DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, Peter M.; Schultz-Fellenz, Emily S.; Kelley, Richard E.

This technical paper presents the most recent and updated catalog of earthquakes measured by the Los Alamos Seismic Network at and around Los Alamos National Laboratory (LANL), with specific focus on the site of the proposed transuranic waste facility (TWF) at Technical Area 63 (TA-63). Any questions about the data presented herein, or about the Los Alamos Seismic Network, should be directed to the authors of this technical paper. LANL and the Los Alamos townsite sit atop the Pajarito Plateau, which is bounded on its western edge by the Pajarito fault system, a 35-mile-long system locally comprised of the down-to-the-eastmore » Pajarito fault (the master fault) and subsidiary down-to-the-west Rendija Canyon, Guaje Mountain, and Sawyer Canyon faults (Figure 1). This fault system forms the local active western margin of the Rio Grande rift near Los Alamos, and is potentially seismogenic (e.g., Gardner et al., 2001; Reneau et al., 2002; Lewis et al., 2009). The proposed TWF area at TA-63 is situated on an unnamed mesa in the north-central part of LANL between Twomile Canyon to the south, Ten Site Canyon to the north, and the headwaters of Canada del Buey to the east (Figure 2). The local bedrock is the Quaternary Bandelier Tuff, formed in two eruptive pulses from nearby Valles caldera, the eastern edge of which is located approximately 6.5 miles west-northwest of the technical area. The older member (Otowi Member) of the Bandelier Tuff has been dated at 1.61 Ma (Izett and Obradovich 1994). The younger member (Tshirege Member) of the Bandelier Tuff has been dated at 1.256 Ma (age from Phillips et al. 2007) and is widely exposed as the mesa-forming unit around Los Alamos. Several discrete cooling units comprise the Tshirege Member. Commonly accepted stratigraphic nomenclature for the Tshirege Member is described in detail by Broxton and Reneau (1995), Gardner et al. (2001), and Lewis et al. (2009). The Tshirege Member cooling unit exposed at the surface at TA-63 is Qbt3. Understanding the subtle differences between Tshirege Member cooling units and the nature of the contacts between cooling units is critical to identifying the presence or absence of faults associated with the Pajarito fault system on the Pajarito Plateau. The Los Alamos Seismic Network (LASN) continuously monitors local earthquake activity in the Los Alamos area in support of LANL's Seismic Hazards program. Seismic monitoring of LANL facilities is a requirement of DOE Order 420.1B (Facility Safety). LASN currently consists of nine permanent seismic instrument field stations that telemeter real-time sensitive ground motion data to a central recording facility. Four of these stations are located on LANL property, with three of those within 2.5 miles of TA-63. The other five stations are in remote locations in the Jemez Mountains, Valles Caldera, St Peters Dome, and the Caja del Rio plateau across the Rio Grande from the Los Alamos area. Local earthquakes are defined as those with locations within roughly 100 miles of Los Alamos. Plate 1 shows the current LASN station locations and all local earthquakes recorded from 1973 through 2011. During this time period, LASN has detected and recorded over 850 local earthquakes in north-central New Mexico. Over 650 of these were located within about 50 miles of Los Alamos, and roughly 60 were within 10 miles. The apparent higher density of earthquakes close to Los Alamos, relative to the rest of north-central New Mexico, is due largely to the fact that LASN is a sensitive local seismic network, recording many very small nearby events (magnitude less than 1.0) that are undetectable at greater distances.« less

Factors Controlling Pre-Columbian and Early Historic Maize Productivity in the American Southwest, Part 2: The Chaco Halo, Mesa Verde, Pajarito Plateau/Bandelier, and Zuni Archaeological Regions

USGS Publications Warehouse

Benson, L.V.

2011-01-01

Chemical and nutrient analyses of 471 soil samples from 161 sites within four archaeological regions (Pajarito Plateau/Bandelier, Zuni, Mesa Verde, and the Chaco Halo) were combined with historical climate data in order to evaluate the agricultural productivity of each region. In addition, maize productivity and field-life calculations were performed using organic-nitrogen (N) values from the upper 50 cm of soil in each region and a range (1-3%/year) of N-mineralization rates. The endmember values of this range were assumed representative of dry and wet climate states. With respect to precipitation and heat, the Pajarito Plateau area has excellent agricultural potential; the agricultural potentials of the Zuni and Mesa Verde regions are good; and the agricultural potential of the Chaco Halo is poor. Calculations of N mineralization and field life indicate that Morfield Valley in Mesa Verde should be able to provide 10 bu/ac of maize for decades (without the addition of N) when organic N-mineralization rates exceed 2%. Productivity and field-life potential decrease in the following order: Zuni, Mesa Verde, Bandelier, Chaco Halo. The Chaco Halo is very unproductive; e. g., 10 bushels per acre can be achieved within the Halo only from soils having the highest organic N concentration (third quartile) and which undergo the highest rate (3%) of N mineralization. ?? 2010 US Government.

Probing the volcanic-plutonic connection and the genesis of crystal-rich rhyolite in a deeply dissected supervolcano in the Nevada Great Basin: Source of the late Eocene Caetano Tuff

USGS Publications Warehouse

Watts, Kathryn E.; John, David A.; Colgan, Joseph P.; Henry, Christopher D.; Bindeman, Ilya N.; Schmitt, Axel K.

2016-01-01

Late Cenozoic faulting and large-magnitude extension in the Great Basin of the western USA has created locally deep windows into the upper crust, permitting direct study of volcanic and plutonic rocks within individual calderas. The Caetano caldera in north–central Nevada, formed during the mid-Tertiary ignimbrite flare-up, offers one of the best exposed and most complete records of caldera magmatism. Integrating whole-rock geochemistry, mineral chemistry, isotope geochemistry and geochronology with field studies and geologic mapping, we define the petrologic evolution of the magmatic system that sourced the >1100 km3Caetano Tuff. The intra-caldera Caetano Tuff is up to ∼5 km thick, composed of crystal-rich (30–45 vol. %), high-silica rhyolite, overlain by a smaller volume of comparably crystal-rich, low-silica rhyolite. It defies classification as either a monotonous intermediate or crystal-poor zoned rhyolite, as commonly ascribed to ignimbrite eruptions. Crystallization modeling based on the observed mineralogy and major and trace element geochemistry demonstrates that the compositional zonation can be explained by liquid–cumulate evolution in the Caetano Tuff magma chamber, with the more evolved lower Caetano Tuff consisting of extracted liquids that continued to crystallize and mix in the upper part of the chamber following segregation from a cumulate-rich, and more heterogeneous, source mush. The latter is represented in the caldera stratigraphy by the less evolved upper Caetano Tuff. Whole-rock major, trace and rare earth element geochemistry, modal mineralogy and mineral chemistry, O, Sr, Nd and Pb isotope geochemistry, sanidine Ar–Ar geochronology, and zircon U–Pb geochronology and trace element geochemistry provide robust evidence that the voluminous caldera intrusions (Carico Lake pluton and Redrock Canyon porphyry) are genetically equivalent to the least evolved Caetano Tuff and formed from magma that remained in the lower chamber after ignimbrite eruption and caldera collapse. Thus, the Caetano Tuff contradicts models for the mutually exclusive origins of voluminous volcanic and plutonic magmas in the upper crust. Crystal-scale O isotope data indicate that the Caetano Tuff is one of the most 18O-enriched rhyolites in the Great Basin (δ18Omagma = 10·2 ± 0·2‰), supporting anatexis of local metasedimentary basement crust. Metapelite xenoliths in the Carico Lake pluton and ubiquitous xenocrystic zircons in the Caetano Tuff provide constraints for the anatexis process; these data point to shallow (<15 km) dehydration melting of a protolith similar to the Proterozoic McCoy Creek Group siliciclastic sediments in eastern Nevada, projected beneath Caetano in fault-stacked shelf sediments that were thickened during Mesozoic crustal shortening. Mean zircon U–Pb ages for different stratigraphic levels of the intra-caldera Caetano Tuff are 34·2–34·5 Ma, 0·2–0·5 Myr older than the caldera sanidine 40Ar/39Ar age of 34·00 ± 0·03 Ma, documenting protracted duration of assembly and homogenization of isotopically diverse upper crustal melts, followed by crystallization and zonation to generate the Caetano Tuff magma chamber. Sanidine rims in the least evolved Caetano Tuff and in the Carico Lake pluton and Redrock Canyon porphyry have sharply zoned Ba domains that point to crystal growth during magmatic recharge events. The recharge magma is inferred to have been compositionally similar to the Caetano Tuff magma, with increased Ba resulting from remelting of Ba-rich sanidine cumulates. Mush reactivation to generate the Caetano Tuff eruption was sufficiently rapid to preserve compositional gradients in the intracaldera ignimbrite, calling into question models that predict homogeneity as a prerequisite for remobilizing crystal-rich ignimbrite magmas.

Tertiary fission-track ages from the Bagua syncline (northern Peru): Stratigraphic and tectonic implications

NASA Astrophysics Data System (ADS)

Naeser, C. W.; Crochet, J.-Y.; Jaillard, E.; Laubacher, G.; Mourier, T.; Sigé, B.

The results of five zircon fission-track ages of volcanic tuffs intercalated within the continental deposits of the Bagua syncline (northern Peru) are reported. These 2500-meter-thick deposits overlie mid-Campanian to lower Maastrichtian fine-grained red beds (Fundo El Triunfo Formation). The disconformable fluvial conglomerates of the Rentema Formation are associated with a 54 Ma tuff (upper Paleocene-lower Eocene?) and would reflect the Inca-1 tectonic phase. The Sambimera Formation (Eocene to mid-Miocene) is a coarsening-upward sequence (from lacustrine to fluvial) that contains three volcanic tuffs of 31, 29, and 12 Ma, respectively. A probable stratigraphic gap, upper Eocene-lower Oligocene, would be related to the late Eocene Inca-2 phase. Neither deformation nor sedimentary discontinuity has been recognized so far. However, the lacustrine to fluvial transition could relate to the late Oligocene Aymara tectonic phase. The unconformable fanglomerates and fluvial deposits of the San Antonio Formation contain in their upper part a 9 Ma tuff (mid-to upper Miocene), and thier base records a major tectonic event (Quechua-2 phase?). The unconformable fanglomerates of the Tambopara Formation date the folding of the Bagua syncline, which could be ascribed to the latest Miocene Quechua-3 tectonics. These formations are correlative with comparable deposits in the sub-Andean basins, suggesting that these eastern areas underwent strong tectonic subsidence of the foreland basin type since mid-Miocene times.

Tertiary fission-track ages from the Bagua syncline (northern Peru): Stratigraphic and tectonic implications

USGS Publications Warehouse

Naeser, C.W.; Crochet, J.-Y.; Jaillard, E.; Laubacher, G.; Mourier, T.; Sige, B.

1991-01-01

The results of five zircon fission-track ages of volcanic tuffs intercalated within the continental deposits of the Bagua syncline (northern Peru) are reported. These 2500-meter-thick deposits overlie mid-Campanian to lower Maastrichtian fine-grained red beds (Fundo El Triunfo Formation). The disconformable fluvial conglomerates of the Rentema Formation are associated with a 54 Ma tuff (upper Paleocene-lower Eocene?) and would reflect the Inca-1 tectonic phase. The Sambimera Formation (Eocene to mid-Miocene) is a coarsening-upward sequence (from lacustrine to fluvial) that contains three volcanic tuffs of 31, 29, and 12 Ma, respectively. A probable stratigraphic gap, upper Eocene-lower Oligocene, would be related to the late Eocene Inca-2 phase. Neither deformation nor sedimentary discontinuity has been recognized so far. However, the lacustrine to fluvial transition could relate to the late Oligocene Aymara tectonic phase. The unconformable fanglomerates and fluvial deposits of the San Antonio Formation contain in their upper part a 9 Ma tuff (mid-to upper Miocene), and thier base records a major tectonic event (Quechua-2 phase?). The unconformable fanglomerates of the Tambopara Formation date the folding of the Bagua syncline, which could be ascribed to the latest Miocene Quechua-3 tectonics. These formations are correlative with comparable deposits in the sub-Andean basins, suggesting that these eastern areas underwent strong tectonic subsidence of the foreland basin type since mid-Miocene times. ?? 1991.

Tephrochronology of Bed II, Olduvai Gorge, Tanzania, and placement of the Oldowan-Acheulean transition.

PubMed

McHenry, Lindsay J; Stanistreet, Ian G

2018-04-12

Tuffaceous marker beds, derived from volcanic products from the Ngorongoro Volcanic Highlands, help define a stratigraphic framework for the world-renowned fossil and stone tool record exposed at Olduvai Gorge, Tanzania. However, previous efforts to constrain this tuff record, especially for Olduvai Bed II, have been limited because of erosion, contamination, reworking, and the alteration of volcanic glass under saline-alkaline conditions. This paper applies previously defined geochemical and mineralogical "fingerprints" for several major Bed II marker tuffs, based on glass (where available) and phenocrysts more resistant to alteration (feldspar, hornblende, augite, and titanomagnetite), to tuffs from stratigraphic sections in the Olduvai Junction Area, including previously and recently excavated Acheulean and Oldowan sites (HWK EE (Locality (Loc) 42), EF-HR (Loc 12a), FLK (Loc 45), and MNK (Loc 88)). The Middle Bed II Bird Print Tuff (BPT) is found to be more compositionally variable than previously reported but is still valuable as a stratigraphic marker over short distances. The confirmation of blocks of Tuff IID in conglomerate helps constrain Upper Bed II stratigraphy at sites where in-situ tuffs are absent. This paper also compiles the results of published geochronological research, providing stratigraphic context and updating previously reported dates using a consistent 40 Ar/ 39 Ar reference standard age. The results of this work support the following paleoanthropologically relevant conclusions: 1) the early Acheulean site EF-HR (Loc 12a) is situated above the level of Hay's Tuff IIC, and thus sits in Upper rather than Middle Bed II, (2) the HWK EE (Loc 42) Oldowan site is constrained between Tuff IIA and Tuff IIB, just above the boundary between Lower and Middle Bed II, and 3) the Acheulean site at FLK W most likely lies within the Middle Augitic Sandstone, above Tuff IIB, similar to the placements by Leakey and Hay for the earliest Acheulean at Olduvai. Copyright © 2018 Elsevier Ltd. All rights reserved.

The effects of wildfire on the peak streamflow magnitude and frequency, Frijoles and Capulin Canyons, Bandelier National Monument, New Mexico

USGS Publications Warehouse

Veenhuis, J.E.

2004-01-01

In June of 1977, the La Mesa fire burned 15,270 acres in and around Frijoles Canyon, Bandelier National Monument and the adjacent Santa Fe National Forest, New Mexico. The Dome fire occurred in April of 1996 in Bandelier National Monument, burned 16,516 acres in Capulin Canyon and the surrounding Dome Wilderness area. Both canyons are characterized by extensive archeological artifacts, which could be threatened by increased runoff and accelerated rates of erosion after a wildfire. The U.S. Geological Survey (USGS) in cooperation with the National Park Service monitored the fires' effects on streamflow in both canyons. Copyright 2004 ASCE.

Trace and rare-earth element characteristics of acidic tuffs from southern Peru and northern Bolivia and a fission-track age for the sillar of Arequipa

NASA Astrophysics Data System (ADS)

Vatin-Perignon, N.; Poupeau, G.; Oliver, R. A.; La Venu, A.; Labrin, F.; Keller, F.; Bellot-Gurlet, L.

1996-03-01

Trace-element and REE data of glass and pumices of acidic tuffs and related fall deposits erupted in southern Peru and northern Bolivia between 20 and 0.36 Ma display typical characteristics of subduction related continental arc magmatism of the CVZ with strong LILE/HFSE enrichment and non enrichment of HREE and Y. Geochemical variations of these tuffs are linked to subduction processes and controlled by changes in tectonic regimes which occured with each Quechua tectonic pulse and affected the astenospheric wedge and both the dowgoing and the overriding lithospheres. During Neogene — Pleistocene times, tuffs erupted in northern Bolivia are typically enriched in Zr, Hf, Th, Ba, LREEs and other incompatible elements and incompatible /Yb ratios are much higher relative to those erupted from southern Peru, at a given SiO 2 content (65-67 wt. for dacites, 72-73 wt.% for rhyolites). {Zr}/{Hf} ratios increase eastward from 27 to 30 and {Ce}/{Yb N} ratios from 11 to 19 reflecting the variation of degree of wedge contribution. Fractionation of the LREE over the HREE and fractionation of incompatible elements may be due to their heterogeneous distribution in the magma source. More highly fractionated REE patterns of Bolivian tuffs than Peruvian tuffs are attributed to variable amounts of contamination of magmas by lower crust. After the Quechua compressional event at 7 Ma, {Sr}/{Y} ratios of tuffs of the same age, erupted at 150-250 km or 250-400 km from the Peru-Chile trench, increase from southern Peru to northern Bolivia. These differences may be attributed to the subduction of a swarm oceanic lithosphere under the Bolivian Alti-plano, leading to partial melting of the sudbucted lithosphere. New FT dating of obsidian fragments of the sillar of Arequipa at 2.42 ± 0.11 Ma. This tuff dates the last Quechua compressional upper Pliocene phase ( 2.5 Ma) and confirms that the sillar is not contemporaneous with the Toba 76 tuff or the Perez ignimbrite of northern Bolivia. Geochemical characteristics of tuffs erupted before and after this last compressional phase remained the same and provide evidence that the upper Miocene ( 7 Ma) compressional deformations played the most important role on the variability of the geochemical characteristics of the southern Peruvian and northern Bolivian tuffs.

Trace elements reconnaissance investigations in New Mexico and adjoining states in 1951

USGS Publications Warehouse

Bachman, George O.; Read, Charles B.

1952-01-01

In the summer and fall of 1951, a reconnaissance search was made in New Mexico and adjacent states for uranium in coal and carbonaceous shale, chiefly of Mesozoic age, and black marine shale of Paleozoic age. Tertiary volcanic rocks, considered to be a possible source for uranium in the coal and associated rocks, were examined where the volcanic rocks were near coal-bearing strata. Uranium in possibly commercial amounts was found at La Ventana Mesa, Sandoval County, New Mexico. Slightly uranifeous coal and carbonaceous shale were found near San Ysidro, Sandoval County, and on Beautiful Mountain, San Juan County, all in New Mexico, and at Keams Canyon, Navajo County, and near Tuba City, Coconino County, in Arizona. Except for La Ventana deposit, none appeared to be of economic importance at the time this report was written, but additional reconnaissance investigations have been underway this field season, in the area where the deposits occur. Marine black shale of Sevonian age was examined in Otero and Socorro Counties, New Mexico and Gila County, Arizona. Mississippian black shale in Socorro County and Pennsylvanian black shale in Taos County, New Mexico were also tested. Equivalent uranium content of samples of these shales did not exceed 0.004 percent. Rhyolitic tuff from the Mount Taylor region is slightly radioactive as is the Bandelier tuff in the Nacimiento region and in the Jemez Plateau. Volcanic rocks in plugs and dikes in the northern Chuska Mountains and to the north in New Mexico as well as in northeastern Arizona and southeastern Utah are slightly radioactive. Coal and carbonaceous rocks in the vicinity of these and similar intrusions are being examined.

Geology and Geochemistry of the 25.0 Ma Underdown Caldera Tuffs and tuff of Clipper Gap, Western Nevada Volcanic Field caldera belt, north-central Nevada

NASA Astrophysics Data System (ADS)

Cousens, B.; Klausen, K. B.; Henry, C.

2016-12-01

The 25.0 Ma Underdown Caldera of the Shoshone Mountains near Austin, Nevada, is part of the Ignimbrite Flare-up suite of calderas in north-central Nevada. Our goal is to characterize the geochemistry and geochronology of the tuffs, determine magma sources, and contrast Underdown with nearby contemporaneous caldera suites. The caldera is contained within a single, mildly west-tilted fault block (Bonham, 1970). The basement rocks are altered intermediate volcanic rocks, rarely intruded by rhyolite veins. The lowermost caldera unit, exposed only on the east side of the fault block, is the sparsely qtz-feld-phyric Underdown Tuff, a high-silica rhyolite (Bonham, 1970) that is columnar-jointed, densely welded, commonly includes aphyric pumice, but locally includes porphyritic pumice. Stretched pumice, flow folds, and foliations that reach nearly vertical demonstrate significant rheomorphism. A densely-welded porphyritic tuff is also present along the southeast side of the exposed caldera, and may be either blocks of an older tuff or a porphyritic phase of the Underdown Tuff. Correlative outflow, the tuff of Clipper Gap, emplaced east of the caldera, is petrographically similar with the same two pumice types. Overlying the Underdown Tuff is the Bonita Canyon Formation, which is moderately welded, commonly lithic- and pumice-rich with minor biotite, quartz and feldspar crystals, and contains reworked lenses; megabreccia of intermediate volcanic rocks and abundantly porphyritic tuff are common. This formation may be an upper part of the Underdown Tuff. On the west side of the Shoshone Mountains, the Bonita Canyon units are overlain by a more porphyritic, variably pumiceous, commonly vitrophyric, and densely welded tuff. At 24.7 Ma, this tuff is petrographically similar to and may be a younger part of the 25.2 Ma tuff of Arc Dome exposed to the east in the Toiyabe Range. Ongoing dating and geochemical analyses will constrain the timing and relationships between the tuffs.

76 FR 8326 - Approval and Promulgation of State Implementation Plans; State of Colorado; Interstate Transport...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-14

... nitrate extinction was 6.9% and 5.1%, respectively. Total nitrates from all source regions are projected to comprise 9.5% of the extinction in Canyonlands and 6.6% of the extinction in Bandelier. Thus, Colorado's nitrate contribution to the overall extinction in 2018 is 0.3% at Bandelier (0.051 x 0.066) and...

Berriasian (Early Cretaceous) radiometric ages from the Grindstone Creek Section, Sacramento Valley, California

USGS Publications Warehouse

Bralower, T.J.; Ludwig, K. R.; Obradovich, J.D.

1990-01-01

The Grindstone Creek Section, Glenn County, Northern California is a sequence of hemipelagic mudstone, siltstone and sandstone interbedded with concretionary limestone and a few thin tuffs and bentonites. Two tuffs have been collected from a narrow interval of this sequence and subjected to mineralogical and isotopic analyses. UPb isotopic analyses of zircon fractions from these volcanic horizons indicate an age of 137.1 + 1.6/-0.6 Ma. A detailed investigation has been conducted on the calcareous nannofossil stratigraphy of this section based on numerous samples with moderately preserved assemblages. The nannoflora is largely of Tethyan affinity, and allows direct correlation with the Berriasian stratotype section, with sections with published magnetostratigraphies and with a DSDP site drilled between known magnetic anomalies. The dated tuffs lie in the lower part of the upper Berriasian Cretarhabdus angustiforatus Zone (Assipetra infracretacea Subzone) and within the narrow range of Rhagodiscus nebulosus. At three different sections, this subzone can be correlated with M-sequence Polarity Zones M16 and M16n. An independent magnetostratigraphic correlation is provided at DSDP Site 387, drilled between anomalies M15 and M16, where basal sediments contain R. nebulosus. Buchia collected within a meter of the lower tuff lie within the B. uncitoides Zone which is Berriasian in age. The upper tuff level, which occurs 65 m above the lower tuff, is situated within the overlying B. pacifica Zone. This zone had previously been correlated with the early Valanginian, but is clearly also partly of Berriasian age based on nannofossil stratigraphy. Our results allow an estimate of the age of the Berriasian-Valanginian and Jurassic-Cretaceous boundaries of 135.1 Ma and 141.1 Ma, respectively, and these fall within the range of, but differ significantiy from, several published time-scales. ?? 1990.

Slanic Tuff and associated Miocene evaporite deposits, Eastern Carpathians, Romania

NASA Astrophysics Data System (ADS)

Bojar, Ana-Voica; Halas, Stanislaw; Barbu, Victor; Bojar, Hans-Peter; Wojtowicz, Artur; Duliu, Octavian

2017-04-01

Miocene tuffs of calcalkaline composition are widespread in the Carpathians, Pannonian and Eastern Alpine realm. Their occurrences are described in outcrops as well as in the subsurface. The presence of such tuffs may offer important criteria for stratigraphic correlations and help to establish the absolute age of deposits and associated climatic and environmental changes. The Green Stone Hill (Muntele Piatra Verde) is situated to the north of Slanic-Prahova salt mine, in the bend region of the Eastern Carpathians, Romania. From bottom to top the section is composed of: marls with Globigerina followed by the so called Slanic tuff, gypsum and salt breccia and, on the top, radiolarian bearing shales. The stratigraphic age of the section is Middle to Upper Badenian (nannoplankton zones NN5 to NN6). XRD investigations of the green Slanic tuff show that the main mineralogical component is clinoptilolite (zeolite) followed by quartz and plagioclase. For this type of tuff there is no crystalline phase, which may be used for radiometric dating. In the middle part of the green tuff interval, we found discrete layers of a much coarser white tuff, with mineralogy consisting of quartz, plagioclase, biotite and clinoptilolite. The white tuff forming distinct layers within the green tuff, has an andesitic composition. 40Ar/39Ar dating of biotite concentrates from the white tuff gives an age of 13.6±0.2Ma, the dated layer being situated below the gypsum and salt breccia. We consider that the age is well constraining the time when the green tuffs were formed at the border of the basin. From this level upwards discrete gypsum layers occurs within the green tuffs, the age may be considered as indicating the base of the evaporitic sequence. To the south-east, from this level upwards evaporites, mainly salt formed. The age suggests that evaporitic deposits formed after the Mid Badenian climatic optimum, evaporitic formation being related to restricted circulation due the drop of sea-level and tectonism.

Distribution of rubidium, strontium, and zirconium in tuff from two deep coreholes at Yucca Mountain, Nevada

USGS Publications Warehouse

Spengler, Richard W.; Peterman, Zell E.; ,

1991-01-01

Variations in concentrations of trace elements Rb, Sr, and Zr within the sequence of high-silica tuff and dacitic lava beneath Yucca Mountain reflect both primary composition and secondary alteration. Rb and K concentrations have parallel trends. Rb concentrations are significantly lower within intervals containing zeolitic nonwelded to partially welded and bedded tuffs and are higher in thick moderately to densely welded zones. Sr concentrations increase with depth from about 30 ppm in the Topopah Spring Member of the Paintbrush Tuff to almost 300 ppm in the older tuffs. Zr concentrations are about 100 ppm in the Topopah Spring Member and also increase with depth to about 150 ppm in the Lithic Ridge Tuff and upper part of the older tuffs. Conspicuous local high concentrations of Sr in the lower part of the Tram Member, in the dacite lava, and in unit c of the older tuffs in USW G-1, and in the densely welded zone of the Bullfrog Member in USW GU-3/G-3 closely correlate with high concentrations of less-mobile Zr and may reflect either primary composition or elemental redistribution resulting largely from smectitic alteration. Initial 87Sr/86Sr values from composite samples increase upward in units above the Bullfrog Member of the Crater Flat Tuff. The progressive tenfold increase in Sr with depth coupled with the similarity of initial 87Sr/86Sr values within the Bullfrog Member and older units to those of Paleozoic marine carbonates are consistent with a massive influx of Sr from water derived from a Paleozoic carbonate aquifer.

The age of volcanic tuffs from the Upper Freshwater Molasse (North Alpine Foreland Basin) and their possible use for tephrostratigraphic correlations across Europe for the Middle Miocene

NASA Astrophysics Data System (ADS)

Rocholl, Alexander; Schaltegger, Urs; Gilg, H. Albert; Wijbrans, Jan; Böhme, Madelaine

2018-03-01

The Middle Miocene Upper Freshwater Molasse sediments represent the last cycle of clastic sedimentation during the evolution of the North Alpine Foreland Basin. They are characterized by small-scale lateral and temporal facies changes that make intra-basin stratigraphic correlations at regional scale difficult. This study provides new U-Pb zircon ages as well as revised 40Ar/39Ar data of volcanic ash horizons in the Upper Freshwater Molasse sediments from southern Germany and Switzerland. In a first and preliminary attempt, we propose their possible correlation to other European tephra deposits. The U-Pb zircon data of one Swiss (Bischofszell) and seven southern German (Zahling, Hachelstuhl, Laimering, Unterneul, Krumbad, Ponholz) tuff horizons indicate eruption ages between roughly 13.0 and 15.5 Ma. The stratigraphic position of the Unterneul and Laimering tuffs, bracketing the ejecta of the Ries impact (Brockhorizon), suggests that the Ries impact occurred between 14.93 and 15.00 Ma, thus assigning the event to the reversed chron C5Bn1r (15.032-14.870 Ma) which is in accordance with paleomagnetic evidence. We combine our data with published ages of tuff horizons from Italy, Switzerland, Bavaria, Styria, Hungary, and Romania to derive a preliminary tephrochronological scheme for the Middle Miocene in Central Europe in the age window from 13.2 to 15.5 Ma. The scheme is based on the current state of knowledge that the Carpathian-Pannonian volcanic field was the only area in the region producing explosive calc-alkaline felsic volcanism. This preliminary scheme will require verification by more high-quality ages complemented by isotopic, geochemical and paleomagnetic data.

Elk response to the La Mesa fire and current status in the Jemez Mountains

USGS Publications Warehouse

Allen, Craig D.; Allen, Craig D.

1996-01-01

Faunal remains in local archeological sites and historic information suggest that elk populations in the Jemez Mountains were low from ca. 1200 A.D. through ca. 1900 A.D., when they were extirpated from this region. Elk were reintroduced to the Jemez country in 1948 and 1964- 1965, and their population apparently grew exponentially, reaching 1000 animals in the 1970's and about 7000 by 1991.Elk populations in Bandelier National Monument and adjoining areas increased rapidly after the 1977 La Mesa Fire. Winter use by elk in the La Mesa Fire area, centered on Bandelier, grew from about 100 animals in .1978 to around 1500 elk by 1992. The dramatic increase in the Bandelier elk herd (an annual growth rate of 21.3% and a 3.6 year population doubling time) was due in part to the creation of about 6000 hectares of grassy winter range in and around the park by the La Mesa Fire. Some of this local population increase reflects concentration of elk into this favorable wintering habitat from surrounding portions of the Jemez Mountains.Existing data are inadequate to determine whether elk populations are still growing rapidly in the Jemez Mountains. While annual aerial surveys since 1990 in Bandelier reveal no clear population trend, a variety of observations demonstrate increasing elk use of lower elevation areas. Negative resource impacts from today's high elk populations are beginning to be widely noted across the Jemez Mountains, especially in high-use portions of the Bandelier National Monument area. Affected resources range from plant communities to soils and even archeological sites. Given the large uncertainties associated with the current data on elk populations, care should be taken to avoid further population increases until the resource impacts of this new phenomenon (large numbers of elk) can be identified, desirable population levels identified (based to a significant degree upon ecological information and resource carrying capacities, as well as social considerations), and appropriate cooperative management strategies implemented.

A Cultural Resources Survey of the Proposed Recreational Development Areas and Wildlife Subimpoundments at the B. Everett Jordan Dam and Lake. Volume 1.

DTIC Science & Technology

1984-03-01

containing flow banding, light-gray felsite, felsic- porphyries , crystal tuffs, and rare mafic porphyries and crystal tuffs (Conley and Bain 1965:12Z). The...goods are also present in the form of glass beads, gunflints, iron axes, copper hawk bells and white clay trade pipes. HISTORICAL BACKGROUND The...points manufactured on two rock types occur most frequently: andesitic felsite in the lower valley and grey latite porphyry in the upper valley. The

Geohydrology of test well USW H-3, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Thordarson, William; Rush, F.E.; Waddell, S.J.

1985-01-01

Test well USW H-3 is one of several wells drilled in the southwestern part of the Nevada Test Site for hydraulic testing, hydrologic monitoring, and geophysical logging. The work was performed in cooperation with the U.S. Department of Energy. The rocks penetrated by the well to a total depth of 1,219 meters were volcanic tuffs of Tertiary age. The most transmissive zone in this well is in the upper part of the Tram Member of the Crater Flat Tuff that was penetrated at a depth from 809 to 841 meters; transmissivity is about 7 x 10 -1 meter squared per day. The remainder of the rocks penetrated between the depths of 841 to 1,219 meters have a transmissivity of about 4 x 10 -1 meter squared per day and are predominatly in the Tram Member of the Crater Flat Tuff and the Lithic Ridge Tuff in the depths from 841 to 1,219 meters. (USGS)

Fossil and active fumaroles in the 1912 eruptive deposits, Valley of ten thousand smokes, Alaska

USGS Publications Warehouse

Keith, T.E.C.

1991-01-01

Fumaroles in the ash-flow sheet emplaced during the 1912 eruption of Novarupta were intensely active throughout the Valley of Ten Thousand Smokes (VTTS) when first studied in 1917. Fumarole temperatures recorded in 1919 were as hot as 645??C. Influx of surface waters into the hot ash-flow sheet provided the fluid flow to sustain the fumaroles but also enhanced cooling so that by the mid-1930's vigorous activity survived only in the vent region. Configuration and distribution of high-temperature fissure fumaroles tens of meters long, that are prevalent in the middle and upper VTTS, were controlled largely by sintering and degree of welding, which in turn controlled fracturing and permeability of the ash-flow tuff. One fracture type developed parallel to the enclosing valley walls during compaction of the ash-flow sheet. Another type extends across the VTTS nearly perpendicular to the flow direction. A third type of randomly oriented fractures developed as cooling contraction cracks during vapor-phase devitrification. In distal parts of the ash-flow sheet where the tuff is nonwelded, prominent fumaroles have irregular funnel-shaped morphologies. Fumarole distribution in the nonwelded part of the ash-flow sheet is concentrated above pre-emplacement river channels. The hottest, longest-lived fumaroles occurred in the upper VTTS near the 1912 vent where the ash-flow sheet is thicker, more indurated, and on average more mafic (richer in dacite and andesite) in contrast to the thinner, nonwelded rhyolitic tuff in the distal part of the sheet. Fumarolic activity was less intense in the distal part of the tuff because of lower emplacement temperatures, more diffuse fumarole conduits in the nonwelded tuff, and the thinness of the ash-flow sheet. Chemical leaching of ash-flow tuff by hot rising fluids took place adjacent to fumarolic conduits in deep parts of the fumaroles. Deposition of incrustation minerals, the components of which were carried upward by fumarolic gases, took place in the upper part of the ejecta, mostly in the fallout layers. The permeability difference between the ash-flow tuff and the overlying coarse dacite fallout was a critical factor in promoting the abrupt gradients in temperature, pressure, and fO2 that resulted in deposition of minerals from the fumarolic gases. The permeability difference between nonwelded ash-flow tuff and overlying fine-grained fall layers in the lower VTTS is less pronounced. The total mass of fumarolically deposited minerals appears large at first glance owing to the conspicuous coloration by Fe minerals; the mass is appreciably less than is apparent, however, because most incrustations are composed largely of ejecta coated or cemented by fine-grained fumarolic minerals. A large mass of unstable incrustation minerals, mainly chlorides and sulfates, reported during the 1917-1919 studies have since been removed by dissolution and weathering. In the vent region, argillic alteration that followed high-temperature degassing is localized along arcuate subsidence fractures in fallback ejecta. At widely scattered residual orifices, fumarolic gases presently are near-neutral steam, and temperatures are as hot as 90??C. ?? 1991.

Nd, Sr, and O isotopic variations in metaluminous ash-flow tuffs and related volcanic rocks at the Timber Mountain/Oasis Valley Caldera, Complex, SW Nevada: implications for the origin and evolution of large-volume silicic magma bodies

USGS Publications Warehouse

Farmer, G.L.; Broxton, D.E.; Warren, R.G.; Pickthorn, W.

1991-01-01

Nd, Sr and O isotopic data were obtained from silicic ash-flow tuffs and lavas at the Tertiary age (16-9 Ma) Timber (Mountain/Oasis Valley volcanic center (TMOV) in southern Nevada, to assess models for the origin and evolution of the large-volume silicic magma bodies generated in this region. The large-volume (>900 km3), chemically-zoned, Topopah Spring (TS) and Tiva Canyon (TC) members of the Paintbrush Tuff, and the Rainier Mesa (RM) and Ammonia Tanks (AT) members of the younger Timber Mountain Tuff all have internal Nd and Sr isotopic zonations. In each tuff, high-silica rhyolites have lower initial e{open}Nd values (???1 e{open}Nd unit), higher87Sr/86Sr, and lower Nd and Sr contents, than cocrupted trachytes. The TS, TC, and RM members have similar e{open}Nd values for high-silica rhyolites (-11.7 to -11.2) and trachytes (-10.5 to -10.7), but the younger AT member has a higher e{open}Nd for both compositional types (-10.3 and -9.4). Oxygen isotope data confirm that the TC and AT members were derived from low e{open}Nd magmas. The internal Sr and Nd isotopic variations in each tuff are interpreted to be the result of the incorporation of 20-40% (by mass) wall-rock into magmas that were injected into the upper crust. The low e{open}Nd magmas most likely formed via the incorporation of low ??18O, hydrothermally-altered, wall-rock. Small-volume rhyolite lavas and ash-flow tuffs have similar isotopic characteristics to the large-volume ash-flow tuffs, but lavas erupted from extracaldera vents may have interacted with higher ??18O crustal rocks peripheral to the main magma chamber(s). Andesitic lavas from the 13-14 Ma Wahmonie/Salyer volcanic center southeast of the TMOV have low e{open}Nd (-13.2 to -13.8) and are considered on the basis of textural evidence to be mixtures of basaltic composition magmas and large proportions (70-80%) of anatectic crustal melts. A similar process may have occurred early in the magmatic history of the TMOV. The large-volume rhyolites may represent a mature stage of magmatism after repeated injection of basaltic magmas, crustal melting, and volcanism cleared sufficient space in the upper crust for large magma bodies to accumulate and differentiate. The TMOV rhyolites and 0-10 Ma old basalts that erupted in southern Nevada all have similar Nd and Sr isotopic compositions, which suggests that silicic and mafic magmatism at the TMOV were genetically related. The distinctive isotopic compositions of the AT member may reflect temporal changes in the isotopic compositions of basaltic magmas entering the upper crust, possibly as a result of increasing "basification" of a lower crustal magma source by repeated injection of mantle-derived mafic magmas. ?? 1991 Springer-Verlag.

Early miocene bimodal volcanism, Northern Wilson Creek Range, Lincoln County, Nevada

USGS Publications Warehouse

Willis, J.B.; Willis, G.C.

1996-01-01

Early Miocene volcanism in the northern Wilson Creek Range, Lincoln County, Nevada, produced an interfingered sequence of high-silica rhyolite (greater than 74% SiO2) ash-flow tuffs, lava flows and dikes, and mafic lava flows. Three new potassium-argon ages range from 23.9 ?? 1.0 Ma to 22.6 ?? 1.2 Ma. The rocks are similar in composition, stratigraphic character, and age to the Blawn Formation, which is found in ranges to the east and southeast in Utah, and, therefore, are herein established as a western extension of the Blawn Formation. Miocene volcanism in the northern Wilson Creek Range began with the eruption of two geochemically similar, weakly evolved ash-flow tuff cooling units. The lower unit consists of crystal-poor, loosely welded, lapilli ash-flow tuffs, herein called the tuff member of Atlanta Summit. The upper unit consists of homogeneous, crystal-rich, moderately to densely welded ash-flow tuffs, herein called the tuff member of Rosencrans Peak. This unit is as much as 300 m thick and has a minimum eruptive volume of 6.5 km3, which is unusually voluminous for tuffs in the Blawn Formation. Thick, conspicuously flow-layered rhyolite lava flows were erupted penecontemporaneously with the tuffs. The rhyolite lava flows have a range of incompatible trace element concentrations, and some of them show an unusual mixing of aphyric and porphyritic magma. Small volumes of alkaline, vesicular, mafic flows containing 50 weight percent SiO2 and 2.3 weight percent K2O were extruded near the end of the rhyolite volcanic activity. The Blawn Formation records a shift in eruptive style and magmatic composition in the northern Wilson Creek Range. The Blawn was preceded by voluminous Oligocene eruptions of dominantly calc-alkaline orogenic magmas. The Blawn and younger volcanic rocks in the area are low-volume, bimodal suites of high-silica rhyolite tuffs and lava flows and mafic lava flows.

Calibration of the Permo-Triassic Magnetostratigraphic Time Scale: Constraints from the Dewey Lake Formation, West Texas

NASA Astrophysics Data System (ADS)

Chang, S.; Knight, K. B.; Renne, P. R.

2005-12-01

Magnetostratigraphy is potentially a powerful tool for deciphering the high resolution chronostratigraphy of events across the Permo-Triassic boundary, but few well-dated polarity reversals exist to serve as calibration. Red beds of the Dewey Lake Formation (DLF) of West Texas span three reversed polarity intervals (Steiner, 2001) in a section of the DLF at Caprock Canyons State Park, where two tuffs occur. Sanidine separated from these tuffs was analyzed by 40Ar/39Ar methods. Single crystal laser fusion 40Ar/39Ar analyses of 40 grains from the upper tuff yield a weighted mean age of 249.9 ± 2.4 Ma (2σ errors here and throughout). The clustering of single crystal data provides some assurance against xenocrystic contamination. Two age spectra from multigrain sanidine separates from the lower tuff yielded integrated ages of 248.9 ± 2.8 Ma and 249.7 ± 2.8 Ma and consistent plateau ages of 249.2 ± 2.4 Ma and 249.6 ± 2.4 Ma. Two age spectra from multigrain upper tuff sanidines lack strict plateaus but with overall flat age spectra, with integrated ages of 249.7 ± 2.8 Ma and 250.3 ± 2.8 Ma and plateau-like segments (>70% of 39Ar released) with ages of 249.9 ± 2.6 Ma and 249.9 ± 2.6 Ma, respectively. These results, compared with 40Ar/39Ar data (using the same FCs = 28.02 Ma standard calibration) from the GSSP section at Meishan, China, suggest that the Permo-Triassic boundary (249.8 Ma; recalculated from Renne et al., 1995) definitely occurs within the lower Dewey Lake Formation. The two tuffs, which bracket a normal to reverse geomagnetic polarity transition polarity (Steiner, 2001), have indistinguishable ages. The age of this Permo-Triassic polarity transition is thus best represented by the weighed average of their ages, ca. 249.7 Ma (based on accepted calibrations of the 40Ar/39Ar system). Further such constraints will facilitate high-resolution comparison of terrestrial and marine records across this critical time interval.

Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estimates of its fossil mammals, including hominins.

PubMed

Gathogo, Patrick N; Brown, Francis H

2006-11-01

Recent geologic study shows that all hominins and nearly all other published mammalian fossils from Paleontological Collection Area 123, Koobi Fora, Kenya, derive from levels between the KBS Tuff (1.87+/-0.02 Ma) and the Lower Ileret Tuff (1.53+/-0.01 Ma). More specifically, the fossils derive from 53 m of section below the Lower Ileret Tuff, an interval in which beds vary markedly laterally, especially those units containing molluscs and algal stromatolites. The upper Burgi Member (approximately 2.00-1.87 Ma) crops out only in the southwestern part of Area 123. Adjacent Area 110 contains larger exposures of the member, and there the KBS Tuff is preserved as an airfall ash in lacustrine deposits and also as a fluvially redeposited ash. We observed no mammalian fossils in situ in this member in Area 123, but surface specimens have been documented in some monographic treatments. Fossil hominins from Area 123 were attributed to strata above the KBS Tuff in the 1970s, but later they were assigned to strata below the KBS Tuff (now called the upper Burgi Member). This study definitively places the Area 123 hominins in the KBS Member. Most of these hominins are between 1.60 and 1.65 myr in age, but the youngest may date to only 1.53 Ma, and the oldest, to 1.75 Ma. All are 0.15-0.30 myr younger than previously estimated. The new age estimates, in conjunction with published taxonomic attributions of fossils, suggest that at least two species of Homo coexisted in the region along with A. boisei until at least 1.65 Ma. Comparison of crania KNM-ER 1813 and KNM-ER 1470, which were believed to be of comparable age, is at the focus of the debate over whether Homo habilis sensu lato is in fact composed of two species: Homo habilis and Homo rudolfensis. These two crania are separated in time by approximately 0.25 myr, and therefore, arguments for their conspecificity no longer need to confront the issue of unusually high contemporaneous variation within a single species.

Chemical correlation of some late Cenozoic tuffs of Northern and Central California by neutron activation analysis of glass and comparison with X-ray fluorescence analysis

USGS Publications Warehouse

Sarna-Wojcicki, Andrei M.; Bowman, Harry W.; Russell, Paul C.

1979-01-01

Glasses separated from several dacitic and rhyolitic late Cenozoic tuffs of northern and central California were analyzed by neutron activation for more than 43 elemental abundances. Eighteen elements--scandiurn, manganese, iron, zinc, rubidium, cesium, barium, lanthanum, cerium, samarium, europium, terbiurn, dysprosiurn, ytterbiurn, hafniurn, tantalurn, thorium and uranium--were selected as most suitable for purposes of chemical correlation on the basis of their natural variability in silicic tuffs and the precision obtainable in analysis. Stratigraphic relations between tuffs and replicate chemical analyses on individual tuffs make it possib1e to calibrate a quantitative parameter, the similarity coefficient, which indicates the degree of correlation for the tuffs studied. The highest similarity coefficient (0.99) was obtained for analyses of two tuffs (potassium-argon dated at about' 6.0 m.y.) exposed in the Merced(?) and Petaluma Formations of Sonoma County, which represent different paleoenvironments, shallow-water marine and fresh water or brackish marine, respectively. Corre1ation of these formations on the basis of criteria other than tephrochronoloqy would be difficult. Results of neutron activation analysis in general confirm earlier correlations made on the basis of analysis by X-ray fluorescence but also make it possible to resolve small compositional differences between chemically simi1ar tuffs in stratigraphic proximity. The Lawlor Tuff (potassium-argon dated at about 4.0 m.y.) is identified at two new localities: in a core sample obtained from a bore hole east of Suisun Bay, and from the Kettleman Hills of western San Joaquin Valley. This identification permits correlation of the uppermost part of the marine Etchegoin Formation in the San Joaquin Valley with the continental Livermore Gravels of Clark, the Tassajara Formation, and the upper part of the Sonoma Volcanics in the cel1tral Coast Ranges of California. A younger tuff near the top of the marine San Joaquin Formation in the Kettleman Hills has been identified at both new 1oca1ities .

Trondhjemite and metamorphosed quartz keratophyre tuff of the Ammonoosuc volcanics (Ordovician), western New Hampshire and adjacent Vermont and Massachusetts.

USGS Publications Warehouse

Leo, G.W.

1985-01-01

These volcanic rocks consist of a lower, mainly mafic unit of hornblende-plagioclase amphibolite and an upper, mainly felsic metamorphosed quartz keratophyre tuff. They are intruded by sills, dykes and plugs of trondhjemite; which is highly silicic (SiO2, 73-81%), low in Al2O3 (11.3-13.5%) and generally contains <1% K2O. Both trondhjemite and volcanics are calc-alkaline. The major- and minor-element geochemistry of the trondhjemites is closely similar to that of the quartz keratophyre tuff. These rocks were probably produced by partial melting of basaltic source rocks, rather than by fractional crystallization, in view of the virtually bimodal nature of the Ammonoosuc assemblage. The generation of the felsic rocks occurred at deeper levels along a subduction zone dipping eastward.-L.C.H.

The Laramide Mesa formation and the Ojo de Agua caldera, southeast of the Cananea copper mining district, Sonora, Mexico

USGS Publications Warehouse

Cox, Dennis P.; Miller, Robert J.; Woodbourne, Keith L.

2006-01-01

The Mesa Formation extends from Cananea, Mexico, southeast to the Sonora River and is the main host rock of Laramide porphyry copper deposits in the Cananea District and at the Alacran porphyry prospect to the east. The Mesa consists of two members-a lower andesite and an upper dacite. The lowest part of the dacite member is a crystal tuff about 100 m thick. This tuff is the outfall of a caldera centered near the village of Ojo de Agua, dated by 40Ar/39Ar at 65.8 Ma ?0.4. The Ojo de Agua Caldera is about 9 km in diameter and is filled by a light gray biotite dacite tuff with abundant flattened pumice fragments. The volume of the caldera is estimated to be 24 km3.

(40)Ar/(39)Ar dating of Bed I, Olduvai Gorge, Tanzania, and the chronology of early Pleistocene climate change.

PubMed

Deino, Alan L

2012-08-01

(40)Ar/(39)Ar dating of tuffs and lavas of the late Pleistocene volcanic and sedimentary sequence of Olduvai Gorge, north-central Tanzania, provides the basis for a revision of Bed I chronostratigraphy. Bed I extends from immediately above the Naabi Ignimbrite at 2.038 ± 0.005 Ma to Tuff IF at 1.803 ± 0.002 Ma. Tuff IB, a prominent widespread marker tuff in the basin and a key to understanding hominin evolutionary chronologies and paleoclimate histories, has an age of 1.848 ± 0.003 Ma. The largest lake expansion event in the closed Olduvai lake basin during Bed I times encompassed the episode of eruption and emplacement of this tuff. This lake event is nearly coincident with the maximum precessional insolation peak of the entire Bed I/Lower Bed II interval, calculated from an astronomical model of the boreal summer orbital insolation time-series. The succeeding precessional peak also apparently coincides with the next youngest expansion of paleo-Lake Olduvai. The extreme wet/dry climate shifts seen in the upper part of Bed I occur during an Earth-orbital eccentricity maximum, similar to episodic lake expansions documented elsewhere in the East African Rift during the Neogene. Copyright © 2012 Elsevier Ltd. All rights reserved.

Ash-flow tuffs of the Galiuro Volcanics in the northern Galiuro Mountains, Pinal County, Arizona

USGS Publications Warehouse

Krieger, Medora Louise Hooper

1979-01-01

The upper Oligocene and lower Miocene Galiuro Volcanics in the northern part of the Galiuro Mountains contains two distinctive major ash-flow tuff sheets, the Holy Joe and Aravaipa Members. These major ash-flows illustrate many features of ash-flow geology not generally exposed so completely. The Holy Joe Member, composed of a series of densely welded flows of quartz latite composition that make up a simple cooling unit. is a rare example of a cooling unit that has a vitrophyre at the top as well as at the base. The upper vitrophyre does not represent a cooling break. The Aravaipa Member. a rhyolite, is completely exposed in Aravaipa and other canyons and on Table Mountain. Remarkable exposures along Whitewash Canyon exhibit the complete change from a typical stacked-up interior zonation of an ash flow to a non welded distal margin. Vertical and horizontal changes in welding, crystallization, specific gravity, and lithology are exposed. The ash flow can be divided into six lithologic zones. The Holy Joe and Aravaipa Members of the Galiuro Volcanics are so well exposed and so clearly show characteristic features of ash-flow tuffs that they could be a valuable teaching aid and a source of theses for geology students.

2.8-Ma ash-flow caldera at Chegem River in the northern Caucasus Mountains (Russia), contemporaneous granites, and associated ore deposits

USGS Publications Warehouse

Lipman, P.W.; Bogatikov, O.A.; Tsvetkov, A.A.; Gazis, C.; Gurbanov, A.G.; Hon, K.; Koronovsky, N.V.; Kovalenko, V.I.; Marchev, P.

1993-01-01

Diverse latest Pliocene volcanic and plutonic rocks in the north-central Caucasus Mountains of southern Russia are newly interpreted as components of a large caldera system that erupted a compositionally zoned rhyolite-dacite ash-flow sheet at 2.83 ?? 0.02 Ma (sanidine and biotite 40Ar/39Ar). Despite its location within a cratonic collision zone, the Chegem system is structurally and petrologically similar to typical calderas of continental-margin volcanic arcs. Erosional remnants of the outflow Chegem Tuff sheet extend at least 50 km north from the source caldera in the upper Chegem River. These outflow remnants were previously interpreted by others as erupted from several local vents, but petrologic similarities indicate a common origin and correlation with thick intracaldera Chegem Tuff. The 11 ?? 15 km caldera and associated intrusions are superbly exposed over a vertical range of 2,300 m in deep canyons above treeline (elev. to 3,800 m). Densely welded intracaldera Chegem Tuff, previously described by others as a rhyolite lava plateau, forms a single cooling unit, is > 2 km thick, and contains large slide blocks from the caldera walls. Caldera subsidence was accommodated along several concentric ring fractures. No prevolcanic floor is exposed within the central core of the caldera. The caldera-filling tuff is overlain by andesitic lavas and cut by a 2.84 ?? 0.03-Ma porphyritic granodiorite intrusion that has a cooling age analytically indistinguishable from that of the tuffs. The Eldjurta Granite, a pluton exposed low in the next large canyon (Baksan River) 10 km to the northwest of the caldera, yields variable K-feldspar and biotite ages (2.8 to 1.0 Ma) through a 5-km vertical range in surface and drill-hole samples. These variable dates appear to record a prolonged complex cooling history within upper parts of another caldera-related pluton. Major W-Mo ore deposits at the Tirniauz mine are hosted in skarns and hornfels along the roof of the Eldjurta Granite, and associated aplitic phases have textural features of Climax-type molybdenite porphyries in the western USA. Similar 40Ar/39Ar ages, mineral chemistry, and bulk-rock compositions indicate that the Chegem Tuff, intracaldera intrusion, and Eldjurta Granite are all parts of a large magmatic system that broadly resembles the middle Tertiary Questa caldera system and associated Mo deposits in northern New Mexico, USA. Because of their young age and superb three-dimensional exposures, rocks of the Chegem-Tirniauz region offer exceptional opportunities for detailed study of caldera structures, compositional gradients in volcanic rocks relative to cogenetic granites, and the thermal and fluid-flow history of a large young upper-crustal magmatic system. ?? 1993.

Oxygen isotopic and geochemical evidence for a short-lived, high-temperature hydrothermal event in the Chegem caldera, Caucasus Mountains, Russia

USGS Publications Warehouse

Gazis, C.; Taylor, H.P.; Hon, K.; Tsvetkov, A.

1996-01-01

Within the 2.8 Ma Chegem ash-flow caldera (11 ?? 15 km), a single cooling unit of rhyolitic to dacitic welded tuff more than 2 km thick is exposed in deep valleys incised during recent rapid uplift of the Caucasus Mountains. The intracaldera tuff is mineralogically fresh and unaltered, and is overlain by andesite lavas and cut by a resurgent granodiorite intrusion. Major- and trace-element compositions for a 1405-m stratigraphic section of intracaldera tuff display trends of upwardly increasing Na2O, CaO, Al2O3, total Fe, MgO, TiO2, Sr and Zr and decreasing SiO2, K2O and Rb. This mafic-upward zoning (from 76.1 to 69.9% SiO2) reflects an inverted view of the upper part of the source magma chamber. Oxygen isotope studies of 35 samples from this 1405-m section define a striking profile with "normal" igneous ??18O values (+7.0 to +8.5) in the lower 600 m of tuff, much lower ??18O values (-4.0 to +4.3) in a 700-m zone above that and a shift to high ??18O values (+4.4 to -10.9) in the upper 100 m of caldera-fill exposure. Data from two other partial stratigraphic sections indicate that these oxygen isotope systematics are probably a caldera-wide phenomenon. Quartz and feldspar phenocrysts everywhere have "normal" igneous ??18O values of about +8.5 and +7.5, respectively, whereas groundmass and glass ??18O values range from -7.7 to +12.3. Consequently, the ??18O values of coexisting feldspar, groundmass and glass form a steep array in a plot of ??feldspar vs. ??groundmass/glass. Such pronounced disequilibrium between coexisting feldspar and groundmass or glass has never before been observed on this scale. It requires a hydrothermal event involving large amounts of low-18O H2O at sufficiently high temperatures and short enough time (tens of years or less) that glass exchanges thoroughly but feldspar does not. The most likely process responsible for the O depletions at Chegem is a very high temperature (500-600??C), short-lived, vigorous meteoric-hydrothermal event that was focused within the upper 750 m of intracaldera tuff. Mass balance calculations indicate fluid fluxes of = 6 ?? 10-6 mol cm-2 s-1. We believe that the closest historical analogue to this Chegem hydrothermal event is the situation observed in the Valley of Ten Thousand Smokes (Alaska, USA), where hundreds of steam fumaroles with measured temperatures as high as 645??C persisted for 10 to 15 years in the much smaller welded ash-flow tuff sheet (??? 200 m thick) produced by the 1912 Katmai eruption.

A survey of macromycete diversity at Los Alamos National Laboratory, Bandelier National Monument, and Los Alamos County; A preliminary report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jarmie, N.; Rogers, F.J.

The authors have completed a 5-year survey (1991--1995) of macromycetes found in Los Alamos County, Los Alamos National Laboratory, and Bandelier National Monument. The authors have compiled a database of 1,048 collections, their characteristics, and identifications. The database represents 123 (98%) genera and 175 (73%) species reliably identified. Issues of habitat loss, species extinction, and ecological relationships are addressed, and comparisons with other surveys are made. With this baseline information and modeling of this baseline data, one can begin to understand more about the fungal flora of the area.

40Ar/(39)Ar dating of the Kapthurin Formation, Baringo, Kenya.

PubMed

Deino, Alan L; McBrearty, Sally

2002-01-01

The(40)Ar/(39)Ar radiometric dating technique has been applied to tuffs and lavas of the Kapthurin Formation in the Tugen Hills, Kenya Rift Valley. Two variants of the(40)Ar/(39)Ar technique, single-crystal total fusion (SCTF) and laser incremental heating (LIH) have been employed to date five marker horizons within the formation: near the base, the Kasurein Basalt at 0.61+/-0.04 Ma; the Pumice Tuff at 0.543+/-0.004 Ma; the Upper Kasurein Basalt at 0.552+/-0.015 Ma; the Grey Tuff at 0.509+/-0.009 Ma; and within the upper part of the formation, the Bedded Tuff at 0.284+/-0.012 Ma. The new, precise radiometric age determination for the Pumice Tuff also provides an age for the widespread Lake Baringo Trachyte, since the Pumice Tuff is the early pyroclastic phase of this voluminous trachyte eruption. These results establish the age of fossil hominids KNM-BK 63-67 and KNM-BK 8518 at approximately 0.510-0.512 Ma, a significant finding given that few Middle Pleistocene hominids are radiometrically dated. The Kapthurin hominids are thus the near contemporaries of those from Bodo, Ethiopia and Tanzania. A flake and core industry from lacustrine sediments in the lower part of the formation is constrained by new dates of 0.55-0.52 Ma, a period during which the Acheulian industry, characterized by handaxes, is known throughout East Africa. Points, typical of the Middle Stone Age (MSA), are found in Kapthurin Formation sediments now shown to date to between 0.509+/-0.009 Ma and 0.284+/-0.012 Ma. This date exceeds previous estimates for the age of the MSA elsewhere in East Africa by 49 ka, and establishes the age of Acheulian to MSA transition for the region. Evidence of the use of the Levallois technique for the manufacture of both small flakes and biface preforms, the systematic production of blades, and the use and processing of red ochre also occurs in this interval. The presence of blades and red ochre at this depth is important as blades signify a high degree of technical competence and red ochre suggests symbolic behavior. Copyright 2002 Academic Press.

Unraveling the volcanic and post-volcanic history at Upsal Hogback, Fallon, Nevada, USA

NASA Astrophysics Data System (ADS)

Anderson, E.; Cousens, B.

2013-12-01

Upsal Hogback is a < 25 ka phreatomagmatic volcanic center situated near Fallon, Nevada. The volcano neighbors two other young volcanic complexes: the Holocene Soda Lakes maars and Rattlesnake Hill, a ~ 1 Ma volcanic neck (Shevenell et al., 2005). These volcanoes lie on the transition between the Sierra Nevada and the Basin and Range province, as well as on the edge of the Walker Lane. Upsal Hogback includes two to four vents, fewer than mapped by Morrison (1964), and can be divided into north (one vent) and south (three potential vents) complexes. The vents all produced phreatomagmatic eruptions resulting in tuff rings composed primarily of coarse, indurated lapilli tuffs with abundant volcanic bombs. Ash tuffs are infrequent, as are structures such as crossbedding. The bombs and lapilli include olivine and plagioclase phenocrysts. The basalts are alkaline and have intraplate-type normalized incompatible element patterns. Both complexes are enriched in LREE compared to HREE, though the north complex overall has lower concentrations of the REE. The flat HREE pattern is indicative of spinel peridotite mantle source. Epsilon Nd values for the north complex are +2.50+/-0.02 and for the south complex are +2.83+/-0.02. The magmas appear to have an enriched asthenospheric mantle source. Bomb samples show that eruptions from the two complexes are geochemically distinguishable both in major and trace elements, suggesting that the two complexes tapped different magma types during eruptions that likely occurred at slightly different times. The proximity of Upsal Hogback to Fallon makes constraining its age important to characterize the hazard to the city. It lies above the Wono ash bed, dated at 25,000 years (Fultz et al., 1983), and tufa deposited over the edifice is dated at 11,100 +/- 100 and 8,600 +/- 200 years (Benson et al., 1992; Broecker and Kaufman, 1965). 40Ar/39Ar total gas age by Shevenell et al. (2005) dated the volcano at 0.60 +/- 0.09 Ma, but with no plateau or isochron, and is thus unreliable. The ash bed and tufa ages show that the eruptions would have occurred during the late history of glacial Lake Lahontan. The evidence for primarily subaerial or shallow subaqueous eruptions, including abundant bomb sags and armored lapilli, demonstrate that most of the volcanism occurred during a low stand in lake level history. Some upper tuff units have been heavily altered to palagonite, which establishes that there was substantial water present during some of the later eruptions. The upper edifice has been significantly modified by slumping of the lapilli tuffs during or after of the eruptions, as indicated by the wildly varying strikes and dips found in adjacent lapilli tuff blocks. Lake Lahontan has substantially altered the morphology of the volcano through wave action and shoreline erosion, as well as tufa deposition, since the eruption and emplacement of the tuffs. The edifice has gone through significant changes during its post-eruptive history that mask many of its original features; it was possible that it was a tuff cone that has been modified into a tuff ring.

SHRIMP U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana: Evidence for rapid deposition of sedimentary strata

USGS Publications Warehouse

Evans, K.V.; Aleinikoff, J.N.; Obradovich, J.D.; Fanning, C.M.

2000-01-01

New sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon analyses from two tuffs and a felsic flow in the middle and upper Belt Supergroup of northwestern Montana significantly refine the age of sedimentation for this very thick (15-20 km) Middle Proterozoic stratigraphic sequence. In ascending stratigraphic order, the results are (1) 1454 ?? 9 Ma for a tuff in the upper part of the Helena Formation at Logan Pass, Glacier National Park; (2) 1443 ?? 7 Ma for a regionally restricted porphyritic rhyolite to quartz latite flow of the Purcell Lava in the Yaak River region; and (3) 1401 ?? 6 Ma for a tuff in the very thin transition zone between the Bonner Quartzite and Libby Formation, west of the town of Libby. Combining these ages with those previously published by other workers for ca. 1470-Ma sills in the lower Belt in Montana and Canada indicates that all but the uppermost Belt strata (about 1700 m) were deposited over a period of about 70 million years, considerably reducing the time span from longstanding estimates ranging from 250 to 600 million years. Calculated sediment accumulation rates between dated samples indicates rapid, but not unreasonable, values for early Belt strata, with decreasing rates through time. These ages also suggest the inadequacy of previously published paleomagnetic data to resolve Belt Supergroup chronology at an appropriate level of accuracy.

The influence of water on the strength of Neapolitan Yellow Tuff, the most widely used building stone in Naples (Italy)

NASA Astrophysics Data System (ADS)

Heap, Michael J.; Farquharson, Jamie I.; Kushnir, Alexandra R. L.; Lavallée, Yan; Baud, Patrick; Gilg, H. Albert; Reuschlé, Thierry

2018-06-01

Neapolitan Yellow Tuff (NYT) has been used in construction in Naples (Italy) since the Greeks founded the city—then called Neapolis—in the sixth century BCE. We investigate here whether this popular building stone is weaker when saturated with water, an issue important for assessments of weathering damage and monument preservation. To this end, we performed 28 uniaxial compressive strength measurements on dry and water-saturated samples cored from a block of the lithified Upper Member of the NYT. Our experiments show that the strength of the zeolite-rich NYT is systematically reduced when saturated with water (the ratio of wet to dry strength is 0.63). Complementary experiments show that two other common Neapolitan building stones—Piperno Tuff and the grey Campanian Ignimbrite (both facies of the Campanian Ignimbrite deposit devoid of zeolites)—do not weaken when wet. From these data, and previously published data for tuffs around the globe, we conclude that the water-weakening in NYT is a consequence of the presence of abundant zeolites (the block tested herein contains 46 wt.% of zeolites). These data may help explain weathering damage in NYT building stones (due to rainfall, rising damp, and proximity to the sea or water table) and the observed link between rainfall and landslides, rock falls, and sinkhole formation in Naples, and the weathering of other buildings built from zeolite-rich tuffs worldwide.

Tephra layers of blind Spring Valley and related upper pliocene and pleistocene tephra layers, California, Nevada, and Utah: isotopic ages, correlation, and magnetostratigraphy

USGS Publications Warehouse

Sarna-Wojcicki, Andrei M.; Reheis, Marith C.; Pringle, Malcolm S.; Fleck, Robert J.; Burbank, Doug; Meyer, Charles E.; Slate, Janet L.; Wan, Elmira; Budahn, James R.; Troxel, Bennie; Walker, James P.

2005-01-01

Numerical ages have been determined for a stratigraphic sequence of silicic tephra layers exposed at the Cowan Pumice Mine in Blind Spring Valley, near Benton Hot Springs, east-central California, as well as at Chalk Cliffs, north of Bishop, Calif. The tephra layers at these sites were deposited after eruptions from nearby sources, most of them from near Glass Mountain, and some from unknown sources. The ages were determined primarily by the laser-fusion 40Ar/39Ar method, mostly on sanidine feldspar; two were determined by conventional K-Ar analysis on obsidian clasts. These tephra layers, all underlying the Bishop ash bed and listed in order of concordant age and stratigraphic position, are: Tephra Unit Method Material Age Bishop Tuff (air-fall pumice) Ar/Ar sanidine 0.759?0.002 Ma* Upper tuffs of Glass Mountain Ar/Ar sanidine 0.87?0.02 Ma Upper tuffs of Glass Mountain Ar/Ar sanidine 1.13?0.19 Ma Lower tuffs of Glass Mountain K-Ar obsidian 1.86?0.09 Ma (avg of 2 dates) Ar/Ar sanidine 1.92?0.02 Ma (avg of 2 dates) Tuffs of Blind Spring Valley Ar/Ar sanidine 2.135?0.02 to sanidine 2.219?0.006 Ma (10 dates) Tuffs of Benton Hot Springs Ar/Ar plagioclase 2.81?0.02 Ma *Date published previously The above tephra layers were also petrographically examined and the volcanic glass shards of the layers were chemically analyzed using the electron microprobe and, for some samples, instrumental neutron activation analysis and X-ray fluorescence. The same types of chemical and petrographic analyses were conducted on stratigraphic sequences of tephra layers of suspected upper Pliocene and Pleistocene age in several past and present depositional basins within the region outside of Blind Spring Valley. Chemical characterization, combined with additional dates and with magnetostratigraphy of thick sections at two of the distal sites, allow correlation of the tephra layers at the Cowan Pumice Mine with layers present at the distal sites and provide age constraints for other intercalated tephra layers and sediments for which age data were previously lacking. The identification at several sections of the widespread Huckleberry Ridge ash bed, derived from the Yellowstone eruptive source area in Wyoming, as well as a new 40Ar/39Ar age on this ash bed from a proximal locality, provide additional age constraints to several of the distal sections. The dated or temporally bracketed distal units, in order of concordant age and stratigraphic position, are: Tephra Unit Method Material Age Tephra layers of Glass Mountain (undiff.) P-mag.*; correlation N/A 1.78 , 1.96, 1.96, 2.22, 2.57, <2.89 Ma Tephra layers of Benton Hot Springs Ar/Ar; correlation plagioclase 2.89?0.03 Ma *Magnetostratigraphic polarity determination At the Cowan Pumice Mine, only a partial section of the eruptive record is preserved, but the best materials for laser-fusion 40Ar/39Ar and other isotopic dating methods were obtained. In the more distal Willow Wash and Confidence Hills sections, both persistent depositional basins for most of late Pliocene time, more complete sections of upper Pliocene tephra layers were preserved. In the region of Glass Mountain, the tephra layers that make up each of the mapped and dated pyroclastic units are multiple and complex, but a progressive simplification of the stratigraphy away from the source area was observed for more distal sites in southern and southwestern California and in Utah. This progressive

High-resolution record of the Matuyama–Brunhes transition constrains the age of Javanese Homo erectus in the Sangiran dome, Indonesia

PubMed Central

Hyodo, Masayuki; Matsu'ura, Shuji; Kamishima, Yuko; Kondo, Megumi; Takeshita, Yoshihiro; Kitaba, Ikuko; Danhara, Tohru; Aziz, Fachroel; Kurniawan, Iwan; Kumai, Hisao

2011-01-01

A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama–Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands’ lavas, which have a mean 40Ar/39Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area. PMID:22106291

High-resolution record of the Matuyama-Brunhes transition constrains the age of Javanese Homo erectus in the Sangiran dome, Indonesia.

PubMed

Hyodo, Masayuki; Matsu'ura, Shuji; Kamishima, Yuko; Kondo, Megumi; Takeshita, Yoshihiro; Kitaba, Ikuko; Danhara, Tohru; Aziz, Fachroel; Kurniawan, Iwan; Kumai, Hisao

2011-12-06

A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama-Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands' lavas, which have a mean (40)Ar/(39)Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area.

Rapid pre-eruptive thermal rejuvenation in a large silicic magma body: the case of the Masonic Park Tuff, Southern Rocky Mountain volcanic field, CO, USA

NASA Astrophysics Data System (ADS)

Sliwinski, J. T.; Bachmann, O.; Dungan, M. A.; Huber, C.; Deering, C. D.; Lipman, P. W.; Martin, L. H. J.; Liebske, C.

2017-05-01

Determining the mechanisms involved in generating large-volume eruptions (>100 km3) of silicic magma with crystallinities approaching rheological lock-up ( 50 vol% crystals) remains a challenge for volcanologists. The Cenozoic Southern Rocky Mountain volcanic field, in Colorado and northernmost New Mexico, USA, produced ten such crystal-rich ignimbrites within 3 m.y. This work focuses on the 28.7 Ma Masonic Park Tuff, a dacitic ( 62-65 wt% SiO2) ignimbrite with an estimated erupted volume of 500 km3 and an average of 45 vol% crystals. Near-absence of quartz, titanite, and sanidine, pronounced An-rich spikes near the rims of plagioclase, and reverse zoning in clinopyroxene record the reheating (from 750 to >800 °C) of an upper crustal mush in response to hotter recharge from below. Zircon U-Pb ages suggest prolonged magmatic residence, while Yb/Dy vs temperature trends indicate co-crystallization with titanite which was later resorbed. High Sr, Ba, and Ti concentrations in plagioclase microlites and phenocryst rims require in-situ feldspar melting and concurrent, but limited, mass addition provided by the recharge, likely in the form of a melt-gas mixture. The larger Fish Canyon Tuff, which erupted from the same location 0.7 m.y. later, also underwent pre-eruptive reheating and partial melting of quartz, titanite, and feldspars in a long-lived upper crustal mush following the underplating of hotter magma. The Fish Canyon Tuff, however, records cooler pre-eruptive temperatures ( 710-760 °C) and a mineral assemblage indicative of higher magmatic water contents (abundant resorbed sanidine and quartz, euhedral amphibole and titanite, and absence of pyroxene). These similar pre-eruptive mush-reactivation histories, despite differing mineral assemblages and pre-eruptive temperatures, indicate that thermal rejuvenation is a key step in the eruption of crystal-rich silicic volcanics over a wide range of conditions.

Geochronological and Taxonomic Revisions of the Middle Eocene Whistler Squat Quarry (Devil’s Graveyard Formation, Texas) and Implications for the Early Uintan in Trans-Pecos Texas

PubMed Central

Campisano, Christopher J.; Kirk, E. Christopher; Townsend, K. E. Beth; Deino, Alan L.

2014-01-01

The Whistler Squat Quarry (TMM 41372) of the lower Devil’s Graveyard Formation in Trans-Pecos Texas is a middle Eocene fossil locality attributed to Uintan biochronological zone Ui1b. Specimens from the Whistler Squat Quarry were collected immediately above a volcanic tuff with prior K/Ar ages ranging from ∼47–50 Ma and below a tuff previously dated to ∼44 Ma. New 40Ar/39Ar analyses of both of the original tuff samples provide statistically indistinguishable ages of 44.88±0.04 Ma for the lower tuff and 45.04±0.10 Ma for the upper tuff. These dates are compatible with magnetically reversed sediments at the site attributable to C20r (43.505–45.942 Ma) and a stratigraphic position above a basalt dated to 46.80 Ma. Our reanalysis of mammalian specimens from the Whistler Squat Quarry and a stratigraphically equivalent locality significantly revises their faunal lists, confirms the early Uintan designation for the sites, and highlights several biogeographic and biochronological differences when compared to stratotypes in the Bridger and Uinta Formations. Previous suggestions of regional endemism in the early Uintan are supported by the recognition of six endemic taxa (26% of mammalian taxa) from the Whistler Squat Quarry alone, including three new taxa. The revised faunal list for the Whistler Squat Quarry also extends the biostratigraphic ranges of nine non-endemic mammalian taxa to Ui1b. PMID:24988115

Eruptive history, petrology, and petrogenesis of the Joe Lott Tuff Member of the Mount Belknap Volcanics, Marysvale volcanic field, west-central Utah

USGS Publications Warehouse

Budding, Karin E.

1982-01-01

The Joe Lott Tuff Member of the Mount Belknap Volcanics is the largest rhyolitic ash-flow tuff sheet in the Marysvale volcanic field. It was erupted 19 m.y. ago, shortly after the changeover from intermediate-composition calc-alkalic volcanism to bimodal basalt-rhyolite volcanism. Eruption of the tuff resulted in the formation of the Mount Belknap Caldera whose pyroclastic intracaldera stratigraphy parallels that in the outflow facies. The Joe Loft Tuff Member is a composite ash-flow sheet that changes laterally from a simple cooling unit near the source to four distinct cooling units toward the distal end. The lowest of these units is the largest and most widespread; it is 64 m thick and contains a basal vitrophyre. Eruption of the lower unit led to the initial collapse of the caldera. The lower unit is followed upward by a 43 m middle unit, a 26 m pink-colored unit which is separated by a prominent air- fall layer, and a 31 m upper unit. The Joe Loft Tuff Member is an alkali rhyolite with 75.85-77.31 wt. % silica and 8.06-9.32 wt. % K2O+Na2O; the agpaitic index (Na2O+ K2O/Al2O3) is .77-.98. The tuff contains about I% phenocrysts of quartz, sanidine, oligoclase, augite, apatite, zircon, sphene, biotite, and oxidized Fe-Ti oxides. The basal vitrophyre contains accessory allanite, chevkinite, and magnesiohastingsite. The main cooling units are chemically and mineralogically zoned indicating that the magma chamber restratified prior to each major eruption. Within each of the two thickest cooling units, the mineralogy changes systematically upwards; the Or content and relative volume of sanidine decreases and An content of plagioclase increases. The basal vitrophyre of the lower unit has a bulk composition that lies in the thermal trough near the minima of Or-Ab-Q at 1 kb PH2O. Microprobe analyses of feldspar and chemical modeling on experimental systems indicate that pre-eruption temperatures were near 750?C and that the temperature increased during the eruption of the cooling units. The chemical gradients in the apatite and whole-rock data in the Joe Loft Tuff Member and the consistent mineral assemblages throughout the ash-flow cannot be explained by crystal settling. The fractionation of the Joe Lott Tuff Member appears to closer fit the model of convection-driven thermogravitational diffusion.

Secondary Mineral Deposits and Evidence of Past Seismicity and Heating of the Proposed Repository Horizon at Yucca Mountain, Nevada

USGS Publications Warehouse

Whelan, Josheph F.

2004-01-01

The Drift Degradation Analysis (DDA) (BSC, 2003) for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, describes model simulations of the effects of pre- and post-closure seismicity and waste-induced heating on emplacement drifts. Based on probabilistic seismic hazard analyses of the intensity and frequency of future seismic events in the region (CRWMS M&O, 1998), the DDA concludes that future seismicity will lead to substantial damage to emplacement drifts, particularly those in the lithophysal tuffs, where some simulations predict complete collapse of the drift walls. Secondary mineral studies conducted by the U.S. Geological Survey since 1995 indicate that secondary calcite and silica have been deposited in some fractures and lithophysal cavities in the unsaturated zone (UZ) at Yucca Mountain during at least the past 10 million years (m.y.), and probably since the tuffs cooled to less than 100?C. Tuff fragments, likely generated by past seismic activity, have commonly been incorporated into the secondary mineral depositional sequences. Preliminary observations indicate that seismic activity has generated few, if any, tuff fragments during the last 2 to 4 m.y., which may be inconsistent with the predictions of drift-wall collapse described in the DDA. Whether or not seismicity-induced tuff fragmentation occurring at centimeter to decimeter scales in the fracture and cavity openings relates directly to failure of tuff walls in the 5.5-m-diameter waste emplacement drifts, the deposits do provide a potential record of the spatial and temporal distribution of tuff fragments in the UZ. In addition, the preservation of weakly attached coatings and (or) delicate, upright blades of calcite in the secondary mineral deposits provides an upper limit for ground motion during the late stage of deposition that might be used as input to future DDA simulations. Finally, bleaching and alteration at a few of the secondary mineral sites indicate that they were subjected to heated gases at approximately the temperatures expected from waste emplacement. These deposits provide at least limited textural and mineralogic analogs for waste-induced, high-humidity thermal alteration of emplacement drift wall rocks.

Volcanism at 1.45 Ma within the Yellowstone Volcanic Field, United States

NASA Astrophysics Data System (ADS)

Rivera, Tiffany A.; Furlong, Ryan; Vincent, Jaime; Gardiner, Stephanie; Jicha, Brian R.; Schmitz, Mark D.; Lippert, Peter C.

2018-05-01

Rhyolitic volcanism in the Yellowstone Volcanic Field has spanned over two million years and consisted of both explosive caldera-forming eruptions and smaller effusive flows and domes. Effusive eruptions have been documented preceding and following caldera-forming eruptions, however the temporal and petrogenetic relationships of these magmas to the caldera-forming eruptions are relatively unknown. Here we present new 40Ar/39Ar dates for four small-volume eruptions located on the western rim of the second-cycle caldera, the source of the 1.300 ± 0.001 Ma Mesa Falls Tuff. We supplement our new eruption ages with whole rock major and trace element chemistry, Pb isotopic ratios of feldspar, and paleomagnetic and rock magnetic analyses. Eruption ages for the effusive Green Canyon Flow (1.299 ± 0.002 Ma) and Moonshine Mountain Dome (1.302 ± 0.003 Ma) are in close temporal proximity to the eruption age of the Mesa Falls Tuff. In contrast, our results indicate a period of volcanism at ca 1.45 Ma within the Yellowstone Volcanic Field, including the eruption of the Bishop Mountain Flow (1.458 ± 0.002 Ma) and Tuff of Lyle Spring (1.450 ± 0.003 Ma). These high-silica rhyolites are chemically and isotopically distinct from the Mesa Falls Tuff and related 1.3 Ma effusive eruptions. The 40Ar/39Ar data from the Tuff of Lyle Spring demonstrate significant antecrystic inheritance, prevalent within the upper welded ash-flow tuff matrix, and minimal within individual pumice. Antecrysts are up to 20 kyr older than the eruption, with subpopulations of grains occurring every few thousand years. We interpret these results as an indicator for the timing of magmatic pulses into a growing magmatic system that would ultimately erupt the Tuff of Lyle Spring, and which we more broadly interpret as the tempo of crustal accumulation associated with bimodal magmatism. We propose a system whereby chemically, isotopically, and temporally distinct, isolated small-volume magma batches are periodically generated and erupted in a low magmatic flux state, which is punctuated by larger volume caldera-forming eruptions.

Miocene calc-alkaline magmatism, calderas, and crustal extension in the Kofa and Castle Dome Mountains, southwestern Arizona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grubensky, M.J.; Bagby, W.C.

1990-11-10

Two widespread lower Miocene rhyolite ash flow tuffs in the Kofa and Castle Dome Mountains of southwestern Arizona are products of caldera-forming eruptions. These closely erupted tuffs, the tuff of Yaqui Tanks and the tuff of Ten Ewe Mountain, are approximately 22 Ma in age and their eruptions culminate a 1- to 2-m.y.-long burst of calc-alkaline volcanic activity centered on the northern Castle Dome Mountains. Exotic blocks of Proterozoic and Mesozoic crystalline rocks up to 20 m across are present in exposures of the tuff of Yaqui Tanks exposed in the central Castle Dome Mountains and the southern Kofa Mountains.more » A single, thick cooling unit of the tuff of Ten Ewe Mountain that includes thick lenses of mesobreccia marks the location of the younger caldera that extends from Palm Canyon in the western Kofa Mountains eastward more than 7 km along strike to the central part of the range. Large residual Bouguer gravity anomalies, one beneath each inferred caldera, are interpreted as batholithic rocks or low-density caldera fill. Caldera-related volcanism in the Kofa region occurred during a transition in extensional tectonic regimes: From a regime of east-west trending uplifts and basins to a regime manifest primarily by northwest striking normal faults. A narrow corridor of folding and strike-slip faulting formed during volcanism in the southern Kofa Mountains. Upper Oligocene or lower Miocene coarse sedimentary rocks along the southern flank of the Chocolate Mountains anticlinorium in the southern Castle Dome Mountains mark the periphery of a basin similar to other early and middle Tertiary basins exposed in southern California. The volcanic section of the Kofa region was dissected by high-angle normal faults related to northeast-southwest oriented crustal extension typical of the southern Basin and Range province.« less

Volcanic Stratigraphy of the Quaternary Rhyolite Plateau in Yellowstone National Park

USGS Publications Warehouse

Christiansen, Robert L.; Blank, H. Richard

1972-01-01

The volcanic sequence of the Quaternary Yellowstone plateau consists of rhyolites and basalts representing three volcanic cycles. The major events of each cycle were eruption of a voluminous ash-flow sheet and formation of a large collapse caldera. Lesser events of each cycle were eruption of precaldera and postcaldera rhyolitic lava flows and marginal basaltic lavas. The three major ash-flow sheets are named and designated in this report as formations within the Yellowstone Group. The lavas are assigned to newly named formations organized around the three ash-flow sheets of the Yellowstone Group to represent the volcanic cycles. Rocks of the first volcanic cycle comprise the precaldera Junction Butte Basalt and rhyolite of Broad Creek; the Huckleberry Ridge Tuff of the Yellowstone Group; and the postcaldera Lewis Canyon Rhyolite and basalt of The Narrows. Rocks of the second volcanic cycle do not crop out within Yellowstone National Park, and only the major unit, the Mesa Falls Tuff of the Yellowstone Group, is named here. The third volcanic cycle is represented by the precaldera Mount Jackson Rhyolite and Undine Falls Basalt; the Lava Creek Tuff of the Yellowstone Group; and the postcaldera Plateau Rhyolite and five post-Lava Creek basaltic sequences. Collapse to form the compound and resurgent Yellowstone caldera was related to eruption of the Lava Creek Tuff. The Plateau Rhyolite is divided into six members - the Mallard Lake, Upper Basin, Obsidian Creek, Central Plateau, Shoshone Lake Tuff, and Roaring Mountain Members; all but the Mallard Lake postdate resurgent doming of the caldera. The basalts are divided into the Swan Lake Flat Basalt, Falls River Basalt, basalt of Mariposa Lake, Madison River Basalt, and Osprey Basalt. Sediments are intercalated in the volcanic section below the Huckleberry Ridge and Mesa Falls Tuffs and within the Junction Butte Basalt, sediments and basalts of The Narrows, Undine Falls Basalt, Plateau Rhyolite, and Osprey Basalt.

Low-(18)O Silicic Magmas: Why Are They So Rare?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balsley, S.D.; Gregory, R.T.

1998-10-15

LOW-180 silicic magmas are reported from only a small number of localities (e.g., Yellowstone and Iceland), yet petrologic evidence points to upper crustal assimilation coupled with fractional crystallization (AFC) during magma genesis for nearly all silicic magmas. The rarity of 10W-l `O magmas in intracontinental caldera settings is remarkable given the evidence of intense 10W-l*O meteoric hydrothermal alteration in the subvolcanic remnants of larger caldera systems. In the Platoro caldera complex, regional ignimbrites (150-1000 km3) have plagioclase 6180 values of 6.8 + 0.1%., whereas the Middle Tuff, a small-volume (est. 50-100 km3) post-caldera collapse pyroclastic sequence, has plagioclase 8]80 valuesmore » between 5.5 and 6.8%o. On average, the plagioclase phenocrysts from the Middle Tuff are depleted by only 0.3%0 relative to those in the regional tuffs. At Yellowstone, small-volume post-caldera collapse intracaldera rhyolites are up to 5.5%o depleted relative to the regional ignimbrites. Two important differences between the Middle Tuff and the Yellowstone 10W-180 rhyolites elucidate the problem. Middle Tuff magmas reached water saturation and erupted explosively, whereas most of the 10W-l 80 Yellowstone rhyolites erupted effusively as domes or flows, and are nearly devoid of hydrous phenocrysts. Comparing the two eruptive types indicates that assimilation of 10W-180 material, combined with fractional crystallization, drives silicic melts to water oversaturation. Water saturated magmas either erupt explosively or quench as subsurface porphyrins bejiire the magmatic 180 can be dramatically lowered. Partial melting of low- 180 subvolcanic rocks by near-anhydrous magmas at Yellowstone produced small- volume, 10W-180 magmas directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.« less

Mesozoic ash-flow caldera fragments in southeastern Arizona and their relation to porphyry copper deposits.

USGS Publications Warehouse

Lipman, P.W.; Sawyer, D.A.

1985-01-01

Jurassic and Upper Cretaceous volcanic and associated granitic rocks in SE Arizona are remnants of large composite silicic volcanic fields, characterized by voluminous ash-flow tuffs and associated calderas. Presence of 10-15 large caldera fragments is inferred primarily from 1) ash-flow deposits over 1 km thick, having features of inter-caldera ponding; 2) 'exotic-block' breccia within a tuff matrix, interpreted as caldera-collapse megabreccia; and 3) local granitic intrusion along arcuate structural boundaries of the thick volcanics. Several major porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins. Such close spatial and temporal association casts doubt on models that associate porphyry copper deposits exclusively with intermediate composition strato-volcanoes. -L.C.H.

Magnetic properties and emplacement of the Bishop tuff, California

USGS Publications Warehouse

Palmer, H.C.; MacDonald, W.D.; Gromme, C.S.; Ellwood, B.B.

1996-01-01

Anisotropy of magnetic susceptibility (AMS) and characteristic remanence were measured for 45 sites in the 0.76 Ma Bishop tuff, eastern California. Thirty-three sites were sampled in three stratigraphic sections, two in Owens gorge south of Long Valley caldera, and the third in the Adobe lobe north of Long Valley. The remaining 12 sites are widely distributed, but of limited stratigraphic extent. Weakly indurated, highly porous to dense, welded ash-flow tuffs were sampled. Saturation magnetization vs temperature experiments indicate two principal iron oxide phases: low Ti magnetites with 525-570 ??C Curie temperatures, and maghemite with 610??-640??C Curie temperatures. AF demagnetization spectra of isothermal remanent magnetizations are indicative of magnetite/maghemite predominantly in the multidomain to pseudo-single domain size ranges. Remeasurement of AMS after application of saturating direct fields indicates that randomly oriented single-domain grains are also present. The degree of anisotropy is only a few percent, typical of tuffs. The AMS ellipsoids are oblate with Kmin axes normal to subhorizontal foliation and Kmax axes regionally aligned with published source vents. For 12 of 16 locality means, Kmax axes plunge sourceward, confirming previous observations regarding flow sense. Topographic control on flow emplacement is indicated by the distribution of tuff deposits and by flow directions inferred from Kmax axes. Deposition east of the Benton range occurred by flow around the south end of the range and through two gaps (Benton notch and Chidago gap). Flow down Mammoth pass of the Sierra Nevada is also evident. At least some of the Adobe lobe in the northeast flowed around the west end of Glass mountain. Eastward flow directions in the upper Owens gorge and southeast directions in the lower Owens gorge are parallel to the present canyon, suggesting that the present drainage has been established along the pre-Bishop paleodrainage. Characteristic remanence directions from 45 sites (267 samples) yield an overall mean of D = 348??, I = 53?? for the Bishop tuff. A correlation is found in two of the three profiles between density and remanence inclination. A mean remanence direction based on 13 localities together with data from uncompacted xenoliths and data from the ash-fall tuff at Lake Tecopa is: D = 353??, I = 54??, k = 172, ??95 = 2.9??, N = 15.

Magnetic properties and emplacement of the Bishop tuff, California

NASA Astrophysics Data System (ADS)

Palmer, H. C.; MacDonald, W. D.; Gromme, C. S.; Ellwood, B. B.

1996-09-01

Anisotropy of magnetic susceptibility (AMS) and characteristic remanence were measured for 45 sites in the 0.76 Ma Bishop tuff, eastern California. Thirty-three sites were sampled in three stratigraphic sections, two in Owens gorge south of Long Valley caldera, and the third in the Adobe lobe north of Long Valley. The remaining 12 sites are widely distributed, but of limited stratigraphic extent. Weakly indurated, highly porous to dense, welded ash-flow tuffs were sampled. Saturation magnetization vs temperature experiments indicate two principal iron oxide phases: low Ti magnetites with 525 570 °C Curie temperatures, and maghemite with 610° 640 °C Curie temperatures. AF demagnetization spectra of isothermal remanent magnetizations are indicative of magnetite/maghemite predominantly in the multidomain to pseudo-single domain size ranges. Remeasurement of AMS after application of saturating direct fields indicates that randomly oriented single-domain grains are also present. The degree of anisotropy is only a few percent, typical of tuffs. The AMS ellipsoids are oblate with Kmin axes normal to subhorizontal foliation and Kmax axes regionally aligned with published source vents. For 12 of 16 locality means, Kmax axes plunge sourceward, confirming previous observations regarding flow sense. Topographic control on flow emplacement is indicated by the distribution of tuff deposits and by flow directions inferred from Kmax axes. Deposition east of the Benton range occurred by flow around the south end of the range and through two gaps (Benton notch and Chidago gap). Flow down Mammoth pass of the Sierra Nevada is also evident. At least some of the Adobe lobe in the northeast flowed around the west end of Glass mountain. Eastward flow directions in the upper Owens gorge and southeast directions in the lower Owens gorge are parallel to the present canyon, suggesting that the present drainage has been established along the pre-Bishop paleodrainage. Characteristic remanence directions from 45 sites (267 samples) yield an overall mean of D=348°, I=53° for the Bishop tuff. A correlation is found in two of the three profiles between density and remanence inclination. A mean remanence direction based on 13 localities together with data from uncompacted xenoliths and data from the ash-fall tuff at Lake Tecopa is: D=353°, I=54°, k=172, α95=2.9°, N=15.

Physical and Thermal Structure of the Bishop Tuff, California

NASA Astrophysics Data System (ADS)

Wilson, C. J.; Hildreth, W.

2001-12-01

The 0.76 Ma Bishop Tuff, California, includes an ignimbrite constructed from a series of overlapping packages of material erupted sequentially and simultaneously from multiple sources around the ring fracture of Long Valley caldera (Wilson, C.J.N., Hildreth, W., 1997, Journal of Geology 105, 407-439). Exceptionally good continuous exposures of the ignimbrite in the walls of Owens Gorge to the east of Long Valley provide a cross-section through the east-side packages (Ig1E and Ig2E). We have measured 10 sections up the gorge walls to draw up a cross section of the ignimbrite down Owens Gorge, using lithic abundances and lithologies to define the physical eruptive packages and their subdivisions, and measurements of tuff bulk density (as an easily measured proxy for welding intensity) to define the thermal eruptive packages. The physically emplaced bodies of ignimbrite represent an overlapping, shingling suite of material such that successively later ignimbrite occurs most prominently farther away from source. Two major and two lesser zones of maximum density (welding) are present, the lower two (in Ig1Ea and lower Ig1Eb) in upper Owens Gorge, and the two most prominent (upper Ig1Eb and Ig2Eb) in middle and lower parts of the gorge. Welding fluctuations are controlled by bulk temperatures of individual batches of hotter and cooler material, but the intensity of the welding also depends on deposit thickness (i.e. load stress). Physically defined contacts between ignimbrite packages show that time breaks inferred to be of hours may not result in formation of any visible parting or flow unit boundary. Furthermore, positions of density (welding) minima between zones of higher density tuff do not coincide with horizons of stratigraphic significance. These observations lead to two conclusions. (1) The absence of clear partings or flow unit boundaries in an ignimbrite sequence is not diagnostic either of the material representing a single flow unit, or of the material being continuously progressively aggraded. (2) Use of the density (welding) minimum to locate the boundaries of cooling units and in measuring and modelling the emplacement and thermal history of compound cooling units may lead to errors.

Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling

NASA Astrophysics Data System (ADS)

Pritchard, Chad J.; Larson, Peter B.

2012-08-01

An array of samples from the eastern Upper Basin Member of the Plateau Rhyolite (EUBM) in the Yellowstone Plateau, Wyoming, were collected and analyzed to evaluate styles of deposition, geochemical variation, and plausible sources for low δ18O rhyolites. Similar depositional styles and geochemistry suggest that the Tuff of Sulphur Creek and Tuff of Uncle Tom's Trail were both deposited from pyroclastic density currents and are most likely part of the same unit. The middle unit of the EUBM, the Canyon flow, may be composed of multiple flows based on a wide range of Pb isotopic ratios (e.g., 206Pb/204Pb ranges from 17.54 to 17.86). The youngest EUBM, the Dunraven Road flow, appears to be a ring fracture dome and contains isotopic ratios and sparse phenocrysts that are similar to extra-caldera rhyolites of the younger Roaring Mountain Member. Petrologic textures, more radiogenic 87Sr/86Sr in plagioclase phenocrysts (0.7134-0.7185) than groundmass and whole-rock ratios (0.7099-0.7161), and δ18O depletions on the order of 5‰ found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving an initial source rock formed by assimilation and fractional crystallization processes, which cooled and was hydrothermally altered. The source rock was then lowered to melting depth by caldera collapse and remelted and erupted. The presence of a low δ18O extra-caldera rhyolite indicates that country rock may have been hydrothermally altered at depth and then assimilated to form the Dunraven Road flow.

Absolute Paleointensity Study of Miocene Tiva Canyon Tuff, Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Patiman, A.; Bowles, J.

2014-12-01

Unoriented samples from the ~12.7 Ma Tiva Canyon (TC) tuff from Yucca Mountain, Nevada are studied in terms of magnetic properties and geomagnetic paleointensity. The magnetic mineralogy and magnetic properties of the TC tuff have previously been well documented, and the remanence-carrier in ~15-m thick zones at the top and bottom of the unit is dominantly is single domain (SD) to superparamagnetic (SP) magnetite, which may be considered ideal for absolute paleointensity studies. Among one of the several episodic volcanic eruptions of the Southwestern Nevada Volcanic Field (SWNVF), the welded TC tuff belongs to the Paintbrush Group. Here we present magnetic properties from two previously unreported sections of the TC tuff, as well as Thellier-type absolute paleointensity estimates. Samples were collected from the lower ~7 m at the base of the flow. Magnetic properties studied include hysteresis, bulk magnetic susceptibility, frequency-dependent susceptibility, and anhysteretic remanent magnetization acquisition. Magnetic property results are consistent with earlier work, showing that the main magnetic mineral is magnetite. SP samples are dominant from the lower ~1 m to ~3.6 m basal unit while the middle unit of ~3.7 m to 7.0 m mainly consists of SD samples. The paleointensity results are closely tied to the stratigraphic height and magnetic properties linked to domain state. The SD samples have consistent absolute paleointensity values 32.40±0.22 uT, VADM 5.74*1022 A.m2 and behaved ideally during paleointensity experiments. The SP samples have consistently higher paleointensity and less ideal behavior, but would likely pass many traditional quality-control tests. Since the magnetite has been interpreted to form by precipitation out of the glass post-emplacement, but at temperatures higher than the Curie temperature, we tentatively interpret the SD remanence to be a primary thermal remanent magnetization and the paleointensity result to be a valid estimate of geomagnetic paleointensity for the Miocene. Post-emplacement vapor-phase alteration might be expected to alter magnetic mineralogy and magnetization, and has been reported in the upper portions of the TC tuff, but not in the lower sections discussed here.

Dacitic ash-flow sheet near Superior and Globe, Arizona

USGS Publications Warehouse

Peterson, Donald W.

1961-01-01

Remnants of a dacitic ash-flow sheet near Globe, Miama, and Superia, Arizona cover about 100 square miles; before erosion the area covered by the sheet was at least 400 square miles and perhaps as much as 1,500 square miles. Its maximum thickness is about 2,000 feet, its average thickness is about 500 feet, and its original volume was at least 40 cubic miles. It was erupted on an eroded surface with considerable relief. The main part of the deposit was thought by early workers to be a lava flow. Even after the distinctive character of welded tuffs and related rocks was discovered, the nature and origin of this deposit remained dubious because textures did not correspond to those in other welded tuff bodies. Yet a lava flow as silicic as this dacite would be viscous instead of spreading out as an extensive sheet. The purpose of this investigation has been to study the deposit, resolve the inconsistencies, and deduce its origin and history. Five stratigraphic zones are distinguished according to differences in the groundmass. From bottom to top the zones are basal tuff, vitrophyre, brown zone, gray zone, and white zone. The three upper zones are distinguished by colors on fresh surfaces, for each weathers to a similar shade of light reddish brown. Nonwelded basal tuff grades upward into the vitrophyre, which is a highly welded tuff. The brown and gray zones consist of highly welded tuff with a lithoidal groundmass. Degree of welding decreases progressively upward through the gray and the white zones, and the upper white zone is nonwelded. Textures are clearly outlined in the lower part of the brown zone, but upward they become more diffuse because of increasing devitrification. In the white zone, original textures are essentially obliterated, and the groundmass consists of spherulites and microcrystalline intergrowths. The chief groundmass minerals are cristobalite and sanidine, with lesser quartz and plagioclase. Phenocrysts comprise about 40 percent of the rock, and their relative proportions are fairly uniform. Almost three-fourths of the phenocrysts are plagioclase, one-tenth quartz, one-tenth biotite, and the remainder sanidine, magnetite, and hornblende, with accessory sphene, zircon, and appetite. Pumice fragments are nearly equidimensional near the top of the sheet, and downward they become progressively more flattened until they finally disappear. The zones and the pumice fragment flattening ration (ratio of length to height) provide means for recognizing several faults within the sheet. Twelve new chemical analyses are nearly uniform in composition. If named according to chemical composition, the rock would be a quartz latite, but when named according to phenocrysts, it is a dacite. From the field occurrence and the interpretation of relict textures, it is concluded that the deposit is an ash-flow sheet containing large amounts of welded tuff, and that it was emplaced by a type of nuee ardente instead of a lava flow or air-fall shower. The nature of zoning and trend of flattening ratios indicate a series of eruptions in rapid enough succession for the sheet to form a single cooling unit. Except in the lower part of the sheet, original textures were obscured by devitrification and crystallization during cooling. Nearly uniform mineralogy and chemistry suggest a single magnetic source. A nearly circular area, about 3? miles in diameter, of altered dacite and earlier volcanic rocks, bounded by intricately faulted and brecciated older rocks, may be the site of a caldera that represents the source of the eruptions.

Geohydrology of Test Well USW H-3, Yucca Mountain, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thordarson, W.; Rush, F.E.; Waddell, S.J.

Test well USW H-3 is one of several test wells drilled in the southwestern part of the Nevada Test Site in cooperation with the US Department of Energy for investigations related to the isolation of high-level radioactive wastes. All rocks penetrated by the well to a total depth of 1219 meters are volcanic tuff of Tertiary age. The composite hydraulic head in the zone 751 to 1219 meters was 733 meters above sea level, and at a depth below land surface of 751 meters. Below a depth of 1190 meters, the hydraulic head was 754 meters above sea level ormore » higher, suggesting an upward component of groundwater flow at the site. The most transmissive part of the saturated zone is in the upper part of the Tram Member of the Crater Flat Tuff in the depth interval from 809 to 841 meters, with an apparent transmissivity of about 7 x 10{sup -1} meter squared per day. The remainder of the penetrated rocks in the saturated zone, 841 to 1219 meters, has an apparent transmissivity of about 4 x 10{sup -1} meter squared per day. The most transmissive part of the lower depth interval is in the bedded tuff and Lithic Ridge Tuff, in the depth interval from 1108 to 1120 meters. The apparent hydraulic conductivity of the rocks in the lower depth interval from 841 to 1219 meters commonly ranges from about 10{sup -1} to 10{sup -4} meter per day. 32 references, 20 figures, 4 tables.« less

A model for microbially induced precipitation of vadose-zone calcites in fractures at LOS Alamos, New Mexico, USA

NASA Astrophysics Data System (ADS)

Newman, Brent D.; Campbell, Andrew R.; Norman, David I.; Ringelberg, David B.

1997-05-01

Fractures are unique environments that can concentrate the flow of water, nutrients, and contaminants. As such, fractures play an important role in controlling the flux of various substances into and through the vadose zone. Calcite fracture fillings are present in the near surface in the Bandelier Tuff Formation at Los Alamos, New Mexico, and provide a record of the geochemical and hydrologic processes that have occurred in fractures. The objective of this study was to examine calcite fracture fills in order to improve understanding of processes within fractures, and in particular those that lead to precipitation of calcite. Samples of calcite fillings were collected from vertical and horizontal fractures exposed in a shallow waste-burial pit. Scanning electron microscopy show morphologies which suggest that plants, fungi, and bacteria were important in the precipitation process. Quadrupole mass spectrometric analyses of fluid inclusion gases show predominantly methane (17-99%) and little to no oxygen (0-8%), suggesting the development of anaerobic conditions in the fractures. Ester-linked phospholipid biomarkers are evidence for a diverse microbial community in the fractures, and the presence of di-ether lipids indicate that the methane was generated by anaerobic bacteria. The calcite fillings apparently resulted from multiple biological and chemical processes in which plant roots in the fractures were converted to calcite. Roots grew into the fractures, eventually died, and were decomposed by bacteria and fungi. Anaerobic gases were generated from encapsulated organic material within the calcite via microbial decomposition, or were generated by microbes simultaneously with calcite precipitation. It is likely that the biological controls on calcite formation that occurred in the Los Alamos fractures also occurs in soils, and may explain the occurrence of other types of pedogenic calcites.

Investigating the thermophysical properties of indurated materials on Mars

NASA Astrophysics Data System (ADS)

Murphy, Nathaniel William

Indurated materials have been observed on the surface of Mars at every landing site and inferred from orbital remote-sensing data by the Viking, Mars Global Surveyor, and Mars Odyssey spacecraft. However, indurated materials on Mars are poorly understood because there is no ground truth for the indurated surfaces inferred from thermal remote-sensing data. I adopted two approaches to investigate indurated materials on Mars: (1) remote-sensing analysis of the Isidis basin, which shows some of the highest thermal inertia values derived from TES 1 observations, and (2) laboratory analyses of terrestrial indurated materials. To characterize the surface of the Isidis basin, I combined a variety of remote-sensing datasets, including thermal inertia data derived from TES and MO-THEMIS, TES albedo, THEMIS thermal and visible imaging, and Earth-based radar observations. From these observations I concluded that the thermal inertia values in the Isidis basin are likely the result of variations in the degree of cementation of indurated materials. To examine the thermophysical properties of indurated materials I collected four examples of terrestrial indurated materials. These included two types of gypcrete collected from a gypcrete deposit near Upham Hills, NM, clay-materials from Lunar Lake Playa, NV, and a pyroclastic material from the Bandelier Tuff near Los Alamos, NM. Despite significant differences in their physical properties and origins, all of these materials have thermal inertia values consistent with inferred indurated surfaces on Mars. There are no strong correlations between the thermal and physical properties of the collected samples due to thermal effects of the fabrics of the indurated materials. 1 Thermal Emission Spectrometer onboard the Mars Global Surveyor spacecraft. 2 Thermal Emission Imaging System onboard the Mars Odyssey spacecraft

Magmatism, ash-flow tuffs, and calderas of the ignimbrite flareup in the western Nevada volcanic field, Great Basin, USA

USGS Publications Warehouse

Christopher D. Henry,; John, David A.

