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Sample records for sangsang ophiolitic massifs

  1. The ophiolite massif of Kahnuj (western Makran, Southern Iran): new geological and geochronological data

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    Kananian, A.; Juteau, Th.; Bellon, H.; Darvishzadeh, A.; Sabzehi, M.; Whitechurch, H.; Ricou, L.E.

    2001-01-01

    The ophiolite massif of Kahnuj (600 km 2 ) consists, from bottom to top, of layered gabbros, isotropic gabbros and ouralite gabbros, agmatites of dioritic to plagio-granitic composition, a sheeted dyke complex and lastly a basaltic pillow lava unit. Amphiboles from gabbros were dated ( 40 K- 40 Ar ages) between 156 and 139 Ma and the agmatites are nearly contemporaneous. Potassic granitic veins dated at 93-88 Ma are related to the development of the Ganj arc complex. (authors)

  2. Mineral compositions of plutonic rocks from the Lewis Hills massif, Bay of Islands ophiolite

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    Smith, Susan E.; Elthon, Don

    1988-01-01

    Mineral compositions of residual and cumulate rocks from the Lewis Hills massif of the Bay of Islands ophiolite complex are reported and interpreted in the context of magnetic processes involved in the geochemical evolution of spatially associated diabase dikes. The mineral compositions reflect greater degrees of partial melting than most abyssal peridotites do and appear to represent the most depleted end of abyssal peridotite compositions. Subsolidus equilibration between Cr-Al spinal and olivine generally has occurred at temperatures of 700 to 900 C. The spinel variations agree with the overall fractionation of basaltic magmas producing spinels with progressively lower Cr numbers. The compositions of clinopyroxenes suggest that the fractionation of two different magma series produced the various cumulate rocks.

  3. Contrasting thermal and melting histories for segments of mantle lithosphere in the Nahlin ophiolite, British Columbia, Canada

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    McGoldrick, Siobhan; Canil, Dante; Zagorevski, Alex

    2018-03-01

    The Permo-Triassic Nahlin ophiolite is the largest and best-preserved ophiolite in the Canadian Cordillera of British Columbia and Yukon, Canada. The ophiolite is well-exposed along its 150 km length with mantle segments divisible into the Hardluck and Menatatuline massifs. Both massifs comprise mostly depleted spinel harzburgite (exchange temperatures in the mantle of the ophiolite also change systematically along strike with the degree of partial melt depletion. The temperatures recorded by REE and Ca-Mg exchange between coexisting pyroxenes require markedly higher peak temperatures and cooling rates for the Menatatuline massif (1250 °C, 0.1-0.01 °C/year) compared to the Hardluck massif (rates controlled by presence or absence of a crustal section above the mantle lithosphere, or by rapid exhumation along a detachment.

  4. The ophiolite massif of Kahnuj (western Makran, Southern Iran): new geological and geochronological data; Le massif ophiolitique de Kahnuj (Makran occidental, Iran meridional): nouvelles donnees geologiques et geochronologiques

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    Kananian, A. [University of Tarbiat Modarress, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Juteau, Th.; Bellon, H. [Universite de Bretagne Occidentale, IUEM, 29 - Brest (France); Darvishzadeh, A. [University of Teheran, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Sabzehi, M. [Geological Survey of Iran, Teheran (Iran, Islamic Republic of); Whitechurch, H. [Universite Louis Pasteur, EOST, Institut de Physique du Globe, 67 - Strasbourg (France); Ricou, L.E. [Institut de Physique du Globe, 75 - Paris (France)

    2001-05-01

    The ophiolite massif of Kahnuj (600 km{sup 2}) consists, from bottom to top, of layered gabbros, isotropic gabbros and ouralite gabbros, agmatites of dioritic to plagio-granitic composition, a sheeted dyke complex and lastly a basaltic pillow lava unit. Amphiboles from gabbros were dated ({sup 40}K-{sup 40}Ar ages) between 156 and 139 Ma and the agmatites are nearly contemporaneous. Potassic granitic veins dated at 93-88 Ma are related to the development of the Ganj arc complex. (authors)

  5. New Paleomagnetic Data From Upper Gabbros Supports Limited Rotation of Central Semail Massif in Oman Ophiolite

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    Horst, A. J.; Sarah, T.; Hartley, E.; Martin, J.

    2017-12-01

    Paleomagnetic data from northern massifs of the Oman ophiolite demonstrate substantial clockwise rotations prior to or during obduction, yet data from southern massifs are recently suggested to be remagnetized during obduction and show subsequent smaller counterclockwise rotations. To better understand paleomagnetic data from the southern massifs, we conducted a detailed paleomagnetic and rock magnetic study of 21 sites in upper gabbros and 5 sites in lower crustal gabbros within the central Semail massif. Samples treated with progressive thermal demagnetization yield interpretable magnetizations with dominant unblocking between 500-580°C that implies characteristic remanent magnetization (ChRM) components carried by low-titanium magnetite and nearly pure magnetite. Rock magnetic and scanning electron microscopy data provide additional support of the carriers of magnetization. ChRMs from sites with samples containing partially-serpentinized olivine are similar to sites with samples lacking olivine, where the carriers appear to be fine magnetite intergrowths in pyroxene. The overall in situ and tilt-corrected mean directions from upper gabbros are distinct from the lower gabbros, from previous data within the massif, and also directions from similar crustal units in adjacent Rustaq and Wadi Tayin massifs. After tilt correction for 10-15° SE dip of the crust-mantle boundary, the mean direction from upper gabbros is nearly coincident with in situ lower gabbros. The tilt-corrected direction from upper gabbros is also consistent with an expected direction from the Late Cretaceous apparent polar wander path for Arabia at the age of crustal accretion ( 95Ma). These results suggest the upper crustal section in Semail has likely only experienced minor tilting since formation and acquisition of magnetization. Due to slow cooling of middle to lower gabbros in fast-spread crust, the lower gabbro sites likely cooled later or after obduction, and thus yield a distinct

  6. Distribution and PGE mineralization in the formation of chromitite in ophiolite complexes (Ospina-Kitoi Kharanur and ultrabasic massifs of Eastern Sayan, Sousern Siberia)

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    Kiseleva, Olga; Zhmodik, Sergei

    2015-04-01

    New study of PGE in restitic ultrabasic (Kharanur and Ospin-Kitoi) massifs from North and South branches (Dobretsov et al., 1985) of the ophiolite complexes in south-eastern part of the Eastern Sayan show their presence in chromitites of both branches belonging to the different geodynamic settings. Modern concepts model includes several mechanisms of podiform chromitite origin reflected in the chemistry of Cr-spinels (Arai, Yurimoto, 1994; Ballhaus, 1998; Uysal et al., 2009 et al.): 1) partial melting of upper mantle rocks, 2) mixing of primitive melts with melts enriched in SiO2, 3) melt-rock interaction. We estimated the types of interaction of mafic melts with mantle peridotites, with the formation of chromite bodies. For ore chrome spinelides from northern branch (Al2O3) melt = 8 - 14 wt%, (TiO2) melt = 0 - 0,4 wt%, (Fe/Mg) melt = 0,5 - 2,4; Southern branch (Al2O3) melt = 10 - 13 wt%, (TiO2) melt = 0,1 wt%, (Fe/Mg) melt = 0,3 - 1 (Kiseleva, 2014). There are two types of PGE distribution Os-Ir-Ru (I) and Pt-Pd (II). Type I chromitites (mid-Al#Cr-spinels) revealed only Os-Ir-Ru distributions; type II (low-Al#Cr spinelides) show both Os-Ir-Ru and (Pt-Pd) distributions (Kiseleva et al., 2012, 2014). PGE distribution in ultramafic peridotites and chromitites reflects PGE fractionation during partial melting (Barnes et al., 1985; Rehkämper et al., 1997). Processes bringing to extreme fractionation of PGE, may be associated with fluid-saturated supra subduction environment where melting degree near 20% and above is sufficient for the release of PGE from the mantle source (Dick, Bullen, 1984; Naldrett, 2010). Enrichment in PPGE together with a high content of IPGE in same chromite bodies is attributed to the second step of melting, and formation of S-enriched and saturated in PGE melts (Hamlyn, Keays, 1986; Prichard et al., 1996). For type I chromitites platinum group minerals (PGM) are presented by Os-Ir-Ru system. In type II chromitites PGM are represented by Os

  7. Geology of the Menderes Massif and the Lycian Nappes South of Denizli, Western Taurides

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    Aral İ. OKAY

    1989-06-01

    Full Text Available Mount Honaz region in the Western Taurides is made up of superimposed several tectonic units. In the west, monotonous green metashales called the Honaz shale occur at the base of the tectonic stack. Honaz shale is tectonically overlain by weakly metamorphosed, massif white limestone, thinly bedded cherty limestone and shale which covers the Mendercs massif. Menderes massif is in turn tectonically overlain by the Sandak complex of the Lycian nappes made up of Mesozoic dolomites and limestones and ophiolite mainly of harzburgite lies oven the Sandak complex. All these tectonic units form an eastward overturned major anticline called the Honaz anticline; a pelagic sedimentary sequence of Late Cretaceous—Middle/Late Eocene age, called the Göbecik Tepe complex, occurs tectonically beneath the overturned limb of the Honaz anticline. The Göbecik Tepe complex constitutes the relative autochthonous in the region of the Mount Honaz. Different tectonic units in the Mount Honaz region show effects of Late Cretaceous, Middle Eocene and Late Eocene/Oligocene tectonics. Obduction of the ophiolite over the Sandak complex probably occurred during the Late Cretaceous, while the age of thrusting of the Sandak complex over the Menderes massif is probably Middle Eocene. Emplacement of these tectonic units over the Göbecik Tepe complex and the formation of the Honaz anticline is of Late Eocene/Oligocene age.

  8. A Fragment of Ophiolite Assemblage of Kasargi Lake Area: East-Urals Megazone, Northern Part of the Southern Urals

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    D. E. Saveliev

    2014-03-01

    Full Text Available The results of study of rocks of ophiolite assemblage exposed on the east coast of Kasargi Lake are presented. The ophiolite assemblage is formed with the serpentinised ultramafic rocks of dunite-harzburgite association, which are residual and the shlirenbanded gabbros with a number of later dikes of diabases and porphiritic gabbros. The chemical content of mafic and ultramafic rocks of Kasargi massif shows that they are likely the equivalent rocks encountered within the backarc spreading ridges.

  9. Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

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    Amelin, Yuri V.; Ritsk, Eugeni Yu.; Neymark, Leonid A.

    1997-04-01

    Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/ 144Nd- 143Nd/ 144Nd and 238U/ 204Pb- 206Pb/ 204Pb mineral isochrons, corresponding to ages of 640 ± 58 Ma (95% confidence level) and 620 ± 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ± 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites withɛ Nd = +6.6 to +7.1 andɛ Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit:ɛ Nd = +4.6 to +6.1 andɛ Sr = -8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/ 204Pb= 16.994 ± 0.023 and 207Pb/ 204Pb= 15.363 ± 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with

  10. Orogenic, Ophiolitic, and Abyssal Peridotites

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    Bodinier, J.-L.; Godard, M.

    2003-12-01

    "Tectonically emplaced" mantle rocks include subcontinental, suboceanic, and subarc mantle rocks that were tectonically exhumed from the upper mantle and occur:(i) as dispersed ultramafic bodies, a few meters to kilometers in size, in suture zones and mountain belts (i.e., the "alpine," or "orogenic" peridotite massifs - De Roever (1957), Thayer (1960), Den Tex (1969));(ii) as the lower ultramafic section of large (tens of kilometers) ophiolite or island arc complexes, obducted on continental margins (e.g., the Oman Ophiolite and the Kohistan Arc Complex - Coleman (1971), Boudier and Coleman (1981), Burg et al. (1998));(iii) exhumed above the sea level in ocean basins (e.g., Zabargad Island in the Red Sea, St. Paul's islets in the Atlantic and Macquarie Island in the southwestern Pacific - Tilley (1947), Melson et al. (1967), Varne and Rubenach (1972), Bonatti et al. (1981)).The "abyssal peridotites" are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974; Prinz et al., 1976; Hamlyn and Bonatti, 1980).Altogether, tectonically emplaced and abyssal mantle rocks provide insights into upper mantle compositions and processes that are complementary to the information conveyed by mantle xenoliths (See Chapter 2.05). They provide coverage to vast regions of the Earth's upper mantle that are sparsely sampled by mantle xenoliths, particularly in the ocean basins and beneath passive continental margins, back-arc basins, and oceanic island arcs.Compared with mantle xenoliths, a disadvantage of some tectonically emplaced mantle rocks for representing mantle compositions is that their original geodynamic setting is not exactly known and their significance is sometimes a subject of speculation. For instance, the provenance of orogenic lherzolite massifs (subcontinental lithosphere versus upwelling asthenosphere) is still debated (Menzies and Dupuy, 1991, and references herein), as is the original setting

  11. Late Precambrian Balkan-Carpathian ophiolite — a slice of the Pan-African ocean crust?: geochemical and tectonic insights from the Tcherni Vrah and Deli Jovan massifs, Bulgaria and Serbia

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    Savov, Ivan; Ryan, Jeff; Haydoutov, Ivan; Schijf, Johan

    2001-10-01

    The Balkan-Carpathian ophiolite (BCO), which outcrops in Bulgaria, Serbia and Romania, is a Late Precambrian (563 Ma) mafic/ultramafic complex unique in that it has not been strongly deformed or metamorphosed, as have most other basement sequences in Alpine Europe. Samples collected for study from the Tcherni Vrah and Deli Jovan segments of BCO include cumulate dunites, troctolites, wehrlites and plagioclase wehrlites; olivine and amphibole-bearing gabbros; anorthosites; diabases and microgabbros; and basalts representing massive flows, dikes, and pillow lavas, as well as hyaloclastites and umbers (preserved sedimentary cover). Relict Ol, Cpx and Hbl in cumulate peridotites indicate original orthocumulate textures. Plagioclase in troctolites and anorthosites range from An60 to An70. Cumulate gabbro textures range from ophitic to poikilitic, with an inferred crystallization order of Ol-(Plag+Cpx)-Hbl. The extrusive rocks exhibit poikilitic, ophitic and intersertal textures, with Cpx and/or Plag (Oligoclase-Andesine) phenocrysts. The major opaques are Ti-Magnetite and Ilmenite. The metamorphic paragenesis in the mafic samples is Chl-Trem-Ep, whereas the ultramafic rocks show variable degrees of serpentinization, with lizardite and antigorite as dominant phases. Our samples are compositionally and geochemically similar to modern oceanic crust. Major element, trace element and rare earth element (REE) signatures in BCO basalts are comparable to those of MORB. In terms of basalt and dike composition, the BCO is a 'high-Ti' or 'oceanic' ophiolite, based on the classification scheme of Serri [Earth Planet. Sci. Lett. 52 (1981) 203]. Our petrologic and geochemical results, combined with the tectonic position of the BCO massifs (overlain by and in contact with Late Cambrian island arc and back-arc sequences), suggest that the BCO may have formed in a mid-ocean ridge setting. If the BCO records the existence of a Precambrian ocean basin, then there may be a relationship

  12. Stratigraphic units overlying the Zambales Ophiolite Complex (ZOC) in Luzon, (Philippines): Tectonostratigraphic significance and regional implications

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    Queaño, Karlo L.; Dimalanta, Carla B.; Yumul, Graciano P.; Marquez, Edanjarlo J.; Faustino-Eslava, Decibel V.; Suzuki, Shigeyuki; Ishida, Keisuke

    2017-07-01

    The Zambales Ophiolite Complex (ZOC) on the island of Luzon, Philippines is one of the most well-studied crust-mantle sequences in the region. Several massifs comprise the ZOC, one of which is the Coto Block overlain by clastic sedimentary units previously dated as Eocene. Geochronologic studies from diabase, granodiorites and other late-stage magmatic products similarly yielded the same age. Succeeding tectonic models have therefore all been grounded on the assumption that the entire ZOC is Eocene. Recent investigations, however, revealed the presence of chert blocks within the Early to Middle Miocene clastic formation overlying the Acoje Block in the northern part of the ophiolite complex. Radiolarians extracted from the cherts yielded a stratigraphic range that suggests a Late Jurassic to Early Cretaceous age. The recognition of a much older age than previously reported of the ZOC warrants a re-examination of its actual distribution and genesis. Correlating with other similarly-aged ophiolites, we suggest defining a western Mesozoic ophiolite belt, largely extending from the west-central portion of the archipelago to the northeastern tip of Luzon island. Tentatively, we attribute the Mesozoic ophiolitic and associated rocks in western Luzon to an arc-continent collision involving the Philippine Mobile Belt and the Palawan Microcontinental Block. In addition, differences in the clastic compositions of the Cenozoic sedimentary formations provide material not only for deciphering the ZOC's unroofing history but also for constraining the timing of province linkage. The intermittent appearance of lithic fragments and detrital minerals from the ophiolite in the units of the Middle Miocene Candelaria Limestone and the Late Miocene to Early Pliocene Sta. Cruz Formation indicates significant but geographically variable contributions from the ophiolite complex. In the northern Zambales Range, the Sta. Cruz Formation caps the Coto Block and the Acoje Block of the ZOC

  13. From ocean depths to mountain tops: uplift of the Troodos Massif (Cyprus) constrained by (U-Th)/He thermochronology and geomorphic analysis

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    Morag, N.; Haviv, I.; Katzir, Y.

    2013-12-01

    The Troodos Massif of Cyprus, rising to nearly 2000 meters above sea level, encompasses one of the world's classic ophiolites. Following its formation at a seafloor spreading center in Late Cretaceous times, this slice of the NeoTethyan oceanic lithosphere was uplifted and eventually exposed on mountain tops during the Neogene. The final uplift and exhumation of the Troodos was previously assigned to Pleistocene age by observations in the circum-Troodos sedimentary strata. However, quantitative thermochronological and geomorphological data from the Massif itself were not available. Here we use apatite (U-Th)/He low-temperature thermochronology complemented by zircon (U-Th)/He and apatite fission track data, and combined with geomorphic analysis to constrain the exhumation and uplift history of the Troodos ophiolite. Apatite (U-Th)/He ages vary with depth from ~ 22 Ma at the top of the Gabbro sequence to ~ 6 Ma at the bottom of the sequence. The deepest sample from a Gabbro pegmatitic dyke intruding the ultramafic sequence yielded an age of ~ 3 Ma. Thermal modeling of apatite (U-Th)/He and fission track data delineates Plio - Pleistocene initiation of rapid uplift and exhumation of the Troodos ophiolite. The estimated cumulative exhumation since its initiation is 2-3 km. No evidence was found for significant uplift of the central Troodos area prior to that time. The geomorphic analysis delineates a bull's-eye zone at the center of the Troodos Massif, where local relief and channel steepness index are highest. The boundaries of this zone roughly correspond with the Mt. Olympus mantle outcrop and suggest recent, differential uplift of this zone relative to its surroundings. The most likely mechanism, which could drive such a focused bull's-eye uplift pattern is hydration of ultramafic rocks (serpentinization) leading to a decrease in rock density and subsequent diapiric uplift of the serpentinized lithospheric mantle.

  14. Vestiges of Submarine Serpentinization Recorded in the Microbiology of Continental Ophiolite Complexes

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    Schrenk, M. O.; Sabuda, M.; Brazelton, W. J.; Twing, K. I.

    2017-12-01

    The study of serpentinization-influenced microbial ecosystems at and below the seafloor has accelerated in recent years with multidisciplinary drilling expeditions to the Atlantis Massif (X357), Southwest Indian Ridge (X360) and Mariana Forearc (X366). In parallel, a number of studies have surveyed serpentinizing systems in ophiolite complexes which host a range of geologic histories, geochemical characteristics, fluid pathways, and consequently microbiology. As ophiolite complexes originate as seafloor materials, it is likely that a microbiological record of seafloor serpentinization processes is maintained through the emplacement and weathering of continental serpentinites. This hypothesis was evaluated through a global comparison of continental serpentinite springs and groundwater, ranging from highly brackish (saline) to freshwater. One of the most saline sites, known as the Coast Range Ophiolite Microbial Observatory (CROMO), was used as a point-of-comparison to marine serpentinizing systems, such as the Lost City Hydrothermal Field. Although there was little taxonomic overlap between microbial populations in marine and terrestrial systems, both communities harbored an abundance of genes involved in sulfur metabolism, including sulfide oxidation, thiosulfate disproportionation, and sulfate reduction. The phylogeny of key genes involved in these metabolic processes was evaluated relative to published studies and compared between sites. Together, these data provide insights into both the functioning of microbial communities in modern-day serpentinizing systems, and the transport processes that disperse microorganisms between marine and terrestrial serpentinites.

  15. 87Sr enrichment of ophiolitic sulphide deposits in Cyprus confirms ore formation by circulating seawater

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    Chapman, H.J.; Spooner, E.T.C.

    1977-01-01

    The hypothesis that seawater was the source of the hydrothermal fluid which formed the Upper Cretaceous ophiolitic cupriferous pyrite ore deposits of the Troodos Massif (Cyprus) has been tested by analysing the strontium isotopic composition of thirteen mineralized samples from four mines. Initial 87 Sr/ 86 Sr ratios range from 0.7052+-0.0001 to 0.7075+-0.00002, the latter value being indistinguishable from that of Upper Cretaceous seawater at 0.7076+-0.0006 (2 sigma). Hence, the mineralized metabasalt samples have been contaminated with 87 Sr, relative to initial magmatic strontium isotope ratios of the Troodos ophiolitic complex (0.70338+-0.00010 to 0.70365+-0.00005). Since seawater was the only source of strontium available during formation of the Troodos Complex which was isotopically relatively enriched in 87 Sr, the data confirm that seawater was the source of the hydrothermal oreforming fluid. (Auth.)

  16. Influence of the Istranca-Rhodope Massifs and strands of the North Anatolian Fault on oil potential of Thrace Basin, NW Turkey

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    Coskun, B.

    2000-01-01

    The Thrace Basin (NW Turkey) is an intermontane trough bounded to the north and west by the granitic and metamorphic rocks of the Istranca and Rhodope Massifs. Recent subsurface studies of the NW portion of the Thrace Basin have led to the identification of two trends in geothermal gradient, both of which are oriented approximately NW-SE (i.e. parallel to the depositional axis of the basin). Geological and geophysical data indicate that, due to the thrust of the Istranca Massif upon the Rhodope Massif, the subsurface temperature may have increased in the northern part of the basin. Other controls were wrench-fault activity of the Splays of the North Anatolian Fault (SNAF) and continuing basinal subsidences. The thermal history of the southern part of the basin was affected by Miocene ophiolitic emplacement to the west in Greece. The presence of a belt of intrabasinal palaeotopography (mainly Palaeozoic rocks) also contributed to increased geothermal gradients in the southern part of the study area. The basin is divisible into northern and southern zones of subsidence, which are separated by the Kuleli-Babaeski High. During the Oligocene, subsidence rates were highest in the northern zone and in the western sector of the southern zone. Later, during the Miocene, basin subsidence was associated with intense tectonic activity of the SNAF and with the emplacement of ophiolites to the west. A map of the top of the oil generation zone, based on TTI values calculated by the Lopatin method, indicates the presence of two maturation zones in the basin ; these were separated by the Late Oligocene Kuleli-Babaeski High. Oil generation in these zones was influenced by rapid subsidence, by a NW-SE oriented wrench fault system associated with the NAF and also by tectonic activity of the Istranca and Rhodope Massifs in the study area

  17. Serpentinization and fluid-rock interaction in Jurassic mafic and ultramafic sea-floor: constraints from Ligurian ophiolite sequences

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    Vogel, Monica; Früh-Green, Gretchen L.; Boschi, Chiara; Schwarzenbach, Esther M.

    2014-05-01

    The Bracco-Levanto ophiolitic complex (Eastern Liguria) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge, such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of deformation processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to modern oceanic hydrothermal systems, such as the Lost City Hydrothermal Field hosted in ultramafic rocks on the Atlantis Massif. A focus is on investigating mass transfer and fluid flow paths during high and low temperature hydrothermal activity, and on processes leading to hydrothermal carbonate precipitation and the formation of ophicalcites, which are characteristic of the Bracco-Levanto sequences. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread SiO2 metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater and high fluid-rock ratios in the shallow ultramafic-dominated portions of the Jurassic seafloor. We observe regional variations in MgO, SiO2 and Al2O3, suggesting Si-flux towards stratigraphically higher units. In general, the ophicalcites have higher Si, Al and Fe concentrations and lower Mg than the serpentinite basement rocks or serpentinites with minimal carbonate veins. Bulk rock trace element data and Sr isotope ratios indicate seawater reacting with rocks of more mafic composition, then channeled towards stratigraphically higher

  18. Chromitites of the Akkarginskiy massif (the Southern Urals

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    D. E. Saveliev

    2018-03-01

    Full Text Available We consider the geological features of ultramafic rock and chrome ore deposits. It is shown that all studied deposits are podiform in morphology that is typical for the ophiolite ultramafic rocks. Morphological and chemical features of the accessory and oreforming spinels are described. Accessory chrome spinels from ultramafic rocks are middle-Cr and high-Cr in chemistry (>42% Cr2O3. All studied ore-forming chrome spinels from deposits in the Main Ore Zone are high-Cr (54–63% Cr2O3. Some middle-Cr oreforming spinels were found in deposit of the East Ore Zone (48% Cr2O3. We adduce a proof of the tectonic origin of present-day structure of the Akkarginskiy massif and its chrome ore deposits.

  19. Overview of Hole GT2A: Drilling middle gabbro in Wadi Tayin massif, Oman ophiolite

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    Takazawa, E.; Kelemen, P. B.; Teagle, D. A. H.; Coggon, J. A.; Harris, M.; Matter, J. M.; Michibayashi, K.

    2017-12-01

    Hole GT2A (UTM: 40Q 655960.7E / 2529193.5N) was drilled by the Oman Drilling Project (OmDP) into Wadi Gideah of Wadi Tayin massif in the Samail ophiolite, Oman. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole GT2A was diamond cored in 25 Dec 2016 to 18 Jan 2017 to a total depth of 406.77 m. The outer surfaces of the cores were imaged and described on site before being curated, boxed and shipped to the IODP drill ship Chikyu, where they underwent comprehensive visual and instrumental analysis. 33 shipboard scientists were divided into six teams (Igneous, Alteration, Structural, Geochem, Physical Properties, Paleomag) to describe and analyze the cores. Hole GT2A drilled through the transition between foliated and layered gabbro. The transition zone occurs between 50 and 150 m curation corrected depth (CCD). The top 50 m of Hole GT2A is foliated gabbro whereas the bottom 250 m consists of layered gabbro. Brittle fracture is observed throughout the core. Intensity of alteration vein decreases from the top to the bottom of the hole. On the basis of changes in grain size and/or modal abundance and/or appearance/disappearance of igneous primary mineral(s) five lithological units are defined in Hole GT2A (Unit I to V). The uppermost part of Hole GT2A (Unit I) is dominated by fine-grained granular olivine gabbro intercalated with less dominant medium-grained granular olivine gabbro and rare coarse-grained varitextured gabbro. The lower part of the Hole (Units II, III and V) is dominated by medium-grained olivine gabbro, olivine melagabbro and olivine-bearing gabbro. Modally-graded rhythmic layering with

  20. Magnetic properties of serpentinized peridotites from the Zedong ophiolite, Yarlung-Zangbo suture zone, SE Tibet

    Science.gov (United States)

    Li, Z.; Zheng, J.; Moskowitz, B. M.; Xiong, Q.; Liu, Q.

    2017-12-01

    Serpentinized mantle peridotites are widely supposed to be significant sources of the magnetic, gravity and seismic anomalies in mid-oceanic ridges, forearcs and suture zones. However, the relationship between the magnetic properties of variably serpentinized peridotites and the serpentinization process is still under debate. Ophiolite outcrops commonly comprise peridotites in different stages of serpentinization and these ophiolitic peridotites are ideal to investigate the magnetic signatures of suture zones. The Zedong ophiolite locates in the eastern part of the Yarlung-Zangbo suture zone, SE Tibet (China), and the peridotite massif represents the remnants of the Neo-Tethyan lithospheric mantle. The harzburgite and lherzolite samples show densities between 3.316 and 2.593 g cm-3, and vary from the freshest to >90% serpentinized peridotites. The magnetic susceptibility curves from room temperature to 700ºC mainly show the Curie temperatures of 585ºC for pure magnetite. The low-temperature (20-300 K) demagnetization curves show the Verwey transitions at 115-125 K, suggesting that magnetite is also the dominant remanence-carrying phase. The hysteresis data of the peridotites fall in the region of pseudo-single-domain (PSD) and follow the theoretical trends for mixtures of single domain (SD) and multidomain (MD) magnetite. The first-order reversal curve (FORC) diagrams suggest that the magnetite is dominantly interacting SD + PSD particles for S 40% serpentinized samples. The susceptibility and saturation magnetization of the Zedong peridotites range from 0.9 to 30.8 × 10‒3 (SI) and 14.1 to 1318 × 10‒3 Am2 kg‒1, respectively, and both show consistent trends with increasing degrees of serpentinization. The S serpentinization of ophiolitic peridotites, whereas the S > 40% peridotites have higher susceptibilities of 0.02-0.03 (SI) and fall in the region of abyssal peridotites. Our results suggest that the Zedong ophiolitic peridotites probably experienced a

  1. Sm-Nd age of ultrabasite-basite massifs of east part of Baikal-Mujya ophiolite belt

    International Nuclear Information System (INIS)

    Izokh, A.Eh.; Gibsher, A.S.; Zhuravlev, D.Z.; Balykin, P.A.

    1998-01-01

    Two stratified ultrabasite-basite massifs of the Urals mountains were selected for isotope-geochemical studies. The intrusives, related to plutonic members of the island-arc associations, were used for dating. The Sm-Nd method indicated that one more belt, namely the Vend belt, is taking shape in the Baikal-Mujya tectonic collage alongside with the later Riphean (pre-Baikal) episubconduction belt of stratified intrusives [ru

  2. From an ocean floor wrench zone origin to transpressional tectonic emplacement of the Sithonia ophiolite, eastern Vardar Suture Zone, northern Greece

    Science.gov (United States)

    Bonev, Nikolay; Filipov, Petyo

    2017-12-01

    In the Hellenides of northern Greece, the Sithonia back-arc ophiolite constitute an element of the Vardar suture zone against the Chortiatis island arc magmatic suite, the Melissochori Formation and the Serbo-Macedonian Massif further north at the Mesozoic continental margin of Eurasia. A granodiorite from the Chortiatis island arc magmatic suite crystallized at 160 Ma as derived from new U-Pb zircon geochronology and confirms the end of arc magmatic activity that started at around 173 Ma. Located southerly of the Chortiatis island arc magmatic suite, the Sithonia ophiolite had igneous life from 159 to 149 Ma, and the ophiolite interfinger with clastic-carbonate Kimmeridgian sediments. Magmatic structures (i.e., sheeted dykes) in the ophiolite witness for NE-trending rift axis, while the transform faults and fracture zones sketch NW-SE transcurrent transtension-like propagation of the rift-spreading center at Sithonia that is consistent with a dextral wrench corridor already proposed for the ophiolite origin in the eastern Vardar zone. The tectonic emplacement of the Sithonia ophiolite involved dextral ENE to SE strike-slip sense of shear and SW and NE reverse thrust sense of shear on mostly steep foliation S1, subhorizontal lineation L1 and associated variably inclined F1 fold axes. This structural grain and kinematics are shared by adjacent Chortiatis island arc magmatic suite and the Melissochori Formation. The coexistence of strike-parallel and thrust components of displacement along discrete dextral strike-slip shear zones and internal deformation of the mentioned units is interpreted to result from a bulk dextral transpressive deformation regime developed in greenschist-facies metamorphic conditions. The back-arc ocean floor previous structural architecture with faults and fracture zones where Kimmeridgian sediments deposited in troughs was used by discrete strike-slip shear zones in which these sediments involved, and the shear zones become the sites for

  3. An oceanic core complex (OCC) in the Albanian Dinarides? Preliminary paleomagnetic and structural results from the Mirdita Ophiolite (northern Albania)

    Science.gov (United States)

    Maffione, M.; Morris, A.; Anderson, M.

    2010-12-01

    Oceanic core complexes (OCCs) are dome-shaped massifs commonly associated with the inside corners of the intersection of transform faults and slow (and ultra-slow) spreading centres. They represent the uplifted footwalls of large-slip oceanic detachment faults (e.g. Cann et al., 1997; Blackman et al., 1998) and are composed of mantle and lower crustal rocks exhumed during fault displacement (Smith et al., 2006, 2008). Recent paleomagnetic studies of core samples from OCCs in the Atlantic Ocean (Morris et al., 2009; MacLeod et al., in prep) have confirmed that footwall sections undergo substantial rotation around (sub-) horizontal axes. These studies, therefore, support “rolling hinge” models for the evolution of OCCs, whereby oceanic detachment faults initiate at a steep angle at depth and then “roll-over” to their present day low angle orientations during unroofing (Buck, 1988; Wernicke & Axen, 1988; Lavier et al., 1999). However, a fully integrated paleomagnetic and structural analysis of this process is hampered by the one-dimensional sampling provided by ocean drilling of OCC footwalls. Therefore, ancient analogues for OCCs in ophiolites are of great interest, as these potentially provide 3-D exposures of these important structures and hence a more complete understanding of footwall strain and kinematics (providing that emplacement-related phases of deformation can be accounted for). Recently, the relationship between outcropping crustal and upper mantle rocks led Tremblay et al. (2009) to propose that an OCC is preserved within the Mirdita ophiolite of the Albanian Dinarides (northern Albania). This is a slice of Jurassic oceanic lithosphere exposed along a N-S corridor which escaped the main late Cenozoic Alpine deformation (Robertson, 2002, 2004; Dilek et al., 2007). Though in the eastern portion of the Mirdita ophiolite a Penrose-type sequence is present, in the western portion mantle rocks are in tectonic contact with upper crustal lithologies

  4. Petrology and geochemistry of the high-Cr podiform chromitites of the Köycegiz ophiolite, southwest Turkey: implications for the multi-stage evolution of the oceanic upper mantle

    Science.gov (United States)

    Xiong, Fahui; Yang, Jingsui; Dilek, Yildirim; Wang, ChunLian; Hao, Xiaolin; Xu, Xiangzhen; Lian, Dongyang

    2018-03-01

    Ophiolites exposed across the western Tauride belt in Turkey represent tectonically emplaced fragments of oceanic lithosphere obducted onto the continental margin following the closure of the Neotethys Ocean during the Late Cretaceous. The ultramafic massif of Köycegiz, which is located in the ophiolitic belt of southwestern Turkey, is a major source of metallurgical chromitite ore. The massif comprises a base of tectonized harzburgite with minor dunite overlain by a magmatic sequence of wehrlite, pyroxenite, troctolite and gabbro. Only sparse refractory chromitites occur within the harzburgites; in contrast, the upper and middle sections of the peridotite sequence contain abundant metallurgical chromitites. The peridotites record abundant evidence of mantle metasomatism on various scales, as the Fo values of olivine in harzburgite are 90.1-95.4, whereas those in dunite are 90.1-91.8. The compositions of the melts passing through the peridotites changed gradually from arc tholeiite to boninite due to melt-rock reactions, thus producing more Cr-rich chromitites in the upper part of the body. Most of the chromitites have high Cr numbers (77-78), although systematic changes in the compositions of the olivine and chromian spinel occur from the harzburgites to the dunite envelopes to the chromitites, reflecting melt-rock reactions. The calculated ΔlogfO2 (FMQ) values range from - 2.77 to + 1.03 in the chromitites, - 2.73 to -0.01 in the harzburgites, and - 1.65 to + 0.45 in the dunites. All of the available evidence suggests that the Köycegiz ophiolite formed in a supra-subduction zone (SSZ) mantle wedge. These models indicate that the harzburgites represent the products of first-stage melting and low degrees of melt-rock interaction that occurred in a mid-ocean ridge (MOR) environment. In contrast, the chromitites and dunites represent the products of second-stage melting and related refertilization, which occurred in an SSZ environment.

  5. Multi-stage origin of the Coast Range ophiolite, California: Implications for the life cycle of supra-subduction zone ophiolites

    Science.gov (United States)

    Shervais, J.W.; Kimbrough, D.L.; Renne, P.; Hanan, B.B.; Murchey, B.; Snow, C.A.; Zoglman, Schuman M.M.; Beaman, J.

    2004-01-01

    The Coast Range ophiolite of California is one of the most extensive ophiolite terranes in North America, extending over 700 km from the northernmost Sacramento Valley to the southern Transverse Ranges in central California. This ophiolite, and other ophiolite remnants with similar mid-Jurassic ages, represent a major but short-lived episode of oceanic crust formation that affected much of western North America. The history of this ophiolite is important for models of the tectonic evolution of western North America during the Mesozoic, and a range of conflicting interpretations have arisen. Current petrologic, geochemical, stratigraphic, and radiometric age data all favor the interpretation that the Coast Range ophiolite formed to a large extent by rapid extension in the forearc region of a nascent subduction zone. Closer inspection of these data, however, along with detailed studies of field relationships at several locales, show that formation of the ophiolite was more complex, and requires several stages of formation. Our work shows that exposures of the Coast Range ophiolite preserve evidence for four stages of magmatic development. The first three stages represent formation of the ophiolite above a nascent subduction zone. Rocks associated with the first stage include ophiolite layered gabbros, a sheeted complex, and volcanic rocks vith arc tholeiitic or (roore rarely) low-K calc-alkaline affinities. The second stage is characterized by intrusive wehrlite-clinopyroxenite complexes, intrusive gabbros, Cr-rich diorites, and volcanic rocks with high-Ca boninitic or tholeiitic ankaramite affinities. The third stage includes diorite and quartz diorite plutons, felsic dike and sill complexes, and calc-alkaline volcanic rocks. The first three stages of ophiolite formation were terminated by the intrusion of mid-ocean ridge basalt dikes, and the eruption of mid-ocean ridge basalt or ocean-island basalt volcanic suites. We interpret this final magmatic event (MORB

  6. Hydrogen Gas from Serpentinite, Ophiolites and the Modern Ocean Floor as a Source of Green Energy

    Science.gov (United States)

    Coveney, R. M.

    2008-12-01

    Hydrogen gas is emitted by springs associated with serpentinites and extensive carbonate deposits in Oman, The Philippines, the USA and other continental locations. The hydrogen springs contain unusually alkaline fluids with pH values between 11 and 12.5. Other workers have described off-ridge submarine springs with comparably alkaline fluid compositions, serpentinite, abundant free hydrogen gas, and associated carbonate edifices such as Lost City on the Atlantis Massif 15 km west of the Mid-Atlantic Ridge (D.S. Kelley and associates, Science 2005). The association of hydrogen gas with ultramafites is a consistent one that has been attributed to a redox couple involving oxidation of divalent iron to the trivalent state during serpentinization, although other possibilities exist. Some of the hydrogen springs on land are widespread. For example in Oman dozens of alkaline springs (Neal and Stanger, EPSL 1983) can be found over thousands of sq km of outcropping ophiolite. While the deposits in Oman and the Philippines are well-known to much of the geochemical community, little interest seems to have been displayed toward either the ophiolitic occurrences or the submarine deposits for energy production. This may be a mistake as the showings because they could lead to an important source of green energy. Widespread skepticism currently exists about hydrogen as a primary energy source. It is commonly said that free hydrogen does not occur on earth and that it is therefore necessary to use other sources of energy to produce hydrogen, obviating the general environmental benefit. However the existence of numerous occurrences of hydrogen gas associated with ophiolites and submarine occurrences of hydrogen suggests the likelihood that natural hydrogen gas may be an important source of clean energy for modern society remaining to be tapped. Calculations in progress should establish whether or not this is likely to be the case.

  7. Compositional Variation of Chrome Spinels in the Ore-bearing Zones of the Kraka Ophiolite and the Chromitite Origin

    Directory of Open Access Journals (Sweden)

    D. E. Saveliev

    2017-07-01

    Full Text Available The article considers a chemical variation of accessory and ore-forming chrome spinels from the Kraka ultramafic massif at the different scales, from the deposit to the thin section. A correlation analysis of compositional and structural features of ultramafic rocks and ores was performed. The ultramafic rocks and chromitites in the studied massif show the distinct deformation structures and tectonite olivine fabric. A typical chemical gap (i.e. Cr#=Cr/(Cr+Al was observed between peridotite, on the one hand, and dunite and chromitite, on the other hand, on the scale of deposits and ore-bearing zones. The location and size of this gap depend on the type of deposit. The gap becomes wider from the disseminated tabular bodies to the typical podiform ones. It has been found that in the thin initial dunite veinlets in peridotite the chrome spinels chemistry changes gradually and there is no Cr# gap between peridotite and dunite. The dunite venlets show a strong olivine fabric, which is an evidence of their high-temperature plastic flow origin. It has been revealed that new chrome spinel grains previously formed as rods or needles and then coarsened. We explained this observation as the result of impurity segregation, coalescence and spheroidization induced by the plastic deformation of olivine. It is inferred that a solid crystal flow is the main requirement for the dunite and chromitite body formation in the Kraka ophiolite massif. In the solid stream, the mineral phase separation takes place. For example, olivine and orthopyroxene grains of parental peridotite separate from one another, and weaker (more mobile olivine grains form dunite bodies in which chromitite appears as a result of impurity segregation.

  8. 222Rn activity concentration differences in groundwaters of three Variscan granitoid massifs in the Sudetes (NE Bohemian Massif, SW Poland)

    International Nuclear Information System (INIS)

    Przylibski, Tadeusz A.; Gorecka, Joanna

    2014-01-01

    Based on research conducted in three Variscan granitoid massifs located within the crystalline Bohemian Massif, the authors confirmed that the higher the degree of their erosional dissection, the smaller the concentration of 222 Rn in groundwaters circulating in these massifs. This notion implies that radon waters and high-radon waters, from which at least some of the dissolved radon should be removed before feeding them as drinking water to the water-supply system, could be expected in granitoid massifs which have been poorly exposed by erosion. At the same time, such massifs must be taken into account as the areas of possible occurrence of radon medicinal waters, which in some countries can be used for balneotherapy in health resorts. Slightly eroded granitoid massifs should be also regarded as very probable radon prone areas or areas of high radon potential. - Highlights: • The concentration of 222 Rn in groundwater depends on the zone of the granitoid massif which is exposed on the ground surface. • The highest 222 Rn concentrations occur in the least eroded granitoid massifs, the lowest in massifs with exposed root parts. • The stronger the erosional dissection of a granitoid massif, the lower 222 Rn concentration in groundwaters in this massif. • Not all granitoid massifs are areas with groundwaters containing high concentrations of 222 Rn. • The least eroded granitoid massifs are radon prone areas with the occurrence of high-radon and radon groundwaters

  9. Isotopic and trace element constraints on the genesis of a boninitic sequence in the Thetford Mines ophiolitic complex, Quebec, Canada

    International Nuclear Information System (INIS)

    Olive, V.; Hebert, R.; Loubet, M.

    1997-01-01

    The Mont Ham Massif (part of the Thetford Mines ophiolite, south Quebec) represents a magmatic sequence made up of tholeiitic and boninitic derived products. A geochemical study confirms the multicomponent mixing models that have been classically advanced for the source of boninites, with slab-derived components added to the main refractory harzburgitic peridotite. An isochron diagram of the boninitic rocks is interpreted as a mixing trend between two components: (i) a light rare earth element (LREE) enriched component (A), interpreted as slab-derived fluid-melts equilibrated with sedimentary materials (ε Nd = -3, 147 Sm/ 144 Nd = 0.140), and (ii) a LREE-depleted component (B) (0.21 147 Sm/ 144 Nd Nd = 9). A multicomponent source is also necessary to explain the Nd-isotope and trace element composition of the tholeiites, which are explained by the melting of a more fertile, Iherzolitic mantle and (or) mid-ocean ridge basalt source (component C), characterized by a large-ion lithophile element depicted pattern and an lapetus mantle Nd isotopic composition (ε Nd = 9), mixed in adequate proportions with the two previously infered slab-derived components (A and B). The genesis of the boninites of Mont Ham is not significantly different from those of boninites located in the Pacific. An intraoceanic subduction zone appears to be an appropriate geodynamic environment for the Mont Ham ophiolitic sequence. (author)

  10. Masirah – the other Oman ophiolite: A better analogue for mid-ocean ridge processes?

    Directory of Open Access Journals (Sweden)

    Hugh Rollinson

    2017-11-01

    Full Text Available Oman has two ophiolites – the better known late Cretaceous northern Oman (or Semail ophiolite and the lesser known and smaller, Jurassic Masirah ophiolite located on the eastern coast of the country adjacent to the Indian Ocean. A number of geological, geochronological and geochemical lines of evidence strongly suggest that the northern Oman ophiolite did not form at a mid-ocean ridge but rather in a supra-subduction zone setting by fast spreading during subduction initiation. In contrast the Masirah ophiolite is structurally part of a series of ophiolite nappes which are rooted in the Indian Ocean floor. There are significant geochemical differences between the Masirah and northern Oman ophiolites and none of the supra-subduction features typical of the northern Oman ophiolite are found at Masirah. Geochemically Masirah is MORB, although in detail it contains both enriched and depleted MORB reflecting a complex source for the lavas and dykes. The enrichment of this source predates the formation of the ophiolite. The condensed crustal section on Masirah (ca. 2 km contains a very thin gabbro sequence and is thought to reflect its genesis from a cool mantle source associated with the early stages of sea-floor spreading during the early separation of eastern and western Gondwana. These data suggest that the Masirah ophiolite is a suitable analogue for an ophiolite created at a mid-ocean ridge, whereas the northern Oman ophiolite is not. The stratigraphic history of the Masirah ophiolite shows that it remained a part of the oceanic crust for ca. 80 Ma. The chemical variability and enrichment of the Masirah lavas is similar to that found elsewhere in Indian Ocean basalts and may simply reflect a similar provenance rather than a feature fundamental to the formation of the ophiolite.

  11. The geology of uranium in the Saint-Sylvestre granite district (Limousin, Massif Central, France); La geologie de l'uranium dans le massif granitique de Saint-Sylvestre (Limousin - Massif Central Francais)

    Energy Technology Data Exchange (ETDEWEB)

    Marquaire, C; Moreau, M; Barbier, J; Ranchin, G; Carrat, H G; Coppens, R; Senecal, J; Koszotolanyi, C; Dottin, H

    1969-07-01

    This report concerns the geology of uranium in Limousin, more particularly in the St-Sylvestre massif, and the related phenomena: regional geology, petrographic and geochemical zonal distribution observed in various granite massifs, uranium movement in connection with surface alteration, geochronology of uranium ore. The work is made up of six articles covering the various scientific aspects listed above. Each article is headed with an abstract. The paper comprises the following chapters: Foreword by Marcel ROUBAULT. 1. Ch. MARQUAIRE, M. MOREAU Outline of geological conditions in Northern Limousin and distribution of uraniferous occurrences. 2. J. BARBIER, G. RANCHIN, H. G. CARRAT and R. COPPENS Geology of the St-Sylvestre Massif and uranium geochemistry - Introduction to laboratory studies - Problems of methodology. 3. J. BARBIER and G. RANCHIN Petrographical and geochemical zones in the St-Sylvestre granite massif (Limousin - French 'Massif Central'). 4. J. BARBIER and G. RANCHIN Uranium geochemistry in the St-Sylvestre Massif (Limousin - French 'Massif Central') - Occurrences of primary geochemical uranium and replacement processes. 5. J. SENEGAL Monograph of the Brugeaud orebody. 6. R. COPPENS, Ch. KOSZTOLANYI and H. DOTTIN Geochronological study of the Brugeaud mine. 1969. (authors) [French] Ce memoire est consacre a la geologie de l'uranium dans le Limousin, plus specialement dans le massif de St-Sylvestre, et aux phenomenes qui s'y rattachent: geologie regionale, phenomenes de zonalite petrographique et geochimique dans certains massifs granitiques, mouvements de l'uranium lies a l'alteration superficielle, geochronologie du minerai d'uranium. L'ouvrage comprend six articles qui recouvrent les differents aspects scientifiques enumeres. Chacun de ces six articles est precede d'un resume. La composition du memoire st la suivante: Marcel ROUBAULT, Preface. 1. Ch. MARQUAIRE, M. MOREAU Esquisse geologique du Nord Limousin et repartition des mineralisations

  12. Ophiolitic detritus in Kimmeridgian resedimented limestones and its provenance from an eroded obducted ophiolitic nappe stack south of the Northern Calcareous Alps (Austria

    Directory of Open Access Journals (Sweden)

    Gawlick Hans-Jürgen

    2015-12-01

    Full Text Available The causes for the Middle to Late Jurassic tectonic processes in the Northern Calcareous Alps are still controversially discussed. There are several contrasting models for these processes, formerly designated “Jurassic gravitational tectonics”. Whereas in the Dinarides or the Western Carpathians Jurassic ophiolite obduction and a Jurassic mountain building process with nappe thrusting is widely accepted, equivalent processes are still questioned for the Eastern Alps. For the Northern Calcareous Alps, an Early Cretaceous nappe thrusting process is widely favoured instead of a Jurassic one, obviously all other Jurassic features are nearly identical in the Northern Calcareous Alps, the Western Carpathians and the Dinarides. In contrast, the Jurassic basin evolutionary processes, as best documented in the Northern Calcareous Alps, were in recent times adopted to explain the Jurassic tectonic processes in the Carpathians and Dinarides. Whereas in the Western Carpathians Neotethys oceanic material is incorporated in the mélanges and in the Dinarides huge ophiolite nappes are preserved above the Jurassic basin fills and mélanges, Jurassic ophiolites or ophiolitic remains are not clearly documented in the Northern Calcareous Alps. Here we present chrome spinel analyses of ophiolitic detritic material from Kimmeridgian allodapic limestones in the central Northern Calcareous Alps. The Kimmeridgian age is proven by the occurrence of the benthic foraminifera Protopeneroplis striata and Labyrinthina mirabilis, the dasycladalean algae Salpingoporella pygmea, and the alga incertae sedis Pseudolithocodium carpathicum. From the geochemical composition the analysed spinels are pleonastes and show a dominance of Al-chromites (Fe3+–Cr3+–Al3+ diagram. In the Mg/(Mg+ Fe2+ vs. Cr/(Cr+ Al diagram they can be classified as type II ophiolites and in the TiO2 vs. Al2O3 diagram they plot into the SSZ peridotite field. All together this points to a harzburgite

  13. Four billion years of ophiolites reveal secular trends in oceanic crust formation

    Directory of Open Access Journals (Sweden)

    Harald Furnes

    2014-07-01

    Full Text Available We combine a geological, geochemical and tectonic dataset from 118 ophiolite complexes of the major global Phanerozoic orogenic belts with similar datasets of ophiolites from 111 Precambrian greenstone belts to construct an overview of oceanic crust generation over 4 billion years. Geochemical discrimination systematics built on immobile trace elements reveal that the basaltic units of the Phanerozoic ophiolites are dominantly subduction-related (75%, linked to backarc processes and characterized by a strong MORB component, similar to ophiolites in Precambrian greenstone sequences (85%. The remaining 25% Phanerozoic subduction-unrelated ophiolites are mainly (74% of Mid-Ocean-Ridge type (MORB type, in contrast to the equal proportion of Rift/Continental Margin, Plume, and MORB type ophiolites in the Precambrian greenstone belts. Throughout the Phanerozoic there are large geochemical variations in major and trace elements, but for average element values calculated in 5 bins of 100 million year intervals there are no obvious secular trends. By contrast, basaltic units in the ophiolites of the Precambrian greenstones (calculated in 12 bins of 250 million years intervals, starting in late Paleo- to early Mesoproterozoic (ca. 2.0–1.8 Ga, exhibit an apparent decrease in the average values of incompatible elements such as Ti, P, Zr, Y and Nb, and an increase in the compatible elements Ni and Cr with deeper time to the end of the Archean and into the Hadean. These changes can be attributed to decreasing degrees of partial melting of the upper mantle from Hadean/Archean to Present. The onset of geochemical changes coincide with the timing of detectible changes in the structural architecture of the ophiolites such as greater volumes of gabbro and more common sheeted dyke complexes, and lesser occurrences of ocelli (varioles in the pillow lavas in ophiolites younger than 2 Ga. The global data from the Precambrian ophiolites, representative of nearly 50

  14. Thermo-mechanical models of obduction applied to the Oman ophiolite

    Science.gov (United States)

    Thibault, Duretz; Philippe, Agard; Philippe, Yamato; Céline, Ducassou; Taras, Gerya; Evguenii, Burov

    2015-04-01

    During obduction regional-scale fragments of oceanic lithosphere (ophiolites) are emplaced somewhat enigmatically on top of lighter continental lithosphere. We herein use two-dimensional thermo-mechanical models to investigate the feasibility and controlling parameters of obduction. The models are designed using available geological data from the Oman (Semail) ophiolite. Initial and boundary conditions are constrained by plate kinematic and geochronological data and modeling results are validated against petrological and structural observations. The reference model consists of three distinct stages: (1) initiation of oceanic subduction initiation away from Arabian margin, (2) emplacement of the Oman Ophiolite atop the Arabian margin, (2) dome-like exhumation of the subducted Arabian margin beneath the overlying ophiolite. A parametric study suggests that 350-400 km of shortening allows to best fit both the peak P-T conditions of the subducted margin (1.5-2.5 GPa / 450-600°C) and the dimensions of the ophiolite (~170 km width), in agreement with previous estimations. Our results further confirm that the locus of obduction initiation is close to the eastern edge of the Arabian margin (~100 km) and indicate that obduction is facilitated by a strong continental basement rheology.

  15. The geology of uranium in the Saint-Sylvestre granite district (Limousin, Massif Central, France); La geologie de l'uranium dans le massif granitique de Saint-Sylvestre (Limousin - Massif Central Francais)

    Energy Technology Data Exchange (ETDEWEB)

    Marquaire, C.; Moreau, M.; Barbier, J.; Ranchin, G.; Carrat, H.G.; Coppens, R.; Senecal, J.; Koszotolanyi, C.; Dottin, H

    1969-07-01

    This report concerns the geology of uranium in Limousin, more particularly in the St-Sylvestre massif, and the related phenomena: regional geology, petrographic and geochemical zonal distribution observed in various granite massifs, uranium movement in connection with surface alteration, geochronology of uranium ore. The work is made up of six articles covering the various scientific aspects listed above. Each article is headed with an abstract. The paper comprises the following chapters: Foreword by Marcel ROUBAULT. 1. Ch. MARQUAIRE, M. MOREAU Outline of geological conditions in Northern Limousin and distribution of uraniferous occurrences. 2. J. BARBIER, G. RANCHIN, H. G. CARRAT and R. COPPENS Geology of the St-Sylvestre Massif and uranium geochemistry - Introduction to laboratory studies - Problems of methodology. 3. J. BARBIER and G. RANCHIN Petrographical and geochemical zones in the St-Sylvestre granite massif (Limousin - French 'Massif Central'). 4. J. BARBIER and G. RANCHIN Uranium geochemistry in the St-Sylvestre Massif (Limousin - French 'Massif Central') - Occurrences of primary geochemical uranium and replacement processes. 5. J. SENEGAL Monograph of the Brugeaud orebody. 6. R. COPPENS, Ch. KOSZTOLANYI and H. DOTTIN Geochronological study of the Brugeaud mine. 1969. (authors) [French] Ce memoire est consacre a la geologie de l'uranium dans le Limousin, plus specialement dans le massif de St-Sylvestre, et aux phenomenes qui s'y rattachent: geologie regionale, phenomenes de zonalite petrographique et geochimique dans certains massifs granitiques, mouvements de l'uranium lies a l'alteration superficielle, geochronologie du minerai d'uranium. L'ouvrage comprend six articles qui recouvrent les differents aspects scientifiques enumeres. Chacun de ces six articles est precede d'un resume. La composition du memoire st la suivante: Marcel ROUBAULT, Preface. 1. Ch. MARQUAIRE, M. MOREAU Esquisse geologique du

  16. Mineralogy, composition and PGM of chromitites from Pefki, Pindos ophiolite complex (NW Greece): evidence for progressively elevated fAs conditions in the upper mantle sequence

    Science.gov (United States)

    Kapsiotis, Argirios; Grammatikopoulos, Tassos A.; Tsikouras, Basilios; Hatzipanagiotou, Konstantin; Zaccarini, Federica; Garuti, Giorgio

    2011-01-01

    The Pindos ophiolite complex, located in the northwestern part of continental Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. The Pefki chromitites are banded and sub-concordant to the surrounding serpentinized dunites. The Cr# [Cr/(Cr + Al)] of magnesiochromite varies between 0.75 and 0.79. The total PGE grade ranges from 105.9 up to 300.0 ppb. IPGE are higher than PPGE, typical of mantle hosted ophiolitic chromitites. The PGM assemblage in chromitites comprises anduoite, ruarsite, laurite, irarsite, sperrylite, hollingworthite, Os-Ru-Ir alloys including osmium and rutheniridosmine, Ru-bearing oxides, braggite, paolovite, platarsite, cooperite, vysotskite, and palladodymite. Iridarsenite and omeiite were also observed as exsolutions in other PGM. Rare electrum and native Ag are recovered in concentrates. This PGM assemblage is of great petrogenetic importance because it is significantly different from that commonly observed in podiform mantle-hosted and banded crustal-hosted ophiolitic chromitites. PGE chalcogenides of As and S are primary, and possibly crystallized directly from a progressively enriched in As boninitic melt before or during magnesiochromite precipitation. The presence of Ru-bearing oxides implies simultaneous desulfurization and dearsenication processes. Chemically zoned laurite and composite paolovite-electrum intergrowths are indicative of the relatively high mobility of certain PGE at low temperatures under locally oxidizing conditions. The PGM assemblage and chemistry, in conjunction with geological and petrologic data of the studied chromitites, indicate that it is characteristic of chromitites found within or close to the petrologic Moho. Furthermore, the strikingly different PGM assemblages between the high-Cr chromitites within the Pindos massif is suggestive of non-homogeneous group of ores.

  17. Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France)

    Science.gov (United States)

    Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jérémie; Li, Xian-Hua; Lin, Wei; Blein, Olivier; Bruguier, Olivier; Poujol, Marc

    2018-02-01

    A structural and petrochronological study was carried out in the southern part of the Belledonne crystalline massif. A first tectonometamorphic event, Dx, corresponds to the eastward thrusting of the Chamrousse ophiolitic complex characterized by a low-temperature-moderate-pressure metamorphism reaching 0.535 ± 0.045 GPa and 427.5 ± 17.5 °C. A subsequent D1 deformation is defined by a penetrative S1 foliation that mostly dips toward the west and displays an E-W- to NE-SW-trending mineral and stretching lineation L1. D1 is associated with a top-to-the east shearing and is responsible for the crustal thickening accommodated by the eastward nappe stacking and the emplacement of the Chamrousse ophiolitic complex upon the Rioupéroux-Livet unit. This event is characterized by an amphibolite facies metamorphism (0.58 GPa ± 0.06; 608 ± 14 °C) that attains partial melting at the base of the nappe pile (0.78 ± 0.07 GPa; 680.5 ± 11.5 °C). LA-ICP-MS U-Pb dating of monazite grains from the mica schists of the Rioupéroux-Livet unit constrain the age of D1 to 337 ± 7 Ma. The D2 tectono-metamorphic event is characterized by NE-SW trending, upright to NE-verging synfolial folding. Folding associated with D2 is pervasively developed in all lithotectonic units with the development of a steeply-dipping S2 foliation. In particular, D2 involves the uppermost weakly metamorphosed Taillefer unit. LA-ICP-MS U-Pb dating performed on detrital zircon grains shows that the Taillefer conglomerates was deposited during the Visean. A zircon SIMS U-Pb age of 352 ± 1 Ma from a plagioglase-rich leucocratic sill of the Rioupéroux-Livet unit is interpreted as the age of magmatic emplacement. Our results suggest that the D2 event took place between 330 Ma and 310 Ma. We propose a new interpretation of the tectonometamorphic evolution of the southern part of the Belledonne massif, focusing on the Middle Carboniferous stages of the Variscan orogeny.

  18. Lead isotopic studies of the Samail ophiolite, Oman

    Energy Technology Data Exchange (ETDEWEB)

    Chen, J.H.; Pallister, J.S.

    1981-04-10

    The isotopic composition of Pb and the concentrations of U, Th, and Pb have been determined for samples from various lithologic units and massive sulfides of the Samail ophiolite. The observed /sup 206/Pb//sup 204/Pb ratios range from 17.90 to 19.06, /sup 207/Pb//sup 204/Pb ratios from 15.43 to 15.63, and /sup 208/Pb//sup 204/Pb from 37.66 to 38.78. In Pb isotopic evolution diagrams, the initial Pb isotopic compositions of most of the samples from the Samail ophiolite plot within the field of oceanic basalt, clearly distinct from island arc data, and define some of the least radiogenic Pb observed from oceanic rocks. Lead data from the Samail are compatible with a model involving magma generation from an oceanic mantle source and formation of the ophiolite at an oceanic spreading center. U--Th--Pb isotopic systematics demonstrate that vertical heterogeneity in the oceanic crust can be created through differential concentration of U, Th, and Pb during crystal fractionation and alteration at, or near, the spreading ridge. Calcite form amygdules in the ophiolite basalt has similar Pb isotopic composition to the igneous rocks, suggesting precipitation of the calcite from seawater which contained Pb derived mostly from the oceanic crust. Lead isotopic data on Fe--Cu sulfides are also similar to the results from the igneous suite suggesting that the source of the sulfides is predominently from the oceanic crust. Lead data from serpentinized peridotite and a galena sample from below the ophiolite suggest that part of the serpentinization process and the formation of galena could involve addition of radiogenic Pb from either a continental source or from oceanic sediments.

  19. Neodymium and strontium isotope study of ophiolite and orogenic lherzolite petrogenesis

    International Nuclear Information System (INIS)

    Richard, P.; Allegre, C.J.; Paris-7 Univ., 75

    1980-01-01

    Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. Epsilonsub(Nd) varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a epsilonsub(Nd)-epsilonsub(Sr) correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high 87 Sr/ 86 Sr ratios and as such lie to the right of the correlation line towards seawater compositions. From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago. (orig.)

  20. TRANSITION FROM CARBONATE PLATFORM TO PELAGIC DEPOSITION (MID JURASSIC- LATE CRETACEOUS, VOURINOS MASSIF, NORTHERN GREECE

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    NICOLAOS CARRAS

    2004-03-01

    Full Text Available A Jurassic- Cretaceous carbonate succession crops out along the Zyghosti Rema, Kozani (Northern Greece. The substratum consists of the ophiolitic succession of the Vourinos Massif (Pelagonian Domain: serpentinites tectonically overlain by basalts, with thin lenses of radiolarian cherts of middle Bathonian age. The contact with the overlying Jurassic limestones is tectonic. Eight informal units have been distinguished within the Mesozoic limestones, from the base upwards. (A bioclastic, intraclastic and oolitic packstone (Callovian- Oxfordian. (B bioclastic packstone and coral boundstone (Oxfordian . (C bioclastic and oncoidal wackestone with Clypeina jurassica (Oxfordian- Upper Kimmeridgian. (D (Upper Kimmeridgian- Portlandian: oncoidal packstone and rudstone (facies D1; intraclastic and bioclastic grainstone and packstone (facies D2; neptunian dykes with intraclastic and bioclastic wackestone and packstone filling (facies D3; neptunian dykes with Fe-Mn rich laterite filling and with pink silty filling of early Late Cretaceous age. An unconformity surface, due to emersion and erosion of the platform during the latest Jurassic- Early Cretaceous, is overlain by (E intraclastic, bioclastic packstone and grainstone (Cenomanian. (F massive body of debrites with coral, echinoderm, algae and rudist large clasts (facies F1 (Cenomanian; turbiditic beds of bioclastic, intraclastic and lithoclastic rudstone and grainstone (facies F2. (G thin bedded bioclastic mudstone and wackestone with planktonic foraminifers and radiolarians, alternating with turbiditic beds of bioclastic, intraclastic packstone and rudstone and with conglomeratic levels and slumped beds of the previous turbidites (upper Santonian- lower Campanian. (H: bioclastic packstone with planktonic foraminifers (facies H1 (lower Campanian - ?Maastrichtian; amalgamated turbiditic beds of bioclastic wackestone and packstone with planktonic foraminifers (facies H2; turbiditic beds of bioclastic

  1. Geochronological and geochemical constraints on the origin of the Yunzhug ophiolite in the Shiquanhe-Yunzhug-Namu Tso ophiolite belt, Lhasa Terrane, Tibetan Plateau

    Science.gov (United States)

    Zeng, Yun-Chuan; Xu, Ji-Feng; Chen, Jian-Lin; Wang, Bao-Di; Kang, Zhi-Qiang; Huang, Feng

    2018-02-01

    The formation of the Shiquanhe-Yunzhug-Namu Tso ophiolite mélange zone (SNMZ) within the Lhasa Terrane, Tibetan Plateau, is key to understanding the Mesozoic tectonic evolution of this terrane, which remains controversial. We show that the Yunzhug ophiolite in the central segment of the SNMZ formed at 150 Ma, based on U-Pb dating of zircons from a gabbroic sample in a well-developed sheeted dike complex. Geochemically, these mafic rocks are dominated by E-MORB-type compositions, along with minor amounts of rocks with P-MORB-type compositions. The samples also exhibit high εNd(t) values and lack negative Nb and Ta anomalies. Data for all the samples plot within the MORB array on a Th/Yb-Nb/Yb diagram. Therefore, these mafic rocks most likely formed in either a slow spreading oceanic setting or an embryonic ocean, and not in a back-arc basin as has been previously assumed. Taking into account the regional geology, we propose that the Yunzhug ophiolite is part of a distinct ophiolitic belt and represents material formed in an embryonic ocean within the Lhasa Terrane, which provides new insights into the Jurassic tectonic evolution of the Lhasa Terrane.

