Sample records for cenozoic tholeiitic volcanism

  1. Cenozoic tholeiitic volcanism in the Colbún area, Linares Precordillera, central Chile (35º35'-36ºS

    Mario Vergara


    énesis y evolución, se mantuvieron relativamente constantes durante este lapso de tiempo de 20 millones de años.ABSTRACT Upper Eocene to Middle Miocene volcanic rocks are found in the Colbún area, Linares Precordillera, central Chile (35º35'-36ºS. Based on stratigraphic characteristics, K-Ar and Ar-Ar dating, two different units are recognized: 1-a Lower Unit (Upper Eocene to Upper Oligocene, in which silicic volcanic rocks predominate in the lower level and basic volcanic rocks in the upper, and 2- an Upper Unit (Lower to Middle Miocene, consisting of aphanitic basalts and rhyolitic welded tuffs. Geochemical characteristics of the Colbún volcanic rocks, such as their low K, O contents, high MgO/FeO ratios, flat REE patterns, MORB normalized Nb to Sc close to unity, relatively low initial Sr isotopic ratios (0.703575-0.704028 and high initial Nd isotopic ratios (0.512919-0.513003 are all consistent with a tholeiitic affinity and a low degree of crustal involvement in the evolution of the parental magmas. Pb isotopic relationships and the enrichment of some incompatible elements such as K, Rb, Sr and Ba suggest recycling of subducting Nazca plate material. This was accompanied by crustal thinning and development of caldera type structures. The Colbún rocks are the isotopically most primitive rocks of the Chilean Andes. Geochemical relationships suggest that these rocks were emplaced in a back-arc, intracontinental, postorogenic extensional geotectonic environment. The Colbún magmas evolved mainly by closed crystal fractionation from primary magmas generated in the mantle. The chemical and isotopic similarities exhibited by rocks ranging in age from the Late Eocene to Middle Miocene suggest that the sources and processes, involved in the generation and evolution of these magmas, were more or less constant during this time span of 20 m. y.

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

    王慧芬; 杨学昌; 等


    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.



    This paper is concentrated on Cenozoic volcanism and geothermal resources in Northeast China. There are a lot of Cenozoic volcanoes, a large area of volcanic rocks, a large number of active faults and rich geothermal resources in Northeast China. The time and space characteristics of Cenozoic volcanism and the space distribution characters of hot springs and high geothermal flux regions in Northeast China are described and discussed on the basis of geological, geothermal, drilling and volcanological data. It is revealed that the hot springs and high geothermal flux regions are re lated to the Cenozoic volcanism, rifting and faulting in Northeast China. It is especially emphasized that the hot springs and high geothermal anomaly areas are controlled by active deep faults. It is proposed that the Cenozoic volcanism re gions, rift basins, active fault belts, activated plate suture zones and large earthquake occurrence points are the best areas for prospecting geothermal resources. The geothermal resources in younger volcanic zones are richer than those in older volcanic belts. The hot springs and active or activated faults might be a very good clue for looking for geothermal resources.

  4. Paleomagnetic results from Cenozoic volcanics of Lusatia, NW Bohemian Massif

    Schnabl, Petr; Cajz, Vladimír; Tietz, O.; Buechner, J.; Suhr, P.; Pécskay, Z.; Čížková, Kristýna

    s. l: American Geophysical Union, 2013. [AGU Meeting of the Americas. 14.05.2013-17.05.2013, Cancun] Institutional support: RVO:67985831 Keywords : paleomagnetism * Cenozoic * volcanics Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  5. Recurrent Cenozoic volcanic activity in the Bohemian Massif (Czech Republic)

    Ulrych, Jaromír; Dostal, J.; Adamovič, Jiří; Jelínek, E.; Špaček, Petr; Hegner, E.; Balogh, K.


    Roč. 123, 1/4 (2011), s. 133-144. ISSN 0024-4937 R&D Projects: GA AV ČR(CZ) IAA300130902; GA ČR(CZ) GA205/09/1170 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z30120515 Keywords : Bohemian Massif * Cenozoic * alkaline volcanism * paleostress fields * rift * mantle Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.246, year: 2011

  6. Radiometric age of Cenozoic volcanism and paleomagnetic research

    Cajz, Vladimír; Schnabl, Petr; Radoň, M.

    [Praha]: Česká geologická společnost, 2011 - (Verner, K.; Buriánek, D.; Budil, P.). s. 24-24 ISBN 978-80-87487-00-6. [Otevřený kongres České geologické společnosti a Slovenskej geologickej spoločnosti /2./. 21.09.2011-25.09.2011, Monínec] Institutional research plan: CEZ:AV0Z30130516 Keywords : volcanism * paleomagnetism * Cenozoic Subject RIV: DB - Geology ; Mineralogy

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

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


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

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

    陈道公; 李彬贤; 等


    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.

  9. Effect of volatiles erupted from Mesozoic and Cenozoic volcanic activities on paleo-environmental changes in China


    Based on the determination of composition of volcanic volatiles and petrologic estimation of the total mass of volatiles erupted,we showed important advances in the study of the impact of Mesozoic and Cenozoic volcanic activities on paleo-environmental changes in China.The volcanic activities include western Liaoning and Zhangjiakou Mesozoic intermediate-acidic explosive eruptions,southern Tibet and Shanwang Cenozoic volcanism,and Mt.Changbai volcanic eruption around one thousand years ago.The paper predominantly discusses the earth's surface temperature changes,ozone depletion,acidic rain formation and mass mortalities of vertebrate induced by the Mesozoic and Cenozoic volcanism in China.


    WANG; Xi-kui


    Ke-qin, 1997. Paleoclimatic and environmental change since 2000a B. P. recorded in ice Core[J]. The Front of Ceo-science, 4(1): 95-100.(in Chiniese)[13]ZHANG Zhen-ke, WU Rui-jin, WANG Su-min, 1998. Paleoenvironmeal evolution during historic time reflected by frequency susceptibility of the lacustrine sediment in Daihai[J]. Geography Reaserch. 17(3) :297-300. (in Chinese)[14]ZHANG Pi-yuan, 1996. Climatic Changes During Historic Time in China[J]. Jinan: Shandong Science and Technology Press, 434-435. (in Chinese)[15]ZHANG Pi-yuan, GE Quan-sheng, 1997. The stage and abrupt ness of climatic evolution[J]. The Front of Geo-science, 4(1):122-126. (in Chinese)[16]ZHONG Wei, XIONG Hei-gang, Tashplati etal., 1998a. The preliminary study on the Spore-pollen combination of the Tagele section in Cele oasis[J]. Arid Zone Research, 15 (3):14-17. (in Chinese)[17]ZHONG Wei, XIONG Hei-gang, 1998b. Preliminary study on paleoclimatic evolution since about 12ka B.P. in Bosten Lake, southern Xinjiang, China[J]. Journal of Arid Land Resources and Enviorment, 12(3) :28-35. (in Chinese)[18]ZHU Ke-zhen. 1973, Preliminary study of climatic changes since about 5000 years in China[J]. Science in China, (2):291-296. (in Chinese)[19]CHEN Mo-xiang, WANG Ji-yang, DENG Xiao, 1994. Geothermal Resources in China[M] . Beijing: Science Press, 139 -159. (in Chinese)[20]CHEN Wen-ji, LI Da-ming, LI Qi et al. , 1992. Chronology and geochemistry of basalts in Lower Liaohe Basin[A] . In: LIU Ruo-xin. Chronology and Geochemistry of Cenozoic Volcanic Rocks in China [C] . Beijing: Seismological Press, 44-80. (in Chinese)[21]E Mo-lan, ZHAO Da-sheng, 1987. Cenozoic Basalts and Deep Source Rock Inclusions[M] . Beijing: Science Press, 86-132. (in Chinese)[22]LIU Jia-qi, 1987. Research on chronology of Cenozoic volcanic rocks in Northeast China[J]. Acta Petrologica Sinica, 3(4):21-31. (in Chinese)[23]MACHIDA H, ARAI F, 1983. Extensive ash falls in and around the Sea of Japan

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


    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. Cenozoic Volcanism and Intraplate Subduction at the Northern Margin of the Tibetan Plateau



    Developed in the Mt.Kunlun orogenic belt at the northern margin of the Tibetan Plateau is an active Cenozoic volcanic zone which is more than 1000km in length and some ten to hundred kilometers in width.It extends east-westwards and is roughly parallet to the strike of Mt.Kunlun.The Cenozoic volcanic rocks are divided into the northern(N-)and southern(S-)subzones.Eruptions of volcanic lavas in the S-subzone are related to an initial rift zone within the north Qiangtang terrane,but the volcanic rocks in the N-subzone are relatively close to the contact zone between the Mt.Kunlun and the Tarim terrane.The space-time distribution,petrological and geochemical features can be explained by a model of southward intraplate subduction of the Tarim terrane.

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

    SU Benxun; ZHANG Hongfu; XIAO Yan; ZHAO Xinmiao


    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.

  14. Cenozoic alkaline volcanic rocks with carbonatite affinity in the Bohemian Massif: Their sources and magma generation

    Ulrych, Jaromír; Štěpánková-Svobodová, Jana


    Roč. 46, 1/2 (2014), s. 45-58. ISSN 0369-2086 R&D Projects: GA AV ČR(CZ) IAA300130902 Institutional support: RVO:67985831 Keywords : alkaline volcanic rocks * melilitic rocks * carbonatite s * magma generation * metasomatism * Cenozoic * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  15. Cenozoic Volcanism in South China Sea and Its Vicinity and South China Sea Spreading


    The rock series, rock types and Sr-Nd isotopic dating of the Cenozoic volcanic rocks in the South China Sea are similar to those in its vicinity. On the basis of the spreading age of the South China Sea, the Cenozoic volcanic rocks are divided into three stages: the pre-spreading stage, the spreading stage and the post-spreading stage. The deep process characteristics of the asthenosphere and lithosphere may be inferred from the study on primary basaltic magma. The top layers of the asthenosphere both in the spreading stage and in the pre-spreading stage are closer to the earth surface than that in the post-spreading stage. From the pre-spreading stage to the spreading stage, the top layer of the asthenosphere decreased in depth, while the amount of interstitial partial melts increased. The evolution of the primary basaltic magma shows a progressive evolution sequence of the rifting volcanism and a faster lithospheric spreading velocity. From the spreading stage to the post-spreading stage, the top layer of the asthenosphere gradually increased in depth, but the amount of interstitial partial melts decreased. The evolution of primary basaltic magma shows a retrogressive evolution sequence of the rifting volcanism and a gradual decrease in the lithospheric spreading velocity. The depth recognized by the study on the Cenozoic volcanism demonstrates the deep environment for the formation and evolution of the South China Sea.

  16. The Achkal Oligocene ring complex: Sr, Nd, Pb evidence for transition between tholeiitic and alkali cenozoic magmatism in Central Hoggar (South Algeria)

    The Achkal Oligocene ring complex-cuts the Upper Eocene tholeiitic traps located on the top of the Hoggar swell. The plutonic rocks range from tholeiitic gabbros to alkali essexites, monzonites and syenites, whereas the volcanites are restricted to late per-alkaline rhyolites. The affinity change linked to the large isotopic heterogeneities (from EM1 to HIMU) suggests that the parental magmas are issued from two district mantle sources, first lithospheric then deeper. The Achkal has recorded the magmatic evolution of the Hoggar hot spot, between Eocene and Miocene. (authors)

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

    Sommer Carlos A.


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

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

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


    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources. PMID:16936944

  19. 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

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


    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

  20. Magmatic zoning of Late Cenozoic volcanism in Central Mongolia: Relation with the mantle plume

    Kudryashova, E. A.; Yarmolyuk, V. V.; Kozlovsky, A. M.; Savatenkov, V. M.


    The concentric zonal structure of the Late Cenozoic volcanism areal in Central Mongolia which is situated on the territory of the Khangai vault has been educed. The central part of the structure conforms to the axial part of the vault and is presented with volcanic fields of the Watershed graben and newest valley flows. The peripheral zone is presented with volcanic fields located along the vault frame (Taryat graben, Lake Valley graben, and grabens of the Orkhon-Selenga interfluve). The structural zoning of the areal comports with the substantial zoning of volcanism products. The rocks of the central part have isotopic (Sr, Nd, Pb) and geochemical characteristics conforming to the most primitive (like PREMA) compositions of mantle sources of magmatism. Magmatism sources in the peripheral zone of the volcanic areal, besides the PREMA mantle, contained a substance of enriched mantle like EMI. The character of substantial and structural zoning of volcanism is caused by the influence of the mantle plume on the Central Asia lithosphere. According to geophysical and isotopic-geochemical data, this plume had a lower mantle nature.

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

    TAN Fuwen; PAN Guitang; XU Qiang


    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.

  2. Hot Spot Induced Cenozoic Volcanism in the Upper Rajang Valley, Sarawak - Is Borneo Rifting?

    Taib, N.


    The Upper Rajang Valley covers a large area in the northern interior of the island of Borneo, in the Malaysian state of Sarawak . It is underlain by the Cretaceous to Late Eocene deep to shallow marine sediments of the Rajang Group. Within this area are several Cenozoic volcanic edifices, which to date have been sparsely studied. Two distinct episodes of volcanism are recognized - the first, dated early Eocene, consists of K-rich basalts, and is represented by the Bukit Mersing volcanics, which were erupted conformably onto deep water turbidites of the Rajang Group. The second, far more extensive, is dated Pliocene to Quaternary, and is bimodal, consisting mainly of early dacite and rhyodacite tuffs, with a smaller amount of later basalt, forming several volcanic plateaus and massifs (Hose Mountains, Usun Apau, Linau-Balui, Nieuwenhuis Mountains and others). They lie unconformably over pre-Miocene sediments, the Linau-Balui basalts having been erupted onto Quaternary river terraces. Mantle-normalized REE and incompatible trace element spider plots reveal that the Bukit Mersing basalts have geochemical affinity with Oceanic Island Basalts (OIB) and rift basalts, being enriched in LREEs and Most Incompatible Elements, and no Eu anomaly. Preliminary trace element data for several basalt samples from Usun Apau also show Oceanic Island/Rift affinity. Bimodal volcanism is most often associated with rift environments. Efforts are being made to radiometrically date the volcanics, in part to determine the possibility of future eruptions. The Upper Rajang Valley is remote, covered in tropical rainforest and is very sparsely populated. At this time, there is no information concerning signs of imminent volcanism, such as hot springs and microseismicity.

  3. The Cenozoic volcanic province of Tibesti (Sahara of Chad): major units, chronology, and structural features

    Deniel, C.; Vincent, P. M.; Beauvilain, A.; Gourgaud, A.


    Using both field relationships and some absolute ages, the sequence of volcanic units in the Cenozoic Tibesti Volcanic Province (TVP) (Chad) is established as follows: (1) plateau volcanism, between at least 17 and 8 Ma, consisting of flood basalts and silicic lava plugs, with intercalated ignimbritic sheets in the upper basalt succession increasing in amount upwards. Ages decrease from NE to SW, following the migration of the small NW-SE flexures concentrating the feeding dike swarms; (2) Late Miocene large central composite volcanoes exhibiting diverse and original structures. Some of them (Tarso Toon, Ehi Oyé, and Tarso Yéga) are located along a major NNE fault, representing the main tectonic direction in Tibesti since Precambrian times; (3) construction of three large ignimbritic volcanoes, associated with significant updoming of the basement, ending with the collapse of large calderas: Voon (about 5-7 Ma), Emi Koussi (2.4-1.33 Ma), and Yirrigué (0.43 Ma); (4) basaltic activity, starting at about 5-7 Ma, and essentially consisting of cinder cones and associated lava flows (Tarso Tôh, Tarso Ahon, and Tarso Emi Chi); and (5) final volcanic activity represented by post-Yirrigué caldera activity in the Tarso Toussidé Volcanic Complex, and especially Ehi Toussidé (the only active volcano in Tibesti), plus Ehi Timi and Ehi Mousgou volcanoes, similar to Ehi Toussidé. The two tectonic directions controlling some volcanic features of the province correspond to the major old lithospheric structures delimiting the volcanic province, namely, the great NW-SE Tassilian flexure to the SW and a major NE-NNE fault zone to the E. Unusual conditions of uplift and erosion in the TVP enable exceptional exposure of the internal structure of its volcanoes.

  4. Late Cenozoic volcanism, geochronology, and structure of the Coso Range, Inyo County, California

    Duffield, W.A.; Bacon, C.R.; Dalrymple, G.B.


    The Coso Range lies at the west edge of the Great Basin, adjacent to the southern part of the Sierra Nevada. A basement complex of pre-Cenozoic plutonic and metamorphic rocks is partly buried by approx.35 km/sup 3/ of late Cenozoic volcanic rocks that were erupted during two periods, as defined by K-Ar dating: (1) 4.0--2.5 m.y., approx.31 km/sup 3/ of basalt, rhyodacite, dacite, andesite, and rhyolite, in descending order of abundance, and (2) < or =1.1 m.y., nearly equal amounts of basalt and rhyolite, most of the rhyolite being < or =0.3 m.y. old. Vents for the volcanic rocks of the younger period are localized on and near a horst of basement rocks within a concavity defined by the distribution of vents of the older period. The alignment of many vents and the presence of a considerable number of roughly north-trending normal faults of late Cenozoic age reflect basin and range tectonics dominated by roughly east-west lithospheric extension. Fumaroles, intermittently active thermal springs, and associated altered rocks occur within and immediately east of the central part of the field of Quaternary rhyolite, in an area characterized by various geophysical anomalies that are evidently related to an active hot-water geothermal system. This system apparently is heated by a reservoir of silicic magma at > or =8-km depth, itself produced and sustained through partial melting of crustal rocks by thermal energy contained in mantle-derived basaltic magma that intrudes the crust in repsonse to lithospheric extension.

  5. Cenozoic intraplate volcanism in Mongolia; if not a mantle plume then what?

    Barry, T. L.; Saunders, A. D.; Kempton, P. D.


    Diffuse, small-volume basaltic volcanism has occurred throughout Mongolia for the past 30 My. This region provides an excellent opportunity to study intraplate volcanism because it is clearly on continental crust and far removed from the effects of subduction-related processes. Although magma has been erupted onto 45 km thick crust, there appears to be very little crustal contamination (Barry et al., 2003). The volcanism also provides an important link between the basaltic volcanism to the north around the Baikal rift zone, which has often been related to a mantle plume and Cenozoic basaltic volcanism that infills extensional grabens within NE China. Very clear chemical similarities within all the Baikal-Mongolia-NE China Cenozoic basalts exists (Barry &Kent, 1998) suggesting that the mantle source region beneath this vast area may be the same. Therefore, one general model should be able to explain all the volcanism. Trace element, REE and isotopic modeling of Mongolian basalt compositions indicate that the melts most likely formed within the lowermost lithospheric mantle from recently metasomatised lithosphere. There is no evidence for high heat flow within the mantle (Khutorskoy &Yarmolyuk, 1989), but geophysical studies infer anomalously dense material to be present at the base of the lithospheric mantle (Petit et al., 2002) which is coincident with a low velocity zone at ~200 km depth (Villaseñor et al., 2001). However, there does not appear to be anomalous low velocity material within the asthenospheric mantle. Geochemistry of the basalts give no positive indication for the presence of an underlying mantle plume. Conversely, whilst localized extensional tectonics may have aided the extrusion of basaltic melts, the small amount of extension cannot account for the generation of the basalts (McKenzie &Bickle, 1988). Lacking evidence for a high heat flux mantle plume, we may suggest the presence of a thermal anomaly, i.e. additional heat within the asthenosphere

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

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


    The distinctive tectono-magmatic characteristics of rift volcanism in the Apennines/Adria domains are discussed focussing attention on the nature of mantle sources, stress regimes, and conditions of magma generation. Post-collisional intensive lithospheric rifting and tectonic collapse of the Apennines generate large amounts of Pliocene-Quaternary orogenic magmas which overlie a nearly vertical subducted slab along the peri-Tyrrhenian border. This magmatism includes the Roman Magmatic Province sensu lato (RMP-s.l.) and the Internal Apennines Volcanism (IAV), and consists of high-K calcalkaline, potassic (shoshonitic) and ultrapotassic (leucitites, leucite basanite and minor lamproites and kamafugites) products. Integrated petrological and geochemical studies of these rocks (and associated mantle xenoliths) indicate that most of them could have been generated by a restricted partial melting range ( F ≤ 5-10%) of extremely inhomogeneous phlogopite-veined lithospheric mantle sources, resulting from subduction related K-metasomatic processes. Moreover, the presence of both intermediate anorogenic and subduction related geochemical features in Mt. Vulture magmas support the existence of a slab window beneath the central-southern Apennines, which could have allowed inflow of subduction components to intraplate mantle sources. This slab discontinuity may mark the transition between the already collisioned Adriatic and the still subducting Ionian lithospheric slabs. By contrast, the Paleogene intraplate magmatism of the Adriatic foreland (i.e., the Veneto Province (VVP) and the minor Mt. Queglia and Pietre Nere magmatic bodies) is characterized by small volumes of basic magmas, varying from tholeiitic to strongly Na-alkaline in composition. This magmatism appears to be related to a limited extensional regime typical of the low volcanicity rifts. Petrogenetic modelling of the intraplate Adriatic foreland magmas indicates that their composition is remarkably depth

  7. Cenozoic volcanism and lithospheric tectonic evolution in Qiangtang area, northern Qinghai-Tibet Plateau

    CHI; Xiaoguo; LI; Cai; JIN; Wei


    Following the collision between the Indian and Eurasian plates, the Cenozoic volcanic activities are rather frequent in the Qiangtang area of northern Qinghai-Tibet Plateau. They can be divided into four series: alkaline basalt series, high-K calc-alkaline series, shoshonitic series and peralkaline potassic-ultrapotassic series. Geochemical data suggest that the magma sources of Cenozoic volcanic rocks have transferred from spinel Iherzolite mantle in the early stage to garnet peridotite enriched mantle (EM2) in the later stage. The high Mg# number and extremely high Cr-Ni-Co abundance of high-K calc-alkaline and shoshonitic series andesites in the Qiangtang area indicate that the primary magma might be derived from subduction of continent lithosphere from the Lhasa block. Incompatible element ratios of La/Rb, Zr/Rb, Rb/Nb, K/Nb,Pb/La and K/La of peralkaline potassic-ultrapotassic series lavas in northern Qinghai-Tibet Plateau are lower than island arc volcanic rocks and higher than and similar to oceanic island basalts. This signature indicates that the primary magma derive from a paleo-mantle wedge interfused by fluids derived from asthenosphere and/or subducted mantle lithosphere. But the above element ratios of ultrapotassic lavas in southern Tibet and ultrapotassic lamprophyres in eastern Tibet are higher than and similar to island arc volcanic rocks, which means that the primary magma sources contained a large quantity of crust contaminant from fluids and/or melts derived from subducted continent lithosphere. The studies result supports that the indian continental .lithosphere has underthrust beneath Tibet to about the middle of the plateau, and Eurasian (Qaidam basin) mantle lithosphere has underthrust beneath the Qiangtang area of northern Tibet Plateau. In the paper we demonstrate further that the pulsing cycles of potassic-ultrapotassic volcanism of the Qinghai-Tibet Plateau result from an asthenospher pulsing upwelling caused by the intraplate subduction

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


    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.

  9. Deep Mechanical Background for the Cenozoic Volcanism in the Tibetan Plateau

    Xiong Xiong; Wang Jiye; Teng Jiwen


    The principle prerequisite for the formation of a volcano is the generation of a channel for magma transportation. There is little research on the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau.Based on the subcrustal mantle convection-generated stress field inversed by gravity anomalies, together with its relationship to the Cenozoic volcanism in the plateau, and the mechanism of crustal fracture formation, as well as the numerical results of the evolution of mantle convection beneath the plateau, this paper investigates the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau. There are two significant extensional convection-generated stress zones beneath the plateau, in which the volcanic rocks in the central and northern parts of the plateau are distributed. The Linzizong volcanism in southern Tibet correlates the upwelling mantle flow prior to the India-Asia collision or during the early stage of the collision. The magnitude of the stress is ~100 MPa, which is the same order of force that causes crustal fractures. The evidence implies that the mantle convection-generated stress is one of the principle causes of crustal fractures, and furthermore, the formation of the magma transportation channel in the Tibetan plateau.

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

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


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

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

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


    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.

  12. Late Cenozoic volcanism in central Myanmar: Geochemical characteristics and geodynamic significance

    Lee, Hao-Yang; Chung, Sun-Lin; Yang, Hsiao-Ming


    Late Cenozoic volcanism occurred in the central Myanmar basin, a region that is marked by the existence of the dextral Sagaing fault linking the eastern Himalayan Syntaxis to the north and the Andaman Sea to the south. Here we report new geochemical data of volcanic rocks from Monywa, Mt. Popa and Singu areas erupting in two distinct stages, i.e., mid-Miocene and Quaternary, respectively. While calc-alkaline rocks showing arc-like geochemical features are abundant, an apparent change in magma composition is observed between these two stages. The mid-Miocene rocks are mainly dominated by intermediate compositions (SiO2 = 53-61 wt.%) and typical of high-K calc-alkaline nature. They exhibit uniform Sr and Nd isotopic ratios (ISr ≈ ~ 0.705; εNd(T) = + 2.7 to + 1.6), suggesting a juvenile mantle origin related to the subduction of Indian oceanic lithosphere beneath this part of Asia. The Quaternary rocks consist mainly of basalts that, however, show variations in geochemical features. Three suites in this stage are observed: (1) calc-alkaline suite (basalts and basaltic andesites from Monywa and Mt. Popa: SiO2 = 48-56 wt.%; ISr = 0.704 to 0.705; εNd(T) = + 3.1 to + 2.1), originating from partial melting of a "remnant" juvenile mantle wedge, (2) alkali basalt suite I (basanites from Monywa: SiO2 ≈ 45 wt.%; MgO = 10-12 wt.%; K2O ≈ 2.0 wt.%; ISr = 0.704 to 0.705; εNd(T) ≈ + 3.6), interpreted as the product of small-degree melting from an amphibole lherzolite in the lithospheric mantle, and (3) alkali basalt suite II (trachybasalts from Singu: SiO2 ≈ 51 wt.%; K2O = 2.6-3.5 wt.%; ISr ≈ 0.706; εNd(T) = + 1.6 to + 0.9), interpreted as the product of partial melting from the asthenosphere. All processes of magma generation were related to the India-Asia collision that caused regional plate reorganization, a transition from oblique subduction to dextral movement in the Miocene, and subsequent "rollback" of the subducted Indian oceanic lithosphere in the

  13. First paleomagnetic results from Cenozoic volcanics of Lusatian region, Saxony/Bohemia

    Cajz, Vladimír; Schnabl, Petr; Büchner, J.; Tietz, O.; Suhr, P.; Pécskay, Z.; Čížková, Kristýna; Šlechta, Stanislav

    Prague: Czech Geological Survey ; Senckenberg museum of natural History Görlitz, 2013 - (Büchner, J.; Rapprich, V.; Tietz, O.). s. 189-190 ISBN 978-80-7075-806-9. [Basalt 2013: Cenozoic magmatism in Central Europe. 24.04.2013-28.04.2013, Görlitz] Institutional support: RVO:67985831 Keywords : Cenozoic * paleomagnetism * Lusation region Subject RIV: DB - Geology ; Mineralogy

  14. Late Mesozoic-Cenozoic intraplate magmatism in Central Asia and its relation with mantle diapirism: Evidence from the South Khangai volcanic region, Mongolia

    Yarmolyuk, Vladimir V.; Kudryashova, Ekaterina A.; Kozlovsky, Alexander M.; Lebedev, Vladimir A.; Savatenkov, Valery M.


    The South Khangai volcanic region (SKVR) comprises fields of Late Mesozoic-Cenozoic volcanic rocks scattered over southern and central Mongolia. Evolution of the region from the Late Jurassic to the Late Cenozoic includes 13 successive igneous episodes that are more or less evenly distributed in time. Major patterns in the distribution of different-aged volcanic complexes were controlled by a systematic temporal migration of volcanic centers over the region. The total length of their trajectory exceeds 1600 km. Principle characteristics of local magmatism are determined. The composition of igneous rocks varies from basanites to rhyolites (predominantly, high-K rocks), with geochemistry close to that of OIB. The rock composition, however, underwent transformations in the Mesozoic-Cenozoic. Rejuvenation of mafic rocks is accompanied by decrease in the contents of HREE and increase of Nb and Ta. According to isotope data, the SKVR magmatic melts were derived from three isotope sources that differed in the Sr, Nd, and Pb isotopic compositions and successively alternated in time. In the Early Cretaceous, the predominant source composition was controlled by interaction of the EMII- and PREMA-type mantle materials. The PREMA-type mantle material dominated quantitatively in the Late Cretaceous and initial Early Cenozoic. From the latest Early Cenozoic to Late Cenozoic, the magma source also contained the EMI-type material along with the PREMA-type. The structural fabric, rock composition, major evolutionary pattern, and inner structure of SKVR generally comply with the criteria used to distinguish the mantle plume-related regions. Analogous features can be seen in other regions of recent volcanism in Central Asia (South Baikal, Udokan, Vitim, and Tok Stanovik). The structural autonomy of these regions suggests that distribution of the Late Mesozoic-Cenozoic volcanism in Central Asia was controlled by a group of relatively small hot finger-type mantle plumes associated with

  15. Tracing the boundaries of Cenozoic volcanic edifices from Sardinia (Italy): a geomorphometric contribution

    Melis, M. T.; F. Mundula; DessÌ, F.; Cioni, R; Funedda, A.


    Unequivocal delimitation of landforms is an important issue for different purposes, from science-driven morphometric analysis to legal issues related to land conservation. This study is aimed at giving a new contribution to the morphometric approach for the delineation of the boundaries of volcanic edifices, applied to 13 monogenetic volcanoes (scoria cones) related to the Pliocene–Pleistocene volcanic cycle in Sardinia (Italy). External boundary delimitation of the edifices...

  16. Pervasive, tholeiitic refertilisation and heterogeneous metasomatism in Northern Victoria Land lithospheric mantle (Antarctica)

    Pelorosso, Beatrice; Bonadiman, Costanza; Coltorti, Massimo; Faccini, Barbara; Melchiorre, Massimiliano; Ntaflos, Theodoros; Gregoire, Michel


    The petrology of peridotite xenoliths in the Cenozoic volcanics from Greene Point (Northern Victoria Land, Antarctica) provides new constraints on the characterisation of the lithospheric mantle beneath the West Antarctic Rift. Based on mineral major and trace element models, this mantle domain is proposed to represent a residuum after 10% and 20% partial melting. Moreover, melting models and isotopic results for Sr and Nd systematics highlight the substantial contribution of tholeiitic melts percolating through peridotites. Close correlation with trace element contents in clinopyroxene phenocrysts from Ferrar and Karoo tholeiites allows us to ascribe this refertilisation event to the Jurassic. This asthenospheric melt was also able to transfer a garnet signature to the Northern Victoria Land mantle segment. The rare presence of glass and secondary phases indicate that Greene Point xenoliths were heterogeneously affected by alkaline metasomatism, probably related to the West Antarctic Rift System opening; this has also been widely observed in other Northern Victoria Land localities (i.e., Baker Rocks). Temperature and fO2 were calculated (950 °C; Δlog fO2 (QFM), - 1.70 to - 0.39) at a fixed pressure of 15 kbar, confirming the tendency of the anhydrous Greene Point xenolith population to have higher equilibration temperatures and comparable redox conditions, compared to the nearby amphibole-bearing peridotites from Baker Rocks.

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


    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.

  18. Cenozoic alkaline volcanic series in W Bohemia: Age relations and geochemical constraints

    Ulrych, Jaromír; Lloyd, F. E.; Balogh, K.

    Prague : Czech Geological Survey, 2002 - (Ulrych, J.; Cajz, V.; Adamovič, J.; Bosák, P.). s. 114 ISBN 80-7075-579-2. [Hibsch 2002 Symposium. 03.06.2002-08.06.2002, Teplá near Třebenice, Ústí nad Labem, Mariánské Lázně] Institutional research plan: CEZ:AV0Z3013912 Keywords : alkaline volcanic series * age relations Subject RIV: DB - Geology ; Mineralogy

  19. The stratigraphic significance of fission-track ages on volcanic ashes in the marine Late Cenozoic of southern California

    Fission-track dates and planktonic microfossil datum levels provide a revised chronology for the marine Late Cenozoic of southern California. In southern California, the Pliocene/Pleistocene boundary has been placed at the first appearance of Globorotalia truncatulinoides within the Pico Formation, Balcom Canyon, Ventura County. A fission-track age on glass shards from the Bailey Ash close to this level yields a result of 1.12 +- 0.36m.y.B.P. (millions of years before present). In tropical deep-sea cores, however, G. truncatulinoides has been shown to evolve within the Gilsa Paleomagnetic event with an estimated age of 1.8 m.y.B.P. Thus, the appearance of G. truncatulinoides in southern California is cryptogenic and probably related to the delayed migration into this region of water-mass conditions suitable for this species. Two volcanic ashes from the upper part of the Malaga Formation, Malaga Cove, Los Angeles County, yielded fission-track data on glass shards of 4.42+- 0.57 m.y.B.P. (lower ash) and 3.364 +- 0.69 m.y.B.P. (upper ash). These dates in addition to inferred paleomagnetic ages of planktonic microfossil datum levels suggest that the Delmontian Stage of California ranges in age from approximately 6 to approximately 3 m.y.B.P. Therefore, the Miocene/Pliocene boundary considered by Berggren and Van Couvering to be approximately 5 m.y.B.P. must lie in the lower Delmontian Stage but paleontologic criteria for its recognition in California are not yet available. (Auth.)

  20. Plate flexure and volcanism: Late Cenozoic tectonics of the Tabar-Lihir-Tanga-Feni alkalic province, New Ireland Basin, Papua New Guinea

    Lindley, I. D.


