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Sample records for cretaceous volcanic rocks

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

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    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.

  2. Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry

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    Skála Roman

    2015-06-01

    Full Text Available Upper Cretaceous to Pleistocene volcanic rocks of the Bohemian Massif represent the easternmost part of the Central European Volcanic Province. These alkaline volcanic series include rare melilitic rocks occurring as dykes, sills, scoria cones and flows. They occur in three volcanic periods: (i the Late Cretaceous to Paleocene period (80–59 Ma in northern Bohemia including adjacent territories of Saxony and Lusatia, (ii the Mid Eocene to Late Miocene (32.3–5.9 Ma period disseminated in the Ohře Rift, the Cheb–Domažlice Graben, Vogtland, and Silesia and (iii the Early to Late Pleistocene period (1.0–0.26 Ma in western Bohemia. Melilitic magmas of the Eocene to Miocene and Pleistocene periods show a primitive mantle source [(143Nd/144Ndt=0.51280–0.51287; (87Sr/86Srt=0.7034–0.7038] while those of the Upper Cretaceous to Paleocene period display a broad scatter of Sr–Nd ratios. The (143Nd/144Ndt ratios (0.51272–0.51282 of the Upper Cretaceous to Paleocene rocks suggest a partly heterogeneous mantle source, and their (87Sr/86Srt ratios (0.7033–0.7049 point to an additional late- to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr- and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~1 to 2 GPa and between 1000 to 1200 °C, respectively. Nepheline crystallized at about 500 to 770 °C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source.

  3. Zircon U/Pb Dating of Cretaceous Adakitic Volcanic Rocks in the Eastern Part of North Dabie Mountains

    Institute of Scientific and Technical Information of China (English)

    薛怀民; 董树文; 刘晓春

    2003-01-01

    Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains are rich inNa ( Na2O=4.03%, Na2O/K2O = 1.31 ), Sr (865μg/g) and Ba ( 1361μg/g) , and high inSr/Y ratio (66.1) but low in Nb, Y and HREE. They have experienced strong fractionation ofREE [ (La/Yb)N = 26.6 ], and are similar to adakite in geochemical characteristics. The U-Pbdating of zircon from the volcanic rocks is ( 129.2 + 2.6) Ma, belonging to Early Cretaceous.These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth el-ement and trace element geochemistry, but also in the formation temperature and pressure of theminerals. The results indicated that the delamination of mountain root and underplating of mafic-ultramafic magma had happened in the Dabie orogen before Early Cretaceous. Mesozoic mag-matism was intense in the North Dabie Mountains, including the intrusion of mafic-ultramaficmagma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma.The Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains may be one part ofthe Mesozoic volcano-intrusive complex belt of North Huaiyang. The existence of Mesozoic vol-canic remnant cap means the denudation of the Dabie orogenic belt was not very strong sinceEarly Cretaceous.

  4. Late Cretaceous lithospheric extension in SE China: Constraints from volcanic rocks in Hainan Island

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    Zhou, Yun; Liang, Xinquan; Kröner, Alfred; Cai, Yongfeng; Shao, Tongbin; Wen, Shunv; Jiang, Ying; Fu, Jiangang; Wang, Ce; Dong, Chaoge

    2015-09-01

    Petrological, geochemical and in-situ zircon U-Pb dating and Hf-isotope analyses have been carried out on a suite of basalt-andesite-rhyolite volcanic rocks exposed in the Liuluocun area, Hainan Island, SE China. Zircon analyses show that these volcanic rocks crystallized in the Early Cretaceous (ca. 102 Ma). The basalts are characterized by low MgO contents and mg-numbers but high rare earth element, high field strength element and large ion lithophile element contents and Nb-Ta negative anomalies. They have relatively uniform Sr-Nd isotope compositions with εNd(t) values of - 4.09 to - 3.63. The andesites show enrichment of high field strength element and rare earth element with negligible Eu anomalies. They have εNd(t) values of - 2.35 to - 3.88 and εHf(t) values of - 9.73 to - 1.13. The rhyolites have high K2O and SiO2 contents. They are characterized by prominent Eu, P and Ti negative anomalies and enrichment in large ion lithophile element, and show εHf(t) values of - 7.51 to + 0.47 and εNd(t) values of - 2.49 to - 2.69. Petrogenetic analysis indicates that the Liuluocun volcanic rocks were produced by incomplete reaction of the mantle wedge peridotite with felsic melts derived from partial melting of subducted sediment. All these characteristics, combined with geological observations, suggest that their formation was related to regional lithospheric extension in the South China Craton during the Early Cretaceous, which may have been caused by subduction of the Paleo-Pacific plate beneath the continental plate of China.

  5. Paleomagnetic data from Early Cretaceous volcanic rocks of West Liaoning:Evidence for intracontinental rotation

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Detailed rock magnetic studies of 55 lavas from Yixian and Fuxin area, West Liaoning, show the primary carriers of remanence to be pseudo-single domain titanomagnetite. K/Ar dating indicates that the volcanic sequence spans 93 to 133 Ma. Stepwise thermal demagnetization successfully isolated well-defined characteristic magnetization (ChRM) in all lavas thermal-treated above 250℃. The mean paleodirections are D/I = 5.9°/58.8° (α95 = 2.9°) and D/I =179.2°/-59.9° (α95 = 5.2°) for 27 normally magnetized flows and 28 reversibly magnetized flows, respectively. It indicates that since the Early Cretaceous there is no significant horizontal movement and rotation between the Yixian-Fuxin area and Eurasia. However, Korea Peninsula may have undergone a clockwise rotation of 33.9° relative to the Yixian-Fuxin area during the Cretaceous. On the basis of characteristics of hotspot origins (core-mantle boundary or upper mantle), the clockwise rotation of Korea Peninsula relative to Eurasia is assumed to be mainly caused by an extensional force in the crust of eastern China, which was corresponding to intensive surface volcanic activities in this area.

  6. Early Cretaceous bimodal volcanic rocks in the southern Lhasa terrane, south Tibet: Age, petrogenesis and tectonic implications

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    Wang, Chao; Ding, Lin; Liu, Zhi-Chao; Zhang, Li-Yun; Yue, Ya-Hui

    2017-01-01

    Limited geochronological and geochemical data from Early Cretaceous igneous rocks of the Gangdese Belt have resulted in a dispute regarding the subduction history of Neo-Tethyan Ocean. To approach this issue, we performed detailed in-situ zircon U-Pb and Hf isotopic, whole-rock elemental and Sr-Nd isotopic analyses on Late Mesozoic volcanic rocks exposed in the Liqiongda area, southern Lhasa terrane. These volcanic rocks are calc-alkaline series, dominated by basalts, basaltic andesites, and subordinate rhyolites, with a bimodal suite. The LA-ICPMS zircon U-Pb dating results of the basaltic andesites and rhyolites indicate that these volcanic rocks erupted during the Early Cretaceous (137-130 Ma). The basaltic rocks are high-alumina (average > 17 wt.%), enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), showing subduction-related characteristics. They display highly positive zircon εHf(t) values (+ 10.0 to + 16.3) and whole-rock εNd(t) values (+ 5.38 to + 7.47). The silicic suite is characterized by low Al2O3 (extracted from a source metasomatized by slab-derived components for the petrogenesis of mafic rocks, whereas the subsequent mafic magma underplating triggered partial melting of the juvenile crust to generate acidic magma. Our results confirm the presence of Early Cretaceous volcanism in the southern Lhasa terrane. Combined with the distribution of the contemporary magmatism, deformation style, and sedimentary characteristics in the Lhasa terrane, we favor the suggestion that the Neo-Tethyan oceanic lithosphere was flat-lying beneath the Lhasa terrane during the Early Cretaceous.

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

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    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

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

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    Oguz, Simge; Aydin, Faruk; Baser, Rasim

    2015-04-01

    In this study, we have reported for lithological, petrographical and geochemical features of late Cretaceous volcanic rocks from the Çanakçı and the Karabörk areas in the south-eastern part of Görele (Giresun, NE Turkey) in order to investigate their origin and magmatic evolution. Based on the previous ages and recent volcano-stratigraphic studies, the late Cretaceous time in the study area is characterized by an intensive volcanic activity that occurred in two different periods. The first period of the late Cretaceous volcanism (Cenomanian-Santonian; 100-85 My), conformably overlain by Upper Jurassic-Lower Cretaceous massive carbonates (Berdiga Formation), is represented by bimodal units consisting of mainly mafic rock series (basaltic-andesitic lavas and hyaloclastites, dikes and sills) in the lower part (Çatak Formation), and felsic rock series (dacitic lavas and hyaloclastites, crystal- and pyrite-bearing tuffs) in the upper part (Kızılkaya Formation). The second period of the late Cretaceous volcanism (Santonian-Late Campanian; 85-75 Ma) is also represented by bimodal character and again begins with mafic rock suites (basaltic-basaltic andesitic lavas and hyaloclastites) in the lower part (Çağlayan Formation), and grades upward into felsic rock suites (biotite-bearing rhyolitic lavas, ignimbrites and hyaloclastites) through the upper part (Tirebolu Formation). These bimodal units are intercalated with volcanic conglomerates-sandstones, claystones, marl and red pelagic limestones throughout the volcanic sequence, and the felsic rock series have a special important due to hosting of volcanogenic massive sulfide deposits in the region. All volcano-sedimentary units are covered by Tonya Formation (Late Campanian-Paleocene) containing calciturbidites, biomicrites and clayey limestones. The mafic rocks in the two volcanic periods generally include basalt, basaltic andesite and minor andesite, whereas felsic volcanics of the first period mainly consists of

  9. Chronology and Geochemistry of Volcanic Rocks in the Cretaceous Suifenhe Formation in Eastern Heilongjiang, China

    Institute of Scientific and Technical Information of China (English)

    JI Weiqiang; XU Wenliang; YANG Debin; PEI Fuping; JIN Ke; LIU Xiaoming

    2007-01-01

    Zircon U-Pb ages and geochemical data of volcanic rocks in the Suifenhe Formation in eastern Heilongjiang Province are reported, and their petrogenesis is discussed in this paper. The Suifenhe Formation mainly consists of basalt, andesite, and dacite. Zircon from andesite and dacite are euhedral in shape and show typical oscillatory zoning with high Th/U ratios (0.18-0.57), implying its magmatic origin. Zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) indicate that the 206Pb/238U ages of zircons from andesite range within 105-106 Ma, yielding a weighted mean age of 105.5±0.8 Ma (n=14), and that 206Pb/238U ages of zircons from dacite are between 90-96 Ma, yielding a weighted mean age of 93.2±1.3 Ma (n =13). The volcanic rocks from the Suifenhe Formation are subalkaline series and show a calc-alkaline evolutionary trend with SiO2 content of 47.69%-65.47%, MgO contents of 1.42%-6.80% (Mg#= 45-53), and Na2O/K2O ratios of 1.83-3.63. They are characterized by enrichment in large ion lithophile elements (LILE) and lightrare-earth elements (LREE), depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE) (e.g., Nb, Ta, Ti), and low initial 87Sr/86Sr ratios (0.7041-0.7057) and positive εNd(t)values (0.39-4.08), implying that they could be derived from a depleted magma source. Taken together,these results suggest that the primary magma of the volcanic rocks might originate from partial melting of the mantle wedge metasomatized by fluids derived from subducted slab under a tectonic setting of active continental margin.

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

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    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

  11. Recognition and Significance of Volcanic Rocks of the Anda Depression of the Songliao Basin in Jurassic-Cretaceous

    Institute of Scientific and Technical Information of China (English)

    Fuhong Gao; Dongpo Wang; Xinrong Zhang; Guixia Ji; Jian Zhao

    2003-01-01

    A series of volcanic rocks were developed in the deep part of Anda faulting depression. The reflection of therocks are mainly stratiform and hummocky. Three kinds of volcanic facies, e.g. explosion facies, effusion facies andsub-volcanic facies,were recognized by different reflecting characteristics in the seismic profile. The volcanic rocks areformed during three episodes of volcanic activities from Shahezi Formation to Yingcheng Formation. The volcanismshave relation to the formation of Songliao Basin and regional tectonics of northeastern China. Some of the volcanic rocksare good oil and gas reservoirs.

  12. Thermal and geotectonic setting of Cretaceous volcanic rocks near Ica, Peru, in relation to Andean crustal thinning

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    Atherton, M. P.; Aguirre, L.

    1992-01-01

    The Cretaceous volcanic rocks of the Ica region, Peru, were deposited in the Cañete marginal basin developed on the Precambrian Arequipa Massif, which was split and thinned along southwardpropagating faults. They are compositionally bimodal, calc-alkaline, high-Al 2O 3 rocks with shoshonitic affinities and a pronounced enriched within-plate character. This contrasts markedly with the equivalent rocks of the Huarmey Basin to the north, which lie directly on mantle-derived material and are chiefly low-K, thleiitic basalts and basaltic andesites, with trace-element abundances related to subduction and/or asthenospheric components. The Ica rocks also show a characteristic very low-grade, nondeformational prehnite-pumpellyite to zeolite facies metamorphism formed under moderate thermal gradients. This contrasts strongly with the high thermal gradient of the rocks to the north, which relates to the more extensive crustal splitting and/or thinning in that direction. These metamorphic patterns, together with the lava chemistry, are important elements in modeling the thermal and geotectonic setting, which has close affinities to a model of the Icelandic rifting system. The source of the Ica rocks is thought to be old enriched mantle beneath the Precambrian Arequipa Massif, in contrast to the mantle beneath the basin to the north, which is much younger and less enriched. This change along the axis of the basin is similar to the K-h relationships suggested at subduction zones. However, the direction of subduction along this sector has been approximately E-W, and the enrichment, which is a right angles to this, relates to the history of the subcontinental mantle along the Andean margin. It is also associated with an abrupt compositional change in the Peruvian Coastal Batholith rocks of slightly younger age, marking a major segmental difference in Mesozoic magma composition along the axis of the Andes. Crustal contributions are not considered to be important, certainly not

  13. Paralavas in the Cretaceous Paraná volcanic province, Brazil - A genetic interpretation of the volcanic rocks containing phenocrysts and glass

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    SÉRGIO B. BAGGIO

    Full Text Available ABSTRACT The occurrences of glassy rocks containing long and curved phenocrysts in the Paraná volcanic province, South America, are here interpreted as paralavas. The large number of thin (0.1-0.5 m dikes and sills of glassy volcanic rocks with hopper, hollow or curved, large crystals of clinopyroxene (up to 10 cm, plagioclase (up to 1 cm, magnetite and apatite are contained in the core of thick (>70 m pahoehoe flows. They are strongly concentrated in the state of Paraná, coincident with the presence of the large number of dikes in the Ponta Grossa arch. These rocks were previously defined as pegmatites, although other names have also been used. A paralava is here interpreted as the product of melting of basaltic rocks following varied, successive processes of sill emplacement in high-kerogen bituminous shale and ascent of the resultant methane. As the gas reached the lower portion of the most recent lava flow of the volcanic pile, the methane reacted with the silicate and oxide minerals of the host volcanic rock (1,000 ºC and thus elevated the local temperature to 1,600 ºC. The affected area of host rock remelted (possibly 75 wt.% and injected buoyantly the central and upper portion of the core. This methane-related mechanism explains the evidence found in the paralavas from this volcanic province, one of the largest in the continents.

  14. Paleomagnetic study on orogenic belt:An example from Early Cretaceous volcanic rocks,Inner Mongolia,China

    Institute of Scientific and Technical Information of China (English)

    REN; Shoumai; ZHU; Rixiang; HUANG; Baochun; ZHANG; Fuqin

    2004-01-01

    We report paleomagnetic results for Early Cretaceous lava flows collected from the Suhongtu area of Inner Mongolia, the middle part of the Tianshan-Mongolia Fold Belt (TMFB).Rock-magnetic experiments for different lava flows indicate that the main magnetic mineral is pseudo-single-domain (PSD) magnetite. The characteristic high-temperature remanence component is isolated by thermal demagnetization temperature steps between 300℃ and 585℃,which yields a mean direction of D= 23.6°, /= 56.0° with α95 = 2.3°. We interpret this high-temperature remanence component as primary magnetization based mainly upon the petrographic analysis, which shows that the shape of magnetite crystal is relatively rounded square or polygon without internal reflection and deuterogenous phenomenon. The corresponding pole of the high-temperature remanence component is at 71.1°N, 200.5°E with A95 = 2.7°.This Early Cretaceous pole is in good agreement with those for Siberia, North China, and Inner Mongolia, suggesting that these continental blocks had already sutured together in the Early Cretaceous, which would further provide constraints on better understanding of the formation and evolution of the TMFB.

  15. Geochemistry, geochronology, and tectonic setting of Early Cretaceous volcanic rocks in the northern segment of the Tan-Lu Fault region, northeast China

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    Ling, Yi-Yun; Zhang, Jin-Jiang; Liu, Kai; Ge, Mao-Hui; Wang, Meng; Wang, Jia-Min

    2017-08-01

    We present new geochemical and geochronological data for volcanic and related rocks in the regions of the Jia-Yi and Dun-Mi faults, in order to constrain the late Mesozoic tectonic evolution of the northern segment of the Tan-Lu Fault. Zircon U-Pb dating shows that rhyolite and intermediate-mafic rocks along the southern part of the Jia-Yi Fault formed at 124 and 113 Ma, respectively, whereas the volcanic rocks along the northern parts of the Jia-Yi and Dun-Mi faults formed at 100 Ma. The rhyolite has an A-type granitoid affinity, with high alkalis, low MgO, Ti, and P contents, high rare earth element (REE) contents and Ga/Al ratios, enrichments in large-ion lithophile (LILEs; e.g., Rb, Th, and U) and high-field-strength element (HFSEs; e.g., Nb, Ta, Zr, and Y), and marked negative Eu anomalies. These features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment. The basaltic rocks are enriched in light REEs and LILEs (e.g., Rb, K, Th, and U), and depleted in heavy REEs, HFSEs (e.g., Nb, Ta, Ti, and P), and Sr. These geochemical characteristics indicate that these rocks are calc-alkaline basalts that formed in an intraplate extensional tectonic setting. The dacite is a medium- to high-K, calc-alkaline, I-type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc. Therefore, the volcanic rocks along the Jia-Yi and Dun-Mi faults were formed in an extensional regime at 124-100 Ma (Early Cretaceous), and these faults were extensional strike-slip faults at this time.

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

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    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

  17. Petrology and chemistry of late Cretaceous volcanic rocks from the southernmost segment of the Western Cordillera of Colombia (South America)

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    Spadea, P.; Espinosa, A.

    1996-03-01

    This paper presents new data on the petrology and chemistry of the igneous rocks composing the Mesozoic basement of southernmost Western Cordillera of Colombia along the Ricaurte-Altaquer section. The studied sequence includes variably metamorphosed submarine lavas, breccias, tuffs and dykes of basalt to andesite composition, and minor, shallow quartz microdiorite intrusives. A Campanian age is recorded by radiolarian faunas from chert strata capping the lavas. Two different tholeiitic suites and a younger calc-alkaline suite, represented by hornblende andesite, are distinguished. One tholeiitic suite, represented by plagioclase and pyroxene phyric lavas, evolves from basalt to basaltic andesite. It is characterized by the occurrence of diopsidic pyroxene as early crystallising phase, by depletion in high-field strength elements, particularly Nb and by relative enrichment in light REE and Th. The second tholeiitic suite, which includes aphyric or poorly phyric lavas of basalt to dacite composition, differs from the first group in having moderately low {FeO tot}/{MgO} ratio and lower P 2O 5 content for a given SiO 2, and higher {Ti}/{Zr}and{Y}/{Zr} ratios. The pyroxene chemistry of the two suites also differs. The primary geochemical characteristics of the two suites suggest a similarity with tholeiitic suites generated in island-arc environment. The hornblende andesite has mineralogical and chemical characteristics of calc-alkaline lavas erupted in an oceanic setting in an evolved island-arc. Petrologic and geochemical evidence suggests that the volcanic rocks from the Ricaurte-Altraquer section are similar to the island-arc tholeiite volcanics from the upper Macuchi Formation of northern Ecuador and can be correlated partly with this unit. Conversely, they are petrochemically dissimilar from the typical Diabase Group volcanic rocks, characterized by transitional MORB lavas, extensively present to the north in the Western Cordillera of Colombia.

  18. Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuejun; SUN Chunlin; SUN Yuewu; SUN Wei

    2008-01-01

    Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area. Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China. Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning, a number of researchers have focused on Mesozoic volcanic events. The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb. The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age, the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma, the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma, respectively. Combined with the data of recent publication on volcanic rocks ages; the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods: 119 Ma, 113 Ma and 103 Ma. The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province, establishing Mesozoic volcanic event sequence, discussing geological tectonic background, and surveying the relation between noble metals to the Cretaceous volcanic rocks, but also otters important information of Mesozoic volcanism in northeastern China.

  19. Uranium series, volcanic rocks

    Science.gov (United States)

    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).

  20. Volcanic Rocks and Features

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. The...

  1. Cretaceous volcanic-intrusive magmatism in western Guangdong and its geological significance

    Institute of Scientific and Technical Information of China (English)

    GENG; Hongyan; XU; Xisheng; S.Y.O'Reilly; ZHAO; Ming; SUN; Tao

    2006-01-01

    Systematic zircon LA-ICPMS U-Pb dating reveals that Cretaceous volcanic-intrusive activities developed in western Guangdong. Representative volcanic rocks, i.e. Maanshan and Zhougongding rhyodacites, have zircon U-Pb isotopic ages of 100±1 Ma, and the intrusive ones including the Deqing monzonitic granite body and the Xinghua granodiorite body in the Shidong complex, as well as the Tiaocun granodiorite body in the Guangping complex yield ages of 99±2 Ma, ca.100 Ma, and 104±3 Ma respectively. The biotite-granites of the Shidong complex main body (461±35 Ma) and that of the Guangping complex (444±6 Ma) are Caledonian. In spite of the big time interval between Cretaceous volcanic-intrusive magmatisms and Caledonian intrusive ones, both of them are characterized by enrichment in Rb, Th, Ce, Zr, Hf, Sm, depletion in Ba, Nb, Ta, P, Ti, Eu, and weakly REE tetrad effect. Eu negative anomalies are: Cretaceous volcanic rocks (Eu/Eu*=0.74), Cretaceous intrusive rocks (Eu/Eu*=0.35-0.58), Caledonian biotite granites (Eu/Eu*=0.31-0.34). Studies of Sr-Nd isotope data show that all these igneous rocks have high initial 87Sr/86Sr ratios (0.7105-0.7518), and low εNd(t) values (-7.23--11.39) with their Nd two-stage model ages ranging from 1.6-2.0 Ga, which suggest that they all derived from the Proterozoic crustal basement of southeast China.The occurrence of Cretaceous volcanic-intrusive magmatisms in western Guangdong is related with the important lithospheric extension event in southeast China (including Nanling region) at ca. 100 Ma.The "volcanic line" defined by the large scale Mesozoic intermediate-acidic volcanic magmatisms in southeast China may further extend to the southwest margin of Nanling region.

  2. Cretaceous alkaline volcanism in south Marzanabad, northern central Alborz, Iran: Geochemistry and petrogenesis

    Directory of Open Access Journals (Sweden)

    Roghieh Doroozi

    2016-11-01

    Full Text Available The alkali-basalt and basaltic trachy-andesites volcanic rocks of south Marzanabad were erupted during Cretaceous in central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Based on petrography and geochemistry, en route fractional crystallization of ascending magma was an important process in the evolution of the volcanic rocks. Geochemical characteristics imply that the south Marzanabad alkaline basaltic magma was originated from the asthenospheric mantle source, whereas the high ratios of (La/YbN and (Dy/YbN are related to the low degree of partial melting from the garnet bearing mantle source. Enrichment pattern of Nb and depletion of Rb, K and Y, are similar to the OIB pattern and intraplate alkaline magmatic rocks. The K/Nb and Zr/Nb ratios of volcanic rocks range from 62 to 588 and from 4.27 to 9 respectively, that are some higher in more evolved samples which may reflect minor crustal contamination. The isotopic ratios of Sr and Nd respectively vary from 0.70370 to 0.704387 and from 0.51266 to 0.51281 that suggest the depleted mantle as a magma source. The development of south Marzanabad volcanic rocks could be related to the presence of extensional phase, upwelling and decompressional melting of asthenospheric mantle in the rift basin which made the alkaline magmatism in Cretaceous, in northern central Alborz of Iran.

  3. Geochemistry and petrogenesis of Early Cretaceous volcanic rocks from Mengyin basin%蒙阴盆地早白垩世火山岩地球化学特征及其岩石成因

    Institute of Scientific and Technical Information of China (English)

    牛漫兰; 傅朋远; 吴齐; 朱光; 夏文静

    2012-01-01

    蒙阴盆地早白垩世火山岩主要出露于青山群八亩地组和方戈庄组中.火山岩SiO2含量为53.71% ~ 69.08%,主要为安山质岩石和流纹岩,以钙碱性系列为主(σ平均3.42);富集Rb、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、P、Ti等高场强元素和重稀土元素;具有富集的Sr-Nd-Pb同位素组成(87Sr/86Sr(t)=0.7051~ 0.7110,εNd(t)=-5.16~-16.4).根据MgO含量和Mg#值,可将安山质火山岩划分为高镁(Mg #>60)和低镁(Mg#<60)两个系列.高镁安山质岩石的MgO、Cr、Ni及不相容元素的含量明显高于低镁安山质岩石,且具有相对高的87Sr/86Sr(t)和较低的εNd(t)值,Sr-Nd同位素组成趋向于EMⅡ型富集地慢端元.低镁安山质岩石地球化学特征类似于埃达克岩,其同位素组成介于EM Ⅰ型富集地幔端元与华北麻粒岩相下地壳之间.流纹岩具有较低的MgO、Cr、Ni含量和明显的负Eu、Sr异常,同位素组成类似于扬子中、上地壳.研究表明,蒙阴盆地高镁安山质岩石由曾遭受俯冲扬子陆壳熔体改造的华北岩石圈地幔部分熔融形成,且岩浆在上升过程中经历了华北下地壳物质一定程度的混染或混合作用;低镁安山质岩石主要由华北下地壳部分熔融形成;流纹岩为岩石圈伸展减薄背景下仰冲至华北克拉通之上的扬子中、上地壳部分熔融的产物.地质现象显示,郯庐断裂带的伸展活动控制着蒙阴断陷盆地的发育,与蒙阴盆地早白垩世火山岩的成因有着密切的联系,在华北克拉通破坏中可能起到了重要的作用.%Early Cretaceous volcanic rocks in Mengyin basin are exposed in Bamudi and Fanggezhuang formations. These rocks are mainly andesitic rocks and rhyolites with SiO2 contents varied between 53.71% ~69. 08% , belong to calc-alkaline to alkaline series ( with a average of σ = 3. 42). These volcanic rocks are characterized by large ion lithophile element ( LILE) , light

  4. Geochemical Characteristics and Metallogenesis of Volcanic Rocks as Exemplified by Volcanic Rocks in Ertix,Xinjiang

    Institute of Scientific and Technical Information of China (English)

    刘铁庚; 叶霖

    1997-01-01

    Volcanic rocks in Ertix,Xinjiang,occurring in the collision zone between the Siberia Plate and the Junggar Plate,are distributed along the Eritix River Valley in northern Xinjiang.The volcanic rocks were dated at Late Paleozoic and can be divided into the spilite-keratophyre series and the basalt-andesite series.The spilite-keratophyre series volcanic rocks occur in the Altay orogenic belt at the southwest margin of the Siberia Plate.In addition to sodic volcanic rocks.There are also associated potassic-sodic volcanic rocks and potassic volcanic rocks.The potassic-sodic volcanic rocks occur at the bottom of the eruption cycle and control the distribution of Pb and Zn deposits.The potassic volcanic rocks occur at the top of the eruption cycle and are associated with Au and Cu mineralizations.The sodic volcanic rocks occur in the middle stage of eruption cycle and control the occurrence of Cu(Zn) deposits.The basalt-andesite series volcanic rocks distributed in the North Junggar orogenic belt at the north margin of the Junggar-Kazakstan Plate belong to the potassic sodic volcain rocks.The volcanic rocks distributed along the Ulungur fault are relatively rich in sodium and poor in potassium and are predominated by Cu mineralization and associated with Au mineralization.Those volcanic rocks distributed along the Ertix fault are relatively rich in K and poor in Na,with Au mineralization being dominant.

  5. Cenozoic volcanic rocks of Saudi Arabia

    Science.gov (United States)

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

    2016-01-01

    The Cenozoic volcanic rocks of Saudi Arabia cover about 90,000 km2, one of the largest areas of alkali olivine basalt in the world. These volcanic rocks are in 13 separate fields near the eastern coast of the Red Sea and in the western Arabian Peninsula highlands from Syria southward to the Yemen Arab Republic.

  6. Late Cretaceous volcanic arc system in Southwest Korea: Occurrence, lithological characteristics, SHRIMP zircon U-Pb age, and tectonic implications

    Science.gov (United States)

    Koh, Hee Jae; Kwon, Chang Woo

    2017-04-01

    In the southwest region of the Korean Peninsula, four large volcanoes, the Buan, Seonunsan, Wido, and Beopseongpo, with a maximum diameter of ca 20 km, form a distinct topographic undulation along the NE-SW-trending Hamyeol Fault. These volcanics comprise various types of pyroclastic, sedimentary, and lava/intrusive rocks, and are interpreted as remnants of calderas resulting from various volcanic eruptions, indicating that Hamyeol Fault, together with crustal extension, played an important role in volcano formation in this region. SHRIMP U-Pb ages of zircon isolated from each volcanics are as follows. For Buan Volcanics, Cheonmasan Tuff 87.23 ±0.92 Ma, Udongje Tuff 86.79 ±0.71 Ma, Seokpo Tuff 87.30 ±0.99 Ma and Yujeongje Tuff 86.66 ±0.93 Ma. For Seonunsan Volcanics, Gyeongsusan Tuff 84.9 ±1.1 Ma and Yeongije Tuff 86.61 ±0.67 Ma. These ages indicate that the four volcanics were formed in the Late Cretaceous. The ages are comparable to those of the volcanic rocks of the Aioi and Arima groups in Southwestern Japan, suggesting that the Late Cretaceous volcanic arc systems developed in a NE-SW direction from the Japanese Islands to the southwestern part of the Korean Peninsula caused by regional magmatism together with crustal deformation as reflected by occurrence of the volcanic rocks along the Hamyeol Fault.

  7. Evidence For Volcanic Initiation Of Cretaceous Ocean Anoxic Events (Invited)

    Science.gov (United States)

    Sageman, B. B.; Hurtgen, M. T.; McElwain, J.; Adams, D.; Barclay, R. S.; Joo, Y.

    2010-12-01

    Increasing evidence from studies of Cretaceous ocean anoxic events (OAE’s) has suggested that major changes in volcanic activity may have played a significant role in their genesis. Numerous specific mechanisms of have been proposed, including increases in atmospheric CO2 and surface temperature, leading to enhanced chemical weathering and terrestrial nutrient release, or increases in reduced trace metal fluxes, leading to oxygen depletion and possibly providing micronutrients for enhanced primary production. An additional pathway by which the byproducts of enhanced volcanic activity may have contributed to OAE genesis involves relationships between the biogeochemical cycles sulfur, iron, and phosphorus. Recent analysis of S-isotope data from carbonate-associated sulfate and pyrite collected across the Cenomanian-Turonian OAE2 in the Western Interior basin suggest that increases in sulfate to an initially sulfate-depleted ocean preceded onset of the event. Modern lake data support the idea that increases in sulfate concentration drive microbial sulfate reduction, leading to more efficient regeneration of P from sedimentary organic matter. If the early Cretaceous opening of the South Atlantic was accompanied by evaporite deposition sufficient to draw down global marine sulfate levels, and widespread anoxia leading to elevated pyrite burial helped maintain these low levels for the succeeding 30 myr, during which most Cretaceous OAE’s are found, perhaps pulses of volcanism that rapidly introduced large volumes of sulfate may have played a key role in OAE initiation. The eventually burial of S in the form of pyrite may have returned sulfate levels to a low background, thus providing a mechanism to terminate the anoxic events. This talk will review the evidence for volcanic initiation of OAE’s in the context of the sulfate-phosphorus regeneration model.

  8. Deccan volcanism at the Cretaceous-Tertiary boundary

    Science.gov (United States)

    Courtillot, V.; Vandamme, D.; Besse, J.

    1988-01-01

    The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as

  9. Volcanic rock properties control sector collapse events

    Science.gov (United States)

    Hughes, Amy; Kendrick, Jackie; Lavallée, Yan; Hornby, Adrian; Di Toro, Giulio

    2017-04-01

    Volcanoes constructed by superimposed layers of varying volcanic materials are inherently unstable structures. The heterogeneity of weak and strong layers consisting of ash, tephra and lavas, each with varying coherencies, porosities, crystallinities, glass content and ultimately, strength, can promote volcanic flank and sector collapses. These volcanoes often exist in areas with complex regional tectonics adding to instability caused by heterogeneity, flank overburden, magma movement and emplacement in addition to hydrothermal alteration and anomalous geothermal gradients. Recent studies conducted on the faulting properties of volcanic rocks at variable slip rates show the rate-weakening dependence of the friction coefficients (up to 90% reduction)[1], caused by a wide range of factors such as the generation of gouge and frictional melt lubrication [2]. Experimental data from experiments conducted on volcanic products suggests that frictional melt occurs at slip rates similar to those of plug flow in volcanic conduits [1] and the bases of mass material movements such as debris avalanches from volcanic flanks [3]. In volcanic rock, the generation of frictional heat may prompt the remobilisation of interstitial glass below melting temperatures due to passing of the glass transition temperature at ˜650-750 ˚C [4]. In addition, the crushing of pores in high porosity samples can lead to increased comminution and strain localisation along slip surfaces. Here we present the results of friction tests on both high density, glass rich samples from Santaguito (Guatemala) and synthetic glass samples with varying porosities (0-25%) to better understand frictional properties underlying volcanic collapse events. 1. Kendrick, J.E., et al., Extreme frictional processes in the volcanic conduit of Mount St. Helens (USA) during the 2004-2008 eruption. J. Structural Geology, 2012. 2. Di Toro, G., et al., Fault lubrication during earthquakes. Nature, 2011. 471(7339): p. 494-498. 3

  10. Source rock evaluation of Cretaceous and Tertiary series in Tunisia

    Energy Technology Data Exchange (ETDEWEB)

    Oudin, J. (TOTAL-CFP, Pessac (France))

    1988-08-01

    Tunisia represents a mature hydrocarbon province with a long exploration history. In the Sfax-Kerkennah and Gabes Gulf areas, the hydrocarbon accumulations are located in series of Cretaceous and Tertiary age. To estimate the petroleum potential of this region, an evaluation of the source rock quality of the Cretaceous and Tertiary series was undertaken. In the Sfax-Kerkennak area, most of the wells studied indicate that, in the Tertiary, Ypresian and lower Lutetian show good organic content but, taking into account the potential productivity, only the Ypresian can be considered as a potential source rock. In the Cretaceous, mainly studies in the offshore area of the Gabes Gulf, the amount of organic matter is fair and it is chiefly located in Albian and Cenomanian. The Vraconian with its quite good potential is a valuable source rock. Due to the difference in the environment of deposition for these two possible source rocks - the Ypresian with its lagoon facies being carbonate and the Vraconian shaly - variations in the type of organic matter can be noted, although both are of marine origin. The hydrocarbons generated from these source rocks reflect these variations and permit them to correlate the different crude oils found in this area with their original source beds.

  11. Geologic Features of Wangjiatun Deep Gas Reservoirs of Volcanic Rock in Songliao Basin

    Institute of Scientific and Technical Information of China (English)

    SHAN Xuanlong; CHEN Shumin; WU Dawei; Zang Yudong

    2001-01-01

    Wangjiatun gas pool is located at the north part of Xujiaweizi in Songliao basin. Commercial gas flow has been found in the intermediate and acid volcanic rock of upper Jurassic - lower Cretaceous, which makes a breakthrough in deep nature gas prospecting in Songliao basin. The deep natural gas entrapment regularity is discussed in the paper by the study of deep strata, structure and reservoir. Andesite, rhyolite and little pyroclastic rock are the main reservoirs. There are two types of volcanic reservoir space assemblage in this area: the pore and fissure and the pure fissure. Changes had taken place for volcanic reservoir space during long geologic time, which was controlled by tectonic movement and geologic environment.The developed degree of reservoir space was controlled by tectonic movement, weathering and filtering, corrosion and Filling. There are three types of source- reservoir-caprock assemblage in this area: lower source- upper reservoir model,upper source - lower reservoir model and lateral change model. Mudstone in Dengluoku formation and the compacted volcanic rock of upper Jurassic - lower Cretaceous are the caprock for deep gas reservoirs. Dark mudstone of deep lacustrine facies in Shahezi formation and lower part of Dengluoku formation are the source rock of deep gas. It can be concluded that deep gas pools are mainly volcanic lithologic reservoirs.

  12. The geochemistry of volcanic, plutonic and turbiditic rocks from Sumba, Indonesia

    Science.gov (United States)

    Lytwyn, J.; Rutherford, E.; Burke, K.; Xia, C.

    2001-06-01

    Rocks that reveal the geology of Sumba for times before the Later Miocene (˜16 Ma) are relatively few and are not particularly well exposed. This has led to uncertainty about the nature of the basement rocks of the island and especially about whether Sumba originated as a fragment of Australia, or of that part of southeastern Eurasia which many authors have called Sundaland. A third possibility is that Sumba is underlain by arc material generated on the ocean floor and is not a fragment of either continent. We have studied the geochemistry of volcanic, plutonic and turbiditic rocks collected from Sumba in an attempt to provide additional insight into the island's origin and history between Late Cretaceous (˜86 Ma) and Early Miocene (˜16 Ma) times. Late Cretaceous to Early Oligocene (˜31 Ma) volcanic rocks on Sumba range compositionally from basalts to andesites, and are of typical oceanic island-arc affinity, exhibiting geochemical characteristics similar to those of high-Al basalts and their derivatives. Compositions indicate evolution along both calc-alkaline and tholeiitic trends. Some samples show indications of possible modifications by slab-derived melts and/or related fluids and also of contamination by turbiditic sediments. Gabbros and diorites collected from the Paleocene Tanadaro intrusion are compositionally similar to the associated volcanic rocks and, we consider, represent the plutonic equivalents of high-Al basalt. The geochemistry of Cretaceous turbiditic sedimentary rocks on Sumba indicates close proximity to an intra-oceanic island-arc environment. These results are consistent with the geochemical, sedimentological, stratigraphic, paleontological and paleomagnetic results of other investigators which together indicate that: (1) Late Cretaceous to Early Oligocene volcanic, plutonic and volcaniclastic rocks of Sumba are island-arc- and forearc-related; (2) the arc involved appears to have been what we refer to as the Great Indonesian Volcanic

  13. Upper Jurassic to Lower Cretaceous(?) synorogenic sedimentary rocks in the southern Spring Mountains, Nevada

    Science.gov (United States)

    Carr, Michael D.

    1980-08-01

    A newly recognized sequence of Upper Jurassic to Lower Cretaceous(?) terrigenous rocks in the Good-springs district, Nevada, was deposited during the emplacement of the Contact thrust plate. Two facies are recognized: (1) interbedded conglomerate and sandstone derived from Mesozoic igneous and terrigenous platform rocks and (2) interbedded carbonate and sandstone-clast conglomerate, quartz sandstone, and red shale. No igneous detritus occurs in the facies with carbonate-clast conglomerate. Carbonate clasts could only have been derived from the Paleozoic carbonate sequence, which was exposed in the area by latest Jurassic to earliest Cretaceous thrusting. The age of rocks from a volcanic unit within the synorogenic sequence was determined radiometrically to be 150 ± 10 m.y. (K-Ar on biotite). The sequence was deposited disconformably on deeply eroded rocks of the early Mesozoic platform and ultimately overridden from the west by the Contact thrust plate. Information from the sequence corroborates previously reported regional data regarding the timing and nature of the Contact-Red Springs thrust event. *Present address: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025

  14. Volcanic Rocks As Targets For Astrobiology Missions

    Science.gov (United States)

    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.

  15. Geochemical characteristics of Early Cretaceous source rocks in Boli Basin

    Institute of Scientific and Technical Information of China (English)

    Hongmei Gao; Fuhong Gao; Fu Fan; Yueqiao Zhang

    2006-01-01

    The Early Cretaceous deposits are composed of important source rocks in Boli Basin. The types of the source rocks include black mudstones and coal (with carbonaceous mudstone). By the organic geochemical analysis methods, the authors discussed the organic petrological characters, abundance of organic matter, degree of maturity and the type of source rocks. The main micro-component of black mudstone is exinite or vitrinite, and the content of vitrinite is high in coal. The weathering of the outcrop is very serious. The abundance of organic matter in source rock reaches the poor to better rank. The major kerogens in mudstone are type-Ⅲ, type-Ⅱ2 and some type-Ⅱ1; the organic type of coal is type-Ⅲ. The thermal evolution of the source rocks in every structural unit is very different, from low-maturity to over-maturity. The depositional environment is reductive, which is good for the preservation of organic matter. The organic matter in source rocks is mainly from aquatic organisms and terrigenous input.

  16. Zircon U-Pb geochronology of the volcanic rocks from Fanchang-Ningwu volcanic basins in the Lower Yangtze region and its geological implications

    Institute of Scientific and Technical Information of China (English)

    YAN Jun; LIU HaiQuan; SONG ChuanZhong; XU XiSheng; AN YaJun; LIU Jia; DAI LiQun

    2009-01-01

    The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation,respectively.The representative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating.The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks.The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation,and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation.These U-Pb ages are interpreted to represent the formation times of the volcanic rocks.In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region,it is proposed that the latest volcanic activations in the Jinniu,Luzong,Fanchang and Ningwu volcanic basins probably came to end prior to ca.128 Me.There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins,suggesting e short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region.Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension,followed by delaminating of the lower part of the thickened lithosphere,lithospheric thinning,asthenosphere upwelling,and crust-mantle interaction.

  17. Paleomagnetism of Jurassic and Cretaceous rocks bounding the Santa Marta massif - NW corner of Colombia, South America

    Science.gov (United States)

    Bayona, G.; Jimenez, G.; Silva, C.

    2008-12-01

    The Santa Marta massif (SMM) is a complex terrain located in the NW margin of South America, bounded by the left-lateral Santa Marta fault to the west and the right-lateral Oca fault to the north. The SMM is cored by Precambrian metamorphic and Jurassic intrusive rocks, whereas along the SE flank crop out Jurassic volcanic rocks overlying unconformably by Limestones of Cretaceous age. Paleomagnetic analysis of 30 sites in the Jurassic and Cretaceous units in the SE region uncovered two principal magnetic components. The component "a", isolated in low coercivity and temperatures, has declinations to the north and moderate positive inclinations representing the actual field direction (n=11, D=347.6 I=23 K=30.77, a95=8.4). The component "c", with high coercivity and temperatures, has two orientations. After two-step tilt corrections, the first has northward declination and positive, low inclination (n=9, D=12, I=3, K=18.99, a95=12.1); this direction was uncovered in Cretaceous and some Jurassic rocks near to the Santa Marta fault, and we consider it as a Cretaceous component. The second direction was uncovered only in Jurassic rocks and has NNE declinations with negative-low inclinations (n=9, D=11.3 I=-14.3 K=12.36, a95=15.2); this direction represents a Jurassic component. Jurassic and Cretaceous directions isolated in areas faraway of the Santa Marta Fault suggest slight clockwise vertical-axes rotation. The Jurassic component suggests northward translation of the SMM from Paleolatitude -7.3, to near the magnetic equador in the Cretaceous, and to northern latitudes in the Cenozoic.

  18. SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications

    Institute of Scientific and Technical Information of China (English)

    XIE Guiqing; MAO Jingwen; LI Ruiling; ZHOU Shaodong; YE Huishou; YAN Quanren; ZHANG Zusong

    2006-01-01

    The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important volcanic basins in East China. Volcanic rocks in the Jinniu Basin are distributed mainly in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation, consisting of rhyolite, basalt and basaltic andesite, (trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively, in which the Dasi volcanism is volumetrically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indicate that there exist a large amount of magmatic zircons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128±1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios, this age is considered to represent the crystallization time of the Dasi volcanism. The volcanic rocks in the Dasi, Majiashan and Lingxiang Formations share similar trace element and REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geology, it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Cretaceous, just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also suggested for tectonic regime in this region in the Cretaceous Period.

  19. Paleointensity of the geomagnetic field in the Cretaceous (from Cretaceous rocks of Mongolia)

    Science.gov (United States)

    Shcherbakova, V. V.; Kovalenko, D. V.; Shcherbakov, V. P.; Zhidkov, G. V.

    2011-09-01

    A representative collection of Cretaceous rocks of Mongolia is used for the study of the magnetic properties of the rocks and for determination of the paleodirections and paleointensities H anc of the geomagnetic field. The characteristic NRM component in the samples is recognized in the temperature interval from 200 to 620-660°C. The values of H anc are determined by the Thellier-Coe method with observance of all present-day requirements regarding the reliability of such kind of results. Comparison of data in the literature on paleointensity in the Cretaceous superchron and in the Miocene supports the hypothesis of the inverse correlation between the average intensity of the paleofield and the frequency of geomagnetic reversals. The increase in the average intensities is accompanied by an appreciable increase in the variance of the virtual dipole moment (VDM). We suggest that the visible increase in the average VDM value in the superchron is due to the greater variability of VDM in this period compared to the Miocene.

  20. Petrology, Magnetic susceptibility, Tectonic setting and mineralization associated with Plutonic and Volcanic Rocks, Eastern Bajestan and Taherabad, Iran

    Directory of Open Access Journals (Sweden)

    Malihe Ghoorchi

    2009-09-01

    Full Text Available Study area is located in district of Bajestan and Ferdows cities, NE of Iran. Structurally, this area is part of Lut block. The oldest exposed rocks, to the north of intrusive rocks and in Eastern Bajestan, are meta-chert, slate, quartzite, thin-bedded crystalline limestone and meta-argillite. The sedimentary units are: Sardar Formation (Carboniferous, Jamal Formation (Permian, Sorkh Shale and Shotori Formations (Triassic, carbonateous rocks (Cretaceous and lithostratigraphically equivalent to Kerman conglomerate (Cretaceous-Paleocene are exposed in this area. Based on relative age, magmatism in eastern Bajestan and Taherabad started after Late Cretaceous and it has been active and repeated during Tertiary time. At least, three episodes of volcanic activities are recognized in this area. The first stage was mainly volcanic flow with mafic composition and minor intermediate. The second episode was mainly intermediate in composition. The third stage was changed to acid-intermediate in composition. Since the plutonic rocks intruded the volcanic rocks, therefore they may be Oligo-Miocene age. Bajestan intrusive rocks are granite-granodiorite-quartz monzonite. Taherabad intrusive rocks are diorite-quartz diorite- monzonite-latite. Bajestan intrusive rocks are reduced type (ilmenite series and Taherabad intrusive rocks are oxidized type (magnetite series.Based on geochemical analysis including trace elements, REE and isotopic data, Bajestan intrusive rocks formed in continental collision zone and the magma has crustal origin. Taherabad intrusive rocks were formed in subduction zone and magma originated from oceanic crust. Taherabad intrusive rock has exploration potential for Cu-Au and pb.

  1. Geology, Geochemistry and Geochronology of the Upper Cretaceous high-K volcanics in the southern Part of the Eastern Pontides: Implications for Mesozoic Geodynamic Evolution of NE Turkey

    Science.gov (United States)

    Eyuboglu, Y.

    2009-04-01

    The Eastern Pontide Orogenic Belt is one of the most complex geodynamic settings in the Alpine-Mediterranean region. Its geodynamic evolution is very controversial due to lack of systematic, quantitative structural, geochemical and geochronological data. This belt is divided into three subgroups: northern, southern and axial zones, distinguished from north to south by different lithological units, facies changes and tectonic characteristics. Especially, the southern zone is very attractive with its numerous rock associations such as alaskan-type mafic-ultramafic intrusions, shoshonitic and ultrapotassic volcanics, adakitic magmatics, glaucophane-bearing gabbros, metamorphic and ultramafic massifes. This study focuses on the petrology, geotectonic setting and evidence for subduction polarity of the Upper Cretaceous shoshonitic and ultrapotassic volcanics exposed in the most southerly part of the eastern Pontide magmatic arc. Geological, geochemical and isotopic data indicate that there were two distinct cycles of high-K volcanic activity in the southern part of the eastern Pontide magmatic arc during the Late Cretaceous. The first cycle (Early Campanian), represented by shoshonitic trachyandesites and associated pyroclastics, containing high K2O (2.74-4.81 wt %) and Na2O (3.60-5.51 wt %), overlies the Middle-Cretaceous ophiolitic-olistostromal melange formed during the rifting stage of a back-arc basin (Neotethys). The second cycle of high-K volcanism is characterized by potassic or ultrapotassic analcime-bearing volcanics, erupted in a lagoonal environment during the Maastrichtian. Progressive shallowing of the basin indicates that Upper Cretaceous high-K volcanism developed during the final stage of pull-apart basin development in the southern zone of the eastern Pontides. These volcanic rocks, intercalated with continental detritus, are characterized by high Na2O (3.22-7.16 wt %) concentrated in secondary analcime crystals. Their K2O contents also range between 0

  2. Basement faults and volcanic rock distributions in the Ordos Basin

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Volcanic rocks in the Ordos Basin are of mainly two types: one in the basin and the other along the margin of the basin. Besides those along the margin, the marginal volcanic rocks also include the volcanic rocks in the Yinshanian orogenic belt north of the basin. Based on the latest collection of gravitational and aeromagnetic data, here we interpret basement faults in the Ordos Basin and its peripheral region, compare the faults derived from aeromagnetic data with those from seismic data, and identify the geological ages of the fault development. Two aeromagnetic anomaly zones exist in the NE-trending faults of the southern basin, and they are in the volcanic basement formed in pre-Paleozoic. These NE-trending faults are the channel of volcanic material upwelling in the early age (Archean-Neoproterozoic), where igneous rocks and sedimentary rocks stack successively on both sides of the continental nucleus. In the Cambrian, the basin interior is relatively stable, but in the Late Paleozoic and Mesozoic, the basin margin underwent a number of volcanic activities, accompanied by the formation of nearly north-south and east-west basement faults in the basin periphery and resulting in accumulation of great amount of volcanic materials. Volcanic tuff from the basin periphery is discovered in the central basin and volcanic materials are exposed in the margins of the basin. According to the source-reservoir-cap rock configuration, the basin peripheral igneous traps formed in the Indosinian-Early Yanshanian and Late Hercynian are favorable exploration objectives, and the volcanic rocks in the central basin are the future target of exploration.

  3. Strength and deformation properties of volcanic rocks in Iceland

    DEFF Research Database (Denmark)

    Foged, Niels Nielsen; Andreassen, Katrine Alling

    2016-01-01

    rock from Iceland has been the topic for rock mechanical studies carried out by Ice-landic guest students at the Department of Civil Engineering at the Technical University of Den-mark over a number of years in cooperation with University of Iceland, Vegagerðin (The Icelandic Road Directorate......) and Landsvirkjun (The National Power Company of Iceland). These projects involve engineering geological properties of volcanic rock in Iceland, rock mechanical testing and parameter evaluation. Upscaling to rock mass properties and modelling using Q- or GSI-methods have been studied by the students......Tunnelling work and preinvestigations for road traces require knowledge of the strength and de-formation properties of the rock material involved. This paper presents results related to tunnel-ling for Icelandic water power plants and road tunnels from a number of regions in Iceland. The volcanic...

  4. Geochronology and Geochemistry of Cretaceous Volcanic Rocks from Liuluo Formation in Hainan Island and Their Tectonic Implications%海南白垩纪六罗村组火山岩的年代学、地球化学特征及其大地构造意义

    Institute of Scientific and Technical Information of China (English)

    周云; 梁新权; 梁细荣; 蒋英; 蔡运花; 邹水长; 王策; 付建刚; 董超阁

    2015-01-01

    A large number of volcanic rocks outcrops have been reported in the southern Hainan Island, but their geochronology, petrogenesis and tectonic implications are still unclear. In this study, we present detailed zircon U-Pb dating results and major and trace elemental compositions of the Liuluocun Formation volcanic rocks in the Liuluo area of Sanya, Hainan Island. LA-ICP-MS zircon U-Pb dating of the rhyolite from the upper Liuluocun Formation yields an age of 102±1 Ma, basaltic andesite from the lower Liuluocun Formation also shows an age of 102±1 Ma, indicating late stage of the Early Cretaceous volcanic activity occurred in southern Hainan Island. The rhyolites are characterized by high contents of silicon (SiO2=73.77%‒74.79%) and potassium (K2O=5.09%‒6.77%) and K2O/Na2O ratios (1.71‒2.80), and low Mg# (22‒28). They show negative Ti, P, Nb and Ta anomalies, obvious depletion of Eu (δEu=0.51‒0.61), enrichment in Rb, Ba and LILE and strong fractionation between LREE and HREE (La/YbCN=15.05‒16.97). The basalts-andesites have SiO2 ranging from 49.82%to 57.93%and lower value of K2O/Na2O (0.32‒1.11) and higher value of Mg# (46‒58) than those of the rhyolites. They show slight Eu anomalies (δEu=0.86~0.94), depletion of Nb and Ta, and enrichment of LILE. They have lower degree fractionation between LREE and HREE (La/YbCN=9.42‒12.24) and weaker negative P, Ti anomalies than those of the rhyolites. Besides, rhyolite and basalt-andesite samples show similar (87Sr/86Sr)i (0.708222‒0.708965 and 0.707532‒0.708401, respectively) andεNd(t) values (‒2.49‒‒2.69 and‒2.35‒‒4.09, respectively), indicating that they may have derived mainly from the same source. Combining with the regional geological data, we propose that these volcanic rocks are most likely generated from continental lithospheric mantle which had been modified by subduction component, and their formation was closely related to the regional lithospheric extension in the South

  5. Integrated Geophysical Techniques for Exploring Deep Volcanic Rock Reservoir

    Institute of Scientific and Technical Information of China (English)

    LiuXuejun; UDechun; ZhangChangjiang; RanXuefeng

    2003-01-01

    The Carboniferous and Pre-Carboniferous formations in Ludong, Zhungar basin, contain favorable oil/gas reservoirs. The Carboniferous formations, however, are complex in structure and exhibit lateral variations in lithology. Seismic reflections from Pre-Triassic formations are poor and the volcanic reservoirs are very difficult to identify. The analysis of physical properties concluded that the major targets in this region, i.e., the top of the Jurassic and Carboniferous formations, provide distinct density interfaces. The basic, intermediate and acid volcanic rocks were also different in density,resulting in distinguishable gravity anomalies. The differences in magnetism in this region existed not only between the volcanic rocks and clastic sedimentary rocks but also among volcanic rocks with different compositions. All formations and volcanic rocks of different lithologies presented high and low resistance interbeds, which are characterized by regional trends.The modeling study demonstrated that non-seismic integrated geophysical techniques should be feasible in this region, especiaUy the high-precision gravity/magnetic methods combined with long offset transient electromagnetic sounding.

  6. SHRIMP dating of volcanic rock in the Zhangwu-Heishan area, West Liaoning province, China: Its relationship with coal-bearing strata

    Institute of Scientific and Technical Information of China (English)

    Cai Houan; Xu Debin; Li Baofang; Shao Longyi

    2011-01-01

    The Zhangwu-Heishan area is located to the east of the Fuxin-Yixian Basin and is mostly covered with volcanic rock.At various periods,different geologists had varying opinions about their age and periods of volcanic eruptions,especially on sequences between volcanic rock and main coal-beating strata,which affect the direction of searching for coal,as well as prospecting the entire research area.During our study,we carried out detailed field investigations in this research area; observed and recorded the main representative outcrops of volcanic rock.We collected over 20 volcanic rock samples and tested the Sensitive High Resolution Ion Microprobe Ⅱ (SHRIMP Ⅱ) U-Pb isotope age of 11 samples.The age of our volcanic rock samples ranged between 56.0 ± 2.9 and 132.3 ± 2.3 Ma.After taking earlier investigations into consideration,we concluded that,except for a suite of paleogene olivine basalt,the volcanic rock in the Zhangwu-Heishan area is younger than the coal-beating Shahai Formation.It is therefore most unlikely to find coal seams equivalent to those of the early Cretaceous Shahai Formation in Fuxin Basin below volcanic rock.