  2. Evaluation of Heterotrophy in in Serpentinite-Associated Waters from the Coast Range Ophiolite, Northern California, USA and the Zambales Ophiolite, Philippines

    Science.gov (United States)

    Scott, T. J.; Arcilla, C. A.; Cardace, D.; Hoehler, T. M.; McCollom, T. M.; Meyer-Dombard, D. R.; Schrenk, M. O.

    2013-12-01

    The deep biosphere in cold, dark sub-seafloor ultramafic rocks (i.e., those rocks rich in Fe and Mg) is stressed by exceedingly high pH, transient, if any, inorganic carbon availability, and little known organic carbon inventories. As a test of heterotrophic carbon use, serpentinite-associated waters (from groundwater sampling wells and associated surface seepages in tectonically uplifted mantle units in ophiolites) were tested for differences with respect to aqueous geochemistry and performance in EcoPlates™ - Biolog Inc. .. This work focuses on two field locations for water sampling: the Coast Range Ophiolite, CA, USA, and the Zambales Ophiolite, Philippines. Characteristics of each sampling site are presented (pH, mineral substrate, Ca2+/Mg2+ ratio, aqueous metal loads, etc.). Complementary EcoPlate™ results [prefabricated 96-well plates, seeded with triplicate experiments for determining microbiological community response to difference organic carbon sources; a triplicate control experiment with just water is built in to the plate also] are also presented. We found that waters from selected California [groundwater wells (7 discrete wells) and related surface seeps (5 hydrologically connected sites)] and Philippines [4 Zambales Ophiolite springs/seepages] sourced in serpentinites were analyzed. EcoPlate™ average well-color development (AWCD), which demonstrates microbial activities averaged per plate (as in Garland and Mills, 1991), differs across sites. Correlations of AWCD with environmental data (such as pH, oxidation-reduction potential or ORP, Ca2+/Mg2+ ratio, and Fe contents) are evaluated. Clarifying the geochemical-biological relationships that bear out in these analyses informs discourse on the energetic limits of life in serpentinizing systems, with relevance to ultramafic-hosted life on continents and in the seabed.

  3. Endolithic microbial communities in carbonate precipitates from serpentinite-hosted hyperalkaline springs of the Voltri Massif (Ligurian Alps, Northern Italy).

    Science.gov (United States)

    Quéméneur, Marianne; Palvadeau, Alexandra; Postec, Anne; Monnin, Christophe; Chavagnac, Valérie; Ollivier, Bernard; Erauso, Gaël

    2015-09-01

    The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmospheric carbon dioxide forms brownish carbonate precipitates covering the bedrock at the springs. Diverse archaeal and bacterial communities were detected in these carbonate precipitates using 454 pyrosequencing analyses of 16S ribosomal RNA (rRNA) genes. Archaeal communities were dominated by members of potential methane-producing and/or methane-oxidizing Methanobacteriales and Methanosarcinales (Euryarchaeota) together with ammonia-oxidizing Nitrososphaerales (Thaumarchaeota) similar to those found in other serpentinization-driven submarine and terrestrial ecosystems. Bacterial communities consisted of members of the Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, Chloroflexi, and Verrucomicrobia phyla, altogether accounting for 92.2% of total retrieved bacterial 16S rRNA gene sequences. Amongst Bacteria, potential chemolithotrophy was mainly associated with Alpha- and Betaproteobacteria classes, including nitrogen-fixing, methane-oxidizing or hydrogen-oxidizing representatives of the genera Azospirillum, Methylosinus, and Hydrogenophaga/'Serpentinomonas', respectively. Besides, potential chemoorganotrophy was attributed mainly to representatives of Actinobacteria and Planctomycetales phyla. The reported 16S rRNA gene data strongly suggested that hydrogen, methane, and nitrogen-based chemolithotrophy can sustain growth of the microbial communities inhabiting the carbonate precipitates in the hyperalkaline springs of the Voltri Massif, similarly to what was previously observed in other serpentinite-hosted ecosystems.

  4. Petrography and mineral chemistry of metamorphosed mantle peridotites of Nain Ophiolite (Central Iran

    Directory of Open Access Journals (Sweden)

    Nargess Shirdashtzadeh

    2017-07-01

    Full Text Available Introduction Study of the petrology of the ophiolites as the relics of ancient oceanic lithosphere, is a powerful tool to reconstruct Earth’s history. Mantle peridotites have mostly undergone alteration and serpentinization to some extent. Thus, the relics of metamorphic signatures from the upper mantle and crustal processes from most of the peridotites have been ruined. Several recent papers deal with the mantle peridotites of Nain Ophiolite (e.g. Ghazi et al., 2010. However, no scientific work has been carried out on the metamorphosed mantle peridotites. The study area of the Darreh Deh that is located in the east of the Nain Ophiolite, is composed of huge massifs of metamorphosed mantle peridotites (i.e. lherzolite, clinopyroxene-bearing harzburgite, and harzburgite, and small volumes of dunite, characterized by darker color, higher topographic relief, smaller number of basic intrusives, lower serpentinization degree, and amphibolite-facies metamorphism. In this study, the petrography and mineralogy of metamorphosed peridotites in the Darreh Deh has been considered based on geochemical data. Geological Setting The Mesozoic ophiolitic mélange of Nain is located in the west of CEIM, along the Nain-Baft fault. As a part of a metamorphosed oceanic crust, it is mainly composed of harzburgite, lherzolite, dunite and their serpentinized varieties, chromitite, pyroxenite, gabbro, diabasic dike, spilitized pillow lava, plagiogranite, amphibolite, metaperidotites, schist, skarn, marble, rodingite, metachert and listwaenite (Shirdashtzadeh et al., 2010, 2014a, 2014b. Geochemical investigations indicate a suprasubduction zone in the eastern branch of the Neo-Tethys Ocean (Ghasemi and Talbot, 2006; Shirdashtzadeh et al., 2010, 2014a, 2014b. Materials and Methods Chemical analyses of mineral compositions were carried out using a JEOL JXA8800R wavelength-dispersive electron probe micro-analyzer (accelerating voltage of 15 kV and a beam current of 15 n

  5. Mineral textures in Serpentine-hosted Alkaline Springs from the Oman ophiolite

    Science.gov (United States)

    Giampouras, Manolis; Garcia-Ruiz, Juan Manuel; Bach, Wolfgang; Garrido, Carlos J.; Los, Karin; Fussmann, Dario; Monien, Monien

    2017-04-01

    Meteoric water infiltration in ultramafic rocks leads to serpentinization and the formation of subaerial, low temperature, hydrothermal alkaline springs. Here, we present a detailed investigation of the mineral precipitation mechanisms and textural features of mineral precipitates, along as the geochemical and hydrological characterization, of two alkaline spring systems in the Semail ophiolite (Nasif and Khafifah sites, Wadi Tayin massif). The main aim of the study is to provide new insights into mineral and textural variations in active, on-land, alkaline vents of the Oman ophiolite. Discharge of circulating fluids forms small-scale, localized hydrological catchments consisting in unevenly interconnected ponds. Three different types of waters can be distinguished within the pond systems: i) Mg-type; alkaline (7.9 11.6), Ca-OH-rich waters; and iii) Mix-type waters arising from the mixing of Mg-type and Ca-type waters (9.6 ponds were carried out by X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscopy coupled to dispersive energy spectroscopy (FE-SEM-EDS). Aragonite and calcite are the dominant minerals (95 vol.%) of the total mineralogical index in all sites. Mg-type waters host hydrated magnesium carbonates (nesquehonite) and magnesium hydroxycarbonate hydrates (artinite) due to evaporation. Brucite, hydromagnesite and dypingite presence in Mix-type waters is spatially controlled by the hydrology of the system and is localized around mixing zones between Ca-type with Mg-type waters. Residence time of discharging waters in the ponds before mixing has an impact on fluid chemistry as it influences the equilibration time with the atmosphere. Acicular aragonite is the main textural type in hyper-alkaline Ca-type waters, acting as a substratum for the growth of calcite and brucite crystals. Low crystallinity, dumbbell shaped and double pyramid aragonite dominates in Mix-type water precipitates. Rate of supersaturation is essential

  6. The Behaviour of Fe Stable Isotopes Accompanying Fluid Migration in Subducted Serpentinite from the Zermatt-Saas Ophiolite of the Swiss Alps

    Science.gov (United States)

    Inglis, E.; Bouilhol, P.; Burton, K. W.; Debret, B.; Millet, M. A.; Williams, H. M.

    2016-12-01

    During subduction the destabilisation of hydrous serpentine group phases can generate significant fluid fluxes between the subducting slab and the overlying mantle wedge. Despite our knowledge of this, the exact process and nature of the fluids released during serpentinite devolatilisation remain poorly understood. This study presents new field observations alongside petrographic and geochemical data for metamorphic veins and host serpentinite from the Zermatt-Saas ophiolite from the Swiss Alps, which underwent high-pressure metamorphism during the Alpine orogeny. Samples were collected from the serpentinised ultramafic section of the Zermatt-Saas ophiolite, which is mainly comprised of variably foliated and sheared antigorite serpentine. High-pressure metamorphic veins hosted within the antigorite serpentinite, are observed within the least deformed part of the massif, occurring as cm scale laterally continuous channels or mm scale interconnected anastomosing networks. Preliminary high-precision Fe isotope data for the host antigorite serpentine yield a mean δ56Fe value of -0.09‰ ± 0.04‰ (n=3), notably lighter than previously measured Alpine and abyssal serpentinites (Debret et al., 2016). In contrast, samples of cm scale olivine-bearing veins display a mean δ56Fe value of 0.07 ± 0.05‰ (n=3), resolvably heavier than that of the host serpentinite. These preliminary results suggest preferential mobility of isotopically heavy Fe within the vein forming fluids, but at this stage it is unclear if this fluid is related to local devolatilisation of the host serpentinite or input from an external source. Debret et al., 2016. Isotopic evidence for iron mobility during subduction. Geology, v. 44, no. 3, pp. 215 -218.

  7. Geology of the Zambales ophiolite, Luzon, Philippines

    Science.gov (United States)

    Rossman, D.L.; Castanada, G.C.; Bacuta, G.C.

    1989-01-01

    The Zambales ophiolite of western Luzon, Philippines, exposes a typical succession of basalt flows, diabasic dikes, gabbro and tectonized harzburgite. The age established by limiting strata is late Eocene. Lack of evidence of thrust faulting and the general domal disposition of the lithologie units indicate that the ophiolitic rocks are exposed by uplift. Highly complex internal layered structures within the complex are related to processes developed during formation of the ophiolite and the Zambales ophiolite may be one of the least disturbed (by emplacement) ophiolitic masses known. The exposed mass trends north and the upper surface plunges at low angles (a few degrees) to the north and south. The chemistry and composition of the rocks in the northwest part of the Zambales area (Acoje block) is distinct from that in the southeastern segment (Coto block). The Acoje block, according to Evans (1983) and Hawkins and Evans (1983), resembles (on a chemical basis) arc-tholeiite series rocks from intra-island arcs and the rocks in the Coto block are typical back-arc basin rock series. The present writer believes that the ophiolite composes a single genetic unit and that the changes in composition are the result of changes that took place during the initial formation. The gabbro probably formed below a spreading center in an elongate, in cross section, V-shaped, magma chamber. The gabbro is estimated by the writer to be less than 2 km thick and may be less than 1 km in places. Numerous erosional windows through the gabbro in the northern and eastern side of the Zambales area show that the gabbro remaining in those areas is likely to be only a few hundred meters thick. Harzburgite is exposed to a depth of about 800 m in the Bagsit River area and this may be the deepest part of the ophiolite accessible for study on which there is any control on depth. A transitional zone, about 200 m thick lying between the gabbro and harzburgite, is composed of serpentinized dunite

  8. Beginning the Modern Regime of Subduction Tectonics in Neoproterozoic time: Inferences from Ophiolites of the Arabian-Nubian Shield

    Science.gov (United States)

    Stern, R.

    2003-04-01

    It is now clear that the motive force for plate tectonics is provided by the sinking of dense lithosphere in subduction zones. Correspondingly, the modern tectonic regime is more aptly called ``subduction tectonics" than plate tectonics, which only describes the way Earth's thermal boundary layer adjusts to subduction. The absence of subduction tectonics on Mars and Venus implies that special circumstances are required for subduction to occur on a silicate planet. This begs the question: When did Earth's oceanic lithosphere cool sufficiently for subduction to began? This must be inferred from indirect lines of evidence; the focus here is on the temporal distribution of ophiolites. Well-preserved ophiolites with ``supra-subduction zone" (SSZ) affinities are increasingly regarded as forming when subduction initiates as a result of lithospheric collapse (± a nudge to get it started), and the formation of ophiolitic lithosphere in evolving forearcs favors their emplacement and preservation. The question now is what percentage of ophiolites with ``supra-subduction zone" (SSZ) chemical signatures formed in forearcs during subduction initiation events? Most of the large, well-preserved ophiolites (e.g., Oman, Cyprus, California, Newfoundland) may have this origin. If so, the distribution in space and time of such ophiolites can be used to identify ``subduction initiation" events, which are important events in the evolution of plate tectonics. Such events first occurred at the end of the Archean (˜2.5Ga) and again in the Paleoproterozoic (˜1.8 Ga), but ophiolites become uncommon after this. Well-preserved ophiolites become abundant in Neoproterozoic time, at about 800±50 Ma. Ophiolites of this age are common and well-preserved in the Arabian-Nubian Shield (ANS) of Egypt, Sudan, Ethiopia, Eritrea, and Saudi Arabia. ANS ophiolites mostly contain spinels with high Cr#, indicating SSZ affinities. Limited trace element data on pillowed lavas supports this interpretation

  9. The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge

    NARCIS (Netherlands)

    Barth, M.G.; Mason, P.R.D.; Davies, G.R.; Drury, M.R.

    2008-01-01

    The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris

  10. Massification to Marketization of Higher Education: Private University Education in Bangladesh

    Science.gov (United States)

    Ahmed, Jashim Uddin

    2016-01-01

    Massification of higher education is a contemporary phenomenon, and Bangladesh is an excellent example of massification in the sector. With increased alertness worldwide among nations, policy-makers and development bodies, massification of higher education is a requirement of time. Increasing number of youth also contribute to the phenomenon…

  11. Multi-scale Onland-Offshore Investigations of the New Caledonia Ophiolite, SW Pacific

    Science.gov (United States)

    Clerc, C. N.; Collot, J.; Sevin, B.; Patriat, M.; Etienne, S.; Iseppi, M.; Lesimple, S.; Jeanpert, J.; Mortimer, N. N.; Poli, S.; Pattier, F.; Juan, C.; Robineau, B.; Godard, M.; Cluzel, D.

    2017-12-01

    The Peridotite Nappe of New Caledonia is one of the largest ultramafic ophiolite in the World: it represents about one quarter of the 500 x 80 km island of Grande Terre. This extensive upper mantle unit was tectonically emplaced during the Eocene onto the northeastern edge of Zealandia continent. It is weakly deformed because it was not involved in a collision belt after obduction. A dome-shaped Eocene HP/LT metamorphic complex was exhumed across the fore-arc mantle lithosphere in the northern tip of the island. Post-obduction Miocene to Present coral reefs developed in shallow waters around Grande Terre and surrounding islands. In the perspective of a possible onshore/offshore drilling project (IODP/ICDP), we present recent advances in our understanding of offshore extensions of this ophiolite. To the south of New Caledonia, the offshore continuation of the ultramafic allochthon has been identified by dredges and by its geophysical signature as a continuous linear body that extends over a distance of more than 400 km at about 2000m bsl. Such water depths allow an unprecedented seismic reflection imaging of a drowned and well-preserved ophiolite. Seismic profiles show that the nappe has a flat-top, and is capped by carbonate reefs and dissected by several major normal faults. To the east of this presumed ultramafic body, Felicité Ridge is a 30 km wide, 350 km long, dome-shaped ridge, which may be interpreted as the possible southern extension of the HP/LT metamorphic complex observed onshore. Onshore, several 150 to 200 m long cores were drilled in the ophiolite and airborne electromagnetic allowed high-resolution imaging down to 400 m depth. These recent results allow identification of internal thrusts within the peridotite body and more superficial landslides. The analysis of polyphase fracturation and associated serpentinization brings new constraints on the tectonic evolution of the ophiolite and its subsequent weathering pattern. We integrate these data and

  12. Geodynamic interpretation of the 40Ar/39Ar dating of ophiolitic and arc-related mafics and metamafics of the northern part of the Anadyr-Koryak region

    Science.gov (United States)

    Palandzhyan, S.A.; Layer, P.W.; Patton, W.W.; Khanchuk, A.I.

    2011-01-01

    Isotope datings of amphibole-bearing mafics and metamafics in the northern part of the Anadyr-Koryak region allow clarification of the time of magmatic and metamorphic processes, which are synchronous with certain stages of the geodynamic development of the northwest segment of the Pacific mobile belt in the Phanerozoic. To define the 40Ar/39Ar age of amphiboles, eight samples of amphibole gabbroids and metamafics were selected during field work from five massifs representing ophiolites and mafic plutons of the island arc. Rocks from terranes of three foldbelts: 1) Pekulnei (Chukotka region), 2) Ust-Belaya (West Koryak region), and 3) the Tamvatnei and El'gevayam subterranes of the Mainits terrane (Koryak-Kamchatka region), were studied. The isotope investigations enabled us to divide the studied amphiboles into two groups varying in rock petrographic features. The first was represented by gabbroids of the Svetlorechensk massif of the Pekulnei Range and by ophiolites of the Tamvatnei Mts.; their magmatic amphiboles show the distribution of argon isotopes in the form of clearly distinguished plateau with an age ranging within 120-129 Ma. The second group includes metamorphic amphiboles of metagabbroids and apogabbro amphibolites of the Ust-Belaya Mts., Pekulnei and Kenkeren ranges (El'gevayam subterranes). Their age spectra show loss of argon and do not provide well defined plateaus the datings obtained for them are interpreted as minimum ages. Dates of amphiboles from the metagabbro of the upper tectonic plate of the Ust-Belaya allochthon points to metamorphism in the suprasubduction environment in the fragment of Late Neoproterozoic oceanic lithosphere in Middle-Late Devonian time, long before the Uda-Murgal island arc system was formed. The amphibolite metamorphism in the dunite-clinopyroxenite-metagabbro Pekulnei sequence was dated to occur at the Permian-Triassic boundary. The age of amphiboles from gabbrodiorites of the Kenkeren Range was dated to be Early

  13. Structural evolution of the Semail Ophiolite metamorphic sole, Wadi Hawasina and Northern Jebel Nakhl Culmination, Oman

    Science.gov (United States)

    Hurtado, C.; Bailey, C.; Visokay, L.; Scharf, A.

    2017-12-01

    The Semail ophiolite is the world's largest and best-exposed ophiolite sequence, however the processes associated with both oceanic detachment and later emplacement onto the Arabian continental margin remain enigmatic. This study examines the upper mantle section of the ophiolite, its associated metamorphic sole, and the autochthonous strata beneath the ophiolite at two locations in northern Oman. Our purpose is to understand the structural history of ophiolite emplacement and evaluate the deformation kinematics of faulted and sheared rocks in the metamorphic sole. At Wadi Hawasina, the base of the ophiolite is defined by a 5- to 15-m thick zone of penetratively-serpentinized mylonitic peridotite. Kinematic indicators record top-to-the SW (reverse) sense-of-shear with a triclinic deformation asymmetry. An inverted metamorphic grade is preserved in the 300- to 500-m thick metamorphic sole that is thrust over deep-water sedimentary rocks of the Hawasina Group. The study site near Buwah, in the northern Jebel Nakhl culmination, contains a N-to-S progression of mantle peridotite, metamorphic sole, and underlying Jurassic carbonates. Liswanite crops out in NW-SE trending linear ridges in the peridotite. The metamorphic sole includes well-foliated quartzite, metachert, and amphibolite. Kinematic evidence indicates that the liswanite and a serpentinized mélange experienced top to-the north (normal) sense-of-shear. Two generations of E-W striking, N-dipping normal faults separate the autochthonous sequence from the metamorphic sole, and also cut out significant sections of the metamorphic sole. Fabric analysis reveals that the metamorphic sole experienced flattening strain (K<0.2) that accumulated during pure shear-dominated general shear (Wk<0.4). Normal faulting and extension at the Buwah site indicates that post-ophiolite deformation is significant in the Jebel Akhdar and Jebel Nakhl culminations.

  14. Sulfide mineralization in ultramafic rocks of the Faryab ophiolite complex, southern Kerman

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Rajabzadeh

    2015-10-01

    Full Text Available Introduction Worldwide, Ni-Cu and PGE magmatic sulfide deposits are confined to the lower parts of stratiform mafic and ultramafic complexes. However, ophiolite mafic and ultramafic complexes have been rarely explored for sulfide deposits despite the fact that they have been extensively explored and exploited for chromite. Sulfide saturation during magmatic evolution is necessary for sulfide mineralization, in which sulfide melts scavenge chalcophile metals from the parent magma and concentrate them in specific lithological zones. The lack of exploration for sulfides in this environment suggests that sulfide saturation is rarely attained in ophiolite-related magmas. Some ophiolites, however, contain sulfide deposits, such as at Acoje in Philippines, and Cliffs in Shetland, U.K. (Evans, 2000; Naldrett, 2004. The Faryab ophiolite complex in southern Kerman Province, the most important mining area for chromite deposits in Iran, is located in the southwest part of the Makran Zone. Evidence of sulfide mineralization has been reported there by some authors (e.g. Rajabzadeh and Moosavinasab, 2013. This paper discusses the genesis of sulfides in the Faryab ophiolite using mineral chemistry of the major mineral phases in different rocks of the ophiolite column in order to determine the possible lithological location of sulfide deposits. Materials and methods Seventy three rock samples from cumulate units were collected from surficial occurrences and drill core. The samples were studied using conventional microscopic methods and the mineralogy confirmed by x-ray diffraction. Electron microprobe analysis was carried out on different mineral phases in order to determine the chemistry of the minerals used in the interpretation of magma evolution in the Faryab ophiolite. Lithologically, the Faryab ophiolite complex is divided into two major parts: the northern part includes magmatic rocks and the southern part is comprised of rocks residual after partial

  15. Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc : Evidence from paleomagnetism, sediment provenance, and stratigraphy

    NARCIS (Netherlands)

    Huang, Wentao; van Hinsbergen, Douwe J J; Maffione, Marco; Orme, Devon A.; Dupont-Nivet, Guillaume; Guilmette, Carl; Ding, Lin; Guo, Zhaojie; Kapp, Paul

    2015-01-01

    The India-Asia suture zone of southern Tibet exposes Lower Cretaceous Xigaze ophiolites and radiolarian cherts, and time-equivalent Asian-derived clastic forearc sedimentary rocks (Xigaze Group). These ophiolites have been interpreted to have formed in the forearc of the north-dipping subduction

  16. The ophiolitic North Fork terrane in the Salmon River region, central Klamath Mountains, California

    Science.gov (United States)

    Ando, C.J.; Irwin, W.P.; Jones, D.L.; Saleeby, J.B.

    1983-01-01

    The North Fork terrane is an assemblage of ophiolitic and other oceanic volcanic and sedimentary rocks that has been internally imbricated and folded. The ophiolitic rocks form a north-trending belt through the central part of the region and consist of a disrupted sequence of homogeneous gabbro, diabase, massive to pillowed basalt, and interleaved tectonitic harzburgite. U-Pb zircon age data on a plagiogranite pod from the gabbroic unit indicate that at least this part of the igneous sequence is late Paleozoic in age.The ophiolitic belt is flanked on either side by mafic volcanic and volcaniclastic rocks, limestone, bedded chert, and argillite. Most of the chert is Triassic, including much of Late Triassic age, but chert with uncertain stratigraphic relations at one locality is Permian. The strata flanking the east side of the ophiolitic belt face eastward, and depositional contacts between units are for the most part preserved. The strata on the west side of the ophiolitic belt are more highly disrupted than those on the east side, contain chert-argillite melange, and have unproven stratigraphic relation to either the ophiolitic rocks or the eastern strata.Rocks of the North Fork terrane do not show widespread evidence of penetrative deformation at elevated temperatures, except an early tectonitic fabric in the harzburgite. Slip-fiber foliation in serpentinite, phacoidal foliation in chert and mafic rocks, scaly foliation in argillite, and mesoscopic folds in bedded chert are consistent with an interpretation of large-scale anti-formal folding of the terrane about a north-south hinge found along the ophiolitic belt, but other structural interpretations are tenable. The age of folding of North Fork rocks is constrained by the involvement of Triassic and younger cherts and crosscutting Late Jurassic plutons. Deformation in the North Fork terrane must have spanned a short period of time because the terrane is bounded structurally above and below by Middle or Late

  17. Petrography and mineral chemistry of metamorphosed mantle peridotites of Nain Ophiolite (Central Iran)

    OpenAIRE

    Nargess Shirdashtzadeh; Ghodrat Torabi; Ramin Samadi

    2017-01-01

    Introduction Study of the petrology of the ophiolites as the relics of ancient oceanic lithosphere, is a powerful tool to reconstruct Earth’s history. Mantle peridotites have mostly undergone alteration and serpentinization to some extent. Thus, the relics of metamorphic signatures from the upper mantle and crustal processes from most of the peridotites have been ruined. Several recent papers deal with the mantle peridotites of Nain Ophiolite (e.g. Ghazi et al., 2010). However, no scientif...

  18. Eclogite nappe-stack in the Grivola-Urtier Ophiolites (Southern Aosta Valley, Western Alps)

    Science.gov (United States)

    Tartarotti, Paola

    2013-04-01

    In the Western Alpine chain, ophiolites represent a section of the Mesozoic Tethys oceanic lithosphere, involved in subduction during the convergence between the paleo-Africa and paelo-Europe continents during the Cretaceous - Eocene. The Western Alpine ophiolites consist of several tectonic units, the most famous being the Zermatt-Saas and Combin nappes, and other major ophiolite bodies as the Voltri, Monviso, and Rocciavrè that show different rock assemblages and contrasting metamorphic imprints. The Grivola-Urtier (GU) unit is exposed in the southern Aosta Valley, covering an area of about 100 km2; it is tectonically sandwiched between the continentally-derived Pennidic Gran Paradiso Nappe below, and the Austroalpine Mount Emilius klippe above. This unit has been so far considered as part of the Zermatt-Saas nappe extending from the Saas-Fee area (Switzerland) to the Aosta Valley (Italy). The GU unit consists of serpentinized peridotites that include pods and boudinaged layers of eclogitic Fe-metagabbro and trondhjemite, rodingites and chloriteschists transposed in the main foliation together with calcschists and micaschists. All rocks preserve particularly fresh eclogitic mineral assemblages. The contact between the serpentinites and calcshists is marked by a tectonic mélange consisting of mylonitic marble and calcschist with stretched and boudinaged serpentinite blocks. Continentally-derived allochthonous blocks ranging in size from100 meters to meters are also included within the ophiolites. New field, petrographic and geochemical data reveal the complex nature of the fossil Tethyan oceanic lithosphere exposed in the southern Aosta Valley, as well as the extent and size of the continental-oceanic tectonic mélange. The geological setting of the GU unit is here inferred as a key tool for understanding the complex architecture of the ophiolites in the Western Alps.

  19. Tracing alteration of mantle peridotite in the Samail ophiolite using Mg isotopes

    Science.gov (United States)

    de Obeso, J. C.; Kelemen, P. B.; Higgins, J. A.

    2017-12-01

    Magnesium is one of the main constituents of mantle peridotite ( 22.8 wt%), which has a homogeneous Mg isotopic composition (d26Mg = -0.25 ± 0.04 ‰ (2 sd) DSM3, Teng et al 2010 GCA). Mg isotopes are used as tracers of continental and oceanic weathering as they exhibit variable degrees of fractionation during alteration depending on the lithology. Here we report some of the first Mg isotopic compositions of the mantle section of the Samail ophiolite in Oman and its alteration products. The mantle section of the ophiolite is composed mainly of depleted harzburgites and dunites with mantle-like d26Mg (-0.25, -0.21 ‰). Mantle peridotite is far from equilibrium in near surface conditions leading to rapid, extensive serpentinization, carbonation and oxidation, as well as other geochemical changes. Our analyzed samples encompass most of the alteration of peridotite products observed in Oman including listvenites (completely carbonated peridotite) near the basal thrust of the ophiolite, massive magnesite veins within peridotite outcrops, and heavily altered harzburgites. Magnesite listvenites have d26Mg slightly below mantle values (-0.33, -0.33‰) while dolomite listvenites are significantly lighter (-1.46, -0.89‰). This suggests that heavy Mg isotopes were removed from the listvenites during ophiolite emplacement. Heavily altered peridotite from Wadi Fins exhibit alteration halos with drastic changes in composition. The most oxidized areas are enriched in Fe and depleted in Mg compared to the cores of the samples. These variations in Mg concentrations are complemented by a shift to heavy Mg isotopic compositions (0.74, 0.86‰), among the heaviest d26Mg values that have been reported in altered peridotite. Potential sinks for light isotopes removed from such alteration zones are massive magnesite veins with very light compositions (-3.39, -3.14‰). The fractionation of Mg isotopes observed in the mantle section of the ophiolite spans more than 50% of the known

  20. The basal part of the Oman ophiolitic mantle: a fossil Mantle Wedge?

    Science.gov (United States)

    Prigent, Cécile; Guillot, Stéphane; Agard, Philippe; Godard, Marguerite; Chauvet, Alain; Dubacq, Benoit; Monié, Patrick; Yamato, Philippe

    2014-05-01

    Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. Fluids involved in the hydration of the oceanic lithosphere and in the presence of a secondary boninitic and andesitic volcanism may provide a way to discriminate between these two interpretations: are they descending near-axis hydrothermal fluxes (first model) or ascending from a subducting slab (second model)? We herein focus on the base of the ophiolitic mantle in order to characterize the origin of fluids and decipher hydration processes. Samples were taken along hecto- to kilometre-long sections across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that, unlike the generally refractory character of Oman harzburgites, all the basal mantle rocks display secondary crystallization of clinopyroxene and amphibole through metasomatic processes. The microstructures and the chronology of these secondary mineralizations (clinopyroxene, pargasitic amphibole, antigorite and then lizardite/chrysotile) suggest that these basal rocks have been affected by cooling from mantle temperatures (serpentines (B, Sr, Rb, Ba, As), are consistent with amphibolite-derived fluids (Ishikawa et al., 2005) and cannot be easily explained by other sources. Based on these observations, we propose a geodynamic model in which intense and continuous metasomatism of the cooling base of the ophiolitic mantle is due to the release of fluids coming from the progressive dehydration of underlying amphibolitic rocks. This process is compatible with the progressive subduction of the Arabian margin during the Upper

  1. Re–Os geochemistry and geochronology of the Ransko gabbro–peridotite massif, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Pašava, J.; Erban, V.

    2013-01-01

    Roč. 48, č. 7 (2013), s. 799-804 ISSN 0026-4598 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Re–Os * geochronology * gabbro * Bohemian Massif * Ni–Cu mineralization Subject RIV: DD - Geochemistry Impact factor: 2.667, year: 2013

  2. Local Seismicity of the Rainbow Massif on the Mid-Atlantic Ridge

    Science.gov (United States)

    Horning, G.; Sohn, R. A.; Canales, J. P.; Dunn, R. A.

    2018-02-01

    The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid-Atlantic Ridge (36°N), is notable for hosting high-temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013-2014. High rates ( 300 per day) of low-magnitude (average ML 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low-magnitude deformation at relatively shallow (serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.

  3. Origin of Manipur Ophiolite Complex, Indo-Myanmar Range ...

    Indian Academy of Sciences (India)

    r b

    2017-11-20

    Nov 20, 2017 ... The Manipur. Ophiolite. Complex: Varying degree of serpentinization and relict pyroxenes. 11/20/2017. 13. Page 14. Serpentinization process preserves the protolith elemental signatures. 11/20/2017. 14 ... The range of Nd isotope ratios in the serpentinized peridotites. 11/20/2017. 17. Kingson et al.

  4. Carboniferous and Permian evolutionary records for the Paleo-Tethys Ocean constrained by newly discovered Xiangtaohu ophiolites from central Qiangtang, central Tibet

    Science.gov (United States)

    Zhang, Xiu-Zheng; Dong, Yong-Sheng; Wang, Qiang; Dan, Wei; Zhang, Chunfu; Deng, Ming-Rong; Xu, Wang; Xia, Xiao-Ping; Zeng, Ji-Peng; Liang, He

    2016-07-01

    Reconstructing the evolutionary history of the Paleo-Tethys Ocean remains at the center of debates over the linkage between Gondwana dispersion and Asian accretion. Identifying the remnants of oceanic lithosphere (ophiolites) has very important implications for identifying suture zones, unveiling the evolutionary history of fossil oceans, and reconstructing the amalgamation history between different blocks. Here we report newly documented ophiolite suites from the Longmu Co-Shuanghu Suture zone (LSSZ) in the Xiangtaohu area, central Qiangtang block, Tibet. Detailed geological investigations and zircon U-Pb dating reveal that the Xiangtaohu ophiolites are composed of a suite of Permian (281-275 Ma) ophiolites with a nearly complete Penrose sequence and a suite of Early Carboniferous (circa 350 Ma) ophiolite remnants containing only part of the lower oceanic crust. Geochemical and Sr-Nd-O isotopic data show that the Permian and Carboniferous ophiolites in this study were derived from an N-mid-ocean ridge basalts-like mantle source with varied suprasubduction-zone (SSZ) signatures and were characterized by crystallization sequences from wet magmas, suggesting typical SSZ-affinity ophiolites. Permian and Carboniferous SSZ ophiolites in the central Qiangtang provide robust evidence for the existence and evolution of an ancient ocean basin. Combining with previous studies on high-pressure metamorphic rocks and pelagic radiolarian cherts, and with tectonostratigraphic and paleontological data, we support the LSSZ as representing the main suture of the Paleo-Tethys Ocean which probably existed and evolved from Devonian to Triassic. The opening and demise of the Paleo-Tethys Ocean dominated the formation of the major framework for the East and/or Southeast Asia.

  5. Timing of pyroxenite formation in supra-subduction Josephine Ophiolite, Oregon.

    Science.gov (United States)

    Hough, T.; Le Roux, V.; Kurz, M. D.

    2017-12-01

    The Josephine ophiolite is a partly dismembered ophiolite located in southern Oregon and northwestern California (USA). It displays a large ( 640 km2) mantle section that is mostly composed of depleted spinel harzburgite and lherzolite re-equilibrated at temperatures of 900 °C. In addition, the peridotite section of the ophiolite contains minor dunites and pyroxenite veins ranging from orthopyroxenites to clinopyroxenites. Using field, petrological and geochemical data, previous studies have shown that the peridotite experienced 10-20% of hydrous flux melting. In addition, clinopyroxene and orthopyroxene in harzburgites show variable degrees of light rare-earth element (LREE) enrichment, which suggests percolation and re-equilibration with small fractions of boninite melt. Overall, the trace element concentrations of pyroxenes indicate that the harzburgites experienced particularly high degrees of melting in the mantle wedge. We collected a number of orthopyroxenite and clinopyroxenite veins in the mantle section of the Josephine Ophiolite. Here we present the major and rare-earth element (REE) contents of pyroxene in 4 orthopyroxenites and 2 clinopyroxenites and calculate the major element and REE closure temperatures for individual veins. We show that individual pyroxenites record drastic variations in their degree of REE depletion, indicating that multiple generations of melts percolated the peridotite. The pyroxenite veins also record higher REE closure temperatures (>1200 ºC) compared to the surrounding peridotite, potentially indicating rapid cooling after emplacement. REE closure temperatures are also higher than major element closure temperatures. In parallel, we analyzed Sr isotopes by MC-ICPMS in pyroxene separates from 4 veins. Results indicate that the maximum age of emplacement of orthopyroxenite veins corresponds to the age of exhumation. Some clinopyroxenites may have formed during earlier melt percolation events. This study supports the idea that

  6. PGE mineralization and melt composition of chromitites in Proterozoic ophiolite complexes of Eastern Sayan, Southern Siberia

    Directory of Open Access Journals (Sweden)

    O. Kiseleva

    2017-07-01

    Full Text Available The Ospino-Kitoi and Kharanur ultrabasic massifs represent the northern and southern ophiolite branches respectively of the Upper Onot ophiolitic nappe and they are located in the southeastern part of the Eastern Sayan (SEPES ophiolites. Podiform chromitites with PGE mineralization occur as lensoid pods within dunites and rarely in harzburgites or serpentinized peridotites. The chromitites are classified into type I and type II based on their Cr#. Type I (Cr# = 59–85 occurs in both northern and southern branches, whereas type II (Cr# = 76–90 occurs only in the northern branch. PGE contents range from ∑PGE 88–1189 ppb, Pt/Ir 0.04–0.42 to ∑PGE 250–1700 ppb, Pt/Ir 0.03–0.25 for type I chromitites of the northern and southern branches respectively. The type II chromitites of the northern branch have ∑PGE contents higher than that of type I (468–8617 ppb, Pt/Ir 0.1–0.33. Parental melt compositions, in equilibrium with podiform chromitites, are in the range of boninitic melts and vary in Al2O3, TiO2 and FeO/MgO contents from those of type I and type II chromitites. Calculated melt compositions for type I chromitites are (Al2O3melt = 10.6–13.5 wt.%, (TiO2melt = 0.01–0.44 wt.%, (Fe/Mgmelt = 0.42–1.81; those for type II chromitites are: (Al2O3melt = 7.8–10.5 wt.%, (TiO2melt = 0.01–0.25 wt.%, (Fe/Mgmelt = 0.5–2.4. Chromitites are further divided into Os-Ir-Ru (I and Pt-Pd (II based on their PGE patterns. The type I chromitites show only the Os-Ir-Ru pattern whereas type II shows both Os-Ir-Ru and Pt-Pd patterns. PGE mineralization in type I chromitites is represented by the Os-Ir-Ru system, whereas in type II it is represented by the Os-Ir-Ru-Rh-Pt system. These results indicate that chromitites and PGE mineralization in the northern branch formed in a suprasubduction setting from a fluid-rich boninitic melt during active subduction. However, the chromitites and PGE mineralization of the southern

  7. The geology of uranium in the Saint-Sylvestre granite district (Limousin, Massif Central, France)

    International Nuclear Information System (INIS)

    Marquaire, C.; Moreau, M.; Barbier, J.; Ranchin, G.; Carrat, H.G.; Coppens, R.; Senecal, J.; Koszotolanyi, C.; Dottin, H.

    1969-01-01

    This report concerns the geology of uranium in Limousin, more particularly in the St-Sylvestre massif, and the related phenomena: regional geology, petrographic and geochemical zonal distribution observed in various granite massifs, uranium movement in connection with surface alteration, geochronology of uranium ore. The work is made up of six articles covering the various scientific aspects listed above. Each article is headed with an abstract. The paper comprises the following chapters: Foreword by Marcel ROUBAULT. 1. Ch. MARQUAIRE, M. MOREAU Outline of geological conditions in Northern Limousin and distribution of uraniferous occurrences. 2. J. BARBIER, G. RANCHIN, H. G. CARRAT and R. COPPENS Geology of the St-Sylvestre Massif and uranium geochemistry - Introduction to laboratory studies - Problems of methodology. 3. J. BARBIER and G. RANCHIN Petrographical and geochemical zones in the St-Sylvestre granite massif (Limousin - French 'Massif Central'). 4. J. BARBIER and G. RANCHIN Uranium geochemistry in the St-Sylvestre Massif (Limousin - French 'Massif Central') - Occurrences of primary geochemical uranium and replacement processes. 5. J. SENEGAL Monograph of the Brugeaud orebody. 6. R. COPPENS, Ch. KOSZTOLANYI and H. DOTTIN Geochronological study of the Brugeaud mine. 1969. (authors) [fr

  8. Deformation of the Songshugou ophiolite in the Qinling orogen

    Science.gov (United States)

    Sun, Shengsi; Dong, Yunpeng

    2017-04-01

    The Qinling orogen, middle part of the China Central Orogenic Belt, is well documented that was constructed by multiple convergences and subsequent collisions between the North China and South China Blocks mainly based on geochemistry and geochronology of ophiolites, magmatic rocks as well as sedimentary reconstruction. However, this model is lack of constraints from deformation of subduction/collision. The Songshugou ophiolite outcropped to the north of the Shangdan suture zone represents fragments of oceanic crust and upper mantle. Previous works have revealed that the ophiolite was formed at an ocean ridge and then emplaced in the northern Qinling belt. Hence, deformation of the ophiolite would provide constraints for the rifting and subduction processes. The ophiolite consists chiefly of metamorphosed mafic and ultramafic rocks. The ultramafic rocks contain coarse dunite, dunitic mylonite and harzburgite, with minor diopsidite veins. The mafic rocks are mainly amphibolite, garnet amphibolite and amphibole schist, which are considered to be eclogite facies and retrograde metamorphosed oceanic crust. Amphibole grains in the mafic rocks exhibit a strong shape-preferred orientation parallel to the foliation, which is also parallel to the lithologic contacts between mafic and ultramafic rocks. Electron backscattered diffraction (EBSD) analyses show strong olivine crystallographic preferred orientations (CPO) in dunite including A-, B-, and C-types formed by (010)[100], (010)[001] and (100)[001] dislocation slip systems, respectively. A-type CPO suggests high temperature plastic deformation in the upper mantle. In comparison, B-type may be restricted to regions with significantly high water content and high differential stress, and C-type may also be formed in wet condition with lower differential stress. Additionally, the dunite evolved into amphibolite facies metamorphism with mineral assemblages of olivine + talc + anthophyllite. Assuming a pressure of 1.5 GPa

  9. Origin of ophiolite complexes related to intra-oceanic subduction initiation: implications of IODP Expedition 352 (Izu-Bonin fore arc)

    Science.gov (United States)

    Robertson, Alastair; Avery, Aaron; Carvallo, Claire; Christeson, Gail; Ferré, Eric; Kurz, Walter; Kutterolf, Steffen; Morgan, Sally; Pearce, Julian; Reagan, Mark; Sager, William; Shervais, John; Whattam, Scott; International Ocean Discovery Program Expedition 352 (Izu-Bonin-Mariana Fore Arc), the Scientific Party of

    2015-04-01

    Ophiolites, representing oceanic crust exposed on land (by whatever means), are central to the interpretation of many orogenic belts (e.g. E Mediterranean). Based mostly on geochemical evidence, ophiolites are widely interpreted, in many but by no means all cases, as having formed within intra-oceanic settings above subduction zones (e.g. Troodos ophiolite, Cyprus). Following land geological, dredging and submersible studies, fore arcs of the SW Pacific region became recognised as likely settings of supra-subduction zone ophiolite genesis. This hypothesis was tested by recent drilling of the Izu-Bonin fore arc. Four sites were drilled, two on the outer fore arc and two on the upper trench slope. Site survey seismic data, combined with borehole data, indicate that three of the sites are located in fault-controlled sediment ponds that formed in response to dominantly down-to the-west extensional faulting (with hints of preceding top-to-the-east compressional thrusting). The sediments overlying the igneous basement, of maximum Late Eocene to Recent age, document ash and aeolian input, together with mass wasting of the fault-bounded sediment ponds. At the two more trenchward sites (U1440 and U1441), mostly tholeiitic basalts were drilled, including massive and pillowed lavas and hyaloclastite. Geochemically, these extrusives are of near mid-oceanic ridge basalt composition (fore arc basalts). Subtle chemical deviation from normal MORB can be explained by weakly fluid-influenced melting during decompression melting in the earliest stages of supra-subduction zone spreading (not as 'trapped' older MORB). The remaining two sites, c. 6 km to the west (U1439 and U1442), penetrated dominantly high-magnesian andesites, known as boninites, largely as fragmental material. Their formation implies the extraction of highly depleted magmas from previously depleted, refractory upper mantle in a supra-subduction zone setting. Following supra-subduction zone spreading, the active

  10. ECOLOGY-ECONOMICAL ASSESSMENT OF NEW RECLAMATION METHOD FOR CURRENTLY WORKING TECHNOGENIC MASSIFS

    Directory of Open Access Journals (Sweden)

    Alexey Strizhenok

    2017-01-01

    Full Text Available One of the most relevant problems of the mining industry is the need to reduce the negative impact of technogenic massifs formed by wastes of extraction and processing of mineral raw materials. This problem has a significant meaning for currently used massifs, because traditional ways of reclamation are not suitable for them. The article describes the results of a scientific study on the development of the most efficient reclamation method for currently used technogenic massifs. Described in detail the main results of the field observations, methods and equipment of laboratory experiments conducted to determine agro-chemical properties of the soil and optimal composition of binder agent. The article also provides ecological and economic assessment of the proposed method of reclamation. The study was conducted on the example of the real technogenic massif, formed by wastes of phosphorus ore processing.

  11. Peridote-water interaction generating migration pathways of H2-rich fluids in subduction context: Common processes in the ophiolites of Oman, New-Caledonia, Philippines and Turkey

    Science.gov (United States)

    Deville, E. P.; Prinzhofer, A.; Pillot, D.; Vacquand, C.; Sissmann, O.

    2010-12-01

    The occurrence of H2 flows which were punctually known notably in the ophiolites of Oman, Zambales (Philippines) and Antalya (Turkey) appears to be a widespread phenomenon in these major peridotite massifs associated with ancient or active subduction processes. Similar H2-rich gas flows have been discovered also in the peridotite of New-Caledonia. H2 concentrations are locally high (commonly 60 to90% in Oman). H2 is frequently degassing in hyperalkaline springs but the highest flows were found directly expelled from fractures in the peridotites. Obviously, within the fracture systems, gas and associated hyperalkaline water separate at shallow depth close to the top of the upper aquifer level. Locally high flows of gas migrate vertically in the fractures, whereas water with degassing H2 tends to migrate laterally in the fracture network toward the creeks where most of the hyperalkaline springs are found. The genesis of natural H2 is interpreted as the result of the interaction, at depth, between ultrabasic mantle rocks in the upper plate and water expelled by the subducted sediments by oxidation of metals (Fe2+, Mn2+) and reduction of water during serpentinisation. CH4 is commonly associated to the H2-rich fluids and it is interpreted as the result of the reduction of available CO2 at depth. N2 is also commonly associated to the H2-rich fluids in the ophiolites, whereas N2 flows (within H2) were found in the subducted sediments (below the sole décollement of the peridotite) where it can be observed (Oman and New-Caledonia). Within the peridotites, the hyperalkaline water is rich in ions OH- and Ca2+ and characterized by high pH (between 11 and 12). Most alkaline springs are found in the vicinity of major faults and/or lithological discontinuities like the basal décollement of the ophiolites and the peridotite-gabbro contact (Moho). This hyperalkaline water migration induces a chain of diagenetic reactions starting at depth within the fracture systems by the

  12. Slab and Sediment Melting during Subduction Initiation: Mantle Plagiogranites from the Oman Ophiolite

    Science.gov (United States)

    Rollinson, H. R.

    2014-12-01

    Granitoid dykes up to several hundred metres wide and 2 km long are found in depleted harzburgites in the mantle section of the Oman ophiolite. They vary in composition from tonalite to potassic granite and are generally more potassic than the crustal plagiogranites found within the sheeted dyke complex higher up within the ophiolite stratigraphy. Some granites are strongly peraluminous and contain garnet and andalusite. They are geochemically variable, some with REE that are relatively unfractionated ((La/Yb)n= 3.5-6.0, flat middle to heavy REE, steep light REE) to those which are highly fractionated ((La/Yb)n= 28-220). On primitive-mantle normalised plots some have very high concentrations of fluid-mobile elements - Cs, Rb, Th, U and Pb. Few have significant Ta-Nb anomalies. On the Ca-Fe-Mg-Ti discrimination diagram of Patino Douce (J. Petrol., 1999) whole-rock compositions define a spectrum between felsic-pelite derived melts and amphibolite-derived melts. There is a chemical similarity between the least REE fractionated plagiogranites (generally tonalites and granodiorites) and melts of an amphibolitic parent. This is supported by the occurrence of mafic xenoliths in some dykes, the presence of hornblende and highly calcic cores (up to An85) in some plagioclase grains. Trace element modelling using Oman Geotimes lavas as the starting composition indicates that melting took place in the garnet stability field, although enrichment in the melt in Cs, Rb, Ba and Pb suggests that there was another component present in addition to the mafic parent. Other plagiogranites (trondhjemites and granites) have a strongly peraluminous chemistry and mineralogy and geochemical similarities with the Himalayan leucogranites implying that they were derived from a sedimentary protolith. These mantle plagiogranites are more prevalent in the northern outcrops of the ophiolite. The volume of granitoid melt and the depth of melting preclude their derivation from the sole of the

  13. Syndeformation Chrome Spinels Inclusions in the Plastically Deformed Olivine Aggregates (Kraka Ophiolites, the Southern Urals

    Directory of Open Access Journals (Sweden)

    D. E. Saveliev

    2015-12-01

    Full Text Available This article presents the results of structural, petrographic, mineralogical and chemical studies of dunite veinlets in spinel peridotite from the Kraka ophiolites. It is demonstrated that plastic deformation of polycrystalline olivine, which form dunite, was accompanied by precipitation of impurities (aluminum and chrome as newly formed chrome spinels. The thinnest acicular inclusions of 0.3-0.5 micron thick are aligned in olivine grains along [010] axis. Bigger elongated irregular chrome spinel grains usually occur along grain and sub-grain olivine boundaries, and, occasionally, inside the grains along [100] axis. Alteration from the fine xenomorphic grains of chrome spinels to the bigger idiomorphic crystals was observed. Analogically to dynamic ageing (dispersion hardening in metals, the structural and chemical alterations in dunites are interpreted as deformation induced segregation of impurities. It is suggested that the euhedral chrome spinel grains typical for ophiolitic dunites were formed by coalescence and spheroidization. This process may be a key factor in the formation of ophiolitic chrome ore deposits.

  14. Social Class Barriers of the Massification of Higher Education in Taiwan

    Science.gov (United States)

    Ru-Jer, Wang

    2012-01-01

    In recent years, the rapid growth of higher education in Taiwan has led to an essential shift from education for the elite to the massification of higher education. Although this massification is making higher education more accessible, one of the main concerns is whether opportunities for higher education are the same among all social classes in…

  15. Heat flow map of the Bohemian massif

    Energy Technology Data Exchange (ETDEWEB)

    Cermak, V [Geophys. Inst., CS Acad. of Sci.

    1977-01-01

    Forty seven heat flow values for the Bohemian massif were used to determine the heat flow pattern of the area. By including data from neighboring countries it was possible to draw an isothermal map outlining the geothermal activity. As a result, it is possible to closely correlate the heat flow and the tectonic structure. It is obvious that the areas of high geothermal activity correspond to zones of crustal weakness associated with two major faults bordering the rigid central section of the massif. The highest heat flow values coincide with the axis of the sedimentary basin. The development of these heat flow patterns should assist in the recognition of probable areas of geothermal resources and several promising sites are readily discernible.

  16. Detection of rock strength at Branisko massif

    Directory of Open Access Journals (Sweden)

    Lazarová Edita

    2000-09-01

    Full Text Available When monitoring and optimizing the driving proces of the exploratory gallery by a computer system, conditions for verification of the interaction between desintegrating head of driving machine and rock massif were created. One of the output values of this mathematical model is the model strength at a simple pressure ótlH, which is defined as a pressure at the discus and the massif contact during the desintigration (a near limit of massif strength. By geological and geological engineering exploration, the section of length 2340 m was divided into fourty-two geological sections and five quasi-homogeneous massif enviroments. In the article, results of scleroscopic strength óCI , the strength in a simple pressure determined from the point load test and the strength at simple pressure ótlH are confronted . The main advance of the electronic geomechanical monitoring is the density of gained information. The two-seconds sample period of input and output data during the driving process makes it possible to describe driving circumstances in an almost continual way for each millimeter of the built tunnel. Then the information about changes of disintegrated rock properties, have the same density (frequency. By comparing a quantity of data gained by examining the index of point strength, scleroscopic strength and the model strength in a simple pressure from the monitoring process of driving process it is obvious that during the driving of exploratory gallery of motorway tunnel Branisko, a proportion of data number from the three “type examinations” of strength was reached and it was approximately 1:7:5000. Approximately in the same proportion, there were determined values for the 42 geologic sections (I. – XLII., which were defined in detail by the geologic, engineering geologic, hydrogeologic and geotechnic research.. The presented quantity values of presented rock mass strength for each geologic section are presented by their arithmetic average

  17. Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

    Science.gov (United States)

    Godfrey, N.J.; Beaudoin, B.C.; Klemperer, S.L.; Levander, A.; Luetgert, J.; Meltzer, A.; Mooney, W.; Tréhu, A.

    1997-01-01

    The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

  18. Massification of Higher Education and Students' Accommodation ...

    African Journals Online (AJOL)

    Massification of Higher Education and Students' Accommodation: The ... of students' accommodation at the University of Dar es salaam (UDSM) over the past 50 years. ... and the quality of learning, as well as the quality of students' life.

  19. Primary discussion on the characteristics and metallogenesis of Lingshan composite massif in northeastern Jiangxi province

    International Nuclear Information System (INIS)

    Zhang Ping; Tian Bangsheng

    2005-01-01

    A large amount of measured data has been applied to elaborate magmatic metallogenesis of Lingshan composite massif in northeastern Jiangxi Province, and to set up a metallogenetic model for polymetallic deposits, the detailed description on the characteristics of Nb-Ta, W-Sn and Pb-Zn deposits have been given. It is suggested that the Lingshan composite massif is of a ring-like multiphase batholith. Both differences and regular changes exist in following aspects such as spatial distribution, petrology, petrochemistry, microelements, REE and so on. The genetic type of the massif is regarded as A-type granite. Important mineral resources associated with the massif are Nb-Ta, W-Sn and Pb-Zn deposits. (authors)

  20. Chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange, Xinjiang, NW China

    Science.gov (United States)

    Qiu, Tian; Zhu, Yongfeng

    2018-06-01

    The Sartohay ophiolitic mélange is located in western Junggar (Xinjiang province, NW China), which is a major component of the core part of the Central Asian Orogenic Belt (CAOB). Chromian spinels in serpentinite, talc schist, carbonate-talc schist and listwaenite in Sartohay ophiolitic mélange retain primary compositions with Cr# of 0.39-0.65, Mg# = 0.48-0.67, and Fe3+# evolution of chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange. Chromian spinels in serpentinite and talc schist were rimmed by Cr-magnetite, which was dissolved completely during transformation from serpentinite/talc schist to listwaenite. Chromian spinels were then transformed into Fe2+-rich chromite in shear zones, which characterized by high fluid/rock ratios. This Fe2+-rich chromite and/or chromian spinels could then be transformed into Fe3+-rich chromite in oxidizing conditions at shallow levels.

  1. Origin of multiple serpentinization events in New Caledonia

    Science.gov (United States)

    Ulrich, M.; Guillot, S.; Muñoz, M.; Picard, C.

    2011-12-01

    Studies on serpentinites around the world have shown that various polymorphs can coexist depending on the temperature, pressure and chemistry of the formation environment. Identifying serpentine polymorphs can thus provide significant constrains on the geodynamic environment at the time of formation. The New Caledonia ophiolite (Southwest Pacific) is one of the world's largest (500 km long, 50 km wide and 2 km thick). Emplaced during Eocene, it is thrust upon the continental Norfolk ridge, which derived from the splitting of the East Gondwana margin during Lower Late Cretaceous. The ophiolite consists of a large continuous massif occurring in the south of the island and some smaller isolated klippes located along the West coast. The peridotites are mostly harzburgite, related to a supra-subduction zone environment. The northernmost massifs are also composed of lherzolites, inherited from the opening of the South Loyalty Basin where the ophiolite was formed. Serpentinization is ubiquitous (usually >50%) independently from the nature of the peridotite. However, numerous studies have focused on the ophiolite but very few on the serpentinite. In this study, we use the Raman spectroscopy to identify serpentine polymorph in each part of the ophiolite. In situ trace element measurements were performed to constrain the behavior of fluid mobile element (FME: As, Sb, B, Li, Cs, Pb, U, Ba, Sr), and we are currently analyzing stable isotopic ratios to investigate the origin of fluids. Our results show that lizardite represents ~90% of the serpentine in the New Caledonia ophiolite. Only the serpentine sole has recorded multiple serpentinization events. In this horizon, the lizardite is crosscut by millimeter to centimeter antigorite veins. Chrysotile is the last polymorph to crystallize in millimeter crackseals. If the formation of the lizardite can be easily related to abyssal history of the ophiolite for the lherzolite and its supra-subduction history for the harzburgite, the

  2. Complejo Ojosmin: fragment of ophiolite transamazonian

    International Nuclear Information System (INIS)

    Bossi, J.; Pineyro, D. . Email geologia@fagro.edu.uy

    2004-01-01

    A preliminary geological survey of a previously unknown basic igneous complex in the Padre Alta Terrane (Pat) is presented. We report petrographic, geochemical and stratigraphic data for more than 200 outcrops. Geological evolution of the complex can be described in terms of four main events: (1) formation Pat units around 2000 Ma; (2) granodiorite thrusting onto possible ophiolite ca 1900 Ma ; (3) granophyric magmatism around 1700 Ma(4) intrusion of trachyte dykes. Data available suggest thrusting onto fragment of oceanic crust. Since the described structure presupposes the existence of pre transamazonian continental fragments in the TPA, it is very important to study the area in detail in the future [es

  3. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    Science.gov (United States)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  4. Crustal Accretion at Subduction Initiation Along Izu-Bonin-Mariana Arc and the Link to SSZ Ophiolites

    Science.gov (United States)

    Ishizuka, O.; Tani, K.; Reagan, M. K.; Kanayama, K.; Umino, S.; Harigane, Y.; Sakamoto, I.

    2014-12-01

    The Izu-Bonin-Mariana (IBM) forearc preserves the earliest arc magmatic history from subduction initiation to the establishment of the arc. Recent investigations have established a bottom to top igneous stratigraphy of: 1) mantle peridotite, 2) gabbroic rocks, 3) a sheeted dyke complex, 4) basaltic pillow lavas (forearc basalts: FAB), 5) boninites and magnesian andesites, 6) tholeiites and calcalkaline arc lavas. This stratigraphy has many similarities to supra-subduction zone (SSZ) ophiolites. One of the most important common characteristics between the SSZ ophiolites and the forearc crust is the occurrence of MORB-like basaltic lavas underlying or accompanying boninites and early arc volcanic suites. A key observation from the IBM forearc is that FAB differs from nearby back-arc lavas in chemical characteristics, including a depletion in moderately incompatible elements. This indicates that FAB is not a pre-existing oceanic basement of the arc, but the first magmatic product after subduction initiation. Sheeted dikes of FAB composition imply that this magmatism was associated with seafloor spreading, possibly triggered by onset of slab sinking. Recognition of lavas with transitional geochemical characteristics between the FAB and the boninites strongly implies genetic linkage between these two magma types. The close similarity of the igneous stratigraphy of SSZ ophiolites to the IBM forearc section strongly implies a common magmatic evolutionary path, i.e., decompressional melting of a depleted MORB-type mantle is followed by melting of an even more depleted mantle with the addition of slab-derived fluid/melt to produce boninite magma. Similarity of magmatic process between IBM forearc and Tethyan ophiolites appears to be reflected on common characteristics of upper mantle section. Peridotite from both sections show more depleted characteristics compared to upper mantle rocks from mid-ocean ridges. Age determinations reveal that first magmatism at the IBM arc

  5. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe J. J.; de Gelder, Giovanni I. N. O.; van der Goes, Freek C.; Morris, Antony

    2017-05-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distributed in the eastern Mediterranean region along three E-W trending ophiolitic belts. Several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra-Neo-Tethyan subduction zone. Here we present new paleospreading directions from six Upper Cretaceous ophiolites of Turkey, Cyprus, and Syria, calculated by using new and published paleomagnetic data from sheeted dyke complexes. Our results show that NNE-SSW subduction zones were formed within the Neo-Tethys during the Late Cretaceous, which we propose were part of a major step-shaped subduction system composed of NNE-SSW and WNW-ESE segments. We infer that this subduction system developed within old (Triassic?) lithosphere, along fracture zones and perpendicular weakness zones, since the Neo-Tethyan spreading ridge formed during Gondwana fragmentation would have already been subducted at the Pontides subduction zone by the Late Cretaceous. Our new results provide an alternative kinematic model of Cretaceous Neo-Tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old (and cold) lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges.

  6. Petrographical and geochemical properties of plagiogranites and gabbros in Guleman ophiolite

    Directory of Open Access Journals (Sweden)

    Ayşe Didem KILIÇ

    2009-06-01

    Full Text Available Petrographical and geochemical properties of gabbros and plagiogranites of Guleman ophiolite are determined. It was concluded that gabbros can be basic rocks on subduction zone and plagioclase-rich leucocratic rocks (plagiogranite are differentiation products of fractional crystallization of a basic magma in the magma chamber.

  7. An overview on geochemistry of Proterozoic massif-type ...

    Indian Academy of Sciences (India)

    A critical study of 311 published WR chemical analyses, isotopic and mineral chemistry of ... Keywords. Massif anorthosite complexes; overview; geochemistry; high-Al gabbro. J. Earth ...... (123–2920 ppm) unlike the experimental results of.

  8. TOURISTIC POTENTIAL, MANAGEMENT AND DEVELOPMENT IN THE RARĂU MASSIF

    Directory of Open Access Journals (Sweden)

    Dinu OPREA-GANCEVICI

    2011-06-01

    Full Text Available As a socio-economic activity, tourism is strongly influenced by numerous factors that determine the size and direction of tourist flows. Mountain tourism is no exception; the mountainous land relief, which generates this type of tourism, possesses a large array of factors which, by definition, represent true attractions for tourists (morphometric elements, types and landforms, oxygen-rich air, specific flora and fauna, but also several factors that may inhibit tourist activity proper (development capacity, climate, natural phenomena hazards.In particular, with reference to the Rarău Massif, we shall emphasize its tourist potential, especially the geomorphologic one, but we shall also highlight the evolution and the present state of infrastructure (accommodation facilities, tourist paths. The cartographic analysis and representation were obtained using dedicated software, generically called Geographic Informatics Systems (GIS, and a social research method as well – the questionnaire. As such, our research features several maps that highlight the differentiated land relief potential as well as the potential resulted from the application of questionnaires, thus bringing into the foreground the areas with maximal morphologic attractiveness and implicitly potential for tourist activity. In order to make the most of the entire massif and to diversify tourist routes we propose new itineraries with a view to covering the entire area more effectively and offering new exploration variants for the massif. The applied questionnaire proves the connection between the tourist potential of land relief and tourists’ perceptions of the tourist sights in the Rarău Massif.

  9. Tourist Activities-Disturbance Factors of Natural Environment in Ciucaș Massif

    Directory of Open Access Journals (Sweden)

    Luminița Costina SĂFTOIU

    2014-10-01

    Full Text Available The study outlines how tourism activities can disturb the natural environment in Ciucaș Massif. Methods used are based on bibliographic research and GIS analysis of morphometric features. Results show that the Ciucaș Massif, as one of the most important mountain in central Romania, is made of conglomerates, which lend specific features to topography. Having several natural sights (The Old Ladies Council, The Sphinx of Bratocea, Zăganului Ridge this massif is declared a protected natural area. The geomorphologic processes: compactions, mudflows, the deepening of tourist paths, rills and gully erosion have a negative impact on the landscape and even on the entire environment, causing erosion and loss of soil and vegetation. Also, the increased number of tourist accommodation facilities and 21 marked tourist trails have resulted in shrinking of forest areas, hayfields and pastures.These numerous changes which occur in this mountain area, lead, in time, to radical, irreversible changes and can affect the local economic development.