    Late Cenozoic Tabar-Lihir-Tanga-Feni (TLTF) alkaline volcanism, New Ireland Basin, PNG, is associated with extensional cracks along the crests of flexed ridges developed on the New Ireland Microplate (New name). The tectonic alignment of the TLTF volcanic arc is essentially perpendicular to the flexed ridges, suggesting that fractures parallel to the direction of maximum horizontal compression facilitated the rapid ascent of alkaline magmas from the mantle region, perhaps 60-70 km depth. The mainly Pliocene to Pleistocene volcanoes were localized at the intersection of ridge-parallel Kabang structures and arc-parallel Niffin structures, suggesting that the Kabang-Niffin structural intersections underlying each of the TLTF island groups provided a well developed, clustered network of open conduits which tapped the mantle source region. Periodic post-Miocene locking and unlocking along the strike-slip Kilinailau Fault (New name) are thought to have functioned as a valve, turning on (Pliocene) and then turning off (Pleistocene) volcanic activity, respectively. Partial locking of the Kilinailau Fault during the Pliocene resulted in the accumulation of intraplate stresses within the New Ireland Microplate, and caused plate flexure and ridge development, plate-cracking along ridge crests and the development of arc-parallel regional fractures parallel to the direction of maximum compression. Unlocking of the Kilinailau Fault in the Pleistocene resulted in the release of intraplate stresses in the New Ireland Microplate and a cessation of volcanic activity across most of the TLTF arc. The style and scale of plate flexure and cracking, accompanied by within-plate alkaline volcanism from equally spaced ridge-top eruptive centers confined to a narrow, linear volcanic arc are unknown from any other tectonic province.

  1. Geochemistry of Cenozoic volcanic rocks of the Faroe Islands with a focus on their ultra-trace contents of Hg

    Šišková, P.; Krmíček, Lukáš; Coufalík, Pavel

    Brno: Department of Geography, Faculty of Science, Masaryk University, 2016 - (Hrbáček, F.; Ondruch, J.; Ambrožová, K.; Ondráčková, L.; Nývlt, D.), s. 41-42 ISBN 9788021082038. [Students in Polar and Alpine Research Conference 2016. Brno (CZ), 25.04.2016-27.04.2016] Institutional support: RVO:68081715 ; RVO:67985831 Keywords : Faroe Islands * tholeiitic basalt * mercury content * continental crust Subject RIV: CB - Analytical Chemistry, Separation; DB - Geology ; Mineralogy (GLU-S)

  2. Distinctly different parental magmas for calc-alkaline plutons and tholeiitic lavas in the central and eastern Aleutian arc

    Cai, Yue; Rioux, Matthew; Kelemen, Peter B.; Goldstein, Steven L.; Bolge, Louise; Kylander-Clark, Andrew R. C.


    Cenozoic calc-alkaline plutons that comprise the middle crust of the central and eastern Aleutians have distinct isotopic and elemental compositions compared to Holocene tholeiitic lavas in the same region, including those from the same islands. Therefore the Holocene lavas are not representative of the net magmatic transfer from the mantle into the arc crust. Compared to the lavas, the Eocene to Miocene (9-39 Ma) intermediate to felsic plutonic rocks show higher SiO2 at a given Fe/Mg ratio, and have higher εNd-εHf values and lower Pb-Sr isotope ratios. However, the plutonic rocks strongly resemble calc-alkaline Holocene volcanics with more "depleted" isotope ratios in the western Aleutians, whose composition has been attributed to significant contributions from partial melting of subducted basaltic oceanic crust. These data could reflect a temporal variation of central and eastern Aleutian magma source compositions, from predominantly calc-alkaline compositions with more "depleted" isotope ratios in the Paleogene, to tholeiitic compositions with more "enriched" isotopes more recently. Alternatively, the differences between central Aleutian plutonic and volcanic rocks may reflect different transport and emplacement processes for the magmas that form plutons versus lavas. Calc-alkaline parental magmas, with higher SiO2 and high viscosity, are likely to form plutons after extensive mid-crustal degassing of initially high water contents. This conclusion has overarching importance because the plutonic rocks are chemically similar to bulk continental crust. Formation of similar plutonic rocks worldwide may play a key role in the genesis and evolution of continental crust.

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

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


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

  4. Cenozoic alkaline volcanic series in Western Ohře (Eger) Rift: Age relations and geochemical constraints

    Ulrych, Jaromír; Balogh, K.; Cajz, Vladimír; Novák, Jiří Karel; Frána, Jaroslav

    21 (125), - (2002), s. 55-76. ISSN 1211-1910 R&D Projects: GA ČR GA205/99/0907 Grant ostatní: Hungarian Academy of Science Foundation(HU) T 014961 (Hungarian-Czech Project: Comparative volcanostratigraphy of Neoidic volcanism of the Bohemian Massif and Pannonian Basin. Institutional research plan: CEZ:AV0Z3013912 Keywords : alcaline volcanic rock * Ohře (Eger) Rift * geochemistry Subject RIV: DB - Geology ; Mineralogy

  5. Petrological and geochemical characteristics of Cenozoic high-K calc-alkaline volcanism in Konya, Central Anatolia, Turkey

    Temel, Abidin; Gündoğdu, M. Niyazi; Gourgaud, Alain


    Late Miocene to Pliocene volcanic rocks outcrop west, northwest and southwest of the Konya area in Central Anatolia, Turkey. Volcanic products are lava domes, nuée ardentes and ignimbrite deposits, predominantly andesitic to dasitic in composition, together with rare basalt, basaltic andesite, basaltic trachyandesite and trachyandesite (50.35-69.39% SiO 2). The serie exhibits high-K calc-alkaline affinities. Fractional crystallization of pyroxene, plagioclase and Fe-Ti oxides is the main process in the magmatic evolution of Konya volcanic rocks. Volcanic units exhibit typical high-K calc-alkaline character. Their geochemical characteristics (e.g., enrichments in LIL elements such as K, Rb, Ba, Sr, depletion in HFSE such as Ti, Nb, and high Ba/Nb and Low Nb/Y ratios) are consistent with those of active continental margin regions. High 87Sr/ 86Sr (0.704841-0.707340) and low 143Nd/ 144Nd (0.512390-0.512618) ratios suggest crustal involvement in their petrogenesis. Correlations between 86Sr/ 87Sr isotope with Rb, Rb/Nb, Rb/Ba, and Rb/Sr also emphasize the effect of crustal contamination on the andesitic and dacitic magmas. As a consequence, Konya volcanic rocks are products of assimilation and fractional crystallization (AFC) processes of a magma which seems to be linked to the subduction of the African plate underneath the Anatolian plate during Miocene.

  6. Upper mantle structure under western Saudi Arabia from Rayleigh wave tomography and the origin of Cenozoic uplift and volcanism on the Arabian Shield

    Park, Y; Nyblade, A; Rodgers, A; Al-Amri, A


    The shear velocity structure of the shallow upper mantle beneath the Arabian Shield has been modeled by inverting new Rayleigh wave phase velocity measurements between 45 and 140 s together with previously published Rayleigh wave group velocity measurement between 10 and 45 s. For measuring phase velocities, we applied a modified array method that minimizes the distortion of raypaths by lateral heterogeneity. The new shear velocity model shows a broad low velocity region in the lithospheric mantle across the Shield and a low velocity region at depths {ge} 150 km localized along the Red Sea coast and Makkah-Madinah-Nafud (MMN) volcanic line. The velocity reduction in the upper mantle corresponds to a temperature anomaly of {approx}250-330 K. These finding, in particular the region of continuous low velocities along the Red Sea and MMN volcanic line, do not support interpretations for the origin of the Cenozoic plateau uplift and volcanism on the Shield invoking two separate plumes. When combined with images of the 410 and 660 km discontinuities beneath the southern part of the Arabian Shield, body wave tomographic models, a S-wave polarization analysis, and SKS splitting results, our new model supports an interpretation invoking a thermal upwelling of warm mantle rock originating in the lower mantle under Africa that crosses through the transition zone beneath Ethiopia and moves to the north and northwest under the eastern margin of the Red Sea and the Arabian Shield. In this interpretation, the difference in mean elevation between the Platform and Shield can be attributed to isostatic uplift caused by heating of the lithospheric mantle under the Shield, with significantly higher region along the Red Sea possibly resulting from a combination of lithosphere thinning and dynamic uplift.

  7. The Achkal Oligocene ring complex: Sr, Nd, Pb evidence for transition between tholeiitic and alkali cenozoic magmatism in Central Hoggar (South Algeria); Le complexe annulaire d`age Oligocene de l`Achkal (Hoggar Central, Sud Algerie): temoin de la transition au cenozoique entre magmatismes tholeitique et alcalin. Evidence par les isopopes du Sr, Nd et Pb

    Maza, M.; Dautria, J.M. [Montpellier-2 Univ., 34 (France); Briqueu, L.; Bosch, D. [Montpellier-2 Univ., 34 (France). Laboratoire de Geochimie Isotopique; Maza, M. [Office National de la Recherche Geologique et Miniere, Boumerdes (Algeria)


    The Achkal Oligocene ring complex-cuts the Upper Eocene tholeiitic traps located on the top of the Hoggar swell. The plutonic rocks range from tholeiitic gabbros to alkali essexites, monzonites and syenites, whereas the volcanites are restricted to late per-alkaline rhyolites. The affinity change linked to the large isotopic heterogeneities (from EM1 to HIMU) suggests that the parental magmas are issued from two district mantle sources, first lithospheric then deeper. The Achkal has recorded the magmatic evolution of the Hoggar hot spot, between Eocene and Miocene. (authors)

  8. The late Mesozoic-Cenozoic tectonic evolution of the South China Sea: A petrologic perspective

    Yan, Quanshu; Shi, Xuefa; Castillo, Paterno R.


    This paper presents a review of available petrological, geochonological and geochemical data for late Mesozoic to Recent igneous rocks in the South China Sea (SCS) and adjacent regions and a discussion of their petrogeneses and tectonic implications. The integration of these data with available geophysical and other geologic information led to the following tectono-magmatic model for the evolution of the SCS region. The geochemical characteristics of late Mesozoic granitic rocks in the Pearl River Mouth Basin (PRMB), micro-blocks in the SCS, the offshore continental shelf and Dalat zone in southern Vietnam, and the Schwaner Mountains in West Kalimantan, Borneo indicate that these are mainly I-type granites plus a small amount of S-type granites in the PRMB. These granitoids were formed in a continental arc tectonic setting, consistent with the ideas proposed by Holloway (1982) and Taylor and Hayes (1980, 1983), that there existed an Andean-type volcanic arc during later Mesozoic era in the SCS region. The geochonological and geochemical characteristics of the volcanics indicate an early period of bimodal volcanism (60-43 Ma or 32 Ma) at the northern margin of the SCS, followed by a period of relatively passive style volcanism during Cenozoic seafloor spreading (37 or 30-16 Ma) within the SCS, and post-spreading volcanism (tholeiitic series at 17-8 Ma, followed by alkali series from 8 Ma to present) in the entire SCS region. The geodynamic setting of the earlier volcanics was an extensional regime, which resulted from the collision between India and Eurasian plates since the earliest Cenozoic, and that of the post-spreading volcanics may be related to mantle plume magmatism in Hainan Island. In addition, the nascent Hainan plume may have played a significant role in the extension along the northern margin and seafloor spreading in the SCS.

  9. Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

    Baltuck, M.; Dixon, T. H.


    The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

  10. Gravity and aeromagnetic constraints on the extent of Cenozoic volcanic rocks within the Nefza Tabarka region, northwestern Tunisia

    Jallouli, Chokri; Mickus, Kevin; Turki, Mohamed Moncef; Rihane, Chedly


    Bouguer gravity and aeromagnetic data are analyzed to determine the extent of Miocene magmatism in the Nefza and Tabarka regions of northwestern Tunisia. Construction of magnetic intensity and enhanced analytic signal (EAS) maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the Nefza and Tabarka regions. Because of the lack of lateral resolution of the EAS techniques, 3-D magnetic and 2.5-D gravity models were constructed over the anomalies at Nefza and Tabarka. The final models indicate that the maximum depths of the igneous bodies are between 2.5 and 2.7 km with maximum widths between 15 and 22 km. The final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust (at least 3 km). These widths greatly expand the region of known Miocene magmatism in northwestern Tunisia. Combined with geochemical and petrological data of the surface volcanic rocks, the gravity and magnetic models imply a wider range of Miocene volcanic activity in northern Tunisia, probably related to a subduction zone.

  11. Geochemical Characteristics of Cenozoic Jining Basalts of the Western North China Craton: Evidence for the Role of the Lower Crust, Lithosphere, and Asthenosphere in Petrogenesis

    Kung-Suan Ho


    Full Text Available The Jining volcanic field located in the southern margin of the Mongolian plateau and the western North China Block consists of four rock types: quartz tholeiite, olivine tholeiite, alkali olivine basalt and basanite. These rocks have a wide range of K-Ar ages from ~36 to < 0.2 Ma. The early volcanism was voluminous and dominated by flood-type fissure eruptions of tholeiites, whereas the later phase was represented by sparse eruptions of basanitic lavas. Thirty-six samples analyzed in this study show a wide range in SiO2 contents from 44% ~ 54%. They all are sodium-rich and high-Ti basalts that, however, show marked isotopic variations between two end-members: (1 tholeiites that have higher 87Sr/86Sr of 0.7048 ~ 0.7052, and lower _ of -0.8 to -2.4 and Pb isotope ratios (206Pb/204Pb of 16.9 ~ 17.2, 207Pb/204Pb of 15.3 ~ 15.4 and 208Pb/204Pb of 37.1 ~ 37.7; and (2 basanites that have lower 87Sr/86Sr of 0.7035 ~ 0.7044, and higher _ of +1.3 to +4.9 and Pb isotope ratios (206Pb/204Pb of 17.7 ~ 18.0, 207Pb/204Pb of 15.4 ~ 15.5 and 208Pb/204Pb of 37.8 ~ 38.2. Alkali olivine basalt that occurs as a subordinate rock type is geochemically similar to the basanites, but isotopically similar to the tholeiites, characterized by the highest 87Sr/86Sr ratio among the three basaltic suites, coupled with a low Nb/U value (~33. In Sr-Nd-Pb isotopic plots, the tholeiites extend toward the EM1 (i.e., enriched mantle type 1 component, whereas the basanites trend toward the Indian Ocean mid-ocean ridge basalt (MORB field. Adopting the _ model by Morris and Hart (1983, we suggest that the Oligocene tholeiites were generated by high degree melting of an ascended asthenospheric mantle that was contaminated with a large amount of EM1-type continental lithospheric material during the early Cenozoic. On the other hand, the late Tertiary and Quaternary basanites may have originated predominantly from a depleted asthenosphere component with small but variable degrees of

  12. Bimodal tholeiitic-dacitic magmatism and the Early Precambrian crust

    Barker, F.; Peterman, Z.E.


    Interlayered plagioclase-quartz gneisses and amphibolites from 2.7 to more than 3.6 b.y. old form much of the basement underlying Precambrian greenstone belts of the world; they are especially well-developed and preserved in the Transvaal and Rhodesian cratons. We postulate that these basement rocks are largely a metamorphosed, volcanic, bimodal suite of tholeiite and high-silica low-potash dacite-compositionally similar to the 1.8-b.y.-old Twilight Gneiss - and partly intrusive equivalents injected into the lower parts of such volcanic piles. We speculate that magmatism in the Early Precambrian involved higher heat flow and more hydrous conditions than in the Phanerozoic. Specifically, we suggest that the early degassing of the Earth produced a basaltic crust and pyrolitic upper mantle that contained much amphibole, serpentine, and other hydrous minerals. Dehydration of the lower parts of a downgoing slab of such hydrous crust and upper mantle would release sufficient water to prohibit formation of andesitic liquid in the upper part of the slab. Instead, a dacitic liquid and a residuum of amphibole and other silica-poor phases would form, according to Green and Ringwood's experimental results. Higher temperatures farther down the slab would cause total melting of basalt and generation of the tholeiitic member of the suite. This type of magma generation and volcanism persisted until the early hydrous lithosphere was consumed. An implication of this hypothesis is that about half the present volume of the oceans formed before about 2.6 b.y. ago. ?? 1974.

  13. Potassium, thorium, and uranium contents of upper Cenozoic basalts of the southern Rocky Mountain region, and their relation to the Rio Grande depression

    Lipman, Peter W.; Bunker, Carl M.; Bush, Charles A


    Late Cenozoic basaltic volcanism in southern Colorado and northern New Mexico was most intense near the Rio Grande rift depression but extended onto stable platforms to the west (Colorado Plateau) and to the east (High Plains). Tholeiitic rocks are largely confined to the Rio Grande depression, and the basalts become increasingly alkalic with distance from the depression. The K, Th, and U contents and the Th/K and U/K ratios consistently increase away from the depression, and Th/U ratios also tend to increase slightly. Geographically distinct suites of petrographicaUy related basalts that are very similar in major-oxide compositions are readily distinguishable by K, Th, and U contents. Sialic crustal contamination did not contribute significantly to development of these compositional variations, and the lateral change from tholeiitic to alkalic basaltic volcanism may be related to different depths of or degrees of partial melting in the mantle. The compositions and compositional ranges of basalts in the southern Rocky Mountain region are similar to those of many Pacific islands, despite the contrasting geologic settings.

  14. Geochronology and geochemistry of the Dunedin Volcanic Group, eastern Otago, New Zealand

    Fifty-six previously unpublished K-Ar ages for the Dunedin Volcanic Group and previously published K-Ar and 40Ar/39Ar ages demonstrate that activity in the centrally situated Dunedin Volcano (here given formal lithostratigraphic status) lasted from 16.0 ± 0.4 to c. 10.1 Ma, and that of the surrounding Waipiata Volcanics lasted from 24.8 ± 0.6 to 8.9 ± 0.9 Ma. Apart from a gap at c. 20 Ma, recorded Waipiata activity climaxed at c. 16-14 Ma when activity of the Dunedin Volcano was beginning; it outlasted that of the Dunedin Volcano by c. 1 m.y. The total volume erupted by the Dunedin Volcano may have exceeded that of the largely monogenetic Waipiata Volcanics by an order of magnitude. New major- and trace-element analyses are given for 87 whole-rock samples and kaersutite. The whole-rock data demonstrate the exclusively alkalic nature of the group, the Waipiata Volcanics being more strongly alkalic than most of the mafic members of the central volcano. This fractionated to give a much greater volume of phonolitic differentiates than the Waipiata Volcanics. As for other intraplate Cenozoic volcanism in the New Zealand region, ranging overall from tholeiitic to highly alkalic, major- and trace-element patterns support an origin from a garnet-bearing ocean island basalt source region with high U/Pb mantle characteristics. (author). 77 refs., 13 figs., 4 tabs

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

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


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

  16. Volcanism and Oil & Gas In Northeast China

    Shan Xuanlong


    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.

  17. The origin of Cenozoic magmatism of Libya

    Stuart, Finlay; Masoud, Abdelmoniem; Mark, Darren


    Cenozoic volcanic provinces cover 66,000 km2 of Libya. The main fields are aligned NNW-SSE where NE-SW trending structural features intersect the main regional uplift structures. They form some of the largest volcanic provinces in North Africa yet despite their size and relative accessibility they have been not studied in detail. We are engaged in a new study of the geochemistry (major-trace elements, REE, Sr-Nd-Pb isotopes) and geochronology (40Ar/39Ar and cosmogenic 3He) of basalts of the four main Cenozoic volcanic provinces (Garian, Jabal Al Hasawinah, Jabal As Sawda and Jabal Al Haruj) in order to elucidate the nature and origin of the volcanism. The volcanic fields are dominated by basaltic flows, with small volumes of phonolites present at Garian and Jabal Al Hasawinah. Basalt piles rarely exceed a few 10s metres thick and the presence of NW-SE trending dykes on the periphery of most fields implies that existing flows probably represent the latest phase of a protracted volcanic history in each region. The basalts tend to be alkali to mildly alkali. Compositional variation is dominated by fractional crystalisation with little indication of crustal contamination. Trace element and REE support an origin in 5 to 15 % melts of heterogeneous sub-lithosphere mantle. Nd and Sr isotopic composition of the Garian and Jabal Al Haruj basalts (0.5128-0.51294 and 0.703-0.704) overlap the Cenozoic volcanism of southern Italy characterized by Etna and Pantelleria. This is typical of the common European asthenosphere mantle reservoir, and lacks the influence of enriched mantle present in other North African Cenozoic basalt provinces. There has been no systematic change in the location of volcanism with time that is indicative of plate movement over a fixed mantle hotspot. The major pulse of basaltic volcanism in the northern (Garian) and southern (Jabal Al Haruj) provinces overlap in time (6-1 Ma,) while Jabal Al Hasawinah and Jabal As Sawda basalts were erupted

  18. Minerogenesis of Shilu Iron Ores with Special Reference to Sm—Nd Isotope Geochemical Characteristics of Shilu Group Bimodal Volcanic Rocks in Hainan Island

    方中; 赵建新; 等


    Presented in this paper are Sm-Nd isotope and major, trace and rare-earth element analyses of bimodal volcanic rocks of the Shilu Group and other stratigraphic units in northwestern Hainan Is-land ,South China. It is shown that there are some N-MORB-type basalts(spilites) in the western part of the bimodal volcanic belt, in addition to some E-MORB-type and initial rift-type tholeiites (IRT) in th emiddle and eastern parts.Sm-Nd model ages of these basalts range from 545 Ma to 460Ma .The other extremes of the bimodal volcanics are porphyritic quartz rhyolites, which are characteristic of crustal material source.Sm-Nd model ages of the rhyolites range from 1562 Ma to 1371 Ma .The bimodal volcanic rocks are almost distributed in fifts or faulted depressions,as well as in the Upper Paleozoic rift of Hainan Island.Tholeiites of the Shilu Group can be compared with Cenozoic basalts in the middle and south-ern parts of the Red Sea Rift Belt in petrology, elemental geochemistry and Sm-Nd isotope geology. Shilu iron ores are closely associated with N-MORB-type basalts located in the western bimodal vol-canic belt.It is very interesting to note that the Shilu Fe-Co-Cu deposit can also be compared with Atlantis II Deep in the Red Sea Rift Belt.Therefore ,the present authors believe that the Shilu depos-it is a kind of hydrothermal deposit related to ocean volcanic belt ,where the geotectonic setting be-longs to initial extensional rifts in the oceanic crust.On the other hand, the largest Fe-Co-Cu ore de-posit in China used to be influenced by Hercynian granites after mineralization ,as is clearly observed on both εNd(T)-1/Nd and εNd(T)-147Sm/144Nd diagrams.

  19. 腾冲新生代火山区温泉CO2气体排放通量研究%CO2 flux estimations of hot springs in the Tengchong Cenozoic volcanic field, Yunnan Province, SW China

    成智慧; 郭正府; 张茂亮; 张丽红


    近期研究表明,不仅火山喷发期会向当时的大气圈输送大量的温室气体,火山间歇期同样会释放大量的温室气体.在火山活动间歇期,火山区主要以喷气孔、温(热)泉以及土壤微渗漏等形式向大气圈释放温室气体.腾冲是我国重要的新生代火山区,同时也是重要的水热活动区,那里出露大量的温泉,然而目前未见腾冲火山区温泉气体排放通量的研究报道.本文利用数字皂膜通量仪测量了腾冲新生代火山区温泉中CO2的排放通量.研究结果表明,腾冲新生代火山区温泉向当今大气圈输送的CO2通量达3.58×103t· a-1,相当于意大利锡耶纳Bassoleto地热区温泉中CO2的排放规模.腾冲火山区温泉的CO2释放通量主要受深部岩浆囊、断裂分布、地下水循环、围岩成分等多方面因素的影响.本文根据温泉中CO2的排放特征,将腾冲温泉分为南北两区,南区温泉CO2通量远高于北区的温泉,热海地热区的通量为腾冲CO2通量的最大值.在北温泉区,CO2通量主要受控于断裂的分布;而在南温泉区,除受到断裂控制外,热海地热区底部的岩浆囊及其与围岩的相互作用成为CO2气体的重要物质来源,同时高温的岩浆囊为温泉及CO2的形成提供了重要热源.%Recent research results have indicated that, beside volcanic eruption periods, dormant periods in the intermittent between the volcanic activities can emit a large amount of the greenhouse gases into atmosphere. In the intermittent between volcanic eruptions, greenhouse gases are erupted from the volcanic eruptive fields in the forms of fumaroles, hot springs, soil micro-seepage and so oa Tengchong volcanic and geothermal system is one of the most important Cenozoic volcanic activity fields in China whereas the estimates of the greenhouse gases emitted from Tengchong have been poorly understood. Using a new apparatus named digital bubble flowmeter, we have measured the flux of

  20. North Kona slump: Submarine flank failure during the early(?) tholeiitic shield stage of Hualalai Volcano

    Lipman, P.W.; Coombs, M.L.


    The North Kona slump is an elliptical region, about 20 by 60 km (1000-km2 area), of multiple, geometrically intricate benches and scarps, mostly at water depths of 2000-4500 m, on the west flank of Hualalai Volcano. Two dives up steep scarps in the slump area were made in September 2001, using the ROV Kaiko of the Japan Marine Science and Technology Center (JAMSTEC), as part of a collaborative Japan-USA project to improve understanding of the submarine flanks of Hawaiian volcanoes. Both dives, at water depths of 2700-4000 m, encountered pillow lavas draping the scarp-and-bench slopes. Intact to only slightly broken pillow lobes and cylinders that are downward elongate dominate on the steepest mid-sections of scarps, while more equant and spherical pillow shapes are common near the tops and bases of scarps and locally protrude through cover of muddy sediment on bench flats. Notably absent are subaerially erupted Hualalai lava flows, interbedded hyaloclastite pillow breccia, and/or coastal sandy sediment that might have accumulated downslope from an active coastline. The general structure of the North Kona flank is interpreted as an intricate assemblage of downdropped lenticular blocks, bounded by steeply dipping normal faults. The undisturbed pillow-lava drape indicates that slumping occurred during shield-stage tholeiitic volcanism. All analyzed samples of the pillow-lava drape are tholeiite, similar to published analyses from the submarine northwest rift zone of Hualalai. Relatively low sulfur (330-600 ppm) and water (0.18-0.47 wt.%) contents of glass rinds suggest that the eruptive sources were in shallow water, perhaps 500-1000-m depth. In contrast, saturation pressures calculated from carbon dioxide concentrations (100-190 ppm) indicate deeper equilibration, at or near sample sites at water depths of -3900 to -2800 m. Either vents close to the sample sites erupted mixtures of undegassed and degassed magmas, or volatiles were resorbed from vesicles during

  1. The Cenozoic Volcanoes in Northeast China

    LIU Jiaqi; HAN Jingtai; GUO Zhengfu


    There are more than 600 Cenozoic volcanic cones and craters with abeut 50 000 km2of lava flows in northeast China, which formed many volcanic clusters and shown the features of the continental rift - type volcanoes. Most volcanic activities in this area, especially in the east part of Songliao graben, were usually controlled by rifts and faults with the main direction of NE / NNE in parallel and become younger from the central graben towards its both sides, especially to the east continental margin. It is revealed that the volcanism occurred in northeast China was as strong as that occurred in Japan during the Miocene and the Quaternary. The Quaternary basalt that is usually distributed along river valley is called "valley basalt"while Neogene basalt usually distributed in the top of mounts is called "high position basalt". These volcanoes and volcanic rocks are usually composed of alkaline basalts with ultramafic inclusions, except Changbaishan volcano that is built by trachyte and pantellerite.

  2. Spatio-temporal autocorrelation of Neogene-Quaternary volcanic and clastic sedimentary rocks in SW Montana and SE Idaho: Relationship to Cenozoic tectonic and thermally induced extensional events

    Davarpanah, A.; Babaie, H. A.; Dai, D.


    Two systems of full and half grabens have been forming since the mid-Tertiary through tectonic and thermally induced extensional events in SW Montana and neighboring SE Idaho. The earlier mid-Tertiary Basin and Range (BR) tectonic event formed the NW- and NE-striking mountains around the Snake River Plain (SRP) in Idaho and SW Montana, respectively. Since the mid-Tertiary, partially synchronous with the BR event, diachronous bulging and subsidence due to the thermally induced stress field of the Yellowstone hotspot (YHS) has produced the second system of variably-oriented grabens through faulting across the older BR fault blocks. The track of the migration of the YHS is defined by the presence of six prominent volcanic calderas along the SRP which become younger toward the present location of the YHS. Graben basins bounded by both the BR faults and thermally induced cross-faults (CF) systems are now filled with Tertiary-Quaternary clastic sedimentary and volcanic-volcaniclastic rocks. Neogene mafic and felsic lava which erupted along the SRP and clastic sedimentary units (Sixmile Creek Fm., Ts) deposited in both types of graben basins were classified based on their lithology and age, and mapped in ArcGIS 10 as polygon using a combination of MBMG and USGS databases and geological maps at scales of 1:250.000, 1:100,000, and 1:48,000. The spatio-temporal distributions of the lava polygons were then analyzed applying the Global and Local Moran`s I methods to detect any possible spatial or temporal autocorrelation relative to the track of the YHS. The results reveal the spatial autocorrelation of the lithology and age of the Neogene lavas, and suggest a spatio-temporal sequence of eruption of extrusive rocks between Miocene and late Pleistocene along the SRP. The sequence of eruptions, which progressively becomes younger toward the Yellowstone National Park, may track the migration of the YSH. The sub-parallelism of the trend of the SRP with the long axis of the

  3. Gem-bearing basaltic volcanism, Barrington, New South Wales: Cenozoic evolution, based on basalt K-Ar ages and zircon fission track and U-Pb isotope dating

    Based on basalt K-Ar and zircon fission track dating, Barrington shield volcano was active for 55 million years. Activity in the northeast, at 59 Ma, preceded more substantial activity between 55 and 51 Ma and more limited activity on western and southern flanks after 45 Ma. Eruptions brought up megacrystic gemstones (ruby, sapphire and zircon) throughout the volcanism, particularly during quieter eruptive periods. Zircon fission track dating (thermal reset ages) indicates gem-bearing eruptions at 57, 43, 38, 28 and 4-5 Ma, while U-Pb isotope SHRIMP dating suggests two main periods of zircon crystallisation between 60 and 50 Ma and 46-45 Ma. Zircons show growth and sector twinning typical of magmatic crystallisation and include low-U, moderate-U and high-U types. The 46 Ma high-U zircons exhibit trace and rare-earth element patterns that approach those of zircon inclusions in sapphires and may mark a sapphire formation time at Barrington. Two Barrington basaltic episodes include primary lavas with trace-element signatures suggesting amphibole/apatite-enriched lithospheric mantle sources. Other basalts less-enriched in Th, Sr, P and light rare-earth elements have trace-element ratios that overlap those of HIMU-related South Tasman basalts. Zircon and sapphire formation is attributed to crystallisation from minor felsic melts derived by incipient melting of amphibole-enriched mantle during lesser thermal activity. Ruby from Barrington volcano is a metamorphic type, and a metamorphic/metasomatic origin associated with basement ultramafic bodies is favoured. Migratory plate/plume paths constructed through Barrington basaltic episodes intersect approximately 80% of dated Palaeogene basaltic activity (65-30 Ma) along the Tasman margin (27-37 deg S) supporting a migratory plume-linked origin. Neogene Barrington activity dwindled to sporadic gem-bearing eruptions, the last possibly marking a minor plume trace. The present subdued thermal profile in northeastern New South

  4. Abanico East Formation: petrology and geochemistry of volcanic rocks behind the Cenozoic arc front in the Andean Cordillera, central Chile (33°50'S

    Marcia Muñoz


    Full Text Available The stratigraphy, chemistry and age of rocks assigned to the eastern portion of the Abanico Formation exposed along the El Volcán river valley, Principal Cordillera east of Santiago (30º50'S/70º12'-70º5'W, are reported and discussed. This ca. 3,300 m thick succession is mainly composed of basalts, basaltic andesites and volcaniclastic rocks. 40Ar/39Ar radiometric dates on plagioclase from the lava flows yield Oligocene-lower Miocene ages with a maximum age of 34.3 ±0.4 Ma for the lower part and a plateau age of 21.4±1.0 Ma for the upper part of the succession. The lava flows show calc-alkaline affinities and have chemical characteristics that are typical of arc volcanic rocks erupted in an active continental margin. A temporal chemical evolution in the sequence is indicated by upward increases in concentrations of LILE and LREE elements and LaN/YbN ratios. This pattern can be attributed to increasing contributions of fluids derived from the subducted lithosphere with time. A chemical comparison of these rocks with Oligocene-lower Miocene volcanic rocks from the Cerro Abanico and Chacabuco areas on the western border of the Principal Cordillera, east of Santiago, and at the northern end of the Central Depression reveals west to east compositional variations. From west to east these variations include: (1 increasing LILE and LREE concentrations, LaN/YbN ratios and Sr and Nd initial isotopic ratios, and (2 decreasing LILE/HFSE and LREE/HFSE ratios. These pattern can be attributed to a west to east decrease in the contribution of slab derived fluids and increase in the influence of crustal contamination processesLa formación Abanico Este: petrología y geoquímica de las rocas volcánicas detrás del arco Cenozoico en la Cordillera Andina, Chile central (33º50'S. Se presentan los resultados del estudio de la estratigrafía, química y edades de rocas asignadas a la franja oriental de la Formación Abanico expuestas en la ladera sur del R

  5. Uranium and thorium in Cenozoic basaltods of Kamchatka

    Regularities in distribution of radioactive elements (RAE) in basaltoids of Kamchatka have been analyzed. The RAE concentration in samples was determined by γ-spectrometric method. The results compared with the instrumental neutron-activation analysis data are found to be in agreement. Results of evaluating the average contents of U, Th and roch-forming elements in ce-- nozoic basaltoids are presented. The radiogeochemical data enable to associate the origin of the Kamchatka Cenozoic basaltoids with both fractional melting of the upper mantle depleted of radioactive elements and the development of magmatic chambers in submerged blocks of the Pre-Cretaceous melanocratic basement the composition of which is close to oceanic tholeiite

  6. East Mariana Basin tholeiites: Cretaceous intraplate basalts or rift basalts related to the Ontong Java plume?

    Castillo, P.R.; Pringle, M.S.; Carlson, R.W.