  7. Geochronology of the volcanic rocks in the Lu-Zong basin and its significance

    Institute of Scientific and Technical Information of China (English)

    David; COOKE; Sebastien; MEFFRE

    2008-01-01

    The Lu-Zong (Lujiang-Zongyang) basin is one of the most important volcanic basins in the middle and lower reaches of the Yangtze River area, China. It comprises four shoshonitic volcanic units, which are, in an ascending order, the Longmenyuan, Zhuanqiao, Shuangmiao and Fushan Groups. The LA-ICP MS U-Pb zircon ages of the four units are: 134.8±1.8 Ma for the Longmenyuan Group, 134.1±1.6 Ma for the Zhuanqiao Group, 130.5±0.8 Ma for the Shuangmiao Group, and 127.1±1.2 Ma for the Fushan Group. The results indicate that all volcanic rocks in the Lu-Zong basin were formed in the Early Cretaceous from about 135 Ma to 127 Ma, lasting 8-10 Ma. There were no Jurassic volcanic activities in all the volcanic basins including the Lu-Zong basin in the middle and lower reaches of the Yangtze River area. This work has provided new chronological results for the further study and understanding of the tec- tonic, magmatic and metallogenic processes of eastern China in the Mesozoic.

  8. Geochronology of the volcanic rocks in the Lu-Zong basin and its significance

    Institute of Scientific and Technical Information of China (English)

    ZHOU TaoFa; FAN Yu; YUAN Feng; LU SanMing; SHANG ShiGui; David COOKE; Sebastien MEFFRE; ZHAO GuoChun

    2008-01-01

    The Lu-Zong (Lujiang-Zongyang) basin is one of the most important volcanic basins in the middle and lower reaches of the Yangtze River area, China. It comprises four shoshonitic volcanic units, which are,in an ascending order, the Longmenyuan, Zhuanqiao, Shuangmiao and Fushan Groups. The LA-ICP MS U-Pb zircon ages of the four units are: 134.8±1.8 Ma for the Longmenyuan Group, 134.1±1.6 Ma for the Zhuanqiao Group, 130.5±0.8 Ma for the Shuangmiao Group, and 127.1+1.2 Ma for the Fushan Group. The results indicate that all volcanic rocks in the Lu-Zong basin were formed in the Early Cretaceous from about 135 Ma to 127 Ma, lasting 8-10 Ma. There were no Jurassic volcanic activities in all the volcanic basins including the Lu-Zong basin in the middle and lower reaches of the Yangtze River area.This work has provided new chronological results for the further study and understanding of the tectonic, magmatic and metallogenic processes of eastern China in the Mesozoic.

  9. Geology, mineralization, Rb-Sr & Sm-Nd geochemistry, and U–Pb zircon geochronology of Kalateh Ahani Cretaceous intrusive rocks, southeast Gonabad

    Directory of Open Access Journals (Sweden)

    Mohammad Hassan Karimpour

    2013-10-01

    Full Text Available Kalateh Ahani is located 27 km southeast of Gonabad within the Khorasan Razavi province. The area is part of Lut Block. Sub-volcanic monzonitic rocks intruded regional metamorphosed Shemshak Formation (Jurassic age. Magnetic susceptibility of less altered monzonitic rocks is 0.6%., As, Pb and Zn > 1%, Au up to 150 ppb and Sn = 133 ppm. The Sn content of vein in the northern part of Kalateh Ahani (Rud Gaz is > 1%. Based on mineralization, alteration and geochemistry, it seems that Sn mineralization is associated with the Cretaceous monzonitic rocks. Zircon U–Pb dating indicates that the age of the monzonitic rocks associated with mineralization is 109 Ma (Lower Cretaceous. Based on (87Sr/86Sri = 0.71089-0.710647 and (143Nd/144Ndi = 0.512113-0.51227 of the monzonitic rocks, the magma for these rocks were originated from the continental crust. This research has opened new window with respect to Sn-Cu mineralization and exploration within the Lut Block which is associated with Cretaceous granitoid rocks (reduced type, ilmenite series originated from the continental crust.

  10. Fluorine geochemistry in volcanic rock series

    DEFF Research Database (Denmark)

    Stecher, Ole

    1998-01-01

    A new analytical procedure has been established in order to determine low fluorine concentrations (30–100 ppm F) in igneous rocks, and the method has also proven successful for higher concentrations (100–4000 ppm F). Fluorine has been measured in a series of olivine tholeiites from the Reykjanes...... Peninsula, a tholeiite to rhyolitic rock series from Kerlingarfjöll, central Iceland, and an alkaline rock series from Jan Mayen that ranges from ankaramites to trachytes. Fluorine is not appreciably degassed during extrusion and appears to be insensitive to slight weathering. The olivine tholeiites from...... the Reykjanes Peninsula have F contents of 30–300 ppm and exhibit linear increases proportional to the incompatible elements K, P, and Ti. Such incompatible behaviour for F has been confirmed for the less evolved rocks of the other series. The tholeiites from Kerlingarfjöll (100–2000 ppm F) show a linear...

  11. Applications of Terrestrial Remote Sensing to Volcanic Rock Masses

    Science.gov (United States)

    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.

  12. Pore Structure of Cement Pastes Blended with Volcanic Rock

    Institute of Scientific and Technical Information of China (English)

    YU Lehua; ZHOU Shuangxi; LI Liling

    2016-01-01

    The pore parameters of cement pastes blended with volcanic rock at the curing age of 1, 28 and 90 d were de-termined by a mercury intrusion porosimetry. The pore structure of the pastes was characterized through the analysis of porosity, average pore diameter, the most probable pore aperture, pore size distribution, as well as total pore volume. For the improvement of mechanical property and durability of cement-based material, the correlation of the formed pore structure with hydration time and replacement level of volcanic rock for cement was revealed. The results indicate that volcanic rock can diminish porosity and reduce pore size in cement paste when curing time prolongs, which is particu-larly prominent with replacement level of less than 20% in late period. The more harmful pores (i.e., capillary pore) are gradually transformed into harmless pore (i.e., gel pores or micropore), even fully filled and disappeared when hydration products increase. The pore structure of the cement paste is thus refined. The beneficial effect of volcanic rock on the pore structure of cement paste could enhance the mechanical property and durability of cement-based material.

  13. The evolution of pore connectivity in volcanic rocks

    Science.gov (United States)

    Colombier, Mathieu; Wadsworth, Fabian B.; Gurioli, Lucia; Scheu, Bettina; Kueppers, Ulrich; Di Muro, Andrea; Dingwell, Donald B.

    2017-03-01

    Pore connectivity is a measure of the fraction of pore space (vesicles, voids or cracks) in a material that is interconnected on the system length scale. Pore connectivity is fundamentally related to permeability, which has been shown to control magma outgassing and the explosive potential of magma during ascent in the shallowest part of the crust. Here, we compile a database of connectivity and porosity from published sources and supplement this with additional measurements, using natural volcanic rocks produced in a broad range of eruptive styles and with a range of bulk composition. The database comprises 2715 pairs of connectivity C and porosity ϕ values for rocks from 35 volcanoes as well as 116 products of experimental work. For 535 volcanic rock samples, the permeability k was also measured. Data from experimental studies constrain the general features of the relationship between C and ϕ associated with both vesiculation and densification processes, which can then be used to interpret natural data. To a first order, we show that a suite of rocks originating from effusive eruptive behaviour can be distinguished from rocks originating from explosive eruptive behaviour using C and ϕ. We observe that on this basis, a particularly clear distinction can be made between scoria formed in fire-fountains and that formed in Strombolian activity. With increasing ϕ, the onset of connectivity occurs at the percolation threshold ϕc which in turn can be hugely variable. We demonstrate that C is an excellent metric for constraining ϕc in suites of porous rocks formed in a common process and discuss the range of ϕc values recorded in volcanic rocks. The percolation threshold is key to understanding the onset of permeability, outgassing and compaction in shallow magmas. We show that this threshold is dramatically different in rocks formed during densification processes than in rocks formed in vesiculating processes and propose that this value is the biggest factor in

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

    Science.gov (United States)

    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.

  15. A detailed paleomagnetic investigation of Cretaceous igneous rocks: New contributions from Colombia and Paraguay

    Science.gov (United States)

    Kapper, Lisa; Calvo-Rathert, Manuel; Cejudo Ruiz, Ruben; Sanchez Bettucci, Leda; Irurzun, Alicia; Carrancho, Ángel; Gogichaishvili, Avto; Morales, Juan; Sinito, Ana; Mejia, Victoria; Nivia Guevara, Alvaro

    2016-04-01

    We present rock magnetic results, paleodirections and -intensities from Cretaceous samples from two locations from South America. On the one hand we report paleomagnetic results from the Western Cordillera of Colombia from 15 sites north of Cali. These volcanic rock samples were related to age determinations from close localities of 92.5 ± 1.1 Ma on average, occuring during the Cretaceous Normal Superchron (CNS). On the other hand we show results from an alkaline dike swarm in the Asunción Rift, Eastern Paraguay. Previous investigations suggest that these dikes extruded in a rather short period of 126-127 Ma, during normal and reversed polarity field configuration, right before the onset of the CNS. Rock magnetic measurements of both sites show that the main magnetic component is a low-coercivity mineral, e.g., (titanium)magnetite, with a large range of grain sizes from multi- to single domain, or mixtures of several grain sizes in a sample. For the Colombian site we obtained an average Virtual Geomagnetic Pole (VGP), whose latitude compares well with those for South and North America of Besse and Courtillot (2002) with a similar age. For the determination of the Virtual Dipole Moments (VDMs) the Thellier-Coe method did not give successful results, probably due to minerals in the range of multidomain grain size. Therefore, we applied the multispecimen protocol on ten specimens. Six successful determinations produced an average VDM of 2.3 x 10-22 Am2. This value is rather low, but in good agreement with other data from the same time period. Directional investigation of the Eastern Paraguayan dike swarm show highly clustered promising results with six out of 22 sites having an α95 ≤ 10.0° . Most of these sites show a reversed polarity; however, one intermediate polarity site has a very reliable direction as well. This and the occurrence of normal polarity sites suggest that the dikes may have not appeared at the same time but rather during the transition from

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

    Science.gov (United States)

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

    2015-04-01

    Yıldızeli region to the south of İzmir Ankara Erzincan suture zone is situated on the large Sivas Tertiary sedimentary basin. After the northern branch of the Neotethyan Ocean was northerly consumed beneath the Sakarya Continent, a continent - continent collision occurred between the Anatolide- Tauride platform and Pontides and followed a severe intermediate magmatism during the Late Cretaceous- Tertiary period. This created an east-west trending volcanic belt along the whole Pontide range. In the previous studies different models are suggested for the Eocene volcanic succession such as post-collisional, delamination and slab-breakoff models as well as the arc model for its westernmost parts. We will present our field and geochemical data obtained from the Yıldızeli and its surroundings for its petrogenesis, and will discuss the tectonic model(s) on the basis of their geochemical/petrological aspects. Cenozoic volcanic sequences of Yıldızeli region which is the main subject of this study, overlie Pre-Mesozoic crustal meta-sedimentary group of Kırşehir Massif, Ophiolitic mélange and Cretaceous- Paleocene? flysch-like sequences. In the northern part of Yıldızeli region, north vergent thrust fault trending E-W seperates the ophiolitic mélange complex from the Upper Cretaceous-Paleocene and Tertiary formations. Volcano-sedimentary units, Eocene in age, of the Yıldızeli (Sivas-Turkey) which are intercalated with sedimentary deposits related to the collision of Anatolide-Tauride and a simultaneous volcanic activity (i.e. the Yıldızeli volcanics), exposed throughout a wide zone along E-W orientation. Yıldızeli volcanics consist of basalts, basaltic-andesites and andesitic lavas intercalated flow breccias and epiclastic, pyroclastic deposits. Basaltic andesite lavas contain Ca-rich plagioclase + clinopyroxene ± olivine with minor amounts of opaque minerals in a matrix comprised of microlites and glass; andesitic lavas are generally contain Ca

  17. Western Alborz Volcanic Rocks, a new Geochemical Viewpoint

    Science.gov (United States)

    Ghorbani, M.

    2001-12-01

    Volcanic and pyroclastic rocks of Eocene age comprise vast outcrops of Alborz Mountain Range, a fold-thrusted structural unit extending across northern Iran for 2000 km in a curvilinear pattern. In his account of structural evolution of Iranian plateau, Berberian (1983; p. 55) ascribed these rocks to a subduction-type magmatism. Based on a tectonostratigraphic study, these rocks are attributed to an arc-type magmatism (Alavi; 1996, p. 29). Recently a new data set of major and trace element (including REE) analyses of volcanic rocks from western Alborz, some 50 km west of city of Qazvin, has been made available (Asiabanha, 2001). Careful examination of the data (i.e., those of basic-intermediate rocks) in present study revealed, for the first time, some geochemical characteristics which have important implications on the geodynamic synthesis of this structural unit. The rocks contain 50-60 wt% SiO2. They lie in the midalkaline-to-subalkaline domain of TAS diagram (Middlemost, 1997; p.216) and fall in the calcalkaline field of AFM diagram. The volcanic rocks display two distinct chondrite-normalized REE patterns, one is MREE-depleted while the other is a rather smooth uniform M-HREE pattern. These are called MREE-depleted and smooth M-HREE series. Basic rocks from the latter contain higher silica than the former (>53 vs. >50 wt%), yet they show lower incompatible elements (e.g., K and Rb) and HFSE contents. These features can not be explained by differentiation and might be interpreted as implying the involvement of two source regions. Chondrite-normalized trace element patterns of the MREE-depleted series is more akin to the island arc calcalkaline (IACA) basic rocks than the basic rocks from any other tectonic settings. However, island arc products, known for being depleted in HFSE relative to other incompatible elements, differ from the MREE-depleted series which is rich in both HFSE and incompatible elements. One may advocate the role of OIB-type mantle

  18. Hydrocarbon- Generating Model of the Area Covered With Volcanic Rock

    Institute of Scientific and Technical Information of China (English)

    Guo Zhanqian; Zhang Yuwei

    2000-01-01

    The distribution of Oil & gas fields shows their close relationship with the most active tectonic regions. This is not a coincidence but having a scientific reasons. The crustal active regions, refer to the places where the active natural earthquake, volcanic activities, underground water happened, and the areas of the leaking off of natural gas to the surface of the crust. The magma of volcanic activities brings the organic "kitchen range body" hydrocarbon- generating model and inorganic genetic hydrocarbon to the regions covered by volcanic rock. Underground water brings a catalytic hydrocarbongenerating model for organic matter, and the leaking- off of H2 and CO2 contributes a synthetic hydrocarbon - generating model. Volcanic activities bring the assemblage of Source, Reservoir and Seal formed by the sediments and magma the sedimentary basins, and the hydrocarbon - generating system with a "water - volcano" binary structure is formed. All these conditions are favorable and excellent for the formation of oil & gas fields. The distribution of American oil & gas fields have very close relationship with the mines of Fe, Mn, Ct, Mo, W and V, deposits of Zn, Cu, V, Pb, Al and Hg, and the deposits of fluorite, sulfur, potassium salt, phosphate and halite, and the distribution of sulfate- chloride of river water. The reason why few oil & gas fields discovered in the regions covered by volcanic rock in western America maybe because of the view of "inconsistency between petroleum and volcano". Further more, It's very difficult to carry out a geophysical exploration in such kinds of regions.This paper examined a few hydrocarbon-generating models (systems) mentioned above and came up with some fresh ideas on the exploration in the areas covered with volcanic rocks.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  1. Geochemical characteristics and petrogenesis of volcanic rocks from Baiyingaolao Formation in northeastern Hailar Basin

    Institute of Scientific and Technical Information of China (English)

    LI Xu; SUN Deyou; GOU Jun

    2016-01-01

    The volcanic rocks from Baiyingaolao Formation in the northeastern Hailar Basin are mainly com-posed of rhyolite and trachydacite.U-Pb dating of zircon shows these volcanic rocks formed in Early Cretaceous (128-124 Ma).Geochemical data indicate that they are sub-alkaline series in composition and rich in alkali and potassium.All samples have similar rare earth element patterns characterized by high total rare earth ele-ments contents (∑REE=113.96 ×10 -6-204.33 ×10 -6),significant fractionation of heavy and light rare earth elements (∑LREE/∑HREE =3.10-4.52)with middle negative Eu anomalies (δEu=0.46-0.76). The trace elements are characterized by enrichment in large-ion lithophile elements such as K,Rb,LREE and depletion in high field strength elements e.g.Nb,Ta,HREE,P and Ti,while enriched in Th and U.Rhyolite and trachydacite contain low initial 87Sr/86Sr ratios (0.704 9-0.7 053)and positive εNd(t)values (ca.4. 15).These data suggest that the magma of rhyolite and trachydacite were derived from mafic lower crust newly accreted from mantle,with the evolutional trend of comagmatic fractional crystallization.

  2. An Early Cretaceous volcanic arc/marginal basin transition zone, Peninsula hardy, southernmost Chile

    Science.gov (United States)

    Miller, Christopher A.; Barton, Michael; Hanson, Richard E.; Fleming, Thomas H.

    1994-10-01

    The Hardy Formation represents a latest Jurassic-Early Cretaceous volcanic arc that was located along the Pacific margin of southern South America. It was separated from the continent by a marginal basin floored by portions of an ophiolite sequence (the Rocas Verdes ophiolites). The transition between the arc and marginal basin occurs on Peninsula Hardy, southernmost Chile, where there is a lateral facies transition from arc deposits of the Hardy Formation into proximal marginal basin fill of the Yahgan Formation. Interfingering of arc and marginal basin sequences demonstrates that subduction-related arc magmatism was concurrent with marginal basin formation. The lateral facies transition is reflected in the geochemistry of volcanic rocks from the Hardy and Yahgan formations. Basalts, andesites and dacites of the arc sequence follow a calc-alkaline differentiation trend whereas basalts from the marginal basin follow a tholeiitic differentiation trend. Estimates of temperature and oxygen fugacity for crystallization of the arc andesites are similar to values reported for other calc-alkaline andesites. It is suggested that water activity influenced the early or late crystallization of Ti-magnetite and this controlled the style of differentiation of the magmas erupted on Peninsula Hardy. Magmas with high water contents evolved along the calc-alkaline differentiation trend whereas those with low water contents evolved along the tholeiitic differentiation trend. Some rhyolites are differentiated from the calc-alkaline andesites and dacites, but most appear to be the products of crustal anatexis on the basis of trace-element evidence. The arc basalts and some marginal basin basalts show relative enrichment in LILE, relative depletion in HFSE, and enrichment in LREE. Other marginal basin basalts are LREE depleted and show small relative depletions in HFSE. Basalts with both calc-alkaline and tholeiitic affinities can also be recognized in the Rocas Verdes ophiolites

  3. Subaqueous environment and volcanic evolution of the Late Cretaceous Chelopech Au-Cu epithermal deposit, Bulgaria

    Science.gov (United States)

    Chambefort, Isabelle; Moritz, Robert

    2014-12-01

    A detailed field and petrographic study constrains the volcanic evolution and environment setting of the volcano-sedimentary-hosted Chelopech Cu-Au epithermal deposit, Bulgaria. Magmatic activity and associated high-sulfidation epithermal mineralization occurred at about 91 Ma in the Panagyurishte ore district of the Eastern European Banat-Timok-Srednogorie metallogenic belt. Volcanic and hydrothermal activity took place in a complex subaqueous setting, resulting in the intercalation of quartz sandstone with andesitic volcanic and volcaniclastic breccia. There are also hypabyssal andesite intrusion, phreatomagmatic breccia and interbeds of pyroclastic, oolithic and bioclastic rocks. The presence of altered cerebroid ooid-bearing sedimentary units characteristic of salty environment is in accordance with a lagoon environment predating the mineralization at Chelopech. Four principal stages of evolution for the Chelopech district are proposed based on field and petrographic observations. Initial volcanism occurred in a lake or in a coastal, shallow lagoon environment above crystalline basement. The Chelopech "phreatomagmatic" breccia and subsurface andesites were emplaced at this time. Subsequent hydrothermal activity produced the different hydrothermal breccia types, advanced argillic and quartz-phyllic alteration, and Au-Cu vein and replacement mineralization. The end of volcanism and hydrothermal activity was associated with opening of a pull-apart basin that covered the Chelopech environment with a sedimentary flysch. Tertiary compression faulting juxtaposed various rocks and tilted the ore deposit during the Alpine orogeny.

  4. Trace Element Geochemistry of Cenozoic Volcanic Rocks in Shandong Province

    Institute of Scientific and Technical Information of China (English)

    陈道公; 李彬贤; 等

    1989-01-01

    The Cenozoic volcanic rock of Shandong Province are mainly alkalic and strongly alkalic basaltic rocks.The Contents of major and trace elements including transitional,incompatible and rare-earth elements were determined.The chemical characterisitics of major and trace elements indicate that these basaltic rocks were derived from a mantle source and probably represent a primary magma,I,e.,unmodifiecd partical melts of mantle peridotite in terms of Mg values,correlatione between P2O5 and Ce,Sr,Ni and Rb concentrations,mantle xenoliths,etc.The abundances of trace elements vary systematically from west to east.The compatible transition elements such as Co,Ni,and Cr show a remarkable depletion,whereas the incompatible and rare-earth elements are abundant as viewed from the chondrite-nor-malized patterns.The chemical composition and correlation are consistent with the tectonic setting.According to the batch and fractional partial melting theory,the trace element contents of Shandong volcanic rocks can be calculated from the two-component mixing model.

  5. Petrography, geochemistry and tectonic setting of Salmabad Tertiary volcanic rocks, southeast of Sarbisheh, eastern Iran

    Directory of Open Access Journals (Sweden)

    Masoumeh Goodarzi

    2014-10-01

    Full Text Available Introduction The area reviewed and studied in this paper is located 5 km southeast of Sarbisheh city at eastern border of the Lut block (Jung et al., 1983; Karimpour et al., 2011; Richards et al., 2012 in eastern Iran between 59° 47′ and 59° 53′ E longitude and 32°30′ and 32°34′ N latitude. The magmatic activity in the Lut block began in middle Jurassic (165-162 Ma and reached its peak in Tertiary (Jung et al., 1983. Volcanic and subvolcanic rocks of Tertiary age cover over half of Lut block with up to 2000 m thickness and formed due to subduction prior to the collision of the Arabian and Asian plates (Camp and Griffis, 1982; Tirrul et al., 1983; Berberianet et al., 1982. Most of magmatic activity in the Lut block formed in middle Eocene (Karimpour et al., 2011 The andesitic volcanics were erupted together with the dacites and rhyodacites during a time interval of some 50 Ma from early Cretaceous to early Neogene. It can be assumed that the intensity of the volcanic activity was varying significantly during this time span (Jung et al., 1983.Tertiary volcanic rocks (Eocene-Oligocene to Pliocene with intermediate composition associated with pyroclastic rocks cropped out in eastern parts of Salmabad village, southeast of Sarbisheh. The main purpose of this paper is better understand the tectono-magmatic setting of the Tertiary volcanic rocks in southeast of Sarbisheh, eastern Iran based on geochemical characteristics. Materials and methods Eleven samples were analyzed for major elements by inductively coupled plasma (ICP technologies and trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP-MS, following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the SGS Laboratories, Toronto, Canada. Results In the Salmabad area, Tertiary volcanic rocks with mainly intermediate (andesitic composition are exposed associated with pyroclastic deposits such as tuff, breccia and agglomerate

  6. Latest Cretaceous and Cenozoic magmatic rocks of Alaska: polygon data

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This map is a statewide summary of magmatic (igneous) rocks grouped into geologic units that can be portrayed cartographically at 1:2,500,000. This dataset consists...

  7. Petrography, Geochemistry and Petrogenesis of Volcanic Rocks, NW Ghonabad, Iran

    Directory of Open Access Journals (Sweden)

    Sedigheh Zirjanizadeh

    2016-07-01

    Full Text Available Introduction The study area is located in NW Gonabad, Razavi Khorasan Province, northern Lut block and eastern Iran north of the Lut Block. Magmatism in NW Gonabad produced plutonic and volcanic rock associations with varying geochemical compositions. These rocks are related to the Cenozoic magmatic rocks in Iran and belong to the Lut Block volcanic–plutonic belt. In this study, petrogenesis of volcanic units in northwest Gonabad was investigated. The volcanic rocks are andesites/trachyandesites, rhyolites, dacites/ rhyodacites and pyroclastics.These rocks show porphyritic, trachytic and embayed textures in phenocrysts with plagioclase, sanidine and quartz (most notably in dacite and rhyolite, hornblende and rare biotite. The most important alteration zones are propylitic, silicification and argillic.Four kaolinite- bearing clay deposits have been located in areas affectedby hydrothermal alteration of Eocene rhyolite, dacite and rhyodacite. Analytical techniques Five samples were analyzed for major elements by wavelength dispersive X-ray fluorescence (XRF and six samples were analyzed for trace elements using inductively coupled plasma-mass spectrometry (ICP-MS in the Acme Laboratories, Vancouver (Canada.Sr and Nd isotopic compositions were determined for four whole-rock samples at the Laboratório de GeologiaIsotópica da Universidade de Aveiro, Portugal. Results Petrography. The rocks in this area are consist of trachyte, andesite/ trachyandesite, dacite/ rhyodacite, principally as ignimbrites and soft tuff. The textures of phenocrysts are mainly porphyritic, glomerophyric, trachytic and embayed textures in plagioclase, hornblende and biotite. The groundmasses consist of plagioclase and fine-grainedcrystals of hornblende. Plagioclase phenocrysts and microlitesare by far the most abundant textures in andesite - trachyandesites (>25% and in size from 0.01 to 0.1mm. Euhedral to subhedral hornblende phenocrysts areabundant (3-5%and 0.1 to 0

  8. Cretaceous source rock sedimentation and its relation to transgressive peaks and geodynamic events for the Central Tethys

    Energy Technology Data Exchange (ETDEWEB)

    Flexer, A. (Tel Aviv Univ. (Israel)); Honigstein, A.; Rosenfeld, A. (Geological Survey of Israel, Jerusalem (Israel)); Lipson, S. (Institute of petroleum and energy, Tel Aviv (Israel)); Tarnenbaum, E. (Consultant, Tel Aviv (Israel))

    1993-02-01

    The reconstruction of the Mesozoic continents shows a wide triangle-shaped Tethys (or Neotethys) between Africa and Eurasia. The Arabian Craton comprised the central part of its southern margins. The Cretaceous period started with extension, volcanism, continued by accelerated divergence during Aptian-Turonian and terminated by convergence and folding. The sea level stand, after a major fall at the commencement, is characterized by a steady stepwise rise with some minor retreats. The global oceanic anoxic events correspond to large-extent transgressions and associated with organic rich sedimentation. The accelerated building up of mid-oceanic ridges is possibly connected to a mantle plume, active around 120-80 Ma. Sea level rise and sea floor spreading is felt mainly at these times in the passive southern margins of the central Tethys. The Senonian compressive tectonic regime transforms them into active margins (destruction of oceanic crust, obduction and thrusting); sea level highstands control dysoxic sedimentation. Dysoxic sediments were observed in the Gevaram shales (Tithonian-Hauterivian). Talme Yafe marls (Late Aptian-Albian), Daliyya Formation (latest Cenomanian-Turonian) and the Mount Scopus Group (Santonian-Maastrichtian). The organic matter in the Gevaram shales is mixed marine and terrestrial (2.6% TOC) and in the Daliyya marls mostly marine (2.5% TOC). Both units have source rock possibilities and yield petroleum upon appropriate burial. The Senonian bituminous rocks (oil shales) are rich in marine organic matter (20% TOC) and are excellent source rocks in the Dead Sea area.

  9. Paleomagnetism, rock-magnetism and geochemical aspects of early Cretaceous basalts of the Paraná Magmatic Province, Misiones, Argentina

    Science.gov (United States)

    Mena, Mabel; Orgeira, María Julia; Lagorio, Silvia

    2006-10-01

    The basalts of the Posadas Formation were extruded during the huge continental volcanism that affected the Paraná Basin in the Lower Cretaceous. We have carried out a paleomagnetic and rock-magnetic study on samples collected along a basalt outcrop section in Misiones, Argentina and determined that rocks classified as tholeiitic basalts and andesi-basalts are characterized by a low to intermediate content of Ti. Paleomagnetic and rock-magnetic studies suggest that the main magnetic mineral is low-Ti titanomagnetite of superparamagnetic (SP) to single-domain (SD) sizes, and very low amounts of multi-domain (MD) particles. The stable magnetic remanence enabled us to define characteristic remanent magnetizations (ChRMs) with a maximum angular deviation (MAD) <5° in most cases; and in all the cases, a MAD <10°. The sequence has registered at least two polarity reversions, starting from a normal polarity at the base. The calculated virtual geomagnetic poles (VGPs) present an elongated distribution similar to other distributions of VGPs published for the Paraná Magmatic Province. The elongated distribution of the VGPs could be a real feature of the geomagnetic field at a time of frequent changes of polarity.

  10. Study on Mechanism of Formation of Volcanic Rock in North Altay by Using Rare Earths

    Institute of Scientific and Technical Information of China (English)

    袁峰; 周涛发; 岳书仓

    2003-01-01

    The characteristics of rare earth elements in the Devonian and Carboniferous volcanic rocks were studied in the north Altay. And the mechanism of formation of volcanic rocks were discussed by using the rare earth elements. The correlativity of rare earth elements and major elements shows that the fractional crystallization is undistinguishable during the formation of Devonian and Carboniferous volcanic rocks, and the mechanism of formation of volcanic rocks may be the partial melting. The further study of the relationship of manifold rare earth elements shows that the mechanism of formation of Devonian and Carboniferous volcanic rocks in the north Altay is the partial melting. And the result also shows that the rare earth elements in the Devonian and Carboniferous volcanic rocks inherited the characteristics of those in its source materiels.

  11. Cretaceous basaltic phreatomagmatic volcanism in West Texas: Maar complex at Peña Mountain, Big Bend National Park

    Science.gov (United States)

    Befus, K. S.; Hanson, R. E.; Lehman, T. M.; Griffin, W. R.

    2008-06-01

    A structurally complex succession of basaltic pyroclastic deposits produced from overlapping phreatomagmatic volcanoes occurs within Upper Cretaceous floodplain deposits in the Aguja Formation in Big Bend National Park, West Texas. Together with similar basaltic deposits recently documented elsewhere in the Aguja Formation, these rocks provide evidence for an episode of phreatomagmatic volcanism that predates onset of arc magmatism in the region in the Paleogene. At Peña Mountain, the pyroclastic deposits are ≥ 70 m thick and consist dominantly of tabular beds of lapillistone and lapilli tuff containing angular to fluidal pyroclasts of altered sideromelane intermixed with abundant accidental terrigenous detritus derived from underlying Aguja sediments. Tephra characteristics indicate derivation from phreatomagmatic explosions involving fine-scale interaction between magma and sediment in the shallow subsurface. Deposition occurred by pyroclastic fall and base-surge processes in near-vent settings; most base-surge deposits lack tractional sedimentary structures and are inferred to have formed by suspension sedimentation from rapidly decelerating surges. Complexly deformed pyroclastic strata beneath a distinct truncation surface within the succession record construction and collapse of an initial volcano, followed by a shift in the location of the conduit and excavation of another maar crater into Aguja strata nearby. Preserved portions of the margin of this second crater are defined by a zone of intense soft-sediment disruption of pyroclastic and nonvolcanic strata. U-Pb isotopic analyses of zircon grains from three basaltic bombs in the succession reveal the presence of abundant xenocrysts, in some cases with ages > 1.0 Ga. The youngest concordant analyses for all three samples yield a weighted mean age of 76.9 ± 1.2 Ma, consistent with the presence of Late Campanian vertebrate fossils in the upper Aguja Formation. We infer that the volcanism is related to the

  12. Case Study of Volcanic Rock Reservoir--Beibao Area of Nanbao Sag

    Institute of Scientific and Technical Information of China (English)

    Guo Qijun; Wan Zhimin; Jiao Shouquan; Liu Laixiang

    1997-01-01

    @@ Preface Crude has been produced from volcanic rock reservoirs inAmerica, Libya, Indonesia and Japan, according to the available data. Oil and gas Production from volcanic rock reservoirs in Japan accounts for 30% of the total, with the recoverable reserves estimated at 48% of the total. Oil and gas traps of volcanic rock reservoir with better reservoir properties and flow potential have been discovered in Liaohe, Erlian, Jizhong, Huanghua, Jiyang, Linqing,Jiangsu and Xinjiang of China since the 1970's. However,the systematic study of volcanic rock reservoir is just in the beginning.

  13. Extensional Lower Cretaceous volcanism in the Coastal Range (29°20'-30°S), Chile: geochemistry and petrogenesis

    Science.gov (United States)

    Morata, D.; Aguirre, L.

    2003-12-01

    Lower Cretaceous volcanism in the Coastal Range (29°20'-30°S) of Chile is mainly represented by highly porphyritic (20-30% phenocrysts) lavas with unzoned Ca-rich plagioclase (An 57-54Ab 40-42Or 3-4), clinopyroxene (Wo 40En 43Fs 17), magnetite, and minor idiomorphic, altered olivines. Geochemically, these lavas are characterized by a relative homogeneity with high Al 2O 3 and low MgO contents, and classified as high-K to shoshonitic basaltic andesites to andesites generated in an intra-arc extensional setting due to oblique subduction. Their isotopic geochemistry is characterized by highly homogeneous low initial Sr ratios (( 87Sr/ 86Sr) 0˜0.7036) and positive ɛNd values ( ɛNd=+2.9 to +4.7 ( 143Nd/ 144Nd) 0˜0.5127) that are very different from those proposed as representative of 'Andean-type' magmatism. A non-Andean modern setting dominated by subduction associated with intra-arc extension is proposed. On a ( 87Sr/ 86Sr) 0 versus ɛNd diagram, these lavas fit a model mixing curve for which the end members are Pacific MORB and Jurassic plutonic rocks from the Coastal Range. Coeval granitoids from the Coastal Range and lavas from the High Andes plot on the same field. Isotopically depleted mafic magmas could be metasomatized by the subducted sediments, which would increase their LILE content, and then partially contaminated by Jurassic plutonic rocks. The genesis of this magmatism may be related to a global low-spreading rate of 5 cm yr -1 in the southeast Pacific during 125-110 Ma.

  14. Fragmentation Speed and Permeability of hot Volcanic Rocks

    Science.gov (United States)

    Scheu, B.; Mueller, S.; Spieler, O.; Dingwell, D. B.

    2002-12-01

    The speed of fragmentation may control the explosive behaviour of silicic volcanoes. It is directly affected by the gas pressure within the volcano, which else influences the eruptive behaviour of the volcano. We used two techniques to analyse the speed of fragmentation. At both the fragmentation is triggered by the rapid decompression inside a high-pressure autoclave. Firstly at room temperature a set of two pressure transducers record the differential pressure loss above and below the cylindrical sample (d = 25mm, l = 60 mm). Secondly at temperatures of 850°C two platinum wires are inserted at known distance into the sample cylinder and used as electrical conductors to record the rupture time. The recorded time difference and the distance between the conductors are used to recalculate the speed of the fragmentation wave. This speed depends on porosity, texture and initial pressure difference. Further, the results show a decrease of fragmentation speed while propagating through the rock sample. We propose this effect to be linked to the density changes of the gas and therefore the reducing flow rates through the rock sample (gas permeability). Up to today permeability measurements have only been performed on cold porous rocks (e.g. Eichelberger et al. 1986, Klug & Cashman 1996), because measurements with higher temperatures are not possible with common gas permeameters. Investigating the permeability of volcanic rocks in a hot state (up to 850°C) provides a better insight into the degassing processes under natural conditions. Therefore, any new experimental set-up is expected to yield information about the temperature dependency of permeability in volcanic rocks. The present experiments have been performed on samples with a wide range of porosities, collected from block-and-ash flows on Merapi (Indonesia), Unzen (Japan) and from pumices on Lipari Island (Italy). Permeability was measured using a modified set-up of the fragmentation apparatus. Below the sample a

  15. LA-ICP-MS U-Pb apatite dating of Lower Cretaceous rocks from teschenite-picrite association in the Silesian Unit (southern Poland

    Directory of Open Access Journals (Sweden)

    Szopa Krzysztof

    2014-08-01

    Full Text Available The main products of volcanic activity in the teschenite-picrite association (TPA are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre and subalkaline (dolerite. Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7. The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128-120 Ma.

  16. Petrogenesis of Volcanic Rocks in the Khabr-Marvast Tectonized Ophiolite: Evidence for Subduction Processes in the South-Western Margin of Central Iranian Microcontinent

    Institute of Scientific and Technical Information of China (English)

    Azam SOLTANMOHAMMADI; Mohammad RAHGOSHAY; Morteza KHALATBARI-JAFARI

    2009-01-01

    The Late Cretaceous Khabr-Marvast tectonized ophiolite is located in the middle part of the Nain-Baft ophiolite belt, at the south-western edge of the central Iranian microcontinent. Although all the volcanic rocks in the study area indicate subduction-related magmatism (e.g. high LILE (large ion lithophile elements)/ HFSE (high field strenght elements) ratios and negative anomalies in Nb and Ta), geological and geochemical data clearly distinguish two distinct groups of volcanic rocks in the tectonized association: (1) group 1 is comprised of hyaloclustic breccias, basaltic pillow iavas, and andesite sheet flows. These rocks represent the Nain-Baft oceanic crust; and (2) group 2 is alkaline iavas from the top section of the ophiolite suite. These lavas show shoshonite affinity, but do not support the propensity of ophiolite.

  17. SHRIMP U-Pb dating and geochemistry of the Cretaceous plutonic rocks in the Korean Peninsula: A new tectonic model of the Cretaceous Korean Peninsula

    Science.gov (United States)

    Kim, Sung Won; Kwon, Sanghoon; Park, Seung-Ik; Lee, Changyeol; Cho, Deung-Lyong; Lee, Hong-Jin; Ko, Kyoungtae; Kim, Sook Ju

    2016-10-01

    The Cretaceous tectonomagmatism of the Korean Peninsula was examined based on geochemical and geochronological data of the Cretaceous plutonic rocks, along with distribution of volcano-sedimentary nonmarine N- to NE-trending fault bounded sedimentary basins. We conducted sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages and whole-rock geochemical compositions of 21 Cretaceous plutonic rocks, together with previously published data, from the central to southern Korean Peninsula. Four age groups of plutonic rocks were identified: Group I (ca. 119-106 Ma) in the northern to central area, Group II (ca. 99-87 Ma) in the central southern area, Group III (ca. 85-82 Ma) in the central to southern area, and Group IV (ca. 76-67 Ma) in the southernmost area. These results indicate a sporadic trenchward-younging trend of the Cretaceous magmatism in the Korean Peninsula. The Group I, II, and III rocks are dominated by high-K calc-alkaline I-type rocks with rift-related A-type granitoids. In contrast, the Group IV rocks are high-K calc-alkaline I-type plutonic rocks with no A-type rocks. The geochemical signatures of the entire groups indicated LREEs (light rare earth elements) enrichments and negative Nb, Ta, and Ti anomalies, indicating normal arc magmatism. A new tectonic model of the Cretaceous Korean Peninsula was proposed based on temporal and spatial distribution of the Cretaceous plutons represented by four age groups; 1) magmatic quiescence throughout the Korean Peninsula from ca. 160 to 120 Ma, 2) intrusions of the I- and A-type granitoids in the northern and central Korean Peninsula (Group I plutonic rocks from ca. 120 to 100 Ma) resulted from the partial melting of the lower continental crust due to the rollback of the Izanagi plate expressed as the conversion from flat-lying subduction to normal subduction. The Gyeongsang nonmarine sedimentary rift basin in the Korean Peninsula and adakite magmatism preserved in the present-day Japanese Islands

  18. Cooling-dominated cracking in thermally stressed volcanic rocks

    Science.gov (United States)

    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.

  19. Partial melting of subducted paleo-Pacific plate during the early Cretaceous: Constraint from adakitic rocks in the Shaxi porphyry Cu-Au deposit, Lower Yangtze River Belt

    Science.gov (United States)

    Deng, Jianghong; Yang, Xiaoyong; Li, Shuang; Gu, Huangling; Mastoi, Abdul Shakoor; Sun, Weidong

    2016-10-01

    A large porphyry Cu-Au deposit associated with early Cretaceous intrusive rocks has been discovered and explored in the Shaxi area, Lower Yangtze River Belt (LYRB), eastern China. We studied two types of intrusive rocks in the Shaxi area: Cu-Au mineralization related diorites and quartz-diorites (adakitic rocks), and newly found high Sr/Y ratio biotite-gabbros. They were formed almost simultaneously with crystallization ages of ca. 130 to 129 Ma, younger than the early stage shoshonitic rocks (Longmenyuan, Zhuanqiao and Shuangmiao Fm.) in the Luzong volcanic basin, ~ 10 km south of the Shaxi area. These intrusive rocks show similar distribution patterns of trace elements (enriched in LILEs and depleted in HFSEs) and REEs (enriched in LREEs and depleted in HREEs, no Eu negative anomaly, flat HREE patterns). The diorites and quartz-diorites are adakitic rocks with calc-alkaline affinity, distinguished from other adakitic rocks in the LYRB which are high-K calc-alkaline series. The biotite-gabbros are not adakitic rocks, although they are characterized by high Sr/Y ratios. Shaxi adakitic rocks show positive zircon εHf(t) values, which may be attributed to the contribution of subducted oceanic crust, while the εHf(t) values of the biotite-gabbros are mostly negative, indicating the involvement of old crustal materials. Although Sr-Nd-Pb isotopes of Shaxi adakitic rocks are more depleted than those of other adakitic rocks in the LYRB, they are still slightly enriched, similar to continental arc adakites in the Andean Austral Volcanic Zone. The Shaxi adakitic rocks are characterized by high Sr contents and Sr/Y ratios, medium (La/Yb)N, MgO contents and Mg#, and low K2O/Na2O ratios, decoupling of Sr/Y and (La/Yb)N, low Th/U values, exhibiting characteristics of slab-derived adakitic rocks. They were not produced by fractional crystallization of basaltic magmas like adakitic rocks in Edong-Jiurui and Tongling but originally generated from partial melting of subducted

  20. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    Energy Technology Data Exchange (ETDEWEB)

    Villamil, T.; Arango, C. (Univ. of Colorado, Boulder, CO (United States))

    1996-01-01

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

  1. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    Energy Technology Data Exchange (ETDEWEB)

    Villamil, T.; Arango, C. [Univ. of Colorado, Boulder, CO (United States)

    1996-12-31

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

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

    Science.gov (United States)

    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.

  3. Contrasting geochemistry of the Cretaceous volcanic suites in Shandong province and its implications for the Mesozoic lower crust delamination in the eastern North China craton

    Science.gov (United States)

    Ling, Wen-Li; Duan, Rui-Chun; Xie, Xian-Jun; Zhang, Yong-Qing; Zhang, Jun-Bo; Cheng, Jian-Ping; Liu, Xiao-Ming; Yang, Hong-Mei

    2009-12-01

    The Qingshan volcanic sequences occur in the Mengyin and Jiaozhou basins, west and east of the Tan-Lu fault zone, respectively, were formed at 128 ± 2 and 106 - 98 Ma. Lithologically the Mengyin succession comprises unimodal andesite (53 - 65 wt.% SiO 2), whereas the Jiaozhou succession consists of bimodal andesite (56-59 wt.% SiO 2) and rhyolite (69-77 wt.% SiO 2). High-Mg (Mg# >60) and low-Mg (Mg# andesitic suites are recognized in the Mengyin volcanic rocks. They show tholeiitic and calc-alkaline trends, respectively. Though the two suites share common trace element features of LILE enrichment and HFSE depletion, higher incompatible element contents in the high-Mg andesite relative to the low-Mg andesite rule out their genetic connection by magmatic differentiation. Similarly, the Jiaozhou andesites also possess higher incompatible element contents compared to their interbedded rhyolites, suggesting their distinct source rocks. The Qingshan mafic volcanic suites are characterized by radiogenic Sr and unradiogenic Nd isotopic compositions, of which the Mengyin high-Mg andesitic rocks display the lowest ɛ Nd(t) and highest initial Sr ratio. By contrast, the Jiaozhou rhyolites possess a positive correlation between Sr-Nd isotopes and relatively unradiogenic Sr isotopic ratios. The Qingshan mafic rocks exhibit geochemical characteristics distinct from those of mantle peridotite- or pyroxenite-derived melt as well as from Fangcheng basalts, the only basalts documented in the Cretaceous volcanic suites in Shandong province. They are inferred to be crust-derived melts. However, a clear decreasing trend in ACNK with Mg# increasing and the elevated MgO, Cr and Ni contents relative to basalt-derived melts indicate assimilation with mantle peridotite during their pristine magmatic evolution. Such a two-step process can be best explained by the Archean lower crust delamination of the North China craton with a ~35% partial melting followed by a variable extent of

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

    Science.gov (United States)

    Wobus, Reinhard A.; Mochel, David W.; Mertzman, Stanley A.; Eide, Elizabeth A.; Rothwarf, Miriam T.; Loeffler, Bruce M.; Johnson, David A.; Keating, Gordon N.; Sultze, Kimberly; Benjamin, Anne E.; Venzke, Edward A.; Filson, Tammy

    1990-07-01

    The Guffey volcanic center is the largest within the 2000 km2 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 represent 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 and tuff breccias chemically identical to the small rhyolitic plutons are locally preserved. Whole-rock major and trace element analyses of 80 samples, ranging almost continuously from 47% to 78%SiO2, indicate that the rocks of the Guffey center are among the most highly enriched in K2O (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.

  5. Magmatic Source Composition and Magmatism of the Volcanic Rocks in the Area of Kuruktag, Southern Xinjiang

    Institute of Scientific and Technical Information of China (English)

    JIANG Changyi; BAI Kaiyin; HI Aizhi; ZHAO Xiaoning; ZHANG Hongbo

    2001-01-01

    In the Sinian-Cambrian strata in the area of Kuruktag, southern Xingjiang, four layers of volcanic rocks occurred in the Early Sinian Beiyixi Formation, Late Sinian Zhamoketi Formation and Shuiquan Formation, and Early Cambrian Xishanbulake Formation, respectively. Volcanics of the Shuiquan Formation and Xishanbulake Formation are of alkali basalt series, those of the Zhamoketi Formation are of alkali basalt series and tholeiite series, and those of the Beiyixi Formation are obviously characterized by bimodal assemblage and mostly belong to alkali volcanics. Multi-element distribution patterns of the rocks show continental tumescence characters of interplate basalt.Fractional crystallization of plagioclase led to negative Eu-anomalies of some volcanics and the cumulation of olivine resulted in high MgO and low SiO2 content of some volcanic rocks. The SiO2 saturability of volcanic rocks of the Xishanbulake Formation and Shuiquan Formation is lower than that of tholeiite of the Zhamoketi Formation. Correspondingly, the abundance of incompatible elements in the first two formations is higher than those in the last formation, and the differences can be attributed to the different degrees of partial melting. The intense fractionation of REE and the obvious depletion of HREE suggest that these volcanic rocks were derived from garnet Iherzolite of the mantle in the continental lithosphere. The Ba/Nb, La/Nb, Ba/La, Ba/Th and Rb/Nb rations demonstrate that these volcanic rocks were exclusively derived from the enriched mantle, mainly the EMI type mantle.

  6. Deccan Volcanism, Chicxulub Impact, Climate Change and the end-Cretaceous Mass Extinction

    Science.gov (United States)

    Keller, Gerta; Punekar, Jahnavi; Mateo, Paula; Adatte, Thierry; Spangenberg, Jorge

    2015-04-01

    Age control for Deccan volcanism, associated global climate changes, high-stress conditions and the KTB mass extinction is excellent based on biostratigraphy and corroborated by new U-Pb dating providing new evidence for a complex mass extinction scenario. The massive Deccan eruptions of phase-2 began in the latest Maastrichtian C29r and ended at or near the Cretaceous-Tertiary boundary (KTB) depositing ~3000 m of stacked lava flows or 80% of the total Deccan eruptions over a period of just 250 ky. The onset of phase-2 eruptions coincided with rapid global warming on land (8°C) and oceans (4°C) and increasingly high-stress environments evident by dwarfed species and decreased diversity preceding the mass extinction in planktic foraminiferal zones CF2-CF1. Deep cores in the Krishna-Godavari Basin, SE India, document the rapid mass extinction of planktic foraminifera in intertrappean sediments between four major volcanic eruptions known as the longest lava flows on Earth. Maximum stress is observed globally approaching the end of the Maastrichtian with faunal assemblages dominated (~90%) by the disaster opportunist Guembelitria cretacea. This interval correlates with the massive eruptions of the world's longest lava flows, renewed rapid global warming and ocean acidification during the last ~50 ky of the Maastrichtian. The Chicxulub impact occurred during the global warming near the base of zone CF1 preceding the mass extinction by Chicxulub impact. Any KTB mass extinction scenario must take into account both Deccan volcanism and the Chicxulub impact. The age of this impact is controversial though generally assumed to be precisely at the KTB and the sole cause of the mass extinction. This assumption is no longer valid given the short duration of massive Deccan eruptions, and the dramatic climatic and environmental effects over just 250 ky ending with the mass extinction. The pre-KTB age of the Chicxulub impact rules out a direct role in the mass extinction

  7. A Petrographic and Mineralogical Study of Volcanic Rocks from the Mayaxueshan Area, North Qilian Fold Belt, NW China

    Institute of Scientific and Technical Information of China (English)

    徐达伟; 萧炎宏

    2002-01-01

    The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosedand contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz,and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assem-blages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. Thisindicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result ofCaledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks shouldbe re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age:prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpellyite to lowergreenschist facies for the lower part of the Middle Ordovician volcanic rocks, and lower greenschist facies for the LowerOrdovician volcanic rocks. The P-T conditions are estimated as T = 240 - 290C and P = 1.5 - 4.5 kbar for the lower partof the Middle Ordovician rocks, and T = ~ 300~C for the Lower Ordovician rocks. The variations of mineral assemblagesoccurring at different domains of the volcanic rocks were controlled by the variations of the effective bulk composition inthose domains during metamorphism. The geochemical characteristics of Mg-Al chromite in the Mayaxueshan volcanicrocks are consistent with an origin of island arc environment.

  8. Rare Earths, Trace Element Characteristics of High-Mg Volcanic Rocks of Yixian Formation in Sihetun West Liaoning Province and Its Apocalypse

    Institute of Scientific and Technical Information of China (English)

    Zhang Hong; Zhang Qi

    2005-01-01

    The high-Mg volcanic rocks of the Yixian Formation in the Sihetun area have the obvious characteristics of mantle-derived lava in rare earth, trace element characteristics with high Mg# (62~70) and high content of compatible elements. In the meantime, the volcanic rocks also have the obvious characteristics of Crust-source material in rare earth, trace element characteristics with high ∑REE (158.78×10-6~359.66×10-6), high (La/Yb)N (14.61~29.60), high La/Nb(2.37~7.52) and high Ba/Nb(67.58~205.96), obvious positive anomaly of Pb and negative anomaly of Nb, Ta in trace element spider-gram. In Sr-Nd-Pb isotope the (87Sr/86Sr)i ratio is higher than 0.706 and the εNd(t) ratio is from -3.4 to -13, both reflect enriched Mantle characteristics. The characteristics above of the volcanic rocks combined with the content of Sr, Ba, Y, Yb and the ratio of Sr/Y show that the volcanic rocks have the property of the Sanukite rocks in Setouchi Japan beside subduction zone, and illuminate that the Sanukite rocks can be formed not only in island-arc near subduction zone but also in intro-plate. The analysis indicates that the high-Mg volcanic rocks in the Sihetun area result from the collective function of mantle-derived lava and crust-source materials. The result illuminates that the West Liaoning region is very special in tectonic geochemical background in Cretaceous in East China, and is an ideal region for us to further study the characteristics of magmatic activity as well as the process of Crust-Mantle interaction in Eastern China.

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

    Science.gov (United States)

    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 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, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock, which itself formed in the mid-crust by emplacement of magma that

  10. Fracture Detection in Geothermal Wells Drilled in Volcanic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Gonfalini, Mauro; Chelini, Walter; Cheruvier, Etienne; Suau, Jean; Klopf, Werner

    1987-01-20

    The Phlegrean Fields, close to Naples, are the site of important geothermal activity. The formations are volcanic and mostly tuffites. They are originally very tight but the geothermal alteration locally produces fractures with large increase in permeability. The lack of geological markers makes well-to-well correlation quite difficult. Thus the local detection of fractured zones in each well is very important for the evaluation of its potential. The Mofete 8 D well is a typical example. A rather complete logging program was run for fracture detection. Standard methods turned out to be disappointing. However several non-standard detectors were found to be very consistent and, later on, in excellent agreement with the analysis of cuttings. They are derived from the Dual Laterolog, the SP, the Temperature log and, most particularly, the Acoustic Waveforms from the Long Spacing Sonic. The Dual Laterolog and the Temperature Log indicate invasion by fresh and cold mud filtrate; the SP behaves as in a typical Sand-Shale sequence. Sonic Waveforms were first analyzed by a purely empirical method derived from consistent log patterns. A practical algorithm compares the total energy measured in each of the two fixed time windows located the one before, the other after the fluid arrivals. The altered zones (i.e. fractured and permeable) are clearly shown by a complete reversal of the relative energy of these two windows. A more scientific method was then applied to the Waveforms; it is based on both logging experiments and physical considerations. The energy carried by the tube wave is separated by a frequency discrimination: it correlates very well with formation alteration, thus also with the other indicators including the empirical Waveform method. It should have two advantages: – It should permit at least a semi quantitative permeability evaluation – It seems to be promising in other formations: non-volcanic geothermal wells and even hydrocarbon-bearing rocks. 10 refs

  11. Discovery of Enclaves from Cenozoic Pulu Volcanic Rocks in West Kunlun Mountains and Its Geological Implications

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In this paper, we present the occurrence and mineral components of the enclaves firstly discovered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains, and propose that the enclave is accumulated by fractional crystallization within high-level magma chamber. In addition, the chemical compositions of its primary magma are calculated. The calculated compositions are similar to those of the Kangxiwa volcanic rocks that belong to the same volcanic belt in the Pulu volcanic region, suggesting their origin from the same source region. However, the temperatures and oxygen fugacity of magmas at high-level magma chamber decreased along with fractional crystallization.

  12. Chronology and Geochemistry of Mesozoic Volcanic Rocks in the Linjiang Area, Jilin Province and their Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    YU Yang; XU Wenliang; PEI Fuping; YANG Debin; ZHAO Quanguo

    2009-01-01

    Zircon U-Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean 206Pb/238U age for 13 zircon grains is 2224±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean 206Pb/238U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean 206Pb/238U age of113±4 Ma. The volcanic rocks have SiO2=60.24%-77.46%, MgO=0.36%-1.29% (Mg#=0.32-0.40) for the Naozhigou Formation, SiO2=51.60%-59.32 %, MgO=3.70 %-5.54% (Mg#=0.50-0.60) for the Ergulazi Formation, and SiO2=58.28%-76.32%, MgO=0.07%-1.20% (Mg#=0.14-0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial 87Sr/86Sr ratios (0.7053-0.7083) and low eNd(t) values (-8.38 to -2.43), and display an EMII trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward snbduction of

  13. Paleomagnetic study of Jurassic and Cretaceous rocks from the Mixteca terrane (Mexico)

    Science.gov (United States)

    Böhnel, Harald

    1999-11-01

    Three sites from Cretaceous limestone and Jurassic sandstone in northern Oaxaca, Mexico, were studied paleomagnetically. Thermal demagnetization isolated site-mean remanence directions which differ significantly from the recent geomagnetic field. The paleopole for the Albian-Cenomanian Morelos formation is indistinguishable from the corresponding reference pole for stable North America, indicating tectonic stability of the Mixteca terrane since the Cretaceous. Rock magnetic properties and a positive reversal test for the Bajocian Tecomazuchil sandstone suggest that the remanence could be of primary origin, although no fold test could be applied. The Tecomazuchil paleopole is rotated 10°±5° clockwise and displaced 24°±5° towards the study area, with respect to the reference pole for stable North America. Similar values were found for the Toarcien-Aalenian Rosario Formation, with 35°±6° clockwise rotation and 33°±6° latitudinal translation. These data support a post-Bajocian southward translation of the Mixteca terrane by around 25°, which was completed in mid-Cretaceous time.

  14. Cretaceous plutonic rocks in the Donner Lake-Cisco Grove area, northern Sierra Nevada, California

    Science.gov (United States)

    Kulow, Matthew J.; Hanson, Richard E.; Girty, Gary H.; Girty, Melissa S.; Harwood, David S.

    1998-01-01

    The northernmost occurrences of extensive, glaciated exposures of the Sierra Nevada batholith occur in the Donner Lake-Cisco Grove area of the northern Sierra Nevada. The plutonic rocks in this area, which are termed here the Castle Valley plutonic assemblage, crop out over an area of 225 km2 and for the most part are shown as a single undifferentiated mass on previously published geological maps. In the present work, the plutonic assemblage is divided into eight separate intrusive units or lithodemes, two of which each consist of two separate plutons. Compositions are dominantly granodiorite and tonalite, but diorite and granite form small plutons in places. Spectacular examples of comb layering and orbicular texture occur in the diorites. U-Pb zircon ages have been obtained for all but one of the main units and range from ~120 to 114 Ma, indicating that the entire assemblage was emplaced in a narrow time frame in the Early Cretaceous. This is consistent with abundant field evidence that many of the individual phases were intruded penecontemporaneously. The timing of emplacement correlates with onset of major Cretaceous plutonism in the main part of the Sierra Nevada batholith farther south. The emplacement ages also are similar to isotopic ages for gold-quartz mineralization in the Sierran foothills west of the study area, suggesting a direct genetic relationship between the voluminous Early Cretaceous plutonism and hydrothermal gold mineralization.

  15. Provenance and drainage system of the Early Cretaceous volcanic detritus in the Himalaya as constrained by detrital zircon geochronology

    Institute of Scientific and Technical Information of China (English)

    Xiu-Mian Hu; Eduardo Garzanti; Wei An

    2015-01-01

    The age range of the major intra-plate volcanic event that affected the northern Indian margin in the Early Cretaceous is here deifned precisely by detrital zircon geochronol-ogy. U–Pb ages of Early Cretaceous detrital zircons found in the Cretaceous to the Paleocene sandstones cluster mainly between 142 Ma and 123 Ma in the northern Tethys Himalayan unit, and between 140 Ma and 116 Ma in the southern Tethys Himalayan unit. The youngest and oldest detrital zircons within this group indicate that volcanism in the source areas started in the latest Jurassic and ended by the early Albian. Stratigraphic data indicate that volcaniclastic sedimentation began signiifcantly earlier in southern Tibet (Tithonian) than in Nepal (Valangin-ian), and considerably later in Spiti and Zanskar (Aptian/Albian) to the west. This apparent westward migration of magmatism was explained with progressive westward propagation of extensional/transtensional tectonic activity and development of fractures cutting deeply across the Indian continental margin crust. However, detrital zircon geochronology provides no indi-cation of heterochroneity in magmatic activity in the source areas from east to west, and thus lends little support to such a scenario. Westward migration of volcaniclastic sedimentation may thus relfect instead the westward progradation of major drainage systems supplying vol-canic detritus sourced from the same volcanic centers in the east. Development of multiple radial drainage away from the domal surface uplift associated with magmatic upwelling, as observed for most large igneous provinces around the world, may also explain why U–Pb ages of detrital zircons tend to cluster around 133–132 Ma (the age of the Comei igneous province) in Tethys Himalayan units, but around 118–117 Ma (the age of the Rajmahal igneous province) in Lesser Himalayan units.

  16. The Late Cretaceous igneous rocks of Romania (Apuseni Mountains and Banat): the possible role of amphibole versus plagioclase deep fractionation in two different crustal terranes

    Science.gov (United States)

    Vander Auwera, Jacqueline; Berza, Tudor; Gesels, Julie; Dupont, Alain

    2016-04-01

    We provide new whole-rock major and trace elements as well as 87Sr/86Sr and 143Nd/144Nd isotopic data of a suite of samples collected in the Late Cretaceous volcanic and plutonic bodies of the Apuseni Mts. (Romania) that belong to the Banatitic Magmatic and Metallogenic Belt, also called the Apuseni-Banat-Timok-Srednogorie belt. The samples define a medium- to high-K calc-alkaline differentiation trend that can be predicted by a three-step fractional crystallization process which probably took place in upper crustal magma chambers. Published experimental data indicate that the parent magma (Mg# = 0.47) of the Apuseni Mts. trend could have been produced by the lower crustal differentiation of a primary (in equilibrium with a mantle source) magma. The Late Cretaceous magmatic rocks of the Apuseni Mts. and Banat display overlapping major and trace element trends except that Sr is slightly lower and Ga is higher in the Apuseni Mts. parent magma. This difference can be accounted for by fractionating plagioclase-bearing (Apuseni Mts.) or amphibole-bearing (Banat) cumulates during the lower crustal differentiation of the primary magma to the composition of the parent magma of both trends. This, together with results obtained on the Late Cretaceous igneous rocks from the Timok area in Eastern Serbia, further suggests variation of the water content of the primary magma along and across the belt. The Apuseni Mts. versus the Banat samples display different isotopic compositions that likely resulted from the assimilation of two distinct crustal contaminants, in agreement with their emplacement in two separate mega-units of Alpine Europe.

  17. Palaeointensity and palaeomagnetic study of Cretaceous and Palaeocene rocks from Western Antarctica

    Science.gov (United States)

    Shcherbakova, V. V.; Bakhmutov, V. G.; Shcherbakov, V. P.; Zhidkov, G. V.; Shpyra, V. V.

    2012-04-01

    A combined palaeodirectional and palaeointensity study of a representative collection of plutonic rocks from the Antarctic Peninsula batholith from the western part of the Antarctic Peninsula, near the Ukrainian Antarctic base 'Academik Vernadsky' were carried out. Petrographically, the collection includes gabbros, diorites and quartz diorites, tonalities, granodiorites and granites. The ages of igneous complex emplacement vary from 50 to 117 Ma with most of the rocks belonging to the Cretaceous Normal Superchron. The characteristic remanent magnetizations were isolated by stepwise thermal demagnetization over the temperature interval 440-590°C and their intensities amount to 95 per cent of the NRM. The geographic positions of palaeopoles do not contradict the 'key poles' of the Antarctic Peninsula between 90 and 60 Ma. A significant part of the collection was subjected to Coe-modified Thellier palaeointensity experiments with the pTRM checks, which yielded seven reliable palaeointensity determinations for seven different locations. The obtained VDMs are relatively low for all sites, being on average about half of the present day VDM. The analysis of available palaeointensity data for the Cretaceous, Miocene and Middle Jurassic indicates the existence of strong correlations between the mean VDM and VDM scatter versus the rate of reversals. However, due to the shortage of data, the correlations are not significant at the 5 per cent significance level.

  18. Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area,NE China and tectonic implications

    Institute of Scientific and Technical Information of China (English)

    LI ChaoWen; GUO Feng; FAN WeiMing; GAO XiaoFeng

    2007-01-01

    Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined "Triassic-Jurassic" volcanic rocks(including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.)were erupted during 118-106Ma,corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage(130-120 Ma)of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. Were extruded at ca.55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as:Tuopangou Fm., Sanxianling/Tuntianying Fm.(118-115 Ma),Malugou/Tianqiaoling Fm.(K1),Huoshanyan/Jingouling Fm.(108-106 Ma),Changcai Fm.(K2),Quanshuicun Fm.(~55 Ma)and Dalazi Fm. Our results suggest that subduction of the Palaeo-Pacific Ocean beneath the East Asian continental margin occurred during 106to 55 Ma. Consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95-65 Ma.

  19. Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area, NE China and tectonic implications

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.

  20. Petrogenesis of Cretaceous adakitic and shoshonitic igneous rocks in the Luzong area, Anhui Province (eastern China): Implications for geodynamics and Cu Au mineralization

    Science.gov (United States)

    Wang, Qiang; Wyman, Derek A.; Xu, Ji-Feng; Zhao, Zhen-Hua; Jian, Ping; Xiong, Xiao-Lin; Bao, Zhi-Wei; Li, Chao-Feng; Bai, Zheng-Hua

    2006-07-01

    Both adakitic and shoshonitic igneous rocks in the Luzong area, Anhui Province, eastern China are associated with Cretaceous Cu-Au mineralization. The Shaxi quartz diorite porphyrites exhibit adakite-like geochemical features, such as light rare earth element (LREE) enrichment, heavy REE (HREE) depletion, high Al 2O 3, MgO, Sr, Sr / Y and La / Yb values, and low Y and Yb contents. They have low ɛNd( t) values (- 3.46 to - 6.28) and high ( 87Sr / 86Sr) i ratios (0.7051-0.7057). Sensitive High-Resolution Ion Microprobe (SHRIMP) zircon analyses indicate a crystallization age of 136 ± 3 Ma for the adakitic rocks. Most volcanic rocks and the majority of monzonites and syenites in the Luzong area are K-rich (or shoshonitic) and were also produced during the Cretaceous (140-125 Ma). They are enriched in LREE and large-ion lithophile elements, and depleted in Ti, and Nb and Ba and exhibit relatively lower ɛNd( t) values ranging from - 4.65 to - 7.03 and relatively higher ( 87Sr / 86Sr) i ratios varying between 0.7057 and 0.7062. The shoshonitic and adakitic rocks in the Luzong area have similar Pb isotopic compositions ( 206Pb / 204Pb = 17.90-18.83, 207Pb / 204Pb = 15.45-15.62 and 208Pb / 204Pb = 38.07-38.80). Geological data from the Luzong area suggest that the Cretaceous igneous rocks are distributed along NE fault zones (e.g., Tanlu and Yangtze River fault zones) in eastern China and were likely formed in an extensional setting within the Yangtze Block. The Shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of > 50 km (i.e., ˜1.5 GPa), possibly leaving rutile-bearing eclogitic residue. The shoshonitic magmas, in contrast, originated mainly from an enriched mantle metasomatized by subducted oceanic sediments. They underwent early high-pressure (> 1.5 GPa) fractional crystallization at the boundary between thickened (> 50 km) lower crust and lithospheric mantle and late low

  1. Characteristics and geological significance of olivine xenocrysts in Cenozoic volcanic rocks from western Qinling

    Institute of Scientific and Technical Information of China (English)

    SU Benxun; ZHANG Hongfu; XIAO Yan; ZHAO Xinmiao

    2006-01-01

    Cenozoic volcanic rocks from the Haoti, Dangchang County of the western Qinling Mountains, contain a few clearlyzoned olivines. These olivines are relatively big in grain sizes and usually have cracks or broken features. Their cores have similar compositions (Mg# = 90.4- 91.0) to those for the peridotitic xenoliths entrained in host volcanic rocks and their rims are close to the compositions of olivine phenocrysts (Mg# = 85.5 81.9). The CaO contents in these zoned olivines are lower than 0.1%. These features demonstrate that the clearly zoned olivines are xenocrysts and disaggregated from mantle peridotites. The zoned texture was the result of the interaction between the olivine and host magma. Available data show that the volcanic rocks would have been derived from the mantle source metasomatized by subducted hydrathermally-altered oceanic crust. The formation of these Cenozoic volcanic rocks was perhaps related to the rapid uplift of the Tibetan Plateau.

  2. Influence of mesostasis in volcanic rocks on the alkali-aggregate reaction

    KAUST Repository

    Tiecher, Francieli

    2012-11-01

    Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites. © 2012 Elsevier Ltd. All rights reserved.

  3. Source rock contributions to the Lower Cretaceous heavy oil accumulations in Alberta: a basin modeling study

    Science.gov (United States)

    Berbesi, Luiyin Alejandro; di Primio, Rolando; Anka, Zahie; Horsfield, Brian; Higley, Debra K.

    2012-01-01

    The origin of the immense oil sand deposits in Lower Cretaceous reservoirs of the Western Canada sedimentary basin is still a matter of debate, specifically with respect to the original in-place volumes and contributing source rocks. In this study, the contributions from the main source rocks were addressed using a three-dimensional petroleum system model calibrated to well data. A sensitivity analysis of source rock definition was performed in the case of the two main contributors, which are the Lower Jurassic Gordondale Member of the Fernie Group and the Upper Devonian–Lower Mississippian Exshaw Formation. This sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals, and in the case of the Exshaw Formation, variations of thickness in areas beneath the Rocky Mountains were also considered. All of the modeled source rocks reached the early or main oil generation stages by 60 Ma, before the onset of the Laramide orogeny. Reconstructed oil accumulations were initially modest because of limited trapping efficiency. This was improved by defining lateral stratigraphic seals within the carrier system. An additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas, but not to the east of Athabasca. In the latter case, the main trapping controls are dominantly stratigraphic and structural. Our model, based on available data, identifies the Gordondale source rock as the contributor of more than 54% of the oil in the Athabasca and Peace River accumulations, followed by minor amounts from Exshaw (15%) and other Devonian to Lower Jurassic source rocks. The proposed strong contribution of petroleum from the Exshaw Formation source rock to the Athabasca oil sands is only reproduced by assuming 25 m (82 ft) of mature Exshaw in the kitchen areas, with original total organic carbon of 9% or more.

  4. End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change.

    Science.gov (United States)

    Petersen, Sierra V; Dutton, Andrea; Lohmann, Kyger C

    2016-07-05

    The cause of the end-Cretaceous (KPg) mass extinction is still debated due to difficulty separating the influences of two closely timed potential causal events: eruption of the Deccan Traps volcanic province and impact of the Chicxulub meteorite. Here we combine published extinction patterns with a new clumped isotope temperature record from a hiatus-free, expanded KPg boundary section from Seymour Island, Antarctica. We document a 7.8±3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.

  5. End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change

    Science.gov (United States)

    Petersen, Sierra V.; Dutton, Andrea; Lohmann, Kyger C.

    2016-07-01

    The cause of the end-Cretaceous (KPg) mass extinction is still debated due to difficulty separating the influences of two closely timed potential causal events: eruption of the Deccan Traps volcanic province and impact of the Chicxulub meteorite. Here we combine published extinction patterns with a new clumped isotope temperature record from a hiatus-free, expanded KPg boundary section from Seymour Island, Antarctica. We document a 7.8+/-3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.

  6. Basic and ultrabasic volcanic rocks from the Argyll Group (Dalradian) of NE Scotland

    OpenAIRE

    2005-01-01

    The Dalradian Supergroup of the Scottish Highlands is a largely metasedimentary succession of Neoproterozoic to Early Cambrian age, metamorphosed during the Caledonian Orogeny. The rocks were deposited on the Laurentian margin during and following the break-up of Rodinia. This rift setting is evidenced, in the upper half of the succession, by the presence of several volcanic sequences. A significant development of these volcanic rocks occurs in the NE Grampian Highlands. There, the Blackwater...

  7. K—Ar Geochronology and Evolution of Cenozoic Volcanic Rocks in Eastrn China

    Institute of Scientific and Technical Information of China (English)

    王慧芬; 杨学昌; 等

    1989-01-01

    Cenozoic volcanic rocks widespread in eastern China constitute an important part of the circum-Pacific volcanic belt.This paper presents more than 150K-Ar dates and a great deal of petrochemical analysis data from the Cenozoic volcanic rocks distributed in Tengchong,China's southeast coast,Shandong,Hebei,Nei Monggol and Northeast China.An integrated study shows that ubiquitous but uneven volcanic activities prevailed from the Eogene to the Holocene,characterized as being multi-eqisodic and multicycled.For example,in the Paleocene(67-58Ma),Eocene(57-37.5Ma),Miocene(22-18,16-19Ma),Pliocene(8-3Ma),and Early Pleistocene-Middle Pleistocene(1.2-0.5Ma) there were upsurges of volcanism,while in the Oligocene there was a repose period.In space,the older Eogene volcanic rocks are distributed within the region or in the central part of the NE-NNE-striking fault depression,while the younger Neogene and Quaternary volcanic rocks are distributed in the eastern and western parts.Petrologically,they belong essentially to tholeiite-series and alkali-series basalts,with alkalinity in the rocks increasing from old to youg.The above regularities are controlled by both global plate movement and regional inherent tectonic pattern.

  8. Petrology of the alkaline rocks of the Macau Volcanic Field, NE Brazil

    Science.gov (United States)

    Ngonge, Emmanuel Donald; de Hollanda, Maria Helena Bezerra Maia; Pimentel, Márcio Martins; de Oliveira, Diógenes Custódio

    2016-12-01

    The Macau Volcanic Field (MVF) in the Borborema Province, NE Brazil, contains multiple centres of volcanic activity of Early to Late Cenozoic ages. We present element and Sr-Nd-Pb isotope geochemical data for four of the few most prominent basalt types of this volcanic field: Serrote Preto-type, Serra Aguda-type, Pico do Cabugi-type and Serra Preta-type, in order to assess their magmatic history from source to crystallization and the evolution of the mantle beneath the Borborema Province. The basalts are basically sodic nephelinitic-basanitic-alkali olivine basalts enriched in LILE and in Nb-Ta. The Serra Preta, Cabugi and Serra Aguda types demonstrate compositions close to primitive characteristics with 10% < MgO < 15 wt.% and 200 ppm < Ni < 500 ppm, and experienced limited fractional crystallization of olivine-clinopyroxene-plagioclase-oxides with negligible wall-rock assimilation. Rb/Sr and Ba/Rb constraints support the generation of SiO2-undersaturated magmas from mantle melting of amphibole-bearing peridotites with minor phlogopite. The source for the basanites and alkali basalts is estimated to be a garnet-bearing domain around the lithosphere-asthenosphere boundary (80-93 km deep), while the nephelinites are derived from the adiabatic asthenosphere at 105 km with temperatures of 1480 °C. Their incompatible trace element patterns and Sr-Nd-Pb isotopic compositions are similar to FOZO and EM-type OIB magmas. From the comparison of data with those of the Ceará-Mirim dyke swarm we propose that there is a ubiquitous FOZO reservoir in the SCLM beneath the Borborema Province. This FOZO signature characterized the upwelling asthenosphere during the lithospheric extension and thinning at the opening of the Equatorial Atlantic and is clearly represented in the Mesozoic olivine tholeiites of Ceará-Mirim. The upwelled asthenosphere cooled as a rigid SCLM since the Cretaceous and has preserved its FOZO signature evident in the Macau Cenozoic basalts. The EM signatures

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

    Science.gov (United States)

    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.

  10. Reverse Polarity Magnetized Melt Rocks from the Cretaceous/Tertiary Chicxulub Structure, Yucatan Peninsula, Mexico

    Science.gov (United States)

    Urrutia-Fucugauchi, J.; Marin, Luis; Sharpton, Virgil L.

    1994-01-01

    We report paleomagnetic results for core samples of the breccia and andesitic rocks recovered from the Yucatan-6 Petrolcos Mexicanos exploratory well within the Chicxulub structure (about 60 km SSW from its center), northern Yucatan, Mexico. A previous study has shown that the rocks studied contain high iridium levels and shocked breccia clasts and an Ar/Ar date of 65.2 +/- 0.4 Ma. Andesitic rocks are characterized by stable single-component magnetizations with a mean inclination of -42.6 deg +/- 2.4 deg. Breccias present a complex paleomagnetic record characterized by multivectorial magnetizations with widely different initial NRM inclinations. However, after alternating field demagnetization, well defined characteristic components with upward inclinations are defined. IRM acquisition experiments, comparison of IRM and NRM coercivity spectra and the single component magnetization of the andesitic rocks indicate the occurrence of iron-rich titanomagnetites of single or pseudo-single domain states as the dominant magnetic carriers. Mean inclinations from the andesitic rocks and most of the breccia samples give a mean inclination of about -40 deg to -45 deg, indicating a reverse polarity for the characteristic magnetization that is consistent with geomagnetic chron 29R, which spans the Cretaceous/Tertiary (K/T) boundary. The inclination is also consistent with the expected value (and corresponding paleolatitude) for the site estimated from the reference polar wander curve for North America. We suggest that the characteristic magnetizations for the andesitic and breccia rocks are the result of shock heating at the time of formation of the impact structure and that the age, polarity and pateolatitude are consistent with a time at the K/T boundary.

  11. Uranium mineralization in fluorine-enriched volcanic rocks

    Energy Technology Data Exchange (ETDEWEB)

    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).

  12. Induced polarization of volcanic rocks. 1Surface versus quadrature conductivity

    Science.gov (United States)

    Revil, A.; Breton, M. Le; Niu, Q.; Wallin, E.; Haskins, E.; Thomas, D. M.

    2016-11-01

    We performed complex conductivity measurements on 28 core samples from the hole drilled for the Humu´ula Groundwater Research Project (Hawai´i Island, HI, USA). The complex conductivity measurements were performed at 4 different pore water conductivities (0.07, 0.5, 1.0 or 2.0, and 10 S m-1 prepared with NaCl) over the frequency range 1 mHz to 45 kHz at 22 ± 1°C. The in-phase conductivity data are plotted against the pore water conductivity to determine, sample by sample, the intrinsic formation factor and the surface conductivity. The intrinsic formation factor is related to porosity by Archie's law with an average value of the cementation exponent m of 2.45, indicating that only a small fraction of the connected pore space controls the transport properties. Both the surface and quadrature conductivities are found to be linearly related to the cation exchange capacity of the material, which was measured with the cobalt hexamine chloride method. Surface and quadrature conductivities are found to be proportional to each other like for sedimentary siliclastic rocks. A Stern layer polarization model is used to explain these experimental results. Despite the fact that the samples contain some magnetite (up to 5% wt.), we were not able to identify the effect of this mineral on the complex conductivity spectra. These results are very encouraging in showing that galvanometric induced polarization measurements can be used in volcanic areas to separate the bulk from the surface conductivity and therefore to define some alteration attributes. Such a goal cannot be achieved with resistivity alone.

  13. Induced polarization of volcanic rocks - 1. Surface versus quadrature conductivity

    Science.gov (United States)

    Revil, A.; Le Breton, M.; Niu, Q.; Wallin, E.; Haskins, E.; Thomas, D. M.

    2017-02-01

    We performed complex conductivity measurements on 28 core samples from the hole drilled for the Humu'ula Groundwater Research Project (Hawai'i Island, HI, USA). The complex conductivity measurements were performed at 4 different pore water conductivities (0.07, 0.5, 1.0 or 2.0, and 10 S m-1 prepared with NaCl) over the frequency range 1 mHz to 45 kHz at 22 ± 1 °C. The in-phase conductivity data are plotted against the pore water conductivity to determine, sample by sample, the intrinsic formation factor and the surface conductivity. The intrinsic formation factor is related to porosity by Archie's law with an average value of the cementation exponent m of 2.45, indicating that only a small fraction of the connected pore space controls the transport properties. Both the surface and quadrature conductivities are found to be linearly related to the cation exchange capacity of the material, which was measured with the cobalt hexamine chloride method. Surface and quadrature conductivities are found to be proportional to each other like for sedimentary siliclastic rocks. A Stern layer polarization model is used to explain these experimental results. Despite the fact that the samples contain some magnetite (up to 5 per cent wt.), we were not able to identify the effect of this mineral on the complex conductivity spectra. These results are very encouraging in showing that galvanometric induced polarization measurements can be used in volcanic areas to separate the bulk from the surface conductivity and therefore to define some alteration attributes. Such a goal cannot be achieved with resistivity alone.

  14. REE Geochemical Characteristics of Volcanic Rocks in Zhejiang and Jiangxi Provinces and Their Gological Significance

    Institute of Scientific and Technical Information of China (English)

    王剑锋

    1991-01-01

    Based on the data of 64 samples ,the REE geochemical characteristics of volcanic rocks in northern Zhejiang and eastern Jiangxi provinces are discussed in this paper.The REE distribution patterns in acid and intermediate-acid volcanic rocks in these areas display some similarities,as indicated by rightward-inclined V-shaped curves with negative Eu anomalies,which are parallel to earch other.In addi-tion,their REE parameters(ΣREE,ΣLREE/ΣHREE,δEu,Ce/Yb,La/Sm,La/Yb,etc)also va-ry over a narrow range with small deviations.HREE are particularly concentrated in the volcanic rocks as-sociated with uranium mineralization.The initial 87Sr/86Sr ratio in the volcanic rocks is about 0.7056-0.7139.All these features in conjunction with strontium isotopic data indicate that the rock-forming materials come from the sialic crust.The REE distribution patterns and REE geochemical parameters of the volcanic rocks ,as well as La/Sm-La and Ce/Yb-Eu/Yb diagrams may be applied to the sources of rock-forming and ore-forming materials.

  15. Geochemistry of the Ophiolite and Island-Arc Volcanic Rocks in the Mianxian-Lueyang Suture Zone,Southern Qinling and Their Tectonic Significance

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly.The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly.Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V,Th/Ta,Th/Yb and Ta/Yb.One is ths MORB-type basalt with LREE depletion,representing the fragments of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic-Early Mesozoic era.The oter comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount of calc-alkaline intermediate-acic volcanic rock,which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin.This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole process of development,evolution and vanishing from Devonian-Cretaceous to Permian.And the Qinling area had becone an independent lithospheric microplate,on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic-Early Mesozoic.That is to say.the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.

  16. 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

    Science.gov (United States)

    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.

  17. Petrographic analysis and correlation of volcanic rocks in Bostic 1-A well near Mountain Home, Idaho

    Energy Technology Data Exchange (ETDEWEB)

    Arney, B.H.; Gardner, J.N.; Belluomini, S.G.

    1984-01-01

    Detailed examination of volcanic rock cuttings from the Bostic 1-A well near Mountain Home, Idaho, provides data that correlate the stratigraphy of the well with the regional stratigraphy of the western Snake River Plain. The Bostic 1-A well penetrates basalt of the Middle Pleistocene Bruneau Formation and underlying sedimentary rocks of the Upper Pliocene Glenns Ferry Formation. Basalt underlying the Glenns Ferry Formation is most likely Banbury Basalt of Middle Pliocene age or Banbury equivalent. A 350-ft interval of felsic volcanics is then intersected above another 600 ft of basalt. The well bottoms in altered felsic volcanics. The lowest 600 ft of basalt flows has not been correlated with any basalt observed on the surface. From the established stratigraphy of the region, and from petrographic evidence, the silicic volcanic rocks occurring both above and below the lowermost basalts in the well are probably lower Pliocene Idavada Volcanics. North of the well, in the Mt. Bennett Hills, Idavada Volcanics overlie crystalline rocks of the Idaho batholith. No estimate of depth to plutonic bedrock can be made from the well data alone. Stratigraphic comparisons suggest as little as 0.2 to 0.3 km more of Idavada lie beneath the Bostic 1-A well. Results of geophysical studies suggest additional basalt lies beneath the Bostic 1-A rather than granitic rocks of the batholith.

  18. Geochemistry and geochronology from Cretaceous magmatic and sedimentary rocks at 6°35‧ N, western flank of the Central cordillera (Colombian Andes): Magmatic record of arc growth and collision

    Science.gov (United States)

    Jaramillo, J. S.; Cardona, A.; León, S.; Valencia, V.; Vinasco, C.

    2017-07-01

    The spatio-temporal, compositional and deformational record of magmatic arcs are sensible markers of the long-term evolution of convergent margins including collisional events. In this contribution, field relations, U-Pb LA-ICP-MS zircon geochronology from magmatic and sedimentary rocks, and whole-rock geochemistry from volcanic and plutonic rocks are used to reconstruct the Cretaceous arc growth and collision in the awakening of the Northern Andean orogeny in northwestern Colombia. The Quebradagrande Complex that includes a sequence of volcanic rocks intercalated with quartz-rich sediments is a tholeiitic arc characterized by an enrichment in LREE and Nb-Ti anomalies that document crustal thickening in an arc system that was already active by ca. 93 Ma. This arc was built associated with thin continental and newly formed oceanic crust, as suggested by the presence of Triassic and older detrital zircons in the associated sandstones. This fringing arc subsequently experienced deformation and a major switch to and enriched calc-alkaline high-k plutonism between 70 and 73 Ma. The deformation record and changes in composition are related to an opposite double-vergence Molucca-sea type arc-arc collision that ended with the accretion to the continental margin of an allochthonous island arc built on an oceanic plateau associated with the Caribbean plate. The new time-framework suggest that the Late Cretaceous to Paleocene collisional tectonics include various stages before the switching to a subduction-dominated regime in most of the Cenozoic.

  19. Time interval between volcanism and burial metamorphism and rate of basin subsidence in a Cretaceous Andean extensional setting

    Science.gov (United States)

    Aguirre, L.; Féraud, G.; Morata, D.; Vergara, M.; Robinson, D.

    1999-11-01

    40Ar/ 39Ar ages were obtained from basaltic flows belonging to a 9-km-thick sequence generated in an extensional ensialic setting of an arc/back-arc basin type during the Early Cretaceous and presently exposed along the Coastal Range of central Chile. The basalts have been affected by very low- to low-grade burial metamorphism, mostly under prehnite-pumpellyite facies. Age values obtained from primary (volcanic) and secondary (metamorphic) minerals permit to quantify the time interval between volcanism and burial metamorphism. A plateau age of 119±1.2 Ma from primary plagioclase represents the best estimation of the age of the volcanism, whereas adularia, in low-variance assemblages contained in amygdules, gave a plateau age of 93.1±0.3 Ma which is interpreted as the age of the metamorphism. Considering the P- T conditions estimated for this metamorphic event, the c. 25 Ma time interval between volcanic emplacement and prehnite-pumpellyite facies metamorphism, the rate of basin subsidence in this extensional geodynamic setting would be comprised in the interval 150-180 m/Ma.

  20. Implications of Late Cretaceous U-Pb zircon ages of granitic intrusions cutting ophiolitic and volcanogenic rocks for the assembly of the Tauride allochthon in SE Anatolia (Helete area, Kahramanmaraş Region, SE Turkey)

    Science.gov (United States)

    Nurlu, Nusret; Parlak, Osman; Robertson, Alastair; von Quadt, Albrecht

    2016-01-01

    An assemblage of NE-SW-trending, imbricate thrust slices (c. 26 km E-W long × 6.3 km N-S) of granitic rocks, basic-felsic volcanogenic rocks (Helete volcanics), ophiolitic rocks (Meydan ophiolite) and melange (Meydan melange) is exposed near the Tauride thrust front in SE Anatolia. The volcanogenic rocks were previously assumed to be Eocene because of associated Nummulitic limestones. However, ion probe U-Pb dating of zircons extracted from the intrusive granitic rocks yielded ages of 92.9 ± 2.2-83.1 ± 1.5 Ma (Cenomanian-Campanian). The Helete volcanic unit and the overlying Meydan ophiolitic rocks both are intruded by granitic rocks of similar age and composition. Structurally underlying ophiolite-related melange includes similar-aged, but fragmented granitic intrusions. Major, trace element and rare earth element analyses coupled with electron microprobe analysis of the granitic rocks show that they are metaluminus to peraluminus and calc-alkaline in composition. A magmatic arc setting is inferred from a combination of tectonomagmatic discrimination, ocean ridge granite-normalized multi-element patterns and biotite geochemistry. Sr-Nd-Pb isotope data further suggest that the granitoid rocks were derived from variably mixed mantle and crustal sources. Granitic rocks cutting the intrusive rocks are inferred to have crystallized at ~5-16 km depth. The volcanogenic rocks and granitic rocks originated in a supra-subduction zone setting that was widely developed throughout SE Anatolia. Initial tectonic assembly took place during the Late Cretaceous probably related to northward subduction and accretion beneath the Tauride continent (Keban and Malatya platforms). Initial tectonic assembly was followed by exhumation and then transgression by shelf-depth Nummulitic limestones during Mid-Eocene, as documented in several key outcrops. Final emplacement onto the Arabian continental margin took place during the Early Miocene.

  1. Archaeological calibration of remagnetized volcanic rocks from pottery firing kilns in Cuentepec, Morelos, Mexico

    OpenAIRE

    L. M. Alva-Valdivia; J. A. González-Rangel; A. M. Soler-Arechalde; S. L. López-Varela; H. López-Loera

    2006-01-01

    Ethnoarchaeological research at the site of Cuentepec, Mexico includes experimental pottery dating in which social knowledge is obtained from archaeometric techniques. At Cuentepec, open kilns are used for firing pottery. Samples from volcanic rocks in the kilns were taken to verify the reliability of the magnetic direction in these rocks as compared with data from Teoloyucan Geomagnetic Observatory, near Mexico City. In the laboratory, forty-seven cores from eight hand oriented rock samples ...

  2. 231Pa systematics in postglacial volcanic rocks from Iceland

    Science.gov (United States)

    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

  3. Trace element and isotope geochemistry of Cretaceous-Tertiary boundary sediments: identification of extra-terrestrial and volcanic components

    Science.gov (United States)

    Margolis, S. V.; Doehne, E. F.

    1988-01-01

    Trace element and stable isotope analyses were performed on a series of sediment samples crossing the Cretaceous-Tertiary (K-T) boundary from critical sections at Aumaya and Sopelano, Spain. The aim is to possibly distinguish extraterrestrial vs. volcanic or authigenic concentration of platinum group and other elements in K-T boundary transitional sediments. These sediments also have been shown to contain evidence for step-wise extinction of several groups of marine invertebrates, associated with negative oxygen and carbon isotope excursions occurring during the last million years of the Cretaceous. These isotope excursions have been interpreted to indicate major changes in ocean thermal regime, circulation, and ecosystems that may be related to multiple events during latest Cretaceous time. Results to date on the petrographic and geochemical analyses of the Late Cretaceous and Early Paleocene sediments indicate that diagenesis has obviously affected the trace element geochemistry and stable isotope compositions at Zumaya. Mineralogical and geochemical analysis of K-T boundary sediments at Zumaya suggest that a substantial fraction of anomalous trace elements in the boundary marl are present in specific mineral phases. Platinum and nickel grains perhaps represent the first direct evidence of siderophile-rich minerals at the boundary. The presence of spinels and Ni-rich particles as inclusions in aluminosilicate spherules from Zumaya suggests an original, non-diagenetic origin for the spherules. Similar spherules from southern Spain (Caravaca), show a strong marine authigenic overprint. This research represents a new approach in trying to directly identify the sedimentary mineral components that are responsible for the trace element concentrations associated with the K-T boundary.

  4. Isotopic data for Late Cretaceous intrusions and associated altered and mineralized rocks in the Big Belt Mountains, Montana

    Science.gov (United States)

    du Bray, Edward A.; Unruh, Daniel M.; Hofstra, Albert H.

    2017-03-07

    The quartz monzodiorite of Mount Edith and the concentrically zoned intrusive suite of Boulder Baldy constitute the principal Late Cretaceous igneous intrusions hosted by Mesoproterozoic sedimentary rocks of the Newland Formation in the Big Belt Mountains, Montana. These calc-alkaline plutonic masses are manifestations of subduction-related magmatism that prevailed along the western edge of North America during the Cretaceous. Radiogenic isotope data for neodymium, strontium, and lead indicate that the petrogenesis of the associated magmas involved a combination of (1) sources that were compositionally heterogeneous at the scale of the geographically restricted intrusive rocks in the Big Belt Mountains and (2) variable contamination by crustal assimilants also having diverse isotopic compositions. Altered and mineralized rocks temporally, spatially, and genetically related to these intrusions manifest at least two isotopically distinct mineralizing events, both of which involve major inputs from spatially associated Late Cretaceous igneous rocks. Alteration and mineralization of rock associated with the intrusive suite of Boulder Baldy requires a component characterized by significantly more radiogenic strontium than that characteristic of the associated igneous rocks. However, the source of such a component was not identified in the Big Belt Mountains. Similarly, altered and mineralized rocks associated with the quartz monzodiorite of Mount Edith include a component characterized by significantly more radiogenic strontium and lead, particularly as defined by 207Pb/204Pb values. The source of this component appears to be fluids that equilibrated with proximal Newland Formation rocks. Oxygen isotope data for rocks of the intrusive suite of Boulder Baldy are similar to those of subduction-related magmatism that include mantle-derived components; oxygen isotope data for altered and mineralized equivalents are slightly lighter.

  5. Evolution of volcanically-induced palaeoenvironmental changes leading to the onset of OAE1a (early Aptian, Cretaceous)

    Science.gov (United States)

    Keller, Christina E.; Hochuli, Peter A.; Giorgioni, Martino; Garcia, Therese I.; Bernasconi, Stefano M.; Weissert, Helmut

    2010-05-01

    During the Cretaceous, several major volcanic events occurred that initiated climate warming, altered marine circulation and increased marine productivity, which in turn often resulted in the widespread black shale deposits of the Oceanic Anoxic Events (OAE). In the sediments underlying the early Aptian OAE1a black shales, a prominent negative carbon isotope excursion is recorded. Its origin had long been controversial (e.g. Arthur, 2000; Jahren et al., 2001) before recent studies attributed it to the Ontong Java volcanism (Méhay et al., 2009; Tejada et al., 2009). Therefore the negative C-isotope excursion covers the interval between the time, when volcanic activity became important enough to be recorded in the C-isotope composition of the oceans to the onset of widespread anoxic conditions (OAE1a). We chose this interval at the locality of Pusiano (N-Italy) to study the effect of a volcanically-induced increase in pCO2 on the marine palaeoenvironment and to observe the evolving palaeoenvironmental conditions that finally led to OAE1a. The Pusiano section (Maiolica Formation) was deposited at the southern continental margin of the alpine Tethys Ocean and has been bio- and magnetostratigraphically dated by Channell et al. (1995). We selected 18 samples from 12 black shale horizons for palynofacies analyses. Palynofacies assemblages consist of several types of particulate organic matter, providing information on the origin of the organic matter (terrestrial/marine) and conditions during deposition (oxic/anoxic). We then linked the palynofacies results to high-resolution inorganic and organic C-isotope values and total organic carbon content measurements. The pelagic Pusiano section consists of repeated limestone-black shale couplets, which are interpreted to be the result of changes in oxygenation of bottom waters. Towards the end of the negative C-isotope excursion we observe enhanced preservation of the fragile amorphous organic matter resulting in increased

  6. Geochemical characteristics of the oceanic island- type volcanic rocks in the Chiang Mai zone, northern Thailand

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; ZHANG Zhibin; CHONGPAN Chonglakmani

    2009-01-01

    The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt being the main rock types. The alkaline series is dominant with sub-alkaline series occurring in few cases. The geochemical characteristics are described as follows: the major chemical compositions are characterized by high TiO2, high P2O5 and medium K2O; the rare-earth elements are characterized by right-inclined strong LREE-enrichment patterns; the trace element patterns are of the upward-bulging K-Ti enrichment type; multi-component plots falling within the fields of oceanic island basalts and alkali basalts, belonging to the oceanic island-type volcanic rocks, which are similar to the equivalents in Deqin and Gengma (the Changning-Menglian zone) of Yunnan Province, China.

  7. Spatial variation of volcanic rock geochemistry in the Virunga Volcanic Province: Statistical analysis of an integrated database

    Science.gov (United States)

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

    2017-10-01

    We present an integrated, spatially-explicit database of existing geochemical major-element analyses available from (post-) colonial scientific reports, PhD Theses and international publications for the Virunga Volcanic Province, located in the western branch of the East African Rift System. This volcanic province is characterised by alkaline volcanism, including silica-undersaturated, alkaline and potassic lavas. The database contains a total of 908 geochemical analyses of eruptive rocks for the entire volcanic province with a localisation for most samples. A preliminary analysis of the overall consistency of the database, using statistical techniques on sets of geochemical analyses with contrasted analytical methods or dates, demonstrates that the database is consistent. We applied a principal component analysis and cluster analysis on whole-rock major element compositions included in the database to study the spatial variation of the chemical composition of eruptive products in the Virunga Volcanic Province. These statistical analyses identify spatially distributed clusters of eruptive products. The known geochemical contrasts are highlighted by the spatial analysis, such as the unique geochemical signature of Nyiragongo lavas compared to other Virunga lavas, the geochemical heterogeneity of the Bulengo area, and the trachyte flows of Karisimbi volcano. Most importantly, we identified separate clusters of eruptive products which originate from primitive magmatic sources. These lavas of primitive composition are preferentially located along NE-SW inherited rift structures, often at distance from the central Virunga volcanoes. Our results illustrate the relevance of a spatial analysis on integrated geochemical data for a volcanic province, as a complement to classical petrological investigations. This approach indeed helps to characterise geochemical variations within a complex of magmatic systems and to identify specific petrologic and geochemical investigations

  8. Geochemical characteristics of island-arc volcanic rocks in the Nan-Nam Pat-Phetchabun zone, northern Thailand

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; YANG Wenqiang; ZHANG Zhibin; Chongpom Chonglakmani

    2010-01-01

    Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.

  9. Petrogenesis of Cenozoic Potassic Volcanic Rocks in the Nangqên Basin

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Nangqên basin is one of the Tertiary pull-apart basins situated in the east of the Qiangtang block. Similar to the adjacent Dengqên basin and Baxoi basin, there occurred a series of potassic volcanic and sub-volcanic rocks, ranging from basic, intermediate to intermediate-acid in lithology. Based on the study of petrology, mineralogy and geochemistry, including REEs, trace elements, isotopic elements and chronology, the authors concluded that the Cenozoic potassic volcanic rocks in the Nangqên basin were formed in the post-collisional intraplate tectonic settings. The relations between the basic, intermediate and intermediate-acid rocks are neither differentiation nor evolution, but instead the geochemical variability is mainly attributable to the different partial melting degrees of the mantle sources formed at depths of 50(80 km. The sources of the potassic rocks are enriched metasomatic mantle that has experienced multiple mixing of components mainly derived from the crust. The recycling model can be described as follows: after they had subducted to the mantle wedge, the crust-derived rocks were metasomatized with the mantle materials. In view of the fact that the ratio of crust-derived rocks increases by the age of volcanism, it can be concluded that the sources of the potassic rocks moved upwards progressively with time. The underplating of small scattered magmas upwelling from the asthenosphere may have induced partial melting of the sources of the volcanic rocks in some pull-apart basins in the Hengduanshan area and the intense tectonic movements of large-scale strike-slip belts provided conduits for the ascending melts.

  10. Petrogenesis of Cenozoic Volcanic Rocks in Tengchong Region of Western Yunnan Province,China

    Institute of Scientific and Technical Information of China (English)

    从柏林; 陈秋媛; 张儒瑷; 吴根耀; 徐平

    1994-01-01

    The Tengchong Cenozoic volcanic rocks belong to the high-K calc-alkaline rock series.They are strongly depleted in high field strength (HFS) elements and enriched in large-ion lithophile(LIL) elements and LREE.The generation of Tengchong volcanic rocks has been considered to be relatedto the evolution of the Neo-Tethys.The Indian Plate was subducted beneath the southeastern Asia conti-nent,which resulted in the formation of Indo-Burman Arc in the Late Cretaeeous-Palaeocene time.Thecollision between the Indian continent and Indo-Burman Arc started in Eocene and lasted to the present.The Andaman Sea and the Inner Burman Tertiary Basin are a back-arc basin that has been extended sincethe Late Miocene.A distinct characteristic of Tengchong volcanics is that they show a chemical affinityrelated to island arc but their generation postdated the subduetion of the ocean plate.

  11. Origin of the ca. 90 Ma magnesia-rich volcanic rocks in SE Nyima, central Tibet: Products of lithospheric delamination beneath the Lhasa-Qiangtang collision zone

    Science.gov (United States)

    Wang, Qing; Zhu, Di-Cheng; Zhao, Zhi-Dan; Liu, Sheng-Ao; Chung, Sun-Lin; Li, Shi-Min; Liu, Dong; Dai, Jin-Gen; Wang, Li-Quan; Mo, Xuan-Xue

    2014-06-01

    Bulk-rock major and trace element, Sr-Nd-Hf isotope, zircon U-Pb age, and zircon Hf isotopic data of the Late Cretaceous Zhuogapu volcanic rocks in the northern Lhasa subterrane provide a new insight into tectonic processes following the collision of the terrane with the Qiangtang zone. SHRIMP zircon U-Pb dating reveals that the Zhuogapu volcanic rocks crystallized at ca. 91 Ma, postdating the development of a regional angular unconformity between the Upper Cretaceous and the underlying strata in the Lhasa-Qiangtang collision zone. Compared to the Andean arc-type andesites and dacites, the Zhuogapu volcanic rocks are characterized by higher MgO of 2.78-5.86 wt.% and Mg# of 54-64 for andesites and MgO of 2.30-2.61 wt.% and Mg# of 55-58 for dacites. Eight andesite samples have whole-rock (87Sr/86Sr)i of 0.7054-0.7065, εNd(t) of - 3.2 to - 1.7, and εHf(t) of + 3.8-+ 6.4, similar to those of the three dacite samples with (87Sr/86Sr)i = 0.7056-0.7060, εNd(t) of - 2.7 to - 2.2, and εHf(t) of + 5.6-+ 7.0. Thirteen analyses from a dacite sample give positive zircon εHf(t) of + 5.6 to + 8.7. These signatures indicate that the Zhuogapu Mg-rich andesites were most likely derived from partial melting of a delaminated mafic lower crust (including the lowermost crust straddling the northern and central Lhasa subterranes) that led to the generation of the Zhuogapu primary melts with adakitic signatures and small negative εNd(t). Such melts subsequently experienced interaction of melt-asthenospheric mantle peridotite followed by the modification of highly fractionated magmas in shallow crustal magma chamber. Hornblende-controlled fractionation results in the change of geochemical composition from Mg-rich andesitic to Mg-rich dacitic magmas. Field observations, together with geochronological and geochemical data, indicate that the Zhuogapu Mg-rich volcanic rocks and coeval magmatism in the northern Lhasa subterrane may be the result of thickened lithospheric delamination

  12. Geochemical Characteristics of Danfeng Meta-Volcanic Rocks in Shangzhou Area,Shaanxi Province

    Institute of Scientific and Technical Information of China (English)

    1995-01-01

    The Danfeng meta-volcanics in the Shangzhou area, Shaanxi Province are characterized by oceanic island arc volcanic geochemistry. They are a suite of low-K tholeiitic series and calc-alkaline series meta-volcanic rocks derived from different sources respectively.These meta-volcanics have high Th/Ta ratios and low contents of Ni,Ta,Ti,Y and Yb, suggesting that they were influenced by the subduction zone components.Many lines of evidence show that the Danfeng meta-volcanics were produced in an oceanic island are setting of the supra-subduction zone at the southern margin of the North China Block during the Early Paleozoic.

  13. Paleomagnetic Results of the Red Soil-Volcanic Rock Series of Yingfengling Section, Southern Leizhou Peninsula

    Institute of Scientific and Technical Information of China (English)

    王俊达; 梁池生

    2002-01-01

    The Yingfengling section composed of red soil and volcanic rocks can be distinguished into 8 stratigraphic units and 4 red soil-volcanic rock cycles. 64 paleomagnetic-orientated sam ples were collected from the bottom to the top of the section. Natural remanent magnetization and magnetic susceptibility were firstly measured. All the samples were stepwisely treated with thermal or/and alternating fields. Four clear polarity segments were recorded in the section.Compared with the geo-magnetic polarity scale, the section was formed since the late Olduvai subchron, about 1.37 Ma. B. P.

  14. Natural gas accumulations in low-permeability Tertiary, and Cretaceous (Campanian and Maastrichtian) rock, Uinta Basin, Utah. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Fouch, T.D.; Wandrey, C.J.; Pitman, J.K.; Nuccio, V.F.; Schmoker, J.W.; Rice, D.D.; Johnson, R.C.; Dolton, G.L.

    1992-02-01

    This report characterizes Upper Cretaceous Campanian and Maastrichtian, and lower Tertiary gas-bearing rocks in the Uinta Basin with special emphasis on those units that contain gas in reservoirs that have been described as being tight. The report was prepared for the USDOE whose Western Tight Gas Sandstone Program cofunded much of this research in conjunction with the US Geological Survey`s Evolution of Sedimentary Basins, and Onshore Oil and Gas Programs. (VC)

  15. Natural gas accumulations in low-permeability Tertiary, and Cretaceous (Campanian and Maastrichtian) rock, Uinta Basin, Utah

    Energy Technology Data Exchange (ETDEWEB)

    Fouch, T.D.; Wandrey, C.J.; Pitman, J.K.; Nuccio, V.F.; Schmoker, J.W.; Rice, D.D.; Johnson, R.C.; Dolton, G.L.

    1992-02-01

    This report characterizes Upper Cretaceous Campanian and Maastrichtian, and lower Tertiary gas-bearing rocks in the Uinta Basin with special emphasis on those units that contain gas in reservoirs that have been described as being tight. The report was prepared for the USDOE whose Western Tight Gas Sandstone Program cofunded much of this research in conjunction with the US Geological Survey's Evolution of Sedimentary Basins, and Onshore Oil and Gas Programs. (VC)

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. A preliminary evaluation of volcanic rock powder for application in agriculture as soil a remineralizer

    Energy Technology Data Exchange (ETDEWEB)

    Ramos, Claudete G., E-mail: claudeterms@brturbo.com.br [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Querol, Xavier [Institute of Environmental Assessment and Water Research (IDÆA-CSIC), C/Luis Solé y Sabarís s/n, 08028 Barcelona (Spain); Oliveira, Marcos L.S. [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Pires, Karen [Departamento Nacional de Produção Mineral (DNPM), Washington Luiz, 815, Centro, 90010-460 Porto Alegre, RS (Brazil); Kautzmann, Rubens M. [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Oliveira, Luis F.S., E-mail: felipeqma@hotmail.com [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil)

    2015-04-15

    Mineralogical and geochemical characteristics of volcanic rock residue, from a crushing plant in the Nova Prata Mining District, State of Rio Grande do Sul (RS), Brazil, in this work named rock powder, were investigated in view of its potential application as soil ammendment in agriculture. Abaut 52,400 m{sup 3} of mining waste is generated annually in the city of Nova Prata without a proper disposal. The nutrients potentially available to plants were evaluated through leaching laboratory tests. Nutrient leaching tests were performed in Milli-Q water; citric acid solution 1% and 2% (AC); and oxalic acid solution 1% and 5% (AO). The bulk and leachable contents of 57 elements were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Mining waste were made up by CaO, K{sub 2}O, SiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3}, and P{sub 2}O{sub 5}. The analysis by X-ray diffraction (XRD) showed the major occurence of quartz, anorthite, cristobalite, sanidine, and augite. The water leachable concentrations of all elements studied were lower than 1.0 mg/kg, indicating their low solubility. Leaching tests in acidic media yield larger leachable fractions for all elements being studied are in the leachate of the AO 1%. These date usefulness of volcanic rock powder as potential natural fertilizer in agriculture in the mining district in Nova Prata, Rio Grande do Sul, Brazil to reduce the use of chemical fertilizers. - Highlights: • Volcanic rock powder as fertilizer in agriculture • Volcanic rock powder as a source of nutrients to plants • This technology may favor the use of volcanic rock in agriculture.

  18. Paleontologic and stratigraphic relations of phosphate beds in Upper Cretaceous rocks of the Cordillera Oriental, Colombia

    Science.gov (United States)

    Maughan, Edwin K.; Zambrano O., Francisco; Mojica G., Pedro; Abozaglo M., Jacob; Pachon P., Fernando; Duran R., Raul

    1979-01-01

    Phosphorite crops out in the Cordillera Oriental of the Colombian Andes in rocks of Late Cretaceous age as strata composed mostly of pelletal carbonate fluorapatite. One stratum of Santonian age near the base of the Galembo Member of the La Luna Formation crops out at many places in the Departments of Santander and Norte de Santander and may be of commercial grade. This stratum is more than one meter thick at several places near Lebrija and near Sardinata, farther south it is locally one meter thick or more near the base of the Guadalupe Formation in the Department of Boyaca. Other phosphorite beds are found at higher stratigraphic levels in the Galembo Member and the Guadalupe Formation, and at some places these may be commercial also. A stratigraphically lower phosphorite occurs below the Galembo Member in the Capacho Formation (Cenomanian age) in at least one area near the town of San Andres, Santander. A phosphorite or pebbly phosphate conglomerate derived from erosion of the Galembo Member forms the base of the Umir Shale and the equivalent Colon Shale at many places. Deposition of the apatite took place upon the continental shelf in marine water of presumed moderate depth between the Andean geosyncline and near-shore detrital deposits adjacent to the Guayana shield. Preliminary calculations indicate phosphorite reserves of approximately 315 million metric tons in 9 areas, determined from measurements of thickness, length of the outcrop, and by projecting the reserves to a maximum of 1,000 meters down the dip of the strata into the subsurface. Two mines were producing phosphate rock in 1969; one near Turmeque, Boyaca, and the other near Tesalia, Huila.

  19. Plesiosaur-bearing rocks from the Late Cretaceous Tahora Fm, Mangahouanga, New Zealand - a palaeoenvironmental study

    Science.gov (United States)

    Vajda, Vivi; Raine, J. Ian

    2010-05-01

    Mangahouanga Stream, Hawkes Bay, New Zealand is world-famous for its high southern latitude vertebrate fossils including plesiosaurs, mosasaurs and more rarely, dinosaurs. The fossils are preserved in the conglomeratic facies of the Maungataniwha Sandstone Member of the Tahora Formation. A palynological investigation of sediments from the boulders hosting vertebrate fossils reveals well-preserved palynological assemblages dominated by pollen and spores from land plants but also including marine dinoflagellate cysts in one sample. The palynofacies is strongly dominated by wood fragments including charcoal, and the sample taken from a boulder hosting plesiosaur vertebrae is entirely terrestrially derived, suggesting a fresh-water habitat for at least some of these plesiosaurs. The key-pollen taxa Nothofagidites senectus and Tricolpites lilliei, together with the dinocyst Isabelidinium pellucidum and the megaspore Grapnelispora evansii, strongly indicate an early Maastrichtian age for the host rock. The terrestrial palynoflora reflects a mixed vegetation dominated by podocarp conifers and angiosperms with a significant tree-fern subcanopy component. The presence of taxa with modern temperate distributions such as Nothofagus (southern beech), Proteaceae and Cyatheaceae (tree-ferns), indicates a mild-temperate climate and lack of severe winter freezing during the latest Cretaceous, providing an ecosystem which most probably made it possible for polar dinosaurs to overwinter. The paper is dedicated to Mrs Joan Wiffen who with her great persistence, enthusiasm and courage put Mangahouanga on the world map, becoming a role model for many young scientists.

  20. Search for magnetic monopoles in polar volcanic rocks

    CERN Document Server

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

    2013-01-01

    For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside the 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 analysed. No monopoles were found and a 90% confidence level upper limit of $1.6\\cdot 10^{-28}$ is set on the monopole to nucleon ratio in the search samples.

  1. Search for Magnetic Monopoles in Polar Volcanic Rocks

    DEFF Research Database (Denmark)

    Bendtz, K.; Milstead, D.; Hächler, H. -P.

    2013-01-01

    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 x...... 10(-5)/g is set on the monopole density in the search samples. DOI:10.1103/PhysRevLett.110.121803...

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

    Science.gov (United States)

    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.

  3. Chronology and geochemistry of the volcanic rocks in Woruo Mountain region,Northern Qiangtang depression:Implications to the Late Triassic volcanic-sedimentary events

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A suite of sedimentary-volcaniclastic rocks intercalated with the volcanic rocks unconformably overlies the Triassic Xiaochaka Formation in the Woruo Mountain region, Qiangtang Basin, northern Tibet. The vitric tuff from the base of these strata gives a SHRIMP zircon U-Pb age of 216 ± 4.5 Ma, which represents the age of the Late Triassic volcanic-sedimentary events in the Woruo Mountain region, and is consistent with that of the formation of the volcanic rocks from the Nadi Kangri Formation in the Nadigangri-Shishui River zone. There is a striking similarity in geochemical signatures of the volcanic rocks from the Woruo Mountain region and its adjacent Nadigangri-Shishui River zone, indicating that all the volcanic rocks from the Qiangtang region might have the same magmatic source and similar tectonic setting during the Late Triassic. The proper recognition of the Late Triassic large-scale volcanic eruption and volcanic-sedimentary events has important implications for the interpretation of the Late Triassic biotic extinction, climatic changes and regressive events in the eastern Tethyan domain, as well as the understanding of the initiation and nature, and sedimentary features of the Qiangtang Basin during the Late Triassic-Jurassic.

  4. Chronology and geochemistry of the volcanic rocks in Woruo Mountain region, Northern Qiangtang depression: Implications to the Late Triassic volcanic-sedimentary events

    Institute of Scientific and Technical Information of China (English)

    WANG Jian; FU XiuGen; CHEN WenXi; WANG ZhengJiang; TAN FuWen; CHEN Ming; ZHUO JieWen

    2008-01-01

    A suite of sedimentary-volcaniclastic rocks intercalated with the volcanic rocks unconformably overlies the Triassic Xiaochaka Formation in the Woruo Mountain region, Qiangtang Basin, northern Tibet. The sents the age of the Late Triassic volcanic-sedimentary events in the Woruo Mountain region, and is consistent with that of the formation of the volcanic rocks from the Nadi Kangri Formation in the Nadigangri-Shishui River zone. There is a striking similarity in geochemical signatures of the volcanic rocks from the Woruo Mountain region and its adjacent Nadigangri-Shishui River zone, indicating that all the volcanic rocks from the Qiangtang region might have the same magmatic source and similar tectonic setting during the Late Triassic. The proper recognition of the Late Triassic large-scale volcanic eruption and volcanic-sedimentary events has important implications for the interpretation of the Late Triassic biotic extinction, climatic changes and regressive events in the eastern Tethyan domain,as well as the understanding of the initiation and nature, and sedimentary features of the Qiangtang Basin during the Late Triassic-Jurassic.

  5. Mineral Chemistry and Geochemistry of Volcanic Rocks in The North of Pasinler (Erzurum

    Directory of Open Access Journals (Sweden)

    Oktay KILIÇ

    2009-02-01

    Full Text Available In the north of Pasinler (Erzurum, Upper Miocene-Pliocene volcanic rocks crop out. These volcanites are composed of basaltic andesite, andesite, dacite, rhyolite lavas and rhyolitic pyroclastics. The rocks show porphyritic, microlitic porphyritic, hyalo-microlitic porphyritic, vitrophyric, glomeroporphyritic, pilotaxitic and hyalopilitic textures. The investigated volcanites contain plagioclase (An29-80, olivine (Fo65-82, clinopyroxene (augite, orthopyroxene (enstatite, amphibole (Mg#: 0.57-0.71, biotite (phlogopite: 0.44-0.47, annite: 0.33-0.37, sanidine, quartz and opaque mineral (titano-magnetite and ilmenite. The volcanic rocks are calc-alkaline in character and have medium to high-K contents. Major oxide and trace element variations point out open-system magmatic differentiation in the evolution of rocks. Geochemical data indicate an important role of fractionation of phenocryst phases in the rocks during differentiation process. However, it is considered that assimilation±magma mixing might have accompanied to the process. High LILE (K, Rb, Ba, Th and relatively low HFSE (Nb, Ta, Hf, Zr contents of the rocks indicate that these rocks derived from parental magmas carrying subduction signature.

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

    Science.gov (United States)

    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.

  7. Engineering geological characterization of volcanic rocks of ethiopian and sardinian highlands to be used as construction materials

    OpenAIRE

    Engidasew, Tesfaye Asresahagne

    2014-01-01

    This thesis presents the results of the study conducted on the “Geoengineering characterization of volcanic rocks from Ethiopian and Sardinian highlands to be used as construction materials”. Though, the two project areas are geographically far apart, both are partly covered with volcanic rocks mainly consisting of basic and subordinate felsic rocks. The research was conducted in two countries; part I, the Ethiopian Project area located on the northwestern central Highlands of ...

  8. Supracrustal rocks in the Kuovila area, Southern Finland: structural evolution, geochemical characteristics and the age of volcanism

    OpenAIRE

    Pietari Skyttä; Asko Käpyaho; Irmeli Mänttäri

    2005-01-01

    The supracrustal rocks of the Kuovila area in the Palaeoproterozoic Svecofennian Uusimaa Belt, southern Finland, consist mainly of volcaniclastic rocks associated with banded iron formations (BIFs) and marbles. Small ZnS and PbS mineralizations are occasionally located within the marbles. Some primary features are well preserved in the sedimentary and volcanic rocks, including lamination in tuffites and banded iron formations. Geochemical results show that the volcanism was bimodal and it mai...

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

    Science.gov (United States)

    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

  10. Fractal approach in petrology: Small-angle neutron scattering experiments with volcanic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Lucido, G.; Triolo, R.; Caponetti, E.

    1988-11-01

    Following Mandelbrot's pioneering work in 1977, we attempt to use the concept of fractal dimension in petrology. Fractal dimension is an intensive property of matter which offers a quantitative measure of the degree of surface roughness. Neutron scattering experiments have been performed on 18 volcanic rocks from different localities. The scattered intensity as a function of the momentum transfer obeys a power law whose exponent varies, for the rock samples presented, between -3 and -4. We conclude that, at the molecular level, our volcanic rocks are not fractal volumes. With regard to the particle-matrix interface, it is not possible to provide a determination at the present stage of research. Our findings suggest it is feasible to verify the degree of surface irregularity at a resolution which is relevant to many aspects of petrology.

  11. Holocene volcanic rocks in Jingbo Lake region--Diversity of magmatism

    Institute of Scientific and Technical Information of China (English)

    FAN Qicheng; SUN Qian; LI Ni; WANG Tuanhua

    2006-01-01

    During the time from 5500 a to 5200 a BP more than 10 Holocene volcanoes in Jingbo Lake region erupted and the volcanic rocks covered an area of about 500 km2. Holocene volcanic rocksin Jingbo Lake region belong to the potassium-rich rocks and contain three rock types: trachybasalts, basanites and phonotephrites. Various types of magmatism formed in a small area and in a short period of time came from partial melting of potassically-metasomatised lithospheric mantle. The diversity of magmatism can be explained by that Jingbo Lake is situated in the back-arc extensional region of East Asian continent subducted by the Pacific Ocean, and potassic fluid derived from mantle wedge or dehydration of subducted slab can result in a high heterogeneity of the mantle beneath this region. Based on the pressure estimation of clinopyroxene megacrysts, we estimate that phonotephrite magma fractionally crystallize at ca. 52-54 km down the earth.

  12. Petrography and petrology of Quaternary volcanic rocks from Ghezel Ghaleh, northwest Qorveh

    Directory of Open Access Journals (Sweden)

    Alireza Bajelan

    2014-10-01

    Full Text Available Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985. Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997. Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985. A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993. According to SiO2 against Na2O + K2O (TAS diagram (Irvine and Baragar , 1971 and cationic R1 and R2 diagram (De La Roche et el., 1980, volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram

  13. Geochemical Characteristics of the Cenozoic Volcanic Rocks in Central Qiangtang, Tibet: Relation with the Uplift of the Qinghai Tibet Plateau

    Institute of Scientific and Technical Information of China (English)

    TAN Fuwen; PAN Guitang; XU Qiang

    2001-01-01

    The Cenozoic volcanic rocks in central Qiangtang are tectonically outcropped in the transitional area where crust of the Qinghai-Tibet Plateau thins northwards and the Passion's ratios of the crust increases abnormally northwards. Of all Cenozoic volcanic rocks of northern Tibet, the volcanic rocks in Qiangtang area is the oldest one with ages from 44.1±1.0 Ma to 32.6±0.8 Ma. Petrological and geochemical studies of the volcanic rocks in central Qiangtang suggest they formed in the extension environment of post collision-orogeny and were the product of mixture of magmas from crust and mantle. The uplift of the northern plateau is closely related to decoupling of mantle lithosphere,crustal extension and thinning as well as volcanism. Therefore, it is inferred that the main uplift of the northern plateau began from about 40 Ma ago.

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

    Science.gov (United States)

    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.

  15. Anisotropy of Anhysteretic Remanent Magnetization: A Tool To Estimate Trm Deviations In Volcanic Rocks

    Science.gov (United States)

    Gattacceca, J.; Rochette, P.

    In order to assess the paleomagnetic direction deviations due to anisotropy in volcanic rocks, we studied the anisotropies of magnetic susceptibility (AMS), of anhysteretic remanent magnetization (AARM) and of thermoremanent magnetization (ATRM) of a set of Miocene pyroclastic rocks from Sardinia (Italy). The main magnetic carrier is pseudo-single domain titanomagnetite. AARM and ATRM were determined with a 3-position measurement scheme. The measurements show that there is no general relation between the degrees of AMS and ATRM (as this relation depends on the ti- tanomagnetite grain size spectrum), while the degree of AARM and ATRM are almost identical. Measuring the AMS is thus nearly irrelevant to quantitatively estimate TRM deviations due to anisotropy in volcanic rocks. Instead, measuring the AARM provides a reliable and relatively fast method to correct paleomagnetic direction deviations in volcanic rocks (inclination shallowing due to horizontal planar fabric in most cases). This is confirmed by a case study on a succession of four welded pyroclastic flows : an apparent paleosecular variation pattern is almost entirely explained by the effect of ATRM.

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

    Science.gov (United States)

    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.

  17. 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

    Science.gov (United States)

    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

  18. Geochemistry of the Neoarchaean Volcanic Rocks of the Kilimafedha Greenstone Belt, Northeastern Tanzania

    Directory of Open Access Journals (Sweden)

    Charles W. Messo

    2012-01-01

    Full Text Available The Neoarchaean volcanic rocks of the Kilimafedha greenstone belt consist of three petrological types that are closely associated in space and time: the predominant intermediate volcanic rocks with intermediate calc-alkaline to tholeiitic affinities, the volumetrically minor tholeiitic basalts, and rhyolites. The tholeiitic basalts are characterized by slightly depleted LREE to nearly flat REE patterns with no Eu anomalies but have negative anomalies of Nb. The intermediate volcanic rocks exhibit very coherent, fractionated REE patterns, slightly negative to absent Eu anomalies, depletion in Nb, Ta, and Ti in multielement spidergrams, and enrichment of HFSE relative to MORB. Compared to the other two suites, the rhyolites are characterized by low concentrations of TiO2 and overall low abundances of total REE, as well as large negative Ti, Sr, and Eu anomalies. The three suites have a εNd (2.7 Ga values in the range of −0.51 to +5.17. The geochemical features of the tholeiitic basalts are interpreted in terms of derivation from higher degrees of partial melting of a peridotite mantle wedge that has been variably metasomatized by aqueous fluids derived from dehydration of the subducting slab. The rocks showing intermediate affinities are interpreted to have been formed as differentiates of a primary magma formed later by lower degrees of partial melting of a garnet free mantle wedge that was strongly metasomatized by both fluid and melt derived from the subducting oceanic slab. The rhyolites are best interpreted as having been formed by shallow level fractional crystallization of the intermediate volcanic rocks involving plagioclase and Ti-rich phases like ilmenite and magnetite as well as REE-rich phases like apatite, zircon, monazite, and allanite. The close spatial association of the three petrological types in the Kilimafedha greenstone belt is interpreted as reflecting their formation in an evolving late Archaean island arc.

  19. Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina

    Science.gov (United States)

    Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo

    2017-05-01

    We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. Geochemistry and petrology of Late Cretaceous subvolcanic rocks (Macka-Trabzon) in the north of the eastern Black Sea region, NE-Turkey

    Science.gov (United States)

    Aydin, Faruk

    2013-04-01

    In this study, geochronological, geochemical and isotopical data for the early Campanian subvolcanic rocks (Macka-Trabzon) in the north of the eastern Blacksea region, northeastern Turkey, have initially been presented with the aim of determining its magma source and geodynamic evolution. The subvolcanic rocks cutting the subduction-related Late Cretaceous volcano-sedimantary rocks in the region are characterized by several sills and dykes with columnar structures and they consist of amphibole-rich quartz-diorite and quartz-tonalite porphyries, with some dioritic mafic microgranular enclaves. The host rocks have a microgranular porphyritic texture, and they contain 15-25% phenocryst of plagioclase and amphibole and have a matrix that is composed primarily of fine-grained quartz, orthoclase, and plagioclase. Accessory apatite, zircon and Fe-Ti oxides are present in all of the rocks. Secondary minerals such as epidote, calcite, sericite and clays are sometimes observed in the matrix or as hydothermal alteration products of some amphibole and plagioclase phenocrysts. When compared to the host rocks, the magmatic enclaves without quartz are fine-grained, and they contain higher ferromagnesian phases and lower feldspar minerals. Ar-Ar geochronology studies on the amphibole separates reveal that the porphyries have a crystallization ages of 81±0.5 Ma. All samples show a high-K calc-alkaline differentiation trend and I-type features with metaluminous character. The rocks and magmatic enclaves are characterized by enrichment of LILE and depletion of HFSE with negative Nb, Ti, Zr and P anomalies. The chondrite-normalized REE patterns are not fractionated [(La/Yb)N = 9-11] and do not display Eu anomalies (Eu/Eu* = 0.7-0.9). The porphyritic rocks and their enclaves are almost isotopically similar. Sr-Nd isotopic data for all of the samples display initial Sr = 0.7085-0.7087, epsilon Nd (81 Ma) = -6.0 to -6.9, with TDM = 1.38-1.63 Ga. The lead isotopic ratios are (206Pb/204Pb

  2. Geochemistry and Petrogenesis of Volcanic Rocks in the Yeba Formation on the Gangdise Magmatic Arc, Tibet

    Institute of Scientific and Technical Information of China (English)

    Geng Quanru; Pan Guitang; Jin Zhenmin; Wang Liquan; Liao Zhongli

    2005-01-01

    The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagzê and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4 % and 64 %-69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66 %-1.01 %, much lower than those of continental tholeiite. The ΣREE contents of basalt and dacite are 60.3-135 μg/g and 126.4-167.9 μg/g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb*=0.54-1.17 averaging 0.84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb*=0.74-1.06 averaging 0.86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal lherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.

  3. Methane-rich fluid inclusions and their hosting volcanic reservoir rocks of the Songliao Basin, NE China

    Institute of Scientific and Technical Information of China (English)

    WANG Pu-Jun; HOU Qi-jun; CHENG Ri-hui; LI Quan-lin; GUO Zhen-hua; HUANG Yu-long

    2004-01-01

    Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions.Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ12C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb,suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.

  4. Geochemical study of volcanic and associated granitic rocks from Endau Rompin, Johor, Peninsular Malaysia

    Indian Academy of Sciences (India)

    Azman A Ghani; Ismail Yusoff; Meor Hakif Amir Hassan; Rosli Ramli

    2013-02-01

    Geochemical studies and modelling show that both volcanic and granitic magmas from the western part of the Johor National Park, Endau Rompin are different and probably have different sources. The geochemical plot suggests that both dacite/rhyolite and andesite probably have a common origin as in many of the geochemical plots, these two groups form a similar trend. Volcanic rocks have a transitional geochemical character between tholeiite and calc alkaline on a Y versus Zr plot. (La/Yb)N versus La and TiO2 versus Zr modelling show that the crystallization of both granitic and volcanic magmas are controlled by a different set of minerals. The rare earth elements (REE) patterns of some of the granite and volcanic samples have pronounced negative Eu anomaly indicating plagioclase fractionation. The difference between both profiles is that the granite samples show a concave shape profile which is consistent with liquids produced by partial melting of quartz feldspathic rocks containing amphibole among the residual phase. Both magmas were generated at a different time during the subduction of Sibumasu beneath the Indochina blocks.

  5. K-Ar dating, whole-rock and Sr-Nd isotope geochemistry of calc-alkaline volcanic rocks around the Gümüşhane area: implications for post-collisional volcanism in the Eastern Pontides, Northeast Turkey

    Science.gov (United States)

    Aslan, Zafer; Arslan, Mehmet; Temizel, İrfan; Kaygusuz, Abdullah

    2014-04-01

    Volcanic rocks from the Gümüşhane area in the southern part of the Eastern Pontides (NE Turkey) consist mainly of andesitic lava flows associated with tuffs, and rare basaltic dykes. The K-Ar whole-rock dating of these rocks range from 37.62 ± 3.33 Ma (Middle Eocene) to 30.02 ± 2.84 Ma (Early Oligocene) for the andesitic lava flows, but are 15.80 ± 1.71 Ma (Middle Miocene) for the basaltic dykes. Petrochemically, the volcanic rocks are dominantly medium-K calc-alkaline in composition and show enrichment of large ion lithophile elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magmas derived from an enriched mantle source. Chondrite-normalized rare-earth element patterns of the volcanic rocks are concave upwards with low- to-medium enrichment (LaCN/LuCN = 3.39 to 12.56), thereby revealing clinopyroxene- and hornblende-dominated fractionations for andesitic-basaltic rocks and tuffs, respectively. The volcanic rocks have low initial 87Sr/86Sr ratios (0.70464 to 0.70494) and ɛNd(i) values (+1.11 to +3.08), with Nd-model ages (TDM) of 0.68 to 1.02 Ga, suggesting an enriched lithospheric mantle source of Proterozoic age. Trace element and isotopic data, as well as the modelling results, show that fractional crystallization and minor assimilation played an important role in the evolution of the volcanic rocks studied. The Eocene to Miocene volcanism in the region has resulted from lithospheric delamination and the associated convective thinning of the mantle, which led to the partial melting of the subduction-metasomatized lithospheric mantle.

  6. Basic-ultrabasic and volcanic rocks in Chagbu-Shuanghu area of northern Xizang (Tibet),China

    Institute of Scientific and Technical Information of China (English)

    邓万明; 尹集祥; 呙中平

    1996-01-01

    The widespread Early Permian and Triassic sequences outcropping in the Chagbu-Shuanghu area of northern Xizang, China, are mainly characterized by volcanic rocks belonging to tholeiite with subordinate veins of diallagite. wehrlite and limburgites schlierens. These ultrabasic rocks do not carry plastic deformational fabrics from upper mantle and may result from the crystallization of fused mass derived from mantle under condition of deeper crust or earlier segregation of tholeiitic magma. These volcanic rocks, as interlayers or lens, are generally involved in slates, limestones and pebbly slates or breccia and geochemically different from MORB. It is reasonable to conclude from research results that the volcanic activities during the Early Permian and Late Triassic would be able to occur in an intraplale environment suffering initial extension of continental crust or an aulacogen. Therefore, these basic-ultrabasic and volcanic rocks did not constitute an ophiolitic association with an occurrence 6f the

  7. Geochemistry and geodynamics of a Late Cretaceous bimodal volcanic association from the southern part of the Pannonian Basin in Slavonija (Northern Croatia)

    Science.gov (United States)

    Pamic, J.; Belak, M.; Bullen, T.D.; Lanphere, M.A.; McKee, E.H.

    2000-01-01

    In this paper we present petrological and geochemical information on a bimodal basaltrhyolite suite associated with A-type granites of Late Cretaceous age from the South Pannonian Basin in Slavonija (Croatia). Basalts and alkali-feldspar rhyolites, associated in some places with ignimbrites, occur in volcanic bodies that are interlayered with pyroclastic and fossiliferous Upper Cretaceus sedimentary rocks. The petrology and geochemistry of the basalts and alkali-feldspar rhyolites are constrained by microprobe analyses, major and trace element analyses including REE, and radiogenic and stable isotope data. Basalts that are mostly transformed into metabasalts (mainly spilites), are alkalic to subalkalic and their geochemical signatures, particularly trace element and REE patterns, are similar to recent back-arc basalts. Alkali-feldspar rhyolites have similar geochemical features to the associated cogenetic A-type granites, as shown by their large variation of Na2O and K2O (total 8-9%), very low MgO and CaO, and very high Zr contents ranging between 710 and 149ppm. Geochemical data indicate an amphibole lherzolite source within a metasomatized upper mantle wedge, with the influence of upper mantle diapir with MORB signatures and continental crust contamination. Sr incorporated in the primary basalt melt had an initial 87Sr/86Sr ratio of 0.7039 indicating an upper mantle origin, whereas the 87Sr/86Sr ratio for the alkalifeldspar rhyolites and associated A-type granites is 0.7073 indicating an apparent continental crust origin. However, some other geochemical data favour the idea that they might have mainly originated by fractionation of primary mafic melt coupled with contamination of continental crust. Only one rhyolite sample appears to be the product of melting of continental crust. Geological and geodynamic data indicate that the basalt-rhyolite association was probably related to Alpine subduction processes in the Dinaridic Tethys which can be correlated with

  8. Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná Magmatic Province, Brazil

    Directory of Open Access Journals (Sweden)

    Liza Angélica Polo

    2014-06-01

    Full Text Available This article presents the first map in detail scale for an area covered by Palmas type volcanic rocks in the south border of the eocretaceous Paraná Magmatic Province, south Brazil. The study of the structural features coupled with petrography and geochemistry made it possible to separate these rocks into three main volcanic sequences and recognize their stratigraphy. The older Caxias do Sul sequence rests directly over the first low-Ti basalt flows (Gramado type, and corresponds to the stacking of lobated lava flows, laminar flows and lava domes, mostly emitted as continuous eruptions; only the latest eruptions are intercalated with thin sandstone deposits. These rocks have dacitic composition (~ 68 wt% SiO2 with microphenocrysts of plagioclase and subordinate pyroxenes and Ti-magnetite immersed in glassy or devitrified matrix. A second volcanic sequence, named Barros Cassal, is composed of several lava flows of basaltic andesite, andesitic and dacitic composition (~ 54; ~ 57 and ~ 63 wt% SiO2 , respectively, with microphenocrysts of plagioclase, pyroxenes and Ti-magnetite. The frequent intercalation of sandstone between the flows attests to the intermittent behaviour of this event. The upper sequence, Santa Maria, is made up of more silica-rich (~ 70 wt% SiO2 rocks occurring as laminar flows, lobated flows and lava-domes. These rocks have rhyolitic composition with microphenocrysts of plagioclase and Ti-magnetite set in a glassy or devitrified matrix with microlites. The structures and textures of all three silicic sequences favor the interpretation that they had a predominantly effusive character, which is thought to be a reflection of the remarkably high temperatures of the lavas (~ 1,000 ºC.

  9. Mineral chemistry and petrogenesis of the Gurgur Mount volcanic rocks (Northeast Takab

    Directory of Open Access Journals (Sweden)

    Dariush Esmaeily

    2016-12-01

    Full Text Available Andesitic and andesitic-basaltic lavas are widespread over most of the ground surface of the Gurgur area altered mostly by the hydrothermal solutions. The main rock forming minerals in these rocks are plagioclase, pyroxene and olivine affected by the hydrothermal solutions. The altered rocks do contain minerals including calcite, sericite and chlorite. Given the results obtained and the mineral chemistry studies, the clinopyroxenes formed in the area are, chemically, calkalkaline and of diopside-augite type formed in subvolcanic to near surface levels contemporaneous with magma ascending. Plagioclase minerals show zoning textures and lie within the two andesine and albite-oligoclase fields. These units, in terms of total rock chemistry, are classified as the calk-alkaline volcanic rocks formed in the continental arcs. On the other hand, on the trace elements chondrite-normalized diagrams and enriched mantle-normalized multi- element diagrams, the LREE enrichment relative to the HREE is observed. The LILE (i.e. Rb, K and Th and the LREE (e.g. La, Ce and Nd show an enrichment in comparison to the HFSE (Zr, Hf, Nb, Yb, Y and Sm. Given the Nd/Th (1.42-1.15, Zr/Nb (12.27-21.22, Ba/La (18.64-29.77 as well as LILE enrichment associated with depletion in Nb, Ta and Ti, an environment related to the subduction zones can be proposed for the area under study. Moreover, the similarity between the REE distribution pattern and the incompatible elements point to the genetic relationship between these rocks. Finally, on the base of the obtained data, it can be concluded that the volcanic rocks in the Gurgur Mountain were likely formed during the extended magmatism of the Urumieh-Dokhtar in the Cenozoic.

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

    Science.gov (United States)

    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 rock properties due to their wide range of porosity (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 heat capacity increases. The data presented in this paper are expected to improve the statistical confidence on

  11. Petrogenesis of the Cenozoic Volcanic Rocks from the Northern Par of Qinghai-Xizang(Tibet) Plateau

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Based on electron probe analyses of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil lithodistricts,Qinghai-Xizang plateau,the forming conditions including the temperature and pressure of those rocks are studied in this paperAccording to the thermodynamic calculation results of mineral-melt equilibrium,the depth of the asthenosphere superface(about 75-130km)for the northern part of the Qinghai-Xizang plateau during the Cenozoic is suggested.Finally,this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai-Xizang plateau mainly consist of shoshonite series.Their forming temperature is 630-1039℃ and forming pressure is between 2.3-4.0GPa .The rocks were formed in the intracontinental orogenic belt,of which the primary magma was originated from a particular enrichment upper mantle and accreted crust-mantle belt of directly from asthenospheric superface as a result of partial of pyrolite.

  12. 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

    Science.gov (United States)

    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.

  13. Diatreme-forming volcanism in a deep-water faulted basin margin: Lower Cretaceous outcrops from the Basque-Cantabrian Basin, western Pyrenees

    Science.gov (United States)

    Agirrezabala, L. M.; Sarrionandia, F.; Carracedo-Sánchez, M.

    2017-05-01

    Deep-water diatremes and related eruption products are rare and they have been mainly interpreted from seismic-based data. We present lithofacies and geochemistry analysis of two Lower Cretaceous (Albian) deep-water diatremes and associated extra-diatreme volcaniclastic deposits at a well-exposed outcrop of the northern margin of the Basque-Cantabrian Basin (north Iberia). The studied diatremes are located along a N-S trending Albian fault and present sub-circular to elongate sections, inward-dipping steep walls and smooth to very irregular contacts with the host rocks. They are filled by un-bedded mixed breccias constituted by juvenile and lithic (sedimentary, igneous and metamorphic) clasts. Their textural and structural characteristics indicate that they represent lower diatreme and root zones of the volcanic system. Mapping, geochemical and petrologic data from diatreme-fills support their genetic relationship with the extra-diatreme volcaniclastic beds, which would be generated by the eruption of an incipiently vesicular trachytic magma. Studied diatremes result from multiple explosions that lasted over an estimated period of 65 k.y. during the Late Albian (H. varicosum ammonite Zone, pro parte), and reached up to a maximum subsurface depth of ca. 370 m, whereas extra-diatreme volcaniclastic beds were formed by eruption-fed gravity-driven flows on the deep-water (200-500 m) paleoseabed. Petrological features suggest that these diatremes and related extra-diatreme deposits resulted mainly from phreatomagmatic explosions. In addition, organic geochemistry data indicate that the thermal effect of the trachytic melts on the sedimentary host caused the conversion of the abundant organic matter to methane and CO2 gases, which could also contribute significantly to the overpressure necessary for the explosive fragmentation of the magma and the host rocks. Considering the inferred confining pressures (ca. 8-11 MPa) and the possible participation of unvesiculated (or

  14. The Dras arc Complex: lithofacies and reconstruction of a Late Cretaceous oceanic volcanic arc in the Indus Suture Zone, Ladakh Himalaya

    Science.gov (United States)

    Robertson, Alastair; Degnan, Paul

    1994-08-01

    The purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the Ladakh Himalayas. The mainly Late Cretaceous (Aptian—Paleocene?) Dras arc Complex in the Indus Suture Zone (N. India) is reconstructed as an oceanic arc, passing southwards into a proximal to distal forearc apron. The arc complex comprises three structural units. From west to east these are the Suru unit, the Naktul unit and the Nindam Formation. The Suru unit and the Naktul unit are unconformably underlain by dissected Late Jurassic? oceanic crust and mantle. The Suru unit preserves the interior of the arc and is divided into Dras 1 and Dras 2 sub-units. The Dras 1 Sub-unit, of mid-Late Cretaceous age, was intruded by arc plutonics, deformed, then unconformably overlain by the poorly dated Dras 2 Sub-unit (Lower Tertiary). The Dras 1 Sub-unit comprises arc extrusives, volcaniclastic and tuffaceous sedimentary rocks, and mainly redeposited shallow-water limestones. The Dras 2 Sub-unit is dominated by coarse volcaniclastics and lava flows, passing up into rhythmically layered acidic extrusives, with interbedded turbiditic siltstones and siliceous pelagic limestones. Further east, the Naktul unit is mainly clastic, with large volumes of massive volcaniclastic talus, thick-bedded debris flows, volcaniclastic turbidites and reworked shallow-water carbonates. Pillowed extrusives and ribbon radiolarites are present, mainly low in the succession in some areas, while pelagic carbonates are abundant near the top. The Naktul unit is interpreted as a proximal forearc apron. The Nindam Formation in the east is dominated by deep-water volcaniclastic turbidites, tuffaceous sediments and pelagic carbonates, with subordinate debris flows and is interpreted as a distal deep-water forearc succession. Cyclical alternations of mainly volcaniclastics and pelagic carbonates in the Nindam Formation

  15. Simulated Lunar Environment Spectra of Silicic Volcanic Rocks: Application to Lunar Domes

    Science.gov (United States)

    Glotch, T. D.; Shirley, K.; Greenhagen, B. T.

    2016-12-01

    Lunar volcanism was dominated by flood-style basaltic volcanism associated with the lunar mare. However, since the Apollo era it has been suggested that some regions, termed "red spots," are the result of non-basaltic volcanic activity. These early suggestions of non-mare volcanism were based on interpretations of rugged geomorphology resulting from viscous lava flows and relatively featureless, red-sloped VNIR spectra. Mid-infrared data from the Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter have confirmed that many of the red spot features, including Hansteen Alpha, the Gruithuisen Domes, the Mairan Domes, Lassell Massif, and Compton Belkovich are silicic volcanic domes. Additional detections of silicic material in the Aristarchus central peak and ejecta suggest excavation of a subsurface silicic pluton. Other red spots, including the Helmet and Copernicus have relatively low Diviner Christiansen feature positions, but they are not as felsic as the features listed above. To date, the SiO2 content of the silicic dome features has been difficult to quantitatively determine due to the limited spectral resolution of Diviner and lack of terrestrial analog spectra acquired in an appropriate environment. Based on spectra of pure mineral and glass separates, preliminary estimates suggest that the rocks comprising the lunar silicic domes are > 65 wt.% SiO2. In an effort to better constrain this value, we have acquired spectra of andesite, dacite, rhyolite, pumice, and obsidian rock samples under a simulated lunar environment in the Planetary and Asteroid Regolith Spectroscopy Environmental Chamber (PARSEC) at the Center for Planetary Exploration at Stony Brook University. This presentation will discuss the spectra of these materials and how they relate to the Diviner measurements of the lunar silicic dome features.

  16. Petrogenesis and tectonic implications of Early Jurassic volcanic rocks of the Raohe accretionary complex, NE China

    Science.gov (United States)

    Wang, Zhi-Hui; Ge, Wen-Chun; Yang, Hao; Bi, Jun-Hui; Ji, Zheng; Dong, Yu; Xu, Wen-Liang

    2017-02-01

    The Raohe accretionary complex, located at the border between the Russian Far East and Northeastern China, is a significant part of the western Pacific Oceanic tectonic regime. Due to lack of precise age and geochemical constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area remain undefined, resulting in debate about crustal growth mechanisms and subduction-related accretionary processes in Northeastern China. Here, we report whole-rock major and trace element and Sr-Nd isotope data, together with zircon U-Pb ages and in situ zircon Hf isotope data for calc-alkaline andesites, dacites, rhyolites, rhyolitic crystal tuffs, Nb-enriched andesites and basaltic andesites, and high-Mg andesites of the Raohe accretionary complex in NE China. Samples were collected from Late Triassic to Early Jurassic strata. However, geochronological results in this study indicated that the studied magmatism occurred in the Early Jurassic (187-174 Ma). The calc-alkaline volcanic rocks possess geochemical characteristics typical of arc magmas that form at active continental margins, such as moderate enrichments in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs). They have positive εHf(t) values of +3.4 to +10.6 and relatively high (87Sr/86Sr)i values of 0.7047-0.7102. While the Nb-enriched andesites and basaltic andesites have higher TiO2, Hf, Nb, and Zr contents and higher Nb/Ta (24.0-87.6), Nb/U (11.9-75.9), (Nb/Th)PM (0.67-2.70), and (Nb/La)PM (1.95-5.00) ratios than typical arc basalts. They have negative εNd(t) values (-5.5 to -6.0) and relatively variable (87Sr/86Sr)i values of 0.7047-0.7114, suggesting an origin via the partial melting of mantle wedge peridotite that had been metasomatized by slab-derived melt. The high-Mg volcanic rocks, characterized by high MgO and Mg#, TiO2, Al2O3, Cr, Ni, (La/Yb)N and (La/Sm)N, but low Ba/Th ratios, are geochemically similar to

  17. Strontium isotopic ratios of the volcanic rocks from Dogo of the Oki Islands, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Kurasawa, Hajime

    1984-12-01

    The isotopic composition of strontium and the abundances of rubidium and strontium in volcanic rocks from Dogo of the Oki Islands and Takashima in the northwest Kyushu, West Japan, and Ulrungdo of Korea, have been determined. The rubidium and strontium contents for alkakine basalts range from 27.6 to 51.2 ppm and 444 to 723 ppm, and 148 to 208 ppm and 3.7 to 205 ppm for intermediate to felsic suites, respectively. The alkaline basalts are divided into two groups with /sup 87/Sr//sup 86/Sr ratios of the restricted ranges of 0.70481 - 0.70496 and 0.70540 - 0.70575, respectively. However, the /sup 87/Sr//sup 86/Sr ratios of intermediate to felsic rocks of Dogo are relatively high and variable ranging from 0.70706 to 0.71019, which probably reflect the contamination and/or produced by body or partial melting of the basement rocks in this area without crustal assimilation of basaltic magma. In addition, the lead isotopic results indicate that the melting of Precambrian basement rocks possibly yields less radiogenic lead. In the southwest Japan, the /sup 87/Sr//sup 86/Sr ratios of Cenozoic basaltic rocks are clearly different between the San-in and the northwest Kyushu regions, which includes Jeju island. The higher /sup 87/Sr//sup 86/Sr ratios of basalts from the San-in region than that of basalts from the northwest Kyushu region also reflect the different properties of the upper mantle, which means there is regional heterogeneity of Sr isotopic ratios under the southwest Japan arcs. Furthermore, the relatively high and variable /sup 87/Sr//sup 86/Sr ratios of volcanic rocks are particularly concentrated in the southwestern Japan arcs which has probably more continental properties than northeastern Japan arcs.

  18. Geochemical and Sr Nd Pb isotopic evidence for a combined assimilation and fractional crystallisation process for volcanic rocks from the Huichapan caldera, Hidalgo, Mexico

    Science.gov (United States)

    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

  19. Petrogenesis of meta-volcanic rocks from the Maimón Formation (Dominican Republic): Geochemical record of the nascent Greater Antilles paleo-arc

    Science.gov (United States)

    Torró, Lisard; Proenza, Joaquín A.; Marchesi, Claudio; Garcia-Casco, Antonio; Lewis, John F.

    2017-05-01

    Metamorphosed basalts, basaltic andesites, andesites and plagiorhyolites of the Early Cretaceous, probably pre-Albian, Maimón Formation, located in the Cordillera Central of the Dominican Republic, are some of the earliest products of the Greater Antilles arc magmatism. In this article, new whole-rock element and Nd-Pb radiogenic isotope data are used to give new insights into the petrogenesis of the Maimón meta-volcanic rocks and constrain the early evolution of the Greater Antilles paleo-arc system. Three different groups of mafic volcanic rocks are recognized on the basis of their immobile element contents. Group 1 comprises basalts with compositions similar to low-Ti island arc tholeiites (IAT), which are depleted in light rare earth elements (LREE) and resemble the forearc basalts (FAB) and transitional FAB-boninitic basalts of the Izu-Bonin-Mariana forearc. Group 2 rocks have boninite-like compositions relatively rich in Cr and poor in TiO2. Group 3 comprises low-Ti island arc tholeiitic basalts with near-flat chondrite-normalized REE patterns. Plagiorhyolites and rare andesites present near-flat to subtly LREE-depleted chondrite normalized patterns typical of tholeiitic affinity. Nd and Pb isotopic ratios of plagiorhyolites, which are similar to those of Groups 1 and 3 basalts, support that these felsic lavas formed by anatexis of the arc lower crust. Geochemical modelling points that the parental basic magmas of the Maimón meta-volcanic rocks formed by hydrous melting of a heterogeneous spinel-facies mantle source, similar to depleted MORB mantle (DMM) or depleted DMM (D-DMM), fluxed by fluids from subducted oceanic crust and Atlantic Cretaceous pelagic sediments. Variations of subduction-sensitive element concentrations and ratios from Group 1 to the younger rocks of Groups 2 and 3 generally match the geochemical progression from FAB-like to boninite and IAT lavas described in subduction-initiation ophiolites. Group 1 basalts likely formed at magmatic

  20. Quaternary Basanitic Rocks within the Eastern Anatolian Volcanism (Turkey): Petrological and Geochemical Constrains

    Science.gov (United States)

    Özdemir, Yavuz; Mercan, Çaǧrı; Oyan, Vural; Atakul-Özdemir, Ayşe

    2017-04-01

    The Eastern Anatolian Cenozoic continental intraplate volcanism was initiated in Middle Miocene as a result of the convergence between the Arabian and Anatolian plates. The origin of Eastern Anatolian volcanism has been the focus of many petrological studies that have aimed to resolve the relative contributions of asthenospheric mantle and/or lithospheric mantle with/without subduction component in the genesis of magmas that compositionally have many affinities to ocean island basalts (OIB) and volcanic arcs. Volcanism in the region characterized by mainly stratovolcanoes, basaltic lava plateaus and are dominantly spread at the northern parts of Bitlis Pötürge Massif (BPM). Our study focuses on a small scale Quaternary basaltic system that firstly observed within the BPM. The volcanic rocks of our study located 50 km to the south of Lake Van and are basanitic in composition. They exposed along K-G striking tensional fissures and crosscut the Upper unit of the Bitlis Massif. Initial products of the volcanism are scoria fall deposits. Thick basanitic lava flows overly the pyroclastics and formed columnar structures. The basanites are generally fine-grained with phenocrysts of olivine+clinopyroxene. The groundmass is typically of clinopyroxene, olivine and Ti magnetite and Cr spinel with interstitial nepheline. The olivine phenocrysts are typically euhedral to subhedral with Forsterite contents of Fo73-83. Clinopyroxenes are highly calcic and show modest variations in Wo47-52-En34-42-Fs10-15 and are weakly zoned with mg# 89-87 at cores to 86-84 at rims. Nephelines occur as minor minerals within the networks of other groundmass minerals. Ti rich and Fe-Cr spinels occur as inclusions in olivine and clinopyroxenes as well as within the groundmass. LILE and LREE enrichments over HFSE and HREE suggest similarities with magmas generated from enriched mantle sources. EC-AFC modeling of trace element and isotope compositions indicates that assimilation of crustal

  1. Distribution and characteristics of volcanic reservoirs in China

    Institute of Scientific and Technical Information of China (English)

    HUANG Yulong; WANG Pujun; CHEN Shuming

    2009-01-01

    About forty productive oil/gas fields hosted in volcanic reservoirs have been found since 1957 in fourteen basins of China. They can be simply subdivided into two groups, the east and the west. Reservoir volcanic rocks of the east group are predominantly composed of Late Jurassic to Early Cretaceous rhyolite and Tertiary basalt, preferred being considered as rift type volcanics developed in the circum-Pacific tectonic regime. Those of the west are Permo-Carboniferous intermediate/basic volcanic rocks, being island-arc type ones developed in paleo-Asian Ocean tectonic regime.

  2. Geology and geochemistry of palaeoproterozoic low-grade metabasic volcanic rocks from Salumber area, Aravalli Supergroup, NW India

    Indian Academy of Sciences (India)

    L S Shekhawat; M K Pandit; D W Joshi

    2007-12-01

    The Palaeoproterozoic Aravalli Supergroup in Salumber region includes a basal unit of metabasic volcanic rocks (Salumber volcanic rocks) overlain by a volcaniclastic/conglomerate one. Although these volcanic rocks have been metamorphosed to green-schist facies, some primary volcanic features are still preserved. This metabasic volcanic sequence can be further differentiated on the basis of textural variations, and the mineral assemblages are: (a) oligoclase + actinolite + chlorite + epidote; and (b) oligoclase + hornblende+ chlorite + biotite + Fe-Ti oxides. The SiO2 content ranges from ∼47.7 to 55.8% and MgO from ∼4.2 to 12.8%. Geochemical characteristics allow their subdivision into high Mg and Fe tholeiites. Inverse relationship of MgO with silica, alkalis and Zr is generally consistent with fractionation mechanism, also suggested by a change in colour of the rocks from dark greenish to light greenish towards the upper parts of the sequence. These metabasic volcanic rocks are enriched in incompatible trace elements and LREE (La = 30 − 40 × chondrite, Lu = 2 − 5 × chondrite), and demonstrate affinity mainly with MORB and within plate settings in geochemical tectonic discrimination schemes. The geochemical characteristics suggest a complex evolutionary history envisaging derivation of the melt from an enriched heterogeneous lithospheric source.

  3. Research on isotope geology: Isotopes ages of volcanic rocks from Ryeongnam Massif, Korea

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Seong Cheon; Chi, Se Jung; Kim, Yoo Sook [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)

    1997-12-01

    Chronostratigraphy of most volcanic rocks in the Ryeongnam Massif have been undefined or mis-classified in different geological maps due to total absence of reported isotope ages. Twenty-four new isotope ages are given for age-undefined volcanic units and some related igneous bodies. Most of volcanic rocks show high [La/Yb]n ratios and LREE enrichments which are characteristics of subduction-related high-K calc-alkali volcanic rocks occurred in the active continental margin. Preliminary results on carbon and oxygen stable isotope ratios({delta}{sup 13}C=-1.7{approx}-6.2 per mil; {delta}{sup 18} O=-21.6{approx}-24.7 per mil) of druse- or phenocryst-calcite from andesitic and basaltic rocks in the southern coastal region indicate a magmatic origin. Based on new K-Ar whole-rock ages, chronological guidelines are established as follows: 1) Gayasan andesite (78{+-}4Ma) - Gurye andesitic tuff (81{+-}4Ma); 2) Gurye andesite (68{+-}4Ma) - Suncheon andesitic tuff (67{+-}3Ma) - Yeosu basaltic andesite (67{+-}3Ma) - Narodo andesite (70{+-}3Ma); 3) Taebaeg Baegbyeongsan basaltic andesite (62{+-}3Ma) - Gurye Obongsan andesite (64{+-}3Ma) - Yeosu dacite (63{+-}3Ma) - Dolsando andesite (62{+-}3Ma) - Jangheung Buyongsan andesite (65{+-}3Ma); 4) Suncheon Joryedong andesite (55{+-}2Ma) - Goheung andesite (56{+-}3Ma); 5) Taebaeg Baegbyeonsan basaltic andesite (48{+-}2Ma) - Yeosu basalt (51{+-}3Ma). Resetted age (49{+-}2Ma) of an intrusive rhyolite implies the timing of thermal alteration in the Wondong Fe-Mine of the Taebaegsan Mineralized Belt. K-Ar hornblende ages of two hornblendite stocks in the southern Jangsu suggests apparent emplacement-ages of late Triassic (210{+-}9Ma) and early Permian (274{+-}10Ma), independently. K-Ar hornblende age (1023{+-}37Ma) of the Ogbang amphibolite implies a reduction of original age due to later thermal effect probably attributed to either later intrusion or regional metamorphism. (author). 56 refs., 19 tabs., 14 figs.

  4. Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China

    Directory of Open Access Journals (Sweden)

    Tian H.S.

    2014-07-01

    Full Text Available The Yishu Fault Zone runs through the centre of Shandong Province (E China; it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5-8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft-sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. These palaeo-earthquake records are dated around 14-10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.

  5. A new genetic interpretation for the Caotaobei uranium deposit associated with the shoshonitic volcanic rocks in the Hecaokeng ore field, southern Jiangxi, China

    Directory of Open Access Journals (Sweden)

    Dong-Sheng Yang

    2017-03-01

    ± 5.7 Ma in the shoshonitic volcanic rock is broadly coeval with main-stage U mineralization, which is probably attributable to a tectonothermal event related to the intrusion of the granite porphyries and further supports our genetic reinterpretation. It is thus concluded that the granite porphyry intrusions and associated magma may provide the fluids, ore components, and the thermal energy for U mineralization. However, some other types of fluids and metal sources (e.g., meteoric-derived fluids, which are yet to be identified could have been substantially involved in the mineralization process. Our new genetic explanation may point to significant potential for mid-Cretaceous granite-related hydrothermal U deposits in Jiangxi and other parts of Southeast China.

  6. Geochemistry of Mesoproterozoic Volcanic Rocks in the Western Kunlun Mountains:Evidence for Plate Tectonic Evolution

    Institute of Scientific and Technical Information of China (English)

    ZHANG Chuanlin; DONG Yongguan; ZHAO Yu; WANG Aiguo; GUO Kunyi

    2003-01-01

    Mesoproterozoic volcanic rocks occurring in the north of the western Kunlun Mountains can be divided into two groups. The first group (north belt) is an reversely-evolved bimodal series. Petrochemistry shows that the alkalinity of the rocks decreases from early to late: alkaline→calc-alkaline→tholeiite, and geochemistry proves that the volcanic rocks were formed in rifting tectonic systems. The sedimentary facies shows characteristics of back-arc basins. The second (south belt) group, which occurs to the south of Yutian-Minfeng-Cele, is composed of calc-alkaline island arc (basaltic) andesite and minor rhyolite. The space distribution, age and geochemistry of the two volcanite groups indicate that they were formed in a back-arc basin (the first group) and an island arc (the second group) respectively and indicate the plate evolution during the Mesoproterozoic. The orogeny took place at ~1.05 Ga, which was coeval with the Grenville orogeny. This study has provided important geological data for exploring the position of the Paleo-Tarim plate in the Rodinia super-continent.

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

    Science.gov (United States)

    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

  8. The Effect of Degassing Efficiency on the Fragmentation Behavior of Volcanic Rocks

    Science.gov (United States)

    Mueller, S.; Scheu, B.; Spieler, O.; Dingwell, D. B.

    2005-12-01

    The degassing efficiency of volcanic rocks is a decisive measure for the eruptive style and thus the explosivity of a volcano, since it directly affects magma fragmentation behaviour. Vesicles in ascending magma may bear overpressure if the relevant magma viscosity entails a relaxation time scale which is significantly larger than the time scale of ambient pressure reduction due to magma ascent. As long as this overpressure does not overcome the tensile strength of the magma, the system is in a structurally stable state, eventually degassing quiescently via an interconnected pore network. However, if a decompressive event (e.g. sector collapse) disturbs this stable pressure situation, two possible scenarios are conceivable: (1) An interconnected pore network has been established whose permeability is sufficiently high, so vesicle overpressure can be reduced efficiently by gas filtration. (2) The permeability of the network (or cluster of isolated pores, respectively) is low and gas overpressure can not be reduced within the required time scale. In this case the expansion of the pressurized gas may cause bubble wall failure and magma fragmentation into pyroclasts. This study compares experimentally derived fragmentation threshold values of volcanic rock samples, determined with a shock-tube based setup, to unsteady-state permeability values of the same sample sets. In order to cover a wide range in rock properties, we analysed samples from a broad variety of volcanic deposits. Among the treated volcanoes were Colima (Mexico), Bezymianny (Russia), Krakatoa and Merapi, (both Indonesia), Unzen (Japan), Lipari and Campi Flegrei (both Italy), Pinatubo (Philippines), and Santorini (Greece). The correlation of extensive databases of both investigated parameters revealed that permeabilities above a transition zone between 10-13 and 10-12 m2 shift the fragmentation threshold towards higher values. By means of this dataset the influence of the permeability on fragmentation

  9. What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou basin, Tibet)

    Science.gov (United States)

    Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; van Hinsbergen, Douwe J. J.; Dekkers, Mark J.; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

    2015-03-01

    The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus, here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou basin. The lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of 52 Ma for the upper Linzizong, and 40Ar/39Ar dates ( 51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent paleolatitude of 5°N, compared to the upper part ( 20°N) and to underlying Cretaceous strata ( 20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by 52 Ma at 20°N.

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

    Science.gov (United States)

    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. Clinopyroxene application in petrogenesis identification of volcanic rocks associated with salt domes from Shurab (Southeast Qom

    Directory of Open Access Journals (Sweden)

    Somayeh Falahaty

    2016-07-01

    Full Text Available Introduction The study area is located in the Shurab area that is about 50 Km Southeast of Qom. Volcanic rocks of the Shurab area have basaltic composition that is associated with salt and marl units. Igneous rocks of the Shurab area have not been comprehensively studied thus far. Clinopyroxene composition of volcanic rocks, and especially the phenocrysts show Magma chemistry and can help to identify magma series (Lebas, 1962; Verhooge, 1962; Kushiro, 1960, Leterrier et al., 1982, tectonic setting (Leterrier et al., 1982; Nisbet and Pearce, 1977 as well as temperature formation and pressure of rock formation. Some geologists have estimated temperature of clinopyroxene formation by clinopyroxene composition (Adams and Bishop, 1986 and clinopyroxene-olivine couple. So, clinopyroxene is used in this study in order to identify magma series, tectonic setting, plus the temperature and pressure of volcanic rocks of the Shurab. Material and method Clinopyroxene analyses were conducted by wavelength-dispersive EPMA (JEOL JXA-8800R at the Cooperative Centre of Kanazawa University (Japan. The analyses were performed under an accelerating voltage of 15 kV and a beam current of 20 nA. The ZAF program was used for data corrections. Natural and synthetic minerals of known composition were used as standards. The Fe3+ content in minerals was estimated by Droop method (Droop, 1987. Discussion In the Shurab area, the volcanic rocks area with basaltic composition are located 50 km Southeast of Qom. Their age is the early Oligocene and they are associated with the salty marl units of the Lower Red Formation (LRF. The hand specimens of the studied rocks look green. These rocks are intergranular, microlitic, porphyric, vitrophyric and amygdaloidal and they consist of olivine, pyroxene and plagioclase. Accessory minerals contain sphene, apatite and opaque. According to Wo-En-Fs diagram (Morimoto, 1988, clinopyroxenes indicate diopside composition. Clinopyroxenes are

  12. Paleomagnetism of Jurassic and Cretaceous rocks in central Patagonia: a key to constrain the timing of rotations during the breakup of southwestern Gondwana?

    Science.gov (United States)

    Geuna, Silvana E.; Somoza, Rubén; Vizán, Haroldo; Figari, Eduardo G.; Rinaldi, Carlos A.

    2000-08-01

    A paleomagnetic study in Jurassic and Cretaceous rocks from the Cañadón Asfalto basin, central Patagonia, indicates the occurrence of about 25-30° clockwise rotation in Upper Jurassic-lowermost Cretaceous rocks, whereas the overlying mid-Cretaceous rocks do not show evidence of rotation. This constrains the tectonic rotation to be related to a major regional unconformity in Patagonia, which in turn seems to be close in time with the early opening of the South Atlantic Ocean. The sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern Gondwana, suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent. On the other hand, the mid-Cretaceous rocks in the region yield a paleopole located at Lat. 87° South, Long. 159° East, A95=3.8°. This pole position is consistent with coeval high-quality paleopoles of other plates when transferred to South American coordinates, implying it is an accurate determination of the Aptian (circa 116 Ma) geomagnetic field in South America.

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

    Science.gov (United States)

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

    2015-04-01

    Mafic xenoliths coexisting with the peridotitic ones in rocks from Polish part of Cenozoic European Volcanic Province have been scarcely examined. (Bakun-Czubarow and Białowolska, 2003, Mineralogical Society of Poland- Spec. Pap. and references therein; Matusiak, 2006, Min. Polonica- Spec. Pap.; Puziewicz et al., 2011, JoP). In this study we present new results on mafic and ultramafic xenolithic rocks from the Wilcza Góra, Winna Góra, Góra Świątek, Mnisia Górka and Grodziec volcanic rocks in the Złotoryja-Jawor Volcanic Complex. The studied xenoliths are either plagioclase-free (clinopyroxenite, websterite) or plagioclase-bearing (anorthosite, gabbro, olivine-bearing gabbro and norite). Both the types may occur in the same volcanic rock. The cumulative xenoliths are smaller than peridotitic ones, blackish and show clear cumulative, coarse grained textures. Beside the rock-forming phases, the xenoliths occasionally contain spinel, sulfides and amphibole. Usually clinopyroxene grains occurring in gabbros are strongly corroded or disintegrated, while other phases are well-preserved. Contacts between xenolith and host volcanic rock are usually sharp with subhedral crystals of clinopyroxene growing at the xenolith surface. The mineral grains are usually zoned and chemical equilibrium between phases is scarce. Clinopyroxene in plagioclase-free rocks has composition of diopside with occasionally elevated Al, Ti and Cr contents. It's mg# varies from 0.89 to 0.79. It is slightly to moderately enriched in LREE; the REE patterns are concave, and the normalized values vary significantly between localities. It shows negative Sr anomaly, depth of Ti anomaly is variable. Orthopyroxene is Al-rich enstatite with mg# varying from 0.85 down to 0.75. Orthopyroxene in websterites is LREE depleted and show strong positive Ti and Zr-Hf anomalies. Opaques are ilmenite - Ti-magnetite solid solution and/or sulfides Clinopyroxene forming plagioclase-bearing rocks also has composition

  14. 40Ar-39Ar dating and tectonic implications of volcanic rocks recovered at IODP Hole U1342A and D on Bowers Ridge, Bering Sea

    Science.gov (United States)

    Sato, Keiko; Kawabata, Hiroshi; W. Scholl, David; 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.

  15. An integrated petrophysical and rock physics analysis to improve reservoir characterization of Cretaceous sand intervals in Middle Indus Basin, Pakistan

    Science.gov (United States)

    Azeem, Tahir; Chun, Wang Yan; MonaLisa; Khalid, Perveiz; Xue Qing, Liu; Ehsan, Muhammad Irfan; Jawad Munawar, Muhammad; Wei, Xie

    2017-03-01

    The sand intervals of the Lower Goru Formation of the Cretaceous age, widely distributed in the Middle and Lower Indus Basin of Pakistan, are proven reservoirs. However, in the Sawan gas field of the Middle Indus Basin, these sandstone intervals are very deep and extremely heterogeneous in character, which makes it difficult to discriminate lithologies and fluid saturation. Based on petrophysical analysis and rock physics modeling, an integrated approach is adopted to discriminate between lithologies and fluid saturation in the above-mentioned sand intervals. The seismic velocities are modeled using the Xu–White clay–sand mixing rock physics model. The calibrated rock physics model shows good consistency between measured and modeled velocities. The correlation between measured and modeled P and S wave velocities is 92.76% and 84.99%, respectively. This calibrated model has been successfully used to estimate other elastic parameters, even in those wells where both shear and sonic logs were missing. These estimated elastic parameters were cross-plotted to discriminate between the lithology and fluid content in the target zone. Cross plots clearly separate the shale, shaly sand, and gas-bearing sand clusters, which was not possible through conventional petrophysical analysis. These data clusters have been exported to the corresponding well for the purpose of interpolation between wells and to analyze the lateral and vertical variations in lithology and fluid content in the reservoir zone.

  16. Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

    Science.gov (United States)

    Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

    2008-07-01

    Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges betweenCampanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment

  17. The character and significance of basement rocks of the southern Molucca Sea region

    Science.gov (United States)

    Hall, Robert; Nichols, Gary; Ballantyne, Paul; Charlton, Tim; Ali, Jason

    Pre-Neogene basement rocks in the southern Molucca Sea region include ophiolitic rocks, arc volcanic rocks and continental rocks. The ophiolitic complexes are associated with arc and forearc igneous and sedimentary rocks. They are interpreted as the oldest parts of the Philippine Sea Plate with equivalents in the ridges and plateaux of the northern Philippine Sea. In the Molucca Sea region igneous components include rocks with a "supra-subduction zone" character, bonintic volcanic rocks and basic volcanic rocks with a "within-plate" character; "MORB-type" rocks are rare or absent. The ophiolitic rocks are overlain by Upper Cretaceous and Eocene sedimentary and volcanic rocks. Plutonic rocks of island arc origin which intrude the ophiolites yield Late Cretaceous radiometric ages and amphibolites with ophiolitic protoliths yield Eocene ages. The "supra-subduction zone" ophiolites are speculated to have originated during a mid-Cretaceous plate reorganization event. For the Late Cretaceous and Eocene the present-day Marianas arc and forearc provides an attractive model. Volcanic rocks from the basement of Morotai, western Halmahera and much of Bacan. These also have an island arc character and are probably of Late Cretaceous-Paleogene age. Both the arc volcanic rocks and the ophiolitic complexes are overlain by shallow water Eocene limestones and an Oligocene rift sequence including basaltic pillow lavas and volcaniclastic turbidites. The distribution of the Eocene-Oligocene sequences indicate pre-Mid/Late Eocene amalgamation of the ophiolitic and arc terranes. Mid Eocene-Oligocene extension appears to be synchronous with opening of the central West Philippine Basin. Continental crust probably arrived in this region in the Late Paleogene-Early Neogene, either due to collision of the Australian margin with Pacific arc-ophiolite terranes or by terrane movement along the Sorong Fault Zone.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  1. Altered volcanic ash layers of the Late Cretaceous San Felipe Formation, Sierra Madre Oriental (Northeastern Mexico): Usbnd Pb geochronology, provenance and tectonic setting

    Science.gov (United States)

    Velasco-Tapia, Fernando; Martínez-Paco, Margarita; Iriondo, Alexander; Ocampo-Díaz, Yam Zul Ernesto; Cruz-Gámez, Esther María; Ramos-Ledezma, Andrés; Andaverde, Jorge Alberto; Ostrooumov, Mikhail; Masuch, Dirk

    2016-10-01

    A detailed petrographic, geochemical, and Usbnd Pb geochronological study of altered volcanic ash layers, collected in eight outcrops of the Late Cretaceous San Felipe Formation (Sierra Madre Oriental, Northeastern Mexico), has been carried out. The main objectives have been: (1) to establish a deposit period, and (2) to propose a reliable provenance-transport-deposit-diagenetic model. These volcano-sedimentary strata represent the altered remains of vitreous-crystalline ash (main grains: quartz + K-feldspar (sanidine) + Na-plagioclase + zircon + biotite; groundmass: glass + calcite + clinochlore + illite) deposited and preserved in a shallow, relatively large in area, open platform environment. Major and trace element geochemistry indicate that parent volcanism was mainly rhyodacitic to rhyolitic in composition. Discrimination diagrams suggest a link to continental arc transitional to extension tectonic setting. Usbnd Pb geochronology in zircon has revealed that the volcanic ash was released from their sources approximately during the range 84.6 ± 0.8 to 73.7 ± 0.3 Ma, being transported to the depocenters. Burial diagenesis process was marked by: (a) a limited recycling, (b) the partial loss of original components (mainly K-feldspar, plagioclase, biotite and glass), and (c) the addition of quartz, calcite, illite and clinochlore. The location of the source area remains uncertain, although the lack of enrichment in Zr/Sc ratio suggests that ashes were subjected to relatively fast and short-distance transport process. El Peñuelo intrusive complex, at 130-170 km west of the depocenters, is the nearest known zone of active magmatism during the Upper Cretaceous. This intermediate to felsic pluton, characterized by a geochemical affinity to post-orogenic tectonic setting, could be linked to the volcanic sources.

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

    Science.gov (United States)

    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.

  3. Properties of middle-late Proterozoic volcanic rocks in South Qinling and the Precambrian continental break-up

    Institute of Scientific and Technical Information of China (English)

    夏林圻; 夏祖春; 徐学义

    1996-01-01

    In South Qinling, the volcanic series of the middle-late Proterozoic Yunxi Group, Yaolinghe Group, Xi.xiang Group and Bikou Group have characteristics of the continental rift volcanic rocks or continental flood basalts and are formed in continental intraplate tensional setting. The enrichment of incompatible elements, high εNd values and low-medium 87Sr/86Sr initial ratios of these volcanic rocks indicate that they were derived from asthenospheric plume. Under the action of the intense pull-apart in lithosphere, the mantle plume upwelled, quickly decompressed and melted, and finally produced magma. This tensional process made the continental crust break and eventually led to an oceanic basin in late Proterozoic. The middle-late Proterozoic volcanism is a precursor of Precarabrian continental break-up in the South Qinling.

  4. Hot climate inhibits volcanism on Venus: Constraints from rock deformation experiments and argon isotope geochemistry

    Science.gov (United States)

    Mikhail, Sami; Heap, Michael J.

    2017-07-01

    The disparate evolution of sibling planets Earth and Venus has left them markedly different. Venus' hot (460 °C) surface is dry and has a hypsometry with a very low standard deviation, whereas Earth's average temperature is 4 °C and the surface is wet and has a pronounced bimodal hypsometry. Counterintuitively, despite the hot Venusian climate, the rate of intraplate volcano formation is an order of magnitude lower than that of Earth. Here we compile and analyse rock deformation and atmospheric argon isotope data to offer an explanation for the relative contrast in volcanic flux between Earth and Venus. By collating high-temperature, high-pressure rock deformation data for basalt, we provide a failure mechanism map to assess the depth of the brittle-ductile transition (BDT). These data suggest that the Venusian BDT likely exists between 2 and 12 km depth (for a range of thermal gradients), in stark contrast to the BDT for Earth, which we find to be at a depth of ∼25-27 km using the same method. The implications for planetary evolution are twofold. First, downflexing and sagging will result in the sinking of high-relief structures, due to the low flexural rigidity of the predominantly ductile Venusian crust, offering an explanation for the curious coronae features on the Venusian surface. Second, magma delivery to the surface-the most efficient mechanism for which is flow along fractures (dykes; i.e., brittle deformation)-will be inhibited on Venus. Instead, we infer that magmas must stall and pond in the ductile Venusian crust. If true, a greater proportion of magmatism on Venus should result in intrusion rather than extrusion, relative to Earth. This predicted lower volcanic flux on Venus, relative to Earth, is supported by atmospheric argon isotope data: we argue here that the anomalously unradiogenic present-day atmospheric 40Ar/36Ar ratio for Venus (compared with Earth) must reflect major differences in 40Ar degassing, primarily driven by volcanism. Indeed

  5. Discovery and Significance of High CH4 Primary Fluid Inclusions in Reservoir Volcanic Rocks of the Songliao Basin, NE China

    Institute of Scientific and Technical Information of China (English)

    WANG Pujun; HOU Qijun; WANG Keyong; CHEN Shumin; CHENG Rihui; LIU Wanzhu; LI Quanlin

    2007-01-01

    Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that: (1) up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; (2) high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bearing CO2 reservoirs that are rich in helium and with a high 3He/4He ratio and which show reversed order of δ13C in alkane; (3) in gas reservoirs of such abiotic methane (>80%)and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42mole%, and the reversed order of δ13C in alkane is sometimes irregular in the corresponding gas pools;(4) a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.

  6. Petrology, Geochemistry and Nd-Sr-Pb Isotopic Properties of Volcanic Rocks in Daheishan Island, Penglai, Shandong Province

    Institute of Scientific and Technical Information of China (English)

    Fu Yongtao; Li Anchun

    2003-01-01

    The major elements, trace elements, K-Ar age and Sr-Nd-Pb isotopic systems of the Cenozoic volcanic rocks in Daheishan Island and Cishan, Penglai, Shandong Province are measured. The volcanic rocks ( olivine-nephelinite and nepheline-basanite ) in Daheishan Island erupted periodically in an interval of 0.32 Ma, from 8.72 Ma, 8.39 Ma, 8.08 Ma to 7.73 Ma. The volcanic rocks are all rich in light REEs. They are similar to the OIB-type alkali basalt in the trace elements normalized model by primordial mantle: rich in high field elements such as Nb and Ta, and imcompatible elements such as Cs, Rb, Ba, Th, U. The volcanic rocks show a depletion of K and Rb elements. It is suggested by the trace elements that the olivine-nephelinite in Daheishan Island is originated from deep resources under the continental mantle. ε Nd (0) values of the volcanic rocks in Daheishan Island and Cisban are 5.31 ~ 8.51 and 7.33 respectively, suggesting that the volcanic rocks are from the depleted mantle resources, which have higher Sm/Nd ratios than the CHUR. 143Nd /144Nd ratios of Daheishan Island olivine-nephelinite and Cishan alkali basalts are 0.512 910 ~ 0.513 074 and 0.513 014 respectively. The 87Sr /86Sr of Daheishan Island volcanic rocks are lower than that of Cishan, 0.703 427 ~ 0.703 482 and 0.703 895 respectively. The Daheishan Island olivinenephelinite has the Pb isotopic values as follows: 206Pb /204pb = 18.028 9 ~ 17.972 8, 207Pb /204pb= 15.435 8 ~ 15.402 2 and 208Pb /204Pb = 38.087 6 ~ 37.997 5, lower than those of Cishan basanite. The Cishan basanite has 206Pb /204pb = 18.240 1, 207Pb /204Pb = 15.564 5 and 208Pb /204pb = 38.535. The authors suggest that the olivine-nephelinite in Daheishan Island is similar to the E-type MORB or Hawaii OIB, and the alkali basalts in Cishan similar to the Kerguelen OIB. The dominant mantle components of DM+PREMA and perhaps DM ( Dupal type ) are the dominant mantle components for volcanic rocks in Daheishan Island and Cishan. The

  7. Potash-rich volcanic rocks and lamprophyres in western Shandong Province: 40Ar39Ar dating and source tracing

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Highly precise 40Ar39Ar dating results demonstrate that the ages of potash-rich volcanic rocks in western Shandong Province are 114.7-124.3 Ma, and that of the lamprophyres is 119.6 Ma. The potash-rich volcanic rocks have relatively high (87Sr/86Sr)i ratios ( 0.708715-0.711418)and distinctly negative εNd values ( -11.47 - -17.54), and are enriched in radiogenic lead (206Pb/204pb=17.341-17.622,207pb/204Pb=15.525-15.538, 208Pb/204pb = 37.563-37.684).Similarly, the lamprophyres also have quite low εNd values ( -11.57 - -19.64). Based on the fact that the Sr, Nd and Pb isotopic compositions of potash-rich volcanic rocks are very consistent with that of the clinopyroxene separates, and by integrating comprehensive analyses of their tectonic settings,and extensive comparisons of the Sr, Nd isotopic compositions with that of the related simultaneous rocks, it is concluded that the potash-rich volcanic rocks and lamprophyres in western Shandong Province were most possibly derived from the partial melting of enriched mantle which was caused by source contamination and metasomatism of subducted continental crustal materials.``

  8. In situ Laser Induced Breakdown Spectroscopy as a tool to discriminate volcanic rocks and magmatic series, Iceland

    Energy Technology Data Exchange (ETDEWEB)

    Roux, C.P.M., E-mail: clement.roux@u-bourgogne.fr [Laboratoire interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, BP 47 870, F-21078 Dijon Cedex (France); Rakovský, J.; Musset, O. [Laboratoire interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, BP 47 870, F-21078 Dijon Cedex (France); Monna, F. [Laboratoire ARTéHIS, UMR 6298 CNRS-Université de Bourgogne, 6 Boulevard Gabriel, F-21000 Dijon (France); Buoncristiani, J.-F.; Pellenard, P.; Thomazo, C. [Laboratoire Biogéosciences, UMR 6282 CNRS-Université de Bourgogne, 6 Boulevard Gabriel, F-21000 Dijon (France)

    2015-01-01

    This study evaluates the potentialities of a lab-made pLIBS (portable Laser-Induced Breakdown Spectroscopy) to sort volcanic rocks belonging to various magmatic series. An in-situ chemical analysis of 19 atomic lines, including Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Na, Si, Sr and Ti, from 21 sampled rocks was performed during a field exploration in Iceland. Iceland was chosen both for the various typologies of volcanic rocks and the rugged conditions in the field in order to test the sturdiness of the pLIPS. Elemental compositions were also measured using laboratory ICP-AES measurements on the same samples. Based on these latter results, which can be used to identify three different groups of volcanic rocks, a classification model was built in order to sort pLIBS data and to categorize unknown samples. Using a reliable statistical scheme applied to LIBS compositional data, the classification capability of the pLIBS system is clearly demonstrated (90–100% success rate). Although this prototype does not provide quantitative measurements, its use should be of particular interest for future geological field investigations. - Highlights: • Portable LIBS applied to field geology • Fast semi-quantitative geochemical analysis of volcanic rocks and magmatic series • Discriminant analysis and statistical treatments for LIBS compositional data.

  9. Petrology and U-Pb zircon geochronology of bimodal volcanic rocks from the Maierze Group, northern Tibet: Constraints on the timing of closure of the Banggong-Nujiang Ocean

    Science.gov (United States)

    Fan, Jian-Jun; Li, Cai; Xie, Chao-Ming; Wang, Ming; Chen, Jing-Wen

    2015-06-01

    We present new zircon U-Pb dates, major and trace element chemistry, and Hf isotopic compositions for bimodal volcanic rocks of the Maierze Group (MG) in the Maierze area of the Southern Qiangtang-Baoshan block, northern Tibet. We discuss the implications of these data for the evolution of this region. The MG bimodal volcanic rocks consist of basalts and dacites that yield LA-ICP-MS zircon U-Pb ages of 122 and 120 Ma, respectively. The MG basalts have light rare earth element (LREE)-enriched chondrite-normalized REE patterns (LaN/YbN = 13-14), high Ti/V ratios (45-64), high Zr (190-270 ppm) and Nb (22-41 ppm) concentrations, and Zr/Y ratios (7-9) that are similar to those of within-plate basalts. The MG basalts also have low MgO and total Fe2O3 (TFe2O3) concentrations, significant enrichments in the LREE and the light ion lithophile elements (LILEs; Rb, Ba, Th, U and Pb), and weak depletions in the high field strength elements (HFSE; Nb, Ta, and Ti), all of which are clearly evident in primitive-mantle-normalized multi-element variation diagrams. The MG dacites are more enriched in the LILE (e.g., Rb, Ba, Th, U, K, and Pb) and more depleted in the HFSE (e.g., Nb, Ta, and Ti) than the MG basalts. Moreover, the dacites have variable zircon εHf(t) values (- 6.3 to + 6.3). These features indicate that the parental magma for the MG basalts was likely derived from an enriched lithospheric mantle source that was contaminated by subduction-related fluids or melts. In contrast, the MG dacites were derived from mixing of the MG basaltic magma with a second magma derived from partial melting of the continental crust. The geochemical and Hf isotopic characteristics of the MG bimodal volcanic rocks suggest that they formed during the initial stages of development of a back-arc basin. From south to north, the Bangong-Nujiang suture zone, the Duolong gold-rich porphyry copper deposit, and the Maierze bimodal rocks are interpreted to represent a remnant of a complete volcanic arc

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

    Science.gov (United States)

    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.

  11. A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; WEI Qirong; ZHANG Zhibin; ZHANG Hu

    2006-01-01

    Geochemical characteristics of the Upper Permian ( P2 ) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks; the volcanic rocks are characterized by high Al2O3 and low TiO2 , with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt.

  12. The Cretaceous System in China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper provides an outline of Cretaceous stratigraphy and paleogeography in China,which is based on rich data obtained from recent researches. Cretaceous deposits are widespread in China. Most strata are of nonmarine origin and marine sediments occur only in Tibet, western Tarim Basin of Xinjiang, Taiwan and limited localities of eastern Heilongjiang. All deposits are rich in fossils and well-constrained biostratigraphically. The stratigraphic successions of different regions are illustrated, and general stratigraphic division and correlation have been introduced. The marine deposits are described in the Tibetan Tethys, Kashi-Hotan Region of Xinjiang, eastern Heilongjiang,western Yunnan and Taiwan; the nonmarine deposits are outlined from northeast China, southeast China, southern interior China, southwest China, the Shaanxi-Gansu-Ningxia region, and northwestern China intermontane basins. The sedimentary facies and paleogeography are diversified.In Tibet the basin evolution is largely related to the subduction and collision of the Indian Plate against the Eurasian Continent, and shows a tectonic evolution in the Cretaceous. Foraminifera are a dominant biota in the Tibet Tethys. Nonmarine sediments include variegated and red beds, coal- or salt-bearing horizons, and volcanic rocks. These deposits contain diverse and abundant continental faunas and floras, as well as important coal and oil resources. The Cretaceous stratigraphy and paleogeography in China have presented a foundation for geological studies.

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

    Science.gov (United States)

    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.

  14. Exotic lamproites or normal ultrapotassic rocks? The Late Miocene volcanic rocks from Kef Hahouner, NE Algeria, in the frame of the circum-Mediterranean lamproites

    Science.gov (United States)

    Lustrino, Michele; Agostini, Samuele; Chalal, Youcef; Fedele, Lorenzo; Stagno, Vincenzo; Colombi, Francesco; Bouguerra, Abdellah

    2016-11-01

    The late Miocene (11-9 Ma) volcanic rocks of Kef Hahouner, 40 km NE of Constantine (NE Algeria), are commonly classified as lamproites in literature. However, these rocks are characterized by an anhydrous paragenesis with plagioclase and Mg-rich olivine phenocrysts, set in a groundmass made up of feldspars, pyroxenes and opaque minerals. Thus, we classify the Kef Hahouner rocks as ultrapotassic shoshonites and latites, having K2O > 3 wt.%, K2O/Na2O > 2.5, MgO > 3-4 wt.%, SiO2 < 55-57 wt.% and SiO2/K2O < 15. All the investigated samples show primitive mantle-normalized multi-element patterns typical of orogenic (arc-type) magmas, i.e. enriched in LILE (e.g. Cs, Rb and Ba) and LREE (e.g. La/Yb = 37-59) with respect to the HFSE, peaks at Pb and troughs at Nb and Ta. Initial isotopic ratios are in the range of 87Sr/86Sr = 0.70874-0.70961, 143Nd/144Nd = 0.51222-0.51223, 206Pb/204Pb = 18.54-18.60, 207Pb/204Pb = 15.62-15.70 and 208Pb/204Pb = 38.88-39.16. The Kef Hahouner volcanic rocks show multi-element patterns similar to the other circum-Mediterranean lamproites and extreme Sr, Nd and Pb isotopic compositions. Nevertheless, the abundant plagioclase, the presence of Al-rich augite coupled with high Al2O3 whole rock compositions (9.6-21.4 wt.%), and the absence of phlogopite are all at inconsistent with the definition of lamproite. We reviewed the rocks classified as lamproites worldwide, and found that many of these rocks, as for the Kef Hahouner samples, should be actually defined as "normal" potassic to ultrapotassic volcanic rocks. Even the grouping of lamproites into "orogenic" and "anorogenic" types appears questionable.

  15. Newly developed evidence for the original Tethysan island-arc volcanic rocks in the southern segment of the South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.

  16. Carboniferous Bimodal Volcanic Rocks and Their Plate Tectonic Setting,Hainan Island

    Institute of Scientific and Technical Information of China (English)

    夏邦栋; 施光宇; 等

    1992-01-01

    The Carboniferous volcanic rocks in western Hainan Island consist of a series of oceanic tholeite and rhyoporphyrite,showing bimodal nature.Similar geochemical characters,in terms of abun-daces and relative rations of incompatible elements and REE and the REE patterns,between the basalt and continental rift-associated tholeiite indicate the occurrence of Late Paleozoic rifting in the area.The basaltic magma,with a low degree of evolution,was originated from deep mantle,show-ing contamination by low crustal material.The rhyolite is thought to be formed from partial melting of the continental crust by higher thermal flow in a rift environment rather than from fractional crystallization of a basaltic magma.

  17. Discovery of the granulite xenoliths in Cenozoic volcanic rocks from Hoh Xil, Tibetan plateau

    Institute of Scientific and Technical Information of China (English)

    LAI Shaocong; YI Haisheng; LIN Jinhui

    2003-01-01

    Two-pyroxene granulite and clinopyroxene granulite xenoliths have been recently discovered in the Late Paleogene to Neogene volcanic rocks (with ages in the range of 4.27~44.60 Ma) that outcropped in Hoh Xil, central Tibetan plateau. Based on the electron microprobe analysis data, the xenoliths provide constraints for the formation equilibrium temperatures of the two-pyroxene granulite being about 783 to 818 ℃ as determined by two-pyroxene thermometry and the forming pressure of the clinopyroxene granulite being about 0.845 to 0.858 GPa that is equivalent to 27.9~28.3 km depth respectively. It indicates that these granulite xenoliths represent the samples from the middle part of the thickened Tibetan crust. This discovery is important and significant to making further discussion on the component and thermal regime of the deep crust of the Tibetan plateau.

  18. K-Ar geochronology of the late cenozoic volcanic rocks of the Cordillera Occidental, southernmost Peru

    Science.gov (United States)

    Tosdal, Richard M.; Farrar, Edward; Clark, Alan H.

    1981-05-01

    Twenty-four K-Ar radiometric ages are presented for late Cenozoic continental volcanic rocks of the Cordillera Occidental of southernmost Perú (lat. 16° 57'-17° 36'S). Rhyodacitic ignimbrite eruptions began in this transect during the Late Oligocene and continued episodically through the Miocene. The development of andesitic-dacitic strato volcanoes was initiated in the Pliocene and continues to the present. The earliest ignimbrite flows (25.3-22.7 Ma) are intercalated in the upper, coarsely-elastic member of the Moquegua Formation and demonstrate that this sedimentary unit accumulated in a trough, parallel to Andean tectonic trends, largely in the Oligocene. More voluminous ash-flow eruptions prevailed in the Early Miocene (22.8-17.6 Ma) and formed the extensively preserved Huaylillas Formation. This episode was coeval with a major phase of Andean uplift, and the pyroclastics overlie an erosional surface of regional extent incised into a Paleogene volcano-plutonic arc terrain. An age span of 14.2-8.9 Ma (mid-Late Miocene) is indicated for the younger Chuntacala Formation, which again comprises felsic ignimbrite flows, largely restricted to valleys incised into the pre-Huaylillas Formation lithologies, and, at lower altitudes, an extensive aggradational elastic facies. The youngest areally extensive ignimbrites, constituting the Sencca Formation, were extruded during the Late Miocene. In the earliest Pliocene, the ignimbrites were succeeded by more voluminous calcalkaline, intermediate flows which generated numerous large and small stratovolcanoes; these range in age from 5.3 to 1.6 Ma. Present-day, or Holocene, volcanism is restricted to several large stratovolcanoes which had begun their development during the Pleistocene (by 0.7 Ma). The late Oligocene/Early Miocene (ca. 22-23 Ma) reactivation of the volcanic arc coincided with a comparable increase in magmatic activity throughout much of the Cordilleras Occidental and Oriental of the Central Andes.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  20. Physical Volcanology and Hazard Analysis of a Young Volcanic Field: Black Rock Desert, Utah, USA

    Science.gov (United States)

    Hintz, A. R.

    2009-05-01

    The Black Rock Desert volcanic field, located in west-central Utah, consists of ~30 small-volume monogenetic volcanoes with compositions ranging from small rhyolite domes to large basaltic lava flow fields. The field has exhibited bimodal volcanism for > 9 Ma with the most recent eruption of Ice Springs volcano ˜ 600 yrs ago. Together this eruptive history along with ongoing geothermal activity attests to the usefulness of a hazard assessment. The likelihood of a future eruption in this area has been calculated to be ˜ 8% over the next 1 Ka (95% confidence). However, many aspects of this field such as the explosivity and nature of many of these eruptions are not well known. The physical volcanology of the Tabernacle Hill volcano, suggests a complicated episodic eruption that may have lasted up to 50 yrs. The initial phreatomagmatic eruptions at Tabernacle Hill are reported to have begun ~14 Ka. This initial eruptive phase produced a tuff cone approximately 150 m high and 1.5 km in diameter with distinct bedding layers. Recent mapping and sampling of Tabernacle Hill's lava field, tuff cone and intra-crater deposits were aimed at better constraining the eruptive history, physical volcanology, and explosive energy associated with this eruption. Blocks ejected during the eruption were mapped and analyzed to yield minimum muzzle velocities of 60 - 70 meters per second. These velocities were used in conjunction with an estimated shallow depth of explosion to calculate an energy yield of ˜ 0.5 kT.

  1. Paleomagnetism of basalts from Alborz: Iran part of Asia in the Cretaceous

    NARCIS (Netherlands)

    Wensink, H.; Varekamp, J.C.

    1980-01-01

    Paleomagnetic results are reported from 20 sites within three units of volcanic rocks of Cretaceous age from the Central Albon Mountains, Iran. After application of progressive demonetization either with alternating magnetic fields or with heating, the mean characteristic remanence direction is foun

  2. Evaluation of the nature, origin and potentiality of the subsurface Middle Jurassic and Lower Cretaceous source rocks in Melleiha G-1x well, North Western Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed M. El Nady

    2015-09-01

    Full Text Available The present work aims to evaluate the nature and origin of the source rock potentiality of subsurface Middle Jurassic and Lower Cretaceous source rocks in Melleiha G-1x well. This target was achieved throughout the evaluation of total organic carbon, rock Eval pyrolysis and vitrinite reflectance for fifteen cutting samples and three extract samples collected from Khatatba, Alam El Bueib and Kharita formations in the studied well. The result revealed that the main hydrocarbon of source rocks, for the Middle Jurassic (Khatatba Fm. is mainly mature, and has good capability of producing oil and minor gas. Lower Cretaceous source rocks (Alam El Bueib Fm. are mature, derived from mixed organic sources and have fair to good capability to generate gas and oil. Kharita Formation of immature source rocks originated from terrestrial origin and has poor to fair potential to produce gas. This indicates that Khatatba and Alam El Bueib formations take the direction of increasing maturity far away from the direction of biodegradation and can be considered as effective source potential in the Melleiha G-1x well.

  3. Late Cretaceous source rocks of a section in the Eastern Venezuelan Basin

    Energy Technology Data Exchange (ETDEWEB)

    Truskowski, I.I. (Intevep S.A., Caracas (Venezuela))

    1993-02-01

    Micropaleontological and geochemical studies of Querecual and San Antonio formations were carried on a section (Cerro Negro) of the Serrania del Interior, in order to establish the imprint of the late Cretaceous [open quotes]Oceanic Anoxic Events[close quotes] (OAE), mentioned by numerous authors. For this purpose, the distribution patterns of microfossil assemblages, variations of organic matter content and, V/Ni ratios have been taken into account to recognize anoxic conditions. This stratigraphic section is characterized by the following: [open quotes]Anaerobic[close quotes] bottom conditions with oxigenated surface waters, indicated by the presence of a well-developed planktonic forms and virtually no benthic foraminifera. These conditions fluctuated along the section, prevailing at its base. Dysaerobic bottom conditions indicated by a low-diversity benthic foraminifera and, a well oxigenated surface waters suggested by high concentration of planktonic biota (foraminifer, radiolaria, and nannoplankton). An increase of organic matter content (TOC: 5-6%) and V/Ni ratios (3.7-4.2) are related to the [open quotes]anaerobic[close quotes] levels. Marine sediments of Brazilian continental margin display similar characteristics, which indicate that deposition of anoxic sediments was extended to the North of South America.

  4. Paleostress analysis of the Cretaceous rocks in the eastern margin of the Dead Sea transform, Jordan

    Science.gov (United States)

    Dead Sea transform, the; Diabat, Jordan A. A.; Atallah, M.; Salih, M. R.

    2004-04-01

    This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes ( σ1, σ2 and σ3) and the ratio of the principal stress differences ( R) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first is characterized by NNW-SSE compression and ENE-WSW extension and related to Middle Miocene-Recent sinistral movement along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW-ESE compression and NNE-SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.

  5. Paleotemperatures and paleodepths of the Upper Cretaceous rocks in El Qusaima, Northeastern Sinai, Egypt

    Science.gov (United States)

    Orabi, O. H.; Zahran, E.

    2014-03-01

    The planktonic foraminiferal morphogroups and planktonic quantitative analysis as well as the lithological variations across the Coniacian to Maastrichtian sediments of El Qusaima section (Northeastern Sinai, Egypt) are studied in detail in order to detect the prevailing paleoecological conditions along these sediments. At the studied area of El Qusaima section there is a gradual cooling started at the base of Globotruncana elevata Zone (early-middle Campanian) of the lower part of the Markha Member and continued till Globotruncana aegyptiaca Zone (Late Campanian) of the upper part of the Markha Member. This trend corresponds to the onset of a global cooling that began at about 73 Ma (Late Campanian) and ended the Cretaceous greenhouse climate mode. At El Qusaima section, a gradual warming started at the base of Pseudogumbelina palpebra Zone (Late Maastrichtian) and continued till Plummerita hantkeninoides Zone (latest Maastrichtian) due to the high abundance of Plummerita hantkeninoides and Plummeritareicheli, which have been flourishing in warm waters. So this warming near the end of the Maastrichtian is a global event as shown by many authors.

  6. Discovery of Late Permian Jianshanzi volcanic rocks in Qinghe valley of northern Liaoning and its geologic significance

    Institute of Scientific and Technical Information of China (English)

    Yuejun CHEN; Chunlin SUN; Yuewu SUN

    2008-01-01

    Jianshanzi volcanic rocks at Qinghe valley in the northern Liaoning were considered belonging to Early Proterozoic Gaojiayu Formation of Liaohe Group, or to Early Cambrian Beidagou Formation of Qinghezhen Group, or Middle-Late Proterozoic Shenjiapu Formation-Complex of Kaiyuan Group-complex. Dating the zircons from the dacite with schistosity is 2 506 Ma in method of U-Pb (SHRIMP). This evidence indicates the rocks may be referred to Late Permian in age. Discovery of the rocks is significant to re-recognize stratigraphic property of "Liaohe Group", regional geotectonic location and revolution of orogenic zone in Qinghe valley of the northern Liaoning.

  7. Geophysical, geochemical, mineralogical, and enivronmental data for rock samples collected in a mineralized volcanic environment, upper Animas River watershed, Colorado

    Science.gov (United States)

    McCafferty, A.E.; Horton, R.J.; Stanton, M.R.; McDougal, R.R.; Fey, D.L.

    2011-01-01

    This report provides analyses of 90 rock samples collected in the upper Animas River watershed near Silverton, Colo., from 2001 to 2007. The samples are analyzed for geophysical, geochemical, mineralogical, and environmental rock properties of acid neutralizing capacity and net acid production. The database is derived from both published (n=68) and unpublished (n=32) data. New for all samples are geophysical measurements of electrical resistivity, density, and porosity. Rock samples were acquired from 12 geologic units that include key Tertiary volcanic and plutonic lithologies, all with varying degrees of alteration.

  8. Upper cretaceous magmatic suites of the Timok magmatic complex

    Directory of Open Access Journals (Sweden)

    Banješević Miodrag

    2010-01-01

    Full Text Available The Upper Cretaceous Timok Magmatic Complex (TMC developed on a continental crust composed of different types of Proterozoic to Lower Cretaceous rocks. The TMC consists of the magmatic suites: Timok andesite (AT - Turonian-Santonian, Metovnica epiclastite (EM - Coniacian-Campanian, Osnić basaltic andesite (AO and Ježevica andesite (AJ - Santonian-Campanian, Valja Strž plutonite (PVS - Campanian and Boljevac latite (LB. The sedimentary processes and volcanic activity of the TMC lasted nearly continuously throughout nearly the whole Late Cretaceous. The sedimentation lasted from the Albian to the Maastrichtian and the magmatism lasted for 10 million years, from the Upper Turonian to the Upper Campanian. The volcanic front migrated from East to West. The volcanic processes were characterized by the domination of extrusive volcanic facies, a great amount of volcanic material, a change in the depositional environment during the volcanic cycle, sharp facial transitions and a huge deposition of syn- and post-eruptive resedimented volcaniclastics.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Mineralogy and geochemistry of xenoliths in the Eocene volcanic rocks from southwest of Jandaq

    Directory of Open Access Journals (Sweden)

    Samineh Rajabi

    2013-04-01

    Full Text Available The Eocene volcanic rocks from the southwest of the Jandaq (Kuh-e-Godar-e-Siah, Central-East Iran micro-continent are andesitic basalt and andesite in composition. These rocks contain xenoliths with granulitic mineralogy. Mineral assemblage of these xenoliths is plagioclase + phlogopite + corundum + sillimanite + chlorite + phengite with granublastic, poiklioblastic and foliated textures in the pick metamorphic condition. Thermometry of phlogopite in these xenoliths suggests the average temperature 782oC. The characteristics of the xenoliths are consistent with the granolitic facies metamorphism of the Al-saturated Si-undersaturated crustal sediments at the lower crust condition. Melting of these granulites forms the magma which crystallized the S-type granitoids. Differentiation and crystallization of this magma causes the S-type granite formation. Therefore, the S-type granites in the study area are probably generated from melting of the granulites parts of which brought to the surface as xenoliths by Eocene magmatism in south of the Jandaq (Kuh-e-Godar-e-Siah. S-type granites in the study area are located along the Doruneh, Chupanan and Aeirakan faults in the Aeirakan area and Jandaq ophiolite. These granites are the source of uranium, thorium and uranium ore in southwest of the Aeirakan mountain.

  11. Crystallisation condition of the Quaternary basanites of volcanic centre Black Rock, monogenetic field Lunar Crater

    Science.gov (United States)

    Turova, Mariia; Plechov, Pavel; Scherbakov, Vasily; Larin, Nikolay

    2017-04-01

    The Lunar Crater volcanic field is located in a tension zone Basin and Range Province (USA). This tension is connected with dives oceanic plate under the continental plate [1]. Lunar Crater consists of flows basalt, basanite, trachybasalt has a different age [2]. In this work we investigate the youngest rock - basanite. The basanite is highly crystalline consisting of about megacrysts (3-10 cm) 30-60 wt% phenocrysts ( 800-1500 µm) and microphenocrysts (100-800 µm) and 40-60% microlites (stress and style of tectonism of the Basin and Range province of the western United States //Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences. - 1981. - T. 300. - №. 1454. - C. 407-434. 2. Wood, X., and Keinle, Y., 1990, Volcanoes of North America: Cambridge,United Kingdom, Cambridge University Press, 354 p. 3. Nimis P. Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems //Contributions to Mineralogy and Petrology. - 1999. - T. 135. - №. 1. - C. 62-74. 4. Ballhaus C., Berry R. F., Green D. H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle //Contributions to Mineralogy and Petrology. - 1991. - T. 107. - №. 1. - C. 27-40.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

    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.

  14. Cenozoic Adakite-type Volcanic Rocks in Qiangtang,Tibet and Its Significance

    Institute of Scientific and Technical Information of China (English)

    LIU Shen; HU Ruizhong; FENG Caixia; CHI Xiaoguo; LI Cai; YANG Rihong; WANG Tianwu; JIN Wei

    2003-01-01

    Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that therocks are characterized by SiO2>59%, enrichment in Al2O3 (15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g)and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg#<0.35),weak Eu anomaly (Eu/Eu*=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd andSr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magmaresulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and thepetrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will givean insight into the uplift mechanism of the Tibetan plateau.

  15. The role of pore fluids on deforming volcanic rocks: an experimental study

    Science.gov (United States)

    Fazio, Marco; Benson, Philip; Vinciguerra, Sergio; Meredith, Philip

    2015-04-01

    Pore fluids play an important role on the process of the deformation of rocks. Not only it affects the mechanical properties and the elastic velocities of the material, but it is also responsible in the generation of a whole kind of seismicity, characterized by lower frequency and longer tail (i.e. Long Period, LP, and Hybrid events) than the Volcano-Tectonic (VT) signals, generated by simple shear. While great progress has been made in understanding VT events, LPs, Hybrid signals and the transition between these types of activity are not fully understood yet. This study, aiming in particular on the transition between VT and Hybrid events, shows the results of triaxial experiments on a volcanic rock, run both in dry and wet conditions, to better understand the role of the pore fluids on the final stage of the deformation tests, when the sample is approaching failure. This is achieved through a servo-controlled triaxial testing machine and a state-of the-art acoustic emissions (AEs) kit, composed by an array of 12 piezoelectric sensors surrounding the sample and by both a "triggered" unit, where the events are recorded only if a certain threshold is reached, and a "continuous" unit, where the data is recorded from the beginning to the end of the acquisition, fundamental when the AEs grow exponentially and the triggered unit cannot store at the same rate. The use of sensors of different dominant frequency allows us to better investigate the events occurring as the sample is approaching failure. In both conditions we observe a decrease of the dominant frequency of the seismic activity, due to two different processes: in dry conditions the coalescence of fractures, eventually leading to the major shear zone, creates relatively low-frequency VT events; the same occurs in wet conditions, but the movement of fluids, eased by the merging of the cracks, generates hybrid events. These two type of seismicity are then distinguished in terms of their source mechanism components

  16. Supracrustal rocks in the Kuovila area, Southern Finland: structural evolution, geochemical characteristics and the age of volcanism

    Directory of Open Access Journals (Sweden)

    Pietari Skyttä

    2005-01-01

    Full Text Available The supracrustal rocks of the Kuovila area in the Palaeoproterozoic Svecofennian Uusimaa Belt, southern Finland, consist mainly of volcaniclastic rocks associated with banded iron formations (BIFs and marbles. Small ZnS and PbS mineralizations are occasionally located within the marbles. Some primary features are well preserved in the sedimentary and volcanic rocks, including lamination in tuffites and banded iron formations. Geochemical results show that the volcanism was bimodal and it mainly had volcanic arc affinity. Specific geochemical indicators suggesting a volcanic arc origin for the Kuovila volcanic rocks include: 1 Enrichment of LILE over the HFSE elements and 2 Distinctly low Nb and Ta contents in relation to Th, Ce and LREE. Geochemistry of the Kuovila area volcanic rocks is very similar to those of the Orijärvi and Kisko formations, located ~15 km NE of Kuovila. Felsic tuff in the Kuovila area was dated at 1891±4 Ma by the U-Pb system on zircons. Consequently volcanism was contemporaneous with magmatism in the adjacent Orijärvi area, thus representing the earliest identified volcanic stage in the southern Svecofennian Uusimaa Belt. Early deformation structures within the Kuovila area are suggested to relate to low-metamorphic or localized low-angle thrusting during D1. F1 folds were recumbent and the S1 cleavages are generally weak. Thrusting was followed by approximately N–S contraction with upright, peak-metamorphic F2 folding overprinting D1 structures and defining the Kuovila synform. Two separate intrusive phases include a synvolcanic granodiorite-diorite-gabbro association and a weakly S2-foliated syn-D2 granodiorite. Anatectic granites and associated migmatizing veins are absent, therefore suggesting that D2 pre-dates the ~1.84–1.82 Ga metamorphic event in the Southern Svecofennian Arc Complex (SSAC. D2 structuresin the Kuovila area are suggested to correlate with the early structures with associated axial planar

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

    Science.gov (United States)

    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.

  18. SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Early Paleozoic volcanic rocks in Nuomuhong area occurred as basalt slice and meta-volcanic slice. SHRIMP zircon U-Pb dating of the basalt slice and the meta-volcanic slice show that the age of the basalt slice is 419±5 Ma, and that of the meta-volcanic slice is 401± 6 Ma. These ages directly testify that there existed Early Paleozoic ocean-continent transform in East Kunlun, the basalt slice was formed in an extensional mid-ocean ridge setting and the meta-volcanic rock slice was formed in an extrusion subduction and collision setting. The inherited zircon age of 1734 Ma in volcanic rocks reflects that the base of East Kunlun may be Middle Proterozoic.

  19. Geologic assessment of undiscovered oil and gas resources—Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups, United States Gulf of Mexico Coastal Plain and State Waters

    Science.gov (United States)

    Swanson, Sharon M.; Enomoto, Catherine B.; Dennen, Kristin O.; Valentine, Brett J.; Cahan, Steven M.

    2017-02-10

    In 2010, the U.S. Geological Survey (USGS) assessed Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups and their equivalent units for technically recoverable, undiscovered hydrocarbon resources underlying onshore lands and State Waters of the Gulf Coast region of the United States. This assessment was based on a geologic model that incorporates the Upper Jurassic-Cretaceous-Tertiary Composite Total Petroleum System (TPS) of the Gulf of Mexico basin; the TPS was defined previously by the USGS assessment team in the assessment of undiscovered hydrocarbon resources in Tertiary strata of the Gulf Coast region in 2007. One conventional assessment unit (AU), which extends from south Texas to the Florida panhandle, was defined: the Fredericksburg-Buda Carbonate Platform-Reef Gas and Oil AU. The assessed stratigraphic interval includes the Edwards Limestone of the Fredericksburg Group and the Georgetown and Buda Limestones of the Washita Group. The following factors were evaluated to define the AU and estimate oil and gas resources: potential source rocks, hydrocarbon migration, reservoir porosity and permeability, traps and seals, structural features, paleoenvironments (back-reef lagoon, reef, and fore-reef environments), and the potential for water washing of hydrocarbons near outcrop areas.In Texas and Louisiana, the downdip boundary of the AU was defined as a line that extends 10 miles downdip of the Lower Cretaceous shelf margin to include potential reef-talus hydrocarbon reservoirs. In Mississippi, Alabama, and the panhandle area of Florida, where the Lower Cretaceous shelf margin extends offshore, the downdip boundary was defined by the offshore boundary of State Waters. Updip boundaries of the AU were drawn based on the updip extent of carbonate rocks within the assessed interval, the presence of basin-margin fault zones, and the presence of producing wells. Other factors evaluated were the middle

  20. Formation Conditions and Distribution Regularities of Oil—gas Pools in Tertiary Volcanic Rocks in Western Huimin Depression,Shandong Province

    Institute of Scientific and Technical Information of China (English)

    刘泽容; 王永杰; 等

    1989-01-01

    The formation conditions and distribution regularities of oil-gas pools in volcanic rocks in western Huimin Depression have been studied in terms of geolgic,sesmic and well logging information,This paper discusses the types and lithofacies,development and distribution of Tertiary volcanic rocks in the area.The results demonstrate that volcanic activity occurred mainly during the period from the Sha-4 stage to the Guantao episode,i.e.,before the oil-generating period(before the end of the Guantao episode and the Minghuazhen episode).The activity did not destroy oil and gas formation and accumulation,but was favourable for the concentration of organic matter and its conversion to hydrocarbons;besides,volcanic rocks can serve as reservoir rocks and cap rocks,playing a role very similar to that of a syndepositional anticline,The volcanic rocks are distributed near the margins of the oil-generating depression;there are many secondary interstices in the rocks,which are connected with each other.These are the leading conditions for the formation of oil-generating period and their self-sealing or good combination with other cap rocks are important factors for forming volcanic rock-hosted oil and gas pools.The oil-gas pools associated with volcanic rocks in western Huimin are mainly distributed around the deep oil-generating depression,in the central up lift or the high structural levels on the margins of the depression.In particular,the sites where several faults cross are usually locatons where hith-yielding oil-gas pools in volcanic rocks are concentrated.

  1. Age, petrogenesis, and tectonic setting of the Permian bimodal volcanic rocks in the eastern Jiamusi Massif, NE China

    Science.gov (United States)

    Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Dong, Yu; Liu, Xi-Wen; Ji, Zheng

    2017-02-01

    We present new in situ zircon U-Pb and Hf isotope, whole-rock geochemical, and Sr-Nd isotopic data for volcanic rocks from the Jiejinkou and Baoqing areas in the eastern Jiamusi Massif. These volcanic rocks are bimodal and consist of basalts, basaltic andesites, rhyolites, and rhyolitic tuffs that can be subdivided into mafic and silicic groups. Zircon U-Pb dating by LA-ICP-MS indicates that these volcanic rocks were erupted between the Early and Middle Permian (290-267 Ma). The mafic rocks in this area have positive εNd(t) (+0.07 to +6.43) values, and are enriched in light rare earth elements (LREEs) and depleted in heavy REE, Nb, and Ta. From these rocks, the meta-basalt of Jinlu and basaltic andesite of Taipinggou and Haojiatun were derived from parental magmas generated by the partial melting of depleted mantle wedge material that was metasomatized by subduction-related melts. These magmas then underwent variable degrees of fractional crystallization and assimilated insignificant amounts of crustal material. The meta-basalt of Liming likely originated from the metasomatized mantle-derived melts hybridized by the convective asthenosphere during the evolution of the magmas. In comparison, the silicic rocks have negative εNd(t) and variable zircon εHf(t) values, are enriched in the large-ion lithophile elements (LILEs) and LREE, and are depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), yielding arc-like geochemical signatures. The geochemical and zircon εHf(t) characteristics of Jiangfeng and Longtouqiao rhyolites are indicative of formation from magmas generated by the partial melting of mafic lower crustal material, whereas the Liming meta-rhyolite was probably produced from a source involving some depleted mantle components. The bimodal volcanic rocks provide convincing evidence that the Early-Middle Permian volcanism in the Jiamusi Massif occurred in an extensional environment probably associated with slab break-off during the westward

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

    Science.gov (United States)

    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

  3. Mapping local singularities using magnetic data to investigate the volcanic rocks of the Qikou depression, Dagang oilfield, eastern China

    Directory of Open Access Journals (Sweden)

    G. Chen

    2013-07-01

    Full Text Available The spatial structural characteristics of geological anomaly, including singularity and self-similarity, can be analysed using fractal or multifractal modelling. Here we apply the multifractal methods to potential fields to demonstrate that singularities can characterise geological bodies, including rock density and magnetic susceptibility. In addition to enhancing weak gravity and magnetic anomalies with respect to either strong or weak background levels, the local singularity index (α ≈ 2 can be used to delineate the edges of geological bodies. Two models were established to evaluate the effectiveness of mapping singularities for extracting weak anomalies and delineating edges of buried geological bodies. The Qikou depression of the Dagang oilfield in eastern China has been chosen as a study area for demonstrating the extraction of weak anomalies of volcanic rocks, using the singularity mapping technique to analyse complex magnetic anomalies caused by complex geological background. The results have shown that the singularities of magnetic data mapped in the paper are associated with buried volcanic rocks, which have been verified by both drilling and seismic survey, and the S–N and E–W faults in the region. The targets delineated for deeply seated faults and volcanic rocks in the Qikou depression should be further investigated for the potential application in undiscovered oil and gas reservoirs exploration.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  6. Petrology, mineral chemistry and tectono-magmatic setting of volcanic rocks from northeast Farmahin, north of Arak

    Directory of Open Access Journals (Sweden)

    Reza Zarei Sahamieh

    2014-10-01

    Full Text Available Introduction The study area is a small part of the Urumieh-Dokhtar structural zone in the Markazi province, located in the northeastern part of the Farmahin, north of Arak (Hajian, 1970. The volcanic rocks studied from the area include andesite, dacite, rhyodacite, ignimbrite and tuff of Middle to Late Eocene age (middle Lutetian to upper Lutetian (Ameri et al., 2009. It seems that folding and faulting is caused in sedimentary basin and volcanic activities. On the other hand, except of orogeny maybe rifting had rule in eruption so that this case has seen in the other area such as Taft and Khezrabad in central Iran (Zarei Sahamieh et al., 2008. The oldest formation in the studied area is Triassic limestones. The dominant textures of these rocks are porphyritic, microlite porphyritic, microlitic and rarely sieve-texture. Sieve texture and dusty texture (dusty plagioclases indicates magma mixing. Mineralogically, they contain plagioclases, clinopyroxenes, amphiboles, quartz and biotite as the main constituents and zircon, apatite, and opaque minerals as accessories. Plagioclases in the andesitic and basaltic- andesite rocks are labradorite, bytownite and anorthite (based on electron microprobe .Moreover, plagioclases in andesitic rocks show that H2O is lesser than 2.5 precent. Amphibole is found in both plagioclases and groundmass. Materials and methods In this article are used different analyses methods such as XRF, ICP-MS and EPMA. Whole-rock major and trace element analyses were determined with ICP-MS method. The major and trace element composition of some rock was determined by electron probe micro-analysis (EPMA using a Cameca SX100 instrument in Iran Mineral Processing Research Center (IMPRC. Moreover, whole-rock major and some trace element analyses for some samples were obtained by X-ray fluorescence (XRF, using an ARL Advant-XP automated X-ray spectrometer. Results Chemical data based on electron micro probe studies of minerals indicate

  7. Characteristics of Rare Earth Elements of Zircons from Mesozoic Volcanic Rocks in Luanping Region, Hebei

    Institute of Scientific and Technical Information of China (English)

    Zhang Hong; Yuan Hongli; Hu Zhaochu; Liu Xiaoming

    2005-01-01

    Rare earth elements of the zircons from the Mesozoic volcanic rocks in Luanping region, Hebei, were analyzed the results reflect that the average values of δEu and (Lu/Gd)N are 0.49 and 21.8 respectively in the zircons from the top part of Tiaojishan Formation;but the average values of δEu and (Lu/Gd)N are 0.15, 0.06, 0.09 and 14.51, 15.66, 16.25 respectively in the zircons from the lower, and upper part of the Tuchengzi Formation and the bottom bed of the Zhangjiakou Formation. The results show that the characteristics of the zircons from the Tuchengzi Formation are coincident with those of the zircons from the Zhangjiakou Formation, but are different from those of the zircons from the Tiaojishan Formation, and imply that the Tuchengzi Formation has close relation with the Zhangjiakou Formation. Combining the results above with the former isotopic dating results of the volcanic rocks, the authors draw the conclusions as follows: The Tuchengzi Formation not only has a long interval period with the Tiaojishan Formation, but also is very different from the Tiaojishan Formation in zircon geochemical characteristics. The Tuchengzi Formation not only is nearly continuous with the Zhangjiakou Formation in time, but also is coincident with the Zhangjiakou Formation in geochemistry of zircons. The results imply that the Tuchengzi Formation and the Zhangjiakou Formation were formed in the same geological background, that is, there are not the boundary of the J3-K1 and the interface of the transition of tectonic framework between the Tuchengzi Formation and the Zhangjiakou Formation in the Luanping region. The research shows that the (Lu/Gd)N, δEu are two important parameters which are relatively stable in the analysis of zircons from Crust-source;but the values of ∑LREE of zircons from Crust-source change greatly, especially the abundance of La element, so some ratios of rare earth elements related with La (or ∑LREE) are not usable in determining the characteristics

  8. Pb, Nd, Sr and Os isotopic systematics of Brazilian cretaceous potassic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Araujo, Ana Lucia Novaes; Sichel, Susanna Eleonora [Universidade Federal Fluminense, Niteroi, RJ (Brazil). Inst. de Geociencias. Laboratorio de Geologia Marinha (LAGEMAR)]. E-mail: alna@zaz.com.br; Gaspar, Jose Carlos; Costa, Vicente Sergio [Brasilia Univ., DF (Brazil). Inst. de Geociencias; Carlson, Richard Walter [Carnegie Institution of Washington, Washington, DC (United States). DTM; Teixeira, Noevaldo Araujo [NTX Consultoria, Brasilia, DF (Brazil)

    2001-12-01

    Mafic potassic rocks of the Alto Paranaiba (Minas Gerais), Juina (Mato Grosso), and Pimenta BUeno (Mato Grosso) belong to a large lineament of rocks that crosses from western to southeastern Brazil and have been associated to a hot spot track by several authors. These provinces intruded the Neoproterozoic Brasilia and Paraguay fold belts (Alto Paranaiba, Paranatinga), and the Mesoproterozoic Rio Negro-Jurema belt (Juina, Pimenta Vueno). Pb isotopic compositions of the studied provinces show a wide variation. {sup 206} Pb/{sup 204} Pb of kimberlites (18.47-19.23) and kamafugities (17.79-18.71) from the Alto Paranaiba Province are close to the Tristaan/Walvis Ridge composition. The {sup 206} Pb/{sup 204} Pb of the paranatinga (19.38-19.87) and Pimenta Bueno (19.78-21.00) provinces are similar to the South African Group I Kimberlite compositional fields, while Juina is displaced to higher Pb isotopic ratios (21.38.22.26), close to those shown ny HIMU ocean island +(OIB).Although the Pb isotopic composition of the more northern alkalic provinces ranges towards the values seen for HIMU OIB, the Sr andNd isotopic composition of these samples is not like HIMU, nor in combination with Pb, like any other ocean island basalt. With the exception of the limberlites from the Alto Paranaiba, which range to quite unradiogenic compositions, most of the samples have {sup 187} Os/{sup 188} Os between 0.13 and 0.15. The Nd model ages of Juina kimberlites vary from 1.70-1.73 Ga, and could be indicating a prior accretion period into the mobile belt. Nd model ages for paranatinga kimberlites vary between 0.56 and 0.64 Ga and Pimenta Bueno kimberlites from 0.72 to 1.05 Ga. Minimum Re depletion model ages for Paranatinga kimberlites vary between 0.74 and 0.93 and Pimenta Bueno kimberlites from 0.9 to 1.3 Ga, indicating that the Nd isotopic signartures could have been affected by metasomatic overprint in Neoroterozoic. (author)

  9. 浙东南地区磨石山群祝村组地层及其区域对比%Lithological Characteristics and Regional Comparison of the Zhucun Formation of the Early Cretaceous Moshishan Group Volcanics in Southeastern Zhejiang

    Institute of Scientific and Technical Information of China (English)

    陈小友; 王加恩; 汪发祥

    2012-01-01

      早白垩世期间浙东南地区火山岩地层磨石山群的祝村组的建组一直存有争议。近年在浙江宁海地区深入开展的1:50000区域地质调查,发现此套中—酸性火山碎屑岩、凝灰质沉积岩夹酸性或中性熔岩地层,在岩性组合、岩相类型、岩石化学成分、火山活动类型等方面与下伏的九里坪组存在较大差异,并在宁海水车、永嘉大箬岩、丽水祝村等地出露广泛、厚度较大。依火山岩地层划分原则,这套地层可作为一个组级岩石地层单位——祝村组。通过对浙东南地区祝村组地层的区域对比认为:祝村组属早白垩世火山活动产物;岩性组合随当时火山活动强度及所处位置有所不同:分布于火山活动较强的破火山口内的祝村组地层,以火山碎屑流相为主,另有崩落相、火山泥石流相、空落相等岩相类型,岩石化学类型属中—酸性;分布于火山活动时喷时歇的火山洼地内的祝村组,以空落相火山碎屑岩与湖相、冲积扇相沉积岩互层产出为主,并有少量火山碎屑流相与喷溢相岩相类型,岩石化学类型属酸性。%  The Zhucun Formation is a constituent part of the Early Cretaceous-aged Moshishan Group volcanics within southeastern Zhejiang Province, and is of controversial origin. Recent mapping at 1:50,000 scale by the Zhejiang Province regional geological survey has identified a set of acidic pyroclastic rocks and tuffaceous sedimentary rocks associated with acid or mafic lavas. This set of pyroclastics and tuffaceous sediments is lithological y, geochemical y, and volcanological y distinct from the underlying Jiliping Formation, and contains significantly different lithofacies units. These rocks are widely exposed in the study area, with units thickening towards the Shuiche area of Ninghai County, the Daruoyan area of Yongjia County, and the Zhucun area of the city of Lishui. Here, we define

  10. Cretaceous Environments of Afghanistan:A Synthesis Based on Selected Sections

    Institute of Scientific and Technical Information of China (English)

    Abdul Rahman Ashraf; Ashok Sahni

    2003-01-01

    The Cretaceous of Afghanistan is marked by great facies diversity. The evolution of Cretaceous basins is part of a complex accretionary history involving three distinct tectonic units namely the Asian (Russian) Block separated from the Indian plate by a rather well defined transcurrent fault (Chaman-Nuski). The southwestern component is representedby the Iran-Afghanistan plate. The Lower Cretaceous of the Asian Block is represented by the Red-Grit Series which isconformable to the underlying Upper Jurassic sequences. The transition is marked by evaporitic facies dominated by salt,gypsum and marl deposits. In south Afghanistan volcanic rocks occur at Farah, with the emplacement of plutonics inwest-central Afghanistan. The Upper Cretaceous of north Afghanistan is marked by richly fossiliferous, lime stone-dominated sequences. The Upper Cretaceous of southern Afghanistan is marked by strong ophiolitic magrmatism.

  11. The discovery of Middle Jurassic volcanic rocks in north-ern Fujian Province and its geological significance%闽北地区中侏罗世火山岩的发现及其地质意义

    Institute of Scientific and Technical Information of China (English)

    李亚楠; 邢光福; 邢新龙; 陈世忠; 段政; 杨东; 胡凌云

    2015-01-01

    There are only very few Middle Jurassic volcanic rocks exposed along the southeast coast of China, but they are very im-portant for the study of the regional Mesozoic tectonic magmatic activiy and tectonic evolution. The authors discovered for the first time the Middle Jurassic volcanic rocks in the Tieshan area of Zhenghe during the survey of large area of Cretaceous volcanic rocks in northern Fujian Province. The zircon U-Pb age obtained by LA-ICP-MS technique is 173.63 ± 0.80Ma. The volcanic rocks are welded tuff, belonging to the calc-alkaline series. Geochemical data show that they are peraluminous rocks rich in potassium and large ion lithophile elements but poor in high field strength elements. Therefore, these rocks must have been formed in a continental margin arc environment, related to the subduction of the paleo-Pacific plate.%中侏罗世火山岩在东南沿海分布极少,但对区域中生代构造-岩浆活动过程及大地构造演化的研究具有重要意义.在闽北地区大面积白垩纪火山岩区调查中,在政和铁山地区发现中侏罗世火山岩,用LA-ICP-MS同位素测试技术测得的锆石U-Pb年龄为173.63±0.80Ma.火山岩属钙碱性系列流纹质熔结凝灰岩,显示过铝质、富钾、富集大离子亲石元素,亏损高场强元素等地球化学特征,推断其形成于陆缘弧环境,与古太平洋板块早期俯冲作用有关.

  12. Mechanisms of aggradation in fluvial systems influenced by explosive volcanism: An example from the Upper Cretaceous Bajo Barreal Formation, San Jorge Basin, Argentina

    Science.gov (United States)

    Umazano, Aldo M.; Bellosi, Eduardo S.; Visconti, Graciela; Melchor, Ricardo N.

    2008-01-01

    The Late Cretaceous succession of the San Jorge Basin (Patagonia, Argentina) records different continental settings that interacted with explosive volcanism derived from a volcanic arc located in the western part of Patagonia. This paper discusses the contrasting aggradational mechanisms in fluvial systems strongly influenced by explosive volcanism which took place during sedimentation of the Bajo Barreal Formation. During deposition of the lower member of the unit, common ash-fall events and scarce sandy debris-flows occurred, indicating syn-eruptive conditions. However, the record of primary pyroclastic deposits is scarce because they were reworked by river flows. The sandy fluvial channels were braided and show evidence of important variations in water discharge. The overbank flows (sheet-floods) represent the main aggradational mechanism of the floodplain. In places, subordinate crevasse-splays and shallow lakes also contributed to the floodplain aggradation. In contrast, deposition of the upper member occurred in a fluvial-aeolian setting without input of primary volcaniclastic detritus, indicating inter-eruptive conditions. The fluvial channels were also braided and flowed across low-relief floodplains that mainly aggraded by deposition of silt-sized sediments of aeolian origin (loess) and, secondarily by sheet-floods. The Bajo Barreal Formation differs from the classic model of syn-eruptive and inter-eruptive depositional conditions in the presence of a braided fluvial pattern during inter-eruptive periods, at least at one locality. This braided fluvial pattern is attributed to the high input of fine-grained pyroclastic material that composes the loessic sediments.

  13. Geochemistry of meta-volcanic rocks from the Longbohe Cu deposit, Yunnan Province, China: Implications for the genesis and tectonic setting

    Institute of Scientific and Technical Information of China (English)

    CUI Yinliang; QING Dexian; CHEN Yaoguang

    2007-01-01

    The Longbohe Cu deposit, which is located in the southern part of the Honghe ore-forming zone, Yunnan Province, China, belongs to a typical ore field where volcanic rocks are of wide distribution and are associated with Cu mineralization in time and space. The volcanic rocks in the ore field, which have experienced varying degree of alteration or regional metamorphism, can be divided into three types, i.e., meta-andesite, meta-subvolcanic rock and meta-basic volcanic rock in accordance with their mineral assemblages. These three types of volcanic rocks in the ore field are relatively rich in Na and the main samples plot in the area of alkali basalts in the geochemical classification diagram. With the exception of very few elements, these three types of volcanic rocks are similar in the content of trace elements. In comparison to the basalts of different tectonic settings, the meta-volcanic rocks in the ore field are rich in high field strength elements (HFSE) such as Th, Nb, etc. and depleted in large ion lithophile elements (LILE) such as Sr, Ba, etc. and their primary mantle-normalized trace element patterns show remarkable negative Th and Nb anomalies and negative Sr and Ba anomalies. These three types of volcanic rocks are similar in REE content range and chondrite-normalized REE patterns with the exception of Eu anomaly. Various lines of evidence show that these three types of volcanic rocks in the ore field have the same source but are the products of different stages of magmatic evolution, their original magma is a product of partial melting of the metasomatically enriched mantle in the tensional tectonic setting within the continent plate, and the crystallization differentiation plays an important role in the process of magmatic evolution.

  14. U-Th-He age determinations on volcanic rocks: A new tool for Quaternary geochronology.

    Science.gov (United States)

    Aciego, S. M.; Kennedy, B. M.; Christensen, J. N.; Depaolo, D. J.; Hutcheon, I. D.

    2002-12-01

    The U-Th/He system, which has been used successfully for thermochronology, also has potential for dating young volcanic rocks. To test this possibility the age of garnet phenocrysts from the 79 AD eruption of Mt. Vesuvius was measured. The samples consisted of 600-1000 μm diameter andradite-grossular garnet crystals separated from a volcanic tuff previously dated by Ar-Ar (Renne et al, 1997). Our age calculation accounts for diffusive loss of radiogenic He since eruption, loss of He by alpha ejection from the garnet grains, U series disequilibrium, and non-uniform U-Th distribution within the mineral grains. The effect of diffusion was investigated using existing diffusivity and activation energy data for almandine rich garnet (Dunai and Roselieb, 1996), and by step-wise degassing of the Vesuvius garnets. Diffusivity was measured over 7 temperature steps ranging from 800oC to 1300oC with one additional 1500oC step for complete extraction. Even up to the 1300oC step the diffusivity remains linear, indicating an Arrhenius relationship with an activation energy of approximately 427 kJ/mol and a frequency factor, Do/a2 = 0.578 s-1. Alpha emission is accounted for by modeling the garnet grains as spheres with the injection and ejection of alphas from the sphere depending on the concentration and distribution of the U and Th inside and outside of the mineral grain. Distribution of U, Th was determined by ion-probe analysis across garnet grains in thin section. While the overall concentration of U and Th within the garnets is quite high (approximately 16-19ppm and 23-27ppm, respectively), there is a deficiency in 230Th and 226Ra. The 234U/238U and 230Th/238U activity we measure directly, while the 226Ra/238U activity ratio was estimated by assuming Ra follows barium. Due to machine limitations, U, Th concentrations and He concentrations were determined on different aliquots. The measured concentration of 4He in the garnet grains varies from 3.72x10-9 to 4.16x10-9 cc STP

  15. Use of terrestrial laser scanning for engineering geological applications on volcanic rock slopes - an example from Madeira island (Portugal)

    Science.gov (United States)

    Nguyen, H. T.; Fernandez-Steeger, T. M.; Wiatr, T.; Rodrigues, D.; Azzam, R.

    2011-03-01

    This study focuses on the adoption of a modern, widely-used Terrestrial Laser Scanner (TLS) application to investigate volcanic rock slopes in Ribeira de João Gomes valley (Funchal, Madeira island). The TLS data acquisition in May and December 2008 provided information for a characterization of the volcanic environment, detailed structural analysis and detection of potentially unstable rock masses on a slope. Using this information, it was possible to determine specific parameters for numerical rockfall simulations such as average block size, shape or potential sources. By including additional data, such as surface roughness, the results from numerical rockfall simulations allowed us to classify different hazardous areas based on run-out distances, frequency of impacts and related kinetic energy. Afterwards, a monitoring of hazardous areas can be performed in order to establish a rockfall inventory.

  16. Petrology of Karoo volcanic rocks in the southern Lebombo monocline, Mozambique

    Science.gov (United States)

    Melluso, Leone; Cucciniello, Ciro; Petrone, Chiara M.; Lustrino, Michele; Morra, Vincenzo; Tiepolo, Massimo; Vasconcelos, Lopo

    2008-11-01

    The Karoo volcanic sequence in the southern Lebombo monocline in Mozambique contains different silicic units in the form of pyroclastic rocks, and two different basalt types. The silicic units in the lower part of the Lebombo sequence are formed by a lower unit of dacites and rhyolites (67-80 wt.% SiO 2) with high Ba (990-2500 ppm), Zr (800-1100 ppm) and Y (130-240 ppm), which are part of the Jozini-Mbuluzi Formation, followed by a second unit, interlayered with the Movene basalts, of high-SiO 2 rhyolites (76-78 wt.%; the Sica Beds Formation), with low Sr (19-54 ppm), Zr (340-480 ppm) and Ba (330-850 ppm) plus rare quartz-trachytes (64-66 wt.% SiO 2), with high Nb and Rb contents (240-250 and 370-381 ppm, respectively), and relatively low Zr (450-460 ppm). The mafic rocks found at the top of the sequence are basalts and ferrobasalts belonging to the Movene Formation. The basalts have roughly flat mantle-normalized incompatible element patterns, with abundances of the most incompatible elements not higher than 25 times primitive mantle. The ferrobasalt has TiO 2 ˜ 4.7 wt.%, Fe 2O 3t = 16 wt.%, and high Y (100 ppm), Zr (420 ppm) and Ba (1000 ppm). The Movene basalts have initial (at 180 Ma) 87Sr/ 86Sr = 0.7052-0.7054 and 143Nd/ 144Nd = 0.51232, and the Movene ferrobasalt has even lower 87Sr/ 86Sr (0.70377) and higher 143Nd/ 144Nd (0.51259). The silicic rocks show a modest range of initial Sr-( 87Sr/ 86Sr = 0.70470-0.70648) and Nd-( 143Nd/ 144Nd = 0.51223-0.51243) isotope ratios. The less evolved dacites could have been formed after crystal fractionation of oxide-rich gabbroic cumulates from mafic parental magmas, whereas the most silica-rich rhyolites could have been formed after fractional crystallization of feldspars, pyroxenes, oxides, zircon and apatite from a parental dacite magma. The composition of the Movene basalts imply different feeding systems from those of the underlying Sabie River basalts.

  17. Attempts of whole-rock K/Ar dating of mesozoic volcanic and hypabissal igneous rocks from the Central Subbetic (Southern Spain: A case of differential Argon loss related to very low-grade metamorphism

    Directory of Open Access Journals (Sweden)

    Sanz de Galdeano, C.

    1988-04-01

    Full Text Available 12 samples of basic intrusives within Triassic rocks «ophites» and 11 samples of volcanic and associated intrusives within Jurassic to Early Cretaceous sequences of the Subbetic Zone were subjected to whole-rock K/Ar dating in combination with chemical/petrological analysis. Satisfactory results were obtained only from a number of samples of volcanic rocks, however, analytical ages commonly agree, within about 10 relative percent, with those deduced from stratigraphic location. «Ophite» samples, on the other hand, may reveal considerably lower analytic ages than the volcanics and show much stronger scattering, even among samples collected within a small area. It is argued that the inferred loss of Ar results from very-low-grade alpine metamorphic alteration, which affected the «ophites» more intensely than the higher volcanic rocks. Other post-emplacement chemical changes, such as the degree of secondary oxidation of Fe, are also distintive among the two groups of samples, and are to some extent consistent with the above view in that the alteration environment of the ophites should have produced conditions for more penetrative fluid-rock interactions and homogeneous recrystallization. Overall, the magmatic activity from which the ophitic rocks originated might have started in the Late Triassic and continued in the Lower Jurassic. 80th, the «ophites» and the volcanics are though to be the result of magmatic events Collowing tensional to transtensive crustal movements affecting the external basins of the Betic Cordilleras Crom Late Triassic to Early Cretaceous times.Doce muestras de cuerpos básicos intrusivos en rocas triásicas («ofitas» y 11 muestras de volcanitas y rocas intrusivas asociadas en secuencias jurásico-cretáceas de la zona Subbética han sido objeto de datación radiométrica K/Ar (roca total en combinación con análisis químico-petrográfico. Las edades analíticas obtenidas son 's

  18. Characteristics of rare earth elements of lacustrine exhalative rock in the Xiagou Formation of Lower Cretaceous in Qingxi sag, Jiuxi basin

    Institute of Scientific and Technical Information of China (English)

    WEN Huaguo; ZHENG Rongcai; GENG Wei; FAN Mingtao; WANG Manfu

    2007-01-01

    The exhalative rock occurring in the Xiagou Formation of Lower Cretaceous in Qingxi sag, Jiuxi basin is a sort of a rare lacustrine white smoke type, rich in ferrodolo-mites and albites. This paper introduces the geological back-ground, mineral association, and lithology of the exhalative rock, and discusses its REE geochemical characteristics and connection with hydrothermal environment. It is shown that the exhalative rock has basal characteristics of hydrothermal depositional formation of LREE>HREE, with positive δCe and negative δEu, which is different from the character-istics of marine exhalative rock. Since the REE pattern and exceptional distribution of δEu and δCe are highly similar to the characteristics of alkalescent tholeiitic basalt in the same layer, the exhalative rock of Xiagou Formation isconsidered to be closely related to the origin of basalt in the same horizon. The fact that the amount of REE of exhala-tive rock decreases outwards indicates that exhalative rock in the Xiagou Formation may be connected with lacustrine hydrothermal convection circulation.

  19. High-precision thermal ionization mass spectrometry dating of young volcanic rocks by using U-series method

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A high precision thermal ionization mass spectrometric (HP-TIMS) technique is used to determine 238U,234U,232Th,230Th concentrations and their ratios in whole rocks and minerals separated from Quaternary Maanshan,Dayingshan and Heikongshan volcanic rocks of Tengchong volcanic field,Yunnan Province,China.The 238U-230Th isochrons are given,yielding four age values (227± 20) ka (D-1,Dayingshan),(79.6± 5.5) ka (D-7,Dayingshan),(21.9± 3.0) ka (h-1,Heikongshan),and (7.5± 1.0) ka (M-1,Maanshan).The result is not only consistent with but also preciser than those measured by the K-Ar method and the alpha spectrometry U-series method,indicating that the HP-TIMS method is reliable and has high precision.Besides,a procedure of HP-TIMS analysis of young volcanic rocks in China is set up preliminarily.

  20. Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China: Petrochemical evidence for partial melting of the mantle-crust transition zone

    Institute of Scientific and Technical Information of China (English)

    LAI Shaocong; QIN Jiangfeng; LI Yongfeng; LIU Xin

    2007-01-01

    Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2=52%-62%, Al2O3>15%, Na2O/K2O>1 and MgO<3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10-13, (La/Yb)N=15-19, and show a weak negative Eu anomaly with δEu=0.71-0.89. The close relationship between Mg# and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.23-3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.

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

    Science.gov (United States)

    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

  2. Origin of marine petroleum source rocks from the Late Jurassic to Early Cretaceous Norwegian Greenland Seaway - evidence for stagnation and upwelling

    Energy Technology Data Exchange (ETDEWEB)

    Langrock, U.; Stein, R. [Alfred Wegener Inst. for Polar and Marine Research, Bremerhaven (Germany)

    2004-02-01

    Forty samples were selected from Upper Jurassic to Lower Cretaceous black shales of IKU sites 6307/07-U-02 and 6814/04-U-02, located on the mid-Norwegian shelf, for a detailed maceral analysis. The penetrated rocks include the Spekk and Hekkingen Formations, which represent major potential petroleum source rocks in the region. It was our first objective to reveal the type of organic material that is responsible for the source rock potential of these sediments. The results suggest that black shale formation has occurred in two different paleoceanographic settings; (1) in a 'high-productive' and (2) an 'anoxic/stagnant' environment. This conclusion is supported by inorganic and sedimentological data. In addition, sedimentation rates (SR) from recent biostratigraphic and sedimentological work on these sequences gave impulse for using accumulation rates to estimate the original organic carbon flux to the sediment. Organic carbon accumulation rates are relatively low but similar to mid-Cretaceous black shales from other ocean areas (average 10-300 mg/cm{sup 2}/ka). Supported by redox-sensitive Re/Mo ratios, SR/TOC relationships, and paleoproductivity estimates we suggest that the formation and preservation of organic carbon during black shale formation in the Spekk Formation has followed largely the conditions of the 'stagnation model', whereas the Hekkingen Formation is likely one possible example for the 'productivity model'. (Author)

  3. K-Ar ages for the Yahazudake volcanic rocks from southwest Kyushu, Japan; Kyushu nanseibu yahazudake kazanganrui no K-Ar nendai

    Energy Technology Data Exchange (ETDEWEB)

    Yokose, H.; Kikuchi, W. [Kumamoto Univ. (Japan)] Nagao, K. [Okayama Univ. (Japan)264000] Kodama, K. [Kochi Univ. (Japan)

    1998-05-05

    Many volcanic rocks, seemed to be erupted during the period from the Pliocene epoch to the Pleistocene epoch, are distributed abounding in Kyushu, Japan. In this study, K-Ar ages determination about the 4 samples which represents the Hisatsu volcanic rocks distributed around Yahazudake and rhyolite distributed in Gesujima placed in the southernmost extremity of Amakusa Shimojima, was conducted. And consideration of time/space distribution of the Hisatsu volcanic rocks upon collecting the data which were reported until now and the data obtained by the present K-Ar age determination, was done. In the result of the present measurement, the absolute age of the Hisatsu volcanic rocks distributed around Minamata-shi became clear. I was clarified that Yahazudake volcanic rocks consisted of andesite, which is comparatively lacking in potassium, were formed during about 100 thousand years from 1.98 to 2.08 Ma, and Ontake volcanic rocks which exists for the bottom erupted at about 2.15 Ma. And, the age value of 2.89 Ma was obtained from Ushibuka rhyolite distributed in Gesujima. 35 refs., 4 figs., 3 tabs.

  4. Geochemistry of the Cenozoic Potassic Volcanic Rocks in the West Kunlun Mountains and Constraints on Their Sources

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhaochong; XIAO Xuchang; WANG Jun; WANG Yong; LUO Zhaohua

    2004-01-01

    The geochemical characteristics of the Cenozoic volcanic rocks from the north Pulu, east Pulu and Dahongliutan regions in the west Kunlun Mountains are somewhat similar as a whole. However, the volcanic rocks from the Dahongliutan region in the south belt are geochemically distinguished from those in the Pulu region (including the north and east Pulu) of the north belt. The volcanic rocks of the Dahongliutan region are characterized by relatively low TiO2 abundance, but more enrichment in alkali, much more enrichment in light rare earth elements and large ion lithosphile elements than those from the Pulu region. Compared with the Pulu region, volcanic rocks from the Dahongliutan region have relatively low 87Sr/86Sr ratios, and high εNd, 207pb/204Pb and 208Pb/204Pb. Their trace elements and isotopic data suggest that they were derived from lithospheric mantle, consisting of biotite- and hornblende-bearing garnet lherzolite, which had undertaken metasomatism and enrichment. On the primitive mantle-normalized patterns, they display remarkably negative Nb and Ta anomalies, indicating the presence of early-stage subducted oceanic crust. The metasomatism and enrichment resulted from the fluid released from the crustal materials enclosed in the source region in response to the uplift of asthenospheric mantle. Based on the previous experiments it can be inferred that the thickness of the lithosphere ranges from 75 to 100 km prior to the generation of the magmas. However, the south belt differs from the north one by its thicker lithosphere and lower degree of partial melting. The different thickness of the lithosphere gives rise to corresponding variation of the degree of crustal contamination. The volcanic rocks in the south belt are much more influenced by crustal contamination. In view of the tectonic setting, the generation of potassic magmas is linked with the uplift of asthenosphere resulted from large-scale thinning of the lithosphere after the collision of Indian

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

    Science.gov (United States)

    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

  6. Isotopic Ages of the Carbonatitic Volcanic Rocks in the Kunyang Rift Zone in Central Yunnan,China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yongbei; WANG Guilan; NIE Jianfeng; ZHAO Chongshun; XU Chengyan; QIU Jiaxiang; Wang Hao

    2003-01-01

    The Mesoproterozoic Kunyang rift, which is located on the western margin of the Yangtze platform and the southern section of the Kangdian axis, is a rare massive Precambrian iron-copper polymetallic mineralization zone in China. The Mesoproterozoic Wulu (Wuding(Lufeng) basin in the middle of the rift is an elliptic basin controlled by a ring fracture system. Moreover, volcanic activities in the basin display zonation of an outer ring, a middle ring and an inner ring with carbonatitic volcanic rocks and sub-volcanic dykes discovered in the outer and middle rings. The Sm-Nd isochron ages have been determined for the outer-ring carbonatitic lavas (1685 Ma) and basaltic porphyrite of the radiating dyke swarm (1645 Ma) and the Rb-Sr isochron ages for the out-ring carbonatitic lavas (893 Ma) and the middle-ring dykes (1048 Ma). In combination of the U-Pb concordant ages of zircon (1743 Ma) in trachy-andesite of the corresponding period and stratum (1569 Ma) of the Etouchang Formation, as well as the Rb-Sr isochron age (1024 Ma) and K-Ar age (1186 Ma) of the dykes in the middle ring, the age of carbonatites in the basin is preliminarily determined. It is ensured that all of these carbonatites were formed in the Mesoproterozoic period, whereby two stages could be identified as follows: in the first stage, carbonatitic volcanic groups, such as lavas, pyroclastic rocks and volcaniclastic sedimentary rocks, were formed in the outer ring; in the second stage, carbonatitic breccias and dykes appeared in the middle ring. The metamorphic age of the carbonatitic lavas in the outer ring was determined to be concurrent with the end of the first stage of the Neoproterozoic period, corresponding to the Jinning movement in central Yunnan.

  7. Geology and petrology of Tertiary volcanic rocks of Sarbisheh perlite mine area (eastern Iran and industrial applications

    Directory of Open Access Journals (Sweden)

    Seayad Sayid Mohammadi

    2012-04-01

    Full Text Available The study area is located at northwest of Sarbisheh in South Khorasan province and eastern border of Lut block. In this area, Tertiary (Eocene-Oligocene to Pliocene volcanic rocks consisting of basaltic andesite, dacite, rhyodacite, vitreous rhyolite (perlitic in some parts, tuff and ignimbrite are exposed. In the Daghar Mountain, A, B and C perlite layers with thicknesses of 102, 7 and 58 meters respectively, occur alternatively with volcanic-pyroclastic rocks. Zoning, sieve texture and embayment of plagioclase and roundness of minerals in the lavas indicate disequilibrium conditions during magma crystallization. Chemically, these are meta-aluminous, medium to high-K calc-alkaline, enriched in LILE and negative anomaly for Nb and Ti. Chondrite-normalized Rare Earth Elements (REE plots indicate enrichment of light REE in comparison with heavy REE, (La/YbN of 9.14-12.64, low negative anomaly for Eu in basaltic andesite (Eu/Eu*=0.91 and dacite (Eu/Eu*=0.78-0.87 and strong negative anomaly for Eu in the rhyolites (Eu/Eu*=0.18-0.35. Negative anomaly for Eu indicates calc-alkaline nature for these rocks. On the basis of chemical characteristics and magnetic susceptibility, these are I-type. Tectonically, the rocks belong to subduction zone and active continental margin and their parental magma originated from partial melting of enriched mantle and then crustal contamination during differentiation process. Dacites have an initial 87Sr/86Sr between 0.7048 and 0.7050 (average 0.7049 that confirm mantle source for the magma. Volcanic glasses of rhyolitic composition altered by hydration (likely meteoric water and formed perlite. Physical tests and chemical analyses show that perlite of Sarbisheh is suitable as raw material for production of expanded perlite.

  8. Geochemical Signature of Mesozoic Volcanic and Granitic Rocks in Madina Regency Area, North Sumatra, Indonesia, and its Tectonic Implication

    Directory of Open Access Journals (Sweden)

    Iskandar Zulkarnain

    2014-06-01

    Full Text Available http://dx.doi.org/10.17014/ijog.vol4no2.20094Five samples consisting of two Permian-Triassic basalts, two Triassic-Jurassic granitic rocks, and a Miocene andesite were collected from the Madina Regency area in North Sumatra that is regionally situated on the West Sumatra Block. Previous authors have proposed three different scenarios for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, namely an island-arc, subduction related continental margin arc, and continental break-up. Petrographic analysis of the Mesozoic basaltic samples indicates that they are island-arcs in origin; however their trace element spider diagram patterns (Rock/MORB ratio also show the character of back-arc marginal basin, besides the island-arc. Furthermore, their REE spider diagram patterns (Rock/ Chondrite ratio clearly reveal that they were actually generated in a back-arc marginal basin tectonic setting. Meanwhile, the two Mesozoic granitic rocks and the Miocene andesite reflect the character of an active continental margin. Their spider diagram patterns show a significant enrichment on incompat- ible elements, usually derived from fluids of the subducted slab beneath the subduction zone. The high enrichment on Th makes their plots on Ta/Yb versus Th/Yb diagram are shifted to outside the active continental margin field. Although the volcanic-plutonic products represent different ages, their La/Ce ratio leads to a probability that they have been derived from the same magma sources. This study offers another different scenario for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, where the magmatic activities started in a back-arc marginal basin tectonic setting during the Permian-Triassic time and changed to an active continental margin during Triassic to Miocene. The data are collected through petrographic and chemical analyses for major, trace, and REE includ- ing literature studies.  

  9. Geochemical Signature of Mesozoic Volcanic and Granitic Rocks in Madina Regency Area, North Sumatra, Indonesia, and its Tectonic Implication

    Directory of Open Access Journals (Sweden)

    Iskandar Zulkarnain

    2014-06-01

    Full Text Available http://dx.doi.org/10.17014/ijog.vol4no2.20094Five samples consisting of two Permian-Triassic basalts, two Triassic-Jurassic granitic rocks, and a Miocene andesite were collected from the Madina Regency area in North Sumatra that is regionally situated on the West Sumatra Block. Previous authors have proposed three different scenarios for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, namely an island-arc, subduction related continental margin arc, and continental break-up. Petrographic analysis of the Mesozoic basaltic samples indicates that they are island-arcs in origin; however their trace element spider diagram patterns (Rock/MORB ratio also show the character of back-arc marginal basin, besides the island-arc. Furthermore, their REE spider diagram patterns (Rock/ Chondrite ratio clearly reveal that they were actually generated in a back-arc marginal basin tectonic setting. Meanwhile, the two Mesozoic granitic rocks and the Miocene andesite reflect the character of an active continental margin. Their spider diagram patterns show a significant enrichment on incompat- ible elements, usually derived from fluids of the subducted slab beneath the subduction zone. The high enrichment on Th makes their plots on Ta/Yb versus Th/Yb diagram are shifted to outside the active continental margin field. Although the volcanic-plutonic products represent different ages, their La/Ce ratio leads to a probability that they have been derived from the same magma sources. This study offers another different scenario for the geological setting of West Sumatra Permian Plutonic-Volcanic Belt, where the magmatic activities started in a back-arc marginal basin tectonic setting during the Permian-Triassic time and changed to an active continental margin during Triassic to Miocene. The data are collected through petrographic and chemical analyses for major, trace, and REE includ- ing literature studies.  

  10. The origin of volcanic rock fragments in Upper Pliocene Grad Member of the Mura Formation, North-Eastern Slovenia

    Directory of Open Access Journals (Sweden)

    Polona Kralj

    2006-12-01

    Full Text Available Fresh-water, coarse-grained and detritus-dominated Mura Formation in North Eastern Slovenia includes pyroclastic and volcaniclastic deposits originating from Upper Pliocene volcanic activity of basaltic geochemical character. Although localized in occurrence at the hamlet Grad, these pyroclastic and volcaniclastic sediments forma distinctive depositional unit, for which the term “Grad Member” is proposed and introduced in this paper.In the Grad area no lavas or cinder cones are preserved, and the origin of volcaniclastic fragments still uncertain. For this reason, chemical composition of basaltic rock fragments from the Grad Member volcaniclastics has been studied and compared with basaltic rocks from the neighboring locations at Klöch, Kindsberg, Dölling and Neuhaus. The Grad Member pyroclastic and volcaniclastic deposits seem to be fed from the same source which is different from the occurrences in Austria. That supports the idea about the existence of a local volcanic centre in the present Grad area. The old volcanic edificeswerepossiblydestroyed by the late-stage hydrovolcanic eruptions, and pyroclastic and volcaniclastic deposits subjected to constant reworking by fluvial currents in a dynamic sedimentary environment of alluvial fan and braided river systems.

  11. Potassic volcanic rocks and adakitic intrusions in southern Tibet: Insights into mantle-crust interaction and mass transfer from Indian plate

    Science.gov (United States)

    Liu, Dong; Zhao, Zhidan; DePaolo, Donald J.; Zhu, Di-Cheng; Meng, Fan-Yi; Shi, Qingshang; Wang, Qing

    2017-01-01

    Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rock types have contrasting temporal-spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K2O/Na2O tend to display lower Y and higher SiO2, suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, the unradiogenic 143Nd/144Nd and the dramatic decrease of zircon εHf(t) values since 35 Ma shown by postcollisional adakites should be interpreted as reflecting the crustal input from Indian plate. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian continental crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that

  12. Dating and source determination of volcanic rocks from Khunik area (South of Birjand, South Khorasan using Rb-Sr and Sm-Nd isotopes

    Directory of Open Access Journals (Sweden)

    Somayeh Samiee

    2016-12-01

    Full Text Available The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma. These rocks have initial 87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.

  13. Age of Tertiary volcanic rocks on the West Greenland continental margin

    DEFF Research Database (Denmark)

    Larsen, Lotte M.; Pedersen, Asger K.; Tegner, Christian

    2016-01-01

    Radiometric ages for undated parts of the volcanic succession and intrusions in West Greenland were obtained by the 40Ar–39Ar incremental heating method. Acceptable crystallization ages were obtained for 27 samples. Combined with published results the new data provide a volcanic stratigraphy corr...

  14. Seismic properties of volcanic rocks from Montagne Pelée (Martinique, Lesser Antilles) and their relations to transport properties

    Science.gov (United States)

    Bernard, M.-L.; Zamora, M.

    2012-04-01

    Numerous laboratory and theoretical studies on the physical properties of rocks and their relationships - lead mainly in the framework of petroleum exploration - show that rock physics is necessary for an accurate quantitative interpretation of geophysical observations. Moreover joint inversion of different geophysical datasets is emerging as an important tool to enhance resolution and decrease inversion artifacts in imaging of structurally complex areas such as volcanoes. In many cases, the coupling between the inverted parameters is based on empirical or theoretical relationships derived from laboratory data. Consequently rock physics can be used to: interpret simultaneously several geophysical datasets on volcanoes when they are available, improve the imaging of volcano structures, and better understand the coupled processes that can occur during volcanic unrest. It's in this context that we lead a laboratory study on the transport properties (permeability, thermal and electrical conductivities) and seismic properties (velocity and attenuation of P and S waves) of volcanic rocks representative of Montagne Pelée (Martinique) deposits. In this presentation we will focus on (1) the seismic properties and (2) the relations between seismic and transport properties. The 43 samples collected are representative of the main lithological units of this volcano: vesicular lava blocks and indurated ashed from indurated block-and-ash flows also called breccias, vesicular lava blocks from "Pelean nuee ardente" flows, scoriae from scoria flows, pumices from ash-and-pumices flows, and dense lava blocks from lava flows and lava domes. Their total porosity varies over a wide range from 4 to 73%. Since the samples present similar chemical and mineralogical compositions (andesites), the main difference between the samples comes from their pore structure and reflects differences in the mechanisms of magma degassing and vesiculation during their formation (Bernard et al., 2007). This

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

    Science.gov (United States)

    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. Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

    Science.gov (United States)

    Walker, R.J.; Echeverria, L.M.; Shirey, S.B.; Horan, M.F.

    1991-01-01

    The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (??Nd+9??1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (??Os) ranged from 0 to +22, and model-initial ?? values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re - Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions. ?? 1991 Springer-Verlag.

  17. Late Cretaceous Volcaniclastics in NW Turkey

    Science.gov (United States)

    Boehm, Katharina; Wolfgring, Erik; Omer Yilmaz, Ismail; Tüysüz, Okan; Wagreich, Michael

    2015-04-01

    On the southwestern coast of the Black Sea, in the western Pontides Upper Cretaceous tuff layers are present. The tuffs are intercalated with limestones, marls and turbidites and were investigated with focus on their geochemistry, to get new insights to the arrangement of terranes and ocean basins at this time. In the region two Upper Cretaceous volcanic units can be distinguished, separated by distinct red pelagic limestone successions, belonging to the Unaz Formation. The lower volcanic unit is named Dereköy Formation and is Turonian to Santonian in age. It is thought to be deposited within extension structures, contemporaneously with rifting in the western Black Sea basin. The upper volcanic unit is called Cambu Formation. According to biostratigraphic data it is deposited throughout Campanian, when spreading in the western Black Sea basin started. Interpreted as submarine deposits, element mobility has to be taken into account when interpreting geochemical ICP-MS data of the volcaniclastics. Multiple discrimination diagrams with suitable proxies elucidate the type of volcanism and contribute to reconstruction of the tectonic setting. The classified rock types range from basaltic to rhyodacitic in both volcanic formations. Basically degree of differentiation and alkalinity are the parameters looked at, when determining rock types of the volcanic eruption. Further volcanic series are specified as calc-alkaline to shoshonitic. Moreover, a volcanic arc setting seems to be the most likely case, following several discrimination diagrams, as well as normalized multi-element plots. This tectonic setting can be discussed in connection with paleo-tectonic reconstructions. Most cited in literature nowadays are models favoring a northward subduction of the northern branch of Neotethys, creating an extensional setting north of the Pontides. This kind of back arc extension is interpreted as the reason of a southward drift of the Istanbul continental fragment from Eurasia

  18. The Ajo Mining District, Pima County, Arizona--Evidence for Middle Cenozoic Detachment Faulting, Plutonism, Volcanism, and Hydrothermal Alteration

    Science.gov (United States)

    Cox, Dennis P.; Force, Eric R.; Wilkinson, William H.; More, Syver W.; Rivera, John S.; Wooden, Joseph L.

    2006-01-01

    Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Gries, R.R. [Priority Oil & Gas, Denver, CO (United States); Clayton, J.L. [Geological Survey, Denver, CO (United States); Leonard, C. [Platte River Associates, Denver, CO (United States)

    1997-07-01

    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 southwest 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 (S{sub 1} + S{sub 2} = 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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  3. Geological and geophysical interpretation of the Espirito Santo Basin and the Abrolhos region: petrography, radiometric dating and seismic visualization of volcanic rocks; Interpretacao geologica e geofisica da Bacia do Espirito Santo e da regiao de Abrolhos: petrografia, datacao radiometrica e visualizacao sismica das rochas vulcanicas

    Energy Technology Data Exchange (ETDEWEB)

    Mohriak, Webster Ueipass [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). E e P. Gestao de Projetos Exploratorios Sul-Sudeste], E-mail: webmohr@petrobras.com.br

    2005-11-15

    Geologic and geophysical interpretation of structural, magmatic and sedimentological features outcropping in the Abrolhos Archipelago (offshore of the Espirito Santo - Mucuri basins along the eastern Brazilian margin), and petrographic and geochronologic studies of igneous rocks, characterized a sequence of volcanic (basalts, diabase, breccia, etc.) and sedimentary rocks (fine grained to coarse grained sandstones and conglomerates in channels, sandstones with concordant stratification and locally discordant with the volcanic rocks, siltites, silty shales, etc.) which were uplifted after their original deposition between the Late Cretaceous and the Paleogene. The geochronological dating, based on the Ar-Ar method, suggests an interval of magmatism between 40 and 60 Ma. The field works suggest that siliciclastic rocks outcropping in the islands constitute a unique example of Paleogene Tertiary turbidity sedimentation in the Brazilian continental margin. Thick layers of massive sandstones with an external lobate geometry, overlying silty rhythmites, particularly in the eastern portion of the Santar Barbara Island, are probable deposits of dense flows (hyperpycnal) deposited in mid platform to upper bathyal environments. The tectonic and seismic stratigraphic interpretation suggests that these rocks were uplifted in a compressional event, probably associated with salt tectonics, affecting the sedimentary layers and creating angular unconformities that reach up to the Neogene. (author)

  4. Late Cretaceous to Middle Eocene Geological Evolution of the Northwestern Caribbean - Constraints from Cuban Data

    Science.gov (United States)

    Cobiella, J.; Hueneke, H.; Meschede, M.; Sommer, M.

    2006-05-01

    Cuba acts as the northwestern boundary of the Caribbean Sea. However it is not part of the Caribbean plate, its geological development is deeply related to the plate history. In fact, its Cretaceous volcanic arc rocks tightly correlate with coeval sections in Hispaniola and Puerto Rico, and the same probably occurs with the ophiolites. The early Palaeogene events in Cuba were also involved in the Caribbean plate history. In general, two principal structural levels can be distinguished in the geological structure of Cuba. The rocks belonging to the upper level (Eocene to Quaternary) are little disturbed and can be referred to as the cover. Below it occurs the great complex of the Cuban orogenic belt, which consists mainly of rocks of Jurassic to Eocene age. In addition, small outcrops of Proterozoic metamorphic rocks also occur in north central Cuba. The Palaeocene-Eocene section contains volcanic arc sequences in SE Cuba and northward thrusted piggy back and foreland basins in central and western Cuba. The Mesozoic rocks lies unconformably below. The contacts between the major Mesozoic elements are always tectonic. With the exception of the rocks of the passive Mesozoic margin of North America in northern Cuba, the remaining units represent tectonostratigraphic terranes extending parallel to the axis of the present main island of Cuba. The northernmost unit is the Mesozoic passive continental margin of North America. It consists of a Jurassic- Cretaceous mainly marine sedimentary sequence now exposed as a thrust and fold belt along the northern edge of the Cuban mainland. The other units are, from north to south: the Northern Ophiolitic Belt, the Volcanic Arc Terrane and the Southern Metamorphic Terranes. The ophiolites and the Cretaceous volcanic arc terranes belong to the Proto-Caribbean plate and were accreted to the palaeomargin during Late Cretaceous and early Palaeogene episodes. Some constrains to Caribbean plate origin and evolution according to data from

  5. Chemostratigraphy of Late Cretaceous deltaic and marine sedimentary rocks from high northern palaeolatitudes in the Nuussuaq Basin, West Greenland

    DEFF Research Database (Denmark)

    Lenniger, Marc; Pedersen, Gunver Krarup; Bjerrum, Christian J.

    The Nuussuaq Basin in the Baffin Bay area in West Greenland formed as a result of the opening of the Labrador Sea in Late Mesozoic to Early Cenozoic times. The first rifting and the development of the Nuussuaq Basin took place during the Early Cretaceous and was followed by a second rifting phase...

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  8. Composition of plagioclases in volcanic rocks of King George Island, Antarctica with reference to the petrogenetic significance

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Plagioclases occur mainly as phenocrysts in volcanic rocks of King George Island, South Shetland Islands, West Antarctica. In basaltic andesites and andesites of Keller Peninsula and Ullman Spur (Admiralty Bay), they are high structure state labradorite-andesines; and in high-A1 basalts and basaltic andesites of Barton and Weaver peninsulas (Maxwell Bay), they are high structure state bytownite-anorthites.∑REE, La/Yb ratios and δEu values of plagioclases from Admiralty Bay are higher than those from Maxwell Bay. All plagioclases have rather identical chondritenormalized transitional element distribution patterns, probably reflecting that crystal structure rather than composition of plagioclase controls their diversity. Compositions of plagioclases depend chiefly on those of their host rocks, compositional differences of plagioclases reveal that basaltic magmas in the Admiralty Bay area are more evolved than in the Maxwell Bay area.

  9. The Ediacaran volcanic rocks and associated mafic dykes of the Ouarzazate Group (Anti-Atlas, Morocco): Clinopyroxene composition, whole-rock geochemistry and Sr-Nd isotopes constraints from the Ouzellarh-Siroua salient (Tifnoute valley)

    Science.gov (United States)

    Belkacim, Said; Gasquet, Dominique; Liégeois, Jean-Paul; Arai, Shoji; Gahlan, Hisham A.; Ahmed, Hassan; Ishida, Yoshito; Ikenne, Moha

    2017-03-01

    Belonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley volcanic rocks are located within a rigid salient of the Anti-Atlas that gives them special extreme characteristics. Due to the heavy greenschist alteration that affects this volcanic group, we focused the more immobile elements, but as REE can also be affected, we used the composition of unaltered clinopyroxene crystals to determine the nature of these volcanic rocks. The clinopyroxene is an augite diopside in the basalt, an augite in the andesite and an augite-salite in the dolerite. Petrography of the Tifnoute mafic volcanic rocks and clinopyroxene compositions indicate the presence of two magmatic series: (i) older high-K calc-alkaline (alkali-calcic) andesite and basalt characterized by the early crystallization of Fe-Ti oxides and of the late fractionation of plagioclase, the modal proportion of the latter increasing from the basalt to the andesite and (ii) younger alkalic dolerite dykes. With clinopyroxene trace element compositions obtained using laser ablation ICP-MS, we calculated the composition of the melts in equilibrium with the pyroxenes. The volcanic rocks of the Tifnoute Valley have positive εNd570 (+1.7 to +5.0), low Sri (volcanic rocks emplaced in a Pan-African transtensive post-collisional environment that evolved towards the major rifting event that will give rise to the Rheic ocean, in a similar way to what occurred just after the Variscan orogeny during the Triassic period that evolved to the Tethys ocean opening.

  10. Geochemistry of the volcanic rocks from Bioko Island (“Cameroon Hot Line”: Evidence for plume-lithosphere interaction

    Directory of Open Access Journals (Sweden)

    Fadimatou Ngounouno Yamgouot

    2016-09-01

    Full Text Available Bioko Island (3008 m a.s.l is located in the presently more active volcanic zone of the Cameroon Line and composed essentially of alkaline basalts and hawaiites, and lesser mugearites. The rocks show microlitic porphyritic texture with phenocrysts of olivine (83% < Fo < 87% and clinopyroxene in a matrix of plagioclase, clinopyroxene and oxides. Hawaiites and mugearites also include phenocrysts of plagioclase (An62-67Ab35-32Or3-1. Major element variation diagrams show an increase in SiO2, Al2O3, Na2O and K2O with increasing MgO for the studied rock groups. The rocks are characterized by low (86Sr/87Sri ratios (0.70320–0.70406, high ɛNd(t values (2.56–4.33 and high (206Pb/204Pbi ratios (20.032–20.035 values. Basalts are enriched in LILE and LREE, and have (Hf/SmN = 0.57–1.16. These geochemical signatures are similar to those of the Mount Cameroon rocks, and might be attributed to low degrees of partial melting from a garnet-amphibole-bearing mantle source. The trace elements and isotopic compositions suggest that the parental magma source might have involved HIMU- and EM1-components.

  11. Hydrothermal alteration in volcanic rocks, eastern part of the Lukavice Group, Železné Hory Mountains, Czech Republic

    Science.gov (United States)

    Pertold, Z.; Watkinson, D. H.; Novotný, L.

    1993-06-01

    Many rocks mapped as felsic metavolcanics in the eastern part of the Lukavice Group are shown to be altered mafic metavolcanics, similar to those in the Noranda and Flin Flon-Snow Lake mining districts, Canada. The relatively fresh rocks of the Lukavice Group are rhyolite, dacite-andesite, and andesite-basalt of calcalka-line character. Assuming no substantial volume change during alteration, Ti, P, La, Ce, Yb, Lu, Th (partly), Sc and V contents remained unchanged. Altered rocks are enriched in (Fe + Mg), K and Si and depleted in Na, Ca and Zr. Some elements show both increased and decreased contents in altered rocks (Mg, Ba, Sm, eu, Tb and Hf). Although hydrothermal alteration in the Lukavice Group is of large extent, it is of the proximal Kuroko style and not of regional ‘Amulet Rhyolite’ style. Implications for a large hydrothermal system within a volcanic pile are discussed in relation to the Ordovician Lukavice Group and its mineral deposits and to some other parts of the Bohemian Massif with volcanosedimentary sequences of the same age.

  12. Geology along southwest coast of Mexico - implications for Cretaceous Paleogeography

    Energy Technology Data Exchange (ETDEWEB)

    Campa, U.M.F.

    1986-04-01

    The coast of Mexico between Puerto Vallarta (lat. 21/sup 0/N) and the Bay of Tehuantepec (long. 94/sup 0/) rises steeply from the Middle America Trench to expose deeply eroded terranes of metamorphosed ophiolitic, basinal to terrigenous sedimentary, and arc volcanic rocks of Pennsylvanian to middle Cretaceous age, in part lying on older Paleozoic and Proterozoic rocks. Granitic intrusios are of Late Cretaceous to early Cenozoic age. The terranes are overlapped by volcanic rocks of middle Cenozoic age and locally, along the coast, by marine Miocene strata. It is particularly significant to paleogeographic reconstructions that there are no known marine coastal deposits of Late Cretaceous or early Cenozoic age. Eight tectono-stratigraphic units are currently recognized. The Colima terrane is a complete sequence of red colvaniclastic beds and limestones from Neocomian to Aptian (ammonites, rudistids). The Tumbiscatio terrane is comprised of lavas and radiolarian cherts, at least in part Triassic. The Huetamo terrane is formed of turbiditic, volcaniclastic, and calcareous sequences of Late Jurassic and Early Cretaceous age (ammonites), locally containing fragments of ophiolite. The fourth unit is comprised of ophiolite terranes. Guerrero terranes are gently metamorphosed lavas, tuffs, and sediments of Late Jurassic to Aptian-Albian age. The Mixteca terrane is comprised of terrigenous calcareous sequences of Pennsylvanian and Early Jurassic ages lying on early Paleozoic basement. The Oaxaca terrane is a Paleozoic sedimentary sequence overlying metamorphic precambrian basement, and the Xalapa terrane is formed of migmatitic, gneissic rocks of Jurassic(.) age. However, this preliminary breakdown does not convey the chaotic complexity of the region.

  13. Geochemistry and tectonic setting of alkaline volcanic rocks in the Antarctic Peninsula: A review

    Science.gov (United States)

    Smellie, J. L.

    1987-06-01

    The numerous Miocene-Recent alkaline volcanic outcrops in the Antarctic Peninsula form a substantial volcanic province, the least well-known part of a major belt of alkaline volcanism that extends between South America and New Zealand. The outcrops consists mainly of aa and pahoehoe lavas and hyaloclastites which locally contain accidental nodules of spinel lherzolite and other mantle-derived lithologies. The province is predominantly basaltic with two major differentiation lineages: (1) a sodic series of olivine and alkali basalt, hawaiite, mugearite, trachy-phonolite and trachyte; and (2) a relatively potassic, highly undersaturated series of basanite, tephrite and phono-tephrite. All the lavas show varying effects of fractionation by crystallization of olivine and clinopyroxene, joined by plagioclase in the hawaiites to trachytes. Fractional crystallization can probably explain most of the chemical variation observed within each outcrop, but variable partial melting is necessary to account for the differences in incompatible element enrichment between the two series, and between the individual outcrops. The degree of partial melting may not have exceeded 3%, as is the case for many other alkaline magmas. The volcanism is an intraplate phenomenon but there is no correlation in timing between the cessation of subduction and the inception of alkaline volcanism. The activity cannot be related to the passage of the coupled Pacific-Antarctic plate over a stationary mantle hot-spot. Although the precise causal relationship with tectonic setting is unknown, regional extension was a prerequisite for giving the magmas rapid access to the surface.

  14. Chronological dating and tectonic implications of late Cenozoic volcanic rocks and lacustrine sequence in Oiyug Basin of southern Tibet

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Reconstruction of uplift history of the Tibetan Plateau is crucial for understanding its environmental impacts. The Oiyug Basin in southern Tibet contains multiple periods of sedimentary sequences and volcanic rocks that span much of the Cenozoic and has great potential for further studying this issue. However, these strata were poorly dated. This paper presents a chronological study of the 145 m thick and horizontally-distributed lacustrine sequence using paleomagnetic method as well as a K-Ar dating of the underlying volcanic rocks. Based on these dating results, a chronostratigraphic framework and the basin-developmental history have been established for the past 15 Ma, during which three tectonic stages are identified. The period of 15-8.1 Ma is characterized by intense volcanic activities involving at least three major eruptions. Subsequently, the basin came into a tectonically quiescent period and a lacustrine sedimentary sequence was developed. Around 2.5 Ma, an N-S fault occurred across the southern margin of the basin, leading to the disappearance of the lake environment and the development of the Oiyug River. The Gyirong basin on northern slope of the Himalayas shows a similar basin developmental history and thus there is a good agreement in tectonic activities between the Himalayan and Gangdise orogenic belts. Therefore, the tectonic evolution stages experienced by the Oiyug Basin during the past 15 Ma could have a regional significance for southern Tibet. The chronological data obtained from this study may provide some constraints for further studies with regard to the tectonic processes and environmental changes in southern Tibetan Plateau.

  15. Geologic framework of pre-Cretaceous rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico

    Science.gov (United States)

    Condon, Steven M.

    1992-01-01

    This report is a discussion and summary of Jurassic and older rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico, and is based on analysis of geophysical logs and observations of outcrops. The Reservation, which is located in the northern San Juan Basin, has been the site of deposition of sediments for much of the Phanerozoic. Geologic times represented on the Reservation are the Precambrian, Cambrian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary. Rocks of Ordovician and Silurian age have not been reported in this region. Thicknesses of pre-Cretaceous sedimentary rocks range from about 750 feet (229 meters) on the Archuleta arch, east of the Reservation, to more than 8,300 feet (2,530 meters) just northwest of the Reservation. About 5,500 feet (1,676 meters) of pre-Cretaceous sedimentary rocks occur in the central part of the Reservation, near Ignacio. At Ignacio the top of the Jurassic lies at a depth of 7,600 feet (2,316 meters) below the surface, which is composed of Tertiary rocks. As much as 2,500 feet (762 meters) of Tertiary rocks occur in the area. More than 10,000 feet (3,048 meters) of Cretaceous and younger rocks, and 15,600 feet (4,755 meters) of all Phanerozoic sedimentary rocks occur in the vicinity of the Reservation. In the early Paleozoic the area that includes the Southern Ute Reservation was on the stable western shelf of the craton. During this time sediments that compose the following shallow-marine clastic and carbonate rocks were deposited: the Upper Cambrian Ignacio Quartzite (0-150 feet; 0-46 meters), Upper Devonian Elbert Formation (50-200 feet; 15-61 meters), Upper Devonian Ouray Limestone (10-75 feet; 3-23 meters), and Mississippian Leadville Limestone (0-250 feet; 0-76 meters). Mixed carbonate and clastic deposition, which was punctuated by a unique episode of deposition of evaporite sediments, continued through

  16. 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

    Science.gov (United States)

    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

  17. Geochronology and Petrogenesis of Intermediate-Basic Volcanic Rocks from Changling Depression in the Songliao Basin%松辽盆地长岭断陷中基性火山岩的时代与其成因

    Institute of Scientific and Technical Information of China (English)

    温升福; 刘曼丽; 刘玮; 李瑞磊; 苟军; 武鹏飞; 王天豪; 柳小明; 孙德有

    2013-01-01

    锆石 U Pb 定年结果显示,松辽盆地长岭断陷松南180井中基性火山岩形成于101~116 Ma 的早白垩世晚期,属于营城组,非火石岭组火山岩。岩相学观察主要由安山岩和橄榄玄武岩组成,化学成分显示为玄武岩、粗面玄武岩和玄武质粗面安山岩,属碱性系列,镁质量分数较低,镁值较小(Mg#=0.27~0.53)。稀土元素总量较高(w (∑ REE)=(164.98~257.27)×10-6),轻重稀土分馏明显((La/Yb)N =6.60~10.96),铕异常微弱(δEu=0.85~1.02)。富集大离子亲石元素和轻稀土元素,Rb,K 相对亏损,相容元素(Cr、Co、Ni)质量分数低,高场强元素 Nb、Ta 弱富集,整体表现出与 OIB(洋岛玄武岩)一致的稀土图谱和微量元素特征。岩浆源区为软流圈地幔,经历了深部地幔流体的交代富集作用,岩浆未遭受地壳物质的混染。%Zircon U Pb dating results show that the intermediate-basic volcanic rocks from Changling depression in the Songliao basin formed at Early Cretaceous,rangingd from 101 Ma to 116 Ma,which belong to Yingcheng Formation rather than Huoshiling Formation.Petrologically,the volcanic rocks are composed dominantly of olivine basalt and andesite,but geochemical data show that the volcanic rocks belong to alkaline series and are composed mainly of basalt,trachybasalt and basaltic trachyandesite.The intermediate-basic volcanic rocks have low contents of MgO and small Mg#(0.27 0.53);The chondrite-normalized rare earth element (REE)patterns indicate that the volcanic rocks show significant fractionation of HREE and LREE [(La/Yb)N = 6.60 10.96]and weak Eu anoalies (δEu=0.85 1.02);The trace element geochemistry are characterized by enrichment in large ionic lithophile elements and LREEs,weak positive anomalies in Nb,Ta,depletion in compatible elements (Cr,Co,Ni)and Rb,K.All of the samples display highly consistent REE patterns and

  18. Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

    Institute of Scientific and Technical Information of China (English)

    WANG Jian; LI Xianhua; DUAN Taizhong; LIU Dunyi; SONG Biao; LI Zhongxiong; GAO Yonghua

    2003-01-01

    The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that overlie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 ( 12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Formation. This age is younger than previously reported values of 921-933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: (1) Lower Neoproterozoic strata (814-1000 Ma) are missing in the studied area; (2) the Nanhua rift system was initiated at about 820 Ma; and (3) an age of ~820 Ma may be taken as the lower boundary timing of the Nanhua System (even Neoproterozoic) in South China.

  19. Coeval 40Ar/39Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites.

    Science.gov (United States)

    Swisher, C C; Grajales-Nishimura, J M; Montanari, A; Margolis, S V; Claeys, P; Alvarez, W; Renne, P; Cedillo-Pardoa, E; Maurrasse, F J; Curtis, G H; Smit, J; McWilliams, M O

    1992-08-14

    (40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

  20. Coeval Ar-40/Ar-39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites

    Science.gov (United States)

    Swisher, Carl C., III; Grajales-Nishimura, Jose M.; Montanari, Alessandro; Margolis, Stanley V.; Claeys, Philippe; Alvarez, Walter; Renne, Paul; Cedillo-Pardo, Esteban; Maurrasse, Florentin J.-M. R.; Curtis, Garniss H.

    1992-01-01

    Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

  1. Searching for Rich Uranium Layers of Volcanic Rocks by Measuring Potential Difference%测定电位差圈定火山岩富铀层位

    Institute of Scientific and Technical Information of China (English)

    袁富蕴; 刘峰

    2000-01-01

    (2.岩石的电位差(△Eh)控制着变价元素的地球化学行为,用差减电位法对330铀矿区393个火山岩△Eh值测量结果表明:火山岩的△Eh值可以准确地圈出铀的富集层位,铀矿化只产在△Eh值高的岩石中。%The potential difference(P.D) of rocks controls geochemical behavior of the element whose valence can change.393volcanic rocks are survied in the 330 uranium ore district by the potential difference method. The result shows: volcanic rocks P.D. accuratly the concetration place of uranium accumtly and uranium mineralize only in the rocks where P.D. value is high.

  2. Mineral chemistry of clinopyroxene: guidance on geo- thermobarometry and tectonomagmatic setting of Nabar volcanic rocks, South of Kashan

    Directory of Open Access Journals (Sweden)

    Rezvan Mehvari

    2017-02-01

    Full Text Available Introduction The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993 and Abbasi (Abbasi, 2012 have been done about the geology of this area. Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternary travertine and recent alluvium (Emami, 1993. The volcanic and sub volcanic rocks of this area are composed of andesite, trachyandesite, dacite, rhyolite and porphyric pyroxene diorite along with pyroclastic rocks. Materials and methods In order to achieve the aims of this work, at first field surveying and sampling were done. Then, thin and polished thin sections were prepared. Some of the samples were selected for microprobe analysis and clinopyroxene minerals were analyzed by using JEOL- JXA-8800 analyzer with a voltage of 20 Kv and a current of 12 nA in the Kanazava University of Japan and Cameca-Sx100 analyzer with a voltage of 15 Kv and a current of 15 nA in the Iranian mineral processing research center, Karaj. Discussion On the basis of petrographic investigations, porphyritic, porphyroid, fluidal, amygdaloidal and porphyry with microlitic groundmass are common textures of these rocks. Also plagioclase, clinopyroxene, amphibole, biotite, sanidine and quartz are essential minerals, opaque, zircon and apatite as accessory minerals are observed in the studied rocks. Clinopyroxenes are observed with corona texture that resulted during the uralitization process. On the basis of minerals’ chemistry, pyroxenes are Fe- Mg- Ca type in composition (Morimoto et al., 1988. These clinopyroxenes are augite. Investigations indicate that mineral composition of clinopyroxene can be effectively used to evaluation the P-T conditions during crystallization. Previous research

  3. 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)

    Science.gov (United States)

    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

  4. Magma-derived gas influx and water-rock interactions in the volcanic aquifer of Mt. Vesuvius, Italy

    Science.gov (United States)

    Federico, C.; Aiuppa, A.; Allard, P.; Bellomo, S.; Jean-Baptiste, P.; Parello, F.; Valenza, M.

    2002-03-01

    We report in this paper a systematic investigation of the chemical and isotopic composition of groundwaters flowing in the volcanic aquifer of Mt. Vesuvius during its current phase of dormancy, including the first data on dissolved helium isotope composition and tritium content. The relevant results on dissolved He and C presented in this paper reveal that an extensive interaction between rising magmatic volatiles and groundwaters currently takes place at Vesuvius. Vesuvius groundwaters are dilute (mean TDS ˜ 2800 mg/L) hypothermal fluids ( mean T = 17.7°C) with a prevalent alkaline-bicarbonate composition. Calcium-bicarbonate groundwaters normally occur on the surrounding Campanian Plain, likely recharged from the Apennines. δD and δ 18O data evidence an essentially meteoric origin of Vesuvius groundwaters, the contribution from either Tyrrhenian seawater or 18O-enriched thermal water appearing to be small or negligible. However, the dissolution of CO 2-rich gases at depth promotes acid alteration and isochemical leaching of the permeable volcanic rocks, which explains the generally low pH and high total carbon content of waters. Attainment of chemical equilibrium between the rock and the weathering solutions is prevented by commonly low temperature (10 to 28°C) and acid-reducing conditions. The chemical and isotope (C and He) composition of dissolved gases highlights the magmatic origin of the gas phase feeding the aquifer. We show that although the pristine magmatic composition may vary upon gas ascent because of either dilution by a soil-atmospheric component or fractionation processes during interaction with the aquifer, both 13C/ 12C and 3He/ 4He measurements indicate the contribution of a magmatic component with a δ 13C ˜ 0‰ and R/R a of ˜2.7, which is consistent with data from Vesuvius fumaroles and phenocryst melt inclusions in olivine phenocrysts. A main control of tectonics on gas ascent is revealed by data presented in this paper. For example

  5. Geochemistry and tectonomagatic setting of Tertiary volcanic rocks of the Kangan area, northeast of Sarbisheh, southern Khorasan

    Directory of Open Access Journals (Sweden)

    Mahshid Malekian Dastjerdi

    2017-02-01

    Full Text Available Introduction The study area is located 12km away from the north east of Sarbisheh at the eastern border of the Lut block (Karimpour et al., 2011; Richards et al., 2012. The magmatic activity in the Lut blockhas begun in the middle Jurassic (165-162 Ma and reached its peak in the Tertiary age (Jung et al., 1983; Karimpour et al., 2011. Volcanic and subvolcanic rocks in the Tertiary age cover over half of the Lut block with up to 2000 m thickness and they were formed due to subduction prior to the collision of the Arabian and Asian plates (Jung et al., 1983; Karimpour et al., 2011. In the Kangan area, the basaltic lavas cropped out beyond the above intermediate to acid volcanic rocks. In this area, bentonite and perlite deposits have an economic importance. The main purpose of this paper is to present a better understanding of the tectono-magmatic settings of volcanic rocks in the northeast of Sarbisheh, east of Iran based on their geochemical characteristics. Materials and methods Fifteen samples were analyzed for major elements by inductively coupled plasma (ICP technologies and trace elements by using inductively coupled plasma mass spectrometry (ICP-MS, following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the Acme laboratories, Vancouver, Canada. Results The Kangan area is located at the northeast of Sarbishe, Southern Khorasan and the eastern border of the Lut block. In this area, basaltic lavas have cropped out above intermediate to acid lavas such as andesite, dacite, rhyolite (sometimes perlitic .The main minerals in the basalt are plagioclase, olivine and pyroxene, in andesite contain plagioclase, pyroxene, biotite and amphibole and in acid rocks include plagioclase, quartz, sanidine, biotite and amphibole. Intermediate to acid rocks have medium to high-K calc-alkaline nature and basalt is alkaline. Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7, high ratio of Zr/Y(4.79- 10.81, enrichment in LILE

  6. Paleomagnetic results of the Cretaceous marine sediments in Tongyouluke, southwest Tarim

    Institute of Scientific and Technical Information of China (English)

    SHEN Zhongyue; CHEN Hanlin; FANG Dajun; DING Jinghai; ZHANG Shiben; HUANG Zhibin; LI Meng

    2005-01-01

    Paleomagnetic and rock magnetic studies on samples of 18 sites from the Cretaceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim,China show that the magnetic carriers of the Lower Cretaceous are dominated by hematite with some magnetite, while the magnetic carriers of the Upper Cretaceous are characterized by a combination of magnetite and titanomagnetite as well as hematite and goethite. Stepwise thermal demagnetization is performed and vector analysis is used to isolate magnetic components, which illustrates a single magnetic component or double magnetic components. The high temperature stable components are dual polarities and pass polarity test, reversal test and consistency test.The overall mean direction of the Lower Cretaceous is D = 27.0° , I = 42.0°, α95=6.5° with pole position at φ = 190.3° , λ=63.1 °, dp=4.9° , dm=8.0° . The overall mean direction of the Upper Cretaceous is D = 29.1 °, I = 39.4° , α95=11.2° with pole position at φ =190.9° , λ=60.3° , dp=8.0° , dm=13.4° . Compared with the inclination of the Early Cretaceous from red beds of north Tarim, the contemporary inclination of southwest Tarim is 10.0°±7.8° sharper, but it is still 8.1 °±8.9°, shallower than that of Early Cretaceous basalts in southwest Tarim. Although these paleomagnetic data show slightly larger confidence limit, the paleolatitude of the marine Cretaceous tends to lie between that of terrestrial red beds and volcanic rocks.

  7. Laser step-heating 40Ar/39Ar dating on young volcanic rocks

    Institute of Scientific and Technical Information of China (English)

    WANG Fei; HE Huaiyu; ZHU Rixiang; YANG Liekun; SANG Haiqing; WANG Yinglan

    2006-01-01

    An attempt was made to use CO2 laser step-heating method to date the late Pleistocene basaltic groundmass (DF-2) from Tengchong volcanic field. Among the fourteen heating steps, ten define a good inverse isochron (MSWD = 1.4) with an age of 32.2 ± 7.1 ka (2 σ).The inverse isochron also shows that the initial argon isotopic ratio is 297.1±2.0 (2σ)which is the same as the atmospheric argon at the 2σ error level. Study indicates that it is a useful means to date young volcanic groundmass with low K content by using CO2 laser step-heating 40Ar/39Ar method.

  8. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Indian Academy of Sciences (India)

    Ashima Saikia; Bibhuti Gogoi; Mansoor Ahmad; Talat Ahmad

    2014-07-01

    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, crosscutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

  9. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Science.gov (United States)

    Saikia, Ashima; Gogoi, Bibhuti; Ahmad, Mansoor; Ahmad, Talat

    2014-06-01

    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, cross-cutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

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

    Science.gov (United States)

    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

  11. Stable isotope compositions and water contents of boninite series volcanic rocks from Chichi-jima, Bonin Islands, Japan

    Science.gov (United States)

    Dobson, P.F.; O'Neil, J.R.

    1987-01-01

    Measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of Chichi-jima, Bonin Islands, Japan, confirm that a large amount (1.6-2.4 wt.%) of primary water was present in these unusual magmas. An enrichment of 0.6??? in 18O during differentiation is explained by crystallization of 18O-depleted mafic phases. Silicic glasses have elevated ??18O values and relatively low ??D values indicating that they were modified by low-temperature alteration and hydration processes. Mafic glasses, on the other hand, have for the most part retained their primary isotopic signatures since Eocene time. Primary ??D values of -53 for boninite glasses are higher than those of MORB and suggest that the water was derived from subducted oceanic lithosphere. ?? 1987.

  12. Textural variations and fragmentation processes in peperite formed between felsic lava flow and wet substrate: An example from the Cretaceous Buan Volcanics, southwest Korea

    Science.gov (United States)

    Gihm, Yong Sik; Kwon, Chang Woo

    2017-02-01

    Multiple exposures of peperite within the Cretaceous Buan Volcanics, southwest Korea, have been examined in order to determine variations in their textural characteristics and to investigate their mode of formation. Along undulating boundaries between rhyolite (lava flow) and deformed host sediment expressed as a series of load and flame structures, exposures commonly contain two distinct types of peperite. Type-1 peperites are composed mostly of rounded juvenile clasts at their base and polyhedral juvenile clasts at their upper levels, interpreted to have formed via a two-stage process. Firstly, abrasion of juvenile clasts occurred after their fragmentation due to shear stress imparted by the overlying and still-moving lava flow, forming rounded juvenile clasts. Subsequent in situ quenching fragmentation of the lava flow produced clasts with platy to polyhedral shapes immediately after emplacement of the lava flow. Type-2 peperites laterally extend into the interior of featureless rhyolite as layers that decrease in thickness with increasing distance away from the flame zone. These layers exhibit horizontal textural variations, ranging from poorly sorted mixtures of ash- to block-sized angular juvenile clasts in the proximal zone, to closely packed polyhedral and tabular juvenile clasts with jigsaw-crack textures in the middle and distal zones. Type-2 peperite are inferred to have formed due to internal steam explosions that resulted from an expansion of heated pore water (leading to an increase in pore fluid pressure) that had been vertically injected into the interior of the rhyolite from the flame zone. The proximal zone, composed mainly of poorly sorted mixtures of juvenile clasts, represents the explosion sites. Juvenile clasts in the middle and distal zones are interpreted to have formed due to three separate processes: the development of fractures in the rhyolite during the internal steam explosions, injection of the host sediment through the fractures, and

  13. Volcanism and Oil & Gas In Northeast China

    Institute of Scientific and Technical Information of China (English)

    Shan Xuanlong

    2000-01-01

    Based on study on the relation with volcanic rock and oil & gas in Songliao Basin and Liaohe Basin in northeast China, author proposes that material from deep by volcanism enrichs the resources in basins, that heat by volcanism promotes organic matter transforming to oil and gas, that volcanic reservoir is fracture, vesicular, solution pore, intercrystal pore.Lava facies and pyroclastic facies are favourable reservoir. Mesozoic volcanic reservoir is majority of intermediate, acid rock,but Cenozoic volcanic reservoir is majority of basalt. Types of oil and gas pool relating to volcanic rock include volcanic fracture pool, volcanic unconformity pool, volcanic rock - screened pool, volcanic darpe structural pool.

  14. Mineralogy of Rock Flour in Glaciated Volcanic Terrains: An Analog for a Cold and Icy Early Mars

    Science.gov (United States)

    Rampe, E. B.; Horgan, B.; Scudder, N.; Smith, R. J.; Rutledge, A. M.

    2017-01-01

    Geomorphological and mineralogical data from early Martian surfaces indicate liquid water was present on ancient Mars. The relative surface temperatures, however, remain a subject of debate. Was early Mars warm and wet or cold and icy with punctuated periods of warmth and ice melt? By characterizing the mineralogy and geochemistry of modern icy mafic terrains on Earth, we can search for these characteristics in early Martian terrains to better constrain the early Martian climate. Here, we describe the mineralogy of glacial flour in a modern glaciated volcanic terrain in Oregon, USA. We are particularly interested in secondary phases that form in these environments, and we hypothesize that poorly crystalline phases may preferentially form in these terrains because of the low temperatures and the seasonality of melt water production. A description of the mineralogy of the moraines, the composition of the amorphous materials, and the geochemistry of the glacial melt waters are presented elsewhere. Glacial flour is made up of silt- and clay-sized particles that form from the physical weathering of rock underlying a wet-based glacier as the glacier slides over it. Flour is usually transported from underneath a glacier by melt water streams. The geochemistry of glacial melt water streams has been studied extensively and has been used to infer weathering reactions within glacial systems. However, the mineralogy of these environments, especially on mafic volcanic terrains, is not well studied. Rock flour is a ubiquitous physical weathering product in glaciated terrains and, therefore, affects microbial habitats, stream and lake chemistry, and chemical weathering processes. and by studying the mineralogy of glacial flour, we can better understand geochemical and microbiological processes in subglacial and proglacial terrains.

  15. Late Jurassic-Early Cretaceous episodic development of the Bangong Meso-Tethyan subduction: Evidence from elemental and Sr-Nd isotopic geochemistry of arc magmatic rocks, Gaize region, central Tibet, China

    Science.gov (United States)

    Zhang, Yu-Xiu; Li, Zhi-Wu; Yang, Wen-Guang; Zhu, Li-Dong; Jin, Xin; Zhou, Xiao-Yao; Tao, Gang; Zhang, Kai-Jun

    2017-03-01

    The Bangong Meso-Tethys plays a critical role in the development of the Tethyan realm and the initial elevation of the Tibetan Plateau. However, its precise subduction polarity, and history still remain unclear. In this study, we synthesize a report for the Late Jurassic-Early Cretaceous two-phase magmatic rocks in the Gaize region at the southern margin of the Qiangtang block located in central Tibet. These rocks formed during the Late Jurassic-earliest Cretaceous (161-142 Ma) and Early Cretaceous (128-106 Ma), peaking at 146 Ma and 118 Ma, respectively. The presence of inherited zircons indicates that an Archean component exists in sediments in the shallow Qiangtang crust, and has a complex tectonomagmatic history. Geochemical and Sr-Nd isotopic data show that the two-phase magmatic rocks exhibit characteristics of arc magmatism, which are rich in large-ion incompatible elements (LIIEs), but are strongly depleted in high field strength elements (HFSEs). The Late Jurassic-earliest Cretaceous magmatic rocks mixed and mingled among mantle-derived mafic magmas, subduction-related sediments, or crustally-derived felsic melts and fluids, formed by a northward and steep subduction of the Bangong Meso-Tethys ocean crust. The magmatic gap at 142-128 Ma marks a flat subduction of the Meso-Tethys. The Early Cretaceous magmatism experienced a magma MASH (melting, assimilation, storage, and homogenization) process among mantle-derived mafic magmas, or crustally-derived felsic melts and fluids, as a result of the Meso-Tethys oceanic slab roll-back, which triggered simultaneous back-arc rifting along the southern Qiangtang block margin.

  16. What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou basin, Tibet)

    NARCIS (Netherlands)

    Huang, Wentao; Dupont-Nivet, Guillaume|info:eu-repo/dai/nl/313092559; Lippert, Peter C.; Van Hinsbergen, Douwe J J; Dekkers, Mark J.|info:eu-repo/dai/nl/073463744; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

    2015-01-01

    The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus, here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong

  17. What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou basin, Tibet)

    NARCIS (Netherlands)

    Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; Van Hinsbergen, Douwe J J; Dekkers, Mark J.; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

    2015-01-01

    The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus, here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Gr

  18. Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous

    Science.gov (United States)

    Hyppolito, Thais; Angiboust, Samuel; Juliani, Caetano; Glodny, Johannes; Garcia-Casco, Antonio; Calderón, Mauricio; Chopin, Christian

    2016-11-01

    Few localities in the Patagonian Andes expose remnants of the Mesozoic Chilean paleo-accretionary complex. We focus on the Diego de Almagro Island high-pressure/low-temperature (HP/LT) Complex, a pluri-kilometer thick sequence comprising metavolcanic rocks with oceanic affinities and metasedimentary rocks. In this study, the deepest segments of the Chilean subduction interface in Patagonia are characterized for the first time. Despite its apparent homogeneity, the complex is actually composed of two tectonic units with distinct ages of metamorphism and thermal evolution: the garnet amphibolite (GA) and the underlying blueschist (BS) units. The GA unit mafic rocks exhibit epidote, phengite, titanite, rutile, chloritoid and paragonite inclusions in prograde garnet I, diopside + albite intergrows replacing omphacite inclusions in garnet II, and relict omphacite (XJd45) included in edenitic-pargasitic amphiboles. Thermobarometric results show that these rocks were buried along a relatively cold prograde path (c. 11 °C/km) and reached eclogite-facies near peak pressure conditions (c. 550-600 °C, 1.6 GPa). The GA unit underwent a pervasive stage of amphibolitization during decompression at c. 1.3 GPa. Field and petrological observations, together with multi-mineral Rb-Sr dating, indicate that amphibolitization of the GA unit took place along the subduction interface at c. 120 Ma in a slightly warmer subduction regime (c. 13-14 °C/km), in agreeement with the formation of coetanoeus amphibolites at c. 35 km. The underlying BS unit (i) yields four consistent Rb-Sr deformation ages of c. 80 Ma, i.e. 40 Ma younger than the overlying rocks from the GA unit; (ii) exhibits slightly cooler peak metamorphic conditions (c. 520-550 °C, 1.6 GPa) indicating burial along a prograde path of c. 10 °C/km (iii) does not show amphibolite-facies overprint as seen in the GA unit. After a long residence time under amphibolite-facies conditions, the amphibolitized rocks of the GA unit

  19. Ontong Java volcanism initiated long-term climate warming that caused substantial changes in terrestrial vegetation several tens of thousand years before the onset of OAE1a (Early Aptian, Cretaceous)

    Science.gov (United States)

    Keller, Christina E.; Hochuli, Peter A.; Giorgioni, Martino; Garcia, Therese I.; Bernasconi, Stefano M.; Weissert, Helmut

    2010-05-01

    During Cretaceous times, several intense volcanic episodes are proposed as trigger for episodic climate warming, for changes in marine circulation patterns and for elevated marine productivity, which resulted in the widespread black shale deposits of the Oceanic Anoxic Events (OAE). In the sediments underlying the early Aptian OAE1a black shales, a prominent negative carbon isotope excursion is recorded. Its origin had long been controversial (e.g. Arthur, 2000; Jahren et al., 2001) before recent studies attributed it to the Ontong Java volcanism (Méhay et al., 2009; Tejada et al., 2009). Volcanic outgassing results in an increased pCO2 and should lead to a rise in global temperatures. We therefore investigated if the volcanically-induced increase in pCO2 at the onset of OAE1a in the early Aptian led to a temperature rise that was sufficient to affect terrestrial vegetation assemblages. In order to analyse changes in terrestrial palynomorph assemblages, we examined 15 samples from 12 black shale horizons throughout the early Aptian negative C-isotope spike interval of the Pusiano section (Maiolica Formation; N-Italy). These sediments were deposited at the southern continental margin of the alpine Tethys Ocean and have been bio- and magnetostratigraphically dated by Channell et al. (1995). In order to obtain a continuous palynological record of the negative C-isotope spike interval and the base of OAE1a, we combined this pre-OAE1a interval of Pusiano with the OAE1a interval of the nearby Cismon section (Hochuli et al., 1999). The sporomorph assemblages at the base of this composite succession feature abundant bisaccate pollen, which reflects a warm-temperate climate. Rather arid conditions are inferred from low trilete spore percentages. Several tens of thousand years before the onset of OAE1a, C-isotope values started to decrease. Some thousand years later, bisaccate pollen began to decrease, whereas an increase of Classopollis spp. and Araucariacites spp

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

    Science.gov (United States)

    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

  1. Geochemistry and zircon U-Pb geochronology of the rhyolitic tuff on Port Island, Hong Kong: Implications for early Cretaceous tectonic setting

    Directory of Open Access Journals (Sweden)

    Longlong Zhao

    2017-05-01

    Full Text Available Early Cretaceous rhyolitic tuffs, widely distributed on Port Island, provide insights into the volcanism and tectonic setting of Hong Kong. In this paper we present petrological, geochronological and geochemical data of the rhyolitic tuff to constrain the diagenesis age and petrogenesis of the rocks, tectonic setting and early Cretaceous volcanism of Hong Kong. The first geochronological data show that the zircons in the volcanic rocks have U-Pb age of 141.1–139.5 Ma, which reveals that the rhyolitic tuff on Port Island was formed in the early Cretaceous (K1. Geochemically, these acid rocks, which are enriched in large ion lithophile elements (LILEs and light rare earth elements (LREEs, and depleted in high field strength elements (HFSEs, belong to the high K calc-alkaline to shoshonite series with strongly-peraluminous characteristic. The geochemical analyses suggest that the volcanic rocks were derived from deep melting in the continental crust caused by basaltic magma underplating. Based on the geochemical analysis and previous studies, we concluded that the rhyolitic tuffs on Port Island were formed in a back-arc extension setting in response to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.

  2. Petrology and Geochemistry of Boninite Series Volcanic Rocks,Chichi-jima, Bonin Islands, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Dobson, Patrick F.; Blank, Jennifer G.; Maruyama, Shigenori; Liou, J.G.

    1977-01-01

    An Eocene submarine boninite series volcanic center isexposed on the island of Chichi-jima, Bonin Islands, Japan. Five rocktypes, boninite, bronzite andesite, dacite, quartz dacite, and rhyolite,were distinguished within the boninite volcanic sequence on the basis ofpetrographic and geochemical observations. Boninite lavas contain highmagnesium, nickel, and chromium contentsindicative of primitive melts,but have high silica contents relative to other mantle-derived magmas.All boninite series lavas contain very low incompatible elementconcentrations, and concentrations of high-field strength elements inprimitive boninite lavas are less than half of those found in depletedmid-ocean ridge basalts. Abundances of large-ion lithophile elements arerelatively high in boninite series lavas, similar to the enrichmentsobserved in many island arc lavas. Trends for both major and traceelement data suggest that the more evolved lavas of the boninite magmaseries were derived primarily through high-level fractionalcrystallization of boninite. Textural features, such as resorption andglomeroporphyrocrysts, and reverse chemical zonations suggest that magmamixing contributed to the development of the quartz dacitelavas.

  3. Petrogenesis of the Neoproterozoic bimodal volcanic rocks along the western margin of the Yangtze Block: New constraints from Hf isotopes and Fe/Mn ratios

    Institute of Scientific and Technical Information of China (English)

    LI Xianhua; QI Changshi; LIU Ying; LIANG Xirong; TU Xianglin; XIE Liewen; YANG Yueheng

    2005-01-01

    High-precision major element and Hf isotope data are reported for the Neoproterozoic Suxiong volcanic rocks along the western margin of the Yangtze Block. These volcanic rocks have variable εHf(T) values and Fe/Mn ratios. The relatively primitive basalts have high Fe/Mn ratios and high Hf-Nd isotopic compositions, indicating that they were generated by partial melting of garnet clinopyroxene in mantle plume at high pressure. Thus, the Suxiong basalts are genetically related to the proposed Neoproterozoic superplume. On the contrary, a few differentiated basalts have low Fe/Mn ratios and low Hf-Nd isotopic compositions. They are likely to experience assimilation-fractional crystallization process. The Suxiong rhyolites have consistent Hf and Nd model ages of 1.3-1.4 Ga. They are likely generated by shallow dehydration melting of pre-existing young arc igneous rocks associated with the basaltic underplating/intrusion in a continental rift.

  4. Insights from Pb and O isotopes into along-arc variations in subduction inputs and crustal assimilation for volcanic rocks in Java, Sunda arc, Indonesia

    Science.gov (United States)

    Handley, Heather K.; Blichert-Toft, Janne; Gertisser, Ralf; Macpherson, Colin G.; Turner, Simon P.; Zaennudin, Akhmad; Abdurrachman, Mirzam

    2014-08-01

    New Pb isotope data are presented for Gede Volcanic Complex, Salak and Galunggung volcanoes in West Java, Merbabu and Merapi volcanoes in Central Java and Ijen Volcanic Complex in East Java of the Sunda arc, Indonesia. New O isotope data for Merbabu and new geochemical and radiogenic isotope data (Sr-Nd-Hf-Pb) for three West Javanese, upper crustal, Tertiary sedimentary rocks are also presented. The data are combined with published geochemical and isotopic data to constrain the relative importance of crustal assimilation and subducted input of crustal material in petrogenesis in Java. Also discussed are the significance of limestone assimilation in controlling the geochemical and isotopic characteristics of erupted Javanese rocks and the geochemical impact upon central and eastern Javanese arc rocks due to the subduction of Roo Rise between 105 and 109°E. The negative correlation between Pb isotopes and SiO2, combined with mantle-like δ18O values in Gede Volcanic Complex rocks, West Java, are most likely explained by assimilation of more isotopically-primitive arc rocks and/or ophiolitic crust known to outcrop in West Java. The negative Pb isotope-SiO2 trend cannot be explained by assimilation of the known compositions of the upper crustal rocks. A peak in δ18O whole-rock and mineral values in Central Javanese volcanic rocks (Merbabu and Merapi) combined with along-arc trends in Sr isotope ratios suggest that a different or additional crustal assimilant exerts control on the isotopic composition of Central Javanese volcanic rocks. This assimilant (likely carbonate material) is characterised by high δ18O and high Sr isotope ratio but is not particularly elevated in its Pb isotopic ratio. Once the effects of crustal assimilation are accounted for, strong East to West Java regional variations in Ba concentration, Ba/Hf ratio and Pb isotopic composition are evident. These differences are attributed to heterogeneity in the subducted source input component along the

  5. Correlations between silicic volcanic rocks of the St Mary's Islands (southwestern India) and eastern Madagascar

    DEFF Research Database (Denmark)

    Melluso, Leone; Sheth, Hetu C.; Mahoney, John J.;

    2009-01-01

    , clinopyroxene, orthopyroxene and opaque oxide, Moderate enrichment in the incompatible elements, (e.g. Zr 580 720 ppm, Nb 43 53 ppan, La/Yb-a 0.9 7.2), relatively low initial Sr-87/Sr-86 (0.7052 0.7055) and near-chondritic initial Nd-143/Nd-144 (0.51248 0.51249), They have mineral chemical, whole-rock chemical...

  6. Distribution and significance of C40+ alkanes in the extracts of Cretaceous source rocks from the Songliao Basin

    Institute of Scientific and Technical Information of China (English)

    FENG; ZiHui; FANG; Wei; ZHANG; JuHe; LI; ZhenGuang; HUANG; ChunYan; WANG; Xue; ZHAO; QinLing; HUO; QiuLi

    2007-01-01

    Source rock extracts and crude oils from the Songliao Basin were analyzed by high-temperature gas chromatography (HTGC), gas chromatography-mass spectrometry (HTGC-MS) and gas chromatography-isotope ratio-mass spectrometry (GC-IRMS), for high molecular-weight alkanes. The distributions of n-alkanes in the Nenjiang Formation extracts are in the C14―C63 range; a bimodal distribution occurs in the and C21―40 regions. The C30―C37 n-alkanes are accompanied by C29―C35 hopanes, whereas the high molecular-weight C45―C47 n-alkanes co-occur with abundant isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The high δ13C values of the n-alkanes and the microscopic maceral compositions indicate a highly diversified organic source input for the Nenjiang Formation source rocks, ranging from aquatic plants, blue alge-bacteria, to land plant material. In contrast, n-alkanes in the rock extracts of the Qingshankou Formation are characterized by a single modal distribution, with relatively low abundances of C29―C35 hopanes, but high molecular-weight isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The relatively low δ13C values of C22―C44 n-alkanes and organic material compositions indicate that the source rocks in the Qingshankou Formation contain dominantly type I algal organic matter. The relative abundance of compounds in source rocks changes little at low maturity stage, but decreases drastically at higher maturity levels, with a concurrent reduction in the odd/even carbon predominance. In crude oils, in contrast, the relative abundance of compounds appears to relate closely with the oil source and oil viscosity.

  7. 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

    Science.gov (United States)

    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.

  8. Mesozoic tectonic regimes and regional ore-forming background in NE China: Constraints from spatial and temporal variations of Mesozoic volcanic rock associations%中国东北中生代构造体制与区域成矿背景:来自中生代火山岩组合时空变化的制约

    Institute of Scientific and Technical Information of China (English)

    许文良; 王枫; 裴福萍; 孟恩; 唐杰; 徐美君; 王伟

    2013-01-01

    空分布特征,可以判定:1)环太平洋构造体系对东亚大陆下的俯冲始于早侏罗世,中生代期间存在早侏罗世、早白垩世晚期和晚白垩世三次俯冲事件,其影响的空间范围主要在松辽盆地及其以东地区,陆缘和古俯冲带是寻找斑岩型矿床的有利场所,而陆内的伸展区域主要与浅成低温热液矿床有关;2)蒙古-鄂霍茨克构造体系经历了中生代早期的俯冲事件和中侏罗世及早白垩世早期两次陆内推覆事件,其影响的空间范围主要在松辽盆地以西地区和华北地块北缘,中生代早期的俯冲事件主要与活动陆缘背景下的斑岩型矿床关系密切,而晚侏罗世和早白垩世两次与加厚陆壳拆沉有关的伸展背景有利于多金属矿床的形成.%This paper summarizes geochronology and association of Mesozoic volcanic rocks and their spatial and temporal variations, with the aim of constraining evolutionary history, and ore-forming background of the circum Pacific and Mongol-Okhotsk tectonic systems in NE China. Zircon U-Pb dating results indicate that Mesozoic volcanisms in NE China can be subdivided into six stages, i. e. , Late Triassic (200 ~ 228Ma) , Early-Middle Jurassic (173 ~ 190Ma) , Middle-Late Jurassic ( 158 ~ 166Ma) , early Early Cretaceous (138 ~ l45Ma) , late Early Cretaceous (106 ~ 133Ma) , and Late Cretaceous (88 ~ 97Ma). Late Triassic volcanic rocks in NE China mainly distribute in the eastern Jilin-Heilongjiang provinces and the Lesser Xing' an-Zhangguangcai Ranges. The former consists of A-type rhyolite, the latter is composed of bimodal volcanic rocks, implying that they formed under an extensional environment after the final closure of the Paleo-Asian Ocean. Early-Middle Jurassic volcanic rocks occur in the eastern Jilin-Heilongjiang provinces, the Lesser Xing'an-Zhangguangcai Ranges, and the Erguna district Those in the eastern Jilin- Heilongjiang provinces and the Erguna district are composed of calc-alkaline volcanic

  9. Permian, Jurassic and Early Cretaceous palynofloral assemblages from subsurface sedimentary rocks in Chuperbhita Coalfield, Rajmahal Basin, India.

    Science.gov (United States)

    Tripathi, A

    2001-04-01

    The results of a palynological analysis of the sedimentary sequence of Borehole RCH-151, Chuperbhita Coalfield, Rajmahal Basin, Bihar are presented here. The borehole penetrated the Rajmahal Formation (comprising two traps sandwiching an intertrappean bed), the thinly represented Dubrajpur Formation and in its lower part, the Coal Measures. The coal-bearing interval is associated with Scheuringipollenites barakarensis, Faunipollenites varius, Densipollenites indicus, Gondisporites raniganjensis and Densipollenites magnicorpus Assemblage Zones. The presence of these biostratigraphic units indicates correlation with the Barakar Formation (Early Permian) and the Barren Measures and Raniganj Formations (both Late Permian). This is the first record, in the Chuperbhita Coalfield, of Late Permian strata, which appear to represent a condensed sequence. Prior to the present study, the Permian succession was thought to have been associated entirely with the Barakar Formation. The overlying Dubrajpur Formation yielded a distinct spore-pollen assemblage (in association with the first report of dinoflagellate, Phallocysta), which is assigned to the newly identified Callialasporites turbatus palynozone of latest Early to early Middle Jurassic age. The diverse spore-pollen flora of the intertrappean bed (Rajmahal Formation) incorporates several age marker taxa, viz. Undulatisporites, Leptolepidites, Klukisporites, Ruffordiaspora, and Coptospora. The assemblages from intertrappean beds are correlated with the Ruffordiaspora australiensis palynozone of Australia. Thus the palynodating indicates Permian, latest Early to early Mid-Jurassic and Early Cretaceous age for the strata studied. This is the first record of definite Jurassic microfossils from the non-marine sequence of Rajmahal Basin, India.

  10. New records of rare lichenicolous and lichen-forming fungi from volcanic rocks in SW Poland

    Directory of Open Access Journals (Sweden)

    Katarzyna Szczepańska

    2015-08-01

    Full Text Available Records of two lichenicolous and nine lichen-forming fungi found in the southwestern part of Poland are presented. All of the reported species are very rare and they have only a few scattered localities in the country. One of them, Lecanora pannonica, is reported for the second time from Poland. Additionally, the new, contemporary records of Cercidospora macrospora, Rhizocarpon disporum, R. viridiatrum and Stereocaulon pileatum in Lower Silesia were noted. These species were known only from historical collections in the study area. Furthermore, Lecidea fuscoatra has been found a new host for Sagediopsis barbara. All of the localities of recorded species were found on natural outcrops of basalt rocks.

  11. Water-rock interaction during mineral carbonation and volcanic ash weathering

    OpenAIRE

    Helgi Arnar Alfreðsson 1984

    2015-01-01

    The reduction of atmospheric carbon dioxide (CO2) is considered one of the greatest challenges of this century. Carbon capture and storage (CCS) is one of the means proposed to lower the atmospheric CO2 content. The aim of the CarbFix project in Iceland was to design and test a CO2 re-injection system, in which CO2 from the Hellisheidi geothermal power plant was injected, fully dissolved in water, into basaltic rocks. In this way the carbon is mineralized upon basalt dissolution by the precip...

  12. 226Ra or 226Ra/Ba dating of Holocene volcanic rocks: application to Mt. Etna and Merapi volcanoes

    Science.gov (United States)

    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

  13. How temperature-dependent elasticity alters host rock/magmatic reservoir models: A case study on the effects of ice-cap unloading on shallow volcanic systems

    Science.gov (United States)

    Bakker, Richard R.; Frehner, Marcel; Lupi, Matteo

    2016-12-01

    In geodynamic numerical models of volcanic systems, the volcanic basement hosting the magmatic reservoir is often assumed to exhibit constant elastic parameters with a sharp transition from the host rocks to the magmatic reservoir. We assess this assumption by deriving an empirical relation between elastic parameters and temperature for Icelandic basalts by conducting a set of triaxial compression experiments between 200 °C and 1000 °C. Results show a significant decrease of Young's modulus from ∼38 GPa to less than 4.7 GPa at around 1000 °C. Based on these laboratory data, we develop a 2D axisymmetric finite-element model including temperature-dependent elastic properties of the volcanic basement. As a case study, we use the Snæfellsjökull volcanic system, Western Iceland to evaluate pressure differences in the volcanic edifice and basement due to glacial unloading of the volcano. First, we calculate the temperature field throughout the model and assign elastic properties accordingly. Then we assess unloading-driven pressure differences in the magma chamber at various depths in models with and without temperature-dependent elastic parameters. With constant elastic parameters and a sharp transition between basement and magma chamber we obtain results comparable to other studies. However, pressure changes due to surface unloading become smaller when using more realistic temperature-dependent elastic properties. We ascribe this subdued effect to a transition zone around the magma chamber, which is still solid rock but with relatively low Young's modulus due to high temperatures. We discuss our findings in the light of volcanic processes in proximity to the magma chamber, such as roof collapse, dyke injection, or deep hydrothermal circulation. Our results aim at quantifying the effects of glacial unloading on magma chamber dynamics and volcanic activity.

  14. Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    ZENG Zhigang; YU Shaoxiong; WANG Xiaoyuan; FU Yongtao; YIN Xuebo; ZHANG Guoliang; WANG Xiaomei; CHEN Shuai

    2010-01-01

    Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements (HFSE).These rocks are higher in Large Ion Lithophile Elements (LILE),thorium and uranium contents,positive lead anomalies,negative Nb-Ta anomalies,and enrichment in Light Rare Earth Elements (LREE).Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB),and rhyolites from the northern Okinawa Trough have the highest 207Pb/204Pb and 208Pb/204Pb ratios.The NECS shelf margin basalts have lower 87Sr/86Sr ratios,εNd and σ18O than the northern Okinawa Trough silicic rocks.According to 40K-40Ar isotopic ages of basalts from the NECS shelf margin,rifting of the Okinawa Trough may have been active since at least 3.65-3.86 Ma.The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere.The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough,and the formation of basaltic magmas closely relates to the thinning of continental crust.The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough,which could have been generated by the interaction of basaltic melt with an enriched crustal component.From the Ryukyu island arc to East China,the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE),suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate,and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.

  15. Relative Roles of Source Composition, Fractional Crystallization and Crustal Contamination in the Petrogenesis of Andean Volcanic Rocks

    Science.gov (United States)

    Thorpe, R. S.; Francis, P. W.; O'Callaghan, L.

    1984-04-01

    There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt--andesite--decite--rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt--trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of `within-plate' character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust. Active Andean volcanoes of the calc-alkaline basalt--andesite--dacite rhyolite association occur within a northern (n.v.z.), central (c.v.z.) and southern volcanic zone (s.v.z.) (figure 9). Alkaline volcanic rocks occur within and to the east of these zones. The n.v.z. and s.v.z. lavas have chemical and isotope characteristics consistent with an origin by

  16. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

    Science.gov (United States)

    Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan

    2017-05-01

    Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

  17. A Clinopyroxene-Plagioclase Geobarometer for A-type Silicic Volcanic Rocks

    Science.gov (United States)

    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.

  18. Helium isotopic variations in volcanic rocks from Loihi Seamount and the Island of Hawaii

    Science.gov (United States)

    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.

  19. Isotopic composition of salt efflorescence from the sandstone castellated rocks of the Bohemian Cretaceous Basin (Czech Republic)

    Science.gov (United States)

    Schweigstillová, Jana; Přikryl, Richard; Novotná, Miroslava

    2009-07-01

    The origin of sulphates in sulphate-rich efflorescences on quartz sandstones with a clay matrix, exposed in rural areas of the Czech Republic is interpreted, based upon an isotopic study of S and O. Sulphates such as gypsum and/or alums exhibit δ34S ranging from +1.3 to +6.1‰ and δ18O from +5.3 to +8.8‰. The low variability of S and O isotopes indicates a common source of the sulphur and a similar mode of sulphate formation. Atmospheric sulphates with a similar isotopic signature occur in the area, due to the combustion of sulphurous coal in power plants, located a few tens of kilometres from the sampling points. The sulphates crystallize from supersaturated pore waters that represent atmospheric precipitation, rich in sulphates, having percolated through the porous sandstone system. The previously proposed model of efflorescence growth (that it is due to the oxidation of pyrite) can be excluded, due to both the rare occurrence of pyrite and also to its different isotopic signature (δ34S about -22‰). Although gypsum prevails in the central and eastern part of the studied area, the north and north-west of the Bohemian Cretaceous Basin (the most polluted region) exhibits a significant presence of alums (NH4 + or K+-NH4 +-rich). Formation of alums can be explained by the partial dissolution of clay minerals or feldspars present in the sandstone matrix. Release of alumina from these phases is facilitated by the low pH of the precipitation (pH 4-4.5) and also locally by organic acids, traces of which were found in the studied efflorescences by the use of infrared spectroscopy.

  20. Uranium, yttrium, and rare earth elements accumulation during the Cretaceous anoxic events in carbonaceous rocks in the Pacific Ocean

    Science.gov (United States)

    Savelyeva, Olga; Philosofova, Tatyana; Bergal-Kuvikas, Olga; Savelyeva, Svetlana

    2017-04-01

    We have studied the carbonate-siliceous section of paleooceanic Albian-Cenomanian deposits on the Kamchatsky Mys peninsula (Eastern Kamchatka, Russia) [1].The section is represented by a rhythmic alternation of planktonic limestones and jaspers, accumulated in the open ocean environment. The rhythmicity can be attributed to climate variations that reflect a fluctuation of astronomical parameters (Milankovitch cycles) [2, 3].The section contains two beds enriched in organic carbon, corresponding to the two oceanic anoxic events - MCE and OAE2 [3]. The maximum content of organic matter in those beds reaches 68%. Our geochemical studies revealed an enrichment of the carbonaceous rocks in some major and trace elements including PGE, in comparison with the surrounding limestone and jasper [4].The accumulation of the ore elements in carbonaceous beds is caused by euxinic conditions during sedimentation.The content of uranium, yttrium, and rare earth elements in carbonaceous rocks is up to 60, 142 and 312 ppm respectively. Phosphate grains (bone detritus) with microinclusions of yttrium and uranium minerals were revealed in the carbonaceous rocks using the scanning electron microscope. These data prove the hypothesis of the sorbtion of U and Y by phosphate detritus from seawater. Microprobe analysis also showed an increased content of Cu, Zn, V in some pyrite framboids, which indicates that these elements are fixed in rocks by Fe-sulphide phase or organic matter under euxinic conditions. Our research may bring us closer to understanding the mechanism of syngenetic accumulation of metals in the black shales. This work was supported by the RFBR (No. 16-05-00546). [1] Palechek, T.N., Savelyev, D.P., Savelyeva, O.L. (2010) Stratigraphy and Geological Correlation 18, (1) 63-82. [2] Savelyeva, O.L. (2010). Vestnik Kraunts. Nauki o zemle 1 (15), 45-55 (in Russian). [3] Savelyev, D.P., Savelyeva, O.L., Palechek, T.N., Pokrovsky, B.G. (2012) Geophysical Research Abstracts, 14, EGU

  1. 3.5 billion years of glass bioalteration: Volcanic rocks as a basis for microbial life?

    Science.gov (United States)

    Staudigel, Hubert; Furnes, Harald; McLoughlin, Nicola; Banerjee, Neil R.; Connell, Laurie B.; Templeton, Alexis

    2008-08-01

    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.

  2. 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

    Science.gov (United States)

    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

  3. Rock magnetism and magnetic anisotropy in folded sills and basaltic flows: A case study of volcanics from the Taimyr Peninsula, Northern Russia

    Institute of Scientific and Technical Information of China (English)

    ZHANG ShuWei; J. Harald WALDERHAUG; YANG YueJun

    2008-01-01

    Magnetic measurements were performed on apparently deformed igneous rocks of 23 sites from the southeastern part of the Taimyr Peninsula. Rock magnetism and reflected light microscopy analyses reveal that fine-grained titanomagnetites up to pure magnetites mainly carry the majority of magnetic fabrics in the sills, and that the slightly coarser Ti-poor or-medium titanomagnetites carry most mag-netic fabrics in the basaltic flows. Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) on 180 unheated samples and 128 samples that had been pre-viously heated to 600℃ during a paleomagnetic study to detect heating effects on the anisotropy of magnetic susceptibility (AMS) properties of volcanic rocks. Laboratory heating significantly affects anisotropy variations of these igneous rocks corresponding to the mineralogical changes during the heat treatment.

  4. Petrogenesis of Middle-Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: Implications for early subduction of Neo-Tethyan oceanic lithosphere

    Science.gov (United States)

    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.

  5. Iron and Zinc isotope fractionation during magmatism in the continental crust: Evidence from bimodal volcanic rocks from Hailar basin, NE China

    Science.gov (United States)

    Xia, Ying; Li, Shuangqing; Huang, Fang

    2017-09-01

    This study presents Fe-Zn isotope data for a suite of well-characterized bimodal volcanic rocks from Hailar Basin, northeast China to understand the mechanism of Fe isotope fractionation in highly differentiated igneous rocks. The samples range from basaltic trachyandesites to trachytes-rhyodacites, and rhyolites. The δ56Fe values increase with increasing SiO2 contents with the rhyolites having the highest δ56Fe (up to 0.64 ± 0.02‰) among the previously reported data for igneous rocks at a similar SiO2. The lack of correlation between δ56Fe and Rb/La argues against the effect of fluid exsolution on Fe isotopes. The δ56Fe do not show a clear correlation with δ66Zn and radiogenic isotopes, suggesting that thermal diffusion or crustal contamination cannot produce the high δ56Fe in Hailar volcanic rocks. Fe isotopic variation in Hailar volcanic rocks can be explained by two steps of magmatism. During the first step, partial melting of basaltic trachyandesites with an average δ56Fe of 0.09 ± 0.14‰ produced trachytes-rhyodacites with an average δ56Fe of 0.24 ± 0.27‰. Modelling using rhyolite-MELTS shows that Fe isotopes can be fractionated by preferential partitioning of isotopically different Fe3+ and Fe2+ between the solid residue and partial melt. The second step involves formation of rhyolites with significantly high δ56Fe through partial melting or extensive crystallization of crust materials, during which isotopically heavy Fe preferentially partition into the rhyolitic melt. Therefore, fractionation of Fe isotopes between melts and minerals can result in high δ56Fe in SiO2-rich igneous rocks and apparent Fe isotope heterogeneity within the continental crust.

  6. Late sodic metasomatism evidences in bimodal volcanic rocks of the Acampamento Velho Alloformation, Neoproterozoic III, southern Brazil

    Directory of Open Access Journals (Sweden)

    Delia Del Pilar M. de Almeida

    2007-12-01

    Full Text Available A mineralogical study was carried out in mafic and felsic volcanic rocks of the Acampamento Velho Alloformation at Cerro do Bugio, Perau and Serra de Santa Bárbara areas (Camaquã Basin in southern Brazil. The Acampamento Velho bimodal event consists of two associations: lower mafic at the base and upper felsic at the top. Plagioclase and alkali-feldspar were studied using an electronic microprobe, and magnetite, ilmenite, rutile, illite and alkali-feldspar were investigated through scanning electron microscopy. The rocks were affected by a process of late sodic autometasomatism. In mafic rocks, Ca-plagioclase was transformed to albite and pyroxenes were altered. In felsic rocks, sanidine was partially pseudomorphosed, generating heterogeneous alkali-feldspar. In this association, unstable Ti-rich magnetite was replaced by rutile and ilmenite. In mafic rocks, the crystallization sequence was: (1 Ti-rich magnetite (?, (2 pyroxene and Ca-plagioclase, (3 albite (alteration to Ca-plagioclase, (4 sericite, chlorite and calcite (alteration to pyroxene, and kaolinite (alteration to plagioclase/albite. In felsic rocks: (1 zircon, (2 Ti-rich magnetite, (3 sanidine, (4 quartz. The introduction of late Na-rich fluids, generated the formation of (5 heterogeneous alkali-feldspar, (6 ilmenite and rutile from the Ti-rich magnetite, (7 albite in the spherulites. Finally, alteration of sanidine, vitroclasts and pumice to (8 illite.Um estudo mineralógico de detalhe foi realizado nas rochas vulcânicas da Aloformação Acampamento Velho nos Cerros do Bugio, Perau e Serra de Santa Bárbara (Bacia do Camaquã, sudeste do Brasil. Este evento bimodal é constituído por duas associações: máfica inferior na base e félsica superior no topo. Foram estudados grãos de plagioclásio e feldspato alcalino com o uso de microssonda eletrônica, sendo que, magnetita,ilmenita, rutilo e ilita além de feldspato alcalino foram pesquisados através do microscópio eletr

  7. Geochemical discrimination of the geotectonic environment of basaltic-andesitic volcanic rocks associated with the Laochang polymetallic ore deposit at Lancang, Yunnan

    Institute of Scientific and Technical Information of China (English)

    GAO Jianguo

    2006-01-01

    The Laochang polymetallic ore deposit at Lancang is one of the well known ancient ore deposits associated with volcanic rocks in the Sanjiang (Tri-river) region of Southwest China. Volcanic rocks are dominated by alkali basalt and trachyte basalt. There has long been a controversy on the environment of formation of basalts. Some scholars hold that the basalts were formed in a continental environment, some thought they were formed in an oceanic environment and others considered that the basalts were emplaced in a back-arc basin. This study focuses on the geochemical characteristics of the basalts on the basis of their major elements, REEs and trace elements. At the same time, strongly incompatible elements such as Ta, Th and Hf and their ratios were used to differentiate the geotectonic settings of basalts. The results showed that the basalts in the region studied were formed in a continental rift environment.

  8. Petrography and geochemistry of volcanic rocks in the east of Nabar (SW of Kashan with emphasis on the role of crustal contamination

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    Seyed Mohsen Tabatabaei Manesh

    2016-09-01

    Full Text Available The studied area is located in the east of Nabar village and southwest of Kashan, a part of the Urumieh – Dokhtar magmatic arc. The volcanic rocks belonging to Eocene age, are composed of pyroxene andesites, andesites, dacites and rhyolites. Porphyritic, glomeroporphyric, microlitic, and sieved textures are the most common textures of these rocks. Plagioclase, clinopyroxene and amphibole are the predominant minerals in the pyroxene andesites and andesites, whereas dacites and rhyolites are characterized by the presence of plagioclase, amphibole, quartz, biotite, and K-feldspar. Inequilibrium textures including embayed plagioclases and quartz with rounded margins, and oscillatory zoning in the plagioclases, sieved texture, and dusty rims are evidences of magma mixing. The enrichment in LREE and LILE and the HREE and HFSE depletion in the chondrite and primitive mantle normalized diagrams point to calc-alkaline nature of the rocks studied and they are related to volcanic arcs setting. High ratio of La/Nb (2-4.36 and negative Ti and Nb anomalies in spider diagrams can support crustal contamination hypotheses of these rocks. Also, low ratio of Nb/La (0.23-0.5 and high ratio of Sr/Ce (8.4-19 indicate contamination of parental magma with crustal materials. The rocks studied are formed from magma which is derived from enriched-mantle with 1-5 percent partial melting of spinel-lehrzolite.

  9. Isotope and trace element systematics in a spinel-lherzolite-bearing suite of basanitic volcanic rocks from San Luis Potosi, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Pier, J.E.G.

    1989-01-01

    Lherzolite-bearing basanitic magmas of Quaternary age have erupted to form maars, lava/cinder cones and lava flows in two volcanic fields (Ventura and Santo Domingo) in the central Mexican state of San Luis Potosi. The systematics of the radiogenic isotopes of Sr, Nd, and Pb and the relationship between these parameters and elemental compositions are used to investigate the petrogenesis of the volcanic rocks and the nature of their mantle sources. Sr and Nd isotopic data are presented for 19 basanitic rocks, 5 kaersutites, and 6 lherzolitic xenoliths; Pb data presented for the same 19 volcanic rocks and 4 of the 5 kaersutites. The isotopic compositions for all of these samples fall within the mantle range defined by MORBs and OIBs. The basanites generally plot within the OIB field on isotopic diagrams; most of the kaersutites are displaced to slightly more-depleted (i.e. MORB-like) values than the volcanic samples and the xenoliths, with one exception, are significantly more-depleted than either of these sample-types. As crustal contamination is considered unlikely for most of the volcanic samples, these trends are thought to arise from mixing multiple mantle components. The absence of similar isotopic elemental relationships for Epsilon Nd and the lack of correlation between {sup 206}Pb/{sup 204}Pb and the other Pb isotopes require a mixture of at least three mantle reservoirs: a depleted reservoir analogous to that of the MORBs, a St. Helena-type component, and a third component, which primarily affects Sr and {sup 208}Pb/{sup 204}Pb composition. This third component carries relatively radiogenic Sr and {sup 208}Pb/{sup 204}Pb and appears to be correlated with the degree of melting.

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

    Science.gov (United States)

    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

  11. Paleointensities of the Auckland Excursion from Volcanic Rocks in New Zealand

    Science.gov (United States)

    Mochizuki, N.; Tsunakawa, H.; Shibuya, H.; Cassidy, J.; Smith, I. E.

    2001-12-01

    Shibuya et al. (1992) reported the Auckland excursion from several basaltic lava flows of monogenetic volcanic centers (forced to introduce correction for thermal alterations in laboratory heating, using low temperature part of the Arai plot. We, therefore, applied the double heating technique (DHT) of Shaw method (Tsunakawa and Shaw, 1994), which was capable of detecting inappropriate results by the ARM correction, to the samples. The low temperature demagnetization (LTD) was combined with DHT (Yamamoto et al., submitted) before AF demagnetization and samples were heated in a vacuum of 10-100 Pa. Sixty-one samples from the five lava flows were subjected to the LTD-DHT Shaw method. Twenty-three of these samples yielded successful results passing the selection criteria. Five out of six paleointensities from the Crater Hill lava were consistent with each other. A mean paleointensity was given to be 10.9+/- 1.9 μ T (N=5) for the Crater Hill lava. Five out of seven paleointensities from the Wiri lava, were consistent and a mean was 10.8+/- 1.2 μ T (N=5). Three samples from the Puketutu lava gave a mean paleointensity of 11.4+/- 0.8 μ T (N=3). These three lava flows, Crater Hill, Wiri and Puketutu lava, all recorded the north-down paleodirection and gave almost the same paleointensities of ~ 11 μ T. This concordance of paleointensities and paleodirections supports the reliability of the paleointensity determination. Four paleointensities were obtained from the Hampton Park lava of the west paleodirection, and gave a mean paleointensity of 10.1+/- 1.1 μ T (N=4). The field strength was comparable to that of the north-down group. Three samples from the McLennan Hills lava of the south paleodirection gave quite low paleointensities, a mean of which was calculated to be 2.4+/- 0.6 μ T (N=3). These five paleointensities from the Auckland excursion are no more than one-fifth of the present-field intensity. The corresponding VDMs range from 0.6x1022 to 2.3*E22Am2, which

  12. Segmentation of the Cascade Arc Based on Compositional and Sr and Nd Isotopic Variations in Primitive Volcanic Rocks

    Science.gov (United States)

    Schmidt, M. E.; Grunder, A. L.

    2006-12-01

    We define four segments in the Cascade Volcanic Arc based on 87Sr/86Sr and 143Nd/144Nd of primitive volcanic rocks: 1) The North segment extends 450 km from Mt. Meager to Glacier Peak; 2) the 350-km Columbia segment includes volcanoes from Mt. Rainier to Mt. Jefferson; 3) the 250 km Central segment comprises the portion of the arc between the Three Sisters and Crater Lake; and 4) the 350-km South segment includes Mt. Shasta to Mt. Lassen. Isotopic data were compiled for primitive bulk composition (MgO concentrations >8 wt.% MgO) as a fingerprint mantle sources. The North segment has a range in 87Sr/86Sr of 0.7030-0.7037 and is distinguished by the predominance of calcalkaline basalts (CAB) and few low K tholeiites (LKT). The North segment lies on the North Cascade craton where convergence is near orthogonal. Oblique subduction occurs beneath the Columbia, Central, and South segments. The Columbia segment (87Sr/86Sr of 0.7028-0.7037) has both LKT and CABs as well as enriched ocean island-like basalts (OIB) that are found both on the arc axis and, especially at the Simcoe Volcanic Field, behind the arc. This segment lies primarily on the accreted Tertiary oceanic plateau terrane of the Columbia Embayment. The Central segment is dominated by LKT with lesser CAB and has the most restricted Sr isotopic range (0.7034- 0.7038). Like the South segment, the Central segment mainly overlies accreted terranes stitched by Mesozoic plutons and has Basin and Range (B&R) extension behind as well as locally within the arc. Medicine Lake Volcano, on the margin of the B&R behind Mt. Shasta is also dominated by LKT and has a narrow isotopic range like the Central segment. This suggests that the LKT's are related to extension in the arc. The South segment is distinguished by the widest Sr isotopic range (0.7028-0.7042) and the presence of high Mg basaltic andesite and andesite compositions in addition to LKT and CABs. These arc segments broadly correspond to physical segments that were

  13. Zircon age and geochemistry of the Tost bimodal volcanic rocks: Constraints on the Early Carboniferous tectonic evolution of the South Mongolia

    Science.gov (United States)

    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.

  14. 松辽盆地断陷层系地震火山地层学研究:典型火山岩地震相与地质解释模式%Seismic Volcanostratigraphy of the Songliao Basin,Early Cretaceous:Typical Volcanic Seismic Facies and Geological Interpretation Pattern

    Institute of Scientific and Technical Information of China (English)

    衣健; 王璞珺; 李瑞磊; 赵然磊; 陈崇阳; 孙玥

    2014-01-01

    为了研究松辽盆地火山岩盆地充填模式及在无井或少井区寻找火山岩有利储层,需要对盆地火山岩地震相及其反射特征和地质内涵进行系统性的总结和分析。基于盆内钻井和过井地震剖面,应用火山地层学理论和地震火山地层学方法将松辽盆地火山岩地震相单元划分为火山岩丘、火山岩台地、洼地火山充填、穿切等4类10种亚类。通过井震对比,结合野外火山地层研究相关文献资料,阐述了这些地震相单元的地质解释模式和响应关系。火山岩地震相单元通常对应于以某种盆地火山充填类型(相或相组合)为主的火山岩体,火山岩丘地震相多可解释为侵出岩穹、酸性简单熔岩流和酸性复合熔岩流等具有丘状外形的充填类型,火山岩台地地震相多代表中基性岩的简单熔岩流和火山碎屑流等具有席状外形的充填类型,洼地火山充填多代表充填在先存洼地中的简单熔岩流和火山碎屑流,穿切地震相多可解释为岩席、岩墙。除了这些典型的地震相单元以外,对地震反射特征(外形、物理参数、反射结构)与火山岩地质属性的响应关系的分析可有助于更好地解释地震相单元所反映的地质含义。%In order to understand the volcanic rocks filling model in basin and explore favorable volcanic reservoir in less or no well area,the systematically study of seismic facies units,their reflection characteristics and geological interpretation is necessary.With volcanostratigraphy theory and seismic volcanostratigraphy method,the typical seismic facies of the volcanic rocks were studied based on wells and inter-well seismic profiles in the Songliao volcanic rifted grabens,Early Cretaceous.The facies can be divided into 4 types and 10 subtypes of typical seismic facies units,such as the volcanic dome unit, the volcanic platform unit,the volcanic filling unit and the cutting units

  15. Vulnerability of shallow ground water and drinking-water wells to nitrate in the United States: Model of predicted nitrate concentration in shallow, recently recharged ground water -- Input data set for basalt and volcanic rocks (gwava-s_vrox)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This data set represents the presence or absence of basalt and volcanic rocks in the conterminous United States. The data set was used as an input data layer for a...

  16. Magmatism in the Tsagaandelger, Eastern Mongolian volcanic belt: Petrological, geochemical and isotopic constraints on Mesozoic geodynamic setting

    Science.gov (United States)

    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

  17. The Pelona-Pico Duarte basalts Formation, Central Hispaniola: an on-land section of Late Cretaceous volcanism related to the Caribbean large igneous province

    National Research Council Canada - National Science Library

    Escuder Viruete, J; Perez-Estaun, A; Joubert, Marc; Weis, D

    2011-01-01

    .... The Pelona-Pico Duarte basalts Fm. was emplaced onto Turonian-Lower Campanian island-arc volcanic and sedimentary sequences, and is overlain by Maastrichtian platformal carbonates. Two (40)Ar/(39...

  18. Geochemistry of Late Cretaceous (60- 67 Ma) igneous activities in the Hebrides Terrace seamount (guyot) area, Scotland

    Institute of Scientific and Technical Information of China (English)

    M. El-Tokhi; M. Omran; A. El-Muslem

    2005-01-01

    Tholeiitic basalts in various stages of alteration were dredged from Late Cretaceous volcanic rocks (60 -67 Ma) in the Hebrides Terrace seamount area in the Atlantic Ocean. These rocks are extrusive olivine basalts, including high- and low-Al basalts. High-Al basalts are depleted in MgO, CaO, Cr,Sc, V, Sr, Zr and enriched in TiO2, Na2 O, Nb, Rb as compared with low-Al basalts. Petrography and bulk-rock composition (major, trace and rare-earth elements) data defined clear tholeiitic suites displaying possible liquid lines of descent related to different degrees of crystal fractionation and partial melting.Isotopic dating of dredged samples gave the guyot an age of 60 - 67 Ma, in support of the assumption that it was formed during the Late Cretaceous.

  19. 赣东北晚白垩世橄榄玄粗岩(Shoshonite)系列火山岩厘定的地质证据%Shoshonite Series Volcanic Rocks in Northern Jiangxi Province

    Institute of Scientific and Technical Information of China (English)

    项媛馨; 巫建华; 余达淦; 刘帅

    2012-01-01

    赣东北广泛发育晚白垩世红色沉积盆地,并常伴有镁铁质火山活动.位于东乡-广丰断裂带南侧的广丰盆地产有上、下两套镁铁质火山岩,而位于该断裂带北侧的玉山盆地产有一套镁铁质火山岩.研究表明,广丰盆地上部的镁铁质火山岩和玉山盆地的镁铁质火山岩均呈块状构造,多气孔,气孔内常充填硅质、碳酸盐、绿泥石;斑晶矿物含量为15%左右,以斜长石和单斜辉石为主,并有少量橄榄石和斜方辉石,斜长石斑晶常见钾长石环边;基质为似粗面结构,斜长石定向排列,也具有钾长石环边;岩石SiO2含量为49.8% ~53.6%(平均51.7%),富碱(Na2O+ K2O为5.00% ~ 6.94%,平均6.35%)、富钾(K2O为2.40% ~ 3.99%,平均2.98%)、K2O/Na2O(0.68 ~ 1.08,平均0.79)比值高,在SiO2 -( Na2O+K2O)图解上落入碱性系列范围,在SiO2 - K2O和SiO2 - K2O/Na2O图解上均落入橄榄玄粗岩范围;全铁含量(7.10%~9.99%,平均8.26%)低,但具有高的Fe2 O3/FeO比值,在AFM图解中具有钙碱性系列特征,在MgO -∑Fe图解上落入钙碱性系列趋势范围内,且大多数位于Lesser Antilles( CA-1)和Cascades( CA-2)两钙碱性趋势线之间,表现出亲钙碱性特征;其地球化学总体特征与典型橄榄玄粗岩系列一致.本文通过对矿物学和地球化学这两方面特征的总结,厘定其为橄榄玄粗岩系列火山岩.%The red sedimentary basin was appeared extensively with large scare of mafic volcanic rocks in Late Cretaceous. Guangfeng basin has two sets of mafic volcanic rocks, which located in the south of Dongxiang-Guangfeng fault line. Yushan basin has one set of mafic volcanic rocks, which located in the north of Dongxiang-Gua.ngfeng fault line. Results show that the mafic volcanic rocks are lump structure, and filled silicious, carbonate and chlorite in many blowholes in Guangfeng and Yushan basins. The content of its phenocrysts is about 15% , the main

  20. Matrix diffusion coefficients in volcanic rocks at the Nevada test site: Influence of matrix porosity, matrix permeability, and fracture coating minerals

    Science.gov (United States)

    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.

  1. Oil-bearing sediments beneath San Juan volcanics - Colorado's newest frontier

    Energy Technology Data Exchange (ETDEWEB)

    Gries, R.R.

    1985-05-01

    During the Tertiary, the western part of the northern Sange de Cristo Range dropped 16,000 ft (4877 m) to become what is now known as the San Luis basin. The foreland basin formerly adjacent to and west of the range remained intact but was subsequently concealed by 10,000 ft (3048 m) of volcanic deposits. The existence of this concealed basin, a northeastern arm of the San Juan basin, was first suggested by Vincent Kelly who named it the San Juan sag. Oil, which was generated in the underlying Mancos Shale, migrated upward into vesicles and fractures in volcanic rocks. In at least two places, oil is currently seeping onto the volcanic surface or into overlying soil. These oil occurrences encouraged geologic and geophysical exploration and have led to confirmation by drilling that the basin exists. Porous reservoirs in both tertiary sedimentary rocks and volcanic rocks overlie a 2000 ft (610 m) Cretaceous Mancos Shale source rock. Within the Mancos Shale are fractured reservoirs, volcanic sills that have reservoir potential where fractured or porous, and stray sandstones. The Dakota Formation underlies the Mancos Shale and is about 200 ft (61 m) thick in this area. In addition, the Jurassic section has potential for source rocks in the Todilto Formation and reservoir rocks in the Entrada and Junction Creek Sandstones. The San Juan sag, a newly discovered basin of 2600 miS (6734 kmS) is a frontier for Colorado oil and gas exploration.

  2. Geochronology and geochemistry of Permian bimodal volcanic rocks from central Inner Mongolia, China: Implications for the late Palaeozoic tectonic evolution of the south-eastern Central Asian Orogenic Belt

    Science.gov (United States)

    Zhang, Zhicheng; Chen, Yan; Li, Ke; Li, Jianfeng; Yang, Jinfu; Qian, Xiaoyan

    2017-03-01

    Zircon U-Pb ages, geochemical data and Sr-Nd isotopic data are presented for volcanic rocks from the lower Permian Dashizhai Formation. These rocks are widely distributed in the south-eastern Central Asian Orogenic Belt in central Inner Mongolia, China. The volcanic rocks mainly consist of basaltic andesite and rhyolite, subordinate dacite and local andesite, and exhibit bimodal geochemical features. The results of zircon U-Pb dating indicate that the volcanic rocks formed during the early Permian (292-279 Ma). The mafic volcanic rocks belong to low-K tholeiitic to medium-K calc-alkaline series. These mafic volcanic rocks are also characterised by moderately enriched light rare earth element (LREE) patterns; high abundances of Th, U, Zr and Hf; negative Nb, Ta and Ti anomalies; initial 87Sr/86Sr ratios of 0.70514-0.70623; and positive εNd(t) values (+1.9 to +3.8). These features indicate that the mafic volcanic rocks were likely derived from the high-percentage partial melting of subduction-related metasomatised asthenospheric mantle. The felsic rocks show an A-type affinity, with enrichments in alkalis, Th, U and LREEs. The felsic rocks are depleted in Ba, Sr, Nb, Ta and Ti and exhibit moderately LREE-enriched patterns (LaN/YbN = 2.09-6.45) and strongly negative Eu anomalies (Eu/Eu∗ = 0.04-0.25). These features, along with the positive εNd(t) values (+2.6 to +7.7) and young TDM2 ages (TDM2 = 435-916 Ma), indicate that the felsic rocks were likely derived from a juvenile crustal source that mainly consisted of juvenile mid-ocean ridge basalt-related rocks. The volcanic association in this study and in previously published work widely distributed in central Inner Mongolia. The observations in this study suggest that the lower Permian volcanic rocks formed in an identical tectonic environment. The regional geological data indicate that the bimodal volcanic rocks from the lower Permian Dashizhai Formation in the study area formed in an extensional setting that was

  3. Age, geochemical and isotopic variations in volcanic rocks from the Coastal Range of Taiwan: Implications for magma generation in the Northern Luzon Arc

    Science.gov (United States)

    Lai, Yu-Ming; Song, Sheng-Rong; Lo, Ching-Hua; Lin, Te-Hsien; Chu, Mei-Fei; Chung, Sun-Lin

    2017-02-01

    This paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the Coastal Range of Taiwan, the Northern Luzon Arc. The rocks, recovered from four main volcanoes, vary from low-K tholeiitic to medium-K calc-alkaline basalts to dacites. The rocks are typical of arc magmatic products, exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements. Our new 40Ar/39Ar age data constrain the youngest eruption time in each of the four volcanoes, i.e., from north to south, at 7.2 Ma (Yuemei), 4.2 Ma (Chimei), 6.2 Ma (Chengkuang'ao) and 8.5 Ma (Tuluanshan), respectively. These data indicate that volcanism in the Northern Luzon Arc did not cease progressively from north to south, as previously alleged. The high and broadly uniform Nd isotope ratios [εNd = + 10.1 to + 8.8] and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge. Their overall geochemical variations are ascribed to magma chamber processes. The effects of magmatic differentiation and crustal contamination differ among each volcano, most likely owing to the discrepancy of residence time in individual magma chambers. Consequently, we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5% crustal contamination with a continental fragment split off from the Eurasian margin.

  4. Numerical modelling of gas-water-rock interactions in volcanic-hydrothermal environment: the Ischia Island (Southern Italy) case study.

    Science.gov (United States)

    Di Napoli, R.; Federico, C.; Aiuppa, A.; D'Antonio, M.; Valenza, M.

    2012-04-01

    Hydrothermal systems hosted within active volcanic systems represent an excellent opportunity to investigate the interactions between aquifer rocks, infiltrating waters and deep-rising magmatic fluids, and thus allow deriving information on the activity state of dormant volcanoes. From a thermodynamic perspective, gas-water-rock interaction processes are normally far from equilibrium, but can be represented by an array of chemical reactions, in which irreversible mass transfer occurs from host rock minerals to leaching solutions, and then to secondary hydrothermal minerals. While initially developed to investigate interactions in near-surface groundwater environments, the reaction path modeling approach of Helgeson and co-workers can also be applied to quantitative investigation of reactions in high T-P environments. Ischia volcano, being the site of diffuse hydrothermal circulation, is an ideal place where to test the application of reaction-path modeling. Since its last eruption in 1302 AD, Ischia has shown a variety of hydrothermal features, including fumarolic emissions, diffuse soil degassing and hot waters discharges. These are the superficial manifestation of an intense hydrothermal circulation at depth. A recent work has shown the existence of several superposed aquifers; the shallowest (near to boiling) feeds the numerous surface thermal discharges, and is recharged by both superficial waters and deeper and hotter (150-260°C) hydrothermal reservoir fluids. Here, we use reaction path modelling (performed by using the code EQ3/6) to quantitatively constrain the compositional evolution of Ischia thermal fluids during their hydrothermal flow. Simulations suggest that compositions of Ischia groundwaters are buffered by interactions between reservoir rocks and recharge waters (meteoric fluids variably mixed - from 2 to 80% - with seawater) at shallow aquifer conditions. A CO2 rich gaseous phase is also involved in the interaction processes (fCO2 = 0.4-0.6 bar

  5. Origin and age of the Volcanic Rocks of Tláloc Volcano, Sierra Nevada, Central Mexico

    Science.gov (United States)

    Meier, M.; Grobéty, B.; Arce, J. L.; Rueda, H.

    2007-05-01

    The Tláloc volcano (TV) is a 4125 m high stratovolcano of the Trans Mexican Volcanic Belt (TMVB) and is located in the northern end of the N-S trending Sierra Nevada, 30 km NE of Mexico City. Few data on the petrological and temporal evolution of TV have been published to date. Recently dated deposits gave ages between 32'000 and 34'500±500 years BP (Huddart and Gonzalez, 2004). Mapping and sampling of extrusive rocks in the summit region of TV revealed a dome structure with radiating lava flows consisting of dacitic rocks containing plagioclase and hornblende phenocrysts. Some flows, however, seem to be associated with a collapse structure E of the main summit. Crossing relationships indicate that this structure is older (“Paleo Tláloc”). A stratigraphy of the pyroclastic deposits was established along the northern slope of TV. From the numerous pyroclastic flows, separated by paleosoils and fluviatile deposits, only two pumice and one block and ash flow (BAF) have regional extent. Their thickness - distance relationship and their granulometry point to major explosive events. A carbonized wood sample from the BAF deposit gave ages similar to the previous ages (33'180±550 yr BP and 23'170±270 yr BP), a sample from a pyroclastic flow gave even a younger age (16'620±110 yr BP), suggesting that TV remained active also after the volcanoes Iztaccíhuatl and Popocatépetl further to the South started their activity. Based on these preliminary data it may be necessary to reconsider the accepted scenario of the temporal evolution of the central section of the TMVB, which assumes that the activity migrates from North to South with time. Huddart, D. and Gonzalez, S., 2004. Pyroclastic flows and associated sediments, Tláloc-Telapón, piedmont fringe of the eastern basin of Mexico. In: G.J. Aguirre-Diaz, Macías, J.L., and Siebe, C., (Editor), Penrose Conference. UNAM, Metepec, Puebla, Mexico, pp. 35.

  6. Petrogenesis of Cretaceous shoshonitic rocks in the northern Wuyi Mountains, South China: A result of the roll-back of a flat-slab?

    Science.gov (United States)

    Li, Wu-Xian; Li, Xian-Hua; Wang, Xuan-Ce; Yang, Dong-Sheng

    2017-09-01

    Potassic magmatism is commonly linked to post-/late-orogenic environments, such as foundering or convection thinning of continental lithosphere. Their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub-continental lithospheric mantle. Here we report new SHRIMP zircon U-Pb ages, whole rock geochemical results and Sr-Nd and zircon Hf isotope data from four potassic plutons (the Da'an, Yingcheng, Zixi and Honggong plutons) in the northern Wuyi Mountains, South China. SHRIMP U-Pb zircon analyses indicate that these potassic rocks formed at 139-126 Ma. They are characterized by high SiO2 (56-73%) and K2O (3.8-6.7%), with a K2O/Na2O ratio of 2.18-2.04, plotting within the field of high-SiO2 shoshonites. Their ISr and εNd(t) values vary from 0.7077 to 0.7162 and - 5.66 to - 10.52, respectively. The initial zircon εHf(t) values range from 2.3 to - 13.1, corresponding to TDM modal ages between 707 and 1330 Ma. These geochemical and isotope characteristics indicate that these shoshonites derived from a subduction-modified ancient subcontinental lithospheric mantle, and then underwent significantly fractional crystallization of K-feldspar, plagioclase, and accessory minerals, such as apatite and Fe-Ti oxides during magma ascent. We interpret that asthenospheric mantle upwelling (caused by eastward roll-back of a flat-slab?) triggered partial melting of the metasomatized lithospheric mantle to result in the Early Cretaceous shoshonitic magmatism in the northern Wuyi Mountains. An integration of our new results with compiled data from the interior of the South China Block reveals that the arc-like geochemical signature is confined to the Wuyi Mountains region, but becomes little or even invisible toward inland in South China. This implies that the far-field effects of the early Mesozoic subduction only reached the Wuyi Mountains, ca. 500 km away from the trench, consistent with flat or shallow subduction models.

  7. Immiscibility of high salinity fluids in volcanic rocks and the mechanism of magma degassing in the Dongying sag, eastern China

    Institute of Scientific and Technical Information of China (English)

    CHEN Yong; ZHOU Yaoqi; XIAO Huanqin; REN Yongjun; SUN Xinian; WANG Qiang; YAN Shiyong; LIU Chaoying

    2007-01-01

    Fluid inclusions that bear halite daughter min- erals were discovered in volcanic rocks at Pingnan area in the Dongying sag. The samples of the fluid inclusions collected from the BGX-15 well drill cores are hosted in quartz of diorite-porphyrite. The daughter minerals are identified as NaCl crystals after being observed under a microscope and analyzed by in situ Raman spectroscopy at -185℃. The results of micro-thermal analysis show that the homogeniza- tion temperatures of primary fluid inclusions are between 359 and 496℃, and the salinities of fluid inclusions are from 43.26 to 54.51 wt-%. All fluid inclusions in the studied sam- ples can be divided into five types including primary fluid inclusions and secondary fluid inclusions. The fact that five types of fluid inclusions were symbiotic in the same quartz grain implies that immiscibility happened in magma. Due to the decrease in temperature and pressure during the ascent of magma, the fluids became intensively immiscible. This pro- cess accelerates the degassing of CO2 from magma, but the remnant fluids with high salinity are preserved in fluid inclu- sions. Thus, the primary fluid inclusions are mainly in NaCl- H2O fluids and poor in CO2. The results of our study indicate that the degassing of magma and accumulation of CO2 gas at the Pingnan area are relative to the immiscibility of high salinity fluids. This discovery is important because it can help us have a further understanding of the mechanism of magma degassing and accumulation of the inorganic CO2 in eastern China.

  8. The Quaternary volcanic rocks of the northern Afar Depression (northern Ethiopia): Perspectives on petrology, geochemistry, and tectonics

    Science.gov (United States)

    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).

  9. 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

    Science.gov (United States)

    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

  10. Petrogenesis and its significance to continental dynamics of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang, Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    赖绍聪; 刘池阳; S.Y.O’Reilly

    2001-01-01

    Detailed studies indicate that the main rock type of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang is andesite, dacite and rhyolite. They belong to typical crust-generation magmatic system and originate from the special thickened crust of the Tibetan Plateau by dehydration melting. This group of rocks exhibits LREE enrichment but no remarkable Eu anomaly that shows their source region should be a thickened deep crust consisting of eclogitic mass group, implying that the crust had been thickened and an eclogitic deep crust had been formed during the Neogene period in Qiangtang area. This understanding is important and significant to making further discussion on the uplift mechanism and continental dynamics of the Tibetan Plateau.

  11. Soft-sediment deformation structures related to volcanic earthquakes of the Lower Cretaceous Qingshan Group in Lingshan Island, Shandong Province, East China

    Directory of Open Access Journals (Sweden)

    Yao-Qi Zhou

    2017-04-01

    The SSDS types in the Qingshan Group includes load and flame structure, ball and pillow structure, water-escape structure, hydroplastic deformation structure, plastic sandstone breccia structure, volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types: (1 seismic waves, (2 gravity and inertia effect of pyroclastic flows, (3 instant differential air pressure; which is different from slumping and tectonic earthquakes occurred in the Laiyang Group. In addition, with the lithofacies association analysis between pyroclastic flow and SSDS beds, a distribution model of SSDS related to volcanic earthquakes can be established: SSDS types changed gradually with their distance further away from the volcanic activity core. Brittle deformation which was common in the proximal zone disappeared gradually; liquefied and plastic SSDS continued to dominate in the medial zone; and slightly liquefied SSDS were developed in the distal zone. Meanwhile, the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent.

  12. Stratigraphic and Petrological Constraints of Cretaceous Subduction Initiation and Arc-Continent Collision in the Northern Andes

    Science.gov (United States)

    Leon, S.; Cardona, A.; Mejia, D.; Parra, M.

    2014-12-01

    Middle to Late-Cretaceous orogenic events in the northern Andes have been commonly reconstructed from the analysis of inland basins or the integration of regional scale thermochronological, geochronological and geochemical datasets from the accreted blocks. In contrast, limited studies have been developed on the stratigraphic and deformational record of magmatic and sedimentary sequences exposed near the suture zones. New field and petrologic data are used to characterize an ophiolite type sequence that outcrops in the western flank from the northwestern segment of the Central Cordillera of Colombia. Stratigraphic analysis indicate the existence of Albian-Aptian deep marine pelitic sequence interbedded with minor chert and thin quartz sandstone beds that apparently change to a volcanic dominate stratigraphy. Deformed ophiolite-like mafic and ultramafic plutonic rocks and isolated pillow lavas are also exposed to the east in fault contact with the pelitic sequence. The pelitic and interlayered volcanic rocks represent the growth of an extensional Early-Cretaceous basin that followed a Late-Jurassic magmatic quiescence in the Northern Andes. The volcano-sedimentary record is probably related to the growth of a fore-arc basin in a new subduction zone that extends until the Late Cretaceous. The deformation and obduction of the ophiolitic association and the fore-arc basin were probably triggered by the Late Cretaceous collision with an allocthonous plateau-arc associated to the migration of the Caribbean plate.

  13. The Maar-Diatreme System in a Mixed "Hard/Soft-Rock" Setting: an Example from the Pali Aike Volcanic Field, Argentina

    Science.gov (United States)

    Delpit, S.; Ross, P.

    2009-05-01

    The eruptive processes in diatremes remain poorly understood compared to those at other volcano types, because these processes occur at depth. Except for maar-diatreme volcanoes formed during kimberlitic eruptions, volcanologists agree that these systems are of phreatomagmatic origin. The origin of kimberlitic diatremes is more contentious, but studying non kimberlitic equivalents can be a good approach to better understand kimberlitic diatremes considering their numerous common characteristics. The geometry of maar-diatreme systems is strongly influenced by their setting in "hard-rock" or "soft-rock" environments (Lorenz, 2003, Geolines 15:72-83). Formation of maar-diatreme systems in "hard-rock" environments, like in the West Eifel Volcanic Field of Germany, is largely described in the literature but emplacement in "soft-rock" environments or mixed settings is not. In the case of "hard-rock" environments external water is provided by fracture aquifers. The eruption products are juvenile clasts and country rock fragments. The inner crater walls of the maar, and the diatreme walls, have steep slopes. In the case of "soft- rock" environments, water is contained in the sediment pores and the walls tend to be at lower angles. We recently conducted field work on maars, cinder cones and spatter rings of the Pali Aike Volcanic Field of southern Argentina as part of the Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO). These Quaternary monogenetic volcanoes were emplaced in a mixed "hard/soft-rock" environment containing young glacial sediments, basaltic lava flows, partly consolidated fluviatile sediments, and older indurated sedimentary rocks. The mixed environment of emplacement is reflected in a phreatomagmatic deposit on the inner slope of a tephra ring exposing some lapilli-tuff layers. The lapilli fraction comprises approximately 40% lithics on average (visual estimate): at least half of the fraction is composed of basaltic lava derived from a pre

  14. Volcanic rock-hosted gold and base-metal mineralization associated with neoproterozoic-early Paleozoic back-arc extension in the Carolina terrane, southern Appalachian Piedmont

    Energy Technology Data Exchange (ETDEWEB)

    Feiss, P.G. (Univ. of North Carolina, Chapel Hill (United States)); Vance, R.K. (Georgia Southern Univ., Statesboro (United States)); Wesolowski, D.J. (Oak Ridge National Lab., TN (United States))

    1993-05-01

    Volcanogenic mineral deposits in the Carolina terrane, southern Appalachian Piedmont, include Kuroko-type polymetallic massive sulfide deposits and disseminated gold-pyrite deposits associated with propylitic, silicic, argillic, and advanced argillic alteration. Host rocks are metavolcaniclastic and metaepiclastic rocks of a Neoproterozoic-Early Cambrian magmatic arc. The favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroelastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows. Kuroko-type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence. Whole-rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light ([delta][sup 18]O = -6% to -10%) waters, typical of high-latitude subaerial systems, to seawater ([delta][sup 18]O = 0%). Plots of [delta][sup 18]O vs. SiO[sub 2] of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition. Values of [delta][sup 18]O for the hydrothermal waters, lithostratigraphic analyses, and tectonic models of the Carolina terrane demonstrate that mineralization coincided with extension in a rifted arc. 34 refs., 3 figs.

  15. Discovery of double-peaking potassic volcanic rocks in Langshan Group of the Tanyaokou hydrothermal-sedimentary deposit, Inner Mongolia, and its indicating significance

    Institute of Scientific and Technical Information of China (English)

    PENG; Runmin; ZHAI; Yusheng; WANG; Zhigang; HAN; Xuefeng

    2005-01-01

    It is revealed that the protolith of gray-light brown potash-feldspar-leucogranulites and granulites in the 2nd formation of the LG in Tanyaokou deposit are quartz kerotophyre of synsedimentary eruption based on the following facts and features: (1) The rocks look compact and homogeneous without obvious crystals with naked eyes; (2) they contain blastoporphyritic or glomeroporphyritic and blasto-crystalloclastic crystals consisting of quartz with wavy extinction and albite with obvious alteration and deformation; (3) they also contain radiated and fibrous blasto-microspherulitic texture and swallow-tailed bifurcate and blasto-hollow-skeleton crystal texture, representing the rapid cooling characteristic of the magma during submarine volcanic eruption; (4) the major chemical compositions of the rocks are: SiO2 = 70.80%―76.00%, K2O (4.83%―6.22%)>Na2O(2.78%―3.80%), and K2O+Na2O = 8.63%―9.00%; and (5) their petrochemical diagrams indicate that they are volcanic rocks. Together with the characteristic that they occur in the same sequence with potassic spilite (SiO2 = 46.12%―50.68%, K2O = 4.23%―5.93%>Na2O = 2.15%―3.14%, K2O+Na2O = 6.51%―8.08%), it can be confirmed that the volcanics occurring in the 2nd Formation of the LG in Tanyaokou district are double-peaking potassic volcanic rocks. The discovery, together with the tuffs with ore minerals and the distribution of lead isotopic as well as the value of Co/Ni of pyrites >1 showing the obvious endogenic metalization, can prove that the Tanyaokou deposit is an untypical SEDEX-type deposit formed in the extension fault basin in the Mesoproterozonic aulacogen of the northern margin of the North China Platform, and its metallogenesis is related to the synsedimentary volcanic activities and the hydrothermal exhalation, and both the ore-forming material source and volcanics came from mantle or lower crust. These facts mentioned above, together with the meta-volcanic rocks (double-peaking) found in the

  16. The anatomy of a cinder cone: preliminary paleomagnetic, rock magnetic, structural, and petrologic data from the La Cienega volcano, Cerros del Rio volcanic field, northern New Mexico

    Science.gov (United States)

    Petronis, M. S.; Foucher, M.; Lineline, J.; Van Wyk de Vries, B.

    2011-12-01

    The Cerros del Rio volcanic field is one of several middle Pliocene to Pleistocene basaltic volcanic fields of the axial Rio Grande Rift in central and northern New Mexico. It is a monogenetic volcanic field that comprises about 60 cinder-spatter cones, occupies ~ 700 km2, and ranges in age from 2.7 Ma to 1.1 Ma. Eruptive centers are typically central vent volcanoes, ranging from low-relief shields to steep-sided, breached cinder and spatter cone remnants. They represent short eruptive events that likely were derived from rapidly evolving reservoir-conduit systems. Mining activity has exposed the volcanic plumbing system of the Cienega Mine cinder cone, just west of Santa Fe, NM. Here, geologists from France and USA have been investigating the exposed roots of this eviscerated Pliocene volcano to investigate magma conduit geometry, magma flow structures, and eruption patterns. We are testing models for magma transport and volcano construction using a variety of field and laboratory tools. Common models of volcanic construction envision the magma feeder as a dike or pipe-like conduit transporting molten rock from a deep reservoir to the eruptive vent. We posit that small volcanic pluming systems are inherently more complex and actually involve numerous feeder geometries throughout the volcano lifespan. Our preliminary work suggests that the simple exteriors of some cinder cones hide a long life and complex history, both of which would change the appreciation of the related volcanic hazards in active systems. The Cienega Mine cinder cone consists of several meter- to decimeter-wide intrusions that connect to eruptive centers. These intrusions show a continuity of brittle to ductile structures from their margins to interiors. We have collected samples across each intrusion as well as along strike for anisotropy of magnetic susceptibility (AMS) and petrographic analysis in order to establish magma flow patterns. AMS results yield a remarkably consistent dataset that

  17. Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems

    Science.gov (United States)

    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

  18. Earth history. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction.

    Science.gov (United States)

    Schoene, Blair; Samperton, Kyle M; Eddy, Michael P; Keller, Gerta; Adatte, Thierry; Bowring, Samuel A; Khadri, Syed F R; Gertsch, Brian

    2015-01-09

    The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.

  19. Zircon U-Pb dating, geochemical and Sr-Nd-Hf isotopic characteristics of the Jintonghu monzonitic rocks in western Fujian Province, South China: Implication for Cretaceous crust-mantle interactions and lithospheric extension

    Science.gov (United States)

    Li, Bin; Jiang, Shao-Yong; Lu, An-Huai; Zhao, Hai-Xiang; Yang, Tang-Li; Hou, Ming-Lan

    2016-09-01

    Comprehensive petrological, in situ zircon U-Pb dating, Ti-in-zircon temperature and Hf isotopic compositions, whole rock geochemical and Sr-Nd isotopic data are reported for the Jintonghu monzonitic intrusions in the western Fujian Province (Interior Cathaysia Block), South China. The Jintonghu monzonitic intrusions were intruded at 95-96 Ma. Their Sr-Nd-Hf isotopic compositions are similar to the coeval and nearby enriched lithospheric mantle-derived mafic and syenitic rocks, indicating that the Jintonghu monzonitic rocks were likely derived from partial melting of the enriched mantle sources. Their high Nb/Ta ratios (average 21.6) suggest that the metasomatically enriched mantle components were involved, which was attributed to the modification of slab-derived fluid and melt by the subduction of the paleo-Pacific Plate. The presence of mafic xenoliths, together with geochemical and isotopic features indicates a mafic-felsic magma mixing. Furthermore, the Jintonghu intrusions may have experienced orthopyroxene-, biotite- and plagioclase-dominated crystallization. Crust-mantle interaction can be identified as two stages, including that the Early Cretaceous mantle metasomatism and lithospheric extension resulted from the paleo-Pacific slab subduction coupled with slab rollback, and the Late Cretaceous crustal activation and enhanced extension induced by dip-angle subduction and the underplating of mantle-derived mafic magma.

  20. 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

    Science.gov (United States)

    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

  1. Sedimentary and tectonic evolution of the arc zone of Southwestern Ecuador during Late Cretaceous and early Tertiary times

    Science.gov (United States)

    Jaillard, Etienne; Ordoñez, Martha; Berrones, Gerardo; Bengtson, Peter; Bonhomme, Michel; Jimenez, Nelson; Zambrano, Italo

    1996-03-01

    The eastern part of the "Celica basin" of southwesternmost Ecuador exhibits Late Cretaceous to Tertiary sediments which belong to the magmatic arc paleogeographic zone. Important N-S to NE-trending faults separate a western, mainly Late Cretaceous series (Río Playas) from an eastern succession (Catamayo-Gonzanamá) of (?) Late Cretaceous to early Tertiary age. The analysis of these sediments indicates a complex geologic history, which recorded the main stages of the early tectonic evolution of the Andes. In the Río Playas area, a submarine andesitic volcanic pile (Celica Fm) represents the products of a volcanic arc of probably Albian age. It is apparently overlain by a thick, early Late Cretaceous series of volcanic flows and coarse-grained volcaniclastic high-density turbiditic beds (Alamor Fm), the deposition of which might result from the Mochica phase (late Albian-early Cenomanian) Deformation, uplift and erosion (early Peruvian phase) are followed by the sedimentation of unconformable marls and greywackes of marine open shelf to deltaic environment. These comprise Santonian and/or Campanian fine- to mediumgrained deposits (Naranjo Fm), abruptly overlain (late Peruvian phase ?) by fan-delta coarse-grained marine deposits of latest Cretaceous age (Casanga Fm) They are locally capped by undated, partly volcaniclastic red beds, indicating an important regression/uplift of latest Cretaceous-early Tertiary age. In the Catamayo-Gonzanamá area, thick subaerial andesitic volcanic rocks (Sacapalca Fm) are intruded by Paleocene to early Eocene plutons and are overlain by undated fluvial red beds. They express uplift movements of latest Cretaceous-early Tertiary age. To the South, these are capped by slumped lacustrine black shales and greywackes of possible Maastrichtian-Paleocene age (Gonzanamá Fm) Farther north, the Sacapalca volcanics and red beds are overlain by variegated shales, sandstones and conglomerates, dated as latest Oligocene-early Miocene (Catamayo Fm

  2. Discovery of the boninite series volcanic rocks in the Bangong Lake ophiolite mélange,western Tibet,and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    SHI Rendeng; YANG Jingsui; XU Zhiqin; QI Xuexiang

    2004-01-01

    The boninite series volcanic rocks, mainly composed of basaltic andesite, andesitic lava breccia and andesite porphyrite, were recognized for the first time in the Bangong Lake ophiolite mé1ange, western Tibet. These rocks have a strong boninitic affinity, with high SiO2 (55.61%-59.23%,weight percent), MgO (6.63%-13.08%, 9.13% on average (weight percent)), A1203/1iO2 ratios (36-54), Mg# (0.61-0.74), Ni (116 ppm on average) and Cr (354 ppm on average)low TiO2 (0.23%-0.39%, weight percent), and strong LILEs enrichment relative to the depleted HFSEs. C1-chondrite normalized (La/Gd)N and (Gd/Yb)N ratios of about 1.70 and 0.83, respectively, produce prominent“U-shaped” normalized REE (rare earth element) patterns. Such a close compositional affinity to boninite indicates that these volcanic rocks were formed in a forearc setting produced by the intra-oceanic subduction.

  3. Geochemistry of the Caledonian Basic Volcanic Rocks at the South Margin of the Qinling Orogenc Belt,and Its Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt(SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of contimental flood basalt.All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting.The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qingling block and the Yangtze block in the Caledonian epoch.The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian.As a result of spreading of the Tethys and geodynamic processes in deep mantle ,the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian,and the Qinling microplate was separated from the northern part of the Yangtze plate.

  4. Paleomagnetic and rock-magnetic study on volcanic units of the Valsequillo Basin: implications for early human occupation in central Mexico

    Science.gov (United States)

    Goguitchaichvili, Avto; Pozzo, Ana Lillian Martin-Del; Rocha-Fernandez, Jose Luis; Urrutia-Fucugauchi, Jaime; Soler-Arechalde, Ana Maria

    2009-01-01

    Alleged human and animal footprints were found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in the Valsequillo Basin, south of Puebla, Mexico (Gonzalez et al, 2005). The ash has been dated at 40 ka by optically stimulated luminescence analysis, thereby providing new evidence that America was colonized earlier than the Clovis culture (about 13.5 Ma). We carried out paleomagnetic and rock magnetic analysis on 18 Xalnene ash block and core samples collected at two distinct localities and 19 standard paleomagnetic cores belonging to nearby monogenetic volcanoes. Our data provide evidence that both the volcanic lava flow and Xalnene ash were emplaced during the Laschamp geomagnetic event spanning from about 45 to 39 ka.

  5. Volcanic stratigraphy and geochemical variations in Miocene-age rocks in western and southeastern Fort Irwin, California

    Science.gov (United States)

    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 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 Fort Irwin also has distinct compositions. Chemical variations indicate the region had similar general evolution of magma sources, but (1) there were numerous small, isolated chambers that fed flows along the edges of the field, (2) several tuffs are similar to local lavas but some differ and might have distant sources, and (3) basalt flows locally encroached into adjacent areas.

  6. 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

    Science.gov (United States)

    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.

  7. What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou Basin, Tibet)

    OpenAIRE

    Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; Van Hinsbergen, Douwe J.J.; Dekkers, Mark J.; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

    2015-01-01

    International audience; The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou Basin. The lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes. We report consistent 40Ar/39Ar and U-P...

  8. Late Cretaceous ARC to MORB compositional switch in the Quebradagrande Complex, Colombian Andes: understanding the long term tectonic evolution of a magmatic arc.

    Science.gov (United States)

    Jaramillo, J. S.; Cardona, A.; Zapata, S.; Valencia, V.

    2014-12-01

    The spatial and compositional characters of arc rocks are sensible markers of the tectonic changes experienced by convergent margins and therefore provide a fundamental view to the continuous tectonic evolution of active margins. The Early to Late Cretaceous tectonic evolution of the Northern Andes have been related to the growth and accretion of different continental and oceanic arc systems that were juxtaposed at the beginning of the Andean Orogeny in the Late Cretaceous. The Quebradagrande Complex is a tectonostratigraphic unit made of mafic to intermediate plutonic rocks, basic to intermediate volcanic flows and associated marine sedimentary rocks that have been related to a single Albian arc or back-arc environment that discontinuously outcrops along the western margin of the Central Cordillera of Colombia. New field, geochronological and geochemical data from the plutonic and volcanic rocks of the Quebradagrande complex shows that the pre-90-80 Ma volcanic arc rocks are intruded by ca. 90 Ma pyroxene gabbroic and hornblende dioritic plutons with medium to pegmatitic grain size characterized by a contrasting MORB-type signature. We related the compositional change to a transient modification of the convergent margin system, where and extensional roll-back related configuration or the subduction of an oceanic ridge allows the flux of the astenospheric mantle. This continental magmatic arc was subsequently deformed due to the collision and accretion of an allocthonous oceanic arc that migrate from the southeast Pacific at the beginning of the Andean orogeny.

  9. Characteristics and hydrocarbon accumulation patterns of volcanic rocks in the Yixin Formation Zhangqiang depression,southern Songliao Basin%松辽盆地南部张强凹陷义县组火山岩储层特征及成藏规律

    Institute of Scientific and Technical Information of China (English)

    张斌

    2013-01-01

    松辽盆地南部辽河外围探区的义县组广泛发育中-基性火山岩,并在张强凹陷获得了工业油流。依据岩心观察和薄片分析,可将义县组火山岩归纳为14种岩石类型,安山岩类揭示厚度最大、分布范围最广。火山岩主要发育3类岩相7种亚相,喷溢相约占84%。研究区共发育6类主要的原生、次生储集空间类型,4种主要的孔隙组合方式。岩性、岩相和断裂共同控制了储层的平面分带和纵向展布,成岩作用和构造作用决定了储层的储集空间类型、储集性、渗透性和连通性。物性和油藏资料分析表明,火山碎屑熔岩、气孔杏仁状熔岩和火山通道相(火山颈亚相、隐爆角砾岩亚相)、喷溢相上部亚相是最有利的储集岩性、岩相带。在靠近或紧邻生烃洼陷和靠近大断裂的构造高部位,寻找火山口-近火山口相带、以及火山岩喷发旋回的上部和顶部,火山岩油气成藏几率最大。%Mafic-intermediate volcanic rocks are widely developed in the Cretaceous Yixian Formation ( K1y ) in the pe-riphery of Liaohe oilfield in southern Songliao Basin ,and commercial oil flow has been tested in these volcanic rocks in Zhangqiang depression .Based on core observation and slice analysis ,14 different rock types have been recognized in the Yixian Fm vocanic rocks.Among them,andesitic lava and andesitic volcanoclastic rocks have the greatest thickness and most extensive distribution .The volcanic lithofacies can be divided into 3 lithofacies and 7 subfacies , of which effusive lithofacies accounts for about 84%.The volcanic reservoirs have 6 main types of primary and secondary reservoir spaces and 4 kinds of pore associations .The plane and vertical distribution of reservoirs are jointly controlled by lithology ,litho-facies and faults .The reservoir space types ,reservoir capacity ,permeability and connectivity are determined by diagenesis and tectonism

  10. Metamorphic pattern of the Cretaceous Celica Formation, SW Ecuador, and its geodynamic implications

    Science.gov (United States)

    Aguirre, Luis

    1992-04-01

    The volcanic rocks of the Cretaceous Celica Formation of southern Ecuador are affected by a weak although widespread alteration. The chemical study of the secondary chemical phases present in andesitic and basaltic lava flows reveals that this alteration corresponds to very low-grade metamorphism comprising the zeolite and the prehnite-pumpellyite facies. Main features of this metamorphism are: weak lithostatic pressure, moderate to steep thermal gradient, high ƒ O2, low value of the seawater/rock ratio and total absence of deformation. These characteristics are typically present in other volcanic suites of similar age and composition along the Andes and correspond to the pattern of metamorphism developed in extensional settings (diastathermal metamorphism) linked to various degrees of thinning of the continental crust. Based on this metamorphic pattern, a geodynamic model is proposed in which the Celica Formation is interpreted as an ensialic, aborted, marginal basin developed on strongly attenuated continental crust at the border of the South American plate. The relationship between the Ecuadorian and Colombian volcanic suites of Cretaceous age present along the Western Cordillera is discussed in the light of the model suggested.

  11. Cretaceous Crocodyliforms from the Sahara

    Directory of Open Access Journals (Sweden)

    Paul Sereno

    2009-11-01

    Full Text Available Diverse crocodyliforms have been discovered in recent years in Cretaceous rocks on southern landmasses formerly composing Gondwana.  We report here on six species from the Sahara with an array of trophic adaptations that significantly deepen our current understanding of African crocodyliform diversity during the Cretaceous period.  We describe two of these species (Anatosuchus minor, Araripesuchus wegeneri from nearly complete skulls and partial articulated skeletons from the Lower Cretaceous Elrhaz Formation (Aptian-Albian of Niger. The remaining four species (Araripesuchus rattoides sp. n., Kaprosuchus saharicus gen. n. sp. n., Laganosuchus thaumastos gen. n. sp. n., Laganosuchus maghrebensis gen. n. sp. n. come from contemporaneous Upper Cretaceous formations (Cenomanian in Niger and Morocco.

  12. 支持向量机与微电阻率成像测井识别火山岩岩性%THE APPLICATION OF SVM AND FMI TO THE LITHOLOGIC IDENTIFICATION OF VOLCANIC ROCKS

    Institute of Scientific and Technical Information of China (English)

    张莹; 潘保芝

    2011-01-01

    针对火山岩储层,从岩石化学成分分类和岩石结构分类两个角度出发,提出了一种利用测井资料识别火山岩岩性的方法.基于取芯薄片鉴定资料获得对应井段的常规测井数据,利用统计学习理论中的支持向量机方法对其处理,得到地质上按岩石化学成分分类的火山岩岩性类别.建立地层微电阻率成像测井图像与不同结构火山岩岩性之间的对应关系,归纳出典型的微电阻率图像模式,从而得到地质上按岩石结构分类的火山岩岩性类别,结合上述两者结论确定最终岩性,实现了运用支持向量机算法处理常规测井资料与微电阻率图像模式相结合的火山岩岩性测井识别新方法.%From the viewpoint of chemical composition categorization and structure classification of rocks, an effective method was proposed to identify the lithology of volcanic rocks by using logging data. On the one hand, the conventional logging data could be obtained by core wafer identification. Thus, after processing the data with Support Vector Machines (SVM) method of statistical theory, we could get the lithologic type of the volcanic rocks, which are classified according to the chemical composition of rocks. On the other hand, the volcanic rocks can be classified as volcanic lava, pyroclastic lava and pyroclastic rock according to the rock structure. Typical formation micro-resistivity imaging logging (FMI) image mode can be concluded by establishing the corresponding relationship between FMI images and lithology of volcanic rocks with different structures. As a result, the lithologic type of the volcanic rock classified by rock structure can be determined. Finally, by combining these two kinds of lithology, the ultimate rock lithology can be determined, too. In this paper, the authors presented a novel method to identify the lithology of volcanic rocks by combining SVM processed logging data and FMI image mode.

  13. Soils Developed from Different Volcanic Rocks from the Fernando de Noronha Island: Rare-Earth Element Patterns and Isotopic Lead Composition

    Directory of Open Access Journals (Sweden)

    Sonia Maria Barros de Oliveira

    2011-12-01

    Full Text Available This study examines the infl uence of pedogenesis on the distribution of rare earth elements in soils derived fromdifferent rock types and formed under tropical humid climate, as well as the possible contribution of airborne Pb to thesesoils. We studied 5 soil profi les developed from different volcanic rocks cropping out in the Fernando de Noronha island.Results show that in the course of weathering, the soils were enriched in REE. The REE patterns of the soils are similarto those of the parent material, except for a slight HREE enrichment. Lead-isotope data indicate the presence of a nonradiogenicanthropogenic component in the upper horizons of the soil profi les.

  14. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau: Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)

    LAI ShaoCong; QIN JiangFeng; LI YongFei; LONG Ping

    2007-01-01

    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt, both characterized by the lower SiO2 (51%-54%), high refractory elements (i.e. Mg, Cr, Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE, i.e. Nb, Ta, Ti). Besides, the fairly low Sm/Yb value (3.07-4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383), and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to-0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 , △7/4Pb = 9.88 to 11.42, △Sr>50, implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area, this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block, and induced its partial melting, and then the melt underplated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  15. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau:Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt,both characterized by the lower SiO2 (51%―54%),high refractory elements (i.e. Mg,Cr,Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE,i.e. Nb,Ta,Ti). Be-sides,the fairly low Sm/Yb value (3.07―4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383),and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to -0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 ,△7/4Pb = 9.88 to 11.42,△Sr>50,implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area,this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block,and induced its partial melting,and then the melt under-plated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  16. 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

    Science.gov (United States)

    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.

  17. Permeability and continuous gradient temperature monitoring of volcanic rocks: new insights from borehole and laboratory analysis at the Campi Flegrei caldera (Southern Italy).

    Science.gov (United States)

    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.

  18. Petrogenesis of the Early Permian volcanic rocks in the Chinese South Tianshan: Implications for crustal growth in the Central Asian Orogenic Belt

    Science.gov (United States)

    Huang, He; Zhang, Zhaochong; Santosh, M.; Zhang, Dongyang; Wang, Tao

    2015-07-01

    The Paleozoic and Early Mesozoic magmatic suites in the Central Asian Orogenic Belt (CAOB) provide important insights on the crustal growth and reworking process associated with the construction of the largest Phanerozoic orogen on the Earth. Among the tectonic blocks of the CAOB, the South Tianshan Terrane (STT) occupies the southwestern margin and is located adjacent to the Tarim Craton. Here we investigate the Early Permian Xiaotikanlike Formation in the central part of the Chinese STT in Xinjiang in Northwest China. The formation is composed of a series of terrestrial volcanic lava flows and volcanic breccia, interbedded with siltstones, sandstones and sandy conglomerates. Zircon U-Pb and Lu-Hf isotopic analysis, whole-rock major oxide, trace element and Sr-Nd isotopic data are presented for the volcanic lava flows of the Xiaotikanlike Formation exposed in the Boziguo'er, Laohutai and Wensu regions. The new zircon ages from our study, together with those reported in previous investigations on the rhyolitic lava flow from the Wensu region, suggest that the volcanic rocks of the Xiaotikanlike Formation simultaneously erupted at ca. 285 Ma. The lavas of the formation show a wide range of SiO2 (49.88 to 78.56 wt.%). The basaltic rocks show SiO2 from 49.88 to 53.78 wt.%, MgO from 3.73 to 7.01 wt.% and Mg# from 41 to 61. They possess slightly enriched Sr-Nd isotope signature [(87Sr/86Sr)t = 0.70495-0.70624 and εNd(t) = - 0.5 to + 0.6], and have trace and rare earth element patterns similar to those of oceanic island basalts (OIBs). Petrographic and whole-rock chemical characteristics indicate that the basaltic lava flows are dominantly tholeiitic, and were likely derived from a spinel-dominated peridotite asthenospheric mantle source. The felsic lavas of the Xiaotikanlike Formation show SiO2 in the range of 60.71 to 78.56 wt.% and display overall similar immobile element pattern characterized by notable troughs at Nb-Ta, P and Ti and gently sloping REEs. Zircon Lu

  19. Laser fusion 40Ar/39Ar dating on young volcanic rocks.%(极)年轻火山岩激光熔蚀40Ar/39Ar定年

    Institute of Scientific and Technical Information of China (English)

    周晶; 季建清; Alan DEINO; 龚俊峰; 韩宝福; 涂继耀; 桑海清; 徐剑光

    2013-01-01

    It is extremely difficult to date young volcanic rocks.Accurate 40Ar/39Ar dating research and practice of young volcanic rocks in China put forward several notable and important points during the process of 40Ar/39 Ar dating for young volcanic rocks.Because of the low background level,small sample quantity,and high sensitivity of modem noble gas isotope mass spectrometry device,laser ablation 40Ar/39Ar dating technique has been used in depth application in volcanic rocks dating.With the laser in 40Ar/39Ar dating of young and modern volcanic rocks,the discrepancy of Nier value and initial argon isotope ratio in Quaternary samples may cause a remarkable deviation between K-Ar apparent age and 40 Ar/39 Ar apparent age.The deviation show exponential increase for samples younger than 0.2Ma,but it is not so notable for samples older than 2Ma.There out,the boundary of young and modern volcanic rocks,which is applied to 40 Ar/39 Ar system,is assigned at 0.2Ma:rocks aged 2 ~ 0.2Ma is defined as young volcanic rock,while rocks aged younger than 0.2Ma is defined as modem volcanic rock.The phenocrysts,which are from different argon isotope fractionation system,should be rejected from the sample during 40Ar/39 Ar dating.According to rock texture and grain size of mineral,the matrix should be picked with ideal grain size.In normal cases,about 0.2mm (or 60 ~ 80 mesh) is recommended; Cooling time after irradiation of fast neutron reactor should not be no more than three months,or else it may cause an error on 37 Ar measurement,and consequently on final results.As neutron-flux monitor,standards should be characteristic of high homogeneity during laser 40Ar/39Ar dating.In calibrating the international and domestic standards we have,we find that SB-778-Bi,Bern4M and BT-1 can be ideal standard samples with good homogeneity.We also find that the isochron age calculated from the laser 40Ar/39Ar data of the phenocryst and matrix,which were cooled and crystallized at the same time

  20. Late Cretaceous-early Eocene counterclockwise rotation of the Fueguian Andes and evolution of the Patagonia-Antarctic Peninsula system

    Science.gov (United States)

    Poblete, F.; Roperch, P.; Arriagada, C.; Ruffet, G.; Ramírez de Arellano, C.; Hervé, F.; Poujol, M.

    2016-02-01

    The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New paleomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of magnetic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. These characteristic directions are similar to those recorded by mid Cretaceous intrusives suggesting a remagnetization event during the normal Cretaceous superchron and describe a large (> 90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the Fueguian Batholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagnetic results are interpreted as evidence of a large counterclockwise rotation of the Fueguian Andes related to the closure of the Rocas Verdes Basin and the formation of the Darwin Cordillera during the Late Cretaceous and Paleocene. The tectonic evolution of the Patagonian Bend can thus be described as the formation of a progressive arc from an oroclinal stage during the closure of the Rocas Verdes basin to a mainly primary arc during the final stages of deformation of the Magallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsula would have formed a continuous margin with Patagonia between the Early Cretaceous and the Eocene, and acted as a non-rotational rigid block facilitating the development of the Patagonian Bend.

  1. Compositional Trends of Cretaceous Conglomerate Provenance: Tracing The Evolving Nature of Tectonic Environments in the Northwestern Colombian Andes

    Science.gov (United States)

    Patino, A. M.; Zapata, S.; Cardona, A.; Jaramillo, J. S.

    2014-12-01

    The composition and provenance of the sedimentary record is a sensible marker of the evolving nature of source , basin paleogeography and tectonic assemblage. The Cretaceous geological evolution of the northern Andes is characterized by the succession of different tectonic environments that include: An early Cretaceous magmatic quiescence that follow former Jurassic arc magmatism, Albian-Aptian subduction resume and associated arc - back-arc formation and the late Cretaceous collision with an allocthonous oceanic arc that marks the beginning of the Andean orogeny. Such tectonic evolution had been mostly reconstructed from the magmatic record or the stratigraphic analysis of inland basin far from the arcs and suture zones. Along the western flank of the central cordillera outcrops two different stratigraphic units with notable differences in the provenance and timing of accumulation. The Abejorral Formation is the oldest sedimentary sequence (Albian-Aptian) that discordantly overlies the Triassic continental margin. this unit include two lithofacies clearly distinguishable, a lithofacies consist mostly of conglomerate, characterized by abundant quartz content , low compaction, rounded clasts and moderate sorting ; and the other is a interbedded of fine size sandstone, mudstone and chert; also with abundant quartz content further muscovite, containing basement and volcanic material . To the west, sedimentary rocks including within the Quebradagrande Formation conform a turbidite sequence with a well defined Bouma type succession that concordantly overlied a Campanian marine volcanic arc succession. The conglomerates associated to this unit are characterized by containing mainly sedimentary and volcanic rock fragments ,high compaction, subrounded clast, and low sorting. This sequence is overlying by the volcanic component in a concord contact. Whereas the Albian-Aptian record of the Abejorral Formation exhibit the unroofing of the continental basement and deepening of

  2. K-Ar age of young volcanic rocks and excess argon--Binary mixing model and quantitative study of excess argon effect

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A binary mixing model for excess argon is suggested in the note. According to this model and the data of excess argon component obtained in our experiment , a quantitative study of the effect of excess argon on real K-Ar age of young volcanic rocks is done. The result indicates that the effect of 5% excess argon component in samples on K-Ar age of the samples more than 2 Ma is less than 7.36% and can lead K-Ar age of 0.5 Ma samples to increase by 32.4%, while 1% excess argon component leads K-Ar age of 0.5 Ma samples to increase by 6.26%. Therefore, when pre-processed excess argon component is ≤1%, K-Ar age of the samples more than 0.5 Ma should be credible. On this basis we suggest a principal opinion for evaluation of previous K-Ar dating results and propose that the matrix is used to determine K-Ar age of young volcanic rocks. For the samples less than 0.2 Ma, in the case of high excess argon content, even if only 1% excess argon component exists in their matrix, it can also greatly affect their K-A age. Thus it must be careful to treat the dating result.

  3. Late Cretaceous and Paleogene evolution of the Greater Antilles fold- and thrustbelt: structure and stratigraphy in the Camagüey region, Cuba

    Science.gov (United States)

    van Hinsbergen, D. J.; Iturralde-Vinent, M. A.; van Geffen, P. W.; Garcia-Casco, A.

    2007-12-01

    The northern Caribbean margin underwent arc-continent collision in the late Cretaceous and Paleogene. On Cuba this les to the stacking of tectonic slices that comprise from top to bottom a volcanic arc unit, an ophiolite complex, a deformed belt of sedimentary rocks (the Camajuaní and Placetas belts) and finally rocks correlative to the Bahamas platform on the southern North American continental margin. On south-central and western Cuba, HP-LT metasedimentary rocks, on the Isle of Pines including a HT-LP overprint, were exhumed in the course of the late Cretaceous, probably at least partly added by extensional unroofing. These metamorphic rocks are exhumed in tectonic windows in the ophiolite and volcanic arc tectonic slices. Their exhumation quite surprisingly coincided with the arrest in arc volcanism in the Cuban periphery. Here, we present an integrated structural geological and stratigraphic study of the sedimentary units incorporated in the basal parts and underlying the ophiolite unit in the Camagüey province in northern central Cuba. Aim of this study was to constrain the direction and timing of compressional deformation contemporaneous with and following the exhumation and possibly extension in the southern internal parts of the Cuban fold-and thrust belt, and with the arrest in arc volcanism. Our results indicate that the Placetas belt in the Camagüey region consist of tightly, polyphase folded deep marine upper Jurassic to upper Cretaceous limestones, forming isolated blocks incorporated in a tectonic mélange at the base of the ophiolite unit. Timing of their deformation is likely late Cretaceous and younger. The Bahamas platform-related carbonates in the Sierra de Cubitas at the base of the Cuban nappe stack are characterized by a single, open folding phase trending sub-parallel to the main NW-SE trending structural grain of the fold- and thrust belt. This deformation marks the arrest in emplacement of the Cuban nappe stack onto the southern North

  4. [Micro-area characteristics of laminated chert in the volcanic rocks of Xionger Group of Ruyang area and its geological significances].

    Science.gov (United States)

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

    Science.gov (United States)

    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

  6. Resrarch on Lithology Identification for Volcanic Rock Based on Logging in Santanghu Basin%三塘湖盆地火山岩岩性测井识别方法

    Institute of Scientific and Technical Information of China (English)

    邢贝贝; 马世忠

    2011-01-01

    火山岩岩性的准确识别是火山岩储层描述与评价的基础.通过对三塘湖盆地火山岩测井相应特征进行的分析归纳,建立了火山岩岩性识别流程.首先利用取芯井段标定准确岩性,然后利用交会图法、模糊聚类分析法以及微电阻率成像测井资料对研究区内储层岩性进行综合识别.将研究区岩性划分为火山熔岩、火山碎屑岩、火山碎屑沉积岩和沉积岩4大类、11小类.通过22口井的资料进行处理验证,岩性识别符合率平均达84.7%.%Accurate identification of volcanic rocks in volcanic reservoir description and evaluation is an important basis. Santanghu basin by volcanic rocks of the corresponding log analysis of the characteristics of induction, the establishment of a volcanic lithology identification process. Firstly, accurate calibration of core lithology well section, then use the intersection graph, fuzzy clustering analysis, and micro-resistivity imaging log lithology of the study area, a comprehensive identification, the study area was divided into the volcanic rock lava, pyroclastic rocks, volcanic rocks and clastic sedimentary rocks 4 categories, 11 categories. 22 wells through the processing of data validation, lithology identification consistent with the average rate of 84.7%.

  7. 滇西腾冲新生代火山岩岩石地球化学特征%GEOCHEMISTRY OF CENOZOIC VOLCANIC ROCKS FROM TENGCHONG, WESTERN YUNNAN

    Institute of Scientific and Technical Information of China (English)

    徐翠玲; 赵广涛; 何雨旸; 李德平

    2012-01-01

    Tengchong Cenozoic volcanic rocks, which consist of basaltic trachy-andesite, trachy-andesite, and basaltic andesite, belonging to the high-K and calc-alkaline series, are continental intraplate volcanic rocks erupted after the Tethys Ocean was closed. They are distributed near the collision zone of the Indian plate and the Eurasian plate. The geochemical features of the rocks can be used to define the tectonic properties and magma sources. The systematic geochemical study of the typical rock samples by XRF and ICP MS shows that the rocks are characterized by high K2O,CaO, low TiO2,and high Mg # (averaging about 46). REE shows a LREE-enriched pattern with significantly negative Eu. Large ion lithophilc elements (LILE) and high field strength elements (HFSE) are enriched compared to the primitive mantle, and the LILE have higher enrichment than the HFSE. Th shows a significantly positive anomaly. The geochemical composition of the studied volcanic rocks is similar to the volcanic arc magma, suggesting that the magmat-ic activity was triggered by the subduction of the Indian plate down to the Eurasian plate. Characteristic element ratios show that the magma may be derived from the subduction-related EM I mantle.%腾冲新生代火山岩位于印度板块和欧亚板块碰撞带附近,但是喷发时大洋已经闭合,属于大陆板内火山岩.对其进行地球化学研究,可以用来划分构造属性和推测岩浆来源.采用XRF和ICP-MS对典型岩石样品进行了较系统的岩石地球化学研究,结果表明,岩石类型有玄武质粗面安山岩、粗面安山岩和玄武安山岩,属高钾钙碱性系列;岩石化学显示高K2O、CaO和低TiO2,Mg#较高,平均约为46;稀土元素分布呈右倾,显示明显的Eu负异常;相对于原始地幔富集大离子亲石元素和高场强元素,并具有明显的Th正异常;地球化学组成总体上与岛弧岩浆岩相似,推测其成因与印度板块向欧亚板块俯冲引发的岩浆活

  8. SHRIMP Geochronology of Volcanics of the Zhangjiakou and Yixian Formations, Northern Hebei Province, with a Discussion on the Age of the Xing'anling Group of the Great Hinggan Mountains and Volcanic Strata of the Southeastern Coastal Area of China

    Institute of Scientific and Technical Information of China (English)

    NIU Baogui; HE Zhengjun; SONG Biao; REN Jishun; XIAO Liwei

    2004-01-01

    A zircon U-Pb geochronological study on the volcanic rocks reveals that both of the Zhangjiakou and Yixian Formations, no