  10. The influence of tectonical structures on the stability rock massif in the area of the magnesite deposit Jelšava of the Dúbrava massif

    Directory of Open Access Journals (Sweden)

    Sasvári Tibor

    2002-12-01

    Full Text Available Magnesite deposits Dúbrava and Miková are located in Carboniferous formations between Brádno and Ochtiná (Dúbrava massif. Carboniferous magnesites are, according to the lithostratigraphic division of Early Paleozoic complexes of Gemericum by Bajaník et al. (1983, situated in the Dobšiná Group, more precisely in the upper part of the Ochtiná Formation, in the environment of black schists with intercalation of metabasalts and their pyroclastics. In the lower parts of the formation are small-pebble conglomerates and polymict sandstones. Carbonatic bodies of the Dúbrava massif has the directional length, 4 500 m, course NE-SW, inclination 55-60o to SE and maximal thickness 600 m. A calculation in 1967 indicated above 500 millions kt of reserves whish after a modification of conditional parameters was reduced to its three fifths. Reserves excluded during the second calculation had a higher content of Fe2O3 causing the lowering of fireproof products quality.In the text the structural and stability conditions in the area of the Dúbrava deposit and the Miková deposit of the Dúbrava massif are analysed.

  11. Research of dynamical Characteristics of slow deformation Waves as Massif Responses on Explosions

    Science.gov (United States)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2013-04-01

    The research of massif state with use of approaches of open system theory [1-3] was developed for investigation the criterions of dissipation regimes for real rock massifs, which are under heavy man-caused influence. For realization of that research we used the data of seismic catalogue of Tashtagol mine. As a result of the analyze of that data we defined character morphology of phase trajectories of massif response, which was locally in time in a stable state: on the phase plane with coordinates released by the massif during the dynamic event energy E and lg(dE/dt) there is a local area as a ball of twisted trajectories and some not great bursts from that ball, which are not greater than 105 joules. In some time intervals that burst can be larger, than 105 joules, achieving 106 joules and yet 109 joules. [3]. Evidently there are two reciprocal depend processes: the energy accumulation in the attracted phase trajectories area and resonance fault of the accumulated energy. But after the fault the system returns again to the same attracted phase trajectories area. For analyzing of the thin structure of the chaotic area we decided to add the method of processing of the seismic monitoring data by new parameters. We shall consider each point of explosion as a source of seismic or deformation waves. Using the kinematic approach of seismic information processing we shall each point of the massif response use as a time point of the first arrival of the deformation wave for calculation of the wave velocity, because additionally we know the coordinates of the fixed response and the coordinates of explosion. The use of additional parameter-velocity of slow deformation wave propagation allowed us with use method of phase diagrams identify their hierarchic structure, which allow us to use that information for modeling and interpretation the propagation seismic and deformation waves in hierarchic structures. It is researched with use of that suggested processing method the thin

  12. Alteration, age, and emplacement of the Tangihua Complex ophiolite, New Zealand

    International Nuclear Information System (INIS)

    Nicholson, K.N.; Black, P.M.; Picard, C.; Cooper, P.; Hall, C.M.; Itaya, T.

    2007-01-01

    The Tangihua Complex, New Zealand, represents an upper sequence of Late Cretaceous oceanic crustal material: massive basalt flows, pillow lavas, and dolerites. Three phases of alteration are preserved within the complex, each characterised by zeolite precipitation, which correlate to stratigraphic position. The mylonitised sole contains greenschist assemblages (c. 325 degrees C) grading upwards into the initial phase of alteration (250-300 degrees C), and is characterised by actinolite, epidote, albite, and Na-rich zeolites. This phase is cut by lower temperature veins of chlorite-smectite and Ca-rich zeolites. The final alteration phase ( + and Ca 2+ rich minerals, including apophyllite and calcite. Disruption of Ar/Ar spectra around 50 Ma correlate with rifting in the Loyalty Basin and initiation of obduction along the Loyalty-Three Kings Ridge system. We suggest that these events resulted in initial dismemberment, alteration, and movement of the ophiolite, whereas Ar/Ar plateaux at 25-35 Ma correspond to ophiolite emplacement and the last phases of alteration. (author). 49 refs., 5 figs., 3 tabs

  13. Structural and kinematic evolution of a Miocene to Recent sinistral restraining bend: the Montejunto massif, Portugal

    Science.gov (United States)

    Curtis, Michael L.

    1999-01-01

    The Montejunto massif lies in the apex of a large-scale restraining bend at the southern termination of a sinistral transpressive fault system, in the Lusitanian basin of Portugal. Cenozoic deformation within the Montejunto massif initiated with southerly directed thrusting along the southern boundary of the massif, in association with the development of the E-W oriented Montejunto anticline, probably during the Langhian. Deformation switched to the northern boundary of the massif, in association with a change to NW-directed thrusting and continued development of the Montejunto anticline. The youngest set of structures within the massif is related to the sinistral reactivation of the Arieiro fault system, and steeply inclined bedding. This late phase of deformation represents the accommodation of a component of sinistral displacement across the restraining bend along mechanical anisotropies formed during this progressive Cenozoic deformation event. Variation in the kinematic style of the Main Arieiro fault is related to the angle ( α) between the fault plane and the displacement vector. Where α≈20°, abrupt pene-contemporaneous switches in displacement direction are recorded along the fault, whereas strike-slip kinematics predominate where α<20°. The timing of deformation events in the Montejunto massif is uncertain. However, correlation with the established Cenozoic Africa/Europe plate convergence directions may provide potential temporal constraints.

  14. Strongly foliated garnetiferous amphibolite clasts in ophiolitic melanges, Yarlung Zangbo Suture Zone, Tibet; Early Cretaceous disruption of a back-arc basin?

    Science.gov (United States)

    Guilmette, C.; Hebert, R.; Wang, C.; Indares, A. D.; Ullrich, T. D.; Dostal, J.; Bedard, E.

    2007-12-01

    Metre to decameter-size clasts of amphibolite are found embedded in ophiolitic melanges underlying the Yarlung Zangbo Suture Zone Ophiolites, South Tibet, China. These ophiolites and melanges occur at the limit between Indian and Tibetan-derived rocks and represent remnants of an Early Cretaceous intraoceanic supra-subduction zone domain, the Neo-Tethys. In the Saga-Dazuka segment (500 km along-strike), we discovered new occurrences of strongly foliated amphibolites found as clasts in the ophiolitic melange. In garnet-free samples, hornblende is green-blue magnesio-hornblende and cpx is low-Al diopside. In garnet- bearing samples, garnet is almandine with a strong pyrope component (up to 30 mol%) whereas coexisting hornblende is brown Ti-rich tschermakite and clinopyroxene is Al-diopside. Plagioclase composition was ubiquitously shifted to albite during a late metasomatic event. Geochemistry of these rocks indicates that their igneous protoliths crystallized from a slightly differentiated tholeiitic basaltic liquid that did not undergo major fractionation. Trace element patterns reveal geochemical characteristics identical to those of the overlying ophiolitic crust. These are 1) trace element abundances similar to that of N-MORBs or BABBs, 2) a slight depletion of LREE and 3) a moderate to strong Ta-Nb negative anomaly and a slight Ti anomaly. Such characteristics suggest genesis over a spreading center close to a subduction zone, possibly a back-arc basin. Step-heating Ar/Ar plateau ages were obtained from hornblende separates. All ages fall in the range of 123-128 Ma, overlapping the crystallization ages from the overlying ophiolite (126-131 Ma). Pseudosections were built with the THERMOCALC software in the system NCFMASH. Results indicate that the observed assemblage Hb+Pl+Gt+Cpx is stable over a wide range of P-T conditions, between 10-18 kbars and at more than 800°C. Measured mineral modes and solid solution compositions were successfully modeled, indicating

  15. Hydrogeology of the Olševa massif (Slovenia

    Directory of Open Access Journals (Sweden)

    Jure Krivic

    2002-12-01

    Full Text Available Olševa consists of highly pervious carbonates, forming a relatively big fractured and karstified aquifer. Due to its high-altitude mountainous nature, the aquifer is unpolluted and therefore has to be regarded as a potential source of drinking water for the future.The Olševa aquifer is tectonically divided into three parts. Groundwater from the two smaller aquifers, covering areas of 1,9 and 0,8 km2, located in eastern part of Ol{eva massif, flows toward Northeast into Meža river basin. In spite of several transversal faults, the rest of Olševa massif forms a relatively uniform aquifer that is conveying groundwater in westerly direction towards Rjavica valley. Rjavica valley in Austria represents the discharge area of a majority of groundwater from the main Ol{eva aquifer.

  16. Tethyan Anhydrite Preserved in the Lower Ocean Crust of the Samail Ophiolite? Evidence from Oman Drilling Project Holes GT1A and 2A

    Science.gov (United States)

    Teagle, D. A. H.; Harris, M.; Crispini, L.; Deans, J. R.; Cooper, M. J.; Kelemen, P. B.; Alt, J.; Banerjee, N.; Shanks, W. C., III

    2017-12-01

    Anhydrite is important in mid-ocean ridge hydrothermal systems because of the high concentrations of calcium and sulfate in modern seawater and anhydrite's retrograde solubility. Because anhydrite hosts many powerful tracers of fluid-rock interactions (87Sr/86Sr, δ18O, δ34S, trace elements, fluid inclusions) it is useful for tracing the chemical evolution of hydrothermal recharge fluids and estimating time-integrated fluid fluxes. Anhydrite can form from heated seawater (>100°C), through water-rock reaction, or by mixing of seawater and hydrothermal fluids. Although abundant in active hydrothermal mounds, and predicted to form from downwelling, warming fluids during convection, anhydrite is rare in drill core from seafloor lavas, sheeted dikes and upper gabbros, with only minor amounts in ODP Holes 504B and 1256D. Because anhydrite can dissolve during weathering, its occurrence in ophiolites is unexpected. Instead, gypsum is present in Macquarie Island lavas and Miocene gypsum fills cavities within the Cretaceous Troodos ore deposits. Thus, the occurrence of numerous anhydrite veins in cores from the gabbroic lower crust of the Samail ophiolite in Oman was unanticipated. To our knowledge, anhydrite in Oman gabbros has not been previously reported. Oman Drilling Project Holes GT1A and GT2A were drilled into the Wadi Gideah section of the Wadi Tayin massif. Both recovered 400 m of continuous core from sections of layered gabbros (GT1) and the foliated-layered gabbro transition (GT2). Anhydrite is present throughout both holes, some in vein networks but more commonly as isolated 1-110 mm veins (>60 mm ave). Anhydrite is mostly the sole vein filling but can occur with greenschist minerals such as epidote, quartz, chlorite and prehnite. Anhydrite commonly exhibits prismatic and bladed textures but can also be capriciously microcrystalline. Though definitive cross cutting relationships are elusive, anhydrite veins cut across some greenschist veins. Anhydrite is

  17. Uranium mineralization in the Bohemian Massif and its exploration

    International Nuclear Information System (INIS)

    Matolin, M.; Pluskal, O.; Rene, M.

    1981-01-01

    Long-term systematic and planned uranium survey including airborne, carborne, ground, logging and laboratory radiometric measurements as well as geological and geochemical investigations have shown a difference in radioactivity of two regional geological units in Czechoslovakia. The higher regional radioactivity of the Variscan granitoid rocks of the Bohemian Massif differs from that of the West Carpathians and is associated with more frequent uranium mineralization. Endogenous vein-type uranium mineralization has a spatial association with high-radioactivity granitoids in the Bohemian Massif. Airborne prospection defined rock radioactivity features on a regional scale while surface and subsurface radiometric and geological investigations using various techniques localized important uranium deposits. Complex statistical evaluation of numerous geophysical and geological data was studied in order to delineate uranium-favourable areas. (author)

  18. Petrology, geochemistry and source characteristics of the Burpala alkaline massif, North Baikal

    Directory of Open Access Journals (Sweden)

    N.V. Vladykin

    2017-07-01

    Full Text Available The Burpala alkaline massif contains rocks with more than 50 minerals rich in Zr, Nb, Ti, Th, Be and rare earth elements (REE. The rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite and contain up to 10% LILE and HSFE, 3.6% of REE and varying amounts of other trace elements (4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th and 0.1% U. Geological and geochemical data suggest that all the rocks in the Burpala massif were derived from alkaline magma enriched in rare earth elements. The extreme products of magma fractionation are REE rich pegmatites, apatite–fluorite bearing rocks and carbonatites. The Sr and Nd isotope data suggest that the source of primary melt is enriched mantle (EM-II. We correlate the massif to mantle plume impact on the active margin of the Siberian continent.

  19. Spring and surface water quality of the Cyprus ophiolites

    Directory of Open Access Journals (Sweden)

    C. Neal

    2002-01-01

    Full Text Available A survey of surface, spring and borehole waters associated with the ophiolite rocks of Cyprus shows five broad water types (1 Mg-HCO3, (2 Na-SO4-Cl-HCO3, (3 Na-Ca-Cl-SO4-OH-CO3, (4 Na-Cl-SO4 and (5 Ca-SO4. The waters represent a progression in chemical reactivity from surface waters that evolve within a groundwater setting due to hydrolysis of the basic/ultrabasic rock as modified by CO2-weathering. An increase in salinity is also observed which is due to mixing with a saline end-member (modified sea-water and dissolution of gypsum/anhydrite. In some cases, the waters have pH values greater than 11. Such high values are associated with low temperature serpentinisation reactions. The system is a net sink for CO2. This feature is related not only to the hydrolysis of the primary minerals in the rock, but also to CaCO3 or Ca-Mg-CO3 solubility controls. Under hyperalkaline conditions, virtually all the carbon dioxide is lost from the water due to the sufficiently high calcium levels and carbonate buffering is then insignificant. Calcium sulphate solubility controls may also be operative when calcium and sulphate concentrations are particularly high. Keywords: Cyprus, Troodos, ophiolite, serpentinisation, spring, stream, water quality, bromide, iodine, boron, trace elements, hyperalkaline.

  20. The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine ophiolites

    Science.gov (United States)

    Inglis, Edward C.; Debret, Baptiste; Burton, Kevin W.; Millet, Marc-Alban; Pons, Marie-Laure; Dale, Christopher W.; Bouilhol, Pierre; Cooper, Matthew; Nowell, Geoff M.; McCoy-West, Alex J.; Williams, Helen M.

    2017-07-01

    Arc lavas display elevated Fe3+/ΣFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidized or oxidizing components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride, and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex, and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S-bearing and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilized from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in proximity to metasediments display a significant Fe isotope fractionation. The covariation of δ56Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.

  1. Lytostratigraphy of the eocene sediments in the Serbian-Macedonian Massif, Republic of Macedonia

    OpenAIRE

    Stojanova, Violeta; Petrov, Gose; Sijakova-Ivanova, Tena

    2017-01-01

    This paper presents the lithostratography of the eocene sedimentary series in the Serbian Macedonian massif on the territory of the Republic of Macedonia. Sediments of Eocene age in the Serbian Macedonian massif are represented in the Delchevo, Deve Bair and Strumi ca basin, with the orientation of NW-SE to S-J. With lithostratigraphic studies of eocene sediments in the basins in SMM, 3 superposition lithostratigraphic units (lithozones) were isolated:...

  2. Behaviour of uranium during late-Hercynian and alpine metamorphisms in the Aiguilles rouges and Belledonne (Valorcine, Lauziere) massifs. Western Alps

    International Nuclear Information System (INIS)

    Negga, H.S.

    1984-01-01

    The purpose of this research thesis is to define the origin of numerous uranium anomalies in the external crystalline Alpine massifs, more precisely the massif of the Aiguilles Rouges and the massif of Belledonne. The primary cause of uranium mineralization in the first massif appears to have been the retrograde metamorphism events of the late-Hercynian age. In the second massif, the same conditions of uranium mineralization appear to have been realised, but with a much higher calcium activity in the fluids. After having explained the choice of the selected areas, the sampling and the chemical analysis performed, the author describes the geological and structural framework of Western Alps: geological history of the paleozoic platform, regional geology of the studied massifs. The next part reports the petrographic and geochemical study, the analysis of the mineral chemistry, of the alteration and the metamorphism. Then the author describes the geochemistry of uranium and thorium within the studied structures

  3. Petrology and Rock Magnetism of the peridotites of Pindos Ophiolite (Greece), insights into the serpentinization process

    Science.gov (United States)

    Bonnemains, D.; Carlut, J. H.; Mevel, C.; Andreani, M.; Escartin, J.; Debret, B.

    2015-12-01

    We present a petrological and magnetic study of a suite of serpentinized peridotites from the Pindos ophiolite spanning a wide range in the degree of serpentinization (from ~10 to 100%). The Pindos ophiolite, in Northern Greece, is a portion of Late Triassic oceanic lithosphere obducted during the convergence of the Apulian and Pelagonian micro-continents. This ophiolite is interpreted mainly as the result of a supra-subduction zone spreading process but its complete history remains largely unknown. Therefore, it is not clear when the ultramafic section was exposed to fluid circulation that resulted in its serpentinization. Element partitioning during serpentinization reactions is dependent on parameters such as temperature and water-rock ratio. In particular, they affect the behavior of the iron released by olivine, which can be taken up either by magnetite, serpentine and/or brucite. Analyses of the reaction products are therefore a key to constrain the conditions during the main stage of the alteration. Our study was designed to gain insight on the conditions prevailing during hydration. Our results indicate that even fully serpentinized samples have a very low magnetization and magnetite content. Moreover, microprobe and μXanes results show that serpentine is the main host of iron in the divalent but also trivalent form. These results are compared with a set of data from serpentinized ultramafics sampled from the ocean floors, as well as from various other ophiolites. We suggest that serpentinization at Pindos occurred at relatively low-temperature (less than 200 °C), therefore not at a ridge environment. In addition, we stress that the presence of trivalent iron in serpentine indicates that serpentinization may remain a producer of hydrogen even when very little magnetite is formed.

  4. U-Pb geochronology by La-CIP-MS and petrography of Sao Carlos massif - stanniferous province of Rondonia

    International Nuclear Information System (INIS)

    Debowski, Beatriz P.; Geraldes, Mauro Cesar; Nogueira, Camila; Almeida, Bruna Saar de

    2015-01-01

    U-Pb dating by ICP-MS-LA were performed in four samples of the Massif Sao Carlos massif, representative of the younger Granites of Rondonia belonging to the stanniferous province of the same State. Dated samples are granites of pink in colour and coarse-grained to porphyry with main mineralogy consisting of feldspar pertitic to mesopertitic, quartz, plagioclase in lower proportion, biotite and amphibole in some cases. Ages obtained were 986 ± 14 Ma, 974 ± 10 Ma, ± 8 Ma 992.7 and 996 ± 8 Ma and represent the age of crystallization of the Massif. Such ages are concordant with others reported on the bibliography ratifying the inclusion of the massif in the younger Granites of Rondonia, which are directly associated with the most significant mineralization of cassiterite in the State

  5. Reduced gas seepages in ophiolitic complexes: Evidences for multiple origins of the H2-CH4-N2 gas mixtures

    Science.gov (United States)

    Vacquand, Christèle; Deville, Eric; Beaumont, Valérie; Guyot, François; Sissmann, Olivier; Pillot, Daniel; Arcilla, Carlo; Prinzhofer, Alain

    2018-02-01

    This paper proposes a comparative study of reduced gas seepages occurring in ultrabasic to basic rocks outcropping in ophiolitic complexes based on the study of seepages from Oman, the Philippines, Turkey and New Caledonia. This study is based on analyses of the gas chemical composition, noble gases contents, stable isotopes of carbon, hydrogen and nitrogen. These seepages are mostly made of mixtures of three main components which are H2, CH4 and N2 in various proportions. The relative contents of the three main gas components show 4 distinct types of gas mixtures (H2-rich, N2-rich, N2-H2-CH4 and H2-CH4). These types are interpreted as reflecting different zones of gas generation within or below the ophiolitic complexes. In the H2-rich type, associated noble gases display signatures close to the value of air. In addition to the atmospheric component, mantle and crustal contributions are present in the N2-rich, N2-H2-CH4 and H2-CH4 types. H2-bearing gases are either associated with ultra-basic (pH 10-12) spring waters or they seep directly in fracture systems from the ophiolitic rocks. In ophiolitic contexts, ultrabasic rocks provide an adequate environment with available Fe2+ and alkaline conditions that favor H2 production. CH4 is produced either directly by reaction of dissolved CO2 with basic-ultrabasic rocks during the serpentinization process or in a second step by H2-CO2 interaction. H2 is present in the gas when no more carbon is available in the system to generate CH4. The N2-rich type is notably associated with relatively high contents of crustal 4He and in this gas type N2 is interpreted as issued mainly from sediments located below the ophiolitic units.

  6. Enriched and depleted characters of the Amnay Ophiolite upper crustal section and the regionally heterogeneous nature of the South China Sea mantle

    Science.gov (United States)

    Perez, Americus d. C.; Faustino-Eslava, Decibel V.; Yumul, Graciano P.; Dimalanta, Carla B.; Tamayo, Rodolfo A.; Yang, Tsanyao Frank; Zhou, Mei-Fu

    2013-03-01

    The volcanic section of the Middle Oligocene Amnay Ophiolite in Mindoro, Philippines has previously been shown to be of normalmid-oceanic ridge basalt (NMORB) composition. Here we report for the first time an enriched mantle component that is additionally recorded in this crustal section. New whole rock major and trace element data are presented for nine mafic volcanic rocks from a section of the ophiolite that has not been previously examined. These moderately evolved tholeiitic basalts were found to have resulted from the bulk mixing of ˜10% ocean island basalt components with depleted mantle. Drawing together various geochemical characteristics reported for different rock suites taken as representatives of the South China Sea crust, including the enriched MORB (EMORB) and NMORB of the East Taiwan Ophiolite, the NMORB from previous studies of the Amnay Ophiolite and the younger ocean floor eruptives of the Scarborough Seamount-Reed Bank region, a veined mantle model is proposed for the South China Sea mantle. The NMORB magmatic products are suggested to have been derived from the more depleted portions of the mantle whereas the ocean island basalt (OIB) and EMORB-type materials from the mixing of depleted and veined/enriched mantle regions.

  7. Comment on "Timing and nature of the Xinlin-Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing'an Range, eastern Central Asian Orogenic Belt" by Feng et al. (2016)

    Science.gov (United States)

    Ni, Dong-Hong

    2017-09-01

    We disagree the transitional supra-subduction zone model of Feng et al. (Int J Earth Sci (Geol Rundsch) 105:491-505, 2016) for the tectonic setting of Jifeng ophiolite suite in NE China. Existence of the komatiite in the Jifeng ophiolite indicates an oceanic plateau environment for this ophiolite suite within the so-called Xinlin-Xiguitu ocean.

  8. Massification and Quality Assurance in Tertiary Education: The ...

    African Journals Online (AJOL)

    The study sets out to examine massification and its impact on quality assurance in tertiary education and the extent to which lecturer–student ratio, adequacy of infrastructure and pedagogical resources affect quality in tertiary institutions. Two research questions and one hypothesis were posed to guide the investigation.

  9. Interpretation of recent gravity profiles over the ophiolite belt, Northern Oman Mountains, United Arab Emirates

    Science.gov (United States)

    Khattab, M. M.

    1993-04-01

    The compiled Bouguer gravity anomaly map over parts of the ophiolite rocks of the Northern Oman Mountains suggests the existence of three partially serpentinized nappes: two along the Gulf of Oman coast with axes near Dadnah, near Fujira and the third 17 km SSE of Masafi. Modeling of the subsurface geology, beneath two gravity profiles (Diba-Kalba and Masafi-Fujira), is based on the occurrence (field evidence) of multiphase low-angle thrusting of the members of the Tethyan lithosphere in northern and Oman Mountains. An assumed crustal model at the Arabian continental margin, beneath the Masafi-Fujira profile, is made to explain an intense gravity gradient. Gravity interpretation is not inconsistent with a gliding mechanism for obduction of the ophiolite on this part of the Arabian continental margin.

  10. Sm-Nd dating of the Verkhneundytkansky massif of autonomous anorthosites (Aldanian Shield)

    International Nuclear Information System (INIS)

    Sukhanov, M.K.; Lennikov, A.M.; Zhuravlev, D.Z.

    1991-01-01

    Geochronological investigation of four typical rocks of the Verkhneundyransky anorthosite massif as well as rock-forming minerals of one of the samples is carried out by the method of Sm-Nd dating. Model ayes of the investigated rocks which were calculated with respect to the depleted mantle, constitute 2.22-2.35 bullion ylars which well agrees with the isochronous age. The experimental points fall well on the regression line which attests that the crystallization of the investigated massif proceeded rather fast and the latter could not assimilate the crustal matter to a considerable extent

  11. Controls on rheology of peridotite at a palaeosubduction interface: a transect across the base of the Oman-UAE ophiolite

    Science.gov (United States)

    Ambrose, T. K.; Wallis, D.; Hansen, L. N.; Waters, D. J.; Searle, M. P.

    2017-12-01

    Studies of experimentally deformed rocks and small-scale natural shear zones have demonstrated that volumetrically minor phases can control strain localisation by limiting grain growth and promoting grain-size sensitive deformation mechanisms. Such studies are often used to infer a critical role for minor phases in the development of plate boundaries. However, the role of of minor phases in strain localisation at plate boundaries remains to be tested by direct observation. To test the hypothesis that minor phases control strain localisation at plate boundaries, we conducted microstructural analyses of peridotite samples collected across the base of the Oman-UAE ophiolite. The base of the ophiolite is marked by the Semail thrust, which represents the now exhumed contact between subducted oceanic crust and the overlying mantle wedge. As such, the base of the ophiolite provides the opportunity to directly examine a former plate boundary. Our results demonstrate that the mean olivine grain size is inversely proportional to the abundance of minor phases (primarily pyroxene), consistent with suppression of grain growth by grain-boundary pinning. Our results also reveal that mean olivine grain size is proportional to CPO strength, suggesting that the fraction of strain accommodated by different deformation mechanisms varied spatially. Experimentally-derived flow laws indicate that under the inferred deformation conditions the viscosity of olivine was grain-size sensitive. As such, grain size, and thereby the abundance of minor phases, influenced viscosity during subduction-related deformation along the base of the mantle wedge. We calculate that viscosity and strain rate respectively decrease and increase by approximately an order of magnitude towards the base of the ophiolite. Our data indicate that this rheological weakening was primarily the result of more abundant secondary phases near the base of the ophiolite. Our interpretations are consistent with those of

  12. Les Gammaridae (Crustaces, Amphipodes) du Massif Central

    NARCIS (Netherlands)

    Goedmakers, Annemarie

    1974-01-01

    Une prospection systématique des eaux courantes du Massif Central a permis de reconnaître le nombre d’espèces des Gammaridés présentes dans cette région. On a trouvé les espèces suivantes: Gammarus pulex (Linnaeus, 1758), G. fossarum Koch, 1835, et G. ibericus Margalef, 1951. G. ibericus, espèce

  13. Petrography and mineral chemistry of wehrlites in contact zone of gabbro intrusions and mantle peridotites of the Naein ophiolite

    Directory of Open Access Journals (Sweden)

    Farhad Ghaseminejad

    2014-10-01

    Full Text Available Introduction Geological background Ophiolites have played a major role in our understanding of Earth’s processes ranging from seafloor spreading, melt evolution and magma transport in oceanic spreading centers, and hydrothermal alteration and mineralization of oceanic crust to collision tectonics, mountain building processes, and orogeny. They provide the essential structural, petrological, geochemical, and geochronological evidence to document the evolutionary history of ancient continental margins and ocean basin. Ophiolites include a peridotitic mantle sequence, generally characterized by high-temperature plastic deformation and residual chemistry, and a comagmatic crustal sequence (gabbros, diabase dikes, and submarine basalts, weakly or not deformed. According to this interpretation, ophiolites were allochthonous with respect to their country rocks. They were assembled during a primary accretion stage at an oceanic spreading center, and later tectonically emplaced on a continental margin or island arc (Dilek, 2003. The indigenous dikes of pyroxenites and gabbros that were injected into a melting peridotite, or intrusive dikes of pyroxenite and gabbro that injected when the peridotite was fresh and well below its solidus, are discussed in different ophiolite papers. Pyroxenite formation and contact of gabbro and mantle peridotite are discussed in different articles (Dilek, 2003. When a gabbro intrude a fresh mantle peridotite could not significantly react with it, but if intrusion occurs during the serpentinization, the gabbro will change to rodingite. Geological setting The Naein ophiolitic melanges comprise the following rock units: mantle peridotites (harzburgite, lherzolite, dunite, with associated chromitite, gabbro, pyroxenite, sheeted and swarm dikes, massive basalts, pillow lava, plagiogranite, radiolarian chert, glaubotruncana limestone, rodingite, listvenite, and metamorphic rocks (foliated amphibolitic dike, amphibolite, skarn

  14. The internal structure of eclogite-facies ophiolite complexes: Implications from the Austroalpine outliers within the Zermatt-Saas Zone, Western Alps

    Science.gov (United States)

    Weber, Sebastian; Martinez, Raul

    2016-04-01

    The Western Alpine Penninic domain is a classical accretionary prism that formed after the closure of the Penninic oceans in the Paleogene. Continental and oceanic nappes were telescoped into the Western Alpine stack associated with continent-continent collision. Within the Western Alpine geologic framework, the ophiolite nappes of the Zermatt-Saas Zone and the Tsate Unit are the remnants of the southern branch of the Piemonte-Liguria ocean basin. In addition, a series of continental basement slices reported as lower Austroalpine outliers have preserved an eclogitic high-pressure imprint, and are tectonically sandwiched between these oceanic nappes. Since the outliers occur at an unusual intra-ophiolitic setting and show a polymetamorphic character, this group of continental slices is of special importance for understanding the tectono-metamorphic evolution of Western Alps. Recently, more geochronological data from the Austroalpine outliers have become available that make it possible to establish a more complete picture of their complex geological history. The Lu-Hf garnet-whole rock ages for prograde growth of garnet fall into the time interval of 52 to 62 Ma (Weber et al., 2015, Fassmer et al. 2015), but are consistently higher than the Lu-Hf garnet-whole rock ages from several other locations throughout the Zermatt-Saas zone that range from 52 to 38 Ma (Skora et al., 2015). This discrepancy suggests that the Austroalpine outliers may have been subducted earlier than the ophiolites of the Zermatt-Saas Zone and therefore have been tectonically emplaced into their present intra-ophiolite position. This points to the possibility that the Zermatt-Saas Zone consists of tectonic subunits, which reached their respective pressure peaks over a prolonged time period, approximately 10-20 Ma. The pressure-temperature estimates from several members of the Austroalpine outliers indicate a complex distribution of metamorphic peak conditions, without ultrahigh

  15. Uranium and thorium in rocks and minerals of Zaangarsk alkaline massif

    International Nuclear Information System (INIS)

    Zhmodin, S.M.; Gofman, A.M.; Ksenzova, V.I.; Malmova, Z.V.; Nemirovskaya, N.A.

    1981-01-01

    U and Th distribution in rocks of the massif of alkaline-granitoid formation is studied using the methods of γ-spectrometry and neutron- fragment radiography. Predominant accumulation of U and Th in final products of magmatic differentiation - foyaites - is established. U and Th concentrations increased sharply during postmagmatic stage of alkaline massif formation - in permatites and metasomatically alterated rocks (Th/U and U/K ratios can serve as criteria for identification of such formations). The increase of U part, connected with accessory minerals in pegmatites and metasomatically alterated rocks, is pointed out. For U in postmagmatically alterated rocks high concentrations due to microcracks are characteristic [ru

  16. Si-Metasomatism During Serpentinization of Jurassic Ultramafic Sea-floor: a Comparative Study

    Science.gov (United States)

    Vogel, M.; Frueh-Green, G. L.; Boschi, C.; Schwarzenbach, E. M.

    2014-12-01

    The Bracco-Levanto ophiolitic complex (northwestern Italy) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge (MAR), such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of serpentinization processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to published data from modern oceanic hydrothermal systems, such as the Lost City hydrothermal field hosted in serpentinites on the Atlantis Massif. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread Si-metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater in the shallow ultramafic-dominated portions of the Jurassic seafloor, resulting in the formation of ophicalcites. In detail, regional variations in Si, Mg and Al content are observed in zones of ophicalcite formation, indicating metasomatic reactions and Si-Al transport during long-lived fluid-rock interaction and channelling of hydrothermal fluids. Rare earth element and isotopic analysis indicate that the Si-rich fluids are derived from alteration of pyroxenes to talc and tremolite in ultramafic rocks at depth. Comparison with serpentinites from the Atlantis Massif and 15°20'N indicates a similar degree of Si-enrichment in the modern seafloor and suggests that Si-metasomatism may be a fundamental process associated with serpentinization at slow-spreading ridge environments

  17. Paleomagnetism of the Oman Ophiolite: New Results from Oman Drilling Project Cores

    Science.gov (United States)

    Horst, A. J.; Till, J. L.; Koornneef, L.; Usui, Y.; Kim, H.; Morris, A.

    2017-12-01

    The Oman Drilling Project drilled holes at four sites in a transect through the southern massifs of the Samail ophiolite, and recovered 1500 m of igneous and metamorphic rocks. We focus on three sites from the oceanic crustal section including lower layered gabbros (GT1A), the mid-crustal layered to foliated gabbro transition (GT2A), and the shallower transition from sheeted dikes to varitextured gabbros (GT3A). Detailed core descriptions, analyses, and paleomagnetic measurements, were made on D/V Chikyu from July to September 2017 to utilize the core laboratory facilities similar to IODP expeditions. Shipboard measurements included anisotropy of magnetic susceptibility (AMS) and alternating field and thermal demagnetization of 597 discrete samples. Sample demagnetization behavior is varied from each of the cores, with some revealing multiple components of magnetization, and others yielding nearly univectorial data. The interpretation of results from the lower crustal cores is complicated by the pervasive presence of secondary magnetite. In almost all samples, a stable component was resolved (interpreted as a characteristic remanent magnetization) after removal of a lower-coercivity or lower unblocking-temperature component. The inclinations of the stable components in the core reference frame are very consistent in Hole GT1A. However, a transition from negative to positive inclinations in GT2A suggests some structural complexity, possibly as a result of intense late faulting activity. Both abrupt and gradual transitions between multiple zones of negative and positive inclinations occur in Hole GT3A. Interpretation and direct comparison of remanence between drill sites is difficult as recovered core pieces currently remain azimuthally unoriented, and GT2A was drilled at a plunge of 60°, whereas GT1A and GT3A were both drilled vertically. Work is ongoing to use borehole imagery to reorient the core pieces and paleomagnetic data into a geographic in situ reference

  18. Plagiogranites as late-stage immiscible liquids in ophiolite and mid-ocean ridge suites - An experimental study

    Science.gov (United States)

    Dixon, S.; Rutherford, M. J.

    1979-01-01

    A study of relationships between basic and acidic rocks was made by fractionating primitive basalt at low pressure anhydrous conditions at various fugacities. Fractionally crystallized basalt became increasingly enriched in iron which became silicate liquid immiscible, producing Fe-enriched basaltic and granitic liquids. The latter is similar to plagiogranites found in mid-oceanic rift (MOR) regions, showing that silicate liquid immiscibility could be the petrogenic process which produces plagiogranites in some MOR regions and ophiolites. The major problem in considering plagiogranites as products of silicate liquid immiscibility is absence of any description of the Fe-enriched conjugate liquid in the ophiolite or MOR literature, and the identification of this magma is essential for a definite case of silicate liquid immiscibility.

  19. The peculiarities of structurizing enclosing rock massif while developing a coal seam

    Science.gov (United States)

    Kozyreva, E. N.; Shinkevich, M. V.

    2017-09-01

    Different concepts of the development of geo-mechanical processes during longwall mining of a seam which are fundamentally different from the conventional ones are introduced in the article. Fundamental principles of the model for structurizing enclosing rock mass while longwall mining along the strike are described. The model was developed on the bases of non-linear geomechanical laws. According to the model, rock mass in the area of mining operation is organized as rock geomechanical layers with shifting arches. And the formation period of shifting arches in disintegrated rock mass is divisible by the length of the stope. Undulate characteristic of a massif as a peculiarity of man-made structurization of a massif is defined. It is shown that structuring the broken massif causes the formation of block-structured system and it can be detected while monitoring the ground pressure in powered support props. The results of the research allow decreasing the negative influence of a ground pressure and can be applied to specify parameters for controlling the roof, defining geometrical dimensions of a mining section and positioning of holing chute (face entry).

  20. A-type granites from the Guéra Massif, Central Chad: Petrology, geochemistry, geochronology, and petrogenesis.

    Science.gov (United States)

    Pham, Ngoc Ha T.; Shellnutt, J. Gregory; Yeh, Meng-Wan; Lee, Tung-Yi

    2017-04-01

    The poorly studied Saharan Metacraton of North-Central Africa is located between the Arabian-Nubian Shield in the east, the Tuareg Shield in the west and the Central African Orogenic Belt in the south. The Saharan Metacraton is composed of Neoproterozoic juvenile crust and the relics of pre-Neoproterozoic components reactivated during the Pan-African Orogeny. The Republic of Chad, constrained within the Saharan Metacraton, comprises a Phanerozoic cover overlying Precambrian basement outcroppings in four distinct massifs: the Mayo Kebbi, Tibesti, Ouaddaï, and the Guéra. The Guéra massif is the least studied of the four massifs but it likely preserves structures that were formed during the collision between Congo Craton and Saharan Metacraton. The Guéra Massif is composed of mostly granitic rocks. The granitoids have petrologic features that are consistent with A-type granite, such as micrographic intergrowth of sodic and potassic feldspar, the presence of sodic- and iron-rich amphibole, and iron-rich biotite. Compositionally, the granitic rocks of the Guéra Massif have high silica (SiO2 ≥ 68.9 wt.%) content and are metaluminous to marginally peraluminous. The rocks are classified as ferroan calc-alkalic to alkali-calcic with moderately high to very high Fe* ratios. The first zircon U/Pb geochronology of the silicic rocks from the Guéra Massif yielded three main age groups: 590 Ma, 570 Ma, 560 Ma, while a single gabbro yielded an intermediate age ( 580 Ma). A weakly foliated biotite granite yielded two populations, in which the emplacement age is interpreted to be 590 ± 10 Ma, whereas the younger age (550 ± 11 Ma) is considered to be a deformation age. Furthermore, inherited Meso- to Paleoproterozoic zircons are found in this sample. The geochemical and geochronology data indicate that there is a temporal evolution in the composition of rocks with the old, high Mg# granitoids shifting to young, low Mg# granitoids. This reveals that the A-type granites in

  1. Reconstructing Plate Boundaries in the Jurassic Neo-Tethys From the East and West Vardar Ophiolites (Greece and Serbia)

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe J. J.

    2018-03-01

    Jurassic subduction initiation in the Neo-Tethys Ocean eventually led to the collision of the Adria-Africa and Eurasia continents and the formation of an 6,000 km long Alpine orogen spanning from Iberia to Iran. Reconstructing the location and geometry of the plate boundaries of the now disappeared Neo-Tethys during the initial moments of its closure is instrumental to perform more realistic plate reconstructions of this region, of ancient ocean basins in general, and on the process of subduction initiation. Neo-Tethyan relics are preserved in an ophiolite belt distributed above the Dinaric-Hellenic fold-thrust belt. Here we provide the first quantitative constraints on the geometry of the spreading ridges and trenches active in the Jurassic Neo-Tethys using a paleomagnetically based net tectonic rotation analysis of sheeted dykes and dykes from the West and East Vardar Ophiolites of Serbia (Maljen and Ibar) and Greece (Othris, Pindos, Vourinos, and Guevgueli). Based on our results and existing geological evidence, we show that initial Middle Jurassic ( 175 Ma) closure of the western Neo-Tethys was accommodated at a N-S trending, west dipping subduction zone initiated near and parallel to the spreading ridge. The West Vardar Ophiolites formed in the forearc parallel to this new trench. Simultaneously, the East Vardar Ophiolites formed above a second N-S to NW-SE trending subduction zone located close to the European passive margin. We tentatively propose that this second subduction zone had been active since at least the Middle Triassic, simultaneously accommodating the closure of the Paleo-Tethys and the back-arc opening of Neo-Tethys.

  2. Quaternary glaciation of the Lato Massif, Zanskar Range of the NW Himalaya

    Science.gov (United States)

    Orr, Elizabeth N.; Owen, Lewis A.; Saha, Sourav; Caffee, Marc W.; Murari, Madhav K.

    2018-03-01

    The glacial chronostratigraphy and history of the Lato Massif of Zanskar northern India is defined for the first time using geomorphic mapping and 10Be surface exposure dating. Three local glacial stages, the Lato, Shiyul and Kyambu, are dated to 244-49, 25-15 and 3.4-0.2 ka, respectively. The Lato glacial stage was the most extensive period of glaciation, characterized by expanded ice caps with glaciers advancing to ∼16 km from their present position. Large till deposits are associated with this glacial stage, which represent a time of heightened glacial erosion and localized incision, and increased rates of sediment transfer and deposition. The glacial style transitioned to entrenched valley glaciation during the Shiyul glacial stage. Hummocky moraine complexes reflecting fluctuating glacier margins characterize this glaciation. Glaciers have been confined to the cirques and headwalls of the massif during and since the Kyambu glacial stage. Equilibrium-line altitude (ELA) reconstructions help define the shifts in glaciation over time, with ELA depressions changing from 470 ± 140, 270 ± 80 to 100 ± 30 m for the Lato, Shiyul and Kyambu glacial stages, respectively. The change of glacial style during the latter part of the Quaternary is similar to other regions of the Transhimalaya and Tibet suggesting that this pattern of glaciation may reflect regional climatic forcing. The evolution of the Lato Massif from an isolated alpine plateau to a steeply incised massif over the last several glacial-interglacial cycles may have also influenced the shifts from ice cap to valley glaciation.

  3. Three steps of serpentinization in an eclogitized oceanic serpentinization front (Lanzo Massif - Western Alps)

    OpenAIRE

    DEBRET, Baptiste; NICOLLET, christian; ANDREANI, Muriel; SCHWARTZ, Stéphane; GODARD, Marguerite

    2013-01-01

    The Lanzo peridotite massif is a fragment of oceanic lithosphere generated in an ocean-continent transition context and eclogitized during alpine collision. Despite the subduction history, the massif has preserved its sedimentary oceanic cover, suggesting that it may have preserved its oceanic structure. It is an exceptional case for studying the evolution of a fragment of the lithosphere from its oceanization to its subduction and then exhumation. We present a field and petrological study re...

  4. Structural Characterization of the Foliated-Layered Gabbro Transition in Wadi Tayin of the Samail Ophiolite, Oman; Oman Drilling Project Holes GT1A and GT2A

    Science.gov (United States)

    Deans, J. R.; Crispini, L.; Cheadle, M. J.; Harris, M.; Kelemen, P. B.; Teagle, D. A. H.; Matter, J. M.; Takazawa, E.; Coggon, J. A.

    2017-12-01

    Oman Drilling Project Holes GT1A and GT2A were drilled into the Wadi Tayin massif, Samail ophiolite and both recovered ca. 400 m of continuous core through a section of the layered gabbros and the foliated-layered gabbro transition. Hole GT1A is cut by a discrete fault system including localized thin ultracataclastic fault zones. Hole GT2A is cut by a wider zone of brittle deformation and incipient brecciation. Here we report the structural history of the gabbros reflecting formation at the ridge to later obduction. Magmatic and high temperature history- 1) Both cores exhibit a pervasive, commonly well-defined magmatic foliation delineated by plagioclase, olivine and in places clinopyroxene. Minor magmatic deformation is present. 2) The dip of the magmatic foliation varies cyclically, gradually changing dip by 30o from gentle to moderate over a 50 m wavelength. 3) Layering is present throughout both cores, is defined by changes in mode and grain size ranging in thickness from 2 cm to 3 m and is commonly sub-parallel to the foliation. 4) There are no high temperature crystal-plastic shear zones in the core. Key observations include: no simple, systematic shallowing of dip with depth across the foliated-layered gabbro transition and layering is continuous across this transition. Cyclic variation of magmatic foliation dip most likely reflects the process of plate separation at the ridge axis. Near-axis faulting- i) On or near-axis structures consist of epidote-amphibole bearing hydraulic breccias and some zones of intense cataclasis with intensely deformed epidote and seams of clay and chlorite accompanied by syntectonic alteration of the wall rock. Early veins are filled with amphibole, chlorite, epidote, and anhydrite. ii) The deformation ranges from brittle-ductile, causing local deflection of the magmatic foliation, to brittle offset of the foliation and core and mantle structures in anhydrite veins. iii) The prevalent sense of shear is normal and slickenfibers

  5. Uranium-lead isotopic ages of the Samail ophiolite, Oman, with applicatons to Tethyan ocean ridge tectonics

    International Nuclear Information System (INIS)

    Tilton, G.R.; Hopson, C.A.; Wright, J.E.

    1981-01-01

    Plagiogranites are a minor but widespread component of the Samail ophiolite plutonic member. They crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the Tethyan spreading ocean ridge, and their ages are thought to mark the time of ocean crust formation. Isotopic U--Pb ages of zircons from 13 plagiogranites collected along a 270-km segment of the Samail ophiolite subparallel to the regional trend of the sheeted dike complex (the former spreading ridge axis direction) define a narrow time interval of 93.5--97.9 m.y., with a pronounced clustering about 95 m.y. The zircon ages of the plagiogranites agree remarkably well with the early Cenomanian to early Turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them (Tippit et al., 1981). The agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite U--Pb ages closely date the time span of ocean crust formation. No step changes in age patterns are observed along the ridge axis (sheeted dike) direction, suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse. One possible exception occurs at the southeastern end of the sampled interval (Ibra area), where a 3 m.y. discontinuity might be caused by an unmapped fault. Assuming that the regional trend of the sheeted dikes (N10 0 --25 0 W) marks the direction of the former spreading ridge axis, the present array of sample localities spans a distance of 130 to 195 km normal to that axis (i.e., in the spreading direction). The data as a whole do not define a clear-cut age trend normal to the spreading axis, but by eliminating samples that may be aberrant due to faulting, the data array suggests a pattern of increasing ages from east to west

  6. VARIATION OF MACROMYCETES SPECIES COMPOSITION IN TWO FOREST HABITATS FROM GIUMALĂU MASSIF (EASTERN CARPATHIANS, ROMANIA

    Directory of Open Access Journals (Sweden)

    BÎRSAN Ciprian

    2013-12-01

    Full Text Available Norway spruce (Picea abies is the most common species with a large spreading in forests from Giumalău Massif. In this study the authors investigated the macromycetes species composition in two forest communities from Giumalău Massif: Hieracio transsilvanico-Piceetum and Leucanthemo waldsteinii-Fagetum. A total of 243 macromycetes species in 30 sampling areas have been identified. Changes in macromycetes species composition have been related to environmental factors (altitude and vegetation (canopy cover, plant species diversity. The results suggest that variation in macromycetes species composition in the two forests types from Giumalău Massif is directly related to abiotic factors (altitude, woody species composition and plants communities’ structure.

  7. Chemistry of chromites from Arroio Grande Ophiolite (Dom Feliciano Belt, Brazil) and their possible connection with the Nama Group (Namibia)

    Science.gov (United States)

    Ramos, Rodrigo Chaves; Koester, Edinei; Porcher, Carla Cristine

    2017-12-01

    The present paper shows a mineral chemistry study in chromites found in serpentine-talc schists of the Arroio Grande Ophiolite, located in the southeastern Dom Feliciano Belt, near the Brazil/Uruguay border. Using electron microscope scanning and electron microprobe techniques, this study found a supra-subduction zone signature in the chromites, together with evidence of metasomatism. It corroborates previous hypothesis that suggested a supra-subduction zone origin for the protoliths of the Arroio Grande meta-igneous rocks and a metasomatic origin for the chromite-bearing magnesian schists. The studied chromites present high Cr# (0.65-0.77) and Fe2+# (0.88-0.95), low MgO (0.85-2.47 wt%) and TiO2 (0.01-0.19 wt%) and anomalous high concentration of ZnO (up to 1.97 wt%). The results were compared with chemical data from detrital chromites from the Schwarzrand and Fish River Subgroups of the Nama Group (Namibia), demonstrating that they are compositionally similar with those found in the latter. These chromites, in turn, are believed to have been derived from the oceanic Marmora Terrane (Gariep Belt) in the west (present-day coordinates). Taking into consideration that oceanic metamafites from both the latter and the Arroio Grande Ophiolite share common bulk-rock geochemical features (in this paper interpreted as fragments of the same paleo-ocean floor - the Marmora back-arc basin), it is possible to raise the hypothesis that detrital material derived from the studied ophiolite might also be found in Nama Group. It is reinforced by the fact that sediments (related to the Pelotas-Aiguá Batholith granitoids) derived from the easternmost Dom Feliciano Belt, i.e. the region where Arroio Grande Ophiolite is located, is found in both Schwarzrand and Fish River Subgroups. Thus, we suggest that Arroio Grande Ophiolite detrital sediments might also have contributed to the Nama Basin infilling during Late Ediacaran-Lower Cambrian.

  8. Synthesis of inverse ringwoodite sheds light on the subduction history of Tibetan ophiolites.

    Science.gov (United States)

    Bindi, Luca; Griffin, William L; Panero, Wendy R; Sirotkina, Ekaterina; Bobrov, Andrey; Irifune, Tetsuo

    2018-04-03

    Tibetan ophiolites are shallow mantle material and crustal slabs that were subducted as deep as the mantle transition zone, a conclusion supported by the discovery of high-pressure phases like inverse ringwoodite in these sequences. Ringwoodite, Mg 2 SiO 4 , exhibits the normal spinel structure, with Mg in the octahedral A site and Si in the tetrahedral B site. Through A and B site-disorder, the inverse spinel has four-coordinated A cations and the six-coordinated site hosts a mixture of A and B cations. This process affects the density and impedance contrasts across the boundaries in the transition zone and seismic-wave velocities in this portion of the Earth. We report the first synthesis at high pressure (20 GPa) and high temperature (1600 °C) of a Cr-bearing ringwoodite with a completely inverse-spinel structure. Chemical, structural, and computational analysis confirm the stability of inverse ringwoodite and add further constraints to the subduction history of the Luobusa peridotite of the Tibetan ophiolites.

  9. Geophysical research results of buried relief and distribution groundwater runoff of the Aragats massif

    OpenAIRE

    V.P. Vardanyan; A.H. Hovhannisyan

    2017-01-01

    Based on the synthesis and reinterpretation of long-term data of geophysical studies together with the hydrology - hydrological materials it has been received new data about the buried topography and spatial distribution of groundwater runoff of the Aragats massif. First of all, it requires to determine the structure of its buried relief, which is basically a regional relief aquitard. The underground water sources are considered to be precipitation on the massif (approximately 83% of the tota...

  10. Defining conditions of garnet growth across the central and southern Menderes Massif, western Turkey

    Science.gov (United States)

    Etzel, T. M.; Catlos, E. J.; Kelly, E. D.; Cemen, I.; Ozerdem, C.; Atakturk, K. R.

    2017-12-01

    Here we apply thermodynamic modeling using Theriak-Domino to garnet-bearing rocks from the central and southern portions of the Menderes Massif to gain insight into the dynamics of western Turkey as the region experienced a transition from collisional to extensional tectonics. To this end, we report new pressure-temperature (P-T) paths from garnet-bearing rocks collected along the Alasehir detachment fault, a prominent exhumation structure in the central portion of the Menderes Massif in western Turkey, constituting the southern margin of the Alasehir Graben. These paths are compared to those from the Selimiye shear zone in the Southern (Cine) Massif. Two Alasehir garnets collected from the same outcrop record two P-T paths: 1) a prograde path beginning at 565oC and 6.4 kbar increasing to 592 oC and 7.5 kbar; and 2) near isobaric growth initiating at 531oC and 7.1 kbar and terminating at 571oC and 7.3 kbar. High-resolution P-T paths could not be modeled for the majority of Alasehir samples due to diffusional modification of garnet. However, conditions were estimated by garnet isopleth thermobarometry at the point of highest spessartine content for each crystal. Calculated P-T values for this subset of samples range between 566-651oC and 6.2-6.8 kbar. Despite this broad range, these P-T conditions are consistent with what is observed in the modeled paths. Th-Pb ages of matrix monazite range from 35.8±3.0 to 20.6±2.4 Ma, suggesting metamorphism in the central Menderes Massif occurred over a 15 m.y. period. Selimiye shear zone rocks show distinct N-shaped P-T paths, suggesting garnets in the central and southern portion of the Menderes Massif record distinctly different tectonic histories.

  11. Geochemical and Geophysical Characteristics of the Balud Ophiolitic Complex (BOC, Masbate Island, Philippines: Implications for its Generation, Evolution and Emplacement

    Directory of Open Access Journals (Sweden)

    Pearlyn C. Manalo

    2015-01-01

    Full Text Available This paper presents the first field, geochemical and geophysical information on the recently recognized Early Cretaceous Balud Ophiolitic Complex (BOC in the island of Masbate in the Central Philippines. Mapping of the western limb of the island revealed that only the upper crustal section of the BOC is exposed in this area. Geochemically, the pillow basalts are characterized by transitional mid-oceanic ridge basalt-island arc tholeiitic compositions. Gravity surveys yielded low Bouguer anomaly values that are consistent with the highly dismembered nature of the BOC. Short wavelength, high amplitude magnetic anomalies registered across the study area are attributed to shallow magnetic sources. This is taken to support the model that the ophiolitic complex occurs as thin crustal slivers that are not deeply-rooted in the mantle. Comparing BOC with other ophiolites in the Central Philippines, such as those in the islands of Sibuyan, Leyte and Bohol, suggests the possibility of a common or contiguous source for similarly-aged and geochemically composed crust-mantle sequences in the region.

  12. Early fracturing in argillaceous massifs and related carbonate transfer

    International Nuclear Information System (INIS)

    Beaudoin, B.; Dennebouy, S.; Parize, O.; Brulhet, J.; Trouiller, A.

    2004-01-01

    To be sure of the stability in the future of underground storage in argillaceous massifs needs to understand the present-day properties of the sediment in the light of its history. It is why early fracturing and associated carbonate transfer in shaly-marly massifs is one of the major themes of the MINANDRA Partnership (Ecole des Mines de Paris + ANDRA + some collaborators). That joint program involves tens of geo-scientists, and we would like to present here the main objects we study and the methods we apply. The base of the project is made of selected large reference-outcrops where an early fracturing is undoubtedly visible in the field. Two sets of such outcrops are presently worked in south-eastern France: - Aptian-albian marls (Marnes Bleues), at Bevons (near 04-Sisteron) and Saint-Andre de Rosans (W. of 05-Serres). - Domerian marls, at Clue du Vancon (E. of 04-Sisteron). Both are made of thick marls and intercalated limestone beds and nodules. (authors)

  13. First-order similarities and differences between Alps, Dinarides, Hellenides and Anatolides-Taurides

    Science.gov (United States)

    Schmid, Stefan M.; Bernoulli, Daniel; Fügenschuh, Bernhard; Matenco, Liviu; Schefer, Senecio; Oberhänsli, Roland; van Hinsbergen, Douwe; Ustaszewski, Kamil

    2013-04-01

    We correlated tectonic units across several circum-Mediterranean orogen strands between the Alps, Carpathians, the Balkan Peninsula, the Aegean and Western Turkey. Our compilation allows discussing fundamental along-strike similarities and differences. One first-order difference is that Dinarides-Hellenides, Anatolides and Taurides represent orogens of opposite subduction polarity and age with respect to the Alps and Carpathians. The internal Dinarides are linked to the Alps and Western Carpathians along the Mid-Hungarian fault zone, a suspected former trench-trench transform fault; its lithospheric root was obliterated during Neogene back-arc extension that formed the Pannonian Basin. Dinarides and Hellenides alike consist of far-travelled nappes detached from the Adriatic continental margin along décollement horizons in Paleozoic or younger stratigraphic levels during Cretaceous and Cenozoic orogeny. The more internal nappes (i.e. Jadar-Kopaonik, Drina-Ivanjica, East Bosnian-Durmitor and their Pelagonian and Almopias equivalents in the Hellenides) are composite nappes whereby the allochthonous Adriatic margin sequences passively carry ophiolites (Western Vardar Ophiolitic Unit) obducted during the latest Jurassic-earliest Cretaceous. These obducted ophiolitic units, as well as ophiolites obducted onto Europe-derived units presently found in the East Carpathians (Eastern Vardar Ophiolitic Unit obducted onto the Dacia continental block), root in one single Neotethys ocean that started closing with the initiation of obduction in the latest Jurassic; final suturing occurred during Cretaceous times, terminating with the formation of the Sava-Izmir-Ankara suture in the latest Cretaceous. Ophiolitic "massifs" found outside the Sava-Izmir-Ankara suture zone do not mark oceanic sutures, nor do the Drina-Ivanjica and Pelagonian "massifs" represent independent continental fragments (terranes). The same logic applies to Western Turkey with the difference that the ophiolites

  14. An Andean type Palaeozoic convergence in the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Schulmann, K.; Konopásek, J.; Janoušek, V.; Lexa, O.; Lardeaux, J.-M.; Edel, J.-B.; Štípská, P.; Ulrich, Stanislav

    2009-01-01

    Roč. 341, č. 2-3 (2009), s. 266-286 ISSN 1631-0713 Institutional research plan: CEZ:AV0Z30120515 Keywords : Bohemian Massif * Saxothuringian oceanic subduction * building of Variscan orogenic root system * channel flow Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.931, year: 2009

  15. First data on Sm-Nd systematization of Khanka Massif metamorphic rocks, Primor'e

    International Nuclear Information System (INIS)

    Mishkin, M.A.; Khanchuk, A.I.; Zhuravlev, D.Z.; Lavrik, S.N.

    2000-01-01

    The age of the metamorphic rocks of the Khanka massif, Primor'e, is determined through the method of the Sm-Nd isotopic dating. The results of the isotopic studies on the amphibolites of the Nakhimov suite of the Khanka massif indicated that the rocks of this suite are not older than 1.7 billion years. The obtained age corresponds to the time of the amphibolite protolith formation, the source whereof is the moderately depleted mantle. The isotopic age of the amphibole and plagioclase mineral fractions constitutes 733 ± 25 mln years, which reflects the time of the Nakhimov suite rocks metamorphism [ru

  16. Man-induced transformation of mountain meadow soils of Aragats mountain massif (Armenia)

    Science.gov (United States)

    Avetisyan, M. H.

    2018-01-01

    The article considers issues of degradation of mountain meadow soils of the Aragats mountain massif of the Republic of Armenia and provides the averaged research results obtained for 2013 and 2014. The present research was initiated in the frames of long-term complex investigations of agroecosystems of Armenia’s mountain massifs and covered sod soils of high mountain meadow pasturelands and meadow steppe grasslands lying on southern slope of Mt. Aragats. With a purpose of studying the peculiarities of migration and transformation of flows of major nutrients namely carbon, nitrogen, phosphorus in study mountain meadow and meadow steppe belts of the Aragats massif we investigated water migration of chemical elements and regularities of their leaching depending on different belts. Field measurement data have indicated that organic carbon and humus in a heavily grazed plot are almost twice as low as on a control site. Lysimetric data analysis has demonstrated that heavy grazing and illegal deforestation have brought to an increase in intrasoil water acidity. The results generated from this research support a conclusion that a man’s intervention has brought to disturbance of structure and nutrient and water regimes of soils and loss of significant amounts of soil nutrients throughout the studied region.

  17. Age and microfacies of oceanic Upper Triassic radiolarite components from the Middle Jurassic ophiolitic mélange in the Zlatibor Mountains (Inner Dinarides, Serbia and their provenance

    Directory of Open Access Journals (Sweden)

    Gawlick Hans-Jürgen

    2017-08-01

    Full Text Available Oceanic radiolarite components from the Middle Jurassic ophiolitic mélange between Trnava and Rožanstvo in the Zlatibor Mountains (Dinaridic Ophiolite Belt west of the Drina–Ivanjica unit yield Late Triassic radiolarian ages. The microfacies characteristics of the radiolarites show pure ribbon radiolarites without crinoids or thin-shelled bivalves. Beside their age and the preservation of the radiolarians this points to a deposition of the radiolarites on top of the oceanic crust of the Neo-Tethys, which started to open in the Late Anisian. South of the study area the ophiolitic mélange (Gostilje–Ljubiš–Visoka–Radoševo mélange contains a mixture of blocks of 1 oceanic crust, 2 Middle and Upper Triassic ribbon radiolarites, and 3 open marine limestones from the continental slope. On the basis of this composition we can conclude that the Upper Triassic radiolarite clasts derive either from 1 the younger parts of the sedimentary succession above the oceanic crust near the continental slope or, more convincingly 2 the sedimentary cover of ophiolites in a higher nappe position, because Upper Triassic ribbon radiolarites are only expected in more distal oceanic areas. The ophiolitic mélange in the study area overlies different carbonate blocks of an underlying carbonate-clastic mélange (Sirogojno mélange. We date and describe three localities with different Upper Triassic radiolarite clasts in a mélange, which occurs A on top of Upper Triassic fore-reef to reefal limestones (Dachstein reef, B between an Upper Triassic reefal limestone block and a Lower Carnian reef limestone (Wetterstein reef, and C in fissures of an Upper Triassic lagoonal to back-reef limestone (Dachstein lagoon. The sedimentary features point to a sedimentary and not to a tectonic emplacement of the ophiolitic mélange (= sedimentary mélange filling the rough topography of the topmost carbonate-clastic mélange below. The block spectrum of the underlying and

  18. Age and microfacies of oceanic Upper Triassic radiolarite components from the Middle Jurassic ophiolitic mélange in the Zlatibor Mountains (Inner Dinarides, Serbia) and their provenance

    Science.gov (United States)

    Gawlick, Hans-Jürgen; Djerić, Nevenka; Missoni, Sigrid; Bragin, Nikita Yu.; Lein, Richard; Sudar, Milan; Jovanović, Divna

    2017-08-01

    Oceanic radiolarite components from the Middle Jurassic ophiolitic mélange between Trnava and Rožanstvo in the Zlatibor Mountains (Dinaridic Ophiolite Belt) west of the Drina-Ivanjica unit yield Late Triassic radiolarian ages. The microfacies characteristics of the radiolarites show pure ribbon radiolarites without crinoids or thin-shelled bivalves. Beside their age and the preservation of the radiolarians this points to a deposition of the radiolarites on top of the oceanic crust of the Neo-Tethys, which started to open in the Late Anisian. South of the study area the ophiolitic mélange (Gostilje-Ljubiš-Visoka-Radoševo mélange) contains a mixture of blocks of 1) oceanic crust, 2) Middle and Upper Triassic ribbon radiolarites, and 3) open marine limestones from the continental slope. On the basis of this composition we can conclude that the Upper Triassic radiolarite clasts derive either from 1) the younger parts of the sedimentary succession above the oceanic crust near the continental slope or, more convincingly 2) the sedimentary cover of ophiolites in a higher nappe position, because Upper Triassic ribbon radiolarites are only expected in more distal oceanic areas. The ophiolitic mélange in the study area overlies different carbonate blocks of an underlying carbonate-clastic mélange (Sirogojno mélange). We date and describe three localities with different Upper Triassic radiolarite clasts in a mélange, which occurs A) on top of Upper Triassic fore-reef to reefal limestones (Dachstein reef), B) between an Upper Triassic reefal limestone block and a Lower Carnian reef limestone (Wetterstein reef), and C) in fissures of an Upper Triassic lagoonal to back-reef limestone (Dachstein lagoon). The sedimentary features point to a sedimentary and not to a tectonic emplacement of the ophiolitic mélange (= sedimentary mélange) filling the rough topography of the topmost carbonate-clastic mélange below. The block spectrum of the underlying and slightly older

  19. Gold in Accessory Zircon (the Kozhim Massif, Subpolar Urals)

    Science.gov (United States)

    Denisova, Yuliya; Pystin, Aleksandr

    2017-12-01

    The crystals of zircon due to their resistance to external impact of various processes can reveal information about the environment of their formation and the inclusions observed of them. Zircon contains different mineral inclusions: biotite, plagioclase, quartz, apatite, etc. However, there is no information about gold inclusions in the zircons from granites of the Sudpolar Urals. The study results of the inclusions of gold in accessory zircon of the Kozhim granitic massif are presented in this paper. The studied mineral is a dark-brown translucent short-prismatic crystal containing the inclusion of gold and the allocations of quartz. According to studies, the inclusion of gold formed during the growth of zircon and it is the gold covered with a thin film of oxide gold. It was confirmed that the crystallization of the studied zircon occurred at a temperature of 800°C and above on the stage of formation of granites of Kozhim massif. The assumption is made about the additional temperature in the course of which was caused by decreasing of temperature up to 700° C and below during postmagmatic stage.