    Studies of seafloor magnetic anomaly patterns suggest the presence of Jurassic oceanic crust in a large area in the western Pacific that includes the East Mariana, Nauru and Pigafetta Basins. Sampling of the igneous crust in this area by the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) allows direct evaluation of the age and petrogenesis of this crust. ODP Leg 129 drilled a 51 m sequence of basalt pillows and massive flows in the central East Mariana Basin. 40Ar 39Ar ages determined in this study for two Leg 129 basalts average 114.6 ?? 3.2 Ma. This age is in agreement with the Albian-late Aptian paleontologic age of the overlying sediments, but is distinctively younger than the Jurassic age predicted by magnetic anomaly patterns in the basin. Compositionally, the East Mariana Basin basalts are uniformly low-K tholeiites that are depleted in highly incompatible elements compared to moderately incompatible ones, which is typical of mid-ocean ridge basalts (MORB) erupted near hotspots. The Sr, Nd and Pb isotopic compositions of the tholeiites ( 87Sr 86Srinit = 0.70360-0.70374; 143Nd 144Ndinit = 0.512769-0.512790; 206Pb 204Pbmeas = 18.355-18.386) also overlap with some Indian Ocean Ridge MORB, although they are distinct from the isotopic compositions of Jurassic basalts drilled in the Pigafetta Basin, the oldest Pacific MORB. The isotopic compositions of the East Mariana Basin tholeiites are also similar to those of intraplate basalts, and in particular, to the isotopic signature of basalts from the nearby Ontong Java and Manihiki Plateaus. The East Mariana Basin tholeiites also share many petrologic and isotopic characteristics with the oceanic basement drilled in the Nauru Basin at DSDP Site 462. In addition, the new 110.8 ?? 1.0 Ma 40Ar 39Ar age for two flows from the bottom of Site 462 in the Nauru Basin is indistinguishable from the age of the East Mariana Basin flows. Thus, while magnetic anomaly patterns predict that the igneous

  7. Cenozoic Intraplate Alkaline Volcanism of Western Bohemia

    Ulrych, Jaromír; Cajz, Vladimír; Pivec, Edvín; Novák, Jiří Karel; Nekovařík, Č.; Balogh, K.

    Praha : Geophysical Institute Academy of Sciences of the Czech Republic, 1999. s. 13-14. [Workshop Seismic Processes and Associated Phenomena in West Bohemia and in the Vogtland.. 13.10.1999-15.10.1999, Teplá] Subject RIV: DB - Geology ; Mineralogy

  8. Development of continental lithospheric mantle as reflected in the chemistry of the Mesozoic Appalachian Tholeiites, U.S.A

    Geochemical analyses of dikes, sills, and volcanic rocks of the Meoszoic Appalachian Tholeiite (MAT) Province of the easternmost United States provide evidence that continental tholeiites are derived from continental lithospheric mantle sources that are genetically and geochronologically related to the overlying continental crust. Nineteen olivine tholeiites and sixteen quartz tholeiites from the length of this province, associated in space and time with the last opening of the Atlantic, display significant isotopic heterogeneity: initial εNd = +3.8 to -5.7; initial 87Sr/86Sr = 0.7044-0.7072; 206Pb/204Pb = 17.49-19.14; 207Pb/204Pb = 15.55-15.65; 208Pb/204Pb = 37.24-39.11. In Pb-Pb space, the MAT define a linear array displaced above the field for MORB and thus resemble oceanic basalts with DUPAL Pb isotopic traits. A regression of this array yields a secondary Pb-Pb isochron age of ≅ 1000 Ma (μ1 = 8.26), similar to Sm/Nd isochrons from the southern half of the province and to the radiometric age of the Grenville crust underlying easternmost North America. The MAT exhibit significant trace element ratio heterogeneity (e.g., Sm/Nd = 0.226-0.327) and have trace element traits similar to convergent margin magmas [e.g., depletions of Nb and Ti relative to the rare earth elements on normalized trace element incompatibility diagrams, Ba/Nb ratios (19-75) that are significantly greater than those of MORB, and low TiO2 (0.39-0.69%)]. Geochemical and geological considerations were strongly suggest that the MAT were not significantly contaminated during ascent through the continental crust. Further, isotope and trace element variations are not consistent with the involvement of contemporaneous MORB or OIB components. Rather, the materials that control the MAT incompatible element chemistry were derived from subcontinental lithospheric mantle. (orig./WB)

  9. Timing and Composition of Continental Volcanism, Harrat Hutaymah, Western Saudi Arabia

    Schlieder, T.; Duncan, R. A.; Al-Amri, A. M.; Al-Shaltoni, S.


    One of the largest alkali basalt provinces in the world (area: 180,000 km2) is located in the western part of the Arabian Peninsula. These extensive Cenozoic basaltic lava fields ('harrats') erupted from N-S oriented volcanic centers that lie within 200 km of the NW-trending eastern margin of the Red Sea. The origin of these fields is partially related to regional extension of thick, Pan-African craton that began ~30 Ma, but there is no reflection of these volcanic centers on the western margin (African Plate). Lava compositions in the region include alkali ol-basalts, ol-transitional basalts, hawaiites, and more evolved compositions, which contrast with the tholeiitic basalts of the Red Sea. In the harrat province early, Red Sea-parallel volcanism (>12 Ma) was dominated by tholeiitic to transitional compositions, but has become more alkalic with younger, N-S oriented eruptive centers (shield, beginning ~15 Ma. Therefore flexure and/or asthenospheric flow may explain the timing, distribution and variable depth and degree of partial melting across the region. We selected the lava field of Harrat Hutaymah, on the northeastern-most edge of the harrat province for high-resolution age and compositional investigation. Previous dating at this harrat (a single K/Ar age; 1.8 Ma) is suspiciously old given the common occurrence of xenolithic material in the lava flows and the field measurement of only normal magnetic polarity. We report new age determinations by the 40Ar-39Ar incremental step heating method and major, trace and rare earth element compositions to better constrain the time frame of volcanism and chemical variation at Harrat Hutaymah. We use these new data to model the depth and degree of partial melting beneath Harrat Hutaymah (65-80 km; ~5%). This compares with contemporaneous Harrat Rahat (20-40 km; 10-15%), part of the central MMN axis, Harrat Lunayyir (60-75 km; 7-12%), 100 km east of the Red Sea, and the Red Sea spreading axis (0-10 km; 25%). This

  10. 40Ar/39Ar dating of alkaline and tholeiitic magmatism of Saudi Arabia related to the early Red Sea Rifting

    40Ar/39Ar plateau-ages at 27-28 Ma obtained on feeder dykes and one lava flow of the alkaline massif of Harrat Hadan are in agreement with the assumed age partly deduced from the conventional K/Ar data of the early activity of other alkaline volcanic massifs from Saudi Arabia. This magmatic activity is spatially distributed over a large area, along the western edge of the Arabian plate, and their N-S to NW-SE volcano-tectonic directions are similar to those of the future Red Sea Rift. Preliminary results obtained on tholeiitic lava flows, dykes and plutons gave 17 plateau-ages which, combined with 6 ages deduced from more disturbed age-spectra, display a main histogram peak from 24 to 21 Ma, much narrower than that obtained with conventional K/Ar ages on the same formations. Therefore, a strong tholeiitic activity affected a narrow linear area following the actual eastern Red Sea coast, over nearly 1700 km, during a brief period of time, and without showing any apparent migration. The main volcano-tectonic features of the future Red Sea are strongly outlined during this event. Such brief magmatic episodes related to continental rifts have also been documented by precise 40Ar/39Ar analyses on the British Tertiary Igneous Province, the Deccan traps and the eastern Central Atlantic. (orig.)

  11. Amygdaloid and hydrothermal mineralization in the Cenozoic volcanic series of eastern part of Jilin Prvince%吉林省东部新生代火山岩系中的杏仁体与热水成矿作用

    吕鹏; 惠艳梅


    吉林省东部山区大面积出露新生代火山岩,但多年以来地质科技人员很少在新生代火山岩中找矿。作者收集了近几年的有关资料,分析了杏仁体的主要特征、杏仁体形态特点、杏仁体的内部构造、杏仁体的矿物组成及其与热水成矿作用关系。供同仁们在火山岩找矿方面参考。%There are large Cenozoic volcano rock outcropping in the eastern mountain area of Jilin Province, but for many years, geological workers rarely prospect in Cenozoic volcano rock. The authors collect the relevant data in recent years, and analyze the main features of the amygdaloid, morphological characteristics, the internal structure, mineral composition and the relation with hot water mineralization. These are reference for colleagues in the volcano rock prospecting.

  12. Viscous flow behavior of tholeiitic and alkaline Fe-rich martian basalts

    Chevrel, Magdalena Oryaëlle; Baratoux, David; Hess, Kai-Uwe; Dingwell, Donald B.


    The chemical compositions of martian basalts are enriched in iron with respect to terrestrial basalts. Their rheology is poorly known and liquids of this chemical composition have not been experimentally investigated. Here, we determine the viscosity of five synthetic silicate liquids having compositions representative of the diversity of martian volcanic rocks including primary martian mantle melts and alkali basalts. The concentric cylinder method has been employed between 1500 °C and the respective liquidus temperatures of these liquids. The viscosity near the glass transition has been derived from calorimetric measurements of the glass transition. Although some glass heterogeneity limits the accuracy of the data near the glass transition, it was nevertheless possible to determine the parameters of the non-Arrhenian temperature-dependence of viscosity over a wide temperature range (1500 °C to the glass transition temperature). At superliquidus conditions, the martian basalt viscosities are as low as those of the Fe-Ti-rich lunar basalts, similar to the lowest viscosities recorded for terrestrial ferrobasalts, and 0.5 to 1 order of magnitude lower than terrestrial tholeiitic basalts. Comparison with empirical models reveals that Giordano et al. (2008) offers the best approximation, whereas the model proposed by Hui and Zhang (2007) is inappropriate for the compositions considered. The slightly lower viscosities exhibited by the melts produced by low degree of mantle partial melting versus melts produced at high degree of mantle partial melting (likely corresponding to the early history of Mars), is not deemed sufficient to lead to viscosity variations large enough to produce an overall shift of martian lava flow morphologies over time. Rather, the details of the crystallization sequence (and in particular the ability of some of these magmas to form spinifex texture) is proposed to be a dominant effect on the viscosity during martian lava flow emplacement and

  13. Geochemistry of tholeiitic to alkaline lavas from the east of Lake Van (Turkey): Implications for a late Cretaceous mature supra-subduction zone environment

    Özdemir, Yavuz


    Arc-related rocks of the Yüksekova Complex extend from Kahramanmaraş to Hakkari throughout the Southeast Anatolia representing the remnants of the Southern Branch of Neotethys. The volcanic members of this zone from the eastern parts of Lake Van suggest three different types of rock chemistry; tholeiitic (type I), calc-alkaline (type II) and alkaline (type III). Tholeiitic and calc-alkaline members suggest a subduction-related environment with their HFS and LIL element distributions. RE and trace element systematics and modelings indicate that i) the intermediate and the felsic calc-alkaline rocks are the result of fractional crystallization from a basic endmember, ii) alkaline members have originated from enriched mantle source relative to the tholeiitic and calc-alkaline lavas. Overall data from Yüksekova Complex suggest a mature supra-subduction zone environment within the southern Neotethyan Ocean during Upper Cretaceous time. The existence of Lutetian OIB like asthenospheric lavas at the upper parts of the ophiolitic assemblage in the eastern parts of Lake Van proposes the end of the normal ophiolite formation and the possible continuation of the magmatism with OIB like lavas during Middle Eocene.

  14. Recycling of oceanic crust from a stagnant slab in the mantle transition zone: Evidence from Cenozoic continental basalts in Zhejiang Province, SE China

    Li, Yan-Qing; Ma, Chang-Qian; Robinson, Paul T.; Zhou, Qin; Liu, Ming-Liang


    Cenozoic continental basalts from Zhejiang Province, southeast China are tholeiitic to weakly alkalic in composition, with moderate MgO contents (6-11 wt.%) and an average Mg# of 62. They display typical OIB-like trace element features, including enrichment in most incompatible elements, both LILE and LREE, and negative K, Pb, Zr, Hf anomalies. In particular, they are characterized by high Fe/Mn (73 ± 5), La/Yb (19 ± 6) and Nb/Ta (18.8 ± 0.4) ratios, which can be attributed to the presence of residual clinopyroxene, garnet and rutile in the mantle source. Based on these minerals, the following hybrid source rocks are hypothesized: garnet pyroxenite/eclogite and peridotite. Clinopyroxene-liquid thermobarometry indicates clinopyroxene crystallization temperatures of > 1257 °C. This is higher than the assumed temperature at the base of the sub-continental lithospheric mantle (SCLM) (~ 1220 °C) beneath Zhejiang, thus the magmas were presumably derived from the asthenosphere. Some typical geochemical features such as negative K, Pb anomalies, positive Ba, Sr, Nb, Ta anomalies and the extremely high Os isotopic signatures, suggest participation of EM-like mantle sources, indicative of ancient subducted oceanic crust. (87Sr/86Sr)i (0.7037-0.7046) and 143Nd/144Nd (0.512832-0.512990) isotope ratios point to the presence of mixed components in the source region, i.e., DMM, EM1 and EM2. Recent seismic tomographic images of the mantle beneath Zhejiang suggest the presence of a subducted slab of oceanic lithosphere in the transition zone. Based on the combined geophysical and geochemical evidence, we propose that the major source of the Zhejiang basaltic magmas was the ancient subducted oceanic slab in the transition zone with an EM-like signature. The other magma sources include depleted asthenospheric peridotite possessing a DMM-like signature. The dynamics of this upwelling hybrid magma was apparently related to westward subduction of the Pacific plate underneath the

  15. Aeromagnetic search for Cenozoic magmatism over the Admiralty Mountains Block (East Antarctica)

    Armadillo; E.; Ferraccioli, F.; Zunino, A.; Bozzo, E.; Rocchi, S.; Armienti, P.


    Cenozoic magmatic rocks of the Transantarctic Mountains provide an important window on the tectonic and magmatic processes of the West Antarctic Rift System. Previous aeromagnetic investigations in northern Victoria Land have delineated Cenozoic volcanic and intrusive complexes assigned to the McMurdo Volcanic Group and Meander Intrusives over the Transantarctic Mountains. We present a new aeromagnetic anomaly map for the region north of the Mariner Glacier to study the extent and spatial distribution of these Cenozoic rocks over the previously unexplored Admiralty Mountains. The new map shows that the Meander Intrusives are restricted to the coastal region between the Malta Plateau and the Daniell Peninsula. However, the McMurdo Volcanic Group rocks extend further inland, and may delineate a hitherto unrecognised volcano-tectonic rift zone, extending as far north as the Trafalgar Glacier.

  16. Research Advances in Greenhouse Gases Degassing from Cenozoic Volcanic Active Fields%火山温室气体释放通量与观测的研究进展

    郭正府; 张茂亮; 孙玉涛; 成智慧; 张丽红; 刘嘉麒


    Volcanic activities are of great importance to the global deep carbon cycle,which could release large amount of greenhouse gases during both eruptive and quiescent stages,resulting in climatic and environmental changes on local and even global scales.Under the context of global warming,quantitative studies on the contribution of volcanic activities to rising of atmospheric greenhouse gases concentration are critical to discriminating carbon emissions associated with nature and human and to accumulating essential data for geological carbon budget.In this study,we briefly reviewed types,char-acteristics and research methods of greenhouse gases emissions,and the current status of research on fluxes and origin of greenhouse gases emitting from volcanic fields of China.Based on internationally accepted theory in volcanic-related green-house gases,we proposed that,systematic studies on fluxes and origin of greenhouse gases emitting from volcanic activities would contribute to estimating scale of greenhouse gases emissions,volcanic monitoring and magma degassing.%火山活动是地球深部碳循环的重要环节,火山区不仅在火山喷发期能够释放温室气体,而且在休眠期也能向大气圈中释放大量的温室气体。在当前全球温室气体减排的背景下,定量化地研究火山区对大气圈温室气体含量增加的贡献,对于识别自然因素和人类因素碳排放的相对规模、为国际碳排放谈判积累基础数据等均具有至关重要的科学价值和现实意义。本文对火山区温室气体的排放方式与特征、温室气体释放通量与成因的研究方法进行了简要概括,并综述了中国新生代典型火山区温室气体释放通量与成因的研究成果。结合国外温室气体排放研究现状,指出深入研究活火山(包括休眠火山)区的温室气体释放通量与成因对于估算火山来源温室气体的释放规模、建立火山未来喷发预测-预警体系

  17. From mantle roots to surface eruptions: Cenozoic and Mesozoic continental basaltic magmatism

    Kämpf, H.; Németh, K.; Puziewicz, J.; Mrlina, Jan; Geissler, W.H.


    Roč. 104, č. 8 (2015), s. 1909-1912. ISSN 1437-3254 Institutional support: RVO:67985530 Keywords : continental basaltic volcanism * BASALT 2013 conference * Cenozoic * Mesozoic Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.093, year: 2014

  18. Eocene to Miocene back-arc basin basalts and associated island arc tholeiites from northern Sulawesi (Indonesia): Implications for the geodynamic evolution of the Celebes basin

    Eocene BABB basalts intruded by tholeiitic and calk-alkalic island arc magmatic rocks are reported from the north arm of Sulawesi (Indonesia). Age and geochemical similarities between these basalts and those drilled in the Celebes Sea indicate this North Sulawesi volcanic arc was built on the same oceanic crust. The 25 deg late Neogene clockwise rotation of the north arm of Sulawesi following its collision with fragments of Australia (Sula, Buton) is not sufficient to explain the asymmetrical magnetic anomalies in the Celebes basin. The North Sulawesi island arc could be interpreted as having progressively retreated northward on its own Celebes sea back arc basin, during an episode of Palaeogene-early Neogene tectonic erosion along the trench. (authors)

  19. Magma/metal compatibility study: compatibility of metals in molten degassed tholeiitic basalt

    The compatibility of ten commercially available alloys with molten (13000C) degassed tholeiitic basalt was studied. Results can be explained on the basis of (1) the relative free energies of formation of pertinent oxides and (2) shifts in the chemical equilibrium among iron species. (auth)

  20. Petrogenesis of Late Cenozoic basalts from North Hainan Island: Constraints from melt inclusions and their host olivines

    Liu, Jian-Qiang; Ren, Zhong-Yuan; Nichols, Alexander R. L.; Song, Mao-Shuang; Qian, Sheng-Ping; Zhang, Yan; Zhao, Pei-Pei


    Melt inclusions and their host olivines in basaltic lavas provide important information about the nature of their mantle source. We present the first analyzed chemical data of olivine-hosted melt inclusions in Cenozoic basalts from the North Hainan Island and report the discovery of both tholeiitic and alkalic melt inclusions in a single rock sample. Cenozoic basalts from the Hainan Island are predominantly tholeiites with only small amounts of alkali basalts. There is a much broader compositional variation in melt inclusions than whole rocks. Compared to partial melts of mantle peridotite, the Hainan basalts have lower CaO, Na2O/TiO2, CaO/Al2O3 and Co/Fe, and higher TiO2, FeO∗, Fe/Mn, Zn/Fe and Zn/Mn. The olivine phenocrysts from the Hainan basalts contain lower Ca and Mn, and higher Ni and Fe/Mn than those of olivines crystallized from partial melts of peridotite. Projections from or towards olivine into the plane CS-MS-A for melt inclusions and whole rocks with MgO >7.5 wt% imply that the residual minerals in the source of the tholeiites are mainly clinopyroxene and garnet, possibly with some orthopyroxene, while in the source of the alkali basalts they are dominated by clinopyroxene and garnet. This indicates that a pyroxenite component could serve as the source lithology of the Hainan basalts. The OIB-like trace element compositions, with Ba, Sr, Nb and Ta positive anomalies, and Th and U negative anomalies, of the Hainan basalts suggest that a recycled oceanic crust component was involved in the source of the Hainan basalts. Based on a CMAS projection of primary magma compositions of the whole rocks and melt inclusions, we infer that a stage-2 silica-deficient pyroxenite derived from melt-peridotite reaction or mechanical mixing between recycled oceanic crust and peridotite can serve as the source lithology. Partial melts derived from such a source can match the overall compositions of the Hainan basalts better than those of MORB-eclogite and fertile

  1. Cenozoic Uplift, Erosion and Dynamic Support of Madagascar

    Stephenson, Simon; White, Nicky


    The physiography of Madagascar is characterised by high-elevation but low-relief topography; 42% of the landscape is above 500 m in elevation. Eocene (marine) nummulitic (marine) limestones at elevations of ˜400 m above sea level and newly dated, emergent 125 ka coral reefs suggest that Madagascar has experienced differential vertical motions during Cenozoic times. Malagasy rivers are often deeply incised and contain steepened reaches, implying that they have responded to changes in regional uplift rate. However, low temperature thermochronology and 10Be derived erosion rates suggest that both Cenozoic and Recent average denudation rates have been low. Extensive laterite-capped, low-relief surfaces also suggest that there have been long periods of tectonic quiescence. In contrast, the modern landscape is characterised by erosional gullies (i.e. lavaka), with very high local erosion rates. To bridge the gap between this disparate evidence, we inverted 2566 longitudinal river profiles using a damped non-negative, least-squares linear inversion to determine the history of regional uplift. We used a simplified version of the stream power erosional law. River profiles were extracted from the 3 arc-second Shuttle Radar Topography Mission (SRTM) digital elevation model. Calibration of the stream power erosional law is based upon Cenozoic limestones and new radiometrically dated marine terraces. The residual misfit between observed and calculated river profiles is small. Results suggest that Malagasy topography grew diachronously by 1-2 km over the last 15-20 Ma. Calculated uplift and denudation are consistent with independent observations. Thus drainage networks contain coherent signals that record regional uplift. The resultant waves of incision are the principal trigger for modern erosional processes. Admittance calculations, the history of basaltic volcanism and nearby oceanic residual age-depth measurements all suggest that as much as 0.8 - 1.1 km of Cenozoic uplift

  2. Cenozoic volcanic series in western part of the Bohemian Massif

    Ulrych, Jaromír; Novák, Jiří Karel; Lloyd, F. E.; Balogh, K.; Hegner, E.; Viereck-Götte, L. G.

    Prague : Geophysical Institute of Academy of Sciences of the Czech Republic, 2004, s. 35-36. [Drilling the Eger Rift (International Continental Drilling Program Workshop. Chateau of Býkov (CZ), 03.10.2004-07.10.2004] Institutional research plan: CEZ:AV0Z3013912 Keywords : Eger Rift * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  3. Petrogenesis of Miocene alkaline volcanic suites from western Bohemia. Whole rock geochemistry and Sr-Nd-Pb isotopic signatures.

    Ulrych, Jaromír; Krmíček, Lukáš; Tomek, Č.; Lloyd, F. E.; Ladenberger, A.; Ackerman, Lukáš; Balogh, K.


    Roč. 76, č. 1 (2106), s. 77-93. ISSN 0009-2819 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cenozoic alkaline volcanism * Geochemistry * K-Ar ages * Sr-Nd-Pb isotopes Subject RIV: DD - Geochemistry

  4. Eocene volcanism during the incipient stage of Izu–Ogasawara Arc: Geology and petrology of the Mukojima Island Group, the Ogasawara Islands.

    Kanayama, Kyoko; Umino, Susumu; Ishizuka, Osamu


    The Ogasawara Islands mainly comprise Eocene volcanic strata formed when the Izu-Ogasawara-Mariana Arc began. We present the first detailed volcanic geology, petrography and geochemistry of the Mukojima Island Group, northernmost of the Ogasawara Islands, and show that the volcanic stratigraphy consists of arc tholeiitic rocks, ultra-depleted boninite-series rocks, and less-depleted boninitic andesites, which are correlatable to the Maruberiwan, Asahiyama and Mikazukiyama Formations on the Ch...

  5. Origin of low δ26Mg Cenozoic basalts from South China Block and their geodynamic implications

    Huang, Jian; Li, Shu-Guang; Xiao, Yilin; Ke, Shan; Li, Wang-Ye; Tian, Ye


    Origin of low δ26Mg basalts is a controversial subject and has been attributed to interaction of isotopically light carbonatitic melts derived from a subducted oceanic slab with the mantle (Yang et al., 2012), or alternatively, to accumulation of isotopically light ilmenite (FeTiO3) in their mantle source (Sedaghatpour et al., 2013). To study the origin of low δ26Mg basalts and evaluate whether Mg isotope ratios of basalts can be used to trace deeply recycled carbon, high-precision major and trace element and Mg isotopic analyses on the Cenozoic alkaline and tholeiitic basalts from the South China Block (SCB), eastern China have been carried out in this study. The basalts show light Mg isotopic compositions, with δ26Mg ranging from -0.60 to -0.35. The relatively low TiO2 contents (eclogite transformed from carbonate-bearing oceanic crust during plate subduction. As only the Pacific slab has an influence on both the North China Block (NCB) and SCB, our results together with the study of Yang et al. (2012) demonstrate that the recycled carbonatitic melts might have originated from the stagnant Pacific slab beneath East Asia in the Cretaceous and Cenozoic and that a widespread carbonated upper mantle exists beneath eastern China, which may serve as the main source for the <110 Ma basalts in this area. Thus, our study demonstrates that Mg isotope ratios of basalts are a powerful tool to trace deeply recycled carbon.

  6. Catastrophic volcanism

    Lipman, Peter W.


    Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

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

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


    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.

  8. Analysing the Cenozoic depositional record

    Goledowski, Bartosz; Clausen, O.R.; Nielsen, S.B.

    between the global climate record (oxygen isotopes) and lithology variations on the Eocene-Oligocene transition in the eastern North Sea. Due to the strongly limited time resolution of low temperature thermochronology, the Cenozoic sedimentary record potentially provides the most detailed history of...... lower limit to erosion rate in source areas of the respective sedimentary bodies. The lower limit arises because some erosional products are transported out of the mapped area, and some erosion is caused by chemical dissolution. The development of the source areas will be modelled using surface process...... models. The matrix mass deposition history will be compared with the paleoclimate record (e.g. oxygen isotope curves) to see if the previously observed correlation in the eastern North Sea can be extended to other ages and locations.  ...

  9. Geochemistry of Spencer-High Point Volcanic Field Lava Flows, Idaho

    Iwahashi, G. S.; Hughes, S. S.


    Lava flows in Spencer-High Point (SHP) volcanic field, an ~1700 sq km mafic volcanic rift zone located near Yellowstone in the eastern Snake River Plain (ESRP), have been compared physically and chemically to other ESRP olivine tholeiites. Overall, SHP lavas are geochemically similar to other ESRP olivine tholeiites but their geomorphology is entirely different. The structural alignment of vents and fissures in an east-west direction in the Spencer-High Point region contrasts with most of the ESRP volcanic features aligned northwest-southeast. Numerous cinder cones at SHP, features that characterize Craters of the Moon volcanic field, are unusual on most of the eastern Snake River Plain. This study agrees with preliminary geochemical data by Leeman (1982) and Kuntz et al. (1992) suggesting that SHP lavas are typical ESRP basalts. However, a broad range of geochemical compositions exists in the SHP field that is similar to the entire range of ESRP olivine tholeiites. A few of the samples are actually closer in composition to lavas present at Craters of the Moon but only a limited number of samples from vents with physically higher relief, in the central and eastern portions of the field show these evolved chemical compositions. Typically Ta ranges 0.5-4.5ppm, La 20-90ppm, Ba 200-1100ppm and Cr 7-550ppm. Some lava flows in the central and eastern sections of SHP volcanic field also contain crustal xenoliths, implying a prolonged crustal history. These results although preliminary, suggest that the SHP system represents a possible petrologic transition between the dominant ESRP tholeiites and the evolved compositions found at Craters of the Moon.

  10. Geochemistry of cenozoic basaltic rocks from Shandong province and its implication for mantle process in North China

    Cenozoic (Miocene to Pleistocene) basaltic rocks found in Shandong province of northern China include tholeiite, olivine tholeiite and alkali basalt. We present major, trace and rare earth elements data of these basalts and together with Sr-Nd isotopic data in the literatures to discuss the petrogenesis of these basalts. The basalts from Penglai area have higher K, Na and P and incompatible elements, but lower Ca, Mg and compatible elements contents than those from Changle area of Shandong province. Spidergrams indicate that Cenozoic basalts from Shandong province have geochemical characteristics similar to those of ocean island basalts (OIB) with slight positive Nb anomaly. The negative Ba, Rb and K anomalies found in the alkali basalts suggest the presence of residual phlogopite in the mantle source, indicating a metasomatic event occurred before the partial melting. The 143Nd/144Nd vs. 87Sr/86Sr plot suggested that basalts from Shandong province can be produced by MORB and EM-I components mixing. We propose that the EM-I type lithospheric mantle may have been produced by the recent H2O-CO2 -fluids metasomatism and the fluids may be derived from dehydration of the subducted slab. Based on Shaw's equation, the basalts from eastern and central Shandong province have undergone different degrees of particle melting from the mantle source. Degrees of partial melting and chemical composition of basalts from Shandong province suggest that the lithosphere has thickened progressively since the Miocene. On the basis of Ar-Ar ages of this study and the fractional crystallization model proposed by Brooks and Nielsen (1982), we suggest that basalts from Changle and Penglai areas belong to different magmatic systems which have undergone fractional crystallization and evolved progressively to produce other types of basalts. (author)

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

    Charles W. Messo


    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.

  12. Timing of the volcanism of the southern Kivu province: Implications for the evolution of the western branch of the East African rift system

    New K-Ar datings of a large rock sampling from the South Kivu volcanic province (Zaire, Rwanda, Burundi) are reported. No ages older than 10 Ma have been obtained. This result contrasts with older assumptions and puts severe constraints on the relations between volcanism and rift evolution. From 10 to 7.5 Ma tholeiitic volcanism predominates corresponding to an episode of fissural eruptions; from 7.5 to 5 Ma alkali basalts and their differentiates are mainly erupted in localized rifts. A culmination of activity occurs between 6.0 and 5.5 Ma ago. Pleistocene alkalic volcanism is restricted to localized areas. The transition from tholeiites to alkali-basaltic volcanism dated around 7.5 Ma would correspond to a major rifting phase which corresponds with the initiation of Lake Kivu Basin formation. The distribution of tholeiitic rocks in the central part of the rift, and predominantly alkalic rocks along the western active border fault, strengthens the idea that the former are associated with tension, the latter with vertical, possibly also strike-slip movements. Volcanism in the Western Rift is restricted to areas where tension occurs in a zone which is located between two zones of strike-slip. In the South Kivu area normal faults intersect strike-slip faults and this seems to have determined the location of volcanic activity. Magma formation is considered to be related with shear heating combined with adiabatic decompression in ascending diapirs. This implies heating at the lithosphere-asthenosphere boundary as a result of extension. Generation of tholeiitic or alkalic magmas is connected with the variable ascent velocity of mantle diapirs or with variable shear heating along the shear zone. Changes in both magma composition and intensity of volcanic activity with time are considered to be related to major phases of rift evolution. (orig.)

  13. Late Cenozoic structure and stratigraphy of south-central Washington

    The structural framework of the Columbia Basin began developing before Columbia River Basalt Group (CRBG) volcanism. Prior to 17.5 Ma, the eastern part of the basin was a relatively stable area, with a basement of Paleozoic and older crystalline rock. The western part was an area of subsidence in which large volumes of sediment and volcanic rocks accumulated. Concurrent with eruption of the CRBG, anticlinal ridges of the Yakima Fold Belt (YFB) were growing under north-south compression. Topographic expression of these features was later masked by the large volume of CRBG basalt flowing west from fissures in the eastern Columbia Basin. The folds continued to develop after cessation of volcanism, leading to as much as 1,000 m of structural relief in the past 10 million years. Post-CRBG evolution of the Columbia Basin is recorded principally in folding and faulting in the YFB and sediments deposited in the basins. The accompanying tectonism resulted in lateral migration of major depositional systems into subsiding structural lows. Although known late Cenozoic faults are on anticlinal ridges, earthquake focal mechanisms and contemporary strain measurements indicate most stress release is occurring in the synclinal areas under north-south compression. There is no obvious correlation between focal mechanisms for earthquakes whose foci are in the CRBG and the location of known faults. High in situ stress values help to explain the occurrence of microseismicity in the Columbia Basin but not the pattern. Microseismicity appears to occur in unaltered fresh basalt. Faulted basalt associated with the YFB is highly brecciated and commonly altered to clay. The high stress, abundance of ground water in confined aquifers of the CRBG, and altered basalt in fault zones suggest that the frontal faults on the anticlinal ridges probably have some aseismic deformation. 85 refs

  14. Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?

    G. Hoareau


    Full Text Available The 58–51 Ma interval was characterized by a long-term increase of global temperatures (+4 to +6 °C up to the Early Eocene Climate Optimum (EECO, 52.9–50.7 Ma, the warmest interval of the Cenozoic. It was recently suggested that sustained high atmospheric pCO2, controlling warm early Cenozoic climate, may have been released during Neo-Tethys closure through the subduction of large amounts of pelagic carbonates and their recycling as CO2 at arc volcanoes ("carbonate subduction factory". To analyze the impact of Neo-Tethys closure on early Cenozoic warming, we have modeled the volume of subducted sediments and the amount of CO2 emitted at active arc volcanoes along the northern Tethys margin. The impact of calculated CO2 fluxes on global temperature during the early Cenozoic have then been tested using a climate carbon cycle model (GEOCLIM. We first show that CO2 production may have reached up to 1.55 × 1018 mol Ma−1 specifically during the EECO, ~ 4 to 37 % higher that the modern global volcanic CO2 output, owing to a dramatic India–Asia plate convergence increase. In addition to the background CO2 degassing, the subduction of thick Greater Indian continental margin carbonate sediments at ~ 55–50 Ma may also have led to additional CO2 production of 3.35 × 1018 mol Ma−1 during the EECO, making a total of 85 % of the global volcanic CO2 outgassed. However, climate modelling demonstrates that timing of maximum CO2 release only partially fit with the EECO, and that corresponding maximum pCO2 values (750 ppm and surface warming (+2 °C do not reach values inferred from geochemical proxies, a result consistent with conclusions arise from modelling based on other published CO2 fluxes. These results demonstrate that CO2 derived from decarbonation of Neo-Tethyan lithosphere may have possibly contributed to, but certainly cannot account alone for early Cenozoic warming, including the EECO. Other commonly cited sources of excess CO2 such as

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


    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.

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

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


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

  17. Jurassic Volcanism in the Eastern Pontides: Is it Rift Related or Subduction Related?

    Şen, Cüneyt


    The Jurassic volcanic rocks in the centre of the northern zone (south of Trabzon City) provide important constraints on the evolution of Pontides. The investigated volcanic rocks form a transitional series between tholeiitic and calc-alkaline, and is dominated by basalt, basaltic andesite and andesite. Geochemically, they are enriched in LILE and LREE contents and depleted in HFSE [(La/Yb)N= 2.2 - 8.5; (Nb/La)N= 0.1 - 0.77)] compared to mid-ocean ridge basalts and have radiogenic Nd isotope r...

