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Sample records for alkaline volcanic rocks

  1. Discovery of Alkaline Volcanic Rocks on Mars

    NASA Astrophysics Data System (ADS)

    McSween, H. Y.; Team, A. S.

    2006-05-01

    Based on remote sensing measurements and the compositions of martian meteorites, the surface of Mars is inferred to be dominated by subalkaline mafic volcanic rocks. However, the Spirit rover has recently discovered lavas of alkalic composition. Picritic (Adirondack class) basalts with high alkali and low silica contents were previously analyzed on the plains of Gusev Crater, and two new classes of dark, fine-grained, relatively unaltered volcanic rocks with distinctive thermal emission spectra have now been found as float and in a possible dike at high elevations in the Columbia Hills. Chemical analyses indicate that these rocks are mildly alkaline basalt and trachybasalt, respectively. Their mineralogy consists of Na- and K-rich feldspar(s), low- and high-Ca pyroxenes, ferroan olivine, Fe-Ti (and possibly Cr) oxides, phosphate, and possibly glass. Chemical compositions of these rocks lie along a MELTS-calculated liquid line of descent for Adirondack class basalt. Systematic changes in normative mineralogy are consistent with the calculated magmatic fractionation. We infer that Backstay- and Irvine-class magmas may have formed by low-pressure fractionation of primitive, oxidized Adirondack-class magmas and were possibly emplaced coevally with the plains basalts. The compositions of these rocks reveal that the Gusev magmatic province is alkaline, distinct from the subalkaline volcanic rocks thought to dominate most of the planet's surface. This discovery may have implications for the composition of the martian mantle source region and the conditions under which it melted.

  2. Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars

    NASA Astrophysics Data System (ADS)

    McSween, H. Y.; Ruff, S. W.; Morris, R. V.; Bell, J. F.; Herkenhoff, K.; Gellert, R.; Stockstill, K. R.; Tornabene, L. L.; Squyres, S. W.; Crisp, J. A.; Christensen, P. R.; McCoy, T. J.; Mittlefehldt, D. W.; Schmidt, M.

    2006-09-01

    Irvine, Backstay, and Wishstone are the type specimens for three classes of fine-grained or fragmental, relatively unaltered rocks with distinctive thermal emission spectra, found as float on the flanks of the Columbia Hills. Chemical analyses indicate that these rocks are mildly alkaline basalt, trachybasalt, and tephrite, respectively. Their mineralogy consists of Na- and K-rich feldspar(s), low- and high-Ca pyroxenes, ferroan olivine, Fe-Ti (and possibly Cr) oxides, phosphate, and possibly glass. The texture of Wishstone is consistent with a pyroclastic origin, whereas Irvine and Backstay are lavas or possibly dike rocks. Chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for Adirondack class rocks (olivine-rich basalts from the Gusev plains) at various pressures from 0.1 to 1.0 GPa. We infer that Wishstone-, Backstay-, and Irvine-class magmas may have formed by fractionation of primitive, oxidized basaltic magma similar to Adirondack-class rocks. The compositions of all these rocks reveal that the Gusev magmatic province is alkaline, distinct from the subalkaline volcanic rocks thought to dominate most of the planet's surface. The fact that differentiated volcanic rocks were not encountered on the plains prior to ascending Husband Hill may suggest a local magma source for volcanism beneath Gusev crater.

  3. Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars

    USGS Publications Warehouse

    McSween, H.Y.; Ruff, S.W.; Morris, R.V.; Bell, J.F.; Herkenhoff, K.; Gellert, Ralf; Stockstill, K.R.; Tornabene, L.L.; Squyres, S. W.; Crisp, J.A.; Christensen, P.R.; McCoy, T.J.; Mittlefehldt, D. W.; Schmidt, M.

    2006-01-01

    Irvine, Backstay, and Wishstone are the type specimens for three classes of fine-grained or fragmental, relatively unaltered rocks with distinctive thermal emission spectra, found as float on the flanks of the Columbia Hills. Chemical analyses indicate that these rocks are mildly alkaline basalt, trachybasalt, and tephrite, respectively. Their mineralogy consists of Na- and K-rich feldspar(s), low- and high-Ca pyroxenes, ferroan olivine, Fe-Ti (and possibly Cr) oxides, phosphate, and possibly glass. The texture of Wishstone is consistent with a pyroclastic origin, whereas Irvine and Backstay are lavas or possibly dike rocks. Chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for Adirondack class rocks (olivine-rich basalts from the Gusev plains) at various pressures from 0.1 to 1.0 GPa. We infer that Wishstone-, Backstay-, and Irvine-class magmas may have formed by fractionation of primitive, oxidized basaltic magma similar to Adirondack-class rocks. The compositions of all these rocks reveal that the Gusev magmatic province is alkaline, distinct from the subalkaline volcanic rocks thought to dominate most of the planet's surface. The fact that differentiated volcanic rocks were not encountered on the plains prior to ascending Husband Hill may suggest a local magma source for volcanism beneath Gusev crater. Copyright 2006 by the American Geophysical Union.

  4. 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

  5. Age, geochemical characteristics and petrogenesis of Cenozoic intraplate alkaline volcanic rocks in the Bafang region, West Cameroon

    NASA Astrophysics Data System (ADS)

    Tchuimegnie Ngongang, Nicaise Blaise; Kamgang, Pierre; Chazot, Gilles; Agranier, Arnaud; Bellon, Hervé; Nonnotte, Philippe

    2015-02-01

    The origin of the volcanism in the Cameroon Volcanic Line and the nature of its mantle sources are still highly controversial. We present major and trace element compositions as well as Sr-Nd-Pb-Hf isotopic results on mafic and intermediate lavas from the Bafang area in the central part of the Cameroon Volcanic Line. The lavas range from basanites and basalts to hawaiites and mugearites with an alkaline affinity and were emplaced between 10 and 6 Ma ago. The evolution from basalts and basanites to more differentiated rocks involved fractionation of olivine, clinopyroxene and Fe-Ti oxides, but the isotopic compositions show that crustal contamination processes affected some magmas during their ascent in the crust. Basalts and basanites originated from a garnet-bearing mantle source and their differences are mostly due to variable degrees of partial melting. The isotopic composition of the uncontaminated samples imply the participation of three distinct mantle components, the depleted MORB mantle (not dominant), an enriched component and a Pb radiogenic component similar to the source of the Mount Cameroon. Combined with previously published isotopic data from the Cameroon Volcanic Line, our new results indicate that the source of the volcanism mostly reside in the lithospheric mantle and is different from what can be expected from the melting of a mantle accreted from or modified during the emplacement of the St. Helena mantle plume.

  6. Mobility of elements during K-metasomatism of volcanic rocks by alkaline, saline brines

    SciTech Connect

    Chapin, C.E. )

    1992-01-01

    Silicic ignimbrites and interbedded mafic lavas of Oligocene age were altered by alkaline, saline brines in the Popotosa basin of the Rio Grande rift near Socorro, New Mexico. Alteration was toward a fine-grained assemblage of adularia + hematite [+-] quartz irrespective of initial rock composition. Elevated [delta][sup 18]O and the occurrence of zeolites, gypsum, and salt casts in overlying play a deposits indicates that the altering fluids were basin brines. Preliminary analysis of secondary inclusions in fractured quartz phenocrysts indicates temperatures near 100 C and salinities near 20 wt. % NaCl equivalent. To test element mobility, pairs of fresh and altered samples from each of 7 ignimbrite units plus 4 samples of interbedded mafic lavas were analyzed by XRF, INAA, and AA. The elements showing the greatest mobility during alteration of ignimbrites are listed below along with their enrichment factors (altered rock/fresh rock). Ignimbrites: enriched--K[sub 2]O 1.99, Rb 1.89, Ba 1.43, As 12.14, Sb 18.30, Pb 1.23; depleted--Na[sub 2]O 0.25, MgO 0.57, CaO 0.27, MnO 0.50, P[sub 2]O[sub 5] 0.75, Sr 0.54, Li 0.57, U 0.78, Br 0.67, Cu 0.90, Zn 0.69. The dramatic enrichment of As and Sb in both ignimbrites and mafic lavas indicates that these elements are highly mobile in oxidizing basin brine systems. K-metasomatism is a common type of alteration in rift basins, detachment terranes, aquifers through which brines have migrated.

  7. Crystal accumulation and compositional trends in a calc-alkaline batholith: implications for correlation of plutonic and volcanic rocks

    NASA Astrophysics Data System (ADS)

    Barnes, C. G.; Coint, N.

    2013-12-01

    The Wooley Creek batholith is a tilted, calc-alkaline intrusive complex in the Klamath Mountain province, California, that can be divided into two main zones: lower (~159.2 × 0.2 Ma) and upper (~158.2 × 0.3 Ma), separated by a central transition zone. The lower zone consists of multiple intrusive units of gabbro through tonalite, with minor mafic synplutonic dikes and intrusive melagabbro and pyroxenite. Major and trace element data plot in two groups: a mafic group that encompasses pyroxenite to diorite, and a tonalitic group. For each group, Mg/Fe in augite was used to determine the approximate composition of equilibrium melt and then major element mass balance was used to calculate proportions of cumulate phases and melt. For the mafic group, no single parental magma can be identified, which is consistent with assembly via many magma batches. However, the most mafic rocks were derived from basaltic andesite magmas and represent 30 to 100% cumulate augite + opx × plagioclase × olivine. Interstitial melt in the tonalitic group was dacitic, and mass balance indicates from 30 to 80% cumulate pyroxenes + plagioclase × accessory apatite and Fe-Ti oxides. The parental magma was probably silicic andesite. The upper zone varies gradationally from structurally low quartz diorite to uppermost granite. Upper zone magmas ';leaked' to form dacitic to rhyodacitic ';roof dikes'. Previous work (Coint et al., Geosphere, in press) showed that the upper zone formed from an approximately homogeneous magma body and that compositional variation was related to upward percolation of melt. Mass balance supports this interpretation and indicates that (1) the parental magmas were andesitic, (2) structurally low rocks are 15 to 65 % cumulate hornblende + plagioclase × pyroxene, and (3) high-level granite and granodiorite are the fractionated products of this accumulation. These results show that the upper zone is a good example of fractional crystallization within a moderate

  8. Controls on the PGE distribution of Permian Emeishan alkaline and peralkaline volcanic rocks in Longzhoushan, Sichuan Province, SW China

    NASA Astrophysics Data System (ADS)

    Qi, Liang; Wang, Christina Yan; Zhou, Mei-Fu

    2008-12-01

    The ~ 260-Ma Emeishan large igneous province in SW China and northern Vietnam contains low-Ti tholeiitic basalts, high-Ti alkaline basalts and minor peralkaline volcanic rocks. The flood basalts in Longzhoushan, Sichuan Province, SW China, comprise four units, each of which has volcanic breccia at the base. From the base upward, rocks of Units 1 and 2 are high-Ti basalts with relatively high MgO (7.6-11.0 wt.%), TiO 2 (1.7-4.5 wt.%) and Ti/Y ratios (420-790). Unit 3 is composed of tephrites with lower MgO (0.87-6.2 wt.%), TiO 2 (0.96-2.14 wt.%) and Ti/Y ratios (190-530), whereas Unit 4 consists of basaltic andesites with moderate MgO (3.5-4.8 wt.%), TiO 2 (2.2-3.1 wt.%) and Ti/Y ratios (383-606). The high-Ti basalts may have been derived from an OIB-like mantle source and the basaltic andesites were probably generated by crustal contamination and fractionation of high-Ti basaltic magmas. The tephrites show high Nb/Y (1.2 to 2.7) and Th/Y (0.31 to 0.55) ratios, variable Zr/Hf ratios (40 to 49) and relatively low ɛNd( t) (- 0.7 to + 0.28) values, suggesting an asthenospheric mantle contribution modified by carbonate-rich fluids. The high-Ti basalts contain relatively high and variable PGE and their Cu/Pd ratios are relatively constant (compared to the tephrites) and vary from 8,500 to 86,000. We attribute such relative constancy of the Cu/Pd ratios to the presence of residual sulphide in the source of the high-Ti rocks and subsequent crystallization from S-undersaturated melts. The basaltic andesites have relatively high and constant Cu/Pd ratios (130,000-370,492) and the lowest PGE contents (average 0.12 ppb for Pd, 0.20 ppb for Pt), suggesting an earlier removal of sulfide due to crustal contamination before emplacement. The tephrites have PGE abundances (0.057 to 1.89 ppb for Pt and 0.11 to 2.10 ppb for Pd) higher than those for basaltic andesites, however, the Cu/Pd ratios (33,300 to 429,000) of the rocks are more variable than those for the basaltic andesites

  9. The Volatile Element Evolution of Intra-plate Alkaline Rocks as Recorded by Apatite: An Example from the Hegau Volcanic Field (Southwest Germany)

    NASA Astrophysics Data System (ADS)

    Von Der Handt, A.; Rahn, M. K. W.; Wang, L. X.; Marks, M. A. W.

    2014-12-01

    The role of volatiles in the petrogenesis of alkaline intra-plate magmas has been the subject of an increasing number of experimental studies. The study of naturally occurring rocks and their volatile contents is often complicated by syn- and post-eruptive degassing and alteration processes. Minerals that incorporate volatiles into their structure such as apatites are often more faithful recorders of the pre-eruptive volatile budget. The Hegau volcanic field in Southwest Germany is part of the Central European Volcanic Province, lies around 60-70 km to the east of the Upper Rhine graben and of Miocene age. Three main lithological units can be distinguished (1) olivine melilites (2) phonolites and (3) the "Deckentuff" series referring to a series of diatreme-filling pipe breccias and lapilli tuff layers. Carbonatites occur subordinately in the Hegau province. Earlier radiometric age dating suggested distinct phases of volcanic activity of Deckentuffs, melilites and phonolites with little overlap, but new apatite fission-track and (U-Th)/He age data suggest a synchronous activity. Apatite is an abundant accessory phase in the Deckentuff and phonolite series and we investigated its major, trace and volatile element composition by EPMA, SIMS and cathodoluminescence imaging. Pronounced core-rim zoning of apatite in places attests that diffusional equilibration was very limited and they likely retained their primary compositions. This allows us to trace the entire magmatic evolution of the Hegau province from its most primitive to most evolved products as well as resolve it in time by combining age dating with compositional analysis. Apatite compositions fall along the OH-F join with low Cl-contents (<0.5 wt%). Volatile contents (Cl, OH, S) are highest in most primitive compositions and decrease with further evolution while F increases. Multiple magmatic cycles can be discerned with a general trend to the more evolved phonolite compositions toward the end of volcanic

  10. Uranium series, volcanic rocks

    USGS Publications Warehouse

    Vazquez, Jorge A.

    2014-01-01

    Application of U-series dating to volcanic rocks provides unique and valuable information about the absolute timing of crystallization and differentiation of magmas prior to eruption. The 238U–230Th and 230Th-226Ra methods are the most commonly employed for dating the crystallization of mafic to silicic magmas that erupt at volcanoes. Dates derived from the U–Th and Ra–Th methods reflect crystallization because diffusion of these elements at magmatic temperatures is sluggish (Cherniak 2010) and diffusive re-equilibration is insignificant over the timescales (less than or equal to 10^5 years) typically associated with pre-eruptive storage of nearly all magma compositions (Cooper and Reid 2008). Other dating methods based on elements that diffuse rapidly at magmatic temperatures, such as the 40Ar/39Ar and (U–Th)/He methods, yield dates for the cooling of magma at the time of eruption. Disequilibrium of some short-lived daughters of the uranium series such as 210Po may be fractionated by saturation of a volatile phase and can be employed to date magmatic gas loss that is synchronous with volcanic eruption (e.g., Rubin et al. 1994).

  11. The Quaternary calc-alkaline volcanism of the Patagonian Andes close to the Chile triple junction: geochemistry and petrogenesis of volcanic rocks from the Cay and Maca volcanoes (˜45°S, Chile)

    NASA Astrophysics Data System (ADS)

    D'Orazio, M.; Innocenti, F.; Manetti, P.; Tamponi, M.; Tonarini, S.; González-Ferrán, O.; Lahsen, A.; Omarini, R.

    2003-08-01

    Major- and trace-element, Sr-Nd isotopes, and mineral chemistry data were obtained for a collection of volcanic rock samples erupted by the Cay and Maca Quaternary volcanoes, Patagonian Andes (˜45°S, Chile). Cay and Maca are two large, adjacent stratovolcanoes that rise from the Chiloe block at the southern end of the southern volcanic zone (SVZ) of the Andes. Samples from the two volcanoes are typical medium-K, calc-alkaline rocks that form two roughly continuous, largely overlapping series from subalkaline basalt to dacite. The overall geochemistry of the samples studied is very similar to that observed for most volcanoes from the southern SVZ. The narrow range of Sr-Nd isotope compositions ( 87Sr/ 86Sr=0.70389-0.70431 and 143Nd/ 144Nd=0.51277-0.51284) and the major- and trace-element distributions indicate that the Cay and Maca magmas differentiated by crystal fractionation without significant contribution by crustal contamination. This is in accordance with the thin (<30 km), relatively young (Paleozoic or more recent) continental crust beneath the volcanoes. The nature of the subduction-derived materials involved in the genesis of the Cay and Maca magmas is investigated by means of the relative concentration of fluid mobile (e.g. Ba) and fluid immobile (e.g. Nb, Ta, Zr, Y) elements and other relevant trace-element ratios (e.g. Sr/Y). The results indicate that small amounts (<1 wt%) of both subducted sediments and slab-released fluids were added to the mantle sources of the Cay and Maca volcanoes and that, despite the very young age (<10 Ma) of the oceanic lithosphere subducted beneath the volcanoes, slab melts were not involved in the magma genesis. Notwithstanding the proximity of the Cay and Maca magma sources to the northern edge of the slab window generated by the subduction of the Chile ridge under the South American plate, we did not find any geochemical evidence for a contribution of a subslab asthenospheric mantle. However, this mantle has been used

  12. Petrology and geochemistry of the ultrapotassic rocks from the Sabatini Volcanic District, central Italy: the role of evolutionary processes in the genesis of variably enriched alkaline magmas

    NASA Astrophysics Data System (ADS)

    Conticelli, Sandro; Francalanci, Lorella; Manetti, Piero; Cioni, Raffaello; Sbrana, Alessandro

    1997-01-01

    The Sabatini Volcanic District (SVD) is a large volcanic field characterised by the lack of any major volcanic center. Its activity, spread over a wide area, started at 0.6 Ma and developed through five main phases, during which several calderas and the Bracciano lake volcano-tectonic depression were formed. All the volcanic rocks belong to the Roman-type ultrapotassic series (HKS), ranging from leucite tephrites to leucite and haüyne phonolites. Although the major- and compatible-element contents indicate a single series of evolution, there are differences in the incompatible trace-element abundances. A high-Ba series (HBaS) has been distinguished from a low-Ba series (LBaS), with the former also enriched in all other incompatible elements (e.g., REE, Nb, Zr, Th) except Rb. The HBaS rocks are plagioclase-free, leucite-bearing lavas and were abundantly outpoured from the Bracciano volcanoes during the third and fifth phase of activity. Plagioclase- and phlogopite-bearing rocks constitute the LBaS and were erupted during the other phases generally from smaller and eccentric volcanic centers. The initial 87Sr/ 86Sr values are higher in the HBaS rocks and do not vary significantly with magma evolution (0.71047-0.71080), but cover a wider range in the LBaS rocks (0.70944-0.71038), with the lowest Sr isotope ratios occurring in the least evolved lavas. The higher Ca content in the olivine and Ti and Al IV in the clinopyroxene, and the lower ulvöspinel content of the Ti-magnetites of the HBaS rocks suggest an evolution at lower pressure and higher temperature for this magma. The observed petrologic characteristics suggest that the HBaS magma evolved at lower depths by processes of refilling, tapping, fractionation and probably assimilation (RTFA), where the crystallisation rate of clinopyroxene+leucite±olivine dominates over the input rate of the fresh magma. The LBaS magma evolved at slightly higher pressure, in separate and small magma bodies, by fractional

  13. Cenozoic volcanic rocks of Saudi Arabia

    USGS Publications Warehouse

    Coleman, R.G.; Gregory, R.T.; Brown, G.F.

    2016-01-01

    The historical record of volcanic activity in Saudi Arabia suggests that volcanism is dormant. The harrats should be evaluated for their potential as volcanic hazards and as sources of geothermal energy. The volcanic rocks are natural traps for groundwater; thus water resources for agriculture may be significant and should be investigated.

  14. Trace element geochemistry of Archean volcanic rocks

    NASA Technical Reports Server (NTRS)

    Jahn, B.-M.; Shih, C.-Y.; Murthy, V. R.

    1974-01-01

    The K, Rb, Sr, Ba and rare-earth-element contents of some Archean volcanic rocks from the Vermilion greenstone belt, northeast Minnesota, were determined by the isotopic dilution method. The characteristics of trace element abundances, supported by the field occurrences and major element chemistry, suggest that these volcanic rocks were formed in an ancient island arc system.

  15. Alkaline basaltic volcanism of the Sea of Japan and the Philippine Sea: Similar and distinct geochemical and genetic features

    NASA Astrophysics Data System (ADS)

    Lelikov, E. P.; Emelyanova, T. A.

    2016-05-01

    The results of study of the deep sources of volcanic rocks from the Sea of Japan and the Philippine Sea with continental and oceanic basements, respectively, are presented. This problem is considered with the example of alkaline volcanic rocks of the Middle Miocene to Pliocene complex of the Sea of Japan and the Eocene-Oligocene Urdaneta Plateau of the Philippine Sea. The rocks have a similar geochemistry typical of OIBs, which indicates their deep (plume) origin. The presence of the Oligocene calc-alkaline volcanic rocks, which were formed prior to the marginal sea volcanism in the Sea of Japan, however, is the main difference in volcanism of the Sea of Japan from that of the Urdaneta Plateau, and this is explained by the different basements of these seas.

  16. Fluid and rock interaction in permeable volcanic rock

    SciTech Connect

    Lindley, J.I.

    1985-02-01

    Four types of interrelated changes -geochemical, mineralogic, isotopic, and physical - occur in Oligocene volcanic units of the Mogollon-Datil volcanic field, New Mexico. These changes resulted from the operation of a geothermal system that, through fluid-rock interaction, affected 5 rhyolite ash-flow tuffs and an intercalated basaltic andesite lava flow causing a potassium metasomatism type of alteration. (1) Previous studies have shown enrichment of rocks in K/sub 2/O as much as 130% of their original values at the expense of Na/sub 2/O and CaO with an accompanying increase in Rb and decreases in MgO and Sr. (2) X-ray diffraction results of this study show that phenocrystic plagioclase and groundmass feldspar have been replaced with pure potassium feldspar and quartz in altered rock. Phenocrystic potassium feldspar, biotite, and quartz are unaffected. Pyroxene in basaltic andesite is replaced by iron oxide. (3) delta/sup 18/O increases for rhyolitic units from values of 8-10 permil, typical of unaltered rock, to 13-15 permil, typical of altered rock. Basaltic andesite, however, shows opposite behavior with a delta/sup 18/ of 9 permil in unaltered rock and 6 permit in altered. (4) Alteration results in a density decrease. SEM revealed that replacement of plagioclase by fine-grained quartz and potassium feldspar is not a volume for volume replacement. Secondary porosity is created in the volcanics by the chaotic arrangement of secondary crystals.

  17. Volcanic Rocks As Targets For Astrobiology Missions

    NASA Astrophysics Data System (ADS)

    Banerjee, N.

    2010-12-01

    Almost two decades of study highlight the importance of terrestrial subaqueous volcanic rocks as microbial habitats, particularly in glass produced by the quenching of basaltic lava upon contact with water. On Earth, microbes rapidly begin colonizing glassy surfaces along fractures and cracks exposed to water. Microbial colonization of basaltic glass leads to enhanced alteration through production of characteristic granular and/or tubular bioalteration textures. Infilling of formerly hollow alteration textures by minerals enable their preservation through geologic time. Basaltic rocks are a major component of the Martian crust and are widespread on other solar system bodies. A variety of lines of evidence strongly suggest the long-term existence of abundant liquid water on ancient Mars. Recent orbiter, lander and rover missions have found evidence for the presence of transient liquid water on Mars, perhaps persisting to the present day. Many other solar system bodies, notably Europa, Enceladus and other icy satellites, may contain (or have once hosted) subaqueous basaltic glasses. The record of terrestrial glass bioalteration has been interpreted to extend back ~3.5 billion years and is widespread in modern oceanic crust and its ancient metamorphic equivalents. The terrestrial record of glass bioalteration strongly suggests that glassy or formerly glassy basaltic rocks on extraterrestrial bodies that have interacted with liquid water are high-value targets for astrobiological exploration.

  18. Petrogenesis of coeval silica-saturated and silica-undersaturated alkaline rocks: Mineralogical and geochemical evidence from the Saima alkaline complex, NE China

    NASA Astrophysics Data System (ADS)

    Zhu, Yu-Sheng; Yang, Jin-Hui; Sun, Jin-Feng; Zhang, Ji-Heng; Wu, Fu-Yuan

    2016-03-01

    A combined study of zircon U-Pb ages, mineral chemistry, whole-rock elements and Sr-Nd-Hf isotopes was carried out for the Saima alkaline complex in the northeastern China, in order to investigate the source and petrogenesis of coeval silica-saturated and silica-undersaturated alkaline rocks. The Saima alkaline complex consists of nepheline syenites, quartz-bearing syenites and alkaline volcanic rocks (i.e., phonolite and trachyte), with minor mafic dikes and carbonatitic veins. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and secondary ion mass spectrometry (SIMS) zircon U-Pb dating gives consistent ages of 230-224 Ma for these rocks, suggesting that they are coeval. All alkaline rocks in the Saima complex are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs) with significant negative Nb, Ta and Ti anomalies. Geochemical data and Sr-Nd-Hf isotopic compositions indicate that the various alkaline rocks were all derived from partial melting of an ancient, re-enriched lithospheric mantle in the garnet stability field, but experienced variable siliceous- or carbonate-rich crustal contamination. Based on petrographic evidence, mineral compositions, and whole-rock geochemical data, two distinct magmatic evolutionary trends are proposed to explain the coeval emplacement of the various rock types within the Saima alkaline complex. The silica-undersaturated rocks (nepheline syenites and phonolites) result from alkali feldspar + apatite + titanite crystal fractionation of an alkaline mafic parental melt combined with assimilation of marine carbonate host rocks. In contrast, the generation of silica-saturated rocks (quartz-bearing syenites and trachytes) may be attributed to subsequent and continued clinopyroxene + apatite + biotite crystal fractionation coupled with assimilation of siliceous sediments.

  19. K-alkaline rocks and lamproites of Tomtor massif

    NASA Astrophysics Data System (ADS)

    Vladykin, Nikolai

    2015-04-01

    Tomtor massif of the largest volcano-plutonic deep alkaline-carbonatite massifs world central type. Area of massif occupy 240 km2 and carbonatites stock is 40 km2. The super large deposit of Nb, TR, Y, Sc, Sr ,REE (Frolov et al. 2001)is found within the massif. The numerical publication are devoted to the ore mineralization there. But the geological struc-ture of the massif and the chemistry of its constituting rocks are not well understood. We obtained new ages based on U-Pb zircon and mica Ar-Ar method (Kotov, Vladykin et al. 2014 Vladykin et al. 2015). The massif was created in 2 stages: 700 and 400 Ma. We (Vla-dykin et al 1998) found rocks of lamproite series and proposed a new scheme of magmatism and the ore.genesis (Vladykin 2007, 2009). Biotite - pyroxenite, peridotite originated in first stage and then intruded iolites, nepheline and alkali syenite. Syenites occupy 70% of -massif and contain 12-13% K2O and 2-4% Na2O showing the K-alkaline-ultramafic nature of Tomtor volcano-plutonic massif (Vladykin 2009). The first stage was accomplished by nelsonitov calcite, dolomite and ankerite carbonatites. Second stage (400Ma) volcanics picrite - lamproite veins and eruptive breccias meli-lite, melanephelinites, tinguaites appered. These rocks are cut by carbonatites of second stage. It was finished by intensive explosive eruption of a silicate (lamproite) tuffs lavobrec-cia kimberlite formed Ebelyakhdiamondiferous placer, melilite rocks in diatremes (feeders), as well as carbonate-phosphate (kamaforite) explosive tuffs with siderite ores. This carbona-tite complex is preserved within the subsidence caldera. Tuff eruption in conjunction with gas and hydrothermal activity determined its rare metal mineralization. These rocks contain to: Nb- 21%, TR-15%, Y-1.5%, Sc-1%, Zr- 0,5% Zn-, Sr-6%, Ti-8%, Ba-4%, V - 8000 ppm, Be- 300 ppm, Ga- 80 ppm, Cr- 1200ppm, Ni- 230 ppm, Mo- 145 ppm, Pb- 4300 ppm, Th- 1500 ppm, U-193 ppm. Picrite - olivine (rare leucite) lamproite and

  20. Transition from alkaline to calc-alkaline volcanism during evolution of the Paleoproterozoic Francevillian basin of eastern Gabon (Western Central Africa)

    NASA Astrophysics Data System (ADS)

    Thiéblemont, Denis; Bouton, Pascal; Préat, Alain; Goujou, Jean-Christian; Tegyey, Monique; Weber, Francis; Ebang Obiang, Michel; Joron, Jean Louis; Treuil, Michel

    2014-11-01

    We report new geochemical data for the volcanic and subvolcanic rocks associated with the evolution of the Francevillian basin of eastern Gabon during Paleoproterozoic times (c. 2.1-2 Ga). Filling of this basin has proceeded through four main sedimentary or volcano-sedimentary episodes, namely FA, FB, FC and FD. Volcanism started during the FB episode being present only in the northern part of the basin (Okondja sub-basin). This volcanism is ultramafic to trachytic in composition and displays a rather constant alkaline geochemical signature. This signature is typical of a within-plate environment, consistent with the rift-setting generally postulated for the Francevillian basin during the FB period. Following FB, the FC unit is 10-20 m-thick silicic horizon (jasper) attesting for a massive input of silica in the basin. Following FC, the FD unit is a c. 200-400 m-thick volcano-sedimentary sequence including felsic tuffs and epiclastic rocks. The geochemical signatures of these rocks are totally distinct from those of the FB alkaline lavas. High Th/Ta and La/Ta ratios attest for a calc-alkaline signature and slight fractionation between heavy rare-earth suggests melting at a rather low pressure. Such characteristics are comparable to those of felsic lavas associated with the Taupo zone of New Zealand, a modern ensialic back-arc basin. Following FD, the FE detrital unit is defined only in the Okondja region, probably associated with a late-stage collapse of the northern part of the basin. It is suggested that the alkaline to calc-alkaline volcanic transition reflects the evolution of the Francevillian basin from a diverging to a converging setting, in response to the onset of converging movements in the Eburnean Belt of Central Africa.

  1. Strontium isotopic evidence for an enriched source for post-subduction volcanic rocks, Dominican Republic

    SciTech Connect

    Wertz, W.K.; Perfit, M.R.; Shuster, R.D.

    1985-01-01

    Later Cenozoic volcanic rocks from the eastern Las Cuevas region (ELCR), Dominican Republic are dominantly shoshonitic and are associated with a series of east-west trending faults. The ELCR rocks are highly enriched in Sr, Ba, and light REE, but contain relatively low amounts of Rb and HFS ions. Several basalts appear to be unfractionated and have Mg-numbers of >75. These transitional to alkalic volcanic rocks are atypical of Caribbean igneous rocks and are more similar to alkaline centers associated with late-stage, island arc volcanism in other regions. Elevated /sup 87/Sr//sup 86/Sr ratios (0.7041-0.7048) are high in comparison to most other igneous rocks from the Caribbean region and indicate that they were derived from a source relatively enriched in LIL and REE in comparison to the sources which gave rise to the majority of Caribbean igneous rocks. /sup 87/Sr//sup 86/Sr values increase linearly with increasing Sr contents, suggesting mixing of sources with relatively low Sr contents and depleted /sup 87/Sr//sup 86/Sr with material that is highly enriched in Sr and with /sup 87/Sr//sup 86/Sr values around 0.706. This enriched component may be a fluid derived from melting/dehydrating subducted oceanic crust and sediment which metasomatically veined the sub-arc mantle. Small degrees of partial melting (<7%) of this source may be responsible for the unusual and enriched chemical composition of the ELCR volcanic rocks.

  2. Strain-dependent permeability of volcanic rocks.

    NASA Astrophysics Data System (ADS)

    Farquharson, Jamie; Heap, Michael; Baud, Patrick

    2016-04-01

    We explore permeability evolution during deformation of volcanic materials using a suite of rocks with varying compositions and physical properties (such as porosity ϕ). 40 mm × 20 mm cylindrical samples were made from a range of extrusive rocks, including andesites from Colima, Mexico (ϕ˜0.08; 0.18; 0.21), Kumamoto, Japan (ϕ˜0.13), and Ruapehu, New Zealand (ϕ˜0.15), and basalt from Mt Etna, Italy (ϕ˜0.04). Gas permeability of each sample was measured before and after triaxial deformation using a steady-state benchtop permeameter. To study the strain-dependence of permeability in volcanic rocks, we deformed samples to 2, 3, 4, 6, and 12 % axial strain at a constant strain rate of 10‑5 s‑1. Further, the influence of failure mode - dilatant or compactant - on permeability was assessed by repeating experiments at different confining pressures. During triaxial deformation, porosity change of the samples was monitored by a servo-controlled pore fluid pump. Below an initial porosity of ˜0.18, and at low confining pressures (≤ 20 MPa), we observe a dilatant failure mode (shear fracture formation). With increasing axial strain, stress is accommodated by fault sliding and the generation of ash-sized gouge between the fracture planes. In higher-porosity samples, or at relatively higher confining pressures (≥ 60 MPa), we observe compactant deformation characterised by a monotonous decrease in porosity with increasing axial strain. The relative permeability k' is given by the change in permeability divided by the initial reference state. When behaviour is dilatant, k' tends to be positive: permeability increases with progressive deformation. However, results suggest that after a threshold amount of strain, k' can decrease. k' always is negative (permeability decreases during deformation) when compaction is the dominant behaviour. Our results show that - in the absence of a sealing or healing process - the efficiency of a fault to transmit fluids is

  3. Contemporaneous trachyandesitic and calc-alkaline volcanism of the Huerto Andesite, San Juan Volcanic Field, Colorado, USA

    USGS Publications Warehouse

    Parat, F.; Dungan, M.A.; Lipman, P.W.

    2005-01-01

    Locally, voluminous andesitic volcanism both preceded and followed large eruptions of silicic ash-flow tuff from many calderas in the San Juan volcanic field. The most voluminous post-collapse lava suite of the central San Juan caldera cluster is the 28 Ma Huerto Andesite, a diverse assemblage erupted from at least 5-6 volcanic centres that were active around the southern margins of the La Garita caldera shortly after eruption of the Fish Canyon Tuff. These andesitic centres are inferred, in part, to represent eruptions of magma that ponded and differentiated within the crust below the La Garita caldera, thereby providing the thermal energy necessary for rejuvenation and remobilization of the Fish Canyon magma body. The multiple Huerto eruptive centres produced two magmatic series that differ in phenocryst mineralogy (hydrous vs anhydrous assemblages), whole-rock major and trace element chemistry and isotopic compositions. Hornblende-bearing lavas from three volcanic centres located close to the southeastern margin of the La Garita caldera (Eagle Mountain - Fourmile Creek, West Fork of the San Juan River, Table Mountain) define a high-K calc-alkaline series (57-65 wt % SiO2) that is oxidized, hydrous and sulphur rich. Trachyandesitic lavas from widely separated centres at Baldy Mountain-Red Lake (western margin), Sugarloaf Mountain (southern margin) and Ribbon Mesa (20 km east of the La Garita caldera) are mutually indistinguishable (55-61 wt % SiO2); they are characterized by higher and more variable concentrations of alkalis and many incompatible trace elements (e.g. Zr, Nb, heavy rare earth elements), and they contain anhydrous phenocryst assemblages (including olivine). These mildly alkaline magmas were less water rich and oxidized than the hornblende-bearing calc-alkaline suite. The same distinctions characterize the voluminous precaldera andesitic lavas of the Conejos Formation, indicating that these contrasting suites are long-term manifestations of San Juan

  4. A Videotape Short Course on Volcanic Rock Textures.

    ERIC Educational Resources Information Center

    Chesner, Craig A.; Rose, William I.

    1987-01-01

    Reviews the objectives, themes, and content of a series of five color videotapes on volcanic rock textures. Explains how the tapes, which integrate petrographic observations of textures with computer graphics, can be used in undergraduate and graduate level courses. (ML)

  5. Petrology and Geochemistry of the Eocene Volcanic Rocks in the Kahrizak Mountains, Central Iran

    NASA Astrophysics Data System (ADS)

    Yazdani, S.; Castillo, P.; Tutti, F.

    2013-12-01

    The Eocene volcanic rocks in the Kahrizak (KH) Mountains in the northern part of Central Iran were mainly formed by magmatism that accompanied block-faulting tectonism in the region. In the KH area, the volcanic rocks are nonconformably overlain by Oligocene-Pliocene sedimentary deposits, suggesting that the Eocene magmatic activity in the region was followed by a sequence of uplift and shallow marine regression. The volcanic rocks consist of pyroclastics (tuff and ignimbrites) and lava flows (basalt, basaltic trachyandesite, trachyandesite, and rhyolite); superposition indicates an earlier explosive volcanic phase that caused the widespread distribution of rhyolitic ignimbrites and tuffs, and this was followed by a quieter phase of lava eruptions. Petrographic evidence such as mineral zoning, sieve texture and rounded crystals of plagioclase and pyroxene phenocrysts indicate non-equilibrium conditions between melt and crystals during magma cooling. These textures suggest magma mixing, although these may also be due to rapid decompression, where heat loss is minor relative to the ascent rate. The geochemistry of KH samples indicates their subalkaline to alkaline affinity. In terms of trace element contents, most samples exhibit the distinct geochemical trait of arc volcanism, i.e., Nb and Ta depletions relative to LILE (e.g., Ba, Rb) enrichment and positive Sr anomaly; however, Zr and Ti depletions are not prominent. The samples have a light-REE enriched but flat heavy-REE pattern and negative Eu anomaly in the rhyolites and trachyandesites. They have a ~narrow to ~moderate range of Pb isotopic ratios (206Pb/204Pb ~18.6-18.9, 207Pb/204Pb ~15.5-15.6, and 208Pb/204Pb ~38.5-38.8), with basaltic rocks somewhat higher than rhyolitic rocks. Available geochemical and isotopic data suggest a complex origin and evolution of the KH magmas. The magmas originated from an intrinsically ~heterogeneous source and, in addition to fractional crystallization, some of the

  6. 40Ar/ 39Ar ages for the alkaline volcanism and the basement of Gorringe Bank, North Atlantic ocean

    NASA Astrophysics Data System (ADS)

    Féraud, Gilbert; Gastaud, Janine; Auzende, Jean-Marie; Olivet, Jean-Louis; Cornen, Guy

    1982-01-01

    Gorringe Bank is situated on the Europe-Africa plate boundary at the eastern end of the Azores-Gibraltar fracture zone. It has two summits, Gettysburg Bank to the Southwest and Ormonde Bank to the northeast. We applied the 40Ar/ 39Ar stepwise heating method to date six samples of the alkaline volcanic rocks, two gabbros from the Ormonde Bank and a dolerite from the Gettysburg Bank. The results that the alkaline volcanism lasted probably for less than 6 Ma(66-60 Ma). Although the nature of this volcanism precludes any subduction feature during its setting, the alkaline volcanism of Ormonde is probably linked to Upper Cretaceous/Eocene compressive tectonic events. The basement rocks of Gorringe Bank reveal distrubed 40Ar/ 39Ar age spectra. One plagioclase and one biotite from a gabbro give evidence for a thermic event whose age is tentatively estimated at about 75 Ma, and related to a variation in the direction of the relative movement between Europe and Africa. The more probable age given by a plagioclase of another gabbro and by a dolerite (110 Ma) corresponds to tilting northeastward of the Gorringe massif.

  7. Volcanic rocks cored on hess rise, Western Pacific Ocean

    USGS Publications Warehouse

    Vallier, T.L.; Windom, K.E.; Seifert, K.E.; Thiede, Jorn

    1980-01-01

    Large aseismic rises and plateaus in the western Pacific include the Ontong-Java Plateau, Magellan Rise, Shatsky Rise, Mid-Pacific Mountains, and Hess Rise. These are relatively old features that rise above surrounding sea floors as bathymetric highs. Thick sequences of carbonate sediments overlie, what are believed to be, Upper Jurassic and Lower Cretaceous volcanic pedestals. We discuss here petrological and tectonic implications of data from volcanic rocks cored on Hess Rise. The data suggest that Hess Rise originated at a spreading centre in the late early Cretaceous (Aptian-Albian stages). Subsequent off-ridge volcanism in the late Albian-early Cenomanian stages built a large archipelago of oceanic islands and seamounts composed, at least in part, of alkalic rocks. The volcanic platform subsided during its northward passage through the mid-Cretaceousequatorial zone. Faulting and uplift, and possibly volcanism, occurred in the latest Cretaceous (Campanian-Maastrichtian stages). Since then, Hess Rise continued its northward movement and subsidence. Volcanic rocks from holes drilled on Hess Rise during IPOD Leg 62 (Fig. 1) are briefly described here and we relate the petrological data to the origin and evolution of that rise. These are the first volcanic rocks reported from Hess Rise. ?? 1980 Nature Publishing Group.

  8. Martian alkaline basites chemically resemble basic rocks of the Lovozero alkaline massif, Kola peninsula

    NASA Astrophysics Data System (ADS)

    Kochemasov, G.

    " (syenite, granite) for Mars [5]. Actually the martian missions successively discovered andesite, dacite, low-Fe highlands. Now "Spirit" has found on a small outlier of highlands -Columbia Hills -a batch of thinly layered gently dipping light rocks that surely are not impact melts as at very short distance there is a sharp transition from light Fe-poor to ultrabasic rocks (on opposite slopes of this small hill) [6]. This layered sequence of more or less altered and weathered rocks resembles differentiated sequences of Lovozero and other alkaline and UB-alkaline massifs of Kola Peninsula (though fresh and much richer in alkalis). Here we compare compositions of alkaline basic rocks of Columbia Hills (dyke or sill [4]) with that of basic volcanics and a later dyke at Lovozero. 5 analyses in wt.%: 1-Backstay (tra1 chybasalt) & 2-Irvine (basalt) of CH, 3-augiteporphyrite, 4-essexite-porphyrite, 5- alkali- lamprophyre dyke of Lovozero. SiO2 -49.9, 47.7, 45.78, 48.09, 41.57; TiO2 - 0.93, 1.07, 7.80, 2.35, 2.92; Al2 O3 -13.2; 10.8, 8.08; 13.74; 11.77; Fe2 O3 -3.40, 7.79 (4.99), 5.90, 6.00, 4.53; FeO -10.6, 12.5 (15.0), 8.65, 7.60, 8.28; MnO -0.25, 0.37, 0.12, 0.17, 0.28; MgO -8.36, 10.8, 7.61, 7.19, 10.59; CaO -6.09, 6.12, 10.73, 8.77, 11.24; Na2 O -4.02, 2.72, 2.80, 2.84, 3.63; K2 O -1.02, 0.69, 1.97, 2.09, 1.38. Compositional similarities between basites occurring in alkaline conditions on both planets can be found. References: [1] Kochemasov G.G. (1999) Theorems of wave planetary tectonics // Geophys. Res. Abstr., v. 1, # 3, 700; [2] Gellert R. et al. (2006) JGR Planets, v. 111, #E2, EO2505; [3] Squyres S.W. et al. (2006) JGR Planets, v.111, #E2, EO2511; [4] McSween H.Y. et al. (2006) JGR Planets, submitted ; [5] Kochemasov G. G. (1995) Golombek M.P., Edgett K.S., Rice J.W. Jr. (Eds). Mars Pathfinder Landing Site Workshop II: Characteristics of the Ares Vallis Region and Field trips to the Channeled Scabland, Washington. LPI Tech. Rpt. 95-01. Pt.1.LPI, Houston, 1995, 63 pp.; [6

  9. The calc-alkaline and adakitic volcanism of the Sabzevar structural zone (NE Iran): Implications for the Eocene magmatic flare-up in Central Iran

    NASA Astrophysics Data System (ADS)

    Moghadam, Hadi Shafaii; Rossetti, Federico; Lucci, Federico; Chiaradia, Massimo; Gerdes, Axel; Martinez, Margarita Lopez; Ghorbani, Ghasem; Nasrabady, Mohsen

    2016-04-01

    A major magmatic flare-up is documented along the Bitlis-Zagros suture zone in Eocene-Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U-Pb and mica Ar-Ar ages of ca. 45 Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around ~ 0.2-0.3 Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole-plagioclase-titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic "flare-up" in Iran.

  10. Petrogenesis of extension-related alkaline volcanism in Karaburhan (Sivrihisar-Eskisehir), NW Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Sarıfakıoğlu, Ender; Özen, Hayrettin; Hall, Chris

    2009-08-01

    Alkaline lavas were erupted as phonolites and trachytes around Karaburhan (Sivrihisar-Eskisehir, NW Anatolia) within the Izmir-Ankara-Erzincan suture zone. These volcanic rocks were emplaced as domes, close and parallel to the ophiolite thrust line. According to 40Ar/ 39Ar geochronological analyses of sanidine crystals from the phonolites, the age of the alkaline volcanics is 25 Ma (Late Oligocene-Early Miocene). The flow-textured phonolites are porphyritic and consist mainly of sanidine, clinopyroxene, and feldspathoid crystals. The clinopyroxenes show compositional zoning, with aegirine (Na 0.82-0.96Fe +30.68-0.83) rims and aegirine-augite cores (containing calcium, magnesium, and Fe +2). Some aegirine-augites are replaced with sodium-, calcium-, and magnesium-rich amphibole (hastingsite). Feldspathoid (hauyne) crystals enriched with elemental Na and Ca have been almost completely altered to zeolite and carbonate minerals. The fine-grained trachytes with a trachytic texture consist of feldspar (oligoclase and sanidine) phenocrystals and clinopyroxene microphenocrystals within a groundmass made up largely of alkali feldspar microlites. Although there are some differences in their element patterns, the phonolites and trachytes exhibit enrichment in LILEs (Sr, K, Rb, Ba, Th) and LREEs (La, Ce, Pr, Nd) and negative anomalies in Nb and Ta. These geochemical characteristics indicate a lithospheric mantle enriched by fluids extracted from the subduction component. In addition, the high 87Sr/ 86Sr (0.706358-0.708052) and low 143Nd/ 144Nd (0.512546-0.512646) isotope concentrations of the alkaline lavas reflect a mantle source that has undergone metasomatism by subduction-derived fluids. Petrogenetic modeling indicates that the alkaline lavas generated from the subduction-modified lithospheric mantle have undergone assimilation, fractional crystallization, and crustal contamination, acquiring high Pb, Ba, Rb, and Sr contents and Pb isotopic compositions during their ascent

  11. Lithium Isotope Systematics of Rift-related Alkaline Igneous Rocks

    NASA Astrophysics Data System (ADS)

    Halama, R.; McDonough, W. F.; Rudnick, R. L.; Trumbull, R.; Klaudius, J.; Keller, J.; Taubald, H.

    2006-05-01

    Intracontinental alkaline igneous rocks from the Proterozoic Gardar Province (Greenland), the Cretaceous Damaraland Province (Namibia), the Tertiary Kaiserstuhl complex (Germany) and from the Holocene volcano Oldoinyo Lengai (Tanzania) were analyzed to characterize Li isotopic compositions of their mantle sources and to determine the processes affecting δ7Li in alkaline igneous rocks. The inferred mantle Li isotope signatures of the primitive alkaline rocks (δ7Li = +1 to +7) are similar to those of present- day MORB, OIB and carbonatites, and appear to be relatively constant in time and space. Gabbros from the Gardar Province define a relatively small field of Li isotope compositions (δ7Li = +4 to +7). Mineral separates (clinopyroxene, plagioclase) mostly overlap with the whole-rock values, which we interpret to reflect the δ7Li of the mantle sources of the gabbros. Mantle-like δ7Li values are also observed for primitive alkaline rocks from the other regions. Li isotope compositions in more differentiated rocks (syenites, phonolites and rhyolites) are highly variable (+11 to -22 per mil) and reflect a diversity of evolutionary processes that may vary from complex to complex. δ7Li values vary independently of Sr and Nd isotope values and indices of differentiation (e.g. MgO content) or weathering (e.g. LOI). Consistently light δ7Li values (+2 to -22) occur in Gardar syenites associated with a carbonatite. These may be explained by weathering and sub-solidus alteration, as indicated by petrographic observations. Alternatively, fluid-assisted diffusion processes, related to a fenitizing fluid from the carbonatite, may have led to extreme Li isotope fractionation. Whole-rock oxygen isotope analyses will be carried out to evaluate interaction with meteoric water, which would be reflected in a decrease in δ18O compared to magmatic values. The heaviest Li isotopic composition (+11 per mil) was obtained for a rhyolite, probably related to the presence of quartz

  12. Geochemistry of volcanic rocks from the Wawa greenstone belt

    NASA Technical Reports Server (NTRS)

    Schulz, K. J.; Sylvester, P. J.; Attoh, K.

    1983-01-01

    The Wawa greenstone belt is located in the District of Algoma and extends east-northeast from Lake Superior to the western part of the Sudbury District in Ontario, Canada. Recent mapping by Attoh has shown that an unconformity at the base of the Dore' Formation and equivalent sedimentary rocks marks a significant stratigraphic break which can be traced throughout the volcanic belt. This break has been used to subdivide the volcanic-sedimentary into pre- and post-Dore' sequences. The pre-Dore' sequence includes at least two cycles of mafic-to-felsic volcanism, each capped by an iron-formation unit. The post-Dore' sequence includes an older mafic-to-felsic unit, which directly overlies sedimentary rocks correlated with the Dore' Formation, and a younger felsic breccia unit interpreted to have formed as debris flows from a felsic volcanic center. In the present study, samples of both the pre-and post-Dore' volcanic sequences were analyzed for major and trace elements, incuding rare earths (REE). This preliminary study is part of an ongoing program to assess the petrogenesis of the volcanic rocks of the Wawa greenstone belt.

  13. Discrimination of alkalinity in granitoid Rocks: A potential TIMS application

    NASA Technical Reports Server (NTRS)

    Ruff, Steven W.

    1995-01-01

    In mineral exploration, the ability to distinguish and map petrochemical variations of magmatic rocks can be a useful reconnaissance tool. Alkalinity is one such petrochemical parameter and is used in the characterization of granitoid rocks. In quartz normative plutonic rocks, alkalinity is related to the composition and abundance of feldspars. Together with quartz abundance, knowledge of feldspar modes allows the classification of these igneous rocks according to the Streckeisen diagram. Alternative classification schemes rely on whole rock geochemistry instead of mineral identifications. The relative ease of obtaining whole rock analyses means that geochemical classifications tend to be favored in exploration geology. But the technique of thermal infrared spectroscopy of rocks yields information on mineralogy and is one that can be applied remotely. The goal of the current work then is to establish whether data from TIMS can be used to distinguish the mineralogical variations that relate to alkalinity. An ideal opportunity to test this thesis arises from the work presented in a paper by Dewitt (1989). This paper contains the results of mapping and analysis of Proterozoic plutonic rocks in north-central Arizona. The map resulting from this work delineates plutons according to alkalinity in an effort to establish a trend or polarity in the regional magmatism. Also contained within this paper are brief descriptions of the mineralogy of half of the region's plutons. This combination of mineralogical and geochemical information was the rationale behind choosing this area as a site for TIMS over flights. A portion of the region centered on the northern Bradshaw Mountains was selected because it contains plutons of all three alkalinity classifications (alkali-calcic, calc-alkalic, and calic) present on DeWitt's map within a relatively small area. The site was flown in August of 1994 and the data received a few days before the writing of this manuscript. Most of this

  14. Evolution of volcanic rocks and associated ore deposits in the Marysvale volcanic field, Utah

    USGS Publications Warehouse

    Cunningham, Charles G.; Steven, Thomas A.; Rowley, Peter D.; Naeser, Charles W.; Mehnert, Harald H.; Hedge, Carl E.; Ludwig, Kenneth R.

    1994-01-01

    A geological account on the igneous activity and associated mineral deposition in the volcanic field of Marysvale in Utah is presented. Three episodes (34-22 Ma, 22-14 Ma and 9-5 Ma) involved in the volcanic rock eruption and associated mineralization are described. The first episode is believed to have occurred during the time of tectonic convergence when two contrasting suites of rocks, Mount Dutton Formation and Bullion Canyon Volcanics, erupted concurrently. Mineralization during this period was sparse. In the second episode, change from intermediate to bimodal volcanism occurred. During the third episode, basaltic compositions did not change. Although major element constituent had rhyolites similar to that of the second episode, rhyolites had a marked radiogenic isotope characteristic difference.

  15. Mantle xenocrysts of Chompolo field of the alkaline volcanics, Aldan shield, South Yakutia.

    NASA Astrophysics Data System (ADS)

    Nikolenko, Evgeny; Tychkov, Nikolay; Afanasiev, Valentin

    2015-04-01

    New mineralogical and chemical constraints for 10 dikes, veins (360-800m) and pipes (60-110 m) of Chompolo field discovered in 1957-1958 are discussed. Feld is located within Central Aldan Archean and Paleoproterozoic granulite-orthogneiss superterrane of Aldan-Stanovoy Shield, with peak of metamorphism - 2.1-1.9 Ga (Smelov, Timofeev, 2007). Originally (Shilina and Zeitlin 1959) and later (Kostrovitsky and Garanin 1992, Ashchepkov, Vladykin et al. 2001) these rocks were classified as kimberlites by mineralogy including pyrope, Cr spinel, and Cr diopside. Panina and Vladykin (1994), Davies et al, (2006) identified them as lamprophyres and lamproites. The age of Chompolo rocks is pre-Jurassic (Vladimirov et. al., 1989) dated by 40Ar/39Ar as 164.7±1 Ma (233.7±2.2 next plato)(unpublished Ashchepkov). The Rb-Sr isochron for lamprophyre "intrusions 104" indicate later age of 131±4 Ma (Zaitsev, Smelov, 2010). Magmatic bodies (Aldanskaya, Sputnik, Gornaya, Ogonek, Perevalnaya, Kilier-E) were studied during 2012-2013 fieldworks. Most of igneous rocks occur as inequigranular volcanic breccias with micro- or crypto-crystalline groundmass of K feldspar (up to 16.3 wt.% K2O, up to 3.2 wt.% FeO), chlorite, opaque minerals, melanocratic xenocrysts and phenocrysts (garnet, pyroxene, amphibole, Cr spinel, apatite, zircon, mica), and abundant xenogenic fragments of wallrock and crystalline basement. Garnet chemistry records the presence of mantle and crustal material. Mantle garnets lack the common megacryst, wehrlite, and high-temperature lherzolite varieties. Mantle mineralization prevails in the Aldan dike and the Sputnik, Gornaya, and Ogonek pipes, while crustal and elcogitic material is in the Perevalnaya and Kilier-E pipes. The Cr spinel consists of (in wt%) 3.5 to 50.9 Al2O3, 18.6-63.5 wt% Cr2O3, 6.1 to 19.1 MgO, and 0 to 1.61 TiO2. Al and Cr in spinels are in inverse proportion. The Chompolo alkaline volcanic rocks are most similar to the Central Aldan lamproites in trace

  16. Applications of Terrestrial Remote Sensing to Volcanic Rock Masses

    NASA Astrophysics Data System (ADS)

    Dewit, M.; Williams-Jones, G.; Stead, D.; Kremsater, R.; So, M.; Francioni, M.

    2015-12-01

    Remote sensing methods are widely used in geological applications today. The physical properties of rock such as composition, texture and structure have previously been difficult to accurately quantify through remote sensing, however, new research in the fields of terrestrial LiDAR and infrared thermography has proven useful in the differentiation of lithology in sedimentary outcrops. This study focuses on the application of these methods, in conjunction with digital photogrammetry, to a number of volcanic rock masses in the Garibaldi Volcanic Belt (GVB) and Chilcotin Group (CG) of British Columbia. The GVB is a chain of volcanoes and related features extending through southwestern British Columbia and is the northern extension of the Cascade Volcanic Arc. The CG is an assemblage of Neogene-aged lavas covering nearly 36,500 km2 in central British Columbia. We integrate infrared chronothermography, which enables the characterization of temporal change in the thermal signature, laser waveform attributes such as amplitude and intensity, and digital photogrammetry, in order to distinguish between a range of rock types, lithologies and structures. This data is compared to laboratory experiments on field samples and ground-truth information collected by classical geological and geotechnical methods. Our research clearly shows that it is possible to remotely map, in 3D, otherwise inaccessible volcanic rock masses.

  17. Petrography and chemical evidence for multi-stage emplacement of western Buem volcanic rocks in the Dahomeyide orogenic belt, southeastern Ghana, West Africa

    NASA Astrophysics Data System (ADS)

    Nude, Prosper M.; Kwayisi, Daniel; Taki, Naa A.; Kutu, Jacob M.; Anani, Chris Y.; Banoeng-Yakubo, Bruce; Asiedu, Daniel K.

    2015-12-01

    The volcanic rocks of the Buem Structural Unit in the Dahomeyide orogenic belt of southeastern Ghana, constitute a unique assemblage among the monocyclic sedimentary formations of this structural unit. Representative volcanic rock samples were collected from the Asukawkaw, Bowiri-Odumase and Nkonya areas which form a roughly north-south trend. The volcanic rocks comprise spherulitic, amygdaloidal, vesicular, phyric and aphyric varieties. Whole rock geochemistry shows that these volcanic rocks exhibit both alkaline and subalkaline characteristics. The alkaline varieties are relatively enriched in REE and incompatible trace element concentrations, similar to OIB; the subalkaline varieties show E-MORB and N-MORB REE and incompatible element characteristics. The rocks have low La/Nb (<1), low K/Nb (<450) and high Nb/U (averagely 47.3) values, suggesting no significant effect of crustal contamination. The key characteristics of these volcanic rocks are the distinct petrography and geochemistry, shown from the three separate localities, which may suggest source fractionation at different depths or modes of emplacement. The association of volcanic rocks of OIB, E-MORB and N-MORB affinities, with no significant crustal contamination, may suggest mantle derived magma that may have been related to rifting event and eventual emplacement at the eastern passive margin of the West African Craton.

  18. Can Rock Deformation Experiments Help us to Forecast Volcanic Eruptions?

    NASA Astrophysics Data System (ADS)

    Smith, R.; Kilburn, C. R.; Sammonds, P. R.

    2009-05-01

    Volcanic eruption forecasting models show that the strength and mechanical properties of volcanic rocks are a primary control on the behaviour of volcanic systems, especially during the approach to eruptions. The progressive failure of these rocks, recorded as sequences of small volcano tectonic earthquakes, can lead to the formation of new magma pathways, allowing eruptions to begin at volcanoes that have not erupted in hundreds of years. Rates and patterns of these small earthquakes, which are typically located within a few km of the volcano summit, are monitored at many volcanoes and used to forecast eruptions. Models of crack growth and interaction have been used to constrain expected patterns in accelerating earthquake rates before the first eruption after a long repose interval. These deterministic models rely on laboratory mechanical data from volcanic rocks tested under the temperature and pressure conditions expected within and beneath a volcanic edifice. Here, we present data from high temperature uniaxial and triaxial deformation of andesite and dacite at temperatures of up to 1000°C, and under confining pressures of up to 50 MPa. These are typical rock types for volcanoes likely to erupt violently after hundreds of years of repose, where these forecasting models have previously been applied. The conditions tested cover the full range of temperatures and pressures expected within the upper 2-3 km of volcanic systems. The eruption forecasting model, with new constraints from this laboratory data, is applied to sequences of VT earthquakes before eruptions and to sequences of acoustic emissions before laboratory sample failure. Both types of data showed accelerating trends within the limits defined in the model, whilst sequences of earthquakes and acoustic emissions not resulting in eruption or sample failure exhibited accelerations outside the model limits. These results support the scaling of laboratory data to field scale and the use of laboratory data

  19. Deriving spatial patterns from a novel database of volcanic rock geochemistry in the Virunga Volcanic Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Barette, Florian; Smets, Benoît; Benbakkar, Mhammed; Kervyn, Matthieu

    2016-04-01

    The Virunga Volcanic Province (VVP) is situated within the western branch of the East-African Rift. The geochemistry and petrology of its' volcanic products has been studied extensively in a fragmented manner. They represent a unique collection of silica-undersaturated, ultra-alkaline and ultra-potassic compositions, displaying marked geochemical variations over the area occupied by the VVP. We present a novel spatially-explicit database of existing whole-rock geochemical analyses of the VVP volcanics, compiled from international publications, (post-)colonial scientific reports and PhD theses. In the database, a total of 703 geochemical analyses of whole-rock samples collected from the 1950s until recently have been characterised with a geographical location, eruption source location, analytical results and uncertainty estimates for each of these categories. Comparative box plots and Kruskal-Wallis H tests on subsets of analyses with contrasting ages or analytical methods suggest that the overall database accuracy is consistent. We demonstrate how statistical techniques such as Principal Component Analysis (PCA) and subsequent cluster analysis allow the identification of clusters of samples with similar major-element compositions. The spatial patterns represented by the contrasting clusters show that both the historically active volcanoes represent compositional clusters which can be identified based on their contrasted silica and alkali contents. Furthermore, two sample clusters are interpreted to represent the most primitive, deep magma source within the VVP, different from the shallow magma reservoirs that feed the eight dominant large volcanoes. The samples from these two clusters systematically originate from locations which 1. are distal compared to the eight large volcanoes and 2. mostly coincide with the surface expressions of rift faults or NE-SW-oriented inherited Precambrian structures which were reactivated during rifting. The lava from the Mugogo

  20. Loss of halogens from crystallized and glassy silicic volcanic rocks

    USGS Publications Warehouse

    Noble, D.C.; Smith, V.C.; Peck, L.C.

    1967-01-01

    One hundred and sixty-four F and Cl analyses of silicic welded tuffs and lavas and glass separates are presented. Comparison of the F and Cl contents of crystallized rocks with those of nonhydrated glass and hydrated glassy rocks from the same rock units shows that most of the halogens originally present were lost on crystallization. An average of about half of the F and four-fifths of the Cl originally present was lost. Analyses of hydrated natural glasses and of glassy rocks indicate that in some cases significant amounts of halogens may be removed from or added to hydrated glass through prolonged contact with ground water. The data show that the original halogen contents of the groundmass of a silicic volcanic rock can be reliably determined only from nonhydrated glass. ?? 1967.

  1. Relationships between ultrapotassic and carbonate-rich volcanic rocks in central Italy: petrogenetic and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Peccerillo, Angelo

    1998-09-01

    The Pleistocene intra-Apennine volcanic (IAV) centres occurring east of the potassium-rich Roman comagmatic province show variable petrological and geochemical composition. Some rocks have a strongly undersaturated ultrapotassic kamafugitic affinity with K 2O/Na 2O=8-20, whereas the rocks from the southern center of Mt. Vulture are still strongly undersaturated in silica but are enriched in both Na 2O and K 2O with K/Na around unity. Carbonate-rich pyroclastic rocks, believed to represent carbonatitic magmas, are found in the IAV centers. Kamafugites have high abundances of LILE and high LILE/HFSE ratios, and their incompatible element patterns resemble closely those of ultrapotassic rocks from the adjoining Roman province. The Vulture volcanics also display high contents of LILE, but their LILE/HFSE ratios are intermediate between intraplate alkaline rocks and kamafugites. The carbonate-rich rocks exhibit an exotic mineralogy and high enrichments in LILE, which speaks for a carbonatitic affinity. However, they have similar incompatible element patterns but consistently lower abundances of almost all the elements than the associated silicate volcanics. These data favour the hypothesis that the IAV carbonate rocks may represent mixtures of silicate magmas and geochemically depleted carbonate material. The sedimentary carbonates that crop out extensively along the Apennine chain may be the source of barren carbonate material. Overall, geochemical data of IAV centres and of the rocks from the Roman province display strong geochemical and isotopic evidence of being generated in an upper mantle that was modified by addition of upper crustal material brought down by subduction processes. A possible exception is represented by Mt. Vulture which, however, occurs east of the main axis of the Apennines, on the western margin of the foreland Adria plate. The occurrence of strongly undersaturated alkaline rocks requires magma generation at high pressures and XCO 2. This is in

  2. Petrographic and geochemical characterization of the Triassic and Jurassic magmatic and volcanic rocks of southeastern Ecuador

    NASA Astrophysics Data System (ADS)

    Villares, Fabián; Eguez, Arturo; Yanez, Ernesto

    2014-05-01

    porphyritic andesites and coarse volcanic breccias. Three geochemical analysis of the lavas show andesitic composition, have medium to high-K calc-alkaline and represent the products of a subduction zone. All intrusions in the area were mapped as Zamora Batholith. Nevetheless, the field observations confirm a large Jurassic batholith but also other significant minor intrusion that intrudes the cretaceous sedimentary formations of the area. Thus, magmatic rocks in the area are named as Zamora batholithic complex. Petrography of the Zamora Batholith ranges from tonalite to monzo-granite with the same qualitative mineralogy. Rocks are composed by different proportions of plagioclase, amphibole, K-feldspar, quartz, biotite, opaques and epidote, as accessory minerals has zircon, sphene and apatite. Zamora Granitoids ranged from dioritic to granitic compositions ( 60.09 - . 73.6 wt % SiO2). The Zamora Granitoids have medium to high-K calc-alkaline and represent the products of a subduction zone. Products are generated within a magmatic arc in normal conditions of maturity. The Zamora Granitoids are I - type intrusions.

  3. Magmatism at the Eurasian–North American modern plate boundary: Constraints from alkaline volcanism in the Chersky Belt (Yakutia)

    PubMed Central

    Tschegg, Cornelius; Bizimis, Michael; Schneider, David; Akinin, Vyacheslav V.; Ntaflos, Theodoros

    2011-01-01

    The Chersky seismic belt (NE-Russia) forms the modern plate boundary of the Eurasian−North American continental plate. The geodynamic evolution of this continent−continent setting is highly complex and remains a matter of debate, as the extent and influence of the Mid-Arctic Ocean spreading center on the North Asian continent since the Eocene remains unclear. The progression from a tensional stress regime to a modern day transpressional one in the Chersky seismic belt, makes the understanding even more complicated. The alkaline volcanism that has erupted along the Chersky range from Eocene through to the Recent can provide constraints on the geodynamic evolution of this continental boundary, however, the source and petrogenetic evolution of these volcanic rocks and their initiating mechanisms are poorly understood. We studied basanites of the central Chersky belt, which are thought to represent the first alkaline volcanic activity in the area, after initial opening of the Arctic Ocean basin. We present mineral and bulk rock geochemical data as well as Sr–Nd–Pb–Hf isotopes of the alkaline suite of rocks combined with new precise K–Ar and 40Ar/39Ar dating, and discuss an integrated tectono-magmatic model for the Chersky belt. Our findings show that the basanites were generated from a homogeneous asthenospheric mantle reservoir with an EM-1 isotopic flavor, under relatively ‘dry’ conditions at segregation depths around 110 km and temperatures of ~ 1500 °C. Trace element and isotope systematics combined with mantle potential temperature estimates offer no confirmation of magmatism related to subduction or plume activity. Mineral geochemical and petrographical observations together with bulk geochemical evidence indicate a rapid ascent of melts and high cooling rates after emplacement in the continental crust. Our preferred model is that volcanism was triggered by extension and thinning of the lithosphere combined with adiabatic upwelling of the

  4. Late Cenozoic alkaline volcanism in the northwestern Caribbean - Tectonic setting and Sr isotopic characteristics

    NASA Technical Reports Server (NTRS)

    Wadge, G.; Wooden, J. L.

    1982-01-01

    The northwestern corner of the Caribbean plate has at least sixteen centers of alkalic volcanism, most of which is Quaternary in age. Sr-87/Sr-86 ratios of the rocks in these centers are used to distinguish three geographical groups: a low-ratio group (0.7026-0.7031) at the Nicaraguan Rise, an intermediate-ratio group (0.7036-0.7038) in northeastern Costa Rica, and a high-ratio group (0.7047-0.7063) in Hispaniola. It is suggested that the increased radiogenic strontium in both Costa Rica and Hispaniola may have come from volatile-rich fluids escaping from adjacent subducting slabs of oceanic crust. The isotopic differences between the two areas is explained by the relative longevity and high rate of subduction in Costa Rica compared to that in Hispaniola. The Costa Rican alkaline rocks cover a segment of the Cocos plate which is being subducted at a smaller angle (about 35 deg) than at the rest of the Central American arc.

  5. Geochemical tectonomagnetic discrimination of metamorphosed Middle Jurassic volcanic rocks, northern Sierra Nevada, California

    SciTech Connect

    Templeton, J.H. . Dept. of Geosciences); Hanson, R.E. . Dept. of Geology); Harwood, D.S. )

    1993-04-01

    Jurassic island-arc rocks in the Northern Sierra terrane (NSt) are represented by the Lower to Middle Jurassic Sailor Canyon Formation, consisting mainly of distal andesitic turgidities, and the overlying, Middle Jurassic Tuttle Lake Formation (TLF); both units were metamorphosed to lower greenschist facies during Mesozoic orogenesis. The TLF is a 1.6-km-thick sequence of submarine tuff-breccia debris-flow deposits intercalated with minor isolated-pillow breccias and intruded by numerous cogenetic hypabyssal intrusions that underwent extensive interaction with wet sediments in near-vent setting. Here the authors report the first geochemical studies of these regionally significant arc rocks. Pillow breccias, hypabyssal intrusions, and clasts within debris-flow deposits are predominantly basalt to basaltic andesite in composition and contain abundant plagioclase and clinopyroxene phenocrysts. Although cpx is intensely altered to actinolite, microprobe analyses were carried out on relict cpx cores. Compositions are typical of cpx from orogenic lavas and fall in combined calc-alkaline and tholeiitic fields on cpx discrimination diagrams. Most major elements show significant scatter on Harker and AFM variation diagrams, reflecting the metamorphic overprint. Immobile trace element contents (Ti, Cr, Y, Yb, Zr, Hf, Ta, Th) clearly indicate volcanic arc and calc-alkaline affinities when plotted on a variety of discrimination diagrams. REE patterns show LREE-enrichment typical of calc-alkaline lavas, commonly with small negative Eu anomalies consistent with plagioclase fractionation. The TLF shows marked petrologic and stratigraphic differences from broadly coeval Jurassic arc rocks exposed in the fault-bounded Kettle Rock sequence in the northeastern part of the NSt. This may reflect relatively rapid along-strike variations within the Jurassic arc, or that the Kettle Rock sequence and the TLF arc rocks have been brought into proximity by later faulting.

  6. The strength of heterogeneous volcanic rocks: A 2D approximation

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Wadsworth, Fabian B.; Xu, Tao; Chen, Chong-feng; Tang, Chun'an

    2016-06-01

    Volcanic rocks typically contain heterogeneities in the form of crystals and pores. We investigate here the influence of such heterogeneity on the strength of volcanic rocks using an elastic damage mechanics model in which we numerically deform two-dimensional samples comprising low-strength elements representing crystals and zero-strength elements representing pores. These circular elements are stochastically generated so that there is no overlap in a medium representing the groundmass. Our modelling indicates that increasing the fraction of pores and/or crystals reduces the strength of volcanic rocks, and that increasing the pore fraction results in larger strength reductions than increasing the crystal fraction. The model also highlights an important weakening role for pore diameter, but finds that crystal diameter has a less significant influence for strength. To account for heterogeneity (pores and crystals), we propose an effective medium approach where we define an effective pore fraction ϕp‧ = Vp/(Vp + Vg) where Vp and Vg are the pore and groundmass fractions, respectively. Highly heterogeneous samples (containing high pore and/or crystal fractions) will therefore have high values of ϕp‧, and vice-versa. When we express our numerical samples (more than 200 simulations spanning a wide range of crystal and pore fractions) in terms of ϕp‧, we find that their strengths can be described by a single curve for a given pore diameter. To provide a predictive tool for the strength of heterogeneous volcanic rocks, we propose a modified version of 2D solution for the Sammis and Ashby (1986) pore-emanating crack model, a micromechanical model designed to estimate strength using microstructural attributes such as porosity, pore radius, and fracture toughness. The model, reformulated to include ϕp‧ (and therefore crystal fraction), captures the strength curves for our numerical simulations over a sample heterogeneity range relevant to volcanic systems. We find

  7. Volcanic rock petrochemistry as an exploration technique for geothermal energy

    SciTech Connect

    Fultz, L.A.; Bell, E.J.; Trexler, D.T.

    1983-12-01

    Large high-level silicic magma chambers offer a high potential for economically viable geothermal systems. While purely basic volcanic systems rarely form thermal anomalies, they may provide the necessary long-term heat input to silicic systems, by underplating, to sustain a high-temperature geothermal system. Petrographic and microprobe, geochemical, geochronologic, and isotopic data on young volcanic rocks in west-central Nevada indicate compositions that may result from magmatic differentiation, crystal fractionation, variation in magmatic source regions and in particular, magma mixing. Analysis of the petrochemistry and the recognition of magma mixing textures of extrusive rocks may indicate interacting mafic magma with buried shallow silicic magma systems. These systems may provide a shallow heat source for development of geothermal resources.

  8. 40Ar/39Ar Geochronology, Isotope Geochemistry (Sr, Nd, Pb), and petrology of alkaline lavas near Yampa, Colorado: migration of alkaline volcanism and evolution of the northern Rio Grande rift

    USGS Publications Warehouse

    Cosca, Michael A.; Thompson, Ren A.; Lee, John P.; Turner, Kenzie J.; Neymark, Leonid A.; Premo, Wayne R.

    2014-01-01

    Volcanic rocks near Yampa, Colorado (USA), represent one of several small late Miocene to Quaternary alkaline volcanic fields along the northeast margin of the Colorado Plateau. Basanite, trachybasalt, and basalt collected from six sites within the Yampa volcanic field were investigated to assess correlations with late Cenozoic extension and Rio Grande rifting. In this paper we report major and trace element rock and mineral compositions and Ar, Sr, Nd, and Pb isotope data for these volcanic rocks. High-precision 40Ar/39Ar geochronology indicates westward migration of volcanism within the Yampa volcanic field between 6 and 4.5 Ma, and the Sr, Nd, and Pb isotope values are consistent with a primary source in the Proterozoic subcontinental lithospheric mantle. Relict olivine phenocrysts have Mg- and Ni-rich cores, whereas unmelted clinopyroxene cores are Na and Si enriched with finely banded Ca-, Mg-, Al-, and Ti-enriched rims, thus tracing their crystallization history from a lithospheric mantle source region to one in contact with melt prior to eruption. A regional synthesis of Neogene and younger volcanism within the Rio Grande rift corridor, from northern New Mexico to southern Wyoming, supports a systematic overall southwest migration of alkaline volcanism. We interpret this Neogene to Quaternary migration of volcanism toward the northeast margin of the Colorado Plateau to record passage of melt through subvertical zones within the lithosphere weakened by late Cenozoic extension. If the locus of Quaternary alkaline magmatism defines the current location of the Rio Grande rift, it includes the Leucite Hills, Wyoming. We suggest that alkaline volcanism in the incipient northern Rio Grande rift, north of Leadville, Colorado, represents melting of the subcontinental lithospheric mantle in response to transient infiltration of asthenospheric mantle into deep, subvertical zones of dilational crustal weakness developed during late Cenozoic extension that have been

  9. The geochemistry of primitive volcanic rocks of the Ankaratra volcanic complex, and source enrichment processes in the genesis of the Cenozoic magmatism in Madagascar

    NASA Astrophysics Data System (ADS)

    Melluso, L.; Cucciniello, C.; le Roex, A. P.; Morra, V.

    2016-07-01

    The Ankaratra volcanic complex in central Madagascar consists of lava flows, domes, scoria cones, tuff rings and maars of Cenozoic age that are scattered over 3800 km2. The mafic rocks include olivine-leucite-nephelinites, basanites, alkali basalts and hawaiites, and tholeiitic basalts. Primitive samples have high Mg# (>60), high Cr and Ni concentrations; their mantle-normalized patterns peak at Nb and Ba, have troughs at K, and smoothly decrease towards the least incompatible elements. The Ankaratra mafic rocks show small variation in Sr-Nd-Pb isotopic compositions (e.g., 87Sr/86Sr = 0.70377-0.70446, 143Nd/144Nd = 0.51273-0.51280, 206Pb/204Pb = 18.25-18.87). These isotopic values differ markedly from those of Cenozoic mafic lavas of northern Madagascar and the Comoro archipelago, typical Indian Ocean MORB and oceanic basalt end-members. The patterns of olivine nephelinitic magmas can be obtained through 3-10% partial melting of a mantle source that was enriched by a Ca-rich alkaline melt, and that contained garnet, carbonates and phlogopite. The patterns of tholeiitic basalts can be obtained after 10-12% partial melting of a source enriched with lower amounts of the same alkaline melt, in the spinel- (and possibly amphibole-) facies mantle, hence in volumes where carbonate is not a factor. The significant isotopic change from the northernmost volcanic rocks of Madagascar and those in the central part of the island implicates a distinct source heterogeneity, and ultimately assess the role of the continental lithospheric mantle as source region. The source of at least some volcanic rocks of the still active Comoro archipelago may have suffered the same time-integrated geochemical and isotopic evolution as that of the northern Madagascar volcanic rocks.

  10. Different sources involved in generation of continental arc volcanism: The Carboniferous-Permian volcanic rocks in the northern margin of the North China block

    NASA Astrophysics Data System (ADS)

    Zhang, Shuan-Hong; Zhao, Yue; Liu, Jian-Min; Hu, Zhao-Chu

    2016-01-01

    New zircon U-Pb dating results on the Carboniferous-Permian volcanic rocks in the northern margin of the North China block (NCB) indicate their eruption during the Early Carboniferous to Late Permian from 347 ± 3 Ma to 258 ± 1 Ma and a slight decrease of the upper limits of the volcanic sequences from west to east. They have a main rock association of basalt, basaltic andesite, andesite, dacite, rhyolite, tuff, and tufaceous sandstone. Most of them have calc-alkaline compositions and exhibit variable SiO2 contents from 48.2 wt.% to 77.1 wt.%. There is no significant gap between the mafic and felsic volcanic rocks in major and trace element classification diagrams, indicating that they are not bimodal in composition. The Carboniferous-Permian volcanic rocks exhibit subduction-related geochemical features such as negative Nb and Ta anomalies of mafic to intermediate rocks on primitive mantle-normalized diagrams, indicating they were formed in an Andean-type continental arc during southward subduction of the Paleo-Asian oceanic plate beneath the northern NCB. However, their wide range of whole-rock Sr-Nd and zircon Hf isotopic compositions indicate that their source areas are very complex and different sources were involved in generation of these volcanic rocks. Geochemical and Sr-Nd-Hf isotopic results show that the basalt and some andesite were produced by fractional crystallization of mafic magma derived from partial melting of mantle wedge and subducted oceanic crust; however, most of the intermediate to felsic volcanic rocks were derived from partial melting of lower continental crust. There is an increasing input of crustal materials from the Carboniferous to Permian as indicated by increasing volumes of felsic volcanic rocks in the volcanic sequences. The results show that origin of the continental arc volcanism is very complex and both materials from the subducted oceanic crust and sediments, mantle wedge and arc continental crust could be involved in their

  11. Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada

    USGS Publications Warehouse

    du Bray, Edward A.; John, David A.; Box, Stephen E.; Vikre, Peter G.; Fleck, Robert J.; Cousens, Brian L.

    2013-04-23

    Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada // // This report presents petrographic and geochemical data for samples collected during investigations of Tertiary volcanism in the Bodie Hills of California and Nevada. Igneous rocks in the area are principally 15–6 Ma subduction-related volcanic rocks of the Bodie Hills volcanic field but also include 3.9–0.1 Ma rocks of the bimodal, post-subduction Aurora volcanic field. Limited petrographic results for local basement rocks, including Mesozoic granitoid rocks and their metamorphic host rocks, are also included in the compilation. The petrographic data include visual estimates of phenocryst abundances as well as other diagnostic petrographic criteria. The geochemical data include whole-rock major oxide and trace element data, as well as limited whole-rock isotopic data.

  12. Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada

    USGS Publications Warehouse

    du Bray, Edward A.; John, David A.; Box, Stephen E.; Vikre, Peter G.; Fleck, Robert J.; Cousens, Brian L.

    2013-01-01

    Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada // // This report presents petrographic and geochemical data for samples collected during investigations of Tertiary volcanism in the Bodie Hills of California and Nevada. Igneous rocks in the area are principally 15–6 Ma subduction-related volcanic rocks of the Bodie Hills volcanic field but also include 3.9–0.1 Ma rocks of the bimodal, post-subduction Aurora volcanic field. Limited petrographic results for local basement rocks, including Mesozoic granitoid rocks and their metamorphic host rocks, are also included in the compilation. The petrographic data include visual estimates of phenocryst abundances as well as other diagnostic petrographic criteria. The geochemical data include whole-rock major oxide and trace element data, as well as limited whole-rock isotopic data.

  13. Cenozoic Bimodal Volcanic Rocks of the Northeast boundary of Tibetan Plateau: implication for the collision-induced mantle flow beneath the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Yu, X.; Mo, X.; Zhao, Z.

    2011-12-01

    Cenozoic bimodal volcanic rocks of the Northeastern boundary of Tibetan Plateau are found in the area of West Qinling in China, E104°30'-105°36' and N33°35'-34°40',which located tectonically to the western boundary of Ordos block and also the north section of the N-S trending Helan mountain-Liupan mountain-Yunnan tectonic belt. The geological setting of the bimodal volcanic rocks belongs to an assemblage of Cratonic blocks composed of many small blocks linked by oroginic belts(Deng et al., 1996). The bimodal volcanic rocks, similar to those in East African rift, are consisted of kamafugite, volcanic eruption carbonatite, shoshonite, rhyolite and/or trachyte. The age of the bimodal volcanic rocks is between 23Ma to 7.1Ma according to isotopic dating of K/Ar and 39Ar/40Ar. All of these volcaic rocks in the volcanic assemblage have the characteristics rich in LREE and LIL. Not only that, the HFS, especially Nb, Zr and P in the volcanic rocks are higher than other Cenozoic alkaline volcanic rocks in Tibetan Plateau. The 87Sr/86Sr=0.704031-0.70525, 206Pb/204Pb=18.408-19.062, 207Pb/204Pb=15.476-15.677, 208Pb/204Pb=38.061-39.414 and ɛ(Nd) =0.3-5.3 of the volcanic rocks, all of these are akin to the feature of Neo-Tethyan mantle geochemical end member as represented by Yaluzangbu ophiolites defined by Zhao and Mo et al (2009), and also akin to the volcanic rocks related to Ontong Java and FOZO mantle plum(Yu et al.,2009). Cenozoic bimodal volcanic rocks in Western Qinling, Northeastern boundary of Tibetan Plateau provide ideal lithoprobes for understanding of the mantle beneath Tibetan Plateau and showed that the Cenozoic bimodal volcanic rocks bear the geochemical feature of Indian ocean mantle domain, and its genesis may be related to mantle plum, the magmatic source of the bimodal volcanic rocks should be a depleted mantle. For this reason, we suggest the bimodal volcaic rock is a rifting magmatisim, and its origin and genesis of the bimodal volcaic rocks of

  14. Paleogene volcanic rocks of the Matanuska Valley area and the displacement history of the Castle Mountain fault

    NASA Astrophysics Data System (ADS)

    Silberman, M. L.; Grantz, A.

    Primitive strontium-isotopic composition and overall bimodal distribution of silica in upper Paleocene and Eocene subalkalic tholeiitic to calc-alkaline basalt and low-potassium rhyolite of the Matanuska Valley and southern Talkeetna Mountains suggest that these rocks were derived from the mantle with little contamination by continental crust. The volcanic rocks consist of rhyolite tuff and ash flows, as well as basalt flows and dikes, in the nonmarine Arkose Ridge Formation of the southwestern Talkeetna Mountains; of subaerial basalt and andesite flows, tuff, and mafic intrusions in the southeastern Talkeetna Mountains; and of felsic and mafic dikes, sills, and small plutons in the Matanuska Valley. The generalized geology of the area in which the volcanic rocks occur and the localities sampled for potassium-argon-age determinations and for chemical and strontinum-isotopic analysis are shown. The analytical results are listed.

  15. Examining ash fall sequences in calk-alkaline subduction related volcanism, southern New Mexico

    NASA Astrophysics Data System (ADS)

    Rentz, S. P.; Michelfelder, G.; Salings, E. E.; Sikes, E. R.

    2015-12-01

    The Mogollon-Datil volcanic field (MDVF) is a 40-20 ma cluster of caldera activity in southern New Mexico tied to the subduction of oceanic lithosphere beneath the North American continental plate. The calk-alkaline magmatism of the three calderas in this field (Mogollon, Bursum, and Gila Cliff Dwellings) produced several voluminous regionally dispersed ash flow tuffs. This study will specifically examine the volcanic rocks: Cooney Formation (a compositionally zoned rhyolitic to quartz latite ash flow tuff containing quartz>k-feldspar>plagioclase>biotite, and pumice and lithic fragments. Rb ranges from 213-317ppm, Sr from 104-108ppm, and 87Sr/86Srm from 0.71326-0.71534), Davis Canyon Tuff (a phenocryst poor, high-silica rhyolite ash flow tuff containing sanidine>quartz>sodic plagioclase. Rb ranges from 214-230ppm, Sr from 42.2-63.2ppm, and 87Sr/86Srm from 0.71383-0.71464), and the Shelley Peak Tuff (a compositionally zoned, crystal-rich rhyolite tuff containing sodic plagioclase>minor sanidine>biotite>cpx. Rb ranges from 154-213ppm, Sr from 105-245ppm, and 87Sr/86Srm from 0.70944-0.7112) to further elucidate their petrogenic origins, attempt to determine if they may be of the same magmatic source, and yield data that could help model processes that would generate magma of these particular compositions. This study will examine compositional variation between the Davis Canyon, Shelley Peak and Cooney Tuffs and help with understanding the magma plumbing system during each eruption. More specifically, we will evaluate possible crustal components of these units, along with looking for geochemical signatures of arc or rift related magmatism. We will compare previous geochronology results (K-Ar and U-Pb fission track) and whole rock major and trace element geochemistry to data obtained via 40Ar/39Ar and U/Pb dates and new whole rock Sr, Nd and Pb isotopic ratios.

  16. Evaluation of ASR potential of quartz-rich rocks by alkaline etching of polished rock sections

    NASA Astrophysics Data System (ADS)

    Šachlová, Šárka; Kuchařová, Aneta; Pertold, Zdeněk; Přikryl, Richard

    2015-04-01

    Damaging effect of alkali-silica reaction (ASR) on concrete structures has been observed in various countries all over the World. Civil engineers and real state owners are demanding reliable methods in the assessment of ASR potential of aggregates before they are used in constructions. Time feasible methods are expected, as well as methods which enable prediction of long-term behaviour of aggregates in concrete. The most frequently employed accelerated mortar bar test (AMBT) quantifies ASR potential of aggregates according to the expansion values of mortar bars measured after fourteen days testing period. Current study aimed to develop a new methodical approach facilitating identification and quantification of ASR potential of aggregates. Polished rock sections of quartz and amorphous SiO2 (coming from orthoquartzite, quartz meta-greywacke, pegmatite, phyllite, chert, and flint) were subjected to experimental leaching in 1M NaOH solution at 80°C. After 14 days of alkaline etching, the rock sections were analyzed employing scanning electron microscope combined with energy dispersive spectrometer. Representative areas were documented in back scattered electron (BSE) images and measured using fully-automatic petrographic image analysis (PIA). Several features connected to alkaline etching were observed on the surface of polished rock sections: deep alkaline etching, partial leach-out of quartz and amorphous particles, alkaline etching connected to quartz grain boundaries, and alkaline etching without any connection to grain boundaries. All features mentioned above had significant influence on grey-scale spectrum of BSE images. A specific part of the grey-scale spectrum (i.e. grey-shade 0-70) was characteristic of areas affected by alkaline etching (ASR area). By measuring such areas we quantified the extent of alkaline etching in studied samples. Very good correlation was found between the ASR area and ASR potential of investigated rocks measured according to the

  17. Calc-alkaline mafic rocks of the Black Dyke Formation: Remnants of the final activity of a submerged Permian volcano

    SciTech Connect

    Blein, O.; Lapierre, H.; Pecher, A. ); Schweickert, R.A. . Dept. of Geological Science)

    1993-04-01

    The Permian Black Dyke Fm., which occurs as large tectonic slices within the Luning allochthon in the Excelsior Mountains, NV, forms an E-W trending anticline at Black Dyke Mountain. The 800-m thick stratigraphic succession consists of volcanic and pyroclastic rocks overlain conformably by volcaniclastic sediments. Along the northern limb of the anticline, the rocks consist of mafic porphyritic lavas, breccias, and graded and ungraded pyroclastic beds. The sedimentary unit consists of thick volcaniclastic turbidites overlain by conglomerates, sandstones, and mudstones. Along the southern limb of the anticline, the sequence is replaced by reworked breccia, tuffs, and sandstones. Mafic plutonic rocks occur as xenoliths in the lavas and breccias, and as coeval plugs intruding the section. Gabbros show cumulate or porphyritic textures and are composed of amph, cpx, and zoned plag. Their Ti/V (14.5--15) and Nb/Y (0.25--0.3) ratios fall in the range commonly found in calc-alkaline rocks. Diorite porphyry shows high Al[sub 2]O[sub 3], ZrO[sub 2], and REE abundances indicating that this rock is more fractionated. Basalts and andesites are plag-cpx-opx phyric. They often include glomeroporphyritic clots of cpx with amph coronas. Some rocks exhibit fluidal textures. Both volcanic and plutonic rocks show homogeneous geochemical features and similar crystallization sequences: Fe-Ti oxides---->plag---->opx + cpx----> brown zoned hbl, suggesting that they are cogenetic. Thus, the lower part of the Black Dyke Fm. likely represents the final products formed in a calc-alkaline magma chamber because pyroclastic rocks prevail over lava flows and abundant early crystal cumulates occur as plugs or as inclusions in the lavas and breccias.

  18. Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds

    NASA Astrophysics Data System (ADS)

    Pearson, D. G.; Canil, D.; Shirey, S. B.

    2003-12-01

    Occurrence and ClassificationFragments of the Earth's mantle are frequently transported to the surface via volcanic rocks that are dominantly alkaline in nature. These fragments range up to sizes in excess of 1 m across. The term "mantle xenoliths" or "mantle nodules" is applied to all rock and mineral inclusions of presumed mantle derivation that are found within host rocks of volcanic origin. The purpose of this contribution is to review the geochemistry of mantle xenoliths. For detailed petrological descriptions of individual locations and suites, together with their geological setting, the reader is referred to the major reference work by Nixon (1987).Despite peridotite xenoliths in basalts being recognized for several centuries and comparisons being made to lherzolite massifs (Lacroix, 1893), it was not until work on garnet peridotites and diamonds in kimberlites by Fermor (1913) and Wagner (1914) that such xenoliths were conceptually associated with a peridotite zone in the Earth beneath the crust, i.e., the zone that we now identify as the mantle. Mantle xenoliths provide snapshots of the lithospheric mantle beneath particular regions at the time of their eruption and hence are crucial direct evidence of the nature of the mantle beneath regions where no samples have been exposed by tectonic activity. As such, xenoliths are an essential compliment to tectonically exposed bodies of mantle (orogenic peridotites and ophiolites) that occur at plate boundaries (see Chapter 2.04). One obvious contrast between the mantle samples provided by xenoliths and those provided by peridotite massifs is the lack of field relationships available for xenoliths. Other drawbacks include the small size of many xenoliths. This makes accurate estimation of bulk compositions difficult and accentuates modal heterogeneities. The frequent infiltration of the host magma also complicates their chemical signature. Despite these drawbacks, xenoliths are of immense value, being the only

  19. Erratic Continental Rocks on Volcanic Seamounts off California and Oregon

    NASA Astrophysics Data System (ADS)

    Paduan, J. B.; Clague, D. A.; Davis, A. S.

    2006-12-01

    The seamounts off the California continental margin, and those well offshore of California and Oregon that formed near mid-ocean ridges, are all constructed of basaltic lava flows and volcanic breccias and sandstones. However, explorations of these seamounts using dredges, and more recently, the remotely operated vehicle Tiburon, frequently recover rocks of a wide assortment of continental lithologies including gabbro, granodiorite, silicic volcanics, limestone, dolomite, and metamorphic rocks. These rocks are often rounded like river and beach cobbles, and the softer rocks are bored as by worms or bivalves. They are covered with manganese oxide crusts of thicknesses that range from a patina to several cm, approaching the thickness on the in-situ basaltic rocks. These rocks are often easier to collect than the basalts. We recognize these rocks to be erratics of continental origin. Erratics have been documented as being transported by icebergs at higher latitudes, but this mechanism is unlikely to be responsible for the erratics we have found as far south as 31.9° N. Three brief papers published by K.O. Emery from 1941 to 1954 proposed that such erratics found in many thick sections of fine-grained sedimentary sequences such as the Monterey Formation, were transported long distances by kelp holdfasts, tree roots, or in the guts of pinnipeds. We propose that these vectors also transport erratics to seamounts, where they have been accumulating since the seamounts formed millions of years ago. Those seamounts that were once islands would have intercepted even more erratics along their shorelines while they stood above sea level. We have recovered or observed such erratics on the Vance Seamounts; Gumdrop, Pioneer, Guide, Davidson, Rodriguez, San Juan, Little Joe, and San Marcos Seamounts; on the muddy bottom of Monterey Bay; and on Northeast Bank and along the Patton Escarpment at the western edge of the California Borderland. These locations are as far as 250 nautical

  20. Petrology and geochemistry of mafic and ultramafic cumulates occurring as xenoliths in volcanic rocks from Polish part of Central European Volcanic Province.

    NASA Astrophysics Data System (ADS)

    Dajek, Michał; Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros

    2015-04-01

    of diopside, but its mg# is lower than in other rocks (0.68-0.88). It is always LREE enriched and shows negative Eu, Ti and Sr anomalies. Orthopyroxene occurs only in norite from Wilcza Góra. It composition is strongly heterogenous and the mg# vary from 0.60 to 0.75. Fo- and NiO-poor (62-69% and 0.04-0.10 wt.%, respectively) olivine is present in gabbro from Winna Góra. Feldspar is typically plagioclase (An30-60), but in rims the composition grades toward ternary feldspar (Or up to 45%). Plagioclase is LREE enriched and shows strong positive Eu anomaly. It is enriched in Sr and depleted in Zr-Hf. Composition of opaques is similar to that in plagioclase-free rocks. Modelling based on the trace element composition of clinopyroxene suggest that all the studied xenoliths are precipitates from alkaline silicate magmas, usually similar to the host volcanic-rock. Relatively high content of iron in silicates suggest crystallization at crustal depths or at crust/mantle boundary, but ratios between AIV and AlVI in clinopyroxene suggest that plagioclase¬-bearing rocks crystalized in different conditions than pyroxenites (Aoki and Shiba, 1976). Origin of xenoliths from Złotoryja-Jawor Volcanic Complex is different than that of clinopyroxene-rich mafic rocks from Lutynia basanite (Lądek Zdrój Volcanic Complex (Ackerman et al., 2012; J. of Geosciences). This study was possible thanks to the project NCN 2011/03/B/ST10/06248 of Polish National Centre for Science.

  1. 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.

  2. Uranium and thorium decay series disequilibria in young volcanic rocks

    SciTech Connect

    Williams, R.W.

    1988-01-01

    Two of the central questions in igneous geochemistry that study of radioactive disequilibria can help to answer are: what are the rates of magma genesis; and what are the timescales of magma separation and transport. In addition to the temporal information that may be extracted from disequilibria data, the {sup 230}Th/{sup 232}Th of a young rock may be used as a tracer of the Th/U ratio of its source region. Measurements were made by isotope dilution alpha-spectrometry of {sup 238}U, {sup 234}U, {sup 230}Th, and {sup 232}Th in 20 subduction related, 3 oceanic intraplate, and 10 continental intraplate volcanics. {sup 210}Pb was measured in all, {sup 226}Ra was measured in about half, and {sup 228}Th was measured in 10 of the most recent samples. Disequilibrium between {sup 228}Th and {sup 232}Th was found only in the Nacarbonatite samples from Oldoinyo Lengai volcano in Tanzania, which is attributable to {sup 228}Ra/{sup 232}Th {approximately} 27 at the time of eruption. These rocks also have {sup 226}Ra/{sup 230}Th > 60. Three Ra-enrichment models are developed which constrain carbonatite magma formation at less than 20 years before eruption. The effects of different partial melting processes on the {sup 238}U decay series are investigated. If mid-ocean ridge basalts are formed by a dynamic melting process, the {sup 230}Th/{sup 232}Th of the basalts provides a minimum estimate of the Th/U ratio of the source region. The {sup 238}U enrichment in arc volcanics is probably the results of metasomatism of the source by fluids derived from the subducting slab, and the {sup 230}Th enrichment observed for other volcanics is probably due to the partial melting process in the absence of U-bearing fluids.

  3. Suprasubduction volcanic rocks of the Char ophiolite belt, East Kazakhstan: new geochemical and first geochronological data

    NASA Astrophysics Data System (ADS)

    Safonova, Inna; Simonov, Vladimir; Seltmann, Reimar; Yamamoto, Shinji; Xiao, Wenjiao

    2016-04-01

    The Char ophiolite belt is located in the western Central Asian Orogenic Belt, a world largest accretionary orogen, which has evolved during more than 800 Ma. The Char belt formed during Kazakhstan - Siberia collision. It has been known for hosting fragments of Late Devonian-Early Carboniferous oceanic crust, MORB, OPB and OIB, of the Paleo-Asian Ocean (Safonova et al., 2012). The Char is surrounded by two Paleozoic island-arc terranes: Zharma-Saur in the west and Rudny Altai in the east, however, until recent times, no island-arc units have been found within it. We were the first to find island-arc units as tectonic sheets occurring adjacent to those consisting of oceanic rocks. In places, island-arc andesites cut oceanic basalts. The Char volcanic and subvolcanic rocks of a probable suprasubduction origin are basalt, microgabbro, dolerite, andesite, tonalite and dacite. The mafic to andesitic volcanics possessing low TiO2 (0.85 wt.%av.) and show MgO vs. major elements crystallization trends suggesting two magma series: tholeiitic and calc-alkaline. The tholeiitic varieties are less enriched in incompatible elements then the calc-alkaline ones. Two samples are high-Mg and low-Ti andesibasalts similar to boninites. The rocks possess moderately LREE enriched rare-earth element patterns and are characterized by negative Nb anomalies present on the multi-element spectra (Nb/Lapm = 0.14-0.47; Nb/Thpm = 0.7-1.6).The distribution of rare-earth elements (La/Smn = 0.8-2.3, Gd/Ybn = 0.7-1.9) and the results of geochemical modeling in the Nb-Yb system suggest high degrees of melting of a depleted harzburgite-bearing mantle source at spinel facies depths. Fractional crystallization of clinopyroxene, plagioclase and opaque minerals also affected the final composition of the volcanic rocks. Clinopyroxene monomineral thermometry indicates crystallization of melts at 1020-1180°C. Melt inclusion composition based numerical calculations show that primary melts were derived at 1350

  4. Geochemistry and petrogenesis of late Ediacaran (605-580 Ma) post-collisional alkaline rocks from the Katherina ring complex, south Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Azer, M. K.; Obeid, M. A.; Ren, M.

    2014-10-01

    The Katherina ring complex (KRC) in the central part of south Sinai, Egypt, is a typical ring complex of late Neoproterozoic age (605-580 Ma). It was developed during the final tectono-magmatic stage of the north Arabian-Nubian Shield (ANS) during evolution of the Pan-African crust. The KRC includes Katherina volcanics, subvolcanic bodies, ring dykes and Katherina granitic pluton. The Katherina volcanics represent the earliest stage of the KRC, which was subsequently followed by emplacement of the subvolcanic bodies and ring dykes. The Katherina granitic pluton depicts as the latest evolution stage of the KRC that intruded all the early formed rock units in the concerned area. The Katherina volcanics are essentially composed of rhyolites, ignimbrite, volcanic breccia and tuffs. Mineralogically, the peralkaline rhyolites contain sodic amphiboles and aegirine. The rhyolite whole rock chemistry has acmite-normative character. The subvolcanic bodies of the KRC are represented by peralkaline microgranite and porphyritic quartz syenite. The ring dykes are semicircular in shape and consist mainly of quartz syenite, quartz trachyte and trachybasalt rock types. The Katherina subvolcanic rocks, volcanic rocks as well as the ring dykes are alkaline or/and peralkaline in nature. The alkaline granitic pluton forms the inner core of the KRC, including the high mountainous areas of G. Abbas Pasha, G. Bab, G. Katherina and G. Musa. These mountains are made up of alkaline syenogranite and alkali feldspar granite. The mantle signature recorded in the KRC indicates a juvenile ANS crust partial melting process for the generation of this system. The evolution of the KRC rocks is mainly dominated by crystal fractionation and crustal contamination. Mineral geothermometry points to the high temperature character of the KRC, up to 700-1100 °C.

  5. Late Cenozoic calc-alkaline volcanism over the Payenia shallow subduction zone, South-Central Andean back-arc (34°30‧-37°S), Argentina

    NASA Astrophysics Data System (ADS)

    Litvak, Vanesa D.; Spagnuolo, Mauro G.; Folguera, Andrés; Poma, Stella; Jones, Rosemary E.; Ramos, Víctor A.

    2015-12-01

    A series of mesosilicic volcanic centers have been studied on the San Rafael Block (SRB), 300 km to the east of the present-day volcanic arc. K-Ar ages indicate that this magmatic activity was developed in at least two stages: the older volcanic centers (˜15-10 Ma) are located in the central and westernmost part of the SRB (around 36°S and 69°W) and the younger centers (8-3.5 Ma) are located in an eastern position (around 36°S and 69°30‧W) with respect to the older group. These volcanic rocks have andesitic to dacitic compositions and correspond to a high-K calc-alkaline sequence as shown by their SiO2, K2O and FeO/MgO contents. Elevated Ba/La, Ba/Ta and La/Ta ratios show an arc-like signature, and primitive mantle normalized trace element diagrams show typical depletions of high field strength elements (HFSE) relative to large ion lithophile elements (LILE). Rare earth element (REE) patterns suggest pyroxene and amphibole crystallization. Geochemical data obtained for SRB volcanic rocks support the proposal for a shallow subduction zone for the latest Miocene between 34°30″-37°S. Regionally, SRB volcanism is associated with a mid-Miocene to early Pliocene eastward arc migration caused by the shallowing of the subducting slab in the South-Central Andes at these latitudes, which represents the evolution of the Payenia shallow subduction segment. Overall, middle Miocene to early Pliocene volcanism located in the Payenia back-arc shows evidence for the influence of slab-related components. The younger (8-3.5 Ma) San Rafael volcanic rocks indicate the maximum slab shallowing and the easternmost extent of slab influence in the back-arc.

  6. Volcanological, petrographical and geochemical characteristics of Late Cretaceous volcanic rocks around Borçka-Artvin region (NE Turkey)

    NASA Astrophysics Data System (ADS)

    Baser, Rasim; Aydin, Faruk; Oguz, Simge

    2015-04-01

    This study presents volcanological, petrographical and geochemical data for late Cretaceous volcanic rocks from the Borçka-Artvin region (NE Turkey) in order to investigate their origin and magmatic evolution. Based on the previous ages and recent field studies, the late Cretaceous time in the study area is characterized by two different bimodal volcanic periods. The first bimodal period of the late Cretaceous volcanism is mainly represented by mafic rock series (basaltic-basaltic andesitic pillow lavas and hyaloclastites) in the lower part, and felsic rock series (dacitic lavas, hyaloclastites, and pyrite-bearing tuffs) in the upper part. The second bimodal period of the late Cretaceous volcanism begins with mafic rock suites (basaltic-andesitic lavas and dikes-sills) and grades upward into felsic rock suites (biotite-bearing rhyolitic lavas and hyaloclastites), which are intercalated with hyaloclastites and red pelagic limestones. All volcano-sedimentary units are covered by Late Campanian-Paleocene clayey limestones and biomicrites with lesser calciturbidites. The mafic volcanic series of the study area, which comprise basaltic and andesitic rocks, generally show amygdaloidal and aphyric to porphyritic texture with phenocrysts of calcic to sodic plagioclase and augite in a hyalopilitic matrix of plag+cpx+mag. Zircon and magnetite are sometimes observed as accessory minerals, whereas chlorite, epidote and calcite are typical alteration products. On the other hand, the felsic volcanic series consisting of dacitic and rhyolitic rocks mostly display porphyritic and glomeroporphyritic textures with predominant feldspar, quartz and some biotite phenocrysts. The microgranular to felsophyric groundmass is mainly composed of aphanitic plagioclase, K-feldspar and quartz. Accessory minerals such as zircon, apatite and magnetite are common. Typical alteration products are sericite and clay minerals. Late Cretaceous Artvin-Borçka bimodal rock series generally display a

  7. Major and EDXRF Trace Element Chemical Analyses of Volcanic Rocks from Lassen Volcanic National Park and Vicinity, California

    USGS Publications Warehouse

    Clynne, Michael A.; Muffler, L.J.P.; Siems, D.F.; Taggart, J.E.; Bruggman, Peggy

    2008-01-01

    This open-file report presents WDXRF major-element chemical data for late Pliocene to Holocene volcanic rocks collected from Lassen Volcanic National Park and vicinity, California. Data for Rb, Sr, Ba, Y, Zr, Nb, Ni, Cr, Zn and Cu obtained by EDXRF are included for many samples. Data are presented in an EXCEL spreadsheet and are keyed to rock units as displayed on the Geologic Map of Lassen Volcanic National Park and vicinity (Clynne and Muffler, in press). Location of the samples is given in latitude and longitude in degrees and decimal minutes and in decimal degrees.

  8. Geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington

    USGS Publications Warehouse

    Smith, James G.

    1993-01-01

    For geothermal reasons, the maps emphasize Quaternary volcanic rocks. Large igneous-related geothermal systems that have high temperatures are associated with Quaternary volcanic fields, and geothermal potential declines rapidly as age increases (Smith and Shaw, 1975). Most high-grade recoverable geothermal energy is likely to be associated with silicic volcanism less than 1 Ma. Lower grade (= lower temperature) geothermal resources may be associated with somewhat older rocks; however, volcanic rocks older than about 2 Ma are unlikely geothermal targets (Smith and Shaw, 1975).

  9. Oligocene caldera complex and calc-alkaline tuffs and lavas of the Indian Peak volcanic field, Nevada and Utah

    USGS Publications Warehouse

    Best, M.G.; Christiansen, E.H.; Blank, H.R.

    1989-01-01

    The Indian Peak volcanic field is representative of the more than 50 000 km3 of ashflow tuff and tens of calderas in the Great Basin that formed during the Oligocene-early Miocene "ignimbrite flareup' in southwestern North America. These dominantly high-K calc-alkaline rocks are a record of the birth, maturation, and death of a large, open, continental magma system that was probably initiated and sustained by influx of mafic magma derived from a southward-migrating locus of magma production in the mantle. Recurrent production of very large batches (some greater than 3000 km3) of quite uniform dacite magmas appears to have required combination of andesite magma and crustal silicic material in vigorously convecting chambers. Compositional data indicate that rhyolites are polygenetic. As the main locus of mantle magma production shifted southward, trachydacite magma could have been produced by fractionation of andesitic magma within the crust. -from Author

  10. Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. G.; Lee, T.-Y.; Torng, P.-K.; Yang, C.-C.; Lee, Y.-H.

    2016-07-01

    Silicic volcanic rocks at Hadjer el Khamis, near Lake Chad, are considered to be an extension of the Cameroon volcanic line (CVL) but their petrogenetic association is uncertain. The silicic rocks are divided into peraluminous and peralkaline groups with both rock types chemically similar to within-plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma indicating the magmas erupted ˜10 million years before the next oldest CVL rocks (i.e., ˜66 Ma). The Sr isotopes (i.e., ISr = 0.7021-0.7037) show a relatively wide range but the Nd isotopes (i.e., 143Nd/144Ndi = 0.51268-0.51271) are uniform and indicate that the rocks were derived from a moderately depleted mantle source. Thermodynamic modeling shows that the silicic rocks likely formed by fractional crystallization of a mafic parental magma but that the peraluminous rocks were affected by low temperature alteration processes. The silicic rocks are more isotopically similar to Late Cretaceous basalts identified within the Late Cretaceous basins (i.e., 143Nd/144Ndi = 0.51245-0.51285) of Chad than the uncontaminated CVL rocks (i.e., 143Nd/144Ndi = 0.51270-0.51300). The age and isotopic compositions suggest the silicic volcanic rocks of the Lake Chad region are related to Late Cretaceous extensional volcanism in the Termit basin. It is unlikely that the silicic volcanic rocks are petrogenetically related to the CVL but it is possible that magmatism was structurally controlled by suture zones that formed during the opening of the Central Atlantic Ocean and/or the Pan-African Orogeny.

  11. Cooling-dominated cracking in thermally stressed volcanic rocks

    NASA Astrophysics Data System (ADS)

    Browning, John; Meredith, Philip; Gudmundsson, Agust

    2016-08-01

    Most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion. Both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating. We present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite. Results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating. Seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic. These new data are important for assessing the contribution of cooling-induced damage within volcanic structures and layers such as dikes, sills, and lava flows.

  12. Paleointensity determinations from Middle Miocene volcanic rocks, Far East, Russia

    NASA Astrophysics Data System (ADS)

    Shcherbakov, Valeriy; Shcherbakova, Valentina; Zhidkov, Grigoriy; Bretstein, Yury

    2010-05-01

    Paleomagnetic and paleointensity studies of a representative collection of Middle Miocene volcanic rocks of (12.4-10.0) Ma age from Far East, Russia were carried out. A comprehensive rock magnetic investigation has been performed in order to determine the mineralogy of magnetic fraction and to identify the origin of NRM. Successful Thellier palaeointensity determinations with pTRM checks were obtained for 4 sites (33 samples). The Thellier experiments were complimented by the Wilson's express method. Values of the VDMs range from 3.1 to 7.5 (10^22 Am^2) with the mean VDM = 5.5×10^22 Am^2. A total 88 Thellier-type palaeointensity determinations were found in the World Paleointensity database for the 5-23 Ma period with the overall mean VDM = 5×10^22 Am^2. The VDM distribution is characterized by high variance from 1.5 to 12 (10^22 Am^2). No significant difference between the VDM distributions for the normal and reverse polarity intervals was revealed.

  13. Early Jurassic Volcanic Rocks from the Raohe Accretionary Complex of NE China: Petrogenesis and Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Wang, Zhihui; Ge, Wenchun

    2016-04-01

    The Raohe accretionary complex is located at the boundary between the Russian Far East and Northeast China, and is an important part of the Western Pacific Ocean tectonic regime. However, owing to the lack of precise age and geochemical constraints, the tectonic setting and petrogenesis of magmatic rocks in this area have been controversial, which has led to the debate on crustal growth mechanisms and subduction accretionary processes in the Northeast China. Herein, we report newly-defined calc-alkaline andesites, dacites, rhyolites, Nb-enriched basaltic-andesites and andesites, and N-MORB type basalts and basaltic-andesites from the Raohe accretionary complex, NE China. All these volcanic rocks are collected from rocks mapped previously as the Late Triassic to Early Jurassic stratums. LA-ICP-MS zircon U-Pb dating for one andesite, one dacites and three rhyolites indicate the occurrence of magmatic events in the Early Jurassic (186-174 Ma). They have positive ɛHf(t) values of +3.4 to +10.6 and relatively high (87Sr/86Sr)i values of 0.704711 to 0.710235. The calc-alkaline andesites, dacites and rhyolites are typical arc magmas, with moderately enriched LILEs and LREEs, distinctly negative HFSEs, consistent with the chemistry of volcanic rocks from an active continental margin setting. The Nb-enriched basaltic-andesites and andesites have higher TiO2, Nb, and Zr contents, higher Nb/Ta (24.03-87.60), Nb/U (11.89-75.94), (Nb/Th)PM (0.67-2.70), and (Nb/La)PM (1.95-5.00) ratios than typical arc basalts. They are relatively enriched in Nb, Zr, Hf and Ti. They have negative ɛNd(t) values of -5.47 to -6.04 and relatively variable (87Sr/86Sr)i values of 0.704648 to 0.711430, suggesting that they were possibly generated by a partial melting of mantle wedge peridotites metasomatized by slab-derived adakitic melts and minor fluids. The N-MORB type basalts and basaltic-andesites have comparatively low TiO2 concentrations (1.18-1.42 wt.%), show almost flat REE patterns with

  14. Petrology and petrogenesis of the Eocene Volcanic rocks in Yildizeli area (Sivas), Central Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Doğa Topbay, C.; Karacık, Zekiye; Genç, S. Can; Göçmengil, Gönenç

    2015-04-01

    -Na plagioclase + hornblend ± pyroxene ± biotite + opaques in a matrix comprised of mostly glass, microlites or crypto to micro crystalline feldspars. All the lavas show mainly pilotaxitic, intersertal, cumulophyric and poikilitic textures. Geochemically, Yıldızeli lavas ranging in composition from basalt to trachyandesite displaying the calc-alkaline affinity with medium-K and shoshonitic character. All intermediate and basic volcanic rocks show enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements (HFSE) such as Nb, Ta, Zr and Ti. Volcanic rocks of the Yıldızeli region display the following range in Sr and Nd initial isotope ratios: 87Sr/86Sr = 0.704389 to 0.706291 and 143Nd/144Nd = 0.512671. The major- trace element geochemistry and isotopic values suggest that Yıldızeli volcanics derived possibly from a mantle source which was modified by subduction related fluids or was contaminated by the continental crustal components.

  15. Volcanostratigraphy, petrography and petrochemistry of Late Cretaceous volcanic rocks from the Görele area (Giresun, NE Turkey)

    NASA Astrophysics Data System (ADS)

    Oguz, Simge; Aydin, Faruk; Baser, Rasim

    2015-04-01

    dacite but those of the second period have biotite-bearing rhyolite. The basalts and basaltic andesites exhibit subaphyric to porphyritic texture with phenocrysts of calcic plagioclase and augite in a fine-grained to microcrystalline groundmass, consisting of plag+cpx+mag. Andesite samples display a porphyritic texture with phenocrysts of calcic to sodic plagioclase and augite in a hyalopilitic matrix of plag+cpx±amph+mag. Zircon and magnetite are common accessory minerals, whereas chlorite, epidote and calcite are typical alteration products. On the other hand, the dacitic and rhyolitic rocks commonly show a porphyritic texture with predominant feldspar, quartz and some biotite phenocrysts. The microgranular to felsophyric groundmass is mainly composed of aphanitic plagioclase, K-feldspar and quartz. Accessory minerals include zircon, apatite and magnetite. Typical alteration minerals include late-formed sericite, albite and clay minerals. Late Cretaceous mafic and felsic volcanic rocks have a largely sub-alkaline character with typical arc geochemical signatures. N-MORB-normalised multi-element patterns show that all rock samples are enriched in LILEs (e.g. Rb, Ba, Th) but depleted in Nb and Ti. The chondrite-normalized REE patterns are concave shapes with low to medium enrichment, suggesting a common mantle source for the studied bimodal rock series. All geochemical data reflecting typical characteristics of subduction-related magmas are commonly attributed to a depleted mantle source, which has been previously enriched by fluids or sediments. Acknowledgments This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK, grant 112Y365)

  16. Evolution and genesis of volcanic rocks from Mutnovsky Volcano, Kamchatka

    NASA Astrophysics Data System (ADS)

    Simon, A.; Yogodzinski, G. M.; Robertson, K.; Smith, E.; Selyangin, O.; Kiryukhin, A.; Mulcahy, S. R.; Walker, J. D.

    2014-10-01

    This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite (60-80% by volume), but each has also produced small volumes of andesite and dacite. Across centers of all ages, Mutnovsky lavas define a tholeiitic igneous series, from 48-70% SiO2. Basalts and basaltic andesites have relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm < 1.0. Andesites have generally higher REE abundances and are more enriched in light REEs, some showing negative Eu anomalies. All samples are depleted in field strength elements (HFSEs) relative to similarly incompatible REEs (e.g., low La/Ta, Nd/Hf compared to MORB), similar to island arc volcanic rocks worldwide. Radiogenic isotope ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene and olivine from a parental basalt, combined with assimilation of a melt composition similar to dacite lavas present at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic andesite, combined with assimilation of dacite. Dacites erupted from Mutnovsky I and II have low abundances of REEs

  17. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins.

    PubMed

    Sommer, Carlos A; Lima, Evandro F; Nardi, Lauro V S; Liz, Joaquim D; Waichel, Breno L

    2006-09-01

    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

  18. Meso-cenozoic volcanic rocks in east China and adjacent areas with relation to plate tectonics

    NASA Astrophysics Data System (ADS)

    Zheng, Xuezheng

    1985-03-01

    Meso-Cenozoic calc-alkaline volcanic rocks and granites in the East China region are composed of four NE belts from west to east; the Trassic belt in the middle and east Mongolia, the Jurassic-Creta-ceous belt in East China, the Paleogene belt in the East China Sea and the Neogene-Quaternary belt in southwestern Japan-Okinawa and northeastern Japan-Izu-Bonin-Mariana volcanic arcs. They are nearly parallel to the Benioff zones of the ancient Pacific Plate on one hand and become older as the distance from the Pacific Ocean increases on the other hand. This sequence is in reverse order to that in South and North America. There are two age-peaks among them: one is in the early Cretaceous and the other in the Miocene, in good agreement with the time when the sea-floor spreading of the ancient Pacific Plate became fast during 115-85 Ma and after 25 Ma (Hilde et al., 1977). The second belt in East China consists of three paralleled NE sub-belts and two E-W sub-belts on which the volcanoes erupted throughout the Jurassic-Cretaceous period but the strong eruption centres were moving eastward with time. The continental rift-type basalts occurred in the middle of East China in Paleogene time. The Neogene-Quaternary basalts in East China belong to crack-type (Zheng and Zao, 1984). These ages and types of rocks suggest that subduction of the ancient Pacific Plate began at Triassic time and became stronger later. The Meso-Cenozoic volcanic belts, from north to south, can be divided into three different regions by the Tianshan-Xinganling and the Qinling tectonic lines in the middle of East Asia and two regions in the middle of the western Pacific. This difference has been getting clear since the Triassic time. On the whole, the Meso-Cenozoic volcanism in the middle of the western Pacific records reaction between the Asian Plate and the ancient Pacific Plate or the Indian Plate.

  19. Geochemistry of high-potassium rocks from the mid-Tertiary Guffey volcanic center, Thirtynine Mile volcanic field, central Colorado

    SciTech Connect

    Wobus, R.A.; Mochel, D.W. ); Mertzman, S.A.; Eide, E.A.; Rothwarf, M.T. ); Loeffler, B.M.; Johnson, D.A. ); Keating, G.N.; Sultz, K. ); Benjamin, A.E. ); Venzke, E.A. ); Filson, T. )

    1990-07-01

    The Guffey volcanic center is the largest within the 2000 km{sup 2} mid-Tertiary Thirtynine Mile volcanic field of central Colorado. This study is the first to provide extensive chemical data for these alkalic volcanic and subvolcanic rocks, which present the eroded remnants of a large stratovolcano of Oligocene age. Formation of early domes and flows of latite and trachyte within the Guffey center was followed by extrusion of a thick series of basalt, trachybasalt, and shoshonite flows and lahars. Plugs, dikes, and vents ranging from basalt to rhyolite cut the thick mafic deposits, and felsic tuffs breccias chemically identical to the small rhyolitic plutons are locally preserved. Whole-rack major and trace element analyses of 80 samples, ranging almost continuously from 47% to 78% SiO{sub 2}, indicate that the rocks of the Guffey center are among the most highly enriched in K{sub 2}O (up to 6%) and rare earth elements (typically 200-300 ppm) of any volcanic rocks in Colorado. These observations, along with the relatively high concentrations of Ba and Rb and the depletion of Cr and Ni, suggest an appreciable contribution of lower crustal material to the magmas that produced the Thirtynine Mile volcanic rocks.

  20. Reservoir Space Evolution of Volcanic Rocks in Deep Songliao Basin, China

    NASA Astrophysics Data System (ADS)

    Zheng, M.; Wu, X.; Zheng, M.; HU, J.; Wang, S.

    2015-12-01

    Recent years, large amount of natural gas has been discovered in volcanic rock of Lower Crataceous of Songliao basin. Volcanic reservoirs have become one of the important target reservoir types of eastern basin of China. In order to study the volcanic reservoirs, we need to know the main factors controlling the reservoir space. By careful obsercation on volcanic drilling core, casting thin sections and statistical analysis of petrophysical properties of volcanic reservoir in Songliao basin, it can be suggested that the igneous rock reservoir in Yingcheng formation of Lower Crataceous is composed of different rock types, such ad rohylite, rohylitic crystal tuff, autoclastic brecciation lava and so on. There are different reservoirs storage space in in various lithological igneous rocks, but they are mainly composed of primary stoma, secondary solution pores and fractures.The evolution of storage space can be divided into 3 stage: the pramary reservoir space,exogenic leaching process and burial diagenesis.During the evolution process, the reservoir space is effected by secondary minerals, tectonic movement and volcanic hydrothermal solution. The pore of volcanic reservoirs can be partially filled by secondary minerals, but also may be dissoluted by other chemical volcanic hydrothermal solution. Therefore, the favorable places for better-quality volcanic reservoirs are the near-crater facies of vocanic apparatus and dissolution zones on the high position of paleo-structures.

  1. Triple junction magmatism: a geochemical study of Neogene volcanic rocks in western California

    USGS Publications Warehouse

    Johnson, C.M.; O'Neil, J.R.

    1984-01-01

    Inception of volcanism at late Oligocene to Recent centers in the eastern Coast Ranges of California (ECR suite) regularly decreases in age northward and is correlated with the northward migration of the transform-transform-trench Mendocino triple junction (MTJ). Miocene volcanism in the southern California basin (SCB suite) is spatially and temporally associated with the transform-ridge-trench Rivera triple junction (RTJ). The tholeiitic to calc-alkaline rocks in both suites were erupted through older trench melange while arc magmatism was occurring several hundred kilometers to the east. Therefore they are not related to subduction zone magmatism, but instead to interactions of the MTJ and RTJ with the continental margin. The ECR rocks, dominantly intermediate to silicic in composition, have relatively high ??18O values up to 11.3, 87Sr 86Sr ratios up to 0.7055, as well as relatively high Th contents, suggesting that crustal anatexis played a dominant role in their generation. Coupled crystal fractionation and crustal assimilation by an initially basaltic magma cannot explain the high ??18O values and 87Sr 86Sr ratios because greater than 95% of the basalt would need to crystallize. In contrast, the SCB rocks, dominantly mafic to intermediate in composition, have relatively low ??18O values down to 5.2 and 87Sr 86Sr ratios down to 0.7025 suggesting that these rocks were derived dominantly from a mantle source. Whether crustal anatexis occurs is determined largely by the type of stress a triple junction imposes upon the continental margin. Both the MTJ and RTJ are associated with high heat flow and magma fluxes from the mantle. The transform-transform-trench MTJ is associated with locally variable mild extension to compression and therefore allows pooling of basaltic magma in the crust to initiate crustal melting. The high rates of continental extension associated with the transform-ridge-trench RTJ prevents such pooling of magma. The space created by decoupling

  2. Fission-track dating of volcanically derived sedimentary rocks

    SciTech Connect

    Kowallis, B.J.; Heaton, J.S.; Bringhurst, K.

    1986-01-01

    Depositional ages of sedimentary rocks can be determined using fission-track single grain ages on zircons from layers of volcanic ash or bentonite, even when the layers have been contaminated by older grains. This is done by compiling an age probability distribution or age spectrum for a sample from individual grain ages. An age spectrum is a simple and unambiguous way of testing for contamination and extracting useful age information. The youngest peak in the age spectrum approximates the time of deposition. In most contaminated samples, 30 or more grains should be counted to produce a reliable spectrum. However, useful, reproducible ages can be obtained by counting less than 10 grains in samples where most of the older, contaminating grains can be removed. The few older grains that remain after removing the obviously abraded ones may then be eliminated by examining the age spectrum. Although ages determined in this way are probably not precise enough for use in defining stratigraphic boundaries, they still provide a means of obtaining an isotopic age in sediments that cannot be dated by other radiometric methods. 18 references, 3 figures, 3 tables.

  3. Geology, geochronology and tectonic setting of late Cenozoic volcanism along the southwestern Gulf of Mexico: The Eastern Alkaline Province revisited

    NASA Astrophysics Data System (ADS)

    Ferrari, Luca; Tagami, Takahiro; Eguchi, Mugihiko; Orozco-Esquivel, Ma. Teresa; Petrone, Chiara M.; Jacobo-Albarrán, Jorge; López-Martínez, Margarita

    2005-09-01

    A NNW-trending belt of alkaline mafic volcanic fields parallels the Gulf of Mexico from the U.S. border southward to Veracruz state, in eastern Mexico. Previous studies grouped this volcanism into the so-called "Eastern Alkaline Province" (EAP) and suggested that it resulted from Gulf-parallel extensional faulting migrating from north to south from Oligocene to Present. On the basis of new geologic studies, forty-nine unspiked K-Ar and two 40Ar- 39Ar ages, we propose a new geodynamic model for the volcanism along the southwestern Gulf of Mexico. We studied in detail four of the six recognized fields of mafic alkaline volcanism in Veracruz state: 1) The lavas flows of Tlanchinol area (7.3-5.7 Ma), 2) the Alamo monogenetic field and Sierra de Tantima (7.6-6.6 Ma), 3) the Poza Rica and Metlatoyuca lava flows (1.6-1.3 Ma) and 4) the Chiconquiaco-Palma Sola area (6.9-3.2 Ma). Other two mafic volcanic fields may represent the continuation of alkaline volcanism to the southeast: the Middle Miocene lavas at Anegada High, offshore port of Veracruz, and the Middle to Late Miocene volcanism at the Los Tuxtlas. The existence of major Neogene extensional faults parallel to the Gulf of Mexico (i.e., ˜N-S to NNW-SSE) proposed in previous works was not confirmed by our geological studies. Elongation of volcanic necks, vent alignment, and faults mapped by subsurface data trend dominantly NE to ENE and NW to NNW. These directions are parallel to transform and normal faults that formed during the Late Jurassic opening of the Gulf of Mexico. Ascent of mafic magmas was likely facilitated and controlled by the existence of these pre-existing basement structures. Coupled with previous studies, our data demonstrate the occurrence of three magmatic episodes in Veracruz: 1) A Middle Miocene (˜15-11 Ma) episode in southern Veracruz (Palma Sola, Anegada, and Los Tuxtlas); 2) A Late Miocene to Early Pliocene (˜7.5-3 Ma) pulse of mafic alkaline volcanism throughout the study region; and 3) A

  4. Identification of kaolins and associated minerals in altered volcanic rocks by infrared spectroscopy.

    USGS Publications Warehouse

    Hunt, G.R.; Hall, R.B.

    1981-01-01

    Examples of visible and near-infrared spectra of altered volcanic rocks and their mineral constituents from Utah and Arizona are presented here to illustrate the potential of this spectral range. -from Authors

  5. Evaluation of early Archean volcaniclastic and volcanic flow rocks as possible sites for carbonaceous fossil microbes.

    PubMed

    Walsh, Maud M

    2004-01-01

    Sedimentary rocks have traditionally been the focus of the search for Archean microfossils; the Earth's oldest fossil bacteria are associated with carbonaceous matter in sedimentary cherts in greenstone belts in the eastern Pilbara block of Western Australia and Barberton greenstone belt of South Africa. Reports of possible fossils in a martian meteorite composed of igneous rock and the discovery of modern bacteria associated with basalts have stimulated a new look at Archean volcanic rocks as possible sites for fossil microbes. This study examines silicified volcaniclastic rocks, near-surface altered volcanic flow rocks, and associated stromatolite- like structures from the Archean Barberton greenstone belt to evaluate their potential for the preservation of carbonaceous fossils. Detrital carbonaceous particles are widely admixed with current-deposited debris. Carbonaceous matter is also present in altered volcanic flow rocks as sparse particles in silica veins that appear to be fed by overlying carbonaceous chert layers. Neither microfossils nor mat-like material was identified in the altered volcanic rocks or adjacent stromatolite-like structures. Ancient volcanic flow and volcaniclastic rocks are not promising sites for carbonaceous fossil preservation.

  6. Evaluation of early Archean volcaniclastic and volcanic flow rocks as possible sites for carbonaceous fossil microbes.

    PubMed

    Walsh, Maud M

    2004-01-01

    Sedimentary rocks have traditionally been the focus of the search for Archean microfossils; the Earth's oldest fossil bacteria are associated with carbonaceous matter in sedimentary cherts in greenstone belts in the eastern Pilbara block of Western Australia and Barberton greenstone belt of South Africa. Reports of possible fossils in a martian meteorite composed of igneous rock and the discovery of modern bacteria associated with basalts have stimulated a new look at Archean volcanic rocks as possible sites for fossil microbes. This study examines silicified volcaniclastic rocks, near-surface altered volcanic flow rocks, and associated stromatolite- like structures from the Archean Barberton greenstone belt to evaluate their potential for the preservation of carbonaceous fossils. Detrital carbonaceous particles are widely admixed with current-deposited debris. Carbonaceous matter is also present in altered volcanic flow rocks as sparse particles in silica veins that appear to be fed by overlying carbonaceous chert layers. Neither microfossils nor mat-like material was identified in the altered volcanic rocks or adjacent stromatolite-like structures. Ancient volcanic flow and volcaniclastic rocks are not promising sites for carbonaceous fossil preservation. PMID:15684724

  7. Sr, Nd, Pb Isotope geochemistry and magma evolution of the potassic volcanic rocks, Wudalianchi, Northeast China

    USGS Publications Warehouse

    Junwen, W.; Guanghong, X.; Tatsumoto, M.; Basu, A.R.

    1989-01-01

    Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in eastern China. Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolution. They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.87Sr /86 Sr is higher and143Nd/144Nd is lower than the undifferentiated global values. In comparison to continental potash volcanic rocks, Pb isotopes are apparently lower. These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material. The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition. ?? 1989 Institute of Geochemistry, Chinese Academy of Sciences.

  8. Uranium mineralization in fluorine-enriched volcanic rocks

    SciTech Connect

    Burt, D.M.; Sheridan, M.F.; Bikun, J.; Christiansen, E.; Correa, B.; Murphy, B.; Self, S.

    1980-09-01

    Several uranium and other lithophile element deposits are located within or adjacent to small middle to late Cenozoic, fluorine-rich rhyolitic dome complexes. Examples studied include Spor Mountain, Utah (Be-U-F), the Honeycomb Hills, Utah (Be-U), the Wah Wah Mountains, Utah (U-F), and the Black Range-Sierra Cuchillo, New Mexico (Sn-Be-W-F). The formation of these and similar deposits begins with the emplacement of a rhyolitic magma, enriched in lithophile metals and complexing fluorine, that rises to a shallow crustal level, where its roof zone may become further enriched in volatiles and the ore elements. During initial explosive volcanic activity, aprons of lithicrich tuffs are erupted around the vents. These early pyroclastic deposits commonly host the mineralization, due to their initial enrichment in the lithophile elements, their permeability, and the reactivity of their foreign lithic inclusions (particularly carbonate rocks). The pyroclastics are capped and preserved by thick topaz rhyolite domes and flows that can serve as a source of heat and of additional quantities of ore elements. Devitrification, vapor-phase crystallization, or fumarolic alteration may free the ore elements from the glassy matrix and place them in a form readily leached by percolating meteoric waters. Heat from the rhyolitic sheets drives such waters through the system, generally into and up the vents and out through the early tuffs. Secondary alteration zones (K-feldspar, sericite, silica, clays, fluorite, carbonate, and zeolites) and economic mineral concentrations may form in response to this low temperature (less than 200 C) circulation. After cooling, meteoric water continues to migrate through the system, modifying the distribution and concentration of the ore elements (especially uranium).

  9. Geochronology and geochemistry of Eocene-aged volcanic rocks around the Bafra (Samsun, N Turkey) area: Constraints for the interaction of lithospheric mantle and crustal melts

    NASA Astrophysics Data System (ADS)

    Temizel, İrfan; Arslan, Mehmet; Yücel, Cem; Abdioğlu, Emel; Ruffet, Gilles

    2016-08-01

    40Ar-39Ar age, whole-rock chemical, and Sr-Nd isotope data are presented for the post-collisional, Eocene (51.3-44.1 Ma)-aged volcanic rocks from the Bafra (Samsun) area in the western part of the Eastern Pontides (N Turkey) aiming to unravel their sources and evolutionary history. The studied Eocene volcanic rocks can be divided into two groups: analcime-bearing (tephritic lava flows and dykes) and analcime-free (basaltic to trachytic lava flows and basaltic dykes). The analcime-bearing volcanic rocks have a fine-grained porphyritic texture with clinopyroxene phenocrysts, whereas analcime-free volcanic rocks show a variety of textures including hyalo-microlitic microgranular porphyritic, intersertal, trachytic, fluidal, and glomeroporphyritic. The volcanic rocks also show evidence of mineral-melt disequilibrium textures such as sieved, rounded, and corroded plagioclases, partially melted and dissolved clinopyroxenes and poikilitic texture. Petrochemically, the parental magmas of the volcanic rocks evolved from alkaline to calc-alkaline lava suites and include high-K and shoshonitic compositions. They display enrichments in light rare earth and large ion lithophile elements such as Sr, K, and Rb, as well as depletions in high field strength elements such as Nb, Ta, Zr, and Ti, resembling subduction-related magmas. The analcime-bearing and -free volcanic rocks share similar incompatible element ratios and chondrite-normalised rare rearth element patterns, indicating that they originated from similar sources. They also have relatively low to moderate initial 87Sr/86Sr (0.7042-0.7051), high positive εNd(t) values (+ 0.20 to + 3.32), and depleted mantle Nd model ages (TDM1 = 0.63-0.93 Ga, TDM2 = 0.58-0.84 Ga). The bulk-rock chemical and Sr-Nd isotope features as well as the high Rb/Y and Th/Zr, but low Nb/Zr and Nb/Y ratios, indicate that the volcanic rocks were derived from a lithospheric mantle source that had been metasomatised by slab-derived fluids. Trace element

  10. Relation of Volcanism to Crustal Deformation in Klamath Falls, Oregon: Transition from Calc-alkaline Basaltic Andesite to High Alumina Olivine Tholeiite

    NASA Astrophysics Data System (ADS)

    Priest, G. R.; Hladky, F. R.; Murray, R. B.

    2009-12-01

    This paper is based on geologic mapping by Priest et al. (2008) at Klamath Falls, Oregon on the southernmost end of the Klamath Graben. Northeast-southwest extension across this area caused northeast tilting of fault blocks on the east side and southwest tilting of blocks on the west side of the Graben. Dominant strike of these Basin and Range fault blocks is N. 30-40° W. At Klamath Falls the two opposing groups of tilted blocks are separated not by a keystone graben but by a complex of bounding faults striking ~N. 65° W. The bounding faults appear to have components of right-lateral or reverse motion, cut rocks dated at ~4 Ma, and terminate to the northwest against northeast-striking faults at the southern boundary of the Graben. Normal faults within the study area cut basalt dated at 1.8 Ma on the west side of the Graben. Holocene talus is cut on the east side of the Graben immediately north of the study area. The 1993 magnitude 5.9 and 6.0 earthquakes on the west margin of the Klamath Graben are evidence that extensional deformation is continuing there. The youngest proven deformation in the map area south of the Graben boundary is offset Pleistocene alluvial fans at the base of Hogback Mountain. These fans are now preserved as discontinuous hills but once filled the local Altamont basin by up to 150 m higher than its present surface. Much of this sand and gravel has been eroded, possibly coincident with breaching of the basin at ~1 Ma by headward erosion of the Klamath River. Magmatic composition changed as crustal extension in the area progressed and the width of the Cascade volcanic arc decreased. Between ~6 and 4 Ma, calc-alkaline basaltic andesite and andesite from local volcanic centers of the volcanic arc flowed unimpeded across the area, thus the current Basin and Range topography had not developed. Angular unconformities within sequences of volcanic and volcaniclastic rocks dated at 4-2.7 Ma indicate contemporaneous tilting of fault blocks, but much

  11. Whole-rock geochemistry and Sr-Nd-Pb isotope systematics of the Late Carboniferous volcanic rocks of the Awulale metallogenic belt in the western Tianshan Mountains (NW China): Petrogenesis and geodynamical implications

    NASA Astrophysics Data System (ADS)

    Ge, Songsheng; Zhai, Mingguo; Safonova, Inna; Li, Dapeng; Zhu, Xiyan; Zuo, Pengfei; Shan, Houxiang

    2015-07-01

    The Awulale metallogenic belt (AMB) of the western Tianshan (NW China) includes Late Carboniferous (ca. 320 Ma) ore-bearing volcanic rocks of the Dahalajunshan Formation. The petrogenesis and tectonic setting of these volcanic rocks are important for the understanding of the tectonic evolution and metallogeny of the western Tianshan. This paper presents new major and trace elements and Sr-Nd-Pb isotope data from the Dahalajunshan volcanic rocks, which are mainly calc-alkaline basaltic trachy-andesite and trachy-andesite with subordinate basalt, trachy-basalt and rhyolite. The variations of major and trace elements in the mafic and intermediate volcanic rocks indicate the fractionation of pyroxene and magnetite or hornblende, magnetite, apatite and plagioclase, respectively, during their petrogenesis. The Dahalajunshan volcanic rocks have similar primitive mantle-normalized diagrams and chondrite-normalized rare-earth element (REE) patterns suggesting their similar mantle source(s). They are characterized by enrichment in large ion lithophile elements (LILEs) and light REEs (LREEs), depletion in heavy REEs (LaN/YbN ≈ 2.80 to 9.59) and high field strength elements (HFSEs) and εNd(t) ranging from + 1.2 to + 6.0 at 86Sr/87Sr(t) = 0.7047-0.7063 and 206Pb/204Pbi = 17.49-18.19. Both the geochemical and isotopic data indicate that the volcanic rocks were probably derived by low-degree melting of sub-arc lithospheric mantle modified by fluids in a continental arc setting. Our obtained results, in conjunction with previous published data, allow us to suggest that the southward subduction of Junggar oceanic crust continued until the Late Carboniferous and was followed by a tectonic shift from continental arc to post-collisional extension environment.

  12. Influence of hydrothermal processes on changes of volcanic rocks (data of physical modelling)

    NASA Astrophysics Data System (ADS)

    Shanina, V. V.; Bychkov, A. Y.

    2009-04-01

    Due to active development of geothermal energy, in middle of the last century have begun papers devoted to experiments, directed on study of transformations of minerals [4] and rocks [1, 2, 5] under action of geothermal processes. But any researcher did not estimate thus change of their physical and physico-mechanical properties. The purpose of job - to study character and dynamics changes of volcanic rocks (to simulate conditions of geothermal transformations). Tasks: creation of the whole series of experiments in autoclavs at various temperatures, pressure and composition of solutions, preparation of samples, study of chemical and mineral composition, structure and properties of rocks and solutions before and after experiments. In 2006 the first similar experiments were begun [3]. Researched rocks basalts, hyaloclasites and obsidian, selected from Iceland and tuffs Payzhetka Geothermal Field, Southern Kamchatka, Russia. Were used autoclavs, consisting from titanic of an alloy ВТ-8, volume 116-119 мл, in each of which was located from 2 up to 4 samples of rocks of the investigated structure and properties. The heating was made in OVEN ТРМ-10 with accuracy + 1 °С, the constancy of temperature was supervised by thermocouples. 15 experiences (temperature 200, 300 and 450 °С; pressure 16, 86 and 1000 bars accordingly now are carried out; 4 solutions (1 alkaline and 3 acid); duration 14, 15, 30 and 60 days). All four groups of the investigated rocks appreciablly react under geothermal influence. The changes are observed in colour of samples (brighten in acid solutions), their microstructure, that for basalts is visible only in raster electronic microscope, and in education of new mineral phases, is especially active in a acid solution, the X-Ray analysis (has executed by Dr. Krupskaya V.V., apparatuses - DRON- UM1) has shown, that 94,2 % is smectite, 3,5 % - kaolinite, 1,2 % - crisrobalite, 1,1 % - diopside (?), in others pores fills chlorite, and in an

  13. Influence of hydrothermal processes on changes of volcanic rocks (data of physical modelling)

    NASA Astrophysics Data System (ADS)

    Shanina, V. V.; Bychkov, A. Y.

    2009-04-01

    Due to active development of geothermal energy, in middle of the last century have begun papers devoted to experiments, directed on study of transformations of minerals [4] and rocks [1, 2, 5] under action of geothermal processes. But any researcher did not estimate thus change of their physical and physico-mechanical properties. The purpose of job - to study character and dynamics changes of volcanic rocks (to simulate conditions of geothermal transformations). Tasks: creation of the whole series of experiments in autoclavs at various temperatures, pressure and composition of solutions, preparation of samples, study of chemical and mineral composition, structure and properties of rocks and solutions before and after experiments. In 2006 the first similar experiments were begun [3]. Researched rocks basalts, hyaloclasites and obsidian, selected from Iceland and tuffs Payzhetka Geothermal Field, Southern Kamchatka, Russia. Were used autoclavs, consisting from titanic of an alloy ВТ-8, volume 116-119 мл, in each of which was located from 2 up to 4 samples of rocks of the investigated structure and properties. The heating was made in OVEN ТРМ-10 with accuracy + 1 °С, the constancy of temperature was supervised by thermocouples. 15 experiences (temperature 200, 300 and 450 °С; pressure 16, 86 and 1000 bars accordingly now are carried out; 4 solutions (1 alkaline and 3 acid); duration 14, 15, 30 and 60 days). All four groups of the investigated rocks appreciablly react under geothermal influence. The changes are observed in colour of samples (brighten in acid solutions), their microstructure, that for basalts is visible only in raster electronic microscope, and in education of new mineral phases, is especially active in a acid solution, the X-Ray analysis (has executed by Dr. Krupskaya V.V., apparatuses - DRON- UM1) has shown, that 94,2 % is smectite, 3,5 % - kaolinite, 1,2 % - crisrobalite, 1,1 % - diopside (?), in others pores fills chlorite, and in an

  14. Precursors predicted by artificial neural networks for mass balance calculations: Quantifying hydrothermal alteration in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Trépanier, Sylvain; Mathieu, Lucie; Daigneault, Réal; Faure, Stéphane

    2016-04-01

    This study proposes an artificial neural networks-based method for predicting the unaltered (precursor) chemical compositions of hydrothermally altered volcanic rock. The method aims at predicting precursor's major components contents (SiO2, FeOT, MgO, CaO, Na2O, and K2O). The prediction is based on ratios of elements generally immobile during alteration processes; i.e. Zr, TiO2, Al2O3, Y, Nb, Th, and Cr, which are provided as inputs to the neural networks. Multi-layer perceptron neural networks were trained on a large dataset of least-altered volcanic rock samples that document a wide range of volcanic rock types, tectonic settings and ages. The precursors thus predicted are then used to perform mass balance calculations. Various statistics were calculated to validate the predictions of precursors' major components, which indicate that, overall, the predictions are precise and accurate. For example, rank-based correlation coefficients were calculated to compare predicted and analysed values from a least-altered test dataset that had not been used to train the networks. Coefficients over 0.87 were obtained for all components, except for Na2O (0.77), indicating that predictions for alkali might be less performant. Also, predictions are performant for most volcanic rock compositions, except for ultra-K rocks. The proposed method provides an easy and rapid solution to the often difficult task of determining appropriate volcanic precursor compositions to rocks modified by hydrothermal alteration. It is intended for large volcanic rock databases and is most useful, for example, to mineral exploration performed in complex or poorly known volcanic settings. The method is implemented as a simple C++ console program.

  15. 231Pa systematics in postglacial volcanic rocks from Iceland

    NASA Astrophysics Data System (ADS)

    Turner, Simon; Kokfelt, Thomas; Hoernle, Kaj; Lundstrom, Craig; Hauff, Folkmar

    2016-07-01

    Several recent studies have highlighted the potential of combined 238U-230Th and 235U-231Pa systematics to constrain upwelling rates and the role of recycled mafic lithologies in mantle plume-derived basalts. Accordingly, we present measurements of the 231Pa concentrations from 26 mafic volcanic rocks from Iceland, including off-axis basalts from the Snaefellsnes Peninsula, to complement previously published 238U-230Th-226Ra data. 231Pa concentrations vary from 27 to 624 fg/g and (231Pa/235U) ratios from 1.12 to 2.11 with the exception of one anomalous sample from the Southeast Rift which has a 231Pa deficit with (231Pa/235U) = 0.86. An important new result is that basalts from the Southeast Rift and the Snaefellsnes Peninsula define a trend at relatively low (231Pa/235U) for a given (230Th/238U) ratio. Many of the remaining samples fall in or around the global field for ocean island basalts but those from the Mid-Iceland Belt and the Southwest Rift/Reykjanes Peninsula extend to higher (231Pa/235U) ratios at a given (230Th/238U), similar to mid-ocean ridge basalts. In principle, these lavas could result from melting of peridotite at lower pressures. However, there is no reason to suspect that the Mid-Iceland Belt and the Southwest Rift lavas reflect shallower melting than elsewhere in Iceland. In our preferred model, these lavas reflect melting of garnet peridotite whereas those from the Southeast Rift and the Snaefellsnes Peninsula contain a significant contribution (up to 20%) of melt from garnet pyroxenite. This is consistent with incompatible trace element and radiogenic isotope evidence for recycled oceanic crust in these lavas. There is increasing agreement that the displacement of ocean island basalts to lower (231Pa/235U) ratios at a given (230Th/238U), compared to mid-ocean ridge basalts, reflects the role of recycled mafic lithologies such as garnet pyroxenite as well as higher average pressures of melting. It now seems likely that this interpretation may

  16. Observations of 231Pa/ 235U disequilibrium in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Pickett, David A.; Murrell, Michael T.

    1997-04-01

    We present here the first survey of ( 231Pa/ 235U) ratios in volcanic rocks; such measurements are made possible by new mass spectrometric techniques. The data place new constraints on the timing and extent of magma source and evolutionary processes, particularly due to the sensitivity of the 231Pa- 235U pair and its intermediate time scale ( 231Pat 1/2 = 33 ky). ( 231Pa/ 235U) is found to vary widely, from 0.2 in carbonatites to 1.1-2.9 in basalts and 0.9-2.2 in arcs. Substantial Pa enrichment is nearly ubiquitous, suggestive of the relative incompatibility of Pa, qualitatively consistent with available partitioning data. The level of 231Pa- 235U disequilibrium typically far exceeds that of 230Th- 238U and is comparable to 226Ra- 230Th. The high ( 231Pa/ 235U) ratios in MORB and other basalts reflect a large degree of discrimination between two incompatible elements, posing challenges for modelling of melt generation and migration. Fundamental differences in ( 231Pa/ 235U) among different basaltic environments are likely related to contrasts in melting zone conditions (e.g., melting rate). Strong ( 231Pa/ 235U) disequilibria in continental basalts, for which ( 230Th/ 238U) disequilibria are small or absent, demonstrate that Pa-U fractionation is possible in both garnet and spinel mantle stability fields. In arcs, correlation of ( 231Pa/ 235U) and ( 230Th/ 238U) is consistent with U enrichment via slab-derived fluids, a process which is additional to the still dominant Pa enrichment. An important new constraint is provided by the observation that the near-equilibrium ( 230Th/ 238U) common to arcs and continental basalts is not typically accompanied by near-equilibrium ( 231Pa/ 235U), arguing against the influence of long magma history, crustal material, or equilibrium mantle sources in affecting decay-series ratios. Small sample sets from two silicic centers illustrate: (1) recent, rapid U enrichment in the magma chamber (El Chichón); and (2) the failure of

  17. Late Middle Eocence Nanny Creek calc-alkaline volcanic field, NE Nevada and NW Utah: Age, extent, and implications for Eocene tectonics

    SciTech Connect

    Thorman, C.H.; Brooks, W.E.; Snee, L.W.; Potter, C.J.; Dubiel, R.J.; Ketner, K.B. )

    1993-04-01

    Eighteen new [sup 40]Ar/[sup 39]Ar dates indicate that widespread rhyolitic to andesitic calc-alkaline volcanic rocks in NE Nevada and NW Utah are part of a distinct eruptive sequence that is late Middle Eocene in age, considerably older than previously believed. Most of the rocks were erupted at 41--39 Ma. The presently recognized extent of the field spans 11 ranges from near Elko on the west to the Silver Island Mts on the east and from 20 miles north of Wells to the southern Deep Creek Range. The authors informally designate this the Nanny Creek volcanic field, the type area being Nanny Creek, in the northern Pequop Mts, where compositional and stratigraphic features of the field are clearly displayed. Typically, the base of the sequence includes one or more rhyolite ash-flow tuffs and (or) dacite flows; sources for the tuffs probably were outside the study area as they all appear to be outflow-facies rocks. The similarities in age, chemistry, and mode of occurrence of these rocks throughout their extent indicate that they are all part of the same eruptive sequence. The widespread occurrence of ash-flows in the lower part of the eruptive cycle suggests that the region initially was one of moderate to low relief. The central part of the field rests with angular discordance on Devonian to Triassic rocks, whereas the western and eastern parts rest with angular discordance on lower Eocene rocks (Elko and White Sage basinal rocks, respectively). Ostracode-bearing limestones at several localities in the central part of the field are parallel to the overlying volcanics rocks; the authors interpret the limestones to be correlative with the Elko and White Sage and the limestone/volcanic contact to be a disconformity that is correlative with the angular unconformities to the east and west. These relationships identify a widespread pre-late Middle Eocene deformational event during which the Elko and White Sage basins, but not the intervening area, were deformed.

  18. The Implications of Petit-Spot Volcanism for the Origin of Alkaline Intraplate Magmas

    NASA Astrophysics Data System (ADS)

    Pilet, S.; Rochat, L.; Abe, N.

    2014-12-01

    The compositions of alkaline lavas are mostly similar even though they are observed in various tectonic contexts. This similarity has been used to suggest that these rocks are all produced by deep processes. Nevertheless, the formation of petit-spot seamounts, which are interpreted as low-degree melts extracted from the base of the lithosphere in response to plate flexure, demonstrates that alkaline lavas could also be produced by shallow tectonic processes. In this presentation, petit-spot lavas will be compared to intraplate basalts to reveal the processes that control the petrogenesis of intraplate lavas. Petit-spot lavas are characterized by an alkaline basaltic composition rich in potassium (K2O/Na2O>0.7). This distinguishes them from oceanic island basalts, which are characterized by a lower alkali ratio. The K-rich nature of petit-spot melts is explained either by the melting of an asthenospheric mantle domain enriched in K2O, TiO2 and trace elements, or by the interaction of low-degree melts extracted from the low velocity zone (LVZ) with phlogopite-rich metasomatic lithologies present in the lower part of the lithospheric mantle; metasomatic cumulates formed during an early stage of LVZ melt migration. The latter model is supported by the recent discovery of metasomatized peridotite xenoliths in petit-spot lavas which demonstrates that low degree melts, similar in composition to the melts responsible for the formation of phlogopite-rich cumulates in continental lithospheric mantle, percolate through the oceanic lithospheric mantle producing a metasomatic enrichment. The involvement of metasomatic processes in the formation of petit-spot lavas provides a link to the metasomatic lithospheric model for the origin of alkaline magmas, a model that suggests that these rocks are not produced directly from the asthenosphere, but by the melting of hydrous veins produced by the percolation and differentiation of low degree asthonospheric melts across the

  19. Anorthosites and alkaline rocks from the deep crust of peninsular India

    NASA Technical Reports Server (NTRS)

    Leelanandam, C.; Ratnakar, J.; Reddy, M. Narsimha

    1988-01-01

    The anorthosite and alkaline rock localities in the Precambrian Shield of Peninsular India were reviewed. There are approximately 50 localities of such rocks, generally restricted to the Eastern Ghats mobile belt. The alkaline plutons are typically confined to the margin of the Eastern Ghats. The anorthosites are all greater than 500 sq km, but many exhibit similarities to one another. It was suggested that the anorthosites are associated with cryptic sutures, and are thought to have originated as a result of ponding of basaltic magmas. An analogy was drawn between the Eastern Ghats belt and the Grenville Province of the Canadian Shield.

  20. Petrology and geochemistry of the Late Cenozoic volcanic rocks of the Dominican Republic

    SciTech Connect

    Vespucci, P.D.

    1988-01-01

    Late Cenozoic rocks of Hispaniola are subdivided into two petrographically and geochemically contrasting series, a calc-alkaline series (CA-series), and a mafic alkaline series (MA-series). The CA-series are basalts, basaltic andesites, trachyandesites, and dacites occurring in several eruptive centers in the southern part of the Cordillera Central of the Dominican Republic. MA-series basalts are alkali-olivine basalts and limburgitic basalts occurring in the San Juan Valley of the Dominican republic and in the Cul de Sac of south central Haiti. Olivine, clinopyroxene, amphibole, mica, feldspar, and titanomagnetite were analyzed for major element chemical composition. MA-series basalts are slightly to moderately silica undersaturated, have high TiO2 (>1.5%) and MgO (>5.0%) and moderately high total alkalis (>2.0%). MA-series basalts are enriched in K, Rb, Sr, Ba, U, Th and LREEs with Ba/La ratios around 0.98. REE patterns are fractionated (chrondrite normalized La/Yb ratios around 62, and La/Sm ratios around 6). HFS elements Zr, Hf, Nb, and Ta are high resembling intraplate basalts. 86SR/87SR ratios are high (0.7060-0.7070) with low Rb/Sr ratios (0.03 to 0.15). Basalts, basaltic andesites, trachyandesites, and dacites of the CA-series show low MgO (<5.0%) and TiO2(<2.0%), and moderately high total alkali contents (2 to 7%). Enrichment is seen in K Rb, Sr, Ba, Th, U, and LREEs with Ba/La ratios as high as 5.6 REE patterns are fractionated to a lesser degree compared to the MA-series (chondrite normalized La/Yb around 23, and La/Sm ratios less than 5). HFS elements are lower resembling typical island arc volcanic rocks. CA-series have 87Sr/86Sr ratios (.7043-.7053), with low Rb/Sr ratios as in the MA-series.

  1. Geochronology and geochemistry of Early Jurassic volcanic rocks in the Erguna Massif, northeast China: Petrogenesis and implications for the tectonic evolution of the Mongol-Okhotsk suture belt

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Tang, Jie; Xu, Wen-Liang; Wang, Feng

    2015-03-01

    The Mongol-Okhotsk suture belt played an important role in the tectonic evolution of northeast Asia during the Mesozoic. However, few studies have examined the influence of this tectonic belt on the geological evolution of northeast China. In this paper, we present zircon U-Pb geochronology, major and trace element geochemistry, and zircon Hf-O isotopic data for Early Jurassic volcanic rocks in the Erguna Massif of northeast China, with the aim of constraining the evolution of the Mongol-Okhotsk suture belt and its influence on the tectonic history of China during the Early Jurassic. Zircon U-Pb dating indicates that the trachybasalt and basaltic andesite in the study area were erupted between 193 ± 5 Ma and 181 ± 9 Ma (i.e., in the Early Jurassic). These Early Jurassic volcanic rocks belong to the high-K calc-alkaline series and are enriched in large ion lithophile elements and light rare earth elements, as well as being depleted in heavy rare earth elements and high field strength elements such as Nb and Ta. The rocks show a small negative Eu anomaly. The zircon εHf (182 Ma) values of the volcanic rocks range from - 1.9 to + 5.1, corresponding to TDM1 values of 640-901 Ma and TDM2 values of 901-1345 Ma. Zircons from two volcanic rocks yield δ18O values of 7.2‰ ± 1.5‰ (n = 19) and 6.6‰ ± 0.7‰ (n = 35). Geochemically, these Early Jurassic volcanic rocks are similar to those from active continental margin settings, and their primary magmas could have been derived from the partial melting of a lithospheric mantle wedge modified by fluid from a subducted slab. The discovery of Early Jurassic calc-alkaline volcanic rocks in the Erguna Massif, together with the coeval porphyry Cu-Mo deposits, indicates that an active continental margin existed in the Erguna area during the Early Jurassic. Taken together, we conclude that southward subduction of the Mongol-Okhotsk oceanic plate took place beneath the Erguna Massif during the Early Jurassic.

  2. Preliminary results of wildcat drilling in Absaroka volcanic rocks, Hot Springs County, Wyoming

    SciTech Connect

    Bailey, M.H.; Sundell, K.A.

    1986-08-01

    Recent drilling of three remote, high-elevation wildcat wells has proven that excellent Paleozoic reservoirs are present at shallow depths beneath Eocene volcaniclastic rocks. The Tensleep and Madison Formations are fluid filled above an elevation of 8000 ft, and all Paleozoic formations exhibit shows of oil and gas. These prolific reservoir rocks have produced billions of barrels of oil from the adjacent Bighorn and Wind river basins, and they pinch out with angular unconformity against the base of the volcanics, providing enormous potential for stratigraphic oil accumulations. Vibroseis and portable seismic data have confirmed and further delineate large anticlines of Paleozoic rocks, which were originally discovered by detailed surface geologic mapping. These structures can be projected along anticlinal trends from the western Owl Creek Mountains to beneath the volcanics as well. The overlying volcanics are generally soft, reworked sediments. However, large, hard boulders and blocks of andesite-dacite, which were previously mapped as intrusives, are present and are the result of catastrophic landslide/debris flow. The volcanics locally contain highly porous and permeable sandstones and abundant bentonite stringers. Oil and gas shows were observed throughout a 2400-ft thick interval of the Eocene Tepee Trail and Aycross Formations. Shows were recorded 9100 ft above sea level in the volcanic rocks. A minimum of 10 million bbl of oil (asphaltum) and an undetermined amount of gases and lighter oils have accumulated within the basal volcanic sequence, based on the evaluation of data from two drill sites. Significant amounts of hydrocarbons have migrated since the volcanics were deposited 50 Ma. Large Laramide anticlines were partially eroded and breached into the Paleozoic formations and resealed by overlying volcanics with subsequent development of a massive tar seal.

  3. Age and tectonic significance of volcanic rocks in the northern Los Angeles Basin, California

    USGS Publications Warehouse

    McCulloh, Thane H.; Fleck, Robert J.; Denison, Rodger E.; Beyer, Larry A.; Stanley, Richard G.

    2002-01-01

    Volcanic rocks, mostly basalts and some andesites, are interbedded with middle Miocene strata and are overlain by younger rocks throughout the greater part of the Los Angeles Basin, California. Roughly correlative flows, previously dated radiometrically (or paleontologically) at about 16.4 to 10.7 Ma, crop out in five separate regions around the basin perimeter. Los Angeles Basin volcanic rocks have special meaning because they offer clues to tectonomagmatic events associated with onset of clockwise transrotation of the western Transverse Ranges region and to the timing and locus of the initial basin opening. Whole-rock 40Ar/39Ar dating of near-tholeiitic olivine basalts of the Topanga Formation (Hoots, 1931) from three sites in the easternmost Santa Monica Mountains, combined with 87Sr/86Sr dating of fossil carbonates from interstratified marine beds at nine sites, establish a new age of 17.4 Ma for these oldest known Topanga-age volcanics of the Los Angeles Basin. We also record three new 40Ar/39Ar ages (15.3 Ma) from andesitic flows of the lower Glendora Volcanics at the northeast edge of the basin, 70 km east of the Santa Monica Mountains. A whole-rock determination of 17.2±0.5 Ma for nearby altered olivine basalt in the unfossiliferous Glendora volcanic sequence is questionable because of a complex 40Ar/39Ar age spectrum suggestive of 39Ar recoil, but it may indicate an older volcanic unit in this eastern area. We hypothesize that the 17.4-Ma volcanics in the eastern Santa Monica Mountains are an early expression of deep crustal magmatism accompanying the earliest extensional tectonism associated with rifting. The extremely thick younger volcanic pile in the western and central parts of the range may suggest that this early igneous activity in the eastern area was premonitory. Paleomagnetic declination data are needed to determine the pre-transrotational orientation of the eastern Santa Monica Mountains volcanic sequence. The new age determinations do not

  4. Marano volcanic rocks, East Azarbaijan Province, Iran, and associated Fe mineralisation

    NASA Astrophysics Data System (ADS)

    Karimzadeh Somarin, A.

    2004-10-01

    There are two main types of economic iron ore deposits in Iran: (1) magmatic segregation deposits and (2) skarns. Most of the hydrothermal iron deposits in Iran, except for the skarns, are uneconomic. One of these uneconomic hydrothermal deposits is the Marano Fe deposit, located in East Azarbaijan Province (NW Iran). This deposit is considered to have been formed by an epithermal style of mineralisation related to a volcanic-dome. There are 5 volcanic domes in the Marano area, ranging in composition from dacite to rhyolite. The volcanic rocks show geochemical evidence of fractionation of biotite, hornblende, magnetite, apatite and feldspars. The Marano volcanic domes crystallised from an I-type magma, formed in a volcanic arc setting. Fe mineralisation has occurred around one of these Marano domes (MA dome) in which the igneous rocks contain more biotite and hornblende and are less fractionated than in the other domes. The main Fe oxide, hematite, occurs as veins and disseminations in sedimentary wall rocks. Alteration of the minerals in the host rocks suggests aS2<10-9.5, aO2>10-34.2 and pH<5.5. The small size and shallow-level of emplacement of magma, together with the absence of extensive hydrothermally altered zones, shows that the hydrothermal system was not voluminous enough to form an economic iron deposit.

  5. Evidence of crustal contamination, sediment, and fluid components in the campanian volcanic rocks

    USGS Publications Warehouse

    Paone, A.

    2004-01-01

    The Campanian Volcanic Subprovince is part of the classic western potassic volcanic province of the Italian Peninsula. The Campanian volcanic products show the effects of shallow assimilation and fractional crystallisation, and the contribution of regional crustal sources (e.g., Hercynian basement-Calabrian crust). The Roccamonfina, Campi Flegrei, and Ventotene volcanic rocks are characterised by wide isotopic and geochemical variations. Such variations appear to reflect both AFC processes and chemical heterogeneity in the upper mantle that may be linked to subduction processes. Mixing curves (Th/Ce-, Ba/K- and Eu/Eu*-143Nd/144Nd) linking sediments and mantle end-members account for the variations in the Campanian Subprovince volcanic rocks with a sediment contribution of 2-10%. The upper mantle sources for the low- and high-K rocks at Roccamonfina have been constrained on the basis of a multi-element normalised diagram. The two sources require different amounts of sediment in the mantle wedge (LK???2% versus HK???10%) and a fluid component probably from altered ocean crust to explain the fluid mobile elements. Low-K Roccamonfina rocks are geochemically similar to those from Campi Flegrei, Ventotene, and Somma-Vesuvius, suggesting a similar proportion of sediment in their upper mantle source regions. ?? 2004 B.V. All rights reserved.

  6. Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

    USGS Publications Warehouse

    Asmeroma, Y.; Damon, P.; Shafiqullah, M.; Dickinson, W.R.; Zartman, R.E.

    1991-01-01

    We report a nine-point RbSr whole-rock isochron age of 70??3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ?? 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism. ?? 1991.

  7. Relationship between Los Angeles attrition test and Nordic abrasion test of volcanic rocks

    NASA Astrophysics Data System (ADS)

    Krutilová, Kateřina; Prikryl, Richard

    2015-04-01

    Various volcanic rocks contribute significantly to the production of crushed stone in the Czech Republic. When used for road surfacing, results of Los Angeles attrition test (LA value below 25 or 30 depending on the mode of use) together with polished stone value are required. In the recent study, we have focused on the search for possible correlation between results obtained by Los Angeles attrition test and Nordic abrasion test, a test widely employed in Scandinavia. For the experimental study, a set of volcanic rocks from 36 active quarries was used. The rocks under study represent range of volcanic rocks from ultrabasic to acid members, formed form Neoproterozoic to Tertiary. The most favourable results of Los Angeles attrition test (i.e. the lowest LA values) were obtained for basalts (range of values 9.4-19.4) and spilites (range of values 8.4-14.9) which are in fact Neoproterozoic to Late Palaeozoic basalts affected by low grade metamorphism. Nordic abrasion test exhibited much broader range of values (6.4 to 36.9) with average value at 15.2 for basalts, resulting in weak coefficient of determination (0.19). . On contrary, narrow range of values from Nordic abrasion test of spilites (7.2-15.9), very similar to the range of LA values, is reflect in higher coefficient of determination (0.56). On contrary, the least favourable properties (LA values 12.3-29.2, Nordic abrasion 16.8-43.3) have been observed for a group of basic to intermediate rocks classified in older literature as melaphyres and diabases (ranging from basalts to trachyndesites and/or trachybasalts) of Palaeozoic age. However, in this specific group of volcanic rocks, the highest coefficient of determination (0.89) between both tests has been achieved. For volcanic rocks exhibiting acid composition (rhyolites and quartz porphyry), coefficient of determination between LA values (15.1-19.3) and Nordic abrasion test (7.3-21.9) is weak (0.42). The weakest relationship between LA values (14

  8. Geochemistry of intrusive rocks associated with the Latir volcanic field, New Mexico, and contrasts between evolution of plutonic and volcanic rocks

    USGS Publications Warehouse

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

    1989-01-01

    Plutonic rocks associated with the Latir volcanic field comprise three groups: 1) ???25 Ma high-level resurgent plutons composed of monzogranite and silicic metaluminous and peralkaline granite, 2) 23-25 Ma syenogranite, and alkali-feldspar granite intrusions emplaced along the southern caldera margin, and 3) 19-23 Ma granodiorite and granite plutons emplaced south of the caldera. Major-element compositions of both extrusive and intrusive suites in the Latir field are broadly similar; both suites include high-SiO2 rocks with low Ba and Sr, and high Rb, Nb, Th, and U contents. Moreover, both intermediateto siliciccomposition volcanic and plutonic rocks contain abundant accessory sphene and apatite, rich in rare-earth elements (REE), as well as phases in which REE's are essential components. Strong depletion in Y and REE contents, with increasing SiO2 content, in the plutonic rocks indicate a major role for accessory mineral fractionation that is not observed in volcanic rocks of equivalent composition. Considerations of the rheology of granitic magma suggest that accessory-mineral fractionation may occur primarily by filter-pressing evolved magmas from crystal-rich melts. More limited accessory-mineral crystallization and fractionation during evolution of the volcanic magmas may have resulted from markedly lower diffusivities of essential trace elements than major elements. Accessory-mineral fractionation probably becomes most significant at high crystallinities. The contrast in crystallization environments postulated for the extrusive and intrusive rocks may be common to other magmatic systems; the effects are particularly pronounced in highly evolved rocks of the Latir field. High-SiO2 peralkaline porphyry emplaced during resurgence of the Questa caldera represents non-erupted portions of the magma that produced the Amalia Tuff during caldera-forming eruption. The peralkaline porphyry continues compositional and mineralogical trends found in the tuff. Amphibole

  9. Biogeochemical impacts of volcanic eruptions on alkaline lake environments: A case study on Lake Van in the eastern Turkey

    NASA Astrophysics Data System (ADS)

    Olgun, Nazli; Çagatay, Namık; Aksu, Abdullah; Balkıs, Nuray; Kaiser, Jerome; Öveçoglu, Lütfi; Özcan, Mustafa

    2014-05-01

    Volcanic ashes ejected during explosive volcanic eruptions can release more than fifty-five soluble elements in contact with water, most of which have environmental significance such as fluoride, chloride, the nutrients like the fixed-nitrogen, phosphate, silica and a variety of key trace metals including iron. Deposition of volcanic ash onto the aqueous environments can therefore affect the water geochemistry and eventually the phytoplankton growth in the ash fallout regions. Alkaline (soda) lakes are distributed world-wide and located almost exclusively in the volcanic regions, which have been related to the long term dissolution of volcanic products. However, although alkali lakes are found in the high volcanic impact regions, the way in which the biogeochemistry of the alkaline lake waters is affected by the volcanic eruptions still remains unknown. Lake Van, located in the eastern Turkey, is the largest of the alkaline lakes on Earth and had been exposed to various volcanic ash fallouts produced by the historical eruptions of neighbouring semi-active volcanoes Nemrut, Süphan and Tendürek. Here, we present new data from geochemical analyses of Lake Van sediments, aiming to determine the potential changes in the primary productivity related to the volcanic eruptions, by using organic biomarkers such as pigments chlorin and fucoxanthin, long chain alkenons, total organic and inorganic carbon contents of sediment layers above and below the ten selected tephra fallout deposits dating back from 1 ka to 82 ka. Furthermore, we have performed microscopic observations of the microfossils (diatoms and coccoliths) in the Lake Van sediments. Our data pointed out variable changes related to different fallout deposits including significant positive (fertilizing affect) and negative (toxic affect) impacts and as well as nearly negligible changes in the biomarker concentrations in the sediments overlying the ten tephra layers compared to the underlying sediments. We suggest

  10. Fluorine in the rocks and sediments of volcanic areas in central Italy: total content, enrichment and leaching processes and a hypothesis on the vulnerability of the related aquifers.

    PubMed

    De Rita, Donatella; Cremisini, Carlo; Cinnirella, Alessandro; Spaziani, Fabio

    2012-09-01

    Rock, sediment and water samples from areas characterised by hydrothermal alterations in the Sabatini and Vico Volcanic Districts, near Rome and the large city of Viterbo, respectively, were collected and analysed to determine the total fluorine (F) content and to understand the F geochemical background level in the volcanic districts of central Italy. Leaching and alteration processes controlling the high concentration of F in water were also investigated. Fluorine concentrations were directly determined (potentiometrically) by an F selective electrode in water samples, while the procedure for rock samples included preliminary F dissolution through alkaline fusion. F concentrations higher than 800 mg kg(-1) were commonly found in the analysed rocks and sediments; the concentration depended on the lithology and on the distance from the alteration areas. A specific successive sampling campaign was conducted in three areas where the F content in sediments was particularly high; in the same areas, measurements of CO(2) flux were also performed to investigate the possible deep origin of F. To verify the relationships among the high F contents in rocks and sediments, the leaching processes involved and the presence of F in the aquifer, we also collected water samples in the western sector of the Sabatini Volcanic District, where hydrothermal manifestations and mineral springs are common. The data were processed using a GIS system in which the F distribution was combined with morphological and geological observations. The main results of our study are that (1) F concentrations are higher in volcanic and recently formed travertine (especially in hydrothermally altered sediments) than in sedimentary rocks and decrease with distance from hydrothermal alteration areas, (2) F is more easily leached from hydrothermally altered rocks and from travertine and (3) sediments enriched with F may indicate the presence of deep regional fractures that represent direct pathways of

  11. Fluorine in the rocks and sediments of volcanic areas in central Italy: total content, enrichment and leaching processes and a hypothesis on the vulnerability of the related aquifers.

    PubMed

    De Rita, Donatella; Cremisini, Carlo; Cinnirella, Alessandro; Spaziani, Fabio

    2012-09-01

    Rock, sediment and water samples from areas characterised by hydrothermal alterations in the Sabatini and Vico Volcanic Districts, near Rome and the large city of Viterbo, respectively, were collected and analysed to determine the total fluorine (F) content and to understand the F geochemical background level in the volcanic districts of central Italy. Leaching and alteration processes controlling the high concentration of F in water were also investigated. Fluorine concentrations were directly determined (potentiometrically) by an F selective electrode in water samples, while the procedure for rock samples included preliminary F dissolution through alkaline fusion. F concentrations higher than 800 mg kg(-1) were commonly found in the analysed rocks and sediments; the concentration depended on the lithology and on the distance from the alteration areas. A specific successive sampling campaign was conducted in three areas where the F content in sediments was particularly high; in the same areas, measurements of CO(2) flux were also performed to investigate the possible deep origin of F. To verify the relationships among the high F contents in rocks and sediments, the leaching processes involved and the presence of F in the aquifer, we also collected water samples in the western sector of the Sabatini Volcanic District, where hydrothermal manifestations and mineral springs are common. The data were processed using a GIS system in which the F distribution was combined with morphological and geological observations. The main results of our study are that (1) F concentrations are higher in volcanic and recently formed travertine (especially in hydrothermally altered sediments) than in sedimentary rocks and decrease with distance from hydrothermal alteration areas, (2) F is more easily leached from hydrothermally altered rocks and from travertine and (3) sediments enriched with F may indicate the presence of deep regional fractures that represent direct pathways of

  12. Influence of water saturation on rock failure - Implications for volcanic environments

    NASA Astrophysics Data System (ADS)

    Scheu, B.; Feneis, C.; Lavallee, Y.; Heap, M. J.; Dingwell, D. B.

    2011-12-01

    Water plays several important roles in the grand scheme of volcanism. As magmatic water, it influences magma generation transport and emplacement/eruption via its influence on the physicochemical properties of melts (e.g. rheology, diffusion, surface tension). As external water, it's role is manifold: (1) it is the driving force for the phreatic explosions which often are precursory to volcanic eruptions, (2) it may mix with magma and fuel phreatomagmatic eruptions, and (3) it has the ability to weaken and destabilize volcanic structures. Previous studies have shown that even small amounts of water may substantially weaken the strength of rocks. However the study of volcanic rocks is, in this respect, sparse. For this study we chose both volcanic rocks and volcanic host rocks (ranging from volcaniclastic sandstone to dacite) and compare their behaviour to that of Bentheim sandstone, an iconic rock type in rock mechanics. Two different experimental approaches are combined in this study. Firstly, we investigated the failure of rock specimens by rapid decompression using a shock-tube apparatus. Therein a rock sample is slowly pressurized with argon gas up to a maximum pressure of 50 MPa and then rapidly decompressed to atmospheric conditions. The decompression rates in this facility reach the order of 10 GPa/s and higher, allowing us to interpret these experiments as dynamic direct tensile strength tests. The experiments were carried out with varying degrees of water saturation in a temperature range from 20 to 300 °C. The degree of water saturation influences the fragmentation threshold (the minimum applied pressure required to fully fragment a sample) as well as the speed of the fragmentation process. Secondly, uniaxial compressive strength (UCS) tests and Brazilian tests were carried out to investigate, respectively, the compressive and (indirect) tensile strengths of dry and water-saturated samples. UCS tests were performed on 80 x 40mm cylinders under a strain

  13. Geochemistry and geochronology of late Mesozoic volcanic rocks in the northern part of the Eastern Pontide Orogenic Belt (NE Turkey): Implications for the closure of the Neo-Tethys Ocean

    NASA Astrophysics Data System (ADS)

    Özdamar, Şenel

    2016-04-01

    This paper presents 40Ar/39Ar and U-Pb age data, Sr-Nd isotopes, whole-rock and mineral compositions of Upper Cretaceous volcanic rocks from the Ordu area of the Eastern Pontide Orogenic Belt (EPOB) in northeastern Turkey. The volcanic rocks exhibit a wide compositional range: basalt, basaltic-andesites, andesites and a rhyodacite suite; they are characterized by subparallel light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with Eu anomalies and moderate fractionation [average (La/Yb)N = 8.55]. The geochemical results show that the volcanic rocks have calc-alkaline affinity consistent with arc volcanic rocks erupted in an active continental margin. Initial 87Sr/86Sr values vary between 0.70569 and 0.70606, while initial 143Nd/144Nd values lie between 0.51244 and 0.51249. Crustal contamination affected the mantle-originated primary magma, as indicated by increased 87Sr/86Sr and decreased 143Nd/144Nd ratios with increasing SiO2. New precise laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) 206Pb-238U age analyses of zircon and 40Ar/39Ar age data of plagioclase from the volcanics enable a more precise reconstruction of the EBOP. The ages provide insight into the timing of arc formation in this region, constrain the volcanic activity between 86 My (Coniacian) and 75 My (Campanian) and constrain the timing of closure of the Neo-Tethys.

  14. Late Jurassic to Eocene geochemical evolution of volcanic rocks in Puerto Rico

    SciTech Connect

    Schellekens, J.H. )

    1991-03-01

    The Late Jurassic to Eocene deformed volcanic, volcaniclastic and sedimentary rocks of Puerto Rico are divided into three igneous provinces, the southwestern, central, and northeastern igneous province. Based on the stratigraphic position approximate ages could be assigned to the flow rocks in these provinces. Ba/Nb and La/Sm diagrams are presented to illustrate the origin and evolution of the flow rocks. The oldest rock in the southwestern province may include MORB. Early Cretaceous volcanic rocks in the central and northeastern province have low Ba/nb and La/Sm, that are interpreted as an early island arc stage, with none or only minor contribution of slab-derived material. The Late Cretaceous to Eocene volcanic rocks have a wide range of values for the Ba/Nb and La/Sm that are interpreted as the result of admixture of a variable amount of slab-derived material. The Maricao Basalt (Maastrichtian to Eocene) in the southeastern igneous province has the geochemical signature of magmas formed in an extensional setting.

  15. Location, age, and rock type of volcanic rocks younger than 5 million years in Arizona and New Mexico

    SciTech Connect

    Aldrich, M.J. Jr.; Laughlin, A.W.

    1981-04-01

    As part of the assessment of the Hot Dry Rock geothermal energy potential of Arizona and New Mexico, a compilation of the locations and ages of volcanic rocks less than 5 Myr was made. The locations of those rocks less than 3 Myr are shown on a map of the region. Because the compiled information has many uses in addition to geothermal exploration, the entire compilation is presented as a tabulation. The table is organized first by state and secondly by latitude and longitude within each state. Rock type, age and error, method of dating, and original reference are also given. The K-Ar dates have not been recalculated using the most recent decay constants for /sup 40/K. A few references gave only verbal descriptions of sample location; these locations were converted to approximate latitude and longitude.

  16. Clastic sedimentary rocks of the Michipicoten Volcanic-sedimentary belt, Wawa, Ontario

    NASA Technical Reports Server (NTRS)

    Ojakangas, R. W.

    1983-01-01

    The Wawa area, part of the Michipicoten greenstone belt, contains rock assemblages representative of volcanic sedimentary accumulations elsewhere on the shield. Three mafic to felsic metavolcanic sequences and cogenetic granitic rocks range in age from 2749 + or - 2Ma to 2696 + or - 2Ma. Metasedimentary rocks occur between the metavolcanic sequences. The total thickness of the supracrustal rocks may be 10,000 m. Most rocks have been metamorphosed under greenschist conditions. The belt has been studied earlier and is currently being remapped by Sage. The sedimentrologic work has been briefly summarized; two mainfacies associations of clastic sedimentary rocks are present - a Resedimented (Turbidite) Facies Association and a Nonmarine (Alluvial Fan Fluvial) Facies Association.

  17. Search for magnetic monopoles in polar volcanic rocks.

    PubMed

    Bendtz, K; Milstead, D; Hächler, H-P; Hirt, A M; Mermod, P; Michael, P; Sloan, T; Tegner, C; Thorarinsson, S B

    2013-03-22

    For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside Earth would be expected to be enhanced in the mantle beneath the geomagnetic poles. A search for magnetic monopoles was conducted using the signature of an induced persistent current following the passage of igneous rock samples through a SQUID-based magnetometer. A total of 24.6 kg of rocks from various selected sites, among which 23.4 kg are mantle-derived rocks from the Arctic and Antarctic areas, was analyzed. No monopoles were found, and a 90% confidence level upper limit of 9.8 × 10(-5)/g is set on the monopole density in the search samples. PMID:25166793

  18. Search for magnetic monopoles in polar volcanic rocks.

    PubMed

    Bendtz, K; Milstead, D; Hächler, H-P; Hirt, A M; Mermod, P; Michael, P; Sloan, T; Tegner, C; Thorarinsson, S B

    2013-03-22

    For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside Earth would be expected to be enhanced in the mantle beneath the geomagnetic poles. A search for magnetic monopoles was conducted using the signature of an induced persistent current following the passage of igneous rock samples through a SQUID-based magnetometer. A total of 24.6 kg of rocks from various selected sites, among which 23.4 kg are mantle-derived rocks from the Arctic and Antarctic areas, was analyzed. No monopoles were found, and a 90% confidence level upper limit of 9.8 × 10(-5)/g is set on the monopole density in the search samples.

  19. Geochemistry and petrology of the Early Miocene lamproites and related volcanic rocks in the Thrace Basin, NW Anatolia

    NASA Astrophysics Data System (ADS)

    Ersoy, Yalçın E.; Palmer, Martin R.; Uysal, İbrahim; Gündoğan, İbrahim

    2014-08-01

    The extensional Thrace basin (NW Anatolia) contains an association of early Miocene diopside-leucite-phlogopite (Doğanca) and diopside-phlogopite (Korucuköy) lamproites with Oligocene medium-K calc-alkaline andesites (Keşan volcanics), early Miocene shoshonitic rocks (Altınyazı trachyte) and middle Miocene Na-alkaline basalts (Beğendik basalts). The Doğanca lamproite (K2O = 5.1-5.5 wt.%; K/Na = 2.78-2.89; MgO = 11.4-11.8 wt.%) consists of olivine (Fo71-86), diopside (Al2O3 = 1.0-5.0, Na2O = 0.2-0.6), phlogopite (TiO2 = 1.1-9.4, Al2O3 = 11.1-13.9), spinel (Mg# = 22.9-32.6; Cr# = 64-83.4), leucite, apatite, zircon, Fe-Ti-oxides and magnetite in a poikilitic sanidine matrix. The potassic volcanic units (lamproites and trachytes) in the region have similarly high Sr and low Nd isotopic compositions (87Sr/86Sr(i) = 0.70835-0.70873 and 143Nd/144Nd(i) = 0.51227-0.51232). The major and trace element compositions and Sr-Nd-Pb isotopic ratios of the shoshonitic, ultrapotassic and lamproitic units closely resemble those of other Mediterranean ultrapotassic lamproites (i.e., orogenic lamproites) from Italia, Serbia, Macedonia and western Anatolia. The Beğendik basalts show intraplate geochemical signatures with an Na-alkaline composition, an absence of Nb negative anomalies on primitive mantle-normalized multi-element diagrams, as well as low Sr (~ 0.70416) and high Nd (0.51293) isotopic ratios; and include olivine (Fo72-84), diopside, spinel, Fe-Ti-oxides and magnetite. The Oligocene Keşan volcanics were emplaced in the earlier stages of extension in Thrace, and represent the typical volcanic products of post-collisional volcanism. The continental crust-like trace element abundances and isotopic compositions of the most primitive early Miocene ultrapotassic rocks (Mg# up to 74) indicate that their mantle sources were intensely contaminated by the continental material. By considering the geodynamic evolution of the region, including oceanic subduction, crustal

  20. Geochemical variation with time in the Cenezoic volcanic rocks of southwest Hokkaido, Japan

    NASA Astrophysics Data System (ADS)

    Okamura, S.

    1987-06-01

    Abundances of major and trace elements were determined for the Tertiary volcanic rocks from SW Hokkaido. The Late Miocene to Pliocene volcanic rocks of this region show geochemical features similar to those of the Quaternary rocks, that is, K/Si, Th/Si and LREE/HREE ratios increasing across the arc, east to west, from the Pacific to the Japan Sea side. In contrast, the Early Miocene volcanic rocks, which are geographically restricted to the Japan Sea coast, are distinct from all later volcanics and show "within-plate" characteristics — in particular, high concentrations of HFS elements. The Quaternary basalts have low Hf/Yb ratios and Hf contents, whereas the Early Miocene basalts are high in Hf/Yb and Hf, similar to Hawaiian alkali basalts. The compositional variation with time may result from the progressive depletion of incompatible HFS elements in the mantle source. Th/Yb ratios increase from Early Miocene to Quaternary, possibly reflecting increase in the LIL element contribution to the mantle source during that time.

  1. Nature and origin of secondary mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs Wash volcanic centers, southern, Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, James V.; Hsu, Liang C.; Spatz, David M.; Chenevey, Michael J.

    1989-01-01

    The following subject areas are covered: (1) genetic, spectral, and LANDSAT Thematic Mapper imagery relationship between desert varnish and tertiary volcanic host rocks, southern Nevada; (2) reconnaissance geologic mapping of the Kane Springs Wash Volcanic Center, Lincoln County, Nevada, using multispectral thermal infrared imagery; (3) interregional comparisons of desert varnish; and (4) airborne scanner (GERIS) imagery of the Kane Springs Wash Volcanic Center, Lincoln County, Nevada.

  2. Bimodal Silurian and Lower Devonian volcanic rock assemblages in the Machias-Eastport area, Maine

    USGS Publications Warehouse

    Gates, Olcott; Moench, R.H.

    1981-01-01

    Exposed in the Machias-Eastport area of southeastern Maine is the thickest (at least 8,000 m), best exposed, best dated, and most nearly complete succession of Silurian and Lower Devonian volcanic strata in the coastal volcanic belt, remnants of which crop out along the coasts of southern New Brunswick, Canada, and southeastern New England in the United States. The volcanics were erupted through the 600-700-million-year-old Avalonian sialic basement. To test the possibility that this volcanic belt was a magmatic arc above a subduction zone prior to presumed Acadian continental collision, samples representing the entire section in the Machias-Eastport area of Maine were chemically analyzed. Three strongly bimodal assemblages of volcanic rocks and associated intrusives are recognized, herein called the Silurian, older Devonian, and younger Devonian assemblages. The Silurian assemblage contains typically nonporphyritic high-alumina tholeiitic basalts, basaltic andesites, and diabase of continental characterand calc-alkalic rhyolites, silicic dacites, and one known dike of andesite. These rocks are associated with fossiliferous, predominantly marine strata of the Quoddy, Dennys, and Edmunds Formations, and the Leighton Formation of the Pembroke Group (the stratigraphic rank of both is revised herein for the Machias-Eastport area), all of Silurian age. The shallow marine Hersey Formation (stratigraphic rank also revised herein) of the Pembroke Group, of latest Silurian age (and possibly earliest Devonian, as suggested by an ostracode fauna), contains no known volcanics; and it evidently was deposited during a volcanic hiatus that immediately preceded emergence of the coastal volcanic belt and the eruption of the older Devonian assemblage. The older Devonian assemblage, in the lagoonal to subaerial Lower Devonian Eastport Formation, contains tholeiitic basalts and basaltic andesites, typically with abundant plagioclase phenocrysts and typically richer in iron and

  3. Isotopic ages for alkaline igneous rocks, including a 26 Ma ignimbrite, from the Peshawar plain of northern Pakistan and their tectonic implications

    NASA Astrophysics Data System (ADS)

    Ahmad, Irshad; Khan, Shuhab; Lapen, Thomas; Burke, Kevin; Jehan, Noor

    2013-01-01

    New isotopic ages on zircons from rocks of the Peshawar Plain Alkaline Igneous Province (PPAIP) reveal for the first time the occurrence of ignimbritic Cenozoic (Oligocene) volcanism in the Himalaya at 26.7 ± 0.8 Ma. Other new ages confirm that PPAIP rift-related igneous activity was Permian and lasted from ˜290 Ma to ˜250 Ma. Although PPAIP rocks are petrologically and geochemically typical of rifts and have been suggested to be linked to rifting on the Pangea continental margin at the initiation of the Neotethys Ocean, there are no documented rift-related structures mapped in Permian rocks of the Peshawar Plain. We suggest that Permian rift-related structures have been dismembered and/or reactivated during shortening associated with India-Asia collision. Shortening in the area between the Main Mantle Thrust (MMT) and the Main Boundary Thrust (MBT) may be indicative of the subsurface northern extension of the Salt Range evaporites. Late Cenozoic sedimentary rocks of the Peshawar Plain deposited during and after Himalayan thrusting occupy a piggy-back basin on top of the thrust belt. Those sedimentary rocks have buried surviving evidence of Permian rift-related structures. Igneous rocks of the PPAIP have been both metamorphosed and deformed during the Himalayan collision and Cenozoic igneous activity, apart from the newly recognized Gohati volcanism, has involved only the intrusion of small cross-cutting granitic bodies concentrated in areas such as Malakand that are close to the MMT. Measurements on Chingalai Gneiss zircons have confirmed the occurrence of 816 ± 70 Ma aged rocks in the Precambrian basement of the Peshawar Plain that are comparable in age to rocks in the Malani igneous province of the Rajasthan platform ˜1000 km to the south.

  4. Sr, Nd and Pb Isotope Geochemistry for the Volcanic Rocks From the Aono and Abu Volcanic Groups in the SW Japan arc

    NASA Astrophysics Data System (ADS)

    Shimoda, G.; Morishita, Y.; Nohda, S.

    2002-12-01

    Although, there is no deep seismic activity beneath the W. Honshu Island in the SW Japan arc, recent seismic studies have revealed the existence of an aseismic slab beneath the area. Thus, the volcanism in the W. Honshu Island is considered to be related to the subduction. Since the subducting Philippine Sea plate caused inter-arc spreading, the volcanism of the Aono and Abu volcanic groups in the W. Honshu Island are inferred to be produced at the high temperature condition. The Aono volcanic group is one of volcanic groups, which comprise the volcanic front on the SW Japan arc, while the Abu volcanic group is on rather backarc side of the Aono volcanic group. In order to evaluate the origin of the volcanic rocks from the Aono and Abu volcanic groups, Sr, Nd and Pb isotopic and trace element compositions were determined. Nb troughs on a spider diagram indicate that these rocks are related to subduction process. Furthermore, high Sr/Y ratios and low Y concentrations of these rocks indicate that these are adakitic magma, which suggests that the magmas were produced by altered oceanic crust melting. Isotopic compositions of these rocks are situated between those of the Shikoku basin basalt and mantle xenoliths from the SW Japan arc on 87Sr/86Sr vs. 143Nd/144Nd and Pb-Pb diagrams. These show that geochemical characteristics of these rocks were produced by the mixing of a depleted slab derived component with an enriched mantle component. A 1/Sr vs. 87Sr/86Sr diagram designates that the depleted and enriched components have high and low Sr concentrations, respectively. Considering phase assemblages during melting processes of mantle peridotite and subducting altered oceanic crust, lower and higher Sr concentrations reflect lherzolite and eclogite melting respectively. This is consistent with the isotopic composition. To test the altered oceanic crust melting as a possible mechanism for the production of Aono and Abu volcanic rocks, melting calculations were conducted

  5. Primary alkaline magmas associated with the Quaternary Alligator Lake volcanic complex, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Eiché, G. E.; Francis, D. M.; Ludden, J. N.

    1987-02-01

    The Alligator Lake complex is a Quaternary alkaline volcanic center located in the southern Yukon Territory of Canada. It comprises two cinder cones which cap a shield consisting of five distinct lava units of basaltic composition. Units 2 and 3 of this shield are primitive olivine-phyric lavas (13.5 19.5 cation % Mg) which host abundant spinel lherzolite xenoliths, megacrysts, and granitoid fragments. Although the two lava types have erupted coevally from adjacent vents and are petrographically similar, they are chemically distinct. Unit 2 lavas have considerably higher abundances of LREE, LILE, and Fe, but lower HREE, Y, Ca, Si, and Al relative to unit 3 lavas. The 87Sr/86Sr and 143Nd/144Nd isotopic ratios of these two units are, however, indistinguishable. The differences between these two lava types cannot be explained in terms of low pressure olivine fractionation, and the low concentrations of Sr, Nb, P, and Ti in the granitoid xenoliths relative to the primitive lavas discounts differential crustal contamination. The abundance of spinel lherzolite xenoliths and the high Mg contents in the lavas of both units indicates that their compositional differences originated in the upper mantle. The Al and Si systematics of these lavas suggests that, compared to unit 3 magmas, the unit 2 magmas may have segregated at greater depths from a garnet lherzolite mantle. The identical isotopic composition and similar ratios of highly incompatible elements in these two lava units argues against their differences being a consequence of random metasomatism or mantle heterogeneity. The lower Y and HREE contents but higher concentrations of incompatible elements in the unit 2 lavas relative to unit 3 can be most simply explained by differential partial melting of similar garnet-bearing sources. The unit 2 magmas thus appear to have been generated by smaller degrees of melting at a greater depth than the unit 3 magmas. The contemporaneous eruption of two distinct but

  6. Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Davidson, J.

    2013-12-01

    Results from separate volcanic and plutonic studies have led to inconsistent conclusions regarding the origins and thus links between volcanic and plutonic systems in continental arcs and the magmatic processes and time scales responsible for their compositional variations. Some have suggested that there is a geochemical and geochronological disconnect between volcanic and plutonic rocks and hence have questioned the existence of magma mush columns beneath active volcanoes. Investigating contemporary volcanic and plutonic rocks that are spatially connected is thus critical in exploring these issues. The ca. 36 Ma Organ Mountains caldera in New Mexico, USA, represents such a system exposing contemporaneous volcanic and plutonic rocks juxtaposed at the surface due to tilting during extensional tectonics along the Rio Grande Rift. Detailed geologic and structural mapping [1] and 40Ar/39Ar ages of both volcanics and plutons [2] demonstrate the spatial and temporal connection of both rock types with active magmatism over >2.5 myr. Three caldera-forming ignimbrites erupted within 600 kyr [2] from this system with a total erupted volume of 500-1,000 km3 as well as less voluminous pre- and post-caldera trachyte and andesite lavas. The ignimbrite sequence ranges from a crystal-poor, high-SiO2 rhyolite at the base to a more crystal-rich, low-SiO2 rhyolite at the top. Compositional zoning with quartz-monzonite at the base grading to syenite and alaskite at the top is also found in the Organ Needle pluton, the main intrusion, which is interpreted to be the source for the ignimbrites [1]. Other contemporaneous and slightly younger plutons have dioritic to leucogranitic compositions. We examined both volcanic and plutonic rocks with petrography and their textural variations with color cathodoluminescence, and used whole rock element and Sr, Nd and Pb isotope geochemistry to constrain magma compositions and origins. Electron microprobe analyses on feldspars have been completed to

  7. Analysis of well logging methods in volcanic and volcano sedimentary rocks from Pina petroleum field

    SciTech Connect

    Rodriquez, N.

    1996-09-01

    Petrophysical, petrological and geophysical methods have been applied to prospecting and well logging for several petroleum fields in Cuba. The most common reservoir in these fields are carbonate rocks. However, the Pina field, in the Central region of the island, distinguishes itself by the good quality of the oil and the volcano sedimentary and volcanic character of the reservoirs. These rocks have peculiar geophysical responses, which is why the study of these methods and the development of the interpretation methods is very important. Integrated geological and geophysical information was necessary during the drilling of wells in the Pina field in order to evaluate the hydrocarbon potential. GEONUC code permits us to use different ways to solve questions about interpretation of well logging in the volcanic sedimentary rocks. This code gives us the opportunity to analyze complex methods.

  8. Thermal Waters in Maguarichi, Chihuahua, Mexico: Influence on Volcanic Rocks Alteration

    NASA Astrophysics Data System (ADS)

    Mascote, C. R.; Espejel-Garcia, V. V.; Villalobos-Aragon, A.

    2013-05-01

    Piedras de Lumbre, Maguarichi, is located 294 km. to the SW of Chihuahua city, in northern Mexico, in the Sierra Madre Occidental (SMO). The study area is composed of a set of igneous volcanic rocks affected by hydrothermal flows, which apparently run along a fault. Outcrops of hot springs, going out with high pressure, are active all over the year and have no seasonal flow changes. The hydrothermal flows, approximately 20, that reach the surface area at Piedras de Lumbre, are altering the volcanic rocks that surround the hot springs. The study area is highly altered, and evidenced by a variety range of colors in the rock surfaces. The rock samples collected at the region show a crystal growth due to the influence of the salts from the thermal water. The rocks closest to the water openings have a change in its mineralogy, with the mafic minerals, present in andesites, been replaced by carbonates and sulfates, leaving only the clear mineral pseudomorphs. On the crust of the rocks a white layer of material (salts), product of the thermal waters has precipitated. The alteration is perceived only about 5 m. or less around the hot springs. The water, which has high contents of arsenic and sulfates has exerted a strong alteration in rhyolitic and andesitic rocks.

  9. The determination of the acoustic parameters of volcanic rocks from compressional velocity measurements

    USGS Publications Warehouse

    Carroll, R.D.

    1969-01-01

    A statistical analysis was made of the relationship of various acoustic parameters of volcanic rocks to compressional wave velocities for data obtained in a volcanic region in Nevada. Some additional samples, chiefly granitic rocks, were also included in the study to extend the range of parameters and the variety of siliceous rock types sampled. Laboratory acoustic measurements obtained on 62 dry core samples were grouped with similar measurements obtained from geophysical logging devices at several depth intervals in a hole from which 15 of the core samples had been obtained. The effects of lithostatic and hydrostatic load on changing the rock acoustic parameters measured in the hole were noticeable when compared with the laboratory measurements on the same core. The results of the analyses determined by grouping all of the data, however, indicate that dynamic Young's, shear and bulk modulus, shear velocity, shear and compressional characteristic impedance, as well as amplitude and energy reflection coefficients may be reliably estimated on the basis of the compressional wave velocities of the rocks investigated. Less precise estimates can be made of density based on the rock compressional velocity. The possible extension of these relationships to include many siliceous rocks is suggested. ?? 1969.

  10. Petrogenesis and tectonic implication of the Late Triassic post-collisional volcanic rocks in Chiang Khong, NW Thailand

    NASA Astrophysics Data System (ADS)

    Qian, Xin; Wang, Yuejun; Feng, Qinglai; Zi, Jian-Wei; Zhang, Yuzhi; Chonglakmani, Chongpan

    2016-04-01

    The volcanic rocks exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand provide important constraints on the tectonic evolution of the eastern Paleotethys ocean. An andesite sample from the Chiang Khong area yields a zircon U-Pb age of 229 ± 4 Ma, significantly younger than the continental-arc and syn-collisional volcanic rocks (ca. 238-241 Ma). The Chiang Khong volcanic rocks are characterized by low MgO (1.71-6.72 wt.%) and high Al2O3 (15.03-17.76 wt.%). They are enriched in LILEs and LREEs and depleted in HFSEs, and have 87Sr/86Sr (i) ratios of 0.7050-0.7065, εNd (t) of - 0.32 to - 1.92, zircon εHf (t) and δ18O values of 3.5 to - 11.7 and 4.30-9.80 ‰, respectively. The geochemical data for the volcanic rocks are consistent with an origin from the enriched lithospheric mantle that had been modified by slab-derived fluid and recycled sediments. Based on available geochronological and geochemical evidences, we propose that the Late Triassic Chiang Khong volcanic rocks are equivalent to the contemporaneous volcanic rocks in the Lancangjiang igneous zone in SW China. The formation of these volcanic rocks was possibly related to the upwelling of the asthenospheric mantle during the Late Triassic, shortly after slab detachment, which induced the melting of the metasomatized mantle wedge.

  11. New high-precision 40Ar/39Ar ages on Oligocene volcanic rocks of northwestern Kenya

    NASA Astrophysics Data System (ADS)

    Brown, Francis H.; Jicha, Brian R.

    2016-02-01

    New, high-precision 40Ar/39Ar ages from volcanic rocks in northwestern Kenya are provided for some areas of exposure in this remote area. We report seven 40Ar/39Ar ages generated from single crystal total fusion experiments on alkali feldspar separated from volcanic rocks in the Mogila, Songot, and Lokwanamur Ranges and the Gatome valley. A rhyolite from the lower part of the sequence in the Mogila Range yielded ages of 32.31 ± 0.06 Ma and 32.33 ± 0.07 Ma, and a rhyolite near the top of that sequence yielded 31.67 ± 0.04 Ma. A single sample from the Songot Range yielded an age of 32.49 ± 0.07 Ma, slightly older than the rocks collected from Mogila. In both ranges the early Oligocene rhyolites are underlain by basalts, as is also the case in the Labur Range. Ages of 25.95 ± 0.03 Ma, 25.91 ± 0.04 Ma, and 27.15 ± 0.03 Ma were measured on alkali feldspar from rhyolites from the Lokwanamur Range, and the nearby Gatome valley. All of these rocks are part of an episode of widespread volcanism in northwestern Kenya in the mid-to late Oligocene that is not currently known from the Ethiopian Rift Valley.

  12. Saturated Zone Plumes in Volcanic Rock: Implications for Yucca Mountain

    SciTech Connect

    S. Kelkar; R. Roback; B. Robinson; G. Srinivasan; C. Jones; P. Reimus

    2006-02-14

    This paper presents a literature survey of the occurrences of radionuclide plumes in saturated, fractured rocks. Three sites, Idaho National laboratory, Hanford, and Oak Ridge are discussed in detail. Results of a modeling study are also presented showing that the length to width ratio of a plume starting within the repository footprint at the Yucca Mountain Project site, decreases from about 20:1 for the base case to about 4:1 for a higher value of transverse dispersivity, indicating enhanced lateral spreading of the plume. Due to the definition of regulatory requirements, this lateral spreading does not directly impact breakthrough curves at the 18 km compliance boundary, however it increases the potential that a plume will encounter reducing conditions, thus significantly retarding the transport of sorbing radionuclides.

  13. Conditions of accumulation of radioactive metals in the process of differentiation of ultrabasic alkaline-carbonatite rock associations

    NASA Astrophysics Data System (ADS)

    Kogarko, L. N.

    2014-07-01

    The distribution of radioactive elements in alkaline rocks from Polar Siberia and Ukraine shows that U and Th are markedly concentrated in carbonatite complex and nepheline syenite as final products of magma fractionation. Peralkaline nepheline syenites from Polar Siberia are characterized by very high contents of radioactive elements, which are close to the economic level. Radioactive elements are also concentrated in rocks of the carbonatite complex. For example, some soevites contain up to 294 × 10-4%U and 916 × 10-4% Th. In late dolomite carbonatites, the contents of radioactive elements are appreciably lower. The Th/U ratio in alkaline rocks of Polar Siberia is close to the chondrite value in primary high-Mg rocks and increases in late derivatives: phoscorite, calcite and dolomite carbonatites. The main amount of radioactive elements is contained in rare-metal accessory minerals: perovskite, pyrochlore, calzirtite, and apatite. Rock-forming minerals are distinguished by very low concentrations of radioactive elements. In alkaline series of the Chernigovka massif (Ukraine), U and Th also accumulate in the course of crystal fractionation, especially in phoscorites from the carbonatite complex. Mantle xenoliths and alkaline rocks from Ukraine reveal uranium specialization. Most likely, the discrepancy in fractionation of radioactive elements between Polar Siberia and Ukraine is caused by different geodynamic regimes of these provinces. The Mesozoic alkaline magmatism of Polar Siberia is a part of the Siberian superplume, whereas the Proterozoic alkaline complex in Ukraine is related to subduction of the oceanic crust.

  14. K-Ar dating of young volcanic rocks

    SciTech Connect

    Damon, P.E.; Shafiqullah, M.

    1991-01-31

    Potassium-Argon (K-Ar) age dates were determined for forty-two young geologic samples by the Laboratory of Isotope Geochemistry, Department of Geosciences, in the period February 1, 1986 to June 30, 1989. Under the terms of Department of Energy Grant No. FG07-86ID12622, The University of Arizona was to provide state-of-the-art K-Ar age dating services, including sample preparation, analytical procedures, and computations, for forty-two young geologic samples submitted by DOE geothermal researchers. We billed only for forty samples. Age dates were determined for geologic samples from five regions with geothermal potential: the Cascade Mountains (Oregon); the Cascade Mountains (Washington); Ascension Island, South Atlantic Ocean; Cerro Prieto, Mexico; and Las Azufres, Mexico. The ages determined varied from 5.92 m.a. to 0.62 m.a. The integration of K-Ar dates with geologic data and the interpretation in terms of geologic and geothermal significance has been reported separately by the various DOE geothermal researchers. Table 1 presents a detailed listing of all samples dated, general sample location, researcher, researcher's organization, rock type, age, and probable error (1 standard deviation). Additional details regarding the geologic samples may be obtained from the respective geothermal researcher. 1 tab.

  15. A Holocene paleosecular variation from 14C-dated volcanic rocks in Western North America

    USGS Publications Warehouse

    Hagstrum, J.T.; Champion, D.E.

    2002-01-01

    A paleosecular variation (PSV) curve for western North America is presented on the basis of 94 virtual geomagnetic poles (VGPs) from dated volcanic rocks sampled at 446 sites. Approximately 60% of the paleomagnetic database has been previously published. A curve defined by "spherical smoothed splines" is fitted to the VGPs, ranked by the quality of the age determinations, where the data density is highest between 3690 and -30 years before present (B.P.) (A.D. 1950), between 7800 and 7050 years B.P., and between 14,060 and 12,700 years B.P. The younger segments of the curve derived from volcanic rocks are similar but less complex than other high-resolution PSV curves derived from lacustrine sediments, particularly the record at Fish Lake, Oregon. The PSV record from lava flows (PSVL), however, is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14C dates. The new PSVL record provides a partial Holocene master curve for western North America and will be of particular value in dating geological and archeological materials using paleomagnetic directions.

  16. Timescales and mechanisms of plume-lithosphere interactions: 40Ar/ 39Ar geochronology and geochemistry of alkaline igneous rocks from the Paraná-Etendeka large igneous province

    NASA Astrophysics Data System (ADS)

    Gibson, S. A.; Thompson, R. N.; Day, J. A.

    2006-11-01

    We have determined high-precision 40Ar/ 39Ar ages for alkaline igneous rocks from the western margin of the Early-Cretaceous Paraná-Etendeka large igneous province (Paraguay). These show that small-fraction melt generation occurred beneath the region in two phases; at 145 Ma and 127.5 Ma, i.e. before and at the end of the 139-127.5 Ma Paraná-Etendeka flood-basalt eruptions. Previously published 40Ar/ 39Ar ages for alkaline igneous rocks on the proto-Atlantic coastal margins range from 134 to 128 Ma and indicate that small-fraction melt generation in the east of the province was either synchronous or slightly later than the main pulse of tholeiitic volcanism (between 134 and 132 Ma). Our new 40Ar/ 39Ar phlogopite ages confirm that: (i) the earliest melts associated with the initial impact of the Tristan plume were generated in the west of the Paraná-Etendeka large igneous province and (ii) igneous activity was long lived and immediately predates continental break-up. The Early-Cretaceous Paraguayan alkaline magmas are silica-undersaturated, enriched in incompatible-trace elements, have very-low initial ɛNd values and probably represent melts of phlogopite-bearing, carbonate-metasomatised peridotite in the subcontinental lithospheric mantle. Our simple one-dimensional, conductive-heating models suggest that the early-phase (145 Ma) alkaline magmas were emplaced on the margins of the Rio de La Plata craton at the time of sublithospheric impact of the proto-Tristan plume. The late phase (127.5 Ma) of Paraguayan alkaline magmatism is concentrated in an intra-cratonic rift zone and melt generation appears to have been triggered by lithospheric extension, perhaps facilitated by conductive heating and thermal weakening associated with the upwelling Tristan plume. The location and timing of both alkaline and tholeiitic melt generation in the Paraná-Etendeka province appear to have been significantly influenced by the non-uniform composition and thickness of the South

  17. Rock thermal conductivity at the cap rock and initial conditions in two-phase volcanic hydrothermal systems

    SciTech Connect

    Mario Cesar Suarez Arriaga

    1993-01-28

    Numerical experiments are performed to investigate the rock thermal conductivity influence in the formation of the thermodynamic initial conditions of two-phase systems located in volcanic rocks. These systems exhibit pressure and temperature profiles characterized by a sudden change or discontinuity in their vertical gradients. Vapor dominated, two-phase fluids are found at the upper reservoir's levels. Liquid is the dominated phase within the layers below some critical point. Numerical results presented in this paper, suggest that the vertical location of this point of discontinuity be controlled by the thermal conductivity existing between the limit of the reservoir and the caprock. Too high values could originate liquid dominated reservoirs. Small values would be at the origin of vapor dominated reservoirs. A characteristic middle value could be responsible for the formation of a counter flow mechanism originating the initial conditions observed at some locations of the Los Azufres, Mexico, geothermal field.

  18. Geochemical and isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy

    USGS Publications Warehouse

    Ayuso, R.A.; de Vivo, B.; Rolandi, G.; Seal, R.R.; Paone, A.

    1998-01-01

    Alkaline volcanism produced by Monte Somma-Vesuvius volcano includes explosive plinian and subplinian activity in addition to effusive lava flows. Pumice, scoria, and lava (150 samples) exhibit major- and trace-element gradients as a function of SiO2 (58.9-47.2 wt%) and MgO (0-7.8 wt%); Mg value are ???50. Internally gradational chemical groups or cycles are distinguished by age: (1) 25 000 to 14 000 yr B.P.; (2) 8000 yr B.P. to A.D. 79; and (3) A.D. 79 to 1944. A small number of lavas, dikes and scora were also analysed from the Somma formation (~ 35 000 to 25 000 yr B.P.). Within each group, contents of Na2O + K2O increas with decreasing MgO along distinct rocks. Nb/Y values are variable from 0.66 to 3.14 (at SiO2 ??? 50 wt%) generally in the range of alkaline and ultra-alkaline rocks. Variations in contents of some majro elements (e.g., P and Ti), and trace elements (e.g., Th, Nb, Ta, Zr, Hf, Pb, La, and Sc), as well as contrasting trends in ratios of various elements (e.g., Ta/Yb, Hf/U, Th/Ta, Th/Hf, Th/Yb, etc.) are also generally consistent with the group subdivisions. For example, Th/Hf increases from ??? 5 to ??? 10 with decreasing age for the Vesuvius system as a whole, yielding similar compositions in the least evolved rocks (low-silica, high-MgO, imcompatible element-poor) erupted at the end of each cycle. Internal variations within individual eruptions also systematically changed generally towards a common mafic composition at the end of each cycle, thus reflecting the dominanit volume in the magma chamber. At the start of a new eruptive cycle, the rocks are relatively enriched in incompatible elements; younger groups also contain higher abundances than other groups. N-MORB-normalized multielement diagrams exhibit selective enrichments of Sr, K, Rb, Th, and the light rare-earth elements; deep Nb and Ta negative anomalies commonly seen in rocks generated at orogenic margins are absent in the light rare-earth elements; deep Nb and Ta netgative anomalies

  19. Potassium metasomatism of volcanic and sedimentary rocks in rift basins, calderas and detachment terranes

    NASA Technical Reports Server (NTRS)

    Chapin, C. E.; drographic basins.

    1985-01-01

    The chemical, mineralogical, and oxygen-isotopic changes accompanying K-metasomatism are described. The similarities with diagenetic reactions in both deep marine and alkaline, saline-lake environments are noted. The common occurrence of K-metasomatism in upper-plate rocks of detachment terranes indicates that the early stage of severe regional extension causes crustal downwarping and, in arid to semi-arid regions, development of closed hydrographic basins.

  20. Barremian rift-related turbidites and alkaline volcanism in southern Mexico and their role in the opening of the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Mendoza-Rosales, Claudia C.; Centeno-García, Elena; Silva-Romo, Gilberto; Campos-Madrigal, Emiliano; Bernal, Juan Pablo

    2010-07-01

    The Chivillas Formation is the easternmost record of Mesozoic marine volcanism in Mexico. It consists of thick intervals of pillow lavas interbedded with siliciclastic turbidites, and debrites, containing clasts derived from metamorphic, sedimentary and volcanic sources. Clast composition and detrital zircon geochronology indicate a continental provenance, with sources located south of the studied rocks. Detrital zircon ages range from 1573 ± 60 to 125 ± 1.6 Ma. The probability curves have peaks at 124 to 130 Ma (mean 126 Ma); 188 Ma and 921-1236 Ma (the latter with peaks at ˜ 1022 and ˜ 1157 Ma). Subordinate peaks at 277, 419 and 535 Ma are also present. We interpret the youngest zircon population ˜ 126 Ma (Barremian), as the maximum depositional age. Other peaks suggest Grenvillian-type basement and Permo-Triassic arc sources. Late Jurassic detrital zircons were probably derived from the Sierra de Juárez Mylonitic belt. Pillow lavas are mostly alkaline basalts, with SiO 2 46%-53%, and alkali oxide (K 2O + Na 2O) 5-8 wt.%; all samples have low-TiO 2 (< 1.6 wt.%) and low V (180-242 ppm), with Ti/V between 30 and 50. 206Pb/ 204Pb isotopic ratios are 18.6-20.5, and 208Pb/ 204Pb are 38.4-40.3, within OIB and MORB ranges. Initial ɛNd(126) are 0.3 to 4.1, and TDM are 632-1520 Ma. Lava compositions are similar to alkaline basalts along the margins of the Atlantic Ocean, particularly to basalts from the Central Atlantic Magmatic Province (CAMP), and to the Cretaceous Peri-Atlantic Alkaline Pulse (PAAP). Volcano-sedimentary rocks from Chivillas Formation probably formed in a subsiding marine rift basin, at a ridge-transform intersection. This basin received sediments transported throughout longitudinal canyons along the major Jurassic-Cretaceous strike-slip fault. In this model, extension of the rift basin was controlled by right-lateral displacement of the strike-slip fault, which acted as a transform fault at this time. This rift is interpreted as a segment of the

  1. Thermo-physical rock properties of greywacke basement rock and intrusive lavas from the Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Mielke, P.; Weinert, S.; Bignall, G.; Sass, I.

    2016-09-01

    Greywacke of the Waipapa and Torlesse (Composite) Terrane form the basement of the Taupo Volcanic Zone (TVZ), New Zealand. Together with inferred buried lavas, domes and igneous complexes they are likely to be the dominant rock type prevailing at depths > 4 km beneath the TVZ. A fundamental understanding of the rock properties of the deep formations is of utmost importance for the exploration of deep unconventional geothermal resources. An outcrop analogue study was conducted to improve the understanding of the thermo-physical rock properties of likely deep buried rock formations beneath the TVZ. A total of 145 core samples were taken at 10 locations inside and outside the TVZ and their grain and bulk density, porosity, matrix permeability, bulk thermal conductivity and specific heat capacity, and the compressional and shear wave velocities measured on oven-dry samples. Additional tests of the unconfined compressive strength were conducted for selected greywacke samples to quantify their mechanical rock strength. The obtained data indicates that the thermo-physical rock properties are mainly controlled by porosity, and minor by mineralogy, texture and grain size. Samples from Waipapa-type and Torlesse-type greywacke exhibit minor rheological differences, with Waipapa-type greywacke having lowest porosity (about 1% vs. 3%) and highest bulk thermal conductivity (2.5 W m- 1 K- 1 vs. 1.7 W m- 1 K- 1) and specific heat capacity (0.8 kJ kg- 1 K- 1 vs. 0.7 kJ kg- 1 K- 1). Matrix permeability is < 1E-16 m2 for all greywacke samples. Tested lavas exhibit heterogeneous rock properties due to their wide range of porosity (< 1% up to 32%). The thermo-physical rock properties were tested at laboratory conditions (ambient temperature and pressure), which do not reflect the in situ conditions at greater depth. With depth, thermal conductivity and acoustic wave velocity are likely to decrease caused by micro fractures resulting from thermal cracking of the rock, while specific

  2. Composition and evolution of submarine volcanic rocks from the central and western Canary Islands

    NASA Astrophysics Data System (ADS)

    Abratis, M.; Schmincke, H.-U.; Hansteen, T. H.

    2002-08-01

    Submarine volcanic rocks dredged during RV Meteor cruise M43-1 comprise alkali basalts, basanites, nephelinites and their differentiates representing both basement-shield and young post-shield volcanics of Gran Canaria, Tenerife, La Palma and El Hierro. The primitive lavas vary widely in trace element composition (e.g., Zr/Y=6.6-11.7, (La/Sm)N=2.3-5.4, and Ba/Yb=71-311), and they are characterized by steep, rare-earth element patterns with mean (La/Yb)N=16, and by pronounced, positive primitive mantle-normalized Nb and Ta and negative K anomalies similar to HIMU-type basalts. Rocks from the submarine flanks west and north of Gran Canaria are isotopically and geochemically identical to rocks of the subaerial Miocene shield stage, but they are distinct from rocks of the post-shield stages (Zr/Nb=6.3-8.9, 87Sr/86Sr=0.70327-0.70332, 143Nd/144Nd=0.51289-0.51293, 206Pb/204Pb=19.55-19.88). Most rocks dredged from the submarine flanks of Tenerife are isotopically and geochemically similar to rocks of the adjacent subaerial shield remnants, but a few resemble rocks of the subaerial post-shield stages (total range in Zr/Nb=4.6-6.1, 87Sr/86Sr=0.70300-0.70329, 143Nd/144Nd=0.51281-0.51292, 206Pb/204Pb=19.51-19.96). Rocks from the southern submarine ridge of La Palma cover the entire compositional range of the subaerial rocks of that ridge. Additionally, they comprise a high Zr/Nb group which resembles rocks of the ca. 1-Ma-old Taburiente shield of northern La Palma (total range in Zr/Nb=3.0-6.4, 87Sr/86Sr=0.70297-0.70314, 143Nd/144Nd=0.51288-0.51296, 206Pb/204Pb=19.21-19.79). Rocks from the southern submarine ridge of El Hierro compositionally resemble subaerial rocks of the island (Zr/Nb=4.1-6.2, 87Sr/86Sr=0.70296-0.70314, 143Nd/144Nd=0.51291-0.51297, 206Pb/204Pb=19.25-19.91). The degree of melting in the subcanarian mantle is interpreted to decrease from east to west across the archipelago whereas the proportion of depleted mantle component in the melting anomaly increases

  3. The nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain and Kane Springs Wash volcanic centers in southern Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, J. V.; Noble, D. D.; Hsu, L. C.; Hutsinpiller, A.

    1986-01-01

    Four LANDSAT thematic mapping scenes in southern Nevada were requested at two different acquisition times in order to assess the effect of vegetation on the signature of the volcanic units. The remote sensing data acquisition and analysis portion are nearly completed. The LANDSAT thematic mapping data is of good quality, and image analysis techniques are so far successful in delineating areas with distinct spectral characteristics. Spectrally distinct areas were correlated with variations in surface coating and lithologies of the volcanic rocks.

  4. Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain and Kane Springs Wash volcanic centers, southern Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, J. V.; Noble, D. C.; Hsu, L. C.; Hutsinpiller, A.; Spatz, D.

    1986-01-01

    Surface coatings on volcanic rock assemblages that occur at select tertiary volcanic centers in southern Nevada were investigated using LANDSAT 5 Thematic Mapper imagery. Three project sites comprise the subject of this study: the Kane Springs Wash, Black Mountain, and Stonewall Mountain volcanic centers. LANDSAT 5 TM work scenes selected for each area are outlined along with local area geology. The nature and composition of surface coatings on the rock types within the subproject areas are determined, along with the origin of the coatings and their genetic link to host rocks, geologic interpretations are related to remote sensing units discriminated on TM imagery. Image processing was done using an ESL VAX/IDIMS image processing system, field sampling, and observation. Aerial photographs were acquired to facilitate location on the ground and to aid stratigraphic differentiation.

  5. Determination of trace elements in volcanic rock samples collected from cenozoic lava eruption sites using LIBS.

    PubMed

    Gondal, Mohammed A; Nasr, Mohamed M; Ahmed, Zulfiqar; Yamani, Zain H

    2009-04-01

    Trace elements of environmental significance present in the volcanic rock samples collected from sites of the Cenozoic era flood basalt flows and eruptions were detected using locally developed laser-induced breakdown spectrometer. For spectro-chemical analysis of these samples, the plasma was generated by focusing a pulsed Nd: YAG laser radiation at 1064 nm wavelength on the target rock samples. These samples were collected from four widely separated locations surrounding the volcanic eruption sites belonging to the Harrat Hutaymah volcanic field in the vicinity of Taba town, situated to the east of Hail city of northern Saudi Arabia. These samples represent the scoria basalt lava flows as well as a large tuff-ring crater and it contains xenoliths. These flows occur widespread over the Earth's surface in this region, and their contained xenoliths are brought up from depths of a few tens of kilometers. This volcanic field has received much less attention in the previous geological studies; and consequently, its effects on the environment are not well defined. The concentration of different elements of environmental significance like Cr, Pb, Mn, Cd, Sr and other trace metals like Cu, Al, Ca, Mg, Zn, Ti and Fe in these rock samples were determined by spectral analysis. Parametric dependence for improvement of LIBS sensitivity for detection of these elements was also carried out. The highest concentration detected of environmentally significant elements like Cr, Mn, Pb, Sr and Ni are 1910, 1399, 90.5, 12412 and 461.5 ppm, respectively in four different lava samples which are considered to be much higher than the safe permissible limits. The LIBS results were compared with the results obtained using other analytical techniques such as the inductively coupled plasma atomic emission spectroscopy (ICP-AES).

  6. Application Of Continuous Wavelet Transform On Aeromagnetic Data To Identify Volcanic Rocks

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Li, Y.; Liu, T.

    2008-12-01

    This paper focuses on the application of continuous wavelet transform on aeromagnetic data, to locate and characterize volcanic rocks. The studied structure is sited in the north centre of the Huanghua depression in the Bohaiwan basin of east China. As channels of magmatism activities, the faults have caused multi-stage magma outpouring and intrusion, forming igneous rocks of different series of strata. As a traditional frequency decomposition method, the discrete wavelet transform is unable to localize frequency variations over time. To handle this problem, the short time Fourier transform method is widely used for the decomposition of non-stationary signals. One problem with this approach is that the fixed width `window function' results in limited resolution. Therefore, the continuous wavelet transform decomposition was used as an alternative approach to overcome this resolution problem. In the continuous wavelet transform, the signal is multiplied with a function similar to a `window function' but the width of the window is not fixed. The time window width is allowed to vary depending upon the frequency that is being considered. As for the magnetic anomalies of igneous rocks, they have different frequencies due to their depths; by analyzing the complex wavelet-based time-frequency characteristics of certain frequencies, we can identify the residual anomalies caused by volcanic rocks in different depths. The theoretical results show that local high frequency spectrum anomalies are the reflection of magnetic sources, and different scales (or different center frequencies) reflect different source depths, with larger scales for deeper sources. Therefore, by analyzing the complex wavelet-based frequency spectrum under different centre frequencies, we can analyze the distribution of magnetic field sources. Then the continuous wavelet transform was applied on the RTP aeromagnetic data of our study area. The data processing results present a detailed description of the

  7. Raman spectroscopic and scanning electron microscopic analysis of a novel biological colonisation of volcanic rocks

    NASA Astrophysics Data System (ADS)

    Jorge Villar, Susana E.; Edwards, Howell G. M.; Benning, Liane G.

    2006-09-01

    A novel type of colonisation of a basaltic rock, collected on the Arctic island of Svalbard, Norway, during the AMASE expedition in 2004, was characterised using Raman spectroscopy and Scanning Electron Microscopy (SEM). The sample contains two different types of extremophile communities, one occurring behind a radial white crystallisation and the other occurring inside a dark vacuole. Several types of minerals and microbial colonies have been identified by both Raman spectroscopy and SEM analyses. It is the first time that photosynthetic communities have been documented to colonise the inside of dark basaltic rocks. Our discovery has important implications for planetary exploration because it extends the analytical capability and our understanding of microbial rock colonisations to subaerial volcanic outcrops and has wide implications towards the search for life in extraterrestrial planets. In this work we also demonstrate that the use of different laser wavelengths for Raman spectroscopic studies and complementary microscopic analysis are critical for a comprehensive organic and inorganic compound identification.

  8. New insights into the petrogenesis of volcanic rocks in the Shanghang Basin in the Fujian Province, China

    NASA Astrophysics Data System (ADS)

    Jiang, Si-Hong; Bagas, Leon; Liang, Qing-Ling

    2015-06-01

    The Mesozoic Shanghang Basin in southeastern China consists of Early Cretaceous mottled coarse-grained clastic and volcanic rocks, and Late Cretaceous clastic rocks. The volcanic rocks are intermediate-mafic to felsic and spatially close to the famous Zijinshan Mineral Field. In order to better understand the timing, petrogenesis and tectonic setting of these volcanic rocks and the relationship between magmatism and metallogeny in the mineral field, U-Pb zircon geochronological, geochemical and Sr-Nd-Pb-Hf isotopic studies were completed on the volcanic rocks. Fifteen LA-MC-ICP-MS U-Pb zircon analyses of the volcanic rocks yield weighted mean ages of between 105 and 99 Ma. Major and trace element geochemistry shows that these rocks are mostly high-K to shoshonitic, enriched in LREE and Th, U, and depleted in Ba, Nb, Sr, P and Ti. The volcanic rocks have 87Sr/86Sri ratios of between 0.70732 and 0.70977, 206Pb/204Pb isotope ratios of 18.57-19.77, 207Pb/204Pb isotope ratios of 15.64-15.71, 208Pb/204Pb isotope ratios of 38.87-40.62, 176Hf/177Hf ratios of 0.282589-0.282823, εNdT values of -7.5 to -4.7, and εHf(t) values of -4.2 to 4. Such characteristics, with similarities to coeval volcanic and intrusive rocks adjacent to the basin, suggest that the parent magma of the Cretaceous volcanic rocks in the basin and their contemporaneous intrusives originated from crustal melts with a juvenile component. Petrogenetically, fractional crystallization with minor wall-rock assimilation is the controlling process in deriving a wide range of more evolved rocks. With reference to the ore-forming events and isotopic features of ore-related intrusions in the Zijinshan Mineral Field, we propose that volcanism in the Shanghang Basin and coeval magmatism in the mineral field are related to the formation of the regional porphyry and epithermal Cu-Au-Mo-Ag deposits in an extension tectonic setting related to the subduction of the Paleo-Pacific Plate.

  9. Petrology of lower Permian volcanic rocks from the Larne No. 2 (geothermal) Borehole, Co. , Antrim, Northern Ireland

    SciTech Connect

    Harrison, R.K.; Styles, M.T.; Penn, I.E.; Davis, A.E.

    1985-01-01

    The isotopically-dated, Permian volcanic succession penetrated by the Larne No.2 Borehole, Co. Antrim, Northern Ireland was examined petrographically, by electron microprobe analyses of selected samples and by major oxide and trace element chemistry of the only substantial rock fragment recovered. The succession comprises eight stratigraphical units defined by characteristic and predominant lithology and by characteristic gamma-ray and sonic log signatures. The lowest unit penetrated, Breccio-Conglomerate and Sandstone, includes volcanic rocks ranging from olivine-basalt, olivine-free basalt, intermediate lavas, to rhyolite and felsite. These indicate denudation of a predominantly volcanic terrain probably deposited in a proximal alluvial-fan environment.

  10. Some geochemical features of Caledonian volcanism recorded in sedimentary rocks of the East Baltic area

    NASA Astrophysics Data System (ADS)

    Soesoo, Alvar; Kiipli, Tarmo; Kallaste, Toivo

    2013-04-01

    The Caledonian rocks have formed as a result of a multitude of magmatic and tectonic processes. All these major processes have generated a set of volcanic and magmatic products. While products of intrusive magmatism can still be well recognised in Caledonian mountains, some of the volcanic products can be found in a wide area of the Baltica paleocontinent. The best record of the ancient explosive volcanism can be traced in sedimentary sections adjacent to tectonically active areas. The aim of this study is to describe geochemical evolution of the volcanism near the Baltica plate using bulk geochemistry and phenocryst compositions of the Caledonian volcanic ashes stored in the Lower Palaeozoic sections of the Eastern Baltica. The bentonite samples were collected from several drill cores from Estonia, Latvia and Lithuania. Thickness of the ash beds varies mostly between 0.1 and 10 cm, rarely reaching 20-70 cm. Constructed isopach schemes indicate increase of thickness of ash beds towards the northwest and west. Original sanidine composition in ca 400 samples and biotite from 13 ash beds were analysed from grain fraction of bentonites using X-ray diffractometry. Stratigraphical distribution of volcanic ash beds in the East Baltic area can be subdivided into four major intervals separated by intervals with less frequent signs of volcanism. The above intervals show characteristic geochemical signatures. Over 175 thin altered volcanic ash beds have been recognised by authors in the East Baltic sedimentary sections from the Upper Ordovician (ca. 458 Ma) to the Upper Silurian (ca. 421 Ma). There separate ash units may correspond to distinct volcanic eruptions in Caledonides. Volcanic ashes which reached the East Baltic area fall into four time periods (time intervals distinguished by micro-paleontological methods): (1) Sandbian with main sources at the margins of the Avalonian microcontinent; (2) Katian with sources at the margin of the Baltica in Iapetus Palaeo

  11. Uranium geochemistry of selected rock units from the Marysvale Volcanic Field, Piute County, Utah

    SciTech Connect

    Hoffer, R.L.

    1982-01-01

    The Marysvale Volcanic Field is an area rich in uranium. This study was undertaken to determine if the uranium deposits might be of volcanogenic origin. This geochemical study consisted of determining the major, minor and trace element concentrations of the major volcanic units, and the relationships of the rock chemistry to uranium mineralization. The units in the Marysvale Volcanic Field, consist of ash-flow tuffs, intermediate lava flows, and associated intrusives of the Bullion Canyon volcanics and ash-flow tuffs, volcaniclastic deposits, domes and stocks of the Mount Belknap volcanics. When compared to overlaying welded tuff or rhyolitic units, the vitrophyric samples from the Mount Belknap volcanic units, are all enriched in F, Cs, and U, and that 50% of the vitrophyres are enriched in Cr, Cu, Mo, Ni, Zr, Pb, Sr, V, and Zn. Overlying untis have been devitrified and have released U as well as other trace elements into the volcanogenic system. This study has reevaluated the Marysvale Central Mining District and has proposed another theory as to the origin of the uranium deposits in that area. This hypothesis places a previously unidentified caldera around the area, and this author has named it the Marysvale caldera. Evidence for this caldera includes: arcurate faults which surround the region; alteration patterns which appear to form a circular pattern along the boundary of the proposed caldera; the presence of small monzonite intrusive bodies appear to ring the caldera; the presence of ash-flow tuffs which thicken appreciably along the northeast boundary of the caldera; and the central intrusive which may represent a resurgent phase of the proposed caldera. This seems to be a viable alternative to the magmatic hydrothermal origin for the uranium deposits presently proposed for the Central Mining District.

  12. Interpretation of volcanic gas data from tholeiitic and alkaline mafic lavas

    SciTech Connect

    Gerlach, T. M.

    1980-01-01

    Data are tabulated for approximately 150 previously reported collections of high-temperature volcanic gases from basic lavas using computational techniques recently introduced by the author. Research problems dealing with the composition of volcanic gases and their relation to lava chemistry are outlined. The need for more accurate data on the volume of gases released during eruptions is also noted. (PCS)

  13. Geochemistry and tectonic setting of the Central Loei volcanic rocks, Pak Chom area, Loei, northeastern Thailand

    NASA Astrophysics Data System (ADS)

    Panjasawatwong, Y.; Zaw, Khin; Chantaramee, S.; Limtrakun, P.; Pirarai, K.

    2006-01-01

    The Central Loei volcanic rocks, as evidenced by those in the Pak Chom area, were formed in the Late Devonian-Early Carboniferous and can be separated into three magmatic groups: transitional tholeiitic basalt, tholeiitic microgabbro and calc-alkalic basalt/andesite on the basis of immobile-element contents and ratios of least altered samples. All the tholeiitic microgabbro possibly occurred as dikes. Chemically, the transitional tholeittic basalt and tholeiitic microgabbro have higher abundances of TiO 2, Ni and Cr relative to the calc-alkalic basalt/andesite at similar values for FeO*/MgO; they also contain higher Ti/Zr but lower Zr/Nb. The transitional tholeiitic basalt has higher concentrations of P 2O 5 and Nb relative to the tholeiitic microgabbro at similar levels of FeO*/MgO, and also has higher ratios of Nb/Y and Ti/V, but lower values for Ti/Zr and Zr/Nb. In terms of chondrite normalized REE and N-MORB normalized patterns, the transitional tholeiitic basalt, tholeiitic basalt and calc-alkalic basalt/andesite are analogous to those from North Atlantic, Southwest Indian Ridge and New Britain Arc. On this basis, the Central Loei volcanic rocks are comprised of MORBs and oceanic island-arc lavas. These arc lavas may have erupted on an oceanic basement in the same ocean basin as those in the Chiang Rai-Chiang Mai volcanic belt.

  14. Beryllium systematics in young volcanic rocks: implications for /sup 1/Be

    SciTech Connect

    Ryan, J.G.; Langmuir, C.H.

    1988-01-01

    Beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior. Be analyses conducted on well-characterized oceanic and arc volcanic rock suites, as well as on marine sediments, suggest a bulk solid/liquid distribution coefficient of 0.03-0.06 for melting of the mantle and crystallization of basalts. The Be/Nd ratio for many volcanic rocks from diverse tectonic environments is approximately .05, similar to the ratio in chondrites. Be data for samples from volcanic arcs show that there are significant variations in /sup 10/Be//sup 9/Be among different arcs, and that variations in /sup 10/Be are not due to variations in Be concentration alone. For at least one volcano (Bogoslof), the /sup 10/Be//sup 9/Be ratio is constant for samples that vary by a factor of three in both their Be and /sup 10/Be concentrations, suggesting that /sup 10/Be is an inherited magmatic signature and not simply a result of contamination near the surface. In addition, the Be, Nd and Pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the Bogoslof source region - provided the mantle wedge has the isotopic characteristics of depleted MORB. Since /sup 10/Be exists only in the uppermost tens of meters of oceanic sediments, the data suggest an efficient return flux of sediment to the mantle at subduction zones.

  15. Th isotope and U-series studies of subduction-related volcanic rocks

    NASA Astrophysics Data System (ADS)

    Gill, James B.; Williams, Ross W.

    1990-05-01

    The activities of 6-7 radionuclides measured by alpha spectrometry are reported for 35 samples of recent volcanic rocks from 24 volcanoes in 9 arcs. These include continental margins (Cascades, Alaska, Costa Rica), island arcs (the Sunda, Banda, and Sangihe arcs of Indonesia, Marianas, Japan, Aleutians, Antilles, Tonga), and a backarc basin (Lau Basin). Enrichment of 238U over 230Th is more common (over 2/5 of the samples) and greater (up to 59%) in these subduction-related volcanics than in those from other tectonic environments. 230Th /232Th ratios also extend to higher values, both in absolute numbers and relative to other isotope ratios. Enrichment of 210Po and 226Ra over 230Th is widespread and is more common and greater in island arcs than continental margins. The level of Po or Ra enrichment (50-300% in island arcs, 10-50% at continental margins) is similar to that in ocean island and ridge basalts and decreases with differentiation. The differences in Th-U systematics between subduction-related and other volcanic rocks are attributed to variations in the process of melt extraction, changes in bulk partition coefficients within the mantle wedge, or preferential addition of U from subducted lithosphere. Ra enrichments are attributed to partial melting processes which are similar to those at ocean ridges. Smaller excesses at continental margins are attributed either to slower ascent or to differences in the process of melt formation beneath continents.

  16. Microimaging VIS-IR spectroscopy of ancient volcanic rocks as Mars analogues

    NASA Astrophysics Data System (ADS)

    Manzari, Paola; De Angelis, Simone; De Sanctis, Maria Cristina; Di Iorio, Tatiana; Ammannito, Eleonora; Bost, Nicolas; Foucher, Frédéric; Westall, Frances

    2016-07-01

    The SPectral Imager (SPIM) facility is a laboratory VIS-IR spectrometer developed to support spaceborne observations of rocky bodies of the solar system. Currently, this laboratory setup is used to support the Dawn NASA mission and to support the 2018 ExoMars mission in the spectral investigation of Martian subsurface. Specifically, for this mission, a selection of relevant Mars analogue materials has been characterized and stored in the International Space Analogue Rockstore (ISAR), hosted in Orléans, France. In this investigation, two volcanic rock samples from the ISAR collection were analyzed. These two samples were chosen because of their similarity in mineralogical composition and age with Martian basalts and volcanic sands. Moreover, volcanic sands are particularly interesting because they can contain fossils of primitive life forms. The analysis of data collected by SPIM resulted in good agreement with the mineralogical phases detected in these two samples by mineralogical and petrographical techniques, demonstrating the effectiveness of the high spatial and spectral resolution of SPIM for identifying and for mapping different mineralogical species on cut rock and mineral samples.

  17. Matrix diffusion of some alkali- and alkaline earth-metals in granitic rock

    SciTech Connect

    Johansson, H.; Byegaard, J.; Skarnemark, G.; Skaalberg, M.

    1997-12-31

    Static through-diffusion experiments were performed to study the diffusion of alkali- and alkaline earth-metals in fine-grained granite and medium-grained Aespoe-diorite. Tritiated water was used as an inert reference tracer. Radionuclides of the alkali- and alkaline earth-metals (mono- and divalent elements which are not influenced by hydrolysis in the pH-range studied) were used as tracers, i.e., {sup 22}Na{sup +}, {sup 45}Ca{sup 2+} and {sup 85}Sr{sup 2+}. The effective diffusivity and the rock capacity factor were calculated by fitting the breakthrough curve to the one-dimensional solution of the diffusion equation. Sorption coefficients, K{sub d}, that were derived from the rock capacity factor (diffusion experiments) were compared with K{sub d} determined in batch experiments using crushed material of different size fractions. The results show that the tracers were retarded in the same order as was expected from the measured batch K{sub d}. Furthermore, the largest size fraction was the most representative when comparing batch K{sub d} with K{sub d} evaluated from the diffusion experiments. The observed effective diffusivities tended to decrease with increasing cell lengths, indicating that the transport porosity decreases with increasing sample lengths used in the diffusion experiments.

  18. Major element, REE, and Pb, Nd and Sr isotopic geochemistry of Cenozoic volcanic rocks of eastern China: implications for their origin from suboceanic-type mantle reservoirs

    USGS Publications Warehouse

    Basu, A.R.; Wang, Junwen; Huang, Wankang; Xie, Guanghong; Tatsumoto, M.

    1991-01-01

    Major- and rare-earth-element (REE) concentrations and UThPb, SmNd, and RbSr isotope systematics are reported for Cenozoic volcanic rocks from northeastern and eastern China. These volcanic rocks, characteristically lacking the calc-alkaline suite of orogenic belts, were emplaced in a rift system which formed in response to the subduction of the western Pacific plate beneath the eastern Asiatic continental margin. The rocks sampled range from basanite and alkali olivine basalt, through olivine tholeiite and quartz tholeiite, to potassic basalts, alkali trachytes, pantellerite, and limburgite. These rock suites represent the volcanic centers of Datong, Hanobar, Kuandian, Changbaishan and Wudalianchi in northeastern China, and Mingxi in the Fujian Province of eastern China. The major-element and REE geochemistry is characteristic of each volcanic suite broadly evolving through cogenetic magmatic processes. Some of the outstanding features of the isotopic correlation arrays are as follows: (1) NdSr shows an anticorrelation within the field of ocean island basalts, extending from the MORB end-member to an enriched, time-averaged high Rb Sr and Nd Sr end-member (EM1), (2) SrPb also shows an anticorrelation, similar to that of Hawaiian and walvis Ridge basalts, (3) NdPb shows a positive correlation, and (4) the 207Pb 204Pb vs 206Pb 204Pb plot shows linear arrays parallel to the general trend (NHRL) for MORB on both sides of the geochron, although in the 208Pb 204Pb vs 206Pb 204Pb plot the linear array is significantly displaced above the NHRL in a pattern similar to that of the oceanic island basalts that show the Dupal signatures. In all isotope correlation patterns, the data arrays define two different mantle components-a MORB-like component and an enriched mantle component. The isotopic data presented here clearly demonstrate the existence of Dupal compositions in the sources of the continental volcanic rocks of eastern China. We suggest that the subcontinental mantle

  19. Plutonic rocks of intermediate composition on Gran Canaria: the missing link of the bimodal volcanic rock suite

    NASA Astrophysics Data System (ADS)

    Freundt-Malecha, B.

    2001-07-01

    Analysis of abundant plutonic fragments in the voluminous Miocene rhyolitic-basaltic composite ignimbrite P1, the initial felsic cooling unit overlying the basaltic shield on Gran Canaria, helps to solve the problem of bimodal volcanism. Syenogabbros dominate the plutonic suite and provide evidence that magmas of intermediate composition formed abundantly at depth but did not erupt. The entire suite of plutonic fragments comprises (1) pyroxenitic to gabbroic cumulates that directly influenced the liquid line of descent of P1 magmas, (2) gabbro, syenogabbro, syenodiorite and quartz-syenite fragments showing moderate degrees of hydrothermal alteration (chloritization, partial melting), and (3) diverse xenoliths differing significantly in bulk-rock composition and texture from the erupted P1 magmas. The compositions of plutonic series (2) overlap with both bulk-rock and mineral compositions of the erupted magmas, whereas series (1) rocks show lower alkali and silica contents. Compositional variations among the plutonic rocks are compatible with fractional crystallization as the major petrogenetic process, locally modified by magma mixing and selective element contamination. Variations in trace element concentrations of the plutonic rocks, however, are inferred to be the result of evolved interstitial melts penetrating into, or draining out of, crystalline mushes during slow intratelluric solidification. The presence of F-rich amphibole suggests that crystalline mushes were invaded by F-bearing fluids. Overall compositional similarity, and the fact that selective contamination effects are similar, support the interpretation that the series (2) plutonic fragments represent solidified portions of the magmatic system that ultimately produced the erupted P1 magmas. This system extended from the zone of underplating at the mantle-crust boundary through the lower and into the upper crust of Gran Canaria and was roughly vertically zoned in composition as shown by

  20. Pan-African adakitic rocks of the north Arabian-Nubian Shield: petrological and geochemical constraints on the evolution of the Dokhan volcanics in the north Eastern Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Obeid, Mohamed A.; Azer, Mokhles K.

    2015-04-01

    The Precambrian basement of Egypt is part of the Red Sea Mountains and represents the north-western part of the Arabian-Nubian Shield (ANS). Five volcanic sections are exposed in the Egyptian basement complex, namely El Kharaza, Monqul, Abu Had, Mellaha and Abu Marwa. They are located in the north Eastern Desert (ED) of Egypt and were selected for petrological and geochemical studies as they represent the Dokhan volcanics. The volcanics divide into two main pulses, and each pulse was frequently accompanied by deposition of immature molasse type sediments, which represent a thick sequence of the Hammamat group in the north ED. Compositionally, the rocks form a continuum from basaltic andesite, andesite, dacite (lower succession) to rhyodacite and rhyolite (upper succession), with no apparent compositional gaps. These high-K calc-alkaline rocks have strong affinities to subduction-related rocks with enriched LILEs (Rb, Ba, K, Th, Ce) relative to high field strength elements (Nb, Zr, P, Ti) and negative Nb anomalies relative to NMORB. The lower succession displays geochemical characteristics of adakitic rocks with SiO2 >53 wt%, Al2O3 >15 wt%, MgO >2.5 wt%, Mg# >49, Sr >650 ppm, Y <17 ppm, Yb <2 ppm, Ni >25 ppm, Cr >50 ppm and Sr/Y >42.4. They also have low Nb, Rb and Zr compared to the coexisting calc-alkaline rhyodacites and rhyolites. The highly fractionated rhyolitic rocks have strong negative Eu anomalies and possess the geochemical characteristics of A-type suites. Trace element geochemical signatures indicate a magma source consistent with post-collisional suites that retain destructive plate signatures associated with subduction zones. The adakitic rocks in the northern ANS are generated through partial melting of delaminated mafic lower crust interacting with overlying mantle-derived magma. The Dokhan volcanics were likely generated by a combination of processes, including partial melting, crystal fractionation and assimilation.

  1. Geochronological and geochemical constraints on the petrogenesis of late Cretaceous volcanic rock series from the eastern Sakarya zone, NE Anatolia-Turkey

    NASA Astrophysics Data System (ADS)

    Aydin, Faruk; Oǧuz, Simge; Şen, Cüneyt; Uysal, İbrahim; Başer, Rasim

    2016-04-01

    New SHRIMP zircon U-Pb ages and whole-rock geochemical data as well as Sr-Nd-Pb and δ18O isotopes of late Cretaceous volcanic rock series from the Giresun and Artvin areas (NE Anatolia, Turkey) in the northern part of the eastern Sakarya zone (ESZ) provide important evidence for northward subduction of the Neo-Tethyan oceanic lithosphere along the southern border of the ESZ. In particular, tectonic setting and petrogenesis of these subduction-related volcanites play a critical role in determining the nature of the lower continental crust and mantle dynamics during late Mesozoic orogenic processes in this region. The late Cretaceous time in the ESZ is represented by intensive volcanic activities that occurred in two different periods, which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic to rhyolitic) within each period. Although there is no geochronological data for the lower mafic-intermediate rock series of the first volcanic period, U-Pb zircon dating from the first cycle of felsic rocks yielded ages ranging from 88.6±1.8 to 85.0±1.3 Ma (i.e. Coniacian-Early Santonian). The first volcanic period in the region is generally overlain by reddish biomicrite-rich sedimentary rocks of Santonian-Early Campanian. U-Pb zircon dating for the second cycle of mafic-intermediate and felsic rocks yielded ages varying from 84.9±1.7 to 80.8±1.5Ma (i.e. Early to Middle Campanian). The studied volcanic rocks have mostly transitional geochemical character changing from tholeiitic to calc-alkaline with typical arc signatures. N-MORB-normalised multi-element and chondrite-normalised rare earth element (REE) patterns show that all rocks are enriched in LILEs (e.g. Rb, Ba, Th) and LREEs (e.g. La, Ce) but depleted in Nb and Ti. In particular, the felsic samples are characterised by distinct negative Eu anomalies. The samples are characterized by a wide range of Sr-Nd-Pb isotopic compositions (initial ɛNd values from -7

  2. Solid Inclusions in Au-nuggets, genesis and derivation from alkaline rocks of the Guli Massif, Northern Siberia

    NASA Astrophysics Data System (ADS)

    Dvorani, Sami N.

    2016-04-01

    A total of 112 Au-nuggets, collected from alluvial placer deposits of the Ingarinda River from the Guli massif, located in northem Siberia, Russia, were investigated. The Guli massif consists of a huge dunite-clinopyroxenite complex (the largest complex in the world), an alkaline to highly alkaline rock suite (melilite, nephelinite, ijolite) enveloping the dunite and carbonatite intrusions, associated with disseminated schlieren type chromitite and Au-Ag, Pt placer deposits. The nuggets are characterized by various sizes and shapes and show chemical compositions Au, Au-Ag and AuCu, typical for a derivate of carbon-atites and/or ultramafic complexes. A great variety of oxide, silicate, REE-minerals, carbonate and sulphide inclusions have been detected in the nuggets, which are identical in mineralogy and chemical composition to mineral constituents of the alkaline to highly alkaline rock suite surrounding the Guli dunite core complex thus, considered as the source for Au-nuggets.

  3. Direct determination of total mercury in phosphate rock using alkaline fusion digestion.

    PubMed

    D'Agostino, Fabio; Oliveri, Elvira; Bagnato, Emanuela; Falco, Francesca; Mazzola, Salvatore; Sprovieri, Mario

    2014-12-10

    The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473. Therefore, to improve the recovery of total Hg, we performed alkaline fusion digestion (AFD) directly inside the furnace of the instrument, using BCR(32) as a certified reference material (Moroccan phosphate rock--phosphorite). The salts used for the AFD were a mixture of Na2CO3, K2CO3 and Li2CO3, which melt at about 400°C, due to their ability to form a ternary eutectic and to decompose the phosphorite matrices at 700°C. By adopting this analytical approach, the Hg recovery in BCR(32) was about 100%, compared to 40% when the reference material was analysed without using the alkaline fusion salt. We suggest that the AFD allowed the decomposition of the sample matrix and that some Hg compounds linked with other functional groups may be transformed in carbonates that sublimate at lower temperatures than other Hg compounds. This original method was tested on a number of different geological samples to compare the differences between the AFD method and the thermal treatment in order to verify the working range and to check the robustness of the new approach.

  4. A Backarc Basin Origin for the Eocene Volcanic Rocks North of Abbas Abad, East of Shahrud, Northeast Iran

    NASA Astrophysics Data System (ADS)

    Khalatbari Jafari, M.; Mobasher, K.; Davarpanah, A.; Babaie, H.; La Tour, T.

    2008-12-01

    The region in northeastern Iran, bordered by the Miami fault and the Doruneh fault, mainly exposes the Eocene volcanic and Tertiary sedimentary rocks and sporadic outcrops of pre- Jurassic metamorphic rocks such as gneiss and mica-schist. We have divided the volcanic and volcanic-sedimentary rocks into six main units: E1 through the youngest E6. North of Abbas Abad, the Lower Eocene is conglomerate, sandstone, and red shale with lenses of nummulite-bearing limestone at the base, and dacitic lava (E1) at the top. The nummulites give an Early Eocene age for the limestone lenses. The E2 unit includes vesicular basalt, intercalated, intraformational conglomerate, and lenses of nummulite-bearing limestone. E3 is volcanic- sedimentary, and is made of green tuff, tuffite, shale, and nummulite bearing limestone. E4 includes basalt and vesicular trachy-basalt, and E5 is mostly sedimentary, made of tan marl, sandstone, shale, and lenses of Middle Eocene nummulite-bearing limestone. The E6 unit is the most extensive, with at least three levels of nummulite-bearing limestone lenses which give a Middle to Early Eocene age. The volcanic rocks of the E6 unit include few hundred meters of epiclastic to hyaloclastic breccia, with intercalations of lava at the base. These are overlain by four horizons of aphyric olivine basalt and basalt, and phyric trachy-andesite and trachy-basalt. The volume of the aphyric lavas decreases, and that of the phyric lavas increases upsection. The Eocene volcanic sequence is covered by turbidite; the marl washings give an Eocene-Oligocene age range. Chondrite-normalized multi-element plots indicate enrichment of the Eocene Abbas Abad volcanic rocks in the LILE elements, with variable ratios of La/Yb (4.36-19.33) and La/Sm (3.10-7.91). These plots show a gentle slope, and the volcanic rocks in the E1 to E4 units are less enriched than those in the E6 unit, probably reflecting the difference in the original source for the melt. The multi-element plots

  5. The Role Of Low-Pressure Fractination In The Petrogenesis Of The Kula Volcanic Province, Western Turkey

    NASA Astrophysics Data System (ADS)

    Kilinc, A. I.; Solpuker, U.

    2005-12-01

    Experimental data show that diversity of alkaline rocks in different tectonic environments is controlled by low-pressure fractionation of their magmas. In order to test this hypothesis we studied the alkaline rocks of the Kula Volcanic Province (KVP) in western Turkey. KVP experienced three episodes of volcanic activity (Burgaz Volcanism (1.1 ma), Elekcitepe Volcanism (0.3 ma) and Divlittepe Volcanism (0.03 ma)), which exposed the alkaline volcanic rocks of KVP to north of the Alasehir graben. An area of approximately 300 km2 exhibits a volcanic rock suite of basanites, phonotephrites, tephriphonolites and trachybasalts. Major, trace and REE modeling of the Quaternary alkaline volcanic rocks of the Kula Volcanic Province (KVP), show that chemical spectrum shown by the rocks is the result of low-pressure fractionation of parental magmas. Bulk compositions of the KVP rocks, when projected on the normative pseudoternary olivine - clinopyroxene - nepheline diagram, follow a path parallel to and just below of the experimentally derived 1 atmosphere cotectic. This further supports the conclusion that KVP rocks represent low-pressure fractionation of alkaline parental magmas of the KVP.

  6. Nature and occurrence of cooling-induced cracking in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Browning, John; Meredith, Philip G.; Gudmundssom, Agust

    2015-04-01

    Several hypotheses have been proposed regarding the role of thermo-mechanical contraction in producing cracks and joints in volcanic rocks. Nevertheless, most studies of thermally-induced cracking to date have focused on the generation of cracks formed during heating. In this latter case, the cracks are formed under an overall compressional regime. By contrast, cooling cracks are formed under an overall tensile regime. Therefore, both the nature and mechanism of crack formation during cooling are hypothesised to be different from those for crack formation during heating. Furthermore, it remains unclear whether cooling simply reactivates pre-existing cracks, induces the growth of new cracks, or both. We present results from experiments based on a new method for testing ideas on cooling-induced cracking. Cored samples of volcanic rock (basaltic to dacitic in composition) were heated at varying rates to different maximum temperatures inside a tube furnace. In the highest temperature experiments samples of both rocks were raised to the liquidus temperature appropriate to their composition, forcing melt interaction and crack annealing. We present in-situ seismic velocity and acoustic emission data, which were recorded throughout each heating and cooling cycle. It is found consistently that the rate of acoustic emission is much higher during cooling than during heating. In addition, acoustic emission events produced on cooling tend to be significantly higher in energy than those produced during heating. We therefore suggest that cracks formed during cooling are significantly larger than those formed during heating. Thin-section and crack morphology analysis of our cyclically heated samples provide further evidence of contrasting fracture morphologies. These new data are important for assessing the contribution of cooling-induced damage within volcanic structures and layers such as sills and lava flows. Our observations may also help to constrain evolving ideas regarding

  7. Crystal chemistry of clinopyroxene from alkaline undersaturated rocks of the Monte Vulture Volcano, Italy

    NASA Astrophysics Data System (ADS)

    Bindi, Luca; Cellai, Daniela; Melluso, Leone; Conticelli, Sandro; Morra, Vincenzo; Menchetti, Silvio

    1999-02-01

    The Monte Vulture is a Late Pleistocene stratovolcano, composed of highly undersaturated alkaline potassic to ultrapotassic rocks belonging to the Roman Magmatic Province. These rocks are notably richer in Na 2O if compared to similar rocks of the Roman Province. Two distinct magmatic Series have been recognized: (1) feldspar-bearing series, ranging from basanite to phonolite, and a volumetrically subordinate (2) feldspar-free series, consisting of melilitite, melafoidite, and haüynophyre. The clinopyroxene compositions of the feldspar-bearing series ranges from diopside to ferro-salite (hedenbergite), and shows, from basanite to phonotephrite, increasing FeO tot, Al 2O 3, and TiO 2 and decreasing of MgO contents. Clinopyroxene in basanites and tephrites has generally high Fe 3+ contents, which is typical for clinopyroxene from the Roman Province. Clinopyroxene of the feldspar-free series shows a more restricted variation in MgO, and has often very high Al 2O 3, FeO tot, and TiO 2 contents. In all the crystals examined the Al 3+ content is high and is present mostly on the T site and for a minor part on the M1 site. The M1-O2 distance shows a good correlation with the R M13+ content; clinopyroxene from basanites (feldspar-bearing series) has the lowest R M13+ and that from melilitite and haüynophyre (feldspar-free series) the highest R M13+ contents. Clinopyroxene crystals from feldspar-free rocks have smaller M1 and larger T polyhedral volumes when compared to those in olivine-melilitites and melilitites (kamafugites) from Umbria, but they show similar polyhedral volumes as clinopyroxene crystals from leucite-bearing rocks. Although clinopyroxene from feldspar-free rocks has small M1 volumes due to the high R 3+ contents, M1 volumes of clinopyroxene from melilitites are larger than expected because of the higher (Fe 3+/Al 3+) M1 values. This larger M1 volume of clinopyroxene in melilitites causes a shortening of and a lengthening of the M2-O3 distance

  8. Orogenic potassic mafic magmatism, a product of alkaline-peraluminous mixing ? Variscan 'calc-alkaline' rocks from the Central Iberian and Ossa Morena Zones, Central Spain.

    NASA Astrophysics Data System (ADS)

    Scarrow, Jane H.; Cambeses, Aitor; Bea, Fernando; Montero, Pilar; Molina, José F.; Moreno, Juan Antonio

    2013-04-01

    Orogenic magmatic rocks provide information about mantle and crust melt-generation and -interaction processes. In this context, minor potassic mafic stocks which are formed of enriched mantle and crustal components and are common as late-orogenic intrusions in granitic plutons give insight into the timing of new crust formation and crustal recycling. Potassic mafic stocks are prevalent, albeit low volume, constituents of granite batholiths all through the European Variscan (350-280 Ma). In the Central Iberia Zone, Spanish Central System, crustal-melt, S-type, granitoid plutons are intruded by minor concomitant ultramafic-intermediate appinitic-vaugneritic stocks. Notwithstanding their whole-rock calc-alkaline composition, the stocks apparently did not have a subduction-related origin. Recent studies have attributed their genesis to mixing of alkaline mantle and peraluminous crustal melts. Their primary alkaline character, as indicated by amphibole and biotite mineral chemistry data, points, rather, towards an extension-related genesis. In the Ossa Morena Zone, south of the Central Iberian Zone, the igneous rocks also have a whole-rock calc-alkaline composition which has been considered to be the result of northward subduction of the South Portuguese Zone. Nevertheless, identification of a 'sill' of significant volume of mafic magma in the middle crust, the ´IBERSEIS reflective body', in a seismic profile across the Ossa Morena and South Portuguese Zones has cast doubt upon the calc-alkaline magmatism-subduction model; leading, instead, to the magmatism being attributed to intra-orogenic extension related to a mantle plume active from 340 Ma to 330 Ma. The aim here, then, is to reinvestigate the petrogenesis and age of the calc-alkaline rocks of the Ossa Morena Zone to determine their tectonomagmatic context be it subduction-, plume- or extension-related, and establish what they may reveal about mantle-crust interactions. Focussing, initially, on the Valencia del

  9. Cenozoic Volcanic Rocks of the Devils Postpile Quadrangle, Eastern Sierra Nevada, California

    USGS Publications Warehouse

    Huber, N. King; Rinehart, C. Dean

    1967-01-01

    Cenozoic volcanic rocks of the Devils Postpile quadrangle are of late Pliocene to Recent age and are divided into 11 map units. The suite is alkalic-calcic and ranges in composition from basalt to rhyolite. It includes a rhyolitic welded ash-flow tuff which is probably correlative with the Bishop Tuff, although the two units are geographically isolated by the Sierra Nevada drainage divide. The Devils Postpile itself is a classic example of columnar jointing in the lower part of a lava flow.

  10. Geology and stratigraphy of the Challis Volcanic Group and related rocks, Little Wood River area, south-central Idaho

    USGS Publications Warehouse

    Sandford, Richard F.; Snee, Lawrence W.

    2005-01-01

    The southwestern part of the Challis volcanic field occupies the valley of the Little Wood River and its tributaries in the Hailey and Idaho Falls 1??2? quadrangles of south-central Idaho. The Little Wood River area is a structurally controlled topographic basin that is partly filled by Eocene Challis Volcanic Group and younger rocks. Rock types in the Challis Volcanic Group of the Little Wood River area include, in order of decreasing abundance, andesite lava flows and tuff breccia, dacite lava flows and flow breccia, volcaniclastic sedimentary rocks, lithic tuff, nonvolcanic conglomerate, and rhyolite dikes. A basal nonvolcanic conglomerate, that locally rests on upper Paleozoic sedimentary rocks at a regional unconformity, was deposited prior to eruption of volcanic rocks. Andesite was the first volcanic rock erupted and is a voluminous sequence as thick as 3,000 ft (1,000 m). Locally thick volcaniclastic sedimentary rocks accumulated in topographic lows. A sharp transition marks the beginning of dacite eruption from fissures and flow-dome complexes. Dacite flows and breccias are as thick as 2,000 ft (600 m). An upper volcaniclastic unit was deposited in paleotopographic lows following emplacement of the main dacite unit. Next, a widespread, distinctive, lithic rich ash flow tuff, correlated with the tuff of Stoddard Gulch, was deposited over much of the area. Deposition of the tuff was followed by eruption of thin andesite and dacite lava flows and deposition of conglomeratic sedimentary rocks. The entire sequence was then intruded by a dacite flow-dome complex composed of at least three separate intrusions. The Challis Volcanic Group in the study area is calcalkaline. Andesitic rocks are typically high potassium basaltic andesite, high potassium andesite, shoshonite, and banakite (latite). Dacitic rocks are high potassium dacite and trachyte. Tuffs and vitrophyres range in composition from basaltic andesite to trachyte. The paleotopographic basin in which the

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

    USGS Publications Warehouse

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

    2004-01-01

    Middle Tertiary volcanic rocks of the central Chiricahua Mountains in southeast Arizona are the westernmost constituents of the Eocene-Oligocene Boot Heel volcanic field of southwestern New Mexico and southeastern Arizona. About two dozen volumetric ally and stratigraphically significant volcanic units are present in this area. These include large-volume, regionally distributed ash-flow tuffs and smaller volume, locally distributed lava flows. The most voluminous of these units is the Rhyolite Canyon Tuff, which erupted 26.9 million years ago from the Turkey Creek caldera in the central Chiricahua Mountains. The Rhyolite Canyon Tuff consists of 500-1,000 cubic kilometers of rhyolite that was erupted from a normally zoned reservoir. The tuff represents sequential eruptions, which became systematically less geochemically evolved with time, from progressively deeper levels of the source reservoir. Like the Rhyolite Canyon Tuff, other ashflow tuffs preserved in the central Chiricahua Mountains have equivalents in nearby, though isolated mountain ranges. However, correlation of these other tuffs, from range to range, has been hindered by stratigraphic discontinuity, structural complexity, and various lithologic similarities and ambiguities. New geochemical and geochronologic data presented here enable correlation of these units between their occurrences in the central Chiricahua Mountains and the remainder of the Boot Heel volcanic field. Volcanic rocks in the central Chiricahua Mountains are composed dominantly of weakly peraluminous, high-silica rhyolite welded tuff and rhyolite lavas of the high-potassium and shoshonitic series. Trace-element, and to a lesser extent, major-oxide abundances are distinct for most of the units studied. Geochemical and geochronologic data depict a time and spatial transgression from subduction to within-plate and extensional tectonic settings. Compositions of the lavas tend to be relatively homogeneous within particular units. In

  12. Lead and strontium isotopes in rocks of the Absaroka volcanic field, Wyoming

    USGS Publications Warehouse

    Peterman, Z.E.; Doe, B.R.; Prostka, H.J.

    1970-01-01

    The Absaroka volcanic field is comprised of predominant andesitic volcaniclastic rocks and less abundant potassium-rich mafic lavas (shoshonites and absarokites). Strontium and lead isotopic variations preclude a simple derivation from an isotopically uniform source: Sr87/Sr86, 0.7042 to 0.7090; Pb206/Pb204, 16.31 to 17.30; Pb208/Pb204, 36.82 to 37.64. We postulate that these rocks were derived from a lower crust or upper mantle which underwent a preferential loss of uranium relative to lead approximately 2800??200 m.y. ago. Variations in lead and strontium isotopic compositions are thought to reflect small inhomogeneities in U/Pb and Rb/Sr ratios in the source. ?? 1970 Springer-Verlag.

  13. Weathering and deterioration of volcanic tuff rocks used as natural building stone caused by moisture expansion

    NASA Astrophysics Data System (ADS)

    Wedekind, W.; Lopez-Doncel, R.; Dohrmann, R.; Siegesmund, S.

    2012-04-01

    Volcanic tuff rocks are one of the most frequently used natural building rocks. Tuff rocks show great assortment in composition, grain size, sorting and textures, however scaling, flaking and cracking mostly affect all of them. Diverse authors suggest, that the swelling ability of clay minerals provoke moisture expansion contributing for the weathering and deterioration of the rocks and finally for the construction. Fourteen building volcanic tuff rocks from Germany, Hungary and Mexico of different ages, with diverse compositions and weathering conditions were studied in order to determine the influence of the moisture content regarding their deterioration. Hydric (water saturated) and hygric (related to the relative humidity) wetting experiments realized on the tuffs show that the phenomenon of the expansion certainly can be related to the content on clay minerals, which were clearly identified by XRD analysis. The moisture contents also dependents on the porosity, principally effective porosity and the radii distribution of the pores, because more water can be adsorbed and transported into the rock. However, there are tuff samples, which show a moderate or none expansion, although they have an important amount of clay minerals. Petrographic and geochemical analysis show, that the presence of other phyillosilicate minerals, like muscovite (sericite) and biotite, plays likewise an important role during the moisture expansion. On the other hand we identified a tuff type rich in clay minerals, which shows important hygric expansion but it is not so clear by the hydric water immersion experiment, because this tuff contains a high amount of calcium carbonate, principally in the fine grained matrix causing dissolution of the matrix and crumbling of the non-soluble particles including the clay-silt fraction. In this case it seems to be that the dissolution of the carbonate matrix causes a secondary porosity, which accelerates and favors the expansion and in consequent

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

    USGS Publications Warehouse

    Lindsey, David A.

    1982-01-01

    The Thomas Range and northern Drum Mountains have a history of volcanism, faulting, and mineralization that began about 42 m.y. (million years) ago. Volcanic activity and mineralization in the area can be divided into three stages according to the time-related occurrence of rock types, trace-element associations, and chemical composition of mineral deposits. Compositions of volcanic rocks changed abruptly from rhyodacite-quartz latite (42-39 m.y. ago) to rhyolite (38-32 m.y. ago) to alkali rhyolite (21 and 6-7 m.y. ago); these stages correspond to periods of chalcophile and siderophile metal mineralization, no mineralization(?), and lithophile metal mineralization, respectively. Angular unconformities record episodes of cauldron collapse and block faulting between the stages of volcanic activity and mineralization. The youngest angular unconformity formed between 21 and 7 m.y. ago during basin-and-range faulting. Early rhyodacite-quartz latite volcanism from composite volcanoes and fissures produced flows, breccias, and ash-flow tuff of the Drum Mountains Rhyodacite and Mt. Laird Tuff. Eruption of the Mt. Laird Tuff about 39 m.y. ago from an area north of Joy townsite was accompanied by collapse of the Thomas caldera. Part of the roof of the magma chamber did not collapse, or the magma was resurgent, as is indicated by porphyry dikes and plugs in the Drum Mountains. Chalcophile and siderophile metal mineralization, resulting in deposits of copper, gold, and manganese, accompanied early volcanism. Te middle stage of volcanic activity was characterized by explosive eruption of rhyolitic ash-flow tuffs and collapse of the Dugway Valley cauldron. Eruption of the Joy Tuff 38 m.y. ago was accompanied by subsidence of this cauldron and was followed by collapse and sliding of Paleozoic rocks from the west wall of the cauldron. Landslides in The Dell were covered by the Dell Tuff, erupted 32 m.y. ago from an unknown source to the east. An ash flow of the Needles Range

  15. Preliminary Numerical Simulations of Nozzle Formation in the Host Rock of Supersonic Volcanic Jets

    NASA Astrophysics Data System (ADS)

    Wohletz, K. H.; Ogden, D. E.; Glatzmaier, G. A.

    2006-12-01

    Recognizing the difficulty in quantitatively predicting how a vent changes during an explosive eruption, Kieffer (Kieffer, S.W., Rev. Geophys. 27, 1989) developed the theory of fluid dynamic nozzles for volcanism, utilizing a highly developed predictive scheme used extensively in aerodynamics for design of jet and rocket nozzles. Kieffer's work shows that explosive eruptions involve flow from sub to supersonic conditions through the vent and that these conditions control the erosion of the vent to nozzle shapes and sizes that maximize mass flux. The question remains how to predict the failure and erosion of vent host rocks by a high-speed, multiphase, compressible fluid that represents an eruption column. Clearly, in order to have a quantitative model of vent dynamics one needs a robust computational method for a turbulent, compressible, multiphase fluid. Here we present preliminary simulations of fluid flowing from a high-pressure reservoir through an eroding conduit and into the atmosphere. The eruptive fluid is modeled as an ideal gas, the host rock as a simple incompressible fluid with sandstone properties. Although these simulations do not yet include the multiphase dynamics of the eruptive fluid or the solid mechanics of the host rock, the evolution of the host rock into a supersonic nozzle is clearly seen. Our simulations show shock fronts both above the conduit, where the gas has expanded into the atmosphere, and within the conduit itself, thereby influencing the dynamics of the jet decompression.

  16. A Comprehensive Study on Dielectric Properties of Volcanic Rock/PANI Composites

    NASA Astrophysics Data System (ADS)

    Kiliç, M.; Karabul, Y.; Okutan, M.; İçelli, O.

    2016-05-01

    Basalt is a very well-known volcanic rock that is dark colored and relatively rich in iron and magnesium, almost located each country in the world. These rocks have been used in the refused rock industry, to produce building tiles, construction industrial, highway engineering. Powders and fibers of basalt rocks are widely used of radiation shielding, thermal stability, heat and sound insulation. This study examined three different basalt samples (coded CM-1, KYZ-13 and KYZ-24) collected from different regions of Van province in Turkey. Polyaniline (PANI) is one of the representative conductive polymers due to its fine environmental stability, huge electrical conductivity, as well as a comparatively low cost. Also, the electrical and thermal properties of polymer composites containing PANI have been widely studied. The dielectric properties of Basalt/Polyaniline composites in different concentrations (10, 25, 50 wt.% PANI) have been investigated by dielectric spectroscopy method at the room temperature. The dielectric parameters (dielectric constants, loss and strength) were measured in the frequency range of 102 Hz-106 Hz at room temperature. The electrical mechanism change with PANI dopant. A detailed dielectrically analysis of these composites will be presented.

  17. Geochemical and isotopic composition of volcanic rocks of the heterogeneous Miocene (~ 23-19 Ma) Tepoztlán Formation, early Transmexican Volcanic Belt, Mexico

    NASA Astrophysics Data System (ADS)

    Torres-Alvarado, Ignacio S.; Lenhardt, Nils; Arce, José Luis; Hinderer, Matthias

    2016-04-01

    We present the first geochemical data (major and trace elements, as well as Sr, Nd, and Pb isotopes) on volcanic rocks from the Tepoztlán Formation in the central Transmexican Volcanic Belt. The Tepoztlán Formation is up to 800 m thick and comprises a wide range of primary volcanic rocks (lavas, pyroclastic density current deposits, pyroclastic fall deposits), and their secondary reworked products due to mass flow (lahars) and fluvial processes. Magnetostratigraphy combined with K/Ar and Ar/Ar geochronology suggests an age of Early Miocene (23-19 Ma) for this Formation. Lava flows, pyroclastic rocks, dykes and volcanic clasts range from basaltic andesite to rhyolite, with a clear dominance of andesites and dacites. All samples are subalkaline and hy-normative. These rocks show homogeneous REE patterns with LREE enrichment and higher LILE concentrations with respect to HFSE, notably the typical negative anomaly of Nb, Ta, and Ti, suggesting a subduction-related magma genesis. Major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the Tepoztlán Formation magmas. Isotopic compositions of the Tepoztlán Formation samples range from (87Sr/86Sr)t = 0.703693 to 0.704355 and (143Nd/144Nd)t = 0.512751 to 0.512882, falling within the mantle array. All geochemical characteristics indicate that these rocks originated from a heterogeneous mantle, modified and evolved through assimilation of country rock and fractional crystallization in the upper crust.

  18. Origin and accumulation mechanisms of petroleum in the Carboniferous volcanic rocks of the Kebai Fault zone, Western Junggar Basin, China

    NASA Astrophysics Data System (ADS)

    Chen, Zhonghong; Zha, Ming; Liu, Keyu; Zhang, Yueqian; Yang, Disheng; Tang, Yong; Wu, Kongyou; Chen, Yong

    2016-09-01

    The Kebai Fault zone of the West Junggar Basin in northwestern China is a unique region to gain insights on the formation of large-scale petroleum reservoirs in volcanic rocks of the western Central Asian Orogenic Belt. Carboniferous volcanic rocks are widespread in the Kebai Fault zone and consist of basalt, basaltic andesite, andesite, tuff, volcanic breccia, sandy conglomerate and metamorphic rocks. The volcanic oil reservoirs are characterized by multiple sources and multi-stage charge and filling history, characteristic of a complex petroleum system. Geochemical analysis of the reservoir oil, hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source, the petroleum filling history, and the dominant mechanisms controlling the petroleum accumulation. Reservoir oil geochemistry indicates that the oil contained in the Carboniferous volcanic rocks of the Kebai Fault zone is a mixture. The oil is primarily derived from the source rock of the Permian Fengcheng Formation (P1f), and secondarily from the Permian Lower Wuerhe Formation (P2w). Compared with the P2w source rock, P1f exhibits lower values of C19 TT/C23 TT, C19+20TT/ΣTT, Ts/(Ts + Tm) and ααα-20R sterane C27/C28 ratios but higher values of TT C23/C21, HHI, gammacerane/αβ C30 hopane, hopane (20S) C34/C33, C29ββ/(ββ + αα), and C29 20S/(20S + 20R) ratios. Three major stages of oil charge occurred in the Carboniferous, in the Middle Triassic, Late Triassic to Early Jurassic, and in the Middle Jurassic to Late Jurassic periods, respectively. Most of the oil charged during the first stage was lost, while moderately and highly mature oils were generated and accumulated during the second and third stages. Oil migration and accumulation in the large-scale stratigraphic reservoir was primarily controlled by the top Carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity. Secondary dissolution

  19. New Insights to the Mid Miocene Calc-alkaline Lavas of the Strawberry Volcanics, NE Oregon Surrounded by the Coeval Tholeiitic Columbia River Basalt Province

    NASA Astrophysics Data System (ADS)

    Steiner, A. R.; Streck, M. J.

    2013-12-01

    The Strawberry Volcanics (SV) of NE Oregon were distributed over 3,400 km2 during the mid-Miocene and comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The predominant composition of this volcanic suite is calc-alkaline (CA) basaltic andesite and andesite, although tholeiitic (TH) lavas of basalt to andesite occur as well. The coeval flood basalts of the Columbia River province surround the SV. Here we will discuss new ages and geochemical data, and present a new geologic map and stratigraphy of the SV. The SV are emplaced on top of pre-Tertiary accreted terranes of the Blue Mountain Province, Mesozoic plutonic rocks, and older Tertiary volcanic rocks thought to be mostly Oligocene of age. Massive rhyolites (~300 m thick) are exposed mainly along the western flank and underlie the intermediate composition lavas. In the southern portion of this study area, alkali basaltic lavas, thought to be late Miocene to early Pliocene in age, erupted and overlie the SV. In addition, several regional ignimbrites reach into the area. The 9.7 Ma Devine Canyon Tuff and the 7.1 Ma Rattlesnake Tuff also overlie the SV. The 15.9-15.4 Ma Dinner Creek Tuff is mid-Miocene, and clear stratigraphic relationships are found in areas where the tuff is intercalated between thick SV lava flows. All of the basalts of the SV are TH and are dominated by phenocryst-poor (≤2%) lithologies. These basalts have an ophitic texture dominated by plagioclase, clinopyroxene and olivine (often weathered to iddingsite). Basalts and basaltic andesites have olivine Fo #'s ranging from 44 at the rims (where weathered to iddingsite) and as high as 88 at cores. Pyroxene Mg #'s range from 65 to 85. Andesites of the SV are sub-alkaline, and like the basalts, are exceedingly phenocryst-poor (≤3%) with microphenocrysts of plagioclase and lesser pyroxene and olivine, which occasionally occur as crystal clots of ~1-3 mm instead of single crystals. In addition, minimal

  20. Unusual evolution of silica-under- and -oversaturated alkaline rocks in the Cenozoic Ambohimirahavavy Complex (Madagascar): Mineralogical and geochemical evidence

    NASA Astrophysics Data System (ADS)

    Estrade, Guillaume; Béziat, Didier; Salvi, Stefano; Tiepolo, Massimo; Paquette, Jean-Louis; Rakotovao, Soatsitohaina

    2014-10-01

    The almost unknown Ambohimirahavavy ring complex in the Cenozoic alkaline province of northwestern Madagascar has recently attracted considerable interest because of the discovery of important rare-metal mineralization. The complex consists of arc-shaped bodies made up of silica-under- and -oversaturated syenites and extremely evolved peralkaline granitic dykes, as well as several mafic to felsic volcanic units, including basalt, phonolite and trachyte, all of which have an alkaline affinity. Uranium-lead zircon ages of 24.2 ± 0.6 Ma and 23.5 ± 6.8 Ma have been obtained for nepheline syenites and peralkaline granitic dykes, respectively, which, together with field data and ages of neighboring complexes, support emplacement controlled by regional lithospheric structures, rather than an evolving hot spot. Whole-rock major and trace-element and Sr-Nd isotopic data for the mafic suite suggest that the parental melt of this complex was generated by low degrees of melting of a metasomatized mantle source with residual amphibole. Fractional crystallization of this alkali basaltic melt likely produced the silica-undersaturated suite. We propose that the silica-oversaturated suite evolved from the undersaturated melt after contamination of the latter by crustal material. Further evolution to peralkaline compositions in both suites is attributed mainly to plagioclase and alkali feldspar segregation. Nepheline and feldspar compositions, as well as considerations of mineral equilibria among mafic silicates and Fe-Ti oxide minerals indicate crystallization temperatures of 1000 to 700 °C and an oxygen fugacity of 0.4 to 0.8 log units below the fayalite-magnetite-quartz (FMQ) buffer at 1 kbar for the silica-undersaturated melt, and temperatures of 860 to 570 °C and an oxygen fugacity of 1.5 to 3.8 log units below FMQ for the oversaturated syenitic melt. The undersaturated melt evolved towards a more peralkaline composition. Crystallization of arfvedsonite plus aegirine

  1. The occurrence of a complete continental rift type of volcanic rocks suite along the Yerer-Tullu Wellel Volcano Tectonic Lineament, Central Ethiopia

    NASA Astrophysics Data System (ADS)

    Abebe Adhana, Tsegaye

    2014-11-01

    The Yerer-Tullu Wellel Volcano-tectonic Lineament (YTVL) is an E-W trending fault system or aborted rift that intercepts the Main Ethiopian Rift (MER) at Debre Zeyt (Bishoftu)/Yerer, in the eastern periphery of Addis Ababa. The structure is in correspondence with the westward extension of the southern margin of the Gulf of Aden rift. The YTVL extends for more than 500 km with a very clear northern fault margin, between Addis Ababa and Ambo known as the “Ambo Fault”. The southern margin is indicated by an E-W trending segmented lineaments at the latitude of about N 8°30‧, the Bedele-Metu being the most clear segment. In between these limits there are several evolved central volcanoes and cinder cones. The central volcanoes range in age from 12 to 7 Ma in the western most (Tullu Wellel) and gradually the upper limit get younger towards East to less than 1 Ma in the Wenchi and Debre Zeyt (Bishoftu) areas. These volcanic products cover the whole spectrum of a continental rift volcanic rocks suite: (1) in the eastern zone (Yerer-Bishoftu) the suite is silica over-saturated, ranging in composition from transitional basalt to peralkaline rhyolite, (2) moving westwards, between Wechacha and Wenchi, the rocks suite is silica saturated ranging in composition from alkali basalt to trachyte, (3) further West between Ijaji-Konchi and Nekemt the rocks suite is silica under-saturated ranging in composition from basanite to phonolite. Crossing the Dedessa lineament, the Tullu Wellel rocks appear to be silica saturated. Within a single suite fractional crystallization is the predominant evolutional process even in the silica over-saturated suite. The westwards progressive silica under-saturation and increase in alkalinity (except for the Tullu Wellel volcanic centers) is interpreted by the gradual deepening of an anomalous mantle where partial fusion took place. Therefore, as distance increases from the MER junction to the West, the amount of melt on the upper mantle was

  2. Tectonic implications of paleomagnetic poles from Lower Tertiary Volcanic Rocks, south central Alaska

    NASA Astrophysics Data System (ADS)

    Hillhouse, John W.; Grommé, C. Sherman; Csejtey, Bela, Jr.

    1985-12-01

    We have determined the paleolatitude of lower Tertiary volcanic rocks in southern Alaska to measure possible poleward translation of the Wrangellia and the Peninsular terranes after 50 m.y. ago. Previous paleomagnetic studies have shown that in Triassic and Jurassic time these terranes were located near the equator and have moved at least 3000 km poleward relative to the North American craton. Our sample localities are in the northern Talkeetna Mountains in mildly deformed andesite and dacite flows (50.4, 51.3, 53.9, and 56.3 m.y. by K-Ar) that overlap Lower Cretaceous flysch, Lower Permian volcanic rocks of Wrangellia, and Upper Triassic pillow basalt of the Susitna terrane. Results from 26 cooling units (23 of reversed polarity and 3 of normal polarity) give a mean paleomagnetic pole at 69.5°N, 179.6°E, α95 = 12.2°. Stratigraphic sections from opposite limbs of a syncline yield directional paths that pass the fold test, satisfying a necessary condition for primary origin of the magnetization. The corresponding mean paleolatitude (76°N) of the northern Talkeetna Mountains is 8°±10° higher than the latitude predicted from the Eocene reference pole for North America. Therefore, northward drift of the Talkeetna superterrane, which is the amalgamation of the Wrangellia and Peninsular terranes during and after Middle Jurassic time, was probably complete by 50 m.y. ago. Our results are consistent with paleomagnetic poles from uppermost Cretaceous and Paleocene volcanic sequences in Denali National Park, the Lake Clark region, northern Bristol Bay region, and near McGrath. These poles generally lie south of the cratonic poles, suggesting that the region between the Kaltag, Bruin Bay, and Castle Mountain faults has rotated counterclockwise relative to North America since the early Eocene.

  3. Lichen-rock interaction in volcanic environments: evidences of soil-precursor formation

    NASA Astrophysics Data System (ADS)

    Vingiani, S.; Adamo, P.; Terribile, F.

    2012-04-01

    , according to the young age of the basaltic lava the recent lichen colonization results in a physical reorganization and chemical modification of the interface materials, which are not necessarily produced by the lichen action on the rock substrate. In volcanic environment, the ability of lichens to retain considerable amount of unconsolidated material, which becomes mixed with organic matter, produced by decomposition of the thallus, and trap atmospheric dust may contribute to the andosolization process. Accumulation of Al and Fe, found at the rock-lichen interface likely as organo-metal complexes, can be considered initial stage of Al and Fe active phases formation, distinguishing features of Andosols development. The simple chelating oxalic acid, produced by the lichens, may be involved in the formation of organo-metal complexes.

  4. Geochemistry of the Yangla volcanic rocks and its relationship to Cu mineralization in the Yangla copper deposit, western Yunnan, China

    NASA Astrophysics Data System (ADS)

    Yang, Xian; Liu, Jiajun; Zhai, Degao; Han, Siyu; Wang, Huan; Yang, Longbo; Huo, Dongliang

    2012-10-01

    The Yangla copper deposit is a recently discovered, giant copper deposit with an estimated Cu reserve of about 1,200,000 tons. Development is now underway. Previous studies have reported that the Yangla copper deposit is a VMS-type deposit related to the Yangla volcanic rocks. Volcanic bulk-rock analyses shows high contents of Si (49.3%-58.7%), Na2O (Na2O = 3.3%-4.9%), MgO (MgO = 3.7%-8.6%), and CaO(CaO = 6.8%-9.0%), low TiO2 (TiO2 = 0.9%-2.1%) and K2O(K2O = 0.2%-1.4%) contents. The geochemistry of the volcanic represent forearc basalts. Four molybdenites samples from the ore bodies in the deposit yield Re-Os model ages ranging from 229.7 ± 3.3 Ma to 233 ± 3.4 Ma. The REE distribution patterns and the primitive-mantle-normalized trace element patterns of the volcanic rocks are similar to the ores, indicating the Yangla copper deposit are closely associated with the Yangla volcanic rocks. The results contribute to our understanding of the genesis of the Yangla copper deposit and will guide further exploration in the region.

  5. Volcanic and structural history of the rocks exposed at Pickering Crater (Daedalia Planum, Mars)

    NASA Astrophysics Data System (ADS)

    Caprarelli, Graziella; Leitch, Evan C.

    2009-08-01

    In the western hemisphere of Mars Amazonian volcanism from Arsia Mons produced the smooth surfaces of Daedalia Planum and masks older rocks. Close to the southern termination of Daedalia Planum basement rocks are exposed in which are preserved craters that escaped or were only partially filled by this most recent volcanism. Pickering Crater is an approximately 130 km diameter crater. The youngest lavas flowed into this crater from Daedalia Planum by way of a NW rim breach, covering its western part. East of a well-defined flow front an older lava sequence with a distinctive platy surface and derived from a more proximal unestablished source to the northeast is exposed. Several units are identified within this sequence on the basis of surface texture, which is more subdued in progressively older rocks. Only local mapping of the flow front boundaries of these units is possible because of incomplete coverage by high resolution imagery. During emplacement of the older lavas a NE-SW striking en echelon graben system and parallel smaller troughs and dikes formed under inferred regional NW-SE extension. A much earlier strike-slip regime pre-dating the lavas exposed in the crater floor is postulated, based on the highly fretted nature of the rim of Pickering Crater and an elongated smaller crater to its northeast, approximately 40 km long in the NE-SW direction. The rims of these craters contrast with that of a smoother rimmed impact crater in the southeast that was excavated subsequent to strike-slip deformation but prior to the emplacement of platy surfaced lavas.

  6. The Fukuyama volcanic rocks: Submarine composite volcano in the Late Miocene to Early Pliocene Akita-Yamagata back-arc basin, northeast Honshu, Japan

    NASA Astrophysics Data System (ADS)

    Yagi, Masahiko; Ohguch, Takeshi; Akiba, Fumio; Yoshida, Takeyoshi; Tiba, Tokiko

    2009-10-01

    The Fukuyama Volcanic Rocks are composed of pyroxene andesite (FKV-1), hornblende-pyroxene andesite (FKV-2), biotite-hornblende dacite (FKV-3) and volcaniclastic debris-flow deposits and/or turbidites. FKV-1, FKV-2 and FKV-3 are medium-K calc-alkaline rocks depleted in Nd, similar to other back-arc volcanic rocks of the northeast Japan arc and constitute a dome cluster at Fukuyama. Volcaniclastic beds surround the dome cluster and thin and fine upwards. The predominant clast type in the volcaniclastic beds changes upwards from pyroxene andesite, through hornblende-pyroxene andesite, to biotite-hornblende dacite, consistent with the stratigraphic relationships of FKV-1, FKV-2 and FKV-3 lavas. All the siltstones inter-bedded with the volcaniclastic beds and overlying the whole succession contain diatom fossils indicative of the lower part of the Thalassionema schraderi zone (7.8 Ma to 8.5 Ma), compatible with the isotopic ages of FKV-1, FKV-2 and FKV-3. The Fukuyama volcano has a total eruption volume of 60-100 km 3, with a lifetime of the order of 10 5 years, as typically observed for volcanoes in the present back-arc region of northeast Honshu. FKV-1 erupted in deep water and partly disintegrated into hyaloclastite breccias due to direct contact with water. FKV-2 lava repeatedly effused over the FKV-1 lava and produced a volcanic apron of breccias that eventually grew above wave base and was eroded by wave action. The magma of FKV-3 was probably hydrous as it contains biotite and hornblende. The FKV-3 magma could have explosively erupted from a shallow-water dome or vent emergent above the wave base, followed by growth of a degassing lava dome. Repose between eruptions allowed accumulation of silt, and after the Fukuyama eruptions ceased silt entirely mantled the volcano. A small magma supply rate perhaps allowed a relatively long period of quiescence between eruptions of FKV-1, FKV-2 and FKV-3 magmas, resulting in abrasion and reworking of volcanic fragments and

  7. Following the kinetics: iron-oxidizing microbial mats in cold icelandic volcanic habitats and their rock-associated carbonaceous signature.

    PubMed

    Cockell, Charles S; Kelly, Laura C; Summers, Stephen; Marteinsson, Viggo

    2011-09-01

    Icelandic streams with mean annual temperatures of less than 5 °C, which receive the cationic products of basaltic rock weathering, were found to host mats of iron-cycling microorganisms. We investigated two representative sites. Iron-oxidizing Gallionella and iron-reducing Geobacter species were present. The mats host a high bacterial diversity as determined by culture-independent methods. β-Proteobacteria, Actinobacteria, α-Proteobacteria, and Bacteroidetes were abundant microbial taxa. The mat contained a high number of phototroph sequences. The carbon compounds in the mat displayed broad G and D bands with Raman spectroscopy. This signature becomes incorporated into the weathered oxidized surface layer of the basaltic rocks and was observed on rocks that no longer host mats. The presence of iron-oxidizing taxa in the stream microbial mats, and the lack of them in previously studied volcanic rocks in Iceland that have intermittently been exposed to surface water flows, can be explained by the kinetic limitations to the extraction of reduced iron from rocks. This type of ecosystem illustrates key factors that control the distribution of chemolithotrophs in cold volcanic environments. The data show that one promising sample type for which the hypothesis of the existence of past life on Mars can be tested is the surface of volcanic rocks that, previously, were situated within channels carved by flowing water. Our results also show that the carbonaceous signatures of life, if life had occurred, could be found in or on these rocks.

  8. Magmatic origin of alkaline meta-igneous rocks from Chamberlindalen, SW Svalbard

    NASA Astrophysics Data System (ADS)

    Goluchowska, Karolina; Barker, Abigail; Manecki, Maciej; Czerny, Jerzy; Majka, Jaroslaw

    2014-05-01

    This study focuses on the late Neoproterozoic meta-igneous rocks of SW Svalbard to determine their magmatic evolution, conditions of magma storage and origin. The samples from the Chamberlindalen area form an alkaline igneous suite, from which thin dikes and intrusive bodies have been collected. The rocks in question intrude Late Neoproterozoic metasediments and are surrounded by occurrences of Neoproterozoic metabasalts in contrast to highly alkaline the Chamberlindalen intrusions. The rocks from Chamberlindalen are divided into two groups based on their geochemistry, mineralogy and field relationships. The dikes, classify as minettes, belonging to the lamprophyre group and contain mainly euhedral, elongated phlogopite and additionally clinopyroxene and feldspar. The rest of the samples are highly magnesian and are classified as alkali gabbro. The alkali gabbros contain primary magmatic minerals such as clinopyroxene, calcic amphibole and mica in different proportions. The alkali gabbros are enriched in LREE and HFSE and depleted in P, K and HREE. The minette dikes are always more enriched in HFSE and REE in comparison to the alkali gabbros. The mineral chemistry of the alkali gabbros reveals that pyroxenes are represented by diopside with Wo46-51 En35-46 Fs6-14, and calcic amphibole by kaersutite. The Mg# number for diopside is from 72 - 88, whereas for kaersutite Mg# number is 51 - 74. Thermobarometry calculations for diopside and kaersutite have been performed. In the alkali gabbros from Chamberlindalen, diopside crystallized between 0.7 - 8 kbar and 1152 - 1233°C. Results for kaersutite reveal that they crystallized between 5 - 17 kbar and 1043 - 1215°C. For diopside the main crystallization was between 10 and 38 km, whereas for kaersutite, the main crystallization was between 30 and 50 km. Clinopyroxene and minor kaersutite also show a zone of crystallization at 2 to 10 km. This reflects a main crystallization zone at 10 - 50 km throughout the continental

  9. Xenoliths of mafic/ultramafic igneous rocks as carriers of information on lower crust beneath Złotoryja - Jawor volcanic complex (SW Poland).

    NASA Astrophysics Data System (ADS)

    Dajek, Michał; Matusiak-Malek, Magdalena; Puziewicz, Jacek; Lipa, Danuta; Ntaflos, Theodors

    2016-04-01

    The Cenozoic alkaline volcanic rocks in Lower Silesia (SW Poland) are known for their mantle peridotite xenoliths. However, the mafic and ultramafic xenoliths with cumulative textures and of composition of olivine- or hornblende clinopyroxenite, clinopyroxenite, websterite, norite and gabbro occur in some of the lavas (6 sites) of the Złotoryja-Jawor volcanic complex. The xenoliths are anhydrous, only in Wilcza Góra minor amount of amphibole occurs. The Mg# of clinopyroxene varies from 0.54 (Ostrzyca Proboszczowicka clinopyroxenite) to 0.89 (Góra Świątek clinopyroxenite). Forsterite content in olivine varies from 64% (Winna Góra gabbro) to 86% (Wilcza Góra hornblende clinopyroxenite). Anortite content in plagioclase in nortite and gabbros is 33-56%. The Mg# in amphibole is 0.43 to 0.76. Clinopyroxene trace element composition is typically LREE enriched, but in Wilcza Góra norite and Mnisza Góra clinopyroxenite it is LREE-depleted. The calculated pressures of clinopyroxene crystallization (calculated by the algorithm of Nimis and Ulmer, 1998, CMP, 1998, 122-135, assuming all Fe to be 2+) is from 0.45 to 0.96 GPa pointing to crystallization of the pyroxenitic rocks in lower crust or at crust/mantle boundary. Theoretical melts in equilibrium with clinopyroxene enriched in LREE resemble the alkaline lavas from the area and we suggest they are cognate with host magmas. We explain variations in composition of mafic xenoliths from Wilcza Góra, Winna Góra and Grodziec to be a result of magma fractionation. Xenoliths containing clinopyroxene impoverished in LREE may represent lithologies inherited from Variscan oceanic crust. Megacrysts of clinopyroxene present in some of the localities cannot result from disintegration of mafic xenoliths This study was possible thanks to project NCN UMO-2014/15/B/ST10/00095 of Polish National Centre for Science.

  10. Rock magnetic studies on marine volcaniclastic sediments off Martinique, Lesser Antilles volcanic arc, IODP Expedition 340

    NASA Astrophysics Data System (ADS)

    Saito, T.; Kataoka, K.

    2013-12-01

    Large numbers of marine volcaniclastic sediments with various origins were recovered from the sites U1397 and U1398 during IODP Expedition 340. They were most likely derived from volcanoes on Martinique and possibly from Dominica, Lesser Antilles volcanic arc. Some volcaniclastic units were transported and deposited as turbidites, some were as thin tephra fall deposits and others show both characteristics. They contain various amounts of bioclastic component, pumice and lithic fragments and hemipelagic mud clasts. Therefore, these volcaniclastic sediments are suitable for investigating transport and emplacement mechanisms of volcanic materials and the resultant sedimentary and petro-facies in marine settings. In this study, we focused on magnetic minerals in the marine volcaniclastic sediments and carried out rock magnetic measurements. Thermomagnetic measurements showed almost reversible curves and induced magnetization decayed to almost zero below 580 °C, suggesting little contribution of maghemite or hematite. Two Curie temperatures (Tc) with 350-400 °C and 500-550°C indicate that the main magnetic carriers are Ti-rich titanomagnetite and Ti-poor titanomagnetite. The proportion of low-Tc titanomagnetite in central and bottom part of turbidite units was larger than that in hemipelagic sediments and in the topmost part of turbidite units, suggesting Ti-rich titanomagnetite is derived from volcanic events. Magnetic susceptibility and hysteresis measurements showed that heavy and large magnetic minerals in most turbidite units were concentrated at the lower part of the unit. Samples from the topmost and bottom part of turbidites showed higher degrees of anisotropy than those from the central part, indicating strong influence of suspension settling at the topmost part and shearing at the bottom part. However, in some turbidite units such features cannot be observed and hysteresis parameters and susceptibility values were almost concentrated. Probably the units

  11. Textural and Mineralogical Analysis of Volcanic Rocks by µ-XRF Mapping.

    PubMed

    Germinario, Luigi; Cossio, Roberto; Maritan, Lara; Borghi, Alessandro; Mazzoli, Claudio

    2016-06-01

    In this study, µ-XRF was applied as a novel surface technique for quick acquisition of elemental X-ray maps of rocks, image analysis of which provides quantitative information on texture and rock-forming minerals. Bench-top µ-XRF is cost-effective, fast, and non-destructive, can be applied to both large (up to a few tens of cm) and fragile samples, and yields major and trace element analysis with good sensitivity. Here, X-ray mapping was performed with a resolution of 103.5 µm and spot size of 30 µm over sample areas of about 5×4 cm of Euganean trachyte, a volcanic porphyritic rock from the Euganean Hills (NE Italy) traditionally used in cultural heritage. The relative abundance of phenocrysts and groundmass, as well as the size and shape of the various mineral phases, were obtained from image analysis of the elemental maps. The quantified petrographic features allowed identification of various extraction sites, revealing an objective method for archaeometric provenance studies exploiting µ-XRF imaging.

  12. Textural and Mineralogical Analysis of Volcanic Rocks by µ-XRF Mapping.

    PubMed

    Germinario, Luigi; Cossio, Roberto; Maritan, Lara; Borghi, Alessandro; Mazzoli, Claudio

    2016-06-01

    In this study, µ-XRF was applied as a novel surface technique for quick acquisition of elemental X-ray maps of rocks, image analysis of which provides quantitative information on texture and rock-forming minerals. Bench-top µ-XRF is cost-effective, fast, and non-destructive, can be applied to both large (up to a few tens of cm) and fragile samples, and yields major and trace element analysis with good sensitivity. Here, X-ray mapping was performed with a resolution of 103.5 µm and spot size of 30 µm over sample areas of about 5×4 cm of Euganean trachyte, a volcanic porphyritic rock from the Euganean Hills (NE Italy) traditionally used in cultural heritage. The relative abundance of phenocrysts and groundmass, as well as the size and shape of the various mineral phases, were obtained from image analysis of the elemental maps. The quantified petrographic features allowed identification of various extraction sites, revealing an objective method for archaeometric provenance studies exploiting µ-XRF imaging. PMID:27160144

  13. Constraints on the Jurassic time scale by /sup 40/Ar//sup 39/Ar dating of North Caucasian volcanic rocks

    SciTech Connect

    Hess, J.C.; Lippolt, H.J.; Borsuk, A.M.

    1987-07-01

    /sup 40/Ar//sup 39/Ar age measurements on biotites and high-temperature plagioclases of Jurassic basaltic to rhyolitic subvolcanic rocks from the Northern Great Caucasus (USSR) yielded plateau and total argon ages between 190 and 180 Ma. The dated rocks are intrusive sills, dikes and laccoliths in sediments of the middle to upper Pliensbachian and of the lower Toarcian (Lower Jurassic). Pebbles of the volcanic rocks exist in the basal conglomerates of the Aalenian (base of the Middle Jurassic). Thus, their stratigraphic age is restricted to the Lower Jurassic stages of middle to upper Pliensbachian and Toarcian. Because of the scarcity of tie-points in the Lower Jurassic, the isotopic ages of these volcanic rocks, in spite of their rather large stratigraphic range, may serve as new calibration points for the improvement of the Jurassic time-scale.

  14. Kaersutite-bearing xenoliths and megacrysts in volcanic rocks from the Funk Seamount in the souhtwest Indian Ocean

    NASA Technical Reports Server (NTRS)

    Reid, Arch M.; Le Roex, Anton P.

    1988-01-01

    The petrography, mineral chemistry, and whole-rock compositions of volcanic rocks dredged from the Funk Seamount, located 60 km NW of Marion Island in the southwestern Indian Ocean, are presented together with the mineral chemistry of their inclusions. On the basis of these characteristics, the possible relationships between the Funk Seamount's volcanic rocks and the megacrysts and xenoliths in these rocks are discussed. It is argued that the Funk Seamount lavas derive from a similar mantle source region as that of the Marion Island and Prince Edward Island hotspot lavas. The geochemical signature of these lavas implies derivation from a source that is enriched (e.g., in Ti, K, P, and Nb) over the depleted mantle source regions for the adjacent mid-ocean ridge basalts.

  15. Increasing Interaction of Alkaline Magmas with Lower Crustal Gabbroic Cumulates over the Evolution of Mt. Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schmidt, M. E.; Crumpler, L. S.; Schrader, C.

    2010-12-01

    The Mount Taylor Volcanic Field at the southeastern edge of the Colorado Plateau, New Mexico erupted diverse alkaline magmas from ~3.8 to 1.5 Ma (Crumpler, 1980; Perry et al., 1990). The earliest eruptions include high silica topaz rhyolites of Grants Ridge (plagioclase, quartz, biotite) and Si-under saturated basanites and trachytes at Mt Taylor stratovolcano. Mt. Taylor was later constructed of stacks of thick, trachyandesitic to rhyolitic lava flows that were subsequently eroded into a ~4-km across amphitheatre opening toward the southeast. Early Mt. Taylor rhyolitic lavas exposed within the amphitheatre contain quartz, plagioclase, hornblende, and biotite (± sanidine) phenocrysts. Later cone-building trachydacite to trachyandesite lavas are crystal-rich with plagioclase and augite megacrysts (± hornblende, ± quartz) and record an overall trend of decreasing SiO2 with time. The last eruptions ~1.5 Ma from the stratovolcano (Perry et al. 1990) produced thick (>70 m), viscous lava flows that contain up to 50% zoned plagioclase phenocrysts. While SiO2 decreased among the silicic magmas, the degree of silica saturation increased among peripheral basaltic magmas from basanite to ne-normative hawaiite to hy-normative basalts. Evidence of increasing crustal contamination within the basalts includes zoned plagioclase megacrysts, augite and plagioclase cumulate texture xenoliths with accompanying xenocrysts. These textures within the basalts combined with abundant, complex plagioclase among the cone-building silicic magmas imply interaction and mixing with gabbroic cumulate mush in the lower crust beneath Mt. Taylor Volcano. Contemporaneous basanitic to trachytitc volcanism in the northern part of the volcanic field at Mesa Chivato (Crumpler, 1980) was more widely distributed, smaller volume, and produced mainly aphyric magmas. The lower crustal gabbroic cumulates either do not extend northward beneath Mesa Chivato, or they were not accessed by lower magma flux rate

  16. Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs Wash volcanic centers, Southern Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, James V.; Hsu, Liang C.; Spatz, David

    1988-01-01

    Comparative lab spectra and Thematic Mapper imagery investigations at 3 Tertiary calderas in southern Nevada indicate that desert varnish is absorbant relative to underlying host rocks below about 0.7 to 1.3 microns, depending on mafic affinity of the sample, but less absorbant than mafic host rocks at higher wavelengths. Desert varnish occurs chiefly as thin impregnating films. Distribution of significant varnish accumulations is sparse and localized, occurring chiefly in surface recesses. These relationships result in the longer wavelength bands and high 5/2 values over felsic units with extensive desert varnish coatings. These lithologic, petrochemical, and desert varnish controlled spectral responses lead to characteristic TM band relationships which tend to correlate with conventionally mappable geologic formations. The concept of a Rock-Varnish Index (RVI) is introduced to help distinguish rocks with a potentially detectable varnish. Felsic rocks have a high RVI, and those with extensive desert varnish behave differently, spectrally, from those without extensive varnish. The spectrally distinctive volcanic formations at Stonewall Mountain provide excellent statistical class segregation on supervised classification images. A binary decision rule flow-diagram is presented to aid TM imagery analysis over volcanic terrane in semi-arid environments.

  17. Petrochemistry of late miocene peraluminous silicic volcanic rocks from the Morococala field, Bolivia

    USGS Publications Warehouse

    Morgan, VI G.B.; London, D.; Luedke, R.G.

    1998-01-01

    Late Miocene peraluminous volcanic rocks of the Morococala field, Bolivia, define a layered stratigraphy of basal andalusite-, biotite-(?? Muscovite)-bearing rhyolite tuffs (AR), overlain by cordierite-, biotite-bearing rhyolite tuffs (CR), and capped by biotite-beanng quartz latite tuffs, lavas, and late domal flows (QL). Mineral and whole-rock compositions become more evolved from top to bottom, with differentiation reflected by decreasing Ca, Ba, Mg, Fe, and rare earth elements (REE) versus increasing F, Na/K, and aluminosity from QL to AR. Mineral, whole-rock, and glass inclusion compositions are consistent with derivation of all three rock types from a single stratified magma reservoir, but age and spatial relations between the three units make this unlikely. Genesis of the QL involved biotite-dehydration melting of an aluminous source at T > 750??C and P ??? 4-6 kbar. If not co-magmatic with QL, the other units were generated primarily by muscovite-dehydration melting at T = 730-750??C and P ??? 3??5-4??5 kbar for CR, and T ??? 750??C for AR with pre-emptive residence at low pressure (1??5-3??0 kbar). Low hematite contents (XHem ??? 0??06) of ilmenite grains in AR, CR, and early grains (as inclusions in plagioclase and sanidine cores) in QL indicate reduced conditions imposed by a graphite-bearing source. Compositional variability among texturally later oxides (ilmenite with XHem = 0??06-0??50, primary magnetite), however, apparently records progressive increases in pre-eruptive f(O2) in QL. Plagioclase-melt equilibria and electron microprobe analysis difference for quartz-hosted glass inclusions suggest pre-emptive melt H2O contents ??? 5-7 wt % for the AR, ???4-6 wt % for the CR, and ???3-5 wt % for the QL.

  18. Geochemistry of middle Tertiary volcanic rocks in the northern Aquarius Mountains, west-central Arizona

    SciTech Connect

    Simmons, A.M.; Haxel, G.B.

    1993-04-01

    The northern Aquarius Mountains volcanic field ([approximately]50km east of Kingman) covers an area of 400 km[sup 2], bounded by upper Trout Creek (S), the Truxton Valley (N), the Big Sandy Valley (W), and Cross Mountain (E). The volcanic sequence rests upon a pre-middle Eocene erosional surface. The lowest units is a 250 m-thick unit of rhyolitic pyroclastic breccias and airfall tuffs. Successively younger units are: basanite flows and cinder cones; hornblende latite flows and domes; porphyritic dacite flows, domes, and breccias; alkali basalt intrusions; and low-silica rhyolite domes and small high=silica rhyolite flows. Dacite is volumetrically dominant, and erupted primarily from vents in and around Cedar Basin (Penitentiary Mtn 7.5[prime] quad.). Other geologists have obtained K-Ar dates [approximately]24--20 Ma for the basanites and latites. The alkali basalts, latites, dacites, and rhyolites evidently constitute a genetically-related high-K to shoshonitic calcalkaline suite with chemistry typical of subduction-related magmatism: enrichment in LILE and LREE, and depletion of Nb and Ta relative to K and La and of Ti relative to Hf and Yb. Each rock type is unique and distinguishable in K/Rb and Rb/Sr. The basanites are primitive (mg=0.75--0.78), have intraplate affinities (La/Nb[<=]1), and show consistent and distinctive depletion of K relative to the other LILE. The presence of these basanites in an early Miocene volcanic sequence is unusual or unexpected, as they predate (by [approximately]10 m.y.) the regional eruption of asthenosphere-derived basalts associated with Basin-and-Range extension.

  19. Rock types of South Pole-Aitken basin and extent of basaltic volcanism

    USGS Publications Warehouse

    Pieters, C.M.; Head, J. W.; Gaddis, L.; Jolliff, B.; Duke, M.

    2001-01-01

    The enormous pre-Nectarian South Pole-Aitken (SPA) basin represents a geophysically and compositionally unique region on the Moon. We present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution. Rock types are derived from Clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials. Individual areas are characterized as noritic (dominated by low-Ca pyroxene), gabbroic/basaltic (dominated by high-Ca pyroxene), feldspathic (<3-6% FeO), and olivine-gabbro (dominated by high-Ca pyroxene and olivine). The anorthositic crust has effectively been removed from the interior of the basin. The style of volcanism within the basin extends over several 100 Myr and includes mare basalt and pyroclastic deposits. Several areas of ancient (pre-Orientale) volcanism, or cryptomaria, have also been identified. The nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically. We interpret this to represent impact melt/breccia deposits derived from the lower crust. A few localized areas are identified within the basin that contain more diverse lithologies (gabbro, olivine-gabbro), some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the SPA event. Copyright 2001 by the American Geophysical Union.

  20. Compilation of modal analyses of volcanic rocks from the Nevada Test Site area, Nye County, Nevada

    SciTech Connect

    Page, W.R.

    1990-10-01

    Volcanic rock samples collected from the Nevada Test Site, Nye County, Nevada, between 1960 and 1985 were analyzed by thin section to obtain petrographic mode data. In order to provide rapid accessibility to the entire database, all data from the cards were entered into a computerized database. This computer format will enable workers involved in stratigraphic studies in the Nevada Test Site area and other locations in southern Nevada to perform independent analyses of the data. The data were compiled from the mode cards into two separate computer files. The first file consists of data collected from core samples taken from drill holes in the Yucca Mountain area. The second group of samples were collected from measured sections and surface mapping traverses in the Nevada Test Site area. Each data file is composed of computer printouts of tables with mode data from thin section point counts, comments on additional data, and location data. Tremendous care was taken in transferring the data from the cards to computer, in order to preserve the original information and interpretations provided by the analyzer. In addition to the data files above, a file is included that consists of Nevada Test Site petrographic data published in other US Geological Survey and Los Alamos National Laboratory reports. These data are presented to supply the user with an essentially complete modal database of samples from the volcanic stratigraphic section in the Nevada Test Site area. 18 refs., 4 figs.

  1. Volcanic rocks of the McDermitt Caldera, Nevada-Oregon

    USGS Publications Warehouse

    Greene, Robert C.

    1976-01-01

    The McDermitt caldera, a major Miocene eruptive center is locatedin the northernmost Great Basin directly west of McDermitt, Nev. The alkali rhyolite of Jordan Meadow was erupted from the caldera and covered an area of about 60,000 sq km; the volume of rhyolite is about 960 cubic km. Paleozoic and Mesozoic sedimentary rocks and Mesozoic granodiorite form the pre-Tertiary Basement in this area.. Overlying these is a series of volcanic rocks, probably all of Miocene age. The lowest is a dacite welded tuff, a reddish-brown rock featuring abundant phenocrysts of plagioclase, hornblende, and biotite; next is a heterogeneous unit consisting of mocks ranging from basalt to dacite. Overlying these is the basalt and andesite of Orevada View, over 700 m thick and consisting of a basal unit of cinder agglutinate overlain by basalt and andesite, much of which contains conspicuous large plagioclase phenocrysts. Near Disaster Peak and Orevada View, the basalt and andesite are overlain by additional units of silicic volcanic rocks. The lower alkali rhyolite welded tuff contains abundant phenocrysts of alkali feldspar and has a vitric phase with obvious pumice and shard texture. The rhyolite of Little Peak consists of a wide variety of banded flows or welded ruffs and breccias, mostly containing abundant alkali feldspar phenocrysts. It extends south from Disaster Peak and apparently underlies the alkali rhyolite of Jordan Meadow. The quartz latite of Sage Creek lies north of Disaster Peak and consists mostly of finely mottled quartz latite with sparse minute plagioclase phenocrysts. Volcanic rock units in the east part of the area near the Cordero mine include trachyandesite, quartz labile of McConnell Canyon, and rhyolite of McCormick Ranch. The trachyandesite is dark gray and contains less than 1 percent microphenocrysts plagioclase. It is the lowest unit exposed and may correlate with part of the basalt and andesite of Orevada View. The quartz latite of McConnell Canyon is

  2. Geology, geochemistry, geochronology, and economic potential of Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes segments of the Archibarca lineament, northwest Argentina

    NASA Astrophysics Data System (ADS)

    Richards, J. P.; Jourdan, F.; Creaser, R. A.; Maldonado, G.; DuFrane, S. A.

    2013-05-01

    This study presents new geochemical, geochronological, isotopic, and mineralogical data, combined with new geological mapping for a 2400 km2 area of Neogene volcanic rocks in northwestern Argentina near the border with Chile, between 25°10‧S and 25°45‧S. The area covers the zone of intersection between the main axis of the Cordillera Occidental and a set of NW-SE-trending structures that form part of the transverse Archibarca lineament. This lineament has localized major ore deposits in Chile (e.g., the late Eocene La Escondida porphyry Cu deposit) and large volcanic centers such as the active Llullaillaco and Lastarría volcanoes on the border between Chile and Argentina, and the Neogene Archibarca, Antofalla, and Cerro Galán volcanoes in Argentina. Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes areas are mostly high-K calc-alkaline in composition, and range from basaltic andesites, through andesites and dacites, to rhyolites. Magmatic temperatures and oxidation states, estimated from mineral compositions, range from ~ 1000 °C and ∆FMQ ≈ 1.0-1.5 in andesites, to ~ 850 °C and ∆FMQ ≈ 1.5-2.0 in dacites and rhyolites. The oldest rocks consist of early-middle Miocene andesite-dacite plagioclase-pyroxene-phyric lava flows and ignimbrites, with 40Ar/39Ar ages ranging from 17.14 ± 0.10 Ma to 11.76 ± 0.27 Ma. Their major and trace element compositions are typical of the Andean Central Volcanic Zone, and show strong crustal contamination trends for highly incompatible elements such as Cs, Rb, Th, and U. These rocks are geochemically grouped as sub-suite 1. This widespread intermediate composition volcanism was followed in the middle-late Miocene by a period of more focused rhyodacitic flow-dome complex formation. These felsic rocks are characterized by less extreme enrichments in highly incompatible elements, and increasing depletion of heavy rare earth elements. These rocks are geochemically grouped as sub-suite 2. The

  3. The questa magmatic system: Petrologic, chemical and isotopic variations in cogenetic volcanic and plutonic rocks of the latir volcanic field and associated intrusives, northern New Mexico

    SciTech Connect

    Johnson, C.M.

    1986-01-01

    Field, chemical and isotopic data demonstrate that nearly all igneous rocks at Questa resulted from interactions between mantle-derived parental magmas and the crust. Strontium, neodymium and lead isotope ratios of early andesites to rhyolites (28 to 26 Ma) indicate that these magmas assimilated > 25% lower crust. Injection of basaltic magmas extensively modified the strontium and neodymium but not the lead isotope compositions of the lower crust. Eruption of comendite magmas and the peralkaline Amalia Tuff 26 Ma is correlated with inception of regional extension. Lead isotope ratios identify different sources for the metaluminous granites and the peralkaline rocks. 26 Ma metaluminous granite to granodiorite intrusions have chemical and isotopic compositions to those of the precaldera intermediate-composition rocks, and are interpreted as representing the solidified equivalents of the precaldera magmatic episode. However, both conventional and ion-microprobe isotopic data prohibit significant assimilation of crustal rocks at the level of exposure, suggesting that the plutons were emplaced a relatively crystal-rich mushes which did not have sufficient heat to assimilate country rocks. This suggest that in some cases plutonic rocks are better than volcanic rocks in representing the isotopic compositions of their source regions, because the assimilation potential of crystal-rich magmas is significantly less than that of largely liquid magmas.

  4. Geochronology and geochemistry of the Triassic volcanic rocks at the eastern margin of the Xing'an Massif, NE China: constraints on the spatial-temporal extent of the influence of the Mongol-Okhotsk tectonic regime

    NASA Astrophysics Data System (ADS)

    Yu, L.; Xu, W.; Wang, F.

    2015-12-01

    The Mongol-Okhotsk suture belt is located between the Siberian and the North China cratons and played an important role in the formation and tectonic evolution of the eastern part of the Eurasian continent during the Mesozoic. It was previously thought that subduction of the Mongol-Okhotsk oceanic plate beneath the Siberian Craton was north-directed throughout the entire period of subduction, but recent research has provided evidence of southward subduction beneath the Central Mongolia and Erguna massifs during the late Permian and early Mesozoic. However, the spatial and temporal extent of the influence of the Mongol-Okhotsk tectonic regime on NE China remains unclear. In this paper, we present new zircon U-Pb and geochemical data for Triassic volcanic rocks that crop out on the eastern margin of the Xing'an Massif to address the above-mentioned question. Zircon U-Pb dating indicates that the Triassic volcanism in the Xing'an Massif occurred in two stages during the Middle (~240 Ma) and Late (~224 Ma) Triassic. Triassic volcanism consists of a suite of calc-alkaline trachybasalt and andesite, and are enriched in light rare earth elements (LREE) and depleted in high field strength elements (HFSE; e.g., Nb, Ta, Zr, and Hf), indicating an affinity to arc-type volcanic rocks. The Triassic volcanic rocks formed in an active continental margin setting associated with southward subduction of the Mongol-Okhotsk oceanic plate. Combined with the spatial and temporal variations of late Mesozoic igneous rocks in NE China, we conclude that the spatial extent of the influence of the Mongol-Okhotsk tectonic regime reached at least the eastern margin of the Xing'an Massif, and the temporal influence of this tectonism spanned from the late Permian to the early Early Cretaceous. This research was financially supported by the National Natural Science Foundation of China (Grant 41330206) and Graduate Innovation Fund of Jilin University (Project 2015038).

  5. Origin of andesitic rocks: Geochemical constraints from Mesozoic volcanics in the Luzong basin, South China

    NASA Astrophysics Data System (ADS)

    Chen, Long; Zhao, Zi-Fu; Zheng, Yong-Fei

    2014-03-01

    A combined study of whole-rock major-trace elements and Sr-Nd-Pb-Hf isotopes as well as zircon U-Pb ages and Hf-O isotopes was carried out for Mesozoic andesitic-basaltic volcanics from the Luzong basin in the Middle-Lower Yangtze River Belt, South China. The results provide insights into the origin of mantle sources above fossil Andes-type oceanic subduction zone and thus into the petrogenesis of andesitic rocks on fossil and modern continental margins. These volcanics are primarily composed of basaltic trachyandesite and trachyandesite, with small amounts of trachybasalt and trachyte. They exhibit variable contents of SiO2 (48.66-63.43 wt.%), MgO (0.39-4.85 wt.%), Na2O (1.22-6.07 wt.%) and K2O (2.53-10.10 wt.%), with highly variable K2O/Na2O ratios from 0.45 to 7.39. They are characterized by arc-like trace element distribution patterns, with significant enrichment of LILE, Pb and LREE but depletion of HFSE. They exhibit relatively enriched Sr-Nd-Pb-Hf isotope compositions, with initial 87Sr/86Sr ratios of 0.7050 to 0.7066, negative ɛNd(t) values of - 8.0 to - 3.1, negative ɛHf(t) values of - 11.1 to - 1.1, and elevated 207Pb/204Pb and 208Pb/204Pb ratios at given 206Pb/204Pb ratios. Zircon U-Pb dating yields consistent ages of 127 ± 2 to 137 ± 1 Ma for magma emplacement through volcanic eruption. The zircon exhibits slightly high δ18O values of 5.3 to 7.6‰ and variable ɛHf(t) values of - 13.1 to 2.6. An integrated interpretation of all these geochemical data leads to the conclusion that the Luzong andesitic-basaltic volcanics were primarily derived from partial melting of fertile and enriched, mafic-ultramafic mantle sources that are similar to those of continental arc andesites. Such mantle sources are hypothesized to form by reaction of the mantle wedge peridotite not only with hydrous felsic melts derived from partial melting of seafloor sediment but also with aqueous fluid derived from metamorphic dehydration of altered oceanic basalt during

  6. Interpretation of volcanic gas data from tholeiitic and Alkaline Mafic Lavas

    NASA Astrophysics Data System (ADS)

    Gerlach, T. M.

    1982-09-01

    The analyses of approximately 100 high temperature gas samples from erupting lavas of Surtsey, Erta Ale, Ardoukoba, Kilauea, Mount Etna and Nyiragongo exhibit erratic compositions resulting from analytical errors, condensation effects, reactions with sampling devices, and contamination by atmospheric gases, meteoric water and organic material. Computational techniques have been devised to restore reported analyses to compositions representative of the erupted gases. The restored analyses show little evidence of short-term variations. The principal species are H2O, CO2, SO2, H2, CO, H2S, S2, and HCl. The O2 fugacities range from nickel-nickel oxide to a half order of magnitude below quartz-magnetite-fayalite. There is no evidence for a unique magmatic gas composition; instead, the erupted gases show regular compositional trends characterized by decreasing CO2 with progressive outgassing. The gases from more alkaline lavas (Etna, Nyiragongo) are distinctly richer in CO2, while those from less alkaline (Surtsey) or tholeiitic lavas (Erta Ale, Ardoukoba) tend to be richer in H2O. Kilauean gases range from CO2-rich to H2O-rich. The total sulfur contents of the erupted gases show an excellent positive correlation with lava O2 fugacity. All restored analyses are significantly lower in H2O and enriched in sulfur and CO2 compared to the «excess volatiles».

  7. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    Donald Sweetkind; Ronald M. Drake II

    2007-11-27

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  8. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    USGS Publications Warehouse

    Sweetkind, Donald S.; Drake II, Ronald M.

    2007-01-01

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  9. Geochemical analyses, age dates, and flow-volume estimates for quaternary volcanic rocks, Southern Cascade Mountains, Washington

    SciTech Connect

    Hammond, P.E.; Korosec, M.A.

    1983-12-01

    Data collected over the last three years as part of a continuing study of the Quaternary volcanic rocks of the southern Cascade Mountains are presented. Whole-rock chemical analyses, selected trace element geochemistry, volume approximations, specific gravity determinations, and locations are provided for most of the 103 samples collected, and 21 radiometric age dates are included. In addition, partial information, including names and flow-volumes, are presented for 98 additional samples, collected for related studies. The study extends from the Columbia River north to the Cowlitz River and Goat Rocks Wilderness area, and from the Klickitat River west to the Puget-Willamette Trough. The volcanic rocks are all younger than 3 million years and consist primarily of tholeiitic and high-alumina basalts and basaltic-andesites erupted from numerous shield volcanoes and cinder cones. A few analyses of more silicic rocks, including hornblende and/or pyroxene andesites and dacites characteristic of the stratovolcanoes of the region, are also presented. However, systematic sampling of the stratovolcanoes in the study area, Mount Adams and Mount St. Helens, was not conducted. A map of the areal extent of Quaternary volcanic units and sample locations is included. It has been based on the 1:125,000 reconnaissance geologic map of the southern Cascade Range by Hammond (1980).

  10. The influence of porosity and vesicle size on the brittle strength of volcanic rocks and magma

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Xu, Tao; Chen, Chong-feng

    2014-09-01

    Volcanic rocks and magma display a wide range of porosity and vesicle size, a result of their complex genesis. While the role of porosity is known to exert a fundamental control on strength in the brittle field, less is known as to the influence of vesicle size. To help resolve this issue, here, we lean on a combination of micromechanical (Sammis and Ashby's pore-emanating crack model) and stochastic (rock failure and process analysis code) modelling. The models show, for a homogenous vesicle size, that an increase in porosity (in the form of circular vesicles, from 0 to 40 %) and/or vesicle diameter (from 0.1 to 2.0 mm) results in a dramatic reduction in strength. For example, uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 %. The presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle-emanating microcracks that grow in the direction of the applied macroscopic stress. As strain increases, these microcracks continue to grow and eventually coalesce leading to macroscopic failure. Vesicle clustering, which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles, and the increased ease of microcrack interaction, is encouraged at higher porosity and reduces sample strength. Once a microcrack nucleates at the vesicle wall, larger vesicles impart higher stress intensities at the crack tips, allowing microcracks to propagate at a lower applied macroscopic stress. Larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture. This explains the reduction in strength at higher vesicle diameters (at a constant porosity). The modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear; the largest reductions are observed at low porosity and small vesicle diameters. In detail, we find that vesicle diameter can play an

  11. Implications for the Upper Cycladic Unit: petrological, mineralogical and structural study of intrusive rocks from the Late-Cretaceous volcanic-arc in Anafi Island, Cyclades, Greece

    NASA Astrophysics Data System (ADS)

    Koutsovitis, P.; Soukis, K.; Lozios, S.

    2012-04-01

    Anafi Island is located at the southeastern edge of the Attic-Cycladic complex and is one of the few Cycladic islands composed solely by upper plate units, which are now found in the form of scattered relics in the central Aegean. The structure of the island consists of a series of thrust sheets which include from bottom to top: a non-metamorphosed flysch of partly Eocene age; greenschist facies metabasites; massive to plate amphibolites; a sequence of upper amphibolite facies meta-sediments and ophiolitic rocks, intruded by intermediate magmatic rocks; marbles and large bodies of felsic intrusive magmatic rocks. The age of the intrusive rocks within the two uppermost thrust sheets is late Cretaceous, (~85 Ma[1]). Mineral chemistry analyses of the intermediate and felsic rocks show that they include quartz, plagioclases (andesines, oligoclases and rarely labradorites), K-feldspars, amphiboles (magnesiohornblendes rarely tremolite), and biotite. The presence of quartz and biotite increases in the most felsic rocks while hornblendes less often appear. These rocks present subophitic textural features, between amphiboles and plagioclases, but also granitic textures in rocks where quartz is in a relatively high modal percentage. Structural observations reveal minor or no ductile deformation (rare undulose extinction in quartz). Based on CIPW and whole-rock chemistry results intrusive rocks are classified as quartz monzodiorites and granodiorites of calc-alkaline affinity[2]. They present subparallel REE patterns, enriched in LREE [(La/Yb)CN=6.1-20.3], with slight to moderate negative Eu anomalies (EuCN/Eu*=0.75-0.97). Their primitive mantle normalized patterns are also subparallel, enriched in LILE elements, such as Cs, Rb, Ba and K. Their Nb and Ta normalized values are lower than the normalized Th, U, K and La. Positive anomalies are noticed for Pb, negative for Ti and slightly negative to none for Zr. These features, along with their high Th/Yb ratios relative to Nb

  12. Effect of the specimen length on ultrasonic P-wave velocity in some volcanic rocks and limestones

    NASA Astrophysics Data System (ADS)

    Karaman, Kadir; Kaya, Ayberk; Kesimal, Ayhan

    2015-12-01

    Ultrasonic P-wave velocity (UPV) is commonly used in different fields such as civil, mining, geotechnical, and rock engineering. One of the significant parameters which affect the UPV of rock materials is likely to be the length of test cores although it is not mentioned in the literature. In this study, in order to explore the influence of the specimen length on the UPV, rock samples were collected from eight different locations in Turkey. The NX-sized core specimens having different length of 50, 75, 100, 125, and 150 mm were prepared. Before the analyses, rocks were divided into two groups in terms of their geological origins such as volcanic and chemical sedimentary (limestone) rocks. The UPV tests were carried out under dry and saturated conditions for each 200 core specimens. By evaluating the test results, it was shown that the length of the specimens significantly affects the UPV values. Based on the regression analyses, a method was developed to determine the threshold specimen length of studied rocks. Fluctuations in UPVdry and UPVsat values were generally observed for cores smaller than the threshold specimen length. In this study, the threshold specimen length was determined as 79 mm for volcanic rocks and 109 mm for limestones.

  13. Spectral characterization of volcanic rocks in the VIS-NIR for martian exploration

    NASA Astrophysics Data System (ADS)

    De Angelis, Simone; Carli, Cristian; Manzari, Paola; De Sanctis, Maria Cristina; Capaccioni, Fabrizio

    2016-10-01

    Igneous effusive rocks cover much of the surface of Mars [1,2,3]. Initially only two types of lithologies were thought to constitute the Martian crust, i.e. a basaltic one and a more andesitic one [1,2], while more evolved lithologies were ruled out.Nevertheless a more complex situation is appearing in the last years. Recently several observations have highlighted the presence of evolved, acidic rocks. High-silica dacite units were identified in Syrtis Major caldera by thermal IR data [4]. Outcrops in Noachis Terra were interpreted as constituted of felsic (i.e. feldspar-rich) rocks essentially by the observation of a 1.3-µm spectral feature in CRISM data, attributed to Fe2+ in feldspars [5]. However different interpretations exist, invoking plagioclase-enriched basalts [6] rather than felsic products.The increasing of high-resolution and in-situ rover-based observations datasets and the changing of the initial paradigm justify a new systematic spectral study of igneous effusive rocks. In this work we focus on the spectral characterization of volcanic effusive rocks in the 0.35-2.5-µm range. We are carrying out measurements and spectral analyses on a wide ensemble of effusive samples, from mafic to sialic, with variable alkali contents, following the classification in the Total-Alkali-Silica diagram, and discussing the influence on spectral characteristics of different mineral assemblages and/or texture ([7], [8]). [1] Bandfield J.L., et al., Science, 287, 1626, 2000; [2] Christensen P.R., et al., J. Geophys. Res., 105, N.E4, 9609-9621, 2000; [3] Ehlmann B.L. & Edwards C.S., Annu. Rev. Earth Planet. Sci., 42, 291-315, 2014; [4] Christensen P.R., et al., Nature, 436, 504-509, 2005; [5] Wray J.J., et al., 44th LPSC, abs. n.3065, 2013; [6] Rogers A.D. & Nekvasil H., Geophys. Res. Lett., 42, 2619-2626, 2015; [7] Carli C. and Sgavetti M.,Icarus, 211, 1034–1048, 2011; [7] Carli C. et al., SGL, doi 10.1144/SP401.19, 2015.

  14. Suitability of alkaline leaching and etching experiments in the quantification of ASR potential of quartz-rich rocks

    NASA Astrophysics Data System (ADS)

    Kuchařová, Aneta; Šachlová, Šárka; Pertold, Zdeněk; Přikryl, Richard

    2015-04-01

    Three groups of methods are conventionally applied in the assessment of the susceptibility of aggregates used in concrete to be affected by alkali-silica reaction (ASR). The most frequently employed expansion tests (accelerated mortar bar test and concrete prism test, e.g. ASTM C1260, RILEM AAR2, RILEM AAR4.1) quantify ASR potential of aggregates according to the expansion values of mortar bars (resp. concrete prisms) measured after certain testing time period. Petrographic methods are based on the quantification of alkali-reactive phases by polarizing microscopy (e.g. RILEM AAR1). Chemical methods quantify ASR potential according to the amount of Si4+ dissolved into alkaline solution combined with the reduction of alkalinity of the solution (e.g. ASTM C289). The current study focused on the comparison of three approaches: the alkaline etching of polished rock sections and standard chemical method (following ASTM C289) with the measuring of expansion values of mortar bars (following ASTM C1260). Various types of quartz and amorphous SiO2 used for the experiments were separated from rock samples of orthoquartzite, quartz meta-greywacke, pegmatite, phyllite, chert, and flint. Polished rock sections (resp. crushed fraction 0.125/0.250) were used and subjected to leaching in 1M NaOH solution at 80°C for 14 days (resp. 24 hours). After alkaline etching in alkaline solution, the rock sections were analyzed by scanning electron microscopy combined with energy dispersive spectrometer. Representative areas were documented in back scattered electron images and quantified using fully-automatic petrographic image analysis. ASR potential of the polished rock sections was evaluated by the vol. % of area affected by alkaline etching. ASR potential of crushed aggregate was estimated by measurements of Si4+ dissolved into the solution versus the reduction of alkalinity of the solution (following ASTM C289). Classification according to the ASTM C289 indicated three of investigated

  15. Age constraints on late Mesozoic lithospheric extension and origin of bimodal volcanic rocks from the Hailar basin, NE China

    NASA Astrophysics Data System (ADS)

    Li, Shuang-Qing; Hegner, Ernst; Yang, Yi-Zeng; Wu, Jia-De; Chen, Fukun

    2014-03-01

    Following the amalgamation of the late Mesoproterozoic-Carboniferous Central Asian Orogenic Belt with the Siberian and North China cratons, NE China underwent late Mesozoic lithospheric extension and widespread formation of volcano-sedimentary basins. We report U-Pb zircon ages and geochemical data for mafic and felsic volcanic rocks from the Hailar basin, located about 1000 km north of Beijing. Zircon populations of six felsic rock samples analyzed by laser ablation ICP-MS yielded similar U-Pb age spectra ranging from 158 to 125 Ma. The youngest zircon ages are interpreted as time of magma eruption and the xenocrystic zircon-age spectra as evidence for a protracted melting of lower crust due to the underplating of mantle-derived magmas during lithospheric extension. The volcanic assemblage has a bimodal composition comprising geochemically evolved trachybasalts and felsic volcanic rocks of I- and subordinate A-type compositions. The mafic volcanic rocks have negative Nb-anomalies, high Th/Nb and Ce/Pb ratios, low initial ɛNd values of + 0.4 to + 3.4, and radiogenic Pb and Sr isotopes all interpreted as evidence for the melting of passively upwelling asthenosphere and lithospheric mantle previously modified by plate subduction. The xenocrystic zircon ages and chemical/isotopic data of the felsic rocks support an origin from juvenile crustal protoliths: the data of I-type felsic rocks are consistent with the melting of underplated mafic protoliths and those of the A-type rhyolites support the melting of a crustal source with a composition similar to the I-type felsites with apatite controlling their Nb anomaly. The evidence for the persistent melting of a subduction-modified mantle in NE China is in agreement with a model of an extending coupled upper mantle-crust system due to a retreating Paleo-Pacific trench.

  16. Geochemistry of mafic Paleocene volcanic rocks in the Valle del Cura region: Implications for the petrogenesis of primary mantle-derived melts over the Pampean flat-slab

    NASA Astrophysics Data System (ADS)

    Litvak, Vanesa D.; Poma, Stella

    2010-04-01

    Mafic volcanism of Paleocene age was recently reported in the Valle del Cura region and the El Indio Belt in the aphanitic and very homogenous well-preserved lavas flows of the Río Frío Basalts unit. These are high-K basalts, with high Fe 2O 3 and TiO 2 contents that imply an alkaline tendency and show typical intraplate-type patterns on a MORB normalized trace elements plot. Sr and Nd isotopic ratios evidence a mantle affinity. The chemistry indicates that these rocks are high temperature melts that result from a low degree of melting of an enriched portion of lithospheric mantle, with no contamination from crustal derived components. The alkaline back-arc Las Máquinas Basalts of Lower Miocene age are derived from more primitive magmas closer to the original source. Mantle composition was relatively constant from Paleocene to Lower Miocene in the studied latitudes over the Pampean flat-slab. Both mafic units share the isotopic trend of pre-Miocene mafic lavas from the Central Andes that were not affected by crustal contamination. Post-Miocene mafic lavas show a strong influence from crust-related processes.

  17. Age and Sr isotopic composition of volcanic rocks in the Maricunga Belt, Chile: implications for magma sources

    USGS Publications Warehouse

    McKee, E.H.; Robinson, A.C.; Rybuta, J.J.; Cuitino, L.; Moscoso, R.D.

    1994-01-01

    K-Ar and 40Ar/39Ar dating of volcanic rocks from the Maricunga belt of north-central Chile indicate that igneous activity took place throughout most of Miocene time at various places in the 150 by 30 km belt. No migration patterns of volcanism appear in the Miocene rocks of the belt. Volcanic activity ceased by the end of the Miocene. All the Miocene volcanic rocks studied are calcic andesites to dacites with about 62% SiO2, 18% A12O3, 4% Fe2O3 (total), and 2% K2O. Initial 87Sr/86Sr (Sri) values fall into two groups, one of lower values around 0.7050 to the west and the other of higher values around 0.7060 to the east. It is postulated that the two Sri groups reflect two adjoining coherent lower-crustal magma sources of possibly different age and subtly different composition that form part of the western edge of the South American craton. ?? 1994.

  18. Role of crustal assimilation and basement compositions in the petrogenesis of differentiated intraplate volcanic rocks: a case study from the Siebengebirge Volcanic Field, Germany

    NASA Astrophysics Data System (ADS)

    Schneider, K. P.; Kirchenbaur, M.; Fonseca, R. O. C.; Kasper, H. U.; Münker, C.; Froitzheim, N.

    2016-06-01

    The Siebengebirge Volcanic Field (SVF) in western Germany is part of the Cenozoic Central European Volcanic Province. Amongst these volcanic fields, the relatively small SVF comprises the entire range from silica-undersaturated mafic lavas to both silica-undersaturated and silica-saturated differentiated lavas. Owing to this circumstance, the SVF represents a valuable study area representative of intraplate volcanism in Europe. Compositions of the felsic lavas can shed some new light on differentiation of intraplate magmas and on the extent and composition of potential crustal assimilation processes. In this study, we provide detailed petrographic and geochemical data for various differentiated SVF lavas, including major and trace element concentrations as well as Sr-Nd-Hf-Pb isotope compositions. Samples include tephriphonolites, latites, and trachytes with SiO2 contents ranging between 53 and 66 wt%. If compared to previously published compositions of mafic SVF lavas, relatively unradiogenic 143Nd/144Nd and 176Hf/177Hf coupled with radiogenic 87Sr/86Sr and 207Pb/204Pb lead to the interpretation that the differentiated volcanic rocks have assimilated significant amounts of lower crustal mafic granulites like the ones found as xenoliths in the nearby Eifel volcanic field. These crustal contaminants should possess unradiogenic 143Nd/144Nd and 176Hf/177Hf, radiogenic 87Sr/86Sr, and highly radiogenic 207Pb/204Pb compositions requiring the presence of ancient components in the central European lower crust that are not sampled on the surface. Using energy-constrained assimilation-fractional crystallisation (EC-AFC) model calculations, differentiation of the SVF lithologies can be modelled by approximately 39-47 % fractional crystallisation and 6-15 % crustal assimilation. Notably, the transition from silica-undersaturated to silica-saturated compositions of many felsic lavas in the SVF that is difficult to account for in closed-system models is also well explained by

  19. Alkaline Basalts of The Quaternary Buffalo Valley Volcanic Field, NW Fish Creek Mountains, North-central Nevada, Great Basin

    NASA Astrophysics Data System (ADS)

    Cousens, B.; Henry, C. D.

    2008-12-01

    The Buffalo Valley volcanic field, 5 km southwest of Battle Mountain, consists of approximately 11 cinder cones and associated flows. Youthful volcanoes are rare in the region, and thus this field offers the opportunity to investigate mantle sources currently beneath the central Great Basin. Most of the eruptive centers are distributed along the northwestern margin of the Fish Creek Mountains, a mid-Tertiary caldera complex, along a 13-km-long northeasterly trend that is perpendicular to the regional stress field (or GPS velocity field), suggesting fault control or eruption from a now-buried fissure. The cones are geomorphologically youthful, with well-defined, commonly breached craters. At least one cone, situated slightly east of the main trend, consists of only a thin mantle of scoria and bombs overlying grey Paleozoic limestone. Previous K-Ar and Ar-Ar dating indicate that the cones are between 1.29 and 0.95 Ma in age. Two other nearby Quaternary volcanic centers lie northeast of the Fish Creek Mountains (K-Ar date of 3.3 Ma) and in the center of the Fish Creek caldera (age unknown). Rare Tertiary basalts and more common Tertiary andesites lie around the margin of the caldera. Lavas from the Buffalo Valley cones have vesicular flow tops and more massive interiors. All Quaternary centers are similar petrographically, including 1-2% olivine phenocrysts and megacrysts up to 1 cm in size, and characteristic plagioclase megacrysts that are rarely up to 4 cm long, commonly in a glassy matrix. Two cone samples are alkalic basalt and tephrite with Mg numbers of 0.55, high TiO2 (2.4%), K2O (2.0%), light REE, Nb (60 ppm), but low Cr and Ni (80 ppm), Pb (2 ppm), Ba (450 ppm) and 87Sr/86Sr (0.70375) compared to Late Pliocene/Quaternary volcanic rocks from the western Great Basin near Reno/Carson City/Fallon. The Buffalo Valley cones are similar chemically to lavas from the Pliocene-Quaternary Lunar Craters volcanic field in central Nevada, and are melts of mantle that is

  20. Geology, thermal maturation, and source rock geochemistry in a volcanic covered basin: San Juan sag, south-central Colorado

    USGS Publications Warehouse

    Gries, R.R.; Clayton, J.L.; Leonard, C.

    1997-01-01

    The San Juan sag, concealed by the vast San Juan volcanic field of south-central Colorado, has only recently benefited from oil and gas wildcat drilling and evaluations. Sound geochemical analyses and maturation modeling are essential elements for successful exploration and development. Oil has been produced in minor quantities from an Oligocene sill in the Mancos Shale within the sag, and major oil and gas production occurs from stratigraphically equivalent rocks in the San Juan basin to the south-west and in the Denver basin to the northeast. The objectives of this study were to identify potential source rocks, assess thermal maturity, and determine hydrocarbon-source bed relationships. Source rocks are present in the San Juan sag in the upper and lower Mancos Shale (including the Niobrara Member), which consists of about 666 m (2184 ft) of marine shale with from 0.5 to 3.1 wt. % organic carbon. Pyrolysis yields (S1 + S2 = 2000-6000 ppm) and solvent extraction yields (1000-4000 ppm) indicate that some intervals within the Mancos Shale are good potential source rocks for oil, containing type II organic matter, according to Rock-Eval pyrolysis assay. Oils produced from the San Juan sag and adjacent part of the San Juan basin are geochemically similar to rock extracts obtained from these potential source rock intervals. Based on reconstruction of the geologic history of the basin integrated with models of organic maturation, we conclude that most of the source rock maturation occurred in the Oligocene and Miocene. Little to no maturation took place during Laramide subsidence of the basin, when the Animas and Blanco Basin formations were deposited. The timing of maturation is unlike that of most Laramide basins in the Rocky Mountain region, where maturation occurred as a result of Paleocene and Eocene basin fill. The present geothermal gradient in the San Juan sag is slightly higher (average 3.5??C/100 m; 1.9??F/100 ft) than the regional average for southern Rocky

  1. /sup 230/Th - /sup 238/U disequilibrium systematics in young volcanic rocks

    SciTech Connect

    Newman, S.

    1983-01-01

    Radioactive disequilibrium between /sup 230/Th (t/sub .5/ = 75,200 years) and its parent, /sup 238/U, has two major applications to the study of young volcanic rocks: 1) geochronology and 2) geochemical tracer studies. Geochronological investigations include both the dating of young (< approx.250,000 year-old) lavas by the internal isochron method and the study of the temporal evolution of magma systems feeding volcanoes. Older, K-Ar-dated lavas from Mauna Kea, Hawaii and Marion Island (Prince Edward hot spot) exhibit constant initial (/sup 230/Th//sup 232/Th) (activity) ratios for the past 100,000-275,000 years. At Mt. Shasta, California, a general decrease in (/sup 230/Th//sup 232/Th)/sub 0/ through time, with evidence of possible mixing corroborated by other geochemical data, is observed. Geochemical tracer studies depend on the observations that Th/U and (/sup 230/Th//sup 238/U) can be changed by such processes as partial melting, mixing, or fluid transport, whereas (/sup 230/Th//sup 232/Th) can only be modified by mixing or the passage of time. The (/sup 230/Th//sup 238/U) ratio can be used to identify possible petrogenetic processes. All lavas exhibit (/sup 230/Th//sup 238/U) greater than or equal to 1 except for some from the Aleutians and Marianas. These observations suggest that subduction-related volcanism is the only type in which U may behave as a more incompatible element than Th, although it need not (Cascades). Recent vapor transport of U or retention of Th may explain the U-enrichment in island arc lavas.

  2. Paleomagnetism of Jurassic volcanic rocks in southeastern Arizona and North American Jurassic apparent polar wander

    SciTech Connect

    May, S.R.

    1985-01-01

    The Corral Canyon sequence in the Patagonia Mountains is a 650 meter thick homoclinal sequence consisting of interbedded volcaniclastic red-beds, welded ash-flow tuff, and lavas. Rb/Sr isotopic analysis of eight whole rock tuff samples yields an isochron age of 171 +/- 3 Ma. Welded tuffs in the Corral Canyon sequence possess a stable, primary magnetization carried in both magnetite and hematite that defines a paleomagnetic pole at 61.8/sup 0/N, 116.0/sup 0/E. Paleomagnetic study of the Canelo Hills volcanics welded tuff member also yields a stable, primary magnetization throughout a stratigraphic thickness of 600 meters. Various aspects of the paleomagnetic data indicate that discordance of the Canelo Hills volcanics pole is probably due to acquisition of remanent magnetization during a period of non-dipole behavior of the geomagnetic field. Dispersion of paleomagnetic directions suggests that the welded tuff member represents at most two cooling units and can be interpreted as a caldera-fill sequence. A revised Jurassic APW path differs significantly from available paths and has important implications for North American plate motion and paleolatitude. The spatio-temporal progression of reliable Jurassic paleopoles, in conjunction with Triassic and Early Cretaceous poles, is well described by paleomagnetic Euler pole analysis. The APW path is divided into three tracks, separated by two cusps. These cusps represent changes in the direction of North American absolute plate motion and can be correlated with global plate motion and intraplate deformation events at approximately 200-210 Ma and 150 Ma. Finally, the APW path presented herein predicts more southerly Late Triassic and Jurassic paleolatitudes for North America than have been suggested by previous authors.

  3. Deciphering the Western Mediterranean mantle heterogeneities through a statistical approach of the erupted volcanic rocks.

    NASA Astrophysics Data System (ADS)

    Fernandez, M.; Melchiorre, M.; Verges, J.; Coltorti, M.; Torne, M.; Casciello, E.

    2015-12-01

    The Western Mediterranean (We-Me) is characterized by a complex geodynamic history related to subduction events that can be explained by three different models: A) N-NW dipping slab extending from the Gibraltar arc to the Balearic promontory retreating in S-SE direction; B) NW dipping slab under the Balearic promontory, retreating in SE direction towards the Gibraltar strait C) two opposite-directed subductions separated by a transform fault subparellel to the Pierre Fallot Fault Since Oligocene the geological evolution of this part of the Mediterranean is characterized by widespread volcanic activity, related to subductive (orogenic) or intraplate (anorogenic) settings. We merged two huge orogenic and anorogenic datasets containing over 14,000 chemical analyses and processed them through factor analysis, in order to reduce the large number of geochemical parameters describing each sample (major/trace elements, isotopic ratios) through a smaller number of factors. Binary diagrams obtained combining seven resulting factors allow to distinguish the anorogenic field from the orogenic one. Anorogenic rocks usually fall in a narrow range of variation, while orogenic are characterized by a greater variability and by alignment along different trends. These different trends account for large heterogeneities of the sub lithospheric mantle due to extensive recycling of geochemically different materials through time, supporting the idea that different reservoirs are responsible for the Mediterranean volcanism [1]. The spatio-temporal evolution of the We-Me lamproites allows us to speculate a two-step evolution of the mantle beneath southern Spain. This evolution has been evaluated in light of the three models. We therefore propose that a type C model accounting for the presence of two juxtaposed slabs beneath the We-Me is the most feasible model to describe the geodynamic evolution of this area. [1] Conticelli et al. (2009). Lithos 107, 68-92.

  4. Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks of Burpala massi, Northern Baikal folded zone

    NASA Astrophysics Data System (ADS)

    Sotnikova, Irina; Vladykin, Nikolai

    2015-04-01

    Burpalinsky rare metal alkaline massif in the Northern Baikal folded zone in southern margin of Siberian Platform, is a of intrusion central type, created 287 Ma covering area of about 250 km2. It is composed of nepheline syenites and pulaskites grading to quartz syenites in the contacts. Veines and dykes are represented by shonkinites, sodalite syenite, leucocratic granophyres, alkali granites and numerous rare metal alkaline syenite pegmatites and two dykes of carbonatites. All rocks except for granites are cut by a large apatite-fluorite dyke rocks with mica and magnetite, which in turn is cut by alaskite granites dyke. The massif has been studied by A.M. Portnov, A.A. Ganzeev et al. (1992) Burpalinsky massif is highly enriched with trace elements, which are concentrated in pegmatite dykes. About 70 rare-metal minerals we found in massif. Zr-silicates: zircon, eudialyte, lovenite, Ti-lovenite, velerite, burpalite, seidozerite, Ca- seidozerite, Rosenbuschite, vlasovite, katapleite, Ca-katapleite, elpidite. Ti- minerals:- sphene, astrophyllite, ramsaite, Mn-neptunite bafertisite, chevkinite, Mn-ilmenite, pirofanite, Sr-perrerit, landauite, rutile, anatase, brookite; TR- minerals - loparite, metaloparite, britolite, rinkolite, melanocerite, bastnesite, parisite, ankilite, monazite, fluocerite, TR-apatite; Nb- minerals - pyrochlore, loparite. Other rare minerals leucophanite, hambergite, pyrochlore, betafite, torite, thorianite, tayniolite, brewsterite, cryolite and others. We have proposed a new scheme massif: shonkinites - nepheline syenites - alkaline syenite - quartz syenites - veined rocks: mariupolites, rare-metal pegmatites, apatite, fluorite rock alyaskite and alkaline granites and carbonatites (Sotnikova, 2009). Apatite-fluorite rocks are found in the central part of massif. This is a large vein body of 2 km length and a 20 m width cutting prevailing pulaskites. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and

  5. Uranium-series disequilibrium in volcanic rocks from the Northeast Japan Arc

    NASA Astrophysics Data System (ADS)

    Yokoyama, T.; Iwamori, H.; Ueki, K.

    2011-12-01

    Subducting slabs are considered to release fluid components as a result of mineralogical reactions during progressive metamorphic dehydration. The fluid released from the slab subsequently induces melting in the mantle wedge as it ascends, resulting in island arc volcanism [1]. To understand the characteristics of slab-derived materials, geochemical tracers such as trace elements, radiogenic isotopes (e.g., Sr, Nd, Pb), and stable isotopes (e.g., B, Li) have been commonly used [2-3]. U-series disequilibria of island arc volcanic rocks have been used to understand melt generation in the source mantle and the timescales of fluid/melt migration in subduction zones. This is possible because of the short half-lives of daughter nuclides of 238U, 235U and 232Th (e.g., 75 kyr for 230Th, and 1.6 kyr for 226Ra). We report our preliminary measurements on 238U-230Th disequilibrium in volcanic rocks from the Northeast Japan Arc. Lava samples of basalts and basaltic andesites were collected from four volcanoes (Iwate, Akita-Komagatake, Yakeyama and Kampu). The eruption ages of these rocks are estimated to be range from 0 to 30 ka. The frontal-arc lavas (Iwate and Akita-Komagatake) are characterized by 238U-230Th disequilibrium with moderate 238U enrichments (5-10%). This is due to the addition to the mantle wedge of slab-derived fluids enriched in fluid-mobile elements (U) relative to less fluid-mobile elements (Th). The extent of 238U enrichment decreases as the slab depth increases, and the rear-arc lavas (Kampu) show 230Th enrichments relative to 238U (~5%). This generally reflects gradual decrease of the amount of slab derived fluid mixed into the wedge mantle. Thus, the 230Th excesses in rear-arc lavas may be predominantly produced by the melting of garnet-bearing upwelling mantle as observed in MORB (dynamic melting). However, our data show 230Th excess with an extremely low (230Th/232Th) ratio (~0.8) that plots outside the MORB data. This strongly argues against a model

  6. A New Hygrometer based on the Europium Anomaly in Clinopyroxene Phenocrysts in Arc Volcanic Rocks

    NASA Astrophysics Data System (ADS)

    Plank, T.; Benjamin, E.; Wade, J.; Grove, T.

    2004-12-01

    Water is arguably the most important chemical component in arc magmas, affecting everything from liquidus temperatures to crystal fractionation trends to melt rheology. Water concentrations in arc magmas provide a first-order constraint on water contents in the mantle wedge, and the mechanisms of wet mantle melting. However, measuring the water content of primary arc magmas has been difficult, or in some cases impossible, due to the near complete degassing of volcanic rocks, and the scarcity of olivine-hosted melt inclusions in many arc volcanoes. We have thus developed a new hygrometer using the composition of clinopyroxene phenocrysts, which are common in arc basalts and andesites. The hygrometer is based on the well-known suppression of plagioclase by water dissolved in the melt, and the effect on the rare earth element (REE) pattern of coexisting phases, such as clinopyroxene. Dry melts saturate in plagioclase early, and the preferential partitioning of Eu2+ in plagioclase causes a negative Eu anomaly to develop in coexisting melts and clinopyroxene. In wet magmas, clinopyroxene crystallizes before plagioclase, and so initially appears with a negligible Eu anomaly. Clinopyroxenes then record water content in the delayed development of their negative Eu anomaly, caused by the delayed appearance of plagioclase along the cotectic with increasing water. We have tested this model using tephras from the 1723 eruption of Irazu, the ET3 unit of Arenal and the 1995 eruption of Cerro Negro volcanoes in Central America, with known water contents of ˜ 3, 4 and 5 wt%, respectively, based on olivine-hosted melt inclusions. Clinopyroxene phenocrysts separated from these samples vary in Mg# from 86-72, and in some cases span the entire liquid line of descent of the volcano. REE patterns were determined by laser ablation ICPMS on 150 micron spots. A marked increase in the magnitude of the negative Eu anomaly occurs in clinopyroxenes with Mg# < 84 in Irazu, < 82 in Arenal and

  7. Strontium isotopic geochemistry of the volcanic rocks and associated megacrysts and inclusions from Ross Island and vicinity, Antarctica

    USGS Publications Warehouse

    Stuckless, J.S.; Ericksen, R.L.

    1976-01-01

    Twelve whole-rock samples of volcanic rocks and a composite of 11 basanitoid samples from Ross Island and vicinity, Antarctica show a narrow range of 87Sr/86Sr ratios from 0.70305 to 0.70339. This range is consistent with a model of differentiation from a single parent magma, but the data allow a 30% variation in the 87Rb/86Sr ratio in the source region if the average ratio is less than 0.057 and if the source region has existed as a closed system for 1.5 b.y. Megacrysts of titaniferous augite, kaersutite, and anorthoclase are isotopically indistinguishable from the host volcanic rocks and therefore are probably cogenetic with the volcanic sequence. A single trachyte sample is isotopically distinct from the rest of the volcanic rocks and probably was contaminated with crustal strontium. Ultramafic and mafic nodules found in association with basanitoids and trachybasalts have 87Sr/86Sr ratios ranging from 0.70275 to 0.70575. Several of these nodules exhibit evidence of reaction with the melt and are isotopically indistinguishable from their hosts, but data for seven granulite-facies nodules show an apparent isochronal relationship. Although this isochron may be fortuitous, the resulting age of 158??22 m.y. is similar to ages reported for the voluminous Ferrar Dolerites, and suggests isotopic re-equilibration within the lower crust and upper mantle. These nodules are not genetically related to the Ferrar Dolerites, as evidenced by their lower initial 87Sr/86Sr ratios. Three ultramafic nodules are texturally and isotopically distinct from the rest of the analyzed nodules. These are friable, have larger 87Sr/86Sr ratios, and may represent a deeper sampling of mantle rock than the granulite-facies nodules. They were, however, derived at a shallower depth than the alkalic magma. Thus they are not genetically related to either the magma or the granulite-facies nodules. ?? 1976 Springer-Verlag.

  8. Upper Paleozoic mafic and intermediate volcanic rocks of the Mount Pleasant caldera associated with the Sn-W deposit in southwestern New Brunswick (Canada): Petrogenesis and metallogenic implications

    NASA Astrophysics Data System (ADS)

    Dostal, Jaroslav; Jutras, Pierre

    2016-10-01

    Upper Paleozoic (~ 365 Ma) mafic and intermediate volcanic rocks of the Piskahegan Group constitute a subordinate part of the Mount Pleasant caldera, which is associated with a significant polymetallic deposit (tungsten-molybdenum-bismuth zones ~ 33 Mt ore with 0.21% W, 0.1% Mo and 0.08% Bi and tin-indium zones ~ 4.8 Mt with 0.82% Sn and 129 g/t In) in southwestern New Brunswick (Canada). The epicontinental caldera complex formed during the opening of the late Paleozoic Maritimes Basin in the northern Appalachians. The mafic and intermediate rocks make up two compositionally distinct associations. The first association includes evolved rift-related continental tholeiitic basalts, and the second association comprises calc-alkaline andesites, although both associations were emplaced penecontemporaneously. The basalts have low Mg# ~ 0.34-0.40, smooth chondrite-normalized REE patterns with (La/Yb)n ~ 5-6, primitive mantle-normalized trace element patterns without noticeable negative Nb-Ta anomalies, and their ɛNd(T) ranges from + 2.5 to + 2.2. The basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of ~ 70-90 km. The calc-alkaline andesites of the second association have chondrite-normalized REE patterns that are more fractionated, with (La/Yb)n ~ 7-8.5, but without significant negative Eu anomalies. Compared to the basaltic rocks, they have lower ɛNd(T) values, ranging from + 0.5 to + 1.9, and their mantle-normalized trace element plots show negative Nb-Ta anomalies. The ɛNd(T) values display negative correlations with indicators of crustal contamination, such as Th/La, Th/Nb and SiO2. The andesitic rocks are interpreted to have formed by assimilation-fractional crystallization processes, which resulted in the contamination of a precursor basaltic magma with crustal material. The parent basaltic magma for both suites underwent a different evolution. The tholeiitic basalts experienced shallow

  9. Temporal variation of isotope and rare earth element abundances in volcanic rocks from Guam: implications for the evolution of the Mariana Arc

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, Rosemary; Reagan, Mark K.

    1987-12-01

    Volcanic rocks exposed on Guam were erupted during the Late Middle Eocene (Facpi Fm.), Late Eocene-Oligocene (Alutom Fm.) and Miocene (Umatac Fm.). Four magma series are recognized: the boninite series (44 m.y.b.p.), the tholeiite and calc-alkaline series, which were erupted along with boninite series lavas at 32 36 m.y.b.p. and high-K lavas of the Umatac Fm. (14 m.y.b.p.). Isotope and and rare earth element (REE) characteristics of the four magma series are distinct. Boninite series lavas have U-shaped REE patterns, relatively low 143Nd/144Nd (0.51294 0.51298), and high 206Pb/204Pb (19.0 19.2). Tholeiite series lavas are LREE (light REE) depleted, and have high 143Nd/144Nd (0.51304 0.51306) and low 206Pb/204Pb (18.4 18.5). Calc-alkaline series lavas have Sr, Nd and Pb isotope ratios similar to tholeiite series lavas, but flat to U-shaped REE patterns. Umatac Fm. lavas are strongly LREE-enriched, and have higher 87Sr/ 86Sr (0.70375 0.70380) and 207Pb/204Pb relative to 206Pb/ 204Pb than Facpi and Alutom Fm. lavas. Boninite and tholeiite series magmas, erupted in the position of the Palau-Kyushu Ridge, were probably derived from distinct mantle sources having OIB and N-MORB-like isotopic characteristics, together with fluids derived from subducted Pacific plate basalt. Calc-alkaline series lavas were most likely derived from the tholeiite series by extensive crystal fractionation, wallrock contamination and magma mixing. Lavas of the Umatac Fm., erupted in the position of the West Mariana Ridge, may include up to 2 3% subducted sediment, similar to some active Mariana arc lavas.

  10. Geochemistry of the mafic volcanic rocks of the Buzwagi gold mine in the Neoarchaean Nzega greenstone belt, northern Tanzania

    NASA Astrophysics Data System (ADS)

    Manya, Shukrani

    2016-11-01

    The Buzwagi gold mine, found in the Neoarchaean Nzega greenstone belt of northern Tanzania; is underlain by mafic volcanic rocks which are associated with a massive body of ultramafic rocks that are considered to be cumulates. The mafic-ultramafic rocks association are cross-cut by ~ 2.71 Ga grey TTG and ~ 2.67 Ga pink microcline K-rich granites. The Buzwagi mine mafic volcanic rocks are Fe-rich tholeiites (MgO = 3.59-7.67 wt.%, Fe2O3 = 12.5-17.7 wt.% and Mg# = 30-56) that are characterized by flat REE (La/SmCN = 0.78-1.12) and N-MORB like patterns except for moderate negative anomalies of Nb (Nb/Lapm = 0.46-1.13) and Ta, Zr and Hf. The rocks exhibit sub-chondritic Zr/Hf ratios of 28.5-40.5 (average = 32.6) and Ti/Zr ratios of 102-136 (average = 124) and suggest that they are mantle-derived. Their La/Nb ratios of 0.85-2.10 encompass the range of oceanic ridge/plateau (La/Nb < 1.4) and arc-like (La/Nb > 1.4) basalts. The Buzwagi mine mafic volcanic rocks have been interpreted as products of 4-10% (average = 5%) non-modal partial melting of the DMM source leaving a residual mineralogy comprised of olivine (57%), orthopyroxene (28%), clinopyroxene (13%) and spinel (2%). The DMM source was metasomatized by the slab-derived hydrous fluids in a back arc setting. This study corroborates previous evidence that crustal growth in the late Archaean Tanzania Craton occurred at convergent margins.

  11. Measurement of cosmogenic /sup 36/Cl/Cl in young volcanic rocks: An application of accelerator mass spectrometry in geochronology

    SciTech Connect

    Leavy, B.D.; Phillips, F.M.; Elmore, D.; Kubik, P.W.

    1987-01-01

    We have measured /sup 36/Cl/Cl ratios in a number of young volcanic rocks in order to test the feasibility of using /sup 36/Cl buildup as a geochronometer for materials less than about 700,000 years old. All of the analyzed rocks have been dated independently using K-Ar or other radiometric dating methods and have exposure histories that are known or can be reasonably assumed. Measured /sup 36/Cl/Cl ratios in these rocks are in good agreement with the calculated in-situ /sup 36/Cl buildup curve. These analyses indicate that AMS measurement of /sup 36/Cl buildup in young rocks is a potentially powerful new method for dating materials that had previously been undatable, and as such will have broad applications in volcanology, tectonics, geophysics, and Quaternary research.

  12. Oxygen isotope geochemistry of the silicic volcanic rocks of the Etendeka-Parana province: Source constraints

    SciTech Connect

    Harris, C.; Milner, S.C.; Armstrong, R.A. ); Whittingham, A.M. )

    1990-11-01

    Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Parana flood basalt province (Namibia, South America) are believed to reflect the {delta}{sup 18}O values of the original magmas. The authors recognize a high {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +10{per thousand}) found in the south of both regions, and a low {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +6.5{per thousand}) found in the north. Other differences between thee two rhyolite types include higher concentrations of incompatible elements and lower initial {sup 87}Sr/{sup 86}Sr ratios in the low {delta}{sup 18}O value type. The authors suggest that the regional distribution of rhyolite types reflects differences in source composition, which can best be explained if the sources are lower crustal, Late Proterozoic mobile belt material (high {delta}{sup 18}O) and Archean lower crust (low {delta}{sup 18}O).

  13. Geochemistry and petrogenesis of volcanic rocks from Daimao Seamount (South China Sea) and their tectonic implications

    NASA Astrophysics Data System (ADS)

    Yan, Quanshu; Castillo, Paterno; Shi, Xuefa; Wang, Liaoliang; Liao, Lin; Ren, Jiangbo

    2015-03-01

    The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6 Ma) was formed 10 my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr-Nd-Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a 'Dupal' isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6 Ma. The seamount subsided rapidly (> 0.12 mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (< 0.12 mm/y). We propose that the parental magmas of SCS seamount lavas originated from the Hainan mantle plume. In contrast, lavas from contemporaneous seamounts in other marginal basins in the western Pacific are subduction-related.

  14. Ar-40-Ar-39 and Rb-Sr age determinations on Quaternary volcanic rocks

    NASA Technical Reports Server (NTRS)

    Radicati Di Brozolo, F.; Huneke, J. C.; Papanastassiou, D. A.; Wasserburg, G. J.

    1981-01-01

    Ages of leucite and biotite separates from samples of the potassic volcanics of the Roman Comagmatic region are derived by the stepwise degassing variant of the Ar-39-Ar-40 dating method and compared with those derived from Rb-Sr dating in order to evaluate the abilities of the methods to date Quaternary geological events. Six of the leucite separates are found to contain Ar with very high bulk 40/36 ratios and to have well correlated Ar-40 and Ar-39 contents, yielding ages of approximately 338,000 years. Two leucites observed to contain Ar with lower bulk 40/36 ratios and Ar-40/Ar-36 ratios significantly lower than atmospheric are found to have ages in substantial agreement with those of the other leucites despite the uncertainty in the composition of the trapped component. Ages obtained for the biotites are not as precise as those of the leucites, due to difficulties in obtaining a good separation of in situ radiogenic Ar-40 from trapped Ar-40. Ages determined from Rb-Sr measurements for selected tuff samples are found to be in good agreement with the Ar-40-Ar-39 ages of the leucites. Results demonstrate the possibility of attaining precisions of better than 5% in the dating of rocks 350,000 years old by both the Ar-40-Ar-39 and the Rb-Sr methods.

  15. Rocks of the Thirtynine Mile volcanic field as possible sources of uranium for epigenetic deposits in central Colorado, USA.

    USGS Publications Warehouse

    Dickinson, K.A.

    1987-01-01

    The most likely volcanic source rock for uranium in epigenetic deposits of the Tallahassee Creek uranium district and nearby areas is the Wall Mountain Tuff. The widespread occurrence of the Tuff, its high apparent original uranium content, approx 11 ppm, and its apparent loss of uranium from devitrification and other alteration suggest its role in providing that element. An estimate of the original Th/U ratio is based on the present thorium and uranium contents of the basal vitrophyre of the Tuff from Castle Rock Gulch, Hecla Junction and other areas.-from Author

  16. Geochemical analyses, age dates, and flow-volume estimates for quaternary volcanic rocks, Southern Cascade Mountains, Washington

    NASA Astrophysics Data System (ADS)

    Hammond, P. E.; Korosec, M. A.

    1983-12-01

    Data collected over the last three years as part of a continuing study of the Quaternary volcanic rocks of the southern Cascade Mountains are presented. Whole-rock chemical analyses, selected trace element geochemistry, volume approximations, specific gravity determinations, and locations are provided for most of the 103 samples collected, and 21 radiometric age dates are included. In addition, partial information, including names and flow-volumes, are presented for 98 additional samples, collected for related studies. The study extends from the Columbia River north to the Cowlitz River and Goat Rocks Wilderness area, and from the Klickitat River west to the Puget-Williamette Trough. The volcanic rocks are all younger than 3 million years and consist primarily of tholeitic and high-alumina basalts and basaltic-andesites erupted from numerous shield volcanoes and cinder cones. A few analyses of more silicic rocks, including hornblende and/or pyroxene andesites and dacites characteristic of the stratovolcanoes of the region, are also presented.

  17. Pleistocene volcaniclastic units from North-Eastern Sicily (Italy): new evidence for calc-alkaline explosive volcanism in the Southern Tyrrhenian Sea

    NASA Astrophysics Data System (ADS)

    Di Bella, Marcella; Italiano, Francesco; Sabatino, Giuseppe; Tripodo, Alessandro; Baldanza, Angela; Casella, Sergio; Pino, Paolo; Rasa', Riccardo; Russo, Selma

    2016-08-01

    A well-preserved volcaniclastic sequence crops out in Pleistocene marine sediments along the Tyrrhenian coastline of the Calabrian-Peloritani arc (Sicily, Italy), testifying the occurrence of Lower-Middle Pleistocene volcanic activity in Southern Tyrrhenian Sea. The presence of dominant highly vesicular and minor blocky glassy particles indicates that the volcanic clasts were originated by explosive events related to the ascent and violent emission of volatile-rich magmas accompanied by and/or alternated with hydromagmatic fragmentation due to magma-sea water interaction. Field investigations and sedimentological features of the studied volcaniclastic units suggest a deposition from sediment-water density flows. The chemical classification of the pumice clasts indicates prevalent rhyolitic and dacitic compositions with calc-alkaline to high-K calc-alkaline affinity. The geochemical features of immobile trace elements together with the presence of orthopyroxene are indicative of a provenance from an arc-type environment. The age (from 980-910 to 589 ka), the chemical composition and the evidence of subaerial explosive volcanic activity constrain the origin nature and temporal evolution of the arc-type volcanism in the Southern Tyrrhenian domain. Finally, the new information here provided contribute to a better understanding of the temporal geodynamic evolution of this sector of the Mediterranean domain.

  18. Mineral chemical compositions of late Cretaceous volcanic rocks in the Giresun area, NE Turkey: Implications for the crystallization conditions

    NASA Astrophysics Data System (ADS)

    Oǧuz, Simge; Aydin, Faruk; Uysal, İbrahim; Şen, Cüneyt

    2016-04-01

    This contribution contains phenocryst assemblages and mineral chemical data of late Cretaceous volcanic (LCV) rocks from the south of Görele and Tirebolu areas (Giresun, NE Turkey) in order to investigate their crystallization conditions. The LCV rocks in the study area occur in two different periods (Coniasiyen-Early Santonian and Early-Middle Campanian), which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic and rhyolitic) within each period. The basaltic and andesitic rocks in both periods generally exhibit porphyritic to hyalo-microlitic porphyritic texture, and contain phenocrysts of plagioclase and pyroxene, whereas the dacitic and rhyolitic rocks of the volcanic sequence usually show a vitrophyric texture with predominant plagioclase, K-feldspar, quartz and lesser amphibole-biotite phenocrysts. Zoned plagioclase crystals of the mafic and felsic rocks in different volcanic periods are basically different in composition. The compositions of plagioclase in the first-stage mafic rocks range from An52 to An78 whereas those of plagioclase from the first-stage felsic rocks have lower An content varying from An38 to An50. Rim to core profile for the zoned plagioclase of the first-stage mafic rocks show quite abrupt and notable compositional variations whereas that of the first-stage felsic rocks show slight compositional variation, although some of the grains may display reverse zoning. On the other hand, although no zoned plagioclase phenocryst observed in the second-stage mafic rocks, the compositions of microlitic plagioclase show wide range of compositional variation (An45-80). The compositions of zoned plagioclase in the second-stage felsic rocks are more calcic (An65-81) than those of the first-stage felsic rocks, and their rim to core profile display considerable oscillatory zoning. The compositions of pyroxenes in the first- and second-stage mafic-intermediate rocks vary over a wide range from

  19. Mineral chemical compositions of late Cretaceous volcanic rocks in the Giresun area, NE Turkey: Implications for the crystallization conditions

    NASA Astrophysics Data System (ADS)

    Oǧuz, Simge; Aydin, Faruk; Uysal, İbrahim; Şen, Cüneyt

    2016-04-01

    This contribution contains phenocryst assemblages and mineral chemical data of late Cretaceous volcanic (LCV) rocks from the south of Görele and Tirebolu areas (Giresun, NE Turkey) in order to investigate their crystallization conditions. The LCV rocks in the study area occur in two different periods (Coniasiyen-Early Santonian and Early-Middle Campanian), which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic and rhyolitic) within each period. The basaltic and andesitic rocks in both periods generally exhibit porphyritic to hyalo-microlitic porphyritic texture, and contain phenocrysts of plagioclase and pyroxene, whereas the dacitic and rhyolitic rocks of the volcanic sequence usually show a vitrophyric texture with predominant plagioclase, K-feldspar, quartz and lesser amphibole-biotite phenocrysts. Zoned plagioclase crystals of the mafic and felsic rocks in different volcanic periods are basically different in composition. The compositions of plagioclase in the first-stage mafic rocks range from An52 to An78 whereas those of plagioclase from the first-stage felsic rocks have lower An content varying from An38 to An50. Rim to core profile for the zoned plagioclase of the first-stage mafic rocks show quite abrupt and notable compositional variations whereas that of the first-stage felsic rocks show slight compositional variation, although some of the grains may display reverse zoning. On the other hand, although no zoned plagioclase phenocryst observed in the second-stage mafic rocks, the compositions of microlitic plagioclase show wide range of compositional variation (An45‑80). The compositions of zoned plagioclase in the second-stage felsic rocks are more calcic (An65‑81) than those of the first-stage felsic rocks, and their rim to core profile display considerable oscillatory zoning. The compositions of pyroxenes in the first- and second-stage mafic-intermediate rocks vary over a wide range

  20. Comparison of conventional K-Ar and 40Ar/39Ar dating of young mafic volcanic rocks

    USGS Publications Warehouse

    Lanphere, M.A.

    2000-01-01

    K-Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K-Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K-Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K-Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K-Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene.

  1. Geochronology and geochemistry of the Triassic bimodal volcanic rocks and coeval A-type granites of the Olzit area, Middle Mongolia: Implications for the tectonic evolution of Mongol-Okhotsk Ocean

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Zhang, Fochin; Miao, Laicheng; Baatar, Munkhtsengel; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo

    2016-05-01

    The Olzit volcanism in Middle Mongolia comprises a bimodal suite of basalts and peralkaline rhyolites adjacent to the Main Mongolia Lineament. The basalts are characterized by enrichment in LILE and LREE, and depletion in HFSE with typical Sr-Nd isotopic signatures (εNd(t) = -2.50 to -0.38 and (87Sr/86Sr)i = 0.7058-0.7063), indicating they were likely derived from partial melting of an enriched lithospheric mantle, modified by subducted slab-derived fluids. The rhyolites show a close affinity to A-type granites with enrichment in LILE and LREE, and depletion in Nb, Ta and Ti. They also show a significant negative Eu anomaly, and have εNd(t) values ranging from 0.50 to 1.38 and initial 87Sr/86Sr ratios ranging from 0.7022 to 0.7200, suggesting the rhyolites stem from partial melting of crustal rocks rather than fractional crystallization of the basaltic melt. The rhyolite porphyry yields a SHRIMP zircon U-Pb age of 207 ± 2 Ma (MSWD = 1.42), indicating the bimodal volcanic suite formed in the Late Triassic. The miarolitic per-alkaline granite and biotite-bearing granite, which are associated with the bimodal volcanic rocks, show typical A-type granitic geochemical affinity with εNd(t) = 0.89-0.91 and (87Sr/86Sr)i = 0.7021-0.7043, indicating they are likely generated by partial melting of crustal rocks similar to the rhyolitic end-member of bimodal suite. The miarolitic per-alkaline granite and biotite-bearing granite yielded SHRIMP zircon U-Pb ages of 209 ± 2 Ma (MSWD = 0.91) and 213 ± 3 Ma (MSWD = 1.65) respectively, which are nearly coeval with the age of the bimodal volcanic suites. In view of the new geochemical and chronological data in this study, we suggest the Olzit Late Triassic bimodal volcanic rocks together with the coeval A-type granites represent a back-arc basin extensional environment, which probably related to the roll-back of Mongol-Okhotsk oceanic plate during the southward subduction under the Central Mongolia microcontinent.

  2. Petrology and Geochemistry of Hydrothermally Altered Volcanic Rocks in the Iheya North Hydrothermal Field, Middle Okinawa Trough

    NASA Astrophysics Data System (ADS)

    Yamasaki, T.

    2015-12-01

    The Iheya North hydrothermal field is located in the middle Okinawa Trough, a young and actively spreading back-arc basin extending behind the Ryukyu arc-trench system in the southeastern margin of the East China Sea. In this hydrothermal field, two scientific drilling expeditions (IODP Exp 331 and SIP CK14-04) were conducted using a deep-sea drilling vessel "Chikyu," and samples from a total of 27 holes were taken. Through these expeditions, Kuroko-type volcanogenic massive sulfide deposits (VMS), hydrothermally altered volcanic rocks, and pumiceous and pelagic sediments were recovered. The recovered core provided important information about the relationship between hydrothermal activity, alteration, and ore mineralization. Whole-rock major element composition and trace element (TE) patterns of pumices were very similar to those of rhyolites in the middle Okinawa Trough (RMO). However, pumices were relatively enriched in chalcophile elements Sr and Nb, which suggest incipient mineralization. Volcanic rock generally demonstrated strong silicification and was greenish pale gray in color. Regardless of severe alteration, some rock displayed major element composition broadly similar to the RMO. Alteration was evidenced by an increase in the content of SiO2 and MgO, and decrease in Al2O3, Na2O, and K2O content. The most striking geochemical feature of altered volcanic rock was the discordance between texture and the degree of modification of TEs. Some samples showed decussate texture occupied by petal-like quartz with severe silicification, but no prominent disturbance of concentration and patterns of TEs were observed. In contrast, samples with well-preserved igneous porphyritic texture showed very low TE content and modification of TE patterns. These results suggest that the modification of texture and composition of TEs, as well as silicification, do not occur by a uniform process, but several processes. This may reflect the differences in temperature and the

  3. Geology of volcanic and subvolcanic rocks of the Raton-Springer area, Colfax and Union Counties, New Mexico

    SciTech Connect

    Scott, G.R.; Wilcox, R.E.; Mehnert, H.H.

    1990-01-01

    The most prominent geomorphic features of the Raton-Springer area are the widely distributed volcanic and subvolcanic rock formations, consisting of cinder cones, domes, lava-capped mesas, a domed sill complex, and dikes. Rock compositions range from mafic to salic, and many are alkalic. Rock names used in this report are based on the classification of La Roche and others (1980). Sixteen new K-Ar age determinations and three new fission-track age determinations are given here for selected rocks in this area. Reconnaissance geologic mapping of the Springer and Raton 30 feet x 60 feet quadrangles (September 1980 to May 1982) and preparation of the resulting maps provided much field and laboratory data about the igneous rocks of this part of the Great Plains. No published geologic map or report describes adequately the distribution and character of the alkalic rocks of this area. This report presents new descriptive information on field relations, chemical analyses, and K-Ar ages of igneous rocks in the area with the hope that others will be encouraged to investigate the geology of this interesting area in greater detail.

  4. The alkaline and alkaline-carbonatite magmatism from Southern Brazil

    NASA Astrophysics Data System (ADS)

    Ruberti, E.; Gomes, C. D. B.; Comin-Chiaramonti, P.

    2015-12-01

    Early to Late Cretaceous lasting to Paleocene alkaline magmatism from southern Brazil is found associated with major extensional structural features in and around the Paraná Basin and grouped into various provinces on the basis of several data. Magmatism is variable in size, mode of occurrence and composition. The alkaline rocks are dominantly potassic, a few occurrences showing sodic affinity. The more abundant silicate rocks are evolved undersaturated to saturated in silica syenites, displaying large variation in igneous forms. Less evolved types are restricted to subvolcanic environments and outcrops of effusive suites occur rarely. Cumulatic mafic and ultramafic rock types are very common, particularly in the alkali-carbonatitic complexes. Carbonatite bodies are represented by Ca-carbonatites and Mg-carbonatites and more scarcely by Fe-carbonatites. Available radiometric ages for the alkaline rocks fit on three main chronological groups: around 130 Ma, subcoveal with the Early Cretaceous flood tholeiites of the Paraná Basin, 100-110 Ma and 80-90 Ma (Late Cretaceous). The alkaline magmatism also extends into Paleocene times, as indicated by ages from some volcanic lavas. Geochemically, alkaline potassic and sodic rock types are distinguished by their negative and positive Nb-Ta anomalies, respectively. Negative spikes in Nb-Ta are also a feature common to the associated tholeiitic rocks. Sr-Nd-Pb systematics confirm the contribution of both HIMU and EMI mantle components in the formation of the alkaline rocks. Notably, Early and Late Cretaceous carbonatites have the same isotopic Sr-Nd initial ratios of the associated alkaline rocks. C-O isotopic Sr-Nd isotopic ratios indicate typical mantle signature for some carbonatites and the influence of post-magmatic processes in others. Immiscibility of liquids of phonolitic composition, derived from mafic alkaline parental magmas, has been responsible for the origin of the carbonatites. Close association of alkaline

  5. Animated tectonic reconstruction of the Southern Pacific and alkaline volcanism at its convergent margins since Eocene times

    NASA Astrophysics Data System (ADS)

    Eagles, Graeme; Gohl, Karsten; Larter, Robert D.

    2009-01-01

    An animated reconstruction shows South Pacific plate kinematics, in the reference frame of West Antarctica, between 55 Ma and the present-day. The ocean floor in the region formed due to seafloor spreading between the Antarctic, Pacific, Phoenix and Nazca plates (a plate formed by fragmentation of the Farallon plate early in Oligocene times). The Pacific-Antarctic Ridge remained fairly stable throughout this time, migrating relatively northwestwards, by various mechanisms, behind the rapidly-moving Pacific plate. The Nazca and Phoenix plates also moved quickly, but relatively towards the east or southeast, and were subducted in these directions beneath the South American and Antarctic plates. Segments of spreading centres forming at the trailing edges of the Nazca and Phoenix plates periodically collided with these subduction zones, resulting in the total destruction of the Nazca-Phoenix spreading centre and the partial destruction of the Nazca-Antarctica spreading centre (the Chile Ridge) and Antarctic-Phoenix Ridge, which ceased to operate shortly before its northeasternmost three segments could collide with the Antarctic margin. Following collision of segments of the Chile Ridge, parts of the Antarctic plate underwent subduction at the Chile Trench. After these collisions, slab windows should have formed beneath both the South American and Antarctic convergent margins, and the animation shows occurrences of alkaline volcanism that have been, or can newly be, related to them. Further occurrences of alkali basalts, at the margins of the Powell Basin and, more speculatively, James Ross Island, can be related to the formation of a slab window beneath them following the collision of segments of the South America-Antarctica spreading centre in the northwest Weddell Sea.

  6. Compilation of Stratigraphic Thicknesses for Caldera-Related Tertiary Volcanic Rocks, East-Central Nevada and West-Central Utah

    USGS Publications Warehouse

    Sweetkind, D.S.; Du Bray, E.A.

    2008-01-01

    The U.S. Geological Survey (USGS), the Desert Research Institute (DRI), and a designee from the State of Utah are currently conducting a water-resources study of aquifers in White Pine County, Nevada, and adjacent areas in Nevada and Utah, in response to concerns about water availability and limited geohydrologic information relevant to ground-water flow in the region. Production of ground water in this region could impact water accumulations in three general types of aquifer materials: consolidated Paleozoic carbonate bedrock, and basin-filling Cenozoic volcanic rocks and unconsolidated Quaternary sediments. At present, the full impact of extracting ground water from any or all of these potential valley-graben reservoirs is not fully understood. A thorough understanding of intermontane basin stratigraphy, mostly concealed by the youngest unconsolidated deposits that blanket the surface in these valleys, is critical to an understanding of the regional hydrology in this area. This report presents a literature-based compilation of geologic data, especially thicknesses and lithologic characteristics, for Tertiary volcanic rocks that are presumably present in the subsurface of the intermontane valleys, which are prominent features of this area. Two methods are used to estimate volcanic-rock thickness beneath valleys: (1) published geologic maps and accompanying descriptions of map units were used to compile the aggregate thicknesses of Tertiary stratigraphic units present in each mountain range within the study areas, and then interpolated to infer volcanic-rock thickness in the intervening valley, and (2) published isopach maps for individual out-flow ash-flow tuff were converted to digital spatial data and thickness was added together to produce a regional thickness map that aggregates thickness of the individual units. The two methods yield generally similar results and are similar to volcanic-rock thickness observed in a limited number of oil and gas exploration

  7. Geochemistry of ultrapotassic volcanic rocks in Xiaogulihe NE China: Implications for the role of ancient subducted sediments

    NASA Astrophysics Data System (ADS)

    Sun, Yang; Ying, Jifeng; Zhou, Xinhua; Shao, Ji'an; Chu, Zhuyin; Su, Benxun

    2014-11-01

    The unique eruptions of ultrapotassic volcanic rocks in eastern China reported so far took place in the Xiaogulihe area of western Heilongjiang Province, NE China. These ultrapotassic rocks are characterized by extremely high K2O contents (> 7 wt.%), abnormally unradiogenic Pb isotopic compositions (206Pb/204Pb = 16.44-16.55; 207Pb/204Pb = 15.39-15.46; 208Pb/204Pb = 36.35-36.61), and moderately high 87Sr/86Sr ratios (0.7053-0.7057), which can be basically correlated with those of ultrapotassic igneous rocks distributed widely in northwestern America and Aldan Shield. The positive correlation between 187Os/188Os and 1/Os argues that these ultrapotassic rocks have probably experienced negligible lower continental crust addition (less than 1%) during magma ascent. The high contents of K2O and negative correlation between 87Sr/86Sr and 206Pb/204Pb of these ultrapotassic rocks indicate the presence of a potassic phase, mostly phlogopite, in their mantle source. Their strong fractionation of rare earth elements and lack of Nd-Hf isotopic decoupling reveal a low-degree partial melting of garnet-bearing source rocks. In addition, the low CaO and Al2O3 contents of whole-rock compositions and low Fe/Mn ratios of olivine phenocryst chemistries suggest peridotites rather than pyroxenites as dominant source rocks for the Xiaogulihe ultrapotassic rocks. Based on these distinctive geochemical characteristics, we thus propose that the ultimate mantle source of the Xiaogulihe ultrapotassic volcanic rocks is phlogopite-bearing garnet peridotite within the lower part of the sub-continental lithospheric mantle (SCLM) that had been metasomatized by potassium-rich silicate melts. Combined with the unradiogenic Pb compositions, the most likely source of these potassium-rich silicate melts is the ancient subducted continental-derived sediments (> 1.5 Ga). These ancient subducted sediments, possessing relatively low initial Pb isotopic compositions, had experienced large U/Pb fractionation

  8. Geomagnetic Secular Variation Recorded in Volcanic Rocks: The End of the Geocentric Axial Dipole

    NASA Astrophysics Data System (ADS)

    Champion, D. E.; Turrin, B. D.; Robinson, J. E.

    2015-12-01

    Most paleomagnetic textbooks ascribe secular variation (SV) to the movement and waxing/waning of non-dipole magnetic features in the fluid core, perhaps joined by wobble of a geocentric axial dipole (GAD). The actuality of a GAD is profoundly limited by the existence of the static, solid inner core, and the dynamic nature of the fluid outer core. A study of >560 Brunhes Epoch Virtual Geomagnetic Poles (VGP) suggests that geomagnetic field behavior arises from the waxing/waning of three approximately "stationary" offset dipoles (OD) situated in the middle of the ring of the outer core. These OD have been loosely fixed to preferred longitudes of 40°E, 120°E, and 280°E for at least the past 17Ma. The three offset dipoles in these positions determine transitional and excursional paths, and also normal SV. An extended literature documents these longitude corridors as paths of preferred VGP movement, guided by the polarity inversion of one of the three OD. Analysis of volcanic rock and archeomagnetic SV records shows a three-fold symmetric movement of local magnetic directions, guided by the variation in strength of the three OD. Preliminary data indicates that in the recent past the dominant OD at a given time yields to the next OD in movement toward greater east longitude. The frequency of OD dominance exchange is ~400 years, with return to the original OD in ~1200 years. Archeomagnetic "jerks", not easily explained by a single dominant, inertial GAD, are more easily understood with 3 waxing/waning and exchanging OD. The particular analysis of Hawaiian SV with regard to the three OD suggests that tropical locales, far from the three spin axis-parallel OD, may still record true non-dipole influences.

  9. Distribution of anomalously high K2O volcanic rocks in Arizona: metasomatism at the Picacho Peak detachment fault.

    USGS Publications Warehouse

    Brooks, W.E.

    1986-01-01

    Metasomatized Tertiary lavas with anomalously high K2O and lower Na2O content are distributed within the NW-trending extensional terrain of SW Arizona. These rocks are common near core-complex-related detachment faults at Picacho Peak and the Harcuvar Mountains and in listric-faulted terrain at the Vulture Mountains. These rocks are also enriched in Zr but depleted in MgO. Fine-grained, euhedral orthoclase (adularia) is the dominant K-mineral; other secondary introduced minerals are quartz and calcite. Spatial association of metasomatism with the detachment faults suggests that detachment provided a conduit for hydrothermal fluids that altered the initial chemistry of the Tertiary volcanics and charged the upper plate rocks with mineralizing fluids that carried Zr and Ba, along with Au, Ag and Cu during detachment 17-18 m.y. ago.-L.C.H.

  10. A typical cross section based on magnetic data of lower and middle Keweenawan volcanic rocks, Ironwood area, Michigan

    USGS Publications Warehouse

    King, Elizabeth R.

    1975-01-01

    A north-trending aeromagnetic profile of a sequence of east-striking Keweenawan volcanic rocks near Ironwood, Mich., can be matched to a calculated profile over a model consisting of a series of dipping layers. (The dips were those measured by H. A. Hubbard along the north-trending valley of the Black River.) Remanent and induced magnetizations of 39 oriented cores from the Black River valley were determined by K. G. Books; felsite from Chippewa Hill and basalt from Algonquin Falls of middle Keweenawan age have normal Keweenawan magnetization and lower Keweenawan Powder Mill rocks have reverse magnetization. In the model these magetizations were assigned to 26 layers which alternated with very weakly magnetized layers. The best match of the calculated composite anomalies of remanent and induced magnetization and the aeromagnetic profile occurs if a deeper block of steeply dipping Powder Mill rocks is assumed to underlie the middle Keweenawan flows.

  11. Whole rock major element chemistry of KREEP basalt clasts in lunar breccia 15205: Implications for the petrogenesis of volcanic KREEP basalts

    NASA Technical Reports Server (NTRS)

    Vetter, Scott K.; Shervais, John W.

    1993-01-01

    KREEP basalts are a major component of soils and regolith at the Apollo 15 site. Their origin is controversial: both endogenous (volcanic) and exogenous (impact melt) processes have been proposed, but it is now generally agreed that KREEP basalts are volcanic rocks derived from the nearby Apennine Bench formation. Because most pristine KREEP basalts are found only as small clasts in polymict lunar breccias, reliable chemical data are scarce. The primary aim of this study is to characterize the range in chemical composition of pristine KREEP basalt, and to use these data to decipher the petrogenesis of these unique volcanic rocks.

  12. Mapping argillic and advanced argillic alteration in volcanic rocks, quartzites, and quartz arenites in the western Richfield 1° x 2 ° quadrangle, southwestern Utah, using ASTER satellite data

    USGS Publications Warehouse

    Rockwell, Barnaby W.; Hofstra, Albert H.

    2012-01-01

    The Richfield quadrangle in southwestern Utah is known to contain a variety of porphyry Mo, skarn, polymetallic replacement and vein, alunite, and kaolin resources associated with 27-32 Ma calc-alkaline or 12-23 Ma bimodal volcano-plutonic centers in Neoproterozoic to Mesozoic carbonate and siliciclastic rocks. Four scenes of visible to shortwave-infrared image data acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor were analyzed to generate maps of exposed clay, sulfate, mica, and carbonate minerals, and ASTER thermal infrared data were analyzed to identify quartz and carbonate minerals. Argillic and advanced argillic alteration minerals including alunite, pyrophyllite, dickite, and kaolinite were identified in both undocumented (U) and known (K) areas, including in the southern Paradise Mtns. (U); in calc-alkaline volcanic rocks in the Wah Wah Mtns. between Broken Ridge and the NG area (U/K); at Wah Wah Summit in a small zone adjacent to 33.1 Ma diorite and marble (U); in fractures cutting quartzites surrounding the 20-22 Ma Pine Grove Mo deposit (U); in volcanic rocks in the Shauntie Hills (U/K); in quartzites in the west-central San Francisco Mtns. (U); in volcanic rocks in the Black Mtns. (K); and in mainly 12-13 Ma rhyolitic rocks along a 20 km E-W belt that includes the Bible Spring fault zone west of Broken Ridge, with several small centers in the Escalante Desert to the south (U/K). Argillized Navajo Sandstone with kaolinite and (or) dickite ± alunite was mapped adjacent to calc-alkaline intrusions in the Star Range (U). Intense quartz-sericite alteration (K) with local kaolinite was identified in andesite adjacent to calc-alkaline intrusions in the Beaver Lake Mountains. Mo-bearing phyllic alteration was identified in 22.2 Ma rhyolite plugs at the center of the NG alunite area. Limestones, dolomites, and marbles were differentiated, and quartz and sericite were identified in most unaltered quartzites. Halos of

  13. Trace element partitioning in rock forming minerals of co-genetic, subduction-related alkaline and tholeiitic mafic rocks in the Ural Mountains, Russia

    NASA Astrophysics Data System (ADS)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

    2009-04-01

    The partitioning of trace elements between rock forming minerals in igneous rocks is largely controlled by physical and chemical parameters e.g. temperature, pressure and chemical composition of the minerals and the coexisting melt. In the present study partition coefficients for REE between hornblende, orthopyroxene, feldspars, apatite and clinopyroxene in a suite of co-genetic alkaline and tholeiitic mafic rocks from the Ural Mountains (Russia) were calculated. The results give insights to the influence of the chemical composition of the parental melt on the partitioning behaviour of the REE. Nepheline-bearing, alkaline melanogabbros (tilaites) are assumed to represent the most fractionated products of the melt that formed the ultramafic cumulates in zoned mafic-ultramafic complexes in the Ural Mountains. Co-genetic with the latter is a suite of olivine gabbros, gabbronorites and hornblende gabbros formed from a tholeiitic parental melt. Negative anomalies for the HFSE along with low Nb and Ta contents and a positive Sr anomaly indicate a subduction related origin of all parental melts. The nepheline gabbros consist predominantly of coarse-grained clinopyroxene phenocrysts in a matrix of fine grained clinopyroxene, olivine, plagioclase, K-feldspar and nepheline with accessory apatite. The tholeiitic gabbros have equigranular to porphyric textures with phenocrysts of olivine, pyroxene and hornblende in a plagioclase rich matrix with olivine hornblende, pyroxene and accessory apatite. Element concentrations of adjacent matrix grains and rims of phenochrysts were measured with LA-ICPMS. The distribution of REE between hornblende and clinopyroxene in the tholeiitic rocks is similar for most of the elements (DHbl•Cpx(La-Tm) = 2.7-2.8, decreasing to 2.6 and 2.4 for Yb and Lu, respectively). These values are about two times higher than published data (e.g. Ionov et al. 1997). Partition coefficients for orthopyroxene/clinopyroxene systematically decrease from the HREE

  14. Halogen content in Lesser Antilles arc volcanic rocks : exploring subduction recycling

    NASA Astrophysics Data System (ADS)

    Thierry, Pauline; Villemant, Benoit; Caron, Benoit

    2016-04-01

    Halogens (F, Cl, Br and I) are strongly reactive volatile elements which can be used as tracers of igneous processes, through mantle melting, magma differentiation and degassing or crustal material recycling into mantle at subduction zones. Cl, Br and I are higly incompatible during partial melting or fractional cristallization and strongly depleted in melts by H2O degassing, which means that no Cl-Br-I fractionation is expected through magmatic differenciation [current thesis]. Thus, Cl/Br/I ratios in lavas reflect the halogen content of their mantle sources. Whereas these ratios seemed quite constant (e.g. Cl/Br =300 as seawater), recent works suggest significant variations in arc volcanism [1,2]. In this work we provide high-precision halogen measurements in volcanic rocks from the recent activity of the Lesser Antilles arc (Montserrat, Martinique, Guadeloupe, Dominique). Halogen contents of powdered samples were determined through extraction in solution by pyrohydrolysis and analysed by Ion Chromatography for F and Cl and high performance ICP-MS (Agilent 8800 Tripe Quad) for Cl, Br and I [3,4]. We show that lavas - and mantle sources - display significant vraiations in Cl/Br/I ratios along the Lesser Antilles arc. These variations are compared with Pb, Nd and Sr isotopes and fluid-mobile elements (Ba, U, Sr, Pb etc.) compositions which vary along the arc from a nothern ordinary arc compositions to a southern 'crustal-like' composition [5,6]. These characteristics are attributed to subducted sediments recycling into the mantle wedge, whose contribution vary along the arc from north to south [7,8]. The proportion of added sediments is also related to the distance to the trench as sediment melting and slab dehydration may occur depending on the slab depth [9]. Further Cl-Br-I in situ measurements by LA-ICP-MS in Lesser Antilles arc lavas melt inclusions will be performed, in order to provide better constraints on the deep halogen recycling cycle from crust to

  15. Experiments and Spectral Studies of Martian Volcanic Rocks: Implications for the Origin of Pathfinder Rocks and Soils

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.; Mustard, Jack; Weitz, Catherine

    2002-01-01

    The composition and spectral properties of the Mars Pathfinder rocks and soils together with the identification of basaltic and andesitic Mars terrains based on Thermal Emission Spectrometer (TES) data raised interesting questions regarding the nature and origin of Mars surface rocks. We have investigated the following questions: (1) are the Pathfinder rocks igneous and is it possible these rocks could have formed by known igneous processes, such as equilibrium or fractional crystallization, operating within SNC magmas known to exist on Mars? If it is possible, what P (depth) and PH2O conditions are required? (2) whether TES-based interpretations of plagioclase-rich basalt and andesitic terrains in the south and north regions of Mars respectively are unique. Are the surface compositions of these regions plagioclase-rich, possibly indicating the presence of old AI-rich crust of Mars, or are the spectra being affected by something like surface weathering processes that might determine the spectral pyroxene to plagioclase ratio?

  16. Porosity and permeability in volcanic rocks: a case study on the Serie Tobı´fera, South Patagonia, Argentina

    NASA Astrophysics Data System (ADS)

    Sruoga, P.; Rubinstein, N.; Hinterwimmer, G.

    2004-04-01

    The Middle to Late Jurassic Serie Tobı´fera belongs to the Chon-Aike Province and extends all over Patagonia and the Antarctic Peninsula. It consists largely of ignimbrites, epiclastics and rhyolitic lavas and was considered only a minor reservoir rock for oil with fracture permeability. Petrographic and petrophysical data in selected core samples from the Austral Basin were collected to determine the processes controlling the porosity and permeability of these volcanic rocks. The sequence of processes occurring during cooling and in the post-cooling stages can modify, sometimes substantially, their original petrophysic characteristics. The results show that the highest porosity and permeability occur in rocks with quench fractured glasses and in non-welded ignimbrites with gas-pipe structures, followed by autobrecciated rhyolites. Welded ignimbrites, massive glasses and fresh rhyolites have the lowest permeabilities. The new data indicate that tectonic fracturing is not as significant as was considered before and application of these concepts are relevant in the assesment of volcanic reservoir quality.

  17. Application of support vector machines and relevance vector machines in predicting uniaxial compressive strength of volcanic rocks

    NASA Astrophysics Data System (ADS)

    Ceryan, Nurcihan

    2014-12-01

    The uniaxial compressive strength (UCS) of intact rocks is an important and pertinent property for characterizing a rock mass. It is known that standard UCS tests are destructive, expensive and time-consuming task, which is particularly true for thinly bedded, highly fractured, foliated, highly porous and weak rocks. Consequently, prediction models have become an attractive alternative for engineering geologists. In the last several years, a new, alternative kernel-based technique, support vector machines (SVMs), has been popular in modeling studies. Despite superior SVM performance, this technique has certain significant, practical drawbacks. Hence, the relevance vector machines (RVMs) approach has been proposed to recast the main ideas underlying SVMs in a Bayesian context. The primary purpose of this study is to examine the applicability and capability of RVM and SVM models for predicting the UCS of volcanic rocks from NE Turkey and comparing its performance with ANN models. In these models, the porosity and P-durability index representing microstructural variables are the input parameters. The study results indicate that these methods can successfully predict the UCS for the volcanic rocks. The SVM and RVM performed better than the ANN model. When these kernel based models are considered, RVM model found successful in terms of statistical performance criterions (e.g., performance index, PI values for training and testing data are computed as 1.579 and 1.449). These values for SVM are 1.509 and 1.307. Although SVM and RVM models are powerful techniques, the RVM run time was considerably faster, and it yielded the highest accuracy.

  18. Analysis of Micro-Seismic Signals and Source Parameters of Eruptions Generated by Rapid Decompression of Volcanic Rocks

    NASA Astrophysics Data System (ADS)

    Arciniega-Ceballos, A.; Alatorre-Ibarguengoitia, M. A.; Scheu, B.; Dingwell, D. B.; Delgado Granados, H.

    2010-12-01

    Seismic evaluation of well-controlled experimental volcanic simulations offers the hope of a better understanding of source mechanisms in natural volcanic seismicity. Here, we have performed the first investigation of the dynamics of explosive volcanic eruption of magma under controlled laboratory conditions. Specifically, we analyzed the micro-seismicity generated by the rapid depressurization of volcanic rocks in a shock tube apparatus, which represents the seismic mechanism. The source parameters and the force system have been analyzed considering the relationship F=πr2 Po. Our well-constrained physical mechanism consists of the slow pressurization of the system (using Argon gas) followed by rapid depressurization of natural volcanic samples (ash, pumice and fragmented particles of pumice) contained in a steel pipe-like conduit of radius r and height ~2r. Several experiments with samples with different porosities were performed under controlled pressure conditions (ranging from 4 to 20 MPa), at room temperature. We calculated the magnitude of the vertical and downward forces and forces at the walls of the reservoir, and the kinetic energy involved during decompression and fragmentation processes from the micro-seismic signals detected at several points in the apparatus using highly dynamic piezo-film transducers. We first characterized the frequencies of the apparatus in order to distinguish in the signals between the waves produced by the natural resonance of the system due to the pressure shock and the waves generated by the rapid depressurization of the samples. In the micro-seismic records the inflation-deflation states of the pipe-like conduit and the fragmentation process after the rapid removal of the diaphragm can be recognized clearly. The decompression time is directly measured from the pressure drop curves of the system recorded by dynamic pressure transducers and correlates well with the duration of maximum amplitudes of micro-seismic waves

  19. Experimental and textural constraints on mafic enclave formation in volcanic rocks

    USGS Publications Warehouse

    Coombs, M.L.; Eichelberger, J.C.; Rutherford, M.J.

    2002-01-01

    We have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at Southwest Trident volcano, Alaska. Andesite enclaves are present throughout the four dacite lava flows produced by the eruption, and resemble mafic enclaves commonly found in other volcanic rocks. Our experiments replicate the pressure-temperature-time path taken by enclave-forming andesite magma as it is engulfed in dacite during magma mixing. Pressure and temperature information for the andesite and dacite are from [Coombs et al., Contrib. Mineral. Petrol. 140 (2000) 99-118]. The andesite was annealed at 1000??C, and then cooled to 890??C at rates of 110??C h1, 10??C h1 and 2??C h1. Once cooled to 890??C, andesite was held at this lower temperature from times ranging from 1 to 40 h. The andesite that was cooled at the slower rates of 2??C h1 and 10??C h1 most resembles enclave groundmass texturally and compositionally. Based on simple thermal calculations, these rates are more consistent with cooling of the andesite groundmass below an andesite-dacite interface than with cooling of enclave-sized spheres. If enclaves do crystallize as spheres, post-crystallization disaggregation must occur. Calculations using the MELTS algorithm [Ghiorso and Sack, Contrib. Mineral. Petrol. 119 (1995) 197-212] show that for incoming andesite to become less dense than the dacite to become less dense ???34 volume % of its groundmass must crystallize to undergo~18 volume % vesiculation; these values are similar to those determined for Southwest Trident enclaves. Thus such crystallization may lead to 'flotation' of enclaves and be a viable mechanism for enclave formation and dispersal. The residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments. Decompression experiments on Southwest Trident dacite suggest an average ascent rate for the eruption of ???2

  20. Preparation of Al-Si Master Alloy by Electrochemical Reduction of Volcanic Rock in Cryolite Molten Salt

    NASA Astrophysics Data System (ADS)

    Liu, Aimin; Shi, Zhongning; Xu, Junli; Hu, Xianwei; Gao, Bingliang; Wang, Zhaowen

    2016-06-01

    Volcanic rock found in the Longgang Volcano Group in Jilin Province of China has properties essentially similar to Apollo lunar soils and previously prepared lunar soil simulants, such as Johnson Space Center Lunar simulant and Minnesota Lunar simulant. In this study, an electrochemical method of preparation of Al-Si master alloy was investigated in 52.7 wt.%NaF-47.3 wt.%AlF3 melt adding 5 wt.% volcanic rock at 1233 K. The cathodic electrochemical process was studied by cyclic voltammetry, and the results showed that the cathodic reduction of Si(IV) is a two-step reversible diffusion-controlled reaction. Si(IV) is reduced to Si(II) by two electron transfers at -1.05 V versus platinum quasi-reference electrode in 52.7 wt.%NaF-47.3 wt.%AlF3 molten salt adding 5 wt.% volcanic rock, while the reduction peak at -1.18 V was the co-deposition of aluminum and silicon. In addition, the cathodic product obtained by galvanostatic electrolysis for 4 h was analyzed by means of x-ray diffraction, x-ray fluorescence, scanning electron microscopy and energy dispersive spectrometry. The results showed that the phase compositions of the products are Al, Si, Al5FeSi, and Al3.21Si0.47, while the components are 90.5 wt.% aluminum, 4.4 wt.% silicon, 1.9 wt.% iron, and 0.2 wt.% titanium.

  1. Rock phosphate solubilization under alkaline conditions by Aspergillus japonicus and A. foetidus.

    PubMed

    Singal, R; Gupta, R; Saxena, R K

    1994-01-01

    Aspergillus japonicus and A. foetidus were found to solubilize five types of Indian rock phosphates at pH 8 and 9. Solubilization was higher in the presence of pyrite than in controls lacking either pyrite or fungal inoculum. Both the aspergilli were found to be good pyrite solubilizers and could grow over a wide pH range. Solubilization of rock phosphates was the result of organic acid release and pyrite oxidation.

  2. Geologic and grade-tonnage information on Tertiary epithermal precious- and base-metal vein districts associated with volcanic rocks

    USGS Publications Warehouse

    Mosier, Dan L.; Menzie, W. David; Kleinhampl, Frank J.

    1986-01-01

    Data on grades, tonnages, and geology of selected Tertiary epithermal precious- and base-metal vein districts associated with volcanic rocks were tabulated for ease of examination and comparison of characteristics between districts. There are 215 districts listed, with a cumulative tonnage of 709 million metric tons and average grades of 4.7 g/t Au, 224 g/t Ag, 0.16 percent Cu, 0.55 percent Pb, and 0.83 percent Zn, representing about 60 percent of world districts.

  3. The Early Andean Magmatic Province (EAMP): 40Ar/ 39Ar dating on Mesozoic volcanic and plutonic rocks from the Coastal Cordillera, northern Chile

    NASA Astrophysics Data System (ADS)

    Oliveros, Verónica; Féraud, Gilbert; Aguirre, Luis; Fornari, Michel; Morata, Diego

    2006-10-01

    The Early Andean Magmatic Province (EAMP), consists of about 150 000 km 3 of volcanic and plutonic units in the Coastal Cordillera of northern Chile and southern Peru and represents a major magmatic Mesozoic event in the world, for which the precise age of the thick volcanic series was unknown. Thirty 40Ar/ 39Ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern Chile (18°30'-24°S). Reliable plateau and "mini plateau" ages were obtained on plagioclase, amphibole and biotite from volcanic and plutonic rocks, despite widespread strong alteration degree. In the Arica, Tocopilla and Antofagasta (700 km apart) regions, the ages obtained on lava flows constrain the volcanic activity between 164 and 150 Ma and no N-S migration of volcanism is observed. The uppermost lava flows of the volcanic sequence at the type locality of the La Negra Formation extruded at ca. 153-150 Ma, suggesting the end of the volcanic activity of the arc at that time. The oldest volcanic activity occurred probably at ca. 175-170 Ma in the Iquique area, although no plateau age could be obtained. The plutonic bodies of the same regions were dated between ca. 160 and 142 Ma, indicating that they were partly contemporaneous with the volcanic activity. At least one volcanic pulse around 160 Ma is evidenced over the entire investigated reach of the EAMP, according to the ages found in Arica, Tocopilla, Michilla and Mantos Blancos regions. The episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole Andean history and particularly during the Jurassic (southern Peru, northern Chile and southern Argentina). These events probably correspond to periodic extensional geodynamic episodes, as a consequence of particular subduction conditions, such as change of obliquity of the convergence, change in the subduction angle, slab roll back effect or lower convergence rate, that remain to be precisely defined.

  4. Along-arc geochemical and isotopic variations in Javanese volcanic rocks: 'crustal' versus 'source' contamination at the Sunda arc, Indonesia

    NASA Astrophysics Data System (ADS)

    Handley, H.; Blichert-Toft, J.; Turner, S.; Macpherson, C. G.

    2012-12-01

    Understanding the genesis of volcanic rocks in subduction zone settings is complicated by the multitude of differentiation processes and source components that exert control on lava geochemistry. Magma genesis and evolution at the Sunda arc is controlled and influenced by 1) along arc changes in the composition and thickness of the overriding Eurasian plate, 2) the variable age of the subducting oceanic crust and, 3) changes in the type and amount of sediment deposited on the subducting plate. Along-arc changes in geochemistry have long been recognised in the Sunda arc (Whitford, 1975), but debate still prevails over the cause of such variations and the relative importance of shallow (crustal) versus deep (subduction) contamination at the Sunda arc, Indonesia. Detailed study of individual Sunda arc volcanic centres is, therefore, a prerequisite in order to establish the relative importance and contributions of various potential source components and composition modifying differentiation processes at individual volcanoes, prior to an along arc comparative petrogenetic investigation. We present new radiogenic isotope data for Javanese volcanoes, which is combined with our recently published (Handley et al., 2007; Handley et al., 2008, Handley et al., 2010; Handley et al., 2011) geochemical and isotopic data of Javanese volcanic rocks along with data from other detailed geochemical studies to establish whether variable contributions from the subducting slab, or a change in crustal architecture of the overriding plate, best explain along-arc variations in isotope ratios and trace element characteristics. In West and Central Java Sr isotope ratios of the volcanic rocks broadly correlate with inferred lithospheric thickness implicating a shallow level control on isotopic composition. However, key trace element ratios combined with Hf isotope data indicate that the subducted slab and slab thermal regime also exert major control on the composition of the erupted Javanese

  5. Dissolution of glass wool, rock wool and alkaline earth silicate wool: morphological and chemical changes in fibers.

    PubMed

    Campopiano, Antonella; Cannizzaro, Annapaola; Angelosanto, Federica; Astolfi, Maria Luisa; Ramires, Deborah; Olori, Angelo; Canepari, Silvia; Iavicoli, Sergio

    2014-10-01

    The behavior of alkaline earth silicate (AES) wool and of other biosoluble wools in saline solution simulating physiological fluids was compared with that of a traditional wool belonging to synthetic vitreous fibers. Morphological and size changes of fibers were studied by scanning electron microscopy (SEM). The elements extracted from fibers were analyzed by inductively coupled plasma atomic emission spectrometry. SEM analysis showed a larger reduction of length-weighted geometric mean fiber diameter at 4.5 pH than at 7.4 pH. At the 7.4 pH, AES wool showed a higher dissolution rate and a dissolution time less than a few days. Their dissolution was highly non-congruent with rapid leaching of calcium. Unlike rock wool, glass wool dissolved more rapidly at physiological pH than at acid pH. Dissolution of AES and biosoluble rock wool is accompanied by a noticeable change in morphology while by no change for glass wool. Biosoluble rock wool developed a leached surface with porous honeycomb structure. SEM analysis showed the dissolution for glass wool is mainly due to breakage transverse of fiber at pH 7.4. AES dissolution constant (Kdis) was the highest at pH 7.4, while at pH 4.5 only biosoluble rockwool 1 showed a higher Kdis.

  6. A Special Issue (Part-II): Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization - dedication to Lia Nikolaevna Kogarko

    NASA Astrophysics Data System (ADS)

    Kogarko, Lia N.; Gwalani, Lalchand G.; Downes, Peter J.; Randive, Kirtikumar R.

    2015-10-01

    This is the second part of a two-volumespecial issue of Open Geoscience (formerly Central European Journal of Geosciences) that aims to be instrumental in providing an update of Mafic-Ultramafic Rocks and Alkaline- Carbonatitic Magmatism and Associated Hydrothermal Mineralization. Together, these two volumes provide a detailed and comprehensive coverage of the subjects that are relevant to the research work of P.Comin-Chiaramonti (Italy) and LiaN. Kogarko (Russia) towhomPart-I and Part- II have been respectively dedicated. To a significant extent, the development of advanced sampling technologies related to alkaline and carbonatitic magmatism by Lia N. Kogarko, has allowed geoscientists to measure and sample the deep crust of the planet not only for the exploration for the mineral deposits, but also to answer basic scientific questions about the origin and evolution of alkaline rocks (kimberlites, lamproites and related rocks associated with carbonatites). The papers presented in this Part-II of the special issue cover the petrology and geochemistry of the rocks collected from the surface and penetrated by drilling. Lia Kogarko proposed a new theory for the evolution of alkaline magmatism in the geological history of the Earth - that the appearance of alkaline magmatism at the Archaean-Proterozoic boundary (~2.5 - 2.7 Ga), and its growing intensity, was related to changes in the geodynamic regime of the Earth and oxidation of the mantle due to mantle-crust interaction.

  7. Age, petrogenesis and tectonic implications of Early Devonian bimodal volcanic rocks in the South Altyn, NW China

    NASA Astrophysics Data System (ADS)

    Kang, Lei; Xiao, Pei-Xi; Gao, Xiao-Feng; Xi, Ren-Gang; Yang, Zai-Chao

    2015-11-01

    In this paper, we report zircon U-Pb dating, Hf isotopes, geochemical and Sr-Nd isotopic data, with the aim the petrogenesis and regional tectonic evolution of Early Devonian bimodal volcanic rock in the South Altyn, NW China. New LA-ICPMS zircon U-Pb isotopic data constrained them at ca. 406 Ma. The mafic samples are characterized by high Fe, Cr and Ni contents, low Ti and Mg contents, slightly enriched LREE patterns, and low (La/Yb)N, La/Nb and La/Ta ratios, and positive εNd(t) values (+3.3 to +3.4), indicating that they were likely derived from strong batch-melting of the asthenosphere in the spinel facies field. The felsic rocks show an A-type affinity, with high alkalis, Fe, Ga, Zr, Nb, Ce and Y contents, low Mg, Sr content, high Rb/Sr and Ga/Al ratios, enrichment in LILE (e.g., Rb, K, Th, U and LREE) and depletion in Ba, Sr, Nb, Ta, P and Ti, and fractionated REE patterns with very strong negative Eu anomalies. These features, along with distinct εNd(t) values (-0.5 to +2.3) and mostly positive εHf(t) (-0.29 to +5.18), indicate that the felsic rocks were mainly generated by partial melting of the crust in low pressure and high temperature conditions, and simultaneously underwent slight magma mixing of such melts with mantle magma. According to the petrogenetic schemes and geological background of the Early Devonian bimodal volcanic rocks (tholeiite and A-type dacite-rhyolite), they should have formed in a post-collisional extensional setting. Moreover, on the basis of spatial and temporal distribution, and formation mechanism, the tectonic magmatic evolution of the early Paleozoic South Altyn Tagh could be divided into three stages: - 505-472 Ma (continental collision), the magmatite formed under high-pressure conditions due to the deep subduction and initial tearing of continental slab; - 467-450 Ma (continental slab break-off), the magmatite formed at high temperature and low pressure in virtue of felsic upper crust uplifting and mantle magma

  8. Short-Wavelength Infrared (SWIR) spectroscopy of low-grade metamorphic volcanic rocks of the Pilbara Craton

    NASA Astrophysics Data System (ADS)

    Abweny, Mohammad S.; van Ruitenbeek, Frank J. A.; de Smeth, Boudewijn; Woldai, Tsehaie; van der Meer, Freek D.; Cudahy, Thomas; Zegers, Tanja; Blom, Jan-Kees; Thuss, Barbara

    2016-05-01

    This paper shows the results of Short-Wavelength Infrared (SWIR) spectroscopy investigations of volcanic rocks sampled from low-grade metamorphic greenstone belts of the Archean Pilbara Craton in Western Australia. From the reflectance spectra a range of spectrally active minerals were identified, including chlorites, hornblende, actinolite, epidote and white micas. The rock samples were grouped into mineral assemblages based on their spectrally identified minerals and stratigraphic positions. The metamorphic amphibolite and greenschist facies could be identified from the SWIR spectroscopic data as well as three sub zones of the greenschist facies: 1) a zone containing Fe-chlorite; 2) a zone containing intermediate chlorite and epidote; and 3) a zone containing intermediate chlorite, actinolite and hornblende. Spectral parameters were calculated from the reflectance spectra to assess the metamorphic grade and zones. Plots of the depth parameters of the Fe-OH feature near 2250 nm versus the Mg-OH feature near 2390 nm differentiate the metamorphic amphibolite and greenschist facies and a transition zone between the two. The wavelength position parameter of the Mg-OH absorption feature near 2340 nm also serves to discriminate between the various metamorphic sub zones. The identification of the metamorphic grades of the volcanic sequences in greenstone belts with SWIR spectroscopy is useful for regional geological field studies, exploration for metamorphic mineral deposits hosted in the greenstone belts and the interpretation of hyperspectral remote sensing data sets covering similar types of terranes.

  9. K-Ar ages and Pb, Sr isotopic characteristics of Cenozoic volcanic rocks in Shandong Province, China

    USGS Publications Warehouse

    Daogong, C.; Zicheng, P.; Lanphere, M.A.; Zartman, R.E.

    1985-01-01

    28 samples of Cenozoic volcanic rocks collected from Shandong Province have been dated by K-Ar method. They are mainly Neogene with an age range of 4-19 m. y. The basalts from Linqu and Yishui in west Shandong Province are Miocene and those from Penglai and Qixia in east Shandong Province are Miocene and Pliocene in age. The basalts from Wudi in north Shandong Province are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2-3 m. y. Pb and Sr isotopic compositions and U, Th, Pb, Rb, Sr, and major elements in most of the samples were determined. The isotopic compositions are:206Pb/204Pb-16.92-18.48,207Pb/204Pb-15.30-15.59,208Pb/204Pb-37.83-38.54, and (87Sr/86Sr)i-0.70327-0.70632. There are some positive or negative linear correlations between206Pb/204Pb and207Pb/204Pb, Pb isotopes and Pb content, Pb isotopes and Sr isotopes, and Sr isotopes and other elements. The basaltic rocks from east and west Shandong Province have somewhat differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source, although they were influenced, to some extent, by the contamination of crustal materials. ?? 1985 Institute of Geochemistry, Chinese Academy of Sciences.

  10. Rock-Forming feldspars of the Khibiny alkaline pluton, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Ivanyuk, G. Yu.; Pakhomovsky, Ya. A.; Konopleva, N. G.; Kalashnikov, A. O.; Korchak, Yu. A.; Selivanova, E. A.; Yakovenchuk, V. N.

    2010-12-01

    This paper describes the structural-compositional zoning of the well-known Khibiny pluton in regard to rock-forming feldspars. The content of K-Na-feldspars increases inward and outward from the Main foidolite ring. The degree of coorientation of tabular K-Na-feldspar crystals sharply increases in the Main ring zone, and microcline-dominant foyaite turns into orthoclase-dominant foyaite. The composition of K-Na-feldspars in the center of the pluton and the Main ring zone is characterized by an enrichment in Al. This shift is compensated by a substitution of some K and Na with Ba (the Main ring zone) or by an addition of K and Na cations to the initially cation-deficient microcline (the central part of the pluton). Feldspars of volcanosedimentary rocks occurring as xenoliths in foyaite primarily corresponded to plagioclase An15-40, but high-temperature fenitization and formation of hornfels in the Main ring zone gave rise to the crystallization of anorthoclase subsequently transformed into orthoclase and albite due to cooling and further fenitization. Such a zoning is the result of filling the Main ring fault zone within the homogeneous foyaite pluton with a foidolite melt, which provided the heating and potassium metasomatism of foyaite and xenoliths of volcanosedimentary rocks therein. The process eventually led to the transformation of foyaite into rischorrite-lyavochorrite, while xenoliths were transformed into aluminum hornfels with anorthoclase, annite, andalusite, topaz, and sekaninaite.

  11. Distribution of anomalously high K2O volcanic rocks in Arizona: Metasomatism at the Picacho Peak detachment fault

    NASA Astrophysics Data System (ADS)

    Brooks, William E.

    1986-04-01

    Metasomatized Tertiary lavas with anomalously high K2O and low Na2O content are distributed within the northwest-trending Miocene extensional terrane of southwestern Arizona. These rocks are common near core-complex related detachment faults at Picacho Peak and the Harcuvar Mountains and in listric-faulted terrane at the Vulture Mountains. In addition to systematic changes in K2O and Na2O, the rocks have been enriched in Zr and depleted in MgO. Secondary, introduced minerals include orthoclase, quartz, and calcite. Fine-grained, euhedral orthoclase (var. adularia), from 2 to 10 μm, is the dominant potassium mineral. Metasomatic changes at Picacho Peak are spatially associated with a major detachment fault. Thus, it is interpreted that detachment provided a conduit for hydrothermal fluids that altered the initial chemical composition of the Tertiary volcanics by potassium metasomatism and charged the upper-plate rocks with mineralizing fluids that carried Zr and Ba, along with Au, Ag, and Cu, during detachment 17 18 Ma.

  12. Palaeomagnetism, Potassium-argon ages and petrology of some volcanic rocks

    USGS Publications Warehouse

    Dalrymple, G.B.; Cox, A.

    1968-01-01

    Geological evidence obtained from samples of rocks from Cocos Island, Costa Rica, seems to agree with the idea that this island could have been a stepping stone for organisms migrating to the Galapagos Islands. ?? 1968 Nature Publishing Group.

  13. Stratigraphy and major element geochemistry of the Lassen Volcanic Center, California

    SciTech Connect

    Clynne, M.A.

    1984-01-01

    Detailed geologic mapping of 200 km/sup 2/ in and near Lassen Volcanic National Park, California and reconnaissance of the surrounding area, combined with reinterpretation of data in the literature, allow definition of the Lassen Volcano Center and provide the stratigraphic framework necessary for interpretation of major-element chemical data. The Lassen Volcanic Center developed in three stages. Stage I and II produced Brokeoff Volcanic, an andesitic composite cone that erupted mafic andesite to dacite 0.6 to 0.35 my ago. Volcanism then shifted in character and locale. Domes and flows of dacite and rhyodacite, and flows of hybrid andesite were erupted on the northern flank of Brokeoff Volcano during the period from 0.25 my ago to the present; these rocks comprise Stage III of the Lassen Volcanic Center. Rocks of the Lassen Volcanic Center are typical of subduction-related calc-alkaline volcanic rocks emplaced on a continental margin overlying sialic crust. Porphyritic andestic and dacite with high Al/sub 2/O/sub 3/, low TiO/sub 2/, medium K/sub 2/O, and FeO/MgO 1.5-2.0 are the most abundant rock types. Major-element chemical trends of rock sequences indicate a mafic to silicic evolution for magmas of the Lassen Volcanic Center, probably owing to crystal fractionation of calc-alkaline basalt. 23 figs., 5 tabs.

  14. The relationship between carbonate facies, volcanic rocks and plant remains in a late Palaeozoic lacustrine system (San Ignacio Fm, Frontal Cordillera, San Juan province, Argentina)

    NASA Astrophysics Data System (ADS)

    Busquets, P.; Méndez-Bedia, I.; Gallastegui, G.; Colombo, F.; Cardó, R.; Limarino, O.; Heredia, N.; Césari, S. N.

    2013-07-01

    The San Ignacio Fm, a late Palaeozoic foreland basin succession that crops out in the Frontal Cordillera (Argentinean Andes), contains lacustrine microbial carbonates and volcanic rocks. Modification by extensive pedogenic processes contributed to the massive aspect of the calcareous beds. Most of the volcanic deposits in the San Ignacio Fm consist of pyroclastic rocks and resedimented volcaniclastic deposits. Less frequent lava flows produced during effusive eruptions led to the generation of tabular layers of fine-grained, greenish or grey andesites, trachytes and dacites. Pyroclastic flow deposits correspond mainly to welded ignimbrites made up of former glassy pyroclasts devitrified to microcrystalline groundmass, scarce crystals of euhedral plagioclase, quartz and K-feldspar, opaque minerals, aggregates of fine-grained phyllosilicates and fiammes defining a bedding-parallel foliation generated by welding or diagenetic compaction. Widespread silicified and silica-permineralized plant remains and carbonate mud clasts are found, usually embedded within the ignimbrites. The carbonate sequences are underlain and overlain by volcanic rocks. The carbonate sequence bottoms are mostly gradational, while their tops are usually sharp. The lower part of the carbonate sequences is made up of mud which appear progressively, filling interstices in the top of the underlying volcanic rocks. They gradually become more abundant until they form the whole of the rock fabric. Carbonate on volcanic sandstones and pyroclastic deposits occur, with the nucleation of micritic carbonate and associated production of pyrite. Cyanobacteria, which formed the locus of mineral precipitation, were related with this nucleation. The growth of some of the algal mounds was halted by the progressive accumulation of volcanic ash particles, but in most cases the upper boundary is sharp and suddenly truncated by pyroclastic flows or volcanic avalanches. These pyroclastic flows partially destroyed the

  15. Petrogenetic implications from Pleistocene volcanic rocks of Psathoura Island, Greece: Mineral chemistry and geochemical data

    NASA Astrophysics Data System (ADS)

    Koutsovitis, Petros; Vougioukalakis, Georgios; Economou, Georgios; Xirokostas, Nikolaos; Tarenidis, Dimitrios; Ioakim, Chrysanthi; Karageorgis, Aristomenis

    2015-04-01

    Psathoura Island in the North Aegean area (39.498/24.181) is the only subaerial Quaternary (0.7 Ma) volcanic center along the extension of the North Anatolian Fault (NAF) in the Aegean area. Outcrops consist of a small number of overlapping subaerial basaltic lava flows. These lavas are enriched in LREE [(La/Yb)CN=12.2-18.1], with no Eu anomaly. The Psathoura volcanics are porphyritic with a fine grained holocrystalline trachytic groundmass. Olivine phenocryst cores (Fo=75.4-85.6), differ from phenocryst rims and groundmass olivines, which have lower Fo compositions. Few anhedral olivine xenocrysts are more Fo rich (Fo=86.2-88.5, CaO

  16. Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain and Kane Springs wash volcanic centers, southern Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, James V.; Noble, Donald C.; Hsu, Liang C.; Spatz, David M.

    1987-01-01

    Mineral coatings, including desert varnish on volcanic rocks of the semi-arid Basin and Range province are composted of amorphous, translucent films of Fe, Mn, Si, and Al rich compounds. Coatings are chiefly thin films that impregnate intergranularly to depths of about 0.1 to 0.3 mm, rarely deeper. Sixteen coating sections and subsurface interiors were probed by SEM; 20 samples were scanned by infrated spectrometry; 10 samples were scanned for visible-near IR spectra; inductin coupling plasma analyses were collected on 34 samples; 2 desert varnish surgaces were investigated by optical density slice imagery; a few XRD analyses were conducted in addition to the 50 reported in the last period; thin section observation continued; and imagery processing focused on classification techniques. In late May, approximately 10 field days were spent at the Stonewall and Black Mountain study sited conducting more detailed mapping and observation base on imagery results and collecting spectra with the Collins Field Spectrometer. Approximately 100 spectral analyses were collected and are currently being processed.

  17. Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs, Wash volcanic centers, Southern Nevada

    NASA Technical Reports Server (NTRS)

    Taranik, James V.; Noble, Donald C.; Hsu, Liang C.; Spatz, David M.

    1987-01-01

    LANDSAT Thematic Mapper imagery was evaluated over 3 Tertiary calderas in southern Nevada. Each volcanic center derived from a highly evolved silici magmatic system represented today by well exposed diverse lithologies. Distinctive imagery contrast between some of the late ash flows and earlier units follows from the high relative reflectance in longer wavelength bands (bands 5 and 7) of the former. Enhancement techniques provide color composite images which highlight some of the units in remarkable color contrast. Inasmuch as coatings on the tuffs are incompletely developed and apparently largely dependent spectrally on rock properties independent of petrochemistry, it is felt that the distinctive imagery characteristics are more a function of primary lithologic or petrochemical properties. Any given outcrop is backdrop for a variety of cover types, of which coatings, at various stages of maturity, are one. Petrographic and X-ray diffraction analysis of the outer air-interface zone of coatings reveal they are composed chiefly of amorphous compounds, probably with varying proportions of iron and manganese. Observations support an origin for some outer (air-interface) coating constituents exogenous to the underlying host.

  18. Rock magnetism and microscopy of the Jacupiranga alkaline-carbonatitic complex, southern Brazil

    NASA Astrophysics Data System (ADS)

    Alva-Valdivia, Luis M.; Perrin, M.; Rivas-Sánchez, María L.; Goguitchaichvili, Avto; López-Loera, Héctor; Lopes, Omar Ferreira; Bonás, Thiago Bastos

    2009-01-01

    This study of the Cajati deposit provides evidence that the ore was neither purely hydrothermal, nor volcanic in origin, as previous workers have proposed. The ores were formed from magnetite-rich magmas, hydrothermally altered and intruded at an indicated crustal depth in excess of 500 m. The mineralogical and textural association between magnetite and magnesioferrite in the carbonatite, and between the titanomagnetite and magnesioferrite-Ti mineralization in the pyroxenite of hedenbergite, seems to be analog mineralizations strongly related to the ionic substitution of Fe2+ by Mg. Relatively high Q ratios (≥5) for Jacupirangite-pyroxenite may indicate a thermo remanent magnetization (TRM) by the ore during post-metamorphic cooling, however it can also be developed from chemical remanent magnetization (CRM). Vector plots for the pyroxenite samples show reasonably linear and stable magnetic components. The intensity decay curves show that only two components of magnetizations are likely present. Continuous susceptibility measurements with increasing temperature show that the main magnetic phase seems to be magnetite. Maghemite is probably produced during the cooling process. Susceptibility recorded from low temperature (liquid nitrogen (-196°C)) to room temperature produces typical curves, indicating Verwey transition of magnetite. Hysteresis parameters point out that nearly all values fall in a novel region of the Day plot, parallel to but below magnetite SD + MD mixing curves.

  19. Petrogenesis of the Late Triassic volcanic rocks in the Southern Yidun arc, SW China: Constraints from the geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Leng, Cheng-Biao; Huang, Qiu-Yue; Zhang, Xing-Chun; Wang, Shou-Xu; Zhong, Hong; Hu, Rui-Zhong; Bi, Xian-Wu; Zhu, Jing-Jing; Wang, Xin-Song

    2014-03-01

    Studies on zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf-Pb isotopic geochemistry of intermediate volcanic rocks from the Southern Yidun arc, Sanjiang-Tethyan Orogenic Belt, SW China have been undertaken in this paper. They are used to discuss the petrogenesis of these rocks and to constrain the tectonic setting and evolution of the Yidun arc. These intermediate volcanic rocks were erupted at ca. 220 Ma (U-Pb zircon ages). Trachyandesite is the dominant lithology among these volcanic rocks, and is mainly composed of hornblende and plagioclase, with minor clinopyroxene and biotite. A hornblende geobarometer suggests that the stagnation of magma in the lower crust, where plagioclase crystallization was suppressed while hornblende crystallized, giving rise to high Sr/Y ratios that are one of the distinguishing features of adakites, after the primary magma originated from the lithospheric mantle wedge. Steeply right-inclined Rare Earth Element (REE) pattern combined with high La/Yb ratios suggests adakitic affinity of these volcanic rocks, implying that slab-melt from the subducting oceanic crust is a necessary component in the primary magma. Besides, trace element geochemistry and isotopic geochemistry also indicate that partial melting of pelagic sediments in the subduction zone and noticeable contamination with the lower crust were involved in the evolution of parental magma of these volcanic rocks. Based on previous work on the Northern Yidun arc and this study, we propose that the subduction was initiated in the Northern Yidun arc and extended to the southern part and that the Northern Yidun arc is an island arc while the Southern Yidun arc represents a continental arc, probably caused by the existence of the Zhongza Massif, that was invoked to be derived from Yangtze Block, as a possible basement of the Southern Yidun arc.

  20. Alkaline fluid circulation in ultramafic rocks and formation of nucleotide constituents: a hypothesis

    PubMed Central

    Holm, Nils G; Dumont, Marion; Ivarsson, Magnus; Konn, Cécile

    2006-01-01

    Seawater is constantly circulating through oceanic basement as a low-temperature hydrothermal fluid (<150°C). In cases when ultramafic rocks are exposed to the fluids, for instance during the initial phase of subduction, ferromagnesian minerals are altered in contact with the water, leading to high pH and formation of secondary magnesium hydroxide, among other – brucite, that may scavenge borate and phosphate from seawater. The high pH may promote abiotic formation of pentoses, particularly ribose. Pentoses are stabilized by borate, since cyclic pentoses form a less reactive complex with borate. Analyses have shown that borate occupies the 2' and 3' positions of ribose, thus leaving the 5' position available for reactions like phosphorylation. The purine coding elements (adenine, in particular) of RNA may be formed in the same general hydrothermal environments of the seafloor. PMID:16867193

  1. New data on Mesozoic Radiolaria of Serbia and Bosnia, and implications for the age and evolution of oceanic volcanic rocks in the Central and Northern Balkans

    NASA Astrophysics Data System (ADS)

    Vishnevskaya, V. S.; Djeric, N.; Zakariadze, G. S.

    2009-03-01

    The Dinaridic Ophiolite Belt (DOB) includes Middle Triassic cherty limestones, Upper Triassic radiolarian cherts associated with basaltic lavas and volcaniclastic sediments, and also Jurassic continental slope sequences. Sedimentary sequences grade upwards into Cretaceous red limestones with planktonic foraminifers of the Genus Hedbergella. Many of the Late Triassic to Late Jurassic cherts probably accumulated in an oceanic setting, and now crop out as blocks in olistostromal deposits. Jurassic radiolarite sequences of the margin of the Dinaride Ophiolite Belt are represented by Aalenian, Upper Bajocian-Lower Bathonian and Upper Bathonian-Lower Callovian, Middle Callovian-Oxfordian, Upper Callovian-Upper Oxfordian and Kimmeridgian-Tithonian-aged strata. These are overlain by Upper Tithonian-Valanginian sedimentary sequences with spongolite-radiolarites, volcaniclastic sediments and other continental slope deposits. The oldest units outcropping in the DOB are Mid-Triassic (Ladinian) red cherts and limestones. These are associated with alkaline and tholeiitic basalts in the Bistrica area, and with tholeiitic basalts in the Visoka area. In contrast, in the Vardar Zone Western Belt the oldest basalt-radiolarite formation is represented by cherts associated with tholeiitic basalt in the Ovčar Banja area. Upper Triassic red radiolarites of the Čačak area lie in direct stratigraphical contact with MORB-type pillow lavas and contain a Carnian-Norian radiolarian assemblage. The youngest radiolarian-bearing units are in the Upper Cretaceous part of the Vardar Zone Western Belt, in the Struganik area, where Coniacian-Santonian radiolarians occur in chert-clay-tuff sediments. In addition, cherty limestones from the northern slope of Kozara Mt. contain a Campanian radiolarian assemblage, together with Campanian-Maastrichtian planktonic foraminifers. Volcanic units associated with the siliceous sediments of Dinaride Ophiolite Belt and the Vardar Zone Western Belt are of MOR

  2. Lithologic discrimination of volcanic and sedimentary rocks by spectral examination of Landsat TM data from the Puma, Central Andes Mountains

    NASA Technical Reports Server (NTRS)

    Fielding, E. J.

    1986-01-01

    The Central Andes are widely used as a modern example of noncollisional mountain-building processes. The Puna is a high plateau in the Chilean and Argentine Central Andes extending southward from the altiplano of Bolivia and Peru. Young tectonic and volcanic features are well exposed on the surface of the arid Puna, making them prime targets for the application of high-resolution space imagery such as Shuttle Imaging Radar B and Landsat Thematic Mapper (TM). Two TM scene quadrants from this area are analyzed using interactive color image processing, examination, and automated classification algorithms. The large volumes of these high-resolution datasets require significantly different techniques than have been used previously for the interpretation of Landsat MSS data. Preliminary results include the determination of the radiance spectra of several volcanic and sedimentary rock units and the use of the spectra for automated classification. Structural interpretations have revealed several previously unknown folds in late Tertiary strata, and key zones have been targeted to be investigated in the field. The synoptic view of space imagery is already filling a critical gap between low-resolution geophysical data and traditional geologic field mapping in the reconnaissance study of poorly mapped mountain frontiers such as the Puna.

  3. Analysis of source characteristics of experimental gas burst and fragmentation explosions generated by rapid decompression of volcanic rocks

    NASA Astrophysics Data System (ADS)

    Arciniega-Ceballos, A.; Alatorre-Ibargüengoitia, M.; Scheu, B.; Dingwell, D. B.

    2015-07-01

    Gas burst and fragmentation explosions induced by rapid decompression of volcanic rocks in a high-pressure autoclave have been analyzed. We performed experiments from 4 to 20 MPa on (1) loose pyroclasts and (2) pumice from recent eruptions of Popocatépetl volcano. Our aim is to characterize the source mechanism distinguishing the physical processes that operate in the conduit which determine the dynamics of explosive volcanoes. For this aim we have analyzed experimentally the parameters that indicate the state and behavior of the conduit (i.e., decompression time, fragmentation threshold and speed, forces, and the partitioning of energy), using microseismic monitoring, the decompression time curves, and the sample rheological properties. The initial available potential energy in the system and its partitioning into different types of energies are correlated in space and time with specific stages of the explosive phenomenon. Such correlations, taken together with the energy distribution, enable the distinction of the individual physical processes involved and their causal sequence and relationships. Our observations suggest that in volcanic conduits with regular explosive activity, a source mechanism may operate whereby a causal sequence of processes results in a system that undergoes both rapid and stable transitions. Such behavior may persist over long periods of time.

  4. The association of endemic elephantiasis of the lower legs in East Africa with soil derived from volcanic rocks.

    PubMed

    Price, E W

    1976-01-01

    Endemic elephantiasis of the lower legs in Ethiopia, which reaches a maximum of 86-7 per 1,000 adults in affected areas, is related to the distribution of red clay soil derived from volcanic rocks, particularly basalt. Prevalence falls rapidly on leaving these areas. This observation has been tested in regions of non-filarial elephantiasis reported in Kanya and north-western Tanzania and further investigated in volcanic areas of Rwanda where the disease had not previously been reported. The same relationship is found to occur in these areas. The limitation to the lower legs of the barefooted section of the farming community suggests that the aetiological factor or factors enter by the feet. The occurrence at high altitude (over 1,200 metres) is noted and the predominance of basalt or basalt-like lava in each case is considered significant. The altitude governs rainfall and temperature and thus governs the type of soil produced. The soil produced from these rocks is rich in colloidal iron oxide, alumina and silica, to which a number of metallic ions are adsorbed. This soil is a reddish-brown clay which, when wet, is strongly adherent to the skin. The derived ions are known to be toxic to human tissue and absorption through intact human skin has been shown to occur experimentally. It is suggested that absorption of these irritants through the bare feet is responsible for the irreversible damage to the lymphatic channels. The present studies support the hypothesis that "high-altitude" elephantiasis of the lower legs in East Africa is a geochemical disease. PMID:1006757

  5. Alkaline igneous rocks of Magnet Cove, Arkansas: Mineralogy and geochemistry of syenites

    USGS Publications Warehouse

    Flohr, M.J.K.; Ross, M.

    1990-01-01

    Syenites from the Magnet Cove alkaline igneous complex form a diverse mineralogical and geochemical suite. Compositional zoning in primary and late-stage minerals indicates complex, multi-stage crystallization and replacement histories. Residual magmatic fluids, rich in F, Cl, CO2 and H2O, reacted with primary minerals to form complex intergrowths of minerals such as rinkite, fluorite, V-bearing magnetite, F-bearing garnet and aegirine. Abundant sodalite and natrolite formed in pegmatitic segregations within nepheline syenite where Cl- and Na-rich fluids were trapped. During autometasomatism compatible elements such as Mn, Ti, V and Zr were redistributed on a local scale and concentrated in late-stage minerals. Early crystallization of apatite and perovskite controlled the compatible behavior of P and Ti, respectively. The formation of melanite garnet also affected the behaviour of Ti, as well as Zr, Hf and the heavy rare-earth elements. Pseudoleucite syenite and garnet-nepheline syenite differentiated along separate trends, but the two groups are related to the same parental magma by early fractionation of leucite, the presumed precursor of intergrowths of K-feldspar and nepheline. The Diamond Jo nepheline syenite group defines a different differentiation trend. Sphene-nepheline syenite, alkali syenite and several miscellaneous nepheline syenites do not consistently plot with the other syenite groups or each other on element and oxide variation diagrams, indicating that they were derived from still other parental syenite magmas. Mineral assemblages indicate that relatively high f{hook};O2, at or above the fayalite-magnetite-quartz buffer, prevailed throughout the crystallization history of the syenites. ?? 1990.

  6. Origin and geodynamic relationships of the Late Miocene to Quaternary alkaline basalt volcanism in the Pannonian basin, eastern-central Europe

    NASA Astrophysics Data System (ADS)

    Harangi, Szabolcs; Jankovics, M. Éva; Sági, Tamás; Kiss, Balázs; Lukács, Réka; Soós, Ildikó

    2015-11-01

    Alkaline basaltic volcanism has been taking place in the Carpathian-Pannonian region since 11 Ma and the last eruptions occurred only at 100-500 ka. It resulted in scattered low-magma volume volcanic fields located mostly at the margins of the Pannonian basin. Many of the basalts have compositions close to those of the primitive magmas and therefore can be used to constrain the conditions of the magma generation. Low-degree (2-3 %) melting could occur in the convective asthenosphere within the garnet-spinel transition zone. Melting started at about 100 km depth and continued usually up to the base of the lithosphere. Thus, the final melting pressure could indicate the ambient lithosphere-asthenosphere boundary. The asthenospheric mantle source regions of the basalts were heterogeneous, presumably in small scale, and included either some water or pyroxenite/eclogite lithology in addition to the fertile to slightly depleted peridotite. Based on the prevailing estimated mantle potential temperature (1,300-1,400 °C) along with the number of further observations, we exclude the existence of mantle plume or plume fingers beneath this region. Instead, we propose that plate tectonic processes controlled the magma generation. The Pannonian basin acted as a thin spot after the 20-12 Ma syn-rift phase and provided suction in the sublithospheric mantle, generating asthenospheric flow from below the adjoining thick lithospheric domains. A near-vertical upwelling along the steep lithosphere-asthenosphere boundary beneath the western and northern margins of the Pannonian basin could result in decompressional melting producing low-volume melts. The youngest basalt volcanic field (Perşani) in the region is inferred to have been formed due to the dragging effect of the descending lithospheric slab beneath the Vrancea zone that could result in narrow rupture at the base of the lithosphere. Continuation of the basaltic volcanism cannot be excluded as inferred from the still fusible

  7. Late Albian ammonites from the carbonate cover of the Teloloapan arc volcanic rocks (Guerrero State, Mexico)

    NASA Astrophysics Data System (ADS)

    Monod, O.; Busnardo, R.; Guerrero-Suastegui, M.

    2000-10-01

    In the Guerrero province of Mexico, the calc-alcaline lavas of the Teloloapan volcanic arc unit are overlain by carbonates with reworked neritic faunas of Aptian-Albian age (La Evolucion Geologica y la Metalogénesis del Noroccidente de Guerrero. Universidad Autonoma de Guerrero, Serie Técnico-Cientifica, 1 (1979) 84). The discovery of an ammonite fauna at the top of the Teloloapan limestone provides a latest Albian age assignment for that horizon. The fauna includes: Pervinquieriarostrata,P. gr. inflata,Turrilitoideshugardianus,Stoliczkaia cf. blancheti, S. cf. tenuis,Desmoceraslatidorsatum,Oxytropidoceras cf. cantianum,Puzosia aff. mayoriana,Lechitesmoreti,Hamites cf. gardneri, H. cf. maximus, and Falciferellacampae n. sp. A pelagic microfauna is associated with the ammonites and contains Hedbergella sp. and Colomiellarecta. The fossiliferous horizon may thus be restricted to the Inflatum and lower Dispar zones. The overlying flysch contains Hamites sp. gr. intermedius near the base. Therefore, volcanism in the Teloloapan arc ceased before the end of the Early Cretaceous, while flysch deposition began in latest Albian times.

  8. 40Ar/39Ar ages and Sr-Nd-Pb isotopic compositions of alkaline and tholeiitic rocks from the northern Deccan Traps

    NASA Astrophysics Data System (ADS)

    Marzoli, A.; Parisio, L.; Jourdan, F.; Melluso, L.; Sethna, S. F.; Bellieni, G.

    2015-12-01

    The Deccan large igneous province in India was emplaced close to the Cretaceous-Paleogene boundary (K-Pg; 66.0 Ma) and is formed by tholeiitic and alkaline rocks. Definition of the origin of Deccan magmatism and of its environmental impact relies on precise and accurate geochronological analyses. We present new 40Ar/39Ar ages from the northern sector of the province. In this area, tholeiitic and alkaline rocks were contemporaneously emplaced at 66.60±0.35 to 65.25±0.29 Ma in the Phenai Mata area, while rocks from Rajpipla and Mt. Pavagadh yielded ages ranging from 66.40±2.80 to 64.90±0.80 Ma. Indistinguishable ages for alkaline and tholeiitic magmatism, coupled with distinct major and trace element and Sr-Nd-Pb isotopic compositions suggest that distinct mantle sources, necessary for the two magmatic series were synchronously active. The new ages are compared with previous ages, which were carefully screened and filtered and then recalculated in order to be comparable. The entire data set of geochronological data does not support a time-related migration of the magmatism related to the northward Indian Plate movement relative to the Reunion mantle plume. The main phase of magmatism, including the newly dated rocks from the Northern Deccan occurred across the K-Pg boundary, confirming a causal link between the emplacement of the province and the K-Pg mass extinction.

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

    USGS Publications Warehouse

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

    2014-01-01

    Extensive volcanic and intrusive igneous activity, partly localized along regional structural zones, characterized the southern Toquima Range, Nevada, in the late Eocene, Oligocene, and Miocene. The general chronology of igneous activity has been defined previously. This major episode of Tertiary magmatism began with emplacement of a variety of intrusive rocks, followed by formation of nine major calderas and associated with voluminous extrusive and additional intrusive activity. Emplacement of volcanic eruptive and collapse megabreccias accompanied formation of some calderas. Penecontemporaneous volcanism in central Nevada resulted in deposition of distally derived outflow facies ash-flow tuff units that are interleaved in the Toquima Range with proximally derived ash-flow tuffs. Eruption of the Northumberland Tuff in the north part of the southern Toquima Range and collapse of the Northumberland caldera occurred about 32.3 million years ago. The poorly defined Corcoran Canyon caldera farther to the southeast formed following eruption of the tuff of Corcoran Canyon about 27.2 million years ago. The Big Ten Peak caldera in the south part of the southern Toquima Range Tertiary volcanic complex formed about 27 million years ago during eruption of the tuff of Big Ten Peak and associated air-fall tuffs. The inferred Ryecroft Canyon caldera formed in the south end of the Monitor Valley adjacent to the southern Toquima Range and just north of the Big Ten Peak caldera in response to eruption of the tuff of Ryecroft Canyon about 27 million years ago, and the Moores Creek caldera just south of the Northumberland caldera developed at about the same time. Eruption of the tuff of Mount Jefferson about 26.8 million years ago was accompanied by collapse of the Mount Jefferson caldera in the central part of the southern Toquima Range. An inferred caldera, mostly buried beneath alluvium of Big Smoky Valley southwest of the Mount Jefferson caldera, formed about 26.5 million years

  10. Crustal evolution in a cratonic nucleus: Granitoids and felsic volcanic rocks of the North Caribou Terrane, Superior Province Canada

    NASA Astrophysics Data System (ADS)

    Wyman, Derek A.; Hollings, Pete; Biczok, John

    2011-04-01

    Attempts to decipher the petrogenesis of Archean Trondhjemite-Tonalite-Granodiorite (TTG) and establish trends in their compositions over time typically do not assess the possible role of assimilation-crystal fractionation processes. Studies of TTG suites worldwide, however, demonstrate that reprocessing of older crust is common. Felsic volcanic and intrusive rocks from the North Caribou Lake area, located in the nucleus of the Superior Province, exhibit a range of compositions that are not accounted for by variable degrees of amphibolite melting alone. Characteristic of Archean TTG, the rocks mainly fall in the lower right hand quadrant of a Nb/Ta vs Zr/Sm plot but they also show clear trends between ɛNd T and ratios such as Al 2O 3/TiO 2, Th/Nb, [Tb/Yb] N and Eu/Eu*. The lowest Nb/Ta values in the TTG likely result from crystal fractionation including titanite, which strongly partitions and fractionates these elements.

  11. Isotopic compositions of volcanic arc rocks in the Southern Volcanic Zone (33°-43°S), Chile: along- and across-arc variations

    NASA Astrophysics Data System (ADS)

    Jacques, Guillaume; Hoernle, Kaj; Gill, Jim; Wehrmann, Heidi

    2014-05-01

    We investigate young, olivine-bearing volcanic arc (VA) rocks from the Southern Volcanic Zone (33-43°S; SVZ) in Chile, and from the backarc (BA) in Argentina for their major and trace element, and Sr-Nd-Hf-Pb-O isotope geochemistry. The compositional data are processed to identify the source components contributing to the arc magmas and to estimate their proportions, with the aim to better understand the effects of the large-scale along-arc tectonic variations onto melt generation and erupted compositions. The Transitional (T) SVZ (34.5-38°S; Jacques et al., 2013) samples overlap the BA samples in Sr and Nd isotopes, whereas the Central (C) SVZ (38-43°S; Jacques et al., submitted, Chemical Geology) samples are shifted to slightly higher Sr and/or Nd isotope ratios. All samples form a tight correlation on the Pb isotope diagrams. The VA samples plot at the radiogenic end of the positive BA array and overlap trench sediment, indicating mixing between a South Atlantic MORB-type source and a slab component derived from subducted trench sediments and altered oceanic crust. On the Nd versus Hf isotope diagram, the VA and BA form two sub parallel linear trends, neither pointing to subducting sediment. The VA may display an asthenospheric mantle array, whereas enriched Proterozoic lithospheric mantle may be involved in the BA. The CSVZ samples have higher fluid-mobile to fluid-immobile element ratios and lower more- to less-incompatible fluid-immobile element ratios than the TSVZ samples, consistent with higher hydrous melt flux and higher degrees of melting resulting in higher magma production and eruption rates in the CSVZ. Low δ18O(melt) of CSVZ lavas suggests that the source of the enhanced water flux is likely to be hydrated lower crust and serpentinized upper mantle of the incoming plate, resulting from the multiple large fracture zones in this part of the SVZ. The δ18O(melt) values of the NSVZ, TSVZ and BA, on the other hand, largely overlap the MORB mantle

  12. Petrological and geochemical data of volcanic rocks from the southern Afar Depression, Ethiopia.

    NASA Astrophysics Data System (ADS)

    Urbanek, Ch.; Faupl, P.; Richter, W.; Seidler, H.

    2003-04-01

    The geological and petrological investigations (FWF Project P15196) in the southern Afar Depression of Ethiopia support an international palaeoanthropological research-team (PAR) under the leadership of Horst Seidler. Mount Galila is the conspicuous centre of the research area [N 9° 44.101', E 40° 27.368'], situated about 20 km E of the NNE-SSW striking, recently active Hertale Graben, which represents a northernmost segment of the Main Ethiopian Rift (MER). Stratigraphically, the fossiliferous lacustrine and fluvial deposits, as well as the intercalated volcanic layers of the Galila area, belong to the "Upper Stratoid Series" (5-1.4 Ma) and will be named the Mount Galila Formation. They are similar to the Awash Group, from which very famous early hominid fossils have been described. In the Mount Galila Fm., 7 main volcanic horizons serve as marker beds comprising basalts, ignimbrites, tuffs and tuffaceous sands. The basalt horizons in the research area represent basaltic lava flows each consisting of one single flow unit c. 5 meters thick with maximum 5 cooling units. A first set of geochemical data from XRF spectrometry comprising main and trace element analysis shows characteristics for the volcanic marker beds as following: The basalts are clearly tholeiitic in the main elements (FeO/MgO/Alk) and show typical trace element distributions (e.g. Zr/Y-Zr; Ti/100-Yx3-Zr) as Within Plate Tholeiit Basalts. All basalt samples contain access 40Ar which can be explained by specific erruption mechanisms that leads to analytical problems for 40Ar/39Ar dating. In the TAS diagram after LeMaitre 1984 the ignimbrites vary at high alkali levels (7-9%) from trachytic to dacitic and rhyolitic composition, whereas at low alkali contents (<7%) they plot into the andesitic field. Compared to the basalts, the geochemistry of the ignimbrites is much more inhomogenous. Tuffs and tuffaceous sands are relevant as marker beds especially for the palaeoanthropological excavations in the

  13. Physical and hydraulic properties of volcanic rocks from Yucca Mountain, Nevada

    USGS Publications Warehouse

    Flint, L.E.

    2003-01-01

    A database of physical and hydraulic properties was developed for rocks in the unsaturated zone at Yucca Mountain, Nevada, a site under consideration as a geologic repository for high-level radioactive waste. The 5320 core samples were collected from 23 shallow (<100 m) and 10 deep (500-1000 m) vertical boreholes. Hydrogeologic units have been characterized in the unsaturated zone [Flint, 1998] that represent rocks with ranges of welding, lithophysae, and high and low temperature alteration (as a result of the depositional, cooling, and alterational history of the lithostratigraphic layers). Lithostratigraphy, the hydrogeologic unit, and the corresponding properties are described. In addition, the physical properties of bulk density, porosity, and particle density; the hydraulic properties of saturated hydraulic conductivity and moisture retention characteristics; and the field water content were measured and compiled for each core sample.

  14. Monitoring of the volcanic rock compositions during the 2012-2013 fissure eruption at Tolbachik volcano, Kamchatka

    NASA Astrophysics Data System (ADS)

    Volynets, Anna O.; Edwards, Benjamin R.; Melnikov, Dmitry; Yakushev, Anton; Griboedova, Irina

    2015-12-01

    Here we present the results from monitoring of the composition of rocks produced during the 2012-2013 fissure eruption at Tolbachik volcano (FTE). Major and trace element concentrations in 75 samples are reported. Products of this eruption are represented by high alumina basaltic trachyandesites with higher alkalis and titanium contents than in all previously studied rocks of the Tolbachik monogenetic volcanic field. Rocks erupted during the first three days (27-30 November) from the northern (also called Menyailov) group of vents are the most silica- and alkali-rich (SiO2 concentrations up to 55.35 wt.% and K2O up to 2.67 wt.%). From December onwards, when the eruptive activity switched from the Menyailov vents to the southern (Naboko) group of vents, silica content dropped by 2 wt.%, concentrations of MgO, FeO, TiO2 and Mg# increased, and K2O and Na2O concentrations and K2O/MgO ratio decreased. For the rest of the eruption the compositions of rocks remained constant and homogeneous; no systematic compositional differences between lava, bombs and scoria samples are evident. Trace element distributions in the rocks of the Menyailov and Naboko vent lavas are relatively uniform; Menyailov lavas have slightly higher Th, Nb, Hf, Y, and HREE concentrations than the Naboko vent lavas at more or less constant element ratios. We explain the initial change in geochemistry by tapping of a slightly cooler and fractionated (~ 3% Mt and 8% Cpx) upper part of the magma storage zone before the main storage area began to feed the eruption. Thermodynamic constraints show that apparent liquidus temperatures varied from 1142 °C to 1151 °C, and thermodynamic modeling shows that variations in compositions are consistent with a high degree of low pressure (100-300 MPa), nominally anhydrous fractionation of a parent melt compositionally similar to the 1975 Northern Breakthrough high-Mg basalt. Geochemistry, petrological observations and modeling are in agreement with the newly erupted

  15. Genetic implications of minor-element and Sr-isotope geochemistry of alkaline rock complexes in the Wet Mountains area, Fremont and Custer counties, Colorado

    USGS Publications Warehouse

    Armbrustmacher, T.J.; Hedge, C.E.

    1982-01-01

    Concentrations of Rb, Sr, and REE (rare earth elements), and Sr-isotopic ratios in rocks of the Cambrian alkaline complexes in the Wet Mountains area, Colorado, show that rocks formed as end-products of a variety of magmas generated from different source materials. The complexes generally contain a bimodal suite of cumulus mafic-ultramafic rocks and younger leucocratic rocks that include nepheline syenite and hornblende-biotite syenite in the McClure Mountain Complex, nepheline syenite pegmatite in the Gem Park Complex, and quartz syenite in the complex at Democrat Creek. The nepheline syenite and hornblende-biotite syenite at McClure Mountain (535??5m.y.) are older than the syenitic rocks at Democrat Creek (511??8m.y.). REE concentrations indicate that the nepheline syenite at McClure Mountain cannot be derived from the hornblende-biotite syenite, which it intrudes, or from the associated mafic-ultramafic rocks. REE also indicate that mafic-ultramafic rocks at McClure Mountain have a source distinct from that of the mafic-ultramafic rocks at Democrat Creek. In the McClure Mountain Complex, initial87Sr/86Sr ratios for mafic-ultramafic rocks (0.7046??0.0002) are similar to those of hornblende-biotite syenite (0.7045??0.0002), suggesting a similar magmatic source, whereas ratios for carbonatites (0.7038??0.0002) are similar to those of nepheline syenite (0.7038??0.0002). At Democrat Creek, initial ratios of syenitic rocks (0.7032??0.0002) and mafic-ultramafic rocks (0.7028??0.0002) are different from those of corresponding rocks at McClure Mountain. ?? 1982 Springer-Verlag.

  16. Geochronology and geochemistry of Cretaceous Nanshanping alkaline rocks from the Zijinshan district in Fujian Province, South China: Implications for crust-mantle interaction and lithospheric extension

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong

    2014-10-01

    In situ zircon U-Pb ages and Hf isotopic data, major and trace elements, and Sr-Nd-Pb isotopic compositions are reported for Nanshanping alkaline rocks from the Zijingshan district in southwestern Fujian Province (the Interior or Western Cathaysia Block) of South China. The Nanshanping alkaline rocks, which consist of porphyritic quartz monzonite, porphyritic syenite, and syenite, revealed a Late Cretaceous age of 100-93 Ma. All of the rocks show high SiO2, K2O + Na2O, and LREE but low CaO, Fe2O3T, MgO, and HFSE (Nb, Ta, P, and Ti) concentrations. These rocks also exhibit uniform initial 87Sr/86Sr ratios of 0.7078 to 0.7087 and εNd(t) values of -4.1 to -7.2, thus falling within the compositional field of Cretaceous basalts and mafic dikes occurring in the Cathaysia Block. Additionally, these rocks display initial Pb isotopic compositions with a 206Pb/204Pbi ratio of 18.25 to 18.45, a 207Pb/204Pbi ratio of 15.63 to 15.67, and a 208Pb/204Pbi ratio of 38.45 to 38.88. Combined with the zircon Hf isotopic compositions (εHf(t) = -11.7 to -3.2), which are different from those of the basement rocks, we suggest that Nanshanping alkaline rocks were primarily derived from a subduction-related enriched mantle source. High Rb/Sr (0.29-0.65) and Zr/Hf (37.5-49.2) but relatively low Ba/Rb (4.4-8.1) ratios suggest that the parental magmas of these rocks were most likely formed via partial melting of a phlogopite-bearing mantle source with carbonate metasomatism. The relatively high SiO2 (62.35-70.79 wt.%) and low Nb/Ta (10.0-15.3) ratios, positive correlation between SiO2 and (87Sr/86Sr)I, and negative correlation between SiO2 and εNd(t) of these rocks suggest that the crustal materials were also involved in formation of the Nanshanping alkaline rocks. Combined with geochemical and isotopic features, we infer magmatic processes similar to AFC (assimilation and fractional crystallization) involving early fractionation of clinopyroxene and olivine and subsequent fractionation of

  17. Numerical Calculation of LP Seismic Signals Modeling the Fluid-Rock Interaction in Simulated Volcanic Conduits

    NASA Astrophysics Data System (ADS)

    Arciniega-Ceballos, Alejandra; Corona-Romero, Pedro; Sanchez-Sesma, Francisco

    2010-05-01

    We present an investigation of the fluid-solid dynamic interaction of a fluid-driven cylindrical conduit embedded within an infinite, homogeneous elastic space with physical properties similar to those encountered in volcanic environments. In our model, a pressure transient is applied at the bottom of the conduit, which perturbs the steady flow of incompressible viscous fluid, driven by a pressure gradient. The model includes radial variation of a cylindrical fluid-filled conduit driven by changes in the flow velocity of a Newtonian fluid and a pressure gradient. Both fluid and solid are dynamically coupled by the continuity of radial velocities and shear and radial stresses at the conduit wall. The conduit dynamics are governed by three ordinary non-linear differential equations of second order, which are solved numerically by applying a fifth-order Runge-Kutta scheme. Our model allows for any number of pipe segments of different sizes coupled in series, thus representing an extended source region, which closely mimics the geometry of realistic volcanic conduits. Various examples of fluid-filled pipe-systems, starting from the simplest penny-shape geometries up to conduits of hundreds of meters in length, are presented. The values assumed for the fluid density and viscosity are in the mean range of basaltic and andesitic composition. Far-field velocity synthetics radiated by the motion of the conduit and fluid flows ascending to the surface display characteristic waveforms and frequency contents that closely resemble those of long-period (LP) signals observed at active volcanoes.

  18. Trace Elements in Olivine in Italian Potassic Volcanic Rocks Distinguish Between Mantle Metasomatism by Carbonatitic and Silicate Melts

    NASA Astrophysics Data System (ADS)

    Foley, S. F.; Ammannati, E.; Jacob, D. E.; Avanzinelli, R.; Conticelli, S.

    2014-12-01

    The Italian Peninsula is the site of intense subduction-related potassic magmatism with bimodal character in terms of silica activity: Ca-poor silica-saturated lamproitic rocks and Ca-enriched silica-undersaturated leucitites. Lamproitic magmas formed in the early phases of magmatic activity and were followed by leucititic magmas. The primary magmas are generated in the sub-continental lithospheric mantle at the destructive plate margin, and both series have olivine as the first crystallizing phenocrysts. Trace elements in olivine phenocrysts are important in recognizing metasomatic effects on the mineralogy of the mantle source. Since Ni is the most compatible trace element in olivine, particularly in alkaline melts, modal changes of olivine in the source strongly affect its bulk partition coefficient, and therefore its content in primary melts and in olivine that crystallizes from them.The concentration of other compatible trace elements (e.g. Mn, Co) in olivine phenocrysts also depends on the abundance of olivine in the magma source. Ni contents in olivine of the Italian rocks show a clear bimodal distribution. Olivine from lamproitic samples has systematically higher Fo and Ni contents, whereas olivine from leucititic rocks never exceeds Fo92 and has markedly lower Ni, reaching among the lowest levels ever observed in olivine phenocrysts in primitive melts. The Mn/Fe ratio of olivine is also sensitive to changes of the modal abundance of olivine in the source, 100*Mn/Fe of olivine from lamproitic rocks never exceeds 2, while it is always >1.8 in leucititic rocks, meaning that the leucitite source regions are much richer in olivine. Lithium is generally enriched in the crust and in sediments compared to the lithospheric mantle and to mantle-derived melts,so that Li in olivine above 10 ppm is suggested to indicate recycled sediments. Li contents are up to 35 ppm in leucititic olivines and up to >50 ppm in lamproitic olivines, confirming the recycling of crustal

  19. Quantitative petrogenetic constraints on the Pliocene alkali basaltic volcanism of the SE Spain Volcanic Province

    NASA Astrophysics Data System (ADS)

    Cebriá, J. M.; López-Ruiz, J.; Carmona, J.; Doblas, M.

    2009-09-01

    Alkali basalts of Pliocene age are the last episode of volcanism in the SE Spain Volcanic Province, postdating a complex series of Miocene calc-alkaline to ultrapotassic rocks. This volcanism is represented by small outcrops and vents NW of Cartagena that has been interpreted as a volcanic episode similar to the contemporaneous monogenetic alkaline basaltic volcanism of the Iberian Peninsula and Western/Central Europe. However, their geochemical signature is characterised by relatively higher 87Sr/ 86Sr ratios as well as distinct trace element anomalies which, at different scale, are only found in the spatially related calc-alkaline to ultrapotassic volcanism. Quantitative modelling of these data demonstrate that the geochemical signature of the Pliocene alkali basalts of Cartagena can be explained by the interaction between primitive melts generated from a sublithospheric mantle source similar to that identified for other volcanic regions of Spain, and liquids derived from the overlying lithospheric mantle. This interaction implies that the alkali basalts show some geochemical features only observed in mantle lithosphere-derived melts (e.g. Sr isotope enrichment and Th-U-Pb positive anomalies), while retaining an overall geochemical signature similar to other Iberian basalts (e.g. Rb-K negative anomalies). This model also implies that beneath the SEVP, enriched (metasomatized) portions were still present within the lithospheric mantle after the Miocene magmatic episodes. Comparison of this model with those already developed for other alkaline basaltic volcanic regions of western/central Europe supports the idea that the interaction of primitive magmas derived from a common sublithospheric mantle source with liquids derived from the overlying regionally heterogeneous lithospheric mantle is a relatively frequent scenario in the European realm.

  20. 226Ra or 226Ra/Ba dating of Holocene volcanic rocks: application to Mt. Etna and Merapi volcanoes

    NASA Astrophysics Data System (ADS)

    Condomines, M.; Gauthier, P. J.; Tanguy, J. C.; Gertisser, R.; Thouret, J. C.; Berthommier, P.; Camus, G.

    2005-02-01

    This paper shows how 226Ra- 230Th disequilibria can be used to date Holocene volcanic rocks from some well selected volcanoes. A systematic study of these disequilibria on historical or well-dated volcanic samples is indeed first required to test the applicability of this method. Two examples are described here to illustrate its potential. In the case of Mt. Etna, the good correlation observed between ( 226Ra) 0 activities at the time of eruption and Th contents in lava flows from the last two millennia [M. Condomines, J.C. Tanguy, V. Michaud, Magma dynamics at Mt. Etna: constraints from U-Th-Ra-Pb radioactive disequilibria and Sr isotopes in historical lavas, Earth Planet. Sci. Lett. 132 (1995) 25-41] is used to infer the ages of several newly analysed lava flows. The calculated ages are in good agreement with those deduced from the archaeomagnetic curve describing the variation of the geomagnetic field direction in southern Italy [J.C. Tanguy, I. Bucur, J.F.C. Thompson, Geomagnetic secular variation in Sicily and revised ages of historic lavas from Mt. Etna, Nature 318 (1985) 453-455, J.C. Tanguy, M. Le Goff, V. Chillemi, A. Paiotti, C. Principe, S. La Delfa, G. Patane, Variation séculaire de la direction du champ géomagnétique enregistrée par les laves de l'Etna et du Vésuve pendant les deux derniers millénaires, C. R. Acad. Sci. Paris 329 (1999) 557-564, J.C. Tanguy, M. Le Goff, C. Principe, S. Arrighi, V. Chillemi, A. Paiotti, S. La Delfa, G. Patane, Archaeomagnetic dating of Mediterranean volcanics of the last 2100 years: validity and limits. Earth Planet. Sci. Lett. 211 (2003) 111-124]. We also present a whole set of new U-series data on historical, recent, and older samples from Merapi (Indonesia), and show that the ( 226Ra)/Ba ratio has probably maintained a quasi-steady state value during at least the past four millennia, and can be used to infer the ( 226Ra) 0/Ba ratio of old volcanics at the time of eruption, and thus their ages. Comparison with

  1. U-Th-Pb geochronology of meta-carbonatites and meta-alkaline rocks in the southern Canadian Cordillera: A geodynamic perspective

    NASA Astrophysics Data System (ADS)

    Millonig, Leo J.; Gerdes, Axel; Groat, Lee A.

    2012-11-01

    U-Pb and Th-Pb ages of zircons from seven meta-carbonatite and three meta-alkaline rock samples provide evidence for three distinct episodes of carbonatite and alkaline magmatism in the southern Canadian Cordillera spanning a period of ~ 460 Ma. The earliest, Neoproterozoic event occurred at ~ 800-700 Ma and coincides with the postulated initial break-up of Rodinia. The second, previously undocumented, event of carbonatitic magmatism is constrained to the Late Cambrian at ~ 500 Ma and corresponds to a period of extensional tectonics that affected the western continental margin of North America from the Canadian Cordillera to the southwestern United States. The youngest and most prevalent period of alkaline igneous activity occurred in Late Devonian to Early Carboniferous times at ~ 360-340 Ma and resulted from extensional tectonics, presumably caused by slab rollback. In addition, different episodes of amphibolite-facies metamorphism subsequently affected the igneous rocks between ~ 155 and 50 Ma. This dataset puts new constraints on the timing of carbonatite and alkaline igneous activity and the evolution of (ancestral) North America's western continental margin from Neoproterozoic to Carboniferous times.

  2. Volcanic facies, structure, and geochemistry of the marginal basin rocks of central Peru

    NASA Astrophysics Data System (ADS)

    Atherton, M. P.; Webb, S.

    The western part of the Mesozoic Peruvian Trough, the Huarmey Basin, has a fill of pillow lavas, sheet lavas, hyaloclastites, tuffs and minor cherts, siliceous and calcareous oozes. Maximum subsidence occurred in the Albian when 9000 meters of basin fill accumulated. This was later intruded by gabbros and dikes and then the Coastal Batholith. The basin is an extensional marginal basin continuous with other basins of similar age to the south. Facies analyses indicate that the basin was relatively deep, with no continental influx, and not dissimilar to spreading and off-axis systems on the ocean floor. Structures at the surface and at depth indicate the crust has split and the basin was floored by mantle material. The basin shows a marked polarity, with tholeiitic basaltic rocks at the center and high-K acid rocks at the eastern margin, with intermediate types between. These changes in petrology and chemistry relate to lateral changes in source composition. Secular variations are also present and indicate a calcalkali source giving way to a more MORB-like source with a variable continental component. The basin is part of the major rifting event in the Cretaceous which affected the whole western margin of South America and was an important and necessary precursor to major batholith intrusion.

  3. Petrology and geochemistry of Early Permian volcanic rocks in South Tian Shan, NW China: implications for the tectonic evolution and Phanerozoic continental growth

    NASA Astrophysics Data System (ADS)

    Liu, Dongdong; Guo, Zhaojie; Jolivet, Marc; Cheng, Feng; Song, Yan; Zhang, Ziya

    2014-04-01

    Situated in the southwest of the Central Asian Orogenic Belt (CAOB), the South Tian Shan (STS) Block is a key area for understanding the final accretion of the CAOB. A suite of volcanic rocks interbedded with continental sediments from the Xiaotikanlike Formation lies along the southwestern edge of the Tian Shan orogen. Laser-ablation-inductively coupled plasma-mass spectrometer U-Pb dating provided a crystallization age of 295.0 ± 2.8 Ma (MSWD = 1.3), suggesting an Early Permian magmatic event. The volcanic rocks show a variable composition, with dominant rhyolites and dacites, subordinate basaltic andesites and few basalts. The felsic rocks are enriched in K and exhibit remarkably negative anomalies in Ba, Sr, Eu, P and Ti. These anomalies associated with their high negative ɛ Nd( t) values and old Nd model ages suggest that they are most likely sourced from ancient lower crustal rocks. The mafic rocks are characterized by high Mg#, Cr, Ni contents, negative Nb, Ta anomalies and pronounced enrichment in light rare earth elements as well as mild enrichment in large-ion lithophile elements. The mafic rocks are thus inferred to derive from enriched subcontinental lithospheric mantle. The petrographic and geochemical characteristics of the Xiaotikanlike Formation volcanic rocks indicate that they were generated under a post-collisional regime. Therefore, the final collision between the Tarim Craton and the Kazakhstan-Yili terrane took place before Early Permian, most probably at Late Carboniferous. Differing from other tectonic units of the CAOB, the recycling of ancient lithospheric crust played a significant role in the continental growth of the STS Block.

  4. New 40Ar/39Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada

    USGS Publications Warehouse

    Harlan, S.S.; Duebendorfer, E.M.; Deibert, J.E.

    1998-01-01

    New 40Ar/39Ar dates on volcanic rocks interlayered with synextensional Miocene sedimentary rocks in the western Lake Mead area and southern end of the Las Vegas Range provide tight constraints on magmatism, basin formation, and extensional deformation in the Basin and Range province of southern Nevada. Vertical axis rotations associated with movement along the Las Vegas Valley shear zone occurred after 15.67??0.10 Ma (2??), based on a 40Ar/39Ar date from a tuff in the Gass Peak formation in the southern Las Vegas Range. Basaltic magmatism in the western Lake Mead area began as early as 13.28??0.09 Ma, based on a date from a basalt flow in the Lovell Wash Member of the Horse Spring Formation. Isotopic dating of a basalt from the volcanic rocks of Callville Mesa indicates that these rocks are as old as 11.41??0.14 Ma, suggesting that volcanic activity began shortly after formation of the Boulder basin, the extensional basin in which the informally named red sandstone unit was deposited. The red sandstone unit is at least as old as 11.70??0.08 Ma and contains megabreccia deposits younger than 12.93??0.10 Ma. This results shows that formation of the Boulder basin was associated with development of topographic relief that was probably generated by movement along the Saddle Island low-angle normal fault. Stratal tilting associated with extension occurred both prior to and after 11.5 Ma.

  5. Helium isotopic variations in volcanic rocks from Loihi Seamount and the Island of Hawaii

    USGS Publications Warehouse

    Kurz, M.D.; Jenkins, W.J.; Hart, S.R.; Clague, D.

    1983-01-01

    Helium isotopic ratios ranging from 20 to 32 times the atmospheric 3He 4He(RA) have been observed in a suite of 15 basaltic glasses from the Loihi Seamount. These ratios, which are up to four times higher than those of MORB glasses and more than twice those of nearby Kilauea, are strongly suggestive of a primitive source of volatiles supplying this volcanism. The Loihi glasses measured span a broad compositional range, and the 3He/4He ratios were found to be generally lower for the alkali basalts than for the tholeiites. The component with a lower 3He 4He ratio appears to be associated with olivine xenocrysts, within which fluid inclusions are probably the carrier of contaminant helium. One Loihi sample has a much lower isotopic ratio ( 30 RA) helium with some (variable) component of lithospheric contamination added during "breakthrough", while the later stages are characterized by a relaxation toward lithospheric 3He 4He ratios (??? 8 RA) due to isolation of the diapir from the mantle below (as the plate moves on), and subsequent mining of the inherited helium and contamination from the surrounding lithosphere. The abrupt contrast in 3He 4He ratios between Kilauea and Loihi, despite their close proximity, is indicative of the small lateral extent of the plume. ?? 1983.

  6. A Clinopyroxene-Plagioclase Geobarometer for A-type Silicic Volcanic Rocks

    NASA Astrophysics Data System (ADS)

    Wolff, J.; Iveson, A. A.; Davis, K.; Johnson, T. A.; Gahagan, S.; Ellis, B. S.

    2015-12-01

    Constraining the crustal storage depths of magmas is important in understanding volcanism. The reaction: anorthite (pl) = Ca-Tschermak's (cpx) + silica (Q or liq) has a large volume change and hence offers potential as a geobarometer, but has not been extensively exploited as such. One of the chief barriers to its wide application is consistent estimation of melt silica activity for assemblages that lack quartz. We have skirted this problem by confining attention to metaluminous silicic compositions (SiO2 > 60% by weight), for which silica activity during crystallization is presumed to be close to 1, and calibrated the barometer for the range 0 - 2 GPa using the LEPR database and additional experiments from the literature. Additional improvement is obtained by excluding hydrous phase-bearing assemblages. Despite the analytical uncertainties present in older experimental investigations, with knowledge of temperature, and clinopyroxene, plagioclase and host melt compositions, pressures for amphibole- and biotite-free dacites and rhyolites can be estimated to ±0.17 GPa (1 sigma). The limitations of the barometer render it most applicable to intraplate, A-type rhyolites. Application to one such system, the Snake River Plain rhyolites, indicate that both melt-hosted phenocrysts and clinopyroxene-plagioclase aggregate grains found in these rhyolites formed at low pressures, <0.5 GPa. This is consistent with isotopic evidence for a shallow crustal origin for Snake River Plain rhyolites.

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

    USGS Publications Warehouse

    Lanphere, M.A.

    1988-01-01

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

  8. Laboratory and Remote Spectroscopy of Volcanic Rocks from Mauna Iki, Hawaii

    NASA Astrophysics Data System (ADS)

    Varriale, J. A.; Rogers, D.; Arnold, J. A.; Glotch, T. D.

    2012-12-01

    Previous studies have shown that remotely measured thermal infrared spectra of Hawaiian basalt flows are dominated by thin alteration coatings. The objectives of this work are to characterize the spectral properties of natural surfaces from flows of varying emplacement age as well as from flows of varying crystallinity and primary mineralogy to understand how duration of exposure and primary rock characteristics influence the alteration assemblages and their spectral properties. We have collected samples from the Mauna Iki-area lava flows that represent primary compositional variation across the flows, and that exhibit a range of alteration coatings. Samples were cataloged and prepared for spectral measurements. Mid-IR (5-50 μm) emissivity spectra and VNIR (~0.85-2.5 μm) reflectance spectra were collected. We also directly compared atmospherically corrected spectra from AVIRIS and ASTER at the sample locations to VNIR and mid-IR laboratory spectra, respectively. In most cases, a spectrally representative sample was collected, and the thin (10's of microns) alteration coatings dominate the spectral signatures of the remotely acquired data. Some sand samples were also collected. As expected, the sands are spectrally similar to fresh-cut rock surfaces in laboratory spectra, suggesting that remote measurements of sand could provide an indication of the unaltered surface mineralogy. However, remote-lab spectral comparisons showed that although widespread regions of sediment cover are apparent from the ground, the sand was not the spectrally dominant material in the regions where it was sampled and thus the primary mineralogy could not be identified remotely. Mid-IR spectra were modeled using a linear least-squares minimization routine to estimate modal abundances in fresh-cut and natural surfaces. The modeling identified key mineral groups within the composition of the altered and freshly cut surfaces; with basalt glass, olivine and plagioclase accounting for 59% of

  9. Comparison of the Brunhes epoch geomagnetic secular variation recorded in the volcanic and sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Shcherbakov, V. P.; Khokhlov, A. V.; Sycheva, N. K.

    2014-03-01

    The results of numerical modeling of the geomagnetic secular variation by the method of the Giant Gaussian Process (GGP) are presented and compared with the information derived from the presentday databases for paleointensity. The variances of the positions of the virtual geomagnetic pole (VGP) calculated from the synthetic and experimental data (Brunhes epoch, effusive rocks) are nearly similar, which supports the validity of the theoretical model. The average value of the virtual axial geomagnetic dipole (VADM) calculated from the PINT world database on paleointensity and the Sint-2000 model is lower than VADM calculated by the GGP model; at the same time, the estimates based on the archaeomagnetic data give the VADM value slightly above the model prediction. The largest difference is observed in the variances of VADM, which is for all the three databases noticeably higher than the value calculated from the GGP model. Most probably, this is due to the contribution of the neglected measurement errors of VADM.

  10. Multiple isotopic components in Quaternary volcanic rocks of the Cascade Arc near Crater lake, Oregon

    USGS Publications Warehouse

    Bacon, C.R.; Gunn, S.H.; Lanphere, M.A.; Wooden, J.L.

    1994-01-01

    Quaternary lavas and pyroclastic rocks of Mount Mazama, Crater lake caldera, and the surrounding area have variable Sr, Nd, and Pb isotopic compositions. High-alumina olivine tholeiites have 87Ar/86Ar ratios of 0.70346-0.70364; basaltic andesite, 0.70349-0.70372; shoshonitic basaltic andesite, 0.70374-0.70388; and andesite, 0.70324-0.70383. Dacites of Mount Mazama have 87Sr/ 86Sr ratios of 0.70348-0.70373. Most rhyodacites converge on 0.7037. Andesitic to mafic-cumulate scoriae of the climatic eruption, and enclaves in pre-climactic rhyodacites, cluster in two groups but show nearly the entire 87Sr/86Sr range of the data set, confirming previously suggested introduction of diverse parental magmas into the growing climactic chamber. Magma evolution is described. -from Authors

  11. 3.5 billion years of glass bioalteration: Volcanic rocks as a basis for microbial life?

    SciTech Connect

    Staudigel, H.; Furnes, H.; McLoughlin, N.; Banerjee, N.R.; Connell, L.B.; Templeton, A.

    2009-04-07

    Alteration textures in volcanic glass from the seafloor fall into two classes, one suggestive of abiotic/diffusive hydration and chemical exchange, and another likely to be caused by microbial, cavity-forming, congruent dissolution. Glass bioalteration is common in submarine lavas throughout the world's ocean, dominant in the upper 300 m of the oceanic crust, and found in all well-preserved ophiolites and greenstone belts dating back to 3.5 Ga. It may yield a significant fraction of the global biomass and geochemical fluxes and is relevant to the development of the earliest life on Earth. We present a critical review concerning these glass bioalteration textures and present new data on their microchemical environment. We explore arguments for their biogenicity and further develop the prevalent model for their formation by relating corrosion morphology to the mechanism of microbial dissolution. Biological alteration produces conspicuous micron-scale granular and tubular textures. Granular glass alteration is well explained by colonizing microbes that selectively dissolve the glass in their contact area, forming a sponge-like interconnected network of micron-sized cavities along glass surfaces. Tubular alteration meanwhile, is more likely to be caused by filamentous cell extensions in a process similar to fungal tunneling of soil feldspars and marine carbonates. While we see clear functional similarities to fungal dissolution behavior, we do not know whether fungal or prokaryotic organisms are involved. However, this functional constraint may eventually help to identify potential microbes responsible for these features, potentially including eukaryotic or prokaryotic organisms. Yet, we caution that these organisms may be difficult to identify and to study, because they are likely to be sparsely distributed, slow growing, and difficult to cultivate.

  12. Petrochemical Results for Volcanic Rocks recovered from SHINKAI 6500 diving on the Bonin Ridge (27°15'N-28°25'N): submarine extension of Ogasawara forearc volcanism

    NASA Astrophysics Data System (ADS)

    Bloomer, S. H.; Kimura, J.; Stern, R. J.; Ohara, Y.; Ishii, T.; Ishizuka, O.; Haraguchi, S.; Machida, S.; Reagan, M.; Kelley, K.; Hargrove, U.; Wortel, M.; Li, Y. B.

    2004-12-01

    Four SHINKAI 6500 submersible dives (dive #823 to #826) were performed along the Bonin Ridge escarpment west of Ogasawara (Bonin) Islands in the West Pacific during May 2004, in the hopes of finding exposures of lower crust of the IBM forearc. The Ogasawara Islands are located on the Bonin ridge, exposing 48-40 Ma boninites on Chichi-jima and depleted arc tholeiite lavas of the same age on Haha-jima. These extremely depleted lavas are believed to have been generated when subduction began beneath the Izu-Bonin-Mariana oceanic arc system. Subsequent rifting (35-30 Ma) formed the Bonin Trough and a 350 km long N-S trending eastern escarpment (Bonin Ridge), where we concentrated our dives. We observed lavas and volcaniclastic sequences by the four SHINKAI dives along the escarpment, and 16 fresh basaltic to andesitic lava samples have been recovered. The first three dives appear to have sampled volcanic constructs, of presumed Oligocene age, along the escarpment, whereas the last dive sampled exposures similar to Eocene rocks of the Bonin islands, including nummulitic limestone. The lava samples were analyzed by ICP-MS at Shimane University for 30 incompatible trace elements. All samples show arc-like chemical signatures, including elevated concentrations of LIL elements, depletions in Ta and Nb, and spikes in Pb, Sr, and Li. All samples show modest enrichments in LREE. A lava sample from the northernmost dive #824 is identical with the depleted tholeiite from Haha-jima Islands at the southernmost end of the Bonin Ridge in terms of trace element characteristics. Other lava samples from northern three dives (#823, #824, #825) have tholeiitic affinities with more elevated highly incompatible elements. This suggests derivation of the series of lavas by different degree of partial melting of a similar source mantle. Samples from southernmost dive site #826, immediately northwest of Chichi-jima Islands, are boninites with U-shaped REE patterns and relatively enriched Zr and

  13. Helium- and lead-isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic. Doctoral thesis

    SciTech Connect

    Graham, D.W.

    1987-01-01

    Glassy basalts erupted at young Pacific seamounts and along the mid-ocean ridge in the South Atlantic, and volcanic rocks from the island of St. Helena were studied for He and Pb isotopes. (U+TH)/He ages of seamount alkali basalts were determined from the isotope disequilibrium of (3)He/(4)He between He trapped in vesicles and that dissolved in the glass phase. The method allows alkalic lavas to be dated in the age range of 103 to 106 years. Tholclites at the EPR seamounts have He, Pb, Sr and Nd isotope compositions indistinguishable from MORB, while associated alkali basalts show more radiogenic signatures. The low (3)He/(4)He in the vesicles of alkali basalts (1.2-2.6 RA), their low helium concentrations, and systematic variations with extent of differentiation suggest that magmatic processes influence (3)He/(4)He in these alkalic lavas. Pb-Sr-Nd isotopes at Shimada seamount (17 deg N, 117 deg W) indicate the presence of enriched mantle beneath the East Pacific which resembles that beneath Samoa. Low (3)He/(4)He (4-5 RA) appears to be an inherent characteristic of the component. Much of the South Atlantic ridge axis displays (3)He/(4)He lower than normal MORB, and is apparently contaminated by off-axis hotspots. He-Pb systematics along the ridge suggest that (3)He/(4)He at St. Helena is less than MORB, consistent with values measured by in vacuo crushing of olivine and pyroxene in St. Helena rocks (approx. 5.8 RA).

  14. Tectonic implications of space-time patterns of Cenozoic volcanism in the Palo Verde Mountain volcanic field, southeastern California

    SciTech Connect

    Murray, K.S.

    1981-01-01

    Variations in Cenozoic volcanism in the western United States are believed to correlate closely with changes in tectonic setting. A transition in volcanic association from calc-alkaline to fundamentally basaltic volcanism and subsequent crustal extension, appears to have coincided temporally with the initial collision of the East Pacific Rise with the continental margin trench off western North America, between 28 and 25 Ma. The volcanic stratigraphy of the Palo Verde Mountain volcanic field is broadly similar to other volcanic centers in southeastern California and can be divided into tripartite regional stratigraphy. A basal sequence of andesitic to rhyolitic lava flows, plugs, domes, and extensive pyroclastic deposits rests unconformably on pre-Cenozoic basement rocks. The basal sequence is intruded by cogenetic Cenozoic plutonic rocks and overlain by basaltic to rhyolitic lava flows, dikes, and a second widespread assemblage of pyroclastic deposits, cumulatively referred to as the silicic sequence. The youngest volcanic rocks of the field include olivine basalt flows and breccia which occur at scattered localities in the Palo Verde Mountains. The age, stratigraphy, and chemistry of the intermediate and basaltic composition volcanic rocks broadly supports previously cited volcanic-tectonic models, if modified to incorporate modern plate reconstruction theory. This modification results in a southeast migration of the transition to basaltic volcanism to southeastern California occurring significantly later in time than the previously cited ages of transition. Moreover, this southeast migration of the volcanic transition is coincident with the inception of Basin and Range faulting and the initiation of movement on the San Andreas fault south of the Transverse Ranges, corresponding to the southward migration of the Pacific-Cocos Ridge.

  15. Geochemistry of Phosphorus and Nitrogen in Volcanic Rocks Altered by Submarine Hydrothermal Activities at the Suiyo Seamount in Japan

    NASA Astrophysics Data System (ADS)

    Noda, M.; Kakegawa, T.; Naraoka, H.; Marumo, K.; Urabe, T.

    2002-12-01

    Phosphorus and nitrogen are essential major elements for all microorganisms. In order to understand the ecological conditions of subvent microorganisms and thermophilic microorganisms on ocean floor, it is necessary to understand the behavior of bio-essential elements not only in hydrothermal fluids but also in the subvent environment. Nine sites of hydrothermal discharging area were drilled in the Suiyo volcanic caldera, Izu-Ogasawara (Bonin) island-arc, western Pacific. Approximately 2 to 10 m deep drill core samples were recovered in the last two years. Chemical compositions and hydrothermal mineral assemblages in the drilled core samples were determined by XRF, ICP-MS, and XRD. Morphology of phosphorous-bearing minerals and their chemistry were examined by electron microprobe. Nitrogen isotopes were measured by the EA-IRMS system. Primary igneous-rock texture (such as euhedral plagioclase phenocryst) is found in the less altered rocks. They often associated with montmorillonite. Highly altered rocks are divided into two groups. First group is characterized by extensive (up to 90%) replacement of primary igneous mineral assemblage by chlorite, mica and sulfide. Second group is cemented with large amounts of sulfates with sulfide (mainly pyrite). It is found in a few drill core sections that hydrothermal hydrous silicate minerals change with depth from montmorillonite to chlorite and mica through mixed layer of chlorite/montmorillonite. This may suggest the more extensive and higher temperature alteration in deeper zones in a certain area. Electron microprobe analyses and bulk chemical composition indicate that the depletion of phosphorous in altered rocks (below 0.1 wt%) but enrichment of phosphorous in sulfide zones. This suggests that phosphorous was easily dissolved from igneous rocks by hydrothermal process, but readily precipitated with sulfides. The reason for co-precipitation of phosphates with sulfides is not certain, but such co-precipitation mechanism

  16. Petrogenesis of the early Cretaceous volcanic rocks in the North Huaiyang tectono-magmatic unit of the Dabie Orogen, eastern China: Implications for crust-mantle interaction

    NASA Astrophysics Data System (ADS)

    Gao, Xin-Yu; Zhao, Tai-Ping; Zhao, Jun-Hong

    2016-03-01

    New elemental and isotopic data are presented for the early Cretaceous felsic to mafic volcanic rocks in the North Huaiyang tectono-magmatic unit (NHY) of the Dabie Orogen, in order to investigate their petrogenesis and provide insights into the nature of the late Mesozoic lithosphere mantle beneath the region and its tectonic relationship with neighboring blocks. LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Jingangtai Formation erupted in a quite short interval about 5 Mys during the Early Cretaceous (128-123 Ma). The rocks have wide ranges of SiO2 (48-68 wt.%) and MgO (0.6-5.6 wt.%) contents. They are enriched in large-ion-lithophile-elements (LILE) (e.g. Rb, Ba) and light rare-earth-elements (LREE), and depleted in high field strength elements (e.g. Nb, Ta and Ti) with weak negative Eu anomalies (Eu/Eu∗ = 0.71-0.94). Meanwhile, the rocks show relatively high whole-rock initial 87Sr/86Sr ratios (0.7074-0.7094), strong negative εNd(t) (-19.1 to -15.8) and zircon εHf values (-20.7 to -14.1). Such typical "continental" geochemical characteristics did not result from crustal contamination during magma ascent, but from an enriched mantle source modified by materials from the subducted Yangtze Craton during the Triassic continental collision. We propose that the petrogenesis of the large-scale contemporaneous magmatism of Dabie Orogen including felsic to mafic volcanic rocks in the NHY reflects an intensive lithospheric thinning and extension during the early Cretaceous as a tectonic response to the change of plate motion of westward subducted Pacific Plate beneath the Eurasian continent.

  17. Petrogenesis of Middle-Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: Implications for early subduction of Neo-Tethyan oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Ding, Lin; Zhang, Li-Yun; Kapp, Paul; Pullen, Alex; Yue, Ya-Hui

    2016-10-01

    The Gangdese belt is dominantly composed of igneous rocks that formed during the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane and has played a crucial role in understanding the pre-collisional evolution of southern Tibet. This paper presents new geochronological and geochemical (whole-rock major and trace element and Sr-Nd and zircon Hf isotope) data for recently identified volcanic rocks exposed in Changguo area, southernmost part of the Lhasa terrane. Zircon U-Pb dating from six samples yields consistent ages of 237.1 ± 1.1 Ma to 211.7 ± 1.5 Ma for magma emplacement through volcanic eruption, showing the Middle-Late Triassic magmatic activity in the southernmost Gangdese Belt. The Changguo volcanic rocks are mainly composed of basaltic and andesitic rocks and exhibit LILE enrichment and HFSE depletion. They also exhibit relatively uniform Nd-Hf isotopic compositions (εNd(t) = + 5.20 to + 7.74 and εHf(t)zircon = + 10.2 to + 15.9). The basaltic magmas were likely sourced from partial melting of sub-arc mantle wedge that was metasomatized by not only the aqueous fluid derived from subducting altered oceanic crust but also hydrous melt derived from subducting seafloor sediments, and subsequently experienced fractional crystallization and juvenile crustal contamination during ascent. The andesitic magmas were generated by partial melting of mafic-ultramafic metasomes through melt/fluid-peridotite reaction at slab-mantle interface. Taking into account the temporal and spatial distribution of the Early Mesozoic magmatic rocks and regional detrital zircon data, we further propose that the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane commenced by Middle Triassic.

  18. Petrogenesis of Challis Volcanic Group, east-central Idaho

    NASA Astrophysics Data System (ADS)

    Schleiffarth, W. K.; Larson, P. B.

    2013-12-01

    The Eocene Challis-Kamloops volcanic belt (CKVB) extends south and east from northern British Columbia to central Idaho and is related to the paleotectonic plate interaction between the Farallon and North American plates. Numerous volcanic fields are scattered throughout the CKVB and show a wide range of eruption styles, tectonic environments, and geochemical compositions. Several volcanic fields produced calc-alkaline rocks, while others produced moderately to strongly alkaline rocks. Some volcanic fields have a significant slab component, while others show no direct evidence of subduction-related magmatism. Proposed models for tectonic controls on the CKVB include continental volcanic arc delamination of subducted slab, rifted arc, slab window, and extensional continental tectonism. However, there is no generally accepted explanation for the petrogenesis of the CKVB. The Challis Volcanic Group (CVG) of central Idaho, located in the southern portion of the belt, is the largest of the Eocene volcanic fields (25,000 km2). The CVG is of interest because it exhibits very diverse volcanic deposits and compositions and may accurately represent the CKVB. Challis volcanism was synchronous with extension along the NE-SW-trending trans-Challis fault system and resulted in similarly oriented normal faults, dikes, calderas, and exhumation of the Pioneer core complex. The CVG covers much of central Idaho with exposures extending from the Sawtooth Mountains in the west to the Lemhi and Beaverhead ranges to the east. The CVG has high alkaline contents relative to calc-alkaline subduction-related volcanic rocks, varying isotopic signatures, and prevalent extensional features. These facts, coupled with the lack of obvious orientation of volcanic fields throughout the CKVB, explain why the petrogenesis of Eocene volcanism of the inland Pacific Northwest is controversial. Rare earth element concentrations and Sr, Nd, and Pb isotope ratios show that the CVG represents a mixture of

  19. Quantifying effects of humans and climate on groundwater resources through modeling of volcanic-rock aquifers of Hawaii

    NASA Astrophysics Data System (ADS)

    Rotzoll, K.; Izuka, S. K.; Nishikawa, T.; Fienen, M. N.; El-Kadi, A. I.

    2015-12-01

    The volcanic-rock aquifers of Kauai, Oahu, and Maui are heavily developed, leading to concerns related to the effects of groundwater withdrawals on saltwater intrusion and streamflow. A numerical modeling analysis using the most recently available data (e.g., information on recharge, withdrawals, hydrogeologic framework, and conceptual models of groundwater flow) will substantially advance current understanding of groundwater flow and provide insight into the effects of human activity and climate change on Hawaii's water resources. Three island-wide groundwater-flow models were constructed using MODFLOW 2005 coupled with the Seawater-Intrusion Package (SWI2), which simulates the transition between saltwater and freshwater in the aquifer as a sharp interface. This approach allowed relatively fast model run times without ignoring the freshwater-saltwater system at the regional scale. Model construction (FloPy3), automated-parameter estimation (PEST), and analysis of results were streamlined using Python scripts. Model simulations included pre-development (1870) and current (average of 2001-10) scenarios for each island. Additionally, scenarios for future withdrawals and climate change were simulated for Oahu. We present our streamlined approach and preliminary results showing estimated effects of human activity on the groundwater resource by quantifying decline in water levels, reduction in stream base flow, and rise of the freshwater-saltwater interface.

  20. Database for the geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington

    USGS Publications Warehouse

    Barron, Andrew D.; Ramsey, David W.; Smith, James G.

    2014-01-01

    This digital database contains information used to produce the geologic map published as Sheet 1 in U.S. Geological Survey Miscellaneous Investigations Series Map I-2005. (Sheet 2 of Map I-2005 shows sources of geologic data used in the compilation and is available separately). Sheet 1 of Map I-2005 shows the distribution and relations of volcanic and related rock units in the Cascade Range of Washington at a scale of 1:500,000. This digital release is produced from stable materials originally compiled at 1:250,000 scale that were used to publish Sheet 1. The database therefore contains more detailed geologic information than is portrayed on Sheet 1. This is most noticeable in the database as expanded polygons of surficial units and the presence of additional strands of concealed faults. No stable compilation materials exist for Sheet 1 at 1:500,000 scale. The main component of this digital release is a spatial database prepared using geographic information systems (GIS) applications. This release also contains links to files to view or print the map sheet, main report text, and accompanying mapping reference sheet from Map I-2005. For more information on volcanoes in the Cascade Range in Washington, Oregon, or California, please refer to the U.S. Geological Survey Volcano Hazards Program website.

  1. Comprehensive Paleomagnetic Study of the Oligocene-Miocene Rocks from the San Luis Potosí Volcanic Field, Mexico

    NASA Astrophysics Data System (ADS)

    Alva-Valdivia, L. M.; Gonzalez-Rangel, J. A.; Torres-Hernandez, J. R.

    2014-12-01

    Comprehensive paleomagnetic study of the Oligocene-Miocene sequence of lithological units from the San Luis Potosí volcanic field in central Mexico was accomplished to set up the magnetostratigraphic record. Two hundred and one oriented standard paleomagnetic cores corresponding to twenty-eight paleomagnetic sites were collected from all units. Rock-magnetic properties are characteristic for each unit. Isothermal remanent magnetization acquisition curves and continuous susceptibility vs. temperature experiments point from low to medium-Ti content in titanomagnetite as the main opaque magnetic minerals, presumably result from oxy-exsolution processes during the initial flow cooling. Opaque mineral microscopy supports this assumption. Unblocking temperature and hysteresis parameters suggests predominance of pseudo-single domain magnetic grain size. Thermal and alternating field demagnetizations show mostly well-defined univectorial magnetizations. Most sites present a mean direction with small angular dispersion. The overall mean direction (N=10, Dec=1.1°, Inc=34.1°, k=531 and α95=2.1°) is characterized by small angular dispersion and inclination close to dipolar value for the locality. Anisotropy of magnetic susceptibility lineation match the geologically inferred flow direction.

  2. Chlorine isotope composition of volcanic gases and rocks at Mount Etna (Italy) and inferences on the local mantle source

    NASA Astrophysics Data System (ADS)

    Rizzo, Andrea L.; Caracausi, Antonio; Liotta, Marcello; Paonita, Antonio; Barnes, Jaime D.; Corsaro, Rosa A.; Martelli, Mauro

    2013-06-01

    We present the first chlorine isotope compositional data for gases and lavas from Mount Etna (Italy), and to our knowledge, of active Mediterranean volcanism. We investigated lavas erupted and gases discharged during 2008-2011 from a high-temperature fumarole (HT; >300 °C) and plume gases from both North East and Central Craters. Most of the samples vary in a narrow range of chlorine isotope composition (δ37Cl values≈0±0.7‰) with gases partially overlapping with rocks. Only HT gases sampled in 2009 have been clearly affected by secondary processes (δ37Cl values>15.9‰), resulting in partial removal of chlorine and isotopic fractionation producing a 37Cl enrichment in the residual gaseous HCl. These secondary processes also affect, although to a lesser extent, plume gases from North East Crater (NEC). Although post-magmatic processes are able to modify the chlorine isotope composition, δ37Cl values are not affected by magma degassing for residual fractions ≥0.3 in the melt, or any effect is within our data variability. Finally, δ37Cl values and Cl/K ratios of magmatic chlorine constrain the Etnean source to be compatible with depleted mantle (DMM) contaminated by altered oceanic crust (AOC), in agreement with indications from more common isotopic tracers of mantle processes.

  3. U-series disequilibria in volcanic rocks from the Futuna spreading centre (North Fiji Basin)

    NASA Astrophysics Data System (ADS)

    Le Faouder, A.; Hemond, C.; Benoit, M.; Lagabrielle, Y.; Guivel, C.; Pelletier, B.; Bollinger, C.

    2005-05-01

    The North Fiji basin is the largest active back arc basin of the SW Pacific. It is 12 m.y. old and characterised by a regional upper mantle thermal anomaly (Garel, 2001). The 200Km long Futuna spreading centre (Pelletier et al., 2001) is located west of Futuna and Alofi islands at the border between Lau and North Fijian Basins. This ridge is composed of an axial valley spotted with numerous seamounts. It starts from the north of the Fiji platform (15° 40'S) and ends in the north Fiji transform zone, northwest of the Futuna and Alofi islands (13° 35'S). New U series measurements were performed by TIMS on fresh dredged glassy samples. As the topography of this spreading centre exhibits a peculiar structure, the geochemical signature is also unusual. U and Th concentrations range between 0,0930%, six have a 230Th excess within 25 ± 5% and three have 230Th excess of about 15%. These 230Th excesses are typical of MORB or OIB source melting and not a back arc volcanic processes. It is also symptomatic of a melting in presence of garnet. In the equiline diagram, samples fall on a linear correlation indicating a mixing between two end-members with different Th/Usources ratios. The trend observed in this diagram requires the involvement of an enriched component, likely an EMII component, as defined by the trace elements and Sr-Nd-Pb isotope compositions (Benoit et al., in prep). This trend falls within the OIB field and plots close to Samoan samples analysed by Newman et al. (1984). This trend demonstrates the influence of a melt may be even more enriched than the samples of Savai'i volcano. This EMII melt mixes, within the upper mantle, with the Indian ocean like component as it was already established that

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

    NASA Astrophysics Data System (ADS)

    Fragoulis, Dimitris; Stamatakis, Michael; Anastasatou, Marianthi

    2015-04-01

    Cements currently produced, include a variety of pozzolanic materials, aiming for lower clinker addition and utilization of vast deposits of certain raw materials and/or mining wastes and byproducts. The major naturally occurring pozzolanic materials include glassy tuffs, zeolitic tuffs, diatomites and volcanic lavas rich in glassy phase, such as perlites. Therefore, based on the available raw materials in different locations, the cement composition might vary according to the accessibility of efficient pozzolanic materials. In the present investigation, the behavior of pozzolanic cements produced with representative samples of the aforementioned materials was studied, following the characterization of the implemented pozzolanas with respect to their chemical and mineralogical characteristics. Laboratory cements were produced by co-grinding 75% clinker, 5% gypsum and 20% pozzolana, for the same period of time (45 min). Regarding pozzolanic materials, four different types of pozzolanas were utilized namely, diatomite, perlite, zeolite tuff and glassy tuff. More specifically, two diatomite samples originated from Australia and Greece, with high and low reactive silica content respectively, two perlite samples originated from Turkey and from Milos Island, Greece, with different reactive silica contents, a zeolite tuff sample originated from Turkey and a glassy tuff sample originated from Milos Island, Greece. The above pozzolana samples, which were ground in the laboratory ball mill for cement production performed differently during grinding and that was reflected upon the specific surface area (cm2/gr) values. The perlites and the glassy tuff were the hardest to grind, whereas, the zeolite tuff and the Australian diatomite were the easiest ones. However, the exceedingly high specific surface area of the Australian diatomite renders cement difficult to transport and tricky to use for concrete manufacturing, due to the high water demand of the cement mixture. Regarding

  5. A simple model of 222Rn accumulation leading to 210Pb excesses in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Condomines, M.; Sigmarsson, O.; Gauthier, P. J.

    2010-05-01

    While most rocks from active volcanoes display (210Pb/226Ra) activity ratios lower than or close to the equilibrium value of 1, several other have ratios much higher than 1. Transfer of 222Rn by magmatic volatiles has often been advocated to explain both 210Pb deficits and excesses. We develop here a model to account for 210Pb excesses through 222Rn accumulation. We show that large 210Pb excesses can be readily obtained, even for moderate ratios of degassing magma over accumulating magma, in a closed-system model where the 222Rn atoms produced by decay of 226Ra in the degassing magma are continuously extracted by a gas phase. For a given duration of volatile transfer, relative 210Pb excesses are expected to be much larger than 210Pb deficits. This model is applied to samples from Santorini (Aegean arc) and Surtsey (Iceland) both of which show high (210Pb/226Ra) ratios of 6.7 and 2.3 respectively at the time of eruption. The agreement with field data suggests that 222Rn accumulation leading to 210Pb excesses might be a rather common process in zoned magma chambers as well as in individual lava flows, and that it can be described by a closed-system model.

  6. Analysis of the rock mechanics properties of volcanic tuff units from Yucca Mountain, Nevada Test Site

    SciTech Connect

    Price, R. H.

    1983-08-01

    Over two hundred fifty mechanical experiments have been run on samples of tuff from Yucca Mountain, Nevada Test Site. Cores from the Topopah Spring, Calico Hills, Bullfrog and Tram tuff units were deformed to collect data for an initial evaluation of mechanical (elastic and strength) properties of the potential horizons for emplacement of commercial nuclear wastes. The experimental conditions ranged in sample saturation from room dry to fully saturated, confining pressure from 0.1 to 20 MPa, pore pressure from 0.1 to 5 MPa, temperature from 23 to 200{sup 0}C, and strain rate from 10{sup -7} to 10{sup -2} s{sup -1}. These test data have been analyzed for variations in elastic and strength properties with changes in test conditions, and to study the effects of bulk-rock characteristics on mechanical properties. In addition to the site-specific data on Yucca Mountain tuff, mechanical test results on silicic tuff from Rainier Mesa, Nevada Test Site, are also discussed. These data both overlap and augment the Yucca Mountain tuff data, allowing more definitive conclusions to be reached, as well as providing data at some test conditions not covered by the site-specific tests.

  7. The Eldivan ophiolite and volcanic rocks in the İzmir-Ankara-Erzincan suture zone, Northern Turkey: Geochronology, whole-rock geochemical and Nd-Sr-Pb isotope characteristics

    NASA Astrophysics Data System (ADS)

    Çelik, Ömer Faruk; Chiaradia, Massimo; Marzoli, Andrea; Billor, Zeki; Marschik, Robert

    2013-07-01

    Gabbros and dolerite dikes of the Eldivan ophiolite and basaltic volcanic rocks of the ophiolitic mélange in the central part of the İzmir-Ankara-Erzincan (IAE) suture zone were investigated for their 40Ar/39Ar age and whole-rock-major-trace element and Sr-Nd-Pb isotope compositions. Based on geological and geochemical characteristics basaltic volcanic rocks in the ophiolitic mélange are subdivided into two groups (Groups I and II) with ocean island basalts or enriched mid-ocean ridge basalt characteristics, respectively. Gabbros and dolerite dikes of the Eldivan ophiolite (Groups III and IV) have instead geochemical compositions indicative of a subduction-related environment. The volcanic rocks of Group I have 87Sr/86Sr(i) between 0.7037 and 0.7044, ƐNd(i)-DM of - 4.5 to - 5.6, and 206Pb/204Pb(i) ranging between 18.35 and 18.75. Group II volcanic rocks have higher 87Sr/86Sr(i) values (0.7049-0.7055), ƐNd(i)-DM ranging between - 5.4 and - 6.0, and 206Pb/204Pb(i) between 18.14 and 18.62. The Nd isotopic signatures and 207Pb/204Pb(i) values of the volcanic rocks of both groups point to a different source with respect to those of the Eldivan ophiolite. The low 206Pb/204Pb(i) values relative to the ophiolitic rocks seem to exclude a significant contribution from a HIMU reservoir, whereas the 207Pb/204Pb(i) values slightly above the NHRL might indicate some contribution from an EM2-type reservoir. Gabbros (Group III) of the Eldivan ophiolite and dolerite dikes (Group IV) cross-cutting the ultramafic part of the ophiolite show 87Sr/86Sr(i) between 0.7038 and 0.7053, ƐNd(i)-DM from - 2 to - 3.6 and 206Pb/204Pb(i) between 18.10 and 18.80. The gabbros yield ca. 150 Ma 40Ar/39Ar amphibole-plateau ages, which, together with the geochemical data, indicate that they were produced above subducted oceanic lithosphere in the IAE ocean domain in Late Jurassic times. Therefore, the Eldivan ophiolite in the IAE suture zone constitutes a link between the Hellenide

  8. Petrology and age of volcanic-arc rocks from the continental margin of the Bering Sea: implications for Early Eocene relocation of plate boundaries

    USGS Publications Warehouse

    Davis, A.S.; Pickthorn, L.-B.G.; Vallier, T.L.; Marlow, M. S.

    1989-01-01

    Eocene volcanic flow and dike rocks from the Beringian margin have arc characteristics, implying a convergent history for this region during the early Tertiary. Chemical and mineralogical compositions are similar to those of modern Aleutian-arc lavas. They also resemble volcanic-arc compositions from western mainland Alaska, although greater chemical diversity and a stronger continental influence are observed in the Alaskan mainland rocks. Early Eocene ages of 54.4-50.2 Ma for the Beringian samples are well constrained by conventional K-Ar ages of nine plagioclase separates and by concordant 40Ar/39Ar incremental heating and total-fusion experiments. A concordant U-Pb zircon age of 53 Ma for the quartz-diorite dike is in good agreement with the K-Ar data. Plate motion studies of the North Pacific Ocean indicate more northerly directed subduction prior to the Tertiary and a continuous belt of arc-type volcanism extending from Siberia, along the Beringian margin, into mainland Alaska. Around 56 Ma (chron 25-24), subduction changed to a more westerly direction and subduction-related volcanism ceased for most of mainland Alaska. The increasingly oblique angle of convergence should have ended subduction along the Beringian margin as well. However, consistent ages of 54-50 Ma indicate a final pulse in arc-type magmatism during this period of plate adjustment. -from Authors

  9. Stratigraphy, regional distribution, and reconnaisance geochemistry of Oligocene and Miocene volcanic rocks in the Paradise Range and northern Pactolus Hills, Nye County, Nevada

    SciTech Connect

    Not Available

    1992-01-01

    In this paper, stratigraphy, geochronology, and geochemistry of about 40 units of Oligocene and Miocene silicic ash-flow tuff, intermediate to silicic lava, and minor sedimentary rock exposed in three stratigraphic sections are described. The distribution and sources of five regionally widespread ash-flow tuff units were delineated. The late Cenozoic volcanic and tectonic history of the Paradise Range and northern Pactolus Hills was compared to other areas in the Great Basin.

  10. Zircon age and geochemistry of the Tost bimodal volcanic rocks: Constraints on the Early Carboniferous tectonic evolution of the South Mongolia

    NASA Astrophysics Data System (ADS)

    Yang, Shunhu; Miao, Laicheng; Zhang, Fochin; Meng, Qingren; Zhu, Mingshuai; Baatar, Munkhtsengel; Anaad, Chimedtseren

    2016-04-01

    SIMS zircon U-Pb dating, geochemical and Sr-Nd isotopic data are presented for the Late Paleozoic volcanic rocks from Tost area in Mongolia, the southern portion of the Central Asian Orogenic Belt (CAOB). The Tost volcanic rocks show a bimodal feature characterized by a mafic member of basalt and a felsic component of rhyolite, which are temporally and spatially related each other, implying a genetic relationship. Zircon U-Pb isotopic data of the rhyolite constrain the Tost bimodal magmatism occurring from 355 Ma to 320 Ma. The Tost basalt is characterized by high abundances in Th, U and Pb, slightly enriched LREE patterns and low HFSE/LREE ratios. These features, together with their OIB-like isotopic signature ((87Sr/86Sr)i = 0.7039378-0.704397, εNd(t) = 3.55-5.02), suggest that they were likely derived from low-degree partial melting of a metasomatized asthenospheric mantle source with subordinate input of subduction components. The Tost rhyolite, which displays an intimate affinity to Tost basalt, with enrichment in Th, U and Pb, depleted in Nb, Ta and Ti, and gently right-tilted REE patterns, is inferred to be generated by partial melting of a juvenile lower crustal source heated by underplating mafic magmas which rise from asthenosphere during continued rifting. The Tost bimodal volcanic rocks are comparable both in age and composition with those in the East Tianshan, which together constitute an E-W-oriented belt of bimodal volcanic rocks, marking an Early Carboniferous rifting event. Considering regional geology, we propose that the rifting took place in a back-arc extensional setting, probably induced by the subduction of the Dzungaria Ocean between the East Tianshan and Junggar-Kazakhstan plate during the Early Carboniferous.

  11. In-situ petrophysical properties of volcanic rocks from Detroit Seamount (ODP-Leg 197, Site 1203A)

    NASA Astrophysics Data System (ADS)

    Kock, I.; Buysch, A.; Pechnig, R.

    2002-12-01

    During Leg 197 an extensive logging program was performed on Site 1203A after drilling was completed on Detroit Seamount to a total depth of 914.6 mbsf. Logging comprised measurements with the ODP/LDEO standard logging tool strings triple combo and FMS/sonic (see: http://www.ldeo.columbia.edu/BRG/ODP/). Logging data imply a classification of the drilled lithology into five groups: three types of sedimentary rocks and two types of basaltic rocks. Non-volcanic sediments, determined down to a depth of 457 mbsf, exhibit constant and low gamma ray values (<15 gAPI). A strong increase in p-wave velocity (3.12 \\pm1.15 km/s) between 388.2-393.5 mbsf correlates with the 388-mbsf reflector in seismic profiles. A gradual increase in density from 1.3 g/ccm to 1.8 g/ccm, and a decrease in porosity from 92.7 % to 69 % with depth record expected consolidation and compaction effects. FMS pictures and standard logging tool data mark the sediment - basement boundary at 464.5 mbsf. A transition zone between 464.5-468.5 mbsf reveals high porosity/low density, high gamma-ray/low resistivity data, which is probably caused by alteration. The basement is characterised by an interlayered succession of volcanoclastic rocks and basaltic lava flows. Lava flows of type B-I are marked by a bimodal data distribution of resistivity (68.80 +/-2.41 ohmm) and porosity (21.71 +/-8.27 %) with maximum values for resistivity at 32 ohmm and 100 ohmm, and for porosity at 11 % and 19.5 %. Usually, basaltic lava exhibits low gamma-ray values as observed for rocks of the B-I flow type (18.75 +/-7.32 gAPI). Instead, lava flows of type B-II show higher gamma-ray data of 28 gAPI (\\pm5.92). This flow type occurs in the lower basement part between 761-920 mbsf and could be target of an increased alteration. It reveals higher porosity (36.56 +/-10.03 %), caused by a high vesicularity, and lower density (2.33 +/-0.18 g/ccm) values than the B-I flows (density = 2.60 \\pm0.16 g/ccm). Resistivity and porosity data

  12. An insight to the eruption mechanism of volcanic rocks in North Tibet: Project TITAN

    NASA Astrophysics Data System (ADS)

    He, R.; Gao, R.; Li, Q.

    2013-12-01

    Since Cenozoic continent-continental collision between India and Asia [Yin and Harrison, 2000], many surface features happened within the plateau were prominent. As one of them, high-to-ultra potassic lavas of Neogene, even younger, are widely distributed in NW Tibet, as shown in Figure1. Obvious petrological and geochemical characteristics of those lavas [Turner et al., 1993; Deng et al., 1996; Hacker et al., 2000; Ding et al., 2003; Williams et al., 2004; Chung et al., 2005; Luo et al., 2006; Guo et al., 2006] were presumably associated with extensional collapse of the lithospheric mantle [Deng et al., 1998; Li et al., 2000; Ding et al., 2003; Williams et al., 2004; Chung et al., 2005; Luo et al., 2006; Guo et al., 2006], which started at about 4Ma [Yin et al., 1999] and still goes on [Lin et al., 2002]. (1) What kinetics happened within the lithosphere beneath the lava region since Late Neogene? (2) What kind of mechanism leads to the lava eruption, it is only the result of far-long effect of northward subduction of the India plate, or directly related to the south margin of the Asian lithosphere, or bilaterally affected by India and Asia plate, or other factors? (3) Why did the strong volcanic activities only wrecked the North Qiangtang terrane, Jinshajiang suture and Hoh Xil terrane, instead of going northward across Altyn Tagh Fault and East Kunlun? As is known, to reveal the scientific secret concealed in lavas within NW Tibet geophysical observations are very necessary and urgent. NW Tibet including North Qiangtang and Hoh Xil is a very tough region for human beings. The project for geophysical observatory in the region is named as TITAN. TITAN has currently made some great progress, such as 103 broadband Seismic observation stations were deployed along longitude 88.5E in recent 5 years, as shown in Figure 1. Some primary results were got, such as (1) P-velocity structure from teleseismic tomography around Shuanghu in central Qiangtang (Figure 2) showed

  13. Using high-resolution aeromagnetic data to recognise and map intra-sedimentary volcanic rocks and geological structures across the Cretaceous middle Benue Trough, Nigeria

    NASA Astrophysics Data System (ADS)

    Anudu, Goodluck K.; Stephenson, Randell A.; Macdonald, David I. M.

    2014-11-01

    Recently acquired high-resolution aeromagnetic data over the Cretaceous middle Benue Trough of Nigeria have been analysed employing various edge-enhancement (magnetic derivative) methods: vertical derivatives, total horizontal derivative, analytic signal, and total horizontal derivative of tilt derivative. The study was aimed at mapping intra-sedimentary volcanic rocks and their areal extents/distribution as well as delineating geological structures, their structural trends and tectonic implications. The magnetic derivative anomaly maps produced in this project greatly enhanced the high amplitude, short-wavelength (high wavenumber) anomalies associated with the surface/near-surface intra-sedimentary volcanic rocks and associated geological structures. The maps show that volcanic rocks of Late Cretaceous to Palaeocene age are much more widespread than implied by surface geological mapping, with an areal extent of greater than 12,000 km2 in the relatively shallow subsurface. The results also highlight some known and several previously unknown geological lineaments. Rose (azimuth-frequency) plots of orientations of geological structures show trends being predominantly NE-SW, NW-SE and ESE-WNW with minor ENE-WSW and N-S trends. These main groups of structural trends are associated with the Brasiliano/Pan-African orogeny (600 ± 200 Ma) and likely predate rifting of the Gondwana supercontinent. They may have been enhanced during continental break-up in Late Jurassic to Early Cretaceous.

  14. The quality of our Nation's waters: groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers and the Hawaiian volcanic-rock aquifers, Washington, Idaho, and Hawaii, 1993-2005

    USGS Publications Warehouse

    Rupert, Michael G.; Hunt, Charles D.; Skinner, Kenneth D.; Frans, Lonna M.; Mahler, Barbara J.

    2015-01-01

    The Columbia Plateau, Snake River Plain, and Hawaii are large volcanic areas in the western United States and mid-Pacific ocean that contain extensive regional aquifers of a hard, gray, volcanic rock called basalt. Residents of the Columbia Plateau, the Snake River Plain, and the island of Oahu depend on groundwater as their primary source of drinking water. Although the depth to the water table can be several hundred feet, the groundwater is highly vulnerable to contamination because the permeable sediments and rocks allow contaminants to move readily down to the water table. Intense agricultural and urban activities occur above the drinking-water supply and are increasing in some areas. Contaminants, such as nitrate, pesticides, and volatile organic compounds, associated with agricultural and urban activities, have adversely affected groundwater quality.

  15. Tectonic and magmatic evolution of the northwestern Basin and Range and its transition to unextended volcanic plateaus: Black Rock Range, Nevada

    USGS Publications Warehouse

    Lerch, D.W.; Miller, E.; McWilliams, M.; Colgan, J.

    2008-01-01

    The seismically active eastern and western margins of the northern Basin and Range have been extensively studied, yet the northwestern margin of the province remains incompletely understood. The Black Rock Range of northwestern Nevada straddles the transition from the Basin and Range province to the south and east, and flat-lying volcanic plateaus to the west. This poorly understood range preserves a remarkably complete record of Cenozoic magmatism and provides an important window into the pre-Miocene history of the unextended volcanic plateaus of northeastern California and southern Oregon. Geologic mapping and 40Ar/39Ar geochronology from the northern Black Rock Range document three significant episodes of Eocene to middle Miocene volcanism. Eocene (35 Ma) basalts directly overlie Mesozoic granites and arc-related volcanic and sedimentary rocks. Locally erupted Oligocene to early Miocene (27-21 Ma) bimodal volcanic rocks comprise the bulk of the Cenozoic section and conformably overlie the Eocene basalt flows. These bimodal units include rhyolitic lavas, variably welded rhyolitic ash flows, unwelded ash-fall deposits, and thin basalt flows. In the neighboring Pine Forest Range ???20 km to the north, similar Oligocene to early Miocene units are overlain by more than 500 m of ca. 16.4 Ma Steens-equivalent basalt flows and are capped by ca. 16 Ma rhyolitic ash-flow tuffs. In the northern Black Rock Range, the ca. 16.4 Ma middle Miocene basalts are absent from the section, and a 16.2 Ma rhyolitic ash-flow tuff directly overlies the early Miocene flows. Basaltic and rhyolitic volcanic products in the northern Black Rock Range span 35-16 Ma, with many of the Oligocene volcanic units derived from local vents and dikes. Despite the map-scale complexities of locally derived lava flows, the Cenozoic section is broadly conformable and dips gently (???5??-10??) to the northwest. The region experienced no significant tilting between 35 and 16 Ma, with moderate tilting (???5

  16. Rocks.

    ERIC Educational Resources Information Center

    Lee, Alice

    This science unit is designed for limited- and non-English speaking students in a Chinese bilingual education program. The unit covers rock material, classification, characteristics of types of rocks, and rock cycles. It is written in Chinese and simple English. At the end of the unit there is a list of main terms in both English and Chinese, and…

  17. Spirit Discovers New Class of Igneous Rocks

    NASA Technical Reports Server (NTRS)

    2006-01-01

    During the past two-and-a-half years of traversing the central part of Gusev Crater, NASA's Mars Exploration Rover Spirit has analyzed the brushed and ground-into surfaces of multiple rocks using the alpha particle X-ray spectrometer, which measures the abundance of major chemical elements. In the process, Spirit has documented the first example of a particular kind of volcanic region on Mars known as an alkaline igneous province. The word alkaline refers to the abundance of sodium and potassium, two major rock-forming elements from the alkali metals on the left-hand side of the periodic table.

    All of the relatively unaltered rocks -- those least changed by wind, water, freezing, or other weathering agents -- examined by Spirit have been igneous, meaning that they crystallized from molten magmas. One way geologists classify igneous rocks is by looking at the amount of potassium and sodium relative to the amount of silica, the most abundant rock-forming mineral on Earth. In the case of volcanic rocks, the amount of silica present gives scientists clues to the kind of volcanism that occurred, while the amounts of potassium and sodium provide clues about the history of the rock. Rocks with more silica tend to erupt explosively. Higher contents of potassium and sodium, as seen in alkaline rocks like those at Gusev, may indicate partial melting of magma at higher pressure, that is, deeper in the Martian mantle. The abundance of potassium and sodium determines the kinds of minerals that make up igneous rocks. If igneous rocks have enough silica, potassium and sodium always bond with the silica to form certain minerals.

    The Gusev rocks define a new chemical category not previously seen on Mars, as shown in this diagram plotting alkalis versus silica, compiled by University of Tennessee geologist Harry McSween. The abbreviations 'Na2O' and 'K2O' refer to oxides of sodium and potassium. The abbreviation 'SiO2' refers to silica. The abbreviation 'wt

  18. Matrix diffusion coefficients in volcanic rocks at the Nevada test site: influence of matrix porosity, matrix permeability, and fracture coating minerals.

    PubMed

    Reimus, Paul W; Callahan, Timothy J; Ware, S Doug; Haga, Marc J; Counce, Dale A

    2007-08-15

    Diffusion cell experiments were conducted to measure nonsorbing solute matrix diffusion coefficients in forty-seven different volcanic rock matrix samples from eight different locations (with multiple depth intervals represented at several locations) at the Nevada Test Site. The solutes used in the experiments included bromide, iodide, pentafluorobenzoate (PFBA), and tritiated water ((3)HHO). The porosity and saturated permeability of most of the diffusion cell samples were measured to evaluate the correlation of these two variables with tracer matrix diffusion coefficients divided by the free-water diffusion coefficient (D(m)/D*). To investigate the influence of fracture coating minerals on matrix diffusion, ten of the diffusion cells represented paired samples from the same depth interval in which one sample contained a fracture surface with mineral coatings and the other sample consisted of only pure matrix. The log of (D(m)/D*) was found to be positively correlated with both the matrix porosity and the log of matrix permeability. A multiple linear regression analysis indicated that both parameters contributed significantly to the regression at the 95% confidence level. However, the log of the matrix diffusion coefficient was more highly-correlated with the log of matrix permeability than with matrix porosity, which suggests that matrix diffusion coefficients, like matrix permeabilities, have a greater dependence on the interconnectedness of matrix porosity than on the matrix porosity itself. The regression equation for the volcanic rocks was found to provide satisfactory predictions of log(D(m)/D*) for other types of rocks with similar ranges of matrix porosity and permeability as the volcanic rocks, but it did a poorer job predicting log(D(m)/D*) for rocks with lower porosities and/or permeabilities. The presence of mineral coatings on fracture walls did not appear to have a significant effect on matrix diffusion in the ten paired diffusion cell experiments

  19. Matrix diffusion coefficients in volcanic rocks at the Nevada test site: Influence of matrix porosity, matrix permeability, and fracture coating minerals

    NASA Astrophysics Data System (ADS)

    Reimus, Paul W.; Callahan, Timothy J.; Ware, S. Doug; Haga, Marc J.; Counce, Dale A.

    2007-08-01

    Diffusion cell experiments were conducted to measure nonsorbing solute matrix diffusion coefficients in forty-seven different volcanic rock matrix samples from eight different locations (with multiple depth intervals represented at several locations) at the Nevada Test Site. The solutes used in the experiments included bromide, iodide, pentafluorobenzoate (PFBA), and tritiated water ( 3HHO). The porosity and saturated permeability of most of the diffusion cell samples were measured to evaluate the correlation of these two variables with tracer matrix diffusion coefficients divided by the free-water diffusion coefficient ( Dm/ D*). To investigate the influence of fracture coating minerals on matrix diffusion, ten of the diffusion cells represented paired samples from the same depth interval in which one sample contained a fracture surface with mineral coatings and the other sample consisted of only pure matrix. The log of ( Dm/ D*) was found to be positively correlated with both the matrix porosity and the log of matrix permeability. A multiple linear regression analysis indicated that both parameters contributed significantly to the regression at the 95% confidence level. However, the log of the matrix diffusion coefficient was more highly-correlated with the log of matrix permeability than with matrix porosity, which suggests that matrix diffusion coefficients, like matrix permeabilities, have a greater dependence on the interconnectedness of matrix porosity than on the matrix porosity itself. The regression equation for the volcanic rocks was found to provide satisfactory predictions of log( Dm/ D*) for other types of rocks with similar ranges of matrix porosity and permeability as the volcanic rocks, but it did a poorer job predicting log( Dm/ D*) for rocks with lower porosities and/or permeabilities. The presence of mineral coatings on fracture walls did not appear to have a significant effect on matrix diffusion in the ten paired diffusion cell experiments.

  20. Zircon age range and sources of alkaline rocks from the Kurgusul intrusion, Kuznetsk Alatau: The first U-Pb (SHRIMP II) and Sm-Nd isotope data

    NASA Astrophysics Data System (ADS)

    Vrublevskii, V. V.; Gertner, I. F.; Tishin, P. A.; Bayanova, T. B.

    2014-12-01

    U-Pb isotope analysis of basic feldspathoid rocks (juvites) of the Kurgusul intrusion, NE Kuznetsk Alatau, revealed three generations of zircons of various ages (˜1.3-1.5 Ga; 484.3 ± 5.5 and 393.6 ± 9.2Ma). This suggests several stages of regional alkaline basic magmatism in the Middle Cambrian-Early Ordovician and Early-Middle Devonian and melting of the Mesoproterozoic continental crust, which form part of the basement of the Kuznetsk Alatau terrane. The trace element geochemical data indicate a continental margin setting characterized by the complex interaction of a plume-related, supra-subduction zone and crustal materials. A possible model of the magmatic evolution assumes that the ascent of a plume at the Cambrian-Ordovician boundary induced generation of the initial alkaline basaltic magmas and metasomatism and erosion of the lower lithosphere. Repeated partial melting of the lower crust after a 100 Myr period produced new magma batches of alkaline composition, which inherited zircons from the preceding episode of magma generation. The inherited juvenile magmatic source (PREMA + E-type MORB + EM) is confirmed by similarities in the Sm-Nd isotopic signatures (ɛNd( T) ≈ +4.5 to +5.7, T(Nd)DM ≈ 0.8-0.9 Ga) of derivatives of regional alkaline basic complexes of different ages.

  1. Geochemistry of the Newbury Volcanic Complex, northeastern, Massachusetts

    SciTech Connect

    McKenna, J.M.; Hepburn, J.C.; Hon, R. . Dept. of Geology and Geophysics)

    1993-03-01

    The Newbury Volcanic Complex consists of 3,000+ meters of subaerial volcanic flows, tuffs and minor admixed sediment (Shride, 1976), contained entirely within fault blocks between the Nashoba and Boston-Avalon tectonic terrane. Fossils date these essentially unmetamorphosed and unpenetratively deformed volcanic rocks as latest Silurian to earliest Devonian. The rocks fall into two general compositional groups: a more mafic group of basalts, basaltic andesites and andesites with SiO[sub 2] values ranging from 50% to 59%; and a second, rhyolitic group with SiO[sub 2] ranging from 75% to 77%. The mafic rocks have high Al[sub 2]O[sub 3] (15% to 19%) and Zr/Hf ratios between 38 and 41. The REE abundances of both groups show marked LREE enrichment with La/Lu ratios ranging from 4.7 to 11. Tectonic discrimination diagrams, including, AFM, Ti-Zr-Y, Hf-Th-Ta, and Nb-Zr-Y, applied to the mafic rocks, all indicate a calc-alkaline chemistry and a volcanic arc origin for the Newbury Volcanic Complex. Depletions in Ta and Nb on MORB-normalized spidergrams further support this conclusion. High Zr/Y ratios suggest that the arc was erupted through continental crust. The authors geochemical data strengthens correlations along the eastern margin of the Appalachians and reinforces the existence of Silurian arc volcanism on or adjacent to the Avalon Zone.

  2. Tectonic Setting and Bimodal Magmatic Evolution of Eocene Volcanic Rocks of the Bijgerd-Kuh-e Kharchin area, Uromieh-Dokhtar Zone, Iran

    NASA Astrophysics Data System (ADS)

    Davarpanah, A.; Khalatbari-Jafari, M.; Babaie, H. A.; Krogstad, E. J.; Mobasher, K.; La Tour, T. E.; Deocampo, D. M.

    2008-12-01

    Geochemical composition and texture of the Middle and Late Eocene volcanic, volcaniclastic, and volcanic- sedimentary rocks in the Bijgerd-Kuh-e Kharchin area, northwest of Saveh, provide significant geochemical and geological clues for the tectonic and magmatic evolution of the Uromieh-Dokhtar volcanic-plutonic zone of Iran. The Middle Eocene volcanic rocks have an intermediate composition and include green tuff and tuffaceous sandstone with intercalated sandstone, sandy tuff, and shale. The shale has lenses of nummulite- bearing limestone with a Middle Eocene detrital age. The time between the Middle and Late Eocene volcanic activities in this area is marked by the presence of andesite and rhyolitic tuff. The Late Eocene succession is distinguished by the presence of four alternating levels (horizons) of intermediate lava and ignimbrite which we designate as Eig. The ignimbrites of the Eig sequence have a rhyolitic composition and include ignimbrite- breccia, ignimbrite-tuff, and ignimbrite-lava pairs. The volume of the felsic volcanic rocks in this sequence far exceeds that of the intermediate rocks, which makes it unlikely that they evolved through the magmatic differentiation of a basaltic magma. The presence of the nummulite-bearing limestone lenses, and sandstone and conglomerate interbeds between the ignimbrites, suggests a shallow marine environment for the pyroclastic deposition and probably the eruptions. The tuff and siltstone of the Est unit that sits above the first ignimbrite may represent deep water, Late Eocene deposit. Oligo-Miocene limestone of the Qom Formation unconformably overlies the uppermost Late Eocene ignimbrite. Washings from red marls give microfossils with Late Eocene age for the Eig sequence, which is synchronous with other paleontological evidence that puts the peak volcanic activity as Late Eocene in the Bijgerd-Kuh-e Kharchin area. Field and petrographic evidence for magma mixing/mingling is given by the presence of mafic

  3. A First Look at Airborne Imaging Spectrometer (AIS) Data in an Area of Altered Volcanic Rocks and Carbonate Formations, Hot Creek Range, South Central Nevada

    NASA Technical Reports Server (NTRS)

    Feldman, S. C.; Taranik, J. V.; Mouat, D. A.

    1985-01-01

    Three flight lines of Airborne Imaging Spectrometer (AIS) data were collected in 128 bands between 1.2 and 2.4 microns in the Hot Creek Range, Nevada on July 25, 1984. The flight lines are underlain by hydrothermally altered and unaltered Paleozoic carbonates and Tertiary rhyolitic to latitic volcanics in the Tybo mining district. The original project objectives were to discriminate carbonate rocks from other rock types, to distinguish limestone from dolomite, and to discriminate carbonate units from each other using AIS imagery. Because of high cloud cover over the prime carbonate flight line and because of the acquisition of another flight line in altered and unaltered volcanics, the study has been extended to the discrimination of alteration products. In an area of altered and unaltered rhyolites and latites in Red Rock Canyon, altered and unaltered rock could be discriminated from each other using spectral features in the 1.16 to 2.34 micron range. The altered spectral signatures resembled montmorillonite and kaolinite. Field samples were gathered and the presence of montmorillonite was confirmed by X-ray analysis.

  4. The Quaternary volcanic rocks of the northern Afar Depression (northern Ethiopia): Perspectives on petrology, geochemistry, and tectonics

    NASA Astrophysics Data System (ADS)

    Hagos, Miruts; Koeberl, Christian; van Wyk de Vries, Benjamin

    2016-05-01

    The northern Afar Depression is one of the most volcano-tectonically active parts of the East African Rift system, a place where oceanic rifting may be beginning to form an incipient oceanic crust. In its center, over an area that is ∼80 km long and ∼50 km wide, there are seven major NNW-SSE-aligned shield volcanoes/volcanic edifices surrounded by compositionally distinct fissure-fed basalts. The Quaternary lavas in this area range from transitional to tholeiitic basalts, with significant across-axis variation both in mineralogy and chemistry. The variation in the contents of the major elements (TiO2, Al2O3, and Fe2O3), incompatible trace elements (Nd, Hf, Th, Ta), and the contents and ratios of the rare earth elements (REE) (e.g., (La/Yb)n = 5.3-8.9) indicate some variation in the petrogenetic processes responsible for the formation of these basalts. However, the variation in isotopic compositions of the mafic lavas is minimal (87Sr/86Sr = 0.7036-0.7041, 143Nd/144Nd = 0.51286-0.51289), which suggests only one source for all the Danakil Depression basalts. These basalts have isotope and incompatible trace element ratios that overlap with those of the Oligocene High-Ti2 flood basalts from the Ethiopian Plateau, interpreted as being derived from the last phase/tail of the Afar mantle plume source. Moreover, the Ce/Pb, Ba/U ratios indicate that the involvement of continental crust in the petrogenesis of the basaltic rocks is minimal; instead, both depth and degree of melting of the source reservoir underneath the northern Afar Depression played a major role for the production of incompatible element-enriched basalts (e.g., AleBagu Shield basalts) and the incompatible element-depleted tholeiitic basalts (e.g., Erta'Ale and Alu Shield basalts).

  5. Zircon U-Pb geochronology and geochemistry of low-grade metamorphosed volcanic rocks from the Dantazi Complex: Implications for the evolution of the North China Craton

    NASA Astrophysics Data System (ADS)

    Ge, Songsheng; Zhai, Mingguo; Li, Tiesheng; Peng, Peng; Santosh, M.; Shan, Houxiang; Zuo, Pengfei

    2015-11-01

    The late Neoarchean witnessed the cratonization of the North China Craton (NCC) through amalgamation of several micro-blocks to form a coherent basement. The Archean orthogneisses and supracrustal rocks in this craton have experienced various grades of metamorphism ranging up to upper amphibolite and granulite facies at ∼2500 Ma. Recently, a suite of low-grade metamorphosed (greenschist to lower amphibolite facies) volcanic rocks was discovered in the late Neoarchean Dantazi Complex in northern Hebei province. These meta-volcanic rocks consist of bimodal basalt-andesite and trachyte-dacite with a SiO2 gap between 54.4 wt.% and 60.7 wt.%. Here we report SHRIMP zircon U-Pb ages of 2490 ± 19 Ma (MSWD = 2.0) and 2502 ± 8 Ma (MSWD = 0.83) from the meta-mafic and meta-felsic volcanics, respectively, representing the timing of igneous activity. All the meta-mafic volcanic rocks display coherent trace element and REE patterns which are characterized by enriched LILE and LREE but depleted HFSE and HREE ((La/Yb)N = 6.29-15.10). Combining these trace element features with the positive zircon εHf(t) values (+1.3 to +6.6), we propose that the mafic rocks were likely derived from partial melting of a previously metasomatized lithospheric mantle. In the primitive mantle-normalized diagram, the felsic rocks display uniform patterns enriched in LILE but depleted in Nb and Ta, similar to those of lower crust. Furthermore, their strongly fractionated REE ((La/Yb)N = 15.24-61.20), lower HREE concentrations (Yb = 0.47-1.65 ppm) and positive zircon εHf(t) values (+1.6 to +5.3) suggest that they were derived from partial melting of the lower crust with garnet in the residue. This coeval occurrence of metasomatized mantle-derived mafic magmas and potassic felsic magmas from different source regions reflects an intracontinental extensional setting during the late Neoarchean to earliest Paleoproterozoic following the cratonization of the NCC. Our new data, combined with previous

  6. Volcanology, geochemistry and age of the Lausitz Volcanic Field

    NASA Astrophysics Data System (ADS)

    Büchner, J.; Tietz, O.; Viereck, L.; Suhr, P.; Abratis, M.

    2015-11-01

    The Lausitz (Lusatia) Volcanic Field is part of the Central European Volcanic Province, and its magmas represent an alkaline trend from olivine nephelinites and basanites to trachytes and phonolites, typical for intraplate settings. Neighbouring volcanic fields are the České Středohoří Mountains to the south-west and the Fore-Sudetic Basin in Lower Silesia to the east. More than 1000 volcanic structures associated with approximately 500 vents have been located within this volcanic field. Residuals of scoria cones, lava lakes, lava flows and maar-diatreme in filling occur in situ near the level of the original syn-volcanic terrain. In more deeply eroded structures, volcanic relicts outcrop as plugs or feeders. Evolved rocks occur as monogenetic domes or intrusions in diatremes, while their volcaniclastic equivalents are rare. Twenty-three localities were dated using the 40Ar/39Ar method. The ages range from 35 to 27 Ma, with a focus around 32-29 Ma, indicating Late Eocene and mainly Oligocene volcanism for the LVF. Differentiated rocks appear to be slightly younger than less differentiated. No geographical age clusters are apparent.

  7. Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems

    NASA Astrophysics Data System (ADS)

    Portnyagin, Maxim; Duggen, Svend; Hauff, Folkmar; Mironov, Nikita; Bindeman, Ilya; Thirlwall, Matthew; Hoernle, Kaj

    2015-12-01

    We present new major and trace element, high-precision Sr-Nd-Pb (double spike), and O-isotope data for the whole range of rocks from the Holocene Tolbachik volcanic field in the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent mostly Late Holocene eruptions (using tephrochronological dating), including historic ones in 1941, 1975-1976 and 2012-2013. Major compositional features of the Tolbachik volcanic rocks include the prolonged predominance of one erupted magma type, close association of middle-K primitive and high-K evolved rocks, large variations in incompatible element abundances and ratios but narrow range in isotopic composition. We quantify the conditions of the Tolbachik magma origin and evolution and revise previously proposed models. We conclude that all Tolbachik rocks are genetically related by crystal fractionation of medium-K primary magmas with only a small range in trace element and isotope composition. The primary Tolbachik magmas contain ~ 14 wt.% of MgO and ~ 4% wt.% of H2O and originated by partial melting (~ 6%) of moderately depleted mantle peridotite with Indian-MORB-type isotopic composition at temperature of ~ 1250 °C and pressure of ~ 2 GPa. The melting of the mantle wedge was triggered by slab-derived hydrous melts formed at ~ 2.8 GPa and ~ 725 °C from a mixture of sediments and MORB- and Meiji-type altered oceanic crust. The primary magmas experienced a complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization (REFC). First the original primary magmas underwent open-system crystal fractionation combined with periodic recharge of the magma chamber with more primitive magma, followed by mixing of both magma types, further fractionation and finally eruption. Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic trachyandesites erupted in 2012-2013 approach steady-state REFC

  8. Stratigraphy and composition of volcanic rocks cropping out along the northern walls of the Valle del Bove, Mount Etna, Italy.

    NASA Astrophysics Data System (ADS)

    Cristofolini, R.; de Rosa, R.; Ferlito, C.; Niceforo, G. A. M.

    2003-04-01

    The Valle del Bove cuts the eastern sector of Mount Etna and represents a key area for understanding of the most recent history of this complex volcano. Lava flows and tuffs related to the volcanic activity preceding the building of the most recent center (Recent Mongibello) outcrop along its sheer slopes. In this work 14 stratigraphic sections, comprising products of the Ellittico center at elevations between 1300 and 2400 m a.s.l., have been examined. In each section lava flows alternate with volcaniclastic deposits, with their thickness varying from less than 1 to 30 m. The matrix ash in thin tephra levels is commonly deeply weathered. Some of these layers show graded bedding and some others plane-parallel and cross-laminated structures, whereas thicker deposits do not show any clear internal structures and are poorly sorted.. The lithic component is always igneous in origin and is represented by dark or reddish, massive lava fragments either rounded or angular in shape, with their size attaining up to 1 m across in the massive beds. The juvenile fraction is represented by dark, vesiculated scoria. Isolated crystals of pyroxene are also present. The limited lateral distribution of the thick massive beds and their textural and compositional characters suggests their emplacement as Lahar-type highly concentrated flows, probably of secondary origin. A primary fall-out pyroclastic origin is inferred for the thin laminated and graded beds . Lavas, light to dark grey in colour, are commonly massive, and only rarely slightly vesicular; their massive portion is 0.5 to 5 m. thick. Plagioclase and pyroxene phenocrysts may be recognised by naked eye; smaller crystals of olivine are present too. Whole rock compositions, obtained by XRF analysis, vary from hawaiites to mugeariites, and. are consistent with those of the Ellittico products. Lateral and vertical variations of some chemical characters of lavas in different stratigraphic sections suggest slight changes of the

  9. Geochemical and Sr Nd Pb isotopic evidence for a combined assimilation and fractional crystallisation process for volcanic rocks from the Huichapan caldera, Hidalgo, Mexico

    NASA Astrophysics Data System (ADS)

    Verma, Surendra P.

    2001-03-01

    This study reports new geochemical and Sr-Nd-Pb isotopic data for Miocene to Quaternary basaltic to andesitic, dacitic, and rhyolitic volcanic rocks from the Huichapan caldera, located in the central part of the Mexican Volcanic Belt (MVB). The initial Sr and Nd isotopic ratios, except for one rhyolite, range as follows: 87Sr/ 86Sr 0.70357-0.70498 and 143Nd/ 144Nd 0.51265-0.51282. The Sr-Nd-Pb isotopic ratios are generally similar to those for volcanic rocks from other areas of the central and eastern parts of the MVB. The isotopic ratios of one older pre-caldera rhyolite (HP30) from the Huichapan area, particularly its high 87Sr/ 86Sr, are significantly different from rhyolitic rocks from this and other areas of the MVB, but are isotopically similar to some felsic rocks from the neighbouring geological province of Sierra Madre Occidental (SMO), implying an origin as a partial melt of the underlying crust. The evolved andesitic to rhyolitic magmas could have originated from a basaltic magma through a combined assimilation and fractional crystallisation (AFC) process. Different compositions, representing lower crust (LC) and upper crust (UC) as well as a hypothetical crust similar to the source of high 87Sr/ 86Sr rhyolite HP30, were tested as plausible assimilants for the AFC process. The results show that the UC represented by granitic rocks from a nearby Los Humeros area or by Cretaceous limestone (L) rocks outcropping in the northern part of the study area, and the LC represented by granulitic xenoliths from a nearby San Luis Potosı´ (SLP) area are not possible assimilants for Huichapan magmas, whereas a hypothetical crust (HA) similar in isotopic compositions to rhyolite HP30 could be considered a possible assimilant for the AFC process. Chemical composition of assimilant HA, although not well constrained at present, was inferred under the assumption that HP30 type partial melts could be generated from its partial melting. These data were then used to evaluate

  10. Petrogenetic connections between volcanic rocks and intrusive suites in the California arc - toward an integrated model for upper-crustal magma system evolution

    NASA Astrophysics Data System (ADS)

    Barth, A. P.; Riggs, N.; Walker, J. D.; Andrew, J.; Jacobson, C. E.; Miller, D. M.; Robert, J.

    2014-12-01

    Volcanic and clastic sedimentary rocks in deeply eroded, predominantly plutonic arcs provide records of arc development and the links between volcanic and plutonic processes. We are analyzing existing and new geochronologic and petrologic data from volcanic breccias, ignimbrites and intrusive suites in the Sierra Nevada and Mojave Desert sectors of the Mesozoic California arc, in an effort to construct an integrated volcano-plutonic model for silicic magmatism in arc upper crust. SIMS and TIMS U-Pb zircon ages, immobile element abundances in whole rocks, and trace element abundances in zircons allow us to interpret the magmatic heritage of ignimbrites and components of underlying granodioritic to granitic intrusive suites. Preliminary results suggest several conclusions: (1) first-order magma production was episodic, with plutonic, forearc and retro-arc detrital zircons defining three magmatic pulses of ~40-60 m.y. duration that are largely mimicked by the more limited record of zircons in ignimbrites; (2) in the Triassic and Jurassic, second-order pulses on 2-10 m.y. time scales are recorded in both the intrusive and ignimbrite records, suggesting that eruption of ignimbrites was synchronous at the shortest resolvable time scales with assembly of underlying incrementally emplaced intrusive suites; (3) ignimbrites range from dacite to rhyolite in bulk composition, and are petrographically similar to modern "monotonous intermediate" dacite or phenocryst-poor low-silica rhyolite; (4) these tuffs are as fractionated as intrusive rocks, and commonly, though not always, contain zircons with similarly complex, multi-stage growth histories. Thus ignimbrites and felsic granodiorites in this arc are complementary elements recording lengthy and episodic evolutionary histories in cool and hydrous upper-crustal arc magma systems.

  11. Dikes, sills, and stress-regime evolution during emplacement of the Jagged Rocks Complex, Hopi Buttes Volcanic Field, Navajo Nation, USA

    NASA Astrophysics Data System (ADS)

    Re, Giuseppe; White, J. D. L.; Ort, M. H.

    2015-03-01

    The dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of the simplest volcanic plumbing systems. Their geometry is controlled by interaction of magma-driven cracks with country rock, and reveals regional structural and stress patterns at the time of their emplacement. The shallow stress field, however, may change during the time an intrusion complex is emplaced, in response to addition or removal of magma and country rock during associated surface eruptions. The Jagged Rocks Complex, in the Miocene Hopi Buttes Volcanic Field, Navajo Nation, Arizona, is exposed 300-350 m below the pre-eruptive surface. It comprises a group of generally NW-SE striking dikes, punctuated in places by buds, a saucer-like intrusion, larger pyroclastic massifs and a diatreme. We made measurements of 13 dikes, divided into 172 segments, with thicknesses from 8 to 122 cm (mean 43 cm) and lengths of 60 to 780 m. Several sills and inclined sheets in places are thicker than dikes, having mean thicknesses of 48 cm and 73 cm respectively. Dikes typically show straight, parallel, and en echelon patterns, while sills and inclined sheets are curved. The northwestern dikes differ from the rest in containing large mafic crystals, and are inferred to have been emplaced after the others. We find that the strike of the overall complex (dikes and other sheets, elongate massifs and aligned sub-cylindrical bodies) reflects a crystalline-basement control that is evident throughout Hopi Buttes. Over the period of the complex's emplacement, local stress patterns were not stable. We infer that excavation of deep maar craters, and perhaps the construction of a scoria cone at the surface, modified the local stress patterns to favor emplacement of sills and en echelon dikes later in the complex's evolution, in contrast to simple straight dikes as the complex first formed.

  12. Paleomagnetic secular variation study of Ar-Ar dated lavas flows from Tacambaro area (Central Mexico): Possible evidence of Intra-Jaramillo geomagnetic excursion in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Peña, Rafael Maciel; Goguitchaichvili, Avto; Guilbaud, Marie-Noëlle; Martínez, Vicente Carlos Ruiz; Rathert, Manuel Calvo; Siebe, Claus; Reyes, Bertha Aguilar; Morales, Juan

    2014-04-01

    More than 350 oriented paleomagnetic cores were obtained for rock-magnetic and paleomagnetic analysis from radiometrically dated (40Ar-39Ar) magmatic rocks occurring in the southern segment (Jorullo and Tacámbaro areas) of the Michoacán-Guanajuato Volcanic Field in the Trans-Mexican Volcanic Belt. Most of the lavas (37) stem from monogenetic volcanoes dated at less than 4 Ma. Two additional sites were sampled from the plutonic basement dated at 33-30 Ma. Primary remanences carried by low-Ti titanomagnetites allowed to determining 34 reliable site-mean directions of mostly normal (27) but also reversed (7) polarities. The mean directions of these two populations are antipodal, and suggest neither major vertical-axis rotations with respect to the North America craton nor tilting in the region for the last 4 Ma (rotation and flattening of the inclination parameters being less than -5.9 ± 3.8 and 0.1 ± 3.9, respectively). The corresponding paleomagnetic pole obtained for Pliocene-Pleistocene times is PLAT = 83.4°, PLON = 2.4° (N = 32, A95 = 2.7°). Virtual geomagnetic poles also contribute to the time averaged field global database and to the paleosecular variation (PSV) investigations at low latitudes from lavas for the last 5 Ma, showing a geomagnetic dispersion value that is in agreement with available PSV models. When comparing the magnetic polarities and corresponding radiometric ages of the studied sites with the Cenozoic geomagnetic polarity time scale (GPTS), a good correlation is observable. This finding underscores the suitability of data obtained on lavas in Central Mexico for contributing to the GPTS. Furthermore, the detection of short-lived geomagnetic features seems possible, since the possible evidence of Intra-Jaramillo geomagnetic excursion could be documented for the first time in these volcanic rocks.

  13. Geomagnetic imprint of the Persani volcanism

    NASA Astrophysics Data System (ADS)

    Besutiu, Lucian; Seghedi, Ioan; Zlagnean, Luminita; Atanasiu, Ligia; Popa, Razvan-Gabriel; Pomeran, Mihai; Visan, Madalina

    2016-04-01

    The Persani small volume volcanism is located in the SE corner of the Transylvanian Depression, at the north-western edge of the intra-mountainous Brasov basin. It represents the south-easternmost segment of the Neogene-Quaternary volcanic chain of the East Carpathians. The alkaline basalt monogenetic volcanic field is partly coeval with the high-K calc-alkaline magmatism south of Harghita Mountains (1-1.6 Ma). Its eruptions post-dated the calc-alkaline volcanism in the Harghita Mountains (5.3-1.6 Ma), but pre-dated the high-K calc-alkaline emissions of Ciomadul volcano (1.0-0.03 Ma). The major volcanic forms have been mapped in previous geological surveys. Still, due to the small size of the volcanoes and large extent of tephra deposits and recent sediments, the location of some vents or other volcanic structures has been incompletely revealed. To overcome this problem, the area was subject to several near-surface geophysical investigations, including paleomagnetic research. However, due to their large-scale features, the previous geophysical surveys proved to be an inappropriate approach to the volcanological issues. Therefore, during the summers of 2014 and 2015, based on the high magnetic contrast between the volcanic rocks and the hosting sedimentary formations, a detailed ground geomagnetic survey has been designed and conducted, within central Persani volcanism area, in order to outline the presence of volcanic structures hidden beneath the overlying deposits. Additionally, information on the rock magnetic properties was also targeted by sampling and analysing several outcrops in the area. Based on the acquired data, a detailed total intensity scalar geomagnetic anomaly map was constructed by using the recent IGRF12 model. The revealed pattern of the geomagnetic field proved to be fully consistent with the direction of magnetisation previously determined on rock samples. In order to enhance the signal/noise ratio, the results were further processed by

  14. Petrogenesis and tectonic settings of volcanic rocks of the Ashele Cu-Zn deposit in southern Altay, Xinjiang, Northwest China: Insights from zircon U-Pb geochronology, geochemistry and Sr-Nd isotopes

    NASA Astrophysics Data System (ADS)

    Wu, Yufeng; Yang, Fuquan; Liu, Feng; Geng, Xinxia; Li, Qiang; Zheng, Jiahao

    2015-11-01

    The Early-Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu-Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U-Pb geochronology, geochemistry, and Sr-Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U-Pb ages of 402 ± 6 Ma and 403 ± 2 Ma. The dacites are calc-alkaline, and characterized by high Na2O/K2O ratios (3.6-9.3), and high Mg# values (47-63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive εNd(t) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe-Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66-73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive εNd(t) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction.

  15. Melting of the primitive martian mantle at 0.5-2.2 GPa and the origin of basalts and alkaline rocks on Mars

    NASA Astrophysics Data System (ADS)

    Collinet, Max; Médard, Etienne; Charlier, Bernard; Vander Auwera, Jacqueline; Grove, Timothy L.

    2015-10-01

    We have performed piston-cylinder experiments on a primitive martian mantle composition between 0.5 and 2.2 GPa and 1160 to 1550 °C. The composition of melts and residual minerals constrain the possible melting processes on Mars at 50 to 200 km depth under nominally anhydrous conditions. Silicate melts produced by low degrees of melting (<10 wt.%) were analyzed in layers of vitreous carbon spheres or in micro-cracks inside the graphite capsule. The total range of melt fractions investigated extends from 5 to 50 wt.%, and the liquids produced display variable SiO2 (43.7-59.0 wt.%), MgO (5.3-18.6 wt.%) and Na2O + K2O (1.0-6.5 wt.%) contents. We provide a new equation to estimate the solidus temperature of the martian mantle: T (°C) = 1033 + 168.1 P (GPa) - 14.22P2 (GPa), which places the solidus 50 °C below that of fertile terrestrial peridotites. Low- and high-degree melts are compared to martian alkaline rocks and basalts, respectively. We suggest that the parental melt of Adirondack-class basalts was produced by ∼25 wt.% melting of the primitive martian mantle at 1.5 GPa (∼135 km) and ∼1400 °C. Despite its brecciated nature, NWA 7034/7533 might be composed of material that initially crystallized from a primary melt produced by ∼10-30 wt.% melting at the same pressure. Other igneous rocks from Mars require mantle reservoirs with different CaO/Al2O3 and FeO/MgO ratios or the action of fractional crystallization. Alkaline rocks can be derived from mantle sources with alkali contents (∼0.5 wt.%) similar to the primitive mantle.

  16. Quaternary volcanics from the Broken Top volcano area, Oregon High Cascades: Varied low pressure processes in calc-alkaline magma chambers

    SciTech Connect

    Webster, J.R. . Div. of Science and Math)

    1992-01-01

    Broken Top (BT) is a Quaternary composite volcano in the central Oregon High Cascades. Volcanics in the vicinity of BT range from basalt to rhyodacite with a paucity of andesite. Most pre- and syn-BT lavas were generated through low pressure crystal fractionation (CF) in small, short-lived chambers. Mixing superimposed on CF generally involved magmas with minimal compositional differences. Lavas erupted from BT are dominantly phenocryst-rich bas. andesite which exhibits evidence for a mixing origin. Whole-rock and phenocryst compositions suggest mixing between basalt and andesite. The andesite can be explained by low pressure CF of the basalt. Latest BT activity consisted of bas. andesite, dacite, and rhyodacite lavas which were generated through CF. During BT activity, andesite was produced by CF during rapid sidewall crystallization and ponded at the top of the chamber. Mixing most likely took place during eruptive events, but evidence for a persistent presence of mixed (hybrid) magma in the chamber suggests incomplete evacuation of mixed magma. With time, the andesite layer became less significant due to decreasing rates of sidewall crystallization and/or frequent eruption/replenishment, more widespread crystal settling resulted in eruption of CF-generated bas. andesite and low-Si dacite. Rapid crystallization of dacitic magma followed by buoyant segregation yielded rhyodacite. These processes operating during the latest stages of the BT activity were likely similar to those operating in the short-lived chambers. Paucity of CF-generated andesite is explained by: (1) low density crust which retards andesite ascent, and (2) rapid crystallization over the dacite range. While significant amounts of andesite were produced in the longer-lived BT system, it rarely erupted unmixed.

  17. Anomalous Seismic Velocity Drop in Iron and Biotite Rich Amphibolite to Granulite Facies Transitional Rocks from Deccan Volcanic Covered 1993 Killari Earthquake Region, Maharashtra (India): a Case Study

    NASA Astrophysics Data System (ADS)

    Pandey, O. P.; Tripathi, Priyanka; Vedanti, Nimisha; Srinivasa Sarma, D.

    2016-07-01

    65 Ma Deccan Volcanic Province of western India forms one of the largest flood basaltic eruptions on the surface of the earth. The nature of the concealed crust below this earthquake prone region, which is marked by several low velocity zones at different depths has hardly been understood. These low velocity zones have been invariably interpreted as fluid-filled zones, genetically connected to earthquake nucleation. While carrying out detailed geological and petrophysical studies on the Late Archean basement cores, obtained from a 617 m deep KLR-1 borehole, drilled in the epicentral zone of 1993 Killari earthquake region of the southern Deccan Volcanic Province, we came across several instances where we observed remarkable drop in measured P-wave velocity in a number of high density cores. We provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid-crustal amphibolite to granulite facies transitional rocks. They are associated with a mean P-wave velocity of 6.02 km/s (range 5.82-6.22 km/s) conforming to granitic upper crust, but in contrast have a high mean density of 2.91 g/cm3 (range 2.75-3.08 g/cm3), which characterise mid to lower crust. This velocity drop, which is as much as 15 % in some cores, is primarily attributed to FeOT enrichment (up to about 23 wt%) during the course of mantle-fluid driven retrogressive metasomatic reactions, caused by exhumation of deep-seated mafic rocks. Presence of Iron content (mainly magnetite), widely seen as opaques in thin sections of the rocks, seems to have resulted into sharp increase in density, as well as mean atomic weight. Our study indicates that the measured V p is inversely related to FeOT content as well as mean atomic weight of the rock.

  18. Permeability and continuous gradient temperature monitoring of volcanic rocks: new insights from borehole and laboratory analysis at the Campi Flegrei caldera (Southern Italy).

    NASA Astrophysics Data System (ADS)

    Carlino, Stefano; Piochi, Monica; Tramelli, Anna; Troise, Claudia; Mormone, Angela; Montanaro, Cristian; Scheu, Bettina; Klaus, Mayer; Somma, Renato; De Natale, Giuseppe

    2016-04-01

    The pilot borehole recently drilled in the eastern caldera of Campi Flegrei (Southern Italy), during the Campi Flegrei Deep Drill Project (CFDDP) (in the framework of the International Continental Scientific Drilling Program) allowed (i) estimating on-field permeability and coring the crustal rocks for laboratory experiments, and (ii) determining thermal gradient measurements down to ca. 500 m of depth. We report here a first comparative in situ and laboratory tests to evaluate the rock permeability in the very high volcanic risk caldera of Campi Flegrei, in which ground deformations likely occur as the persistent disturbance effect of fluid circulation in the shallower geothermal system. A large amount of petro-physical information derives from outcropping welded tuffs, cores and geophysical logs from previous AGIP's drillings, which are located in the central and western part of the caldera. We discuss the expected scale dependency of rock permeability results in relation with well-stratigraphy and core lithology, texture and mineralogy. The new acquired data improve the database related to physical property of Campi Flegrei rocks, allowing a better constrain for the various fluid-dynamical models performed in the tentative to understand (and forecast) the caldera behavior. We also present the first data on thermal gradient continuously measured through 0 - to 475 m of depth by a fiber optic sensor installed in the CFDDP pilot hole. As regards, we show that the obtained values of permeability, compared with those inferred from eastern sector of the caldera, can explain the different distribution of temperature at depth, as well as the variable amount of vapor phase in the shallow geothermal system. The measured temperatures are consistent with the distribution of volcanism in the last 15 ka.

  19. Magmatism in the Tsagaandelger, Eastern Mongolian volcanic belt: Petrological, geochemical and isotopic constraints on Mesozoic geodynamic setting

    NASA Astrophysics Data System (ADS)

    Oidov, M.; Fujimaki, H.

    2008-12-01

    The vast territory of Mongolia lies in the heart of the Central Asian Orogenic Belt, one of largest provinces of the Phanerozoic continental growth on Earth (Jahn et al., 2004). We present new petrographic, geochemical and Sr-Nd isotopic analyses on Mesozoic igneous rocks emplaced in Central Mongolia. The Mesozoic igneous suites, those exposed in the Tsagaandelger area, pass upwards from alkaline series trachytic rocks and overlain by tuffaceous sediments. Those are intruded by calc alkaline leucocratic granites and covered by Late Mesozoic calc alkaline bimodal volcanic rocks consisting of basalts and rhyolite. Alkaline series volcanic sequences were erupted in Early-Middle Triassic (241 Ma) and characterized by LILE, LREE enrichment and significant Nb-Ta depletion. Rocks have weakly enriched initial 87Sr86Sr ratios of 0.705 to 0.706 and positive ɛNd(t) values (0.7 to 4). The crystallization age of intrusive rocks is 231 Ma. The majority of samples is slightly peraluminous and can be classified as granite, including monzogranite, granodiorite and aplite. Granites are characterized by near- zero ɛNd(t) values (0.7 to 2) and tetrad effect in their REE distribution patterns. Further Cretaceous volcanic sequences have lower contents of LILE and higher contents of HFS and REE, comparing with Triassic volcanic sequences. The Cretaceous volcanic rocks have the initial 87Sr86Sr ratios between 0.705 and 0.719 and near-zero ɛNd(t) values (-0.7 to 1.6). Trace element geochemistry indicates that Mesozoic volcanic rocks from the studied area are arc related. The Triassic volcanic and plutonic rocks could be emplaced in active continental margin settings. Post collisional extensional regime could be started with Early Cretaceous volcanism. The mass balance calculation suggests that the all Mesozoic volcanic and plutonic rocks were derived from sources composed of more than 80% juvenile mantle-derived component. Our data confirm the earlier observations of similar isotopic

  20. Diagenetic Iron Cycling in Ancient Alkaline Saline Lacustrine Sedimentary Rocks: A Case Study on the Jurassic Brushy Basin Member of the Morrison Formation, Colorado Plateau, USA

    NASA Astrophysics Data System (ADS)

    Potter-McIntyre, S. L.; Chan, M. A.; McPherson, B. J. O. L.

    2014-12-01

    The upper part of the Brushy Basin Member in the Four Corners region of the U.S. was deposited in an ephemeral alkaline saline lake system with copious input of volcanic ash. The variegated shale formation provides a setting for the study of early diagenetic iron cycling that records the action of alkaline saline fluid chemistries reacting with volcaniclastic sediments in the presence of microbes. A bull's-eye pattern of authigenic minerals with increasing alteration towards the basinal center similar to modern alkaline saline lakes provides evidence for an extreme paleoenvironmental interpretation. The purpose of this research is to document specific factors, such as reactive sediments, microbial influences, and grain size that affect concretion formation and iron cycling in an ancient extreme environment. Three broad diagenetic facies are interpreted by color and associated bioturbation features: red, green and intermediate. Diagenetic facies reflect meter-scale paleotopography: red facies represent shallow water to subaerial, oxidizing conditions; green facies reflect saturated conditions and reducing pore water chemistry shortly after deposition, and intermediate facies represent a combination of the previous two conditions. Evidence of biotic influence is abundant and trace fossils exhibit patterns associated with the diagenetic facies. Red diagenetic facies typically contain burrows and root traces and green diagenetic facies exhibit restricted biotic diversity typically limited to algal molds (vugs). Microbial fossils are well-preserved and are in close proximity to specific iron mineral textures suggesting biotic influence on the crystal morphology. Three categories of concretions are characterized based on mineralogy: carbonate, iron (oxyhydr)oxide and phosphate concretions. Concretion mineralogy and size vary within an outcrop and even within a stratigraphic horizon such that more than one main category is typically present in an outcrop. Variation in

  1. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    NASA Astrophysics Data System (ADS)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but

  2. Volcanic stratigraphy and geochemical variations in Miocene-age rocks in western and southeastern Fort Irwin, California

    NASA Astrophysics Data System (ADS)

    Buesch, D.

    2015-12-01

    Lava flows and tuffaceous deposits ranging in composition from basalt to rhyolite, including basaltic trachyandesite to trachyte, are exposed in 800 km2 of western Fort Irwin area, California, and form the eastern edge of the Eagle Crags volcanic field (ECVF). The main ECVF has 40Ar/39Ar ages from ~18.7-12.4 Ma (mostly 18.7-18.5 Ma; Sabin et al. 1994), and on Fort Irwin, the ages are from 21.0-15.8 Ma (mostly 18.6-15.8 Ma; Schermer et al. 1996). 68 samples (56 lava flow, 4 dome-collapse breccia, 3 ignimbrite, and 5 fallout tephra) were analyzed for major, minor, and trace elements. Typically, stratigraphic sequences dip <30° (mostly <15°) except near faults, with local buttress unconfomities and no large unconfomities. Compositions are moderate-to-high-K type, and similar to Na2O+K2O from Sabin et al. (1994) but with slightly smaller ranges. The generalized stratigraphic sequence is rhyolite (R), dacite (D), or trachyte (T) that form domes, lava flows (up to 3.5 km long), dome-collapse deposits, or pyroclastic deposits, overlain by andesite (A), trachyandesite (TA), basaltic andesite (BA), basaltic trachyandesite (BT), or basalt (B) lava flows (up to 7 km long), and minor cinder cones. A general upward felsic to mafic compositional sequence occurs throughout the area, but is not continuous as B is locally in a R-D sequence and B is at the base of and interstratified with a BA-A sequence. Also, there are compositional variations at different locations along the edges of the field. In the Goldstone Mesa, Pink Canyon, and Stone Ridge areas (~70 km2), B-BA forms the youngest lava flows, but ~21 km to the north in the Garry Owen area (~25 km2), BTA forms the youngest lava flows. Compared to the Stone Ridge area with a D-A-TA-BA trend, ~6 km west in the Pioneer Plateau area is R-TA-D, ~3 km south in the Pink Canyon area is R-B-BA-A, and ~8 km east at Dacite Dome is D only (all areas have slightly different Na2O+K2O in each rock type). A non-ECVF, 5.6 Ma BA flow in SE

  3. Crustal contamination versus subduction zone enrichment: Examples from the Lesser Antilles and implications for mantle source compositions of island arc volcanic rocks

    NASA Astrophysics Data System (ADS)

    Davidson, Jon P.

    1987-08-01

    Isotopic and geochemical data are presented from the northern and central Lesser Antilles arc. Island arc tholeiites from the northern islands are restricted in 143Nd /144Nd and 87Sr /86Sr and show large enrichments in LILE relative to other trace elements, as exemplified particularly in high Ba/La ratios. These volcanic rocks represent typical island arc compositions, similar to those described from the Aleutians, Marianas and South Sandwich Islands. In contrast, samples from the central islands (Martinique and St. Lucia) are highly variable in isotopic and trace element ratios, and reflect overprinting of primitive island arc magma chemistry by subsequent crustal contamination. Such magmas therefore do not represent island arc mantle source characteristics. Northern Lesser Antilles arc mantle sources are displaced from MORB Pb isotopic compositions towards the higher 207Pb /204Pb ratios characteristic of sediments. Also, Sr and Nd isotopic compositions are highly restricted and distinct from those of MORB. As a result, mixing models between MORB source and subducted sediment are tightly constrained in terms of the allowable proportion of sediment. The characteristically high LILE/REE and LILE/HFSE ratios of island arc volcanics cannot be easily reconciled with sediment + MORB source mixing. Buffering of isotopic compositions together with considerable relative LILE enrichment might be achieved by mixing between mantle and a hydrous fluid which has equilibrated with not only sediment but also a large proportion of variably altered oceanic crust. The fluid has isotopic compositions closer to those of MORB, thereby permitting a greater range of mixing proportions. At the same time, the LILE characteristics of the modified mantle source are dominated by the very high concentrations of these elements in the fluid. High degrees of partial melting of mantle modified by a hydrous fluid reproduce the trace element pattern of the source in the derivative volcanic rocks and

  4. [Micro-area characteristics of laminated chert in the volcanic rocks of Xionger Group of Ruyang area and its geological significances].

    PubMed

    Luo, An; Li, Hong-zhong; Zhao, Ming-zhen; Yang, Zhi-jun; Liang, Jin; He, Jun-guo

    2014-12-01

    The Xionger Group was originated from the volcanic eruption and sedimentation in Precambrian, whose sedimentary strata at the top were named Majiahe Formation. In the Majiahe Formation, there were hydrothermal chert widely distributed, which were exhibited to be interlayers in the volcanic rocks. The polarized microscope, X-ray diffraction (XRD), Raman and electron back scatter diffraction (EBSD) were conducted to study the characteristics in micro area of the jasperite samples, which were from the sedimentary interlayers in the volcanic rocks of Majiahe Formation in Xionger Group. As shown in the microphotographs and EBSD images, the quartz in the chert had small grain size, low degree of crystallinity and close packed structure, which quite agreed with the characteristics of hydrothermal sedimentary chert. In the chert of Xionger Group, there were clear banded (or lamellar) structures which were contributed by the diversities of the grain size and mineral composition. The different bands (or lamellars) had alternative appearance repeatedly, and denoted the diversities and periodic changes in the substance supply during the precipitation. According to the results of the XRD analysis, the majority minerals of the chert was low temperature quartz, whose lattice parameters were a=b=0.4913 nm, c=0.5405 nm and Z=3. As denoted in the EBSD image and result of Raman analysis, several impurity minerals were formed in the chert in different stages, whose geneses and formation time were quite different. The clay minerals and pyrite were scattered in distribution, and should be contributed by the original sedimentation. On contrary, the felsic minerals and mafic silicate minerals were originated from the sedimentation of tuffaceous substance during the volcanic eruption. The minerals of volcanic genesis had relatively larger grain size, and they deposited together with the hydrothermal sediments to form the bands (or lamellars) of coarse minerals. However, the hydrothermal

  5. [Micro-area characteristics of laminated chert in the volcanic rocks of Xionger Group of Ruyang area and its geological significances].

    PubMed

    Luo, An; Li, Hong-zhong; Zhao, Ming-zhen; Yang, Zhi-jun; Liang, Jin; He, Jun-guo

    2014-12-01

    The Xionger Group was originated from the volcanic eruption and sedimentation in Precambrian, whose sedimentary strata at the top were named Majiahe Formation. In the Majiahe Formation, there were hydrothermal chert widely distributed, which were exhibited to be interlayers in the volcanic rocks. The polarized microscope, X-ray diffraction (XRD), Raman and electron back scatter diffraction (EBSD) were conducted to study the characteristics in micro area of the jasperite samples, which were from the sedimentary interlayers in the volcanic rocks of Majiahe Formation in Xionger Group. As shown in the microphotographs and EBSD images, the quartz in the chert had small grain size, low degree of crystallinity and close packed structure, which quite agreed with the characteristics of hydrothermal sedimentary chert. In the chert of Xionger Group, there were clear banded (or lamellar) structures which were contributed by the diversities of the grain size and mineral composition. The different bands (or lamellars) had alternative appearance repeatedly, and denoted the diversities and periodic changes in the substance supply during the precipitation. According to the results of the XRD analysis, the majority minerals of the chert was low temperature quartz, whose lattice parameters were a=b=0.4913 nm, c=0.5405 nm and Z=3. As denoted in the EBSD image and result of Raman analysis, several impurity minerals were formed in the chert in different stages, whose geneses and formation time were quite different. The clay minerals and pyrite were scattered in distribution, and should be contributed by the original sedimentation. On contrary, the felsic minerals and mafic silicate minerals were originated from the sedimentation of tuffaceous substance during the volcanic eruption. The minerals of volcanic genesis had relatively larger grain size, and they deposited together with the hydrothermal sediments to form the bands (or lamellars) of coarse minerals. However, the hydrothermal

  6. Alteration mapping at Goldfield, Nevada, by cluster and discriminant analysis of Landsat digital data. [mapping of hydrothermally altered volcanic rocks

    NASA Technical Reports Server (NTRS)

    Ballew, G.

    1977-01-01

    The ability of Landsat multispectral digital data to differentiate among 62 combinations of rock and alteration types at the Goldfield mining district of Western Nevada was investigated by using statistical techniques of cluster and discriminant analysis. Multivariate discriminant analysis was not effective in classifying each of the 62 groups, with classification results essentially the same whether data of four channels alone or combined with six ratios of channels were used. Bivariate plots of group means revealed a cluster of three groups including mill tailings, basalt and all other rock and alteration types. Automatic hierarchical clustering based on the fourth dimensional Mahalanobis distance between group means of 30 groups having five or more samples was performed using Johnson's HICLUS program. The results of the cluster analysis revealed hierarchies of mill tailings vs. natural materials, basalt vs. non-basalt, highly reflectant rocks vs. other rocks and exclusively unaltered rocks vs. predominantly altered rocks. The hierarchies were used to determine the order in which sets of multiple discriminant analyses were to be performed and the resulting discriminant functions were used to produce a map of geology and alteration which has an overall accuracy of 70 percent for discriminating exclusively altered rocks from predominantly altered rocks.

  7. Distribution of chemical elements in calc-alkaline igneous rocks, soils, sediments and tailings deposits in northern central Chile

    NASA Astrophysics Data System (ADS)

    Oyarzún, Jorge; Oyarzun, Roberto; Lillo, Javier; Higueras, Pablo; Maturana, Hugo; Oyarzún, Ricardo

    2016-08-01

    This study follows the paths of 32 chemical elements in the arid to semi-arid realm of the western Andes, between 27° and 33° S, a region hosting important ore deposits and mining operations. The study encompasses igneous rocks, soils, river and stream sediments, and tailings deposits. The chemical elements have been grouped according to the Goldschmidt classification, and their concentrations in each compartment are confronted with their expected contents for different rock types based on geochemical affinities and the geologic and metallogenic setting. Also, the element behavior during rock weathering and fluvial transport is here interpreted in terms of the ionic potentials and solubility products. The results highlight the similarity between the chemical composition of the andesites and that of the average Continental Crust, except for the higher V and Mn contents of the former, and their depletion in Mg, Ni, and Cr. The geochemical behavior of the elements in the different compartments (rocks, soils, sediments and tailings) is highly consistent with the mobility expected from their ionic potentials, their sulfates and carbonates solubility products, and their affinities for Fe and Mn hydroxides. From an environmental perspective, the low solubility of Cu, Zn, and Pb due to climatic, chemical, and mineralogical factors reduces the pollution risks related to their high to extremely high contents in source materials (e.g., rocks, altered zones, tailings). Besides, the complex oxyanions of arsenic get bound by colloidal particles of Fe-hydroxides and oxyhydroxides (e.g., goethite), thus becoming incorporated to the fine sediment fraction in the stream sediments.

  8. A multianalytical approach to investigate stone biodeterioration at a UNESCO world heritage site: the volcanic rock-hewn churches of Lalibela, Northern Ethiopia

    NASA Astrophysics Data System (ADS)

    Schiavon, Nick; De Caro, Tilde; Kiros, Alemayehu; Caldeira, Ana Teresa; Parisi, Isabella Erica; Riccucci, Cristina; Gigante, Giovanni Ettore

    2013-12-01

    A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rock-hewn churches ( Bete Gyorgis and Bete Amanuel) at the UNESCO's World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite-zeolite-smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural "geological" weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited "geological" features, biological attack by micro- (bacteria) and/or macro- (lichens) organisms is currently responsible for severe stone surface physical and chemical weathering leading to significant weakening of the stone texture and to material loss at the surface of the churches walls. A prompt and careful removal of the biological patinas with the correct biocidal treatment is therefore recommended.

  9. Geochemical, petrographic and physical characterizations and associated alterations of the volcanic rocks of the Romanesque San Nicola Church (Ottana, central Sardinia, Italy)

    NASA Astrophysics Data System (ADS)

    Columbu, Stefano; Palomba, Marcella; Sitzia, Fabio

    2015-04-01

    In this research, the volcanic rocks belonging to the Sardinia Oligo-Miocene volcanic cycle (32 - 11 Ma) and building up the structure of the San Nicola church, one of the most representative churches of the Romanesque architecture, were studied. These stones were widely used in medieval architecture for the excellent workability, but they present some disadvantages, since they are greatly affected by alteration phenomena. The main objectives of this research are i) to focus the mineral, chemical and petrographic compositions of the San Nicola stones, ii) the chemical and physical alteration processes affecting these materials, and iii) to establish the exactly provenance of the volcanic rocks. Furthermore, a comparative study between the rocks from the ancient quarries and those forming the structure of the church was performed. In the ancient quarries, where presumably a more advanced alteration occurs due to the vertical alteration gradient, different facies of the same volcanic lithology, characterized by macroscopical evidences of chemical-physical degradation degree, were sampled. Petrographic, geochemical (both major elements that the traces) and physical-mechanical features of the collected samples were determined to highlight the compositional differences (density, porosity, water-absorption kinetics, mechanical resistance) as a function of the different alteration degree. Moreover, chemical-mineralogical analysis of the sample surfaces from the church, was performed, to highlight possible presence and nature of secondary newly-formed phases (e.g., salt efflorescence). Several methodologies were applied to carry out physical-chemical and petrographic analysis: X-Ray fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS), X-Ray Diffractometry (XRD) for chemical and mineral composition; Optical and Scanning Electron Microscopy (SEM) for textures, mineral assemblages and microstructures studies; He-picnometry, water-absorption and mechanical

  10. Sphene (Titanite) as Both Monitor and Driver of Evolution of Felsic Magma: Miocene Volcanic Plutonic and Rocks of the Colorado River Region, NV-AZ, USA

    NASA Astrophysics Data System (ADS)

    Miller, C. F.; Colombini, L. L.; Wooden, J. L.; Mazdab, F. K.; Gualda, G. A.; Claiborne, L. E.; Ayers, J. C.

    2009-05-01

    Sphene is commonly the most abundant accessory mineral in metaluminous to weakly peraluminous igneous rocks. Its relatively large crystals preserve a wide array of zoning patterns and inclusions - notably, abundant other accessories and melt inclusions - and it is a major host for REE, U, Th, and HFSE. Thus it is a valuable repository of information about the history of the magmas from which it forms. Recent development of a Zr-in- sphene thermometer (Hayden et al CMP 155:529 2008) and of sensitive and precise in situ trace element analysis by SHRIMP-RG (Mazdab et al GSA abst 39:6:406 2007) permit more powerful exploitation of this repository. We have initiated a study of sphene in Miocene intrusive and extrusive rocks of the Colorado River extensional corridor for which extensive field, geochemical, and geochronological data provide context. Sphene is present as a late interstitial phase in some gabbros and diorites and common in quartz monzonites and granites. Among extrusive rocks, it occurs as phenocrysts in rhyolite lavas and tuffs that are products of small to giant eruptions (Peach Spring Tuff, >600 km3). Glasses that host sphene in the rhyolites are highly evolved (>76 wt% SiO2). Applying the Zr-in-sphene thermometer (TZr), SHRIMP-RG analyses indicate crystallization T between 730 and 810 C in both plutonic and volcanic rocks. This range is narrower than T estimates for zircon growth (Ti thermometry) for the same suite, which extend to somewhat lower and considerably higher values; zircons also tend to record more events and, evidently, longer histories. Ranges of REE patterns are variable and to some extent sample-specific, but all reveal common characteristics: (1) extremely high concentrations, especially for middle REE (maximum Sm in interiors 10-40x103 x chondrite); (2) deep negative Eu anomalies (Eu/Eu* ca. 0.1-0.2); (3) TZr and REE dropping toward rims - especially pronounced for MREE. Estimated Kds for REE from sphene rims and rhyolite glass or

  11. Volcanic rocks and subglacial volcanism beneath the West Antarctic Ice Sheet in the West Antarctic Rift System, (WAIS) from aeromagnetic and radar ice sounding - Thiel Subglacial Volcano as possible source of the ash layer in the WAISCORE

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.

    2012-12-01

    Radar ice sounding and aeromagnetic surveys reported over the West Antarctic Ice Sheet (WAIS) have been interpreted as evidence of subglacial volcanic eruptions over a very extensive area (>500,000 km2 ) of the volcanically active West Antarctic rift system interpreted as caused by subglacial volcanic rocks. Several active volcanoes have shown evidence of eruption through the WAIS and several other active volcanoes are present beneath the WAIS reported from radar and aeromagnetic data. Five-kilometer spaced coincident aeromagnetic and radar ice sounding surveys since 1990 provide three dimensional characterization of the magnetic field and bed topography beneath the ice sheet. These 5-50-km-width, semicircular magnetic anomalies range from 100->1000 nT as observed ~1 km over the 2-3 km thick ice have been interpreted as evidence of subglacial eruptions. Comparison of a carefully selected subset of ~400 of the >1000 high-amplitude anomalies in the CWA survey having topographic expression at the glacier bed, showed >80% had less than 200-m relief. About 18 high-amplitude subglacial magnetic sources also have high topography and bed relief (>600 m) interpreted as subaerially erupted volcanic peaks when the WAIS was absent, whose competent lava flows protected their edifices from erosion. All of these would have high elevation above sea-level, were the ice removed and glacial rebound to have occurred. Nine of these subaerially erupted volcanoes are concentrated in the WAIS divide area. Behrendt et al., 1998 interpreted a circular ring of positive magnetic anomalies overlying the WAIS divide as caused by a volcanic caldera. The area is characterized by high elevation bed topography. The negative regional magnetic anomaly surrounding the caldera anomalies was interpreted as the result of a shallow Curie isotherm. High heat flow inferred from temperature logging in the WAISCORE (G. Clow 2012, personal communication; Conway, 2011) and a prominent volcanic ash layer in the

  12. Chemical, mineralogical and textural systematics of non-mare melt rocks: Implications for lunar impact and volcanic processes

    NASA Technical Reports Server (NTRS)

    Irving, A. J.

    1975-01-01

    Based on a synthesis of chemical data for over 200 samples, the nonmare rocks with fine grained melt textures can be classified into 7 major groups: anorthositic basalts, troctolitic basalts, VHA basalts, Apollo 14-type KREEP basalts, Apollo 15-type KREEP basalts, Apollo 17-type KREEP basalts, and aluminous mare basalts. Review of chemical, mineralogical, textural and experimental evidence leads to preferred hypotheses for the origins of these rocks; those hypotheses are discussed in detail.

  13. Geological investigations of volcanic rocks at Mount Discovery, Mount Morning, and Mason Spur, McMurdo Sound

    SciTech Connect

    Wright, A.C.; Kyle, P.R.; More, J.A.; Meeker, K.

    1986-01-01

    This work includes mapping of volcanic geology, description of geologic sections, and collection of samples for geochemical analysis and potassium-argon dating. Reconnaissance mapping of Mount Discovery shows that this 2681-meter-high composite volcano comprises a core of plagioclase-phyric nepheline-benmoreite flows, lahars, and volcanoclastic fluviatile sediments, which are thought to be the unit dated at 5.44 million years. Reconnaissance mapping of Mount Morning shows that this is a young volcano principally composed of kaersutite-bearing phonolite flows erupted both from the summit crater and from small parasitic domes on the upper northern slopes of the mountain. A sample from one of these parasitic domes has been dated at 1.15 million years. Description of five geologic sections at Mason Spur has provided a more detailed understanding of the older trachytic volcanic complex, which is now dated at 11.5 to 12.8 years and is divided into seven mapped units.

  14. Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

    NASA Astrophysics Data System (ADS)

    Oda, Hirokuni; Miyagi, Isoji; Kawai, Jun; Suganuma, Yusuke; Funaki, Minoru; Imae, Naoya; Mikouchi, Takashi; Matsuzaki, Takuya; Yamamoto, Yuhji

    2016-03-01

    Nondestructive magnetic detection of tephra layers in ice cores will be an important method to identify and correlate stratigraphic horizons of ice bearing volcanic ash particles. Volcanic ash particles were extracted from tephra-bearing ice samples collected from Nansen Ice Field south of the Sør Rondane Mountains, Antarctica. Particles are fresh glassy volcanic ash with diameters of ~50 μm, and chemical composition of the matrix glass belongs to a low-K basaltic andesite group, ranging from SiO2 60-62 wt% and K2O 0.40-0.50 wt%. Considering the grain size of ash particles and chemical composition of volcanic glass, the ash in tephra-bearing ice samples might be originated from the South Sandwich Islands located 2800 km northwest of the sampling sites. Correlations on major element concentrations with tephra layers associated with South Sandwich Islands in EPICA-Dome C, Vostok, and Dome Fuji ice cores show high similarity. Rock magnetic experiments show that the magnetic mineral is pseudo-single-domain titanomagnetite with ulvospinel content of 0.2-0.35 mixed with single-domain to superparamagnetic (titano)magnetite. Small blocks of the tephra-bering ice were measured with a SQUID gradiometer at 1-mm intervals with a spatial resolution of ~3 mm. With DC magnetic field of 25 mT, magnetic signal could be enhanced and detected for all the samples including the one with invisible amount of tephra particles. In order to simulate a thin ash layer in ice core, volcanic ash particles extracted from the tephra-bearing ice were used to fabricate a thin ash layer, which were subsequently magnetized, measured with the gradiometer. The noise level for Z axis gradiometer was about 0.6 pT. Detection limit for a half-cylinder with 29 mm radius and a thickness of 1 mm uniformly magnetized in X axis direction is ~9 × 10-5 A/m, which could be improved down to ~2 × 10-6 A/m by reducing the sensor-to-sample distance to 0.5 mm.

  15. Petrogenesis of the Miocene felsic volcanism from the south of Izmir (Western Turkey) and its regional tectono-magmatic implications

    NASA Astrophysics Data System (ADS)

    Karacik, Z.; Genç, C.

    2013-12-01

    Miocene volcanism, mainly intermediate and rarely mafic and felsic in composition, was produced under the effects of the extensional tectonic regime in western Turkey. The Karaburun and Cumaovasi volcanics are the cases for understanding the magma source(s) and petrological processes, producing the extension-related mafic and felsic bimodal volcanism. The Karaburun volcanics (KV) are mainly distributed north to south direction within the Karaburun peninsula and span a wide compositional spectrum from basalt (20 Ma) to rhyolite (16 Ma), and younger trachyte and trachydacites (13 Ma). The products of the subaerial felsic volcanism (the Cumaovasi volcanics, CV; 17 Ma) which are represented by cluster of topaz bearing rhyolite domes, related pyroclastic rocks occur within the NE-SW trending Cubukludag graben. The intermediate and mafic volcanic rocks are lack in the volcanic succession of CV. The lavas of the Cumaovasi volcanics are silicic which are calc alkaline, peralumious and enriched significantly in LILE. Extremely low Sr, Ba values, Eu depletions and very low LaN/YbN ratios are typical for rhyolites. The Karaburun volcanics, with the exception of the minor alkaline basaltic and trachytic lavas, are mainly calc alkaline and metaluminous intermediate lavas. The petrological data revealed that the KV and CV were formed in extensional tectonic setting, but evolved by different petrological processes in different magma chambers. The Cumaovasi lavas have a unique chemical composition, and closely similar to the extension related topaz bearing rhyolites formed from small magma bodies. Our data reveal that extension related mafic injections caused crustal anatectic melting and produced felsic melts that rapidly ascended into the upper crust.

  16. 40Ar-39Ar dating and tectonic implications of volcanic rocks recovered at IODP Hole U1342A and D on Bowers Ridge, Bering Sea

    NASA Astrophysics Data System (ADS)

    Sato, Keiko; Kawabata, Hiroshi; Scholl, David W.; Hyodo, Hironobu; Takahashi, Kozo; Suzuki, Katsuhiko; Kumagai, Hidenori

    2016-03-01

    During the Integrated Ocean Drilling Program (IODP), a total of 41.54 m of basement rock, consolidated volcaniclastic sediment, was recovered beneath a thin sediment cover. The drilled site is at the eastern end of the crestal area of Bowers Ridge, a north and westward sweeping offshoot of the Aleutian Arc into the Bering Sea. The volcanic sequence recovered from Holes U1342A and U1342D was divided into six major lithologic units. We used the single grain 40Ar-39Ar dating method performed by step-wise heated laser fusion technique to date andesites of Unit 1. Thereby two ages of Oligocene volcanism (34-32 Ma, 28-26 Ma) were distinguished each other according to our 40Ar-39Ar data. These ages refute a hypothesized Cretaceous origin in the North Pacific as an exotic arc massif or sector of the Hawaiian-Emperor chain and indicate that the Bowers Ridge is a Bering-Sea formed arc or remnant arc that ceased forming in the latest Oligocene to the earliest Miocene time.

  17. Geochemistry of subalkaline and alkaline extrusives from the Kermanshah ophiolite, Zagros Suture Zone, Western Iran: implications for Tethyan plate tectonics

    NASA Astrophysics Data System (ADS)

    Ghazi, A. Mohamad; Hassanipak, A. A.

    1999-06-01

    The Kermanshah ophiolite is a highly dismembered ophiolite complex that is located in western Iran and belongs to the Zagros orogenic system. The igneous rocks of this complex consist of both mantle and crustal suites and include peridotites (dunite and harzburgite), cumulate gabbros, diorites, and a volcanic sequence that exhibits a wide range in composition from subalkaline basalts to alkaline basalts to trachytes. The associated sedimentary rocks include a variety of Upper Triassic to Lower Cretaceous deep- and shallow-water sedimentary rocks (e.g., dolomite, limestone, and pelagic sediments, including umber). Also present are extensive units of radiolarian chert. The geochemical data clearly identifies some of the volcanic rocks to have formed from two distinct types of basaltic melts: (i) those of the subalkaline suite, which formed from an initial melt with a light rare earth elements (LREE) enriched signature and incompatible trace element patterns that suggest an island arc affinity; and (ii) those of the alkaline suite with LREE-enriched signature and incompatible trace element patterns that are virtually identical to typical oceanic island basalt (OIB) pattern. The data also suggests that the trachytes were derived from the alkaline source, with fractionation controlled by extensive removal of plagioclase and to a lesser extent clinopyroxene. The presence of compositionally diverse volcanics together with the occurrence of a variety of Triassic-Cretaceous sedimentary rocks and radiolarian chert indicate that the studied volcanic rocks from the Kermanshah ophiolite represent off-axis volcanic units that were formed in intraplate oceanic island and island arc environments in an oceanic basin. They were located on the eastern and northern flanks of one of the spreading centers of a ridge-transform fault system that connected Troodos to Oman prior to its subduction under the Eurasian plate.

  18. Geophysical, geochemical, mineralogical, and enivronmental data for rock samples collected in a mineralized volcanic environment, upper Animas River watershed, Colorado

    USGS Publications Warehouse

    McCafferty, A.E.; Horton, R.J.; Stanton, M.R.; McDougal, R.R.; Fey, D.L.

    2011-01-01

    * provide measurements to study the geochemical, mineralogical, and geophysical characteristics of rocks having weak to extreme degrees of alteration and to develop an understanding of how these characteristics change with alteration type. Data are provided in two digital formats: an Arc/Info geodatabase and a Microsoft Excel spreadsheet.

  19. Volcanic rocks of the Mendeleev Ridge (Arctic Ocean) - evidences for existence of the large igneous provinces within Arctic region: on the data of the High Arctic Russian Expedition "Arctic-2012"

    NASA Astrophysics Data System (ADS)

    Sergeev, Sergey; Petrov, Oleg; Morozov, Andrey; Kremenetsky, Alexander; Gusev, Evgeny; Shevchenko, Sergey; Krymsky, Robert; Belyatsky, Boris; Antonov, Anton; Rodionov, Nikolay

    2013-04-01

    During the complex geological-geophysical survey within August-October 2012 cruise of the Russian Expedition "Arctica-2012" on 9 sampling station (dredge, box-corer, drill-core) spaced on 450 km from the south to north alongside the Mendeleev Ridge were recovered more than 100 kg submarine volcanic rocks (which is represented about 10-15% of the total recovered bottom material), from calc-alkaline basalts, normal and subalkaline tholeites till andesite-dacites, typical lavas with glassy matrix and volcanic breccias, tuff-breccias and subvolcanic dolerites. We have studied 4 volcanic samples which are drill-cored (30-60 cm) of basement rocks at the depths of 2000-2500 m (79° and 83°N) or consolidate fragments of 30 kg weight collected at the steep escarpments with >45° slopes, three of them are tholeitic basalts (SiO2: 45.4-50.7, Al2O3: 13.7-21.7, MgO: 3.4-4.8, TiO2: 2.5-2.8, CaO: 4.7-11.4, Fe2O3: 5.9-14.4, Na2O: 2.9-3.8, K2O: 0.5-2.1 %), but the other one - is tuffobreccia with angular fragments of crystallized basalts and dolerites, and hydrated carbonatized (LOI up to 20%, ??2 - 35%) matrix. Isotopic and geochemical characteristics of the sample studied (low degree of REE fractionation: Cen/Ybn 1.6-2.2, moderate enrichment of HREE - 10-15×?1, low ratios of highly incompatible trace elements: Th/Ce = 0.03-0.04, Th/Nb = 0.14-0.16, Ce/Nb = 1.0-4.1) are very similar to those of high-Ti alkaline basalts of continental traps (CFB) connected with large mantle plume activities [Arndt et al., 1998; Hofmann, 1988] and close to the earlier discovered basalts from Chukcha borderland [Mukasa et al., 2009, 2012]. Measured Sr, Nd ? Pb isotope compositions of basalts vary from moderately enriched to moderately depleted compositions (143Nd/144Nd= 0.512706 - 0.512887, 87Sr/86Sr=0.704127-0.708580, 206Pb/204Pb=18.66-19.07, 207Pb/204Pb= 15.51-15.65, 208Pb/204Pb=38.42-39.20), reflecting different stages of secondary alterations, melt contamination by sedimentary material of host

  20. Mineralization on the moon? Theoretical considerations of Apollo 16 'rusty rocks', sulfide replacement in 67016, and surface-correlated volatiles on lunar volcanic glass

    NASA Astrophysics Data System (ADS)

    Colson, Russell O.

    Theoretical considerations of vapor-rock interactions in the lunar environment are a useful supplement to petrologic studies of mineralization or alteration in rocks from the moon. They also provide insights into the potential for the existence of more extensive mineralization on the moon than is found in the limited sample set. Discussed in this paper are the coexistence and textural association in 66095 of the phases lawrencite, troilite, schreibersite, iron metal, and sphalerite; the replacement of olivine in certain clasts of 67016 by troilite and enstatite; and the existence of Zn + S deposits on the surfaces of volcanic glass beads. Particular attention is given in each case to whether the observed mineralization implies that metals, as well as S, P, or Cl, have been mobilized in the vapor. Vapor species that might mobilize metals in the absence of H2O are considered. Most importantly, the suggestion is made that in the dry lunar environment carbonyl species may be important carriers of S and metals. The implications of this possibility are discussed.

  1. Mineralization on the moon? Theoretical considerations of Apollo 16 'rusty rocks', sulfide replacement in 67016, and surface-correlated volatiles on lunar volcanic glass

    NASA Technical Reports Server (NTRS)

    Colson, Russell O.

    1992-01-01

    Theoretical considerations of vapor-rock interactions in the lunar environment are a useful supplement to petrologic studies of mineralization or alteration in rocks from the moon. They also provide insights into the potential for the existence of more extensive mineralization on the moon than is found in the limited sample set. Discussed in this paper are the coexistence and textural association in 66095 of the phases lawrencite, troilite, schreibersite, iron metal, and sphalerite; the replacement of olivine in certain clasts of 67016 by troilite and enstatite; and the existence of Zn + S deposits on the surfaces of volcanic glass beads. Particular attention is given in each case to whether the observed mineralization implies that metals, as well as S, P, or Cl, have been mobilized in the vapor. Vapor species that might mobilize metals in the absence of H2O are considered. Most importantly, the suggestion is made that in the dry lunar environment carbonyl species may be important carriers of S and metals. The implications of this possibility are discussed.

  2. The pre-Kos Plateau Tuff Volcanic Rocks on Kefalos Peninsula (Kos Island, Dodecanese, Greece): Crescendo to the Largest Eruption of the Modern Aegean Arc

    NASA Astrophysics Data System (ADS)

    Bachmann, O.; Schnyder, C.

    2006-12-01

    Young volcanic rocks (K-Ar ages of 3 to 0.5 Ma) from the Kefalos Peninsula (Kos Island, Dodecanese, Greece) erupted prior to the voluminous (>60 km\\ 3) Kos Plateau Tuff (KPT; Ar-Ar age of 0.16 Ma) were studied in order to better define the conditions that led to the paroxysmal eruption of the modern Aegean Arc. Two different whole-rock compositions were sampled on Kefalos peninsula; dacites (63-65 wt% SiO2) and rhyolites (75-77 wt% SiO2). Kefalos dacites are crystal-rich (>40% crystals), show high Sr-Ba contents compared to other continental arcs, and have "adakitic" Sr/Y ratios (>40). Kefalos rhyolites are typical high- SiO2 arc magmas, similar in composition and mineralogy to the KPT, but displaying lower crystallinities (<5 vol% instead of >30% in most of the KPT). The high Sr/Y ratios of the dacites is surprising in an area where the subducting slab is not particularly hot and the continental crust relatively thin (~30 km). If the low Y and high Sr-Ba contents result from the fact that magma formed deep enough to supress plagioclase and have garnet present, dacite magma generation must have occurred in the mantle. There is geochemical and mineralogical evidence for the Kefalos and KPT rhyolites being generated by fractional crystallization from magmas similar to the Kefalos dacites. However, the few distinctions between KPT and Kefalos rhyolites (KPT is more voluminous, contains more crystals, has lower whole-rock U and Th contents, and lower MgO-SiO2, but higher Al2O3-FeOtot in biotite) suggest slightly different conditions in the magma chambers. These observations, together with increasing explosivity of the volcanic products from ~3 Ma to 0.16 Ma, may indicate that the build-up to the large KPT eruption could be the result of an increase in magmatic water input in the system through time.

  3. Trace elements and REE fractionation in subsoils developed on sedimentary and volcanic rocks: case study of the Mt. Vulture area, southern Italy

    NASA Astrophysics Data System (ADS)

    Mongelli, Giovanni; Paternoster, Michele; Rizzo, Giovanna; Sinisi, Rosa

    2014-06-01

    There is an increasing interest in the distribution of rare earth elements (REEs) within soils, primarily as these elements can be used to identify pedogenetic processes and because soils may be future sources for REE extraction, despite much attention should be paid to the protection and preservation of present soils. Here, we evaluate the processes that control the distribution of REEs in subsoil horizons developed over differing lithologies in an area of low anthropogenic contamination, allowing estimates of the importance of source rocks and weathering. Specifically, this study presents new data on the distribution of REEs and other trace elements, including transition and high-field-strength elements, in subsoils developed on both Quaternary silica-undersaturated volcanic rocks and Pliocene siliciclastic sedimentary rocks within the Mt. Vulture area of the southern Apennines in Italy. The subsoils in the Mt. Vulture area formed during moderate weathering (as classified using the chemical index of alteration) and contain an assemblage of secondary minerals that is dominated by trioctahedral illite with minor vermiculite. The REEs, high-field-strength elements, and transition metals have higher abundances in subsoils that developed from volcanic rocks, and pedogenesis caused the Mt. Vulture subsoils to have REE concentrations that are an order of magnitude higher than typical values for the upper continental crust. This result indicates that the distribution of REEs in soils is a valuable tool for mineral exploration. A statistical analysis of inter-elemental relationships indicates that REEs are concentrated in clay-rich fractions that also contain significant amounts of low-solubility elements such as Zr and Th, regardless of the parent rock. This suggests that low-solubility refractory minerals, such as zircon, play a significant role in controlling the distribution of REEs in soils. The values of (La/Yb)N and (Gd/Yb)N fractionation indices are dependent on

  4. Dual-porosity analysis of conservative tracer testing in saturated volcanic rocks at Yucca Mountain in Nye County, Nevada

    USGS Publications Warehouse

    Fahy, M.F.

    1997-01-01

    A radially convergent conservative tracer injection test was conducted between boreholes UE-25 #2 and UE-25 c #3 of the C-hole complex at Yucca Mountain to determine effective porosity and longitudinal dispersivity. Approximately 47% of the tracer mass was recovered and a dual-porosity analytical model replicates the breakthrough curve. Fractured-rock analyses focus on the fracture-porosity and geometry as the controlling factors in transport.

  5. Rock magnetic studies on sediments from Erlongwan maar lake, Long Gang Volcanic Field, Jilin province, NE China

    NASA Astrophysics Data System (ADS)

    Frank, Ute

    2007-01-01

    Detailed rock magnetic investigations were carried out on two 23-m-long sediment cores from Erlongwan maar lake, NE China. The completely laminated sediment sequence of the lake is interrupted by 410 graded layers with thicknesses between 0.1 and 150 cm. Magnetite of PSD-size was identified as the main magnetic carrier mineral by temperature-dependent measurements of the saturation magnetization and determination of hysteresis parameters. The minerogenic components in the laminated sediments and the graded layers are nearly identical, and their rock magnetic characteristics reflect the prevailing conditions, anoxic or oxic, during deposition. The most reliable criteria for estimating the availability of oxygen is whether an increase in minerogenic influx is linked to a shift in the magnetic grain size spectrum to coarser (oxic) or finer (anoxic) grains. Comparison of different rock magnetic parameters indicative for magnetic grain size and coercitivity revealed, that the S-ratio which is known to reflect the presence of high coercive minerals, is grain size indicative in sediments with a monomineralic magnetic composition.

  6. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater

    PubMed Central

    Morris, Richard V.; Vaniman, David T.; Blake, David F.; Gellert, Ralf; Chipera, Steve J.; Rampe, Elizabeth B.; Ming, Douglas W.; Morrison, Shaunna M.; Downs, Robert T.; Treiman, Allan H.; Yen, Albert S.; Grotzinger, John P.; Achilles, Cherie N.; Bristow, Thomas F.; Crisp, Joy A.; Des Marais, David J.; Farmer, Jack D.; Fendrich, Kim V.; Graff, Trevor G.; Morookian, John-Michael; Stolper, Edward M.; Schwenzer, Susanne P.

    2016-01-01

    Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO2 and Fe2O3T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin’s tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill. PMID:27298370

  7. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater.

    PubMed

    Morris, Richard V; Vaniman, David T; Blake, David F; Gellert, Ralf; Chipera, Steve J; Rampe, Elizabeth B; Ming, Douglas W; Morrison, Shaunna M; Downs, Robert T; Treiman, Allan H; Yen, Albert S; Grotzinger, John P; Achilles, Cherie N; Bristow, Thomas F; Crisp, Joy A; Des Marais, David J; Farmer, Jack D; Fendrich, Kim V; Frydenvang, Jens; Graff, Trevor G; Morookian, John-Michael; Stolper, Edward M; Schwenzer, Susanne P

    2016-06-28

    Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides-perchlorates-chlorates), and has minor TiO2 and Fe2O3T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a "Lake Gale" catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

  8. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater

    NASA Astrophysics Data System (ADS)

    Morris, Richard V.; Vaniman, David T.; Blake, David F.; Gellert, Ralf; Chipera, Steve J.; Rampe, Elizabeth B.; Ming, Douglas W.; Morrison, Shaunna M.; Downs, Robert T.; Treiman, Allan H.; Yen, Albert S.; Grotzinger, John P.; Achilles, Cherie N.; Bristow, Thomas F.; Crisp, Joy A.; Des Marais, David J.; Farmer, Jack D.; Fendrich, Kim V.; Frydenvang, Jens; Graff, Trevor G.; Morookian, John-Michael; Stolper, Edward M.; Schwenzer, Susanne P.

    2016-06-01

    Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ˜40 wt.% crystalline and ˜60 wt.% X-ray amorphous material and a bulk composition with ˜74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (˜17 wt.% of bulk sample), tridymite (˜14 wt.%), sanidine (˜3 wt.%), cation-deficient magnetite (˜3 wt.%), cristobalite (˜2 wt.%), and anhydrite (˜1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (˜39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides‑perchlorates‑chlorates), and has minor TiO2 and Fe2O3T oxides (˜5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

  9. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater

    NASA Astrophysics Data System (ADS)

    Morris, Richard V.; Vaniman, David T.; Blake, David F.; Gellert, Ralf; Chipera, Steve J.; Rampe, Elizabeth B.; Ming, Douglas W.; Morrison, Shaunna M.; Downs, Robert T.; Treiman, Allan H.; Yen, Albert S.; Grotzinger, John P.; Achilles, Cherie N.; Bristow, Thomas F.; Crisp, Joy A.; Des Marais, David J.; Farmer, Jack D.; Fendrich, Kim V.; Frydenvang, Jens; Graff, Trevor G.; Morookian, John-Michael; Stolper, Edward M.; Schwenzer, Susanne P.

    2016-06-01

    Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ˜40 wt.% crystalline and ˜60 wt.% X-ray amorphous material and a bulk composition with ˜74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (˜17 wt.% of bulk sample), tridymite (˜14 wt.%), sanidine (˜3 wt.%), cation-deficient magnetite (˜3 wt.%), cristobalite (˜2 wt.%), and anhydrite (˜1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (˜39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides-perchlorates-chlorates), and has minor TiO2 and Fe2O3T oxides (˜5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

  10. Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater.

    PubMed

    Morris, Richard V; Vaniman, David T; Blake, David F; Gellert, Ralf; Chipera, Steve J; Rampe, Elizabeth B; Ming, Douglas W; Morrison, Shaunna M; Downs, Robert T; Treiman, Allan H; Yen, Albert S; Grotzinger, John P; Achilles, Cherie N; Bristow, Thomas F; Crisp, Joy A; Des Marais, David J; Farmer, Jack D; Fendrich, Kim V; Frydenvang, Jens; Graff, Trevor G; Morookian, John-Michael; Stolper, Edward M; Schwenzer, Susanne P

    2016-06-28

    Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides-perchlorates-chlorates), and has minor TiO2 and Fe2O3T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a "Lake Gale" catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill. PMID:27298370

  11. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

    USGS Publications Warehouse

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.

    2009-01-01

    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  12. Complementary trace-element fractionation in volcanic and plutonic rocks: imperfect examples from ocean-floor basalts and gabbros

    NASA Astrophysics Data System (ADS)

    Delong, Stephen E.; Chatelain, Carole

    1989-06-01

    A simple trace-element model that is generalized from one devised by Albarede (1976) can be used to treat plutonic rocks as mixtures of cumulate phases and trapped liquid. The model is based on the Rayleigh fractionation law, mass balance, and modal data and, with certain assumptions, can give estimates of the mass fraction of the liquid component ( X l) in a cumulate rock and of some of the characteristics of that liquid, including trace-element concentrations and the mass fraction of the original liquid ( F) that remained in the magma chamber when some of it was trapped. Application of the model to Cr and Zr data for ten dredged gabbros from the Oceanographer Fracture Zone (OFZ) in the North Atlantic yields results in the range X l=0.014 0.17 and F=0.04 0.22. A more complex model extends the equations developed by Greenland (1970) and combines them with constraints from 1-atm experiments on ocean-floor basalts to effectively map phase-saturation boundaries onto trace-element variation diagrams. On a Zr-Sr plot, the model is capable of mimicking mixing chords and differences in liquid lines of descent (or parental compositions) inferred from major-element chemistry for several OFZ basalts. Qualitatively, the associated gabbros can also be rationalized as cumulate/melt mixtures on this diagram, although the allowable range of liquid compositions is large. In addition, there is some suggestion that the Zr-Sr liquid line of descent fitted to the OFZ basalts may have more general relevance to other ocean-floor rocks (e.g., Galapagos and FAMOUS glasses).

  13. Evidence From Adakitic Rocks For Lithosphere Recycling At The U.S. East Coast Volcanic Rifted Margin

    NASA Astrophysics Data System (ADS)

    Meyer, R.; Van Wijk, J. W.

    2014-12-01

    Magmatism at magmatic rifted margins is dominated by asthenospheric melts generated during decompression melting from the upwelling asthenosphere. However reported magma compositions are diverse, giving clues about additional processes during rifting and continental rupture. We report here on adakites from the U.S. East Coast that are related to breakup of the North Atlantic. The sampled adakites are bi-modal, and show a clear high-Si and low-Si major and trace element chemistry. During the closure of the proto-Atlantic and its related back-arc basins, the Appalachian lithosphere sampled an ophiolitic mélange within major sutures. Subsequent metamorphic events in the Blue Ridge province of the U.S. East Coast increased the rock density of the ophiolites (eclogite) and partly hydrated these mafic to ultramafic rocks. Such a preconditioned lithosphere will likely develop gravitational instabilities at the asthenosphere-lithosphere boundary during rifting. We use geodynamic models to show when gravitational instabilities form below the East Coast margin, and how they eventually delaminate mantle lithosphere and lower crust material. After foundering, the delaminated lithosphere undergoes metamorphism, heats up, and interacts with fluids and melts in the surrounding convecting mantle. Partial melting of this metamorphic lithology produces high-Si adakitic melts. These melts percolated upwards through the mantle and were partially injected into the Valley and Ridge province. Where melt-to-peridotite (asthenosphere) ratios were small, the melts and fluids leaving the sinking lithospheric block became fixed within the peridotites. Geochemical modeling suggests, that 5 to 10% melting degrees of such a metasomatically overprinted and fertile asthenosphere produced the low-Si adakitic rocks of the Virginia adakites.

  14. Geology of Volcan Las Navajas, a pleistocene trachyte/peralkaline rhyolite volcanic center in Nayarit, Mexico

    SciTech Connect

    Hegre, J.A.; Nelson, S.A.

    1985-01-01

    Volcan Las Navajas, located in the northwestern portion of the Mexican Volcanic Belt has produced a sequence of volcanic rocks with compositions in marked contrast to the predominantly calc-alkaline volcanoes which predominate in this part of Mexico. The oldest exposed lavas consist of trachytes with 63% SiO/sub 2/, 6% FeO*, and 500 ppm Zr along with comenditic rhyolites with 68% SiO/sub 2/, 5% FeO*, 800 ppm Zr, and an agpaitic index of 1.0. These lavas were followed by the eruption of a comenditic ash-flow tuff and the formation of a caldera 2.7 km in diameter. This caldera was subsequently filled by eruptions of pantelleritic rhyolite obsidian lava flows with 72% SiO/sub 2/, 8% FeO*, 1100 ppm Zr, and an agpaitic index of 1.5 to 1.9. A second caldera was then formed which is offset to the south of the main eruptive vents for previous eruptions. This younger caldera has a diameter of about 4.8 km and its southern walls have been covered by calc-alkaline andesitic lavas erupted from nearby Sanganguey volcano. Volcanoclastic sediments in the floor of the younger caldera have been tilted and faulted in a manner suggestive of late stage resurgence. Subsequent eruptions within the caldera, however, have been restricted to calc-alkaline andesites. Tectonically, the area in which this volcano occurs appears to have been undergoing a crustal rifting event since the Pliocene. The occurrence of these peralkaline rocks lends further support to such a hypothesis.

  15. Earthquake-induced seismic tremor explained by Krauklis wave resonance in fractured reservoir rocks: A case study of Salse di Nirano mud volcanic field (Italy)

    NASA Astrophysics Data System (ADS)

    Frehner, Marcel; Lupi, Matteo

    2014-05-01

    For seismic studies of fractured fluid-filled reservoir rocks, the so-called Krauklis wave is of particular interest. It is a special guided wave mode that is bound to and propagates along fluid-filled fractures. It can repeatedly propagate back and forth along a fracture and eventually fall into resonance. This resonant behavior has been speculated to be the source of narrow-band seismic tremor and long-period events in volcanic areas. However, it remains unstudied whether Krauklis waves may be initiated by body waves and therefore be relevant for active seismic surveys or earthquake signals in fractured reservoir rocks. The presented study consists of two parts: A combined theoretical-numerical study on the possible initiation of Krauklis wave resonance in fractures by an incident body wave Application of the theoretical resonance frequency of Krauklis waves to narrow-band seismic tremor signals recorded above a mud volcanic system to determine fracture size within the fluid-filled reservoir. In the first part, we study Krauklis wave initiation by an incident plane P- or S-wave using numerical finite-element simulations. Both wave modes initiate two Krauklis waves, one at each fracture tip, with significant amplitudes that strongly depend on the orientation of the facture. S-waves generally lead to larger-amplitude Krauklis waves, with maximum amplitudes at fracture angles of 50º, while P-waves initiate large-amplitude Krauklis waves at moderate (12°-40°) and high (>65°) fracture angles. The fact that large-amplitude Krauklis waves are initiated by body waves has severe implications for earthquake signals propagating through fractured reservoirs, because Krauklis wave-related signals are expected to be present in seismic recordings. The second part is a case study of the Salse di Nirano mud volcanic field in northern Italy. Immediately after a M4.4 earthquake with a dominant frequency of 2 Hz, the recorded seismic tremor increased significantly with a

  16. The Satah Mountain and Baldface Mountain volcanic fields: Pleistocene hot spot volcanism in the Anahim Volcanic Belt, west-central British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Kuehn, Christian; Guest, Bernard; Russell, James K.; Benowitz, Jeff A.

    2015-03-01

    The Satah Mountain and Baldface Mountain volcanic fields (SMVF, BMVF) comprise more than three dozen small volcanic centers and erosional remnants thereof. These fields are located in the Chilcotin Highland of west-central British Columbia, Canada, and are spatially associated with the Anahim Volcanic Belt (AVB), a linear feature of alkaline to peralkaline plutonic and volcanic centers of Miocene to Holocene ages. The AVB has been postulated to be the track of a hot spot passing beneath the westward moving Cordilleran lithosphere. We test the AVB hot spot model by applying whole-rock 40Ar/39Ar geochronology ( n = 24) and geochemistry. Whole-rock chemical compositions of volcanic rock samples ( n = 59) from these two fields suggest a strong geochemical affinity with the nearby Itcha Range shield volcano; however, SMVF and BMVF centers are mostly small in volume (<1 km3) and differ in composition from one another, even where they are in close spatial proximity. Trace element and REE patterns of mafic AVB lavas are similar to ocean island basalts (OIB), suggesting a mantle source for these lavas. The age ranges for the SMVF ( n = 11; ~2.21 to ~1.43 Ma) and BMVF ( n = 7; ~3.91 to ~0.91 Ma) are largely coeval with the Itcha Range. The distribution of volcanoes in these two volcanic fields is potentially consistent with the postulated AVB hot spot track. Eruption rates in the SMVF were high enough to build an elongated ridge that deviates from the E-W trend of the AVB by almost 90°. This deviation might reflect the mechanisms and processes facilitating magma generation and ascent through the lithosphere in this tectonically complex region and may also indicate interaction of the potential hot spot with (pre)existing fracture systems in vicinity of the Itcha Range.

  17. Geologic and chemical evolution of volcan tepetiltic, Nayarit, Mexico

    SciTech Connect

    Deremer, L.A.; Nelson, S.A.

    1985-01-01

    Volcan Tepetiltic is located in the northwestern segment of the Mexican Volcanic Belt, about 40 km SW of the city of Tepic. The structure is a calc-alkaline stratovolcano composed primarily of andesite and dacite lava flows topped by an elliptical caldera measuring approximately 5 by 2.5 km. At least two cycles of andesite volcanism followed by rapid differentiation into volumetrically subordinate dacite flows and dikes built the majority of the complex. The second pulse of andesitic lavas were more basic than the first and appear to have been the result of reinjection of mafic magma into the shallow andesitic magma chamber. This was closely followed by the emplacement of two rhyolite domes and associated ash deposits on the eastern flank of the volcano. Finally, two small hornblende andesite domes were erupted on the floor of the caldera, and a lake formed in the northeastern corner of the caldera. Cinder cones on the flanks of the volcano have erupted alkaline lavas of mugearitic affinity. These are chemically unrelated to the calc-alkaline lavas erupted from Tepetiltic itself. The latest activity of Tepetiltic was the emplacement of a crystal rich rhyolite domes on the southern flank, which has blocked stream drainages to form a coulee lake. This last event has occurred within the last several thousand years. The rocks erupted from Tepetiltic form a chemically continuous suite which could have been derived through crystal fractionation of andesitic magma. No basic parental magmas, however, have erupted throughout the area.

  18. Volcanics oil bearing in Indonesia

    SciTech Connect

    Lukman, K.A.; Nyak, B.R.; Anditya, I.M. )

    1996-01-01

    The volcanic rock is seldom considered as good reservoir rocks. However, in Indonesia there is a volcanic layer called the Jatibarang Formation in Jatibarang Field, West Java, that has proven to be a producer of oil and gas of adequate amount. The lateral development of this rock extent along the whole of the basin, about 400 km over a Tertiary block-faulting system of the North West Java Basin. It is estimated that the volume of the spread is about 2360 km[sup 3]. Beside from the primary volcanic rock, the developing reservoir rock could also resulted from rework of massive volcanics or agglomerate, and other volcanic product resedimented as clastic deposits. The hydrocarbon is sourced from the younger Talang Aker Formation that is in direct contact with the reservoir rock. It migrated through the faults. Present cumulative production has reached 1.2 BBC and 2.7 TCFG, while speculative reserve is estimated at 4.0 BBO and 3 TCFG. Regionally, the volcanic rock of the Jatibarang Formation where the hydrocarbon is found is the result of eruptions along the magmatic trend during Late Cretaceous. In North West Java Basin, the trapping system includes both the structural and stratigraphic traps. Reservoir analysis yields pororsity values of around 16-25% and permeability of around 10 Darcies. It is concluded that there are good opportunities still left for hydrocarbon exploration in volcanic rocks. The study is discussed in detail, supported by data from cores and laboratories.

  19. Volcanics oil bearing in Indonesia

    SciTech Connect

    Lukman, K.A.; Nyak, B.R.; Anditya, I.M.

    1996-12-31

    The volcanic rock is seldom considered as good reservoir rocks. However, in Indonesia there is a volcanic layer called the Jatibarang Formation in Jatibarang Field, West Java, that has proven to be a producer of oil and gas of adequate amount. The lateral development of this rock extent along the whole of the basin, about 400 km over a Tertiary block-faulting system of the North West Java Basin. It is estimated that the volume of the spread is about 2360 km{sup 3}. Beside from the primary volcanic rock, the developing reservoir rock could also resulted from rework of massive volcanics or agglomerate, and other volcanic product resedimented as clastic deposits. The hydrocarbon is sourced from the younger Talang Aker Formation that is in direct contact with the reservoir rock. It migrated through the faults. Present cumulative production has reached 1.2 BBC and 2.7 TCFG, while speculative reserve is estimated at 4.0 BBO and 3 TCFG. Regionally, the volcanic rock of the Jatibarang Formation where the hydrocarbon is found is the result of eruptions along the magmatic trend during Late Cretaceous. In North West Java Basin, the trapping system includes both the structural and stratigraphic traps. Reservoir analysis yields pororsity values of around 16-25% and permeability of around 10 Darcies. It is concluded that there are good opportunities still left for hydrocarbon exploration in volcanic rocks. The study is discussed in detail, supported by data from cores and laboratories.

  20. Magnetotelluric survey for exploration of a volcanic-rock reservoir in the Yurihara oil and gas field, Japan

    SciTech Connect

    Mitsuhata, Yuji; Matsuo, Koichi; Minegishi, Masato

    1999-03-01

    The Yurihara oil and gas field is located on the southern edge of Akita Prefecture, northeastern Japan. In this area, drilling, surface geological surveys and many seismic surveys have been used to investigate the geological structure. Wells drilled into the Nishikurosawa Basalt Group (NBG) of Miocene age found oil and gas reservoirs at depths of 1.5--2 km. Oil and gas are now being produced commercially and further exploration is required in the surrounding areas. However, since the neighboring areas are covered with young volcanic products from the Chokai volcano, and have a rough topography, the subsurface distribution of the NBG must be investigated using other methods in addition to seismic reflection. According to the well data, the resistivity of the NBG is comparatively higher than that of the overlying sedimentary formations, and therefore the magnetotelluric (MT) method is expected to be useful for the estimation of the distribution of the NBG. An MT survey was conducted along three survey lines in this area. Each line trended east-west, perpendicular to the regional geological strike, and was composed of about 25 measurement sites. Induction vectors evaluated from the magnetic field show that this area has a two-dimensional structure. The evaluated resistivity sections are in agreement with the log data. In conclusion, the authors were able to detect resistive layers (the NBG) below conductive layers. The results indicate that the NBG becomes gradually less resistive from north to south. In the center of the northern line, an uplifted resistive area is interpreted as corresponding to the reservoir. By comparison with a seismic section, the authors prove the effectiveness of the integration of seismic and MT surveys for the investigation of the morphology and internal structure of the NBG. On other survey lines, the resistive uplifted zones are interpreted as possible prospective areas.

  1. Subterranean fragmentation of magma during conduit initiation and evolution in the shallow plumbing system of the small-volume Jagged Rocks volcanoes (Hopi Buttes Volcanic Field, Arizona, USA)

    NASA Astrophysics Data System (ADS)

    Re, Giuseppe; White, James D. L.; Muirhead, James D.; Ort, Michael H.

    2016-08-01

    Monogenetic volcanoes have limited magma supply and lack long-lived sustained magma plumbing systems. They erupt once, often from multiple vents and sometimes over several years, and are rarely or never re-activated. Eruptive behavior is very sensitive to physical processes (e.g., volatile exsolution, magma-water interaction) occurring in the later stages of magma ascent at shallow crustal depths (<1 km), which yield a spectrum of eruptive styles including weak to moderate explosive activity, violent phreatomagmatism, and lava effusion. Jagged Rocks Complex in the late Miocene Hopi Buttes Volcanic field (Arizona, USA) exposes the frozen remnants of the feeding systems for one or a few monogenetic volcanoes. It provides information on how a shallow magmatic plumbing system evolved within a stable non-marine sedimentary basin, and the processes by which magma flowing through dikes fragmented and conduits were formed. We have identified three main types of fragmental deposits, (1) buds (which emerge from dikes), (2) pyroclastic massifs, and (3) diatremes; these represent three different styles and intensities of shallow-depth magma fragmentation. They may develop successively and at different sites during the evolution of a monogenetic volcano. The deposits consist of a mixture of pyroclasts with varying degrees of welding and country-rock debris in various proportions. Pyroclasts are commonly welded together, but also reveal in places features consistent with phreatomagmatism, such as blocky shapes, dense groundmasses, and composite clasts (loaded and cored). The extent of fragmentation and the formation of subterranean open space controlled the nature of the particles and the architecture and geometry of these conduit structures and their deposits.

  2. 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

  3. Volcanic gas

    USGS Publications Warehouse

    McGee, Kenneth A.; Gerlach, Terrance M.

    1995-01-01

    In Roman mythology, Vulcan, the god of fire, was said to have made tools and weapons for the other gods in his workshop at Olympus. Throughout history, volcanoes have frequently been identified with Vulcan and other mythological figures. Scientists now know that the “smoke" from volcanoes, once attributed by poets to be from Vulcan’s forge, is actually volcanic gas naturally released from both active and many inactive volcanoes. The molten rock, or magma, that lies beneath volcanoes and fuels eruptions, contains abundant gases that are released to the surface before, during, and after eruptions. These gases range from relatively benign low-temperature steam to thick hot clouds of choking sulfurous fume jetting from the earth. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other volcanic gases are hydrogen sulfide, hydrochloric acid, hydrogen, carbon monoxide, hydrofluoric acid, and other trace gases and volatile metals. The concentrations of these gas species can vary considerably from one volcano to the next.

  4. Petrochemical features of Miocene volcanism around the Çubukludağ graben and Karaburun peninsula, western Turkey: Implications for crustal melting related silicic volcanism

    NASA Astrophysics Data System (ADS)

    Karacık, Z.; Genç, Ş. C.; Gülmez, F.

    2013-09-01

    Widespread Neogene volcanism, mainly intermediate and rarely mafic and felsic in composition, was controlled by the extensional tectonic regime in western Turkey. The Karaburun and Cumaovası volcanics are the cases for understanding the magma source(s) and petrological processes, producing the extension-related mafic and felsic volcanism. The Karaburun volcanics (KV) are mainly oriented north to south in the Karaburun peninsula and span a wide spectrum from basalt (20 Ma) to rhyolite (16 Ma), and younger trachyte and trachydacites (13 Ma). The products of the subaerial silicic volcanism (the Cumaovası volcanics, CV; 17 Ma) which are represented by cluster of rhyolite domes, related pyroclastics occur within the NE-SW trending Çubukludağ graben, and intermediate and mafic volcanic rocks are lack in this area. The lavas of the Cumaovası volcanics are high silica rhyolites and rare dacites which are calc alkaline, peralumious and enriched significantly in LILE. Extremely low Sr, Ba values, extremely Eu depletions and very low LaN/YbN ratios are typical for the rhyolites of CV, similar to the topaz rhyolites. The Karaburun volcanics, with the exception of the minor alkaline basaltic and trachytic lavas, are mainly calc alkaline and metaluminous intermediate lavas. 87Sr/86Sr ratios of the KV and dacitic samples of CV are close to each other and range from 0.708 to 0.709; while Sr isotopic ratios of the rhyolites are significantly high and variable (0.724-0.786). 143Nd/144Nd ratios of the CV and KV, except for the alkaline samples, are similar for both sequences vary from 0.51230 to 0.51242. Geological, geochemical, isotopic and radiochronologic data reveal that the KV and CV were formed in extensional tectonic setting, but evolved by different petrological processes in different magma chambers. During the Neogene, underplated mafic magma was injected into the crust and hybridized by mantle and crustal derived materials. Geochemical features and trace element

  5. Basaltic rocks from the Andean Southern Volcanic Zone: Insights from the comparison of along-strike and small-scale geochemical variations and their sources

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, Rosemary; Holbik, Sven; Tormey, Daniel; Frey, Frederick A.; Moreno Roa, Hugo

    2016-08-01

    The origin of spatial variations in the geochemical characteristics of volcanic rocks erupted in the Andean Southern Volcanic Zone (SVZ) has been studied by numerous researchers over the past 40 years. Diverse interpretations for along-strike, across-strike, and small-scale variations have been proposed. In this paper, we review geochemical data showing along-strike geochemical variations and address the processes causing such trends. We compare large- and small-scale changes of the same geochemical parameters in basaltic rocks in order to use spatial scale as a tool for isolating processes that may have the same result. Along-strike geochemical variations in the SVZ are expected, due to 1) greater thickness or age of the sub-arc continental crust and mantle lithosphere in the Northern SVZ (NSVZ; 33°S-34°30‧S) and Transitional SVZ (TSVZ; 34°30‧S-37°S) compared with the Central SVZ (CSVZ; 37°S-41.5°S) and Southern SVZ (SSVZ: 41.5°S-46°S); and 2) along-strike changes of the subducting Nazca plate and overlying asthenosphere. Basalts and basaltic andesites erupted at volcanic front stratovolcanoes define several along-strike geochemical trends: 1) higher 87Sr/86Sr and lower 143Nd/144Nd at volcanoes in the NSVZ compared with the TSVZ, CSVZ, and SSVZ; 2) higher and more variable La/Yb at volcanoes in the NSVZ and TSVZ compared with the CSVZ and SSVZ; 3) lower 87Sr/86Sr for a given 143Nd/144Nd at volcanoes in the TSVZ compared with the CSVZ and SSVZ; and 4) large values for time-sensitive subduction tracers such as 10Be/9Be and (238U/230Th) at some volcanoes in the CSVZ, but not in the NSVZ and TSVZ. Geochemical parameters that distinguish the TSVZ from the CSVZ and SSVZ are also found within the CSVZ at small basaltic eruptive centers (SEC) aligned with the Liquiñe-Ofqui Fault System (LOFS), which extends from 38°S to the southernmost SVZ. Our interpretation is that CSVZ magmas with strong time-sensitive subduction tracers represent the ambient subduction

  6. Database for the Geologic Map of Upper Eocene to Holocene Volcanic and Related Rocks of the Cascade Range, Oregon

    USGS Publications Warehouse

    Nimz, Kathryn; Ramsey, David W.; Sherrod, David R.; Smith, James G.

    2008-01-01

    Since 1979, Earth scientists of the Geothermal Research Program of the U.S. Geological Survey have carried out multidisciplinary research in the Cascade Range. The goal of this research is to understand the geology, tectonics, and hydrology of the Cascades in order to characterize and quantify geothermal resource potential. A major goal of the program is compilation of a comprehensive geologic map of the entire Cascade Range that incorporates modern field studies and that has a unified and internally consistent explanation. This map is one of three in a series that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of rock units distinguished by composition and age; map sheets of the Cascade Range in Washington (Smith, 1993) and California will complete the series. The complete series forms a guide to exploration and evaluation of the geothermal resources of the Cascade Range and will be useful for studies of volcano hazards, volcanology, and tectonics. This digital release contains all the information used to produce the geologic map published as U.S. Geological Survey Geologic Investigations Series I-2569 (Sherrod and Smith, 2000). The main component of this digital release is a geologic map database prepared using ArcInfo GIS. This release also contains files to view or print the geologic map and accompanying descriptive pamphlet from I-2569.

  7. Results of analyses performed on basalt adjacent to penetrators emplaced into volcanic rock at Amboy, California, April 1976

    NASA Technical Reports Server (NTRS)

    Blanchard, M.; Bunch, T.; Davis, A.; Shade, H.; Erlichman, J.; Polkowski, G.

    1977-01-01

    The physical and chemical modifications found in the basalt after impact of four penetrators were studied. Laboratory analyses show that mineralogical and elemental changes are produced in the powdered and crushed basalt immediately surrounding the penetrator. Optical microscopy studies of material next to the skin of the penetrator revealed a layer, 0-2 mm thick, of glass and abraded iron alloy mixed with fractured mineral grains of basalt. Elemental analysis of the 0-2 mm layer revealed increased concentrations of Fe, Cr, Ni, No, and Mn, and reduced concentrations of Mg, Al, Si, and Ca. The Fe, Cr, Ni, and Mo were in fragments abraded from the penetrator. Mineralogical changes occurring in the basalt sediment next to the penetrator include the introduction of micron-size grains of alpha-iron, magnetite, and hematite. The newly formed silicate minerals include metastable phases of silica (tridymite and cristobalite). An increased concentration of Fe, Cr, Ni, and Mo occurred in the 2-mm to 1-cm layer of penetrator no. 1, which impacted at the highest velocity. No elemental concentration increase was noted for penetrators nos. 2 and 3 in the 2-mm to 1-cm layer. Contaminants introduced by the penetrator occur up to 1 cm away from the penetrator's skin. Although volatile elements do migrate and new minerals are formed during the destruction of host minerals in the crushed rock, no changes were observed beyond the 1-cm distance.

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

    USGS Publications Warehouse

    Maldonado, Florian; Koether, S.L.

    1983-01-01

    A continuously cored drill hole designated as USW G-2, located at Yucca Mountain in southwestern Nevada, penetrated 1830.6 m of Tertiary volcanic strata composed of abundant silicic ash-flow tuffs, minor lava and flow breccias, and subordinate volcaniclastic rocks. The volcanic strata penetrated are comprised of the following in descending order: Paintbrush Tuff (Tiva Canyon Member, Yucca Mountain Member, bedded tuff, Pah Canyon Member, and Topopah Spring Member), tuffaceous beds of Calico Hills, Crater Flat Tuff (Prow Pass Member, Bullfrog Member, and Tram unit), lava and flow breccia (rhyodacitic), tuff of Lithic Ridge, bedded and ash-flow tuff, lava and flow breccia (rhyolitic, quartz latitic, and dacitic), bedded tuff, conglomerate and ash-flow tuff, and older tuffs of USW G-2. Comparison of unit thicknesses at USW G-2 to unit thicknesses at previously drilled holes at Yucca Mountain indicate the following: (1) thickening of the Paintbrush Tuff members and tuffaceous beds of Calico Hills toward the northern part of Yucca Mountain; (2) thickening of the Prow Pass Member but thinning of the Bullfrog Member and Tram unit; (3) thinning of the tuff of Lithic Ridge; (4) presence of approximately 280 m of lava and flow breccia not previously penetrated by any drill hole; and (5) presence of an ash-flow tuff unit at the bottom of the drill hole not previously intersected, apparently the oldest unit penetrated at Yucca Mountain to date. Petrographic features of some of the units include: (1) decrease in quartz and K-feldspar and increases in biotite and plagioclase with depth in the tuffaceous beds of Calico Hills; (2) an increase in quartz phenocrysts from the top to the bottom members of the Crater Flat Tuff; (3) a low quartz content in the tuff of Lithic Ridge, suggesting tapping of the magma chamber at quartz-poor levels; (4) a change in zeolitic alteration from heulandite to clinoptilolite to mordenite with increasing depth; (5) lavas characterized by a rhyolitic

  9. Revealing magma degassing below closed-conduit active volcanoes: Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy)

    NASA Astrophysics Data System (ADS)

    Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.

    2016-04-01

    The elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions have been measured for rocks at various degrees of evolution and belonging to high-K calcalkaline-shoshonitic and shoshonitic-potassic series in order to cover the entire volcanological history of Vulcano Island (Italy). The major- and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the theoretical value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic history of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-erupted Vulcanello latites (Punta del Roveto), which have anomalously high He isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs, since an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He-isotope ratios between fluid inclusions and fumarolic gases shows that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that the most probable magma which actually feeds the fumarolic emissions is a latitic body that ponded at about 3-3.5 km of depth and is flushed by fluids coming from a deeper and basic magma.

  10. Effect of Weathering Processes on Mineralogical and Mechanical Properties of Volcanic Rocks Used as Ballast Material for Railway Between Sabuncupinar and Kütahya in Western Turkey

    NASA Astrophysics Data System (ADS)

    Abiddin Erguler, Zeynal; Adıgüzel, Ömer; Derman, Mustafa

    2015-04-01

    Geomaterials used in engineering projects and man-made structures such as railway ballasts, buildings, historical structures, monuments and tombstones naturally weather as a result of various physico-chemical factors. Due to being long-term exposure to the anthroposphere, geomaterials used for these purposes provides important information to the researchers for understanding the effect of weathering processes on their time dependent physical, mineralogical and mechanical changes. Thus, researchers frequently can take advantage of available engineering time of man-made structures to assess weathering properties of the geomaterials used in their construction in terms of time dependent durability and stability of these structures. Considering the fact that railway ballasts produced from natural deposits of limestone, dolomite, granite, basalt etc., supply an important contribution for evaluation weathering processes, a research was carried out to determine the effect of weathering as a function of time on physical, mineralogical and mechanical properties of ballasts used for railway between Kütahya and Sabuncupınar in western Turkey. For this purpose, fresh and weathered rock samples exposed to physical and chemical weathering processes at different times were collected from quarry located in Sabuncupınar and nearby railway. This volcanic rock was previously classified as basalt based on the detailed mineralogical and geochemical analyses performed at the laboratories of the Mineral Research & Exploration General Directorate located in Ankara (Turkey). In-situ characteristics of sampling site were also investigated at different locations of quarry site by line surveying technique to describe the influence of discontinuity conditions on the weathering rate of selected rocks. Several techniques were utilized to determine time dependent deterioration in mineralogical and chemical composition of these samples for understanding their weathering rate. The porosity, water

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

    USGS Publications Warehouse

    Leo, G.W.

    1985-01-01

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

  12. Paleoproterozoic andesitic volcanism in the southern Amazonian craton (northern Brazil); lithofacies analysis and geodynamic setting

    NASA Astrophysics Data System (ADS)

    Roverato, Matteo; Juliani, Caetano; Capra, Lucia; Dias Fernandes, Carlos Marcelo

    2016-04-01

    Precambrian volcanism played an important role in geological evolution and formation of new crust. Most of the literature on Precambrian volcanic rocks describes settings belonging to subaqueous volcanic systems. This is likely because subaerial volcanic rocks in Proterozoic and Archean volcano-sedimentary succession are poorly preserved due to erosive/weathering processes. The late Paleoproterozoic Sobreiro Formation (SF) here described, seems to be one of the rare exceptions to the rule and deserves particular attention. SF represents the subaerial expression of an andesitic magmatism that, linked with the upper felsic Santa Rosa F., composes the Uatumã Group. Uatumã Group is an extensive magmatic event located in the Xingú region, southwestern of Pará state, Amazonian Craton (northern Brazil). The Sobreiro volcanism is thought to be related to an ocean-continent convergent margin. It is characterized by ~1880 Ma well-preserved calc-alkaline basaltic/andesitic to andesitic lava flows, pyroclastic rocks and associated reworked successions. The superb preservation of its rock-textures allowed us to describe in detail a large variety of volcaniclastic deposits. We divided them into primary and secondary, depending if they result from a direct volcanic activity (pyroclastic) or reworked processes. Our study reinforces the importance of ancient volcanic arcs and rocks contribution to the terrestrial volcaniclastic sedimentation and evolution of plate tectonics. The volcanic activity that produced pyroclastic rocks influenced the amount of detritus shed into sedimentary basins and played a major role in the control of sedimentary dispersal patterns. This study aims to provide, for the first time, an analysis of the physical volcanic processes for the subaerial SF, based in field observation, lithofacies analysis, thin section petrography and less geochemical data. The modern volcanological approach here used can serve as a model about the evolution of Precambrian

  13. Geochemistry and zircon U-Pb-Hf isotopes of Early Paleozoic arc-related volcanic rocks in Sonid Zuoqi, Inner Mongolia: Implications for the tectonic evolution of the southeastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan

    2016-11-01

    An Early Paleozoic acid volcanic sequence has been recently detected southeast of Sonid Zuoqi in central Inner Mongolia to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. First, the volcanic rocks have zircon U-Pb ages of 439-445 Ma. They are characterized by (a) a high silica content, moderate alkali content and low iron content; (b) enrichment in light rare earth elements, depletion of heavy rare earth elements, and negative Eu anomalies; and (c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic samples yield εHf(t) values of - 4.7 to + 9.2 with TDM2 ages of 835-1724 Ma. For petrogenesis, they were possibly arc derived, from predominant juvenile materials with subordinate ancient continental crust. Combined with previous studies, the Early Paleozoic Sonid Zuoqi arc magmatism can be divided into three stages: a primitive arc stage represented by 464-490 Ma low-K, calcic granitoids; a normal continental arc stage represented by 439-445 Ma medium-K, calcic to calcic-alkalic plutons and volcanic rocks and a syn-collisional stage represented by 423-424 Ma high-K granites. Furthermore, the timing and tectonic settings of the above magmatic rocks show similarities to those in Xilinhot and other areas of the northern Early to Mid-Paleozoic orogenic belt (NOB), although the rock assemblies and their proportions vary more or less in different areas. Accordingly, the NOB that formed on this arc was probably attributed to the northward subduction of the Paleo-Asian Ocean beginning at ~ 500 Ma, which experienced this type of arc development and was terminated by a soft collision before the Late Devonian.

  14. Sr, Nd, and Pb isotopes of ultramafic xenoliths in volcanic rocks of Eastern China: enriched components EMI and EMII in subcontinental lithosphere

    USGS Publications Warehouse

    Tatsumoto, M.; Basu, A.R.; Wankang, H.; Junwen, W.; Guanghong, X.

    1992-01-01

    The UThPb, SmNd, and RbSr isotopic systematics of mafic and ultramafic xenolithic rocks and associated megacrystic inclusions of aluminous augite and garnet, that occur in three alkalic volcanic suites: Kuandian in eastern Liaoning Province, Hanluoba in Hebei Province, and Minxi in western Fujian Province, China are described. In various isotopic data plots, the inclusion data invariably fall outside the isotopic ranges displayed by the host volcanic rocks, testifying to the true xenolithic nature of the inclusions. The major element partitioning data on Ca, Mg, Fe, and Al among the coexisting silicate minerals of the xenoliths establish their growth at ambient mantle temperatures of 1000-1100??C and possible depths of 70-80 km in the subcontinental lithosphere. Although the partitioning of these elements reflects equilibrium between coexisting minerals, equilibria of the Pb, Nd, and Sr isotopic systems among the minerals were not preserved. The disequilibria are most notable with respect to the 206Pb 204Pb ratios of the minerals. On a NdSr isotopic diagram, the inclusion data plot in a wider area than that for oceanic basalts from a distinctly more depleted component than MORB with higher 143Nd 144Nd and a much broader range of 87Sr 86Sr values, paralleling the theoretical trajectory of a sea-water altered lithosphere in NdSr space. The garnets consistently show lower ?? and ?? values than the pyroxenes and pyroxenites, whereas a phlogopite shows the highest ?? and ?? values among all the minerals and rocks studied. In a plot of ??207 and ??208, the host basalts for all three areas show lower ??207 and higher ??208 values than do the xenoliths, indicating derivation of basalts from Th-rich (relative to U) sources and xenoliths from U-rich sources. The xenolith data trends toward the enriched mantle components, EMI and EMII-like, characterized by high 87Sr 86Sr and ??207 values but with slightly higher 143Nd 144Nd. The EMI trend is shown more distinctly by the host

  15. Sorption and desorption of lead (Pb) and europium (Eu) on volcanic rocks at the Nevada Test Site

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Papelis, C.; Yu, Z.

    2005-12-01

    Previous research has shown that sorption/desorption reactions frequently control the concentration of solutes in the groundwater system at the Nevada Test Site (NTS). The hysteresis between the sorption and desorption processes determines the techniques of simulating radionuclide transport under field conditions. In this study, batch sorption and desorption experiments of lead (Pb) and europium (Eu) were conducted to study the partitioning of dissolved radionuclides at the groundwater-rock interface. Lead, showing the stronger binding affinity, can be used to evaluate conservatively the retardation of strongly binding radionuclides, such as plutonium. Europium can be used as the natural analog of transuranic radioactive solutes because of its similar valance and geochemical characteristics. Samples, including matrix and fracture cut from cores, were collected from the Western Pahute Mesa (WPM) at NTS. Based on the results of sorption and desorption batch experiments with Pb and Eu, adsorption envelops and fractional desorption were obtained, as a function of time. The sorption behavior of both cations was pH-dependent, with sorption uptake increasing with increasing pH. The sorption uptake of Pb was always higher, compared to Eu, for the same pH value, while Pb fractional desorption was lower, compared to Eu. These data suggest that Pb forms stronger binding and less reversible complexes than Eu. To simulate the specific sorption process of Pb and Eu, two surface complexation models (SCM), the diffuse-layer model (DLM) and the triple-layer model (TLM), were used to derive the primary sorption modeling parameters. Based on results of sorption data simulation, the TLM was selected to quantify the sorption behavior of Pb and Eu at the NTS.

  16. Cenozoic basaltic volcanism in W Turkey: Implications for lithospheric thinning and extension

    NASA Astrophysics Data System (ADS)

    Altunkaynak, S.

    2013-05-01

    Western Anatolia (Turkey) is regarded as an eastern extension of the Alpine collision belt and was affected dominantly by convergent tectonics preceding current extensional tectonics. Three major episodes of magmatic flare-up were identified in western Anatolia: the Early to late Eocene, late Oligocene to middle Miocene and late Miocene to Quaternary. Ranging from basalt, basaltic andesite to basaltic trachyandesite, Early to late Eocene volcanic rocks include both calc-alkaline and transitional (calc-alkaline to tholeiitic) affinity. They are slightly-moderately enriched in large ion lithophile elements and light rare earth elements with respect to high field strength elements and show negative Nb, Ta, and Ti anomalies. Basaltic lavas and dikes are characterized by 87Sr/86Sr(i) compositions ranging from 0.70530 to 0.70415, positive ɛNd (2.7-6.6) and restricted Pb-isotope compositions. Late Oligocene to Middle Miocene volcanic activity produced High-K calc-alkaline basic to acid lava flows/dikes and associated pyroclastic rocks that exhibit features similar to those of Early Cenozoic Western U.S Cordillera, Great Basin, where magmatism and crustal extension overlapped in space and time. The geochemical and Sr-Nd-Pb isotopic features of the Late Oligocene-Middle Miocene volcanic units suggest that both lithospheric and asthenospheric mantle melts were involved in the evolution of volcanism during this episode, with a decreasing lithospheric geochemical fingerprint by the middle Miocene, when the asthenospheric mantle source became more dominant. Late Miocene to Quaternary volcanism produced alkaline basalts that show OIB-type trace-element patterns and 87Sr/86Sr (i) (0.7033 to 0.7030) and ɛNd (i) (+6.5 to +2.5) values. These features suggest enriched asthenospheric mantle-derived melts as their main magma source. Geochemical and temporal evolution of basaltic volcanism in western Turkey indicate that the geochemical changes in the nature of volcanism from calc-alkaline

  17. Volcanic signature of Basin and Range extension on the shrinking Cascade arc, Klamath Falls-Keno area, Oregon

    NASA Astrophysics Data System (ADS)

    Priest, George R.; Hladky, Frank R.; Mertzman, Stanley A.; Murray, Robert B.; Wiley, Thomas J.

    2013-08-01

    geologic mapping of the Klamath Falls-Keno area revealed the complex relationship between subduction, crustal extension, and magmatic composition of the southern Oregon Cascade