  20. Rainwater chemistry at the summit and southern flank of the Itatiaia massif, Southeastern Brazil

    International Nuclear Information System (INIS)

    Mello, William Z. de; Almeida, Marcelo D. de

    2004-01-01

    Wet deposition and related rainwater chemistry were studied at the Itatiaia massif, on which is settled the Itatiaia National Park (INP). Samples were simultaneously collected on a weekly basis over 12 months, using automated wet and dry samplers, at the INP-Headquarters (INP-Hq; altitude=820 m) and the Itatiaia Plateau (It-Pt; altitude=2460 m). Conductivity, pH, Na + , K + , Mg 2+ , Ca 2+ , NH 4 + , Cl - , NO 3 - and SO 4 2- were determined in 36 rainwater samples. Volume-weighted mean (VWM) pH was lower at the INP-Hq (4.9) than at the It-Pt (5.3). Very strong correlation between Cl - and Na + was found for the INP-Hq (r=0.99). At the Itatiaia massif, SO 4 2- , NO 3 - , and NH 4 + comprised together about 60% of the total inorganic ions and appear to exert the major control on rainwater pH. - Rainwater chemistry at the Itatiaia massif in SE Brazil is strongly dominated by S and N inorganic species, and influenced by human activities

  1. Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East: Petrogenesis and tectonic implications

    Science.gov (United States)

    Xu, Ting; Xu, Wen-Liang; Wang, Feng; Ge, Wen-Chun; Sorokin, A. A.

    2018-02-01

    This paper presents new geochronological and geochemical data for early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East, with the aim of elucidating the Paleozoic evolution and tectonic attributes of the Khanka Massif. New U-Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages: 502, 492, 462-445, and 430 Ma. The 502 Ma pyroxene diorites contain 58.28-59.64 wt% SiO2, 2.84-3.69 wt% MgO, and relatively high Cr and Ni contents. Negative εHf(t) values (- 1.8 to - 0.4), along with other geochemical data, indicate that the primary magma was derived from partial melting of mafic lower crust with the addition of mantle material. The 492 Ma syenogranites have high SiO2 and K2O contents, and show positive Eu anomalies, indicating the primary magma was generated by partial melting of lower crust at relatively low pressure. The 445 Ma Na-rich trondhjemites display high Sr/Y ratios and positive εHf(t) values (+ 1.8 to + 3.9), indicating the primary magma was generated by partial melting of thickened hydrous mafic crust. The 430 Ma granitoids have high SiO2 and K2O contents, zircon εHf(t) values of - 5.4 to + 5.8, and two-stage model ages of 1757-1045 Ma, suggesting the primary magma was produced by partial melting of heterogeneous Proterozoic lower crustal material. The geochemistry of these early Paleozoic intrusive assemblages indicates their formation in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif. The εHf(t) values show an increasingly negative trend with increasing latitude, revealing a lateral heterogeneity of the lower crust beneath the Khanka Massif. Regional comparisons of the magmatic events indicate that the Khanka Massif in the Russian Far East has a tectonic affinity to the Songnen-Zhangguangcai Range Massif rather than the adjacent Jiamusi Massif.

  2. Geochemistry of reduced gas related to serpentinization of the Zambales ophiolite, Philippines

    Science.gov (United States)

    Abrajano, T.A.; Sturchio, N.C.; Kennedy, B.M.; Lyon, G.L.; Muehlenbachs, K.; Böhlke, J.K.

    1990-01-01

    Methane-hydrogen gas seeps with mantle-like C and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the Zambales ophiolite, Philippines. New measurements of noble gas and 14C isotope abundances, rock/mixed-volatile equilibrium calculations, and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration. The gas seeps are produced in rock-dominated zones of serpentinization, and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization.

  3. Grass survey of the Itremo Massif records endemic central highland ...

    African Journals Online (AJOL)

    Twenty species are endemic to the central highlands, and a further 1 4 species are restricted to Madagascar. Five ecological groups of grasses were identified in the Itremo Massif: shade species in gallery forests, open wet area species, fire grasses, anthropogenic disturbance associated grasses and rock-dwelling grasses.

  4. Thermo-mechanical modeling of the obduction process based on the Oman ophiolite case

    OpenAIRE

    Duretz , Thibault; Agard , Philippe; Yamato , Philippe; Ducassou , Céline; Burov , Evgenii ,; Gerya , T. V.

    2016-01-01

    International audience; Obduction emplaces regional-scale fragments of oceanic lithosphere (ophiolites) over continental lithosphere margins of much lower density. For this reason, the mechanisms responsible for obduction remain enigmatic in the framework of plate tectonics. We present two-dimensional (2D) thermo-mechanical models of obduction and investigate possible dynamics and physical controls of this process. Model geometry and boundary conditions are based on available geological and g...

  5. Mineral chemistry and petrology of highly magnesian ultramafic cumulates from the Sarve-Abad (Sawlava) ophiolites (Kurdistan, NW Iran): New evidence for boninitic magmatism in intra-oceanic fore-arc setting in the Neo-Tethys between Arabia and Iran

    Science.gov (United States)

    Allahyari, Khalil; Saccani, Emilio; Rahimzadeh, Bahman; Zeda, Ottavia

    2014-01-01

    The Sarve-Abad (Sawlava) ophiolitic complex consists of several tectonically dismembered ophiolitic sequences. They are located along the Main Zagros Thrust Zone, which marks the ophiolitic suture between the Arabian and Sanandaj-Sirjan continental blocks. They represent a portion of the southern Neo-Tethyan oceanic lithosphere, which originally existed between the Arabian (to the south) and Eurasian (to the north) continental margins. The Sarve-Abad ophiolites include cumulitic lherzolites bearing minor dunite and chromitite lenses in places. The main rock-forming minerals in ultramafic cumulates are cumulus olivine and inter-cumulus clinopyroxene and orthopyroxene. Minor (<5%) chromian spinel occurs as both cumulus and inter-cumulus phases.

  6. Potential Hydrogen Yields from Ultramafic Rocks of the Coast Range Ophiolite and Zambales Ophiolite: Inferences from Mössbauer Spectroscopy

    Science.gov (United States)

    Stander, A.; Nelms, M.; Wilkinson, K.; Dyar, M. D.; Cardace, D.

    2013-12-01

    The reduced status of mantle rocks is a possible controller and indicator of deep life habitat, due to interactions between water and ultramafic (Fe, Mg-rich) minerals, which, under reducing conditions, can yield copious free hydrogen, which is an energy source for rock-hosted chemosynthetic life. In this work, Mössbauer spectroscopy was used to parameterize the redox status of Fe in altering peridotites of the Coast Range Ophiolite (CRO) in California, USA and Zambales Ophiolite (ZO) in the Philippines. Fe-bearing minerals were identified and data were collected for the percentages of Fe(III)and Fe(II)and bulk Fe concentration. Thin section analysis shows that relict primary olivines and spinels generally constitute a small percentage of the ZO and CRO rock, and given satisfactory estimates of the volume of the ultramafic units of the ZO and CRO, a stoichiometric H2 production can be estimated. In addition, ZO serpentinites are ~63,000 ppm Fe in bulk samples; they contain ~41-58% Fe(III)and ~23-34% Fe(II) in serpentine and relict minerals along with ~8-30% of the total Fe as magnetite. CRO serpentinites are ~42,000 ppm Fe in bulk samples; they contain ~15-50% Fe(III), ~22-88% Fe(II) in serpentine and relict minerals, and ~0-52% of total Fe is in magnetite (Fe(II)Fe(III)2O4). Assuming stoichiometric production of H2, and given the following representation of serpentinization 2(FeO)rock + H2O → (Fe2O3)rock +H2, we calculated the maximum quantity of hydrogen released and yet to be released through the oxidation of Fe(II). Given that relatively high Fe(III)/Fetotal values can imply higher water:rock ratios during rock alteration (Andreani et al., 2013), we can deduce that ZO ultramafics in this study have experienced a net higher water:rock ratio than CRO ultramafics. We compare possible H2 yields and contrast the tectonic and alteration histories of the selected ultramafic units. (M. Andreani, M. Muñoz, C. Marcaillou, A. Delacour, 2013, μXANES study of iron

  7. The Armenian and NW Anatolian ophiolites: new insights for the closure of the Tethys domain and obduction onto the South Armenian Block and Anatolian-Tauride Platform before collision through dynamic modeling

    Science.gov (United States)

    Hässig, Marc; Rolland, Yann; Sosson, Marc; Hassani, Riad; Topuz, Gultekin; Faruk Çelik, Ömer; Gerbault, Muriel; Galoyan, Ghazar; Müller, Carla; Sahakyan, Lilit; Avagyan, Ara

    2013-04-01

    In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the South Armenian Block (SAB), a Gondwanian-derived continental terrane; (2) scattered outcrops of ophiolites coming up against the Sevan-Akera suture zone; and (3) the Eurasian plate. The Armenian ophiolites represent remnants of an oceanic domain which disappeared during Eurasia-Arabia convergence. Previous works using geochemical whole-rock analyses, 40Ar/39Ar and paleontological dating have shown that the ophiolite outcrops throughout this area were emplaced during the Late Cretaceous as one non-metamorphic preserved ophiolitic nappe of back-arc origin that formed during Middle to Late Jurassic. From these works, tectonic reconstructions include two clearly identified subductions, one related to the Neotethys subduction beneath the Eurasian margin and another to intra-oceanic subduction responsible for the opening of the back-arc basin corresponding to the ophiolites of the Lesser Caucasus. The analysis of the two stages of metamorphism of the garnet amphibolites of the ophiolite obduction sole at Amasia (M1: HT-LP peak of P = 6-7 kbar and T > 630°C; M2; MP-MT peak at P = 8-10 kbar and T = 600°C) has allowed us to deduce the onset of subduction of the SAB at 90 Ma for this locality, which age coincides with other paleontological ages at the obduction front. A preliminary paleomagnetic survey has also brought quantification to the amount of oceanic domain which disappeared by subduction between the SAB and Eurasia before collision. We propose a dynamic finite element model using ADELI to test the incidence of parameters such as the density of the different domains (or the interval between the densities), closing speed (or speeds if sporadic), the importance and interactions of mantle discontinuities with the subducting lithosphere and set a lithospheric model. Our field observations and analyses are used to validate combinations of factors. The aim is to better qualify the

  8. Seismic Constraints on Shallow Crustal Processes at the East Pacific Rise.

    Science.gov (United States)

    1994-02-01

    travel to Cyprus, Iceland, the Canary Islands , and Oregon. These field trips have given me a first hand look at what the oceanic crust might be like. Plus...A.J. Harding and J.A. Orcutt, Distribution of magma beneath the East Pacific Rise between the Clipperton Transform and the 9󈧕’N deval from forward...The structure of sheeted dikes and associated rocks in North Arm massif, Bay of Islands ophiolite complex, and the intrusive process at oceanic

  9. Paleomagnetic Constraints on the Tectonic History of the Mesozoic Ophiolite and Arc Terranes of Western Mexico

    Science.gov (United States)

    Boschman, L.; Van Hinsbergen, D. J. J.; Langereis, C. G.; Molina-Garza, R. S.; Kimbrough, D. L.

    2017-12-01

    The North American Cordillera has been shaped by a long history of accretion of arcs and other buoyant crustal fragments to the western margin of the North American Plate since the Early Mesozoic. Accretion of these terranes resulted from a complex tectonic history interpreted to include episodes of both intra-oceanic subduction within the Panthalassa/Pacific Ocean, as well as continental margin subduction along the western margin of North America. Western Mexico, at the southern end of the Cordillera, contains a Late Cretaceous-present day long-lived continental margin arc, as well as Mesozoic arc and SSZ ophiolite assemblages of which the origin is under debate. Interpretations of the origin of these subduction-related rock assemblages vary from far-travelled exotic intra-oceanic island arc character to autochthonous or parautochthonous extended continental margin origin. We present new paleomagnetic data from four localities: (1) the Norian SSZ Vizcaíno peninsula Ophiolite; (2) its Lower Jurassic sedimentary cover; and (3) Barremian and (4) Aptian sediments derived from the Guerrero arc. The data show that the Mexican ophiolite and arc terranes have a paleolatitudinal plate motion history that is equal to that of the North American continent. This suggests that these rock assemblages were part of the overriding plate and were perhaps only separated from the North American continent by temporal fore- or back-arc spreading. These spreading phases resulted in the temporal existence of tectonic plates between the North American and Farallon Plates, and upon closure of the basins, in the growth of the North American continent without addition of any far-travelled exotic terranes.

  10. Geodynamic movements and deformations of the Sudetic structural unit of the Bohemian Massif

    Science.gov (United States)

    Schenk, V.; Jechumtálová, Z.; Schenková, Z.; Kottnauer, P.

    2003-04-01

    The African plate pushes to European orogenic Alpine structures that transfer the compression further to Variscan structural units, including the Bohemian Massif. Central parts of the Bohemian Massif are relatively deep-seated and, therefore, some of marginal parts of the Massif and its border geological structures should be affected intensively and moved distinctly with respect to the central parts. The geodynamical GPS network EAST SUDETEN is located just over the area mentioned above, i.e. it covers both kinetically quasi-effected and quasi-non-effected structural blocks. GPS data observed already for six annual campaigns (1997-2002) were processed and movement vectors of individual network sites were assessed. Applied data processing did not allow errors in the horizontal direction 2 mm and in the vertical direction 5-6 mm to be exceeded. Since time series of coordinate changes for several network sites gave rather pronounce movement trends, preliminary deformations among individual structural blocks were evaluated and compared to other geological, geophysical and geodetic materials. The investigation has been supported by the Grant Agency of the Czech Republic, projects 205/97/0679 and 205/01/0480, and by the research programme of the Ministry of Education, Youth and Sport of the Czech Republic, project LN00A005 "Dynamics of the Earth".

  11. The hydrothermal alteration in the context of geologic evolution from Pocos de Caldas Alkaline Massif, MG-SP

    International Nuclear Information System (INIS)

    Garda, G.M.

    1990-01-01

    The Pocos de Caldas Alkaline Massif covers 800 km 2 , a quarter of which is hydrothermally altered. Such proportion is uncommon, when compared to the know alkaline massifs of the world. The hydrothermal alteration is associated with Zr, U and Mo mineralizations which are predominantly located in the central-southern portion of the massif, in the central-eastern circular structure. The colour of the altered rock (and its soil) in that area is typically whitish beige to yellowish white and is regionally called potassic rock. The Osamu Utsumi Mine, also referred to as the uranium ore of Campo do Cercado, is located 25 Km to the south of Pocos de Caldas City and was explored, from 1977 to 1989, through the open pit method. A sequence of alteration minerals adapted to lowering temperatures should be expected; however, only illite and alkaline feldspar are observed in the hydrothermally altered portions of the massif, and their formation must have been controlled mainly by kinetic, other than thermal factors. The irrestrict circulation of relatively hotter hydrothermal fluids must have happened at the beginning of the process, diminishing immediately after the cooling of the brecciated areas (and the subjacent magmatic body), leading the system to kinetics levels that made subsequent hydrothermal alteration impossible. (author)

  12. Magmatic Diversity of the Wehrlitic Intrusions in the Oceanic Lower Crust of the Northern Oman Ophiolite

    Science.gov (United States)

    Kaneko, R.; Adachi, Y.; Miyashita, S.

    2014-12-01

    The Oman ophiolite extends along the east coast of Oman, and is the world's largest and best-preserved slice of obducted oceanic lithosphere. The magmatic history of this ophiolite is complex and is generally regarded as having occurred in three stages (MOR magmatism, subduction magmatism and intraplate magmatism). Wehrlitic intrusions constitute an important element of oceanic lower crust of the ophiolite, and numerous intrusions cut gabbro units in the northern Salahi block of this ophiolite. In this study area, we identified two different types of wehrlitic intrusions. One type of the intrusions mainly consists of dunite, plagioclase (Pl) wehrlite and mela-olivine (Ol) gabbro, in which the crystallization sequence is Ol followed by the contemporaneous crystallization of Pl and clinopyroxene (Cpx). This type is called "ordinary" wehrlitic intrusions and has similar mineral compositions to host gabbros (Adachi and Miyashita 2003; Kaneko et al. 2014). Another type of the intrusions is a single intrusion that crops out in an area 250 m × 150 m along Wadi Salahi. This intrusion consists of Pl-free "true" wehrlite, in which the crystallization sequence is Ol and then Cpx. The forsterite contents (Fo%) of Ol from the "ordinary" wehrlitic intrusions and "true" wehrlitic intrusions have ranges of 90.8-87.0 (NiO = 0.36-0.13 wt%) and 84.7 (NiO = 0.31 wt%), respectively. Cr numbers (Cr#) of Cr-spinel from the "true" wehrlitic intrusions show higher Cr# value of 0.85 than those of the "ordinary" wehrlitic intrusions (0.48-0.64). But the former is characterized by very high Fe3+ values (YFe3+ = 0.49-0.68). Kaneko et al. (2014) showed that the "ordinary" ubiquitous type has similar features to MOR magmatism and the depleted type in the Fizh block (Adachi and Miyashita 2003) links to subduction magmatism. These types are distinguished by their mineral chemistries (TiO2 and Na2O contents of Cpx). The TiO2 and Na2O contents of Cpx from the "true" wehrlitic intrusions have 0

  13. Influence of geotechnical properties of the rocks of massif Vajarska on the technology of used blasting operations

    Directory of Open Access Journals (Sweden)

    Oreská ¼udmila

    1997-12-01

    Full Text Available Geotechnical properties of a rock massif have a decisive influence on the technology of blasting operations and on the resulting fragmentation of the blast. Parameters of the blasting operations were given for the limestone deposit Vajarska on the base of knowledge about fractures of the massif Vajarska. The computer programm is used to choice new para-meters for the blasting operations in HIROCEM, a.s., Rohožník.

  14. N-S crustal shear system in the Bundelkhand massif: a unique ...

    Indian Academy of Sciences (India)

    56

    In the light of our detailed geological studies of the massif (Singh and Bhattacharya,. 2010 .... relations with, and displace, the earlier shear systems, i.e. BS1, BS2 and BS3 (Fig. 3D), (3) ..... and shear zone patterns: The South Indian case. Jour.

  15. A middle Permian ophiolite fragment in Late Triassic greenschist- to blueschist-facies rocks in NW Turkey: An earlier pulse of suprasubduction-zone ophiolite formation in the Tethyan belt

    Science.gov (United States)

    Topuz, Gültekin; Okay, Aral I.; Schwarz, Winfried H.; Sunal, Gürsel; Altherr, Rainer; Kylander-Clark, Andrew R. C.

    2018-02-01

    The Eastern Mediterranean region within the Tethyan belt is characterised by two main pulses of suprasubduction-zone ophiolite formation during the Early-Middle Jurassic and Late Cretaceous. Despite vast exposures of the Permo-Triassic accretionary complexes, related suprasubduction-zone ophiolites and the timing of subduction initiation leading to the formation of Permo-Triassic accretionary complexes are unknown so far. Here we report on a 40 km long and 0.3 to 1.8 km wide metaophiolite fragment within transitional greenschist- to blueschist-facies oceanic rocks from NW Turkey. The metaophiolite fragment is made up mainly of serpentinite and minor dykes or stocks of strongly sheared metagabbro with mineral assemblages involving actinolite/winchite, chlorite, epidote, albite, titanite and phengite. The metagabbro displays (i) variable CaO and MgO contents, (ii) anomalously high Mg# (= 100 ∗ molar MgO/(MgO + FeOtot)) of 75-88, and (iii) positive Eu anomalies, together with low contents of incompatible elements such as Ti, P and Zr, suggesting derivation from former plagioclase cumulates. The serpentinites comprise serpentine, ± chlorite, ± talc, ± calcite and relict Cr-Al spinel surrounded by ferrichromite to magnetite. Relict Cr-Al spinels are characterised by (i) Cr/(Cr + Al) ratios of 0.45-0.56 and Mg/(Mg + Fe2 +) ratio of 0.76-0.22, (ii) variable contents of ZnO and MnO, and (iii) extremely low TiO2 contents. Zn and Mn contents are probably introduced into Cr-Al spinels during greenschist- to blueschist metamorphism. Compositional features of the serpentinite such as (i) Ca- and Al-depleted bulk compositions, (ii) concave U-shaped, chondrite-normalised rare earth element patterns (REE) with enrichment of light and heavy REEs, imply that serpentinites were probably derived from depleted peridotites which were refertilised by light rare earth element enriched melts in a suprasubduction-zone mantle wedge. U-Pb dating on igneous zircons from three metagabbro

  16. Neogene Uplift and Exhumation of Plutonic Bodies in the Beni Bou Ifrour Massif (Nador, northeastern Morocco)

    Science.gov (United States)

    Lebret, Noëmie; Jolivet, Laurent; Branquet, Yannick; Bourdier, Jean-Louis; Jolivet, Marc; Marcoux, Eric

    2013-04-01

    In Neogene times, the whole Mediterranean Sea was the center of an intense magmatic activity. This post-collisional magmatism produced a large amount of volcanic edifices through the Alpine belts, together with some intrusives. These plutonic bodies can be associated with skarn-type mineralization, well-known in Elba Island or Serifos Island (Cyclades), where they are generally exhumed by detachment faults. In Morocco, the plutons hosted by the Beni Bou Ifrour massif are connected to the biggest skarn-type iron concentrations of the country (production > 60 Mt, reserves ≈ 25 Mt). The purpose of this work is to explain the late uplift of this massif and subsequent exhumation of the intrusives. As a final product of the Africa-Eurasia plate convergence since ca. 70 Ma, the Rif Mountains constitute the westernmost segment of the Mediterranean Alpine belts. In the oriental part of this range, volcanic summits and Paleozoic to Mesozoic massifs outcrop in the surrounding Mio-Pliocene plains. The Beni Bou Ifrour massif, in the Nador province, consists in a dome-shaped folded Mesozoic series (Domerian to Barremian) affected by a slight epizonal regional metamorphism (ca. 14-12 Ma), dislocated by Neogene NE-SW faults and eventually sealed by upper Miocene transgressive sediments. The hosted intrusives (7.58 ± 0.03 Ma; Duggen et al., 2005) are the plutonic equivalents to the potassic calc-alkaline lavas (andesites mainly) from the surrounding "satellite" volcanic massifs. They turn out to stand in higher topographic position than the younger shoshonitic lavas of the neighboring Gourougou stratovolcano (6.12 ± 0.01 Ma; Duggen et al., 2005). Previous studies have attributed this uplift to the action of normal faults (pull-apart basins; Guillemin & Houzay, 1982), thrusting (Kerchaoui, 1985; 1995) or even of a caldeira resurgence (El Bakkali, 1995). To discriminate against those exhumation mechanisms, field work has been performed, coming along with new cross-sections to

  17. New data for paleoprotherozoic PGE-bearing anorthosite of Kandalaksha massif (Baltic shield): U-Pb and Sm-Nd ages

    Science.gov (United States)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

    2015-04-01

    The aims of this researches were to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) on Kandalaksha anorthosite massif due to study of polimetamorphic history. In marginal zone firstly have been obtained the presence of sulphide mineralization with PGE (Chashchin, Petrov , 2013). Kandalaksha massif is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate polymetamorphism. Two fractions of single grains from anorthosite of the massif gave precise U-Pb age, which is equal to 2450± 3 Ma. Leucocratic gabbro-norite were dated by U-Pb method, with age up to 2230 ± 10 Ma. This age reflects the time of granulite metamorphism according to data of (Mitrofanov, Nirovich, 2003). Two fractions of rutile have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile is 400-450 ° C (Mezger et.al., 1989), thus cooling processes of massif rocks to these temperatures was about 1.7 Ga. These data reflect one of the stages of metamorphic alteration of the massif. Three stages of metamorphism are distinguished by Sm-Nd method. Isotope Sm-Nd dating on Cpx-WR line gives the age of 2311 Ma which suggested of high pressure granulite metamorphism. Moreover Cpx-Pl line reflect the age 1908 Ma of low pressure granulite metamorphism. Also two-points (Grt-Rt) Sm-Nd isochrone yield the age 1687 Ma of the last metamorphic alterations in Kandalaksha anorthosite massif. Model Sm-Nd age of the leucocratic gabbro-norite is 2796 Ma with positive ɛNd (+0.32). It means that the source of gabbro-norite was mantle reservoir. All investigations are devoted to memory of academician PAS F. MItrofanov which was a leader of scientific school for

  18. N-S crustal shear system in the Bundelkhand massif: A unique crustal evolution signature in the northern Indian peninsula

    Science.gov (United States)

    Singh, S. P.; Bhattacharya, A. R.

    2017-12-01

    The Bundelkhand massif, located in the northern part of the Indian shield, is a poly-deformed and poly-metamorphic terrain. This paper reports a new shear system developed throughout the massif in the form of N-S trending quartz veins that are sometimes quartzo-feldspathic and rarely granitic in composition. The veins are vertical and commonly occur in conjugate sets. This tectono-magmatic event appears to represent the youngest shear system of the massif as it cross-cuts all the earlier shear systems (E-W, NE-SE and NW-SE). Emplacement of this N-S vein system may have taken place due to extensional processes that developed some cracks along which siliceous magma was vertically emplaced. The complete absence of signature of the N-S event from the surrounding sedimentary cover of Vindhyan Supergroup, Bijawar and Gwalior Groups suggests that this shear system is pre-tectonic to the nearly E-W trending passive basins developed at the margins of the Bundelkhand craton. Further, several workers have considered the Bundelkhand massif as a part of the Aravalli craton. However, due to the absence of N-S, as well as the other (i.e., E-W, NW-SE and NW-SE), tectonic fabrics of the Bundelkhand massif in other cratons of the Peninsular India, and vice versa, makes the Bundelkhand block a separate and unique craton of its own and is not part of the Aravalli craton.

  19. Biodiversity impact of the aeolian periglacial geomorphologic evolution of the Fontainebleau Massif (France)

    Science.gov (United States)

    Thiry, M.; Liron, M. N.

    2009-04-01

    Landscape features The geomorphology of the Fontainebleau Massif is noteworthy for its spectacular narrow ridges, up to 10 km long and 0.5 km wide, armored by tightly cemented sandstone lenses and which overhang sandy depressions of about 50m. Denudation of the sandstone pans lead to a highly contrasted landscape, with sandstone ridges ("platières") towering sandy depressions ("vallées") and limestone plateaus ("monts"). This forms the geological frame of the spectacular sceneries of the Fontainebleau Massif (Thiry & Liron, 2007). Nevertheless, there is little know about the erosive processes that have built-up these landscapes. Periglacial processes, and among them aeolian ones, appear significant in the development of the Fontainebleau Massif physiography. The periglacial aeolian geomorphology Dunes and dune fields are known since long and cover about 15% to 25% of the Fontainebleau Massif. The aeolian dunes developed as well on the higher parts of the landscape, as well as in the lower parts of the landscape. The dunes are especially well developed in the whole eastern part of the massif, whereas the western part of the massif is almost devoid of dunes. Nevertheless, detailed mapping shows that dunes can locally be found in the western district, they are of limited extension, restricted to the east facing backslope of outliers. Loamy-sand covers the limestone plateaus of the "monts". The loam cover is of variable thickness: schematically thicker in the central part of the plateaus, where it my reach 3 m; elsewhere it may thin down to 0,20-0,30 m, especially at the plateau edges. Blowout hollows are "negative" morphologies from where the sand has been withdrawed. Often these blowouts are decametric sized and well-delimited structures. Others, more complex structures, are made up of several elongated hectometric hollows relaying each other from and which outline deflation corridor more than 1 km long. A characteristic feature of these blowout hollows is the

  20. Geochemistry and petrogenesis of serpentinite from the Ingalls ophiolite complex, central Cascades, Washington

    Science.gov (United States)

    MacDonald, J. H., Jr.; Milliken, S. H.; Zalud, K. M.

    2017-12-01

    The Jurassic Ingalls ophiolite complex is located in the central Cascades, Washington State. This ophiolite predominantly consists of three variably serpentinized mantle units. Serpentinite occurs as massive replacing peridotite, or as highly sheared fault zones cutting other rocks. Mylonitic serpentinite forms a large-scale mélange in the middle of the ophiolite, and is interpreted as a fracture zone. Whole-rock and mineral geochemistry of the massive serpentinite was done to understand the metasomatic process and identify the possible protoliths of these rocks. Whole-rock major and trace elements of the massive serpentinite are similar to modern peridotites. The majority of samples analyzed are strongly serpentinized, while a few were moderately to weakly altered. Ca, Mg, and Al suggest these rocks formed from serpentinized harzburgite and dunite with minor lherzolite. All samples have positive Eu/Eu*. Serpentinites plot in fields defined by modern abyssal and forearc peridotites. Trace elements suggests the protoliths underwent variable amounts of mantel depletion (5-20%). Serpentine and relic igneous minerals were analyzed by EPMA at the Florida Center for Analytical Electron Microscopy. The serpentine dose not chemically display brucite mixing, has minor substitution of Fe, Ni, and Cr for Mg, and minor Al substitution for Si. Bastites have higher Ni than replaced olivine. Mineral chemistry, high LOI, and X-ray diffraction suggest lizardite is the primary serpentine polymorph, with minor chrysotile also occurring. Relic Al-chromite and Cr-spinel commonly have Cr-magnetite rims. These relic cores have little SiO2 and Fe3+, suggesting the spinels are well preserved. Most spinels plot in overlap fields defined by abyssal and arc peridotite, while two samples plot entirely in arc fields. Relic olivine have Fo90 to Fo92 and plot along the mantle array. Relic pyroxene are primarily enstatite, with lesser high-Ca varieties. Relic minerals plot near fields defined by

  1. Hydrogeologic characterization of the Cachoeira Deposit Massif, Caetite, state of Bahia, Brazil

    International Nuclear Information System (INIS)

    Bottura, J.A.; Albuquerque Filho, J.L.; Ojima, L.M.

    1984-01-01

    The hydrogeologic applications for the characterization of rock massifs in future mining activity areas are presented. The study was performed in the Cachoeira uranium deposit (Anomaly no.13 - Lagoa Real Project) located in the south-central portion of the state of Bahia, Caetite municipality, belonging to the Brazilian Nuclear Enterprise - NUCLEBRAS. The massif occuring in the area is composed of a group or series of rocks classified generically as gneisses, displaying different geotechnical classes. In order to consubstantiate the hydrogeologic/ hydrogeotechnical characterization, pumping and infiltration tests were performed, as well as periodic water level measurements in piezometers and drill-holes. In this manner, a hydrogeotechnical classification was made possible and a quantitative evaluation of the volume of water that will be drained was elaborated, orviding necessary contributions for research diggings and exploration. (D.J.M.) [pt

  2. Geologic-geochemical characteristics of Guidong granitic massif and recognition of geo-tectonic environment at the time of its emplacement

    Energy Technology Data Exchange (ETDEWEB)

    Jianhong, Li; Shanyuan, Wei; Mingyue, Feng [Beijing Research Inst. of Uranium Geology, Beijing (China); Liang, Liang [East China Inst. of Technology, Fuzhou (China)

    2004-11-01

    Based on the study of geologic characteristics, such as mineralogic assemblage, structural and textural features of granite of Guidong granitic massif, and by using petrochemical, trace-element and isotopic data, and some petrochemical, trace-element and isotopic diagrams widely applied to the identification of geo-tectonic environments, authors recognize that Guidong granitic massif was emplaced in post-orogenic collision environment. (authors)

  3. Genesis and transport of hexavalent chromium in the system ophiolitic rocks - groundwater

    Science.gov (United States)

    Shchegolikhina, Anastasia; Guadagnini, Laura; Guadagnini, Alberto

    2015-04-01

    Our study aims at contributing to the quantification and characterization of chromium transport processes from host rocks and soil matrices to groundwater. We focus on dissolved hexavalent chromium detected in groundwaters of geological regions with ophiolitic rocks (ophiolites and serpentinites) inclusions due to its critical ecological impact. (Oze et al., 2004). Despite the large number of analyses on the occurrence of high concentrations of hazardous hexavalent chromium ions in natural waters, only few studies were performed with the objective of identifying and investigating the geochemical reactions which could occur in the natural system rock - groundwater - dissolved chromium (Fantoni et al., 2002, Stephen and James, 2004, Lelli et al., 2013). In this context, there is a need for integration of results obtained from diverse studies in various regions and settings to improve our knowledge repository. Our theoretical analyses are grounded and driven by practical scenarios detected in subsurface reservoirs exploited for civil and industrial use located in the Emilia-Romagna region (Italy). Available experimental datasets are complemented with data from other international regional-scale settings (Altay mountains region, Russia). Modeling of chromium transformation and migration particularly includes characterization of the multispecies geochemical system. A key aspect of our study is the analysis of the complex competitive sorption processes governing heavy metal evolution in groundwater. The results of the research allow assessing the critical qualitative features of the mechanisms of hexavalent chromium ion mobilization from host rocks and soils and the ensuing transformation and migration to groundwater under the influence of diverse environmental factors. The study is then complemented by the quantification of the main sources of uncertainty associated with prediction of heavy metal contamination levels in the groundwater system explored. Fantoni, D

  4. Controls on the rheological properties of peridotite at a palaeosubduction interface: A transect across the base of the Oman-UAE ophiolite

    Science.gov (United States)

    Ambrose, Tyler K.; Wallis, David; Hansen, Lars N.; Waters, Dave J.; Searle, Michael P.

    2018-06-01

    Studies of experimentally deformed rocks and small-scale natural shear zones have demonstrated that volumetrically minor phases can control strain localisation by limiting grain growth and promoting grain-size sensitive deformation mechanisms. These small-scale studies are often used to infer a critical role for minor phases in the development of plate boundaries. However, the role of minor phases in strain localisation at an actual plate boundary remains to be tested by direct observation. In order to test the hypothesis that minor phases control strain localisation at plate boundaries, we conducted microstructural analyses of peridotite samples collected along a ∼1 km transect across the base of the Oman-United Arab Emirates (UAE) ophiolite. The base of the ophiolite is marked by the Semail thrust, which represents the now exhumed contact between subducted oceanic crust and the overlying mantle wedge. As such, the base of the ophiolite provides the opportunity to directly examine a former plate boundary. Our results demonstrate that the mean olivine grain size is inversely proportional to the abundance of minor phases (primarily orthopyroxene, as well as clinopyroxene, hornblende, and spinel), consistent with suppression of grain growth by grain-boundary pinning. Our results also reveal that mean olivine grain size is proportional to CPO strength (both of which generally decrease towards the metamorphic sole), suggesting that the fraction of strain produced by different deformation mechanisms varied spatially. Experimentally-derived flow laws indicate that under the inferred deformation conditions, the viscosity of olivine was grain-size sensitive. As such, grain size, and thereby the abundance of minor phases, influenced viscosity during subduction-related deformation along the base of the mantle wedge. We calculate an order of magnitude decrease in the viscosity of olivine towards the base of the ophiolite, which suggests strain was localised near the

  5. Massification and Diversity of Higher Education Systems: Interplay of Complex Dimensions

    Science.gov (United States)

    Guri-Rosenblit, Sarah; Sebkova, Helena; Teichler, Ulrich

    2007-01-01

    This paper provides a synthetic overview of the complex dimensions that shape the interrelations between the massification of higher education systems and their structure and composition. Many higher education systems worldwide expanded extensively in the last decades, and have undergone wide and deep structural changes. Most notably, the…

  6. Microbial Community Structure in a Serpentine-Hosted Abiotic Gas Seepage at the Chimaera Ophiolite, Turkey.

    Science.gov (United States)

    Neubeck, Anna; Sun, Li; Müller, Bettina; Ivarsson, Magnus; Hosgörmez, Hakan; Özcan, Dogacan; Broman, Curt; Schnürer, Anna

    2017-06-15

    The surface waters at the ultramafic ophiolitic outcrop in Chimaera, Turkey, are characterized by high pH values and high metal levels due to the percolation of fluids through areas of active serpentinization. We describe the influence of the liquid chemistry, mineralogy, and H 2 and CH 4 levels on the bacterial community structure in a semidry, exposed, ultramafic environment. The bacterial and archaeal community structures were monitored using Illumina sequencing targeting the 16S rRNA gene. At all sampling points, four phyla, Proteobacteria , Actinobacteria , Chloroflexi , and Acidobacteria , accounted for the majority of taxa. Members of the Chloroflexi phylum dominated low-diversity sites, whereas Proteobacteria dominated high-diversity sites. Methane, nitrogen, iron, and hydrogen oxidizers were detected as well as archaea and metal-resistant bacteria. IMPORTANCE Our study is a comprehensive microbial investigation of the Chimaera ophiolite. DNA has been extracted from 16 sites in the area and has been studied from microbial and geochemical points of view. We describe a microbial community structure that is dependent on terrestrial, serpentinization-driven abiotic H 2 , which is poorly studied due to the rarity of these environments on Earth. Copyright © 2017 Neubeck et al.

  7. Crystal structure of modular sodium-rich and low-iron eudialyte from Lovozero alkaline massif

    Energy Technology Data Exchange (ETDEWEB)

    Rozenberg, K. A.; Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru; Aksenov, S. M. [Federal Scientific Research Center “Crystallography and Photonics”, Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

    2016-09-15

    The structure of the sodium-rich representative of the eudialyte group found by A.P. Khomyakov at the Lovozero massif (Kola Peninsula) is studied by X-ray diffraction. The trigonal cell parameters are: a = 14.2032(1) and c = 60.612(1) Å, V = 10589.13 Å3, space group R3m. The structure is refined to the final R = 5.0% in the anisotropic approximation of atomic displacement parameters using 3742|F| > 3σ(F). The idealized formula (Z = 3) is Na{sub 37}Ca{sub 10}Mn{sub 2}FeZr{sub 6}Si{sub 50}(Ti, Nb){sub 2}O{sub 144}(OH){sub 5}Cl{sub 3} · H{sub 2}O. Like other 24-layer minerals of the eudialyte group, this mineral has a modular structure. Its structure contains two modules, namely, “alluaivite” (with an admixture of “eudialyte”) and “kentbrooksite,” called according to the main structural fragments of alluaivite, eudialyte, and kentbrooksite. The mineral found at the Lovozero alkaline massif shows some chemical and symmetry-structural distinctions from the close-in-composition labyrinthite modular mineral from the Khibiny massif. The difference between the minerals stems from different geochemical conditions of mineral formation in the two regions.

  8. HT-LP thermometamorphism modelling : Agly massif, French Pyrenees.

    Science.gov (United States)

    Tournaire Guille, Baptiste; Pascal, Marie-Lola; Lejeune, Anne-Marie; Annen, Catherine

    2017-04-01

    Owing to the strongly anomalous thermal gradients implied, HT-LP metamorphism is a worldwide type of processes in which magma emplacement and solidification at relatively high levels in the crust must be considered as a potentially major heat source. Thermal modelling (e.g. Annen et al. 2005) is an appropriate tool for constraining the part played by such processes in practical cases of thermometamorphism. We study the Agly massif, an exhumed part of middle crust from the Variscan belt in the French Pyrenees. This massif is a classical example of HT-LP metamorphism (Vielzeuf 1996), composed of a metasedimentary cover, mainly micaschists aged from upper Cambrian to Devonian, unconformably overlying an older basement of para- and orthogneisses. The Variscan metamorphic facies extend from greenschists, in the upper part of the cover, to granulites in the basement (Fonteilles 1976). The apparent geotherm of about 110°/km in the metasedimentary cover (amphibolite and greenschist facies) has given way to contrasting interpretations. Magmatic activity partly synchronous with and probably related to the Variscan thermometamorphism is observed at the outcropping level as at least 4 magmatic bodies of mantle origin (Touil 1994), of Stephanian age, including granodiorites and subordinate diorites and gabbros. Recent U/Pb datations on zircons (Tournaire-Guille et al., in prep) also reveal the presence of lower Cambrian magmatism in the gneisses, therefore confirming their interpretation as a pre-Variscan basement. The location (depth), volume (thickness), temperature (composition) and timing of magma emplacement are the parameters controlling the thermal effect to be modelled with a Matlab® code (Annen et al. 2005). In order to constrain these parameters, we have updated the lithostratigraphy and the PT conditions of the Variscan metamorphism in the Agly area. Mineralogic and petrologic data exploited in thermobarometric analyses compared with thermodynamic PerpleX modelling

  9. Musa massif: mapping, petrology and petrochemical, Rio Maria, SE from Para State

    International Nuclear Information System (INIS)

    Gastal, M.C.P.

    1987-01-01

    The petrological, geochemical and geochronological studies allow some insight on the genesis and evolution of the Musa Massif. The different facies of the granitic body are cogenetic, although each of these facies presents some peculiarities in its genesis and evolution. These data suggests that the granite magma evolution was complex or, alternatively, that the facies were generated by liquids derived from different sources. A model of magmatic emplacement, genesis and differentiation is proposed and discussed. The granitic facies show a calc-alkaline compositions, exhibiting strong analogies with cordilleran granites or magnetite granites. An age of 1692 +- 11 Ma (Rb/Sr) with IR of 0,70777 +- 0,00023 was obtained for different facies of Massif. A preliminary attempt to individualize geochronology the principal facies was done and showed that there is a coincidence between the ages and the emplacement sequence of these facies of the pluton. (author)

  10. Characterization of ophiolites from northern Havana-Matanzas petroleum fields using instrumental neutron activation analysis

    Energy Technology Data Exchange (ETDEWEB)

    Montero Cabrera, M.E. E-mail: montero@yakko.cimav.edu.mx; Ortueta Milan, M.; Herrera Peraza, E.F.; Herrera Hernandez, H.; Rodriguez Martinez, N.; Olivares Rieumont, S.; Lopez Reyes, M.C

    2001-01-15

    Concentrations of 16 elements from 14 serpentinitic samples from Basilio and Cantel petroleum fields were obtained by instrumental neutron activation analysis (INAA): Cr, Co, Ni, La, Nd, Sm, Eu, Gd, Tb, Ce Yb, Lu, Rb, Cs, Hf and Th. Relative INAA was performed using certified reference materials and laboratory standards. Average elemental concentrations showed that the ophiolites have a basic character, suggesting the use of a well-logging method designed for volcano-sedimentary petroleum fields.

  11. Characterization of ophiolites from northern Havana-Matanzas petroleum fields using instrumental neutron activation analysis

    International Nuclear Information System (INIS)

    Montero Cabrera, M.E.; Ortueta Milan, M.; Herrera Peraza, E.F.; Herrera Hernandez, H.; Rodriguez Martinez, N.; Olivares Rieumont, S.; Lopez Reyes, M.C.

    2001-01-01

    Concentrations of 16 elements from 14 serpentinitic samples from Basilio and Cantel petroleum fields were obtained by instrumental neutron activation analysis (INAA): Cr, Co, Ni, La, Nd, Sm, Eu, Gd, Tb, Ce Yb, Lu, Rb, Cs, Hf and Th. Relative INAA was performed using certified reference materials and laboratory standards. Average elemental concentrations showed that the ophiolites have a basic character, suggesting the use of a well-logging method designed for volcano-sedimentary petroleum fields

  12. Extensional ductile tectonics of the Sioule metamorphic series (Variscan French Massif Central)

    Science.gov (United States)

    Faure, M.; Grolier, J.; Pons, J.

    1993-09-01

    In the Northern part of the Variscan French Massif Central, the Sioule series, from top to bottom, consists of a pre-Viséan granite, migmatite, gneiss and mica schist. Two ductile deformations have been recognized. The earlier phase is characterized by a north-east-south-west trending stretching lineation; the second phase, characterized by a north-west-south-east trending mineral, stretching and crenulation lineation, is better marked in the lower mica schist part than in the upper granito-gneissic part. This second phase occurred during retrogression of the metamorphic rocks; related shear criteria indicate a top to the south-west shear. The Namurian-Westphalian magmatic bodies such as the Echassières leucogranite, Pouzol-Servant microgranite and numerous north-east -south-west trending microgranite dykes are emplaced in extensional fractures related to the same north-west-south-east maximum stretching direction. The asymmetrical shapes of the two granitic massifs indicate that they intruded towards the south-east. The synkinematic retrogression of the metamorphic rocks, the shape of the magmatic bodies and a re-examination of the numerous available data support the interpretation that the deformation is due to the extensional tectonic regime related to the Variscan crustal re-quilibration. This interpretation is in agreement with the correlation of the Sioule series with the Chavanon series. The two series belong to a unique tectono-metamorphic unit left-laterally offset by the Stephanian motion of the Sillon Houiller fault. This study also shows that the Sillon Houiller did not play a significant part during the Namurian-Westphalian extensional tectonics of the Massif Central.

  13. Permian fauna of the Krkonoše Piedmont Basin (Bohemian Massif, Central Europe)

    Czech Academy of Sciences Publication Activity Database

    Zajíc, Jaroslav

    2014-01-01

    Roč. 70, 3/4 (2014), s. 131-142 ISSN 0036-5343 Institutional support: RVO:67985831 Keywords : faunal lists * palaeogeography * palaeoenvironment * stratigraphy * Early Permian * Krkonoše Piedmont Basin * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  14. Assessment of flora condition and transformation extent at the Degelen mountain massif

    International Nuclear Information System (INIS)

    Tuleubaev, B.A.; Sejsebaev, A.T.; Sultanova, B.M.; Dzhanin, B.T.

    2000-01-01

    The article describes current condition of vegetation at the Degelen mountain massif and assessment of vegetation disturbance in areas of underground nuclear testing. It also presents results of studying flora transformation, species and cinotic composition, structural and spatial distribution within the Degelen technical site. (author)

  15. Petrology of Ortsog-Uul peridotite-gabbro massif in Western Mongolia

    Science.gov (United States)

    Shapovalova, M.; Tolstykh, N.; Shelepaev, R.; Cherdantseva, M.

    2017-12-01

    The Ortsog-Uul mafic-ultramafic massif of Western Mongolia is located in a tectonic block with overturned bedding. The massif hosts two intrusions: a rhythmically-layered peridotite-gabbro association (Intrusion 1) and massive Bt-bearing amphibole-olivine gabbro (Intrusion 2). Intrusions 1 and 2 have different petrology features. Early Intrusion 1 (278±2.5Ma) is characterized by lower concentrations of alkalis, titanium and phosphorus than late Intrusion 2 (272±2Ma). The chondrite-normalized REE and primitive mantle-normalized rare elements patterns of Ortsog-Uul intrusions have similar curves of elements distribution. However, Intrusion 2 is characterized higher contents of REE and rare elements. High concentrations of incompatible elements are indicative of strong fractionation process. It has been suggested that Intrusions 1 and 2 derived from compositionally different parental melts. Model calculations (COMAGMAT-3.57) show that parental melts of two intrusions were close to high-Mg picrobasaltic magmas. The concentration of MgO in melt is 16.21 (Intrusion 1) and 16.17 (Intrusion 2). Isotopic data of Ortsog-Uul magmatic rocks exhibit different values of εNd (positive and negative) for Intrusion 1 and 2, respectively.

  16. Quelques phases granitiques intrusives dans le Massif des Trois Seigneurs

    NARCIS (Netherlands)

    Nieuwenhuys, W.H.

    1956-01-01

    Pendant les étés de 1953, 1954 et 1955 j’ai effectué des travaux de terrain dans le Massif des Trois Seigneurs, Pyrénées orientales, sous la direction du Professeur L.U. de Sitter. Ces travaux de terrain comprennent entre autres le levé d’une carte géologique de la partie centrale et Sud-Ouest de ce

  17. From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

    Science.gov (United States)

    Paquette, J.-L.; Ballèvre, M.; Peucat, J.-J.; Cornen, G.

    2017-12-01

    In the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples. Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism.

  18. Expedition 357 Preliminary Report: Atlantis Massif Serpentinization and Life

    OpenAIRE

    Früh-Green, GL; Orcutt, BN; Green, S; Cotterill, C; McCaig, AM; Expedition 357 Scientists,

    2016-01-01

    International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpent...

  19. Incipient boninitic arc crust built on denudated mantle: the Khantaishir ophiolite (western Mongolia)

    Science.gov (United States)

    Gianola, Omar; Schmidt, Max W.; Jagoutz, Oliver; Sambuu, Oyungerel

    2017-12-01

    The 570 Ma old Khantaishir ophiolite is built by up to 4 km harzburgitic mantle with abundant pyroxenites and dunites followed by 2 km of hornblende-gabbros and gabbronorites and by a 2.5 km thick volcanic unit composed of a dyke + sill complex capped by pillow lavas and some volcanoclastics. The volcanics are mainly basaltic andesites and andesites (or boninites) with an average of 58.2 ± 1.0 wt% SiO2, X Mg = 0.61 ± 0.03 ( X Mg = molar MgO/(MgO + FeOtot), TiO2 = 0.4 ± 0.1 wt% and CaO = 7.5 ± 0.6 wt% (errors as 2 σ). Normalized trace element patterns show positive anomalies for Pb and Sr, a negative Nb-anomaly, large ion lithophile elements (LILE) concentrations between N- and E-MORB and distinctly depleted HREE. These characteristics indicate that the Khantaishir volcanics were derived from a refractory mantle source modified by a moderate slab-component, similar to boninites erupted along the Izu-Bonin-Mariana subduction system and to the Troodos and Betts Cove ophiolites. Most strikingly and despite almost complete outcrops over 260 km2, there is no remnant of any pre-existing MORB crust, suggesting that the magmatic suite of this ophiolite formed on completely denudated mantle, most likely upon subduction initiation. The architecture of this 4-5 km thick early arc crust resembles oceanic crust formed at mid ocean ridges, but lacks a sheeted dyke complex; volcanic edifices are not observed. Nevertheless, low melting pressures combined with moderate H2O-contents resulted in high-Si primitive melts, in abundant hornblende-gabbros and in a fast enrichment in bulk SiO2. Fractional crystallization modeling starting from the observed primitive melts (56.6 wt% SiO2) suggests that 25 wt% pyroxene + plagioclase fractionation is sufficient to form the average Khantaishir volcanic crust. Most of the fractionation happened in the mantle, the observed pyroxenite lenses and layers in and at the top of the harzburgites account for the required cumulate volumes. Finally

  20. A deep hydrothermal fault zone in the lower oceanic crust, Samail ophiolite Oman

    Science.gov (United States)

    Zihlmann, B.; Mueller, S.; Koepke, J.; Teagle, D. A. H.

    2017-12-01

    Hydrothermal circulation is a key process for the exchange of chemical elements between the oceans and the solid Earth and for the extraction of heat from newly accreted crust at mid-ocean ridges. However, due to a dearth of samples from intact oceanic crust, or continuous samples from ophiolites, there remain major short comings in our understanding of hydrothermal circulation in the oceanic crust, especially in the deeper parts. In particular, it is unknown whether fluid recharge and discharge occurs pervasively or if it is mainly channeled within discrete zones such as faults. Here, we present a description of a hydrothermal fault zone that crops out in Wadi Gideah in the layered gabbro section of the Samail ophiolite of Oman. Field observations reveal a one meter thick chlorite-epidote normal fault with disseminated pyrite and chalcopyrite and heavily altered gabbro clasts at its core. In both, the hanging and the footwall the gabbro is altered and abundantly veined with amphibole, epidote, prehnite and zeolite. Whole rock mass balance calculations show enrichments in Fe, Mn, Sc, V, Co, Cu, Rb, Zr, Nb, Th and U and depletions of Si, Ca, Na, Cr, Zn, Sr, Ba and Pb concentrations in the fault rock compared to fresh layered gabbros. Gabbro clasts within the fault zone as well as altered rock from the hanging wall show enrichments in Na, Sc, V, Co, Rb, Zr, Nb and depletion of Cr, Ni, Cu, Zn, Sr and Pb. Strontium isotope whole rock data of the fault rock yield 87Sr/86Sr ratios of 0.7046, which is considerably more radiogenic than fresh layered gabbro from this locality (87Sr/86Sr = 0.7030 - 0.7034), and similar to black smoker hydrothermal signatures based on epidote, measured elsewhere in the ophiolite. Altered gabbro clasts within the fault zone show similar values with 87Sr/86Sr ratios of 0.7045 - 0.7050, whereas hanging wall and foot wall display values only slightly more radiogenic than fresh layered gabbro.The secondary mineral assemblages and strontium isotope

  1. Quantification of Tremolite in Friable Material Coming from Calabrian Ophiolitic Deposits by Infrared Spectroscopy

    Directory of Open Access Journals (Sweden)

    Antonella Campopiano

    2015-01-01

    Full Text Available The aim of this study is to identify the infrared absorption band suitable for quantifying tremolite in three powdered samples (fine, medium, and large size classes coming from a quarry of ophiolitic friable rocks in the western part of the Calabria region of Italy. Three IR bands were considered: OH stretching band between 3700 and 3650 cm−1, the stretching bands of the Si-O-Si linkage between 1200 and 900 cm−1, and the absorbance band at 756 cm−1 attributable to tremolite. The amount of tremolite in the test samples was quantified by using the curve parameters of the three analytical bands. The quantitative analysis of tremolite using the band due to OH stretchings (3700–3650 cm−1 and the bands attributed to the Si-O-Si stretchings (1200–900 cm−1 showed high values for all test samples. Their use overestimated the tremolite amount because both bands were affected at the interfering mineral silicates such as talc, kaolinite, chlorite, and serpentinites. The abundant presence of antigorite in studied samples mainly in medium size class sample had a key role in our findings. The band at 756 cm−1 was not affected at the interfering minerals and can be used for quantitative analysis of tremolite in sample coming from ophiolitic deposits.

  2. The Gondwana Orogeny in northern North Patagonian Massif: Evidences from the Caita Có granite, La Seña and Pangaré mylonites, Argentina

    Directory of Open Access Journals (Sweden)

    Daniel A. Gregori

    2016-07-01

    Full Text Available Structural analyses in the northern part of the North Patagonia Massif, in the foliated Caita Có granite and in La Seña and Pangaré mylonites, indicate that the pluton was intruded as a sheet-like body into an opening pull-apart structure during the Gondwana Orogeny. Geochronological studies in the massif indicate a first, lower to middle Permian stage of regional deformation, related to movements during indentation tectonics, with emplacement of foliated granites in the western and central areas of the North Patagonian Massif. Between the upper Permian and lower Triassic, evidence indicates emplacement of undeformed granitic bodies in the central part of the North Patagonian Massif. A second pulse of deformation between the middle and upper Triassic is related to the emplacement of the Caita Có granite, the development of mylonitic belts, and the opening of the Los Menucos Basin. During this pulse of deformation, compression direction was from the eastern quadrant.

  3. The Massification of Higher Education in the UK: Aspects of Service Quality

    Science.gov (United States)

    Giannakis, Mihalis; Bullivant, Nicola

    2016-01-01

    This article explores several aspects of service quality for the provision of higher education. Alongside the trend of the massification of higher education over the past two decades, higher education institutions are required to review quality across a range of outputs, besides teaching and learning. The study was undertaken within the…

  4. Fission track and petrostructural analysis of carbonatic massif of Tamazert ( high central Atlas, Morocco) and neogene reactivation of the north-atlasic fault

    International Nuclear Information System (INIS)

    Ziad, N.; Khazrouni, S.; Tayebi, M.; Bouabdli, A.; Poupeau, G.

    2001-01-01

    The uranium fission-track dating method is used in geochronological survey of basic apatites extracted from the Tamazert complex. The result of this survey coupled with those of petrostructural analysis of this massif enabled as to distinguish three age groups: 32.4 Myr, 23.3 Myr and 12.6 Myr. The first age corresponds to the setting up of the massif, whereas the two other ages indicate later emissions. The setting up of the sill whose age is 12.6 Myr induced a partial rejuvenation of the emission age og the massif. This late volcanic emission is probably related to the north-atlasic fault activity. 4 figs., 1 tab., 30 refs. (au)

  5. Environmental characterization of lake ecosystems located in Serbo Macedonian massif (FYRM)

    OpenAIRE

    Dolenec, Tadej; Serafimovski, Todor; Lojen, Sonja; Dolenec, Matej; Tasev, Goran; Kramar, Sabina; Rogan Šmuc, Nastja; Vrhovnik, Petra

    2015-01-01

    This mineralogical, geochemical and isotopic characteristics of recent lacustrine sediments, of Anodonta cygnea shells and of fish species Rutilus rutilus dojranensis from the Lake Dojran (FY Republic of Macedonia, southern part of the Serbo-Macedonian Massif (SMM)), which provide indirect evidence regarding biomineralization and calcification processes as well as various geological problems. Environmental pollution can seriously impair physiological functions such as the secre...

  6. The recycling of chromitites in ophiolites from southwestern North America

    Science.gov (United States)

    González-Jiménez, José M.; Camprubí, Antoni; Colás, Vanessa; Griffin, William L.; Proenza, Joaquín A.; O'Reilly, Suzanne Y.; Centeno-García, Elena; García-Casco, Antonio; Belousova, Elena; Talavera, Cristina; Farré-de-Pablo, Júlia; Satsukawa, Takako

    2017-12-01

    Podiform chromitites occur in mantle peridotites of the Late Triassic Puerto Nuevo Ophiolite, Baja California Sur State, Mexico. These are high-Cr chromitites [Cr# (Cr/Cr + Al atomic ratio = 0.61-0.69)] that contain a range of minor- and trace-elements and show whole-rock enrichment in IPGE (Os, Ir, Ru). That are similar to those of high-Cr ophiolitic chromitites crystallised from melts similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction-zone mantle wedges. Crystallisation of these chromitites from S-undersaturated melts is consistent with the presence of abundant inclusions of platinum-group minerals (PGM) such as laurite (RuS2)-erlichmanite (OsS2), osmium and irarsite (IrAsS) in chromite, that yield TMA ≈ TRD model ages peaking at 325 Ma. Thirty-three xenocrystic zircons recovered from mineral concentrates of these chromitites yield ages (2263 ± 44 Ma to 278 ± 4 Ma) and Hf-O compositions [ɛHf(t) = - 18.7 to + 9.1 and 18O values the mantle via subduction. They were captured by the parental melts of the chromitites when the latter formed in a supra-subduction zone mantle wedge polluted with crustal material. In addition, the Puerto Nuevo chromites have clinopyroxene lamellae with preferred crystallographic orientation, which we interpret as evidence that chromitites have experienced high-temperature and ultra high-pressure conditions (the formation of chromitite in the supra-subduction zone mantle wedge underlying the Vizcaino intra-oceanic arc ca. 250 Ma ago, deep-mantle recycling, and subsequent diapiric exhumation in the intra-oceanic basin (the San Hipólito marginal sea) generated during an extensional stage of the Vizcaino intra-oceanic arc ca. 221 Ma ago. The TRD ages at 325 Ma record a partial melting event in the mantle prior to the construction of the Vizcaino intra-oceanic arc, which is probably related to the Permian continental subduction, dated at 311 Ma.

  7. Paleocene-Eocene Sediments Interbedded With Volcanics Within the Lycian Nappes: Faralya Formation

    Directory of Open Access Journals (Sweden)

    Mustafa Şenel

    1991-06-01

    Full Text Available The presumably allochthonous structural units in the Southwestern Turkey between the Menderes massif and Beydağları autochthon are known as the Lycian nappes. Some of these units particularly beneath the ophiolite nappe end up with the Faralya formation of Paleocene-Lutetian age. The striking feature of this formation which includes micrite, clayey micrite, claystone, sandstone and conglomerate, is the presence of basic volcanite interbeds of Eocene age, This volcanite bearing formation exhibits a strong similarity to those of the other formations in Southwestern Turkey most of which include similar basic volcanites. Eocene basic volcanites are also known in the Akseki autochthon to the south of Seydişehir (Geyikdağ unit in broad sense. Similar extensive lateral movements (Eocene mountain building processes developed over the Faralya formation are seen over the volcanite bearing formations to the south of Menderes massif as well as to the north of Isparta angle and the Akseki autochthon. These features indicate that the area between the Menderes massif and Akseki autochthon (Geyikdağ unit reflects common basinal characters in terms of depositional conditions, volcanism and the traces of Eocene mountain building process.

  8. Plutonic rocks in the Mineoka-Setogawa ophiolitic mélange, central Japan: Fragments of middle to lower crust of the Izu-Bonin-Mariana Arc?

    Science.gov (United States)

    Ichiyama, Yuji; Ito, Hisatoshi; Hokanishi, Natsumi; Tamura, Akihiro; Arai, Shoji

    2017-06-01

    A Paleogene accretionary complex, the Mineoka-Setogawa Belt, is distributed around the Izu Collision Zone, central Japan. Plutonic rocks of gabbro, diorite and tonalite compositions are included as fragments and dykes in an ophiolitic mélange in this belt. Zircon U-Pb dating of the plutonic rocks indicates that they were formed at ca. 35 Ma simultaneously. These ages are consistent with Eocene-Oligocene tholeiite and calc-alkaline arc magmatism in the Izu-Bonin-Mariana (IBM) Arc and exclude several previous models for the origin of the Mineoka-Setogawa ophiolitic rocks. The geochemical characteristics of these plutonic rocks are similar to those of the Eocene-Oligocene IBM tholeiite and calc-alkaline volcanic rocks as well as to the accreted middle crust of the IBM Arc, the Tanzawa Plutonic Complex. Moreover, their lithology is consistent with those of the middle and lower crust of the IBM Arc estimated from the seismic velocity structure. These lines of evidence strongly indicate that the plutonic rocks in the Mineoka-Setogawa ophiolitic mélange are fragments of the middle to lower crust of the IBM Arc. Additionally, the presence of the Mineoka-Setogawa intermediate to felsic plutonic rocks supports the hypothesis that intermediate magma can form continental crust in intra-oceanic arcs.

  9. Rapakivi texture in porphyritic dikes within the Karavanke Granitic Massif (Slovenia

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    Giuliano Bellieni

    2002-01-01

    Full Text Available The northern Karavanke Granitic Massif straddles the Slovenian–Austrian border. The investigated area lies in northern Slovenia, and extends from the western Slovenian–Austrian border to the east for about 30 km, with a maximum width of 2 km. The massif exhibits a bimodal magmatic association comprising mainly syenogranite and syenite with contemporaneous gabbroic rocks. Rocks of intermediate composition are less abundant and show field, textural and chemical features suggesting that they have formed as a result of the interaction (mixing and mingling between felsic and mafic magmas. Plagioclasemantled alkali feldspars occur in dikes of porphyritic syenite, which cut larger bodies of gabbroic rocks. Field, mineralogical, petrographic and geochemical evidences suggest that the porphyritic syenite is a hybrid rock, formed by the interaction of mafic and felsic magmas. The formation of plagioclase-mantled alkali feldspar can be explained by the introduction of alkali feldspar from felsic, syenogranitic magma into more mafic magma, causing local undercooling in the portion of mafic magma surrounding the crystals. This resulted in the growth of cellular plagioclase, with quartz infilling, in a thermally and compositionally equilibrating system.

  10. Constraining the deformation and exhumation history of the Ronda Massif, Southern Spain

    Science.gov (United States)

    Myall, Jack; Donaldson, Colin

    2016-04-01

    The Ronda peridotite, southern Spain is comprised of four peridotite units hosted within metasedimentary units of the Betic Cordillera, Western Alps. These four areas of differing mineral facies are termed: the Garnet Mylonite , the Foliated Spinel Peridotite, the Granular Spinel Peridotite and the Foliated Plagioclase Peridotite. Whilst two of these units show a strong NE-SW foliation, the granular unit has no foliation and the Plagioclase facies shows a NW-SE foliation. The massif is separated from the metasedimentary host through a mylonite shear zone to the NW and thrust faults to the SE. The Garnets contain rims of Kelyphite which when combined with the rims of Spinel on the Plagioclase crystals illustrate the complicated exhumation of this massif. The Kelyphite shows the breakdown of garnet back to spinel and pyroxene showing the deeper high pressure high temperature mineral is under shallowing conditions whereas in contrast to this the low pressure low temperature plagioclase crystals have spinel rims showing that they have been moved into deeper conditions. The P-T-t pathway of the massif suggests slow exhumation to allow for partial recrystallisation of not only the garnets and plagioclases but of a 100m band of peridotite between the Foliated Spinel Peridotite and the Granular Spinel Peridotite facies. The tectonic model for the Ronda Peridotite that best describes the field data and subsequent lab work of this study is Mantle Core complex and slab roll back models. These models support mantle uprising during an extensional event that whereby slab roll back of the subducting lithosphere provides uplift into a void and emplacement into the crust. Further extension and final exhumation causes rotation of a mantle wedge into its present day position.