  18. Metallogenic systems related to Mesozoic and Cenozoic granitoids in South China

    HUA; Renmin; (华仁民); CHEN; Peirong; (陈培荣); ZHANG; Wenlan; (张文兰); LIU; Xiaodong; (刘晓东); LU; Jianjun; (陆建军); LIN; Jinfu; (林锦富); YAO; Junming; (姚军明); QI; Huawen; (戚华文); ZHANG; Zhanshi; (张展适); GU; Shengyan; (顾晟彦)


    Large scale mineralizations of nonferrous, precious, and rare metals took place in South China in Mesozoic and Cenozoic Eras, which were mostly closely related with granitic magmatisms of different sources and features. Four metallogenic systems related to Mesozoic and Cenozoic granitoids are put forward in this paper. They are: (i) the porphyry-epithermal copper-gold system related to calc-alkaline volcanic-intrusive magmatism, (ii) rare metal (mainly W, Sn, Ta, Nb, etc) metallogenic system related with continental crust re-melting type granitoids, (iii) copper and polymetallic metallogenic system related with intra-plate high potassium calc-alkaline and shoshonitic magmatism, and (iv) Au-Cu and REE metallogenic system related to A-type granites. The main characteristics of these systems are briefly discussed. These Mesozoic and Cenozoic granitoids of different sources were the products of different periods of lithosphere evolution in that area under different tectonic-dynamic environments. Fundamentally speaking, however, the granitoids and related metallogeneses are the results of mantle-crust interactions under a tensile tectonic environment in South China.

  19. Construction of the seawater 87Sr/86Sr curve for the Cenozoic and Cretaceous: supporting data

    We present the data used to construct the Cenozoic and Cretaceous portion of the Phanerozoic curve of seawater 87Sr/86Sr that had been given in summary form by W.H. Burke and coworkers. All Cenozoic samples (128) and 22 Cretaceous samples are foram-nannofossil oozes and limestones from DSDP cores distributed among 13 sites in the Atlantic, Pacific and Indian Oceans, and the Caribbean Sea. Non-DSDP Cretaceous samples (126) include limestone, anhydrite and phosphate samples from North America, Europe and Asia. Determination of the 87Sr/86Sr value of seawater at particular times in the past is based on comparison of ratios derived from coeval marine samples from widely separated geographic areas. The general configuration of the Cenozoic and Cretaceous curve appears to be strongly influenced by the history of plate interactions and sea-floor spreading. Specific rises and falls in the 87Sr/86Sr of seawater, however, may be caused by a variety of factors such as variation in lithologic composition of the crust exposed to weathering, configuration and topographic relief of continents, volcanic activity, rate of sea-floor spreading, extent of continental inundation by epeiric seas, and variations in both climate and paleo-oceanographic conditions. Many or all of these factors are probably related to global tectonic processes, yet their combined effect on the temporal variation of seawater 87Sr/86Sr can complicate a direct plate-tectonic interpretation for portions of the seawater curve. (Auth.)

  20. Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: Constraints of geochemical and isotopic data

    Ngonge, Emmanuel Donald; de Hollanda, Maria Helena Bezerra Maia; Archanjo, Carlos José; de Oliveira, Diógenes Custódio; Vasconcelos, Paulo Marcosde Paula; Muñoz, Patrício Rodrigo Montecinos


    The Ceará Mirim dyke swarm (northeastern Brazil) is composed of Cretaceous tholeiites with plagioclase, clinopyroxene (± olivine), Fe-Ti oxides and pigeonite in their groundmass. These tholeiites have been subdivided into three groups: high-Ti olivine tholeiites, evolved high-Ti tholeiites (TiO2 ≥ 1.5 wt.%; Ti/Y > 360), and low-Ti tholeiites (TiO2 ≤ 1.5 wt%; Ti/Y ≤ 360), with all exhibiting distinct degrees of enrichment in incompatible elements relative to Primitive Mantle. Negative Pb anomalies are found in all three groups, while Nb-Ta abundances similar to those of OIB-type magmas are found in the olivine tholeiites, with moderate to high depletions being observed, respectively, in the evolved high-Ti and low-Ti tholeiites. The low-Ti tholeiites exhibit some contamination with crustal (felsic) materials during ascent. The initial isotopic compositions of the olivine tholeiites show uniform and unradiogenic 87Sr/86Sr (~ 0.7035-0.7039) combined with (in part) radiogenic 143Nd/144Nd and 206Pb/204Pb (> 19.1) ratios, which together reveal a likely contribution of FOZO (FOcalZOne) component in their genesis. The other tholeiite groups show variable Sr-Nd ratios with relatively consistent 206Pb/204Pb ratios clustering towards an isotopically enriched mantle (EM1) component. Taken in conjunction with the Nb, this enriched signature reflects the involvement of a subduction-modified lithospheric mantle in the source of the evolved high-Ti and low-Ti tholeiites. Thus, we propose that FOZO and EMI components coexisted (including minor mixing with E-MORB magmas) and contributed in varying extents to the generation of the Ceará-Mirim dyke swarm primary melts, which segregated at 75 to 60 km in depth around the garnet-spinel facies transition zone. The mechanism that promoted melting was most likely non-plume related. We suggest that plate-boundary forces linked to the opening of the Atlantic Ocean promoted passive rifting and that the resulting asthenospheric

  1. Potassium, rubidium, strontium, thorium, uranium, and the ratio of strontium-87 to strontium-86 in oceanic tholeiitic basalt

    Tatsumoto, M.; Hedge, C.E.; Engel, A.E.J.


    The average concentrations of potassium, rubidium, strontium, thorium, and uranium in oceanic tholeiitic basalt are (in parts per million) K, 1400; Rb, 1.2; Sr, 120; Th, 0.2; and U, 0.1. The ratio Sr87 to Sr86 is about 0.702, that of K to U is 1.4 ?? 104, and of Th to U is 1.8. These amounts of K, Th, U, and radiogenic Sr87 are less than in other common igneous rocks. The ratios of Th to U and Sr87 to Sr 86 suggest that the source region of the oceanic tholeiites was differentiated from the original mantle material some time in the geologic past.

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

    Skála, Roman; Ulrych, Jaromír; Krmíček, Lukáš; Fediuk, F.; Balogh, K.; Hegner, E.


    Roč. 66, č. 3 (2015), s. 197-216. ISSN 1335-0552 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cenozoic volcanism * isotope geochemistry * melilitic rock * mineralogy * petrology Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.761, year: 2014

  3. Meso-Cenozoic evolution of the Tuareg Shield (Algeria, Sahara): insights from new thermochronological data

    Rougier, Sylvain; Missenard, Yves; Gautheron, Cécile; Barbarand, Jocelyn; Zeyen, Hermann; Pinna, Rosella; Liégeois, Jean-Paul; Bonin, Bernard; Ouabadi, Aziouz; El-Messaoud Derder, Mohammed; Frizon de Lamotte, Dominique; Kettouche, Djouher


    In North Africa, Meso-Cenozoic large scale topographic swells, such as Hoggar, Tibesti or Darfur domes, are superimposed to a Paleozoic arch and basin morphology which characterizes this region. Although these topographic highs are associated to Cenozoic intraplate volcanism, their development remains poorly constrained, both from temporal and spatial points of view. This study is focused on the Tuareg Shield bulge, a topographic high where Precambrian rocks, exposed over 500000 km², can reach 2400 m above sea level (Atakor district, Hoggar, South Algeria). While presumed Cretaceous sedimentary remnants, resting unconformably over the basement, suggest a possible stage of weak topography during the Mesozoic, current high topography is emphasized by time-temperature history were performed. As previously deduced from apatite (U-Th)/He analyzes, these modelings show that samples underwent a heating to at least 80°C before their Late Eocene exhumation. Moreover, they also indicate that samples underwent another cooling stage during Lower Cretaceous, prior to Upper Cretaceous/Paleogene heating. We interpret these results as an evidence of a large-scale subsidence stage after the Cretaceous and until the Eocene, which allowed the deposition of a 1.5 to 3 km thick sedimentary cover and a heating at ~80°C of the currently outcropping basement. During the Eocene, the establishment of a thermal anomaly beneath the Tuareg Shield lithosphere resulted in erosion of the major part of this cover and, since 35 Ma, the development of intraplate volcanism.

  4. Cenozoic stratigraphy and geologic history of the Tucson Basin, Pima County, Arizona

    Anderson, S.R.


    This report was prepared as part of a geohydrologic study of the Tucson basin conducted by the U.S. Geological Survey in cooperation with the city of Tucson. Geologic data from more than 500 water supply and test wells were analyzed to define characteristics of the basin sediments that may affect the potential for land subsidence induced by groundwater withdrawal. The Tucson basin is a structural depression within the Basin and Range physiographic province. The basin is 1,000 sq mi in units area and trends north to northwest. Three Cenozoic stratigraphic unit--the Pantano Formation of Oligocene age, the Tinaja beds (informal usage) of Miocene and Pliocene age, and the Fort Lowell Formation of Pleistocene age--fill the basin. The Tinaja beds include lower, middle, and upper unconformable units. A thin veneer of stream alluvium of late Quaternary age overlies the Fort Lowell Formation. The Pantano Formation and the lower Tinaja beds accumulated during a time of widespread continental sedimentation, volcanism, plutonism, uplift, and complex faulting and tilting of rock units that began during the Oligocene and continued until the middle Miocene. Overlying sediments of the middle and upper Tinaja beds were deposited in response to two subsequent episodes of post-12-million-year block faulting, the latter of which was accompanied by renewed uplift. The Fort Lowell Formation accumulated during the Quaternary development of modern through-flowing the maturation of the drainage. The composite Cenozoic stratigraphic section of the Tucson basin is at least 20,000 ft thick. The steeply tilted to flat-lying section is composed of indurated to unconsolidated clastic sediments, evaporites, and volcanic rocks that are lithologically and structurally complex. The lithology and structures of the section was greatly affected by the uplift and exhumation of adjacent metamorphic core-complex rocks. Similar Cenozoic geologic relations have been identified in other parts of southern

  5. Paleocene initiation of cenozoic uplift in Norway

    Nielsen, S.B.; Paulsen, G.E.; Hansen, D.L.; Gemmer, L.; Clausen, O.R.; Jacobsen, B.H.; Balling, N.; Huuse, M.; Gallagher, K.


    The timing of Cenozoic surface uplift in NW Europe relies on the assumption that the sedimentary response in basins is synchronous with tectonic processes in the source areas. However, many of the phenomena commonly used to infer recent uplift may as well be a consequence of climate change and sea-level fall. The timing of surface uplift therefore remains unconstrained from the sedimentary record alone, and it becomes necessary to consider the constraints imposed by physically and geologically plausible tectonic mechanisms, which have a causal relation to an initiating agent. The gradual reversal of the regional stress field following the break-up produced minor perturbations to the thermal subsidence on the Norwegian Shelf and in the North Sea. Pulses of increased compression cannot be the cause of Cenozoic land surface uplift and accelerated Neogene basin subsidence. Virtually deformation-free regional vertical movements could have been caused by changes in the density column of the lithosphere and asthenosphere following the emplacement of the Iceland plume. A transient uplift component was produced as the plume displaced denser asthenosphere at the base of the lithosphere. This component decayed as the plume material cooled. Permanent uplift as a result of igneous underplating occurred in areas of a thin lithosphere (some Palaeozoic and Mesozoic basins) or for lithosphere under extension at the time of plume emplacement (the ocean-continent boundary). In areas of a thicker lithosphere (East Greenland, Scotland and Norway) plume emplacement may have triggered a Rayleigh-Taylor instability, causing partial lithospheric delamination and associated transient surface uplift at a decreasing rate throughout Cenozoic time. A possible uplift history for the adjacent land areas hence reads: initial transient surface uplift around the break-up time at 53 Ma caused by plume emplacement, and permanent tectonic uplift caused by lithospheric delamination and associated

  6. Pacific Plate slab pull and intraplate deformation in the early Cenozoic

    N. P. Butterworth


    Full Text Available Large tectonic plates are known to be susceptible to internal deformation, leading to a range of phenomena including intraplate volcanism. However, the space and time dependence of intraplate deformation and its relationship with changing plate boundary configurations, subducting slab geometries, and absolute plate motion is poorly understood. We utilise a buoyancy driven Stokes flow solver, BEM-Earth, to investigate the contribution of subducting slabs through time on Pacific Plate motion and plate-scale deformation, and how this is linked to intraplate volcanism. We produce a series of geodynamic models from 62 to 42 Ma in which the plates are driven by the attached subducting slabs and mantle drag/suction forces. We compare our modelled intraplate deformation history with those types of intraplate volcanism that lack a clear age progression. Our models suggest that changes in Cenozoic subduction zone topology caused intraplate deformation to trigger volcanism along several linear seafloor structures, mostly by reactivation of existing seamount chains, but occasionally creating new volcanic chains on crust weakened by fracture zones and extinct ridges. Around 55 Ma subduction of the Pacific-Izanagi ridge reconfigured the major tectonic forces acting on the plate by replacing ridge push with slab pull along its north-western perimeter, causing lithospheric extension along pre-existing weaknesses. Large scale deformation observed in the models coincides with the seamount chains of Hawaii, Louisville, Tokelau, and Gilbert during our modelled time period of 62 to 42 Ma. We suggest that extensional stresses between 72 and 52 Ma are the likely cause of large parts of the formation of the Gilbert chain and that localised extension between 62 and 42 Ma could cause late-stage volcanism along the Musicians Volcanic Ridges. Our models demonstrate that early Cenozoic changes in Pacific plate driving forces only cause relatively minor changes in Pacific

  7. Cenozoic coupled basin-mountain and prospecting direction for sandstone-type uranium deposits in western Yunnan

    The initial forming time of Cenozoic basins in western Yunnan is at 14 Ma or so, it was coupling in the later period tectonic activity time of Lushui-Ruili arc dextral strike-slip fault belt in the eastern fringe and Nabang dextral strike-slip fault belt in the western fringe of Tengchong microplate. The evolution of Cenozoic basins is divided into two stages of sedimentary basin and reformed basin, the former was coupling in the strike-slip tectonic activity of orogen, and formed strike-slip basins, the latter was closely related with the uplift of the whole basins, and formed residual basins. It is considered that there exists two sorts of Cenozoic basins, and they are different in sedimentary evolution, volcanic activity and geographic sight etc., the metallogenic conditions of sandstone-type uranium deposits are also different. The most favourable basins for prospecting sandstone-type uranium deposits are those basins that keeps on uplifting in reformed basin stages, exists volcanic activity and deep incised low mountain-hill-river valley terraces in northern Tengchong area. (authors)

  8. Assessment of the atmospheric impact of volcanic eruptions

    Sigurdsson, H.


    The dominant global impact of volcanic activity is likely to be related to the effects of volcanic gases on the Earth's atmosphere. Volcanic gas emissions from individual volcanic arc eruptions are likely to cause increases in the stratospheric optical depth that result in surface landmass temperature decline of 2 to 3 K for less than a decade. Trachytic and intermediate magmas are much more effective in this regard than high-silica magmas, and may also lead to extensive ozone depletion due to effect of halogens and magmatic water. Given the assumed relationship between arc volcanism and subduction rate, and the relatively small variation in global spreading rates in the geologic record, it is unlikely that the rates of arc volcanism have varied greatly during the Cenozoic. Hotspot related basaltic fissure eruptions in the subaerial environment have a higher mass yield of sulfur, but lofting of the valcanic aerosol to levels above the tropopause is required for a climate impact. High-latitude events, such as the Laki 1783 eruption can easily penetrate the tropopause and enter the stratosphere, but formation of a stratospheric volcanic aerosol form low-latitude effusive basaltic eruptions is problematical, due to the elevated low-latitude tropopause. Due to the high sulfur content of hotspot-derived basaltic magmas, their very high mass eruption rates and the episodic behavior, hotspots must be regarded as potentially major modifiers of Earth's climate through the action of their volcanic volatiles on the chemistry and physics of the atmosphere.

  9. A synthesis of Cenozoic sedimentation in the North Sea

    Anell, Ingrid Anna Margareta; Thybo, Hans; Rasmussen, E.S.


    sediment influx into the North Sea during the Cenozoic is more complex than previously suggested clockwise rotation from early northwestern to late southern sources. The Shetland Platform supplied sediment continuously, although at varying rates, until the latest Cenozoic. Sedimentation around Norway...... changed from early Cenozoic influx from the southwestern margin, to almost exclusively from the southern margin in the Oligocene and from all of southern Norway in the latest Cenozoic. Thick Eocene deposits in the Central Graben are sourced mainly from a western and a likely southern source, indicating...

  10. Low-K Tholeiitic Signatures in Calayan Island (Northern Luzon, Philippines)

    Pendón, R. R.; Corretgé, Luis Guillermo; Ordaz, J.


    The Calayan island is a Tertiary (7-4 Ma) volcanic island situated in the northern portion of the Philippine archipelago, a part of Babuyan segment of the Luzon arc. It is a product of subduction of South China Sea oceanic crust underneath the Philippine terrane. Rock spectrum in the island ranges from basalt to rhyolite with andesite as the most predominating lava. Geochemical signatures are characterized by low concentrations of large-ion lithophile and flat behavior of rare-earth elements,...

  11. Petrology and geochemistry and K-Ar ages for Cenozoic tinguaites from the Ohře/Eger Rift (NW Bohemia)

    Ulrych, Jaromír; Novák, Jiří Karel; Lang, Miloš; Balogh, K.; Hegner, E.; Řanda, Zdeněk


    Roč. 183, č. 1 (2006), s. 41-61. ISSN 0077-7757 R&D Projects: GA AV ČR IAA3048201 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505 Keywords : České středohoří Mts. * Ohře/Eger Rift * Roztoky Intrusive Center * tinguaite dikes * Cenozoic volcanism Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.577, year: 2006

  12. Early cenozoic differentiation of polar marine faunas.

    J Alistair Crame

    Full Text Available The widespread assumption that the origin of polar marine faunas is linked to the onset of major global cooling in the Late Eocene-Early Oligocene is being increasingly challenged. The Antarctic fossil record in particular is suggesting that some modern Southern Ocean taxa may have Early Eocene or even Paleocene origins, i.e. well within the Early Cenozoic greenhouse world. A global analysis of one of the largest marine clades at the present day, the Neogastropoda, indicates that not only is there a decrease in the number of species from the tropics to the poles but also a decrease in the evenness of their distribution. A small number of neogastropod families with predominantly generalist trophic strategies at both poles points to the key role of seasonality in structuring the highest latitude marine assemblages. A distinct latitudinal gradient in seasonality is temperature-invariant and would have operated through periods of global warmth such as the Early Cenozoic. To test this concept a second global analysis was undertaken of earliest Cenozoic (Paleocene neogastropods and this does indeed show a certain degree of faunal differentiation at both poles. The Buccinidae, s.l. is especially well developed at this time, and this is a major generalist taxon at the present day. There is an element of asymmetry associated with this development of Paleocene polar faunas in that those in the south are more strongly differentiated than their northern counterparts; this can in turn be linked to the already substantial isolation of the southern high latitudes. The key role of seasonality in the formation of polar marine faunas has implications for contemporary ecosystem structure and stability.

  13. Cenozoic stratigraphy of the Sahara, Northern Africa

    Swezey, Christopher S.


    This paper presents an overview of the Cenozoic stratigraphic record in the Sahara, and shows that the strata display some remarkably similar characteristics across much of the region. In fact, some lithologies of certain ages are exceptionally widespread and persistent, and many of the changes from one lithology to another appear to have been relatively synchronous across the Sahara. The general stratigraphic succession is that of a transition from early Cenozoic carbonate strata to late Cenozoic siliciclastic strata. This transition in lithology coincides with a long-term eustatic fall in sea level since the middle Cretaceous and with a global climate transition from a Late Cretaceous–Early Eocene “warm mode” to a Late Eocene–Quaternary “cool mode”. Much of the shorter-term stratigraphic variability in the Sahara (and even the regional unconformities) also can be correlated with specific changes in sea level, climate, and tectonic activity during the Cenozoic. Specifically, Paleocene and Eocene carbonate strata and phosphate are suggestive of a warm and humid climate, whereas latest Eocene evaporitic strata (and an end-Eocene regional unconformity) are correlated with a eustatic fall in sea level, the build-up of ice in Antarctica, and the appearance of relatively arid climates in the Sahara. The absence of Oligocene strata throughout much of the Sahara is attributed to the effects of generally low eustatic sea level during the Oligocene and tectonic uplift in certain areas during the Late Eocene and Oligocene. Miocene sandstone and conglomerate are attributed to the effects of continued tectonic uplift around the Sahara, generally low eustatic sea level, and enough rainfall to support the development of extensive fluvial systems. Middle–Upper Miocene carbonate strata accumulated in northern Libya in response to a eustatic rise in sea level, whereas Upper Miocene mudstone accumulated along the south side of the Atlas Mountains because uplift of the

  14. Integrating geological and geophysical data to improve probabilistic hazard forecasting of Arabian Shield volcanism

    Runge, Melody G.; Bebbington, Mark S.; Cronin, Shane J.; Lindsay, Jan M.; Moufti, Mohammed R.


    During probabilistic volcanic hazard analysis of volcanic fields, a greater variety of spatial data on crustal features should help improve forecasts of future vent locations. Without further examination, however, geophysical estimations of crustal or other features may be non-informative. Here, we present a new, robust, non-parametric method to quantitatively determine the existence of any relationship between natural phenomena (e.g., volcanic eruptions) and a variety of geophysical data. This provides a new validation tool for incorporating a range of potentially hazard-diagnostic observable data into recurrence rate estimates and hazard analyses. Through this study it is shown that the location of Cenozoic volcanic fields across the Arabian Shield appear to be related to locations of major and minor faults, at higher elevations, and regions where gravity anomaly values were between - 125 mGal and 0 mGal. These findings support earlier hypotheses that the western shield uplift was related to Cenozoic volcanism. At the harrat (volcanic field)-scale, higher vent density regions are related to both elevation and gravity anomaly values. A by-product of this work is the collection of existing data on the volcanism across Saudi Arabia, with all vent locations provided herein, as well as updated maps for Harrats Kura, Khaybar, Ithnayn, Kishb, and Rahat. This work also highlights the potential dangers of assuming relationships between observed data and the occurrence of a natural phenomenon without quantitative assessment or proper consideration of the effects of data resolution.

  15. Synopsis of volcanic stratigraphy

    Hammond, P. E.


    Volcanic stratigraphic units are mappable layered units composed of volcanic rocks that are formed on land (subaerially) or under water (subaqueously) by volcanic processes. At least ten different types of volcanic stratigraphic units are recognized. The characteristics for each are discussed briefly and some typical examples are illustrated by diagrams to show their salient features.

  16. Le volcanisme cambrien du Maroc central : implications géodynamiquesThe Central Morocco Cambrian volcanism: geodynamic implications

    Ouali, Houssa; Briand, Bernard; Bouchardon, Jean-Luc; Capiez, Paul


    In southeastern Central Morocco, the Bou-Acila volcanic complex is considered of Cambrian age. In spite of low-grade metamorphic effect, initial volcanic texture and mineralogy can be recognized and volcanic rocks are dominated by dolerites and porphyric dolerites. The initial mineralogy is composed of plagioclases, pyroxenes and dark minerals. A secondary mineral assemblage is composed of albite, epidote, chlorite and calcite. According to their immobile elements compositions, the southeastern central Morocco metavolcanites are of within-plate continental tholeiites. This volcanism and those recognized in many other areas in Morocco confirm a Cambrian extensive episode within the Gondwana supercontinent. To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).

  17. Origin and geodynamic setting of Late Cenozoic granitoids in Sulawesi, Indonesia

    Maulana, Adi; Imai, Akira; Van Leeuwen, Theo; Watanabe, Koichiro; Yonezu, Kotaro; Nakano, Takanori; Boyce, Adrian; Page, Laurence; Schersten, Anders


    Late Cenozoic granitoids are widespread in a 1600 km long belt forming the Western and Northern Sulawesi tectono-magmatic provinces. They can be divided into three rock series: shoshonitic (HK), high-K felsic calc-alkaline (CAK), and normal calc-alkaline to tholeiitic (CA-TH). Representative samples collected from eleven plutons, which were subjected to petrography, major element, trace element, Sr, Nd, Pb isotope and whole-rock δ18O analyses, are all I-type and metaluminous to weakly peraluminous. The occurrence of the two K-rich series is restricted to Western Sulawesi, where they formed in an extensional, post-subduction tectonic setting with astenospheric upwelling providing thermal perturbation and adiabatic decompression. Two parental magma sources are proposed: enriched mantle or lower crustal equivalent for HK magmas, and Triassic igneous rocks in a Gondwana-derived fragment thrust beneath the cental and northern parts of Western Sulawesi for CAK magmas. The latter interpretation is based on striking similarities in radiogenic isotope and trace element signatures. CA-TH granitoids are found mostly in Northern Sulawesi. Partial melting of lower-middle crust amphibolites in an active subduction environment is the proposed origin of these rocks. Fractional crystallization and crustal contamination have played a significant role in magma petrogenesis, particularly in the case of the HK and CAK series. Contamination by organic carbon-bearing sedimentary rocks of the HK and CAK granitoids in the central part of Western Sulawesi is suggested by their ilmenite-series (reduced) character. The CAK granitoids further to the north and CA-TH granitoids in Northern Sulawesi are typical magnetite-series (oxidized). This may explain differences in mineralization styles in the two regions.

  18. High-pressure melting experiments on garnet clinopyroxenite and the alkalic to tholeiitic transition in ocean-island basalts

    Keshav, Shantanu; Gudfinnsson, Gudmundur H.; Sen, Gautam; Fei, Yingwei


    It has been suggested, on the basis of recent high-pressure melting experiments, that high-Mg garnet clinopyroxenite is the most important lithology controlling the major-element budget of ocean-island lavas [Geology 31 (2003) 481-484]. To clarify these claims and further our understanding of the petrogenesis of ocean-island basaltic (OIB) lavas, we present the results of a high-pressure (2.0-2.5 GPa) melting study on a high-Mg garnet-clinopyroxenite mantle nodule (77SL-582) from Hawaii. Major-element compositions of the partial melts as a function of pressure ( P), temperature ( T), and degree of melting ( F), mineral chemistry of the coexisting crystalline phases, and the solidus/liquidus brackets of this particular garnet clinopyroxenite are reported. The solidus of 77SL-582, which resembles a tholeiitic picrite in terms of its bulk composition, is bracketed at 1295±15 and 1335±15 °C at 2.0 and 2.5 GPa, respectively, which is ˜60-70 °C lower than the solidus of mantle lherzolite at identical pressures [Geochem. Geophys. Geosystems 1 (2000) 2000GC000070]. The solidus of 77SL-582 is also lower by ˜30-40 °C than reported for a slightly alkalic, high-Mg garnet clinopyroxenite [Geology 31 (2003) 481]. At both pressures, the moderate degree (˜18-20%) partial melts of 77SL-582 are strongly alkalic with ˜8-12 wt.% nepheline in the norm. Even at a degree of melting as high as ˜60%, moderately alkalic basaltic liquids are produced. With further melting, however, partial melts become hypersthene-normative. In the CaO-MgO-Al 2O 3-SiO 2 (CMAS) system, the eclogite surface is restricted to the tholeiitic part of the basalt tetrahedron [D.C. Presnall, Effect of pressure on fractional crystallization of basaltic magma, in: Y. Fei, C. Bertka, and B. Mysen (eds.) Mantle Petrology: Field observations and High Pressure Experimentation: A Tribute to Francis (Joe) R. Boyd, The Geochemical Society Special Publication no. 6, 1999, pp. 209-224.]. A comparison with high

  19. Straddling the tholeiitic/calc-alkaline transition: the effects of modest amounts of water on magmatic differentiation at Newberry Volcano, Oregon

    Mandler, Ben E.; Donnelly-Nolan, Julie M.; Grove, Timothy L.


    Melting experiments have been performed at 1 bar (anhydrous) and 1- and 2-kbar H2O-saturated conditions to study the effect of water on the differentiation of a basaltic andesite. The starting material was a mafic pumice from the compositionally zoned tuff deposited during the ~75 ka caldera-forming eruption of Newberry Volcano, a rear-arc volcanic center in the central Oregon Cascades. Pumices in the tuff of Newberry caldera (TNC) span a continuous silica range from 53 to 74 wt% and feature an unusually high-Na2O content of 6.5 wt% at 67 wt% SiO2. This wide range of magmatic compositions erupted in a single event makes the TNC an excellent natural laboratory in which to study the conditions of magmatic differentiation. Our experimental results and mineral-melt hygrometers/thermometers yield similar estimates of pre-eruptive H2O contents and temperatures of the TNC liquids. The most primitive (mafic) basaltic andesites record a pre-eruptive H2O content of 1.5 wt% and a liquidus temperature of 1,060-1,070 °C at upper crustal pressure. This modest H2O content produces a distinctive fractionation trend that is much more enriched in Na, Fe, and Ti than the calc-alkaline trend typical of wetter arc magmas, but slightly less enriched in Fe and Ti than the tholeiitic trend of dry magmas. Modest H2O contents might be expected at Newberry Volcano given its location in the Cascade rear arc, and the same fractionation trend is also observed in the rim andesites of the rear-arc Medicine Lake volcano in the southern Cascades. However, the Na-Fe-Ti enrichment characteristic of modest H2O (1-2 wt%) is also observed to the west of Newberry in magmas erupted from the arc axis, such as the Shevlin Park Tuff and several lava flows from the Three Sisters. This shows that modest-H2O magmas are being generated directly beneath the arc axis as well as in the rear arc. Because liquid lines of descent are particularly sensitive to water content in the range of 0-3 wt% H2O, they provide a

  20. Inversion of Gravity Data to Define the Pre-Cenozoic Surface and Regional Structures Possibly Influencing Groundwater Flow in the Rainier Mesa Region, Nye County, Nevada.

    Thomas G. Hildenbrand; Geoffrey A. Phelps; Edward A. Mankinen


    A three-dimensional inversion of gravity data from the Rainier Mesa area and surrounding regions reveals a topographically complex pre-Cenozoic basement surface. This model of the depth to pre-Cenozoic basement rocks is intended for use in a 3D hydrogeologic model being constructed for the Rainier Mesa area. Prior to this study, our knowledge of the depth to pre-Cenozoic basement rocks was based on a regional model, applicable to general studies of the greater Nevada Test Site area but inappropriate for higher resolution modeling of ground-water flow across the Rainier Mesa area. The new model incorporates several changes that lead to significant improvements over the previous regional view. First, the addition of constraining wells, encountering old volcanic rocks lying above but near pre-Cenozoic basement, prevents modeled basement from being too shallow. Second, an extensive literature and well data search has led to an increased understanding of the change of rock density with depth in the vicinity of Rainier Mesa. The third, and most important change, relates to the application of several depth-density relationships in the study area instead of a single generalized relationship, thereby improving the overall model fit. In general, the pre-Cenozoic basement surface deepens in the western part of the study area, delineating collapses within the Silent Canyon and Timber Mountain caldera complexes, and shallows in the east in the Eleana Range and Yucca Flat regions, where basement crops out. In the Rainier Mesa study area, basement is generally shallow (< 1 km). The new model identifies previously unrecognized structures within the pre-Cenozoic basement that may influence ground-water flow, such as a shallow basement ridge related to an inferred fault extending northward from Rainier Mesa into Kawich Valley.

  1. Midcontinent rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin

    Nicholson, S.W. (Geological Survey, Reston, VA (USA) Univ. of Minnesota, MN (USA)); Shirey, S.B. (Carnegie Institution of Washington, DC (USA))


    Between 1091 and 1098 Ma, most of a 15- to 20-km thickness of dominantly tholeiitic basalt erupted in the Midcontinent Rift System of the Lake Superior region, North American. The Portage Lake Volcanics in Michigan, which are the youngest MRS flood basalts, fall into distinctly high- and low-TiO{sub 2} types having different liquid lines of descent. Incompatible trace elements in both types of tholeiites are enriched compared to depleted or primitive mantle (La/Yb = 4.3-5.3; Th/Ta = 2.12-2.16; Zr/Y = 4.3-4.4), and both basalt types are isotopically indistinguishable. Sr, Nd, and Pb isotopic compositions of the Portage Lake tholeiites have {sup 87}Sr/{sup 86}Sr{sub i} {approx}0.7038, {epsilon}{sub Nd(1095 Ma)} {approx}0 {plus minus} 2, and {mu}{sub 1} {approx}8.2. Model ages with respect to a depleted mantle source (T{sub DM}) average about 1950-2100 Ma. Portage Lake rhyolits fall into two groups. Type I rhyolites have Nd and Pb isotopic characteristics ({epsilon}{sub Nd(1095 Ma)} {approx}0 to {minus}4.7; {mu}{sub 1} {approx}8.2-7.8) consistent with contamination of tholeiitic rocks by 5-10% Archean crust. The one type II rhyolite analyzed has Nd and Pb isotopic compositions ({epsilon}{sub Nd(1095 Ma)} {approx}{minus}13 to {minus}16; {mu}{sub 1} {approx}7.6-7.7) which are consistent with partial melting of Archean crust. Early Proterozoic crust was not a major contaminant of MRS rocks in the Lake Superior region. Most reported Nd and Pb isotopic compositions of MRS tholeiites from the main stage of volcanism in the Lake Superior region and of the Duluth Complex are comparable to the Nd and Pb isotopic data for Portage lake tholeiites. The isotopic enrichment of the MRS source compared to depleted mantle is striking and must have occurred at least 700 m.y. before 1100 Ma.

  2. Transition of magma genesis estimated by change of chemical composition of Izu-bonin arc volcanism associated with spreading of Shikoku Basin

    Haraguchi, S.; Ishii, T.


    Arc volcanism in the Izu-Ogasawara arc is separated into first and latter term at the separate of Shikoku Basin. Middle to late Eocene early arc volcanism formed a vast terrane of boninites and island arc tholeiites that is unlike active arc systems. A following modern-style arc volcanism was active during the Oligocene, along which intense tholeiitic and calc-alkaline volcanism continued until 29Ma, before spreading of the back- arc basin. The recent arc volcanism in the Izu-Ogasawara arc have started in the middle Miocene, and it is assumed that arc volcanism were decline during spreading of back-arc basin. In the northern Kyushu-Palau Ridge, submarine bottom materials were dredged during the KT95-9 and KT97-8 cruise by the R/V Tansei-maru, Ocean Research Institute, university of Tokyo, and basaltic to andesitic volcanic rocks were recovered during both cruise except for Komahashi-Daini Seamount where recovered acidic plutonic rocks. Komahashi-Daini Seamount tonalite show 37.5Ma of K-Ar dating, and this age indicates early stage of normal arc volcanism. These volcanic rocks are mainly cpx basalt to andesite. Two pyroxene basalt and andesite are only found from Miyazaki Seamount, northern end of the Kyushu-Palau Ridge. Volcanic rocks show different characteristics from first term volcanism in the Izu-Ogasawara forearc rise and recent arc volcanism. The most characteristic is high content of incompatible elements, that is, these volcanics show two to three times content of incompatible elements to Komahashi-Daini Seamount tonalite and former normal arc volcanism in the Izu outer arc (ODP Leg126), and higher content than recent Izu arc volcanism. This characteristic is similar to some volcanics at the ODP Leg59 Site448 in the central Kyushu- Palau Ridge. Site448 volcanic rocks show 32-33Ma of Ar-Ar ages, which considered beginning of activity of Parece Vela Basin. It is considered that the dredged volcanic rocks are uppermost part of volcanism before spreading of

  3. Chemical versus temporal controls on the evolution of tholeiitic and calc-alkaline magmas at two volcanoes in the Alaska-Aleutian arc

    George, R.; Turner, S.; Hawkesworth, C.; Bacon, C.R.; Nye, C.; Stelling, P.; Dreher, S.