2013-01-01

The western Nevada volcanic field is the western third of a belt of calderas through Nevada and western Utah. Twenty-three calderas and their caldera-forming tuffs are reasonably well identified in the western Nevada volcanic field, and the presence of at least another 14 areally extensive, apparently voluminous ash-flow tuffs whose sources are unknown suggests a similar number of undiscovered calderas. Eruption and caldera collapse occurred between at least 34.4 and 23.3 Ma and clustered into five ∼0.5–2.7-Ma-long episodes separated by quiescent periods of ∼1.4 Ma. One eruption and caldera collapse occurred at 19.5 Ma. Intermediate to silicic lavas or shallow intrusions commonly preceded caldera-forming eruptions by 1–6 Ma in any specific area. Caldera-related as well as other magmatism migrated from northeast Nevada to the southwest through time, probably resulting from rollback of the formerly shallow-dipping Farallon slab. Calderas are restricted to the area northeast of what was to become the Walker Lane, although intermediate and effusive magmatism continued to migrate to the southwest across the future Walker Lane.Most ash-flow tuffs in the western Nevada volcanic field are rhyolites, with approximately equal numbers of sparsely porphyritic (≤15% phenocrysts) and abundantly porphyritic (∼20–50% phenocrysts) tuffs. Both sparsely and abundantly porphyritic rhyolites commonly show compositional or petrographic evidence of zoning to trachydacites or dacites. At least four tuffs have volumes greater than 1000 km3, with one possibly as much as ∼3000 km3. However, the volumes of most tuffs are difficult to estimate, because many tuffs primarily filled their source calderas and/or flowed and were deposited in paleovalleys, and thus are irregularly distributed.Channelization and westward flow of most tuffs in paleovalleys allowed them to travel great distances, many as much as ∼250 km (original distance) to what is now the western foothills of the Sierra Nevada, which was not a barrier to westward flow of ash flows at that time. At least three tuffs flowed eastward across a north-south paleodivide through central Nevada. That tuffs could flow significant distances apparently uphill raises questions about the absolute elevation of the region and the elevation, relief, and location of the paleodivide.Calderas are equant to slightly elongate, at least 12 km in diameter, and as much as 35 km in longest dimension. Exceptional exposure of two caldera complexes that resulted from extensional faulting and tilting show that calderas subsided as much as 5 km as large piston-like blocks; caldera walls were vertical to steeply inward dipping to depths ≥4–5 km, and topographic walls formed by slumping of wall rock into the caldera were only slightly outboard (≤1 km) of structural margins.Most calderas show abundant post-collapse magmatism expressed as resurgent intrusions, ring-fracture intrusions, or intracaldera lavas that are closely related temporally (∼0–0.5 Ma younger) to caldera formation. Granitoid intrusions, which were emplaced at paleodepths ranging from <1 to ∼7 km, are compositionally similar to both intracaldera ash-flow tuffs and post-caldera lavas. Therefore in the western Nevada volcanic field, erupted caldera-forming tuffs commonly were the upper parts of large magma chambers that retained considerable volumes of magma after tuff eruption.Several calderas in the western Nevada volcanic field hosted large hydrothermal systems and underwent extensive hydrothermal alteration. Different types of hydrothermal systems (neutral-pH alkali-chloride and acid or low-pH magmatic-hydrothermal) may reflect proximity to (depth of) large resurgent intrusions. With the exception of the giant Round Mountain epithermal gold deposit, few known caldera-related hydrothermal systems are strongly mineralized. Major middle Cenozoic precious and base metal mineral deposits in and along the margins of the western Nevada volcanic field are mostly related to intrusive rocks that preceded caldera-forming eruptions.

Differentiating the Bishop ash bed and related tephra layers by elemental-based similarity coefficients of volcanic glass shards using solution inductively coupled plasma-mass spectrometry (S-ICP-MS)

USGS Publications Warehouse

Knott, J.R.; Sarna-Wojcicki, A. M.; Montanez, I.P.; Wan, E.

2007-01-01

Volcanic glass samples from the same volcanic center (intra-source) often have a similar major-element composition. Thus, it can be difficult to distinguish between individual tephra layers, particularly when using similarity coefficients calculated from electron microprobe major-element measurements. Minor/trace element concentrations in glass can be determined by solution inductively coupled plasma mass spectrometry (S-ICP-MS), but have not been shown as suitable for use in large tephrochronologic databases. Here, we present minor/trace-element concentrations measured by S-ICP-MS and compare these data by similarity coefficients, the method commonly used in large databases. Trial samples from the Bishop Tuff, the upper and lower tuffs of Glass Mountain and the tuffs of Mesquite Spring suites from eastern California, USA, which have an indistinguishable major-element composition, were analyzed using S-ICP-MS. The resulting minor/trace element similarity coefficients clearly separated the suites of tephra layers and, in most cases, individual tephra layers within each suite. Comparisons with previous instrumental neutron activation analysis (INAA) elemental measurements were marginally successful. This is important step toward quantitative correlation in large tephrochronologic databases to achieve definitive identification of volcanic glass samples and for high-resolution age determinations. ?? 2007 Elsevier Ltd and INQUA.

A study of bat populations at Los Alamos National Laboratory and Bandelier National Monument, Jemez Mountains, New Mexico: FY95--97 report to Los Alamos National Laboratory and Bandelier National Monument

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bogan, M.A.; O`Shea, T.J.; Cryan, P.M.

In 1995, a three-year study was initiated to assess the current status of bat species of concern, elucidate distribution and relative abundance, and obtain information on roosting sites of bats. The authors captured and released 1532 bats of 15 species (Myotis californicus, M. ciliolabrum, M. evotis, M. thysanodes, M. volans, M. yumanensis, Lasiurus cinereus, Lasionycteris noctivagans, Pipistrellus hesperus, Eptesicus fuscus, Euderma maculatum, Corynorhinus townsendii, Antrozous pallidus, Tadarida brasiliensis, and Nyctinomops macrotis) and followed 32 bats of eight species (M. evotis, M. thysanodes, M. volans, E. fuscus, E. maculatum, C. townsendii, A. pallidus, and N. macrotis) to 51 active diurnal roosts.more » The most abundant species were L. noctivagans, E. fuscus, L. cinereus, M. evotis, M. volans, and M. ciliolabrum. Most of these species are typical inhabitants of ponderosa pine-mixed coniferous forests.« less

Genesis of a regionally widespread celadonitic chert ironstone bed overlying upper Lias manganese deposits, Hungary

USGS Publications Warehouse

Polgari, Marta; Hein, J.R.; Toth, M.; Brukner-Wein, A.; Vigh, T.; Biro, L.; Cserhati, C.

2010-01-01

Mineralogy and chemical composition are presented for a chert-ironstone bed that overlies the ??rk??t Mn deposit. This bed is mottled green-brown in its lower and upper parts, which are composed of quartz, goethite and celadonite. These parts of the bed are interpreted to be strongly altered tuffs, reflecting oxidic, low-temperature alteration of a hydrated, Fe-rich, Al-poor tuff, and K and Mg uptake from seawater. The middle part of the bed is a mineralized bacterial mat (quartz, goethite). Textures resembling bacterial cells and colonies are common, with wavy, bulbous laminations composed of mounds overlying a mesh-work stromatolite-like texture constructed of micrometre-size Fe oxides. This bed is concordant with the underlying Mn deposit and marks the termination of Mn accumulation. Although no genetic connection exists between the two, the rocks adjacent to the contact record the oceanographic and bottom-water conditions extant when accumulation of one of the major Mn deposits of Europe ended, when the Transdanubian Range was located in the middle of the Adria-Apulian microcontinent between the Neotethys and Atlantic-Ligurian seaways. A pyroclastic origin for part of the bed has significance for the Toarcian of Central Europe because evidence of volcanism occurring at that time is otherwise sparse. ?? 2010 Geological Society of London.

A Revised Clinopyroxene-Liquid Geothermometer for Silicic Igneous Systems with Applications to Diffusion Chronometry of the Scaup Lake Rhyolite, Yellowstone Caldera, WY

NASA Astrophysics Data System (ADS)

Brugman, K. K.; Till, C. B.

2017-12-01

Eruption of the Scaup Lake Rhyolite (SCL) ended 220,000 years of dormancy at Yellowstone caldera and initiated the volcano's youngest sequence of eruptions [Christiansen et al., USGS, 2007]. SCL contains 14% phenocrysts (e.g., feldspar, quartz, pyroxene, zircon, Fe-Ti oxides) which exhibit disequilbrium textures that indicate multiple rejuvenation events occurred shortly before eruption. Our previous work using NanoSIMS elemental concentration profiles from clinopyroxene (cpx) intracrystalline zone boundaries as a diffusion dating tool supported our hypothesis that different minerals may not record the same series of pre-eruptive events, with the cpx rims recording older magmatic events (100s of years prior to eruption [Brugman et al., AGU, 2016]) relative to the sanidine rims (< 10 months and 10-40 years prior to eruption [Till et al., Geology, 2015]). However, diffusion chronometry results are highly dependent on the temperature at which the concentration profile was modeled, necessitating the employment of an appropriate geothermometer. SCL cpx is moderately high in FeOtot (Mg# = 56) but very low in Al2O3 (0.53-0.73 wt%), which is similar to cpx from other high-silica systems (e.g., Rattlesnake Tuff cpx = 0.35 wt% Al2O3, Bandelier Tuff cpx = 0.28-0.91 wt% Al2O3, Paektu Millenium eruption pumice cpx = 0.14-1.78 wt% Al2O3, and Pantelleria trachyte cpx = 0.25-0.72 wt% Al2O3). This range of cpx compositions is not well represented in historical experimental data, and thus has not been included in existing cpx and cpx-liquid geothermometer calibrations. These geothermometers predict temperatures >40°C in error of low-Al cpx-saturated experiments. A new regression of Putirka's [RiMG, 2008] cpx-liquid geothermometer calibrated with 64 experimentally-derived cpx of a similar composition to that of SCL increases the geothermometer's dependence on the Mg# and Na+K component of the liquid and decreases its dependence on the Ca+Si component of the liquid. This revised geothermometer reproduces experimental conditions to ±20°C. This updated thermometer returns temperatures for SCL cpx 30°C lower than the Putirka [RiMG, 2008] cpx-liquid geothermometer, thereby increasing the timescales previously reported for SCL cpx, and increasing the difference in timescales recorded by the SCL cpx and sanidine rims.

Barite aerosol particles from volcanic plumes and fumaroles - FESEM/EDS analysis

NASA Astrophysics Data System (ADS)

Obenholzner, J. H.; Schroettner, H.; Delgado, H.

2003-04-01

Studies of aerosol particles (AP) contained in volcanic plumes has been enormously benefited by the use of field emission scanning electron microscope (FESEM/EDS; responsability by H. Schroettner) permitting morphological, mineralogical and chemical detailed observations and opening new scientific questions. This work shows the ubiquitous presence of Ba in volcanic emissions. We sampled e.g. a volcanic plume (Popocatepetl v.; 1997, 2002) revealing Ba-S-O particles, interpreteted as barite (BaSO4) and Sr-bearing barite with Fe-rich rim (w=1µm). The ca. 500 nm - 4 µm long crystals are +/- euhedral, anhedral and/or partially etched. The µm-sized crystals had been collected on a Teflon fiber filter (1997), the nm-sized on borosilicate fiber filter (BFF, 2002); one set of crystals (ca. l=500-800 nm) is scattered on Fe-hydr/oxide(?). APs collected from the degassing lava flow of Etna (2001) revealed barite (l= ca. 100 nm) on a rounded NaCl (d= 500 nm) and on Fe-hydr/oxides (?). BFF exposed to the F0 fumarole at Vulcano (2001) showed incrustations of barite (l=ca.200 nm) on fibers indicating barite formation during 5 min sampling. At Solfatra we observed almost euhedral barite particles (l=ca.300 nm) of unusual pseudo-trigonal shape. APs from Alpine air masses (A) did not reveal barite. Sources for barite could be vesicle fillings of lavas (known from continental-crust settings), vapor-phase crystallization of ignimbrites (Bandelier Tuff, USA), Ba-rich fumarolic incrustations, rock coatings in the vicinity of fumaroles (Vulcano, I.), sinter of hot springs (Akita-Yaka-Yama v., J.), barite veins (Milos, Gr.), contact-metamorphosed sedimentary xenoliths (Kloech, A.) or lithics associated with hydrovolcanic eruptions (Alban Hills v., I.). Barite has been observed in many Si-tube experiments. Stratospheric APs (1985) of the El Chichon eruption (1982) revealed barite. Ba is known as a trace element in fumarole gases of Vulcano (F11) and TOF mass spectrometry studies detected 138Ba++ in the upper troposphere over Mexico (1998). Barite APs being the product of fragmented rocks would be very rare. The incrustations on fibrous filters at Vulcano indicate that Ba species exist in fumarolic gases. Can barite be used as a proxy for volcanic signals in ice cores or other environments? Do Ba species exist in all volcanic gases or are there speciations according to plate tectonic settings? What the effects might be of Ba in fumaroles, plumes interacting with the atmosphere? Ba-rich particles are known as natural ice-forming nuclei.

Volcano-tectonic evolution of the Castle Mountains: 22 to 14 MA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capps, R.C.

1993-04-01

The alkali-calcic Castle Mountains Volcanic rocks (CMV) are host to major gold mineralization. They are located about 100 km south of Las Vegas, Nevada and are on the boundary between the Basin and Range Province and Colorado River extensional corridor (35[degree]18 minutes 45 seconds N, 115[degree]05 minutes 10 seconds W). New data show the following chronology. 22 Ma. A regional rhyolite ash-flow tuff, the Castle Mountain Tuff member, was deposited on a Proterozoic-Paleozoic basement of low relief. <22 Ma - > 17 Ma. Normal faulting (N30--60[degree]W, 60--65[degree]NE) formed half-grabens. Latite and basalt flows, minor ash-flow tuffs, lahars and sediments (Jacksmore » Well member - JW) were deposited unconformably. JW magmas are enriched in light REE compared to the younger CMV. <17 Ma to 15.5 Ma. Oxidizing upper portions (796 C) of a shallowly emplaced silicic melt erupted to form the high-silica rhyolite dome complexes and intrusives (Linder Peak member - LP) of the NNE-striking Castle Mountains. NW-striking transverse structures caused discontinuities in strike direction of the subvolcanic intrusive and domes and helped form a synvolcanic depression. During a hiatus in volcanism, early Hart Peak member (HP) sediments were deposited marginal to the Castle Mountains. Major gold mineralization and widespread hydrothermal alteration occurred at about 15.5 Ma. 16 Ma to 14 Ma. Early HP volcaniclastic sediments, rhyolite pyroclastic-surge tuff, and basaltic flows, were deposited during late hydrothermal alteration and then fractured and displaced by NNE-striking normal faults, especially in the eastern and northeastern CMV. < 14 Ma. Tectonically significant flat-lying boulder conglomerate and unconformably overlying, largely andesitic flows fill depressions in the Castle Mountains and the Piute Range to the east.« less

Specific surface area of a crushed welded tuff before and after aqueous dissolution

USGS Publications Warehouse

Reddy, M.M.; Claassen, H.C.

1994-01-01

Specific surface areas were measured for several reference minerals (anorthoclase, labradorite and augite), welded tuff and stream sediments from Snowshoe Mountain, near Creede, Colorado. Crushed and sieved tuff had an unexpectedly small variation in specific surface area over a range of size fractions. Replicate surface area measurements of the largest and smallest tuff particle size fractions examined (1-0.3 mm and <0.212 mm) were 2.3 ?? 0.2 m2/g for each size fraction. Reference minerals prepared in the same way as the tuff had smaller specific surface areas than that of the tuff of the same size fraction. Higher than expected tuff specific surface areas appear to be due to porous matrix. Tuff, reacted in solutions with pH values from 2 to 6, had little change in specific surface area in comparison with unreacted tuff. Tuff, reacted with solutions having high acid concentrations (0.1 M hydrochloric acid or sulfuric-hydrofluoric acid), exhibited a marked increase in specific surface area compared to unreacted tuff. ?? 1994.

Chemistry of diagenetically altered tuffs at a potential nuclear waste repository, Yucca Mountain, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broxton, D.E.; Warren, R.G.; Hagan, R.C.

1986-10-01

The chemistry of diagenetically altered tuffs at a potential nuclear waste repository, Yucca Mountain, Nevada is described. These tuffs contain substantial amounts of zeolites that are highly sorptive of certain radionuclides. Because of their widespread distribution, the zeolitic tuffs could provide important barriers to radionuclide migration. Physical properties of these tuffs and of their constituent zeolites are influenced by their chemical compositions. This study defines the amount of chemical variability within diagenetically altered tuffs and within diagenetic minerals at Yucca Mountain. Zeolitic tuffs at Yucca Mountain formed by diagenetic alteration of rhyolitic vitric tuffs. Despite their similar starting compositions, thesemore » tuffs developed compositions that vary both vertically and laterally. Widespread chemical variations were the result of open-system chemical diagenesis in which chemical components of the tuffs were mobilized and redistributed by groundwaters. Alkalies, alkaline earths, and silica were the most mobile elements during diagenesis. The zeolitic tuffs can be divided into three compositional groups: (1) calcium- and magnesium-rich tuffs associated with relatively thin zones of alteration in the unsaturated zone; (2) tuffs in thick zones of alteration at and below the water table that grade laterally from sodic compositions on the western side of Yucca Mountain to calcic compositions on the eastern side; and (3) potassic tuffs at the north end of Yucca Mountain. Physical properties of tuffs and their consistuent zeolites at Yucca Mountain may be affected by variations in compositions. Properties important for assessment of repository performance include behavior and ion exchange.« less

Stable Isotopes of Tilted Ignimbrite Calderas in Nevada

NASA Astrophysics Data System (ADS)

John, D. A.; Watts, K. E.; Hofstra, A. H.; Colgan, J. P.; Henry, C.; Bindeman, I. N.

2013-12-01

Mid-Tertiary calderas are exceptionally well exposed in tilted fault blocks of the northern Great Basin, facilitating detailed evolutionary models of their magmatic-hydrothermal systems. The 29.4 Ma Job Canyon caldera, the oldest of 3 overlapping calderas in the Stillwater Range, west-central Nevada, is tilted ~90° exposing a 10-km-thick section of the crust. Large parts of the >7 km-diameter caldera system, including >2 km thickness of intracaldera rhyolitic tuff, lower parts of an ~2 km thick sequence of post-caldera intermediate lavas, and the upper 500 m of the resurgent granodioritic IXL pluton, were pervasively altered to propylitic, argillic, and sericitic assemblages. Sparse quartz×calcite veins cut the tuff. δ18O values of altered whole rock samples range from +4.8 to -9.1‰ but are mostly -6 to -9‰ at paleodepths >2 km. Calculated magmatic δ18O and δD values range from +6.4 to 8.2‰ and ~-70‰, respectively. Calculated fluid compositions using temperatures from fluid inclusions and mineral assemblages are δ18OH2O=-9.5 to -15‰ and δDH2O=-125 to -135‰ (chlorite) and -70 to -80‰ (epidote). Chlorite-whole rock data suggest fluids that were derived from moderately 18O-exchanged meteoric water. Fault blocks in north-central Nevada expose a >5 km upper crustal cross section through the 12-17 x 20 km, 34 Ma Caetano caldera, including >3 km thickness intracaldera rhyolitic Caetano Tuff. Asymmetric caldera subsidence left a depression >1 km deep partly filled with a lake. Magma resurgence and emplacement of shallow granite porphyry plutons drove a hydrothermal system that altered >120 km2 of the caldera to depths >1.5 km. Alteration was focused in an early granite porphyry intrusion and surrounding upper Caetano Tuff and lacustrine sediments. Early pervasive quartz-kaolinite-pyrite alteration grades outward and downward into more restricted quartz-illite/smectite-pyrite alteration. Hematite, quartz, and barite veins and hydrothermal breccias cut early alteration. Whole rock δ18O values of kaolinite-altered tuff and intrusions are +1.7 to +4.7‰. Magmatic δ18O values of Caetano rocks calculated from zircon and major phenocrysts range narrowly from +10.0 to +10.5‰. Calculated fluid compositions from kaolinite are δ18OH2O=-3 to -7‰ and δDH2O=-148 to -160‰, and from quartz and barite veins are δ18OH2O=-4 to -11‰, indicating that hydrothermal fluids also were dominantly 18O-exchanged meteoric water. Compared to the Job Canyon caldera, δDH2O values for Caetano hydrothermal fluids are ~25‰ lower, suggesting that Caetano formed at an elevation about 1 km higher than Job Canyon along the crest of the Nevadaplano. Both calderas hosted vigorous hydrothermal systems driven by heat from magma resurgence that pervasively altered and exchanged 18O and D with 10s to 100s km3 of rock. However, significant assimilation of low-18O hydrothermally altered rocks is not apparent by the exclusively normal-δ18O values of Job Canyon, Caetano, and adjacent younger magmas. Neither caldera is strongly mineralized, probably in part due to low sulfur contents of the hydrothermal fluids. More acidic fluids at Caetano suggest a larger magmatic gas (HCl) input likely resulting from degassing of shallow resurgent magma into the caldera lake.

Early postcaldera rhyolite and structural resurgence at Long Valley Caldera, California

NASA Astrophysics Data System (ADS)

Hildreth, Wes; Fierstein, Judy; Calvert, Andrew

2017-04-01

After the 767-ka caldera-forming eruption of 650 km3 of rhyolite magma as the Bishop Tuff, 90-100 km3 of similar rhyolite erupted in the west-central part of Long Valley caldera in as many as 40 batches spread over the 110,000-year interval from 750 ka to 640 ka. Centrally, this Early Rhyolite (ER) is as thick as 622 m, but it spread radially to cover much of the caldera floor, where half its area is now concealed by post-ER sediments and lavas. At least 75% of the ER is aphyric rhyolite tuff. Drillholes encountered 22 (altered) ER lava flows intercalated in the pyroclastic pile, and another 11 units of (largely fresh) ER lava are exposed on the caldera's resurgent dome and at Lookout Mountain. Exposed units have been distinguished, mapped, studied petrographically and chemically, and radioisotopically dated; each is described in detail. Their phenocryst contents range from 0 to 2.5 wt%. All the phyric units have plagioclase, orthopyroxene, and ilmenite; most have biotite and rare tiny magnetite, and a few contain rare zircon. The compositional range of fresh obsidians is narrow-74.3-75.0% SiO2, 1.21-1.37% FeO*, and 5.12-5.26% K2O, but wider variations in Ti, Ba, Sr, and Zr permit distinction of individual units and eruptive groups. The limited chemical and petrographic variability shown by so many ER batches released episodically for 110,000 years suggests a thermally buffered and well-stirred reservoir. The ER central area, where ER eruptions had taken place, was uplifted 400 m to form a structural dome 10 km in diameter. Most of the inflation is attributable to 10 sills of ER that intrude the Bishop Tuff beneath the uplift, but other processes potentially contributing to resurgence are also considered. As shown by erratics of Mesozoic rocks ice-rafted from the Sierra Nevada and dropped on ER lavas, much of the ER had erupted early enough and at low enough elevation to be inundated by the intracaldera lake and was only later lifted by the resurgence that also raised clusters of the erratics hundreds of meters higher than any shoreline. Most of the uplift was over by 570 ka, but dome-crossing faults that exhibit normal throw of 10-30 m cut lavas as young as 175-125 ka. For most elements, chemical ranges of the ER lie within those of the zoned Bishop Tuff, which had erupted earlier from the same place. Only Ba, Zr, Hf, and Eu/Eu* extend to ranges outside those of the Bishop Tuff, nominally to less evolved compositions. Initial 87Sr/86Sr values of ER are likewise within the range of the Bishop Tuff, but ER ratios of 143Nd/144Nd and 206Pb/204Pb extend beyond those of the Bishop Tuff to values slightly more influenced by upper-crustal contributions. FeTi-oxide geothermometry yields 752°-844 °C for ER, compared to 700°-820 °C for the Bishop Tuff. ER fO2 values are 0.5-1.0 log units more reduced than those of the T-fO2 array of the Bishop Tuff. The postcaldera reduction may reflect reaction with graphite from the black lithics of Paleozoic graphitic metapelite so abundant in the Bishop Tuff. Much of the pumice emplaced during the later half of the Bishop Tuff eruption has 10-25 wt% phenocrysts, dominantly quartz and sanidine, but the 100 km3 of ER has only 0-2.5 wt% and completely lacks quartz and sanidine. Postcaldera processes, including mixing, volatile ascent, and crystal resorption, as well as potential contaminants and magmatic inputs, are all considered.

Geochemical correlation and 40Ar/39Ar dating of the Kern River ash bed and related tephra layers: Implications for the stratigraphy of petroleum-bearing formations in the San Joaquin Valley, California

USGS Publications Warehouse

Baron, D.; Negrini, R.M.; Golob, E.M.; Miller, D.; Sarna-Wojcicki, A.; Fleck, R.J.; Hacker, B.; Erendi, A.

2008-01-01

The Kern River ash (KRA) bed is a prominent tephra layer separating the K and G sands in the upper part of the Kern River Formation, a major petroleum-bearing formation in the southern San Joaquin Valley (SSJV) of California. The minimum age of the Kern River Formation was based on the tentative major-element correlation with the Bishop Tuff, a 0.759??0.002 Ma volcanic tephra layer erupted from the Long Valley Caldera. We report a 6.12??0.05 Ma 40Ar/39Ar date for the KRA, updated major-element correlations, trace-element correlations of the KRA and geochemically similar tephra, and a 6.0??0.2 Ma 40Ar/39Ar age for a tephra layer from the Volcano Hills/Silver Peak eruptive center in Nevada. Both major and trace-element correlations show that despite the similarity to the Bishop Tuff, the KRA correlates most closely with tephra from the Volcano Hills/Silver Peak eruptive center. This geochemical correlation is supported by the radiometric dates which are consistent with a correlation of the KRA to the Volcano Hills/Silver Peak center but not to the Bishop Tuff. The 6.12??0.05 Ma age for the KRA and the 6.0??0.2 Ma age for the tephra layer from the Volcano Hills/Silver Peak eruptive center suggest that the upper age of the Kern River Formation is over 5 Ma older than previously thought. Re-interpreted stratigraphy of the SSJV based on the new, significantly older age for the Kern River Formation opens up new opportunities for petroleum exploration in the SSJV and places better constraints on the tectonostratigraphic development of the SSJV. ?? 2007 Elsevier Ltd and INQUA.

Geologic Map of the Clark Peak Quadrangle, Jackson and Larimer Counties, Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Ruleman, Chester A.; Shroba, Ralph R.; Braddock, William A.

2008-01-01

The Clark Peak quadrangle encompasses the southern end of the Medicine Bow Mountains and the northernmost end of the Mummy Range. The Continental Divide traverses the map area and Highway 14 cross the Divide at Cameron Pass, in the southeastern corner of the map. Approximately the eastern half of the map, and a few areas to the west, are underlain by Early Proterozoic plutonic and metamorphic rocks. Most of these basement rocks are part of the ~1,715 Ma Rawah batholith, composed mostly of pinkish, massive to moderately foliated monzogranite and granodiorite intruded by numerous, large pegmatite- aplite bodies. The metamorphic rocks, many of which form large inclusions in the granitic rocks of the Rawah batholith, include biotite-hornblende gneiss, hornblende gneiss, amphibolite, and biotite schist. The crystalline basement rocks are thrust westward along the Medicine Bow thrust over a sequence of sedimentary rocks as old as the Upper Permian Satanka Shale. The Satanka Shale, Middle and Lower Triassic Chugwater group, and a thin sandstone tentatively correlated with the Lower Jurassic and Upper Triassic Jelm Formation are combined as one map unit. This undivided unit is overlain sequentially upward by the Upper Jurassic Sundance Formation, Upper Jurassic Morrison Formation, Lower Cretaceous Dakota Group, Upper and Lower Cretaceous Benton Group, Upper Cretaceous Niobrara Formation, and the Eocene and Paleocene Coalmont Formation. The Late Cretaceous to early Eocene Medicine Bow thrust is folded in places, and several back thrusts produced a complicated thrust pattern in the south part of the map. Early Oligocene magmatism produced rhyolite tuff, dacite and basalt flows, and intermediate dikes and small stocks. A 40Ar/39Ar date on sanidine from one rhyolite tuff is ~28.5 Ma; a similar whole-rock date on a trachybasalt is ~29.6 Ma. A very coarse, unsorted probably pre-Quaternary ridge-top diamicton crops out in the southern part of the quadrangle. Numerous glacial deposits (mostly of Pinedale age), rock glaciers, block-slope deposits, landslide deposits, talus deposits, fan deposits, colluvium, and alluvium comprise the surficial deposits of the map area.

Spectroscopic examinations of hydro- and glaciovolcanic basaltic tuffs: Modes of alteration and relevance for Mars

NASA Astrophysics Data System (ADS)

Farrand, W. H.; Wright, S. P.; Glotch, T. D.; Schröder, C.; Sklute, E. C.; Dyar, M. D.

2018-07-01

Hydro- and glaciovolcanism are processes that have taken place on both Earth and Mars. The amount of materials produced by these processes that are present in the martian surface layer is unknown, but may be substantial. We have used Mars rover analogue analysis techniques to examine altered tuff samples collected from multiple hydrovolcanic features, tuff rings and tuff cones, in the American west and from glaciovolcanic hyaloclastite ridges in Washington state and in Iceland. Analysis methods include VNIR-SWIR reflectance, MWIR thermal emissivity, thin section petrography, XRD, XRF, and Mössbauer spectroscopy. We distinguish three main types of tuff that differ prominently in petrography and VNIR-SWIR reflectance: minimally altered sideromelane tuff, gray to brown colored smectite-bearing tuff, and highly palagonitized tuff. Differences are also observed between the tuffs associated with hydrovolcanic tuff rings and tuff cones and those forming glaciovolcanic hyaloclastite ridges. For the locations sampled, hydrovolcanic palagonite tuffs are more smectite and zeolite rich while the palagonitized hyaloclastites from the sampled glaciovolcanic sites are largely devoid of zeolites and relatively lacking in smectites as well. The gray to brown colored tuffs are only observed in the hydrovolcanic deposits and appear to represent a distinct alteration pathway, with formation of smectites without associated palagonite formation. This is attributed to lower temperatures and possibly longer time scale alteration. Altered hydro- or glaciovolcanic materials might be recognized on the surface of Mars with rover-based instrumentation based on the results of this study.

Identification of mineral composition and weathering product of tuff using reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Hyun, C.; Park, H.

2009-12-01

Tuff is intricately composed of various types of rock blocks and ash matrixes during volcanic formation processes. Qualitative identification and quantitative assessment of mineral composition of tuff usually have been done using manual inspection with naked-eyes and various chemical analyses. Those conventional methods are destructive to objects, time consuming and sometimes carry out biased results from subjective decision making. To overcome limits from conventional methods, assessment technique using reflectance spectroscopy was applied to tuff specimens. Reflectance spectroscopy measures electromagnetic reflectance on rock surface and can extract diagnostic absorption features originated from chemical composition and crystal structure of constituents in the reflectance curve so mineral species can be discriminated qualitatively. The intrinsic absorption feature from particular mineral can be converted to absorption depth representing relative coverage of the mineral in the measurement area by removing delineated convex hull from raw reflectance curve. The spectral measurements were performed with field spectrometer FieldSpec®3 of ASD Inc. and the wavelength range of measurement was form 350nm to 2500nm. Three types of tuff blocks, ash tuff, green lapilli tuff and red lapilli tuff, were sampled from Hwasun County in Korea and the types of tuffs. The differences between green tuff and red tuff are from the color of their matrixes. Ash tuff consists of feldspars and quartz and small amount of chalcedony, calcite, dolomite, epidote and basalt fragments. Green lapilli tuff consists of feldspar, quartz and muscovite and small amount of calcite, chalcedony, sericite, chlorite, quartzite and basalt fragments. Red lapilli tuff consists of feldspar, quartz and muscovite and small amount of calcite, chalcedony, limonite, zircon, chlorite, quartzite and basalt fragments. The tuff rocks were coarsely crushed and blocks and matrixes were separated to measure standard spectral reflectance of each constituent. Unmixing of mineral composition and their weathering products of blocks and matrixes in tuff were conducted and the ratio of mineral composition was calculated for each specimen. This study was supported by National Research Institute of Cultural Heritage (project title: Development on Evaluation Technology for Weathering Degree of Stone Cultural Properties, project no.: 09B011Y-00150-2009).

Newly combined 40Ar/39Ar and U-Pb ages of the Upper Cretaceous timescale from Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Gaylor, J. R.; Heredia, B. D.; Quidelleur, X.; Takashima, R.; Nishi, H.; Mezger, K.

2011-12-01

The main targets for GTS next project (www.gtsnext.eu) are to develop highly refined geological time scales, including the Upper Cretaceous. The Cretaceous period is characterised by numerous global anoxic events in the marine realm, rich ammonitic fossil assemblages and specialised foraminifera. However, lack of age diagnostic macro and micro fossils in the North Pacific sections has made it difficult to link these with global sections such as the Western Interior Basin (North America). Using advances with terrestrial C-isotope and planktic foraminifera records within Central Hokkaido we are able to correlate these sections globally. The Cretaceous Yezo group in Central Hokkaido comprises deep marine mudstones and turbidite sandstones interbedded with acidic volcanic tuffs. Using various sections within the Yezo group, we radiometrically dated tuffs at the main stage boundaries in the Upper Cretaceous. The samples derive from the Kotanbetsu, Shumarinai, Tiomiuchi and the Hakkin river sections, spanning the time from the Albian-Cenomanian up until the Campanian-Santonian boundaries, and were dated using 40Ar/39Ar, K/Ar and U-Pb techniques. Recent age constraints in the Hokkaido counterparts (Kotanbetsu sections) show good coherence between radiometric chronometers on the various Upper Cretaceous stage boundaries. These additional ages together with our isotope ages from the different sections around the Hokkaido basin are well linked by the various faunal assemblages and C-isotope curves. The combined radio isotope ages contribute to previous attempts (such as those focused in the Western Interior Basin) supporting the synchronicity of events such as global oceanic anoxic events. Finally, the ages obtained here also compliment the previous C-isotope and planktic foraminifera records allowing for a more precise climatic history of the Northwest Pacific during the Cretaceous. The research within the GTSnext project is funded by the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement no. 215458.

Geochronology, stratigraphy and geochemistry of Cambro-Ordovician, Silurian and Devonian volcanic rocks of the Saxothuringian Zone in NE Bavaria (Germany)—new constraints for Gondwana break up and ocean-island magmatism

NASA Astrophysics Data System (ADS)

Höhn, Stefan; Koglin, Nikola; Klopf, Lisa; Schüssler, Ulrich; Tragelehn, Harald; Frimmel, Hartwig E.; Zeh, Armin; Brätz, Helene

2018-01-01

Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were sampled for geochemical characterisation and U-Pb zircon dating. The oldest rock suite comprises quartz keratophyre, brecciated keratophyre, quartz keratophyre tuff and basalt, formed in Upper Cambrian to Tremadocian time (c. 497-478 Ma). Basaltic volcanism continued until the Silurian. Quartz keratophyre shows post-collisional calc-alkaline signature, the Ordovician-Silurian basalt has alkaline signature typical of continental rift environments. The combined datasets provide evidence of Cambro-Ordovician bimodal volcanism and successive rifting until the Silurian. This evolution very likely resulted from break-up of the northern Gondwana margin, as recorded in many terranes throughout Europe. The position at the northern Gondwana margin is supported by detrital zircon grains in some tuffs, with typical Gondwana-derived age spectra mostly recording ages of 550-750 Ma and minor age populations of 950-1100 and 1700-2700 Ma. The absence of N-MORB basalt in the Frankenwald area points to a retarded break-off of the Saxothuringian terrane along a continental rift system from Uppermost Cambrian to Middle Silurian time. Geochemical data for a second suite of Upper Devonian basalt provide evidence of emplacement in a hot spot-related ocean-island setting south of the Rheic Ocean. Our results also require partial revision of the lithostratigraphy of the Frankenwald area. The basal volcanic unit of the Randschiefer Formation yielded a Tremadocian age and, therefore, should be attributed to the Vogtendorf Formation. Keratophyre of the Vogtendorf Formation, previously assigned to the Tremadoc, is most likely of Upper Devonian age.

Upper Neogene stratigraphy and tectonics of Death Valley - A review

USGS Publications Warehouse

Knott, J.R.; Sarna-Wojcicki, A. M.; Machette, M.N.; Klinger, R.E.

2005-01-01

New tephrochronologic, soil-stratigraphic and radiometric-dating studies over the last 10 years have generated a robust numerical stratigraphy for Upper Neogene sedimentary deposits throughout Death Valley. Critical to this improved stratigraphy are correlated or radiometrically-dated tephra beds and tuffs that range in age from > 3.58 Ma to < 1.1 ka. These tephra beds and tuffs establish relations among the Upper Pliocene to Middle Pleistocene sedimentary deposits at Furnace Creek basin, Nova basin, Ubehebe-Lake Rogers basin, Copper Canyon, Artists Drive, Kit Fox Hills, and Confidence Hills. New geologic formations have been described in the Confidence Hills and at Mormon Point. This new geochronology also establishes maximum and minimum ages for Quaternary alluvial fans and Lake Manly deposits. Facies associated with the tephra beds show that ???3.3 Ma the Furnace Creek basin was a northwest-southeast-trending lake flanked by alluvial fans. This paleolake extended from the Furnace Creek to Ubehebe. Based on the new stratigraphy, the Death Valley fault system can be divided into four main fault zones: the dextral, Quaternary-age Northern Death Valley fault zone; the dextral, pre-Quaternary Furnace Creek fault zone; the oblique-normal Black Mountains fault zone; and the dextral Southern Death Valley fault zone. Post -3.3 Ma geometric, structural, and kinematic changes in the Black Mountains and Towne Pass fault zones led to the break up of Furnace Creek basin and uplift of the Copper Canyon and Nova basins. Internal kinematics of northern Death Valley are interpreted as either rotation of blocks or normal slip along the northeast-southwest-trending Towne Pass and Tin Mountain fault zones within the Eastern California shear zone. ?? 2005 Elsevier B.V. All rights reserved.

Constraints for recently discovered ignimbrites in the Altiplano-Puna Volcanic Complex (APVC), northern Chile

NASA Astrophysics Data System (ADS)

Layana, S.; Aguilera, F.

2014-12-01

One of most voluminous ignimbrite provinces in the world (>30.000 km3) is located in the Central Andean Volcanic Zone (CAVZ), which has been continuously active since Upper Oligocene. Altiplano-Puna Volcanic Complex (APVC), located between 21 and 24ºS, is a volcano-tectonic province constituted by diverse caldera complexes and ignimbrite deposits (Upper Miocene - Lower Pleistocene) that covers an area ~50.000 km2. In this work, we present data from three new ignimbrites discovered in a portion of APVC (22°-22,4°S), with the objective to establish its origin and provenance. Were identified 3 new ignimbrites: 1) Cabana ignimbrite (>7.5 Ma), constituted by 3 pyroclastic flow and 1 pyroclastic surge units of crystal-glass rich dacitic tuffs, 80 m maximum thick, 0.18 km3 volume and 0.14 km3 DRE; 2) Inacaliri ignimbrite (7.5 Ma) constituted by two members, corresponding to glassy dacitic (basal member) and basaltic andesites (upper member) tuffs, the total thick reach up 20 m, 0.003 km3 volume and 0.002 km3 DRE; 3) Tolar ignimbrite (>1.3 Ma), constituted by a single pyroclastic flow and a basal fall glassy dacitic deposits, 50 m maximum thick, 0.04 km3 volume and 0.03 km3 DRE. Cabana ignimbrite seems to have been originated from a single caldera complex, whose cannot be recognized in the field. Inacaliri ignimbrite could be related to initial phases of building of Inacaliri and Apacheta-Aguilucho volcanic complexes, or originated to a buried caldera located below both volcanic complexes. Finally, Tolar ignimbrite corresponds to initial building stage of Toconce volcano, located 2 km at NE from these deposits.

Preliminary hydrogeologic assessment of boreholes UE-25c #1, UE-25c #2, and UE-25c #3, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Geldon, A.L.

1993-01-01

Boreholes UE-25c #1, UE-25c #2, and UE-25c #3 (collectively called the C-holes) each were drilled to a depth of 914.4 meters at Yucca Mountain, on the Nevada Test Site, in 1983 and 1984 for the purpose of conducting aquifer and tracer tests. Each of the boreholes penetrated the Paintbrush Tuff and the tuffs and lavas of Calico Hills and bottomed in the Crater Flat Tuff. The geologic units penetrated consist of devitrified to vitrophyric, nonwelded to densely welded, ash-flow tuff, tuff breccia, ash-fall tuff, and bedded tuff. Below the water table, which is at an average depth of 401.6 meters below land surface, the rocks are argillic and zeolitic. The geologic units at the C-hole complex strike N. 2p W. and dip 15p to 21p NE. They are cut by several faults, including the Paintbrush Canyon Fault, a prominent normal fault oriented S. 9p W., 52.2p NW. The rocks at the C-hole complex are fractured extensively, with most fractures oriented approximately perpendicular to the direction of regional least horizontal principal stress. In the Crater Flat Tuff and the tuffs and lavas of Calico Hills, fractures strike predominantly between S. 20p E. and S. 20p W. and secondarily between S. 20p E. and S. 60p E. In the Topopah Spring Member of the Paintbrush Tuff, however, southeasterly striking fractures predominate. Most fractures are steeply dipping, although shallowly dipping fractures occur in nonwelded and reworked tuff intervals of the Crater Flat Tuff. Mineral-filled fractures are common in the tuff breccia zone of the Tram Member of the Crater Flat Tuff, and, also, in the welded tuff zone of the Bullfrog Member of the Crater Flat Tuff. The fracture density of geologic units in the C-holes was estimated to range from 1.3 to 7.6 fractures per cubic meter. Most of these estimates appear to be the correct order of magnitude when compared to transect measurements and core data from other boreholes 1.3 orders of magnitude too low. Geophysical data and laboratory analyses were used to determine matrix hydrologic properties of the tuffs and lavas of Calico Hills and the Crater Flat Tuff in the C-holes. The porosity ranged from 12 to 43 percent and, on the average, was larger in nonwelded to partially welded, ash-flow tuff, ashfall tuff, and reworked tuff than in moderately to densely welded ash-flow tuff. The pore-scale horizontal permeability of nine samples ranged from 5.7x10'3 to 2.9 millidarcies, and the pore-scale vertical permeability of these samples ranged from 3.7x10'* to 1.5 millidarcies. Ratios of pore-scale horizontal to vertical permeability generally ranged from 0.7 to 2. Although the number of samples was small, values of pore-scale permeability determined were consistent with samples from other boreholes at Yucca Mountain. The specific storage of nonwelded to partially welded ash-flow tuff, ash-fall tuff, and reworked tuff was estimated from porosity and elasticity to' be 2xlO'6 per meter, twice the specific storage of moderately to densely welded ash-flow tuff and tuff breccia. The storativity of geologic units, based on their average thickness (corrected for bedding dip) and specific storage, was estimated to range from 1xlO's to 2xlO'4. Ground-water flow in the Tertiary rocks of the Yucca Mountain area is not confined by strata but appears to result from the random intersection of water-bearing fractures and faults. Even at the C-hole complex, an area of only 1,027 square meters, water-producing zones during pumping tests vary from borehole to borehole. In borehole UE-25c #1, water is produced mainly from the lower, nonwelded to welded zone of the Bullfrog Member of the Crater Flat Tuff and secondarily from the tuff-breccia zone of the Tram Member of the Crater Flat Tuff. In borehole UE-25c #3, water is produced in nearly equal proportions from these two intervals and the central, moderately to densely welded zone of the Bullfrog Member. In borehole UE-25c #2, almost all production comes from the moderately to dense

Geohydrologic data from test hole USW UZ-7, Yucca Mountain area, Nye County, Nevada

USGS Publications Warehouse

Kume, Jack; Hammermeister, D.P.

1990-01-01

This report contains a description of the methods used in drilling and coring of the test-hole USW UZ-7, a description of the methods used in collecting, handling, and testing of test-hole samples; Lithologic information from the test hole; and water-content, water-potential, bulk-density, grain-density, porosity, and tritium data for the test hole. Test-hole USW UZ-7 was drilled and cored to a total depth of 62.94 m. The drilling was done using air as a drilling fluid to minimize disturbance to the water content of cores, drill-bit cuttings, and borehole wall-rock. Beginning at the land surface, the unsaturated-zone rock that was penetrated consisted of alluvium; welded and partially to nonwelded ash-flow tuff; bedded and reworked ash-fall tuff; nonwelded ash-flow tuff; and welded ash-flow tuff. Values of gravimetric water content and water potential of alluvium were intermediate between the extreme values in welded and nonwelded units of tuff. Gravimetric water content was largest in bedded and nonwelded ash-fall tuffs and was smallest in welded ash-flow tuff. Values of water potential were more negative in densely welded ash-flow tuffs and were less negative in bedded and nonwelded ash-fall tuffs. Bulk density was largest in densely welded ash-flow tuffs and smallest in nonwelded and bedded ash-fall tuffs. Grain density was uniform but was slightly larger in nonwelded and bedded ash-fall tuffs than in welded ash-flow tuffs. Porosity trends were opposite to bulk-density trends. Tritium content in alluvium was smallest near the alluvium-bedrock contact, markedly increased in the middle of the deposit, and decreased in the near-surface zone of the deposit. (Author 's abstract)

Late Cenozoic tephrochronology, stratigraphy, geomorphology, and neotectonics of the Western Black Mountains Piedmont, Death Valley, California: Implications for the spatial and temporal evolution of the Death Valley fault zone

NASA Astrophysics Data System (ADS)

Knott, Jeffrey Rayburn

This study presents the first detailed tephrochronologic study of the central Death Valley area by correlation of a Nomlaki-like tuff (>3.35 Ma), tuffs of the Mesquite Spring family (3.1 -- 3.35 Ma), a tuff of the lower Glass Mountain family (1.86 -- 2.06 Ma), and tephra layers from the upper Glass Mountain family (0.8 -- 1.2 Ma), the Bishop ash bed (0.76 Ma), the Lava Creek B ash bed (~0.66 Ma), and the Dibekulewe ash bed (~0.51 Ma). Correlation of these tuffs and tephra layers provides the first reliable numeric-age stratigraphy for late Cenozoic alluvial fan and lacustrine deposits for Death Valley and resulted in the naming of the informal early to middle Pleistocene Mormon Ploint formation. Using the numeric-age stratigraphy, the Death Valley fault zone (DVFZ) is interpreted to have progressively stepped basinward since the late Pliocene at Mormon Point and Copper Canyon. The Mormon Point turtleback or low-angle normal fault is shown to have unequivocal late Quaternary slip at its present low angle dip. Tectonic geomorphic analysis indicates that the (DVFZ) is composed of five geomorphic segments with the most persistent segment boundaries being the en-echelon step at Mormon Point and the bedrock salient at Artists Drive. Subsequent geomorphic studies resulting from the numeric-age stratigraphy and structural relations include application of Gilberts field criteria to the benches at Mormon Point indicating that the upper bench is a lacustrine strandline and the remaining topographically-lower benches are fault scarps across the 160--185 ka lake abrasion platform. In addition, the first known application of cosmogenic 10Be and 26Al exposure dating to a rock avalanche complex south of Badwater yielded an age of 29.5 +/- 1.9 ka for the younger avalanche. The 28 meter offset of the older avalanche may be interpreted as post-160--185 ka yielding a 0.1 mm/year slip rate, or post-29.5 +/- 1.9 ka yielding a maximum slip rate of 0.9 nun/year for the DVFZ. A consequence of these studies is the hypothesis that the turtleback or low-angle normal faults represent a thermally-warped detachment fault related to the Black Mountains igneous complex and do not conform with the present domino or a rolling-hinge models of low-angle normal fault development.

Welded tuff porosity characterization using mercury intrusion, nitrogen and ethylene glycol monoethyl ether sorption and epifluorescence microscopy

USGS Publications Warehouse

Reddy, M.M.; Claassen, H.C.; Rutherford, D.W.; Chiou, C.T.

1994-01-01

Porosity of welded tuff from Snowshoe Mountain, Colorado, was characterized by mercury intrusion porosimetry (MIP), nitrogen sorption porosimetry, ethylene glycol monoethyl ether (EGME) gas phase sorption and epifluorescence optical microscopy. Crushed tuff of two particle-size fractions (1-0.3 mm and less than 0.212 mm), sawed sections of whole rock and crushed tuff that had been reacted with 0.1 N hydrochloric acid were examined. Average MIP pore diameter values were in the range of 0.01-0.02??m. Intrusion volume was greatest for tuff reacted with 0.1 N hydrochloric acid and least for sawed tuff. Cut rock had the smallest porosity (4.72%) and crushed tuff reacted in hydrochloric acid had the largest porosity (6.56%). Mean pore diameters from nitrogen sorption measurements were 0.0075-0.0187 ??m. Nitrogen adsorption pore volumes (from 0.005 to 0.013 cm3/g) and porosity values (from 1.34 to 3.21%) were less than the corresponding values obtained by MIP. More than half of the total tuff pore volume was associated with pore diameters < 0.05??m. Vapor sorption of EGME demonstrated that tuff pores contain a clay-like material. Epifluorescence microscopy indicated that connected porosity is heterogeneously distributed within the tuff matix; mineral grains had little porosity. Tuff porosity may have important consequences for contaminant disposal in this host rock. ?? 1994.

Commercial geophysical well logs from the USW G-1 drill hole, Nevada Test Site, Nevada

USGS Publications Warehouse

Muller, D.C.; Kibler, J.E.

1983-01-01

Drill hole USW G-1 was drilled at Yucca Mountain, Nevada Test Site, Nevada, as part of the ongoing exploration program for the Nevada Nuclear Waste Storage Investigations. Contract geophysical well logs run at USW G-1 show only limited stratigraphic correlations, but correlate reasonably well with the welding of the ash-flow and ash-fall tuffs. Rocks in the upper part of the section have highly variable physical properties, but are more uniform and predictably lower in the section.

Pretest thermal analysis of the Tuff Water Migration/In-Situ Heater Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bulmer, B.M.

This report describes the pretest thermal analysis for the Tuff Water Migration/In-Situ Heater Experiment to be conducted in welded tuff in G-tunnel, Nevada Test Site. The parametric thermal modeling considers variable boiling temperature, tuff thermal conductivity, tuff emissivity, and heater operating power. For nominal tuff properties, some near field boiling is predicted for realistic operating power. However, the extent of boiling will be strongly determined by the ambient (100% water saturated) rock thermal conductivity. In addition, the thermal response of the heater and of the tuff within the dry-out zone (i.e., bounded by boiling isotherm) is dependent on the temperaturemore » variation of rock conductivity as well as the extent of induced boiling.« less

Surface water data at Los Alamos National Laboratory: 2009 water year

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz, David; McCullough, Betsy

2010-05-01

The principal investigators collected and computed surface water discharge data from 73 stream-gage stations that cover most of Los Alamos National Laboratory and one at Bandelier National Monument. Also included are discharge data from three springs— two that flow into Cañon de Valle and one that flows into Water Canyon.

Surface water data at Los Alamos National Laboratory: 2008 water year

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz, David; Cata, Betsy; Kuyumjian, Gregory

2009-09-01

The principal investigators collected and computed surface water discharge data from 69 stream-gage stations that cover most of Los Alamos National Laboratory and one at Bandelier National Monument. Also included are discharge data from three springs— two that flow into Cañon de Valle and one that flows into Water Canyon.

Wildfire in the valley of the wild roses

Treesearch

Linda Moon Stumpff

2015-01-01

Santa Clara Indian Pueblo lands are adjacent to the Jemez National Forest, Bandelier National Monument and Valles Caldera National Preserve. This paper explores Pueblo vulnerability and resilience after repeated and devastating fires in this century as a result of drought and climate change. Santa Clara Pueblo holds a rich store of traditional knowledge about the fire-...

Paleomagnetism and tectonic rotation of the lower Miocene Peach Springs Tuff: Colorado Plateau, Arizona, to Barstow, California

USGS Publications Warehouse

Wells, Ray E.; Hillhouse, John W.

1989-01-01

We have determined remanent magnetization directions of the lower Miocene Peach Springs Tuff at 41 localities in western Arizona and southeastern California. An unusual northeast and shallow magnetization direction confirms the proposed geologic correlation of isolated outcrops of the tuff from the Colorado Plateau to Barstow, California, a distance of 350 km. The Peach Springs Tuff was apparently emplaced as a single cooling unit about 18 or 19 Ma and is now exposed in 4 tectonic provinces west of the Plateau, including the Transition Zone, Basin and Range, Colorado River extensional corridor, and central Mojave Desert strike-slip zone. As such, the tuff is an ideal stratigraphic and structural marker for paleomagnetic assessment of regional variations in tectonic rotations about vertical axes. From 4 sites on the stable Colorado Plateau, we have determined a reference direction of remanent magnetization (I = 36.4°, D = 33.0°, α95 = 3.4°) that we interpret as a representation of the ambient magnetic field at the time of eruption. A steeper direction of magnetization (I = 54.8°, D = 22.5°, α95 = 2.3°) was observed at Kingman where the tuff is more than 100 m thick, and similar directions were determined at 7 other thick exposures of the Peach Springs Tuff. The steeper component is presumably a later-stage magnetization acquired after prolonged cooling of the ignimbrite. When compared to the Plateau reference direction, tilt-corrected directions from 3 of 6 sites in the central Mojave strike-slip zone show localized rotations up to 13° in the vicinity of strike-slip faults. The other three sites show no significant rotations with respect to the Colorado Plateau. Both clockwise and counterclockwise rotations were measured, and no systematic regional pattern is evident. Our results do not support kinematic models which require consistent rotation of large regions to accommodate the cumulative displacement of major post-middle Miocene strike-slip faults in the central Mojave Desert. Most of our sites in the Transition Zone and Basin and Range province have had no significant rotation, although small counterclockwise rotation in the McCullough and New York Mountains may be related to sinistral shear along en echelon faults southwest of the Lake Mead shear zone. The larger rotations occur in the Colorado River extensional corridor, where 8 of 14 sites show rotations ranging from 37° clockwise to 51° counterclockwise. These rotations occur in allochthonous tilt blocks which have been transported northeastward above the Chemehuevi-Whipple Mountains detachment fault. Upper-plate blocks within 1 km of the exposed detachment unexpectedly show no significant rotation. From this relation, we infer that rotations are accommodated along numerous low-angle faults at higher structural levels above the detachment surface.

The palaeogeographic setting and the local environmental impact of the 130 ka Falconiera tuff-cone eruption (Ustica island, Italy)

NASA Astrophysics Data System (ADS)

de Vita, Sandro; Foresta Martin, Franco

2017-04-01

This research focuses on the effects of the last eruption at Ustica (Suthern Tyrrhenian Sea, Italy), which formed the Falconiera tuff-cone at around 130 ka BP in the north-eastern tip of the island. This eruption was mainly explosive and phreatomagmatic, and emplaced a series of pyroclastic surge beds that formed an asymmetric tuff cone. This is the most easily recognizable volcanic edifice on Ustica, although its north-eastern sector has been partially eroded. A section of the feeding conduit is exposed northward, and is composed of lavas that fed the last stages of the eruption characterized by an intracrateric lava lake and a Strombolian scoria-fallout deposit. The eruption occurred during Upper Pleistocene Marine Isotopic Substage 5.5, a warm period characterized by a high sea-level stand (6±3 m above the present sea level in stable areas) and the diffusion of subtropical flora and fauna across the Mediterranean sea. This eruption slightly modified the morphology of Ustica, but impacted both marine and terrestrial environments, burying beach deposits rich in mollusk shells (i.e. Strombus bubonius, Conus testudinarius, Brachidontes puniceus), colonies of corals (Cladocora caespitosa) and subaerial plants (Chamaerops humilis). These organisms, found in some cases in their life position, along with other lines of evidence, provide information on the palaeogeography of this sector of the island at the time of the eruption, and on the local impact of this event on the environment.

Unconventional maar diatreme and associated intrusions in the soft sediment-hosted Mardoux structure (Gergovie, France)

NASA Astrophysics Data System (ADS)

Valentine, Greg A.; van Wyk de Vries, Benjamin

2014-03-01

A Miocene age volcanic-hypabyssal structure comprising volcaniclastic deposits and mafic intrusions is exposed with vertical relief of ˜110 m on the side of Gergovie Plateau (Auvergne, France). Three main volcaniclastic facies are: (1) Fluidal tuff breccia composed of juvenile basalt and sediment clasts with dominantly fluidal shapes, with several combinations of basalt and sediment within individual clasts. (2) Thickly bedded lapilli tuff composed of varying proportions of fine-grained sediment derived from Oligocene-Miocene lacustrine marls and mudstones and basaltic lapilli, blocks, and bombs. (3) Planar-bedded tuff forming thin beds of fine to coarse ash-size sedimentary material and basalt clasts. Intrusive bodies in the thickly bedded lapilli tuff range from irregularly shaped and anastomosing dikes and sills of meters to tens of meters in length, to a main feeder dike that is up to ˜20 m wide, and that flares into a spoon-shaped sill at ˜100 m in diameter and 10-20 m thick in the eastern part of the structure. Volcaniclastic deposits and structural features suggest that ascending magma entrained soft, saturated sediment host material into the feeder dike and erupted fluidal magma and wet sediment via weak, Strombolian-like explosions. Host sediment and erupted material subsided to replace the extracted sediments, producing the growth subsidence structure that is similar to upper diatreme facies in typical maar diatremes but lacks evidence for explosive disruption of diatreme fill. Irregularly shaped small intrusions extended from the main feeder dike into the diatreme, and many were disaggregated due to shifting and subsidence of diatreme fill and recycled via eruption. The Mardoux structure is an "unconventional" maar diatreme in that it was produced mainly by weak explosive activity rather than by violent phreatomagmatic explosions and is an example of complex coupling between soft sediment and ascending magma.

Fault evolution in volcanic tuffs and quartz-rich eolian sandstone as mechanical analogs for faulting in Martian pyroclastic deposits

NASA Astrophysics Data System (ADS)

Okubo, C. H.

2014-12-01

In order to establish a foundation for studies of faulting in Martian rocks and soils in volcanic terrain, the distribution of brittle strain around faults within the North Menan Butte Tuff in the eastern Snake River Plain, Idaho and the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah, has been recently described. These studies employed a combination of macroscopic and microscopic observations, including measurements of in situ permeability as a proxy for non-localized brittle deformation of the host rock. In areas where the tuff retained its primary granular nature at the time of deformation, initial plastic yielding in both tuffs occurred along deformation bands. Both compactional and dilational types of deformation bands were observed, and faulting occurred along clusters of deformation bands. Where secondary alteration processes imparted a massive texture to the tuff, brittle deformation was accommodated along fractures. Host-rock permeability exhibits little variation from non-deformed values in the North Menan Butte Tuff, whereas host rock permeability is reduced by roughly an order of magnitude through compaction alone (no alteration) in the Joe Lott Tuff. To create a bridge between these observations in tuff and the more substantial body of work centered on deformation band formation and faulting in quartz-rich sandstones, the same techniques employed in the North Menan Butte Tuff and the Joe Lott Tuff have also been applied to a kilometer-scale fault in the Jurassic Navajo Sandstone in the Waterpocket Fold, Utah. These observations demonstrate that the manifestation of strain and evolution of faulting in the Mars-analog tuffs are comparable to that in quartz-rich sandstones. Therefore, current understanding of brittle deformation in quartz-rich sandstones can be used to inform investigations into fault growth within porous tuffs on Mars. A discussion of these observations, practical limitations, and directions for future work are presented here.

Revised ages for tuffs of the Yellowstone Plateau volcanic field: Assignment of the Huckleberry Ridge Tuff to a new geomagnetic polarity event

USGS Publications Warehouse

Lanphere, M.A.; Champion, D.E.; Christiansen, R.L.; Izett, G.A.; Obradovich, J.D.

2002-01-01

40Ar/39Ar ages were determined on the three major ash-flow tuffs of the Yellowstone Plateau volcanic field in the region of Yellowstone National Park in order to improve the precision of previously determined ages. Total-fusion and incremental-heating ages of sanidine yielded the following mean ages: Huckleberry Ridge Tuff-2.059 ?? 0.004 Ma; Mesa Falls Tuff-1.285 ?? 0.004 Ma; and Lava Creek Tuff-0.639 ?? 0.002 Ma. The Huckleberry Ridge Tuff has a transitional magnetic direction and has previously been related to the Reunion Normal-Polarity Subchron. Dating of the Reunion event has been reviewed and its ages have been normalized to a common value for mineral standards. The age of the Huckleberry Ridge Tuff is significantly younger than lava flows of the Reunion event on Re??union Island, supporting other evidence for a normal-polarity event younger than the Reunion event.

The hydrothermal system of Long Valley Caldera, California

USGS Publications Warehouse

Sorey, M.L.; Lewis, Robert Edward; Olmsted, F.H.

1978-01-01

Long Valley caldera, an elliptical depression covering 450 km 2 on the eastern front of the Sierra Nevada in east-central California, contains a hot-water convection system with numerous hot springs and measured and estimated aquifer temperatures at depths of 180?C to 280?C. In this study we have synthesized the results of previous geologic, geophysical, geochemical, and hydrologic investigations of the Long Valley area to develop a generalized conceptual and mathematical model which describes the gross features of heat and fluid flow in the hydrothermal system. Cenozoic volcanism in the Long Valley region began about 3.2 m.y. (million years) ago and has continued intermittently until the present time. The major event that resulted in the formation of the Long Valley caldera took place about 0.7 m.y. ago with the eruption of 600 km 3 or more of Bishop Tuff of Pleistocene age, a rhyolitic ash flow, and subsequent collapse of the roof of the magma chamber along one or more steeply inclined ring fractures. Subsequent intracaldera volcanism and uplift of the west-central part of the caldera floor formed a subcircular resurgent dome about 10 km in diameter surrounded by a moat containing rhyolitic, rhyodacitic, and basaltic rocks ranging in age from 0.5 to 0.05 m.y. On the basis of gravity and seismic studies, we estimate an aver- age thickness of fill of 2.4 km above the precaldera granitic and metamorphic basement rocks. A continuous layer of densely welded Bishop Tuff overlies the basement rocks, with an average thickness of 1.4 km; the fill above the welded Bishop Tuff consists of intercalated volcanic flows and tuffs and fluvial and lacustrine deposits. Assuming the average grain density of the fill is between 2.45 and 2.65 g/cm 3 , we calculate the average bulk porosity of the total fill as from 0.11 to 0.21. Comparison of published values of porosity of the welded Bishop Tuff exposed southeast of the caldera with calculated values indicates average bulk porosity for the welded tuff (including fracture porosity) from 0.05 to 0.10. Because of its continuity and depth and the likelihood of significant fracture permeability in the more competent rocks such as the welded tuff, our model of the hydrothermal system assumes that the Bishop Tuff provides the principal hot-water reservoir. However, because very little direct information exists from drill holes below 300 m, this assumption must be considered tentative. Long Valley caldera is drained by the Owens River and several tributaries which flow into Lake Crowley in the southeast end of the caldera. Streamflow and springflow measurements for water years 1964-74 indicate a total inflow to Lake Crowley of about 10,900 L/s. In contrast, the total discharge of hot water from the hydrothermal reservoir is about 300 L/s. For modeling purposes, the ground-water system is considered as comprising a shallow subsystem in the fill above the densely welded Bishop Tuff containing relatively cold ground water, and a deep subsystem or hydrothermal reservoir in the welded tuff containing relatively hot ground water. Hydrologic, isotopic, and thermal data indicate that recharge to the hydrothermal reservoir occurs in the upper Owens River drainage basin along the western periphery of the caldera. Temperature profiles in a 2.11- km-deep test well drilled by private industry in the southeastern part of the caldera suggest that an additional flux of relatively cool ground water recharges the deep subsystem around the northeast rim. Flow in the shallow ground-water subsystem is neglected in the model except in recharge areas and along Hot Creek gorge, where approximately 80 percent of the hot-water discharge from the hydrothermal reservoir moves upward along faults toward springs in the gorge. Heat-flow data from the Long Valley region indicate that the resurgent dome overlies a residual magma chamber more circular in plan than the original magma chamber that supplied the Bishop Tuff

Stratigraphic and volcano-tectonic relations of Crater Flat Tuff and some older volcanic units, Nye County, Nevada

USGS Publications Warehouse

Carr, W.J.; Byers, F.M.; Orkild, Paul P.

1984-01-01

The Crater Flat Tuff is herein revised to include a newly recognized lowest unit, the Tram Member, exposed at scattered localities in the southwest Nevada Test Site region, and in several drill holes in the Yucca Mountain area. The overlying Bullfrog and Prow Pass Members are well exposed at the type locality of the formation near the southeast edge of Crater Flat, just north of U.S. Highway 95. In previous work, the Tram Member was thought to be the Bullfrog Member, and therefore was shown as Bullfrog or as undifferentiated Crater Flat Tuff on published maps. The revised Crater Flat Tuff is stratigraphically below the Topopah Spring Member of the Paintbrush Tuff and above the Grouse Canyon Member of the Belted Range Tuff, and is approximately 13.6 m.y. old. Drill holes on Yucca Mountain and near Fortymile Wash penetrate all three members of the Crater Flat as well as an underlying quartz-poor unit, which is herein defined as the Lithic Ridge Tuff from exposures on Lithic Ridge near the head of Topopah Wash. In outcrops between Calico Hills and Yucca Flat, the Lithic Ridge Tuff overlies a Bullfrog-like unit of reverse magnetic polarity that probably correlates with a widespread unit around and under Yucca Flat, referred to previously as Crater Flat Tuff. This unit is here informally designated as the tuff of Yucca Flat. Although older, it may be genetically related to the Crater Flat Tuff. Although the rocks are poorly exposed, geophysical and geologic evidence to date suggests that (1) the source of the Crater Flat Tuff is a caldera complex in the Crater Flat area between Yucca Mountain and Bare Mountain, and (2) there are at least two cauldrons within this complex--one probably associated with eruption of the Tram, the other with the Bullfrog and Prow Pass Members. The complex is named the Crater Flat-Prospector Pass caldera complex. The northern part of the Yucca Mountain area is suggested as the general location of the source of pre-Crater Flat tuffs, but a caldera related to the Lithic Ridge Tuff has not been specifically identified.

Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs

USGS Publications Warehouse

Lipman, P.W.; Dungan, M.A.; Brown, L.L.; Deino, A.

1996-01-01

Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite erupted from separate source calderas has important implications for evolution of the multicyclic Platoro caldera complex and for caldera-forming processes generally. Masonic Park Tuff in central parts of the San Juan field, including the type area, was erupted from a concealed source at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youngest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the "Chiquito Peak Tuff," is the last-erupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y. interval (29.5-28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km3 each, and five more have volumes of 50-150 km3. The total volume of ash-flow tuff exceeds 2500 km3, and caldera-related lavas of dominantly andesitic composition make up 250-500 km3 more. A much greater volume of intermediate-composition magma must have solidified in subcaldera magma chambers. Most preserved features of the Platoro complex - including postcollapse asymmetrical trap-door resurgent uplift of the ponded intracaldera tuff and concurrent infilling by andesitic lava flows - postdate eruption of the Chiquito Peak Tuff. The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompanied by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse. Repeated syneruptive collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the sustained presence of an andesitic subcaldera magma reservoir, or its rapid replenishment, during the 1 m.y. life span of the Platoro complex. Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.

Cenozoic Ignimbrites, Source Calderas, Relict Magma Chambers, and Tectonic Settings: Perspectives from Cordilleran North America (Invited)

NASA Astrophysics Data System (ADS)

Lipman, P. W.

2009-12-01

In the early 1960s, new concepts and innovative techniques coalesced spectacularly to improve understanding of Tertiary pyroclastic volcanism in North America. Spotty recognition of welded tuff, among rocks mostly described as silicic lava flows, exploded with identification of individual ignimbrite sheets, some having volumes >103 km3 and extending >100 km from source calderas. R.l. Smith, during study of the Bandelier Tuff in New Mexico, documented complexities of welding and crystallization zones that provided a genetic framework (cooling units) for ignimbrite studies (even while confusion continues in some areas where talus and vegetation obscure bench-forming contact zones between densely welded cliffs). Also in the 1960s, application of isotopic age determinations (initially K-Ar, now largely superceded by 40Ar/39Ar laser fusion) and precise paleomagnetic pole directions became key tools for correlating ignimbrites, deciphering eruptive histories, and determining volcano-tectonic patterns. Dated ignimbrites provide unique stratigraphic markers within volcanic field, as well as datums for regional structures and the shifting patterns of volcanism related to global plate motions--another happy coincidence in the 1960s as plate-tectonic models were formulated. Tertiary ignimbrite flare-ups along the Cordilleran margin increasingly are recognized as coinciding with inception of regional extension, especially during transitions from episodes of low-angle convergence. Many large caldera sources for the Tertiary ignimbrites have now been identified, in place of prior vague concepts of “volcano-tectonic depressions”, especially as the contrasts between thin outflow and thickly ponded intracaldera ignimbrite with interleaved collapse breccia became appreciated. Multi-km-thick fills in many calderas document that collapse begins early during large ignimbrite eruptions, and downsag inception was succeeded by breakage along ring faults. Resurgent uplift has been identified at many ignimbrite calderas, building on the pioneering observations of van Bemmelen at Lake Toba, Indonesia. Still many Tertiary caldera systems remain poorly understood where buried beneath younger rocks, others completely eroded to levels of subvolcanic granitic plutons. Links between silicic volcanism and batholith formation in continental crust continue a major research focus; improved petrologic, isotopic, and geophysical techniques are helping evaluate compositional and age relations between extrusive and intrusive components, as well as present-day intrusion geometry relative to times of peak volcanism. Ignimbrites that preserve quenched compositional gradients, commonly from rhyolite upward into crystal-rich dacite, were early recognized as special opportunities for magma-chamber studies, especially as analytical methods improved (XRF and INAA rock chemistry, microprobe mineral compositions, radiogenic and stable isotope geochemistry). These demonstrated the importance of mafic magma from the mantle, melting/assimilation in the lower crust, and mixing of diverse magmas during rise and eruption, even as recent studies by electron and/or ion probe documented complex crystal cargos (mixed phenocrysts, xenocrysts, and antecrysts).

U-Pb Geochronology of Hydrous Silica (Siebengebirge, Germany)

NASA Astrophysics Data System (ADS)

Tomaschek, Frank; Nemchin, Alexander; Geisler, Thorsten; Heuser, Alexander; Merle, Renaud

2015-04-01

Low-temperature, hydrous weathering eventually leads to characteristic products such as silica indurations. Elevated U concentrations and the ability of silica to maintain a closed system permits silica to be dated by the U-Pb method, which, in turn, will potentially allow constraining the timing of near-surface processes. To test the feasibility of silica U-Pb geochronology, we sampled opal and chalcedony from the Siebengebirge, Germany. This study area is situated at the terminus of the Cenozoic Lower Rhine Basin on the Rhenish Massif. The investigated samples include silicified gravels from the Mittelbachtal locality, renowned for the embedded wood opal. Structural characterization of the silica phases (Raman spectroscopy) was combined with in situ isotopic analyses, using ion microprobe and LA-ICPMS techniques. In the Siebengebirge area fluviatile sediments of Upper Oligocene age were covered by an extended trachyte tuff at around 25 Ma. Silica is known to indurate some domains within the tuff and, in particular, certain horizons within the subjacent fluviatile sediments ('Tertiärquarzite'). Cementation of the gravels occurred during at least three successive growth stages: early paracrystalline silica (opal-CT), fibrous chalcedony, and late microcrystalline quartz. It has traditionally been assumed that this silica induration reflects intense weathering, more or less synchronous with the deposition of the volcanic ashes. Results from U-Pb geochronology returned a range of discrete 206Pb-238U ages, recording a protracted silicification history. For instance, we obtained 22 ± 1 Ma for opal-CT cement from a silicified tuff, 16.6 ± 0.5 Ma for silicified wood and opal-CT cement in the fluviatile gravels, as well as 11 ± 1 Ma for texturally late chalcedony. While silicification of the sampled tuff might be contemporaneous with late-stage basalts, opaline silicification of the subjacent sediments and their wood in the Mittelbachtal clearly postdates active Siebengebirge volcanism, and the clastic sedimentation by about 8 Myr. To account for the age discrepancies, opal-CT formation might be a local and episodic phenomenon, reflecting progressive denudation of the trachyte tuff cover. Alternatively, the dominant silicification event of the Mittelbachtal silcretes could be of regional significance (Middle Miocene Climatic Optimum). Our relatively fast approach by LA-ICPMS analysis will be used to further expand the database.

An investigation of volcanic depressions. Part 3: Maars, tuff-rings, tuff-cones, and diatremes

NASA Technical Reports Server (NTRS)

Lorenz, V.; Mcbirney, A. R.; Williams, H.

1970-01-01

A classification of maars, tuff-rings, tuff-cones, and diatremes is given along with a summary of their lithologic and structural characteristics at the surface and at depth, and their probable manner of formation. Particular emphasis is placed on the roles of fluidization and groundwater.

Surface Water Data at Los Alamos National Laboratory: 2002 Water Year

DOE Office of Scientific and Technical Information (OSTI.GOV)

D.A. Shaull; D. Ortiz; M.R. Alexander

2003-03-03

The principal investigators collected and computed surface water discharge data from 34 stream-gaging stations that cover most of Los Alamos National Laboratory and one at Bandelier National Monument. Also included are discharge data from three springs--two that flow into Canon de Valle and one that flows into Water Canyon--and peak flow data from 16 stations.

Surface Water Data at Los Alamos National Laboratory 2006 Water Year

DOE Office of Scientific and Technical Information (OSTI.GOV)

R.P. Romero, D. Ortiz, G. Kuyumjian

2007-08-01

The principal investigators collected and computed surface water discharge data from 44 stream-gaging stations that cover most of Los Alamos National Laboratory and one at Bandelier National Monument. Also included are discharge data from three springs--two that flow into Canon de Valle and one that flows into Water Canyon--and peak flow data for 44 stations.

Chapter 6. Ranching history

Treesearch

Thomas Merlan; Kurt F. Anschuetz

2007-01-01

Adolf Bandelier described the Valles Caldera in the mid-1880s: The Valles Mountains separate the northern section of the Queres district from that claimed by the Jémez tribe. Against the chain of gently sloping summits which forms the main range from the peak of Abiquiu to the Sierra de la Palisada in the south abuts in the west an elevated plateau, containing a series...

Ecohydrology of pinon-juniper woodlands in the Jemez Mountains, New Mexico: Runoff, erosion, and restoration

Treesearch

Craig D. Allen

2008-01-01

(Please note, this is an extended abstract only) Woodlands of pinon (Pinus edulis) and oneseed juniper (Juniperus monosperma) in the Jemez Mountains at Bandelier National Monument in northern New Mexico exhibit greatly accelerated rates of soil erosion, triggered by historic land use practices (livestock grazing and fire suppression). This erosion is degrading these...

Chloride Diffusion and Acid Resistance of Concrete Containing Zeolite and Tuff as Partial Replacements of Cement and Sand

PubMed Central

Mohseni, Ehsan; Tang, Waiching; Cui, Hongzhi

2017-01-01

In this paper, the properties of concrete containing zeolite and tuff as partial replacements of cement and sand were studied. The compressive strength, water absorption, chloride ion diffusion and resistance to acid environments of concretes made with zeolite at proportions of 10% and 15% of binder and tuff at ratios of 5%, 10% and 15% of fine aggregate were investigated. The results showed that the compressive strength of samples with zeolite and tuff increased considerably. In general, the concrete strength increased with increasing tuff content, and the strength was further improved when cement was replaced by zeolite. According to the water absorption results, specimens with zeolite showed the lowest water absorption values. With the incorporation of tuff and zeolite, the chloride resistance of specimens was enhanced significantly. In terms of the water absorption and chloride diffusion results, the most favorable replacement of cement and sand was 10% zeolite and 15% tuff, respectively. However, the resistance to acid attack reduced due to the absorbing characteristic and calcareous nature of the tuff. PMID:28772737

Age, composition, and areal distribution of the Pliocene Lawlor Tuff, and three younger Pliocene tuffs, California and Nevada

USGS Publications Warehouse

Sarna-Wojcicki, Andrei M.; Deino, Alan L.; Fleck, Robert J.; McLaughlin, Robert J.; Wagner, David; Wan, Elmira; Wahl, David B.; Hillhouse, John W.; Perkins, Michael

2011-01-01

The Lawlor Tuff is a widespread dacitic tephra layer produced by Plinian eruptions and ash flows derived from the Sonoma Volcanics, a volcanic area north of San Francisco Bay in the central Coast Ranges of California, USA. The younger, chemically similar Huichica tuff, the tuff of Napa, and the tuff of Monticello Road sequentially overlie the Lawlor Tuff, and were erupted from the same volcanic field. We obtain new laser-fusion and incremental-heating 40Ar/39Ar isochron and plateau ages of 4.834 ± 0.011, 4.76 ± 0.03, ≤4.70 ± 0.03, and 4.50 ± 0.02 Ma (1 sigma), respectively, for these layers. The ages are concordant with their stratigraphic positions and are significantly older than those determined previously by the K-Ar method on the same tuffs in previous studies.Based on offsets of the ash-flow phase of the Lawlor Tuff by strands of the eastern San Andreas fault system within the northeastern San Francisco Bay area, total offset east of the Rodgers Creek–Healdsburg fault is estimated to be in the range of 36 to 56 km, with corresponding displacement rates between 8.4 and 11.6 mm/yr over the past ∼4.83 Ma.We identify these tuffs by their chemical, petrographic, and magnetic characteristics over a large area in California and western Nevada, and at a number of new localities. They are thus unique chronostratigraphic markers that allow correlation of marine and terrestrial sedimentary and volcanic strata of early Pliocene age for their region of fallout. The tuff of Monticello Road is identified only near its eruptive source.

Relationship between the Porco, Bolivia, Ag-Zn-Pb-Sn deposit and the Porco Caldera

USGS Publications Warehouse

Cunningham, C.G.

1994-01-01

The Porco Ag-Zn-Pb-Sn deposit, a major Ag producer in the 16th century and currently the major Zn producer in Bolivia, consists of a swarm of fissure-filling veins in the newly recognized Porco caldera. The caldera measures 5 km by 3 km and formed in response to the eruption of the 12 Ma crystal-rich dacitic Porco Tuff. The mineralization is associated with, and is probably genetically related to, the 8.6 Ma Huayna Porco stock. The Porco deposit consists of steeply dipping irregular and curvilinear veins that cut the intracaldera Porco Tuff about 1 km east of the Huayna Porco stock. Most of the veins are aligned along the structural margin (ring fracture) of the caldera. The ore deposit is zoned around the Huayna Porco stock. The primary Ag minerals are most abundant in the upper parts of the viens. Fluid inclusions in sphalerite stalactites have homogenization temperatures of about 225??C and salinities of about 8 wt% NaCl equiv. The stalactites and the presence of sparse vapor-rich inclusions suggest deposition of sphalerite under boiling conditions. -from Authors

Geohydrology of rocks penetrated by test well USW H-4, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Whitfield, M.S.; Eshom, E.P.; Thordarson, William; Schaefer, D.H.

1985-01-01

Test well USW H-4 is one of several wells drilled in the southwestern part of the Nevada Test Site for hydraulic testing, hydrologic monitoring, and geophysical logging. The work was performed in cooperation with the U.S. Department of Energy. The rocks penetrated by the well to a total depth of 1,219 m were volcanic tuffs of Tertiary age. Hydraulic coefficients calculated from pumping test data indicate that transmissivity ranged from 200 to 790 sq m/day. A radioactive tracer, borehole flow survey indicated that the two most productive zones during this borehole flow survey occurred in the upper part of the Bullfrog Member of the Crater Flat Tuff, depth interval from 721 to 731.5m, and in the underlying part of the Tram Member, depth interval from 864 to 920m. The water is predominantly a sodium biocarbonate type with small concentrations of calcium, magnesium, and sulfate. The apparent age of this composite water sample was determined by carbon-14 date of 17,200 years before present. (USGS)

Rock geochemistry in the Mahd adh Dhahab district, Kingdom of Saudi Arabia

USGS Publications Warehouse

Worl, R.G.; Doebrich, J.L.; Allen, M.S.; Afifi, A.M.; Ebens, R.J.

1987-01-01

Anomalous values of gold, silver, lead, and to a lesser extent copper and zinc in surface rock samples clearly delineated the northern mineralized zone in the upper agglomerate, and an east-vein area and west-vein area of the southern mineralized zone in the lower agglomerate. A third geochemically anomalous area occurs farther to the west in the lower agglomerate, suggesting that mineralization may have extended at least to this area along the lower agglomerate-lower tuff contact, and possibly even further to the west.

Geochronologic and paleomagnetic evidence defining the relationship between the Miocene Hiko and Racer Canyon tuffs, eccentric outflow lobes from the Caliente caldera complex, southeastern Great Basin, USA

USGS Publications Warehouse

Gromme, S.; Deino, A.M.; Best, M.G.; Hudson, M.R.

1997-01-01

Outflow sheets of the Hiko tuff and the Racer Canyon tuff, which together extend over approximately 16000 km2 around the Caliente caldera complex in southeastern Nevada, have long been considered to be products of simultaneous or near-simultaneous eruptions from inset calderas in the west and east ends, respectively, of the caldera complex. New high-precision 40Ar/39Ar geochronology and paleomagnetic data demonstrate that emplacement of the uppermost part of the Racer Canyon tuff at 18.33??0.03 Ma was nearly synchronous with emplacement of the single outflow cooling unit of the much larger overlying Hiko tuff at 18.32??0.04 Ma. Based on comparison with the geomagnetic polarity time scale derived from the sea-floor spreading record, we conclude that emplacement of the first of several outflow cooling units of the Racer Canyon tuff commenced approximately 0.5 m.y. earlier. Only one paleomagnetic polarity is found in the Hiko tuff, but at least two paleomagnetic reversals have been found in the Racer Canyon tuff. The two formations overlap in only one place, at and near Panaca Summit northeast of the center of the Caliente caldera complex; here the Hiko tuff is stratigraphically above the Racer Canyon tuff. This study demonstrates the power of combining 40Ar/39Ar and paleomagnetic data in conjunction with phenocryst compositional modes to resolve problematic stratigraphic correlations in complex ash-flow sequences where use of one method alone might not eliminate ambiguities.

Perched Ground Water in Zeolitized-Bedded Tuff, Rainier Mesa and Vicinity, Nevada Test Site, Nevada

USGS Publications Warehouse

Thordarson, William

1965-01-01

Rainier Mesa--site of the first series of underground nuclear detonations--is the highest of a group of ridges and mesas within the Nevada Test Site. The mesa is about 9.5 square miles in area and reaches a maximum altitude of 7,679 feet. The mesa is underlain by welded tuff, friable-bedded tuff, and zeolitized-bedded tuff of the Piapi Canyon Group and the Indian Trail Formation of Tertiary age. The tuff--2,000 to 9,000 feet thick--rests unconformably upon thrust-faulted miogeosynclinal rocks of Paleozoic age. Zeolitic-bedded tuff at the base of the tuff sequence controls the recharge rate of ground water to the underlying and more permeable Paleozoic aquifers. The zeolitic tuff--600 to 800 feet thick--is a fractured aquitard with high interstitial porosity, but with very low interstitial permeability and fracture transmissibility. The interstitial porosity ranges from 29 to 38 percent, the interstitial permeability is generally less than 0.009 gpd/ft3, and the fracture transmissibility ranges from 10 to 100 gpd/ft for 900 feet of saturated rock. The tuff is generally fully saturated interstitially hundreds of feet above the regional water table, yet no appreciable volume of water moves through the interstices because of the very low permeability. The only freely moving water observed in miles of underground workings occurred in fractures, usually fault zones.

Geological and 40Ar/39Ar age constraints on late-stage Deccan rhyolitic volcanism, inter-volcanic sedimentation, and the Panvel flexure from the Dongri area, Mumbai

NASA Astrophysics Data System (ADS)

Sheth, Hetu C.; Pande, Kanchan

2014-04-01

Post-K-Pg Boundary Deccan magmatism is well known from the Mumbai area in the Panvel flexure zone. Represented by the Salsette Subgroup, it shows characters atypical of much of the Deccan Traps, including rhyolite lavas and tuffs, mafic tuffs and breccias, spilitic pillow basalts, and "intertrappean" sedimentary or volcanosedimentary deposits, with mafic intrusions as well as trachyte intrusions containing basaltic enclaves. The intertrappean deposits have been interpreted as formed in shallow marine or lagoonal environments in small fault-bounded basins due to syn-volcanic subsidence. We report a previously unknown sedimentary deposit underlying the Dongri rhyolite flow from the upper part of the Salsette Subgroup, with a westerly tectonic dip due to the Panvel flexure. We have obtained concordant 40Ar/39Ar ages of 62.6 ± 0.6 Ma (2σ) and 62.9 ± 0.2 Ma (2σ) for samples taken from two separate outcrops of this rhyolite. The results are significant in showing that (i) Danian inter-volcanic sedimentary deposits formed throughout Mumbai, (ii) the rock units are consistent with the stratigraphy postulated earlier for Mumbai, (iii) shale fragments known in some Dongri tuffs were likely derived from the sedimentary deposit under the Dongri rhyolite, (iv) the total duration of extrusive and intrusive Deccan magmatism was at least 8-9 million years, and (v) Panvel flexure formed, or continued to form, after 63 Ma, possibly even 62 Ma, and could not have formed by 65-64 Ma as concluded in a recent study.

Petrography of the Paleogene Volcanic Rocks of the Sierra Maestra, Southeastern Cuba

NASA Astrophysics Data System (ADS)

Bemis, V. L.

2006-12-01

This study is a petrographic analysis of over 200 specimens of the Paleogene volcanic rocks of the Sierra Maestra (Southerneastern Cuba), a key structure in the framework of the northern Caribbean plate boundary evolution. The purpose of this study is to understand the eruptive processes and the depositional environments. The volcanic sequence in the lower part of the Sierra Maestra begins with highly porphyritic pillow lavas, topped by massive tuffs and autoclastic flows. The presence of broken phenocrystals, palagonitic glass and hyaloclastites in this section of the sequence suggests that the prevalent mode of eruption was explosive. The absence of welding in the tuffs suggests that the rocks were emplaced in a deep submarine environment. Coherent flows, much less common than the massive tuffs, show evidence of autoclastic fracturing, also indicating low temperature-submarine environments. These observations support the hypothesis that the Sierra Maestra sequence may be neither part of the Great Antilles Arc of the Mesozoic nor any other fully developed volcanic arc, rather a 250 km long, submarine eruptive system of dikes, flows and sills, most likely a back-arc structure. The volcanic rocks of the upper sequence are all very fine grained, reworked volcaniclastic materials, often with the structures of distal turbidities, in mode and texture similar to those drilled on the Cayman Rise. This study suggests that the Sierra Maestra most likely records volcanism of diverse sources: a local older submarine source, and one or more distal younger sources, identifiable with the pan-Caribbean volcanic events of the Tertiary.

Fire effects in southwestern forests: Proceedings of the second La Mesa Fire Symposium

Treesearch

Craig D. Allen

1996-01-01

In 1977, the La Mesa Fire burned across 15,444 acres of ponderosa pine forests on the adjoining lands of Bandelier National Monument, the Santa Fe National Forest, and Los Alamos National Laboratory. Following this event, several fire effects studies were initiated. The 16 papers herein document longer-term knowledge gained about the ecological effects of the fire and...

Mechanics of brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho

NASA Astrophysics Data System (ADS)

Okubo, C. H.

2013-12-01

The Menan Volcanic Complex consists of phreatomagmatic tuff cones that were emplaced as part of the regional volcanic activity in the Snake River Plain during the late Pleistocene. These tuff cones, the ';Menan Buttes', resulted from the eruption of basaltic magma through water-saturated alluvium and older basalts along the Snake River. The tuffs are composed primarily of basaltic glass with occasional plagioclase and olivine phenocrysts. The tuff is hydrothermally altered to a massive palagonitic tuff at depth but is otherwise poorly welded. Mass movements along the flanks of the cones were contemporaneous with tuff deposition. These slope failures are manifest as cm- to meter-scale pure folds, faults and fault-related folds, as well as larger slumps that are tens to a few hundred meters wide. Previous investigations classified the structural discontinuities at North Menan Butte based on orientation and sense of displacement, and all were recognized as opening-mode or shear fractures (Russell and Brisbin, 1990). This earlier work also used a generalized model of static (i.e., aseismic) gravity-driven shear failure within cohesionless soils to infer a possible origin for these fractures through slope failure. Recent work at North Menan Butte has provided novel insight into the styles of brittle deformation present, the effect of this deformation on the circulation of subsurface fluids within the tuff cone, as well as the mechanisms of the observed slope failures. Field observations reveal that the brittle deformation, previously classified as fractures, is manifest as deformation bands within the non-altered, poorly welded portions of the tuff. Both dilational and compactional bands, with shear, are observed. Slumps are bounded by normal faults, which are found to have developed within clusters of deformation bands. Deformation bands along the down-slope ends of these failure surfaces are predominantly compactional in nature. These bands have a ~3800 millidarcy permeability, a decrease from the ~9400 millidarcy permeability typical of the non-deformed, poorly-welded tuff. As such, these bands would have acted to slow to the circulation of local fluids through the tuff cone, possibly reducing the slopes' stability further. Future work will employ slope stability models to investigate the tendency for slumping of these tuffs shortly after their emplacement, accounting for water-saturated conditions and the effects of eruption-related seismicity. These results will improve current understanding of the mechanics of fault growth within basaltic tuff and enable more rigorous assessments of the hazards posed by slope instability on active phreatomagmatic tuff cones.

Hydrogeology of rocks penetrated by test well JF-3, Jackass Flats, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plume, R.W.; La Camera, R.J.

1996-12-31

The U.S. Department of Energy and U.S. Geological Survey are monitoring water levels in southern Nevada and adjacent parts of California in response to concern about the potential effects of pumping ground water to support the Yucca Mountain Site-Characterization Program. Well JF-3 was drilled in the western part of Jackass Flats for monitoring water levels, for determining the likelihood of a hydraulic connection between well JF-3 and production wells J-12 and J-13, and for measuring the hydraulic properties of the Topopah Spring Tuff. The borehole for JF-3 penetrated about 480 feet of alluvium and 818 feet of underlying volcanic rock.more » The well was finished at a depth of 1,138 feet below land surface near the base of the Topopah Spring Tuff, which is the principal volcanic-rock aquifer in the area. The Topopah Spring Tuff at well JF-3 extends from depths of 580 feet to 1,140 feet and consists of about 10 feet of partly to moderately welded ash-flow tuff; 10 feet of vitrophyre; 440 feet of devitrified, moderately to densely welded ash-flow tuff; 80 feet of densely welded ash-flow tuff; 10 feet of vitric, nonwelded to partly welded ash-flow tuff; and 10 feet of ashfall tuff. Fractures and lithophysae are most common in the devitrified tuff, especially between depths of 600 feet and 1,040 feet. Much of the water produced in well JF-3 probably comes from the sequence of these devitrified tuffs that is below the water table. The transmissivity of the aquifer is an estimated 140,000-160,000 feet squared per day and hydraulic conductivity is 330-370 feet per day. These values exceed estimates made at well J-13 by two orders of magnitude. Such large differences may be accounted for by differences in the development of fractures and lithophysae in the Topopah Spring Tuff at the two wells.« less

Triaxial- and uniaxial-compression testing methods developed for extraction of pore water from unsaturated tuff, Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mower, T.E.; Higgins, J.D.; Yang, I.C.

1989-12-31

To support the study of hydrologic system in the unsaturated zone at Yucca Mountain, Nevada, two extraction methods were examined to obtain representative, uncontaminated pore-water samples from unsaturated tuff. Results indicate that triaxial compression, which uses a standard cell, can remove pore water from nonwelded tuff that has an initial moisture content greater than 11% by weight; uniaxial compression, which uses a specifically fabricated cell, can extract pore water from nonwelded tuff that has an initial moisture content greater than 8% and from welded tuff that has an initial moisture content greater than 6.5%. For the ambient moisture conditions ofmore » Yucca Mountain tuffs, uniaxial compression is the most efficient method of pore-water extraction. 12 refs., 7 figs., 2 tabs.« less

Batch sorption results for neptunium transport through Yucca Mountain tuffs. Yucca Mountain Site Characterization Program milestone 3349

DOE Office of Scientific and Technical Information (OSTI.GOV)

Triay, I.R.; Cotter, C.R.; Huddleston, M.H.

1996-09-01

We studied the sorption of neptunium onto tuffs characteristic of the proposed nuclear waste repository at Yucca Mountain, Nevada. The neptunium was in the Np(V) oxidation state under oxidizing conditions in groundwaters from two wells located close to the repository site (J-13 and UE-25 p No.1). We used devitrified, vitric, zeolitic (with emphasis on clinoptilolite-rich samples), and calcite-rich tuffs characteristic of the geology of the site. Neptunium sorbed well onto calcite and calcite-rich tuffs, indicating that a significant amount of neptunium retardation can be expected under fractured-flow scenarios because of calcite coating of the fractures. Neptunium sorption onto clinoptilolite-rich zeoliticmore » tuffs in J-13 well water (pH from 7 to 8.5) was moderate, increased with decreasing pH, and correlated to surface area and amount of clinoptilolite. Neptunium sorbed poorly onto zeolitic tuffs from UE-25 p No.1 groundwater (pH from 7 to 9) and onto devitrified and vitric tuffs from J-13 and UE-25 p No.1 waters (pH from 7 to 9). Iron oxides appeared to be passivated in tuffs, not seeming to contribute to the observed neptunium sorption, even though neptunium sorption onto synthetic iron oxide is significant.« less

The submarine record of a large-scale explosive eruption in the Vanuatu Arc: ˜1 Ma Efaté Pumice Formation

NASA Astrophysics Data System (ADS)

Raos, Alison M.; McPhie, Jocelyn

The Efaté Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efaté Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ˜500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efaté Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95% glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efaté Pumice Breccias were largely generated by magmatic-volatile-driven ("dry"), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

Plio-Pleistocene synsedimentary fault compartments, foundation for the eastern Olduvai Basin paleoenvironmental mosaic, Tanzania.

PubMed

Stollhofen, Harald; Stanistreet, Ian G

2012-08-01

Normal faults displacing Upper Bed I and Lower Bed II strata of the Plio-Pleistocene Lake Olduvai were studied on the basis of facies and thickness changes as well as diversion of transport directions across them in order to establish criteria for their synsedimentary activity. Decompacted differential thicknesses across faults were then used to calculate average fault slip rates of 0.05-0.47 mm/yr for the Tuff IE/IF interval (Upper Bed I) and 0.01-0.13 mm/yr for the Tuff IF/IIA section (Lower Bed II). Considering fault recurrence intervals of ~1000 years, fault scarp heights potentially achieved average values of 0.05-0.47 m and a maximum value of 5.4 m during Upper Bed I, which dropped to average values of 0.01-0.13 m and a localized maximum of 0.72 m during Lower Bed II deposition. Synsedimentary faults were of importance to the form and paleoecology of landscapes utilized by early hominins, most traceably and provably Homo habilis as illustrated by the recurrent density and compositional pattern of Oldowan stone artifact assemblage variation across them. Two potential relationship factors are: (1) fault scarp topographies controlled sediment distribution, surface, and subsurface hydrology, and thus vegetation, so that a resulting mosaic of microenvironments and paleoecologies provided a variety of opportunities for omnivorous hominins; and (2) they ensured that the most voluminous and violent pyroclastic flows from the Mt. Olmoti volcano were dammed and conduited away from the Olduvai Basin depocenter, when otherwise a single or set of ignimbrite flows might have filled and devastated the topography that contained the central lake body. In addition, hydraulically active faults may have conduited groundwater, supporting freshwater springs and wetlands and favoring growth of trees. Copyright © 2011 Elsevier Ltd. All rights reserved.

Landscape ecology: a concept for protecting park resources

USGS Publications Warehouse

Allen, Craig D.; Lissoway, John; Yarborough, Keith

1990-01-01

The Southwest Region has been supporting Resource Basic Inventory (RBI) efforts to establish baseline data for comparisons with long-term monitoring results to be conducted in the future. This “pulse taking” is a part of the Servicewide initiative being fostered so that resource managers, scientists, and park managers will be able to track the health of park resources by determining changes and trends. The RBI work is being linked with the development of Geographic Information Systems (GIS) at Bandelier, Big Thicket, Big Bend, Padre Island, and Guadalupe Mountains. Many of the parks in the southwest Region have only partially completed RBIs. This informational shortcoming is a pervasive threat to the parks because without detailed knowledge of the parks’ respective resources the Service cannot protect them adequately. To overcome this deficiency, the SWRO’s Division of Natural Resources Management and Science has fostered at Bandelier a pilot research effort, which started in FY ’87 and utilizes a landscape ecology paradigm. This concept links the RBI, GIS, and research activities in a park to present an overall picture of the park in its regional ecosystem setting. The flowchart diagrams this project’s concept. The results have been encouraging. A final report was recently completed (Allen 1989). This concept may now be applied to other Southwest Region parks.

Temporal evolution of the Roccamonfina volcanic complex (Pleistocene), Central Italy

NASA Astrophysics Data System (ADS)

Rouchon, V.; Gillot, P. Y.; Quidelleur, X.; Chiesa, S.; Floris, B.

2008-10-01

The Roccamonfina volcanic complex (RVC), in southern Italy, is an Early to Middle Pleistocene stratovolcano sharing temporal and morphological characteristics with the Somma-Vesuvius and the Alban Hills; both being associated with high volcanic hazard for the cities of Naples and Rome, respectively. The RVC is important for the understanding of volcanic evolution in the Roman and Campanian volcanic provinces. We report a comprehensive study of its evolution based on morphological, geochemical and K-Ar geochronological data. The RVC was active from c.a. 550 ka to 150 ka. Its evolution is divided into five stages, defining a volcanic pulse recurrence time of c.a. 90-100 kyr. The two initial stages, consisted in the construction of two successive stratovolcanoes of the tephrite-phonolite, namely "High-K series". The first stage was terminated by a major plinian eruption emplacing the trachytic Rio Rava pumices at 439 ± 9 ka. At the end of the second stage, the last High-K series stratovolcano was destroyed by a large sector collapse and the emplacement of the Brown Leucitic Tuff (BLT) at 353 ± 5 ka. The central caldera of the RVC is the result of the overlapping of the Rio Rava and of the BLT explosions. The plinian eruption of the BLT is related to the emptying of a stratified, deep-seated HKS magma chamber during the upwelling of K series (KS) magma, marking a major geochemical transition and plumbing system re-organization. The following stage was responsible for the emplacement of the Lower White Trachytic Tuff at 331 ± 2 ka, and of basaltic-trachytic effusive products erupted through the main vent. The subsequent activity was mainly restricted to the emplacement of basaltic-shoshonitic parasitic cones and lava flows, and of minor subplinian deposits of the Upper White Trachytic Tuff between 275 and 230 ka. The northern crater is most probably a maar that formed by the phreatomagmatic explosion of the Yellow Trachytic Tuff at 230 ka. The latest stage of activity featured the edification of the central shoshonitic domes at c.a. 150 ka.

Deformation of the Wineglass Welded Tuff and the timing of caldera collapse at Crater Lake, Oregon

USGS Publications Warehouse

Kamata, H.; Suzuki-Kamata, K.; Bacon, C.R.

1993-01-01

Four types of deformation occur in the Wineglass Welded Tuff on the northeast caldera rim of Crater Lake: (a) vertical tension fractures; (b) ooze-outs of fiamme: (c) squeeze-outs of fiamme; and (d) horizontal pull-apart structures. The three types of plastic deformation (b-d) developed in the lower part of the Wineglass Welded Tuff where degree of welding and density are maximum. Deformation originated from concentric normal faulting and landsliding as the caldera collapsed. The degree of deformation of the Wineglass Welded Tuff increases toward the northeast part of the caldera, where plastic deformation occurred more easily because of a higher emplacement temperature probably due to proximity to the vent. The probable glass transition temperature of the Wineglass Welded Tuff suggests that its emplacement temperature was ???750??C where the tuff is densely welded. Calculation of the conductive cooling history of the Wineglass Welded Tuff and the preclimactic Cleetwood (lava) flow under assumptions of a initially isothermal sheet and uniform properties suggests that (a) caldera collapse occurred a maximum of 9 days after emplacement of the Wineglass Welded Tuff, and that (b) the period between effusion of the Cleetwood (lava) flow and onset of the climactic eruption was <100 years. If cooling is controlled more by precipitation during quiescent periods than by conduction, these intervals must be shorter than the calculated times. ?? 1993.

Methods for pore water extraction from unsaturated zone tuff, Yucca Mountain, Nevada

USGS Publications Warehouse

Scofield, K.M.

2006-01-01

Assessing the performance of the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, requires an understanding of the chemistry of the water that moves through the host rock. The uniaxial compression method used to extract pore water from samples of tuffaceous borehole core was successful only for nonwelded tuff. An ultracentrifugation method was adopted to extract pore water from samples of the densely welded tuff of the proposed repository horizon. Tests were performed using both methods to determine the efficiency of pore water extraction and the potential effects on pore water chemistry. Test results indicate that uniaxial compression is most efficient for extracting pore water from nonwelded tuff, while ultracentrifugation is more successful in extracting pore water from densely welded tuff. Pore water splits collected from a single nonwelded tuff core during uniaxial compression tests have shown changes in pore water chemistry with increasing pressure for calcium, chloride, sulfate, and nitrate. Pore water samples collected from the intermediate pressure ranges should prevent the influence of re-dissolved, evaporative salts and the addition of ion-deficient water from clays and zeolites. Chemistry of pore water splits from welded and nonwelded tuffs using ultracentrifugation indicates that there is no substantial fractionation of solutes.

LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece)

NASA Astrophysics Data System (ADS)

Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.

2014-12-01

Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

40Ar/(39)Ar dating of Chemeron Formation strata encompassing the site of hominid KNM-BC 1, Tugen Hills, Kenya.

PubMed

Deino, Alan L; Hill, Andrew

2002-01-01

A fossil hominid temporal bone (KNM-BC 1) from surface exposures at Baringo Paleontological Research Project site BPRP#2 in the Chemeron Formation outcropping in a tributary drainage of the Kapthurin River west of Lake Baringo, Kenya has been attributed to Homo sp. indet. K-feldspar phenocrysts from lapilli tuffs bracketing the inferred fossiliferous horizon yield single-crystal(40)Ar/(39)Ar ages of 2.456+/-0.006 and 2.393+/-0.013 Ma. These age determinations are supported by stratigraphically consistent ages on higher tuff horizons and from nearby sections. In addition, new(40)Ar/(39)Ar ages on tuffaceous units near the base and top of the formation along the Kapthurin River yield 3.19+/-0.03 and 1.60+/-0.05 Ma respectively. The base of the formation along the Kapthurin River is thus approximately 0.5 Ma younger than the uppermost Chemeron Formation strata exposed at Tabarin, 23 km to the north-northwest. The upper half of the formation along the Kapthurin River was deposited at an average rate of approximately 11 cm/ka, compared to 21-23 cm/ka at Tabarin. Copyright 2002 Academic Press.

Task IV: Groundshock-Induced Hydrogeologic Response: Volume 2. Hydrologic Response of Deep Based Systems to Blast Loading

DTIC Science & Technology

1994-09-01

north-south. Width of the cap rock is approximately 1.5 miles, length about 3 miles and area about 4.4 square miles. According to Thordarson (1965...The volcanic tuffs making up the mesa are of moderately recent (Miocene) to very recent (Pliocene) origin. Thordarson (1965) identifies 11 layered tuff...various degrees of welded or partially welded tuff can be formed during cooling. The tuff units identified by Thordarson (1965) making up Rainier

Petrology and trace element geochemistry of the Honolulu volcanics, Oahu: implications for the oceanic mantle below Hawaii.

USGS Publications Warehouse

Clague, D.A.; Frey, F.A.

1982-01-01

These volcanic rocks are the products of small-volume, late-stage vents along rifts cutting the older massive Koolan tholeiitic shield on Oahu. Most of the lavas and tuffs have the geochemical features expected of near-primary magmas derived from a peridotite source with olivine Fo87-89, e.g. 100 Mg/(Mg + Fe2+) > 65, Ni > 250 p.p.m. and the presence of ultramafic mantle xenoliths at 18 of the 37 vents. Thus the geochemistry of the alkali olivine basalt, basanite, nephelinite and nepheline melilitite lavas and tuffs of these Honolulu volcanic rocks has been used to deduce the composition of their mantle source and the conditions under which they were generated by partial melting in the mantle. New major- and trace-element analyses for 31 samples are tabulated and indicate derivation by partial melting of a garnet (<10%) lherzolite source which was isotopically homogeneous and compositionally uniform for most major and trace elements, though apparently heterogeneous in TiO2, Zr, Hf, Nb and Ta (due perhaps to the low inferred degrees of melting which failed to exhaust the source in minor residual phases). In comparison with estimates of a primordial mantle composition and the mantle source of MORB, the garnet peridotite source of these Honolulu volcanics was increasingly enriched in the sequence heavy REE, Y, Tb, Ti, Sm, Zr and Hf, for which a multi-stage history is required. This composition differs from the source of the previously erupted tholeiitic shield, nor is it represented in the upper-mantle xenoliths in the lavas and tuff of the unit.-R.A.H.

Radionuclide sorption in Yucca Mountain tuffs with J-13 well water: Neptunium, uranium, and plutonium. Yucca Mountain site characterization program milestone 3338

DOE Office of Scientific and Technical Information (OSTI.GOV)

Triay, I.R.; Cotter, C.R.; Kraus, S.M.

1996-08-01

We studied the retardation of actinides (neptunium, uranium, and plutonium) by sorption as a function of radionuclide concentration in water from Well J-13 and of tuffs from Yucca Mountain. Three major tuff types were examined: devitrified, vitric, and zeolitic. To identify the sorbing minerals in the tuffs, we conducted batch sorption experiments with pure mineral separates. These experiments were performed with water from Well J-13 (a sodium bicarbonate groundwater) under oxidizing conditions in the pH range from 7 to 8.5. The results indicate that all actinides studied sorb strongly to synthetic hematite and also that Np(V) and U(VI) do notmore » sorb appreciably to devitrified or vitric tuffs, albite, or quartz. The sorption of neptunium onto clinoptilolite-rich tuffs and pure clinoptilolite can be fitted with a sorption distribution coefficient in the concentration range from 1 X 10{sup -7} to 3 X 10{sup -5} M. The sorption of uranium onto clinoptilolite-rich tuffs and pure clinoptilolite is not linear in the concentration range from 8 X 10{sup -8} to 1 X 10{sup -4} M, and it can be fitted with nonlinear isotherm models (such as the Langmuir or the Freundlich Isotherms). The sorption of neptunium and uranium onto clinoptilolite in J-13 well water increases with decreasing pH in the range from 7 to 8.5. The sorption of plutonium (initially in the Pu(V) oxidation state) onto tuffs and pure mineral separates in J-13 well water at pH 7 is significant. Plutonium sorption decreases as a function of tuff type in the order: zeolitic > vitric > devitrified; and as a function of mineralogy in the order: hematite > clinoptilolite > albite > quartz.« less

Fission-track dating of pumice from the KBS Tuff, East Rudolf, Kenya

USGS Publications Warehouse

Hurford, A.J.; Gleadow, A.J.W.; Naeser, C.W.

1976-01-01

Fission-track dating of zircon separated from two pumice samples from the KBS Tuff in the Koobi Fora Formation, in Area 131, East Rudolf, Kenya, gives an age of 2.44??0.08 Myr for the eruption of the pumice. This result is compatible with the previously published K-Ar and 40Ar/ 39Ar age spectrum estimate of 2.61??0.26 Myr for the KBS Tuff in Area 105, but differs from the more recently published K-Ar date of 1.82??0.04 Myr for the KBS Tuff in Area 131. This study does not support the suggestion that pumice cobbles of different ages occur in the KBS Tuff. ?? 1976 Nature Publishing Group.

Bed II Sequence Stratigraphic context of EF-HR and HWK EE archaeological sites, and the Oldowan/Acheulean succession at Olduvai Gorge, Tanzania.

PubMed

Stanistreet, Ian G; McHenry, Lindsay J; Stollhofen, Harald; de la Torre, Ignacio

2018-04-20

Archaeological excavations at EF-HR and HWK EE allow reassessment of Bed II stratigraphy within the Junction Area and eastern Olduvai Gorge. Application of Sequence Stratigraphic methods provides a time-stratigraphic framework enabling correlation of sedimentary units across facies boundaries, applicable even in those areas where conventional timelines, such as tephrostratigraphic markers, are absent, eroded, or reworked. Sequence Stratigraphically, Bed II subdivides into five major Sequences 1 to 5, all floored by major disconformities that incise deeply into the underlying succession, proving that simple "layer cake" stratigraphy is inappropriate. Previous establishment of the Lemuta Member has invalidated the use of Tuff IIA as the boundary between Lower and Middle Bed II, now redefined at the disconformity between Sequences 2 and 3, a lithostratigraphic contact underlying the succession containing the Lower, Middle, and Upper Augitic Sandstones. HWK EE site records Oldowan technology in the Lower Augitic Sandstone at the base of Sequence 3, within Middle Bed II. We suggest placement of recently reported Acheulean levels at FLK W within the Middle Augitic Sandstone, thus emphasizing that handaxes are yet to be found in earlier stratigraphic units of the Olduvai sequence. This would place a boundary between the Oldowan and Acheulean technologies at Olduvai in the Tuff IIB zone or earliest Middle Augitic Sandstone. A major disconformity between Sequences 3 and 4 at and near EF-HR cuts through the level of Tuff IIC, placing the main Acheulean EF-HR assemblage at the base of Sequence 4, within Upper rather than Middle Bed II. Sequence stratigraphic methods also yield a more highly resolved Bed II stratigraphic framework. Backwall and sidewall surveying of archaeological trenches at EF-HR and HWK EE permits definition of "Lake-parasequences" nested within the major Sequences that record downcutting of disconformities associated with lake regression, then sedimentation associated with lake transgression, capped finally by another erosional disconformity or hiatal paraconformity caused by the next lake withdrawal. On a relative time-scale rather than a vertical metre scale, the resulting Wheeler diagram framework provides a basis for recognizing time-equivalent depositional episodes and the position of time gaps at various scales. Relative timing of archaeological assemblage levels can then be differentiated at a millennial scale within this framework. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pore-water extraction from unsaturated tuff by triaxial and one-dimensional compression methods, Nevada Test Site, Nevada

USGS Publications Warehouse

Mower, Timothy E.; Higgins, Jerry D.; Yang, In C.; Peters, Charles A.

1994-01-01

Study of the hydrologic system at Yucca Mountain, Nevada, requires the extraction of pore-water samples from welded and nonwelded, unsaturated tuffs. Two compression methods (triaxial compression and one-dimensional compression) were examined to develop a repeatable extraction technique and to investigate the effects of the extraction method on the original pore-fluid composition. A commercially available triaxial cell was modified to collect pore water expelled from tuff cores. The triaxial cell applied a maximum axial stress of 193 MPa and a maximum confining stress of 68 MPa. Results obtained from triaxial compression testing indicated that pore-water samples could be obtained from nonwelded tuff cores that had initial moisture contents as small as 13 percent (by weight of dry soil). Injection of nitrogen gas while the test core was held at the maximum axial stress caused expulsion of additional pore water and reduced the required initial moisture content from 13 to 11 percent. Experimental calculations, together with experience gained from testing moderately welded tuff cores, indicated that the triaxial cell used in this study could not apply adequate axial or confining stress to expel pore water from cores of densely welded tuffs. This concern led to the design, fabrication, and testing of a one-dimensional compression cell. The one-dimensional compression cell used in this study was constructed from hardened 4340-alloy and nickel-alloy steels and could apply a maximum axial stress of 552 MPa. The major components of the device include a corpus ring and sample sleeve to confine the sample, a piston and base platen to apply axial load, and drainage plates to transmit expelled water from the test core out of the cell. One-dimensional compression extracted pore water from nonwelded tuff cores that had initial moisture contents as small as 7.6 percent; pore water was expelled from densely welded tuff cores that had initial moisture contents as small as 7.7 percent. Injection of nitrogen gas at the maximum axial stress did not produce additional pore water from nonwelded tuff cores, but was critical to recovery of pore water from densely welded tuff cores. Gas injection reduced the required initial moisture content in welded tuff cores from 7.7 to 6.5 percent. Based on the mechanical ability of a pore-water extraction method to remove water from welded and nonwelded tuff cores, one-dimensional compression is a more effective extraction method than triaxial compression. However, because the effects that one-dimensional compression has on pore-water chemistry are not completely understood, additional testing will be needed to verify that this method is suitable for pore-water extraction from Yucca Mountain tuffs.

Degraded dryland rehabilitation: boosting seedling survival using zeolitic tuff

NASA Astrophysics Data System (ADS)

Alhamad, Mohammad Noor; Alrbabah, Mohammad; Athamneh, Hana

2016-04-01

More than 90% of Jordan is broadly defined as rangelands. Most rangelands are located within the arid zone of the country. Extensive grazing occurs across much of the natural pastures resulting in serious environmental degradation of natural resources in these rangelands. Several programs were carried out for rangeland conservation and rehabilitation in the country. However, these programs face a major challenge of the low survival rate of transplanted shrub seedlings. Seeking innovative approaches to assure healthy establishment of seedling is a big challenge to achieve successful rehabilitation programs. Drought is considered one of the major problems in rehabilitation. Promoting survival and growth, using zeolitic tuff added to planting holes is suggested to be a possible solution. The experiment was conducted on a factorial arrangement within RCBD design. Two shrub species (Atriplex halimus, Atriplex nummularia) were transplanted into holes prepared with three levels of tuff treatments (mulching, mixing and control) under rainfed condition. The result showed insignificant effect of tuff on seedling survival percentage, when mixing tuff with plantation soil or adding tuff as mulch. Also, the two species showed similar survival percentages over two measured dates. However, mixing tuff with soil during hole preparation significantly enhanced seedling heights. Furthers, The Australian atriplex (Atriplex nummularia) species significantly grow higher than Atriplex halimus. The study results suggested that mixing zeoltic tuff with soil during transplantation of seedling is promising in improving the success of rangeland rehabilitation in dry areas in Jordan.

Influences of Sedimentary Environments and Volcanic Sources on Diagenetic Alteration of Volcanic Tuffs in South China.

PubMed

Gong, Nina; Hong, Hanlie; Huff, Warren D; Fang, Qian; Bae, Christopher J; Wang, Chaowen; Yin, Ke; Chen, Shuling

2018-05-16

Permian-Triassic (P-Tr) altered volcanic ashes (tuffs) are widely distributed within the P-Tr boundary successions in South China. Volcanic altered ashes from terrestrial section-Chahe (CH) and marine section-Shangsi (SS) are selected to further understand the influence of sedimentary environments and volcanic sources on diagenetic alterarion on volcanic tuffs. The zircon 206 Pb/ 238 U ages of the corresponding beds between two sections are almost synchronous. Sedimentary environment of the altered tuffs was characterized by a low pH and did not experience a hydrothermal process. The dominant clay minerals of all the tuff beds are illite-smectite (I-S) minerals, with minor chlorite and kaolinite. I-S minerals of CH (R3) are more ordered than SS (R1), suggesting that CH also shows a higher diagenetic grade and more intensive chemical weathering. Besides, the nature of the volcanism of the tuff beds studied is derived from different magma sources. The clay mineral compositions of tuffs have little relation with the types of source volcanism and the depositional environments. Instead, the degree of the mixed-layer clay minerals and the REE distribution are mainly dependent upon the sedimentary environments. Thus, the mixed-layer clay minerals ratio and their geochemical index can be used as the paleoenvironmental indicator.

Contrasting perspectives on the Lava Creek Tuff eruption, Yellowstone, from new U–Pb and 40Ar/39Ar age determinations

USGS Publications Warehouse

Wilson, Colin J. N.; Stelten, Mark; Lowenstern, Jacob B.

2018-01-01

The youngest major caldera-forming event at Yellowstone was the ~ 630-ka eruption of the Lava Creek Tuff. The tuff as mapped consists of two major ignimbrite packages (members A and B), linked to widespread coeval fall deposits and formation of the Yellowstone Caldera. Subsequent activity included emplacement of numerous rhyolite flows and domes, and development of two structurally resurgent domes (Mallard Lake and Sour Creek) that accommodate strain due to continual uplift/subsidence cycles. Uplifted lithologies previously mapped on and adjacent to Sour Creek dome were thought to include the ~ 2.08-Ma Huckleberry Ridge Tuff, cropping out beneath Lava Creek Tuff members A and B. Mapped outcrops of this Huckleberry Ridge Tuff material were sampled as welded ignimbrite (sample YR345) on Sour Creek dome, and at nearby Bog Creek as welded ignimbrite (YR311) underlain by an indurated lithic lag breccia containing blocks of another welded ignimbrite (YR324). Zircon near-rim U–Pb analyses from these samples yield weighted mean ages of 661 ± 13 ka (YR345: 95% confidence), 655 ± 11 ka (YR311), and 664 ± 15 ka (YR324) (combined weighted mean of 658.8 ± 6.6 ka). We also studied two samples of ignimbrite previously mapped as Huckleberry Ridge Tuff on the northeastern perimeter of the Yellowstone Caldera, ~ 12 km ENE of Sour Creek dome. Sanidines from these samples yield 40Ar/39Ar age estimates of 634.5 ± 6.8 ka (8YC-358) and 630.9 ± 4.1 ka (8YC-359). These age data show that all these units represent previously unrecognized parts of the Lava Creek Tuff and do not have any relationship to the Huckleberry Ridge Tuff. Our observations and data imply that the Lava Creek eruption was more complex than is currently assumed, incorporating two tuff units additional to those currently mapped, and which themselves are separated by a time break sufficient for cooling and some reworking. The presence of a lag breccia suggests that a source vent lay nearby (< ~ 3 km) for some of the tuffs and that the Yellowstone Caldera boundary in this area could be reconsidered.

Contrasting perspectives on the Lava Creek Tuff eruption, Yellowstone, from new U-Pb and 40Ar/39Ar age determinations

NASA Astrophysics Data System (ADS)

Wilson, Colin J. N.; Stelten, Mark E.; Lowenstern, Jacob B.

2018-06-01

The youngest major caldera-forming event at Yellowstone was the 630-ka eruption of the Lava Creek Tuff. The tuff as mapped consists of two major ignimbrite packages (members A and B), linked to widespread coeval fall deposits and formation of the Yellowstone Caldera. Subsequent activity included emplacement of numerous rhyolite flows and domes, and development of two structurally resurgent domes (Mallard Lake and Sour Creek) that accommodate strain due to continual uplift/subsidence cycles. Uplifted lithologies previously mapped on and adjacent to Sour Creek dome were thought to include the 2.08-Ma Huckleberry Ridge Tuff, cropping out beneath Lava Creek Tuff members A and B. Mapped outcrops of this Huckleberry Ridge Tuff material were sampled as welded ignimbrite (sample YR345) on Sour Creek dome, and at nearby Bog Creek as welded ignimbrite (YR311) underlain by an indurated lithic lag breccia containing blocks of another welded ignimbrite (YR324). Zircon near-rim U-Pb analyses from these samples yield weighted mean ages of 661 ± 13 ka (YR345: 95% confidence), 655 ± 11 ka (YR311), and 664 ± 15 ka (YR324) (combined weighted mean of 658.8 ± 6.6 ka). We also studied two samples of ignimbrite previously mapped as Huckleberry Ridge Tuff on the northeastern perimeter of the Yellowstone Caldera, 12 km ENE of Sour Creek dome. Sanidines from these samples yield 40Ar/39Ar age estimates of 634.5 ± 6.8 ka (8YC-358) and 630.9 ± 4.1 ka (8YC-359). These age data show that all these units represent previously unrecognized parts of the Lava Creek Tuff and do not have any relationship to the Huckleberry Ridge Tuff. Our observations and data imply that the Lava Creek eruption was more complex than is currently assumed, incorporating two tuff units additional to those currently mapped, and which themselves are separated by a time break sufficient for cooling and some reworking. The presence of a lag breccia suggests that a source vent lay nearby (< 3 km) for some of the tuffs and that the Yellowstone Caldera boundary in this area could be reconsidered.

Geochronology and correlation of Tertiary volcanic and intrusive rocks in part of the southern Toquima Range, Nye County, Nevada

USGS Publications Warehouse

Shawe, Daniel R.; Snee, Lawrence W.; Byers, Frank M.; du Bray, Edward A.

2014-01-01

Extensive volcanic and intrusive igneous activity, partly localized along regional structural zones, characterized the southern Toquima Range, Nevada, in the late Eocene, Oligocene, and Miocene. The general chronology of igneous activity has been defined previously. This major episode of Tertiary magmatism began with emplacement of a variety of intrusive rocks, followed by formation of nine major calderas and associated with voluminous extrusive and additional intrusive activity. Emplacement of volcanic eruptive and collapse megabreccias accompanied formation of some calderas. Penecontemporaneous volcanism in central Nevada resulted in deposition of distally derived outflow facies ash-flow tuff units that are interleaved in the Toquima Range with proximally derived ash-flow tuffs. Eruption of the Northumberland Tuff in the north part of the southern Toquima Range and collapse of the Northumberland caldera occurred about 32.3 million years ago. The poorly defined Corcoran Canyon caldera farther to the southeast formed following eruption of the tuff of Corcoran Canyon about 27.2 million years ago. The Big Ten Peak caldera in the south part of the southern Toquima Range Tertiary volcanic complex formed about 27 million years ago during eruption of the tuff of Big Ten Peak and associated air-fall tuffs. The inferred Ryecroft Canyon caldera formed in the south end of the Monitor Valley adjacent to the southern Toquima Range and just north of the Big Ten Peak caldera in response to eruption of the tuff of Ryecroft Canyon about 27 million years ago, and the Moores Creek caldera just south of the Northumberland caldera developed at about the same time. Eruption of the tuff of Mount Jefferson about 26.8 million years ago was accompanied by collapse of the Mount Jefferson caldera in the central part of the southern Toquima Range. An inferred caldera, mostly buried beneath alluvium of Big Smoky Valley southwest of the Mount Jefferson caldera, formed about 26.5 million years ago with eruption of the tuff of Round Mountain. The Manhattan caldera south of the Mount Jefferson caldera and northwest of the Big Ten Peak caldera formed in association with eruption of a series of tuffs, principally the Round Rock Formation, mostly ash-flow tuff, about 24.4 million years ago. Extensive 40Ar/39Ar dating of about 60 samples that represent many of the Tertiary extrusive and intrusive rocks in the southern Toquima Range provides precise ages that refine the chronology of previously dated units. New geochronologic data indicate that the petrogenetically related Corcoran Canyon, Ryecroft Canyon, and Mount Jefferson calderas formed during a period of about 560,000 years. Electron microprobe analyses of phenocrysts from 20 samples of six dated units underscore inferred petrogenetic relations among some of these units. In particular, compositions of augite, hornblende, and biotite in tuffs erupted from the Corcoran Canyon, Ryecroft Canyon, and Mount Jefferson calderas are similar, which suggests that magmas represented by these tuffs have similar petrogenetic histories. The unique occurrence of hypersthene in Isom-type tuff confirms its derivation from a source beyond the southern Toquima Range.

The volcanic-plutonic connection unveiled

NASA Astrophysics Data System (ADS)

Hartung, E.; Caricchi, L.; Floess, D.; Wallis, S.; Harayama, S.

2017-12-01

Are upper crustal plutons solidified magma bodies or residues from extracted and erupted liquids? This remains one of the key questions to address to understand the construction and eruption of upper crustal magmatic systems. We have investigated the Takidani Pluton and contemporaneous volcanic deposits (Nyukawa PFD, Chayano Tuff and Ebisutoge PD) distributed around this crustal intrusion to understand whether they were sourced from this pluton. The Takidani Pluton is a good candidate because it contains petrographic and geochemical evidences for residual melt extraction, and pressure quenching associated with eruptive activity (Hartung et al., 2017). We analysed major and trace element concentrations of 18 plagioclase phenocrysts (core to rim) from the Takidani Pluton and Nyukawa-Chayano-Ebisutoge eruptions. Major elements were first analysed using an electron microprobe and trace elements were subsequently determined by laser ablation inductively coupled mass spectrometry in the same spot. Plagioclase chemistry shows that the Chayano and Ebisutoge rhyolitic deposits are not petrogenetically related to either the Takidani Pluton or the Nyukawa PFD. However, plagioclase of the Nyukawa PDF and the Takidani Pluton show indistinguishable REE patterns suggesting a common source domain for plagioclase from the two units. Ebisutoge plagioclase grains commonly contain xenocrystic cores that have major and trace element compositions comparable to the plagioclase grains observed in the Takidani Pluton and Nyukawa PFD. Our data show that the Nyukawa and Takidani plagioclase are geochemically indistinguishable, suggesting that the Takidani pluton was the magma reservoir that fed this large eruptive unit (400 km3, Oikawa, 2003). The Ebisutoge magma was not extracted directly from the pluton, but interacted with Takidani-Nyukawa when it was still molten. We have no evidence to suggest that the Takidani Pluton was the source of either the Chayano Tuff or the Ebisutoge PD.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater - Clan Alpine caldera complex, western Nevada, USA

NASA Astrophysics Data System (ADS)

Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

2018-01-01

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4-28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3-24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1-2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500-5000 km3.

Stratigraphic and geochemical evolution of an oceanic arc upper crustal section: The Jurassic Talkeetna Volcanic Formation, south-central Alaska

USGS Publications Warehouse

Clift, P.D.; Draut, A.E.; Kelemen, P.B.; Blusztajn, J.; Greene, A.

2005-01-01

The Early Jurassic Talkeetna Volcanic Formation forms the upper stratigraphic level of an oceanic volcanic arc complex within the Peninsular Terrane of south-central Alaska. The section comprises a series of lavas, tuffs, and volcaniclastic debris-How and flow turbidite deposits, showing significant lateral facies variability. There is a general trend toward more volcaniclastic sediment at the top of the section and more lavas and tuff breccias toward the base. Evidence for dominant submarine, mostly mid-bathyal or deeper (>500 m) emplacement is seen throughout the section, which totals ???7 km in thickness, similar to modern western Pacific arcs, and far more than any other known exposed section. Subaerial sedimentation was rare but occurred over short intervals in the middle of the section. The Talkeetna Volcanic Formation is dominantly calc-alkatine and shows no clear trend to increasing SiO2 up-section. An oceanic subduction petrogenesis is shown by trace element and Nd isotope data. Rocks at the base of the section show no relative enrichment of light rare earth elements (LREEs) versus heavy rare earth elements (REES) or in melt-incompatible versus compatible high field strength elements (HFSEs). Relative enrichment of LREEs and HFSEs increases slightly up-section. The Talkeetna Volcanic Formation is typically more REE depleted than average continental crust, although small volumes of light REE-enriched and heavy REE-depleted mafic lavas are recognized low in the stratigraphy. The Talkeetna Volcanic Formation was formed in an intraoceanic arc above a north-dipping subduction zone and contains no preserved record of its subsequent collisions with Wrangellia or North America. ?? 2005 Geological Society of America.

Geochemistry of waters in the Valley of Ten Thousand Smokes region, Alaska

USGS Publications Warehouse

Keith, T.E.C.; Thompson, J.M.; Hutchinson, R.A.; White, L.D.

1992-01-01

Meteoric waters from cold springs and streams outside of the 1912 eruptive deposits filling the Valley of Ten Thousand Smokes (VTTS) and in the upper parts of the two major rivers draining the 1912 deposits have similar chemical trends. Thermal springs issue in the mid-valley area along a 300-m lateral section of ash-flow tuff, and range in temperature from 21 to 29.8??C in early summer and from 15 to 17??C in mid-summer. Concentrations of major and minor chemical constituents in the thermal waters are nearly identical regardless of temperature. Waters in the downvalley parts of the rivers draining the 1912 deposits are mainly mixtures of cold meteoric waters and thermal waters of which the mid-valley thermal spring waters are representative. The weathering reactions of cold waters with the 1912 deposits appear to have stabilized and add only subordinate amounts of chemical constituents to the rivers relative to those contributed by the thermal waters. Isotopic data indicate that the mid-valley thermal spring waters are meteoric, but data is inconclusive regarding the heat source. The thermal waters could be either from a shallow part of a hydrothermal system beneath the 1912 vent region or from an incompletely cooled, welded tuff lens deep in the 1912 ash-flow sheet of the upper River Lethe area. Bicarbonate-sulfate waters resulting from interaction of near-surface waters and the cooling 1953-1968 southwest Trident plug issue from thermal springs south of Katmai Pass and near Mageik Creek, although the Mageik Creek spring waters are from a well-established, more deeply circulating hydrothermal system. Katmai caldera lake waters are a result of acid gases from vigorous drowned fumaroles dissolving in lake waters composed of snowmelt and precipitation. ?? 1992.

Recent advances in the cretaceous stratigraphy of Korea

NASA Astrophysics Data System (ADS)

Chang, Ki-Hong; Suzuki, Kazuhiro; Park, Sun-Ok; Ishida, Keisuke; Uno, Koji

2003-06-01

A subrounded, accidental, zircon grain from a rhyolite sample of the Oknyobong Formation has shown an U-Pb CHIME isochron age, 187 Ma, implying its derivation from a Jurassic felsic igneous rock. Such a lower limit of the geologic age of the Oknyobong Formation, combined with its pre-Kyongsang upper limit, constrains that the Oknyobong Formation belongs to the Jasong Synthem (Late Jurassic-early Early Cretaceous) typified in North Korea. The Jaeryonggang Movement terminated the deposition of the Jasong Synthem and caused a shift of the depocenter from North Korea to the Kyongsang Basin, Southeast Korea. The Cretaceous-Paleocene Kyongsang Supergroup of the Kyongsang Basin is the stratotype of the Kyongsang Synthem, an unconformity-bounded unit in the Korean Peninsula. The unconformity at the base of the Yuchon Volcanic Group is a local expression of the interregionally recognizable mid-Albian tectonism; it subdivides the Kyongsang Synthem into the Lower Kyongsang Subsynthem (Barremian-Early Albian) and the Upper Kyongsang Subsynthem (Late Albian-Paleocene). The latter is unconformably overlain by Eocene and younger strata. The Late Permian to Early Jurassic radiolarian fossils from the chert pebbles of the Kumidong and the Kisadong conglomerates of the Aptian-Early Albian Hayang Group of the Kyongsang Basin are equivalent with those of the cherts that constitute the Jurassic accretionary prisms in Japan, the provenance of the chert pebbles in the Kyongsang Basin. Bimodal volcanisms throughout the history of the Kyongsang Basin is exemplified by the felsic Kusandong Tuff erupted abruptly and briefly in the Late Aptian when semi-coeval volcanisms were of intermediate and mafic compositions. The mean paleomagnetic direction shown by the Kusandong Tuff is in good agreement with the Early Cretaceous directions known from North China, South China and Siberia Blocks.

Geohydrology of rocks penetrated by test well USW H-4, Yucca Mountain, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitfield, M.S. Jr.; Eshom, E.P.; Thordarson, W.

This report presents the results of hydraulic testing of rocks penetrated by USW H-4, one of several test wells drilled in the southwestern part of the Nevada Test Site, in cooperation with the US Department of Energy, for investigations related to the isolation of high-level radioactive wastes in volcanic tuffs of Tertiary age. All rocks penetrated by the test well to its total depth of 1219 meters were volcanic. Static water level was at a depth of 519 meters below land surface. Hydraulic-head measurements made at successively lower depths during drilling in this test hole indicate no noticeable head change.more » A radioactive-tracer, borehole-flow survey indicated that the two most productive zones in this borehole occurred in the upper part of the Bullfrog Member, depth interval from 721 to 731.5 meters, and in the underlying upper part of the Tram Member, depth interval from 864 to 920 meters, both in the Crater Flat Tuff. Hydraulic coefficients calculated from pumping-test data indicate that transmissivity ranged from 200 to 790 meters squared per day. The hydraulic conductivity ranged from 0.29 to 1.1 meters per day. Chemical analysis of water pumped from the saturated part of the borehole (composite sample) indicates that the water is typical of water produced from tuffaceous rocks in southern Nevada. The water is predominantly a sodium bicarbonate type with small concentrations of calcium, magnesium, and sulfate. The apparent age of this composite water sample was determined by a carbon-14 date to be 17,200 years before present. 24 refs., 10 figs., 8 tabs.« less

Eruptive style and construction of shallow marine mafic tuff cones in the Narakay Volcanic Complex (Proterozoic, Hornby Bay Group, Northwest Territories, Canada)

NASA Astrophysics Data System (ADS)

Ross, Gerald M.

1986-03-01

The Early Proterozoic (1663 Ma) Narakay Volcanic Complex, exposed in Great Bear Lake (Northwest Territories, Canada), is a bimodal suite of basalt and rhyolite erupted in a continental setting and consisting largely of pyroclastic rocks interlayered with shallow marine sedimentary rocks of the Hornby Bay Group. Mafic pyroclastic rocks consist of lapilli tuff, tuff, tuff breccia and agglomerate that represent the remnants of small subaerial tuff cones (0.5 to 2 km in diameter) that in most cases have subsided into the volcanic conduit. Stratification styles, sedimentary structures and grain morphologies in pyroclastic rocks reflect variations in the water:magma ratio during eruptions and have been used to help elucidate eruptive mechanisms and reconstruct volcanic edifices. Basaltic pyroclasts are commonly bounded by fracture surfaces and are morphologically similar to modern pyroclasts produced by thermal quench fragmentation or steam-blast disruption of magma. Most fragments have low vesicularity and scoria is only locally abundant which indicates that eruptive energy was supplied mostly by water—melt interaction rather than exsolution of magmatic gases. Cored bombs and lapilli, fusiform bombs, and pyroclasts similar in texture to those of Strombolian cinder and agglutinate spatter, are uncommon but are stratigraphically widespread and imply the occurrence of Strombolian eruptions, presumably when water access to the vent was impeded. Massive bedding is typical of the tuffs and, in addition to the poorly sorted ash-rich nature of the tuffs, implies deposition from water- and/or steam-rich hydrovolcanic eruption clouds and cypressoid jets by airfall and dense pyroclastic flows. Uncommon well-stratified and sorted ash and lapilli tuff record airfall and pyroclastic flow(?) deposition from eruption clouds rich in magmatic gases. Base surge deposits are uncommon and occur only in the subaerial portion of a sequence of tuffs inferred to record the progradation of a cone-margin surge platform into standing water. Few of the tuff cone deposits display a systematic vertical sequence of stratification styles, structures and grain morphologies. This indicates that either the eruptive style varied irregularly between hydrovolcanic and Strombolian and/or that pyroclasts of different origin were mixed during eruptions.

Reconnaissance geochronology of tuffs in the Miocene Barstow Formation: implications for basin evolution and tectonics in the central Mojave Desert

USGS Publications Warehouse

Miller, David M.; Leslie, Shannon R.; Hillhouse, John W.; Wooden, Joseph L.; Vazquez, Jorge A.; Reynolds, R.E.

2010-01-01

Early to middle Miocene lacustrine strata of the Barstow Formation are well dated in just a few places, limiting our ability to infer basin evolution and regional tectonics. At the type section in the Mud Hills, previous studies have shown that the lacustrine interval of the Barstow Formation is between ~16.3 Ma and ~13.4 Ma. Elsewhere, lake beds of the Barstow Formation have yielded vertebrate fossils showing the Hemingfordian/Barstovian transition at ~16 Ma but are otherwise poorly dated. In an attempt to clarify the age and depositional environments of the lake deposits, we are mapping the Barstow Formation and dating zircons from interbedded tuffs, as well as testing ash-flow tuffs for the distinctive remanent magnetization direction of the widespread Peach Spring Tuff. Thus far, our new U-Pb zircon ages indicate that the Barstow lake beds contain tuff beds as old as 19.1 Ma and as young as 15.3 Ma. At Harvard Hill, Barstow lake beds contain a thick tuff dated at 18.7 Ma. On the basis of zircon ages, mineralogy, zircon chemistry, and paleomagnetic results, we consider the thick tuff to be a lacustrine facies of the Peach Spring Tuff. We have identified the Peach Spring Tuff by similar methods at eight localities over a broad area, providing a timeline for several fluvial and lacustrine sections. The new dates indicate that long-lived lacustrine systems originated before 19 Ma and persisted to at least 15 Ma. The onset of lacustrine conditions predates the Peach Spring Tuff in most Barstow Formation sections and may be older than 19.5 Ma in some places. The new data indicate that the central Mojave Desert contained narrow to broad lake basins during and after extension, and that Barstow lacustrine deposits did not exclusively postdate extensional tectonics. At present, it is unclear whether several separate, small lake basins coexisted during the early to middle Miocene, or if instead several small early Miocene basins gradually coalesced over about 6 million years to form one or two large middle Miocene lake basins.

Reconnaissance geochronology of tuffs in the Miocene Barstow Formation: implications for basin evolution and tectonics in the central Mojave Desert

USGS Publications Warehouse

Miller, D.M.; Leslie, S.R.; Hillhouse, J.W.; Wooden, J.L.; Vazquez, J.A.; Reynolds, R.E.

2010-01-01

Early to middle Miocene lacustrine strata of the Barstow Formation are well dated in just a few places, limiting our ability to infer basin evolution and regional tectonics. At the type section in the Mud Hills, previous studies have shown that the lacustrine interval of the Barstow Formation is between ~16.3 Ma and ~13.4 Ma. Elsewhere, lake beds of the Barstow Formation have yielded vertebrate fossils showing the Hemingfordian/Bartovian transition at ~16 Ma but are otherwise poorly dated. In an attempt to clarify the age and depositional environments of the lake deposits, we are mapping the Barstow Formation and dating zircons from interbedded tuffs, as well as testing ash-flow tuffs for the distinctive remanent magnetization direction of the widespread Peach Spring Tuff. Thus far, our new U-Pb zircon ages inficate that the Barstow lake beds contain tuff beds as old as 19.1 Ma and as young as 15.3 Ma. At Harvard Hill, Barstow lake beds contain a thick tuff dated at 18.7 Ma. On the basis of zircon ages, mineralogy, zircon chemistry, and paleomagnetic results, we consider the thick tuff to be a lacustrine facies of the Peach Spring Tuff. We have identified the Peach Spring Tuff by similar methods at eight localities over a broad area, providing a timeline for several fluvial and lacustrine sections. The new dates indicate that long-lived lacustrine systems originated before 19 Ma and persisted to at least 15 Ma. The onset of lacustrine conditions predates the Peach Spring Tuff in most Barstow Formation sections and may be older than 19.5 Ma in some places. The new data indicate that the central Mojave Desert contained narrow to broad lake basins during and after extension, and that Barstow lacustrine deposits did not exclusively postdate extensional tectonics. At present, it is unclear whether several separate, small lake basins coexisted during the early to middle Miocene, or if instead several small early Miocene basins gradually coalesced over about 6 millions years to form one or two large middle Miocene lake basins.

Radioelements and their occurrence with secondary minerals in heated and unheated tuff at the Nevada Test Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flexser, S.; Wollenberg, H.A.

1992-06-01

Samples of devitrified welded tuff near and away from the site of a heater test in Rainier Mesa were examined with regard to whole-rock radioelement abundances, microscopic distribution of U, and oxygen isotope ratios. Wholerock U averages between 4 and 5 ppM, and U is concentrated at higher levels secondary opaque minerals as well as in accessory grains. U in primary and secondary sites is most commonly associated with Mn phases, which average {approximately}30 ppM U in more uraniferous occurrences. This average is consistent and apparently unaffected by proximity to the heater. The Mn phases differ compositionally from Mn mineralsmore » in other NTS tuffs, usually containing abundant Fe, Ti, and sometimes Ce, and are often poorly crystalline. Oxygen isotope ratios show some depletion in {delta}{sup 18}O in tuff samples very close to the heater; this depletion is consistent with isotopic exchange between the tuff and interstitial water, but it may also reflect original heterogeneity in isotopic ratios of the tuff unrelated to the heater test. Seismic properties of several tuff samples were measured. Significant differences correlating with distance from the heater occur in P- and S-wave amplitudes; these may be due to loss of bound water. Seismic velocities are nearly constant and indicate a lack of significant microcracking. The absence of clearer signs of heater-induced U mobilization or isotopic variations may be due to the short duration of the heater test, and to insufficient definition of pre-heater-test heterogeneities in the tuff.« less

Geochronology of the mammal-bearing late Cenozoic on the northern Altiplano, Bolivia

NASA Astrophysics Data System (ADS)

Marshall, L. G.; Swisher, C. C.; Lavenu, A.; Hoffstetter, R.; Curtis, G. H.

1992-01-01

Samples of seven tuff or ignimbrite units associated with known land mammal faunas of late Miocene and Pliocene age were collected from 17 localities on the northern Altiplano of western Bolivia. Mineral separates dated by the classic 40K- 40Ar technique (35 dates) and by single crystal laser fusion (SCLF) 40Ar/ 39Ar analysis (84 dates) indicate the following preferred ages based on SCLF 40Ar/ 39Ar dates on sanidine for six of these units: Ulloma Tuff, 10.35±0.06 Ma; Callapa Tuff, 9.03±0.07 Ma; Toba 76, 5.348±0.003 Ma; Ayo Ayo Tuff, 2.896±0.006 Ma; Perez Ignimbrite, 2.815±0.005 Ma; and Chijini Tuff, 2.650±0.012 Ma. Land mammal faunas of early Huayquerian age are bracketed below by the Callapa Tuff (9.0 Ma) and above the base of the Cerke Formation (7.6 Ma); faunas of Montehermosan age are bracketed below by the Toba 76 and Cota Cota Tuffs ( ca. 5.4 Ma), and above by the Ayo Ayo and Chijini Tuffs ( ca. 2.8 Ma) of the Umala and La Paz Formations, respectively; and faunas of Ensenadan and Lujanian age occur in rocks younger than 1.6 Ma. Hiatuses identified by the absence of late Huayquerian and Chapadmalalan-Uquian faunas correlate with unconformities which are interpreted as deformation phases: the first with Q3 (8.0-5.5 Ma) and the second with Q4 (2.8-1.6 Ma) of the Quechua Orogeny.

Would ecological landscape restoration make the Bandelier Wilderness more or less of a wilderness?

Treesearch

Charisse A. Sydoriak; Craig D. Allen; Brian F. Jacobs

2000-01-01

The purpose of this paper is to foster discussion on the basic issue of whether it is appropriate or not to intervene in designated wilderness areas that have been “trammeled by man” and, as a result, no longer retain their “primeval character and influence.” We explore this wilderness management dilemma (whether we can or should actively manage wilderness conditions...

Re-collection of Fish Canyon Tuff for fission-track standardization

USGS Publications Warehouse

Naeser, C.W.; Cebula, G.T.

1984-01-01

The PURPOSE of this note is to announce the availability of apatite and zircon from a third collection of the Oligocene Fish Canyon Tuff (FC-3). Apatite and zircon separated from the Fish Canyon Tuff have prove to be a useful standard for fission-track dating, both for interlaboratory comparisons and for checking procedures within a laboratory. In May 1981, about 540 kg of Fish Canyon Tuff were collected for mineral separation. Approximately 7. 5 g of apatite, 6. 5 g of zircon, and 89 g of sphene were recovered from this collection. This new material is now ready for distribution.

Moderate-temperature zeolitic alteration in a cooling pyroclastic deposit

USGS Publications Warehouse

Levy, S.S.; O'Neil, J.R.

1989-01-01

The locally zeolitized Topopah Spring Member of the Paintbrush Tuff (13 Myr.), Yucca Mountain, Nevada, U.S.A., is part of a thick sequence of zeolitized pyroclastic units. Most of the zeolitized units are nonwelded tuffs that were altered during low-temperature diagenesis, but the distribution and textural setting of zeolite (heulandite-clinoptilolite) and smectite in the densely welded Topopah Spring tuff suggest that these hydrous minerals formed while the tuff was still cooling after pyroclastic emplacement and welding. The hydrous minerals are concentrated within a transition zone between devitrified tuff in the central part of the unit and underlying vitrophyre. Movement of liquid and convected heat along fractures from the devitrified tuff to the ritrophyre caused local devitrification and hydrous mineral crystallization. Oxygen isotope geothermometry of cogenetic quartz confirms the nondiagenetic moderate temperature origin of the hydrous minerals at temperatures of ??? 40-100??C, assuming a meteoric water source. The Topopah Spring tuff is under consideration for emplacement of a high-level nuclear waste repository. The natural rock alteration of the cooling pyroclastic deposit may be a good natural analog for repository-induced hydrothermal alteration. As a result of repository thermal loading, temperatures in the Topopah Spring vitrophyre may rise sufficiently to duplicate the inferred temperatures of natural zeolitic alteration. Heated water moving downward from the repository into the vitrophyre may contribute to new zeolitic alteration. ?? 1989.

Stratigraphy, structure, and some petrographic features of Tertiary volcanic rocks in the USW G-2 drill hole, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Maldonado, Florian; Koether, S.L.

1983-01-01

A continuously cored drill hole designated as USW G-2, located at Yucca Mountain in southwestern Nevada, penetrated 1830.6 m of Tertiary volcanic strata composed of abundant silicic ash-flow tuffs, minor lava and flow breccias, and subordinate volcaniclastic rocks. The volcanic strata penetrated are comprised of the following in descending order: Paintbrush Tuff (Tiva Canyon Member, Yucca Mountain Member, bedded tuff, Pah Canyon Member, and Topopah Spring Member), tuffaceous beds of Calico Hills, Crater Flat Tuff (Prow Pass Member, Bullfrog Member, and Tram unit), lava and flow breccia (rhyodacitic), tuff of Lithic Ridge, bedded and ash-flow tuff, lava and flow breccia (rhyolitic, quartz latitic, and dacitic), bedded tuff, conglomerate and ash-flow tuff, and older tuffs of USW G-2. Comparison of unit thicknesses at USW G-2 to unit thicknesses at previously drilled holes at Yucca Mountain indicate the following: (1) thickening of the Paintbrush Tuff members and tuffaceous beds of Calico Hills toward the northern part of Yucca Mountain; (2) thickening of the Prow Pass Member but thinning of the Bullfrog Member and Tram unit; (3) thinning of the tuff of Lithic Ridge; (4) presence of approximately 280 m of lava and flow breccia not previously penetrated by any drill hole; and (5) presence of an ash-flow tuff unit at the bottom of the drill hole not previously intersected, apparently the oldest unit penetrated at Yucca Mountain to date. Petrographic features of some of the units include: (1) decrease in quartz and K-feldspar and increases in biotite and plagioclase with depth in the tuffaceous beds of Calico Hills; (2) an increase in quartz phenocrysts from the top to the bottom members of the Crater Flat Tuff; (3) a low quartz content in the tuff of Lithic Ridge, suggesting tapping of the magma chamber at quartz-poor levels; (4) a change in zeolitic alteration from heulandite to clinoptilolite to mordenite with increasing depth; (5) lavas characterized by a rhyolitic top and dacitic base, suggesting reverse compositional zoning; and (6) presence of hydrothermal mineralization in the lavas that could be related to an intrusive under Yucca Mountain or to volcanism associated with the Timber Mountain-Claim Canyon caldera complex. A fracture analysis of the core resulted n tabulation of 7,848 fractures, predominately open and high angle. The fractures were filled or coated with material in various combinations and include the following in decreasing abundance: CaCo3, iron oxides and hydroxides, SiO2, manganese oxides and hydroxides, clays and zeolites. An increase in the intensity of fracturing can be correlated with the following: (1) densely welded zones, (2) lithophysal zones, (3) vitrophyre, (4) silicified zones, (5) fault zones, and (6) cooling joints. Numerous fault zones were penetrated by the drill hole, predominately in the lithophysal zone of the Topopah Spring Member and below the tuffaceous beds of Calico Hills. The faults are predominately high angle with both a vertical and lateral component. Three major faults were penetrated, two of which intersect the ground surface, with displacements of at least 20 m and possibly as much as 52 m. The faults and some fractures are probably related to the regional doming of the area associated with the volcanism-tectonism of the Timber Mountain-Claim Canyon caldera complex, and to Basin and Range tectonism.

Geological monitoring of Surtsey, Iceland, 1967-1998

USGS Publications Warehouse

Jakobsson, Sveinn P.; Gudmundsson, Gudmundur; Moore, James G.

2000-01-01

Aspects of the geological monitoring of the volcanic island of Surtsey 1967-1998, are described. A hydrothermal system was developed within the tephra craters in late 1966 to early 1967. Temperatures in a drill hole, situated at the eastern border of the hydrothermal area, indicate that the hydrothermal system at that site has been cooling at an average rate of ≤ 1°C per year since 1980. The tephra was altered rapidly within the hydrothermal area, producing the first visible palagonite tuff in 1969. A substantial part of the tephra pile above sea level was probably converted to tuff by 1972. The visible area of tuff has gradually increased since then, primarily due to erosion of tephra at the surface. By 1998 52% of the exposed tephra area had been converted to palagonite tuff. By volume, however, some 80-85% of the tephra pile above sea level has been converted to tuff in 1998. The area of Surtsey has shrunk from its original 2.65 km2 (1967) to 1.47 km2 (1998) due to marine abrasion. The geological formations on Surtsey have, however, responded quite variably to erosion. The tephra pile was easily eroded, but marine abrasion. The central core of palagonite tuff is estimated to be ≤0.39 km2. Statistical estimation of models of the decreases of Surtsey indicate that it will last for a long time. The numerical experiments indicate that it will take over 100 years until only the palagonite tuff core is left. It is postulated that the final remnany of Surtsey before complete destruction will be a palagonite tuff crag, comparable to those of the other islands in the Vestmannaeyjar archipelago.

Recrystallization and anatexis along the plutonic-volcanic contact of the Turkey Creek caldera, Arizona

USGS Publications Warehouse

du Bray, E.A.; Pallister, J.S.

1999-01-01

Unusual geologic and geochemical relations are preserved along the contact between intracaldera tuff and a resurgent intrusion within the 26.9 Ma Turkey Creek caldera of southeast Arizona. Thick intracaldera tuff is weakly argillically altered throughout, except in zones within several hundred meters of its contact with the resurgent intrusion, where the groundmass of the tuff has been variably converted to granophyre and unaltered sanidine phenocrysts are present. Dikes of similarly granophyric material originate at the tuff-resurgent intrusion contact and intrude overlying intracaldera megabreccia and tuff. Field relations indicate that the resurgent intrusion is a laccolith and that it caused local partial melting of adjacent intracaldera tuff. Geochemical and petrographic relations indicate that small volumes of partially melted intracaldera tuff assimilated and mixed with dacite of the resurgent intrusion along their contact, resulting in rocks that have petrographic and compositional characteristics transitional between those of tuff and dacite. Some of this variably contaminated, second-generation magma coalesced, was mobilized, and was intruded into overlying intracaldera rocks. Interpretation of the resurgent intrusion in the Turkey Creek and other calderas as intracaldera laccoliths suggests that intrusions of this type may be a common, but often unrecognized, feature of calderas. Development of granophyric and anatectic features such as those described here may be equally common in other calderas. The observations and previously undocumented processes described here can be applied to identification and interpretation of similarly enigmatic relations and rocks in other caldera systems. Integration of large-scale field mapping with detailed petrographic and chemical data has resulted in an understanding of otherwise intractable but petrologically important caldera-related features.

Structure, stratigraphy, and eruption chronology of the Hanauma Bay Tuff Ring, Oahu, Hawaii

NASA Astrophysics Data System (ADS)

Rottas, K. M.; Houghton, B. F.

2010-12-01

The Hanauma Bay-Koko Head Complex is one of several volcanic landforms along the Koko fissure, in southeastern Oahu, that formed during rejuvenated volcanism. The Hanauma Bay region of the complex is comprised of two nested tuff rings. The internal structure of the inner tuff ring is well exposed due to subsequent breaching and wave erosion and is described in detail here for the first time. The inner tuff ring is currently believed to have formed during a single eruption episode. However, field observations, detailed photography, structural mapping in both the vertical and horizontal planes, extensive measurements of bedding attitudes, and stratigraphic analysis suggest that there were a minimum of five distinct intervals of deposition, which also blanketed the deposits of the outer tuff ring with ejecta. These intervals of sedimentation were separated by significant collapses, generating major unconformities that cross the inner wall of the inner ring. The planes of failure are marked by smaller steep-walled channels and gullies, eroded by rainfall-induced runoff and suggesting the failures were each followed by short time breaks with erosion. Within each pyroclastic sequence there are also smaller slump scars and local unconformities. The inner tuff ring was predominately formed by pyroclastic surges, although the beds of Phase 3 are primarily fall deposits. From ballistic trajectories and bedding features, it is apparent that the eruption locus shifted a minimum of two times during tuff ring growth. Ballistic blocks in the final Phase 5 indicate that the Hanauma Bay eruption was contemporaneous with a separate eruption to the north, most likely that of the Kahauloa tuff ring 880 meters away.

Petrology and geochemistry of the Grouse Canyon Member of the Belted Range Tuff, Rock-Mechanics Drift, U12g Tunnel, Nevada Test Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connolly, J.R.; Mansker, W.L.; Hicks, R.

1983-04-01

G-Tunnel at Nevada Test Site (NTS) is the site of thermal and thermomechanical experiments examining the feasibility of emplacing heat-producing nuclear wastes in silicic tuffs. This report describes the general stratigraphy, mineralogy, and bulk chemistry of welded portions of the Grouse Canyon Member of the Belted Range Tuff, the unit in which most of these experiments will be performed. The geologic characteristics of the Grouse Canyon Member are compared with those of the Topopah Spring Member of the Paintbrush Tuff, presently the preferred horizon for an actual waste repository at Yucca Mountain, near the southwest boundary of Nevada Test Site.more » This comparison suggests that test results obtained in welded tuff from G-Tunnel are applicable, with limitations, to evaluation of the Topopah Spring Member at Yucca Mountain.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connolly, J.R.

Petrologic, bulk chemical, and mineralogic data are presented for 49 samples of tuffaceous rocks from core holes USW G-1 and UE-25a{number_sign}1 at Yucca Mountain, Nevada. Included, in descending stratigraphic order, are 11 samples from the Topopah Spring Member of the Paintbrush Tuff, 12 samples from the Tuffaceous Beds of Calico Hills, 3 samples from the Prow Pass Member of the Crater Flat Tuff, 20 samples from the Bullfrog Member of the Crater Flat Tuff and 3 samples from the Tram Member of the Crater Flat Tuff. The suite of samples contains a wide variety of petrologic types, including zeolitized, glassy,more » and devitrified tuffs. Data vary considerably between groups of samples, and include thin section descriptions (some with modal analyses for which uncertainties are estimated), electron microprobe analyses of mineral phases and matrix, mineral identifications by X-ray diffraction, and major element analyses with uncertainty estimates.« less

Determining the physical and chemical processes behind four caldera-forming eruptions in rapid succession in the San Juan caldera cluster, Colorado, USA

NASA Astrophysics Data System (ADS)

Curry, A. C.; Caricchi, L.; Lipman, P. W.

2017-12-01

A primary goal of volcanology is to understand the frequency and magnitude of large, explosive volcanic eruptions to mitigate their impact on society. Recent studies show that the average magma flux and the time between magma injections into a given magmatic-volcanic system fundamentally control the frequency and magnitude of volcanic eruptions, yet these parameters are unknown for many volcanic regions on Earth. We focus on major and trace element chemistry of individual phases and whole-rock samples, initial zircon ID-TIMS analyses, and zircon SIMS oxygen isotope analyses of four caldera-forming ignimbrites from the San Juan caldera cluster in the Southern Rocky Mountain volcanic field, Colorado, to determine the physical and chemical processes leading to large eruptions. We collected outflow samples along stratigraphy of the three caldera-forming ignimbrites of the San Luis caldera complex: the Rat Creek Tuff ( 150 km3), Cebolla Creek Tuff ( 250 km3), and Nelson Mountain Tuff (>500 km3); and we collected samples of both outflow and intracaldera facies of the Snowshoe Mountain Tuff (>500 km3), which formed the Creede caldera. Single-crystal sanidine 40Ar/39Ar ages show that these large eruptions occurred in rapid succession between 26.91 ± 0.02 Ma (Rat Creek Tuff) and 26.87 ± 0.02 Ma (Snowshoe Mountain Tuff), providing an opportunity to investigate the temporal evolution of magmatic systems feeding large, explosive volcanic eruptions. Major and trace element analyses show that the first and last eruption of the San Luis caldera complex (Rat Creek Tuff and Nelson Mountain Tuff) are rhyolitic to dacitic ignimbrites, whereas the Cebolla Creek Tuff and Snowshoe Mountain Tuff are crystal-rich, dacitic ignimbrites. Trace elements show enrichment in light rare-earth elements (LREEs) over heavy rare-earth elements (HREEs), and whereas the trace element patterns are similar for each caldera cycle, trace element values for each ignimbrite show variability in HREE concentrations. This variability indicates that these large eruptions sampled a magmatic system with some degree of internal heterogeneity. These results have implications for the chemical and physical processes, such as magmatic flux and injection periodicity, leading to the formation of large magmatic systems prior to large, explosive eruptions.

Moisture Monitoring at Area G, Technical Area 54, Los Alamos National Laboratory, 2016 Status Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levitt, Daniel Glenn; Birdsell, Kay Hanson; Jennings, Terry L.

Hydrological characterization and moisture monitoring activities provide data required for evaluating the transport of subsurface contaminants in the unsaturated and saturated zones beneath Area G, and for the Area G Performance Assessment and Composite Analysis. These activities have been ongoing at Area G, Technical Area 54 of the Los Alamos National Laboratory since waste disposal operations began in 1957. This report summarizes the hydrological characterization and moisture monitoring activities conducted at Area G. It includes moisture monitoring data collected from 1986 through 2016 from numerous boreholes and access tubes with neutron moisture meters, as well as data collected by automatedmore » dataloggers for water content measurement sensors installed in a waste disposal pit cover, and buried beneath the floor of a waste disposal pit. This report is an update of a nearly identical report by Levitt et al., (2015) that summarized data collected through early 2015; this report includes additional moisture monitoring data collected at Pit 31 and the Pit 38 extension through December, 2016. It also includes information from the Jennings and French (2009) moisture monitoring report and includes all data from Jennings and French (2009) and the Draft 2010 Addendum moisture monitoring report (Jennings and French, 2010). For the 2015 version of this report, all neutron logging data, including neutron probe calibrations, were investigated for quality and pedigree. Some data were recalculated using more defensible calibration data. Therefore, some water content profiles are different from those in the Jennings and French (2009) report. All of that information is repeated in this report for completeness. Monitoring and characterization data generally indicate that some areas of the Area G vadose zone are consistent with undisturbed conditions, with water contents of less than five percent by volume in the top two layers of the Bandelier tuff at Area G. These data also indicate that other areas of the vadose zone are affected by waste disposal activities that have been ongoing at Area G since 1957, a period of nearly 60 years. In some areas, water content profiles indicate increases in water content to depths of tens of meters, especially in areas covered by asphalt and structures.« less

Patchy distribution of magma that fed the Bishop Tuff supereruption: Evidence from matrix glass major and trace-element compositions

NASA Astrophysics Data System (ADS)

Gualda, G. A. R.; Ghiorso, M. S.; Hurst, A. A.; Allen, M. C.; Bradshaw, R. W.

2017-12-01

For more than 40 years, the Bishop Tuff has been the archetypical example of a singular, zoned magma body that fed a supereruption. Early-erupted material is pyroxene-free and crystal poor (<20 wt. %), presumably erupted from the upper parts of the magma body; late-erupted material is orthopyroxene and clinopyroxene-bearing, commonly more crystal rich (up to 30 wt. % crystals), and presumably tapped magma from the lower portions of the magma body. Fe-Ti oxide compositions suggest higher crystallization temperatures for late-erupted magmas (as high as 820 °C) than for early-erupted magmas (as low as 700 °C). Pressures and temperatures derived from major element compositions of glass inclusions led Gualda & Ghiorso (2013, CMP) to suggest an alternative model of lateral juxtaposition of two main magma bodies - each one feeding early-erupted and late-erupted units. Chamberlain et al. (2015, JPet) and Evans et al. (2016, AmMin) recently disputed this interpretation. We present a large dataset of matrix glass compositions for 161 pumice clasts that span the stratigraphy of the deposit. We calculate crystallization pressures based on major-element glass compositions using rhyolite-MELTS geobarometry, and crystallization temperatures based on Zr in glass using zircon saturation geothermometry. We apply the same methods to 1538 major-element and 615 trace-element analyses from Chamberlain et al. The results overwhelmingly demonstrate that there is no difference in crystallization temperature or pressure between early and late-erupted magmas. Crystallization pressures and temperatures are unimodal, with modes of 150 MPa and 730 °C (calibration of Watson & Harrison). Our results strongly support lateral juxtaposition of two main magma bodies. Smaller units recognized by Chamberlain et al. crystallized at the same pressures as the main bodies - this suggests the coexistence of larger and smaller magma bodies at the time of the Bishop Tuff supereruption. We compare our findings for the Bishop Tuff with results for very large and supereruptions elsewhere in the world. We argue that supereruptions typically mobilize a complex patchwork of magma bodies that reside within specific levels of the crust. They reveal moments of high-melt productivity in the crust, unlike what we observe in the Earth today.

Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporation

NASA Technical Reports Server (NTRS)

Kruener, Alfred; Byerly, Gary R.; Lowe, Donald R.

1991-01-01

Precise Pb-207/Pb-206 single zircon evaporating ages are reported for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, as well as for granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group are shown to yield ages between 3445 + or - 3 and 3416 + or - 5 Ma and to contain older crustal components represented by a 3504 + or - 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 + or - 3 Ma in age which are interpreted to reflect the time of crystallization. The comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites are keynoted. The data adduced show that the Onverwacht and Fig Tree felsic units have distinctly different ages and thus do not constitute a single, tectonically repeated unit as proposed by others. It is argued that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones, and that the BGB in the Kaapval craton of southern Africa and greenstones in the Pilbara Block of Western Australia may have been part of a larger crustal unit in early Archaean times.

Geoengineering characterization of welded tuffs from laboratory and field investigations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zimmerman, R.M.; Nimick, F.B.; Board, M.P.

1984-12-31

Welded tuff beneath Yucca Mountain adjacent to the Nevada Test Site (NTS) is being considered for development as a high-level radioactive waste repository by the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. Because access into Yucca Mountain has been limited to borehole explorations, early geoengineering materials characterizations have been derived from laboratory tests on cores from Yucca Mountain and from laboratory and field tests on welded tuffs located in G-Tunnel on the NTS. G-Tunnel contains welded tuffs that have similar properties and stress states to those at Yucca Mountain and has been the location for in situ rock mechanics testing.more » The purpose of this paper is to summarize the geoengineering material property data obtained to date and to compare appropriate laboratory and field data from G-Tunnel to findings from Yucca Mountain. Geomechanical and thermal data are provided and are augmented by limited geological and hydrological data. A comparison of results of laboratory measurements on tuffs from Yucca Mountain and G-Tunnel indicates good agreement between the bulk densities, saturations, moduli of elasticity, Poisson`s ratios, and P-wave velocities. The G-Tunnel tuff has slightly lower thermal conductivity, tensile strength, compressive strength and slightly higher matrix permeability than does the welded tuff near the proposed repository horizon at Yucca Mountain. From a laboratory-to-field scaling perspective, the modulus of deformation shows the most sensitivity to field conditions because of the presence of the joints found in the field. 14 references, 1 table.« less

Geoengineering characterization of welded tuffs from laboratory and field investigations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zimmerman, R.M.; Nimick, F.B.; Board, M.P.

1984-12-31

Welded tuff beneath Yucca Mountain adjacent to the Nevada Test Site (NTS) is being considered for development as a high-level radioactive waste repository by the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. Because access into Yucca Mountain has been limited to borehole explorations, early geoengineering materials characterizations have been derived from laboratory tests on cores from Yucca Mountain and from laboratory and field tests on welded tuffs located in G-Tunnel on the NTS. G-Tunnel contains welded tuffs that have similar properties and stress states to those at Yucca Mountain and has been the location for in situ rock mechanics testing.more » The purpose of this paper is to summarize the geoengineering material property data obtained to date and to compare appropriate laboratory and field data from G-Tunnel to findings from Yucca Mountain. Geomechanical and thermal data are provided and are augmented by limited geological and hydrological data. A comparison of results of laboratory measurements on tuffs from Yucca Mountain and G-Tunnel indicates good agreement between the bulk densities, saturations, moduli of elasticity, Poisson`s ratios, and P-wave velocities. The G-Tunnel tuff has slightly lower thermal conductivity, tensile strength, compressive strength and slightly higher matrix permeability than does the welded tuff near the proposed repository horizon at Yucca Mountain. From a laboratory-to-field scaling perspective, the modulus of deformation shows the most sensitivity to field conditions because of the presence of joints found in the field. 14 refs., 1 tab.« less

Geology and ground-water resources of upper Grande Ronde River Basin, Union County, Oregon

USGS Publications Warehouse

Hampton, E.R.; Brown, S.G.

1964-01-01

The upper Grande Ronde River basin is a 1,400-square-mile area in northeastern Oregon, between the Blue Mountains to the west and the Wallowa Mountains to the east. The area is drained by the Grande Ronde River, which flows northeast through this region and is tributary to the Snake River. The climate is generally moderate; temperature extremes recorded at La Grande are 22?F. below zero and 108?F. above. The average annual precipitation ranges from 13 to 20 inches in the Grande Ronde Valley to . more than 35 inches in the mountain highlands surrounding the valley. The topography of. the area is strongly controlled by the geologic structures, principally those related to block faulting. The terrain ranges from the nearly flat floors of the Grande Ronde and Indian Valleys, whose elevations are 2,600 to about 2,750 feet, to the mountainous uplands, whose average elevations are about 5,000 feet and which have local prominences exceeding 6,500 feet. The rocks in the upper Grande Ronde River basin, from oldest to youngest, are metamorphic rocks of pre-Tertiary age; igneous masses of diorite and granodiorite that intruded the metamorphic rocks; tuff-breccia, welded and silicified tuff, and andesite and dacite flows, of Tertiary age; the Columbia River basalt of Miocene and possibly early Pliocene age; fanglomerate and lacustrine deposits of Pliocene and Pleistocene age; and younger deposits . of alluvium, colluvium, and welded tuff. In the graben known as the Grande Ronde Valley, which is the principal populated district in the area, the valley fill deposits are as thick as 2,000 feet. The valley is bordered by the scarps of faults, the largest of which have displacements of more than 4.000 feet. Most of the wells in the area obtain small to moderate supplies of water from unconfined aquifers in the val1ey fill and alluvial fan deposits. Moderate to large quantities of water are obtained from aquifers carrying artesian water in the fan alluvium and the Columbia River basalt. The available supplies of ground water greatly exceed the relatively small amounts that are being used, and the natural supplies are ..adequate for foreseeable domestic, industrial, irrigation, and municipal. requirements. Yields of future wells probably could be improved appreciably over those of present wells by exercising close attention to subsurface conditions during construction, and by greater use of well screens, gravel envelopes, and well development techniques. The chemical quality of the ground water in general is excellent. All waters sampled are potable and are within the desired ranges of hardness and salinity for most public, industrial, and irrigation uses. The average temperature of shallow ground water drawn from, the alluvial fill was 3?F. above the mean annual air temperature. That of water obtained from the basalt is 6?F. above the temperatures computed from the 'normal' gradient of 1.8?F. per 100 feet of increased depth.

The behavior of biogenic silica-rich rocks and volcanic tuffs as pozzolanic additives in cement

NASA Astrophysics Data System (ADS)

Fragoulis, Dimitris; Stamatakis, Michael; Anastasatou, Marianthi

2015-04-01

Cements currently produced, include a variety of pozzolanic materials, aiming for lower clinker addition and utilization of vast deposits of certain raw materials and/or mining wastes and byproducts. The major naturally occurring pozzolanic materials include glassy tuffs, zeolitic tuffs, diatomites and volcanic lavas rich in glassy phase, such as perlites. Therefore, based on the available raw materials in different locations, the cement composition might vary according to the accessibility of efficient pozzolanic materials. In the present investigation, the behavior of pozzolanic cements produced with representative samples of the aforementioned materials was studied, following the characterization of the implemented pozzolanas with respect to their chemical and mineralogical characteristics. Laboratory cements were produced by co-grinding 75% clinker, 5% gypsum and 20% pozzolana, for the same period of time (45 min). Regarding pozzolanic materials, four different types of pozzolanas were utilized namely, diatomite, perlite, zeolite tuff and glassy tuff. More specifically, two diatomite samples originated from Australia and Greece, with high and low reactive silica content respectively, two perlite samples originated from Turkey and from Milos Island, Greece, with different reactive silica contents, a zeolite tuff sample originated from Turkey and a glassy tuff sample originated from Milos Island, Greece. The above pozzolana samples, which were ground in the laboratory ball mill for cement production performed differently during grinding and that was reflected upon the specific surface area (cm2/gr) values. The perlites and the glassy tuff were the hardest to grind, whereas, the zeolite tuff and the Australian diatomite were the easiest ones. However, the exceedingly high specific surface area of the Australian diatomite renders cement difficult to transport and tricky to use for concrete manufacturing, due to the high water demand of the cement mixture. Regarding late compressive strength, the worst performing cement was the one with the lowest reactive silica content with biogenic opal-A as the only reactive pozzolana constituent. Cements produced with perlites, raw materials consisting mainly of a glassy phase, were characterized by higher strength and a rather ordinary specific surface area. Cements produced with Turkish zeolite tuff and Milos glassy tuff exhibited higher late compressive strength than those mentioned above. The highest strength was achieved by the implementation of Australian diatomite for cement production. Its 28 day strength exceeded that of the control mixture consisting of 95% clinker and 5% gypsum. That could be attributed to both, high specific surface of cement and reactive SiO2 of diatomite. Therefore, a preliminary assessment regarding late strength of pozzolanic cements could be obtained by the consideration of two main parameters, namely: specific surface area of cement and reactive silica content of pozzolana.

Thoughts Regarding the Dimensions of Faults at Rainier and Aqueduct Mesas, Nye County, Nevada, Based on Surface and Underground Mapping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drellack, S.L.; Prothro, L.B.; Townsend, M.J.

2011-02-01

The geologic setting and history, along with observations through 50 years of detailed geologic field work, show that large-displacement (i.e., greater than 30 meters of displacement) syn- to post-volcanic faults are rare in the Rainier Mesa area. Faults observed in tunnels and drill holes are mostly tight, with small displacements (most less than 1.5 meters) and small associated damage zones. Faults are much more abundant in the zeolitized tuffs than in the overlying vitric tuffs, and there is little evidence that faults extend downward from the tuff section through the argillic paleocolluvium into pre-Tertiary rocks. The differences in geomechanical characteristicsmore » of the various tuff lithologies at Rainier Mesa suggest that most faults on Rainer Mesa are limited to the zeolitic units sandwiched between the overlying vitric bedded tuffs and the underlying pre-Tertiary units (lower carbonate aquifer–3, lower clastic confining unit–1, and Mesozoic granite confining unit).« less

H, O, Sr, Nd, and Pb isotope geochemistry of the Latir volcanic field and cogenetic intrusions, New Mexico, and relations between evolution of a continental magmatic center and modifications of the lithosphere

USGS Publications Warehouse

Johnson, C.M.; Lipman, P.W.; Czamanske, G.K.

1990-01-01

Over 200 H, O, Sr, Nd, and Pb isotope analyses, in addition to geologic and petrologic constraints, document the magmatic evolution of the 28.5-19 Ma Latir volcanic field and associated intrusive rocks, which includes multiple stages of crustal assimilation, magma mixing, protracted crystallization, and open- and closed-system evolution in the upper crust. In contrast to data from younger volcanic centers in northern New Mexico, relatively low and restricted primary ??18O values (+6.4 to +7.4) rule out assimilation of supracrustal rocks enriched in 18O. Initial 87Sr/86Sr ratios (0.705 to 0.708), ??18O values (-2 to-7), and 206Pb/204Pb ratios (17.5 to 18.4) of metaluminous precaldera volcanic rocks and postcaldera plutonic rocks suggest that most Latir rocks were generated by fractional crystallization of substantial volumes of mantle-derived basaltic magma that had near-chondritic Nd isotope ratios, accompanied by assimilation of crustal material in two main stages: 1) assimilation of non-radiogenic lower crust, followed by 2) assimilation of middle and upper crust by inter-mediate-composition magmas that had been contaminated during the first stage. Magmatic evolution in the upper crust peaked with eruption of the peralkaline Amalia Tuff (???26 Ma), which evolved from metaluminous parental magmas. A third stage of late, roofward assimilation of Proterozoic rocks in the Amalia Tuff magma is indicated by trends in initial 87Sr/86Sr and 206Pb/204Pb ratios from 0.7057 to 0.7098 and 19.5 to 18.8, respectively, toward the top of the pre-eruptive magma chamber. Highly evolved postcaldera plutons are generally fine grained and are zoned in initial 87Sr/86Sr and 206Pb/204Pb ratios, varying from 0.705 to 0.709 and 17.8 to 18.6, respectively. In contrast, the coarser-grained Cabresto Lake (???25 Ma) and Rio Hondo (???21 Ma) plutons have relatively homogeneous initial 87Sr/86Sr and 206Pb/204Pb ratios of approximately 0.7053 and 17.94 and 17.55, respectively. ??18O values for all the postcaldera plutons overlap those of the precaldera rocks and Amalia Tuff, except for those for two late-stage rhyolite dikes associated with the Rio Hondo pluton that have ??18O values of-8.6 and-9.5; these dikes are the only Latir rocks which may be largely crustal melts. Chemical and isotopic data from the Latir field suggest that large fluxes of mantle-derived basaltic magma are necessary for developing and sustaining large-volume volcanic centers. Development of a detailed model suggests that 6-15 km of new crust may have been added beneath the volcanic center; such an addition may result in significant changes in the chemical and Sr and Nd isotopic compositions of the crust, although Pb isotope ratios will remain relatively unchanged. If accompanied by assimilation, crystallization of pooled basaltic magma near the MOHO may produce substantial cumulates beneath the MOHO that generate large changes in the isotopic composition of the upper mantle. The Latir field may be similar to other large-volume, long-lived intracratonal volcanic fields that fundamentally owe their origins to extensive injection of basaltic magma into the lower parts of their magmatic systems. Such fields may overlie areas of significant crustal growth and hybridization. ?? 1990 Springer-Verlag.

The distribution and mobility of uranium in glassy and zeolitized tuff, Keg Mountain area, Utah, U.S.A.

USGS Publications Warehouse

Zielinski, R.A.; Lindsey, D.A.; Rosholt, J.N.

1980-01-01

The distribution and mobility of uranium in a diagenetically altered, 8 Ma old tuff in the Keg Mountain area, Utah, are modelled in this study. The modelling represents an improvement over similar earlier studies in that it: (1) considers a large number of samples (76) collected with good geologic control and exhibiting a wide range of alteration; (2) includes radiometric data for Th, K and RaeU (radium equivalent uranium) as well as U; (3) considers mineralogic and trace-element data for the same samples; and (4) analyzes the mineral and chemical covariation by multivariate statistical methods. The variation of U in the tuff is controlled mainly by its primary abundance in glass and by the relative abundance of non-uraniferous detritus and uraniferous accessory minerals. Alteration of glass to zeolite, even though extensive, caused no large or systematic change in the bulk concentration of U in the tuff. Some redistribution of U during diagenesis is indicated by association of U with minor alteration products such as opal and hydrous Fe-Mn oxide minerals. Isotopic studies indicate that the zeolitized tuff has been open to migration of U decay products during the last 0.8 Ma. The tuff of Keg Mountain has not lost a statistically detectable fraction of its original U, even though it has a high (??? 9 ppm) trace U content and has been extensively altered to zeolite. Similar studies in a variety of geological environments are required in order to identify the particular combination of conditions most favorable for liberation and migration of U from tuffs. ?? 1980.

Hydraulic characterization of overpressured tuffs in central Yucca Flat, Nevada Test Site, Nye County, Nevada

USGS Publications Warehouse

Halford, Keith J.; Laczniak, Randell J.; Galloway, Devin L.

2005-01-01

A sequence of buried, bedded, air-fall tuffs has been used extensively as a host medium for underground nuclear tests detonated in the central part of Yucca Flat at the Nevada Test Site. Water levels within these bedded tuffs have been elevated hundreds of meters in areas where underground nuclear tests were detonated below the water table. Changes in the ground-water levels within these tuffs and changes in the rate and distribution of land-surface subsidence above these tuffs indicate that pore-fluid pressures have been slowly depressurizing since the cessation of nuclear testing in 1992. Declines in ground-water levels concurrent with regional land subsidence are explained by poroelastic deformation accompanying ground-water flow as fluids pressurized by underground nuclear detonations drain from the host tuffs into the overlying water table and underlying regional carbonate aquifer. A hydraulic conductivity of about 3 x 10-6 m/d and a specific storage of 9 x 10-6 m-1 are estimated using ground-water flow models. Cross-sectional and three-dimensional ground-water flow models were calibrated to measured water levels and to land-subsidence rates measured using Interferometric Synthetic Aperture Radar. Model results are consistent and indicate that about 2 million m3 of ground water flowed from the tuffs to the carbonate rock as a result of pressurization caused by underground nuclear testing. The annual rate of inflow into the carbonate rock averaged about 0.008 m/yr between 1962 and 2005, and declined from 0.005 m/yr in 2005 to 0.0005 m/yr by 2300.

Evidence for large-magnitude, post-Eocene extension in the northern Shoshone Range, Nevada, and its implications for Carlin-type gold deposits in the lower plate of the Roberts Mountains allochthon

USGS Publications Warehouse

Colgan, Joseph P.; Henry, Christopher D.; John, David A.

2014-01-01

The northern Shoshone and Toiyabe Ranges in north-central Nevada expose numerous areas of mineralized Paleozoic rock, including major Carlin-type gold deposits at Pipeline and Cortez. Paleozoic rocks in these areas were previously interpreted to have undergone negligible postmineralization extension and tilting, but here we present new data that suggest major post-Eocene extension along west-dipping normal faults. Tertiary rocks in the northern Shoshone Range crop out in two W-NW–trending belts that locally overlie and intrude highly deformed Lower Paleozoic rocks of the Roberts Mountains allochthon. Tertiary exposures in the more extensive, northern belt were interpreted as subvertical breccia pipes (intrusions), but new field data indicate that these “pipes” consist of a 35.8 Ma densely welded dacitic ash flow tuff (informally named the tuff of Mount Lewis) interbedded with sandstones and coarse volcaniclastic deposits. Both tuff and sedimentary rocks strike N-S and dip 30° to 70° E; the steeply dipping compaction foliation in the tuffs was interpreted as subvertical flow foliation in breccia pipes. The southern belt along Mill Creek, previously mapped as undivided welded tuff, includes the tuff of Cove mine (34.4 Ma) and unit B of the Bates Mountain Tuff (30.6 Ma). These tuffs dip 30° to 50° east, suggesting that their west-dipping contacts with underlying Paleozoic rocks (previously mapped as depositional) are normal faults. Tertiary rocks in both belts were deposited on Paleozoic basement and none appear to be breccia pipes. We infer that their present east tilt is due to extension on west-dipping normal faults. Some of these faults may be the northern strands of middle Miocene (ca. 16 Ma) faults that cut and tilted the 34.0 Ma Caetano caldera ~40° east in the central Shoshone Range (

Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

USGS Publications Warehouse

Bryan, C.R.; Helean, K.B.; Marshall, B.D.; Brady, P.V.

2009-01-01

Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (???60 wt%) and quartz polymorphs (???35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10-16 to 10-17 mol s-1 kg tuff-1 with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10-15 to 10-16 mol s-1 kg tuff-1 for percolation fluxes of 15 mm a-1 and 1 mm a-1, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a-1 or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (???50 mg L-1) may inhibit feldspar dissolution. ?? 2009 Elsevier Ltd. All rights reserved.

Petrologic evolution of the Caetano magmatic system: What can we learn from a dissected, 34 Ma caldera in the northern Great Basin, western U.S.A.?

NASA Astrophysics Data System (ADS)

Watts, K. E.; Colgan, J. P.; John, D. A.; Henry, C. D.

2012-12-01

Eruption of the >1,100 km3 Caetano Tuff and formation of the Caetano caldera occurred during the mid-Tertiary ignimbrite flare-up in the Great Basin. Post-collapse extension and faulting created a series of tilted fault blocks that expose >4 km thick intracaldera tuff, two generations of resurgent granitic plutons, silicic ring-fracture intrusions, a tuff dike that fed the early eruption, and pre- and post-caldera andesites. We integrate new petrologic data for extrusive and intrusive Caetano units with geologic mapping and geochronology to provide an exceptional view into the inner workings of a large caldera center. The Caetano Tuff is a phenocryst-rich (~30-50%) ignimbrite with a mineralogy of plagioclase + sanidine + quartz + biotite + orthopyroxene + Fe-Ti oxides ± hornblende + accessory zircon and allanite. Plagioclase crystals in the Caetano Tuff and cogenetic intrusive units span a wide compositional range (>30 mol% An) and have diverse petrographic textures ranging from euhedral phenocrysts to anhedral, sieved crystals with melt-rich cores. Plagioclase compositions measured by electron microprobe for whole rock thin sections are consistent with compositional zoning of the intracaldera tuff shown by XRF whole rock analyses, oligoclase (~10-30 mol% An) and andesine (~30-50 mol% An) in the most evolved (75-77% SiO2) and least evolved (72-74% SiO2) tuff units, respectively. However, orthopyroxene compositions are apparently decoupled from the host tuff composition, with the highest Mg#s (~60-70%) occurring in the most evolved tuff samples. In the Caetano Tuff, equilibrium pairs of Fe-Ti oxides yield an average eruption temperature of 745°C, which is consistent with the average Ti-in-zircon temperature of 750±70°C (1 stdev, n=90 spots) obtained from Ti concentrations measured by SHRIMP for single zircons. Application of Al-in-hornblende geobarometry indicates an average equilibration pressure of 4.5±0.1 kbar, corresponding to mid-crustal magma storage depths of ~14-15 km. In light of our new petrologic data, we highlight the following key points: (1) Diverse crystal cargoes, disequilibrium textures, and wide compositional oscillations in single phenocrysts and among discrete mineral populations indicate prolonged and complex episodes of magma assembly and growth. Based on zircon U-Pb SHRIMP ages that range from ~34-37 Ma, assembly and growth may have spanned ~2-3 Ma, or a 34 Ma Caetano magma chamber may have assimilated older igneous rocks in and around the caldera. (2) Mineral chemistry, U-Pb and Ar-Ar geochronology, O isotope geochemistry, and whole rock major and trace element geochemistry indicate a genetic connection between the Caetano Tuff and resurgent granitic plutons, supporting the role of linked volcanic-plutonic components in caldera settings. (3) Generation and eruption of crystal-rich "monotonous" rhyolite calls into question the prevailing paradigms of crystal-poor rhyolites derived from crystal mushes, or crystal-rich "monotonous intermediates" derived from homogeneous dacitic magma reservoirs. The Caetano Tuff may be a representative end member of caldera-forming eruptions that is important for understanding large-volume rhyolite genesis in the shallow-middle crust.

Evaluation of the potential for debris and hyperconcentrated flows in Capulin Canyon as a result of the 1996 Dome fire, Bandelier National Monument, New Mexico

USGS Publications Warehouse

Cannon, Susan H.

1997-01-01

The Dome fire of April 1996 burned 6684 ha in Bandelier National Monument and the adjacent Sante Fe National Forest. The potential for significant debris- and hyperconcentrated-flow activity in Capulin Canyon is evaluated through 1) a systematic consideration of geologic and geomorphic factors that characterize the condition of the hillslope materials and channels following the fire, 2) examination of sedimentologic evidence for past debris-flow activity in the canyon, and 3) evaluation of the response of the watershed through the 1996 summer monsoon season. The lack of accumulations of dry-ravel material on the hillslopes or in channels, the absence of a continuous hydrophobic layer, the relatively intact condition of the riparian vegetation and of the fibrous root mat on the hillslopes, and the lack of evidence of widespread past debris- and hyperconcentrated-flow activity, even with evidence of past fires, indicate a low potential for debris-flow activity in Capulin Canyon. In addition, thunderstorms during the summer monsoon of 1996 resulted in abundant surface overland flow on the hillslopes which transported low-density pumice, charcoal, ash and some mineral soil downslope as small-scale and non-erosive debris flows. In some places cobble- and boulder-sized material was moved short distances. A moderate potential for debris- and hyperconcentrated-flow activity is identified for the two major tributary canyons to Capulin Canyon based on evidence of both summer of 1996 and possible historic significant debris-flow activity.

Pneumatic testing in 45-degree-inclined boreholes in ash-flow tuff near Superior, Arizona

USGS Publications Warehouse

LeCain, G.D.

1995-01-01

Matrix permeability values determined by single-hole pneumatic testing in nonfractured ash-flow tuff ranged from 5.1 to 20.3 * 1046 m2 (meters squared), depending on the gas-injection rate and analysis method used. Results from the single-hole tests showed several significant correlations between permeability and injection rate and between permeability and test order. Fracture permeability values determined by cross-hole pneumatic testing in fractured ash-flow tuff ranged from 0.81 to 3.49 * 1044 m2, depending on injection rate and analysis method used. Results from the cross-hole tests monitor intervals showed no significant correlation between permeability and injection rate; however, results from the injection interval showed a significant correlation between injection rate and permeability. Porosity estimates from the 'cross-hole testing range from 0.8 to 2.0 percent. The maximum temperature change associated with the pneumatic testing was 1.2'(2 measured in the injection interval during cross-hole testing. The maximum temperature change in the guard and monitor intervals was O.Ip C. The maximum error introduced into the permeability values due to temperature fluctuations is approximately 4 percent. Data from temperature monitoring in the borehole indicated a positive correlation between the temperature decrease in the injection interval during recovery testing and the gas-injection rate. The thermocouple psychrometers indicated that water vapor was condensing in the boreholes during testing. The psychrometers in the guard and monitor intervals detected the drier injected gas as an increase in the dry bulb reading. The relative humidity in the test intervals was always higher than the upper measurement limit of the psychrometers. Although the installation of the packer system may have altered the water balance of the borehole, the gas-injection testing resulted in minimal or no changes in the borehole relative humidity.

Spatial variability of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, southwestern Utah: An analog to faulting in tuff on Mars

NASA Astrophysics Data System (ADS)

Okubo, C. H.

2011-12-01

The equatorial layered deposits on Mars exhibit abundant evidence for the sustained presence of groundwater, and therefore insight into past water-related processes may be gained through the study of these deposits. Pyroclastic and evaporitic sediments are two broad lithologies that are known or inferred to comprise these deposits. Investigations into the effects of faulting on fluid flow potential through such Mars analog lithologies have been limited. Thus a study into the effects of faulting on fluid flow pathways through fine-grained pyroclastic sediments has been undertaken, and the results of this study are presented here. Faults and their damage zones can influence the trapping and migration of fluids by acting as either conduits or barriers to fluid flow. In clastic sedimentary rocks, the conductivity of fault damage zones is primarily a function of the microstructure of the host rock, stress history, phyllosilicate content, and cementation. The chemical composition of the host rock influences the mechanical strength of the grains, the susceptibility of the grains to alteration, and the availability of authigenic cements. The spatial distribution of fault-related damage is investigated within the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah. Damage is characterized by measuring fracture densities along the fault, and by mapping the gas permeability of the surrounding rock. The Joe Lott Tuff is a partially welded, crystal-poor, rhyolite ash-flow tuff of Miocene age. While the rhyolitic chemical composition of the Joe Lott Tuff is not analogous to the basaltic compositions expected for Mars, the mechanical behavior of a poorly indurated mixture of fine-grained glass and pumice is pertinent to understanding the fundamental mechanics of faulting in Martian pyroclastic sediments. Results of mapping around two faults are presented here. The first fault is entirely exposed in cross-section and has a down-dip height of ~10 m. The second fault is partially exposed, with ~21 m visible in cross-section. Both faults have a predominantly normal sense of offset and a minor dextral strike-slip component. The 10 m fault has a single well-defined surface, while the 21 m fault takes the form of a 5-10 cm wide fault core. Fracture density at the 10 m fault is highest near its upper and lower tips, forming distinct near-tip fracture damage zones. At the 21 m fault, fracture density is broadly consistent along the exposed height of the fault, with the highest fracture densities nearest to the fault core. Fracture density is higher in the hanging walls than in the footwalls of both faults, and the footwall of the 21 m fault exhibits m-scale areas of significant distributed cataclasis. Gas permeability has a marked decrease, several orders of magnitude relative to the non-deformed host rock, at 1.5 m on either side of the 10 m fault. Permeability is lowest outboard of the fault's near-tip fracture damage zones. A similar permeability drop occurs at 1-5 m from the center of the 21 m fault's core, with the permeability drop extending furthest from the fault core in the footwall. These findings will be used to improve existing numerical methods for predicting subsurface fluid flow patterns from observed fault geometries on Mars.

Brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho

USGS Publications Warehouse

Okubo, Chris H.

2014-01-01

The manifestation of brittle deformation within inactive slumps along the North Menan Butte, a basaltic tuff cone in the Eastern Snake River Plain, is investigated through field and laboratory studies. Microstructural observations indicate that brittle strain is localized along deformation bands, a class of structural discontinuity that is predominant within moderate to high-porosity, clastic sedimentary rocks. Various subtypes of deformation bands are recognized in the study area based on the sense of strain they accommodate. These include dilation bands (no shear displacement), dilational shear bands, compactional shear bands and simple shear bands (no volume change). Measurements of the host rock permeability between the deformation bands indicate that the amount of brittle strain distributed throughout this part of the rock is negligible, and thus deformation bands are the primary means by which brittle strain is manifest within this tuff. Structural discontinuities that are similar in appearance to deformation bands are observed in other basaltic tuffs. Therefore deformation bands may represent a common structural feature of basaltic tuffs that have been widely misclassified as fractures. Slumping and collapse along the flanks of active volcanoes strongly influence their eruptive behavior and structural evolution. Therefore characterizing the process of deformation band and fault growth within basaltic tuff is key to achieving a more complete understanding of the evolution of basaltic volcanoes and their associated hazards.

Geohydrology of Monitoring Wells Drilled in Oasis Valley near Beatty, Nye County, Nevada, 1997

USGS Publications Warehouse

Robledo, Armando R.; Ryder, Philip L.; Fenelon, Joseph M.; Paillet, Frederick L.

1999-01-01

Twelve monitoring wells were installed in 1997 at seven sites in and near Oasis Valley, Nevada. The wells, ranging in depth from 65 to 642 feet, were installed to measure water levels and to collect water-quality samples. Well-construction data and geologic and geophysical logs are presented in this report. Seven geologic units were identified and described from samples collected during the drilling: (1) Ammonia Tanks Tuff; (2) Tuff of Cutoff Road; (3) tuffs, not formally named but informally referred to in this report as the 'tuff of Oasis Valley'; (4) lavas informally named the 'rhyolitic lavas of Colson Pond'; (5) Tertiary colluvial and alluvial gravelly deposits; (6) Tertiary and Quaternary colluvium; and (7) Quaternary alluvium. Water levels in the wells were measured in October 1997 and February 1998 and ranged from about 18 to 350 feet below land surface. Transmissive zones in one of the boreholes penetrating volcanic rock were identified using flowmeter data. Zones with the highest transmissivity are at depths of about 205 feet in the 'rhyolitic lavas of Colson Pond' and 340 feet within the 'tuff of Oasis Valley.'

Geology of the Ulugh Muztagh area, northern Tibet

USGS Publications Warehouse

Burchfiel, B.C.; Molnar, P.; Zhao, Ziyun; Liang, K'uangyi; Wang, Shuji; Huang, Minmin; Sutter, J.

1989-01-01

Within the Ulugh Muztagh area, north central Tibet, an east-west-trending ophiolitic melange marks a suture that apparently was formed during a late Triassic or slightly younger collision between a continental fragment to the south and the rest of Asia. The southern continental fragment carries a thick sequence of upper Triassic sandstone, but the contact between the sandstone and the ophiolitic melange is covered by a younger redbed sequence of unknown age. A suite of 2-mica, tourmaline-bearing leucogranite plutons and dikes intruded the Triassic sandstone at shallow crustal levels 10.5 to 8.4 Ma. These rocks range from granite to tonalite in composition, are geochemically very similar to slightly older High Himalayan leucogranite and are interpreted to have been derived by the partial melting of crustal material. We interpret this to mean that crustal thickening began in this part of the Tibetan plateau at least by 10.5 Ma. Welded rhyolitic tuff rests on a conglomerate that consists of abundant debris from the Ulugh Muztagh intrusive rocks and has yielded Ar Ar ages of about 4 Ma. The tuffs are geochemically identical to the intrusive rocks suggesting that crustal thickening may have continued to 4 Ma. Crustal thickening probably occurred by distributed crustal shortening similar to shortening now occurring north of Ulugh Muztagh along the northern margin of the Tibetan Plateau. ?? 1989.

Magma storage and evolution of the most recent effusive and explosive eruptions from Yellowstone Caldera

NASA Astrophysics Data System (ADS)

Befus, Kenneth S.; Gardner, James E.

2016-04-01

Between 70 and 175 ka, over 350 km3 of high-silica rhyolite magma erupted both effusively and explosively from within the Yellowstone Caldera. Phenocrysts in all studied lavas and tuffs are remarkably homogenous at the crystal, eruption, and caldera-scale, and yield QUILF temperatures of 750 ± 25 °C. Phase equilibrium experiments replicate the observed phenocryst assemblage at those temperatures and suggest that the magmas were all stored in the upper crust. Quartz-hosted glass inclusions contain 1.0-2.5 % H2O and 50-600 ppm CO2, but some units are relatively rich in CO2 (300-600 ppm) and some are CO2-poor (50-200 ppm). The CO2-rich magmas were stored at 90-150 MPa and contained a fluid that was 60-75 mol% CO2. CO2-poor magmas were stored at 50-70 MPa, with a more H2O-rich fluid (X_{{{text{CO}}2 }} = 40-60 %). Storage pressures and volatiles do not correlate with eruption age, volume, or style. Trace-element contents in glass inclusions and host matrix glass preserve a systematic evolution produced by crystal fractionation, estimated to range from 36 ± 12 to 52 ± 12 wt%. Because the erupted products contain <10 wt% crystals, crystal-poor melts likely separated from evolving crystal-rich mushes prior to eruption. In the Tuffs of Bluff Point and Cold Mountain Creek, matrix glass is less evolved than most inclusions, which may indicate that more primitive rhyolite was injected into the reservoir just before those eruptions. The presence and dissolution of granophyre in one flow may record evidence for heating prior to eruption and also demonstrate that the Yellowstone magmatic system may undergo rapid changes. The variations in depth suggest the magmas were sourced from multiple chambers that follow similar evolutionary paths in the upper crust.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

USGS Publications Warehouse

Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

2018-01-01

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of ~ 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000 km3.

Petrogenesis and U-Pb zircon chronology of felsic tuffs interbedded with turbidites (Eastern Pontides Orogenic Belt, NE Turkey): Implications for Mesozoic geodynamic evolution of the eastern Mediterranean region and accumulation rates of turbidite sequences

NASA Astrophysics Data System (ADS)

Eyuboglu, Yener

2015-01-01

The Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt, which is one of the key areas of the Alpine-Himalayan system, is still controversial due to lack of systematic geological, geophysical, geochemical and chronological data. The prevailing interpretation is that this belt represents the southern margin of Eurasia during the Mesozoic and its geodynamic evolution is related to northward subduction of oceanic lithosphere. This paper reports the first detailed geological, geochemical and chronological data from felsic tuffs interbedded with late Cretaceous turbidites in the Southern Zone of the Eastern Pontides Orogenic Belt. Individual tuff layers are thin, mostly < 2 m in thickness, implying that these are dominantly air-fall tuffs. Petrographic data indicate that the felsic tuffs, which exhibit various degrees of alteration, can be classified as crystal-rich and crystal-poor tuffs. The crystal-poor tuffs consist mainly of 45-65% devitrified glass shards and 10-20% broken quartz crystals, whereas the crystal-rich tuffs consist of > 50% crystals. The zircon U-Pb data show three statistically distinct ages at 84, 81 and 77 Ma, with uncertainties of about 1 Ma, suggesting that tuff-forming late Cretaceous magmatism started about 84 Ma ago and was episodically active over a minimum of 7 Ma. The age data also indicate that the average accumulation rate of the turbiditic sequence that hosts the felsic tuffs remained constant between 36 and 40 cm/10 ky. Their enrichment in LIL and LRE elements relative to HFS and HRE elements, and also strongly negative Nb, Ta and Ti anomalies, are consistent with those of magmas generated by subduction-related processes. The tuffs have relatively low initial ratios of 143Nd/144Nd (0.512296-0.512484; εNd: - 2.1 and - 7.2) and 87Sr/86Sr (0.704896-0.706159). Their initial Pb isotopic compositions range from 18.604 to 18.646 for 206Pb/204Pb, from 15.644 to 15.654 for 207Pb/206Pb and from 38.712 to 38.763 for 208Pb/204Pb. The distribution of Sr-Nd isotopic compositions in the late Cretaceous igneous rocks from different locations of the Eastern Pontides Orogenic Belt is consistent with two-component mixing between depleted mantle and crust. However, the Pb isotopic data are not compatible with two-component mixing and require at least a third component. Considering all of the new data and also previous data such as southward migration and increasing potassium content of the late Cretaceous arc volcanism, the northward migration of Cenozoic igneous activity, northward drift of the belt since the late Cretaceous and the existence of south-dipping reverse fault systems in the whole region, the Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt can be best explained by southward subduction of Tethys oceanic lithosphere, rather than northward subduction.

Geology, ore facies and sulfur isotopes geochemistry of the Nudeh Besshi-type volcanogenic massive sulfide deposit, southwest Sabzevar basin, Iran

NASA Astrophysics Data System (ADS)

Maghfouri, Sajjad; Rastad, Ebrahim; Mousivand, Fardin; Lin, Ye; Zaw, Khin

2016-08-01

The southwest Sabzevar basin is placed in the southwestern part of a crustal domain known as the Sabzevar zone, at the north of Central Iranian microcontinent. This basin hosts abundant mineral deposits; particularly of the Mn exhalative and Cu-Zn volcanogenic massive sulfide (VMS) types. The evolution of this basin is governed by the Neo-tethys oceanic crust subduction beneath the Central Iranian microcontinent and by the resulting continental arc (Sanandaj-Sirjan) and back-arc (Sabzevar-Naien). This evolution followed two major sequences: (I) Lower Late Cretaceous Volcano-Sedimentary Sequence (LLCVSS), which is indicated by fine-grained siliciclastic sediments, gray basic coarse-grained different pyroclastic rocks and bimodal volcanism. During this stage, tuff-hosted stratiform, exhalative Mn deposits (Nudeh, Benesbourd, Ferizy and Goft), oxide Cu deposits (Garab and Ferizy) and Cu-Zn VMS (Nudeh, Chun and Lala) deposits formed. (II) Upper Late Cretaceous Sedimentary Dominated Sequence (ULCSS), including pelagic limestone, marly tuff, silty limestone and marl with minor andesitic tuff rocks. The economically most important Mn (Zakeri and Cheshmeh-sefid) deposits of Sabzevar zone occur within the marly tuff of this sequence. The Nudeh Cu-Zn volcanogenic massive sulfide (VMS) deposit is situated in the LLCVSS. The host-rock of deposits consists of alkali olivine basalt flow and tuffaceous silty sandstone. Mineralization occurs as stratiform blanket-like and tabular orebodies. Based on ore body structure, mineralogy, and ore fabric, we recognize three different ore facies in the Nudeh deposit: (1) a stringer zone, consisting of a discordant mineralization of sulfides forming a stockwork of sulfide-bearing quartz veins cutting the footwall volcano-sedimentary rocks; (2) a massive ore, consisting of massive replacement pyrite, chalcopyrite, sphalerite and Friedrichite with magnetite; (3) bedded ore, with laminated to disseminated pyrite, and chalcopyrite. Chloritization, silicification, sericitization and epidotization are the main wall-rock alterations; alteration intensity increases towards the stringer zone. The δ34S composition of the sulfides ranges from -1.5‰ to +3.69‰ with a general increase of δ34S ratios of massive ore facies to stockwork zone. The heavier values indicate that some of the sulfur was derived from seawater sulfate that was ultimately thermochemically reduced in deep hydrothermal reaction zones. Sulfur isotopes, along with sedimentological, textural, petrological, mineralogical, and geochemical evidences, suggest that this deposit should be classified as a Besshi-type VMS ore deposit.

Comparison of neptunium sorption results using batch and column techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Triay, I.R.; Furlano, A.C.; Weaver, S.C.

1996-08-01

We used crushed-rock columns to study the sorption retardation of neptunium by zeolitic, devitrified, and vitric tuffs typical of those at the site of the potential high-level nuclear waste repository at Yucca Mountain, Nevada. We used two sodium bicarbonate waters (groundwater from Well J-13 at the site and water prepared to simulate groundwater from Well UE-25p No. 1) under oxidizing conditions. It was found that values of the sorption distribution coefficient, Kd, obtained from these column experiments under flowing conditions, regardless of the water or the water velocity used, agreed well with those obtained earlier from batch sorption experiments undermore » static conditions. The batch sorption distribution coefficient can be used to predict the arrival time for neptunium eluted through the columns. On the other hand, the elution curves showed dispersivity, which implies that neptunium sorption in these tuffs may be nonlinear, irreversible, or noninstantaneous. As a result, use of a batch sorption distribution coefficient to calculate neptunium transport through Yucca Mountain tuffs would yield conservative values for neptunium release from the site. We also noted that neptunium (present as the anionic neptunyl carbonate complex) never eluted prior to tritiated water, which implies that charge exclusion does not appear to exclude neptunium from the tuff pores. The column experiments corroborated the trends observed in batch sorption experiments: neptunium sorption onto devitrified and vitric tuffs is minimal and sorption onto zeolitic tuffs decreases as the amount of sodium and bicarbonate/carbonate in the water increases.« less

The link between volcanism and plutonism in epizonal magma systems; high-precision U–Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

USGS Publications Warehouse

Rioux, Matthew; Farmer, Lang; Bowring, Samuel; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.

2016-01-01

The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U–Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the final eruption. Calculated magmatic fluxes for the Organ Needle pluton range from 0.0006 to 0.0030 km3/year, in agreement with estimates from other well-studied plutons. The petrogenetic evolution proposed here may be common to many small-volume silicic volcanic systems.

Eruption and emplacement of a laterally extensive, crystal-rich, and pumice-free ignimbrite (the Cretaceous Kusandong Tuff, Korea)

NASA Astrophysics Data System (ADS)

Sohn, Y. K.; Son, M.; Jeong, J. O.; Jeon, Y. M.

2009-10-01

The Cretaceous Kusandong Tuff, Korea, is a thin (1-5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55-73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin.

Geologic evaluation of six nonwelded tuff sites in the vicinity of Yucca Mountain, Nevada for a surface-based test facility for the Yucca Mountain Project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broxton, D.E.; Chipera, S.J.; Byers, F.M. Jr.

1993-10-01

Outcrops of nonwelded tuff at six locations in the vicinity of Yucca Mountain, Nevada, were examined to determine their suitability for hosting a surface-based test facility for the Yucca Mountain Project. Investigators will use this facility to test equipment and procedures for the Exploratory Studies Facility and to conduct site characterization field experiments. The outcrops investigated contain rocks that include or are similar to the tuffaceous beds of Calico Hills, an important geologic and hydrologic barrier between the potential repository and the water table. The tuffaceous beds of Calico Hills at the site of the potential repository consist of bothmore » vitric and zeolitic tuffs, thus three of the outcrops examined are vitric tuffs and three are zeolitic tuffs. New data were collected to determine the lithology, chemistry, mineralogy, and modal petrography of the outcrops. Some preliminary data on hydrologic properties are also presented. Evaluation of suitability of the six sites is based on a comparison of their geologic characteristics to those found in the tuffaceous beds of Calico Hills within the exploration block.« less

Differentiation of colloidal and dissolved silica: Analytical separation using spectrophotometry and inductively coupled plasma atomic emission spectrometry

USGS Publications Warehouse

Lewis-Russ, A.; Ranville, J.; Kashuba, A.T.

1991-01-01

A method is described that differentiates between solutions containing silica-dominated colloids and solutions that are essentially free of colloids. Suspensions of tuff particles were treated to remove colloids by centrifugation, filtration or both. Agreement of silica concentrations determined by inductively coupled plasma atomic emission spectrometry and by a spectrophotometric method was taken as an indication of colloid-free solutions. For two tuffs, centrifugation was effective for removing colloids. For the third, highly altered tuff, filtration was more effective for removing colloids.

Are there Tuffs from Toba Supereruptions in Singapore?

NASA Astrophysics Data System (ADS)

Bergal-Kuvikas, O.; Bouvet de Maisonneuve, C.; Vazquez, J. A.

2016-12-01

Singapore is a dense transportation hub and the most highly populated area of SE Asia. In order to assess volcanic hazards for Singapore, we compiled a database of Quaternary eruptions from neighboring volcanoes and we investigated samples from 20 boreholes collected across 11 reservoirs and several natural outcrops in the NW parts of the city. We identified a deposit of white to slightly yellow clay with a visible thickness of 6-8 meters in the western part of Singapore. This deposit of very fine ash is silicic (SiO2 72-75 wt.%) and calk-alkaline (K2O 3.7-4.5 wt.%). The ash layer is clearly weathered as the LOI is around 5 wt.% and SEM images show the presence of clay minerals almost exclusively. Geochemical mapping shows that quartz crystals are characterized by textures similar to volcanic deposits. N-MORB normalized spiderdiagrams of whole-rocks show minimums in Nb and Ti, enrichments in LREE, and depletions of HREE. This suggests a subduction origin. One possible source for this voluminous weathered ash layer is the Toba caldera, which produced several super eruptions in the Quaternary (the Young Toba Tuff at 0.074 Ma, Middle Toba Tuff at 0.5 Ma, Old Toba Tuff at 0.84 Ma, and Haranggoal Dacite Tuff at 1.2 Ma). Recognizing distal Toba tuffs is problematic because most deposits are underwater. Most of the analyzed samples have geochemical compositions that are statistically similar to the Toba tuffs and characterized by high contents of HREE elements (e.g. Y, Er, Yb) and some REE (e.g. Eu, Ba, La, Th). Preliminary dating shows the presence of Triassic zircons, possibly due to geologic contamination. Additional dating is needed to ascertain the source and age of this ash. Our new geochemical data of likely distal Toba deposits will be an important component for tephrochronological and paleoenvironmental studies in addition to being of importance for hazards assessments in Singapore.

Carbonatite tuffs in the Laetolil Beds of Tanzania and the Kaiserstuhl in Germany

USGS Publications Warehouse

Hay, R.L.; O'Neil, J.R.

1983-01-01

Carbonatite lava and tephra are now well known. The only modern eruptive carbonatites, from Oldoinyo Lengai, Tanzania, are of alkali carbonatite, whereas all of the pre-modern examples are of calcite or dolomite. Chemical and stable isotope analyses were made of separate phases of Pliocene carbonatite tuffs of the Laetolil Beds in Tanzania and of Miocene carbonatite tuffs of the Kaiserstuhl in Germany in order to understand the reasons for this major difference. The Laetolil Beds contain numerous carbonatite and melilitite-carbonatite tuffs. It is proposed that the carbonatite ash was originally of alkali carbonate composition and that the alkali component was dissolved, leaving a residuum of calcium carbonate. The least recrystallized melilitite-carbonatite tuff contains early-deposited calcite cement and calcite pseudomorphs after nyerereite (?) that have contents of strontium and barium and ??18O and ??13C values suggestive of incomplete chemical and isotopic exchange during alteration and replacement of alkali carbonatite ash. Carbonatite tuffs of the Kaiserstuhl contain globules composed of calcite phenocrysts and microphenocrysts in a groundmass of calcite with a small amount of clay, apatite, and magnetite. The SrO contents of phenocrysts, microphenocrysts, and groundmass calcite average 0.90, 1.42, and 0.59 percent, respectively. The average ??18O and ??13C values of globules (+14.3 and -9.0, respectively) fall between those of coarse-grained intrusive Kaiserstuhl carbonatite (avg. +6.6, -5.8) and those of low-temperature calcite cement in the carbonatite tuffs (+21.8, -14.9). The phenocrysts and microphenocrysts are primary magmatic calcite, but several features indicate that the groundmass has been recrystallized and altered in contact with meteoric water, resulting in weathering of silicate to clay, leaching of strontium, and isotopic exchange. The weight of evidence favors an original high content of alkali carbonatite in the groundmass, with recrystallization following leaching of the alkalies. ?? 1983 Springer-Verlag.

Preliminary geological interpretation and lithologic log of the exploratory geothermal test well (INEL-1), Idaho National Engineering Laboratory, eastern Snake River Plain, Idaho

USGS Publications Warehouse

Doherty, David J.; McBroome, Lisa Ann; Kuntz, Mel A.

1979-01-01

A 10,365 ft (3,159 m) geothermal test well was drilled in the spring of 1979 at the Idaho National Engineering Laboratory, eastern Snake River Plain, Idaho: The majority of rock types encountered in the borehole are of volcanic origin. An upper section above 2,445 ft (745 m) consists of basaltic lava flows and interbedded .sediments of alluvial, lacustrine, and volcanic origin. A lower section below 2,445 ft (745 m) consists exclusively of rhyolitic welded ash-flow tuffs, air-fall ash deposits, nonwelded ash-flow ruffs, and volcaniclastic sediments. The lithology and thickness of the rhyolitic rocks suggest that they are part of an intracaldera fill.

Pore-water extraction from unsaturated tuff by triaxial and one-dimensional compression methods, Nevada Test Site, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mower, T.E.; Higgins, J.D.; Yang, In C.

1994-07-01

The hydrologic system in the unsaturated tuff at Yucca Mountain, Nevada, is being evaluated for the US Department of Energy by the Yucca Mountain Project Branch of the US Geological Survey as a potential site for a high-level radioactive-waste repository. Part of this investigation includes a hydrochemical study that is being made to assess characteristics of the hydrologic system such as: traveltime, direction of flow, recharge and source relations, and types and magnitudes of chemical reactions in the unsaturated tuff. In addition, this hydrochemical information will be used in the study of the dispersive and corrosive effects of unsaturated-zone watermore » on the radioactive-waste storage canisters. This report describes the design and validation of laboratory experimental procedures for extracting representative samples of uncontaminated pore water from welded and nonwelded, unsaturated tuffs from the Nevada Test Site.« less

Effect of the addition of by-product ash of date palms on the mechanical characteristics of gypsum-calcareous materials used in road construction

NASA Astrophysics Data System (ADS)

Khellou, A.; Kriker, A.; Hafssi, A.; Belbarka, K.; Baali, K.

2016-07-01

The gypsum-calcareous materials, also known as the crusting tuff, are used in the pavement layers of low -traffic road and considered as the materials of first choice in the Saharan region of Algeria. The objective of this paper is to study the mechanical characteristics of tuff of Ouargla town that is situated in the Southeast of Algeria, by adding different percentage of ash resulted from the combustion of by-products of date palms, such as 4%, 8% and l2%, to the tuff. The results obtained have shown a remarkable improvement both in compressive strength at different ages and in the bearing index in the two cases immediate and after immersion in water. These characteristics of the mixture (tuff+ash) reach their maximum values at the 8% of ash addition.

Paleoflow of the Tuff of San Felipe on Isla Angel de la Guarda

NASA Astrophysics Data System (ADS)

Skinner, S. M.; Stock, J. M.; Martin Barajas, A.

2013-05-01

The Tuff of San Felipe is a widespread 12.5 Ma ignimbrite in northwestern Mexico that has a proven potential in reconstructing the rifting history of the Gulf of California. Previous studies have used the Tuff of San Felipe to correlate Isla Tiburon to the Sierra San Felipe on the Baja California Peninsula, and to correlate central Isla Angel de la Guarda to Baja California in the region of Cataviña. However, because only scattered outcrops are preserved in this latter region, paleoflow directions are an important additional constraint for reconstructing its past position relative to Isla Angel de la Guarda. We have confirmed the presence of the Tuff of San Felipe on Isla Angel de la Guarda and collected rocks from 44 sites for paleomagnetic and AMS analysis. Our work on the Tuff of San Felipe has revealed discrepancies in the magnetic fabric, and resulting flow direction, on the scale of hundreds of meters. The lack of a uniform flow direction from a single mesa impairs our ability to correlate offset channelized flows over large distances. To investigate the robustness of the AMS fabric we have performed a spatially dense sampling of the unit. Rigorous rock magnetic experiments will be used to investigate any correlation between changes in the magnetic mineralogy of the samples and any irregularities or constancies in the measured fabrics and flow directions. With this study we aim to characterize the variability of the AMS ellipsoid in natural volcanic samples and the scale at which AMS can be used as a meaningful indicator of paleoflow in the Tuff of San Felipe.

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

USGS Publications Warehouse

Moscati, Richard J.; Johnson, Craig A.

2014-01-01

Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magma-derived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe1.46Mn1.45Mg0.03Ca0.10)(Al1.93Ti0.02)Si3.01O12 and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4‰. The associated quartz (after tridymite) has δ18O values of 17.4 and 17.6‰, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ18O of 11.1‰ which, when coupled with the garnet δ18O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ~600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50–70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

USGS Publications Warehouse

Dai, S.; Wang, X.; Chen, W.; Li, D.; Chou, C.-L.; Zhou, Y.; Zhu, Chen; Li, H.; Zhu, Xudong; Xing, Y.; Zhang, W.; Zou, J.

2010-01-01

The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5??g/g), V (121??g/g), Cr (33.6??g/g), Co (27.2??g/g), Ni (83.5??g/g), Cu (48.5??g/g), Ga (17.3??g/g), Y (68.3??g/g), Zr (444??g/g), Nb (23.8??g/g), and REE (392??g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that enriched trace elements above were largely derived from mafic tuffs, in addition to a minor amount from the Kandian Oldland. ?? 2010 Elsevier B.V.

Tertiary volcanic rocks and uranium in the Thomas Range and northern Drum Mountains, Juab County, Utah

USGS Publications Warehouse

Lindsey, David A.

1982-01-01

The Thomas Range and northern Drum Mountains have a history of volcanism, faulting, and mineralization that began about 42 m.y. (million years) ago. Volcanic activity and mineralization in the area can be divided into three stages according to the time-related occurrence of rock types, trace-element associations, and chemical composition of mineral deposits. Compositions of volcanic rocks changed abruptly from rhyodacite-quartz latite (42-39 m.y. ago) to rhyolite (38-32 m.y. ago) to alkali rhyolite (21 and 6-7 m.y. ago); these stages correspond to periods of chalcophile and siderophile metal mineralization, no mineralization(?), and lithophile metal mineralization, respectively. Angular unconformities record episodes of cauldron collapse and block faulting between the stages of volcanic activity and mineralization. The youngest angular unconformity formed between 21 and 7 m.y. ago during basin-and-range faulting. Early rhyodacite-quartz latite volcanism from composite volcanoes and fissures produced flows, breccias, and ash-flow tuff of the Drum Mountains Rhyodacite and Mt. Laird Tuff. Eruption of the Mt. Laird Tuff about 39 m.y. ago from an area north of Joy townsite was accompanied by collapse of the Thomas caldera. Part of the roof of the magma chamber did not collapse, or the magma was resurgent, as is indicated by porphyry dikes and plugs in the Drum Mountains. Chalcophile and siderophile metal mineralization, resulting in deposits of copper, gold, and manganese, accompanied early volcanism. Te middle stage of volcanic activity was characterized by explosive eruption of rhyolitic ash-flow tuffs and collapse of the Dugway Valley cauldron. Eruption of the Joy Tuff 38 m.y. ago was accompanied by subsidence of this cauldron and was followed by collapse and sliding of Paleozoic rocks from the west wall of the cauldron. Landslides in The Dell were covered by the Dell Tuff, erupted 32 m.y. ago from an unknown source to the east. An ash flow of the Needles Range(?) Formation was erupted 30-31 m.y. ago from an unknown source. Mineralization probably did not occur during the rhyolitic stage of volcanism. The last stage of volcanism was contemporaneous with basin-and-range faulting and was characterized by explosive eruption of ash and pumice, forming stratified tuff, and by quiet eruption of alkali rhyolite as viscous flows and domes. The first episode of alkali rhyolite volcanism deposited the beryllium tuff and porphyritic rhyolite members of the Spor Mountain Formation 21 m.y. ago. After a period of block faulting, the stratified tuff and alkali rhyolite of the Topaz Mountain Rhyolite were erupted 6-7 m.y. ago along faults and fault intersections. Erosion of Spor Mountain, as well as explosive eruptions through dolomite, provided abundant dolomite detritus to the beryllium tuff member. The alkali rhyolite of both formations is fluorine rich, as is evident from abundant topaz, and contains anomalous amounts of lithophile metals. Alkali rhyolite volcanism was accompanied by lithophile metal mineralization which deposited fluorite, beryllium, and uranium. The structure of the area is dominated by the Thomas caldera and the younger Dugway Valley cauldron, which is nested within the Thomas caldera; the Thomas caldera is surrounded by a rim of Paleozoic rocks at Spor Mountain and Paleozoic to Precambrian rocks in the Drum Mountains. The Joy fault and Dell fault system mark the ring-fracture zone of the Thomas caldera. These structural features began to form about 39 m.y. ago during eruption of the Mt. Laird Tuff and caldera subsidence. The Dugway Valley cauldron sank along a series of steplike normal faults southeast of Topaz Mountain in response to collapse of the magma chamber of the Joy Tuff. Caldera structure was modified by block faulting between 21 and 7 m.y. ago, the time of widespread extensional faulting in the Basin and Range Province. Vents erupted alkali rhyolite 6-7 m.y. ago along basin-and-range faults.

Permian U-Pb (CA-TIMS) zircon ages from Australia and China: Constraining the time scale of environmental and biotic change

NASA Astrophysics Data System (ADS)

Denyszyn, S. W.; Mundil, R.; Metcalfe, I.; He, B.

2010-12-01

In eastern Australia, the interconnected Bowen and Sydney Basins are filled with terrestrial sediments of late Paleozoic to early Mesozoic age. These sedimentary units record significant evolutionary events of eastern Gondwana during the time interval between two major mass extinctions (end Middle Permian and Permian-Triassic), and also provide lithological evidence for the Carboniferous-Permian Late Paleozoic Ice Age of southern Pangea, considered to be divisible into up to seven discrete glaciation events in Australia [e.g., 1]. These glaciations are currently assigned ages that indicate that the last of the glaciations predate the end Middle Permian mass extinction at ca. 260 Ma. However, the estimates for the time and durations are largely based on biostratigraphy and lithostratigraphy that, in the absence of robust and precise radioisotopic ages, are unacceptably fragile for providing an accurate high-resolution framework. Interbedded with the sediments are numerous tuff layers that contain zircon, many of which are associated with extensive coal measures in the Sydney and Bowen Basins. Published SHRIMP U-Pb zircon ages [2, 3] have been shown to be less precise and inaccurate when compared to ages applying the CA-TIMS method to the same horizons. Also within the late Middle Permian, the eruption of the Emeishan flood basalts in SW China has been proposed to have caused the end Middle Permian mass extinction [e.g., 4], though a causal link between these events demands a rigorous test that can only be provided by high-resolution geochronology. We present new U-Pb (CA-TIMS) zircon ages on tuff layers from the Sydney and Bowen Basins, with the purpose of generating a timescale for the Upper Permian of Australia to allow correlation with different parts of the world. Initial results, with permil precision, date a tuff layer within the uppermost Bandanna Fm. to ca. 252 Ma, a tuff within the Moranbah Coal Measures to ca. 256 Ma, and a tuff within the Ingelara Fm. to ca. 257 Ma, the latter two units lying stratigraphically below the latest identified glacial deposits. U-Pb (CA-TIMS) results on zircons from the Emeishan flood basalts and related volcanic products confirm the end-Guadalupian age (ca. 260 Ma) of the magmatism, and based on present data, place the Emeishan volcanic event (and its possibly associated mass extinction) within the occurrence of the Late Paleozoic Ice Age. This study’s primary goal is the establishment of a chronostratigraphic framework that would allow the integration of calibrated records from both terrestrial and marine units from different parts of the world in order to constrain the timing and rates of extinctions and recoveries in different locations and physical environments. [1] Fielding et al. (2008), J. Geol Soc. Lon., v. 165, pp. 129-140 [2] Michaelsen et al. (2001), Aus. J. Earth Sci., v. 48, pp. 183-192 [3] Roberts et al. (1996), Aus. J. Earth Sci., v. 43, pp. 401-421 [4] He et al. (2007), EPSL, v. 255, pp. 306-323

Explosive shaped charge penetration into tuff rock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vigil, M.G.

1988-10-01

Analysis and data for the use of Explosive Shaped Charges (ESC) to generate holes in tuff rock formation is presented. The ESCs evaluated include Conical Shaped Charges (CSC) and Explosive Formed Projectiles (EFP). The CSCs vary in size from 0.158 to 9.1 inches inside cone diameter. The EFPs were 5.0 inches in diameter. Data for projectile impact angles of 30 and 90 degrees are presented. Analytically predicted depth of penetration data generally compared favorably with experimental data. Predicted depth of penetration versus ESC standoff data and hole profile dimensions in tuff are also presented. 24 refs., 45 figs., 6 tabs.

Correlation of the KHS Tuff of the Kibish Formation to volcanic ash layers at other sites, and the age of early Homo sapiens (Omo I and Omo II).

PubMed

Brown, Francis H; McDougall, Ian; Fleagle, John G

2012-10-01

Hominin specimens Omo I and Omo II from Member I of the Kibish Formation, Ethiopia are attributed to early Homo sapiens, and an age near 196 ka has been suggested for them. The KHS Tuff, within Member II of the Kibish Formation has not been directly dated at the site, but it is believed to have been deposited at or near the time of formation of sapropel S6 in the Mediterranean Sea. Electron microprobe analyses suggest that the KHS Tuff correlates with the WAVT (Waidedo Vitric Tuff) at Herto, Gona, and Konso (sample TA-55), and with Unit D at Kulkuletti in the Ethiopian Rift Valley. Konso sample TA-55 is older than 154 ka, and Unit D at Kulkuletti is dated at 183 ka. These correlations and ages provide strong support for the age originally suggested for the hominin remains Omo I and Omo II, and for correlation of times of deposition in the Kibish region with formation of sapropels in the Mediterranean Sea. The Aliyo Tuff in Member III of the Kibish Formation is dated at 104 ka, and correlates with Gademotta Unit 15 in the Ethiopian Rift Valley. Copyright © 2012 Elsevier Ltd. All rights reserved.

Structure, stratigraphy, and eruption dynamics of a young tuff ring: Hanauma Bay, O'ahu, Hawai'i

NASA Astrophysics Data System (ADS)

Rottas, K. M.; Houghton, B. F.

2012-09-01

The Hanauma Bay-Koko Head complex is one of several young volcanic landforms along the Koko fissure, in southeastern O'ahu. The Hanauma Bay region of the complex comprises two nested tuff rings, inner and outer Hanauma Bay, and multiple smaller vents. The internal structure of the inner tuff ring, well exposed due to subsequent breaching by the ocean and wave erosion, indicates that it formed during a minimum of five distinct phases of deposition that produced five mappable units. Significant inward collapses generated major unconformities that separate the units exposed in the inner wall. The planes of failure are cut by narrow steep-walled, locally overhung channels and gullies, suggesting that the collapse events were each followed by short time breaks during which the deposits were eroded by rainfall runoff. Within each pyroclastic unit, there are many local slump scars and unconformities, suggesting that minor instability of the inner wall was a near-constant feature. From bedding sags and surge bed forms, it is apparent that the vent shifted at least twice during tuff ring growth. Ballistic blocks in the youngest unit indicate that the eruption overlapped in time with a separate eruption to the north, most likely to be that of the Kahauloa tuff ring 880 m away.

Analysis of Conservative Tracer Tests in the Bullfrog, Tram, and Prow Pass Tuffs, 1996 to 1998, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Umari, Amjad; Fahy, Michael F.; Earle, John D.; Tucci, Patrick

2008-01-01

To evaluate the potential for transport of radionuclides in ground water from the proposed high-level nuclear-waste repository at Yucca Mountain, Nevada, conservative (nonsorbing) tracer tests were conducted among three boreholes, known as the C-hole Complex, and values for transport (or flow) porosity, storage (or matrix) porosity, longitudinal dispersivity, and the extent of matrix diffusion were obtained. The C-holes are completed in a sequence of Miocene tuffaceous rock, consisting of nonwelded to densely welded ash-flow tuff with intervals of ash-fall tuff and volcaniclastic rocks, covered by Quaternary alluvium. The lower part of the tuffaceous-rock sequence includes the Prow Pass, Bullfrog, and Tram Tuffs of the Crater Flat Group. The rocks are pervaded by tectonic and cooling fractures. Paleozoic limestone and dolomite underlie the tuffaceous rocks. Four radially convergent and one partially recirculating conservative (nonsorbing) tracer tests were conducted at the C-hole Complex from 1996 to 1998 to establish values for flow porosity, storage porosity, longitudinal dispersivity, and extent of matrix diffusion in the Bullfrog and Tram Tuffs and the Prow Pass Tuff. Tracer tests included (1) injection of iodide into the combined Bullfrog-Tram interval; (2) injection of 2,6 difluorobenzoic acid into the Lower Bullfrog interval; (3) injection of 3-carbamoyl-2-pyridone into the Lower Bullfrog interval; and (4) injection of iodide and 2,4,5 trifluorobenzoic acid, followed by 2,3,4,5 tetrafluorobenzoic acid, into the Prow Pass Tuff. All tracer tests were analyzed by the Moench single- and dual-porosity analytical solutions to the advection-dispersion equation or by superposition of these solutions. Nonlinear regression techniques were used to corroborate tracer solution results, to obtain optimal parameter values from the solutions, and to quantify parameter uncertainty resulting from analyzing two of the three radially convergent conservative tracer tests conducted in the Bullfrog and Tram intervals. Longitudinal dispersivity values in the Bullfrog and Tram Tuffs ranged from 1.83 to 2.6 meters, flow-porosity values from 0.072 to 0.099, and matrix-porosity values from 0.088 to 0.19. The flow-porosity values indicate that the pathways between boreholes UE-25 c#2 and UE-25 c#3 in the Bullfrog and Tram intervals are not connected well. Tracer testing in the Prow Pass interval indicates different transport characteristics than those obtained in the Bullfrog and Tram intervals. In the Prow Pass Tuff, longitudinal dispersivity was 0.27 meter, flow porosity was 4.5 ? 10?4, and matrix porosity was 0.01. This indicates that the flow network in the Prow Pass is dominated by interconnected fractures, whereas in the Bullfrog and Tram, the flow network is dominated by discontinuous fractures with connecting segments of matrix.

High-temperature, large-volume, lavalike ash-flow tuffs without calderas in southwestern Idaho

USGS Publications Warehouse

Ekren, E.B.; McIntyre, David H.; Bennett, Earl H.

1984-01-01

Rhyolitic rocks were erupted from vents in and adjacent to the Owyhee Mountains and Owyhee Plateau of southwestern Idaho from 16 m.y. ago to about 10 m.y. ago. They were deposited on a highly irregular surface developed on a variety of basement rocks that include granitic rocks of Cretaceous age, quartz latite and rhyodacite tuffs and lava flows of Eocene age, andesitic and basaltic lava flows of Oligocene age, and latitic and basaltic lava flows of early Miocene age. The rhyolitic rocks are principally welded tuffs that, regardless of their source, have one feature in common-namely internal characteristics indicating en-masse, viscous lavalike flowage. The flowage features commonly include considerable thicknesses of flow breccia at the bases of various cooling units. On the basis of the tabular nature of the rhyolitic deposits, their broad areal extents, and the local preservation of pyroclastic textures at the bases, tops, and distal ends of some of the deposits, we have concluded that the rocks were emplaced as ash flows at extremely high temperatures and that they coalesced to liquids before final emplacement and cooling. Temperatures of l090?C and higher are indicated by iron-titanium oxide compositions. Rhyolites that are about 16 m.y. old are preserved mostly in the downdropped eastern and western flanks of the Silver City Range and they are inferred to have been erupted from the Silver City Range. They rarely contain more than about 2 percent phenocrysts that consist of quartz and subequal amounts of plagioclase and alkali feldspar; commonly, they contain biotite, and they are the only rhyolitic rocks in the area to do so. The several rhyolitic units that are 14 m.y. to about 10 m.y. old contain only pyroxene-principally ferriferous and intermediate pigeonites-as mafic constituents. The rhyolites of the Silver City Range comprise many cooling units, none of which can be traced for great distances. Rocks erupted from the Owyhee Plateau include two sequences that were traced over areas having diameters of about 100 km. These two sheets are the herein-named Swisher Mountain Tuff, which is about 13.8 m.y. old, and the Little Jacks Tuff, which is about 10 m.y. old. The Swisher Mountain Tuff was erupted from the Juniper Mountain volcanic center, a gentle dome that is not bounded by arcuate faults indicative of cauldron subsidence. The tuff is 200 m thick over a considerable area in and adjacent to its source. It apparently thins gradually toward its distal edges, and it is inferred to be uniformly distributed around its source at Juniper Mountain. The unit contains vitrophyres at various intervals from base to top, and, although the vitrophyres are, in general, flow layered and commonly flow brecciated, they occasionally contain well-defined pumice clasts. The vitrophyres indicate compound cooling, and, near the distal edges of the sheet, some of them probably represent complete cooling breaks. The Little Jacks Tuff onlaps the Swisher Mountain Tuff in expo sures east of Juniper Mountain, and it is inferred to have been erupted from a source on the part of the Owyhee Plateau that lies just east of the area studied. This inferred source area, like that at Juniper Mountain, is also expressed today as a gentle dome without structural features indicative of cauldron subsidence. The Little Jacks Tuff, in most exposures in the deep canyons of the Plateau, consists of at least four cooling units, and, in places in the eastern part of the studied area near the source area, it possibly comprises as many as six. Although there is no obvious evidence of erosion between the various cooling units, magnetic polarity measurements indicate that there were at least two magnetic reversals during the eruption interval of the Little Jacks Tuff. Like the Swisher Mountain Tuff, the Little Jacks has flattened pumice clasts in a few outcrops-principally at the bases of the various cooling units. The two tuff sequences are calc-a

Fire effects in southwestern forests: Proceedings of the Second La Mesa Fire symposium

USGS Publications Warehouse

Allen, Craig D.

1996-01-01

In 1977, the La Mesa Fire burned across 15,444 acres of ponderosa pine forests on the adjoining lands of Bandelier National Monument, the Santa Fe National Forest, and Los Alamos National Laboratory. Following this event, several fire effects studies were initiated. The 16 papers herein document longer-term knowledge gained about the ecological effects of the fire and about Southwestern fire ecology in general. The presentations are also designed to give resource managers practical information for managing fire in local landscapes. Studies presented range from fire histories and avifauna to geomorphology and arthropods.

Preliminary examination of uranium deposits near Marysvale, Piute County, Utah

USGS Publications Warehouse

Granger, Harry C.; Bauer, Herman L.

1950-01-01

Autunite and other uranium minerals were discovered in 1948 by Pratt Seegmiller about 3 1/4 miles north of Marysvale, Piute County, Utah. Mining operations were begun in the summer of 1949 by the Vanadium Corporation of America on the Prospector and the Freedom claims, and by the Bullion Monarch Mining Company a the Bullion Monarch claims. These claims were examined briefly in December 1949 and January 1950 by the writers. The uranium deposits of the Marysvale district are in north-easterly striking fault zones in quartz monzonite that intrudes rocks of the "older" Tertiary volcanic sequence. Flows and tuffs of the "younger" Tertiary volcanic sequence uncomfortably overlie the earlier rocks. Autunite, tobernite, uranophane, schroeckingerite, and at least one unidentified secondary uranium mineral occur in the upper parts of the deposits. Pitchblende has been mined from the underground workings of the Prospector No. 1 mine. The uranium minerals are associated with dense quartz veins and intensely argillized wall rock. In the upper parts of the deposits pyrite is completely oxidized. The secondary uranium minerals probably were formed by the alteration of primary pitchblende by circulating meteoric waters.

Altered tuffaceous rocks of the Green River Formation in the Piceance Creek Basin, Colorado

USGS Publications Warehouse

Griggs, Roy Lee

1968-01-01

More than 50 ash-fall tuff beds which have altered to analcitized or feldspathized rocks have been found in the upper 500-600 feet of the Parachute Creek Member of the Green River Formation in the Piceance Creek Basin of northwestern Colorado. Similarly altered water-washed tuff occurs as tongues in the uppermost part of this member, and forms most of the lower 400-600 feet of the overlying Evacuation Creek Member of the Green River Formation. 'The altered ash-fall beds of the Parachute Creek Member are all thin and show a characteristic pattern of alteration. Most beds range in thickness from a fraction of an inch to a few inches. One bed reaches a maximum thickness of 5 feet, and, unlike the other beds, is composed of several successive ash falls. The pattern of alteration changes from the outer part to the center of the basin. Most beds in the outer part of the basin contain about 50 to 65 percent analcite,with the interstices between the crystals filled mainly by microlites of feldspar, opal, and quartz, and small amounts of carbonate. At the center of the basin .essentially all the beds -are composed of microlites of feldspar, opal, and quartz, and small amounts of carbonate. The tongues of water-washed tuff in the uppermost part of the Parachute Creek Member and the similar rocks composing the lower 400-600 feet of the Evacuation Creek Mewber are feldspathized rocks composed mainly of microlites of feldspar, opal, and quartz, varying amounts of carbonate, and in some specimens tiny subrounded crystals of analcite. The general trend in alteration of the tuffaceous rocks from analcitization near the margin to feidspathization near the center of the Piceance Creek Basin is believed to have taken place at shallow depth during diagenesis , as indicated by field observations and laboratory work. It is believed that during sedimentation and diagenesis the waters of the central part of the basin were more alkaline and following the breakdown of the original tuffaceous glass to a colloidal gel during diagenesis analcitized rocks crystallized near the basin margin and feldspathized rocks crystallized near the center of the basin.

Experimental investigation of time dependent behavior of welded Topopah Spring Tuff

NASA Astrophysics Data System (ADS)

Ma, Lumin

Four types of laboratory tests have been performed. Specimens were attained from four lithophysal zones of the welded Topopah Spring Tuff unit at Yucca Mountain, Nevada: upper lithophysal, middle nonlithophysal, lower lithophysal and lower nonlithophysal zones. Two types of tests are conducted to study time-dependent behavior: constant strain rate and creep tests. Sixty-five specimens from the middle nonlithophysal zone were tested at six strain rates: 10-2, 10-4, 10-5, 10-6, 10-7, and 10-8 s-1. Test durations range from 2 seconds to 7 days. Fourteen specimens from middle nonlithophysal, lower lithophysal and lower nonlithophysal zones are creep tested by incremental stepwise loading. All the tests are conducted under uniaxial compression at room temperature and humidity. Specimens exhibit extremely brittle fracture and fail by axial splitting, and show very little dilatancy if any. It is assumed that microfracturing dominates the inelastic deformation and failure of the tuff. Nonlinear regression is applied to the results of the constant strain rate tests to estimate the relations between peak strength, peak axial strain, secant modulus and strain rate. All three these parameters decrease with a decrease of strain rate and follow power functions: sigmapeak = 271.37 3˙0.0212 0.0212, epsilonpeak = 0.006 3˙0.0083 , ES = 41985.4 3˙0.015 . Secant modulus is introduced mainly as a tool to analyze strain rate dependent axial strain. Two threshold stresses define creep behavior. Below about 50% of peak strength, a specimen does not creep. Above about 94% of peak strength, a specimen creeps at an accelerating rate. Between the two threshold stresses, a power law relates strain rate and stress. One hundred fifty-eight Brazilian (Indirect tensile splitting) tests have been performed at six different constant strain rates. Nineteen lithophysal specimens were tested in uniaxial compression to study their fracture pattern. These specimens have a far less brittle failure mode. They slowly crumble, collapse, and maintain considerable relative strength beyond the peak. Due to the presence of multiple relatively large lithophysal cavities, they are far weaker and softer than the nonlithophysal specimens.

Stratigraphy, correlation, depositional setting, and geophysical characteristics of the Oligocene Snowshoe Mountain Tuff and Creede Formation in two cored boreholes

USGS Publications Warehouse

Larsen, Daniel; Nelson, Philip H.

2000-01-01

Core descriptions and geophysical logs from two boreholes (CCM-1 and CCM-2) in the Oligocene Snowshoe Mountain Tuff and Creede Formation, south-central Colorado, are used to interpret sedimentary and volcanic facies associations and their physical properties. The seven facies association include a mixed sequence of intracaldera ash-flow tuffs and breccias, alluvial and lake margin deposits, and tuffaceous lake beds. These deposits represent volcanic units related to caldera collapse and emplacement of the Snowshoe Mountain Tuff, and sediments and pyroclastic material deposited in the newly formed caldera basin, Early sedimentation is interpreted to have been rapid, and to have occurred in volcaniclastic fan environments at CCM-1 and in a variery of volcaniclastic fan, braided stream shallow lacustrine, and mudflat environments at CCM-2. After an initial period of lake-level rise, suspension settling, turbidite, and debris-flow sedimentation occurred in lacustrine slope and basin environments below wave base. Carbonate sedimentation was initially sporadic, but more continuous in the latter part of the recorded lake history (after the H fallout tuff). Sublacustrine-fan deposition occurred at CCM-1 after a pronounced lake-level fall and subsequent rise that preceded the H tuff. Variations in density, neutron, gamma-ray, sonic, and electrical properties of deposits penetrated oin the two holes reflect variations in lithology, porosity, and alteration. Trends in the geophysical properties of the lacustrine strata are linked to downhole changes in authigenic mineralology and a decrease in porosity interpreted to have resulted primarily from diagenesis. Lithological and geophysical characteristics provide a basis for correlation of the cores; however, mineralogical methods of correlation are hampered by the degree of diagenesis and alteration.

Paleoflow of the Tuff of San Felipe on Isla Angel de la Guarda

NASA Astrophysics Data System (ADS)

Skinner, S. M.; Stock, J. M.; Martin, A.

2013-12-01

The Tuff of San Felipe is a widespread 12.5 Ma ignimbrite in northwestern Mexico that has a proven potential in reconstructing the rifting history of the Gulf of California. Previous studies have used the Tuff of San Felipe to correlate Isla Tiburon to the Sierra San Felipe on the Baja California Peninsula, and to correlate central Isla Angel de la Guarda to Baja California in the region of Cataviña. However, because only scattered outcrops are preserved in this latter region, paleoflow directions are an important additional constraint for reconstructing its past position relative to Isla Angel de la Guarda. We have confirmed the presence of the Tuff of San Felipe on Isla Angel de la Guarda and collected rocks from 44 sites for paleomagnetic and AMS analysis. Our work on the Tuff of San Felipe has revealed discrepancies in the magnetic fabric, and resulting flow direction. The azimuth of flow directions observed at 27 sites over 1.5 square kilometers ranges from 8° to 355° with a mean direction of 195° and an α95 of 27°. The lack of a uniform flow direction from a single mesa impairs our ability to correlate offset channelized flows over large distances. To investigate the robustness of the AMS fabric we have performed a spatially dense sampling of the unit. Rigorous rock magnetic experiments will be used to investigate any correlation between changes in the magnetic mineralogy of the samples and any irregularities or constancies in the measured fabrics and flow directions. With this study we aim to characterize the variability of the AMS ellipsoid in natural volcanic samples and the scale at which AMS can be used as a meaningful indicator of paleoflow in the Tuff of San Felipe.

Assessment of the geothermal potential of southwestern New Mexico. Final report, July 1, 1978-April 30, 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elston, W.E.

1981-07-01

Results are reported of geologic mapping of geothermal anomalies in the Gila Hot Springs KGRA/Mimbres Hot Springs area, Grant County. They suggest that both hot-spring occurrences are structurally controlled by the intersection of a major Basin and Range fault and the disturbed margin of an ash-flow tuff cauldron. Hydrothermal alteration in both areas is related to mid-Tertiary volcanism, not to modern hot springs. At Gila Hot Springs, the geothermal aquifer is a zone at the contact between the unwelded top of a major ash-flow tuff sheet (Bloodgood Canyon Rhyolite Tuff) and a succession of interlayered vesicular basaltic andesite flows andmore » thin sandstone beds (Bearwallow Mountain Formation). Scattered groups of natural hot springs occur at intersections of this zone and the faults bordering the northeastern side of the Gila Hot Springs graben. Hydrothermal alteration of Bloodgood Canyon Rhyolite Tuff near major faults seems to have increased its permeability. At Mimbres Hot Springs, a single group of hot springs is controlled by the intersection of the Mimbres Hot Springs fault and a fractured welded ash-flow tuff that fills the Emory cauldron (Kneeling Nun Tuff). Gila Hot Springs and Mimbres Hot Springs do not seem to be connected by throughgoing faults. At both localities, hot spring water is used locally for space heating and domestic hot water; at Gila Hot Springs, water of 65.6/sup 0/C (150/sup 0/F) is used to generate electricity by means of a 10 kw freon Rankine Cycle engine. This is the first such application in New Mexico.« less

Geochronology and Regional Correlation of Continental Permo-Triassic Sediments in West Texas

NASA Astrophysics Data System (ADS)

Mitchell, W.; Renne, P. R.; Mundil, R.; Chang, S.; Geissman, J. W.; Tabor, N. J.; Mack, G.

2011-12-01

Although many aspects of marine sections spanning the Permian-Triassic boundary (PTB) have been studied in great detail across a broad paleogeographic area, less is known about the timing, pace, and extent of environmental changes and extinctions across this boundary in continental environments, particularly along the Panthalassa margin. Extensive outcrops in the Ochoan Series of west Texas provide an opportunity to investigate the terrestrial record spanning the PTB. The presence of several silicic tuffs in these sections allows for precise radioisotopic dating using both U-Pb and 40Ar/39Ar techniques. Dated strata then serve as a calibration basis for paleomagnetic and lithostratigraphic studies and facilitate stratigraphic correlation across the few to hundreds of kilometers separating study sites. Depending on the possible correlations, as many as seven tuffs have been identified in this region, the ages of which are within about a million years of the chronometrically-defined PTB at the Meishan section in China at ca. 252 Ma. Data obtained thus far indicate that the PTB occurs within the Quartermaster/Dewey Lake Formation. With the aims of determining the number and ages of distinct tuffs found and facilitating a well-correlated regional stratigraphy among the studied sections, we present preliminary radioisotopic age determinations of, and correlations among, these tuffs using the zircon U-Pb system, 40Ar/39Ar dating where possible, as well as mineral chemistry. Our results include the first dated tuff in the Ochoan Series that lies within the Alibates Formation which underlies the Dewey Lake Fm. Other samples in progress from the various tuffs in the region, in combination with results from magneto- and chemostratigraphy, will significantly expand the areal coverage of these strata and lead towards a greatly improved chronostratigraphic framework.

Vegetation during UMBI and deposition of Tuff IF at Olduvai Gorge, Tanzania (ca. 1.8 Ma) based on phytoliths and plant remains.

PubMed

Albert, Rosa Maria; Bamford, Marion K

2012-08-01

As part of ongoing research at Olduvai Gorge, Tanzania, to determine the detailed paleoenvironmental setting during Bed I and Bed II times and occupation of the basin by early hominins, we present the results of phytolith analyses of Tuff IF which is the uppermost unit of Bed I. Phytoliths were identified in most of the levels and localities on the eastern paleolake margin, but there are not always sufficient numbers of identifiable morphologies to infer the specific type of vegetation due to dissolution. Some surge surfaces and reworked tuff surfaces were vegetated between successive ash falls, as indicated by root-markings and the presence of a variety of phytolith morphotypes. Dicotyledonous wood/bark types were dominant except at the FLK N site just above Tuff IF when monocots are dominant and for the palm-dominated sample from the reworked channel cutting down into Tuff IF at FLK N. The area between the two fault scarps bounding the HWK Compartment, approximately 1 km wide, was vegetated at various time intervals between some of the surges and during the reworking of the Tuff. By lowermost Bed II times the eastern margin was fully vegetated again. Climate and tectonic activity probably controlled the fluctuating lake levels but locally the paleorelief and drainage were probably the controlling factors for the vegetation changes. These data support a scenario of small groups of hominins making brief visits to the paleolake during uppermost Bed I times, followed by a more desirable vegetative environment during lowermost Bed II times. Copyright © 2011 Elsevier Ltd. All rights reserved.

40Ar/39Ar ages for the fossil-bearing Gyeongsang Supergroup in South Korea

NASA Astrophysics Data System (ADS)

Chang, S. C.; Hemming, S. R.

2016-12-01

Since the 1970s, abundant vertebrate fossils have been documented from the Cretaceous Gyeongsang Supergroup in the Gyeongsang Basin and some small nearby basins of the Korean Peninsula, including dinosaurs, pterosaurs, crocodilians, turtles and fish. In addition to body fossils, well-preserved dinosaur, bird and pterosaur tracks have been found from these formations. Well-preserved and extensive vertebrate ichnofaunas from the Gyeongsang Supergroup represent the largest known concentration of Cretaceous vertebrate track sites reported from the Asian continent. Determining the age of the Gyeongsang Supergroup is critical to understanding several fundamental questions related to evolution and paleo-biogeography. However, limited radioisotopic studies for the Gyeongsang Supergroup have been previously reported. Additionally, the large uncertainties of previous data and the incomplete stratigraphic description of the samples limit their value for high-resolution chronostratigraphy. In this study, we aim to establish high-precision 40Ar/39Ar ages for two well-known tuffs from the middle and the upper part of the Gyeongsang Supergroup, and one rhyolite from the uppermost Gyeongsang Supergroup. Our preliminary 40Ar/39Ar data for the Kusandong Tuff indicates that the middle part of the Gyeongsang Supergroup is 78-82 Ma. This is consistent with the hypothesized extension of the Jehol biota into Korea and the preliminary results suggest that refinement of the time scale for these strata is a practical goal. The Gyeongsang Supergroup sample has great potential for substantially increasing our knowledge of Mesozoic terrestrial ecosystems.

Dating the Naisiusiu Beds, Olduvai Gorge, by electron spin resonance

NASA Astrophysics Data System (ADS)

Skinner, A. R.; Hay, R. L.; Masao, F.; Blackwell, B. A. B.

2003-05-01

The lower beds at Olduvai Gorge are well known for containing early hominid fossils and Oldowan stone tools, and their ages have been established by 40Ar/ 39Ar dating and paleomagnetic stratigraphy. Ages are generally less certain for the upper deposits at Olduvai Gorge because of the scarcity of datable tuffs. The youngest archaeologically significant site at Olduvai is microlithic LSA, which lies in the type section of the Naisiusiu Beds. The age for the site is controversial, with 14C dates of 17,000-17,550 (Hay, R.L., 1976 Geology of Olduvai Gorge, University of California Press, Berkeley) and >42,000 BP (Manega, P.C., 1993. Geochronology, geochemistry, and isotopic study of the Plio-Pleistocene Hominid sites and the Ngorongoro Volcanic Highland in Northern Tanzania. Unpublished Ph.D. Thesis, University of Colorado, Boulder, CO). The tuff bed in the zone with artifacts does not contain materials datable by 40Ar/ 39Ar, and some other dating method was needed. In the summer of 2001, five equid teeth were collected from the type Naisiusiu site. Another tooth had previously been collected. ESR ages have been determined for three teeth from the archaeological level and their ages cluster around 62±5 ka, assuming linear uranium uptake. Another tooth from a level without artifacts and believed to be significantly younger dated to 39±5 ka, again assuming LU. These dates are considerably older than previous estimates and suggest that the East African MSA/LSA transition occurred very early.

Interstratified arkosic and volcanic rocks of the Miocene Spanish Canyon Formation, Alvord Mountain area, California: descriptions and interpretations

USGS Publications Warehouse

Buesch, David C.

2014-01-01

The Spanish Canyon Foundation in the Alvord Mountain area, California, varies from about 50 to 120 m thick and records the interstratification of arkosic sandstone and conglomerate with tuffaceous deposits and lava flows. In the lower third of the formation, arkosic sandstone and conglomerate are interstratified with tuffaceous deposits. Some tuffs might have been deposited as primary, nonwelded to partially welded ignimbrites or fallout tephra. Many of the tuffaceous deposits represent redeposited material that formed tuffaceous sandstone, and many of these deposits contain arkosic grains that represent mixing of different source matieral. Arkosic sandstone, and especially conglomerate (some with maximum clast lengths up to 1 m), represent intermittent incursions of coarser plutoniclastic fan deposits into other finer grained and mostly volcaniclastic basin deposits. After deposition of the 18.78 Ma Peach Spring Tuff, the amount of tuffaceous material decreased. The upper two-thirds of the formation has arkosic sandstone and conglomerate interstratified with two olivine basalt lave flows. locally, conglomerate clasts in this part of the section have maximum lengths up to 1 m. Many tuffaceous and arkosic sandstone beds of the Spanish Canyon Formation have tabular to broad (low-relief) lenticular geometry, and locally, some arkosic conglomerate fills channels as much as 1.5 m deep. These bedforms are consistent with deposition in medial to distal alluvial-fan or fluvial environments; some finer-grained deposits might have formed in lacustrine environments.

Publications - GMC 145 | Alaska Division of Geological & Geophysical

Science.gov Websites

DGGS GMC 145 Publication Details Title: Analytical results of x-ray diffraction studies on tuff beds , Analytical results of x-ray diffraction studies on tuff beds from core of the following 5 NPRA wells: U.S

Removal of ammonium from aqueous solutions with volcanic tuff.

PubMed

Marañón, E; Ulmanu, M; Fernández, Y; Anger, I; Castrillón, L

2006-10-11

This paper presents kinetic and equilibrium data concerning ammonium ion uptake from aqueous solutions using Romanian volcanic tuff. The influence of contact time, pH, ammonium concentration, presence of other cations and anion species is discussed. Equilibrium isotherms adequately fit the Langmuir and Freundlich models. The results showed a contact time of 3h to be sufficient to reach equilibrium and pH of 7 to be the optimum value. Adsorption capacities of 19 mg NH(4)(+)/g were obtained in multicomponent solutions (containing NH(4)(+), Zn(2+), Cd(2+), Ca(2+), Na(2+)). The presence of Zn and Cd at low concentrations did not decrease the ammonium adsorption capacity. Comparison of Romanian volcanic tuff with synthetic zeolites used for ammonium removal (5A, 13X and ZSM-5) was carried out. The removal efficiciency of ammonium by volcanic tuff were similar to those of zeolites 5A and 13X at low initial ammonium concentration, and much higher than those of zeolite ZSM-5.

Petrographic and geochemical characteristics of a section through the Tiva Canyon Tuff at Antler Ridge, Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singer, F.R.; Widmann, B.L.; Dickerson, R.P.

1994-12-31

The Tiva Canyon Tuff of the Paintbrush Group of Miocene age caps much of Yucca Mountain, Nevada and is a compositionally zoned, compound cooling, pyroclastic flow that ranges from a dominantly high-silica rhyolitic base to a quartz-latitic caprock. Petrographic and geochemical studies have focused on rigorously defining the internal stratigraphy of this unit to support the detailed mapping of the Ghost Dance fault and other structures in the central fault block of Yucca Mountain. This study shows that devitrification textures and vapor phase mineralogy, in addition to other physical attributes such as pumice variability (flattening) and crystal content, can bemore » used as distinguishing criteria to better define lithologic zones within the Tiva Canyon Tuff. In addition, the study also shows that the petrographic textures and chemistry of the groundmass vary systematically within recognizable lithologic zones and may be used to characterize and vertically divide litho-stratigraphic zones within the Tiva Canyon Tuff.« less

Volcanotectonic history of Crater Flat, southwestern Nevada, as suggested by new evidence from drill hole USW-VH-1 and vicinity

USGS Publications Warehouse

Carr, W.J.

1982-01-01

New evidence for a possible resurgent dome in the caldera related to eruption of the Bullfrog Member of the Crater Flat Tuff has been provided by recent drilling of a 762-meter (2,501-foot) hole in central Crater Flat. Although no new volcanic units were penetrated by the drill hole (USW-VH-1), the positive aeromagnetic anomaly in the vicinity of the drill hole appears to result in part from the unusually thick, densely welded tuff of the Bullfrog. Major units penetrated include alluvium, basalt of Crater Flat, Tiva Canyon and Topopah Spring Members of the Paintbrush Tuff, and Prow Pass and Bullfrog Members of the Crater Flat Tuff. In addition, the drill hole provided the first subsurface hydrologic information for the area. The water table in the hole is at about 180 meters (600 feet), and the temperature gradient appears slightly higher than normal for the region.

Correlation of Pliocene and Pleistocene tephra layers between the Turkana Basin of East Africa and the Gulf of Aden

USGS Publications Warehouse

Brown, F.H.; Sarna-Wojcicki, A. M.; Meyer, C.E.; Haileab, B.

1992-01-01

Electron-microprobe analyses of glass shards from volcanic ash in Pliocene and Pleistocene deep-sea sediments in the Gulf of Aden and the Somali Basin demonstrate that most of the tephra layers correlate with tephra layers known on land in the Turkana Basin of northern Kenya and southern Ethiopia. Previous correlations are reviewed, and new correlations proposed. Together these data provide correlations between the deep-sea cores, and to the land-based sections at eight levels ranging in age from about 4 to 0.7 Ma. Specifically, we correlate the Moiti Tuff (???4.1 Ma) with a tephra layer at 188.6 m depth in DSDP hole 231 and with a tephra layer at 150 m depth in DSDP hole 241, the Wargolo Tuff with a tephra layer at 179.7 m in DSDP Hole 231 and with a tephra layer at 155.3 m depth in DSDP Hole 232, the Lomogol Tuff (defined here) with a tephra layer at 165 m in DSDP Hole 232A, the Lokochot Tuff with a tephra layer at 140.1 m depth in DSDP Hole 232, the Tulu Bor Tuff with a tephra layer at 160.8 m depth in DSDP Hole 231, the Kokiselei Tuff with a tephra layer at 120 m depth in DSDP Hole 231 and with a tephra layer at 90.3 m depth in DSDP Hole 232, the Silbo Tuff (0.74 Ma) with a tephra layer at 35.5 m depth in DSDP Hole 231 and possibly with a tephra layer at 10.9 m depth in DSDP Hole 241. We also present analyses of other tephra from the deep sea cores for which correlative units on land are not yet known. The correlated tephra layers provide eight chronostratigraphic horizons that make it possible to temporally correlate paleoecological and paleoclimatic data between the terrestrial and deep-sea sites. Such correlations may make it possible to interpret faunal evolution in the Lake Turkana basin and other sites in East Africa within a broader regional or global paleoclimatic context. ?? 1992.

Examining patterns of bat activity in Bandelier National Monument, New Mexico, using walking point transects

USGS Publications Warehouse

Ellison, L.E.; Everette, A.L.; Bogan, M.A.

2005-01-01

We conducted a preliminary study using small field crews, a single Anabat II detector coupled with a laptop computer, and point transects to examine patterns of bat activity at a scale of interest to local resource managers. The study was conducted during summers of 1996–1998 in Bandelier National Monument in the Jemez Mountains of northern New Mexico, a landscape with distinct vegetation zones and high species richness of bats. We developed simple models that described general patterns of acoustic activity within 4 vegetation zones based primarily on nightly variation and a qualitative index of habitat complexity. Bat acoustic activity (number of bat passes&sol point) did not vary dramatically among a limited sample of transects within a vegetation zone during 1996. In 1997 and 1998, single transects within each vegetation zone were established, and bat activity did not vary annually within these zones. Acoustic activity differed among the 4 vegetation zones of interest, with the greatest activity occurring in riparian canyon bottomland, intermediate activity in coniferous forest and a 1977 burned zone, and lowest activity in piñon-juniper woodlands. We identified 68.5% of 2,529 bat passes recorded during point-transect surveys to species using an echolocation call reference library we established for the area and qualitative characteristics of bat calls. Bat species richness and composition differed among vegetation zones. Results of these efforts were consistent with general knowledge of where different bat species typically forage and with the natural history of bats of New Mexico, suggesting such a method might have value for drawing inferences about bat activity in different vegetation zones.

Research Spotlight: New evidence could let supereruption off the hook

NASA Astrophysics Data System (ADS)

Schultz, Colin

2011-02-01

It’s a case of forensic analysis on the grandest scale: the possible near-extinction of the entire human race at the hands of one volcanic supereruption. The Younger Toba Tuff (YTT) eruption 74,000 years ago has been accused of blanketing the sky with sulfate aerosols and driving the world into a long-lasting winter. In a new study, Timmreck et al. have given the Sumatran volcano a climatological alibi. The authors used a global circulation model to simulate the YTT eruption, including for the first time an analysis of the small-scale interactions between sulfate particles. Sulfate particles in the upper atmosphere strongly reflect incoming solar radiation, which has a cooling effect on the Earth. (Geophysical Research Letters, doi:10.1029/2010GL045464, 2010)

Water chemistry at Snowshoe Mountain, Colorado: mixed processes in a common bedrock

USGS Publications Warehouse

Hoch, A.R.; Reddy, M.M.

2001-01-01

At Snowshoe Mountain the primary bedrock is quite homogeneous, but weathering processes vary as waters moves through the soils, vadose zone and phreatic zone of the subsurface. In the thin soil, physical degradation of tuff facilitates preferential dissolution of potassium ion from glass within the rock matrix, while other silicate minerals remain unaltered. In the vadose zone, in the upper few meters of fractured bedrock, dilute water infiltrates during spring snowmelt and summer storms, leading to preferential dissolution of augite exposed on fracture surfaces. Deeper yet, in the phreatic zone of the fractured bedrock, Pleistocene calcite fracture fillings dissolve, and dioctahedral and trioctahedral clays form as penetrative weathering alters feldspar and pyroxene. Alkalinity is generated and silica concentrations are buffered by mineral alteration reactions.

Experimental study on the Neapolitan Yellow Tuff: Salt weathering and consolidation

NASA Astrophysics Data System (ADS)

La Russa, Mauro Francesco; Ruffolo, Silvestro Antonio; Alvarez de Buergo, Monica; Ricca, Michela; Belfiore, Cristina Maria; Pezzino, Antonino; Mirocle Crisci, Gino

2016-04-01

Salt crystallization is one of the major weathering agents in porous building materials due to the crystallization pressure exerted by salt crystals growing in confined pores. The consolidation of such degraded stone materials is a crucial issue in the field of Cultural Heritage restoration. This contribution deals with laboratory experimentation carried out on the Neapolitan Tuff, a pyroclastic rock largely used in the Campanian architecture. Several specimens, collected from a historical quarry nearby the city of Naples, were treated with two different consolidating products: a suspension of nanosilica in water (Syton X30®) and ethyl silicate (Estel 1000®) dispersed in organic solvent (TEOS). Then, in order to assess the effectiveness of consolidation treatments, both treated and untreated samples underwent accelerated degradation through salt crystallization tests. A multi-analytical approach, including mercury intrusion porosimetry, peeling tests and point load test, was employed to evaluate the correlation between the salt crystallization and the micro-structural features of the examined tuff specimens. In addition, the calculation of the crystallization pressures was also performed in order to make a correlation between the porous structure of the tuff and its susceptivity to salt crystallization. Obtained results show that both the tested products increase the resistance of tuff to salt crystallization, although inducing an increase of crystallization pressure. Ethyl silicate, however, shows a better behaviour in terms of superficial cohesion, even after several degradation cycles.

A field method for making a quantitative estimate of altered tuff in sandstone

USGS Publications Warehouse

Cadigan, R.A.

1954-01-01

The use of benzidine to identify altered tuff in sandstone is practical for field or field laboratory studies associated with stratigraphic correlations, mineral deposit investigations, or paleogeographic interpretations. The method is based on the ability of saturated benzidine (C12H12N2) solution to produce a blue stain on montmorillonite-bearing tuff grains. The method is substantiated by the results of microscopic, X-ray spectrometer, and spectrographic tests which lead to the conclusion that: (1) the benzidine stain test differentiates grains of different composition, (2) the white or gray grains which are stained a uniform blue color are fragments of altered tuff, and (3) white or gray grains which stain in a few small spots are probably silicified tuff. The amount of sand grains taken from a hand specimen or an outcrop which will be held by a penny is spread out on a nonabsorbent white surface and soaked with benzidine for 5 minutes. The approximate number blue grains and the average grain size are used in a chart to determine a reference number which measures relative order of abundance. The chart, based on a volume relationship, corrects for the variation in the number of grains in the sample as the grain size varies. Practical use of the method depends on a knowledge of several precautionary measures as well as an understanding of the limitations of benzidine staining tests.

Evolution Of An Upper Crustal Plutonic-Volcanic Plumbing System:Insights From High Precision U-Pb Zircon Geochronology Of Intracaldera Tuff And Intrusions In Silver Creek Caldera, Arizona, USA

NASA Astrophysics Data System (ADS)

Zhang, T.; Mundil, R.; Miller, C. F.; Miller, J. S.; Paterson, S. R.

2010-12-01

Study of both plutonic and volcanic regimes in one single magmatic system is a powerful approach towards obtaining a more complete view of the long-term evolution of magma systems. The recently discovered Silver Creek caldera is the source of the voluminous Peach Spring Tuff (PST) (Ferguson, 2008) and presents a unique opportunity to study a field laboratory of a linked plutonic-volcanic system. This relict west-facing half caldera is predominantly filled with trachytic intracaldera tuff with the caldera margin intruded by several petrologically distinct hypabyssal intrusions. These include porphyritic granite with granophyric texture, felsic leucogranite, porphyritic monzonite exposed on NE side of the caldera that is zoned from more felsic to more mafic, and quartz-phyric dikes that intrude the caldera fill. We present preliminary single zircon ages from 4 samples that have been analyzed using the CA-TIMS method after thermal annealing and chemical leaching (Mattinson 2005), including 1 sample from intracaldera tuff and 3 samples from caldera-related intrusions. 3-D total U/Pb isochron ages from all four samples fall within a range of 18.32-18.90 Ma with uncertainties between 0.09 and 0.39 Ma, although some of them lack precision and are compromised by elevated common Pb. For example, zircon from the dated porphyritic monzonite yields an age of 18.32±0.42 Ma (MSWD=2.7) where the excess scatter may result from real age dispersion and/or different compositions of the common Pb contribution. The PST had been dated to ~18.5 Ma by 40Ar/39Ar techniques (Nielson et al., 1990). In order to be compared to U/Pb ages the 40Ar/39Ar age must be adjusted for a revised age for the then used flux monitor (MMbh-1) and corrected for the now quantified systematic bias between 40Ar/39Ar and U/Pb ages (Renne et al., 2010), which results in a corrected age of 18.8 Ma. Thus, the ages for our samples match that of the PST within error. Based on current results, the age difference between the different phases of the intrusion is very small and the ages of the intrusion match within errors the age of the PST. This tight time range indicates that the super-eruption and the subsequent reactivation of the caldera by hypabyssal intrusions happened on a much shorter timescale than the evolution of large magma systems that have been described with durations of up to 10 m.y. Additional geochronology in combination with geochemical and AMS analyses are aimed at a more detailed reconstruction of the emplacement and eruption history of this plutonic-volcanic system.

Dating the Gaofan and Hutuo Groups - Targets to investigate the Paleoproterozoic Great Oxidation Event in North China

NASA Astrophysics Data System (ADS)

Peng, Peng; Feng, Lianjun; Sun, Fengbo; Yang, Shuyan; Su, Xiangdong; Zhang, Zhiyue; Wang, Chong

2017-05-01

There are several sedimentary units in North China that are proposed to be associated with the Paleoproterozoic Great Oxidation Event (GOE) and/or subsequent events; however, few of them have been precisely dated. In this study, deposition age of the greenschist facies Gaofan and Hutuo Groups is determined. Zircon grains liberated from a tuff layer (metamorphosed to sericite-quartz schist) in the upper part of the Mohe Formation (the second of the three formations of the Gaofan Group) yield a weighted average 207Pb/206Pb age of 2186 ± 8 Ma (n = 7, MSWD = 1.3), representing time of deposition. This age and the detrital zircon U-Pb ages of the basal feldspar quartzite (meta-siltstone), as well as the initial deposition age of the unconformably overlying Hutuo Group, confine the deposition age of the Gaofan Group to 2350-2150 Ma. This result negates the Gaofan Group as one subgroup of the 2560-2510 Ma Wutai greenstone belt. Zircons from the Banlaoyao mafic sill (meta-diabase) that intruded the Dongye Subgroup of the Hutuo Group yield an upper intercept U-Pb age of 2057 ± 25 Ma (n = 14, MSWD = 1.3), representing time of crystallization. Considering the age of the basalt in the first formation of the Doucun Subgroup and the tuff in the first formation of the Dongye Subgroup, the deposition age of the Doucun and Dongye Subgroups of the Hutuo Group is confined to 2150-2090 Ma and 2090-2060 Ma, respectively. These age brackets, as well as the available carbon and nitrogen isotope data indicate that the Zhangxianbu Formation of the Gaofan Group possibly recorded the GOE; whereas the Mohe-Yaokouqian Formations of the Gaofan Group and the Doucun-Dongye Subgroups of the Hutuo Group recorded the subsequent Lomagundi-Jatuli Event (LJE). However, the Lomagundi-Jatuli carbon excursions are hardly distinguishable from the Gaofan Group and the Doucun Subgroup (Hutuo Group) as both units consist of little inorganic carbon but terrestrial clastic turbidites.

Lithology, Geochemistry and Paleomagnetism of the Table Mountain Formation at the Little Walker Caldera

NASA Astrophysics Data System (ADS)

Schubert, R.; Pluhar, C. J.; Carlson, C. W.; Jones, S. A.

2015-12-01

West of Bridgeport Valley near the Central Sierra Nevada crest, the Little Walker Caldera (LWC) erupted Stanislaus Group lavas and tuffs during the Late Miocene. Remnants of these rocks are now distributed from the western Sierra Nevada foothills across the range and into the Walker Lane. This wide distribution is attributed to the lavas flowing down paleochannels, which provide an excellent marker for deformation over the last 10 Ma. Priest (1978) identified a thick section of these lavas along Flatiron Ridge, the southeast margin of the LWC, which our preliminary data suggests may correlate with lavas in the Sweetwater Mountains to the northeast and at Rancheria Mtn near Hetch Hetchy to the southwest. The oldest unit in the Stanislaus group is the Table Mountain Formation, a trachyandesite. At Priest's measured section it is divided into three members. By our measurements, the Lower Member (Tmtl) is 256 meters thick, has a fine-grained groundmass with plagioclase and augite phenocrysts (<0.5 cm), and the presence of augite phenocrysts distinguishes it from the other members. Some Tmtl flows have chalcedony amigdules. Overlying this, the Large Plagioclase member (Tmtp) is 43.5 meters thick. Distinguished by (~1 cm) plagioclase and occasional small olivine phenocrysts. The Upper Member (Tmtu) is 116 meters thick, very fine-grained and often platy. Tmtl has a distinctive northwest-oriented normal polarity and geochemistry, similar to several localities at Rancheria Mtn. Tmtu has a reversed polarity similar to the polarity of Table Mountain Formation in the Sweetwater Mountains and lavas that directly underlie the ~9.5 Ma Tollhouse Flat member of the Eureka Valley Tuff at Rancheria Mtn. Thus, our preliminary data suggest that the lower member at Priest's Measured Section could correlate to the normal polarity samples at Rancheria Mtn. Also, that the upper Member reversed-polarity samples may correlate with lavas both at the Sweetwater Mountains and Rancheria Mtn. This correlation across about 60 km allows us to assess rotation between sites as well as estimate throw across some faults of the Eastern Sierra range front.

The Fish Canyon magma body, San Juan volcanic field, Colorado: Rejuvenation and eruption of an upper-crustal batholith

USGS Publications Warehouse

Bachmann, Olivier; Dungan, M.A.; Lipman, P.W.

2002-01-01

More than 5000 km3 of nearly compositionally homogeneous crystalrich dacite (~68 wt % SiO2: ~45% Pl + Kfs + Qtz + Hbl + Bt + Spn + Mag + Ilm + Ap + Zrn + Po) erupted from the Fish Canyon magma body during three phases: (1) the pre-caldera Pagosa Peak Dacite (an unusual poorly fragmented pyroclastic deposit, ~ 200 km3); (2) the syn-collapse Fish Canyon Tuff (one of the largest known ignimbrites, ~ 5000 km3); (3) the post-collapse Nutras Creek Dacite (a volumetrically minor lava). The late evolution of the Fish Canyon magma is characterized by rejuvenation of a near-solidus upper-crustal intrusive body (mainly crystal mush) of batholithic dimensions. The necessary thermal input was supplied by a shallow intrusion of more mafic magma represented at the surface by sparse andesitic enclaves in late-erupted Fish Canyon Tuff and by the post-caldera Huerto Andesite. The solidified margins of this intrusion are represented by holocrystalline xenoliths with Fish Canyon mineralogy and mineral chemistry and widely dispersed partially remelted polymineralic aggregates, but dehydration melting was not an important mechanism in the rejuvenation of the Fish Canyon magma. Underlying mafic magma may have evolved H2O-F-S-Cl-rich fluids that fluxed melting in the overlying crystal mush. Manifestations of the late up-temperature magma evolution are: (1) resorbed quartz, as well as feldspars displaying a wide spectrum of textures indicative of both resorption and growth, including Rapakivi textures and reverse growth zoning (An27-28 to An32-33) at the margins of many plagioclase phenocrysts; (2) high Sr, Ba, and Eu contents in the high-SiO2 rhyolite matrix glass, which are inconsistent with extreme fractional crystallization of feldspar; (3) oscillatory and reverse growth zoning toward the margins of many euhedral hornblende phenocrysts (rimward increases from ~5??5-6 to 7??7-8??5 wt % Al2O3). Homogeneity in magma composition at the chamber-wide scale, contrasting with extreme textural and chemical complexities at the centimeter-millimeter scale, is consistent with a dynamic environment, wherein crystals with a variety of growth and resorption histories were juxtaposed shortly before eruption by convective currents.

Cerro Xalapaxco: An Unusual Tuff Cone with Multiple Explosion Craters, in Central Mexico (Puebla)

NASA Technical Reports Server (NTRS)

Abrams, M. J.; Siebe, C.

1994-01-01

The Xalapaxco tuff cone is located on the northeast flank of La Malinche stratovolcano in central Mexico. An unusually large number (10) of explosion craters, concentrated on the central and on the uphill side of the cone, expose alternating beds of stratified surge deposits and massive fall deposits.

Stochastic Model of Fracture Frequency Heterogeneity in a Welded Tuff EGS reservoir, Snake River Plain, Idaho, USA

NASA Astrophysics Data System (ADS)

Moody, A.; Fairley, J. P., Jr.

2014-12-01

In light of recent advancements in reservoir enhancement and injection tests at active geothermal fields, there is interest in investigating the geothermal potential of widespread subsurface welded tuffs related to caldera collapse on the Snake River Plain (SRP). Before considering stimulation strategies, simulating heat extraction from the reservoir under in-situ fracture geometries will give a first-order estimation of extractable heat. With only limited deep boreholes drilled on the SRP, few analyses of the bulk hydrologic properties of the tuffs exist. Acknowledging the importance of the spatial heterogeneity of fractures to the permeability and injectivity of reservoirs hosted in impermeable volcanic units, we present fracture distributions from ICDP hole 5036-2A drilled as a part of Project HOTSPOT. The core documents more than 1200 m of largely homogeneous densely welded tuff hosting an isothermal warm-water reservoir at ~60˚ C. Multiple realizations of a hypothetical reservoir are created using sequential indicator algorithms that honor the observed vertical fracture frequency statistics. Results help form criteria for producing geothermal energy from the SRP.

Green-tuff landslide areas are beneficial for rice nutrition in Japan.

PubMed

Tazaki, Kazue

2006-12-01

Japanese Islands are covered with weathered volcanic rocks and soils. Terraced rice field are located in green-tuff areas which are very fertile but where landslides occur associated to strong earthquakes. The Xray diffraction and X-ray fluorescence analyses of the soils in landslide area identified predominant smectite and Mg, Al, Si, K, Ti, Mn and Fe are main components. The rice leaf showed that S, Cl, K and Ca play important roles for nutrients in the area. Drainpipe systems have set up in the green- tuff areas to reduce the risks of landslides. Reddish brown microbial mats inhabited bacteria and diatom in the drainpipe outlets. The microbial mats are rich in Fe and PO4(3-). The iron bacteria in the ground water have a high metabolic rate suggesting that the weathering materials were produced by not only physical and chemical influence but also by microorganism. Many microorganisms attach to mineral surfaces and show their high impact in the water mineral chemistry in the landslide area. Bacteria in the green-tuff over landslide area play important roles for sustainable agriculture including rice nutrition.

3D Model of the McGinness Hills Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

The McGinness Hills geothermal system lies in a ~8.5 km wide, north-northeast trending accommodation zone defined by east-dipping normal faults bounding the Toiyabe Range to the west and west-dipping normal faults bounding the Simpson Park Mountains to the east. Within this broad accommodation zone lies a fault step-over defined by north-northeast striking, west-dipping normal faults which step to the left at roughly the latitude of the McGinness Hills geothermal system. The McGinness Hills 3D model consists of 9 geologic units and 41 faults. The basal geologic units are metasediments of the Ordovician Valmy and Vininni Formations (undifferentiated in the model) which are intruded by Jurassic granitic rocks. Unconformably overlying is a ~100s m-thick section of Tertiary andesitic lava flows and four Oligocene-to-Miocene ash-flow tuffs: The Rattlesnake Canyon Tuff, tuff of Sutcliffe, the Cambell Creek Tuff and the Nine Hill tuff. Overlying are sequences of pre-to-syn-extensional Quaternary alluvium and post-extensional Quaternary alluvium. 10-15º eastward dip of the Tertiary stratigraphy is controlled by the predominant west-dipping fault set. Geothermal production comes from two west dipping normal faults in the northern limb of the step over. Injection is into west dipping faults in the southern limb of the step over. Production and injection sites are in hydrologic communication, but at a deep level, as the northwest striking fault that links the southern and northern limbs of the step-over has no permeability.

Spatial distribution of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah: A mechanical analog for faulting in pyroclastic deposits on Mars

USGS Publications Warehouse

Okubo, Chris H.

2012-01-01

Volcanic ash is thought to comprise a large fraction of the Martian equatorial layered deposits and much new insight into the process of faulting and related fluid flow in these deposits can be gained through the study of analogous terrestrial tuffs. This study identifies a set of fault-related processes that are pertinent to understanding the evolution of fault systems in fine-grained, poorly indurated volcanic ash by investigating exposures of faults in the Miocene-aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah. The porosity and granularity of the host rock are found to control the style of localized strain that occurs prior to and contemporaneous with faulting. Deformation bands occur in tuff that was porous and granular at the time of deformation, while fractures formed where the tuff lost its porous and granular nature due to silicic alteration. Non-localized deformation of the host rock is also prominent and occurs through compaction of void space, including crushing of pumice clasts. Significant off-fault damage of the host rock, resembling fault pulverization, is recognized adjacent to one analog fault and may reflect the strain rate dependence of the resulting fault zone architecture. These findings provide important new guidelines for future structural analyses and numerical modeling of faulting and subsurface fluid flow through volcanic ash deposits on Mars.

The Tala Tuff, La Primavera caldera Mexico. Pre-eruptive conditions and magma processes before eruption

NASA Astrophysics Data System (ADS)

Sosa-Ceballos, G.

2015-12-01

La Primavera caldera, Jalisco Mexico, is a Pleistocenic volcanic structure formed by dome complexes and multiple pyroclastic flows and fall deposits. It is located at the intersection of the Chapala, Colima, and Tepic grabens in western Mexico. The first volcanic activity associated to La Primavera started ~0.1 Ma with the emission of pre-caldera lavas. The caldera collapse occurred 95 ka and is associated to the eruption of ~20 km3of pumice flows known as the Tala tuff (Mahood 1980). The border of the caldera was replaced by a series of domes dated in 75-30 ky, which partially filled the inner depression of the caldera with pyroclastic flows and falls. For more than a decade the Federal Commission of Electricity in Mexico (CFE) has prospected and evaluated the geothermal potential of the Cerritos Colorados project at La Primavera caldera. In order to better understand the plumbing system that tapped the Tala tuff and to investigate its relation with the potential geothermal field at La Primavera we performed a series of hydrothermal experiments and studied melt inclusions hosted in quartz phenocrysts by Fourier Infra red stectroscopy (FTIR). Although some post caldera products at La Primavera contain fayalite and quartz (suggesting QFM conditions) the Tala tuff does not contain fayalite and we ran experiments under NNO conditions. The absence of titanomagnetite does not allowed us to calculate pre-eruptive temperature. However, the stability of quartz and plagioclase, which are natural phases, suggest that temperature should be less than 750 °C at a pressure of 200 MPa. The analyses of H2O and CO2 dissolved in melt inclusions yielded concentrations of 2-5 wt.% and 50-100 ppm respectively. This data confirm that the pre-eruptive pressure of the Tala tuff is ~200 MPa and in addition to major elements compositions suggest that the Tala tuff is either, compositionally zoned or mixed with other magma just prior to eruption.

Substorm wave base felsic hydroclastic deposits in the Archean Lac des Vents volcanic complex, Abitibi belt, Canada

NASA Astrophysics Data System (ADS)

Mueller, Wulf; Chown, E. H.; Potvin, Robin

1994-05-01

Volcaniclastic deposits of the 2.3-km-thick Archean Lac des Vents volcanic complex are an integral part of major submarine volcanic construction. The volcanic edifice, which formed on a subaqueous basalt plain, is comparable to modern seamounts resting on the ocean floor. The initial 770 m of the mafic-felsic edifice, subject of this study, is composed of massive, brecciated and pillowed basalts, massive to brecciated felsic lava flows and abundant felsic fragmental rocks of hydroclastic origin. Four distinct volcaniclastic lithofacies constitute the latter: (1) the pumice lapilli-tuff lithofacies; (2) the lapilli-tuff breccia lithofacies characterized by two sublithofacies; (3) the turbidite tuff and tuff-breccia lithofacies; and (4) the volcanic sandstone and breccia lithofacies. These four volcaniclastic lithofacies are considered to be the result of explosive and non-explosive hydrovolcanic fragmentation processes operating at depths below storm wave base (> 200 m). Primary deposition or limited remobilization of unconsolidated hydroclastic debris is shown by the preservation of delicate clasts and volcanic textures, and heat retention structures. The principal transport agents are high-concentration sediment gravity flows occurring under laminar and turbulent flow conditions. High- and low-density turbiditic tuffs and fine-grained tuff fallout deposits, are related to either the dissipating stages of volcanic eruptions or slumping of syneruptive volcanic debris on the flanks of a subaqueous volcanic edifice. Ubiquitous interstratification of volcaniclastic turbidites, shale, and pillowed basalt flows with the felsic lava flows and fragmental debris favours subaqueous deposition. These features combined with the absence of wave-induced sedimentary structures, imply deposition in water depths in excess of 200 m. Viscous feldspar-phyric massive and brecciated felsic flows, and associated volcaniclastics cross cut by felsic dykes, suggest vent proximity. The abundance of breccia-size hydroclastic debris is consistent with this interpretation. Collectively, these criteria argue for subaqueous fragmentation and deposition of volcaniclastics of inferred hydroclastic origin close to the central vent area at depths below storm wave base.

Neogene Fallout Tuffs from the Yellowstone Hotspot in the Columbia Plateau Region, Oregon, Washington and Idaho, USA

PubMed Central

Nash, Barbara P.; Perkins, Michael E.

2012-01-01

Sedimentary sequences in the Columbia Plateau region of the Pacific Northwest ranging in age from 16–4 Ma contain fallout tuffs whose origins lie in volcanic centers of the Yellowstone hotspot in northwestern Nevada, eastern Oregon and the Snake River Plain in Idaho. Silicic volcanism began in the region contemporaneously with early eruptions of the Columbia River Basalt Group (CRBG), and the abundance of widespread fallout tuffs provides the opportunity to establish a tephrostratigrahic framework for the region. Sedimentary basins with volcaniclastic deposits also contain diverse assemblages of fauna and flora that were preserved during the Mid-Miocene Climatic Optimum, including Sucker Creek, Mascall, Latah, Virgin Valley and Trout Creek. Correlation of ashfall units establish that the lower Bully Creek Formation in eastern Oregon is contemporaneous with the Virgin Valley Formation, the Sucker Creek Formation, Oregon and Idaho, Trout Creek Formation, Oregon, and the Latah Formation in the Clearwater Embayment in Washington and Idaho. In addition, it can be established that the Trout Creek flora are younger than the Mascall and Latah flora. A tentative correlation of a fallout tuff from the Clarkia fossil beds, Idaho, with a pumice bed in the Bully Creek Formation places the remarkably well preserved Clarkia flora assemblage between the Mascall and Trout Creek flora. Large-volume supereruptions that originated between 11.8 and 10.1 Ma from the Bruneau-Jarbidge and Twin Falls volcanic centers of the Yellowstone hotspot in the central Snake River Plain deposited voluminous fallout tuffs in the Ellensberg Formation which forms sedimentary interbeds in the CRBG. These occurrences extend the known distribution of these fallout tuffs 500 km to the northwest of their source in the Snake River Plain. Heretofore, the distal products of these large eruptions had only been recognized to the east of their sources in the High Plains of Nebraska and Kansas. PMID:23071494

Eruption and deposition of the Fisher Tuff (Alaska)--Evidence for the evolution of pyroclastic flows

USGS Publications Warehouse

Burgisser, Alain; Gardner, J.E.; Stelling, P.

2007-01-01

Recognition that the Fisher Tuff (Unimak Island, Alaska) was deposited on the leeside of an ∼500–700‐m‐high mountain range (Tugamak Range) more than 10 km away from its source played a major role in defining pyroclastic flows as momentum‐driven currents. We reexamined the Fisher Tuff to evaluate whether deposition from expanded turbulent clouds can better explain its depositional features. We studied the tuff at 89 sites and sieved bulk samples from 27 of those sites. We find that the tuff consists of a complex sequence of deposits that record the evolution of the eruption from a buoyant plume (22 km) that deposited ∼0.2 km3 of dacite magma as a pyroclastic fall layer to erupting ∼10–100 km3 of andesitic magma as Scoria‐rich pyroclastic falls and flows that were mainly deposited to the north and northwest of the caldera, including those in valleys within the Tugamak Range. The distribution of the flow deposits and their welding, internal stratification, and the occurrence of lithic breccia all suggest that the pyroclastic flows were fed from a fountaining column that vented from an inclined conduit, the first time such a conduit has been recognized during a large‐volume caldera eruption. Pyroclastic flow deposits before and after the mountain range and thin veneer deposits high in the range are best explained by a flow that was stratified into a dense undercurrent and an overriding dilute turbulent cloud, from which deposition before the range was mainly from the undercurrent. When the flow ran into the mountain range, however, the undercurrent was blocked, but the turbulent cloud continued on. As the flow continued north, it restratified, forming another undercurrent. The Fisher Tuff thus records the passing of a flow that was significantly higher (800–1100 m thick) than the mountain range and thus did not require excessive momentum.

Neogene fallout tuffs from the Yellowstone hotspot in the Columbia Plateau region, Oregon, Washington and Idaho, USA.

PubMed

Nash, Barbara P; Perkins, Michael E

2012-01-01

Sedimentary sequences in the Columbia Plateau region of the Pacific Northwest ranging in age from 16-4 Ma contain fallout tuffs whose origins lie in volcanic centers of the Yellowstone hotspot in northwestern Nevada, eastern Oregon and the Snake River Plain in Idaho. Silicic volcanism began in the region contemporaneously with early eruptions of the Columbia River Basalt Group (CRBG), and the abundance of widespread fallout tuffs provides the opportunity to establish a tephrostratigrahic framework for the region. Sedimentary basins with volcaniclastic deposits also contain diverse assemblages of fauna and flora that were preserved during the Mid-Miocene Climatic Optimum, including Sucker Creek, Mascall, Latah, Virgin Valley and Trout Creek. Correlation of ashfall units establish that the lower Bully Creek Formation in eastern Oregon is contemporaneous with the Virgin Valley Formation, the Sucker Creek Formation, Oregon and Idaho, Trout Creek Formation, Oregon, and the Latah Formation in the Clearwater Embayment in Washington and Idaho. In addition, it can be established that the Trout Creek flora are younger than the Mascall and Latah flora. A tentative correlation of a fallout tuff from the Clarkia fossil beds, Idaho, with a pumice bed in the Bully Creek Formation places the remarkably well preserved Clarkia flora assemblage between the Mascall and Trout Creek flora. Large-volume supereruptions that originated between 11.8 and 10.1 Ma from the Bruneau-Jarbidge and Twin Falls volcanic centers of the Yellowstone hotspot in the central Snake River Plain deposited voluminous fallout tuffs in the Ellensberg Formation which forms sedimentary interbeds in the CRBG. These occurrences extend the known distribution of these fallout tuffs 500 km to the northwest of their source in the Snake River Plain. Heretofore, the distal products of these large eruptions had only been recognized to the east of their sources in the High Plains of Nebraska and Kansas.

Fractures in outcrops in the vicinity of drill hole USW G-4. Yucca Mountain, Nevada; data analysis and compilation

USGS Publications Warehouse

Barton, Christopher C.; Page, William R.; Morgan, Terrance L.

1989-01-01

Fractures on outcrops in the vicinity of drill hole USW G-4, Yucca Mountain, Nevada, were studied in order to contribute to characterization of fractures for hydrologjc, geomechanical, and tectonic modeling of the Yucca Mountain block and to characterize fractures prior to the excavation of a proposed exploratory shaft located near USW G-4. Yucca Mountain is a prospective site for the construction of an underground repository for high-level nuclear waste.Measurements were taken and recorded on 5,000 fractures at 50 outcrop stations primarily in the upper lithophysal unit of the Tiva Canyon Member of the Miocene Paintbrush Tuff. Fracture orientation and surface roughness were recorded for each fracture. Additionally, notes were taken on fracture abutting, crossing, and offsetting relations, swarming, curvature, brecciation, slickensides, and fracture fillings. Frequency distributions of orientation and roughness were plotted and analyzed. Fractures with low roughness coefficients (0-4) group tightly into two sets based on orientation. We conclude that such fractures are cooling joints and that all other fractures are tectonic. The development of small-scale fractures adjacent, subparallel, and possibly related to the Ghost Dance fault has been addressed in a preliminary way based on data collected in this study. Such sympathetic fractures are abundant in the upper cliff unit but not in the upper lithophysal unit.

Picrite "Intelligence" from the Middle-Late Triassic Stikine arc: Composition of mantle wedge asthenosphere

NASA Astrophysics Data System (ADS)

Milidragovic, D.; Zagorevski, A.; Weis, D.; Joyce, N.; Chapman, J. B.

2018-05-01

Primitive, near-primary arc magmas occur as a volumetrically minor ≤100 m thick unit in the Canadian Cordillera of northwestern British Columbia, Canada. These primitive magmas formed an olivine-phyric, picritic tuff near the base of the Middle-Late Triassic Stuhini Group of the Stikine Terrane (Stikinia). A new 40Ar/39Ar age on hornblende from a cross-cutting basaltic dyke constrains the tuff to be older than 221 ± 2 Ma. An 87Sr/86Sr isochron of texturally-unmodified tuff samples yields 212 ± 25 Ma age, which is interpreted to represent syn-depositional equilibration with sea-water. Parental trace element magma composition of the picritic tuff is strongly depleted in most incompatible trace elements relative to MORB and implies a highly depleted ambient arc mantle. High-precision trace element and Hf-Nd-Pb isotopic analyses indicate an origin by mixing of a melt of depleted ambient asthenosphere with ≤2% of subducted sediment melt. Metasomatic addition of non-conservative incompatible elements through melting of subducted Panthalassa Ocean floor sediments accounts for the arc signature of the Stuhini Group picritic tuff, enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) and high field strength elements (HFSE), and anomalous enrichment in Pb. The inferred Panthalassan sediments are similar in composition to the Neogene-Quaternary sediments of the modern northern Cascadia Basin. The initial Hf isotopic composition of the picritic tuff closely approximates that of the ambient Middle-Late Triassic asthenosphere beneath Stikinia and is notably less radiogenic than the age-corrected Hf isotopic composition of the Depleted (MORB) Mantle reservoir (DM or DMM). This suggests that the ambient asthenospheric mantle end-member experienced melt depletion (F ≤ 0.05) a short time before picrite petrogenesis. The mantle end-member in the source of the Stuhini Group picritic tuff is isotopically similar to the mantle source of enriched mid-ocean ridge basalts (E-MORB) erupted today at the southern end of the Explorer Ridge in northeastern Pacific Ocean. The isotopic similarity between the Middle-Late Triassic ambient mantle under Stikinia, and mantle presently tapped at the southern Explorer Ridge suggests that enriched domains in the northeastern Pacific mantle are long-lived (≥222 million years).

Magma batches in the Timber Mountain magmatic system, Southwestern Nevada Volcanic Field, Nevada, USA

NASA Astrophysics Data System (ADS)

Mills, James G.; Saltoun, Benjamin W.; Vogel, Thomas A.

1997-09-01

The common occurrence of compositionally and mineralogically zoned ash flow sheets, such as those of the Timber Mountain Group, provides evidence that the source magma bodies were chemically and thermally zoned. The Rainier Mesa and Ammonia Tanks tuffs of the Timber Mountain Group are both large volume (1200 and 900 km 3, respectively) chemically zoned (57-78 wt.% SiO 2) ash flow sheets. Evidence of distinct magma batches in the Timber Mountain system are based on: (1) major- and trace-element variations of whole pumice fragments; (2) major-element variations in phenocrysts; (3) major-element variations in glass matrix; and (4) emplacement temperatures calculated from Fe-Ti oxides and feldspars. There are three distinct groups of pumice fragments in the Rainier Mesa Tuff: a low-silica group and two high-silica groups (a low-Th and a high-Th group). These groups cannot be related by crystal fractionation. The low-silica portion of the Rainier Mesa Tuff is distinct from the low-silica portion of the overlying Ammonia Tanks Tuff, even though the age difference is less than 200,000 years. Three distinct groups occur in the Ammonia Tanks Tuff: a low-silica, intermediate-silica and a high-silica group. Part of the high-silica group may be due to mixing of the two high-silica Rainier Mesa groups. The intermediate-silica group may be due to mixing of the low- and high-silica Ammonia Tanks groups. Three distinct emplacement temperatures occur in the Rainier Mesa Tuff (869, 804, 723 °C) that correspond to the low-silica, high-Th and low-Th magma batches, respectively. These temperature differences could not have been maintained for any length of time in the magma chamber (cf. Turner, J.S., Campbell, I.H., 1986. Convection and mixing in magma chambers. Earth-Sci. Rev. 23, 255-352; Martin, D., Griffiths, R.W., Campbell, I.H., 1987. Compositional and thermal convection in magma chambers. Contrib. Mineral. Petrol. 96, 465-475) and therefore eruption must have occurred soon after emplacement of the magma batches into the chamber. Emplacement temperatures of the pumice fragments from the Ammonia Tanks Tuff show a continuous gradient of temperatures with composition. This continuous temperature gradient is consistent with the model of storage of magma batches in the Ammonia Tanks group that have undergone both thermal and chemical diffusion.

In defense of Magnetite-Ilmenite Thermometry in the Bishop Tuff and its implication for gradients in silicic magma reservoirs

USGS Publications Warehouse

Evans, Bernard W; Hildreth, Edward; Bachmann, Olivier; Scaillet, Bruno

2016-01-01

Despite claims to the contrary, the compositions of magnetite and ilmenite in the Bishop Tuff correctly record the changing conditions of T and fO2 in the magma reservoir. In relatively reduced (∆NNO < 1) siliceous magmas (e.g., Bishop Tuff, Taupo units), Ti behaves compatibly (DTi ≈ 2-3.5), leading to a decrease in TiO2 activity in the melt with cooling and fractionation. In contrast, FeTi-oxides are poorer in TiO2 in more oxidized magmas (∆NNO > 1, e.g., Fish Canyon Tuff, Pinatubo), and the d(aTiO2)/dT slope can be negative. Biotite, FeTi-oxides, liquid, and possibly plagioclase largely maintained equilibrium in the Bishop Tuff magma (unlike the pyroxenes, and cores of quartz, sanidine, and zircon) prior ro and during a mixing event triggered by a deeper recharge, which, based on elemental diffusion profiles in minerals, took place at least several decades before eruption. Equilibrating phases and pumice compositions show evolving chemical variations that correlate well with mutually consistent temperatures based on the FeTi-oxides, sanidine-plagioclase, and ∆18O quartz-magnetite pairs. Early Bishop Tuff (EBT) temperatures are lower (700 to ~780‎°C) than temperatures (780 to >820°C) registered in Late Bishop Tuff (LBT), the latter defined here not strictly stratigraphically, but by the presence of orthopyroxene and reverse-zoned rims on quartz and sanidine. The claimed similarity in compositions, Zr-saturation temperatures and thermodynamically calculated temperatures (730-740°C) between EBT and less evolved LBT reflect the use of glass inclusions in quartz cores in LBT that were inherited from the low temperature rhyolitic part of the reservoir characteristic of the EBT. LBT temperatures as high as 820°C, the preservation of orthopyroxene, and the presence of reverse-zoned minerals (quartz, sanidine, zircons) are consistent with magma recharge at the base of the zoned reservoir, heating the cooler rhyolitic melt, partly remelting cumulate mush, and introducing enough CO2 (0.4-1.4 wt%, mostly contained in the exsolved fluid phase) to significantly lower H2O-activity in the system.

Stratigraphy, age, and depositional setting of the Miocene Barstow Formation at Harvard Hill, central Mojave Desert, California

USGS Publications Warehouse

Leslie, Shannon R.; Miller, David M.; Wooden, Joseph L.; Vazquez, Jorge A.

2010-01-01

New detailed geologic mapping and geochronology of the Barstow Formation at Harvard Hill, 30 km east of Barstow, CA, help to constrain Miocene paleogeography and tectonics of the central Mojave Desert. A northern strand of the Quaternary ENE-striking, sinistral Manix fault divides the Barstow Formation at Harvard Hill into two distinct lithologic assemblages. Strata north of the fault consist of: a green rhyolitic tuff, informally named the Shamrock tuff; lacustrine sandstone; partially silicified thin-bedded to massive limestone; and alluvial sandstone to pebble conglomerate. Strata south of the fault consist of: lacustrine siltstone and sandstone; a rhyolitic tuff dated at 19.1 Ma (U-Pb); rock-avalanche breccia deposits; partially silicified well-bedded to massive limestone; and alluvial sandstone and conglomerate. Our U-Pb zircon dating of the Shamrock tuff by SHRIMP-RG yields a peak probability age of 18.7 ± 0.1 Ma. Distinctive outcrop characteristics, mineralogy, remanent magnetization, and zircon geochemistry (Th/U) suggest that the Shamrock tuff represents a lacustrine facies of the regionally extensive Peach Spring Tuff (PST). Here we compare zircon age and geochemical analyses from the Shamrock tuff with those of the PST at Stoddard Wash and provide new insight into the age of zircon crystallization in the PST rhyolite. Results of our field studies show that Miocene strata at Harvard Hill mostly accumulated in a lacustrine environment, although depositional environments varied from a relatively deep lake to a very shallow lake or even onshore setting. Rock-avalanche breccias and alluvial deposits near the base of the exposed section indicate proximity to a steep basin margin and detrital studies suggest a southern source for coarse-grained deposits; therefore, we may infer a southern basin-margin setting at Harvard Hill during the early Miocene. Our geochronology demonstrates that deposition of the Barstow Formation at Harvard Hill extended from before ~19.1 Ma until well after ~18.7 Ma, similar to timing of Barstow Formation lake deposition in the Calico Mountains but at least 3 million years older than comparable lacustrine facies in the Mud Hills type section. These observations are consistent with either of two paleogeographic models: westward transgression of lacustrine environments within a single large basin, or sequential development of geographically distinct eastern and western sub-basins.

Mega-features at the Table Rock phreatomagmatic complex in Christmas Valley, Oregon; Law of original horizontality need not apply

NASA Astrophysics Data System (ADS)

Brand, B. D.; Clarke, A.

2006-12-01

The Table Rock Complex (TRC; Pliocene-Pleistocene), first documented and described by (Heiken, 1971, J. Geophy Res, 76, 5615-5626) is a large and well exposed phreatomagmatic complex in the Fort Rock- Christmas Lake Valley Basin, south-central Oregon. It is ~7 by 5 km and contains two large phreatomagmatic edifices; a large southern tuff cone with a capping lava lake (TRC1), and a large broad tuff ring in the northeast (TRC2). At least five additional, smaller tuff rings were identified along the flanks of the complex, yielding a complicated network of tuff ring-tuff cone deposits. Based on the low accidental component and evidence for a lake during this time, the cause of the explosive eruptions is interpreted to be due to interaction of magma with shallow standing water. The TRC1 consists of fining-up sequences, large erosive channel scour and fill deposits, massive tuff breccias, and abundant soft sediment deformation, which suggests deposition within a standing body of water. Subaerial TRC1 deposits are found south of the edifice, but are not exposed in the north. A significant repose period occurred between the TRC1 and TRC2 eruptions, evidenced by a wave-cut terrace and 25-50 cm of diatomitic lake sediments. TRC2 produced multiple, extremely erosive pyroclastic surges, which cut and scour the TRC1 deposits. Surge deposits consist of 50-200 m wavelength cross-beds, in some areas form large U-shaped features (10-100 m deep), and can be seen plastering up and around large obstacles from previous vents. The surge-deposits blanket all other sequences and create a hummocky topography around the edifice. This suggests that TRC2 was the last eruption in the sequence. The weight of the TRC2 sediments caused the water-saturated TRC1 sediments to plastically deform into large ball and pillow features and overturned slump blocks on the order of 20-50 m thick. The smaller flank tuff-ring eruptions likely occurred sometime between the TRC1 and TRC2 events. The inner-craters of these vents are well exposed and show features such as near-vertical plastered beds, large-scale convolute bedding, and in some places deformed and folded slump blocks up to 20-120 m thick. The features observed in both TRC deposits and in the smaller flank tuff rings (e.g., large-scale soft sediment deformation, plastered-vertical bedding, accretionary/armored lapilli) are consistent with a high water-magma ratio. The highly erosive surge beds of TRC2 represent the most energetic pulse of the eruptions.

The oligocene Lund Tuff, Great Basin, USA: A very large volume monotonous intermediate

USGS Publications Warehouse

Maughan, L.L.; Christiansen, E.H.; Best, M.G.; Gromme, C.S.; Deino, A.L.; Tingey, D.G.

2002-01-01

Unusual monotonous intermediate ignimbrites consist of phenocryst-rich dacite that occurs as very large volume (> 1000 km3) deposits that lack systematic compositional zonation, comagmatic rhyolite precursors, and underlying plinian beds. They are distinct from countless, usually smaller volume, zoned rhyolite-dacite-andesite deposits that are conventionally believed to have erupted from magma chambers in which thermal and compositional gradients were established because of sidewall crystallization and associated convective fractionation. Despite their great volume, or because of it, monotonous intermediates have received little attention. Documentation of the stratigraphy, composition, and geologic setting of the Lund Tuff - one of four monotonous intermediate tuffs in the middle-Tertiary Great Basin ignimbrite province - provides insight into its unusual origin and, by implication, the origin of other similar monotonous intermediates. The Lund Tuff is a single cooling unit with normal magnetic polarity whose volume likely exceeded 3000 km3. It was emplaced 29.02 ?? 0.04 Ma in and around the coeval White Rock caldera which has an unextended north-south diameter of about 50 km. The tuff is monotonous in that its phenocryst assemblage is virtually uniform throughout the deposit: plagioclase > quartz ??? hornblende > biotite > Fe-Ti oxides ??? sanidine > titanite, zircon, and apatite. However, ratios of phenocrysts vary by as much as an order of magnitude in a manner consistent with progressive crystallization in the pre-eruption chamber. A significant range in whole-rock chemical composition (e.g., 63-71 wt% SiO2) is poorly correlated with phenocryst abundance. These compositional attributes cannot have been caused wholly by winnowing of glass from phenocrysts during eruption, as has been suggested for the monotonous intermediate Fish Canyon Tuff. Pumice fragments are also crystal-rich, and chemically and mineralogically indistinguishable from bulk tuff. We postulate that convective mixing in a sill-like magma chamber precluded development of a zoned chamber with a rhyolitic top or of a zoned pyroclastic deposit. Chemical variations in the Lund Tuff are consistent with equilibrium crystallization of a parental dacitic magma followed by eruptive mixing of compositionally diverse crystals and high-silica rhyolite vitroclasts during evacuation and emplacement. This model contrasts with the more systematic withdrawal from a bottle-shaped chamber in which sidewall crystallization creates a marked vertical compositional gradient and a substantial volume of capping-evolved rhyolite magma. Eruption at exceptionally high discharge rates precluded development of an underlying plinian deposit. The generation of the monotonous intermediate Lund magma and others like it in the middle Tertiary of the western USA reflects an unusually high flux of mantle-derived mafic magma into unusually thick and warm crust above a subducting slab of oceanic lithosphere. ?? 2002 Elsevier Science B.V. All rights reserved.

Mid-tertiary ash flow tuff cauldrons, southwestern New Mexico

NASA Technical Reports Server (NTRS)

Elston, W. E.

1984-01-01

Characteristics of 28 known or suspected mid-Tertiary ash-flow tuff cauldrons in New Mexico are described. The largest region is 40 km in diameter, and erosional and block faulting processes have exposed levels as far down as the plutonic roots. The study supports a five-stage process: precursor, caldera collapse, early post-collapse, volcanism, major ring-fracture volcanism, and hydrothermal activity. The stages can repeat or the process can stop at any stage. Post-collapse lavas fell into two categories: cauldron lavas, derived from shallow defluidized residues of caldera-forming ash flow tuff eruption, and framework lavas, evolved from a siliceous pluton below the cauldron complex. The youngest caldera was shallow and formed from asymmetric subsidence and collapse of the caldera walls.

Zeolite-clay mineral zonation of volcaniclastic sediments within the McDermitt caldera complex of Nevada and Oregon

USGS Publications Warehouse

Glanzman, Richard K.; Rytuba, James J.

1979-01-01

Volcaniclastic sediments deposited in the moat of the collapsed McDermitt caldera complex have been altered chiefly to zeolites and potassium feldspar. The original rhyolitic and peralkaline ash-flow tuffs are included in conglomerates at the caldera rims and grade into a lacustrine series near the center of the collapse. The tuffs show a lateral zeolitic alteration from almost fresh glass to clinoptilolite, clinoptilolite-mordenite, and erionite; to analcime-potassium feldspar; and finally to potassium feldspar. Vertical zonation is in approximately the same order. Clay minerals in associated mudstones, on the other hand, show little lateral variation but a distinct vertical zonation, having a basal dioctahedral smectite, a medial trioctahedral smectite, and an upper dioctahedral smectite. The medial trioctahedral smectite is enriched in lithium (as much as 6,800 ppm Li). Hydrothermal alteration of the volcaniclastic sediments, forming both mercury and uranium deposits, caused a distinct zeolite and clay-mineral zonation within the general lateral zonation. The center of alteration is generally potassium feldspar, commonly associated with alunite. Potassium feldspar grades laterally and vertically to either clinoptilolite or clinoptilolite-mordenite, generally associated with gypsum. This zone then grades vertically and laterally into fresh glass. The clay minerals are a dioctahedral smectite, a mixed-layer clay mineral, and a 7-A clay mineral. The mixed-layer and 7-A clay minerals are associated with the potassium feldspar-alunite zone of alteration, and the dioctahedral smectite is associated with clinoptilolite. This mineralogical zonation may be an exploration guide for mercury and uranium mineralization in the caldera complex environment.

Paleontology, sedimentology and paleoenvironment of a new fossiliferous locality of the Jurassic Cañadón Asfalto Formation, Chubut Province, Argentina

NASA Astrophysics Data System (ADS)

Gallego, Oscar F.; Cabaleri, Nora G.; Armella, Claudia; Volkheimer, Wolfgang; Ballent, Sara C.; Martínez, Sergio; Monferran, Mateo D.; Silva Nieto, Diego G.; Páez, Manuel A.

2011-02-01

A new Late Jurassic assemblage of “conchostracans”, ostracods, bivalves and caddisfly cases from the locality “Estancia La Sin Rumbo”, Chubut Province (Patagonia, Argentina) is recorded. The fossils occur in the upper part of an outcropping 45 m thick volcaniclastic lacustrine sequence of yellowish tuffs and tuffites of the Puesto Almada Member, which is the upper member of the Cañadón Asfalto Formation with U/Pb age of 161 ± 3 Ma. The sequence represents one sedimentary cycle composed of a (lower) hemicycle of expansion and a (higher) hemicycle of contraction of the water body. The invertebrates lived in small freshwater bodies during the periods of expansion of the lake. The occurrence of a great number of small spinicaudatans, associated with mud-cracks, is evidence of dry climatic conditions and suggests several local mortality events. The spinicaudatan record of the fushunograptid-orthestheriid (component of the Eosestheriopsis dianzhongensis fauna) and the presence of Congestheriella rauhuti Gallego and Shen, suggest a Late Jurassic (Oxfordian to Tithonian) age. Caddisfly cases are recorded for the first time in the Cañadón Asfalto Basin.

Geology of the Yucca Mountain region

USGS Publications Warehouse

Stuckless, J.S.; O'Leary, Dennis W.

2006-01-01

Yucca Mountain has been proposed as the site for the nation's first geologic repository for high-level radioactive waste. This chapter provides the geologic framework for the Yucca Mountain region. The regional geologic units range in age from late Precambrian through Holocene, and these are described briefly. Yucca Mountain is composed dominantly of pyroclastic units that range in age from 11.4 to 15.2 Ma. The proposed repository would be constructed within the Topopah Spring Tuff, which is the lower of two major zoned and welded ash-flow tuffs within the Paintbrush Group. The two welded tuffs are separated by the partly to nonwelded Pah Canyon Tuff and Yucca Mountain Tuff, which together figure prominently in the hydrology of the unsaturated zone. The Quaternary deposits are primarily alluvial sediments with minor basaltic cinder cones and flows. Both have been studied extensively because of their importance in predicting the long-term performance of the proposed repository. Basaltic volcanism began ca. 10 Ma and continued as recently as ca. 80 ka with the eruption of cones and flows at Lathrop Wells, ???10 km south-southwest of Yucca Mountain. Geologic structure in the Yucca Mountain region is complex. During the latest Paleozoic and Mesozoic, strong compressional forces caused tight folding and thrust faulting. The present regional setting is one of extension, and normal faulting has been active from the Miocene through to the present. There are three major local tectonic domains: (1) Basin and Range, (2) Walker Lane, and (3) Inyo-Mono. Each domain has an effect on the stability of Yucca Mountain. ?? 2007 Geological Society of America. All rights reserved.

Research on the Log Interpretation Method of Tuffaceous Sandstone Reservoirs of X Depression in Hailar-Tamtsag Basin

NASA Astrophysics Data System (ADS)

Liu, S.; Pan, B.

2015-12-01

The logging evaluation of tuffaceous sandstone reservoirs is always a difficult problem. Experiments show that the tuff and shale have different logging responses. Since the tuff content exerts an influence on the computation of shale content and the parameters of the reservoir, and the accuracy of saturation evaluation is reduced. Therefore, the effect of tuff on the calculation of saturation cannot be ignored. This study takes the tuffaceous sandstone reservoirs in the X depression of Hailar-Tamtsag basin as an example to analyze. And the electric conduction model of tuffaceous sandstone reservoirs is established. The method which combines bacterial foraging algorithm and particle swarm optimization algorithm is used to calculate the content of reservoir components in well logging for the first time, and the calculated content of tuff and shale corresponds to the results analysis of thin sections. The experiment on cation exchange capacity (CEC) proves that tuff has conductivity, and the conversion relationship between CEC and resistivity proposed by Toshinobu Iton has been improved. According to the rock electric experiment under simulated reservoir conditions, the rock-electro parameters (a, b, m and n) are determined. The improved relationship between CEC and resistivity and the rock-electro parameters are used in the calculation of saturation. Formula (1) shows the saturation equation of the tuffaceous reservoirs:According to the comparative analysis between irreducible water saturation and the calculated saturation, we find that the saturation equation used CEC data and rock-electro parameters has a better application effect at oil layer than Archie's formulas.

Geohydrologic data and test results from Well J-13, Nevada Test Site, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thordarson, W.

Well J-13 was drilled to a depth of 1063.1 meters by using air-hydraulic-rotary drilling equipment. The well penetrated 135.6 meters of alluvium of Quaternary and Tertiary age and 927.5 meters of tuff of Tertiary age. The Topopah Spring Member of the Paintbrush Tuff, the principal aquifer, was penetrated from depths of 207.3 to 449.6 meters; a pumping test indicated its transmissivity is 120 meters squared per day, and its hydraulic conductivity is 1.0 meters per day. Below the Topopah Spring Member, tuff units are confining beds; transmissivities range from 0.10 to 4.5 meters squared per day, and hydraulic conductivities rangemore » from 0.0026 to 0.15 meter per day. Confining beds penetrated below a depth of 719.3 meters had the smallest transmissivities (0.10 to 0.63 meter squared per day) and hydraulic conductivities (0.0026 to 0.0056 meter per day). A static water level of about 282.2 meters was measured for the various water-bearing tuff units above a depth of 645.6 meters. Below a depth of 772.7 meters, the static water level was slightly deeper, 283.3 to 283.6 meters. Ground water sampled from well J-13 is a sodium bicarbonate water containing small concentrations of calcium, magnesium, silica, and sulfate, which is a typical analysis of water from tuff. Apparent age of the ground water, derived from carbon-14 age dating, is 9900 years. 15 references, 24 figures, 13 tables.« less

Late Paleozoic transpression in Buenos Aires and northeast Patagonia ranges, Argentina

NASA Astrophysics Data System (ADS)

Rossello, E. A.; Massabie, A. C.; López-Gamundí, O. R.; Cobbold, P. R.; Gapais, D.

1997-12-01

Paleozoic sediments are present in three regions in eastern central Argentina: (1) the Sierras Australes of Buenos Aires, (2) Sierras Septentrionales of Buenos Aires and (3) Northeast Patagonia. All of these deposits share a common deformational imprint imparted by late Paleozoic Gondwanan deformation. Exposures of these rocks are scattered, variably deformed, and isolated by younger sediments deposited in basins related to the Mesozoic through Tertiary opening of the South Atlantic such as the offshore Colorado Basin. The Sierras Australes of Buenos Aires outcrops are the best preserved. They are mostly located along the Sierras Australes foldbelt, with minor outliers distributed in the adjacent Claromec-basin. The Tunas Formation (early-early late? Permian) is the uppermost unit of the Pillahuincó Group (late Carboniferous-Permian) and is crucial to the understanding of the tectono-sedimentary evolution of the region during the late Paleozoic. The underlying units of the Pillahuincó Group (Sauce Grande, Piedra Azul and Bonete Formations) exhibit a depositional and compositional history characterized by glaciomarine sedimentation and postglacial transgression. They are also characterized by rather uniform quartz-rich compositions indicative of a cratonic provenance from the La Plata craton to the NE. In contrast, the sandstone-rich Tunas Formation has low quartz contents, and abundant volcanic and metasedimentary fragments; paleocurrents are consistently from the SW. Glassrich tuffs are interbedded with sandstone in the upper half of the Tunas Formation. The age of the deformation in the Sierras Australes is Permian and early-middle Triassic. This is based on metamorphic events indicated by formation of illite at 282 ± 3 Ma, 273 ± 8 Ma, 265 ± 3 Ma, and 260 ± 3 Ma ( {K}/{Ar} illite) in the Silurian Curamalal Group. Evidence of syntectonic magmatism is provided by a radiometric date of 245 ± 12 Ma ( {K}/{Ar} hornblende) for the López Lecube Granite, immediately west of the Sierras Australes. In the Sierras Septentrionales of Buenos Aires, Precambrian through early Paleozoic deposits of La Tinta, Sierras Bayas, Las Aguilas and Balcarce Formations rest on Precambrian crystalline basement of the La Plata craton. These exposed rocks are affected by subordinate, right lateral wrench faulting; some thrusting indicates tectonic transport toward the NE. In northeast Patagonia (Sierra Grande region) synkinematic deformation of early Permian (261 ± 5 Ma, {Rb}/{Sr} whole rock) age has been identified in Silurian metasediments of the Sierra Grande Formation. Bands of deformation in Sierra Grande quartzites indicate right lateral wrenching in a N-S direction. Contraction in a NE-SW direction is evidenced by folding. Three stages of tectonic evolution can be discerned for the above regions: (1) Early Paleozoic platform sedimentation, punctuated by episodes of accelerated subsidence during the Silurian and early Devonian, as shown by transgressive episodes, (2) late Paleozoic sedimentation and deformation, and (3) Meso-Cenozoic extensional inversion due to the South Atlantic opening. The late Paleozoic sedimentation and deformation (stage 2) includes late Carboniferous-earliest Permian glacial deposits of the Sierras Australes and Colorado offshore basin, deposited during an initial phase of extension, and cratonward foreland subsidence triggered sedimentation of the synorogenic deposits of the Permian Tunas Formation. Tuffs are intercalated in the upper half of this unit. These tuffs are associated with the silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) that peaked between the late early Permian and late Permian. Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late early Permian (260 Ma) age. The deformation described in this paper can be considered as part of a large scale intracontinental deformation in SW Gondwanaland inboard of an Andean-type compressive margin. This deformation is characterized by transpression (right lateral wrenching) combined with overthrusting to the NE and N-S horizontal contraction.

Publications - GMC 146 | Alaska Division of Geological & Geophysical

Science.gov Websites

concentrates from the following 2 NPRA core tuff samples: U.S. Navy Umiat Test #1 (510.5 feet); Umiat Test #11 geochronology studies on biotite concentrates from the following 2 NPRA core tuff samples: U.S. Navy Umiat Test #1 (510.5 feet); Umiat Test #11 (488 feet): Alaska Division of Geological & Geophysical Surveys

High-resolution 40Ar 39Ar chronology of Oligocene volcanic rocks, San Juan Mountains, Colorado

USGS Publications Warehouse

Lanphere, M.A.

1988-01-01

The central San Juan caldera complex consists of seven calderas from which eight major ash-flow tuffs were erupted during a period of intense volcanic activity that lasted for approximately 2 m.y. about 26-28 Ma. The analytical precision of conventional K-Ar dating in this time interval is not sufficient to unambiguously resolve this complex history. However, 40Ar 39Ar incremental-heating experiments provide data for a high-resolution chronology that is consistent with stratigraphie relations. Weighted-mean age-spectrum plateau ages of biotite and sanidine are the most precise with standard deviations ranging from 0.08 to 0.21 m.y. The pooled estimate of standard deviation for the plateau ages of 12 minerals is about 0.5 percent or about 125,000 to 135,000 years. Age measurements on coexisting minerals from one tuff and on two samples of each of two other tuffs indicate that a precision in the age of a tuff of better than 100,000 years can be achieved at 27 Ma. New data indicate that the San Luis caldera is the youngest caldera in the central complex, not the Creede caldera as previously thought. ?? 1988.

Dynamic tunable notch filters for the Antarctic Impulsive Transient Antenna (ANITA)

NASA Astrophysics Data System (ADS)

Allison, P.; Banerjee, O.; Beatty, J. J.; Connolly, A.; Deaconu, C.; Gordon, J.; Gorham, P. W.; Kovacevich, M.; Miki, C.; Oberla, E.; Roberts, J.; Rotter, B.; Stafford, S.; Tatem, K.; Batten, L.; Belov, K.; Besson, D. Z.; Binns, W. R.; Bugaev, V.; Cao, P.; Chen, C.; Chen, P.; Chen, Y.; Clem, J. M.; Cremonesi, L.; Dailey, B.; Dowkontt, P. F.; Hsu, S.; Huang, J.; Hupe, R.; Israel, M. H.; Kowalski, J.; Lam, J.; Learned, J. G.; Liewer, K. M.; Liu, T. C.; Ludwig, A. B.; Matsuno, S.; Mulrey, K.; Nam, J.; Nichol, R. J.; Novikov, A.; Prohira, S.; Rauch, B. F.; Ripa, J.; Romero-Wolf, A.; Russell, J.; Saltzberg, D.; Seckel, D.; Shiao, J.; Stockham, J.; Stockham, M.; Strutt, B.; Varner, G. S.; Vieregg, A. G.; Wang, S.; Wissel, S. A.; Wu, F.; Young, R.

2018-06-01

The Antarctic Impulsive Transient Antenna (ANITA) is a NASA long-duration balloon experiment with the primary goal of detecting ultra-high-energy (> 1018eV) neutrinos via the Askaryan Effect. The fourth ANITA mission, ANITA-IV, recently flew from Dec 2 to Dec 29, 2016. For the first time, the Tunable Universal Filter Frontend (TUFF) boards were deployed for mitigation of narrow-band, anthropogenic noise with tunable, switchable notch filters. The TUFF boards also performed second-stage amplification by approximately 45 dB to boost the ∼ μV-level radio frequency (RF) signals to ∼ mV-level for digitization, and supplied power via bias tees to the first-stage, antenna-mounted amplifiers. The other major change in signal processing in ANITA-IV is the resurrection of the 90 ° hybrids deployed previously in ANITA-I, in the trigger system, although in this paper we focus on the TUFF boards. During the ANITA-IV mission, the TUFF boards were successfully operated throughout the flight. They contributed to a factor of 2.8 higher total instrument livetime on average in ANITA-IV compared to ANITA-III due to reduction of narrow-band, anthropogenic noise before a trigger decision is made.

Radionuclide Gas Transport through Nuclear Explosion-Generated Fracture Networks

PubMed Central

Jordan, Amy B.; Stauffer, Philip H.; Knight, Earl E.; Rougier, Esteban; Anderson, Dale N.

2015-01-01

Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gas breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. Seasonal and location-based effects on breakthrough, which occur due to differences in barometric forcing, are stronger where the barometric signal is highly variable. PMID:26676058

Radionuclide Gas Transport through Nuclear Explosion-Generated Fracture Networks.

PubMed

Jordan, Amy B; Stauffer, Philip H; Knight, Earl E; Rougier, Esteban; Anderson, Dale N

2015-12-17

Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gas breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. Seasonal and location-based effects on breakthrough, which occur due to differences in barometric forcing, are stronger where the barometric signal is highly variable.

Eruptive history of Earth's largest Quaternary caldera (Toba, Indonesia) clarified

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesner, C.A.; Rose, W.I.; Drake, R.

1991-03-01

Single-grain laser-fusion {sup 40}Ar/{sup 39}Ar analyses of individual sanidine phenocrysts from the two youngest Toba (Indonesia) tuffs yield mean ages of 73{plus minus}4 and 501{plus minus}5 ka. In addition, glass shards from Toba ash deposited in Malaysia were dated at 68{plus minus}7 ka by the isothermal plateau fission-track technique. These new determinations, in conjunction with previous ages for the two oldest tuffs at Toba, establish the chronology of four eruptive events from the Toba caldera complex over the past 1.2 m.y. Ash-flow tuffs were erupted from the complex every 0.34 to 0.43 m.y., culminating with the enormous (2500-3000 km{sup 3})more » Youngest Toba tuff eruption, caldera formation, and subsequent resurgence of Samosir Island. Timing of this last eruption at Toba is coincident with the early Wisconsin glacial advance. The high-precision {sup 40}Ar/{sup 39}Ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions.« less

Construction of the North Head (Maungauika) tuff cone: a product of Surtseyan volcanism, rare in the Auckland Volcanic Field, New Zealand

NASA Astrophysics Data System (ADS)

Agustín-Flores, Javier; Németh, Károly; Cronin, Shane J.; Lindsay, Jan M.; Kereszturi, Gábor

2015-02-01

The Auckland Volcanic Field (AVF) comprises at least 52 monogenetic eruption centres dispersed over ˜360 km2. Eruptions have occurred sporadically since 250 ka, predominantly when glacio-eustatic sea levels were lower than today. Now that around 35 % of the field is covered by shallow water (up to 30 m depth), any eruption occurring in the present or near future within this area may display Surtseyan dynamics. The North Head tuff cone evidences eruptive dynamics caused by magma interaction with seawater. The first stages of the eruption comprise a phreatomagmatic phase that built a 48-m-high tuff cone. North Head tuff deposits contain few lithic fragments (<10 vol%) and are characterized by deposits from collapsing tephra jets and fall from relatively wet tephra columns. The conditions needed for this eruption existed between 128 and 116 ka, when the sea level in the Auckland area was at least 10-12 m above the pre-eruptive surface. The hazards associated with this type of eruption pose a risk to the densely populated coastal residential zones and the activities of one of the busiest harbours in New Zealand.

Geochemistry and Geochronology of Middle Tertiary Volcanic Rocks of the Central Chiricahua Mountains, Southeast Arizona

USGS Publications Warehouse

du Bray, Edward A.; Pallister, John S.; Snee, Lawrence W.

2004-01-01

Middle Tertiary volcanic rocks of the central Chiricahua Mountains in southeast Arizona are the westernmost constituents of the Eocene-Oligocene Boot Heel volcanic field of southwestern New Mexico and southeastern Arizona. About two dozen volumetric ally and stratigraphically significant volcanic units are present in this area. These include large-volume, regionally distributed ash-flow tuffs and smaller volume, locally distributed lava flows. The most voluminous of these units is the Rhyolite Canyon Tuff, which erupted 26.9 million years ago from the Turkey Creek caldera in the central Chiricahua Mountains. The Rhyolite Canyon Tuff consists of 500-1,000 cubic kilometers of rhyolite that was erupted from a normally zoned reservoir. The tuff represents sequential eruptions, which became systematically less geochemically evolved with time, from progressively deeper levels of the source reservoir. Like the Rhyolite Canyon Tuff, other ashflow tuffs preserved in the central Chiricahua Mountains have equivalents in nearby, though isolated mountain ranges. However, correlation of these other tuffs, from range to range, has been hindered by stratigraphic discontinuity, structural complexity, and various lithologic similarities and ambiguities. New geochemical and geochronologic data presented here enable correlation of these units between their occurrences in the central Chiricahua Mountains and the remainder of the Boot Heel volcanic field. Volcanic rocks in the central Chiricahua Mountains are composed dominantly of weakly peraluminous, high-silica rhyolite welded tuff and rhyolite lavas of the high-potassium and shoshonitic series. Trace-element, and to a lesser extent, major-oxide abundances are distinct for most of the units studied. Geochemical and geochronologic data depict a time and spatial transgression from subduction to within-plate and extensional tectonic settings. Compositions of the lavas tend to be relatively homogeneous within particular units. In contrast, compositions of the ash-flow tuffs, including the Rhyolite Canyon Tuff, vary significantly owing to eruption from compositionally zoned reservoirs. Reservoir zonation is consistent with fractional crystallization of observed phenocryst phases and resulting residual liquid compositional evolution. Rhyolite lavas preserved in the moat of the Turkey Creek caldera depict compositional zonation that is the reverse of that expected of magma extraction from progressively deeper parts of a normally zoned reservoir. Presuming that the source reservoir was sequentially tapped from its top downward, development of reverse zonation in the rhyolite lava sequence may indicate that later erupted, more evolved magma contains systematically less wallrock contamination derived from the geochemically primitive margins of its incompletely mixed reservoir. New 40Ar/39Ar geochronology data indicate that the principal middle Tertiary volcanic rocks in the central Chiricahua Mountains were erupted between about 34.2 and 26.2 Ma, and that the 5.2 m.y. period between 33.3 and 28.1 Ma was amagmatic. The initial phase of eruptive activity in the central Chiricahua Mountains, between 34.2 and 33.3 Ma, was associated with a regional tectonic regime dominated by subduction along the west edge of North America. We infer that the magmatic hiatus, nearly simultaneous with a hiatus of similar duration in parts of the Boot Heel volcanic field east of the central Chiricahua Mountains, is related to a period of more rapid convergence and therefore shallower subduction that may have displaced subduction-related magmatic activity to a position east of the present-day Boot Heel volcanic field. The hiatus also coincides with a major plate tectonic reorganization along the west edge of North America that resulted in cessation of subduction and initiation of transform faulting along the San Andreas fault. The final period of magmatism in the central Chiricahua Mountains, between 28.1 and 23.2 Ma, ap

Chemical data and variation diagrams of igneous rocks from the Timber Mountain-Oasis Valley Caldera Complex, southern Nevada

USGS Publications Warehouse

Quinlivan, W.D.; Byers, F.M.

1977-01-01

Silica variation diagrams presented here are based on 162 chemical analyses of tuffs, lavas, and intrusives, representative of volcanic centers of the Timber Mountain-Oasis Valley caldera complex and cogenetic rocks of the Silent Canyon ca1dera. Most of the volcanic units sampled are shown on the U.S. Geological Survey geologic map of the Timber Mountain caldera area (I-891) and are described in U.S. Geological Survey Professional Paper 919. Early effusives of the complex, although slightly altered, are probably chemically, and petrographically, more like the calc-alkalic Fraction Tuff (Miocene) of the northern Nellis Air Force Base Bombing and Gunnery Range to the north, whereas effusives of later Miocene age, such as the Paintbrush and Timber Mountain Tuffs, are alkali-calcic.

Pyroxene thermometry of rhyolite lavas of the Bruneau-Jarbidge eruptive center, Central Snake River Plain

NASA Astrophysics Data System (ADS)

Cathey, Henrietta E.; Nash, Barbara P.

2009-11-01

The Bruneau-Jarbidge eruptive center of the central Snake River Plain in southern Idaho, USA produced multiple rhyolite lava flows with volumes of <10 km 3 to 200 km 3 each from ~11.2 to 8.1 Ma, most of which follow its climactic phase of large-volume explosive volcanism, represented by the Cougar Point Tuff, from 12.7 to 10.5 Ma. These lavas represent the waning stages of silicic volcanism at a major eruptive center of the Yellowstone hotspot track. Here we provide pyroxene compositions and thermometry results from several lavas that demonstrate that the demise of the silicic volcanic system was characterized by sustained, high pre-eruptive magma temperatures (mostly ≥950 °C) prior to the onset of exclusively basaltic volcanism at the eruptive center. Pyroxenes display a variety of textures in single samples, including solitary euhedral crystals as well as glomerocrysts, crystal clots and annealed microgranular inclusions of pyroxene ± magnetite ± plagioclase. Pigeonite and augite crystals are unzoned, and there are no detectable differences in major and minor element compositions according to textural variety — mineral compositions in the microgranular inclusions and crystal clots are identical to those of phenocrysts in the host lavas. In contrast to members of the preceding Cougar Point Tuff that host polymodal glass and mineral populations, pyroxene compositions in each of the lavas are characterized by single rather than multiple discrete compositional modes. Collectively, the lavas reproduce and extend the range of Fe-Mg pyroxene compositional modes observed in the Cougar Point Tuff to more Mg-rich varieties. The compositionally homogeneous populations of pyroxene in each of the lavas, as well as the lack of core-to-rim zonation in individual crystals suggest that individual eruptions each were fed by compositionally homogeneous magma reservoirs, and similarities with the Cougar Point Tuff suggest consanguinity of such reservoirs to those that supplied the polymodal Cougar Point Tuff. Pyroxene thermometry results obtained using QUILF equilibria yield pre-eruptive magma temperatures of 905 to 980 °C, and individual modes consistently record higher Ca content and higher temperatures than pyroxenes with equivalent Fe-Mg ratios in the preceding Cougar Point Tuff. As is the case with the Cougar Point Tuff, evidence for up-temperature zonation within single crystals that would be consistent with recycling of sub- or near-solidus material from antecedent magma reservoirs by rapid reheating is extremely rare. Also, the absence of intra-crystal zonation, particularly at crystal rims, is not easily reconciled with cannibalization of caldera fill that subsided into pre-eruptive reservoirs. The textural, compositional and thermometric results rather are consistent with minor re-equilibration to higher temperatures of the unerupted crystalline residue from the explosive phase of volcanism, or perhaps with newly generated magmas from source materials very similar to those for the Cougar Point Tuff. Collectively, the data suggest that most of the pyroxene compositional diversity that is represented by the tuffs and lavas was produced early in the history of the eruptive center and that compositions across this range were preserved or duplicated through much of its lifetime. Mineral compositions and thermometry of the multiple lavas suggest that unerupted magmas residual to the explosive phase of volcanism may have been stored at sustained, high temperatures subsequent to the explosive phase of volcanism. If so, such persistent high temperatures and large eruptive magma volumes likewise require an abundant and persistent supply of basalt magmas to the lower and/or mid-crust, consistent with the tectonic setting of a continental hotspot.

Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin-Ventana foldbelt (Argentina) and Karoo basin-Cape foldbelt (South Africa) revisited

NASA Astrophysics Data System (ADS)

López-Gamundí, O. R.; Rossello, E. A.

As integral parts of du Toit's (1927) ``Samfrau Geosyncline'', the Sauce Grande basin-Ventana foldbelt (Argentina) and Karoo basin-Cape foldbelt (South Africa) share similar paleoclimatic, paleogeographic, and paleotectonic aspects related to the Late Paleozoic tectono-magmatic activity along the Panthalassan continental margin of Gondwanaland. Late Carboniferou-earliest Permian glacial deposits were deposited in the Sauce Grande (Sauce Grande Formation) and Karoo (Dwyka Formation) basins and Falkland-Malvinas Islands (Lafonia Formation) during an initial (sag) phase of extension. The pre-breakup position of the Falkland (Malvinas) Islands on the easternmost part of the Karoo basin (immediately east of the coast of South Africa) is supported by recent paleomagnetic data, lithofacies associations, paleoice flow directions and age similarities between the Dwyka and the Lafonia glacial sequences. The desintegration of the Gondwanan Ice Sheet (GIS) triggered widespread transgressions, reflected in the stratigraphic record by the presence of inter-basinally correlatable, open marine, fine-grained deposits (Piedra Azul Formation in the Sauce Grande basin, Prince Albert Formation in the Karoo basin and Port Sussex Formation in the Falkland Islands) capping glacial marine sediments. These early postglacial transgressive deposits, characterised by fossils of the Eurydesma fauna and Glossopteris flora, represent the maximum flooding of the basins. Cratonward foreland subsidence was triggered by the San Rafael orogeny (ca. 270 Ma) in Argentina and propogated along the Gondwanan margin. This subsidence phase generated sufficient space to accommodate thick synorogenic sequences derived from the orogenic flanks of the Sauce Grande and Karoo basins. Compositionally, the initial extensional phase of these basins was characterized by quartz-rich, craton-derived detritus and was followed by a compressional (foreland) phase characterized by a paleocurrent reversal and dominance of arc/foldbelt-derived material. In the Sauce Grande basin, tuffs are interbedded in the upper half of the synorogenic, foldbelt-derived Tunas Formation (Early-early Late? Permian). Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late Early Permian (260 Ma) age. Silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) peaked between the late Early Permian and Late Permian. A link between these volcanics and the consanguineous airborne tuffs present in the Sauce Grande and Karoo basins is suggested on the basis of their similar compositions and ages.

Geology and Volcanology of Kima'Kho Mountain, Northern British Columbia: A Pleistocene Glaciovolcanic Edifice

NASA Astrophysics Data System (ADS)

Turnbull, M.; Porritt, L. A.; Edwards, B. R.; Russell, K.

2014-12-01

Kima'Kho Mountain is a 1.8 Ma (40Ar/39Ar of 1.82 +/- 40 ka) Pleistocene an alkali-olivine basaltic tuya situated in northern British Columbia. The volcanic edifice rises 460 m from its base and comprises a central vent, dominated by lapilli-tuff and minor pillow lava and dykes; and a surrounding plateau underlain by a sequence of dipping beds of basaltic tuff-breccia and capped by a series of flat-lying, subaerial lava flows. We present a 1:10,000 geological map for Kima'Kho Mountain building on the preliminary work of Ryane et al. (2010). We use the volcanic stratigraphy to explore the implications of three unique features. (1) The central cone comprises massive to crudely-bedded lapilli tuffs containing abundant armoured lapilli - cores of highly-vesicular pyroclasts coated with blocky to cuspate vitric ash. These units suggest an explosive origin from within an ice-enclosed lake, and deposited by wet, dilute pyroclastic surge events. (2) The entire stratigraphic sequence hosts at least two "passage zones" (cf. Jones, 1969); the presence and geometry of these passage zones constrain ice thicknersses at the time of eruption and inform on the englacial lake dynamics. (3) Lastly, our field-based stratigraphic relationships are at odds with the classic tuya model (i.e. an effusive onset to the eruption, forming pillow basalts, followed by explosive activity). Our field mapping suggests an alternative model of tuya architecture, involving a highly-energetic, sustained explosive onset creating a tephra cone that become emergent followed by effusive eruption to create lavas and a subaqueous lava-fed delta. Jones, J. G. Intraglacial volcanoes of the Laugarvatn region, south-west Iceland-I. Geological Society of London Quarterly Journal 124, 197-211 (1969). Ryane, C., Edwards, B. R. & Russell, J. K. The volcanic stratigraphy of Kima'Kho Mountain: A Pleistocene tuya, northwestern British Columbia. Geological Survey of Canada, Current Research 2011-104, 12p, doi:10.4095/289196 (2011). Figure 1. (Upper Figure) Geological cross-section showing projected distribution of volcanic lithofacies used to define 3 passage zones (PZ#). (Lower Figure) Dynamic evolution and interplay between the rates of volcano growth vs. rise of englacial lake and relationship to passage zones (PZ) mapped at Kima'Kho.

Field occurrence and lithology of Archean hydrothermal systems in the 3.2Ga Dixon Island Formation, Western Australia

NASA Astrophysics Data System (ADS)

Aihara, Y.; Kiyokawa, S.; Ito, T.; Ikehara, M.; Yamaguchi, K. E.; Horie, K.; Sakamoto, R.; Miki, T.

2013-12-01

Stratigraphic transition of black chert to iron-rich sedimentary rocks above volcanic sequences with hydrothermal systems is common and characteristic feature of Archean greenstone belts. The 3.2 Ga Dixon Island Formation, exposed along the northern coast of Dixon Island located in the coastal Pilbara terrane, Western Australia, is one of such units and the focus of our study. We introduce field occurrence and lithology of the Dixon Island Formation that preserves features of paleohydrohermal environment in the Mesoarchean ocean. The Dixon Island Formation is composed of the following three members (in ascending order): Komatiite-Rhyolite Tuff, Black Chert, and Varicolored Chert members (Kiyokawa and Taira, 1998). Here we focus on the Komatiite-Rholite Tuff member. It preserves two cycles of highly altered komatiite lavas and well-stratified rhyolite tuff. Komatiite lavas include dendritic crystals of chrome spinel and ghosts of spinifex, euhedral and sheet-like olivines and pyroxenes. These rocks are now composed of granular microcrystalline quartz with chromian muscovite, chrome spinel and chrorite that formed by intense silicification. Its upper part contains hydrothermal veining and alteration (i.e., many vein swarms composed of veins of quartz and organic carbon-rich black chert). Most black chert veins intrude vertically into overlying layers, and contain barite, pyrite, monazite and clay minerals which were least affected by silicificatio. Based on the cross-cutting relationship seen in the outcrops, we recognized two generations of black chert veins (type 1 and type 2 veins; Kiyokawa et al., 2006). Type 1 veins are mainly composed of carbonaceous peloids in a microcrystalline quartz matrix. Euhedral and xenocrystic tourmaline are found only in Type1 veins. Type 2 veins are organic carbon-poor and contain fragments of black chert and siliceous volcanic breccia (Kiyokawa et al., 2006). Intense silicification of komatiitic volcaniclastics and lava, enriched in Si and K and depleted in Mg, occurred earlier than the formation of black chert veins and probably during sedimentation of the overlying Black Chert member. Petrographycally, tourmaline in Type1 veins formed by hydrothermal processes and can be used to infer physicochemical conditions of the hydrothermal activity. Fragmentation of black chert and volcanic rocks within Type 2 veins was probably due to high pressure caused by hydrothermal activity.

Earth Observations

NASA Image and Video Library

2010-08-22

ISS024-E-012425 (22 Aug. 2010) --- This photograph, featuring a landscape in the central Andes mountains near the Chile/Argentina border dominated by numerous volcanoes and associated landforms, was photographed by an Expedition 24 crew member on the International Space Station. Layers of older sedimentary rocks are visible to the southeast (upper right). Many of the volcanic cones show grooves eroded by water to form gullies. Such erosion has occurred since the host volcano was built up, indicating that most volcanoes in this view have been inactive for centuries or millennia. A few volcanoes exhibit much less erosion, and even show tongues of recent, dark lava flows (top left). According to scientists, two of these volcanoes, Cerro el Condor and Peinado have likely erupted within approximately the last 12,000 years (the Holocene Epoch). Also visible in the image is the world’s highest active volcano, Nevado Ojos del Salado, with a summit at 6,887 meters above sea level. The most recent confirmed eruption of this volcano has been dated to 700 (approximately 300 years), but minor eruptive activity may have occurred as recently as 1993. Stratovolcanoes such as Cerro el Condor, Peinado, and Nevado Ojos del Salado are formed partly by buildup of lava flows and partly by buildup of explosively vented material dropping back down onto the surface. One type of material associated with explosive eruptions is welded tuff, which is formed by molten and fragmented rock that accumulates on the ground and later solidifies. A large tuff sheet is visible at top left. Formed very rapidly, these sheets have been termed “instant landscapes.” So active has the Andean volcanic system been that the origin of many of the tuffs in the Andes cannot be pinpointed since source vents have been overprinted by subsequent volcanic events. The volcanic landscape also shows that the erosive work of rivers—and glaciers repeatedly in the recent past—is slower than the opposite processes of the upward building of the volcanoes. The bright blue, nearly 7-kilometer-long lake near the center of the image is known as Laguna Verde. This and other less obvious lakes indicate that water (snowmelt or direct precipitation) is unable to reach the sea, but is rather impounded in the depressions between the volcanic edifices.

The Pioneer Ultramafic Complex of the Barberton Greenstone Belt, South Africa

NASA Astrophysics Data System (ADS)

Cooper, M. R.; Byerly, G. R.; Lowe, D. R.; Thompson, M. E.

2005-12-01

The 3.55-3.22 Ga Barberton Greenstone Belt is an approximately 100km x 30km northeast trending, isoclinally folded, volcanic and sedimentary succession surrounded by intrusive granitic rocks. It is perhaps Earth's best preserved mid-Archean supracrustal sequence and also among the most magnesian, making it an ideal location for studying compositionally distinct rocks of the Archean, such as komatiites. The Pioneer Ultramafic Complex has been interpreted as a komatiitic intrusion but we argue that it is a sequence of layered komatiitic flows and interbedded tuffs correlative with other komatiitic extrusive units of the 3.29 Ga Weltevreden Formation, the uppermost formation of the Onverwacht Group. The Pioneer Ultramafic Complex contains at least 900m of section in the study area, including at least 5 flow sets, with individual flows up to 100 m thick, sections of tuff up to 100m thick and additional thinner tuff units. The base of the sequence is in fault contact with the Sawmill Ultramafic Complex, which is similar to and perhaps correlative with the Pioneer. The top of the sequence is bounded by the Moodies Fault and slightly younger sedimentary rocks of the Fig Tree and Moodies Groups. Typical flows of the Pioneer have highly serpentinized olivine-rich cumulate bases, fresh olivine bearing peridotitic lithologies in central portions, and increasing pyroxene content, pyroxene size, and elongation of grains toward the flow tops. Three of the five flows are capped with random and/or oriented spinifex layers. The tuffs within this and other layered ultramafic complexes of the Barberton Greenstone Belt are mostly fine grained, slaty serpentinites that were previously interpreted as bedding horizontal zones of shearing. However, rare preservation of angular and vesicular lapilli, and more commonly cross-stratification in finer grained layers, provide strong evidence that these layers represent tuffs. High chromium and other trace element contents suggest they are komatiitic tuffs likely co-magmatic with the interbedded komatiitic lava flows. Compositions of fresh olivines range between 91 to 93 percent forsterite, indicating a komatiitic melt composition. In addition to olivine phenocrysts, fresh chromite, orthopyroxene, pigeonite, and augite are all present as smaller intercumulus crystals or microphenocrysts. The pyroxenes have Mg numbers up to 89 and Al/Ti ratios approximately 10-15. The latter are consistent with the Al/Ti ratios of 20-30 found within the komatiites and tuffs analyzed thus far. These ratios indicate the flows belong to the aluminium undepleted group of komatiites. The rock and mineral chemistry of these flows allow us to determine melt compositions and explore correlations and relationships with other komatiitic flows and layered ultramafic complexes of the Barberton Greenstone Belt. Field studies of these flows help characterize an Archean igneous complex believed to represent shallow marine deposition of komatiitic tuffs and coeval emplacement of thick vertically differentiated komatiitic flows.

Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from?

USGS Publications Warehouse

Lipman, P.W.; McIntosh, W.C.

2008-01-01

The northeastern San Juan Mountains, the least studied portion of this well-known segment of the Southern Rocky Mountains Volcanic Field are the site of several newly identified and reinterpreted ignimbrite calderas. These calderas document some unique eruptive features not described before from large volcanic systems elsewhere, as based on recent mapping, petrologic data, and a large array of newly determined high-precision, laser-fusion 40Ar/39Ar ages (140 samples). Tightly grouped sanidine ages document exceptionally brief durations of 50-100 k.y. or less for individual Oligocene caldera cycles; biotite ages are more variable and commonly as much as several hundred k.y. older than sanidine from the same volcanic unit. A previously unknown ignimbrite caldera at North Pass, along the Continental Divide in the Cochetopa Hills, was the source of the newly distinguished 32.25-Ma Saguache Creek Tuff (???400-500 km3). This regionally, distinctive crystal-poor alkalic rhyolite helps fill an apparent gap in the southwestward migration from older explosive activity, from calderas along the N-S Sawatch locus in central Colorado (youngest, Bonanza Tuff at 33.2 Ma), to the culmination of Tertiary volcanism in the San Juan region, where large-volume ignimbrite eruptions started at ca. 29.5 Ma and peaked with the enormous Fish Canyon Tuff (5000 km3) at 28.0 Ma. The entire North Pass cycle, including caldera-forming Saguache Creek Tuff, thick caldera-filling lavas, and a smaller volume late tuff sheet, is tightly bracketed at 32.25-32.17 Ma. No large ignimbrites were erupted in the interval 32-29 Ma, but a previously unmapped cluster of dacite-rhyolite lava flows and small tuffs, areally associated with a newly recognized intermediate-composition intrusion 5 ?? 10 km across (largest subvolcanic intrusion in San Juan region) centered 15 km north of the North Pass caldera, marks a near-caldera-size silicic system active at 29.8 Ma. In contrast to the completely filled North Pass caldera that has little surviving topographic expression, no voluminous tuffs vented directly from the adjacent Cochetopa Park caldera, which is morphologically beautifully preserved. Instead, Cochetopa Park subsided passively as the >500 km3 Nelson Mountain Tuff vented at 26.9 Ma from an "underfit" caldera (youngest of the San Luis complex) 30 km to the SW. Three separate regional ignimbrites were erupted sequentially from San Luis calderas within an interval of less than 50-100 k.y., a more rapid recurrence rate for large explosive eruptions than previously documented elsewhere. In eruptive processes, volcanic compositions, areal extent, duration of activity, and magmatic production rates and volumes, the Southern Rocky Mountains Volcanic Field represents present-day erosional remnants of a composite volcanic field, comparable to younger ignimbrite terranes of the Central Andes. ?? 2008 Geological Society of America.

HIGH EXPLOSIVE CRATER STUDIES: TUFF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphey, B.F.

1961-04-01

Spherical charges of TNT, each weighing 256 pounds, were exploded at various depths in tuff to determine apparent crater dimensions in a soft rock. No craters were obtained for depths of burst equal to or greater than 13.3 feet. It was deduced that rock fragments were sufficiently large that charges of greater magnitude should be employed for crater experiments intended as models of nuclear explosions. (auth)

The effect of dilatancy on the unloading behavior of Mt. Helen tuff

DOE Office of Scientific and Technical Information (OSTI.GOV)

Attia, A.V.; Rubin, M.B.

1993-11-01

In order to understand the role of rock dilatancy in modeling the response of partially saturated rock formations to underground nuclear explosions, we have developed a thermodynamically consistent model for a porous material, partially saturated with fluid. This model gives good predictions of the unloading behavior of dry, partially saturated, and fully saturated Mt. Helen tuff, as measured by Heard.

Effect of reducing groundwater on the retardation of redox-sensitive radionuclides

PubMed Central

Hu, QH; Zavarin, M; Rose, TP

2008-01-01

Laboratory batch sorption experiments were used to investigate variations in the retardation behavior of redox-sensitive radionuclides. Water-rock compositions were designed to simulate subsurface conditions at the Nevada Test Site (NTS), where a suite of radionuclides were deposited as a result of underground nuclear testing. Experimental redox conditions were controlled by varying the oxygen content inside an enclosed glove box and by adding reductants into the testing solutions. Under atmospheric (oxidizing) conditions, radionuclide distribution coefficients varied with the mineralogic composition of the sorbent and the water chemistry. Under reducing conditions, distribution coefficients showed marked increases for 99Tc (from 1.22 at oxidizing to 378 mL/g at mildly reducing conditions) and 237Np (an increase from 4.6 to 930 mL/g) in devitrified tuff, but much smaller variations in alluvium, carbonate rock, and zeolitic tuff. This effect was particularly important for 99Tc, which tends to be mobile under oxidizing conditions. A review of the literature suggests that iodine sorption should decrease under reducing conditions when I- is the predominant species; this was not consistently observed in batch tests. Overall, sorption of U to alluvium, devitrified tuff, and zeolitic tuff under atmospheric conditions was less than in the glove-box tests. However, the mildly reducing conditions achieved here were not likely to result in substantial U(VI) reduction to U(IV). Sorption of Pu was not affected by the decreasing Eh conditions achieved in this study, as the predominant sorbed Pu species in all conditions was expected to be the low-solubility and strongly sorbing Pu(OH)4. Depending on the aquifer lithology, the occurrence of reducing conditions along a groundwater flowpath could potentially contribute to the retardation of redox-sensitive radionuclides 99Tc and 237Np, which are commonly identified as long-term dose contributors in the risk assessment in various radionuclide environmental contamination scenarios. The implications for increased sorption of 99Tc and 237Np to devitrified tuff under reducing conditions are significant as the fractured devitrified tuff serves as important water flow path at the NTS and the horizon for a proposed repository to store high-level nuclear waste at Yucca Mountain. PMID:19077277

A Remotely Sensed and Paleomagnetic Perspective on the Bonelli Tuff of NW AZ and SE CA

NASA Astrophysics Data System (ADS)

Gomez, C. D.

2015-12-01

The southern Black and Cerbat Mountains of NW AZ and the Sacramento Mountains of SE CA preserve ignimbrites associated with multiple episodes of volcanic activity that span at least a million years. Unraveling the stratrigraphy of these deposits, as well as their eruptive centers, is critical for constraining the volcanic history of this ignimbrite, the 18.8 Ma Peach Spring Tuff, is the recently identified 17.7 Ma Tuff of Bonelli House (TB) (Ferguson & Cook 2015) and may also occur in the southern Black and Sacramento Mountains. To help determine the extent and possible source of the TB, we have performed a combined remote sensing and paleomagnetic study of this unit, including possible correlatives. Paleomagnetic work involved Remanence and anisotropic magnetic susceptibility methods. Drill samples were collected and processed at Scripps Institute of Oceanography & Pomona College. An AC current was run to obtain the Paleomag current, as opposed to the traditional of heating up the cores at specific intervals. Sacramento Mountains samples produced an average direction of 200.9 / -26.4, which contrasts the Peach Spring Tuff paleodirection of 036.4/33 (Wells & Hillhouse, 1989). An AMS direction was determined using a MFK1 Kappabridge instrument and consistently showed similar flow direction to that of the PST. In compiling our data on a map, we took into account the Whipple Detachment Fault, ~40 km westward (Lister & Davis, 1989). We were able to identify a spectral signature and remnant paleomagnetic direction for the TB and identify potential additional outcrops in the southern Black mountains. AMS showed us that the ignimbrites originated from a source in the Silver Creek Caldera, which may indicate the PST at TB were produced from a similar source. The remnant paleomagnetic direction allows us to closely correlate these tuff units as occurring within a similar timeframe. The contrasting paleodirection of the TB and the PST allows us to confidently say that the Peach Spring and Bonelli Tuffs occurred at different times when the Earth's magnetic field directions were different.

The Yucca Mountain Project prototype air-coring test, U12g tunnel, Nevada test site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ray, J.M.; Newsom, J.C.

1994-12-01

The Prototype Air-Coring Test was conducted at the Nevada Test Site (NTS) G-Tunnel facility to evaluate standard coring techniques, modified slightly for air circulation, for use in testing at a prospective nuclear waste repository at Yucca Mountain, Nevada. Air-coring technology allows sampling of subsurface lithology with minimal perturbation to ambient characteristic such as that required for exploratory holes near aquifers, environmental applications, and site characterization work. Two horizontal holes were cored, one 50 ft long and the other 150 ft long, in densely welded fractured tuff to simulate the difficult drilling conditions anticipated at Yucca Mountain. Drilling data from sevenmore » holes on three other prototype tests in nonwelded tuff were also collected for comparison. The test was used to establish preliminary standards of performance for drilling and dust collection equipment and to assess procedural efficiencies. The Longyear-38 drill achieved 97% recovery for HQ-size core (-2.5 in.), and the Atlas Copco dust collector (DCT-90) captured 1500 lb of fugitive dust in a mine environment with only minor modifications. Average hole production rates were 6-8 ft per 6-h shift in welded tuff and almost 20 ft per shift on deeper holes in nonwelded tuff. Lexan liners were successfully used to encapsulate core samples during the coring process and protect core properties effectively. The Prototype Air-Coring Test demonstrated that horizontal air coring in fractured welded tuff (to at least 150 ft) can be safely accomplished by proper selection, integration, and minor modification of standard drilling equipment, using appropriate procedures and engineering controls. The test also indicated that rig logistics, equipment, and methods need improvement before attempting a large-scale dry drilling program at Yucca Mountain.« less

Permian plate margin volcanism and tuffs in adjacent basins of west Gondwana: Age constraints and common characteristics

NASA Astrophysics Data System (ADS)

López-Gamundí, Oscar

2006-12-01

Increasing evidence of Permian volcanic activity along the South American portion of the Gondwana proto-Pacific margin has directed attention to its potential presence in the stratigraphic record of adjacent basins. In recent years, tuffaceous horizons have been identified in late Early Permian-through Middle Permian (280-260 Ma) sections of the Paraná Basin (Brazil, Paraguay, and Uruguay). Farther south and closer to the magmatic tract developed along the continental margin, in the San Rafael and Sauce Grande basins of Argentina, tuffs are present in the Early to Middle Permian section. This tuff-rich interval can be correlated with the appearance of widespread tuffs in the Karoo Basin. Although magmatic activity along the proto-Pacific plate margin was continuous during the Late Paleozoic, Choiyoi silicic volcanism along the Andean Cordillera and its equivalent in Patagonia peaked between the late Early Permian and Middle Permian, when extensive rhyolitic ignimbrites and consanguineous airborne tuffaceous material erupted in the northern Patagonian region. The San Rafael orogenic phase (SROP) interrupted sedimentation along the southwestern segment of the Gondwana margin (i.e., Frontal Cordillera, San Rafael Basin), induced cratonward thrusting (i.e., Ventana and Cape foldbelts), and triggered accelerated subsidence in the adjacent basins (Sauce Grande and Karoo) located inboard of the deformation front. This accelerated subsidence favored the preservation of tuffaceous horizons in the syntectonic successions. The age constraints and similarities in composition between the volcanics along the continental margin and the tuffaceous horizons in the San Rafael, Sauce Grande, Paraná, and Karoo basins strongly suggest a genetic linkage between the two episodes. Radiometric ages from tuffs in the San Rafael, Paraná, and Karoo basins indicate an intensely tuffaceous interval between 280 and 260 Ma.

Geochemistry, strontium isotope data, and potassium-argon ages of the andesite-rhyolite association in the Padang area, West Sumatra

USGS Publications Warehouse

Leo, G.W.; Hedge, C.E.; Marvin, R.F.

1980-01-01

Quaternary volcanoes in the Padang area on the west coast of Sumatra have produced two-pyroxene, calc-alkaline andesite and volumetrically subordinate rhyolitic and andesitic ash-flow tuffs. A sequence of andesite (pre-caldera), rhyolitic tuff and andesitic tuff, in decreasing order of age, is related to Maninjau caldera. Andesite compositions range from 55.0 to 61.2% SiO2 and from 1.13 to 2.05% K2O. Six K-Ar whole-rock age determinations on andesites show a range of 0.27 ?? 0.12 to 0.83 ?? 0.42 m.y.; a single determination on the rhyolitic ashflow tuff gave 0.28 ?? 0.12 m.y. Eight 57Sr/26Sr ratios on andesites and rhyolite tuff west of the Semangko fault zone are in the range 0.7056 - 0.7066. These ratios are higher than those elsewhere in the Sunda arc but are comparable to the Taupo volcanic zone of New Zealand and calc-alkaline volcanics of continental margins. An 87Sr/86Sr ratio of 0.7048 on G. Sirabungan east of the Semangko fault is similar to an earlier determination on nearby G. Marapi (0.7047), and agrees with 87Sr/86Sr ratios in the rest of the Sunda arc. The reason for this distribution of 87Sr/86Sr ratios is unknown. The high 87Sr/86Sr ratios are tentatively regarded to reflect a crustal source for the andesites, while moderately fractionated REE patterns with pronounced negative Eu anomalies suggest a residue enriched in plagioclase with hornblende and/or pyroxenes. Generation of associated andesite and rhyolite could have been caused by hydrous fractional melting of andesite or volcanogenic sediments under adiabatic decompression. ?? 1980.

Ce-Fe-modified zeolite-rich tuff to remove Ba(2+)-like (226)Ra(2+) in presence of As(V) and F(-) from aqueous media as pollutants of drinking water.

PubMed

Olguín, María Teresa; Deng, Shuguang

2016-01-25

The sorption behavior of the Ba(2+)-like (226)Ra(2+) in the presence of H2AsO4(-)/HAsO4(2-) and F(-) from aqueous media using Ce-Fe-modified zeolite-rich tuff was investigated in this work. The Na-modified zeolite-rich tuff was also considered for comparison purposes. The zeolite-rich tuff collected from Wyoming (US) was in contact with NaCl and CeCl3-FeCl3 solutions to obtain the Na- and Ce-Fe-modified zeolite-rich tuffs (ZUSNa and ZUSCeFe). These zeolites were characterized by scanning electron microscopy and X-ray diffraction. The BET-specific surface and the points of zero charge were determined as well as the content of Na, Ce and Fe by neutron activation analysis. The textural characteristics and the point of zero charge were changed by the presence of Ce and Fe species in the zeolitic network. A linear model described the Ba(2+)-like (226)Ra(2+) sorption isotherms and the distribution coefficients (Kd) varied with respect to the metallic species present in the zeolitic material. The As(V) oxianionic chemical species and F(-) affected this parameter when the Ba(2+)-like (226)Ra(2+)-As(V)-F(-) solutions were in contact with ZUSCeFe. The H2AsO4(-)/HAsO4(2-) and F(-) were adsorbed by ZUSCeFe in the same amount, independent of the concentration of Ba(2+)-like (226)Ra(2+) in the initial solution. Copyright © 2015 Elsevier B.V. All rights reserved.

Pleistocene hydrovolcanism in the Tule Lake Basin, N. E. California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavine, A.

1993-04-01

The Prisoners Rock and The Peninsula tuff cones and the North Crater tuff ring, located in the Tule Lake Basin of northeastern California formed along a north-trending fissure approximately 270 ka when basaltic magma interacted with abundant groundwater or shallow lake water, resulting in phreatomagmatic eruptions. Diatomite inclusions in the tuff ring and correlations with the corresponding depth and diatoms in a drill core taken in the center of the basin, 2.5 km to the west of the cones, indicate shallow, marshy or shallow, alkaline-open conditions at Tule Lake around 270 ka. Deposits at Prisoners Rock and The Peninsula indicatemore » subaerial emplacement, which allowed the deposits to lithify with little erosion by the lake. Subsequent wave erosion caused undercutting and breaking off of large blocks along mainly north-trending fractures forming vertical cliff faces on the east and west sides of the cones. The cones are elongated north-south with a greater thickness of deposits on the north and northeast, probably due to prevailing southwesterly winds at the time of eruptions. Deposits of the tuff cones at Prisoners Rock and The Peninsula resulted from deep explosions caused by water-magma ratios of around 3:1. The deposits are mainly inversely graded planar surge beds, ranging in thickness from 5 to 30 cm, and grading from very fine ash to 2 cm-diameter accretionary lapilli. Emplacement by highly steam-saturated, poorly inflated pyroclastic surges is indicated by the abundance of accretionary lapilli, vesiculated tuffs, soft-sediment deformation structures, steep bedding angles (20 to 40 degrees) lack of structures beneath country rock inclusions, massive bedding, and cementation of the deposits by alteration of basaltic glass to calcite, zeolites, clays, and chlorite.« less

A tuff cone erupted under frozen-bed ice (northern Victoria Land, Antarctica): linking glaciovolcanic and cosmogenic nuclide data for ice sheet reconstructions

NASA Astrophysics Data System (ADS)

Smellie, J. L.; Rocchi, S.; Johnson, J. S.; Di Vincenzo, G.; Schaefer, J. M.

2018-01-01

The remains of a small volcanic centre are preserved on a thin bedrock ridge at Harrow Peaks, northern Victoria Land, Antarctica. The outcrop is interpreted as a monogenetic tuff cone relict formed by a hydrovolcanic (phreatomagmatic) eruption of mafic magma at 642 ± 20 ka (by 40Ar-39Ar), corresponding to the peak of the Marine Isotope Stage 16 (MIS16) glacial. Although extensively dissected and strewn with glacial erratics, the outcrop shows no evidence for erosion by ice. From interpretation of the lithofacies and eruptive mechanisms, the weight of the evidence suggests that eruptions took place under a cold-based (frozen-bed) ice sheet. This is the first time that a tuff cone erupted under cold ice has been described. The most distinctive feature of the lithofacies is the dominance of massive lapilli tuff rich in fine ash matrix and abraded lapilli. The lack of stratification is probably due to repeated eruption through a conduit blasted through the ice covering the vent. The ice thickness is uncertain but it might have been as little as 100 m and the preserved tephra accumulated mainly as a crater (or ice conduit) infill. The remainder of the tuff cone edifice was probably deposited supraglacially and underwent destruction by ice advection and, particularly, collapse during a younger interglacial. Dating using 10Be cosmogenic exposure of granitoid basement erratics indicates that the erratics are unrelated to the eruptive period. The 10Be ages suggest that the volcanic outcrop was most recently exposed by ice decay at c. 20.8 ± 0.8 ka (MIS2) and the associated ice was thicker than at 642 ka and probably polythermal rather than cold-based, which is normally assumed for the period.

Paleogeographic insights based on new U-Pb dates for altered tuffs in the Miocene Barstow Formation, California

USGS Publications Warehouse

Miller, David; Rosario, Jose E.; Leslie, Shannon R.; Vazquez, Jorge A.

2013-01-01

The type section of the Barstow Formation in the Mud Hills, north of Barstow, is a reference section for early to middle Miocene paleontology, magnetostratigraphy, and dated volcanic episodes. Thanks to this robust chronologic framework, much of the interpretation of the paleogeography of the region from about 18 Ma to 13 Ma is based on study of the rocks in the Mud Hills. Eastward from the type section, the Barstow Formation typically is altered and structurally complex, and therefore it is hard to fit into the patterns inferred for sedimentation at the type section. We have studied ten tuff beds in five locations, extracting zircons that are partly eruptive components of the volcanic ash and partly detrital. Ion microprobe dating of the zircons associated with the ashes allows us to improve stratigraphic correlations. Dated tuffs range from 19.3 Ma to ~14.8 Ma. In several of the sections, we dated tuffs in the range 16.2-16.5 Ma, about the same age as the ~16.3 Ma Rak Tuff in the type section. The beginning of lacustrine limestone, shale, and siltstone deposition varies significantly, from ~16.3 Ma in the type section to ~18.5 Ma in hills to the east and the Calico Mountains, and greater than 19.3 Ma at Harvard Hill. At ~16.3 Ma, the sedimentary rocks ranged (west to east) from silty sandstone and limestone, to mudstone with gypsum, to massive mudstone, and then to sandstone. If the sections have not been greatly shuffled by subsequent faulting, the picture that emerges is one of a broad basin whose center near the Yermo Hills was occupied by a lake that was much longer lived and deeper than to the east and west.

Studies of the mobility of uranium and thorium in Nevada Test Site tuff

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wollenberg, H.A.; Flexser, S.; Smith, A.R.

1991-06-01

Hydro-geochemical processes must be understood if the movement of radionuclides away from a breached radioactive waste canister is to be modeled and predicted. In this respect, occurrences of uranium and thorium in hydrothermal systems are under investigation in tuff and in rhyolitic tuff that was heated to simulate the effects of introduction of radioactive waste. In these studies, high-resolution gamma spectrometry and fission-track radiography are coupled with observations of alteration mineralogy and thermal history to deduce the evidence of, or potential for movement of, U and Th in response to the thermal environment. Observations to date suggest that U wasmore » mobile in the vicinity of the heater but that localized reducing environments provided by Fe-Ti-Mn-oxide minerals concentrated U and thus attenuated its migration.« less

Salt efflorescence due to water-rock interaction on the surface of tuff cave in the Yoshimi-Hyakuana Historic Site, central Japan

NASA Astrophysics Data System (ADS)

Oguchi, Chiaki T.; Kodama, Shogo; Mohammad, Rajib; Tharanga Udagedara, Dashan

2016-04-01

Artificial cave walls in Yoshimi Hyakuana Historic Site have been suffering from salt weathering since 1945 when the caves were made. To consider the processes of weathering and subsequent crystallization of secondary minerals, water-rock experiment using tuff from this area was performed. Rocks, surface altered materials, groundwater and rainwater were collected, and chemical and mineralogical characteristics of those samples were investigated. The XRD and SEM-EDS analyses were carried out for the solid samples and ICP-OES analysis was performed for the solution generated from the experiment, groundwater and rainwater. Gypsum is detected in original tuff, and on grey and whiter coloured altered materials. General chemical changes were observed on this rock. However, it is found that purple and black altered materials were mainly made due to microbiological processes.

[sup 40]Ar/[sup 39]Ar ages of Challis volcanic rocks and the initiation of Tertiary sedimentary basins in southwestern Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

M'Gonigle, J.W.; Dalrymple, G.B.

1993-10-01

[sup 40]Ar/[sup 39]Ar ages on single sanidine crystals from rhyolitic tuffs and ash flow tuffs within the uppermost and lowermost parts of the volcanic sequence of the Horse Prairie and Medicine Lodge topographic basins, southwestern Montana, show that these volcanic rocks were emplaced between about 48.8[+-]0.2 Ma and 45.9[+-]0.2 Ma, and are correlative with the Eocene Challis Volcanic Group of central Idaho. Sanidine ages on tuffs at the base of the Tertiary lacustrine, paludal, and fluvial sedimentary sequence, which unconformably overlies the volcanic sequence, suggest that sedimentation within an ancestral sedimentary basin that predated the development of the modern Horsemore » Prairie and Medicine Lodge basins began in the middle Eocene. 22 refs., 3 figs., 2 tabs.« less

Synchronism of the Siberian Traps and the Permian-Triassic boundary

USGS Publications Warehouse

Campbell, I.H.; Czamanske, G.K.; Fedorenko, V.A.; Hill, R.I.; Stepanov, V.

1992-01-01

Uranium-lead ages from an ion probe were taken for zircons from the ore-bearing Noril'sk I intrusion that is comagmatic with, and intrusive to, the Siberian Traps. These values match, within an experimental error of ??4 million years, the dates for zircons extracted from a tuff at the Permian-Triassic (P-Tr) boundary. The results are consistent with the hypothesis that the P-Tr extinction was caused by the Siberian basaltic flood volcanism. It is likely that the eruption of these magmas was accompanied by the injection of large amounts of sulfur dioxide into the upper atmosphere, which may have led to global cooling and to expansion of the polar ice cap. The P-Tr extinction event may have been caused by a combination of acid rain and global cooling as well as rapid and extreme changes in sea level resulting from expansion of the polar ice cap.

Geohydrology of volcanic tuff penetrated by test well UE-25b#1, Yucca Mountain, Nye County, Nevada

USGS Publications Warehouse

Lahoud, R.G.; Lobmeyer, D.H.; Whitfield, M.S.

1984-01-01

Test well UE-25bNo1, located on the east side of Yucca Mountain in the southwestern part of the Nevada Test Site, was drilled to a total depth of 1,220 meters and hydraulically tested as part of a program to evaluate the suitability of Yucca Mountain as a nuclear-waste repository. The well penetrated almost 46 meters of alluvium and 1,174 meters of Tertiary volcanic tuffs. The composite hydraulic head for aquifers penetrated by the well was 728.9 meters above sea level (471.4 meters below land surface) with a slight decrease in loss of hydraulic head with depth. Average hydraulic conductivities for stratigraphic units determined from pumping tests, borehole-flow surveys, and packer-injection tests ranged from less than 0.001 meter per day for the Tram Member of the Crater Flat Tuff to 1.1 meters per day for the Bullfrog Member of the Crater Flat Tuff. The small values represented matrix permeability of unfractured rock; the large values probably resulted from fracture permeability. Chemical analyses indicated that the water is a soft sodium bicarbonate type, slightly alkaline, with large concentrations of dissolved silica and sulfate. Uncorrected carbon-14 age dates of the water were 14,100 and 13,400 years. (USGS)

Preliminary report on the geology and geophysics of drill hole UE25a-1, Yucca Mountain, Nevada Test Site

USGS Publications Warehouse

Spengler, Richard W.; Muller, D.C.; Livermore, R.B.

1979-01-01

A subsurface geologic study in connection with the Nevada Nuclear Waste Storage Investigations has furnished detailed stratigraphic and structural information about tuffs underlying northeastern Yucca Mountain on the Nevada Test Site. Drill hole UE25a-1 penetrated thick sequences of nonwelded to densely welded ash-flow and bedded tuffs of Tertiary age. Stratigraphic units that were identified from the drill-hole data include the Tiva Canyon and Topopah Spring Members of the Paintbrush Tuff, tuffaceous beds of Calico Hills, and the Prow Pass and Bullfrog Members of the Crater Flat Tuff. Structural analysis of the core indicated densely welded zones to be highly fractured. Many fractures show near-vertical inclinations and are commonly coated with secondary silica, manganese and iron oxides, and calcite. Five fault zones were recognized, most of which occurred in the Topopah Spring Member. Shear fractures commonly show oblique-slip movement and some suggest a sizable component of lateral compression. Graphic logs are included that show the correlation of lithology, structural properties, and geophysical logs. Many rock units have characteristic log responses but highly fractured zones, occurring principally in the Tiva Canyon and Topopah Spring Members, restricted log coverage to the lower half of the drill hole.

Radionuclide gas transport through nuclear explosion-generated fracture networks

DOE PAGES

Jordan, Amy B.; Stauffer, Philip H.; Knight, Earl E.; ...

2015-12-17

Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gasmore » breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. In conclusion, seasonal and location-based effects on breakthrough, which occur due to differences in barometric forcing, are stronger where the barometric signal is highly variable.« less

Removal and recovery of p-phenylenediamines developing compounds from photofinishing lab-washwater using clinoptilolite tuffs from Greece.

PubMed

Vlessidis, A G; Triantafillidis, C S; Evmiridis, N P

2001-04-01

Clinoptilolite tuffs from areas in Thrace region of Greece are compared with synthetic zeolites NaY and NH4Y for the uptake of N4-ethyl-N4-(2-methansulphonamidoethyl)-2-methyl-1,4-phenylenediamin (sesquisulphate, monohydrate) with the trade name CD-3 for the purpose to be used for clean-up and recycling photo-finishing and photo-developing washwaters. The cation-exchange capacity is found to be 6.15-11.1 mg/g for zeoliferous tuffs at equilibrium concentration of 50 ppm CD-3 in aqueous solution compared to 65.0 mg/g of NaY and 48.2 mg/g for NH4Y synthetic zeolites corresponding to the removal of CD-3 from 120 to 2001 of 50 ppm aqueous solution per kg of natural zeoliferous tuff; this capacity is only 6-10 times lower than type-Y synthetic zeolite. Initial rates of uptake are 20.8 mg/l/min for natural and 38.5 mg/l/min for synthetic zeolites. Regeneration levels of 55, 23, 35, and 33% are obtained for MCH, SF, NaY, and NH4Y, respectively. The rapid and almost complete uptake of CD-3 from its aqueous solutions at low CD-3 concentrations by the natural zeolites is promising for such an application.

Radionuclide gas transport through nuclear explosion-generated fracture networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jordan, Amy B.; Stauffer, Philip H.; Knight, Earl E.

Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gasmore » breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. In conclusion, seasonal and location-based effects on breakthrough, which occur due to differences in barometric forcing, are stronger where the barometric signal is highly variable.« less

Sonication Enables Effective Iron Leaching from Green Tuff at Low Temperature

NASA Astrophysics Data System (ADS)

Nakamura, Takashi; Okawa, Hirokazu; Kawamura, Youhei; Sugawara, Katsuyasu

2011-07-01

Ultrasound irradiation (28 and 200 kHz) was applied to iron leaching from green tuff into a low temperature solution (20 °C) using oxalic acid. Ultrasound irradiation increased the amount of iron leached from the green tuff and was greater than that leached by stirring. It is thought that the jet flow caused by the collapse of cavities during ultrasound irradiation prevents and strips the deposits of iron oxalate from the green tuff particles. The extraction of iron at 28 kHz displayed better performance than that at 200 kHz for three reasons. The first is that the jet flow generated by cavitation bubble collapse at 28 kHz is thought to be stronger than that at 200 kHz. The second is that the crushing action of ultrasound irradiation at 28 kHz is greater than that at 200 kHz. The third is that 200 kHz irradiation generates OH radicals, which prevents the generation of FeH(C2O4)+ and oxidizes FeH(C2O4)+ to Fe(C2O4), creating a cover layer on the surface of the stone. Thus, to leach iron from the ore, it is effective to use ultrasound irradiation at 28 kHz, which prevents the creation of radicals and breaks down the grain size.

Yucca Mountain Project Subsurface Facilities Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

A. Linden; R.S. Saunders; R.J. Boutin

2002-11-19

Four units of the Topopah Springs formation (volcanic tuff) are considered for the proposed repository: the upper lithophysal, the middle non-lithophysal, the lower lithophysal, and the lower non-lithophysal. Yucca Mountain was recently designated the site for a proposed repository to dispose of spent nuclear fuel and high-level radioactive waste. Work is proceeding to advance the design of subsurface facilities to accommodate emplacing waste packages in the proposed repository. This paper summarized recent progress in the design of subsurface layout of the proposed repository. The original Site Recommendation (SR) concept for the subsurface design located the repository largely within the lowermore » lithophysal zone (approximately 73%) of the Topopah The Site Recommendation characterized area suitable for emplacement consisted of the primary upper block, the lower block and the southern upper block extension. The primary upper block accommodated the mandated 70,000 metric tons of heavy metal (MTHM) at a 1.45 kW/m hear heat load. Based on further study of the Site Recommendation concept, the proposed repository siting area footprint was modified to make maximum use of available site characterization data, and thus, reduce uncertainties associated with performance assessment. As a result of this study, a modified repository footprint has been proposed and is presently being review for acceptance by the DOE. A panel design concept was developed to reduce overall costs and reduce the overall emplacement schedule. This concept provides flexibility to adjust the proposed repository subsurface layout with time, as it makes it unnecessary to ''commit'' to development of a large single panel at the earliest stages of construction. A description of the underground layout configuration and influencing factors that affect the layout configuration are discussed in the report.« less

The Tunas Formation (Permian) in the Sierras Australes foldbelt, east central Argentina: evidence for syntectonic sedimentation in a foreland basin

NASA Astrophysics Data System (ADS)

Lopez-Gamundi, O. R.; Conaghan, P. J.; Rossello, E. A.; Cobbold, P. R.

1995-04-01

The Tunas Formation, extensively exposed in the Sierras Australes foldbelt of eastern central Argentina, completes the sedimentation of the Gondwanan (Late Carboniferous-Permian) sequence, locally known as the Pillahuincó Group. The underlying units of the Group show an integrated depositional history which can be explained in terms of glaciomarine sedimentation (Sauce Grande Formation) and postglacial transgression (Piedra Azul and Bonete Formations). This succession also has a rather uniform quartz-rich, sand-sized composition indicative of a cratonic provenance from the Tandilia Massif to the northeast. Early to Late Permian deformation folded and thrusted the southwestern basin margin (Sierras Australes) and triggered the deposition of a 1,500 m — thick, synorogenic prograding wedge, the Tunas Formation, in the adjacent foreland basin (Sauce Grande or Claromecó Basin). Sandstone detrital modes for the Tunas deposits show moderate to low contents of quartz and abundant lithics, mostly of volcanic and metasedimentary origin. Paleocurrents are consistently from the SW. Tuffs interbedded with sandstones in the upper half of Tunas Formation (Early — early Late? Permian) are interpreted as being derived from volcanic glass-rich tuffs settled in a body of water. Extensive rhyolitic ignimbrites and consanguineous airborne tuffaceous material erupted in the northern Patagonian region during that period. The age constraints and similarities in composition between these volcanics and the tuffaceous horizons present in the Sauce Grande, Parana and Karoo Basins suggest a genetic linkage between these two episodes. The intimate relationship between volcanic activity inboard of the paleo-Pacific margin, deformation in the adjacent orogenic belt and subsidence and sedimentation in the contiguous foreland basin constitutes a common motif in the Sauce Grande and Karoo Basins of southwestern Gondwana.

Pressurized Slot Testing to Determine Thermo-Mechanical Properties of Lithophysal Tuff at Yucca Mountain Nevada.

DOE Office of Scientific and Technical Information (OSTI.GOV)

George, James T.; Sobolik, Steven R.; Lee, Moo Y.

The study described in this report involves heated and unheated pressurized slot testing to determine thermo-mechanical properties of the Tptpll (Tertiary, Paintbrush, Topopah Spring Tuff Formation, crystal poor, lower lithophysal) and Tptpul (upper lithophysal) lithostratigraphic units at Yucca Mountain, Nevada. A large volume fraction of the proposed repository at Yucca Mountain may reside in the Tptpll lithostratigraphic unit. This unit is characterized by voids, or lithophysae, which range in size from centimeters to meters, making a field program an effective method of measuring bulk thermal-mechanical rock properties (thermal expansion, rock mass modulus, compressive strength, time-dependent deformation) over a range ofmore » temperature and rock conditions. The field tests outlined in this report provide data for the determination of thermo-mechanical properties of this unit. Rock-mass response data collected during this field test will reduce the uncertainty in key thermal-mechanical modeling parameters (rock-mass modulus, strength and thermal expansion) for the Tptpll lithostratigraphic unit, and provide a basis for understanding thermal-mechanical behavior of this unit. The measurements will be used to evaluate numerical models of the thermal-mechanical response of the repository. These numerical models are then used to predict pre- and post-closure repository response. ACKNOWLEDGEMENTS The authors would like to thank David Bronowski, Ronnie Taylor, Ray E. Finley, Cliff Howard, Michael Schuhen (all SNL) and Fred Homuth (LANL) for their work in the planning and implementation of the tests described in this report. This is a reprint of SAND2004-2703, which was originally printed in July 2004. At that time, it was printed for a restricted audience. It has now been approved for unlimited release.« less

Volcaniclastic dykes tell on fracturing, explosive eruption and lateral collapse at Stromboli volcano (Italy)

NASA Astrophysics Data System (ADS)

Vezzoli, Luigina; Corazzato, Claudia

2016-05-01

In the upper part of the Stromboli volcano, in the Le Croci and Bastimento areas, two dyke-like bodies of volcanic breccia up to two-metre thick crosscut and intrude the products of Vancori and Neostromboli volcanoes. We describe the lithofacies association of these unusual volcaniclastic dykes, interpret the setting of dyke-forming fractures and the emplacement mechanism of internal deposits, and discuss their probable relationships with the explosive eruption and major lateral collapse events that occurred at the end of the Neostromboli period. The dyke volcaniclastic deposits contain juvenile magmatic fragments (pyroclasts) suggesting a primary volcanic origin. Their petrographic characteristics are coincident with the Neostromboli products. The architecture of the infilling deposits comprises symmetrically-nested volcaniclastic units, separated by sub-vertical boundaries, which are parallel to the dyke margins. The volcanic units are composed of distinctive lithofacies. The more external facies is composed of fine and coarse ash showing sub-vertical laminations, parallel to the contact wall. The central facies comprises stratified, lithic-rich breccia and lapilli-tuff, whose stratification is sub-horizontal and convolute, discordant to the dyke margins. Only at Le Croci dyke, the final unit shows a massive tuff-breccia facies. The volcaniclastic dykes experienced a polyphasic geological evolution comprising three stages. The first phase consisted in fracturing, explosive intrusion related to magma rising and upward injection of magmatic fluids and pyroclasts. The second phase recorded the dilation of fractures and their role as pyroclastic conduits in an explosive eruption possibly coeval with the lateral collapse of the Neostromboli lava cone. Finally, in the third phase, the immediately post-eruption mass-flow remobilization of pyroclastic deposits took place on the volcano slopes.

Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

NASA Astrophysics Data System (ADS)

Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

2016-12-01

Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

Multiscalar approach to archaeological site formation at GaJj17, East Turkana, Kenya

NASA Astrophysics Data System (ADS)

Murray, B. M.; Ranhorn, K. L.; Colarossi, D.; Mavuso, S. S.; Dogandžić, T.; Ziegler, M. J.; Warren, S. L.; Braun, D. R.; Harris, J. W. K.

2017-12-01

Kenya's East Turkana region hosts a rich Plio­Pleistocene record of fossils, archaeological artifacts, and sedimentary features whose chronostratigraphic histories are often obscured by landscape changes from erosional events and tectonic activity. The Middle Stone Age (MSA) record of the Koobi Fora Formation (KF Fm.) has particularly been subjected to this complex depositional history, making it a sparse unit and, consequently, widely understudied. Stratigraphically located in between the maximum capping unconformity of the KF Fm.'s Chari tuff ( 1.39 Ma) and that of the Galana Boi Fm. ( 10 ka), the unit provides a unique window into understanding the Late Pleistocene of the region. The MSA surface scatters at archaeological site GaJj17 prompted further study into the site's age and depositional chronology. The GaJj17 ridge is locally distinguished by its cap of Late Pleistocene sands overlying strata containing tuffs likely of the Upper Burgi (2.0­-1.87 Ma) or KBS (1.87­-1.56 Ma) members. To investigate whether GaJj17's preservation is due to tectonic deformation, a broader scale examination of the structural geology was conducted through surveys and aerial imagery. Regions of deformation were identified and mapped to establish the geological history of the locality. Resultant observations and elevation data offer insight into regional faults at the root of prolonged structural alterations which have facilitated the unique preservation of MSA materials. Through a multiscalar approach it is possible to understand both the formation of GaJj17 and the underlying processes behind preservation and destruction in the changing landscape of the Turkana basin, enabling future identification of archaeological sites through proxies of elevation, regional stratigraphy, and fault mapping. This research was supported by IRES grants 1358178 and 1358200 from the U.S. National Science Foundation.

A strategy to seal exploratory boreholes in unsaturated tuff; Yucca Mountain Site Characterization Project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fernandez, J.A.; Case, J.B.; Givens, C.A.

1994-04-01

This report presents a strategy for sealing exploratory boreholes associated with the Yucca Mountain Site Characterization Project. Over 500 existing and proposed boreholes have been considered in the development of this strategy, ranging from shallow (penetrating into alluvium only) to deep (penetrating into the groundwater table). Among the comprehensive list of recommendations are the following: Those boreholes within the potential repository boundary and penetrating through the potential repository horizon are the most significant boreholes from a performance standpoint and should be sealed. Shallow boreholes are comparatively insignificant and require only nominal sealing. The primary areas in which to place sealsmore » are away from high-temperature zones at a distance from the potential repository horizon in the Paintbrush nonwelded tuff and the upper portion of the Topopah Spring Member and in the tuffaceous beds of the Calico Hills Unit. Seals should be placed prior to waste emplacement. Performance goals for borehole seals both above and below the potential repository are proposed. Detailed construction information on the boreholes that could be used for future design specifications is provided along with a description of the environmental setting, i.e., the geology, hydrology, and the in situ and thermal stress states. A borehole classification scheme based on the condition of the borehole wall in different tuffaceous units is also proposed. In addition, calculations are presented to assess the significance of the boreholes acting as preferential pathways for the release of radionuclides. Design calculations are presented to answer the concerns of when, where, and how to seal. As part of the strategy development, available technologies to seal exploratory boreholes (including casing removal, borehole wall reconditioning, and seal emplacement) are reviewed.« less

A ground-based magnetic survey of Frenchman Flat, Nevada National Security Site and Nevada Test and Training Range, Nevada: data release and preliminary interpretation

USGS Publications Warehouse

Phillips, Jeffrey D.; Burton, Bethany L.; Curry-Elrod, Erika; Drellack, Sigmund

2014-01-01

Question 2—Does basin and range normal faulting observed in the hills north of Frenchman Flat continue southward under alluvium and possibly disrupt the Topopah Spring Tuff of the Paintbrush Group (the Topopah Spring welded tuff aquifer or TSA) east of the Pin Stripe underground nuclear test, which was conducted in Emplacement hole U11b?

Drill-back studies examine fractured, heated rock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wollenberg, H.A.; Flexser, S.; Myer, L.R.

1990-01-01

To investigate the effects of heating on the mineralogical, geochemical, and mechanical properties of rock by high-level radioactive waste, cores are being examined from holes penetrating locations where electric heaters simulated the presence of a waste canister, and from holes penetration natural hydrothermal systems. Results to date indicate the localized mobility and deposition of uranium in an open fracture in heated granitic rock, the mobility of U in a breccia zone in an active hydrothermal system in tuff, and the presence of U in relatively high concentration in fracture-lining material in tuff. Mechanical -- property studies indicate that differences inmore » compressional- and shear-wave parameters between heated and less heated rock can be attributed to differences in the density of microcracks. Emphasis has shifted from initial studies of granitic rock at Stripa, Sweden to current investigations of welded tuff at the Nevada Test Site. 7 refs., 8 figs.« less

Oligocene lacustrine tuff facies, Abu Treifeya, Cairo-Suez Road, Egypt

NASA Astrophysics Data System (ADS)

Abdel-Motelib, Ali; Kabesh, Mona; El Manawi, Abdel Hamid; Said, Amir

2015-02-01

Field investigations in the Abu Treifeya area, Cairo-Suez District, revealed the presence of Oligocene lacustrine volcaniclastic deposits of lacustrine sequences associated with an Oligocene rift regime. The present study represents a new record of lacustrine zeolite deposits associated with saponite clay minerals contained within reworked clastic vitric tuffs. The different lithofacies associations of these clastic sequences are identified and described: volcaniclastic sedimentary facies represent episodic volcaniclastic reworking, redistribution and redeposition in a lacustrine environment and these deposits are subdivided into proximal and medial facies. Zeolite and smectite minerals are mainly found as authigenic crystals formed in vugs or crusts due to the reaction of volcanic glasses with saline-alkaline water or as alteration products of feldspars. The presence of abundant smectite (saponite) may be attributed to a warm climate, with alternating humid and dry conditions characterised by the existence of kaolinite. Reddish iron-rich paleosols record periods of non-deposition intercalated with the volcaniclastic tuff sequence.

Influence of temperature on the adsorption of α-tocopherol from ethanol solutions on acid-activated clinoptilolite tuff

NASA Astrophysics Data System (ADS)

Kotova, D. L.; Vasilyeva, S. Yu.; Krysanova, T. A.

2014-08-01

Patterns in the adsorption of α-tocopherol on acid-activated clinoptilolite tuff at 283, 295, 305, and 333 K are established and explained. It is found that the selectivity of the sorbent toward the vitamin rises as the temperature of the process falls. The adsorption of α-tocopherol from dilute solutions is described in terms of the Langmuir adsorption theory. It is shown that the fixing of vitamin E monolayers in the structural matrix of clinoptilolite tuff is due to the formation of hydrogen bonds between isolated silanol groups of the adsorbent and oxygen atoms of the chromane ring and the phenol residue of α-tocopherol. The thermodynamic functions of monolayer adsorption of the vitamin are estimated. It is concluded that the formation of polymolecular layers in the form of associates is due to hydrophobic interactions between side substituents of α-tocopherol.

Diatreme evolution during the phreatomagmatic eruption of the Songaksan tuff ring, Jeju Island, Korea

NASA Astrophysics Data System (ADS)

Go, S. Y.; Kim, G. B.; Jeong, J. O.; Sohn, Y. K.

2017-03-01

The Songaksan tuff ring, Jeju Island, Korea, which erupted ca. 3.7 ka BP in a coastal setting, provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well-preserved ejecta beds and well-known subsurface geology. The tuff sequence can be divided into four units (A to D), which have distinctly different accidental componentry (quartz-rich vs. quartz-poor), grain surface features (abraded and ash-coated vs. unabraded and uncoated), and chemical compositions of juvenile particles. The basal tephra bed of unit A, which probably erupted after the removal of the relatively hard shallow-level (<120 m deep) substrate by initial cratering, comprises only unabraded and uncoated grains and contains abundant relatively deep-derived (>120 m deep) accidental grains, suggesting that the early erupted tephra had not yet experienced recycling and pre-eruption mixing in the diatreme. On the other hand, the overlying tephra beds of units A, B, and D contain an abundance of abraded and ash-coated juvenile/accidental grains, suggesting that the tephra comprised significant proportions of "recycled" or "premixed" materials from previous eruptions or subsurface explosions, which participated in the explosion-driven mixing in the diatreme before eventual ejection from the diatreme. Unit C is unusual in that it comprises extremely rare accidental grains and ash-coated juvenile/accidental grains. We interpret that the supply of solid materials, either accidental or juvenile, to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme. The diatreme is therefore envisaged to have been filled with a water-saturated slurry, in which particle abrasion and adhesion were inhibited. We also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit C on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit C. The ratio of tachylite to sideromelane grains generally increases up-section of the tuff sequence with two abrupt drops across the tuff unit boundaries. These variations are coincident with the changes in the chemical composition of juvenile particles, suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches. The textural and compositional variations of the Songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring, including removal and renewal of the diatreme fill, and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust.

Uranium-series disequilibrium in tuffs from Yucca Mountain, Nevada, as evidence of pore-fluid flow over the last million years

USGS Publications Warehouse

Gascoyne, M.; Miller, N.H.; Neymark, L.A.

2002-01-01

Samples of tuff from boreholes drilled into fault zones in the Exploratory Studies Facility (ESF) and relatively unfractured rock of the Cross Drift tunnels, at Yucca Mountain, Nevada, have been analysed by U-series methods. This work is part of a project to verify the finding of fast flow-paths through the tuff to ESF level, indicated by the presence of 'bomb' 36Cl in pore fluids. Secular radioactive equilibrium in the U decay series, (i.e. when the radioactivity ratios 234U/238U, 230Th/234U and 226Ra/230Th all equal 1.00) might be expected if the tuff samples have not experienced radionuclide loss due to rock-water interaction occurring within the last million years. However, most fractured and unfractured samples were found to have a small deficiency of 234U (weighted mean 234U/238U=0.95??0.01) and a small excess of 230Th (weighted mean 230Th/234U 1.10??0.02). The 226Ra/230Th ratios are close to secular equilibrium (weighted mean = 0.94??0.07). These data indicate that 234U has been removed from the rock samples in the last ???350 ka, probably by pore fluids. Within the precision of the measurement, it would appear that 226Ra has not been mobilized and removed from the tuff, although there may be some localised 226Ra redistribution as suggested by a few ratio values that are significantly different from 1.0. Because both fractured and unfractured tuffs show approximately the same deficiency of 234U, this indicates that pore fluids are moving equally through fractured and unfractured rock, More importantly, fractured rock appears not to be a dominant pathway for groundwater flow (otherwise the ratio would be more strongly affected and the Th and Ra isotopic ratios would likely also show disequilibrium). Application of a simple mass-balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at ESF level is about 400 a. Processes of U sorption, precipitation and re-solution are believed to be occurring and would account for these anomalous results but have not been included in the model. Despite the difficulties, the U-series data suggest that fractured rock, specifically the Sundance and Drill Hole Wash faults, are not preferred flow paths for groundwater flowing through the Topopah Spring tuff and, by implication, rapid-flow, within 50 a, from the surface to the level of the ESF is improbable. ?? 2002 Elsevier Science Ltd. All rights reserved.

Geologic map and upper Paleozoic stratigraphy of the Marble Canyon area, Cottonwood Canyon quadrangle, Death Valley National Park, Inyo County, California

USGS Publications Warehouse

Stone, Paul; Stevens, Calvin H.; Belasky, Paul; Montañez, Isabel P.; Martin, Lauren G.; Wardlaw, Bruce R.; Sandberg, Charles A.; Wan, Elmira; Olson, Holly A.; Priest, Susan S.

2014-01-01

This geologic map and pamphlet focus on the stratigraphy, depositional history, and paleogeographic significance of upper Paleozoic rocks exposed in the Marble Canyon area in Death Valley National Park, California. Bedrock exposed in this area is composed of Mississippian to lower Permian (Cisuralian) marine sedimentary rocks and the Jurassic Hunter Mountain Quartz Monzonite. These units are overlain by Tertiary and Quaternary nonmarine sedimentary deposits that include a previously unrecognized tuff to which we tentatively assign an age of late middle Miocene (~12 Ma) based on tephrochronologic analysis, in addition to the previously recognized Pliocene tuff of Mesquite Spring. Mississippian and Pennsylvanian rocks in the Marble Canyon area represent deposition on the western continental shelf of North America. Mississippian limestone units in the area (Tin Mountain, Stone Canyon, and Santa Rosa Hills Limestones) accumulated on the outer part of a broad carbonate platform that extended southwest across Nevada into east-central California. Carbonate sedimentation was interrupted by a major eustatic sea-level fall that has been interpreted to record the onset of late Paleozoic glaciation in southern Gondwana. Following a brief period of Late Mississippian clastic sedimentation (Indian Springs Formation), a rise in eustatic sea level led to establishment of a new carbonate platform that covered most of the area previously occupied by the Mississippian platform. The Pennsylvanian Bird Spring Formation at Marble Canyon makes up the outer platform component of ten third-order (1 to 5 m.y. duration) stratigraphic sequences recently defined for the regional platform succession. The regional paleogeography was fundamentally changed by major tectonic activity along the continental margin beginning in middle early Permian time. As a result, the Pennsylvanian carbonate shelf at Marble Canyon subsided and was disconformably overlain by lower Permian units (Osborne Canyon and Darwin Canyon Formations) representing part of a deep-water turbidite basin filled primarily by fine-grained siliciclastic sediment derived from cratonal sources to the east. Deformation and sedimentation along the western part of this basin continued into late Permian time. The culminating phase was part of a regionally extensive late Permian thrust system that included the Marble Canyon thrust fault just west of the present map area.

Regional stratigraphy, sedimentology, and tectonic significance of Oligocene-Miocene sedimentary and volcanic rocks, northern Baja California, Mexico

NASA Astrophysics Data System (ADS)

Dorsey, Rebecca J.; Burns, Beverly

1994-01-01

Upper Oligocene (?) to middle Miocene sedimentary and volcanic rocks in northern Baja California were deposited along the western margin of North America during subduction of the Guadalupe plate and southward migration of the Rivera Triple Junction. Regional mapping and compilation of stratigraphic data reveal a sequence of three regionally traceable stratigraphic units. (1) Oligocene (?) to lower Miocene Mesa Formation: basal quartz-rich fluvial sandstone, grus, conglomerate, and accessory facies, whose detrital compositions reflect the composition of local pre-Tertiary basement rock. (2) Lower to middle Miocene Comondú Formation: laterally variable sequence of volcaniclastic conglomerate, breccia, sandstone, tuff and minor volcanic flow units. (3) Widespread mesa-capping rhyolite tuff, typically welded and crystal-rich, probably upper Miocene in age. The Mesa Formation overlies a highly irregular and deeply dissected erosional surface developed on pre-Tertiary basement rock. The shift from pre-Mesa erosion to widespread (though localized) deposition and valley-filling records the final phase of late Cretaceous to middle Tertiary regional subsidence and eastward transgression that resulted from slow cooling and thermal contraction of Cretaceous arc crust during a temporal gap in magmatic activity along the western Cordilleran margin. Nonmarine sediments of the Mesa Formation were deposited in small, steep-walled paleovalleys and basins that gradually filled and evolved to form through-going, low-energy ephemeral stream systems. The gradational upward transition from the Mesa to Comondú Formation records the early to middle Miocene onset of subduction-related arc magmatism in eastern Baja California and related westward progradation of alluvial volcaniclastic aprons shed from high-standing eruptive volcanic centers. Pre-existing streams were choked with the new influx of volcanic detritus, causing the onset of rapid sediment deposition by stream flows and dilute to viscous sediment gravity flows. Deposits of the Comondú Formation thin and fine systematically westward, from proximal volcanic conglomerate and breccia with thin basalt and andesite flows in the east, to distal volcaniclastic fluvial sandstone in the west. These proximal—distal relationships help to define the location and paleogeography of active arc-flanking volcaniclastic alluvial aprons of the Miocene magmatic arc in northern Baja California. A substantial late Miocene drop in regional base level (relative sea level) is best attributed to regional uplift caused by the renewal of magmatic and thermal activity in northern Baja California, which has continued to the present day.

Composition of the crust beneath the Kenya rift

USGS Publications Warehouse

Mooney, W.D.; Christensen, N.I.

1994-01-01

We infer the composition of the crust beneath and on the flanks of the Kenya rift based on a comparison of the KRISP-90 crustal velocity structure with laboratory measurements of compressional-wave velocities of rock samples from Kenya. The rock samples studied, which are representative of the major lithologies exposed in Kenya, include volcanic tuffs and flows (primarily basalts and phonolites), and felsic to intermediate composition gneisses. This comparison indicates that the upper crust (5-12 km depth) consists primarily of quartzo-feldspathic gneisses and schists similar to rocks exposed on the flanks of the rift, whereas the middle crust (12-22 km depth) consists of more mafic, hornblende-rich metamorphic rocks, probably intruded by mafic rocks beneath the rift axis. The lower crust on the flanks of the rift may consist of mafic granulite facies rocks. Along the rift axis, the lower crust varies in thickness from 9 km in the southern rift to only 2-3 km in the north, and has a seismic velocity substantially higher than the samples investigated in this study. The lower crust of the rift probably consists of a crust/mantle mix of high-grade metamorphic rocks, mafic intrusives, and an igneous mafic residuum accreted to the base of the crust during differentiation of a melt derived from the upper mantle. ?? 1994.

Experimental and textural investigation of welding: effects of compaction, sintering, and vapor-phase crystallization in the rhyolitic Rattlesnake Tuff

NASA Astrophysics Data System (ADS)

Grunder, Anita L.; Laporte, Didier; Druitt, Tim H.

2005-04-01

The abrupt changes in character of variably welded pyroclastic deposits have invited decades of investigation and classification. We conducted two series of experiments using ash from the nonwelded base of the rhyolitic Rattlesnake Tuff of Oregon, USA, to examine conditions of welding. One series of experiments was conducted at atmospheric pressure (1 At) in a muffle furnace with variable run times and temperature and another series was conducted at 5 MPa and 600 °C in a cold seal apparatus with variable run times and water contents. We compared the results to a suite of incipiently to densely welded, natural samples of the Rattlesnake Tuff. Experiments at 1 At required a temperature above 900 °C to produce welding, which is in excess of the estimated pre-eruptive magmatic temperature of the tuff. The experiments also yielded globular clast textures unlike the natural tuff. During the cold-seal experiments, the gold sample capsules collapsed in response to sample densification. Textures and densities that closely mimic the natural suite were produced at 5 MPa, 600 °C and 0.4 wt.% H 2O, over run durations of hours to 2 days. Clast deformation and development of foliation in 2-week runs were greater than in natural samples. Both more and less water reduced the degree of welding at otherwise constant run conditions. For 5 MPa experiments, changes in the degree of foliation of shards and of axial ratios of bubble shards and non-bubble (mainly platy) shards, are consistent with early densification related to compaction and partial rotation of shards into a foliation. Subsequent densification was associated with viscous deformation as indicated by more sintered contacts and deformation of shards. Sintering (local fusion of shard-shard contacts) was increasingly important with longer run times, higher temperatures, and greater pressures. During runs with high water concentrations, sintering was rare and adhesion between clasts was dominated by precipitation of sublimates in pore spaces. A few tenths wt.% H 2O in the rhyolite glass promote the development of welding by sharp reduction of glass viscosity. Large amounts of water inhibit welding by creating surface sublimates that interfere with sintering and may exert fluid pressure counter to lithostatic load if sintering and vapor-phase sublimates seal permeability in the tuff.

Geology of the Mid-Miocene Rooster Comb Caldera and Lake Owyhee Volcanic Field, eastern Oregon: Silicic volcanism associated with Grande Ronde flood basalt

NASA Astrophysics Data System (ADS)

Benson, Thomas R.; Mahood, Gail A.

2016-01-01

The Lake Owyhee Volcanic Field (LOVF) of eastern Oregon consists of rhyolitic caldera centers and lava fields contemporaneous with and spatially related to Mid-Miocene Columbia River flood basalt volcanism. Previous studies delineated two calderas in the southeastern part of LOVF near Owyhee Reservoir, the result of eruptions of two ignimbrites, the Tuff of Leslie Gulch and the Tuff of Spring Creek. Our new interpretation is that these two map units are differentially altered parts of a single ignimbrite produced in a major phreatomagmatic eruption at 15.8 Ma. Areas previously mapped as Tuff of Spring Creek are locations where the ignimbrite contains abundant clinoptilolite ± mordenite, which made it susceptible to erosion. The resistant intracaldera Tuff of Leslie Gulch has an alteration assemblage of albite ± quartz, indicative of low-temperature hydrothermal alteration. Our new mapping of caldera lake sediments and pre- and post-caldera rhyolitic lavas and intrusions that are chemically similar to intracaldera Tuff of Leslie Gulch point to a single 20 × 25 km caldera, which we name the Rooster Comb Caldera. Erosion of the resurgently uplifted southern half of the caldera created dramatic exposures of intracaldera Tuff of Leslie Gulch cut by post-caldera rhyolite dikes and intrusions that are the deeper-level equivalents of lava domes and flows that erupted into the caldera lake preserved in exposures to the northeast. The Rooster Comb Caldera has features in common with more southerly Mid-Miocene calderas of the McDermitt Volcanic Field and High Rock Caldera Complex, including formation in a basinal setting shortly after flood basalt eruptions ceased in the region, and forming on eruption of peralkaline ignimbrite. The volcanism at Rooster Comb Caldera postdates the main activity at McDermitt and High Rock, but, like it, begins 300 ky after flood basalt volcanism begins in the area, and while flood basalts don't erupt through the silicic focus, are contemporaneous with the latest stages of eruptions nearby. High Rock and McDermitt rhyolites are associated with propagation of Steens Basalt dikes to the south, and LOVF rhyolites with later propagation of Grande Ronde Basalt dikes to the north and north-northwest.

Paleomagnetic and Anisotropy of Magnetic Susceptibility (AMS) Documentation of the Formation of Large-Scale Rheomorphic Structures in the 2.06 Ma Huckleberry Ridge Tuff, Eastern Idaho

NASA Astrophysics Data System (ADS)

Geissman, J. W.; Holm, D.; Harlan, S. S.

2006-12-01

In the Teton River Valley, east of Rexburg, Idaho, the ca. 2.06 Ma Huckleberry Ridge Tuff is about 130 m thick, exceedingly well-exposed, and displays large-scale (100-150 m+ amplitude) rheomorphic folds, with eutaxitic fabrics that are parallel to inferred primary internal zonation (e.g. boundary between basal vitrophyre and overlying devitrified part of the pyroclastic deposit) as well as the basal contact with older deposits defining the fold geometries. One 150 m amplitude fold , is well-exposed on the north side of the valley about 2.5 km east of Teton Dam, has a NW trending fold axis and has a southwest limb that is overturned by about 45o. Samples were collected from 16 sites in this fold, on both limbs and the hinge area, to test the hypothesis that folding took place above maximum TRM blocking temperatures (about 580C). Progressive AF and thermal demagnetization both yield characteristic magnetizations of southwest to south-southwest declination and shallow inclination removed over a range of peak fields (typically between 20 and 80 mT) and laboratory unblocking temperatures (typically between 350 and 580C). The preliminary determination of an in situ mean based on the 16 sites is about D = 215°, I = -5°, a95= 5°, N = 16 site means). The direction of this ChRM is statistically indistinguishable from that reported by previous studies of the tuff (e.g. Reynolds, 1977, JGR; Byrd et al., 1994, JGR). The trend of the fold axis is orthogonal to this declination; the paleomagnetic fold test applied to these data is negative, with k values continuously decreasing upon unfolding, thus indicating that the entire structure in the tuff formed after the well-developed compaction fabric was acquired, at a temperature above maximum blocking temperatures of the ChRM. Post-compaction, high temperature deformation is consistent with field evidence indicating plastic secondary deformation of much of the tuff prior to devitrification. Rapid strain rates probably contributed to the formation of brittle features in the uppermost parts of the tuff (joints and fissures). AMS fabrics, at the site level, are typically very well-defined, with AMS foliations roughly parallel to compaction fabric, with K1 (maximum principal susceptibility) axes typically directed in a southwest-northeast orientation.

Rockfall hazard assessment of nearly vertical rhyolite tuff cliff faces by using terrestrial laser scanner, UAV and FEM analyses

NASA Astrophysics Data System (ADS)

Török, Ákos; Barsi, Árpád; Görög, Péter; Lovas, Tamás; Bögöly, Gyula; Czinder, Balázs; Vásárhelyi, Balázs; Molnár, Bence; József Somogyi, Árpád

2017-04-01

Nearly vertical rhyolite tuff cliff faces are located in NE-Hungary representing rock fall hazard in the touristic region of Sirok. Larger blocks of the cliff have fallen in recent years menacing tourists and human lives. The rhyolite tuff, that forms the Castle Hill was formed during Miocene volcanism and comprises of brecciated lapilli tuffs and tuffs with intercalating ignimbritic horizons. The paper focuses on the 3D mapping of cliff faces and modeling of rock fall hazard. The topography and 3D model of the cliff was obtained by using GNSS supported terrestrial laser scanner and UAV. With imaging techniques of UAV a Triangulated Irregular Network (TIN) model was developed that contained triangles with 5-10 cm side lengths. GNSS supported terrestrial laser scanning allowed the observation with a resolution 1-5 cm of point spacing. The point clouds were further processed and with the combination of laser scanner and UAV data a 3D model of the studied cliff faces were obtained. Geological parameters for rock fall analyses included both field observations and laboratory tests. The lithotypes were identified on the field and were sampled for rock mechanical laboratory analyses. Joint- and fault system was mapped and visualized by using Rocscience Dip. EN test methods were used to obtain the density properties of various lithotypes of rhyolite tuff. Other standardized EN tests included ultrasonic pulse velocity, water absorption, indirect tensile strength (Brasilian), uniaxial compressive strength and modulus of elasticity of air dry and of water saturated samples. GSI values were denoted based on filed observations and rock mass properties. The stability analyses of cliff faces were made by using 2D FEM software (Phase 2). Cross sections were evaluated and global factor of safety was also calculated. The modeled displacements were in the order of few centimeters; however several locations were pinpointed where wedge failure and planar slip surfaces were identified as major cliff stability hazards. These were associated with the major joint systems dissecting cliff faces. This research have proved that the combined methods of field surveying, imaging techniques, data processing and FEM modelling with rock mechanical laboratory analyses allowed the identification of major rock fall hazards even at areas which are difficult to access.

Geology of the Humboldt region and the Iron King mine, Bigbug mining district, Yavapai County, Arizona

USGS Publications Warehouse

Creasey, Saville Cyrus

1951-01-01

The Humboldt region is in central Yavapai County, Arizona. The intersection of the 112? 15' meridian and the 34? 30' N parallel is in the approximate geographical center of the region, and the Iron King mine is about 2000 feet west-northwest of the intersection. Pre-Cambrian rocks form the bedrock in the Humboldt region. Late Cenozoic unconsolidated river wash and valley fill, including some interbedded basalt, locally mantle the pre-Cambrian rocks, especially in the north-central part of the region (Lonesome Valley). The pre-Cambrian rocks consist of five newly defined metavolcanic formations derived from flows and tuff s, and of six intrusive units ranging in composition from granite to gabbro or perhaps more mafic types. Relic bedding-and pillow structures are locally prominent in the metavolcanics; geopetal structures are uncommon, but where present, generally indicate that the top is toward the west, though the evidence is too meager to be conclusive. Low-grade dynamothermal metamorphism altered the metavolcanics and to a lesser extent the intrusive rocks, forming textures, structures, and mineral assemblages characteristic of low temperature and moderate stress. The Texas Gulch formation, which is the easternmost metavolcanic formation, consists of five lithologic units. Arranged in the general order of their appearance from east to west they are meta-andesite breccia, purple slate, metarhyolite tuff, meta-andesite, and green slate. The boundary between the Texas Gulch formation and the Iron King meta-andesite is apparently gradational. The Iron King meta-andesite consists of three meta-andesite tuff units, two meta-andesite flow units and one metarhyolite tuff and conglomerate unit. The assemblage chlorite-albite-epitode with or without quartz is dominant in the meta-andesites. Mafic intrusive rocks, which may be approximately contemporaneous with metamorphism, may explain the presence of actinolitic hornblende in the central part of the formation. Toward the west the Iron King meta-andesite appears to grade into the Spud Mountain metabreccia through a zone containing beds characteristic of either one formation or the other. The Spud Mountain metabreccia consists of interbedded metabreccia and metatuff beds. The metatuffs are largely andesitic in composition, but a few thin beds of metarhyolite tuff occur. The fragments in the metabreccia beds consist chiefly or porphyritic meta-andesites and the matrix is meta-andesite tuff. Pre-Cambrian faults now marked by dikes separate the Chaparral Gulch metavolcanics, which lie west of the Spud Mountain metabreccia, from underlying and overlying formations. The Chaparral Gulch metavolcanics contain metarhyolite tuff, metarhyolite flow, and meta-andesite tuff that locally was contaminated by rhyolitic detritus. The Indian Hills metavolcanics, which are northeast of the Chaparral Gulch metavolcanics, consist of two broad units, one composed of metarhyolites and the other of meta-andesites. Metamorphosed tuffs and flows are believed to be represented in both units and flow breccia in the meta-andesites. Granite and alaskite; granodiorite and quartz diorite; diorite, mafic quartz diorite, gabbro and diabase; metarhyolite (?); and quartz porphyry comprise the pre-Cambrian intrusive units mapped. They include both deep-seated and hypabyssal types. Dynamothermal metamorphism has foliated the smaller bodies and the margins of the larger masses and partly converted them into mineral assemblages stable under low-grade metamorphic conditions. Planar structures (chiefly foliation) are omnipresent and linear structures are common in the pre-Cambrian meta-volcanic rocks. North-trending planar structures dominate in the Indian Hills metavolcanics, and in the Spud Mountain metabreccia, whereas northeast-trending planar structures are dominant in the Texas Gulch formation, Iron King meta-andesite, and Chaparral Gulch metavolcanics. To a lesser extent northeast-trending st

MX Siting Investigation. Geotechnical Evaluation. Verification Study - Pahroc Valley, Nevada. Volume I. Synthesis.

DTIC Science & Technology

1981-06-30

Range both consist of Paleozoic limestone and dolomite overlain by Tertiary ash-flow tuffs and undiffer- entiated volcanic rocks. The central portion...andesite, detrital material, volcanic tuff, pumice). FAULT - A plane or zone of fracture along which there has been * I displacement. FAULT BLOCK...D2850-70). To conduct the test, a cylindrical specimen of soil is surrounded by a fluid in a pressure chamber and subjected to an isotropic pressure . An

Additional results on palaeomagnetic stratigraphy of the Koobi Fora Formation, east of Lake Turkana (Lake Rudolf), Kenya

USGS Publications Warehouse

Hillhouse, J.W.; Ndombi, J.W.M.; Cox, A.; Brock, A.

1977-01-01

The magnetostratigraphy of the hominid-bearing sediments exposed east of Lake Turkana has been strengthened by new palaeomagnetic results. Ages obtained from several tuffs by the 40Ar/39Ar method suggest an approxmate match between the observed magnetozones and the geomagnetic polarity time scale; however, the palaeomagnetic results are also compatible with a younger chronology suggested by conventional K-Ar dating of the KBS Tuff. ?? 1977 Nature Publishing Group.

A subaqueous eruption model for shallow-water, small volume eruptions: Evidence from two Precambrian examples

NASA Astrophysics Data System (ADS)

Mueller, Wulf U.

Ancient, shallow-water, pyroclastic deposits are identified in the Paleoproterozoic Ketilidian Mobile belt, southeast Greenland at Kangerluluk and in the Neoproterozoic Gariep belt of Namibia in the Schakalsberg Mountains. The 1-30 m-thick tuff and lapilli tuff deposits are interpreted as eruption-fed density current deposits emanating from tephra jets that collapsed under subaqueous conditions due to water ingress. The presence of 1-10 mm diameter armoured lapilli, with a central vesicular lapillus or shard, suggests the existence of high velocity, gas, water vapour, and particle-rich tephra jets. A transition from a gas-steam supported tephra jet to a cold water-laden density current without an intermediate stage of storage and remobilization is inferred. Interpretation of a 5-15 m-thick lapilli tuff breccia further supports explosive subaqueous mechanisms. Pyroclasts in the lapilli tuff breccia are interpreted as bombs emplaced ballistically. Multiple bomb sags produced by the impact of rounded juvenile crystal-rich pyroclasts required a water-exclusion zone formed either by a continuous magma uprush or multiple jet activity occurring concurrently, rather than as isolated tephra jets. Intercalated density current deposits indicate uprush events of limited duration and their recurrence with rapid collapse after each pulse. A new subaqueous Surtseyan-type eruption model is proposed based on observations from these two Precambrian study areas.

Hydrology of Yucca Mountain, Nevada

USGS Publications Warehouse

Flint, A.L.; Flint, L.E.; Kwicklis, E.M.; Bodvarsson, G.S.; Fabryka-Martin, J. M.

2001-01-01

Yucca Mountain, located in southern Nevada in the Mojave Desert, is being considered as a geologic repository for high-level radioactive waste. Although the site is arid, previous studies indicate net infiltration rates of 5-10 mm yr-1 under current climate conditions. Unsaturated flow of water through the mountain generally is vertical and rapid through the fractures of the welded tuffs and slow through the matrix of the nonwelded tuffs. The vitric-zeolitic boundary of the nonwelded tuffs below the potential repository, where it exists, causes perching and substantial lateral flow that eventually flows through faults near the eastern edge of the potential repository and recharges the underlying groundwater system. Fast pathways are located where water flows relatively quickly through the unsaturated zone to the water table. For the bulk of the water a large part of the travel time from land surface to the potential repository horizon (~300 m below land surface) is through the interlayered, low fracture density, nonwelded tuff where flow is predominately through the matrix. The unsaturated zone at Yucca Mountain is being modeled using a three-dimensional, dual-continuum numerical model to predict the results of measurements and observations in new boreholes and excavations. The interaction between experimentalists and modelers is providing confidence in the conceptual model and the numerical model and is providing researchers with the ability to plan further testing and to evaluate the usefulness or necessity of further data collection.

Rejuvenation Stage Volcanics at Laeo Kilauea, Kauai, Hawaii

NASA Astrophysics Data System (ADS)

Thordarson, T.; Garcia, M.; Wanless, D.; Tagami, T.; Sano, H.

2005-12-01

The Plio-Pleistocene Koloa volcanic series represents the rejuvenated volcanism on Kauai, one of the oldest main Hawaiian Islands. The Koloa series is made up of highly alkalic basalt and associated sedimentary rocks that rest unconformably on the shield-building Waimea Canyon volcanic series. Koloa vents are dispersed across the eastern two-thirds of the island and typically consist of scoria or lava cones that fed broad lava flow fields blanketing the marginal lowlands on the south, east and north side of the island. The northernmost subaerial Koloa vents are found at Laeo Kilauea on the north shore of the island. At Laeo Kilauea the volcanic succession is unusual in that it contains the only phreatomagmatic vent structures of the Koloa series. Here an ~2-km-long costal cliff face reveals a bedded phreatomagmatic tephra sequence that is >90-m-thick and represents the remnant of an a much large tuff cone (>2-km in diameter). The tuff cone sequence is characterized by decimeter to meters thick layers, where cross-bedded ash beds alternate with massive and poorly sorted lapilli tuff beds. The cross-bedded deposits were produced by dry and wet surges, whereas the poorly sorted beds represent fall deposits produced by sustained eruption column (i.e. continuous up-rush) or tephra jets (i.e. rooster-tail explosions). The juvenile clast population of the tephra consists of olivine-phyric foidite, but it also contains abundant wall-rock lithics, including fragments of reef-limestone. The base of the tuff cone outcrops at Mokolea point on the east side of the outcrop, where phreatomagmatic tephra rests directly on an older Koloa pahoehoe flow, a olivine- and mellelite-phyric foidite lava. The tephra sequence is cut by an ~1-m-thick olivine-bearing basanite dike, which acted as a feeder for the fountain-fed spatter and lava (up to 100-m-thick) that cap the phreatomagmatic tephra sequence. These units are separated by a 2-3 m thick soil horizon formed by weathering of the tuff. These three formations have been dated by Ar-Ar giving 2.65 +/- 0.35 Ma for the age of the basal foidite lava, 1.68 +/- 0.11 Ma for the tuff cone and 0.69 +/- 0.03 Ma for the overlying fountain-fed basanite lava. Important conclusions that can be drawn from the results of this study include: (1) The characteristics of the phreatomagmatic tephra indicate that at times the tuff cone crater was filled with water implying that the eruption site was submarine and most likely located in shallow coastal waters. The presence of reef-limestone fragments in the tephra supports this notion. On the other hand, the underlying and overlying lava flows, which do extend an unknown distance beyond the current shoreline, were clearly deposited on dry land. This implies that Kauai experienced significant changes in sea level in early to mid Pleistocene times. (2) The eruptions that produced the tuff cone and the overlying fountain-fed basanite lava are one million years apart, yet the dikes that fed these eruptions appear to have followed a similar path to the surface. This indicates that the magma is utilizing preexisting structural weaknesses to reach the surface.

New 40Ar/39Ar age of the Bishop Tuff from multiple sites and sediment rate calibration for the Matuyama-Brunhes boundary

USGS Publications Warehouse

Sarna-Wojcicki, A. M.; Pringle, M.S.; Wijbrans, J.

2000-01-01

Precise dating of sanidine from proximal ash flow Bishop Tuff and air fall Bishop pumice and ash, California, can be used to derive an absolute age of the Matuyama Reversed-Brunhes Normal (M-B) paleomagnetic transition, identified stratigraphically close beneath the Bishop Tuff and ash at many sites in the western United States. An average age of 758.9 ?? 1.8 ka, standard error of the mean (SEM), was obtained for individual sanidine crystals or groups of several crystals, determined from ???70 individual analyses of sanidine separates from 11 sample groups obtained at five localities. The basal air fall pumice (757.7 ?? 1.8 ka) and overlying ash flow tuff (762.2 ?? 4.7 ka) from near the source yield essentially the same dates within errors of analysis, suggesting that the two units were emplaced close in time. A date on distal Bishop air fall ash bed at Friant, California, ???100 km to the west of the source area, is younger, 750.1 ?? 4.3 ka, but not significantly different within analytical error (??1 standard deviation). Previous dates of the Bishop Tuff, obtained by others using conventional K-Ar and the fission track method on zircons, ranged from ???650 ka to ???1.0 Ma. The most recent, generally accepted date by the K-Ar method on sanidine was 738 ?? 3 ka. We infer, as others before, that many K-Ar dates on sanidine feldspar are too young owing to incomplete degassing of radiogenic Ar during fusion in the K-Ar technique and that many older K-Ar dates are too old owing to detrital or xenocrystic contamination in the larger samples that are necessary for the technique. The new dates are similar to recent 40Ar/39Ar ages of the Bishop Tuff determined on individual samples by others but are derived from a larger proximal sample population and from multiple analysis of each sample. The results provide a definitive and precise age calibration of this widespread chronostratigraphic marker in the western United States and northeastern Pacific Ocean. We calculated the age of the M-B transition at five sites, assuming constant sedimentation rates, the age of the Bishop ash bed and one or more well-dated chronostratigraphic horizons above and below the Bishop Tuff ash bed and M-B transition, and stratigraphic separations between these datum levels. The age of the M-B transition is 774.2 ?? 2.8 ka, based on the average of eight such calculations, close to other recent determinations, and similar to that determined from the astronomically tuned polarity timescale. Our approach provides an alternative and surprisingly precise method for determining the age of the M-B and other chronostratigraphic levels. The above dates, calculated using U.S. Geological Survey values of 27.92 Ma for the Taylor Creek (TC) sanidine can be recalculated to other widely used values for these monitors. For example, using recently published values of 28.34 Ma (TC) and 523.1 Ma (McLure Mountain hornblende, MMhb-1), the resulting ages are ???774 ka for the Bishop Tuff and ash bed and ???789 ka for the M-B transition. Copyright 2000 by the American Geophysical Union.

Petrology and geochemistry of samples from bed-contact zones in Tunnel Bed 5, U12g-Tunnel, Nevada Test Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connolly, J.R.; Keil, K.; Mansker, W.L.

1984-10-01

This report summarizes the detailed geologic characterization of samples of bed-contact zones and surrounding nonwelded bedded tuffs, both within Tunnel Bed 5, that are exposed in the G-Tunnel complex beneath Rainier Mesa on the Nevada Test Site (NTS). Original planning studies treated the bed-contact zones in Tunnel Bed 5 as simple planar surfaces of relatively high permeability. Detailed characterization, however, indicates that these zones have a finite thickness, are depositional in origin, vary considerably over short vertical and horizontal distances, and are internally complex. Fluid flow in a sequence of nonwelded zeolitized ash-flow or bedded tuffs and thin intervening reworkedmore » zones appears to be a porous-medium phenomenon, regardless of the presence of layering. There are no consistent differences in either bulk composition or detailed mineralogy between bedded tuffs and bed-contact zones in Tunnel Bed 5. Although the original bulk composition of Tunnel Bed 5 was probably peralkaline, extensive zeolitization has resulted in a present peraluminous bulk composition of both bedded tuffs and bed-contact zones. The major zeolite present, clinoptilolite, is intermediate (Ca:K:Na = 26:35:39) and effectively uniform in composition. This composition is similar to that of clinoptilolite from the tuffaceous beds of Calico Hills above the static water level in hole USW G-1, but somewhat different from that reported for zeolites from below the static water level in USW G-2. Tunnel Bed 5 also contains abundant hydrous manganese oxides. The similarity in composition of the clinoptilolites from Tunnel Bed 5 and those above the static water level at Yucca Mountain indicates that many of the results of nuclide-migration experiments in Tunnel Bed 5 would be transferrable to zeolitized nonwelded tuffs above the static water level at Yucca Mountain.« less

On the physics of unstable infiltration, seepage, and gravity drainage in partially saturated tuffs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.; Bodvarsson, G.S.; Salve, R.

2002-04-01

To improve understanding of the physics of dynamic instabilities in unsaturated flow processes within the Paintbrush nonwelded unit (PTn) and the middle nonlithophysal portion of the Tonopah Spring welded tuff unit (TSw) of Yucca Mountain, we analyzed data from a series of infiltration tests carried out at two sites (Alcove 4 and Alcove 6) in the Exploratory Studies Facility, using analytical and empirical functions. The analysis of infiltration rates measured at both sites showed three temporal scales of infiltration rate: (1) a macro-scale trend of overall decreasing flow, (2) a meso-scale trend of fast and slow motion exhibiting three-stage variationsmore » of the flow rate (decreasing, increasing, and [again] decreasing flow rate, as observed in soils in the presence of entrapped air), and (3) micro-scale (high frequency) fluctuations. Infiltration tests in the nonwelded unit at Alcove 4 indicate that this unit may effectively dampen episodic fast infiltration events; however, well-known Kostyakov, Horton, and Philip equations do not satisfactorily describe the observed trends of the infiltration rate. Instead, a Weibull distribution model can most accurately describe experimentally determined time trends of the infiltration rate. Infiltration tests in highly permeable, fractured, welded tuff at Alcove 6 indicate that the infiltration rate exhibits pulsation, which may have been caused by multiple threshold effects and water-air redistribution between fractures and matrix. The empirical relationships between the extrinsic seepage from fractures, matrix imbibition, and gravity drainage versus the infiltration rate, as well as scaling and self-similarity for the leading edge of the water front are the hallmark of the nonlinear dynamic processes in water flow under episodic infiltration through fractured tuff. Based on the analysis of experimental data, we propose a conceptual model of a dynamic fracture flow and fracture-matrix interaction in fractured tuff, incorporating the time dependent processes of water redistribution in the fracture-matrix system.« less

Records of Triassic volcanism in Pangean Great Lakes, and implications for reconstructing the distal effects of Large Igneous Provinces

NASA Astrophysics Data System (ADS)

Whiteside, J. H.; Percival, L.; Kinney, S.; Olsen, P. E.; Mather, T. A.; Philpotts, A.

2017-12-01

Documentation of the precise timing of volcanic eruptions in sedimentary records is key for linking volcanic activity to both historical and geological episodes of environmental change. Deposition of tuffs in sediments, and sedimentary enrichment of trace metals linked to igneous processes, are both commonly used for such correlations. In particular, sedimentary mercury (Hg) enrichments have been used as a marker for volcanic activity from Large Igneous Provinces (LIPs) to support their link to episodes of major climate change and mass extinction in the geological record. However, linking such enrichments to a specific eruption or eruption products is often challenging or impossible. In this study, the mercury records from two exactly contemporaneous latest Triassic-earliest Jurassic rift lakes are presented. Both sedimentary records feature igneous units proposed to be related to the later (Early Jurassic) stages of volcanism of the Central Atlantic Magmatic Province (CAMP). These CAMP units include a small tuff unit identified by thin-section petrology and identified at 10 localities over a distance of over 200 km, and a major CAMP basalt flow overlying this tuff (and dated at 200.916±0.064 Ma) which is also known across multiple sedimentary basins in both North America and Morocco and is thought to have been emplaced about 120 kyr after the tuff. A potential stratigraphic correlation between Hg enrichments and the igneous units is considered, and compared to the established records of mercury enrichments from the latest Triassic that are thought to be coeval with the earlier stages of CAMP volcanism. Investigating the Hg records of sedimentary successions containing tuffs and basalt units is an important step for demonstrating whether the mercury emissions from specific individual volcanic eruptions in the deep past can be identified in the geological record, and are thus important tools for interpreting the causes of associated past geological events, such as mass extinctions.

Water supply for the Nuclear Rocket Development Station at the U.S. Atomic Energy Commission's Nevada Test Site

USGS Publications Warehouse

Young, Richard Arden

1972-01-01

The Nuclear Rocket Development Station, in Jackass Flats, occupies about 123 square miles in the southwestern part of the U.S. Atomic Energy Commission's Nevada Test Site. Jackass Flats, an intermontane valley bordered by highlands on all sides except for a drainage outlet in the southwestern corner, has an average annual rainfall of 4 inches. Jackass Flats is underlain by alluvium, colluvium, and volcanic rocks of Cenozoic age and, at greater depth, by sedimentary rocks of Paleozoic age. The alluvium and the colluvium lie above the saturated zone throughout nearly all of Jackass Flats. The Paleozoic sedimentary rocks contain limestone and dolomite units that are excellent water producers elsewhere ; however, these units are too deep in Jackass Flats to be economic sources of water. The only important water-producing unit known in the vicinity of the Nuclear Rocket Development Station is a welded-tuff aquifer, the Topopah Spring Member of the Paintbrush Tuff, which receives no significant recharge. This member contains about 500 feet of highly fractured rock underlying an area 11 miles long and 3 miles wide in western Jackass Flats. Permeability of the aquifer is derived mostly from joints and fractures; however, some permeability may be derived from gas bubbles in the upper part of the unit. Transmissivity, obtained from pumping tests, ranges from 68,000 to 488,000 gallons per day per foot. Volume of the saturated part of the aquifer is about 3.5 cubic miles, and the average specific yield probably ranges from 1 to 5 percent. The volume of ground water in storage is probably within the range of 37-187 billion gallons. This large amount of water should be sufficient to supply the needs of the Nuclear Rocket Development Station for many years. Water at the Nuclear Rocket Development Station is used for public supply, construction, test-cell coolant, exhaust cooling, and thermal shielding during nuclear reactor and engine testing, and washdown. Present (1967) average consumption of water is 520,000 gallons per day--all supplied by one well. This supply well and a standby well have a production capability of 1.6 million gallons per day--adequate for present needs. Water in the welded-tuff aquifer is of the sodium bicarbonate type. Dissolved-solids content of the water in Jackass Flats is in the general range 230 milligrams per liter in the western part to 890 milligrams per liter in the eastern part.

Observations on the geology and petroleum potential of the Cold Bay-False Pass area, Alaska Peninsula

USGS Publications Warehouse

McLean, Hugh James

1979-01-01

Upper Jurassic strata in the Black Hills area consist mainly of fossiliferous, tightly cemented, gently folded sandstone deposited in a shallow marine environment. Upper Cretaceous strata on Sanak Island are strongly deformed and show structural features of broken formations similar to those observed in the Franciscan assemblage of California. Rocks exposed on Sanak Island do not crop out on the peninsular mainland or on Unimak Island, and probably make up the acoustic and economic basement of nearby Sanak basin. Tertiary sedimentary rocks on the outermost part of the Alaska Peninsula consist of Oligocene, Miocene, and lower Pliocene volcaniclastic sandstone, siltstone, and conglomerate deposited in nonmarine and very shallow marine environments. Interbedded airfall and ash-flow tuff deposits indicate active volcanism during Oligocene time. Locally, Oligocene strata are intruded by quartz diorite plutons of probable Miocene age. Reservoir properties of Mesozoic and Tertiary rocks are generally poor due to alteration of chemically unstable volcanic rock fragments. Igneous intrusions have further reduced porosity and permeability by silicification of sandstone. Organic-rich source rocks for petroleum generation are not abundant in Neogene strata. Upper Jurassic rocks in the Black Hills area have total organic carbon contents of less than 0.5 percent. Deep sediment-filled basins on the Shumagin Shelf probably contain more source rocks than onshore correlatives, but reservoir quality is not likely to be better than in onshore outcrops. The absence of well-developed folds in most Tertiary rocks, both onshore and in nearby offshore basins, reduces the possibility of hydrocarbon entrapment in anticlines.

Occurrence model for volcanogenic beryllium deposits: Chapter F in Mineral deposit models for resource assessment

USGS Publications Warehouse

Foley, Nora K.; Hofstra, Albert H.; Lindsey, David A.; Seal, Robert R.; Jaskula, Brian W.; Piatak, Nadine M.

2012-01-01

Current global and domestic mineral resources of beryllium (Be) for industrial uses are dominated by ores produced from deposits of the volcanogenic Be type. Beryllium deposits of this type can form where hydrothermal fluids interact with fluorine and lithophile-element (uranium, thorium, rubidium, lithium, beryllium, cesium, tantalum, rare earth elements, and tin) enriched volcanic rocks that contain a highly reactive lithic component, such as carbonate clasts. Volcanic and hypabyssal high-silica biotite-bearing topaz rhyolite constitutes the most well-recognized igneous suite associated with such Be deposits. The exemplar setting is an extensional tectonic environment, such as that characterized by the Basin and Range Province, where younger topaz-bearing igneous rock sequences overlie older dolomite, quartzite, shale, and limestone sequences. Mined deposits and related mineralized rocks at Spor Mountain, Utah, make up a unique economic deposit of volcanogenic Be having extensive production and proven and probable reserves. Proven reserves in Utah, as reported by the U.S. Geological Survey National Mineral Information Center, total about 15,900 tons of Be that are present in the mineral bertrandite (Be4Si2O7(OH)2). At the type locality for volcanogenic Be, Spor Mountain, the tuffaceous breccias and stratified tuffs that host the Be ore formed as a result of explosive volcanism that brought carbonate and other lithic fragments to the surface through vent structures that cut the underlying dolomitic Paleozoic sedimentary rock sequences. The tuffaceous sediments and lithic clasts are thought to make up phreatomagmatic base surge deposits. Hydrothermal fluids leached Be from volcanic glass in the tuff and redeposited the Be as bertrandite upon reaction of the hydrothermal fluid with carbonate clasts in lithic-rich sections of tuff. The localization of the deposits in tuff above fluorite-mineralized faults in carbonate rocks, together with isotopic evidence for the involvement of magmatic water in an otherwise meteoric water-dominated hydrothermal system, indicate that magmatic volatiles contributed to mineralization. At the type locality, hydrothermal alteration of dolomite clasts formed layered nodules of calcite, opal, fluorite, and bertrandite, the latter occurring finely intergrown with fluorite. Alteration assemblages and elemental enrichments in the tuff and surrounding volcanic rocks include regional diagenetic clays and potassium feldspar and distinctive hydrothermal halos of anomalous fluorine, lithium, molybdenum, niobium, tin, and tantalum, and intense potassium feldspathization with sericite and lithium-smectite in the immediate vicinity of Be ore. Formation of volcanogenic Be deposits is due to the coincidence of multiple factors that include an appropriate Be-bearing source rock, a subjacent pluton that supplied volatiles and heat to drive convection of meteoric groundwater, a depositional site characterized by the intersection of normal faults with permeable tuff below a less permeable cap rock, a fluorine-rich ore fluid that facilitated Be transport (for example, BeF42- complex), and the existence of a chemical trap that caused fluorite and bertrandite to precipitate at the former site of carbonate lithic clasts in the tuff.

In Situ Measurement of Permeability in the Vicinity of Faulted Nonwelded Bishop Tuff, Bishop, CA

NASA Astrophysics Data System (ADS)

Dinwiddie, C. L.; Fedors, R. W.; Ferrill, D. A.; Bradbury, K. K.

2002-12-01

The nonwelded Bishop Tuff includes matrix-supported massive ignimbrites and clast-supported bedded deposits. Fluid flow through such faulted nonwelded tuff is likely to be influenced by a combination of host rock properties and the presence of deformation features, such as open fractures, mineralized fractures, and fault zones that exhibit comminuted fault rock and clays. Lithologic contacts between fine- and coarse-grained sub-units of nonwelded tuff may induce formation of capillary and/or permeability barriers within the unsaturated zone, potentially leading to down-dip lateral diversion of otherwise vertically flowing fluid. However, discontinuities (e.g., fractures and faults) may lead to preferential sub-vertical fast flow paths in the event of episodic infiltration rates, thus disrupting the potential for both (1) large-scale capillary and/or permeability barriers to form and for (2) redirection of water flow over great lateral distances. This study focuses on an innovative technique for measuring changes in matrix permeability near faults in situ--changes that may lead to enhancement of vertical fluid flow and disruption of lateral fluid flow. A small-drillhole minipermeameter probe provides a means to eliminate extraction of fragile nonwelded tuffs as a necessity for permeability measurement. Advantages of this approach include (1) a reduction of weathering-effects on measured permeability, and (2) provision of a superior sealing mechanism around the gas injection zone. In order to evaluate the effect of faults and fault zone deformation on nonwelded tuff matrix permeability, as well as to address the potential for disruption of lithologic barrier-induced lateral diversion of flow, data were collected from two fault systems and from unfaulted host rock. Two hundred and sixty-seven gas-permeability measurements were made at 89 locations; i.e. permeability measurements were made in triplicate at each location with three flow rates. Data were collected at the first fault and perpendicularly away from it within the hanging wall to a distance of 6 m [20 ft] along one transect, and perpendicular to the fault from the foot wall to the hanging wall for a distance of 6 m [20 ft] along a second transect. Additionally, eight water-permeameter tests were conducted in order to augment the gas-permeability data. Gas-permeability measurements were collected along two transects at the main fault of the second fault system and perpendicularly away from it within the foot wall to a distance of 10.5 m [34 ft], crossing several secondary faults in the process. Data were also collected within the fault gouge of the main fault, and were found to vary therein by an order of magnitude. This Bishop Tuff study supports the U.S. Nuclear Regulatory Commission (NRC) review of hydrologic property studies at Yucca Mountain, Nevada, which are conducted by the U.S. Department of Energy. This abstract is an independent product of the CNWRA and does not necessarily reflect the views or regulatory position of the NRC.

Show Me the Mush! - Constraints From Voluminous Rhyolitic Ignimbrites of Bimodal and Calc-alkaline Settings on the Applicability of a Mush Model

NASA Astrophysics Data System (ADS)

Streck, M. J.

2012-12-01

Mush models have been popular in explaining crystal-poor rhyolites of a variety of settings. The classical mush model requires an abundance of very crystal-rich (>50%), intermediate (dacitic) magmas that upon compaction expel their interstitial liquids that erupt to give rise to rhyolitic lava flows and ignimbrites. In volcanic systems, a critical part in evaluating a mush model rests on providing evidence for the existence of suitable crystal-rich intermediate magmas that are consistent with the petrology of the erupted rhyolites. In my evaluation, I focus on providing constraints of whether or not suitable crystal mushes are likely to have existed and were instrumental in the production of a select series of voluminous (>100 km3) rhyolitic ignimbrites. Furthermore, the volcanic framework of each selected ignimbrite is used for assessing questions of "eruptibility" of magma types. The three main evaluated units representing 'hot-dry-reduced' rhyolites of bimodal settings are the 16-15.4 Ma Dinner Creek Tuff, the 9.7 Ma Devine Canyon Tuff, and 7.1 Ma Rattlesnake Tuff. All three tuffs erupted in eastern Oregon within a basalt-rhyolite suite. The key feature that makes them particularly valuable for this discussion is that each of the tuffs erupted a co-magmatic component that tracks the intermediate to mafic underpinnings to the rhyolitic magma. This allows a direct assessment of what intermediate magmas residing in close spatial proximity to the rhyolites looked like. On the other hand, other characteristics such as degree of chemical zoning, element trends, single or multiple cooling units, etc., vary considerably among the three tuffs thus covering a wide spectrum of rhyolites from bimodal settings. As representative of 'cool-wet-oxidized' rhyolites, I test applicability of the mush model on the tuffs and associated lavas of the Oligocene San Luis caldera system. This system represents strongly confocal and voluminous eruptions that are closely spaced in time at the end of the activity period of the Central Caldera Cluster of the Oligocene San Juan volcanic field, Colorado. Compositional intermediate underpinnings of each of the 'hot-dry-reduced' rhyolites fail geochemical requirements to represent suitable intermediate magmas. In addition, these underpinnings are crystal-poor and this is inconsistent with the required high crystallinity of magma mushes. Remelting scenarios to reduce crystallinities in intermediate magmas are excluded - again on geochemical grounds. Other complications with a model of voluminous crystal mushes beneath such rhyolites are the production of strong trace-element chemical gradation within single magma batches as well as multi-cyclic eruptions of crystal-poor rhyolites from the same system. For the system of 'cold-wet-oxidized' rhyolites, one of the challenges for a mush model is that interstitial melts of crystal-rich intermediate magmas compositionally deviate from erupted rhyolites when abundant amphibole (±sphene) is present, yet both phases are commonly expected phenocrystic phases at crystallinities when extraction of rhyolite from mush can take place.

In-Situ Tuff Water Migration/Heater Experiment: posttest thermal analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eaton, R.R.; Johnstone, J.K.; Nunziato, J.W.

This report describes posttest laboratory experiments and thermal computations for the In-Situ Tuff Water Migration/Heater Experiment that was conducted in Grouse Canyon Welded Tuff in G-Tunnel, Nevada Test Site. Posttest laboratory experiments were designed to determine the accuracy of the temperatures measured by the rockwall thermocouples during the in-situ test. The posttest laboratory experiments showed that the measured in-situ rockwall temperatures were 10 to 20{sup 0}C higher than the true rockwall temperatures. The posttest computational results, obtained with the thermal conduction code COYOTE, were compared with the experimentally obtained data and with calculated pretest results. Daily heater output power fluctuationsmore » (+-4%) caused by input power line variations and the sensitivity of temperature to heater output power required care in selecting the average heater output power values used in the code. The posttest calculated results compare reasonably well with the experimental data. 10 references, 14 figures, 5 tables.« less

Geophysical methods as mapping tools in a strata-bound gold deposit: Haile mine, South Carolina slate belt.

USGS Publications Warehouse

Wynn, J.C.; Luce, R.W.

1984-01-01

The Haile mine is the largest gold producer in the eastern USA. It is postulated to be a strata-bound gold deposit formed by a fumarolic or hot-spring system in felsic tuffs of Cambrian(?) age. Two mineralized zones occur, each composed of a sericitic part overlain by a siliceous part. Au is concentrated in especially silicified horizons and in pyrite horizons in the siliceous part of each mineralized zone. The tuffs are metamorphosed to greenschist facies and intruded by diabase and other mafic dykes. Weathering is deep and the mineralized tuffs are partly covered by coastal-plain sediments. It is suggested that certain geophysical methods may be useful in mapping and exploring Haile-type deposits in the Carolina slate belt. Very low frequency electromagnetic resistivity surveys help define alteration and silicified zones. A magnetic survey found sharp highs that correlate with unexposed mafic and ultramafic dykes. Induced polarization proved useful in giving a two-dimensional view of the structure.-G.J.N.

Nonmarine facies in the Late Triassic(?) to Early Jurassic Horn Mountain Tuff member of the Talkeetna Formation, Horn Mountain, lower Cook Inlet basin, Alaska

USGS Publications Warehouse

LePain, D.L.; Stanley, Richard G.; Helmold, K.P.

2016-01-01

The Talkeetna Formation is a prominent lithostratigraphic unit in south-central Alaska. In the Iniskin–Tuxedni area, Detterman and Hartsock (1966) divided the formation into three mappable units including, from oldest to youngest, the Marsh Creek Breccia, the Portage Creek Agglomerate, and the Horn Mountain Tuff Members. The Horn Mountain Tuff Member was thought to include rocks deposited in a nonmarine setting based on the presence of “tree stumps in an upright position” (Detterman and Hartsock, 1966, p. 19) near the top of the type section at Horn Mountain. Bull (2015) recognized possible nonmarine volcaniclastic rocks in the member during the 2014 field season in a saddle on the north side of Horn Mountain (figs. 2-1 and 2-2). The authors visited this location in 2015 and measured a short stratigraphic section to document facies, interpret depositional setting, and constrain age. This report summarizes our field observations and presents preliminary interpretations.

Post-middle Miocene Tuffs of Bodie Hills and Mono Basin, California: Paleomagnetic Reference Directions and Vertical Axis Rotation

NASA Astrophysics Data System (ADS)

Lindeman, J. R.; Pluhar, C. J.; Farner, M. J.

2013-12-01

The relative motions of the Pacific and North American plates about the Sierra Nevada-North American Euler pole is accommodated by dextral slip along the San Andreas Fault System (~75%) and the Walker Lane-Eastern California Shear Zone system of faults, east of the Sierra Nevada microplate (~25%). The Bodie Hills and Mono Basin regions lie within the Walker Lane and partially accommodate deformation by vertical axis rotation of up to 60o rotation since ~9.4 Ma. This region experienced recurrent eruptive events from mid to late Miocene, including John et al.'s (2012) ~12.05 Ma Tuff of Jack Springs (TJS) and Gilbert's (1968) 11.1 - 11.9 Ma 'latite ignimbrite' east of Mono Lake. Both tuffs can be identified by phenocrysts of sanidine and biotite in hand specimens, with TJS composed of a light-grey matrix and the latite ignimbrite composed of a grey-black matrix. Our paleomagnetic results show these units to both be normal polarity, with the latite ignimbrite exhibiting a shallow inclination. TJS's normal polarity is consistent with emplacement during subchron C5 An. 1n (12.014 - 12.116 Ma). The X-ray fluorescence analyses of fiamme from TJS in Bodie Hills and the latite ignimbrite located east of Mono Lake reveal them both to be rhyolites with the latite ignimbrite sharing elevated K composition seen in the slightly younger Stanislaus Group (9.0 - 10.2 Ma). We establish a paleomagnetic reference direction of D = 352.8o I = 42.7o α95 = 7.7o n = 5 sites (42 samples) for TJS in the Bodie Hills in a region hypothesized by Carlson (2012) to have experienced low rotation. Our reference for Gilbert's latite ignimbrite (at Cowtrack Mountain) is D = 352.9o I = 32.1o α95 = 4.7o. This reference locality is found on basement highland likely to have experienced less deformation then the nearby Mono Basin since ignimbrite emplacement. Paleomagnetic results from this latite ignimbrite suggests ~98.2o × 5.5o of clockwise vertical axis rotation of parts of eastern Mono Basin since unit emplacement. A welded 11.7 Ma (K-Ar; Drake, 1979) rhyolitic tuff near Trafton Mountain appears similar in composition to TJS. Drake's tuff exhibits a reversed polarity, consistent with reversed polarity subchron C5r.3r (11.614 - 12.014 Ma) and distinguishes this tuff from TJS and Gilbert's latite ignimbrite.

Evidence for an abrupt transition in the mantle-derived source to the Long Valley Caldera rhyolites after the climactic eruption: from subduction-modified lithosphere to asthenosphere

NASA Astrophysics Data System (ADS)

Waters, L.; Lange, R. A.

2014-12-01

Shortly after the climactic eruption of ~600 km3 of Bishop Tuff zoned rhyolitic magma, ~100 km3 of crystal-poor Early Rhyolite erupted inside Long Valley Caldera between ~750-650 ka as domes, glassy lavas, and tuffs (Hildreth, 2004). Despite similarities in bulk composition (e.g., 73-75 wt% SiO2; ~100 ppm Sr), there are marked differences between the Late (≥ 790°C) Bishop Tuff and postcaldera Early Rhyolites. Although crystal-poor (<5%), the Early Rhyolites are often saturated with 7-8 mineral phases (plag + opx + ilm + tmte + biotite + apatite + zircon ± pyrrhotite), but without the quartz, sanidine, and cpx additionally found in the more crystal-rich (12-24%) Late Bishop Tuff. Pre-eruptive temperatures, on the basis of two Fe-Ti oxides, range from 720-860°C, and ΔNNO values range from-0.4 to -0.9 (consistent with abundant ilmenite). Thus the Early Rhyolites record fO2 values that are nearly two orders of magnitude lower than those in the Late Bishop Tuff (ΔNNO = +1; Hildreth and Wilson, 2007). Application of the plagioclase-liquid hygrometer to Early Rhyolites gives pre-eruptive water contents ≤ 4.4 wt% H2O. The phenocrysts in Early Rhyolite obsidians often display euhedral and/or diffusion-limited growth textures, suggesting degassing-induced crystallization during rapid ascent. Isotopic data from the literature (e.g., Simon et al., 2014 and references therein) show that Long Valley rhyolites were derived from both crustal and mantle sources. We hypothesize that the drop in fO2 between the Late Bishop Tuff and Early Rhyolites may reflect a transition in their respective mantle source, from subduction-modified lithosphere to asthenosphere. Such a time-progressive transition in the mantle source of erupted basalts is seen throughout the Great Basin, occurring earliest in its central region and more recently toward its western margin (e.g. Cousens et al., 2012). Although the geochemistry of Quaternary basalts erupted around Long Valley indicate a subduction-modified lithosphere source (Cousens, 1996), the Early Rhyolites may be recording the crustal emplacement of basalts from the asthenosphere before any have yet erupted. If so, the Early Rhyolites may be derived from a greater proportion of crustal sources than calculated from isotopic data on the assumption of a lithospheric mantle source.

Recognition of primary and diagenetic magnetizations to determine the magnetic polarity record and timing of deposition of the moat-fill rocks of the Oligocene Creede Caldera, Colorado

USGS Publications Warehouse

Reynolds, Richard L.; Rosenbaum, Joseph G.; Sweetkind, Donald S.; Lanphere, Marvin A.; Robert, Andrew P.; Verosub, Kenneth L.

2000-01-01

Sedimentary and volcaniclastic rocks of the Oligocene Creede Formation fill the moat of the Creede caldera, which formed at about 26.9 Ma during the eruption of the Snowshoe Mountain Tuff. Paleomagnetic and rock magnetic studies of two cores (418 and 703 m long) that penetrated the lower half of the Creede Formation, in addition to paleomagnetic and isotopic dating studies of stratigraphically bracketing volcanic units, provide information on the age and the time span of sedimentation of the caldera fill. Normal polarity magnetization are found in Snowshoe Mountain Tuff beneath the moat sediments; in detrital-magnetite-bearing graded tuffs near the bottom of the moat fill; in an ash-fall deposit about 200 m stratigraphically about the top of core 2; and in postcaldera lava flows of the Fisher Dacite that overlie the Creede Formation. Normal polarity also characterizes detrital-magnetite-bearing tuff and sandstone unites within the caldera moat rocks that did not undergo severe sulfidic alteration. The combination of initially low magnitude of remanent magnetization and the destructive effects of subsequent diagenetic sulfidization on detrital iron oxides results in a poor paleomagnetic record for the fine-grained sedimentary rocks of the Creede Formation. these fine-grained rocks have either normal or revered polarity magnetizations that are carried by magnetite and/or maghemite. Many more apparent reversals are found that can be accommodated by any geomagnetic polarity time scale over the interval spanned by the ages of the bracketing extrusive rocks. Moreover, opposite polarity magnetization are found in specimens separated by only a few centimeters, without intervening hiatuses, and by specimens in several tuff beds, each of which represents a single depositional event. These polarity changes cannot, therefore, be attributed to detrital remanent magnetization. Many polarity changes are apparently related to chemical remanent magnetizations carried by postdepositional magnetite and maghemite that formed in rocks in which most or all detrital megnetic iron oxide was destroyed. Incipient oxidation of early diagenetic pyrite may have normal polarity Snowshoe Mountain Tuff (26.89 ± 0.0 Ma, 1 δ) and on the normal polarity postcaldera Fisher lava flows (as young as 26.23 ± 0.05 Ma, 1 δ) indicate that deposition of the Creede Formation spanned about 340-660 k.y. The intermittently defined normal polarity magnetization for the caldera-fill sequence, compared with different versions of the geomagnetic polarity time scale, is consistent with the shorter time span.

Cape Wanbrow: A stack of Surtseyan-style volcanoes built over millions of years in the Waiareka-Deborah volcanic field, New Zealand

NASA Astrophysics Data System (ADS)

Moorhouse, B. L.; White, J. D. L.; Scott, J. M.

2015-06-01

Volcanic fields typically include many small, monogenetic, volcanoes formed by single eruptions fed by short-lived magma plumbing systems that solidify after eruption. The Cape Wanbrow coastline of the northeast Otago region in the South Island of New Zealand exposes an Eocene-Oligocene intraplate basaltic field that erupted in Surtseyan style onto a submerged continental shelf, and the stratigraphy of Cape Wanbrow suggests that eruptions produced multiple volcanoes whose edifices overlapped within a small area, but separated by millions of years. The small Cape Wanbrow highland is shown to include the remains of 6 volcanoes that are distinguished by discordant to locally concordant inter-volcano contacts marked by biogenic accumulations or other slow-formed features. The 6 volcanoes contain several lithofacies associations: (a) the dominantly pyroclastic E1 comprising well-bedded tuff and lapilli-tuff, emplaced by traction-dominated unsteady, turbulent high-density currents; (b) E2, massive to diffusely laminated block-rich tuff deposited by grain-dominant cohesionless debris flows; (c) E3, broadly cross-stratified tuff with local lenses of low- to high-angle cross-stratification which was deposited by either subaerial pyroclastic currents or subaqueously by unstable antidune- and chute-and-pool-forming supercritical flows; (d) E4, very-fine- to medium-grained tuff deposited by turbidity currents; (e) E5, bedded bioclast-rich tuff with increasing glaucony content upward, emplaced by debris flows; (f) E6, pillow lava and inter-pillow bioclastic sediment; and (g) E7, hyaloclastite breccia. These lithofacies associations aid interpretation of the eruptive evolution of each separate volcano, which in turn grew and degraded during build-up of the overall volcanic pile. Sedimentary processes played a prominent role in the evolution of the volcanic pile with both syn- and post-eruptive re-mobilization of debris from the growing pile of primary pyroclastic deposits of multiple volcanoes separated by time. An increase in bioclastic detritus upsequence suggests that the stack of deposits from overlapping volcanoes built up into shallow enough waters for colonization to occur. This material was periodically shed from the top of the edifice to form bioclast-rich debris flow deposits of volcanoes 4, 5 and 6. Since the eruption of Surtsey (1963-1965) many studies have been made of the resulting island, but the pre-emergent base remains submarine, unincised and little studied. Eruption-fed density currents that formed deposits of the volcanoes of Cape Wanbrow are inferred to be typical products of submarine processes such as those that built Surtsey to the sea surface.

Effects of Wildfire on the Hydrology of Capulin and Rito de los Frijoles canyons, Bandelier National Monument, New Mexico

USGS Publications Warehouse

Veenhuis, Jack E.

2002-01-01

In June of 1977, the La Mesa wildfire burned 15,270 acres in and around Frijoles Canyon in Bandelier National Monument and the adjacent Santa Fe National Forest, New Mexico. The Dome wildfire in April of 1996 in Bandelier National Monument burned 16,516 acres in Capulin Canyon and the surrounding Dome Wilderness area. Both watersheds are characterized by abundant and extensive archeological sites that could be affected by increased runoff and accelerated rates of erosion, which typically occur after a wildfire. The U.S. Geological Survey in cooperation with the National Park Service monitored the wildfires' effects on streamflow in both canyons. The magnitude of large stormflows increased dramatically after these wildfires; peak flows at the most downstream streamflow-gaging station in Frijoles and Capulin Canyons increased to about 160 times the maximum recorded flood prior to the fire. Maximum peak flow was 3,030 cubic feet per second at the gaging station in Frijoles Canyon (drainage area equals 18.1 square miles) and 3,630 cubic feet per second at the most downstream crest-stage gage in Capulin Canyon (drainage area equals 14.1 square miles). The pre-fire maximum peak flow recorded in these two canyons was 19 and an estimated 25 cubic feet per second, respectively. As vegetation reestablished itself during the second year, the post-fire annual maximum peak flow decreased to about 10 to 15 times the pre-fire annual maximum peak flow. During the third year, maximum annual peak flows decreased to about three to five times the pre-fire maximum peak flow. In the 22 years since the La Mesa wildfire, flood magnitudes have not completely returned to pre-fire size. Post-fire flood magnitudes in Frijoles and Capulin Canyons do not exceed the maximum floods per drainage area for physiographic regions 5 and 6 in New Mexico. For a burned watershed, however, the peak flows that occur after a wildfire are several orders of magnitude larger than normal forested watershed peak flows. The frequency of larger stormflows also increased in response to the effects of the wildfires in both canyons. In Frijoles Canyon, the number of peak stormflows greater than the pre-fire maximum flow of 19 cubic feet per second was 15 in 1977, 9 in 1978, and 5 in 1979, which is about the magnitude of the maximum pre-fire peak flow in both canyons. Again the hydrologic effects of a wildfire seem to be more pronounced for the 3 years following the date of the fire. Likewise, larger peakflows occurred more frequently in Capulin Canyon for the first 3 years after the 1996 wildfire. Median suspended-sediment concentrations in samples collected in Frijoles Canyon in 1977 were 1,330 milligrams per liter; median concentrations were 16 milligrams per liter after the watershed stabilized in 1993-95. The annual load calculated from regression equations for load compared to flow for the first year after the wildfire was 220 times the annual load for the post-recovery period. To convey the increased frequency and magnitude of average flows in Capulin Canyon after the 1996 Dome wildfire, the stream channel in Capulin Canyon increased in flow capacity by widening and downcutting. As Capulin Canyon peak flows have decreased in both magnitude and frequency with vegetative recovery, the stream channel also has slowly begun to readjust. The channel at the most downstream crest-stage gage, which has the shallowest initial valley slope, is showing the first signs of aggradation.

Experimental Analyses of Yellow Tuff Spandrels of Post-medieval Buildings in the Naples Area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calderoni, B.; Cordasco, E. A.; Lenza, P.

2008-07-08

Experimental analyses have been carried out on tuff masonry specimens in order to investigate the structural behaviour of historical buildings in the Naples area (Southern Italy). Spandrels of post-medieval buildings (late XVI to early XX century) have been analysed, with emphasis on morphological characteristics according to chronological indicators. Results of the experimentation on scaled models (1:10) are discussed and the better behaviour of historical masonry typologies on respect to the modern one is highlighted. Comparison with theoretical formulations of ultimate shear resistance are provided too.

Geology of the Bir Nifazi Quadrangle, Kingdom of Saudi Arabia

USGS Publications Warehouse

Quick, James E.; Bosch, Paul S.

1990-01-01

A north-trending, 10-km-long belt of gossans crops out within the ophiolite beneath the upper-basalt sequence at Jabal Mardah. Reconnaissance drilling indicates that one of the larger gossans is underlain by a steeply dipping, 15-m-thick, sulfide-rich volcanic wacke that averages 1 percent nickel locally. The ore is composed of pyrite, millerite, polydymite, and minor sphalerite that fill interstices between clasts of the wacke and are intimately intergrown with quartz and nickel-rich epidote and chlorite. These textures and assemblages suggest that the sulfides crystallized in situ from infiltrating hydrothermal fluids. Tuffs and basalt flows appear to have acted as impermeable barriers that channeled the hydrothermal fluids through the more permeable wacke where sulfides were deposited. Carbonate-replaced serpentinized peridotite at the base of the ophiolite is considered a potential source for the nickel. In contrast to most nickel deposits, the mineralized rocks at Jabal Mardah have extremely high Ni/Cu (130 to 260) and negligible concentrations (< 5 ppb) of platinum-group elements.

Eruptive history, geochronology, and post-eruption structural evolution of the late Eocene Hall Creek Caldera, Toiyabe Range, Nevada

USGS Publications Warehouse

Colgan, Joseph P.; Henry, Christopher D.

2017-02-24

The magmatic, tectonic, and topographic evolution of what is now the northern Great Basin remains controversial, notably the temporal and spatial relation between magmatism and extensional faulting. This controversy is exemplified in the northern Toiyabe Range of central Nevada, where previous geologic mapping suggested the presence of a caldera that sourced the late Eocene (34.0 mega-annum [Ma]) tuff of Hall Creek. This region was also inferred to be the locus of large-magnitude middle Tertiary extension (more than 100 percent strain) localized along the Bernd Canyon detachment fault, and to be the approximate location of a middle Tertiary paleodivide that separated east and west-draining paleovalleys. Geologic mapping, 40Ar/39Ar dating, and geochemical analyses document the geologic history and extent of the Hall Creek caldera, define the regional paleotopography at the time it formed, and clarify the timing and kinematics of post-caldera extensional faulting. During and after late Eocene volcanism, the northern Toiyabe Range was characterized by an east-west trending ridge in the area of present-day Mount Callaghan, probably localized along a Mesozoic anticline. Andesite lava flows erupted around 35–34 Ma ponded hundreds of meters thick in the erosional low areas surrounding this structural high, particularly in the Simpson Park Mountains. The Hall Creek caldera formed ca. 34.0 Ma during eruption of the approximately 400 cubic kilometers (km3) tuff of Hall Creek, a moderately crystal-rich rhyolite (71–77 percent SiO2) ash-flow tuff. Caldera collapse was piston-like with an intact floor block, and the caldera filled with thick (approximately 2,600 meters) intracaldera tuff and interbedded breccia lenses shed from the caldera walls. The most extensive exposed megabreccia deposits are concentrated on or close to the caldera floor in the southwestern part of the caldera. Both silicic and intermediate post-caldera lavas were locally erupted within 400 thousand years of the main eruption, and for the next approximately 10 million years sedimentary rocks and distal tuffs sourced from calderas farther west ponded in the caldera basin surrounding low areas nearby. Patterns of tuff deposition indicate that the area was characterized by east-west trending paleovalleys and ridges in the late Eocene and Oligocene, which permitted tuffs to disperse east-west but limited their north-south extent. Although a low-angle fault contact of limited extent separates Cambrian and Ordovician strata in the southwestern part of the study area, there is no evidence that this fault cuts overlying Tertiary rocks. Total extensional strain across the caldera is on the order of 15 percent, and there is no evidence for progressive tilting of 34–25 Ma rocks that would indicate protracted Eocene–Oligocene extension. The caldera appears to have been tilted as an intact block after 25 Ma, probably during the middle Miocene extensional faulting well documented to the north and south of the study area.

Graphite in the Bishop Tuff and its effect on postcaldera oxygen fugacity

USGS Publications Warehouse

Hildreth, Edward; Ryan-Davis, Juliet; Harlow, Benjamin

2017-01-01

Several cubic kilometers of Paleozoic graphite-bearing argillitic country rocks are present as lithic fragments in Bishop Tuff ignimbrite and fallout. The lithics were entrained by the 650 km3 of rhyolite magma that vented during the 5- to 6-day-long, caldera-forming eruption at Long Valley, California. The caldera is floored by a 350 km2 roof plate that collapsed during the eruption and consists in large part of the Paleozoic strata that provided the abundant hornfelsed metapelitic lithic clasts in the tuff. Graphite has been identified by Raman spectroscopy, electron-dispersive spectroscopy, and X-ray diffraction as an irregularly dispersed component in the small fraction of Bishop Tuff pumice that is dark-colored. Carbon concentration has been determined in pumice, lithics, and wall rocks. Values of δ13C range from –21‰ to –29‰ Vienna Peedee Belemnite (VPDB) for pumice, lithics, and argillitic wall rocks, reflecting the biogenic origin of the reduced carbon in oxygen-limited black Paleozoic marine mudrocks. Carbonate contents, measured separately, are negligible in fresh pumice and lithics. Microprobe analyses of titanomagnetite-ilmenite pairs show that oxygen-fugacity values of numerous batches of postcaldera Early Rhyolite (750–640 ka; ~100 km3) are up to one log unit more reduced than those of the temperature–oxygen fugacity (T-fO2) array of the Bishop Tuff (767 ka), despite similar major-element compositions and Fe-Ti–oxide temperature ranges. All of the many batches of Early Rhyolite, which erupted episodically over an interval of ~125,000 years, yield the reduced fO2 values, indicating that reaction with graphite lowered magmatic fO2 after the caldera-forming eruption but before the first eruption of Early Rhyolite. It is inferred that reaction of postcaldera rhyolite magma with the reduced carbon in a great mass of subsided roof rocks lowered its fO2. It is suggested that comparable effects could have attended caldera collapse of other magma chambers hosted in continental sedimentary rocks.

Soft sediment deformation structures in a lacustrine sedimentary succession induced by volcano-tectonic activities: An example from the Cretaceous Beolgeumri Formation, Wido Volcanics, Korea

NASA Astrophysics Data System (ADS)

Ko, Kyoungtae; Kim, Sung Won; Lee, Hong-Jin; Hwang, In Gul; Kim, Bok Chul; Kee, Won-Seo; Kim, Young-Seog; Gihm, Yong Sik

2017-08-01

The Cretaceous Beolgeumri Formation is composed of laminated mudstones intercalated with sandstones, chert, and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike-slip fault systems on the southwestern Korean Peninsula. The Beolgeumri Formation contains various types of soft sediment deformation (SSD) structures that are characterized by a wide extent (< 4 km), lateral continuity (< 200 m), and vertical repetition. The SSD structures can be classified into six categories based on their morphological features and deformation styles: 1) fold structures, 2) load structures, 3) water-escape structures, 4) rip-down structures, 5) boudin structures, and 6) synsedimentary fault structures. Field examination of SSD structures together with an analysis of the sedimentological records of the Beolgeumri Formation indicate that the SSD structures formed largely by liquefaction and/or fluidization triggered by ground shaking during earthquakes. To constrain the timing of the development of SSD structures in the Beolgeumri Formation, we conducted sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age dating of block sized lithic clasts bearing volcaniclastic deposits that conformably underlie (the Mangryeongbong Tuff) and overlie (the Ttandallae Tuff) the Beolgeumri Formation. The Mangryeongbong and Ttandallae Tuffs have ages of 86.63 ± 0.83 Ma and 87.24 ± 0.36 Ma, respectively, indicating that the Beolgeumri Formation was deposited during a short interval between major volcanic eruptions. The large lithic clasts of volcaniclastic deposits suggest that the Beolgeumri Formation was deposited adjacent to an active volcanic edifice(s). Syndepositional magmatic activities are suggested by the occurrence of a lapilli tuff bed in the Beolgeumri Formation and an igneous intrusion (intermediate sill) that is crosscut by a sand dike, as well as the similar age results of the underlying and overlying volcaniclastic deposits. Thus, we infer that the earthquakes that caused the development of SSD structures in the study area were closely related to syndepositional magmatic activities, as is the case for modern tectonic earthquakes around active volcanoes.

The Lake Forest Tuff Ring, Lake Tahoe, CA: Age and Geochemistry of a Post-arc Phreatomagmatic Eruption

NASA Astrophysics Data System (ADS)

Cousens, B. L.; Henry, C. D.; Pauly, B. D.

2007-12-01

The Lake Tahoe region of the northern Sierra Nevada consists of Mesozoic plutonic rocks blanketed by Mio- Pliocene arc volcanic rocks and locally overlain by < 2.5 Ma post-arc lavas. Several volcanic features along the Lake Tahoe shoreline indicate that magmas commonly erupted into shallow regions of the lake during the last 2.5 Ma, including the Eagle Rock vent (Kortemeier and Schweickert 2007), Tahoe City pillow lavas and palagonite layers, and the Lake Forest tuff ring (Sylvester et al., 2007). Here we report on the age and composition of the rocks at Lake Forest, aiming to identify the source of the volcanic rocks compared to arc and post-arc lavas in the area. The low-relief Lake Forest tuff ring, located on the lakeshore west of Dollar Point, consists of radially outward-dipping layers composed primarily of loosely-cemented angular, microvesicular lava fragments with minor basaltic bombs and a scoria pile at the east end of the exposed ring. Most fragments are poorly phyric, and two samples are andesites similar to post-arc lavas sampled at higher elevations. The bombs are vesicular, poorly olivine/plagioclase-phyric basaltic andesites with chilled margins and glassy matrices. Scoria in the scoria pile, which we tentatively interpret as a slump, are similar texturally to the bombs but are more silica-rich. Chemically, the fragments, bombs and scoria are more primitive (higher Mg number) than local post-arc and arc lavas, and have trace element ratios and normalized incompatible element patterns similar to, but not identical to, local post-arc lava flows. Thus the Lake Forest tuff ring was the product of a shoreline eruptive event and did not form from lavas flowing downslope into the water. The fragments, bombs and scoria each have different radiogenic isotopic compositions and incompatible element ratios, indicating that primary magma compositions varied during the eruption(s) that produced the tuff ring. Our ongoing geochronological analyses will help constrain the timing of magmatism and the formation of Lake Tahoe.

Numerical Simulation of Tuff Dissolution and Precipitation Experiments: Validation of Thermal-Hydrologic-Chemical (THC) Coupled-Process Modeling

NASA Astrophysics Data System (ADS)

Dobson, P. F.; Kneafsey, T. J.

2001-12-01

As part of an ongoing effort to evaluate THC effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation. To replicate mineral dissolution by condensate in fractured tuff, deionized water equilibrated with carbon dioxide was flowed for 1,500 hours through crushed Yucca Mountain tuff at 94° C. The reacted water was collected and sampled for major dissolved species, total alkalinity, electrical conductivity, and pH. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/L; silica was the dominant dissolved constituent. A portion of the steady-state reacted water was flowed at 10.8 mL/hr into a 31.7-cm tall, 16.2-cm wide vertically oriented planar fracture with a hydraulic aperture of 31 microns in a block of welded Topopah Spring tuff that was maintained at 80° C at the top and 130° C at the bottom. The fracture began to seal within five days. A 1-D plug-flow model using the TOUGHREACT code developed at Berkeley Lab was used to simulate mineral dissolution, and a 2-D model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The fracture-plugging simulations result in the precipitation of amorphous silica at the base of the boiling front, leading to a hundred-fold decrease in fracture permeability in less than 6 days, consistent with the laboratory experiment. These results help validate the use of the TOUGHREACT code for THC modeling of the Yucca Mountain system. The experiment and simulations indicate that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. The TOUGHREACT code will be used to evaluate larger-scale silica sealing observed in a portion of the Yellowstone geothermal system, a natural analog for the precipitation-experiment processes.

Paleomagnetism and Lithostratigraphy of the Miocene Tuff of Huntoon Creek Type Section

NASA Astrophysics Data System (ADS)

Johnson, S.; Pluhar, C. J.; Lindeman, J. R.

2014-12-01

Here we define the Tuff of Huntoon Creek (THC), previously identified and mapped in Mono Basin, CA by Gilbert et al. (1968) as "latite ignimbrite" (K-Ar date of 11.1-11.9 Ma). Formally defining this formation and its paleomagnetic characteristics, can help reveal the spatial and temporal relationships of the Walker Lane and Mina Deflection structural features, including distribution of vertical axis rotation. THC is composed of four tuffs with an intercalated volcaniclastic sandstone giving a total stratigraphic thickness of ~300 m. We define THC in a gorge of Huntoon Creek, where the stratigraphic section is capped by Pliocene basalt. The lowest and most extensive stratigraphic unit, the Huntoon Valley member of THC, is ~243 m thick and can be distinguished from other units by the presence of sanidine and biotite phenocrysts and normal polarity. A 7-meter-thick volcaniclastic sandstone overlies the Huntoon Valley member, straddling a magnetic polarity reversal within the section. The 3 overlying members of THC are reversed-polarity, biotite-bearing, sanidine-free tuffs of variable degrees of welding. Their paleomagnetic directions are each statistically distinguishable from the others, indicating that the deposition of each tuff is separated by a significant amount of time and can be used as a geologically instantaneous measure of Earth's magnetic field for purposes of averaging out secular variation. The capping Pliocene olivine basalt was emplaced over an erosional unconformity of significant relief, as evidenced by the complete absence at some locations of the uppermost biotite-bearing THC member. The tilt corrected mean paleomagnetic direction for the 4 members of THC indicate a clockwise rotation magnitude of 77.5°±40.3°. The absolute rotation results of this locality are statistically indistinguishable from the relative rotation results of this locality compared to Cowtrack Mountain (Lindeman et al. 2013). The corroboration of these data suggests that this region of the Mina Deflection has undergone large magnitude clockwise rotation since the emplacement of THC. However, the capping basalt exhibits a magnetic declination of due north, suggesting that this unit experienced little rotation and that rotational deformation in this region had mostly ended by the time of its emplacement at ~3.5 Ma.

Chemical-abrasion SIMS dating of zircon from the Eocene Caetano caldera, Nevada

NASA Astrophysics Data System (ADS)

Colgan, J.; Watts, K. E.; John, D. A.; Henry, C. D.; Coble, M. A.; Vazquez, J. A.

2012-12-01

The Eocene Caetano caldera in northern Nevada formed during eruption of ~1100 km3 of crystal-rich rhyolite. Miocene extension cut the caldera into a set of fault blocks that expose minor pre-caldera volcanic rocks, two units of intracaldera Caetano Tuff up to 4 km thick, ash-flow tuff feeder dikes and ring-fracture intrusions, caldera collapse breccias, and post-collapse resurgent intrusions. Single-crystal 40Ar/39Ar sanidine dates on all parts of the caldera system overlap, yielding a 34.01 ± 0.05 Ma (n=17, Fish Canyon sanidine = 28.201 Ma) age for the eruption. 40Ar/39Ar dating also documents several preceding episodes of magmatism: 35.69 ± 0.06 Ma (sanidine, n =13) rhyolite dikes in the nearby Cortez gold district, 35.21 ± 0.18 Ma (plagioclase, n=1) andesite lava underlying Caetano Tuff, and a 38.90 ± 0.11 Ma (biotite, n=1), dacite dike in the northeastern caldera wall. Extensive U-Pb SHRIMP dating of zircon from both the Cortez dikes and all phases of the Caetano system suggests continuous magmatism from 40-34 Ma. However, all samples contain at least some—sometimes many—zircons with U-Pb ages younger than the 34.0 Ma argon age. To determine if anomalously young zircon ages are due to Pb-loss, we analyzed representative samples of the upper Caetano Tuff and the Redrock Canyon resurgent pluton with and without chemical abrasion to mitigate Pb-loss. Bulk zircon separates were annealed at 850°C for 48 hours, then chemically abraded with 10:1 HF/HNO3 vapor in a Parr bomb at 225°C for 8 hours, based on protocols outlined by Mattinson (2005). Both treated and untreated zircons from the same sample were mounted in epoxy and polished to their midsections, then imaged on the SEM using BSE and CL. The SHRIMP-RG at Stanford University was used to determine U-Pb ages and trace element concentrations in single spots for ~25 to 30 individual zircons per sample, using a round-robin procedure and two zircon age standards (R33 and 080) to monitor external precision. Analyses revealed distinctly different age populations for the abraded and untreated zircons. The chemically abraded populations yielded unimodal zircon age distributions with mean ages that overlap with the 40Ar/39Ar age. Untreated zircon populations yielded mean ages 0.9-1.5 Ma younger than the 40Ar/39Ar. In the untreated populations, 50-60% of zircon ages are younger than 34.0 Ma at 1σ, versus 15-20% in the chemically abraded populations. Comparison of trace element data from treated and untreated populations indicates that trace element concentrations are apparently unaffected by the chemical abrasion procedure. Further experiments are underway, but we tentatively conclude that chemical abrasion is effective for removing damaged Pb-loss portions of zircons while still enabling high spatial resolution U-Pb dating and trace element analysis. It appears to be a relatively fast and low-cost way to improve the accuracy of SIMS dating of large populations of zircon from Tertiary and older plutonic and volcanic rocks where Pb-loss is frequently an issue.

The Nopal 1 Uranium Deposit: an Overview

NASA Astrophysics Data System (ADS)

Calas, G.; Allard, T.; Galoisy, L.

2007-05-01

The Nopal 1 natural analogue is located in the Pena Blanca uranium district, about 50 kms north of Chihuahua City, Mexico. The deposit is hosted in tertiary ignimbritic ash-flow tuffs, dated at 44 Ma (Nopal and Colorados formations), and overlying the Pozos conglomerate formation and a sequence of Cretaceous carbonate rocks. The deposit is exposed at the ground surface and consists of a near vertical zone extending over about 100 m with a diameter of 40 m. An interesting characteristic is that the primary mineralization has been exposed above the water table, as a result of the uplift of the Sierra Pena Blanca, and subsequently oxidized with a remobilization of hexavalent uranium. The primary mineralization has been explained by various genetic models. It is associated to an extensive hydrothermal alteration of the volcanic tuffs, locally associated to pyrite and preserved by an intense silicification. Several kaolinite parageneses occur in fissure fillings and feldspar pseudomorphs, within the mineralized breccia pipe and the barren surrounding rhyolitic tuffs. Smectites are mainly developed in the underlying weakly welded tuffs. Several radiation-induced defect centers have been found in these kaolinites providing a unique picture of the dynamics of uranium mobilization (see Allard et al., this session). Another evidence of this mobilization is given by the spectroscopy of uranium-bearing opals, which show characteristic fluorescence spectra of uranyl groups sorbed at the surface of silica. By comparison with the other uranium deposits of the Sierra Pena Blanca and the nearby Sierra de Gomez, the Nopal 1 deposit is original, as it is one of the few deposits hving retained a reduced uranium mineralization.

OSL dating of a Pleistocene maar: Birket Ram, the Golan heights

USGS Publications Warehouse

Shaanan, U.; Porat, N.; Navon, O.; Weinberger, R.; Calvert, A.; Weinstein, Y.

2011-01-01

Direct dating of maars and their phreatomagmatic deposits is difficult due to the dominance of lithic (host rock) fragments and glassy particles of the juvenile magma. In this paper we demonstrate that optically stimulated luminescence (OSL) dating can be successfully used for age determination of phreatomagmatic deposits. We studied the tuff deposit of Birket Ram, a basanitic maar located at the northern edge of the Golan heights on the western Arabian plate. The maar is underlain by a thick section of Pleistocene basalts, and currently hosts a small lake. It is filled by approximately 90m of lacustrine sediments with radiocarbon ages extrapolated to 108ka at the base. OSL was applied to quartz grains extracted from tuffs and paleosols in order to set the time frame of the phreatomagmatism at the site. A maximum age constraint of 179??13ka was determined for a paleosol that underlies the maar ejecta. Quartz grains from two layers in the tuff section yielded a direct age of 129??6ka for the phreatomagmatic eruption. A younger age of 104??7ka, which was determined for a tuff layer underlying a basaltic flow, was attributed to thermal resetting during the lava emplacement. This was confirmed by an 40Ar/39Ar age of 101??3ka determined on the overlying basalt. The internal consistency of the OSL ages and the agreement with the 40Ar/39Ar age determination as well as with previous estimates demonstrates the potential of OSL for maar dating. ?? 2010 Elsevier B.V.

Freeze-Thaw Cycle Test on Basalt, Diorite and Tuff Specimens with the Simulated Ground Temperature of Antarctica

NASA Astrophysics Data System (ADS)

Park, J.; Hyun, C.; Cho, H.; Park, H.

2010-12-01

Physical weathering caused by freeze-thaw action in cold regions was simulated with artificial weathering simulator in laboratory. Physical weathering of rock in cold regions usually depends on the temperature, rock type and moisture content. Then these three variables were considered in this study. The laboratory freeze-thaw tests were conducted on the three types of rocks, e.g. diorite, basalt and tuff, which are the major rock types around Sejong Station, King George Island, Antarctica. Nine core samples composed of three samples from each rock type were prepared in NX core, and 50 cycles of freeze-thaw test was carried out under dried and saturated water conditions. In this study, the physical weathering of rocks was investigated after each 10 cycles by measuring P-wave velocity, bulk density, effective porosity, Schmidt hardness and uniaxial compression strength(UCS). The experimental result of the diorite and the tuff specimens showed that P-wave velocity, bulk density, effective porosity, Schmidt hardness and UCS were gradually decreased as weathering progresses, but the result of the basalt specimens did not show typical trends due to the characteristics of irregular pore distribution and various pore sizes. Scanning electron microscopy(SEM) photographs of diorite, basalt and tuff specimens weathered in dried and saturated conditions were also acquired to investigate the role of water during physical weathering processes. The number and size of microcracks were increased as weathering progresses. This work was supported by the National Research Foundation of Korea(NRF) Grant(NRF-2010-0027753).

Actinide Sorption in Rainier Mesa Tunnel Waters from the Nevada Test Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, P; Zavarin, M; Leif, R

2007-12-17

The sorption behavior of americium (Am), plutonium (Pu), neptunium (Np), and uranium (U) in perched Rainier Mesa tunnel water was investigated. Both volcanic zeolitized tuff samples and groundwater samples were collected from Rainier Mesa, Nevada Test Site, NV for a series of batch sorption experiments. Sorption in groundwater with and without the presence of dissolved organic matter (DOM) was investigated. Am(III) and Pu(IV) are more soluble in groundwater that has high concentrations of DOM. The sorption K{sub d} for Am(III) and Pu(IV) on volcanic zeolitized tuff was up to two orders of magnitude lower in samples with high DOM (15more » to 19 mg C/L) compared to samples with DOM removed (< 0.4 mg C/L) or samples with naturally low DOM (0.2 mg C/L). In contrast, Np(V) and U(VI) sorption to zeolitized tuff was much less affected by the presence of DOM. The Np(V) and U(VI) sorption Kds were low under all conditions. Importantly, the DOM was not found to significantly sorb to the zeolitized tuff during these experiment. The concentration of DOM in groundwater affects the transport behavior of actinides in the subsurface. The mobility of Am(III) and Pu(IV) is significantly higher in groundwater with elevated levels of DOM resulting in potentially enhanced transport. To accurately model the transport behavior of actinides in groundwater at Rainier Mesa, the low actinide Kd values measured in groundwater with high DOM concentrations must be incorporated in predictive transport models.« less

The effect of dissolution of volcanic glass on the water chemistry in a tuffaceous aquifer, Rainier Mesa, Nevada

USGS Publications Warehouse

White, Art F.; Claassen, H.C.; Benson, Larry V.

1980-01-01

Geochemistry of ground water associated with the Tertiary tuffs within Rainier Mesa, southern Nevada, was investigated to determine the relative importance of glass dissolution in controlling water chemistry. Water samples were obtained both from interstitial pores in core sections and from free-flowing fractures. Cation com- positions showed that calcium and magnesium decreased as a function of depth in the mesa, as sodium increased. The maximum effect occurs within alteration zones containing clinoptilolite and montmorillonite, suggesting these minerals effectively remove bivalent cations from the system. Comparisons are made between compositions of ground waters found within Rainier Mesa that apparently have not reacted with secondary minerals and compositions of waters produced by experimental dissolution of vitric and crystalline tufts which comprise the principal aquifers in the area. The two tuff phases have the same bulk chemistry but produce aqueous solutions of different chemistry. Rapid parabolic dissolution of sodium and silica from, and the retention of, potassium within the vitric phase verify previous predictions concerning water compositions associated with vitric volcanic rocks. Parabolic dissolution of the crystalline phase results in solutions high in calcium and magnesium and low in silica. Extrapolation of the parabolic dissolution mechanism for the vitric tuff to long times successfully reproduces, at com- parable pH, cation ratios existing in Rainier Mesa ground water. Comparison of mass- transfer rates of the vitric and crystalline tuffs indicates that the apparent higher glass-surface to aqueous-volume ratio associated with the vitric rocks may account for dominance of the glass reaction.

The age of the Tunas formation in the Sauce Grande basin-Ventana foldbelt (Argentina): Implications for the Permian evolution of the southwestern margin of Gondwana

NASA Astrophysics Data System (ADS)

López-Gamundí, Oscar; Fildani, Andrea; Weislogel, Amy; Rossello, Eduardo

2013-08-01

New SHRIMP radiogenic isotope dating on zircons in tuffs (280.8 ± 1.9 Ma) confirms the Early Permian (Artinskian) age of the uppermost section of the Tunas Formation. Tuff-rich levels in the Tunas Formation are exposed in the Ventana foldbelt of central Argentina; they are part of a deltaic to fluvial section corresponding to the late overfilled stage of the Late Paleozoic Sauce Grande foreland basin. Recent SHRIMP dating of zircons from the basal Choiyoi volcanics exposed in western Argentina yielded an age of 281.4 ± 2.5 Ma (Rocha-Campos et al., 2011). The new data for the Tunas tuffs suggest that the volcanism present in the Sauce Grande basin can be considered as the distal equivalent of the earliest episodes of the Choiyoi volcanism of western Argentina. From the palaeoclimatic viewpoint the new Tunas SHRIMP age confirms that by early Artinskian glacial conditions ceased in the Sauce Grande basin and, probably, in adajacent basins in western Gondwana.

Oxidation of basaltic tephras: Influence on reflectance in the 1 micron region

NASA Technical Reports Server (NTRS)

Farrand, William H.; Singer, Robert B.

1991-01-01

As part of a ongoing study into the products of hydrovolcanism, tuffs were examined from the Cerro Colorado and Pavant Butte tuff cones. The former resides in the northeastern corner of the Pinacate Volcanic Field in Sonara, Mexico and the latter is in the Black Rock Desert of southern Utah. Numerous samples were collected and many of these had their Vis/IR reflectance measured. It seems likely that in the palagonite tuffs there is a combination of nanocrystalline ferric oxide phases contributing to the UV absorption edge, but not to the 1 micron band, plus more crystalline ferric oxides which do contribute to that band as well as ferrous iron within unaltered sideromelane which is skewing the band center to longer wavelengths. This work has implications for the study of Mars. The present work indicates that when ferrous and ferric iron phases are both present, their combined spectral contribution is a single band in the vicinity of 1 micron. The center, depth, and width of that feature has potential to be used to gauge the relative proportions of ferrous and ferric iron phases.

Biogas cleaning and upgrading with natural zeolites from tuffs.

PubMed

Paolini, Valerio; Petracchini, Francesco; Guerriero, Ettore; Bencini, Alessandro; Drigo, Serena

2016-01-01

CO2 adsorption on synthetic zeolites has become a consolidated approach for biogas upgrading to biomethane. As an alternative to synthetic zeolites, tuff waste from building industry was investigated in this study: indeed, this material is available at a low price and contains a high fraction of natural zeolites. A selective adsorption of CO2 and H2S towards CH4 was confirmed, allowing to obtain a high-purity biomethane (CO2 <2 g m(-3), i.e. 0.1%; H2S <1.5 mg m(-3)), suitable for injection in national grids or as vehicle fuel. The loading capacity was found to be 45 g kg(-1) and 40 mg kg(-1), for CO2 and H2S, respectively. Synthetic gas mixtures and real biogas samples were used, and no significant effects due to biogas impurities (e.g. humidity, dust, moisture, etc.) were observed. Thermal and vacuum regenerations were also optimized and confirmed to be possible, without significant variations in efficiency. Hence, natural zeolites from tuffs may successfully be used in a pressure/vacuum swing adsorption process.

Hydrology of the unsaturated zone, Yucca Mountain, Nevada

USGS Publications Warehouse

Lecain, Gary D.; Stuckless, John S.

2012-01-01

The unsaturated zone at Yucca Mountain was investigated as a possible site for the nation's first high-level nuclear waste repository. Scientific investigations included infiltration studies, matrix properties testing, borehole testing and monitoring, underground excavation and testing, and the development of conceptual and numerical models of the hydrologic processes at Yucca Mountain. Infiltration estimates by empirical and geochemical methods range from 0.2 to 1.4 mm/yr and 0.2–6.0 mm/yr, respectively. Infiltration estimates from numerical models range from 4.5 mm/yr to 17.6 mm/yr. Rock matrix properties vary vertically and laterally as the result of depositional processes and subsequent postdepositional alteration. Laboratory tests indicate that the average matrix porosity and hydraulic conductivity values for the main level of the proposed repository (Topopah Spring Tuff middle nonlithophysal zone) are 0.08 and 4.7 × 10−12 m/s, respectively. In situ fracture hydraulic conductivity values are 3–6 orders of magnitude greater. The permeability of fault zones is approximately an order of magnitude greater than that of the surrounding rock unit. Water samples from the fault zones have tritium concentrations that indicate some component of postnuclear testing. Gas and water vapor movement through the unsaturated zone is driven by changes in barometric pressure, temperature-induced density differences, and wind effects. The subsurface pressure response to surface barometric changes is controlled by the distribution and interconnectedness of fractures, the presence of faults and their ability to conduct gas and vapor, and the moisture content and matrix permeability of the rock units. In situ water potential values are generally less than −0.2 MPa (−2 bar), and the water potential gradients in the Topopah Spring Tuff units are very small. Perched-water zones at Yucca Mountain are associated with the basal vitrophyre of the Topopah Spring Tuff or the Calico Hills bedded tuff. Thermal gradients in the unsaturated zone vary with location, and range from ~2.0 °C to 6.0 °C per 100 m; the variability appears to be associated with topography. Large-scale heater testing identified a heat-pipe signature at ~97 °C, and identified thermally induced and excavation-induced changes in the stress field. Elevated gas-phase CO2 concentrations and a decrease in the pH of water from the condensation zone also were identified. Conceptual and numerical flow and transport models of Yucca Mountain indicate that infiltration is highly variable, both spatially and temporally. Flow in the unsaturated zone is predominately through fractures in the welded units of the Tiva Canyon and Topopah Spring Tuffs and predominately through the matrix in the Paintbrush Tuff nonwelded units and Calico Hills Formation. Isolated, transient, fast-flow paths, such as faults, do exist but probably carry only a small portion of the total liquid-water flux at Yucca Mountain. The Paintbrush Tuff nonwelded units act as a storage buffer for transient infiltration pulses. Faults may act as flow boundaries and/or fast pathways. Below the proposed repository horizon, low-permeability lithostratigraphic units of the Topopah Spring Tuff and/or the Calico Hills Formation may divert flow laterally to faults that act as conduits to the water table. Advective transport pathways are consistent with flow pathways. Matrix diffusion is the major mechanism for mass transfer between fractures and the matrix and may contribute to retardation of radionuclide transport when fracture flow is dominant. Sorption may retard the movement of radionuclides in the unsaturated zone; however, sorption on mobile colloids may enhance radionuclide transport. Dispersion is not expected to be a major transport mechanism in the unsaturated zone at Yucca Mountain. Natural analogue studies support the concepts that percolating water may be diverted around underground openings and that the percentage of infiltration that becomes seepage decreases as infiltration decreases.

Geologic map of the Fraser 7.5-minute quadrangle, Grand County, Colorado

USGS Publications Warehouse

Shroba, Ralph R.; Bryant, Bruce; Kellogg, Karl S.; Theobald, Paul K.; Brandt, Theodore R.

2010-01-01

The geologic map of the Fraser quadrangle, Grand County, Colo., portrays the geology along the western boundary of the Front Range and the eastern part of the Fraser basin near the towns of Fraser and Winter Park. The oldest rocks in the quadrangle include gneiss, schist, and plutonic rocks of Paleoproterozoic age that are intruded by younger plutonic rocks of Mesoproterozoic age. These basement rocks are exposed along the southern, eastern, and northern margins of the quadrangle. Fluvial claystone, mudstone, and sandstone of the Upper Jurassic Morrison Formation, and fluvial sandstone and conglomeratic sandstone of the Lower Cretaceous Dakota Group, overlie Proterozoic rocks in a small area near the southwest corner of the quadrangle. Oligocene rhyolite tuff is preserved in deep paleovalleys cut into Proterozoic rocks near the southeast corner of the quadrangle. Generally, weakly consolidated siltstone and minor unconsolidated sediments of the upper Oligocene to upper Miocene Troublesome Formation are preserved in the post-Laramide Fraser basin. Massive bedding and abundant silt suggest that loess or loess-rich alluvium is a major component of the siltstone in the Troublesome Formation. A small unnamed fault about one kilometer northeast of the town of Winter Park has the youngest known displacement in the quadrangle, displacing beds of the Troublesome Formation. Surficial deposits of Pleistocene and Holocene age are widespread in the Fraser quadrangle, particularly in major valleys and on slopes underlain by the Troublesome Formation. Deposits include glacial outwash and alluvium of non-glacial origin; mass-movement deposits transported by creep, debris flow, landsliding, and rockfall; pediment deposits; tills deposited during the Pinedale and Bull Lake glaciations; and sparse diamictons that may be pre-Bull Lake till or debris-flow deposits. Some of the oldest surficial deposits may be as old as Pliocene.

U-Pb detrital zircon dates and provenance data from the Beaufort Group (Karoo Supergroup) reflect sedimentary recycling and air-fall tuff deposition in the Permo-Triassic Karoo foreland basin

NASA Astrophysics Data System (ADS)

Viglietti, Pia A.; Frei, Dirk; Rubidge, Bruce S.; Smith, Roger M. H.

2018-07-01

Detrital zircon U-Pb age dating was used for provenance determination and maximum age of deposition for the Upper Permian (upper Teekloof and Balfour formations) and Lower Triassic (Katberg Formation) lithostratigraphic subdivisions of the Beaufort Group of South Africa's Karoo Basin. Ten samples were analysed using laser ablation - single collector - magnetic sectorfield - inductively coupled plasma - mass spectrometry (LA-SF-ICP-MS). The results reveal a dominant Late Carboniferous-Late Permian population (250 ± 5 Ma - 339 ± 5 Ma), a secondary Cambrian-Neoproterozoic (489 ± 5 Ma to 878 ± 24 Ma) population, a minor Mesoproterozoic (908 ± 24 Ma to 1308 ± 23) population, and minor occurrences of Devonian, Ordovician, Proterozoic and Archean zircon grains. Multiple lines of evidence (e.g. roundness and fragmentary nature of zircons, palaeo-current directions, and previous work), suggest the older zircon populations are related to sedimentary recycling in the Gondwanide Orogeny. The youngest and dominant population contain elongate euhedral grains interpreted to be directly derived from their protolith. Since zircons form in felsic igneous rocks, and no igneous rocks of Late Permian age occur in the Karoo Basin, these findings suggest significant input of volcanic material by ash falls. These results support sedimentological and palaeontological data for a Lopingian (Late Permian) age for the upper Beaufort Group, but contradict previous workers who retrieved Early Triassic dates from zircons in ashes for the Beaufort and Ecca Groups. Pb-loss not revealed by resolvable discordance on the concordia diagram, and metamictization of natural zircons are not factored into the conclusions of earlier workers.

Long Valley Caldera Lake and reincision of Owens River Gorge

USGS Publications Warehouse

Hildreth, Wes; Fierstein, Judy

2016-12-16

Owens River Gorge, today rimmed exclusively in 767-ka Bishop Tuff, was first cut during the Neogene through a ridge of Triassic granodiorite to a depth as great as its present-day floor and was then filled to its rim by a small basaltic shield at 3.3 Ma. The gorge-filling basalt, 200 m thick, blocked a 5-km-long reach of the upper gorge, diverting the Owens River southward around the shield into Rock Creek where another 200-m-deep gorge was cut through the same basement ridge. Much later, during Marine Isotope Stage (MIS) 22 (~900–866 ka), a piedmont glacier buried the diversion and deposited a thick sheet of Sherwin Till atop the basalt on both sides of the original gorge, showing that the basalt-filled reach had not, by then, been reexcavated. At 767 ka, eruption of the Bishop Tuff blanketed the landscape with welded ignimbrite, deeply covering the till, basalt, and granodiorite and completely filling all additional reaches of both Rock Creek canyon and Owens River Gorge. The ignimbrite rests directly on the basalt and till along the walls of Owens Gorge, but nowhere was it inset against either, showing that the basalt-blocked reach had still not been reexcavated. Subsidence of Long Valley Caldera at 767 ka produced a steep-walled depression at least 700 m deeper than the precaldera floor of Owens Gorge, which was beheaded at the caldera’s southeast rim. Caldera collapse reoriented proximal drainages that had formerly joined east-flowing Owens River, abruptly reversing flow westward into the caldera. It took 600,000 years of sedimentation in the 26-km-long, usually shallow, caldera lake to fill the deep basin and raise lake level to its threshold for overflow. Not until then did reestablishment of Owens River Gorge begin, by incision of the gorge-filling ignimbrite.

Facies analysis of tuffaceous volcaniclastics and felsic volcanics of Tadpatri Formation, Cuddapah basin, Andhra Pradesh, India

NASA Astrophysics Data System (ADS)

Goswami, Sukanta; Dey, Sukanta

2018-05-01

The felsic volcanics, tuff and volcaniclastic rocks within the Tadpatri Formation of Proterozoic Cuddapah basin are not extensively studied so far. It is necessary to evaluate the extrusive environment of felsic lavas with associated ash fall tuffs and define the resedimented volcaniclastic components. The spatial and temporal bimodal association were addressed, but geochemical and petrographic studies of mafic volcanics are paid more attention so far. The limited exposures of eroded felsic volcanics and tuffaceous volcaniclastic components in this terrain are highly altered and that is the challenge of the present facies analysis. Based on field observation and mapping of different lithounits a number of facies are categorized. Unbiased lithogeochemical sampling have provided major and selective trace element data to characterize facies types. Thin-section studies are also carried out to interpret different syn- and post- volcanic features. The facies analysis are used to prepare a representative facies model to visualize the entire phenomenon with reference to the basin evolution. Different devitrification features and other textural as well as structural attributes typical of flow, surge and ash fall deposits are manifested in the middle, lower and upper stratigraphic levels. Spatial and temporal correlation of lithologs are also supportive of bimodal volcanism. Felsic and mafic lavas are interpreted to have erupted through the N-S trending rift-associated fissures due to lithospheric stretching during late Palaeoproterozoic. It is also established from the facies model that the volcaniclastics were deposited in the deeper part of the basin in the east. The rifting and associated pressure release must have provided suitable condition of decompression melting at shallow depth with high geothermal gradient and this partial melting of mantle derived material at lower crust must have produced mafic magmas. Such upwelling into cold crust also caused partial heat transfer and associated melting of the surrounding shallow crustal rocks to generate felsic magmas.

Volcanic stratigraphy of large-volume silicic pyroclastic eruptions during Oligocene Afro-Arabian flood volcanism in Yemen

NASA Astrophysics Data System (ADS)

Peate, Ingrid Ukstins; Baker, Joel A.; Al-Kadasi, Mohamed; Al-Subbary, Abdulkarim; Knight, Kim B.; Riisager, Peter; Thirlwall, Matthew F.; Peate, David W.; Renne, Paul R.; Menzies, Martin A.

2005-12-01

A new stratigraphy for bimodal Oligocene flood volcanism that forms the volcanic plateau of northern Yemen is presented based on detailed field observations, petrography and geochemical correlations. The >1 km thick volcanic pile is divided into three phases of volcanism: a main basaltic stage (31 to 29.7 Ma), a main silicic stage (29.7 to 29.5 Ma), and a stage of upper bimodal volcanism (29.5 to 27.7 Ma). Eight large-volume silicic pyroclastic eruptive units are traceable throughout northern Yemen, and some units can be correlated with silicic eruptive units in the Ethiopian Traps and to tephra layers in the Indian Ocean. The silicic units comprise pyroclastic density current and fall deposits and a caldera-collapse breccia, and they display textures that unequivocally identify them as primary pyroclastic deposits: basal vitrophyres, eutaxitic fabrics, glass shards, vitroclastic ash matrices and accretionary lapilli. Individual pyroclastic eruptions have preserved on-land volumes of up to ˜850 km3. The largest units have associated co-ignimbrite plume ash fall deposits with dispersal areas >1×107 km2 and estimated maximum total volumes of up to 5,000 km3, which provide accurate and precisely dated marker horizons that can be used to link litho-, bio- and magnetostratigraphy studies. There is a marked change in eruption style of silicic units with time, from initial large-volume explosive pyroclastic eruptions producing ignimbrites and near-globally distributed tuffs, to smaller volume (<50 km3) mixed effusive-explosive eruptions emplacing silicic lavas intercalated with tuffs and ignimbrites. Although eruption volumes decrease by an order of magnitude from the first stage to the last, eruption intervals within each phase remain broadly similar. These changes may reflect the initiation of continental rifting and the transition from pre-break-up thick, stable crust supporting large-volume magma chambers, to syn-rift actively thinning crust hosting small-volume magma chambers.

Sorption Kinetics Of Selected Heavy Metals Adsorption To Natural And Fe(III) Modified Zeolite Tuff Containing Clinoptilolite Mineral

NASA Astrophysics Data System (ADS)

Sirotiak, Maroš; Lipovský, Marek; Bartošová, Alica

2015-06-01

In the research described in this paper, studied was sorption capacity of natural and ferric modification of zeolite tuff containing mineral clinoptilolite from the Nižný Hrabovec deposit to remove potentially toxic metals (ionic forms of chromium, nickel, copper and aluminium) from their water solutions. We reported that the Fe (III) zeolite has an enhanced ability to sorption of Cu (II), and a slight improvement occurs in the case of Cr (VI) and Ni (II). On the other hand, the deterioration was observed in the case of Al (III) adsorption.

Geochronology, stratigraphy and geochemistry of Cindery Tuff in Pliocene hominid-bearing sediments of the Middle Awash, Ethiopia.

PubMed

Hall, C M; Walter, R C; Westgate, J A; York, D

Cindery Tuff is a subalkaline, rhyolitic air-fall deposit that was probably produced by a mixed-magma eruption. It is a distinctive, datable, regional isochronous marker bed within the Pliocene sediments of the Middle Awash district, and is stratigraphically situated between two new fossil hominid discoveries. Based on 40Ar/39Ar analyses of plagioclase, rhyolitic glass and basaltic glass, as well as fission-track analyses of zircons, we estimate its age to be 3.8-4.0 Myr. This implies that associated hominid skull fragments are at least 3.9 Myr old.

Physical properties of Campi Flegrei tuff from variable depths

NASA Astrophysics Data System (ADS)

Vinciguerra, Sergio; Del Gaudio, Pierdomenico; Iarocci, Alessandro; Mollo, Silvio; Scarlato, Piergiorgio; Freda, Carmela

2010-05-01

A number of measurements on physical properties of volcanic tuff from different volcanic Italian districts (Campi Flegrei, Colli Albani, Lago di Vico) has been performed in the recent years. Petrophysical investigations carried out at increasing/decreasing effective pressure (Vinciguerra et al., 2005; 2008) revealed how, within the same lithology, the different degree of lithification and presence of clasts can affect significantly physical property values. Microstructural analyses revealed that the pressurization and depressurization cycles generate inelastic crack damage/pore collapse and permanent reduction of voids space. When cores from boreholes were investigated, significant variations of physical properties have been found even within the same tuff lithologies (Vinciguerra et al., 2008), which significantly influence the modelling of the overall physics and mechanics, as well as the input parameters for ground deformation and seismicity modelling. In this study we analysed the physical properties of Campi Flegrei tuff (12ka) cores from depths down to 100m, which is the most abundant and widely distributed lithology in the caldera (Rosi and Sbrana, 1987). CF tuff is a strongly heterogeneous pyroclastic flow material, which include cavities, pumice and crystals of sanidine, pyroxene and biotite (Vanorio et al., 2002; Vinciguerra et al., 2005). Total porosity was measured, after drying samples at 80°C for 24 hours, throughout a helium pycnometer (AccuPyc II 1340, Micromeritics Company) with ±0.01% accuracy. Initial total porosity of 52% was found for cores coming from 30m of depth. Total porosity decreases to 46% , when cores from 100m depth are considered. Bench measurements of P-wave and S-wave velocities carried out in dry conditions are of 1.8 and 1.2 km/s respectively for the 30m depth cores and increase up to 2.1 km/s and 1.35 km/s at depth of 100m. Taken together, the measurements of porosity and seismic velocities of P and S wave velocities revealed a significant compaction occurring even at such shallow depths. This observation suggests that pore collapse is a pervasive mechanism affecting such weak lithologies and can be activated even from very modest increase of effective pressure (1-10MPa). In order to proof this we aim to carry out simultaneous seismic velocity and permeability under increasing effective pressure, which simulate the lithostatic increasing load. The results obtained from laboratory measurements and their comparison with field determinations, such as sonic logs, provide crucial information for the interpretation of the inner volcanic district structure, and in turn suggest if/how mechanical and thermal stress can significantly change the rheology and permeability tuffs, opening new perspectives for the interpretation of the caldera dynamics.

Tectonic Setting and Bimodal Magmatic Evolution of Eocene Volcanic Rocks of the Bijgerd-Kuh-e Kharchin area, Uromieh-Dokhtar Zone, Iran

NASA Astrophysics Data System (ADS)

Davarpanah, A.; Khalatbari-Jafari, M.; Babaie, H. A.; Krogstad, E. J.; Mobasher, K.; La Tour, T. E.; Deocampo, D. M.

2008-12-01

Geochemical composition and texture of the Middle and Late Eocene volcanic, volcaniclastic, and volcanic- sedimentary rocks in the Bijgerd-Kuh-e Kharchin area, northwest of Saveh, provide significant geochemical and geological clues for the tectonic and magmatic evolution of the Uromieh-Dokhtar volcanic-plutonic zone of Iran. The Middle Eocene volcanic rocks have an intermediate composition and include green tuff and tuffaceous sandstone with intercalated sandstone, sandy tuff, and shale. The shale has lenses of nummulite- bearing limestone with a Middle Eocene detrital age. The time between the Middle and Late Eocene volcanic activities in this area is marked by the presence of andesite and rhyolitic tuff. The Late Eocene succession is distinguished by the presence of four alternating levels (horizons) of intermediate lava and ignimbrite which we designate as Eig. The ignimbrites of the Eig sequence have a rhyolitic composition and include ignimbrite- breccia, ignimbrite-tuff, and ignimbrite-lava pairs. The volume of the felsic volcanic rocks in this sequence far exceeds that of the intermediate rocks, which makes it unlikely that they evolved through the magmatic differentiation of a basaltic magma. The presence of the nummulite-bearing limestone lenses, and sandstone and conglomerate interbeds between the ignimbrites, suggests a shallow marine environment for the pyroclastic deposition and probably the eruptions. The tuff and siltstone of the Est unit that sits above the first ignimbrite may represent deep water, Late Eocene deposit. Oligo-Miocene limestone of the Qom Formation unconformably overlies the uppermost Late Eocene ignimbrite. Washings from red marls give microfossils with Late Eocene age for the Eig sequence, which is synchronous with other paleontological evidence that puts the peak volcanic activity as Late Eocene in the Bijgerd-Kuh-e Kharchin area. Field and petrographic evidence for magma mixing/mingling is given by the presence of mafic- intermediate enclaves in the ignimbrite, hybrid breccias with felsic and mafic clasts, felsic pseudo-flames filled with intermediate lava, heterogeneity in the ignimbrite texture, and sieve texture and oscillatory zoning of plagioclase and opacitization of olivine in the intermediate lava. Geochemical analyses of the major and trace elements (including the REE) and rock texture and assemblages indicate the bimodal magmatic characteristics of the mafic-intermediate lavas and ignimbrites. The tuff and the breccia show a hybrid elemental distribution between those of rhyolite and basalt. The ignimbrites show more enriched compositions than those of the mafic and intermediate rocks on the chondrite-normalized trace element distribution diagram. The higher enrichment of the LREE in the ignimbrites may be due to a crustal contribution. The primitive mantle-normalized elemental distributions show a distinct depletion of Nb and Ti, which suggests a subduction-related volcanism during Eocene.

Chemical evolution of a pleistocene rhyolitic center: Sierra La Primavera, Jalisco, México

NASA Astrophysics Data System (ADS)

Mahood, Gail A.

1981-06-01

The late Pleistocene caldera complex of the Sierra La Primavera, Jalisco, México, contains well-exposed lava flows and domes, ash-flow tuff, air-fall pumice, and caldera-lake sediments. All eruptive units are high-silica rhyolites, but systematic chemical differences correlate with age and eruptive mode. The caldera-producing unit, the 45-km3 Tala Tuff, is zoned from a mildly peralkaline first-erupted portion enriched in Na, Rb, Cs, Cl, F, Zn, Y, Zr, Hf, Ta, Nb, Sb, HREE, Pb, Th, and U to a metaluminous last-erupted part enriched in K, LREE, Sc, and Ti; Al, Ca, Mg, Mn, Fe, and Eu are constant within analytical errors. The earliest post-caldera lava, the south-central dome, is nearly identical to the last-erupted portion of the Tala Tuff, whereas the slightly younger north-central dome is chemically transitional from the south-central dome to later, moremafic, ring domes. This sequence of ash-flow tuff and domes represents the tapping of progressively deeper levels of a zoned magma chamber 95,000 ± 5,000 years ago. Since that time, the lavas that erupted 75,000, 60,000, and 30,000 years ago have become decreasingly peralkaline and progressively enriched only in Si, Rb, Cs, and possibly U. They represent successive eruption of the uppermost magma in the post-95,000-year magma chamber. Eruptive units of La Primavera are either aphyric or contain up to 15% phenocrysts of sodic sanidine ≧quartz >ferrohedenbergite >fayalite>ilmenite±titanomagnetite. Whereas major-element compositions of sanidine, clinopyroxene, and fayalite phenocrysts changed only slightly between eruptive groups, concentrations of many trace elements changed by factors of 5 to 10, resulting in crystal/glass partition coefficients that differ by factors of up to 20 between successively erupted units. The extreme variations in partitioning behavior are attributed to small changes in bulk composition of the melt because major-element compositions of the phenocrysts and temperature, pressure, and oxygen fugacity of the magma all remained essentially constant. Crystal settling and incremental partial melting by themselves appear incapable of producing either the chemical gradients within the Tala Tuff magma chamber or the trends with time in the post-caldera lavas. Transport of trace metals as volatile complexes within the thermal and gravitational gradient in volatilerich but water-undersaturated magma is considered the dominant process responsible for compositional zonation in the Tala Tuff. The evolution of the post-caldera lavas with time is thought to involve the diffusive emigration of trace elements from a relatively dry magma as a decreasing proportion of network modifiers and/or a decreasing concentration of complexing ligands progressively reduced trace-metal-site availability in the silicate melt.

Timing and development of the Heise volcanic field, Snake River Plain, Idaho, western USA

USGS Publications Warehouse

Morgan, L.A.; McIntosh, W.C.

2005-01-01

The Snake River Plain (SRP) developed over the last 16 Ma as a bimodal volcanic province in response to the southwest movement of the North American plate over a fixed melting anomaly. Volcanism along the SRP is dominated by eruptions of explosive high-silica rhyolites and represents some of the largest eruptions known. Basaltic eruptions represent the final stages of volcanism, forming a thin cap above voluminous rhyolitic deposits. Volcanism progressed, generally from west to east, along the plain episodically in successive volcanic fields comprised of nested caldera complexes with major caldera-forming eruptions within a particular field separated by ca. 0.5-1 Ma, similar to, and in continuation with, the present-day Yellowstone Plateau volcanic field. Passage of the North American plate over the melting anomaly at a particular point in time and space was accompanied by uplift, regional tectonism, massive explosive eruptions, and caldera subsidence, and followed by basaltic volcanism and general subsidence. The Heise volcan ic field in the eastern SRP, Idaho, represents an adjacent and slightly older field immediately to the southwest of the Yellowstone Plateau volcanic field. Five large-volume (>0.5 km3) rhyolitic ignimbrites constitute a time-stratigraphic framework of late Miocene to early Pliocene volcanism for the study region. Field relations and high-precision 40Ar/39Ar age determinations establish that four of these regional ignimbrites were erupted from the Heise volcanic field and form the framework of the Heise Group. These are the Blacktail Creek Tuff (6.62 ?? 0.03 Ma), Walcott Tuff (6.27 ?? 0.04 Ma), Conant Creek Tuff (5.51 ?? 0.13 Ma), and Kilgore Tuff (4.45 ?? 0.05 Ma; all errors reported at ?? 2??). The fifth widespread ignimbrite in the regions is the Arbon Valley Tuff Member of the Starlight Formation (10.21 ?? 0.03 Ma), which erupted from a caldera source outside of the Heise volcanic field. These results establish the Conant Creek Tuff as a distinct and widespread ignimbrite in the Heise volcanic field, eliminating former confusion resulting from previous discordant K/Ar and fission-track dates. New 40Ar/39Ar determinations, when combined wi th geochemical, lithologic geophysical, and field data, define the volcanic and tectonic history of the Heise volcanic field and surrounding areas. Volcanic units erupted from the Heise volcanic field also provide temporal control for tectonic events associated with late Cenozoic extension in the Snake Range and with uplift of the Teton Range, Wyoming. In the Snake Range, movement of large (???0.10 km3) slide blocks of Mississippian limestone exposed 50 km to the east of the Heise field occurred between 6.3 and 5.5 Ma and may have been catastrophically triggered by the caldera eruption of the 5.51 ?? 0.13-Ma Conant Creek Tuff. This slide block movement of ???300 vertical meters indicates that the Snake Range had significant relief by at least 5.5 Ma. In Jackson Hole, the distribution of outflow facies of the 4.45 ?? 0.05-Ma Kilgore caldera in the Heise volcanic field on the eastern SRP indicates that the northern Teton Range was not a significant topographic feature at this time. ?? 2005 Geological Society of America.

Rock-fall hazard in the Etruscan archaeological site of Norchia (Central Italy)

NASA Astrophysics Data System (ADS)

Margottini, Claudio; Spizzichino, Daniele; Argento, Alessia; Russo, Alfonsina

2016-04-01

The ancient Etruscan town of Norchia (Central Italy, 80 km North of Rome) is situated on a long volcanic plateau surrounded by steep slopes, at the confluence of rivers Pile and Acqua Alta into the river Biedano. It has been constructed along the ancient Via Clodia, a short-range route intended for commercial traffic between Rome and the colonies in Etruscan lands. The flourishing of the town, evidenced by the beautiful necropolis, is placed between the end of the fourth and half of the second century BC. With its necropolis Norchia is the most significant example of funerary architecture rock Hellenistic period (IV-II century BC.). Its rock-cut tombs, are among the most important archaeological sites of Etruscan civilisation. They are an important and rare example of rock architecture and one of the few preserved in Italy. Also, the necropolis, with an extension of more than 100 hectares, is composed of rock-cut tombs of various types (façade, half-cube, false-cube and temple type) and dimensions (4-10 m in height), exhibiting a remarkable similarity with Asian tombs. From geological point of view, the area is exhibiting the overly of rigid volcanic products from both Vico and Volsini volcanic apparatus; as a bedrock, a plastic clay formation is positioned. The rock-cut tombs were excavated on two main volcanic levels, following the natural profile of tuff outcrops. The tombs located in the upper part of the necropolis have been excavated in a Red Tuff from Vico volcanic district, while those in lower level are dug in a grey tuff (Nenfro) from Vulsini volcanic apparatus. Recent investigations revealed the presence of many threats affecting the conservation of the site, that are including: surface rock weathering, water percolation and infiltration, surface vegetation and biological colonisation, instability and collapse of the cliff. The purpose of this study is mainly focused to verify whether the geological, geomorphological and geomechanical processes that have allowed the creation of a typical "butte" landscape, later inhabited by Etruscans, are still active. Field survey and historical data collection revealed the presence of many rock slope instabilities that have affected the site. Particularly meaningful is the presence of a large debris fan, just at the toe of the most relevant archaeological place, where the half-cube rock-cut tombs are positioned, testifying important rock-falls after the excavation of the necropolis. The preliminary investigation is revealing the importance of rock-fall hazard as well as the other environmental threats for the future conservation of the site. An integrated approach among different experts is now required, to define processes and causative factors and then to establish priorities for conservation

Straddling the tholeiitic/calc-alkaline transition: the effects of modest amounts of water on magmatic differentiation at Newberry Volcano, Oregon

USGS Publications Warehouse

Mandler, Ben E.; Donnelly-Nolan, Julie M.; Grove, Timothy L.

2014-01-01

Melting experiments have been performed at 1 bar (anhydrous) and 1- and 2-kbar H2O-saturated conditions to study the effect of water on the differentiation of a basaltic andesite. The starting material was a mafic pumice from the compositionally zoned tuff deposited during the ~75 ka caldera-forming eruption of Newberry Volcano, a rear-arc volcanic center in the central Oregon Cascades. Pumices in the tuff of Newberry caldera (TNC) span a continuous silica range from 53 to 74 wt% and feature an unusually high-Na2O content of 6.5 wt% at 67 wt% SiO2. This wide range of magmatic compositions erupted in a single event makes the TNC an excellent natural laboratory in which to study the conditions of magmatic differentiation. Our experimental results and mineral–melt hygrometers/thermometers yield similar estimates of pre-eruptive H2O contents and temperatures of the TNC liquids. The most primitive (mafic) basaltic andesites record a pre-eruptive H2O content of 1.5 wt% and a liquidus temperature of 1,060–1,070 °C at upper crustal pressure. This modest H2O content produces a distinctive fractionation trend that is much more enriched in Na, Fe, and Ti than the calc-alkaline trend typical of wetter arc magmas, but slightly less enriched in Fe and Ti than the tholeiitic trend of dry magmas. Modest H2O contents might be expected at Newberry Volcano given its location in the Cascade rear arc, and the same fractionation trend is also observed in the rim andesites of the rear-arc Medicine Lake volcano in the southern Cascades. However, the Na–Fe–Ti enrichment characteristic of modest H2O (1–2 wt%) is also observed to the west of Newberry in magmas erupted from the arc axis, such as the Shevlin Park Tuff and several lava flows from the Three Sisters. This shows that modest-H2O magmas are being generated directly beneath the arc axis as well as in the rear arc. Because liquid lines of descent are particularly sensitive to water content in the range of 0–3 wt% H2O, they provide a quantitative and reliable tool for precisely determining pre-eruptive H2O content using major-element data from pumices or lava flows. Coupled enrichment in Na, Fe, and Ti relative to the calc-alkaline trend is a general feature of fractional crystallization in the presence of modest amounts of H2O, which may be used to look for “damp” fractionation sequences elsewhere.

The geology and chronology of the Acheulean deposits in the Mieso area (East-Central Ethiopia).

PubMed

Benito-Calvo, Alfonso; Barfod, Dan N; McHenry, Lindsay J; de la Torre, Ignacio

2014-11-01

This paper presents the Quaternary sequence of the Mieso area of Central-East Ethiopia, located in the piedmont between the SE Ethiopian Escarpment and the Main Ethiopian Rift-Afar Rift transition sector.In this region, a piedmont alluvial plain is terraced at þ25 m above the two main fluvial courses, the Mieso and Yabdo Rivers. The piedmont sedimentary sequence is divided into three stratigraphic units separated by unconformities. Mieso Units I and II contain late Acheulean assemblages and a weakly consolidated alluvial sequence, consisting mainly of fine sediments with buried soils and, to a lesser degree, conglomerates. Palaeo-wetland areas were common in the alluvial plain, represented by patches of tufas, stromatolites and clays. At present, the piedmont alluvial surface is preserved mainly on a dark brown soil formed at the top of Unit II. Unit III corresponds to a fluvial deposit overlying Unit II, and is defined by sands, silty clays and gravels, including several Later Stone Age (LSA) occurrences. Three fine-grained tephra levels are interbedded in Unit I (tuffs TBI and TA) and II (tuff CB), and are usually spatially-constrained and reworked. Argon/argon (40Ar/39Ar) dating from tuff TA, an ash deposit preserved in a palustrine environment, yielded an age of 0.212 ± 0.016 Ma (millions of years ago). This date places thetop of Unit I in the late Middle Pleistocene, with Acheulean sites below and above tuff TA. Regional correlations tentatively place the base of Unit I around the Early-Middle Pleistocene boundary, Unit II inthe late Middle Pleistocene and within the Late Pleistocene, and the LSA occurrences of Unit III in the LatePleistoceneeHolocene.

Completion Report for Well ER-EC-5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bechtel Nevada

2004-10-01

Well ER-EC-5 was drilled for the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office in support of the Nevada Environmental Restoration Project at the Nevada Test Site, Nye County, Nevada. This well was drilled in the summer of 1999 as part of the U.S. Department of Energy's hydrogeologic investigation program in the Western Pahute Mesa - Oasis Valley region just west of the Nevada Test Site. A 44.5-centimeter surface hole was drilled and cased off to a depth of 342.6 meters below ground surface. The borehole diameter was then decreased to 31.1 centimeters for drilling to amore » total depth of 762.0 meters. One completion string with three isolated slotted intervals was installed in the well. A preliminary composite, static water level was measured at the depth of 309.9 meters, 40 days after installation of the completion string. Detailed lithologic descriptions with stratigraphic assignments are included in the report. These are based on composite drill cuttings collected every 3 meters, and 18 sidewall samples taken at various depths below 349.6 meters, supplemented by geophysical log data and results from detailed chemical and mineralogical analyses of rock samples. The well penetrated Tertiary-age tuffs of the Thirsty Canyon Group, caldera moat-filling sedimentary deposits, lava of the Beatty Wash Formation, and landslide breccia and tuffs of the Timber Mountain Group. The well reached total depth in welded ashflow tuff of the Ammonia Tanks Tuff after penetrating 440.1 meters of this unit, which is also the main water-producing unit in the well. The geologic interpretation of data from this well constrains the western margin of the Ammonia Tanks caldera to the west of the well location.« less

The Late-Holocene evolution of the Miseno area (south-western Campi Flegrei) as inferred by stratigraphy, petrochemistry and 40Ar/39Ar geochronology:Chapter 6 in Volcanism in the Campania Plain — Vesuvius, Campi Flegrei and Ignimbrites

USGS Publications Warehouse

Insinga, Donatella; Calvert, Andrew T.; Lanphere, Marvin A.; Morra, Vincenzo; Perrotta, Annamaria; Sacchi, Marco; Scarpati, Claudio; Saburomaru, James; Fedele, Lorenzo

2006-01-01

This study on terrestrial and marine successions increases the understanding of the Late-Holocene volcanological and stratigraphical evolution of the south-western part of Campi Flegrei caldera.Stratigraphic data derived from field studies of two major tuff vents located along the coastal zone, namely Porto Miseno and Capo Miseno, clearly indicate that the Porto Miseno tuff ring slightly predates the Capo Miseno tuff cone. 40Ar/39Ar step-heating experiments, carried out on fresh sanidine separates from pumice samples, yielded a plateau age of 5090±140 yr BP for Capo Miseno and 6490±510 yr BP for Porto Miseno vent, thus confirming field observations.The volcanoclastic input derived from this recent and intense eruptive activity played a major role in the inner-shelf stratigraphic evolution of the Porto Miseno Bay deposits that have been drilled up to 40 m depth off the crater rim. The cored succession is characterised by transgressive marine deposits (mostly volcanic sand) with two intercalated peat layers (t1 and t2), dated at 3560±40 yr BP and 7815±55 yr BP (14C), respectively, interbedded with a 1–5 m thick pumice layer (tephra C). Peat layers have been chronostratigraphically correlated with two widespread paleosols onland while petrochemical analyses allowed us to correlate tephra C with the Capo Miseno tuff cone deposits.The results presented in this study imply a Late-Holocene volcanic activity that is also well preserved in the marine record in this sector of the caldera where a new chronostratigraphic reconstruction of the eruptive events is required in order to better evaluate the hazard assessment of the area.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Q; Zavarin, M; Rose, T P

Laboratory batch sorption experiments were used to investigate variations in the retardation behavior of redox-sensitive radionuclides. Water-rock compositions used during these experiments were designed to simulate subsurface conditions at the Nevada Test Site (NTS), where a suite of radionuclides were deposited as a result of underground nuclear testing. Experimental redox conditions were controlled by varying the oxygen content inside an enclosed glove box and by adding reductants into the testing solutions. Under atmospheric (oxidizing) conditions, the radionuclide distribution coefficients varied with the mineralogical composition of the sorbent and the water chemistry. Under reducing conditions, distribution coefficients showed marked increases formore » {sup 99}Tc and {sup 237}Np in devitrified tuff, but much smaller variations in alluvium, carbonate rock, and zeolitic tuff. This effect was particularly important for {sup 99}Tc, which tends to be mobile under oxidizing conditions. Unlike other redox-sensitive radionuclides, iodine sorption may decrease under reducing conditions when I{sup -} is the predominant species. Overall, sorption of U to alluvium, devitrified tuff, and zeolitic tuff under atmospheric conditions was less than in the glove-box tests. However, the mildly reducing conditions achieved here were not likely to result in substantial U(VI) reduction to U(IV). Sorption of Pu was not affected by the decreasing redox conditions achieved in this study, as the predominant sorbed Pu species in all conditions was expected to be the low-solubility and strongly sorbing Pu(OH){sub 4}. Depending on the aquifer lithology, the occurrence of reducing conditions along a groundwater flowpath could potentially contribute to the retardation of redox-sensitive radionuclides {sup 99}Tc and {sup 237}Np, which are commonly identified as long-term dose contributors in the risk assessment in various nuclear facilities.« less

Possible Tuff Cones In Isidis Planitia, Mars

NASA Astrophysics Data System (ADS)

Seabrook, A. M.; Rothery, D. A.; Bridges, J. C.; Wright, I. P.

The Beagle 2 lander of the ESA Mars Express mission will touch down on the martian surface in December 2003 to conduct a primarily exobiological mission. The landing site will be within Isidis Planitia, an 1100 km diameter impact basin. Isidis contains many sub-kilometre-sized cones. These can be found singly, in clusters, and in straight or arcuate chains extending many kilometres. In some areas of the basin these cones can occupy over 10% of the surface, with the most densely populated areas being in the older western half of the basin. There are few cones around the basin rim. There is also variation in the erosional state of the cones both across the basin, and within smaller areas, implying a range in time of formation for the cones. We currently favour a tuff cone origin as an explanation for these features. Tuff cones on Earth are rooted volcanic features formed at vents by the interaction between magma or magmatic heat and surface or near-surface water. Lava flows likely to be associated with at least some of the cones if they had a cinder cone (rooted eruptions at vents in a dry environment) origin are absent. This suggests the involvement of suffi- cient volatiles both to explosively fragment the erupting magma, and to cool the ejecta enough to prevent the formation of clastogenic flows. If our tuff cone interpretation is correct, this has implications for the presence, abundance and long-term persistence of sub-surface volatiles (water or carbon dioxide) on Mars. An understanding of the mechanism of formation of the Isidis cones will assist the characterisation of the basin in preparation for the landing of Beagle 2, by providing information about the history of volatiles and volcanism in the basin, and the processes that resulted in the surface we see today.

Geochemical and Petrological Studies of Peralkaline Rocks from Laborcita de San Javier, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Lozano, J. E.; Espejel-Garcia, V. V.; Villalobos-Aragon, A.

2013-05-01

Peralkaline igneous rocks are characterized by a lower total aluminum content in comparison to the total alkalis content (Na + K), and are important to determine the tectonic environment in which they formed. The majority of the volcanic activity in Chihuahua State, northern Mexico, is mostly related to the formation of the Sierra Madre Occidental (SMO), product of the subduction of the Farallon plate. Volcanic activity of Paleogene age (late Oligocene) to the SW of Chihuahua city, specifically in the towns of Laborcita de San Javier and Cusihuiriachic, includes 27.5 M.a. peralkaline tuffs, capping the older rhyolites and andesites of the SMO. This sequence becomes thicker and more prominent towards the west. A volcanic section of more than 1,000 m thick is exposed in the Laborcita area, which ranges in age from 27 to 35 Ma. The oldest (bottom) unit is a calc-alkaline felsic ash-flow tuff and rhyolitic lavas interbedded with flows of mafic to intermediate composition. Overlying this unit, there is a basaltic andesite with an age of 30 to 33 Ma. Right at the top of this sequence, there is the widespread peralkaline ash-flow tuff (27.5 M.a.), focus of this study. Geochemical analyses performed to rhyolitic tuffs by Mauger and Dayvault (1983), have a peralkalinity index ranging from 0.94 to 1.20, while analyses prepared for this project only reach an index of 0.60. The appearance of peralkaline rocks in the Chihuahua State indicates the change of tectonic regime from compression (Farallon plate subduction) to distension (Basin and Range and/or Rio Grande Rift), about 27 M.a. ago.

The Menengai Tuff: A 36 ka widespread tephra and its chronological relevance to Late Pleistocene human evolution in East Africa

NASA Astrophysics Data System (ADS)

Blegen, Nick; Brown, Francis H.; Jicha, Brian R.; Binetti, Katie M.; Faith, J. Tyler; Ferraro, Joseph V.; Gathogo, Patrick N.; Richardson, Jonathan L.; Tryon, Christian A.

2016-11-01

The East African Rift preserves the world's richest Middle and Late Pleistocene (∼780-12 ka) geological, archaeological and paleontological archives relevant to the emergence of Homo sapiens. This region also provides unparalleled chronological control for many important sites through tephrochronology, the dating and correlation of volcanic ashes as widespread isochronous markers in the geological record. There are many well-characterized Pliocene-Early Pleistocene tephras that are widespread across East Africa. A comparable framework is lacking for the Middle and Late Pleistocene; a period characterized by spatially and temporally complex patterns of climate change, as well as the emergence of modern Homo sapiens and the dispersal of this species across and out of Africa. Unraveling relationships among these spatial and temporally complex phenomena requires a precise chronology. To this end we report the Menengai Tuff, a widespread volcanic ash produced by the large-scale caldera-forming eruption in Kenya and 40Ar/39Ar dated to 35.62 ± 0.26 ka. Geochemical characterization of 565 glass shards from 36 samples by wavelength-dispersive electron probe microanalysis show the Menengai Tuff was deposited over >115,000 km2 and is found in the Baringo, Chalbi, Elmenteita, Nakuru, Olorgesailie, Turkana, and Victoria basins, all of which preserve rich Late Pleistocene paleoenvironmental and archaeological archives. Correlation and dating of the Menengai Tuff demonstrate that it is the most widespread tephra and largest eruption currently known from the Late Pleistocene of East Africa. As such, it is a valuable marker in establishing a Late Pleistocene chronology for paleoclimatic, archeological, and paleontological records relevant to the study of human evolution.

High but balanced sedimentation and subsidence rates (Moodies Group, Barberton Greenstone Belt), followed by basin collapse: Implication for Archaean tectonics

NASA Astrophysics Data System (ADS)

Heubeck, Christoph; Lowe, Donald R.; Byerly, Gary R.

2010-05-01

Archaean tectonophysical models distinguish between thick, rigid and thin, mobile crust; from these the major mechanisms and rates for continental growth are derived. Archaean sedimentary rocks, preserved in metamorphosed and highly deformed greenstone belts, can contribute to constrain these models by estimating subsidence rates, derived from the combination of facies changes and precise age dates. Largely siliciclastic strata of the Moodies Group form the topmost unit of the Barberton Supergroup of the Barberton Greenstone Belt (BGB), South Africa, represent one of the world's oldest unmetamorphosed quartz-rich sedimentary sequences, and reach ca. 3500m thick (Lowe and Byerly, 2007). Large parts of the Moodies Group were deposited in apparent sedimentary continuity in alluvial, fluvial, shoreline and shallow-marine environments (e.g., Eriksson, 1979; Heubeck and Lowe, 1994). Distinctive sources and variations in facies indicate that Moodies deposition occurred at times in several basins. In several now tectonically separated regions, a regional basaltic lava (unit MdL of Anhaeusser, 1968) separates a lower unit (ca. 2000m thick and possibly representing an extensional setting) from an upper unit (ca. 1500m thick and characterized by progressive unconformities, rapidly changing facies, thicknesses, and sandstone petrographic composition). Single zircons separated from a felsic air-fall tuff of the middle Moodies Group and immediately overlying the basaltic lava in the Saddleback Syncline were dated on the Stanford-USGS SHRIMP RG. Out of 24 dated grains, two near-concordant groups have mean ages of 3230,6+-6,1Ma (2σ; n=9) and 3519+-7 Ma (2σ; n=9), respectively. We interpret the former age as representing the depositional age of the tuff, the latter as representing inherited zircons from underlying Onverwacht-age basement. The interpreted depositional age of the Moodies tuff is indistinguishable from numerous similar ages from felsic and dacitic volcanics at the top of the underlying Fig Tree Group (Schoongezicht Fm.; Byerly et al., 1996), implying that ca. 2000m of Moodies sandstones and subordinate siltstones and conglomerates were deposited in not more than a few (0-6) Ma. Their comparatively low degree of facies variation and lithological change implies a balance between rates of sediment supply and of subsidence, creating thick stacked units. Ferruginous shales and thin BIFs of the upper Moodies Group suggest that background 'Fig-Tree-style' sedimentation continued during Moodies time but was mostly overwhelmed by the apparently brief but massive influx of medium- to coarse-grained quartzose sediment. Because two progressive unconformities, marking Moodies basin uplift and onset of renewed overall BGB shortening, occur only 50 m above this dated unit, they are likely of a similar age and imply that dominant NW-SE-directed shortening in the BGB began shortly after 3230+-6 Ma. The combination of these new data with published information thus suggest that the Moodies Basin formed after 3225+-6 Ma (i.e., at the earliest at 3231) but was already largely filled and began to be deformed by 3231+-6 (i.e., at the latest by 3225). Moodies deposition thus happened geologically nearly instantaneously following the end of Fig Tree volcanism, took very little time and deposited large volumes of sediments on a rapidly subsiding basement just prior to large-scale BGB deformation. REFERENCES Byerly, G.R., Kroner, A., Lowe, D.R., Todt W., Walsh, M.M., 1996, Prolonged magmatism and time constraints for sediment deposition in the early Archean Barberton greenstone belt: Evidence from the Upper Onverwacht and Fig Tree groups: Precambrian Research, 78, p. 125-138. Eriksson, K.A., 1979, Marginal marine depositional processes from the Archaean Moodies Group, Barberton Mountain Land, South Africa: Evidence and significance: Precambrian Res., 8, p. 153-182. Heubeck, C. and Lowe, D.R., 1994, Depositional and tectonic setting of the Archaean Moodies Group, Barberton Greenstone Belt, South Africa: Precambrian Res., 68, p. 257-290. Lowe, D.R., and Byerly, G.R., 2007, An overview of the geology of the Barberton Greenstone Belt and vicinity: Implications for early crustal development; in: M.J. von Kranendonk, R.H. Smithies and V.C. Bennett, eds., Earth's Oldest Rocks. - Elsevier (Developments in Precambrian Geology), vol. 15, p. 481-526.

Influence of Air Humidity and Water Particles on Dust Control Using Ultrasonic Atomization

NASA Astrophysics Data System (ADS)

Okawa, Hirokazu; Nishi, Kentaro; Shindo, Dai; Kawamura, Youhei

2012-07-01

The influence of air humidity and water particles on dust control was examined using ultrasonic atomization at 2.4 MHz, an acrylic box (61 L), and four types of ore dust samples: green tuff (4 µm), green tuff (6 µm), kaolin, and silica. It was clearly demonstrated that ultrasonic atomization was effective in raising humidity rapidly. However, at high relative air humidity, the water particles remained stable in the box without changing to water vapor. Ultrasonic atomization was applied to suppress dust dispersion and 40-95% dust reduction was achieved at 83% relative air humidity. Dust dispersion was more effective with ultrasonic atomization than without.

Multiple episodes of zeolite deposition in fractured silicic tuff

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlos, B.A.; Chipera, S.J.; Snow, M.G.

Fractures in silicic tuffs above the water table at Yucca Mountain, Nevada, USA contain two morphologies of heulandite with different compositions. Tabular heulandite is zoned, with Sr-rich cores and Mg-rich rims. Later prismatic heulandite is nearly the same composition as the more magnesian rims. Heulandite and stellerite may occur between layers of calcite, and calcite occurs locally between generations of heulandite. Thermodynamic modeling, using estimated thermodynamic data and observed chemical compositions for heulandite and stellerite, shows that stellerite is the favored zeolite unless Ca concentrations are reduced or Mg and/or Sr concentrations are significantly elevated above current Yucca Mountain waters.

Fractured Rock Permeability as a Function of Temperature and Confining Pressure

NASA Astrophysics Data System (ADS)

Alam, A. K. M. Badrul; Fujii, Yoshiaki; Fukuda, Daisuke; Kodama, Jun-ichi; Kaneko, Katsuhiko

2015-10-01

Triaxial compression tests were carried out on Shikotsu welded tuff, Kimachi sandstone, and Inada granite under confining pressures of 1-15 MPa at 295 and 353 K. The permeability of the tuff declined monotonically with axial compression. The post-compression permeability became smaller than that before axial compression. The permeability of Kimachi sandstone and Inada granite declined at first, then began to increase before the peak load, and showed values that were almost constant in the residual strength state. The post-compression permeability of Kimachi sandstone was higher than that before axial compression under low confining pressures, but lower under higher confining pressures. On the other hand, the permeability of Inada granite was higher than that before axial compression regardless of the confining pressure values. For the all rock types, the post-compression permeability at 353 K was lower than at 295 K and the influence of the confining pressure was less at 353 K than at 295 K. The above temperature effects were observed apparently for Inada granite, only the latter effect was apparent for Shikotsu welded tuff, and they were not so obvious for Kimachi sandstone. The mechanisms causing the variation in rock permeability and sealability of underground openings were discussed.

Stochastic modeling of a lava-flow aquifer system

USGS Publications Warehouse

Cronkite-Ratcliff, Collin; Phelps, Geoffrey A.

2014-01-01

This report describes preliminary three-dimensional geostatistical modeling of a lava-flow aquifer system using a multiple-point geostatistical model. The purpose of this study is to provide a proof-of-concept for this modeling approach. An example of the method is demonstrated using a subset of borehole geologic data and aquifer test data from a portion of the Calico Hills Formation, a lava-flow aquifer system that partially underlies Pahute Mesa, Nevada. Groundwater movement in this aquifer system is assumed to be controlled by the spatial distribution of two geologic units—rhyolite lava flows and zeolitized tuffs. The configuration of subsurface lava flows and tuffs is largely unknown because of limited data. The spatial configuration of the lava flows and tuffs is modeled by using a multiple-point geostatistical simulation algorithm that generates a large number of alternative realizations, each honoring the available geologic data and drawn from a geologic conceptual model of the lava-flow aquifer system as represented by a training image. In order to demonstrate how results from the geostatistical model could be analyzed in terms of available hydrologic data, a numerical simulation of part of an aquifer test was applied to the realizations of the geostatistical model.

Preliminary assessment, by means of Radon exhalation rate measurements, of the bio-sustainability of microwave treatment to eliminate biodeteriogens infesting stone walls of monumental historical buildings.

NASA Astrophysics Data System (ADS)

Mancini, S.; Caliendo, E.; Guida, M.; Bisceglia, B.

2017-10-01

The main purpose of the work described in this paper has been to establish the protocol for a new non-disruptive technique of intervention, based on microwave treatment, for cleaning operations on monumental historical buildings, to eliminate biodeteriogens infesting stones. Non-destructive methods in the cleaning operations, should not only preserve the physical integrity, the chemical-mineralogical and structural identity of materials, but, when the exhalation of pollutant agents (like for example Radon gas) from building materials is considered, also, make the indoor air quality (IAQ) levels healthy. Therefore, one of the main steps of the protocol proposed in this paper is concerned with the assessment of the Radon exhalation rate in order to verify that microwave treatments do not increase the Radon naturally exhalated by building materials. In this paper, the preliminary results of the Radon measurements performed on two different type of tuff samples (grey tuff and yellow tuff), typical of the Italian traditional construction heritage, with the E-PERM passive technique at the Environmental Radioactivity Laboratory (Amb.Ra.), University of Salerno, Italy, ISO 9001:2008 certified, are summarized.

Relative Abundances of Calcite and Silica in Fracture Coatings as a Possible Indicator of Evaporation in a Thick Unsaturated Zone, Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Marshall, B. D.; Moscati, R. J.

2005-12-01

Yucca Mountain, a ridge of shallowly dipping, Miocene-age volcanic rocks in southwest Nevada, is the proposed site for a nuclear waste repository to be constructed in the 500- to 700-m-thick unsaturated zone (UZ). At the proposed repository, the 300-m-thick Topopah Spring Tuff welded unit (TSw) is overlain by approximately 30 m of nonwelded tuffs (PTn); the Tiva Canyon Tuff welded unit (TCw) overlies the PTn with a range in thickness from 0 to approximately 130 m at the site. The amount of water percolation through the UZ is low and difficult to measure directly, but local seepage into mined tunnels has been observed in the TCw. Past water seepage in the welded tuffs is recorded by widespread, thin (0.3 cm) coatings of calcite and silica on fracture surfaces and within cavities. Abundances of calcite and silica in the coatings were determined by X-ray microfluorescence mapping and subsequent multispectral image analysis of over 200 samples. The images were classified into constituent phases including opal-chalcedony-quartz (secondary silica) and calcite. In the TCw samples, the median calcite/silica ratio is 8; in the TSw samples within 35 m below the PTn, median calcite/silica falls to 2, perhaps reflecting an increase in soluble silica from the presence of glass in the nonwelded tuffs. In the deeper parts of the TSw, median calcite/silica reaches 100 and many samples contain no detectable secondary silica phase. Evaporation and changing pCO2 control precipitation of calcite from water percolating downward in the UZ, but precipitation of opal requires only evaporation. Calcite/silica ratios, therefore, can constrain the relative importance of evaporation in the UZ. Although calcite/silica values scatter widely within the TSw, reflecting the spatial variability of gas and water flow, average calcite/silica ratios increase with stratigraphic depth, indicating less evaporation at the deeper levels of the UZ. Coupled with the much smaller calcite/silica ratios observed in coatings from the TCw, these data indicate that evaporation decreases with depth in the UZ. Evaporation at the repository horizon and in the overlying units is an important process that reduces the amount of seepage at the repository horizon.

Paleointensity in ignimbrites and other volcaniclastic flows

NASA Astrophysics Data System (ADS)

Bowles, J. A.; Gee, J. S.; Jackson, M. J.

2011-12-01

Ash flow tuffs (ignimbrites) are common worldwide, frequently contain fine-grained magnetite hosted in the glassy matrix, and often have high-quality 40Ar/39Ar ages. This makes them attractive candidates for paleointensity studies, potentially allowing for a substantial increase in the number of well-dated paleointensity estimates. However, the timing and nature of remanence acquisition in ignimbrites are not sufficiently understood to allow confident interpretation of paleointensity data from ash flows. The remanence acquisition may be a complex function of mineralogy and thermal history. Emplacement conditions and post-emplacement processes vary considerably between and within tuffs and may potentially affect the ability to recover ancient field intensity information. To better understand the relevant magnetic recording assemblage(s) and remanence acquisition processes we have collected samples from two well-documented historical ignimbrites, the 1980 ash flows at Mt. St. Helens (MSH), Washington, and the 1912 flows from Mt. Katmai in the Valley of Ten Thousand Smokes (VTTS), Alaska. Data from these relatively small, poorly- to non-welded historical flows are compared to the more extensive and more densely welded 0.76 Ma Bishop Tuff. This sample set enables us to better understand the geologic processes that destroy or preserve paleointensity information so that samples from ancient tuffs may be selected with care. Thellier-type paleointensity experiments carried out on pumice blocks sampled from the MSH flows resulted in a paleointensity of 55.8 μT +/- 0.8 (1 standard error). This compares favorably with the actual value of 56.0 μT. Excluded specimens of poor technical quality were dominantly from sites that were either emplaced at low temperature (<350°C) or were subject to post-emplacement hydrothermal alteration. The VTTS experienced much more wide-spread low-temperature hydrothermal activity than did MSH. Pumice-bearing ash matrix samples from this locality are characterized by at least two magnetic phases, one of which appears to carry a chemical remanent magnetization. Paleointensities derived from the second phase give results that vary widely but which may be correlated with degree of hydrothermal alteration or hydration. Preliminary data from the Bishop Tuff suggests that vapor-phase alteration at high (>600°C) temperatures does not corrupt the paleointensity signal, and additional data will be presented which explores this more fully.

Stratigraphic architecture of hydromagmatic volcanoes that have undergone vent migration: a review of Korean case studies

NASA Astrophysics Data System (ADS)

Sohn, Y.

2011-12-01

Recent studies show that the architecture of hydromagmatic volcanoes is far more complex than formerly expected. A number of external factors, such as paleohydrology and tectonics, in addition to magmatic processes are thought to play a role in controlling the overall characteristics and architecture of these volcanoes. One of the main consequences of these controls is the migration of the active vent during eruption. Case studies of hydromagmatic volcanoes in Korea show that those volcanoes that have undergone vent migration are characterized by superposition or juxtaposition of multiple rim deposits of partial tuff rings and/or tuff cones that have contrasting lithofacies characteristics, bed attitudes, and paleoflow directions. Various causes of vent migration are inferred from these volcanoes. Large-scale collapse of fragile substrate is interpreted to have caused vent migration in the Early Pleistocene volcanoes of Jeju Island, which were built upon still unconsolidated continental shelf sediments. Late Pleistocene to Holocene volcanoes, which were built upon a stack of rigid, shield-forming lava flows, lack features due to large-scale substrate collapse and have generally simple and circular morphologies either of a tuff ring or of a tuff cone. However, ~600 m shift of the eruptive center is inferred from one of these volcanoes (Ilchulbong tuff cone). The vent migration in this volcano is interpreted to have occurred because the eruption was sourced by multiple magma batches with significant eruptive pauses in between. The Yangpori diatreme in a Miocene terrestrial half-graben basin in SE Korea is interpreted to be a subsurface equivalent of a hydromagmatic volcano that has undergone vent migration. The vent migration here is inferred to have had both vertical and lateral components and have been caused by an abrupt tectonic activity near the basin margin. In all these cases, rimbeds or diatreme fills derived from different source vents are bounded by either prominent or subtle, commonly laterally extensive truncation surfaces or stratigraphic discontinuities. Careful documentation of these surfaces and discontinuities thus appears vital to proper interpretation of eruption history, morphologic evolution, and even deep-seated magmatic processes of a hydromagmatic volcano. In this respect, the technique known as 'allostratigraphy' appears useful in mapping, correlation, and interpretation of many hydrovolcanic edifices and sequences.

The timing and origin of pre- and post-caldera volcanism associated with the Mesa Falls Tuff, Yellowstone Plateau volcanic field

NASA Astrophysics Data System (ADS)

Stelten, Mark E.; Champion, Duane E.; Kuntz, Mel A.

2018-01-01

We present new sanidine 40Ar/39Ar ages and paleomagnetic data for pre- and post-caldera rhyolites from the second volcanic cycle of the Yellowstone Plateau volcanic field, which culminated in the caldera-forming eruption of the Mesa Falls Tuff at ca. 1.3 Ma. These data allow for a detailed reconstruction of the eruptive history of the second volcanic cycle and provide new insights into the petrogenesis of rhyolite domes and flows erupted during this time period. 40Ar/39Ar age data for the biotite-bearing Bishop Mountain flow demonstrate that it erupted approximately 150 kyr prior to the Mesa Falls Tuff. Integrating 40Ar/39Ar ages and paleomagnetic data for the post-caldera Island Park rhyolite domes suggests that these five crystal-rich rhyolites erupted over a centuries-long time interval at 1.2905 ± 0.0020 Ma (2σ). The biotite-bearing Moonshine Mountain rhyolite dome was originally thought to be the downfaulted vent dome for the pre-caldera Bishop Mountain flow due to their similar petrographic and oxygen isotope characteristics, but new 40Ar/39Ar dating suggest that it erupted near contemporaneously with the Island Park rhyolite domes at 1.2931 ± 0.0018 Ma (2σ) and is a post-caldera eruption. Despite their similar eruption ages, the Island Park rhyolite domes and the Moonshine Mountain dome are chemically and petrographically distinct and are not derived from the same source. Integrating these new data with field relations and existing geochemical data, we present a petrogenetic model for the formation of the post-Mesa Falls Tuff rhyolites. Renewed influx of basaltic and/or silicic recharge magma into the crust at 1.2905 ± 0.0020 Ma led to [1] the formation of the Island Park rhyolite domes from the source region that earlier produced the Mesa Falls Tuff and [2] the formation of Moonshine Mountain dome from the source region that earlier produced the biotite-bearing Bishop Mountain flow. These magmas were stored in the crust for less than a few thousand years before being erupted contemporaneously along a 30 km long, structurally controlled vent zone related to extracaldera Basin and Range faults. These data highlight the rapidity with which magma can be generated and erupted over large distances at Yellowstone.

Origin of metaluminous and alkaline volcanic rocks of the Latir volcanic field, northern Rio Grande rift, New Mexico

USGS Publications Warehouse

Johnson, C.M.; Lipman, P.W.

1988-01-01

Volcanic rocks of the Latir volcanic field evolved in an open system by crystal fractionation, magma mixing, and crustal assimilation. Early high-SiO2 rhyolites (28.5 Ma) fractionated from intermediate compositionmagmas that did not reach the surface. Most precaldera lavas have intermediate-compositions, from olivine basaltic-andesite (53% SiO2) to quartz latite (67% SiO2). The precaldera intermediate-composition lavas have anomalously high Ni and MgO contents and reversely zoned hornblende and augite phenocrysts, indicating mixing between primitive basalts and fractionated magmas. Isotopic data indicate that all of the intermediate-composition rocks studied contain large crustal components, although xenocrysts are found only in one unit. Inception of alkaline magmatism (alkalic dacite to high-SiO2 peralkaline rhyolite) correlates with, initiation of regional extension approximately 26 Ma ago. The Questa caldera formed 26.5 Ma ago upon eruption of the >500 km3 high-SiO2 peralkaline Amalia Tuff. Phenocryst compositions preserved in the cogenetic peralkaline granite suggest that the Amalia Tuff magma initially formed from a trace element-enriched, high-alkali metaluminous magma; isotopic data suggest that the parental magmas contain a large crustal component. Degassing of water- and halogen-rich alkali basalts may have provided sufficient volatile transport of alkalis and other elements into the overlying silicic magma chamber to drive the Amalia Tuff magma to peralkaline compositions. Trace element variations within the Amalia Tuff itself may be explained solely by 75% crystal fractionation of the observed phenocrysts. Crystal settling, however, is inconsistent with mineralogical variations in the tuff, and crystallization is thought to have occurred at a level below that tapped by the eruption. Spatially associated Miocene (15-11 Ma) lavas did not assimilate large amounts of crust or mix with primitive basaltic magmas. Both mixing and crustal assimilation processes appear to require development of relatively large magma chambers in the crust that are sustained by large basalt fluxes from the mantle. The lack of extensive crustal contamination and mixing in the Miocene lavas may be related to a decreased basalt flux or initiation of blockfaulting that prevented pooling of basaltic magma in the crust. ?? 1988 Springer-Verlag.

Geology of the Orcopampa 30 minute quadrangle, southern Peru with special focus on the evolution of the Chinchon and Huayta calderas

NASA Astrophysics Data System (ADS)

Swanson, Kirk Edward

The 30 minute Orcopampa quadrangle, southern Peru, was a site of several episodes of Neogene volcanism, hydrothermal activity and precious-metal mineralization. Lavas of pyroxene andesite and associated silicic tuffs of the early Miocene Santa Rosa volcanics are the remnants of stratovolcanoes overlying an irregular erosional surface developed on a transgressive Mesozoic marine succession. Major ash-flow volcanism then resulted in the 20.1 Ma Manto Tuff and the associated Chinchon caldera. Deep dissection, locally >2 km, has exposed the steep caldera margin, slide blocks and related (19.9 Ma) dikes. Flows and domes of hornblende-biotite dacite comprising the Sarpane volcanics were erupted between about 18.5--19.5 Ma over much of the northern part of the quadrangle. Early Miocene rocks were folded during the Quechua I tectonic event, and related ENE-trending normal faults host the 17.8 Ma Ag-Au veins of the Orcopampa district. Eruption of the ca. 11.6 Ma tuffs of Cerro Huayta and Cerro Hospicio resulted in formation of the Huayta caldera, nested within the northern part of the Chinchon caldera. Caldera formation was associated with, and followed by, the eruption of intermediate lavas of Cerro Sahuarque ( ca. 11.4 Ma) and the emplacement of rhyolite domes. The adularia-sericite type Au-Ag veins of Mina Shila were formed along the southern margin of the Huayta caldera several million years after collapse. The 7.3 Ma tuff of Laguna Pariguanas, erupted from vents northeast of the Huayta caldera, appears to be deformed; however, the 6.2 Ma tuff of Umachulco postdates Quechua II/III tectonism. Flows and domes of the ca. 7.2 Ma andesite of Cerro Aseruta were emplaced within the Huayta caldera, and approximately contemporaneous lavas of silicic to intermediate composition were erupted in the northern part of the quadrangle. A large area of largely barren acid-sulfate alteration (Chuchanne) formed within the Huayta caldera shortly after the eruption of the andesite of Cerro Aseruta. Pliocene volcanic activity included the formation of the Cailloma caldera to the east and the Coropuna caldera southwest of the Orcopampa quadrangle. Lava flows, cinder cones and small shield volcanoes of intermediate composition of the Andagua volcanics were formed from late Pliocene to Holocene time.

Geologic Reconnaissance of the Antelope-Ashwood Area, North-Central Oregon: With Emphasis on the John Day Formation of Late Oligocene and Early Miocene Age

USGS Publications Warehouse

Peck, Dallas L.

1964-01-01

This report briefly describes the geology of an area of about 750 square miles in Jefferson, Wasco, Crook, and Wheeler Counties, Oregon. About 16,000 feet of strata that range in age from pre-Tertiary to Quaternary are exposed. These include the following units: pre-Tertiary slate, graywacke, conglomerate, and meta-andesite; Clarno Formation of Eocene age - lava flows, volcanic breccia, tuff, and tuffaceous mudstone, chiefly of andesitic composition; John Day Formation of late Oligocene and early Miocene age - pyroclastic rocks, flows, and domes, chiefly of rhyolitic composition; Columbia River Basalt of middle Miocene age - thick, columnar jointed flows of very fine grained dense dark-gray basalt; Dalles Formation of Pliocene age - bedded tuffaceous sandstone, siltstone, and conglomerate; basalt of Pliocene or Pleistocene age - lava flows of porous-textured olivine basalt; and Quaternary loess, landslide debris, and alluvium. Unconformities separate pre-Tertiary rocks and Clarno Formation, Clarno and John Day Formations, John Day Formation and Columbia River Basalt, and Columbia River Basalt and Dalles Formation. The John Day Formation, the only unit studied in detail, consists of about 4,000 feet of tuff, lapilli tuff, strongly to weakly welded rhyolite ash flows, and less abundant trachyandesite flows and rhyolite flows and domes. The formation was divided into nine mappable members in part of the area, primarily on the basis of distinctive ledge-forming welded ash-flow sheets. Most of the sheets are composed of stony rhyolite containing abundant lithophysae and sparse phenocrysts. One sheet contains 10 to 20 percent phenocrysts, mostly cryptoperthitic soda sanidine, but including less abundant quartz, myrmekitic intergrowths of quartz and sanidine, and oligoclase. The rhyolitic ash flows and lava flows were extruded from nearby vents, in contrast to some of the interbedded air-fall tuff and lapilli tuff of dacitic and andesitic composition that may have been derived from vents in an ancestral Cascade Range. The John Day is dated on the basis of a late Oligocene flora near the base of the formation and early Miocene faunas near the top of the formation. The middle Miocene and older rocks in the Antelope-Ashwood area are broadly folded and broken along northeast-trending faults. Over much of the area the rocks dip gently eastward from the crest of a major fold and are broken along a series of steeply dipping antithetic strike faults. Pliocene and Quaternary strata appear to be undeformed. At the Priday agate deposit, chalcedony-filled spherulites (thunder-eggs) occur in the lower part of a weakly welded rhyolitic ash flow. The so-called thunder-eggs are small spheroidal bodies, about 3 inches in average diameter; each consists of a chalcedonic core surrounded by a shell of welded tuff that is altered to radially oriented fibers of cristobalite and alkalic feldspar.

Gravitational slope-deformation of a resurgent caldera: New insights from the mechanical behaviour of Mt. Nuovo tuffs (Ischia Island, Italy)

NASA Astrophysics Data System (ADS)

Marmoni, G. M.; Martino, S.; Heap, M. J.; Reuschlé, T.

2017-10-01

Ischia Island (Italy) is an impressive example of the rare phenomenon of caldera resurgence. The emplacement and replenishment of magmas at shallow depth resulted in a vertical uplift of about 900 m, concentrated in the western portion of Mt. Epomeo (789 m a.s.l.). As a consequence of this uplift, the island has experienced several slope instabilities at different scales since the Holocene, from shallow mass movements to large rock and debris avalanches. These mass wasting events, which mobilised large volumes of greenish alkali-trachytic tuff (the Mt. Epomeo Green Tuff, MEGT), were strictly related to volcano-tectonic activity and the interaction between the volcanic slopes and the hydrothermal system beneath the island. Deep-Seated Gravitational Slope Deformation (DSGSD) at Mt. Nuovo, located adjacent to densely populated coastal villages, is an ongoing process that covers an area of 1.6 km2. The Mt. Nuovo DSGSD involves a rock mass volume of 190 Mm3 and is accommodated by a main shear zone and a series of sub-vertical fault zones associated with high-angle joint sets. To improve our understanding of this gravity-induced process, we performed a physical (porosity and permeability) and mechanical (uniaxial and triaxial deformation experiments) characterisation of two ignimbrite deposits - both from the MEGT - that form a significant component of the NW sector of Mt. Epomeo. The main conclusions drawn from our experiments are twofold. First, the presence of water dramatically reduces the strength of the tuffs, suggesting that the movement of fluids within the hydrothermal system could greatly impact slope stability. Second, the transition from brittle (dilatant) to ductile (compactant) behaviour in the tuffs of the MEGT occurs at a very low effective pressure, analogous to a depth of a couple of hundred metres, and that this transition is likely moved closer to the surface in the presence of water. We hypothesise that compactant (porosity decreasing) behaviour at the base of the layer could therefore facilitate slope instability. Although our results show that transient exposure to 300 °C does not influence the short-term strength of the tuff, we speculate that the high in-situ temperature could increase the efficiency of brittle and compactant creep and therefore increase the rate of slope deformation. Taken together, our experimental data highlight a potentially important role for the hydrothermal system (that reaches a minimum depth of 1 km) in dictating the DSGSD at Mt. Nuovo. An understanding of this deformation process is not only important for the proximal coastal villages, at risk of engulfment by a large debris avalanche, but also for the towns and cities along the coast of the Gulf of Naples that are at risk to a secondary consequence of such an avalanche - a tsunami wave.

Gastropoda-Bivalvia Fauna And Neogene-Quaternary Stratigraphy of the Southwest of Dardanelles (Çanakkale-NWAnatolia)

NASA Astrophysics Data System (ADS)

Kapan, Sevinç; Kabasakal, Sinem

2016-04-01

Gastropoda-Bivalvia Fauna And Neogene-Quaternary Stratigraphy of the Southwest of Dardanelles (Çanakkale-NWAnatolia) Sevinç KAPAN, Sinem KABASAKAL, Çanakkale Onsekiz Mart University, Engineering Faculty, Geological Engineering Department sevinckapan_yesilyurt@hotmail.com In this study, paleontology and stratigraphy of Neogene and Quaternary units around south of the Dardanelles have been examined using Gastropoda and Bivalvia fauna. In the investigation area, the base of the sediments that belongs to Neogene, consist of the volcanics which are formed with basalts, andesites and tuff. Neogene begins unconformity with basal conglomerate which are formed with basalt and tuff gravels. The measurable thickness of the Neogene sediments is approximately 200meters in total. First fossiliferius level which consist of Lymnocardium (Euxinicardium) nobile Sabba has showed similarities with the Pontian (Late Miocene) fauna of the Eastern Paratethys. The existence of Melanopsis and Psidium species indicate that the basin has been brackish water feeding by fresh water in the Early Pliocene. Theodoxus fluviatilis (Linne), Theodoxus (Calvertia) aff. imbricata Brusina, Theodoxus (Calvertia) licherdopoli scriptus (Stefanescu), Viviparus mammatus (Stefanescu), Valvata (Valavata) sulekiana Brusina, Valvata (Cincinna) crusitensis Fontannes, Hydrobia cf grandis Cobalcescu, Hydrobia ventrosa Monfort, Melanopsis (Melanopsis) cf. bergeroni Stefanescu, , Melanopsis (Melanopsis) sandbergeri rumana Tournouer, Melanopsis (Canthidomus) hybostoma anili Taner, Melanopsis (Canthidomus) hybostoma amaradica Fontannes, Melanopsis (Canthidomus) lanceolata Neumayr, Amphimelania fossariformis (Tournouer), Melanoides tuberculata monolithica (Bukowski), Radix (Radix) peregra (Müller), Planorbarius thiollierei (Michaud), Potamida (Potamida) craiovensis craiovensis (Tournouer), Potamida (Potamida) berbestiensis (Fontannes), Unio pristinus davilai Porumbaru, Unio subexquisitus Jatzko, Anadonta zmaji Brusina, Pisidium amnicum (Müller), species have been determined from the mudstone, claystone, carbonated sandstone lithologies. These fauna are characteristic for the Dasic basin in Late Pliocene (Romanian). Also, Avimactra karabugasica (Andrussow), Avimactra ososkovi (Andrussow), Avimactra subcaspia (Andrussow), Avimactra venjukovi (Andrussow). Dreissena (Dreissena) polymorpha (Pallas), Dreissena rostriformis Deshayes species have been determined from the upper level of the section composed of carbonated sandstone lithology. These fauna are characteristic for the Caspic basin in the Late Pliocene (Aktschaglian). In the Treenean and Monastrian times, the marine fauna (Gibbula (Adriaria) albida (Gmelin), Gibbula (Tunulus) umblicaris (Linneaus), Hydrobia (Hydrobia) acuta (Draparnaud), Alvania (Alvania) reticulata (Montagu), Turritella (Turritella) tricarinata (Brocchi), Pirenella conica (Blainville), Bittium (Bittium) reticulatum (Da Costa), Thericium (Thericium) vulgatum (Brugiere), Radix (Radix) peregra (Müller) are belonging to the Gastropoda and Mytilaster lineatus (Gmelin in Linneaus), Ostrea edulis Linneaus, Ostrea lamellosa Linneaus, Paphia (Polititapes) senescens (Coc.), Timoclea ovata (Pennant), Corbula (Varicorbula) gibba (Olivi)) have been observed. In the Pontian, the Basin has been low salinity and semi-marine conditions. In the Lower Romanian, the Basin was developed as brackish water character feeding by fresh water. Late Lower Romanian=Lower Kujalnikien, Basin was became more brackish character by increasing salinity. During the Upper Kujalnikien=Upper Romanian, feeding by freshwater was increased. The youngest sequence of the basin is Treenean-Monastrian terraces sedimented by increasing sea level. These marine fauna indicate that there was a connection between Black Sea and Mediterranean in that time. Key words: Neogene, Gastropoda-Bivalvia, Romanian, Dasic, Caspic.

Geologic Controls on Geophysics for Tunnel Detection

NASA Astrophysics Data System (ADS)

Kelley, J. R.; Wakeley, L. D.; McKenna, J. R.; Ketcham, S. A.; Weiss, C. A.; Curtis, J. O.

2006-05-01

Properties of soils are critical to using near-surface geophysical techniques to search for clandestine tunnels. We have constructed a database of soils sampled at sites on the northern (N) and southern (S) US borders and at sites in Iraq in conjunction with tunnel searches. Geologic materials at these sites consist of glacial gravels (N), volcanic tuff (S), and alluvial sands interbedded with marine clays (Iraq). The depth of interest for detecting clandestine tunneling is < 30m, and as shallow as 2m at some locations. Mineral composition, grain size, moisture content, conductivity, permittivity, and magnetic susceptibility are critical for assessing the effectiveness of near-surface geophysical techniques. Values for these properties are consistent with soil stratigraphy and with vertical and lateral geologic variability. In some environments, in situ moisture content and the arrangement of conductive and resistive materials in the upper few meters limit significantly the depth of investigation using traditional near-surface techniques (electromagnetic induction, ground-penetrating radar). Geologic factors plus the small physical size of the targets limit the usefulness of commercial off-the-shelf techniques, and warrant an investment in new approaches.

Petrology, sedimentology, and diagenesis of hemipelagic limestone and tuffaceous turbidities in the Aksitero Formation, central Luzon, Philippines

USGS Publications Warehouse

Garrison, Robert E.; Espiritu, E.; Horan, L.J.; Mack, L.E.

1979-01-01

The Aksitero Formation of central Luzon is an upper Eocene and lower Oligocene sequence of evenly bedded hemipelagic limestone with a few thin interlayers of tuffaceous turbidites. The limestone consists chiefly of planktonic foraminifers and calcareous nannofossils, with up to 30 percent of noncarbonate components, chiefly volcaniclastic debris. The tuff layers are graded beds. Composed mainly of glass shards, pumice fragments, crystals, and fine-grained volcanic rock fragments. Hydrocarbons migrated into the pores of the tuffaceous layers early during diagenesis but they were subsequently flushed out and only bitumen remains, chiefly as thin coatings on grains and wthin pumice vesicles. Later during diagenesis, zeolites (mordenite and c1inoptilolite) and secondary calcite preferentially replaced glass shards and pumice fragments. Deposition of the Aksitero Formation probably occurred at depths of at least 1,000 meters within a subsiding basin adjacent to an active island arc system. Submarine ash eruptions of silicic composition caused volcaniclastic turbidity currents that occasionally reached the basin floor. The more proximal facies of these volcaniclastic deposits may be prospective for hydrocarbons.

Background studies in support of a feasibility assessment on the use of copper-base materials for nuclear waste packages in a repository in tuff

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Konynenburg, R.A.; Kundig, K.J.A.; Lyman, W.S.

1990-06-01

This report combines six work units performed in FY`85--86 by the Copper Development Association and the International Copper Research Association under contract with the University of California. The work includes literature surveys and state-of-the-art summaries on several considerations influencing the feasibility of the use of copper-base materials for fabricating high-level nuclear waste packages for the proposed repository in tuff rock at Yucca Mountain, Nevada. The general conclusion from this work was that copper-base materials are viable candidates for inclusion in the materials selection process for this application. 55 refs., 48 figs., 22 tabs.

Mineral resource of the month: natural and synthetic zeolites

USGS Publications Warehouse

Virta, Robert L.

2008-01-01

Volcanic rocks containing natural zeolites — hydrated aluminosilicate minerals that contain alkaline and alkaline-earth metals — have been mined worldwide for more than 1,000 years for use as cements and building stone. For centuries, people thought natural zeolites occurred only in small amounts inside cavities of volcanic rock. But in the 1950s and early 1960s, large zeolite deposits were discovered in volcanic tuffs in the western United States and in marine tuffs in Italy and Japan. And since then, similar deposits have been found around the world, from Hungary to Cuba to New Zealand. The discovery of these larger deposits made commercial mining of natural zeolite possible.

Using AVIRIS Data to Map and Characterize Subaerially and Subaqueously Erupted BasalticVolcanic Tephras: The Challenge of Mapping Low-Albedo Materials

NASA Technical Reports Server (NTRS)

Farrand, William H.

2004-01-01

Increases in the signal-to-noise ratio (SNR) in AVIRIS has enabled the mapping and characterization of low albedo materials. Low albedo materials of interest include certain soils, man-made materials (asphalt, certain building materials, tires, etc.), and basaltic lava flows and ashes. Early in its history, the response of the AVIRIS sensor was not sensitive enough so that these low albedo materials could be reliably mapped. However, as indicated by Green and Pavri (2002) the noise equivalent delta radiance (NEdL) of AVIRIS in the 2001 flight season was below 0.010 in all but the shortest wavelength channels. This is approximately a ten-fold improvement from the 1989 flight season when NEdL was closer to 0.1 (Green et al., 1990). In the current investigation, AVIRIS data from the 2002 flight season collected over the Pavant Butte tuff cone, Tabernacle Hill tuff ring, and an associated lava flow in the Black Rock Desert of west central Utah were examined to determine how well these generally low albedo volcanic lavas and tephras could be discriminated from background materials. The Pavant Butte tuff cone was examined by the author in an earlier study with a 1989 AVIRIS dataset (Farrand and Singer,

Pyroclastic rocks: another manifestation of ultramafic volcanism on Gorgona Island, Colombia

NASA Astrophysics Data System (ADS)

Echeverría, Lina M.; Aitken, Bruce G.

1986-04-01

Tertiary ultramafic volcanism on Gorgona Island, Colombia, is manifested not only by komatiite flows, but also by a more voluminous sequence of tuff breccias, which is cut by comagmatic picrite dikes. The ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically-deformed, glassy globules. The entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst-laden picritic magma. MgO contents of tuff breccias and picrite dikes range from 21 to 27 wt%. Relative to nearby komatiite flows, these rocks are MgO-rich, and FeO-, TiO2- and Ni-poor. HREE concentrations are very low (

Petrologic evolution of divergent peralkaline magmas from the Silent Canyon caldera complex, southwestern Nevada volcanic field

USGS Publications Warehouse

Sawyer, D.A.; Sargent, K.A.

1989-01-01

The Silent Canyon volcanic center consists of a buried Miocene peralkaline caldera complex and outlying peralkaline lava domes. Two widespread ash flow sheets, the Tub Spring and overlying Grouse Canyon members of the Miocene Belted Range Tuff, were erupted from the caldera complex and have volumes of 60-100 km3 and 200 km3, respectively. Eruption of the ash flows was preceded by widespread extrusion of precaldera comendite domes and was followed by extrusion of postcollapse peralkaline lavas and tuffs within and outside the caldera complex. Lava flows and tuffs were also deposited between the two major ash flow sheets. Rocks of the Silent Canyon center vary significantly in silica content and peralkalinity. Weakly peralkaline silicic comendites (PI 1.0-1.1) are the most abundant precaldera lavas. Postcollapse lavas range from trachyte to silicic comendite; some have anomalous light rare earth element (LREE) enrichments. Silent Canyon rocks follow a common petrologic evolution from trachyte to low-silica comendite; above 73% SiO2, compositions of the moderately peralkaline comendites diverge from those of the weakly peralkaline silicic comendites. The development of divergent peralkaline magmas, toward both pantelleritic and weakly peralkaline compositions, is unusual in a single volcanic center. -from Authors

Determining the physical processes behind four large eruptions in rapid sequence in the San Juan caldera cluster (Colorado, USA)

NASA Astrophysics Data System (ADS)

Curry, Adam; Caricchi, Luca; Lipman, Peter

2017-04-01

Large, explosive volcanic eruptions can have both immediate and long-term negative effects on human societies. Statistical analyses of volcanic eruptions show that the frequency of the largest eruptions on Earth (> ˜450 km3) differs from that observed for smaller eruptions, suggesting different physical processes leading to eruption. This project will characterize the petrography, whole-rock geochemistry, mineral chemistry, and zircon geochronology of four caldera-forming ignimbrites from the San Juan caldera cluster, Colorado, to determine the physical processes leading to eruption. We collected outflow samples along stratigraphy of the three caldera-forming ignimbrites of the San Luis caldera complex: the Nelson Mountain Tuff (>500 km3), Cebolla Creek Tuff (˜250 km3), and Rat Creek Tuff (˜150 km3); and we collected samples of both outflow and intracaldera facies of the Snowshoe Mountain Tuff (>500 km3), which formed the Creede caldera. Single-crystal sanidine 40Ar/39Ar ages show that these eruptions occurred in rapid succession between 26.91 ± 0.02 Ma (Rat Creek) and 26.87 ± 0.02 Ma (Snowshoe Mountain), providing a unique opportunity to investigate the physical processes leading to a rapid sequence of large, explosive volcanic eruptions. Recent studies show that the average flux of magma is an important parameter in determining the frequency and magnitude of volcanic eruptions. High-precision isotope-dilution thermal ionization mass spectrometry (ID-TIMS) zircon geochronology will be performed to determine magma fluxes, and cross-correlation of chemical profiles in minerals will be performed to determine the periodicity of magma recharge that preceded these eruptions. Our project intends to combine these findings with similar data from other volcanic regions around the world to identify physical processes controlling the regional and global frequency-magnitude relationships of volcanic eruptions.

LA-ICP-MS Dating and Tectonic Setting of Yeba Formation Lavas in Qulong Area east Part of the Gangdise Belt, Xizang China

NASA Astrophysics Data System (ADS)

Liu, D.

2009-12-01

In China, Xizang Gangdise tectonic belt is a large nonferrous metal and noble metal mineralized zone and in which, it is found that the mineralization correlates with Tethyan Ocean subduction, continent-continent collision and magmatism due to inter-continent extension orogeny. Qulong porphyry copper (molybdenum) deposit is the largest recently found in the Gangdise metallogenic belt and is one of the most large porphyry copper deposit in Asia. In the area of Qulong porphyry copper deposit, the adjacent strata is Yeba Formation and which can be parted into three members. The first member is built up of dacite, rhyolite, andesite, lapilli tuff, volcanic breccia and volcanic agglomerate. The second member widely occur in the area with major rocks of medium-acidic lava, debris-crystallinoclastic volcanic tuff intercalated with tuffaceous sand, tuffaceous slate and limestone. The third member is built up of andesite, liparite, crystallinoclastic tuff intercalated with sillicalite, sericite slate, tuffaceous sandstone and dirty limestone. The volcanic tuff in the second member gives a LA-ICP-MS U-Pb zircon age of 156.2±2.3 Ma, which may represent the age of the Yeba Formation. That is to say, in the study area, the Yeba Formation comes to being in age of Middle and Later Jurassic. The characteristic which comes from the research on geochronology and rockassociations suggests that the Yeba Formation volcanic rocks are built up by a long time ejection and the ejection of the Yeba Formation volcanic rocks comes from west to east in the Gangdise zone. The volcanic rocks in the Yeba Formation can be considered as the products originated from northward subduction and consumption of the Tethyan Ocean. At the same time, it is proposed that the Yeba Formation volcanic rocks have potential significances in evaluating the early Jurassic biotic crisis, climate change, regression or intrusion event and the later mineralizaion.

The Onset of the Sturtian Snowball Earth: New Geochronology and Chemostratigraphy from the Tambien Group of Ethiopia

NASA Astrophysics Data System (ADS)

Park, Y.; MacLennan, S. A.; Swanson-Hysell, N.; Maloof, A. C.; Schoene, B.; Alene, M.; Tremblay, M. M.; Anttila, E.; Haileab, B.

2016-12-01

The Snowball Earth hypothesis proposes that the onset of global glaciation was a rapid event, particularly at low-latitudes, due to a runaway ice-albedo instability in the climate system. Currently, the Neoproterozoic Sturtian Snowball Earth Glaciation is constrained to have been ongoing at low-latitudes in present day NW Canada at 716.47 ± 0.24 Ma based on a U-Pb date from a tuff within glacial diamictite (Macdonald et al., 2010). A date from a rhyolite underlying this diamicitite of 717.43 ± 0.14 Ma has been inferred to precede the glaciation, although this age is not a strict maximum for the initiation of the snowball Earth since evidence of glaciation may have been obscured in volcanic units. The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence deposited in an arc proximal basin that conformably culminates in diamictite associated with the Sturtian Glaciation. This study exploits the presence of tuffs suitable for high precision U-Pb zircon geochronology interbedded with recently discovered exposures of the transition into the snowball Earth. Dates from tuffs stratigraphically <100 m below massive diamictite enable a test of synchronicity for the initiation of the Sturtian Glaciation when compared with data from NW Canada and S China. Furthermore, tuffs in the proximity of the chemostratigraphically defined Islay negative δ13C anomaly give the opportunity to develop new U-Pb dates to test the prediction from Re-Os dating of black shales in NW Canada that the Islay significantly predates the Sturtian ice age, decoupling the sharpest negative downturns in inorganic δ13C values from glacial initiation. These data also augment and temporally constrain the pre-glacial 87Sr/86Sr curve, informing ongoing modeling efforts of global weathering and seawater chemistry as they relate to hypotheses of the role of large igneous province emplacement and paleogeography in the initiation of Snowball Earth glaciation.

Tuff of Bridge Spring: A mid-Miocene ash-flow tuff, northern Colorado River extensional corridor, Nevada and Arizona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, E.I.; Morikawa, S.A.; Martin, M.W.

1993-04-01

The Tuff of Bridge Spring (TBS) (15.19[+-]0.02 Ma; Gans, 1991) is a compositionally variable dacite to rhyolite ash-flow tuff that crops out over 1800 sq. km in the northern Colorado River extensional corridor. The TBS varies in composition from 59.5 to 74 wt. % SiO[sub 2] and typically contains phenocrysts of sanidine, plagioclase, biotite, clinopyroxene, [+-] sphene, [+-] apatite, [+-] zircon, and [+-] hornblende. The TBS is thickest and displays its greatest compositional range in the center of its area of exposure. The McCullough Range section contains at least three chemically distinct flow units that vary in composition from dacitemore » to rhyolite. The basal and uppermost units are normally zoned and the middle unit is reversely zoned. The complex chemical zonation and zoning reversals in the TBS indicate that it erupted from a magma chamber that was periodically injected by both mafic and felsic magmas. Sections at the edge of the exposure area are thin, contain only one or two chemically definable flow units and have a limited compositional range. To the west at Sheep Mountain, TBS is 2.9 m thick and ranges from 70.2--71.7 wt % SiO[sub 2]. To the east in the White Hills, TBS is 14 m thick and ranges from 59.5--65.3 wt % SiO[sub 2]. This chemical and field data indicate that although the TBS is regionally extensive, individual flow units are not. Isotopic data and chemistry suggest that all sections of the TBS are cogenetic. Comparisons of chemical, geochronological and isotopic data between the TBS and nearby coeval plutons indicate that the Aztec Wash (Eldorado Mts., Nevada) and Mt. Perkins (Black Mountain, Arizona) plutons are possible source for the TBS. Both plutons exhibit ample evidence of magma mixing and commingling, processes that may produce compositional zonation such as that observed in the TBS.« less

Quartz phenocrysts preserve volcanic stresses at Long Valley and Yellowstone calderas

NASA Astrophysics Data System (ADS)

Befus, K. S.; Leonhardi, T. C.; Manga, M.; Tamura, N.; Stan, C. V.

2016-12-01

Magmatic processes and eruptions are the consequence of stresses active in volcanic environments. Few techniques are presently available to quantify those stresses because they operate in subsurface and/or hazardous environments, and thus new techniques are needed to advance our understanding of key processes. Here, we provide a dataset of volcanic stresses that were imparted to quartz crystals that traveled through, and were hosted within, pyroclastic and effusive eruptions from Long Valley and Yellowstone calderas. We measured crystal lattice deformation with submicron spatial resolution using the synchrotron X-ray microdiffraction beamline (12.3.2) at the Advanced Light Source, Lawrence Berkeley National Laboratory. Quartz from all units produces diffraction patterns with residual strains locked in the crystal lattice. We used Hooke's Law and the stiffness constants of quartz to calculate the stresses that caused the preserved residual strains. At Long Valley caldera, quartz preserves stresses of 187±80 MPa within pumice clasts in the F1 fall unit of the Bishop Tuff, and preserves stresses of 120±45 MPa from the Bishop Tuff welded ignimbrite. At Yellowstone caldera quartz preserves stresses of 115±30 and 140±60 MPa within pumices from the basal fall units of the Mesa Falls Tuff and the Tuff of Bluff Point, respectively. Quartz from near-vent and flow-front samples from Summit Lake lava flow preserves stresses up to 130 MPa, and show no variation with distance travelled. We believe that subsurface processes cause the measured residual stresses, but it remains unclear if they are relicts of fragmentation or from the magma chamber. The residual stresses from both Long Valley and Yellowstone samples roughly correlate to lithostatic pressures estimated for the respective pre-eruption magma storage depths. It is possible that residual stress in quartz provides a new geobarometer for crystallization pressure. Moving forward, we will continue to perform analyses and experiments on natural and synthetic crystals to better determine the source of residual stresses.

Status Report on the 40Ar/39Ar and U/Pb Dating of Tuffs in the Dewey Lake Formation of West Texas Towards Constraining the Permo-Triassic Magnetostratigraphic Time Scale

NASA Astrophysics Data System (ADS)

Chang, S.; Renne, P. R.; Mundil, R.

2007-12-01

A detailed magnetic polarity time scale for the Permo-Triassic Boundary interval, critical for correlating events in marine and terrestrial paleoenvironments, is not yet well-established. Recently, late Permian magnetostratigraphic studies have been reported for non-marine sections in Europe and South Africa (Szurlies et al., 2003; Nawrocki, 2004; Ward et al., 2005). However, these sections are devoid of index fossil suitable for correlation with marine successions and also lack age constraints from radioisotopic dating methods. In other words, it is dubious to correlate these magnetostratigraphic data with the GSSP Permo-Triassic boundary and mass extinction. The Dewey Lake red beds formation of West Texas, believed to be the youngest Permian formation in North America, has yielded high-quality paleomagnetic data (Molina-Garza et al., 1989; Steiner, 2001) and contains several silicic tuffs potentially enabling high-resolution calibration of the magnetic polarity time scale in this critical age range. The tuffs have yet to be placed into a regional stratigraphic or magnetostratigraphic framework, and it is unclear exactly how many distinct eruptive units are represented by the 7 distinct samples collected to date from widely separated (>160 km) localities. 40Ar/39Ar (sanidine and biotite) and U/Pb (zircon) studies reveal that all 7 sampled tuffs were probably erupted within several hundred ka of the Permo-Triassic boundary as dated at the Meishan GSSP section (Renne et al., 1995; Mundil et al., 2004) but results thus far are inadequate to convincingly resolve age differences between the various samples. U/Pb dating of some samples is severely challenged by Pb-loss from the zircons despite application of the Mattinson (2005) annealing/chemical abrasion technique. 40Ar/39Ar data have been obtained from as many as four different irradiations in order to reduce neutron fluence related error. We observe the familiar ~1% bias between U/Pb and 40Ar/39Ar ages. Biotite microprobe data, zircon U/Th TIMS data, and the absence of sanidine from some samples serve to help correlate or distinguish some samples despite irresolvable age differences; existing data suggest that 4 distinct tuffs are present in the Dewey Lake Formation. Resolving their ages convincingly will require further work, but it is clear from our results combined with previous magnetostratigraphic data that magnetic polarity reversals were relatively frequent in the latest Permian. Thus the uniqueness of correlations elsewhere with the Permo-Triassic boundary based on magnetostratigraphy alone are not well-founded.

Geology of the Anlauf and Drain Quadrangles, Douglas and Lane Counties, Oregon

USGS Publications Warehouse

Hoover, Linn

1963-01-01

The Anlauf and Drain quadrangles, Oregon, lie about 20 miles south of the city of Eugene, in Douglas and Lane Counties. They constitute an area of about 435 square miles that includes parts of both the Cascade Range and Coast Range physiographic provinces. A sequence of lower Tertiary sedimentary and volcanic rocks with a maximum thickness of about 20,000 feet is exposed in the area. The oldest part of this sequence is the Umpqua formation of early Eocene age consisting of a lower member of vesicular and amygdaloidal olivine basalt flows, a middle member of water-laid vitric and lapilli crystal tuff, and an upper member of interbedded fissile siltstone and basaltic sandstone which contains a 300-foot tongue of massive to thick-bedded basaltic sandstone near its top. These rocks are predominantly of marine origin, although the general absence of pillow structures which are common in basaltic lavas of equivalent age elsewhere in the Coast Ranges suggests that some of the flows were poured out subaerially. The overlying tuff member, however, contains Foraminifera and in places has a lime content slightly in excess of 10 percent. Mollusca and Foraminifera indicate that the Umpqua formation is of early Eocene age and is a correlative of the Capay formation of California. The Tyee formation of middle Eocene age overlies the Umpqua formation and consists of more than 5,000 feet of rhythmically deposited sandstone and siltstone in beds 2 to 30 feet thick. The basal part of each bed consists of medium- to coarse-grained sandstone that grades upward into fine-grained sand- stone and siltstone. The principal constituents of the sandstone are quartz, partly a1tered feldspar, mica, clay, and fragments of basalt, fine-grained argillaceous rocks, and mica schist. Other detrital minerals include epidote, garnet, blue-green hornblende, tourmaline, and zoisite. The depositional environment of the Tyee formation is poorly known, although the rhythmic-graded bedding suggests turbidity currents. About 500 feet of sandstone and siltstone assigned to the Spencer formation of late Eocene age unconformably overlies the Tyee formation. The Spencer formation, better exposed in the east-central part of the Coast Ranges, contains marine fossils but also has thin impure coal beds, indicative of strand-line accumulation. The sandstone in the Spencer formation is very similar to that in the Tyee formation, from which it was probably derived. The Fisher formation contains about 5,500 feet of nonmarine pyroclastic and volcanic rocks that are related to the volcanic rock sequences of the western Cascade Range. The formation is characterized by a wide variety of rock types, including conglomerate, tuffaceous sandstone and siltstone, vitric and crystal tuff, waterlaid and mudflow breccia, and andesitic lava flows. These rocks gen- erally occur in lenticular beds that have little stratigraphic significance. The rocks apparently accumulated on a plain slightly above sea level that was subjected alternately to fiooding by running water and to desiccation. Fossil leaves from the lowermost part of the Fisher formation are of late Eocene age; the upper part of the formation is of early, and possibly niiddle, Oligocene age. A few exposures of olivine basalt were mapped in the extreme northern part of the Anlauf quadrangle. The flows, more extensively exposed to the north, overlie the Fisher formation, and, therefore, are tentatively considered to be post-Oligocene in age. All these stratigraphic units, but principally the Fisher formation, are cut by dikes, sills, and stocklike bodies of 'porphyritic basalt, diabase, and norite. Contemporaneously with the emplacement of most of these rocks, in late Miocene (?) time, hydrothermal solutions locailly altered the sedimentary and extrusive igneous racks and deposited cinnabar and other sulfide minerals, carbonates, and silica. Three parallel nartheastward-trending

Geologic map of the Yucca Mountain region, Nye County, Nevada

USGS Publications Warehouse

Potter, Christopher J.; Dickerson, Robert P.; Sweetkind, Donald S.; Drake II, Ronald M.; Taylor, Emily M.; Fridrich, Christopher J.; San Juan, Carma A.; Day, Warren C.

2002-01-01

Yucca Mountain, Nye County, Nev., has been identified as a potential site for underground storage of high-level radioactive waste. This geologic map compilation, including all of Yucca Mountain and Crater Flat, most of the Calico Hills, western Jackass Flats, Little Skull Mountain, the Striped Hills, the Skeleton Hills, and the northeastern Amargosa Desert, portrays the geologic framework for a saturated-zone hydrologic flow model of the Yucca Mountain site. Key geologic features shown on the geologic map and accompanying cross sections include: (1) exposures of Proterozoic through Devonian strata inferred to have been deformed by regional thrust faulting and folding, in the Skeleton Hills, Striped Hills, and Amargosa Desert near Big Dune; (2) folded and thrust-faulted Devonian and Mississippian strata, unconformably overlain by Miocene tuffs and lavas and cut by complex Neogene fault patterns, in the Calico Hills; (3) the Claim Canyon caldera, a segment of which is exposed north of Yucca Mountain and Crater Flat; (4) thick densely welded to nonwelded ash-flow sheets of the Miocene southwest Nevada volcanic field exposed in normal-fault-bounded blocks at Yucca Mountain; (5) upper Tertiary and Quaternary basaltic cinder cones and lava flows in Crater Flat and at southernmost Yucca Mountain; and (6) broad basins covered by Quaternary and upper Tertiary surficial deposits in Jackass Flats, Crater Flat, and the northeastern Amargosa Desert, beneath which Neogene normal and strike-slip faults are inferred to be present on the basis of geophysical data and geologic map patterns. A regional thrust belt of late Paleozoic or Mesozoic age affected all pre-Tertiary rocks in the region; main thrust faults, not exposed in the map area, are interpreted to underlie the map area in an arcuate pattern, striking north, northeast, and east. The predominant vergence of thrust faults exposed elsewhere in the region, including the Belted Range and Specter Range thrusts, was to the east, southeast, and south. The vertical to overturned strata of the Striped Hills are hypothesized to result from successive stacking of three south-vergent thrust ramps, the lowest of which is the Specter Range thrust. The CP thrust is interpreted as a north-vergent backthrust that may have been roughly contemporaneous with the Belted Range and Specter Range thrusts. The southwest Nevada volcanic field consists predominantly of a series of silicic tuffs and lava flows ranging in age from 15 to 8 Ma. The map area is in the southwestern quadrant of the southwest Nevada volcanic field, just south of the Timber Mountain caldera complex. The Claim Canyon caldera, exposed in the northern part of the map area, contains thick deposits of the 12.7-Ma Tiva Canyon Tuff, along with widespread megabreccia deposits of similar age, and subordinate thick exposures of other 12.8- to 12.7-Ma Paintbrush Group rocks. An irregular, blocky fault array, which affects parts of the caldera and much of the nearby area, includes several large-displacement, steeply dipping faults that strike radially to the caldera and bound south-dipping blocks of volcanic rock. South and southeast of the Claim Canyon caldera, in the area that includes Yucca Mountain, the Neogene fault pattern is dominated by closely spaced, north-northwest- to north-northeast-striking normal faults that lie within a north-trending graben. This 20- to 25-km-wide graben includes Crater Flat, Yucca Mountain, and Fortymile Wash, and is bounded on the east by the 'gravity fault' and on the west by the Bare Mountain fault. Both of these faults separate Proterozoic and Paleozoic sedimentary rocks in their footwalls from Miocene volcanic rocks in their hanging walls. Stratigraphic and structural relations at Yucca Mountain demonstrate that block-bounding faults were active before and during eruption of the 12.8- to 12.7-Ma Paintbrush Group, and significant motion on these faults continued unt

Generation of Continental Crust in Central America: New Field and Geochemical Observations on Silicic Magmatism in Costa Rica

NASA Astrophysics Data System (ADS)

Szymanski, D. W.; Patino, L. C.; Vogel, T. A.; Alvarado, G. E.

2002-12-01

Explaining the occurrence of high-silica arc magmatism in the absence of continental crust remains a fundamental problem in igneous petrology. Recent work in the southern portion of the Central American volcanic arc has expanded the database for the abundant high-silica ash-flow tuffs erupted on top of thick oceanic basement in Costa Rica and southern Nicaragua. Regional differences in geochemistry are observed in data from central and northern Costa Rica. In addition, local heterogeneities among units are demonstrated in plots of both major and trace elements. High-silica ash-flow tuffs in central Costa Rica include the Tiribi Tuff (~0.33 Ma) and Alto Palomo formation (~0.56 Ma). In northern Costa Rica, numerous large silicic ash-flow sheets are found in the Guanacaste province, ranging from late Miocene (<10 Ma) to Pleistocene (~0.6 Ma) in age. A frequency histogram of normalized silica content for all analyses to date from these units (n=222) produces a left-skewed curve with a mode occurring at approximately 70 wt.% SiO2. Samples from the northern region (n=107) demonstrate a tighter distribution of silica content (60.1-78.7 wt.% SiO2 with a median of 72.2 wt.% SiO2) compared to samples from the central region (n=115, 55.4-74.2 wt.% SiO2 with a median of 67.1 wt.% SiO2). The least evolved samples come from the Tiribi Formation in the Valle Central and are chemically distinct from rocks in the Guanacaste region. In both chemistry and geographical position, the Alto Palomo formation appears to represent a transition between tuffs in the Valle Central and those in Guanacaste. Incompatible trace element ratios for these units are nearly identical to regional trends observed in basaltic to andesitic lavas of the modern Costa Rican arc (e.g. Ba/Nb). The Papagayo sequence is an example of chemical variation within one vertical section. The sequence is a ~21 m section of well-exposed tuff that represents an essentially continuous sampling of an evolving magma body. Major-element analyses from a systematic vertical sampling of the section support a model of crystal fractionation, eruption, and mafic replenishment of the magma chamber. Samples range from 60.1 to 70.2 wt.% SiO2, with the most mafic sample occurring at the top of sequence as a visibly mafic-silicic mingled pumice. The Rio Liberia (~1.47 Ma) and Salitral (~1.3 Ma) formations in the Guanacaste region form a series of tuffs, related by the same inferred vent. Despite overlapping silica content, the units have distinct mineral compositions. The Salitral formation includes plagioclase- and amphibole-rich units that appear very similar in the field, while the Rio Liberia contains biotite. Chemically, the units are distinct, forming several separate trends in trace element plots. These heterogeneities most likely reflect differences in both source and/or processes of magma evolution.

A summary of the geology and petrology of the Sierra La Primavera, Jalisco, Mexico

NASA Astrophysics Data System (ADS)

Mahood, Gail A.

1981-11-01

The Sierra La Primavera, near Guadalajara, Mexico, is a Late Pleistocene rhyolitic center consisting of lava flows and domes, ash flow tuff, air fall pumice, and caldera lake sediments. All eruptive units are high-silica rhyolites, but systematic compositional differences correlate with age and eruptive mode. The earliest lavas erupted approximately 145,000 years ago and were followed approximately 95,000 years ago by the eruption of about 20 km3 of magma as ash flows that form the Tala Tuff. The Tala Tuff is zoned from a mildly peralkaline first-erupted portion enriched in Na, Rb, Cs, Cl, F, Zn, Y, Zr, Nb, Sb, HREE, Hf, Ta, Pb, Th, and U to a metaluminous last-erupted part enriched in K, LREE, Sc, and Ti; Al, Ca, Mg, Mn, Fe, and Eu are constant within analytical errors. Collapse of the roof zone of the magma chamber led to the formation of a shallow 11-km-diameter caldera in which lake sediments began to collect. The earliest postcaldera lava, the south-central dome, is nearly identical to the last-erupted portion of the Tala Tuff, whereas the slightly younger north-central dome is chemically transitional from the south-central dome to later, more mafic, ring domes. This sequence of ash flow tuff and domes represents the tapping of progressively deeper levels of a zoned magma chamber 95,000 ± 5,000 years ago. Sedimentation continued and a period of volcanic quiescence was marked by the deposition of some 30 m of fine-grained ashy sediments. Approximately 75,000 years ago a new group of ring domes erupted at the southern margin of the lake. These domes are lapped by only 10-20 m of sediments as uplift resulting from renewed insurgence of magma brought an end to the lake. This uplift culminated in the eruption, beginning approximately 60,000 years ago, of aphyric lavas along a southern arc. The youngest of these lavas erupted approximately 30,000 years ago. The lavas that erupted 75,000, 60,000, and 30,000 years ago became decreasingly peralkaline and progressively enriched only in Si, Rb, Cs, and possibly U with time. They represent successive eruption of the uppermost magma in the postcaldera magma chamber. Eruptive units of La Primavera are either aphyric or contain up to 15% phenocrysts of sodic sanidine ≥ quartz ≫ ferrohedenbergite > fayalite > ilmenite ± titanomagnetite. Major element compositions of sanidine, clinopyroxene, and fayalite phenocrysts vary only slightly between eruptive groups, but the concentrations of many trace elements change by factors of 5-10. This is reflected in phenocryst/glass partition coefficients that differ by factors of up to 20 between successively erupted units. Because the major element compositions of the phenocrysts and the pressure, temperature, and ƒO2 of the magmas were essentially constant, the large variations in partitioning behavior are thought to result from small changes in bulk composition of the melt. Crystal settling and incremental partial melting are by themselves incapable of producing either the chemical gradients within the Tala Tuff magma chamber or the trends with time in the post-95,000-year lavas. Rather, diffusional processes in the silicate liquid are thought to have been the dominant differentiation mechanisms. The zonation in the Tala Tuff is attributed to transport of trace metals as volatile complexes within a thermal and gravitational gradient in a volatile-rich but water-undersaturated magma. The evolution of the postcaldera lavas with time is thought to involve the diffusive emigration of trace elements from a relatively dry magma as a decreasing proportion of network modifiers and/or a decreasing concentration of complexing ligands progressively reduced octahedral site availability in the silicate melt.

Early Depositional History of the Eocene Izu-Bonin Mariana Arc, Western Pacific Ocean

NASA Astrophysics Data System (ADS)

Waldman, R.; Marsaglia, K. M.; Tepley, F. J., III

2015-12-01

Expedition 351 of the International Ocean Discovery Program cored an Eocene section at Site U1438 in the Philippine Sea that provides insight into the early history of the Izu-Bonin arc. Subduction here is hypothesized to have initiated spontaneously, leaving a characteristic depositional sequence of post-subduction-initiation localized extension and volcanism. We conducted detailed macroscopic and microscopic study of the cores of the lowermost 100m of volcaniclastic and sedimentary rocks (Unit IV) directly overlying subduction initiation igneous basement, to identify depositional facies and trends. We subdivided Unit IV into three subunits based on lithologic characteristics. Transitions between the subunits are relatively abrupt, occurring within the length of a single core. The lowermost subunit (IVA) consists of 4 meters of laminated pelagic claystone with thin beds of graded volcaniclastic siltstone, and fine-grained tuff laminae composed of plagioclase feldspar and green-brown amphibole. The middle subunit (IVB) comprises 51 meters of texturally variable, thick-bedded, coarse-grained gravity flow deposits. These are composed of volcaniclastic sandstone and conglomerate containing glassy and tachylitic volcanic grains as well as sedimentary lithic fragments, along with traces of shallow-water carbonate bioclasts. Subunit IVB sediments are poorer in feldspar than IVA and contain only trace amphibole. They show variable grain rounding and an upsection increase in vitric components. Tachylite grains range from sub-angular to well rounded throughout, and other volcanic grain types show upward increases in angularity and vesicularity. The abrupt transition from pelagic sediments in subunit IVA to shallow-water-sourced gravity flows in subunit IVB suggests a rapid emergence of shallow-water to subaerial volcanic center early in the arc's development. The upper part of subunit IVB also contains igneous intrusions, providing possible evidence for more proximal volcanism at the site. Subunit IVC consists of 46 meters of fine-grained turbidites composed of tuffaceous siltstone, along with radiolarian mudstone and vitric tuff layers. Ongoing studies of the volcanic components will provide additional insight into the source(s) of volcanics throughout the arc's early development.

The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory

NASA Technical Reports Server (NTRS)

Izett, G. A.

1988-01-01

At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America.

Thermohydrologic modeling of the large-block test in partially saturated fractured tuff at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Lee, K.; Buscheck, T. A.; Glascoe, L. G.; Gansemer, J.; Sun, Y.

2002-12-01

In support of the characterization of Yucca Mountain as a potential site for as a geologic repository for high-level nuclear waste, the US Department of Energy conducted the Large Block Test (LBT) at nearby Fran Ridge. The LBT was conducted in an excavated 3x 3x 4.5m block of partially saturated, fractured nonlithophysal Topopah Spring tuff, which is one of the host-rock units for the potential repository at Yucca Mountain. The LBT was one of a series of field-scale thermohydrologic tests conducted in the repository host-rock units. The LBT was heated by line heaters installed in five boreholes lying in a horizontal plane 2.75 m below the upper surface of the block. The field-scale thermal tests were designed to help investigators better understand the coupled thermohydrologic-mechanical-chemical processes that would occur in the host rock in response to the radioactive heat of decay from emplaced waste packages. The tests also provide data for the calibration and validation of numerical models used to analyze the thermohydrologic response of the near-field host rock and Engineered Barrier System (EBS). Using the NUFT code and the dual-permeability approach to representing fracture-matrix interaction, we simulated the thermohydrologic response of the block to a heating and cooling cycle. The primary goals of the analysis were to study the heat-flow mechanisms and water redistribution patterns in the boiling and sub-boiling zones, and to compare model results with measured temperature and liquid saturation data, and thereby evaluate two rock property data sets available for modeling thermohydrologic behavior in the rock. Model results were also used for model calibration and validation. We obtained a good to excellent match between model and observed temperatures, and found that the distinct dryout and condensation zones modeled above and below the heater level agreed fairly well with the liquid-saturation measurements. We identified the best-fit data set by using a statistical analysis to compare model and field temperatures, and found that heat flow in the block was dominated by conduction.

Undergraduate Field Courses in Volcanology at the University of California, Davis

NASA Astrophysics Data System (ADS)

Schiffman, P.

2002-05-01

At U.C. Davis, undergraduate Geology majors have two opportunities to participate in extended field courses in volcanology: (1) all majors spend one week in a volcanology module during their six-week, "capstone" Summer Field Geology (GEL 110) course, and (2) all majors may enroll in a two-week, Introductory Volcanology course (GEL 138) offered each summer at Kilauea Volcano. The former course is required of all majors in order to fulfill their B.S. degree requirements, whereas the latter fulfills upper division elective units for either the B.A. or B.S. degree in Geology. The volcanology module in GEL 110 is based at U.C.'s White Mountain Research Station in Bishop, California and includes four separate exercises: (1) mapping patterns of consolidation of tephra at the Black Point tuff cone in order to understand the processes of palagonitization, (2) contouring graphic mean and sorting for tephra collected from the Red Cones cinder cone to understand Strombolian processes, (3) measuring a stratigraphic section of the Bishop Tuff in the lower Owens River Gorge to differentiate cooling units in ignimbrites, and (4) mapping the relationships amongst pumice units and obsidian at the Glass Mountain flow to understand evolution of silicic flows. Most exercises require laboratory measurements for grain size or density (Mayfield and Schiffman, 1998). GEL 138, based at the Kilauea Military Camp, includes a daily schedule of morning lectures and afternoon field excursions and exercises. Exercises include: (1) measuring a stratigraphic section of the Keanakako'i Ash Member to interpret pre-1790 periods of hydrovolcanism, (2) measuring and contouring ground temperatures in the Steaming Bluffs thermal area (3) conducting granulometric measurements of tephra from the Nanawale sand hills to understand the genesis of littoral cones, (4) mapping of soil pH around the perimeter of Kilauea Caldera to illuminate climatic effects (i.e.,vog and wind patterns) on the summit region, and (5) mapping lava flows from the SW rift zone of Mauna Loa at South Point. Reference: Mayfield, J. and Schiffman, P., (1998) Measuring the density of porous volcanic rocks in the field using a Saran coating. Journal of Geological Education 46, 460-464.

Sources of Increased Spring and Streamflow Caused by the 2014 South Napa Earthquake

NASA Astrophysics Data System (ADS)

Rytuba, J. J.; Holzer, T. L.

2014-12-01

Seasonally dry springs and creeks began flowing over a broad region in the hills around Napa following the M6.0 South Napa earthquake on August 24, 2014. Flows in hillside creek beds, which were dry before the earthquake, were reported from 19 km west, to 6 km east, and 18 km north of Napa and the epicenter, an area that shook at MMI≥VI. The exact timing of the increased flow is unknown because the earthquake occurred at 3:20 AM PDT. A gaging station on the Napa River, which is downstream from several tributaries that began flowing after the earthquake, showed a sudden increase of flow rate within 45 minutes following the earthquake. The sudden increase at the gaging station suggests flows initiated either contemporaneously with or very soon after the strong shaking. This timing is consistent with eyewitness accounts of other streams and springs at daylight, a few hours after the earthquake. One of the largest increases of streamflow was in Green Valley, where a streamflow rate of about 100 cubic hectometers per day was measured in Wild Horse Creek. Two types of waters are being discharged in the Wild Horse Creek drainage: 1) water with low iron concentration that has exchanged with rhyolitic flows and tuffs in the upper part of the drainage; and 2) high iron concentration water that has exchanged with basaltic andesite in the middle part of drainage (vertical interval of about 75 meters). The high iron waters are depositing FeOOH other iron phases. Mixing of the two water types results in water with pH 6.9 and conductivity of 0.197 mS. This water is used by the Vallejo Water District for domestic purposes after it is mixed with recent surface water runoff stored in Lake Frey reservoir in order to improve its quality. Other drainages that have increased flow since the earthquake have water chemistry consistent with exchange with rhyolitic flows and tuffs that are the dominant rock type in these drainages.

The low-latitude Rapitan glaciation (Invited)

NASA Astrophysics Data System (ADS)

MacDonald, F. A.; Schmitz, M. D.; Crowley, J. L.; Roots, C.; Maloof, A. C.; Jones, D. S.; Strauss, J.

2009-12-01

The snowball Earth hypothesis1 was developed in response to strong palaeomagnetic evidence for low-latitude glaciation from “Marinoan” glacial deposits in the Elatina Formation of Australia. An earlier Cryogenian glaciation, commonly referred to as the “Sturtian” glaciation, has been inferred from the ubiquity of pre-Marinoan glacial deposits; however, the synchroneity and global extent of this event have been questioned due to the lack of precise U/Pb ages and robust paleomagnetic data. Herein we provide new age constraints on the Franklin LIP with revised U/Pb ID-TIMS dates on the the Mt. Harper volcanic complex in the Yukon Territory and the Coronation sills of Victoria Island. Furthermore we present a new age from a tuff interbedded with diamictite in the Upper Mt. Harper Group. A glaciogenic origin of the diamictites is provided by striated clasts and laminae-penetrating dropstones. These glacial deposits can be traced from Alaska westward through the Yukon Territory and into the Northwest Territories, and are correlative to the Rapitan Group. Throughout the Cordillera, the Rapitan Group and its correlatives commonly host iron formation, are the lower of two Cryogenian glacial horizons, and globally are thought to be equivalent to the Sturtian glaciation. The age of the tuff interbedded with the glacial deposits in the Mt. Harper Group is within 1 million years of the revised age on the Franklin LIP. Several paleomagnetic studies on dikes, sills, and basalts spanning >2000 km of NW Canada have agreed that the Franklin LIP erupted when NW Laurentia was in an equatorial position2,3. Consequently, the Sturtian glaciation on Laurentia can now be confidently inferred to have occurred at a very low palaeolatitude. Thus, there were at least two Cryogenian glaciations of global extent. 1 Kirschvink, J.L., in The Proterozoic Biosphere, edited by J. W. Schopf and C. Klein (Cambridge University Press, Cambridge, 1992), pp. 51. 2 Park, J.K., Paleomagnetic constraints on the position of Laurentia from middle Neoproterozoic to Early Cambrian times. Precambrian Research 69, 95 (1994). 3 Evans, D.A.D., Stratigraphic, geochronological, and paleomagnetic constraints upon the Neoproterozoic climatic paradox. American Journal of Science 300, 347 (2000).

Geology of drill hole UE25p No. 1: A test hole into pre-Tertiary rocks near Yucca Mountain, southern Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carr, M.D.; Waddell, S.J.; Vick, G.S.

1986-12-31

Yucca Mountain in southern Nye County, Nevada, has been proposed as a potential site for the underground disposal of high-level nuclear waste. An exploratory drill hole designated UE25p No. 1 was drilled 3 km east of the proposed repository site to investigate the geology and hydrology of the rocks that underlie the Tertiary volcanic and sedimentary rock sequence forming Yucca Mountain. Silurian dolomite assigned to the Roberts Mountain and Lone Mountain Formations was intersected below the Tertiary section between a depth of approximately 1244 m (4080 ft) and the bottom of the drill hole at 1807 m (5923 ft). Thesemore » formations are part of an important regional carbonate aquifer in the deep ground-water system. Tertiary units deeper than 1139 m (3733 ft) in drill hole UE25p No. 1 are stratigraphically older than any units previously penetrated by drill holes at Yucca Mountain. These units are, in ascending order, the tuff of Yucca Flat, an unnamed calcified ash-flow tuff, and a sequence of clastic deposits. The upper part of the Tertiary sequence in drill hole UE25p No. 1 is similar to that found in other drill holes at Yucca Mountain. The Tertiary sequence is in fault contact with the Silurian rocks. This fault between Tertiary and Paleozoic rocks may correlate with the Fran Ridge fault, a steeply westward-dipping fault exposed approximately 0.5 km east of the drill hole. Another fault intersects UE25p No. 1 at 873 m (2863 ft), but its surface trace is concealed beneath the valley west of the Fran Ridge fault. The Paintbrush Canyon fault, the trace of which passes less than 100 m (330 ft) east of the drilling site, intersects drill hole UE25p No. 1 at a depth of approximately 78 m (255 ft). The drill hole apparently intersected the west flank of a structural high of pre-Tertiary rocks, near the eastern edge of the Crater Flat structural depression.« less

Linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved Yellowstone-type supervolcanoes

USGS Publications Warehouse

Wotzlaw, J.F.; Bindeman, I.N.; Watts, Kathryn E.; Schmitt, A.K.; Caricchi, L.; Schaltegger, U.

2014-01-01

The geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations, the A.D. 1815 Tambora (Indonesia) eruption. Perhaps nowhere on Earth are deposits of such supereruptions more prominent than in the Snake River Plain–Yellowstone Plateau (SRP-YP) volcanic province (northwest United States). While magmatic activity at Yellowstone is still ongoing, the Heise volcanic field in eastern Idaho represents the youngest complete caldera cycle in the SRP-YP, and thus is particularly instructive for current and future volcanic activity at Yellowstone. The Heise caldera cycle culminated 4.5 Ma ago in the eruption of the ∼1800 km3 Kilgore Tuff. Accessory zircons in the Kilgore Tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity, and the vast majority are 18O depleted. This suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low-δ18O meteoric-hydrothermal fluids. Prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir. U-Pb geochronology of isotopically diverse zircons using chemical abrasion–isotope dilution–thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206Pb/238U date of 4.4876 ± 0.0023 Ma (MSWD = 1.5; n = 24). These zircon crystallization ages are also indistinguishable from the sanidine 40Ar/39Ar dates, and thus zircons crystallized close to eruption. This requires that shallow crustal melting, assembly of isolated batches into a supervolcanic magma reservoir, homogenization, and eruption occurred extremely rapidly, within the resolution of our geochronology (103–104 yr). The crystal-scale image of the reservoir configuration, with several isolated magma batches, is very similar to the reservoir configurations inferred from seismic data at active supervolcanoes. The connection of magma batches vertically distributed over several kilometers in the upper crust would cause a substantial increase of buoyancy overpressure, providing an eruption trigger mechanism that is the direct consequence of the reservoir assembly process.

Oxygen isotope study of the Long Valley magma system, California: isotope thermometry and convection in large silicic magma bodies

NASA Astrophysics Data System (ADS)

Bindeman, Ilya; Valley, John

2002-07-01

Products of voluminous pyroclastic eruptions with eruptive draw-down of several kilometers provide a snap-shot view of batholith-scale magma chambers, and quench pre-eruptive isotopic fractionations (i.e., temperatures) between minerals. We report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite, pyroxene, and zircon from individual pumice clasts of ignimbrite and fall units of caldera-forming 0.76 Ma Bishop Tuff (BT), pre-caldera Glass Mountain (2.1-0.78 Ma), and post-caldera rhyolites (0.65-0.04 Ma) to characterize the long-lived, batholith-scale magma chamber beneath Long Valley Caldera in California. Values of δ18O show a subtle 1‰ decrease from the oldest Glass Mountain lavas to the youngest post-caldera rhyolites. Older Glass Mountain lavas exhibit larger ( 1‰) variability of δ18O(quartz). The youngest domes of Glass Mountain are similar to BT in δ18O(quartz) values and reflect convective homogenization during formation of BT magma chamber surrounded by extremely heterogeneous country rocks (ranging from 2 to +29‰). Oxygen isotope thermometry of BT confirms a temperature gradient between "Late" (815 °C) and "Early" (715 °C) BT. The δ18O(quartz) values of "Early" and "Late" BT are +8.33 and 8.21‰, consistent with a constant δ18O(melt)=7.8+/-0.1‰ and 100 °C temperature difference. Zircon-melt saturation equilibria gives a similar temperature range. Values of δ18O(quartz) for different stratigraphic units of BT, and in pumice clasts ranging in pre-eruptive depths from 6 to 11 km (based on melt inclusions), and document vertical and lateral homogeneity of δ18O(melt). Worldwide, five other large-volume rhyolites, Lava Creek, Lower Bandelier, Fish Canyon, Cerro Galan, and Toba, exhibit equal δ18O(melt) values of earlier and later erupted portions in each of the these climactic caldera-forming eruptions. We interpret the large-scale δ18O homogeneity of BT and other large magma chambers as evidence of their longevity (>105 years) and convection. However, remaining isotopic zoning in some quartz phenocrysts, trace element gradients in feldspars, and quartz and zircon crystal size distributions are more consistent with far shorter timescales (102-104 years). We propose a sidewall-crystallization model that promotes convective homogenization, roofward accumulation of more evolved and stagnant, volatile-rich liquid, and develops compositional and temperature gradients in pre-climactic magma chamber. Crystal + melt + gas bubbles mush near chamber walls of variable δ18O gets periodically remobilized in response to chamber refill by new hotter magmas. One such episode of chamber refill by high-Ti, Sr, Ba, Zr, and volatile-richer magma happened 103-104 years prior to the 0.76-Ma caldera collapse that caused magma mixing at the base, mush thawing near the roof and walls, and downward settling of phenocrysts into this hybrid melt.

Upper cretaceous (Austin Group) volcanic deposits as a hydrocarbon trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hutchinson, P.J.

1994-12-31

An Upper Cretaceous submarine igneous extrusion occurs in the subsurface of southwestern Wilson County, Texas. The Coniacian-Santonian-aged (Austin Group) volcanic eruption discharged large volumes of magnetite-rich olivine nephelinite that upon quenching formed an extensive nontronitic clay layer. This clay deposit formed a trapping mechanism for hydrocarbon beneath the volcano. Production from volcanic plugs is normally attributed to the shoal-water carbonate facies developed on top of the volcanic, the palagonite tuff ({open_quotes}serpentine{close_quotes}), and overlying sandstones. The heat energy of the volcano may have thermally matured the calcarous sediments of adjacent parts of the Austin Chalk. The normally grayish-colored suggesting thermal alteration.more » The overlying nontronite trapped mobile hydrocarbons, and this early emplacement of oil may have preserved some of the original porosity and permeability of the Austin Chalk. Austin Chalk-aged volcanic deposits produce hydrocarbons from stratigraphic traps within the volcanic material, within the porous beachrock, and structurally within overlying sandstones. The intruded Austin Chalk also behaves as a reservoir because the original porosity and permeability are maintained by early emplacement of oil and the overlying volcanic clay acts as a seal by preventing vertical migration. Marcelina Creek field, discovered in 1980 from an {open_quotes}augen{close_quotes}-shaped seismic signature and an aerial magnetic survey, produces from the fractured chalk beneath the nontronitic clay layer. This field has produced more than 15 million barrels of oil from more than 60 wells in fractured and porous rock beneath the volcano.« less

Complex circular subsidence structures in tephra deposited on large blocks of ice: Varða tuff cone, Öræfajökull, Iceland

NASA Astrophysics Data System (ADS)

Smellie, J. L.; Walker, A. J.; McGarvie, D. W.; Burgess, R.

2016-08-01

Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations.

Transient calcite fracture fillings in a welded tuff, Snowshoe Mountain, Colorado

USGS Publications Warehouse

Hoch, A.R.; Reddy, M.M.; Heymans, M.J.

2000-01-01

The core from two boreholes (13.1 and 19.2 m depth) drilled 500 m apart in the fractured, welded tuff near the summit of the Snowshoe Mountain, Colorado (47??30'N, 106??55'W) had unique petrographic and hydrodynamic properties. Borehole SM-4 had highly variable annual water levels, in contrast to SM-1a, whose water level remained near the land surface. Core samples from both boreholes (n = 10 and 11) were examined petrographically in thin sections impregnated with epoxy containing rhodamine to mark the pore system features, and were analyzed for matrix porosity and permeability. Core from the borehole sampling the vadose zone was characterized by open fractures with enhanced porosity around phenocrysts due to chemical weathering. Fractures within the borehole sampling the phreatic zone were mineralized with calcite and had porosity characteristics similar to Unweathered and unfractured rock. At the top of the phreatic zone petrography indicates that calcite is dissolving, thereby changing the hydrogeochemical character of the rock (i.e. permeability, porosity, reactive surface area, and mineralogy). Radiocarbon ages and C and O stable isotopes indicate that calcite mineralization occurred about 30 to 40 ka ago and that there was more than one mineralization event. Results of this study also provide some relationships between primary porosity development from 3 types of fracture in a welded tuff. (C) 2000 Elsevier Science Ltd.

Experimental constraints on phreatic eruption processes at Whakaari (White Island volcano)

NASA Astrophysics Data System (ADS)

Mayer, Klaus; Scheu, Bettina; Gilg, H. Albert; Heap, Michael J.; Kennedy, Ben M.; Lavallée, Yan; Letham-Brake, Mark; Dingwell, Donald B.

2015-09-01

Vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at Whakaari (White Island volcano), New Zealand. Here, we investigate the influence of sample type (hydrothermally altered cemented ash tuffs and unconsolidated ash/lapilli) and fragmentation mechanism (steam flashing versus gas expansion) on fragmentation and ejection velocities as well as on particle-size and shape. Our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs, cemented by alunite and amorphous opal, increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing. Ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs, as less energy is consumed by fragmentation. Fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles. Particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front. Neither fragmentation mechanisms nor sample type show a significant influence on the shape. Our results emphasize that, under identical pressure and temperature conditions, eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion. Therefore, phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments.

Geoengineering properties of potential repository units at Yucca Mountain, southern Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tillerson, J.R.; Nimick, F.B.

1984-12-01

The Nevada Nuclear Waste Storage Investigations (NNWSI) Project is currently evaluating volcanic tuffs at the Yucca Mountain site, located on and adjacent to the Nevada Test Site, for possible use as a host rock for a radioactive waste repository. The behavior of tuff as an engineering material must be understood to design, license, construct, and operate a repository. Geoengineering evaluations and measurements are being made to develop confidence in both the analysis techniques for thermal, mechanical, and hydrothermal effects and the supporting data base of rock properties. The analysis techniques and the data base are currently used for repository design,more » waste package design, and performance assessment analyses. This report documents the data base of geoengineering properties used in the analyses that aided the selection of the waste emplacement horizon and in analyses synopsized in the Environmental Assessment Report prepared for the Yucca Mountain site. The strategy used for the development of the data base relies primarily on data obtained in laboratory tests that are then confirmed in field tests. Average thermal and mechanical properties (and their anticipated variations) are presented. Based upon these data, analyses completed to date, and previous excavation experience in tuff, it is anticipated that existing mining technology can be used to develop stable underground openings and that repository operations can be carried out safely.« less

Geochronology and geochemistry of tuff beds from the Shicaohe Formation of Shennongjia Group and tectonic evolution in the northern Yangtze Block, South China

NASA Astrophysics Data System (ADS)

Du, Qiuding; Wang, Zhengjiang; Wang, Jian; Deng, Qi; Yang, Fei

2016-03-01

Meso- to Neoproterozoic magmatic events are widespread in the Yangtze Block. The geochronology and tectonic significance of the Shennongjia Group in the Yangtze Block are still highly controversial. An integrated geochronology and geochemistry approach provides new insights into the geochronological framework, tectonic setting, magmatic events, and basin evolution of the northern Yangtze Block. Our new precise sensitive high-resolution ion microprobe U-Pb data indicate a deposition age of 1180 ± 15 Ma for the Shicaohe Formation subalkaline basaltic tuff that is geochemically similar to modern intracontinental rift volcanic rocks. The integration of available geochemical data together with our new U-Pb ages indicates the Shicaohe Formation subalkaline basaltic tuff formed ca. 1180 in a continental rift-related setting on a passive continental margin. The Shennongjia Group is topped by the Zhengjiaya Formation volcanic sequence, indicating arc-related igneous events at 1103 Ma. The transition of the late Mesoproterozoic tectonic regime from intracontinental extension to convergence occurred between ca. 1180 and 1103 Ma in the northern Yangtze Block. Tectonic evolution in the Neoproterozoic led to accretion along the northern margin of the Yangtze Block. These results provide geochronological evidence, which is of utmost importance for reconfiguration of the chronostratigraphic framework and for promoting research on Mesoproterozoic strata in China, thereby increasing understanding of magmatic events and basin evolutionary history in the northern Yangtze Block.

Magnetic properties in an ash flow tuff with continuous grain size variation: a natural reference for magnetic particle granulometry

USGS Publications Warehouse

Till, J.L.; Jackson, M.J.; Rosenbaum, J.G.; Solheid, P.

2011-01-01

The Tiva Canyon Tuff contains dispersed nanoscale Fe-Ti-oxide grains with a narrow magnetic grain size distribution, making it an ideal material in which to identify and study grain-size-sensitive magnetic behavior in rocks. A detailed magnetic characterization was performed on samples from the basal 5 m of the tuff. The magnetic materials in this basal section consist primarily of (low-impurity) magnetite in the form of elongated submicron grains exsolved from volcanic glass. Magnetic properties studied include bulk magnetic susceptibility, frequency-dependent and temperature-dependent magnetic susceptibility, anhysteretic remanence acquisition, and hysteresis properties. The combined data constitute a distinct magnetic signature at each stratigraphic level in the section corresponding to different grain size distributions. The inferred magnetic domain state changes progressively upward from superparamagnetic grains near the base to particles with pseudo-single-domain or metastable single-domain characteristics near the top of the sampled section. Direct observations of magnetic grain size confirm that distinct transitions in room temperature magnetic susceptibility and remanence probably denote the limits of stable single-domain behavior in the section. These results provide a unique example of grain-size-dependent magnetic properties in noninteracting particle assemblages over three decades of grain size, including close approximations of ideal Stoner-Wohlfarth assemblages, and may be considered a useful reference for future rock magnetic studies involving grain-size-sensitive properties.

New geochronologic and palaeomagnetic data for the hominid-bearing Hadar Formation of Ethiopia

USGS Publications Warehouse

Aronson, J.L.; Schmitt, T.J.; Walter, R.C.; Taieb, M.; Tiercelin, J.J.; Johanson, D.C.; Naeser, C.W.; Nairn, A.E.M.

1977-01-01

A 2.6 Myr K/Ar age has been derived for a primary unreworked tuff high in the hominid-bearing Hadar Formation (Kada Hadar Member), stratigraphically above all the important fossil finds. A 2.6 Myr fission track age has been derived on zircons from this tuff. New K/Ar results on the Kadada Moumou basalt (Sidi Hakoma Member) suggest a 3.0 Myr age. Preliminary interpretation of a detailed continuous palaeomagnetic section through the formation indicates the existence of persistent normal and reversed sequences. With the radiometric age control this magnetic sequence appears to correlate with the Gauss Epoch. These initial results imply the fossil-rich Hadar Formation spans from somewhat older than 3.1 Myr to somewhat younger than 2.6 Myr. ?? 1977 Nature Publishing Group.

Paleomagnetism of the Oligocene Kalamazoo Tuff: implications for middle Tertiary extension in east central Nevada

USGS Publications Warehouse

Hagstrum, J.T.; Gans, P.B.

1989-01-01

The Oligocene Kalamazoo Tuff (???35 Ma) was sampled for paleomagnetic analysis across a 100-km-wide zone of highly extended crust in east central Nevada to estimate between-site vertical axis rotations and thus the relative importance of strike-slip faulting to the mechanism of extension. The tilt-corrected data, with sources of error reduced or eliminated, exhibit a 28?? ?? 12?? clockwise rotation of the Schell Creek Range relative to the Kern Mountains region. This rotation implies differential extension accommodated by strike-slip faulting or N-S shortening. The paleomagnetic results also suggest that large changes in strike of layered units near faults with presumed strike-slip movement need not be the result of oroclinal bending, but could result from superimposed sets of orthogonal normal faults. -from Authors

Postwildfire preliminary debris flow hazard assessment for the area burned by the 2011 Las Conchas Fire in north-central New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Darr, Michael J.; Cannon, Susan H.; Michael, John A.

2011-01-01

The Las Conchas Fire during the summer of 2011 was the largest in recorded history for the state of New Mexico, burning 634 square kilometers in the Jemez Mountains of north-central New Mexico. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from 321 basins burned by the Las Conchas Fire. A pair of empirical hazard-assessment models developed using data from recently burned basins throughout the intermountain western United States was used to estimate the probability of debris-flow occurrence and volume of debris flows at the outlets of selected drainage basins within the burned area. The models incorporate measures of burn severity, topography, soils, and storm rainfall to estimate the probability and volume of debris flows following the fire. In response to a design storm of 28.0 millimeters of rain in 30 minutes (10-year recurrence interval), the probabilities of debris flows estimated for basins burned by the Las Conchas Fire were greater than 80 percent for two-thirds (67 percent) of the modeled basins. Basins with a high (greater than 80 percent) probability of debris-flow occurrence were concentrated in tributaries to Santa Clara and Rio del Oso Canyons in the northeastern part of the burned area; some steep areas in the Valles Caldera National Preserve, Los Alamos, and Guaje Canyons in the east-central part of the burned area; tributaries to Peralta, Colle, Bland, and Cochiti canyons in the southwestern part of the burned area; and tributaries to Frijoles, Alamo, and Capulin Canyons in the southeastern part of the burned area (within Bandelier National Monument). Estimated debris-flow volumes ranged from 400 cubic meters to greater than 72,000 cubic meters. The largest volumes (greater than 40,000 cubic meters) were estimated for basins in Santa Clara, Los Alamos, and Water Canyons, and for two basins at the northeast edge of the burned area tributary to Rio del Oso and Vallecitos Creek. The Combined Relative Debris-Flow Hazard Rankings identify the areas of highest probability of the largest debris flows. Basins with high Combined Relative Debris-Flow Hazard Rankings include upper Santa Clara Canyon in the northern section of the burn scar, and portions of Peralta, Colle, Bland, Cochiti, Capulin, Alamo, and Frijoles Canyons in the southern section of the burn scar. Three basins with high Combined Relative Debris-Flow Hazard Rankings also occur in areas upstream from the city of Los Alamos—the city is home to and surrounded by numerous technical sites for the Los Alamos National Laboratory. Potential debris flows in the burned area could affect the water supply for Santa Clara Pueblo and several recreational lakes, as well as recreational and archeological resources in Bandelier National Monument. Debris flows could damage bridges and culverts along State Highway 501 and other roadways. Additional assessment is necessary to determine if the estimated volume of material is sufficient to travel into areas downstream from the modeled basins along the valley floors, where they could affect human life, property, agriculture, and infrastructure in those areas. Additionally, further investigation is needed to assess the potential for debris flows to affect structures at or downstream from basin outlets and to increase the threat of flooding downstream by damaging or blocking flood mitigation structures. The maps presented here may be used to prioritize areas where erosion mitigation or other protective measures may be necessary within a 2- to 3-year window of vulnerability following the Las Conchas Fire.

Spatial variability of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, southwestern Utah

NASA Astrophysics Data System (ADS)

Okubo, C. H.

2012-12-01

In order to yield new insight into the process of faulting in fine-grained, poorly indurated volcanic ash, the distribution of strain around faults in the Miocene-aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah, is investigated. Several distinct styles of inelastic strain are identified. Deformation bands are observed in tuff that is porous and granular in nature, or is inferred to have been so at the time of deformation. Where silicic alteration is pervasive, fractures are the dominant form of localized strain. Non-localized strain within the host rock is manifest as pore space compaction, including crushing of pumice clasts. Distinct differences in fault zone architecture are observed at different magnitudes of normal fault displacement, in the mode II orientation. A fault with cm-scale displacements is manifest as a single well-defined surface. Off-fault damage occurs as pore space compaction near the fault tips and formation of deformation band damage zones that are roughly symmetric about the fault. At a fault with larger meter-scale displacements, a fault core is present. A recognizable fault-related deformation band damage zone is not observed here, even though large areas of the host rock remain porous and granular and deformation bands had formed prior to faulting. The host rock is instead fractured in areas of pervasive alteration and shows possible textural evidence of fault pulverization. The zones of localized and distributed strain have notably different spatial extents around the causative fault. The region of distributed deformation, as indicated by changes in gas permeability of the macroscopically intact rock, extends up to four times farther from the fault than the highest densities of localized deformation (i.e., fractures and deformation bands). This study identifies a set of fault-related processes that are pertinent to understanding the evolution of fault systems in poorly indurated tuff. Not surprisingly, the type of structural discontinuity that forms in the fault environment is found to be a function of the porosity and granularity of the host rock. Non-localized deformation in the form of pore space compaction of the host rock is found to be prominent around the fault tips at First Spring Hollow. Interestingly, the spatial distribution of host rock compaction and the occurrences of dilational deformation bands around this fault do not correlate with the classic pattern of compression and dilation generally anticipated for slipped normal faults when viewed in mode II. Therefore, while broad generalities regarding the types of discontinuities that form around faults in tuff can be drawn based on current principles, additional work is needed to better understand the genesis of the observed spatial distributions of strain.

Summary of the geology of the northern part of the Sierra Cuchillo, Socorroand Sierra Counties, southwestern New Mexico

USGS Publications Warehouse

Maldonado, Florian; Edited by Lucas, Spencer G.; McLemore, Virginia T.; Lueth, Virgil W.; Spielmann, Justin A.; Krainer, Karl

2012-01-01

The northern part of the Sierra Cuchillo is located within the northeastern part of the Mogollon-Datil volcanic field west of the Rio Grande rift in the Basin and Range Province, approximately 50 km northwest of Truth or Consequences in south-central New Mexico. The Sierra Cuchillo is a north-south, elongated horst block composed of Tertiary volcanic and intrusive rocks, sparse outcrops of Lower Permian and Upper Cretaceous rocks, and sediments of the Tertiary-Quaternary Santa Fe Group. The horst is composed mainly of a basal volcanic rock sequence of andesite-latite lava flows and mud-flow breccias with a 40Ar/39Ar isotopic age of about 38 Ma. The sequence is locally intruded by numerous dikes and plugs that range in composition from basaltic andesite through rhyolite and granite. The andesite-latite sequence is overlain by ash-flow tuffs and a complex of rhyolitic lava flows and domes. Some of these units are locally derived and some are outflow sheets derived from calderas in the San Mateo Mountains, northeast of the study area. These locally derived units and outflow sheets range in age from 28 to 24 Ma.

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, G.C.; Lissoway, J.

In June 1977, the holocaustic La Mesa Fire occurred in the eastern Jemez Mountains of New Mexico. The fire and the subsequent reseeding of the area have created a potential 15,000-acre winter range for elk. Winter range generally is considered the limiting factor in control of elk populations; this new abundance may allow a large increase in the eastern Jemez Mountains elk population. The Los Alamos Scientific Laboratory (LASL), located in the area, is interested in elk overpopulation because of the effect on the vegetation, because increased numbers of elk on the roads would increase traffic hazards, and because ofmore » the possibility of elk becoming contaminated with effluents released by the Laboratory. The elk population is difficult to control here because LASL and Bandelier National Monument do not allow hunting on their lands. A 1-day workshop, held June 12, 1979, to discuss problems that might occur with elk population changes, resulted in the research plan outlined here. Participants, including experts on elk and regional land and wildlife managers, are listed in the Appendix.« less

In-situ petrophysical properties of hotspot volcanoes. Results from ODP Leg 197, Detroit Seamount and HSDP II borehole, Hawaii

NASA Astrophysics Data System (ADS)

Kock, I.; Pechnig, R.; Buysch, A.; Clauser, C.

2003-04-01

During ODP Leg 197 an extensive logging program was run on Site 1203, Detroit Seamount. This seamount is part of the Emperor seamount chain, a continuation of the Hawaiian volcanic chain. Standard ODP/LDEO logging tool strings were used to measure porosity, density, resistivity, p- and s-wave velocities and gamma ray activity. The FMS-tool yielded detailed high resolution resistivity images of the borehole wall. By interpretation and statistical analysis of the logging parameters a petrophysical classification of the drilled rock content could be derived. The pillow lava recovered in the cores exhibits low porosity, low resistivity and high density. This indicates no or very little vesicles in the non-fractured rock unit. Compared to the pillow basalts, subaerial basalts show increasing porosity, gamma ray and potassium content and decreasing density, resistivity and velocity. A basalt with no or little vesicles and a basalt with average or many vesicles can clearly be distinguished. The volcaniclastics show lower resistivity, lower sonic velocities, higher porosities and lower densities than the basalts. Three different rock types can be distinguished within the volcaniclastics: Tuffs, resedimented tephra and breccia. The tuff shows medium porosity and density, low gamma ray and potassium content. The log responses from the resedimented tephra suggest that the tephra is more easily altered than the tuff. The log responses from the breccia lie between the tuff and tephra log responses, but the breccia can clearly be identified in the FMS borehole images. A similar rock content was found in the Hawaiian Scientific Drilling Project borehole. Gamma ray activity, electrical resistivity and sonic velocity were measured down to 2700 mbsl.. Compared to the 72-76 Ma old Detroit seamount basalts, the HSDP subaerial and submarine lava flows show a significant lower gamma ray activity, while sonic velocity and electrical resistivity are comparable. Deviations between the gamma ray activity might be due to the different primary compositions of the melt or to long lasting low temperature alteration. Investigations on this topic are in progress.

Stratigraphy and tephra of the Kibish Formation, southwestern Ethiopia.

PubMed

Brown, Francis H; Fuller, Chad R

2008-09-01

The Kibish Formation in southwestern Ethiopia, with an aggregate thickness of approximately 105 m, consists of lacustrine, marginal lacustrine, and deltaic deposits. It is divided into four members numbered I to IV on the basis of erosion surfaces (disconformities) between the strata of each member. It overlies the Mursi and Nkalabong formations, the latter of which is here shown to correlate with the Shungura Formation. Tephra layers in each member allow for secure correlation between geographically separated sections on the basis of the composition of their volcanic glass. Members I, III, and IV of the Kibish Formation appear to have been deposited at the same times as sapropels S7 (197 ka), S4 (104 ka), and S1 (8 ka) in the eastern Mediterranean Sea, respectively. We correlate the KHS Tuff of the Kibish Formation with a >154-kyr-old unnamed tuff in the Konso Formation. Tephra in Member IV may derive from Mount Wenchi, a volcano situated on the divide between the Omo and Blue Nile drainage basins. Thin-bedded sedimentary layers probably represent annual deposition reflecting rapid sedimentation (approximately 30 m/kyr) of parts of the formation. This conclusion is supported by variation in paleomagnetic inclination through a sequence of these layers at KHS. Two fossils of early Homo sapiens (Omo I and Omo II) derive from Member I. Their stratigraphic placement is confirmed by analysis of the KHS Tuff in the lower part of Member II at both fossil sites. The KHS Tuff lies above a disconformity, which itself lies above the fossils at both sites. (40)Ar/(39)Ar dates provide an estimated age of approximately 195 kyr for these fossils. Omo III, a third fossil H. sapiens, probably also derives from Member I of the Kibish Formation and is of similar age. Hominin fossils from AHS, a new site, also derive from Member I. Hominin fossils from CHS can only be placed between 104 ka and 10 ka, the H. sapiens specimen from JHS is most likely 9-13 kyr in age, and a partial skeleton of H. sapiens from Pelvic Corner is most likely approximately 6.6 kyr in age.

Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Dobson, Patrick F.; Kneafsey, Timothy J.; Sonnenthal, Eric L.; Spycher, Nicolas; Apps, John A.

2003-05-01

Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 °C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 °C at the top and 130 °C at the bottom. The fracture began to seal with amorphous silica within 5 days. A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment. These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However, differences in fluid flow rates and thermal gradients between the experimental setup and anticipated conditions at Yucca Mountain need to be factored into scaling the results of the dissolution/precipitation experiments and associated simulations to THC models for the potential Yucca Mountain repository.

The Late Cretaceous Middle Fork caldera, its resurgent intrusion, and enduring landscape stability in east-central Alaska

USGS Publications Warehouse

Bacon, Charles R.; Dusel-Bacon, Cynthia; Aleinikoff, John N.; Slack, John F.

2014-01-01

The Middle Fork is a relatively well preserved caldera within a broad region of Paleozoic metamorphic rocks and Mesozoic plutons bounded by northeast-trending faults. In the relatively downdropped and less deeply exhumed crustal blocks, Cretaceous–Early Tertiary silicic volcanic rocks attest to long-term stability of the landscape. Within the Middle Fork caldera, the granite porphyry is interpreted to have been exposed by erosion of thick intracaldera tuff from an asymmetric resurgent dome. The Middle Fork of the North Fork of the Fortymile River incised an arcuate valley into and around the caldera fill on the west and north and may have cut down from within an original caldera moat. The 70 Ma land surface is preserved beneath proximal outflow tuff at the west margin of the caldera structure and beneath welded outflow tuff 16–23 km east-southeast of the caldera in a paleovalley. Within ∼50 km of the Middle Fork caldera are 14 examples of Late Cretaceous (?)–Tertiary felsic volcanic and hypabyssal intrusive rocks that range in area from <1 km2 to ∼100 km2. Rhyolite dome clusters north and northwest of the caldera occupy tectonic basins associated with northeast-trending faults and are relatively little eroded. Lava of a latite complex, 12–19 km northeast of the caldera, apparently flowed into the paleovalley of the Middle Fork of the North Fork of the Fortymile River. To the northwest of the Middle Fork caldera, in the Mount Harper crustal block, mid-Cretaceous plutonic rocks are widely exposed, indicating greater total exhumation. To the southeast of the Middle Fork block, the Mount Veta block has been uplifted sufficiently to expose a ca. 68–66 Ma equigranular granitic pluton. Farther to the southeast, in the Kechumstuk block, the flat-lying outflow tuff remnant in Gold Creek and a regionally extensive high terrace indicate that the landscape there has been little modified since 70 Ma other than entrenchment of tributaries in response to post–2.7 Ma lowering of base level of the Yukon River associated with advance of the Cordilleran ice sheet.

Voluminous lava-like precursor to a major ash-flow tuff: Low-column pyroclastic eruption of the Pagosa Peak Dacite, San Juan volcanic field, Colorado

USGS Publications Warehouse

Bachmann, Olivier; Dungan, M.A.; Lipman, P.W.

2000-01-01

The Pagosa Peak Dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous Fish Canyon Tuff (~5000 km3) from the La Garita caldera at 28 Ma. The Pagosa Peak Dacite is thick (to 1 km), voluminous (>200 km3), and has a high aspect ratio (1:50) similar to those of silicic lava flows. It contains a high proportion (40-60%) of juvenile clasts (to 3-4 m) emplaced as viscous magma that was less vesiculated than typical pumice. Accidental lithic fragments are absent above the basal 5-10% of the unit. Thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading, despite the very high viscosity of the crystal-rich magma, resulting in a macroscopic appearance similar to flow-layered silicic lava. Although it is a separate depositional unit, the Pagosa Peak Dacite is indistinguishable from the overlying Fish Canyon Tuff in bulk-rock chemistry, phenocryst compositions, and 40Ar/39Ar age. The unusual characteristics of this deposit are interpreted as consequences of eruption by low-column pyroclastic fountaining and lateral transport as dense, poorly inflated pyroclastic flows. The inferred eruptive style may be in part related to synchronous disruption of the southern margin of the Fish Canyon magma chamber by block faulting. The Pagosa Peak eruptive sources are apparently buried in the southern La Garita caldera, where northerly extensions of observed syneruptive faults served as fissure vents. Cumulative vent cross-sections were large, leading to relatively low emission velocities for a given discharge rate. Many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow. Explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits, leading to fracture-dominated magma fragmentation at low vesicularity. Subsequent collapse of the 75 x 35 km2 La Garita caldera and eruption of the Fish Canyon Tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the Pagosa Peak eruption. (C) 2000 Elsevier Science B.V. All rights reserved.

New insights into the explosive history of the Yellowstone super-volcano from high-precision dating and mineral chemistry

NASA Astrophysics Data System (ADS)

Ellis, B. S.; Mark, D. F.; Nix, C.; Rowe, M. C.; Wolff, J. A.; Kent, A. J.; Loewen, M. W.

2012-12-01

Yellowstone is commonly held up as the archetypal 'super-volcano', having had three major eruptive episodes at ~ 2 Ma, 1.3 Ma, and 0.6 Ma. However, given the importance of such large magnitude events on all scales from local to global, this idea has been held up to surprisingly little rigorous testing. Here we combine new high-precision Ar/Ar geochronology and mineral chemistry from multiple phases to shed new light on the explosive history of the Huckleberry Ridge and Lava Creek eruptions from the Yellowstone volcanic field. Recent high precision 40Ar/39Ar geochronology has shown that member C of the Huckleberry Ridge Tuff was erupted at least 6,000 years later than members A and B. This result is supported by significant differences in the compositions of fayalitic olivine, augite, and quartz between the different members. Mafic minerals are compositionally homogeneous with augites and fayalites of member C less magnesian than those found in members A and B. Quartz grains show a variety of textures in CL imaging and have within-grain variations in titanium (determined via EMPA and LA-ICPMS) reaching a factor of 2. Again, member C of the Huckleberry Ridge Tuff has distinct compositions of quartz (with higher Ti up to 242 ppm) than earlier erupted HRT. Quartz from Lava Creek Tuff shows differences in abundance of Ti between members A and B with member A having generally lower Ti (average 55 ppm) than member B (average 102 ppm). The mineral-scale chemistry presented here agrees with the pre-existing field evidence, radiogenic isotopic variation and high-precision geochronology to indicate that member C of Huckleberry Ridge Tuff represents a different magma to that which erupted and formed members A and B. Combining high-precision geochronology and detailed mineral-scale geochemistry from a number of different phases provides a robust method of distinguishing individual magma batches and clarifying the explosive history of a volcano. Our new data suggest that in some cases 'super-eruptions' might be better thought of as a series of large eruptions over a short timespan rather than a single gigantic event.

Storage, Ascent, and Release of Silicic Magma in Caldera-forming Eruptions

NASA Astrophysics Data System (ADS)

Myers, Madison Logan

The mechanisms and timescales associated with the triggering of caldera-forming eruptions remain ambiguous and poorly constrained. Do such eruptions start vigorously, then escalate, or can there be episodicity? Are they triggered through internal processes (e.g. recharge, buoyancy), or can external modulations play an important role? Key to answering these questions is the ability to reconstruct the state of the magma body immediately prior to eruption. My dissertation research seeks to answer these questions through detailed investigation of four voluminous caldera-forming eruptions: (1) 650 km3, 0.767 Ma Bishop Tuff, Long Valley, (2) 530 km3, 25.4 ka Oruanui eruption, Taupo, (3) 2,500 km3, 2.08 Ma Huckleberry Ridge Tuff, Yellowstone and (4) 250 km3, 26.91 Ma Cebolla Creek Tuff, Colorado. The main techniques I applied integrated glass geochemistry (major, trace and volatile), diffusion modeling, and detailed field sampling. In chapters two, three, and four these methods are applied to the initial fall deposits of three supereruptions (Bishop, Oruanui and Huckleberry Ridge) that preserve field-evidence for different opening behaviors. These behaviors range from continuous deposition of fall deposits and ignimbrite (Bishop), to repetitive start/stop behavior, with time breaks between eruptive episodes on the order of weeks to months (Oruanui, Huckleberry Ridge). To reconstruct the timescales of opening activity and relate this to conduit processes, I used two methods that exploit diffusion of volatiles through minerals and melt, providing estimates for the rate at which magmas ascended to the surface. This knowledge is then integrated with the pre-eruptive configuration of the magma body, based on melt inclusion chemistry, to interpret what triggered these systems into unrest. Finally, in chapter five I take a different approach by integrating geochemical data for melt inclusions and phenocryst minerals to test whether the mechanism of heat and volatile recharge often called upon to trigger crystal-rich dacitic magmas (the so-called monotonous intermediates), is applicable to the Cebolla Creek Tuff. This dissertation includes both previously published and unpublished co-authored material, and three online supplementary excel files.

The Blacktail Creek Tuff: an analytical and experimental study of rhyolites from the Heise volcanic field, Yellowstone hotspot system

NASA Astrophysics Data System (ADS)

Bolte, Torsten; Holtz, Francois; Almeev, Renat; Nash, Barbara

2015-02-01

The magma storage conditions of the 6.62 Ma Blacktail Creek Tuff eruption, belonging to the Heise volcanic field (6.62-4.45 Ma old) of the Yellowstone hotspot system, have been investigated by combining thermobarometric and experimental approaches. The results from different geothermometers (e.g., Fe-Ti oxides, feldspar pairs, apatite and zircon solubility, and Ti in quartz) indicate a pre-eruptive temperature in the range 825-875 °C. The temperature estimated using two-pyroxene pairs varies in a range of 810-950 °C, but the pyroxenes are probably not in equilibrium with each other, and the analytical results of melt inclusion in pyroxenes indicate a complex history for clinopyroxene, which hosts two compositionally different inclusion types. One natural Blacktail Creek Tuff rock sample has been used to determine experimentally the equilibrium phase assemblages in the pressure range 100-500 MPa and a water activity range 0.1-1.0. The experiments have been performed at fluid-present conditions, with a fluid phase composed of H2O and CO2, as well as at fluid-absent conditions. The stability of the quartzo-feldspathic phases is similar in both types of experiments, but the presence of mafic minerals such as biotite and clinopyroxene is strongly dependent on the experimental approach. Possible explanations are given for this discrepancy which may have strong impacts on the choice of appropriate experimental approaches for the determination of magma storage conditions. The comparison of the composition of natural phases and of experimentally synthesized phases confirms magma storage temperatures of 845-875 °C. Melt water contents of 1.5-2.5 wt% H2O are required to reproduce the natural Blacktail Creek Tuff mineral assemblage at these temperatures. Using the Ti-in-quartz barometer and the Qz-Ab-Or proportions of natural matrix glasses, coexisting with quartz, plagioclase and sanidine, the depth of magma storage is estimated to be in a pressure range between 130 and 250 MPa.

Utilization of ultrasonic atomization for dust control in underground mining

NASA Astrophysics Data System (ADS)

Okawa, Hirokazu; Nishi, Kentaro; Kawamura, Youhei; Kato, Takahiro; Sugawara, Katsuyasu

2017-07-01

This study examined dust suppression using water particles generated by ultrasonic atomization (2.4 MHz) at low temperature (10 °C). Green tuff (4 µm), green tuff (6 µm), kaolin, and silica were used as dust samples. Even though ultrasonic atomization makes fine water particles, raising relative air humidity immediately was difficult at low temperature. However, remaining water particles that did not change to water vapor contributed to suppression of dust dispersion. Additionally, the effect of water vapor amount (absolute humidity) and water particles generated by ultrasonic atomization on the amount of dust dispersion was investigated using experimental data at temperatures of 10, 20, and 30 °C. Utilization of ultrasound atomization at low temperature has the advantages of low humidity increments in the working space and water particles remaining stable even with low relative air humidity.

A proposed origin of the Olympus Mons escarpment. [Martian volcanic feature

NASA Technical Reports Server (NTRS)

King, J. S.; Riehle, J. R.

1974-01-01

Olympus Mons (Nix Olympica) on Mars is delimited by a unique steep, nearly circular scarp. A pyroclastic model is proposed for the construct's origin. It is postulated that the Olympus Mons plateau is constructed predominantly of numerous ash-flow tuffs which were erupted from central sources over an extended period of time. Lava flows may be intercalated with the tuffs. A schematic radial profile incorporating the inferred compaction zones for an ash sheet is proposed. Following emplacement, eolian (and possibly fluvial) erosion and abrasion during dust storms would act on the ash sheets. Interior portions of the sheets would spall and slump following eolian erosion, generating steep, relatively smooth boundary scarps. The scarp would be circular due to symmetrical distribution of compaction zones. The model implies further that the Olympus Mons plateau rests on a more resistant rock substrate.

Geochemistry of rock units at the potential repository level, Yucca Mountain, Nevada

USGS Publications Warehouse

Peterman, Z.E.; Cloke, P.L.

2002-01-01

The compositional variability of the phenocryst-poor member of the 12.8 Ma Topopah Spring Tuff at the potential repository level was assessed by duplicate analysis of 20 core samples from the cross drift at Yucca Mountain, Nevada. Previous analyses of outcrop and core samples of the Topopah Spring Tuff showed that the phenocryst-poor rhyolite, which includes both lithophysal and nonlithophysal zones, is relatively uniform in composition. Analyses of rock samples from the cross drift, the first from the actual potential repository block, also indicate the chemical homogeneity of this unit excluding localized deposits of vapor-phase minerals and low-temperature calcite and opal in fractures, cavities, and faults. The possible influence of vapor-phase minerals and calcite and opal coatings on rock composition at a scale sufficiently large to incorporate these heterogeneously distributed deposits was evaluated and is considered to be relatively minor. Therefore, the composition of the phenocryst-poor member of the Topopah Spring Tuff is considered to be adequately represented by the analyses of samples from the cross drift. The mean composition as represented by the 10 most abundant oxides in wt. % or g/100 g is: SiO2, 76.29; Al2O3, 12.55; FeO, 0.14; Fe2O3, 0.97; MgO, 0.13; CaO, 0.50; Na2O, 3.52; K2O, 4.83; TiO2, 0.11; and MnO, 0.07. ?? 2002 Published by Elsevier Science Ltd.

SEM-MLA-based Investigation of the Composition of Mafic Volcaniclastic Deposits from the Paraná Large Igneous Province, Brazil

NASA Astrophysics Data System (ADS)

Höfig, D. F.; Höfig, T. W.; Licht, O. A. B.; Haser, S.; Valore, L.

2017-12-01

Mafic volcaniclastic deposits (MVDs) have been widely reported in Large Igneous Provinces around the world, except for the Paraná Province (review by Ross et al., 2005: J Volcanol Geotherm Res, 145, pp. 281-314). Recent geochemical classification for this unit highlights, however, the occurrence of such deposits, connected to basic lava flows, mostly those High Ti - High P ones (Licht.: J Volcanol Geotherm Res, in press). In southern Brazil, MVDs intercalated with lava flows have been reported at 680 sites, showing conspicuous poorly sorted polymictic breccia at the base, grading to tuff breccias and red silicified tuffs at the top. Newly sampled rocks of Paraná mafic volcanoclastic deposits unravel important information about the composition utilizing Scanning Electron Microscopy-based Mineral Liberation Analysis. Overall, they show similar mineralogy presenting obsidian (25-40%), different phases of iron oxide (5-20%), quartz (10-25%), plagioclase (5-25%), celadonite (5-25%), and chlorite (5-10%). The breccias reveal a greater content of celadonite due to the presence of altered hypohyaline and hypocrystalline basaltic shards, whereas the tuffs are more enriched in glass. Different generations of plagioclase are attributed to various basalt shards and clasts as well vitroclasts found in the matrix. It is proposed that the MVDs were generated by explosive events due the interaction between the ascending mafic magma and deep aquifer systems and its siliciclastic matrix represents the country rock, i.e., the underneath Paleozoic sedimentary sequence of Paraná Basin.

Miocene tectono-stratigraphic history of La Mision basin, northwestern Baja California: implications for early tectonic development of southern California continental borderland

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ashby, J.R.; Minch, J.

1988-03-01

The middle Miocene La Mision basin in northwestern Baja California, Mexico, provides a rare opportunity to study an onshore portion of the southern California continental borderland. Stratigraphy, geometry of dispersal, and a variety of lithotypes within the volcanic and volcaniclastic sediments of the Rosarito Beach Formation provide clues to the nature of early tectonic evolution of this area during the Miocene. The elongated, trough-shaped La Mision basin formed in response to peninsular basement uplifts and the formation of volcanic highlands west of the present coastline. Lithologies and depositional environments represented within the basin sediments include: subaerial basalt flows and airfallmore » tuffs, submarine muddy- and sandy-matrix mudflow breccias, lapilli tuffs, crystal tuffs, tuffaceous sandstones,d diatomites, and conglomerates. The environments of deposition range from fluvatile to intertidal to shallow marine. Early basin infilling is characterized by sediments and basalts, with a western source terrane, that were deposited against the faulted seacliffs. progressive infilling against the seacliff resulted in the formation of an extensive eastward-sloping basaltic platform extending eastward to the foothill coastal belt of the Peninsular Ranges. Marine transgression and subsequent regression are recorded by diverse marine volcaniclastic lithologies. Abundant fossils, K-Ar dates, and paleomagnetic data obtained from the La Mision basin allow precise correlation with other areas in the continental borderland and provide conclusive evidence that this block of the borderland was formed and in its present position by 16-14 Ma.« less

Slope stability and rockfall assessment of volcanic tuffs using RPAS with 2-D FEM slope modelling

NASA Astrophysics Data System (ADS)

Török, Ákos; Barsi, Árpád; Bögöly, Gyula; Lovas, Tamás; Somogyi, Árpád; Görög, Péter

2018-02-01

Steep, hardly accessible cliffs of rhyolite tuff in NE Hungary are prone to rockfalls, endangering visitors of a castle. Remote sensing techniques were employed to obtain data on terrain morphology and to provide slope geometry for assessing the stability of these rock walls. A RPAS (Remotely Piloted Aircraft System) was used to collect images which were processed by Pix4D mapper (structure from motion technology) to generate a point cloud and mesh. The georeferencing was made by Global Navigation Satellite System (GNSS) with the use of seven ground control points. The obtained digital surface model (DSM) was processed (vegetation removal) and the derived digital terrain model (DTM) allowed cross sections to be drawn and a joint system to be detected. Joint and discontinuity system was also verified by field measurements. On-site tests as well as laboratory tests provided additional engineering geological data for slope modelling. Stability of cliffs was assessed by 2-D FEM (finite element method). Global analyses of cross sections show that weak intercalating tuff layers may serve as potential slip surfaces. However, at present the greatest hazard is related to planar failure along ENE-WSW joints and to wedge failure. The paper demonstrates that RPAS is a rapid and useful tool for generating a reliable terrain model of hardly accessible cliff faces. It also emphasizes the efficiency of RPAS in rockfall hazard assessment in comparison with other remote sensing techniques such as terrestrial laser scanning (TLS).

Geohydrologic and drill-hole data for test well USW H-4, Yucca Mountain, Nye County, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitfield, M.S. Jr.; Thordarson, W.; Eshom, E.P.

This report presents data on drilling operations, lithology, geophysical well logs, sidewall-core samples, water-level monitoring, pumping tests, injection tests, radioactive-tracer borehole flow survey, and water chemistry for test well USW H-4. The well is one of a series of test wells drilled in the southwestern part of the Nevada Test Site, Nye County, Nevada, in cooperation with the US Department of Energy. These test wells are part of the Nevada Nuclear Waste Storage Investigations to identify sites for storage of high-level radioactive wastes. Test well USW H-4 was drilled in ash-flow tuff to a total depth of 1219 meters. Depthmore » to water below land surface was 519 meters, or at an altitude of 730 meters above sea level. After test pumping at a rate of 17.4 liters per second for approximately 9 days, the drawdown was 4.85 meters. A radioactive borehole-flow survey indicated that the Bullfrog Member of the Crater Flat Tuff (Tertiary age) was the most productive geologic unit, producing 36.5 percent of the water in the well. The second most productive geologic unit was the Tram Member of the Crater Flat Tuff, which produced 32 percent of the water. The water in test well USW H-4 is predominantly a soft, sodium bicarbonate type of water typical of water produced in tuffaceous rocks in southern Nevada. 7 references, 26 figures, 9 tables.« less

Ultrasonic Surface Measurements for the investigation of superficial alteration of natural stones

NASA Astrophysics Data System (ADS)

Meier, Thomas; Auras, Michael; Bilgili, Filiz; Christen, Sandra; Cristiano, Luigia; Krompholz, Rolf; Mosca, Ilaria; Rose, David

2013-04-01

Seismic waveform analysis is applicable also to the centimeter and decimeter scale for non-destructive testing of pavement, facades, plaster, sculptures, or load-bearing structures like pillars. Mostly transmission measurements are performed and travel-times of first arriving P-waves are considered that have limited resolution for the upper centimeters of an object. In contrast, surface measurements are well suited to quantify superficial alterations of material properties e.g. due to weathering. A number of surface measurements have been carried out in the laboratory as well as on real structures in order to study systematically the information content of ultrasonic waveforms and their variability under real conditions. As a preposition for ultrasonic waveform analysis, reproducible, broad-band measurements have to be carried out with a definite radiation pattern and an about 1 mm accuracy of the measurement geometry. We used special coupling devices for effective ultrasonic surface measurements in the laboratory as well as at real objects. Samples of concrete with varying composition and samples of natural stone - marble, tuff, and sandstone - were repeatedly weathered and tested by ultrasonic measurements. The resistance of the samples to weathering and the penetration depth of the weathering are analyzed. Furthermore, material specific calibration curves for changes in velocities of elastic waves due to weathering can be obtained by these tests. Tests on real structures have been carried out for marble (Schlossbrücke, Berlin) and sandstone (Porta Nigra, Trier). Altogether, these test measurements show clearly that despite of the internal inhomogeneity of many real objects, their surface roughness and topography especially ultrasonic Rayleigh waves are well suited to study material alterations in the upper centimeters. Dispersion of Rayleigh waves may be inverted for shear-wave velocity as a function of depth.

Cretaceous planktic foraminiferal biostratigraphy of the Calera Limestone, Northern California, USA

USGS Publications Warehouse

Sliter, W.V.

1999-01-01

The Calera Limestone is the largest, most stratigraphically extensive limestone unit of oceanic character included in the Franciscan Complex of northern California. The aim of this paper is to place the Calera Limestone at its type locality (Rockaway Beach, Pacifica) in a high-resolution biostratigraphy utilizing planktic foraminifers studied in thin section. A section, about 110 m-thick, was measured from the middle thrust slice exposed by quarrying on the southwest side of Calera Hill at Pacifica Quarry. Lithologically, the section is divided in two units; a lower unit with 73 m of black to dark-grey limestone, black chert and tuff, and an upper unit with 36.8 m of light-grey limestone and medium-grey chert. Two prominent black-shale layers rich in organic carbon occur 11 m below the top of the lower black unit and at the boundary with overlying light-grey unit, yielding a total organic content (TOC) of 4.7% and 1.8% t.w., respectively. The fossiliferous Calera Limestone section measured at Pacifica Quarry, from the lower black shale, contains eleven zones and three subzones that span approximately 26 m.y. from the early Aptian to the late Cenomanian. The zones indentified range from the Globigerinelloides blowi Zone to the Dicarinella algeriana Subzone of the Rotalipora cushmani Zone. Within this biostratigraphic interval, the Ticinella bejaouaensis and Hedbergella planispira Zones at the Aptian/Albian boundary are missing as are the Rotalipora subticinensis Subzone of the Biticinella breggiensis Zone and the overlying Rotalipora ticinensis Zone in the late Albian owing both to low-angle thrust faulting and to unconformities. The abundance and preservation of planktic foraminifers are poor in the lower part and improve only within the upper G. algerianus Zone. The faunal relationship indicate that the lower black shale occurs in the upper part of the G. blowi Zone and correlates with the Selli Event recognized at global scale in the early Aptian. The upper black shale occurs at or near the boundary between the G. ferreolensis and G. algerianus Zone in the late Aptian. This black layer, or Thalmann Event as named here, seems to represent the sedimentary expression, at the scale of Permanente Terrane, of a global perturbation of the carbon cycle.

U-Pb ages of secondary silica at Yucca Mountain, Nevada: Implications for the paleohydrology of the unsaturated zone

USGS Publications Warehouse

Neymark, L.A.; Amelin, Y.; Paces, J.B.; Peterman, Z.E.

2002-01-01

Uranium, Th and Pb isotopes were analyzed in layers of opal and chalcedony from individual mm- to cm-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of 206Pb/204Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotope systems in opal samples at Yucca Mountain are complicated by the incorporation of excess 234U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the 207PB/235U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, 207Pb/235U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. 234U and 230Th in most silica layers deeper in the coatings are in secular equilibrium with 238U, which is consistent with their old age and closed system behavior during the past -0.5 Ma. The ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average growth rates of 1 to 5 mm/Ma. These data imply that the deeper parts of the UZ at Yucca Mountain maintained long-term hydrologic stability over the past 10 Ma. despite significant climate variations. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from fractures in the shallower part of the UZ (welded part of the overlying Tiva Canyon Tuff) indicate larger long-term average growth rates up to 23 mm/Ma and an absence of recently deposited materials (ages of outermost layers are 3-5 Ma.). These differences between the characteristics of the coatings for samples from the shallower and deeper parts of the UZ may indicate that the nonwelded tuffs (PTn), located between the welded parts of the Tiva Canyon and Topopah Spring Tuffs, play an important role in moderating UZ flow.

PRE-ORE POTASSIUM METASOMATISM, CREEDE MINING DISTRICT, COLORADO.

USGS Publications Warehouse

Bethke, P.M.; Rye, R.O.; Barton, P.B.

1985-01-01

Rhyolitic welded-tuff wallrocks of the epithermal base and precious metal veins of the Creede district were pervasively altered by the addition of more than two billion metric tons of potassium some 1. 5-2 million years before mineralization. Sodium, calcium and magnesium were strongly depleted, yielding a nearly binary quartz plus potassium feldspar assemblage containing as much as 13 weight percent K//2O. This large-scale metasomatism, originally noted by Steven and Rattle (1965), took place progressively by initial alteration of plagioclase phenocrysts to orthoclase or microcline followed by alteration of the groundmass feldspar to orthoclase and gradual change of the sanidine phenocrysts to more Or-rich compositions. Oxygen isotope and chemical studies show that the metasomatism resulted from the interaction of the tuffs with deeply circulating heated ground water and suggest that the potassium metasomatism of rhyolitic rocks is the facies equivalent of propylitization of volcanic rocks of more basic composition.

Neutron and gamma (density) logging in welded tuff

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, W

This Technical Implementation Procedure (TIP) describes the field operation, and the management of data records pertaining to neutron logging and density logging in welded tuff. This procedure applies to all borehole surveys performed in support of Engineered Barrier System Field Tests (EBSFT), including the Earge Block Tests (LBT) and Initial Engineered Barrier System Field Tests (IEBSFT) - WBS 1.2.3.12.4. The purpose of this TIP is to provide guidelines so that other equally trained and qualified personnel can understand how the work is performed or how to repeat the work if needed. The work will be documented by the use ofmore » Scientific Notebooks (SNs) as discussed in 033-YMP-QP 3.4. The TIP will provide a set of guidelines which the scientists will take into account in conducting the mea- surements. The use of this TIP does not imply that this is repetitive work that does not require profes- sional judgment.« less

The Magnet Cove Rutile Company mine, Hot Spring County, Arkansas

USGS Publications Warehouse

Kinney, Douglas M.

1949-01-01

The Magnet Cove Rutile Company mine was mapped by the U.S. Geological Survey in November 1944. The pits are on the northern edge of Magnet Cove and have been excavated in the oxidized zone of highly weathered and altered volcanic agglomerate. The agglomerate is composed of altered mafic igneous rocks in a matrix of white to gray clay, a highly altered tuff. The agglomerate appears layered and is composed of tuffaceous clay material below and igneous blocks above. The agglomerate is cut by aplite and lamprophyre dikes. Alkalic syenite dikes crop out on the ridge north of the pits. At the present stage of mine development the rutile seems to be concentrated in a narrow zone beneath the igneous blocks of the agglomerate. Rutile, associated with calcite and pyrite, occurs as disseminated acicular crystals and discontinuous vein-like masses in the altered tuff. Thin veins of rutile locally penetrate the mafic igneous blocks of the agglomerate.

Emplacement of Zebín Hill, Jičín Volcanic Field, Bohemian Paradise, Czech Republic: Anisotropy of Magnetic Susceptibility, Ground Magnetometry, Electric Resistivity Tomography, and Paleomagnetic Data

NASA Astrophysics Data System (ADS)

Petronis, M. S.; Rapprich, , V.; Valenta, J.; Leman, J.; Brister, A. R.; van Wyk de Vries, B.

2014-12-01

A well-preserved set of mid-Miocene tuff-cones and their feeders outcrop in the Jičín Volcanic Field, Czech Republic. Zebín Hill is a tuff cone that has been quarried to reveal the volcanoes feeder system. This edifice offers the opportunity to understand how magma is transported through a monogenetic pyroclastic cone. Rock types include a coarse-grained basal phreatomagmatic layer and a stratified upper wall facies both of which are penetrated by feeder dikes. Anisotropy of magnetic susceptibility (AMS) and paleomagnetic data were collected at twenty-one sites from feeder dikes and the main conduit of the volcano. A high-resolution ground magnetometry survey, electric resistivity tomography and seismic tomography were also conducted. Magnetic susceptibility intensity indicates that the dominant magnetic mineral is a ferromagnetic phase with little contribution from paramagnetic minerals. AMS ellipsoids shapes are both oblate and prolate and inferred magma flow directions indicate magma flow away from the central vent area and subhorizontal flow towards and away from the axial conduit; both upward and downward magma flow is evident at some sites. Curie point estimates yield a spectrum of results indicating a mixture of high-Ti titanomagnetite, iron sulfide, and low-Ti titanomagnetite. Ground magnetometry data indicate that both normal and reverse polarity rocks are present at Zebín Hill. Paleomagnetic data confirm the ground magnetic data in that both normal and reverse polarity rocks are present. Most sites yield a single component magnetization that is well grouped at the site level and carried by pseudosingle domain titanomagnetite. The presence of both normal and reverse polarity magnetizations from the volcano indicate that significant time passed during the growth of this monogenic system. Complex system of branching dikes has been also observed from electric resistivity tomography. The simple external structure of monogenetic volcanoes hides a rather complex magmatic plumbing system that dynamically evolves during the life of the volcano. As we show, the well-exposed roots of Zebín Hill reveals that the growth of a volcano occurs not due to simple central axis feeder systems but rather through interplay of local structures, magmatic effects, and construct evolution during the life of the volcano

Pliocene and Pleistocene chronostratigraphy of continental sediments underlying the Altiplano at La Paz, Bolivia

NASA Astrophysics Data System (ADS)

Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.

2018-06-01

Continental sediments underlying the Altiplano plateau provide insight into the late Cenozoic evolution of the Central Andes. We characterize the magnetostratigraphy and lithostratigraphy of the upper part of this fill sequence along a transect extending southwestward from the Cordillera Real at La Paz, Bolivia, where it is best exposed. Multiple polarity reversals and the locally extensive, 2.74-Ma Chijini Tuff enable correlation between our six sections and three previously reported sections. The tuff ties the composite polarity sequence to the geomagnetic polarity time scale, demonstrating that the stratigraphic record extends from the latest Gilbert Chron (ca. 3.8 Ma) to the late Olduvai subchron (ca. 1.8 Ma), or possibly Jaramillo subchron (ca. 1.0 Ma). The sequence provides Earth's longest known record of low-latitude glaciation and the only record of Pliocene tropical glaciation. It includes evidence for 16 late Pliocene and Early Pleistocene glaciations, separated by interglacials of sufficient length (>103-104 a) to produce mature soil profiles. Successively larger ice caps formed directly before, during, and after the globally warm mid-Piacenzian (3.265-3.025 Ma), and throughout Plio-Pleistocene climate deterioration. The late Pliocene glacial units predate the onset of widespread Northern Hemisphere continental glaciation and in most cases unambiguously correspond to specific cool peaks of the astronomically tuned, benthic oxygen isotope (δ18O) record, including marine isotope stages MG2, M2, KM2, and G10. The glacial events broadly coincide with those nearer both poles, suggesting inter-hemispheric climate linkages. The early formation and subsequent expansion of ice caps beyond glacier margins of the Last Glacial Maximum suggest that the Cordillera Real likely attained its modern height before ca. 3.4 Ma. The number and timing of glaciations, and long-term sediment accumulation and incision rates suggest that the local Altiplano surface formed by ca. 1.8 Ma, after which headwaters of the Amazon River system breached the Cordillera Real and began to incise the fill sequence. The sequence spans at least 2 Ma before and during the first main pulses of the Great American Biotic Interchange, providing an important record of faunal migration. The arrival of savanna-adapted North American mammals in the Central Andes during this period points to the influence of glaciation on faunal migration in the southern tropics, similar to influences proposed in North and Central America.

Newly Described Tephra Provide Middle Pleistocene Age Constraints to Stegodon Fossils in West (Indonesian) Timor

NASA Astrophysics Data System (ADS)

Jensen, B. J. L.; Dufrane, A.; Mark, D.; Zaim, Y.; Rizal, Y.; Aswan, A.; Hascaryo, A.; Ciochon, R.; Gunnell, G.; Larick, R.; Zonnveld, J. P.

2017-12-01

As the Asian proboscidian Stegodon dispersed across Island Southeast Asia during the Pleistocene, multiple forms developed. On Timor, a southerly island east of Wallace's Line, the Ainaro gravels have yielded a highly dwarfed S. timorensis and a larger S. `trigonocephalus.' During a half-century of exploration, the age of the fossil bearing gravels remains in question, with only one age determination of >130 ka derived from six 230Th- 238U dates on a tusk fragment found in the Raebia area (Louys et al. 2016). Here we present radiometric ages for two tephra deposits bracketing Ainaro gravels at Raebia, a S. timorensis fossil locality 8 km northeast of Atambua city. The Raebia ravine exposes 2-10 meters of coarse-grained gravels incised into silt and clay deposits, bracketed by two indurated and largely devitrified tephras. Some intact glass was present to geochemically characterize each unit, which are both high-silica rhyolites. Biotite and zircons for 40Ar/39Ar and laser ablation U-Pb dating were extracted from the upper unit (Raebia Tuff 1; RT1), and zircons from the lower unit (Raebia Tuff 2; RT2). RT1 had zircons with two distinct age populations, but the youngest yield a 230Th deficiency corrected 206Pb/238U age of 665 ± 19 ka, (2s, n = 23, MSWD = 0.81), consistent with the 40Ar/39Ar age 614.9 ± 16.4 ka (2s, full external precision). Preliminary zircon dates on RT2 are more problematic, providing a large range that suggests inheritance by xenoliths and/or locally-sourced detrital zircons. However, a single zircon yielded 230Th deficiency corrected 206Pb/238U age of 708 ± 66 ka (2s, n=17, MSWD = 0.41), which is stratigraphically consistent. These are the first reliable age constraints on a higher elevation Ainaro gravel terrace and fossils they contain. The only other direct ages on the gravels are 230Th- 238U dates on lower terraces interbedded with coral, ranging from 130 ka to Holocene in age (Roosmawati and Harris 2009). These two newly described and dated tephra are likely regionally distributed and may represent important stratigraphic horizons for this portion of Southern Wallacea. They also provide useful data for calculating uplift rates for the region from the middle Pleistocene.

Root zone of the Late Proterozoic Salma Caldera, northeastern Arabian Shield, Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Kellogg, Karl S.

1985-11-01

The eroded root of the late Proterozoic Salma caldera crops out in a striking, roughly elliptical feature, about 27 km long and 22 km wide, near the northeastern edge of the Arabian Shield. The caldera is genetically part of an elongate alkalic granitic massif (Jabal Salma) that extends 35 km from the caldera to the southwest. Comenditic ash flow tuff and lava(?) of the caldera fill, probably more than 1 km thick, are the oldest recognized rocks of the caldera complex. These rocks were erupted during caldera collapse associated with the rapid evacuation of the upper, mildly peralkalic part of a zoned magma reservoir. Within the caldera fill, a massive, lithic-rich intracaldera rhyolite, probably a lava in excess of 1 km thick, is overlain by a layered ash flow sequence. Numerous megabreccia blocks, probably derived from the caldera wall, occur in the massive rhyolite. Open folds in the layered volcanic rocks may be due to high-temperature slumping of the rocks toward the center of the caldera following collapse. Later peralkalic granite that intruded the caldera ring fracture zone occurs in an arcuate pattern outside the area of exposed caldera fill. After caldera collapse, metaluminous to peraluminous magma rose beneath the caldera at approximately 580 Ma and solidified as biotite alkali granite, rim syenogranite, and late, high-level granophyre. Rare earth element abundances indicate that the layered rhyolite tuff, peralkalic granite, and granophyre are chemically more evolved than the biotite alkali granite and rim syenogranite. The granophyre intruded the caldera fill as a dome-shaped body composed of numerous sheetlike masses. Granophyric texture resulted from rapid pressure release and quenching accompanying the intrusion of each sheet. Maximum penetration of the granophyre into overlying rocks occurred in the central region and along the west side of the caldera, where the caldera fill volcanic rocks have been removed by erosion. No apparent structural doming of the exposed volcanic rocks along the east side of the caldera took place; the layered ash flows commonly dip steeply toward the center of the caldera. Postemplacement deformation and metamorphism of the caldera are minimal. Small-displacement strike-slip faults cut the complex, which is tilted to the northeast by no more than about 2°.

Climate Proxy Signals in the Plio-Pleistocene Chemeron and Miocene Lukeino Formations, Baringo Basin, Kenya

NASA Astrophysics Data System (ADS)

Deino, A. L.; Kingston, J.; Hill, A.; Wilson, K. E.; Edgar, R.; Goble, E.

2009-12-01

The Chemeron Formation is a hominin-bearing, highly fossiliferous sequence of dominantly alluvial fan and fluvial sedimentary rocks, with climatically significant lacustrine intercalations, exposed within the Tugen Hills of the central Kenya Rift. As we have previously documented (Deino et al., 2006; Kingston et al., 2007), the formation contains a sequence of five 3-7 m thick diatomites in the interval 2.7-2.5 Ma that record, at precessional intervals, the repeated occurrence of deep-lake conditions in the Baringo Basin. These lakes appear abruptly, persist for only about 8,000 years of the ~23,000 year precessional cycle, and recede quickly. The oscillations have been tied to marine core and Mediterranean sapropel sections based on high-precision 40Ar/39Ar dating of K-feldspar in tuffs interspersed through the sequence, and paleomagnetic reversal stratigraphy. Ongoing paleontological investigations in the Tugen Hills are addressing the dynamics of high-resolution faunal and ecological change directly related to the fluctuating climatic background, including its effect on hominin evolution. This specific interval in the Baringo Basin/Tugen Hills has been identified by the Hominid Sites and Paleolakes Drilling Project Steering Committee as one of five target areas in East Africa for high-resolution coring studies. The drilling project is currently moving forward to the funding agency proposal development phase. Further exploration in the Tugen Hills has revealed a similar, older sequence of rhythmic alternating diatomites and non-lacustrine sediments in nearby drainages. These beds may represent a precessionally driven climate response possibly associated with the next older orbital eccentricity maximum from ~3.2-2.9 Ma. Characterization of the lithostratigraphy of this area is in progress, and samples of intercalated tuff beds suitable for high-precision single-crystal 40Ar/39Ar dating have been acquired. We have also extended our search for climate proxy records in the Tugen Hills to diatomaceous sequences between ~8-6 Ma that would specifically implicate precessional control as a pervasive factor in the formation of rift lake systems and by inference climate. Reconnaissance in summer ’09 of these older strata have revealed extensive lacustrine deposits indicating that this portion of the rift was inundated by major lake systems during the upper Miocene.

Deep Vadose Zone Flow and Transport Behavior at T-Tunnel Complex, Rainier Mesa, Nevada National Security Site

NASA Astrophysics Data System (ADS)

Parashar, R.; Reeves, D. M.

2010-12-01

Rainier Mesa, a tuffaceous plateau on the Nevada National Security Site, has been the location of numerous subsurface nuclear tests conducted in a series of tunnel complexes located approximately 450 m below the top of the mesa and 500 m above the regional groundwater flow system. The tunnels were constructed near the middle of an 800 m Tertiary sequence of faulted, low-permeability welded and non-welded bedded, vitric, and zeolitized tuff units. Water levels from wells in the vicinity of the T-tunnel complex indicate the presence of a perched saturation zone located approximately 100 m above the T-tunnel complex. This upper zone of saturation extends downward through most of the Tertiary sequence. The groundwater table is located at an elevation of 1300 m within a thrust sheet of Paleozoic carbonates, corresponding to the lower carbonate aquifer hydrostratigraphic unit (LCA3). The LCA3 is considered to be hydraulically connected to the Death Valley regional flow system. The objective of this project is to simulate complex downward patterns of fluid flow and radionuclide transport from the T-tunnel complex through the matrix and fault networks of the Tertiary tuff units to the water table. We developed an improved fracture characterization and mapping methodology consisting of displacement-length scaling relationships, simulation of realistic fault networks based on site-specific data, and the development of novel fracture network upscaling techniques that preserves fracture network flow and transport properties on coarse continuum grid. Development of upscaling method for fracture continua is based on the concepts of discrete fracture network modeling approach which performs better at honoring network connectivity and anisotropy of sparse networks in comparison to other established methods such as a tensor approach. Extensive flow simulations in the dual-continuum framework demonstrate that the characteristics of fault networks strongly influences the saturation profile and formation of perched zones, although they may not conduct a large amount of flow when compared to the matrix continua. The simulated results are found to be very sensitive to distribution of fracture aperture, density of the network, and spatial pattern of fracture clustering. The faults provide rapid pathways for radionuclide transport and the conceptual modeling of diffusional mass transfer between matrix and fracture continua plays a vital role in prediction of the overall behavior of the breakthrough curve.

Intra-cone plumbing system and eruptive dynamics of small-volume basaltic volcanoes: A case study in the Calatrava Volcanic Field

NASA Astrophysics Data System (ADS)

Carracedo-Sánchez, M.; Sarrionandia, F.; Ábalos, B.; Errandonea-Martin, J.; Gil Ibarguchi, J. I.

2017-12-01

The Manoteras volcano (Tortonian to Pleistocene, Calatrava Volcanic Field, Spain) is composed of a scoria and spatter cone surrounded by a field of pahoehoe lava. The volcanic cone is made essentially of vitreous lapilli-tuffs with intercalations of vitreous tuffs and spatter deposits, without any intercalations of lava flows. Erosion has uncovered an intra-cone plumbing system formed by coherent dykes and pyroclastic dykes (mixed-type dykes). This dyke swarm reflects processes of intrusion at the end of the eruption or even post-eruption. All the volcanic products are nephelinitic in composition. The main dyke is up to 3.4 m thick and has an exposed length of 1000 m. It is composed mostly of coherent nephelinite with some pyroclastic sections at its northern extremity. This dyke is regarded as a feeder dyke of the volcano, although the upper parts of the dike have been eroded, which prevents the observation of the characteristics and nature of the possible overlying vent(s). Mixed-type dykes could also have acted as small linear vents and indicate that the magma fragmentation level during final waning stages of the eruption was located inside the volcanic cone. The pyroclastic deposits that make up the volcanic cone at the current exposure level were probably developed during a major phase of violent Strombolian style that formed the scoria cone, followed by a Hawaiian phase that formed the summital intracrater spatter deposit. Three central-type vents have been identified: one at the highest point of the remnant volcanic cone (summital vent), from where the earlier explosive eruptions took place, and the other two at the fringe of the cone base, from where emissions were only effusive. The lava flows were emitted from these boccas through the scoria cone feeding the lava field. The results obtained, based on careful field observations, add substantial complexity to the proposed eruptive models for small-volume basaltic volcanoes as it appears evident that there may exist and evolution through time from central conduit settings to fissure eruptions. Moreover, it is shown that intracone plumbing systems can integrate coherent and clastic dykes of variable thicknesses, which, in some cases could represent feeder dykes. Table 2. Petrographic characteristics of the coherent rocks (dykes and lava flows) from the Manoteras volcano. See Fig. 2 supplementary.

Ilchulbong tuff cone, Jeju Island, Korea, revisited: A compound monogenetic volcano involving multiple magma batches, shifting vents, and discrete eruptive phases

NASA Astrophysics Data System (ADS)

Sohn, Y.; Brenna, M.; Smith, I. E.; Nemeth, K.; White, J. D.; Murtagh, R.; Jeon, Y.; Kwon, C.; Cronin, S. J.

2010-12-01

Ilchulbong (Sunrise Peak) tuff cone is a UNESCO World Heritage site that owes its scientific importance to the outstanding coastal exposures that surround it. It is also one of the classic sites that provided the sedimentary evidence for the primary pyroclastic processes that occur during phreatomagmatic basaltic eruptions. It has been long considered, based on the cone morphology, that this classic cone was produced via eruption from a single vent site. Reanalysis of the detailed sedimentary sequence has now revealed that two subtle paraconformities occur in this deposition sequence, one representing a significant time break of perhaps days to weeks or months, during which erosion and compaction of the lower cone occurred, the conduit cooled and solidified and a subsequent resumption of eruption took place in a new vent location. Detailed geochemical study of the juvenile clasts through this cone reveals that three separate alkali basaltic magma batches were erupted, the first and third erupted may be genetically related, with the latter showing evidence for longer periods of shallow-level fractionation. The second magma batch erupted was generated in a different mantle source area. Reconstructing the eruption sequence, the lower Ilchulbong cone was formed by eruption of magma 1. Cessation of eruption was accompanied by erosion to generate a volcano-wide unconformity, associated with reworked deposits in the lower cone flanks. The eruption resumed with magma 2 that, due to the cooled earlier conduit, was forced to erupt in a new site to the west of the initial vent. This formed the middle cone sequence over the initially formed structure. The third magma batch erupted with little or no interval after magma 2 from the same vent location, associated with cone instability and slumping, and making up the deposits of the upper cone. These results demonstrate how critical the examination for sedimentary evidence for time breaks in such eruption sequences is for detecting potential shifts in eruption chemistry and vent location. It appears that if eruption breaks are short, successive magma batches follow the same path, whereas if pauses are greater than a critical period, conduit solidification will force vent migration for subsequent magma batches. This has important implications for examining the controls of vent migration at other monogenetic volcanoes and for emergency management planning during future similar types of eruptions.

Sedimentology and paleoenvironments of a new fossiliferous late Miocene-Pliocene sedimentary succession in the Rukwa Rift Basin, Tanzania

NASA Astrophysics Data System (ADS)

Mtelela, Cassy; Roberts, Eric M.; Hilbert-Wolf, Hannah L.; Downie, Robert; Hendrix, Marc S.; O'Connor, Patrick M.; Stevens, Nancy J.

2017-05-01

This paper presents a detailed sedimentologic investigation of a newly identified, fossiliferous Late Neogene sedimentary succession in the Rukwa Rift Basin, southwestern Tanzania. This synrift deposit is a rare and significant new example of a fossiliferous succession of this age in the Western Branch of East Africa Rift System. The unit, informally termed the lower Lake Beds succession, is late Miocene to Pliocene in age based on cross-cutting relationships, preliminary biostratigraphy, and U-Pb geochronology. An angular unconformity separates the lower Lake Beds from underlying Cretaceous and Oligocene strata. Deposition was controlled by rapid generation of accommodation space and increased sediment supply associated with late Cenozoic tectonic reactivation of the Rukwa Rift and synchronous initiation of the Rungwe Volcanic Centre. The lower Lake Beds, which have thus far only been identified in three localities throughout the Rukwa Rift Basin, are characterized by two discrete lithologic members (herein A and B). The lower Member A is a volcanic-rich succession composed mostly of devitrified volcanic tuffs, and volcaniclastic mudstones and sandstones with minor conglomerates. The upper Member B is a siliciclastic-dominated succession of conglomerates, sandstones, mudstones and minor volcanic tuffs. Detailed facies analysis of the lower Lake Beds reveals various distinctive depositional environments that can be grouped into three categories: 1) alluvial fan; 2) fluvial channel; and 3) flood basin environments, characterized by volcanoclastic-filled lakes and ponds, abandoned channel-fills and pedogenically modified floodplains. Member A represents a shallow lacustrine setting filled by tuffaceous sediments, which grade up into a system of alluvial fans and high-energy, proximal gravel-bed braided rivers. An unconformity marks the contact between the two members. Member B shows an upward transition from a high-energy, gravel-bed braided river system to a sandy braided river system with increasingly abundant floodplain deposits and well-developed paleosols. Vertebrate fossils are sparse in member A, but common in member B, preserved both within pedogenic soil horizons and as isolated elements and microsites within fluvial channel facies associations. Faunal remains include fishes, turtles and crocodylians, along with well-preserved mammal cranial and post-cranial remains. In addition, freshwater gastropod shells are locally present in member A and continental trace fossils, including abundant fossilized termite nests, are present in both members.

Holocene phreatomagmatic eruptions alongside the densely populated northern shoreline of Lake Kivu, East African Rift: timing and hazard implications

NASA Astrophysics Data System (ADS)

Poppe, Sam; Smets, Benoît; Fontijn, Karen; Rukeza, Montfort Bagalwa; De Marie Fikiri Migabo, Antoine; Milungu, Albert Kyambikwa; Namogo, Didier Birimwiragi; Kervyn, François; Kervyn, Matthieu

2016-11-01

The Virunga Volcanic Province (VVP) represents the most active zone of volcanism in the western branch of the East African Rift System. While the VVP's two historically active volcanoes, Nyamulagira and Nyiragongo, have built scoria cones and lava flows in the adjacent lava fields, several small phreatomagmatic eruptive centers lie along Lake Kivu's northern shoreline, highlighting the potential for explosive magma-water interaction. Their presence in the densely urbanized Sake-Goma-Gisenyi area necessitates an assessment of their eruptive mechanisms and chronology. Some of these eruptive centers possess multiple vents, and depositional contacts suggest distinct eruptive phases within a single structure. Depositional facies range from polymict tuff breccia to tuff and loose lapilli, often impacted by blocks and volcanic bombs. Along with the presence of dilute pyroclastic density current (PDC) deposits, indicators of magma-water interaction include the presence of fine palagonitized ash, ash aggregates, cross-bedding, and ballistic impact sags. We estimate that at least 15 phreatomagmatic eruptions occurred in the Holocene, during which Lake Kivu rose to its current water level. Radiocarbon dates of five paleosols in the top of volcanic tuff deposits range between ˜2500 and ˜150 cal. year bp and suggest centennial- to millennial-scale recurrence of phreatomagmatic activity. A vast part of the currently urbanized zone on the northern shoreline of Lake Kivu was most likely impacted by products from phreatomagmatic activity, including PDC events, during the Late Holocene, highlighting the need to consider explosive magma-water interaction as a potential scenario in future risk assessments.

Fitful and protracted magma assembly leading to a giant eruption, Youngest Toba Tuff, Indonesia

USGS Publications Warehouse

Reid, Mary R; Vazquez, Jorge A.

2017-01-01

The paroxysmal eruption of the 74 ka Youngest Toba Tuff (YTT) of northern Sumatra produced an extraordinary 2800 km3 of non-welded to densely welded ignimbrite and co-ignimbrite ash-fall. We report insights into the duration of YTT magma assembly obtained from ion microprobe U-Th and U-Pb dates, including continuous age spectra over >50% of final zircon growth, for pumices and a welded tuff spanning the compositional range of the YTT. A relatively large subpopulation of zircon crystals nucleated before the penultimate caldera-related eruption at 501 ka, but most zircons yielded interior dates 100-300 ka thereafter. Zircon nucleation and growth was likely episodic and from diverse conditions over protracted time intervals of >100 to >500 ka. Final zircon growth is evident as thin rim plateaus that are in Th/U chemical equilibrium with hosts, and that give crystallization ages within tens of ka of eruption. The longevity and chemical characteristics of the YTT zircons, as well as evidence for intermittent zircon isolation and remobilization associated with magma recharge, is especially favored at the cool and wet eutectoid conditions that characterize at least half of the YTT, wherein heat fluxes could dissolve major phases but have only a minor effect on larger zircon crystals. Repeated magma recharge may have contributed to the development of compositional zoning in the YTT but, considered together with limited allanite, quartz, and other mineral dating and geospeedometry, regular perturbations to the magma reservoir over >400 ka did not lead to eruption until 74 ka ago.

Comparison of Two Methods for Determination of Strontium Isotopes in Pore Water at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Marshall, B. D.; Futa, K.; Scofield, K. M.

2002-12-01

The proposed radioactive waste repository at Yucca Mountain, Nevada would be constructed in the high-silica rhyolite member of the Topopah Spring Tuff, an ash-flow tuff within the ~500-m-thick unsaturated zone. Dry-drilled rock cores from this unit have been packaged to preserve their water content. Two methods have been used to extract the strontium contained in the pore water for isotopic measurements. In the first method, samples of dried core were crushed, and the 0.25 to 2.4 mm size fractions were leached with ultra-pure water for about 1 hour to dissolve the salts left behind by the evaporated pore water. Concentrations of strontium in the pore water were calculated from determinations of porosity and saturation on adjacent core and the measured strontium concentration in the leachate. In the second method, pore water was extracted from sealed core using an ultracentrifuge, minimizing evaporation of water from the core at all steps in the process. The centrifugation of 150 to 200 g of welded tuff at 15,000 rpm for 6 hours typically results in the recovery of as much as 3 ml of pore water for analysis. Strontium isotope compositions were determined by thermal ionization mass spectrometry; 87Sr /86Sr ratios have a reproducibility of 0.00005. The ranges of 87Sr/86Sr ratios determined by the two methods are identical: 0.71215 to 0.71267 in the leachates (n = 35) and 0.71214 to 0.71266 in the extracted pore waters (n = 21). However, the calculated strontium concentrations in the leachates average 300 μg/L, whereas those in the extracted pore water average 1440 μg/L, indicating that a substantial portion of the pore-water salts remain in the crushed rock after leaching. The strontium data determined on extracted pore water shows that the leaching of pore-water salts results in accurate 87Sr/86Sr, but that a substantial correction to the strontium concentration is required due to the inefficiency of the leaching procedure and the small pore sizes in the welded tuffs. The strontium isotope data obtained on leachates can be used to constrain models of water-rock interaction and estimates of travel times in the unsaturated zone.

Evaluation of Pleistocene groundwater flow through fractured tuffs using a U-series disequilibrium approach, Pahute Mesa, Nevada, USA

USGS Publications Warehouse

Paces, James B.; Nichols, Paul J.; Neymark, Leonid A.; Rajaram, Harihar

2013-01-01

Groundwater flow through fractured felsic tuffs and lavas at the Nevada National Security Site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at Pahute Mesa. To help evaluate fracture flow and matrix–water exchange, we have determined U-series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces, breccia zones, and interiors of unfractured core. The U-series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium-series decay chain due to preferential mobilization of 234U relative to 238U, and U relative to Th. Samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays, silica, Fe–Mn oxyhydroxides, and zeolite. Intact core interiors and breccia fragments were sampled in bulk. In addition, profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture/matrix water exchange. Samples of rock matrix have 234U/238U and 230Th/238U activity ratios (AR) closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix. Greater U mobility was observed in welded-tuff matrix with elevated porosity and in zeolitized bedded tuff. Samples of brecciated core were also in secular equilibrium implying a lack of long-range hydraulic connectivity in these cases. Samples of discrete fracture surfaces typically, but not always, were in radioactive disequilibrium. Many fractures had isotopic compositions plotting near the 230Th-234U 1:1 line indicating a steady-state balance between U input and removal along with radioactive decay. Numerical simulations of U-series isotope evolution indicate that 0.5 to 1 million years are required to reach steady-state compositions. Once attained, disequilibrium 234U/238U and 230Th/238U AR values can be maintained indefinitely as long as hydrological and geochemical processes remain stable. Therefore, many Pahute Mesa fractures represent stable hydrologic pathways over million-year timescales. A smaller number of samples have non-steady-state compositions indicating transient conditions in the last several hundred thousand years. In these cases, U mobility is dominated by overall gains rather than losses of U.

Rhyolitic tephra record of the Gona region, southern Afar Rift, Ethiopia: Characteristics correlation and chronology

NASA Astrophysics Data System (ADS)

Dunbar, N. W.; Brown, F. H.; Levin, N. E.; McIntosh, W. C.; Rogers, M.; Semaw, S.; Simpson, S. W.; Stinchcomb, G. E.

2016-12-01

The Gona region, on the western flank of the southern Afar Rift, in Ethiopia, contains a rich and complex tephra record that provides insight into structural evolution of the region and chronological controls on the local record of human evolution. Despite lack of source volcanoes in the Gona region, thick (up to 80 cm), fine-grained (20-500 µm), fresh, pure, glassy distal tephra layers, which are discontinuous and appear to have undergone significant secondary thickening shortly after deposition, are present in sediments deposited in the last two million years. Altered tephra are present in older sediments. New data are consistent with those reported by Quade et al. (2008), showing that tephra from Gona are typically rhyolitic, consistent with derivation from large, but distant volcanic eruptions. Significant geochemical variation is observed between different tephra layers, particularly with respect to FeO (ranging between 2 and 7.5 wt.% in different rhyolitic tephra), Ca, Mn, and Cl. Elements Na and K are variable, consistent with alkali mobility during glass hydration. Although some tephra layers contain feldspar and are thus datable using the 40Ar/39Ar, others are not directly datable, so must be geochemically linked to dated source eruptions. A unit of particular focus is the widespread marker tuff known locally as the Boolihinan tuff, which is associated with significant hominin fossils and artifacts. This locally aphyric unit, which consists of highly expanded rhyolitic glass, exhibits some geochemical variability, particularly with respect to SiO2 (74-78 wt.%), but yields a robust compositions with respect to Fe, Ca, Mn, and Cl. The Boolihinan tuff was previously tentatively correlated to a 1.6 Ma tephra found in DSDP core DEM-4-1. However, we suggest here a more robust correlation to two samples of an unwelded ignimbrite with 40Ar/39Ar ages of 1.281±0.061 and 1.253±0.041 (27-01 and 27-05 of Morgan et al., 2012) from the Melka Kunture area, which is over 300 km from the Gona field area. The Boolihinan tuff is interpreted to be the ashfall equivalent of the unwelded ignimbrite. This correlation provides a chronological marker which in turn provides improved age constraints to the fossils and artifacts at Gona that are found in association with this tephra.

Erratum to ``Eruption style and petrology of a new carbonatitic suite from the Mt. Vulture (Southern Italy): The Monticchio Lakes Formation'' [Journal of Volcanology and Geothermal Research 78 (1997) 251 265

NASA Astrophysics Data System (ADS)

Stoppa, Francesco; Principe, Claudia

1998-01-01

The Monticchio Lakes Formation (MLF) is a newly identified carbonatite-melilitite tuff sequence which is exposed in the southwestern sector of the Vulture volcano. It is the youngest example (ca. 0.13 m.y.) of this type of volcanism in Italy, although other carbonatites of smaller volume, but with similar characteristics, have been discovered recently. This volcanic event occurred in isolation after a 0.35 m.y. period of inactivity at Vulture. The eruption produced two maar-type vents and formed tuff aprons mainly composed of dune beds of lapilli. Depositional features suggest that a dry surge mechanism, possibly triggered by CO 2 expansion, was dominant during tuff emplacement. The MLF event involved a mixture of carbonatite and melilitite liquids which were physically separated before the eruption. Abundant mantle xenoliths are direct evidence of the deep-seated origin of the parental magma and its high velocity of propagation towards the surface. Often, these nodules form the core of lapilli composed of concentric shells of melilitite and/or porphyritic carbonatite. Coarse-ash beds alternate with lapilli beds and consist of abundant lumps and spherulae of very fine-grained calcite immersed in a welded, highly compacted carbonatite matrix. Porphyritic carbonatite shells of the lapilli and fine-grained spherulae of calcite in the tuff matrix suggest incipient crystallisation of a carbonatite liquid in subvolcanic conditions and eruption of carbonatite-spray droplets. Dark coloured juvenile fragments mainly consist of melilite, phlogopite, calcite, apatite, perovskite, and häuyne crystals in a carbonatite or melilitite matrix. The rocks have an extremely primitive, ultramafic composition with very high Mg# (> 85) and Cr and Ni content (1500 ppm). The calcite contains high SrO, BaO and REE of up to 1.5 wt.%. Similar compositions are typical of primary, magmatic carbonates which are found in both intrusive and extrusive carbonatites. The high modal Sr-Ba-REE-rich calcite, the typical mineralogy, and the high amount of Sr-group elements identify the carbonate component as a carbonatite. The very high Mg#, mantle debris and C, O, He isotope ratios in the range of mantle values indicate a near-primary character for the carbonatite which is distinctive of a restricted group of extrusive carbonatites only found in continental rift areas.

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa

NASA Technical Reports Server (NTRS)

Heubeck, C.; Lowe, D. R.

1994-01-01

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.

Geology and ore deposits of the Pioche district, Nevada

USGS Publications Warehouse

Westgate, L.G.; Knopf, Adolph

1932-01-01

LOCATION AND SURFACE FEATURES The Bristol Range, Highland, and Ely Range quadrangles make up the larger part of a. rectangular area 35 miles north and south by 24 miles east and west, which lies 19 miles west of the Nevada-Utah line and about 250 miles southwest of Salt Lake City. The district lies within the Great Basin, a semiarid region of alternating mountain ranges and intermontane plains floored largely by outwash from the mountains. The plain, which slopes away from the ranges, stands between 4,700 and 6,000 feet above the sea. The Bristol and Highland Ranges, which are separated only by a low gap, form an almost continuous north-south range that rises about 2,500 feet above the highest part of the surrounding plain, to general altitudes of 8,000 to 9,000 feet, though the highest point, Highland Peak, reaches 9,395 feet. A lower range, the Ely Range, with a northwesterly trend, lies farther east and nearly in touch with the Bristol-Highland Range. The town of Pioche lies midway on the. eastern foot of the Ely Range. ROOKS OF THE PIOOHB REGION The rocks of the ranges are Paleozoic sediments, Tertiary (?) lavas and intrusive rocks, and Pliocene (?) tuffs. The Paleozoic sediments have a total thickness of nearly 18,000 feet. Over 8,000 feet of the Cambrian has been measured without reaching its base. The lowest Cambrian formation is a quartzite, of which only the upper 1,500 feet is exposed, and this is followed by 1,200 feet of shale, 400 feet of limestone, aoid 150 feet of shale. Above this second shale the upper three-fourths of the Cambrian consists of limestone and dolomitic limestone. It is in the quartzite and in the limestone interbedded in and bounding the shales that the main ore bodies of the district have been found. Above the Cambrian comes 1,795 feet of Ordovician limestone, with some interbedded dolomite and with a 50-foot quartzite a, third of the way down from the top; 75 feet of Silurian dolomite; 3,000 feet of Middle Devonian dolomite with thin interbedded quartzite near the top, followed by 550 feet of Upper Devonian limestone; 3,775 feet of Mississippian limestone with a heavy quartzitic sandstone just below the middle; then, at the top of the series, 700 feet of Pennsylvania n limestone.The Paleozoic formations are tilted, bent, and faulted, but sharp folding is extremely rare. Dips between 10° and 30° are common, but there are few greater than 40°. The rocks are cut by many large and innumerable small normal faults, which in many parts of the area are difficult to recognize because they cut thick formations of similar rocks. A large thrust fault occurs along the west side of the Bristol-Highland Range. A thick series of lavas with interbedded tuffs lies along the flanks of the ranges and makes up a large part of the hilly northwest corner of the Bristol quadrangle. The lavas lie unconformably on the Paleozoic sediments and consist mainly of dacite, latite, and andesite, with some basalt and a little rhyolite. About 6,000 feet of lavas and tuffs were measured in Condor Canyon, near the south end of the Ely Range. The age of the lavas is not sharply fixed; they may be early Tertiary or even late Mesozoic. It is not unlikely that they are the result of volcanic action extending over a long period. The lavas are tilted and faulted, though their average dip is less than that of the Paleozoic sediments. At Blind Mountain, on the west side of the Bristol Range, stocks of quartz monzonite and dikes of similar composition cut an infaulted block consisting of sediments, chiefly Devonian, and lavas. Both the sediments and the lavas are metamorphosed, and a belt of marked metamorphism extends south along the west base of the Bristol-Highland Range for several miles. The quartz porphyry dikes of the region, including those near Pioche, are believed to have come in at the same time. The plain west of the Bristol-Highland Range is a. valley of interior drainage floored with outwash from the mountains, coarser near the range but finer and making a clay flat along the west side of the Bristol Range and Highland quadrangles. The valley east of the Bristol-Highland Range, however, has outside drainage by way of Meadow Valley to the Virgin and Colorado Rivers. The stream in upper Meadow Valley and its tributaries have cut through the surface wash from the mountains and laid bare several hundred feet of white, yellow, and red water-laid Pliocene tuffs that lie in nearly the position in which they were laid down. This erosion has developed a striking badland topography in the Pliocene beds. HISTORICAL SUMMARY The general succession of events may be summarized as follows: 1. Sedimentation during most of Paleozoic time from Cambrian to Pennsylvanian. 2. Uplift, slight warping, and erosion. 3. Volcanism of perhaps late Mesozoic or early Tertiary time, producing lavas and tuffs. This period of volcanism may have lasted a long time and spanned one or more of the epochs of faulting. 4. Tilting and normal faulting. 5. Thrust faulting. 6. Quartz monzonite intrusions at Blind Mountain. 7. Normal block faulting of the Basin Range type. 8. Erosion of the faulted blocks to maturity and to essen-. tially the topography of to-day. 9. Outbursts of volcanic ash, probably in late Pliocene time, and the deposition of several hundred feet of water-laid tuffs in the valleys. 10. In Meadow Valley, valley cutting, which has produced a badland topography in the soft Pliocene tuffs and canyons where the streams cross the harder Paleozoic limestones. ECONOMIC GEOLOGY The Pioche district during four years in the early seventies was second only to the Comstock district in output of silver. The bonanza ore of those stirring times came from fissure veins in the Prospect Mountain quartzite, of Lower Cambrian age. In recent years the main interest has shifted to the bedded replacement deposits of silver-bearing lead-zinc sulphide ore occurring in the limestone members of the Pioche shale a type of ore body which was discovered accidentally during the prospecting of the fissure veins. The ore deposits of the district comprise three groups (1) silver-bearing fissure veins in quartzite; (2) silver-bearing mineralized granite porphyry; (3) replacement deposits in limestone and dolomite. All of them appear to have been formed at about the same time, in the epoch of mineralization that occurred shortly after the intrusion of the granitic rocks and their allied dikes of granite porphyry and lamprophyre. The entire present output of the district is coming from the replacement deposits in limestone and dolomite, but exploratory work is still in progress on the fissure veins and mineralized porphyry. The replacement deposits include both replacement fissure veins and stratiform ("bedded") replacement deposits. The replacement fissure veins dip steeply and cut across the bedding of the carbonate rocks in which they are inclosed. They are thoroughly oxidized, as deep at least as 1,100 feet, for on none of them have the mine workings penetrated to water level, and they are highly manganiferous and limonitic and low in silica. At-certain horizons stratiform replacement deposits extend out as lateral branches from the fissure veins. Deposits of this kind occur mainly in the Mendha limestone, Highland Peak limestone, and Lyndon limestone. The stratigraphic range is therefore at least 5,500 feet, and as some of the fissure veins extend down through the underlying Pioche shale the indicated range may exceed 6,500 feet. The most notable representatives of the replacement fissure veins are at the Bristol mine, where they yield silver-bearing copper-leadzinc ores. So far unique among the ore bodies of the district is the pipe of wad and pyrolusite ore at the Jackrabbit mine, the periphery of the pipe consisting of a girdle of extraordinarily coarse white calcite spar produced by the recrystallization of the surrounding limestones. The stratiform replacement deposits that are attracting most attention occur at the intersections of steep fissures with the limestone members of the Pioche shale. In recent years the " bedded " ore of the Combined Metals mine has been of main interest. The ore is essentially a.n intimate intergrowth of pyrite, sphalerite, and galena. Although above water level, the ore is unoxidized. It extends on both sides of the mineralizing fissure as far as 100 feet. At the Prince mine ore beds were formed at seven successively higher horizons in the Pioche shale and the overlying Lyndon and Highland Peak limestones. The ore " beds " above water level in the Prince mine are thoroughly oxidized and consist of manganese-iron oxides low in silver, lead, and zinc. About 800,000 tons of ore carrying 2.5 to 3 ounces of silver to the ton, 3 per cent of lead, 35 per cent of iron, and 15 per cent of manganese has been shipped. The Prince mine was in 1915-1918 the premier producer of lead in Nevada. The ore " bed " that occurs here below water level consists of sphalerite, galena, and pyrite in a gangue of manganosiderite and minor quartz. This is the only locality in the district in which the primary source of the abundant oxidized manganese minerals (wad, pyrolusite, and braunite) has so far been found. Some of the stratiform ore bodies the ore beds, as they are locally called were formed adjacent to exceedingly insignificant-looking fissures; and this dependence on inconspicuous mineralizing fissures is beyond doubt one of the most impressive features in the geology of the district. It opens the possibility that there may be many other bedded deposits which, like the Combined Metals ore bed, do not crop out. To find these ore bodies will be difficult, but their discovery will be aided primarily by applying skillfully a knowledge of the geologic column and by determining the faulting that has disturbed or changed the normal sequence of the strata.

Small scale recirculating vertical flow constructed wetland (RVFCW) for the treatment and reuse of wastewater.

PubMed

Gross, A; Sklarz, M Y; Yakirevich, A; Soares, M I M

2008-01-01

The quantity of freshwater available worldwide is declining, revealing a pressing need for its more efficient use. Moreover, in many developing countries and lightly populated areas, raw wastewater is discarded into the environment posing serious ecological and health problems. Unfortunately, this situation will persist unless low-cost, effective and simple technologies are brought in. The aim of this study is to present such a treatment method, a novel setup which is termed recirculating vertical flow constructed wetland (RVFCW). The RVFCW is composed of two components: (i) a three-layer bed consisting of planted organic soil over an upper layer of filtering media (i.e. tuff or beads) and a lower layer of limestone pebbles, and (ii) a reservoir located beneath the bed. Wastewater flows directly into the plant root zone and trickles down through the three-layer bed into the reservoir, allowing passive aeration. From the reservoir the water is recirculated back to the bed, several times, until the desired purification is achieved. The results obtained show that the RVFCW is an effective and convenient strategy to treat (domestic, grey and agro) wastewater for re-use in irrigation. The system performance is expected to be further improved once current optimization experiments and mathematical modeling studies are concluded. IWA Publishing 2008.

Zircon U-Pb Age Distributions in Cogenetic Crystal-Rich Dacitic and Crystal-Poor Rhyolitic Members of Zoned Ignimbrites in the Southern Rocky Mountains by Chemical Abrasion Inductively-Coupled-Plasma Mass Spectrometry (CA-LA-ICP-MS).

NASA Astrophysics Data System (ADS)

Sliwinski, J.; Zimmerer, M. J.; Guillong, M.; Bachmann, O.; Lipman, P. W.

2015-12-01

The San Juan locus of the Southern Rocky Mountain Volcanic Field (SRMVF) in SW Colorado represents an erosional remnant of a mid-Tertiary (~37-23 Ma) ignimbrite flare up that produced some of the most voluminous ignimbrites on Earth. A key feature of many SRMVF ignimbrites is compositional zonation, with many volcanic units comprising both dacitic and rhyolitic horizons. Geochemical, field and petrographic evidence suggests that dacites and rhyolites are cogenetic. Here, we report U-Pb zircon ages by chemical abrasion inductively-coupled-plasma mass spectrometry (CA-LA-ICPMS) for rhyolitic and dacitic components in four units: the Bonanza, Rat Creek, Carpenter Ridge and Nelson Mountain Tuffs. All units show zircon age spectra that are either within analytical uncertainty of Ar/Ar ages or are appreciably older, indicating prolonged magma residence times (~500 ka) prior to eruption. Anomalously young Pb-loss zones in zircon have been largely removed by chemical abrasion. Older, inherited zircons and zircon cores (60-2000 Ma) are rare in all samples, suggesting limited assimilation of upper crustal Precambrian country rock or complete resorption during recharge events and magma chamber growth.

An approach of understanding acid volcanics and tuffaceous volcaniclastics from field studies: A case from Tadpatri Formation, Proterozoic Cuddapah basin, Andhra Pradesh, India

NASA Astrophysics Data System (ADS)

Goswami, Sukanta; Upadhyay, P. K.; Bhagat, Sangeeta; Zakaulla, Syed; Bhatt, A. K.; Natarajan, V.; Dey, Sukanta

2018-03-01

The lower stratigraphic part of the Cuddapah basin is marked by mafic and felsic volcanism. Tadpatri Formation consists of a greater variety of rock types due to bimodal volcanism in the upper part. Presence of bimodal volcanism is an indication of continental rift setting. Various genetic processes involved in the formation of such volcanic sequence result in original textures which are classified into volcaniclastic and coherent categories. Detailed and systematic field works in Tadpatri-Tonduru transect of SW Cuddapah basin have provided information on the physical processes producing this diversity of rock types. Felsic volcanism is manifested here with features as finger print of past rhyolite-dacite eruptions. Acid volcanics, tuffs and associated shale of Tadpatri Formation are studied and mapped in the field. With supporting subordinate studies on geochemistry, mineralogy and petrogenesis of the volcanics to validate field features accurately, it is understood that volcanism was associated with rifting and shallow marine environmental condition. Four facies (i.e., surge, flow, fall and resedimented volcaniclastic) are demarcated to describe stratigraphic units and volcanic history of the mapped area. The present contribution focuses on the fundamental characterization and categorization of field-based features diagnostic of silica-rich volcanic activities in the Tadpatri Formation.

Massive Pyroclastic Eruptions Accompanied the Sector Collapse of Oahu and the Nu`uanu Landslide: Petrological Evidence for a Submarine Directed Blast

NASA Astrophysics Data System (ADS)

Natland, J. H.; Atlas, Z.

2003-12-01

During ODP Leg 200 in December, 2002, a series of thinly bedded volcaniclastic turbidites and silty muds interbedded with two thicker and strongly indurated vitric tuffs was drilled at Site 1223 on the crest of the Hawaiian arch east of the island of Oahu. The massive Nu`uanu landslide debris field, derived from a massive collapse of the eastern half of Oahu at about 2 Ma, lies in the flexural moat between the site and the island. The shipboard interpretation (1) was that the muds and silts are typical turbidites derived by redeposition from beaches and nearshore benches, but that the tuffs represent the distal portions of large submarine pyroclastic eruptions that may have attended the landslide. We report electron probe microanalyses of basaltic glass, olivine, Cr-spinel, palagonite and secondary minerals in the tuffs supporting the shipboard interpretation. In particular, the glass compositions from individual thin sections match precisely the range of compositions obtained from numerous samples of coarse volcaniclastic breccia sampled from the steep flanks of landslide blocks in the moat (2). This includes somewhat higher SiO2 and lower total iron as FeO(T) at given MgO than similar basaltic glasses from other Hawaiian volcanoes, a distinctive attribute of tholeiitic basalt from Oahu's Ko`olau volcano. Key attributes of the glasses in the tuffs and the minerals in them are that they are poly-compositional and they are strongly differentiated, with a range of compositions typical of those erupted from modern Hawaiian volcanic rift systems supplied by lateral diking from central conduits. The finer-grained tuffs at Site 1223 thus are indeed a distal pyroclastic facies that seemingly tapped much of the suddenly exposed, magma-inflated, deep flanking rift system of Ko`olau volcano. Over-steepening of the NE flank of the volcano coupled with internal weakening provided by near saturation of its rift system with magma may have triggered the landslide. This was almost immediately followed by massive submarine pyroclastic eruptions of magma mainly at submarine levels in the rift that, accelerated by steep downslope descent, were directed all the way to the ENE in rapidly-moving debris flows. These sorted themselves by size (mass) with the coarsest material plastering the sides of the landslide blocks, and the finer grained material, mainly glass and olivine grains, reaching the crest of the Hawaiian arch. The palagonite is compositionally-modified glass that probably formed by leaching in response to lateral migration of warm hydrothermal fluids from beneath thicker and still hot proximal pyroclastic material that was abruptly deposited in the moat to the west following the landslide. (1)Shipboard Scientific Party, 2003. Site 1223. In Stephen, R.A., Kasahara, J., Acton, G.D., et al., Proc. ODP, Init. Rept. 200 [CD-ROM], College Station, TX (Ocean Drill. Prog), 1-159. (2)Clague, D.A., Moore, J.G., and Davis, A.S., 2002. In Takahashi, E.,Lipman, P., Garcia, M.O., and Aramaki, S., (Eds.), Geophys. Monog. 128: Washington (AGU), 279-296.

BACTERIOPHAGE TRANSPORT IN SANDY SOIL AND FRACTURED TUFF

EPA Science Inventory

Bacteriophage transport was investigated in laboratory column experiments using sandy soil, a controlled field study in a sandy wash, and laboratory experiments using fractured rock. In the soil columns, the phage MS-2 exhibited significant dispersion and was excluded from 35 to ...

Possible Hydrovolcanic Landforms Observed in MOC NA Imagery: A Preliminary Survey

NASA Technical Reports Server (NTRS)

Farrand, W. H.; Gaddis, L. R.; Blundell, S.

2001-01-01

In a preliminary survey of MOC NA imagery, a number of features resembling table mountains, tuff rings, and near craters have been identified. Their locations and geologic significance will be discussed. Additional information is contained in the original extended abstract.

Crustal-scale recycling in caldera complexes and rift zones along the Yellowstone hotspot track: O and Hf isotopic evidence in diverse zircons from voluminous rhyolites of the Picabo volcanic field, Idaho

USGS Publications Warehouse

Drew, Dana L.; Bindeman, Ilya N.; Watts, Kathryn E.; Schmitt, Axel K.; Fu, Bin; McCurry, Michael

2013-01-01

Rhyolites of the Picabo volcanic field (10.4–6.6 Ma) in eastern Idaho are preserved as thick ignimbrites and lavas along the margins of the Snake River Plain (SRP), and within a deep (>3 km) borehole near the central axis of the Yellowstone hotspot track. In this study we present new O and Hf isotope data and U–Pb geochronology for individual zircons, O isotope data for major phenocrysts (quartz, plagioclase, and pyroxene), whole rock Sr and Nd isotope ratios, and whole rock geochemistry for a suite of Picabo rhyolites. We synthesize our new datasets with published Ar–Ar geochronology to establish the eruptive framework of the Picabo volcanic field, and interpret its petrogenetic history in the context of other well-studied caldera complexes in the SRP. Caldera complex evolution at Picabo began with eruption of the 10.44±0.27 Ma (U–Pb) Tuff of Arbon Valley (TAV), a chemically zoned and normal-δ18O (δ18O magma=7.9‰) unit with high, zoned 87Sr/86Sri (0.71488–0.72520), and low-εNd(0) (−18) and εHf(0) (−28). The TAV and an associated post caldera lava flow possess the lowest εNd(0) (−23), indicating ∼40–60% derivation from the Archean upper crust. Normal-δ18O rhyolites were followed by a series of lower-δ18O eruptions with more typical (lower crustal) Sr–Nd–Hf isotope ratios and whole rock chemistry. The voluminous 8.25±0.26 Ma West Pocatello rhyolite has the lowest δ18O value (δ18Omelt=3.3‰), and we correlate it to a 1,000 m thick intracaldera tuff present in the INEL-1 borehole (with published zircon ages 8.04–8.35 Ma, and similarly low-δ18O zircon values). The significant (4–5‰) decrease in magmatic-δ18O values in Picabo rhyolites is accompanied by an increase in zircon δ18O heterogeneity from ∼1‰ variation in the TAV to >5‰ variation in the late-stage low-δ18O rhyolites, a trend similar to what is characteristic of Heise and Yellowstone, and which indicates remelting of variably hydrothermally altered tuffs followed by rapid batch assembly prior to eruption. However, due to the greater abundance of low-δ18O rhyolites at Picabo, the eruptive framework may reflect an intertwined history of caldera collapse and coeval Basin and Range rifting and hydrothermal alteration. We speculate that the source rocks with pre-existing low-δ18O alteration may be related to: (1) deeply buried and unexposed older deposits of Picabo-age or Twin Falls-age low-δ18O volcanics; and/or (2) regionally-abundant late Eocene Challis volcanics, which were hydrothermally altered near the surface prior to or during peak Picabo magmatism. Basin and Range extension, specifically the formation of metamorphic core complexes exposed in the region, could have facilitated the generation of low-δ18O magmas by exhuming heated rocks and creating the large water-rock ratios necessary for shallow hydrothermal alteration of tectonically (rift zones) and volcanically (calderas) buried volcanic rocks. These interpretations highlight the major processes by which supereruptive volumes of magma are generated in the SRP, mechanisms applicable to producing rhyolites worldwide that are facilitated by plume driven volcanism and extensional tectonics.

Petrochemistry of late miocene peraluminous silicic volcanic rocks from the Morococala field, Bolivia

USGS Publications Warehouse

Morgan, VI G.B.; London, D.; Luedke, R.G.

1998-01-01

Late Miocene peraluminous volcanic rocks of the Morococala field, Bolivia, define a layered stratigraphy of basal andalusite-, biotite-(?? Muscovite)-bearing rhyolite tuffs (AR), overlain by cordierite-, biotite-bearing rhyolite tuffs (CR), and capped by biotite-beanng quartz latite tuffs, lavas, and late domal flows (QL). Mineral and whole-rock compositions become more evolved from top to bottom, with differentiation reflected by decreasing Ca, Ba, Mg, Fe, and rare earth elements (REE) versus increasing F, Na/K, and aluminosity from QL to AR. Mineral, whole-rock, and glass inclusion compositions are consistent with derivation of all three rock types from a single stratified magma reservoir, but age and spatial relations between the three units make this unlikely. Genesis of the QL involved biotite-dehydration melting of an aluminous source at T > 750??C and P ??? 4-6 kbar. If not co-magmatic with QL, the other units were generated primarily by muscovite-dehydration melting at T = 730-750??C and P ??? 3??5-4??5 kbar for CR, and T ??? 750??C for AR with pre-emptive residence at low pressure (1??5-3??0 kbar). Low hematite contents (XHem ??? 0??06) of ilmenite grains in AR, CR, and early grains (as inclusions in plagioclase and sanidine cores) in QL indicate reduced conditions imposed by a graphite-bearing source. Compositional variability among texturally later oxides (ilmenite with XHem = 0??06-0??50, primary magnetite), however, apparently records progressive increases in pre-eruptive f(O2) in QL. Plagioclase-melt equilibria and electron microprobe analysis difference for quartz-hosted glass inclusions suggest pre-emptive melt H2O contents ??? 5-7 wt % for the AR, ???4-6 wt % for the CR, and ???3-5 wt % for the QL.

The Bossoroca Complex, São Gabriel Terrane, Dom Feliciano Belt, southernmost Brazil: Usbnd Pb geochronology and tectonic implications for the neoproterozoic São Gabriel Arc

NASA Astrophysics Data System (ADS)

Gubert, Mauricio Lemos; Philipp, Ruy Paulo; Stipp Basei, Miguel Angelo

2016-10-01

Usbnd Pb LA-ICPMS geochronological analyses were carried out on zircon grains from metavolcanic rocks of the Bossoroca Complex and for one ash tuff of the Acampamento Velho Formation of the Camaquã Basin, in order to understand the evolution of the Neoproterozoic São Gabriel magmatic arc. A total of 42 analyses of igneous zircon grains were performed in three samples. The results yielded Usbnd Pb ages of 767.2 ± 2.9 Ma for the metavolcanic agglomerate (BOS-02); 765 ± 10 Ma for the metacrystal tuff (BOS-03) and 565.8 ± 4.8 Ma for the ash tuff (BOS-04). The Orogenic Cycle in Brazil is characterized by a set of orogenic belts consisting of petrotectonic associations juxtaposed by two collisional events that occurred at the end of the Neoproterozoic. In southern Brazil this orogeny formed the Dom Feliciano Belt, a unit composed of associations of rocks developed during two major orogenic events called São Gabriel (900-680 Ma) and Dom Feliciano (650-540 Ma). The main São Gabriel associations are tectonically juxtaposed as elongated strips according to the N20-30°E direction, bounded by ductile shear zones. The Bossoroca Complex comprises predominantly metavolcano-sedimentary rocks, characterized by medium-K calc-alkaline association generated in a cordillera-type magmatic arc. The volcanism occurred in sub-aerial environment, developing deposits generated by flow, resurgence and fall, sporadically interrupted by subaqueous epiclastic deposits, suggesting an arc related basin. The São Gabriel Terrane contains the petrotectonic units that represent the closure of the Charrua Ocean associated to the subduction period of the Brasiliano Orogenic Cycle in the Sul-rio-grandense Shield.

Radionuclide migration: laboratory experiments with isolated fractures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rundberg, R.S.; Thompson, J.L.; Maestas, S.

Laboratory experiments examining flow and element migration in rocks containing isolated fractures have been initiated at the Los Alamos National Laboratory. Techniques are being developed to establish simple fracture flow systems which are appropriate to models using analytical solutions to the matrix diffusion-flow equations, such as those of I. Neretnieks [I. Neretnieks, Diffusion in the Rock Matrix: An Important Factor in Radionuclide Retardation? J. Geophys. Res. 85, 4379 (1980).] These experiments are intended to be intermediate steps toward larger scale field experiments where it may become more difficult to establish and control the parameters important to nuclide migration in fracturedmore » media. Laboratory experiments have been run on fractures ranging in size from 1 to 20 cm in length. The hydraulic flow in these fractures was studied to provide the effective apertures. The flows established in these fracture systems are similar to those in the granite fracture flow experiments of Witherspoon et al. [P.A. Witherspoon, J.S.Y. Wang, K. Iwai, and J.E. Gale, Validity of Cubic Law for Fluid Flow in a Deformable Rock Fracture, Lawrence Berkeley Laboratory report LBL-9557 (October 1979).] Traced solutions containing {sup 85}Sr and {sup 137}Cs were flowed through fractures in Climax Stock granite and welded tuff (Bullfrog and Tram members, Yucca Mountain, Nevada Test Site). The results of the elutions through granite agree with the matrix diffusion calculations based on independent measurements of K/sub d/. The results of the elutions through tuff, however, agree only if the K/sub d/ values used in the calculations are lower than the K/sub d/ values measured using a batch technique. This trend has been previously observed in chromatographic column experiments with tuff. 5 figures, 3 tables.« less

Geology of the platanares geothermal area, Departamento de Copan, Honduras

USGS Publications Warehouse

Heiken, G.; Ramos, N.; Duffield, W.; Musgrave, J.; Wohletz, K.; Priest, S.; Aldrich, J.; Flores, W.; Ritchie, A.; Goff, F.; Eppler, D.; Escobar, C.

1991-01-01

Platanares is located 16 km west of Santa Rosa de Copan, Honduras, along the Quebrada del Agua Caliente. The thermal manifestations are along faults in tuffs, tuffaceous sedimentary rocks, and lavas of the Padre Miguel Group. These tuffs are silicified near the faults, are fractured, and may provide the fracture permeability necessary for the hydrothermal system. Tuffs are overlain by a wedge of terrace gravels up to 60 m thick. Quaternary conglomerates of the Quebrada del Agua Caliente are cemented by silica sinter. The Platanares area contains numerous faults, all of which appear to be extensional. There are four groups of faults (N80/sup 0/E to N70/sup 0/W, N30/sup 0/ to 60/sup 0/W, N40/sup 0/ to 65/sup 0/E, and N00/sup 0/ to 05/sup 0/W). All hot springs at this site are located along faults that trend mostly northwest and north. Twenty-eight spring groups were described over an area of 0.2 km/sup 2/; half were boiling. Based on surface temperatures and flow rates, between 0.7 and 1.0 MW thermal energy is estimated for the area. The increased temperature of the stream flowing through the thermal area indicates that several megawatts of thermal energy are being added to the stream. We recommend that a dipole-dipole resistivity line be run along the Quebrada del Agua Caliente to identify zones of fracture permeability associated with buried faults and hot water reservoirs within those fault zones. A thermal gradient corehole should be drilled at Platanares to test temperatures, lithologies, and permeability of the hydrothermal system.

Mineral and chemical variations within an ash-flow sheet from Aso caldera, Southwestern Japan

USGS Publications Warehouse

Lipman, P.W.

1967-01-01

Although products of individual volcanic eruptions, especially voluminous ash-flow eruptions, have been considered among the best available samples of natural magmas, detailed petrographic and chemical study indicates that bulk compositions of unaltered Pleistocene ash-flow tuffs from Aso caldera, Japan, deviate significantly from original magmatic compositions. The last major ash-flow sheet from Aso caldera is as much as 150 meters thick and shows a general vertical compositional change from phenocryst-poor rhyodacite upward into phenocryst-rich trachyandesite; this change apparently reflects in inverse order a compositionally zoned magma chamber in which more silicic magma overlay more mafic magma. Details of these magmatic variations were obscured, however, by: (1) mixing of compositionally distinct batches of magma during upwelling in the vent, as indicated by layering and other heterogeneities within single pumice lumps; (2) mixing of particulate fragments-pumice lumps, ash, and phenocrysts-of varied compositions during emplacement, with the result that separate pumice lenses from a single small outcrop may have a compositional range nearly as great as the bulk-rook variation of the entire sheet; (3) density sorting of phenocrysts and ash during eruption and emplacement, resulting in systematic modal variations with distance from the caldera; (4) addition of xenocrysts, resulting in significant contamination and modification of proportions of crystals in the tuffs; and (5) ground-water leaching of glassy fractions during hydration after cooling. Similar complexities characterize ash-flow tuffs under study in southwestern Nevada and in the San Juan Mountains, Colorado, and probably are widespread in other ash-flow fields as well. Caution and careful planning are required in study of the magmatic chemistry and phenocryst mineralogy of these rocks. ?? 1967 Springer-Verlag.

Eruption processes and deposit characteristics at the monogenetic Mt. Gambier Volcanic Complex, SE Australia: implications for alternating magmatic and phreatomagmatic activity

NASA Astrophysics Data System (ADS)

van Otterloo, Jozua; Cas, Raymond A. F.; Sheard, Malcolm J.

2013-08-01

The ˜5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner. The facies are (1) coherent to vesicular fragmental alkali basalt (effusive/Hawaiian spatter and lava flows); (2) massive scoriaceous fine lapilli with coarse ash (Strombolian fallout); (3) bedded scoriaceous fine lapilli tuff (violent Strombolian fallout); (4) thin-medium bedded, undulating very fine lapilli in coarse ash (dry phreatomagmatic surge-modified fallout); (5) palagonite-altered, cross-bedded, medium lapilli to fine ash (wet phreatomagmatic base surges); and (6) massive, palagonite-altered, very poorly sorted tuff breccia and lapilli tuff (phreato-Vulcanian pyroclastic flows). Since most deposits are lithified, to quantify the grain size distributions (GSDs), image analysis was performed. The facies are distinct based on their GSDs and the fine ash to coarse+fine ash ratios. These provide insights into the fragmentation intensities and water-magma interaction efficiencies for each facies. The eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles, except for a "magmatic horizon" of effusive activity occurring at both ends of the volcanic complex simultaneously. The eruption foci are located along NW-SE trending lineaments, indicating that the complex was fed by multiple dykes following the subsurface structures related to the Tartwaup Fault System. Possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates, viscosity, crystallinity, degassing and magma discharge rate, as well as hydrological parameters.

Physical and hydrologic properties of outcrop samples from a nonwelded to welded tuff transition, Yucca Mountain, Nevada

USGS Publications Warehouse

Rautman, C.A.; Flint, L.E.; Flint, A.L.; Istok, J.D.

1995-01-01

Quantitative material-property data are needed to describe lateral and vertical spatial variability of physical and hydrologic properties and to model ground-water flow and radionuclide transport at the potential Yucca Mountain nuclear-waste repository site in Nevada. As part of ongoing site characterization studies of Yucca Mountain directed toward this understanding of spatial variability, laboratory measurements of porosity, bull* and particle density, saturated hydraulic conductivity, and sorptivity have been obtained for a set of outcrop samples that form a systematic,two dimensional grid that covers a large exposure of the basal Tiva Canyon Tuff of the Paintbrush Group of Miocene age at Yucca Mountain. The samples form a detailed vertical grid roughly parallel to the transport direction of the parent ash flows, and they exhibit material-property varia- tions in an interval of major lithologic change overlying a potential nuclear-waste repository at Yucca Mountain. The observed changes in hydrologic properties were systematic and consistent with the changes expected for the nonwelded to welded transition at the base of a major ash-flow sequence. Porosity, saturated hydraulic conductivity, and sorptivity decreased upward from the base of the Tiva Canyon Tuff, indicating the progressive compaction of ash- rich volcanic debris and the onset of welding with increased overburden pressure from the accumulating ash-flow sheet. The rate of decrease in the values of these material properties varied with vertical position within the transition interval. In contrast, bulk-density values increased upward, a change that also is consistent with progressive compaction and the onset of welding. Particle-density values remained almost constant throughout the transition interval, probably indicating compositional (chemical) homogeneity.

New seismo-stratigraphic and marine magnetic data of the Gulf of Pozzuoli (Naples Bay, Tyrrhenian Sea, Italy): inferences for the tectonic and magmatic events of the Phlegrean Fields volcanic complex (Campania)

NASA Astrophysics Data System (ADS)

Aiello, Gemma; Marsella, Ennio; Fiore, Vincenzo Di

2012-06-01

A detailed reconstruction of the stratigraphic and tectonic setting of the Gulf of Pozzuoli (Naples Bay) is provided on the basis of newly acquired single channel seismic profiles coupled with already recorded marine magnetics gathering the volcanic nature of some seismic units. Inferences for the tectonic and magmatic setting of the Phlegrean Fields volcanic complex, a volcanic district surrounding the western part of the Gulf of Naples, where volcanism has been active since at least 50 ka, are also discussed. The Gulf of Pozzuoli represents the submerged border of the Phlegrean caldera, resulting from the volcano-tectonic collapse induced from the pyroclastic flow deposits of the Campanian Ignimbrite (35 ka). Several morpho-depositional units have been identified, i.e., the inner continental shelf, the central basin, the submerged volcanic banks and the outer continental shelf. The stratigraphic relationships between the Quaternary volcanic units related to the offshore caldera border and the overlying deposits of the Late Quaternary depositional sequence in the Gulf of Pozzuoli have been highlighted. Fourteen main seismic units, both volcanic and sedimentary, tectonically controlled due to contemporaneous folding and normal faulting have been revealed by geological interpretation. Volcanic dykes, characterized by acoustically transparent sub-vertical bodies, locally bounded by normal faults, testify to the magma uprising in correspondence with extensional structures. A large field of tuff cones interlayered with marine deposits off the island of Nisida, on the western rim of the gulf, is related to the emplacement of the Neapolitan Yellow Tuff deposits. A thick volcanic unit, exposed over a large area off the Capo Miseno volcanic edifice is connected with the Bacoli-Isola Pennata-Capo Miseno yellow tuffs, cropping out in the northern Phlegrean Fields.

Results from Geothermal Logging, Air and Core-Water Chemistry Sampling, Air Injection Testing and Tracer Testing in the Northern Ghost Dance Fault, YUCCA Mountain, Nevada, November 1996 to August 1998

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lecain, G.D.; Anna, L.O.; Fahy, M.F.

1998-08-01

Geothermal logging, air and core-water chemistry sampling, air-injection testing, and tracer testing were done in the northern Ghost Dance Fault at Yucca Mountain, Nevada, from November 1996 to August 1998. The study was done by the U.S. Geological Survey, in cooperation with the U.S. Department of Energy. The fault-testing drill room and test boreholes were located in the crystal-poor, middle nonlithophysal zone of the Topopah Spring Tuff, a tuff deposit of Miocene age. The drill room is located off the Yucca Mountain underground Exploratory Studies Facility at about 230 meters below ground surface. Borehole geothermal logging identified a temperature decreasemore » of 0.1 degree Celsius near the Ghost Dance Fault. The temperature decrease could indicate movement of cooler air or water, or both, down the fault, or it may be due to drilling-induced evaporative or adiabatic cooling. In-situ pneumatic pressure monitoring indicated that barometric pressure changes were transmitted from the ground surface to depth through the Ghost Dance Fault. Values of carbon dioxide and delta carbon-13 from gas samples indicated that air from the underground drill room had penetrated the tuff, supporting the concept of a well-developed fracture system. Uncorrected carbon-14-age estimates from gas samples ranged from 2,400 to 4,500 years. Tritium levels in borehole core water indicated that the fault may have been a conduit for the transport of water from the ground surface to depth during the last 100 years.« less

Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.

1992-01-01

A combined isotopic and trace-element study of the Late Paleozoic Ouachita Orogenic belt has the following goals: (1) define changing provenance of Ouachita sedimentary systems throughout the Paleozoic; (2) constrain sources feeding into the Ouachita flysch trough during the Late Paleozoic; (3) isolate the geochemical signature of proposed colliding terranes to the south; (4) build a data base to compare with possible Ouachita System equivalents in Mexico. The ultimate aim is to constrain the tectonic setting of the southern margin of North America during the Paleozoic, with particular emphasis on collisional events leading to the final suturing of Pangea. Ndmore » isotopic data identify 3 distinct groups: (1) Ordovician passive margin sequence; (2) Carboniferous proto-flysch (Stanley Fm.), main flysch (Jackfork and Atoka Fms.) and molasse (foreland Atoka Fm.); (3) Mississippian ash-flow tuffs. The authors interpret the Ordovician signature to be essentially all craton-derived, whereas the Carboniferous signature reflects mixed sources from the craton plus orogenic sources to the east and possibly the south, including the evolving Appalachian Orogen. The proposed southern source is revealed by the tuffs to be too old and evolved to be a juvenile island arc terrane. They interpret the tuffs to have been erupted in a continental margin arc-type setting. Surprisingly, the foreland molasse sequence is indistinguishable from the main trough flysch sequence, suggesting the Ouachita trough and the craton were both inundated with sediment of a single homogenized isotopic signature during the Late Carboniferous. The possibility that Carboniferous-type sedimentary dispersal patterns began as early as the Silurian has important implications for the tectonics and paleogeography of the evolving Appalachian-Ouachita Orogenic System.« less

Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

USGS Publications Warehouse

Reid, M.R.; Vazquez, J.A.; Schmitt, A.K.

2011-01-01

Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720??C for zircon rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat ?? chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by-or zircon entrainment in-a less evolved melt from the one in which the zircons had previously resided. ?? 2010 Springer-Verlag.

Formation of a spatter-rich pyroclastic density current deposit in a Neogene sequence of trachytic-mafic igneous rocks at Mason Spur, Erebus volcanic province, Antarctica

NASA Astrophysics Data System (ADS)

Martin, A. P.; Smellie, J. L.; Cooper, A. F.; Townsend, D. B.

2018-01-01

Erosion has revealed a remarkable section through the heart of a volcanic island, Mason Spur, in the southwestern Ross Sea, Antarctica, including an unusually well-exposed section of caldera fill. The near-continuous exposure, 10 km laterally and > 1 km vertically, cuts through Cenozoic alkalic volcanic rocks of the Erebus volcanic province (McMurdo Volcanic Group) and permits the study of an ancient volcanic succession that is rarely available due to subsequent burial or erosion. The caldera filling sequence includes an unusual trachytic spatter-rich lapilli tuff (ignimbrite) facies that is particularly striking because of the presence of abundant black fluidal, dense juvenile spatter clasts of trachytic obsidian up to 2 m long supported in a pale cream-coloured pumiceous lapilli tuff matrix. Field mapping indicates that the deposit is an ignimbrite and, together with petrological considerations, it is suggested that mixing of dense spatter and pumiceous lapilli tuff in the investigated deposit occurred during emplacement, not necessarily in the same vent, with the mixed fragmental material emplaced as a pyroclastic density current. Liquid water was not initially present but a steam phase was probably generated during transport and may represent water ingested during passage of the current as it passed over either wet ground, stream, shallow lake or (possibly) snow. Well-exposed caldera interiors are uncommon and that at Mason Spur is helping understand eruption dynamics associated with a complex large island volcano. The results of our study should help to elucidate interpretations of other, less well exposed, pyroclastic density current deposits elsewhere in Antarctica and globally.

Tectonostratigraphic history of the Neogene Maimará basin, Northwest Argentina

NASA Astrophysics Data System (ADS)

Galli, Claudia I.; Coira, Beatriz L.; Alonso, Ricardo N.; Iglesia Llanos, María P.; Prezzi, Claudia B.; Kay, Suzanne Mahlburg

2016-12-01

This paper presents the tectonostratigraphic evolution of the Maimará Basin and explores the relationship between the clastic sediments and pyroclastic deposits in the basin and the evolution of the adjacent orogeny and magmatic arc. The sedimentary facies in this part of the basin include, in ascending order, an ephemeral fluvial system, a deep braided fluvial system and a medial to distal ephemeral fluvial system. We interpret that Maimará Formation accumulated in a basin that has developed two stages of accumulation. Stage 1 extended from 7 to 6.4 Ma and included accelerated tectonic uplift in the source areas, and it corresponds to the ephemeral fluvial system deposits. Stage 2, which extended from 6.4 to 4.8 Ma, corresponds to a tectonically quiescent period and included the development of the deep braided fluvial system deposits. The contact between the Maimará and Tilcara formations is always characterized by a regional unconformity and, in the study area, also shows pronounced erosion. Rare earth element and other chemical characteristics of the tuff intervals in the Maimará Formation fall into two distinct groups suggesting the tuffs were erupted from two distinct late Miocene source regions. The first and most abundant group has characteristics that best match tuffs erupted from the Guacha, Pacana and Pastos Grandes calderas, which are located 200 and 230 km west of the study area at 22º-23º30‧S latitude. The members the second group are chemically most similar to the Merihuaca Ignimbrite from the Cerro Galán caldera 290 km south-southwest of the studied section. The distinctive geochemical characteristics are excellent tools to reconstruct the stratigraphic evolution of the Neogene Maimará basin from 6.4 to 4.8 Ma.

Lithostratigraphy and shear-wave velocity in the crystallized Topopah Spring Tuff, Yucca Mountain, Nevada

USGS Publications Warehouse

Buesch, D.C.; Stokoe, K.H.; Won, K.C.; Seong, Y.J.; Jung, J.L.; Schuhen, M.D.

2006-01-01

Evaluation of the potential future response to seismic events of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities; rims on lithophysae and some fractures; spots (which are similar to rims but without an associated cavity or aperture); amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization; and fractures. Seismic properties, including shear-wave velocity (Vs), have been measured on 38 pieces of core, and there is a good "first order" correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger Vs values compared to samples from lithophysal zones. Some samples have Vs values that are outside the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, "large" lithophysal cavities, or "missing pieces" relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as Vs data from small-scale samples (typical and "flawed" core) to larger scale transects in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

Postglacial volcanic deposits at Glacier Peak, Washington, and potential hazards from future eruptions; a preliminary report

USGS Publications Warehouse

Beget, J.E.

1982-01-01

Eruptions and other geologic events at Glacier Peak volcano in northern Washington have repeatedly affected areas near the volcano as well as areas far downwind and downstream. This report describes the evidence of this activity preserved in deposits on the west and east flanks of the volcano. On the west side of Glacier Peak the oldest postglacial deposit is a large, clayey mudflow which traveled at least 35 km down the White Chuck River valley sometime after 14,000 years ago. Subsequent large explosive eruptions produced lahars and at least 10 pyroclastic-flow deposits, including a semiwelded vitric tuff in the White Chuck River valley. These deposits, known collectively as the White Chuck assemblage, form a valley fill which is locally preserved as far as 100 km downstream from the volcano in the Stillaguamish River valley. At least some of the assemblage is about 11,670-11,500 radiocarbon years old. A small clayey lahar, containing reworked blocks of the vitric tuff, subsequently traveled at least 15 km down the White Chuck River. This lahar is overlain by lake sediments containing charred wood which is about 5,500 years old. A 150-m-thick assemblage of pyroclastic-flow deposits and lahars, called the Kennedy Creek assemblage, is in part about 5,500-5,100 radiocarbon years old. Lithic lahars from this assemblage extend at least 100 km downstream in the Skagit River drainage. The younger lahar assemblages, each containing at least three lahars and reaching at least 18 km downstream from Glacier Peak in the White Chuck River valley, are about 2,800 and 1,800 years old, respectively. These are postdated by a lahar containing abundant oxyhornblende dacite, which extends at least 30 km to the Sauk River. A still younger lahar assemblage that contains at least five lahars, and that also extends at least 30 km to the Sauk River, is older than a mature forest growing on its surface. At least one lahar and a flood deposit form a low terrace at the confluence of the White Chuck and Sauk Rivers, and were deposited before 300 years ago, but more recently than about 1,800 years ago. Several small outburst floods, including one in 1975, have affected Kennedy and Baekos Creek and the upper White Chuck River in the last hundred years. East of Glacier Peak the oldest postglacial deposits consist of ash-cloud deposits that underlie tephra erupted by Glacier Peak between 12,750 and 11,250 radiocarbon years ago. Although pyroclastic-flow deposits correlative with the ash-cloud deposits have not been recognized, late Pleistocene pumiceous lahars extend at least 50 km downstream in the Suiattle River valley. A younger clayey mudflow extends at least 6 km down Dusty Creek. This lahar is overlain by deposits of lithic pyroclastic flows and lahars that form the Dusty assemblage. This assemblage is at least 300 m thick in the upper valleys of Dusty and Chocolate Creeks, and contains more than 10 km3 of lithic debris. Lahars derived from the Dusty assemblage extend at least 100 km down the Skagit River valley from Glacier Peak. This assemblage is younger than tephra layer 0 from Mount Mazama, and older than tephra layer Yn from Mount St. Helens, and thus was formed between about 7,000 and 3,400 years ago. The Dusty assemblage may have been formed at the same time as the Kennedy Creek assemblage. A 100-m-thick assemblage of pyroclastic flows and lahars preserved in the Chocolate Creek valley is about 1,800 radiocarbon years old. A clayey lahar in the upper Chocolate Creek valley extended at least 2 km downvalley after 1,800 years ago, but before pyroclastic flows and lahars were deposited in upper Chocolate Creek 1,100 radiocarbon years ago. Several clayey lahars in the Dusty Creek valley east of Glacier Peak are also about 1,100 years old. A lahar in the valley of Dusty Creek, which contains rare prismatically jointed blocks of vesiculated dacite, and a white ash that is locally as much as 50 cm thick may be the products of small

Hydrogeological Modelling of Some Geothermal Waters of Ivrindi, Havran and Gönen in the Province Capital of Balikesir, Western Anatolia, Turkey

NASA Astrophysics Data System (ADS)

Özgür, Nevzat; Ugurlu, Zehra; Memis, Ümit; Aydemir, Eda

2017-12-01

In this study, hydrogeological, hydrogeochemical and isotope geochemical features of Havran, Gönen and Ivrindi within the province capital of Balıkesir, Turkey were investigated in detail. The Early Triassic Karakaya formation in the study area of Havran forms the oldest rocks consisting of spilitic basalts, diabases, gabbros, mudstones, cherts and radiolarites. There are limestone blocks in this formation with intercalations with sandstones and with feldspar contents, quartzite, conglomerates and siltstones. Oligocene to Miocene granodiorite intrusions were generated in association with intensively volcanic events in the area. Between Upper Oligocene and Early Miocene, andesitic and dacitic pyroclastic rocks cropped out due to intensively volcanism. Later, conglomerates, sandstones, claystones, marls and limestones as lacustrine sediments formed from Middle to Upper Miocene in the study area. In the study area of Gönen, the Lower Triassic Karakaya formation consists of basalts, diabases, gabbros, mudstones, cherts and radiolarites and forms the basement rocks overlain by Upper Jurassic to Lower Cretaceous sandy limestones. Upper and Middle Miocene volcanics which can be considered intensive Biga Peninsula volcanos outcrop in the area. These andesitic lava flows are of black, gray and red color with intensive fissures. Neogene lacustrine sediments consist of conglomerates, sandstones, marl, claystone and clayey limestones. Upper Miocene to Pliocene rhyolitic pyroclastics and dacitic lava flows are the volcanic rocks which are overlain by Pliocene conglomerates, sandstones and claystones. In the study area of Ivrindi, the Çaldağ limestones are the oldest formation in Permian age. Çavdartepe metamorphic rocks are of Lower Triassic in which can be observed marbles sporadically. The Kınık formation consisting of conglomerates, sandstones, siltstones and limestones are of Lower Triassic age and display a lateral Stratigraphic progress with volcanic rocks. Upper Miocene to Pliocene Yürekli formation consists of dacites and rhyodacites. Upper Miocene to Pliocene Soma formation is composed of clayey limestone, marl, siltstone, intercalations of sandstone, agglomerate and andesitic gravels and blocks cemented by tuffs. Quaternary alluvium is the youngest formation. The samples of geothermal waters in the area of Havran can be considered as Na-Ca-(SO4)-HCO3, Na-(SO4)-HCO3 and Na-SO4 type waters. In comparison, the geothermal waters in Gönen are of Na-(SO4)-HCO3 and Na-HCO3 type waters. The geothermal waters of Ivrindi are considered as Na-Ca-HCO3 type waters. In the area, a groundwater sample is of Ca-Mg-HCO3 type water. The geothermal waters belong to the cations of Na+K>Ca>Mg in Havran, Gönen and Ivrindi and to the anions of SO4>HCO3>Cl in Havran, HCO3>SO4>Cl in Gönen and SO4>HCO3>Cl in Ivrindi. In the diagram of Na-K-Mg1/2, the geothermal waters in Havran, Gönen and Ivrindi of the province capital of Balıkesir can be classified as immature waters.