  11. A new method of discriminating different types of post-Archean ophiolitic basalts and their tectonic significance using Th-Nb and Ce-Dy-Yb systematics

    Directory of Open Access Journals (Sweden)

    Emilio Saccani

    2015-07-01

    Full Text Available In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to post-Archean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram was obtained using >2000 known ophiolitic basalts and was tested using ∼560 modern rocks from known tectonic settings. Ten different basaltic varieties from worldwide ophiolitic complexes have been examined. They include two basaltic types that have never been considered before, which are: (1 medium-Ti basalts (MTB generated at nascent forearc settings; (2 a type of mid-ocean ridge basalts showing garnet signature (G-MORB that characterizes Alpine-type (i.e., non volcanic rifted margins and ocean-continent transition zones (OCTZ. In the Th-Nb diagram, basalts generated in oceanic subduction-unrelated settings, rifted margins, and OCTZ can be distinguished from subduction-related basalts with a misclassification rate <1%. This diagram highlights the chemical variation of oceanic, rifted margin, and OCTZ basalts from depleted compositions to progressively more enriched compositions reflecting, in turn, the variance of source composition and degree of melting within the MORB-OIB array. It also highlights the chemical contributions of enriched (OIB-type components to mantle sources. Enrichment of Th relative to Nb is particularly effective for highlighting crustal input via subduction or crustal contamination. Basalts formed at continental margin arcs and island arc with a complex polygenetic crust can be distinguished from those generated in intra-oceanic arcs in supra-subduction zones (SSZ with a misclassification rate <1%. Within the SSZ group, two sub-settings can be recognized with a misclassification rate <0.5%. They are: (1 SSZ influenced by chemical contribution from subduction-derived components (forearc and intra-arc sub-settings characterized by island arc tholeiitic (IAT and boninitic basalts; (2 SSZ with no contribution from subduction

  12. K-Ar ages of some metamorphic rocks of Oban massif and their implications for the tectonothermal evolution of Southeastern Nigeria

    International Nuclear Information System (INIS)

    Ekwueme, B.N.; Itaya, Tetsumaru; Yabe, Hisatomo

    2000-01-01

    The following K-Ar ages have been obtained on mineral separates from some metamorphic rocks in the Oban massif: amphibolites (592-930 Ma), banded gneisses (492-538 Ma), granodioritic gneiss (502 Ma), schists (514-519 Ma) and charnockite (481 Ma). Comparison of these ages with previous dates obtained by the Rb-Sr whole rock method and the Pb-Pb evaporation technique on single zircon throws light on the cooling history and orogenic events in the Oban massif. The banded gneiss in the Oban massif yields a zircon age of 1932±5 Ma, indicating that it was emplaced during the early Proterozoic (Eburnean orogeny). The K-Ar age of 492-538 Ma suggests that these rocks were metamorphosed during the Pan-African orogeny. This age is similar to the Rb-Sr isochron age of 510±10 Ma earlier suggested to be the age of migmatization in the Oban massif. The amphibolite yielded Rb-Sr isochron ages of 784±31 Ma and 1313±37 Ma. The age of 1313±37 Ma fits into the Kibaran event. The K-Ar hornblende age of 930±37 Ma on the same amphibolite strongly suggests that this amphibolite belongs to an event older than Pan-African (600±150 Ma) and has not been reset perfectly by the Pan-African event. The migmatitic schists in the Oban massif yielded a Rb-Sr isochron age of 527±16 Ma which has been interpreted as the age of its migmatization. One sample of this schist, however, gave a model age of 676±24 Ma. The K-Ar ages for the Oban massif schists (514-519 Ma) are close to the Rb-Sr isochron age of ca. 527 Ma and confirm that a metamorphic event occurred in the area at this time. This was followed by final cooling at 515±10 Ma. Charnockite in the Oban area has yielded a zircon age of 584±20 Ma, which is Pan-African. The age possibly dates the time of formation of the charnockites. The K-Ar age (481 Ma) obtained in this study is approximately 100 Ma younger than the zircon age and possibly dates the subsequent cooling of the charnockite through hornblende blocking temperature. (author)

  13. STRUCTURAL FEATURES OF THE NİĞDE MASSIF IN THE ÇAMARDI (NİĞDE DISTRICT

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    Ramazan DEMİRCİOĞLU

    2017-04-01

    Full Text Available In the Çamardı (Niğde district, the Niğde Massif is composed of marbles, gneisses, quartzites and amphibolites. These rocks of the Massif have been cut by Cretaceous aged granodiorites. The Paleocene-Eocene aged low-grade metamorphic rocks constitute the autochthonous cover of the Massif. These units are tectonically overlain by the Upper Cretaceous-Paleocene aged flyschoid and island arc type rocks. The Oligocene-Quaternary aged terrestrial and volcanic rocks constitute the youngest units in the district. The metamorphics of the Niğde Massif have been subjected to at least four phase ductile deformation (D1, D2, D3, and D4 and folding. Through the D1 phase deformation, the rocks of the Massif have been folded as recumbent-isoclinal folds (F1-F2 phase folding and have gained a structure with a foliation (S1 which is parallel to the axial planes. Owing to the isoclinal and intense folding of the bedding planes (S0 of the rocks, bedding transposition have developed and transposed folding structures have formed. Through the D2 phase deformation, northeast-southwest trending and both northeast and southwest dipping map scale folds (F3 phase folding have developed. As a result of the interference of F1-F2 and F3 phase folds, in the district, folds, generated by Type-2 folding, have formed (mushroom folds. Second phase mesoscopic folds are of tight-isoclinal geometry and display asymmetrical and inclined fold feature. In the study area, as a result of   D3 phase folding a large dome structure has developed in the district. And D4 phase folds have formed map scale synformal and antiformal structures that are trending approximately perpendicular to D2 phase, plunging south-east and trending northwest-southeast. Through D4 phase deformation, the cover rocks have been deformed together with the basement rocks (F5 phase that they overlie. The microscopic observations show that Cretaceous-Eocene aged rocks have been subjected to low

  14. How are the emplacement of rare-element pegmatites, regional metamorphism and magmatism interrelated in the Moldanubian domain of the Variscan Bohemian Massif, Czech Republic?

    Czech Academy of Sciences Publication Activity Database

    Melleton, J.; Gloaguen, E.; Frei, D.; Novák, M.; Breiter, Karel

    2012-01-01

    Roč. 50, č. 6 (2012), s. 1751-1773 ISSN 0008-4476 Institutional support: RVO:67985831 Keywords : LCT pegmatite * rare-element-enriched magma * columbite-tantalite * LA-SF-ICP-MS dating * Variscan orogeny * Bohemian Massif * Moldanubian domain * Bohemian Massif (Czech Republic) Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.180, year: 2012

  15. Modeling the uplift in the Ardennes-Rhenish Massif: Mechanical weakening under the Eifel?

    NARCIS (Netherlands)

    Garcia-Castellanos, D.; Cloetingh, S.A.P.L.; van Balen, R.T.

    2000-01-01

    Middle Pleistocene uplift in the Eifel has been interpreted as the isostatic response of the lithosphere to a deep buoyant hot body. The spatial and temporal distribution of the uplift in the Ardennes-Rhenish Massif Region has recently been constrained by new data of river incision that have been

  16. Characterizing and quantifying superparamagnetic magnetite particles in serpentinized mantle peridotite observed in continental ophiolite complexes.

    Science.gov (United States)

    Ortiz, E.; Vento, N. F. R.; Tominaga, M.; Beinlich, A.; Einsle, J. F.; Buisman, I.; Ringe, E.; Schrenk, M. O.; Cardace, D.

    2017-12-01

    Serpentinization of mantle peridotite has been recognized as one of the most important energy factories for the deep biosphere. To better evaluate the habitability of the deep biosphere, it is crucial to understand the link between in situ peridotite serpentinization processes and associated magnetite and hydrogen production. Previous efforts in correlating magnetite and hydrogen production during serpentinization processes are based primarily on laboratory experiments and numerical modeling, being challenged to include the contribution of superparamagnetic-sized magnetites (i.e., extremely fine-grained magnetite, petrographically observed as a "pepper flake" like texture in many natural serpentinized rock samples). To better estimate the abundance of superparamagnetic grains, we conducted frequency-dependent susceptibility magnetic measurements at the Institute of Rock Magnetism on naturally serpentinized rock samples from the Coast Range Ophiolite Microbial Observatory (CROMO) in California, USA and the Atlin Ophiolite (British Columbia). In addition, we conducted multiscale EDS phase mapping, BackScattered Electron (BSE) scanning, FIB-nanotomography and STEM-EELS to identify and quantify the superparamagnetic minerals that contribute to the measured magnetic susceptibility signals in our rock samples. Utilizing a multidisciplinary approach, we aim to improve the estimation of hydrogen production based on the abundance of magnetite, that includes the contribution of superparamagnetic particle size magnetite, to ultimately provide a more accurate estimation of bulk deep-biomass hosted by in situ serpentinization processes.

  17. Massification and Diversification as Complementary Strategies for Economic Growth in Developed and Developing Countries

    Science.gov (United States)

    Tyndorf, Darryl; Glass, Chris R.

    2016-01-01

    Numerous microeconomic studies demonstrate the significant individual returns to tertiary education; however, little empirical evidence exists regarding the effects of higher education massification and diversification agendas on long-term macroeconomic growth. The researchers used the Uzawa-Lucas endogenous growth model to tertiary education…

  18. Dating an actively exhuming metamorphic core complex, the Suckling Dayman Massif in SE Papua New Guinea

    Science.gov (United States)

    Oesterle, J.; Seward, D.; Little, T.; Stockli, D. F.; Mizera, M.

    2016-12-01

    Low-temperature thermochronology is a powerful tool for revealing the thermal and kinematic evolution of metamorphic core complexes (MCCs). Most globally studied MCCs are ancient, partially eroded, and have been modified by deformation events that postdate their origin. The Mai'iu Fault is a rapidly slipping active low-angle normal fault (LANF) in the Woodlark Rift in Papua New Guinea that has exhumed a >25 km-wide (in the slip direction), and over 3 km-high domal fault surface in its footwall called the Suckling-Dayman massif. Some knowledge of the present-day thermal structure in the adjacent Woodlark Rift, and the pristine nature of this active MCC make it an ideal candidate for thermochronological study of a high finite-slip LANF. To constrain the thermal and kinematic evolution of this MCC we apply the U/Pb, fission-track (FT) and (U-Th)/He methods. Zircon U/Pb analyses from the syn-extensional Suckling Granite that intrudes the footwall of the MCC yield an intrusion age of 3.3 Ma. Preliminary zircon FT ages from the same body indicate cooling below 300 °C at 2.7 Ma. Ages decrease to 2.0 Ma with increasing proximity to the Mai'iu Fault and imply cooling controlled by tectonic exhumation. Almost coincident zircon U/Pb and FT ages from the nearby syn-extensional Mai'iu Monzonite, on the other hand, record extremely rapid cooling from magmatic temperatures to 300 °C at 2 Ma. As apparent from the preliminary He extraction stage, these syn-extensional plutons have young zircon and apatite (U-Th)/He ages. These initial results suggest that the Mai'iu Fault was initiated as an extensional structure by 3.3 Ma. We infer that it reactivated an older ophiolitic suture that had emplaced the Papuan Ultramafic body in the Paleogene. Rapid cooling of the Mai'iu Monzonite indicates that it was intruded into a part of the MCC's footwall that was already shallow in the crust by 2 Ma. This inference is further supported by the mineral andalusite occurring in the contact

  19. Geophysical monitoring as an information source of rock massif behaviour

    Directory of Open Access Journals (Sweden)

    Pavel Bláha

    2008-06-01

    Full Text Available Geophysical measurements are an integral part of engineering-geological investigation where theypresent a wide range of useful information about the tested geological medium and about its geotechnicalqualities. Lately, repeated geophysical measurements in different time intervals have been used to judgethe changes occurring in the rock massif. These measurements bear the characteristics of total monitoring.This total monitoring contains series of repeated measurements and further an integrated spectrum of linkedactivities including evaluation, comparison with the warning state and making a decision about takingprecautions. From the range of geophysical methods and methodologies used for monitoring in full sensewe may mention, for example, continuous seismoacoustic measurements in mining constructions; (whichmay result even in recalling of the personnel, and further, also seismic measurements in the surroundingsof atomic power stations and measurements considering the protection against radioactive elements and their decay components.As a full monitoring we may also classify measurements in dumping sites with the aid of repeated geoelectrical measurements in the system of fixed electrodes under impermeable foils.These measurements are mostly carried out from time to time followed by taking immediate action when the foil is found damaged. In practice the term monitoring is used, although not very correctly, for all periodically repeated measurements, which do not result in taking action or interference, but supply a wide range of information about the rock massif behavior in time.

  20. Geological and geophysical investigations at Sierra del Medio massif - Argentine

    International Nuclear Information System (INIS)

    Perucca, J.C.; Llambias, E.; Puigdomenech, H.H.; Cebrelli, E.; Castro, C.E.; Grassi, I.; Salinas, L.I.

    1987-01-01

    Geological investigations were performed at Sierra del Medio (Chubut Province), a mountainous massif of about 25 km by 8 km of migmatic origin, which emerges from a depressed tectonic trench or graben called Pampa de Gastre. The most ancient rocks belong to biotitic and anphibolic schist that passed almost entirely to tonalitoid migmatites with a second process producing granitic rocks. Boreholes were drilled on the basis of conclusions from Landsat satellites imagery and aerial photographic sets, folowed by field work on geological, petrographic, geophysical and hydrogeological features at surface, structural interpretation supported by geostatistical computations. Two sets of boreholes were drilled to investigate subsurface rock behaviour al 300 m depth and 800 m depth respectively, beginning at peripheral places and ending at the central part or selected site. Basic purposes of boreholes were to define structural and petrographic features of the rock massif by a good comprehension of master joints and faulting distribution with its belts of alteration mylonitization or brecciation, mechanical properties of samples, chemical composition and varitions, petrographic facies and mineralogy. Boreholes provided data to investigate joints, faults and dikes as general discontinuities for hydraulic research like permeability or effective hydraulic conductivity, and their geostatistical modelling. Boreholes are also being prepared for geophysical logging from which logthermal ones have already been completed. (Author) [es

  1. K-Ar cooling age profile from Joinville massif (PR and SC, Brazil) and Dom Feliciano belt (SC, Brazil) - Tectonics entanglement

    International Nuclear Information System (INIS)

    Siga Junior, O.; Basei, M.A.S.; Kawashita, K.

    1990-01-01

    A K-Ar cooling age profile using different minerals from metamorphic rocks of the Joinville Massif and Dom Feliciano Belt is presented. Three main geochronological domains are distinguishable, from NW to SE: 1) Northern part of the Joinville Massif (NJM); 2) Southern part of the Joinville Massif (SJM) and 3) Dom Feliciano Belt (DBF). Geochronological domains 1 and 3 yielded K-Ar values in the range 800-500 Ma and 700-500 Ma, respectively, which show a clear influence of the Brasiliano Cycle. The granulite terrain comprising the SMJ exhibits ages older than 1700 Ma, indicating that this area was cool during the Late Proterozoic Brasiliano Cycle. The SJM and NJM limit is marked by a rapid Transition from Early Proterozoic ages in the SJM to Late Proterozoic ages in the NJM. On the other hand the contact between the SJM and DFB is interpreted as a thrust at a high, relatively cool crustal level. (author)

  2. Geophysical research results of buried relief and distribution groundwater runoff of the Aragats massif

    Directory of Open Access Journals (Sweden)

    V.P. Vardanyan

    2017-03-01

    Overall, the new data concerning the structure of the buried relief of Aragats massif and the distribution of its underground runoff allow to develop effective measures for the selection of underground waters and their rational usage for the purpose of water supply and irrigation.

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

    Czech Academy of Sciences Publication Activity Database

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

    2015-01-01

    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: 1.523, year: 2015

  4. Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

    Science.gov (United States)

    Rubatto, Daniela; Ferrando, Simona; Compagnoni, Roberto; Lombardo, Bruno

    2010-04-01

    The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded H P granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.

  5. Late Paleozoic volcanic rocks of the Intra-Sudetic Basin, Bohemian Massif: Petrological and geochemical characteristics

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Fediuk, F.; Lang, Miloš; Martinec, Petr

    2004-01-01

    Roč. 64, č. 2 (2004), s. 127-153 ISSN 0009-2819 R&D Projects: GA AV ČR(CZ) IAA3013903 Keywords : Late Paleozoic * volcanic rocks * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.643, year: 2004

  6. Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants?

    Science.gov (United States)

    Benzaggagh, Mohamed; Mokhtari, Abdelkader; Rossi, Philippe; Michard, André; El Maz, Abdelkhader; Chalouan, Ahmed; Saddiqi, Omar; Rjimati, Ech-Cherki

    2014-07-01

    The aim of this paper is to describe the mafic rocks that crop out in the central-western Mesorif Zone (External Rif Belt), and discuss their geodynamic signification. Basalt flows, olistoliths and breccias occur in Oxfordian-Berriasian deposits of Mesorif units ascribed to the distal part of the African paleomargin. The climax of volcanic activity is observed at the northern border of a Kimmeridgian carbonate platform progressively dismembered during the Tithonian-Berriasian. In spite of the alteration of the basalts, their petrological and geochemical characters point to E-MORB affinities. The studied gabbro massifs (Bou Adel, Kef el Rhar west and north) occur as restricted slivers or klippes within the Senhadja nappe or mélange of the internal Mesorif, which overlies the basalt-bearing units and other, more external Mesorif units. The compositions range from troctolitic olivine gabbro to ferrogabbro with frequent ortho- to heteradcumulate textures; they display typical tholeiitic affinity. The gabbro massifs are crosscut by trondjhemite dykes and overlain by metabasalts, fault-scarp breccias, ophicalcites, marbles and radiolarites. Composition featuring initial near liquid composition, display multi elements patterns close to those of E-MORB, with a weak Eu negative anomaly and evidence of slight crustal contamination. These gabbro massifs were regarded as Jurassic-Cretaceous intrusions, locally dated (K-Ar) at 166 ± 3 Ma. Conversely, we assume they represent discrete samples of a Jurassic-Cretaceous oceanic basement (ophiolites), emplaced tectonically in the Senhadja nappe (mélange) of the central Mesorif. The correlation of both these types of mafic rock associations (paleomargin basalts and ophiolite klippes) with the serpentinites of the eastern Mesorif (Beni Malek) and Oran mountains (Algeria) is then briefly discussed. We conclude that the previous hypothesis of an intramargin “Mesorif suture zone” must be reconsidered, being challenged by that of a

  7. Instrument-Aided Assessment of the Effect of Natural and Technogenic Factors on the Geomechanical State of a Massif Enclosing an HPP Turbine Room

    Energy Technology Data Exchange (ETDEWEB)

    Abramov, N. N., E-mail: Abramov@goi.kolasc.net.ru; Epimakhov, Yu. A. [Russian Academy of Sciences, Mining Institute, Kola Scientific Center (Russian Federation)

    2016-05-15

    A package of geophysical criteria has been developed using seismic spatiotemporal tomography (SST) of a rock massif to perform an instrument-aided assessment of the effect of natural and technogenic factors on the geomechanical state of a rock massif enclosing an underground turbine room at an HPP. Results are presented for a detailed assessment for the underground turbine room at the Verkhnyaya Tuloma HPP on the Kola peninsula.

  8. Tholeitic basalts and ophiolitic complexes of the Mesorif Zone (External Rif, Morocco) at the Jurassic-Cretaceous boundary and the importance of the Ouerrha Accident in the palaeogeographic and geodynamic evolution of the Rif Mountains

    Energy Technology Data Exchange (ETDEWEB)

    Benzaggagh, M.

    2016-10-01

    The stratigraphical series around the Jurassic-Cretaceous boundary of the External Rif Mountains, in particular those in the Mesorif Zone, exhibits many outcrops with volcanic materials spread westwards over 200 km. These materials show diverse aspects: basalt lithoclasts reworked into calcareous breccia beds or in marly matrix breccia, interstratified lava flows and volcanoclastic complexes incorporated within the Berriasian marls. In the Central Rif, several magmatic blocks outcrop, usually regarded as granite scales from the Paleozoic basement or as intrusive gabbros of Barremian age. Actually these magmatic massifs display typical ophiolitic sequences and they are overlaid by mega-olistoliths of Jurassic materials and locally by radiolarite layers. Geochemical analysis of several basalt and gabbro samples belonging to the Mesorif Zone evidenced that both display a typical E-MORB magma indicating at least partial oceanization of the Mesorif basement. Concerning geodynamics, the Mesorif Zone had undergone, at the Jurassic-Cretaceous boundary interval, two successive palaeogeographic phases: an uplift, close to emersion during the Kimmeridgian-Early Tithonian interval, stressed by important submarine volcanic activities and intense brecciation of the carbonate formations, followed by a general collapse at the Late Tithonian, underlined by lava flows, slumping as mega-olistoliths and the formation of an oceanic crust, at least in the Central Rif. These magmatic materials, distributed on both sides of the Ouerrha Valley, evidence that this westwards extending valley (the Nekor Accident), may correspond in the Central Rif, to two palaeo-subduction planes which become two major overlapping thrusts in the western part of the Rif Mountains. (Author)

  9. Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif

    Science.gov (United States)

    Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Anczkiewicz, Robert; Van Den Driessche, Jean

    2018-05-01

    Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15-20 kbar, 560-630 °C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 ± 13 Ma.

  10. Circum-Pacific accretion of oceanic terranes to continental blocks: accretion of the Early Permian Dun Mountain ophiolite to the E Gondwana continental margin, South Island, New Zealand

    Science.gov (United States)

    Robertson, Alastair

    2016-04-01

    Accretionary orogens, in part, grow as a result of the accretion of oceanic terranes to pre-existing continental blocks, as in the circum-Pacific and central Asian regions. However, the accretionary processes involved remain poorly understood. Here, we consider settings in which oceanic crust formed in a supra-subduction zone setting and later accreted to continental terranes (some, themselves of accretionary origin). Good examples include some Late Cretaceous ophiolites in SE Turkey, the Jurassic Coast Range ophiolite, W USA and the Early Permian Dun Mountain ophiolite of South Island, New Zealand. In the last two cases, the ophiolites are depositionally overlain by coarse clastic sedimentary rocks (e.g. Permian Upukerora Formation of South Island, NZ) that then pass upwards into very thick continental margin fore-arc basin sequences (Great Valley sequence, California; Matai sequence, South Island, NZ). Field observations, together with petrographical and geochemical studies in South Island, NZ, summarised here, provide evidence of terrane accretion processes. In a proposed tectonic model, the Early Permian Dun Mountain ophiolite was created by supra-subduction zone spreading above a W-dipping subduction zone (comparable to the present-day Izu-Bonin arc and fore arc, W Pacific). The SSZ oceanic crust in the New Zealand example is inferred to have included an intra-oceanic magmatic arc, which is no longer exposed (other than within a melange unit in Southland), but which is documented by petrographic and geochemical evidence. An additional subduction zone is likely to have dipped westwards beneath the E Gondwana margin during the Permian. As a result, relatively buoyant Early Permian supra-subduction zone oceanic crust was able to dock with the E Gondwana continental margin, terminating intra-oceanic subduction (although the exact timing is debatable). The amalgamation ('soft collision') was accompanied by crustal extension of the newly accreted oceanic slab, and

  11. A conceptual hydrogeological model of ophiolitic aquifers (serpentinised peridotite): The test example of Mt. Prinzera (Northern Italy)

    NARCIS (Netherlands)

    Segadelli, Stefano; Vescovi, Paolo; Ogata, Kei; Chelli, Alessandro; Zanini, Andrea; Boschetti, Tiziano; Petrella, Emma; Toscani, Lorenzo; Gargini, Alessandro; Celico, Fulvio

    2017-01-01

    © 2016 John Wiley & Sons, Ltd.The main aim of this study is the experimental analysis of the hydrogeological behaviour of the Mt. Prinzera ultramafic massif in the northern Apennines, Italy. The analysed multidisciplinary database has been acquired through (a) geologic and structural survey; (b)

  12. Geochronology and geochemistry of the Niujuanzi ophiolitic mélange, Gansu Province, NW China: implications for tectonic evolution of the Beishan Orogenic Collage

    Science.gov (United States)

    Wang, Shengdong; Zhang, Kexin; Song, Bowen; Li, Shucai; Li, Ming; Zhou, Jie

    2018-01-01

    The Niujuanzi ophiolitic mélange (NOM), located in the Beishan Orogenic Collage, marks the termination between the Huaniushan arc and Mingshui-Hanshan Massifs. The NOM is mainly composed of gabbros, diabases, plagiogranites, basalts, and greywacke. Two gabbros have ages of 433.8 ± 3.1 and 354.0 ± 3.3 Ma, two plagiogranites have ages of 429.8 ± 2 and 448.7 ± 2.0 Ma, and a diabase has an age of 433.4 ± 3.2 Ma. The gabbros and diabases are calc-alkaline and tholeiitic, with high Al2O3, CaO, and TiO2 contents and low FeOT contents. The gabbros have high Mg# values (49-82), while the diabases have relatively low Mg# values (46-61). The plagiogranites are calc-alkaline and metaluminous, with high SiO2 and Na2O contents and low Al2O3 and K2O contents. The gabbros and diabases are enriched in large iron lithophile elements and slightly depleted in high field strength elements relative to N-MORB and their trace element characteristics are similar to E-MORB. With respect to rare earth element (REE), they have slightly enriched LREEs relative to HREEs. The majority of the plagiogranite trace elements approximate those of the volcanic arc granite. The plagiogranites have obviously enriched LREEs relative to HREEs, with a slightly to strongly negative Eu anomaly, which is similar to ORG but distinct from volcanic arc and within plate granite. The NOM was formed from the Ordovician to the Carboniferous, representing the expansion period of the Niujuanzi Ocean. The gabbros, diabases, and plagiogranites were formed in a mid-ocean ridge environment. The gabbros and diabases were generated by different degrees of partial melting of the mantle, and the plagiogranites derived from both the crystallization differentiation of basaltic magma and the partial melting of amphibolites in the crust.

  13. Post-magmatic structural evolution of the Troodos Ophiolite Pillow Lavas revealed by microthermometry within vein precipitates, with application to Alpine-Mediterranean supra-subduction zone settings

    Science.gov (United States)

    Kurz, W.; Quandt, D.; Micheuz, P.; Krenn, K.

    2017-12-01

    The Troodos ophiolite, Cyprus, is one of the best preserved ophiolites. Based on geochemical data a supra-subduction zone (SSZ) setting was proposed. Microtextures and fluid inclusions of veins and vesicles within the Pillow Lavas record the post-magmatic structural and geochemical evolution of this SSZ beginning at 75 Ma. Three different vein types from the Upper and Lower Pillow Lavas are distinguished and imply vein precipitation under a dominant extensional regime: (1) syntaxial calcite-, quartz- and zeolite-bearing veins are interpreted as mineralized extension fractures that were pervaded by seawater. This advective fluid flow in an open system changed later into a closed system characterized by geochemical self-organization. (2) Blocky and (3) antitaxial fibrous calcite veins are associated with brecciation due to hydrofracturing and diffusion-crystallization processes, respectively. Based on aqueous fluid inclusion chemistry with seawater salinities in all studied vein types, representative fluid inclusion isochores crossed with calculated litho- and hydrostatic pressure conditions yield mineral precipitation temperatures between 180 and 210 °C, for veins and vesicles hosted in the Upper and Lower Pillow Lavas. This points to a heat source for the circulating seawater and implies that vein and vesicle minerals precipitated shortly after pillow lava crystallization under dominant isobaric cooling conditions. Compared to previous suggestions derived from secondary mineralization a less steep geothermal gradient of 200 °C from the Sheeted Dyke Complex to the Pillow Lavas of the Troodos SSZ is proposed. Further fossil and recent SSZ like the Mirdita ophiolite, Albania, the South-Anatolian ophiolites, Turkey, and the Izu-Bonin fore arc, respectively, reveal similar volcanic sequences. Vein samples recovered during International Ocean Discovery Program expedition 351 and 352 in the Izu-Bonin back and fore arc, respectively, indicate also seawater infiltration

  14. Serpentinite with and without brucite: A reaction pathway analysis of a natural serpentinite in the Josephine ophiolite, California

    OpenAIRE

    Sonzogni, Yann; Treiman, Allan H.; Schwenzer, Susanne P.

    2017-01-01

    A partially serpentinized peridotite from the Josephine ophiolite has been studied in detail in order to characterize the chemical processes of its serpentinization. The original rock was harzburgite, and its olivine and orthopyroxene are partially replaced by veins and patches of lizardite serpentine and magnetite; brucite and talc are completely absent from the serpentinite, regardless of whether the precursor mineral was olivine or pyroxene. Petrographic and mineral-chemical data suggest a...

  15. Mineralogy of Surface Serpentinite Outcrops in the Coast Range Ophiolite: Implications for the Deep Biosphere and Astrobiology

    Science.gov (United States)

    Mccann, A. R.; Cardace, D.; Carnevale, D.; Ehlmann, B. L.

    2011-12-01

    California contains a number of ultramafic (Fe- and Mg rich) rock bodies, including the Coast Range Ophiolite, a block of oceanic crust and upper mantle tectonically emplaced onto land. These ultramafic rocks are primarily composed of olivine and pyroxene, both of which are stable at the high temperatures and pressures in the deep subsurface where they crystallize but become unstable at low temperature and low pressure conditions near the surface. They are highly reduced rocks, creating chemical disequilibria, which can theoretically provide energy to chemoautotrophic organisms. Serpentinization (serpentine-forming) reactions between the rocks and water produce hydrogen molecules, which can be metabolized by diverse organisms. Earth and Mars have shown evidence of similar early geologic histories, possibly with widespread reducing habitable environments (Schulte et al., 2006). Recent data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) have shown serpentine-bearing outcrops near Nili Fossae (21 N, 282 W) and elsewhere in Mars' cratered highlands. Serpentine-bearing outcrops are rare, but their presence confirms that such systems involving the aqueous alteration of ultramafic rocks were active in the past (specifically during the Noachian epoch (older than ~3.7 billion years), possibly producing aqueous habitats suitable for chemoautotrophic life (Ehlmann et al., 2010). Remotely sensed data cannot confirm whether there is active serpentinization on Mars, however exposed, presently serpentinizing ultramafics in terrestrial ophiolites such as those of the California Coast Range provide points of comparison for similar Martian rocks. Volume expansion during serpentinization fractures the host rock, exposing new reaction surfaces, allowing further serpentinization. If subsurface liquid water is present on Mars, serpentinization may still be occurring. We will provide x-ray diffraction and petrographic data for surface serpentinites from the Coast

  16. Clinopyroxenite dykes within a banded unit in the basal mantle section of the northern part of the Oman ophiolite: A record of the latest deep-seated magmatism

    Science.gov (United States)

    Ishimaru, Satoko; Arai, Shoji; Tamura, Akihiro

    2017-11-01

    We found clinopyroxenite dykes in a banded harzburgite block within the Sumeini area in the uppermost part of the metamorphic sole of the northern part of the Oman ophiolite. The dykes clearly cut the deformational structure of the harzburgite and contain its fragments, indicating dyke formation during obduction of the ophiolite. The Mg# [= Mg / (Mg + total Fe)] of clinopyroxenes in the dykes ranges from 0.81 to 0.91, and increases up to 0.93 proximal to harzburgite fragments. Mantle minerals in the harzburgite fragments were modified chemically through interaction with the magma that formed the dyke, yielding lower clinopyroxene and spinel Mg#, and spinels with higher TiO2 contents than those in the unaltered harzburgite. These geochemical features indicate that the clinopyroxenite dykes are cumulates derived from a relatively deep-seated primitive magma enriched in light rare earth elements (LREE) with an ocean island basalt (OIB)-like affinity, geochemically similar to the V3 lavas of an off-ridge origin. Combining these data with geological observations suggests that the clinopyroxenite dykes represent root system of the V3 lavas. Our analyses of the clinopyroxenite dykes testify to the external nature of the V3 magmas, which was added to the sliced oceanic lithosphere from the outside. It is likely that the V3 magma underwent deep-seated crystallization of clinopyroxene and had limited interaction with mantle peridotite en route to the surface. The mode of occurrence of the Sumeini clinopyroxenites (i.e., emplaced into a banded harzburgite block surrounded by garnet amphibolite) is consistent with the generation of OIB-like magmas (V3 lava) beneath the Oman ophiolite resulting from the break-off of the "subducting slab" and subsequent infiltration of hot asthenospheric mantle. This view is consistent with the limited distribution of V3-related rocks in the Oman ophiolite. The production of such OIB-like magmas during ophiolite obduction is not a rare event

  17. Geology and uranium occurrences in the Forez tertiary plain (in the French 'Massif Central'); Geologie et mineralisations uraniferes de la plaine tertiaire du Forez (Massif Central francais)

    Energy Technology Data Exchange (ETDEWEB)

    Duclos, P [Commissariat a l' Energie Atomique, Fontenay-aux-Roses - 92 (France). Centre d' Etudes Nucleaires

    1967-01-01

    In the first part, the observations made during the geological survey of the Forez Tertiary plain (in the French 'Massif Central') are recalled. Then, using various methods, the author lists the formations according to chronology. Finally, a reconstitution of the geological history of this subsidence basin is attempted. In the second part, the occurrence of 17 uranium bearing geochemical anomalies is commented upon. Each of these various anomalies is given a place on the stratigraphic scale. This enables the author to put the successive phases of uranium deposition into their proper perspective in the history of the plain. In conclusion, the author points out the usefulness of these uraniferous geochemical anomalies. (author) [French] Dans la premiere partie, l'auteur rappelle les observations faites au cours de l'etude geologique de la plaine tertiaire du Forez (Massif Central francais). Puis se servant de differentes methodes, il etablit une chronologie des formations. Enfin, il termine par un essai de reconstitution de l'histoire geologique de ce bassin de subsidence. Dans la deuxieme partie, il commente la decouverte de 17 anomalies geochimiques uraniferes. Il situe ces differentes anomalies dans la serie stratigraphique. Ceci lui permet de replacer les depots successifs de l'uranium dans l'histoire de la plaine. Enfin, il indique l'interet de ces anomalies geochimiques uraniferes. (auteur)

  18. Biofilm formation and potential for iron cycling in serpentinization-influenced groundwater of the Zambales and Coast Range ophiolites.

    Science.gov (United States)

    Meyer-Dombard, D'Arcy R; Casar, Caitlin P; Simon, Alexander G; Cardace, Dawn; Schrenk, Matthew O; Arcilla, Carlo A

    2018-05-01

    Terrestrial serpentinizing systems harbor microbial subsurface life. Passive or active microbially mediated iron transformations at alkaline conditions in deep biosphere serpentinizing ecosystems are understudied. We explore these processes in the Zambales (Philippines) and Coast Range (CA, USA) ophiolites, and associated surface ecosystems by probing the relevance of samples acquired at the surface to in situ, subsurface ecosystems, and the nature of microbe-mineral associations in the subsurface. In this pilot study, we use microcosm experiments and batch culturing directed at iron redox transformations to confirm thermodynamically based predictions that iron transformations may be important in subsurface serpentinizing ecosystems. Biofilms formed on rock cores from the Zambales ophiolite on surface and in-pit associations, confirming that organisms from serpentinizing systems can form biofilms in subsurface environments. Analysis by XPS and FTIR confirmed that enrichment culturing utilizing ferric iron growth substrates produced reduced, magnetic solids containing siderite, spinels, and FeO minerals. Microcosms and enrichment cultures supported organisms whose near relatives participate in iron redox transformations. Further, a potential 'principal' microbial community common to solid samples in serpentinizing systems was identified. These results indicate collectively that iron redox transformations should be more thoroughly and universally considered when assessing the function of terrestrial subsurface ecosystems driven by serpentinization.

  19. Metagenomic identification of active methanogens and methanotrophs in serpentinite springs of the Voltri Massif, Italy

    Directory of Open Access Journals (Sweden)

    William J. Brazelton

    2017-01-01

    Full Text Available The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12. Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif.

  20. Automated data collection based on RoboDiff at the ESRF beamline MASSIF-1

    Energy Technology Data Exchange (ETDEWEB)

    Nurizzo, Didier, E-mail: Didier.nurizzo@esrf.fr; Guichard, Nicolas; McSweeney, Sean; Theveneau, Pascal; Guijarro, Matias; Svensson, Olof; Mueller-Dieckmann, Christoph; Leonard, Gordon [ESRF, The European Synchrotron, 71, Avenue des Martyrs,CS 40220, 38043 Grenoble (France); Bowler, Matthew W. [EMBL Grenoble Outstation, 71 Avenue des Martyrs, CS90181, 38042 Grenoble Cedex 9 (France)

    2016-07-27

    The European Synchrotron Radiation Facility has a long standing history in the automation of experiments in Macromolecular Crystallography. MASSIF-1 (Massively Automated Sample Screening and evaluation Integrated Facility), a beamline constructed as part of the ESRF Upgrade Phase I program, has been open to the external user community since July 2014 and offers a unique completely automated data collection service to both academic and industrial structural biologists.

  1. Compositionally heterogeneous podiform chromitite in the Shetland Ophiolite Complex (Scotland): Implications for chromitite petrogenesis and late-stage alteration in the upper mantle portion of a supra-subduction zone ophiolite

    Science.gov (United States)

    Derbyshire, E. J.; O'Driscoll, B.; Lenaz, D.; Gertisser, R.; Kronz, A.

    2013-03-01

    The mantle sequence of the ~ 492 Ma Shetland Ophiolite Complex (SOC; Scotland) contains abundant compositionally heterogeneous podiform chromitite bodies enclosed in elongate dunite lenses in the vicinity of the petrological Moho. Chromitite petrogenesis and late-stage alteration events recorded in these seams are examined here using petrography, mineral chemistry and crystal structural data. The resistant nature of Cr-spinel to serpentinisation and other late-stage alteration means that primary igneous compositions are preserved in unaltered crystal cores. Chromitite mineralogy and texture from five sampled localities at The Viels, Hagdale, Harold's Grave, Nikka Vord and Cliff reveal significant inter-pod chemical heterogeneity. The Cr-spinel mineral chemistry is consistent with supra-subduction zone melt extraction from the SOC peridotites. The occurrence of chromitite seams in the centres of the dunite lenses combined with variable Cr-spinel compositions at different chromitite seam localities supports a model of chromitite formation from spatially (and temporally?) fluctuating amounts of melt-rock interaction through channelised and/or porous melt flow. Pervasive serpentinisation of the SOC has led to the almost complete replacement of the primary (mantle) silicate mineral assemblages with serpentine (lizardite with minor chrysotile and antigorite). Magmatic sulphide (e.g., pentlandite) in dunite and chromitite is locally converted to reduced Ni-sulphide varieties (e.g., heazlewoodite and millerite). A post-serpentinisation (prograde) oxidisation event is recorded in the extensively altered Cliff chromitite seams in the west of the studied area, where chromitite Cr-spinel is extensively altered to ferritchromit. The ferritchromit may comprise > 50% of the volume of the Cliff Cr-spinels and contain appreciable quantities of 1-2 μm inclusions of sperrylite (PtAs2) and Ni-arsenide, signifying the coeval formation of these minerals with ferritchromit at

  2. Subduction initiation, recycling of Alboran lower crust, and intracrustal emplacement of subcontinental lithospheric mantle in the Westernmost Mediterranean

    Science.gov (United States)

    Varas-Reus, María Isabel; Garrido, Carlos J.; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly; Booth-Rea, Guillermo; Acosta-Vigil, Antonio

    2015-04-01

    Unraveling the tectonic settings and processes involved in the annihilation of subcontinental mantle lithosphere is of paramount importance for our understanding of the endurance of continents through Earth history. Unlike ophiolites -- their oceanic mantle lithosphere counterparts -- the mechanisms of emplacement of the subcontinental mantle lithosphere in orogens is still poorly known. The emplacement of subcontinental lithospheric mantle peridotites is often attributed to extension in rifted passive margins or continental backarc basins, accretionary processes in subduction zones, or some combination of these processes. One of the most prominent features of the westernmost Mediterranean Alpine orogenic arcs is the presence of the largest outcrops worldwide of diamond facies, subcontinental mantle peridotite massifs; unveiling the mechanisms of emplacement of these massifs may provide important clues on processes involved in the destruction of continents. The western Mediterranean underwent a complex Alpine evolution of subduction initiation, slab fragmentation, and rollback within a context of slow convergence of Africa and Europe In the westernmost Mediterranean, the alpine orogeny ends in the Gibraltar tight arc, which is bounded by the Betic, Rif and Tell belts that surround the Alboran and Algero-Balearic basins. The internal units of these belts are mostly constituted of an allochthonous lithospheric domain that collided and overthrusted Mesozoic and Tertiary sedimentary rocks of the Mesozoic-Paleogene, South Iberian and Maghrebian rifted continental paleomargins. Subcontinental lithospheric peridotite massifs are intercalated between polymetamorphic internal units of the Betic (Ronda, Ojen and Carratraca massifs), Rif (Beni Bousera), and Tell belts. In the Betic chain, the internal zones of the allochthonous Alboran domain include, from bottom to top, polymetamorphic rock of the Alpujarride and Malaguide complexes. The Ronda peridotite massif -- the

  3. The Vascular Flora of Rarău Massif (Eastern Carpathians, Romania. Note I

    Directory of Open Access Journals (Sweden)

    Adrian Oprea

    2012-10-01

    Full Text Available The present study is concerned with the flora of the Rarău Massif, an area lying in the northeastern part of Romania, nearby the town of Câmpulung Moldovenesc. This study attempt to list all the vascular plants (i.e. ferns, conifers, and flowering plants from the whole area of Rarău Massif. Till now, there are published several papers on this area, but no paper deals with the whole surface of Rarău Massif. The research was carried out between 2000 to 2011. During the study period, 1377 taxa (1089 species and 288 subspecies, belonging to 95 families and 411 genera; 43 of the species belong to Pteridophytes, 8 belongs to Gymnosperms, and 1038 belongs to Angiosperms (835 Dicotyledons, 203 Monocotyledons subdivisions. The largest families (in terms of the number of species and subspecies included are: Asteraceae (167, Poaceae (78, Brassicaceae (53, Rosaceae and Lamiaceae (50, Scrophulariaceae and Cyperaceae (47, Caryophyllaceae and Ranunculaceae (42. The highest number of species, of a certain genus, is like the next: Carex L. (39, Centaurea L. (25, Hieracium L. (21, Festuca L. (19, Senecio L. (12, Cirsium, Pilosella, and Poa (11, etc. Since the flora of the area is analysed according to Raunkiaer’s life forms, the results are as follows: Hemicryptophytes 605 species (H=55.6%, Cryptophytes (also called Geophytes 137 species (G=12.6%, Therophytes 120 species (11.0%, Phanerophytes 84 species (Ph=7.7%, Chamaephytes 57 species (Ch=5.2%, Hemitherophytes 77 species (Ht=7.1%, Helo-hydatophytes 8 species (HH=0.7%, and Epiphytes 1 species (Ep=0.1%. The phytogeographic elements are the next ones: European=375 species (36.6%, Eurasian=349 species (34.0%, Circumboreal=148 species (14.8%, Cosmopolite=37 species (3.6%, Carpathians=31 species (3.0%, Pontics=19 species (1.9%, Mediterranean-submediterrannean=11 species (1.1%, and Adventitious=2 species (0.2%. The number of endemic and near-endemic taxa (species and subspecies within the study area is 53 (5.2%.

  4. Hydration of the Atlantis Massif: Halogen, Noble Gas and In-Situ δ18O Constraints

    Science.gov (United States)

    Williams, M. J.; Kendrick, M. A.; Rubatto, D.

    2017-12-01

    A combination of halogen (Cl, Br, I), noble gases (He, Ne, Ar, Kr and Xe) and in situ oxygen isotope analysis have been utilized to investigate the fluid-mobile element record of hydration and alteration processes at the Atlantis Massif (30°N on the Mid-Atlantic Ridge). The sample suite investigated includes serpentinite, talc-amphibole ± chlorite schist and hydrated gabbro recovered by seafloor drilling undertaken at sites on a transect across the Atlantis Massif during IODP Expedition 357. Serpentine mesh and veins analysed in-situ by SHRIMP SI exhibit δ18O from 6‰ down to ≈0‰, suggesting serpentinization temperatures of 150 to >280°C and water/rock ratios >5. Differences of 1.5-2.5‰ are observed between adjacent generations of serpentine, but the δ18O range is similar at each investigated drilling site. Halogen and noble gas abundances in serpentinites, talc-amphibole schist and hydrated gabbro have been measured by noble gas mass spectrometry of both irradiated and non-irradiated samples. Serpentinites contain low abundances of halogens and noble gases (e.g. 70-430 ppm Cl, 4.7-12.2 x 10-14 mol/g 36Ar) relative to other seafloor serpentinites. The samples have systematically different Br/Cl and I/Cl ratios related to their mineralogy. Serpentinites retain mantle-like Br/Cl with a wide variation in I/Cl that stretches toward seawater values. Talc-amphibole schists exhibit depletion of Br and I relative to Cl with increasing Cl abundances, suggesting tremolite exerts strong control on halogen abundance ratios. Serpentinites show no evidence of interaction with halogen-rich sedimentary pore fluids. Iodine abundances are variable across serpentinites, and are decoupled from Br and Cl; iodine enrichment (up to 530 ppb) is observed within relatively oxidised and clay-bearing samples. Serpentinized harzburgites exhibit distinct depletion of Kr and Xe relative to atmospheric 36Ar in seawater. Oxygen isotope compositions and low abundances of both halogens

  5. Using remote sensing imagery and GIS to identify land cover and land use within Ceahlau Massif (Romania

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    GEORGE CRACU

    2014-11-01

    Full Text Available Using remote sensing imagery and GIS to identify land cover and land use within Ceahlău Massif (Romania. In this study we considerer land cover and land use asessment within Ceahlău Massif (Romania using satellite imagery and GIS . To achieve this goal, we used a Landsat 7 ETM + satellite image, which was processed using specialized software in analyzing satellite images and GIS software in several stages:  Downloading, importing and layer stack of all spectral bands composing satellite image;  Establishment of areas of interest for each category of land cover and land use, which were digitized on - screen and for which spectral signatures characteristics were established;  Supervised image classification using Maximum Likelihood Method;  Importing the resulting m ap (raster in GIS environment and creating the final land cover/land use map for Ceahlău Massif. In the study area we identified nine land cover/land use classes: deciduous forests, mixed forests, coniferous forests, secondary grasslands, subalpine vegeta tion, alpine meadows, agricultural land, lakes and built area. By analizing the spatial distribution of these classes, it was found that forests are the best represented class, occupying an area of 188.4 km² (56.4% of total, followed by secondary grassl and, which occupies an area of 68.2 km² (20.4% of total, lakes (26.6 km² or 7.98% of total and agricultural land (16.1 km² or 4.86%

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

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Štěpánková-Svobodová, Jana

    2014-01-01

    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 * carbonatites * magma generation * metasomatism * Cenozoic * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  7. Protrusive intrusion, dehydration and polymorphism in minerals as possible reason of seismic activity, relation between ophiolite belts and seismic zonation of the territory of Armenia

    Science.gov (United States)

    Harutyunyan, A. V.; Petrosyan, H. M.

    2010-05-01

    In the basis of multiple geological and geophysical data, also on the results of investigations seismic and density properties of rocks at high termobaric conditions, we proposed the petrophisical section and model of evolution of Earth crust of the territory of Armenia. On the proposed model the following interrelated problems are debated: forming of ophiolite belts and volcanic centers, genesis of hydrocarbons by organic and inorganic ways, and also reasons of originating of seismic centers. The reasons of originating of seismic centers in different depths of Earth crust, are miscellaneous. According to the model of Earth crust evolution the ophiolite belts are formed due to permanent protrusive intrusion of serpentinized masses from the foot of the crust (35-50km) into upper horizons. It is natural to assume, that the permanent intrusion of serpentinizd masses through deep faults has drastically occurred accompanying with seismic shakings. This process encourages the development of deep faults. The protrusive intrusion of serpentinized masse accompanied with partial dehydration of serpentinites and serpentinized ultrabasites and new mineral formation. The processes was accompanied also with drastic change of seismic waves and volumes up to 30%. Experiments at high termobaric conditions show, that some minerals undergone polymorphous transformations, accompanied with phase change and drastic change of rocks volume. Particularly plastic calcite, included in the composition of metamorphic rocks to run into the cracks expends and diversifies them. The process described cause some general effects similar to those of the process of dilatancy. Therefore, the protrusive intrusion of serpentinized masses into upper horizons, it dehydrations and polymorphous transformations in different minerals, may be cause of geo-dynamic processes at different depths of Earth crust. It may be assumed, that those processes permanently occur nowadays as well. Comparing the maps of

  8. Clockwise rotation of the Santa Marta massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and Cesar-Ranchería basins

    Science.gov (United States)

    Montes, Camilo; Guzman, Georgina; Bayona, German; Cardona, Agustin; Valencia, Victor; Jaramillo, Carlos

    2010-10-01

    A moderate amount of vertical-axis clockwise rotation of the Santa Marta massif (30°) explains as much as 115 km of extension (stretching of 1.75) along its trailing edge (Plato-San Jorge basin) and up to 56 km of simultaneous shortening with an angular shear of 0.57 along its leading edge (Perijá range). Extensional deformation is recorded in the 260 km-wide, fan-shaped Plato-San Jorge basin by a 2-8 km thick, shallowing-upward and almost entirely fine-grained, upper Eocene and younger sedimentary sequence. The simultaneous initiation of shortening in the Cesar-Ranchería basin is documented by Mesozoic strata placed on to lower Eocene syntectonic strata (Tabaco Formation and equivalents) along the northwest-verging, shallow dipping (9-12° to the southeast) and discrete Cerrejón thrust. First-order subsidence analysis in the Plato-San Jorge basin is consistent with crustal stretching values between 1.5 and 2, also predicted by the rigid-body rotation of the Santa Marta massif. The model predicts about 100 km of right-lateral displacement along the Oca fault and 45 km of left-lateral displacement along the Santa Marta-Bucaramanga fault. Clockwise rotation of a rigid Santa Marta massif, and simultaneous Paleogene opening of the Plato-San Jorge basin and emplacement of the Cerrejón thrust sheet would have resulted in the fragmentation of the Cordillera Central-Santa Marta massif province. New U/Pb ages (241 ± 3 Ma) on granitoid rocks from industry boreholes in the Plato-San Jorge basin confirm the presence of fragments of a now segmented, Late Permian to Early Triassic age, two-mica, granitic province that once spanned the Santa Marta massif to the northernmost Cordillera Central.

  9. Geochronology and geochemistry of Mesozoic intrusive rocks in the Xing'an Massif of NE China: Implications for the evolution and spatial extent of the Mongol-Okhotsk tectonic regime

    Science.gov (United States)

    Li, Yu; Xu, Wen-Liang; Tang, Jie; Pei, Fu-Ping; Wang, Feng; Sun, Chen-Yang

    2018-04-01

    This study presents new zircon U-Pb-Hf and whole-rock geochemical data for intrusive rocks in the Xing'an Massif of NE China, with the aim of furthering our understanding of the evolution and spatial influence of the Mongol-Okhotsk tectonic regime. Zircon U-Pb dating indicates that five stages of Mesozoic magmatism are recorded in the Xing'an Massif, namely during the Middle Triassic ( 237 Ma), the Late Triassic ( 225 Ma), the Early Jurassic ( 178 Ma), the Middle Jurassic ( 168 Ma), and the late Early Cretaceous ( 130 Ma). The Middle Triassic-Early Jurassic intrusive rocks in the Xing'an Massif are dominantly granodiorites, monzogranites, and syenogranites that formed from magma generated by partial melting of newly accreted continental crust. Geochemistry of the Middle Triassic-Early Jurassic granitoid suites of the Xing'an Massif indicates their formation at an active continental margin setting, related to the southwards subduction of the Mongol-Okhotsk oceanic plate. The Middle Jurassic monzogranites in the Xing'an Massif are geochemically similar to adakites and have εHf(t) values (+3.8 to +5.8) and Hf two-stage model ages (TDM2; 979-850 Ma) that are indicative of derivation from magma generated by partial melting of thickened juvenile lower crust. The Middle Jurassic monzogranites formed in a compressional setting related to the closure of the Mongol-Okhotsk Ocean. The late Early Cretaceous intrusive rocks in the Xing'an Massif are dominated by A-type granitoids that are associated with bimodal volcanic rocks, suggesting their formation in an extensional environment related to either (i) delamination of a previously thickened region of the crust, associated with the Mongol-Okhotsk tectonic regime; (ii) the subduction of the Paleo-Pacific Plate; or (iii) the combined influence of these two tectonic regimes.

  10. Uranium mineralization possibilities in metamorphic Massif of Isla de Juventud, Cuba

    International Nuclear Information System (INIS)

    Gongora Dominguez, L.E.; Llanes Castro, A.I.; Pena Fortes, B.; Capote Rodriguez, G.

    1996-01-01

    The geologic and metallogenic characteristic of the metamorphic Massif shows the presence of possible uranium vein type mineralization as a result of a hidrotermal genetic process. Metalliferous fluids rising along the fault system were responsible for the deposition of the uranium in the reduction zones, i.e. presence of pyrite, organic matter and others. This type of uranium minerization is proposed for the Bibijagua area and for the Revolucion and Lela area the same type is expected. The gamma spectrometric analysis was used to evaluate the geological samples

  11. Granitic magma emplacement and deformation during early-orogenic syn-convergent transtension: The Stare Sedlo complex, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Tomek, Filip; Žák, J.; Chadima, Martin

    2015-01-01

    Roč. 87, JUL (2015), s. 50-66 ISSN 0264-3707 Institutional support: RVO:67985831 Keywords : anisotropy of magnetic susceptibility (AMS) * Bohemian Massif * pluton emplacement * granite * transtension * Variscan orogeny Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.926, year: 2015

  12. The age and emplacement of obducted oceanic crust in the Urals from Sm-Nd and Rb-Sr systematics

    International Nuclear Information System (INIS)

    Edwards, R.L.; Wasserburg, G.J.

    1985-01-01

    The Urals contain a 2000 km belt of mafic-ultramafic bodies. The Sm-Nd and Rb-Sr systematics of two of these bodies, the Kempersai Massif in the South Ural Mountains and the Voykar-Syninsky Ophiolite Complex in the Polar Ural Mountains have been examined. These data confirm the hypothesis that these bodies represent fragments of pre-collision oceanic crust and establish constraints on the nature and timing of events in the Uralian Orogeny. Two Kempersai gabbros define Sm-Nd internal isochrons of 397 +- 20 My and 396 +- 33 My with epsilonsub(Nd)(T) = +8.7 -+ 0.6 and +8.4 -+ 1.3, respectively. Whole rock samples of pillow basalt, diabase, gabbros, troctolite, and a metasediment give Sm-Nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 My. Whole rock samples of Voykar-Syninsky diabase, gabbros, and clinopyroxenite give Sm-Nd values which lie on or within proportional 1 epsilon-unit of this isochron indicating an age and epsilonsub(Nd)(T) virtually identical to those of Kempersai. epsilonsub(Nd)(T) for the Kempersai and Voykar-Syninsky mafic samples range from +7.3 to +9.0 with an average value of +8.4. This indicates that the Urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere. The fact that a metasediment has the same epsilonsub(Nd)(397 My) as the other samples indicates derivation from an oceanic source with negligible continental input. epsilonsub(Nd)(T) for the massifs is proportional 1.5 epsilon-units lower than the average for modern MORBs. (orig./HSI)

  13. Geochemistry and Nd-isotope systematics of chemical and terrigenous sediments from the Dun Mountain Ophiolite, New Zealand

    International Nuclear Information System (INIS)

    Sivell, W.J.

    2002-01-01

    Two sedimentary associations closely related to temporally discrete ophiolitic magma suites occur within the Early Permian Dun Mountain Ophiolite Belt (DMOB), New Zealand. These are: (1) a suite of diverse chemical sediments and turbidite argillites (TA) that bear an intimate depositional relationship to early-formed pillow lavas (back-arc basin basalts); and (2) a younger, lithic-dominated, bimodal, coarse sandstone-ophiolitic rudite assemblage of proximal turbidite/mass-flow origin, rich in clasts of infant-arc magmas which comprise the bulk of the ophiolite. There are four groups of DMOB chemical sediments. Red hematitic chert (group 1) fills interstices between basalt pillows, and black nodular Fe-Mn deposits (group 2) occur along pillow lava/sediment interfaces. These facies are overlain by red mudstones (group 3), and mottled orange-olive brown mudstones (altered hyaloclastites; group 4). Geochemical features (including REE contents, Fe/Ti and transition ratios) indicate that the cherts reflect silica and metalliferous contributions to sea water, promoted by low-temperature hydrothermal alteration of glassy basalt, while group 4 muds represent residual components in halmyrolytically altered volcanic glass. Transition metal and REE enrichments in group 2 nodules (with high Ce/Ce*, Ni/Fe, and Cu/Fe ratios) reflect hydrogenous chemisorption to a hydothermal component (with high Ba and Sr). The nodules possess ε Nd (T) values (c. 0) identical to those calculated for Permian sea water. Group 3 red muds have lower ε Nd (T) = -1 to -2, and Nd model ages (T) Nd DM) that indicate contributions from continentally derived fluvial particulate fallout of mean Proterozoic age. For the nodules and red muds, strong negative correlations between Mn/Fe, Nd, Ce*/Ce, and ε Nd (T) are attributed to increasing diagenetic influence in the muds. ε Nd (T) values (c. +2) in group 4 muds are transitional toward higher values in their (hyaloclastite) basalt glass precursors

  14. Distribution of uranium, thorium and potassium in the alkaline rocks of Pocos de Caldas massif

    International Nuclear Information System (INIS)

    Rocha, E.B.

    1985-01-01

    The Pocos de Caldas massif, with area about 800 Km 2 , represents the greatest complex of alkaline rocks existent in the American continent. Although values of U and Th are well Known in the mineralized areas, few has been registered with respect to the distribution of those elements outside the ore deposits. The rocks of the massif, in general, present high contents of U and Th when confronted with the surrouding country rocks. The distribution of the U and Th appoint a relevant additional data in the discussion on the hypothesis of nepheline syenites bodies formation in Pocos de Caldas by crystal fractionation processes. In this work are provided results of the U, Th and K distribution in the main petrographic facies occurring in the several studies places of the massif, yielded by gamma-ray spectrometric analysis of the samples. Those analysis disclose that khibinites present average values about 38 ppm U and 120 ppm Th; lujavrites, about 14 ppm U and more than 70 ppm Th; U-Th depleted nepheline synites, about 12 ppm U and 38 ppm Th, Th/U ratios are close to 3,0 in the nepheline syenites, about 3,7 in the phonolites, reaching values close to 4,0 in the khibinites. These values are comparable with others Th/U ratios of selected series of alkaline rocks reported in the international literature. Uranium and Th comparative data, attained by delayed neutron counting activation analysis also are given. The results obtained for the fluorimetric analysis show loss of U leaching is greater in the fine-grained rocks (phonolites) than coarse-grained ones (lujavrites, Khibinites). The autoradiographic studies reveal that radioactive elements are found concentrated in mineral phases. A new assessment of the radiogenic heat production it is also available. (Author) [pt

  15. U-Pb zircon geochronology and Sm-Nd-Pb isotopic constraint for precambrian plutonic rocks in the northeastern part of Ryeongnam massif, Korea

    International Nuclear Information System (INIS)

    Chang, Ho-Wan

    2003-01-01

    The Ryeongnam massif is composed of Precambrian gneisses, Paleozoic and Mesozoic sedimentary rocks and extensive Triassic-Jurassic plutonic rocks of felsic to mafic composition. In the northeast Ryeongnam massif, the oldest rocks belong to the Sobaegsan gneiss complex, which is composed of orthogneisses, paragneisses and mafic plutonic rocks. U-Pb zircon ages for the felsic and mafic intrusive bodies within the Sobaegsan gneiss complex are: the Icheon granite gneiss, 2357±43 and 2342±47 Ma; the Buncheon granite gneiss, 1963±5 Ma; the Pyeonghae granite gneiss, 1936±21 Ma; the Ogbang amphibolite, 1918±10 Ma; the Imwon leucogranite gneiss, 1826±20 Ma. The Hyeondong biotite schist, which is intruded by the Buncheon granite gneiss and the Ogbang amphibolite, yielded an age of 2271±44 Ma. The Nd-Sm-Pb isotopic data indicate that the felsic plutonic rocks are derived from an older Archean crust. The Nd T DM ages are Archean, and the εNd values are negative for the felsic rocks and positive for the amphibolite. Common Pb isotope compositions also indicate a crustal source for the felsic intrusives. The U-Pb ages of Precambrian rocks of the Ryeongnam massifs are similar to those in the Gyeonggi massif, and may have a similar crustal evolutionary history. The Precambrian rocks of South Korea could be related either to the North China block or to the South China block, as the isotope ages and patterns are not unique to either block. Similarly, a geologic correlation with Japan, although possible, is tenuous at present. (author)

  16. Geology and uranium occurrences in the Forez tertiary plain (in the French 'Massif Central'); Geologie et mineralisations uraniferes de la plaine tertiaire du Forez (Massif Central francais)

    Energy Technology Data Exchange (ETDEWEB)

    Duclos, P. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses - 92 (France). Centre d' Etudes Nucleaires

    1967-01-01

    In the first part, the observations made during the geological survey of the Forez Tertiary plain (in the French 'Massif Central') are recalled. Then, using various methods, the author lists the formations according to chronology. Finally, a reconstitution of the geological history of this subsidence basin is attempted. In the second part, the occurrence of 17 uranium bearing geochemical anomalies is commented upon. Each of these various anomalies is given a place on the stratigraphic scale. This enables the author to put the successive phases of uranium deposition into their proper perspective in the history of the plain. In conclusion, the author points out the usefulness of these uraniferous geochemical anomalies. (author) [French] Dans la premiere partie, l'auteur rappelle les observations faites au cours de l'etude geologique de la plaine tertiaire du Forez (Massif Central francais). Puis se servant de differentes methodes, il etablit une chronologie des formations. Enfin, il termine par un essai de reconstitution de l'histoire geologique de ce bassin de subsidence. Dans la deuxieme partie, il commente la decouverte de 17 anomalies geochimiques uraniferes. Il situe ces differentes anomalies dans la serie stratigraphique. Ceci lui permet de replacer les depots successifs de l'uranium dans l'histoire de la plaine. Enfin, il indique l'interet de ces anomalies geochimiques uraniferes. (auteur)

  17. Modelling the Middle Pleistocene uplift in the Ardennes-Rhenish Massif: Thermo-mechanical weakening under the Eifel?

    NARCIS (Netherlands)

    Garcia-Castellanos, D.; Cloetingh, S.A.P.L.; van Balen, R.T.

    2000-01-01

    Middle Pleistocene uplift in the Eifel has been interpreted as the isostatic response of the lithosphere to a deep buoyant hot body. The spatial and temporal distribution of the uplift in the Ardennes-Rhenish Massif Region has recently been constrained by new data of river incision that have been

  18. Comparison of support vector machine and neutral network classification method in hyperspectral mapping of ophiolite mélanges–A case study of east of Iran

    Directory of Open Access Journals (Sweden)

    Bahram Bahrambeygi

    2017-06-01

    Full Text Available Ophiolitic regions are one of the most complex geology settings. Mapping in these parts need broad and precise studies and tools because of the mixture rocks and confusion units. Hyperion hyperspectral sensor data are one of the advanced tools for earth surface mapping that containing rich information of shallow electromagnetic reflection in 242 continuous bands. Because of some contaminated noise in tens of these bands we removed 87 most noisy bands and focused our study on 155 low noisy bands. In present study, tow spectral based classification algorithms of support vector machine and neutral network are compared on hyperion image for classification of cluttered units in an ophiolite set. Study area is Mesina region in collision ophiolitic belt of south east of Iran. In this region for design processing results validation rate, lots of random locations and control points were studied in field scale and were sampled for laboratory surveys. Samples were investigated in microscopic section and by electron microprobe system. Based on laboratory-field studies, the lithology of this area can divided into five general groups: (Melange series, metamorphic units, Oligocene – Miocene to Quaternary volcanic units, lime and flysch units. Based on field-laboratory works, some standard points defined for validate processing results accuracy rate. Therefore, the Support Vector Machine and neutral network method as advanced hyperspectral image processing methods respectively have overall accuracies of 52% and 65%. Consequently the method based neutral network theory for hyperspectral classification have acceptable ratio in separation of blended complicated units.

  19. Hydrogen generation during serpentinisation in ophiolite complexes: A comparison of H2-rich gases from Oman, Philippines and Turkey.

    Science.gov (United States)

    Beaumont, Valérie; Vacquand, Christèle; Deville, Eric; Prinzhofer, Alain

    2013-04-01

    H2-rich gas seepages in ultrabasic to basic contexts both in marine and continental environment are by-products of serpentinisation. Hydrothermal systems at MOR expose ultrabasic rocks to thermodynamic conditions favouring oxidation of FeII bearing minerals and water reduction. In continental context such thermodynamic conditions do not exist although active serpentinisation occurs in all known ophiolitic complexes (Barnes et al., 1978; Bruni et al., 2002; Cipolli et al., 2004; Boschetti and Toscani, 2008; Marques et al., 2008). Hyperalkaline springs are reported in these contexts as evidence of this active serpentinisation (Barnes et al., 1967) and are often associated with seepages of reduced gases (Neal and Stanger, 1983; Sano et al., 1993). Dry gas seepages are also observed (Abrajano et al., 1988, 1990; Hosgörmez, 2007; Etiope et al., 2011) Such H2-rich gases from ophiolite complexes were sampled in the Sultanate of Oman, the Philippines and Turkey and were analysed for chemical composition, noble gases contents, stable isotopes of carbon, hydrogen and nitrogen. The conditions for present-day serpentinisation in ophiolites were recognised as low temperature processes in Oman with high rock/water ratios (Neal and Stanger, 1985), while the origin of gases is not as univocal for Philippines and Turkey gas seepages. Although, H2 generation is directly linked with FeII oxidation, different reactions can occur during peridotite hydration (McCollom and Bach, 2009; Marcaillou et al., 2011) and serpentine weathering. Produced H2 can react with carbonate species to produce methane via processes that could be biological or abiotic, while carbon availability depends on water recharge chemistry. In the present study, the geochemical properties of gases sampled from three different ophiolite complexes are compared and provide evidence that weathering reactions producing H2 depend on structural, geological, geomorphologic and hydrological local features. REFERENCES Abrajano

  20. Effect of Hydrochemistry on Mineral Precipitation and Textural Diversity in Serpentinization-driven Alkaline Environments; Insights from Thermal Springs in the Oman Ophiolite.

    Science.gov (United States)

    Bach, W.; Giampouras, M.; Garcia-Ruiz, J. M.; Garrido, C. J.; Los, C.; Fussmann, D.; Monien, P.

    2017-12-01

    Interactions between meteoric water and ultramafic rocks within Oman ophiolite give rise to the formation of thermal spring waters of variable composition and temperature. Discharge of two different types of water forms complex hydrological networks of streams and ponds, in which the waters mix, undergo evaporation, and take up atmospheric CO2. We conducted a pond-by-pond sampling of waters and precipitates in two spring sites within the Wadi Tayin massif, Nasif and Khafifah, and examined how hydrochemistry and associated mineral saturation states affect the variations in mineral phases and textures. Three distinctive types of waters were identified in the system: a) Mg-type (7.9 11.6); Ca-OH-rich waters, and c) Mix-type (9.6 < pH < 11.5); waters arising upon mixing of Mg-type and Ca-type. PHREEQC was used to evaluate the role of mixing in aqueous speciation and the evolution of the saturation index value of different mineral phases. Mineral and textural characterization by X-ray diffraction, Raman spectroscopy and scanning electron microscopy were combined with these hydrogeochemical constraints to determine the factors controlling mineralogical and textural diversity in the system. In Ca-type waters, uptake of CO2 during the exposure of the fluids to the atmosphere is the predominant precipitation mechanism of CaCO3. High Mg:Ca ratios and high supersaturation rate of CaCO3 favor the growth of aragonite over calcite in mixed fluids. Changes in morphology and texture of aragonite crystals and crystal aggregates indicate the variations in the values of supersaturation and supersaturation rate of CaCO3 in the different water types. Brucite precipitation is common and driven by fluid mixing, while interaction with air-derived CO2 causes its alteration to hydromagnesite. The proximity of gabbroic lithologies appears to affect the presence of Al-bearing layered double hydroxides (LDHs). Furthermore, transformation of nesquehonite to dypingite in Mg-type waters record a

  1. Natural flows of H2-rich fluids in the ophiolites of Oman and the Philippines: Tectonic control of migration pathways and associated diagenetic processes

    Science.gov (United States)

    Deville, E. P.; Prinzhofer, A.; Vacquand, C.; Chavagnac, V.; Monnin, C.; Ceuleneer, G.; Arcilla, C. A.

    2009-12-01

    We compare the geological environments of sites of emission of natural hydrogen in the Oman ophiolite and the Zambales ophiolite (Luzon, Philippines). The genesis of natural H2 results from the interaction between ultrabasic rocks and aqueous solutions circulating in deep fracture networks, by oxidation of metals (Fe2+, Mn2+) and reduction of water, probably under high temperature conditions. This process generates very reducing conditions capable of destabilizing other molecules (notably reduction of deep CO2 being transformed into CH4 by Fisher-Tropsch type reactions). Nitrogen is also commonly associated to the H2-rich fluids. H2 flows are associated with the expulsion of hyperalkaline waters rich in ions OH- and Ca2+ and characterized by high pH (between 11 and 12). Most alkaline springs are found in the vicinity of major faults and/or lithological discontinuities like the basal thrust plane of the ophiolites and the peridotite-gabbro contact (Moho). Within the fracture networks, gas and water separate probably at shallow depth, i.e. close to the top of the upper aquifer level. Locally high flows of gas migrate vertically through fracture pathways and they are able to inflame spontaneously on the surface. Aqueous fluids tends to migrate laterally in the fracture network toward the creeks where most of the hyperalkaline springs are found. This water circulation induces a chain of diagenetic reactions starting in the fracture systems and continuing at the surface where it leads to the precipitation of calcite, aragonite, brucite and more rarely portlandite. This chain of diagenetic reactions is associated with the capture of the atmospheric CO2 during the precipitation of carbonates.

  2. Structure and evolution of the northern Oman margin: gravity and seismic constraints over the Zagros-Makran-Oman collision zone

    Science.gov (United States)

    Ravaut, P.; Bayer, R.; Hassani, R.; Rousset, D.; Yahya'ey, A. Al

    1997-09-01

    The obduction process in Oman during Late Cretaceous time, and continental-to-oceanic subduction along the Zagros-Makran region during the Tertiary are consequences of the Arabian-Eurasian collision, resulting in construction of complex structures composed of the Oman ophiolite belt, the Zagros continental mountain belt and the Makran subduction zone with its associated accretionary wedge. In this paper, we jointly interpret Bouguer anomaly and available petroleum seismic profiles in terms of crustal structures. We show that the gravity anomaly in northern Oman is characterized by a high-amplitude negative-positive couple. The negative anomaly is coincident with Late Cretaceous (Fiqa) and Tertiary (Pabdeh) foreland basins and with the Zagros-Oman mountain belts, whereas the positive anomaly is correlated to the ophiolite massifs. The Bouguer anomaly map indicates the presence of a post-Late Cretaceous sedimentary basin, the Sohar basin, centred north of the Batinah plain. We interpret the negative/positive couple in terms of loading of the elastic Arabian lithosphere. We estimate the different Cretaceous-to-Recent loads, including topography, ophiolite nappes, sedimentary fill and the accretionary prism of the Makran trench. A new method, using Mindlin's elastic plate theory, is proposed to model the 2D deflection of the heterogeneous elastic Arabian plate, taking into account boundary conditions at the ends of the subducted plate. We show that remnant ophiolites are isolated from Tethyan oceanic lithosphere in the Gulf of Oman by a continental basement ridge, a NW prolongation of the Saih-Hatat window. Loading the northward-limited ophiolite blocks explains the deflection of the Fiqa foredeep basin. West of the Musandam Peninsula, the Tertiary Pabdeh foredeep is probably related to the emplacement of a 8-km-thick tectonic prism located on the Musandam Peninsula and in the Strait of Hormuz. Final 2D density models along profiles through the Oman mountain belt and

  3. The Atlantis Bank Gabbro Massif, SW Indian Ridge: the Largest Know Exposure of the Lower Crust in the Oceans

    Science.gov (United States)

    Dick, H. J.; Kvassnes, A. J.; Kinoshita, H.; MacLeod, C. J.; Robinson, P. T.

    2017-12-01

    Until the discovery of oceanic core complexes little was known and much inferred about the lower ocean crust at slow-spreading ridges. Their study shows the ocean crust isn't simply a uniform layer-cake of pillow lavas, sheeted dikes and gabbros, but is highly variable in thickness, composition and architecture, and even absent over large regions. The 660 km2 Atlantis Bank Gabbro Massif in the rift-mountains of the SW Indian Ridge flanking the Atlantis II Transform is the magmatic end member for ocean core complexes, and best approximates `average' slow-spread crust. Thus it has been a focus for drilling since its discovery in 1986, leading to the current attempt to drill to Moho there (Project SloMo). There are 3 ODP and IODP drill holes on its crest: 1508-m deep Hole 735B, 158-m deep Hole 1105A, and 809.4-m deep Hole U1473. These provide a 200 Kyr view of lower crustal accretion at a slow-spread ocean ridge. Here we extend this view to 2.7 Myr. Mapping and sampling shows the gabbro massif extends nearly the length of a single 2nd order magmatic ridge segment. With numerous inliers of the dike-gabbro transition at numerous locations, and a crust-mantle boundary, traced for 30-km along the transform wall, it would appear to represent a full section of the lower crust. As Moho is at 5.5 ± 1 km mbsf near Hole 735B, and 4.5 km beneath the transform, it is likely a serpentinization front. The crust-mantle boundary was crossed by dives at 4 locations. In each case gabbros at the base of the crust crystallized from melt that had previously fractionated 50% or more from a likely parent. Thus the gabbro massif must be laterally zoned, and the parental mantle melts had to have been emplaced at the center of the paleo-ridge segment, before intruding laterally to the distal end of the complex. Gabbros on a lithospheric flow line down the center of the massif closely resemble those from the drill holes. This shows that while lateral variations in crustal composition and

  4. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Science.gov (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

    2016-09-01

    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  5. Clinopyroxenite dikes crosscutting banded peridotites just above the metamorphic sole in the Oman ophiolite: early cumulates from the primary V3 lava

    Science.gov (United States)

    Ishimaru, Satoko; Arai, Shoji; Tamura, Akihiro

    2013-04-01

    Oman ophiolite is one of the well-known ophiolites for excellent exposures not only of the mantle section but also of the crustal section including effusive rocks and the underlying metamorphic rocks. In the Oman ophiolite, three types of effusive rocks (V1, V2 and V3 from the lower sequences) are recognized: i.e., V1, MORB-like magma, V2, island-arc type lava, and V3, intra-plate lava (Godard et al., 2003 and references there in). V1 and V2 lavas are dominant (> 95 %) as effusive rocks and have been observed in almost all the blocks of northern part of the Oman ophiolite (Godard et al., 2003), but V3 lava has been reported only from Salahi area (Alabaster et al., 1982). It is clear that there was a time gap of lava eruption between V1-2 and V3 based on the presence of pelagic sediments in between (Godard et al., 2003). In addition, V3 lavas are fed by a series of doleritic dikes crosscutting V2 lava (Alley unit) (Alabaster et al., 1982). We found clinopyroxenite (CPXITE) dikes crosscutting deformation structure of basal peridotites just above the metamorphic sole in Wadi Ash Shiyah. The sole metamorphic rock is garnet amphibolite, which overlies the banded and deformed harzburgite and dunite. The CPXITE is composed of coarse clinopyroxene (CPX) with minor amount of chlorite, garnet (hydrous/anhydrous grossular-andradite) with inclusions of titanite, and serpentine formed at a later low-temperature stage. The width of the CPXITE dikes is 2-5 cm (10 cm at maximum) and the dikes contain small blocks of wall harzburgite. Almost all the silicates are serpentinized in the harzburgite blocks except for some CPX. The Mg# (= Mg/(Mg + Fe) atomic ratio) of the CPX is almost constant (= 0.94-0.95) in the serpentinite blocks but varies within the dikes, highest at the contact with the block (0.94) and decreasing with the distance from the contact to 0.81 (0.85 on average). The contents of Al2O3, Cr2O3, and TiO2 in the CPX of the dikes are 0.5-2.0, 0.2-0.6, and 0

  6. Significance of geological units of the Bohemian Massif, Czech Republic, as seen by ambient noise interferometry

    Czech Academy of Sciences Publication Activity Database

    Růžek, Bohuslav; Valentová, L.; Gallovič, F.

    2016-01-01

    Roč. 173, č. 5 (2016), s. 1663-1682 ISSN 0033-4553 R&D Projects: GA ČR GAP210/12/2336; GA MŠk LM2010008 Institutional support: RVO:67985530 Keywords : ambient noise * geological units * Bohemian Massif * velocity model Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.591, year: 2016

  7. Palaeomagnetic constraints on the evolution of the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N)

    Science.gov (United States)

    Morris, A.; Pressling, N.; Gee, J. S.

    2012-04-01

    Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. They represent a fundamental component of the seafloor spreading system at slow and ultraslow axes. One of the most extensively studied oceanic core complexes is Atlantis Massif, located at 30°N at the intersection of the Atlantis Transform Fault and the Mid Atlantic Ridge (MAR). The central dome of the massif exposes the corrugated detachment fault surface and was drilled during IODP Expedition 304/305 (Hole U1309D). This sampled a 1.4 km faulted and complexly layered footwall section dominated by gabbroic lithologies with minor ultramafic rocks. Palaeomagnetic analyses demonstrate that the gabbroic sequences at Atlantis Massif carry highly stable remanent magnetizations that provide valuable information on the evolution of the section. Thermal demagnetization experiments recover high unblocking temperature components of reversed polarity (R1) throughout the gabbroic sequences. Correlation of structures observed on oriented borehole (FMS) images and those recorded on unoriented core pieces allows reorientation of R1 remanences. The mean remanence direction in true geographic coordinates constrains the tectonic rotation experienced by the Atlantis Massif footwall, indicating a 46°±6° counterclockwise around a MAR-parallel horizontal axis trending 011°±6°. The detachment fault therefore initiated at a steep dip of >50° and then rotated flexurally to its present day low angle geometry (consistent with a 'rolling-hinge' model for detachment evolution). In a number of intervals, the gabbros exhibit a complex remanence structure with the presence of additional intermediate temperature normal (N1) and lower temperature reversed (R2) polarity components, suggesting an extended period of remanence acquisition during different polarity intervals. Sharp break-points between different polarity components suggest

  8. Internal structure of the Aar Massif: What can we learn in terms of exploration for deep geothermal energy?

    Science.gov (United States)

    Herwegh, Marco; Baumberger, Roland; Wehrens, Philip; Schubert, Raphael; Berger, Alfons; Maeder, Urs; Spillmann, Thomas

    2014-05-01

    The successful use of deep geothermal energy requires 3D flow paths, which allow an efficient heat exchange between the surrounding host rocks and the circulating fluids. Recent attempts to exploit this energy resource clearly demonstrate that the new technology is facing sever problems. Some major problems are related to the prediction of permeability, the 3D structure of the flow paths and the mechanical responses during elevated fluid pressures at depths of several kilometers. Although seemingly new in a technical perspective, nature is facing and solving similar problems since the beginning of the Alpine orogeny. Based on detailed studies in the Hasli Valley (Aar Massif) we can demonstrate that deformation and fluid flow are strongly localized along mechanical anisotropies (e.g. lithological variations, brittle and ductile faults). Some of them already evolved during Variscan and post-Variscan times. Interestingly, these inherited structures are reactivated over and over again during the Alpine orogeny. Their reactivation occurred at depths of ~13-15 km with elevated temperatures (400-475°C) and involved both ductile and brittle deformation processes. Brittle deformation in form of hydrofracking was always present due to the circulating fluids. It is this process, which was and still is responsible for seismic activity. With progressive uplift and exhumation of the Aar Massif, ductile deformation structures became replaced by brittle cataclasites and fault gouges during fault activity at shallower crustal levels. Existing hydrotest data from the Grimsel Test Site (Nagra's underground research laboratory) indicate that these brittle successors of the ductile shear zones are domains of enhanced recent fluid percolation. Note that although being exposed today, the continuation of these fault structures are still active at depth in both brittle and ductile deformation modes, a fact that can be inferred from recent uplift rates and the active seismicity. On the

  9. Problems of geologic survey of high level radioactive waste repositories illustrated on the testing site in the Melechov Massif

    International Nuclear Information System (INIS)

    Mlcoch, B.

    1997-01-01

    Major attention is paid to problems associated with the geologic maps of the prospective repository site, which lies within the Bohemian Massif. Structural geology, survey through boreholes, and primary database are also discussed briefly. (P.A.)

  10. Natural analogue studies of bentonite reaction under hyperalkaline conditions. Overview of ongoing work at the Zambales ophiolite, Philippines

    International Nuclear Information System (INIS)

    Fujii, N.; Yanakawa, M.; Arcilla, C.A.; Pascua, C.; Namiki, K.; Sato, T.; Shikazono, N.; Alexander, W.R.

    2011-01-01

    Bentonite is one of the safety-critical components of the engineered barrier system for the disposal concepts developed for many types of radioactive waste. However, bentonite - especially the swelling clay component that contributes to its essential barrier functions - is unstable at high pH. To date, results from laboratory tests on bentonite degradation have been ambiguous as the reaction rates are so slow as to be difficult to observe. As such, a key goal in this project is to examine the reaction of natural bentonites in contact with natural hyperalkaline groundwaters to determine if any long-term alteration of the bentonite occurs. Ophiolites have been identified as sources of hyperalkaline groundwaters that can be considered natural analogues of the leachates produced by some cementitious materials in repositories for radioactive waste. At the Zambales ophiolite in the Philippines, widespread active serpentinisation results in hyperalkaline groundwaters with measured pH values of up to 11.7, falling into the range typical of low-alkali cement porewaters. These cements are presently being developed worldwide to minimise the geochemical perturbations which are expected to result from the use of OPC-based concretes (see Kamei et al., this conference, for details). In particular, it is hoped that the lower pH of the low-alkali cement leachates will reduce, or even avoid entirely, the potential degradation of the bentonite buffer which is expected at the higher pH levels (12.5 and above) common to OPC-based concretes. During recent field campaigns at two sites in the Zambales ophiolite (Mangatarem and Bigbiga), samples of bentonite and the associated hyperalkaline groundwaters have been collected by drilling and trenching. At Mangatarem, qualitative data from a 'fossil' (i.e. no groundwater is currently present) reaction zone indicates some alteration of the bentonite to zeolite, serpentine and CSH phases. Preliminary reaction path modelling suggests that the

  11. Permo-Carboniferous volcanism in late Variscan continental basins of the Bohemian Massif (Czech Republic): geochemical characteristic

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Pešek, J.; Štěpánková-Svobodová, Jana; Bosák, Pavel; Lloyd, F. E.; Seckendorff, von, V.; Lang, Miloš; Novák, Jiří Karel

    2006-01-01

    Roč. 66, č. 1 (2006), s. 37-56 ISSN 0009-2819 R&D Projects: GA AV ČR(CZ) IAA3013903 Institutional research plan: CEZ:AV0Z30130516 Keywords : Permo-Carboniferous * volcanics * continental basin * Bohemian Massif * underplating * crustal anatexis * Sr-Nd isotopes Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.824, year: 2006

  12. Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Haluzová, Eva; Creaser, R. A.; Pašava, J.; Veselovský, F.; Breiter, Karel; Erban, V.; Drábek, M.

    2017-01-01

    Roč. 52, č. 5 (2017), s. 651-662 ISSN 0026-4598 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Re-Os * geochronology * molybdenite * Bohemian Massif * granite Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 3.396, year: 2016

  13. Miocene metamorphism of pan-African granites in the Edough Massif (NE Algeria)

    International Nuclear Information System (INIS)

    Hammor, D.; Lancelot, J.

    1998-01-01

    The Edough Massif is the eastern most crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595± My and 606±55 My and orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18± My U-Pb age that points to a Miocene age of the high-temperature metamorphism. (authors)

  14. The Juchatengo complex: an upper-level ophiolite assemblage of late Paleozoic age in Oaxaca, southern Mexico

    Science.gov (United States)

    Grajales-Nishimura, José Manuel; Ramos-Arias, Mario Alfredo; Solari, Luigi; Murillo-Muñetón, Gustavo; Centeno-García, Elena; Schaaf, Peter; Torres-Vargas, Ricardo

    2018-04-01

    The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated by late Paleozoic magmatism. It consists of mafic and sedimentary rocks that have oceanic affinities, with internal pseudostratigraphic, structural and metamorphic characteristics, which resemble a typical upper-level ophiolite assemblage. New U-Pb zircon and previous hornblende K-Ar analyses yield ages of ca. 291-313 Ma (U-Pb) for plagiogranites and ca. 282-277 Ma for tonalites intruding the entire sequence, including pelagic sediments at the top, with a maximum deposition age of ca. 278 Ma and noteworthy local provenance. These data constrain the age of the JC to the Late Pennsylvanian-Early Permian period. Hf isotopic analyses obtained from zircons in the JC plagiogranite and tonalite show that they come from a similar primitive mantle source (176Hf/177Hf: 0.282539-0.283091; ƐHf(t): + 3.2 to + 15.0). ƐHf(t) values from near 0 to - 2.8 in the tonalites indicate a contribution from the continental crust. Trace elements and REE patterns in whole rock and zircons point to a primitive mantle source for differentiated mafic, plagiogranite dykes and tonalitic plutons. Geochronological and geochemical data address the generation of new oceanic crust above the subduction zone, probably in a backarc setting. In this tectonic scenario, the JC ophiolite originated due to the convergence of the paleo-Pacific plate below the already integrated Oaxacan and Acatlán complexes in western Pangea. The dextral displacement places the deformation in a transtensional regime during the late Paleozoic age.

  15. Geochemical bioenergetics during low-temperature serpentinization: An example from the Samail ophiolite, Sultanate of Oman

    Science.gov (United States)

    Canovas, Peter A.; Hoehler, Tori; Shock, Everett L.

    2017-07-01

    Various classes of microbial and biomolecular evidence from global studies in marine and continental settings are used to identify a set of reactions that appear to support microbial metabolism during serpentinization of ultramafic rocks. Geochemical data from serpentinizing ecosystems in the Samail ophiolite of Oman are used to evaluate the extent of disequilibria that can support this set of microbial metabolisms and to provide a ranking of potential metabolic energy sources in hyperalkaline fluids that are direct products of serpentinization. Results are used to construct hypotheses for how microbial metabolism may be supported in the subsurface for two cases: ecosystems hosted in rocks that have already undergone significant serpentinization and those hosted by deeper, active serpentinization processes.

  16. THE GLACIER COMPLEXES OF THE MOUNTAIN MASSIFS OF THE NORTH-WEST OF INNER ASIA AND THEIR DYNAMICS

    Directory of Open Access Journals (Sweden)

    Kirill Chistyakov

    2011-01-01

    Full Text Available The subject of this paper is the glaciation of the mountain massifs Mongun-Taiga, Tavan-Boghd-Ola, Turgeni-Nuru, and Harhira-Nuru. The glaciation is represented mostly by small forms that sometimes form a single complex of dome-shaped peaks. According to the authors, the modern glaciated area of the mountain massifs is 21.2 km2(Tavan-Boghd-Ola, 20.3 km2 (Mongun-Taiga, 42 km2 (Turgeni-Nuru, and 33.1 km2 (Harhira-Nuru. The area of the glaciers has been shrinking since the mid 1960’s. In 1995–2008, the rate of reduction of the glaciers’ area has grown considerably: valley glaciers were rapidly degrading and splitting; accumulation of morainic material in the lower parts of the glaciers accelerated. Small glaciers transformed into snowfields and rock glaciers. There has been also a degradation of the highest parts of the glaciers and the collapse of the glacial complexes with a single zone of accumulation into isolated from each other glaciers. Reduced snow cover area has led to a rise in the firn line and the disintegration of a common accumulation area of the glacial complex. In the of the Mongun-Taiga massif, in 1995–2008, the firn line rose by 200–300 m. The reduction of the glaciers significantly lagged behind the change in the position of the accumulation area boundary. In the past two years, there has been a significant recovery of the glaciers that could eventually lead to their slower degradation or stabilization of the glaciers in the study area.

  17. Palaeomagnetism in the Sines massif (SW Iberia) revisited: evidences for Late Cretaceous hydrothermal alteration and associated partial remagnetization

    Science.gov (United States)

    Ribeiro, P.; Silva, P. F.; Moita, P.; Kratinová, Z.; Marques, F. O.; Henry, B.

    2013-10-01

    This study revisits the palaeomagnetism of the Sines massif (˜76 Ma) in the southwestern Iberian Margin (Portugal). The palaeomagnetic analysis was complemented by a comprehensive study of the magnetic mineralogy by means of rock magnetic measurements and petrographic observations. The overall dispersion of palaeomagnetic directions (declination ranging between ˜N0° and ˜N50°) and their migration observed during stepwise demagnetizations have revealed the superposition of remanence components. We interpret this complex palaeomagnetic behaviour as related to the regional hydrothermalism associated with the last stages of Late Cretaceous magmatic activity. This environment favoured mineralogical alteration and a partial chemical remagnetization, giving in most samples a composite magnetization, which has been erroneously interpreted as the primary one in a previous study, then leading to a questionable model for Cretaceous Iberia rotation. Nonetheless, for some samples a single component has been isolated. Interesting rock magnetic properties and microscopic observations point to a well-preserved magnetic mineralogy for these samples, with magnetite clearly of primary origin. The associated ChRM mean direction (D/I = 3.9°/46.5°, α95 = 1.7°, N = 31 samples) then represents the true primary magnetization of the Sines massif. This new palaeomagnetic direction and the corresponding palaeomagnetic pole (long = 332.0°, lat = -79.5°, A95 = 1.7°) agrees with those from the other palaeomagnetic works for the same period and region (e.g. the Sintra and Monchique massifs), yielding a lack of significant rotation of Iberia relative to stable Europe since the uppermost Late Cretaceous (Campanian-Maastrichtian).

  18. Sr isotopic tracer study of the Samail ophiolite, Oman

    International Nuclear Information System (INIS)

    Lanphere, M.A.; Coleman, R.G.; Hopson, C.A.

    1981-01-01

    We have measured Rb and Sr concentrations and Sr isotopic compositions in 41 whole-rock samples and 12 mineral separates from units of the Samail ophiolite, including peridotite, gabbro, plagiogranite diabase dikes, and gabbro and websterite dikes within the metamorphic peridotite. Ten samples of cummulate gabbro from the Wadir Kadir section and nine samples from the Wadi Khafifah section have mean 87 Sr/ 86 Sr ratios and standard deviations of 0.70314 +- 0.00030 and 0.70306 +- 0.00034, respectively. The dispersion in Sr isotopic composition may reflect real heterogeneities in the magma source region. The average Sr isotopic composition of cumulate gabbro falls in the range of isotopic compositions of modern midocean ridge basalt. The 87 Sr/ 86 Sr ratios of noncumulate gabbro, plagiogranite, and diabase dikes range from 0.7034 to 0.7047, 0.7038 to 0.7046, and 0.7037 to 0.7061, respectively. These higher 87 Sr/ 86 Sr ratios are due to alteration of initial magmatic compositions by hydrothermal exchange with seawater. Mineral separates from dikes that cut harzburgite tectonite have Sr isotopic compositions which agree with that of cumulate gabbro. These data indicate that the cumulate gabbro and the different dikes were derived from partial melting of source regions that had similar long-term histories and chemical compositions

  19. Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: An integrated geodynamic and petrological modelling approach

    Science.gov (United States)

    Palin, Richard M.; Reuber, Georg S.; White, Richard W.; Kaus, Boris J. P.; Weller, Owen M.

    2017-06-01

    The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India-Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure-temperature-time (P-T-t) path has been derived from thermomechanical simulations tailored for Eocene subduction in the northwestern Himalaya. Phase equilibrium modelling performed along this P-T path has described the petrological evolution of felsic and mafic components of the massif crust, and shows that differences in their fluid contents would have controlled the degree of metamorphic phase transformation in each during subduction. Our model predicts that peak P-T conditions of ∼2.6-2.8 GPa and ∼600-620 ∘C, representative of 90-100 km depth (assuming lithostatic pressure), could have been reached just ∼3 Myr after the onset of subduction of continental crust. This P-T path and subduction duration correlate well with constraints reported for similar UHP eclogite in the Kaghan Valley, Pakistan Himalaya, suggesting that the northwest Himalaya contains dismembered remnants of what may have been a ∼400-km-long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. A maximum overpressure of ∼0.5 GPa was calculated in our simulations for a homogeneous crust, although small-scale mechanical heterogeneities may produce overpressures that are larger in magnitude. Nonetheless, the extremely high pressures for peak metamorphism reported by some workers (up to 4.8 GPa) are unreliable owing to conventional thermobarometry

  20. Two-phase southward subduction of the Mongol-Okhotsk oceanic plate constrained by Permian-Jurassic granitoids in the Erguna and Xing'an massifs (NE China)

    Science.gov (United States)

    Liu, Huichuan; Li, Yinglei; He, Hongyun; Huangfu, Pengpeng; Liu, Yongzheng

    2018-04-01

    Geodynamics of the Mongol-Okhotsk oceanic plate southward subduction are still pending problems. This paper presents new zircon LA-ICP-MS U-Pb age and whole-rock geochemical data for the middle Permian to Middle Jurassic granitoids in the western Erguna and central Xing'an massifs. 267-264 Ma, 241 Ma and 173 Ma I-type granites, and 216 Ma A-type granites were identified in the Erguna and Xing'an massifs (NE China). The I-type granites were produced by partial melting of the lower mafic crust. The 216 Ma A-type granites were derived from partial melting of crustal materials with tonalitic to granodioritic compositions. The 267-264 Ma and 241 Ma I-type granites were generated in an Andean-type arc setting, wheras the 216 Ma A-type and 173 Ma granites were formed in supra subduction extensional setting. We summarized previous age data of the middle Permian to Middle Jurassic magmtaic rocks in the Erguna and Xing'an Massifs and identified two isolated phases of magmatic activity including the ca. 267-225 Ma and ca. 215-165 Ma periods, with a significant magmatic gap at ca. 225-215 Ma. These middle Permian to Middle Jurassic magmatic rocks are closely related to the southward subduction of the Mongol-Okhotsk ocean. A two-stage tectonic evolutionary model was proposed to account for these geological observations in the Erguna and Xing'an massifs, involving Permian to Middle Triassic continuous southward subduction of the Mongol-Okhotsk oceanic plate and Late Triassic to Jurassic slab-rollback and supra subduction extension.

  1. A contribution of airborne magnetic, gamma ray spectrometric data in understanding the structure of the Central Jebilet Hercynian massif and implications for mining

    Science.gov (United States)

    Maacha, Lhou; Jaffal, Mohammed; Jarni, Abdelmajid; Kchikach, Azzouz; Mouguina, El Mostafa; Zouhair, Mohamed; Ennaciri, Aomar; Saddiqi, Omar

    2017-10-01

    The Central Jebilet massif, well-known for its mining potential, has been explored for several years by the Managem Group, in collaboration with the National Office of Hydrocarbons and Mines (ONHYM), Morocco. This massif was surveyed by high-resolution magnetic and gamma-ray spectrometric methods in 1997 as part of a broader exploration program. In order to better exploit the results of this survey in understanding the structure of the Central Jebilet massif, we performed a series of processing of the collected data. The qualitative interpretation of this data highlighted the various magnetic domains, structures (e.g., lineaments and faults), and mafic intrusions. Euler deconvolution calculations provided estimates of the spatial location and depth of the magnetic sources, and spectral analysis of the magnetic data allowed further refinement of these depth estimates. Quantitative interpretation of some anomalies associated with exposed gossans allowed the characterization of their causative bodies, inferred to be sulfide deposits. The magnetic character of both the potential massive-sulfide bodies and the basic magmatic rocks (gabbro) were determined by the aeromagnetic data. Gamma ray spectrometric data has helped facilitate lithological discrimination and alteration zones, based on the radio-elemental distribution in the area. For example, the Thorium to Potassium ratio (Th/K) was used to highlight potassic alteration zones associated with massive-sulfide deposits in the Central Jebilet. The combined magnetic and radiometric study reveals the magnetic character of the Central Jebilet gossans, due to the content of pyrrhotite, which along with potassic alterations, has been recognized in all the known deposits of the Marrakech region. The results of this geophysical campaign supplement the existing geological and structural maps of Central Jebilet massif.

  2. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians

    Science.gov (United States)

    Bąk, Krzysztof; Bąk, Marta

    2013-06-01

    Bąk, K. and Bąk M. 2013. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians. Acta Geologica Polonica, 63 (2), 223-237. Warszawa. The foraminiferal and radiolarian biostratigraphy of selected sections of the Zabijak Formation, the youngest sediments of the Tatra massif (Central Western Carpathians), have been studied. Benthic foraminifers, mainly agglutinated species, occur abundantly and continuously throughout the studied succession, while planktic foraminifers are generally sparse. Five planktic and two benthic foraminiferal zones have been recognized. The marly part of the Zabijak Formation comprises the Pseudothalmanninella ticinensis (Upper Albian) through the Rotalipora cushmani (Upper Cenomanian) planktic foraminiferal zones, and the Haplophragmoides nonioninoides and Bulbobaculites problematicus benthic foraminiferal zones. The radiolarians were recognized exclusively in the Lower Cenomanian part of the formation.

  3. Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    HARTMANN LÉO A.

    2003-01-01

    Full Text Available Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite or compositional (e.g. mantle spinel remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3 and narrow 1-3 m-wide shear zones (M4 containing asbestos.

  4. Listwaenite in the Sartohay ophiolitic mélange (Xinjiang, China): A genetic model based on petrology, U-Pb chronology and trace element geochemistry

    Science.gov (United States)

    Qiu, Tian; Zhu, Yongfeng

    2018-03-01

    Listwaenite lenses in the Sartohay ophiolitic mélange (Xinjiang, China) were formed via reactions between serpentinite and metasomatic fluids. First, serpentinite changed into talc schist via the reaction of serpentine + CO2 → talc + magnesite + H2O. Second, talc schist changed into listwaenite via the reaction of talc + CO2 → magnesite + quartz + H2O. Magnetite was progressively destroyed during transformation from serpentinite to talc schist, and completely consumed in listwaenite. Zircon crystals 30-100 μm long, disseminating in talc schist, undeformed listwaenite and mylonitized listwaenite, coexist with talc, quartz and magnesite, while micron-sized zircon grains (ages (302.9 ± 6.8 Ma, 299.7 ± 5.5 Ma and 296.5 ± 3.5 Ma), and are thought to represent the age of formation of the talc schist and listwaenite. These ages are indistinguishable within errors and suggest a rapid transformation from talc schist to listwaenite. Some zircon rims in samples of the undeformed listwaenite and mylonitized listwaenite give much younger apparent U-Pb ages (280-277 Ma), which could be interpreted as a recrystallization age reflecting late-stage shearing in the Sartohay ophiolitic mélange.

  5. The Oldest Granites of Russia: Paleoarchean (3343 Ma) Subalkali Granites of the Okhotsk Massif

    Science.gov (United States)

    Kuzmin, V. K.; Bogomolov, E. S.; Glebovitskii, V. A.; Rodionov, N. V.

    2018-02-01

    The Paleoarchean age (3.34 Ga) of subalkali granite magmatism first established for the Kukhtui uplift of the Okhotsk Massif suggests a formation time of the mature continental K-rich crust in this region as early as the Paleoarchean. According to the geological structural, mineralogical-geochemical, geochronological, and isotopic-geochemical data, the Kukhtui uplift can be considered as the most ancient Paleoarchean province in Russia: the ancient consolidation core of the sialic protocrust of the Okhotsk-Omolon Craton.

  6. Mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks: A case study of Oman and Ligurian ophiolites

    Science.gov (United States)

    Chavagnac, Valérie; Ceuleneer, Georges; Monnin, Christophe; Lansac, Benjamin; Hoareau, Guilhem; Boulart, Cédric

    2013-07-01

    We report on the mineralogical assemblages found in the hyperalkaline springs hosted on Liguria and Oman ophiolites based on exhaustive X-ray diffraction and scanning electron microprobe analyses. In Liguria, hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric CO2 uptake and neutralization of the hyperalkaline waters. No brucite and portlandite minerals are observed. The discharge of alkaline waters in Oman ophiolite forms white-orange precipitates. Calcium carbonate minerals (calcite and/or aragonite) are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in Liguria. This process is observed as a thin surface crust made of rhombohedral calcite. Morphological features of aragonite vary from needle-, bouquet-, dumbbell-, spheroidal-like habitus according to the origin of carbon, temperature, and ionic composition of the hyperalkaline springs, and the biochemical and organic compounds. Brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo-Moho. The varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation. The layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros. Finally, the dominant mineralogical associations we found in Oman (Ca-bearing carbonates and brucite) in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the Lost City hydrothermal site in a totally marine environment.

  7. PALLADIUM, PLATINUM, RHODIUM, RUTHENIUM AND IRIDIUM IN PERIDOTITES AND CHROMITITES FROM OPHIOLITE COMPLEXES IN NEWFOUNDLAND.

    Science.gov (United States)

    Page, Norman J; Talkington, Raymond W.

    1984-01-01

    Samples of spinel lherzolite, harzburgite, dunite, and chromitite from the Bay of Islands, Lewis Hills, Table Mountain, Advocate, North Arm Mountain, White Hills Periodite Point Rousse, Great Bend and Betts Cove ophiolite complexes in Newfoundland were analyzed for the platinum-group elements (PGE) Pd, Pt, Rh, Ru and Ir. The ranges of concentration (in ppb) observed for all rocks are: less than 0. 5 to 77 (Pd), less than 1 to 120 (Pt), less than 0. 5 to 20 (Rh), less than 100 to 250 (Ru) and less than 20 to 83 (Ir). Chondrite-normalized PGE ratios suggest differences between rock types and between complexes. Samples of chromitite and dunite show relative enrichment in Ru and Ir and relative depletion in Pt and Pd.

  8. The topographic signature of Quaternary tectonic uplift in the Ardennes massif (Western Europe)

    Science.gov (United States)

    Sougnez, N.; Vanacker, V.

    2011-04-01

    Geomorphic processes that produce and transport sediment, and incise river valleys are complex; and often difficult to quantify over longer timescales of 103 to 105 y. Morphometric indices that describe the topography of hill slopes, valleys and river channels have commonly been used to compare morphological characteristics between catchments and to relate them to hydrological and erosion processes. This study aims to analyze the link between tectonic uplift rates and landscape morphology based on slope and channel morphometric indexes. To achieve this objective, we selected 10 catchments of about 150 to 250 km2 across the Ardennes Massif (a Palaeozoic massif of NW Europe, principally located in Belgium) that cover various tectonic domains with uplift rates ranging from about 0.06 to 0.20 mm yr-1 since mid-Pleistocene times. The morphometric analysis indicates that the slope and channel morphology of third-order catchments is not yet in topographic steady-state, and exhibits clear convexities in slope and river profiles. Our analysis indicates that the fluvial system is the main driver of topographic evolution and that the spatial pattern of uplift rates is reflected in the distribution of channel steepness and convexity. The spatial variation that we observe in slope and channel morphology between the 10 third-order catchments suggests that the response of the fluvial system was strongly diachronic, and that a transient signal of adjustment is migrating from the Meuse valley towards the Ardennian headwaters.

  9. Geochemical study of water-rock interaction processes on geothermal systems of alkaline water in granitic massif

    International Nuclear Information System (INIS)

    Buil gutierrez, B.; Garcia Sanz, S.; Lago San Jose, M.; Arranz Yague, E.; Auque Sanz, L.

    2002-01-01

    The study of geothermal systems developed within granitic massifs (with alkaline waters and reducing ORP values) is a topic of increasing scientific interest. These systems are a perfect natural laboratory for studying the water-rock interaction processes as they are defined by three main features: 1) long residence time of water within the system, 2) temperature in the reservoir high enough to favour reaction kinetics and finally, 3) the comparison of the chemistry of the incoming and outgoing waters of the system allows for the evaluation of the processes that have modified the water chemistry and its signature, The four geothermal systems considered in this paper are developed within granitic massifs of the Spanish Central Pyrenes; these systems were studied from a geochemical point of view, defining the major, trace and REE chemistry of both waters and host rocks and then characterizing the composition and geochemical evolution of the different waters. Bicarbonate-chloride-sodic and bicarbonate-sodic compositions are the most representative of the water chemistry in the deep geothermal system, as they are not affected by secondary processes (mixing, conductive cooling, etc). (Author)

  10. Monazite and zircon as major carriers of Th, U, and Y in peraluminous granites: examples from the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Breiter, Karel

    2016-01-01

    Roč. 110, č. 6 (2016), s. 767-785 ISSN 0930-0708 R&D Projects: GA ČR GA14-13600S Institutional support: RVO:67985831 Keywords : zircon * monazite * granites * trace elements * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.236, year: 2016

  11. Features of change of permanent snow patches in the Mongun-Taiga Massif, 1966–2011

    Directory of Open Access Journals (Sweden)

    D. A. Ganyushkin

    2013-01-01

    Full Text Available The article is dedicated to perennial snow patches of Mongun-Taiga mountain massif (south-western Tuva, their morphology, present state and dynamics over the last 45 years. We created a scheme of snow patch classification with regard to genesis of relief and position on the slopes. Dynamics of snow patches is analyzed for periods between several time points – 1966 (on basis of aerial photos, 2000, 2007–2008 and 2011 (on basis of field measurements and observations. From 1966 to 2008 the number of snow patches decreased by 4 times, the total area – by 15 times, the altitudinal zone of snow patches moved 250–300 m up. In 2008–2011 the altitudinal zone of snow patches partly recovered, its lower limit moved 250 m down, periglacial snow patches recovered, a new type – snow patches of buried ice and debris-covered glaciers appeared. It could be the first face of the process of small glaciers recovery in the massif. Using the changes of the altitudinal position of snow patches in comparison with data of the closest meteorological station we estimated the amount of annual precipitation, critical for the existence of local snow patches.

  12. The andean ophiolitic megastructures on the Buga-Buenaventura transverse (Western Cordillera—Valle Colombia)

    Science.gov (United States)

    Bourgois, Jacques; Calle, Bernardo; Tournon, Jean; Toussaint, Jean-François

    1982-02-01

    A structural study of the Buga-Buenaventura transverse in the central part of the Western Cordillera of Colombia, has shown the presence of three structural units which, from bottom to top and from west to east, are: the Rio Dagua unit, the Rio Calima unit, and the Loboguerrero window unit. All three units comprise strata between 120 and 80 m.y. old overlying a basement of green rocks showing the characteristics of submarine flows. The Bolivar ultrabasic and basic massif is geographically linked to the Rio Calima unit, in which green rocks predominate, and is separated from it by a tectonic contact. The upper part of the massif, on the other hand, shows high-temperature metamorphic rocks formed during its emplacement. The Rio Dagua unit shows two tectonic phases with isoclinal folding and development of schistosity. The first phase is contemporaneous with low-grade metamorphism equivalent to lower greenschist facies conditions. The Loboguerrero window unit shows a large recumbent fold oriented towards the southeast. Deformation in the Rio Calima unit is weaker and appears to correspond to a higher structural level than in the two other units. As the attitudes of the S1, schistosity in the Rio Dagua unit and of the shear zones located at the green rocks-sediments contact in this same unit are similar to that of the overthrust at the base of the Rio Calima unit, we are led to postulate that the overthrust belongs to the first phase of deformation, as also does the recumbent fold in the Loboguerrero window unit. We are thus led to propose a southeastward direction of emplacement for the nappes in the Western Cordillera of Colombia. In conclusion, the authors extend their observations and propose a new structural interpretation of the "Occidente Colombiano".

  13. Lateral displacement of crustal units relative to underlying mantle lithosphere: Example from the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Babuška, Vladislav; Plomerová, Jaroslava

    2017-01-01

    Roč. 48, December (2017), s. 125-138 ISSN 1342-937X R&D Projects: GA ČR GAP210/12/2381; GA MŠk(CZ) LD15029; GA MŠk LM2010008; GA MŠk(CZ) LM2015079 Institutional support: RVO:67985530 Keywords : Bohemian Massif * Teplá-Barrandian mantle lithosphere * Zone Erbendorf-Vohenstrauss * Jáchymov Fault Zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Volcanology Impact factor: 6.959, year: 2016

  14. Tourist Traffic In The Aconcagua Massif Area

    Directory of Open Access Journals (Sweden)

    Marek Aneta

    2015-09-01

    Full Text Available The aim of the article is an analysis of tourist traffic in the Aconcagua massif, one of the most popular peaks of the Seven Summits. On the basis of statistical data, the tourist traffic was analysed in a temporal and spatial perspective. The applied data made it possible to capture the dynamics of visits in the period 2000/2001 – 2012/2013 and with a breakdown into months, which helped analyse the tourist traffic in this area. In each of the analysed periods, January dominates. Data concerning the origin of tourists according to countries and continents, their age, gender and type of mountaineering activity were also taken into account. Most tourists came from Argentina, the USA and Germany. These are people of age groups 21–30 (33% and 31–40 (31%. Men account for over 75% of visitors. The favourite mountaineering activity is climbing (about 60%. Aconcagua has invariably been a very popular peak among tourists and climbers. It is a place for training and acclimatisation for alpinists, participating in Himalayan expeditions and climbers collecting peaks of the Seven Summits.

  15. Deciphering the Variscan tectonothermal overprint and deformation partitioning in the Cadomian basement of the Teplá-Barrandian unit, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Hajná, J.; Žák, J.; Kachlík, V.; Chadima, Martin

    2012-01-01

    Roč. 101, č. 7 (2012), s. 1855-1873 ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : Avalonian-Cadomian belt * Bohemian Massif * Shear zone * Teplá-Barrandian unit * transpression * Variscan orogeny Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.261, year: 2012

  16. Metaultramafic schists and dismembered ophiolites of the Ashe Metamorphic Suite of northwestern North Carolina, USA

    Science.gov (United States)

    Raymond, Loren A.; Merschat, Arthur J.; Vance, R. Kelly

    2016-01-01

    both chemical composition and metamorphic history. Spot sampling of heterolithic MUR bodies does not reveal MUR body character or history or allow ‘type’ designations. We recommend that the subdivision of MUR bodies into ‘types’ be abandoned and that the metasomatic hypothesis be carefully applied. AMS MURs and associated metamafic rocks likely represent fragments of dismembered ophiolites from various ophiolite types.

  17. Metabolic Potential and Activity in Fluids of the Coast Range Ophiolite Microbial Observatory, California, USA

    Science.gov (United States)

    Hoehler, T.; Som, S.; Schrenk, M.; McCollom, T.; Cardace, D.

    2016-01-01

    Metabolic potential and activity associated with hydrogen and carbon monoxide were characterized in fluids sampled from the the Coast Range Ophiolite Microbial Observatory (CROMO). CROMO consists of two clusters of science-dedicated wells drilled to varying depths up to 35m in the actively serpentinizing, Jurassic-age Coast Range Ophiolite of Northern California, along with a suite of pre-existing monitoring wells at the same site. Consistent with the fluid chemistry observed in other serpentinizing systems, CROMO fluids are highly alkaline, with pH up to 12.5, high in methane, with concentrations up 1600 micromolar, and low in dissolved inorganic carbon (DIC), with concentrations of 10's to 100's of micromolar. CROMO is conspicuous for fluid H2 concentrations that are consistently sub-micromolar, orders of magnitude lower than is typical of other systems. However, higher H2 concentrations (10's -100's of micromolar) at an earlier stage of fluid chemical evolution are predicted by, or consistent with: thermodynamic models for fluid chemistry based on parent rock composition equivalent to local peridotite and with water:rock ratio constrained by observed pH; the presence of magnetite at several wt% in CROMO drill cores; and concentrations of formate and carbon monoxide that would require elevated H2 if formed in equilibrium with H2 and DIC. Calculated Gibbs energy changes for reaction of H2 and CO in each of several metabolisms, across the range of fluid composition encompassed by the CROMO wells, range from bioenergetically feasible (capable of driving ATP synthesis) to thermodynamically unfavorable. Active consumption relative to killed controls was observed for both CO and H2 during incubation of fluids from the pre-existing monitoring wells; in incubations of freshly cored solids, consumption was only observed in one sample set (corresponding to the lowest pH) out of three. The specific metabolisms by which H2 and CO are consumed remain to be determined.

  18. Perceptions of social and environmental changes in a Mediterranean forest during the last 100 years: the Gavarres Massif.

    Science.gov (United States)

    Rodríguez-Carreras, Roser; Ubeda, Xavier; Outeiro, Luís; Asperó, Francesc

    2014-06-01

    During the last century the landscape of the mid-Mediterranean mountains has undergone major transformations. The precipitous decline in the economic viability of forest products has engendered ever-thickening forests and agricultural lands have reverted to forest land cover. The related exodus of existing inhabitants since 1960 has led to new styles of occupancy: residential and touristic land uses have emerged while the primary and secondary sectors have largely disappeared. The object of the present study is to review how these transformations have developed in a specific area of north-eastern of Catalonia, known as the Gavarres Massif. The study applies a qualitative approach, based on interviews with stakeholders including active members of the local community and others who utilize or visit the area, all of whom are representatives of different social groups with a wide range of interests and points of view with regard to the massif. The information collected from the perspectives and opinions of the participants is coupled with objective data about the area. The result of this investigation is a rich variety of perceptions on landscape and social transformation and its current functional dynamics. Analyzing the information obtained allows us to understand the fact that the disappearance of the rural world is directly related to the collapse of an entire economic system that relied on the environment. In this study, two divergent points of view arise, one which supports recovering past landscapes and another which favours managing changes, conserving the existing landscape. Proposals for the current and future territorial management of Les Gavarres are presented. The diversity of opinions which emerges with regard to managing necessary changes in the massif emphasizes the importance of increased social dialogue. Copyright © 2013 Elsevier Ltd. All rights reserved.

  19. Tectonic evolution of part of the Southern Metamorphic Belt of the Armorican Massif including the Ile de Groix

    Science.gov (United States)

    Richards, Lawrence Edward

    The Southern Metamorphic Belt (SMB) of the Armorican Massifextends 400km along the south coast of Brittany and into Vendee. It is separated from the Central Armorican Domain by a major, late-Hercynian shear belt, known as the South Armorican Shear Zone. In the area studied, belts of metasedimentary and metavolcanic schist of uncertain age are separated by belts of granitic gneiss; areas of migmatite and Hercynian granite plutons cross-cut these belts. Three distinctive lithologic assemblages have been identified in the schist belts, characteristic of different depositional environments: the Le Pouldu Group, Kerleven and Gouesnach formations probably originated as abyssal black shales deposited on oceanic crust; the St. Laurent Formation and Melgven Schists probably formed as distal greywacke deposits on a deep continental shelf; the Nerly and Beg-Meil formations probably formed in a proximal marine or fluviatile environment. These disparate assemblages were tectonically juxtaposed by overthrusting (obduction) before an amphibolite facies metamorphism and deformation during the Cadomian Orogeny. The Moelan Gneiss, a Lower Ordovician alkali-granite intrusion, postdates M1/D1 and probably formed in a rifting environment at the onset of ocean-floor spreading along an axis south of the present Armorican Massif. The famous blueschists of the Ile de Groix probably formed in a subduction zone on the south side of the ocean and were obducted onto the passive southern margin of the Armorican Massif following closure of the ocean and continental collision. A second phase of regional deformation, producing a cataclastic foliation in the Moelan Gneiss, probably resulted from the collision. Large-scale overthrusting of the southern continent onto the Armorican Massif took place, causing metamorphism with partial melting at depth generating migmatites. A third phase of pervasive deformation may correlate with oroclinal bending of the Ibero-Armorican Arc during the Hercynian

  20. Uraninite, coffinite and brannerite from shear-zone hosted uranium deposits of the Bohemian Massif (Central European Variscan belt)

    Czech Academy of Sciences Publication Activity Database

    René, Miloš; Dolníček, Z.

    2017-01-01

    Roč. 7, č. 4 (2017), č. článku 50. ISSN 2075-163X Institutional support: RVO:67985891 Keywords : uranium deposits * mineralogy * uraninite * coffinite * brannerite * Moldanubian Zone * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.088, year: 2016 http://www.mdpi.com/2075-163X/7/4/50

  1. Occurrence of an unknown Atlantic eruption in the Chaîne des Puys volcanic field (Massif Central, France)

    Science.gov (United States)

    Jouannic, G.; Walter-Simonnet, A. V.; Bossuet, G.; Cubizolle, H.; Boivin, P.; Devidal, J. L.; Oberlin, C.

    2014-08-01

    A volcanic ash layer, called MF1, was recently identified in Holocene sediments from the Gourgon and Molhiac peat bogs (Monts du Forez, French Massif Central). This ash layer consists of colorless shards with a heterogeneous trachytic to rhyolitic composition. The trace elements analyzed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) attest to a local origin. Radiocarbon dating of peat samples taken within and below the ash layer indicates the best age at 6339 ± 61 cal yr BP, i.e. an age contemporaneous with the volcanic activity of Montchal, Montcineyre and Pavin volcanoes from the Chaîne des Puys volcanic field. These volcanoes are characterized by basaltic and trachytic products, thus the rhyolitic composition of MF1 tephra suggests that it is likely originated from an unknown eruption. These results again confirm the interest of studying the distal volcanic ash fallouts in order to establish or specify records of past eruptions of volcanic fields. Identification of this new tephra layer also provides an additional tephrochronological marker for Eastern French Massif Central.

  2. Petro-structural, geochemical and carbon and oxygen isotopic study on carbonates crosscuting the Oman Ophiolite peridotites: evidence of polygenic CO2 trapping

    Science.gov (United States)

    Noël, J.; Godard, M.; Martinez, I.; Oliot, E.; Williams, M. J.; Rodriguez, O.; Chaduteau, C.; Gouze, P.

    2017-12-01

    Carbon trapping in ophiolitic peridotites contributes to the global carbon cycle between solid Earth and its outer envelopes (through subduction and/or modern alteration). To investigate this process, we performed petro-structural (microtomography, EBSD, EPMA) and geochemical studies (LA-ICP-MS, carbon and oxygen isotopes on bulk and minerals using SHRIMP) of harzburgites cored in the Oman Ophiolite. Studied harzburgites are highly serpentinized (> 90 %) and crosscut by 3 generations of carbonates (> 20 Vol%) with compositions from calcite to dolomite (Mg/Ca = 0-0.85). Type 1 carbonates are fine penetrative veinlets and mesh core after olivine. They have low REE (e.g., Yb = 0.08-0.23 x CI-chondrite) and negative Ce anomalies. They have δ13CPDB = -15.2 to 1.10‰ and δ18OSMOW = 17.5 to 33.7‰, suggesting precipitation temperatures up to 110°C. Type 2 carbonates are pluri-mm veins bounded by cm-thick serpentinized vein selvages, oriented dominantly parallel to mantle foliation. Dynamic recrystallization is observed, indicating polygenetic formation: well crystallized calcite with REE abundances similar to Type 1 carbonates are locally replaced by small dolomite and calcite grains with higher REE (e.g., Yb = 0.35-1.0 x CI-chondrite) and positive Gd anomaly. Type 2 carbonates have δ13CPDB = -12.6 to -4.1‰ and δ18OSMOW = 25.0 to 32.7‰, suggesting precipitation temperatures from 10 to 60°C. Type 3 carbonates are late pluri-mm to cm veins reactivating Type 2 veins. They consist of small grains of dolomite and calcite with REE abundances similar to recrystallized Type 2 carbonates. Type 3 carbonates have δ13CPDB = -8.3 to -5.8‰ and δ18OSMOW = 28.8 to 32.7‰, suggesting precipitation temperatures 100°C). Formation of carbonate veins (Type 2) indicates localization of fluid flux, while serpentinization remains the dominant alteration process. Low T carbonate veins (Type 3) remain the main flow path through ophiolitic peridotites. Our study suggests that

  3. The topographic signature of Quaternary tectonic uplift in the Ardennes massif (Western Europe

    Directory of Open Access Journals (Sweden)

    N. Sougnez

    2011-04-01

    Full Text Available Geomorphic processes that produce and transport sediment, and incise river valleys are complex; and often difficult to quantify over longer timescales of 103 to 105 y. Morphometric indices that describe the topography of hill slopes, valleys and river channels have commonly been used to compare morphological characteristics between catchments and to relate them to hydrological and erosion processes. This study aims to analyze the link between tectonic uplift rates and landscape morphology based on slope and channel morphometric indexes. To achieve this objective, we selected 10 catchments of about 150 to 250 km2 across the Ardennes Massif (a Palaeozoic massif of NW Europe, principally located in Belgium that cover various tectonic domains with uplift rates ranging from about 0.06 to 0.20 mm yr−1 since mid-Pleistocene times. The morphometric analysis indicates that the slope and channel morphology of third-order catchments is not yet in topographic steady-state, and exhibits clear convexities in slope and river profiles. Our analysis indicates that the fluvial system is the main driver of topographic evolution and that the spatial pattern of uplift rates is reflected in the distribution of channel steepness and convexity. The spatial variation that we observe in slope and channel morphology between the 10 third-order catchments suggests that the response of the fluvial system was strongly diachronic, and that a transient signal of adjustment is migrating from the Meuse valley towards the Ardennian headwaters.

  4. The Dilemma and Solutions for the Conflicts between Equality and Excellence in the Massification of Higher Education in Taiwan

    Science.gov (United States)

    Hsiou-Huai, Wang

    2012-01-01

    Equality and excellence are two core values underlying many educational endeavors; however, they are often in conflict and controversy. This article intends to examine the dilemma created by such controversies in the context of massification of higher education in Taiwan and attempt to provide solutions from both the theoretical and policy…

  5. Plio-Pleistocene basanitic and melilititic series of the Bohemian Massif: K-Ar ages, major/trace element and Sr–Nd isotopic data

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Ackerman, Lukáš; Balogh, K.; Hegner, E.; Jelínek, E.; Pécskay, Z.; Přichystal, A.; Upton, B. G. J.; Zimák, J.; Foltýnová, R.

    2013-01-01

    Roč. 73, č. 4 (2013), s. 429-450 ISSN 0009-2819 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Plio-Pleistocene * Basanite * Melilitite * K-Ar age * Magmatism * Sr–Nd isotopes Subject RIV: DD - Geochemistry Impact factor: 1.397, year: 2013

  6. Late Cenozoic cooling history of the central Menderes Massif and the contribution of erosion to rock exhumation during active continental extension

    Science.gov (United States)

    Nilius, Nils-Peter; Wölfler, Andreas; Heineke, Caroline; Glotzbach, Christoph; Hetzel, Ralf; Hampel, Andrea; Akal, Cüneyt; Dunkl, István

    2017-04-01

    The Menderes Massif constitutes the western part of the Anatolide belt in western Turkey and experienced a prolonged history of post-orogenic extension. A large amount of the extension was accommodated by the two oppositely dipping Gediz and Büyük Menderes detachment faults, which led to the exhumation of the central Menderes Massif (Gessner et al., 2013). Previous studies proposed a synchronous, bivergent exhumation of the central Menderes Massif since the Miocene (Gessner et al., 2001), although only the evolution of the north-dipping Gediz detachment is well constrained (Buscher et al., 2013). Detailed structural and thermochronological investigations from the south-dipping Büyük Menderes detachment have still been missing. Here we present results from different thermochronometers, which constrain the cooling and exhumation history of footwall and hanging wall rocks of the Büyük Menderes detachment. Our new zircon and apatite (U-Th)/He and fission track ages of footwall rocks from the Büyük Menderes detachment document two phases of increased cooling and exhumation (Wölfler et al., in revision). The first episode of increased footwall exhumation ( 0.9 km/Myr) occurred during the middle Miocene, followed by a second phase during latest Miocene and Pliocene ( 1.0 km/Myr). Apatite fission track ages yield a slip rate for the Pliocene movement along the Büyük Menderes detachment of 3.0 (+1.1/-0.6) km/Myr. Thermochronological data of hanging wall units reflect a slow phase of exhumation ( 0.2 km/Myr) in the late Oligocene and an increased exhumation rate of 1.0 km/Myr during the early to middle Miocene, when hanging wall units cooled below 80 °C. In comparison with the Gediz detachment, our thermochronological data from the Büyük Menderes detachment confirms the concurrent activity of both detachments during the late Miocene and Pliocene. With respect to the relative importance of normal faulting and erosion to rock exhumation, a comparison with 10Be

  7. A new species of Pristimantis (Anura, Craugastoridae) from the Cajas Massif, southern Ecuador

    Science.gov (United States)

    Sánchez-Nivicela, Juan C.; Celi-Piedra, Elvis; Posse-Sarmiento, Valentina; Urgiles, Verónica L.; Yánez-Muñoz, Mario; Cisneros-Heredia, Diego F.

    2018-01-01

    Abstract A new species of Pristimantis is described from the highland paramos on the eastern slopes of the Cajas Massif, southern Andes of Ecuador, at 3400 m. This new species is characterized by having a distinctive reddish color, cutaneous macroglands in suprascapular region and surfaces of arm and legs, and by lacking dentigerous processes of vomers. The cutaneous macroglands are similar to those exhibited by several species of the Pristimantis orcesi group, and may suggest a close phylogenetic relationship. The new species could be a latitudinal substitution of Pristimantis orcesi in the southern Andes of Ecuador. PMID:29713233

  8. Development of a Comprehensive Plan for Scientific Research, Exploration, and Design: Creation of an Underground Radioactive Waste Isolation Facility at the Nizhnekansky Rock Massif

    International Nuclear Information System (INIS)

    Jardine, L J

    2005-01-01

    ISTC Partner Project No.2377, ''Development of a General Research and Survey Plan to Create an Underground RW Isolation Facility in Nizhnekansky Massif'', funded a group of key Russian experts in geologic disposal, primarily at Federal State Unitary Enterprise All-Russian Design and Research Institute of Engineering Production (VNIPIPT) and Mining Chemical Combine Krasnoyarsk-26 (MCC K-26) (Reference 1). The activities under the ISTC Partner Project were targeted to the creation of an underground research laboratory which was to justify the acceptability of the geologic conditions for ultimate isolation of high-level waste in Russia. In parallel to this project work was also under way with Minatom's financial support to characterize alternative sections of the Nizhnekansky granitoid rock massif near the MCC K-26 site to justify the possibility of creating an underground facility for long-term or ultimate isolation of radioactive waste (RW) and spent nuclear fuel (SNF). (Reference 2) The result was a synergistic, integrated set of activities several years that advanced the geologic repository site characterization and development of a proposed underground research laboratory better than could have been expected with only the limited funds from ISTC Partner Project No.2377 funded by the U.S. DOE-RW. There were four objectives of this ISTC Partner Project 2377 geologic disposal work: (1) Generalize and analyze all research work done previously at the Nizhnekansky granitoid massif by various organizations; (2) Prepare and issue a declaration of intent (DOI) for proceeding with an underground research laboratory in a granite massif near the MCC K-26 site. (The DOI is similar to a Record of Decision in U.S. terminology). (3) Proceeding from the data obtained as a result of scientific research and exploration and design activities, prepare a justification of investment (JOI) for an underground research laboratory in as much detail as the available site characterization

  9. Le Massif du Taburno-Camposauro, une montagne calcaire en position de charnière à l'échelle de l'Apennin méridional (Italie du Sud

    Directory of Open Access Journals (Sweden)

    Bruno Comentale

    2010-03-01

    Full Text Available Le massif du Taburno-Camposauro, bloc calcaire tectoniquement soulevé, occupe une position de charnière dans l'Apennin méridional, du fait du morcellement orographique qui permet l'établissement d'une communication entre les deux versants, tyrrhénien et adriatique, de la péninsule italienne. En complément de ce morcellement redevable à la néotectonique plio-pléistocène en extension, le massif juxtapose de vigoureux escarpements de faille et des topographies sommitales à aplanissements partiels, ultérieurement karstifiées. En replaçant ce massif dans le contexte géomorphologique régional, et en en soulignant les nombreuses analogies avec le massif voisin du Matese, ce travail conduit une analyse microtectonique des escarpements de faille associés à des déformations de brèches, alors que le lien génétique entre ces dernières et les topographies sommitales fait l'objet d'une discussion.The Taburno-Camposauro limestone faulted block has a key location between tyrrhenian and adriatic sides of the Southern Apennines, because of the relief disruption due to extensional Plio-Pleistocene neotectonics. From this, results a contrasted landscape, with prior gentle erosional landsurfaces (Upper Miocene-Early Pliocene? subsequently disrupted by huge fault scarps. After a microtectonic analysis along these fault scarps, also considering the deformation of breccia – which are regarded as genetically linked with the erosional landsurfaces shaping –, the discussion deals with the regional geomorphic pattern, mainly the nearest Matese mountain.

  10. Late Cretaceous and Cenozoic dynamics of the Bohemian Massif inferred from the paleostress history of the Lusatian Fault Belt

    Czech Academy of Sciences Publication Activity Database

    Coubal, Miroslav; Málek, Jiří; Adamovič, Jiří; Štěpančíková, Petra

    2015-01-01

    Roč. 87, July 1 (2015), s. 26-49 ISSN 0264-3707 R&D Projects: GA ČR GAP210/12/0573 Institutional support: RVO:67985831 ; RVO:67985891 Keywords : paleostress * fault kinematics * Lusatian Fault Belt * Elbe fault system * Bohemian Massif * Alpine foreland Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.926, year: 2015

  11. Behavior of trace elements in quartz from plutons of different geochemical signature: A case study from the Bohemian Massif, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Breiter, Karel; Ackerman, Lukáš; Svojtka, Martin; Müller, A.

    175/176, 15 August (2013), s. 54-67 ISSN 0024-4937 R&D Projects: GA ČR GAP210/10/1105 Institutional support: RVO:67985831 Keywords : Quartz * trace elements * granites * fractionation * Bohemian Massif Subject RIV: DD - Geochemistry Impact factor: 3.654, year: 2013

  12. Origin of the Okrouhlá Radouň episyenite-hosted uranium deposit, Bohemian Massif, Czech Republic: fluid inclusion and stable isotope constraints

    Czech Academy of Sciences Publication Activity Database

    Dolníček, Z.; René, Miloš; Hermannová, S.; Prochaska, W.

    2014-01-01

    Roč. 49, č. 4 (2014), s. 409-425 ISSN 0026-4598 R&D Projects: GA MŠk ME10083 Institutional support: RVO:67985891 Keywords : Bohemian Massif * Uranium mineralization * Episyenite * Fluid inclusions Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.561, year: 2014

  13. U/Pb dating: brioverian age of the Erquy series (Armorican massif, France)

    International Nuclear Information System (INIS)

    Cocherie, A.; Chantraine, J.; Egal, E.; Fanning, C.M.; Dabard, M.P.; Paris, F.; Le Herisse, A.

    2001-01-01

    New U/Pb analyses obtained with a high-resolution ion microprobe (SHRIMP) fix an age of 608 ± 7 Ma for spilites of the Erquy series, in Cadomian rocks of the Armorican massif, France. This Neo-proterozoic age re-integrates this unit into the Brioverian, the age it was initially assigned to. A Rb/sr whole-rock dating in the 1970's had undermined the regional Cadomian model, by suggesting an Ordovician age for these rocks; this was apparently further supported by the discovery of organic remains, interpreted as Paleozoic micro-fossils. The reassessment of this paleontologic attribution and the new isotope dating are a final confirmation of the age of this series. (authors)

  14. Boundaries of mantle–lithosphere domains in the Bohemian Massif as extinct exhumation channels for high-pressure rocks

    Czech Academy of Sciences Publication Activity Database

    Babuška, Vladislav; Plomerová, Jaroslava

    2013-01-01

    Roč. 23, č. 3 (2013), s. 973-987 ISSN 1342-937X R&D Projects: GA ČR GA205/07/1088; GA ČR GAP210/12/2381; GA AV ČR IAA300120709 Institutional research plan: CEZ:AV0Z30120515 Keywords : Bohemian Massif * mantle lithosphere domains * fossil olivine fabric * high pressure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 8.122, year: 2013

  15. Unraveling P-T-t-D Evolution of Zermatt-Saas Ophiolites from Valtournanche: from Ocean Opening to Mountain Building

    Science.gov (United States)

    Rebay, G.; Tiepolo, M.; Zanoni, D.; Langone, A.; Spalla, M. I.

    2015-12-01

    The Zermatt-Saas (ZS) Zone, formerly part of Tethyan oceanic crust and variously affected by oceanic metamorphism, is now part of the orogenic suture that developed in the Western European Alps during the Alpine subduction and collision. The ZS rocks preserve a dominant HP to UHP metamorphic imprint overprinted by greenschist facies metamorphism. The age of the oceanic protoliths is considered to be middle to upper Jurassic whereas the HP metamorphism is mostly considered to be Eocene. In upper Valtournanche ZS ophiolites, the dominant regional S2 foliation is mapped with spatial continuity in serpentinite, metarodingite and eclogite and is defined by HP/UHP parageneses in all lithotypes. It developed at 2.5 ± 0.3 GPa and 600 ± 20°C during Alpine subduction. S2 foliation of serpentinites wraps rare clinopyroxene and zircon relics. Trace element composition of clinopyroxene suggests that they crystallised from a melt in equilibrium with plagioclase: they most likely represent relicts of gabbroic assemblages. The clinopyroxene porphyroclasts have rims indented within S2 and compositions similar to fine-grained clinopyroxeneII defining S2, suggesting that they recrystallised during Alpine subduction. Zircon cores show, under CL, sector zoning typical of magmatic growth. U-Pb dates suggest their crystallisation during Middle Jurassic. Magmatic cores have thin fringe overgrowths parallel to the S2 foliation. U-Pb concordant analyses on these domains reveal an Upper Cretaceous-Paleocene crystallization most likely representing the HP to UHP Alpine re-equilibration. This suggests that some sections of the ZS have experienced HP to UHP metamorphism earlier than previously thought, opening new interpretative geodynamic scenarios. Remarkably, these new dates are similar to those recorded for the HP re-equilibration in the continental crust of the adjacent Austroalpine units (upper plate of the Alpine subduction system) and to those recorded for prograde metamorphism in

  16. Evidence for partial melting of eclogite from the Moldanubian Zone of the Bohemian Massif, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Miyazaki, T.; Nakamura, D.; Tamura, A.; Svojtka, Martin; Arai, S.; Hirajima, T.

    2016-01-01

    Roč. 111, č. 6 (2016), s. 405-419 ISSN 1345-6296 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100131203 Program:Program interní podpory projektů mezinárodní spolupráce AV ČR Institutional support: RVO:67985831 Keywords : partial melting * eclogite * leucocratic pockets * Bohemian Massif * Moldanubian Zone Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.409, year: 2016

  17. Comprenhensive Program of Engineering and Geologic Surveys for Designing and Constructing Radioactive Waste Storage Facilities in Hard Rock Massifs

    International Nuclear Information System (INIS)

    Gupalo, T.; Milovidov, V.; Prokopoca, O.; Jardine, L.

    2002-01-01

    Geological, geophysical, and engineering-geological research conducted at the 'Yeniseisky' site obtained data on climatic, geomorphologic, geological conditions, structure and properties of composing rock, and conditions of underground water recharge and discharge. These results provide suficient information to make an estimate of the suitability of locating a radioactive waste (RW) underground isolation facility at the Nizhnekansky granitoid massif.

  18. Structure, emplacement, and tectonic setting of Late Devonian granitoid plutons in the Teplá–Barrandian unit, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Žák, J.; Kratinová, Zuzana; Trubač, J.; Janoušek, V.; Sláma, Jiří; Mrlina, Jan

    2011-01-01

    Roč. 100, č. 7 (2011), s. 1477-1495 ISSN 1437-3254 R&D Projects: GA AV ČR KJB300120702 Institutional research plan: CEZ:AV0Z30120515; CEZ:AV0Z30130516 Keywords : Bohemian Massif * Teplá-Barrandian unit * Variscan orogeny * granite * pluton * subduction Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.342, year: 2011

  19. Making a report of a short trip in an ophiolitic complex with Google Earth

    Science.gov (United States)

    Aubret, Marianne

    2017-04-01

    Plate tectonics is taught in French secondary school (lower and upper-sixth). According to the curriculum, the comprehension of plate-tectonic processes and concepts should be based on field data. For example, the Alpine's ocean history is studied to understand how mountain ranges are formed. In this context, Corsica is a great open-air laboratory, but unfortunately, the traffic conditions are very difficult in the island and despite the short distances, it's almost impossible for teachers to take their students to the remarkable geologic spots. The «défilé de l'Inzecca» is one of them: there you can see a part of the alpine's ophiolitic complex. The aim of this activity is to elaborate a « KMZ folder » in Google Earth as a report of a short trip thanks to the students' data field; it is also the occasion to enrich the Google Earth KMZ folder already available for our teaching.

  20. Rhenium-osmium isotopes in pervasively metasomatized mantle xenoliths from the Bohemian Massif and implications for the reliability of Os model ages

    Czech Academy of Sciences Publication Activity Database

    Kochergina, Y. V.; Ackerman, Lukáš; Erban, V.; Matusiak-Malek, M.; Puziewicz, J.; Halodová, P.; Špaček, P.; Trubač, J.; Magna, T.

    2016-01-01

    Roč. 430, July 15 (2016), s. 90-107 ISSN 0009-2541 Institutional support: RVO:67985831 Keywords : Bohemian Massif * depletion age * Ohře/Eger rift * Os isotopes * peridotite xenolith * Re-Os * sub-continental lithospheric mantle Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.347, year: 2016

  1. Gammarus orinos n. sp. from the Massif Central (France): its genetic and morphological distinction from Gammarus ibericus Margalef, 1951 (Crustacea, Amphipoda)

    NARCIS (Netherlands)

    Pinkster, Sjouk; Scholl, Adolf

    1984-01-01

    Until 1974 Gammarus ibericus was known only from the type-locality in Spain. In that year, Goedmakers recorded the species from many localities in the Massif Central, France. Indeed, these populations show a great morphological resemblance to the Spanish ones. These French populations were used in

  2. Coeval interaction between magmas of contrasting composition (Late Carboniferous-Early Permian Santa Eulália-Monforte massif, Ossa-Morena Zone): field relations and geochronological constraints

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, M.F.; Gama, C.; Rodríguez, C.

    2017-07-01

    The Santa Eulália-Monforte massif is a post-kinematic Late Carboniferous-Early Permian calc-alkaline composite massif (LC-EP) located in the Ossa-Morena Zone (OMZ, Portugal). This paper examines the field relationships between pinkish granites and mafic-intermediate rocks from the external ring of this massif and presents new U-Pb zircon age determinations. The estimated 206Pb/238U ages, 297±4Ma for the pinkish granite and 303±3Ma for a gabbro-diorite point to a short time interval between the crystallization of both magmas. At outcrop scale, contacts of the mafic-intermediate rocks with the host pinkish granite are sharp and corroborate this age relationship, but do not justify why the host-enclave contacts often has curved and irregular shapes, indicating liquid-liquid interaction. A full analysis of the distribution of U-Pb zircon ages and respective Th/U ratios suggests that the compositionally distinct magmas were roughly contemporaneous. The obtained ages also fit the LC-EP Iberian calc-alkaline suite that was formed contemporaneously to the development of the Iberian-Armorican Arc and when the Paleotethyan oceanic Plate subducted under the Eurasian active margin. Taking this geodynamic setting as a reference, the LC-EP Iberian calc-alkaline magmatism can be interpreted as most probably related to the Cimmerian cycle instead of the traditionally accepted model that ascribe a closer connection of this magmatism with the Variscan cycle. The Santa Eulália-Monforte massif is a post-kinematic Late Carboniferous-Early Permian calc-alkaline composite massif (LC-EP) located in the Ossa-Morena Zone (OMZ, Portugal). This paper examines the field relationships between pinkish granites and mafic-intermediate rocks from the external ring of this massif and presents new U-Pb zircon age determinations. The estimated 206Pb/238U ages, 297±4Ma for the pinkish granite and 303±3Ma for a gabbro-diorite point to a short time interval between the crystallization of both

  3. Coeval interaction between magmas of contrasting composition (Late Carboniferous-Early Permian Santa Eulália-Monforte massif, Ossa-Morena Zone): field relations and geochronological constraints

    International Nuclear Information System (INIS)

    Pereira, M.F.; Gama, C.; Rodríguez, C.

    2017-01-01

    The Santa Eulália-Monforte massif is a post-kinematic Late Carboniferous-Early Permian calc-alkaline composite massif (LC-EP) located in the Ossa-Morena Zone (OMZ, Portugal). This paper examines the field relationships between pinkish granites and mafic-intermediate rocks from the external ring of this massif and presents new U-Pb zircon age determinations. The estimated 206Pb/238U ages, 297±4Ma for the pinkish granite and 303±3Ma for a gabbro-diorite point to a short time interval between the crystallization of both magmas. At outcrop scale, contacts of the mafic-intermediate rocks with the host pinkish granite are sharp and corroborate this age relationship, but do not justify why the host-enclave contacts often has curved and irregular shapes, indicating liquid-liquid interaction. A full analysis of the distribution of U-Pb zircon ages and respective Th/U ratios suggests that the compositionally distinct magmas were roughly contemporaneous. The obtained ages also fit the LC-EP Iberian calc-alkaline suite that was formed contemporaneously to the development of the Iberian-Armorican Arc and when the Paleotethyan oceanic Plate subducted under the Eurasian active margin. Taking this geodynamic setting as a reference, the LC-EP Iberian calc-alkaline magmatism can be interpreted as most probably related to the Cimmerian cycle instead of the traditionally accepted model that ascribe a closer connection of this magmatism with the Variscan cycle. The Santa Eulália-Monforte massif is a post-kinematic Late Carboniferous-Early Permian calc-alkaline composite massif (LC-EP) located in the Ossa-Morena Zone (OMZ, Portugal). This paper examines the field relationships between pinkish granites and mafic-intermediate rocks from the external ring of this massif and presents new U-Pb zircon age determinations. The estimated 206Pb/238U ages, 297±4Ma for the pinkish granite and 303±3Ma for a gabbro-diorite point to a short time interval between the crystallization of both

  4. The timberline as result of the interactions among forest, abiotic environment and human activity in the Babia Gora massif, Western Carpathians

    Science.gov (United States)

    Lajczak, Adam

    2016-04-01

    The timberline is one of the clearest and most easily discernible boundaries in nature (Troll 1973). Among the existing conceptual models clarifying the complex nature of the relationship between the timberline and the environment and human impact, the fullest seems to be the one presented by K. Holtmeier (2009). The quoted author comprehensively characterizes the timberline, taking into account its course, appearance and ecological characteristics. The aim of the work is to quantitatively assess the factors influencing the course of timberline and its changes over the last ca. 400 years in the Babia Góra massif (1725 m a.s.l.), the highest flysch ridge in the Western Carpathians, which is formed as an asymmetric ridge of kuesta type. Forests mainly in the upper montane zone have preserved their natural character in many areas. Old spruce tree growths are a particular advantage of the Babia Góra Mt., being there on the predominant section of the altitude zone of the timberline. In the rest of this zone, spruce forests have been under a direct or indirect influence of changes resulting from grazing with its 400-year history and forestry taking place about 100 years ago. The 60 m difference between the average altitude of the timberline on the northern (1335 m a.s.l.) and the southern slope (1395 m a.s.l.) on the Babia Góra Mt. can be explained with climatic conditions of these areas. The average gradient of the slope within the timberline ecotone on the southern slope of the massif is by 100 smaller, and the amount of solar energy delivered during the growing season is 40% higher (960 kWh/m2) than on the northern slope. The higher position of the timberline on the windward southern slope is favored by the dominant winds from S-W sector, thinner snow cover and earlier melting due to the lower precipitation on the slope and also due to the winnowing of snow onto the steep northern slope of the ridge. On the southern slope of the ridge there are no larger snow

  5. Developing the lithotectonic framework and model for sulphide mineralization in the Jebilet Massif, Morocco: implications for regional exploration

    OpenAIRE

    Lusty, Paul A.J.; Goodenough, Kathryn M.; Essaifi, Abderrahim; Maacha, Lhou

    2015-01-01

    The central Jebilet massif, part of the North African Variscan Belt, hosts significant polymetallic sulphide mineralization. It is generally considered syngenetic and has many features of volcanogenic massive sulphide (VMS) mineralization. However, some characteristics are not compatible with a classic VMS model and two alternative scenarios for formation have been proposed. Our preliminary research favours a complex, multi-stage development of the sulphide deposits...

  6. Iron transformations during low temperature alteration of variably serpentinized rocks from the Samail ophiolite, Oman

    Science.gov (United States)

    Mayhew, Lisa E.; Ellison, Eric T.; Miller, Hannah M.; Kelemen, Peter B.; Templeton, Alexis S.

    2018-02-01

    Partially serpentinized peridotites in the Samail ophiolite in the Sultanate of Oman currently undergo low temperature alteration and hydration both at shallow levels, with water recently in contact with the atmosphere, and at depth, with anoxic, reducing fluids. However, it is unclear how changes in the distribution and oxidation state of Fe are driving the production of energy-rich gases such as hydrogen and methane detected in peridotite catchments. We track the Fe transformations in a suite of outcrop samples representing a subset of the spectrum of least to most altered end-members of the Oman peridotites. We use microscale mineralogical and geochemical analyses including QEMSCAN, Raman spectroscopy, synchrotron radiation X-ray fluorescence (XRF) mapping, and electron microprobe wavelength dispersive spectroscopy. The less-altered peridotites possess a diversity of Fe-bearing phases including relict primary minerals (e.g. olivine, pyroxene, chromite) and secondary phases (e.g. serpentine and brucite). Raman spectroscopy and electron microprobe data (Si/(Mg + Fe)) indicate that much of the serpentine is significantly intergrown with brucite on the sub-micron scale. These data also indicate that the Fe content of the brucite ranges from 10 to 20 wt% FeO. The mineral assemblage of the highly reacted rocks is less diverse, dominated by serpentine and carbonate while olivine and brucite are absent. Magnetite is relatively rare and mainly associated with chromite. Goethite and hematite, both Fe(III)-hydroxides, were also identified in the highly altered rocks. Whole rock chemical analyses reflect these mineralogical differences and show that Fe in the partially serpentinized samples is on average more reduced (∼0.40-0.55 Fe3+/FeTotal) than Fe in the highly reacted rocks (∼0.85-0.90 Fe3+/FeTotal). We propose that olivine, brucite, chromite and, perhaps, serpentine in the less-altered peridotites act as reactive phases during low temperature alteration of the Oman

  7. Crystallization Temperatures of Lower Crustal Gabbros from the Oman Ophiolite and the Persistence of the 'Mush Zone' at Intermediate/Fast Spreading Ridges

    Science.gov (United States)

    VanTongeren, J. A.

    2017-12-01

    Oceanic crust is formed when mantle-derived magmas are emplaced at the ridge axis, a zone of intense rifting and extension. Magmas begin to cool and crystallize on-axis, forming what is termed the "Mush Zone", a region of partially molten rocks. Several attempts have been made to understand the nature of the Mush Zone at fast spreading mid-ocean ridges, specifically how much partial melt exists and how far off-axis the Mush Zone extends. Geophysical estimates of P-wave velocity perturbations at the East Pacific Rise show a region of low velocity approximately 1.5-2.5 km off-axis, which can be interpreted to be the result of higher temperature [e.g. Dunn et al., 2000, JGR] or the existence of partial melt. New petrological and geochemical data and methods allow for the calculation of the lateral extent of the Mush Zone in the lower oceanic crust on exposed sections collected from the Oman ophiolite, a paleo-fast/intermediate spreading center. I will present new data quantifying the crystallization temperatures of gabbros from the Wadi Khafifah section of lower oceanic gabbros from the Oman ophiolite. Crystallization temperatures are calculated with the newly developed plagioclase-pyroxene REE thermometer of Sun and Liang [2017, Contrib. Min. Pet.]. There does not appear to be any systematic change in the crystallization temperature of lower crustal gabbros with depth in the crust. In order to quantify the duration of crystallization and the lateral extent of the Mush Zone of the lower crust, crystallization temperatures are paired with estimates of the solidus temperature and cooling rate determined from the same sample, previously constrained by the Ca diffusion in olivine geothermometer/ geospeedometer [e.g. VanTongeren et al., 2008 EPSL]. There is no systematic variation in the closure temperature of Ca in olivine, or the cooling rate to the 800°C isotherm. These results show that gabbros throughout the lower crust of the Oman ophiolite remain in a partially

  8. Using Telepresence to Connect and Engage Classes and the Public in the Exploration of Tamu Massif, the World's Largest Single Volcano

    Science.gov (United States)

    Nanez-James, S. E.; Sager, W.

    2016-02-01

    Research published in 2013 showed that TAMU Massif, the largest mountain in the Shatsky Rise oceanic plateau, located approximately 1500 kilometers east of Japan, is the "World's Largest Single Volcano." This claim garnered widespread public interest and wonder concerning how something so big could remain so mysterious in the 21st century. This disconnect highlights the fact that oceans are still widely unexplored, especially the middle of the deep ocean. Because there is so much interest in TAMU Massif, a diverse outreach team lead by chief scientist Dr. William Sager from the University of Houston in partnership with the Texas State Aquarium and the Schmidt Ocean Institute (SOI) conducted a multifaceted ship-to-shore outreach project that included secondary school students, formal and informal educators, university students and professors, the aquarium and museum audience, and the general public. The objective was to work in conjunction with SOI and various other partners, including the Texas Regional Collaborative, the Aquarium of the Pacific, and the Houston Museum of Natural Science, to promote science and ocean literacy while inspiring future scientists - especially those from underserved and underrepresented groups - through ocean connections. Participants were connected through live ship-to-shore distance learning broadcasts of ongoing marine research and discovery of TAMU Massif aboard the R/V Falkor, allowing audiences to participate in real-time research and apply real world science to curriculum in the classrooms. These ship-to-shore presentations connected to existing curriculums and standards, lessons, and career interests of the students and educators with special teacher events and professional development workshops conducted from aboard the R/V Falkor.

  9. Peculiarity of rock massif deformation under explosion impact (by the example of Zarechie area of the Semipalatinsk Test Site)

    International Nuclear Information System (INIS)

    Gorbunova, Eh.M.

    2003-01-01

    The paper systematize the results of study of man-caused situation formed outside the central zone of underground nuclear explosion (CZ UNE), at a testing area of the Semipalatinsk Test Site (STS) - Zarechie. The consequence effects of nuclear testing appeared in the rock massif and on the ground surface in the radius of 0.3-5 km from event epicenter are described. (author)

  10. Constraints on the origin of gabbroic rocks from the Moldanubian-Moravian units boundary (Bohemian Massif, Czech Republic and Austria)

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Ackerman, Lukáš; Kachlík, V.; Hegner, E.; Balogh, K.; Langrová, Anna; Luna, J.; Fediuk, F.; Lang, M.; Filip, Jiří

    2010-01-01

    Roč. 61, č. 3 (2010), s. 175-191 ISSN 1335-0552 R&D Projects: GA AV ČR IAA3013403; GA AV ČR IAA300130902 Institutional research plan: CEZ:AV0Z30130516 Keywords : gabbroic rocks * geochemistry * Sr-Nd isotopes * K-Ar ages * Moravian Unit * Moldanubian Unit * Bohemian Massif Subject RIV: DD - Geochemistry Impact factor: 0.909, year: 2010

  11. Mineral chemistry and geothemobarometry of mantle harzburgites in the Eastern Metamorphic Complex of Khoy ophiolite -NW Iran

    Directory of Open Access Journals (Sweden)

    Morovvat Faridazad

    2017-02-01

    Full Text Available Introduction Khoy ophiolite at the global scale is in the middle part of the Alp-Himalaya orogenic belt and it is extended over 3900 Km2 which indicates remnant Neotethys oceanic lithosphere in the Mesozoic era (Kananian et al., 2010. In this paper, in addition to a review of previous investigations about Khoy ophiolite, we will try to determine the nature and kind of minerals, origin and partial melting rate as well as the equilibrium pressure and temperature of harzburgites from the Eastern Metamorphic Complex of Khoy ophiolite. Materials and methods Thin sections microscopy studies were carried out following field investigations. EPMA analysis was carried out with using a Superprobe JEOL, JXA 8200 Microprobe unit at the state of WDS and under condition of 15kv accelerating voltage, 10nA current beam, 1µm beam diameter and collection of natural and synthetic standards for calibration. Results The study area is located at the NW of Iran and north of the Khoy city in the west Azarbaijan province. This area is part of the ophiolitic complex of NW Iran and belongs to its Eastern Metamorphic Complex. This metamorphic zone has large tectonically segments of the metamorphic ophiolites which mainly include serpentinized peridotites with associated metagabbros. There are three types of peridotitic rocks in this area which are: Lherzolites, harzburgites and dunites. Lherzolites are composed of olivine (60-70%, orthopyroxene (10-30% and clinopyroxene (~10-20% with minor amounts (~2% of Cr-spinel mineral. Harzburgites are composed of olivine (70-80%, orthopyroxene (10-20% and clinopyroxene (~5% with minor amounts (~2% of Cr-spinel mineral. Dunites are composed of olivine (90-95%, orthopyroxene (5-10% with minor amounts (~1-2% of Cr-spinel mineral. Composition range of olivines is between Fo89.46 Fa10.37 to Fo89.86 Fa10.0 as well as NiO content range is 018-046 (wt %. The calculated Mg# of olivines is 0.90 and the composition of olivines in Fo-Fa diagram

  12. Seismic refraction technique aplications in the geotechnical characterization of the Cachoeira deposit massif, Caetite, State of Bahia, Brazil

    International Nuclear Information System (INIS)

    Malagutti Filho, W.; Oliveira Braga, T. de.

    1984-01-01

    Geophysical surveys throught the Cachoeira Uranium deposit massif were carried out with the purpose of assisting in the geotechnical characterization for the implantation of the Mining-Industrial Complex projects on the Lagoa Real uranium deposits, Caetite municipality, state of Bahia, Brazil. This study discusses the methodology utilized in the geophysical surveys and their results as well as their applications to the geotechnical characterization as a whole. (D.J.M.) [pt

  13. Multiple fluid sources/pathways and severe thermal gradients during formation of the Jílové orogenic gold deposit, Bohemian Massif, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Zachariáš, J.; Žák, Karel; Pudilová, M.; Snee, L. W.

    2013-01-01

    Roč. 54, October (2013), s. 81-109 ISSN 0169-1368 Institutional research plan: CEZ:AV0Z30130516 Institutional support: RVO:67985831 Keywords : Orogenic gold deposits * Carbon isotopes * Oxygen isotopes * Bismuth * Age * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.383, year: 2013

  14. Sulphide mineralization and wall-rock alteration in ophiolites and modern oceanic spreading centres

    Science.gov (United States)

    Koski, R.A.

    1983-01-01

    Massive and stockwork Fe-Cu-Zn (Cyprus type) sulphide deposits in the upper parts of ophiolite complexes represent hydrothermal mineralization at ancient accretionary plate boundaries. These deposits are probable metallogenic analogues of the polymetallic sulphide deposits recently discovered along modern oceanic spreading centres. Genetic models for these deposits suggest that mineralization results from large-scale circulation of sea-water through basaltic basement along the tectonically active axis of spreading, a zone of high heat flow. The high geothermal gradient above 1 to 2 km deep magma chambers emplaced below the ridge axis drives the convective circulation cell. Cold oxidizing sea-water penetrating the crust on the ridge flanks becomes heated and evolves into a highly reduced somewhat acidic hydrothermal solvent during interaction with basaltic wall-rock. Depending on the temperature and water/rock ratio, this fluid is capable of leaching and transporting iron, manganese, and base metals; dissolved sea-water sulphate is reduced to sulphide. At the ridge axis, the buoyant hydrothermal fluid rises through permeable wall-rocks, and fluid flow may be focussed along deep-seated fractures related to extensional tectonic processes. Metal sulphides are precipitated along channelways as the ascending fluid undergoes adiabatic expansion and then further cooling during mixing with ambient sub-sea-floor water. Vigorous fluid flow results in venting of reduced fluid at the sea-floor/sea-water interface and deposition of massive sulphide. A comparison of sulphide mineralization and wall-rock alteration in ancient and modern spreading centre environments supports this genetic concept. Massive sulphide deposits in ophiolites generally occur in clusters of closely spaced (stacked sequences of pillow basalt and sheet flows, the sea-floor underlying numerous deposits in Guaymas Basin consists of diatomaceous ooze and terrigenous clastic sediment that is intruded by diabase

  15. Use of Digital Elevation Models to understand map landforms and history of the magmatism Khibiny Massif (Kola Peninsula, Russia)

    Science.gov (United States)

    Chesalova, Elena; Asavin, Alex

    2016-04-01

    This work presents an improved geomorphological methodology that uses 3D model of relief, remotely-sensed data, geological, geophysical maps and tools of Geographical Information Systems. On the basis of maps of 1: 50,000 and 1: 200,000 the Digital Elevation model (DEM) of Khibiny massif was developed. We used software ARC / INFO v10.2 ESRI. A DEM was used for analyzing landform by extracting the slope gradient, curvature, valley pro?les, slope, aspect and so on. The results were gradually re?ned from the interpretation of satellite imagery and geological map Geomorphological analysis will allow us to determine spatial regularities in inner massive construction. We try to found areas where gas emissions (CH4/H2) enrich, according to morphometry, geology, tectonic and other environments. The main regional blocks were de?ned by different morphological evidences: impression zone, similar to subsidence caldera; uplift zone, domed area (located in the highest part of massif and zone of intersection of main faults) and others. It says that there are the few stages in the development of the Khibiny massif. There is no common concept of the consequence of intrudes magmatic phases now. And we hope that our geomorphical analysis take a new evidences about this problems. Locations of the blocks' borders (tectonic zones) were recognized by lineament analysis of valleys and tectonic faults presented in relief. Erosion system is represented by valleys of 4 ranks. It inherits the zone of tectonic disturbances 3 groups of faults were recognized: 1) Global lineament system cross whole peninsula - existing before Khibiny massif intrusion; 2) Faults associated with the formation of the intrusive phases sequence and magma differentiation and with later collision history during magma cooling; 3) Crack system related to neotectonic process. We believed that if different magmatic phases intrude in similar tectonic environment, the common spatial system of faults will be formed. Really we

  16. Geochemical and Mineralogical Profiles Across the Listvenite- Metamorphic Transition in the Basal Megathrust of the Oman Ophiolite: First Results from Drilling at Oman Drilling Project Hole BT1B

    Science.gov (United States)

    Godard, M.; Bennett, E.; Carter, E.; Kourim, F.; Lafay, R.; Noël, J.; Kelemen, P. B.; Michibayashi, K.; Harris, M.

    2017-12-01

    The transition from the base of the Oman ophiolite to the underlying metamorphic sole was drilled at Hole BT1B (Sumail Massif) during Phase 1 of Oman Drilling Project (Winter 2016-2017). 74 samples were collected from the 300m of recovered cores for whole rock geochemical and XRD analyses. 55 listvenites, ophicarbonates and serpentinites, and 19 schists and greenstones were analyzed for major and minor elements (XRF) and for CO2 and S concentrations (CHNS) aboard DV Chikyu (ChikyuOman, Summer 2017). Analyses for trace elements (ICP-MS) at the University of Montpellier are in progress. The composition of listvenites, ophicalcites and serpentinites recovered at Hole BT1B record extensive interactions between CO2-rich fluids and the serpentinized peridotites. These reactions involved addition of SiO2 and formation of carbonates at the expense of the serpentinized peridotite protolith. All samples recovered from the mantle section are enriched in fluid mobile and incompatible trace elements compared to the mean composition of the Oman mantle. These enrichments are up to 103 times the Oman mantle for Rb and Ba. They mimic the pattern of the samples from the metamorphic sole. This suggests that the composition of the listvenites in these elements is controlled by that of contaminating fluids that may have originated in the same lithologies as those drilled at the base of Hole BT1B. Listvenites, ophicalcites and serpentinites also show notable downhole chemical variations, with listvenites showing marked variations in Al2O3 and TiO2. Occurrence of lherzolites and cpx-harzburgites has been reported at the base of the Oman dominantly harzburgitic mantle section. The observed variations in the listvenites (Al2O3 and TiO2) could be related to the composition of their protolith, the deepest having more fertile compositions. Alternatively, the observed downhole changes in the composition of listvenites may relate to the progressive equilibration of the reacting ultramafic

  17. Forecast of promising areas for uranium prospection at the metamorphic Massif of Isla de la Juventud

    International Nuclear Information System (INIS)

    Gongora, L.E.; Macola, E.; Sanchez, J.; Torres, J.C.; Alaminos, C.; LLanes, A.; Morales, M.

    1995-01-01

    A mineralization conceptual model for uranium of the metamorphic Massif of Isla de la Juventud was established taking into account the study of the geological and metallogenic characteristic of the territory. The determined indications of mineralization were plotted on the geological map in order to conform a forecasting map and the selection of 22 hypothetical promising areas was carried out. As result of the field words three really promising areas were selected. A group of exploration techniques needed to evaluate the targets areas is presented

  18. The Nysa-Morava Zone: an active tectonic domain with Late Cenozoic sedimentary grabens in the Western Carpathians' foreland (NE Bohemian Massif)

    Czech Academy of Sciences Publication Activity Database

    Špaček, P.; Bábek, O.; Štěpančíková, Petra; Švancara, J.; Pazdírková, J.; Sedláček, J.

    2015-01-01

    Roč. 104, č. 4 (2015), s. 963-990 ISSN 1437-3254 R&D Projects: GA ČR GAP210/12/0573; GA MŠk LM2010008 Institutional support: RVO:67985891 Keywords : Bohemian Massif * Upper Morava Basin * tectonic evolution * seismicity * sedimentary grabens Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.133, year: 2015

  19. Geochemical, petrological and geochronological observations on the metamorphic rocks of the Tauride belt ophiolites (S. Turkey)

    OpenAIRE

    Celik, Omer Faruk

    2002-01-01

    La chaîne du Taurus (sud de la Turquie) comprend une succession de massifs ophiolitiques. Chacun d'eux possède une semelle métamorphique. Les principales roches constituant ces semelles sont des amphibolites qui se caractérisent, grâce à la géochimie des éléments en traces et des Terres Rares, en basaltes d'îles océaniques, en tholéites d'arcs ou en basaltes de rides. Ces roches sont regroupées par des filons doléritiques et gabbroïques tardifs. L'étude géothermobarométrique montre que ces am...

  20. La couverture tertiaire du flanc nord du massif du Troodos et de la partie méridionale de la Mésaoria : étude stratigraphique et micropaléontologique The Terciary Sediments of the Northern Flank of the Stroodos Massif and the Southern Part of Mesaoria : Stratigraphic and Micropaleonlogical Study

    Directory of Open Access Journals (Sweden)

    Baroz F.

    2006-11-01

    Full Text Available Le massif pluto-volcanique du Troodos est ceinturé par une importante série sédimentaire le plus souvent à dominante crayeuse dont l'âge va du Maestrichtien au Messinien, époque à laquelle le Troodos émerge. La mer revient en transgression au Pliocène. Après une recherche bibliographique réinterprétant les principaux résultats des travaux antérieurs, une étude pétrographique, micropaléontologique et stratigraphique est réalisée à partir des échantillons recueillis suivant treize profils, sur le flanc N du Troodos et dans la partie méridionale de la Mésaoria. Cette étude montre que les craies résultent de la lithification de boues à Globigérinidés redéposées dans lesquelles les figures de courant et les slumps sont nombreux. Ces dépôts, qui s'organisent en un système progradantà partir du haut fond sous-marin du Troodos, forment sur son flanc N une série condensée présentant de nombreux et souvent spectaculaires hiatus stratigraphiques. Elle caractérise un environnement qui, bathyal inférieur au Maestrichtien-Paléocène, évolue en un milieu de dépôt néritique au Messinien. The plutonic-volcanic Troodos Massif is surrounded by thick sedimentory series, often developed in a predominantly chalky facies ; their age ranges from Maastrichtian to Messinian during which period the Troodos Massif emerged. The sea transgressively returned in Pliocene times. Hoving studied the references which lead to a reinterpretation of the main findings of previous investigations, a petrogrophic, micropaleontological and stratigrophic study of rock somples hos been made, gathered along thirteen profiles on the northern flank of the Troodos Massif and in the southern part of Mesaoria. The study reveals that the chalky resulted from a lithification of redeposited glogigerina oozes, showing numerous current marks and slump structures. These progroding deposits laid down on a Troodos seamount at the time, form a condensed series

  1. Joint inversion of teleseismic P waveforms and surface-wave group velocities from ambient seismic noise in the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Růžek, Bohuslav; Plomerová, Jaroslava; Babuška, Vladislav

    2012-01-01

    Roč. 56, č. 1 (2012), s. 107-140 ISSN 0039-3169 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709; GA MŠk LM2010008 Institutional research plan: CEZ:AV0Z30120515 Keywords : receiver function * seismic noise * joint inversion * Bohemian Massif * velocity structure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.975, year: 2012

  2. Les variations récentes (1975-2000 de l’englacement dans le Massif de l’Aconcagua (Mendoza, Argentine

    Directory of Open Access Journals (Sweden)

    Julie Le Gall

    2008-03-01

    Full Text Available La région de Mendoza est particulièrement vulnérable au réchauffement climatique. Les glaciers du massif de l’Aconcagua ont amorcé un important retrait depuis la fin du Petit Âge de Glace. Or la disparition de ces glaciers risque d’entraîner une modification des régimes hydrologiques qui, jusqu’à présent, se caractérisaient par de hautes eaux estivales. Ce pic estival pourrait à l’avenir être atténué et remettre en cause les stratégies de gestion de la ressource en eau. Nous faisons ici le point sur les variations récentes de l’englacement et tentons de dessiner un scénario prospectif.Mendoza area is highly vulnerable to the global warming. The glaciers of the Aconcagua massif are currently shrinking, this trend of retreat began at the end of the Little Ice Age. The disappearance of glaciers may modify hydrological regimes. The discharge is currently at maximum during summer (related to glacier melt, but the peak discharge may occur during spring (related to snow melt in the next future. In this paper we synthesize the recent variations of the glaciers and propose a pattern of future variations.

  3. Late Hercynian volcanic and hypovolcanic phenomena in South of the French Massif Central. Associated mineralization: U, F, Ba, Pb, Zn, Sn, W

    International Nuclear Information System (INIS)

    Badia; Fuchs

    1983-01-01

    Volcanism of the Stephanian period produced lava rich in potassium and fluorine with mineralization of U, F, Sn, W without Mo in the French Massif Central. Permian volcanism and associated magmatism are reviewed. Studied elements allow the characterization of their thermalism. These mineralizations are important for prospection [fr

  4. Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history?

    Science.gov (United States)

    Jedlicka, Radim; Faryad, Shah Wali

    2017-08-01

    High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite

  5. Les dykes basiques du massif ancien de l'Ourika (Atlas de Marrakech, Maroc): géochimie et significationThe basic dykes of the Ourika old massif (High Atlas of Marrakech): Geochemistry and significance

    Science.gov (United States)

    Barakat, Ahmed; Marignac, Christian; Bouabdelli, Mohamed

    The Precambrian massif of Ourika is crosscut by two systems of basic dykes, striking N40°E and N90-120°E. Using incompatible trace elements, the two systems form two distinct chemical groups, displaying a continental tholeiitic affinity. The composition variations between the two defined groups can be due to heterogeneities of mantle sources and to contamination, during the magma ascent, by the continental crust. The emplacement of these basic dykes, before the late-PIII formations, can be related to the Neoproterozoic distension generalised to the Anti-Atlas chain. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 827-833.

  6. Tectonic strain changes affecting the development of deep seated gravitational slope deformations in the Bohemian Massif and Outer Western Carpathians

    Czech Academy of Sciences Publication Activity Database

    Stemberk, Josef; Hartvich, Filip; Blahůt, Jan; Rybář, Jan; Krejčí, O.

    2017-01-01

    Roč. 289, SI (2017), s. 3-17 ISSN 0169-555X R&D Projects: GA MŠk(CZ) LG15007; GA MŠk(CZ) LM2015079 Institutional support: RVO:67985891 Keywords : Deep seated gravitational slope deformations * Displacement monitoring * Tectonic strain changes * Bohemian Massif * Outer Western Carpathians Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.958, year: 2016

  7. Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

    Directory of Open Access Journals (Sweden)

    Argyrios Kapsiotis

    2016-11-01

    Full Text Available Several small chromium (Cr ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al = 0.51–0.66] and Mg# [Mg/(Mg + Fe2+ = 0.58–0.76], low Fe3+# [Fe3+/(Fe3+ + Fe2+ ≤ 0.43] and low TiO2 (≤0.21 wt % content. This composition is characteristic of Cr-spinels in equilibrium with melts of intermediate affinity between island-arc tholeiites (IATs and mid-ocean ridge basalts (MORBs. Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe3+# generally increase (0.68–0.87, 0.78–0.88 and 0.55–0.80, respectively, whereas from the core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe3+# generally decrease (0.45–0.74 and ≤0.51, correspondingly. The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (≤30 μm, subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO2 intermediate to mafic

  8. Pleistocene speleothem fracturing in the foreland of the Western Carpathians: a case study from the seismically active eastern margin of the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Bábek, O.; Briestenský, Miloš; Přecechtělová, G.; Štěpančíková, Petra; Hellstrom, J.C.; Drysdale, R.N.

    2015-01-01

    Roč. 59, č. 3 (2015), s. 491-506 ISSN 1641-7291 R&D Projects: GA ČR GAP210/12/0573 Institutional support: RVO:67985891 Keywords : speleothems * U/Th series dating * palaeoseismicity * Pleistocene * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.858, year: 2015

  9. Three-dimensional velocity model of the crust of the Bohemian Massif and its effects on seismic tomography of the upper mantle

    Czech Academy of Sciences Publication Activity Database

    Karousová, Hana; Plomerová, Jaroslava; Babuška, Vladislav

    2012-01-01

    Roč. 56, č. 1 (2012), s. 249-267 ISSN 0039-3169 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709 Institutional research plan: CEZ:AV0Z30120515 Keywords : crustal structure * seismic methods * Bohemian Massif * teleseismic tomography Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.975, year: 2012

  10. Cenozoic extensional tectonics of the Western Anatolia Extended Terrane, Turkey

    International Nuclear Information System (INIS)

    Cemen, I; Catlos, E J; Gogus, O; Diniz, E; Hancer, M

    2008-01-01

    The Western Anatolia Extended Terrane in Turkey is located on the eastern side of the Aegean Extended Terrane and contains one of the largest metamorphic core complexes in the world, the Menderes massif. It has experienced a series of continental collisions from the Late Cretaceous to the Eocene during the formation of the Izmir-Ankara-Erzincan suture zone. Based our field work and monazite ages, we suggest that the north-directed postcollisional Cenozoic extension in the region is the product of three consecutive stages, triggered by three different mechanisms. The first stage was initiated about 30 Ma ago, in the Oligocene by the Orogenic Collapse the thermally weakened continental crust along the north-dipping Southwest Anatolian shear zone. The shear zone was formed as an extensional simple-shear zone with listric geometry at depth and exhibits predominantly normal-slip along its southwestern end. But, it becomes a high-angle oblique-slip shear zone along its northeastern termination. Evidence for the presence of the shear zone includes (1) the dominant top to the north-northeast shear sense indicators throughout the Menderes massif, such as stretching lineations trending N10E to N30E; and (2) a series of Oligocene extensional basins located adjacent to the shear zone that contain only carbonate and ophiolitic rock fragments, but no high grade metamorphic rock fragments. During this stage, erosion and extensional unroofing brought high-grade metamorphic rocks of the Central Menderes massif to the surface by the early Miocene. The second stage of the extension was triggered by subduction roll-back and associated back-arc extension in the early Miocene and produced the north-dipping Alasehir and the south-dipping Bueyuek Menderes detachments of the central Menderes massif and the north-dipping Simav detachment of the northern Menderes massif. The detachments control the Miocene sedimentation in the Alasehir, Bueyuek Menderes, and Simav grabens, containing high

  11. Lithosphere destabilization by melt percolation during pre-oceanic rifting: Evidence from Alpine-Apennine ophiolitic peridotites

    Science.gov (United States)

    Piccardo, Giovanni; Ranalli, Giorgio

    2017-04-01

    Orogenic peridotites from Alpine-Apennine ophiolite Massifs (Lanzo, Voltri, External and Internal Ligurides, - NW Italy, and Mt. Maggiore - Corsica) derive from the mantle lithosphere of the Ligurian Tethys. Field/structural and petrologic/geochemical studies provide constraints on the evolution of the lithospheric mantle during pre-oceanic passive rifting of the late Jurassic Ligurian Tethys ocean. Continental rifting by far-field tectonic forces induced extension of the lithosphere by means of km-scale extensional shear zones that developed before infiltration of melts from the asthenosphere (Piccardo and Vissers, 2007). After significant thinning of the lithosphere, the passively upwelling asthenosphere underwent spinel-facies decompression melting along the axial zone of the extensional system. Silica-undersaturated melt fractions percolated through the lithospheric mantle via diffuse/focused porous flow and interacted with the host peridotite through pyroxenes-dissolving/olivine-precipitating melt/rock reactions. Pyroxene dissolution and olivine precipitation modified the composition of the primary silica-undersaturated melts into derivative silica-saturated melts, while the host lithospheric spinel lherzolites were transformed into pyroxene-depleted/olivine-enriched reactive spinel harzburgites and dunites. The derivative liquids interacted through olivine-dissolving/orthopyroxene+plagioclase-crystallizing reactions with the host peridotites that were impregnated and refertilized (Piccardo et al., 2015). The saturated melts stagnated and crystallized in the shallow mantle lithosphere (as testified by diffuse interstitial crystallization of euhedral orthopyroxene and anhedral plagioclase) and locally ponded, forming orthopyroxene-rich/olivine-free gabbro-norite pods (Piccardo and Guarnieri, 2011). Reactive and impregnated peridotites are characterized by high equilibration temperatures (up to 1250 °C) even at low pressure, plagioclase-peridotite facies

  12. Paleomagnetism of Jurassic radiolarian chert above the Coast Range ophiolite at Stanley Mountain, California, and implications for its paleogeographic origins

    Science.gov (United States)

    Hagstrum, J.T.; Murchey, B.L.

    1996-01-01

    Upper Jurassic red tuffaceous chert above the Coast Range ophiolite at Stanley Mountain, California (lat 35??N, long 240??E), contains three components of remanent magnetization. The first component (A; removed by ???100-???200 ??C) has a direction near the present-day field for southern California and is probably a recently acquired thermoviscous magnetization. A second component (B; removed between ???100 and ???600 ??C) is identical to that observed by previous workers in samples of underlying pillow basalt and overlying terrigenous sedimentary rocks. This component has constant normal polarity and direction throughout the entire section, although these rocks were deposited during a mixed polarity interval of the geomagnetic field. The B magnetization, therefore, is inferred to be a secondary magnetization acquired during accretion, uplift, or Miocene volcanism prior to regional clockwise rotation. The highest temperature component (C; removed between ???480 and 680 ??C) is of dual polarity and is tentatively interpreted as a primary magnetization, although it fails a reversal test possibly due to contamination by B. Separation of the B and C components is best shown by samples with negative-inclination C directions, and a corrected mean direction using only these samples indicates an initial paleolatitude of 32??N ?? 8??. Paleobiogeographic models relating radiolarian faunal distribution patterns to paleolatitude have apparently been incorrectly calibrated using the overprint B component. Few other paleomagnetic data have been incorporated in these models, and faunal distribution patterns are poorly known and mostly unqualified. The available data, therefore, do not support formation of the Coast Range ophiolite at Stanley Mountain near the paleoequator or accretion at ???10??N paleolatitude, as has been previously suggested based on paleomagnetic data, but indicate deposition near expected paleolatitudes for North America (35??N ?? 4??) during Late Jurassic

  13. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

    Science.gov (United States)

    Bonin, Bernard; Tatu, Mihai

    2016-08-01

    The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

  14. The Blaník Gneiss in the southern Bohemian Massif (Czech Republic): a rare rock composition among the early palaeozoic granite of Variscan Central Europe

    Czech Academy of Sciences Publication Activity Database

    René, Miloš; Finger, F.

    2016-01-01

    Roč. 110, č. 4 (2016), 503-514 ISSN 0930-0708 R&D Projects: GA MŠk ME 555 Institutional support: RVO:67985891 Keywords : leucogranite * turmaline * petrology * geochemistry * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.236, year: 2016

  15. Geology and uranium occurrences in the Forez tertiary plain (in the French 'Massif Central')

    International Nuclear Information System (INIS)

    Duclos, P.

    1967-01-01

    In the first part, the observations made during the geological survey of the Forez Tertiary plain (in the French 'Massif Central') are recalled. Then, using various methods, the author lists the formations according to chronology. Finally, a reconstitution of the geological history of this subsidence basin is attempted. In the second part, the occurrence of 17 uranium bearing geochemical anomalies is commented upon. Each of these various anomalies is given a place on the stratigraphic scale. This enables the author to put the successive phases of uranium deposition into their proper perspective in the history of the plain. In conclusion, the author points out the usefulness of these uraniferous geochemical anomalies. (author) [fr

  16. Petrology of the gabbro and sheeted basaltic intrusives at North Cape, New Zealand

    International Nuclear Information System (INIS)

    Hopper, D.J.; Smith, I.E.M.

    1996-01-01

    The North Cape massif consists of a semi-conformable sequence of serpentinite, gabbro, sheeted sill and dike units, and pillow lavas. Although structurally disrupted, they can be interpreted in terms of an idealised ophiolite sequence and represent the most complete sequence in the Northland Ophiolite. Their age is considered to be Late Cretaceous-Paleocene on the basis of microfossils in associated sediments. Early Miocene K-Ar ages from igneous rocks are thought to reflect the time of emplacement as a thrust sheet of oceanic crust and upper mantle. The gabbros are divided into a lower unit characterised by well-developed cumulate layering and an upper unit which is massive; the sheeted sills and dikes are quartz-diorite and microgabbro interleaved with minor pillow lava. Two phases of alteration are observed, a pervasive low-grade greenschist metamorphism attributed to sea-water interaction after formation as oceanic crust, and an overprinting zeolitic alteration which is possibly post-emplacement. Their tholeiitic nature as well as overlapping geochemical compositions suggest that the gabbros and sheeted dikes and sills represent different components of a single magmatic system related by simple fractionation processes. Several lines of evidence suggest that the magmas that formed the North Cape gabbro and sheeted intrusives have subduction-related chemical characteristics. In the gabbro, calcic plagioclase (An 86-92 ) and depleted Zr and Y abundances, and in the sheeted intrusives depleted high field strength element abundances relative to typical MORB, is indicative of a subduction signature. The presence of subduction-related characteristics within the Northland Ophiolite suggests that it may have originated at a back-arc basin rather than a major ocean ridge spreading centre. (author). 64 refs., 12 figs., 7 tabs

  17. Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Bizimis, M.; Haluzová, Eva; Sláma, Jiří; Svojtka, Martin; Hirajima, T.; Erban, V.

    256/257, July (2016), s. 197-210 ISSN 0024-4937 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100131203 Program:Program interní podpory projektů mezinárodní spolupráce AV ČR Institutional support: RVO:67985831 Keywords : Bohemian Massif * Lu-Hf * mantle * pyroxenite * Re-Os Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.677, year: 2016

  18. Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian, Gzhelian, Pennsylvanian, Bohemian Massif), their timing, and possible trigger mechanism

    Czech Academy of Sciences Publication Activity Database

    Stárková, M.; Martínek, K.; Mikuláš, Radek; Rosenau, N.

    2015-01-01

    Roč. 104, č. 5 (2015), s. 1277-1298 ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : soft-sediment deformation structures * bioturbation * early diagenetic carbonate * lacustrine facies * Bohemian Massif * Stephanian C * Krkonoše Piedmont Basin Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.133, year: 2015

  19. Gravimetric structure for the abyssal mantle massif of Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean, and its relation to active uplift

    Directory of Open Access Journals (Sweden)

    KENJI F. MOTOKI

    2014-06-01

    Full Text Available This paper presents gravimetric and morphologic analyses based on the satellite-derived data set of EGM2008 and TOPEX for the area of the oceanic mantle massif of the Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean. The free-air anomaly indicates that the present plate boundary is not situated along the longitudinal graben which cuts peridotite ridge, but about 20 km to the north of it. The high Bouguer anomaly of the peridotite ridge suggests that it is constituted mainly by unserpentinised ultramafic rocks. The absence of isostatic compensation and low-degree serpentinisation of the ultramafic rocks indicate that the peridotite ridge is sustained mainly by active tectonic uplift. The unparallel relation between the transform fault and the relative plate motion generates near north-south compression and the consequent tectonic uplift. In this sense, the peridotite massif is a pressure ridge due to the strike-slip displacement of the Saint Paul Transform Fault.

  20. K-Ar and Rb-Sr dating results of the Malyshevsky leucogranite massif (eastern slope of the Middle Urals)

    International Nuclear Information System (INIS)

    Smirnov, V.N.; Ivanov, K.S.; Ronkin, Yu.L.; Levin, V.Ya.; Bushlyakov, I.N.; Lepikhina, O.P.; Popova, O.Yu.

    2005-01-01

    The age of leucogranites and minerals forming the Malyshevsky massif was identified by the methods of K-Ar- and Rb-Sr dating for refining the sequence of magmatic complexes formation on the eastern slope of the Middle Urals. The obtained isotope age values, i.e. 229-277 mln. years (K-Ar) and 277.1±1.1 mln. years (Rb-Sr), permit considering the age of 277 mln. years as the period of the leucogranites formation and of the associated molybdenum mineralization [ru

  1. Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

    Directory of Open Access Journals (Sweden)

    Federica Zaccarini

    2016-10-01

    Full Text Available An electron microprobe study has been carried out on platinum-group minerals, accessory phases, and chromite in several chromite deposits of the Alapaevsk ophiolite (Central Urals, Russia namely the Bakanov Kluch, Kurmanovskoe, Lesnoe, 3-d Podyony Rudnik, Bol’shaya Kruglyshka, and Krest deposits. These deposits occur in partially to totally serpentinized peridotites. The microprobe data shows that the chromite composition varies from Cr-rich to Al-rich. Tiny platinum-group minerals (PGM, 1–10 µm in size, have been found in the chromitites. The most abundant PGM is laurite, accompanied by minor cuproiridsite and alloys in the system Os–Ir–Ru. A small grain (about 20 μm was found in the interstitial serpentine of the Bakanov Kluch chromitite, and its calculated stoichiometry corresponds to (Ni,Fe5P. Olivine, occurring in the silicate matrix or included in fresh chromite, has a mantle-compatible composition in terms of major and minor elements. Several inclusions of amphibole, Na-rich phlogopite, and clinopyroxene have been identified. The bimodal Cr–Al composition of chromite probably corresponds to a vertical distribution in the ophiolite sequence, implying formation of Cr-rich chromitites in the deep mantle, and Al-rich chromitites close to the Moho-transition zone, in a supra-subduction setting. The presence of abundant hydrous silicate inclusions, such as amphibole and phlogopite, suggests that the Alapaevsk chromitites crystallized as a result of the interaction between a melt enriched in fluids and peridotites. Laurite and cuproiridsite are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at high temperatures. The sulfur fugacity was relatively high to allow the precipitation of Ir-bearing sulfides, but below the Os–OsS2 buffer. The alloys in the system Os–Ir–Ru are classified as secondary PGM, i.e., formed at low temperature during the serpentinization process. The

  2. Lower crustal section of the Oman Ophiolite drilled in Hole GT1A, ICDP Oman Drilling Project

    Science.gov (United States)

    Umino, S.; Kelemen, P. B.; Matter, J. M.; Coggon, J. A.; Takazawa, E.; Michibayashi, K.; Teagle, D. A. H.

    2017-12-01

    Hole GT1A (22° 53.535'N, 58° 30.904'E) was drilled by the Oman Drilling Project (OmDP) into GT1A of the Samail ophiolite, Oman. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole GT1A was diamond cored in 22 Jan to 08 Feb 2017 to a total depth of 403.05 m. The outer surfaces of the cores were imaged and described on site before being curated, boxed and shipped to the IODP drill ship Chikyu, where they underwent comprehensive visual and instrumental analysis. Hole GT1A drilled the lower crustal section in the southern Oman Ophiolite and recovered 401.52 m of total cores (99.6% recovery). The main lithology is dominated by olivine gabbro (65.9%), followed in abundance by olivine-bearing gabbro (21.5%) and olivine melagabbro (3.9%). Minor rock types are orthopyroxene-bearing olivine gabbro (2.4%), oxide-bearing olivine gabbro (1.5%), gabbro (1.1%), anorthositic gabbro (1%), troctolitic gabbro (0.8%); orthopyroxene-bearing gabbro (0.5%), gabbronorite (0.3%); and dunite (0.3%). These rocks are divided into Lithologic Unit I to VII at 26.62 m, 88.16 m, 104.72 m, 154.04 m, 215.22 m, 306.94 m in Chikyu Curated Depth in descending order; Unit I and II consist of medium-grained olivine gabbro with lower olivine abundance in Unit II. Unit III is medium-grained olivine melagabbros, marked by an increase in olivine. Unit IV is relatively homogenous medium-grained olivine gabbros with granular textures. Unit V is identified by the appearance of fine-grained gabbros, but the major rocktypes are medium grained olivine gabbros. Unit VI is medium-grained olivine gabbro, marked by appearance of orthopyroxene. Unit VII

  3. Estimation of surface runoff for calculating recharge in the karstic massif of Ports of Beseit (Tarragona, Spain) combining water balance in the soil and analysis of flow hydrographs

    International Nuclear Information System (INIS)

    Espinosa Martinez, S.; Custodio, E.

    2016-01-01

    For the right estimation of aquifer recharge by precipitation surface taking into account runoff is particularly relevant. Non considering it in the estimation of the groundwater resources can overestimate them. In the Baix Ebre aquifer system, in southern Catalonia, the surface and vadose zone runoff produced in the karstified carbonate formations in the Ports de Beseit massif has to be evaluated in order to achieve a better estimation of the resources transferred from this massif to the Plana de La Galera plain. Starting from the conceptual hydrogeological model, the average annual runoff is estimated. It includes the discharge from temporal perched aquifers in the Ports de Beseit massif, in the Matarraña river basin, and in the SE watershed to the Plana de La Galera plain. This is performed by analyzing the river and tributaries hydrographs, the filling and emptying hydrographs of the Ulldecona reservoir, and the soil water balance using the Visual Balan code applied to obtain the runoff in the Ulldecona reservoir watershed. The runoff has been estimated about 105±20 mm·yr−1, which represents 20–30% of average annual recharge in the Ports, estimated with soil water balance and atmospheric chloride deposition balance, about 350–500 mm·yr−1, which is mostly transferred laterally to the Plana de La Galera plain. (Author)

  4. Estimation of surface runoff for calculating recharge in the karstic massif of Ports of Beseit (Tarragona, Spain) combining water balance in the soil and analysis of flow hydrographs

    Energy Technology Data Exchange (ETDEWEB)

    Espinosa Martinez, S.; Custodio, E.

    2016-07-01

    For the right estimation of aquifer recharge by precipitation surface taking into account runoff is particularly relevant. Non considering it in the estimation of the groundwater resources can overestimate them. In the Baix Ebre aquifer system, in southern Catalonia, the surface and vadose zone runoff produced in the karstified carbonate formations in the Ports de Beseit massif has to be evaluated in order to achieve a better estimation of the resources transferred from this massif to the Plana de La Galera plain. Starting from the conceptual hydrogeological model, the average annual runoff is estimated. It includes the discharge from temporal perched aquifers in the Ports de Beseit massif, in the Matarraña river basin, and in the SE watershed to the Plana de La Galera plain. This is performed by analyzing the river and tributaries hydrographs, the filling and emptying hydrographs of the Ulldecona reservoir, and the soil water balance using the Visual Balan code applied to obtain the runoff in the Ulldecona reservoir watershed. The runoff has been estimated about 105±20 mm·yr−1, which represents 20–30% of average annual recharge in the Ports, estimated with soil water balance and atmospheric chloride deposition balance, about 350–500 mm·yr−1, which is mostly transferred laterally to the Plana de La Galera plain. (Author)

  5. Volcanic and geochemical evolution of the Teno massif, Tenerife, Canary Islands: some repercussions of giant landslides on ocean island magmatism

    OpenAIRE

    Longpré, Marc-Antoine; Troll, Valentin R.; Walter, Thomas R.; Hansteen, Thor H.

    2009-01-01

    Large-scale, catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes. Recent studies, however, have highlighted a possible feedback relationship between flank collapse, or incipient instability, and subsequent episodes of structural rearrangement and/or renewed volcano growth. The Teno massif, located in northwestern Tenerife (Canary Islands), is a deeply eroded Miocene shield volcano that was built in four major eruptive phases punctuated ...

  6. Graptolite assemblages and stratigraphy of the lower Silurian Mrákotín Formation, Hlinsko Zone, NE interior of the Bohemian Massif (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Štorch, Petr; Kraft, P.

    2009-01-01

    Roč. 84, č. 1 (2009), s. 51-74 ISSN 1214-1119 R&D Projects: GA AV ČR IAA3013405 Institutional research plan: CEZ:AV0Z30130516 Keywords : graptolites * stratigraphy * Llandovery * Hlinsko Zone * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.983, year: 2009

  7. Pb-Pb age and Rb-Sr and Sm-Nd isotope signature of paleoproterozoic syenitic plutonism in the south of Salvador-Curaca mobile belt: Sao Felix Syenitic Massif, Bahia-Brazil

    International Nuclear Information System (INIS)

    Rosa, Maria de Lourdes da Silva; Conceicao, Herbet; Leal, Luiz Rogerio Bastos

    2001-01-01

    The Sao Felix Syenitic Massif (MSSF) has a tabular shape with about 32 km 2 that represents the south expression of the aligned syenitic plutonism, which occur in the middle part of Salvador-Curaca mobile belt (CMSC). Single zircon dating by stepwise Pb evaporation methodology yields an age of 2098 ± 1 Ma to SFSM. This data correlate the emplacement of the SFSM with the late stages of SCMB stabilization. This massif is isotopically characterized by negative epsilon neodymium values (-1.45 to -2.89) and low initial strontium ratio (0.701 to 0.704). SFSM isotopic signature is similar to the ones displayed by the others syenites from the belt and reflects an enriched source which should be related to a metasomatic enriched mantle. (author)

  8. Characterization of potassic materials of Pocos de Caldas alkaline massif, Southeastern Brazil

    International Nuclear Information System (INIS)

    Goncalves, P.; Navarro, F.C.; Roveri, C.D.; Bergerman, M.G.

    2016-01-01

    Potassium, which has featured in Brazil's agricultural sector and in the world's in the application of fertilizers, is present in magmatic rocks, such as nepheline syenite and phonolite, found in the Alkaline Massif of Pocos de Caldas (AMPC). The rare earth elements (REE), in turn, also occur in this region and have important uses in various industrial fields. The aim of this study was to investigate the potential of potassic rocks of AMPC in the fertilizer and rare earths industry. Five samples were collected and characterized. It was observed that there was no preferential concentration by granulometric range of potassium oxide, alumina, silica and iron oxide. Feldspathic mass, potash feldspar, and muscovite were found in all samples. The samples show REE with amounts greater than those found in the earth's crust, except for lutetium and scandium and possessed average content of potassium oxide from 8.70 to 14.40%. (author)

  9. Processes Governing Alkaline Groundwater Chemistry within a Fractured Rock (Ophiolitic Mélange Aquifer Underlying a Seasonally Inhabited Headwater Area in the Aladağlar Range (Adana, Turkey

    Directory of Open Access Journals (Sweden)

    Cüneyt Güler

    2017-01-01

    Full Text Available The aim of this study was to investigate natural and anthropogenic processes governing the chemical composition of alkaline groundwater within a fractured rock (ophiolitic mélange aquifer underlying a seasonally inhabited headwater area in the Aladağlar Range (Adana, Turkey. In this aquifer, spatiotemporal patterns of groundwater flow and chemistry were investigated during dry (October 2011 and wet (May 2012 seasons utilizing 25 shallow hand-dug wells. In addition, representative samples of snow, rock, and soil were collected and analyzed to constrain the PHREEQC inverse geochemical models used for simulating water-rock interaction (WRI processes. Hydrochemistry of the aquifer shows a strong interseasonal variability where Mg–HCO3 and Mg–Ca–HCO3 water types are prevalent, reflecting the influence of ophiolitic and carbonate rocks on local groundwater chemistry. R-mode factor analysis of hydrochemical data hints at geochemical processes taking place in the groundwater system, that is, WRI involving Ca- and Si-bearing phases; WRI involving amorphous oxyhydroxides and clay minerals; WRI involving Mg-bearing phases; and atmospheric/anthropogenic inputs. Results from the PHREEQC modeling suggested that hydrogeochemical evolution is governed by weathering of primary minerals (calcite, chrysotile, forsterite, and chromite, precipitation of secondary minerals (dolomite, quartz, clinochlore, and Fe/Cr oxides, atmospheric/anthropogenic inputs (halite, and seasonal dilution from recharge.

  10. A Reference Section through the Lower Fast-spreading Oceanic Crust in the Wadi Gideah (Sumail ophiolite, Sultanate Oman): Drill Sites GT1A and GT2A within the ICDP Oman Drilling Project

    Science.gov (United States)

    Mueller, S.; Koepke, J.; Garbe-Schoenberg, C. D.; Müller, T.; Mock, D.; Strauss, H.; Schuth, S.; Ildefonse, B.

    2017-12-01

    In the absence of a complete profile through fast-spreading oceanic crust in modern oceans, we established a reference profile through the whole paleocrust of the Sumail Ophiolite (Oman), which is regarded as the best analogue for fast-spreading oceanic crust on land. For establishing a coherent data set, we sampled the Wadi Gideah in the Wadi-Tayin massif from the mantle section up to the pillow basalts and performed different analytical and structural investigations on the same suite of samples (pool sample concept). The whole sample set contains about 400 samples focusing on both primary magmatic rocks and hydrothermal fault zones to characterize initial formation processes and cooling of the crust. The Wadi Gideah hosts the sites GT1A (lower crust) and GT2A (foliated / layered gabbro transition) where 400 m long cores have been drilled in the frame of the ICDP Oman Drilling Project (OmanDP). Thus, the Wadi Gideah crustal transect is well-suited for providing a reference frame for these two drill cores. Major and trace element data on minerals and rocks reveal in-situ crystallization in the deep crust, thus strongly supporting a hybrid accretion model that is characterized by sheeted sill intrusion in the lower part of the plutonic crust and gabbro glacier features in the upper section. This hybrid model is also supported by results on crystallographic preferred orientations (CPO) of the minerals within the gabbros, which call for distinct formation mechanisms in the upper and lower gabbro sections. A requirement for our hybrid model is significant hydrothermal cooling in the lower crust for the consumption of the latent heat of crystallization. This was facilitated by channelled hydrothermal flow zones, preserved today in faulted zones of extensively altered gabbro cutting both layered and foliated gabbros. These gabbros show higher Sr87/Sr86 ratios if compared to the background gabbro, the presence of late stage minerals (amphibole, oxides, orthopyroxene

  11. Deforestation Along the Maya Mountain Massif Belize-Guatemala Border

    Science.gov (United States)

    Chicas, S. D.; Omine, K.; Arevalo, B.; Ford, J. B.; Sugimura, K.

    2016-06-01

    In recent years trans-boundary incursions from Petén, Guatemala into Belize's Maya Mountain Massif (MMM) have increased. The incursions are rapidly degrading cultural and natural resources in Belize's protected areas. Given the local, regional and global importance of the MMM and the scarcity of deforestation data, our research team conducted a time series analysis 81 km by 12 km along the Belize-Guatemalan border adjacent to the protected areas of the MMM. Analysis drew on Landsat imagery from 1991 to 2014 to determine historic deforestation rates. The results indicate that the highest deforestation rates in the study area were -1.04% and -6.78% loss of forested area per year in 2012-2014 and 1995-1999 respectively. From 1991 to 2014, forested area decreased from 96.9 % to 85.72 % in Belize and 83.15 % to 31.52 % in Guatemala. During the study period, it was clear that deforestation rates fluctuated in Belize's MMM from one time-period to the next. This seems linked to either a decline in deforestation rates in Guatemala, the vertical expansion of deforestation in Guatemalan forested areas and monitoring. The results of this study urge action to reduce incursions and secure protected areas and remaining forest along the Belize-Guatemalan border.

  12. L'érosion dans les environnements glaciaires : exemple du Glacier des Bossons (Massif du Mont-Blanc, Haute-Savoie, France)

    OpenAIRE

    Godon , Cécile

    2013-01-01

    The study presented in this PhD memory aim at better define and quantify the present timeerosion processes in glacial and proglacial domain. The Glacier des Bossons, situated in theMont-Blanc massif (Haute-Savoie, France), is a good example of a natural and nonanthropizedsystem which allows us to study this topic. This glacier lies on two mainlithologies (the Mont-Blanc granite and the metamorphic bedrock) and this peculiarity is usedto determine the origin of the glacial sediments. The sedim...

  13. Transfer of subduction fluids into the deforming mantle wedge during nascent subduction: Evidence from trace elements and boron isotopes (Semail ophiolite, Oman)

    Science.gov (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Lemarchand, D.; Soret, M.; Ulrich, M.

    2018-02-01

    The basal part of the Semail ophiolitic mantle was (de)formed at relatively low temperature (LT) directly above the plate interface during "nascent subduction" (the prelude to ophiolite obduction). This subduction-related LT deformation was associated with progressive strain localization and cooling, resulting in the formation of porphyroclastic to ultramylonitic shear zones prior to serpentinization. Using petrological and geochemical analyses (trace elements and B isotopes), we show that these basal peridotites interacted with hydrous fluids percolating by porous flow during mylonitic deformation (from ∼850 down to 650 °C). This process resulted in 1) high-T amphibole crystallization, 2) striking enrichments of minerals in fluid mobile elements (FME; particularly B, Li and Cs with concentrations up to 400 times those of the depleted mantle) and 3) peridotites with an elevated δ11B of up to +25‰. These features indicate that the metasomatic hydrous fluids are most likely derived from the dehydration of subducting crustal amphibolitic materials (i.e., the present-day high-T sole). The rapid decrease in metasomatized peridotite δ11B with increasing distance to the contact with the HT sole (to depleted mantle isotopic values in <1 km) suggests an intense interaction between peridotites and rapid migrating fluids (∼1-25 m.y-1), erasing the initial high-δ11B subduction fluid signature within a short distance. The increase of peridotite δ11B with increasing deformation furthermore indicates that the flow of subduction fluids was progressively channelized in actively deforming shear zones parallel to the contact. Taken together, these results also suggest that the migration of subduction fluids/melts by porous flow through the subsolidus mantle wedge (i.e., above the plate interface at sub-arc depths) is unlikely to be an effective mechanism to transport slab-derived elements to the locus of partial melting in subduction zones.

  14. Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China

    Science.gov (United States)

    Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan

    2017-04-01

    Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

  15. Seismic anisotropy of the French Massif Central and predisposition of Cenozoic rifting and volcanism by Variscan suture hidden in the mantle lithosphere

    Czech Academy of Sciences Publication Activity Database

    Babuška, Vladislav; Plomerová, Jaroslava; Vecsey, Luděk; Granet, M.; Achauer, U.

    2002-01-01

    Roč. 21, č. 4 (2002), s. U407-U429 ISSN 0278-7407 R&D Projects: GA ČR GV205/98/K004; GA ČR GA205/01/1154; GA AV ČR IAA3012908 Institutional research plan: CEZ:AV0Z3012916 Keywords : seismic anisotropy * Massif Central * mantle lithosphere Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.697, year: 2002

  16. Chromium-rich lawsonite in high-Cr eclogites from the Făgăras Massif (South Carpathians)

    Science.gov (United States)

    Negulescu, E.; Săbău, G.

    2012-12-01

    Lawsonite is a relatively rare phase in natural rocks, because of its thermal decomposition during exhumation, and Cr-bearing lawsonite being restricted to only a few occurrences worldwide. Here we report Cr-lawsonite in eclogites hosted in a medium-grade metamorphic complex. Several high-Cr eclogite lenses occur in the Topolog Complex (Făgăras Massif) of dominantly gneissic-amphibolitic composition. High Cr contents are the result of emerald-green mm-sized nodules containing Cr-rich minerals, embedded in a gray-green matrix of kyanite, clinopyroxene, garnet, amphibole, zoisite, and rutile. Garnets occur as porphyroblasts or in coronas around clinopyroxene aggregates probably replacing former magmatic pyroxene. Relict gabbroic textures (sometimes pegmatoid) and whole rock geochemistry indicate a gabbroic cumulate origin. The REE pattern, displaying a slight positive Eu anomaly and a tea spoon-shaped LREE depletion is also indicative of a cumulate origin, as also noted by Pe Piper & Piper (2002) for the Othrys gabbro (as well as others in the Vourinos and Pindos ophiolitic suites) with the same unusual REE-pattern. The emerald-green Cr-rich nodules are unevenly distributed in the rock, and always enclosed in Cr-rich clinopyroxenes (up to 5.46% Cr2O3) which may exhibit Cr-diffusion haloes towards normal Cr-free matrix pyroxene. The nodules consist of diablastic chromite, rutile and Cr-rich kyanite of up to 15.67 wt% Cr2O3, Cr-bearing epidote, to which Cr-rich staurolite (up to 10.45% Cr2O3; XMg up to 0.68) and Cr-rich lawsonite (up to 9.17% Cr2O3) may exceptionally associate. Cr concentrations in kyanite and lawsonite are, to our knowledge, the highest reported so far. Cr-lawsonite was identified in a single sample, as small single phase inclusions armoured in Cr-kyanite. Equilibrium PT-conditions of 2.6 GPa and 610o C were derived from the garnet-mantled clinopyroxene aggregates using multi-equilibria calculation with the PTGIBBS routine of Brandelik & Massonne

  17. Thermo chronology by fission tracks of the conjugated rift margins of the Liguro-Provencal basin: Corsica and the Maures-Tanneron Massif

    International Nuclear Information System (INIS)

    Jakni, B.

    2000-01-01

    We have employed apatite fission-track (AFT) thermo-chronology on granitic and metamorphic samples taken from Corsican and Maures-Tanneron basement rocks as well as alpine 'schistes lustres' units in Corsica, in order to constrain the cooling histories and the tectonic evolution of the Liguro-Provencal basin margins. The AFT data indicate that: -) the Tanneron massif (AFT ages 145- 150 My) appears to record the earliest cooling history, reflecting thermal relaxation related to opening of the Tethys; -) the Maures basement (AFT ages 20-25 My) clearly records a thermo- tectonic evolution associated with Liguro-Provencal rifting; -) the island of Corsica, which was the main focus of this work and which shows a complex geomorphology and a poly-phased tectonic evolution. shows a remarkable zoning in the distribution of AFT ages, reflecting the signature of at least two post-Oligocene thermal events. Those events are related to the opening of Liguro-Provencal basin (20-25 My) in the west, and exhumation of the Hercynian basement related to Tyrrhenian extension (12- 16 My) in the east. In the east-Tenda shear zone, which forms the contact between the alpine units and Hercynian basement in northern Corsica, our results indicate that the Tenda Massif was being exhumed from about 21 Ma onwards. (author)

  18. Origin of eclogite and garnet pyroxenite from the Moldanubian Zone of the Bohemian Massif, Czech Republic and its implication to other mafic layers embedded in orogenic peridotites

    Czech Academy of Sciences Publication Activity Database

    Obata, M.; Hirajima, T.; Svojtka, Martin

    2006-01-01

    Roč. 88, 1-2 (2006), s. 321-340 ISSN 0930-0708 R&D Projects: GA AV ČR IAA3013006 Institutional research plan: CEZ:AV0Z30130516 Keywords : eclogite * pyroxenite * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.038, year: 2006

  19. Multiphase formation of the Obří důl polymetallic skarn deposit, West Sudetes, Bohemian Massif: geochemistry and Re–Os dating of sulfide mineralization

    Czech Academy of Sciences Publication Activity Database

    Veselovský, F.; Ackerman, Lukáš; Pašava, J.; Žák, Karel; Haluzová, Eva; Creaser, R. A.; Dobeš, P.; Erban, V.; Tásler, R.

    2018-01-01

    Roč. 53, č. 5 (2018), s. 665-682 ISSN 0026-4598 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Bohemian Massif * polymetallic skarn deposit * West Sudetes * arsenopyrite * Re–Os geochronology Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 3.396, year: 2016

  20. Late Mesoproterozoic to Early Paleozoic history of metamorphic basement from the southeastern Chiapas Massif Complex, Mexico, and implications for the evolution of NW Gondwana

    Science.gov (United States)

    Weber, Bodo; González-Guzmán, Reneé; Manjarrez-Juárez, Román; Cisneros de León, Alejandro; Martens, Uwe; Solari, Luigi; Hecht, Lutz; Valencia, Victor

    2018-02-01

    In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined "El Triunfo Complex" located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at 650 °C and 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian ( 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from 457 to 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of

  1. The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex

    Science.gov (United States)

    Schoolmeesters, Nicole; Cheadle, Michael J.; John, Barbara E.; Reiners, Peter W.; Gee, Jeffrey; Grimes, Craig B.

    2012-10-01

    Oceanic core complexes (OCCs) are domal exposures of oceanic crust and mantle interpreted to be denuded to the seafloor by large slip oceanic detachment faults. We combine previously reported U-Pb zircon crystallization ages with (U-Th)/He zircon thermochronometry and multicomponent magnetic remanence data to determine the cooling history of the footwall to the Atlantis Massif OCC (30°N, MAR) and help establish cooling rates, as well as depths of detachment faulting and gabbro emplacement. We present nine new (U-Th)/He zircon ages for samples from IODP Hole U1309D ranging from 40 to 1415 m below seafloor. These data paired with U-Pb zircon ages and magnetic remanence data constrain cooling rates of gabbroic rocks from the upper 800 m of the central dome at Atlantis Massif as 2895 (+1276/-1162) °C Myr-1 (from ˜780°C to ˜250°C); the lower 600 m of the borehole cooled more slowly at mean rates of ˜500 (+125/-102) °C Myr-1(from ˜780°C to present-day temperatures). Rocks from the uppermost part of the hole also reveal a brief period of slow cooling at rates of ˜300°C Myr-1, possibly due to hydrothermal circulation to ˜4 km depth through the detachment fault zone. Assuming a fault slip rate of 20 mm/yr (from U-Pb zircon ages of surface samples) and a rolling hinge model for the sub-surface fault geometry, we predict that the 780°C isotherm lies at ˜7 km below the axial valley floor, likely corresponding both to the depth at which the semi-brittle detachment fault roots and the probable upper limit of significant gabbro emplacement.

  2. Fore arc tectonothermal evolution of the El Oro metamorphic province (Ecuador) during the Mesozoic

    Science.gov (United States)

    Riel, Nicolas; Martelat, Jean-Emmanuel; Guillot, Stéphane; Jaillard, Etienne; Monié, Patrick; Yuquilema, Jonatan; Duclaux, Guillaume; Mercier, Jonathan

    2014-10-01

    The El Oro metamorphic province of SW Ecuador is a composite massif made of juxtaposed terranes of both continental and oceanic affinity that has been located in a fore-arc position since Late Paleozoic times. Various geochemical, geochronological, and metamorphic studies have been undertaken on the El Oro metamorphic province, providing an understanding of the origin and age of the distinct units. However, the internal structures and geodynamic evolution of this area remain poorly understood. Our structural analysis and thermal modeling in the El Oro metamorphic province show that this fore-arc zone underwent four main geological events. (1) During Triassic times (230-225 Ma), the emplacement of the Piedras gabbroic unit at crustal-root level ( 9 kbar) triggered partial melting of the metasedimentary sequence under an E-W extensional regime at pressure-temperature conditions ranging from 4.5 to 8.5 kbar and from 650 to 900°C for the migmatitic unit. (2) At 226 Ma, the tectonic underplating of the Arenillas-Panupalí oceanic unit (9 kbar and 300°C) thermally sealed the fore-arc region. (3) Around the Jurassic-Cretaceous boundary, the shift from trench-normal to trench-parallel subduction triggered the exhumation and underplating of the high-pressure, oceanic Raspas Ophiolitic Complex (18 kbar and 600°C) beneath the El Oro Group (130-120 Ma). This was followed by the opening of a NE-SW pull-apart basin, which tilted the massif along an E-W subhorizontal axis (110 Ma). (4) In Late Cretaceous times, an N-S compressional event generated heterogeneous deformation due to the presence of the Cretaceous Celica volcanic arc, which acted as a buttress and predominantly affected the central and eastern part of the massif.

  3. A distinctive new frog species (Anura, Mantellidae supports the biogeographic linkage of two montane rainforest massifs in northern Madagascar

    Directory of Open Access Journals (Sweden)

    Mark D. Scherz

    2018-03-01

    Full Text Available We describe a new species of the genus Gephyromantis, subgenus GephyromantisVatomantis (Mantellidae, Mantellinae, from moderately high elevation (1164–1394 m a.s.l. on the Marojejy, Sorata, and Andravory Massifs in northern Madagascar. The new species, Gephyromantis (Vatomantis lomorina sp. n. is highly distinct from all other species, and was immediately recognisable as an undescribed taxon upon its discovery. It is characterised by a granular, mottled black and green skin, reddish eyes, paired subgular vocal sacs of partly white colour, bulbous femoral glands present only in males and consisting of three large granules, white ventral spotting, and a unique, amplitude-modulated advertisement call consisting of a series of 24–29 rapid, quiet notes at a dominant frequency of 5124–5512 Hz. Genetically the species is also strongly distinct from its congeners, with uncorrected pairwise distances ≥10 % in a fragment of the mitochondrial 16S rRNA gene to all other nominal Gephyromantis species. A molecular phylogeny based on 16S sequences places it in a clade with species of the subgenera Laurentomantis and Vatomantis, and we assign it to the latter subgenus based on its morphological resemblance to members of Vatomantis. We discuss the biogeography of reptiles and amphibians across the massifs of northern Madagascar, the evidence for a strong link between Marojejy and Sorata, and the role of elevation in determining community sharing across this landscape.

  4. Late Carboniferous remagnetisation of Palaeozoic rocks in the NE Rhenish Massif, Germany

    Science.gov (United States)

    Zwing, A.; Bachtadse, V.; Soffel, H. C.

    During stepwise thermal and alternating field demagnetisation experiments on Devonian and Lower Carboniferous carbonate and clastic rocks from the north-eastern part of the Rhenish Massif, Germany, three components of magnetisation (A, B, C) are identified. Component A is a recent viscous overprint that parallels the local present day geomagnetic field. Component B is mainly observed from 260 up to 550 °C during thermal demagnetisation and is carried by magnetite. In two localities, where red siltstones and red carbonate rocks were sampled, component B is stable up to 670 °C, indicating the presence of hematite. Three clusters of in situ B directions can be identified, which are controlled by the tectonic position of the sampling areas. These are from NW to SE: the Remscheid anticline (RA), the Lüdenscheid syncline (LS) and the Attendorn and Wittgenstein synclines (AS/WS). Standard and inclination-only fold tests, using parametric resampling, yield optimal statistical parameters at increasing amounts of untilting ranging from 0% in the South up to 57% in the North of the NE Rhenish Massif. Despite the variations in optimal untilting, the resulting site mean directions of component B do not differ significantly in inclination. These results are interpreted to reflect the acquisition of magnetisation during progressive northward migration of the deformation front in Late Carboniferous times. The resulting palaeolatitudes (RA: 1°S +2°-3°; LS: 2°S +3°-2°; AS/WS: 1°S +3°-4°) are in good agreement with the predicted position of the sampling area in the Late Carboniferous, as derived from a published Apparent Polar Wander Path for Baltica and Laurentia. The unblocking temperature spectra and the synfolding nature of B yield strong evidence that chemical processes, possibly driven by fluid migration during orogenesis, caused this remagnetisation. A third component C was observed in zones of tight folding with steeply dipping to overturned bedding planes and is

  5. Large plates and small blocks: The Variscan orogeny in the Bohemian Massif

    Science.gov (United States)

    Kroner, Uwe; Romer, Rolf L.

    2017-04-01

    The Bohemian Massif of the Central European Variscides consists of several late Proterozoic / early Paleozoic low-strain crustal units, namely the Bruno-Vistulian continental block of the Laurussian plate that is juxtaposed with the Tepla-Barrandian Unit and the Lausitz block of the Gondwana plate. These pre-Variscan low-strain units are separated by high-strain zones that contain the mid- and lower crustal record of the Variscan orogeny (400-300 Ma), with nappes reflecting successive subduction exhumation events, voluminous migmatites and a wide range of geochemically contrasting granites. Although the principal constraints are undisputed, there is no consensus regarding the general tectonics of this area. Here we present a plate tectonic model explaining the Bohemian Massif as an orogenic wedge with a Gondwana pro-wedge and a Laurussia retro-wedge area. The principal formation steps are as follows. Subduction of the oceanic crust of the Gondwana plate, i.e. the southern part of the Rheic Ocean eventually followed by continental subduction of the distal Peri-Gondwana shelf produced the early Devonian (U)HP complexes now exposed in the uppermost allochthonous units. The arrival of the Tepla-Barrandian Cadomian block initiates a flip of subduction polarity, leading to the complete closure of the Rheic Ocean in the late Devonian coeval with the exhumation of the early Variscan (U)HP units. Caused by the Lausitz block entering the plate boundary zone in the early Carboniferous, this early subduction accretion stage was followed by continent continent collision. The resulting orogenic wedge is characterized by an intra-continental subduction zone in the pro-wedge area superimposed by the crustal stack of early and mid-Variscan accreted units. Due to heating of the subducted slab in the mantle, the isothermal exhumation of this deeply buried continental crust caused HT-LP metamorphism during the final transpressional stage. Lateral extrusion tectonics coeval with the

  6. Petrogenesis of the Cenozoic alkaline volcanic rock series of the České Středohoří Complex (Bohemian Massif), Czech Republic: A case for two lineages

    Czech Academy of Sciences Publication Activity Database

    Dostal, J.; Schellnutt, J. G.; Ulrych, Jaromír

    2017-01-01

    Roč. 317, June (2017), s. 677-706 ISSN 0002-9599 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Central European volcanic province * continental alcaline volcanism * fractional crystallization * magmatic fluids Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 4.099, year: 2016

  7. Les roches basiques et ultrabasiques des Lacs Robert et le Trias de Chamrousse (Massif de Belledonne) Etude petrologique et geologique

    NARCIS (Netherlands)

    Tex, den E.

    1950-01-01

    La région que j’ai étudiée et relevée est située dans les Alpes françaises, à environ 4° longitude est et 50°15’ latitude nord, et à environ 2000 mètres d’altitude. Elle fait partie de la chaîne dite „chaîne de Belledonne” qui s’étend des massifs de Beaufort et du Grand Mont dans le N N E jusqu’à

  8. DEFORESTATION ALONG THE MAYA MOUNTAIN MASSIF BELIZE-GUATEMALA BORDER

    Directory of Open Access Journals (Sweden)

    S. D. Chicas

    2016-06-01

    Full Text Available In recent years trans-boundary incursions from Petén, Guatemala into Belize’s Maya Mountain Massif (MMM have increased. The incursions are rapidly degrading cultural and natural resources in Belize’s protected areas. Given the local, regional and global importance of the MMM and the scarcity of deforestation data, our research team conducted a time series analysis 81 km by 12 km along the Belize-Guatemalan border adjacent to the protected areas of the MMM. Analysis drew on Landsat imagery from 1991 to 2014 to determine historic deforestation rates. The results indicate that the highest deforestation rates in the study area were −1.04% and −6.78% loss of forested area per year in 2012-2014 and 1995-1999 respectively. From 1991 to 2014, forested area decreased from 96.9 % to 85.72 % in Belize and 83.15 % to 31.52 % in Guatemala. During the study period, it was clear that deforestation rates fluctuated in Belize's MMM from one time-period to the next. This seems linked to either a decline in deforestation rates in Guatemala, the vertical expansion of deforestation in Guatemalan forested areas and monitoring. The results of this study urge action to reduce incursions and secure protected areas and remaining forest along the Belize-Guatemalan border.

  9. Petrology and geochemistry of primary magmas trapped in melt inclusions in scoria of Beaunit Maar (Chaîne des Puys, Massif Central, France)

    Science.gov (United States)

    Jannot, S.; Schiano, P.; Boivin, P.; Clocchiatti, R.; Chazot, G.

    2003-04-01

    The Massif Central area, characterized by a typical intraplate alkaline serie, is the largest magmatic province of the West-European Rift system. Although it has been the subject of several studies, the nature of Massif Central sources is still a matter of debate and many hypotheses are proposed, including deep-rooted continental hotspot, metasomatised spinel lherzolites and an asthenospheric flow linked to the lithospheric root of the Alpine chain. The Chaîne des Puys is the last magmatic province of the French Massif Central and is composed of hundred young well-preserved volcanoes. The present work aims to supply information on the nature and the origin of the source chemistry of alkaline serie from the Chaîne des Puys, by characterizing the trace and major element composition of minute melts preserved as quenched glass inclusions inside olivines phenocrysts in scoria from the Beaunit Maar. Heating stage experiments performed at ambient pressure on partially crystallised primary melt inclusions suggest CO_2 oversaturation of the trapped melt, and an entrapment temperature around 1200^oC±10^oC. Daughter minerals analyses point to a Ti-and Ca-rich basaltic paragenesis, in good agreement with that of erupted basalts from the Chaîne des Puys. Major element compositions show that melts trapped in inclusions evolve by limited fractional crystallization. Inclusions trapped in the more primitive olivine phenocrysts (Fo85) have alkali-basalt compositions that fall on the primitive end of the compositional trend define by the lavas of the Chaîne des Puys. Their major element chemistry rules out the hypothesis of a mantle source in the spinel stability field and requires a garnet-bearing mantle source. Analyzed for trace-element composition by LA-ICP-MS, they display homogeneous, enriched patterns, similar to those characterizing oceanic island and continental basalts. They have high concentration of LILE and LREE/HREE ratios. Such trace-element feature are typical of

  10. Spinel and plagioclase peridotites of the Nain ophiolite (Central Iran): Evidence for the incipient stage of oceanic basin formation

    Science.gov (United States)

    Pirnia, Tahmineh; Saccani, Emilio; Arai, Shoji

    2018-06-01

    The Nain ophiolites crop out along the western border of the central East Iran Microcontinent (CEIM) and consist of an ophiolitic mélange in which pargasite-bearing spinel and plagioclase mantle lherzolites are largely represented. Whole-rock and mineral chemistry data suggest that these rocks record the complex history of the asthenospheric and lithospheric mantle evolution. The spinel lherzolites have experienced low-degree ( 5%) partial melting and contain clinopyroxenes with positive Eu anomalies (Eu/Eu* = 1.10-1.48) suggesting that the partial melting occurred under oxidized conditions (fayalite-magnetite-quartz -0.8 to +1.3). The pargasite and coexisting clinopyroxene in these rocks are depleted in light rare earth elements (LREE) (mean chondrite-normalized CeN/SmN = 0.045). The depleted chemistry of this amphibole reflects metasomatism during interaction with H2O-rich subalkaline mafic melts, most likely concurrently with or after the partial melting of the spinel lherzolites. The plagioclase lherzolites were subsequently formed by the subsolidus recrystallization of spinel lherzolites under plagioclase facies conditions as a result of mantle uprising, as evidenced by: (1) the development of plagioclase rims around the spinels; (2) plagioclase + orthopyroxene exsolution textures within some clinopyroxene grains; (3) an increase in plagioclase modal content coupled with an increase in modal olivine and a decrease in modal pyroxene and pargasite; (4) coincident decreases in Al, Mg, and Ni, and increases in Cr, Ti, and Fe in spinel, as well as decreases in Al and Ca, and increases in Cr and Ti in pyroxene and pargasite; and (5) the identical whole rock compositions of the spinel and plagioclase lherzolites, which rules out a magmatic origin for the plagioclase in these units. The Nain lherzolites have similar whole-rock and mineral geochemical compositions to subcontinental peridotites that are typically representative of Iberia-type rifted continental margins

  11. Application of GIS technologies to monitor secondary radioactive contamination in the Delegen mountain massif

    Science.gov (United States)

    Alipbeki, O.; Kabzhanova, G.; Kurmanova, G.; Alipbekova, Ch.

    2016-06-01

    The territory of the Degelen mountain massif is located within territory of the former Semipalatinsk nuclear test site and it is an area of ecological disaster. Currently there is a process of secondary radioactive contamination that is caused by geodynamic processes activated at the Degelen array, violation of underground hydrological cycles and as a consequence, water seepage into the tunnels. One of the methods of monitoring of geodynamic processes is the modern technology of geographic information systems (GIS), methods of satellite radar interferometry and high accuracy satellite navigation system in conjunction with radioecological methods. This paper discusses on the creation of a GIS-project for the Degelen array, facilitated by quality geospatial analysis of the situation and simulation of the phenomena, in order to maximize an objective assessment of the radiation situation in this protected area.

  12. Metamorphic history of garnet-rich gneiss at Ktiš in the Lhenice shear zone, Moldanubian Zone of the southern Bohemian Massif, inferred from inclusions and compositional zoning of garnet

    Czech Academy of Sciences Publication Activity Database

    Kobayashi, T.; Hirajima, T.; Kawakami, T.; Svojtka, Martin

    2011-01-01

    Roč. 124, 1/2 (2011), s. 46-65 ISSN 0024-4937 Institutional research plan: CEZ:AV0Z30130516 Keywords : Bohemian Massif * Lhenice shear zone * garnet * P-T path * partial melting Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.246, year: 2011

  13. Ultramafites in the Gogolow-Jordanow massif and their predicted raw material evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Ciemniewska, M.; Czemier-Kowalska, M.; Lindner, M.; Salacinski, R.

    1981-01-01

    Based on mineralogical-petrographic analysis, it was established that the primary rocks of ultramafites were dunites and verlites which were exposed to intensive serpentinization, talcing, amphibolization, chloritization and carbonization. The constant components of rocks are ore minerals of paragenesis: chromite-ferrospinel-magnetite. Geochemical studies indicated the content (g/T): Cr 100-4800, Ni 100-3500, Co 30-160, Cu 1-100, while the computed values of the correlation coefficient revealed the existence of a link between Cr Ni, Co and Cr, Co and Ni. The mineralogical-petrographic composition, as well as the geological position of the studied massif indicate its affiliation to the ultramafites of the Alpine type and formation at the early stage of development of the geosyncline in the boundary zone between the consolidated gneiss block of the Archean and the mobile zone in relation to the deep faults. Although industrial concentrations of the expected were not found, the conducted observations make it possible to approach development of new prospecting concepts. Manifestation of the chromite mineralization and the ore accumulation in the region should be considered hydrothermal-metasomatic.

  14. Geochemistry of Spodosols formed in holocene till, Norra Storfjaellet Massif, northern Sweden

    International Nuclear Information System (INIS)

    Earl-goulet, J.R.; Mahaney, W.C.; Milner, M.W.; Hancock, R.G.V.

    1997-01-01

    Silt and clay size fractions of soils, from a transect of six Spodosols formed in the Norra Storfjaellet Massif, were analyzed by neutron activation to determine the degree to which pedogenic processes have influenced the distribution of macro, micro and trace elements. The distributions of Mg, Ca and Fe, together with Co, Cr and other trace elements in the profiles, suggest the presence of different parent materials, with A and E horizons arising from an influx of aeolian sediment. Translocation processes, both physical and chemical, occurred in the soil concentrating Fe and Br in the spodic(Bs) horizons of the profiles. The rare earth elements (REEs) are predominantly associated with the heavy mineral fraction of the soil material. The distributions of chondrite normalized REEs patterns of the profiles indicate that light rare earth element (LREE) concentrations increase with horizon depth. The depletion of LREEs in the upper soil horizons confirms the presence of material that is chemically different from that in the lower horizons, thus indicating a distinct chemical difference from the local glacial deposits. (author)

  15. Tectonic Evolution of Jabal Tays Ophiolite Complex, Eastern Arabian Shield, Saudi Arabia

    Science.gov (United States)

    AlHumidan, Saad; Kassem, Osama; Almutairi, Majed; Al-Faifi, Hussain; Kahal, Ali

    2017-04-01

    Microstructural analysis is important for investigation of tectonic evaluation of Jable Tays area. Furthermore, the Jable Tays ophiolite complex is effected by Al Amar -Idsas fault. The nature of the Al Amar-Idsas fault is a part of the Eastern Arabian Shield, which was subjected to multiple interpretations. Through fieldwork investigation, microscopic examination, and microstructural analysis, we aim to understand the evolution and tectonic setting of the Jable Tays area. Finite-strain data displays that the Abt schist, the metavolcanics and the metagranites are highly to moderately deformed. The axial ratios in the XZ section range from 1.40 to 2.20. The long axes of the finite-strain ellipsoids trend NW- SE and W-E in the Jable Tays area while, their short axes are subvertical to subhorizontal foliations. The strain magnitude does not increase towards the tectonic contacts between the Abt schist and metavolcano-sedimentary. While majority of the obtained data indicate a dominant oblate with minor prolate strain symmetries in the Abt schist, metavolcano-sedimentary and metagranites. The strain data also indicate flattening with some constriction. We assume that the Abt schist and the metavolcano-sedimentry rocks have similar deformation behavior. The finite strain in the studied rocks accumulated during the metamorphism that effected by thrusting activity. Based on these results, we finally concluded that the contact between Abt schist and metavolcano-sedimentary rocks were formed during the progressive thrusting under brittle to semi-ductile deformation conditions by simple shear that also involved a component of vertical shortening, causing subhorizontal foliation in Jable Tays area.

  16. Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

    Science.gov (United States)

    Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

    2017-06-01

    Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

  17. Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

    Science.gov (United States)

    Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.

    2014-03-01

    Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

  18. Magmatism and crustal extension: Constraining activation of the ductile shearing along the Gediz detachment, Menderes Massif (western Turkey)

    Science.gov (United States)

    Rossetti, Federico; Asti, Riccardo; Faccenna, Claudio; Gerdes, Axel; Lucci, Federico; Theye, Thomas

    2017-06-01

    The Menderes Massif of western Turkey is a key area to study feedback relationships between magma generation/emplacement and activation of extensional detachment tectonics. Here, we present new textural analysis and in situ U-(Th)-Pb titanite dating from selected samples collected in the transition from the undeformed to the mylonitized zones of the Salihli granodiorite at the footwall of the Neogene, ductile-to-brittle, top-to-the-NNE Gediz-Alaşheir (GDF) detachment fault. Ductile shearing was accompanied by the fluid-mediated sub-solidus transformation of the granodiorite to orthogneiss, which occurred at shallower crustal levels and temperatures compatible with the upper greenschist-to-amphibolite facies metamorphic conditions (530-580 °C and P system ages during fluid-assisted syn-tectonic re-crystallisation in the transition from magma crystallization and emplacement (at 16-17 Ma) to the syn-tectonic, solid-state shearing (at 14-15 Ma). A minimum time lapse of ca. 1-2 Ma is then inferred between the crustal emplacement of the Salihli granodiorite and nucleation of the ductile extensional shearing along the Gediz detachment. The reconstruction of the cooling history of the Salihli granodiorite documents a punctuated evolution dominated by two episodes of rapid cooling, between 14 Ma and 12 Ma ( 100 °C/Ma) and between 3 and 2 Ma ( 105 °C/Ma). We relate the first episode to nucleation and development of post-emplacement of ductile shearing along the GDF and the second to brittle high-angle faulting, respectively. Our dataset suggests that in the Menderes Massif the activation of ductile extension was a consequence, rather than the cause, of magma emplacement in the extending crust.

  19. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Soejono, I.; Janoušek, V.; Žáčková, E.; Sláma, Jiří; Konopásek, J.; Machek, Matěj; Hanžl, P.

    2017-01-01

    Roč. 106, č. 6 (2017), s. 2109-2129 ISSN 1437-3254 Institutional support: RVO:67985530 ; RVO:67985831 Keywords : Cadomian magmatic arc * Brunovistulian Domain * Bohemian Massif * Gondwana margin * U–Pb geochronology * geochemistry Subject RIV: DB - Geology ; Mineralogy; DC - Siesmology, Volcanology, Earth Structure (GFU-E) OBOR OECD: Geology; Volcanology (GFU-E) Impact factor: 2.283, year: 2016

  20. Mineral chemistry and geochemistry of ophiolitic metaultramafics from Um Halham and Fawakhir, Central Eastern Desert, Egypt

    Science.gov (United States)

    Abdel-Karim, Abdel-Aal M.; Ali, Shehata; El-Shafei, Shaimaa A.

    2018-03-01

    This study is focused on ophiolitic metaultramafics from Um Halham and Fawakhir, Central Eastern Desert of Egypt. The rocks include serpentinized peridotites, serpentinites together with talc- and quartz-carbonates. The primary spinel relict is Al-chromite [Cr# > 60], which is replaced by Cr-magnetite during metamorphism. The high Cr# of Al-chromites resembles supra-subduction zone (SSZ) peridotites and suggests derivation from the deeper portion of the mantle section with boninitic affinity. These mantle rocks equilibrated with boninitic melt have been generated by high melting degrees. The estimated melting degrees ( 19-24%) lie within the range of SSZ peridotites. The high Cr# of spinel and Fo content of olivine together with the narrow compositional range suggest a mantle residual origin. Serpentinized peridotite and serpentinites have low Al2O3/SiO2 ratios (mostly serpentinization process. Moreover, they have very low Nb, Ta, Zr and Hf concentrations along with sub-chondritic Nb/Ta (0.3-16) and Zr/Hf (mostly 1-20) ratios further confirming that their mantle source was depleted by earlier melting extraction event. The high chondrite normalized (La/Sm)N ratios (average 10) reflect input of subduction-related slab melts/fluids into their mantle source.

  1. One-carbon (bio ?) Geochemistry in Subsurface Waters of the Serpentinizing Coast Range Ophiolite

    Science.gov (United States)

    Hoehler, Tori M.; Mccollom, Tom; Schrenk, Matt; Cardace, Dawn

    2011-01-01

    Serpentinization - the aqueous alteration of ultramafic rocks - typically imparts a highly reducing and alkaline character to the reacting fluids. In turn, these can influence the speciation and potential for metabolism of one-carbon compounds in the system. We examined the aqueous geochemistry and assessed the biological potential of one-carbon compounds in the subsurface of the McLaughlin Natural Reserve (Coast Range Ophiolite, California, USA). Fluids from wells sunk at depths of 25-90 meters have pH values ranging from 9.7 to 11.5 and dissolved inorganic carbon (DIC concentrations) generally below 60 micromolar. Methane is present at concentrations up to 1.3 millimolar (approximately one-atmosphere saturation), and hydrogen concentrations are below 15 nanomolar, suggesting active consumption of H2 and production of CH4. However, methane production from CO2 is thermodynamically unfavorable under these conditions. Additionally, the speciation of DIC predominantly into carbonate at these high pH values creates a problem of carbon availability for any organisms that require CO2 (or bicarbonate) for catabolism or anabolism. A potential alternative is carbon monoxide, which is present in these waters at concentrations 2000-fold higher than equilibrium with atmospheric CO. CO is utilized in a variety of metabolisms, including methanogenesis, and bioavailability is not adversely affected by pH-dependent speciation (as for DIC). Methanogenesis from CO under in situ conditions is thermodynamically favorable and would satisfy biological energy requirements with respect to both Gibbs Energy yield and power.

  2. X-ray color maps of the zoned garnets from Silgará Formation metamorphic rocks,SantanderMassif, Eastern Cordillera (Colombia

    Directory of Open Access Journals (Sweden)

    Takasu Akira

    2010-12-01

    Full Text Available

    The metamorphic rocks of the Lower Paleozoic Silgará Formation of the Santander Massif, Eastern Cordillera (Colombia, were affected by a Barrovian-type metamorphism under low to high temperature and medium pressure conditions. These rocks contain garnet porphyroblasts, which show several kinds of chemical zoning patterns. The garnet grains behave as closed systems with respect to the rock matrix. Most of the observed zoning patterns are due to gradual changes in physicochemical conditions during growth. However, some garnet grains show complex zoning patterns during multiple deformation and metamorphic events.

  3. Interpretation of the chemical compositions of the cumulates of the gabro-anorthositic massif of Piau River - Bahia State

    International Nuclear Information System (INIS)

    Cruz, M.J.M.; Demange, M.; Fonteilles, M.

    1989-01-01

    The Rio Piau gabbroic and anorthositic complex is an Archean layered body; intrusive in the charnokitic and enderbitic terrains of the Jequie nucleous (Sao Francisco Craton, Bahia State, Brazil). The geochemical data of the Rio Piau massif consists of two magmatic series, better identified by REE, titanium, phosphorous, niobium and gallium contents. These two magmatic series show an evolution following the typical tholeiitic and several types of cumulatic rocks. The evolution of each magmatic series is made up by differentiation and accumulation, from basic terms (MgO = 10%) up to intermediate terms (MgO = 2%) and shows an evolution similar to the Skaergaard trends. (author) [pt

  4. An eclogite-bearing continental tectonic slice in the Zermatt-Saas high-pressure ophiolites at Trockener Steg (Zermatt, Swiss Western Alps)

    Science.gov (United States)

    Weber, Sebastian; Bucher, Kurt

    2015-09-01

    The Theodul Glacier Unit (TGU) at "Trockener Steg" represents a continental slice, embedded within the ophiolitic Zermatt-Saas Zone. The Zermatt-Saas Zone is the remnant of the Piemonte-Liguria oceanic lithosphere, formed in the middle Jurassic and subducted up to eclogite facies conditions in the Early Tertiary. The close spatial association of the TGU to the Zermatt-Saas Zone permits a comparison of the metamorphic evolution of the units by detailed field mapping and a petrological investigation of eclogites. The eclogites from both tectono-metamorphic units can be clearly distinguished by their textures, mineral assemblages and by mineral and bulk-rock composition. Geothermobarometry and computed assemblage stability diagrams for the TGU eclogites indicate P-T conditions of 2.2 ± 0.1 GPa and 580 ± 50 °C. These derived P-T conditions must be considered as minimum peak metamorphic conditions the rocks achieved during subduction. The P-T data are different from those derived for eclogites of Zermatt-Saas Zone adjacent to the Theodul Glacier Unit, that reached maximal burial depths at 2.3-2.4 GPa and 500 ± 50 °C. While the estimates of the eclogites of Zermatt-Saas Zone are in good agreement with some of the previous studies, the contrasting P-T estimates for the TGU eclogites suggest that the Zermatt-Saas complex must be subdivided into several tectonic subunits. The non-uniform peak conditions over the "Trockener Steg" area and the maximum pressures conditions reported from ultra-high pressure localities within Zermatt-Saas Zone suggest, that individual tectonic slices have been assembled after detachment from the slab at the return-point, i.e. along the exhumation path. Detached packages of rocks may range from small tectonic slices up to several kilometer-sized fragments. The TGU is separated from the surrounding rocks of the ophiolite unit by two major tectonic contacts. In addition, the formation of biotite-rich crusts along the basal contact of the TGU

  5. Aqueous Geochemical Dynamics at the Coast Range Ophiolite Microbial Observatory and The Case for Subsurface Mixing of Regional Groundwaters

    Science.gov (United States)

    Cardace, D.; Schrenk, M. O.; McCollom, T. M.; Hoehler, T. M.

    2017-12-01

    Serpentinization is the aqueous alteration (or hydration) of olivine and pyroxene minerals in ultramafic rocks, occurring in the seabed and ultramafic units on continents, such as at the Coast Range Ophiolite (CRO) in northern California, USA. Mineral products of serpentinization include serpentine, magnetite, brucite, talc, oxyhydroxides, carbonates, and diverse clay minerals. Such mineral transformations generate extremely high pH solutions with characteristic cation and dissolved metal loads, transmitting CH4, H2, and CO gas mixtures from depth; deep life in ultramafic terrains is thought to be fueled by chemical energy derived from these geochemical reactions. The installation of 8 groundwater monitoring wells in the CRO has allowed frequent monitoring since 2011. Influx of deeply sourced, serpentinization-influenced waters is evidenced by related geochemical shifts (e.g., pH, oxidation-reduction potential), but is apparently mixing with other, regionally important groundwater types. Evaluation salinity loads in concert with other parameters, we model the mixing scenario of this site of ongoing scientific study and experimentation.

  6. Endeavor research into evolving paradigms around ophiolites: the case of the oceanic igneous complexes of Costa Rica

    International Nuclear Information System (INIS)

    Alvarado, Guillermo E.; Denyer, Perci; Gazel, Esteban

    2009-01-01

    Studies on the radiolarite igneous (ophiolitic) complexes were done for more than one century in Costa Rica that range from Jurassic to Eocene. These studies can be grouped in four stages of knowledge: 1) from 1904 to 1957 were recognized the cherts, and the mafic and ultramafic igneous complexes, the first regional maps were done, and the first time were recognized ellipsoidal basalts, now widely known as pillow lavas. 2) From 1958 to 1978 the complexes were seen under the concept of the association of ophiolites (serpentine, gabbro, diabase, basalts, and related rocks) and interpreted the radiolarites as deep-sea sediments. The stage is characterized by the seminal work of Gabriel Dengo and by the first geochemical analyses in the framework of the plate tectonics. 3) A huge amount of geochemical data, paleontological and K/Ar ages were published from 1979 to 1994 and it was the stage of more controversial papers, their interpretation varied for the same locality (i.e. (Nicoya Peninsula) from relative simple stratigraphic model to a very complex nappe slices, and from a simple tectonic evolution (in situ and formed by a mid oceanic ridge volcanism) to a multistage evolution (terrains, and mid oceanic ridge, aseismic ridge, intraplate and island arc volcanism). The situation was similar in the other Costa Rican oceanic complexes. 4) The outlook for 1995 to the present it has been clarified and mutual agreement between the different groups. The stage is characterized by joint collaboration, the use of modern laboratory techniques as Sr, Nd, and Pb isotopes, major, trace and complete rare earth elements. 40A r/ 39 Ar dating, and volcanological criteria, together with detailed field mapping. The main new result of these studies was that the radiolarites (164-84 Ma) in the Nicoya Peninsula were significatively older than the basic igneous rocks (140-84 Ma), indicating a complex magmatic event intruding and erupting into the thick sedimentary sequence. For other areas

  7. Petrogenesis and tectonic implications of gabbro and plagiogranite intrusions in mantle peridotites of the Myitkyina ophiolite, Myanmar

    Science.gov (United States)

    Xu, Yang; Liu, Chuan-Zhou; Chen, Yi; Guo, Shun; Wang, Jian-Gang; Sein, Kyaing

    2017-07-01

    Centimeter-size intrusions of gabbros and plagiogranites occur in mantle peridotites of the Myitkyina ophiolite, Myanmar. The gabbros mainly consist of plagioclase and clinopyroxene, whereas orthopyroxene occasionally occurs. The plagiogranites are mainly composed of plagioclase, quartz and amphibole, with small amount of accessory minerals, such as zircon, apatite and rutile. Plagioclase in the gabbros varies from andesine to anorthite (An37-91), whereas plagioclase in the plagiogranites is less calcic (An1-40). Clinopyroxene in the gabbros is pervasively altered to hornblende. The gabbros contain 42.97-52.88 wt% SiO2, which show negative correlations with Al2O3, CaO and MgO, but positive correlations with Na2O, P2O5 and TiO2. Microtextural relations reveal the crystallization of clinopyroxene prior to plagioclase in the Myitkyina gabbros. This suggests that the gabbros were crystallized from hydrous melts, which is also supported by the occurrence of orthopyroxene and anorthitic plagioclase in some gabbros. The gabbros have slightly enriched Sr-Nd isotopes, with initial 87Sr/86Sr ratios of 0.703938-0.706609 and εNd(t) values of + 2.4-+7.2, and relatively variable Hf isotopes, with εHf(t) values of + 13.4-+24.9. A subduction component is required to explain the decoupled Nd-Hf isotopes of the gabbros. Binary mixing suggests that addition of ca 2% subducted sediments to a depleted mantle can account for the Nd-Hf decoupling. Therefore, both petrological and geochemical data of the gabbros support that the Myitkyina ophiolite was originated in a supra-subduction zone setting. The plagiogranites have compositions of tonalites and trondhjemites, containing 56.93-77.93 wt% SiO2, 1.27-10.79 wt% Na2O and 0.05-0.71 wt% K2O. They are slightly enriched in LREE over HREE and display positive anomalies in Eu, Zr, Hf but negative Nb anomalies. Very low TiO2 contents (0.03-0.2 wt%) of the plagiogranites suggest that they were not products of fractional crystallization of MORB

  8. A stable isotope study of serpentinization in the Fengtien ophiolite, Taiwan

    Energy Technology Data Exchange (ETDEWEB)

    Tzen-Fu Yui; Hsueh-Wen Yeh (Univ. of Hawaii, Honolulu (USA)); Chihming Wang Lee (National Taiwan Univ. (Taiwan))

    1990-05-01

    Detailed H- and O-isotopic studies of serpentinites of Fengtien ophiolite have been made in order to enhance our knowledge on the process of serpentinization. Pseudomorphic lizardites have {delta}{sup 18}O = +3.6{per thousand} and {delta}D = {minus}48 to {minus}49{per thousand}; bladed-mat and foliated antigorites have {delta}{sup 18}O = +3.5 to +5.8{per thousand} and {delta}D = {minus}45 to {minus}69{per thousand}; slickensided antigorites have {delta}{sup 18}O = +4.1 to +4.9{per thousand} and {delta}D = {minus}46 to {minus}50{per thousand}; picrolites have {delta}{sup 18}O = +4.2 to +4.3{per thousand} and {delta}D = {minus}65 to {minus}67{per thousand}; and slickensided chrysotiles have {delta}{sup 18}O = +4.1 to +4.5{per thousand} and {delta}D = {minus}80{per thousand}. It is suggested that lizardite might have formed in an oceanic environment, whereas antigorite and chrysotile have formed in continental environments. These results depict complicated multiple serpentinization processes. Isotopic temperatures calculated using {delta}{sup 18}O values of coexisting fissure-filling minerals range from 325 to 370{degree}C, which are consistent with those derived from phase equilibria involving serpentines. The narrow range of {delta}{sup 18}O and wide range of {delta}D values for antigorite and chrysotile also demonstrate that water/rock ratios during these serpentinizations should not have been high. These Fengtien serpentines fall outside either of the continental domains described by Wenner and Taylor (1973, 1974); and fall within their oceanic domain. We suggest that the domains proposed by Wenner and Taylor (1973, 1974) should be extended and that the terms, especially the continental antigorite and the continental lizardite-chrysotile, should be purely occurrence-descriptive.

  9. Fault slip versus slope deformations: Experience from paleoseismic trenches in the region with low slip-rate faults and strong Pleistocene periglacial mass wasting (Bohemian Massif)

    Czech Academy of Sciences Publication Activity Database

    Špaček, P.; Valenta, Jan; Tábořík, Petr; Ambrož, V.; Urban, M.; Štěpančíková, Petra

    2017-01-01

    Roč. 451, 7 SEP (2017), s. 56-73 ISSN 1040-6182 R&D Projects: GA ČR GAP210/12/0573; GA MŠk(CZ) LM2015079; GA MŠk 7AMB13AT023 Institutional support: RVO:67985891 Keywords : Active faulting * Paleoseismology * Slope deformation * Solifluction * Colluvium * Quaternary * Bohemian massif Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.199, year: 2016

  10. Preandean geological configuration of the eastern North Patagonian Massif, Argentina

    Directory of Open Access Journals (Sweden)

    Daniel A. Gregori

    2013-11-01

    Full Text Available The Preandean geological configuration of the eastern North Patagonian Massif is established through the use of geological and geophysical analysis. The positive gravity anomalies located near the Atlantic coast are due to 535 and 540 Ma old rocks belonging to the Pampean Orogeny (Precambrian–middle Cambrian, which are widely recognized in central and northern Argentina. The Famatinian Cycle (Ordovician–Devonian is represented by a Silurian–Devonian marine basin equivalent to those of eastern-central Argentina and South Africa, and which was deformed at the end of the Devonian by an ∼E–W to WNW–ESE compressional event, part of the Famatinian Orogeny. Containing strong gravity gradients, the NW–SE belt is coincident with fault zones which were originated during the Gondwanide Orogeny. This event also produced NW–SE overthrusting of the Silurian–Devonian sequences and strike-slip faults that displaced blocks in the same direction. This deformation event belongs to the Gondwanide Orogeny that includes movements related to a counterclockwise rotation of blocks in northern Patagonia. The strong negative anomalies located in the western part of the area stem from the presence of rocks of the Jurassic Cañadón Asfalto basin interbedded in the Marifil Complex. These volcaniclastic sequences show mild deformation of accommodation zones in a pre-Jurassic paleorelief.

  11. Weathering profiles in granitoid rocks of the Sila Massif uplands, Calabria, southern Italy: New insights into their formation processes and rates

    Science.gov (United States)

    Scarciglia, Fabio; Critelli, Salvatore; Borrelli, Luigi; Coniglio, Sabrina; Muto, Francesco; Perri, Francesco

    2016-05-01

    In this paper we characterized several weathering profiles developed on granitoid rocks in the Sila Massif upland (Calabria, southern Italy), integrating detailed macro- and micromorphological observations with physico-mechanical field tests and petrographic, mineralogical and geochemical analyses. We focused our attention on the main weathering and pedogenetic processes, trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties, and two common weathering indices, such as the micropetrographic index (Ip) and the chemical index of alteration (CIA). Our results showed that sericite on plagioclase and biotite chloritization, that represent inherited features formed during late-stage hydrothermal alteration of granitoid rocks, may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions, especially in lower weathering grade classes. Moreover, the frequent identification of Fe-Mn oxides and clay coatings of illuvial origin (rather than or in addition to those formed in situ), both at the macro- and microscale, may also explain an overestimation of the weathering degree with respect to field-based classifications. Finally, some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes (cryoclastism and thermoclastism), that lead to rock breakdown even when chemical weathering is not well developed. Hence, our study showed that particular caution is needed for evaluating weathering grades, because traditional field and geochemical-petrographic tools may be biased by inherited hydrothermal alteration, physical weathering and illuvial processes. On the basis of chronological constraints to soil formation obtained from a 42 ka-old volcanic input (mixed to granite parent materials) detected in the soil cover of the Sila Massif upland, a first attempt to estimate

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

    Czech Academy of Sciences Publication Activity Database

    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: 3.723, year: 2015

  13. Migmatization and low-pressure overprinting metamorphism as record of two pre-Cretaceous tectonic episodes in the Santander Massif of the Andean basement in northern Colombia (NW South America)

    Science.gov (United States)

    Zuluaga, C. A.; Amaya, S.; Urueña, C.; Bernet, M.

    2017-03-01

    The core of the Santander Massif in the northern Andes of Colombia is dominated by migmatitic gneisses with a 7.5 kbar. Lithologies are overprinted by low-pressure metamorphism, related to extensive Jurassic intrusions and linked with growth of cordierite and equilibration of low-pressure mineral assemblages, recorded metamorphic conditions are Pangaea.

  14. Seismotectonic significance of the 2008–2010 Walloon Brabant seismic swarm in the Brabant Massif, Belgium

    Science.gov (United States)

    Van Noten, Koen; Lecocq, Thomas; Shah, Anjana K.; Camelbeeck, Thierry

    2015-01-01

    Between 12 July 2008 and 18 January 2010 a seismic swarm occurred close to the town of Court-Saint-Etienne, 20 km SE of Brussels (Belgium). The Belgian network and a temporary seismic network covering the epicentral area established a seismic catalogue in which magnitude varies between ML -0.7 and ML 3.2. Based on waveform cross-correlation of co-located earthquakes, the spatial distribution of the hypocentre locations was improved considerably and shows a dense cluster displaying a 200 m-wide, 1.5-km long, NW-SE oriented fault structure at a depth range between 5 and 7 km, located in the Cambrian basement rocks of the Lower Palaeozoic Anglo-Brabant Massif. Waveform comparison of the largest events of the 2008–2010 swarm with an ML 4.0 event that occurred during swarm activity between 1953 and 1957 in the same region shows similar P- and S-wave arrivals at the Belgian Uccle seismic station. The geometry depicted by the hypocentral distribution is consistent with a nearly vertical, left-lateral strike-slip fault taking place in a current local WNW–ESE oriented local maximum horizontal stress field. To determine a relevant tectonic structure, a systematic matched filtering approach of aeromagnetic data, which can approximately locate isolated anomalies associated with hypocentral depths, has been applied. Matched filtering shows that the 2008–2010 seismic swarm occurred along a limited-sized fault which is situated in slaty, low-magnetic rocks of the Mousty Formation. The fault is bordered at both ends with obliquely oriented magnetic gradients. Whereas the NW end of the fault is structurally controlled, its SE end is controlled by a magnetic gradient representing an early-orogenic detachment fault separating the low-magnetic slaty Mousty Formation from the high-magnetic Tubize Formation. The seismic swarm is therefore interpreted as a sinistral reactivation of an inherited NW–SE oriented isolated fault in a weakened crust within the Cambrian core of

  15. Evaluation of Southern Quebec asbestos residues for CO2 sequestration by mineral carbonation

    Energy Technology Data Exchange (ETDEWEB)

    Beaudoin, G.; Hebert, R.; Constantin, M. [Laval Univ., Quebec City, PQ (Canada); Bonin, G. [LAB Chrysotile Inc., Black Lake, PQ (Canada); Dipple, G. [British Columbia Univ., Vancouver, BC (Canada)

    2003-08-01

    One alternative to help reduce carbon dioxide (CO{sub 2}) levels in the atmosphere is to sequester CO{sub 2} by mineral carbonation using ultramafic rock-hosted magnesian silicates (serpentine, olivine, talc). The carbonation process produces magnesite, which is a geologically stable and an environmentally safe magnesium carbonate. Three CO{sub 2} sinks exist in southern Quebec use such silicates. They are: (1) asbestos mill residues, (2) associated mine waste, and (3) ultramafic bedrock. Extraction of asbestos in the region has been accomplished from serpentinized harzburgite located in the Thetford Mines and Asbestos ophiolitic massifs and also from the highly sheared Pennington Sheet. The physical and chemical properties of magnesium silicate deposits greatly determine their carbonation potential. A wide range of properties was observed in samples obtained from almost all asbestos mill residues and waste. The reaction which takes place depends on the mineral content. The kinetics of the reactions are influenced by humidity and grain size.

  16. Evaluation of southern Quebec asbestos residues for CO{sub 2} sequestration by mineral carbonation : preliminary result

    Energy Technology Data Exchange (ETDEWEB)

    Huot, F. [Geo-conseils, Cap-Rouge, PQ (Canada); Beaudoin, G.; Hebert, R.; Constantin, M. [Laval Univ., Dept. of Geology and Geological Engineering, Quebec City, PQ (Canada); Bonin, G. [LAB Chrysotile Inc., Black Lake, PQ (Canada); Dipple, G.M. [British Columbia Univ., Vancouver, BC (Canada). Dept. of Earth and Ocean Sciences

    2003-07-01

    Carbon dioxide (CO{sub 2}) sequestration is one approach that can help reduce CO{sub 2} levels in the atmosphere. This paper discusses CO{sub 2} sequestration by mineral carbonation using ultramafic rock-hosted magnesian silicates (serpentine, olivine, talc). The carbonation process produces magnesite, which is a geologically stable and an environmentally safe magnesium carbonate. There are 3 potential CO{sub 2} sinks in southern Quebec that use such silicates. They are: (1) asbestos mill residues, (2) associated mine waste, and (3) ultramafic bedrock. Asbestos is extracted from serpentinized harzburgite located in the Thetford Mines and Asbestos ophiolitic massifs and also from the highly sheared Pennington Sheet. The physical and chemical properties of magnesium silicate deposits greatly determine their carbonation potential. A wide range of properties was observed in samples obtained from almost all asbestos mill residues and waste. The reaction which takes place depends on the mineral content. The kinetics of the reactions are influenced by humidity and grain size.

  17. Fossil intermediate-depth earthquakes in subducting slabs linked to differential stress release

    Science.gov (United States)

    Scambelluri, Marco; Pennacchioni, Giorgio; Gilio, Mattia; Bestmann, Michel; Plümper, Oliver; Nestola, Fabrizio

    2017-12-01

    The cause of intermediate-depth (50-300 km) seismicity in subduction zones is uncertain. It is typically attributed either to rock embrittlement associated with fluid pressurization, or to thermal runaway instabilities. Here we document glassy pseudotachylyte fault rocks—the products of frictional melting during coseismic faulting—in the Lanzo Massif ophiolite in the Italian Western Alps. These pseudotachylytes formed at subduction-zone depths of 60-70 km in poorly hydrated to dry oceanic gabbro and mantle peridotite. This rock suite is a fossil analogue to an oceanic lithospheric mantle that undergoes present-day subduction. The pseudotachylytes locally preserve high-pressure minerals that indicate an intermediate-depth seismic environment. These pseudotachylytes are important because they are hosted in a near-anhydrous lithosphere free of coeval ductile deformation, which excludes an origin by dehydration embrittlement or thermal runaway processes. Instead, our observations indicate that seismicity in cold subducting slabs can be explained by the release of differential stresses accumulated in strong dry metastable rocks.

  18. Use of isotopes to study groundwater recharge in arid zones: Application to the crystalline Ahaggar massif (central Sahara)

    International Nuclear Information System (INIS)

    Saighi, O.

    1999-01-01

    In the crystalline and igneous Ahaggar massif, the water resources are found in some small-scale phreatic aquifers which are recharged by sporadic wadi floods. The most favourable aquifer zones are localized in the valleys, consisting of three overlying levels of varying importance: the alluvial aquifer, the weathered zone of the underlying substratum, and the deep aquifer of fissured basement, the extent of which is not limited only to wadis. In order to evaluate the recharge to the different aquifers, chemical and isotopic analyses have been carried out on a hundred samples taken at different depths. Measurements of oxygen-18, deuterium, carbon-13, carbon-14 and tritium have been carried out on these samples

  19. Trace element behavior during serpentinization/de-serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)

    OpenAIRE

    DEBRET, Baptiste; ANDREANI, Muriel; GODARD, Marguerite; NICOLLET, Christian; SCHWARTZ, Stéphane; LAFAY, Romain

    2013-01-01

    Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its...

  20. Differences in composition of shallow-water marine benthic communities associated with two ophiolitic rock substrata

    Science.gov (United States)

    Bavestrello, Giorgio; Bo, Marzia; Betti, Federico; Canessa, Martina; Gaggero, Laura; Rindi, Fabio; Cattaneo-Vietti, Riccardo

    2018-01-01

    On marine rocky shores, several physical, chemical and biological processes operate to maintain the benthic assemblages' heterogeneity, but among the abiotic factors, the composition and texture of the rocky substrata have been only sporadically considered. However, biomineralogical studies have demonstrated an unsuspected ability of the benthic organisms to interact at different levels with rocky substrata. Therefore, the mineralogy of the substratum can affect the structure of benthic communities. To evaluate this hypothesis, the macrobenthic assemblages developed on two different ophiolitic rocks (serpentinites and metagabbros) in contact at a restricted stretch of the western Ligurian Riviera (western Mediterranean Sea), with identical environmental and climatic conditions, were analysed. Samplings were carried out at four bathymetric levels (+1m, 0m, -1m, and -3m respect to the mean sea level) and the analysis of the data evidenced differences in terms of species distribution and percent coverage. Algal communities growing on metagabbros were poorer in species richness and showed a much simpler structure when compared to the assemblages occurring on the serpentinites. The most widely distributed animal organism, the barnacle Chthamalus stellatus, was dominant on serpentinites, and virtually absent on metagabbros. Our results suggest a complex pattern of interactions between lithology and benthic organisms operating through processes of inhibition/facilitation related to the mineral properties of the substratum.

  1. High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement

    Science.gov (United States)

    Vilhelm, Jan; Slavík, Lubomír

    2014-05-01

    For the purpose of non-destructive monitoring of rock properties in the underground excavation it is possible to perform repeated high-accuracy P- and S-wave velocity measurements. This contribution deals with preliminary results gained during the preparation of micro-seismic long-term monitoring system. The field velocity measurements were made by pulse-transmission technique directly on the rock outcrop (granite) in Bedrichov gallery (northern Bohemia). The gallery at the experimental site was excavated using TBM (Tunnel Boring Machine) and it is used for drinking water supply, which is conveyed in a pipe. The stable measuring system and its automatic operation lead to the use of piezoceramic transducers both as a seismic source and as a receiver. The length of measuring base at gallery wall was from 0.5 to 3 meters. Different transducer coupling possibilities were tested namely with regard of repeatability of velocity determination. The arrangement of measuring system on the surface of the rock massif causes better sensitivity of S-transducers for P-wave measurement compared with the P-transducers. Similarly P-transducers were found more suitable for S-wave velocity determination then P-transducers. The frequency dependent attenuation of fresh rock massif results in limited frequency content of registered seismic signals. It was found that at the distance between the seismic source and receiver from 0.5 m the frequency components above 40 kHz are significantly attenuated. Therefore for the excitation of seismic wave 100 kHz transducers are most suitable. The limited frequency range should be also taken into account for the shape of electric impulse used for exciting of piezoceramic transducer. The spike pulse generates broad-band seismic signal, short in the time domain. However its energy after low-pass filtration in the rock is significantly lower than the energy of seismic signal generated by square wave pulse. Acknowledgments: This work was partially

  2. Molybdenite-tungstenite association in the tungsten-bearing topaz greisen at Vítkov (Krkonoše-Jizera Crystalline Complex, Bohemian Massif): indication of changes in physico-chemical conditions in mineralizing system

    Czech Academy of Sciences Publication Activity Database

    Pašava, J.; Veselovský, F.; Drábek, M.; Svojtka, Martin; Pour, O.; Klomínský, J.; Škoda, R.; Ďurišová, Jana; Ackerman, Lukáš; Halodová, P.; Haluzová, Eva

    2015-01-01

    Roč. 60, č. 3 (2015), s. 149-161 ISSN 1802-6222 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : LA-ICP-MS * EMPA * molybdenite * tungstenite * transitional Mo–W and W–Mo disulfides * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.326, year: 2015

  3. Transition from island-arc to passive setting on the continental margin of Gondwana: U-Pb zircon dating of Neoproterozoic metaconglomerates from the SE margin of the Teplá-Barrandian Unit, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Dunkley, D. J.; Kachlík, V.; Kusiak, M. A.

    2008-01-01

    Roč. 461, 1-4 (2008), s. 44-59 ISSN 0040-1951 Institutional research plan: CEZ:AV0Z30130516 Keywords : Bohemian Massif * Teplá–Barrandian Unit * Neoproterozoic * Armorican Terrane Assemblage * Gondwana * zircon dating Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.677, year: 2008

  4. Micro-FTIR and EPMA Characterisation of Charoite from Murun Massif (Russia

    Directory of Open Access Journals (Sweden)

    Maria Lacalamita

    2018-01-01

    Full Text Available Combined micro-Fourier transform infrared (micro-FTIR and electron probe microanalyses (EPMA were performed on a single crystal of charoite from Murun Massif (Russia in order to get a deeper insight into the vibrational features of crystals with complex structure and chemistry. The micro-FTIR study of a single crystal of charoite was collected in the 6000–400 cm−1 at room temperature and after heating at 100°C. The structural complexity of this mineral is reflected by its infrared spectrum. The analysis revealed a prominent absorption in the OH stretching region as a consequence of band overlapping due to a combination of H2O and OH stretching vibrations. Several overtones of the O-H and Si-O stretching vibration bands were observed at about 4440 and 4080 cm−1 such as absorption possibly due to the organic matter at about 3000–2800 cm−1. No significant change due to the loss of adsorbed water was observed in the spectrum obtained after heating. The occurrence of well-resolved water bending vibration bands at about 1595 and 1667 cm−1 accounts for more than one structural water molecule as expected by charoite-90 polytype structure model from literature. The chemical composition of the studied crystal is close to the literature one.

  5. Unraveling the Quaternary river incision in the Moselle valley (Rhenish Massif, Germany): new insights from cosmogenic nuclide dating (10Be/26Al) of the Main Terrace complex

    Science.gov (United States)

    Rixhon, Gilles; