Distribution and compositions of magmatic inclusions in the Mount Helen dome, Lassen Volcanic Center, California: Insights into magma chamber processes

NASA Astrophysics Data System (ADS)

Feeley, T. C.; Wilson, L. F.; Underwood, S. J.

2008-11-01

Variations in spatial abundances, compositions, and textures of undercooled magmatic inclusions were determined in a glaciated Pleistocene lava dome (Mt. Helen; ~ 0.6 km 3) at the Lassen volcanic center (LVC), southernmost Cascades. Spatial variations were determined by point-counting at 86 locations separated by ~ 100 m on the dome. Major and trace element compositions of host rocks and inclusions at 12 locations along the flow length of the dome were obtained. Important results include the following. (1) Inclusion abundances range from 3-19 vol.%, with the highest values generally located along the little eroded northwestern margin and flow front of the dome. (2) Host rock compositions are markedly uniform across the dome (65.4 +/- 0.4 wt.% SiO 2) indicating that the degree of inclusion disaggregation was uniform, despite large spatial variations in inclusion abundances. (3) Inclusion sizes range from a maximum of ~ 1 m across to mm-sized crystal clots of phenocrysts plus adhering Ca-rich plagioclase microphenocrysts. (4) Inclusions have variable macroscopic textures indicating that partial undercooling both prior to and following entrapment in cooler dacitic host magma were important processes. (5) Inclusions are variably fractionated magmas with large variations in Ni (79-11 ppm) and Cr (87-7 ppm) contents that are lower than presumed mantle-derived melts. Furthermore, large ranges in incompatible trace elements indicate that inclusion compositions also reflect deep processes involving either melting of variable mantle source rocks or assimilation-fractional crystallization. (6) Inclusions are variably mixed magmas (56-61 wt.% SiO 2) that contain up to 50% host dacitic magma. (7) Correlations between Ni and Cr contents in hosts and inclusions from individual outcrops indicate that the effect of inclusion disaggregation and magma mingling on host dacitic magma was local (e.g., < 50 m). These features are interpreted to reflect protracted recharge of diverse composition mafic magmas into the base of a shallow magma reservoir containing a lower layer of compositionally evolving hybrid mafic magma and an upper layer of rhyodacitic magma. Complex interactions among magmas in the upper and lower layers resulted in formation of mafic inclusions by both pre- and post-entrapment undercooling mechanisms, followed by buoyant rise and accumulation near the roof of the reservoir. The main stage of inclusion disaggregation probably occurred in the conduit during eruptive ascent and largely ceased upon surface eruption. We infer that endogenous growth concentrated inclusions along the margins and top of the dome as more inclusion-poor dacite was progressively tapped from deeper regions of the reservoir.

Final report - Magma Energy Research Project

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

Colp, J.L.

1982-10-01

Scientific feasibility was demonstrated for the concept of magma energy extraction. The US magma resource is estimated at 50,000 to 500,000 quads of energy - a 700- to 7000-yr supply at the current US total energy use rate of 75 quads per year. Existing geophysical exploration systems are believed capable of locating and defining magma bodies and were demonstrated over a known shallow buried molten-rock body. Drilling rigs that can drill to the depths required to tap magma are currently available and experimental boreholes were drilled well into buried molten rock at temperatures up to 1100/sup 0/C. Engineering materials compatiblemore » with the buried magma environment are available and their performances were demonstrated in analog laboratory experiments. Studies show that energy can be extracted at attractive rates from magma resources in all petrologic compositions and physical configurations. Downhole heat extraction equipment was designed, built, and demonstrated successfully in buried molten rock and in the very hot margins surrounding it. Two methods of generating gaseous fuels in the high-temperature magmatic environment - generation of H/sub 2/ by the interaction of water with the ferrous iron and H/sub 2/, CH/sub 4/, and CO generation by the conversion of water-biomass mixtures - have been investigated and show promise.« less

OIB signatures in basin-related lithosphere-derived alkaline basalts from the Batain basin (Oman) - Constraints from 40Ar/39Ar ages and Nd-Sr-Pb-Hf isotopes

NASA Astrophysics Data System (ADS)

Witte, M.; Jung, S.; Pfänder, J. A.; Romer, R. L.; Mayer, B.; Garbe-Schönberg, D.

2017-08-01

Tertiary rift-related intraplate basanites from the Batain basin of northeastern Oman have low SiO2 (< 45.6 wt.%), high MgO (> 9.73 wt.%) and moderate to high Cr and Ni contents (Cr > 261 ppm, Ni > 181 ppm), representing near primary magmas that have undergone fractionation of mainly olivine and magnetite. Rare earth element systematics and p-T estimates suggest that the alkaline rocks are generated by different degrees of partial melting (4-13%) of a spinel-peridotite lithospheric mantle containing residual amphibole. The alkaline rocks show restricted variations of 87Sr/86Sr and 143Nd/144Nd ranging from 0.70340 to 0.70405 and 0.51275 to 0.51284, respectively. Variations in Pb isotopes (206Pb/204Pb: 18.59-18.82, 207Pb/204Pb: 15.54-15.56, 208Pb/204Pb: 38.65-38.98) of the alkaline rocks fall in the range of most OIB. Trace element constraints together with Sr-Nd-Pb isotope composition indicate that assimilation through crustal material did not affect the lavas. Instead, trace element variations can be explained by melting of a lithospheric mantle source that was metasomatized by an OIB-type magma that was accumulated at the base of the lithosphere sometimes in the past. Although only an area of less than 1000 km2 was sampled, magmatic activity lasted for about 5.5 Ma with a virtually continuous activity from 40.7 ± 0.7 to 35.3 ± 0.6 Ma. During this period magma composition was nearly constant, i.e. the degree of melting and the nature of the tapped source did not change significantly over time.

Magma Reservoir Processes Revealed by Geochemistry of the Ongoing East Rift Zone Eruption, Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Thornber, C. R.

2002-12-01

Geochemical data were examined for a suite of 1,000 near-vent lava samples from the Pu`u `O`o-Kupaianaha eruption of Kilauea, collected from January 1983 through October 2001. Bulk lava and glass compositions reveal short- and long-term changes in pre-eruptive magma conditions that can be correlated with changes in edifice deformation, shallow magma transfer and eruptive behavior. Two decades of eruption on Kilauea's east rift zone has yielded ~2 km3 of lava, 97% of which is sparsely olivine-phyric with an MgO range of 6.8 to 9.6 wt%. During separate brief intervals of low-volume, fissure eruption (episodes 1 to 3 and 54), isolated rift-zone reservoirs with lower-MgO and olv-cpx-plg-phryic magma were incorporated by more mafic magma immediately prior to eruption. During prolonged, near-continuous eruption(e.g.,episodes 48-53 and most of 55), steady-state effusion is marked by cyclic variations in olivine-saturated magma chemistry. Bulk lava MgO and eruption temperature vary in cycles of monthly to bi-annual frequency, while olivine-incompatible elements vary inversely to these cycles. However, MgO-normalized values and ratios of highly to moderately incompatible elements (HINCE/MINCE), which nullify olivine fractionation effects, reveal cycles in magma chemistry that occur prior to olivine crystallization over the magmatic temperature range that is tapped by this eruption (1205-1155°C). These short-term cycles are superimposed on a long-term decrease of HINCE/MINCE, which is widely thought to reflect a 20-year change in mantle-source conditions. While HINCE/MINCE variation in primitive recharge magma cannot be ruled out, the short-term fluctuations of this signature may require unreasonably complex mantle variations. Alternatively, the correspondence of HINCE/MINCE cycles with edifice deformation and eruptive behavior suggests that the long-term evolving magmatic condition is a result of prolonged succession of short-term shallow magmatic events. The consistent limits of repeated MgO and temperature variation imply end-member magma conditions that are regulated by open-system recharge of the shallow magmatic plumbing system. The low-end of MgO variation (7 wt%) approaches the low-pressure multiphase cotectic, which is maintained by open-system replenishment of a persistent magma reservoir. The high-temperature end-member (10 wt% MgO) is probably regulated by olivine fractionation in a zone of turbulent mixing between primitive recharge magma (15 wt% MgO) and resident cotectic magma. The highest temperature magmas are associated with eruption pulses that occur in response to intrusive events at the summit and initiate short-term increases of HINCE/MINCE. Subsequent changes toward lower magmatic temperatures are associated with periods of overall summit deflation, relatively low-level effusion, and frequent eruptive pauses. The long-term trends can be explained by episodic mixing of chemically uniform recharge melt with diminishing proportions of pre-1983 summit magma (maintained at cotectic conditions). Decreasing HINCE/MINCE may signify that a greater proportion of recharge magma is being diverted directly to Pu`u `O`o with minimal summit interaction or that the mass ratio of those mixing end-members has changed due to a depleted summit chamber (or both). The coincidence of long-term summit deflation since the 1982 summit eruption suggests that shallow processes related to summit reservoir depletion may be responsible for decreasing HINCE/MINCE and Pb isotopes in post-1982 steady-state eruption products. Magma derived from a uniform mantle-source, after having flushed out older resident magma, may now completely occupy the shallow magmatic plumbing system.

The Acoculco caldera magmas: genesis, evolution and relation with the Acoculco geothermal system

NASA Astrophysics Data System (ADS)

Sosa-Ceballos, G.; Macías, J. L.; Avellán, D.

2017-12-01

The Acoculco Caldera Complex (ACC) is located at the eastern part of the Trans Mexican Volcanic Belt; México. This caldera complex have been active since 2.7 Ma through reactivations of the system or associated magmatism. Therefore the ACC is an excellent case scenario to investigate the relation between the magmatic heat supply and the evolution processes that modified magmatic reservoirs in a potential geothermal field. We investigated the origin and the magmatic processes (magma mixing, assimilation and crystallization) that modified the ACC rocks by petrography, major oxides-trace element geochemistry, and isotopic analysis. Magma mixing is considered as the heat supply that maintain active the magmatic system, whereas assimilation yielded insights about the depth at which processes occurred. In addition, we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped during the caldera collapse. Rocks from the ACC were catalogued as pre, syn and post caldera. The post caldera rocks are peralkaline rhyolites, in contrast to all other rocks that are subalkaline. Our investigation is focus to investigate if the collapse modified the plumbing system and the depth at which magmas stagnate and recorded the magmatic processes.

Origins of cryptic variation in the Ediacaran-Fortunian rhyolitic ignimbrites of the Saldanha Bay Volcanic Complex, Western Cape, South Africa

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Stevens, G.; Frei, D.; Joseph, C. S. A.

2017-12-01

The Saldanha eruption centre, on the West Coast of South Africa, consists of 542 Ma, intracaldera, S-type, rhyolite ignimbrites divided into the basal Saldanha Ignimbrite and the partly overlying Jacob's Bay Ignimbrite. Depleted-mantle Nd model ages suggest magma sources younger than the Early Mesoproterozoic, and located within the Neoproterozoic Malmesbury Group and Swartland complex metasedimentary and metavolcanic rocks that form the regional basement. The Sr isotope systematics suggest that the dominant source rocks were metavolcaniclastic rocks and metagreywackes, and that the magmas formed from separate batches extracted from the same heterogeneous source. No apparent magma mixing trends relate the Saldanha to the Jacob's Bay Ignimbrites, or either of these to the magmas that formed the Plankiesbaai or Tsaarsbank Ignimbrites in the neighbouring Postberg eruption centre. The magmas were extracted from their source rocks carrying small but significant proportions of peritectic and restitic accessory minerals. Variations in the content of this entrained crystal cargo were responsible for most of the chemical variations in the magmas. Although we cannot construct a cogent crystal fractionation model to relate these groups of magmas, at least some crystal fractionation occurred, as an overlay on the primary signal due to peritectic assemblage entrainment (PAE). Thus, the causes of the cryptic chemical variation among the ignimbrite magmas of the Saldanha centre are variable, but dominated by the compositions of the parent melts and PAE. The preservation of clear, source-inherited chemical signatures, in individual samples, calls into question the common interpretation of silicic calderas as having been formed in large magma reservoirs, with magma compositions shaped by magma mingling, mixing, and fractional crystallization. The Saldanha rocks suggest a more intimate connection between source and erupted magma, and perhaps indicate that silicic magmas are too viscous to be significantly modified by magma-chamber processes.

Depth of origin of magma in eruptions.

PubMed

Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

2013-09-26

Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.

Depth of origin of magma in eruptions

PubMed Central

Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

2013-01-01

Many volcanic hazard factors - such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses - relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11–15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011–2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide. PMID:24067336

Extremely Rapid Crystal Fractionation During Episodes 30-31 of the Pu`u O`o Eruption: Implications for Magma Chamber Processes

NASA Astrophysics Data System (ADS)

Garcia, M. O.; Rhodes, J. M.; Pietruszka, A. J.; Rose, W. I.

2002-12-01

The Pu`u O`o eruption offers excellent opportunities to examine petrologic and geochemical processes in shallow, basaltic magma chamber due to the intense, multi-disciplinary monitoring of its activity, frequent sampling and repeated eruptions at the same vent. Strong compositional variations were observed during some of the high fire-fountaining (400 m) episodes in 1985. Following a 20-30 day hiatus in eruptive activity, the shallow magma chamber was largely evacuated during brief (1-2 day) eruptions. Samples collected during these episodes, especially at the beginning and end, document the compositional variation between and during eruptive episodes. Lavas and tephra from episodes 30 and 31 showed a remarkable and systematic variation (2 wt% increase in MgO; 7% decrease in incompatible elements like Ba) during and between these episodes. Most of the intra-episode lava compositional variation was observed during a brief period (<2 hours) with little variation before or after. Olivines in these weakly prophyritic Pu`u O`o lavas are in equilibrium with the host rock composition indicating that compositional variation is not related to magma mixing or accumulation of olivine. We interpret the variation to reflect crystal fractionation within the shallow (tens to hundreds of meter deep) Pu`u O`o magma chamber. This extremely high rate of crystallization (up to 0.3%/day) and cooling (2°C/day), compared to estimates of 1°C/year for the rift zone interior, must reflect the high surface area of the dike-shaped and open topped magma chamber. These features may represent the tapping of a diffusive interface separating well mixed zones of hotter and more primitive magma in the lower part of the chamber from cooler, somewhat evolved magma above.

From Rock to Magmatic Timescales in 25 Hours: Near-Real Time Petrological Volcanic Eruption Monitoring Tested with Basaltic Icelandic Tephras

NASA Astrophysics Data System (ADS)

Couperthwaite, F.; Morgan, D. J.; Thordarson, T.; Shea, T.; Harvey, J.

2016-12-01

Diffusion modeling of erupted crystals is routine for investigating pre-eruptive timescales within magma storage bodies and magma transport systems. The technique typically produces results some time after a volcanic eruption has commenced. This contribution employs a user-friendly, easy-to-use method for deployment in near-real time during an eruption, enabling rapid timescale assessment whilst retaining reliability. A `stress test' was undertaken to simulate analysis during an evolving eruption involving multiple tephra layers, to test method performance and assess the rapidity with which timescale data could be retrieved. The first tephra cycle was completely processed in 25 working hours, significantly faster than current traditional methods. Traditional limitations include slow data processing rates, the measurement of crystal orientations and sectioning angles, crystal shape uncertainties, and the possibilities of crystal growth and/or changing boundary conditions. These constraints have been considered for the new methodology with corrections applied at a crystal population level. Tephra samples from Vatnaöldur, Iceland were the study material for the stress test. 39 magmatic timescales from Mg-Fe interdiffusion across 25 olivine crystals were retrieved from the basal tephra layer representing eruption onset. Timescales range from 400 days to 160 days with olivine cores giving Forsterite (Fo) values of 82-84 and rim values 79 indicating a single olivine population showing normal zoning (Mg-rich core). The distribution of timescales is consistent with a single pulse of magma migrating from depth into a shallow system 1year before eruption onset. Magma arrival slows, then ceases by 5 months before eruption with no new magma entering the system in the days and weeks immediately before eruption. At the time of abstract submission, work is ongoing regarding the signals from later tephra units, but preliminary results indicate tapping of a source with longer crustal residence. Being able to retrieve this information within a day or so of the start of an eruption has exciting implications for eruption monitoring and hazard mitigation.

Venusian pancake domes: Insights from terrestrial voluminous silicic lavas and thermal modeling

NASA Technical Reports Server (NTRS)

Manley, Curtis R.

1993-01-01

The so-called 'pancake' domes, and several other volcanoes on Venus, appear to represent large extrusions of silicic lava. Similar voluminous rhyolite lava flows, often associated with mantle plumes, are known on Earth. Venus' high ambient temperature, and insulation by the dome's brecciated carapace, both act to prolong cooling of a dome's interior, allowing for episodic lava input over an extended period of time. Field relations and aspect ratios of terrestrial voluminous rhyolite lavas imply continuous, non-episodic growth, reflecting tapping of a large volume of dry, anatectic silicic magma. Petrogenetically, the venusian domes may be analogous to chains of small domes on Earth, which represent 'leakage' of evolved material from magma bodies fractionating from much more mafic liquids.

Effects of Host-rock Fracturing on Elastic-deformation Source Models of Volcano Deflation.

PubMed

Holohan, Eoghan P; Sudhaus, Henriette; Walter, Thomas R; Schöpfer, Martin P J; Walsh, John J

2017-09-08

Volcanoes commonly inflate or deflate during episodes of unrest or eruption. Continuum mechanics models that assume linear elastic deformation of the Earth's crust are routinely used to invert the observed ground motions. The source(s) of deformation in such models are generally interpreted in terms of magma bodies or pathways, and thus form a basis for hazard assessment and mitigation. Using discontinuum mechanics models, we show how host-rock fracturing (i.e. non-elastic deformation) during drainage of a magma body can progressively change the shape and depth of an elastic-deformation source. We argue that this effect explains the marked spatio-temporal changes in source model attributes inferred for the March-April 2007 eruption of Piton de la Fournaise volcano, La Reunion. We find that pronounced deflation-related host-rock fracturing can: (1) yield inclined source model geometries for a horizontal magma body; (2) cause significant upward migration of an elastic-deformation source, leading to underestimation of the true magma body depth and potentially to a misinterpretation of ascending magma; and (3) at least partly explain underestimation by elastic-deformation sources of changes in sub-surface magma volume.

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

USGS Publications Warehouse

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-01-01

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

PubMed Central

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-01-01

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

PubMed

Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

2016-08-25

Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

The trigger mechanism of low-frequency earthquakes on Montserrat

NASA Astrophysics Data System (ADS)

Neuberg, J. W.; Tuffen, H.; Collier, L.; Green, D.; Powell, T.; Dingwell, D.

2006-05-01

A careful analysis of low-frequency seismic events on Soufrièere Hills volcano, Montserrat, points to a source mechanism that is non-destructive, repetitive, and has a stationary source location. By combining these seismological clues with new field evidence and numerical magma flow modelling, we propose a seismic trigger model which is based on brittle failure of magma in the glass transition. Loss of heat and gas from the magma results in a strong viscosity gradient across a dyke or conduit. This leads to a build-up of shear stress near the conduit wall where magma can rupture in a brittle manner, as field evidence from a rhyolitic dyke demonstrates. This brittle failure provides seismic energy, the majority of which is trapped in the conduit or dyke forming the low-frequency coda of the observed seismic signal. The trigger source location marks the transition from ductile conduit flow to friction-controlled magma ascent. As the trigger mechanism is governed by the depth-dependent magma parameters, the source location remains fixed at a depth where the conditions allow brittle failure. This is reflected in the fixed seismic source locations.

The Life and Times of Supervolcanoes: Inferences from Long Valley Caldera

NASA Technical Reports Server (NTRS)

Simon, Justin

2014-01-01

Cataclysmic eruptions of silicic magma from "supervolcanoes" are among the most awe-inspiring natural phenomena found in the geologic record, in terms of size, power, and potential hazard. Based on the repose intervals between eruptions of this magnitude, the magmas responsible for them could accumulate gradually in the shallow crust over time scales that may be in excess of a million years (Smith, 1979; Spera and Crisp, 1981; Shaw, 1985). Pre-eruption magma residence time scales can also be inferred from the age difference between eruption (i.e., using 40Ar/39Ar dating to determine the time when hot erupted material cools to below its Ar closure temperature, 200 to 600 degC) and early pre-eruption crystallization (i.e., zircon saturation temperatures; Reid et al., 1997). I will discuss observations from Long Valley a Quaternary volcanic center in California. Long Valley is a voluminous, dominantly silicic caldera system. Based on extensive dating of accessory minerals (e.g., U-Th-Pb dating of zircon and allanite) along with geochemical and isotopic data we find that silicic magmas begin to crystallize 10's to 100's of thousands of years prior to their eruption and that rhyolites record episodes of punctuated and independent evolution rather than the periodic tapping of a long-lived magma. The more punctuated versus more gradual magma accumulation rates required by the absolute and model ages, respectively, imply important differences in the mass and heat fluxes associated with the generation, differentiation, and storage of voluminous rhyolites and emphasize the need to reconcile the magmatic age differences.

Oxidized sulfur-rich mafic magma at Mount Pinatubo, Philippines

USGS Publications Warehouse

de Hoog, J.C.M.; Hattori, K.H.; Hoblitt, R.P.

2004-01-01

Basaltic fragments enclosed in andesitic dome lavas and pyroclastic flows erupted during the early stages of the 1991 eruption of Mount Pinatubo, Philippines, contain amphiboles that crystallized during the injection of mafic magma into a dacitic magma body. The amphiboles contain abundant melt inclusions, which recorded the mixing of andesitic melt in the mafic magma and rhyolitic melt in the dacitic magma. The least evolved melt inclusions have high sulfur contents (up to 1,700 ppm) mostly as SO42, which suggests an oxidized state of the magma (NNO + 1.4). The intrinsically oxidized nature of the mafic magma is confirmed by spinel-olivine oxygen barometry. The value is comparable to that of the dacitic magma (NNO + 1.6). Hence, models invoking mixing as a means of releasing sulfur from the melt are not applicable to Pinatubo. Instead, the oxidized state of the dacitic magma likely reflects that of parental mafic magma and the source region in the sub-arc mantle. Our results fit a model in which long-lived SO2 discharge from underplated mafic magma accumulated in the overlying dacitic magma and immiscible aqueous fluids. The fluids were the most likely source of sulfur that was released into the atmosphere during the cataclysmic eruption. The concurrence of highly oxidized basaltic magma and disproportionate sulfur output during the 1991 Mt. Pinatubo eruption suggests that oxidized mafic melt is an efficient medium for transferring sulfur from the mantle to shallow crustal levels and the atmosphere. As it can carry large amounts of sulfur, effectively scavenge sulfides from the source mantle and discharge SO2 during ascent, oxidized mafic magma forms arc volcanoes with high sulfur fluxes, and potentially contributes to the formation of metallic sulfide deposits. ?? Springer-Verlag 2003.

On precisely modelling surface deformation due to interacting magma chambers and dykes

NASA Astrophysics Data System (ADS)

Pascal, Karen; Neuberg, Jurgen; Rivalta, Eleonora

2014-01-01

Combined data sets of InSAR and GPS allow us to observe surface deformation in volcanic settings. However, at the vast majority of volcanoes, a detailed 3-D structure that could guide the modelling of deformation sources is not available, due to the lack of tomography studies, for example. Therefore, volcano ground deformation due to magma movement in the subsurface is commonly modelled using simple point (Mogi) or dislocation (Okada) sources, embedded in a homogeneous, isotropic and elastic half-space. When data sets are too complex to be explained by a single deformation source, the magmatic system is often represented by a combination of these sources and their displacements fields are simply summed. By doing so, the assumption of homogeneity in the half-space is violated and the resulting interaction between sources is neglected. We have quantified the errors of such a simplification and investigated the limits in which the combination of analytical sources is justified. We have calculated the vertical and horizontal displacements for analytical models with adjacent deformation sources and have tested them against the solutions of corresponding 3-D finite element models, which account for the interaction between sources. We have tested various double-source configurations with either two spherical sources representing magma chambers, or a magma chamber and an adjacent dyke, modelled by a rectangular tensile dislocation or pressurized crack. For a tensile Okada source (representing an opening dyke) aligned or superposed to a Mogi source (magma chamber), we find the discrepancies with the numerical models to be insignificant (<5 per cent) independently of the source separation. However, if a Mogi source is placed side by side to an Okada source (in the strike-perpendicular direction), we find the discrepancies to become significant for a source separation less than four times the radius of the magma chamber. For horizontally or vertically aligned pressurized sources, the discrepancies are up to 20 per cent, which translates into surprisingly large errors when inverting deformation data for source parameters such as depth and volume change. Beyond 8 radii however, we demonstrate that the summation of analytical sources represents adjacent magma chambers correctly.

Lunar ferroan anorthosites and mare basalt sources - The mixed connection

NASA Technical Reports Server (NTRS)

Ryder, Graham

1991-01-01

Global overturn of a hot, gravitationally unstable lunar mantle immediately following the solidification of a magma ocean explains several characteristics of lunar petrology. Lunar mare basalt sources are inferred to be depleted in europium and alumina. These depletions are consensually attributed to complementary plagioclase floating from a magma ocean. However, in contrast to the mare basalt source parent magma, the ferroan anorthosite parent magma was more evolved by virtue of its lower Mg/Fe ratio and Ni abundances, although less evolved in its poverty of clinopyroxene constituents, flat rare earth pattern, and lower incompatible element abundances. The europium anomaly in mare sources is inferred to be present at 400 km depth, too deep to have been directly influenced by plagioclase crystallization. Massive overturning of the post-magma ocean mantle would have carried down clinopyroxene, ilmenite, and phases containing fractionated rare earths, europium anomalies, and some heat-producing radionuclides.

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.

Onset of a basaltic explosive eruption from Kīlauea’s summit in 2008: Chapter 19

USGS Publications Warehouse

Carey, Rebecca J.; Swavely, Lauren; Swanson, Don; Houghton, Bruce F.; Orr, Tim R.; Elias, Tamar; Sutton, Andrew; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

2015-01-01

The onset of a basaltic eruption at the summit of Kīlauea volcano in 2008 is recorded in the products generated during the first three weeks of the eruption and suggests an evolution of both the physical properties of the magma and also lava lake levels and vent wall stability. Ash componentry and the microtextures of the early erupted lapilli products reveal that the magma was largely outgassed, perhaps in the preceding weeks to months. An increase in the juvenile:lithic ratio and size of ash collected from March 23 to April 3 records an increasing level of the magma within the conduit. After April 3 until the explosive eruption of April 9, a trend of decreasing juvenile:lithic ratio suggests that vent wall collapses were more frequent, possibly because lava level increased and destabilized the overhanging wall [Orr et al. 2013]. Despite increasing lake height, the microtextural characteristics of the lapilli suggest that the outgassed end-member was still being tapped between March 26 and April 8. The April 9 rockfall triggered an explosive eruption that produced a new component in the eruption deposits not seen in the preceding weeks; microvesicular juvenile lapilli, the first evidence of an actively vesiculating magma. Two additional dense end-member pyroclast types were also erupted during the April 9 explosion, likely related to outgassed magma with longer residence times than the microvesicular magma. We link these pyroclasts to a stagnant viscous crust at the top of the magma column or to convecting, downwelling magma. Our study of ash componentry and the textures of juvenile lapilli suggests that the April 9 explosive event effectively cleared the conduit of largely outgassed magma. The degassing processes during this eruption are complex and varied: in the period of persistent degassing during March 26-April 8 small resident bubbles at shallow levels in the lava lake were coupled to the magma whereas large bubbles ascended, expanded and fragmented. During the rockfall- triggered explosion of April 9, all bubbles were coupled to the host magma on the timescale of decompression, but additional exsolution, decompression and expansion of deeper, more gas-rich resident magma likely occurred [cf. Carey et al. 2012]. Where external conditions play a significant role in eruption dynamics, e.g., by triggering eruptions, vesiculation and degassing dynamics can be expected to be complex.

40 CFR 141.88 - Monitoring requirements for lead and copper in source water.

Code of Federal Regulations, 2010 CFR

2010-07-01

... the basis of tap samples collected in accordance with § 141.86 shall collect lead and copper source... value or be considered one-half the PQL. (b) Monitoring frequency after system exceeds tap water action level. Any system which exceeds the lead or copper action level at the tap shall collect one source...

Magma-magma interaction in the mantle beneath eastern China

NASA Astrophysics Data System (ADS)

Zeng, Gang; Chen, Li-Hui; Yu, Xun; Liu, Jian-Qiang; Xu, Xi-Sheng; Erdmann, Saskia

2017-04-01

In addition to magma-rock and rock-rock reaction, magma-magma interaction at mantle depth has recently been proposed as an alternative mechanism to produce the compositional diversity of intraplate basalts. However, up to now no compelling geochemical evidence supports this novel hypothesis. Here we present geochemistry for the Longhai basalts from Fujian Province, southeastern China, which demonstrates the interaction between two types of magma at mantle depth. At Longhai, the basalts form two groups, low-Ti basalts (TiO2/MgO < 0.25) and high-Ti basalts (TiO2/MgO > 0.25). Calculated primary compositions of the low-Ti basalts have compositions close to L + Opx + Cpx + Grt cotectic, and they also have low CaO contents (7.1-8.1 wt %), suggesting a mainly pyroxenite source. Correlations of Ti/Gd and Zr/Hf with the Sm/Yb ratios, however, record binary mixing between the pyroxenite-derived melt and a second, subordinate source-derived melt. Melts from this second source component have low Ti/Gd and high Zr/Hf and Ca/Al ratios, thus likely representing a carbonated component. The Sr, Nd, Hf, and Pb isotopic compositions of the high-Ti basalts are close to the low-Ti basalts. The Sm/Yb ratio of the high-Ti basalts, however, is markedly elevated and characterized by crossing rare earth element patterns at Ho, suggesting that they have source components comparable to the low-Ti basalts, but that they have experienced garnet and clinopyroxene fractionation. We posit that mingling of SiO2-saturated tholeiitic magma with SiO2-undersaturated alkaline magma might trigger such fractionation. Therefore, the model of magma-magma interaction and associated deep evolution of magma in the mantle is proposed to explain the formation of Longhai basalts. It may, moreover, serve as a conceptual model for the formation of tholeiitic to alkaline intraplate basalts worldwide.

Hadean silicate differentiation preserved by anomalous 142Nd/144Nd ratios in the Réunion hotspot source

NASA Astrophysics Data System (ADS)

Peters, Bradley J.; Carlson, Richard W.; Day, James M. D.; Horan, Mary F.

2018-03-01

Active volcanic hotspots can tap into domains in Earth’s deep interior that were formed more than two billion years ago. High-precision data on variability in tungsten isotopes have shown that some of these domains resulted from differentiation events that occurred within the first fifty million years of Earth history. However, it has not proved easy to resolve analogous variability in neodymium isotope compositions that would track regions of Earth’s interior whose composition was established by events occurring within roughly the first five hundred million years of Earth history. Here we report 142Nd/144Nd ratios for Réunion Island igneous rocks, some of which are resolvably either higher or lower than the ratios in modern upper-mantle domains. We also find that Réunion 142Nd/144Nd ratios correlate with helium-isotope ratios (3He/4He), suggesting parallel behaviour of these isotopic systems during very early silicate differentiation, perhaps as early as 4.39 billion years ago. The range of 142Nd/144Nd ratios in Réunion basalts is inconsistent with a single-stage differentiation process, and instead requires mixing of a conjugate melt and residue formed in at least one melting event during the Hadean eon, 4.56 billion to 4 billion years ago. Efficient post-Hadean mixing nearly erased the ancient, anomalous 142Nd/144Nd signatures, and produced the relatively homogeneous 143Nd/144Nd composition that is characteristic of Réunion basalts. Our results show that Réunion magmas tap into a particularly ancient, primitive source compared with other volcanic hotspots, offering insight into the formation and preservation of ancient heterogeneities in Earth’s interior.

High-precision Pb isotopes reveal two small magma bodies beneath the summit of Kilauea Volcano

NASA Astrophysics Data System (ADS)

Pietruszka, A. J.; Heaton, D. E.; Marske, J. P.; Garcia, M. O.

2011-12-01

The summit magma storage reservoir of Kilauea Volcano is one of the most important components of the volcano's magmatic pluming system, but the geometry (size and shape) of this reservoir is poorly known. Here we use high-precision Pb isotopic analyses of historical Kilauea summit lavas (1823-2010) to define the minimum number of magma bodies within the summit reservoir and their volumes. The 206Pb/204Pb ratios of these lavas display a systematic temporal fluctuation characterized by low values in 1823, a gradual increase to a maximum in 1921, an abrupt drop to relatively constant intermediate values from 1929 to 1959, and a rapid decrease to 2010. These variations indicate that Kilauea's summit reservoir is being supplied by rapidly changing parental magma compositions derived from a mantle source that is heterogeneous on a small scale. Analyses of multiple lavas from several individual eruptions reveal small but significant differences in 206Pb/204Pb ratios (~0.01-0.03). For example, the extra-caldera lavas from Aug. 1971 and Jul. 1974 display significantly lower Pb isotope ratios and higher MgO contents (10 wt. %) than the intra-caldera lavas (MgO ~7-8 wt. %) from each eruption. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate decreasing temporal trends. The intra-caldera lavas from 1971, 1974, 1975, Apr. 1982 and the lower MgO lavas from Sep. 1982 have consistently higher 206Pb/204Pb ratios at a given time (compared to the extra-caldera lavas and the higher MgO lavas from Sep. 1982). These trends require that the intra- and extra-caldera lavas (and the Sep. 1982 lavas) were supplied from two separate magma bodies. Numerous studies by HVO scientists (e.g., Fiske and Kinoshita, 1969; Klein et al., 1987) have long identified the main locus of Kilauea's summit reservoir ~2 km southeast of Halemaumau (near the caldera rim) at a depth of ~2-7 km, but more recent investigations have discovered a secondary magma body located <1 km below the southeast rim of Halemaumau (e.g., Battaglia et al., 2003; Johnson et al., 2010). The association between the vent locations of the extra-caldera lavas near the southeast rim of the caldera and their higher MgO contents suggest that these lavas tapped into the main (deeper) body of the volcano's summit reservoir. In contrast, the lower MgO intra-caldera lavas were likely derived from the secondary (shallow) body beneath Halemaumau. Residence time modeling based on the Pb isotope ratios of the lavas suggests that the magma volume of the deeper body is ~0.2 km3, whereas the shallow body holds a minimum of ~0.04 km3 of magma. These estimates are much smaller than our previous calculation of ~2-3 km3 for Kilauea's summit reservoir based on trace element ratios (Pietruszka and Garcia, 1999), but are similar to the volume of the magma body that underlies Piton de la Fournaise Volcano on Réunion Island (Albarède, 1993).

40 CFR 63.544 - Standards for process fugitive sources.

Code of Federal Regulations, 2010 CFR

2010-07-01

...) Smelting furnace and dryer charging hoppers, chutes, and skip hoists; (2) Smelting furnace lead taps, and molds during tapping; (3) Smelting furnace slag taps, and molds during tapping; (4) Refining kettles; (5) Dryer transition pieces; and (6) Agglomerating furnace product taps. (b) Process fugitive emission...

S-type granitic magmas—petrogenetic issues, models and evidence

NASA Astrophysics Data System (ADS)

Clemens, J. D.

2003-04-01

Despite a perception that it represents a perverse divergence, it is perfectly possible to believe in the existence of S- and I-type granites (and the implications for the nature of their protoliths), and to disbelieve in the applicability of the restite-unmixing model for chemical variation in granitic magmas. White and Chappell erected the S-I classification with impeccable validity. The isotopic evidence demands contrasting source reservoirs for S- and I-type granitic magmas. However, the major advance was not the classification, but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas. The restite-unmixing model is commonly seen as a companion to the S-I classification, but it is really a separate issue. This model implies that the compositions of granites 'image' those of their source rocks in a simple way. However, there are other equally valid models that can explain the data, and none of them represents a unique solution. The most cogent explanation for the high-grade metasedimentary enclaves in most S-type granites is that they represent mid-crustal xenoliths; restitic enclaves are either rare or absent. Inherited zircons in S-type rocks are certainly restitic. However, the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock. Zircon and zirconium behaviours are controlled by disequilibrium and kinetics, and Zr contents of granitic rocks can rarely be used to infer magma temperatures. Since the dominant ages among inherited zircons in Lachlan Fold Belt (LFB) S-type granites are Ordovician and Proterozoic, it seems likely that crust of this age, but geochemically different from the exposed rocks, not only underlies much of the LFB but also forms a component in the granite magma sources. The evidence is overwhelming that the dark, microgranular enclaves that occur in both S- and I-type granites are igneous in origin. They represent globules of quenched, more mafic magma mingled and modified by exchange with the host granitic magma. However, magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas. Likewise, the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and, in some cases, violate constraints from isotopic studies. S- and I-type magmas commonly retain their distinct identities. This suggests limited source mixing, limited magma mixing and limited wall-rock assimilation. Though intermediate types certainly exist, they are probably relatively minor in volume. Crystal fractionation probably plays the major role in the differentiation of very many granitic magmas, including most S-types, especially those emplaced at high crustal levels or in the volcanic environment. Minor mechanisms include magma mixing, wall-rock assimilation and restite unmixing. Isotopic variations within plutons and in granite suites could be caused by source heterogeneities, magma mixing, assimilation and even by isotopic disequilibrium. However, source heterogeneity, coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity. Normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust, and crustal thickening likewise fails to provide sufficient heat. Generally, the mantle must be the major heat source. This might be provided through mantle upwelling and crustal thinning, and possibly through the intra- and underplating of mafic magmas. Upper crustal extension seems to have been common in regions undergoing granitic magmatism. Migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid-present reactions. Granitic magmas are mostly formed by fluid-absent processes. Where we do see rare evidence for arrested fluid-absent partial melting, the melt fraction is invariably concentrated into small shear zones, veinlets and small dykes. Thus, it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels. However, one major missing link in the chain is the mechanism by which melt fractions, in small-scale segregations occurring over a wide area, can be gathered and focused to efficiently feed much wider-spaced major magma conduits. Answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones. Self-organization almost certainly plays a role.

Mare basalt magma source region and mare basalt magma genesis

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

Binder, A.B.

1982-11-15

Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regionsmore » (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.« less

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.

Compositional zoning of the bishop tuff

USGS Publications Warehouse

Hildreth, W.; Wilson, C.J.N.

2007-01-01

Compositional data for >400 pumice clasts, organized according to eruptive sequence, crystal content, and texture, provide new perspectives on eruption and pre-eruptive evolution of the >4600 km3 of zoned rhyolitic magma ejected as the BishopTuff during formation of Long Valley caldera. Proportions and compositions of different pumice types are given for each ignimbrite package and for the intercalated plinian pumice-fall layers that erupted synchronously. Although withdrawal of the zoned magma was less systematic than previously realized, the overall sequence displays trends toward greater proportions of less evolved pumice, more crystals (0-5 24 wt %), and higher FeTi-oxide temperatures (714-818??C). No significant hiatus took place during the 6 day eruption of the BishopTuff, nearly all of which issued from an integrated, zoned, unitary reservoir. Shortly before eruption, however, the zoned melt-dominant portion of the chamber was invaded by batches of disparate lower-silica rhyolite magma, poorer in crystals than most of the resident magma but slightly hotter and richer in Ba, Sr, andTi. Interaction with resident magma at the deepest levels tapped promoted growth ofTi-rich rims on quartz, Ba-rich rims on sanidine, and entrapment of near-rim melt inclusions relatively enriched in Ba and CO2.Varied amounts of mingling, even in higher parts of the chamber, led to the dark gray and swirly crystal-poor pumices sparsely present in all ashflow packages. As shown by FeTi-oxide geothermometry, the zoned rhyolitic chamber was hottest where crystal-richest, rendering any model of solidification fronts at the walls or roof unlikely.The main compositional gradient (75-195 ppm Rb; 0.8-2.2 ppm Ta; 71-154 ppm Zr; 0.40-1.73% FeO*) existed in the melt, prior to crystallization of the phenocryst suite observed, which included zircon as much as 100 kyr older than the eruption.The compositions of crystals, though themselves largely unzoned, generally reflect magma temperature and the bulk compositional gradient, implying both that few crystals settled or were transported far and that the observed crystals contributed little to establishing that gradient. Upward increases in aqueous gas and dissolved water, combined with the adiabatic gradient (for the 5 km depth range tapped) and the roofward decline in liquidus temperature of the zoned melt, prevented significant crystallization against the roof, consistent with dominance of crystal-poor magma early in the eruption and lack of any roof-rind fragments among the Bishop ejecta, before or after onset of caldera collapse. A model of secular incremental zoning is advanced wherein numerous batches of crystal-poor melt were released from a mush zone (many kilometers thick) that floored the accumulating rhyolitic melt-rich body. Each batch rose to its own appropriate level in the melt-buoyancy gradient, which was selfsustaining against wholesale convective re-homogenization, while the thick mush zone below buffered it against disruption by the deeper (non-rhyolitic) recharge that augmented the mush zone and thermally sustained the whole magma chamber. Crystal-melt fractionation was the dominant zoning process, but it took place not principally in the shallow melt-rich body but mostly in the pluton-scale mush zone before and during batchwise melt extraction. ?? Published by Oxford University Press (2007).

Insights into the evolution of an alkaline magmatic system: An in situ trace element study of clinopyroxenes from the Ditrău Alkaline Massif, Romania

NASA Astrophysics Data System (ADS)

Batki, Anikó; Pál-Molnár, Elemér; Jankovics, M. Éva; Kerr, Andrew C.; Kiss, Balázs; Markl, Gregor; Heincz, Adrián; Harangi, Szabolcs

2018-02-01

Clinopyroxene is a major constituent in most igneous rock types (hornblendite, diorite, syenite, nepheline syenite, camptonite, tinguaite and ijolite) of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. Phenocryst and antecryst populations have been distinguished based on mineral zoning patterns and geochemical characteristics. Major and trace element compositions of clinopyroxenes reflect three dominant pyroxene types including primitive high-Cr Fe-diopside, intermediate Na-diopside-hedenbergite and evolved high-Zr aegirine-augite. Clinopyroxenes record two major magma sources as well as distinct magma evolution trends. The primitive diopside population is derived from an early camptonitic magma related to basanitic parental melts, whilst the intermediate diopside-hedenbergite crystals represent a Na-, Nb- and Zr-rich magma source recognised for the first time in the Ditrău magmatic system. This magma fractionated towards ijolitic and later phonolitic compositions. Field observations, petrography and clinopyroxene-melt equilibrium calculations reveal magma recharge and mingling, pyroxene recycling, fractional crystallisation and accumulation. Repeated recharge events of the two principal magmas resulted in multiple interactions between more primitive and more fractionated co-existing magma batches. Magma mingling occurred between mafic and felsic magmas by injection of ijolitic magma into fissures (dykes) containing phonolitic (tinguaite) magma. This study shows that antecryst recycling, also described for the first time in Ditrău, is a significant process during magma recharge and demonstrates that incorporated crystals can crucially affect the host magma composition and so whole-rock chemical data should be interpreted with great care.

Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan.

PubMed

Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

2016-09-13

Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.

Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan

PubMed Central

Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

2016-01-01

Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide. PMID:27619897

Getting the lead out: understanding risks in the distribution ...

EPA Pesticide Factsheets

This presentation discusses the importance of the water distribution system as a component of the source-to-tap continuum in public health protection. Issues covered include: understanding source water quality changes and their impacts throughout the system; use of mitigation measures such as filters); and holistic approaches and/or strategies that could be used to avoid unintended consequences of decisions from source to tap. Invited presentation on topics indicated as of interest. With exposure to lead as the context, this presentation discusses the importance of the water distribution system as a component of the source-to-tap continuum in public health protection. Issues covered include: understanding source water quality changes and their impacts throughout the system; use of mitigation measures such as filters); and holistic approaches and/or strategies that could be used to avoid unintended consequences of decisions from source to tap.

Relating stress models of magma emplacement to volcano-tectonic earthquakes

NASA Astrophysics Data System (ADS)

Vargas-Bracamontes, D.; Neuberg, J.

2007-12-01

Among the various types of seismic signals linked to volcanic processes, volcano-tectonic earthquakes are probably the earliest precursors of volcanic eruptions. Understanding their relationship with magma emplacement can provide insight into the mechanisms of magma transport at depth and assist in the ultimate goal of forecasting eruptions. Volcano-tectonic events have been observed to occur on faults that experience increases in Coulomb stress changes as the result of magma intrusions. To simulate stress changes associated with magmatic injections, we test different models of volcanic sources in an elastic half-space. For each source model, we look at several aspects that influence the stress conditions of the magmatic system such as the regional tectonic setting, the effect of varying the elastic parameters of the media, the evolution of the magma with time, as well as the volume and rheology of the ascending magma.

Evidence for crustal recycling during the Archean: The parental magmas of the stillwater complex

NASA Technical Reports Server (NTRS)

Mccallum, I. S.

1988-01-01

The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area.

Petrogenesis of the granitic Donkerhuk batholith in the Damara Belt of Namibia: protracted, syntectonic, short-range, crustal magma transfer

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Buick, I. S.; Kisters, A. F. M.; Frei, D.

2017-07-01

The areally extensive (>5000 km2), syn-tectonic, ca. 520 Ma, mainly S-type Donkerhuk batholith was constructed through injection of thousands of mainly sheet-like magma pulses over 20-25 Myr. It intruded schists of the Southern Zone accretionary prism in the Damara Belt of Namibia. Each magma pulse had at least partly crystallised prior to the arrival of the following batch. However, much of the batholith may have remained partially molten for long periods, close to the H2O-saturated granite solidus. The batholith shows extreme variation in chemistry, while having limited mineralogical variation, and seems to be the world's most heterogeneous granitic mass. The Nd model ages of 2 Ga suggest that Eburnean rocks of the former magmatic arc, structurally overlain by the accretionary wedge, are the most probable magma sources. Crustal melting was initiated by mantle heat flux, probably introduced by thermal diffusion rather than magma advection. The granitic magmas were transferred from source to sink, with minimal intermediate storage; the whole process having occurred in the middle crust, resulting in feeble crustal differentiation despite the huge volume of silicic magma generated. Source heterogeneity controlled variation in the magmas and neither mixing nor fractionation was prominent. However, due to the transpressional emplacement régime, local filter pressing formed highly silicic liquids, as well as felsic cumulate rocks. The case of the Donkerhuk batholith demonstrates that emplacement-level tectonics can significantly influence compositional evolution of very large syn-tectonic magma bodies.

High-precision Pb Isotopes Reveal Two Small Magma Bodies Beneath the Summit of Kilauea Volcano

NASA Astrophysics Data System (ADS)

Pietruszka, A. J.; Heaton, D. E.; Marske, J. P.; Garcia, M. O.

2013-12-01

The summit magma storage reservoir of Kilauea Volcano is one of the most important components of the volcano's magmatic plumbing system, but its geometry is poorly known. High-precision Pb isotopic analyses of Kilauea summit lavas (1959-1982) define the minimum number of magma bodies within the summit reservoir and their volumes. The 206Pb/204Pb ratios of these lavas display a temporal decrease due to changes in the composition of the parental magma delivered to the volcano. Analyses of multiple lavas from some individual eruptions reveal small but significant differences in 206Pb/204Pb. The extra-caldera lavas from Aug. 1971 and Jul. 1974 display lower Pb isotope ratios and higher MgO contents (10 wt. %) than the intra-caldera lavas (MgO ~7-8 wt. %) from each eruption. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate decreasing temporal trends. The intra-caldera lavas from 1971, 1974, 1975, Apr. 1982 and the lower MgO lavas from Sep. 1982 have higher 206Pb/204Pb ratios at a given time (compared to the extra-caldera lavas and the higher MgO lavas from Sep. 1982). These trends require that the intra- and extra-caldera lavas (and the Sep. 1982 lavas) were supplied from two separate, partially isolated magma bodies. Numerous studies (Fiske and Kinoshita, 1969; Klein et al., 1987) have long identified the locus of Kilauea's summit reservoir ~2 km southeast of Halemaumau (HMM) at a depth of ~2-7 km, but more recent investigations have discovered a second magma body located <1 km below the east rim of HMM (Battaglia et al., 2003; Johnson et al., 2010). The association between the vent locations of the extra-caldera lavas near the southeast rim of the caldera and their higher MgO contents suggests that these lavas tapped the deeper magma body. In contrast, the lower MgO intra-caldera lavas were likely derived from the shallow magma body beneath HMM. Residence time modeling based on the Pb isotope ratios of the lavas suggests that the magma volume of the deeper body is ~0.2 km3, whereas the shallow body holds a minimum of ~0.04 km3 of magma. These estimates are smaller than a previous calculation of ~2-3 km3 for Kilauea's summit reservoir based on trace element ratios (Pietruszka and Garcia, 1999), but are similar to the volume of the magma body that underlies Piton de la Fournaise Volcano on Réunion Island (Albarède, 1993).

Longitudinal and Source-to-Tap New Orleans, LA, U.S.A. Drinking Water Microbiology.

PubMed

Hull, Natalie M; Holinger, Eric P; Ross, Kimberly A; Robertson, Charles E; Harris, J Kirk; Stevens, Mark J; Pace, Norman R

2017-04-18

The two municipal drinking water systems of New Orleans, LA, U.S.A. were sampled to compare the microbiology of independent systems that treat the same surface water from the Mississippi River. To better understand temporal trends and sources of microbiology delivered to taps, these treatment plants and distribution systems were subjected to source-to-tap sampling over four years. Both plants employ traditional treatment by chloramination, applied during or after settling, followed by filtration before distribution in a warm, low water age system. Longitudinal samples indicated microbiology to have stability both spatially and temporally, and between treatment plants and distribution systems. Disinfection had the greatest impact on microbial composition, which was further refined by filtration and influenced by distribution and premise plumbing. Actinobacteria spp. exhibited trends with treatment. In particular, Mycobacterium spp., very low in finished waters, occurred idiosyncratically at high levels in some tap waters, indicating distribution and/or premise plumbing as main contributors of mycobacteria. Legionella spp., another genus containing potential opportunistic pathogens, also occurred ubiquitously. Source water microbiology was most divergent from tap water, and each step of treatment brought samples more closely similar to tap waters.

Lead Isotope Compositions of Acid Residues from Olivine-Phyric Shergottite Tissint: Implications for Heterogeneous Shergottite Source Reservoirs

NASA Technical Reports Server (NTRS)

Moriwaki, R.; Usui, T.; Yokoyama, T.; Simon, J. I.; Jones, J. H.

2015-01-01

Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions and trace element abundances. These correlations have been interpreted as indicating the presence of a reduced, incompatible element- depleted reservoir and an oxidized, incompatible- element-enriched reservoir. The former is clearly a depleted mantle source, but there is ongoing debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former requires the ancient Martian crust to be the enriched source (crustal assimilation), whereas the latter requires isolation of a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and trace element concentration analyses of sequential acid-leaching fractions (leachates and the final residues) from the geochemically depleted olivine-phyric shergottite Tissint. The results suggest that the Tissint magma is not isotopically uniform and sampled at least two geochemical source reservoirs, implying that either crustal assimilation or magma mixing would have played a role in the Tissint petrogenesis.

Comparison of the Mineral Content of Tap Water and Bottled Waters

PubMed Central

Azoulay, Arik; Garzon, Philippe; Eisenberg, Mark J

2001-01-01

OBJECTIVES Because of growing concern that constituents of drinking water may have adverse health effects, consumption of tap water in North America has decreased and consumption of bottled water has increased. Our objectives were to 1) determine whether North American tap water contains clinically important levels of calcium (Ca2+), magnesium (Mg2+), and sodium (Na+) and 2) determine whether differences in mineral content of tap water and commercially available bottled waters are clinically important. DESIGN We obtained mineral analysis reports from municipal water authorities of 21 major North American cities. Mineral content of tap water was compared with published data regarding commercially available bottled waters and with dietary reference intakes (DRIs). MEASUREMENTS AND MAIN RESULTS Mineral levels varied among tap water sources in North America and among bottled waters. European bottled waters generally contained higher mineral levels than North American tap water sources and North American bottled waters. For half of the tap water sources we examined, adults may fulfill between 8% and 16% of their Ca2+ DRI and between 6% and 31% of their Mg2+ DRI by drinking 2 liters per day. One liter of most moderate mineralization European bottled waters contained between 20% and 58% of the Ca2+ DRI and between 16% and 41% of the Mg2+ DRI in adults. High mineralization bottled waters often contained up to half of the maximum recommended daily intake of Na+. CONCLUSION Drinking water sources available to North Americans may contain high levels of Ca2+, Mg2+, and Na+ and may provide clinically important portions of the recommended dietary intake of these minerals. Physicians should encourage patients to check the mineral content of their drinking water, whether tap or bottled, and choose water most appropriate for their needs. PMID:11318912

Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile

USGS Publications Warehouse

Singer, Brad S.; Andersen, Nathan L.; Le Mével, Hélène; Feigl, Kurt L.; DeMets, Charles; Tikoff, Basil; Thurber, Clifford H.; Jicha, Brian R.; Cardonna, Carlos; Córdova, Loreto; Gil, Fernando; Unsworth, Martyn J.; Williams-Jones, Glyn; Miller, Craig W.; Fierstein, Judith; Hildreth, Edward; Vazquez, Jorge A.

2014-01-01

Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about magma-crust dynamics—are not well known. This is because we have learned how these systems form, grow, and erupt mainly from the study of ash flow tuffs deposited tens to hundreds of thousands of years ago or more, or from the geophysical imaging of the unerupted portions of the reservoirs beneath the associated calderas. The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007, the crust there has been inflating at an astonishing rate of at least 25 cm/yr. This unique opportunity to investigate the dynamics of a large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively under way is stimulating a new international collaboration. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ca. 20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. The next phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics.

Volatile content of Hawaiian magmas and volcanic vigor

NASA Astrophysics Data System (ADS)

Blaser, A. P.; Gonnermann, H. M.; Ferguson, D. J.; Plank, T. A.; Hauri, E. H.; Houghton, B. F.; Swanson, D. A.

2014-12-01

We test the hypothesis that magma supply to Kīlauea volcano, Hawai'i may be affected by magma volatile content. We find that volatile content and magma flow from deep source to Kīlauea's summit reservoirs are non-linearly related. For example, a 25-30% change in volatiles leads to a near two-fold increase in magma supply. Hawaiian volcanism provides an opportunity to develop and test hypotheses concerning dynamic and geochemical behavior of hot spot volcanism on different time scales. The Pu'u 'Ō'ō-Kupaianaha eruption (1983-present) is thought to be fed by essentially unfettered magma flow from the asthenosphere into a network of magma reservoirs at approximately 1-4 km below Kīlauea's summit, and from there into Kīlauea's east rift zone, where it erupts. Because Kīlauea's magma becomes saturated in CO2 at about 40 km depth, most CO2 is thought to escape buoyantly from the magma, before entering the east rift zone, and instead is emitted at the summit. Between 2003 and 2006 Kīlauea's summit inflated at unusually high rates and concurrently CO2emissions doubled. This may reflect a change in the balance between magma supply to the summit and outflow to the east rift zone. It remains unknown what caused this surge in magma supply or what controls magma supply to Hawaiian volcanoes in general. We have modeled two-phase magma flow, coupled with H2O-CO2 solubility, to investigate the effect of changes in volatile content on the flow of magma through Kīlauea's magmatic plumbing system. We assume an invariant magma transport capacity from source to vent over the time period of interest. Therefore, changes in magma flow rate are a consequence of changes in magma-static and dynamic pressure throughout Kīlauea's plumbing system. We use measured summit deformation and CO2 emissions as observational constraints, and find from a systematic parameter analysis that even modest increases in volatiles reduce magma-static pressures sufficiently to generate a 'surge' in magma supply and in CO2 emissions.

Spatial, seasonal, and source variability in the stable oxygen and hydrogen isotopic composition of tap waters throughout the USA

USGS Publications Warehouse

Landwehr, Jurate M.; Coplen, Tyler B.; Stewart, David W.

2013-01-01

To assess spatial, seasonal, and source variability in stable isotopic composition of human drinking waters throughout the entire USA, we have constructed a database of δ18O and δ2H of US tap waters. An additional purpose was to create a publicly available dataset useful for evaluating the forensic applicability of these isotopes for human tissue source geolocation. Samples were obtained at 349 sites, from diverse population centres, grouped by surface hydrologic units for regional comparisons. Samples were taken concurrently during two contrasting seasons, summer and winter. Source supply (surface, groundwater, mixed, and cistern) and system (public and private) types were noted. The isotopic composition of tap waters exhibits large spatial and regional variation within each season as well as significant at-site differences between seasons at many locations, consistent with patterns found in environmental (river and precipitation) waters deriving from hydrologic processes influenced by geographic factors. However, anthropogenic factors, such as the population of a tap’s surrounding community and local availability from diverse sources, also influence the isotopic composition of tap waters. Even within a locale as small as a single metropolitan area, tap waters with greatly differing isotopic compositions can be found, so that tap water within a region may not exhibit the spatial or temporal coherence predicted for environmental water. Such heterogeneities can be confounding factors when attempting forensic inference of source water location, and they underscore the necessity of measurements, not just predictions, with which to characterize the isotopic composition of regional tap waters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry

USGS Publications Warehouse

Lu, Z.; Masterlark, Timothy; Dzurisin, D.; Rykhus, Russ; Wicks, C.

2003-01-01

A group of satellite radar interferograms that span the time period from 1991 to 2000 shows that Westdahl volcano, Alaska, deflated during its 1991-1992 eruption and is reinflating at a rate that could produce another eruption within the next several years. The rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days, respectively. This behavior is consistent with a deep, constant-pressure magma source connected to a shallow reservoir by a magma-filled conduit. An elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath Westdahl Peak. We propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir. The pressure gradient, and hence the flow rate, are greatest immediately after eruptions. Pressurization of the reservoir decreases both the pressure gradient and the flow rate, but eventually the reservoir ruptures and an eruption or intrusion ensues. The eruption rate is controlled partly by the pressure gradient between the reservoir and surface, and therefore it, too, decreases with time. When the supply of eruptible magma is exhausted, the eruption stops, the reservoir begins to repressurize at a high rate, and the cycle repeats. This model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems.

Rhenium-osmium and samarium-neodymium isotopic systematics of the Stillwater complex

NASA Technical Reports Server (NTRS)

Lambert, David D.; Shirey, Steven B.; Carlson, Richard W.; Morgan, John W.; Walker, Richard J.

1989-01-01

The role of magma mixing in the formation of strategic platinum-group element ore deposits is examined using isotopic data from the Stillwater Complex, Montana. Nd and Os isotopic data show that the intrusion formed from at least two distinct magmas: ultramafic (U-type) affinity magmas and anorthositic (A-type) affinity magmas. The U-type magmas formed from a lithospheric mantle source containing recycled crustal materials and the A-type magmas originated either by crustal contamination of basaltic magmas or by partial melting of basalt in the lower crust. The results also suggest that the platinum-group element ore deposits were derived from A-type magmas which were injected into the U-type magma chamber at several stages during the development of the ultramafic series.

Assessing the origin of bacteria in tap water and distribution system in an unchlorinated drinking water system by SourceTracker using microbial community fingerprints.

PubMed

Liu, Gang; Zhang, Ya; van der Mark, Ed; Magic-Knezev, Aleksandra; Pinto, Ameet; van den Bogert, Bartholomeus; Liu, Wentso; van der Meer, Walter; Medema, Gertjan

2018-07-01

The general consensus is that the abundance of tap water bacteria is greatly influenced by water purification and distribution. Those bacteria that are released from biofilm in the distribution system are especially considered as the major potential risk for drinking water bio-safety. For the first time, this full-scale study has captured and identified the proportional contribution of the source water, treated water, and distribution system in shaping the tap water bacterial community based on their microbial community fingerprints using the Bayesian "SourceTracker" method. The bacterial community profiles and diversity analyses illustrated that the water purification process shaped the community of planktonic and suspended particle-associated bacteria in treated water. The bacterial communities associated with suspended particles, loose deposits, and biofilm were similar to each other, while the community of tap water planktonic bacteria varied across different locations in distribution system. The microbial source tracking results showed that there was not a detectable contribution of source water to bacterial community in the tap water and distribution system. The planktonic bacteria in the treated water was the major contributor to planktonic bacteria in the tap water (17.7-54.1%). The particle-associated bacterial community in the treated water seeded the bacterial community associated with loose deposits (24.9-32.7%) and biofilm (37.8-43.8%) in the distribution system. In return, the loose deposits and biofilm showed a significant influence on tap water planktonic and particle-associated bacteria, which were location dependent and influenced by hydraulic changes. This was revealed by the increased contribution of loose deposits to tap water planktonic bacteria (from 2.5% to 38.0%) and an increased contribution of biofilm to tap water particle-associated bacteria (from 5.9% to 19.7%) caused by possible hydraulic disturbance from proximal to distal regions. Therefore, our findings indicate that the tap water bacteria could possibly be managed by selecting and operating the purification process properly and cleaning the distribution system effectively. Copyright © 2018 Elsevier Ltd. All rights reserved.

Magma oceanography. I - Thermal evolution. [of lunar surface

NASA Technical Reports Server (NTRS)

Solomon, S. C.; Longhi, J.

1977-01-01

Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

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).

A mantle-driven surge in magma supply to Kīlauea Volcano during 2003--2007

USGS Publications Warehouse

Poland, Michael P.; Miklius, Asta; Sutton, A. Jeff; Thornber, Carl R.

2012-01-01

The eruptive activity of a volcano is fundamentally controlled by the rate of magma supply. At Kīlauea Volcano, Hawai‘i, the rate of magma rising from a source within Earth’s mantle, through the Hawaiian hotspot, was thought to have been relatively steady in recent decades. Here we show that the magma supply to Kīlauea at least doubled during 2003–2007, resulting in dramatic changes in eruptive activity and the formation of new eruptive vents. An initial indication of the surge in supply was an increase in CO2 emissions during 2003–2004, combined with the onset of inflation of Kīlauea’s summit, measured using the Global Positioning System and interferometric synthetic aperture radar. Inflation was not limited to the summit magma reservoirs, but was recorded as far as 50 km from the summit, implying the existence of a connected magma system over that distance. We also record increases in SO2 emissions, heightened seismicity, and compositional and temperature variations in erupted lavas. The increase in the volume of magma passing through and stored within Kīlauea, coupled with increased CO2 emissions, indicate a mantle source for the magma surge. We suggest that magma supply from the Hawaiian hotspot can vary over timescales of years, and that CO2 emissions could be a valuable aid for assessing variations in magma supply at Kīlauea and other volcanoes.

Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008

USGS Publications Warehouse

Lu, Zhong; Dzurisin, Daniel; Biggs, Juliet; Wicks, Charles; McNutt, Steve

2010-01-01

Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, magma accumulated in a storage zone centered ~3.5 km beneath the caldera floor at a rate that varied with time. A Mogi-type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time-sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, magma storage increased by 3.2–4.5 × 107 m3, which corresponds to 75–85% of the magma volume erupted in 1997. Thereafter, the average magma supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, magma storage had increased by 3.7–5.2 × 107 m3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region. Eventually the effects of continuing magma supply and vesiculation of stored magma caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of magma during the eruptions depressurized the shallow storage zone, causing significant volcano-wide subsidence and initiating a new intereruption deformation cycle.

Biofilm formation in an experimental water distribution system: the contamination of non-touch sensor taps and the implication for healthcare.

PubMed

Moore, Ginny; Stevenson, David; Thompson, Katy-Anne; Parks, Simon; Ngabo, Didier; Bennett, Allan M; Walker, Jimmy T

2015-01-01

Hospital tap water is a recognised source of Pseudomonas aeruginosa. U.K. guidance documents recommend measures to control/minimise the risk of P. aeruginosa in augmented care units but these are based on limited scientific evidence. An experimental water distribution system was designed to investigate colonisation of hospital tap components. P. aeruginosa was injected into 27 individual tap 'assemblies'. Taps were subsequently flushed twice daily and contamination levels monitored over two years. Tap assemblies were systematically dismantled and assessed microbiologically and the effect of removing potentially contaminated components was determined. P. aeruginosa was repeatedly recovered from the tap water at levels above the augmented care alert level. The organism was recovered from all dismantled solenoid valves with colonisation of the ethylene propylene diene monomer (EPDM) diaphragm confirmed by microscopy. Removing the solenoid valves reduced P. aeruginosa counts in the water to below detectable levels. This effect was immediate and sustained, implicating the solenoid diaphragm as the primary contamination source.

Total sulfur dioxide emissions and pre-eruption vapor-saturated magma at Mount St. Helens, 1980-88

NASA Astrophysics Data System (ADS)

Gerlach, T. M.; McGee, K. A.

1994-12-01

SO2 from explosive volcanism can cause significant climatic and atmospheric impacts, but the source of the sulfur is controversial. Total ozone mapping spectrometer (TOMS), correlation spectrometer (COSPEC), and ash leachate data for Mount St. Helens from the time of the climactic eruption on 18 May 1980 to the final stages of non-explosive degassing in 1988 give a total SO2 emission of 2 Mt. COSPEC data show a sharp drop in emission rate that was apparently controlled by a decreasing rate of magma supply. A total SO2 emission of only 0.08 Mt is estimated from melt inclusion data and the conventional assumption that the main sulfur source was pre-eruption melt; commonly invoked sources of 'excess sulfur' (anhydrite decomposition, basaltic magma, and degassing of non-erupted magma) are unlikely in this case. Thus melt inclusions may significantly underestimate SO2 emissions and impacts of explosive volcanism on climate and the atmosphere. Measured CO2 emissions, together with the H2O content of melt inclusions and experimental solubility data, indicate the Mount St. Helens dacite was vapor-saturated at depth prior to ascent and suggest that a vapor phase was the main source of sulfur for the 2-Mt of SO2. A vapor source is consistent with experimental studies on the Mount St. Helens dacite and removes the need for a much debated shallow magma body.

Production of mildly alkaline basalts at complex ocean ridge settings: Perspectives from basalts emitted during the 2010 eruption at the Eyjafjallajökull volcano, Iceland

NASA Astrophysics Data System (ADS)

Viccaro, Marco; Nicotra, Eugenio; Urso, Salvatore

2015-11-01

The early phase of the 2010 eruption at the Eyjafjallajökull volcano (Iceland) produced poorly evolved mildly alkaline basalts that have a signature more enriched with respect to the typically depleted basalts emitted at ocean ridges. The whole rock geochemistry of these basaltic magmas offers a great opportunity to investigate the mantle source characteristics and reasons leading to this enriched fingerprint in proximity of the ocean ridge system. Some basaltic products of Katla volcano, ∼25 km east of Eyjafjallajökull, have been chosen from the literature, as they display a similar mildly alkaline signature and can be therefore useful to explore the same target. Major and trace element variations of the whole rock suggest a very limited evolutionary degree for the 2010 Eyjafjallajökull products and the selected Katla magmas, highlighting the minor role played by differentiation processes such as fractional crystallization. Nevertheless, effects of the limited fractionation have been erased through re-equilibration of the major and trace element abundances at primary conditions. Concentrations of Th after re-equilibration have been assumed as indexes of the partial melting degree, given the high incompatibility of the element, and enrichment ratios calculated for each trace element. Especially for LILE (Rb, Ba, K, Sr), the pattern of resulting enrichment ratios well matches that obtained from fractional melting of peridotite bearing hydrous phases (amphibole/phlogopite). This put forward the idea that magmas have been generated through partial melting of enriched mantle domains where hydrous minerals have been stabilized as a consequence of metasomatic processes. Refertilization of the mantle has been attributed to intrusion of hydrous silicate melts and fractional crystallization of hydrous cumulates. These refertilizing melts, inherited from an ancient subducted oceanic crust, intruded into a depleted oceanic lithosphere that remained stored for a long time (hundreds of Ma or Ga) before being re-entrained in partial melting. This means that magmas could have acquired their main geochemical differences in response of the variable depletion/enrichment degree of the heterogeneous mantle portion tapped at rather shallow depth (≤100 km). Our finding is another tessera in the open debate on the plume-related vs. non plume-related origin of Icelandic magmatism.

Modeling Magma Mixing: Evidence from U-series age dating and Numerical Simulations

NASA Astrophysics Data System (ADS)

Philipp, R.; Cooper, K. M.; Bergantz, G. W.

2007-12-01

Magma mixing and recharge is an ubiquitous process in the shallow crust, which can trigger eruption and cause magma hybridization. Phenocrysts in mixed magmas are recorders for magma mixing and can be studied by in- situ techniques and analyses of bulk mineral separates. To better understand if micro-textural and compositional information reflects local or reservoir-scale events, a physical model for gathering and dispersal of crystals is necessary. We present the results of a combined geochemical and fluid dynamical study of magma mixing processes at Volcan Quizapu, Chile; two large (1846/47 AD and 1932 AD) dacitic eruptions from the same vent area were triggered by andesitic recharge magma and show various degrees of magma mixing. Employing a multiphase numerical fluid dynamic model, we simulated a simple mixing process of vesiculated mafic magma intruded into a crystal-bearing silicic reservoir. This unstable condition leads to overturn and mixing. In a second step we use the velocity field obtained to calculate the flow path of 5000 crystals randomly distributed over the entire system. Those particles mimic the phenocryst response to the convective motion. There is little local relative motion between silicate liquid and crystals due to the high viscosity of the melts and the rapid overturn rate of the system. Of special interest is the crystal dispersal and gathering, which is quantified by comparing the distance at the beginning and end of the simulation for all particle pairs that are initially closer than a length scale chosen between 1 and 10 m. At the start of the simulation, both the resident and new intruding (mafic) magmas have a unique particle population. Depending on the Reynolds number (Re) and the chosen characteristic length scale of different phenocryst-pairs, we statistically describe the heterogeneity of crystal populations on the thin section scale. For large Re (approx. 25) and a short characteristic length scale of particle-pairs, heterogeneity of particle populations is large. After one overturn event, even the "thin section scale" can contain phenocrysts that derive from the entire magmatic system. We combine these results with time scale information from U-series plagioclase age dating. Apparent crystal residence times from the most evolved and therefore least hybridized rocks for the 1846/47 and 1932 eruptions of Volcan Quizapu are about 5000 and about 3000 yrs, respectively. Based on whole rock chemistry as well as textural and crystal-chemical data, both eruptions tapped the same reservoir and therefore should record similar crystal residence times. Instead, the discordance of these two ages can be explained by magma mixing as modeled above, if some young plagioclase derived from the andesitic recharge magma which triggered the 1846/47 AD eruption got mixed into the dacite remaining in the reservoir after eruption, thus lowering the apparent crystal residence time for magma that was evacuated from the reservoir in 1932.

Geophysical Investigations of Magma Plumbing Systems at Cerro Negro Volcano, Nicaragua

NASA Astrophysics Data System (ADS)

MacQueen, Patricia Grace

Cerro Negro near Leon, Nicaragua is a very young (163 years), relatively small basaltic cinder cone volcano that has been unusually active during its short lifespan (recurrence interval 6--7 years), presenting a significant hazard to nearby communities. Previous studies have raised several questions as to the proper classification of Cerro Negro and its relation to neighboring Las Pilas-El Hoyo volcano. Analysis of Bouguer gravity data collected at Cerro Negro has revealed connected positive density anomalies beneath Cerro Negro and Las Pilas-El Hoyo. These findings suggest that eruptions at Cerro Negro may be tapping a large magma reservoir beneath Las Pilas-El Hoyo, implying that Cerro Negro should be considered the newest vent on the Las Pilas-El Hoyo volcanic complex. As such, it is possible that the intensity of volcanic hazards at Cerro Negro may eventually increase in the future to resemble those pertaining to a stratovolcano. Keywords: Cerro Negro; Las Pilas-El Hoyo; Bouguer gravity; magmatic plumbing systems; potential fields; volcano.

Using Intensive Variables to Constrain Magma Source Regions

NASA Astrophysics Data System (ADS)

Edwards, B. R.; Russell, J. K.

2006-05-01

In the modern world of petrology, magma source region characterization is commonly the realm of trace element and isotopic geochemistry. However, major element analyses of rocks representing magmatic compositions can also be used to constrain source region charactertistics, which enhance the results of isotopic and trace element studies. We show examples from the northern Cordilleran volcanic province (NCVP), in the Canadian Cordillera, where estimations of thermodynamic intensive variables are used to resolve different source regions for mafic alkaline magmas. We have taken a non-traditional approach to using the compositions of three groups of mafic, alkaline rocks to characterize the source regions of magmas erupted in the NCVP. Based on measured Fe2O3 and FeO in rocks from different locations, the Atlin volcanic district (AVD), the Fort Selkirk volcanic complex (FSVC), the West Tuya volcanic field, (WTVF), we have estimated oxygen fugacities (fO2) for the source regions of magmas based on the model of Kress and Carmichael (1991) and the computational package MELTS/pMelts (Ghiorso and Sack, 1995; Ghiorso et al., 2002). We also have used Melts/pMelts to estimate liquidus conditions for the compositions represented by the samples as well as activities of major element components. The results of our calculations are useful for distinguishing between three presumably different magma series: alkaline basalts, basanites, and nephelinites (Francis and Ludden, 1990; 1995). Calculated intensive variables (fO2, activities SiO2, KAlSiO4, Na2SiO3) show clear separation of the samples into two groups: i) nephelinites and ii) basanites/alkaline basalts. The separation is especially evident on plots of log fO2 versus activity SiO2. The source region for nephelinitic magmas in the AVD is up to 2 log units more oxidized than that for the basanites/basalts as well as having a distinctly lower range of activities of SiO2. Accepting that our assumptions about the magmas representing source region conditions are valid, these thermodynamic constraints on the source regions clearly indicate two things: the nephelinites and basanites/basalts could not have originated from the same source regions, and the basanites and basalts could have originated from the same source regions. We suggest that computation of intensive variables for magma source regions is a logical complement to standard trace element and isotopic studies. -Francis, D. and Ludden, J., (1990) The mantle source for olivine nephelinite, basanite and alkaline olivine basalts at Fort Selkirk, Yukon, Canada: Journal of Petrology, 31, p. 371-400. -Francis, D. and Ludden, J., (1995) The signature of amphibole in mafic alkaline lavas, a study in the northern Canadian Cordillera: Journal of Petrology, 36, p. 1171-1191. -Ghiorso, MS., and Sack, RO. (1995) Chemical Mass Transfer in Magmatic Processes. IV. A Revised and Internally Consistent Thermodynamic Model for the Interpolation and Extrapolation of Liquid-Solid Equilibria in Magmatic Systems at Elevated Temperatures and Pressures. Contributions to Mineralogy and Petrology, 119, 197-212. -Ghiorso, MS., Hirschmann, MM., Reiners, PW., and Kress, VC. III (2002) The pMELTS: An revision of MELTS aimed at improving calculation of phase relations and major element partitioning involved in partial melting of the mantle at pressures up to 3 GPa. Geochemistry, Geophysics, Geosystems 3(5), 10.1029/2001GC000217.

Oropharyngeal Tularemia Outbreak Associated with Drinking Contaminated Tap Water, Turkey, July-September 2013.

PubMed

Aktas, Dilber; Celebi, Bekir; Isik, Mehmet Emirhan; Tutus, Celal; Ozturk, Huseyin; Temel, Fehminaz; Kizilaslan, Mecit; Zhu, Bao-Ping

2015-12-01

In 2013, an oropharyngeal tularemia outbreak in Turkey affected 55 persons. Drinking tap water during the likely exposure period was significantly associated with illness (attack rate 27% vs. 11% among non-tap water drinkers). Findings showed the tap water source had been contaminated by surface water, and the chlorination device malfunctioned.

A City-wide Investigation of the Isotopic Distribution and Source of Tap Waters for Forensic Human Geolocation Ground-truthing.

PubMed

Ueda, Momoko; Bell, Lynne S

2017-05-01

Human geolocation is prefaced on the accuracy of the geographic precision of mapped isotopic values for drinking water. As most people live in cities, it becomes important to understand city water supplies and how the isotopic values uniquely reflect that city. This study investigated the isotopic distribution of δ 2 H and δ 18 O from sourced tap waters that were collected from across the Metro Vancouver (MV) area (n = 135). The results revealed that the isotopic values reflect their water sources with a range of 5.3‰ for δ 18 O tap and 29.3‰ for δ 2 H tap for MV. The results indicate that individual cities need higher resolution studies to determine their tap water isotopic ranges, and a good understanding of the water supply network itself for human geolocation work. With an extended high-resolution understanding of each city, human tissue may be compared with more certainty for geolocation. © 2016 American Academy of Forensic Sciences.

Magma emplacement in 3D

NASA Astrophysics Data System (ADS)

Gorczyk, W.; Vogt, K.

2017-12-01

Magma intrusion is a major material transfer process in Earth's continental crust. Yet, the mechanical behavior of the intruding magma and its host are a matter of debate. In this study, we present a series of numerical thermo-mechanical experiments on mafic magma emplacement in 3D.In our model, we place the magmatic source region (40 km diameter) at the base of the mantle lithosphere and connect it to the crust by a 3 km wide channel, which may have evolved at early stages of magmatism during rapid ascent of hot magmatic fluids/melts. Our results demonstrate continental crustal response due to magma intrusion. We observe change in intrusion geometries between dikes, cone-sheets, sills, plutons, ponds, funnels, finger-shaped and stock-like intrusions as well as injection time. The rheology and temperature of the host-rock are the main controlling factors in the transition between these different modes of intrusion. Viscous deformation in the warm and deep crust favours host rock displacement and magma pools along the crust-mantle boundary forming deep-seated plutons or magma ponds in the lower to middle-crust. Brittle deformation in the cool and shallow crust induces cone-shaped fractures in the host rock and enables emplacement of finger- or stock-like intrusions at shallow or intermediate depth. A combination of viscous and brittle deformation forms funnel-shaped intrusions in the middle-crust. Low-density source magma results in T-shaped intrusions in cross-section with magma sheets at the surface.

Compositional Variation in Magmas Supplied to the Southern East Pacific Rise, 17°-19° S: Implications for Magma Reservoir Dynamics

NASA Astrophysics Data System (ADS)

Bergmanis, E. C.; Sinton, J. M.; Rubin, K. H.; Gregg, T. K.; Cormier, M.

2002-12-01

Fine-scale observation and sampling of lavas from the southern EPR 17°-19° S reveal both short- and long-term compositional heterogeneity of flows produced in single eruptive episodes. Located between 17° 24' and 17° 36'S, the 140 x 106 m2 Aldo-Kihi flow reaches a maximum width of 2.2 km between 17° 26' and 17° 28'S; the presence of sheet flows, lava channels, and summit collapse troughs imply that the eruption was centered in this area of broad axial morphology. Some lava channels and collapsed lava tubes extend beyond the margins of the recently erupted Aldo-Kihi flow, indicating that lava distribution systems can persist over at least several hundreds of years and multiple separate eruptions were apparently centered in this region. Extensive glass analyses of the Aldo-Kihi flow show that MgO contents range from 7.7-8.4 wt %; all the samples with greater than 8.0 wt % MgO occur south of 17° 30'S. This result is hard to reconcile with along-axis propagation of a single dike, and suggests vertical eruption from a magma chamber that is compositionally zoned along-axis. Twenty-three other samples older than Aldo-Kihi contain > 8.0 wt % MgO; all but two occur south of 17° 28.4'S suggesting that the displacement of eruptive centers from the location of hottest subaxial magma is a long-lived feature of this region. Lack of compositional variation across some contacts indicates that this length of ridge has erupted compositionally similar lavas in separate volcanic episodes. Elsewhere distinctly different lava compositions include the several-hundred-year-old Rehu-Marka Fe-Ti basalt, and local occurrences of incompatible element-enriched T-MORB. The distribution of rock types in this area requires a complex history of mantle melting, recharge, cooling, and eruption that has been spatially systematic over time scales encompassing several eruptive episodes. Between 18° 31.5' and 18° 34.5'S the South Hump lava is distinctly bimodal with highly evolved ferrobasalts (MgO < 6.2 wt %, Na2O < 3.1 wt %) in the south, and basalts (~7.2 wt % MgO, Na2O > 3.1 wt %) in the north. Major and trace element data for these lavas indicate that they cannot be related by low-pressure fractional crystallization and that variations in mantle source composition appears to be required to explain the observed compositional variation. Existing geological evidence indicates that either the axial graben here was resurfaced by a single, chemically bimodal eruption, or by two adjacent eruptions that must be close in age. The boundary between the two chemical types corresponds to discontinuities in the axial magma chamber imaged by seismic reflection, as well as to significant differences in the thickness of seismic layer 2A. This result indicates that magma arising from vastly different melting processes can reside in adjacent crustal magma reservoirs and be tapped, either during a single eruption or during closely spaced eruptions in adjacent regions.

Observations of the eruptions of July 22 and August 7, 1980, at Mount St. Helens, Washington

USGS Publications Warehouse

Hoblitt, Richard P.

1986-01-01

The explosive eruptions of July 22 and August 7, 1980, at Mount St. Helens, Wash., both included multiple eruptive pulses. The beginnings of three of the pulses-two on July 22 and one on August 7-were witnessed and photographed. Each of these three began with a fountain of gases and pyroclasts that collapsed around the vent and generated a pyroclastic density flow. Significant vertical-eruption columns developed only after the density flows were generated. This behavior is attributable to either an increase in the gas content of the eruption jet or a decrease in vent radius with time. An increase in the gas content may have occurred as the vent was cleared (by expulsion of a plug of pyroclasts) or as the eruption began to tap deeper, gas-rich magma after first expelling the upper, gas-depleted part of the magma body. An effective decrease of the vent radius with time may have occurred as the eruption originated from progressively deeper levels in the vent. All of these processes-vent clearing; tapping of deeper, gas-rich magma; and effective decrease in vent radius-probably operated to some extent. A 'relief-valve' mechanism is proposed here to account for the occurrence of multiple eruptive pulses. This mechanism requires that the conduit above the magma body be filled with a bed of pyroclasts, and that the vesiculation rate in the magma body be inadequate to sustain continuous eruption. During a repose interval, vesiculation of the magma body would cause gas to flow upward through the bed of pyroclasts. If the rate at which the magma produced gas exceeded the rate at which gas escaped to the atmosphere, the vertical pressure difference across the bed of pyroclastic debris would increase, as would the gas-flow rate. Eventually a gas-flow rate would be achieved that would suddenly diminish the ability of the bed to maintain a pressure difference between the magma body and the atmosphere. The bed of pyroclasts would then be expelled (that is, the relief valve would open) and an eruption would commence. During the eruption, gas would be lost faster than it could be replaced by vesiculation, so the gas-flow rate in the conduit would decrease. Eventually the gas-flow rate would decrease to a value that would be inadequate to expel pyroclasts, so the conduit would again become choked with pyroclasts (that is, the relief valve would close). Another period of repose would commence. The eruption/repose sequence would be repeated until gas-production rates were inadequate to reopen the valve, either because the depth of the pyroclast bed had become too great, the volatile content of the magma had become too low, or the magma had been expended. A timed sequence of photographs of a pyroclastic density flow on August 7 indicates that, in general, the velocity of the flow front was determined by the underlying topography. Observations and details of the velocity/topography relationship suggest that both pyroclastic flows and pyroclastic surges formed. The following mechanism is consistent with the data. During initial fountain collapse and when the flow passed over steep, irregular terrain, a highly inflated suspension of gases and pyroclasts formed. In this suspension, the pyroclasts underwent rapid differential settling according to size and density; a relatively low-concentration, fine-grained upper phase formed over a relatively high-concentration coarse-grained phase. The low-particle-concentration phase (the pyroclastic surge) was subject to lower internal friction than the basal high-concentration phase (the pyroclastic flow), and so accelerated away from it. The surge advanced until it had deposited so much of its solid fraction that its net density became less than that of the ambient air. At this point it rose convectively off the ground, quickly decelerated, and was overtaken by the pyroclastic flow. The behavior of the flow of August 7 suggests that a pyroclastic density flow probably expands through the ingestion of ai

SNC Oxygen Fugacity Recorded in Pyroxenes and its Implications for the Oxidation State of the Martian Interior: An Experimental and Analytical Study

NASA Technical Reports Server (NTRS)

McCanta, M. C.; Rutherford, M. J.

2003-01-01

Knowledge of the oxidation state of a magma is critical as it is one of the parameters which controls the nature and composition of the resulting crystals. In terrestrial magmatic systems, oxygen fugacity (fo2) is known to vary by over nine orders of magnitude. With variations of this magnitude, understanding the compositional differences, phase changes, and crystallization sequence variations, caused by the magma fo2, is essential in deciphering the origin of all igneous rocks. Magmatic oxidation state is of great importance in that it reflects the degree of oxidation of the source region and can provide insight into magmatic processes, such as metasomatism, degassing, and assimilation, which may have changed them. Carmichael [1991] argues that most magmas are unlikely to have their redox states altered from those of their source region. This assumption allows for estimation of the oxidation state of planetary interiors. Conversely, it is known that the fo2 of the magma can be affected by other processes, which occur outside of the source region and therefore, the oxidation state may record those too. Processes which could overprint source region fugacities include melt dehydrogenation or other volatile loss, water or melt infiltration, or assimilation of oxidized or reduced wallrock. Understanding which of these processes is responsible for the redox state of a magma can provide crucial information regarding igneous processes and other forces active in the region. The composition of the SNC basalts and their widely varying proposed oxidation states raise some interesting questions. Do the SNC meteorites have an oxidized or reduced signature? What was the oxygen fugacity of the SNC source region at the time of melt generation? Is the fugacity calculated for the various SNC samples the fugacity of the magma source region or was it overprinted by later events? Are there different oxidation states in the Martian interior or a single one? This proposal seeks to address all of these questions.

A Chill Sequence to the Bushveld Complex - Insight into the First Stages of Emplacement and the Parental Magmas to the World's Largest Layered Intrusion

NASA Astrophysics Data System (ADS)

Wilson, A.

2012-04-01

Evidence of the initial stages of magma emplacement in large mafic chambers is commonly lacking because of resorption of early-formed chills and complicated by the fact that the first magmas that entered the chamber were usually more evolved than the true parental magma. Deep drilling has revealed a rare occurrence of a chill sequence from the eastern Bushveld Complex at the base of a previously unrecognized thick succession of ultramafic rocks that forms part of the Lower Zone. The chill sequence (1.8 m thick) includes a true chill against quartzite floor rock, crystalline quench textured and orthopyroxene spinifex textured rocks. Importantly the chill composition represents a relatively evolved magma formed by the separation of high-Mg olivines prior to its emplacement, probably in a conduit or a pre-chamber. An overlying pyroxene dunite represents the extract that gave rise to the chill and was emplaced either as a crystal slurry derived from the feeder conduit or as the crystallization product from a slightly later influx of primitive magma of komatiitic composition. This highly-Mg rich pyroxene dunite most likely acted as a barrier to the thermal erosion of the chill sequence as the chamber filled. The olivine in the pyroxene dunite layer is the most primitive yet recorded for the Bushveld Complex at Mg# 0.915, and the cores of associated orthopyroxene are Mg# 0.93. Compositions of the orthopyroxene in the quench and spinifex textured units range from Mg# 0.91 to 0.72 and preserve cores close to the original liquidus as well as tracking the complete in-situ solidification process. Olivine contains abundant dendritic exsolution structures of Cr-spinel and Al-rich clinopyroxene indicating that they formed at high temperature from incorporation of Ca, Al and Cr into olivine, with little time to equilibrate before emplacement. Chromite in the section is the most primitive yet recorded for the Bushveld Complex. The komatiite magma that was initially emplaced into the Bushveld chamber contained 19-20% MgO but trace element analysis indicates that it was derived from melting of a more primitive komatiite source which digested about 40% of typical Kaapvaal basement to give the strong crustal signature represented by trace elements and Sr isotopes. The evolved B1 magma, which compositionally is only broadly constrained, is regarded as the parental magma to the Lower and Critical Zones, but this is shown to represent a number of different magmas also derived from a komatiitic source with relatively high degrees of crustal contamination. The komatiite source to the Bushveld magmas could have been derived from subducted Archean ocean crust such as the silica- rich but highly depleted Commondale-type komatiites, as well as Barberton-type komatiites and komatiitic basalts. A mantle peridotite source is not considered a suitable bulk source because the Ni content in the Bushveld olivines (up to 4000 ppm) is indicative of a pyroxenite source in the mantle.

Timing of magmatism following initial convergence at a passive margin, southwestern U.S. Cordillera, and ages of lower crustal magma sources

USGS Publications Warehouse

Barth, A.P.; Wooden, J.L.

2006-01-01

Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali-calcic Fe- and Sr-enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal-miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo-Triassic intrusion ages, and a prolonged postemplacement thermal history within the long-lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc. ?? 2006 by The University of Chicago. All rights reserved.

Crustal forensics in arc magmas

NASA Astrophysics Data System (ADS)

Davidson, Jon P.; Hora, John M.; Garrison, Jennifer M.; Dungan, Michael A.

2005-01-01

The geochemical characteristics of continental crust are present in nearly all arc magmas. These characteristics may reflect a specific source process, such as fluid fluxing, common to both arc magmas and the continental crust, and/or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment, or via contamination during differentiation. Resolving the relative mass contributions of juvenile, mantle-derived material, versus that derived from pre-existing crust of the upper plate, and providing these estimates on an element-by-element basis, is important because: (1) we want to constrain crustal growth rates; (2) we want to quantitatively track element cycling at convergent margins; and (3) we want to determine the origin of economically important elements and compounds. Traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis. Studies of suites from multiple magmatic systems along arcs, for which differentiation effects can be individually constrained, can be used to extrapolate to potential source compositions. In the Lesser Antilles Arc, for example, differentiation trends from individual volcanoes are consistent with open-system evolution. However, such trends do not project back to a common primitive magma composition, suggesting that differentiation modifies magmas that were derived from distinct mantle sources. We propose that such approaches should now be complemented by petrographically constrained mineral-scale isotope and trace element analysis to unravel the contributing components to arc magmas. This innovative approach can: (1) better constrain true end-member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks; (2) better determine magmatic evolution processes from core-rim isotopic or trace element profiles from the phases contained in magmas; and (3) constrain rates of differentiation by applying diffusion-controlled timescales to element profiles. An example from Nguaruhoe Volcano, New Zealand, underscores the importance of such a microsampling approach, showing that mineral isotopic compositions encompass wide ranges, that whole-rock isotopic compositions are consequently simply element-weighted averages of the heterogeneous crystal cargo, and that open-system evolution is proved by core-rim variations in Sr isotope ratios. Nguaruhoe is just one of many systems examined through microanalytical approaches. The overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic, but are inherited from various sources. The implication of this realization is that the interpretation of whole-rock isotopic data, including the currently popular U-series, needs careful evaluation in the context of petrographic observations.

Variations in magma supply rate at Kilauea Volcano, Hawaii

USGS Publications Warehouse

Dvorak, John J.; Dzurisin, Daniel

1993-01-01

When an eruption of Kilauea lasts more than 4 months, so that a well-defined conduit has time to develop, magma moves freely through the volcano from a deep source to the eruptive site at a constant rate of 0.09 km3/yr. At other times, the magma supply rate to Kilauea, estimated from geodetic measurements of surface displacements, may be different. For example, after a large withdrawal of magma from the summit reservoir, such as during a rift zone eruption, the magma supply rate is high initially but then lessens and exponentially decays as the reservoir refills. Different episodes of refilling may have different average rates of magma supply. During four year-long episodes in the 1960s, the annual rate of refilling varied from 0.02 to 0.18 km3/yr, bracketing the sustained eruptive rate of 0.09 km3/yr. For decade-long or longer periods, our estimate of magma supply rate is based on long-term changes in eruptive rate. We use eruptive rate because after a few dozen eruptions the volume of magma that passes through the summit reservoir is much larger than the net change of volume of magma stored within Kilauea. The low eruptive rate of 0.009 km3/yr between 1840 and 1950, compared to an average eruptive rate of 0.05 km3/yr since 1950, suggests that the magma supply rate was lower between 1840 and 1950 than it has been since 1950. An obvious difference in activity before and since 1950 was the frequency of rift zone eruptions: eight rift zone eruptions occurred between 1840 and 1950, but more than 20 rift zone eruptions have occurred since 1950. The frequency of rift zone eruptions influences magma supply rate by suddenly lowering pressure of the summit magma reservoir, which feeds magma to rift zone eruptions. A temporary drop of reservoir pressure means a larger-than-normal pressure difference between the reservoir and a deeper source, so magma is forced to move upward into Kilauea at a faster rate.

Basalt generation at the Apollo 12 site. Part 2: Source heterogeneity, multiple melts, and crustal contamination

NASA Technical Reports Server (NTRS)

Neal, Clive R.; Hacker, Matthew D.; Snyder, Gregory A.; Taylor, Lawrence A.; Liu, Yun-Gang; Schmitt, Roman A.

1994-01-01

The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and late-stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile.

Geothermal Energy: Tapping the Potential

ERIC Educational Resources Information Center

Johnson, Bill

2008-01-01

Ground source geothermal energy enables one to tap into the earth's stored renewable energy for heating and cooling facilities. Proper application of ground-source geothermal technology can have a dramatic impact on the efficiency and financial performance of building energy utilization (30%+). At the same time, using this alternative energy…

40 CFR 63.11528 - What are the performance test and compliance requirements for new and existing sources?

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 CFR part 60). The test must be conducted for at least 60 minutes and shall include tapping the... of the readings over the furnace cycle (tap to tap) or 60 minutes, whichever is longer. If VE are...

Joint analysis of geodetic and earthquake fault-plane solution data to constrain magmatic sources: A case study from Kīlauea Volcano

USGS Publications Warehouse

Wauthier, Christelle; Roman, Diana C.; Poland, Michael

2016-01-01

A joint analysis of geodetic and seismic datasets from Kīlauea Volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex, multi-source system. At the end of 2003, Kīlauea's summit began a four-year-long period of inflation due to a surge in magma supply to the volcano. In 2006, for the first time since 1982, Kīlauea's Southwest Rift Zone (SWRZ) also experienced inflation. To investigate the characteristics of active magma sources and the nature of their interactions with faults in the SWRZ during 2006, we integrate, through Coulomb stress modeling, contemporary geodetic data from InSAR and GPS with a new catalogue of double-couple fault-plane solutions for volcano-tectonic earthquakes. We define two periods of inflation during 2006 based on the rate of deformation measured in daily GPS data, spanning February to 15 March 2006 (Period 1) and 16 March to 30 September 2006 (Period 2). InSAR data for these two periods are inverted to determine the position, change in size, and shape of inflation sources in each period. Our new models are consistent with microseismic activity from each period. They suggest that, during Period 1, deformation in the SWRZ can be explained by pressurization of magma in a spherical reservoir beneath the south caldera, and that, during Period 2, magma was also aseismically intruded farther to the southwest into the SWRZ along a sub-horizontal plane. Our Coulomb stress analysis shows that the microseismicity recorded in the SWRZ is induced by overpressurization of the south caldera reservoir, and not by magma intrusion into the SWRZ. This study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation.

Joint analysis of geodetic and earthquake fault-plane solution data to constrain magmatic sources: A case study from Kīlauea Volcano

NASA Astrophysics Data System (ADS)

Wauthier, Christelle; Roman, Diana C.; Poland, Michael P.

2016-12-01

A joint analysis of geodetic and seismic datasets from Kīlauea Volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex, multi-source system. At the end of 2003, Kīlauea's summit began a four-year-long period of inflation due to a surge in magma supply to the volcano. In 2006, for the first time since 1982, Kīlauea's Southwest Rift Zone (SWRZ) also experienced inflation. To investigate the characteristics of active magma sources and the nature of their interactions with faults in the SWRZ during 2006, we integrate, through Coulomb stress modeling, contemporary geodetic data from InSAR and GPS with a new catalogue of double-couple fault-plane solutions for volcano-tectonic earthquakes. We define two periods of inflation during 2006 based on the rate of deformation measured in daily GPS data, spanning February to 15 March 2006 (Period 1) and 16 March to 30 September 2006 (Period 2). InSAR data for these two periods are inverted to determine the position, change in size, and shape of inflation sources in each period. Our new models are consistent with microseismic activity from each period. They suggest that, during Period 1, deformation in the SWRZ can be explained by pressurization of magma in a spherical reservoir beneath the south caldera, and that, during Period 2, magma was also aseismically intruded farther to the southwest into the SWRZ along a sub-horizontal plane. Our Coulomb stress analysis shows that the microseismicity recorded in the SWRZ is induced by overpressurization of the south caldera reservoir, and not by magma intrusion into the SWRZ. This study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation.

Incremental growth of an upper crustal, A-type pluton, Argentina: Evidence of a re-used magma pathway

NASA Astrophysics Data System (ADS)

Alasino, Pablo H.; Larrovere, Mariano A.; Rocher, Sebastián; Dahlquist, Juan A.; Basei, Miguel A. S.; Memeti, Valbone; Paterson, Scott; Galindo, Carmen; Macchioli Grande, Marcos; da Costa Campos Neto, Mario

2017-07-01

Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (< 2 kbar). One of these, the San Blas intrusive complex formed over millions of years (≤ 2-3 m.y.) through three periods of magma additions that are characterized by variations in magma sources and emplacement style. The main units, mostly felsic granitoids, have U-Pb zircon crystallization ages within the error range. From older to younger (based on cross-cutting relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNdt = - 5.8 and εHft in zircon = - 2.9 to - 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNdt = + 0.6 to - 4.8 and εHft in zircon = + 3 to - 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include older hot magma mush. The latter results in ductile downward flow of older, during rise of younger magma. Such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted.

Intrusion of granitic magma into the continental crust facilitated by magma pulsing and dike-diapir interactions: Numerical simulations

NASA Astrophysics Data System (ADS)

Cao, Wenrong; Kaus, Boris J. P.; Paterson, Scott

2016-06-01

We conducted a 2-D thermomechanical modeling study of intrusion of granitic magma into the continental crust to explore the roles of multiple pulsing and dike-diapir interactions in the presence of visco-elasto-plastic rheology. Multiple pulsing is simulated by replenishing source regions with new pulses of magma at a certain temporal frequency. Parameterized "pseudo-dike zones" above magma pulses are included. Simulation results show that both diking and pulsing are crucial factors facilitating the magma ascent and emplacement. Multiple pulses keep the magmatic system from freezing and facilitate the initiation of pseudo-dike zones, which in turn heat the host rock roof, lower its viscosity, and create pathways for later ascending pulses of magma. Without diking, magma cannot penetrate the highly viscous upper crust. Without multiple pulsing, a single magma body solidifies quickly and it cannot ascent over a long distance. Our results shed light on the incremental growth of magma chambers, recycling of continental crust, and evolution of a continental arc such as the Sierra Nevada arc in California.

The role of water in the petrogenesis of Marina trough magmas

NASA Astrophysics Data System (ADS)

Stolper, Edward; Newman, Sally

1994-02-01

Most variations in composition among primitive basalts from the Mariana back-arc trough can be explained by melting mixtures of an N-type mid-ocean ridge basalt (NMORB) mantle source and an H2O rich component, provided the degree of melting is positively and approximately linearly correlated with the proportion of the H2O-rich component in the mixture. We conclude that the degrees of melting by which Mariana trough magmas are generated increase from magmas similar to NMORB, through more H2O-enriched basalts, to 'arc-like' basalts, and that this increase is due to the lowering of the solidus of mantle peridotite that accompanies addition of the H2O-rich component. The H2O-rich component is likely to be ultimately derived from fluid from a subducting slab, but we propose that by the time fluids reach the source regions of Mariana trough basalts, they have interacted with sufficient mantle material that for all but the most incompatible of elements (with respect to fluid-mantle interaction), they are in equilibrium with the mantle. In contrast, fluids added to the source regions of Mariana island-arc magmas have typically interacted with less mantle and thus retain the signature of slab-derived fluids to varying degrees for all but the most compatible elements. Primitive Mariana arc basalts can be generated by melting mixtures of such incompletely exchanged slab-derived fluids and sources similar to NMORB-type mantle sources, but the degrees of melting are typically higher than those of Mariana trough NMORB and the sources have been variably depleted relative to the back-arc sources by previous melt extraction. This depletion may be related to earlier extraction of back-arc basin magmas or may evolve by repeated fluxing of the sources as fluid is continually added to them in the regions of arc magma generation. If fluid with partitioning behavior relative to the solid mantle similar to that deduced for the H2O-rich component involved in the generation of Mariana trough basalts were extracted from primitive mantle, the residual mantle would have many of the minor and trace element characteristics of typical oceanic upper mantle; primitive mantle enriched in such fluid would be a satisfactory source for the continental crust in terms of its trace and minor element chemical composition.

Element variations in rhyolitic magma resulting from gas transport

NASA Astrophysics Data System (ADS)

Berlo, K.; Tuffen, H.; Smith, V. C.; Castro, J. M.; Pyle, D. M.; Mather, T. A.; Geraki, K.

2013-11-01

Tuffisite veins are glass-filled fractures formed when magma fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from magma. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study magma degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajökull (Iceland) and Chaitén (Chile) were studied in detail. The tuffisite vein from Torfajökull is from a shallow dissected conduit (∼70 ka) that fed a degassed lava flow, while the sample from Chaitén was a bomb ejected during the waning phases of Plinian activity in May 2008. The results of detailed in situ chemical analyses (synchrotron XRF, FTIR, LA-ICP-MS) show that in both veins larger vesiculated fragments are enriched in volatile elements (Torfajökull: H, Li, Cl; Chaitén: Li, Cl, Cu, Zn, As, Sn, Sb) compared to the host, while the surrounding smaller particles are depleted in the Torfajökull vein (Li, Cl, Zn, Br, Rb, Pb), but enriched in the Chaitén vein (K, Cu, Zn, As, Mo, Sb, Pb). The lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors. The Torfajökull vein had a longer lifespan (∼a day) and low particle velocities (∼cm/s), while the Chaitén vein was shorter lived (<1 h) with a high gas velocity (∼m/s). These differences are consistent with the contrasting eruption mechanisms (effusive vs. explosive). The amount of magma that degassed through the Chaitén vein is more than ten times the volume of the vein itself, requiring the vein to tap into pre-exsolved gas pockets. This study highlights that tuffisite veins are highly efficient gas pathways and thereby impart chemical diversity in volatile elements on the melt.

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth’s oxygenation

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

Brounce, Maryjo; Stolper, Edward; Eiler, John

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The leastmore » degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.« less

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth's oxygenation.

PubMed

Brounce, Maryjo; Stolper, Edward; Eiler, John

2017-08-22

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity ( f O 2 ). Volcanic degassing is a source of these elements to Earth's surface; therefore, variations in mantle f O 2 may influence the f O 2 at Earth's surface. However, degassing can impact magmatic f O 2 before or during eruption, potentially obscuring relationships between the f O 2 of the solid Earth and of emitted gases and their impact on surface f O 2 We show that low-pressure degassing resulted in reduction of the f O 2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher f O 2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower f O 2 than modern magmas. Estimates of f O 2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth’s oxygenation

PubMed Central

Stolper, Edward; Eiler, John

2017-01-01

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere. PMID:28784788

Redox variations in Mauna Kea lavas, the oxygen fugacity of the Hawaiian plume, and the role of volcanic gases in Earth's oxygenation

NASA Astrophysics Data System (ADS)

Brounce, Maryjo; Stolper, Edward; Eiler, John

2017-08-01

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.

Application of Think Aloud Protocols for Examining and Confirming Sources of Differential Item Functioning Identified by Expert Reviews

ERIC Educational Resources Information Center

Ercikan, Kadriye; Arim, Rubab; Law, Danielle; Domene, Jose; Gagnon, France; Lacroix, Serge

2010-01-01

This paper demonstrates and discusses the use of think aloud protocols (TAPs) as an approach for examining and confirming sources of differential item functioning (DIF). The TAPs are used to investigate to what extent surface characteristics of the items that are identified by expert reviews as sources of DIF are supported by empirical evidence…

Extremely High Magma Emplacement Rates Recorded in the Golden Horn Batholith, WA

NASA Astrophysics Data System (ADS)

Eddy, M. P.; Bowring, S. A.; Tepper, J. H.; Miller, R. B.

2015-12-01

High SiO2 rhyolites emplaced during 'super-eruptions' demonstrate that large volumes of eruptible magma can exist in the upper crust. However, the timescale over which the magma reservoirs that source these eruptions are built remains controversial. Thermal models suggest that magma emplacement rates need to be > 0.005-0.01 km3/yr in order to accumulate enough eruptible magma to source a 'super-eruption'. Yet, these rates are higher than the time-averaged rates (< 0.001 km3/yr) for nearly all well-studied granitoid plutonic complexes. This disparity contradicts geologic evidence suggesting that the high SiO2 rhyolites emplaced during 'super-eruptions' are extracted from crystal rich magma chambers that should be preserved in the geologic record as granodioritic and granitic plutons. We quantify time-averaged magma emplacement rates for the upper crustal Golden Horn batholith, WA based on new geologic mapping and U-Pb zircon CA-IDTIMS geochronology. The batholith is exposed over 310 km3 and can be separated in the field into five intrusive units. High topography allows the 3D geometry of each phase to be constrained and their volumes range from < 100 km3 to > 400 km3. U-Pb zircon geochronology reveals that four of the five phases were assembled incrementally and distinct zircon populations from samples within these phases suggest that individual magmatic pulses had fully crystallized before the next arrived. However, six nearly identical U-Pb zircon dates from a > 400 km3 rapakivi granite show that this phase was built in ca. 50 kyr and that large portions may have been emplaced nearly simultaneously. The implied emplacement rate for this phase (≥ 0.008 km3/yr) is in agreement with those predicted for assembly of the upper crustal magma chambers that source 'super-eruptions', and it may provide a rare and unprecedented opportunity to study the processes that occur in such chambers.

Episodic inflation events at Akutan Volcano, Alaska, during 2005-2017

NASA Astrophysics Data System (ADS)

Ji, Kang Hyeun; Yun, Sang-Ho; Rim, Hyoungrea

2017-08-01

Detection of weak volcano deformation helps constrain characteristics of eruption cycles. We have developed a signal detection technique, called the Targeted Projection Operator (TPO), to monitor surface deformation with Global Positioning System (GPS) data. We have applied the TPO to GPS data collected at Akutan Volcano from June 2005 to March 2017 and detected four inflation events that occurred in 2008, 2011, 2014, and 2016 with inflation rates of about 8-22 mm/yr above the background trend at a near-source site AV13. Numerical modeling suggests that the events should be driven by closely located sources or a single source in a shallow magma chamber at a depth of about 4 km. The inflation events suggest that magma has episodically accumulated in a shallow magma chamber.

The Krafla International Testbed (KMT): Ground Truth for the New Magma Geophysics

NASA Astrophysics Data System (ADS)

Brown, L. D.; Kim, D.; Malin, P. E.; Eichelberger, J. C.

2017-12-01

Recent developments in geophysics such as large N seismic arrays , 4D (time lapse) subsurface imaging and joint inversion algorithms represent fresh approaches to delineating and monitoring magma in the subsurface. Drilling at Krafla, both past and proposed, are unique opportunities to quantitatively corroborate and calibrate these new technologies. For example, dense seismic arrays are capable of passive imaging of magma systems with resolutions comparable to that achieved by more expensive (and often logistically impractical) controlled source surveys such as those used in oil exploration. Fine details of the geometry of magma lenses, feeders and associated fluid bearing fracture systems on the scale of meters to tens of meters are now realistic targets for surface seismic surveys using ambient energy sources, as are detection of their temporal variations. Joint inversions, for example of seismic and MT measurements, offer the promise of tighter quantitative constraints on the physical properties of the various components of magma and related geothermal systems imaged by geophysics. However, the accuracy of such techniques will remain captive to academic debate without testing against real world targets that have been directly sampled. Thus application of these new techniques to both guide future drilling at Krafla and to be calibrated against the resulting borehole observations of magma are an important step forward in validating geophysics for magma studies in general.

Composition and origin of basaltic magma of the Hawaiian Islands

USGS Publications Warehouse

Powers, H.A.

1955-01-01

Silica-saturated basaltic magma is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This magma may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma. Silica-deficient basaltic magma, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of magma are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable magma under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.

From Magma Fracture to a Seismic Magma Flow Meter

NASA Astrophysics Data System (ADS)

Neuberg, J. W.

2007-12-01

Seismic swarms of low-frequency events occur during periods of enhanced volcanic activity and have been related to the flow of magma at depth. Often they precede a dome collapse on volcanoes like Soufriere Hills, Montserrat, or Mt St Helens. This contribution is based on the conceptual model of magma rupture as a trigger mechanism. Several source mechanisms and radiation patterns at the focus of a single event are discussed. We investigate the accelerating event rate and seismic amplitudes during one swarm, as well as over a time period of several swarms. The seismic slip vector will be linked to magma flow parameters resulting in estimates of magma flux for a variety of flow models such as plug flow, parabolic- or friction controlled flow. In this way we try to relate conceptual models to quantitative estimations which could lead to estimations of magma flux at depth from seismic low-frequency signals.

Constraints on dike propagation from continuous GPS measurements

USGS Publications Warehouse

Segall, P.; Cervelli, Peter; Owen, S.; Lisowski, M.; Miklius, Asta

2001-01-01

The January 1997 East Rift Zone eruption on Kilauea volcano, Hawaii, occurred within a network of continuous Global Positioning System (GPS) receivers. The GPS measurements reveal the temporal history of deformation during dike intrusion, beginning ??? 8 hours prior to the onset of the eruption. The dike volume as a function of time, estimated from the GPS data using elastic Green's functions for a homogeneous half-space, shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time. These observations are inconsistent with simple models of dike propagation, which predict accelerating dike volume up to the time of the eruption and little or no change thereafter. Deflationary tilt changes at Kilauea summit mirror the inferred dike volume history, suggesting that the rate of dike propagation is limited by flow of magma into the dike. A simple, lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption (rather than intrusion) is favored by high initial dike pressures, compressional stress states, large, compressible magma reservoirs, and highly conductive conduits linking the dike and source reservoirs. Comparison of model predictions to the observed dike volume history, the ratio of erupted to intruded magma, and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits. Interpretation is complicated by the presence of multiple source reservoirs, magma vesiculation and cooling, as well as spatial variations in dike-normal stress. Reinflation of the summit magma chamber following the eruption was measured by GPS and accompanied a rise in the level of the Pu'u O'o lava lake. For a spheroidal chamber these data imply a summit magma chamber volume of ??? 20 km3, consistent with recent estimates from seismic tomography. Continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems. Copyright 2001 by the American Geophysical Union.

Constraints on dike propagation from continuous GPS measurements

NASA Astrophysics Data System (ADS)

Segall, Paul; Cervelli, Peter; Owen, Susan; Lisowski, Mike; Miklius, Asta

2001-09-01

The January 1997 East Rift Zone eruption on Kilauea volcano, Hawaii, occurred within a network of continuous Global Positioning System (GPS) receivers. The GPS measurements reveal the temporal history of deformation during dike intrusion, beginning ˜8 hours prior to the onset of the eruption. The dike volume as a function of time, estimated from the GPS data using elastic Green's functions for a homogeneous half-space, shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time. These observations are inconsistent with simple models of dike propagation, which predict accelerating dike volume up to the time of the eruption and little or no change thereafter. Deflationary tilt changes at Kilauea summit mirror the inferred dike volume history, suggesting that the rate of dike propagation is limited by flow of magma into the dike. A simple, lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption (rather than intrusion) is favored by high initial dike pressures, compressional stress states, large, compressible magma reservoirs, and highly conductive conduits linking the dike and source reservoirs. Comparison of model predictions to the observed dike volume history, the ratio of erupted to intruded magma, and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits. Interpretation is complicated by the presence of multiple source reservoirs, magma vesiculation and cooling, as well as spatial variations in dike-normal stress. Reinflation of the summit magma chamber following the eruption was measured by GPS and accompanied a rise in the level of the Pu'u O'o lava lake. For a spheroidal chamber these data imply a summit magma chamber volume of ˜20 km3, consistent with recent estimates from seismic tomography. Continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems.

Crustal Deformation Associated With the 2000 Eruption and Degassing Process of Miyakejima, Izu Islands, Japan

NASA Astrophysics Data System (ADS)

Nishimura, T.; Ozawa, S.; Murakami, M.; Sagiya, T.; Yarai, H.; Tada, T.; Kaidzu, M.

2001-12-01

Miyakejima is located in the northern part of the Izu Islands lying along the boundary between the Pacific plate and the Philippine Sea plate. Miyakejima volcano erupted on Miyakejima is located in the northern part of the Izu Islands which are a chain of volcanoes lying along the boundary between the Pacific plate and the Philippine Sea plate. Miyakejima volcano erupted on June 27, 2000 after the quiescence of 17 years. First eruption is a small submarine eruption 1.5km off the western coast of Miyakejima. Subsequently, several summit eruptions as tephra ejecta occurred in July and August 2000. The summit collapsed just after the first summit eruption and a caldera was formed for 40 days. Collapsed volume and erupted volume are estimated to be 0.6km3 and 0.02km3, respectively. In September 2000, the collapse caldera started emitting a large amount of volcanic gasses. A peak amount of degassing SO2 is ~70000 ton/day in the period from October to December 2000. Amount of volcanic gas is decreasing gradually and is 15000 ton/day (SO2 ) now. However, it is still larger than other active volcanoes. Permanent GPS data reveals the spatial pattern and time evolution of ground deformation. Inflation of Miyakejima was observed by continuous GPS and leveling before the 2000 eruption. The observed displacements associated with the 2000 eruption show radial pattern suggesting shrinking of the island and subsidence. This pattern continues for 14 months from July 2000. Though the rate of crustal deformation is almost constant from July to August 2000, it is decreasing exponentially with a time constant of ~150days from September 2000. We assumed a point deflation source and inverted the observed displacement to estimate parameters of the point source. Volume decrease and depth of the deflation source is 0.12km3 and 4.2km from July to August 2000. We interpret that it is the squeezing of magma from a magma chamber of Miyakejima volcano. The displacement observed in neighbor islands suggests that the squeezed magma and collapsed material of Miyakejima migrated northwestward by as much as 30km in the form of a dike intrusion. Volume decrease and depth of the deflation source is 2.9km and 0.016km3 from September 2000 to May 2001. Decreasing rate of the deflation source is an order of magnitude smaller than that of the previous period. We considered that degassing from magma mainly causes the deflation of magma chamber after September 2000. The decreasing rate estimated from crustal deformation was quantitatively consistent with that estimated from the rate of the emitting volcanic gasses (Kazahaya, personal communication). This consideration suggests that the magma does not migrate any more and that the magma chamber is in closed system. However, recent rate of the deformation is much smaller than that calculated from the degassing rate. This implies that new magma is supplied to the magma chamber from deeper region or that the depth of magma head becomes deeper in a conduit from the magma chamber to the caldera.

Probing the Source of Explosive Volcanic Eruptions (Sergey Soloviev Medal Lecture)

NASA Astrophysics Data System (ADS)

Eichelberger, John C.

2015-04-01

What if we knew where magma is located under a volcano and its current state? Such information would transform volcanology. For extreme events, we typically know where the vulnerabilities are: people, lifelines, and critical infrastructure, but seldom do we know the 'source term' beforehand. For restless calderas such as Campi Flegrei, Italy and Yellowstone, USA, the threat is silicic magma within the caldera itself. Great effort has gone into finding such bodies through surface measurements. 'Discovery' is declared when consensus is achieved. But there is a difference between consensus and knowledge. By following certain conventions in finding magma bodies (aseismic volume, seismic attenuation, Mogi source location, water and CO2 content of melt inclusions) and depicting them in accepted ways (oblate spheroids or lenses with an impossible solid/liquid boundary discontinuity), we perpetuate myths that mislead even ourselves. The consensus view of the Long Valley Caldera, USA, magma reservoir has evolved over 40 years from a 104 km3 balloon to two tiny pockets of magma, in part because drilling revealed a temperature of 100°C at 3 km depth over the 'balloon'. Oil and gas exploration is free of fanciful reservoirs because there is ground truth. Geophysics and geology define a possible reservoir and a well is drilled. If oil is not there, the model needs revision. The situation is worse for conditions of magma storage. The heretofore-unknowable roof zone of magma chambers has been invoked for separating melt from crystals and/or for accumulating vapor and evolved magma leading to eruption. Anything is possible when there are no data. The accidental (but technically remarkable) drilling discovery of rhyolite magma at 2,100 m depth under Krafla Caldera, Iceland by Landsvirkjun Co. and the Iceland Deep Drilling Project opens the door to properly detect magma and to understand how magma evolves, energizes hydrothermal systems, and erupts. A new project before the International Continental Scientific Drilling Program (ICDP) would continuously core through the margin of the magma body, accompanied by state-of-the-art geophysics, geochemical analyses and 3-D mass/heat transport modeling. Coring of molten rock has been conducted with success in lava lakes. Gradients in phase assemblage and composition will provide definitive tests of models of mass/heat transfer and magma evolution. By knowing 'the answer', techniques for finding magma will likewise be tested, making Krafla an international magma laboratory. In fact, Krafla may resemble the state of neighboring Askja Caldera system prior its 1875 eruption, with hidden rhyolite being brewed in a basalt-fired caldera crucible. Additionally, the observed high permeability and sustained power output from the magma body's margin implies self-sustained thermal fracturing, i.e. an 'Enhanced Geothermal System' an order of magnitude more powerful than conventional geothermal. The cost should be balanced against the higher cost of ignorance. For tsunamis, Sergey Soloviev showed there is no substitute for direct measurements at depth, despite technical and economic obstacles. He also led the way in Russian - American cooperation on natural hazards, thereby mitigating the risk of the ultimate hazard, of humans to each other.

Thermally-assisted Magma Emplacement Explains Restless Calderas.

PubMed

Amoruso, Antonella; Crescentini, Luca; D'Antonio, Massimo; Acocella, Valerio

2017-08-11

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei caldera, Italy. Campi Flegrei experienced at least 4 major unrest episodes in the last decades. Our results indicate that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust. Our thermal models show that this repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth ~3 ka before the last eruption. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks. Our model of thermally-assisted unrest may have a wider applicability, possibly explaining also the dynamics of other restless calderas.

New insights on dyke width and upward velocity

NASA Astrophysics Data System (ADS)

Taisne, B.; Jaupart, C.; Tait, S.

2012-04-01

Striking observations have been made that challenge our understanding of magma migration through the Earth's crust. How may a volatile rich magma stall at shallow depth as a growing crypto-dome such as during the 1980 Mount Saint Helens eruption? How can we explain the width of the 2005 mega-dyke intrusion in Afar, that attained more than 8 meters with a very small amount of magma emitted at the surface? We show that changes in the geometry and the dynamics of the propagation can be attributed to density variations in the host rocks, to solidification, to volatile exsolution and expansion or to changes in the input flux of magma at depth. We focus on the relationship between dyke width and ascent rate. Shallow levels are commonly made of low density rocks or volcanic deposits with strong impact on dyke ascent. The dynamics and width of the upper part of the dyke (the nose region) are determined by a local buoyancy balance, independently of the total buoyancy of the magma column between source and tip. In such conditions, the dyke swells and slows down and, in some cases, may not breach the surface. Using laboratory experiments we show that solidification of the magma may lead to a regime of intermittent propagation, even with constant physical conditions at the source. Interestingly the time between two steps can be related to the input flux at the source region. With volatile-bearing magmas, dyke propagation proceeds in two markedly different ways depending on whether or not fragmentation occurs. With no fragmentation, magma expansion leads to acceleration and thinning of the dyke. With fragmentation, the sharp drop of head loss that occurs in gas-rich fragmented material generates large internal overpressure and swelling of the nose region, leading to deceleration of the dyke. All the above effects lead to rapid and large changes of ascent rate. Large variations of magma flux at the source would be required to have similar impacts on dyke propagation. In an extreme case, arrest of the feeding at depth leads to a gradual decrease of upward velocity and thinning of the dyke. Variations of dyke ascent velocity make monitoring of volcanic unrest and prediction of eruption onset uncertain and potentially erroneous. Our models emphasize, however, that such variations are linked to changes of dyke dimensions and width that can be determined using geophysical networks and that allow identification of the physical mechanism at work. Data and physical models, when used in combination, therefore allow useful diagnostic tools for assessing the likelihood and time of an eruption.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2017-02-01

We model the ascent and eruption of lunar mare basalt magmas with new data on crustal thickness and density (GRAIL), magma properties, and surface topography, morphology and structure (Lunar Reconnaissance Orbiter). GRAIL recently measured the broad spatial variation of the bulk density structure of the crust of the Moon. Comparing this with the densities of lunar basaltic and picritic magmas shows that essentially all lunar magmas were negatively buoyant everywhere within the lunar crust. Thus positive excess pressures must have been present in melts at or below the crust-mantle interface to enable them to erupt. The source of such excess pressures is clear: melt in any region experiencing partial melting or containing accumulated melt, behaves as though an excess pressure is present at the top of the melt column if the melt is positively buoyant relative to the host rocks and forms a continuously interconnected network. The latter means that, in partial melt regions, probably at least a few percent melting must have taken place. Petrologic evidence suggests that both mare basalts and picritic glasses may have been derived from polybaric melting of source rocks in regions extending vertically for at least a few tens of km. This is not surprising: the vertical extent of a region containing inter-connected partial melt produced by pressure-release melting is approximately inversely proportional to the acceleration due to gravity. Translating the ∼25 km vertical extent of melting in a rising mantle diapir on Earth to the Moon then implies that melting could have taken place over a vertical extent of up to 150 km. If convection were absent, melting could have occurred throughout any region in which heat from radioisotope decay was accumulating; in the extreme this could have been most of the mantle. The maximum excess pressure that can be reached in a magma body depends on its environment. If melt percolates upward from a partial melt zone and accumulates as a magma reservoir, either at the density trap at the base of the crust or at the rheological trap at the base of the elastic lithosphere, the excess pressure at the top of the magma body will exert an elastic stress on the overlying rocks. This will eventually cause them to fail in tension when the excess pressure has risen to close to twice the tensile strength of the host rocks, perhaps up to ∼10 MPa, allowing a dike to propagate upward from this point. If partial melting occurs in a large region deep in the mantle, however, connections between melt pockets and veins may not occur until a finite amount, probably a few percent, of melting has occurred. When interconnection does occur, the excess pressure at the top of the partial melt zone will rise abruptly to a high value, again initiating a brittle fracture, i.e. a dike. That sudden excess pressure is proportional to the vertical extent of the melt zone, the difference in density between the host rocks and the melt, and the acceleration due to gravity, and could readily be ∼100 MPa, vastly greater than the value needed to initiate a dike. We therefore explored excess pressures in the range ∼10 to ∼100 MPa. If eruptions take place through dikes extending upward from the base of the crust, the mantle magma pressure at the point where the dike is initiated must exceed the pressure due to the weight of the magmatic liquid column. This means that on the nearside the excess pressure must be at least ∼19 ± 9 MPa and on the farside must be ∼29 ± 15 MPa. If the top of the magma body feeding an erupting dike is a little way below the base of the crust, slightly smaller excess pressures are needed because the magma is positively buoyant in the part of the dike within the upper mantle. Even the smallest of these excess pressures is greater than the ∼10 MPa likely maximum value in a magma reservoir at the base of the crust or elastic lithosphere, but the values are easily met by the excess pressures in extensive partial melt zones deeper within the mantle. Thus magma accumulations at the base of the crust would have been able to intrude dikes part-way through the crust, but not able to feed eruptions to the surface; in order to be erupted, magma must have been extracted from deeper mantle sources, consistent with petrologic evidence. Buoyant dikes growing upward from deep mantle sources of partial melt can disconnect from their source regions and travel through the mantle as isolated bodies of melt that encounter and penetrate the crust-mantle density boundary. They adjust their lengths and internal pressure excesses so that the stress intensity at the lower tip is zero. The potential total vertical extent of the resulting melt body depends on the vertical extent of the source region from which it grew. For small source extents, the upper tip of the resulting dike crossing the crust-mantle boundary cannot reach the surface anywhere on the Moon and therefore can only form a dike intrusion; for larger source extents, the dike can reach the surface and erupt on the nearside but still cannot reach the surface on the farside; for even larger source extents, eruptions could occur on both the nearside and the farside. The paucity of farside eruptions therefore implies a restricted range of vertical extents of partial melt source region sizes, between ∼16 and ∼36 km. When eruptions can occur, the available pressure in excess of what is needed to support a static magma column to the surface gives the pressure gradient driving magma flow. The resulting typical turbulent magma rise speeds are ∼10 to a few tens of m s-1, dike widths are of order 100 m, and eruption rates from 1 to 10 km long fissure vents are of order 105 to 106 m3 s-1. Volume fluxes in lunar eruptions derived from lava flow thicknesses and surface slopes or rille lengths and depths are found to be of order 105 to 106 m3 s-1 for volume-limited lava flows and >104 to 105 m3 s-1 for sinuous rilles, with dikes widths of ∼50 m. The lower end of the volume flux range for sinuous rilles corresponds to magma rise speeds approaching the limit set by the fact that excessive cooling would occur during flow up a 30 km long dike kept open by a very low excess pressure. These eruptions were thus probably fed by partial melt zones deep in the mantle. Longer eruption durations, rather than any subtle topographic slope effects, appear to be the key to the ability of these flows to erode sinuous rille channels. We conclude that: (1) essentially all lunar magmas were negatively buoyant everywhere within the crust; (2) positive excess pressures of at least 20-30 MPa must have been present in mantle melts at or below the crust-mantle interface to drive magmas to the surface; (3) such pressures are easily produced in zones of partial melting by pressure-release during mantle convection or simple heat accumulation from radioisotopes; (4) magma volume fluxes available from dikes forming at the tops of partial melt zones are consistent with the 105 to 106 m3 s-1 volume fluxes implied by earlier analyses of surface flows; (5) eruptions producing thermally-eroded sinuous rille channels involved somewhat smaller volume fluxes of magma where the supply rate may be limited by the rate of extraction of melt percolating through partial melt zones.

Signatures in Martian Volatiles and the Magma Sources of NC Meteorites

NASA Technical Reports Server (NTRS)

Marti, K.; Mathew, K. J.

2004-01-01

We report nitrogen and xenon isotopic signatures in Yamato nakhlites and use the data to assess properties of the magma source of NC meteorites in planet Mars. The Chassigny meteorite was investigated by Floran et al, who classified it as a cumulate dunite with hydrous amphibole-bearing melt inclusions with no preferred orientation of the olivines. Their inferred composition of the parent magma, which was based on electron microprobe analyses, has been questioned. The trace and minor elements in minerals were analyzed in nakhlites and in Chassigny and the authors conclude that nakhlites may represent samples from different horizons of the same lithologic unit, but that Chassigny was not co-magmatic with the nakhlites.

Using cGPS to estimate the magma budget for Soufrière Hills volcano, Montserrat, West Indies

NASA Astrophysics Data System (ADS)

Collinson, Amy; Neuberg, Jurgen; Pascal, Karen

2017-04-01

For over 20 years, Soufrière Hills Volcano, Montserrat has been in a state of volcanic unrest. Intermittent periods of dome building have been punctuated by explosive eruptions and dome collapse events, endangering the lives of the inhabitants of the island. The last episode of active magma extrusion was in February 2010, and the last explosive event (ash venting) in March 2012. Despite a lack of recent eruptive activity, the volcano continues to emit significant volumes of SO2 and shows an ongoing trend of island inflation as indicated by cGPS. Through the aid of three-dimensional numerical modelling, using a finite element method, we model the cGPS data to explore the potential sources of the ongoing island deformation. We consider both magmatic (dykes and chambers) and tectonic sources which result in entirely different interpretations: Whilst a magmatic source suggests the possibility for further eruption, a tectonic source may indicate cessation of volcanic activity. We investigate the effects that different sources (shapes, characters and depths) have on the surface displacement. We demonstrate that whilst a tectonic contribution cannot be completely discounted, the dominant source is magmatic. Consequently, we define a best-fit model which we use to assess the source volume change, and therefore, the potential current magma budget. Based on the similarity in the relative displacement between the cGPS stations at every episode of the eruption, we assume that the displacement for all Phases and Pauses can be explained by the same basic source. Therefore, we interpret the cGPS data with our source model for all the preceding Pauses and Phases to estimate the magma budget feeding the entire eruption. Subsequently, we derive important insights into the potential future eruptive behaviour of the volcano.

Petrology and Physics of Magma Ocean Crystallization

NASA Technical Reports Server (NTRS)

Elkins-Tanton, Linda T.; Parmentier, E. M.; Hess, P. C.

2003-01-01

Early Mars is thought to have been melted significantly by the conversion of kinetic energy to heat during accretion of planetesimals. The processes of solidification of a magma ocean determine initial planetary compositional differentiation and the stability of the resulting mantle density profile. The stability and compositional heterogeneity of the mantle have significance for magmatic source regions, convective instability, and magnetic field generation. Significant progress on the dynamical problem of magma ocean crystallization has been made by a number of workers. The work done under the 2003 MFRP grant further explored the implications of early physical processes on compositional heterogeneity in Mars. Our goals were to connect early physical processes in Mars evolution with the present planet's most ancient observable characteristics, including the early, strong magnetic field, the crustal dichotomy, and the compositional characteristics of the SNC meteorite's source regions as well as their formation as isotopically distinct compositions early in Mars's evolution. We had already established a possible relationship between the major element compositions of SNC meteorite sources and processes of Martian magma ocean crystallization and overturn, and under this grant extended the analysis to the crucial trace element and isotopic SNC signatures. This study then demonstrated the ability to create and end the magnetic field through magma ocean cumulate overturn and subsequent cooling, as well as the feasibility of creating a compositionally- and volumetrically-consistent crustal dichotomy through mode-1 overturn and simultaneous adiabatic melting.

The effects of Venus' thermal structure on buoyant magma ascent

NASA Technical Reports Server (NTRS)

Sakimoto, S. E. H.; Zuber, M. T.

1992-01-01

The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

Long-period seismicity at Redoubt Volcano, Alaska, 1989-1990 related to magma degassing

USGS Publications Warehouse

Morrissey, M.M.

1997-01-01

The mass of exsolved magmatic H2O is estimated and compared to the mass of superheated steam (25-50 Mtons) released through the resonating crack producing the December 13-14, 1989 swarm of long-period seismic events at Redoubt Volcano. Results indicate degassing of a H2O-CO2-SO2-saturated magma upon ascending from at least 12 km to 3-4 km beneath the crater as the source of the superheated steam. The mass of exsolved H2O (3.2-250 Mtons) is estimated from solubility diagrams of H2O-CO2-saturated silicate melts for the ascent history of the Redoubt magmas. Crystal size distribution, seismological, petrological, and geochemical data are used to constrain the ascent history of the two andesitic magmas prior to the eruption. Two stages of crystallization are inferred from crystal size distributions of plagioclase crystals in andesites erupted in December 1989. The first stage occurred 30-150 years before the eruption in both magmas and the second stage occurred at least 8 years and 15 years before the eruption in the dacitic andesite and rhyolitic andesite, respectively. The depths of crystallization are constrained from the spatial and temporal variations of volcano-tectonic earthquakes locations (Lahr et al., 1994) and from the P-wave and S-wave velocity structures (Benz et al., 1996). These data suggest that the rhyolitic andesite magma ascended to a depth of 7-8 km within at least 15 years of the eruption. Within at least 8 years of the eruption, the dacitic andesite magma migrated to a depth just below the other magma body where it resided until hours to days of the eruption. At this time, the dacitic andesite magma mixed with the rhyolitic andesite magma and established the reservoir for the eruption. Near the top of the reservoir, some of the mixed magma was displaced into fractures which extended 4-5 km toward the surface. This displaced magma created the eruption conduit and released the fluids related to the resonating crack. This scenario is consistent with the trends in major-and trace-element chemistry, and the stability of hornblende in the pre-eruption Redoubt magmas. It also provides a source for the SO2 and CO2 emissions measured during the eruption.

Volcanic tremor masks its seismogenic source: Results from a study of noneruptive tremor recorded at Mount St. Helens, Washington

USGS Publications Warehouse

Denlinger, Roger P.; Moran, Seth C.

2014-01-01

On 2 October 2004, a significant noneruptive tremor episode occurred during the buildup to the 2004–2008 eruption of Mount St. Helens (Washington). This episode was remarkable both because no explosion followed, and because seismicity abruptly stopped following the episode. This sequence motivated us to consider a model for volcanic tremor that does not involve energetic gas release from magma but does involve movement of conduit magma through extension on its way toward the surface. We found that the tremor signal was composed entirely of Love and Rayleigh waves and that its spectral bandwidth increased and decreased with signal amplitude, with broader bandwidth signals containing both higher and lower frequencies. Our modeling results demonstrate that the forces giving rise to this tremor were largely normal to conduit walls, generating hybrid head waves along conduit walls that are coupled to internally reflected waves. Together these form a crucial part of conduit resonance, giving tremor wavefields that are largely a function of waveguide geometry and velocity. We find that the mechanism of tremor generation fundamentally masks the nature of the seismogenic source giving rise to resonance. Thus multiple models can be invoked to explain volcanic tremor, requiring that information from other sources (such as visual observations, geodesy, geology, and gas geochemistry) be used to constrain source models. With concurrent GPS and field data supporting rapid rise of magma, we infer that tremor resulted from drag of nearly solid magma along rough conduit walls as magma was forced toward the surface.

Composition of basaltic lavas sampled by phase-2 of the Hawaii Scientific Drilling Project: Geochemical stratigraphy and magma types

NASA Astrophysics Data System (ADS)

Rhodes, J. M.; Vollinger, M. J.

2004-03-01

This paper presents major and trace element compositions of lavas from the entire 3098 m stratigraphic section sampled by phase-2 of the Hawaii Scientific Drilling Project. The upper 245 m are lavas from Mauna Loa volcano, and the lower 2853 m are lavas and volcanoclastic rocks from Mauna Kea volcano. These intervals are inferred to represent about 100 ka and 400 ka respectively of the eruptive history of the two volcanoes. The Mauna Loa tholeiites tend to be higher in SiO2 and lower in total iron, TiO2, alkalis, and incompatible elements at a given MgO content than Mauna Kea lavas. The transition from Mauna Loa to Mauna Kea lavas is all the more pronounced because the Mauna Loa tholeiites overlie a thin sequence of postshield Mauna Kea alkalic to transitional tholeiitic lavas. The Mauna Loa tholeiites display well-developed coherent trends with MgO that are indistinguishable in most respects from modern lavas. With depth, however, there is a slight decline in incompatible element abundances, and small shifts to depleted isotopic ratios. These characteristics suggest small changes in melt production and source components over time, superimposed on shallow melt segregation. The Mauna Kea section is subdivided into a thin, upper 107 m sequence of postshield tholeiites, transitional tholeiites and alkali basalts of the Hamakua volcanics, overlying four tholeiitic magma types that are intercalated throughout the rest of the core. These four magma types are recognized on the basis of MgO-normalized SiO2 and Zr/Nb values. Type-1 lavas (high SiO2 and Zr/Nb) are ubiquitous below the postshield lavas and are the dominant magma type on Mauna Kea. They are inter-layered with the other three lava types. Type-2 lavas (low SiO2 but high Zr/Nb) are found only in the upper core, and especially above 850 m. Type-3 lavas (low SiO2 and Zr/Nb) are very similar to tholeiites from Loihi volcano and are present only below 1974 m. There are only 3 discrete samples of type-4 lavas (high SiO2 and low Zr/Nb), which are present in the upper and lower core. The differences between these magma types are inferred to reflect changes in melt production, depth of melt segregation, and differences in plume source components over about 400 ka of Mauna Kea's eruptive history. At the start of this record, eruption rates were high, and two distinct tholeiitic magmas (type-1 and 3) were erupting concurrently. These two magmas require two distinct source components, one similar to that of modern Loihi tholeiites and the other close to that of Kilauea magmas. Subsequently, the Loihi-like source of the type-3 magmas was exhausted, and these lavas are absent from the remainder of the core. For the next 200 ka or so, the eruptive sequence consists of inter-layered type-1 and -2 lavas that are derived from a common Mauna Kea source, the major difference between the two being the depth at which the melts segregated from the source. At around 440 ka (corresponding with the transition in the core from submarine to subaerial lavas) eruption rates began to decline and low-MgO lavas are suddenly much more abundant in the record. Continuing gradual decline in melting and eruption rates was accompanied by a decline in normalized SiO2 content of the type-1 magmas, and the eventual onset of postshield magmatism.

Explosive volcanism may not be an inevitable consequence of magma fragmentation.

PubMed

Gonnermann, Helge M; Manga, Michael

2003-11-27

The fragmentation of magma, containing abundant gas bubbles, is thought to be the defining characteristic of explosive eruptions. When viscous stresses associated with the growth of bubbles and the flow of the ascending magma exceed the strength of the melt, the magma breaks into disconnected fragments suspended within an expanding gas phase. Although repeated effusive and explosive eruptions for individual volcanoes are common, the dynamics governing the transition between explosive and effusive eruptions remain unclear. Magmas for both types of eruptions originate from sources with similar volatile content, yet effusive lavas erupt considerably more degassed than their explosive counterparts. One mechanism for degassing during magma ascent, consistent with observations, is the generation of intermittent permeable fracture networks generated by non-explosive fragmentation near the conduit walls. Here we show that such fragmentation can occur by viscous shear in both effusive and explosive eruptions. Moreover, we suggest that such fragmentation may be important for magma degassing and the inhibition of explosive behaviour. This implies that, contrary to conventional views, explosive volcanism is not an inevitable consequence of magma fragmentation.

Factors affecting continued use of ceramic water purifiers distributed to tsunami-affected communities in Sri Lanka.

PubMed

Casanova, Lisa M; Walters, Adam; Naghawatte, Ajith; Sobsey, Mark D

2012-11-01

There is little information about continued use of point-of-use technologies after disaster relief efforts. After the 2004 tsunami, the Red Cross distributed ceramic water filters in Sri Lanka. This study determined factors associated with filter disuse and evaluate the quality of household drinking water. A cross-sectional survey of water sources and treatment, filter use and household characteristics was administered by in-person oral interview, and household water quality was tested. Multivariable logistic regression was used to model probability of filter non-use. At the time of survey, 24% of households (107/452) did not use filters; the most common reason given was breakage (42%). The most common household water sources were taps and wells. Wells were used by 45% of filter users and 28% of non-users. Of households with taps, 75% had source water Escherichia coli in the lowest World Health Organisation risk category (<1/100 ml), vs. only 30% of households reporting wells did. Tap households were approximately four times more likely to discontinue filter use than well households. After 2 years, 24% of households were non-users. The main factors were breakage and household water source; households with taps were more likely to stop use than households with wells. Tap water users also had higher-quality source water, suggesting that disuse is not necessarily negative and monitoring of water quality can aid decision-making about continued use. To promote continued use, disaster recovery filter distribution efforts must be joined with capacity building for long-term water monitoring, supply chains and local production. © 2012 Blackwell Publishing Ltd.

U-Th-Pb, Rb-Sr, and Sm-Nd isotopic systematics of lunar troctolitic cumulate 76535 - Implications on the age and origin of this early lunar, deep-seated cumulate

NASA Technical Reports Server (NTRS)

Premo, Wayne R.; Tatsumoto, M.

1992-01-01

The U-Th-Pb, Rb-Sr, and Sm-Nd isotopic systematics of four lightly leached residues of pristine, high-Mg, troctolitic cumulate 76535 were analyzed in order to determine their ages and magma sources. The data indicate that the cumulate was in isotopic equilibrium with a fluid or magma characterized by a high U-238/Pb-204 (mu) value of 600 at 4.236 Ga. Two and three stage Pb evolution calculations define even greater source mu values of about 1000, assuming low lunar initial mu values between 5 and 40 prior to about 4.43 Ga. These results are similar to mu values for KREEP sources and are also consistent with values from 78235, suggesting that at least some high-Mg suite rocks were derived from magma sources with high-mu values similar to KREEP, and support that idea that these rocks postdate primary lunar differentiation and formation of ferroan anorthosites.

Rhenium-osmium and samarium-neodymium isotopic systematics of the stillwater complex

USGS Publications Warehouse

Lambert, D.D.; Morgan, J.W.; Walker, R.J.; Shirey, S.B.; Carlson, R.W.; Zientek, M.L.; Koski, M.S.

1989-01-01

Isotopic data for the Stillwater Complex, Montana , which formed about 2700 Ma (million years ago), were obtained to evaluate the role of magma mixing in the formation of strategic platinum-group element (PGE) ore deposits. Neodymium and osmium isotopic data indicate that the intrusion formed from at least two geochemically distinct magmas. Ultramafic affinity (U-type) magmas had initial ??Nd of -0.8 to -3.2 and a chondritic initial 187Os/186Os ratio of ???0.88, whereas anorthositic affinity (A-type) magmas had ??Nd of -0.7 to +1.7 and an initial 187Os/186Os ratio of ???1.13. These data suggest that U-type magmas were derived from a lithospheric mantle source containing recycled crustal materials whereas A-type magmas originated either by crustal contamination of basaltic magmas or by partial melting of basalt in the lower crust. The Nd and Os isotopic data also suggest that Os, and probably the other PGEs in ore horizons such as the J-M Reef, was derived from A-type magmas. The Nd and Os isotopic heterogeneity observed in rocks below the J-M Reef also suggests that A-type magmas were injected into the Stillwater U-type magma chamber at several stages during the development of the Ultramafic series.

Creep, dike intrusion, and magma chamber deflation model for the 2000 Miyake eruption and the Izu islands earthquakes

NASA Astrophysics Data System (ADS)

Ozawa, S.; Miyazaki, S.; Nishimura, T.; Murakami, M.; Kaidzu, M.; Imakiire, T.; Ji, X.

2004-02-01

Analysis of Global Positioning System data shows shrinkage of Miyake Island and the widening between Nijima and Kozu Islands during the period of the Miyake island volcanic activity and the ensuing Izu islands earthquakes in 2000. The estimated time evolution of a model consisting of a dike, creeping faults, and a Mogi source suggests that a crack opening on Miyake Island occurred immediately after the start of the seismic activities on 26 June and ended within several days at the west coast of Miyake Island. After the seabed eruption on 27 June, magma migrated from Miyake Island to Kozu and Nijima Islands within several days. The estimated volume of intruded magma totals around 1.2 × 109 m3. Associated with the magma intrusion between Miyake and Kozu Islands, left-lateral and right-lateral creep motions occurred in regions off the west coast of Miyake Island and near Kozu Island. The accumulated moment energy is equivalent to an earthquake of Mw 6.6 and 6.6 for right-lateral and left-lateral creeping faults, respectively. The estimated magma chamber continued deflation beneath the southwestern part of Miyake Island from 26 June, totaling around 0.12 × 109 m3 in volume change, in addition to the collapse volume of 0.6 × 109 m3 at the summit of Mount Oyama on Miyake Island. The volume change on Miyake Island can be compensated by the migrated magma toward Kozu Island from the deflation source beneath Miyake Island. The deflation speed of the magma chamber beneath Miyake Island decreased and increased before and after the eruption of 14-15 July and 18 August, suggesting a change in balance of mass influx and draining out rate of the magma chamber.

The Recreational Water Cycle: From Source Water to Tap Water to Spa and Swimming Pool Water: Effects of Disinfectants and Precursors and Implications for Exposure and Toxicity

EPA Science Inventory

The current study investigates the effect of different disinfection treatments on the disinfection by-products (DBPs) formed in finished drinking water vs. tap water vs. swimming pool water vs. spa waters. To this end, complete water pathway samples (untreated source waters ->fi...

A new Mantle Source Tapped During Episode 55 of the Pu'u O'o Eruption From Kilauea Volcano

NASA Astrophysics Data System (ADS)

Marske, J. P.; Pietruszka, A. J.; Garcia, M. O.; Rhodes, J. M.

2005-12-01

Over 22 years of continuous geochemical monitoring of lavas from the current Pu'u O'o eruption allows us to probe the mantle and crustal processes beneath Kilauea Volcano in unparalleled detail. Episode 55 (1997-present) marks the longest and most voluminous Pu'u O'o eruptive interval. Here we present new Pb, Sr, and Nd isotopic ratios and major- and trace-element abundances for the most recent lavas (1999-2005). MgO variation diagrams show that most of the major-element variations are related to olivine fractionation. However, Pu'u O'o lavas display longer-term systematic decreases in their TiO2, K2O, P2O5 and CaO abundances (at a given MgO) due to changes in the parental magma composition. Incompatible element ratios (K2O/TiO2, Nb/Y, Nb/Zr) and MgO-normalized abundances (Sr, Rb, K) in episode 55 lavas delimit the lowest values observed during the Pu'u O'o eruption. Earlier Pu'u O'o lavas displayed a temporal decrease in highly over moderately incompatible trace-element ratios, near constant SiO2 contents, and a gradual increase in 87Sr/86Sr. However, episode 55 lavas (between days 5500-6500) record an increase in MgO-normalized SiO2 contents and even higher 87Sr/86Sr with near constant incompatible trace-element ratios. Neither a single mantle source composition nor a change in partial melting conditions can explain these observations. Based on 226Ra-230Th-238U disequilibria and partial melting modeling of trace elements, we conclude that Pu'u O'o lavas originate from at least two distinct mantle source components: (1) a recently depleted component that was subsequently remelted to explain the overall decreases of incompatible major- and trace-element ratios and abundances, and (2) a compositionally and isotopically distinct mantle component that was not previously melted within the Hawaiian plume to explain the temporal increase in 87Sr/86Sr and SiO2 abundances and the flattening trend of incompatible trace-element ratios. This second component lies within typical Pb, Sr and Nd isotopic space for Kilauea, but represents a new source composition for the Pu'u O'o eruption. These results can be explained by a recent (1999) change in the size or location of Pu'u O'o's melting region, which allowed this new source to be tapped.

Zircon Hf-O isotopic constraints on the origin of Late Mesozoic felsic volcanic rocks from the Great Xing'an Range, NE China

NASA Astrophysics Data System (ADS)

Gong, Mingyue; Tian, Wei; Fu, Bin; Wang, Shuangyue; Dong, Jinlong

2018-05-01

The voluminous Late Mesozoic magmatism was related to extensive re-melting of juvenile materials that were added to the Central East Asia continent in Phanerozoic time. The most favoured magma generation mechanism of Late Mesozoic magmas is partial melting of underplated lower crust that had radiogenic Hf-Nd isotopic characteristics, but this mechanism faces difficulties when interpreting other isotopic data. The tectonic environment controlling the generation of the Late Mesozoic felsic magmas is also in dispute. In this study, we obtained new U-Pb ages, and geochemical and isotopic data of representative Jurassic (154.4 ± 1.5 Ma) and Cretaceous (140.2 ± 1.5 Ma) felsic volcanic samples. The Jurassic sample has inherited zircon cores of Permian age, with depleted mantle-like εHf(t) of +7.4 - +8.5, which is in contrast with those of the magmatic zircons (εHf(t) = +2.4 ± 0.7). Whereas the inherited cores and the magmatic zircons have identical mantle-like δ18O composition ranges (4.25-5.29‰ and 4.69-5.54‰, respectively). These Hf-O isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited Permian zircon core. This mechanism is manifested by the eruption of Jurassic alkaline basalts originated from an enriched mantle source. The Cretaceous sample has high εHf(t) of +7.0 - +10.5, suggesting re-melting of a mafic magma derived from a depleted mantle-source. However, the sub-mantle zircon δ18O values (3.70-4.58‰) suggest the depleted mantle-derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level. Therefore, the Cretaceous felsic magma, if not all, could be generated by re-melting of down-dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration. The two processes, enriched mantle-contribution and supracrustal juvenile material re-melting, are new generation mechanisms of the Late Mesozoic magmas from Central East Asia. Rift settings may have controlled these processes throughout crustal and mantle levels.

Workshop on Mare Volcanism and Basalt Petrogenesis: Astounding Fundamental Concepts (AFC) Developed Over the Last Fifteen Years

NASA Technical Reports Server (NTRS)

Taylor, Lawrence A. (Editor); Longi, John (Editor)

1991-01-01

Papers presented at the workshop on mare volcanism and basalt petrogenesis are compiled. The discussion of recent ideas and concepts within the context of this workshop permitted to catch up on the developments over the last 15 years. The following subject areas were covered: (1) geological setting; (2) magma evolution and source regions; (3) magma source and ascent processes; and (4) history of volcanism.

Survey of possibility for volcanic energy development

NASA Astrophysics Data System (ADS)

1990-03-01

Volcanic areas, clarification of heat source structure, evaluation of resources and problems on utilization techniques were arranged to search the possibility of future volcanic heat source. It is necessary to improve the exploration accuracy by combining geophysical exploration with geological and geochemical surveys in order to explorate a magma reservoir. Especially, seismic exploration is effective. The surveying procedure is as follows: confirmation of magma existence and grasping the whole image, evaluation of resources, clarification of three-dimensional distribution of magma in a promising area, and heat structure survey by heat flow measurement and others to construct more accurate model for resources. This model is verified finally by practical drilling. Promising areas which are worthy of development, are active volcanic areas in Kyushu, Hakkoda nad Hokkaido. It is desirable to make drilling to the depth of 3 km or magma reservoir to develop the future heat source. It is also required to improve the thermal resistance and corrosion resistance of materials to be used. Heat extraction by a single well is most realistic and the closed coaxial double pipe heat exchanger or open heat exchanger in the well will be used to improve the extraction.

Deformation patterns, magma supply, and magma storage at Karymsky Volcanic Center, Kamchatka, Russia, 2000-2010, revealed by InSAR

NASA Astrophysics Data System (ADS)

Ji, Lingyun; Izbekov, Pavel; Senyukov, Sergey; Lu, Zhong

2018-02-01

Under a complex geological region influenced by the subduction of the Pacific plate, Kamchatka Peninsula is one of the most active volcanic arcs in the Pacific Rim. Due to logistical difficulty in instrumentation, shallow magma plumbing systems beneath some of the Kamchatkan volcanoes are poorly understood. InSAR offers a safe and quick method for monitoring volcanic deformation with a high spatial resolution. In this study, a group of satellite radar interferograms that span the time interval from 2000 to 2010 shows eruptive and non-eruptive deformation at Karymsky Volcanic Center (KVC), Kamchatka, Russia. All the interferograms provide details of the activity around the KVC during 2000-2010, as follows: (1) from 2000 to 2004, the Karymsky-AN (Akademia Nauk) area deflated and the MS (Maly Semyachik) area inflated, (2) from 2004 to 2006, the Karymsky-AN area deflated with ongoing eruption, while the MS area subsided without eruption, (3) from 2006 to 2008, as with 2000-2004, the Karymsky-AN area deflated and the MS area inflated, (4) from 2008 to 2010, the Karymsky-AN area inflated up to 3 cm, and the MS area subsided. Point source models suggest that two magma reservoirs provide a good fit to the observed deformation. One source is located beneath the area between Karymsky and AN at a depth of approximately 7.0 km, and the other one is situated beneath MS at a depth of around 5.8 km. Synchronous deformation patterns suggest that two magma systems are fed from the same deep magma source and connected by a fracture zone. The InSAR results are consistent with GPS ground deformation measurements, seismic data, and petrological constraints.

Occurrence and sources of bromate in chlorinated tap drinking water in Metropolitan Manila, Philippines.

PubMed

Genuino, Homer C; Espino, Maria Pythias B

2012-04-01

Significant levels of potentially carcinogenic bromate were measured in chlorinated tap drinking water in Metropolitan Manila, Philippines, using an optimized ion-chromatographic method. This method can quantify bromate in water down to 4.5 μg l⁻¹ by employing a postcolumn reaction with acidic fuchsin and subsequent spectrophotometric detection. The concentration of bromate in tap drinking water samples collected from 21 locations in cities and municipalities within the 9-month study period ranged from 7 to 138 μg l⁻¹. The average bromate concentration of all tap drinking water samples was 66 μg l⁻¹ (n = 567), almost seven times greater than the current regulatory limit in the country. The levels of bromate in other water types were also determined to identify the sources of bromate found in the distribution lines and to further uncover contaminated sites. The concentration of bromate in water sourced from two rivers and two water treatment plants ranged from 15 to 80 and 12 to 101 μg l⁻¹, respectively. Rainwater did not contribute bromate in rivers but decreased bromate level by dilution. Groundwater and wastewater samples showed bromate concentrations as high as 246 and 342 μg l⁻¹, respectively. Bromate presence in tap drinking water can be linked to pollution in natural water bodies and the practice of using hypochlorite chemicals in addition to gaseous chlorine for water disinfection. This study established the levels, occurrence, and possible sources of bromate in local drinking water supplies.

Multiple magma emplacement and its effect on the superficial deformation: hints from analogue models

NASA Astrophysics Data System (ADS)

Montanari, Domenico; Bonini, Marco; Corti, Giacomo; del Ventisette, Chiara

2017-04-01

To test the effect exerted by multiple magma emplacement on the deformation pattern, we have run analogue models with synchronous, as well as diachronous magma injection from different, aligned inlets. The distance between injection points, as well as the activation in time of injection points was varied for each model. Our model results show how the position and activation in time of injection points (which reproduce multiple magma batches in nature) strongly influence model evolution. In the case of synchronous injection at different inlets, the intrusions and associated surface deformation were elongated. Forced folds and annular bounding reverse faults were quite elliptical, and with the main axis of the elongated dome trending sub-parallel to the direction of the magma input points. Model results also indicate that the injection from multiple aligned sources could reproduce the same features of systems associated with planar feeder dikes, thereby suggesting that caution should be taken when trying to infer the feeding areas on the basis of the deformation features observed at the surface or in seismic profiles. Diachronous injection from different injection points showed that the deformation observed at surface does not necessarily reflect the location and/or geometry of their feeders. Most notably, these experiments suggest that coeval magma injection from different sources favor the lateral migration of magma rather than the vertical growth, promoting the development of laterally interconnected intrusions. Recently, some authors (Magee et al., 2014, 2016; Schofield et al., 2015) have suggested that, based on seismic reflection data analysis, interconnected sills and inclined sheets can facilitate the transport of magma over great vertical distances and laterally for large distances. Intrusions and volcanoes fed by sill complexes may thus be laterally offset significantly from the melt source. Our model results strongly support these findings, by reproducing in the laboratory a strong lateral magma migration, and suggesting a possible mechanism. The models also confirmed that lateral magma migration could take place with little or no accompanying surface deformation. The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). References: Magee et al., 2014. Basin Research, v. 26, p. 85-105, doi: 10 .1111 /bre.12044. Magee et al., 2016. Geosphere, v. 12, p. 809-841, ISSN: 1553-040X. Schofield et al., 2015. Basin Research, v. 29, p. 41-63, doi:10.1111/bre.12164.

Sources of drinking water in a pediatric population.

PubMed

Jadav, Urvi G; Acharya, Bhavini S; Velasquez, Gisela M; Vance, Bradley J; Tate, Robert H; Quock, Ryan L

2014-01-01

The purpose of this study was to determine the primary sources of water used for consumption and cooking by the patients of a university-based pediatric dental practice. A simple, prewritten questionnaire-consisting of seven questions and available in English and Spanish-was conducted verbally with the caregivers of 123 pediatric patients during a designated timeframe. Analysis of responses included descriptive statistics and a chi-square test for a single proportion. Nonfiltered tap water accounted for the primary drinking water source in only 10 percent of the respondents. Firty-two percent of the respondents selected bottled water as the primary source of drinking water, and 24 percent selected vended water stations as a primary drinking water source. Nonfiltered tap water was much more likely to be utilized in cooking (58 percent). The majority of the patients in this study's pediatric dental practice do not consume fluoridated tap water. With the vast majority of the patients primarily consuming bottled or vended water, these patients are likely missing out on the caries-protective effects of water fluoridation.

Evaluation of crustal recycling during the evolution of Archean-age Matachewan basaltic magmas

NASA Technical Reports Server (NTRS)

Nelson, Dennis O.

1989-01-01

The simplest model for the Matachewan-Hearst Dike (MHD) magmas is assimilation-fractional crystallization (AFC), presumably occurring at the base of the crust during underplating. Subduction zone enriched mantle sources are not required. Trace elements suggest that the mantle sources for the MHD were depleted, but possessed a degree of heterogeneity. Rates of assimilation were approximately 0.5 (= Ma/Mc); the contaminant mass was less than 20 percent. The contaminant was dominated by tonalites-randodiorites, similar to xenoliths and rocks in the Kapuskasing Structural Zone (KSZ). Assimilation of partial melts of light-rare earth and garnet-bearing basaltic precursors may have produced some the MHD magmas. Apparently, previous underplating-AFC processes had already produced a thick crust. The silicic granitoid assimilant for the MHD magmas was probably produced by earlier processing of underplated mafic crust (4, 5, 10, 21 and 30). Calculations suggest that the derived silicic rocks possess negative Ta and Ti anomalies even though they were not the product of subduction.

Characteristics of Mare Deposits on the Eastern Limb of the Moon: Implications for Magma Transport Mechanisms

NASA Astrophysics Data System (ADS)

Yingst, R. A.; Head, J. W.

1996-03-01

Lunar volcanic history has been examined in light of geomorphological and stratigraphic constraints placed upon the surface features. Compositional and petrological analyses have provided models for the conditions of mare parent magma generation . The connection between lunar magma source regions and volcanic surface features remains unclear, however, both conceptually and quantitatively with respect to our understanding of transport mechanisms. It has been suggested that mare emplacement was controlled by propagation of dikes driven by the overpressurization of diapir-like source regions stalled below the cooling lunar highland crust. Recent analyses of the characteristics of lava ponds in the South Pole/Aitken and Orientale/Mendel-Rydberg basins based on Clementine, Lunar Orbiter and Zond data have provided evidence that supports this theory. In this contribution we report on an analysis of the areas, volumes, modes of occurrence and crustal thicknesses for mare deposits in the Marginis and Smythii basins, and investigate implications for magma transport mechanisms.

Gravity fluctuations induced by magma convection at Kilauea Volcano, Hawai'i

USGS Publications Warehouse

Carbone, Daniele; Poland, Michael P.

2012-01-01

Convection in magma chambers is thought to play a key role in the activity of persistently active volcanoes, but has only been inferred indirectly from geochemical observations or simulated numerically. Continuous microgravity measurements, which track changes in subsurface mass distribution over time, provide a potential method for characterizing convection in magma reservoirs. We recorded gravity oscillations with a period of ~150 s at two continuous gravity stations at the summit of Kīlauea Volcano, Hawai‘i. The oscillations are not related to inertial accelerations caused by seismic activity, but instead indicate variations in subsurface mass. Source modeling suggests that the oscillations are caused by density inversions in a magma reservoir located ~1 km beneath the east margin of Halema‘uma‘u Crater in Kīlauea Caldera—a location of known magma storage.

Gas emissions from failed and actual eruptions from Cook Inlet Volcanoes, Alaska, 1989-2006

USGS Publications Warehouse

Werner, C.A.; Doukas, M.P.; Kelly, P.J.

2011-01-01

Cook Inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled. For the six events studied, mean emission rates for eruptions were ~13,000 t/d CO2 and 5200 t/d SO2, but only ~1200 t/d CO2 and 500 t/d SO2 for non-eruptive events (‘failed eruptions’). Statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t/d for CO2 and SO2, respectively. Emission rates greater than 4000 and 2000 t/d for CO2 and SO2, respectively, almost exclusively resulted during eruptive events (the only exception being two measurements at Fourpeaked). While this analysis could suggest that unerupted magmas have lower pre-eruptive volatile contents, we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions, or that magmas from failed eruptions experience less decompression such that the majority of H2O remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase (or both). In the majority of unrest and eruption sequences, increases in CO2 emission relative to SO2 emission were observed early in the sequence. With time, all events converged to a common molar value of C/S between 0.5 and 2. These geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice (i.e., from 20–35 to ~4–6 km) and perhaps roughly similar initial volatile contents in all cases. Early elevated CO2 levels that we find at these high-latitude, andesitic arc volcanoes have also been observed at mid-latitude, relatively snow-free, basaltic volcanoes such as Stromboli and Etna. Typically such patterns are attributed to injection and decompression of deep (CO2-rich) magma into a shallower chamber and open system degassing prior to eruption. Here we argue that the C/S trends probably represent tapping of vapor-saturated regions with high C/S, and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface. At these volcanoes, however, C/S is often accentuated due to early preferential scrubbing of sulfur gases. The range of equilibrium degassing is consistent with the bulk degassing of a magma with initial CO2 and S of 0.6 and 0.2 wt.%, respectively, similar to what has been suggested for primitive Redoubt magmas.

Magma accumulation or second boiling - Investigating the ongoing deformation field at Montserrat, West Indies

NASA Astrophysics Data System (ADS)

Collinson, Amy; Neuberg, Jurgen; Pascal, Karen

2016-04-01

For over 20 years, Soufriere Hills Volcano, Montserrat has been in a state of volcanic unrest. Intermittent periods of dome building have been punctuated by explosive eruptions and dome collapse events, endangering the lives of the inhabitants of the island. The last episode of active magma extrusion was in February 2010, and the last explosive event (ash venting) in March 2012. Despite a lack of eruptive activity recently, the volcano continues to emit significant volumes of SO2 and shows an ongoing trend of island inflation. Through the aid of three-dimensional numerical modelling, using a finite element method, we explore the potential sources of the ongoing island inflation. We consider both magmatic (dykes and chamber) and tectonic sources. Whilst a magmatic source suggests the possibility for further eruption, a tectonic source may indicate cessation of volcanic activity. We show that a magmatic source is the most likely scenario, and illustrate the effect of different sources (shapes, characters and depths) on the surface displacement. Furthermore, through the inclusion of topographic data, we investigate how the topography may affect the displacement pattern at the surface. We investigate the conflicting scenarios of magma chamber resupply versus second boiling - crystallisation-induced degassing. Based on numerical modelling results, we suggest the required pressurisation is too high for crystallisation-induced degassing to be the dominant process - thereby suggesting magma accumulation may be ongoing. However, we show that second boiling may be a contributing factor, particularly when taking into account the local tectonics and regional stretching.

New perspectives on the eruption of 1912 in the valley of ten thousand smokes, Katmai National Park, Alaska

USGS Publications Warehouse

Hildreth, W.

1987-01-01

New data extend our understanding of the 1912 eruption, its backfilled vent complex at Novarupta, and magma-storage systems beneath adjacent stratovolcanoes. Initial Plinian rhyolite fallout is confined to a narrow downwind sector, and its maximum thickness may occur as far as 13 km from source. In contrast, the partly contemporaneous rhyolite-rich ash flows underwent relatively low-energy emplacement, their generation evidently being decoupled from the high column. Flow veneers 1-13 m thick on near-vent ridge crests exhibit a general rhyolite-to-andesite sequence like that of the much thicker valley-confined ignimbrite into which they merge downslope. Lithics in both the initial Plinian and the ignimbrite are predominantly fragments of the Jurassic Naknek Formation, which extends from the surface to a depth of ca. 1500 m. Absence of lithics from the underlying sedimentary section limits to 100 m thick near source and 10 m thick 3 km away, which dip back into an inner vent <0.5 km wide, nested inside the earlier vent funnel of the ignimbrite. The dacite fallout is poor in Naknek lithics but contains abundant fragments of vitrophyre, most of which was vent-filling, densely welded tuff reejected during later phases of the 3-day eruption. Adjacent to the inner vent, a 225-m-high asymmetrical accumulation of coarse near-vent ejecta is stratigraphically continuous with the regional dacite fallout. Distensional faulting of its crest may reflect spreading related to compaction and welding. Nearby andesite-dacite stratovolcanoes, i.e., Martin, Mageik, Trident, and Katmai, display at least 12 vents that define a linear volcanic front trending N65??E. The 1912 vent and adjacent dacite domes are disposed parallel to the front and ca. 4 km behind it. Mount Griggs, 10 km behind the front, is more potassic than other centers, taps isotopically more depleted source materials, and reflects a wholly independent magmatic plumbing system. Geochemical differences among the stratovolcanoes, characteristically small eruptive volumes ( < 0.1 to 0.4 km3), and the dominance of andesite and low-SiO2 dacite suggest complex crustal reservoirs, not large integrated magma chambers. Linear fractures just outside the 1912 vent strike nearly normal to the volcanic front and may reflect dike transport of magma previously stored beneath Trident 3-5 km away. Caldera collapse at Mount Katmai may have taken place in response to hydraulic transfer of Katmai magma toward Novarupta via reservoir components beneath Trident. The voluminous 1912 eruption (12-15 km3 DRE) was also unusual in producing high-silica rhyolite (6-9 km3 DRE), a composition rare in this arc and on volcanic fronts in general. Isotopic data indicate that rhyolite genesis involved little assimilation of sedimentary rocks, pre-Tertiary plutonic rocks, or hydrothermally altered rocks of any age. Trace-element data suggest nonetheless that the rhyolite contains a nontrivial crustal contribution, most likely partial melts of Late Cenozoic arc-intrusive rocks. Because the three compositions (77%, 66-64.5%, and 61.5-58.5% SiO2) that intermingled in 1912 vented both concurrently and repeatedly (after eruptive pauses hours in duration), the compositional gaps between them must have been intrinsic to the reservoir, not merely effects of withdrawal dynamics. ?? 1987 Springer-Verlag.

Magma chamber cooling by episodic volatile expulsion as constrained by mineral vein distributions in the Butte, Montana Cu-Mo porphyry deposit

NASA Astrophysics Data System (ADS)

Daly, K.; Karlstrom, L.; Reed, M. H.

2016-12-01

The role of hydrothermal systems in the thermal evolution of magma chambers is poorly constrained yet likely significant. We analyze trends in mineral composition, vein thickness and overall volumetric fluid flux of the Butte, Montana porphyry Cu-Mo deposit to constrain the role of episodic volatile discharge in the crystallization of the source magma chamber ( 300 km3of silicic magma). An aqueous fluid sourced from injection of porphyritic dikes formed the Butte porphyry Cu network of veins. At least three separate pulses of fluid through the system are defined by alteration envelopes of [1] gray sericite (GS); [2] early-dark micaceous (EDM), pale-green sericite (PGS), and dark-green sericite (DGS); and [3] quartz-molybdenite (Qmb) and barren-quartz. Previous research using geothermometers and geobarometers has found that vein mineral composition, inferred temperatures and inferred pressures vary systematically with depth. Later fluid pulses are characterized by lower temperatures, consistent with progressive cooling of the source. We have digitized previously unused structural data from Butte area drill cores, and applied thermomechanical modeling of fluid release from the source magma chamber through time. Vein number density and vein thickness increase with depth as a clear function of mineralogy and thus primary temperature and pressure. We identify structural trends in the three fluid pulses which seem to imply time evolution of average vein characteristics. Pulses of Qmb-barren quartz and EDM-PGS-DGS (1st and 2nd in time) exhibit increasing vein number density (157 & 95 veins/50m, respectively) and thickness (300mm & 120mm, respectively) as a function of depth. EDM-PGS-DGS has a shallower peak in vein density (800m) than Qmb-barren quartz (>1600m). These data provide the basis for idealized mechanical models of hydrofractures, to predict driving pressures and to compare with existing source temperatures and total fluid volumes in order to estimate the total enthalpy of each fluid pulse. We then compare with models for conductive cooling and crystallization of the source magma chamber to estimate the importance of hydrothermal fluid expulsion in the total heat budget. Such models should also provide constraints on the timing and ultimately the origin of pulsed volatile release at Butte.

Vaccination and the TAP-independent antigen processing pathways.

PubMed

López, Daniel; Lorente, Elena; Barriga, Alejandro; Johnstone, Carolina; Mir, Carmen

2013-09-01

The cytotoxic CD8(+) T lymphocyte-mediated cellular response is important for the elimination of virus-infected cells and requires the prior recognition of short viral peptide antigens previously translocated to the endoplasmic reticulum by the transporter associated with antigen processing (TAP). However, individuals with nonfunctional TAP complexes or infected cells with TAP molecules blocked by specific viral proteins, such as the cowpoxvirus, a component of the first source of early empirical vaccination against smallpox, are still able to present several HLA class I ligands generated by the TAP-independent antigen processing pathways to specific cytotoxic CD8(+) T lymphocytes. Currently, bioterrorism and emerging infectious diseases have renewed interest in poxviruses. Recent works that have identified HLA class I ligands and epitopes in virus-infected TAP-deficient cells have implications for the study of both the effectiveness of early empirical vaccination and the analysis of HLA class I antigen processing in TAP-deficient subjects.

The 2014-15 eruption and the short-term geochemical evolution of the Fogo volcano (Cape Verde): Evidence for small-scale mantle heterogeneity

NASA Astrophysics Data System (ADS)

Mata, J.; Martins, S.; Mattielli, N.; Madeira, J.; Faria, B.; Ramalho, R. S.; Silva, P.; Moreira, M.; Caldeira, R.; Moreira, M.; Rodrigues, J.; Martins, L.

2017-09-01

Recurrent eruptions at very active ocean island volcanoes provide the ideal means to gain insight on the scale of spatial variations at the mantle source and on temporal changes of magma genesis and evolution processes. In 2014, after 19 years of quiescence, Fogo volcano (Cape Verde Archipelago) experienced a new eruption, with the vents located 200 m from those of the 1995 eruption, and less than 2000 m from those of the 1951 event. This offered a unique opportunity to investigate the existence of small-scale mantle heterogeneities and the short-term compositional evolution of magmas erupted by a very active oceanic volcano like Fogo. Here we present petrological and geochemical data from the early stages of the Fogo's most recent eruption - started on November 23, 2014 - and compare them with the signature of previous eruptions (particularly those of 1995 and 1951). The magmas erupted in 2014 are alkaline (up to 23.4% and 0.94% of normative ne and lc, respectively) with somewhat evolved compositions (Mg # < 56), ranging from tephrites to phonotephrites. The eruption of phonotephritic lavas preceded the effusion of tephritic ones. Lavas carried to the surface clinopyroxene and kaersutite phenocrysts and cognate megacrysts, which indicate that the main stages of magma evolution occurred in magma chambers most probably located at mantle depths (25.6 ± 5.5 km below sea level). This was followed by a shallower (< 1.5 km below sea level) and shorter (≈ 50 days) magma stagnation before the eruption. 2014 magmas have more unradiogenic Sr and more radiogenic Nd compositions than those of the previous 1951 and 1995 eruptions, which generally have less radiogenic Pb ratios. These isotopic differences - coming from quasi-coeval materials erupted almost in the same place - are remarkable and reflect the small-scale heterogeneity of the underlying mantle source. Moreover, they reflect the limited isotopic averaging of the source composition during partial melting events as well as the inefficient homogenization within the plumbing system when on route to the surface. The lid effect of an old and thick lithosphere is considered of utmost importance to the preservation of a significant part of source heterogeneity by erupted magmas. The decrease in the contribution of an enriched component to the Fogo magmas in the 2014 eruption marks a change on the volcano short-term evolution that was characterized by a progressive increase of the importance of such a component. Nb/U ratios of the 2014 lavas are similar, within 2σ, to the mean value of OIB, but significantly lower than those reported for the 1995 and 1951 eruptions. This is considered to reflect the lack of significant mixing of the 2014 magmas with lithospheric melts, as opposed to what is here hypothesised for the two previous eruptions.

Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica

USGS Publications Warehouse

Oppenheimer, C.; Moretti, R.; Kyle, P.R.; Eschenbacher, A.; Lowenstern, J. B.; Hervig, R.L.; Dunbar, N.W.

2011-01-01

Continental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer). ?? 2011 Elsevier B.V.

Volcano deformation source parameters estimated from InSAR: Sensitivities to uncertainties in seismic tomography

USGS Publications Warehouse

Masterlark, Timothy; Donovan, Theodore; Feigl, Kurt L.; Haney, Matt; Thurber, Clifford H.; Tung, Sui

2016-01-01

The eruption cycle of a volcano is controlled in part by the upward migration of magma. The characteristics of the magma flux produce a deformation signature at the Earth's surface. Inverse analyses use geodetic data to estimate strategic controlling parameters that describe the position and pressurization of a magma chamber at depth. The specific distribution of material properties controls how observed surface deformation translates to source parameter estimates. Seismic tomography models describe the spatial distributions of material properties that are necessary for accurate models of volcano deformation. This study investigates how uncertainties in seismic tomography models propagate into variations in the estimates of volcano deformation source parameters inverted from geodetic data. We conduct finite element model-based nonlinear inverse analyses of interferometric synthetic aperture radar (InSAR) data for Okmok volcano, Alaska, as an example. We then analyze the estimated parameters and their uncertainties to characterize the magma chamber. Analyses are performed separately for models simulating a pressurized chamber embedded in a homogeneous domain as well as for a domain having a heterogeneous distribution of material properties according to seismic tomography. The estimated depth of the source is sensitive to the distribution of material properties. The estimated depths for the homogeneous and heterogeneous domains are 2666 ± 42 and 3527 ± 56 m below mean sea level, respectively (99% confidence). A Monte Carlo analysis indicates that uncertainties of the seismic tomography cannot account for this discrepancy at the 99% confidence level. Accounting for the spatial distribution of elastic properties according to seismic tomography significantly improves the fit of the deformation model predictions and significantly influences estimates for parameters that describe the location of a pressurized magma chamber.

Petrologic testament to changes in shallow magma storage and transport during 30+ years of recharge and eruption at Kīlauea Volcano, Hawai‘i: Chapter 8

USGS Publications Warehouse

Thornber, Carl R.; Orr, Tim R.; Heliker, Christina; Hoblitt, Richard P.; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

2015-01-01

Petrologic monitoring of Kīlauea Volcano from January 1983 to October 2013 has yielded an extensive record of glass, phenocryst, melt inclusion, and bulk-lava chemistry from well-quenched lava. When correlated with 30+ years of geophysical and geologic monitoring, petrologic details testify to physical maturation of summit-to-rift magma plumbing associated with sporadic intrusion and prolonged magmatic overpressurization. Changes through time in bulk-lava major- and trace-element compositions, along with glass thermometry, record shifts in the dynamic balance of fractionation, mixing, and assimilation processes inherent to magma storage and transport during near-continuous recharge and eruption. Phenocryst composition, morphology, and texture, along with the sulfur content of melt inclusions, constrain coupled changes in eruption behavior and geochemistry to processes occurring in the shallow magmatic system. For the first 17 years of eruption, magma was steadily tapped from a summit reservoir at 1–4 km depth and circulating between 1180 and 1200°C. Furthermore, magma cooled another 30°C while flowing through the 18 km long rift conduit, before erupting olivine-spinel-phyric lava at temperatures of 1150–1170°C in a pattern linked with edifice deformation, vent formation, eruptive vigor, and presumably the flux of magma into and out of the summit reservoir. During 2000–2001, a fundamental change in steady state eruption petrology to that of relatively low-temperature, low-MgO, olivine(-spinel)-clinopyroxene-plagioclase-phryic lava points to a physical transformation of the shallow volcano plumbing uprift of the vent. Preeruptive comagmatic mixing between hotter and cooler magma is documented by resorption, overgrowth, and compositional zonation in a mixed population of phenocrysts grown at higher and lower temperatures. Large variations of sulfur (50 to >1000 ppm) in melt inclusions within individual phenocrysts and among phenocrysts in most samples provide an unequivocal glimpse of rapid crystal growth amid sulfur degassing at <30 MPa in a turbulent preeruptive environment. We speculate that, during the last decade, one or more shallow open-system reservoirs developed along the conduit between the summit and Pu‘u ‘Ō‘ō and now serve to buffer the magmatic throughput associated with ongoing recharge and eruption. Lava with identical trace-element signatures erupted simultaneously at the summit and at Pu‘u ‘Ō‘ō from 2008 to 2013 confirms magmatic continuity between the vents. Complementary changes in compositions of matrix glasses, phenocrysts, and melt inclusions of summit tephra are mirrored by similar changes in contemporaneous rift lava at eruption temperatures 20–35°C lower than those at the summit. Petrologic parameters measured at opposite ends of the shallow magmatic plumbing system are both correlated with summit deformation, demonstrating that effects of summit magma chamber pressurization are translated throughout interconnected magma pathways in the shallow edifice.

Mantle ingredients for making the fingerprint of Etna alkaline magmas: implications for shallow partial melting within the complex geodynamic framework of Eastern Sicily

NASA Astrophysics Data System (ADS)

Viccaro, Marco; Zuccarello, Francesco

2017-09-01

Mantle ingredients responsible for the signature of Etnean Na- and K-alkaline magmas and their relationships with short-term geochemical changes of the erupted volcanic rocks have been constrained through a partial melting model that considers major, trace elements and water contents in the produced liquids. Characteristics of the Etnean source for alkaline magmas have been supposed similar to those of the mantle accessible at a regional scale, namely below the Hyblean Plateau. The assumption that the Etnean mantle resembles the one beneath the Hyblean Plateau is justified by the large geochemical affinities of the Etnean hawaiites/K-trachybasalts and the Hyblean hawaiites/alkali basalts for what concerns both trace elements and isotope systematics. We have modeled partial melting of a composite source constituted by two rock types, inferred by lithological and geochemical features of the Hyblean xenoliths: 1) a spinel lherzolite bearing metasomatic, hydrous phases and 2) a garnet pyroxenite in form of veins intruded into the spinel lherzolite. The partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. These compositions have been compared with some Etnean alkaline magmas of the post ∼60 ka activity, which were firstly re-equilibrated to mantle conditions through mass balance calculations. Our results put into evidence that concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of the spinel lherzolite with variable modal contents of metasomatic phases and of the garnet pyroxenite can therefore account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time, emphasizing the crucial role played by compositional small-scale heterogeneity of the source. These heterogeneities are able to produce magmas with variable compositions and volatile contents, which can then undergo distinct histories of ascent and evolution, leading to the wide range of eruptive styles observed at Mt. Etna volcano. Being partial melting confined in the spinel facies of the mantle, our model implies that the source of Mt. Etna magmas might be rather shallow (<2 GPa; i.e., lesser than ca. 60 km), excluding the presence of deep, plume-like mantle structures responsible for magma generation. Partial melting should occur consequently as a response of mantle decompression within the framework of regional tectonics affecting the Eastern Sicily, which could be triggered by extensional tectonics and/or subduction-induced mantle upwelling.

Tiny crystals give away the where and when of magma ascent

NASA Astrophysics Data System (ADS)

Ruth, D. C. S.; Costa Rodriguez, F.; Bouvet de Maisonneuve, C.; Franco, L.; Cortes, J. A.; Calder, E.

2016-12-01

Open vent volcanoes exhibit passive degassing and can transition to explosive behavior, with limited or no warning. Melt inclusion chemistry and volatile contents have been used to infer the inner dynamics of magma storage, recharge, degassing, and eruption triggering mechanisms. However, the interpretation of melt inclusion chemistry is ambiguous because it cannot constrain the residence times of the host crystals, which could have various sources and growth histories. To resolve this issue we combine diffusion chronometry and melt inclusion entrapment pressures from olivine crystals sourced from the 2008 eruption of Llaima volcano (Chile). Olivine crystals (core Fo70-84, rim Fo77-84) are dominantly reverse zoned, although normal zoned and complex zoned crystals are observed. These data reflect mixing between the mafic injecting magma and the crystal-rich resident magma. Fe/Mg diffusion timescales range between 16 and 1375 days. The diffusion data show a non-uniform distribution with no discernible peaks, indicating that magma injection is likely progressive, rather than punctuated. Entrapment pressures range between 8 and 151 MPa, overlapping with an inferred crystal-rich region. Longer timescales correspond to higher pressures, strongly suggesting a link between magma residence time and ascent from depth. To our knowledge, this relationship has not been previously demonstrated. We infer that mafic magma intruded at depths of 5 km below the edifice and mingled with a pre-existing crystal-mush 3 yr before the eruption. Magma migration and mingling continued and stalled at 2.5 km depth about a year prior to the eruption. Precursory activity such as volcano-tectonic and long period seismicity, and a series of minor explosions overlap with the diffusion times 6 months before the eruption. Similar diffusion timescales have been reported for eruptions at other open vent volcanoes. Our study provides the first temporal and spatial constraints on magma storage and ascent before an eruption. Furthermore at Llaima, and potentially open vent systems, the progressive nature of magma injection suggests that additional processes (e.g. variable ascent rates, changing viscosity, etc.) are needed to trigger an eruption.

Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions.

PubMed

Wotzlaw, Jörn-Frederik; Bindeman, Ilya N; Stern, Richard A; D'Abzac, Francois-Xavier; Schaltegger, Urs

2015-09-10

Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 10(3) to 10(4) years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption.

Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions

PubMed Central

Wotzlaw, Jörn-Frederik; Bindeman, Ilya N.; Stern, Richard A.; D’Abzac, Francois-Xavier; Schaltegger, Urs

2015-01-01

Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 103 to 104 years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption. PMID:26356304

Stable isotope ratios of tap water in the contiguous United States

NASA Astrophysics Data System (ADS)

Bowen, Gabriel J.; Ehleringer, James R.; Chesson, Lesley A.; Stange, Erik; Cerling, Thure E.

2007-03-01

Understanding links between water consumers and climatological (precipitation) sources is essential for developing strategies to ensure the long-term sustainability of water supplies. In pursing this understanding a need exists for tools to study and monitor complex human-hydrological systems that involve high levels of spatial connectivity and supply problems that are regional, rather than local, in nature. Here we report the first national-level survey of stable isotope ratios in tap water, including spatially and temporally explicit samples from a large number of cities and towns across the contiguous United States. We show that intra-annual ranges of tap water isotope ratios are relatively small (e.g., <10‰ for δ2H) at most sites. In contrast, spatial variation in tap water isotope ratios is very large, spanning ranges of 163‰ for δ2H and 23.6‰ for δ18O. The spatial distribution of tap water isotope ratios at the national level is similar to that of stable isotope ratios of precipitation. At the regional level, however, pervasive differences between tap water and precipitation isotope ratios can be attributed to hydrological factors in the water source to consumer chain. These patterns highlight the potential for monitoring of tap water isotope ratios to contribute to the study of regional water supply stability and provide warning signals for impending water resource changes. We present the first published maps of predicted tap water isotope ratios for the contiguous United States, which will be useful in guiding future research on human-hydrological systems and as a tool for applied forensics and traceability studies.

Magma-sponge hypothesis and stratovolcanoes: Case for a compressible reservoir and quasi-steady deep influx at Soufrière Hills Volcano, Montserrat

NASA Astrophysics Data System (ADS)

Voight, Barry; Widiwijayanti, Christina; Mattioli, Glen; Elsworth, Derek; Hidayat, Dannie; Strutt, M.

2010-02-01

We use well-documented time histories of episodic GPS surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at Soufrière Hills volcano (SHV) on Montserrat, WI. We focus on data from 2003 to 2007, for an inflation succeeded by an episode of eruption-plus-deflation. We examine Mogi-type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre-eruption storage, and geodetic constraints inferring a deeper mean-pressure source. An exsolved phase involving several gas species greatly increases andesite magma compressibility to depths >10 km (i.e., for water content >4 wt%, crystallinity ˜40%), and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma (i.e., the “magma-sponge”). Our results suggest quasi-steady deep, mainly mafic magma influx of the order of 2 m3s-1, and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation. Our magma-sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at SHV, which comprises tens of km3 with radial dimensions of order ˜1-2 km, in turn implying a long-lived eruption.

Beamformer source analysis and connectivity on concurrent EEG and MEG data during voluntary movements.

PubMed

Muthuraman, Muthuraman; Hellriegel, Helge; Hoogenboom, Nienke; Anwar, Abdul Rauf; Mideksa, Kidist Gebremariam; Krause, Holger; Schnitzler, Alfons; Deuschl, Günther; Raethjen, Jan

2014-01-01

Electroencephalography (EEG) and magnetoencephalography (MEG) are the two modalities for measuring neuronal dynamics at a millisecond temporal resolution. Different source analysis methods, to locate the dipoles in the brain from which these dynamics originate, have been readily applied to both modalities alone. However, direct comparisons and possible advantages of combining both modalities have rarely been assessed during voluntary movements using coherent source analysis. In the present study, the cortical and sub-cortical network of coherent sources at the finger tapping task frequency (2-4 Hz) and the modes of interaction within this network were analysed in 15 healthy subjects using a beamformer approach called the dynamic imaging of coherent sources (DICS) with subsequent source signal reconstruction and renormalized partial directed coherence analysis (RPDC). MEG and EEG data were recorded simultaneously allowing the comparison of each of the modalities separately to that of the combined approach. We found the identified network of coherent sources for the finger tapping task as described in earlier studies when using only the MEG or combined MEG+EEG whereas the EEG data alone failed to detect single sub-cortical sources. The signal-to-noise ratio (SNR) level of the coherent rhythmic activity at the tapping frequency in MEG and combined MEG+EEG data was significantly higher than EEG alone. The functional connectivity analysis revealed that the combined approach had more active connections compared to either of the modalities during the finger tapping (FT) task. These results indicate that MEG is superior in the detection of deep coherent sources and that the SNR seems to be more vital than the sensitivity to theoretical dipole orientation and the volume conduction effect in the case of EEG.

Beamformer Source Analysis and Connectivity on Concurrent EEG and MEG Data during Voluntary Movements

PubMed Central

Muthuraman, Muthuraman; Hellriegel, Helge; Hoogenboom, Nienke; Anwar, Abdul Rauf; Mideksa, Kidist Gebremariam; Krause, Holger; Schnitzler, Alfons; Deuschl, Günther; Raethjen, Jan

2014-01-01

Electroencephalography (EEG) and magnetoencephalography (MEG) are the two modalities for measuring neuronal dynamics at a millisecond temporal resolution. Different source analysis methods, to locate the dipoles in the brain from which these dynamics originate, have been readily applied to both modalities alone. However, direct comparisons and possible advantages of combining both modalities have rarely been assessed during voluntary movements using coherent source analysis. In the present study, the cortical and sub-cortical network of coherent sources at the finger tapping task frequency (2–4 Hz) and the modes of interaction within this network were analysed in 15 healthy subjects using a beamformer approach called the dynamic imaging of coherent sources (DICS) with subsequent source signal reconstruction and renormalized partial directed coherence analysis (RPDC). MEG and EEG data were recorded simultaneously allowing the comparison of each of the modalities separately to that of the combined approach. We found the identified network of coherent sources for the finger tapping task as described in earlier studies when using only the MEG or combined MEG+EEG whereas the EEG data alone failed to detect single sub-cortical sources. The signal-to-noise ratio (SNR) level of the coherent rhythmic activity at the tapping frequency in MEG and combined MEG+EEG data was significantly higher than EEG alone. The functional connectivity analysis revealed that the combined approach had more active connections compared to either of the modalities during the finger tapping (FT) task. These results indicate that MEG is superior in the detection of deep coherent sources and that the SNR seems to be more vital than the sensitivity to theoretical dipole orientation and the volume conduction effect in the case of EEG. PMID:24618596

Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan—Constraints from melt inclusions and phase equilibria experiments

NASA Astrophysics Data System (ADS)

Suzuki, Yuki; Yasuda, Atsushi; Hokanishi, Natsumi; Kaneko, Takayuki; Nakada, Setsuya; Fujii, Toshitsugu

2013-05-01

The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2 = 57-58 wt.%; 960-980 °C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2 = 62-63 wt.% and a temperature of 870 °C, and contains 43 vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2 = 55 wt.% and a temperature of 1030 °C, and contains 9 vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles. The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125 MPa, corresponding to a depth of 5 km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6 wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤ 250 MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of < 5 km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8 km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2 km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation. Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871 °C; stage-1 of ≥ 350 h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2 h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

Linking observations at active volcanoes to physical processes through conduit flow modelling

NASA Astrophysics Data System (ADS)

Thomas, Mark; Neuberg, Jurgen

2010-05-01

Low frequency seismic events observed on volcanoes such as Soufriere hills, Montserrat may offer key indications about the state of a volcanic system. To obtain a better understanding of the source of these events and of the physical processes that take place within a volcano it is necessary to understand the conditions of magma a depth. This can be achieved through conduit flow modelling (Collier & Neuberg, 2006). 2-D compressible Navier-Stokes equations are solved through a Finite Element approach, for differing initial water and crystal contents, magma temperatures, chamber overpressures and geometric shapes of conduit. In the fully interdependent modelled system each of these variables has an effect on the magma density, viscosity, gas content, and also the pressure within the flow. These variables in turn affect the magma ascent velocity and the overall eruption dynamics of an active system. Of particular interest are the changes engendered in the flow by relativity small variations in the conduit geometry. These changes can have a profound local effect of the ascent velocity of the magma. By restricting the width of 15m wide, 5000m long vertical conduit over a 100m distance a significant acceleration of the magma is seen in this area. This has implications for the generation of Low-Frequency (LF) events at volcanic systems. The strain-induced fracture of viscoelastic magma or brittle failure of melt has been previously discussed as a possible source of LF events by several authors (e.g. Tuffen et al., 2003; Neuberg et al., 2006). The location of such brittle failure however has been seen to occur at relativity shallow depths (<1000m), which does not agree with the location of recorded LF events. By varying the geometry of the conduit and causing accelerations in the magma flow, localised increases in the shear strain rate of up to 30% are observed. This provides a mechanism of increasing the depth over witch brittle failure of melt may occur. A key observable of the Low frequency events observed on Montserrat is their tightly confined source region. The high degree of similarity of the waveforms from such events indicates a stationary common source within a finite volume of 150m x 150m x 150m (Neuberg et al., 2006). By modelling the physical processes that occur at depth within the volcano it has been possible to identify a potential source region of these events caused by the shape of the conduit, that has a fixed position and will have the potential cause repeatable events whenever magma is moving within the system. Making links of this type is essential to form a better understanding of what the observations made by monitoring systems actually relate to in terms of the volcanoes activity. Tuffen, H., Dingwell, D.B., and Pinkerton, H. 2003. Repeated fracture and healing of silicic magma generate flow banding and earthquakes? Geology, 31(12), 1089-1092. Collier, L. and Neuberg, J. 2006. Incorporating seismic observations into 2D conduit flow modelling. Journal of volcanology and geothermal research, 152, 331-346. Neuberg, J., Tuffen, H., Collier, L., Green, D., Powell, T., and Dingwell, P. 2006. The trigger mechanisms of low-frequency swarms on Montserrat. Journal of volcanology and geothermal research, 153, 37-50.

Persistence of antibiotic resistance genes and bacterial community changes in drinking water treatment system: From drinking water source to tap water.

PubMed

Su, Hao-Chang; Liu, You-Sheng; Pan, Chang-Gui; Chen, Jun; He, Liang-Ying; Ying, Guang-Guo

2018-03-01

As emerging contaminants, antibiotic resistance genes (ARGs) have become a public concern. This study aimed to investigate the occurrence and diversity of ARGs, and variation in the composition of bacterial communities in source water, drinking water treatment plants, and tap water in the Pearl River Delta region, South China. Various ARGs were present in the different types of water. Among the 27 target ARGs, floR and sul1 dominated in source water from three large rivers in the region. Pearson correlation analysis suggested that sul1, sul2, floR, and cmlA could be potential indicators for ARGs in water samples. The total abundance of the detected ARGs in tap water was much lower than that in source water. Sand filtration and sedimentation in drinking water treatment plants could effectively remove ARGs; in contrast, granular activated carbon filtration increased the abundance of ARGs. It was found that Pseudomonas may be involved in the proliferation and dissemination of ARGs in the studied drinking water treatment system. Bacteria and ARGs were still present in tap water after treatment, though they were significantly reduced. More research is needed to optimize the water treatment process for ARG removal. Copyright © 2017 Elsevier B.V. All rights reserved.

Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

USGS Publications Warehouse

Chang, Wu-Lung; Smith, Robert B.; Wicks, Charles; Farrell, J.M.; Puskas, C.M.

2007-01-01

The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

Magma transport and storage at Kilauea volcano, Hawaii I: 1790-1952

NASA Astrophysics Data System (ADS)

Wright, T. L.; Klein, F.

2011-12-01

We trace the evolution of Kilauea from the time of the first oral records of an explosive eruption in 1790 to the long eruption in Halemaumau crater in 1952. The establishment of modern seismic and geodetic networks in the early 1960s showed that eruptions and intrusions were fed from two magma sources beneath the summit at depths of 2-6 and ~1 km respectively (sources 1 and 2), and that seaward spreading of the south flank took place on a decollement at 10-12 km depth at the base of the Kilauea edifice. A third diffuse, pressure-transmitting magma system (source 3) between the shallow East rift zone and the decollement was also identified. We test the null hypothesis that the volcano has behaved similarly throughout its lifetime, and conclude that the null hypothesis is not met for the period preceding the 1952 summit eruption because of changes in magma supply rate and differences in ground deformation patterns. The western missionaries arriving at Kilauea in 1823 were confronted with a caldera-wide lava lake. Filling rates determined by visual observation correspond to magma supply rates that averaged more than 0.3 km3/yr prior to 1840 and declined to 1894, when lava disappeared altogether at Halemaumau crater. The Hawaiian Volcano Observatory (HVO) was established by Thomas A. Jaggar in 1912 adjacent to the Volcano House Hotel on the rim of Kilauea. Instrumental observation at HVO began using a seismometer that doubled as a tiltmeter. A 1912-1924 magma supply rate of 0.024 km3/yr agreed with the rate of filling of Kilauea caldera from 1840-1894. 1924 was a critical year. An intrusion that moved down Kilauea's East rift zone beginning in February culminated beneath the lower East rift zone in April. In May, explosive eruptions accompanied a dramatic draining of Halemaumau. Triangulation results between 1912 and 1921 showed uplift extending far beyond Kilauea caldera and an equally large regional subsidence occurred between 1921 and 1927. HVO tilt narrows the former time to 1918-1919 and the latter to 1924. Qualitative Mogi modeling of the 1921-1927 deformation data yields three centers, two shallow ones corresponding to sources 1 and 2, and a third deeper one that we interpret to represent draining of source 3. During recovery from the 1924 intrusion and collapse the tilt remained low, unlike the aftermath of more recent deflations. Small eruptions in Halemaumau between 1924 and 1934 used up the last of the magma that fed the lava lakes, and three passive East rift intrusions without a tilt signal are considered part of the recovery of source 3. Kilauea began inflating in March 1950, leading up to the long 1952 eruption in Halemaumau. Deep earthquakes occurred in 1950 and 1951, resulting in an increased magma supply rate of 0.062 km3/yr. An intense earthquake swarm occurred beneath the offshore south flank in March-April 1952 that unlocked the south flank to initiate the modern spreading regime. We interpret the 1924 intrusion as a critical event in stabilizing the modern magma system beneath the rift zone. Prior to that time it is probable that major caldera draining events in the 19th century involved the entire magmatic system. Measurements made at HVO are critical to the interpretations made in the pre-1952 period.

Geochemical and Depth Variations at the Galápagos 93.25˚W Propagating Rift

NASA Astrophysics Data System (ADS)

Rotella, M.; Sinton, J.; Mahoney, J.; Chazey, W.

2006-12-01

The 93.25°W propagating rift on the Galápagos Spreading Center (GSC) differs markedly from the better-known propagator at 95.5°W in having the morphology of a classic overlapping spreading center (~24 km of overlap and 7.5 km of offset). It has a higher propagation rate (70 vs 48 mm/yr) [Wilson & Hey, JGR v. 100, 1995] and is breaking through younger crust (260 vs 910 ka); overall magma supply is ~20% greater, as the area is closer to the Galápagos hotspot. The overlapping limbs lack pronounced bathymetric lows, instead they are up to 150 m shallower than the surrounding axial ridges away from the offset. Lavas are T-MORB; failing rift lavas show a slight increase in Mg within the overlap zone but propagating rift lavas lack the strong fractionation anomaly that characterizes the propagating limb at 95.5°W and many other propagating rifts. New major and trace element data on 28 samples from 24 dredge stations along a 175 km section of the GSC spanning the 93.25°W offset indicate significant, systematic variations in mantle sources and melting processes on each limb of the system. Fractionation-corrected ratios of highly to moderately incompatible elements (e.g. La/Yb, Sm/Yb, Zr/Y) show constant values along the propagating rift east of 93.2°W, but within the overlap zone these ratios increase sharply up to a factor of 1.5, then gradually decline to the west. In contrast, the failing rift shows constant to moderately increasing ratios as the overlap zone is approached from the west, with lower overall ratios within the zone. These variations could be interpreted to reflect a counter-intuitive relationship of gradually increasing extent of partial melting with progressive failure of the dying rift, consistent with the striking shoaling of the failing limb, or melting of incompatible-element depleted mantle. Variations along the eastern, propagating rift suggest either a sharp decrease in extent of melting or tapping of a more incompatible-element-enriched mantle source within the overlap zone. Limited Nd-Pb-Sr isotopic data suggest source variations are required in addition to variations in extent of melting. Thus, in contrast to other well-documented propagators where geochemical variations are dominated by magma chamber effects, variations around the 93.25°W system appear to be dominated by melting and source.

Rb-Sr and Sm-Nd Isotopic Studies of Lunar Green and Orange Glasses

NASA Technical Reports Server (NTRS)

Shih, C.-Y.; Nyquist, L. E.; Reese, Y.

2012-01-01

Lunar volcanic glassy beads have been considered as quenched basaltic magmas derived directly from deep lunar mantle during fire-fountaining eruptions [1]. Since these sub-mm size glassy melt droplets were cooled in a hot gaseous medium during free flight [2], they have not been subject to mineral fractionations. Thus, they represent primary magmas and are the best samples for the investigation of the lunar mantle. Previously, we presented preliminary Rb- Sr and Sm-Nd isotopic results for green and orange glassy samples from green glass clod 15426,63 and orange soil 74220,44, respectively [3]. Using these isotopic data, initial Sr-87/Sr-86 and Nd ratios for these pristine mare glass sources can be calculated from their respective crystallization ages previously determined by other age-dating techniques. These isotopic data were used to evaluate the mineralogy of the mantle sources. In this report, we analyzed additional glassy samples in order to further characterize isotopic signatures of their source regions. Also, we'll postulate a relationship between these two major mare basalt source mineralogies in the context of lunar magma ocean dynamics.

Regional and temporal variability of melts during a Cordilleran magma pulse: Age and chemical evolution of the jurassic arc, eastern mojave desert, California

USGS Publications Warehouse

Barth, A.P.; Wooden, J.L.; Miller, David; Howard, Keith A.; Fox, Lydia; Schermer, Elizabeth R.; Jacobson, C.E.

2017-01-01

Intrusive rock sequences in the central and eastern Mojave Desert segment of the Jurassic Cordilleran arc of the western United States record regional and temporal variations in magmas generated during the second prominent pulse of Mesozoic continental arc magmatism. U/Pb zircon ages provide temporal control for describing variations in rock and zircon geochemistry that reflect differences in magma source components. These source signatures are discernible through mixing and fractionation processes associated with magma ascent and emplacement. The oldest well-dated Jurassic rocks defining initiation of the Jurassic pulse are a 183 Ma monzodiorite and a 181 Ma ignimbrite. Early to Middle Jurassic intrusive rocks comprising the main stage of magmatism include two high-K calc-alkalic groups: to the north, the deformed 183–172 Ma Fort Irwin sequence and contemporaneous rocks in the Granite and Clipper Mountains, and to the south, the 167–164 Ma Bullion sequence. A Late Jurassic suite of shoshonitic, alkali-calcic intrusive rocks, the Bristol Mountains sequence, ranges in age from 164 to 161 Ma and was emplaced as the pulse began to wane. Whole-rock and zircon trace-element geochemistry defines a compositionally coherent Jurassic arc with regional and secular variations in melt compositions. The arc evolved through the magma pulse by progressively greater input of old cratonic crust and lithospheric mantle into the arc magma system, synchronous with progressive regional crustal thickening.

Characteristics of Individual Eruptive Events on the Lunar Western Limb and Farside: Implications for Magma Ascent and Eruption Mechanisms

NASA Astrophysics Data System (ADS)

Yingst, R. A.; Head, J. W., III

1996-03-01

The connection between lunar magma source regions and the location and emplacement conditions of volcanic surface features remains unclear, both conceptually and quantitatively with respect to our understanding of transport mechanisms. Investigation of these issues requires use of surface feature characteristics to reconstruct the conditions of transport and eruption, so that thermal evolution models may be tested. Specifically, mare deposits are asymmetrically distributed over the lunar surface, with the nearside displaying the vast majority of surface basalts. Apollo and recent Clementine data have confirmed a dichotomy between the nearside and the farside with respect to crustal thickness. This implies a possible relationship between the efficiency of magma transport and the amount of crust through which magma must pass. It has been suggested that mare emplacement has been controlled by propagation of dikes driven by the overpressurization of diapir-like source regions stalled below the cooling lunar highland crust. Thus, regions of thinner crust would be expected to allow a greater number of dikes to reach the surface under the same source region conditions, than areas with thicker crust. Recent analyses of the characteristics of lava ponds in the South Pole/Aitken and Orientale/Mendel-Rydberg basins based on Clementine, Lunar Orbiter and Zond data have provided evidence that supports this theory.

Contrasting sources of Late Paleozoic rhyolite magma in the Polish Lowlands: evidence from U-Pb ages and Hf and O isotope composition in zircon

NASA Astrophysics Data System (ADS)

Słodczyk, Elżbieta; Pietranik, Anna; Glynn, Sarah; Wiedenbeck, Michael; Breitkreuz, Christoph; Dhuime, Bruno

2018-02-01

The Polish Lowlands, located southwest of the Teisseyre-Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly rhyolitic, magmatism during the Late Paleozoic. Thanks to the inherited zircon they contain, these rhyolitic rocks provide a direct source of information about the pre-Permian rocks underlying the Polish Lowland. This paper presents zircon U-Pb geochronology and Hf and O isotopic results from five drill core samples representing four rhyolites and one granite. Based on the ratio of inherited vs. autocrystic zircon, the rhyolites can be divided into two groups: northern rhyolites, where autocrystic zircon is more abundant and southern rhyolites, where inherited zircon dominates. We suggest that the magma sources and the processes responsible for generating high silica magmas differ between the northern and southern rhyolites. Isotopically distinct sources were available during formation of northern rhyolites, as the Hf and O isotopes in magmatic zircon differ between the two analysed localities of northern rhyolites. A mixing between magmas formed from Baltica-derived mudstone-siltstone sediments and Avalonian basement or mantle can explain the diversity between the zircon compositions from the northern localities Daszewo and Wysoka Kamieńska. Conversely, the southern rhyolites from our two localities contain zircon with similar compositions, and these units can be further correlated with results from the North East German Basin, suggesting uniform source rocks over this larger region. Based on the ages of inherited zircon and the isotopic composition of magmatic ones, we suggest that the dominant source of the southern rhyolites is Variscan foreland sediments mixed with Baltica/Avalonia-derived sediments.

Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

NASA Technical Reports Server (NTRS)

Rapp, J. F.; Draper, D. S.

2015-01-01

The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

The length of channelized lava flows: Insight from the 1859 eruption of Mauna Loa Volcano, Hawai‘i

NASA Astrophysics Data System (ADS)

Riker, Jenny M.; Cashman, Katharine V.; Kauahikaua, James P.; Montierth, Charlene M.

2009-06-01

The 1859 eruption of Mauna Loa Volcano, Hawai'i, produced paired 'a'ā and pāhoehoe flows of exceptional length (51 km). The 'a'ā flow field is distinguished by a long (> 36 km) and well-defined pāhoehoe-lined channel, indicating that channelized lava remained fluid to great distances from the vent. The 1859 eruption was further unusual in initiating at a radial vent on the volcano's northwest flank, instead of along the well-defined rift zone that has been the source of most historic activity. As such, it presents an opportunity both to examine controls on the emplacement of long lava channels and to assess hazards posed by future flank eruptions of Mauna Loa. Here we combine evidence from historical chronicles with analysis of bulk compositions, glass geothermometry, and microlite textures of samples collected along the 1859 lava flows to constrain eruption and flow emplacement conditions. The bulk compositions of samples from the 'a'ā and pāhoehoe flow fields are bimodally distributed and indicate tapping of two discrete magma bodies during eruption. Samples from the pāhoehoe flow field have bulk compositions similar to those of historically-erupted lavas (< 8 wt.% MgO); lava that fed the 'a'ā channel is more primitive (> 8 wt.% MgO), nearly aphyric, and was erupted at high temperatures (1194-1216 °C). We suggest that the physical properties of proximal channel-fed lava (i.e., high-temperature, low crystallinity, and low bulk viscosity) promoted both rapid flow advance and development of long pāhoehoe-lined channels. Critical for the latter was the large temperature decrease (~ 50 °C) required to reach the point at which plagioclase and pyroxene started to crystallize; the importance of phase constraints are emphasized by our difficulty in replicating patterns of cooling and crystallization recorded by high-temperature field samples using common models of flow emplacement. Placement of the 1859 eruption within the context of historic activity at Mauna Loa suggests that the formation of radial vents and eruptions of high-temperature magma may not only be linked, but may also be a consequence of periods of high magma supply (e.g., 1843-1877). Flank eruptions could therefore warrant special consideration in models and hazard mitigation efforts.

Preliminary Report on U-Th-Pb Isotope Systematics of the Olivine-Phyric Shergottite Tissint

NASA Technical Reports Server (NTRS)

Moriwaki, R.; Usui, T.; Yokoyama, T.; Simon, J. I.; Jones, J. H.

2014-01-01

Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions, and trace element abundances.. These correlations have been interpreted as indicating the presence of a reduced, incompatible-element- depleted reservoir and an oxidized, incompatible-element-rich reservoir. The former is clearly a depleted mantle source, but there has been a long debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former clearly requires the ancient martian crust to be the enriched source (crustal assimilation), whereas the latter requires a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and U-Th-Pb concentration analyses of the olivine-phyric shergottite Tissint because U-Th-Pb isotope systematics have been intensively used as a powerful radiogenic tracer to characterize old crust/sediment components in mantle- derived, terrestrial oceanic island basalts. The U-Th-Pb analyses are applied to sequential acid leaching fractions obtained from Tissint whole-rock powder in order to search for Pb isotopic source components in Tissint magma. Here we report preliminary results of the U-Th-Pb analyses of acid leachates and a residue, and propose the possibility that Tissint would have experienced minor assimilation of old martian crust.

Quantifying tap-to-household water quality deterioration in urban communities in Vellore, India: The impact of spatial assumptions.

PubMed

Alarcon Falconi, Tania M; Kulinkina, Alexandra V; Mohan, Venkata Raghava; Francis, Mark R; Kattula, Deepthi; Sarkar, Rajiv; Ward, Honorine; Kang, Gagandeep; Balraj, Vinohar; Naumova, Elena N

2017-01-01

Municipal water sources in India have been found to be highly contaminated, with further water quality deterioration occurring during household storage. Quantifying water quality deterioration requires knowledge about the exact source tap and length of water storage at the household, which is not usually known. This study presents a methodology to link source and household stored water, and explores the effects of spatial assumptions on the association between tap-to-household water quality deterioration and enteric infections in two semi-urban slums of Vellore, India. To determine a possible water source for each household sample, we paired household and tap samples collected on the same day using three spatial approaches implemented in GIS: minimum Euclidean distance; minimum network distance; and inverse network-distance weighted average. Logistic and Poisson regression models were used to determine associations between water quality deterioration and household-level characteristics, and between diarrheal cases and water quality deterioration. On average, 60% of households had higher fecal coliform concentrations in household samples than at source taps. Only the weighted average approach detected a higher risk of water quality deterioration for households that do not purify water and that have animals in the home (RR=1.50 [1.03, 2.18], p=0.033); and showed that households with water quality deterioration were more likely to report diarrheal cases (OR=3.08 [1.21, 8.18], p=0.02). Studies to assess contamination between source and household are rare due to methodological challenges and high costs associated with collecting paired samples. Our study demonstrated it is possible to derive useful spatial links between samples post hoc; and that the pairing approach affects the conclusions related to associations between enteric infections and water quality deterioration. Copyright © 2016 Elsevier GmbH. All rights reserved.

Rare earth patterns in shergottite phosphates and residues

NASA Technical Reports Server (NTRS)

Laul, J. C.

1987-01-01

Leaching experiments with 1M HCl on ALHA 77005 powder show that rare earth elements (REE) are concentrated in accessory phosphate phases (whitlockite, apatite) that govern the REE patterns of bulk shergottites. The REE patterns of whitlockite are typically light REE-depleted with a negative Eu anomaly and show a hump at the heavy REE side, while the REE pattern of apatite (in Shergotty) is light REE-enriched. Parent magmas are calculated from the modal compositions of residues of ALHA 77005, Shergotty, and EETA 79001. The parent magmas lack a Eu anomaly, indicating that plagioclase was a late-stage crystallizing phase and that it probably crystallized before the phosphates. The parent magmas of ALHA 77005 and Shergotty have similar REE patterns, with a subchondritic Nd/Sm ratio. However, the Sm/Nd isotopoics require a light REE-depleted source for ALHA 77005 (if the crystallization age is less than 600 Myr) and a light REE-enriched source for Shergotty. Distant Nd and Sr isotopic signatures may suggest different source regions for shergottites.

Geothermal energy program overview

NASA Astrophysics Data System (ADS)

1991-12-01

The mission of the Geothermal Energy Program is to develop the science and technology necessary for tapping our nation's tremendous heat energy sources contained within the Earth. Geothermal energy is a domestic energy source that can produce clean, reliable, cost-effective heat and electricity for our nation's energy needs. Geothermal energy - the heat of the Earth - is one of our nation's most abundant energy resources. In fact, geothermal energy represents nearly 40 percent of the total U.S. energy resource base and already provides an important contribution to our nation's energy needs. Geothermal energy systems can provide clean, reliable, cost-effective energy for our nation's industries, businesses, and homes in the form of heat and electricity. The U.S. Department of Energy's (DOE) Geothermal Energy Program sponsors research aimed at developing the science and technology necessary for utilizing this resource more fully. Geothermal energy originates from the Earth's interior. The hottest fluids and rocks at accessible depths are associated with recent volcanic activity in the western states. In some places, heat comes to the surface as natural hot water or steam, which have been used since prehistoric times for cooking and bathing. Today, wells convey the heat from deep in the Earth to electric generators, factories, farms, and homes. The competitiveness of power generation with lower quality hydrothermal fluids, geopressured brines, hot dry rock, and magma (the four types of geothermal energy), still depends on the technical advancements sought by DOE's Geothermal Energy Program.

Origin of silicic magmas along the Central American volcanic front: Genetic relationship to mafic melts

NASA Astrophysics Data System (ADS)

Vogel, Thomas A.; Patino, Lina C.; Eaton, Jonathon K.; Valley, John W.; Rose, William I.; Alvarado, Guillermo E.; Viray, Ela L.

2006-09-01

Silicic pyroclastic flows and related deposits are abundant along the Central American volcanic front. These silicic magmas erupted through both the non-continental Chorotega block to the southeast and the Paleozoic continental Chortis block to the northwest. The along-arc variations of the silicic deposits with respect to diagnostic trace element ratios (Ba/La, U/Th, Ce/Pb), oxygen isotopes, Nd and Sr isotope ratios mimic the along-arc variation in the basaltic and andesitic lavas. This variation in the lavas has been interpreted to indicate relative contributions from the slab and asthenosphere to the basaltic magmas [Carr, M.J., Feigenson, M.D., Bennett, E.A., 1990. Incompatible element and isotopic evidence for tectonic control of source mixing and melt extraction along the Central American arc. Contributions to Mineralogy and Petrology, 105, 369-380.; Patino, L.C., Carr, M.J. and Feigenson, M.D., 2000. Local and regional variations in Central American arc lavas controlled by variations in subducted sediment input. Contributions to Mineralogy and Petrology, 138 (3), 265-283.]. With respect to along-arc trends in basaltic lavas the largest contribution of slab fluids is in Nicaragua and the smallest input from the slab is in central Costa Rica — similar trends are observed in the silicic pyroclastic deposits. Data from melting experiments of primitive basalts and basaltic andesites demonstrate that it is difficult to produce high K 2O/Na 2O silicic magmas by fractional crystallization or partial melting of low-K 2O/Na 2O sources. However fractional crystallization or partial melting of medium- to high-K basalts can produce these silicic magmas. We interpret that the high-silica magmas associated Central America volcanic front are partial melts of penecontemporaneous, mantle-derived, evolved magmas that have ponded and crystallized in the mid-crust — or are melts extracted from these nearly completely crystallized magmas.

Water content in intraplate basalt magmas from the Longgang area, NE China

NASA Astrophysics Data System (ADS)

Mizobuchi, F.; Kuritani, T.; Yoshida, T.; Miyamoto, T.; Nagahashi, Y.; Taniguchi, H.

2009-12-01

In northeastern China, intraplate magmatism has been active, and Cenozoic basalts are widely distributed. Beneath the area, the subducted Pacific slab is stagnant in the mantle transition zone, and some previous studies have inferred that the magmatism may have been affected by fluid phases released from the stagnant slab. To test this hypothesis, it is important to know the water content in the source mantle. In this context, the water content in the intraplate magma was estimated using primitive scoria samples from the Longgang area, NE China. Because of the absence of glass inclusions in phenocrysts that enables direct measurement of water content, it was estimated by thermodynamic constraints. During ascent of water-bearing magmas, the water solubility tends to decrease, and water saturation is achieved at depth. Then, crystals can grow rapidly by an increase in the liquidus temperature resulting from water exsolution. Because the microlites in our samples can be regarded as such crystals, the water content in the magma in which the microlites occured was estimated by thermodynamic analyses using the compositions of the microlites and glass. In the calculations, thermodynamic solution models of e.g. Ghiorso&Sack(1995) were used. The calculated water content and the temperature of the magma were about 0.6 wt.% and 1110 degC, respectively. The water content is slightly higher than those of primitive intraplate magmas such as from Hawaii (0.4 wt.%, Wallace & Anderson,1998) and Iceland (0.1-0.4 wt.%, Nichols et al., 2002). Assuming that the degree of melting was 1-2%, the water content of the source asthenospheric mantle was 110-170 ppm. The magma temperature at 80-120 km depth (garnet stability field) was also estimated as 1160-1180 degC, assuming adiabatic ascent. Using the constraints obtained in this study, the effect of stagnant-slab-derived fluids on the magma generation will be evaluated as a future study.

Post-collisional and intraplate Cenozoic volcanism in the rifted Apennines/Adriatic domain

NASA Astrophysics Data System (ADS)

Bianchini, G.; Beccaluva, L.; Siena, F.

2008-02-01

The distinctive tectono-magmatic characteristics of rift volcanism in the Apennines/Adria domains are discussed focussing attention on the nature of mantle sources, stress regimes, and conditions of magma generation. Post-collisional intensive lithospheric rifting and tectonic collapse of the Apennines generate large amounts of Pliocene-Quaternary orogenic magmas which overlie a nearly vertical subducted slab along the peri-Tyrrhenian border. This magmatism includes the Roman Magmatic Province sensu lato (RMP-s.l.) and the Internal Apennines Volcanism (IAV), and consists of high-K calcalkaline, potassic (shoshonitic) and ultrapotassic (leucitites, leucite basanite and minor lamproites and kamafugites) products. Integrated petrological and geochemical studies of these rocks (and associated mantle xenoliths) indicate that most of them could have been generated by a restricted partial melting range ( F ≤ 5-10%) of extremely inhomogeneous phlogopite-veined lithospheric mantle sources, resulting from subduction related K-metasomatic processes. Moreover, the presence of both intermediate anorogenic and subduction related geochemical features in Mt. Vulture magmas support the existence of a slab window beneath the central-southern Apennines, which could have allowed inflow of subduction components to intraplate mantle sources. This slab discontinuity may mark the transition between the already collisioned Adriatic and the still subducting Ionian lithospheric slabs. By contrast, the Paleogene intraplate magmatism of the Adriatic foreland (i.e., the Veneto Province (VVP) and the minor Mt. Queglia and Pietre Nere magmatic bodies) is characterized by small volumes of basic magmas, varying from tholeiitic to strongly Na-alkaline in composition. This magmatism appears to be related to a limited extensional regime typical of the low volcanicity rifts. Petrogenetic modelling of the intraplate Adriatic foreland magmas indicates that their composition is remarkably depth-dependent, with generation of tholeiites to nephelinites/alkaline lamprophyres by decreasing degrees of partial melting ( F = 25 to ≤ 5%) of lherzolite lithospheric sources at progressively increasing depths (ca. 40 to 100 km). Moreover, geochemical features of these anorogenic magmas testify that their mantle sources are remarkable homogeneous, as also confirmed by lack of veining in the VVP mantle xenoliths. This homogeneity suggests that Na-metasomatic agents pervasively affected the overlying Adriatic lithospheric mantle by porous flow mechanisms without causing significant inhomogeneities at a regional scale.

Why Is There an Abrupt Transition from Solid Rock to Low Crystallinity Magma in Drilled Magma Bodies?

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Carrigan, C. R.; Sun, Y.; Lavallée, Y.

2017-12-01

We report on a preliminary evaluation, from basic principles of heat and mass transfer, on the unexpectedly abrupt transition from cuttings of solid rock to fragments of crystal poor glass during drilling into magma bodies. Our analysis is based on conditions determined and inferred for the 2009 IDDP-1 well in Krafla Caldera, which entered apparently liquidus rhyolite magma at about 900oC at a depth of 2104 m. Simple conduction would predict some 30 m of crystallization and partial crystallization since the latest time the magma could have been intruded, approximately 30 years prior to discovery by drilling. Option 1: The expected crystallization of magma has occurred but interstitial melt remains. The pressure difference between lithostatic load of about 50 MPa on the mush and 20 MPa hydrostatic pressure in the well causes pore melt to flow from the permeable mush into the borehole, where it becomes the source of the quenched melt chips. To be viable, this mechanism must work over the time frame of a day. Option 2: The expected crystallization is occurring, but high Rayleigh number thermal convection in the magma chamber continuously displaces crystallizing roof magma by liquidus magma from the interior of the body. To be viable, this mechanism must result in overturning magma in the chamber on a time scale that is much shorter than that of crystallization. Option 3: Flow-induced crystal migration away from zones of high shear created during drilling into magma may preferentially produce low-crystal-content melt at the boundary of the borehole, which is then sampled.

Investigation of healthcare-acquired infections associated with Pseudomonas aeruginosa biofilms in taps in neonatal units in Northern Ireland.

PubMed

Walker, J T; Jhutty, A; Parks, S; Willis, C; Copley, V; Turton, J F; Hoffman, P N; Bennett, A M

2014-01-01

In December 2011 and early 2012 four neonates died from Pseudomonas aeruginosa bacteraemia in hospitals in Northern Ireland. To assess whether P. aeruginosa was associated with the neonatal unit taps and whether waterborne isolates were consistent with patient isolates. Thirty taps and eight flow straighteners from the relevant hospitals were categorized and dismantled into 494 components and assessed for aerobic colony and P. aeruginosa counts using non-selective and selective agars. P. aeruginosa isolates were typed by variable number tandem repeat (VNTR) analysis. Selected tap components were subjected to epifluorescence and scanning electron microscopy to visualize biofilm. The highest P. aeruginosa counts were from the flow straighteners, metal support collars and the tap bodies surrounding these two components. Complex flow straighteners had a significantly higher P. aeruginosa count than other types of flow straighteners (P < 0.05). Highest aerobic colony counts were associated with integrated mixers and solenoids (P < 0.05), but there was not a strong correlation (r = 0.33) between the aerobic colony counts and P. aeruginosa counts. Representative P. aeruginosa tap isolates from two hospital neonatal units had VNTR profiles consistent with strains from the tap water and infected neonates. P. aeruginosa was predominantly found in biofilms in flow straighteners and associated components in the tap outlets and was a possible source of the infections observed. Healthcare providers should be aware that water outlets can be a source of P. aeruginosa contamination and should take steps to reduce such contamination, monitor it and have strategies to minimize risk to susceptible patients. Copyright © 2013 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

Magma volumes and storage in the middle crust

NASA Astrophysics Data System (ADS)

Memeti, V.; Barnes, C. G.; Paterson, S. R.

2015-12-01

Quantifying magma volumes in magma plumbing systems is mostly done through geophysical means or based on volcanic eruptions. Detailed studies of plutons, however, are useful in revealing depths and evolving volumes of stored magmas over variable lifetimes of magma systems. Knowledge of the location, volume, and longevity of stored magma is critical for understanding where in the crust magmas attain their chemical signature, how these systems physically behave and how source, storage levels, and volcanoes are connected. Detailed field mapping, combined with single mineral geochemistry and geochronology of plutons, allow estimates of size and longevity of melt-interconnected magma batches that existed during the construction of magma storage sites. The Tuolumne intrusive complex (TIC) recorded a 10 myr magmatic history. Detailed maps of the major units in different parts of the TIC indicate overall smaller scale (cm- to <1 km) compositional variation in the oldest, outer Kuna Crest unit and mainly larger scale (>10 km) changes in the younger Half Dome and Cathedral Peak units. Mineral-scale trace element data from hornblende of granodiorites to gabbros from the Kuna Crest lobe show distinct hornblende compositions and zoning patterns. Mixed hornblende populations occur only at the transition to the main TIC. This compositional heterogeneity in the first 1-2 myr points to low volume magmatism resulting in smaller, discrete and not chemically interacting magma bodies. Trace element and Sr- and Pb-isotope data from growth zones of K-feldspar phenocrysts from the two younger granodiorites indicate complex mineral zoning, but general isotopic overlap, suggesting in-situ, inter-unit mixing and fractionation. This is supported by hybrid zones between units, mixing of zircon, hornblende, and K-feldspar populations and late leucogranites. Thus, magma body sizes increased later resulting in overall more homogeneous, but complexly mixing magma mushes that fractionated locally.

InSAR observations of deformation associated with new episodes of volcanism at Kilauea Volcano, Hawai'i, 2007

USGS Publications Warehouse

Poland, Michael P.

2008-01-01

In June 2007, the Pu'u 'Ō'ō-Kūpaianaha eruption of Kīlauea Volcano was interrupted when magma intruded the east rift zone (ERZ), resulting in a small extrusion of lava near Makaopuhi Crater. Deformation associated with the activity was exceptionally well-documented by ASAR interferometry, which indicates deflation of the summit and uplift and extension of the ERZ. Models of co-intrusion interferograms suggest that the dike was emplaced in two distinct segments. The modeled volume of the dike greatly exceeds that of the deflation source, raising the possibility that magma from the downrift Pu'u 'Ō'ō vent (dominant extrusion site at Kīlauea since 1983) contributed to the eruption near Makaopuhi, or that the magma that fed the eruption from the summit was compressible. A month following the Makaopuhi eruption, an eruptive fissure opened on the east flank of Pu'u 'Ō'ō. Interferograms, processed within 48 hours of the event, were critical in demonstrating that the magma source feeding the eruption was shallow. The eruption probably resulted from overpressure in Pu'u 'Ō'ō's magmatic system.

Apollo 15 yellow-brown volcanic glass - Chemistry and petrogenetic relations to green volcanic glass and olivine-normative mare basalts

NASA Technical Reports Server (NTRS)

Hughes, S. S.; Schmitt, R. A.; Delano, J. W.

1988-01-01

Electron microprobe and INAA were used to analyze forty spherules of Apollo 15 yellow-brown glass for major and trace elements. The glass is one of twenty-five high-Mg primary magmas emplaced on the lunar surface in pyroclastic eruptions. The abundances show that the magma was produced by partial melting of differentiated cumulates in the lunar mantle. Models to explain the possible source-regions of several Apollo 15 and Apollo 12 low-Ti mare magmas are presented.

Watching magma from space

USGS Publications Warehouse

Lu, Zhong; Wicks, Charles W.; Dzurisin, Daniel; Thatcher, Wayne R.; Freymueller, Jeffrey T.; McNutt, Stephen R.; Mann, Dorte

2000-01-01

Westdahl is a broad shield volcano at the western end of Unimak Island in the Aleutian chain. It has apparently been dormant since a 1991-92 eruption and seismicity levels have been low. However, satellite radar imaging shows that in the years following 1992 the upper flanks of Westdahl have risen several centimeters, probably from the influx of new magma deep below its summit. Until now, deep magma reservoirs have been difficult to detect beneath most volcanoes. But using space geodetic technologies, specifically interferometric synthetic aperture radar (InSAR), we have discovered a deep magmatic source beneath Westdahl. 

Magma degassing triggered by static decompression at Kīlauea Volcano, Hawai‘i

USGS Publications Warehouse

Poland, Michael P.; Jeff, Sutton A.; Gerlach, Terrence M.

2009-01-01

During mid-June 2007, the summit of Kīlauea Volcano, Hawai‘i, deflated rapidly as magma drained from the subsurface to feed an east rift zone intrusion and eruption. Coincident with the deflation, summit SO2 emission rates rose by a factor of four before decaying to background levels over several weeks. We propose that SO2 release was triggered by static decompression caused by magma withdrawal from Kīlauea's shallow summit reservoir. Models of the deflation suggest a pressure drop of 0.5–3 MPa, which is sufficient to trigger exsolution of the observed excess SO2 from a relatively small volume of magma at the modeled source depth beneath Kīlauea's summit. Static decompression may also explain other episodes of deflation accompanied by heightened gas emission, including the precursory phases of Kīlauea's 2008 summit eruption. Hazards associated with unexpected volcanic gas emission argue for increased awareness of magma reservoir pressure fluctuations.

A basal magma ocean dynamo to explain the early lunar magnetic field

NASA Astrophysics Data System (ADS)

Scheinberg, Aaron L.; Soderlund, Krista M.; Elkins-Tanton, Linda T.

2018-06-01

The source of the ancient lunar magnetic field is an unsolved problem in the Moon's evolution. Theoretical work invoking a core dynamo has been unable to explain the magnitude of the observed field, falling instead one to two orders of magnitude below it. Since surface magnetic field strength is highly sensitive to the depth and size of the dynamo region, we instead hypothesize that the early lunar dynamo was driven by convection in a basal magma ocean formed from the final stages of an early lunar magma ocean; this material is expected to be dense, radioactive, and metalliferous. Here we use numerical convection models to predict the longevity and heat flow of such a basal magma ocean and use scaling laws to estimate the resulting magnetic field strength. We show that, if sufficiently electrically conducting, a magma ocean could have produced an early dynamo with surface fields consistent with the paleomagnetic observations.

[Volatile organic compounds of the tap water in the Watarase, Tone and Edo River system].

PubMed

Ohmichi, Kimihide; Ohmichi, Masayoshi; Machida, Kazuhiko

2004-01-01

The chlorination of river water in purification plants is known to produce carcinogens such as trihalomethanes (THMs). We studied the river system of the Watarase, Tone, and Edo Rivers in regard to the formation of THMs. This river system starts from the base of the Ashio copper mine and ends at Tokyo Bay. Along the rivers, there are 14 local municipalities in Gunma, Saitama, Ibaragi and Chiba Prefectures, as well as Tokyo. This area is the center of the Kanto plain and includes the main sources of water pollution from human activities. We also analyzed various chemicals in river water and tap water to clarify the status of the water environment, and we outline the problems of the water environment in the research area (Fig. 1). Water samples were taken from 18 river sites and 42 water faucets at public facilities in 14 local municipalities. We analyzed samples for volatile organic compounds such as THMs, by gas chromatography mass spectrometry (GC-MS), and evaluations of chemical oxygen demand (COD) were made with reference to Japanese drinking water quality standards. Concentrations of THMs in the downstream tap water samples were higher than those in the samples from the upperstream. This tendency was similar to the COD of the river water samples, but no correlation between the concentration of THMs in tap water and the COD in tap water sources was found. In tap water of local government C, trichloroethylene was detected. The current findings suggest that the present water filtration plant procedures are not sufficient to remove some hazardous chemicals from the source water. Moreover, it was confirmed that the water filtration produced THMs. Also, trichloroethylene was detected from the water environment in the research area, suggesting that pollution of the water environment continues.

Alternate energy source usage for in situ heat treatment processes

DOEpatents

Stone, Jr., Francis Marion; Goodwin, Charles R [League City, TX; Richard, Jr., James

2011-03-22

Systems, methods, and heaters for treating a subsurface formation are described herein. At least one system for providing power to one or more subsurface heaters is described herein. The system may include an intermittent power source; a transformer coupled to the intermittent power source, and a tap controller coupled to the transformer. The transformer may be configured to transform power from the intermittent power source to power with appropriate operating parameters for the heaters. The tap controller may be configured to monitor and control the transformer so that a constant voltage is provided to the heaters from the transformer regardless of the load of the heaters and the power output provided by the intermittent power source.

Checking the validity of superimposing analytical deformation models and implications for numerical modelling of dikes and magma chambers

NASA Astrophysics Data System (ADS)

Pascal, K.; Neuberg, J. W.; Rivalta, E.

2011-12-01

The displacement field due to magma movements in the subsurface is commonly modelled using the solutions for a point source (Mogi, 1958), a finite spherical source (McTigue, 1987), or a dislocation source (Okada, 1992) embedded in a homogeneous elastic half-space. When the magmatic system is represented by several sources, their respective deformation fields are summed, and the assumption of homogeneity in the half-space is violated. We have investigated the effects of neglecting the interaction between sources on the surface deformation field. To do so, we calculated the vertical and horizontal displacements for models with adjacent sources and we tested them against the solutions of corresponding numerical 3D finite element models. We implemented several models combining spherical pressure sources and dislocation sources, varying the pressure or opening of the sources and their relative position. We also investigated various numerical methods to model a dike as a dislocation tensile source or as a pressurized tabular crack. In the former case, the dike opening was either defined as two boundaries displaced from a central location, or as one boundary displaced relative to the other. We finally considered two case studies based on Soufrière Hills Volcano (Montserrat, West Indies) and the Dabbahu rift segment (Afar, Ethiopia) magmatic systems. We found that the discrepancies between simple superposition of the displacement field and a fully interacting numerical solution depend mostly on the source types and on their spacing. Their magnitude may be comparable with the errors due to neglecting the topography, the inhomogeneities in crustal properties or more realistic rheologies. In the models considered, the errors induced when neglecting the source interaction can be neglected (<5%) when the sources are separated by at least 4 radii for two combined Mogi sources and by at least 3 radii for juxtaposed Mogi and Okada sources. Furthermore, this study underlines fundamental issues related to the numerical method chosen to model a dike or a magma chamber. It clearly demonstrates that, while the magma compressibility can be neglected to model the deformation due to one source or distant sources, it is necessary to take it into account in models combining close sources.

Kinematic GPS Analysis Gives New Insights on the Origin of the Very-Long-Period Seismic Signals at Miyake-Jima Volcano during the Caldera Formation

NASA Astrophysics Data System (ADS)

Munekane, H.; Oikawa, J.; Kobayashi, T.

2014-12-01

Miyake-jima is an active basaltic stratovolcano that is located 200km south of Tokyo, Japan. Its eruption event in 2000 was remarkable in that the large caldera was formed at the summit in approximately one month. During the caldera forming stage, very-long-period (VLP) seismic pulse waves with a duration of about 50-s that were accompanied by the step-like inflation were repeatedly recorded. Based on the broadband seismometer data, the piston model is proposed in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber located 3-5 km beneath the edific. In this study, we used the kinematic displacements from the continuous GPS observation to obtain additonal insights on the source mechanism of the pulse waves. 　We calculated the kinematic displacements of 15 GPS stations on Miyake-jima that were in operation at that time at 30 sec interval. Then we extracted the displacements associated with each event using 20-hour time window centered at the occurrence of the event, and stacked the whole time series to obtain mean displacement time series. The obtained time series contain: 1) step-like displacements associated with the pulse waves, 2) exponential decay following the events with time constant of approximately half-day, and 3) steady linear displacements indicating continuous contraction of the edifice. The type one displacements can be attributed to the simultaneous inflation of an mogi-type spherical pressure source located at the depth of 3.6 km under the edifice, and the opening of the nearby vertical dike whose top is at the depth of 2.3 km. The type two displacements can be interpreted as the pressure adjustment at the type one source by the outflow of the magma driven by the pressure difference between the type one source and surrounding area. The type three displacements can be interpreted as the steady outflow of the magma from the type one source. The above results support the ``piston model'' for the source of the pulse waves. However, it seems that the pressure increases by the collapse of the piston are not adjusted by the steady magma outflow as the ``piston model'' suggests but by the pressure-driven magma outflow. The steady magma outflow instead seems to be responsible for the long-term shrinkage of the edifice observed at that period.

The 3D Distribution of Magma Bodies that Fed the Paraná Silicic Volcanics, Brazil: A Combination of Field Evidence, Textural Analysis, and Geothermobarometry

NASA Astrophysics Data System (ADS)

Harmon, L.; Gualda, G. A. R.; Gravley, D. M.

2016-12-01

The Paraná Silicic Volcanics include some of the largest eruptive deposits known in the geological record. However, we know very little about the magma bodies that fed these eruptions. Combining physical volcanology, geochemistry, and geothermobarometry techniques, we aim to find the sources of extinct magma bodies to build a 3D view of the magma structure at the time by discovering storage conditions, eruption styles, and post-eruption alteration. The approach elucidates temporal and spatial eruption styles and sequences of the silicic units that make up the Palmas unit of the Serra Geral formation, Brazil. We use field investigations to determine the history of volcanic deposits, domes, and changes in eruptive style; we map and characterize volcanic deposits based on thickness (thicker is proximal to source) and distribution of effusive (proximal to source) and explosive deposits. We focus on several exposed canyons that exhibit either exclusively explosive or effusive, or a clear progression from explosive to effusive deposits. The progression from explosive to effusive indicates a system change from explosively energetic to effusively waning. Additionally, observation of pervasive flow banding in both effusive and explosive deposits indicates rheomorphic flow through many portions of the field area, an indicator of hot emplacement. Geochemical work focuses on the pre-eruptive magma conditions to determine the depth of magma bodies. We utilize glass bearing samples of both the explosively deposited juvenile blob-like structures and obsidian samples to determine crystallization depth. The glass is variably altered, via silicification and devitrification processes, with the blobs more greatly silicified than the obsidian. We use rhyolite-MELTS geothermobarometry when pristine glass can be found. Initial results indicate shallow ( 80 MPa) storage conditions for the explosively erupted blobs. The combination of techniques builds a 3D understanding of extinct super-eruptive systems, and has the potential to unravel both the pre-eruptive and deposition dynamics of the Paraná Silicic Volcanics.

How seismicity and shear stress-generated tilt can indicate imminent explosions on Tungurahua

NASA Astrophysics Data System (ADS)

Neuberg, Jurgen; Mothes, Patricia; Collinson, Amy; Marsden, Luke

2017-04-01

Seismic swarms and tilt measurement on active silicic volcanoes have been successfully used to assess their eruption potential. Swarms of low-frequency seismic events have been associated with brittle failure or stick-slip motion of magma during ascent and have been used to estimate qualitatively the magma ascent. Tilt signals are extremely sensitive indicators for volcano deformation and their interpretation includes shear stress as a generating source as well as inflation or deflation of a shallow magma reservoir. Here we use data sets from different tiltmeters deployed on Tungurahua volcano, Ecuador, and contrast the two source models for different locations and time intervals. We analyse a simultaneously recorded seismic data set and address the question of shear stress partitioning resulting in both the generation of tilt and low-frequency seismicity in critical phases prior to Vulcanion explosions.

Age-related changes in the bimanual advantage and in brain oscillatory activity during tapping movements suggest a decline in processing sensory reafference.

PubMed

Sallard, Etienne; Spierer, Lucas; Ludwig, Catherine; Deiber, Marie-Pierre; Barral, Jérôme

2014-02-01

Deficits in the processing of sensory reafferences have been suggested as accounting for age-related decline in motor coordination. Whether sensory reafferences are accurately processed can be assessed based on the bimanual advantage in tapping: because of tapping with an additional hand increases kinesthetic reafferences, bimanual tapping is characterized by a reduced inter-tap interval variability than unimanual tapping. A suppression of the bimanual advantage would thus indicate a deficit in sensory reafference. We tested whether elderly indeed show a reduced bimanual advantage by measuring unimanual (UM) and bimanual (BM) self-paced tapping performance in groups of young (n = 29) and old (n = 27) healthy adults. Electroencephalogram was recorded to assess the underlying patterns of oscillatory activity, a neurophysiological mechanism advanced to support the integration of sensory reafferences. Behaviorally, there was a significant interaction between the factors tapping condition and age group at the level of the inter-tap interval variability, driven by a lower variability in BM than UM tapping in the young, but not in the elderly group. This result indicates that in self-paced tapping, the bimanual advantage is absent in elderly. Electrophysiological results revealed an interaction between tapping condition and age group on low beta band (14-20 Hz) activity. Beta activity varied depending on the tapping condition in the elderly but not in the young group. Source estimations localized this effect within left superior parietal and left occipital areas. We interpret our results in terms of engagement of different mechanisms in the elderly depending on the tapping mode: a 'kinesthetic' mechanism for UM and a 'visual imagery' mechanism for BM tapping movement.

Acanthamoeba keratitis: the role of domestic tap water contamination in the United Kingdom.

PubMed

Kilvington, Simon; Gray, Trevor; Dart, John; Morlet, Nigel; Beeching, John R; Frazer, David G; Matheson, Melville

2004-01-01

The incidence of acanthamoeba keratitis (AK) in the UK is some 15 times that in the United States and seven times that in Holland. To investigate reasons for this higher frequency, a study of the role of domestic tap water as a potential source of AK was undertaken. Tap outlets from the homes of 27 patients with culture-proven AK were sampled and cultured for free-living amoebae (FLA). For all Acanthamoeba isolates, mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) and cytochrome oxidase (cox 1/2) sequence typing was performed to determine the similarity between corneal and tap water isolates. FLA, including Acanthamoeba, were isolated from 24 (89%) of 27 homes, and the presence within the homes varied significantly with tap water temperature and location: 19 (76%) of 25 bathroom sink cold taps sampled compared with 6 (24%) of 25 hot and 9 (47%) of 19 kitchen cold taps compared with 3 (16%) of 19 of hot kitchen taps. Acanthamoeba were isolated from 8 (30%) of 27 homes (five bathroom sink cold taps, one cloakroom cold tap, one bath, and one bedroom sink mixer [hot/cold] taps). In six cases, identical Acanthamoeba mtDNA profiles were found for the clinical and home tap water isolates. In keeping with UK plumbing practice, 24 of 27 homes had internal roof water storage tanks to supply domestic taps, but the mains fed the kitchen cold tap. Water storage tanks promote colonization of domestic water with FLA, including Acanthamoeba, and hence increase the risk of AK. This accounts for the significantly greater incidence of AK in the UK and supports advice to avoid using tap water in contact lens care routines.

Rapid Mantle Source Variations During the Latest Episode of Kilauea's Prolonged Pu'u O'o Eruption, Hawaii

NASA Astrophysics Data System (ADS)

Marske, J. P.; Garcia, M. O.; Pietruszka, A. J.; Norman, M. D.; Rhodes, J. M.

2006-12-01

Nearly 24 years of continuous geochemical monitoring of lavas from the current Pu'u O'o eruption allow us to probe the mantle processes beneath Kilauea Volcano in unparalleled detail. Here we present new measurements Pb, Sr, and Nd isotope ratios and major- and trace-element abundances for lavas from episode 55 (1997-2006), which marks the longest and most voluminous interval of this eruption. Pu'u O'o lavas erupted since 1985 display systematic decreases in their TiO2, K2O, P2O5 and CaO abundances (normalized to 10 wt. % MgO to correct for olivine control) due to changes in the parental magma composition. Incompatible element ratios (e.g., Ba/Nb and La/Y) also show overall temporal decreases. Earlier erupted Pu'u O'o lavas displayed the most significant decrease in incompatible element ratios with near constant SiO2 contents, and a gradual increase in 87Sr/86Sr ratios. However, episode 55 lavas record significant increases in MgO- normalized SiO2 contents and 87Sr/86Sr with nearly constant (e.g. Ba/Nb) or a slightly reversed (e.g., TiO2 and K2O) trends in incompatible element ratios and abundances. There is little variation of 206Pb/204Pb ratios in lavas (18.38-18.43) erupted since 1985. Neither a single mantle source composition nor a change in partial melting conditions alone can explain these observations. Based on the isotopic and chemical variability, we conclude that early Pu'u O'o lavas originated from two distinct mantle source components: (1) a long-term depleted component (with relatively low 87Sr/86Sr ratios) that originated within the deep source of the Hawaiian plume that characterizes the earlier part of the eruption (1985-1992), and (2) a recently depleted component (i.e. a component that was recently depleted by prior melting) with low abundances of incompatible elements became increasingly important from 1992-1997. More recently, Pu'u O'o has tapped greater proportions of a new (3) long-term less depleted component (with higher 87Sr/86Sr ratios than observed from 1985-1992) that originated within the deep source region of the plume. This third component lies within typical Pb, Sr and Nd isotopic space for Kilauea, but represents a new source composition for the Pu'u O'o eruption. The systematic geochemical evolution of Pu'u O'o lavas reflects changes in the proportions of the mantle source components tapped throughout the eruption. The rapid isotope variations (on a time scale of years) in the most recent lavas suggest the mantle source components are heterogeneous on an extremely small scale, relative to the size of Kilauea's melting region.

Evaluation on the Quality of Bangkok Tap Water with Other Drinking Purpose Water

NASA Astrophysics Data System (ADS)

Kordach, A.; Chardwattananon, C.; Wongin, K.; Chayaput, B.; Wongpat, N.

2018-02-01

The concern of drinking purposed water quality in Bangkok, Nonthaburi, and Samutprakarn provinces has been a problem for over fifteen years. Metropolitan Water Works Authority (MWA) of Thailand is fully responsible for providing water supply to the mentioned areas. The objective of Drinkable Tap Water Project is to make people realize in quality of tap water. Communities, school, government agencies, hotels, hospitals, department stores, and other organizations are participating in this project. MWA have collected at least 3 samples of water from the corresponding places and the samples have to meet the World Health Organization (WHO) guidelines level. This study is to evaluate water quality of tap water, storage water, filtered water, and filtered water dispenser. The water samples from 2,354 attending places are collected and analyzed. From October 2011 to September 2016, MWA analyzed 32,711 samples. The analyzed water parameters are free residual chlorine, appearance color, turbidity, pH, conductivity, total dissolved solids (TDS), and pathogenic bacteria; E.coli. The results indicated that a number of tap water samples had the highest number compliance with WHO guidelines levels at 98.40%. The filtered water, filtered water dispenser, and storage water were received 96.71%, 95.63%, and 90.88%, respectively. However, the several samples fail to pass WHO guideline level because they were contaminated by E.coli. The result is that tap water has the highest score among other sources probably because tap water has chlorine for disinfection and always is monitored by professional team round-the-clock services compared to the other water sources with less maintenance or cleaning. Also, water quality reports are continuously sent to customers by mail addresses. Tap water quality data are shown on MWA websites and Facebook. All these steps of work should enhance the confidence of tap water quality.

Finite Element modelling of deformation induced by interacting volcanic sources

NASA Astrophysics Data System (ADS)

Pascal, Karen; Neuberg, Jürgen; Rivalta, Eleonora

2010-05-01

The displacement field due to magma movements in the subsurface is commonly modelled using the solutions for a point source (Mogi, 1958), a finite spherical source (McTigue, 1987), or a dislocation source (Okada, 1992) embedded in a homogeneous elastic half-space. When the magmatic system comprises more than one source, the assumption of homogeneity in the half-space is violated and several sources are combined, their respective deformation field being summed. We have investigated the effects of neglecting the interaction between sources on the surface deformation field. To do so, we calculated the vertical and horizontal displacements for models with adjacent sources and we tested them against the solutions of corresponding numerical 3D finite element models. We implemented several models combining spherical pressure sources and dislocation sources, varying their relative position. Furthermore we considered the impact of topography, loading, and magma compressibility. To quantify the discrepancies and compare the various models, we calculated the difference between analytical and numerical maximum horizontal or vertical surface displacements.We will demonstrate that for certain conditions combining analytical sources can cause an error of up to 20%. References: McTigue, D. F. (1987), Elastic Stress and Deformation Near a Finite Spherical Magma Body: Resolution of the Point Source Paradox, J. Geophys. Res. 92, 12931-12940. Mogi, K. (1958), Relations between the eruptions of various volcanoes and the deformations of the ground surfaces around them, Bull Earthquake Res Inst, Univ Tokyo 36, 99-134. Okada, Y. (1992), Internal Deformation Due to Shear and Tensile Faults in a Half-Space, Bulletin of the Seismological Society of America 82(2), 1018-1040.

Consumer Perception and Preference of Drinking Water Sources

PubMed Central

Sajjadi, Seyed Ali; Alipour, Vali; Matlabi, Mohammad; Biglari, Hamed

2016-01-01

Introduction Understanding consumer perception of drinking water can contribute to improvements in water management and consumer satisfaction. The aim of this study was to assess the consumer perception of tap water quality and other drinking water sources in Gonabad as a small semiarid city. Methods This study was performed in autumn and winter 2013. For collection data a researcher-made a questionnaire consisting of nine questions, based on demographic information prepared. Questions were asked for participants to provide information regarding household drinking water usage and patterns, opinion about tap water safety, taste and reasons for purchasing bottled water. For statistical analysis, analysis of variance (ANOVA) using SPSS version 16 was applied in this study. Results Results showed that demographic variables had a significant relationship with consumer satisfaction (p < 0.05). Office employees, women and poor families had the most satisfaction from tap water quality. Peoples’ preferences for tap water, commercial softener, domestic softener, ghanat (a type of underground cistern) and bottled water were 27.8, 19, 27.8, 40.4 and 3.5% respectively. Dissatisfaction from production of foam, unsuitable taste, unacceptable appearance and other problems in tap water was 11.1, 95.6, 27.8 and 0.4% respectively. Consumer reasons for using domestic water softeners are: suitable taste (80%), easy availability (71%), economical (56%) and low health side effects (34%). Conclusion According to these results it was clear that each consumer group, based on self-condition, prefers using a specific drinking water source. PMID:28070256

Consumer Perception and Preference of Drinking Water Sources.

PubMed

Sajjadi, Seyed Ali; Alipour, Vali; Matlabi, Mohammad; Biglari, Hamed

2016-11-01

Understanding consumer perception of drinking water can contribute to improvements in water management and consumer satisfaction. The aim of this study was to assess the consumer perception of tap water quality and other drinking water sources in Gonabad as a small semiarid city. This study was performed in autumn and winter 2013. For collection data a researcher-made a questionnaire consisting of nine questions, based on demographic information prepared. Questions were asked for participants to provide information regarding household drinking water usage and patterns, opinion about tap water safety, taste and reasons for purchasing bottled water. For statistical analysis, analysis of variance (ANOVA) using SPSS version 16 was applied in this study. Results showed that demographic variables had a significant relationship with consumer satisfaction (p < 0.05). Office employees, women and poor families had the most satisfaction from tap water quality. Peoples' preferences for tap water, commercial softener, domestic softener, ghanat (a type of underground cistern) and bottled water were 27.8, 19, 27.8, 40.4 and 3.5% respectively. Dissatisfaction from production of foam, unsuitable taste, unacceptable appearance and other problems in tap water was 11.1, 95.6, 27.8 and 0.4% respectively. Consumer reasons for using domestic water softeners are: suitable taste (80%), easy availability (71%), economical (56%) and low health side effects (34%). According to these results it was clear that each consumer group, based on self-condition, prefers using a specific drinking water source.

Enhanced Geothermal System Potential for Sites on the Eastern Snake River Plain, Idaho

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

Robert K Podgorney; Thomas R. Wood; Travis L McLing

2013-09-01

The Snake River volcanic province overlies a thermal anomaly that extends deep into the mantle and represents one of the highest heat flow provinces in North America (Blackwell and Richards, 2004). This makes the Snake River Plain (SRP) one of the most under-developed and potentially highest producing geothermal districts in the United States. Elevated heat flow is typically highest along the margins of the topographic SRP and lowest along the axis of the plain, where thermal gradients are suppressed by the Snake River aquifer. Beneath this aquifer, however, thermal gradients rise again and may tap even higher heat flows associatedmore » with the intrusion of mafic magmas into the mid-crustal sill complex (e.g., Blackwell, 1989).« less

The Breccia Museo formation, Campi Flegrei, southern Italy: Geochronology, chemostratigraphy and relationship with the Campanian Ignimbrite eruption

USGS Publications Warehouse

Fedele, L.; Scarpati, C.; Lanphere, M.; Melluso, L.; Morra, V.; Perrotta, A.; Ricci, G.

2008-01-01

The Breccia Museo is one of the most debated volcanic formations of the Campi Flegrei volcanic district. The deposit, made up of six distinctive stratigraphic units, has been interpreted by some as the proximal facies of the major caldera-forming Campanian Ignimbrite eruption, and by others as the product of several, more recent, independent and localized events. New geochemical and chemostratigraphical data and Ar - Ar age determinations for several units of the Breccia Museo deposits (???39 ka), correlate well with the Campanian Ignimbrite-forming eruption. The chemical zoning of the Breccia Museo deposits is interpreted here to be a consequence of a three-stage event that tapped a vertically zoned trachytic magma chamber. ?? Springer-Verlag 2008.

Two Distinct Sets of Magma Sources in Cretaceous Rocks From Magnet Cove, Prairie Creek, and Other Igneous Centers of the Arkansas Alkaline Province, USA

NASA Astrophysics Data System (ADS)

Duke, G. I.; Carlson, R. W.; Eby, G. N.

2008-12-01

Two distinct sets of magma sources from the Arkansas alkaline province (~106-89 Ma) are revealed by Sr-Nd-Pb isotopic compositions of olivine lamproites vs. other alkalic rock types, including carbonatite, ijolite, lamprophyres, tephrite, malignite, jacupirangite, phonolite, trachyte, and latite. Isotopic compositions of diamond-bearing olivine lamproites from Prairie Creek and Dare Mine Knob point to Proterozoic lithosphere as an important source, and previous Re-Os isotopic data indicate derivation from subcontinental mantle lithosphere. Both sources were probably involved in lamproite generation. Magnet Cove carbonatites and other alkalic magmas were likely derived from an asthenospheric source. Lamproite samples are isotopically quite different from other rock types in Sr-Nd-Pb isotopic space. Although three lamproite samples from Prairie Creek have a large range of SiO2 contents (40-60 wt %), initial values of ɛNd (-10 to -13), 206Pb/204Pb (16.61-16.81), 207Pb/204Pb (15.34-15.36), and 208Pb/204Pb (36.57-36.76) are low and similar. Only 87Sr/86Sr(i) displays a wide range in the Prairie Creek lamproites (0.70627-0.70829). A fourth lamproite from Dare Mine Knob has the most negative ɛNd(i) of -19. Lamproite isotope values show a significant crustal component and isotopically overlap subalkalic rhyolites from the Black Hills (SD), which assimilated Proterozoic crust. Six samples of carbonatite, ijolite, and jacupirangite from Magnet Cove and Potash Sulphur Springs exhibit the most depleted Sr-Nd isotopic signatures of all samples. For these rock types, 87Sr/86Sr(i) is 0.70352 - 0.70396, and ɛNd(i) is +3.8 - +4.3. Eight other rock types have a narrow range of ɛNd(i) (+1.9 - +3.7), but a wide range of 87Sr/86Sr(i) (0.70424 - 0.70629). These 14 samples comprise a fairly tight cluster of Pb isotopic values: 206Pb/204Pb (18.22-19.23), 207Pb/204Pb (15.54-15.62), and 208Pb/204Pb (38.38-38.94), suggesting very little crustal assimilation. They are most similar to EM-2 (sub-group of OIB). Published ages of crustal amphibolite xenoliths from the Prairie Creek lamproite are Proterozoic (~1.32- 1.47 Ga), in keeping with isotopic evidence for crustal assimilation, including Tdm = 1.3-1.7 Ga. Published ages of lamproite (~106 Ma) indicate that these magmas intruded first, whereas carbonatites and other alkalic magmas were later (~102 to ~89 Ma). Asthenospheric upwelling first melted lithospheric mantle and crust, producing lamproitic magmas; asthenospheric magmas followed as swelling of the lithosphere ensued.

Heterogeneity in lunar anorthosite meteorites: implications for the lunar magma ocean model.

PubMed

Russell, Sara S; Joy, Katherine H; Jeffries, Teresa E; Consolmagno, Guy J; Kearsley, Anton

2014-09-13

The lunar magma ocean model is a well-established theory of the early evolution of the Moon. By this model, the Moon was initially largely molten and the anorthositic crust that now covers much of the lunar surface directly crystallized from this enormous magma source. We are undertaking a study of the geochemical characteristics of anorthosites from lunar meteorites to test this model. Rare earth and other element abundances have been measured in situ in relict anorthosite clasts from two feldspathic lunar meteorites: Dhofar 908 and Dhofar 081. The rare earth elements were present in abundances of approximately 0.1 to approximately 10× chondritic (CI) abundance. Every plagioclase exhibited a positive Eu-anomaly, with Eu abundances of up to approximately 20×CI. Calculations of the melt in equilibrium with anorthite show that it apparently crystallized from a magma that was unfractionated with respect to rare earth elements and ranged in abundance from 8 to 80×CI. Comparisons of our data with other lunar meteorites and Apollo samples suggest that there is notable heterogeneity in the trace element abundances of lunar anorthosites, suggesting these samples did not all crystallize from a common magma source. Compositional and isotopic data from other authors also suggest that lunar anorthosites are chemically heterogeneous and have a wide range of ages. These observations may support other models of crust formation on the Moon or suggest that there are complexities in the lunar magma ocean scenario to allow for multiple generations of anorthosite formation. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Heterogeneity in lunar anorthosite meteorites: implications for the lunar magma ocean model

PubMed Central

Russell, Sara S.; Joy, Katherine H.; Jeffries, Teresa E.; Consolmagno, Guy J.; Kearsley, Anton

2014-01-01

The lunar magma ocean model is a well-established theory of the early evolution of the Moon. By this model, the Moon was initially largely molten and the anorthositic crust that now covers much of the lunar surface directly crystallized from this enormous magma source. We are undertaking a study of the geochemical characteristics of anorthosites from lunar meteorites to test this model. Rare earth and other element abundances have been measured in situ in relict anorthosite clasts from two feldspathic lunar meteorites: Dhofar 908 and Dhofar 081. The rare earth elements were present in abundances of approximately 0.1 to approximately 10× chondritic (CI) abundance. Every plagioclase exhibited a positive Eu-anomaly, with Eu abundances of up to approximately 20×CI. Calculations of the melt in equilibrium with anorthite show that it apparently crystallized from a magma that was unfractionated with respect to rare earth elements and ranged in abundance from 8 to 80×CI. Comparisons of our data with other lunar meteorites and Apollo samples suggest that there is notable heterogeneity in the trace element abundances of lunar anorthosites, suggesting these samples did not all crystallize from a common magma source. Compositional and isotopic data from other authors also suggest that lunar anorthosites are chemically heterogeneous and have a wide range of ages. These observations may support other models of crust formation on the Moon or suggest that there are complexities in the lunar magma ocean scenario to allow for multiple generations of anorthosite formation. PMID:25114312

Application of Microbeam Techniques to Identifying and Assessing Comagmatic Mixing Between Summit and Rift Eruptions at Kilauea Volcano (Invited)

NASA Astrophysics Data System (ADS)

Thornber, C. R.; Rowe, M. C.; Adams, D. T.; Orr, T. R.

2010-12-01

Near-continuous eruption of Kilauea Volcano since 1983 has yielded an extensive record of glass, phenocryst and melt-inclusion chemistry from well-quenched lava that can be correlated with geophysical and geological monitoring data. Eruption temperatures are determined using glass thermometry. Microbeam evaluation of phenocryst mineralogy, morphology, texture, zoning and melt inclusions helps to constrain magma storage and transport within the edifice and to track the evolution of shallow magmatic plumbing during this prolonged eruptive era. For most of this eruption up to April 2001, east rift lava was olivine-phyric and olivine-liquid relations indicated equilibrium crystallization during summit-to-rift magma transport. From 2001 to present, most lava erupted from vents near Pu`u O`o has been a relatively low-temperature “hybrid”, characterized by a disequilibrium low-pressure phenocryst assemblage. Olivine (Fo81.5-80.5) coexists with phenocrysts of lower temperature clinopyroxene (±plagioclase, ±Fe-rich olivine). Mixing between hotter and cooler magma is texturally documented by complex pyroxene zoning and resorption and olivine overgrowths on resorbed pyroxene. The co-magmatic mixing is not apparent in bulk lava analyses, since both components are fractionates of parent magmas with indistinguishable trace-element signatures. Post-2001 rift-zone lava indicates perpetual flushing of stored magma by hotter recharge magma rising from the mantle source. Geophysical and gas monitoring data confirm an increase in magma supply to Kilauea Volcano between 2001 and 2008, which we have interpreted as increasing the efficiency of the flushing process. Since March 2008, the petrology of the new summit lava lake and contemporaneously erupted rift zone lava provides new perspective on complexities of magma degassing, crystallization and mixing prior to rift eruption. Bulk lava chemistry, SIMS and LA-ICPMS analyses of matrix glasses and olivine melt-inclusions in both rift zone lava and summit tephra reveal identical trace-element concentrations, thus confirming that both eruption sites share a common magma source. Because Kilauea magma degasses all of its primary sulfur (~1200 to 1500 ppm) at pressures less than 100 bars, shallow summit-to-rift magma mixing and crystallization is quantified by study of relative sulfur concentrations in melt inclusions. For higher temperature magma at the summit, olivine (Fo82.0-83.5) contains melt inclusions with 600-1400 ppm S. A small population of rift zone phenocrysts have similar sulfur contents, while typical rift zone olivine inclusions contain 300-700 ppm S. Complex zoned pyroxene phenocrysts with multiple inclusions have trapped melts of low to high sulfur concentrations ranging from100 to 1000 ppm. Collectively, these microbeam observations provide evidence for dynamic pre-eruptive comingling between hotter, sulfur-rich magma rising beneath the summit with a denser, cooler and degassed pyroxene-bearing magma mush, prior to eruption on the east rift.

Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest

NASA Astrophysics Data System (ADS)

Farrar, C. D.; Sorey, M. L.; Evans, W. C.; Howle, J. F.; Kerr, B. D.; Kennedy, B. M.; King, C.-Y.; Southon, J. R.

1995-08-01

MAMMOTH Mountain, in the western United States, is a large dacitic volcano with a long history of vo lean ism that began 200 kyr ago1 and produced phreatic eruptions as recently as 500 +/- 200 yr BP (ref. 2). Seismicity, ground deformation and changes in fumarole gas composition suggested an episode of shallow dyke intrusion in 1989-90 (refs 3, 4). Areas of dying forest and incidents of near asphyxia in confined spaces, first reported in 1990, prompted us to search for diffuse flank emissions of magmatic CO2, as have been described at Mount Etna5 and Vulcano6. Here we report the results of a soil-gas survey, begun in 1994, that revealed CO2 concentrations of 30-96% in a 30-hectare region of killed trees, from which we estimate a total CO2 flux of >=1,200 tonnes per day. The forest die-off is the most conspicuous surface manifestation of magmatic processes at Mammoth Mountain, which hosts only weak fumarolic vents and no summit activity. Although the onset of tree kill coincided with the episode of shallow dyke intrusion, the magnitude and duration of the CO2 flux indicates that a larger, deeper magma source and/or a large reservoir of high-pressure gas is being tapped.

Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest

USGS Publications Warehouse

Farrar, C.D.; Sorey, M.L.; Evans, William C.; Howle, J.F.; Kerr, B.D.; Kennedy, B.M.; King, C.-Y.; Southon, J.R.

1995-01-01

MAMMOTH Mountain, in the western United States, is a large dacitic volcano with a long history of volcamsm that began 200 kyr ago1 and produced phreatic eruptions as recently as 500 ?? 200 yr BP (ref. 2). Seismicity, ground deformation and changes in fumarole gas composition suggested an episode of shallow dyke intrusion in 1989-90 (refs 3, 4). Areas of dying forest and incidents of near asphyxia in confined spaces, first reported in 1990, prompted us to search for diffuse flank emissions of magmatic CO2, as have been described at Mount Etna5 and Vulcano6. Here we report the results of a soil-gas survey, begun in 1994, that revealed CO2 concentrations of 30-96% in a 30-hectare region of killed trees, from which we estimate a total CO2 flux of ???1,200 tonnes per day. The forest die-off is the most conspicuous surface manifestation of magmatic processes at Mammoth Mountam, which hosts only weak fumarolic vents and no summit activity. Although the onset of tree kill coincided with the episode of shallow dyke intrusion, the magnitude and duration of the CO2 flux indicates that a larger, deeper magma source and/or a large reservoir of high-pressure gas is being tapped.

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.

Magmagenesis at Soufriere volcano St Vincent, Lesser Antilles Arc

USGS Publications Warehouse

Heath, E.; Macdonald, R.; Belkin, H.; Hawkesworth, C.; Sigurdsson, Haraldur

1998-01-01

Soufriere volcano of St Vincent (3 wt %, whereas various projections onto phase diagrams are more consistent with relatively anhydrous magmas. Primary magmas at Soufriere were generated by around 15% melting of mid-ocean ridge basalt type mantle sources which had been modified by addition of fluids released from the slab containing contributions from subducted sediments and mafic crust.

Magma supply rate at kilauea volcano, 1952-1971.

PubMed

Swanson, D A

1972-01-14

The three longest Kilauea eruptions since 1952 produced lava at an overall constant rate of about 9 x 10(6) cubic meters per month (vesicle-free). This is considered to represent the rate of magma supply from a deep source, probably the mantle, because little or no summit deformation indicating high-level storage accompanied any of the three eruptions.

Elastostatic effects around a magma reservoir and pathway due to historic earthquakes: a case study of Mt. Fuji, Japan

NASA Astrophysics Data System (ADS)

Hosono, Masaki; Mitsui, Yuta; Ishibashi, Hidemi; Kataoka, Jun

2016-12-01

We discuss elastostatic effects on Mt. Fuji, the tallest volcano in Japan, due to historic earthquakes in Japan. The 1707 Hoei eruption, which was the most explosive historic eruption of Mt. Fuji, occurred 49 days after the Hoei earthquake (Mw 8.7) along the Nankai Trough. It was previously suggested that the Hoei earthquake induced compression of a basaltic magma reservoir and unclamping of a dike-intruded region at depth, possibly triggering magma mixing and the subsequent Plinian eruption. Here, we show that the 1707 Hoei earthquake was a special case of induced volumetric strain and normal stress changes around the magma reservoir and pathway of Mt. Fuji. The 2011 Tohoku earthquake (Mw 9), along the Japan Trench, dilated the magma reservoir. It has been proposed that dilation of a magma reservoir drives the ascent of gas bubbles with magma and further depressurization, leading to a volcanic eruption. In fact, seismicity notably increased around Mt. Fuji during the first month after the 2011 Tohoku earthquake, even when we statistically exclude aftershocks, but the small amount of strain change (< 1 μ strain) may have limited the ascent of magma. For many historic earthquakes, the magma reservoir was compressed and the magma pathway was wholly clamped. This type of interaction has little potential to mechanically trigger the deformation of a volcano. Thus, Mt. Fuji may be less susceptible to elastostatic effects because of its location relative to the sources of large tectonic earthquakes. As an exception, a possible local earthquake in the Fujikawa-kako fault zone could induce a large amount of magma reservoir dilation beneath the southern flank of Mt. Fuji.

Contrasting Granite Metallogeny through the Zircon Record: A Case Study from Myanmar.

PubMed

Gardiner, Nicholas J; Hawkesworth, Chris J; Robb, Laurence J; Whitehouse, Martin J; Roberts, Nick M W; Kirkland, Christopher L; Evans, Noreen J

2017-04-07

Granitoid-hosted mineral deposits are major global sources of a number of economically important metals. The fundamental controls on magma metal fertility are tectonic setting, the nature of source rocks, and magma differentiation. A clearer understanding of these petrogenetic processes has been forged through the accessory mineral zircon, which has considerable potential in metallogenic studies. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset from the paired Cu-Au (copper) and Sn-W (tin) magmatic belts in Myanmar. Copper arc zircons have juvenile εHf (+7.6 to +11.5) and mantle-like δ 18 O (5.2-5.5‰), whereas tin belt zircons have low εHf (-7 to -13) and heavier δ 18 O (6.2-7.7‰). Variations in zircon Hf and U/Yb reaffirm that tin belt magmas contain greater crustal contributions than copper arc rocks. Links between whole-rock Rb/Sr and zircon Eu/Eu* highlight that the latter can monitor magma fractionation in these systems. Zircon Ce/Ce* and Eu/Eu* are sensitive to redox and fractionation respectively, and here are used to evaluate zircon sensitivity to the metallogenic affinity of their host rock. Critical contents of Sn in granitic magmas, which may be required for the development of economic tin deposits, are marked by zircon Eu/Eu* values of ca. ≤0.08.

Time dependence of volcano inflation: mass influx or viscoelastic relaxation? Insights from Grímsvötn volcano, Iceland

NASA Astrophysics Data System (ADS)

Segall, P.

2017-12-01

Distinguishing magma chamber pressurization from relaxation of a viscoelastic aureole surrounding the chamber based on geodetic measurements has remained challenging. Elastic models with mass inflow proportional to the pressure difference between the chamber and a deep reservoir predict exponentially decaying flux. For a spherical chamber surrounded by a Maxwell viscoelastic shell with pressure dependent recharge, the surface deformation is the sum of two exponentials (Segall, 2016). GPS displacements following eruptions of Grímsvötn, Iceland in 2004 and 2011 exhibit rapid post-eruptive inflation (time scale of 0.1 yr), followed by inflation with a much longer time constant. Markov Chain Monte Carlo inversion with the viscoelastic model shows the GPS time series can be fit with viscosity of 2e16 Pa-s, and a relatively incompressible magma, B = beta_c/ (beta_m + beta_c) > 0.6, where beta_m and beta_c are chamber and magma compressibility. The latter appears to conflict with the ratio of erupted volume to geodetically inferred source volume change, rv 10, obtained for the best fitting spherical (Mogi ) source (Hreinsdóttir, 2014). Since rv = 1/B, this implies a relatively compressible melt, B 0.1. Reexamination of the co-eruptive GPS and tilt data with the more general ellipsoidal model of Cervelli (2013), reveals that the best fitting sources are oblate (b/a 3), deeper, and with larger volume changes, rv 3, relative to spherical models. Oblate magma chambers are consistent with seismic tomography. FEM calculations including free surface effects lead to even larger co-eruptive volume changes, smaller rv and hence larger B. I conclude that the data are consistent with rapid post-eruptive inflation driven by viscoelastic relaxation with a relatively incompressible magma, although other interpretations will be discussed.

Magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase: A new bulk silicate Moon model with sub-chondritic Ti/Ba, Sr/Ba, and Sr/Al ratios

NASA Astrophysics Data System (ADS)

Togashi, Shigeko; Kita, Noriko T.; Tomiya, Akihiko; Morishita, Yuichi

2017-08-01

The compositions of host magmas of ferroan anorthosites (FAN-host magmas) were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks. The evolution of the magmas was investigated by considering phase relations based on the MELTS algorithm and by re-examining partition coefficients for trace elements between plagioclase and melts. Data little affected by post-magmatic processes were selected by using plagioclase with relatively primitive Sc and Co contents. The FAN-host magma contained 90-174 ppm Sr, 40-119 ppm Ba and 0.5-1.3% TiO2, and had sub-chondritic Sr/Ba and Ti/Ba ratios. It is difficult to account for the formation of FAN-host magma on the basis of magma evolution processes of previously proposed bulk silicate Moon models with chondritic ratios for refractory elements at global scale. Therefore, the source of the FAN-host magma must have had primordial sub-chondritic Sr/Ba and Ti/Ba ratios. The FAN-host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites, and some very-low-Ti mare rocks from lunar meteorites. Here, we propose an alternative bulk silicate Moon model (the cBSM model), which is enriched in crustal components of proto-bodies relative to the present whole Earth-Moon system.

Time constraints on the origin of large volume basalts derived from O-isotope and trace element mineral zoning and U-series disequilibria in the Laki and Grímsvötn volcanic system

NASA Astrophysics Data System (ADS)

Bindeman, Ilya N.; Sigmarsson, Olgeir; Eiler, John

2006-05-01

The 1783-1784 AD fissure eruption of Laki (Iceland) produced 15 km 3 of homogeneous basaltic lavas and tephra that are characterized by extreme (3‰) 18O-depletion relative to normal mantle. Basaltic tephra erupted over the last 8 centuries and as late as in November 2004 from the Grímsvötn central volcano, which together with Laki are a part of a single volcanic system, is indistinguishable in δ18O from Laki glass. This suggests that all tap a homogeneous and long-lived low- δ18O magma reservoir. In contrast, we observe extreme oxygen isotope heterogeneity (2.2-5.2‰) in olivine and plagioclase contained within these lavas and tephra, and disequilibrium mineral-glass oxygen-isotope fractionations. Such low- δ18O glass values, and extreme 3‰ range in δ18O olivine have not been described in any other unaltered basalt. The energy constrained mass balance calculation involving oxygen isotopes and major element composition calls for an origin of the Laki-Grímsvötn quartz tholeiitic basaltic melts with δ18O = 3.1‰ by bulk digestion of low- δ18O hydrated basaltic crust with δ18O = - 4‰ to + 1‰, rather than magma mixing with ultra-low- δ18O silicic melt. The abundant Pleistocene hyaloclastites, which were altered by synglacial meltwaters, can serve as a likely assimilant material for the Grímsvötn magmas. The ( 226Ra / 230Th) activity ratio in Laki lavas and 20th century Grímsvötn tephras is 13% in-excess of secular equilibrium, but products of the 20th century Grímsvötn eruptions have equilibrium ( 210Pb / 226Ra). Modeling of oxygen isotope exchange between disequilibrium phenocrysts and magmas, and these short-lived U-series nuclides yields a coherent age for the Laki-Grímsvötn magma reservoir between 100 and 1000 yrs. We propose the existence of uniquely fingerprinted, low- δ18O, homogeneous, large volume, and long-lived basaltic reservoir beneath the Laki-Grímsvötn volcanic system that has been kept alive in its position above the center of the Icelandic mantle plume. Melt generation, crustal assimilation, magma storage and homogenization all took place in only a few thousands of years at most.

Commercializing Defense Technologies and Helping Defense Firms Succeed in Commercial Markets: A Report on the Objectives, Activities, and Accomplishments of the TAP-IN Program

NASA Technical Reports Server (NTRS)

1997-01-01

Technology Access for Product Innovation (TAP-IN), the largest technology deployment project funded by TRP, was competitively selected through a national solicitation for proposals. TAP-IN was created to help companies access and apply defense technologies and help defense-dependent companies enter new commercial markets. Defense technologies included technologies developed by DoD, DOE, NASA, and their contractors. TAP-IN was structured to provide region-based technology access services that were able to draw on technology resources nationwide. TAP-IN provided expert assistance in all stages of the commercialization process from concept through prototype design to capital sourcing and marketing strategy. TAP-IN helped companies locate new technology, identify business partners, secure financing, develop ideas for new products, identify new markets, license technology, solve technical problems, and develop company-specific applications of federal technology. TAP-IN leveraged NASA's existing commercial technology network to create an integrated national network of organizations that assisted companies in every state. In addition to NASA's six regional technology transfer centers (RTTCs), TAP-IN included business and technology development organizations in every state, the Industrial Designers Society of America, and the Federal Laboratory Consortium (FLC).

Monitoring of Emerging and Legacy Contaminants in Groundwater and Tap Water of the Karst Region in Northern Puerto Rico for Assessment of Sources and Fate and Transport Processes

NASA Astrophysics Data System (ADS)

Padilla, I. Y.; Cotto, I.; Torres, P. M.

2014-12-01

The karst aquifer region of northern Puerto Rico is the area with the highest groundwater extraction in the island. Urban and industrial development has led to extensive contamination of the groundwater in the region. Of particular concern, is the presence of emerging and legacy organic contaminants, such as phthalates and chlorinated organic compounds (CVOCs), because there high risk for exposure and adverse health impact. Variable sources and the heterogeneous and dynamic conditions of karst groundwater systems, limits the ability to properly assess and manage the water quality of these precious water resources. This work develops a monitoring and water analysis scheme to assess spatial-temporal exposure of hazardous contaminants trough karst water in northern Puerto Rico. Groundwater and tap water are sampled in the region and analyzed for phthalates, CVOCs, and common ions. Detections and concentrations of phthalates and CVOCs are determined by using modified EPA methods, which rely on liquid-liquid extractions and gas chromatography techniques. The modified methods have reduced the volume of samples and solvent waste, decreased the time of analysis, increased analysis outcomes, and lower potential for hazardous exposure. Results show intermittent presence of di-ethyl, di-butyl and di (2-ethyl hexyl) phthalates in 36% of the groundwater and 53% of tap water samples, with detected concentrations ranging between 0.1-88.7 μg/L. These results indicate that karst groundwater can serve as a route of exposure for phthalates, but there are additional disperse sources in the water system. CVOCs are detected in groundwater at much higher frequencies (50%) than phthalates, and include trichloromethane (TCM), carbon tetrachloride (CT), trichloroethylene (TCE), and tetrachloroethylene (TCE). CVOCs, except for TCM, are found at lower frequencies on tap water (5.8%) than groundwater (27%). TCM is detected more frequently and at higher concentrations in tap water (56.8%) than tap water (30%). Results indicated that most CVOCs on tap water come from groundwater sources. Spatial-temporal analysis of CVOC data shows that transport through karst system is highly heterogeneous variable, and reflect high capacity of the system to store and slowly release contaminants through rate-limited mass transport process.

&LDQUO;FROM THE SOURCE &NDASH; TAP WATER AS A SUSTAINABLE ALTERNATIVE&RDQUO;

EPA Science Inventory

The major technical challenge to sustainability is reduction of use of plastic bottled water and bottled water in general. This will be done by a student administered water assessment survey on campus, coupled with a public education campaign on the benefits of using tap water...

The relationship between the height of a volcano and the depth to its magma source zone - A critical reexamination

NASA Technical Reports Server (NTRS)

Wilson, Lionel; Head, James W., III; Parfitt, Elisabeth A.

1992-01-01

The relationship between the maximum height to which a volcanic edifice is able to grow and the depth at which the partial melts providing its magma supply are formed is used to infer various aspects of the thermal and stress state of the lithosphere beneath volcanic constructs on earth, Mars, Io, and Venus. The assumptions behind this relationship are examined, and it is shown that many of them require geologically unreasonable conditions. The evidence cited in the literature for the relationship is assessed critically, and it is found that there are other factors that may explain the observations. It is concluded that volcano heights on the terrestrial planets cannot be related in any simple way to lithospheric thickness or depth to the magma source zone, and the range of other vectors controlling volcano height are reviewed.

Apollo 15 yellow-brown volcanic glass: Chemistry and petrogenetic relations to green volcanic glass and olivine-normative mare basalts

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

Hughes, S.S.; Schmitt, R.A.; Oregon State Univ., Corvallis

1988-10-01

Apollo 15 yellow-brown glass is one of twenty-five, high Mg, primary magmas emplaced on the lunar surface in pyroclastic eruptions. Forty spherules of this glass were individually analyzed by electron microprobe and INAA for major- and trace-elements. The abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle. Models are developed to explain the possible source-regions of several Apollo 15 and Apollo 12 low-Ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean: (a) early olivine {plus minus} orthopyroxene cumulates; (b) late-stage clinopyroxenemore » + pigeonite + ilmenite + plagioclase cumulates; and (c) late-stage inter-cumulus liquid.« less

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

NASA Astrophysics Data System (ADS)

Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni; Rico, Ciro; Scandone, Roberto; Terrasi, Filippo

2017-04-01

Defining and understanding the shallow transfer of magma at volcanoes is crucial to forecast eruptions, possibly the ultimate goal of volcanology. This is particularly challenging at felsic calderas experiencing unrest, which typically includes significant changes in seismicity, deformation and degassing rates. Caldera unrest is particularly frequent, affects wide areas and often does not culminate in an eruption. Moreover its evidence is usually complicated by the presence of a hydrothermal system. As a result, forecasting any eruption and vent-opening sites within a caldera is very difficult. The Campi Flegrei caldera (CFc), in the densely inhabited area of Naples (Italy), is commonly considered one of the most dangerous active volcanic systems. CFc is a 12 km wide depression hosting two nested calderas formed during the eruptions of the Campanian Ignimbrite ( 39 ka) and the Neapolitan Yellow Tuff ( 15 ka). In the last 5 ka, resurgence, with uplift >60 m close to the central part of the caldera, was accompanied by volcanism between 4.8 and 3.8 ka. After 3 ka of quiescence, increasing seismicity and uplift preceded the last eruption at Monte Nuovo in 1538 for several decades. The most recent activity culminated in four unrest episodes between 1950-1952, 1969-1972, 1982-1984 and 2005-Present, with a cumulative uplift at Pozzuoli of 4.5 m; the present unrest episode has been interpreted as being magma-driven. These unrest episodes are considered the most evident expression of a longer-term (centuries or more) restless activity. The post-1980 deformation largely results from a magmatic oblate or sill-like source at 4 km depth below Pozzuoli. Despite the restless activity of CFc, the recent unrest episodes did not culminate in eruption, so that any possibility to define the pre-eruptive shallow transfer of magma remains elusive. Indeed, this definition is a crucial step in order to identify and understand pre-eruptive processes, and thus to make any forecast. To fill this gap, we focused on the last eruption of 1538, reconstructing its pre-eruptive deformation pattern. For this, we exploited the unique historical, archaeological, geological and long-term geodetic record of the caldera to carefully determine the height variations (and related errors) of 20 selected sites along its coastline. The integration of this large dataset permitted the first reconstruction of pre-eruptive short- and long-term ground deformation of the CFc and to model the magma transfer before the eruption. Our data suggest a progressive magma accumulation from 1251 to 1536 in a 4.6±0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8±0.6 km deep magmatic source 4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4±0.3 km deep. This reconstruction corroborates the existence of a stationary oblate source, below the caldera centre, that was feeding lateral eruptions for the last 5 ka, and suggests: repeated emplacement of magma through intrusions below the caldera centre; occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

Drinking water treatment is not associated with an observed increase in neural tube defects in mice

PubMed Central

Melin, Vanessa E.; Johnstone, David W.; Etzkorn, Felicia A.

2018-01-01

Disinfection by-products (DBPs) arise when natural organic matter in source water reacts with disinfectants used in the water treatment process. Studies have suggested an association between DBPs and birth defects. Neural tube defects (NTDs) in embryos of untreated control mice were first observed in-house in May 2006 and have continued to date. The source of the NTD-inducing agent was previously determined to be a component of drinking water. Tap water samples from a variety of sources were analyzed for trihalomethanes (THMs) to determine if they were causing the malformations. NTDs were observed in CD-1 mice provided with treated and untreated surface water. Occurrence of NTDs varied by water source and treatment regimens. THMs were detected in tap water derived from surface water but not detected in tap water derived from a groundwater source. THMs were absent in untreated river water and laboratory purified waters, yet the percentage of NTDs in untreated river water were similar to the treated water counterpart. These findings indicate that THMs were not the primary cause of NTDs in the mice since the occurrence of NTDs was unrelated to drinking water disinfection. PMID:24497082

Identifying (subsurface) anthropogenic heat sources that influence temperature in the drinking water distribution system

NASA Astrophysics Data System (ADS)

Agudelo-Vera, Claudia M.; Blokker, Mirjam; de Kater, Henk; Lafort, Rob

2017-09-01

The water temperature in the drinking water distribution system and at customers' taps approaches the surrounding soil temperature at a depth of 1 m. Water temperature is an important determinant of water quality. In the Netherlands drinking water is distributed without additional residual disinfectant and the temperature of drinking water at customers' taps is not allowed to exceed 25 °C. In recent decades, the urban (sub)surface has been getting more occupied by various types of infrastructures, and some of these can be heat sources. Only recently have the anthropogenic sources and their influence on the underground been studied on coarse spatial scales. Little is known about the urban shallow underground heat profile on small spatial scales, of the order of 10 m × 10 m. Routine water quality samples at the tap in urban areas have shown up locations - so-called hotspots - in the city, with relatively high soil temperatures - up to 7 °C warmer - compared to the soil temperatures in the surrounding rural areas. Yet the sources and the locations of these hotspots have not been identified. It is expected that with climate change during a warm summer the soil temperature in the hotspots can be above 25 °C. The objective of this paper is to find a method to identify heat sources and urban characteristics that locally influence the soil temperature. The proposed method combines mapping of urban anthropogenic heat sources, retrospective modelling of the soil temperature, analysis of water temperature measurements at the tap, and extensive soil temperature measurements. This approach provided insight into the typical range of the variation of the urban soil temperature, and it is a first step to identifying areas with potential underground heat stress towards thermal underground management in cities.

Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

USGS Publications Warehouse

Hinkley, T.K.; Quick, J.E.; Gregory, R.T.; Gerlach, T.M.

1995-01-01

Condensate samples were collected in 1992 from a high-temperature (300?? C) fumarole on the floor of the Halemaumau Pit Crater at Kilauea. The emergence about two years earlier of such a hot fumarole was unprecedented at such a central location at Kilauea. The condensates have hydrogen and oxygen isotopic compositions which indicate that the waters emitted by the fumarole are composed largely of meteoric water, that any magmatic water component must be minor, and that the precipitation that was the original source to the fumarole fell on a recharge area on the slopes of Mauna Loa Volcano to the west. However, the fumarole has no tritium, indicating that it taps a source of water that has been isolated from atmospheric water for at least 40 years. It is noteworthy, considering the unstable tectonic environment and abundant local rainfall of the Kilauea and Mauna Loa regions, that waters which are sources to the hot fumarole remain uncontaminated from atmospheric sources over such long times and long transport distances. As for the common, boiling point fumaroles of the Kilauea summit region, their 18O, D and tritium concentrations indicate that they are dominated by recycling of present day meteoric water. Though the waters of both hot and boiling point fumaroles have dominantly meteoric sources, they seem to be from separate hydrological regimes. Large concentrations of halogens and sulfur species in the condensates, together with the location at the center of the Kilauea summit region and the high temperature, initially suggested that much of the total mass of the emissions of the hot fumarole, including the H2O, might have come directly from a magma body. The results of the present study indicate that it is unreliable to infer a magmatic origin of volcanic waters based solely on halogen or sulfur contents, or other aspects of chemical composition of total condensates. ?? 1995 Springer-Verlag.

Children's drinking water: parental preferences and implications for fluoride exposure.

PubMed

Sriraman, Natasha K; Patrick, Patricia A; Hutton, Kara; Edwards, Karen S

2009-01-01

The purposes of this study were to: describe children's drinking water sources; determine if any demographic factors are associated with water choice; describe parents' reasons for selecting bottled water; and determine parents' ability to provide enough information about their drinking water for providers to assess children's fluoride exposure. Subjects were parents of children 6 months to 15-years-old. A questionnaire was verbally administered in English or Spanish. Chi-square analyses were used to evaluate associations among study variables. Of 194 parents, 134 (69%) gave their children bottled water either exclusively or with tap water. Bottled water use was not significantly associated with the primary source of tap water, parent's education level, or household income. Reasons for giving children bottled water included: fear of contaminants in tap water; taste and/or smell of tap water; and convenience of bottled water. For parents using bottled water, over 65% did not know the brand's fluoride content. Barriers to an accurate fluoride assessment include frequent bottled water use and parental uncertainty about its fluoride content. By initiating communication with parents and educating them about fluoride sources, health care and dental providers may be able to better evaluate the adequacy of children's fluoride exposure and decide whether fluoride supplementation is necessary.

Making mushy magma chambers in the lower continental crust: Cold storage and compositional bimodality

NASA Astrophysics Data System (ADS)

Jackson, Matthew; Blundy, Jon; Sparks, Steve

2017-04-01

Increasing geological and geophysical evidence suggests that crustal magma reservoirs are normally low melt fraction 'mushes' rather than high melt fraction 'magma chambers'. Yet high melt fractions must form within these mush reservoirs to explain the observed flow and eruption of low crystallinity magmas. In many models, crystallinity is linked directly to temperature, with higher temperature corresponding to lower crystallinity (higher melt fraction). However, increasing temperature yields less evolved (silicic) melt composition for a given starting material. If mobile, low crystallinity magmas require high temperature, it is difficult to explain how they can have evolved composition. Here we use numerical modelling to show that reactive melt flow in a porous and permeable mush reservoir formed by the intrusion of numerous basaltic sills into the lower continental crust produces magma in high melt fraction (> 0.5) layers akin to conventional magma chambers. These magma-chamber-like layers contain evolved (silicic) melt compositions and form at low (close to solidus) temperatures near the top of the mush reservoir. Evolved magma is therefore kept in 'cold storage' at low temperature, but also at low crystallinity so the magma is mobile and can leave the mush reservoir. Buoyancy-driven reactive flow and accumulation of melt in the mush reservoir controls the temperature and composition of magma that can leave the reservoir. The modelling also shows that processes in lower crustal mush reservoirs produce mobile magmas that contain melt of either silicic or mafic composition. Intermediate melt compositions are present but are not within mobile magmas. Silicic melt compositions are found at high melt fraction within the magma-chamber like layers near the top of the mush reservoir. Mafic melt compositions are found at high melt fraction within the cooling sills. Melt elsewhere in the reservoir has intermediate composition, but remains trapped in the reservoir because the local melt fraction is too low to form a mobile magma. The model results are consistent with geochemical data suggesting that lower crustal magma reservoirs supply silicic and mafic melts to arc volcanoes, but intermediate magmas are formed by mixing in shallower reservoirs. We suggest here that lower crustal magma chambers primarily form in response to changes in bulk composition caused by melt migration and chemical reaction in a mush reservoir. This process is different to the conventional and widely applied models of magma chamber formation. Similar processes are likely to operate in shallow mush reservoirs, but will likely be further complicated by the presence of volatile phases, and mixing of different melt compositions sourced from deeper mush reservoirs.

Rapid Inflation Caused by Shallow Magmatic Activities at Okmok Volcano, Alaska, Detected by GPS Campaigns 2000-2003

NASA Astrophysics Data System (ADS)

Miyagi, Y.; Freymueller, J.; Kimata, F.; Sato, T.; Mann, D.

2006-12-01

Okmok volcano is located on Umnak Island in the Aleutian Arc, Alaska. This volcano consists of a large caldera, and there are several post-caldera cones within the caldera. It has erupted more than 10 times during the last century, with the latest eruption occurring in February 1997. Annual GPS campaigns during 2000-2003 have revealed a rapid inflation at Okmok volcano. Surface deformation indicates that Okmok volcano has been inflating during 2000-2003 at a variable inflation rate. Total displacements over three years are as large as 15 cm of maximum radial displacement and more than 35 cm of maximum uplift. Simple inflation pattern after 2001, showing radial outward displacements from the caldera center and significant uplifts, are modeled by a Mogi inflation source, which is located at the depth of about 3.1 km beneath the geometric center of the caldera, and we interpreted the source as a shallow magma chamber. The results from our GPS measurements correspond approximately to the results from InSAR measurement for almost same periods, except for an underestimate of the volume change rate of the source deduced by InSAR data for the period 2002-2003. Taking into consideration the results from InSAR measurements, the amount of volume increase in the source is estimated to be about 0.028 km3 during 1997-2003. This means that 20-54 percent of the volume erupted in the 1997 eruption has been already replenished in the shallow magma chamber. An eruption recurrence time is estimated from the volume change rate of the source to be about 15-30 years for 1997-sized eruptions, which is consistent with about 25 years average time interval between major eruptions at Okmok volcano. An additional modeling using a rectangular tensile source combined to the main spherical source suggests a possibility of other magma storage located between the main source and the active vent, which is associated with lateral magma transportation between them. The combined model improved residuals compared to those from single-source model, and provided significantly better fitting to the deformation data inside the caldera.

Fluoride and bacterial content of bottled drinking water versus municipal tap water.

PubMed

Mythri, H; Chandu, G N; Prashant, G M; Subba Reddy, V V

2010-01-01

Water is a divine gift. People quench their thirst without questioning the source of water. But, apprehension about contaminants in municipal water supplies along with increased fear of fluorosis made bottled drinking water as one of the important tradable commodities. The objectives of the study were to determine and compare the fluoride and bacterial contents of commercially available bottled drinking water and municipal tap water in Davangere city, Karnataka. Fifty samples of 10 categories of bottled drinking water with different batch numbers were purchased and municipal water from different sources were collected. Fluoride levels were determined by an ion-selective electrode. Water was cultured quantitatively and levels of bacteria were calculated as colony-forming units (CFUs) per milliliter. Descriptive analysis of water samples for fluoride concentration was in the range of 0.07-0.33 for bottled drinking water, Bisleri showing the highest of 0.33. A comparison of the mean values of microbial count for bottled drinking water with that of municipal tap water showed no statistically significant difference, but was more than the standard levels along with the presence of fungus and maggots. The fluoride concentration was below the optimal level for both municipal tap water and bottled drinking water. CFUs were more than the recommended level in both municipal tap water and bottled drinking water.

Geodesy - the key for constraining rates of magma supply, storage, and eruption

NASA Astrophysics Data System (ADS)

Poland, Michael; Anderson, Kyle

2016-04-01

Volcanology is an inherently interdisciplinary science that requires joint analysis of diverse physical and chemical datasets to infer subsurface processes from surface observations. Among the diversity of data that can be collected, however, geodetic data are critical for elucidating the main elements of a magmatic plumbing system because of their sensitivity to subsurface changes in volume and mass. In particular, geodesy plays a key role in determining rates of magma supply, storage, and eruption. For example, surface displacements are critical for estimating the volume changes and locations of subsurface magma storage zones, and remotely sensed radar data make it possible to place significant bounds on eruptive volumes. Combining these measurements with geochemical indicators of magma composition and volatile content enables modeling of magma fluxes throughout a volcano's plumbing system, from source to surface. We combined geodetic data (particularly InSAR) with prior geochemical constraints and measured gas emissions from Kīlauea Volcano, Hawai`i, to develop a probabilistic model that relates magma supply, storage, and eruption over time. We found that the magma supply rate to Kīlauea during 2006 was 35-100% greater than during 2000-2001, with coincident increased rates of subsurface magma storage and eruption at the surface. By 2012, this surge in supply had ended, and supply rates were below those of 2000-2001; magma storage and eruption rates were similarly reduced. These results demonstrate the connection between magma supply, storage, and eruption, and the overall importance of magma supply with respect to volcanic hazards at Kīlauea and similar volcanoes. Our model also confirms the importance of geodetic data in modeling these parameters - rates of storage and eruption are, in some cases, almost uniquely constrained by geodesy. Future modeling efforts along these lines should also seek to incorporate gravity data, to better determine magma compressibility and subsurface mass change.

Drilling Magma for Science, Volcano Monitoring, and Energy

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Lavallée, Y.; Blankenship, D.

2017-12-01

Magma chambers are central to understanding magma evolution, formation of continental crust, volcanism, and renewal of hydrothermal systems. Information from geology, petrology, laboratory experiments, and geophysical imagery has led to little consensus except a trend to see magma systems as being crystal-dominant (mush) rather than melt dominant. At high melt viscosities, crystal-liquid fractionation may be achieved by separation of melt from mush rather than crystals from liquid suspension. That the dominant volume has properties more akin to solid than liquid might explain the difficulty in detecting magma geophysically. Recently, geothermal drilling has intersected silicic magma at the following depths and SiO2 contents are: Puna, Hawaii, 2.5 km, 67 wt%; Menengai, Kenya 2.1 km, 67 wt%; Krafla, Iceland, 2.1 km, 75 wt%. Some similarities are: 1) Drillers encountered a "soft", sticky formation; 2) Cuttings or chips of clear quenched glass were recovered; 3) The source of the glass flowed up the well; 4) Transition from solid rock to recovering crystal-poor glass occurred in tens of meters, apparently without an intervening mush zone. Near-liquidus magma at the roof despite rapid heat loss there presents a paradox that may be explained by very recent intrusion of magma, rise of liquidus magma to the roof replacing partially crystallized magma, or extremely skewed representation of melt over mush in cuttings (Carrigan et al, this session). The latter is known to occur by filter pressing of ooze into lava lake coreholes (Helz, this session), but cannot be verified in actual magma without coring. Coring to reveal gradients in phase composition and proportions is required for testing any magma chamber model. Success in drilling into and controlling magma at all three locations, in coring lava lakes to over 1100 C, and in numerical modeling of coring at Krafla conditions (Su, this session) show this to be feasible. Other unprecedented experiments are using the known location and properties of magma to calibrate geophysics (Brown et al, this session) and understand signals of "unrest". How can we not make such observations when there is so much to learn, so much at stake in correctly monitoring volcanoes, and such a need for clean, renewable energy?

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

NASA Astrophysics Data System (ADS)

Harris, Chris; le Roux, Petrus; Cochrane, Ryan; Martin, Laure; Duncan, Andrew R.; Marsh, Julian S.; le Roex, Anton P.; Class, Cornelia

2015-07-01

Oxygen isotope compositions of Karoo and Etendeka large igneous province (LIP) picrites and picrite basalts are presented to constrain the effects of crustal contamination versus mantle source variation. Olivine and orthopyroxene phenocrysts from lavas and dykes (Mg# 64-80) from the Tuli and Mwenezi (Nuanetsi) regions of the ca 180 Ma Karoo LIP have δ18O values that range from 6.0 to 6.7 ‰. They appear to have crystallized from magmas having δ18O values about 1-1.5 ‰ higher than expected in an entirely mantle-derived magma. Olivines from picrite and picrite basalt dykes from the ca 135 Ma Etendeka LIP of Namibia and Karoo-age picrite dykes from Dronning Maud Land, Antarctica, do not have such elevated δ18O values. A range of δ18O values from 4.9 to 6.0 ‰, and good correlations between δ18O value and Sr, Nd and Pb isotope ratios for the Etendeka picrites are consistent with previously proposed models of crustal contamination. Explanations for the high δ18O values in Tuli/Mwenezi picrites are limited to (1) alteration, (2) crustal contamination, and (3) derivation from mantle with an abnormally high δ18O. Previously, a variety of models that range from crustal contamination to derivation from the `enriched' mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as K, and average ɛNd and ɛSr values of -8 and +16 in Mwenezi (Nuanetsi) picrites. However, the primitive character of the magmas (Mg# 73), combined with the lack of correlation between δ18O values and radiogenic isotopic compositions, MgO content, or Mg# is inconsistent with crustal contamination. Thus, an 18O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated. High δ18O values are accompanied by negative Nb and Ta anomalies, consistent with the involvement of the mantle lithosphere, whereas the high δ18O themselves are consistent with an eclogitic source. Magma δ18O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, and the possibility exists that a long-lived 18O-enriched mantle source has existed beneath southern Africa. A mixed eclogite peridotite source could have developed by emplacement of oceanic lithosphere into the cratonic keel during Archaean subduction.

Drinking water consumption patterns among adults-SMS as a novel tool for collection of repeated self-reported water consumption.

PubMed

Säve-Söderbergh, Melle; Toljander, Jonas; Mattisson, Irene; Åkesson, Agneta; Simonsson, Magnus

2018-03-01

Studies have shown that the average drinking water consumption ranges between 0.075 and 3 L/day for adults with both national and regional differences. For exposure assessment of drinking water hazards, country-specific drinking water consumption data including sources of the consumed water may therefore be warranted. To estimate the amount and source of drinking water consumed among adults in Sweden, we collected self-reported estimates using both traditional methods (telephone interviews, web questionnaire) and a novel method (Short Message Service, SMS questionnaires) in a population from an average sized Swedish municipality. Monthly SMS questionnaires were sent out during one year to obtain longitudinal information as well. SMS showed to be a promising tool for collecting self-reported consumption, as most citizens could participate and the method showed high response rate. Data collected via the SMS questionnaire shows an average consumption of cold tap water of 4.9 glasses/24 h (one glass=200 ml), while the average estimates of cold tap water collected by the traditional methods range from 4.5 to 7.0 glasses/24 h. For statistical distributions, the mean daily consumption of cold tap water for the population was best fitted to a gamma distribution. About 70% of the cold tap water is consumed at home. Based on the results from the SMS study, we suggest using 1 l/day for the average adult population and 2.5 l/day for high consumers for risk assessment of cold tap water consumption. As 46% of the tap water consumed is heated, we suggest using 1.85 l/day for total tap water consumption.

Drinking water consumption patterns among adults—SMS as a novel tool for collection of repeated self-reported water consumption

PubMed Central

Säve-Söderbergh, Melle; Toljander, Jonas; Mattisson, Irene; Åkesson, Agneta; Simonsson, Magnus

2018-01-01

Studies have shown that the average drinking water consumption ranges between 0.075 and 3 L/day for adults with both national and regional differences. For exposure assessment of drinking water hazards, country-specific drinking water consumption data including sources of the consumed water may therefore be warranted. To estimate the amount and source of drinking water consumed among adults in Sweden, we collected self-reported estimates using both traditional methods (telephone interviews, web questionnaire) and a novel method (Short Message Service, SMS questionnaires) in a population from an average sized Swedish municipality. Monthly SMS questionnaires were sent out during one year to obtain longitudinal information as well. SMS showed to be a promising tool for collecting self-reported consumption, as most citizens could participate and the method showed high response rate. Data collected via the SMS questionnaire shows an average consumption of cold tap water of 4.9 glasses/24 h (one glass=200 ml), while the average estimates of cold tap water collected by the traditional methods range from 4.5 to 7.0 glasses/24 h. For statistical distributions, the mean daily consumption of cold tap water for the population was best fitted to a gamma distribution. About 70% of the cold tap water is consumed at home. Based on the results from the SMS study, we suggest using 1 l/day for the average adult population and 2.5 l/day for high consumers for risk assessment of cold tap water consumption. As 46% of the tap water consumed is heated, we suggest using 1.85 l/day for total tap water consumption. PMID:28612838

Silica-enriched mantle sources of subalkaline picrite-boninite-andesite island arc magmas

NASA Astrophysics Data System (ADS)

Bénard, A.; Arculus, R. J.; Nebel, O.; Ionov, D. A.; McAlpine, S. R. B.

2017-02-01

Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation. Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith ('hybrid mantle wedge') composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid compositions extracted from these hybrid sources are higher in normative quartz and hypersthene (i.e., they have a more silica-saturated character) in comparison with basalts derived from prior melt-depleted asthenospheric mantle beneath ridges. These primary arc melts range from silica-rich picrite to boninite and high-Mg basaltic andesite along a residual spinel harzburgite cotectic. Silica enrichment in the mantle sources of arc-related, subalkaline picrite-boninite-andesite suites coupled with the amount of water and depth of melting, are important for the formation of medium-Fe ('calc-alkaline') andesite-dacite-rhyolite suites, key lithologies forming the continental crust.

Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption.

PubMed

Sigmundsson, Freysteinn; Hreinsdóttir, Sigrún; Hooper, Andrew; Arnadóttir, Thóra; Pedersen, Rikke; Roberts, Matthew J; Oskarsson, Níels; Auriac, Amandine; Decriem, Judicael; Einarsson, Páll; Geirsson, Halldór; Hensch, Martin; Ofeigsson, Benedikt G; Sturkell, Erik; Sveinbjörnsson, Hjörleifur; Feigl, Kurt L

2010-11-18

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (>5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ∼0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajökull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.

Constraint on the magma sources in Luzon Island Philippines by using P and S wave local seismic tomography

NASA Astrophysics Data System (ADS)

Nghia, N. C.; Huang, B. S.; Chen, P. F.

2017-12-01

The subduction of South China Sea beneath the Luzon Island has caused a complex setting of seismicity and magmatism because of the proposed ridge subduction and slab tearing. To constrain the validity of slab tearing induced by ridge subduction and their effect, we performed a P and S wave seismic tomography travel time inversion using LOTOS code. The dataset has been retrieved from International Seismological Centre from 1960 to 2008. A 1D velocity inverted by using VELEST with a Vp/Vs ratio of 1.74 is used as the starting input velocity for tomographic inversion. Total of 20905 P readings and 8126 S readings from 2355 earthquakes events were used to invert for velocity structure beneath Luzon Island. The horizontal tomographic results show low-velocity, high Vp/Vs regions at the shallow depth less than 50 km which are interpreted as the magmatic chambers of the volcanic system in Luzon. At the suspected region of slab tearing at 16oN to 18oN, two sources of magma have been indentified: slab window magma at shallow depth (< 50 km) and magma induced by mantle wedge partial melting from higher depth. This slab melting may have changed the composition of magmatic to become more silicic with high viscosity, which explains the volcanic gap in this region. At the region of 14oN to 15oN, large magma chambers under active volcanos are identified which explain the active volcanism in this region. Contrast to the region of slab tearing, in this region, the magma chambers are fed by only magma from partial melting of mantle wedge from the depth higher than 100 km. These observations are consistent with previous work on the slab tearing of South China Sea and the activities of volcanism in the Luzon Island.

Imaging the Magmatic System of Erebus Volcano, Antarctica using the Magnetotelluric Method

NASA Astrophysics Data System (ADS)

Hill, G.; Wannamaker, P. E.; Stodt, J. A.; Unsworth, M. J.; Maris, V.; Bedrosian, P.; Wallin, E.; Kordy, M. A.; Ogawa, Y.; Kyle, P. R.; Uhlmann, D. F.

2017-12-01

Erebus volcano, on Ross Island, Antarctica, in the south west Ross Sea, offers a unique opportunity to understand the magmatic system of an active alkaline volcano, and rifting within the West Antarctica Rift System. Erebus has the world's only persistent phonolite lava lake in its summit crater, and thus provides a window into the heart of a degassing volcano's magmatic system. Phonolite magmas like those at Erebus have been responsible for devastating eruptions (e.g. Pompeii 79 AD; Tambora 1815). Petrologic models suggest that Erebus is undergoing fractional crystallisation of deep mantle-derived parental basanite magma in one or more crustal magma chambers. We are using magnetotelluric (MT) methods and instrumentation, especially developed for use in Antarctica, to image the resistivity structure (magmatic system) of Erebus and the older volcanoes forming Ross Island. In addition, we mapping the rifted crustal structure and examining the mantle source of the magma and the role that the Terror Rift system plays in the active volcanism. Data collection occurred over three field seasons from 2014-2017. Measurements were made at 129 locations on Ross Island and vicinity. A pool of 11 Phoenix Geophysics V5 systems coupled with Numeric Resources high impedance preamplifiers were used. A primary goal of this work is to constrain the distribution of melt within and beneath the volcanic edifice. In addition, we are imaging the interpreted mantle source region for Erebus magmas and investigating the role that the Terror Rift system plays in generating and focusing magmatism. Preliminary modelling suggests that we are able to resolve the crustal residence zones and the path taken by the magma as it ascends from the mantle to the surface. Our work provides new insight into the formation of phonolite magma and has implications for understanding the magmatic process occurring in rift systems globally. It further provides an opportunity to compare volcanic processes in both compressional and extensional tectonics settings.

Can basal magma oceans generate magnetic fields?

NASA Astrophysics Data System (ADS)

Stegman, D. R.; Ziegler, L. B.; Davies, C.

2015-12-01

Earth's magnetic field is very old, with recent data now showing the field possibly extended back to 4.1 billion years ago (Tarduno et al., Science, 2015). Yet, based upon our current knowledge there are difficulties in sustained a core dynamo over most of Earth's history. Moreover, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core. We have extended this work by developing a new code, Dynamantle, which is a model with an entropy-based approach, similar to those commonly used in core dynamics models. We present new results using this code to assess the conditions under which basal magma oceans can generate positive ohmic dissipation. This is more generally useful than just considering the early Earth, but also for many silicate exoplanets in which basal magma oceans are even more likely to exist.

Occurrence of nitrosamines and their precursors in drinking water systems around mainland China.

PubMed

Bei, Er; Shu, Yuanyuan; Li, Shixiang; Liao, Xiaobin; Wang, Jun; Zhang, Xiaojian; Chen, Chao; Krasner, Stuart

2016-07-01

N-Nitrosamines (NAs) in drinking water have attracted considerable attention in recent years due to their high carcinogenicity, frequent occurrence, and their potential regulation. During the past three years, we have collected about 164 water samples of finished water, tap water, and source water from 23 provinces, 44 cities from large cities to small towns, and 155 sampling points all over China. The occurrence of NAs in the finished and tap water was much higher in China than that in the U.S. Nine NAs were measured and NDMA had the highest concentration. The occurrence of NDMA was in 33% of the finished waters of water treatment plants and in 41% of the tap waters. The average NDMA concentration in finished and tap waters was 11 and 13 ng/L, respectively. Formation potentials (FPs) of source waters were examined with an average NDMA FP of 66 ng/L. Large variations in NA occurrence were observed geographically in China and temporally in different seasons. The Yangtze River Delta area, one sub-area in East China, had the highest concentrations of NAs, where the average NDMA concentrations in the finished and tap water were 27 and 28.5 ng/L, respectively, and the average NDMA FP in the source water was 204 ng/L. NA control may be achieved by applying breakpoint free chlorination and/or advanced treatment of ozone - granular activated carbon process to remove the NA precursors before disinfection. Copyright © 2016 Elsevier Ltd. All rights reserved.

Oxidation state inherited from the magma source and implications for mineralization: Late Jurassic to Early Cretaceous granitoids, Central Lhasa subterrane, Tibet

NASA Astrophysics Data System (ADS)

Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; McInnes, Brent I. A.; Li, JinXiang; Zhao, JunXing

2018-03-01

Arc magmas are more oxidized than mid-ocean ridge basalts; however, there is continuing debate as to whether this higher oxidation state is inherited from the source magma or developed during late-stage magmatic differentiation processes. Well-constrained Late Jurassic to Early Cretaceous arc-related intermediate to felsic rocks derived from distinct magma sources provide us with a good opportunity to resolve this enigma. A series of granitoids from the western Central Lhasa subterrane were analyzed for whole-rock magnetic susceptibility, Fe2O3/FeO ratios, and trace elements in zircon. Compared to Late Jurassic samples (1.8 ± 2.0 × 10-4 emu g-1 oe-1, Fe3+/Fetotal = 0.32 ± 0.07, zircon Ce4+/Ce3+* = 15.0 ± 13.4), Early Cretaceous rocks show higher whole-rock magnetic susceptibility (5.8 ± 2.5 × 10-4 emu g-1 oe-1), Fe3+/Fetotal ratios (0.43 ± 0.04), and zircon Ce4+/Ce3+* values (23.9 ± 22.3). In addition, positive correlations among whole-rock magnetic susceptibility, Fe3+/Fetotal ratios, and zircon Ce4+/Ce3+* reveal a slight increase in oxidation state from fO2 = QFM to NNO in the Late Jurassic to fO2 = ˜NNO in the Early Cretaceous. Obvious linear correlation between oxidation indices (whole-rock magnetic susceptibility, zircon Ce4+/Ce3+*) and source signatures (zircon ɛHf(t), TDM C ages) indicates that the oxidation state was predominantly inherited from the source with only a minor contribution from magmatic differentiation. Thus, the sources for both the Late Jurassic and Early Cretaceous rocks were probably influenced by mantle wedge-derived magma, contributing to the increased fO2. Compared to ore-forming rocks at giant porphyry Cu deposits, the relatively low oxidation state (QFM to NNO) and negative ɛHf(t) (-16 to 0) of the studied granitoids implies relative infertility. However, this study demonstrates two potential fast and effective indices ( fO2 and ɛHf(t)) to evaluate the fertility of granitoids for porphyry-style mineralization. In an exploration context for the west Central Lhasa subterrane, features indicative of potential fertility might include more oxidized, positive ɛHf(t), young rocks (<130 Ma).

Magmatic controls on eruption dynamics of the 1950 yr B.P. eruption of San Antonio Volcano, Tacaná Volcanic Complex, Mexico-Guatemala

NASA Astrophysics Data System (ADS)

Mora, Juan Carlos; Gardner, James Edward; Macías, José Luis; Meriggi, Lorenzo; Santo, Alba Patrizia

2013-07-01

San Antonio Volcano, in the Tacaná Volcanic Complex, erupted ~ 1950 yr. B.P., with a Pelean type eruption that produced andesitic pyroclastic surges and block-and-ash flows destroying part of the volcano summit and producing a horse-shoe shaped crater open to the SW. Between 1950 and 800 yr B.P. the eruption continued with effusive andesites followed by a dacite lava flow and a summit dome, all from a single magma batch. All products consist of phenocrysts and microphenocrysts of zoned plagioclase, amphibole, pyroxene, magnetite ± ilmenite, set in partially crystallized groundmass of glass and microlites of the same mineral phases, except for the lack of amphibole. Included in the andesitic blocks of the block-and-ash flow deposit are basaltic andesite enclaves with elongated and ellipsoidal forms and chilled margins. The enclaves have intersertal textures with brown glass between microphenocrysts of plagioclase, hornblende, pyroxene, and olivine, and minor proportions of phenocrysts of plagioclase, hornblende, and pyroxene. A compositional range obtained of blocks and enclaves resulted from mixing between andesite (866 °C ± 22) and basaltic andesite (enclaves, 932 °C ± 22), which may have triggered the explosive Pelean eruption. Vestiges of that mixing are preserved as complex compositional zones in plagioclase and clinopyroxene-rich reaction rims in amphibole in the andesite. Whole-rock chemistry, geothermometry, experimental petrology and modeling results suggest that after the mixing event the eruption tapped hybrid andesitic magma (≤ 900 °C) and ended with effusive dacitic magma (~ 825 °C), all of which were stored at ~ 200 MPa water pressure. A complex open-system evolution that involved crustal end-members best explains the generation of effusive dacite from the hybrid andesite. Amphibole in the dacite is rimmed by reaction products of plagioclase, orthopyroxene, and Fe-Ti oxides produced by decompression during ascent. Amphibole in the andesite, however, lacks such rims. Because the andesite was at 866 ± 22 °C and the dacite was at ~ 825 °C, the reaction rims indicate that the andesitic magma ascended at 0.023 m s- 1 during the explosive phase of the eruption, whereas the dacitic magma rose more slowly at ~ 0.002-0.004 m s- 1.

Explosive origin of silicic lava: Textural and δD-H2O evidence for pyroclastic degassing during rhyolite effusion

NASA Astrophysics Data System (ADS)

Castro, Jonathan M.; Bindeman, Ilya N.; Tuffen, Hugh; Ian Schipper, C.

2014-11-01

A long-standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava. A widely cited idea is that the explosive-to-effusive transition manifests a two-stage degassing history whereby lava is the product of non-explosive, open-system gas release following initial explosive, closed-system degassing. Direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive, as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent. This explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava. Here we use precise H-isotope and magmatic H2O measurements and textural evidence to demonstrate that effusion results from explosion(s)-lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels (tuffisites) that repetitively and explosively vent from effusing lava. Our measurements show, specifically that D/H ratios and H2O contents of a broad suite of explosive and effusive samples from Chaitén volcano (hydrous bombs, Plinian pyroclasts, tuffisite veins, and lava) define a single and continuous degassing trend that links wet explosive pyroclasts (∼ 1.6 wt.% H2O, δD = - 76.4 ‰) to dry obsidian lavas (∼ 0.13 wt.% H2O, δD = - 145.7 ‰). This geochemical pattern is best fit with batched degassing model that comprises small repeated closed-system degassing steps followed by pulses of vapour extraction. This degassing mechanism is made possible by the action of tuffisite veins, which, by tapping already vesicular or brecciated magma, allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed-system domains and large tracts of conduit magma by giving them long-range connectivity. Even though tuffisite veins render magma degassed and capable of effusing, they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut. Thus the effusion of silicic lava, traditionally thought to be relatively benign process, presents a particularly hazardous form of explosive volcanism.

Effects of sea-level changes on mid-ocean ridge magmatism and implications for emission rates of carbon.

NASA Astrophysics Data System (ADS)

Cerpa, N.; Katz, R. F.; Keller, T.

2017-12-01

Glacial cycles move water between ice sheets and the ocean, and hence cause regional pressure changes in the solid Earth. The rate of sea-level (SL) change during this cycle is comparable to the rate of mantle upwelling beneath mid-ocean ridges (MORs), and hence we expect the induced pressure variations to modify the rate and depth of silicate melting. SL variations may therefore induce changes in the supply and composition of magma at MORs, which could affect the flux of carbon into the climate system. Likewise, the trace-element geochemistry of magmas tapped by ridge volcanism may vary during these cycles due to variations in melt flux. Such variations may have been recorded by sediment-hosted volcanic glass fragments [Ferguson et al., 2017]. We investigate these questions using computational models of melt production and transport in which volatiles participate in the thermodynamics of melting. Published models of the effect of SL on MORs predict up to 10% variation in carbon emission rates for absolute changes in SL of 50-100 m with possible lag times of several tens of kyrs [Burley et al., 2015; Hasenclever et al., 2017]. A major assumption of those models is that water and carbon are passive, incompatible elements. But small concentrations of those volatiles affect the solidus of mantle peridotite and increase the volume of upper mantle undergoing partial melting. Hence the current predictions of variation in MOR carbon emission might be an underestimate. Moreover, published models neglect the effects of volatiles on melt transport. Recents studies have demonstrated that volatiles can induce channelized transport [Keller and Katz 2016], potentially affecting the rate at which carbon is extracted from the mantle. In this study, we investigate the interplay between SL variations, melting, and segregation of volatile-rich melts. We use two-phase magma/mantle dynamics coupled to melting models that treat water and carbon dioxide as thermodynamic components. We compare models of equilibrium and disequilibrium melting to assess the influence of reaction kinetics on magma productivity at MORs during SL variations. Our calculations provide new estimates of the lag and amplitude of carbon emissions during glacial cycles. We address the impact of SL variations on the trace-element composition of magmas.

Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

USGS Publications Warehouse

Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu

2013-01-01

The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

Miocene silicic volcanism in southwestern Idaho: Geochronology, geochemistry, and evolution of the central Snake River Plain

USGS Publications Warehouse

Bonnichsen, B.; Leeman, W.P.; Honjo, N.; McIntosh, W.C.; Godchaux, M.M.

2008-01-01

New 40Ar-39Ar geochronology, bulk rock geochemical data, and physical characteristics for representative stratigraphic sections of rhyolite ignimbrites and lavas from the west-central Snake River Plain (SRP) are combined to develop a coherent stratigraphic framework for Miocene silicic magmatism in this part of the Yellowstone 'hotspot track'. The magmatic record differs from that in areas to the west and east with regard to its unusually large extrusive volume, broad lateral scale, and extended duration. We infer that the magmatic systems developed in response to large-scale and repeated injections of basaltic magma into the crust, resulting in significant reconstitution of large volumes of the crust, wide distribution of crustal melt zones, and complex feeder systems for individual eruptive events. Some eruptive episodes or 'events' appear to be contemporaneous with major normal faulting, and perhaps catastrophic crustal foundering, that may have triggered concurrent evacuations of separate silicic magma reservoirs. This behavior and cumulative time-composition relations are difficult to relate to simple caldera-style single-source feeder systems and imply complex temporal-spatial development of the silicic magma systems. Inferred volumes and timing of mafic magma inputs, as the driving energy source, require a significant component of lithospheric extension on NNW-trending Basin and Range style faults (i.e., roughly parallel to the SW-NE orientation of the eastern SRP). This is needed to accommodate basaltic inputs at crustal levels, and is likely to play a role in generation of those magmas. Anomalously high magma production in the SRP compared to that in adjacent areas (e.g., northern Basin and Range Province) may require additional sub-lithospheric processes. ?? Springer-Verlag 2007.

The role of magmas in the formation of hydrothermal ore deposits

USGS Publications Warehouse

Hedenquist, Jeffrey W.; Lowenstern, Jacob B.

1994-01-01

Magmatic fluids, both vapour and hypersaline liquid, are a primary source of many components in hydrothermal ore deposits formed in volcanic arcs. These components, including metals and their ligands, become concentrated in magmas in various ways from various sources, including subducted oceanic crust. Leaching of rocks also contributes components to the hydrothermal fluid—a process enhanced where acid magmatic vapours are absorbed by deeply circulating meteoric waters. Advances in understanding the hydrothermal systems that formed these ore deposits have come from the study of their active equivalents, represented at the surface by hot springs and volcanic fumaroles.

The crustal magma storage system of Volcán Quizapu, Chile, and the effects of magma mixing on magma diversity

USGS Publications Warehouse

Bergantz, George W.; Cooper, Kari M.; Hildreth, Edward; Ruprecht, Phillipp

2012-01-01

Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km3) of Volcán Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcán Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An25–40) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcán Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic magma that is the source for most of the 1846–1847 and 1932 erupted magmas. Dacite formation is best explained by mineral–melt separation (crystal fractionation) from an andesitic mush, which is inferred to have thermally and compositionally buffered the dacite magma thereby keeping it at relatively low crystallinity (<30 vol. %). The dominant cause of compositional diversity is melt separation. Back-mixing of mush (i.e. crystals with signatures of growth both in the andesitic mush and in the dacite magma) into the overlying dacite magma is rarely observed. Recharge events that increase crystal and magma diversity in the dacite magma are limited to an episode of mafic recharge and mixing just prior to the 1846–1847 eruption, where evidence for magma mixing is present on all scales. Chamber-wide mixing was incomplete (mixing efficiency of ∼0·53–0·85) as flow lobes vary significantly in composition along the proposed mixing array. Estimates of viscosity variations during the course of magma mixing suggest that mixing dynamics and the degree of magma interaction on all scales were established at the beginning of the recharge event.

Studies on the Effects of High Renewable Penetrations on Driving Point Impedance and Voltage Regulator Performance: National Renewable Energy Laboratory/Sacramento Municipal Utility District Load Tap Changer Driving Point Impedance Project

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

Nagarajan, Adarsh; Coddington, Michael H.; Brown, David

Voltage regulators perform as desired when regulating from the source to the load and when regulating from a strong source (utility) to a weak source (distributed generation). (See the glossary for definitions of a strong source and weak source.) Even when the control is provisioned for reverse operation, it has been observed that tap-changing voltage regulators do not perform as desired in reverse when attempting regulation from the weak source to the strong source. The region of performance that is not as well understood is the regulation between sources that are approaching equal strength. As part of this study, wemore » explored all three scenarios: regulator control from a strong source to a weak source (classic case), control from a weak source to a strong source (during reverse power flow), and control between equivalent sources.« less

Constraints on magma processes, subsurface conditions, and total volatile flux at Bezymianny Volcano in 2007–2010 from direct and remote volcanic gas measurements

USGS Publications Warehouse

Lopez, Taryn; Ushakov, Sergey; Izbekov, Pavel; Tassi, Franco; Cahill, Cathy; Neill, Owen; Werner, Cynthia A.

2013-01-01

Direct and remote measurements of volcanic gas composition, SO2 flux, and eruptive SO2 mass from Bezymianny Volcano were acquired between July 2007 and July 2010. Chemical composition of fumarolic gases, plume SO2 flux from ground and air-based ultraviolet remote sensing (FLYSPEC), and eruptive SO2 mass from Ozone Monitoring Instrument (OMI) satellite observations were used along with eruption timing to elucidate magma processes and subsurface conditions, and to constrain total volatile flux. Bezymianny Volcano had five explosive magmatic eruptions between May 2007 and June 2010. The most complete volcanic gas datasets were acquired for the October 2007, December 2009, and May 2010 eruptions. Gas measurements collected prior to the October 2007 eruption have a relatively high ratio of H2O/CO2 (81.2), a moderate ratio of CO2/S (5.47), and a low ratio of S/HCl (0.338), along with moderate SO2 and CO2 fluxes of 280 and 980 t/d, respectively, and high H2O and HCl fluxes of ~ 45,000 and ~ 440 t/d, respectively. These results suggest degassing of shallow magma (consistent with observations of lava extrusion) along with potential minor degassing of a deeper magma source. Gas measurements collected prior to the December 2009 eruption are characterized by relatively low H2O/CO2 (4.13), moderate CO2/S (6.84), and high S/HCl (18.7) ratios, along with moderate SO2 and CO2 fluxes of ~ 220 and ~ 1000 t/d, respectively, and low H2O and HCl fluxes of ~ 1700 and ~ 7 t/d, respectively. These trends are consistent with degassing of a deeper magma source. Fumarole samples collected ~ 1.5 months following the May 2010 eruption are characterized by high H2O/CO2 (63.0), low CO2/S (0.986), and moderate S/HCl (6.09) ratios. These data are consistent with degassing of a shallow, volatile-rich magma source, likely related to the May eruption. Passive and eruptive SO2 measurements are used to calculate a total annual SO2 mass of 109 kt emitted in 2007, with passive emissions comprising ~ 87–95% of the total. Total annual volatile masses for the study period are estimated to range from 1.1 × 106 to 18 × 106 t/year. Annual CO2 masses are ~ 8 to 40 times larger than can be explained by degassing of dissolved CO2 within eruptive magma, suggesting that the eruptive magma contained a significant quantity of exsolved volatiles sourced either from the eruptive melt or unerupted magma at depth. Variable total volatile fluxes ranging from ~ 3000 t/d in 2009 to ~ 49,000 t/d in 2007 are attributed to variations in the depth of gas exsolution and separation from the melt under open-system degassing conditions. We propose that exsolved volatiles are quickly transported to the surface from ascending magma via permeable flow through a bubble and/or fracture network within the conduit and thus retain their equilibrium composition at the time of segregation from melt. The composition of surface CO2 and H2O emissions from 2007 to 2009 are compared with modeled exsolved fluid compositions for a magma body ascending from entrapment depths to estimate depth of fluid exsolution and separation from the melt. We find that at the time of sample collection magma had already begun ascent from the mid-crustal storage region and was located at maximum depths of ~ 3.7 km in August 2007, approximately 2 months prior to the next magmatic eruption, and ~ 4.6 km in July of 2009 approximately five months prior to the next magmatic eruption. These findings suggest that the exsolved gas composition at Bezymianny Volcano may be used to detect magma ascent prior to eruption.

Finger tapping and pre-attentive sensorimotor timing in adults with ADHD.

PubMed

Hove, Michael J; Gravel, Nickolas; Spencer, Rebecca M C; Valera, Eve M

2017-12-01

Sensorimotor timing deficits are considered central to attention-deficit/hyperactivity disorder (ADHD). However, the tasks establishing timing impairments often involve interconnected processes, including low-level sensorimotor timing and higher level executive processes such as attention. Thus, the source of timing deficits in ADHD remains unclear. Low-level sensorimotor timing can be isolated from higher level processes in a finger-tapping task that examines the motor response to unexpected shifts of metronome onsets. In this study, adults with ADHD and ADHD-like symptoms (n = 25) and controls (n = 26) performed two finger-tapping tasks. The first assessed tapping variability in a standard tapping task (metronome-paced and unpaced). In the other task, participants tapped along with a metronome that contained unexpected shifts (±15, 50 ms); the timing adjustment on the tap following the shift captures pre-attentive sensorimotor timing (i.e., phase correction) and thus should be free of potential higher order confounds (e.g., attention). In the standard tapping task, as expected, the ADHD group had higher timing variability in both paced and unpaced tappings. However, in the pre-attentive task, performance did not differ between the ADHD and control groups. Together, results suggest that low-level sensorimotor timing and phase correction are largely preserved in ADHD and that some timing impairments observed in ADHD may stem from higher level factors (such as sustained attention).

Geochemical characteristics of igneous rocks associated with epithermal mineral deposits—A review

USGS Publications Warehouse

du Bray, Edward A.

2017-01-01

Newly synthesized data indicate that the geochemistry of igneous rocks associated with epithermal mineral deposits varies extensively and continuously from subalkaline basaltic to rhyolitic compositions. Trace element and isotopic data for these rocks are consistent with subduction-related magmatism and suggest that the primary source magmas were generated by partial melting of the mantle-wedge above subducting oceanic slabs. Broad geochemical and petrographic diversity of individual igneous rock units associated with epithermal deposits indicate that the associated magmas evolved by open-system processes. Following migration to shallow crustal reservoirs, these magmas evolved by assimilation, recharge, and partial homogenization; these processes contribute to arc magmatism worldwide.Although epithermal deposits with the largest Au and Ag production are associated with felsic to intermediate composition igneous rocks, demonstrable relationships between magmas having any particular composition and epithermal deposit genesis are completely absent because the composition of igneous rock units associated with epithermal deposits ranges from basalt to rhyolite. Consequently, igneous rock compositions do not constitute effective exploration criteria with respect to identification of terranes prospective for epithermal deposit formation. However, the close spatial and temporal association of igneous rocks and epithermal deposits does suggest a mutual genetic relationship. Igneous systems likely contribute heat and some of the fluids and metals involved in epithermal deposit formation. Accordingly, deposit formation requires optimization of source metal contents, appropriate fluid compositions and characteristics, structural features conducive to hydrothermal fluid flow and confinement, and receptive host rocks, but not magmas with special compositional characteristics.

Insights into Along Strike Variability in the Lau Back Spreading Center and Tonga Arc from Bodywave Tomography

NASA Astrophysics Data System (ADS)

Adams, A. N.; Wiens, D.; Barklage, M.; Conder, J. A.; Wei, S. S.; Cai, C.

2016-12-01

The Lau Backarc Spreading Center (LBSC) and the Tonga Arc offer an excellent location to study the complex interactions between magma production in subduction arcs and backarcs. Although the LBSC is often considered to be an archetype of backarc spreading centers, the system exhibits major along strike changes in surficial and subsurface characteristics - including rift morphology, spreading and subduction rates, rift-arc separation, magma production, and crustal thickness. These variations, together with geochemical evidence, suggest that mixing of arc and backarc magmas may occur at depth beneath the southern LBSC, where the backarc spreading center and the Tonga Arc are most proximal. To investigate magma production and transport beneath the LBSC and the Tonga Arc, this study jointly inverts arrivals from local and teleseismic earthquakes at 51 OBS and 16 land stations to create P- and S-wave upper mantle velocity models. Results from this study show that low velocity zones associated with the LBSC and Tonga Arc are distinctly separated in the north, but merge to a single low velocity zone in the south, supporting prior geochemical evidence for a common source of arc and backarc magmas in the south. Low velocities beneath the LBSC tilt westward with depth, consistent with predictions from numerical models for asymmetrical melting in the mantle wedge. Beneath the central LBSC, low velocities extend to depths of 300 km, suggesting a deep source for melt in some regions.

Compositions of Mars Rocks: SNC Meteorites, Differentiates, and Soils

NASA Technical Reports Server (NTRS)

Rutherford, M. J.; Minitti, M.; Weitz, C. M.

1999-01-01

The 13 samples from Mars identified in the terrestrial meteorite collections vary from dunite to pyroxenite to microgabbro or basalt. All of these rocks appear to have formed from primitive melts with similar major element compositional characteristics; i.e., FeO-rich and Al2O3-Poor melts relative to terrestrial basalt compositions. Although all of the SNC rocks can be derived by melting of the same Al-depleted mantle, contamination of SNC's by a Rb-enriched mantle or crustal source is required to explain the different REE characteristics of SNC rocks. Thus, there are indications of an old crustal rocktype on Mars, and this rock does not appear to have been sampled. This paper focuses primarily on the composition of the SNC basalts, however, and on the compositions of rocks which could be derived from SNC basaltic melt by magmatic processes. In particular, we consider the possible compositions which could be achieved through accumulation of early-formed crystals in the SNC primitive magma. Through a set of experiments we have determined (1) melt (magma) compositions which could be produced by melt evolution as crystals are removed from batches of this magma cooling at depth, and (2) which evolved (Si02enriched, MgO-depleted) rock compositions could be produced from the SNC magma, and how these compare with the Pathfinder andesite composition. Finally, we compare the SNC magma compositions to the Mars soil composition in order to determine whether any source other than SNC is required.

Modelling the petrogenesis of high Rb/Sr silicic magmas

USGS Publications Warehouse

Halliday, A.N.; Davidson, J.P.; Hildreth, W.; Holden, P.

1991-01-01

Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb Sr 100. Mass-balance modelling of source compositions, differentiation and contamination using the trace-element geochemistry of granites are therefore commonly in error because of the failure to account for evolved differentiates that may have been erupted from the system. Rhyolitic magmas with very low Sr concentrations (???1 ppm) cannot be explained by any partial melting models involving typical crustal source compositions. The only plausible mechanism for the production of such rhyolites is Rayleigh fractional crystallization involving substantial volumes of cumulates. A variety of methods for modelling the differentiation of magmas with extremely high Rb/Sr is discussed. In each case it is concluded that the bulk partition coefficients for Sr have to be large. In the simplest models, the bulk DSr of the most evolved types is modelled as > 50. Evidence from phenocryst/glass/whole-rock concentrations supports high Sr partition coefficients in feldspars from high silica rhyolites. However, the low modal abundance of plagioclase commonly observed in such rocks is difficult to reconcile with such simple fractionation models of the observed trace-element trends. In certain cases, this may be because the apparent trace-element trend defined by the suite of cognetic rhyolites is the product of different batches of magma with separate differentiation histories accumulating in the magma chamber roof zone. ?? 1991.

Stability of rift axis magma reservoirs: Spatial and temporal evolution of magma supply in the Dabbahu rift segment (Afar, Ethiopia) over the past 30 kyr

NASA Astrophysics Data System (ADS)

Medynski, S.; Pik, R.; Burnard, P.; Vye-Brown, C.; France, L.; Schimmelpfennig, I.; Whaler, K.; Johnson, N.; Benedetti, L.; Ayelew, D.; Yirgu, G.

2015-01-01

Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression (Ethiopia) using a combination of cosmogenic (36Cl and 3He) surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift (notably the 2005-2010 dyking crises) has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30 kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems. Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 km on the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent (<15 ka) flank volcanism is observed at the surface. Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is maintained by a system of separate relaying reservoirs, which could in return control the location of spreading. This long term (>105 yr) alternation between distinct crustal reservoirs located broadly at the same location relative to the segment appears to be a key feature for organizing and maintaining active spreading centres over stable soft points in the mantle.

Short-circuiting magma differentiation from basalt straight to rhyolite?

NASA Astrophysics Data System (ADS)

Ruprecht, P.; Winslow, H.

2017-12-01

Silicic magmas are the product of varying degrees of crystal fractionation and crustal assimilation/melting. Both processes lead to differentiation that is step-wise rather than continuous for example during melt separation from a crystal mush (Dufek and Bachmann, 2010). However, differentiation is rarely efficient enough to evolve directly from a basaltic to a rhyolitic magma. At Volcán Puyehue-Cordón Caulle, Chile, the magma series is dominated by crystal fractionation where mixing trends between primitive and felsic end members in the bulk rock compositions are almost absent (e.g. P, FeO, TiO2 vs. SiO2). How effective fraction is in this magmatic system is not well-known. The 2011-12 eruption at Cordón Caulle provides new constraints that rhyolitic melts may be derived directly from a basaltic mush. Minor, but ubiquitous mafic, crystal-rich enclaves co-erupted with the predominantly rhyolitic near-aphyric magma. These enclaves are among the most primitive compositions erupted at Puyehue-Cordón Caulle and geochemically resemble closely basaltic magmas that are >10 ka old (Singer et al. 2008) and that have been identified as a parental tholeiitic mantle-derived magma (Schmidt and Jagoutz, 2017) for the Southern Andean Volcanic Zone. The vesiculated nature, the presence of a microlite-rich groundmass, and a lack of a Eu anomaly in these encalves suggest that they represent recharge magma/mush rather than sub-solidus cumulates and therefore have potentially a direct petrogenetic link to the erupted rhyolites. Our results indicate that under some conditions crystal fractionation can be very effective and the presence of rhyolitic magmas does not require an extensive polybaric plumbing system. Instead, primitive mantle-derived magmas source directly evolved magmas. In the case, of the magma system beneath Puyehue-Cordón Caulle, which had three historic rhyolitic eruptions (1921-22, 1960, 2011-12) these results raise the question whether rhyolite magma extraction has been efficient for multiple eruptions? References: Dufek & Bachmann (2010) Geology 38, 687-690; Schmidt & Jagoutz (2017) G-cubed, doi: 10.1002/2016GC006699; Singer et al. (2008) GSA Bulletin 120, 599-618.

Eruption prediction aided by electronic tiltmeter data at Mount St. Helens

USGS Publications Warehouse

Dzurisin, D.; Westphal, J.A.; Johnson, Daniel J.

1983-01-01

Telemetry from electronic tiltmeters in the crater at Mount St. Helens contributed to accurate predictions of all six effusive eruptions from June 1981 to August 1982. Tilting of the crater floor began several weeks before each eruption, accelerated sharply for several days, and then abruptly changed direction a few minutes to days before extrusion began. Each episode of uplift was caused by the intrusion of magma into the lava dome from a shallow source, causing the dome to inflate and eventually rupture. Release of magma pressure and increased surface loading by magma added to the dome combined to cause subsidence just prior to extrusion.

Eruption prediction aided by electronic tiltmeter data at mount st. Helens.

PubMed

Dzurisin, D; Westphal, J A; Johnson, D J

1983-09-30

Telemetry from electronic tiltmeters in the crater at Mount St. Helens contributed to accurate predictions of all six effusive eruptions from June 1981 to August 1982. Tilting of the crater floor began several weeks before each eruption, accelerated sharply for several days, and then abruptly changed direction a few minutes to days before extrusion began. Each episode of uplift was caused by the intrusion of magma into the lava dome from a shallow source, causing the dome to inflate and eventually rupture. Release of magma pressure and increased surface loading by magma added to the dome combined to cause subsidence just prior to extrusion.

Location of Sinabung volcano magma chamber on 2013 using lavenberg-marquardt inversion scheme

NASA Astrophysics Data System (ADS)

Kumalasari, R.; Srigutomo, W.; Djamal, M.; Meilano, I.; Gunawan, H.

2018-05-01

Sinabung Volcano has been monitoring using GPS after his eruption on August 2010. We Applied Levenberg-Marquardt Inversion Scheme to GPS data on 2013 because deformation of Sinabung Volcano in this year show an inflation and deflation, first we applied Levenberg-Marquardt to velocity data on 23 January 2013 then we applied Levenberg-Marquardt Inversion Scheme to data on 31 December 2013. From our analysis we got the depth of the pressure source modeling results that indicate some possibilities that Sinabung has a deep magma chamber about 15km and also shallow magma chamber about 1km from the surface.

Magmatic vapor source for sulfur dioxide released during volcanic eruptions: Evidence from Mount Pinatubo

USGS Publications Warehouse

Wallace, P.J.; Gerlach, T.M.

1994-01-01

Sulfur dioxide (SO2) released by the explosive eruption of Mount Pinatubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO2 released was much greater than the amount dissolved in the magma before the eruption, and thus an additional source for the excess SO2 is required. Infrared spectroscopic analyses of dissolved water and carbon dioxide in glass inclusions from quartz phenocrysts demonstrate that before eruption the magma contained a separate, SO2-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO2 that is released during many volcanic eruptions.

Magma plumbing in the Grímsvötn volcanic system, Iceland: an overview

NASA Astrophysics Data System (ADS)

Thordarson, T.

2016-12-01

The basaltic Grímsvötn volcanic system (GVS) consists of Grímsvötn central volcano (GCV) and an immature fissure swarm extending 70 km to the southwest from GCV. The GCV has the highest eruption frequency of all central volcanos in Iceland, or 7 events per 100 years. In contrast, the GVS fissure swarm has only featured two events in postglacial times, the 1783-4 Laki and the prehistoric Lambavatnsgígar fissure eruptions. These two events account for 25% of the total Holocene magma output from the GVS and 80% of the output in historic time (i.e. last 1100 years). Although GVS magma plumbing has been a topic of research for four decades, its general structure, extent and geometry is still deliberated. Is mantle-derived magma delivered straight up beneath the GCV to an upper crustal magma chamber and then vertically to eruptions at the GCV and laterally to eruption on the GVS fissure swarm? Or does the system feature two levels of crustal storage, one in the upper crust beneath GCV and another at mid-crustal depth? Or is the structure of the GVS plumbing more complex? The data that we have so far and is pertinent to GVS magma plumbing is summarised below: Geophysical measurements imply that shallowest magma storage beneath GCV is at 3-4 km. The Zr and Nb concentrations in the tephra from the 1998 and 2004 GCV plus Laki eruptions show that the parent magmas for each was produced by different degrees of partial melting of a similar mantle source. It also demonstrates transport to the surface via separate pathways and that neither magma can be derived by fractional crystallization from a Laki-like magma. Detailed petrological studies on the Laki tephra and lava indicate polybaric magma evolution within the mid-crust (at 6 to 15 km depth), with further evolution at shallower depths induced either by disequilibrium crystal growth during ascent of magma from the mid-crust storage or a brief residence at 3-6 km depths. The Laki magma contains significant abundances of polymineralic glomerocrysts, signifying that erupted magma interacted with preexisting crystal mushes. These data support the notion of a crustal plumbing system with multiple storage level involving polybaric magma evolution and are inconsistent with the idea that all of the magma erupted within the GVS is delivered from a single upper crustal magma chamber beneath GCV.

Dynamic melting in plume heads: the formation of Gorgona komatiites and basalts

NASA Astrophysics Data System (ADS)

Arndt, Nicholas T.; Kerr, Andrew C.; Tarney, John

1997-01-01

The small Pacific island of Gorgona, off the coast of Colombia, is well known for its spectacular spinifex-textured komatiites. These high-Mg liquids, which have been linked to a late Cretaceous deep mantle plume, are part of a volcanic series with a wide range of trace-element compositions, from moderately enriched basalts ( La/SmN ˜ 1.5) to extremely depleted ultramafic tuffs and picrites ( La/SmN ˜ 0.2). Neither fractional crystallization, nor partial melting of a homogeneous mantle source, can account for this large variation: the source must have been chemically heterogeneous. Low 143Nd/144Nd in the more enriched basalts indicates some initial source heterogeneity but most of the variation in magma compositions is believed to result from dynamic melting during the ascent of a plume. Modelling of major- and trace-element compositions suggests that ultramafic magmas formed at ˜ 60-100 km depth, and that the melt extraction that gave rise to their depleted sources started at still greater depths. The ultra-depleted lavas represent magmas derived directly from the hottest, most depleted parts of the plume; the more abundant moderately depleted basalts are interpreted as the products of pooling of liquids from throughout the melting region.

Real-time source deformation modeling through GNSS permanent stations at Merapi volcano (Indonesia

NASA Astrophysics Data System (ADS)

Beauducel, F.; Nurnaning, A.; Iguchi, M.; Fahmi, A. A.; Nandaka, M. A.; Sumarti, S.; Subandriyo, S.; Metaxian, J. P.

2014-12-01

Mt. Merapi (Java, Indonesia) is one of the most active and dangerous volcano in the world. A first GPS repetition network was setup and periodically measured since 1993, allowing detecting a deep magma reservoir, quantifying magma flux in conduit and identifying shallow discontinuities around the former crater (Beauducel and Cornet, 1999;Beauducel et al., 2000, 2006). After the 2010 centennial eruption, when this network was almost completely destroyed, Indonesian and Japanese teams installed a new continuous GPS network for monitoring purpose (Iguchi et al., 2011), consisting of 3 stations located at the volcano flanks, plus a reference station at the Yogyakarta Observatory (BPPTKG).In the framework of DOMERAPI project (2013-2016) we have completed this network with 5 additional stations, which are located on the summit area and volcano surrounding. The new stations are 1-Hz sampling, GNSS (GPS + GLONASS) receivers, and near real-time data streaming to the Observatory. An automatic processing has been developed and included in the WEBOBS system (Beauducel et al., 2010) based on GIPSY software computing precise daily moving solutions every hour, and for different time scales (2 months, 1 and 5 years), time series and velocity vectors. A real-time source modeling estimation has also been implemented. It uses the depth-varying point source solution (Mogi, 1958; Williams and Wadge, 1998) in a systematic inverse problem model exploration that displays location, volume variation and 3-D probability map.The operational system should be able to better detect and estimate the location and volume variations of possible magma sources, and to follow magma transfer towards the surface. This should help monitoring and contribute to decision making during future unrest or eruption.

Satellite radar interferometry measures deformation at Okmok Volcano

USGS Publications Warehouse

Lu, Zhong; Mann, Dorte; Freymueller, Jeff

1998-01-01

The center of the Okmok caldera in Alaska subsided 140 cm as a result of its February– April 1997 eruption, according to satellite data from ERS-1 and ERS-2 synthetic aperture radar (SAR) interferometry. The inferred deflationary source was located 2.7 km beneath the approximate center of the caldera using a point source deflation model. Researchers believe this source is a magma chamber about 5 km from the eruptive source vent. During the 3 years before the eruption, the center of the caldera uplifted by about 23 cm, which researchers believe was a pre-emptive inflation of the magma chamber. Scientists say such measurements demonstrate that radar interferometry is a promising spaceborne technique for monitoring remote volcanoes. Frequent, routine acquisition of images with SAR interferometry could make near realtime monitoring at such volcanoes the rule, aiding in eruption forecasting.

Neural Tube Defects In Mice Exposed To Tap Water

PubMed Central

Mallela, Murali K; Werre, Stephen R; Hrubec, Terry C

2010-01-01

In May of 2006 we suddenly began to observe neural tube defects (NTDs) in embryos of untreated control mice. We hypothesized the mice were being exposed unknowingly to a teratogenic agent and investigated the cause. Our results suggested that NTDs were not resulting from bedding material, feed, strain or source of the mice. Additionally, mice were negative for routine and comprehensive screens of pathogens. To further test whether the NTDs resulted from infectious or genetic cause localized to our facility, we obtained three strains of timed pregnant mice from commercial suppliers located in 4 different states. All strains and sources of mice arrived in our laboratory with NTDs, implying that commercially available mice were possibly exposed to a teratogen prior to purchase. Our investigation eventually concluded that exposure to tap water was causing the NTDs. The incidence of NTDs was greatest in purchased mice provided tap water and lowest in purchased mice provided distilled deionized water (DDI). Providing mice DDI water for two generations (F2-DDI) eliminated the NTDs. When F2-DDI mice were provided tap water from three different urban areas prior to breeding, their offspring again developed NTDs. Increased length of exposure to tap water significantly increased the incidence of NTDs. These results indicate that a contaminant in municipal tap water is likely causing NTDs in mice. The unknown teratogen appears to have a wide geographic distribution but has not yet been identified. Water analysis is currently underway to identify candidate contaminants that might be responsible for the malformations. PMID:20549630

Observation of Isotope Ratios (δ2H, δ18O, 87Sr/86Sr) of Tap Water in Urban Environments

NASA Astrophysics Data System (ADS)

Mancuso, C. J.; Tipple, B. J.; Ehleringer, J. R.

2014-12-01

Urban environments are centers for rapidly growing populations. In order to meet the culinary water needs of these areas, municipal water departments use water from multiple locations and/or sources, often piped differentially to different locations within a municipality. This practice creates isotopically distinct locations within an urban area and therefore provides insight to urban water management practices. In our study we selected urban locations in the Salt Lake Valley, UT (SLV) and San Francisco Bay Area, CA (SFB) where we hypothesized geographically distinct water isotopic ratio differences existed. Within the SLV, municipal waters come from the same mountainous region, but are derived from different geologically distinct watersheds. In contrast, SFB waters are derived from regionally distinct water sources. We hypothesized that the isotope ratios of tap waters would differ based upon known municipal sources. To test this, tap water samples were collected throughout the urban regions in SLV and SFB and analyzed for δ2H, δ18O and 87Sr/86Sr isotope ratios. Seasonal collections were also made to assess if isotope ratios differed throughout the year. Within SLV and SFB, different regions were characterized by distinct paired δ18O and 87Sr/86Sr values. These different realms also agreed with known differences in municipal water supplies within the general geographic region. Waters from different cities within Marin County showed isotopic differences, consistent with water derived from different local reservoirs. Seasonal variation was observed in paired δ18O and 87Sr/86Sr values of tap water for some locations within SLV and SFB, indicating management decisions to shift from one water source to another depending on demand and available resources. Our study revealed that the δ18O and 87Sr/86Sr values of tap waters in an urban region can exhibit significant differences despite close spatial proximity if districts differ in their use of local versus transported waters.

Assessment of potable water quality including organic, inorganic, and trace metal concentrations.

PubMed

Nahar, Mst Shamsun; Zhang, Jing

2012-02-01

The quality of drinking water (tap, ground, and spring) in Toyama Prefecture, Japan was assessed by studying quality indicators including major ions, total carbon, and trace metal levels. The physicochemical properties of the water tested were different depending on the water source. Major ion concentrations (Ca(2+), K(+), Si(4+), Mg(2+), Na(+), SO(4)(2-), HCO(3)(-), NO(3)(-), and Cl(-)) were determined by ion chromatography, and the results were used to generate Stiff diagrams in order to visually identify different water masses. Major ion concentrations were higher in ground water than in spring and tap water. The relationship between alkaline metals (Na(+) and K(+)), alkaline-earth metals (Ca(2+) and Mg(2+)), and HCO(3)(-) showed little difference between deep and shallow ground water. Toyama ground, spring, and tap water were all the same type of water mass, called Ca-HCO(3). The calculated total dissolved solid values were below 300 mg/L for all water sources and met World Health Organization (WHO) water quality guidelines. Trace levels of As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, V, Zn, Sr, and Hg were detected in ground, spring, and tap water sources using inductively coupled plasma atomic emission spectrometry, and their levels were below WHO and Japanese water quality standard limits. Volatile organic carbon compounds were quantified by headspace gas chromatography-mass spectrometry, and the measured concentrations met WHO and Japanese water quality guidelines. Total trihalomethanes (THMs) were the major contaminant detected in all natural drinking water sources, but the concentration was highest in tap water (37.27 ± 0.05 μg/L). Notably, THMs concentrations reached up to 1.1 ± 0.05 μg/L in deep ground water. The proposed model gives an accurate description of the organic, inorganic, and trace heavy metal indicators studied here and may be used in natural clean water quality management. © Springer Science+Business Media B.V. 2011

From Source Water to Tap Water to Spa and Swimming Pool Water: Effects of Disinfectanta and Precursors and Implications for Exposure and Toxicity

EPA Science Inventory

Introduction The current study investigated the effect of different disinfection treatments on the disinfection by-products (DBPs) formed in finished drinking water vs. tap water vs. swimming pool water vs. spa waters. To this end, samples across the complete water pathway (untr...

A post-implementation evaluation of ceramic water filters distributed to tsunami-affected communities in Sri Lanka.

PubMed

Casanova, Lisa M; Walters, Adam; Naghawatte, Ajith; Sobsey, Mark D

2012-06-01

Sri Lanka was devastated by the 2004 Indian Ocean tsunami. During recovery, the Red Cross distributed approximately 12,000 free ceramic water filters. This cross-sectional study was an independent post-implementation assessment of 452 households that received filters, to determine the proportion still using filters, household characteristics associated with use, and quality of household drinking water. The proportion of continued users was high (76%). The most common household water sources were taps or shallow wells. The majority (82%) of users used filtered water for drinking only. Mean filter flow rate was 1.12 L/hr (0.80 L/hr for households with taps and 0.71 for those with wells). Water quality varied by source; households using tap water had source water of high microbial quality. Filters improved water quality, reducing Escherichia coli for households (largely well users) with high levels in their source water. Households were satisfied with filters and are potentially long-term users. To promote sustained use, recovery filter distribution efforts should try to identify households at greatest long-term risk, particularly those who have not moved to safer water sources during recovery. They should be joined with long-term commitment to building supply chains and local production capacity to ensure safe water access.

Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective

PubMed Central

Chiaradia, Massimo

2015-01-01

Arc magmas originate in subduction zones as partial melts of the mantle, induced by aqueous fluids/melts liberated by the subducted slab. Subsequently, they rise through and evolve within the overriding plate crust. Aside from broadly similar features that distinguish them from magmas of other geodynamic settings (e.g., mid-ocean ridges, intraplate), arc magmas display variably high Sr/Y values. Elucidating the debated origin of high Sr/Y signatures in arc magmas, whether due to mantle-source, slab melting or intracrustal processes, is instrumental for models of crustal growth and ore genesis. Here, using a statistical treatment of >23000 whole rock geochemical data, I show that average Sr/Y values and degree of maturation (MgO depletion at peak Sr/Y values) of 19 out of 22 Pliocene-Quaternary arcs correlate positively with arc thickness. This suggests that crustal thickness exerts a first order control on the Sr/Y variability of arc magmas through the stabilization or destabilization of mineral phases that fractionate Sr (plagioclase) and Y (amphibole ± garnet). In fact, the stability of these mineral phases is function of the pressure at which magma evolves, which depends on crustal thickness. The data presented show also that high Sr/Y Pliocene-Quaternary intermediate-felsic arc rocks have a distinct origin from their Archean counterparts. PMID:25631193

Major and trace element, and Sr isotope compositions of clinopyroxene phenocrysts in mafic dykes on Jiaodong Peninsula, southeastern North China Craton: Insights into magma mixing and source metasomatism

NASA Astrophysics Data System (ADS)

Liang, Yayun; Deng, Jun; Liu, Xuefei; Wang, Qingfei; Qin, Cheng; Li, Yan; Yang, Yi; Zhou, Mian; Jiang, Jieyan

2018-03-01

Early Cretaceous mafic dyke swarms are widely developed on Jiaodong Peninsula in the southeastern part of the North China Craton (NCC), but their petrogenesis remains enigmatic. We have examined the in-situ major element, trace element and Sr isotope compositions of the clinopyroxene phenocrysts in these dykes in order to evaluate the extent of magma mixing and source metasomatism. Depending on the type of mineral zoning, the clinopyroxene phenocrysts in our samples can be classified into two groups: Group I (reverse zoning) and Group II (no zoning). Based on core compositions, the Group I phenocrysts with obvious reverse zoning can be divided into two subgroups: Groups IA and IB. The cores of Group IA clinopyroxenes have low values of Mg#, low Al2O3 contents, high Na2O contents, and high 87Sr/86Sr ratios, and they were probably derived from newly accreted lower crust that formed through the underplating of basaltic magma. In contrast, the cores of Group IB clinopyroxenes have lower Mg# values and lower contents of Al2O3, ΣREE (total rare earth elements), and incompatible elements, but they have similar 87Sr/86Sr ratios; these cores crystallised from crust-derived andesitic-dacitic magma. Group IA and IB clinopyroxene phenocryst rims (Group I rims) all have similar compositions with higher values of Mg# and higher Al2O3, Cr and Ni contents than the cores. The rims have high 87Sr/86Sr ratios, are enriched in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and are depleted in HFSEs (high field strength elements); these characteristics indicate that all the high-Mg rims were derived from a similar magma, possibly a relatively primitive magma derived from lithospheric mantle. We suggest, therefore, that the reversely-zoned clinopyroxene phenocrysts (Group I) in the Jiaodong mafic dykes provide evidence of magma mixing between a magma derived from lithospheric mantle and crust-derived andesitic-dacitic melt alongside with the newly accreted lower crust. The Group II clinopyroxene phenocrysts, which lack zoning, display major and trace element compositions and 87Sr/86Sr ratios that are similar to those of the Group I rims, which indicates that all the high-Mg clinopyroxenes were derived from a common source in the lithospheric mantle. These high-Mg clinopyroxenes exhibit high 87Sr/86Sr ratios, high Sr contents and remarkable depletions in HFSEs, reflecting metasomatism of the mantle source by aqueous fluids derived by dehydration of the subducting slab and its marine sediments. The metasomatism of the source reveals that the lithospheric mantle beneath Jiaodong Peninsula was metasomatised by fluids from the subducting Paleo-Pacific slab. Progressive thinning of the lithosphere mantle under the NCC was induced by continuous thermo-mechanical erosion, promoting the partial melting of lithospheric mantle and generating the mafic dykes at Jiaodong. Table A2 Analytical results for the trace element standards used during LA-ICP-MS analyses of clinopyroxene phenocrysts. Table A3 Analytical results for the Sr isotope standards used during MC-ICP-MS analyses of clinopyroxene phenocrysts. Table A4 Major element contents (wt%) of clinopyroxene phenocrysts from the mafic dykes on Jiaodong Peninsula. Table A5 Representative Sr isotopic compositions of clinopyroxene phenocrysts from the mafic dykes on Jiaodong Peninsula. Table A6 Geochemistry of the mafic dykes on Jiaodong Peninsula. Table A7 Partition coefficients (KD) and end-member components used for REE modeling.

New Insights Into the Genesis and Compositional Evolution of I-type Granitic magmas in the Lachlan Fold Belt (SE Australia) by in situ Hf Isotopic Analysis of Zircon

NASA Astrophysics Data System (ADS)

Kemp, T. I.; Hawkesworth, C. J.; Hergt, J. M.; Woodhead, J.

2004-05-01

Isotope studies have proved of enormous benefit in fingerprinting the source rocks of silicic magmas and tracing open system petrogenetic processes, such as crustal assimilation or magma mixing. Quantification of these processes, especially the role of mantle-derived magmas, is essential to formulating realistic models for the thermal regime and compositional evolution of the continental crust. However, this remains problematic, since whole-rock isotopic data registers the final state of the magmatic system but gives no information on the pathways by which this state was attained. For example, the eNd - initial 87Sr/86Sr isotopic array defined by the classic I- and S-type granites of the Lachlan Fold Belt has been variously interpreted to reflect (1) mixing between two end-member magmas, one depleted mantle-like, the other evolved and continental crust-like, (2) mixing between a juvenile magma and a magma sourced from mafic lower crust, accompanied by sediment assimilation, (3) derivation of the granites from mixed source rocks and (4) derivation from a sequence of protoliths of various ages and sedimentary maturity. The implications of these possibilities for crustal architecture, and whether granitic magmatism was associated with the recycling or growth of new continental crust are drastically different. One way to now resolve such ambiguities is by unravelling the isotopic information encoded in the fine-scale growth zoning of minerals such as zircon, which potentially tracks the processes operative during crystallisation. To this end we report the first laser-ablation ICP-MS study into the Hf isotope stratigraphy of zircons hosted by LFB I-type granites and their mafic enclaves. This is integrated with a prior U-Pb isotope study and trace element concentrations measured on the same zircons. Two suites were investigated, the Cobargo and Why Worry Suites of the Bega Batholith. Although the bulk rock isotopic variation within these suites is restricted, this study reveals remarkable fluctuations in Hf isotopic ratios recorded within and between melt-precipitated zircons of granitic and enclave samples. This can only be reconciled by open-system behaviour, though contrasting patterns of Hf isotope variation within zoned zircons demonstrate that this differed significantly between the two suites. The Cobargo Suite was generated by mixing between two contrasting magmas, followed by crustal assimilation. Zircons from the Why Worry Suite have more evolved Hf isotope ratios, consistent with recycling of older crust during granitic generation, though increase in eHf towards zircon rims manifests interaction with primitive magmas. Globules of these are represented by mafic enclaves, the mantle heritage of which is preserved by high eHf values of zircon cores, even though whole-rock isotope contrasts with the host have been erased by equilibration. Analysis of inherited zircons contained by the Why Worry Suite establishes that the 450-600 Ma age population have evolved eHf values, and thus meta-igneous rocks of this age are appropriate protoliths for these granites. The primitive eHf values of the Cobargo Suite preclude derivation from similar sources, instead suggesting formation from mantle-derived materials. Incorporating the existing geochemical and isotope datasets, the Hf-in-zircon data will be coupled with recent thermal simulations to erect a general model for granite formation and the evolution of the continental crust during Lachlan orogenesis.

Contemporaneous eruption of calc-alkaline and alkaline lavas in a continental arc (Eastern Mexican Volcanic Belt): chemically heterogeneous but isotopically homogeneous source

NASA Astrophysics Data System (ADS)

Carrasco-Núñez, Gerardo; Righter, Kevin; Chesley, John; Siebert, Lee; Aranda-Gómez, José Jorge

2005-11-01

Nearly contemporaneous eruption of alkaline and calc-alkaline lavas occurred about 900 years BP from El Volcancillo paired vent, located behind the volcanic front in the Mexican Volcanic Belt (MVB). Emission of hawaiite (Toxtlacuaya) was immediately followed by calc-alkaline basalt (Río Naolinco). Hawaiites contain olivine microphenocrysts (Fo67-72), plagioclase (An56-60) phenocrysts, have 4-5 wt% MgO and 49.6-50.9 wt% SiO2. In contrast, calc-alkaline lavas contain plagioclase (An64-72) and olivine phenocrysts (Fo81-84) with spinel inclusions, and have 8-9 wt% MgO and 48.4-49.4 wt% SiO2. The most primitive lavas in the region (Río Naolinco and Cerro Colorado) are not as primitive as parental melts in other arcs, and could represent either (a) variable degrees of melting of a subduction modified, garnet-bearing depleted mantle source, followed by AFC process, or (b) melting of two distinct mantle sources followed by AFC processes. These two hypotheses are evaluated using REE, HFSE, and Sr, Os and Pb isotopic data. The Toxtlacuaya flow and the Y & I lavas can be generated by combined fractional crystallization and assimilation of gabbroic granulite, starting with a parental liquid similar to the Cerro Colorado basalt. Although calc-alkaline and alkaline magmas commonly occur together in other areas of the MVB, evidence for subduction component in El Volcancillo magmas is minimal and limited to <1%, which is a unique feature in this region further from the trench. El Volcancillo lavas were produced from two different magma batches: we surmise that the injection of calc-alkaline magma into an alkaline magma chamber triggered the eruption of hawaiites. Our results suggest that the subalkaline and hawaiitic lavas were formed by different degrees of partial melting of a similar, largely depleted mantle source, followed by later AFC processes. This model is unusual for arcs, where such diversity is usually explained by melting of heterogeneous (enriched and depleted) and subduction-modified mantle.

Compositional variation through time and space in Quaternary magmas of the Chyulu Hills Volcanic Province, Kenya

NASA Astrophysics Data System (ADS)

Widom, E.; Kuentz, D. C.

2017-12-01

The Chyulu Hills Volcanic Province, located in southern Kenya >100 km east of the Kenya Rift Valley, has produced mafic, monogenetic eruptions throughout the Quaternary. The volcanic field is considered to be an off-rift manifestation of the East African Rift System, and is known for the significant compositional variability of its eruptive products, which range from nephelinites to basanites, alkali basalts, hawaiites, and orthopyroxene-normative subalkaline basalts [1]. Notably, erupted compositions vary systematically in time and space: Pleistocene volcanism, occurring in the northern Chyulu Hills, was characterized by highly silica-undersaturated magmas, whereas Holocene volcanism, restricted to the southern Chyulu Hills, is less silica-understaturated, consistent with a progressive decrease in depth and increase in degree of melting with time, from north to south [1]. Pronounced negative K anomalies, and enriched trace element and Sr-Nd-Pb isotope signatures have been attributed to a metasomatized, amphibole-bearing, sub-continental lithospheric mantle (SCLM) source [2]. Seismic evidence for a partially molten zone in the SCLM beneath this region [3] may be consistent with such an interpretation. We have analyzed Chyulu Hills samples for Os, Hf and high precision Pb isotopes to further evaluate the magma sources and petrogenetic processes leading to systematic compositional variation in time and space. Sr-Nd-Pb-Hf isotope systematics and strong negative correlations of 206Pb/204Pb and highly incompatible trace element ratios with SiO2 are consistent with the progression from a deeper, HIMU-type source to a shallower, EM-type source. Os isotope systematics, however, suggest a more complex relationship; although all samples are more radiogenic than primitive mantle, the least radiogenic values (similar to primitive OIB) are found in magmas with intermediate SiO2, and those with lower or higher SiO2 are more radiogenic. This may be explained by interaction between mantle plume-derived magmas and heterogeneous metasomatized SCLM, consistent with the radiogenic Os isotope compositions found in some highly metasomatized mantle xenoliths associated with the Tanzanian craton [4]. [1] Spath et al., 2000; [2] Spath et al., 2001; [3] Ritter & Kasper, 1997; [4] Nelson et al., 2012.

Petrogenesis of Cretaceous volcanic-intrusive complex from the giant Yanbei tin deposit, South China: Implication for multiple magma sources, tin mineralization, and geodynamic setting

NASA Astrophysics Data System (ADS)

Li, Qian; Zhao, Kui-Dong; Lai, Pan-Chen; Jiang, Shao-Yong; Chen, Wei

2018-01-01

The giant Yanbei tin ore deposit is the largest porphyry-type tin deposit in South China. The orebodies are hosted by the granite porphyry in the central part of the Yanbei volcanic basin in southern Jiangxi Province. The Yanbei volcanic-intrusive complex mainly consists of dacitic-rhyolitic volcanic rocks, granite, granite porphyry and diabase dikes. In previous papers, the granite porphyry was considered as subvolcanic rocks, which came from the same single magma chamber with the volcanic rocks. In this study, zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemical and Sr-Nd isotopic compositions of different magmatic units in the Yanbei complex are reported. Geochronologic results show that various magmatic units have different formation ages. The dacite yielded a zircon U-Pb age of 143 ± 1 Ma, and the granite porphyry has the emplacement age of 138 ± 1 Ma. Diabase dikes which represented the final stage of magmatism, yielded a zircon U-Pb age of 128 ± 1 Ma. Distinctive whole rock Sr-Nd and zircon Hf isotopic compositions suggest that these magmatic units were derived from different magma sources. The volcanic rocks were mainly derived from the partial melting of Paleoproterozoic metasedimentary rocks without additions of mantle-derived magma. The granite porphyry has an A-type geochemical affinity, and was derived from remelting of Paleo-Mesoproterozoic crustal source with involvement of a subordinate mantle-derived magma. The granite porphyry is also a typical stanniferous granite with high F (4070-6090 ppm) and Sn (7-39 ppm) contents. It underwent strongly crystal fractionation of plagioclase, K-feldspar, and accessory minerals (like apatite, Fe-Ti oxides), which may contribute to the tin mineralization. The diabase was derived by partial melting of enriched lithospheric mantle which had been metasomatised by slab-derived fluids. The change of magmatic sources reflected an increasing extensional tectonic environment, perhaps induced by slab rollback of subducted paleo-Pacific plate.

Bubble accumulation and its role in the evolution of magma reservoirs in the upper crust.

PubMed

Parmigiani, A; Faroughi, S; Huber, C; Bachmann, O; Su, Y

2016-04-28

Volcanic eruptions transfer huge amounts of gas to the atmosphere. In particular, the sulfur released during large silicic explosive eruptions can induce global cooling. A fundamental goal in volcanology, therefore, is to assess the potential for eruption of the large volumes of crystal-poor, silicic magma that are stored at shallow depths in the crust, and to obtain theoretical bounds for the amount of volatiles that can be released during these eruptions. It is puzzling that highly evolved, crystal-poor silicic magmas are more likely to generate volcanic rocks than plutonic rocks. This observation suggests that such magmas are more prone to erupting than are their crystal-rich counterparts. Moreover, well studied examples of largely crystal-poor eruptions (for example, Katmai, Taupo and Minoan) often exhibit a release of sulfur that is 10 to 20 times higher than the amount of sulfur estimated to be stored in the melt. Here we argue that these two observations rest on how the magmatic volatile phase (MVP) behaves as it rises buoyantly in zoned magma reservoirs. By investigating the fluid dynamics that controls the transport of the MVP in crystal-rich and crystal-poor magmas, we show how the interplay between capillary stresses and the viscosity contrast between the MVP and the host melt results in a counterintuitive dynamics, whereby the MVP tends to migrate efficiently in crystal-rich parts of a magma reservoir and accumulate in crystal-poor regions. The accumulation of low-density bubbles of MVP in crystal-poor magmas has implications for the eruptive potential of such magmas, and is the likely source of the excess sulfur released during explosive eruptions.

Deposits, petrology and mechanism of the 2010-2013 eruption of Kizimen volcano in Kamchatka, Russia

NASA Astrophysics Data System (ADS)

Auer, A.; Belousov, A.; Belousova, M.

2018-04-01

Kizimen volcano in Kamchatka is well known as a source of highly heterogeneous poorly mingled magmas ranging from dacites to basaltic andesites. In 2010-2013, the volcano produced its first historical magmatic eruption with the deposition of 0.27 km3 of block and ash pyroclastic flows accompanied by slow extrusion of a 200-m-thick, highly viscous (1010-1011 Pa s) block lava flow with a volume of 0.3 km3. The total volume of erupted magma comprised approximately 0.4 km3 DRE. We provide description of the eruption chronology, as well as the lithology and petrology of eruptive products. The erupted material is represented by banded dacite and high-silica andesite. The dacitic magma was formed during a long dormancy after the previous magmatic eruption several hundred years ago with mineral compositions indicating average pre-eruptive temperatures of 810 °C, fO2 of 0.9-1.6 log units above the nickel-nickel oxide (NNO) buffer and shallow crustal storage conditions at 123 MPa. The silica-rich andesite represents a hybrid magma, which shows signs of recent thermal and compositional disequilibrium. We suggest that the hybrid magma started to form in 1963 when a swarm of deep earthquakes indicated an input of mafic magma from depth into the 6-11-km-deep silicic magma chamber. It took the following 46 years until the magma filling the chamber reached an eruptible state. Poor mingling of the two melts is attributed to its unusually high viscosity that could be associated with the pre-eruptive long-term leakage of volatiles from the chamber through a regional tectonic fault. Our investigations have shown that shallow magma chambers of dormant volcanoes demonstrating strong persistent fumarolic activity can contain highly viscous, degassed magma of evolved composition. Reactivation of such magma chambers by injection of basic magma takes a long time (several decades). Thus, eruption forecasts at such volcanoes should include a possibility of long time lag between a swarm of deep earthquakes (indicating the recharge of basic magma from depth) and the following swarm of shallow earthquakes (indicating final ascent of the hybrid magma towards the surface). Due to the high viscosity of the magma, the shallow swarm can last for more than a year. The forthcoming eruption can be of moderate to low explosivity and include extrusion of viscous lava flows and domes composed of poorly mingled magmas of contrasting compositions.

[Investigation on contamination of Giardia and Cryptosporidium in drinking water in Jiangsu Province].

PubMed

Bi-Xian, N I; Ming-Xue, S; Xiang-Zhen, X U; Xiao-Ting, W; Yang, D; Xiao-Lin, J

2017-05-17

Objective To know the contamination status of Giardia lamblia and Cryptosporidium in drinking water of Jiangsu Province, so as to provide the evidence for producing hygiene and safety drinking water. Methods A total of 28 water plants of 13 cities in Jiangsu Province were selected, and the source water (10 L), chlorinated water (100 L) and tap water (100 L) were collected separately in each site. The water samples were then treated by filtration, washing, centrifuging concentration, immune magnetic separation, and immunofluorescent assay, to detect the numbers of Giardia cysts and Cryptosporidium oocysts. Results Totally 84 samples from 13 cities were collected, including 28 source water, 28 chlorinated water and 28 tap water samples. Among the chlorinated water and tap water samples, no Giardia cysts and Cryptosporidium oocysts were found. However, Giardia cysts were detected in 3 (10.71%, 3/28) source water samples (Yancheng, Lianyungang, Changzhou cities), with the density of 1 cyst/10 L of all. Cryptosporidium oocysts were also detected in 3 (10.71%, 3/28) source water samples (Nanjing, Zhenjiang, Yangzhou cities), with the density of 1 oocyst/10 L of all. Conclusions The source water in partial areas of Jiangsu Province has been contaminated by Giardia and Cryptosporidium . To ensure the safety of drinking, the regulation of source water and surveillance of drinking water should be strengthened.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 2: Predicted emplacement processes and observations)

NASA Astrophysics Data System (ADS)

Head, James W.; Wilson, Lionel

2017-02-01

We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike intrusions, and effusive and explosive eruptions. We make predictions about the intrusion and eruption processes and compare these with the range of observed styles of mare volcanism, and related features and deposits. Density contrasts between the bulk mantle and regions with a greater abundance of heat sources will cause larger heated regions to rise as buoyant melt-rich diapirs that generate partial melts that can undergo collection into magma source regions; diapirs rise to the base of the anorthositic crustal density trap (when the crust is thicker than the elastic lithosphere) or, later in history, to the base of the lithospheric rheological trap (when the thickening lithosphere exceeds the thickness of the crust). Residual diapiric buoyancy, and continued production and arrival of diapiric material, enhances melt volume and overpressurizes the source regions, producing sufficient stress to cause brittle deformation of the elastic part of the overlying lithosphere; a magma-filled crack initiates and propagates toward the surface as a convex upward, blade-shaped dike. The volume of magma released in a single event is likely to lie in the range 102 km3 to 103 km3, corresponding to dikes with widths of 40-100 m and both vertical and horizontal extents of 60-100 km, favoring eruption on the lunar nearside. Shallower magma sources produce dikes that are continuous from the source region to the surface, but deeper sources will propagate dikes that detach from the source region and ascend as discrete penny-shaped structures. As the Moon cools with time, the lithosphere thickens, source regions become less abundant, and rheological traps become increasingly deep; the state of stress in the lithosphere becomes increasingly contractional, inhibiting dike emplacement and surface eruptions. In contrast to small dike volumes and low propagation velocities in terrestrial environments, lunar dike propagation velocities are typically sufficiently high that shallow sill formation is not favored; local low-density breccia zones beneath impact crater floors, however, may cause lateral magma migration to form laccoliths (e.g., Vitello Crater) and sills (e.g., Humboldt Crater) in floor-fractured craters. Dikes emplaced into the shallow crust may stall and produce crater chains due to active and passive gas venting (e.g., Mendeleev Crater Chain) or, if sufficiently shallow, may create a near-surface stress field that forms linear and arcuate graben, often with pyroclastic and small-scale effusive eruptions (e.g., Rima Parry V). Effusive eruptions are modulated by effusion rates, eruption durations, cooling and supply limitations to flow length, and pre-existing topography. Relatively low effusion rate, cooling-limited flows lead to small shield volcanoes (e.g., Tobias Mayer, Milicius); higher effusion rate, cooling-limited flows lead to compound flow fields (e.g., most mare basins) and even higher effusion rate, long-duration flows lead to thermal erosion of the vent, effusion rate enhancement, and thermal erosion of the substrate to produce sinuous rilles (e.g., Rimae Prinz). Extremely high effusion rate flows on slopes lead to volume-limited flow with lengths of many hundreds of kilometers (e.g., the young Imbrium basin flows). Explosive, pyroclastic eruptions are common on the Moon. The low pressure environment in propagating dike crack-tips can cause gas formation at great depths and throughout dike ascent; at shallow crustal depths both the smelting reaction and the recently documented abundant magmatic volatiles in mare basalt magmas contribute to significant shallow degassing and pyroclastic activity associated with the dike as it erupts at the surface. Dikes penetrating to the surface produce a wide range of explosive eruption types whose manifestations are modulated by lunar environmental conditions: (1) terrestrial strombolian-style eruptions map to cinder/spatter cone-like constructs (e.g., Isis and Osiris); (2) Hawaiian-style eruptions map to broad flat pyroclastic blankets (e.g., Taurus-Littrow Apollo 17 dark mantle deposits); (3) gas-rich ultraplinian-like venting can cause Moon-wide dispersal of gas and foam droplets (e.g., many isolated glass beads in lunar soils); (4) vulcanian-like eruptions caused by solidification of magma in the dike tip, buildup of gas pressure and explosive disruption, can form dark-halo craters with mixed country rock (e.g., Alphonsus Crater floor); (5) ionian-like eruptions can be caused by artificial gas buildup in wide dikes, energetic explosive eruption and formation of a dark pyroclastic ring (e.g., Orientale dark ring); (6) multiple eruptions from many gas-rich fissures can form regional dark mantle deposits (e.g., Rima Bode, Sinus Aestuum); and (7) long duration, relatively high effusion rate eruptions accompanied by continuing pyroclastic activity cause a central thermally eroded lava pond and channel, a broader pyroclastic 'spatter' edifice, an even broader pyroclastic glass deposit and, if the eruption lasts sufficiently long, an associated inner thermally eroded vent and sinuous rille channel (e.g., Cobra Head and Aristarchus Plateau dark mantle). The asymmetric nearside-farside distribution of mare basalt deposits is most plausibly explained by crustal thickness differences; intrusion is favored on the thicker farside crust and extrusion is favored on the thinner nearside crust. Second-order effects include regional and global thermal structure (areal variations in lithospheric thickness as a function of time) and broad geochemical anomalies (the Procellarum-KREEP Terrain). Differences in mare basalt titanium content as a function of space and time are testimony to a laterally and vertically heterogeneous mantle source region. The rapidly decreasing integrated flux of mare basalts is a result of the thermal evolution of the Moon; continued cooling decreased diapiric rise and mantle melting, thickened the lithosphere, and caused the global state of stress to be increasingly contractional, all factors progressively inhibiting the generation, ascent and eruption of basaltic magma. Late-stage volcanic eruptions are typically widely separated in time and characterized by high-volume, high-effusion rate eruptions producing extensive volume-limited flows, a predictable characteristic of deep source regions below a thick lithosphere late in lunar history. This improved paradigm for the generation, ascent, intrusion and eruption of basaltic magma provides the basis for the broader interpretation of the lunar volcanic record in terms of variations in eruption conditions in space and time, and their relation to mantle heterogeneity and a more detailed understanding of lunar thermal evolution.

Pigeonholing pyroclasts: Insights from the 19 March 2008 explosive eruption of Kīlauea volcano

USGS Publications Warehouse

Houghton, Bruce F.; Swanson, D.A.; Carey, R.J.; Rausch, J.; Sutton, A.J.

2011-01-01

We think, conventionally, of volcanic explosive eruptions as being triggered in one of two ways: by release and expansion of volatiles dissolved in the ejected magma (magmatic explosions) or by transfer of heat from magma into an external source of water (phreatic or phreatomagmatic explosions). We document here an event where neither magma nor an external water source was involved in explosive activity at K??lauea. Instead, the eruption was powered by the expansion of decoupled magmatic volatiles released from deeper magma, which was not ejected by the eruption, and the trigger was a collapse of near-surface wall rocks that then momentarily blocked that volatile flux. Mapping of the advected fall deposit a day after this eruption has highlighted the difficulty of constraining deposit edges from unobserved or prehistoric eruptions of all magnitudes. Our results suggest that the dispersal area of advected fall deposits could be miscalculated by up to 30% of the total, raising issues for accurate hazard zoning and assessment. Eruptions of this type challenge existing classification schemes for pyroclastic deposits and explosive eruptions and, in the past, have probably been interpreted as phreatic explosions, where the eruptive mechanism has been assumed to involve flashing of groundwater to steam. ?? 2011 Geological Society of America.

Tap water isotope ratios reflect urban water system structure and dynamics across a semiarid metropolitan area

NASA Astrophysics Data System (ADS)

Jameel, Yusuf; Brewer, Simon; Good, Stephen P.; Tipple, Brett J.; Ehleringer, James R.; Bowen, Gabriel J.

2016-08-01

Water extraction for anthropogenic use has become a major flux in the hydrological cycle. With increasing demand for water and challenges supplying it in the face of climate change, there is a pressing need to better understand connections between human populations, climate, water extraction, water use, and its impacts. To understand these connections, we collected and analyzed stable isotopic ratios of more than 800 urban tap water samples in a series of semiannual water surveys (spring and fall, 2013-2015) across the Salt Lake Valley (SLV) of northern Utah. Consistent with previous work, we found that mean tap water had a lower 2H and 18O concentration than local precipitation, highlighting the importance of nearby montane winter precipitation as source water for the region. However, we observed strong and structured spatiotemporal variation in tap water isotopic compositions across the region which we attribute to complex distribution systems, varying water management practices and multiple sources used across the valley. Water from different sources was not used uniformly throughout the area and we identified significant correlation between water source and demographic parameters including population and income. Isotopic mass balance indicated significant interannual and intra-annual variability in water losses within the distribution network due to evaporation from surface water resources supplying the SLV. Our results demonstrate the effectiveness of isotopes as an indicator of water management strategies and climate impacts within regional urban water systems, with potential utility for monitoring, regulation, forensic, and a range of water resource research.

Inflation-predictable behavior and co-eruption deformation at Axial Seamount.

PubMed

Nooner, Scott L; Chadwick, William W

2016-12-16

Deformation of the ground surface at active volcanoes provides information about magma movements at depth. Improved seafloor deformation measurements between 2011 and 2015 documented a fourfold increase in magma supply and confirmed that Axial Seamount's eruptive behavior is inflation-predictable, probably triggered by a critical level of magmatic pressure. A 2015 eruption was successfully forecast on the basis of this deformation pattern and marked the first time that deflation and tilt were captured in real time by a new seafloor cabled observatory, revealing the timing, location, and volume of eruption-related magma movements. Improved modeling of the deformation suggests a steeply dipping prolate-spheroid pressure source beneath the eastern caldera that is consistent with the location of the zone of highest melt within the subcaldera magma reservoir determined from multichannel seismic results. Copyright © 2016, American Association for the Advancement of Science.

Petrogenesis of the Elephant Moraine A79001 meteorite Multiple magma pulses on the shergottite parent body

NASA Technical Reports Server (NTRS)

Mcsween, H. Y., Jr.; Jarosewich, E.

1983-01-01

The EETA 79001 achondrite consists of two distinct igneous lithologies joined along a planar, non-brecciated contact. Both are basaltic rocks composed primarily of pigeonite, augite, and maskelynite, but one contains zoned megacrysts of olivine, orthopyroxene, and chromite that represent disaggregated xenoliths of harzburzite. Both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small, shallow chamber. Many similarities between the two virtually synchronous magmas suggest that they are related. Possible mechanisms to explain their differences involve varying degrees of assimilation, fractionation from similar parental magmas, or partial melting of a similar source peridotite; of these, assimilation of the observed megacryst assemblage seems most plausible. However, some isotopic contamination may be required in any of these petrogenetic models. The meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body.

Devonian magmatism in the Timan Range, Arctic Russia - subduction, post-orogenic extension, or rifting?

NASA Astrophysics Data System (ADS)

Pease, V.; Scarrow, J. H.; Silva, I. G. Nobre; Cambeses, A.

2016-11-01

Devonian mafic magmatism of the northern East European Craton (EEC) has been variously linked to Uralian subduction, post-orogenic extension associated with Caledonian collision, and rifting. New elemental and isotopic analyses of Devonian basalts from the Timan Range and Kanin Peninsula, Russia, in the northern EEC constrain magma genesis, mantle source(s) and the tectonic process(es) associated with this Devonian volcanism to a rift-related context. Two compositional groups of low-K2O tholeiitic basalts are recognized. On the basis of Th concentrations, LREE concentrations, and (LREE/HREE)N, the data suggest two distinct magma batches. Incompatible trace elements ratios (e.g., Th/Yb, Nb/Th, Nb/La) together with Nd and Pb isotopes indicate involvement of an NMORB to EMORB 'transitional' mantle component mixed with variable amounts of a continental component. The magmas were derived from a source that developed high (U,Th)/Pb, U/Th and Sm/Nd over time. The geochemistry of Timan-Kanin basalts supports the hypothesis that the genesis of Devonian basaltic magmatism in the region resulted from local melting of transitional mantle and lower crust during rifting of a mainly non-volcanic continental rifted margin.

The influence of a subduction component on magmatism in the Okinawa Trough: Evidence from thorium and related trace element ratios

NASA Astrophysics Data System (ADS)

Guo, Kun; Zeng, Zhi-Gang; Chen, Shuai; Zhang, Yu-Xiang; Qi, Hai-Yan; Ma, Yao

2017-09-01

The Okinawa Trough (OT) is a back-arc, initial continental marginal sea basin located behind the Ryukyu Arc-Trench System. Formation and evolution of the OT have been intimately related to subduction of the Philippine Sea Plate (PSP) since the late Miocene; thus, the magma source of the trough has been affected by subduction components, as in the case of other active back-arc basins, including the Lau Basin (LB) and Mariana Trough (MT). We review all the available geochemical data relating to basaltic lavas from the OT and the middle Ryukyu Arc (RA) in this paper in order to determine the influence of the subduction components on the formation of arc and back-arc magmas within this subduction system. The results of this study reveal that the abundances of Th in OT basalts (OTBs) are higher than that in LB (LBBs) and MT basalts (MTBs) due to the mixing of subducted sediments and EMI-like enriched materials. The geochemical characteristics of Th and other trace element ratios indicate that the OTB originated from a more enriched mantle source (compared to N-mid-ocean ridge basalt, N-MORB) and was augmented by subducted sediments. Data show that the magma sources of the south OT (SOT) and middle Ryukyu Arc (MRA) basalts were principally influenced by subducted aqueous fluids and bulk sediments, which were potentially added into magma sources by accretion and underplating. At the same time, the magma sources of the middle OT (MOT) and Kobi-syo and Sekibi-Syo (KBS+SBS) basalts were impacted by subducted aqueous fluids from both altered oceanic crust (AOC) and sediment. The variable geochemical characteristics of these basalts are due to different Wadati-Benioff depths and tectonic environments of formation, while the addition of subducted bulk sediment to SOT and MRA basalts may be due to accretion and underplating, and subsequent to form mélange formation, which would occur partial melting after aqueous fluids are added. The addition of AOC and sediment aqueous fluid to MOT and KBS+SBS basalts is therefore the result of cold subducted slab dehydration combined with a rapid subduction rate (82 mm/a), leading to the migration of fluids into the mantle wedge. The presence of these attributes is likely because the OT was a back-arc, initial continental marginal sea basin.

Getting granite dikes out of the source region

NASA Technical Reports Server (NTRS)

Rubin, Allan M.

1995-01-01

Whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow. Various formulations are developed for a viscous fluid at temperature T(sub m) intruding a growing crack in an elastic solid. The initial solid temperature equals T(sub m) at the source and decreases linearly with distance from the source. If T(sub m) is the unique freezing temperature of the fluid, dike growth is initially self-similar and an essentially exact solution is obtained; if T(sub m) is above the solidus temperature, the solution is approximate but is designed to overestimate the distance the dike may propagate. The ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness. Perhaps more intuitively, one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus, necessary for dikes to propagate far into subsolidus rock. It is concluded that for reasonable material properties and source conditions, most basalt dikes will have little difficulty leaving the source region, but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus. While these results can explain why granitic dikes are common near granitic plutons but rare elsewhere, the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes. Nonetheless, these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies.

Two magma bodies beneath the summit of Kīlauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

NASA Astrophysics Data System (ADS)

Pietruszka, Aaron J.; Heaton, Daniel E.; Marske, Jared P.; Garcia, Michael O.

2015-03-01

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas-from 1959 to the active Halema'uma'u lava lake-to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir ∼2-4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body <2 km below the eastern rim of Halema'uma'u pit crater. Residence time modeling suggests that the total volume of magma within Kīlauea's summit reservoir during the late 20th century (1959-1982) was exceedingly small (∼0.1-0.5 km3). Voluminous Kīlauea eruptions, such as the ongoing, 32-yr old Pu'u 'Ō'ō rift eruption (>4 km3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969-1974 Mauna Ulu, 1983-present Pu'u 'Ō'ō and 2008-present Halema'uma'u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

Origin of hybrid ferrolatite lavas from Magic Reservoir eruptive center, Snake River Plain, Idaho

NASA Astrophysics Data System (ADS)

Honjo, Norio; Leeman, William P.

1987-06-01

The mineralogy and geochemical characteristics of intermediate composition ferrolatites and related lavas from the Magic Reservoir eruptive center (central Snake River Plain) have been investigated to evaluate the origin and petrologic significance of these hybrid lavas. The ferrolatites are chemically uniform, but contain a disequilibrium phenocryst/xenocryst assemblage derived in part from mixed rhyolitic and basaltic magmas that are closely represented by extrusive units in the area. The hybrid lavas also contain xenoliths of Archean granulites and have high 87Sr/ 86Sr and low 143Nd/144Nd ratios, all of which suggest significant magma-crust interaction. Quantitative models including magma mixing, minor crystal fractionation, and crustal contamination very closely reproduce the observed compositions of these ferrolatites; closed system fractionation and (or) simple bulk contamination models are not as successful and can be ruled out. It appears that preexisting mafic and silicic magmas from distinct sources (e.g., mantle and crust) encounter one another in crustal-level magma chambers under conditions where intimate mixing may occur despite wide differences in the physical properties of these liquids.

Thermally-assisted Magma Emplacement Explains Restless Calderas

NASA Astrophysics Data System (ADS)

Amoruso, A.; Crescentini, L.; D'Antonio, M.; Acocella, V.

2017-12-01

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei, Italy, which is the best-known, yet most dangerous calderas, lying to the west of Naples and restless since the 1950s at least.Our elaboration of the geodetic data indicates that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust.Our thermal models show that the repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth 3 ka before the last eruption and, in turn, contributed to maintain the thermal anomaly itself. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks.Available information at other calderas highlights similarities to Campi Flegrei, in the pattern and cause of unrest. All monitored restless calderas have either geodetically (Yellowstone, Aira Iwo-Jima, Askja, Fernandina and, partly, Long Valley) or geophysically (Rabaul, Okmok) detected sill-like intrusions inducing repeated unrest. Some calderas (Yellowstone, Long Valley) also show stable deformation pattern, where inflation insists on and mimics the resurgence uplift. The common existence of sill-like sources, also responsible for stable deformation patterns, in restless calderas suggests close similarities to Campi Flegrei. This suggests a wider applicability of our model of thermally-assisted sill emplacement, to be tested by future studies to better understand not only the dynamics of restless calderas and their eruptive potential but also the growth and assemblage of igneous intrusions and plutons.

The PROTEUS Experiment: Active Source Seismic Imaging of the Crustal Magma Plumbing Structure of the Santorini Arc Volcano

NASA Astrophysics Data System (ADS)

Hooft, E. E. E.; Morgan, J. V.; Nomikou, P.; Toomey, D. R.; Papazachos, C. V.; Warner, M.; Heath, B.; Christopoulou, M. E.; Lampridou, D.; Kementzetzidou, D.

2016-12-01

The goal of the PROTEUS seismic experiment (Plumbing Reservoirs Of The Earth Under Santorini) is to examine the entire crustal magma plumbing system beneath a continental arc volcano and determine the magma geometry and connections throughout the crust. These physical parameters control magma migration, storage, and eruption and inform the question of how physical and chemical processing of magma at arc volcanoes forms the andesitic rock compositions that dominate the lower continental crust. These physical parameters are also important to understand volcanic-tectonic interactions and geohazards. Santorini is ideal for these goals because the continental crust has been thinned by extension and so the deep magmatic system is more accessible, also it is geologically well studied. Since the volcano is a semi-submerged, it was possible to collect a unique 3D marine-land active source seismic dataset. During the PROTEUS experiment in November-December of 2015, we recorded 14,300 marine sound sources from the US R/V Langseth on 89 OBSIP short period ocean bottom seismometers and 60 German and 5 Greek land seismometers. The experiment was designed for high-density spatial sampling of the seismic wavefield to allow us to apply two state-of-the-art 3D inversion methods: travel time tomography and full waveform inversion. A preliminary travel time tomography model of the upper crustal seismic velocity structure of the volcano and surrounding region is presented in an accompanying poster. We also made marine geophysical maps of the seafloor using multi-beam bathymetry and of the gravity and magnetic fields. The new seafloor map reveals the detailed structure of the major fault system between Santorini and Amorgos, of associated landslides, and of newly discovered volcanic features. The PROTEUS project will provide new insights into the structure of the whole crustal magmatic system of a continental arc volcano and its evolution within the surrounding tectonic setting.

Geologic History of Asteroid 4 Vesta

NASA Technical Reports Server (NTRS)

Mittlefehldt, David W.

2014-01-01

Some types of meteorites - most irons, stony irons, some achondrites - hail from asteroids that were heated to the point where magmatism occurred within a very few million years of the formation of the earliest solids in the solar system. The largest clan of achondrites, the howardite, eucrite and diogenite (HED) meteorites, represent the crust of their parent asteroid]. Diogenites are cumulate harzburgites and orthopyroxenites from the lower crust whilst eucrites are basalts, diabases and cumulate gabbros from the upper crust. Howardites are impact-engendered breccias mostly of diogenites and eucrites. There remains only one large asteroid with a basaltic crust, 4 Vesta, which is thought to be the source of the HED clan. Differentiation models for Vesta are based on HED compositions. Proto-Vesta consisted of chondritic materials containing Al-26, a potent, short-lived heat source. Inferences from compositional data are that Vesta was melted to high degree (=50%) allowing homogenization of the silicate phase and separation of a metallic core. Convection of the silicate magma ocean allowed equilibrium crystallization, forming a harzburgitic mantle. After convective lockup occurred, melt collected between the mantle and the cool thermal boundary layer and underwent fractional crystallization forming an orthopyroxene-rich (diogenite) lower crust. The initial thermal boundary layer of chondritic material was replaced by a mafic upper crust through impact disruption and foundering. The mafic crust thickened over time as additional residual magma intrudes and penetrates the mafic crust forming plutons, dikes, sills and flows of cumulate and basaltic eucrite composition. This magmatic history may have taken only 2-3 Myr. This magma ocean scenario is at odds with a model of heat and magma transport that indicates that small degrees of melt would be rapidly expelled from source regions, precluding development of a magma ocean. Constraints from radiogenic Mg-26 distibutions suggest that the parent asteroid of HEDs was much smaller than Vesta. Thus, first-order questions regarding asteroid differentiation remain.

Method for sputtering with low frequency alternating current

DOEpatents

Timberlake, John R.

1996-01-01

Low frequency alternating current sputtering is provided by connecting a low frequency alternating current source to a high voltage transformer having outer taps and a center tap for stepping up the voltage of the alternating current. The center tap of the transformer is connected to a vacuum vessel containing argon or helium gas. Target electrodes, in close proximity to each other, and containing material with which the substrates will be coated, are connected to the outer taps of the transformer. With an applied potential, the gas will ionize and sputtering from the target electrodes onto the substrate will then result. The target electrodes can be copper or boron, and the substrate can be stainless steel, aluminum, or titanium. Copper coatings produced are used in place of nickel and/or copper striking.

Method for sputtering with low frequency alternating current

DOEpatents

Timberlake, J.R.

1996-04-30

Low frequency alternating current sputtering is provided by connecting a low frequency alternating current source to a high voltage transformer having outer taps and a center tap for stepping up the voltage of the alternating current. The center tap of the transformer is connected to a vacuum vessel containing argon or helium gas. Target electrodes, in close proximity to each other, and containing material with which the substrates will be coated, are connected to the outer taps of the transformer. With an applied potential, the gas will ionize and sputtering from the target electrodes onto the substrate will then result. The target electrodes can be copper or boron, and the substrate can be stainless steel, aluminum, or titanium. Copper coatings produced are used in place of nickel and/or copper striking. 6 figs.

Mantle source volumes and the origin of the mid-Tertiary ignimbrite flare-up in the southern Rocky Mountains, western U.S.

NASA Astrophysics Data System (ADS)

Farmer, G. Lang; Bailley, Treasure; Elkins-Tanton, Linda T.

2008-04-01

Voluminous intermediate to silicic composition volcanic rocks were generated throughout the southern Rocky Mountains, western U.S., during the mid-Tertiary "ignimbrite flare-up", principally at the San Juan and Mogollon-Datil volcanic fields. At both volcanic centers, radiogenic isotope data have been interpreted as evidence that 50% or more of the volcanic rocks (by mass) were derived from mantle-derived, mafic parental magmas, but no consensus exists as to whether melting was largely of lithospheric or sub-lithospheric mantle. Recent xenolith studies, however, have revealed that thick (> 100 km), fertile, and hydrated continental lithosphere was present beneath at least portions of the southern Rocky Mountains during the mid-Tertiary. The presence of such thick mantle lithosphere, combined with an apparent lack of syn-magmatic extension, leaves conductive heating of lithospheric mantle as a plausible method of generating the mafic magmas that fueled the ignimbrite flare-up in this inland region. To further assess this possibility, we estimated the minimum volume of mantle needed to generate the mafic magmas parental to the preserved mid-Tertiary igneous rocks. Conservative estimates of the mantle source volumes that supplied the Mogollon-Datil and San Juan volcanic fields are ˜ 2 M km 3 and ˜ 7 M km 3, respectively. These volumes could have comprised only lithospheric mantle if at least the lower ˜ 20 km of the mantle lithosphere beneath the entire southern Rocky Mountains region underwent partial melting during the mid-Tertiary and if the resulting mafic magmas were drawn laterally for distances of up to ˜ 300 km into each center. Such widespread melting of lithospheric mantle requires that the lithospheric mantle have been uniformly fertile and primed for melting in the mid-Tertiary, a possibility if the lithospheric mantle had experienced widespread hydration and refrigeration during early Tertiary low angle subduction. Exposure of the mantle lithosphere to hot, upwelling sub-lithospheric mantle during mid-Tertiary slab roll back could have then triggered the mantle melting. While a plausible source for mid-Tertiary basaltic magmas in the southern Rocky Mountains, lithospheric mantle could not have been the sole source for mafic magmas generated to the south in that portion of the ignimbrite flare-up now preserved in the Sierra Madre Occidental of northern Mexico. The large mantle source volumes (> 45 M km 3) required to fuel the voluminous silicic ignimbrites deposited in this region (> 400 K km 3) are too large to have been accommodated within the lithospheric mantle alone, implying that melting in sub-lithospheric mantle must have played a significant role in generating this mid-Tertiary magmatic event.

Assimilation by lunar mare basalts: Melting of crustal material and dissolution of anorthite

NASA Astrophysics Data System (ADS)

Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

1994-07-01

We discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances, kinetic rates, and simple fluid mechanical constraints. Assuming parent magmas of picritic compositions, we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic, troctolitic, noritic, and KREEP (quartz monzodiorite) compositions. Significant melting of the plagioclase-rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt. Even when this occurs, the major element chemistry of the picritic magmas will change by less than 1-2 wt %. Diffusion coefficients measured for Al2O3 from an iron-free basalt and an orange glass composition are 10-12 sq m/s at 1340 C and 10-11 sq m/s at 1390 C. These rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions. Picritic magmas can melt significant quantities of KREEP, which suggests that their trace element chemistry may still be affected by assimilation processes; however, mixing viscous melts of KREEP composition with the fluid picritic magmas could be prohibitively difficult. We conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation/fractional crystallization processes near the lunar surface. Instead, most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle.

Assimilation by lunar mare basalts: Melting of crustal material and dissolution of anorthite

NASA Technical Reports Server (NTRS)

Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

1994-01-01

We discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances, kinetic rates, and simple fluid mechanical constraints. Assuming parent magmas of picritic compositions, we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic, troctolitic, noritic, and KREEP (quartz monzodiorite) compositions. Significant melting of the plagioclase-rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt. Even when this occurs, the major element chemistry of the picritic magmas will change by less than 1-2 wt %. Diffusion coefficients measured for Al2O3 from an iron-free basalt and an orange glass composition are 10(exp -12) sq m/s at 1340 C and 10(exp -11) sq m/s at 1390 C. These rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions. Picritic magmas can melt significant quantities of KREEP, which suggests that their trace element chemistry may still be affected by assimilation processes; however, mixing viscous melts of KREEP composition with the fluid picritic magmas could be prohibitively difficult. We conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation/fractional crystallization processes near the lunar surface. Instead, most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle.

Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

NASA Astrophysics Data System (ADS)

Heinonen, Jussi S.; Kurz, Mark D.

2015-09-01

The massive outpourings of Karoo and Ferrar continental flood basalts (CFBs) ∼180 Ma ago mark the initial Jurassic rifting stages of the Gondwana supercontinent. The origin and sources of these eruptions have been debated for decades, largely due to difficulties in defining their parental melt and mantle source characteristics. Recent findings of Fe- and Mg-rich dikes (depleted ferropicrite suite) from Vestfjella, western Dronning Maud Land, Antarctica, have shed light on the composition of the deep sub-Gondwanan mantle: these magmas have been connected to upper mantle sources presently sampled by the Southwest Indian Ocean mid-ocean ridge basalts (SWIR MORBs) or to high 3He/4He plume-entrained non-chondritic primitive mantle sources formed early in Earth's history. In an attempt to determine their He isotopic composition and relative contributions from magmatic, cosmogenic, and radiogenic He sources, we performed in-vacuo stepwise crushing and melting analyses of olivine mineral separates, some of which were abraded to remove the outer layer of the grains. The best estimate for the mantle isotopic composition is given by a sample with the highest amount of He released (>50%) during the first crushing step of an abraded coarse fraction. It has a 3He/4He of 7.03 ± 0.23 (2σ) times the atmospheric ratio (Ra), which is indistinguishable from those measured from SWIR MORBs (6.3-7.3 Ra; source 3He/4He ∼6.4-7.6 Ra at 180 Ma) and notably lower than in the most primitive lavas from the North Atlantic Igneous Province (up to 50 Ra), considered to represent the epitome magmas from non-chondritic primitive mantle sources. Previously published trace element and isotopic (Sr, Nd, and Pb) compositions do not suggest a direct genetic link to any modern hotspot of Indian or southern Atlantic Oceans. Although influence of a mantle plume cannot be ruled out, the high magma temperatures and SWIR MORB-like geochemistry of the suite are best explained by supercontinent insulation of a precursory Indian Ocean upper mantle source. Such a model is also supported by the majority of the recent studies on the structure, geochronology, and petrology of the Karoo CFBs.

Two types of ore-bearing mafic complexes of the Early Proterozoic East-Scandinavian LIP and their ore potential

NASA Astrophysics Data System (ADS)

Mitrofanov, Felix; Zhirov, Dmitry; Bayanova, Tamara; Korchagin, Alexey; Chaschin, Victor

2015-04-01

Two types of the ore-bearing mafic complexes are allotted in the East-Scandinavian large igneous province (LIP). They differ in geodynamic setting, structure, isotope geochemistry, petrology and mineralogy. The PGE-bearing mafic-ultramafic layered intrusions are associated with the first complex. They have been formed at an initial (pre-rift) stage of LIP. Features of origin of this complex are: 1) large-scale, protracted, and multiple episodes of deep mantle plume or asthenosphere upwelling; 2) the vast non-subduction-type basaltic magma in an intraplate continental setting; 3) low-sulfide Pt-Pd (with Ni, Cu, Au, Co and Rh) mineralization in different geological setting (reef- and contact type etc.); 4) anomalously high concentrations of PGEs in the bulk sulfides, inferred platinum distribution coefficient between silicate and sulfide melts of >100000. Deep mantle magma source is enriched in ore components (fertile source) and lithophile elements. It is reflected in the isotope indicators such as ɛNd(T) from -1 to -3, ISr(87Sr/86Sr) from 0.702 to 0.704, 3Не/4Не = (10 ^-5 ÷ 10 ^-6). Magma and ore sources differ from those of Mid-Ocean Ridge basalts (MORB), subduction-related magma but are similar to EM-I. Ore-bearing mafic complexes formed during a long period of time and by different episodes (2490±10 Ma; 2470±10 Ma; 2450±10 Ma; 2400±10 Ma), and by mixing between the boninitic an anorthositic magmas. It is known about 10 deposits and occurrences in Kola region with total reserves and resources about 2000 tons in palladium equivalent (with an average content ≥2-3 ppm). Intrusions with the rich sulfide Ni-Cu ore (with Co and poor PGE) are associated with the second mafic complex. Ore-controlling mafic-ultramafic intrusions are formed at a final stage of the intracontinental rifting of the Transitional period (2200-1980 Ma). Initial magma is depleted and similar to the MORB in terms of rare earths distribution. Enriched ferropicritic Fe-Ti derivatives of magma generate single volcano-plutonic rock series. For intrusive ore bodies rock differentiation with the formation of syngenetic wehrlite-clinopyroxenite-gabbro- orthoclase gabbro sequence is typical. Upper mantle source of the depleted magma is characterized by the following isotope indicators: ɛNd(T) +0.5 to +4, ISr= 87Sr/86Sr 0.703-0.704. Ore-bearing intrusive bodies are injected in the upper part of the Early Palaeoproterozoic volcano-sedimentary cross-section. Ores are located in the basement of intrusions and in the redeposited veined bodies, including offset setting. Numerous Ni-Cu deposits with total reserves and resources of several million tons of Nickel equivalent (with an average grade ≥ 0,3%) have been explored, and some of them now is mining. As a result of our research, the complex of indicators and criteria is suggested for predicting the occurrence, for regional exploration target selection and for regional resource evaluation of PGE and base metals. The studies are supported by the Russian Foundation for Basic Research (project nos. 13-05-12055).

Evaluating Crustal Contamination Effects on the Lithophile Trace Element Budget of Shergottites

NASA Technical Reports Server (NTRS)

Brandon, A. D.; Ferdous, J.; Peslier, A. H.

2017-01-01

The origin of the incompatible trace element (ITE) enriched compositions of shergottites has been a point of contention for decades [1-2]. Two scenarios have been proposed, the first is that enriched shergottite compositions reflect an ITE-enriched mantle source, whereas in the second, the ITE enrichment reflects crustal contamination of mantle-derived parent magmas. Evidence supporting the first scenario is that the ITE-enriched shergottite compositions are consistent with the outcomes of magma ocean crystallization [3], and that Os-Nd isotope relationships for shergottites cannot be explained by realistic crustal contamination models [4]. In contrast, Cl and S isotopes are consistent with shergottite magmas interacting with Mars crust [5,6], and ITE-enriched olivine-hosted melt inclusions and interstitial glass are found in depleted shergottite Yamato 980459 [7]. These findings indicate that some level of crustal interaction occurred but the question of whether ITE-enrichments in some bulk shergottites reflect crustal contamination remains open. Recently, a Mars crustal breccia meteorite has been found, NWA 7034 and its paired stones, that is our best analogue to an average of Mars ancient crust [8-10]. This allows for better constraints on crustal contamination of shergottite magmas. We modeled magma-crust mixing and assimilation-fractional crystallization (AFC) using ITE-depleted shergottite compositions and bulk NWA 7034 and its clasts as end-members. The results of these models indicate that crustal contamination can only explain the ITE-enriched compositions of some bulk shergottites under unusual circumstances. It is thus likely that the shergottite range of compositions reflects primarily mantle sources.

Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 2. Coeruptive deflation, July-August 2008

USGS Publications Warehouse

Lu, Zhong; Dzurisin, Daniel

2010-01-01

A hydrovolcanic eruption near Cone D on the floor of Okmok caldera, Alaska, began on 12 July 2008 and continued until late August 2008. The eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and ∼3 km below sea level (bsl), which began immediately after Okmok's previous eruption in 1997. In this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar (InSAR) techniques to produce a suite of 2008 coeruption deformation maps. Most of the surface deformation that occurred during the eruption is explained by deflation of a Mogi-type source located beneath the center of the caldera and 2–3 km bsl, i.e., essentially the same source that inflated prior to the eruption. During the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1/e time constant of ∼13 days. We envision a sponge-like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath Okmok caldera. The rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface. A similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring-fracture system.

Pre-eruptive conditions of the Hideaway Park topaz rhyolite: Insights into metal source and evolution of magma parental to the Henderson porphyry molybdenum deposit, Colorado

USGS Publications Warehouse

Mercer, Celestine N.; Hofstra, Albert H.; Todorov, Todor I.; Roberge, Julie; Burgisser, Alain; Adams, David T.; Cosca, Michael A.

2015-01-01

The Hideaway Park tuff is the only preserved extrusive volcanic unit related to the Red Mountain intrusive complex, which produced the world-class Henderson porphyry Mo deposit. Located within the Colorado Mineral Belt, USA, Henderson is the second largest Climax-type Mo deposit in the world, and is therefore an excellent location to investigate magmatic processes leading to Climax-type Mo mineralization. We combine an extensive dataset of major element, volatile, and trace element abundances in quartz-hosted melt inclusions and pumice matrix glass with major element geochemistry from phenocrysts to reconstruct the pre-eruptive conditions and the source and evolution of metals within the magma. Melt inclusions are slightly peraluminous topaz rhyolitic in composition and are volatile-charged (≤6 wt % H2O, ≤600 ppm CO2, ∼0·3–1·0 wt % F, ∼2300–3500 ppm Cl) and metal-rich (∼7–24 ppm Mo, ∼4–14 ppm W, ∼21–52 ppm Pb, ∼28–2700 ppm Zn, <0·1–29 ppm Cu, ∼0·3–1·8 ppm Bi, ∼40–760 ppb Ag, ∼690–1400 ppm Mn). Melt inclusion and pumice matrix glass chemistry reveal that the Hideaway Park magma evolved by large degrees of fractional crystallization (≤60–70%) during quartz crystallization and melt inclusion entrapment at pressures of ≤300 MPa (≤8 km depth), with little to no crystallization upon shallow ascent and eruption. Filter pressing, crystal settling, magma recharge and mixing of less evolved rhyolite melt, and volatile exsolution were important processes during magma evolution; the low estimated viscosities (∼105–1010 Pa s) of these H2O- and F-rich melts probably enhanced these processes. A noteworthy discrepancy between the metal contents in the pumice matrix glass and in the melt inclusions suggests that after quartz crystallization ceased upon shallow magma ascent and eruption, the Hideaway Park magma exsolved an aqueous fluid into which Mo, Bi, Ag, Zn, Mn, Cs, and Y strongly partitioned. Given that the Henderson deposit contains anomalous abundances of not only Mo, but also W, Pb, Zn, Cu, Bi, Ag, and Mn, we suggest that these metals were sourced from similar fluids exsolved from unerupted portions of the same magmatic system. Trace element ratios imply that Mo was sourced deep, from either the lower crust or metasomatized mantle. The origin of sulfur remains unresolved; however, given the extremely low S solubility of rhyolite melts in the shallow crust we favor the possibility that another source of S might supplement or account for that present in the ore deposit, probably the comagmatic, mantle-derived lamprophyres that occur in minor quantities with the voluminous topaz rhyolites in the area. To account for the 437 Mt of MoS2 (∼1·0 × 106 t Mo) present in the Henderson ore deposit, a volume of ∼45 km3 of Hideaway Park rhyolite magma would have been necessary to supply the Mo (a cylindrical pluton measuring 3·1 km × 6·0 km) along with sparging of ∼6·8 × 105 t of S from ∼0·05 km3 of lamprophyre magma. Based on a weighted mean 40Ar/39Ar age of 27·58 ± 0·24 Ma, similar melt geochemistry, and characteristically F-rich biotite phenocrysts, we conclude that the Hideaway Park tuff was cogenetic with the intrusions at Red Mountain that formed the Henderson deposit.

Sombrero uplift above the Altiplano-Puna Magma Body: evidence of a ballooning mid-crustal diapir.

PubMed

Fialko, Yuri; Pearse, Jill

2012-10-12

The Altiplano-Puna ultralow-velocity zone in the central Andes, South America, is the largest active magma body in Earth's continental crust. Space geodetic observations reported an uplift in the Altiplano-Puna proper at a rate of ~10 mm/year; however, the nature of the inferred inflation source has been uncertain. We present data showing that the uplift has persisted at a nearly constant rate over the past two decades, and is surrounded by a broad zone of subsidence. We show that the ongoing uplift and peripheral subsidence may result from a large mid-crustal diapir fed by partial melt from the Altiplano-Puna Magma Body.

CO 2-fluxing collapses metal mobility in magmatic vapour

DOE PAGES

van Hinsberg, V. J.; Berlo, K.; Migdisov, A. A.; ...

2016-05-18

Magmatic systems host many types of ore deposits, including world-class deposits of copper and gold. Magmas are commonly an important source of metals and ore-forming fluids in these systems. In many magmatic-hydrothermal systems, low-density aqueous fluids, or vapours, are significant metal carriers. Such vapours are water-dominated shallowly, but fluxing of CO 2-rich vapour exsolved from deeper magma is now recognised as ubiquitous during open-system magma degassing. Furthermore, we show that such CO 2-fluxing leads to a sharp drop in element solubility, up to a factor of 10,000 for Cu, and thereby provides a highly efficient, but as yet unrecognised mechanismmore » for metal deposition.« less

The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny

NASA Astrophysics Data System (ADS)

Richards, Jeremy P.

2015-09-01

Global data for measured Fe2O3/FeO ratios and Cu contents in unaltered volcanic and intrusive arc rocks indicate that, on average, they are slightly more oxidized than other magmas derived from depleted upper mantle (such as MORB), but contain similar Cu contents across their compositional ranges. Although Cu scatters to elevated values in some intermediate composition samples, the bulk of the data show a steady but gentle trend to lower concentrations with differentiation, reaching modal values of 50-100 ppm in andesitic rocks. These data suggest that Cu is mildly compatible during partial melting and fractionation processes, likely reflecting minor degrees of sulfide saturation throughout the magmatic cycle. However, the volume of sulfides must be small such that significant proportions of the metal content remain in the magma during fractionation to intermediate compositions. Previous studies have shown that andesitic magmas containing 50 ppm Cu can readily form large porphyry-type Cu deposits upon emplacement in the upper crust. A review of the literature suggests that the elevated oxidation state in the asthenospheric mantle wedge source of arc magmas (ΔFMQ ≈ + 1 ± 1) derives from the subduction of seawater-altered and oxidized oceanic crust, and is transmitted into the mantle wedge via prograde metamorphic dehydration fluids carrying sulfate and other oxidizing components. Progressive hydration and oxidation of the mantle wedge may take up to 10 m.y. to reach a steady state from the onset of subduction, explaining the rarity of porphyry deposits in primitive island arcs, and the late formation of porphyries in continental arc magmatic cycles. Magmas generated from this metasomatized and moderately oxidized mantle source will be hydrous basalts containing high concentrations of sulfur, mainly dissolved as sulfate or sulfite. Some condensed sulfides (melt or minerals) may be present due to the high overall fS2, despite the moderately high oxidation state. These sulfides may retain some highly siderophile elements in the source, but are unlikely to be sufficiently voluminous to significantly affect the budget of more modestly sulfide-compatible and more abundant elements such as Cu and Mo. These primary magmas can therefore be considered to be largely Cu-Mo-undepleted, although highly siderophile elements such as Au and platinum group elements (PGE) may be depleted unless no sulfides remain in the source. The latter condition seems unlikely during active subduction because of the continuous flux of fresh sulfur from the slab, but may occur during post-subduction re-melting (leading to potentially Au-rich post-subduction porphyry and alkalic-type epithermal systems). Lower crustal differentiation of main-stage arc magmas results in some loss of Cu to residual or cumulate sulfides, but again the amount appears to be minor, and does not drastically reduce the Cu content of derivative intermediate-composition melts. Fractionation and devolatilization affect the oxidation state of the magma in competing ways, but, while crystallization and segregation of Fe3 +-rich magnetite can cause reduction in reduced to moderately oxidized evolved magmas, this effect appears to be outweighed by the oxidative effects of degassing reduced or weakly oxidized gaseous species such as H2, H2S, and SIVO2, and preferential solvation and removal of Fe2 + in saline hydrothermal fluids. Consequently, most arc magmatic suites show slight increases in oxidation state during differentiation, reaching typical values of ΔFMQ = + 1 to + 2. This oxidation state is significant, because it corresponds to the transition from dissolved sulfide to sulfate dominance in magmas. It has been shown that Cu and Au solubilities in silicate magma increase up to this level (ΔFMQ ≈ + 1), but while Cu solubility continues to increase at higher oxidation states, Au shows a precipitous drop as sulfide, which solvates Au in the melt, is converted to sulfate. This may explain the somewhat restricted distribution of Au-rich porphyry Cu deposits, but the general association of porphyry Cu deposits with relatively oxidized magmas. Exsolution of a saline, high temperature aqueous fluid enables metals to partition from the magma into a highly mobile volatile phase. Sulfur also partitions strongly into this fluid phase, predominantly as SO2 at ΔFMQ = + 1 to + 2. However, as the fluid cools below 400 °C, SIVO2 disproportionates to form reduced H2S- II and oxidized H2SVIO4. The H2S bonds with metals in solution to precipitate as Cu- and Mo-sulfides, while the H2SO4 (and HCl) generates progressively acidic wallrock alteration (phyllic, argillic, advanced argillic). Gold may precipitate with early Cu/Mo-sulfides, but some may also stay in solution as bisulfide complexes, eventually reaching the epithermal environment. Thus, three components, [S], [H2O], and fO2 work together throughout subduction and arc magmatic processes to transport chalcophile and siderophile metals from the mantle into the upper crust, where they may be concentrated by hydrothermal processes to form ore deposits. These processes are far from 100% efficient, and metals (especially highly siderophile elements such as Au and PGE) may be left behind at various stages of the passage of arc magmas through the lithosphere, where they may form potentially metalliferous source rocks for partial melts and subsequent magmatic-hydrothermal ore deposits generated during later tectonomagmatic events.

Temporal constraints on magma generation and differentiation in a continental volcano: Buckland, eastern Australia

NASA Astrophysics Data System (ADS)

Crossingham, Tracey J.; Ubide, Teresa; Vasconcelos, Paulo M.; Knesel, Kurt M.; Mallmann, Guilherme

2018-03-01

The eastern margin of the Australian continent hosts a large number of Cenozoic intraplate volcanoes along a 2000 km long track. Here, we study mafic lavas from the Buckland volcano, Queensland, located in the northern (older) segment of this track, to assess magma generation and differentiation through time. The rocks are aphanitic to microporphyritic basalts, trachy-basalts and basanites. Incompatible element geochemistry together with Sr-Nd-Pb isotope ratios indicate that magmas formed from an enriched mantle I (EMI)-like garnet-bearing source with variable degrees of crustal contamination. Whole rock elemental variations suggest fractionation of olivine, plagioclase, clinopyroxene and/or magnetite. There is no petrographic or geochemical evidence of magma mixing in the studied rocks (e.g., lack of recycled minerals), suggesting a relatively quick ascent from the source to the surface without major storage at shallow levels. 40Ar/39Ar geochronology reveals two stages of volcanism: 30.3 ± 0.1 Ma and 27.4 ± 0.2 Ma. The Old Buckland (30.3 ± 0.1 Ma) melts have negative K anomalies, and incompatible element ratios suggest the occurrence of residual hydrous minerals in a metasomatised mantle source. We therefore infer that at the onset of volcanism, deep-mantle-derived magmas interacted with metasomatised sub-continental lithospheric mantle (SCLM). Major and trace element data, clinopyroxene thermobarometry and thermodynamic modelling indicate magma evolution by assimilation and fractional crystallisation (AFC) during ascent through the crust. Following a hiatus in volcanic activity of 2.5 Ma, eruption of Young Buckland (27.4 ± 0.2 Ma) lavas marked a shift towards more alkaline compositions. Trace element compositions indicate lower degrees of partial melting and a lack of interaction with metasomatic components. Young Buckland lavas become progressively more SiO2-saturated up stratigraphy, suggesting an increase in the degree of partial melting with time. Young Buckland lavas also have more radiogenic 87Sr/86Sr and 207Pb/204Pb ratios and less radiogenic 143Nd/144Nd ratios up stratigraphy. These isotopic variations, together with coupled increases in Pb and K and decreases in Ce/Pb (27.22 to 11.09) and Nb/U (68.30 to 29.96), suggest that crustal contamination also increased with time. By placing absolute age and stratigraphic constraints on the Buckland lavas, we have been able to ascertain differentiation signatures imposed on mantle-derived melts during ascent through the continental lithosphere over 3 Ma. Our study provides new constraints on magma generation and differentiation in continental intraplate volcanic systems.

Mineralogy and composition of the oceanic mantle

USGS Publications Warehouse

Putirka, Keith; Ryerson, F.J.; Perfit, Michael; Ridley, W. Ian

2011-01-01

The mineralogy of the oceanic basalt source region is examined by testing whether a peridotite mineralogy can yield observed whole-rock and olivine compositions from (1) the Hawaiian Islands, our type example of a mantle plume, and (2) the Siqueiros Transform, which provides primitive samples of normal mid-ocean ridge basalt. New olivine compositional data from phase 2 of the Hawaii Scientific Drilling Project (HSDP2) show that higher Ni-in-olivine at the Hawaiian Islands is due to higher temperatures (T) of melt generation and processing (by c. 300°C) related to the Hawaiian mantle plume. DNi is low at high T, so parental Hawaiian basalts are enriched in NiO. When Hawaiian (picritic) parental magmas are transported to shallow depths, olivine precipitation occurs at lower temperatures, where DNi is high, leading to high Ni-in-olivine. Similarly, variations in Mn and Fe/Mn ratios in olivines are explained by contrasts in the temperatures of magma processing. Using the most mafic rocks to delimit Siqueiros and Hawaiian Co and Ni contents in parental magmas and mantle source compositions also shows that both suites can be derived from natural peridotites, but are inconsistent with partial melting of natural pyroxenites. Whole-rock compositions at Hawaii and Siqueiros are also matched by partial melting experiments conducted on peridotite bulk compositions. Hawaiian whole-rocks have elevated FeO contents compared with Siqueiros, which can be explained if Hawaiian parental magmas are generated from peridotite at 4-5 GPa, in contrast to pressures of slightly greater than 1 GPa for melt generation at Siqueiros; these pressures are consistent with olivine thermometry, as described in an earlier paper. SiO2-enriched Koolau compositions are reproduced if high-Fe Hawaiian parental magmas re-equilibrate at 1-1·5 GPa. Peridotite partial melts from experimental studies also reproduce the CaO and Al2O3 contents of Hawaiian (and Siqueiros) whole-rocks. Hawaiian magmas have TiO2 contents, however, that are enriched compared with melts from natural peridotites and magmas derived from the Siqueiros depleted mantle, and consequently may require an enriched source. TiO2 is not the only element that is enriched relative to melts of natural peridotites. Moderately incompatible elements, such as Ti, Zr, Hf, Y, and Eu, and compatible elements, such as Yb and Lu, are all enriched at the Hawaiian Islands. Such enrichments can be explained by adding 5-10% mid-ocean ridge basalt (crust) to depleted mantle; when the major element composition of such a mixture is recast into mineral components, the result is a fertile peridotite mineralogy.

Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

2018-05-01

The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid-ocean-ridge-basalt mantle and enriched-mantle I components. The Permian mafic-ultramafic intrusions in North Xinjiang were formed from tholeiitic basaltic magmas derived from decompression partial melting of the metasomatized mantle in a post-collision extensional tectonic setting. The tholeiitic basaltic magmas are equivalent to the voluminous underplated basaltic magmas that formed during vertical crustal growth of the Central Asian Orogenic Belt in the later Paleozoic.

Can a fractionally crystallized magma ocean explain the thermo-chemical evolution of Mars?

NASA Astrophysics Data System (ADS)

Plesa, A.-C.; Tosi, N.; Breuer, D.

2014-10-01

The impact heat accumulated during the late stage of planetary accretion can melt a significant part or even the entire mantle of a terrestrial body, giving rise to a global magma ocean. The subsequent cooling of the interior causes the magma ocean to freeze from the core-mantle boundary (CMB) to the surface due to the steeper slope of the mantle adiabat compared to the slope of the solidus. Assuming fractional crystallization of the magma ocean, dense cumulates are produced close to the surface, largely due to iron enrichment in the evolving magma ocean liquid. A gravitationally unstable mantle thus forms, which is prone to overturn. We investigate the cumulate overturn and its influence on the thermal evolution of Mars using mantle convection simulations in 2D cylindrical geometry. We present a suite of simulations using different initial conditions and a strongly temperature-dependent viscosity. We assume that all radiogenic heat sources have been enriched during the freezing-phase of the magma ocean in the uppermost 50 km and that the initial steam-atmosphere created by the degassing of the freezing magma ocean was rapidly lost, implying that the surface temperature is set to present-day values. In this case, a stagnant lid quickly forms on top of the convective interior preventing the uppermost dense cumulates to sink, even when allowing for a plastic yielding mechanism. Below this dense stagnant lid, the mantle chemical gradient settles to a stable configuration. The convection pattern is dominated by small-scale structures, which are difficult to reconcile with the large-scale volcanic features observed over Mars' surface and partial melting ceases in less than 900 Ma. Assuming that the stagnant lid can break because of additional mechanisms and allowing the uppermost dense layer to overturn, a stable density gradient is obtained, with the densest material and the entire amount of heat sources lying above the CMB. This stratification leads to a strong overheating of the lowermost mantle, whose temperature increases to values that exceed the liquidus. The iron-rich melt would most likely remain trapped in the lower part of the mantle. The upper mantle in that scenario cools rapidly and only shows partial melting during the first billion year of evolution. Therefore a fractionated global and deep magma ocean is difficult to reconcile with observations. Different scenarios assuming, for instance, a hemispherical or shallow magma ocean, or a crystallization sequence resulting in a lower density gradient than that implied by pure fractional crystallization will have to be considered.

Geochemical and Isotopic Data from Micron to Across-Arc Scales in the Andean Central Volcanic Zone: Applications for Resolving Crustal Magmatic Differentiation and Modification Processes

NASA Astrophysics Data System (ADS)

Michelfelder, G.; Wilder, A.; Feeley, T.

2014-12-01

Plagioclase crystals from silicic (andesitic to dacitic) lavas and domes at Volcán Uturuncu, a potentially active volcano in the back-arc of the Andean CVZ (22.3°S, 67.2°W), exhibit large variations in An contents, textures, and core to rim 87Sr/86Sr ratios. Many of the isotopic variations can not have existed at magmatic temperatures for more than a few thousand years. The crystals likely derived from different locations in the crustal magmatic system and mixed just prior to eruption. Uturuncu magmas initially assimilated crustal rocks with high 87Sr/86Sr ratios. The magmas were subsequently modified by frequent recharge of more mafic magmas with lower 87Sr/86Sr ratios. A typical Uturuncu silicic magma therefore only attains its final composition just prior to or during eruption. In the Lazufre region of active surface uplift (~25˚14'S; Volcán Lastarria and Cordon del Azufre) closed system differentiation processes are not the only factors influencing silicic magma compositions. 87Sr/86Sr (0.70651-0.70715) and 206Pb/204Pb ratios (18.83-18.88) are highly elevated and143Nd/144Nd ratios (0.512364 -0.512493) are low relative to similar composition rocks from the "southern Cordillera domain." These data, along with major and trace element trends, reflect a multitude of differentiation processes and magma sources including crystallization-differentiation of more mafic magmas, melting and assimilation of older crustal rocks, and magma mixing and mingling. On an arc-wide scale silicic lavas erupted from three well-characterized composite volcanoes between 21oS and 22oS (Aucanquilcha, Ollagüe, and Uturuncu) display systematically higher K2O, LILE, REE and HFSE contents and 87Sr/86Sr ratios with increasing distance from the arc-front. In contrast, the lavas have systematically lower Na2O, Sr, and Ba contents; LILE/HFSE ratios; 143Nd/144Nd ratios; and more negative Eu anomalies. Silicic magmas along the arc-front apparently reflect melting of relatively young, mafic composition amphibolitic source rocks with the continental crust becoming increasingly older with a more felsic bulk composition toward the east. We suggest this results from progressively smaller degrees of mantle partial melting, primary melt generation, and crustal hybridization with distance from the arc-front.

Magma supply, storage, and transport at shield-stage Hawaiian volcanoes: Chapter 5 in Characteristics of Hawaiian volcanoes

USGS Publications Warehouse

Poland, Michael P.; Miklius, Asta; Montgomery-Brown, Emily K.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

2014-01-01

Magma supply to Hawaiian volcanoes has varied over millions of years but is presently at a high level. Supply to Kīlauea’s shallow magmatic system averages about 0.1 km3/yr and fluctuates on timescales of months to years due to changes in pressure within the summit reservoir system, as well as in the volume of melt supplied by the source hot spot. Magma plumbing systems beneath Kīlauea and Mauna Loa are complex and are best constrained at Kīlauea. Multiple regions of magma storage characterize Kīlauea’s summit, and two pairs of rift zones, one providing a shallow magma pathway and the other forming a structural boundary within the volcano, radiate from the summit to carry magma to intrusion/eruption sites located nearby or tens of kilometers from the caldera. Whether or not magma is present within the deep rift zone, which extends beneath the structural rift zones at ~3-km depth to the base of the volcano at ~9-km depth, remains an open question, but we suggest that most magma entering Kīlauea must pass through the summit reservoir system before entering the rift zones. Mauna Loa’s summit magma storage system includes at least two interconnected reservoirs, with one centered beneath the south margin of the caldera and the other elongated along the axis of the caldera. Transport of magma within shield-stage Hawaiian volcanoes occurs through dikes that can evolve into long-lived pipe-like pathways. The ratio of eruptive to noneruptive dikes is large in Hawai‘i, compared to other basaltic volcanoes (in Iceland, for example), because Hawaiian dikes tend to be intruded with high driving pressures. Passive dike intrusions also occur, motivated at Kīlauea by rift opening in response to seaward slip of the volcano’s south flank.

Metallogeny by Trans-magmatic Fluids—Theoretical Analysis and Field Evidence

NASA Astrophysics Data System (ADS)

Luo, Zhaohua; Mo, Xuanxue; Lu, Xinxiang; Chen, Bihe; Ke, Shan; Hou, Zengqian; Jiang, Wan

This paper is aimed at introducing and developing the principle of Metallogenic Theory through Trans-magmatic Fluids (MTTF) proposed by the Russian Kozhinskii's school. Some fundamental problems of metallogeny are discussed on geodynamic bases. In this theory, the trans-magmatic fluid is interpreted as a moving fluid passing through magma which is not yet consolidated. The intensive wallrock alteration of most of hydrothermal ore systems suggests that large scale fluid flow accompanies metallogenesis. However, geological observations and experiments imply a very limited solubility of fluids in magmas. In addition, the close relationship between small igneous bodies and large ore systems together with the difficulty of fluids that from the wallrocks might enter a magmatic body, which is under high pressure and temperature, need also to be considered. Those ore-bearing fluids that originate from a deep fluid system, are independent of magmas. Experiments show rapid increases of the solubility of ore-forming elements or their compounds in hydrothermal fluids. Therefore, the essential prerequisites for mineralization are (1) large volumes of deep ore-bearing fluids with high concentration of metals, and (2) the large amounts of metal accumulation depend on the rapid ascent of the deep ore-bearing fluid. Magmas are the favorable medium for the ascending fluids, because these magmas provide conditions that prevent re-equilibrium between the fluid and the wallrocks at different deep levels. The fluids in turn, may provide the driving force for the rapid ascent of magmas. Therefore, the two systems act together to account for the close relationship between magmatism and metallogeny. According to this theory, the scale and location of an ore-forming process are decided by (1) the volumetric ratio of the magma and the fluid systems, (2) the ascending rate of the ore-bearing fluid, (3) the boundary conditions for metal accumulation and (4) the segregation of the fluid from the magma. The field investigations of copper-bearing Melanocratic Macrogranular Enclaves (MME) in the Qushui massif, Gangdise belt are very helpful for understanding of source, transport and precipitation of ore-forming materials. In this example, it can be seen that fluid-rich MMEs is the source of the ore-forming element copper. Copper is transported out from MMEs by the fluid, following dispersal in the granitic magma. The copper-bearing fluid is then transferred through the magma and induced to deposit mineralization elsewhere. These processes have been noted when comparing the metallogenic features in both MME in the Qushui massif and the porphyry copper deposits in Yulong, eastern Tibet. It is obvious that MTTF is a very important theory for metallogeny of endogenic deposits. Using this theory, many paradoxes in metallogenesis can be interpreted in easier manner.

The heartbeat of the volcano: The discovery of episodic activity at Prometheus on Io

USGS Publications Warehouse

Davies, A.G.; Wilson, L.; Matson, D.; Leone, G.; Keszthelyi, L.; Jaeger, W.

2006-01-01

The temporal signature of thermal emission from a volcano is a valuable clue to the processes taking place both at and beneath the surface. The Galileo Near Infrared Mapping Spectrometer (NIMS) observed the volcano Prometheus, on the jovian moon Io, on multiple occasions between 1996 and 2002. The 5 micron (??m) brightness of this volcano shows considerable variation from orbit to orbit. Prometheus exhibits increases in thermal emission that indicate episodic (though non-periodic) effusive activity in a manner akin to the current Pu'u 'O'o-Kupaianaha (afterwards referred to as the Pu'u 'O'o) eruption of Kilauea, Hawai'i. The volume of material erupted during one Prometheus eruption episode (defined as the interval from minimum thermal emission to peak and back to minimum) from 6 November 1996 to 7 May 1997 is estimated to be ???0.8 km3, with a peak instantaneous volumetric flux (effusion rate) of ???140 m3 s-1, and an averaged volumetric flux (eruption rate) of ???49 m3 s-1. These quantities are used to model subsurface structure, magma storage and magma supply mechanisms, and likely magma chamber depth. Prometheus appears to be supplied by magma from a relatively shallow magma chamber, with a roof at a minimum depth of ???2-3 km and a maximum depth of ???14 km. This is a much shallower depth range than sources of supply proposed for explosive, possibly ultramafic, eruptions at Pillan and Tvashtar. As Prometheus-type effusive activity is widespread on Io, shallow magma chambers containing magma of basaltic or near-basaltic composition and density may be common. This analysis strengthens the analogy between Prometheus and Pu'u 'O'o, at least in terms of eruption style. Even though the style of eruption appears to be similar (effusive emplacement of thin, insulated, compound pahoehoe flows) the scale of activity at Prometheus greatly exceeds current activity at Pu'u 'O'o in terms of volume erupted, area covered, and magma flux. Whereas the estimated magma chamber at Prometheus dwarfs the Pu'u 'O'o magma chamber, it fits within expectations if the Pu'u 'O'o chamber were scaled for the greater volumetric flux and lower gravity of Io. Recent volumetric eruption rates derived from Galileo data for Prometheus were considerably smaller than the rate that produced the extensive flows formed in the ???17 years between the Voyager and Galileo missions. These smaller eruption rates, coupled with the fact that flows are not expanding laterally, may mean that the immediate heat source that generates the Prometheus plume is simultaneously running out of available volatiles and the thermal energy that drives mobilization of volatiles. This raises the question of whether the current Prometheus eruption is in its last throes. ?? 2006 Elsevier Inc.

Deep magma transport at Kilauea volcano, Hawaii

USGS Publications Warehouse

Wright, T.L.; Klein, F.W.

2006-01-01

The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5?? and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325??, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0.4 my for Kilauea and 0.8 my for Mauna Loa are consistent with this model. Younger ages would apply if Kilauea began its growth south of the locus of maximum melting, as is true for Loihi seamount. We conclude that Kilauea is fed from below the eastern end of the zone of deep long-period earthquakes. Magma transport is vertical below 30 km, then sub-horizontal, following the oceanic mantle boundary separating plagioclase- and spinel-peridotite, then near-vertical beneath Kilauea's summit. The migration of the melting region within the hotspot and Kilauea's sampling of different sources within the melting region can explain (1) the long-term geochemical separation of Kilauea from neighboring volcanoes Mauna Loa and Loihi, and (2) the short-term changes in trace-element and isotope signatures within Kilauea. ?? 2005 Elsevier B.V. All rigths reserved.

Deep magma transport at Kilauea volcano, Hawaii

NASA Astrophysics Data System (ADS)

Wright, Thomas L.; Klein, Fred W.

2006-03-01

The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5° and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325°, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0.4 my for Kilauea and 0.8 my for Mauna Loa are consistent with this model. Younger ages would apply if Kilauea began its growth south of the locus of maximum melting, as is true for Loihi seamount. We conclude that Kilauea is fed from below the eastern end of the zone of deep long-period earthquakes. Magma transport is vertical below 30 km, then sub-horizontal, following the oceanic mantle boundary separating plagioclase- and spinel-peridotite, then near-vertical beneath Kilauea's summit. The migration of the melting region within the hotspot and Kilauea's sampling of different sources within the melting region can explain (1) the long-term geochemical separation of Kilauea from neighboring volcanoes Mauna Loa and Loihi, and (2) the short-term changes in trace-element and isotope signatures within Kilauea.

Is plagioclase removal responsible for the negative Eu anomaly in the source regions of mare basalts

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

Shearer, C.K.; Papike, J.J.

1989-12-01

The nearly ubiquitous presence of a negative Eu anomaly in the mare basalts has been suggested to indicate prior separation and flotation of plagioclase from the basalt source region during its crystallization from a lunar magma ocean (LMO). Are there any mare basalts derived from a mantle source which did not experience prior plagioclase separation Crystal chemical rationale for REE substitution in pyroxene suggests that the combination of REE size and charge, M2 site characteristics of pyroxene, fO{sub 2}, magma chemistry, and temperature may account for the negative Eu anomaly in the source region of some types of primitive, lowmore » TiO{sub 2} mare basalts. This origin for the negative Eu anomaly does not preclude the possibility of the LMO as many mare basalts still require prior plagioclase crystallization and separation and/or hybridization involving a KREEP component.« less

Late Neoproterozoic to Carboniferous genesis of A-type magmas in Avalonia of northern Nova Scotia: repeated partial melting of anhydrous lower crust in contrasting tectonic environments

NASA Astrophysics Data System (ADS)

Murphy, J. Brendan; Shellnutt, J. Gregory; Collins, William J.

2018-03-01

Avalonian rocks in northern mainland Nova Scotia are characterized by voluminous 640-600 Ma calc-alkalic to tholeiitic mafic to felsic magmas produced in a volcanic arc. However, after the cessation of arc activity, repeated episodes of felsic magmatism between ca. 580 Ma and 350 Ma are dominated by A-type geochemical characteristics. Sm-Nd isotopic data, combined with zircon saturation temperature estimates, indicate that these magmas were formed by high temperature (800-1050 °C) melting of the same anhydrous crustal source. Regional tectonic considerations indicate that A-type felsic magmatism was produced (1) at 580 Ma in a San Andreas-type strike slip setting, (2) at 495 Ma as Avalonia rifted off Gondwana, (3) at 465 and 455 in an ensialic island arc environment and (4) at 360-350 Ma during post-collisional, intra-continental strike-slip activity as Avalonia was translated dextrally along the Laurentian margin. These results attest to the importance of crustal source, rather than tectonic setting, in the generation of these A-type magmas and are an example of how additional insights are provided by comparing the geochemical and isotopic characteristics of igneous suites of different ages within the same terrane. They also suggest that the shallow crustal rocks in northern mainland Nova Scotia were not significantly detached from their lower crustal source between ca. 620 Ma and 350 Ma, a time interval that includes the separation of Avalonia from Gondwana, its drift and accretion to Laurentia as well as post-accretionary strike-slip displacement.

Imaging irregular magma reservoirs with InSAR and GPS observations: Application to Kilauea and Copahue volcanoes

NASA Astrophysics Data System (ADS)

Lundgren, P.; Camacho, A.; Poland, M. P.; Miklius, A.; Samsonov, S. V.; Milillo, P.

2013-12-01

The availability of synthetic aperture radar (SAR) interferometry (InSAR) data has increased our awareness of the complexity of volcano deformation sources. InSAR's spatial completeness helps identify or clarify source process mechanisms at volcanoes (i.e. Mt. Etna east flank motion; Lazufre crustal magma body; Kilauea dike complexity) and also improves potential model realism. In recent years, Bayesian inference methods have gained widespread use because of their ability to constrain not only source model parameters, but also their uncertainties. They are computationally intensive, however, which tends to limit them to a few geometrically rather simple source representations (for example, spheres). An alternative approach involves solving for irregular pressure and/or density sources from a three-dimensional (3-D) grid of source/density cells. This method has the ability to solve for arbitrarily shaped bodies of constant absolute pressure/density difference. We compare results for both Bayesian (a Markov chain Monte Carlo algorithm) and the irregular source methods for two volcanoes: Kilauea, Hawaii, and Copahue, Argentina-Chile border. Kilauea has extensive InSAR and GPS databases from which to explore the results for the irregular method with respect to the Bayesian approach, prior models, and an extensive set of ancillary data. One caveat, however, is the current restriction in the irregular model inversion to volume-pressure sources (and at a single excess pressure change), which limits its application in cases where sources such as faults or dikes are present. Preliminary results for Kilauea summit deflation during the March 2011 Kamoamoa eruption suggests a northeast-elongated magma body lying roughly 1-1.5 km below the surface. Copahue is a southern Andes volcano that has been inflating since early 2012, with intermittent summit eruptive activity since late 2012. We have an extensive InSAR time series from RADARSAT-2 and COSMO-SkyMed data, although both are from descending tracks. Preliminary modeling suggests a very irregular magma body that extends from the volcanic edifice to less than 5 km depth and located slightly north of the summit at shallow depths but to the ENE at greater depths. In our preliminary analysis, we find that there are potential limitations and trade-offs in the Bayesian results that suggest the simplicity of the assumed analytic source may generate systematic biases in source parameters. Instead, the irregular 3-D solution appears to provide greater realism, but is limited in the number and type of sources that can be modeled.

On the plumbing system of volcanic complexes: field constraints from the Isle of Skye (UK) and FEM elasto-plastic modelling including gravity and tectonics.

NASA Astrophysics Data System (ADS)

Bistacchi, A.; Pisterna, R.; Romano, V.; Rust, D.; Tibaldi, A.

2009-04-01

The plumbing system that connects a sub-volcanic magma reservoir to the surface has been the object of field characterization and mechanical modelling efforts since the pioneering work by Anderson (1936), who produced a detailed account of the spectacular Cullin Cone-sheet Complex (Isle of Skye, UK) and a geometrical and mechanical model aimed at defining the depth to the magma chamber. Since this work, the definition of the stress state in the half space comprised between the magma reservoir and the surface (modelled either as a flat surface or a surface comprising a volcanic edifice) was considered the key point in reconstructing dike propagation paths from the magma chamber. In fact, this process is generally seen as the propagation in an elastic media of purely tensional joints (mode I or opening mode propagation), which follow trajectories perpendicular to the least compressive principal stress axis. Later works generally used different continuum mechanics methodologies (analytic, BEM, FEM) to solve the problem of a pressure source (the magma chamber, either a point source or a finite volume) in an elastic (in some cases heterogeneous) half space (bounded by a flat topography or topped by a "volcano"). All these models (with a few limited exceptions) disregard the effect of the regional stress field, which is caused by tectonic boundary forces and gravitational body load, and consider only the pressure source represented by the magma chamber (review in Gudmundsson, 2006). However, this is only a (sometimes subordinate) component of the total stress field. Grosfils (2007) first introduced the gravitational load (but not tectonic stresses) in an elastic model solved with FEM in a 2D axisymmetric half-space, showing that "failure to incorporate gravitational loading correctly" affect the calculated stress pattern and many of the predictions that can be drawn from the models. In this contribution we report on modelling results that include: 2D axisymmetric or true 3D geometry; gravitational body load; anisotropic tectonic stresses; different shapes and depths of the magma chamber; different overpressure levels in the magma chamber; different shapes of the topographic surface (e.g. flat, volcano, caldera); linear-elastic or elasto-plastic Drucker-Prager rheology. The latter point, which in our opinion constitutes a fundamental improvement in the model, has proven necessary because in a purely elastic model the stress state would rise at levels that cannot be sustained by geologic materials. Particularly around and above the magma chamber, yielding is expected, influencing the stress field in the remaining modelling domain. The non-linear problem has been solved with the commercial finite element package Comsol Multiphysics, using a parametric solver. At the same time, a field structural analysis of the classical Cuillin Cone-sheet Complex has been performed. This analysis has shown that four distinct families of cone sheets of different age do exist. Among these, the sheets with the higher dip angle range (80-65°) are confirmed as purely tensional joints, but those with a lower dip angle range (60-40°) are quite often (when suitable markers are available) associated with a measurable shear component. Combining these new field observations with mechanical modelling results, we propose a new interpretation for the Cuillin Cone Sheet Complex. The plumbing system was composed by both purely tensional joints and mesoscopic faults with a shear component, produced in response to the regional stress field perturbed by the magma chamber, and later passively re-used as magma emplacement conduits. Under this assumption, the observed geometry of the Cuillin Cone-sheet Complex is consistent with a relatively shallow magma chamber with a flattened laccolite shape. The shape of the palaeotopography, now completely eroded, has also been considered, but is more weakly constrained by modelling results. References: Anderson E.M., 1936. The dynamics of the formation of cone-sheets, ring-dykes and cauldron subsidences. Proc R Soc Edinburgh, 56, 128-157. Grosfils E.B., 2007. Magma reservoir failure on the terrestrial planets: Assessing the importance of gravitational loading in simple elastic models. Journal of Volcanology and Geothermal Research, 166 (2), 47-75. Gudmundsson A. , 2006. How local stresses control magma-chamber ruptures, dyke injections, and eruptions in composite volcanoes. Earth Science Reviews, 79 (1), 1-31.

Association of Sub-continental and Asthenosphere related Volcanism in NW Iran,Implication forMantle thermal perturbation induced by slab break off and collision event

NASA Astrophysics Data System (ADS)

Jahangiri, A.

2017-12-01

Cenozoic magmatic rocks occur extensively in the north of the Zagros suture zone and constitute a significant component of the continental crust in this segment of the Alpine-Himalayan orogenic belt. They range in age from Eocene to quaternary. Miocene to Plio-Quaternary volcanism with post-collisional related significant is covered vast areas in NW Iran. These volcanic rocks can be divided into three different sub-groups on the basis of their mineralogy, geochemistry and magma sources including: 1. alkaline leucite-bearing mafic rocks, which are characterized with high ratios of K2O/Na2O, high content LILE and low HFS elements like Ti, Nb and Ta. They are display fractionated REE patterns and based on different discrimination diagrams show similarity with subduction related magmas. 2- Olivine basalt to trachy-basaltic samples which shows similarity to within plate basalts with high content of TiO2, Nb, Ta and fractionated REE pattern. However, compared with a global average of OIB, they are display slightly higher LIL elements and lower HFS elements concentrations, features that resemble to the arc magmas and suggest that the source of the magmas may have been contaminated by slab-derived fluids. These rocks have simple mineralogical composition with plagioclase, clinopyroxene and olivine. 3- Dominant dacitic volcanic rocks with adakitic geochemical characteristics such as highly fractionate REE pattern and high Sr/Y ratio. Generation of adakitic magmas can be related to increased temperatures in the subduction zone due to mantle upwelling and slab tearing. Subsequent asthenospheric upwelling could be caused direct melting of sub-continental mantle to produce the alkaline magmas, with high contents of K2O, MgO and volatile rich phase's potassic magmas that led to crystallization of leucite, phlogopite, apatite and olivine in studied samples. Rupture of the continental lithosphere by strike-slip-related transtensional deformation might have caused decompression partial melting of the asthenospheric mantle and generating alkali basalts. Continental lithosphere rupturing is occurred subsequent to slab breakoff/delamination and sub-continental mantle thermal perturbation processes following closure of Neo-Tethys and collision of Arabian plate with microplate of Iran.

Transfer Rates of Magma From Planetary Mantles to the Surface.

NASA Astrophysics Data System (ADS)

Wilson, L.; Head, J. W.; Parfitt, E. A.

2008-12-01

We discuss the speed at which magma can be transferred to a planetary surface from the deep interior. Current literature describes a combination of slow percolation of melt in the mantle where convection-driven pressure-release melting is occurring, concentration of melt by source region deformation, initiation and growth of magma-filled brittle fractures (dikes) providing wider pathways for melt movement, additional growth and interconnection of dikes with decreasing depth, rise of magma to storage zones (reservoirs) located at levels of neutral buoyancy at the base of or within the crust, and transfer from the storage zones in dikes to feed eruptions or intrusions. We do not take issue with these mechanisms but think that their relative importance in various circumstances is poorly appreciated. On Earth, preservation of diamonds in kimberlites implies very rapid (hours) transfer of melts from depths of 100-300 km, and there is strong geochemical evidence that magmas at mid-ocean ridges reach shallow depths faster than is possible by percolation alone. On the Moon, the petrology of pyroclasts involved in dark-mantle-forming eruptions implies rapid (again probably hours) magma transfer from depths of up to 400 km. The ureilite meteorites, samples of the mantle of a disrupted asteroid 200 km in diameter, have compositions only consistent with the rapid (months) extraction of mafic melt from the mantle. All of these examples imply that brittle fractures (dikes) can sometimes be initiated at depths where mantle rheology would normally be expected to be plastic rather than elastic, and that melt can be fed into these dikes extremely efficiently. Further evidence for this is provided by the giant radial dike swarms observed on Earth, Mars and Venus. The dikes observed (on Earth) and inferred from the presence of radiating graben systems (Mars) and radiating fracture and graben systems (Venus) are so voluminous that they can only be understood if they are fed from extremely large magma reservoirs, probably located at the base of the crust, that are supplied from the mantle (i.e. buffered) while the dikes are being emplaced, again implying extremely efficient melt extraction from mantle source regions.

From a long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)

NASA Astrophysics Data System (ADS)

Buret, Yannick; von Quadt, Albrecht; Heinrich, Christoph; Selby, David; Wälle, Markus; Peytcheva, Irena

2016-09-01

The formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system, which provides the source of porphyry magmas, as well as metal and sulphur-charged mineralising fluids. Reading the geochemical record of this large magmatic source region, as well as constraining the time-scales for creating a much smaller porphyry copper deposit, are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits. This study focuses on the Bajo de la Alumbrera porphyry copper deposit in Northwest Argentina. The deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections. To constrain the duration of ore formation, we dated zircons from four porphyry intrusions, including pre-, syn- and post-mineralisation porphyries based on intersection relations between successive intrusion and vein generations, using high precision CA-ID-TIMS. Based on the youngest assemblages of zircon grains, which overlap within analytical error, all four intrusions were emplaced within 29 ka, which places an upper limit on the total duration of hydrothermal mineralisation. Re/Os dating of hydrothermal molybdenite fully overlaps with this high-precision age bracket. However, all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the ∼200 ka preceding the emplacement of the porphyries. Zircon trace element variations, Ti-in-zircon temperatures, and Hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history, and that the four intrusions were derived from the same upper-crustal magma chamber. Trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation. However, zircon cathodoluminescence imaging reveals the presence of intermediate low luminescent (dark) growth zones in many crystals from all intrusions, characterised by anomalously high Th, U and REE concentrations and transient excursions in trace element ratios. A return to the same fractionation trend after this excursion excludes external compositional forcing such as magma mixing. Instead we interpret the ;dark-zones; to record zircon crystallisation during a transient event of rapid growth that resulted from mafic magma injection into the base of the magma chamber, releasing a CO2-rich vapour phase into the dacitic crystal mush. We propose that this vapour phase then migrated upwards to the apical part of the magma chamber from where it was expelled, together with successive batches of magma, to form the porphyry copper deposit within a short time-span of less than a few 10,000 years. The short duration of host rock emplacement, hydrothermal alteration and mineralisation presented in this study provides critical constraints on fluid storage in magma chambers and the genesis of large porphyry copper deposits.

Highly differentiated subalkaline rhyolite from Glass Mountain, Mono County, California.

NASA Technical Reports Server (NTRS)

Noble, D. C.; Korringa, M. K.; Hedge, C. E.; Riddle, G. O.

1972-01-01

Available data on the partition of Sr between coexisting feldspar and melt phases re interpreted as an indication that a rhyolite from Glass Mountain represents about 25% of a hypothetical 'parent' magma of silicic composition having a norm ntent of 150 ppm. Available Sr and Pb isotope data on nearby Pleistocene rhyolite lavas suggest that the 'parent' magmas of volcanic rocks of the area came from mafic or ultramafic source marl.

Making rhyolite in a basalt crucible

NASA Astrophysics Data System (ADS)

Eichelberger, John

2016-04-01

Iceland has long attracted the attention of those concerned with the origin of rhyolitic magmas and indeed of granitic continental crust, because it presents no alternative for such magmas other than deriving them from a basaltic source. Hydrothermally altered basalt has been identified as the progenitor. The fact that rhyolite erupts as pure liquid requires a process of melt-crustal separation that is highly efficient despite the high viscosity of rhyolite melt. Volcanoes in Iceland are foci of basaltic magma injection along the divergent plate boundary. Repeated injection produces remelting, digestion, and sometimes expulsion or lateral withdrawal of material resulting in a caldera, a "crucible" holding down-dropped and interlayered lava flows, tephras, and injected sills. Once melting of this charge begins, a great deal of heat is absorbed in the phase change. Just 1% change in crystallinity per degree gives a melt-present body an effective heat capacity >5 times the subsolidus case. Temperature is thus buffered at the solidus and melt composition at rhyolite. Basalt inputs are episodic ("fires") so likely the resulting generation of rhyolite by melting is too. If frequent enough to offset cooling between events, rhyolite melt extractions will accumulate as a rhyolite magma reservoir rather than as discrete crystallized sills. Evidently, such magma bodies can survive multiple firings without themselves erupting, as the 1875 eruption of Askja Caldera of 0.3 km3 of rhyolite equilibrated at 2-km depth without previous leakage over a ten-millennium period and the surprise discovery of rhyolite magma at 2-km depth in Krafla suggest. Water is required for melting; otherwise melting cannot begin at a temperature lower than that of the heat source. Because the solubility of water in melt is pressure-dependent and almost zero at surface pressure, there must be a minimum depth at which basalt-induced melting can occur and a rhyolite reservoir sustained. In practice, the storage limit is likely near 2-km depth at which IDDP-1 and other Krafla boreholes encountered rhyolite melt. Rearrangement of components within the crucible during brewing produces little in terms of a gravity or deformation signals, hence the surprise in finding newly intruded magma. Below 2 km much of the charge in the crucible is near the basalt solidus, so that pockets, sills, and chambers of near-liquidus rhyolite magma will all be close to thermal and chemical equilibrium. Heat is advected upwards from the mantle first by basalt to the crucible, then by rhyolite magma within the crucible, then by hydrothermal fluid to the surface. A major portion of the thermal energy is stored as latent heat of crystallization of rhyolite magma. Such a view challenges some basic tenets of volcano hazard assessment and geothermal energy. The Krafla Magma Drilling Project of the International Continental Scientific Drilling Program will provide a critical test in 2017 by coring from subsolidus granite to liquidus rhyolite, wherein the transitions of heat advection by hydrothermal fluid, to heat conduction, to heat advection by rhyolite magma must occur.

Occurrence, Source, and Human Infection Potential of Cryptosporidium and Giardia spp. in Source and Tap Water in Shanghai, China▿

PubMed Central

Feng, Yaoyu; Zhao, Xukun; Chen, Jiaxu; Jin, Wei; Zhou, Xiaonong; Li, Na; Wang, Lin; Xiao, Lihua

2011-01-01

Genotyping studies on the source and human infection potential of Cryptosporidium oocysts in water have been almost exclusively conducted in industrialized nations. In this study, 50 source water samples and 30 tap water samples were collected in Shanghai, China, and analyzed by the U.S. Environmental Protection Agency (EPA) Method 1623. To find a cost-effective method to replace the filtration procedure, the water samples were also concentrated by calcium carbonate flocculation (CCF). Of the 50 source water samples, 32% were positive for Cryptosporidium and 18% for Giardia by Method 1623, whereas 22% were positive for Cryptosporidium and 10% for Giardia by microscopy of CCF concentrates. When CCF was combined with PCR for detection, the occurrence of Cryptosporidium (28%) was similar to that obtained by Method 1623. Genotyping of Cryptosporidium in 17 water samples identified the presence of C. andersoni in 14 water samples, C. suis in 7 water samples, C. baileyi in 2 water samples, C. meleagridis in 1 water sample, and C. hominis in 1 water sample. Therefore, farm animals, especially cattle and pigs, were the major sources of water contamination in Shanghai source water, and most oocysts found in source water in the area were not infectious to humans. Cryptosporidium oocysts were found in 2 of 30 tap water samples. The combined use of CCF for concentration and PCR for detection and genotyping provides a less expensive alternative to filtration and fluorescence microscopy for accurate assessment of Cryptosporidium contamination in water, although the results from this method are semiquantitative. PMID:21498768

Evaluation of Kilauea Eruptions By Using Stable Isotope Analysis

NASA Astrophysics Data System (ADS)

Rahimi, K. E.; Bursik, M. I.

2016-12-01

Kilauea, on the island of Hawaii, is a large volcanic edifice with numerous named vents scattered across its surface. Halema`uma`u crater sits with Kilauea caldera, above the magma reservoir, which is the main source of lava feeding most vents on Kilauea volcano. Halema`uma`u crater produces basaltic explosive activity ranging from weak emission to sub-Plinian. Changes in the eruption style are thought to be due to the interplay between external water and magma (phreatomagmatic/ phreatic), or to segregation of gas from magma (magmatic) at shallow depths. Since there are three different eruption mechanisms (phreatomagmatic, phreatic, and magmatic), each eruption has its own isotope ratios. The aim of this study is to evaluate the eruption mechanism by using stable isotope analysis. Studying isotope ratios of D/H and δ18O within fluid inclusion and volcanic glass will provide an evidence of what driven the eruption. The results would be determined the source of water that drove an eruption by correlating the values with water sources (groundwater, rainwater, and magmatic water) since each water source has a diagnostic value of D/H and δ18O. These results will provide the roles of volatiles in eruptions. The broader application of this research is that these methods could help volcanologists forecasting and predicting the current volcanic activity by mentoring change in volatiles concentration within deposits.

Source investigation of two outbreaks of skin and soft tissue infection by Mycobacterium abscessus subsp. abscessus in Venezuela.

PubMed

Torres-Coy, J A; Rodríguez-Castillo, B A; Pérez-Alfonzo, R; DE Waard, J H

2016-04-01

Outbreaks of soft tissue or skin infection due to non-tuberculous mycobacteria are reported frequently in scientific journals but in general the infection source in these outbreaks remains unknown. In Venezuela, in two distinct outbreaks, one after breast augmentation surgery and another after hydrolipoclasy therapy, 16 patients contracted a soft tissue infection due to Mycobacterium abscessus subsp. abscessus. Searching for the possible environmental infection sources in these outbreaks, initially the tap water (in the hydrolipoclasy therapy outbreak) and a surgical skin marker (in the breast implant surgery outbreak), were identified as the infection sources. Molecular typing of the strains with a variable number tandem repeat typing assay confirmed the tap water as the infection source but the molecular typing technique excluded the skin marker. We discuss the results and make a call for the implementation of stringent hygiene and disinfection guidelines for cosmetic procedures in Venezuela.

Magma Reservoirs Feeding Giant Radiating Dike Swarms: Insights from Venus

NASA Technical Reports Server (NTRS)

Grosfils, E. B.; Ernst, R. E.

2003-01-01

Evidence of lateral dike propagation from shallow magma reservoirs is quite common on the terrestrial planets, and examination of the giant radiating dike swarm population on Venus continues to provide new insight into the way these complex magmatic systems form and evolve. For example, it is becoming clear that many swarms are an amalgamation of multiple discrete phases of dike intrusion. This is not surprising in and of itself, as on Earth there is clear evidence that formation of both magma reservoirs and individual giant radiating dikes often involves periodic magma injection. Similarly, giant radiating swarms on Earth can contain temporally discrete subswarms defined on the basis of geometry, crosscutting relationships, and geochemical or paleomagnetic signatures. The Venus data are important, however, because erosion, sedimentation, plate tectonic disruption, etc. on Earth have destroyed most giant radiating dike swarm's source regions, and thus we remain uncertain about the geometry and temporal evolution of the magma sources from which the dikes are fed. Are the reservoirs which feed the dikes large or small, and what are the implications for how the dikes themselves form? Does each subswarm originate from a single, periodically reactivated reservoir, or do subswarms emerge from multiple discrete geographic foci? If the latter, are these discrete foci located at the margins of a single large magma body, or do multiple smaller reservoirs define the character of the magmatic center as a whole? Similarly, does the locus of magmatic activity change with time, or are all the foci active simultaneously? Careful study of giant radiating dike swarms on Venus is yielding the data necessary to address these questions and constrain future modeling efforts. Here, using giant radiating dike swarms from the Nemesis Tessera (V14) and Carson (V43) quadrangles as examples, we illustrate some of the dike swarm focal region diversity observed on Venus and briefly explore some key implications for the questions framed above.

Petrogenesis of coeval sodic and potassic alkaline magmas at Spanish Peaks, Colorado: Magmatism related to the opening of the Rio Grande rift

NASA Astrophysics Data System (ADS)

Lord, A. Brooke Hamil; McGregor, Heath; Roden, Michael F.; Salters, Vincent J. M.; Sarafian, Adam; Leahy, Rory

2016-07-01

Approximately coeval, relatively primitive (∼5-10% MgO with exception of a trachyandesite) alkaline mafic dikes and sills at or near Spanish Peaks, CO are divided into relatively sodic and potassic varieties on the basis of K2O/Na2O. Many of these dikes are true lamprophyres. In spite of variable alkali element ratios, the alkaline rocks share a number of geochemical similarities: high LIL element contents, high Ba and similar Sr, Nd and Hf isotope ratios near that of Bulk Earth. One important difference is that the potassic rocks are characterized by lower Al2O3 contents, typically less than 12 wt.%, than the sodic dikes/sills which typically have more than 13 wt.% Al2O3, and this difference is independent of MgO content. We attribute the distinct Al2O3 contents to varying pressure during melting: a mica-bearing, Al-poor vein assemblage for the potassic magmas melted at higher pressure than an aluminous amphibole-bearing vein assemblage for the sodic magmas. Remarkable isotopic and trace element similarities with approximately contemporaneous, nearby Rio Grande rift-related basalts in the San Luis Valley, indicate that the magmatism at Spanish Peaks was rift-related, and that lithosphere sources were shared between some rift magmas and those at Spanish Peaks. High Zn/Fe ratios in the Spanish Peaks mafic rocks point to a clinopyroxene- and garnet-rich source such as lithosphere veined by pyroxenite or eclogite. Lithospheric melting was possibly triggered by foundering of cool, dense lithosphere beneath the Rio Grande rift during the initiation of rifting with the potassic parent magmas generated by higher pressure melting of the foundered lithosphere than the sodic parent magmas. This process, caused by gravitational instability of the lithosphere (Elkins-Tanton, 2007) may be common beneath active continental rifts.

Two mantle sources, two plumbing systems: Tholeiitic and alkaline magmatism of the Maymecha River basin, Siberian flood volcanic province

USGS Publications Warehouse

Arndt, N.; Chauvel, C.; Czamanske, G.; Fedorenko, V.

1998-01-01

Rocks of two distinctly different magma series are found in a ???4000-m-thick sequence of lavas and tuffs in the Maymecha River basin which is part of the Siberian flood-volcanic province. The tholeiites are typical low-Ti continental flood basalts with remarkably restricted, petrologically evolved compositions. They have basaltic MgO contents, moderate concentrations of incompatible trace elements, moderate fractionation of incompatible from compatible elements, distinct negative Ta(Nb) anomalies, and ??Nd values of 0 to + 2. The primary magmas were derived from a relatively shallow mantle source, and evolved in large crustal magma chambers where they acquired their relatively uniform compositions and became contaminated with continental crust. An alkaline series, in contrast, contains a wide range of rock types, from meymechite and picrite to trachytes, with a wide range of compositions (MgO from 0.7 to 38 wt%, SiO2 from 40 to 69 wt%, Ce from 14 to 320 ppm), high concentrations of incompatible elements and extreme fractionation of incompatible from compatible elements (Al2O3/TiO2 ??? 1; Sm/Yb up to 11). These rocks lack Ta(Nb) anomalies and have a broad range of ??Nd values, from -2 to +5. The parental magmas are believed to have formed by low-degree melting at extreme mantle depths (>200 km). They bypassed the large crustal magma chambers and ascended rapidly to the surface, a consequence, perhaps, of high volatile contents in the primary magmas. The tholeiitic series dominates the lower part of the sequence and the alkaline series the upper part; at the interface, the two types are interlayered. The succession thus provides evidence of a radical change in the site of mantle melting, and the simultaneous operation of two very different crustal plumbing systems, during the evolution of this flood-volcanic province. ?? Springer-Verlag 1998.

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.

Perfluoroalkyl acids (PFAAs) in the Pra and Kakum River basins and associated tap water in Ghana.

PubMed

Essumang, David K; Eshun, Albert; Hogarh, Jonathan N; Bentum, John K; Adjei, Joseph K; Negishi, Junya; Nakamichi, Shihori; Habibullah-Al-Mamun, Md; Masunaga, Shigeki

2017-02-01

Perfluoroalkyl acids (PFAAs) are persistent environmental pollutants that have been detected in various media including human serum. Due to concerns regarding their bioaccumulation and possible negative health effects, an understanding of routes of human exposure is necessary. PFAAs are recalcitrant in many water treatment processes, making drinking water a potential source of human exposure. This study presents the first report on contamination from PFAAs in river and drinking water in Ghana. The targeted PFAAs were perfluoroalkyl carboxylic acids (PFCAs) with C 4-14 carbon chain and perfluoroalkane sulphonic acids (PFSAs) with C 6, 8, 10 . Five PFAA congeners - PFOA, PFOS, PFHxA, PFDA and PFPeA - were commonly detected in river and tap water. The mean concentrations of ∑PFAAs in the Kakum and Pra Rivers were 281 and 398ng/L, while tap water (supplied from the treatment of water from those rivers) contained concentrations of 197 and 200ng/L, respectively. PFOA and PFOS constituted about 99% of the ∑PFAAs. The risk quotient (RQ) attributed to drinking of tap water was estimated at 1.01 and 1.74 for PFOA and PFOS, respectively. For a country that has not produced these compounds, the RQs were unexpectedly high, raising concerns particularly about contamination from such emerging pollutants in local water sources. The study revealed limitations of local tap water treatment in getting rid of these emerging pollutants. Copyright © 2016 Elsevier B.V. All rights reserved.

Perceptional and socio-demographic factors associated with household drinking water management strategies in rural Puerto Rico.

PubMed

Jain, Meha; Lim, Yili; Arce-Nazario, Javier A; Uriarte, María

2014-01-01

Identifying which factors influence household water management can help policy makers target interventions to improve drinking water quality for communities that may not receive adequate water quality at the tap. We assessed which perceptional and socio-demographic factors are associated with household drinking water management strategies in rural Puerto Rico. Specifically, we examined which factors were associated with household decisions to boil or filter tap water before drinking, or to obtain drinking water from multiple sources. We find that households differ in their management strategies depending on the institution that distributes water (i.e. government PRASA vs community-managed non-PRASA), perceptions of institutional efficacy, and perceptions of water quality. Specifically, households in PRASA communities are more likely to boil and filter their tap water due to perceptions of low water quality. Households in non-PRASA communities are more likely to procure water from multiple sources due to perceptions of institutional inefficacy. Based on informal discussions with community members, we suggest that water quality may be improved if PRASA systems improve the taste and odor of tap water, possibly by allowing for dechlorination prior to distribution, and if non-PRASA systems reduce the turbidity of water at the tap, possibly by increasing the degree of chlorination and filtering prior to distribution. Future studies should examine objective water quality standards to identify whether current management strategies are effective at improving water quality prior to consumption.

Perceptional and Socio-Demographic Factors Associated with Household Drinking Water Management Strategies in Rural Puerto Rico

PubMed Central

Jain, Meha; Lim, Yili; Arce-Nazario, Javier A.; Uriarte, María

2014-01-01

Identifying which factors influence household water management can help policy makers target interventions to improve drinking water quality for communities that may not receive adequate water quality at the tap. We assessed which perceptional and socio-demographic factors are associated with household drinking water management strategies in rural Puerto Rico. Specifically, we examined which factors were associated with household decisions to boil or filter tap water before drinking, or to obtain drinking water from multiple sources. We find that households differ in their management strategies depending on the institution that distributes water (i.e. government PRASA vs community-managed non-PRASA), perceptions of institutional efficacy, and perceptions of water quality. Specifically, households in PRASA communities are more likely to boil and filter their tap water due to perceptions of low water quality. Households in non-PRASA communities are more likely to procure water from multiple sources due to perceptions of institutional inefficacy. Based on informal discussions with community members, we suggest that water quality may be improved if PRASA systems improve the taste and odor of tap water, possibly by allowing for dechlorination prior to distribution, and if non-PRASA systems reduce the turbidity of water at the tap, possibly by increasing the degree of chlorination and filtering prior to distribution. Future studies should examine objective water quality standards to identify whether current management strategies are effective at improving water quality prior to consumption. PMID:24586302

Episodic trace element and isotopic variations in historical Mauna Loa Lavas: Implications for magma and plume dynamics

NASA Astrophysics Data System (ADS)

Rhodes, J. M.; Hart, S. R.

Over the past 152 years, Mauna Loa volcano has erupted lavas with almost constant major element, and compatible and moderately incompatible trace element abundances at a given MgO content. This uniformity is attributed to continuing replenishment of a shallow magma reservoir. In contrast, incompatible element abundances and ratios, together with Sr, Nd and Pb isotopic ratios, vary systematically with time. The greatest rate of change occurred at a time (1843-1887) when Mauna Loa was vigorously active with high eruption rates, presumably a consequence of a high magma supply rate. Detailed analysis confirms what is evident from the isotopic data: that this open-system magmatism requires two or more parental magmas. One has the compositional attributes of lavas erupted in 1843, the other the characteristics of lavas erupted at the summit early in 1880. All other historical lavas can be considered as mixtures of these two end-members, modified by contemporaneous eruption and olivine crystallization. Both parental magmas have Sr, Pb and Nd isotopic ratios typical of magmas in the Hawaiian tholeiitic array, and intermediate between those of Kilauea and Koolau lavas, the end-members of the array. The 1843 parental magma has incompatible element ratios that are similar to, and overlap with the Koolau and Kilauea data. The inferred 1880 parental magma, however, is more depleted than the 1843 parental magma (and most other Hawaiian lavas), and is also isotopically closer to the Kilauea end-member of the tholeiitic array. The origin of these parental magmas is discussed in terms of melting within a radially heterogeneous plume in which the heterogeneity may develop at the source or through subsequent mantle entrainment. Two models are explored, both depend on the location of Mauna Loa at, or close to the plume margin. In the simplest case the parental magmas are produced by progressive melting of the heterogeneous outer plume. The second model is more dynamic, involving melt production and re-equilibration in a diverging, or inclined, plume.

The Central-Western Mediterranean: Anomalous igneous activity in an anomalous collisional tectonic setting

NASA Astrophysics Data System (ADS)

Lustrino, Michele; Duggen, Svend; Rosenberg, Claudio L.

2011-01-01

The central-western Mediterranean area is a key region for understanding the complex interaction between igneous activity and tectonics. In this review, the specific geochemical character of several 'subduction-related' Cenozoic igneous provinces are described with a view to identifying the processes responsible for the modifications of their sources. Different petrogenetic models are reviewed in the light of competing geological and geodynamic scenarios proposed in the literature. Plutonic rocks occur almost exclusively in the Eocene-Oligocene Periadriatic Province of the Alps while relatively minor plutonic bodies (mostly Miocene in age) crop out in N Morocco, S Spain and N Algeria. Igneous activity is otherwise confined to lava flows and dykes accompanied by relatively greater volumes of pyroclastic (often ignimbritic) products. Overall, the igneous activity spanned a wide temporal range, from middle Eocene (such as the Periadriatic Province) to the present (as in the Neapolitan of southern Italy). The magmatic products are mostly SiO 2-oversaturated, showing calcalkaline to high-K calcalcaline affinity, except in some areas (as in peninsular Italy) where potassic to ultrapotassic compositions prevail. The ultrapotassic magmas (which include leucitites to leucite-phonolites) are dominantly SiO 2-undersaturated, although rare, SiO 2-saturated (i.e., leucite-free lamproites) appear over much of this region, examples being in the Betics (southeast Spain), the northwest Alps, northeast Corsica (France), Tuscany (northwest Italy), southeast Tyrrhenian Sea (Cornacya Seamount) and possibly in the Tell region (northeast Algeria). Excepted for the Alpine case, subduction-related igneous activity is strictly linked to the formation of the Mediterranean Sea. This Sea, at least in its central and western sectors, is made up of several young (< 30 Ma) V-shaped back-arc basins plus several dispersed continental fragments, originally in crustal continuity with the European plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle 'wedge' regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO 2 and H 2O in the fluid phase released by the subducting plates are the most important. Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) centrifugal wave of both compressive and extensional tectonics starting from a 'pivotal' region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction 'inversion' events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subduction-related magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related 'exotic' (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the hanging-wall of the Late Cretaceous-Eocene Adria-Europe subduction system in the Alps); i) voluminous production of subduction-related magmas coeval with extensional tectonic régimes (e.g., during Oligo-Miocene Sardinian Trough formation). To summarize, these salient central-western Mediterranean features, characterizing a late-stage of the classic 'Wilson Cycle' offer a 'template' for interpreting magmatic compositions in analogous settings elsewhere.

Molybdenum distributions and variability in drinking water from England and Wales.

PubMed

Smedley, P L; Cooper, D M; Lapworth, D J

2014-10-01

An investigation has been carried out of molybdenum in drinking water from a selection of public supply sources and domestic taps across England and Wales. This was to assess concentrations in relation to the World Health Organization (WHO) health-based value for Mo in drinking water of 70 μg/l and the decision to remove the element from the list of formal guideline values. Samples of treated drinking water from 12 water supply works were monitored up to four times over an 18-month period, and 24 domestic taps were sampled from three of their supply areas. Significant (p < 0.05) differences were apparent in Mo concentration between sources. Highest concentrations were derived from groundwater from a sulphide-mineralised catchment, although concentrations were only 1.5 μg/l. Temporal variability within sites was small, and no seasonal effects (p > 0.05) were detected. Tap water samples collected from three towns (North Wales, the English Midlands, and South East England) supplied uniquely by upland reservoir water, river water, and Chalk groundwater, respectively, also showed a remarkable uniformity in Mo concentrations at each location. Within each, the variability was very small between houses (old and new), between pre-flush and post-flush samples, and between the tap water and respective source water samples. The results indicate that water distribution pipework has a negligible effect on supplied tap water Mo concentrations. The findings contrast with those for Cu, Zn, Ni, Pb, and Cd, which showed significant differences (p < 0.05) in concentrations between pre-flush and post-flush tap water samples. In two pre-flush samples, concentrations of Ni or Pb were above drinking water limits, although in all cases, post-flush waters were compliant. The high concentrations, most likely derived from metal pipework in the domestic distribution system, accumulated during overnight stagnation. The concentrations of Mo observed in British drinking water, in all cases less than 2 μg/l, were more than an order of magnitude below the WHO health-based value and suggest that Mo is unlikely to pose a significant health or water supply problem in England and Wales.

Mesozoic invasion of crust by MORB-source asthenospheric magmas, U.S. Cordilleran interior

NASA Astrophysics Data System (ADS)

Leventhal, Janet A.; Reid, Mary R.; Montana, Art; Holden, Peter

1995-05-01

Mafic and ultramafic xenoliths entrained in lavas of the Cima volcanic field have Nd and Sr isotopic ratios indicative of a source similar to that of mid-ocean ridge basalt (MORB). Nd and Sr internal isochrons demonstrate a Late Cretaceous intrusion age. These results, combined with evidence for emplacement in the lower crust and upper mantle, indicate invasion of the lower crust by asthenospheric magmas in the Late Cretaceous. Constituting the first prima facie evidence for depleted-mantle magmatism in the Basin and Range province prior to late Cenozoic volcanism, these results lend key support to models suggesting crustal heating by ascent of asthenosphere in the Mesozoic Cordilleran interior.

Assimilation by Lunar Mare Basalts: Melting of Crustal Material and Dissolution of Anorthite

NASA Technical Reports Server (NTRS)

Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

1994-01-01

We discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances, kinetic rates, and simple fluid mechanical constraints. Assuming parent magmas of picritic compositions, we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic, troctolitic, noritic, and KREEP (quartz monzodiorite) compositions. Significant melting of the plagioclase-rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt. Even when this occurs, the major element chemistry of the picritic magmas will change by less than 1-2 wt %. Diffusion coefficients measured for Al2O3 from an iron-free basalt and an orange glass composition are 10(exp -12) m(exp 2) s(exp -1) at 1340 C and 10(exp -11) m(exp 2) s(exp -1) at 1390 C. These rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions. Picritic magmas can melt significant quantities of KREEP, which suggests that their trace element chemistry may still be affected by assimilation processes; however, mixing viscous melts of KREEP composition with the fluid picritic magmas could be prohibitively difficult. We conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation/fractional crystallization processes near the lunar surface. Instead, most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle.

Volcán Popocatépetl, Mexico. Petrology, magma mixing, and immediate sources of volatiles for the 1994- Present eruption

USGS Publications Warehouse

Witter, J.B.; Kress, V.C.; Newhall, C.G.

2005-01-01

Volcán Popocatépetl has been the site of voluminous degassing accompanied by minor eruptive activity from late 1994 until the time of writing (August 2002). This contribution presents petrological investigations of magma erupted in 1997 and 1998, including major-element and volatile (S, Cl, F, and H2O) data from glass inclusions and matrix glasses. Magma erupted from Popocatépetl is a mixture of dacite (65 wt % SiO2, two-pyroxenes + plagioclase + Fe–Ti oxides + apatite, ∼3 wt % H2O, P = 1·5 kbar, fO2 = ΔNNO + 0·5 log units) and basaltic andesite (53 wt % SiO2, olivine + two-pyroxenes, ∼3 wt % H2O, P = 1–4 kbar). Magma mixed at 4–6 km depth in proportions between 45:55 and 85:15 wt % silicic:mafic magma. The pre-eruptive volatile content of the basaltic andesite is 1980 ppm S, 1060 ppm Cl, 950 ppm F, and 3·3 wt % H2O. The pre-eruptive volatile content of the dacite is 130 ± 50 ppm S, 880 ± 70 ppm Cl, 570 ± 100 ppm F, and 2·9 ± 0·2 wt % H2O. Degassing from 0·031 km3 of erupted magma accounts for only 0·7 wt % of the observed SO2 emission. Circulation of magma in the volcanic conduit in the presence of a modest bubble phase is a possible mechanism to explain the high rates of degassing and limited magma production at Popocatépetl.

Time dependent model of magma intrusion in and around Miyake and Kozu Islands, Central Japan in June August, 2000

NASA Astrophysics Data System (ADS)

Murase, Masayuki; Irwan, Meilano; Kariya, Shinichi; Tabei, Takao; Okuda, Takashi; Miyajima, Rikio; Oikawa, Jun; Watanabe, Hidefumi; Kato, Teruyuki; Nakao, Shigeru; Ukawa, Motoo; Fujita, Eisuke; Okayama, Muneo; Kimata, Fumiaki; Fujii, Naoyuki

2006-02-01

A time-dependent model of magma intrusion is presented for the Miyake-Kozu Island area in central Japan based on global positioning system (GPS) measurements at 28 sites recorded between June 27 and August 27, 2000. A model derived from a precise hypocenter distribution map indicates the presence of three dikes between Miyake and Kozu Islands. Other dike intrusion models, including a dike with aseismic creep and a dike associated with a deep deflation source are also discussed. The optimal parameters for each model are estimated using a genetic algorithm (GA) approach. Using Akaike's information criteria (AIC), the three-dike model is shown to provide the best solution for the observed deformation. Volume changes in spherical inflation and deflation sources, as well as three dikes, are calculated for seven discretized periods after GA optimization of the dike geometry. The optimization suggests a concentration of dike expansion near Miyake Island in the period from June 27 to July 1 associated with large deflation at a depth of about 7 km below Miyake volcano, indicating magma supply from depth below Miyake Island. In the period from July 9 to August 10, a huge dike intrusion near Kozu Island is inferred, accompanied by expansion of the lower parts of a central dike, suggesting magma supply from depth in the region between Miyake and Kozu Islands.

Deep mantle: Enriched carbon source detected

NASA Astrophysics Data System (ADS)

Barry, Peter H.

2017-09-01

Estimates of carbon in the deep mantle vary by more than an order of magnitude. Coupled volcanic CO2 emission data and magma supply rates reveal a carbon-rich mantle plume source region beneath Hawai'i with 40% more carbon than previous estimates.

The origin of Cu/Au ratios in porphyry-type ore deposits.

PubMed

Halter, Werner E; Pettke, Thomas; Heinrich, Christoph A

2002-06-07

Microanalysis of major and trace elements in sulfide and silicate melt inclusions by laser-ablation inductively coupled plasma mass spectrometry indicates a direct link between a magmatic sulfide liquid and the composition of porphyry-type ore deposits. Copper (Cu), gold (Au), and iron (Fe) are first concentrated in a sulfide melt during magmatic evolution and then released to an ore-forming hydrothermal fluid exsolved late in the history of a magma chamber. The composition of sulfide liquids depends on the initial composition and source of the magma, but it also changes during the evolution of the magma in the crust. Magmatic sulfide melts may exert the dominant direct control on the economic metal ratios of porphyry-type ore deposits.

Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea

NASA Astrophysics Data System (ADS)

Ronchin, Erika; Masterlark, Timothy; Dawson, John; Saunders, Steve; Martì Molist, Joan

2017-06-01

We test an innovative inversion scheme using Green's functions from an array of pressure sources embedded in finite-element method (FEM) models to image, without assuming an a-priori geometry, the composite and complex shape of a volcano deformation source. We invert interferometric synthetic aperture radar (InSAR) data to estimate the pressurization and shape of the magma reservoir of Rabaul caldera, Papua New Guinea. The results image the extended shallow magmatic system responsible for a broad and long-term subsidence of the caldera between 2007 February and 2010 December. Elastic FEM solutions are integrated into the regularized linear inversion of InSAR data of volcano surface displacements in order to obtain a 3-D image of the source of deformation. The Green's function matrix is constructed from a library of forward line-of-sight displacement solutions for a grid of cubic elementary deformation sources. Each source is sequentially generated by removing the corresponding cubic elements from a common meshed domain and simulating the injection of a fluid mass flux into the cavity, which results in a pressurization and volumetric change of the fluid-filled cavity. The use of a single mesh for the generation of all FEM models avoids the computationally expensive process of non-linear inversion and remeshing a variable geometry domain. Without assuming an a-priori source geometry other than the configuration of the 3-D grid that generates the library of Green's functions, the geodetic data dictate the geometry of the magma reservoir as a 3-D distribution of pressure (or flux of magma) within the source array. The inversion of InSAR data of Rabaul caldera shows a distribution of interconnected sources forming an amorphous, shallow magmatic system elongated under two opposite sides of the caldera. The marginal areas at the sides of the imaged magmatic system are the possible feeding reservoirs of the ongoing Tavurvur volcano eruption of andesitic products on the east side and of the past Vulcan volcano eruptions of more evolved materials on the west side. The interconnection and spatial distributions of sources correspond to the petrography of the volcanic products described in the literature and to the dynamics of the single and twin eruptions that characterize the caldera. The ability to image the complex geometry of deformation sources in both space and time can improve our ability to monitor active volcanoes, widen our understanding of the dynamics of active volcanic systems and improve the predictions of eruptions.

Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

USGS Publications Warehouse

Pietruszka, Aaron J.; Heaton, Daniel E.; Marske, Jared P.; Garcia, Michael O.

2015-01-01

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir ∼2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body <2 km below the eastern rim of Halema‘uma‘u pit crater. Residence time modeling suggests that the total volume of magma within Kīlauea's summit reservoir during the late 20th century (1959–1982) was exceedingly small (∼0.1–0.5 km3). Voluminous Kīlauea eruptions, such as the ongoing, 32-yr old Pu‘u ‘Ō‘ō rift eruption (>4 km3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

NASA Technical Reports Server (NTRS)

Danielson, Lisa R.; Metcalf, Rodney V.; Miller, Calvin F.; Rhodes Gregory T.; Wooden, J. L.

2013-01-01

The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the crust. Mixing and fractional crystallization of these magmas at various levels in the crust generated a suite of intermediate composition magmas. U-Pb zircon SHRIMP ages of phase 1 (15.7 +/- 0.2 Ma), phase 3 (15.8 +/- 0.2 Ma) and phase 4 (15.4 +/- 0.3 Ma) document a 100-300k year timescale for petrogenetic processes recorded in the Mt Perkins magma system.

Gravimetric control of active volcanic processes

NASA Astrophysics Data System (ADS)

Saltogianni, Vasso; Stiros, Stathis

2017-04-01

Volcanic activity includes phases of magma chamber inflation and deflation, produced by movement of magma and/or hydrothermal processes. Such effects usually leave their imprint as deformation of the ground surfaces which can be recorded by GNSS and other methods, on one hand, and on the other hand they can be modeled as elastic deformation processes, with deformation produced by volcanic masses of finite dimensions such as spheres, ellipsoids and parallelograms. Such volumes are modeled on the basis of inversion (non-linear, numerical solution) of systems of equations relating the unknown dimensions and location of magma sources with observations, currently mostly GNSS and INSAR data. Inversion techniques depend on the misfit between model predictions and observations, but because systems of equations are highly non-linear, and because adopted models for the geometry of magma sources is simple, non-unique solutions can be derived, constrained by local extrema. Assessment of derived magma models can be provided by independent observations and models, such as micro-seismicity distribution and changes in geophysical parameters. In the simplest case magmatic intrusions can be modeled as spheres with diameters of at least a few tens of meters at a depth of a few kilometers; hence they are expected to have a gravimetric signature in permanent recording stations on the ground surface, while larger intrusions may also have an imprint in sensors in orbit around the earth or along precisely defined air paths. Identification of such gravimetric signals and separation of the "true" signal from the measurement and ambient noise requires fine forward modeling of the wider areas based on realistic simulation of the ambient gravimetric field, and then modeling of its possible distortion because of magmatic anomalies. Such results are useful to remove ambiguities in inverse modeling of ground deformation, and also to detect magmatic anomalies offshore.

Experimental Constraints on the Origin of Lunar High-Ti Ultramafic Glasses

NASA Technical Reports Server (NTRS)

Wagner, T. P.; Grove, T. L.

1996-01-01

Phase equilibria and dissolution rate experiments are used to develop a petrogenetic model for the high-Ti lunar ultramafic glasses. Near-liquidus phase relations of the Apollo 14 black glass, the most Ti-rich lunar ultramafic glass, are determined to 2.2-GPa. The liquidus is saturated with Cr-spinel at 1-atm, olivine between approximately 0.5- and 1.5-GPa, and low-Ca pyroxene + Cr-spinel above 1.5-GPa. Ilmenite does not crystallize near the liquidus and implies that high-Ti ultramafic glasses are not produced by melting of an ilmenite-saturated source. We infer that high-Ti ultramafic magmas are derived from low-Ti ultramafic parent magmas by assimilation of ilmenite +/- clinopyroxene +/- urKREEP +/- pigeonite in the shallow lunar interior. Heat is provided by adiabatic ascent of the low-Ti ultramafic primary magmas from the deeper lunar interior and crystallization of olivine during assimilation. The assimilation reaction is modeled by mass balance and requires that ilmenite and high-Ca pyroxene are assimilated in a approximately 3:1 ratio, a much higher ratio than the proportion in which these minerals are thought to exist in the lunar interior. In an effort to understand the kinetic controls on this reaction, the dissolution of ilmenite is examined experimentally in both low- and high-Ti lunar magmas. We find that ilmenite dissolves incongruently to Cr-spinel and a high-Ti melt. The dissolution reaction proceeds by a diffusion-controlled mechanism. An assimilation model for the origin of high-Ti melts is developed that leaves the magma ocean cumulates in their initial stratigraphic positions and obviates source hybridization models that require lunar overturn.

Numerical simulation of plagioclase rim growth during magma ascent at Bezymianny Volcano, Kamchatka

NASA Astrophysics Data System (ADS)

Gorokhova, N. V.; Melnik, O. E.; Plechov, P. Yu.; Shcherbakov, V. D.

2013-08-01

Slow CaAl-NaSi interdiffusion in plagioclase crystals preserves chemical zoning of plagioclase in detail, which, along with strong dependence of anorthite content in plagioclase on melt composition, pressure, and temperature, make this mineral an important source of information on magma processes. A numerical model of zoned crystal growth is developed in the paper. The model is based on equations of multicomponent diffusion with diagonal cross-component diffusion terms and accounts for mass conservation on the melt-crystal interface and growth rate controlled by undercooling. The model is applied to the data of plagioclase rim zoning from several recent Bezymianny Volcano (Kamchatka) eruptions. We show that an equilibrium growth model cannot explain crystallization of naturally observed plagioclase during magma ascent. The developed non-equilibrium model reproduced natural plagioclase zoning and allowed magma ascent rates to be constrained. Matching of natural and simulated zoning suggests ascent from 100 to 50 MPa during 15-20 days. Magma ascent rate from 50 MPa to the surface varies from eruption to eruption: plagioclase zoning from the December 2006 eruption suggests ascent to the surface in less than 1 day, whereas plagioclase zoning from March 2000 and May 2007 eruptions are better explained by magma ascent over periods of more than 30 days). Based on comparison of diffusion coefficients for individual elements a mechanism of atomic diffusion during plagioclase crystallization is proposed.

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8-3.1 Ga detrital zircons

NASA Astrophysics Data System (ADS)

Bolhar, Robert; Hofmann, Axel; Kemp, Anthony I. S.; Whitehouse, Martin J.; Wind, Sandra; Kamber, Balz S.

2017-10-01

Hafnium and oxygen isotopic compositions measured in-situ on U-Pb dated zircon from Archaean sedimentary successions belonging to the 2.9-2.8 Ga Belingwean/Bulawayan groups and previously undated Sebakwian Group are used to characterize the crustal evolution of the Zimbabwe Craton prior to 3.0 Ga. Microstructural and compositional criteria were used to minimize effects arising from Pb loss due to metamorphic overprinting and interaction with low-temperature fluids. 207Pb/206Pb age spectra (concordance >90%) reveal prominent peaks at 3.8, 3.6, 3.5, and 3.35 Ga, corresponding to documented geological events, both globally and within the Zimbabwe Craton. Zircon δ18O values from +4 to +10‰ point to both derivation from magmas in equilibrium with mantle oxygen and the incorporation of material that had previously interacted with water in near-surface environments. In εHf-time space, 3.8-3.6 Ga grains define an array consistent with reworking of a mafic reservoir (176Lu/177Hf ∼0.015) that separated from chondritic mantle at ∼3.9 Ga. Crustal domains formed after 3.6 Ga depict a more complex evolution, involving contribution from chondritic mantle sources and, to a lesser extent, reworking of pre-existing crust. Protracted remelting was not accompanied by significant mantle depletion prior to 3.35 Ga. This implies that early crust production in the Zimbabwe Craton did not cause complementary enriched and depleted reservoirs that were tapped by later magmas, possibly because the volume of crust extracted and stabilised was too small to influence (asthenospheric) mantle isotopic evolution. Growth of continental crust through pulsed emplacement of juvenile (chondritic mantle-derived) melts, into and onto the existing cratonic nucleus, however, involved formation of complementary depleted subcontinental lithospheric mantle since the early Archaean, indicative of strongly coupled evolutionary histories of both reservoirs, with limited evidence for recycling and lateral accretion of arc-related crustal blocks until 3.35 Ga.

Silicic magma differentiation in ascent conduits. Experimental constraints

NASA Astrophysics Data System (ADS)

Rodríguez, Carmen; Castro, Antonio

2017-02-01

Crystallization of water-bearing silicic magmas in a dynamic thermal boundary layer is reproduced experimentally by using the intrinsic thermal gradient of piston-cylinder assemblies. The standard AGV2 andesite under water-undersaturated conditions is set to crystallize in a dynamic thermal gradient of about 35 °C/mm in 10 mm length capsules. In the hotter area of the capsule, the temperature is initially set at 1200 °C and decreases by programmed cooling at two distinct rates of 0.6 and 9.6 °C/h. Experiments are conducted in horizontally arranged assemblies in a piston cylinder apparatus to avoid any effect of gravity settling and compaction of crystals in long duration runs. The results are conclusive about the effect of water-rich fluids that are expelled out the crystal-rich zone (mush), where water saturation is reached by second boiling in the interstitial liquid. Expelled fluids migrate to the magma ahead of the solidification front contributing to a progressive enrichment in the fluxed components SiO2, K2O and H2O. The composition of water-rich fluids is modelled by mass balance using the chemical composition of glasses (quenched melt). The results are the basis for a model of granite magma differentiation in thermally-zoned conduits with application of in-situ crystallization equations. The intriguing textural and compositional features of the typical autoliths, accompanying granodiorite-tonalite batholiths, can be explained following the results of this study, by critical phenomena leading to splitting of an initially homogeneous magma into two magma systems with sharp boundaries. Magma splitting in thermal boundary layers, formed at the margins of ascent conduits, may operate for several km distances during magma transport from deep sources at the lower crust or upper mantle. Accordingly, conduits may work as chromatographic columns contributing to increase the silica content of ascending magmas and, at the same time, leave behind residual mushes that eventually are dragged as enclaves or autoliths.

Recent volcanic history of Irazu volcano, Costa Rica: alternation and mixing of two magma batches, and pervasive mixing

USGS Publications Warehouse

Alvarado, Guillermo E.; Carr, Michael J.; Turrin, Brent D.; Swisher, Carl C.; Schmincke, Hans-Ulrich; Hudnut, Kenneth W.

2006-01-01

40Ar/39Ar dates, field observations, and geochemical data are reported for Irazú volcano, Costa Rica. Volcanism dates back to at least 854 ka, but has been episodic with lava shield construction peaks at ca. 570 ka and 136–0 ka. The recent volcanic record on Irazú volcano comprises lava flows and a variety of Strombolian and phreatomagmatic deposits, with a long-term trend toward more hydrovolcanic deposits. Banded scorias and hybridized rocks reflect ubiquitous magma mixing and commingling. Two distinct magma batches have been identified. One magma type or batch, Haya, includes basalt with higher high field strength (HFS) and rare-earth element contents, suggesting a lower degree melt of a subduction modified mantle source. The second batch, Sapper, has greater enrichment of large ion lithophile elements (LILE) relative to HFS elements and rare-earth elements, suggesting a higher subduction signature. The recent volcanic history at Irazú records two and one half sequences of the following pattern: eruptions of the Haya batch; eruptions of the Sapper batch; and finally, an unusually clear unconformity, indicating a pause in eruptions. In the last two sequences, strongly hybridized magma erupted after the eruption of the Haya batch. The continuing presence of two distinct magma batches requires two active magma chambers. The common occurrence of hybrids is evidence for a small, nearer to the surface chamber for mixing the two batches. Estimated pre-eruptive temperatures based on two-pyroxene geothermometry range from ∼1000–1176 °C in basalts to 922 °C in hornblende andesites. Crystallization occurred mainly between 4.6 and 3 kb as measured by different geobarometers. Hybridized rocks show intermediate pressures and temperatures. High silica magma occurs in very small volumes as banded scorias but not as lava flows. Although eruptions at Irazú are not often very explosive, the pervasiveness of magma mixing presents the danger of larger, more explosive hybrid eruptions.

Buffered and unbuffered dike emplacement on Earth and Venus - Implications for magma reservoir size, depth, and rate of magma replenishment

NASA Technical Reports Server (NTRS)

Parfitt, E. A.; Head, J. W., III

1993-01-01

Models of the emplacement of lateral dikes from magma chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source magma reservoir. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.

Petrogensis of rhyolitic domes of Dastjerd (SE Qom)

NASA Astrophysics Data System (ADS)

Askari, Nasim; Kheirkhah, Monireh; Hashem Emami, Mohamad

2010-05-01

The study area is located in South Eastern Qom; this area is marginal part of SW Central Iran, located in Urumieh- Dokhtar magmatic belt. Rhyolitic domes (Post Eocene) as endogenous (crypto dome) are along Meyem slip-fault, that this fault probably is effective in emplacement and magma ascent. The ryholitic rocks contain some phenocrysts of garnets, plagioclases and biotits. The groundmasses are consisting of plagioclase, K-feldspar and quartz. Rhyolitic rocks have calc alkaline trends and base on chemical composition of rhyolite rocks and mica bearing. The source of magma is S-type and per aluminums which belongs to collision environment. It is suggested the role of continental crust in generation rhyolitic rocks. Because of the garnet area is an early crystallizing phase and is only confined to rhyolite, it is inferred that the garnet did not crystallize in more basic magmas and that the rhyolite could not have been derived from a basic magma by crystal fractionation. Keywords: Rhyolitic, slip-fault, collision, S-type, endogenous

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

Phillips, Benjamin R.; Baldridge, W. Scott; Gable, Carl W.

Finite volume calculations of the flow of rhyolite are presented to investigate the fate of viscous magmas flowing in planar fractures with realistic length to width ratios of up to 2500:1. Heat and mass transfer for a melt with a temperature dependent viscosity and the potential to undergo phase change are considered. Magma driving pressures and dike widths are chosen to satisfy simple elastic considerations. These models are applied within a parameter space relevant to the Banco Bonito rhyolite flow, Valles caldera, New Mexico. We estimate a maximum eruption duration for the event of ~200 days, realized at a minimummore » possible dike width of 5-6 m and driving pressure of 7-8 MPa. Simplifications in the current model may warrant scaling of these results. However, we demonstrate the applicability of our model to magma dynamics issues and suggest that such models may be used to infer information about both the timing of an eruption and the evolution of the associated magma source.« less

Volcanic history, geologic analysis and map of the Prometheus Patera region on Io

USGS Publications Warehouse

Leone, G.; Gerard, Davies A.; Wilson, L.; Williams, D.A.; Keszthelyi, L.P.; Jaeger, W.L.; Turtle, E.P.

2009-01-01

Data from Jupiter's moon Io returned by the Galileo spacecraft have been used to create a geologic map of Prometheus Patera, its associated flow field, and nearby features. We have identified the location of the vent that fed the Prometheus flow field during the Galileo epoch in the north-eastern portion of the main Prometheus flow field. This vent is the probable source of a small sulphur-rich plume. Previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault. It is plausible that, in the past, magma exploited the fault to reach the surface at Prometheus Patera, but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the Prometheus flow field. We also speculate on how a new Prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle. ?? 2009 Elsevier B.V.

Volcanic history, geologic analysis and map of the Prometheus Patera region on Io

USGS Publications Warehouse

Leone, Giovanni; Davies, Ashley G.; Wilson, Lionel; Williams, David A.; Keszthelyi, Laszlo P.; Jaeger, Windy L.; Turtle, Elizabeth P.

2009-01-01

Data from Jupiter's moon Io returned by the Galileo spacecraft have been used to create a geologic map of Prometheus Patera, its associated flow field, and nearby features. We have identified the location of the vent that fed the Prometheus flow field during the Galileo epoch in the north-eastern portion of the main Prometheus flow field. This vent is the probable source of a small sulphur-rich plume. Previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault. It is plausible that, in the past, magma exploited the fault to reach the surface at Prometheus Patera, but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the Prometheus flow field. We also speculate on how a new Prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle.

An experimental and petrologic investigation of the source regions of lunar magmatism in the context of the primordial differentiation of the moon

NASA Astrophysics Data System (ADS)

Elardo, Stephen M.

The primordial differentiation of the Moon via a global magma ocean has become the paradigm under which all lunar data are interpreted. The success of this model in explaining multiple geochemical, petrologic, and isotopic characteristics lunar geology has led to magma oceans becoming the preferred model for the differentiation of Earth, Mars, Mercury, Vesta, and other large terrestrial bodies. The goal of this work is to combine petrologic analyses of lunar samples with high pressure, high temperature petrologic experiments to place new and detailed constraints the petrogenetic processes that operated during different stages of lunar magmatism, the processes that have acted upon these magmas to obscure their relationship to their mantle source regions, and how those source regions fit into the context of the lunar magma ocean model. This work focuses on two important phases of lunar magmatism: the ancient crust-building plutonic lithologies of the Mg-suite dating to ~4.3 Ga, and the most recent known mare basaltic magmas dating to ~3 Ga. These samples provide insight into the petrogenesis of magmas and interior thermal state when the Moon was a hot, juvenile planet, and also during the last gasps of magmatism from a cooling planet. Chapter 1, focusing on Mg-suite troctolite 76535, presents data on chromite symplectites, olivine-hosted melt inclusions, intercumulus mineral assemblages, and cumulus mineral chemistry to argue that the 76535 was altered by metasomatism by a migrating basaltic melt. This process could effectively raise radioisotope systems above their mineral-specific blocking temperatures and help explain some of the Mg-suite-FAN age overlap. Chapter 2 focuses on lunar meteorites NWA 4734, 032, and LAP 02205, which are 3 of the 5 youngest igneous samples from the Moon. Using geochemical and isotopic data combined with partial melting models, it is shown that these basalts do not have a link to the KREEP reservoir, and a model is presented for low-degree partial melting of late-stage LMO cumulates to generate Fe-rich partial melts. Chapter 3 presents datasets from NWA 032 that document one of the only occurrences of oscillatory zoning in lunar minerals. A model is presented that explains the zoning patterns in olivine and pyroxene by convection in a differentially cooling magma chamber. Constraints from mineral chemistry and isotopic compositions show that magma mixing was not a factor during this convection. Lastly, chapter 4 presents the results of high-pressure, high-temperature petrologic experiments on the compositions of the LAP 02205 group basalts, and NEA 003A, the latter of which is also one of the youngest basalts from the Moon. These results show that the LAP group basalts are likely the result of extreme olivine fractionation, whereas NEA 003A not only has the deepest known multiple saturation point amongst crystalline mare basalts, but also may be a near-primary melt. Possible parental melt compositions are calculated for these basalts, and models are presents for the petrogenesis of these basalts and discussed in the context of a cooling lunar mantle. These studies illustrate the importance of different LMO cumulate source regions in lunar magmatism at very different points in the thermal and magmatic evolution of the Moon.

Tracing crustal contamination along the Java segment of the Sunda Arc, Indonesia

NASA Astrophysics Data System (ADS)

Jolis, E. M.; Troll, V.; Deegan, F.; Blythe, L.; Harris, C.; Freda, C.; Hilton, D.; Chadwick, J.; Van Helden, M.

2012-04-01

Arc magmas typically display chemical and petrographic characteristics indicative of crustal input. Crustal contamination can take place either in the mantle source region or as magma traverses the upper crust (e.g. [1]). While source contamination is generally considered the dominant process (e.g. [2]), late-stage crustal contamination has been recognised at volcanic arcs too (e.g. [3]). In light of this, we aim to test the extent of upper crustal versus source contamination along the Java segment of the Sunda arc, which, due its variable upper crustal structure, is an exemplary natural laboratory. We present a detailed geochemical study of 7 volcanoes along a traverse from Anak-Krakatau in the Sunda strait through Java and Bali, to characterise the impact of the overlying crust on arc magma composition. Using rock and mineral elemental geochemistry, radiogenic (Sr, Nd and Pb) and, stable (O) isotopes, we show a correlation between upper crustal composition and the degree of upper crustal contamination. We find an increase in 87Sr/86Sr and δ18O values, and a decrease in 143Nd/144Nd values from Krakatau towards Merapi, indicating substantial crustal input from the thick continental basement present. Volcanoes to the east of Merapi and the Progo-Muria fault transition zone, where the upper crust is thinner, in turn, show considerably less crustal input in their isotopic signatures, indicating a stronger influence of the mantle source. Our new data represent a systematic and high-resolution arc-wide sampling effort that allows us to distinguish the effects of the upper crust on the compositional spectrum of individual volcanic systems along the Sunda arc. [1] Davidson, J.P, Hora, J.M, Garrison, J.M & Dungan, M.A 2005. Crustal Forensics in Arc Magmas. J. Geotherm. Res. 140, 157-170; [2] Debaille, V., Doucelance, R., Weis, D., & Schiano, P. 2005. Geochim. Cosmochim. Acta, 70,723-741; [3] Gasparon, M., Hilton, D.R., & Varne, R. 1994. Earth Planet. Sci. Lett., 126, 15-22.

Gravity-height correlations for unrest at calderas

NASA Astrophysics Data System (ADS)

Berrino, G.; Rymer, H.; Brown, G. C.; Corrado, G.

1992-11-01

Calderas represent the sites of the world's most serious volcanic hazards. Although eruptions are not frequent at such structures on the scale of human lifetimes, there are nevertheless often physical changes at calderas that are measurable over periods of years or decades. Such calderas are said to be in a state of unrest, and it is by studying the nature of this unrest that we may begin to understand the dynamics of eruption precursors. Here we review combined gravity and elevation data from several restless calderas, and present new data on their characteristic signatures during periods of inflation and deflation. We find that unless the Bouguer gravity anomaly at a caldera is extremely small, the free-air gradient used to correct gravity data for observed elevation changes must be the measured or calculated gradient, and not the theoretical gradient, use of which may introduce significant errors. In general, there are two models that fit most of the available data. The first involves a Mogi-type point source, and the second is a Bouguer-type infinite horizontal plane source. The density of the deforming material (usually a magma chamber) is calculated from the gravity and ground deformation data, and the best fitting model is, to a first approximation, the one producing the most realistic density. No realistic density is obtained where there are real density changes, or where the data do not fit the point source or slab model. We find that a point source model fits most of the available data, and that most data are for periods of caldera inflation. The limited examples of deflation from large silicic calderas indicate that the amount of mass loss, or magma drainage, is usually much less than the mass gain during the preceding magma intrusion. In contrast, deflationary events at basaltic calderas formed in extensional tectonic environments are associated with more significant mass loss as magma is injected into the associated fissure swarms.

Deep volcanic tremor and magma ascent mechanism under Kilauea, Hawaii

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

Aki, K.; Koyanagi, R.

1981-08-10

Deep harmonic tremor originating at depths around 40 km under Kilauea was studied using records accumulated since 1962 at the Hawaii Volcano Observatory of the U. S. Geological Survey. The deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island-wide network of seismometers. The period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode. The tremor appeared to be primarilymore » composed of P waves. We interpret the observation period and amplitude in terms of the stationary crack model of Aki et al. (1977) and find that the seismic moment rates for deep tremors are considerably larger than those for shallow-tremors suggesting mor vigorous transport for the former. We propose a kinematic source model which may be more appropriate for deep tremor. According to this model, a measurable quantity called 'reduced displacement' is directly proportional to the rate of magma flow. A systematic search for deep tremor episodes was made for the period from 1962 through 1979, and the amplitude, period, and duration of the tremor were tabulated. We then constructed a cumulative reduced-displacement plot over the 18-year period. The result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface. The total magma flow estimated from the reduced displacement is however, one order of magnitude smaller than that estimated by Swanson (1972). It may be that most channels transport magma aseismically, and only those with strong barriers generate tremor.« less

The implications of gas slug ascent in a stratified magma for acoustic and ground deformation source mechanisms in Strombolian eruptions

NASA Astrophysics Data System (ADS)

Capponi, Antonio; Lane, Stephen J.; James, Mike R.

2017-06-01

The interpretation of geophysical measurements at active volcanoes is vital for hazard assessment and for understanding fundamental processes such as magma degassing. For Strombolian activity, interpretations are currently underpinned by first-order fluid dynamic models which give relatively straightforward relationships between geophysical signals and gas and magma flow. However, recent petrological and high-speed video evidence has indicated the importance of rheological stratification within the conduit and, here, we show that under these conditions, the straightforward relationships break down. Using laboratory analogue experiments to represent a rheologically-stratified conduit we characterise the distinct variations in the shear stress exerted on the upper sections of the flow tube and in the gas pressures measured above the liquid surface, during different degassing flow configurations. These signals, generated by varying styles of gas ascent, expansion and burst, can reflect field infrasonic measurements and ground motion proximal to a vent. The shear stress signals exhibit timescales and trends in qualitative agreement with the near-vent inflation-deflation cycles identified at Stromboli. Therefore, shear stress along the uppermost conduit may represent a plausible source of near-vent tilt, and conduit shear contributions should be considered in the interpretation of ground deformation, which is usually attributed to pressure sources only. The same range of flow processes can produce different experimental infrasonic waveforms, even for similar masses of gas escape. The experimental data resembled infrasonic waveforms acquired from different vents at Stromboli associated with different eruptive styles. Accurate interpretation of near-vent ground deformation, infrasonic signal and eruptive style therefore requires detailed understanding of: a) spatiotemporal magma rheology in the shallow conduit, and b) shallow conduit geometry, as well as bubble overpressure and volume.

Observations and modelling of inflation in the Lazufre volcanic region, South America

NASA Astrophysics Data System (ADS)

Pearse, J.; Lundgren, P.

2010-12-01

The Central Volcanic Zone (CVZ) is an active volcanic arc in the central Andes, extending through Peru, southwestern Bolivia, Chile, and northwestern Argentina [De Silva, 1989; De Silva and Francis, 1991]. The CVZ includes a number of collapsed calderas, remnants of catastrophic eruptions, which are now thought to be inactive. However, recent Interferometric Synthetic Aperture Radar (InSAR) observations [Pritchard and Simons, 2004] show surface deformation occurring at some of these large ancient volcanic regions, indicating that magma chambers are slowly inflating beneath the surface. The mechanisms responsible for the initiation and growth of large midcrustal magma chambers remains poorly understood, and InSAR provides an opportunity for us to observe volcanic systems in remote regions that are otherwise difficult to monitor and observe. The Lastarria-Cordon del Azufre ("Lazufre" [Pritchard and Simons, 2002]) volcanic area is one such complex showing recent deformation, with average surface uplift rates of approximately 2.5 cm/year [Froger et al., 2007; Ruch et al, 2008]. We have processed InSAR data from ERS-1/2 and Envisat in the Lazufre volcanic area, including both ascending and descending satellite tracks. Time series analysis of the data shows steady uplift beginning in about 2000, continuing into 2010. We use boundary-element elastic models to invert for the depth and shape of the magmatic source responsible for the surface deformation. Given data from both ascending and descending tracks, we are able to resolve the ambiguity between the source depth and size, and constrain the geometry of the inflating magma source. Finite element modelling allows us to understand the effect of viscoelasticity on the development of the magma chamber.

Deep volcanic tremor and magma ascent mechanism under Kilauea, Hawaii

USGS Publications Warehouse

Aki, Keiiti; Koyanagi, Robert Y

1981-01-01

Deep harmonic tremor originating at depths around 40 km under Kilauea was studied using records accumulated since 1962 at the Hawaii Volcano Observatory of the U.S. Geological Survey. The deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island-wide network of seismometers. The period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode. The tremor appeared to be primarily composed of P waves. We interpret the observed period and amplitude in terms of the stationary crack model of Aki et al. (1977) and find that the seismic moment rates for deep tremors are considerably larger than those for shallow-tremors suggesting more vigorous transport for the former. We propose a kinematic source model which may be more appropriate for deep tremor. According to this model, a measurable quantity called ‘reduced displacement’ is directly proportional to the rate of magma flow. A systematic search for deep tremor episodes was made for the period from 1962 through 1979, and the amplitude, period, and duration of the tremor were tabulated. We then constructed a cumulative reduced-displacement plot over the 18-year period. The result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface. The total magma flow estimated from the reduced displacement is however, one order of magnitude smaller than that estimated by Swanson (1972). It may be that most channels transport magma aseismically, and only those with strong barriers generate tremor.

Mass Intrusion at Mount St. Helens (WA) From Temporal Gravity Variations

NASA Astrophysics Data System (ADS)

Battaglia, M.; Lisowski, M.; Dzurisin, D.; Poland, M. P.; Schilling, S. P.; Diefenbach, A. K.; Wynn, J.

2015-12-01

Repeated high-precision gravity measurements made at Mount St. Helens (WA) have revealed systematic temporal variations in the gravity field several years after the end of the 2004-2008 dome-building eruption. Changes in gravity with respect to a stable reference station 36 km NW of the volcano were measured at 10 sites on the volcanic edifice and at 4 sites far afield (10 to 36 km) from the summit in August 2010, August 2012 and August 2014. After simulating and removing the gravity signal associated with changes in mass of the crater glacier, the local hydrothermal aquifer, and vertical deformation, the residual gravity field observed at sites near the volcano's summit significantly increased with respect to the stable reference site during 2010-2012 (maximum change 48 ± 15 mgal). No significant change was measured during 2012-2014. The pattern of gravity increase is radially symmetrical, with a half-width of about 2.5 km and a point of maximum change centered at the 2004-2008 lava dome. Forward modeling of residual gravity data using the same source geometry, depth, and location as that inferred from geodetic data (a spheroidal source centered 7.5 km beneath the 2004-2008 dome) indicates a mass increase rate of the order of 1011 kg/year. For a reasonable magma density (~2250 kg/m3), the volume rate of magma intrusion beneath the summit region inferred from gravity (~ 0.1 km3/yr) greatly exceeds the volume inferred from inversion of geodetic data (0.001 km3/yr between 2008-2011), suggesting that either magma compressibility or other processes are important aspects of magma storage at Mount St. Helens, or that the data argue for a different source.

Peruvian Arid Coast and Agriculture, South America

NASA Technical Reports Server (NTRS)

1991-01-01

The coast of Peru, between the Pacific Ocean and the Andes Mountains is very arid (16.5S, 72.5W). For several thousand years, water from numerous small streams has been used for traditional flood and canal irrigation agriculture. However, during the past decade innovative techniques have tapped new water sources for increased agricultural production. Ground water in the porous sedimentary rock formations has been tapped for well irrigation agriculture.

Petrogenesis of ultramafic xenoliths from Hawaii inferred from Sr, Nd, and Pb isotopes

NASA Astrophysics Data System (ADS)

Okano, Osamu; Tatsumoto, Mitsunobu

Isotopic compositions of Nd, Sr, and Pb in xenoliths in the Honolulu volcanic series from the Salt Lake Crater (H-type) are similar to those of the host post-erosional basalts, but are distinct from the magma sources of Koolau shield tholeiites and MORB. In contrast, one spinel Iherzolite (K-type) has isotopic compositions of Nd and Sr that are close to those of Koolau tholeiite rather than to the other Hawaiian basalts. Previous studies have shown that Sr isotopic composition of the xenoliths and the host basalt and that trace element concentrations in minerals of garnet Iherzolites from Honolulu basalt were nearly in equilibrium with the host magma, indicating that Honolulu volcanics were derived from garnet Iherzolite or similar material. However, differences exist among the isotopic compositions (especially Nd) of the xenoliths indicating that they are accidental inclusions from upper layers. The similarity in isotopic compositions between xenoliths and Honolulu basalt suggests that the source areas in the mantle are chemically similar. Correlation of 238U/204Pb vs. 206Pb/204Pb of chrome diopside separated from the H-type spinel Iherzolites indicates that the xenoliths are 80±36 Ma, which corresponds to the lithosphere age of the Hawaiian site. This age is consistent with petrological studies [e.g., Sen and Leeman, 1991] which have found that the spinel Iherzolite inclusions are derived from the lithosphere wall rocks. The ɛNd = ˜+8 of the H-xenoliths is slightly lower than that for the East Pacific Rise MORB indicating that the xenoliths are derived from a trace element depleted source similar to the MORB residue. If the garnet Iherzolite xenoliths are derived from mixture of spinel Iherzolite with intrusive pyroxenite, then the source of the pyroxenite contained little plume component. The one exceptional spinel Iherzolite xenolith may be a residue of Koolau-like tholeiitic magma or may have been metasomatized by Koolau volcanism in the deep lithosphere. Isotopic compositions of gabbro in Kaupulehu are similar to MORB, indicating its derivation from the oceanic crust. The Sr and Nd isotopic compositions of dunite are similar to those of Hualalai alkaline magma, consistent with the theory that the dunite is a cumulate from the Hualalai magma.

Lu-Hf isotopic memory of plume-lithosphere interaction in the source of layered mafic intrusions, Windimurra Igneous Complex, Yilgarn Craton, Australia

NASA Astrophysics Data System (ADS)

Nebel, O.; Arculus, R. J.; Ivanic, T. J.; Nebel-Jacobsen, Y. J.

2013-10-01

Most layered mafic intrusions (LMI) are formed via multiple magma injections into crustal magma chambers. These magmas are originally sourced from the mantle, likely via plume activity, but may interact with the overriding lithosphere during ascent and emplacement in the crust. The magma injections lead to the establishment of different layers and zones with complex macroscopic, microscopic and cryptic compositional layering through magmatic differentiation and associated cumulate formation, sometimes accompanied by crustal assimilation. These complex mineralogical and petrological processes obscure the nature of the mantle sources of LMI, and typically have limited the degree to which parental liquids can be fully characterised. Here, we present Lu-Hf isotope data for samples from distinct layers of the Upper Zone of the Windimurra Igneous Complex (WIC), an immense late-Archean LMI in the West Australian Yilgarn Craton. Lu-Hf isotope systematics of whole rocks are well correlated (MSWD=5.6, n=17) with an age of ˜3.05±0.05 Ga and initial ɛHf˜+8. This age, however, is older than whole rock Sm-Nd and zircon U-Pb ages of the intrusion, both of which are ca. 2.8 Ga. Stratigraphically-controlled initial Hf isotope variations (associated with multiple episodes of emplacement at ca. 2.8 Ga) indicate isotope mixing between a near-chondritic and an ultra-radiogenic component, the latter with ɛHf[2.8 Ga]>+15. This Hf isotope mixing creates a pseudochron-relationship at the time of intrusion of ˜250 Myr that is superimposed on subsequent radiogenic ingrowth after crystallisation, generating an age that predates the actual emplacement event. Mixing between late-stage crystallisation products (melt + crystals) from the Middle Zone and replenishing, plume-derived liquids was followed by crystal accumulation in a chemically evolving magma chamber. The ultra-radiogenic Hf isotope endmember in the WIC mantle source requires parent-daughter ratios consistent with very early formation in Earth history, akin to early Archean komatiitic plume sources. We propose that plume-derived melts that formed the Windimurra LMI reacted with ancient refractory lithospheric keels already underpinning ancient cratons, creating a melt with extremely high ɛHf[t]. Melting a refractory component with super-chondritic, time-integrated high Lu/Hf, in this case by plume-lithosphere interaction, simultaneously accounts for the extreme Hf isotope signals, Hf-Nd isotope decoupling, and difference in radiometric Lu-Hf and Sm-Nd ages.

Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

USGS Publications Warehouse

Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G

2015-01-01

We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to antecrystic zircons require a model where eruptible rhyolites are generated by extracting melt and zircons from a long-lived mush of immobile crystal-rich magma. In this process the larger sanidine crystals remain trapped in the locked crystal network. The extracted melts (plus antecrystic zircon) amalgamate into a liquid dominated (i.e., eruptible) magma body that is maintained as a physically distinct entity relative to the bulk of the long-lived crystal mush. Zircon surfaces and sanidines in each rhyolite crystallize after melt extraction/amalgamation and their ages constrain the residence time of eruptible magmas at Yellowstone. Residence times of the large volume rhyolites (~40 – 70 km3) are ≤ 1 kyr (conservatively < 6 kyr), which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush. Because the lifespan of the crystal mush that sourced the Central Plateau Member rhyolites is two orders of magnitude longer than the residence time of eruptible magma bodies within the reservoir, it is apparent that the Yellowstone magma reservoir spends most of its time in a largely-crystalline (i.e., uneruptible) state, similar to the present-day magma reservoir, and that eruptible magma bodies are ephemeral features.

Generation and Evolution of Quaternary Magmas Beneath Tengchong: Sr-Nd-Pb-Hf Isotope and Zircon U-series Age Constraints

NASA Astrophysics Data System (ADS)

Zou, H.; Ma, M.; Fan, Q.; Xu, B.; Li, S. Q.; Zhao, Y.; King, D. T., Jr.

2017-12-01

The Tengchong volcanic field on the southeastern margin of the Tibetan Plateau represents rare Quaternary volcanic eruptions on the plateau. The Quaternary Tengchong volcanic field formed high-potassium calc-alkaline volcanic rocks that include trachybasalts, basaltic trachyandesites, trachyandesites, and dacites. Herein, we present comprehensive Nd-Sr-Pb-Hf isotopic and elemental data for trachybasalts, basaltic trachyandesites, and trachyandesites from four young Tengchong volcanoes at Maanshan, Dayingshan, Heikongshan, and Laoguipo, in order to understand their magma genesis and evolution. Nd-Sr-Pb-Hf isotopes for the primitive Tengchong magma (trachybasalts with SiO2 <52.5 wt. % and MgO >5.5% wt. %) reflect a heterogeneous enriched mantle source. High Th/U, Th/Ta, and Rb/Nb ratios and Nd-Sr-Pb-Hf isotope characteristics of the primitive magmas suggest that the enriched mantle beneath Tengchong formed as a result of subduction of clay-rich sediments, which probably came from the Indian continental plate. Partial melting of the enriched mantle was generated by deep continental subduction coupled with recent regional extension in the Tengchong area. With regard to the evolved magmas (basaltic trachyandesites and trachyandesites), good correlations between SiO2 content and the ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 177Hf/176Hf strongly suggest that the combined assimilation and fractional crystallization (AFC) was an important process during magma evolution to form these basaltic trachyandesites and trachyandesites. Uranium-series zircon dating on these evolved lavas from Tengchong is used to constrain their magma evolution and residence timescales.

A Geophysical Model for the Origin of Volcano Vent Clusters in a Colorado Plateau Volcanic Field

NASA Astrophysics Data System (ADS)

Deng, Fanghui; Connor, Charles B.; Malservisi, Rocco; Connor, Laura J.; White, Jeremy T.; Germa, Aurelie; Wetmore, Paul H.

2017-11-01

Variation in spatial density of Quaternary volcanic vents, and the occurrence of vent clusters, correlates with boundaries in Proterozoic crust in the Springerville volcanic field (SVF), Arizona, USA. Inverse modeling using 538 gravity measurements shows that vent clusters correlate with gradients in the gravity field due to lateral variation in crustal density. These lateral discontinuities in the crustal density can be explained by boundaries in the North American crust formed during Proterozoic accretion. Spatial density of volcanic vents is low in regions of high-density Proterozoic crust, high in areas of relatively low density Proterozoic crust, and is greatest adjacent to crustal boundaries. Vent alignments parallel these boundaries. We have developed 2-D and 3-D numerical models of magma ascent through the crust to simulate long-term, average magma migration that led to the development of vent clusters in the SVF, assuming that a viscous fluid flow through a porous media is statistically equivalent to magma migration averaged over geological time in the full field scale. The location and flux from the uniform magma source region are boundary conditions of the model. Changes in model diffusivity, associated with changes in the bulk properties of the lithosphere, can simulate preferential magma migration paths and alter estimated magma flux at the surface, implying that large-scale crustal structures, such as inherited tectonic block boundaries, influence magma ascent and clustering of volcanic vents. Probabilistic models of volcanic hazard for distributed volcanic fields can be improved by identifying crustal structures and assessing their impact on volcano distribution with the use of numerical models.

Modulation of magmatic processes by CO2 flushing

NASA Astrophysics Data System (ADS)

Caricchi, Luca; Sheldrake, Tom E.; Blundy, Jon

2018-06-01

Magmatic systems are the engines driving volcanic eruptions and the source of fluids responsible for the formation of porphyry-type ore deposits. Sudden variations of pressure, temperature and volume in magmatic systems can produce unrest, which may culminate in a volcanic eruption and/or the abrupt release of ore-forming fluids. Such variations of the conditions within magmatic systems are commonly ascribed to the injection of new magma from depth. However, as magmas fractionating at depth or rising to the upper crust release CO2-rich fluids, the interaction between carbonic fluids and H2O-rich magmas stored in the upper crust (CO2 flushing), must also be a common process affecting the evolution of subvolcanic magma reservoirs. Here, we investigate the effect of gas injection on the stability and chemical evolution of magmatic systems. We calculate the chemical and physical evolution of magmas subjected to CO2-flushing using rhyolite-MELTS. We compare the calculations with a set of melt inclusion data for Mt. St. Helens, Merapi, Etna, and Stromboli volcanoes. We provide an approach that can be used to distinguish between melt inclusions trapped during CO2 flushing, magma ascent and decompression, or those affected by post-entrapment H2O-loss. Our results show that CO2 flushing is a widespread process in both felsic and mafic magmatic systems. Depending upon initial magma crystallinity and duration of CO2 input, flushing can either lead to volcanic eruption or fluid release. We suggest that CO2 flushing is a fundamental process modulating the behaviour and chemical evolution of crustal magmatic systems.

The iron source in phreatomagmatic pipes in the Tunguska Basin (eastern Siberia): insights into hydrothermal-metasomatic leaching processes from Fe isotopes, microstructures, and mass balances.

NASA Astrophysics Data System (ADS)

John, Timm; Svensen, Henrik; Weyer, Stefan; Polozov, Alexander; Planke, Sverre

2010-05-01

The Siberian iron-bearing phreatomagmatic pipes represent world class Fe-ore deposit, and 5-6 are currently mined in eastern Siberia. The pipes formed within the vast Tunguska Basin, cutting thick accumulations of carbonates (dolostones) and evaporites (anhydrite, halite, dolostone). These sediments were intruded by the sub-volcanic part of the Siberian Traps at 252 Ma, and sills and dykes are abundant throughout the basin. The pipes formed during sediment-magma interactions in the deep parts of the basin, and the degassing is believed to have triggered the end-Permian environmental crisis. A major problem with understanding the pipe formation is related to the source of iron. Available hypotheses state that the iron was leached from a Fe-enriched magmatic melt that incorporated dolostones. It is currently unclear how the magmatic, hydrothermal, and sedimentary processes interacted to form the deposits, as there are no actual constraints to pin down the iron source. We hypothesize two end-member scenarios to account for the magnetite enrichment and deposition, which is testable by analyzing Fe-isotopes of magnetite: 1) Iron sourced from dolerite magma through leaching and metasomatism by chloride brines. 2) Leaching of iron from sedimentary rocks (shale, dolostone) during magma-sediment interactions. We focus on understanding the Fe-isotopic architecture of the pipes in order constrain the source of the Fe and the mechanism that caused this significant Fe redistribution. We further evaluate possible fractionation during fast metasomatic ore-forming process that took place soon after pipe formation.

Prevalence of Giardia lamblia in Different Water Sources of District Nowshehra, Khyber Pakhtunkhwa Pakistan.

NASA Astrophysics Data System (ADS)

khan, Shaukat Ali; Ayaz, Sultan; Khan, Sanaullah; Anees, Muhammad; Khan, Amir Muhammad; Khan, Imran

2012-12-01

Giardia lamblia is a cosmopolitan parasite that occurs worldwide and generally effects gastrointestinal tract. Water played a media for transmission of Giardia to different hosts. A total of 300 water samples were examined from different water sources, i.e. tap, open well, bore well and drain waters and DNA was extracted by trizol method through prescribed protocol. DNA was amplified through PCR. The overall prevalence of G. lamblia was 27.66% (83/300). Among these 2.5% (1/40) in bore well water, 29% (29/100) open well, 18.83% (11/60) tap water and 42% (42/100) drain water. It is concluded from the study that Giardia is frequently found in all water sources and is the main cause of ill health.

Lead Isotopes in Olivine-Phyric Shergottite Tissint: Implications for the Geochemical Evolution of the Shergottite Source Mantle

NASA Technical Reports Server (NTRS)

Moriwaki, R.; Usui, T.; Simon, J. I.; Jones, J. H.; Yokoyama, T.

2015-01-01

Geochemically-depleted shergottites are basaltic rocks derived from a martian mantle source reservoir. Geochemical evolution of the martian mantle has been investigated mainly based on the Rb-Sr, Sm-Nd, and Lu-Hf isotope systematics of the shergottites [1]. Although potentially informative, U-Th- Pb isotope systematics have been limited because of difficulties in interpreting the analyses of depleted meteorite samples that are more susceptible to the effects of near-surface processes and terrestrial contamination. This study conducts a 5-step sequential acid leaching experiment of the first witnessed fall of the geochemically-depleted olivinephyric shergottite Tissint to minimize the effect of low temperature distrubence. Trace element analyses of the Tissint acid residue (mostly pyroxene) indicate that Pb isotope compositions of the residue do not contain either a martian surface or terrestrial component, but represent the Tissint magma source [2]. The residue has relatively unradiogenic initial Pb isotopic compositions (e.g., 206Pb/204Pb = 10.8136) that fall within the Pb isotope space of other geochemically-depleted shergottites. An initial µ-value (238U/204Pb = 1.5) of Tissint at the time of crystallization (472 Ma [3]) is similar to a time-integrated mu- value (1.72 at 472 Ma) of the Tissint source mantle calculated based on the two-stage mantle evolution model [1]. On the other hand, the other geochemically-depleted shergottites (e.g., QUE 94201 [4]) have initial µ-values of their parental magmas distinctly lower than those of their modeled source mantle. These results suggest that only Tissint potentially reflects the geochemical signature of the shergottite mantle source that originated from cumulates of the martian magma ocean

Analytical volcano deformation source models

USGS Publications Warehouse

Lisowski, Michael; Dzurisin, Daniel

2007-01-01

Primary volcanic landforms are created by the ascent and eruption of magma. The ascending magma displaces and interacts with surrounding rock and fluids as it creates new pathways, flows through cracks or conduits, vesiculates, and accumulates in underground reservoirs. The formation of new pathways and pressure changes within existing conduits and reservoirs stress and deform the surrounding rock. Eruption products load the crust. The pattern and rate of surface deformation around volcanoes reflect the tectonic and volcanic processes transmitted to the surface through the mechanical properties of the crust.

Zircon U-Pb geochronology and Sr-Nd-Pb-Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China

NASA Astrophysics Data System (ADS)

Shu, Qihai; Lai, Yong; Zhou, Yitao; Xu, Jiajia; Wu, Huaying

2015-12-01

Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U-Pb dating, trace elements and Hf isotope, and/or whole rock Sr-Nd-Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U-Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re-Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr-Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from - 0.8 to + 10.0, restricted εNd(t) values from - 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03-18.88, (207Pb/204Pb)i = 15.48-15.58 and (208Pb/204Pb)i = 37.72-38.28, in agreement with Sr-Nd-Hf isotopes reflecting the dominance of a mantle component. An integration of geochronological and isotopic data points to three stages of Mo mineralization events (i.e., Triassic, Late Jurassic, and Early Cretaceous) associated with magmas generated from three different source regions in the Xilamulun district, NE China. The variation in the origin of the magmas from which the porphyry Mo systems were generated suggests that the formation of Mo deposit lies not in the composition of magma sources. Other factors, including high magma oxygen fugacity, may have taken a fundamental role in Mo enrichment and subsequent mineralization.

A large community outbreak of gastroenteritis associated with consumption of drinking water contaminated by river water, Belgium, 2010.

PubMed

Braeye, T; DE Schrijver, K; Wollants, E; van Ranst, M; Verhaegen, J

2015-03-01

SUMMARY On 6 December 2010 a fire in Hemiksem, Belgium, was extinguished by the fire brigade with both river water and tap water. Local physicians were asked to report all cases of gastroenteritis. We conducted a retrospective cohort study among 1000 randomly selected households. We performed a statistical and geospatial analysis. Human stool samples, tap water and river water were tested for pathogens. Of the 1185 persons living in the 528 responding households, 222 (18·7%) reported symptoms of gastroenteritis during the time period 6-13 December. Drinking tap water was significantly associated with an increased risk for gastroenteritis (relative risk 3·67, 95% confidence interval 2·86-4·70) as was place of residence. Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. Tap water samples tested positive for faecal indicator bacteria and protozoa. The results support the hypothesis that a point-source contamination of the tap water with river water was the cause of the multi-pathogen waterborne outbreak.

Carbon dioxide in magmas and implications for hydrothermal systems

USGS Publications Warehouse

Lowenstern, J. B.

2001-01-01

This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems. Because some metals, including gold, can be more volatile in vapor phases than coexisting liquids, the presence of CO2 may indirectly aid the process of metallogenesis by inducing phase separation.

Along-strike variability of primitive magmas (major and volatile elements) inferred from olivine-hosted melt inclusions, southernmost Andean Southern Volcanic Zone, Chile

NASA Astrophysics Data System (ADS)

Weller, D. J.; Stern, C. R.

2018-01-01

Glass compositions of melt inclusions in olivine phenocrysts found in tephras derived from explosive eruptions of the four volcanoes along the volcanic front of the southernmost Andean Southern Volcanic Zone (SSVZ) are used to constrain primitive magma compositions and melt generation parameters. Primitive magmas from Hudson, Macá, and Melimoyu have similar compositions and are formed by low degrees (8-18%) of partial melting. Compared to these other three centers, primitive magmas from Mentolat have higher Al2O3 and lower MgO, TiO2 and other incompatible minor elements, and are generated by somewhat higher degrees (12-20%) of partial melting. The differences in the estimated primitive parental magma compositions between Mentolat and the other three volcanic centers are consistent with difference in the more evolved magmas erupted from these centers, Mentolat magmas having higher Al2O3 and lower MgO, TiO2 and other incompatible minor element contents, suggesting that these differences are controlled by melting processes in the mantle source region above the subducted oceanic plate. Parental magma S = 1430-594 and Cl = 777-125 (μg/g) contents of Hudson, Macá, and Melimoyu are similar to other volcanoes further north in the SVZ. However, Mentolat primitive magmas have notably higher concentrations of S = 2656-1227 and Cl = 1078-704 (μg/g). The observed along-arc changes in parental magma chemistry may be due to the close proximity below Mentolat of the subducted Guamblin Fracture Zone that could efficiently transport hydrous mineral phases, seawater, and sediment into the mantle, driving enhanced volatile fluxed melting beneath this center compared to the others. Table S2. Olivine-hosted melt inclusion compositions, host-olivine compositions, and the post-entrapment crystallization corrected melt inclusion compositions. Table S3. Olivine-hosted melt inclusion modeling information. Table S4. Major element compositions of the fractionation corrected melt inclusion in equilibrium with mantle olivine. Table S5. Melting parameters Fm and CoH2O. Table S6. Major element compositions of phenocrysts and glasses occurring with the olivine-hosted melt inclusions.

Stability of volcanic conduits: insights from magma ascent modelling and possible consequences on eruptive dynamics

NASA Astrophysics Data System (ADS)

Aravena, Alvaro; de'Michieli Vitturi, Mattia; Cioni, Raffaello; Neri, Augusto

2017-04-01

Geological evidences of changes in volcanic conduit geometry (i.e. erosive processes) are common in the volcanic record, as revealed by the occurrence of lithic fragments in most pyroclastic deposits. However, the controlling factors of conduit enlargement mechanisms are still partially unclear, as well as the influence of conduit geometry in the eruptive dynamics. Despite physical models have been systematically used for studying volcanic conduits, their mechanical stability has been poorly addressed. In order to study the mechanical stability of volcanic conduits during explosive eruptions, we present a 1D steady-state model which considers the main processes experimented by ascending magmas, such as crystallization, drag forces, fragmentation, outgassing and degassing; and the application of the Mogi-Coulomb collapse criterion, using a set of constitutive equations for studying typical cases of rhyolitic and trachytic explosive volcanism. From our results emerge that conduit stability is mainly controlled by magma rheology and conduit dimensions. Indeed, in order to be stable, feeding conduits of rhyolitic eruptions need larger radii respect to their trachytic counterparts, which is manifested in the higher eruption rates usually observed in rhyolitic explosive eruptions, as confirmed by a small compilation of global data. Additionally, for both magma compositions, we estimated a minimum magma flux for developing stable conduits (˜3ṡ106 kg/s for trachytic magmas and ˜8ṡ107 kg/s for rhyolitic magmas), which is consistent with the unsteady character commonly observed in low-mass flux events (e.g. sub-Plinian eruptions), which would be produced by episodic collapse events of the volcanic conduit, opposite to the mainly stationary high-mass flux events (e.g. Plinian eruptions), characterized by stable conduits. For a given magma composition, a minimum radius for reaching stable conditions can be computed, as a function of inlet overpressure and water content. Under the assumption that magma chamber conditions during a typical volcanic eruption follow a depressurizing trend, a continuous conduit widening process is expected. This process could explain the pervasive and continuous presence of lithic fragments in most pyroclastic deposits, even with stationary properties and conditions of the magma source (e.g. water content, temperature, composition).

Characteristics of Young Rhyolites at Taupo, New Zealand: Implications for the Sub-Surface Plutonic System

NASA Astrophysics Data System (ADS)

Wilson, C. J.; Charlier, B. L.

2007-12-01

The young history of Taupo volcano captures the growth and destruction in the 26.5 ka ca. 530 km3 Oruanui eruption of a large rhyolitic magma body, together with the subsequent rejuvenation of magma sources below the volcano. Integration of field information with petrological and isotopic studies at the whole-pumice and single- crystal scales provide a picture of this history. Several important contrasts are inferred to exist between Taupo and comparably-sized, long-lived silicic foci such at Long Valley and in the Bishop Tuff. At Taupo the following are demonstrable. 1. Even in crystal-poor rhyolites like the Oruanui, many grains are inherited antecrysts or xenocrysts. The Oruanui crystal-poor rhyolite body was an open system, with influxes of crystals (plus melt) from remobilised older crystal mush, melted metasedimentary country rocks and plutonics, and crystal-poor basaltic to andesitic magmas. 2. All the Taupo rhyolites were well mixed prior to eruption, and there are no gradients in the eruption products to suggest that the holding chamber(s) were stratified to any extent. 3. Mafic magmas rose into, interacted with, and ponded on the floors of crystal-poor rhyolite in the Oruanui and Waimihia (3.5 ka) examples, again implying that the chamber floor was sharply defined, not a gradual progression down into a more crystal- rich root zone. 4. Pre-Oruanui activity involved contrasting magma types being generated simultaneously, but erupting from geographically separated vents. Post-Oruanui activity has seen (subtly) contrasting magma groups being erupted from vents in the same geographic area, but separated in time. The Oruanui and post-Oruanui magmas are different and do not appear to be related by consanguinity or by mixing - the Oruanui eruption effectively destroyed its magma body. These features are consistent with rhyolite magma generation at Taupo that is exceptionally fast, driven by high fluxes of mafic magmas into a highly heterogeneous crustal melange of metasedimentary and igneous lithologies. There is no voluminous crystal mush body to act as a buffer for the rhyolite generation processes; the eruption frequency at Taupo gives no chance for such a body to develop.

Intrusion Triggering of Explosive Eruptions: Lessons Learned from EYJAFJALLAJÖKULL 2010 Eruptions and Crustal Deformation Studies

NASA Astrophysics Data System (ADS)

Sigmundsson, F.; Hreinsdottir, S.; Hooper, A. J.; Arnadottir, T.; Pedersen, R.; Roberts, M. J.; Oskarsson, N.; Auriac, A.; Decriem, J.; Einarsson, P.; Geirsson, H.; Hensch, M.; Ofeigsson, B. G.; Sturkell, E. C.; Sveinbjornsson, H.; Feigl, K.

2010-12-01

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic. This eruption was preceded by an effusive flank eruption of olivine basalt from 20 March - 12 April 2010. Geodetic and seismic observations revealed the growth of an intrusive complex in the roots of the volcano during three months prior to eruptions. After initial horizontal growth, modelling indicates both horizontal and sub-vertical growth in three weeks prior the first eruption. The behaviour is attributed to subsurface variations in crustal stress and strength originating from complicated volcano foundations. A low-density layer may capture magma allowing pressure to build before an intrusion can ascend towards higher levels. The intrusive complex was formed by olivine basalt as erupted on the volcano flank 20 March - 12 April; the intrusive growth halted at the onset of this eruption. Deformation associated with the eruption onset was minor as the dike had reached close to the surface in the days before. Isolated eruptive vents opening on long-dormant volcanoes may represent magma leaking upwards from extensive pre-eruptive intrusions formed at depth. A deflation source activated during the summit eruption of trachyandesite is distinct from, and adjacent to, all documented sources of inflation in the volcano roots. Olivine basalt magma which recharged the volcano appears to have triggered the summit eruption, although the exact mode of triggering is uncertain. Scenarios include stress triggering or propagation of olivine basalt into more evolved magma. The trachyandesite includes crystals that can be remnants of minor recent intrusion of olivine basalt. Alternatively, mixing of larger portion of olivine basalt with more evolved magma may have occurred. Intrusions may lead to eruptions not only when they find their way to the surface; at Eyjafjallajökull our observation show how primitive melts in an intrusive complex active since 1992 catalyzed an explosive eruption of trachyandesite. Eyjafjallajökull’s behaviour can be attributed to its off-rift setting with a relatively cold subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes whereas immediate short-term precursors may be subtle and difficult to detect.

Determining pre-eruptive compositions of late Paleozoic magma from kaolinized volcanic ashes: Analysis of glass inclusions in quartz microphenocrysts from tonsteins

NASA Astrophysics Data System (ADS)

Webster, James D.; Congdon, Roger D.; Lyons, Paul C.

1995-02-01

Glass inclusions in quartz microphenocrysts were analyzed for major and minor elements by electron microprobe and H, Li, Be, B, Rb, Sr, Y, Nb, Mo, Sn, Cs, Ce, Th, and U by ion microprobe. The phenocrysts and inclusions occur as fresh relicts in about eleven strongly kaolinized, air-fall volcanic ash units (tonsteins) that outcrop in five states located in the central Appalachian basin; the ashes were erupted during the Pennsylvanian. Even though the whole-rock tonstein samples are extremely altered, the glass trapped in quartz microphenocrysts preserves pre-eruptive melt compositions, and, consequently, the inclusions are useful for determining compositions of source magmas and identifying geochemical trends indicative of magmatic evolution. Interpretation of inclusion compositions indicates the strongly altered tonsteins were derived from potassium-enriched, metaluminous to mildly peraluminous magma(s). The tonsteins can be divided into two groups on the basis of trapped melt compositions: older tonsteins that have inclusions with high Sr and normative quartz contents and comparatively low concentrations of U, Th, Rb, Y, Cs, Nb, F, and Cl (±Be) and younger tonsteins whose inclusions contain low Sr and normative quartz and high concentrations of U, Th, Rb, Y, Cs, Nb, F, and Cl (±Be). In general, as concentrations of Sr decreased, the magmatic abundances of Rb, Y, Cs, Nb, U, Th, Cl, and F (±Be) increased. The associated magma or magmas were highly evolved, volatile enriched, and contained Rb, Nb, and Y abundances characteristic of continental within-plate granites; compositions ranged from high-silica rhyolite to topaz rhyolite. Pre-eruptive volatile abundances in the source magma(s) were generally high but also highly variable. Chlorine contents of melt(s) ranged from 0.02-0.23 wt%, and F ranged from 0.01-0.7 wt%. Concentrations of H 2O in melt(s) ranged from 1.6-6.5 wt%. The high pre-eruptive H 2O contents are consistent with large eruptive volumes indicating the precursor rhyolites, which weathered to tonsteins, were a result of plinian eruptions. Even though pre-eruptive water concentrations exhibit no recognizable trends with any elements studied, magmatic evolution appears to have been a strong function of F and H 2O in melt(s); the thermal stabilities of quartz and feldspar were controlled by F and H 2O activities at pressures of approximately 0.5-1 kbar.

A tale of two magmas: Petrological insights into mafic and intermediate Plinian volcanism at Volcán de Colima, Mexico

NASA Astrophysics Data System (ADS)

Crummy, J. M.; Savov, I. P.; Morgan, D. J.; Wilson, M.; Loughlin, S.; Navarro-Ochoa, C.

2012-12-01

Volcán de Colima in western Mexico explosively erupts basaltic to high-silica andesitic magmas. Detailed petrological and geochemical analyses of Holocene tephra fallout deposits reveal two distinct magma types: I. typical calc-alkaline series magmas; and II. mixed calc-alkaline - alkaline magmas. Group I magmas comprise basalt to high-silica andesite (50.7 to 60.4 wt.% SiO2) and typically contain phenocrysts of plagioclase + clinopyroxene + orthopyroxene + Fe-Ti oxides ± hornblende ± olivine. Crystallinity varies from 10-25 vol.% dominated by plagioclase in a groundmass comprising highly vesiculated glass with abundant microlites. Back-scatter electron (BSE) microscope images together with electron microprobe analyses (EPMA) reveal complex zoning patterns and compositional variations in plagioclase and pyroxene phenocrysts. Large scale resorption events with dissolution surfaces cross-cutting multiple growth zones, combined with large steps in An content of up to 20 mol.% in plagioclase, and Mg# varying from 0.74 to 0.86 in clinopyroxene and orthopyroxene, indicates destabilisation and recrystallisation in a more mafic melt: increases in Cr coincident with step increases in Mg# reveal mafic magma recharge. Many plagioclase and pyroxene phenocrysts record multiple magma recharge events; while small-scale oscillations reveal compositional fluctuations as a result of decompression and degassing. Group II magmas comprise basalt to basaltic-andesite (48.3 to 57.5 wt.% SiO2) and contain 10-15 vol.% crystals comprising clinopyroxene + olivine + phlogopite + plagioclase + Fe-Ti oxides ± hornblende ± orthopyroxene. The groundmass comprises highly vesiculated glass with abundant microlites of the same mineral phases. Clinopyroxene phenocrysts have magnesian cores (Mg# 0.88-0.89) that display strong dissolution with clear resorption and recrystallisation. EPMA analyses reveal large compositional differences with the surrounding growth zone (Mg# 0.80) indicating recrystallisation and re-equilibration within a compositionally different melt. This composition of the clinopyroxene is similar to that of the Group I magmas. Whole-rock geochemical and Sr and Nd isotopic analyses reveal strong trends in the Group II magmas towards the composition of monogenetic cinder cones composed of phlogopite-bearing alkaline lamprophyre situated to the north of Volcán de Colima. The alkaline magmas are thought to have formed from partial melting of metasomatically enriched veins within the lithospheric mantle. We suggest the high Mg clinopyroxene cores of the Group II magmas crystallised from such alkaline melts, which then mixed with the parental mantle-derived melts of the Group I magmas. Geothermometry and hygrometry based on mineral-mineral and mineral-melt equilibria reveal no correlation between variations in eruption temperature (930-1000°C) and magmatic H2O content (3-6 wt.%) with magma composition. This implies magma composition and volatile content are not controlling the highly explosive mafic and intermediate eruptions at Volcán de Colima, but rather, are driven by very fast ascent rates from source to surface.

Evidence for a Light-Rare-Earth-Element-Depleted Source for Some Ferroan Anorthosites

NASA Astrophysics Data System (ADS)

Borg, L. E.; Norman, M.; Nyquist, L. E.; Bogard, D.; Snyder, G.; Taylor, L.

1998-01-01

In the lunar magma ocean model, ferroan anorthosites (FANs) are expected to be derived from a relatively undifferentiated source with chondritic REE abundances and yield the oldest radiometric ages of any lunar rocks. Samarium-neodymium-isotopic analyses of 60025 and 67016 yielded ages of 4.44 +/- 0.02 Ga and 4.53 +/- 0.12 Ga and initial EpsilonNd(sup 143) values in excess of -0.5. These ages are within error of ages determined on some Mg-suite rocks by researchers. Thus, the existing data are not completely consistent with the standard magma ocean model. We have completed isotopic analysis on the pristine FAN 62236 in order to place further constraints on lunar crust-forming processes.

Evidence for a Light-Rare-Earth-Element-Depleted Source for Some Ferroan Anorthosites

NASA Technical Reports Server (NTRS)

Borg, L. E.; Norman, M.; Nyquist, L. E.; Bogard, D.; Snyder, G.; Taylor, L.

1998-01-01

In the lunar magma ocean model, ferroan anorthosites (FANs) are expected to be derived from a relatively undifferentiated source with chondritic REE abundances and yield the oldest radiometric ages of any lunar rocks. Samarium-neodymium-isotopic analyses of 60025 and 67016 yielded ages of 4.44 +/- 0.02 Ga and 4.53 +/- 0.12 Ga and initial Epsilon(sub Nd)(sup 143) values in excess of -0.5. These ages are within error of ages determined on some Mg-suite rocks by researchers. Thus, the existing data are not completely consistent with the standard magma ocean model. We have completed isotopic analysis on the pristine FAN 62236 in order to place further constraints on lunar crust-forming processes.

Igneous proceses and closed system evolution of the Tharsis region of Mars

NASA Astrophysics Data System (ADS)

Finnerty, A. A.; Phillips, R. J.; Banerdt, W. B.

1988-09-01

A quantitative petrologic model for the evolution of the Tharsis region on Mars is presented, which is consistent with global gravity and topography data. It is demonstrated that it is possible to form and support the topographic relief of the Tharsis plateau by a closed-system mass-conservative nearly isostatic process involving generation of magmas from a mantle source region. Extrusion and/or intrusion (or underplating) of such magmas allows low-pressure solidification, with a consequent increase in volume relative to that which would be possible in the high-pressure source region, leading to elevated topology. The distribution of densities with depth obtained by the model is quantitatively consistent with the isostatic models of Sleep and Phillips (1979, 1985).

Effect of the Galapagos Hotspot on Seamount Formation along the Galapagos Spreading Center

NASA Astrophysics Data System (ADS)

Behn, M. D.; Sinton, J. M.; Detrick, R. S.

2002-12-01

Studies along the Mid-Atlantic Ridge (MAR) and East Pacific Rise (EPR) have shown seamount formation to be a strong function of spreading rate. At the MAR, seamounts are a dominant morphologic feature of the inner valley floor, while at the EPR seamounts are rarely observed within the neovolcanic zone. The Galapagos Spreading Center (GSC) provides an excellent location to test the influence of a hotspot on the process of seamount generation at a relatively constant spreading rate. In this study we use multi-beam bathymetry data acquired during the G-PRIME cruise in April-May, 2000 to examine the distribution of axial seamounts along the GSC with distance from the hotspot. We use a numerical algorithm to identify isolated volcanic edifices, by searching bathymetry for closed, concentric contours protruding above the surrounding seafloor. Seamount populations are fit with a maximum likelihood model to estimate the total number of seamounts per unit area, ν o, and the characteristic seamount height, β-1. The number of seamounts in the axial zone decreases significantly as the Galapagos hotspot is approached, suggesting a change from dominantly point-source to fissure-fed volcanism as magma supply increases. West of the 95.5°W propagator, the total number of seamounts per unit area (ν o = 279+/-16 per 103 km2) is similar to values observed at the MAR. In comparison, east of 92.7°W, where magma supply is higher, seamount density (50+/-9 per 103 km2) is similar to observations at the fast-spreading EPR. Our results show that the transition from point-source to fissure-fed eruptions occurs gradually, in contrast to the "threshold" effect observed in axial magma chamber depth and axial morphology in which small changes in magma supply result in large changes in these variables. In summary, the western GSC displays the same range in seamount density observed along the global mid-ocean ridge system suggesting that both spreading rate and magma supply are important factors controlling the style of constructional volcanism (point source vs fissure fed eruptions) at oceanic spreading centers.

Boninite-like intraplate magmas from Manihiki Plateau require ultra-depleted and enriched source components

PubMed Central

Golowin, Roman; Portnyagin, Maxim; Hoernle, Kaj; Hauff, Folkmar; Gurenko, Andrey; Garbe-Schönberg, Dieter; Werner, Reinhard; Turner, Simon

2017-01-01

The Ontong Java and Manihiki oceanic plateaus are believed to have formed through high-degree melting of a mantle plume head. Boninite-like, low-Ti basement rocks at Manihiki, however, imply a more complex magma genesis compared with Ontong Java basement lavas that can be generated by ∼30% melting of a primitive mantle source. Here we show that the trace element and isotope compositions of low-Ti Manihiki rocks can best be explained by re-melting of an ultra-depleted source (possibly a common mantle component in the Ontong Java and Manihiki plume sources) re-enriched by ≤1% of an ocean-island-basalt-like melt component. Unlike boninites formed via hydrous flux melting of refractory mantle at subduction zones, these boninite-like intraplate rocks formed through adiabatic decompression melting of refractory plume material that has been metasomatized by ocean-island-basalt-like melts. Our results suggest that caution is required before assuming all Archaean boninites were formed in association with subduction processes. PMID:28181497

Eruptive stratigraphy of the Tatara-San Pedro complex, 36°S, sourthern volcanic zone, Chilean Andes: reconstruction method and implications for magma evolution at long-lived arc volcanic centers

USGS Publications Warehouse

Dungan, M.A.; Wulff, A.; Thompson, R.

2001-01-01

The Quaternary Tatara-San Pedro volcanic complex (36°S, Chilean Andes) comprises eight or more unconformity-bound volcanic sequences, representing variably preserved erosional remnants of volcanic centers generated during 930 ky of activity. The internal eruptive histories of several dominantly mafic to intermediate sequences have been reconstructed, on the basis of correlations of whole-rock major and trace element chemistry of flows between multiple sampled sections, but with critical contributions from photogrammetric, geochronologic, and paleomagnetic data. Many groups of flows representing discrete eruptive events define internal variation trends that reflect extrusion of heterogeneous or rapidly evolving magna batches from conduit-reservoir systems in which open-system processes typically played a large role. Long-term progressive evolution trends are extremely rare and the magma compositions of successive eruptive events rarely lie on precisely the same differentiation trend, even where they have evolved from similar parent magmas by similar processes. These observations are not consistent with magma differentiation in large long-lived reservoirs, but they may be accommodated by diverse interactions between newly arrived magma inputs and multiple resident pockets of evolved magma and / or crystal mush residing in conduit-dominated subvolcanic reservoirs. Without constraints provided by the reconstructed stratigraphic relations, the framework for petrologic modeling would be far different. A well-established eruptive stratigraphy may provide independent constraints on the petrologic processes involved in magma evolution-simply on the basis of the specific order in which diverse, broadly cogenetic magmas have been erupted. The Tatara-San Pedro complex includes lavas ranging from primitive basalt to high-SiO2 rhyolite, and although the dominant erupted magma type was basaltic andesite ( 52-55 wt % SiO2) each sequence is characterized by unique proportions of mafic, intermediate, and silicic eruptive products. Intermediate lava compositions also record different evolution paths, both within and between sequences. No systematic long-term pattern is evident from comparisons at the level of sequences. The considerable diversity of mafic and evolved magmas of the Tatara-San Pedro complex bears on interpretations of regional geochemical trends. The variable role of open-system processes in shaping the compositions of evolved Tatara-San Pedro complex magmas, and even some basaltic magmas, leads to the conclusion that addressing problems such as are magma genesis and elemental fluxes through subduction zones on the basis of averaged or regressed reconnaissance geochemical datasets is a tenuous exercise. Such compositional indices are highly instructive for identifying broad regional trends and first-order problems, but they should be used with extreme caution in attempts to quantify processes and magma sources, including crustal components, implicated in these trends.

Trans-boundary air pollution in a city under various atmospheric conditions.

PubMed

Luo, Ming; Hou, Xiangting; Gu, Yefu; Lau, Ngar-Cheung; Yim, Steve Hung-Lam

2018-03-15

Trans-boundary air pollution (TAP) is a crucial factor affecting air quality, and its contribution may vary over time and differ under various atmospheric conditions. This study firstly applies an integrated statistical scheme to estimate the contributions of TAP and local sources to air pollutants in a city, and then investigate the influences of tropical cyclones (TC) on TAP. Hong Kong is chosen as an example because of its significant and special TAP characteristics. This study focuses on four major air pollutants, namely, respirable and fine suspended particulates (RSP/PM 10 and FSP/PM 2.5 ), sulfur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ), from 2002 to 2013. Our results show that, on average, TAP is the major contributor of the annual RSP, FSP, SO 2 , and NO 2 in Hong Kong. We estimate that when a TC is approaching, the increase in pollutant concentration in Hong Kong is mainly due to the increase in TAP contribution by the strengthened northerly wind at higher level of atmosphere (≥900hPa). These changes are accompanied by decreases in precipitation and increases in northerly/north-easterly wind, which may prolong the lifetime of pollutants, enhancing pollutant transport from mainland China to Hong Kong. Copyright © 2017 Elsevier B.V. All rights reserved.

Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U-Pb ages, petrography, geochemistry and Nd-Sr-Hf isotopes

NASA Astrophysics Data System (ADS)

Liu, Wei; Liu, Xiu-Jin; Liu, Li-Juan

2013-10-01

Whole rock major and trace element, Nd-Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U-Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar (NW China) were analyzed in this study. The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325-301 Ma) following volcanic eruption of the Batamayi Formation. Zircons from the East Junggar granitoids yielded 210 concordant 206Pb/238U ages which are all younger than 334 Ma and exhibit ɛHf(t) values distinctly higher than Devonian arc volcanic-rocks. Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust (OC). These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source region. The East Junggar granitoids show ɛNd(t) and initial 87Sr/86Sr values substantially overlapping those of the Armantai ophiolite in the area. The Early Paleozoic OC with seamount-like composition as the Zhaheba-Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids. Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea, I-type (I1 and I2 subgroups) mainly in the north and A-type in the south of the southern subarea. The perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase, in the monzogranites (northern subarea), suggest mixing of peralkaline granitic magma with mafic magma. In the north of the southern subarea, the presence of magmatic microdioritic enclaves (MMEs) in the I1 subgroup granitoids, transfer of plagioclase phenocrysts and hornblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plagioclase phenocrysts indicate mixing of crustal magma (I2 subgroup granitoids) with mafic magma. Magma mixing shifted (87Sr/86Sr)i of the I1 subgroup granitoids towards the mantle array. Two generations of hornblende with zonal distribution and similar mineral and geochemical compositions of quartz monzodiorite and hosted MME with unfractionated rare earth elements (REE) suggest extended magma mixing with onset probably at or near source region. These observations imply concurrency of mantle input and the crustal melting and, hence, a causal relationship between underplating/intraplating and the lower OC/upper OC melting. The I-type granitoids experienced plagioclase and hornblende fractionations, whereas fractionated phases of the two groups of A-type granites were alkali feldspar and albite-oligoclase with significant involvement of F--rich fluid. Granodioritic parent magmas of the I2 subgroup granitoids stemmed from the hydrous upper OC. Parent magmas of the two A-type groups possess syenogranitic or quartz syenitic compositions. The peralkaline A-type granites stemmed from the lower OC, whereas the A-type granites from dehydrated upper OC left behind after extensive partial melting and extraction of I-type granitoids. Based on comparison in the ternary system Mg2SiO4-CaAl2SiO6-SiO2, most of the Batamayi volcanic rocks with affinity to ocean-island basalts were derived from asthenospheric upwelling. The gabbro-dioritic rocks with higher light to heavy REE ratios stemmed from metasomatized lithospheric mantle. Both of the above mafic rocks contain subducted slab component.

The nakhlite meteorites: Augite-rich igneous rocks from Mars

NASA Technical Reports Server (NTRS)

Treiman, Allan H.

2005-01-01

The seven nakhlite meteorites are augite-rich igneous rocks that formed in flows or shallow intrusions of basaltic magma on Mars. They consist of euhedral to subhedral crystals of augite and olivine (to 1 cm long) in fine-grained mesostases. The augite crystals have homogeneous cores of Mg' = 63% and rims that are normally zoned to iron enrichment. The core-rim zoning is cut by iron-enriched zones along fractures and is replaced locally by ferroan low-Ca pyroxene. The core compositions of the olivines vary inversely with the steepness of their rim zoning - sharp rim zoning goes with the most magnesian cores (Mg' = 42%), homogeneous olivines are the most ferroan. The olivine and augite crystals contain multiphase inclusions representing trapped magma. Among the olivine and augite crystals is mesostasis, composed principally of plagioclase and/or glass, with euhedra of titanomagnetite and many minor minerals. Olivine and mesostasis glass are partially replaced by veinlets and patches of iddingsite, a mixture of smectite clays, iron oxy-hydroxides and carbonate minerals. In the mesostasis are rare patches of a salt alteration assemblage: halite, siderite, and anhydrite/ gypsum. The nakhlites are little shocked, but have been affected chemically and biologically by their residence on Earth. Differences among the chemical compositions of the nakhlites can be ascribed mostly to different proportions of augite, olivine, and mesostasis. Compared to common basalts, they are rich in Ca, strongly depleted in Al, and enriched in magmaphile (incompatible) elements, including the LREE. Nakhlites contain little pre-terrestrial organic matter. Oxygen isotope ratios are not terrestrial, and are different in anhydrous silicates and in iddingsite. The alteration assemblages all have heavy oxygen and heavy carbon, while D/H values are extreme and scattered. Igneous sulfur had a solar-system isotopic ratio, but in most minerals was altered to higher and lower values. High precision analyses show mass-independent fractionations of S isotopes. Nitrogen and noble gases are complex and represent three components: two mantle sources (Chas-E and Chas-S), and fractionated Martian atmosphere. The nakhlites are igneous cumulate rocks, formed from basaltic magma at approx.1.3 Ga, containing excess crystals over what would form from pure magma. After accumulation of their augite and olivine crystals, they were affected (to various degrees) by crystallization of the magma, element diffusion among minerals and magma, chemical reactions among minerals and magma, magma movement among the crystals, and post-igneous chemical equilibration. The extent of these modifications varies, from least to greatest, in the order: MIL03346, NWA817, Y000593, Nakhla = Governador Valadares, Lafayette, and NWA998. Chemical, isotopic, and chronologic data confirm that the nakhlites formed on Mars, most likely in thick lava flows or shallow intrusions. Their crystallization ages, referenced to crater count chronologies for Mars, suggest that the nakhlites formed on the large volcanic constructs of Tharsis, Elysium, or Syrtis Major. The nakhlites were suffused with liquid water, probably at approx.620 ma. This water dissolved olivine and mesostasis glass, and deposited iddingsite and salt minerals in their places. The nakhlites were ejected from Mars at approx.10.75Ma by an asteroid impact and fell to Earth within the last 10,000 years. Although the nakhlites are enriched in incompatible elements, their source mantle was strongly depleted. This depletion event was ancient, as the nakhlites source mantle was fractionated while short-lived radionuclides (e.g., t(sub 1/2 = 9 my) were still active. This differentiation event may have been core formation coupled with a magma ocean, as is inferred for the moon.

Preference for tap, bottled, and recycled water: Relations to PTC taste sensitivity and personality.

PubMed

Harmon, Daniel; Gauvain, Mary; Z Reisz; Arthur, Isaac; Story, S Drew

2018-02-01

This study investigated people's preferences for different water sources and factors that predict such preferences using a blind taste test. Water preferences of 143 participants for one name-brand bottled water, one groundwater-sourced tap water, and one indirect potable reuse (IDR) water were assessed. For predictors of water preference, we measured each participant's PTC taste sensitivity and assessed two personality traits (Neuroticism, Openness to Experience). We also explored participants' descriptions of each water source. Results indicate a preference for water treated with Reverse Osmosis (RO) (bottled and IDR water) over groundwater-sourced water, which had higher pH levels and lower concentrations of Ca and HCO 3 - . PTC taste sensitivity did not predict preferences, while Openness to Experience and Neuroticism predicted preference for IDR water. Positive relations between Openness to Experience and preferences for bottled and IDR water were moderated by gender and were stronger among females. Participants described water primarily by its taste and texture. Findings suggest that (1) tap water treated by RO is equally preferable to some bottled water, (2) personality traits may affect water preferences, and (3) prior findings of gender differences in preferences for bottled water may reflect personality characteristics. Efforts to increase acceptance for sustainable water alternatives, such as IDR, may be more successful by assuring consumers about taste and addressing personality traits that encourage or inhibit use. Copyright © 2017 Elsevier Ltd. All rights reserved.

Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization

NASA Astrophysics Data System (ADS)

Garcia-Arias, Marcos; Stevens, Gary

2017-04-01

Several fractional crystallization processes (flow segregation, gravitational settling, filter-pressing), as well as batch crystallization, have been investigated in this study using thermodynamic modelling (pseudosections) to test whether they are able to reproduce the compositional trends shown by S-type granites. Three starting compositions comprising a pure melt phase and variable amounts of entrained minerals (0, 20 and 40 wt.% of the total magma) have been used to study a wide range of likely S-type magma compositions. The evolution of these magmas was investigated from the segregation from their sources at 0.8 GPa until emplacement at 0.3 GPa in an adiabatic path, followed by isobaric cooling until the solidus was crossed, in a closed-system scenario. The modelled magmas and the fractionated mineral assemblages are compared to the S-type granites of the Peninsula pluton, Cape Granite Suite, South Africa, which have a composition very similar to most of the S-type granites. The adiabatic ascent of the magmas digests partially the entrained mineral assemblage of the magmas, but unless this entrained assemblage represents less than 1 wt.% of the original magma, part of the mineral fraction survives the ascent up to the chosen pressure of emplacement. At the level of emplacement, batch crystallization produces magmas that only plot within the composition of the granites of the Peninsula pluton if the bulk composition of the original magmas already matched that of the granites. Flow segregation of crystals during the ascent and gravitational settling fractional crystallization produce bodies that are generally more mafic than the most mafic granites of the pluton and the residual melts have an almost haplogranitic composition, producing a bimodal compositional distribution not observed in the granites. Consequently, these two processes are ruled out. Filter-pressing fractional crystallization produces bodies in an onion-layer structure that become more felsic with increasing crystallization, culminating in a haplogranitic melt, and is able to reproduce the compositional trends of the granites, but only if the original magmas already had the composition of the granites. Filter-pressing fractionation produces a mineral assemblage that is 1.5 times more mafic than the magma fraction from which it is derived. However, the mineral assemblages produced by crystallization of an originally pure melt phase are still too felsic to account for the bulk of the granites of the Peninsula pluton. For filter-pressing to produce the most mafic granites of the pluton, the original magmas must already contain an entrained mafic mineral assemblage and have the same composition of the granites, otherwise the modelled trends do not match the maficity (FeO + MgO) or the slope against maficity of the granites. Crystallization of the magma in filter-pressing releases a free water phase, whose amount depends on the amount of water of the original magma, and whose behaviour may be controlled by a water-saturation front. In summary, the main control in the composition of S-type granites is the amount and nature of the entrained mineral assemblage, and filter-pressing fractional crystallization can only modify slightly the compositions of the granitic bodies derived from these magmas.

Post-supereruption recovery at Toba Caldera

NASA Astrophysics Data System (ADS)

Mucek, Adonara E.; Danišík, Martin; de Silva, Shanaka L.; Schmitt, Axel K.; Pratomo, Indyo; Coble, Matthew A.

2017-05-01

Large calderas, or supervolcanoes, are sites of the most catastrophic and hazardous events on Earth, yet the temporal details of post-supereruption activity, or resurgence, remain largely unknown, limiting our ability to understand how supervolcanoes work and address their hazards. Toba Caldera, Indonesia, caused the greatest volcanic catastrophe of the last 100 kyr, climactically erupting ~74 ka. Since the supereruption, Toba has been in a state of resurgence but its magmatic and uplift history has remained unclear. Here we reveal that new 14C, zircon U-Th crystallization and (U-Th)/He ages show resurgence commenced at 69.7+/-4.5 ka and continued until at least ~2.7 ka, progressing westward across the caldera, as reflected by post-caldera effusive lava eruptions and uplifted lake sediment. The major stratovolcano north of Toba, Sinabung, shows strong geochemical kinship with Toba, and zircons from recent eruption products suggest Toba's climactic magma reservoir extends beneath Sinabung and is being tapped during eruptions.

Magma source transition of lunar mare volcanism at 2.3 Ga

NASA Astrophysics Data System (ADS)

Kato, Shinsuke; Morota, Tomokatsu; Yamaguchi, Yasushi; Watanabe, Sei-Ichiro; Otake, Hisashi; Ohtake, Makiko

2017-09-01

Mare basalts provide insights into the composition and thermal history of the lunar mantle. The ages of mare basalts suggest a first peak of magma activity at 3.2-3.8 Ga and a second peak at 2 Ga. In this study, we reassess the correlation between the titanium contents and the eruption ages of mare basalt units using the compositional and chronological data updated by SELENE (Kaguya). Using morphological and geological criteria, we calculated the titanium content of 261 mare units across a representative area of each mare unit. In the Procellarum KREEP Terrane, where the latest eruptions are located, an increase in the mean titanium content is observed during the Eratosthenian period, as reported by previous studies. We found that the increase in the mean titanium content occurred within a relatively short period near approximately 2.3 Ga, suggesting that the magma source of the mare basalts changed at this particular age. Moreover, the high-titanium basaltic eruptions are correlated with a second peak in volcanic activity near 2 Ga. The high-titanium basaltic eruptions occurring during the last volcanic activity period can be explained by the three possible scenarios (1) the ilmenite-bearing cumulate rich layer in the core-mantle boundary formed after the mantle overturn, (2) the basaltic material layers beneath the lunar crust formed through upwelling magmas, and (3) ilmenite-bearing cumulate blocks remained in the upper mantle after the mantle overturn.

Steady state deformation of the Coso Range, east central California, inferred from satellite radar interferometry

USGS Publications Warehouse

Wicks, C.W.; Thatcher, W.; Monastero, F.C.; Hasting, M.A.

2001-01-01

Observations of deformation from 1992 to 1997 in the southern Coso Range using satellite radar interferometry show deformation rates of up to 35 mm yr-1 in an area ???10 km by 15 km. The deformation is most likely the result of subsidence in an area around the Coso geothermal field. The deformation signal has a short-wavelength component, related to production in the field, and a long-wavelength component, deforming at a constant rate, that may represent a source of deformation deeper than the geothermal reservoir. We have modeled the long-wavelength component of deformation and inferred a deformation source at ???4 km depth. The source depth is near the brittle-ductile transition depth (inferred from seismicity) and ???1.5 km above the top of the rhyolite magma body that was a source for the most recent volcanic eruption in the Coso volcanic field [Manley and Bacon, 2000]. From this evidence and results of other studies in the Coso Range, we interpret the source to be a leaking deep reservoir of magmatic fluids derived from a crystallizing rhyolite magma body.

Isotopic and trace element variations in the Ruby Batholith, Alaska, and the nature of the deep crust beneath the Ruby and Angayucham Terranes

USGS Publications Warehouse

Arth, Joseph G.; Zmuda, Clara C.; Foley, Nora K.; Criss, Robert E.; Patton, W.W.; Miller, T.P.

1989-01-01

Thirty-six samples from plutons of the Ruby batholith of central Alaska were collected and analyzed for 22 trace elements, and many were analyzed for the isotopic compositions of Sr, Nd, O, and Pb in order to delimit the processes that produced the diversity of granodioritic to granitic compositions, to deduce the nature of the source of magmas at about 110 Ma, and to characterize the deep crust beneath the Ruby and Angayucham terranes. Plutons of the batholith show a substantial range in initial 87Sr/86Sr (SIR) of 0.7055–0.7235 and a general decrease from southwest to northeast. Initial 143Nd/144Nd (NIR) have a range of 0.51150–0.51232 and generally increase from southwest to northeast. The δ18O values for most whole rocks have a range of +8.4 to +11.8 and an average of +10.3‰. Rb, Cs, U, and Th show large ranges of concentration, generally increase as SiO2 increases, and are higher in southwest than in northeast plutons. Sr, Ba, Zr, Hf, Ta, Sc, Cr, Co, and Zr show large ranges of concentration and generally decrease as SiO2 increases. Rare earth elements (REE) show fractionated patterns and negative Eu anomalies. REE concentrations and anomalies are larger in the southwest than in the northeast plutons. Uniformity of SIR and NIR in Sithylemenkat and Jim River plutons suggests a strong role for fractional crystallization or melting of uniform magma sources at depth. Isotopic variability in Melozitna, Ray Mountains, Hot Springs, and Kanuti plutons suggests complex magmatic processes such as magma mixing and assimilation, probably combined with fractional crystallization, or melting of a complex source at depth. The large variations in SIR and NIR in the batholith require a variation in source materials at depth. The southwestern plutons probably had dominantly siliceous sources composed of metamorphosed Proterozoic and Paleozoic upper crustal rocks. The northeastern plutons probably had Paleozoic sources that were mixtures of siliceous and intermediate to mafic crustal rocks. The inferred sources could well have been the higher-metamorphic-grade lithologic equivalents of the exposed Proterozoic(?) to Paleozoic schists, orthogneisses, and metavolcanic rocks of Ruby terrane, the silicic portions of which are quite radiogenic. The deeper crustal sources that gave rise to most of the batholithic magmas are inferred to be similar under both the Ruby metamorphic terrane and the Angayucham ophiolitic terrane.

Weber (slope) analyses of timing variability in tapping and drawing tasks.

PubMed

Spencer, Rebecca M C; Zelaznik, Howard N

2003-12-01

Timing variability in continuous drawing tasks has not been found to be correlated with timing variability in repetitive finger tapping in recent studies (S. D. Robertson et al., 1999; H. N. Zelaznik, R. M. C. Spencer, & R. B. Ivry, 2002). Furthermore, the central component of timing variability, as measured by the slope of the timing variance versus the square of the timed interval, differed for tapping and drawing tasks. On the basis of those results, the authors posited that timing in tapping is explicit and as such uses a central representation of the interval to be timed, whereas timing in drawing tasks is implicit, that is, the temporal component is an emergent property of the trajectory produced. The authors examined that hypothesis in the present study by determining the linear relationship between timing variance and squared duration for tapping, circle-drawing, and line-drawing tasks. Participants (N = 50) performed 1 of 5 tasks: finger tapping, line drawing in the x dimension, line drawing in the y dimension, continuous circle drawing timed in the x dimension, or continuous circle drawing timed in the y dimension. The slopes differed significantly between finger tapping, line drawing, and circle drawing, suggesting separable sources of timing variability. The slopes of the 2 circle-drawing tasks did not differ from one another, nor did the slopes of the 2 line-drawing tasks differ significantly, suggesting a shared timing process within those tasks. Those results are evidence of a high degree of specificity in timing processes.

Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

NASA Astrophysics Data System (ADS)

Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

2013-12-01

The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible scenarios: 1) only deep gases enter the hydrothermal system, because the shallow magmatic body is now fully crystallized and degassed. 2) The shallow magmatic body, invested by the arrival of deep gases, starts remelting and releasing gases into the hydrothermal system. 3) Magma from the deep reservoir slowly rises to shallow depths, well below the ductile-fragile transition for this area. These three scenarios carry contrasting implications for the volcanic hazard assessment, and demand a comprehensive treatment of geochemical and geophysical data in a way coherent with the knowledge that we have of the 1982-85 unrest

Deep Basalt Aquifers in Orcus Patera, Elysium Basin Mars: Perspectives for Exobiology Exploration

NASA Technical Reports Server (NTRS)

Grin, E. A.; Cabrol, N. A.

1998-01-01

Direct indicators of shorelines, spillways, and terraces allowed to determine the extent of the Elysium Paleolake between the contour-lines 1000 and 500 m below the Martian datum. The Elysium Paleolake is bordered north by Orcus Patera (14N/181W), which lies west of the Tartarus Montes and Tartarus Colles. The Orcus Patera displays an ellipse-shaped collapsed caldera of 360-km long and 100-km wide. Viking topographic data show that the bottom of the caldera is located at 2500 below the Martian datum, and surrounded by a steep-walled ram art which crest is located at about 0 m elevation. Considering the localization of Orcus Patera in the Elysium paleolake, its altimetry, and the magmatic origin of this caldera, we propose the existence of a paleolake in Orcus Patera generated (a) by juvenile water from magma during the Noachian period, and (b) by intermittent influx of the Elysium Basin from Hesperian to Amazonian. Results are encouraging to consider this site as a potential high-energy source environment for microbial communities. are circumscribed by a 50-km wide lava field mapped as Noachian material. The structure of Orcus Patera represents the record of material erupted from a magmatic reservoir. The caldera is enclosed by steep inner walls (25% measured from topographic data), values which could be in agreement with the presence of a deep magmatic reservoir, as suggested by the typology of Crumpler et.al. The depth of the caldera might be due to the collapse of the magma reservoir, and the release of gases accompanying the magma thermal evolution. Origins of water for the paleolake(s): The water that generated a paleolake in Orcus Patera may have come from two origins: (1) Juvenile water: Plescia and Crips estimated a magma H20 content by weight between 0.5% and 1.5% using for the first value a comparison with terrestrial basalt, and for the second values from a Martian meteorite. The amount of H20 can be estimated by the volume of erupted lava, and the lava content of the caldera. In this study, we adopt a water content of 1%. The total volume of magma that has been contained in the caldera, and the volume of lava contained in the observed lava field is about 110 x 10(exp 6) cubic km, that gives a total volume of 1.10 x 10(exp 6) cubic km of water. The juvenile water expelled by the overpressure within the magma chamber charged with desolved water-vapor may have moved into the crust. The decrease in overburden pressure led to bubble formation. The ascent of these bubbles generated a pressurization of the magma, which was sufficient to fracture the overlaying magma layer, (2) Water from Elysium paleolake. During the Amazonian, the rise of the Elysium paleolake level generated an overspilling that supplied the caldera with water. The southern portion of the crest shows a deep gap 12-km wide at -1500 m elevation, locating the gap between 500 to 1000 in below the assumed water of Elysium paleolake, thus facilitating the influx of Elysium paleolake water into Orcus Patera. Bathymetric calculations give a floor area of 25,500 sq km at -2000 m elevation, and a water volume of 42,000 cubic km, with a lake-level at -1500 m. A substantial amount of water may have percolated through the fractured lava, and part of the volume may have overspilled the northern crest of Orcus Patera to debouch in the Tartarus Montes region. We envision the formation of a subsurface aqueous environment in basaltic rocks at the contact of the two water-source origins, possibly the percolating surface lake water, and more likely the juvenile water. Similarly to terrestrial calderas, Orcus Patera might be surrounded by ring-fractures caused by the collapse of the magma chamber that followed the release of gases. These ring-fractures may have been covered later by sedimentation in the caldera (lacustrine, aeolian, and volcanic), and by mass wasting. The detumescence of the magma in the caldera, and the vesiculation of the juvenile water may have operated simultaneously. Comparatively to terrestrial melts, Martian iron-rich melts are denser. This greater density implies greater effusion rates (eight-times terrestrial values), and larger fissuration widths (two-times terrestrial ones). With increasing vesiculation of magma, the bubbles interact with one-another because there are of similar pressure. They make a magma froth at the contact with the caldera surface, and on the walls of the fractures. In the saturated magma, froth, where the volume ratio of gases-to-liquid is about 4:1, the bubbles form a huge surface area of interconnected spaces. Bubbles near the caldera surface disrupt the magma, and fragmentation takes place, which moves downward through the magma column. On Earth, the bubbles are likely to grow between 1 and 50 mm in diameter due to the difference between the magma surface tension, and the bubble supersaturation pressure. The Martian low-pressure at surface level is likely to accelerate the expansion of the bubbles, and increase their final diameter and number, creating more voids in the magma. The strong magma froth with enclosed juvenile water bubbles interconnected with exsolved gas bubbles constitute a potential geothermal environment for geochemical energy production from basalt and water that does not require excessive temperatures. This process can start at +20C. Similar types of environments have been shown on Earth as potential energy sources for microbial metabolism, and could have provided deep aqueous basaltic niches for possible Martian microorganisms, even geologically recently. During the Amazonian, combination of volcanism and water activity still existed on Mars. Moreover, this type of potential niches open ways for investigation of possible oases of extinct or extant life, not only on paleolakes, and surface hydrothermalism spring areas, but also all large systems of fossae, which combine hydrologic and volcanic activities, and which provide an energy source, and an underground shelter to prevent surface UV bombardment. Additional information contained in the original.

Eruption style at Kīlauea Volcano in Hawai‘i linked to primary melt composition

USGS Publications Warehouse

Sides. I.R.,; Edmonds, M.; Maclennan, J.; Swanson, Don; Houghton, Bruce F.

2014-01-01

Explosive eruptions at basaltic volcanoes have been linked to gas segregation from magmas at shallow depths in the crust. The composition of primary melts formed at greater depths was thought to have little influence on eruptive style. Ocean island basaltic volcanoes are the product of melting of a geochemically heterogeneous mantle plume and are expected to give rise to heterogeneous primary melts. This range in primary melt composition, particularly with respect to the volatile components, will profoundly influence magma buoyancy, storage and eruption style. Here we analyse the geochemistry of a suite of melt inclusions from 25 historical eruptions at the ocean island volcano of Kīlauea, Hawai‘i, over the past 600 years. We find that more explosive styles of eruption at Kīlauea Volcano are associated statistically with more geochemically enriched primary melts that have higher volatile concentrations. These enriched melts ascend faster and retain their primary nature, undergoing little interaction with the magma reservoir at the volcano’s summit. We conclude that the eruption style and magma-supply rate at Kīlauea are fundamentally linked to the geochemistry of the primary melts formed deep below the volcano. Magmas might therefore be predisposed towards explosivity right at the point of formation in their mantle source region.

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment.

PubMed

Chiaradia, Massimo; Caricchi, Luca

2017-03-15

Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > ~0.5 GPa) during ≥2-3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<~0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits.

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

PubMed Central

Chiaradia, Massimo; Caricchi, Luca

2017-01-01

Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > ~0.5 GPa) during ≥2–3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<~0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits. PMID:28295045

Abundant carbon in the mantle beneath Hawai`i

NASA Astrophysics Data System (ADS)

Anderson, Kyle R.; Poland, Michael P.

2017-09-01

Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai`i’s active volcanoes is 0.97-0.19+0.25 wt%--roughly 40% higher than previously believed--and is supplied from a mantle source region with a carbon concentration of 263-62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

A review of the recent geochemical evolution of Piton de la Fournaise volcano (1927-2010)

USGS Publications Warehouse

Pietruszka, Aaron J.; Vlastélic, Ivan

2015-01-01

Between 1927 and 2010, more than one hundred eruptions of Piton de la Fournaise produced ~1 km3 of lava, and the volcano’s summit collapsed twice (in 1931 and 2007). These lavas display, respectively, 20 and 65 % of the Sr–Nd and the Pb isotope ranges reported for La Réunion volcanoes over their known eruptive record (3.8 Ma). Variations in major and trace element concentrations and Sr–Pb isotopes do not define a temporal trend at the scale of the century, but display systematic short-term cyclic fluctuations. The positive correlation between 87Sr/86Sr and ratios of trace elements that are more versus less incompatible during partial melting of the mantle (e.g., Nd/Sm, La/Sm) probably results from the sampling of small-scale heterogeneities within the plume source. Changes in the degree of melting and/or crystallization are debated, but these appear ultimately linked to source properties. Lead isotopes do not co-vary with Sr isotopes, in part because of the partitioning of Pb into dense metallic phases that are preferentially sampled during high-flux eruptions. Taken together, Sr–Nd–Pb–Os–Th isotopes do not support contamination of magma with genetically unrelated components, such as the underlying Indian oceanic crust, mantle lithosphere, seawater, or seawater-altered lavas. Yet, in some rare cases (e.g. the 1998 Hudson eruption), the compositional patterns suggest that the parental magma assimilated older volcanic products within the edifice, such as crystal cumulates and/or interstitial differentiated melts. The geochemical fluctuations over the 1927–2010 time period constrain the residence time of magma in the shallow reservoir to 10–30 years and its size to 0.1–0.3 km3. The magma residence time during the course of the long-lived 1998 eruption is estimated to be an order of magnitude shorter, but the reservoir was probably of similar size. Instead, the shorter magma residence for the 1998 eruption was probably due to a higher magma flux.

Regional implications of geochemistry and style of emplacement of Miocene I-type diorite and granite, Delos, Cyclades, Greece

NASA Astrophysics Data System (ADS)

Pe-Piper, Georgia; Piper, David J. W.; Matarangas, Dionysis

2002-01-01

The Miocene plutons of the Cyclades were emplaced in a subduction setting during regional back-arc extension of continental crust, that led to flat-lying mid-crustal detachment faulting. Mapping of the island of Delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction. Mafic magmas were followed by numerous small batches of felsic magma, with magmatic and ductile deformation synchronous with magma emplacement. Late granite dykes occupy brittle fractures in the more deformed rocks. Mafic and intermediate rocks show a bimodal distribution of incompatible trace elements, with one group of broadly tholeiitic character and the other with substantial enrichment in Sr, Nb, and HFSE, but low Th and Ba. These differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern Cyclades. Voluminous granodiorite results from these mafic magmas fractionating and/or mixing with felsic crustal material, some of which was derived by anatexis of a sedimentary protolith, indicated by high B and Mn. Some late granites appear derived from partial melting of Hercynian paragneiss. Regionally, the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones. The shear zones parallel the Mid-Cycladic Lineament, a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the Hellenic subduction zone. Distinctive geochemical features in Miocene igneous rocks suggests that these two blocks had quite different geological histories. The localisation of plutonism and core complexes near the Mid Cycladic Lineament suggests that this crustal-scale shear played a role in bringing subduction-derived magmas to mid-crustal levels. The heat supplied by the mafic magmas promoted ductile deformation high in the crust, where extension was concentrated, leading to the formation of core complexes. The regional extension resulted in progressive shallowing of the position of the granite solidus within the crust, leading to welding of the Mid-Cycladic Lineament, which is no longer seismically active.

Numerical Modeling of Surface Deformation due to Magma Chamber Inflation/Deflation in a Heterogeneous Viscoelastic Half-space

NASA Astrophysics Data System (ADS)

Dichter, M.; Roy, M.

2015-12-01

Interpreting surface deformation patterns in terms of deeper processes in regions of active magmatism is challenging and inherently non-unique. This study focuses on interpreting the unusual sombrero-shaped pattern of surface deformation in the Altiplano Puna region of South America, which has previously been modeled as the effect of an upwelling diapir of material in the lower crust. Our goal is to investigate other possible interpretations of the surface deformation feature using a suite of viscoelastic models with varying material heterogeneity. We use the finite-element code PyLith to study surface deformation due to a buried time-varying (periodic) overpressure source, a magma body, at depth within a viscoelastic half-space. In our models, the magma-body is a penny-shaped crack, with a cylindrical region above the crack that is weak relative to the surrounding material. We initially consider a magma body within a homogeneous viscoelastic half-space to determine the effect of the free surface upon deformation above and beneath the source region. We observe a complex depth-dependent phase relationship between stress and strain for elements that fall between the ground surface and the roof of the magma body. Next, we consider a volume of weak material (faster relaxation time relative to background) that is distributed with varying geometry around the magma body. We investigate how surface deformation is governed by the spatial distribution of the weak material and its rheologic parameters. We are able to reproduce a "sombrero" pattern of surface velocities for a range of models with material heterogeneity. The wavelength of the sombrero pattern is primarily controlled by the extent of the heterogeneous region, modulated by flexural effects. Our results also suggest an "optimum overpressure forcing frequency" where the lifetime of the sombrero pattern (a transient phenomenon due to the periodic nature of the overpressure forcing) reaches a maximum. Through further research we hope to better understand how the parameter space of our forward model controls the distribution of surface deformation and eventually develop a better understanding of the observed pattern of surface deformation in the Altiplano Puna.

Tap water isotopes reveal the San Francisco Bay Area's plumbing and responses to a major drought

NASA Astrophysics Data System (ADS)

Tipple, B. J.; Jameel, M. Y.; Chau, T. H.; Mancuso, C. J.; Bowen, G. J.; Dufour, A.; Chesson, L. A.; Ehleringer, J. R.

2016-12-01

Water availability and sustainability in the Western United States is a major flashpoint among expanding communities, growing industries, and productive agricultural lands. This issue came to a head in 2015 in the State of California, when the State mandated a 25% reduction in urban water use following a multi-year drought that significantly depleted water resources. The demands for and challenges in supplying water are only expected to intensify as climate perturbations, such as the 2012-2015 California Drought, become more common. As a consequence, there is an increased need to understand linkages between population centers, water transport and usage, and the impacts of climate change on water resources and infrastructure. To better understand these relationships within a megalopolis in the Western United States, we collected and analyzed 723 tap waters from the San Francisco Bay Area during seven collection campaigns across 21 months during 2013-2015. San Francisco Bay Area was selected as it has well-known water management strategies and its water resources were dramatically affected by the 2012-2105 drought. Consistent with known water management strategies and previous reports of tap water isotope values, we found large spatiotemporal variations in the δ2H and δ18O values of tap waters, indicative of complex water transport systems and municipality-scale management decisions. We observed δ2H and δ18O values of tap water consistent with waters originating from snowmelt from the Sierra Nevada Mountains, local precipitation, ground water, and partially evaporated reservoir sources. A cluster analysis of measured tap water data grouped waters from 43 static sampling sites that were associated with specific water utility providers within the San Francisco Bay Area and known management practices. Water management responses to the drought, such as source switching, bringing in new sources, and conservation, could be observed within the isotope data from each of collection campaigns. Finally, we used a modified Craig-Gordon model of evaporative loss from one utility's reservoir system during the 2015 water year to estimate the consequences of the drought on this resource. Using these isotope methods, we estimated that approximately 10% of the water in this reservoir system was lost to evaporation.

The Magmatic Plumbing System of the Campi Flegrei Caldera.

NASA Astrophysics Data System (ADS)

Lucia, C.; Ilenia, A.; Massimo, D.; Valeria, D.; Mauro, D.; Giovanni, O.

2006-12-01

The Campi Flegrei caldera is a nested and resurgent structure generated by at least two major collapses. Large sectors of the structural boundary of both calderas resulted from partial reactivation of pre-existing faults generated by regional tectonism. Its magmatic system is still active with the last eruption occurring in 1538 A.D. (Monte Nuovo), widespread fumaroles and hot springs activity, and the unrest episodes in the last 35 years, with a maximum net uplift of about 3.5 m in the Pozzuoli area. The definition of the history of the magmatic feeding system of this caldera, in terms of composition, time- scale and depth of crystallization, relation between composition of the erupted magma and structural position of the vent, and magma chamber processes, is of extreme importance for a better understanding of the dynamic conditions of the present day magma chamber and for evaluating of the extent to which the behavior of the magmatic system can be predicted. The Campi Flegrei caldera magmatic plumbing system is characterized by deep and shallow reservoirs. Campi Flegrei magmas originated in a subduction modified mantle source, stagnate at mid crustal level (20- 10 km depth), where they differentiated and are contaminated with the continental crust. From the "deep reservoir" shoshonitic to latitic magmas rise towards the surface along the NE aligned regional fault reactivated during the caldera collapse, whereas trachytic magmas rise mostly along faults and fractures bordering the resurgent block and the southern part of the Campi Flegrei caldera. Repeated arrival of trachytic to phonolitic magmas form shallow reservoirs at 4-3 km depth, in which differentiation and mixing processes occur before and during the eruption.

Young Prehistoric Kilauea Lava Flows From Uwekahuna Bluff, Hawaii: Mixed Source or Hybrid Magmas?

NASA Astrophysics Data System (ADS)

Marske, J. P.; Pietruszka, A. J.; Garcia, M. O.; Norman, M. D.; Rhodes, J. M.

2004-12-01

For the last 350 kyr, nearly the entire known compositional range of subaerial and submarine Kilauea lavas lie within the range defined by the volcano's historical eruptions. In contrast, Rhodes et al. (1989) discovered that some Kilauea lavas have Mauna Loa-like major-and trace-element signatures and concluded that Mauna Loa magmas may periodically invade Kilauea's shallow plumbing system. Here, we present new major- and trace- element data for 25 sequential prehistoric lava flows (0.5 to <2 ka) from the upper 55 m of the north wall of Kilauea caldera at Uwekahuna Bluff (UB). Although historical Kilauea and Mauna Loa lavas have been compositionally distinct for most of the last 230 kyr, our results show that the UB lavas span the geochemical spectrum between these neighboring volcanoes. At a given MgO content, the abundances of major elements (e.g., SiO2, TiO2, or CaO) in the UB lavas typically plot between historical Mauna Loa and Kilauea values, suggesting that these lavas originated from compositionally intermediate parental magmas or from hybridization between historical Kilauea- and Mauna Loa-type magmas. In contrast to the major element abundances, ratios of highly to moderately incompatible elements (e.g., Nb/Y) in the UB lavas are mostly Mauna Loa-like. These incompatible trace element ratios reveal a rapid fluctuation of Kilauea's lava composition since prehistoric times: (1) two lava flows at the base of the suite record a decrease in Nb/Y from historical Kilauea- to historical Mauna Loa-type values, (2) a weathered hiatus near the middle of the flow sequence coincides with a gradual Nb/Y minimum and reversal, and (3) the top three lava flows transition back into historical Kilauea-type Nb/Y values with a smooth temporal connection to the oldest historical lavas from this volcano. The systematic variations of these UB trace-element ratios may result from gradual mixing between Kilauea- and Mauna Loa-type magmas within the summit reservoir and/or varying degrees of partial melting of a Mauna Loa-like mantle heterogeneity within Kilauea's source region. Highly incompatible element ratios (e.g., Rb/Nb), which are typically unaffected by variable melt fraction, indicate that changes in the degree of partial melting alone cannot explain these Mauna Loa-like lava flows. Pb, Sr and Nd isotopic ratios of the Uwekahuna Bluff lavas will be presented to differentiate mantle source and melting effects from magma chamber processes.

Deep magma accumulation at Nyamulagira volcano in 2011 detected by GNSS observations

NASA Astrophysics Data System (ADS)

Ji, Kang Hyeun; Stamps, D. Sarah; Geirsson, Halldor; Mashagiro, Niche; Syauswa, Muhindo; Kafudu, Benjamin; Subira, Josué; d'Oreye, Nicolas

2017-10-01

People in the area of the Virunga Mountains, along the borders of the Democratic Republic of Congo, Rwanda, and Uganda, are at very high natural risk due to active volcanism. A Global Navigation Satellite System (GNSS) network, KivuGNet (Kivu Geodetic Network), has operated since 2009 for monitoring and research of the deformation of Nyamulagira and Nyiragongo volcanoes as well as tectonic deformation in the region. We detected an inflationary signal from the position time-series observed in the network using our detection method, which is a combination of Kalman filtering and principal component analysis. The inflation event began in October 2010 and lasted for about 6 months prior to the 2011-2012 eruption at Nyamulagira volcano. The pre-eruptive inflationary signal is much weaker than the co-eruptive signal, but our method successfully detected the signal. The maximum horizontal and vertical displacements observed are ∼9 mm and ∼5 mm, respectively. A Mogi point source at a depth >10 km can explain the displacement field. This suggests that a relatively deep source for the magma chamber generated the inflationary signal. The deep reservoir that is the focus of this study may feed a shallower magma chamber, which is the likely source of the 2011-2012 eruption. Continuous monitoring of the volcanic activity is essential for understanding the eruption cycle and assessing potential volcanic hazards.

Hydrogen, Oxygen and Silicon Isotope Systematics of Groundwater-Magma Interaction in Icelandic Hydrothermal Systems

NASA Astrophysics Data System (ADS)

Kleine, B. I.; Stefansson, A.; Halldorsson, S. A.; Martin, W.; Barnes, J.; Jónasson, K.; Franzson, H.

2016-12-01

Magma often encounters groundwater (meteoric or seawater derived) when intruded into the crust. Magma-groundwater interactions result in the formation of hydrothermal fluids which can lead to contact metamorphism and elemental transport in the country rock. In fact, magma-hydrothermal fluid interaction (rather than magma-magmatic fluid interaction) may lead to classic contact metamorphic reactions. In order to explore the importance of hydrothermal fluid during contact metamorphism we use stable isotopes (δD, δ18O, δ30Si) from both active and extinct magma chambers and hydrothermal systems from across Iceland. Quartz grains from various hydrothermal systems, from crustal xenoliths from the Askja central volcano and from the Hafnarfjall pluton, as well as quartz grains associated with low-T zeolites were analysed for δ18O and δ30Si in-situ using SIMS. Whole rock material of these samples was analysed for δD values using a TCEA coupled to an IRMS. Our results indicate that low-T quartz (<150°C) are dominated by negative δ30Si values whereas positive δ30Si values prevail in quartz precipitated at higher T (>300°C). Combining the results from the analyses of δ18O and δD allows further division of samples into (i) seawater and/or rock dominated and (ii) meteoric water dominated hydrothermal systems. In order to isolate the effects of fluid-rock interaction, fluid source and formation temperature at the magma-groundwater contact, δD, δ18O and δ30Si values of rocks and fluids were modeled using the PHREEQC software. Comparison of analytical and model results shows that the isotopic compositions are influenced by multiple processes. In some cases, groundwater penetrates the contact zone and causes alteration at >400°C by groundwater-magma heat interaction. Other cases document "baked" contact zones without groundwater. Our analyses and modeling demonstrates that groundwater flow and permeability are crucial in setting the style of contact metamorphism around high T intrusions.

Why do magmas stall? Insights from petrologic and geodetic data

NASA Astrophysics Data System (ADS)

Zimmer, M. M.; Plank, T.; Freymueller, J.; Hauri, E. H.; Larsen, J. F.; Nye, C. J.

2007-12-01

Magmas stall at various depths in the crust due to their internal properties (magma viscosity, buoyancy) and external crustal controls (local stress regime, wallrock strength). Annen et al. (JPet 2006) propose a petrological model in which buoyant magma ascends through the crust until the depth of water saturation, after which it crystallizes catastrophically and stalls due to the large increase in magma viscosity. Magmas may erupt from this storage region, or viscous death may result in pluton formation. In order to test this model, and constrain magma storage depths, we combine petrological and geodetic data for several active volcanoes along the Aleutian-Alaska arc. We analyzed glassy, primarily olivine-hosted melt inclusions by SIMS in tephra samples for their pre-eruptive volatile contents, which can be related to the depth of entrapment via pressure-dependent H2O-CO2 solubility models (e.g., VolatileCalc). Melt inclusions are not in equilibrium with pure water vapor (all will contain S and C species), but >50% of the inclusion population are in equilibrium with a vapor containing >85% H2O. Geodetic data (InSAR, GPS) record surface deformation related to volcano inflation/deflation, and can be inverted to solve for the depths of volume change (magma storage) in the crust. In the Aleutians, we find that the maximum melt inclusion trapping depths and geodetic depths correlate, suggesting both techniques record crustal magma storage and crystallization. Melt inclusions from the 1997 Okmok eruption are trapped at ≤3 km; deformation during the eruption and subsequent inflation occurred at 3±0.5 km (Miyagi et al., EPSL 2004; Lu & Masterlark, JGR 2005). At Akutan, melt inclusions and GPS data indicate magma storage at ~5-7 km. Inclusions from flank cones of Makushin yield depths of 7 km, similar to inflation observed beneath the main edifice (6.8 km, Lu et al., JGR 2002). Pleistocene inclusions from Augustine volcano indicate magma storage at 10-18 km, in accord with a deep magma source proposed for the 2006 eruption. Melt inclusions from Shishaldin are trapped at depths up to 4 km, coincident with the base of the conduit (Vergnoille & Caplan Auerbach, BVolc 2006). Other volcanoes record similar depths of melt inclusion entrapment and deformation, including Mt. St. Helens, Irazú, Soufriere Hills, Vesuvius, and Etna. Clearly, crystallization will occur where magmas stall, cool, and degas, so it may not be surprising that the depths of deformation correlate with the depths of melt inclusion entrapment. But the question of why magmas stall at various depths remains. In the Aleutians, maximum H2O contents of melt inclusions (from 2 wt% at Shishaldin to 7 wt% at Augustine) negatively correlate with measures of the degree of mantle melting (Ti6.0 and Y6.0), which is expected if water drives mantle melting beneath arcs (e.g. Kelley et al. JGR 2006; Portnyagin et al EPSL 2007). Thus, if magmas stall near the depths where they reach H2O-saturation, as predicted by Annen et al. and observed here, then magma chamber and pluton depths may ultimately be controlled by the primary magmatic water contents set in the mantle.

Olivine-hosted melt inclusions as an archive of redox heterogeneity in magmatic systems

NASA Astrophysics Data System (ADS)

Hartley, Margaret E.; Shorttle, Oliver; Maclennan, John; Moussallam, Yves; Edmonds, Marie

2017-12-01

The redox state of volcanic products determines their leverage on the oxidation of Earth's oceans and atmosphere, providing a long-term feedback on oxygen accumulation at the planet's surface. An archive of redox conditions in volcanic plumbing systems from a magma's mantle source, through crustal storage, to eruption, is carried in pockets of melt trapped within crystals. While melt inclusions have long been exploited for their capacity to retain information on a magma's history, their permeability to fast-diffusing elements such as hydrogen is now well documented and their retention of initial oxygen fugacities (fO2) could be similarly diffusion-limited. To test this, we have measured Fe3+/ΣFe by micro-XANES spectroscopy in a suite of 65 olivine-hosted melt inclusions and 9 matrix glasses from the AD 1783 Laki eruption, Iceland. This eruption experienced pre-eruptive mixing of chemically diverse magmas, syn-eruptive degassing at the vent, and post-eruptive degassing during lava flow up to 60 km over land, providing an ideal test of whether changes in the fO2 of a magma may be communicated through to its cargo of crystal-hosted melt inclusions. Melt inclusions from rapidly quenched tephra samples have Fe3+/ΣFe of 0.206 ± 0.008 (ΔQFM of +0.7 ± 0.1), with no correlation between their fO2 and degree of trace element enrichment or differentiation. These inclusions preserve the redox conditions of the mixed pre-eruptive Laki magma. When corrected for fractional crystallisation to 10 wt.% MgO, these inclusions record a parental magma [Fe3+/ΣFe](10) of 0.18 (ΔQFM of +0.4), significantly more oxidised than the Fe3+/ΣFe of 0.10 that is often assumed for Icelandic basalt magmas. Melt inclusions from quenched lava selvages are more reduced than those from the tephra, having Fe3+/ΣFe between 0.133 and 0.177 (ΔQFM from -0.4 to +0.4). These inclusions have approached equilibrium with their carrier lava, which has been reduced by sulfur degassing. The progressive re-equilibration of fO2 between inclusions and carrier melts occurs on timescales of hours to days, causing a drop in the sulfur content at sulfide saturation (SCSS) and driving the exsolution of immiscible sulfide globules in the inclusions. Our data demonstrate the roles of magma mixing, progressive re-equilibration, and degassing in redox evolution within magmatic systems, and the open-system nature of melt inclusions to fO2 during these processes. Redox heterogeneity present at the time of inclusion trapping may be overprinted by rapid re-equilibration of melt inclusion fO2 with the external environment, both in the magma chamber and during slow cooling in lava at the surface. This can decouple the melt inclusion archives of fO2, major and trace element chemistry, and mask associations between fO2, magmatic differentiation and mantle source heterogeneity unless the assembly of diverse magmas is rapidly followed by eruption. Our tools for understanding the redox conditions of magmas are thus limited; however, careful reconstruction of pre- and post-eruptive magmatic history has enabled us to confirm the relatively oxidised nature of ocean island-type mantle compared to that of mid-ocean ridge mantle.

The temporal evolution of back-arc magmas from the Auca Mahuida shield volcano (Payenia Volcanic Province, Argentina)

NASA Astrophysics Data System (ADS)

Pallares, Carlos; Quidelleur, Xavier; Gillot, Pierre-Yves; Kluska, Jean-Michel; Tchilinguirian, Paul; Sarda, Philippe

2016-09-01

In order to better constrain the temporal volcanic activity of the back-arc context in Payenia Volcanic Province (PVP, Argentina), we present new K-Ar dating, petrographic data, major and trace elements from 23 samples collected on the Auca Mahuida shield volcano. Our new data, coupled with published data, show that this volcano was built from about 1.8 to 1.0 Ma during five volcanic phases, and that Auca Mahuida magmas were extracted from, at least, two slightly different OIB-type mantle sources with a low partial melting rate. The first one, containing more garnet, was located deeper in the mantle, while the second contains more spinel and was thus shallower. The high-MgO basalts (or primitive basalts) and the low-MgO basalts (or evolved basalts), produced from the deeper and shallower lherzolite mantle sources, respectively, are found within each volcanic phase, suggesting that both magmatic reservoirs were sampled during the 1 Myr lifetime of the Auca Mahuida volcano. However, a slight increase of the proportion of low-MgO basalts, as well as of magmas sampled from the shallowest source, can be observed through time. Similar overall petrological characteristics found in the Pleistocene-Holocene basaltic rocks from Los Volcanes and Auca Mahuida volcano suggest that they originated from the same magmatic source. Consequently, it can be proposed that the thermal asthenospheric anomaly is probably still present beneath the PVP. Finally, our data further support the hypothesis that the injection of hot asthenosphere with an OIB mantle source signature, which was triggered by the steepening of the Nazca subducting plate, induced the production of a large volume of lavas within the PVP since 2 Ma.

Earthquake sources near Uturuncu Volcano

NASA Astrophysics Data System (ADS)

Keyson, L.; West, M. E.

2013-12-01

Uturuncu, located in southern Bolivia near the Chile and Argentina border, is a dacitic volcano that was last active 270 ka. It is a part of the Altiplano-Puna Volcanic Complex, which spans 50,000 km2 and is comprised of a series of ignimbrite flare-ups since ~23 ma. Two sets of evidence suggest that the region is underlain by a significant magma body. First, seismic velocities show a low velocity layer consistent with a magmatic sill below depths of 15-20 km. This inference is corroborated by high electrical conductivity between 10km and 30km. This magma body, the so called Altiplano-Puna Magma Body (APMB) is the likely source of volcanic activity in the region. InSAR studies show that during the 1990s, the volcano experienced an average uplift of about 1 to 2 cm per year. The deformation is consistent with an expanding source at depth. Though the Uturuncu region exhibits high rates of crustal seismicity, any connection between the inflation and the seismicity is unclear. We investigate the root causes of these earthquakes using a temporary network of 33 seismic stations - part of the PLUTONS project. Our primary approach is based on hypocenter locations and magnitudes paired with correlation-based relative relocation techniques. We find a strong tendency toward earthquake swarms that cluster in space and time. These swarms often last a few days and consist of numerous earthquakes with similar source mechanisms. Most seismicity occurs in the top 10 kilometers of the crust and is characterized by well-defined phase arrivals and significant high frequency content. The frequency-magnitude relationship of this seismicity demonstrates b-values consistent with tectonic sources. There is a strong clustering of earthquakes around the Uturuncu edifice. Earthquakes elsewhere in the region align in bands striking northwest-southeast consistent with regional stresses.

Petrology of basalts from Loihi Seamount, Hawaii

NASA Astrophysics Data System (ADS)

Hawkins, James; Melchior, John

1983-12-01

Loihi Seamount is the southeasternmost active volcano of the Emperor-Hawaii linear volcanic chain. It comprises a spectrum of basalt compositional varieties including basanite, alkali basalt, transitional basalt and tholeiite. Samples from four dredge collections made on Scripps Institution of Oceanography Benthic Expedition in October 1982 are tholeiite. The samples include highly vesicular, olivine-rich basalt and dense glass-rich pillow fragments containing olivine and augite phenocrysts. Both quartz-normative and olivine-normative tholeiites are present. Minor and trace element data indicate relatively high abundances of low partition coefficient elements (e.g., Ti, K, P. Rb, Ba, Zr) and suggest that the samples were derived by relatively small to moderate extent of partial melting, of an undepleted mantle source. Olivine composition, MgO, Cr and Ni abundances, and Mg/(Mg+Fe), are typical of moderately fractionated to relatively unfractionated "primary" magmas. The variations in chemistry between samples cannot be adequately explained by low-pressure fractional crystallization but can be satisfied by minor variations in extent of melting if a homogeneous source is postulated. Alternatively, a heterogeneous source with variable abundances of certain trace elements, or mixing of liquids, may have been involved. Data for 3He/ 4He, presented in a separate paper, implies a mantle plume origin for the helium composition of the Loihi samples. There is little variation in the helium isotope ratio for samples having different compositions and textures. The helium data are not distinctive enough to unequivocally separate the magma sources for the tholeiitic rocks from the other rock types such as Loihi alkalic basalts and the whole source region for Loihi may have a nearly uniform helium compositions even though other element abundances may be variable. Complex petrologic processes including variable melting, fractional crystallization and magma mixing may have blurred original helium isotopic signatures.

Very slow lava extrusion continued for more than five years after the 2011 Shinmoedake eruption observed from SAR interferometry

NASA Astrophysics Data System (ADS)

Ozawa, T.; Miyagi, Y.

2017-12-01

Shinmoe-dake located to SW Japan erupted in January 2011 and lava accumulated in the crater (e.g., Ozawa and Kozono, EPS, 2013). Last Vulcanian eruption occurred in September 2011, and after that, no eruption has occurred until now. Miyagi et al. (GRL, 2014) analyzed TerraSAR-X and Radarsat-2 SAR data acquired after the last eruption and found continuous inflation in the crater. Its inflation decayed with time, but had not terminated in May 2013. Since the time-series of inflation volume change rate fitted well to the exponential function with the constant term, we suggested that lava extrusion had continued in long-term due to deflation of shallow magma source and to magma supply from deeper source. To investigate its deformation after that, we applied InSAR to Sentinel-1 and ALOS-2 SAR data. Inflation decayed further, and almost terminated in the end of 2016. It means that this deformation has continued more than five years from the last eruption. We have found that the time series of inflation volume change rate fits better to the double-exponential function than single-exponential function with the constant term. The exponential component with the short time constant has almost settled in one year from the last eruption. Although InSAR result from TerraSAR-X data of November 2011 and May 2013 indicated deflation of shallow source under the crater, such deformation has not been obtained from recent SAR data. It suggests that this component has been due to deflation of shallow magma source with excess pressure. In this study, we found the possibility that long-term component also decayed exponentially. Then this factor may be deflation of deep source or delayed vesiculation.

Oscillation of a Shallow Hydrothermal Fissure Inferred from Long-Period Seismic Events at Taal Volcano, the Philippines

NASA Astrophysics Data System (ADS)

Maeda, Y.; Kumagai, H.; Lacson, R.; Figueroa, M. S.; Yamashina, T.

2012-12-01

We installed a multi-parameter monitoring network including five broadband seismometers at Taal volcano, the Philippines, where a high risk of near-future eruption is expected. The network detected more than 40,000 long-period (LP) seismic events which have a peak frequency of 0.8 Hz and a Q value of 6. Most of the events occurred in a 2-month-long swarm period of ~600 events/day. Our travel time analysis pointed to a shallow source (100-200 m) beneath the northeastern flank of the active volcanic island. To determine the source mechanism of the LP events, we performed waveform inversion. We first fixed the source location to that obtained by the travel time analysis, and performed inversion using waveforms with and without site amplification corrections and assuming four simple source geometries (a vertical crack, a horizontal crack, a vertical pipe, and a sphere). We obtained the minimum AIC value for the vertical crack source geometry using the corrected waveforms. We next performed a grid search for dip, azimuth, and the location of the tensile crack source using the corrected waveforms. We obtained small residuals for crack dips between 30 and 60 degrees at similar locations to that of the travel time analysis. We used the fluid-filled crack model to interpret the observed complex frequencies of the events. The observed waveforms of the events show a small Q value (= 6), which may be explained by bubbly basalt, bubbly water, or gas. However, since the source location is estimated to be shallow (100-200 m) and we have no evidence for an ascent of magma to such a shallow depth in the swarm period, bubbly basalt seems to be unrealistic. It seems difficult to maintain bubbly water in the inclined crack. For bubbly water, a peak frequency variation is expected to occur due to a variation of the bubble content, whereas the observed peak frequencies of the events are almost constant. The constant frequency is more easily realized by gas in a crack. We therefore examine H2O gas (vapor) for simplicity. We calculated far-field waveforms generated by an oscillation of a crack containing vapor, and applied the Sompi method to estimate Q and nondimensional frequency. The estimated Q of a fundamental longitudinal mode oscillation was similar to the observation. We obtained a reasonable crack size (188 m) from a comparison of the observed peak frequency (0.8 Hz) with the calculated nondimensional frequency of the mode. In the swarm period of the LP events, other anomalies such as large volcano deformation and significant increase of gas emission from the main crater were not observed. This feature and the crack model result above suggest an active and localized vapor supply from magma at depth to the LP source. Such a localized supply may be realized by a transportation of vapor through a fissure. If we assume that the estimated crack volume (10^2 m^3) corresponds to vapor supplied to the LP source for each event, the total vapor mass supplied throughout the swarm period is ~10^7 kg. If we assume that this amount of vapor was originated by degassing from the magma and transported to the LP source through the fissure, we can estimate a magma volume of ~10^6 m^3. We thus suggest that the LP events at Taal were triggered by degassing and transportation of vapor from a deep magma to a shallow depth through a fissure.

Applying Fractal Dimensions and Energy-Budget Analysis to Characterize Fracturing Processes During Magma Migration and Eruption: 2011-2012 El Hierro (Canary Islands) Submarine Eruption

NASA Astrophysics Data System (ADS)

López, Carmen; Martí, Joan; Abella, Rafael; Tarraga, Marta

2014-07-01

The impossibility of observing magma migration inside the crust obliges us to rely on geophysical data and mathematical modelling to interpret precursors and to forecast volcanic eruptions. Of the geophysical signals that may be recorded before and during an eruption, deformation and seismicity are two of the most relevant as they are directly related to its dynamic. The final phase of the unrest episode that preceded the 2011-2012 eruption on El Hierro (Canary Islands) was characterized by local and accelerated deformation and seismic energy release indicating an increasing fracturing and a migration of the magma. Application of time varying fractal analysis to the seismic data and the characterization of the seismicity pattern and the strain and the stress rates allow us to identify different stages in the source mechanism and to infer the geometry of the path used by the magma and associated fluids to reach the Earth's surface. The results obtained illustrate the relevance of such studies to understanding volcanic unrest and the causes that govern the initiation of volcanic eruptions.

Native gold in Hawaiian alkalic magma

USGS Publications Warehouse

Sisson, T.W.

2003-01-01

Native gold found in fresh basanite glass from the early submarine phase of Kilauea volcano, Hawaii, may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle-derived magma. The gold-bearing glass is a grain in bedded volcanic glass sandstone (Japan Marine Science and Technology Center (JAMSTEC) sample S508-R3) collected by the submersible Shinkai 6500 at 3879 m depth off Kilauea's south flank. Extensive outcrops there expose debris-flow breccias and sandstones containing submarine-erupted alkalic rock fragments and glasses from early Kilauea. Precipitation of an immiscible gold liquid resulted from resorption of magmatic sulfides during crystallization-differentiation, with consequent liberation of sulfide-hosted gold. Elevated whole-rock gold concentrations (to 36 ppb) for fresh lavas and clasts from early Kilauea further show that some magmas erupted at the beginning stages of Hawaiian shield volcanoes were distinctly gold rich, most likely owing to limited residual sulfide in their mantle source. Alkalic magmas at other ocean islands may also be gold rich, and oceanic hot-spot provinces may contain underappreciated gold resources.

Pressurized magma reservoir within the east rift zone of Kīlauea Volcano, Hawai`i: Evidence for relaxed stress changes from the 1975 Kalapana earthquake

NASA Astrophysics Data System (ADS)

Baker, Scott; Amelung, Falk

2015-03-01

We use 2000-2012 InSAR data from multiple satellites to investigate magma storage in Kīlauea's east rift zone (ERZ). The study period includes a surge in magma supply rate and intrusion-eruptions in 2007 and 2011. The Kupaianaha area inflated by ~5 cm prior to the 2007 intrusion and the Nāpau Crater area by ~10 cm following the 2011 intrusion. For the Nāpau Crater area, elastic modeling suggests an inflation source at 5 ± 2 km depth or more below sea level. The reservoir is located in the deeper section of the rift zone for which secular magma intrusion was inferred for the period following the 1975 Mw7.7 décollement earthquake. Reservoir pressurization suggests that in this section of the ERZ, extensional stress changes due to the earthquake have largely been compensated for and that this section is approaching its pre-1975 state. Reservoir pressurization also puts the molten core model into question for this section of Kīlauea's rift zone.

Geochemical and mineralogical analysis of Gruithuisen region on Moon using M3 and DIVINER images

NASA Astrophysics Data System (ADS)

Kusuma, K. N.; Sebastian, N.; Murty, S. V. S.

2012-07-01

Spectral information from the Moon Mineralogy Mapper (M3) onboard Chandrayaan-1 and DIVINER Lunar Radiometer onboard LRO have been used for geochemical and mineralogical characterisation of the Gruithuisen region on Moon along with morphometrical information from LOLA Digital elevation model. The apparent reflectance of M3 on global mode is used for (1) spectral characterisation (2) estimating the abundance of Ti and Fe using Lucey's method and (3) discriminating non-mare region from mare regions by means of Minimum Noise Fraction (MNF) transform and Integrated Band Depth (IBD) parameters. Christensen frequency (CF) value derived from DIVINER data is used to delineate the silica saturated lithology from the undersaturated rocks as well as to delineate their spatial spread. Low values of FeO, TiO2, and IBD indicate non-mare nature of the domes and highland material, also supplemented by CF values. The highland rocks represent signatures of sodic plagioclase, the end result of plagioclase crystallisation from Lunar Magma Ocean. Compositional variations are observed among the domes. NW dome has highest silica concentration than the other two domes and in turn higher viscosity. It is most likely that the three domes tapped residual liquid from different locations of the residual magma chamber which is in constant mixing. The extrusion is probably a localised phenomenon, where urKREEP welled out along the zone of crustal weakness formed by Imbrium Impact. It is likely that δ dome has extruded over a larger time span than other two features.

Mantle helium in ground waters of eastern North America: Time and space constraints on sources

USGS Publications Warehouse

Torgersen, T.; Drenkard, S.; Stute, M.; Schlosser, P.; Shapiro, A.

1995-01-01

Mantle helium in continental environments is generally considered to be the result of active volcanism and/or active extension. The latest episodes of volcanism in northeastern North America are the track of the New England hotspot (95–190 Ma) and the closure of the Iapetus sea (before 300 Ma). Thus, the identification of mantle helium in young ground waters of central New England is counter to the conventional wisdom. On the basis of evaluation of helium evolution in emplaced magmas, we postulate an “aged” mantle source for the excess helium component in ground waters of central New England that is either (1) a local, near-surface–emplaced, gas-rich magma that has retained significant volatiles (e.g., in fluid inclusions) or (2) a deeply emplaced gas-rich magma with high initial 2He/4He (10−5) and helium transport (with dispersion) through the crust over time. This gas-rich initial condition may support the concept of a volatile-enriched mantle wedge and thus explain the increased buoyancy flux of the New England hotspot as it traversed eastern North America, as has been suggested by others.

Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field

USGS Publications Warehouse

Hildreth, W.; Halliday, A.N.; Christiansen, R.L.

1991-01-01

Since 2.2 Ma, the Yellowstone Plateau Volcanic Field has produced ~6000 km3 of rhyolite tuffs and lavas in >60 separate eruptions, as well as ~100 km3 of tholeiitic basalt from >50 vents peripheral to the silicic focus. Intermediate eruptive products are absent. Early postcollapse rhyolites show large shifts in Nd, Sr, Pb, and O isotopic composition caused by assimilation of roof rocks and hydrothermal brines during collapse and resurgence. Younger intracaldera rhyolite lavas record partial isotopic recovery toward precaldera ratios. Thirteen extracaldera rhyolites show none of these effects and have sources independent of the subcaldera magma system. Contributions from the Archaean crust have extreme values and wide ranges of Nd-, Sr, and Pb-isotope ratios, but Yellowstone rhyolites have moderate values and limited ranges. This requires their deep-crustal sources to have been pervasively hybridized by distributed intrusion of Cenozoic basalt, most of which was probably contemporaneous with the Pliocene and Quaternary volcanism. Most Yellowstone basalts had undergone cryptic clinopyroxene fractionation in the lower crust or crust-mantle transition zone and, having also ascended through or adjacent to crustal zones of silicic-magma generation, most underwent some crustal contamination. -from Authors

Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii

USGS Publications Warehouse

Okubo, Paul G.; Benz, Harley M.; Chouet, Bernard A.

1997-01-01

Three-dimensional seismic P-wave traveltime tomography is used to image the magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii. High-velocity bodies (>6.4 km/s) in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro-ultramafic cumulates from which the surface volcanism is derived. The proximity of these high-velocity features to the rift zones is consistent with a ridge-spreading model of the volcanic flank. Southeast of the Hilina fault zone, along the south flank of Kilauea, low-velocity material (<6.0 km/s) is observed extending to depths of 9–11 km, indicating that the Hilina fault may extend possibly as deep as the basal decollement. Along the southeast flank of Mauna Loa, a similar low-velocity zone associated with the Kaoiki fault zone is observed extending to depths of 6–8 km. These two upper crustal low-velocity zones suggest common stages in the evolution of the Hawaiian shield volcanoes in which these fault systems are formed as a result of upper crustal deformation in response to magma injection within the volcanic edifice.

Crustal tomography of the 2016 Kumamoto earthquake area in West Japan using P and PmP data

NASA Astrophysics Data System (ADS)

Wang, Haibo; Zhao, Dapeng; Huang, Zhouchuan; Xu, Mingjie; Wang, Liangshu; Nishizono, Yukihisa; Inakura, Hirohito

2018-05-01

A high-resolution model of three-dimensional (3-D) P-wave velocity (Vp) tomography of the crust in the source area of the 2016 Kumamoto earthquake (M 7.3) in West Japan is determined using a large number of arrival times of first P-waves and reflected P-waves from the Moho discontinuity (PmP). The PmP data are collected from original seismograms of the Kumamoto aftershocks and other local crustal events in Kyushu. Detailed resolution tests show that the addition of the PmP data can significantly improve the resolution of the crustal tomography, especially that of the lower crust. Our results show that significant low-velocity (low-V) anomalies exist in the entire crust beneath the active arc volcanoes, which may reflect the pathway of arc magmas. The 2016 Kumamoto earthquake occurred at the edge of a small low-V zone in the upper crust. A significant low-V anomaly is revealed in the lower crust beneath the source zone, which may reflect the arc magma and fluids ascending from the mantle wedge. These results suggest that the rupture nucleation of the 2016 Kumamoto earthquake was affected by fluids and arc magma.

Formation of Hadean granites by melting of igneous crust

NASA Astrophysics Data System (ADS)

Burnham, A. D.; Berry, A. J.

2017-06-01

The oldest known samples of Earth, with ages of up to 4.4 Gyr, are detrital zircon grains in meta-sedimentary rocks of the Jack Hills in Australia. These zircons offer insights into the magmas from which they crystallized, and, by implication, igneous activity and tectonics in the first 500 million years of Earth’s history, the Hadean eon. However, the compositions of these magmas and the relative contributions of igneous and sedimentary components to their sources have not yet been resolved. Here we compare the trace element concentrations of the Jack Hills zircons to those of zircons from the locality where igneous (I-) and sedimentary (S-) type granites were first distinguished. We show that the Hadean zircons crystallized predominantly from I-type magmas formed by melting of a reduced, garnet-bearing igneous crust. Further, we propose that both the phosphorus content of zircon and the ratio of phosphorus to rare earth elements can be used to distinguish between detrital zircon grains from I- and S-type sources. These elemental discriminants provide a new geochemical tool to assess the relative contributions of primeval magmatism and melting of recycled sediments to the continents over geological time.

An unmetasomatized source for the Malaitan alnoeite (Solomon Islands): Petrogenesis involving zone refining, megacryst fractionation, and assimilation of oceanic lithosphere

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

Neal, C.R.; Davidson, J.P.

The Malaitan alnoite contains a rich and varied megacryst suite of unprecedented compositional range. The authors have undertaken trace element and isotope modeling in order to formulate a petrogenetic scheme which links the host alnoeite to its entrained megacrysts. This requires that a proto-alnoeite magma is the product of zone refining initiated by diapiric upwelling (where the initial melt passes through 200 times its volume of mantle). Isotopic evidence indicates the source of the proto-alnoeite contains a time-integrated LREE-depleted signature. Impingement upon the rigid lithosphere halts or dramatically slows the upward progress of the mantle diapir. At this point, themore » magma cools and megacryst fractionation begins with augites crystallizing first, followed by subcalcic diopsides and finally phlogopites. Garnet probably crystallizes over the entire range of clinopyroxene fractionation. Estimated proportions of fractionating phases are 30% augite, 24.5% subcalcic diopside, 27% garnet, 12.9% phlogopite, 5% bronzite, 0.5% ilmenite, and 0.1% zircon. As this proto-alnoeite magma crystallizes, it assimilates a subducted component of seawater-altered basalt which underplates the Ontong Java Plateau. This is witnessed in the isotopic composition of the megacrysts and alnoeite.« less

Asteroid differentiation - Pyroclastic volcanism to magma oceans

NASA Technical Reports Server (NTRS)

Taylor, G. J.; Keil, Klaus; Mccoy, Timothy; Haack, Henning; Scott, Edward R. D.

1993-01-01

A summary is presented of theoretical and speculative research on the physics of igneous processes involved in asteroid differentiation. Partial melting processes, melt migration, and their products are discussed and explosive volcanism is described. Evidence for the existence of asteroidal magma oceans is considered and processes which may have occurred in these oceans are examined. Synthesis and inferences of asteroid heat sources are discussed under the assumption that asteroids are heated mainly by internal processes and that the role of impact heating is small. Inferences of these results for earth-forming planetesimals are suggested.

Exposure assessment of radon in the drinking water supplies: a descriptive study in Palestine

PubMed Central

2012-01-01

Background Radon gas is considered as a main risk factor for lung cancer and found naturally in rock, soil, and water. The objective of this study was to determine the radon level in the drinking water sources in Nablus city in order to set up a sound policy on water management in Palestine. Methods This was a descriptive study carried out in two phases with a random sampling technique in the second phase. Primarily, samples were taken from 4 wells and 5 springs that supplied Nablus city residents. For each source, 3 samples were taken and each was analyzed in 4 cycles by RAD 7 device manufactured by Durridge Company. Secondly, from the seven regions of the Nablus city, three samples were taken from the residential tap water of each region. Regarding the old city, ten samples were taken. Finally, the mean radon concentration value for each source was calculated. Results The mean (range) concentration of radon in the main sources were 6.9 (1.5-23.4) Becquerel/liter (Bq/L). Separately, springs and wells' means were 4.6 Bq/L and 9.5 Bq/L; respectively. For the residential tap water in the 7 regions, the results of the mean (range) concentration values were found to be 1.0 (0.9-1.3) Bq/L. For the old city, the mean (range) concentration values were 2.3 (0.9-3.9) Bq/L. Conclusions Except for Al-Badan well, radon concentrations in the wells and springs were below the United State Environmental Protection Agency maximum contaminated level (U.S EPA MCL). The level was much lower for tap water. Although the concentration of radon in the tap water of old city were below the MCL, it was higher than other regions in the city. Preventive measures and population awareness on radon's exposure are recommended. PMID:22243625

Exposure assessment of radon in the drinking water supplies: a descriptive study in Palestine.

PubMed

Al Zabadi, Hamzeh; Musmar, Samar; Issa, Shaza; Dwaikat, Nidal; Saffarini, Ghassan

2012-01-13

Radon gas is considered as a main risk factor for lung cancer and found naturally in rock, soil, and water. The objective of this study was to determine the radon level in the drinking water sources in Nablus city in order to set up a sound policy on water management in Palestine. This was a descriptive study carried out in two phases with a random sampling technique in the second phase. Primarily, samples were taken from 4 wells and 5 springs that supplied Nablus city residents. For each source, 3 samples were taken and each was analyzed in 4 cycles by RAD 7 device manufactured by Durridge Company. Secondly, from the seven regions of the Nablus city, three samples were taken from the residential tap water of each region. Regarding the old city, ten samples were taken. Finally, the mean radon concentration value for each source was calculated. The mean (range) concentration of radon in the main sources were 6.9 (1.5-23.4) Becquerel/liter (Bq/L). Separately, springs and wells' means were 4.6 Bq/L and 9.5 Bq/L; respectively. For the residential tap water in the 7 regions, the results of the mean (range) concentration values were found to be 1.0 (0.9-1.3) Bq/L. For the old city, the mean (range) concentration values were 2.3 (0.9-3.9) Bq/L. Except for Al-Badan well, radon concentrations in the wells and springs were below the United State Environmental Protection Agency maximum contaminated level (U.S EPA MCL). The level was much lower for tap water. Although the concentration of radon in the tap water of old city were below the MCL, it was higher than other regions in the city. Preventive measures and population awareness on radon's exposure are recommended.

Geochronology and geochemistry of the Huilvshan gabbro in west Junggar (NW China): Implications for magma process and tectonic regime

NASA Astrophysics Data System (ADS)

Zhang, Huichao; Zhu, Yongfeng

2018-06-01

Gabbro plutons, consisting of clinopyroxene and plagioclase with trace amounts of magnetite, titanite, and apatite, intruded into Early Carboniferous volcanic-sedimentary strata in the Huilvshan gold mining region (west Junggar, China). Samples collected from two gabbro bodies are tholeiitic in composition with low concentrations of Na2O + K2O, showing weak depletions of light rare earth elements with insignificant Eu, Nb, and Ti anomalies. Zircon U-Pb analyses yield a weighted average U-Pb age of 296.1 ± 2.7 Ma (MSWD = 0.98), which could represent the time corresponding to mafic magma emplacement in the Huilvshan region. Geochemical calculations suggest that this mafic magma was derived from a depleted mantle source in a post-collisional tectonic setting corresponding to 4% partial melting of spinel lherzolite.

Getting the lead out: understanding risks in the distribution system

EPA Science Inventory

This presentation discusses the importance of the water distribution system as a component of the source-to-tap continuum in public health protection. Issues covered include: understanding source water quality changes and their impacts throughout the system; use of mitigation me...

Spatio-temporal variation in the tap water isotope ratios of Salt Lake City: a novel indicator of urban water system structure and dynamics.

NASA Astrophysics Data System (ADS)

Jameel, M. Y.; Bowen, G. J.

2015-12-01

Public water supply systems are the life-blood of urban areas. How we use urban water systems affects more than human health and well-being. Our water use can alter a city's energy balance, including how much solar energy is absorbed as heat or reflected back into space. The severity of these effects, and the need to better understand connections between climate, water extraction, water use, and water use impacts, is strongest in areas of climatic aridity and substantial land-use change, such as the rapidly urbanizing areas of Utah. We have gathered and analyzed stable water isotope data from a series of semi-annual hydrological surveys (spring and fall, 2013 and 2014) in urban tap water sampled across the Salt Lake Valley. Our study has led to four major findings thus far: 1) Clear and substantial variation in tap water isotopic composition in space and time that can be linked to different water sources and management practices within the urban area, 2) There is a strong correlation between the range of observed isotope values and the population of water districts, reflecting use of water from multiple local and non-local sources in districts with high water demand, 3) Water isotopes reflect significant and variable loss of water due to evaporation of surface water resources and 4) Overall, tap water contains lower concentrations of the heavy H and O isotopes than does precipitation within the basin, reflecting the connection between city water supplies and mountain water sources. Our results highlight the utility of isotopic data as an indicator of heterogeneities within urban water systems, management practices and their variation across a major metropolitan area, and effects of climate variability on urban water supplies

Drinking water quality assessment.

PubMed

Aryal, J; Gautam, B; Sapkota, N

2012-09-01

Drinking water quality is the great public health concern because it is a major risk factor for high incidence of diarrheal diseases in Nepal. In the recent years, the prevalence rate of diarrhoea has been found the highest in Myagdi district. This study was carried out to assess the quality of drinking water from different natural sources, reservoirs and collection taps at Arthunge VDC of Myagdi district. A cross-sectional study was carried out using random sampling method in Arthunge VDC of Myagdi district from January to June,2010. 84 water samples representing natural sources, reservoirs and collection taps from the study area were collected. The physico-chemical and microbiological analysis was performed following standards technique set by APHA 1998 and statistical analysis was carried out using SPSS 11.5. The result was also compared with national and WHO guidelines. Out of 84 water samples (from natural source, reservoirs and tap water) analyzed, drinking water quality parameters (except arsenic and total coliform) of all water samples was found to be within the WHO standards and national standards.15.48% of water samples showed pH (13) higher than the WHO permissible guideline values. Similarly, 85.71% of water samples showed higher Arsenic value (72) than WHO value. Further, the statistical analysis showed no significant difference (P<0.05) of physico-chemical parameters and total coliform count of drinking water for collection taps water samples of winter (January, 2010) and summer (June, 2010). The microbiological examination of water samples revealed the presence of total coliform in 86.90% of water samples. The results obtained from physico-chemical analysis of water samples were within national standard and WHO standards except arsenic. The study also found the coliform contamination to be the key problem with drinking water.

The Role of Magma Mixing in Creating Magmatic Diversity

NASA Astrophysics Data System (ADS)

Davidson, J. P.; Collins, S.; Morgan, D. J.

2012-12-01

Most magmas derived from the mantle are fundamentally basaltic. An assessment of actual magmatic rock compositions erupted at the earth's surface, however, shows greater diversity. While still strongly dominated by basalts, magmatic rock compositions extend to far more differentiated (higher SiO2, LREE enriched) compositions. Magmatic diversity is generated by differentiation processes, including crystal fractionation/ accumulation, crustal contamination and magma mixing. Among these, magma mixing is arguably inevitable in magma systems that deliver magmas from source-to-surface, since magmas will tend to multiply re-occupy plumbing systems. A given mantle-derived magma type will mix with any residual magmas (and crystals) in the system, and with any partial melts of the wallrock which are generated as it is repeatedly flushed through the system. Evidence for magma mixing can be read from the petrography (identification of crystals derived from different magmas), a technique which is now well-developed and supplemented by isotopic fingerprinting (1,2) As a means of creating diversity, mixing is inevitably not efficient as its tendency is to blend towards a common composition (i.e. converging on homogeneity rather than diversity). It may be surprising then that many systems do not tend to homogenise with time, meaning that the timescales of mixing episodes and eruption must be similar to external magma contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of magma mixing may well bear on eruption triggering. When two magmas mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the magmas (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the magmas (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling these ideas together has suggested that mixing generates volatile release accompanied by geophysical signals, and the petrographic fingerprints of crystal exchange. Crystal overgowths then reflect the composition of the hybrid magma. The compositional profile (overgrowth) can then be inverted provided T and diffusivity are known. This gives a potential characteristic timescales between mixing and eruption (calculated for instance as ~17 years at Vesuvius around the time of Pompeii (5) and 7 weeks at Nea Kameni, Santorini (6)(, These characteristic timescales may represent the time between mixing and eruption and may therefore be useful in prediction, especially so if there is a geophysical signal (earthquakes) associated with it. (1) Davidson, J.P., Morgan, D.J., Charlier, B.L.A., Harlou, R. and Hora, J.M., 2007. Ann. Rev. Earth Planet. Sci. 35, 273-311, (2) Davidson, J.P., Tepley, FJ III, Palacz, Z., and Main, S., 2001, Earth and Planetary Science Lett., 182, 427-44 (3) Pallister, J.S., Hoblitt, R.P, Reyes, A.G., 1992. Nature 356, 426 - 428 (4) Feeley, T.C. and Sharp, Z.D., 1998. Geology, v. 24 no. 11 p. 1021-1024 (5) Morgan, D.J., Blake, S., Rogers, N.W., De Vivo, B., Rolandi, G. and Davidson, J.P., 2006. Geology 34, 845-848 (6) Martin, V.M., Morgan, D.J., Jerram, D.A., Caddick, M.J., Prior, D and Davidson, J.P., 2008. Science, 321, 1178.

Optimal nitrogen and phosphorus codoping carbon dots towards white light-emitting device

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

Zhang, Feng; Wang, Yaling; Miao, Yanqin

Through a one-step fast microwave-assisted approach, nitrogen and phosphorus co-doped carbon dots (N,P-CDs) were synthesized using ammonium citrate (AC) as a carbon source and phosphates as additive reagent. Under the condition of an optimal reaction time of 140 s, the influence of additive with different N and P content on fluorescent performance of N,P-CDs was further explored. It was concluded that high nitrogen content and moderate phosphorus content are necessary for obtaining high quantum yield (QY) N,P-CDs, among which the TAP-CDs (CDs synthesized using ammonium phosphate as additive reagent) show high quantum yield (QY) of 62% and red-green-blue (RGB) spectral compositionmore » of 51.67%. Besides, the TAP-CDs exhibit satisfying thermal stability within 180 °C. By virtue of good optical and thermal properties of TAP-CDs, a white light-emitting device (LED) was fabricated by combining ultraviolet chip with TAP-CDs as phosphor. The white LED emits bright warm-white light with the CIE chromaticity coordinate of (0.38, 0.35) and the corresponding color temperature (CCT) of 4450 K, indicating the potential of TAP-CDs phosphor in white LED.« less

Degassing system from the magma reservoir of Miyakejima volcano revealed by GPS observations

NASA Astrophysics Data System (ADS)

Oikawa, J.; Nakao, S.; Matsushima, T.

2013-12-01

Miyake-jima is a volcanic island located approximately 180 km south of Tokyo. The island is an active basaltic volcano that was dormant for a 17-year period between an eruption in 1983 and June 26, 2000, when it again became active. The volcanic activity that occurred in 2000 is divided into the following four stages: the magma intrusion stage, summit subsidence stage, summit eruptive stage, and degassing stage (Nakada et al., 2001). Earthquake swarm activity began on June 26, 2000, accompanied by large-scale crustal deformation. This led to a summit eruption on July 8, 2000. Based on the pattern of hypocenter migration and the nature of crustal deformation, it was estimated that magma migrated from beneath the summit of Miyake-jima to the northwest during the magma intrusion stage. The rapid collapse of the summit took place between July 8 and the beginning of August 2000 (summit subsidence stage). Large-scale eruptions took place on August 10, 18, and 29, 2000 (explosion stage). The eruptions largely ceased after August 29, followed by the release of large amounts of gas from the summit crater (degassing stage). In this study, we examined the location of the magma reservoir during the degassing stage based on crustal deformation observed by GPS. By comparing the amounts of degassing and volume change of the magma reservoir, as determined from crustal deformation, we determined the mechanism of degassing and the nature of the magma reservoir-vent system. According to observations by the Japan Meteorological Agency, a large amount of volcanic gas began to be released from Miyake-jima in September 2000 (Kazahaya et al., 2003). Approximately 42,000 tons/day of SO2 was released during the period between September 2000 and January 2001. Analysis of GPS data during the period [Figure 1] indicates a source of crustal deformation on the south side of the summit crater wall at a depth of 5.2 km. The rate of volume change was -3.8 x 106 m3/month [Figure 2]. As the volume is equivalent to the volume occupied by the volatile components such as SO2, H2O, CO2 dissolved in the magma, it is proposed that contraction of the magma reservoir reflects degassing of its volatile components. The observations indicate that the magma reservoir is connected to the summit crater by a magma-filled vent. Convection within the vent carries volatile-rich magma upward to the crater, where volcanic gas is released by degassing. The depleted magma is then carried into the magma reservoir, which contracts due to the loss of volume originally occupied by the volcanic gas. Figure 1 shows displacements per month. Vectors show the horizontal movements. Contours and shading indicate vertical displacement. Figure 2 shows theoretical displacement assuming the Mogi model.

Water quality risks of 'improved' water sources: evidence from Cambodia.

PubMed

Shaheed, A; Orgill, J; Ratana, C; Montgomery, M A; Jeuland, M A; Brown, J

2014-02-01

The objective of this study was to investigate the quality of on-plot piped water and rainwater at the point of consumption in an area with rapidly expanding coverage of 'improved' water sources. Cross-sectional study of 914 peri-urban households in Kandal Province, Cambodia, between July-August 2011. We collected data from all households on water management, drinking water quality and factors potentially related to post-collection water contamination. Drinking water samples were taken directly from a subsample of household taps (n = 143), stored tap water (n = 124), other stored water (n = 92) and treated stored water (n = 79) for basic water quality analysis for Escherichia coli and other parameters. Household drinking water management was complex, with different sources used at any given time and across seasons. Rainwater was the most commonly used drinking water source. Households mixed different water sources in storage containers, including 'improved' with 'unimproved' sources. Piped water from taps deteriorated during storage (P < 0.0005), from 520 cfu/100 ml (coefficient of variation, CV: 5.7) E. coli to 1100 cfu/100 ml (CV: 3.4). Stored non-piped water (primarily rainwater) had a mean E. coli count of 1500 cfu/100 ml (CV: 4.1), not significantly different from stored piped water (P = 0.20). Microbial contamination of stored water was significantly associated with observed storage and handling practices, including dipping hands or receptacles in water (P < 0.005), and having an uncovered storage container (P = 0.052). The microbial quality of 'improved' water sources in our study area was not maintained at the point of consumption, possibly due to a combination of mixing water sources at the household level, unsafe storage and handling practices, and inadequately treated piped-to-plot water. These results have implications for refining international targets for safe drinking water access as well as the assumptions underlying global burden of disease estimates, which posit that 'improved' sources pose minimal risks of diarrhoeal diseases. © 2013 John Wiley & Sons Ltd.

Root distribution of Nitraria sibirica with seasonally varying water sources in a desert habitat.

PubMed

Zhou, Hai; Zhao, Wenzhi; Zheng, Xinjun; Li, Shoujuan

2015-07-01

In water-limited environments, the water sources used by desert shrubs are critical to understanding hydrological processes. Here we studied the oxygen stable isotope ratios (δ (18)O) of stem water of Nitraria sibirica as well as those of precipitation, groundwater and soil water from different layers to identify the possible water sources for the shrub. The results showed that the shrub used a mixture of soil water, recent precipitation and groundwater, with shallow lateral roots and deeply penetrating tap (sinker) roots, in different seasons. During the wet period (in spring), a large proportion of stem water in N. sibirica was from snow melt and recent precipitation, but use of these sources declined sharply with the decreasing summer rain at the site. At the height of summer, N. sibirica mainly utilized deep soil water from its tap roots, not only supporting the growth of shoots but also keeping the shallow lateral roots well-hydrated. This flexibility allowed the plants to maintain normal metabolic processes during prolonged periods when little precipitation occurs and upper soil layers become extremely dry. With the increase in precipitation that occurs as winter approaches, the percentage of water in the stem base of a plant derived from the tap roots (deep soil water or ground water) decreased again. These results suggested that the shrub's root distribution and morphology were the most important determinants of its ability to utilize different water sources, and that its adjustment to water availability was significant for acclimation to the desert habitat.

Heterogeneous source components of intraplate basalts from NE China induced by the ongoing Pacific slab subduction

NASA Astrophysics Data System (ADS)

Chen, Huan; Xia, Qun-Ke; Ingrin, Jannick; Deloule, Etienne

2016-04-01

In recent few years, the recycled oceanic slab has been increasingly suggested to be the enriched component in the mantle source of widespread intra-plate small-volume basaltic magmatism in eastern China. The recycled oceanic slab is a mixture of sediment, upper oceanic crust and lower gabbro oceanic crust, and will undergo alteration and dehydration during the recycling progress. The influence of these different components on the mantle source needs to be further constrained. The Chaihe-aershan volcanic field in Northeast China is located close to the surface position of the front edge of the subducted Pacific slab and includes more than 35 small-volume Quaternary basaltic volcanoes, which provides an opportunity to study the evolution of mantle source in detail and the small-scale geochemical heterogeneity of the mantle source. We measured the oxygen isotopes and water content of clinopyroxene (cpx) phenocrysts by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectrometry (FTIR), respectively. The water content of magma was then estimated based on the partition coefficient of H2O between cpx and basaltic melt. The measured δ18O of cpx phenocrysts (4.27 to 8.57) and the calculated H2O content of magmas (0.23-2.70 wt.%) show large variations, reflecting the compositional heterogeneity of the mantle source. The δ18O values within individual samples also display a considerable variation, from 1.28 to 2.31‰ suggesting mixing of magmas or the sustained injection of magmas with different δ18O values during the crystallization. The relationship between the averaged δ18O values of cpx phenocrysts and the H2O/Ce, Ba/Th, Nb/La ratios and Eu anomaly of whole-rocks demonstrates the contribution to three components in the mantle source (hydrothermally altered upper oceanic crust or marine sediments, altered lower gabbroic oceanic crust, ambient mantle). The proportions of these three components varied strongly within a limited period (˜1.27 Ma to ˜0.25 Ma). As only the Pacific slab is constantly subducted to the eastern Asia during that time, we suggested that its ongoing subduction is the only reasonable candidate to result in the compositional heterogeneity and rapid variation of enriched components in such a limited and recent time. Combines with previous studies on other basalt localities of eastern China, these new results confirm that the Pacific slab subduction play a key role in the triggering of the wide spread Cenozoic basaltic volcanism in eastern China.

Into hot water head first: distribution of intentional and unintentional immersion burns.

PubMed

Daria, Sonya; Sugar, Naomi F; Feldman, Kenneth W; Boos, Stephen C; Benton, Scott A; Ornstein, Amy

2004-05-01

Experience with several, previously unreported, intentional face-first immersion burns led us to evaluate the distribution of inflicted and unintentional immersion scald burns in a hospital series. (1) Authors' clinical and legal practices; (2) Burn center at regional Level 1 trauma hospital. : (1) Case series of face-first, inflicted immersion burn victims; (2) Consecutive hospitalized scald burn victims younger than 5 years old, 1/3/1996 to 3/25/2000. (1) Individual case reports; (2) Retrospective records review. Simple descriptive statistics, Fisher Exact test and t test. (1) Six cases of inflicted head and neck immersion injury are described. Four were tap water and 2 food/drink scalds. (2) 22/195 hospitalized victims had sustained immersion burns, 13 from tap water and 9 from other fluids. Six (46%) tap water immersions and no (0%) other immersions had inflicted injuries (P = 0.05). Two of the tap water immersions and one other source immersion included burning of the head and neck. Of these, one tap water immersion, but no other immersion, was inflicted. In no patients were head and neck injuries the sole or predominant site of scalding. In all, 9 children sustained inflicted scalds. Bilateral lower extremity tap water immersion scalds occurred in 100% (6/6) of abusive and 29% (2/7) of unintentional injuries (P = 0.02). Buttock and perineal injuries occurred in 67% (4/6) inflicted versus 29% (2/7) unintentional tap water immersion scalds (P = 0.28). Other fluids caused bilateral lower extremity immersion burns in 3/9 (33 %) unintentionally injured patients, but no abused children (NS). Craniofacial immersion injury, although seen by the authors in legal cases, is infrequent. It was present incidentally in one inflicted tap water burn in the consecutive hospital series. This series affirms the predominance of bilateral lower extremity burns in inflicted tap water immersions. Buttock/perineal immersions were more common with abuse than with unintentional injury.

Geochronology and petrogenesis of the Qibaoshan Cu-polymetallic deposit, northeastern Hunan Province: Implications for the metal source and metallogenic evolution of the intracontinental Qinhang Cu-polymetallic belt, South China

NASA Astrophysics Data System (ADS)

Yuan, Shunda; Mao, Jingwen; Zhao, Panlao; Yuan, Yabin

2018-03-01

The recently recognized Qinhang metallogenic belt (QHMB) is an economically important intracontinental Mesozoic porphyry-skarn Cu-polymetallic metallogenic belt in South China. However, the origin of the ore-bearing magma and the major factors controlling the different metal assemblages in the QHMB are still unclear. The Qibaoshan deposit is a large Cu-Au-Pb-Zn-Ag-Fe deposit located at the juncture between the northern and central parts of the QHMB. In this study, new zircon U-Pb ages, Hf-O isotopic data, molybdenite Re-Os ages, and whole-rock geochemical data are combined to constrain the timing of the mineralization and the origin and petrogenesis of the ore-bearing porphyry in the Qibaoshan deposit. The ages obtained from both zircon U-Pb and molybdenite Re-Os dating fall in the Late Jurassic (between 152.7 and 148.3 Ma), revealing that this deposit is significantly younger than previously estimated (227-184 Ma). The Qibaoshan ore-bearing quartz porphyry shows variable negative zircon εHf(t) values (-14.8 to -5.5), high δ18O values (8.4 to 10.8‰), and high Mg# values (69.1 to 73.0), indicating that it formed via the partial melting of ancient crust triggered by the injection of mantle-derived magma. Zircon Hf-O isotopic modeling of the mixing of two extreme endmembers indicates that the magmatic source comprised 70-80% reworked ancient crustal components and 20-30% depleted mantle components. Based on comparisons with other ore-bearing porphyries in the QHMB, a magmatic source dominated by crust-derived material and relatively low oxygen fugacities (ΔFMQ -1.8 to ΔFMQ +0.8) was responsible for the high (Pb + Zn)/Cu ratio in the Qibaoshan deposit, and the Pb, Zn and Ag were mainly derived from the reworked ancient crust. Although four analyses of inherited Neoproterozoic zircons ( 800 Ma) have variable positive εHf(t) values (0.72 to 11.21), indicating that Neoproterozoic juvenile crust was involved in the formation of the Qibaoshan ore-bearing quartz porphyry, the relatively low oxygen fugacities (ΔFMQ -1.2 to ΔFMQ +0.4) of the parent magma of these inherited zircons suggest that this parent magma could not have provided significant metallic Cu for mineralization in the Qibaoshan Cu-polymetallic deposit. Therefore, the metallic Cu in the Qibaoshan Cu-polymetallic deposit was probably provided by the injection of the mantle-derived magma. Because ore-forming magmas with relatively low oxygen fugacities have low Au solubility, the large Au mineralization in the Qibaoshan deposit may be related to high background values of Au in this area. Our data, integrated with regional petrogeochemical data, indicate that the magmatic source exerted a first-order control on the different metal assemblages in the deposits in the QHMB.

Project Hotspot: Temporal Compositional Variation in Basalts of the Kimama Core and Implications for Magma Source Evolution, Snake River Scientific Drilling Project, Idaho

NASA Astrophysics Data System (ADS)

Potter, K. E.; Shervais, J. W.; Champion, D.; Duncan, R. A.; Christiansen, E. H.

2012-12-01

Project Hotspot produced continuous core from three drill sites in the Snake River plain, including 1912 m of core from the Kimama drill site on the axis of the plain. Ongoing major and trace element chemical characterization of the Kimama core and new 40Ar/39Ar and paleomagnetic age data demonstrate temporal variations in the evolution of Snake River Plain volcanism. Cyclic fluctuations in magma chemistry identify over a hundred chemically distinct basalt flow groups (comprising 550 individual lava flows) within 54 periods of volcanic activity, separated by hiatuses of decades to many millennia. From a surface age of 700 ka to a bottom-hole age of 6.5 Ma, the Kimama core records the presence of several nearly coeval but compositionally different lava flows, ranging from highly evolved lavas to non-evolved tholeiites. Determining whether Kimama lavas are genetically unrelated or extreme differentiates of a single magma batch relies upon a combination of detailed chemostratigraphy and absolute and relative age data. Age and geochemical data introduce new ideas on the role of multiple magma sources and/or differentiation processes in the development of central Snake River Plain volcanic systems. The relatively short gestation of evolved liquids is demonstrated throughout the Kimama core, with evidence for cyclic fractionation of mafic lavas at depths of 318 m, 350 m, 547 m, and 1078 m. Here, highly evolved lava flows (FeOT 16.0-18.4 wt %; TiO2 3.43-4.62 wt %) are stratigraphically bounded by more primitive tholeiitic basalts (FeOT 9.9-14.8 wt%; TiO2 1.22-3.56 wt%) within the same inclination range, suggesting that cyclic fractionation is a regular feature of shield volcano development on the central Snake River Plain. Between 1.60 ± 0.13 Ma (453.5 m depth) and 1.54 ± 0.15 Ma (320.0 m depth), Kimama lavas ranged in composition from primitive tholeiite (FeOT 11.7 wt %; TiO2 1.76 wt %) to evolved basalt (FeOT 16.0 wt %; TiO2 4.00 wt %). At depths of 1119 m and 1138 m, evolved lava flows (FeOT 17.2 and 17.0 wt %; TiO2 4.20 and 4.09 wt %, respectively) of negative polarity are stratigraphically bounded by more primitive tholeittic lava flows (FeOT 13.6 and 14.5 wt %; TiO2 2.92 and 3.24 wt %, respectively) of positive polarity, a chronological transition that may represent many millennia and magma source variability. Kimama core stratigraphy as well as paleomagnetic, and radiometric age data demonstrate that mafic volcanism on the central Snake River Plain has been relatively continuous for the last 6.5 Ma. The compositional variability in Kimama basalts introduces broader implications for the timing of cyclic fractionation processes and the development of regional magma sources.

Heterogeneous source components of intraplate basalts from NE China induced by the ongoing Pacific slab subduction

NASA Astrophysics Data System (ADS)

Chen, Huan; Xia, Qun-Ke; Ingrin, Jannick; Deloule, Etienne; Bi, Yao

2017-02-01

The subduction of oceanic slabs is widely accepted to be a main reason for chemical heterogeneities in the mantle. However, determining the contributions of slabs in areas that have experienced multiple subduction events is often difficult due to possible overlapping imprints. Understanding the temporal and spatial variations of source components for widespread intraplate small volume basalts in eastern China may be a basis for investigating the influence of the subducted Pacific slab, which has long been postulated but never confirmed. For this purpose, we investigated the Chaihe-aershan volcanic field (including more than 35 small-volume Quaternary basaltic volcanoes) in NE China and measured the oxygen isotopes and water content of clinopyroxene (cpx) phenocrysts using secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR), respectively. The water content of magma was then estimated based on the partition coefficient of H2O between cpx and the basaltic melt. The δ18O of cpx phenocrysts (4.28‰ to 8.57‰) and H2O content of magmas (0.19 wt.%-2.70 wt.%) show large variations, reflecting the compositional heterogeneity of the mantle source. The δ18O values and H2O content within individual samples also display considerable variation, suggesting the mixing of magmas and that the magma mixing occurred shortly before the eruption. The relation between the δ18O values of cpx phenocrysts and the H2O/Ce ratio, Ba/Th ratio and Eu anomaly of whole rocks demonstrates the contributions of three components to the mantle source (hydrothermally altered upper oceanic crust and marine sediments, altered lower gabbroic oceanic crust, and ambient mantle). The proportions of these three components have varied widely over time (∼1.37 Ma to ∼0.25 Ma). The Pacific slab is constantly subducted under eastern Asia and continuously transports recycled materials to the deep mantle. The temporal heterogeneity of the source components may be caused by ongoing Pacific slab subduction. Combined with other basalt localities in eastern China (Shuangliao basalts, Taihang basalts and Shangdong basalts), the contributions of recycled oceanic components in their mantle source are heterogeneous. This spatial heterogeneity of mantle sources may be induced by variable alterations and dehydration during the recycling process of the Pacific slab. Our results show that the source components of Cenozoic intraplate small-volume basalts in eastern China are temporally and spatially heterogeneous, which is likely induced by the ongoing subduction of the Pacific slab. This demonstrates that integrating the temporal variations in geochemical characteristics and tectonic history of a study region can identify the subducted oceanic plate that induced enriched components in the mantle source of intraplate basalts.

Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea Volcano, Hawaii

USGS Publications Warehouse

Ohminato, T.; Chouet, B.A.; Dawson, P.; Kedar, S.

1998-01-01

We use data from broadband seismometers deployed around the summit of Kilauea Volcano to quantify the mechanism associated with a transient in the flow of magma feeding the east rift eruption of the volcano. The transient is marked by rapid inflation of the Kilauea summit peaking at 22 ??rad 4.5 hours after the event onset, followed by slow deflation over a period of 3 days. Superimposed on the summit inflation is a series of sawtooth displacement pulses, each characterized by a sudden drop in amplitude lasting 5-10 s followed by an exponential recovery lasting 1-3 min. The sawtooth waveforms display almost identical shapes, suggesting a process involving the repeated activation of a fixed source. The particle motion associated with each sawtooth is almost linear, and its major swing shows compressional motion at all stations. Analyses of semblance and particle motion are consistent with a point source located 1 km beneath the northeast edge of the Halemaumau pit crater. To estimate the source mechanism, we apply a moment tensor inversion to the waveform data, assuming a point source embedded in a homogeneous half-space with compressional and shear wave velocities representative of the average medium properties at shallow depth under Kilauea. Synthetic waveforms are constructed by a superposition of impulse responses for six moment tensor components and three single force components. The origin times of individual impulses are distributed along the time axis at appropriately small, equal intervals, and their amplitudes are determined by least squares. In this inversion, the source time functions of the six tensor and three force components are determined simultaneously. We confirm the accuracy of the inversion method through a series of numerical tests. The results from the inversion show that the waveform data are well explained by a pulsating transport mechanism operating on a subhorizontal crack linking the summit reservoir to the east rift of Kilauea. The crack acts like a buffer in which a batch of fluid (magma and/or gas) accumulates over a period of 1-3 min before being rapidly injected into a larger reservoir (possibly the east rift) over a timescale of 5-10 s. The seismic moment and volume change associated with a typical batch of fluid are approximately 1014 N m and 3000 m3, respectively. Our results also point to the existence of a single force component with amplitude of 109 N, which may be explained as the drag force generated by the flow of viscous magma through a narrow constriction in the flow path. The total volume of magma associated with the 4.5-hour-long activation of the pulsating source is roughly 500,000 m3 in good agreement with the integrated volume flow rate of magma estimated near the eruptive site.

Phase equilibria constraints on models of subduction zone magmatism

NASA Astrophysics Data System (ADS)

Myers, James D.; Johnston, Dana A.

Petrologic models of subduction zone magmatism can be grouped into three broad classes: (1) predominantly slab-derived, (2) mainly mantle-derived, and (3) multi-source. Slab-derived models assume high-alumina basalt (HAB) approximates primary magma and is derived by partial fusion of the subducting slab. Such melts must, therefore, be saturated with some combination of eclogite phases, e.g. cpx, garnet, qtz, at the pressures, temperatures and water contents of magma generation. In contrast, mantle-dominated models suggest partial melting of the mantle wedge produces primary high-magnesia basalts (HMB) which fractionate to yield derivative HAB magmas. In this context, HMB melts should be saturated with a combination of peridotite phases, i.e. ol, cpx and opx, and have liquid-lines-of-descent that produce high-alumina basalts. HAB generated in this manner must be saturated with a mafic phase assemblage at the intensive conditions of fractionation. Multi-source models combine slab and mantle components in varying proportions to generate the four main lava types (HMB, HAB, high-magnesia andesites (HMA) and evolved lavas) characteristic of subduction zones. The mechanism of mass transfer from slab to wedge as well as the nature and fate of primary magmas vary considerably among these models. Because of their complexity, these models imply a wide range of phase equilibria. Although the experiments conducted on calc-alkaline lavas are limited, they place the following limitations on arc petrologic models: (1) HAB cannot be derived from HMB by crystal fractionation at the intensive conditions thus far investigated, (2) HAB could be produced by anhydrous partial fusion of eclogite at high pressure, (3) HMB liquids can be produced by peridotite partial fusion 50-60 km above the slab-mantle interface, (4) HMA cannot be primary magmas derived by partial melting of the subducted slab, but could have formed by slab melt-peridotite interaction, and (5) many evolved calc-alkaline lavas could have been formed by crystal fractionation at a range of crustal pressures.

Late Pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at Crater Lake, Oregon

USGS Publications Warehouse

Bacon, C.R.; Lowenstern, J. B.

2005-01-01

Rhyodacite tephra and three lavas erupted ???27 ka, interpreted to be early leaks from the climactic magma chamber of Mount Mazama, contain ubiquitous resorbed crystals (antecrysts) that were recycled from young granodiorite and related plutonic rocks of the same magmatic system. The shallow composite pluton is represented by blocks ejected in the 7.7-ka climactic eruption that formed Crater Lake caldera. Plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented Fe-oxide needles exsolved at subsolidus conditions. At least 80% of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks. Other crystals in the rhyodacite, notably zircon, also were recycled. SIMS 238U- 230Th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between ???20 ka and ???300 ka with concentrations of analyses near 50-70, ???110, and ???200 ka that correspond to periods of dacitic volcanism dated by K- Ar. U-Th ages of zircon from a rhyodacite sample yield similar results. No analyzed zircons from the granodiorite or rhyodacite are pre-Quaternary. Zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton. Survival of zircon in zircon-undersaturated hydrous magma and of Fe-oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the ???27-ka eruption of the rhyodacite. The ???27-ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high-level magma chamber. In contrast, the voluminous 7.7-ka climactic rhyodacite pumice is virtually lacking in zircon, indicating dissolution of any granodioritic debris in the intervening period. Mineralogical evidence of assimilation may be destroyed in hot, vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of Mount Mazama. ?? 2005 Elsevier B.V. All rights reserved.

A Tale of Two Olivines: Magma Ascent in the Auckland Volcanic Field, New Zealand

NASA Astrophysics Data System (ADS)

Smid, E. R.; McGee, L. E.; Smith, I. E.; Lindsay, J. M.

2013-12-01

The Auckland Volcanic Field (AVF) is a nephelinitic to subalkali basaltic monogenetic field centered on the city of Auckland, New Zealand. Lavas are olivine-phyric, and the deposits of several volcanoes in the field contain olivine crystals with chrome spinel (Cr-spinel) inclusions. Microprobe analyses show at least two populations of olivine, categorised by their Mg# and their spinel inclusion compositions: the first has olivines that are euhedral, have compositions slightly less forsteritic than expected for whole rock Mg#, and have Cr-spinel inclusions with relatively low Cr2O3 contents of ~20%. These are interpreted as antecrysts inherited from the mantle source that yielded their host magma. The second population is characterised by olivines that are sub- to euhedral, are significantly more forsteritic than expected from their host whole rock Mg#, and have Cr-spinel inclusons with relatively high Cr2O3 contents of ~50%. These are interpreted as xenocrysts. The composition of these high Cr2O3 spinels very closely resembles the composition of spinels within olivines in dunite sampled from the Dun Mountain Ophiolite on the South Island of New Zealand. The northward extension of the Dun Mountain complex beneath the North Island is defined by the Junction Magnetic Anomaly, marking a crustal terrane boundary that underlies the Auckland Volcanic Field. These data indicate that the magmas that have risen to produce the volcanoes of the Auckland Volcanic Field have carried crystals from an underlying ultramafic crust as well as from their asthenospheric source. Euhedral olivine crystals which do not contain Cr-spinel are also present in AVF lavas and these are interpreted as true phenocrysts that crystallised directly from their host magmas. The lack of reaction textures at crystal margins suggests rapid ascent rates. A crustal origin for the xenocrysts not only has large implications for ascent rate modelling of olivines, but also for the crustal structure of the Auckland area and possible magma ascent paths under the AVF.

Formation of magmatic brine lenses via focussed fluid-flow beneath volcanoes

NASA Astrophysics Data System (ADS)

Afanasyev, Andrey; Blundy, Jon; Melnik, Oleg; Sparks, Steve

2018-03-01

Many active or dormant volcanoes show regions of high electrical conductivity at depths of a few kilometres beneath the edifice. We explore the possibility that these regions represent lenses of high-salinity brine separated from a single-phase magmatic fluid containing H2O and NaCl. Since chloride-bearing fluids are highly conductive and have an exceptional capacity to transport metals, these regions can be an indication of an active hydrothermal ore-formation beneath volcanoes. To investigate this possibility we have performed hydrodynamic simulations of magma degassing into permeable rock. In our models the magma source is located at 7 km depth and the fluid salinity approximates that expected for fluids released from typical arc magmas. Our model differs from previous models of a similar process because it is (a) axisymmetric and (b) includes a static high-permeability pathway that links the magma source to the surface. This pathway simulates the presence of a volcanic conduit and/or plexus of feeder dykes that are typical of most volcanic systems. The presence of the conduit leads to a number of important hydrodynamic consequences, not observed in previous models. Importantly, we show that an annular brine lens capped by crystallised halite is likely to form above an actively degassing sub-volcanic magma body and can persist for more than 250 kyr after degassing ceases. Parametric analysis shows that brine lenses are more prevalent when the fluid is released at temperatures above the wet granite solidus, when magmatic fluid salinity is high, and when the high-permeability pathway is narrow. The calculated depth, form and electrical conductivity of our modelled system shares many features with published magnetotelluric images of volcano subsurfaces. The formation and persistence of sub-volcanic brine lenses has implications for geothermal systems and hydrothermal ore formation, although these features are not explored in the presented model.

Development of a Test Battery to Assess Mental Flexibility Based on Sternberg’s Theory of Successful Intelligence

DTIC Science & Technology

2008-01-01

on such tests as the Embedded Figures Test ( EFT ) (Witkin et al., 1971) or the Rod and Frame Test (RFT) (Witkin, Dyk, Faterson, Goodenough, & Karp...one starts to tap sources of individual differences measured little or not at all by such tests. Thus, when assessing intelligence, it is important to...in requiring verbal skills or the ability to analyze one’s own ideas-Sternberg & Lubart, 1995) but also tap skills beyond those measured even by

Does improved access to water supply by rural households enhance the concept of safe water at the point of use? A case study from deep rural South Africa.

PubMed

Jagals, P

2006-01-01

The concept of safe water is defined by three principles: the health-related quality must be suitable, the supply/source must be accessible and the water must constantly be available in quantities sufficient for the intended use. If any one (or more) of these three elements is missing from a water services improvement programme, providing safe water is not successfully achieved. A study in a deep rural area in South Africa showed that providing small communities, using untreated river water as their only water source, with good quality water through a piped distribution system and accessible at communal taps did not fall within our parameters of safe water. The parameters for measuring the three principles were: absence of Escherichia coli in drinking water samples; accessibility by improving tap distances to within 200 m from each household; availability by assessing whether households have at least 25 L per person per day. Results show that although E. coli levels were reduced significantly, households were still consuming water with E. coli numbers at non-compliant levels. Access (distance) was improved from an average of 750 m from households to river source to an average of 120 m to new on-tap source points. This did not result in significant increases in household quantities, which on average remained around 18 L per person per day.

CO2 Degassing at Kilauea Volcano: Implications for Primary Magma, Summit Reservoir Dynamics, and Magma Supply Monitoring

NASA Astrophysics Data System (ADS)

Gerlach, T. M.; McGee, K. A.; Elias, T.; Sutton, A. J.; Doukas, M. P.

2001-12-01

We report a new CO2 emission rate of 8,500 tons/day (t/d) for the summit of Kilauea Volcano, a result several times larger than previous estimates. It is based on 12 experiments on three occasions over four years constraining the SO2 emission rate and the average CO2/SO2 of emissions along the 5.4-km summit COSPEC traverse (by COSPEC, NDIR CO2 analyzer, and CP-FTIR). The core of the summit plume is at ground level along the traverse and gives average CO2/SO2 values that are representative of the overall summit emission, even though CO2 and SO2 variations are commonly uncorrelated. CO2 and SO2 concentrations exceed background by 200-1,000 ppm and 1-7 ppm respectively. Nighttime measurements exclude Park auto exhaust as a source of CO2. The summit CO2 emission rate is nearly constant (95% confidence interval = 300 t/d), despite variable summit SO2 emission rates (62-240 t/d) and CO2/SO2 (54-183). Including other known CO2 emissions on the volcano (mainly from the Pu`u `O`o eruption) gives a total emission rate of about 8,800 t/d. Thus summit CO2 emissions comprise 97% of the total known CO2 output, consistent with the hypothesis that all primary magma supplied to Kilauea arrives under the summit caldera and is thoroughly degassed of excess CO2. A persistent large CO2 anomaly of 200-1,000 ppm indicates the entry to the summit reservoir is beneath a km2-area east of Halemaumau. The bulk CO2 content of primary magma is about 0.70 wt%, inferred from the CO2 emission rate and Kilauea's magma supply rate (0.18 km3/y [Cayol et al., Science, 288, 2343, 2000]). Most of the CO2 is present as exsolved vapor (3.6-11.7 vol%) at summit reservoir depths (2-7 km), making the primary magma strongly buoyant. Magma chamber replenishment models show that robust turbulent mixing of primary and reservoir magma prevents frequent eruption of buoyant primary magma in the summit region. The escape of 90-95% of the CO2 from the summit reservoir provides a potential proxy for monitoring the magma supply rate. Streaming CO2-rich vapor causes fractional degassing of H2O and SO2 from reservoir magma, but scrubbing minimizes summit SO2 emissions.

[Survey on the contamination of microcystin-LR in water supply of Shanghai city].

PubMed

Wu, He-yan; Zheng, Li-xing; Su, Jin; Shi, Wei

2005-03-01

To study the pollution level of microcystin-LR in water supply of Shanghai city and the removal efficacy for microcystin-LR through routine water treatment technique. High performance liquid chromatogram (HPLC) was applied to determine the concentration of microcystin-LR in source water, water samples after various water treatment procedures and tap water. The concentration of microcystin-LR varied with sampling seasons and sites and reached peak during summer and fall. The maximum of microcystin-LR was 2.38 microg/L in source water. Coagulation plus chlorine disinfection were found to be effective for the removal of microcystin-LR, while the remove rate through filtration was not significant. And it could also be detected in tap water as high as 1.27 microg/L. The source waters of Shanghai city were polluted by cyanobacteria toxins represented by microcystin-LR. The source water in suburb was more polluted. Routine water treatment techniques can not remove the toxins effectively.

Carbon isotope constraints on degassing of carbon dioxide from Kilauea Volcano

USGS Publications Warehouse

Gerlach, T.M.; Taylor, B.E.

1990-01-01

We examine models for batch-equilibrium and fractional-equilibrium degassing of CO2 from magma at Kilauea Volcano. The models are based on 1. (1) the concept of two-stage degassing of CO2 from magma supplied to the summit chamber, 2. (2) C isotope data for CO2 in eruptive and noneruptive (quiescent) gases from Kilauea and 3. (3) data for the isotopic fractionation of C between CO2 and C dissolved in tholeiitic basalt melt. The results of our study indicate that 1. (1) both eruptive and noneruptive degassing of CO2 most closely approach a batch equilibrium process, 2. (2) the ??13C of parental magma supplied to the summit chamber is in the range -4.1 to-3.4??? and 3. (3) the ??13C of melt after summit chamber degassing is in the range -7 to -8???, depending upon the depth of equilibration. We also present ??13C data for CO2 in eruptive gases from the current East Rift Zone eruption. These are the first C isotope data for CO2 in high-temperature (>900??C) eruptive gases from Kilauea; they have a mean ??13C value of -7.82 ?? 0.24??? and are similar to those predicted for the melt after summit chamber degassing. The minor role played by fractional degassing of ascending magma at Kilauea means that exsolved CO2 tends to remain entrained in and coherent with its host melt during ascent from both mantle source regions and crustal magma reservoirs. This has important implications for magma dynamics at Kilauea. ?? 1990.

Edifice strength and magma transfer modulation at Piton de la Fournaise volcano

NASA Astrophysics Data System (ADS)

Peltier, A.; Got, J.; Staudacher, T.; Kowalski, P.; Boissier, P.

2013-12-01

From 2003 to 2007, eruptive activity at Piton de la Fournaise followed cycles, comprising many summit/proximal eruptions and finishing by a distal eruption. GPS measurements evidenced striking asymmetric deformation between its western and eastern flanks. Horizontal displacements recorded during inter-distal periods showed a characteristic amplitude at the top of the eastern flank. Displacements recorded at the base of the summit cone showed a bimodal distribution, with low amplitudes during inter-distal periods and large ones during distal eruptions. To account for displacement asymmetry, characteristic amplitude and large flank displacement, we modeled the volcanic edifice using a Drücker-Prager elasto-plastic rheology. Friction angles of 15° and >30° were needed to model the displacements respectively during distal eruptions and inter-distal periods; this change shows that strain weakening occurred during distal events. Large plastic displacement that occurred in the eastern flank during distal eruptions relaxed the horizontal elastic stress accumulated during inter-distal periods; it triggered summit deflation, horizontal magma transfer and distal flank eruption, and reset the eruptive cycle. Our elasto-plastic models also show that simple source geometries may induce large eastern flank displacements that would be explained by a complex geometry in a linear elastic edifice. Magma supply is often thought to control volcano's eruptive activity, with surface deformation reflecting changes in magma supply rate, the volcano's response being linear. Our results bring some evidences that on Piton de la Fournaise time-space discretization of magma transfer may be the result of the edifice's non-linear response, rather than changes in magma supply.

Petit-spot geology reveals melts in upper-most asthenosphere dragged by lithosphere

NASA Astrophysics Data System (ADS)

Machida, Shiki; Hirano, Naoto; Sumino, Hirochika; Hirata, Takafumi; Yoneda, Shigekazu; Kato, Yasuhiro

2015-09-01

Petit-spot volcanism is a phenomenon ubiquitous on Earth. It originates from melt in the upper-most mantle asthenosphere, occurring where the plate flexes and fractures before subduction. Recent geochemical and petrological studies of petit-spot volcanism lava have shown that understanding this form of volcanism can contribute to the investigation of mantle dynamics and CO2 degassing of Earth. However, geological information constraining the magma source of petit-spot remains limited. Here, we present a comprehensive dataset of geochemistry (major and trace elements, and Sr and Nd isotopic compositions) and 40Ar/39Ar ages of alkaline basaltic rocks and glasses to define the geological characteristics of petit-spot volcanoes in the northwestern Pacific. The geochemical and geochronological variations of the basalts indicate that petit-spot volcanism is characterized by a petrogenetically and temporally isolated magma system for each volcano. The basalt geochemistry further indicates that the magmas at the volcanoes were derived from the melting of a heterogeneous regional-scale source under a range of conditions. In addition, slight temporal intra-field migration of petit-spot vent fields against the plate motion was detected. These features indicate that the magma originates from isolated melt ponds at the lithosphere-asthenosphere boundary, and that the speed at which the melt ponds are dragged by the plate is only slightly slower than that of the plate motion. Our results provide detailed insight into eruption processes of asthenosphere melts induced by plate-flexure, and also suggest the complete coupling of the lithosphere to the upper-most asthenosphere in the case of large plate subduction.

Variable Sources and Differentiation of Lavas from the Copahue-Caviahue Eruptive Complex, Neuquen Argentina

NASA Astrophysics Data System (ADS)

Todd, E.; Ort, M. H.

2012-12-01

Caldera collapse (˜180 km2) associated with a large Pliocene pyroclastic eruption and subsequent glacial erosion exposed an extensive and complex cross-section of pre-caldera volcanic history (at least 5 My) at the Copahue-Caviahue Eruptive Center (CCEC) in the Andean Southern Volcanic Zone (SVZ) of Argentina. Lava flows in wall exposures range from olivine-rich basaltic andesite to trachyte, are typically horizontal, vary in abundance and thickness at different wall exposures, and rarely correlate with flows in adjacent sections, although some lava and pyroclastic deposits from adjacent sections are similar in petrography, mineral assemblage, and geochemistry. Bulk-rock geochemical and isotopic data indicate at least two distinct primary melt types contributed to pre-caldera CCEC volcanism, and their differentiates produced a high-K and a low-K series. Incompatible element and isotope systematics suggest they are not related by differentiation of a common parental melt, and less-evolved examples of both types occur throughout the pre-caldera stratigraphic section, suggesting long-lived recharge of the local system by variably-sourced magmas. Petrographic and mineral chemistry evidence indicates that mixing of dissimilar magma types produced compositionally intermediate magmas. The location of the CCEC, rear of the volcanic front (VF), yet trenchward of regional backarc basin (BAB) volcanism, is reflected by the composition of CCEC lavas, which are transitional between local VF and BAB types. Thus, contrasting low- and high-K CCEC magmas in the SVZ rear-arc may reflect local focusing of VF-like (low-K) and BAB-like (high-K) melts.

Enhancing Leadership Quality. TQ Source Tips & Tools: Emerging Strategies to Enhance Educator Quality

ERIC Educational Resources Information Center

National Comprehensive Center for Teacher Quality, 2008

2008-01-01

Teaching Quality (TQ) Source Tips & Tools: Emerging Strategies to Enhance Educator Quality is an online resource developed by the TQ Center. It is designed to help education practitioners tap into strategies and resources they can use to enhance educator quality. This publication is based on the TQ Source Tips & Tools topic area "Enhancing…

Growth of continental crust: Clues from Nd isotopes and Nb-Th relationships in mantle-derived magmas

NASA Astrophysics Data System (ADS)

Arndt, N. T.; Chauvel, C.; Jochum, K.-P.; Gruau, G.; Hofmann, A. W.

Isotope and trace element geochemistry of Precambrian mantle derived rocks and implications for the formation of the continental crust is discussed. Epsilon Nd values of Archean komatiites are variable, but range up to at least +5, suggesting that the Archean mantle was heterogeneous and, in part, very depleted as far back as 3.4 to 3.5 Ga. This may be taken as evidence for separation of continental crust very early in Earth history. If these komatiite sources were allowed to evolve in a closed system, they would produce modern day reservoirs with much higher epsilon Nd values than is observed. This implies recycling of some sort of enriched material, perhaps subducted sediments, although other possibilities exist. Archean volcanics show lower Nb/Th than modern volcanics, suggesting a more primitive mantle source than that observed nowadays. However, Cretaceous komatiites from Gorgona island have similar Nb/Th to Archean volcanics, indicating either the Archean mantle source was indeed more primitive, or Archean magmas were derived from a deep ocean island source like that proposed for Gorgona.

Growth of continental crust: Clues from Nd isotopes and Nb-Th relationships in mantle-derived magmas

NASA Technical Reports Server (NTRS)

Arndt, N. T.; Chauvel, C.; Jochum, K.-P.; Gruau, G.; Hofmann, A. W.

1988-01-01

Isotope and trace element geochemistry of Precambrian mantle derived rocks and implications for the formation of the continental crust is discussed. Epsilon Nd values of Archean komatiites are variable, but range up to at least +5, suggesting that the Archean mantle was heterogeneous and, in part, very depleted as far back as 3.4 to 3.5 Ga. This may be taken as evidence for separation of continental crust very early in Earth history. If these komatiite sources were allowed to evolve in a closed system, they would produce modern day reservoirs with much higher epsilon Nd values than is observed. This implies recycling of some sort of enriched material, perhaps subducted sediments, although other possibilities exist. Archean volcanics show lower Nb/Th than modern volcanics, suggesting a more primitive mantle source than that observed nowadays. However, Cretaceous komatiites from Gorgona island have similar Nb/Th to Archean volcanics, indicating either the Archean mantle source was indeed more primitive, or Archean magmas were derived from a deep ocean island source like that proposed for Gorgona.

A Model for the Thermal and Chemical Evolution of the Moon's Interior: Implications for the Onset of Mare Volcanism

NASA Technical Reports Server (NTRS)

Hess, Paul C.; Parmentier, E. M.

1995-01-01

Crystallization of the lunar magma ocean creates a chemically stratified Moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior. Within the magma ocean cumulates the last liquids to crystallize form dense, ilmenite-rich cumulates that contain high concentrations of incompatible radioactive elements. The underlying olivine-orthopyroxene cumulates are also stratified with later crystallized, denser, more Fe-rich compositions at the top. This paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy. Rayleigh-Taylor instability causes the dense ilmenite-rich cumulate layer and underlying Fe-rich cumulates to sink toward the center of the Moon, forming a dense lunar core. After this overturn, radioactive heating within the ilmenite-rich cumulate core heats the overlying mantle, causing it to melt. In this model, the source region for high-TiO2 mare basalts is a convectively mixed layer above the core-mantle boundary which would contain small and variable amounts of admixed ilmenite and KREEP. This deep high-pressure melting, as required for mare basalts, occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the Moon. Regardless of details implied by particular model parameters, gravitational overturn driven by the high density of magma ocean Fe-rich cumulates should concentrate high-TiO2 mare basalt sources, and probably a significant fraction of radioactive heating, toward the center of the Moon. This will have important implications for both the thermal evolution of the Moon and for mare basalt genesis.

Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galán caldera, NW Argentina

NASA Astrophysics Data System (ADS)

Folkes, Chris B.; de Silva, Shanaka L.; Wright, Heather M.; Cas, Raymond A. F.

2011-12-01

By applying a number of analytical techniques across a spectrum of spatial scales (centimeter to micrometer) in juvenile components, we show that the Cerro Galán volcanic system has repeatedly erupted magmas with nearly identical geochemistries over >3.5 Myr. The Cerro Galán system produced nine ignimbrites (˜5.6 to 2 Ma) with a cumulative volume of >1,200 km3 (DRE; dense rock equivalent) of calc-alkaline, high-K rhyodacitic magmas (68-71 wt.% SiO2). The mineralogy is broadly constant throughout the eruptive sequence, comprising plagioclase, quartz, biotite, Fe-Ti oxides, apatite, and titanite. Early ignimbrite magmas also contained amphibole, while the final eruption, the most voluminous Cerro Galán ignimbrite (CGI; 2.08 ± 0.02 Ma) erupted a magma containing rare amphibole, but significant sanidine. Each ignimbrite contains two main juvenile clast types; dominant "white" pumice and ubiquitous but subordinate "grey" pumice. Fe-Ti oxide and amphibole-plagioclase thermometry coupled with amphibole barometry suggest that the grey pumice originated from potentially hotter and deeper magmas (800-840°C, 3-5 kbar) than the more voluminous white pumice (770-810°C, 1.5-2.5 kbar). The grey pumice is interpreted to represent the parental magmas to the Galán system emplaced into the upper crust from a deeper storage zone. Most inter-ignimbrite variations can be accounted for by differences in modal mineralogy and crystal contents that vary from 40 to 55 vol.% on a vesicle-free basis. Geochemical modeling shows that subtle bulk-rock variations in Ta, Y, Nb, Dy, and Yb between the Galán ignimbrites can be reconciled with differences in amounts of crystal fractionation from the "grey" parent magma. The amount of fractionation is inversely correlated with volume; the CGI (˜630 km3) and Real Grande Ignimbrite (˜390 km3) return higher F values (proportion of liquid remaining) than the older Toconquis Group ignimbrites (<50 km3), implying less crystal fractionation took place during the upper-crustal evolution of these larger volume magmas. We attribute this relationship to variations in magma chamber geometry; the younger, largest volume ignimbrites came from flat sill-like magma chambers, reducing the relative proportion of sidewall crystallization and fractionation compared to the older, smaller-volume ignimbrite eruptions. The grey pumice clasts also show evidence of silicic recharge throughout the history of the Cerro Galán system, and recharge days prior to eruption has previously been suggested based on reversely zoned (OH and Cl) apatite phenocrysts. A rare population of plagioclase phenocrysts with thin An-rich rims in juvenile clasts in many ignimbrites supports the importance of recharge in the evolution and potential triggering of eruptions. This study extends the notion that large volumes of nearly identical silicic magmas can be generated repeatedly, producing prolonged geochemical homogeneity from a long-lived magma source in a subduction zone volcanic setting. At Cerro Galán, we propose that there is a zone between mantle magma input and upper crustal chambers, where magmas are geochemically "buffered", producing the underlying geochemical and isotopic signatures. This produces the same parental magmas that are delivered repeatedly to the upper crust. A lower-crustal MASH (melting, assimilation, storage, and homogenization) zone is proposed to act as this buffer zone. Subsequent upper crustal magmatic processes serve only to slightly modify the geochemistry of the magmas.

Abundant carbon in the mantle beneath Hawai`i

USGS Publications Warehouse

Anderson, Kyle R.; Poland, Michael

2017-01-01

Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97−0.19+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263−62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

Chlorine in mid-ocean ridge magmas: Evidence for assimilation of seawater-influenced components

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

Michael, P.J.; Schilling, J.G.

1989-12-01

Suites of depleted MORB glasses from the fast-spreading Pacific-Nazca Ridge at 28{degree}S and 32{degree}S and the slow-spreading eastern boundary of the Juan Fernandez microplate were analyzed for chlorine by electron microprobe. The Cl concentrations in FeTi basalts exceed by a factor of 5 to 10 the amounts that can be generated by fractional crystallization of the primitive magmas. Selective melting or breakdown of amphibole and incorporation of Cl-rich brine contained in the wall rocks may be important processes. A magmatic source for the additional Cl and H{sub 2}O cannot be ruled out on geochemical grounds but is physically unrealistic becausemore » it requires that large volumes of magma have crystallized and exsolved a Cl-rich vapor phase that has somehow migrated to a small magma chamber. Excess Cl in evolved magmas is best developed in evolved MORB from propagating or overlapping spreading centers such as the Galapagos Spreading Center at 85{degree}W and 95{degree}W and the west ridge of the Juan Fernandez microplate. Cl overenrichment has not been observed on slow-spreading ridges including the eastern ridge of the Juan Fernandez microplate, the Southwest Indian Ridge, and the mid-Atlantic Ridge. The assimilation of hydrothermally altered material could influence the concentration and isotopic ratios of other elements which have low abundances in MORB relative to seawater.« less

Jurassic magmatism in Dronning Maud Land: synthesis of results of the MAMOG project

USGS Publications Warehouse

Leat, P.T.; Curtis, M.L.; Riley, T.R.; Ferraccioli, F.

2007-01-01

The Jurassic Karoo large igneous province (LIP) of Antarctica, and its conjugate margin in southern Africa, is critical for investigating important questions about the relationship of basaltic LIPs to mantle plumes. Detailed aerogeophysical, structural, anisotropy of magnetic susceptibility (AMS), geochronological and geochemical investigations completed under the British Antarctic Survey’s MAMOG project have provided some of the answers. Across most of the area, magma volumes were small compared to those in southern Africa. Jurassic dikes intruding the Archean craton are sparse and the Jutulstraumen trough, a Jurassic rift, is interpreted, from aerogeophysical data, as largely amagmatic. The largest volumes of magma were emplaced along the margin of the craton and close to the Africa-Antarctica rift. Although dikes were emplaced by both vertical and horizontal flow, overwhelmingly magmas in Dronning Maud Land were locally derived, and not emplaced laterally from distant sources. Basaltic magmatism was protracted in Dronning Maud Land (several dike emplacement episodes between ~206 and 175 Ma), and the small magma volumes resulted in highly diverse magma compositions, including picrites and ferropicrites interpreted to have been derived from hot mantle in a mantle plume. The protracted magmatism before the locally ~177 Ma flood lava eruptions, and evidence for a radiating dike swarm, favor a model of mantle plume incubation for 20-30 million years before flood lava eruption.

The efficiency of the heat pump water heater, during DHW tapping cycle

NASA Astrophysics Data System (ADS)

Gużda, Arkadiusz; Szmolke, Norbert

2017-10-01

This paper discusses one of the most effective systems for domestic hot water (DHW) production based on air-source heat pump with an integrated tank. The operating principle of the heat pump is described in detail. Moreover, there is an account of experimental set-up and results of the measurements. In the experimental part, measurements were conducted with the aim of determining the energy parameters and measures of the economic efficiency related to the presented solution. The measurements that were conducted are based on the tapping cycle that is similar to the recommended one in EN-16147 standard. The efficiency of the air source heat pump during the duration of the experiment was 2.43. In the end of paper, authors conducted a simplified ecological analysis in order to determine the influence of operation of air-source heat pump with integrated tank on the environment. Moreover the compression with the different source of energy (gas boiler with closed combustion chamber and boiler fired by the coal) was conducted. The heat pump is the ecological friendly source of the energy.

Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar interferometry observations

USGS Publications Warehouse

Lundgren, Paul; Lu, Zhong

2006-01-01

We analyzed RADARSAT-1 synthetic aperture radar (SAR) data to compute interferometric SAR (InSAR) images of surface deformation at Uzon caldera, Kamchatka, Russia. From 2000 to 2003 approximately 0.15 m of inflation occurred at Uzon caldera, extending beneath adjacent Kikhpinych volcano. This contrasts with InSAR data showing no significant deformation during either the 1999 to 2000, or 2003 to 2004, time periods. We performed three sets of numerical source inversions to fit InSAR data from three different swaths spanning 2000 to 2003. The preferred source model is an irregularly shaped, pressurized crack, dipping ∼20° to the NW, 4 km below the surface. The geometry of this solution is similar to the upper boundary of the geologically inferred magma chamber. Extension of the surface deformation and source to adjacent Kikhpinych volcano, without an eruption, suggests that the deformation is more likely of hydrothermal origin, possibly driven by recharge of the magma chamber.

Deploying a Route Optimization EFB Application for Commercial Airline Operational Trials

NASA Technical Reports Server (NTRS)

Roscoe, David A.; Vivona, Robert A.; Woods, Sharon E.; Karr, David A.; Wing, David J.

2016-01-01

The Traffic Aware Planner (TAP), developed for NASA Langley Research Center to support the Traffic Aware Strategic Aircrew Requests (TASAR) project, is a flight-efficiency software application developed for an Electronic Flight Bag (EFB). Tested in two flight trials and planned for operational testing by two commercial airlines, TAP is a real-time trajectory optimization application that leverages connectivity with onboard avionics and broadband Internet sources to compute and recommend route modifications to flight crews to improve fuel and time performance. The application utilizes a wide range of data, including Automatic Dependent Surveillance Broadcast (ADS-B) traffic, Flight Management System (FMS) guidance and intent, on-board sensors, published winds and weather, and Special Use Airspace (SUA) schedules. This paper discusses the challenges of developing and deploying TAP to various EFB platforms, our solutions to some of these challenges, and lessons learned, to assist commercial software developers and hardware manufacturers in their efforts to implement and extend TAP functionality in their environments. EFB applications (such as TAP) typically access avionics data via an ARINC 834 Simple Text Avionics Protocol (STAP) server hosted by an Aircraft Interface Device (AID) or other installed hardware. While the protocol is standardized, the data sources, content, and transmission rates can vary from aircraft to aircraft. Additionally, the method of communicating with the AID may vary depending on EFB hardware and/or the availability of onboard networking services, such as Ethernet, WIFI, Bluetooth, or other mechanisms. EFBs with portable and installed components can be implemented using a variety of operating systems, and cockpits are increasingly incorporating tablet-based technologies, further expanding the number of platforms the application may need to support. Supporting multiple EFB platforms, AIDs, avionics datasets, and user interfaces presents a challenge for software developers and the management of their code baselines. Maintaining multiple baselines to support all deployment targets can be extremely cumbersome and expensive. Certification also needs to be considered when developing the application. Regardless of whether the software is itself destined to be certified, data requirements in support of the application and user interface elements may introduce certification requirements for EFB manufacturers and the airlines. The example of TAP, the challenges faced, solutions implemented, and lessons learned will give EFB application and hardware developers insight into future potential requirements in deploying TAP or similar flight-deck EFB applications.

Magma-tectonic interactions in Kīlauea's Southwest Rift Zone in 2006 through coupled geodetic/seismological analysis

NASA Astrophysics Data System (ADS)

Wauthier, C.; Roman, D. C.; Poland, M. P.

2015-12-01

For much of the first 20 years of Kīlauea's 1983-present Pu'u 'Ō'ō eruption, deformation was characterized by subsidence at the volcano's summit and along both the East Rift Zone (ERZ) and Southwest Rift Zone (SWRZ). At the end of 2003, however, Kīlauea's summit began a 4-year period of inflation due to a surge in magma supply to the volcano. In 2006, the SWRZ also experienced atypical inflation, which was last observed in 1981-82 during a series of dike intrusions. To investigate the active magma sources and their interactions with faulting in the SWRZ during 2006, we integrate contemporary geodetic data from InSAR and GPS with double-couple fault-plane solutions for volcano-tectonic earthquakes and Coulomb stress modeling. According to the rate of deformation measured in daily GPS data, two distinct periods can be defined, spanning January to 15 March 2006 (period 1) and 16 March to 30 September 2006 (period 2). Geodetic models suggest that, during period 1, deformation, due to pressurization of magma in a vertical prolate-spheroidal conduit, in the south caldera area. In addition, a major seismic swarm occurred in both the SWRZ and ERZ. Our preliminary results also suggest that, during period 2, magma was still overpressurizing the same prolate-spheroid but a subhorizontal sill also intruded further to the southwest in the seismic SWRZ (SSWRZ). The beginning of period 2 also corresponds to a switch from subsidence to inflation of the SWRZ. Faulting in the upper ERZ is primarily strike-slip, with no obvious change in FPS orientation between periods 1 and 2. In contrast, faulting in the upper SSWRZ occurs as dip-slip motion on near-vertical faults. SSWRZ FPS show a mix of orientations including NW- and NE-striking faults, which along with relative earthquake locations, suggest a series of right-stepping fault segments, particularly during period 2. Calculated Coulomb stress changes indicate that faulting in the upper SSWRZ may result from stresses produced by inflation of the geodetically modeled sources described above, in particular the prolate spheroid located in the south caldera area. In contrast, earthquakes in the ERZ are generally inhibited by the geodetically modeled sources, suggesting that another process may be responsible for faulting along the ERZ.

The Brava seamount, Cape Verde: Beyond the spatial extent of EM1 and petrogenesis of highly evolved alkaline lavas.

NASA Astrophysics Data System (ADS)

Barker, Abigail; Andersson, Axel; Troll, Valentin; Hansteen, Thor; Ellam, Robert

2010-05-01

Alkaline lavas from the Brava seamount, Cape Verde are investigated to establish the spatial distribution of compositional heterogeneity in the southwest of the Cape Verde archipelago. Highly evolved lavas provide a record of shallow level magma-crust interaction beneath the Brava seamount. The Brava seamount, located southwest of the island of Brava, Cape Verde was sampled during research cruise 8/85 of the R.R.S. Charles Darwin in 1985. Two groups of highly evolved alkaline volcanics are distinguished from the Brava seamount: 1) pyroxene-phonolites containing clinopyroxene, amphibole, nepheline, ±biotite, and minor sanidine and 2) feldspathoid-phonolites containing nepheline, nausean, minor biotite and leucite. All of the samples have MgO between 0.8 and 2 wt%, comparable to the most evolved volcanics sampled in the Cape Verde archipelago. The feldspathoid-phonolites have NaO2 of 12-13 wt%. Alkaline lavas from the Brava seamount have higher 87Sr/87Sr (0.70337 to 0.70347) at ɛNd of +6 to +7 than previously sampled in Cape Verde. Sr isotopes will be integrated with oxygen isotopes to establish magma and crust interactions in the magmatic plumbing system beneath the Brava seamount. Clinopyroxene-melt thermobarometry will be presented to constrain the depths of equilibrium crystallisation. Sr-O isotopes and thermobarometry will be combined to build a picture of the levels of magma stalling and interaction between magmas and the crust beneath the Brava seamount. The Brava seamount phonolitic lavas have high 206Pb/204Pb of 19.5 to 19.8 with negative ?8/4 and high ɛNd of +6 to +7 in contrast to the positive ?8/4 for lavas from nearby Brava and the southern islands of the Cape Verde archipelago. Lavas from the Brava seamount have Pb-Nd isotope systematics comparable to the northern Cape Verde islands, indicating the southwestern boundary in mantle heterogeneity and thereby the spatial extent of the EM1-like source contributing to the southern islands. The extensive crystallisation and stalling of magma batches at crustal depths shown by thermobarometry will be used in conjunction with geochemistry to constrain the origin of assimilants and implies that an EM1-like source is not found in the mantle source, the shallow lithosphere or crust beneath the Brava seamount.

40 CFR 141.703 - Sampling locations.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 23 2011-07-01 2011-07-01 false Sampling locations. 141.703 Section... Monitoring Requirements § 141.703 Sampling locations. (a) Systems required to conduct source water monitoring... a sampling tap is available where the sources are combined prior to treatment, systems must collect...

Initial H2O content and conditions of parent magma origin for Gorely volcano (Southern Kamchatka) estimated by trace element thermobarometry

NASA Astrophysics Data System (ADS)

Nazarova, D. P.; Portnyagin, M. V.; Krasheninnikov, S. P.; Mironov, N. L.; Sobolev, A. V.

2017-01-01

The formation conditions of the parental magmas of Gorely volcano, which is located behind a volcanic front in Southern Kamchatka, have been evaluated using the modern methods of micro-element thermobarometry. These magmas contained 1.7 ± 0.8 (2σ) wt % of H2O, the majority (82%) of which has been lost from inclusions. They crystallized at 1121 ± 17°C and an oxygen fugacity of ΔQFM 1.2 ± 0.2, and could have been produced by about 11% melting of an enriched MORB source (E-DMM) at a temperature of about 1270°C, and a pressure of about 1.5 GPa. A distinctive feature of Gorely volcano, compared with frontal volcanoes of Kamchatka, is the unusually high temperature (925 ± 20°C) of formation of the subduction component corresponding to the region of existence of water-bearing melts.

Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber

PubMed Central

Burchardt, Steffi; Troll, Valentin R.; Mathieu, Lucie; Emeleus, Henry C.; Donaldson, Colin H.

2013-01-01

The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system. PMID:24100542

Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber.

PubMed

Burchardt, Steffi; Troll, Valentin R; Mathieu, Lucie; Emeleus, Henry C; Donaldson, Colin H

2013-10-08

The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system.

Low-frequency seismic events in a wider volcanological context

NASA Astrophysics Data System (ADS)

Neuberg, J. W.; Collombet, M.

2006-12-01

Low-frequency seismic events have been in the centre of attention for several years, particularly on volcanoes with highly viscous magmas. The ultimate aim is to detect changes in volcanic activity by identifying changes in the seismic behaviour in order to forecast an eruption, or in case of an ongoing eruption, forecast the short and longterm behaviour of the volcanic system. A major boost in recent years arose through several attempts of multi-parameter volcanic monitoring and modelling programs, which allowed multi-disciplinary groups of volcanologists to interpret seismic signals together with, e.g. ground deformation, stress field analysis and petrological information. This talk will give several examples of such multi-disciplinary projects, focussing on the joint modelling of seismic source processes for low-frequency events together with advanced magma flow models, and the signs of magma movement in the deformation and stress field at the surface.

NEOview: Near Earth Object Data Discovery and Query

NASA Astrophysics Data System (ADS)

Tibbetts, M.; Elvis, M.; Galache, J. L.; Harbo, P.; McDowell, J. C.; Rudenko, M.; Van Stone, D.; Zografou, P.

2013-10-01

Missions to Near Earth Objects (NEOs) figure prominently in NASA's Flexible Path approach to human space exploration. NEOs offer insight into both the origins of the Solar System and of life, as well as a source of materials for future missions. With NEOview scientists can locate NEO datasets, explore metadata provided by the archives, and query or combine disparate NEO datasets in the search for NEO candidates for exploration. NEOview is a software system that illustrates how standards-based interfaces facilitate NEO data discovery and research. NEOview software follows a client-server architecture. The server is a configurable implementation of the International Virtual Observatory Alliance (IVOA) Table Access Protocol (TAP), a general interface for tabular data access, that can be deployed as a front end to existing NEO datasets. The TAP client, seleste, is a graphical interface that provides intuitive means of discovering NEO providers, exploring dataset metadata to identify fields of interest, and constructing queries to retrieve or combine data. It features a powerful, graphical query builder capable of easing the user's introduction to table searches. Through science use cases, NEOview demonstrates how potential targets for NEO rendezvous could be identified by combining data from complementary sources. Through deployment and operations, it has been shown that the software components are data independent and configurable to many different data servers. As such, NEOview's TAP server and seleste TAP client can be used to create a seamless environment for data discovery and exploration for tabular data in any astronomical archive.

Ignimbrites to batholiths: integrating perspectives from geological, geophysical, and geochronological data

USGS Publications Warehouse

Lipman, Peter W.; Bachmann, Olivier

2015-01-01

Multistage histories of incremental accumulation, fractionation, and solidification during construction of large subvolcanic magma bodies that remained sufficiently liquid to erupt are recorded by Tertiary ignimbrites, source calderas, and granitoid intrusions associated with large gravity lows at the Southern Rocky Mountain volcanic field (SRMVF). Geophysical data combined with geological constraints and comparisons with tilted plutons and magmatic-arc sections elsewhere are consistent with the presence of vertically extensive (>20 km) intermediate to silicic batholiths (with intrusive:extrusive ratios of 10:1 or greater) beneath the major SRMVF volcanic loci (Sawatch, San Juan, Questa-Latir). Isotopic data require involvement of voluminous mantle-derived mafic magmas on a scale equal to or greater than that of the intermediate to silicic volcanic and plutonic rocks. Early waxing-stage intrusions (35–30 Ma) that fed intermediate-composition central volcanoes of the San Juan locus are more widespread than the geophysically defined batholith; these likely heated and processed the crust, preparatory for ignimbrite volcanism (32–27 Ma) and large-scale upper-crustal batholith growth. Age and compositional similarities indicate that SRMVF ignimbrites and granitic intrusions are closely related, but the extent to which the plutons record remnants of former magma reservoirs that lost melt to volcanic eruptions has been controversial. Published Ar/Ar-feldspar and U-Pb-zircon ages for plutons spatially associated with ignimbrite calderas document final crystallization of granitoid intrusions at times indistinguishable from the tuff to ages several million years younger. These ages also show that SRMVF caldera-related intrusions cooled and solidified soon after zircon crystallization, as magma supply waned. Some researchers interpret these results as recording pluton assembly in small increments that crystallized rapidly, leading to temporal disconnects between ignimbrite eruption and intrusion growth. Alternatively, crystallization ages of the granitic rocks are here inferred to record late solidification, after protracted open-system evolution involving voluminous mantle input, lengthy residence (105–106yr) as near-solidus crystal mush, and intermittent separation of liquid to supply volcanic eruptions. The compositions of the least-evolved ignimbrite magmas tend to merge with those of caldera-related plutons, suggesting that the plutons record nonerupted parts of long-lived cogenetic magmatic systems, variably modified prior to final solidification. Precambrian-source zircons are scarce in caldera plutons, in contrast to their abundance in some peripheral waning-stage intrusions of the SRMVF, implying dissolution of inherited crustal zircon during lengthy magma assembly for the ignimbrite eruptions and construction of a subvolcanic batholith. Broad age spans of zircons (to several million years) from individual samples of some ignimbrites and intrusions, commonly averaged and interpreted as “intrusion-emplacement age,” alternatively provide an incomplete record of intermittent crystallization during protracted incremental magma-body assembly, with final solidification only when the system began to wane. Analyses of whole zircons cannot resolve late stages of crystal growth, and early growth in a long-lived magmatic system may be poorly recorded due to periods of zircon dissolution. Overall, construction of a batholith can take longer than recorded by zircon-crystallization ages, while the time interval for separation and shallow assembly of eruptible magma may be much shorter. Magma-supply estimates (from ages and volcano-plutonic volumes) yield focused intrusion-assembly rates sufficient to generate ignimbrite-scale volumes of eruptible magma, based on published thermal models. Mid-Tertiary processes of batholith assembly associated with the SRMVF caused drastic chemical and physical reconstruction of the entire lithosphere, probably accompanied by asthenospheric input.

Mafic mantle sources indicated by the olivine-spinifex basalt-ferropicrite lavas in the accreted Permian oceanic LIP fragments and Miocene low-Ni basalt and adakite lavas in central Japan

NASA Astrophysics Data System (ADS)

Ishiwatari, A.; Ichiyama, Y.; Yamazaki, R.; Katsuragi, T.; Tsuchihashi, H.

2008-12-01

Melting of mafic (eclogitic) rocks in the peridotite mantle diapir may be important to generate a large quantity of magma in a short period of time as required for the LIP basaltic magmatism (e.g. Takahashi et al. 1998; EPSL, 162, 63-). Ferropicritic rocks also occur in some LIPs, and Ichiyama et al. (2006; Lithos, 89, 47-) propose a non-peridotitic, Ti- and Fe-rich eclogitic source (recycled oceanic ferrogabbro?) entrained in the peridotitic LIP mantle plume for the origin of ferropicritic rocks, that occur with olivine-spinifex basalt (Ichiyama et al., 2007; Island Arc, 16, 493-) in a Permian LIP fragment that was captured in the Jurassic Tamba accretionary complex in central Japan. Although Ti-poor ferrokomatiitic magma might form through high- degree melting of a primitive chondritic mantle (25wt% MgO and 25wt% Fe+FeO), Ti- and HFSE-rich ferropicritic and meimechitic magmas can not form in this way. On the other hand, Miocene volcanic rocks distributed along the Japan Sea coast of central Japan also represent a product of large-scale arc magmatism that happened coeval to the spreading of the Japan Sea floor. The chemical and isotopic signatures of the magmas are consistent with the secular change of tectonic setting from continental arc (22- 20 Ma) to island arc (15-11 Ma) (Shuto et al. 2006; Lithos, 86, 1-). Some adakites have already been found from these Miocene volcanic rocks by Shuto"fs group, and mafic rock melting in either subducting slab or lower arc crust has been proposed. We have recently found a wide distribution of low-Ni basalt from Fukui City. The low-Ni basalt contains olivine phenocrysts which are one order of magnitude poorer in Ni (less than 0.02 wt% NiO at Fo87) than those in normal basalt (more than 0.2 wt% NiO at Fo87). The rock is also poor in bulk-rock Ni, rich in K and Ti, and may have formed from an olivine-free pyroxenitic source. Close association of adakite and low-Ni basalt with normal tholeiitic basalt, calc-alkaline andesite-dacite-rhyolite, high-Mg andesite and rare picritic basalt suggests melting of a heterogeneous mantle wedge that was abundantly endorsed with eclogitic and pyroxenitic rocks. Melting pressure greatly differs between the ferropicrite case (5 GPa or more) and the low-Ni basalt-adakite case (2 GPa or less), causing large chemical differences. However, common occurrences of non-peridotite-origin magmas in the LIP and island arc suggest pervasive and voluminous distribution of the mafic materials in the peridotitic mantle and their important role in magma genesis at various tectonic settings.

Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism

NASA Astrophysics Data System (ADS)

Iyer, H. M.

1984-04-01

This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and delineating magma chambers with minimum horizontal and vertical dimensions of about 6 km. This technique has been used successfully to detect low-velocity anomalies, interpreted as magma bodies in the volume range 103-106 km3, in several volcanic centres in the U.S.A. and in Mt Etna, Sicily. Velocity models developed using teleseismic residuals of the Cascades volcanoes of Oregon and California, and Kilauea volcano, Hawaii, do not show appreciable storage of magma in the crust. However, regional models imply that large volumes of parental magma may be present in the upper mantle of these regions. In some volcanic centres, teleseismic delays are accompanied by P-wave attenuation, and linear inversion of spectral data have enabled computation of three-dimensional Q-models for these areas. The use of gravity data for magma chamber studies is illustrated by a study in the Geysers-Clear Lake volcanic field in California, where a strong gravity low has been modelled as a low-density body in the upper crust. This body is approximately in the same location as the low-velocity body delineated with teleseismic delays, and is interpreted as a magma body. In Yellowstone National Park, magnetic field data have been used to map the depth to the Curie isotherm, and the results show that high temperatures may be present at shallow depths beneath the Yellowstone caldera. The main application of electrical techniques in magma-related studies has been to understand the deep structure of continental rifts. Electromagnetic studies in several rift zones of the world provide constraints on the thermal structure and magma storage beneath these regions. Geophysical tools commonly used in resource exploration and earth-structure studies are also suited for the detection of magma chambers. Active seismic techniques, with controlled sources, and passive seismic techniques, with local and regional earthquakes and teleseisms, can be used to detect the drastic changes in velocity and attenuation that occur at the onset of melting of rocks and to delineate in three dimensions the shape of the partly melted zone. Similarly, decreases in density and electrical resistivity in rocks during melting, can be detected. Seismic refraction and reflection are not yet used extensively in magma chamber studies. In a study, in the Yellowstone region, seismic delays occurring in a fan-shooting configuration and time-term modelling show the presence of an intense molten zone in the upper crust. Deep seismic sounding (a combination of seismic refraction and reflection) and modelling amplitude and velocity changes of diffracted seismic waves from explosions and earthquakes, have enabled mapping of small and large magma chambers beneath many volcanoes in Kamchatka, U.S.S.R. Teleseismic P-wave residuals have been used to model low-velocity bodies, interpreted as magma chambers, in several Quaternary volcanic centres in the U.S.A. The results show that magma chambers with volumes of a few hundred to a few thousand cubic kilometres volume seem to be confined to regions of silicic volcanism. Many of the magma bodies seem to have upper-mantle roots implying that they are not isolated pockets of partial melt, but may be deriving their magma supplies from deeper parental sources. Medium or large crustal magma chambers are absent in the andesitic volcanoes of western United States and the basaltic Kilauea volcano, Hawaii. However, regional velocity models of the Oregon Cascades and Hawaii show evidence for the presence of magma reservoirs in the upper mantle. The transport of magma to the upper crust in these regions probably occurs rapidly through narrow conduits, with transient storage occurring in small chambers of a few cubic kilometres volume. Very little use has been made of the gravity and magnetic maps to model magma chambers. The number of available case histories, though few, indicate that these data can be very useful to give constraints on the density and temperature in magma chambers. Seismic, gravity, and electromagnetic techniques have been used to model regional structure in several rift zones of the world. Together the data indicate lithospheric thinning under the rifts with possible subcrustal storage of magma and diapiric intrusions into the crust. The current status of the use of geophysical techniques in magma chamber studies can be summarized as follows. Though powerful experimental methods for data collection and mathematical and computational techniques for modelling are available, the two dozen or so available case histories seem to represent isolated, technique-oriented studies. Only in a few regions, such as Kamchatka, U.S.S.R., and Yellowstone and Socorro, U.S.A., are data from multiple geophysical techniques becoming available. Several studies in different tectonic and volcanic environments, which use a suite of geophysical experiments capable of measuring different physical properties of rocks and having a wide range of resolutions, are needed to understand the problems of magma generation, migration, and storage. Many figures, data and results presented in this paper are from several different publications. I am indebted to the authors and publishers for permitting their use. I am very grateful to some of the authors who supplied photo prints of figures. Tim Hitchcock's help in preparing and organizing the figures was invaluable. Dr F. W. Klein, Dr W. D. Mooney, and Dr R. S. J. Sparks reviewed the manuscript and made useful suggestions.

Role of water source in the growth of kale

NASA Astrophysics Data System (ADS)

Coates, M.

2017-12-01

Over the course of 2 months we watered Kale with tap water, water from turtle bayou, rain water, water from university lake, and deionized water. We found little difference between height and number of seedlings with different water treatments even though nutrient levels were different between these water sources.

40 CFR 63.544 - Standards for process fugitive sources.

Code of Federal Regulations, 2011 CFR

2011-07-01

... National Emission Standards for Hazardous Air Pollutants from Secondary Lead Smelting § 63.544 Standards for process fugitive sources. (a) Each owner or operator of a secondary lead smelter shall control the...) Smelting furnace and dryer charging hoppers, chutes, and skip hoists; (2) Smelting furnace lead taps, and...

Titanium oxidation state and coordination in the lunar high-titanium glass source mantle

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

Krawczynski, M.J.; Sutton, S.R.; Grove, T.L.

2009-03-20

XANES and EXAFS spectra from synthetic HiTi lunar glasses determine coordination of Ti in the HiTi source region. The amount of Ti{sup 3+} present affects the olivine-opx equilibrium, and the total amount of Ti{sup 3+} present requires a pyx bearing source. Lunar high-titanium (HiTi) ultramafic glasses provide us with evidence of the mantle processes that led to the melting of the lunar magma ocean cumulates nearly one billion years after the magma ocean solidified. Constraints on the depth, temperature and melting processes that formed the HiTi glasses are crucial for understanding the melting history of LMO products. The Apollo 17more » orange glass (A17O) and Apollo 15 red glass (A15R) represent two of the HiTi compositions in the spectrum of pristine ultramafic glasses returned from the moon. The difference between these two compositions is that the A15R contains {approx}40% more TiO{sub 2} than the A17O. The low f{sub O2} of the ultramafic glass source regions allows for a certain amount of Ti{sup 3+} in the source mineralogy; however the amount of Ti{sup 3+} in the source and the host mineral for this element remain relatively unconstrained. In addition to the unknown mineralogy of the source region, the high amount of TiO*{sub 2} and FeO* in the HiTi magmas makes the phase relations extremely sensitive to changes in the oxidation state of the source region. We have previously investigated the oxidation state effect on the olivine-orthopyroxene multiple saturations points of the A15R and A17O and shown that the magnitude of the effect is proportional to the amount of Ti in the system. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure (EXAFS) measurements have been made on minerals and glasses in experiments on synthetic analogues to the A17O and A15R. Our results show that Ti{sup 3+} concentration does indeed affect the multiple saturation points, and is an important constituent in the lunar interior.« less

Tapping mode imaging and measurements with an inverted atomic force microscope.

PubMed

Chan, Sandra S F; Green, John-Bruce D

2006-07-18

This report demonstrates the successful use of the inverted atomic force microscope (i-AFM) for tapping mode AFM imaging of cantilever-supported samples. i-AFM is a mode of AFM operation in which a sample supported on a tipless cantilever is imaged by one of many tips in a microfabricated tip array. Tapping mode is an intermittent contact mode whereby the cantilever is oscillated at or near its resonance frequency, and the amplitude and/or phase are used to image the sample. In the process of demonstrating that tapping mode images could be obtained in the i-AFM design, it was observed that the amplitude of the cantilever oscillation decreased markedly as the cantilever and tip array were approached. The source of this damping of the cantilever oscillations was identified to be the well-known "squeeze film damping", and the extent of damping was a direct consequence of the relatively shorter tip heights for the tip arrays, as compared to those of commercially available tapping mode cantilevers with integrated tips. The functional form for the distance dependence of the damping coefficient is in excellent agreement with previously published models for squeeze film damping, and the values for the fitting parameters make physical sense. Although the severe damping reduces the cantilever free amplitude substantially, we found that we were still able to access the low-amplitude regime of oscillation necessary for attractive tapping mode imaging of fragile molecules.

Divergence of stable isotopes in tap water across China

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

Zhao, Sihan; Hu, Hongchang; Tian, Fuqiang

Stable isotopes in water (e.g., δ2H and δ18O) are important indicators of hydrological and ecological patterns and processes. Tap water can reflect integrated features of regional hydrological processes and human activities. China is a large country with significant meteorological and geographical variations. This report presents the first national-scale survey of Stable Isotopes in Tap Water (SITW) across China. 780 tap water samples have been collected from 95 cities across China from December 2014 to December 2015. (1) Results yielded the Tap Water Line in China is δ2H = 7.72 δ18O + 6.57 (r2 = 0.95). (2) SITW spatial distribution presentsmore » typical "continental effect". (3) SITW seasonal variations indicate clearly regional patterns but no trends at the national level. (4) SITW can be correlated in some parts with geographic or meteorological factors. This work presents the first SITW map in China, which sets up a benchmark for further stable isotopes research across China. This is a critical step toward monitoring and investigating water resources in climate-sensitive regions, so the human-hydrological system. These findings could be used in the future to establish water management strategies at a national or regional scale. Title: Divergence of stable isotopes in tap water across China Authors: Zhao, SH; Hu, HC; Tian, FQ; Tie, Q; Wang, LX; Liu, YL; Shi, CX Source: SCIENTIFIC REPORTS, 7 10.1038/srep43653 MAR 2 2017« less

Multiscale magmatic cyclicity, duration of pluton construction, and the paradoxical relationship between tectonism and plutonism in continental arcs

NASA Astrophysics Data System (ADS)

de Saint Blanquat, Michel; Horsman, Eric; Habert, Guillaume; Morgan, Sven; Vanderhaeghe, Olivier; Law, Richard; Tikoff, Basil

2011-03-01

The close relationship between crustal magmatism, an expression of heat dissipation, and tectonics, an expression of stress dissipation, leads to the question of their mutual relationships. Indeed, the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas, and then possible "magmatic" initiation of structures at a wide range of scales. However, new data about 3-d pluton shape and duration of pluton construction perturb this simple geological image, and indicate some independence between magmatism and tectonics. In some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics. In other cases, we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric-plate dynamics. A simple explanation of this complexity follows directly from the pulsed, incremental assembly of plutons and its spatial and temporal characteristics. The size of each pluton is related to a magmatic pulsation at a particular time scale, and each of these coupled time/space scales is related to a specific process: in small plutons, we can observe the incremental process, the building block of plutons; in larger plutons, the incremental process is lost, and the pulsation, which consists of a cycle of injections at different timescales, must be related to the composition and thermal regime of the source region, itself driving magmatic processes (melting, segregation, and transfer) that interact with tectonic boundary conditions. The dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes. From our data and a review of published work, we find a positive corelation between volume and duration of pluton construction. The larger a pluton, the longer its construction time. Large/fast or small/slow plutons have not been identified to date. One consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans. A second consequence of this correlation is that small plutons, which are constructed in a geologically short length of time, commonly record little about tectonic conditions, and result only from the interference between magma dynamics and the local geologic setting. The fast rate of magma transfer in the crust (on the order of cm/s) relative to tectonic rates (on the order of cm/yr) explain why the incremental process of pluton construction is independent of - but not insensitive to - the tectonic setting. However, in large plutonic bodies, which correspond to longer duration magmatic events, regional deformation has time to interact with the growing pluton and can be recorded within the pluton-wall rock structure. Magma transfer operates at a very short timescale (comparable to volcanic timescales), which can be sustained over variable periods, depending on the fertility of the magma source region and its ability to feed the system. The fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below.

Vapor saturation and accumulation in magmas of the 1989-1990 eruption of Redoubt Volcano, Alaska

USGS Publications Warehouse

Gerlach, Terrance M.; Westrich, Henry R.; Casadevall, Thomas J.; Finnegan, David L.

1994-01-01

The 1989–1990 eruption of Redoubt Volcano, Alaska, provided an opportunity to compare petrologic estimates of SO2 and Cl emissions with estimates of SO2 emissions based on remote sensing data and estimates of Cl emissions based on plume sampling. In this study, we measure the sulfur and chlorine contents of melt inclusions and matrix glasses in the eruption products to determine petrologic estimates of SO2 and Cl emissions. We compare the results with emission estimates based on COSPEC and TOMS data for SO2 and data for Cl/SO2 in plume samples. For the explosive vent clearing period (December 14–22, 1989), the petrologic estimate for SO2 emission is 21,000 tons, or ~12% of a TOMS estimate of 175,000 tons. For the dome growth period (December 22, 1989 to mid-June 1990), the petrologic estimate for SO2 emission is 18,000 tons, or ~3% of COSPEC-based estimates of 572,000–680,000 tons. The petrologic estimates give a total SO2 emission of only 39,000 tons compared to an integrated TOMS/COSPEC emission estimate of ~1,000,000 tons for the whole eruption, including quiescent degassing after mid-June 1990. Petrologic estimates also appear to underestimate Cl emissions, but apparent HCl scavenging in the plume complicates Cl emission comparisons. Several potential sources of ‘excess sulfur’ often invoked to explain petrologic SO2 deficits are concluded to be unlikely for the 1989–1990 Redoubt eruption — e.g., breakdown of sulfides, breakdown of anhydrite, release of SO2 from a hydrothermal system, degassing of commingled infusions of basalt in the magma chamber, and syn-eruptive degassing of sulfur from melt present in non-erupted magma. Leakage and/or diffusion of sulfur from melt inclusions do not provide convincing explanations for the petrologic SO2 deficits either. The main cause of low petrologic estimates for SO2 is that melt inclusions do not represent the total sulfur content of the Redoubt magmas, which were vapor-saturated magmas carrying most of their sulfur in an accumulated vapor phase. Almost all the sulfur of the SO2 emissions was present prior to emission as accumulated magmatic vapor at 6–10 km depth in the magma that supplied the eruption; whole-rock normalized concentrations of gaseous excess S in these magmas remained at ~0.2 wt.% throughout the eruption, equivalent to ~0.7 vol.% at depth. Data for CO2 emissions during the eruption indicate that CO2 at whole-rock concentrations of ~0.6 wt.% in the erupted magma was a key factor in creating the vapor saturation and accumulation condition making a vapor phase source of excess sulfur possible at depth. When explosive volcanism involves magma with accumulated vapor, melt inclusions do not provide a sufficient basis for predicting SO2 emissions. Thus, petrologic estimates made for SO2 emissions during explosive eruptions of the past may be too low and may significantly underestimate impacts on climate and the chemistry of the atmosphere.

Strong S-wave attenuation and actively degassing magma beneath Taal volcano, Philippines, inferred from source location analysis using high-frequency seismic amplitudes

NASA Astrophysics Data System (ADS)

Kumagai, H.; Lacson, R. _Jr., Jr.; Maeda, Y.; Figueroa, M. S., II; Yamashina, T.

2014-12-01

Taal volcano, Philippines, is one of the world's most dangerous volcanoes given its history of explosive eruptions and its close proximity to populated areas. A key feature of these eruptions is that the eruption vents were not limited to Main Crater but occurred on the flanks of Volcano Island. This complex eruption history and the fact that thousands of people inhabit the island, which has been declared a permanent danger zone, together imply an enormous potential for disasters. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) constantly monitors Taal, and international collaborations have conducted seismic, geodetic, electromagnetic, and geochemical studies to investigate the volcano's magma system. Realtime broadband seismic, GPS, and magnetic networks were deployed in 2010 to improve monitoring capabilities and to better understand the volcano. The seismic network has recorded volcano-tectonic (VT) events beneath Volcano Island. We located these VT events based on high-frequency seismic amplitudes, and found that some events showed considerable discrepancies between the amplitude source locations and hypocenters determined by using onset arrival times. Our analysis of the source location discrepancies points to the existence of a region of strong S-wave attenuation near the ground surface beneath the east flank of Volcano Island. This region is beneath the active fumarolic area and above sources of pressure contributing inflation and deflation, and it coincides with a region of high electrical conductivity. The high-attenuation region matches that inferred from an active-seismic survey conducted at Taal in 1993. Our results, synthesized with previous results, suggest that this region represents actively degassing magma near the surface, and imply a high risk of future eruptions on the east flank of Volcano Island.

Variable sulfur isotope composition of sulfides provide evidence for multiple sources of contamination in the Rustenburg Layered Suite, Bushveld Complex

NASA Astrophysics Data System (ADS)

Magalhães, Nivea; Penniston-Dorland, Sarah; Farquhar, James; Mathez, Edmond A.

2018-06-01

The Rustenburg Layered Suite (RLS) of the Bushveld Complex (BC) is famous for its platinum group element (PGE) ore, which is hosted in sulfides. The source of sulfur necessary to generate this type of mineralization is inferred to be the host rock of the intrusion. The RLS has a sulfur isotopic signature that indicates the presence of Archean surface-derived material (Δ33 S ≠ 0) in the magma. This signature, with an average value of Δ33 S = 0.112 ± 0.024 ‰, deviates from the expected Δ33 S value of the mantle of 0 ± 0.008 ‰. Previous work suggested that this signature is uniform throughout the RLS, which contrasts with radiogenic isotopes which vary throughout the igneous stratigraphy of the RLS. In this study, samples from key intervals within the igneous stratigraphy were analyzed, showing that Δ33 S values vary in the same stratigraphic levels as Sr and Nd isotopes. However, the variation is not consistent; in some levels there is a positive correlation and in others a negative correlation. This observation suggests that in some cases distinct magma pulses contained assimilated sulfur from different sources. Textural analysis shows no evidence for late addition of sulfur. These results also suggest that it is unlikely that large-scale assimilation and/or efficient mixing of host rock material in a single magma chamber occurred during emplacement. The data do not uniquely identify the source of sulfur in the different layers of the RLS, but the variation in sulfur isotope composition and its relationship to radiogenic isotope data calls for a reevaluation of the models for the formation and evolution of the RLS, which has the potential to impact the knowledge of how PGE deposits form.

Kinetics of Melting and Dissolution in Lunar Materials

NASA Technical Reports Server (NTRS)

Hess, Paul C.

2002-01-01

An understanding of the petrogenesis of lunar magmas, particularly mare basalts and the parent magmas to the Mg-rich suite, remains an unfulfilled goal. The fact is not surprising given the complexity of the problem. On the Moon, the source region for lunar magmas is not primitive mantle but rather a series of cumulate rocks that vary widely in both minerology and major and minor element contents. The stratigraphy of the cumulate mantle is not likely to be very regular given that the culumate pile is formed initially in an unstable configuration and subsequent thermal and compositional heterogeneities on a number of length scales. These lithologic heterogeneities, the large range of pressures and temperatures over which melts are generated on the Moon, and the close juxtaposition of cumulate rock with widely varying solidii introduce significant complications to the nature of the melting relations that control melt generation. These factors, coupled with the likelihood that polybaric fractional melting of varying efficiencies ultimately control the composition of planetary progress, are ample reasons why the lunar magmas remain the enigma they are. To make progress, phase equilibria studies must be coupled with a detailed understanding of the time scales and the dynamics of crystal and melt reequilibration processes.

Oxidation State of Iron in the Izu-Bonin Arc Initial Magma and Its Influence Factors

NASA Astrophysics Data System (ADS)

Li, H.; Arculus, R. J.; Brandl, P. A.; Hamada, M.; Savov, I. P.; Zhu, S.; Hickey-Vargas, R.; Tepley, F. J., III; Meffre, S.; Yogodzinski, G. M.; McCarthy, A.; Barth, A. P.; Kanayama, K.; Kusano, Y.; Sun, W.

2014-12-01

The redox state of mantle-derived magmas is a controversial issue, especially whether island arc basalts are more oxidized than those from mid-ocean ridges. Usually, arc magmas have higher Fe3+/Fe2+ and calculated oxygen fugacity (fO2) than mid-ocean ridge basalts (MORB). It is the high fO2 of arc magma that apparently delays onset of sulfide fractionation and sequestration of precious/base metals thereby facilitating the formation of many giant gold-copper deposits typically associated with subduction zones. But due to a paucity of Fe3+/Fe2+ data for primary mantle-derived arc magmas, the cause for high fO2 of these magma types is still controversial; causes may include inter alia subduction-released oxidized material addition to the mantle wedge source of arc magma, partial melting of subducted slab, and redox changes occurring during ascent of the magma. Fortunately, IODP expedition 351 drilling at IODP Site U1438 in the Amami-Sankaku Basin of the northwestern Philipine Sea, adjacent to the proto-Izu-Bonin Arc at the Kyushu-Palau Ridge (KPR), recovered not only volcaniclastics derived from the inception of Izu-Bonin Mariana (IBM) arc in the Eocene, but also similar materials for the Arc's subsequent evolution through to the Late Oligocene and abandonment of the KPR as a remnant arc. Samples of the pre-Arc oceanic crustal basement were also recovered enabling us to determine the fO2of the mantle preceding arc inception. As the oxidation state of iron in basaltic glass directly relates to the fO2 , the Fe3+/∑Fe ratio [Fe3+/(Fe3++ Fe2+)] of basaltic glass are quantified by synchrotron-facilitated micro X-ray Absorption Near Edge Structure (XANES) spectroscopy to reflect its fO2. Fe K-edge µ-XANES spectra were recorded in fluorescence mode at Beamline 15U1, Shanghai Synchrotron Radiation Facility (SSRF). Synthetic silicate glass with known Fe3+/∑Fe ratio was used in data handling. The experimental results as well as preliminary data from IODP Expedition 351 will be presented

Rethinking Volcanic Plumbing Systems: The Prevalence of Offset Magma Reservoirs at Holocene Volcanoes

NASA Astrophysics Data System (ADS)

Lerner, A. H.; Karlstrom, L.; Hurwitz, S.; Anderson, K. R.; Ebmeier, S. K.

2016-12-01

Mechanical models of volcanic overpressure and interpretations of volcanic deposits are generally rooted in the classic paradigm of a magma reservoir being located directly beneath the main topographic high and central conduit of a volcano. We test this framework against recent decades of research on volcanic deformation, seismic tomography, earthquake hypocenter locations, and magnetotellurics, which have provided unprecedented geophysical views of volcanic plumbing systems. In a literature survey of Holocene strato- and shield volcanoes in arc, backarc, continental rift, and intraplate settings, we find that shallow to mid-crustal (< 20 km) magma reservoirs are equally likely to be laterally offset from principle volcanic edifices (n = 20) as they are to be centrally located beneath volcanic topographic highs (n = 19). We classify offset reservoirs as having imaged or modeled centroids that are at least 2 km laterally offset from the central volcanic edifice. The scale and geometry of offset magma reservoirs range widely, with a number of systems having discrete reservoirs laterally offset up to 15 km from the main volcanic edifice, at depths of 2 to 15 km. Other systems appear to have inclined magmatic reservoirs and/or fluid transport zones that continuously extend from beneath the main edifice to lateral distances up to 20 km, at depths of 3 to 18 km. Additionally, over a third of the studied systems have small, centrally located shallow magma or fluid reservoirs at depths of 1 to 5 km. Overall, we find that offset magma reservoirs are more common than is classically perceived, and offset reservoirs are more prevalent in intermediate to evolved stratovolcanoes (19 of 28) than in basaltic shield volcanoes (2 of 7). The reason for the formation of long-lived edifices that are offset from their source magma reservoir(s) is an open question; correlation to regional principal stresses or local tectonics, edifice size, lithology, and morphology, and climate may provide insights into this phenomenon. The commonality of offset magma reservoirs warrants reassessing the ways that volcanic systems have been traditionally modeled and monitored, which are principally focused around the topographic edifice, but may be missing critical features associated with lateral offset reservoirs and more complex conduit geometries.

The 1994-2001 eruptive period at Rabaul, Papua New Guinea: Petrological and geochemical evidence for basalt injections into a shallow dacite magma reservoir, and significant SO2 flux

NASA Astrophysics Data System (ADS)

Patia, H.; Eggins, S. M.; Arculus, R. J.; McKee, C. O.; Johnson, R. W.; Bradney, A.

2017-10-01

The eruptions that began at Rabaul Caldera on 19 September 1994 had two focal points, the vents Tavurvur and Vulcan, located 6 km apart on opposing sides of the caldera. Vulcan eruptives define a tight cluster of dacite compositions, whereas Tavurvur eruptives span an array from equivalent dacite compositions to mafic andesites. The eruption of geochemically and mineralogically identical dacites from both vents indicates sourcing from the same magma reservoir. This, together with previously reported H2O-CO2 volatile contents of dacite melt inclusions, a caldera-wide seismic low-velocity zone, and a seismically active caldera ring fault structure are consistent with the presence at 3-6 km depth of an extensive, tabular dacitic magma body having volume of about 15-150 km3. The Tavurvur andesites form a linear compositional array and have strongly bimodal phenocryst assemblages that reflect dacite hybridisation with a mafic basalt. The moderately large volume SO2 flux documented in the Tavurvur volcanic plume (and negligible SO2 flux in the Vulcan plume) combined with high dissolved S contents of basaltic melt inclusions trapped in olivine of Tavurvur eruptives, indicate that the amount of degassed basaltic magma was 0.1 km3 and suggest that the injection of this magma was confined to the Tavurvur-side (eastern to northeastern sector) of the caldera. Circumstantial evidence suggests that the eruption was triggered and evolved in response to a series of basaltic magma injections that may have commenced in 1971 and continued up until at least the start of the 1994 eruptions. The presence of zoned plagioclase phenocrysts reflecting older basalt-dacite interaction events (i.e. anorthite cores overgrown with thick andesine rims), evaluation of limited available data for the products of previous eruptions in 1878 and 1937-1943, and the episodic occurrence of major intra-caldera seismo-deformational events indicates that the shallow magma system at Rabaul Caldera is subjected to repeated mafic magma injections at intervals of several years to several decades.

Comparing microbial water quality in an intermittent and continuous piped water supply.

PubMed

Kumpel, Emily; Nelson, Kara L

2013-09-15

Supplying piped water intermittently is a common practice throughout the world that increases the risk of microbial contamination through multiple mechanisms. Converting an intermittent supply to a continuous supply has the potential to improve the quality of water delivered to consumers. To understand the effects of this upgrade on water quality, we tested samples from reservoirs, consumer taps, and drinking water provided by households (e.g. from storage containers) from an intermittent and continuous supply in Hubli-Dharwad, India, over one year. Water samples were tested for total coliform, Escherichia coli, turbidity, free chlorine, and combined chlorine. While water quality was similar at service reservoirs supplying the continuous and intermittent sections of the network, indicator bacteria were detected more frequently and at higher concentrations in samples from taps supplied intermittently compared to those supplied continuously (p < 0.01). Detection of E. coli was rare in continuous supply, with 0.7% of tap samples positive compared to 31.7% of intermittent water supply tap samples positive for E. coli. In samples from both continuously and intermittently supplied taps, higher concentrations of total coliform were measured after rainfall events. While source water quality declined slightly during the rainy season, only tap water from intermittent supply had significantly more indicator bacteria throughout the rainy season compared to the dry season. Drinking water samples provided by households in both continuous and intermittent supplies had higher concentrations of indicator bacteria than samples collected directly from taps. Most households with continuous supply continued to store water for drinking, resulting in re-contamination, which may reduce the benefits to water quality of converting to continuous supply. Copyright © 2013 Elsevier Ltd. All rights reserved.

Asymmetric Post-Magma Ocean Crust-Building on the Lunar Nearside

NASA Astrophysics Data System (ADS)

Elardo, S. M.; Laneuville, M.; McCubbin, F. M.; Shearer, C. K.

2018-05-01

Our experiments show that the KREEP reservoir on the lunar nearside reduces the melting temperature of Mg-suite source rocks, leading to asymmetric crust-building magmatism independent of any contribution from radiogenic heating.

Magma mixing in granite petrogenesis: Insights from biotite inclusions in quartz and feldspar of Mesozoic granites from South China

NASA Astrophysics Data System (ADS)

Gao, Peng; Zhao, Zi-Fu; Zheng, Yong-Fei

2016-06-01

Magma mixing is a common process in granite petrogenesis. The major element composition of biotites in granites is primarily controlled by the composition of magmas from which they crystallized. Biotite grains enclosed in quartz and feldspars of granites are naturally protected by their host minerals, so that their compositions are likely original and can potentially be used to track the magma mixing. This is illustrated by a combined study of matrix and inclusion biotites from Mesozoic granites in the Nanling Range, South China. Three granite samples have been used in this study: one two-mica granite and two biotite granites. The biotites of different occurrences in the two-mica granite have no compositional distinctions. Biotites in the two-mica granite have higher Al2O3 and lower MgO than those in the biotite granites. The former is consistent with biotites from typical S-type granites of metasedimentary origin. In contrast, biotites from the biotite granites can be categorized into different groups based on their paragenetic minerals and geochemical compositions. They have relatively low aluminous saturation indices but higher Mg numbers, falling in the transitional field between typical S- and I-type granites. In addition, there are two contrasting zircon populations with nearly identical U-Pb ages in the biotite granites. One shows clearly oscillatory zonings in CL images, whereas the other is totally dark and often overgrew on the former one. The zircons with oscillatory zonings have higher δ18O values than the dark ones, indicating their growth from two compositionally different magmas, respectively, with different sources. An integrated interpretation of all these data indicates that mixing of two different magmas was responsible for the petrogenesis of biotite granites. Therefore, the study of biotite inclusions provides insights into the magma mixing in granite petrogenesis.

The Campi Flegrei Deep Drilling Project: using borehole measurements to discriminate magmatic and geothermal effects in caldera unrest

NASA Astrophysics Data System (ADS)

De Natale, Giuseppe; Troise, Claudia; Carlino, Stefano; Troiano, Antonio; Giulia Di Giuseppe, Maria; Piochi, Monica; Somma, Renato; Tramelli, Anna; Kilburn, Christopher

2015-04-01

Large calderas are potentially the most risky volcanic areas in the world since they are capable of producing huge eruptions whose major effects can involve human life and activities from regional to global scale. Calderas worldwide are characterized by frequent episodes of unrest which, only in few cases, culminate with eruptions. This ambiguous behavior is generally explained in terms of magma intrusion or disturbance of geothermal fluids in the shallow crust, which are both source of ground deformations and seismicity. A major goal is to determine the relative contribution of each process, because the potential for eruptions significantly enhanced if magma movements emerge as the primary component. A very important case study is the active Campi Flegrei caldera, hosting part of the large city of Naples (Southern Italy). In the framework of the Campi Flegrei Deep Drilling Project new filed data from pilot borehole have been recorded (permeability and in situ stress) by using a novel procedure of Leak Off Test. These new data, particularly the actual permeability, are fundamental to calibrate the caldera unrest models at Campi Flegrei and, , to put constrains to forecast the maximum future eruptive scenario. We show here that these new data, integrated by fluid-dynamical modeling, allow to assess that only about a third of the maximum uplift recorded in 1982-1984 may be due to shallow aquifer perturbation, so that the remaining part should be due to magma inflow, corresponding to about 0.05 Km3 of new magma if we assume a sill-like reservoir located at 4 km of depth. Considering an almost equivalent magma inflow for the 1969-1972 unrest, which showed a similar uplift, we got a total magma inflow of 0.1 Km3. It is then very important to assess the times for cooling of such accumulated magma, in order to assess the eruption hazard.

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 (

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.

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.

New Martian Meteorite Is One of the Most Oxidized Found to Date

NASA Technical Reports Server (NTRS)

Hui, Hejiu; Peslier, Anne; Lapen, Thomas J.; Shafer, John T.; Brandon, Alan D.; Irving, Anthony J.

2014-01-01

As of 2013, about 60 meteorites from the planet Mars have been found and are being studied. Each time a new Martian meteorite is found, a wealth of new information comes forward about the red planet. The most abundant type of Martian meteorite is a shergottite; its lithologies are broadly similar to those of Earth basalts and gabbros; i.e., crustal igneous rocks. The entire suite of shergottites is characterized by a range of trace element, isotopic ratio, and oxygen fugacity values that mainly reflect compositional variations of the Martian mantle from which these magmas came. A newly found shergottite, NWA 5298, was the focus of a study performed by scientists within the Astromaterials Research and Exploration Science (ARES) Directorate at the Johnson Space Center (JSC) in 2012. This sample was found in Morocco in 2008. Major element analyses were performed in the electron microprobe (EMP) laboratory of ARES at JSC, while the trace elements were measured at the University of Houston by laser inductively coupled plasma mass spectrometry (ICPMS). A detailed analysis of this stone revealed that this meteorite is a crystallized magma that comes from the enriched end of the shergottite spectrum; i.e., trace element enriched and oxidized. Its oxidation comes in part from its mantle source and from oxidation during the magma ascent. It represents a pristine magma that did not mix with any other magma or see crystal accumulation or crustal contamination on its way up to the Martian surface. NWA 5298 is therefore a direct, albeit evolved, melt from the Martian mantle and, for its lithology (basaltic shergottite), it represents the oxidized end of the shergottite suite. It is thus a unique sample that has provided an end-member composition for Martian magmas.