    The Alaska-Aleutian island arc is well known for erupting both tholeiitic and calc-alkaline magmas. To investigate the relative roles of chemical and temporal controls in generating these contrasting liquid lines of descent we have undertaken a detailed study of tholeiitic lavas from Akutan volcano in the oceanic A1eutian arc and calc-alkaline products from Aniakchak volcano on the continental A1askan Peninsula. The differences do not appear to be linked to parental magma composition. The Akutan lavas can be explained by closed-system magmatic evolution, whereas curvilinear trace element trends and a large range in 87 Sr/86 Sr isotope ratios in the Aniakchak data appear to require the combined effects of fractional crystallization, assimilation and magma mixing. Both magmatic suites preserve a similar range in 226 Ra-230 Th disequilibria, which suggests that the time scale of crustal residence of magmas beneath both these volcanoes was similar, and of the order of several thousand years. This is consistent with numerical estimates of the time scales for crystallization caused by cooling in convecting crustal magma chambers. During that time interval the tholeiitic Akutan magmas underwent restricted, closed-system, compositional evolution. In contrast, the calc-alkaline magmas beneath Aniakchak volcano underwent significant open-system compositional evolution. Combining these results with data from other studies we suggest that differentiation is faster in calc-alkaline and potassic magma series than in tholeiitic series, owing to a combination of greater extents of assimilation, magma mixing and cooling.

  4. 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

    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.


    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

  5. Cenozoic planktonic marine diatom diversity and correlation to climate change.

    Lazarus, David; Barron, John; Renaudie, Johan; Diver, Patrick; Türke, Andreas


    Marine planktonic diatoms export carbon to the deep ocean, playing a key role in the global carbon cycle. Although commonly thought to have diversified over the Cenozoic as global oceans cooled, only two conflicting quantitative reconstructions exist, both from the Neptune deep-sea microfossil occurrences database. Total diversity shows Cenozoic increase but is sample size biased; conventional subsampling shows little net change. We calculate diversity from a separately compiled new diatom species range catalog, and recalculate Neptune subsampled-in-bin diversity using new methods to correct for increasing Cenozoic geographic endemism and decreasing Cenozoic evenness. We find coherent, substantial Cenozoic diversification in both datasets. Many living cold water species, including species important for export productivity, originate only in the latest Miocene or younger. We make a first quantitative comparison of diatom diversity to the global Cenozoic benthic ∂(18)O (climate) and carbon cycle records (∂(13)C, and 20-0 Ma pCO2). Warmer climates are strongly correlated with lower diatom diversity (raw: rho = .92, p.9, detrended r>.6, all prisk of extinction in future warm oceans, with an unknown but potentially substantial negative impact on the ocean biologic pump and oceanic carbon sequestration. We cannot however extrapolate our my-scale correlations with generic climate proxies to anthropogenic time-scales of warming without additional species-specific information on proximate ecologic controls. PMID:24465441

  6. Ultramafic pre-rift volcanism of the Osečná Complex, northern Bohemia

    Ulrych, Jaromír; Adamovič, Jiří; Paluska, A.; Krmíček, L.; Balogh, K.

    Prague : Czech Geological Survey ; Senckenberg museum of natural History Görlitz, 2013 - (Büchner, J.; Rapprich, V.; Tietz, O.). s. 232-233 ISBN 978-80-7075-806-9. [Basalt 2013: Cenozoic magmatism in Central Europe. 24.04.2013-28.04.2013, Görlitz] Institutional support: RVO:67985831 Keywords : volcanism * geology * Osečná Complex Subject RIV: DB - Geology ; Mineralogy

  7. Quaternary volcanism, tectonics, and sedimentation in the Idaho National Engineering Laboratory area

    Hackett, W.R.; Smith, R.P.


    In this article, we discuss the regional context and describe localities for a two-day field excursion in the vicinity of the Idaho National Engineering Laboratory (INEL). We address several geologic themes: (1) Late Cenozoic, bimodal volcanism of the Eastern Snake River Plain (ESRP), (2) the regional tectonics and structural geology of the Basin and Range province to the northwest of the ESRP, (3) fluvial, lacustrine, and aeolian sedimentation in the INEL area, and (4) the influence of Quaternary volcanism and tectonics on sedimentation near the INEL.

  8. Quaternary volcanism, tectonics, and sedimentation in the Idaho National Engineering Laboratory area

    Hackett, W.R.; Smith, R.P.


    In this article, we discuss the regional context and describe localities for a two-day field excursion in the vicinity of the Idaho National Engineering Laboratory (INEL). We address several geologic themes: (1) Late Cenozoic, bimodal volcanism of the Eastern Snake River Plain (ESRP), (2) the regional tectonics and structural geology of the Basin and Range province to the northwest of the ESRP, (3) fluvial, lacustrine, and aeolian sedimentation in the INEL area, and (4) the influence of Quaternary volcanism and tectonics on sedimentation near the INEL.

  9. Mongolian plateau: Evidence for a late Cenozoic mantle plume under central Asia

    Windley, Brian F.; Allen, Mark B.


    The 2500 x 700 km Mongolian plateau (average elevation 2000 m) is situated between the Altai orogen and the Siberian craton and occupies much of Mongolia and Transbaikalia in Russia. The plateau is characterized by (1) basin and range topography and two major domes(Hentai, 600 x 300 km, and Hangai, 800 x 550 km), where altitudes reach 3905 m; (2) lithosphere that is thinner than adjacent areas (minimum ˜50 km); (3) elevated heat flow (up to 120 mW/m2); (4) dominantly alkaline basaltic volcanism in the form of cones, lava fields, and volcanic plateaus mostly of Miocene-Quaternary age, and (5) rifts, including Baikal (main evolution in the Pliocene-Quaternary), Tunka (Oligocene-early Miocene), and Hobsogol (Pliocene-Quaternary). Existing models explain these features in terms of diapiric upwelling of a mantle asthenolith below the main rifts and/or as a long-distance effect of the India-Asia collision. We propose that the late Cenozoic uplift of the whole Mongolian plateau and associated rifting, magmatism, high heat flow, and lithospherec thinning are not externally driven by the India-Asia collision, but are the expression of the interaction of a mantle plume with overlying lithosphere. Some rifts link and interact with major strike-slip faults, such as the Bolnai. Such faults may be the major expression of the India-Asia collision in this region.

  10. Triple junction magmatism: A geochemical study of Neogene volcanic rocks in western California

    Inception of volcanism at late Oligocene to Recent centers in the eastern Coast Ranges of California (ECR suite) regularly decreases in age northward and is correlated with the northward migration of the transform-transform-trench Mendocino triple junction (MTJ). Miocene volcanism in the southern California basin (SCB suite) is spatially and temporally associated with the transform-ridge-trench Rivera triple junction (RTJ). The tholeiitic to calc-alkaline rocks in both suites were erupted through older trench melange while arc magmatism was occuring several hundred kilometers to the east. Therefore they are not related to subduction zone magmatism, but instead to interactions of the MTJ and RTJ with the continental margin. (orig./WB)

  11. Cenozoic planktonic marine diatom diversity and correlation to climate change.

    David Lazarus

    Full Text Available Marine planktonic diatoms export carbon to the deep ocean, playing a key role in the global carbon cycle. Although commonly thought to have diversified over the Cenozoic as global oceans cooled, only two conflicting quantitative reconstructions exist, both from the Neptune deep-sea microfossil occurrences database. Total diversity shows Cenozoic increase but is sample size biased; conventional subsampling shows little net change. We calculate diversity from a separately compiled new diatom species range catalog, and recalculate Neptune subsampled-in-bin diversity using new methods to correct for increasing Cenozoic geographic endemism and decreasing Cenozoic evenness. We find coherent, substantial Cenozoic diversification in both datasets. Many living cold water species, including species important for export productivity, originate only in the latest Miocene or younger. We make a first quantitative comparison of diatom diversity to the global Cenozoic benthic ∂(18O (climate and carbon cycle records (∂(13C, and 20-0 Ma pCO2. Warmer climates are strongly correlated with lower diatom diversity (raw: rho = .92, p.9, detrended r>.6, all p<.001, but only weakly over the earlier Cenozoic, suggesting increasingly strong linkage of diatom and climate evolution in the Neogene. Our results suggest that many living marine planktonic diatom species may be at risk of extinction in future warm oceans, with an unknown but potentially substantial negative impact on the ocean biologic pump and oceanic carbon sequestration. We cannot however extrapolate our my-scale correlations with generic climate proxies to anthropogenic time-scales of warming without additional species-specific information on proximate ecologic controls.

  12. Application of Clinopyroxene Chemistry to Interpret the Physical Conditions of Ascending Magma, a Case Study of Eocene Volcanic Rocks in the Ghohrud Area (North of Isfahan

    Mohammad Sayari


    Full Text Available Introduction Volcanic rocks with a porphyritic texture have experienced two crystallization stages. The first is slow, resulting in phenocrysts, and the second, which took place at, or near the surface, or during intrusion into a cooler body of rock, result in a groundmass of glass, or fine crystals. The pressure and temperature history of a magma during crystallization is recorded in the chemical composition of the phenocrysts during both stages. These phenocrysts provide valuable data about the physicochemical conditions of the parent magma during the process of crystallization. The composition of clinopyroxene (cpx reflects not only the chemical condition and therefore the magmatic series, but also the physical conditions, i.e., temperature and pressure of a magma at the time when clinopyroxene crystallized. The Ghohrud area lies in the middle part of the Urumieh-Dokhtar Magmatic Arc , which is part of a much larger magmatic province extending in a vast region of convergence between Arabia and Eurasia north of the Zagros-Bitlis suture zone (Dilek et al., 2010. In the Ghohrud area, north of Isfahan, exposed Eocene volcanic rocks belong to the first pulse of Cenozoic volcanism of Iran (Sayari, 2015, ranging in composition from andesitic basalt to basalt. The basaltic rocks of the Ghohrud area are composed mainly of plagioclase phenocrysts surrounded by smaller crystals of clinopyroxene in a groundmass of microlites, glass and opaques. In this study, the clinopyroxene and plagioclase of these rocks were analyzed in order to estimate the physicochemical conditions of the parent magmas. Results Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermobarometry (Sayari

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

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


    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.

  14. Permian to late Cenozoic evolution of northern Patagonia: Main tectonic events, magmatic activity, and depositional trends

    Uliana, M. A.; Biddle, K. T.

    The late Paleozoic to late Cenozoic evolution of northern Patagonia was influenced significantly by events that occurred while the area was part of the South American sector of Gondwanaland. Late Paleozoic to Middle Triassic subduction along the edge of the supercontinent formed a broad convergent-margin system that is the underpinning of northern Patagonia. Deformation (Gondwanidian orogeny) associated with the subduction is recognized in both the forearc and the convergent backarc areas. Regional extension, accompanied by bimodal volcanism, began in the Late Triassic and led to the formation of a number of north-northwest trending rift basins in Patagonia, which generally followed the Gondwanidian basement grain. Continued extension in the Jurassic and Early Cretaceous led to the opening of the Rocas Verdes marginal basin in southern Chile and, ultimately, to the opening of the South Atlantic Ocean. Once oceanic crust began to form, faulting and volcanism declined in Patagonia. During the late Early Cretaceous to the Late Cretaceous, sags over the rift basins coalesced to form a broad backarc basin behind the volcanic arc to the west. These sags are suggestive of thermally driven subsidence. Subsidence of the evolving Atlantic margin allowed extensive marine transgressions to take place from the east. The stratigraphic record of northern Patagonia reflects these events. The upper Paleozoic to upper Mesozoic sedimentary sequences were deposited in basins directly associated with convergent activity along the margin of Gondwanaland or in rift basins created during its breakup. Even though the Tertiary evolution of Patagonia was dominated by events along the western margin of South America, the patterns of sediment transport, thickness, and general shoreline position were still influenced by the locations of the Mesozoic rifts formed during the breakup of Gondwanaland.

  15. Late Cenozoic crustal extension and magmatism, southern Death Valley region, California

    Calzia, J.P.; Rämö, O.T.


    The late Cenozoic geologic history of the southern Death Valley region is characterized by coeval crustal extension and magamatism. Crustal extension is accommodated by numerous listric and planar normal faults as well as right- and left-lateral strike slip faults. The normal faults sip 30°-50° near the surface and flatten and merge leozoic miogeoclinal rocks; the strike-slip faults act as tear faults between crustal blocks that have extended at different times and at different rates. Crustal extension began 13.4-13.1 Ma and migrated northwestward with time; undeformed basalt flows and lacustrine deposits suggest that extension stopped in this region (but continued north of the Death Valley graben) between 5 and 7 Ma. Estimates of crustal extension in this region vary from 30-50 percent to more than 100 percent. Magmatic rocks syntectonic with crustal extension in the southern Death Valley region include 12.4-6.4 Ma granitic rocks as well as bimodal 14.0-4.0 Ma volcanic rocks. Geochemical and isotopic evidence suggest that the granitic rocks get younger and less alkalic from south to north; the volcanic rocks become more mafic with less evidence of crustal interaction as they get younger. The close spatial and temporal relation between crustal extension and magmatism suggest a genetic and probably a dynamic relation between these geologic processes. We propose a rectonic-magmatic model that requires heat to be transported into the crust by mantle-derived mafic magmas. These magmas pond at lithologic or rheologic boundaries, begin the crystallize, and partially melt the surrounding crustal rocks. With time, the thermally weakened crust is extended (given a regional extensional stress field) concurrent with granitic magmatism and bimodal volcanism.

  16. 40Ar/39Ar dating and geochemistry of tholeiitic magmatism related to the early opening of the Central Atlantic rift

    Tholeiitic effusive and intrusive magnetism from Iberia, Morocco, Algeria and Mali, realted to the early opening of the Central Atlantic rift, was dated by the 40Ar/39Ar step-heating method. Four plateau ags, rangin from 203.7±2.7 to 197.1±1.8 Ma, were obtained on plagioclase from dykes from theTaoudenni area (Mali) and two lava flows from Morocco. The Messejana dyke (Iberia), which previously yielded discrepant conventional K-Ar dates, did not furnish any 40Ar/39Ar plateau dates. However, there is a clear inverse relationship between apparent age and K/Ca atio for gas fractions from a plagioclase separate (proportional to the alteration degree) which, combined with dates obtained on amphibole, biotite and pyroxene, allows us to determine an age of around 200 Ma for this body. These data, and those obtained on the Foum Zguid (Morocco) and the Ksi Ksou (Algeria) dykes, give evidence of a brief magmatic event (between 206 and 195 Ma ago) which affected a large area ca. 2500 km long. Trace-element modelling shows that most of these formations originated from a homogeneous, enriched, source material. Such a brief magmatic episode related to the opening of a continental rift is in agreement with findings in other magmatic provinces (e.g. the Deccan traps and the Red Sea rift, precisely dated by the 40Ar/39Ar method as well). (orig.)

  17. Age Relations and Geochemical Constraints of Cenozoic Alkaline Volcanic Series in W Bohemia: A Review

    Ulrych, Jaromír; Lloyd, F. E.; Balogh, K.


    Roč. 15, - (2003), s. 168-180. ISSN 1210-9606. [Hibsch 2002 Symposium. Teplá near Třebenice, Ústí nad Labem, Mariánské Lázně, 03.06.2002-08.06.2002] R&D Projects: GA ČR GA205/99/0907; GA AV ČR IAA3048201 Institutional research plan: CEZ:AV0Z3013912 Keywords : W Bohemia * Cheb-Domažlice Graben * geochemistry Subject RIV: DB - Geology ; Mineralogy

  18. Cenozoic intraplate volcanic rock series of the Bohemian Massif: a review

    Ulrych, Jaromír; Pivec, Edvín; Lang, Miloš; Balogh, K.; Kropáček, V.


    Roč. 9, - (1999), s. 123-129. ISSN 1210-9606. [Magmatism and Rift Basin Evolution. Liblice, 07.09.1998-11.09.1998] Subject RIV: DB - Geology ; Mineralogy

  19. Cenozoic magmatism in the northern continental margin of the South China Sea: evidence from seismic profiles

    Zhang, Qiao; Wu, Shiguo; Dong, Dongdong


    Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. This study identified intrusive and extrusive structures including seamounts and buried volcanoes, and their seismic characteristics. Intrusive features consist of piercement and implicit-piercement type structures, indicating different energy input associated with diapir formation. Extrusive structures are divided into flat-topped and conical-topped seamounts. Three main criteria (the overlying strata, the contact relationship and sills) were used to distinguish between intrusive rocks and buried volcanos. Three criteria are also used to estimate the timing of igneous rock formation: the contact relationship, the overlying sedimentary thickness and seismic reflection characteristics. These criteria are applied to recognize and distinguish between three periods of Cenozoic magmatism in the northern margin of the SCS: before seafloor spreading (Paleocene and Eocene), during seafloor spreading (Early Oligocene-Mid Miocene) and after cessation of seafloor spreading (Mid Miocene-Recent). Among them, greater attention is given to the extensive magmatism since 5.5 Ma, which is present throughout nearly all of the study area, making it a significant event in the SCS. Almost all of the Cenozoic igneous rocks were located below the 1500 m bathymetric contour. In contrast with the wide distribution of igneous rocks in the volcanic rifted margin, igneous rocks in the syn-rift stage of the northern margin of the SCS are extremely sporadic, and they could only be found in the southern Pearl River Mouth basin and NW sub-sea basin. The ocean-continent transition of the northern SCS exhibits high-angle listric faults, concentrated on the seaward side of the magmatic zone, and a sharply decreased crust, with little influence from a mantle plume. These observations provide further evidence to

  20. Late-Paleozoic emplacement and Meso-Cenozoic reactivation of the southern Kazakhstan granitoid basement

    De Pelsmaeker, Elien; Glorie, Stijn; Buslov, Mikhail M.; Zhimulev, Fedor I.; Poujol, Marc; Korobkin, Valeriy V.; Vanhaecke, Frank; Vetrov, Evgeny V.; De Grave, Johan


    The Ili-Balkhash Basin in southeastern Kazakhstan is located at the junction of the actively deforming mountain ranges of western Junggar and the Tien Shan, and is therefore part of the southwestern Central Asian Orogenic Belt. The basement of the Ili-Balkhash area consists of an assemblage of mainly Precambrian microcontinental fragments, magmatic arcs and accretionary complexes. Eight magmatic basement samples (granitoids and tuffs) from the Ili-Balkhash area were dated with zircon U-Pb LA-ICP-MS and yield Carboniferous to late Permian (~ 350-260 Ma) crystallization ages. These ages are interpreted as reflecting the transition from subduction to (post-) collisional magmatism, related to the closure of the Junggar-Balkhash Ocean during the Carboniferous-early Permian and hence, to the final late Paleozoic accretion history of the ancestral Central Asian Orogenic Belt. Apatite fission track (AFT) dating of 14 basement samples (gneiss, granitoids and volcanic tuffs) mainly provides Cretaceous cooling ages. Thermal history modeling based on the AFT data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late Mesozoic and Cenozoic. Late Mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the Cimmerian collisions at the southern Eurasian margin and possibly of the Mongol-Okhotsk Orogeny in SE Siberia during the Jurassic-Cretaceous. Following tectonic stability during the Paleogene, inherited basement structures were reactivated during the Neogene (constrained by Miocene AFT ages of ~ 17-10 Ma). This late Cenozoic reactivation is interpreted as the far-field response of the India-Eurasia collision and reflects the onset of modern mountain building and denudation in southeast Kazakhstan, which seems to be at least partially controlled by the inherited basement architecture.

  1. Tectonic implications of space-time patterns of Cenozoic magmatism in the western United States

    Snyder, W.S.; Dickinson, W.R.; Silberman, M.L.


    Locations of 2,100 radiometrically dated igneous rocks were plotted on a series of 20 maps, each representing an interval within the period 80 m.y. B.P. to present. Derivative maps showing the distributions in space and time of dated granitic intrusive rocks, silicic lavas and domes, ash-flow tuffs, andesitic-dacitic rocks, and basalts depict well the two main petrogenetic assemblages noted previously by others: (1) mainly intermediate andesitic-dacitic suites, including associated granitic intrusive rocks, silicic extrusive rocks, and minor basaltic lavas, are interpreted as reflecting plate interactions related to subduction along the continental margin; and (2) bimodal suites, dominantly basaltic but with minor silicic extrusive rocks, are interpreted as reflecting extensional tectonics. Space-time distribution of the two assemblages suggests that magmatic arcs extended continously parallel to the continental margin from Canada to Mexico in latest Mesozoic and in Oligocene times. An early Cenozoic null in magmatism in the Great Basin may delineate the region where subduction was arrested temporarily by development of the proto-San Andreas fault as a transform in coastal California or, alternatively, may reflect complex subsurface configurations of subducted plates. The late Cenozoic transition from subduction-related magmatism to extention-related basaltic volcanism in the southern Cordillera occurred at different times in different areas in harmony with current concepts about the migration of the Mendocino triple junction as the modern San Andreas transform fault was formed. The plots also reveal the existence of several discrete magmatic loci where igneous activity of various kinds was characteristically more intense and long-lived than elsewhere. ?? 1976.

  2. Relating Cenozoic North Sea sediments to topography in southern Norway:

    Anell, Ingrid Anna Margareta; Thybo, Hans; Stratford, Wanda Rose


    sources for progradational influx of clastic sediments from Scotland, the Shetland platform and, to a lesser degree, southwestern Norway. The Eocene sedimentation pattern was similar to the Palaeocene, with lower rates of accumulation associated with flooding and tectonic quiescence. Sediment influx from...... the Shetland platform continued throughout the Cenozoic while supply from southern Norway increased markedly around the Eocene–Oligocene, coeval with the greenhouse–icehouse transition. Mass balance calculations of sediment and eroded rock volumes suggest that while some topography along the western...... margin of Norway may be pre-Cenozoic, significant uplift of the main Paleic surface in southern Norway occurred around the early Oligocene. Sedimentation rates were almost ten-fold higher than the Cenozoic average in the Plio-Pleistocene, slightly higher than the global average. Mass balance calculations...

  3. Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Guba, Chukotka (NE Russia): Significance for interregional correlations

    Ledneva, G. V.; Pease, V. L.; Sokolov, S. D.


    In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska-Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Guba, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U-Pb zircon age of 252+/-4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Guba region have major and trace element compositions identical the tholeiitic flood basalts of the main plateau stage of the Siberian LIP. They are strongly differentiated, the result of high-pressure equilibrium crystallization of a low-Ti/Y tholeiitic melt, and contaminated. The compositional variations in these rocks, however, neither proves nor disproves a correlation between the Permo-Triassic tholeiitic flood basalts of eastern Chukotka and the Siberian LIP. Thus, two alternative geodynamic interpretations are possible: 1) The hypabyssal mafic rocks and associated tholeiitic flows crystallized from a plume-derived melt; 2) The rocks are not related to plume activity, consequently eastern Chukotka was probably part of a passive rifted or extensional continental margin in the Permo-Triassic. Nonetheless, we prefer the first of these two possibilities. Funding for this work is gratefully acknowledged from the Swedish Polar Research Secretariat ("Beringia-2005"), the Swedish Research Council, the Russian Foundation for Basic Research (grant No 08-05-00547), Leading Scientific School (NSH-3172.2008.5) and ONZ RAS. Thanks are also extended to M.J. Whitehouse and the Nordsim facility - the Nordsim facility is funded by the research councils of Denmark, Norway, Sweden, the Geological Survey of Finland, and the Swedish Museum of

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

    Gates, Olcott; Moench, R.H.


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

  5. Volcanic subsidence triggered by the 2011 Tohoku earthquake in Japan

    Takada, Youichiro; Fukushima, Yo


    The 2011 Mw 9.0 Tohoku earthquake caused an unprecedented level of crustal deformation in eastern parts of Japan. The event also induced seismic activity in the surrounding area, including some volcanic regions, but has not yet triggered any eruptions. Here we use data from satellite radar and the Global Positioning System to show that volcanic regions, located between 150 and 200km from the rupture area, experienced subsidence coincident with the Tohoku earthquake. The volcanic regions subsided by 5-15cm, forming elliptical depressions with horizontal dimensions of up to 15-20km. The depressions are elongated in a direction roughly perpendicular to the axis of maximum coseismic extension. A high concentration of Late Cenozoic calderas, high heat flow, hot thermal waters, and young and hot granite in the subsided regions imply the presence of magmatic and hot plutonic bodies beneath the volcanoes, that may have deformed and subsided in response to stress changes associated with the Tohoku earthquake along with the surrounding, thermally weakened host rocks. Similar subsidence observed in Chile following the 2010 Maule earthquake indicates that earthquake-triggered subsidence could be widespread in active volcanic chains along subduction zones.

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

    L S Shekhawat; M K Pandit; D W Joshi


    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.

  7. Cenozoic structural evolution of the Argentinean Andes at 34°40'S: A close relationship between thick and thin-skinned deformation Evolución estructural Cenozoica de los Andes Argentinos a los 34°40'S: una estrecha relación entre deformación de piel fina y piel gruesa

    Martín Turienzo; Luis Dimieri; Cristina Frisicale; Vanesa Araujo; Natalia Sánchez


    In the Argentinean side of the Andes at 34°40'S, the Cenozoic Andean orogeny produced the thick-skinned Malargüe fold-and-thrust belt and the easternmost basement uplift of the Cordillera Frontal. Integrating balanced structural cross-sections with previous studies of Cenozoic synorogenic rocks and 40Ar/39Ar ages of coeval volcanic and subvolcanic rocks, we propose a Miocene to Quaternary sequential structural evolution of this sector of the Andes. Andean deformation in the study area begun a...

  8. Landscape evolution within a retreating volcanic arc, Costa Rica, Central America

    Marshall, Jeffrey S.; Idleman, Bruce D.; Gardner, Thomas W.; Fisher, Donald M.


    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 40Ar/39Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tárcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

  9. Meso-Cenozoic basin evolution in northern Korean Peninsula

    PAK Hyon Uk; LYANG To Jun; LIU Yongjiang; HYON Yun Su; KIM Gyong Chol


    In the Korean Peninsula the Meso-Cenozoic basins were mainly formed due to fault block and block movement. The Mesozoic fracture structures correspond basically to modern large rivers in direction. Such faults were usually developed to rift and formed lake-type tectonic basin, such as the Amrokgang-, Taedonggang-, Ryesonggang-, Hochongang-, Jangphari-, Susongchon-, Pujon-, and Nampho basins. The Mesozoic strata are considered to be divided into the Lower Jurassic Taedong System, Upper Jurassic Jasong System, Upper Jurassic- -early Lower Cretaceous Taebo System, and the Upper Cretaceous- -Paleocene (Chonjaebong, Hongwon, Jaedok Series). The Cenozoic block movement succeeded the Mesozoic fault block movement. The Kilju-Myongchon Graben and Tumangang Basin, etc, are the basins related to the fault zones developed from the Oligocene to Miocene. In addition, the Tertiary basins were formed in many areas in the Miocene (e.g. Sinhung, Oro, Hamhung, Yonghung, Anbyon, Cholwon, etc). The Cenozoic sedimentation occurred mainly from the late Oligocene to Miocene. The Kilju-Myongchon Graben was the fore deep connected to the sea and the basins inclined in the Chugaryong Fault Zone are intramountain basins. Therefore, coal-bearing beds and clastic rocks in the intramountain basins and rare marine strata and terrigenous clastic rocks are main sedimentary sequences in the Cenozoic.

  10. On the meso-cenozoic mantle plume tectonics, its relationship to uranium metallogenesis and prospecting directions in South China

    The author briefly introduces the research history and trends on mantle plume tectonics, which is considered to be primary origins of geotectonics-volcanism/magmatism-sedimentation-metamorphism and metallogenesis system. The activities of the Meso-Cenozoic mantle plume tectonics, its features and relationship to uranium mineralization in South China are discussed. The classified four main types of uranium deposits in South China must be formed under direct or indirect influence of the mantle plume tectonics, which provides not only dynamic energy for processes of uranium migration, mobilization and enrichment, but also ore sources for mineralization. Those considerations are of important significance to more deeply understanding uranium regional metallogenetic regularity, enlarging resources of the known ore fields and searching for new uranium mineralized areas and mineralization types as well

  11. Temporal evolution of island arc magmatism: geochronology, petrology et geochemistry of mesozoic and cenozoic magmatic rocks from Sumatra (Indonesia)

    Sumatra island (Western Indonesia) belongs to the Sunda magmatic arc, which results from the subduction of the Indian ocean plate beneath the margin of the Eurasiatic continental block. Plutonic and volcanic rocks of Mesozoic and Cenozoic ages are very abundant in Sumatra, where they mainly outcrop in a NNW-SSE trending, 1,650 km-long stripe in the western part of the island. The spatial and temporal distributions of magmatic rocks in Sumatra were not previously investigated in detail. We have performed 175 40K-40Ar datings on bulk rocks and minerals separated from samples which have also been analysed for major and trace elements by ICP-AES. These results allow to discuss the distribution of magmatic events in space of a long subduction period on the chemical composition of the Sunda arc mantle wedge. (author)

  12. Central America arc volcanic geochemistry: What do we know and what more do we need?

    Jordan, E. K.; Stern, R. J.


    This study uses geochemical data for the Central America volcanic arc (CAVA) from the most comprehensive online data portal,, to assess the quality of data available to the scientific community, geographic sampling bias versus volcano volume, and statistical analyses of CAVA geochemistry. These statistical studies use new or underutilized visualization techniques to present and interpret volcanic heterogeneities and trends associated with tectonic features along the arc. CAVA volcanoes range widely in type, volume, and composition within individual volcanoes and between volcanic complexes. Mean volcanic complex SiO2 concentrations range from 50-70% wt% and Mg# from 44-66. El Salvadoran and Nicaraguan samples, some of which erupted through continental crust of the Chortis terrane, are dominated by high- to medium-Fe tholeiitic to calcalkalic lavas. These lavas have lower incompatible trace element concentrations than do Guatemalan and Costa Rican lavas, erupted through accreted oceanic island arc and Chorotega oceanic plateau crust, which define medium- to low-Fe calcalkalic suites. In addition to providing a valuable representation of CAVA geochemistry, this comprehensive study is useful in identifying where data is lacking. Comprehensive volcanic arc studies are difficult to implement due to the complexity of the tectonic system. Sampling sites are limited due to rugged terrain, limited road access, extreme foliage, or political boundaries. For example, the data obtained for this study show that nearly 21% of samples are from Arenal volcano, which represents less than 0.5% of the volume of the volcanic arc complexes in the data set. Meanwhile, Irazú-Turrialba makes up 11% of the arc volume and less than 4% of the sample set. Since most of the volcano volume is buried by younger lavas, only the outer volcanic layers are typically sampled.

  13. Volcanic signals in oceans

    Stenchikov, Georgiy L.


    Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean integrates volcanic radiative cooling and responds over a wide range of time scales. The associated processes, especially ocean heat uptake, play a key role in ongoing climate change. However, they are not well constrained by observations, and attempts to simulate them in current climate models used for climate predictions yield a range of uncertainty. Volcanic impacts on the ocean provide an independent means of assessing these processes. This study focuses on quantification of the seasonal to multidecadal time scale response of the ocean to explosive volcanism. It employs the coupled climate model CM2.1, developed recently at the National Oceanic and Atmospheric Administration\\'s Geophysical Fluid Dynamics Laboratory, to simulate the response to the 1991 Pinatubo and the 1815 Tambora eruptions, which were the largest in the 20th and 19th centuries, respectively. The simulated climate perturbations compare well with available observations for the Pinatubo period. The stronger Tambora forcing produces responses with higher signal-to-noise ratio. Volcanic cooling tends to strengthen the Atlantic meridional overturning circulation. Sea ice extent appears to be sensitive to volcanic forcing, especially during the warm season. Because of the extremely long relaxation time of ocean subsurface temperature and sea level, the perturbations caused by the Tambora eruption could have lasted well into the 20th century.

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

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


    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.

  15. Geochemical characteristics and petrogenesis of phonolites and trachytic rocks from the České Středohoří Volcanic Complex, the Ohře Rift, Bohemian Massif

    Ackerman, Lukáš; Ulrych, Jaromír; Řanda, Zdeněk; Erban, V.; Hegner, E.; Magna, T.; Balogh, K.; Frána, Jaroslav; Lang, Miloš; Novák, Jiří Karel

    224/225, May (2015), s. 256-271. ISSN 0024-4937 R&D Projects: GA AV ČR IAA3048201 Institutional support: RVO:67985831 ; RVO:61389005 Keywords : phonolite * trachyte * Sr–Nd–Li isotopes * Cenozoic alkaline volcanism * Ohře (Eger) Rift * Bohemian Massif Subject RIV: DD - Geochemistry Impact factor: 4.482, year: 2014

  16. Volcanic Rocks and Features

    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...

  17. Thermochronological constraints on two pulses of Cenozoic high-K magmatism in eastern Tibet


    The previously published U-Pb and 40Ar/39Ar ages and our 21 newly-obtained 40Ar/39Ar ages suggest that the Cenozoic magmatism in eastern Tibet and Indochina occurred in two episodes, each with distinctive geochemical signatures, at (40-28) Ma and (16-0) Ma. The older rocks are localized along the major strike-slip faults such as the Jinsha-Red River fault system and erupted synchronously with transpression. The younger rocks are widely distributed in rift basins and coeval with the east-west extension of Tibet and eastern Asia. Combining with their geochemical data, we consider that the earlier magmatic phase was generated by continental subduction, while the later volcanic phase was caused by decompression melting of a recently meta- somatically-altered, depleted mantle source. The magmatic gap between the two igneous pulses represents an important geodynamic transition in the evolution of eastern Tibet, from the processes controlled mainly by crustal deformation to those largely dominated by mantle tectonics.

  18. K-Ar ages, paleomagnetism, and geochemistry of the South Auckland volcanic field, North Island, New Zealand

    The South Auckland volcanic field is one of the Pliocene-Quaternary intraplate basaltic fields in northern North Island. It consists of at least 97 monogenetic volcanic centres covering an area of c. 300 km2 , 38 km south of Auckland. Fifty-nine of the volcanic centres are characterised by mainly magmatic or effusive activity that constructed scoria cones and lava flows, while 38 are mainly phreatomagmatic or explosive that produced tuff rings and maars. Rock types consist of basanites, hawaiites, nepheline hawaiites, transitional basalts, and ol-tholeiitic basalts, with relatively minor amounts of nephelinites, alkali basalts, Q-tholeiitic basalts, and nepheline mugearites. Forty-three new K-Ar ages are presented, which range from 0.51 to 1.59 Ma, and show two peaks of activity at 0.6 and 1.3 Ma. Paleomagnetic determinations at 26 selected sites agree well with the paleomagnetic reversal time scale and support the K-Ar age data. Age data from each of the volcanic fields of Okete, Ngatutura, South Auckland, and Auckland, which constitute the Auckland intraplate basaltic province, show that they have developed within a time span of 0.3-1.1 Ma. After activity ceased in any particular field, a new field then developed 35-38 km to the north. These consistent time/space patterns indicate the possibility of a mantle source migrating northwards at c. 5 cm/yr. There is no correlation of rock composition with time, which is consistent with observations in the Northland intraplate province, but is not consistent with the formerly invoked rising diapir model. (author). 30 refs., 8 figs., 3 tabs

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


    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.

  20. Scientific Drilling in a Central Italian Volcanic District

    Paola Montone


    Full Text Available The Colli Albani Volcanic District, located 15 km SE of Rome (Fig. 1, is part of the Roman Magmatic Province, a belt of potassic to ultra-potassic volcanic districts that developed along the Tyrrhenian Sea margin since Middle Pleistocene time (Conticelli and Peccerillo, 1992; Marra et al., 2004; Giordano et al., 2006 and references therein. Eruption centers are aligned along NW-SE oriented majorextensional structures guiding the dislocation of Meso-Cenozoic siliceous-carbonate sedimentary successions at the rear of the Apennine belt. Volcanic districts developed in structural sectors with most favorable conditions for magma uprise. In particular, the Colli Albani volcanism is located in a N-S shear zone where it intersects the extensional NW- and NE-trending fault systems. In the last decade, geochronological measurements allowed for reconstructions of the eruptive history and led to the classification as "dormant" volcano. The volcanic history may be roughly subdivided into three main phases marked by different eruptive mechanisms andmagma volumes. The early Tuscolano-Artemisio Phase (ca. 561–351 ky, the most explosive and voluminous one, is characterized by five large pyroclastic flow-forming eruptions. After a ~40-ky-long dormancy, a lesser energetic phase of activity took place (Faete Phase; ca. 308–250 ky, which started with peripheral effusive eruptions coupled with subordinate hydromagmatic activity. A new ~50-ky-long dormancypreceded the start of the late hydromagmatic phase (ca. 200–36 ky, which was dominated by pyroclastic-surge eruptions, with formation of several monogenetic or multiple maars and/or tuff rings.

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

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


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

  2. Geologic evolution of the Jemez Mountains and their potential for future volcanic activity

    Burton, B.W.


    Geophysical and geochemical data and the geologic history of the Rio Grande rift and the vicinity of the Jemez Mountains are summarized to determine the probability of future volcanic activity in the Los Alamos, New Mexico area. The apparent cyclic nature of volcanism in the Jemez Mountains may be related to intermittent thermal inputs into the volcanic system beneath the region. The Jemez lineament, an alignment of late Cenozoic volcanic centers that crosses the rift near Los Alamos, has played an important role in the volcanic evolution of the Jemez Mountains. Geophysical data suggest that there is no active shallow magma body beneath the Valles caldera, though magma probably exists at about 15 km beneath this portion of the rift. The rate of volcanism in the Jemez Mountains during the last 10 million years has been 5 x 10/sup -9//km/sup 2//y. Lava or ash flows overriding Laboratory radioactive waste disposal sites would have little potential to release radionuclides to the environment. The probability of a new volcano intruding close enough to a radioactive waste disposal site to effect radionuclide release is 2 x 10/sup -7//y.

  3. Geologic evolution of the Jemez Mountains and their potential for future volcanic activity

    Geophysical and geochemical data and the geologic history of the Rio Grande rift and the vicinity of the Jemez Mountains are summarized to determine the probability of future volcanic activity in the Los Alamos, New Mexico area. The apparent cyclic nature of volcanism in the Jemez Mountains may be related to intermittent thermal inputs into the volcanic system beneath the region. The Jemez lineament, an alignment of late Cenozoic volcanic centers that crosses the rift near Los Alamos, has played an important role in the volcanic evolution of the Jemez Mountains. Geophysical data suggest that there is no active shallow magma body beneath the Valles caldera, though magma probably exists at about 15 km beneath this portion of the rift. The rate of volcanism in the Jemez Mountains during the last 10 million years has been 5 x 10-9/km2/y. Lava or ash flows overriding Laboratory radioactive waste disposal sites would have little potential to release radionuclides to the environment. The probability of a new volcano intruding close enough to a radioactive waste disposal site to effect radionuclide release is 2 x 10-7/y

  4. Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations

    Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (-8 to 10-10 as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the mechanism of waste incorporation in magma, and Strombolian eruption processes

  5. The Cenozoic Tectonic History of the Calabrian Orogen, Southern Italy

    Shimabukuro, David Haruo


    The Cenozoic accretionary wedge of Calabria, Southern Italy, consists of several units of continental and oceanic affinity accreted beneath the former continental margin of the Sardinia-Corsica block. Each of these units bears the imprint of blueschist-facies metamorphism, indicating that it has been subducted to high-pressure/low-temperature conditions during the Alpine Orogeny. Structurally higher units, having been accreted first, record the early metamorphic history of the orogen; lower...

  6. Report on ICDP workshop CONOSC (COring the NOrth Sea Cenozoic)

    Westerhoff, Wim; Donders, Timme; Luthi, Stefan


    ICDP workshop COring the NOrth Sea Cenozoic focused on the scientific objectives and the technical aspects of drilling and sampling. Some 55 participants attended the meeting, ranging from climate scientists, drilling engineers, and geophysicists to stratigraphers and public outreach experts. Discussion on the proposed research sharpened the main research lines and led to working groups and the necessary technical details to compile a full proposal that was submitted in January 2016.

  7. Volcanic hazard assessment for disposal of high-level radioactive waste

    Volcanic hazard studies for disposal of high-level radioactive waste pose a number of unique problems. These include the long time frame of hazard assessment (104 to 106 yr), the limited geologic record of volcanic activity at disposal sites and the political sensitivity of this national problem. The major variables affecting volcanic hazards are the structure of magma feeder systems at repository depths and the magma fragmentation and dispersal energy of eruptions. The latter is generally controlled by magma composition and the presence or absence of groundwater. Long-lived volcanic fields (> 1 m.y.) provide the greatest potential risk for waste disposal, but these can be avoided by proper site selection. Short-lived volcanic fields are more difficult to avoid but are generally mafic in composition, which results in smaller disruption zones and explosive eruptions of lower energy than those of long-lived centers. Volcanic hazards are evaluated through risk assessment, which is a product of probability and consequences. These studies have been completed for a potential waste disposal site in the Nevada Test Site (NTS). Cenozoic volcanism of the NTS region is divided into three distinct episodes. The youngest episode, 3.7 to 0.3 m.y., comprises scattered, monogenetic Strombolian centers of small volume (3). Rates of volcanic activity for the NTS region are estimated to be about 10-6 event/yr, based on vent counts through time and calculation of rates of magma production. The conditions probability of disruption of the possible waste disposal site at the NTS by basaltic volcanism is bounded by the range of 10-8 to 10-10 yr-1. Consequences, expressed as radiological release levels, were evaluated by assuming disruption of a repository by basaltic magmas fed along narrow dikes

  8. Volcanism in Eastern Africa

    Cauthen, Clay; Coombs, Cassandra R.


    In 1891, the Virunga Mountains of Eastern Zaire were first acknowledged as volcanoes, and since then, the Virunga Mountain chain has demonstrated its potentially violent volcanic nature. The Virunga Mountains lie across the Eastern African Rift in an E-W direction located north of Lake Kivu. Mt. Nyamuragira and Mt. Nyiragongo present the most hazard of the eight mountains making up Virunga volcanic field, with the most recent activity during the 1970-90's. In 1977, after almost eighty years of moderate activity and periods of quiescence, Mt. Nyamuragira became highly active with lava flows that extruded from fissures on flanks circumscribing the volcano. The flows destroyed vast areas of vegetation and Zairian National Park areas, but no casualties were reported. Mt. Nyiragongo exhibited the same type volcanic activity, in association with regional tectonics that effected Mt. Nyamuragira, with variations of lava lake levels, lava fountains, and lava flows that resided in Lake Kivu. Mt. Nyiragongo, recently named a Decade volcano, presents both a direct and an indirect hazard to the inhabitants and properties located near the volcano. The Virunga volcanoes pose four major threats: volcanic eruptions, lava flows, toxic gas emission (CH4 and CO2), and earthquakes. Thus, the volcanoes of the Eastern African volcanic field emanate harm to the surrounding area by the forecast of volcanic eruptions. During the JSC Summer Fellowship program, we will acquire and collate remote sensing, photographic (Space Shuttle images), topographic and field data. In addition, maps of the extent and morphology(ies) of the features will be constructed using digital image information. The database generated will serve to create a Geographic Information System for easy access of information of the Eastem African volcanic field. The analysis of volcanism in Eastern Africa will permit a comparison for those areas from which we have field data. Results from this summer's work will permit

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

    夏邦栋; 施光宇; 等


    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.

  10. Olivine and chromian spinel in primitive calc-alkaline and tholeiitic lavas from the southernmost cascade range, California: A reflection of relative fertility of the source

    Clynne, M.A.; Borg, L.E.


    Chromian spinel and coexisting olivine phenocrysts from a geochemically diverse suite of primitive tholeiitic and calc-alkaline basalts and magnesian andesites from the Lassen region, in the southernmost Cascade Range, in California, show that the sub-arc mantle is zoned. Depleted calc-alkaline basalts and magnesian andesites erupt in the forearc region, and calc-alkaline basalts contain increasing abundances of incompatible elements toward the backarc. High-alumina olivine tholeiites erupt from the arc and backarc areas. Olivine from all these lavas displays a limited compositional range, from Fo86 to Fo91, and crystallized at high temperature, generally 1225-1275??C. Chromian spinel trapped in the olivine phenocrysts displays a large range of composition: Cr# values span the range 9-76. Excess Al in the spinel relative to that in 1-atm spinel suggests that it crystallized at elevated pressure. The phenocrysts in these lavas are in equilibrium with their host liquids. The full range of Cr# of the spinel compositions cannot be explained by differentiation or variable pressure, variations in f(O2), subsolidus equilibration or variations in degree of partial melting of a single peridotitic source. Rather, the systematic compositional differences among phenocrysts in these primitive lavas result from bulk chemical variability in their mantle sources. Correlations between spinel and host-rock compositions support the assertion that the geochemical diversity of Lassen basalts reflects the relative fertility of their mantle sources.

  11. Cenozoic carbon cycle imbalances and a variable weathering feedback

    Caves, Jeremy K.; Jost, Adam B.; Lau, Kimberly V.; Maher, Kate


    The long-term stability of Earth's climate and the recovery of the ocean-atmosphere system after carbon cycle perturbations are often attributed to a stabilizing negative feedback between silicate weathering and climate. However, evidence for the operation of this feedback over million-year timescales and in response to tectonic and long-term climatic change remains scarce. For example, the past 50 million years of the Cenozoic Era are characterized by long-term cooling and declining atmospheric CO2 (pCO2). During this interval, constant or decreasing carbon fluxes from the solid Earth to the atmosphere suggest that stable or decreasing weathering fluxes are needed to balance the carbon cycle. In contrast, marine isotopic proxies of weathering (i.e., 87Sr/86Sr, δ7 Li , and 187Os/188Os) are interpreted to reflect increasing weathering fluxes. Here, we evaluate the existence of a negative feedback by reconstructing the imbalance in the carbon cycle during the Cenozoic using the surface inventories of carbon and alkalinity. Only a sustained 0.25-0.5% increase in silicate weathering is necessary to explain the long-term decline in pCO2 over the Cenozoic. We propose that the long-term decrease in pCO2 is due to an increase in the strength of the silicate weathering feedback (i.e., the constant of proportionality between the silicate weathering flux and climate), rather than an increase in the weathering flux. This increase in the feedback strength, which mirrors the marine isotope proxies, occurs as transient, 1 million year timescales remains invariant to match the long-term inputs of carbon. Over the Cenozoic, this results in stable long-term weathering fluxes even as pCO2 decreases. We attribute increasing feedback strength to a change in the type and reactivity of rock in the weathering zone, which collectively has increased the reactivity of the surface of the Earth. Increasing feedback strength through the Cenozoic reconciles mass balance in the carbon cycle with

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

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


    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

  13. Hydrocarbon potential of the Meso-Cenozoic Turkana Depression, northern Kenya. 1. Reservoirs: depositional environments, diagenetic characteristics, and source rock-reservoir relationships

    Tiercelin, J.-J.; Bellon, H.; Rio, A.; Le Gall, B.; Vetel, W. [UMR CNRSUBO, Plouzane (France). Institut Universitaire Europeen de la Mer; Universite de Bretagne Occidentale, Brest (France); Potdevin, J.-L. [Universite des Sciences et Technologies de Lille (France). UFR des Sciences de la Terre; Morley, C.K. [Universiti Brunei Darassalam (Brunei Darussalam). Jalan Tungku Link; Talbot, M.R. [University of Bergen (Norway). Geological Institute


    Major oil exploration efforts started in the 70s in the Meso-Cenozoic Anza Rift and Cenozoic Turkana Depression of northern Kenya. Thick piles of fluvio-lacustrine sandstones and shales infill these different rift basins. West of Lake Turkana, the Auwerwer/Lomerimong Formation is part of the Palaeogene-middle Miocene age, 7 km-thick fluvio-lacustrine infill of the Lokichar half-graben. East of Lake Turkana, the 220 m-thick Sera Iltomia Formation is of possible late Mesozoic-basal Palaeocene age, and comprises sandstones and mudstones with conglomeratic layers. The poorly dated Sera Iltomia Formation may represent either the early phase of Cenozoic East African rifting in northern Kenya or the Meso-Cenozoic Anza Rift. The sandstones of these two formations exhibit different sediment sources and consequent reservoir quality. The Sera litomia sandstones are immature and basement-derived. While the sources of clastic material from the Auwerwer/Lomerimong section originated from both volcanic and basement terrains. Palaeocurrent data for the Sera Iltomia and Auwerwer/Lomerimong basement-derived sandstones suggest a source to the south and south-cast of Lake Turkana. The volcanic-derived clastic rocks forming part of the Auwerwer/Lomerimong section suggest a sediment source to the south-southeast of the Lokichar Basin, linked to the lower Miocene Samburu Basalts Formation. Evidence for significant burial diagenesis is absent in both. In the Auwerwer/Lomerimong sandstones, calcite-analcite precipitation and calcite cementation significantly reduced the porosity from initial values of 40-45% to values which ranges up to 15%. In the Sera Iltomia sandstones, different early diagenetic events are recorded by calcite, quartz or kaolin cements. Quartz overgrowths and kaolin precipitation are local phenomena, and did not induce significant porosity reduction. In some cases, calcite cementation completely occluded the initial porosity, but in other cases it has helped preserve

  14. Modeling volcanic ash dispersal

    CERN. Geneva


    The assessment of volcanic fallout hazard is an important scientific, economic, and political issue, especially in densely populated areas. From a scientific point of view, considerable progress has been made during the last two decades through the use of increasingly powerful computational models and capabilities. Nowadays, models are used to quantify hazard...

  15. Potassium-argon/argon-40-argon-39 geochronology of Cenozoic alkali basalts from the South China Sea

    YAN Quanshu; SHI Xuefa; YANG Yaomin; WANG Kunshan


    Based on the isotopic chronologic results of Cenozoic alkali basalts from the South China Sea,the characteristics of volcanic activi-ty of the South China Sea after spreading were studied.The potassium - argon ages of eight alkali basalt samples from the South China Sea,and the argon - argon ages of two samples among them are reported.Apparent ages of the whole rock are 3.80 to 7.91 Ma with an average value of 5.43 Ma (potassium- argon,whole rock),and there is little difference among samples at the same location,e.g.,4.76~5.78 Ma for location S04-12.The argon - argon ages for the two samples are 6.06 and 4.71 Ma,which lie within the age scope of potassium - argon method.The dating results indicate that rock-forming age is from late Miocene to Pli-ocene,which is consistent with erupting event for alkali basalts from adjacent regions of the South China Sea.Volcanic activities occur after the cessation of spreading of the South China Sea,which are controlled by lithospheric fault and the spreading center formed during the spreading period of the South China Sea.These dating results,combined with geochemical characteristics of these basalts,the published chronological data for the South China Sea and its adjacent regions,and the updated geophysical data near Hainan Island,suggest that after the cessation of spreading of the South China Sea,there occur widely distributing magmatic activities which primarily is alkali basalt,and the volcanic activity continues to Quaternary.The activity may be relative to Hainan mantle plume originated from core/mantle boundary.

  16. Dynamic topography and the Cenozoic carbonate compensation depth

    Campbell, S. M.; Moucha, R.; Raymo, M. E.; Derry, L. A.


    The carbonate compensation depth (CCD), the ocean depth at which the calcium carbonate accumulation rate goes to zero, can provide valuable insight into climatic and weathering conditions over the Cenozoic. The paleoposition of the CCD can be inferred from sediment core data. As the carbonate accumulation rate decreases linearly with depth between the lysocline and CCD, the CCD can be calculated using a linear regression on multiple sediment cores with known carbonate accumulation rates and paleodepths. It is therefore vital to have well-constrained estimates of paleodepths. Paleodepths are typically calculated using models of thermal subsidence and sediment loading and compaction. However, viscous convection-related stresses in the mantle can warp the ocean floor by hundreds of meters over broad regions and can also vary significantly over millions of years. This contribution to paleobathymetry, termed dynamic topography, can be calculated by modeling mantle flow backwards in time. Herein, we demonstrate the effect dynamic topography has on the inference of the late Cenozoic CCD with an example from the equatorial Pacific, considering sites from IODP Expeditions 320/321. The equatorial Pacific, given its large size and high productivity, is closely tied to the global carbon cycle. Accordingly, long-term changes in the equatorial Pacific CCD can be considered to reflect global changes in weathering fluxes and the carbon cycle, in addition to more regional changes in productivity and thermohaline circulation. We find that, when the dynamic topography contribution to bathymetry is accounted for, the equatorial Pacific CCD is calculated to be appreciably shallower at 30 Ma than previous estimates would suggest, implying a greater deepening of the Pacific CCD over the late Cenozoic.

  17. Cenozoic Methane-Seep Faunas of the Caribbean Region.

    Steffen Kiel

    Full Text Available We report new examples of Cenozoic cold-seep communities from Colombia, Cuba, the Dominican Republic, Trinidad, and Venezuela, and attempt to improve the stratigraphic dating of Cenozoic Caribbean seep communities using strontium isotope stratigraphy. Two seep faunas are distinguished in Barbados: the late Eocene mudstone-hosted 'Joes River fauna' consists mainly of large lucinid bivalves and tall abyssochrysoid gastropods, and the early Miocene carbonate-hosted 'Bath Cliffs fauna' containing the vesicomyid Pleurophopsis, the mytilid Bathymodiolus and small gastropods. Two new Oligocene seep communities from the Sinú River basin in Colombia consist of lucinid bivalves including Elongatolucina, thyasirid and solemyid bivalves, and Pleurophopsis. A new early Miocene seep community from Cuba includes Pleurophopsis and the large lucinid Meganodontia. Strontium isotope stratigraphy suggests an Eocene age for the Cuban Elmira asphalt mine seep community, making it the oldest in the Caribbean region. A new basal Pliocene seep fauna from the Dominican Republic is characterized by the large lucinid Anodontia (Pegophysema. In Trinidad we distinguish two types of seep faunas: the mudstone-hosted Godineau River fauna consisting mainly of lucinid bivalves, and the limestone-hosted Freeman's Bay fauna consisting chiefly of Pleurophopsis, Bathymodiolus, and small gastropods; they are all dated as late Miocene. Four new seep communities of Oligocene to Miocene age are reported from Venezuela. They consist mainly of large globular lucinid bivalves including Meganodontia, and moderately sized vesicomyid bivalves. After the late Miocene many large and typical 'Cenozoic' lucinid genera disappeared from the Caribbean seeps and are today known only from the central Indo-Pacific Ocean. We speculate that the increasingly oligotrophic conditions in the Caribbean Sea after the closure of the Isthmus of Panama in the Pliocene may have been unfavorable for such large

  18. Cenozoic sequence stratigraphy in the eastern North Sea

    Michelsen, O.; Thomsen, E.; Danielsen, M.; Heilmann-Clausen, C.; Jordt, H.; Laursen, G.V.


    The Cenozoic evolution of the epicontinental North Sea Basin is described on the basis of sequence stratigraphy, comprising analyses of seismic sections, petrophysical logs, and biostratigraphic studies of foraminifera, dinoflagellates, and calcareous nannofossils. Stratigraphic, palaeogeographic, and palaeoecological information from the Danish onshore area is integrated in the study. The deposits are subdivided into 21 sequences, which groups into seven informal major units. The sequence boundaries are identified by differences in seismic facies and by seismic onlap, toplap, and truncation features. The maximum flooding surface is placed at an internal downlap surface which correlates with high values on the gamma ray log. The source of sediments and the direction of sediment transport changed several times during the Cenozoic. Transport was mainly from the north during the Late Paleocene and Early Eocene, from the west during the Middle and Late Eocene, and from the north and northwest during the Oligocene to quaternary. The depocenters of the seven major units are generally located marginally, probably adjoining the source areas. There is only minor evidence for changes in subsidence rates in the basin. A constant rate is assumed from the Paleocene to the mid Middle Miocene. For the remaining part of the Cenozoic and increased rate is indicated. A tentative relative sea-level curve for the North Sea Basin is proposed. The overall trends of the curve are broadly comparable with the global sea-level curve of Haq et al. Discrepancies may be caused by differences in the biostratigraphic calibrations. The most pronounced Oligocene sea-level fall is dated ot the latest Oligocene. (au) (83 refs.)

  19. Early Cenozoic Multiple Thrust in the Tibetan Plateau

    Zhenhan Wu


    Full Text Available Recently completed regional geological mapping at a scale of 1 : 250,000 or larger across all of the Tibetan Plateau coupled with deep seismic surveys reveals for the first time a comprehensive depiction of the major early Cenozoic thrust systems resulting from the northward subduction of the Indian Continental Plate. These systems define a series of overlapping north-dipping thrust sheets that thickened the Tibetan crust and lead to the rise of the plateau. The few south-dipping thrusts present apparently developed within a sheet when the back moved faster than the toe. Many of the thrusts are shown to extend to the middle-lower crustal depths by seismic data. The regional thrust systems are the Main Central, Renbu-Zedong, Gangdese, Central Gangdese, North Gangdese, Bangoin-Nujiang, Qiangtang, Hohxil, and South Kunlun Thrusts. The minimal southward displacements of the South Kunlun, Hohxil, South Qiangtang, and Central Gangdese Thrusts are estimated to be 30 km, 25 km, 150 km and 50 km, respectively. Deep thrusting began in the Himalaya-Tibetan region soon after India-Eurasia continental collision and led to crustal thickening and subsequent uplift of the Tibetan Plateau during Late Eocene-Early Miocene when the systems were mainly active. The major thrust systems ceased moving in Early Miocene and many were soon covered by lacustrine strata. This activity succeeded in the late Cenozoic to crustal extension and strike-slip movement in the central Tibetan Plateau. The revelation of the full array of the early Cenozoic thrust systems provides a much more complete understanding of the tectonic framework of the Tibetan Plateau.

  20. Structural inheritance and selective reactivation in the central Andes: Cenozoic deformation guided by pre-Andean structures in southern Peru

    Perez, Nicholas D.; Horton, Brian K.; Carlotto, Victor


    Structural, stratigraphic, and geochronologic constraints from the Eastern Cordillera in the central Andean plateau of southern Peru (14-15°S) demonstrate the existence and position of major pre-Andean structures that controlled the accumulation of Triassic synrift fill and guided subsequent Cenozoic deformation. The timing of initial clastic deposition of the Triassic Mitu Group is here constrained to ~ 242-233 Ma on the basis of detrital and volcanic zircon U-Pb geochronology. Regionally distinct provenance variations, as provided by U-Pb age populations from localized synrift accumulations, demonstrate Triassic erosion of multiple diagnostic sources from diverse rift-flank uplifts. Stratigraphic correlations suggest synchronous initiation of extensional basins containing the Mitu Group, in contrast with previous interpretations of southward rift propagation. Triassic motion along the NE-dipping San Anton normal fault accommodated up to 7 km of throw and hanging-wall deposition of a synrift Mitu succession > 2.5 km thick. The contrasting orientation of a non-reactivated Triassic normal fault suggests selective inversion of individual structures in the Eastern Cordillera was dependent on fault dip and strike. Selective preservation of a ~ 4 km thick succession of Carboniferous-Permian strata in the down-dropped San Anton hanging wall, beneath the synrift Mitu Group, suggests large-scale erosional removal in the uplifted footwall. Field and map observations identify additional pre-Andean thrust faults and folds attributed to poorly understood Paleozoic orogenic events preserved in the San Anton hanging wall. Selective thrust reactivation of normal and reverse faults during later compression largely guided Cenozoic deformation in the Eastern Cordillera. The resulting structural compartmentalization and across-strike variations in kinematics and deformation style highlight the influence of inherited Paleozoic structures and Triassic normal faults on the long

  1. Deep geological tectonic features and their control over volcanic activities and uranium metallization in the Bashang region, north Hebei

    The Bashang region of North Hebei is located at the north margin of North China Platform. Two remarkable features have been recognized in deep geological tectonics first, the Moho-surface down-warped with crustal thickening regionally, secondly, the asthenosphere locally inserted the upper part of the lower lithosphere, resulting in the mantle-upwelling and the crust thinning in local regions. Guyuan and Datan volcanic basins formed by volcanic eruption in the upper part of the crust are corresponding to the two areas of mantle upwelling and crust thinning in the lower part. The uranium deposits (occurrences) are regularly distributed along the mobile fault zone of the periphery of mantle upwelling. All above-mentioned facts strongly prove that Mesozoic-Cenozoic volcanic activities and uranium metallization are controlled by the deep geological tectonics. The mobile fault zone along the periphery of mantle upwelling is the favourable site for prospecting uranium and polymetallic mineral resources in the future

  2. Cenozoic crustal shortening and thickening contributions to Andean orogenesis: Preliminary results from structural mapping in the southern Peruvian Andes

    Perez, N.; Horton, B. K.


    Estimates of Cenozoic crustal shortening and thickening from the southern Peruvian Andes are necessary to address ongoing debates regarding growth of the Andes and Altiplano plateau. However, limited regional studies in southern Peru prevent accurate assessments of the structural contributions to high topography. This study provides new structural mapping along a >200 km transect spanning the northernmost Altiplano to Subandes at 13-15.5°S and fills the gap between existing central Peruvian and northern Bolivian studies. New stratigraphic data, fault relationships and fold orientations are used to create an updated geologic map and provide insights into the style, timing and magnitude of crustal deformation. Preliminary cross sections accompanying these map transects illustrate deformation style and provide first-order estimates of shortening. Further cross section analyses will be balanced and provide estimates of total crustal shortening and associated thickening in southern Peru. The study transect is subdivided into belts according to the age of exposed rocks and style of deformation. From west to east these belts include: Cretaceous strata dominated by tight folds, closely spaced faults and multiple detachments; Permo-Triassic strata dominated by thicker thrust sheets and fault-fold orientations departing from typical Andean trends; and Paleozoic rocks characterized by thick thrust sheets and deformation focused near major faults. The Cretaceous belt is composed of marine limestones and upward coarsening, siltstone to coarse sandstone progradational sequences. Disharmonic and detachment folds in the Cretaceous section demonstrate the importance of interbedded gypsum and mudstone layers. Fault relationships suggest local shortening during the Early Cretaceous. The Permo-Triassic belt is composed of thick Permian carbonates (Copacabana Formation) and interbedded sandstones, conglomerates and volcanics of the Mitu Formation. This study defines the orientation of

  3. Thermal state of the Roer Valley Graben, part of the European Cenozoic Rift System

    Luijendijk, E.; Voorde, M. ter; Balen, R. van; Verweij, H.; Simmelink, E.


    We performed a detailed analysis of the thermal state of the Cenozoic Roer Valley Graben, the north-western branch of the European Cenozoic Rift System, based on a new set of temperature data. We developed a numerical technique for correcting bottom hole temperatures, including an evaluation of the

  4. Cenozoic Tectonic Activity of the "Passive" North America Margin: Evidence for Cenozoic Activity on Mesozoic or Paleozoic Faults

    Nedorub, O. I.; Knapp, C. C.


    The tectonic history of the Eastern North American Margin (ENAM) incorporates two cycles of continental assembly, multiple pulses of orogeny, rifting, and post-rift geodynamic evolution. This is reflected in the heterogeneous lithosphere of the ENAM which contains fault structures originated in Paleozoic to Mesozoic eras. The South Georgia Rift basin is probably the largest Mesozoic graben within its boundaries that is associated with the breakup of Pangea. It is composed of smaller sub-basins which appear to be bounded by high-angle normal faults, some of which may have been inverted in late Cretaceous and Cenozoic eras. Paleozoic structures may have been reactivated in Cenozoic time as well. The ENAM is characterized by N-NE maximum horizontal compressive stress direction. This maximum compressional stress field is sub-parallel to the strike of the Atlantic Coast province fault systems. Camden, Augusta, Allendale, and Pen Branch faults are four of the many such reactivated faults along the southern part of ENAM. These faults are now buried under the 0-400 m of loosely consolidated Cretaceous and Cenozoic age sediments and thus are either only partially mapped or currently not recognized. Some of the objectives of this study are to map the subsurface expression and geometry of these faults and to investigate the post Cretaceous deformation and possible causes of fault reactivation on a passive margin. This study employs an integrated geophysical approach to investigate the upper 200 m of identified locations of the above mentioned faults. 2-D high-resolution shallow seismic reflection and refraction methods, gravity surveys, GPR, 2-D electrical resistivity and well data are used for analyses and interpretation. Preliminary results suggest that Camden fault shows signs of Cenozoic reactivation through an approximately 30 m offset NW side up mainly along a steeply dipping fault zone in the basal contact of Coastal Plain sediments with the Carolina Piedmont. Drill

  5. Bimodal magmatism, basaltic volcanic styles, tectonics, and geomorphic processes of the eastern Snake River Plain, Idaho

    Hughes, S.S.; Smith, R.P.; Hackett, W.R.; McCurry, M.; Anderson, S.R.; Ferdock, G.C.


    Geology presented in this field guide covers a wide spectrum of internal and surficial processes of the eastern Snake River Plain, one of the largest components of the combined late Cenozoic igneous provinces of the western United States. Focus is on widespread Quaternary basaltic plains volcanism that produced coalescent shields and complex eruptive centers that yielded compositionally evolved magmas. The guide is constructed in several parts beginning with discussion sections that provide an overview of the geology followed by road directions, with explanations, for specific locations. The geology overview briefly summarizes the collective knowledge gained, and petrologic implications made, over the past few decades. The field guide covers plains volcanism, lava flow emplacement, basaltic shield growth, phreatomagmatic eruptions, and complex and evolved eruptive centers. Locations and explanations are also provided for the hydrogeology, groundwater contamination, and environmental issues such as range fires and cataclysmic floods associated with the region.

  6. Continental arc volcanism as the principal driver of icehouse-greenhouse variability.

    McKenzie, N Ryan; Horton, Brian K; Loomis, Shannon E; Stockli, Daniel F; Planavsky, Noah J; Lee, Cin-Ty A


    Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years. PMID:27102480

  7. Middle to late cenozoic magmatism of the southeastern Colorado plateau and central Rio Grande rift (New Mexico and Arizona, U.S.A.) : a model for continental rifting

    Baldridge, W.S.; Perry, F.V.; Vaniman, D.T.; Nealey, L.D.; Leavy, B.D.; Laughlin, A.W.; Kyle, P.; Bartov, Y.; Steinitz, G.; Gladney, E.S.


    The region of the present Rio Grande rift and southeastern Colorado Plateau underwent lithospheric extension during middle to late Cenozoic deformation affecting the entire southwestern U.S. Lithospheric mantle was disrupted, and in many regions displaced or replaced by asthenospheric mantle at depths from which basaltic magmas were derived and erupted to the surface. Study of the igneous rocks erupted or intruded during this deformation yields insights into processes of magmatism associated with extension of continental lithosphere. Magmatic rocks associated with an early (late Oligocene-early Miocene) ductile phase of extension are dominantly basaltic andesites and related, calc-alkaline intermediate to silicic derivative rocks. Mafic magmas were probably derived from isotopically "enriched" lithospheric mantle. Igneous rocks associated with a later (middle Miocene-Holocene), more brittle phase of extension include widespread basaltic rocks and localized central volcanoes of intermediate to silicic composition. Isotopic compositions of mafic rocks, which include both tholeiitic and alkalic basalts, correlate strongly with tectonic setting and lithospheric structure. Basalts erupted in areas of greatest crustal extension, such as the central and southern rift and Basin and Range province, were derived from isotopically "depleted" (correlated with "asthenospheric") mantle. Also, isotopic compositions of Pliocene to Holocene basalts are slightly more depleted than those of Miocene basalts, suggesting that subcrustal lithospheric mantle was thinned during late Miocene extension. Intermediate rocks of the central volcanoes formed by a complex combination of processes, probably dominated by fractional crystallization and by assimilation of upper and lower crust in isolated, small magma chambers. The petrologic, geochemical, and isotopic data are compatible with a model, derived first from geophysical data, whereby lithosphere is thinned beneath the central rift and

  8. Reducing volcanic risk

    Decker, R.; Decker, B.


    The last two decades have brought major advances in research on how volcanoes work and how to monitor their changing habits. Geologic mapping as well as studies of earthquake patterns and surface deformation associated with underground movement of magma have given scientists a better view of the inner structure and dynamics of active volcanoes. With the next decade, the time has come to focuses more on applying this knowledge toward reducing the risk from volcanic activity on a worldwide basis. 

  9. North Chilean forearc tectonics and cenozoic plate kinematics

    Buddin, Tim S.; Stimpson, Ian G.; Williams, Graham D.


    The continental forearc of northern Chile has been subjected to contemporaneous extension and compression. Here, cross-sections constructed across the forearc are presented which show that since initial shortening, deformation of the forearc has occurred in two tectonically distinct areas. These inner and outer forearc areas are separated by the strain discontinuity of the Atacama fault system and the tectonically neutral Central Depression. The outer forearc, the Coastal Cordillera, exhibits extensional tectonics, with large (up to 300 m) normal fault scarps preserved. These faults cut the earlier thrusts responsible for the elevation of Jurassic rocks at the coast above their regional elevation. The normal faults have been re-activated, displacing Quaternary salt deposits in the Salar Grande. This re-activation of the basement faults is probably due to the subduction of anomalously thick oceanic crust, producing an isostatic imbalance in the outer forearc. In the inner forearc, cross-sections through the Sierra del Medio and Cordillera de Domeyko show that structures of the Pre-Cordillera are best explained by a thick-skinned thrust system, with localized thin-skinned tectonics controlled by evaporite detachment horizons. Current forearc deformation features indicate a strong degree of correlation between subduction zone geometry and forearc tectonics. The timing of Cenozoic tectonism also fits well with established plate motion parameters, and the spatial and temporal variation in the state of stress of the forearc shows a close relationship throughout the Cenozoic to the plate kinematics and morphology of the subducting Nazca plate.

  10. Late Cenozoic Paleoceanography of the Central Arctic Ocean

    The Arctic Ocean is the smallest and perhaps least accessible of the worlds oceans. It occupies only 26% of the global ocean area, and less than 10% of its volume. However, it exerts a disproportionately large influence on the global climate system through a complex set of positive and negative feedback mechanisms directly or indirectly related to terrestrial ice and snow cover and sea ice. Increasingly, the northern high latitude cryosphere is seen as an exceptionally fragile part of the global climate system, a fact exemplified by observed reductions in sea ice extent during the past decades [2]. The paleoceanographic evolution of the Arctic Ocean can provide important insights into the physical forcing mechanisms that affect the form, intensity and permanence of ice in the high Arctic, and its sensitivity to these mechanisms in vastly different climate states of the past. However, marine records capturing the late Cenozoic paleoceanography of the Arctic are limited - most notably because only a single deep borehole exists from the central parts of this Ocean. This paper reviews the principal late Cenozoic (Neogene/Quaternary) results from the Arctic Coring Expedition to the Lomonosov Ridge and in light of recent data and observations on modern sea ice, outlines emerging questions related to three main themes: 1) the establishment of the 'modern' Arctic Ocean and the opening of the Fram Strait 2) the inception of perennial sea ice 3) The Quaternary intensification of Northern Hemisphere glaciations.

  11. Mesozoic and Cenozoic formations uraniferous activity. Chapter 3

    The main features of geological structure and history of forming Mesozoic and Cenozoic structure and formations complexes are given. Forming of Mesozoic-Cenozoic Depressive structures had been going on under the condition of infiltrations regime of artesian basins with forming of regional ground and stratum oxidation zones in Zhalpak and Paleogenic sediments which are including uranium deposits belonging to four uranium ore formation. The main raw materials base and extraction of uranium by in-situ leaching method are connected with deposits of epigenetic uranium-ore formation of regional stratum oxidation zones. There are most important deposits: Maikuduk, Inkai, Zhalpak, Uvanas, Suluchekenskoe, Koldzatskoe, Nizhneilyiskoe. All deposits are described according to same plan: stratigraphy, tectonic structure, hydrogeology, hydrochemics, uranium mineralization, morphology of deposits, mineral compound of ores, geologic characteristics of ores, genetics. Except uranium, the main deposit component, there is an information about the accompanied elements: rhenium, selenium, rare-earth ones, industrial concentration of which are in competitions with the same elements extracted from ores

  12. Algal constraints on the Cenozoic history of atmospheric CO2?

    R. E. M. Rickaby


    Full Text Available An urgent question for future climate, in light of increased burning of fossil fuels, is the temperature sensitivity of the climate system to atmospheric carbon dioxide (pCO2. To date, no direct proxy for past levels of pCO2 exists beyond the reach of the polar ice core records. We propose a new methodology for placing an upper constraint on pCO2 over the Cenozoic based on the living geological record. Specifically, our premise is that the contrasting calcification tolerance of various extant species of coccolithophore to raised pCO2 reflects an "evolutionary memory" of past atmospheric composition. The different times of first emergence of each morphospecies allows an upper constraint of past pCO2 to be placed on Cenozoic timeslices. Further, our hypothesis has implications for the response of marine calcifiers to ocean acidification. Geologically "ancient" species, which have survived large changes in ocean chemistry, are likely more resilient to predicted acidification.

  13. Midcontinent rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin

    Nicholson, S.W.; Shirey, S.B.


    Between 1091 and 1098 Ma, most of a 15- to 20-km thickness of dominantly tholeiitic basalt erupted in the Midcontinent Rift System of the Lake Superior region, North America. The Portage Lake Volcanics in Michigan, which are the younget MRS flood basalts, fall into distinctly high- and low-TiO2 types having different liquid lines of descent. Incompatible trace elements in both types of tholeiites are enriched compared to depleted or primitive mantle and both basalt types are isotopically indistinguishable. The isotopic enrichment of the MRS source compared to depleted mantle is striking and must have occurred at least 700 m.y. before 1100 Ma. There are two likely sources for such magmatism: subcontinental lithospheric mantle enriched during the early Proterozoic or enriched mantle derived from an upwelling plume. Decompression melting of an upwelling enriched mantle plume in a region of lithosphere thinned by extension could have successfully generated the enormous volume (850 ?? 103 km3) of relatively homogeneous magma in a restricted time interval. -from Authors

  14. Subdiffusion of volcanic earthquakes

    Abe, Sumiyoshi


    A comparative study is performed on volcanic seismicities at Mt.Eyjafjallajokull in Iceland and Mt. Etna in Sicily, Italy, from the viewpoint of science of complex systems, and the discovery of remarkable similarities between them regarding their exotic spatio-temporal properties is reported. In both of the volcanic seismicities as point processes, the jump probability distributions of earthquakes are found to obey the exponential law, whereas the waiting-time distributions follow the power law. In particular, a careful analysis is made about the finite size effects on the waiting-time distributions, and accordingly, the previously reported results for Mt. Etna [S. Abe and N. Suzuki, EPL 110, 59001 (2015)] are reinterpreted. It is shown that spreads of the volcanic earthquakes are subdiffusive at both of the volcanoes. The aging phenomenon is observed in the "event-time-averaged" mean-squared displacements of the hypocenters. A comment is also made on presence/absence of long term memories in the context of t...

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

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


    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

  16. The lithospheric shear-wave velocity structure of Saudi Arabia: Young volcanism in an old shield

    Tang, Zheng; Julià, Jordi; Zahran, Hani; Mai, P. Martin


    We investigate the lithospheric shear-wave velocity structure of Saudi Arabia by conducting H-κ stacking analysis and jointly inverting teleseismic P-receiver functions and fundamental-mode Rayleigh wave group velocities at 56 broadband stations deployed by the Saudi Geological Survey (SGS). The study region, the Arabian plate, is traditionally divided into the western Arabian shield and the eastern Arabian platform: The Arabian shield itself is a complicated mélange of crustal material, composed of several Proterozoic terrains separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks (locally known as harrats). The Arabian platform is primarily covered by 8 to 10 km of Paleozoic, Mesozoic and Cenozoic sedimentary rocks. Our results reveal high Vp/Vs ratios in the region of Harrat Lunayyir, which are interpreted as solidified magma intrusions from old magmatic episodes in the shield. Our results also indicate slow velocities and large upper mantle lid temperatures below the southern and northern tips of the Arabian shield, when compared with the values obtained for the central shield. We argue that our inferred patterns of lid velocity and temperature are due to heating by thermal conduction from the Afar plume (and, possibly, the Jordan plume), and that volcanism in western Arabia may result from small-scale adiabatic ascent of magma diapirs.

  17. The lithospheric shear-wave velocity structure of Saudi Arabia: Young volcanism in an old shield

    Tang, Zheng


    We investigate the lithospheric shear-wave velocity structure of Saudi Arabia by conducting H-κ stacking analysis and jointly inverting teleseismic P-receiver functions and fundamental-mode Rayleigh wave group velocities at 56 broadband stations deployed by the Saudi Geological Survey (SGS). The study region, the Arabian plate, is traditionally divided into the western Arabian shield and the eastern Arabian platform: The Arabian shield itself is a complicated mélange of crustal material, composed of several Proterozoic terrains separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks (locally known as harrats). The Arabian platform is primarily covered by 8 to 10 km of Paleozoic, Mesozoic and Cenozoic sedimentary rocks. Our results reveal high Vp/Vs ratios in the region of Harrat Lunayyir, which are interpreted as solidified magma intrusions from old magmatic episodes in the shield. Our results also indicate slow velocities and large upper mantle lid temperatures below the southern and northern tips of the Arabian shield, when compared with the values obtained for the central shield. We argue that our inferred patterns of lid velocity and temperature are due to heating by thermal conduction from the Afar plume (and, possibly, the Jordan plume), and that volcanism in western Arabia may result from small-scale adiabatic ascent of magma diapirs.

  18. Geochemical characteristics of Bikou volcanic group and Sr-Nd-Pb isotopic composition: Evidence for breakup event in the north margin of Yangtze plate, Jining era

    LI; YongFei; LAI; ShaoCong; QIN; JiangFeng; LIU; Xin; WANG; Juan


    The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is composed of several residual oceanic crust units: MORB (mid-ocean ridge basalt), Alk-OIB (alkaline ocean island basalt) and Th-OIB (tholeiitic ocean island basalt) as well as subduction-related volcanic rocks. According to field observation, those distinct rocks occurred collectively in form of tectonic contact, implying that the Bikou volcanic group was an ophiolitic mélange. Coupled with geochronological data, a perished oceanic basin at the northern margin of the Yangtze block during Neoproterozoic was tested by this ophiolitic mélange. Meanwhile, the isogeochemical data suggest that the ocean occurred in the Southern Hemisphere identical to Indian, South Atlantic and South Pacific oceans in terms of their Dupal anomalies, and the original source of the rocks could be probably mixing by EMⅠand EMⅡ component caused by dehydration melting of subducting oceanic crust during subduction process. On the basis of geochemical characteristics of the studied rocks, the Bikou volcanic group could imply that a partial breakup event occurred in the northern margin of Yangtze plate during the Neoproterozoic era.

  19. Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

    Duncan, Robert A.; Kent, Adam J. R.; Thornber, Carl R.; Schlieder, Tyler D.; Al-Amri, Abdullah M.


    Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K-Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar-39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1-7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60-80 km).

  20. Intraplate Harrat Volcanism and Neogene Evolution of the Lithosphere-Asthenosphere Boundary beneath Western Saudi Arabia

    Kent, A. J.; Duncan, R. A.; Graham, D. W.; Al-Amri, A. M.; Alshalntoni, S. A.


    Continental extension is a fundamental plate tectonic process, and extensional environments are associated with significant production of basaltic magmas. Although tholeiitic magmatism produced by mantle decompression is common, dispersed, less voluminous and compositionally variable basaltic and related magmas also occur in association with continental extension. One of the most voluminous, best-preserved and least studied examples of the latter is the volcanic harrats of western Saudi Arabia. Uplift, crustal erosion and harrat volcanism occurred from ~15 Ma to recent over a considerable region of western Arabia. Volcanism trends north from the Red Sea along the Makkah-Madinah-Nafud (MMN) line as a number of discrete harrats, and geophysical evidence suggests this region is underlain by hot upwelling asthenosphere. Larger harrats occur along the central axis of the MMN line, with smaller fields on the periphery. We present initial results of an ongoing study of harrat volcanism, including more than 50 new 40Ar-39Ar ages together with geochemical and isotopic data. Magma storage and fractionation appears to have occurred at a range of crustal levels, including deep storage and transport sufficiently rapid to preserve a range of lithospheric and crustal xenoliths. Melting commenced within the garnet peridotite field, however modeling of REE element abundances suggest that considerable differences exist in the thickness of the overlying lithospheric lid. Thinner lithosphere (line, whereas harrats peripheral to the MMN line have thicker lithosphere (>60-80 km) and magmas result from lower degree melts. The observed variability can be explained by a process of progressively thinning lithosphere along the main axis of the MMN line, as a result of regional lithospheric extension and mantle decompression melting, coupled with northward asthenospheric flow from the Red Sea and/or Afar hot spot.

  1. Geologic and geophysical investigations of the Zuni-Bandera volcanic field, New Mexico

    Ander, M.E.; Heiken, G.; Eichelberger, J.; Laughlin, A.W.; Huestis, S.


    A positive, northeast-trending gravity anomaly, 90 km long and 30 km wide, extends southwest from the Zuni uplift, New Mexico. The Zuni-Bandera volcanic field, an alignment of 74 basaltic vents, is parallel to the eastern edge of the anomaly. Lavas display a bimodal distribution of tholeiitic and alkalic compositions, and were erupted over a period from 4 Myr to present. A residual gravity profile taken perpendicular to the major axis of the anomaly was analyzed using linear programming and ideal body theory to obtain bounds on the density contrast, depth, and minimum thickness of the gravity body. Two-dimensionality was assumed. The limiting case where the anomalous body reaches the surface gives 0.1 g/cm/sup 3/ as the greatest lower bound on the maximum density contrast. If 0.4 g/cm/sup 3/ is taken as the geologically reasonable upper limit on the maximum density contrast, the least upper bound on the depth of burial is 3.5 km and minimum thickness is 2 km. A shallow mafic intrusion, emplaced sometime before Laramide deformation, is proposed to account for the positive gravity anomaly. Analysis of a magnetotelluric survey suggests that the intrusion is not due to recent basaltic magma associated with the Zuni-Bandera volcanic field. This large basement structure has controlled the development of the volcanic field; vent orientations have changed somewhat through time, but the trend of the volcanic chain followed the edge of the basement structure. It has also exhibited some control on deformation of the sedimentary section.

  2. Fluorine geochemistry in volcanic rock series

    Stecher, Ole


    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 ...

  3. Volcanic Ash Nephelometer Probe Project

    National Aeronautics and Space Administration — Advanced dropsondes that could effectively be guided through atmospheric regions of interest such as volcanic plumes may enable unprecedented observations of...

  4. System of Volcanic activity



    Full Text Available A comparison is made among the systems of B. G.
    Escher (3, of R. W. van Bemmelen (1 and that of the author (4. In this
    connection, on the basis of Esclier's classification, the terms of "constructiv
    e " and "destructive" eruptions are introduced into the author's system and
    at the same time Escher's concept on the possible relation between the depth
    of magma-chamber and the measure of the gas-pressure is discussed briefly.
    Three complementary remarks to the first paper (4 011 the subject of system
    of volcanic activity are added.

  5. Patterns of Cenozoic sediment flux from western Scandinavia

    Gołędowski, Bartosz; Nielsen, S.B.; Clausen, O.R.


    tectonism, climate and climate change. Western Scandinavia, the northern British Isles and the Faeroe-Shetland Platform were significant sediment sources during the Paleocene, which is well founded in tectonic causes related to the opening of the North Atlantic. From the Eocene and onward, variations in the...... sediment flux from western Scandinavia correlate better with climate and climate change. During the Eocene, sediment production was low. From the late Eocene onward, increased seasonality may have contributed to stimulating the sediment flux. Significant climatic cooling episodes correlate with Oligocene......The significance of variations in the sediment flux from western Scandinavia during the Cenozoic has been a matter of debate for decades. Here we compile the sediment flux using seismic data, boreholes and results from other publications and discuss the relative importance of causal agents such as...

  6. The 13 million year Cenozoic pulse of the Earth

    Chen, Jiasheng; Kravchinsky, Vadim A.; Liu, Xiuming


    The geomagnetic polarity reversal rate changes radically from very low to extremely high. Such process indicates fundamental changes in the Earth's core reorganization and core-mantle boundary heat flow fluctuations. However, we still do not know how critical such changes are to surface geology and climate processes. Our analysis of the geomagnetic reversal frequency, oxygen isotope record, and tectonic plate subduction rate, which are indicators of the changes in the heat flux at the core mantle boundary, climate and plate tectonic activity, shows that all these changes indicate similar rhythms on million years' timescale in the Cenozoic Era occurring with the common fundamental periodicity of ∼13 Myr during most of the time. The periodicity is disrupted only during the last 20 Myr. Such periodic behavior suggests that large scale climate and tectonic changes at the Earth's surface are closely connected with the million year timescale cyclical reorganization of the Earth's interior.

  7. The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt:Geology, volcanism and neotectonics

    E. Sharkov; V. Lebedev; A. Chugaev; L. Zabarinskaya; A. Rodnikov; N. Sergeeva; I. Safonova


    The Caucasian-Arabian belt is part of the huge late Cenozoic Alpine-Himalayan orogenic belt formed by collision of continental plates. The belt consists of two domains:the Caucasian-Arabian Syntaxis (CAS) in the south and the EW-striking Greater Caucasus in the north. The CAS marks a zone of the indentation of the Arabian plate into the southern East European Craton. The Greater Caucasus Range is located in the south of the Eurasian plate;it was tectonically uplifted along the Main Caucasian Fault (MCF), which is, in turn, a part of a megafault extended over a great distance from the Kopetdag Mts. to the Tornquist-Teisseyre Trans-European Suture Zone. The Caucasus Mts. are bounded by the Black Sea from the west and by the Caspian Sea from the east. The SN-striking CAS is characterized by a large geophysical isostatic anomaly suggesting presence of mantle plume head. A 500 km long belt of late Cenozoic volcanism in the CAS extends from the eastern Anatolia to the Lesser and Greater Caucasus ranges. This belt hosts two different types of volcanic rocks: (1) plume-type intraplate basaltic plateaus and (2) suprasubduction-type calc-alkaline and shoshonite-latite volcanic rocks. As the CAS lacks signatures of subduction zones and is characterized by relatively shallow earthquakes (50e60 km), we suggest that the “supra-subduction-type”magmas were derived by interaction between mantle plume head and crustal material. Those hybrid melts were originated under conditions of collision-related deformation. During the late Cenozoic, the width of the CAS reduced to ca. 400 km due to tectonic “diffluence” of crustal material provided by the continuing Arabia-Eurasia collision.

  8. Analysis of long period magnetotelluric data measured in regions affected by volcanism in Germany

    Complete text of publication follows. In 2008, we carried out an eight months magnetotelluric campaign. The stations were placed along a 400km profile from the middle of Germany to the west of Germany. The profile crosses areas which were affected by extensive intraplate volcanism in the past, like the Leine Valley near Goettingen and the Rhenish Massif in the west. The volcanoes besides the Leine Valley were formed in the Cenozoic whereas some of the Eiffel volcanic formations in the Rhenish Massif belong to the youngest in central Europe. Seismic surveys found evidence for a mantle plume beneath the Eiffel volcanic fields. This conclusion couldn't be ratified with magnetotelluric surveys. But it was found a crustal conductivity anomaly similar to a crustal conductivity anomaly below the volcanoes close to the Leine Valley. Furthermore at long periods there is a consistent WE strike direction in the whole area between the Rhenish Massif and the Leine Valley, which can be identified with an anisotropic structure in the upper mantle. This effect isn't observed in southern Germany as a reference station shows. Using a 3D model that includes the entire area, we hope to uncover more details about the structures in the upper mantle and deeper crust that may be consulted as an explanation of the volcanism.

  9. Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

    Søager, Nina

    The extensive Quaternary volcanism in the Payenia volcanic province, Mendoza, Argentina, is investigated in this study by major and trace element analyses, Sr, Nd, Hf and Pb-isotopic analyses and Zr-Hf isotope dilution data on samples from almost the entire province. The samples are mainly...... basalts from all the studied volcanic fields in Payenia is signs of lower crustal contamination indicating assimilation of, in some cases, large amounts of trace element depleted, mafic, plagioclase-bearing rocks. The northern Payenia is dominated by backarc basalts erupted between late Pliocene to late...... Pleistocene times. These basalts mark the end of a period of shallow subduction of the Nazca slab beneath the Payenia province and volcanism in the Nevado volcanic field apparently followed the downwarping slab in a north-northwest direction ending in the Northern Segment. The northern Payenia basalts are...

  10. Volcanic Eruptions and Climate

    LeGrande, Allegra N.; Anchukaitis, Kevin J.


    Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.

  11. Cenozoic back-arc magmatism of the southern extra-Andean Patagonia (44° 30' - 52° S: A review of geochemical data and geodynamic interpretations

    M. D'Orazio


    Full Text Available Huge amounts of basaltic s.l. lavas were persistently erupted along the eastern side of the Andean Cordillera, throughout Cenozoic time, forming extensive plateaus, hundreds of monogenetic scoria cones and other volcanic structures in a continental back-arc setting. The igneous products exposed in the southern sector of the extra-Andean Patagonia (44° 30' - 52° S are dominantly mafic with minor slightly evolved compositions and rare highly differentiated products. The many published chemical analyses of these rocks, indicate that the mafic lavas range from strongly silica - undersaturated basanites to oversaturated basaltic andesites, and that most of the lavas have a typical within-plate geochemical signature. However, a number of lavas, generally erupted in the western-central sectors of Patagonia, are characterized by different distributions of the incompatible elements with high LILE/HFSE and LREE/HFSE ratios. The REE distribution modelling suggests a low degree of melting of a deep (> 70 km garnet-bearing source for the alkaline magmas, and a higher degree of melting of the same source, or an even higher degree of melting of an enriched source, for the subalkaline magmas. The available Sr-Nd-Pb isotope compositions clearly attest to a major geographic variation: the southernmost lavas have lower 87Sr/86Sr and higher 143Nd/144Nd and 206Pb/204Pb ratios with respect to those erupted to the north. On the whole, the Sr-Nd-Pb isotope compositions of the southern Patagonia lavas fall within the typical range of within-plate continental magmas; in addition the Pb isotope ratios fall in the range of the Southern Hemisphere Dupal Pb isotope anomaly. The geochemical variations of the southern Patagonia lavas are discussed in terms of different geochemical components: depleted and enriched sub-slab asthenosphere, enriched continental lithospheric mantle, continental crust and subducted materials. The geodynamic significance is interpreted with in the

  12. Types of Cenozoic Mollusca from Java in the Martin Collection of Naturalis

    Leloux, J.; Wesselingh, F.P.


    An updated type catalogue of the Martin Collection (fossil Mollusca, predominantly from the Cenozoic of Java, Indonesia) is presented. Type specimen data, updated locality data, and illustrations are given.

  13. Recurrence models of volcanic events

    An assessment of the risk of future volcanism has been conducted for isolation of high-level radioactive waste at the potential Yucca Mountain site in southern Nevada. Volcanism studies for the Yucca Mountain Site Characterization Project have progressed to a sufficient degree that it is now prudent to work toward concluding aspects of the work. An advantage of a probabilistic approach to volcanic risk is that it assigns a structured formalism to the problem. This formalism subdivides a complex issue into logical sections. The significance of uncertainty or differences in scientific opinion concerning volcanism issues can be tested for each section of a probabilistic problem. The perspective for making judgement of significance for volcanism studied are the regulatory requirements for assessing the suitability of the potential Yucca Mountain site. This paper attempts to begin the process of helping establish the probabilistic framework for making those judgement. There are three objectives. First, the authors describe the tripartite probability used to define the risk of volcanism and the geologic assumptions required for the probability model. Second, the authors examine and define the first part of this probability, the recurrence of volcanic events. Studies are reviewed from the volcanological literature where time-volume behavior of volcanic centers and fields have been evaluated. These evaluations include both conventional statistical analysis of time-series of volcanic events and applications using newly developing concepts of fractal analysis and deterministic chaos. Third, the authors tabulate past calculations and derive new values for the recurrence of volcanic events using a simple Poison model

  14. Cenozoic tectonics of the Tuz Gölü Basin (Central Anatolian Plateau, Turkey)

    FERNÁNDEZ-BLANCO, David; BERTOTTI, Giovanni; ÇİNER, T. Attila


    We present a new 3D geologic model for the architecture and Cenozoic tectonic evolution of the Tuz Gölü Basin, a major sedimentary basin in the Central Anatolian orogenic plateau. This model is grounded on 7 depth-converted seismic reflection profiles in combination with the analysis of backstripped subsidence curves, isochore maps, and a palinspastically restored cross-section. Two stages of basin formation are detected during Cenozoic times. During the Palaeogene, around 2 km of basement su...

  15. 40Ar/39Ar Geochronology, Isotope Geochemistry (Sr, Nd, Pb), and petrology of alkaline lavas near Yampa, Colorado: migration of alkaline volcanism and evolution of the northern Rio Grande rift

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


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

  16. Petrogenesis of OIB-like volcanic rocks in a continental collision zone: Late Cenozoic magmatism of eastern Iran

    Kheirkhah, M.; Neill, I.; Allen, M. B.


    Hundreds of compositionally diverse volcanoes have erupted on the Turkish–Iranian Plateau in the last 15 Myr, attributed to one or more of the processes of Middle Miocene Tethyan slab break-off, localised lithospheric delamination and small-scale convection. Magmatism post-dates the initial Late Eocene or Early Oligocene Arabia–Eurasia collision by >10 Myr. By contrast, in the east of the plateau in Eastern Iran there has been intermittent magmatism from the Late Oligocene to the Quaternary. ...

  17. Cenozoic intracontinental deformation of the Kopeh Dagh Belt, Northeastern Iran

    Chu, Yang; Wan, Bo; Chen, Ling; Talebian, Morteza


    Compressional intracontinental orogens represent large tectonic zones far from plate boundaries. Since intracontinental mountain belts cannot be framed in the conventional plate tectonics theory, several hypotheses have been proposed to account for the formations of these mountain belts. The far-field effect of collision/subduction at plate margins is now well accepted for the origin and evolution of the intracontinental crust thickening, as exemplified by the Miocene tectonics of central Asia. In northern Iran, the Binalud-Alborz mountain belt witnessed the Triassic tectonothermal events (Cimmerian orogeny), which are interpreted as the result of the Paleotethys Ocean closure between the Eurasia and Central Iran blocks. The Kopeh Dagh Belt, located to the north of the Binalud-Alborz Belt, has experienced two significant tectonic phases: (1) Jurassic to Eocene rifting with more than 7 km of sediments; and (2) Late Eocene-Early Oligocene to Quaternary continuous compression. Due to the high seismicity, deformation associated with earthquakes has received more and more attention; however, the deformation pattern and architecture of this range remain poorly understood. Detailed field observations on the Cenozoic deformation indicate that the Kopeh Dagh Belt can be divided into a western zone and an eastern zone, separated by a series of dextral strike-slip faults, i.e. the Bakharden-Quchan Fault System. The eastern zone characterized by km-scale box-fold structures, associated with southwest-dipping reverse faults and top-to-the NE kinematics. In contrast, the western zone shows top-to-the SW kinematics, and the deformation intensifies from NE to SW. In the northern part of this zone, large-scale asymmetrical anticlines exhibit SW-directed vergence with subordinate thrusts and folds, whereas symmetrical anticlines are observed in the southern part. In regard to its tectonic feature, the Kopeh Dagh Belt is a typical Cenozoic intracontinental belt without ophiolites or

  18. ACEX: A First Look at Arctic Ocean Cenozoic History

    Moran, K.; Backman, J.


    The first Integrated Ocean Drilling Program mission specificplatform expedition (ACEX - Arctic Coring Expedition) drilled and recovered core from five holes at four sites through Cenozoic sediments draping the crest of the Lomonosov Ridge in the central Arctic Ocean. Coring continued into the underlying Cretaceous sedimentary bedrock. Sites are located only a few nautical miles apart along a single seismic line (AWI-91090), showing an identical and coherent Cenozoic seismostratigraphy. Preliminary results from shipboard investigations of core-catcher-based bio- and lithostratigraphy, pore water analyses and core logger data describe a thick (~160 m) middle Miocene through Pleistocene sequence that shows large amplitude, cyclic variability in the density, magnetic susceptibility and acoustic velocity of the sediments. Sediments are largely carbonate free. Pleistocene sedimentation rates are close to 3 cm/ka, whereas Pliocene sediments are by-and-large missing. A sharp change in physical properties at ~200 m defines the transition into a 200+ m thick Paleogene sequence that is initially dominated by large numbers of dinoflagellate cysts. The early Miocene, Oligocene and late Eocene appear to be largely missing in a hiatus. However, a 32 m thick interval separates the overlying middle Miocene from the underlying middle Eocene and presumably preserves some of the early Neogene and late Paleogene sections. Dinoflagellate cysts, diatoms, ebridians and silicoflagellates are common to abundant in the middle Eocene section, which bottoms in a spectacular layer showing massive occurrences of glochidia and massulae (megaspores) of the freshwater hydropterid fern Azolla (duckweed) at the early/middle Eocene boundary (~306 m), suggesting strongly reduced surface water salinity or perhaps even a brief episode of fresh water conditions at the surface. Biosilica is not present prior to the late early Eocene (~320 m). The (sub-) tropical dinoflagellate species Apectodinium augustum

  19. Late Cretaceous and Cenozoic exhumation history of the Malay Peninsula

    François, Thomas; Daanen, Twan; Matenco, Liviu; Willingshofer, Ernst; van der Wal, Jorien


    The evolution of Peninsular Malaysia up to the collisional period in the Triassic is well described but the evolution since the collision between Indochina and the Sukhothai Arc in Triassic times is less well described in the literature. The processes affecting Peninsular Malaysia during the Jurassic up to current day times have to explain the emplacement multiple intrusions (the Stong Complex, and the Kemahang granite), the Jurassic/Cretaceous onland basins, the Cenozoic offshore basins, and the asymmetric extension, which caused the exhumation of Taku Schists dome. The orogenic period in Permo-Triassic times, which also formed the Bentong-Raub suture zone, resulted in thickening of the continental crust of current day Peninsular Malaysia due to the collision of the Indochina continental block and the Sukhothai Arc, and is related to the subduction of oceanic crust once present between these continental blocks. The Jurassic/Cretaceous is a period of extension, resulting in the onland Jurassic/Cretaceous basins, synchronous melting of the crust, resulting in the emplacement Stong Complex and the Kemahang granite and thinning of the continental crust on the scale of the Peninsular, followed by uplift of the Peninsular. Different models can explain these observations: continental root removal, oceanic slab detachment, or slab delamination. These models all describe the melting of the lower crust due to asthenospheric upwelling, resulting in uplift and subsequent extension either due to mantle convective movements or gravitational instabilities related to uplift. The Cenozoic period is dominated by extension and rapid exhumation in the area as documented by low temperature thermocrological ages The extension in this period is most likely related to the subduction, which resumed at 45 Ma, of the Australian plate beneath the Eurasian plate after it terminated in Cretaceous times due to the collision of an Australian microcontinental fragment with the Sunda margin in the

  20. Closer look at lunar volcanism

    Although the American Apollo and Soviet Luna missions concentrated on mare basalt samples, major questions remain about lunar volcanism. Lunar field work will be indispensable for resolving the scientific questions about ages, compositions, and eruption processes of lunar volcanism. From a utilitarian standpoint, a better knowledge of lunar volcanism will also yield profitable returns in lunar base construction (e.g., exploitation of rille or lava-tube structures) and in access to materials such as volatile elements, pure glass, or ilmenite for lunar industry

  1. Interaction between Cenozoic fault activity and sediment influx in the Arctic region: new thermochronologic data and seismic study

    Bigot-Buschendorf, Maelianna; Mouthereau, Frédéric; Fillon, Charlotte; Loget, Nicolas; Labrousse, Loïc; Werner, Philippe; Bernet, Matthias; Ehlers, Todd


    The Alaskan Brooks Range and its canadian counterpart, the British Mountains result from the Meso-Cenozoic collision of the Arctic continental margin with accreted volcanic arcs and adjacent continental terranes. Because of its location and known potential for oil industries, more attention has been brought to this area for the last few years. While the timing of collisional events, duration, and rates of exhumation associated with mountain building is now better understood, the causes of these exhumation events are still largely unknown. Published constraints and our present data are consistent with progressive cooling from 105 to 25 Ma, with rates of exhumation constant across the range until 35-25 Ma. From 35 Ma onwards, exhumation likely slowed in concomitance with underplating/duplexing in the inner part of the belt (Doonerak window) and activation of the northernmost thrust. The earliest cooling stage (from 100 Ma) marking the onset of the Brookian orogeny is recorded by a low order coarsening upward sequence in the foreland. On the contrary, the latest stage of cooling (at 35 Ma) is not linked to the construction of the range but more likely due to a reorganization of the wedge possibly related to changes in the regional climatic or geodynamic boundary conditions. First, we aim at reconstructing the time-temperature evolution of the British Mountains by combining new (U-Th)/He and fission-tracks ages on zircon and apatite ; our first thermochronological data in the British Mountains show ages ranging from 110 to 25 Ma from range to basin. These data will permit to reconstruct the thermal history of the British Mountains and its basin, and to estimate the exhumation rates associated to the main unities. Then, we also examine the role of climate during the Tertiary period. Some markers indicate a climate change at this period which could be registered in the sedimentation. Therefore we determine the part of climate by analyzing seismic lines in the Beaufort

  2. Evidence for the Mesozoic and Cenozoic Evolution of the Lithosphere in the Trans-European Suture Zone from Surface Wave Tomography

    Meier, Thomas; Soomro, Riaz; Lebedev, Sergei; Weidle, Christian; Viereck, Lothar; Behrmann, Jan; Cristiano, Luigia; Hanemann, Ricarda


    The Trans-European Suture Zone marks the transition between the East European Craton and Phanerozoic central Europe. Subduction of the Thor ocean and collision of Avalonia resulted in a Caledonian terrane assemblage that has been strongly affected by Permian volcanism, sedimentation in Post-Permian basins and recently by Cenozoic inversion tectonics. Whereas the structure of the crust in the area has been extensively studied by Deep Seismic Soundings, properties of the subcontinental mantle lithosphere are less well known. Surface waves are well suited to study the structure of the lithosphere and the sublithospheric mantle being mainly sensitive to the S-wave velocity structure at those depths. It has been shown before that the Tornquist-Teisseyre Zone representing the boundary to the East-European Craton in the southwest of the Trans-European Suture Zone is associated with a sharp transition between thick cratonic lithosphere in the northeast and thinner lithosphere to the southwest. Here we present results of a tomographic surface wave study based on automated broad-band measurements of average inter-station Rayleigh wave phase velocities providing higher resolution especially at lithospheric depths. All available broad-band recordings including data of temporary deployments like the TOR and PASSEQ experiments have been processed. At shorter periods phase velocities are sensitive to the sedimentary basins providing a 3D image of average shear-wave velocities. At intermediate periods differences in the crustal thickness and the structure of the uppermost mantle in the regions of the North German Basin and the Polish Basin become obvious. The latter is characterized by larger crustal thickness and rather low sub-Moho S-wave velocities. Also, lithospheric thickness varies along the Trans-European Suture Zone. In the region of the Sorgenfrei-Tornquist Zone a rather gradual decrease of lithospheric thickness towards central Europe is observed, whereas a shallow

  3. Successor Characteristics of the Mesozoic and Cenozoic Songliao Basins

    LI Zhongquan; Timothy KUSKY; YING Danlin; GUO Xiaoyu; LI Hongkui


    The Songliao basin is a complex successor basin that was initiated in the Mesozoic and experienced multiple periods of reactivation. Based on seismic and drilling data, as well as regional geologic research, we suggest that the Songliao basin contains several different successor basins resting on top of Carboniferous-Permian folded strata forming the basement to the Songliao basin. These basins include the Triassic-Mid Jurassic Paleo-foreland basin, the Late Jurassic-Early Cretaceous downfaulted basin, and an early Cretaceous depressed basin (since the Denglouku Group). This paper presents a systematic study of the basin-mountain interactions, and reveals that there are different types of prototype basin at different geologic times. These prototype basins sequentially superimposed and formed the large Songliao basin. Discovery of the Triassic-early Middle Jurassic paleo-foreland basin fills a Triassic-early Middle Jurassic gap in the geologic history of the Songliao basin. The paleoforeland basin, downfaulted basin, and depressed thermal subsidence basin all together represent the whole Mesozoic-Cenozoic geologic history and deformation of the Songliao basin. Discovery of the Triassic-early Middle Jurassic paleo-foreland basin plays an important role both for deep natural gas exploration and the study of basin-mountain coupling in north China and eastern China in general. This example gives dramatic evidence that we should give much more attention to the polyphase tectonic evolution of related basins for the next phase of exploration and study.

  4. Continental erosion and the Cenozoic rise of marine diatoms

    Cermeño, Pedro; Falkowski, Paul G.; Romero, Oscar E.; Schaller, Morgan F.; Vallina, Sergio M.


    Marine diatoms are silica-precipitating microalgae that account for over half of organic carbon burial in marine sediments and thus they play a key role in the global carbon cycle. Their evolutionary expansion during the Cenozoic era (66 Ma to present) has been associated with a superior competitive ability for silicic acid relative to other siliceous plankton such as radiolarians, which evolved by reducing the weight of their silica test. Here we use a mathematical model in which diatoms and radiolarians compete for silicic acid to show that the observed reduction in the weight of radiolarian tests is insufficient to explain the rise of diatoms. Using the lithium isotope record of seawater as a proxy of silicate rock weathering and erosion, we calculate changes in the input flux of silicic acid to the oceans. Our results indicate that the long-term massive erosion of continental silicates was critical to the subsequent success of diatoms in marine ecosystems over the last 40 My and suggest an increase in the strength and efficiency of the oceanic biological pump over this period.

  5. Late Cenozoic sedimentary and tectonic history of south Buton, Indonesia

    Fortuin, A. R.; De Smet, M. E. M.; Hadiwasastra, S.; Van Marle, L. J.; Troelstra, S. R.; Tjokrosapoetro, S.

    A description and interpretation are given of the Upper Cenozoic sedimentary record of south Buton. Various sections and outcrops were studied and sampled for their microfossil content, to provide age and paleobathymetrical data. Together with information from the literature, these data from the base for a geohistory analysis to evaluate the vertical motions. Deposition started some 11 Ma ago, after the main deformation of the island, which was related to the collision of a microplate carrying Buton, with the southeast arm of Sulawesi. Coarse and fine terrigenous debris accumulated in a rapidly subsiding foreland basin; subsidence may have exceeded 100 cm/ka. When the rate of subsidence decreased a late Miocene-early Pliocene period of quiet pelagic sedimentation followed. From the late Pliocene onwards (around 3.5 Ma BP) an overall uplift took place, with rates between 30-120 cm/ka. This drastic change is explained by the collision of Buton with a submerged microcontinent that presently forms the Tukang Besi platform, situated southeast of Buton, which interaction resulted in wrench type tectonics and a clockwise rotation of over 60° for south Buton.

  6. Mid Cenozoic freshwater wetlands of the Sunda region

    Robert J. Morley


    Full Text Available The Sunda region was the scene of widespread rifting during the mid-Cenozoic, resulting in the development of numerous large lake-filled rifts, analogous in scale to the rift valley system of East Africa. The Tonle Sap in Cambodia forms the closest modern analogue for these lakes in the Southeast Asian region. Many of the palaeolakes were long lived, continuing uninterrupted as open lakes for several millions of years during the Oligocene. Smaller rift systems infilled with fluvial sediments, but the larger ones remained as lakes, and with Late Oligocene subsidence, were transformed by brackish, and in the earliest Miocene, by marine incursion, into large inland seas. These seas reached their greatest extent at the time of the mid Miocene thermal maximum. This paper describes the development and eventual demise of these lakes following marine transgression, and, based on their rich content of pollen and spores, illustrates the variety of fresh and brackish water swamp communities which developed around their margins. The marginal swamps can be divided into: i seasonally inundated swamps, mainly during the Oligocene, characterised by Barringtonia, Lagerstroemia and grasses/sedges; ii fern swamps and iii from the Late Oligocene onward alluvial swamps, often characterised by Pandanus; and iv peat swamps. The latter can be differentiated into kerapah peat swamps, first occurring during the Oligocene, and basinal peat swamps, becoming widespread from the Early Miocene onward.

  7. Detecting Volcanism on Extrasolar Planets

    Kaltenegger, L; Sasselov, D D


    The search for extrasolar rocky planets has already found the first transiting rocky super-Earth, Corot 7b, with a surface temperature that allows for magma oceans. Here we ask if we could distinguish rocky planets with recent major volcanism by remote observation. We develop a model for volcanic eruptions on an Earth-like exoplanet based on the present day Earth, derive the observable features in emergent and transmission spectra for multiple scenarios of gas distribution and cloudcover. We calculate the observation time needed to detect explosive volcanism on exoplanets in primary as well as secondary eclipse and discuss the likelihood of observing volcanism on transiting Earth to super-Earth sized exoplanets. We find that sulfur dioxide from large explosive eruptions does present a spectral signal that is remotely detectable especially for secondary eclipse measurements around the closest stars using ground based telescopes, and report the frequency and magnitude of the expected signatures. Transit probabi...

  8. Volcanology: Volcanic bipolar disorder explained

    Jellinek, Mark


    Eruptions come in a range of magnitudes. Numerical simulations and laboratory experiments show that rare, giant super-eruptions and smaller, more frequent events reflect a transition in the essential driving forces for volcanism.

  9. Monogenetic volcanic hazards and assessment

    Connor, C.; Connor, L. J.; Richardson, J. A.


    Many of the Earth's major cities are build on the products of monogenetic volcanic eruptions and within geologically active basaltic volcanic fields. These cities include Mexico City (Mexico), Auckland (New Zealand), Melbourne (Australia), and Portland (USA) to name a few. Volcanic hazards in these areas are complex, and involve the potential formation of new volcanic vents and associated hazards, such as lava flows, tephra fallout, and ballistic hazards. Hazard assessment is complicated by the low recurrence rate of volcanism in most volcanic fields. We have developed a two-stage process for probabilistic modeling monogenetic volcanic hazards. The first step is an estimation of the possible locations of future eruptive vents based on kernel density estimation and recurrence rate of volcanism using Monte Carlo simulation and accounting for uncertainties in age determinations. The second step is convolution of this spatial density / recurrence rate model with hazard codes for modeling lava inundation, tephra fallout, and ballistic impacts. A methodology is presented using this two-stage approach to estimate lava flow hazard in several monogenetic volcanic fields, including at a nuclear power plant site near the Shamiram Plateau, a Quaternary volcanic field in Armenia. The location of possible future vents is determined by estimating spatial density from a distribution of 18 mapped vents using a 2-D elliptical Gaussian kernel function. The SAMSE method, a modified asymptotic mean squared error approach, uses the distribution of known eruptive vents to optimally determine a smoothing bandwidth for the Gaussian kernel function. The result is a probability map of vent density. A large random sample (N=10000) of vent locations is drawn from this probability map. For each randomly sampled vent location, a lava flow inundation model is executed. Lava flow input parameters (volume and average thickness) are determined from distributions fit to field observations of the low

  10. Volcanic eruption plumes on Io

    The detection of an umbrella-shaped plume extending about 280 km above the bright limb of Io was one of the most important discoveries made during the Voyager 1 encounter with the jovian system. This discovery proves that Io is volcanically active at present, and the number and magnitude of these eruptions indicate that Io is the most volcanically active body so far discovered in the Solar System. Preliminary analyses of these eruptive plumes are presented. (U.K.)

  11. Magmatic sulfide-rich nickel-copper deposits related to picrite and (or) tholeiitic basalt dike-sill complexes-A preliminary deposit model

    Schulz, Klaus J.; Chandler, Val W.; Nicholson, Suzanne W.; Piatak, Nadine M.; Seal, Robert R., II; Woodruff, Laurel G.; Zientek, Michael L.


    Magmatic sulfide deposits containing nickel (Ni) and copper (Cu), with or without (?) platinum-group elements (PGEs), account for approximately 60 percent of the world's Ni production and are active exploration targets in the United States and elsewhere. On the basis of their principal metal production, magmatic sulfide deposits in mafic rocks can be divided into two major types: those that are sulfide-rich, typically with 10 to 90 percent sulfide minerals, and have economic value primarily because of their Ni and Cu contents; and those that are sulfide-poor, typically with 0.5 to 5 percent sulfide minerals, and are exploited principally for PGE. Because the purpose of this deposit model is to facilitate the assessment for undiscovered, potentially economic magmatic Ni-Cu?PGE sulfide deposits in the United States, it addresses only those deposits of economic significance that are likely to occur in the United States on the basis of known geology. Thus, this model focuses on deposits hosted by small- to medium-sized mafic and (or) ultramafic dikes and sills that are related to picrite and tholeiitic basalt magmatic systems generally emplaced in continental settings as a component of large igneous provinces (LIPs). World-class examples (those containing greater than 1 million tons Ni) of this deposit type include deposits at Noril'sk-Talnakh (Russia), Jinchuan (China), Pechenga (Russia), Voisey's Bay (Canada), and Kabanga (Tanzania). In the United States, this deposit type is represented by the Eagle deposit in northern Michigan, currently under development by Kennecott Minerals.

  12. Yanshan, Gaoshan-Two Active Volcanoes of the Volcanic Cluster in Arshan, Inner Mongolia

    Bai Zhida; Tian Mingzhong; Wu Fadong; Xu Debing; Li Tuanjie


    The volcanic cluster in Arshan, Inner Mongolia, is located in the west of the middle section of the Da Hinggan Mountains. There are more than forty Cenozoic volcanoes among which the Yanshan Volcano and Gaoshan Volcano are the active ones in broad sense and basaltic central vents. Arshan is a newly found volcanic active region in the Chinese continent. The volcanoes are perfectly preserved and composed of cinder cones, pyroclastic sheets and lava flows. Their cones are grand and the Gaoshan cone is about 362m high, and the depth of the Yanshan crater is about 140m. The pyroclastic sheet is mainly made up of scoria, and the distribution area of scoria with thickness more than 1m is about 27km2. There are two Carbonized-wood sites in the pyroclastic sheet and the 14C datings indicate ages of 1990 ± 100a B. P and 1900 ±70a B. P, which are rectified by dendrodating. Basaltic lava flows are uncovered, and they change from pahoehoe in the early stage to aa in the later stage. There are lots of perfect fumarolic cones, fumarolic dishes and lava tumulus in the front zones. The spread of lava flow is controlled by the local topography and its main body flowed northwestwards covering the Holocene rivers and swamp deposits and blocked up the Halahahe river and its branches to create six lava-dam lakes. For these distinguishing features, Arshan volcanic cluster could be called another natural "Volcano Museum".

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

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


    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

  14. Various depths of origin of clinopyroxene megacrysts from Cenozoic alkaline lavas of occurrences in Lower Silesia (SW Poland)

    Lipa, Danuta; Puziewicz, Jacek; Ntaflos, Theodoros; Woodland, Alan


    The Polish part of Central European Volcanic Province consists of more than 300 outcrops of Cenozoic volcanic rocks (Badura et al., 2006). Some of these alkaline lavas contain mantle xenoliths and megacrysts of clinopyroxene and plagioclase. We studied clinopyroxene megacrysts from three sites in Lower Silesia: (1) the Księginki nephelinite (Lubań-Frydlant volcanic complex, dated at 34.6  3.1 Ma), (2) the Ostrzyca Proboszczowicka basanite (Złotoryja-Jawor complex, probably of Miocene age) and (3) the Lutynia basanite (Lądek Zdrój volcanic complex, dated at 4.56  0.2 Ma; K-Ar datings after Pécskay & Birkenmajer, 2013). We determined major (electron microprobe) and trace (LA-ICP-MS) element compositions, Fe3+/ƩFe (Mössbauer spectroscopy), as well as 87Sr/86Sr and 143Nd/144Nd isotopic ratios. The megacrysts from Księginki are typically up to 5 cm and have the composition of diopside and augite (Puziewicz et al., 2011), Mg# 0.79 - 0.87, Fe3+/ƩFe 0.31 - 0.36, 87Sr/86Sr 0.703323 - 0.703496 and 143Nd/144Nd 0.512890 - 0.512904. Typical REE concentrations are 0.78 - 10.5 x PM, TE patterns show strong negative Pb and weaker Sr, Zr anomalies. The megacrysts from Ostrzyca are up to 3 cm, have the composition of diopside (Lipa et al., 2014), Mg# 0.61 - 0.70, Fe3+/ƩFe 0.38 - 0.45, 87Sr/86Sr 0.703221 - 0.703226 and 143Nd/144Nd 0.512906 - 0.512911. Typical REE values range from 1.81 to 22.9 x PM, TE patterns show strong negative Pb and weaker Ti anomalies and characteristic positive Ta, Zr, Hf anomalies. Megacrysts from Lutynia, up to 4 cm, have the composition of augite and diopside, Mg# from 0.77 - 0.97, Fe3+/ƩFe 0.33 - 0.37, 87Sr/86Sr 0.703261 - 0.703295 and 143Nd/144Nd 0.512898 - 0.512910. REE concentrations vary from 0.52 to 7.8 x PM, but one megacryst shows strong depletion in LREE (to 0.01 x PM). TE patterns reveal strong negative Pb and weaker Sr, Zr, Y anomalies and the LREE depleted megacryst has positive Pb anomaly. The knowledge on Fe3+/ƩFe allowed

  15. Volcanism, sedimentation, K/Ar and palynology studies, Yayu and Delbi-Moye Basins, Southwestern Plateau of Ethiopia

    Wolela, A.


    Major element, K/Ar, sedimentation and palynology data are reported on Tertiary volcanic and sedimentary rocks from the Yayu and Delbi-Moye Basins, SW Ethiopia. In the Yayu and Delbi-Moye Basins, pre-rift volcanic (basalts) and post-rift volcanic (basalts) are separated by coal and oil shale-bearing sedimentary rocks. The basalts are tholeiitic in composition. The K/Ar data on the volcanic rocks range from 10.98 ± 0.55 Ma (Lower Miocene i.e. Tortonian) to 111.19 ± 2.83 Ma (Early Cretaceous i.e. Aptian). Inter-Trappean coal and oil shale-bearing sedimentary rocks are widely distributed in the Yayu and Delbi-Moye Basins. The NNW-SSE fault system developed grabens and half-grabens for the deposition of coal and oil shale-bearing sedimentary rocks. The sedimentary successions are dominated by fine to medium-grained sandstones, siltstones, mudstones, carbonaceous shales, carbonaceous claystones, coal and oil shale seams, and are characterized by meandering river and lacustrine depositional environments. Fresh water algae Botryococcus brauni, Pediastrum sp., Polypodii sporites favus and Polypodii sporites afavus and Pachydermites diederixi, are common palynomorphs in the studied coal and oil shales, and are indicators of lacustrine environment. The presence of Peregrinipollis nigericus is consistent with Oligocene to Miocene. The presence of Euphorbiaceae, Papilionacae, Melastomtaceae sp., Dodonaea, Martretia quadricornis, Rubiaceae sp. (pollen derived from tropical shrubs), Sapotaceae spp. and Meliaceae spp. are indicative of humid, tropical rainforest conditions. Extensive bio-assemblages confirm that the age of coal and oil shale-bearing sedimentary rocks to be Oligocene to Miocene.

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

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


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

  17. On water in volcanic clouds

    Durant, Adam J.


    Volcanic clouds and tephra fallout present a hazard to aviation, human and animal health (direct inhalation or ingestion, contamination of water supplies), and infrastructure (building collapse, burial of roads and railways, agriculture, abrasive and chemical effects on machinery). Understanding sedimentation processes is a fundamental component in the prediction of volcanic cloud lifetime and fallout at the ground, essential in the mitigation of these hazards. The majority of classical volcanic ash transport and dispersion models (VATDM) are based solely on fluid dynamics. The non-agreement between VATDM and observed regional-scale tephra deposit characteristics is especially obvious at large distances from the source volcano. In meteorology, the processes of hydrometeor nucleation, growth and collection have been long-established as playing a central role in sedimentation and precipitation. Taking this as motivation, the hypothesis that hydrometeor formation drives sedimentation from volcanic clouds was tested. The research objectives of this dissertation are: (1) To determine the effectiveness of tephra particles in the catalysis of the liquid water to ice phase transformation, with application to ice hydrometeor formation in volcanic clouds. (2) To determine the sedimentological characteristics of distal (100s km) tephra fallout from recent volcanic clouds. (3) To assess particle fallout rates from recent volcanic clouds in the context of observed deposit characteristics. (4) To assess the implications of hydrometeor formation on the enhancement of volcanic sedimentation and the potential for cloud destabilization from volcanic hydrometeor sublimation. Dissertation Overview. The following chapters present the analysis, results and conclusions of heterogeneous ice nucleation experiments and sedimentological characterization of several recent tephra deposits. The dissertation is organized in three chapters, each prepared in journal article format. In Chapter 1

  18. Changing source regions of magmas and crustal growth in the Trans-Himalayas: evidence from the Chalt volcanics and Kohistan batholith, Kohistan, northern Pakistan

    Petterson, M. G.; Windley, B. F.


    The Kohistan batholith and Chalt volcanics form a major part of the Kohistan island arc terrane in northern Pakistan. They record some 70-80 Ma of magmatism within the northwestern Himalayan orogen; the Chalt volcanics are Albian-Aptian (mid-Cretaceous), and currently available Rb sbnd Sr age data for the batholith indicate an intrusive age span of 102 to 30 Ma. The volcanics are composed of medium-K, calc-alkaline andesites and low-K, high-Mg, tholeiites, some of which have boninitic and basaltic komatiitic chemistry. Three intrusive stages are recognised in the batholith: (1) (110-90 Ma) comprises low-K trondhjemites and medium-high-K calc-alkaline gabbro-diorites with associated hornblendite cumulates; (2) (85-40 Ma) comprises low-high-K, calc-alkaline gabbro-diorites (with hornblendite cumulates, granodiorites and granites; and (3) (circa 30 Ma) comprises biotite ± muscovite ± garnet leucogranites. 87Sr/ 86Sr 0 for the batholith range between 0.7039 and 0.7052. Four magmatic source regions (Sce 1-Sce 4) have been identified. Sce 1 is a variably metasomatised mantle wedge situated above an active subduction zone during stages 1 and 2. Sce 2 is a harzburgite depleted with respect to major elements and incompatibles, whilst retaining "subduction-related" trace element ratios. Sce 2 melted during stage 1 within a fore-arc position during the subduction of young, hot oceanic crust to provide the necessary extra thermal input for harzburgite anatexis. Melts from Sce 2 produced the high-Mg tholeiitic volcanics. Sce 3 melted during stage 1 to produce the low-K trondhjemites, and it is envisaged as incompatible element-depleted primitive arc crust with a similar composition to the depleted Chalt volcanics. Sce 4 melted at 30 Ma during stage 3 as India underthrust Eurasia: frictional heating and dehydration of the Indian plate caused crustal anatexis within the deep Kohistan arc and these melts formed the stage 3 leucogranites. The low 87Sr/ 86Sr initial ratios for the

  19. Climatic impact of volcanic eruptions

    Rampino, Michael R.


    Studies have attempted to 'isolate' the volcanic signal in noisy temperature data. This assumes that it is possible to isolate a distinct volcanic signal in a record that may have a combination of forcings (ENSO, solar variability, random fluctuations, volcanism) that all interact. The key to discovering the greatest effects of volcanoes on short-term climate may be to concentrate on temperatures in regions where the effects of aerosol clouds may be amplified by perturbed atmospheric circulation patterns. This is especially true in subpolar and midlatitude areas affected by changes in the position of the polar front. Such climatic perturbation can be detected in proxy evidence such as decrease in tree-ring widths and frost rings, changes in the treeline, weather anomalies, severity of sea-ice in polar and subpolar regions, and poor grain yields and crop failures. In low latitudes, sudden temperature drops were correlated with the passage overhead of the volcanic dust cloud (Stothers, 1984). For some eruptions, such as Tambora, 1815, these kinds of proxy and anectdotal information were summarized in great detail in a number of papers and books (e.g., Post, 1978; Stothers, 1984; Stommel and Stommel, 1986; C. R. Harrington, in press). These studies lead to the general conclusion that regional effects on climate, sometimes quite severe, may be the major impact of large historical volcanic aerosol clouds.

  20. Atmospheric chemistry in volcanic plumes.

    von Glasow, Roland


    Recent field observations have shown that the atmospheric plumes of quiescently degassing volcanoes are chemically very active, pointing to the role of chemical cycles involving halogen species and heterogeneous reactions on aerosol particles that have previously been unexplored for this type of volcanic plumes. Key features of these measurements can be reproduced by numerical models such as the one employed in this study. The model shows sustained high levels of reactive bromine in the plume, leading to extensive ozone destruction, that, depending on plume dispersal, can be maintained for several days. The very high concentrations of sulfur dioxide in the volcanic plume reduces the lifetime of the OH radical drastically, so that it is virtually absent in the volcanic plume. This would imply an increased lifetime of methane in volcanic plumes, unless reactive chlorine chemistry in the plume is strong enough to offset the lack of OH chemistry. A further effect of bromine chemistry in addition to ozone destruction shown by the model studies presented here, is the oxidation of mercury. This relates to mercury that has been coemitted with bromine from the volcano but also to background atmospheric mercury. The rapid oxidation of mercury implies a drastically reduced atmospheric lifetime of mercury so that the contribution of volcanic mercury to the atmospheric background might be less than previously thought. However, the implications, especially health and environmental effects due to deposition, might be substantial and warrant further studies, especially field measurements to test this hypothesis. PMID:20368458

  1. Granulite xenoliths from Cenozoic Basalts in SE China provide geochemical fingerprints to distinguish lower crust terranes from the North and South China tectonic blocks

    Yu, Jin-Hai; Xu, Xisheng; O'Reilly, Suzanne Y.; Griffin, W. L.; Zhang, Ming


    A large suite of lower crustal xenoliths from Cenozoic basaltic rocks from three widely spaced localities in the eastern part of the South China Block (SCB; Xilong, Qilin and Leizhou) and two localities (Nushan and Guizishan) close to the suture between the North and South China Blocks in Southeast China has been studied in detail. They are used to define the nature of the lower crust beneath these regions and to define two distinct types of lithospheric domains resulting from different tectonic episodes. Lower crustal xenoliths from the Nushan area have distinctive petrologic and geochemical (including isotopic) characteristics indicating formation by underplating of continental basaltic magmas around the crust-mantle boundary. Geochemistry of these granulites demonstrates that an isotopically enriched old source component had played a significant role in the formation of the Nushan xenoliths. The lower crustal xenoliths from the South China Block reveal different origins and source compositions from those from the Nushan area. The South China Block xenoliths are considered to be derived from the underplating of continental arc-type basaltic magmas, but also show evidence of significant assimilation and fractional crystallisation (AFC) that produced abundant cumulates and fractionated liquids with strong crustal contamination signatures. They are geochemically and isotopically similar to the outcropping Late Mesozoic gabbros and basalts in the same region and are inferred to be their underplated high-pressure analogues and products of AFC with the lower crustal sources parental to the more silicic Mesozoic outcropping magmatic rocks. These Mesozoic basaltic magmas from the South China Block are geochemically distinct from the Cenozoic basaltic volcanics in this region, indicating a secular source change from a continental arc setting to an intraplate extensional regime. This significant change from Mesozoic to Cenozoic may indicate eastward movement of the

  2. Volcanic Eruptions in Kamchatka


    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Sheveluch Stratovolcano Click on the image for full resolution TIFF Klyuchevskoy Stratovolcano Click on the image for full resolution TIFF One of the most volcanically active regions of the world is the Kamchatka Peninsula in eastern Siberia, Russia. It is not uncommon for several volcanoes to be erupting at the same time. On April 26, 2007, the Advanced Spaceborne Thermal Emission and Reflection Radioneter (ASTER) on NASA's Terra spacecraft captured these images of the Klyuchevskoy and Sheveluch stratovolcanoes, erupting simultaneously, and 80 kilometers (50 miles) apart. Over Klyuchevskoy, the thermal infrared data (overlaid in red) indicates that two open-channel lava flows are descending the northwest flank of the volcano. Also visible is an ash-and-water plume extending to the east. Sheveluch volcano is partially cloud-covered. The hot flows highlighted in red come from a lava dome at the summit. They are avalanches of material from the dome, and pyroclastic flows. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra spacecraft. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and

  3. Oligocene and Miocene arc volcanism in northeastern California: evidence for post-Eocene segmentation of the subducting Farallon plate

    Colgan, J.P.; Egger, A.E.; John, D.A.; Cousens, B.; Fleck, R.J.; Henry, C.D.


    The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava flows overlain by hornblende and pyroxene andesite pyroclastic flows and minor lava flows. Both sequences vary in thickness (0–2 km) along strike and are inferred to be the erosional remnants of one or more large, partly overlapping composite volcanoes. No volcanic rocks were erupted in the Warner Range between ca. 24 and 16 Ma, although minor distally sourced silicic tuffs were deposited during this time. Arc volcanism resumed ca. 16 Ma with eruption of basalt and basaltic andesite lavas sourced from eruptive centers 5–10 km south of the relict Oligocene centers. Post–16 Ma arc volcanism continued until ca. 8 Ma, forming numerous eroded but well-preserved shield volcanoes to the south of the Warner Range. Oligocene to Late Miocene volcanic rocks in and around the Warner Range are calc-alkaline basalts to andesites (48%–61% SiO2) that display negative Ti, Nb, and Ta anomalies in trace element spider diagrams, consistent with an arc setting. Middle Miocene lavas in the Warner Range are distinctly different in age, composition, and eruptive style from the nearby Steens Basalt, with which they were previously correlated. Middle to Late Miocene shield volcanoes south of the Warner Range consist of homogeneous basaltic andesites (53%–57% SiO2) that are compositionally similar to Oligocene rocks in the Warner Range. They are distinctly different from younger (Late Miocene to Pliocene) high-Al, low-K olivine tholeiites, which are more mafic (46%–49% SiO2), did not build large edifices, and are thought to be related to backarc extension. The Warner Range is ∼100 km east of the

  4. Occurrence of Tertiary bimodal volcanism in the Mucuri Basin; Ocorrencia de vulcanismo bimodal de idade terciaria na Bacia de Mucuri

    Gomes, Newton Souza; Suita, Marcos Tadeu de Freitas [Universidade Federal de Ouro Preto (UFOP). Escola de Minas. Dept. de Geologia (Brazil)], e-mails:,


    Since the last century two distinct ages of magmatic activity have been recognized in the Espirito Santo and Mucuri basins. The first, interpreted as Cretaceous, is related to the South Atlantic opening and is registered by its tholeiitic basalts of the Barremian aged Cabiunas Formation. The second and most expressive volcanic activity in the basin was formed during Tertiary times and generated basalts described as of an alkaline nature, from the Abrolhos Formation. Recent studies of core samples obtained from two wells made by PETROBRAS in the offshore part of the Mucuri Basin identified volcanic rocks of intermediate to acid nature on the top of the Abrolhos Formation. The presence of rhyolites and trachytes on the top of basalts characterized for the first time a bimodal volcanism in the submersed part of this basin. In both these lithologies, the substitution of the matrix minerals by carbonate and zeolites, is probably due to the interaction of the rocks with seawater. The two sampled wells are something like 120km apart, which suggests that due to small lateral continuity, characteristic of acid to intermediate magmas, these so distant occurrences should reflect proximity with their volcanic conduits. The presence of volcanic rock fragments immediately overlaying the calcarenites, base of the Caravelas Formation, documented in the core samples, supports the registration of the extrusion of intermediate to acid lithotypes in the final stages of the Abrolhos volcanism. Furthermore, other occurrences of rhyolitic and ignimbrite rocks are reported over the Sao Mateus crystalline basement regions, Espirito Santo State and in the northeastern part of Minas Gerais State. Also they appear as intercalated levels in the sandstones of the Rio Doce Formation in the most southern part of Bahia State and could have a cogenetic character and be related to the ending of the Abrolhos Tertiary magmatism the dimension of which has been underestimated until the present

  5. Petrology and geochemistry of the Salma dike, Raniganj coalfield (Lower Gondwana), eastern India: linkage with Rajmahal or Deccan volcanic activity?

    Paul, D.K. [Presidency College, Calcutta (India). Dept. of Geology


    The Gondwana (Early Permian to Early Cretaceous) basins of eastern India have been intruded by ultramafic-ultrapotassic (minette, lamproite and orangeite) and mafic (dolerite) rocks. The Salma dike is the most prominent among mafic intrusives in the Raniganj basin. This dike is tholeiitic in composition; MgO varies from 5.4 to 6.3% and the mg number from 54 to 59. In general, the major and trace element abundances are uniform both along and across the strike. There is geochemical and mineralogical evidence for fractional crystallization. The chondrite normalized REE pattern of the Salma dike (La/Yb{sub n} = 3.5) is similar to that of Deccan dikes of the Son-Narmada rift zone, western India. Sr-87/Sr-86 varies from 0.70552 to 0.70671 suggesting assimilation of crustal material. Some trace element abundances (e.g. Ti, Zr, Y) of the Salma dike are comparable to Group I Rajmahal basalts. The Ar-40/Ar-39 whole rock age of 65 Ma for the Salma dike is less than the ca. 114 Ma age for the Rajmahal basalt, but is similar to the generally accepted age for Deccan volcanic rocks. Despite geographical proximity with the Rajmahal basalt, the Salma dike is believed to be related to late phase of Deccan volcanic activity.

  6. Geopulsation, Volcanism and Astronomical Periods

    Yang Xuexiang; Chen Dianyou; Yang Xiaoying; Yang Shuchen


    Volcanism is mainly controlled by the intermittent release of energy in the earth. As far as the differential rotation of the earth's inner core is concerned, the Galactic Year may change the gravitational constant G, the solar radiative quantity and the moving speed of the solar system and affect the exchange of angular momentum between core and mantle as well as the energy exchange between crust and mantle. As a result, this leads to eruptions of superplumes and magma, and controls the energy flow from core - mantle boundary (CMB) to crust. When the earth' s speed decreases, it will release a huge amount of energy. They are the reason of the correspondence of the volcanic cycles one by one with the astronomical periods one by one. According to the astronomical periods, volcanic eruptions may possibly be predicted in the future.

  7. Volcanic eruption detection with TOMS

    Krueger, Arlin J.


    The Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) is designed for mapping of the atmospheric ozone distribution. Absorption by sulfur dioxide at the same ultraviolet spectral wavelengths makes it possible to observe and resolve the size of volcanic clouds. The sulfur dioxide absorption is discriminated from ozone and water clouds in the data processing by their spectral signatures. Thus, the sulfur dioxide can serve as a tracer which appears in volcanic eruption clouds because it is not present in other clouds. The detection limit with TOMS is close to the theoretical limit due to telemetry signal quantization of 1000 metric tons (5-sigma threshold) within the instrument field of view (50 by 50 km near the nadir). Requirements concerning the use of TOMS in detection of eruptions, geochemical cycles, and volcanic climatic effects are discussed.

  8. Volcanic eruptions and solar activity

    Stothers, Richard B.


    The historical record of large volcanic eruptions from 1500 to 1980 is subjected to detailed time series analysis. In two weak but probably statistically significant periodicities of about 11 and 80 yr, the frequency of volcanic eruptions increases (decreases) slightly around the times of solar minimum (maximum). Time series analysis of the volcanogenic acidities in a deep ice core from Greenland reveals several very long periods ranging from about 80 to about 350 yr which are similar to the very slow solar cycles previously detected in auroral and C-14 records. Solar flares may cause changes in atmospheric circulation patterns that abruptly alter the earth's spin. The resulting jolt probably triggers small earthquakes which affect volcanism.

  9. The Lathrop Wells volcanic center

    The Lathrop Wells volcanic center is located 20 km south of the potential Yucca Mountain site, at the south end of the Yucca Mountain range. This paper discusses a detailed Study Plan which was prepared describing planned geochronology and field studies to assess the chronology of the Lathrop Wells volcanic center and other Quaternary volcanic centers in the region. A paper was published discussing the geomorphic and soil evidence for a late Pleistocene or Holoceno age for the main cone of the center. The purpose of this paper was to expose the ideas concerning the age of the Lathrop Wells center to scientific scrutiny. Additionally, field evidence was described suggesting the Lathrop Wells center may have formed from multiple eruptive events with significant intervals of no activity between events. This interpretation breaks with established convention in the volcanological literature that small volume basalt centers are monogenetic

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

    Hagos, Miruts; Koeberl, Christian; van Wyk de Vries, Benjamin


    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).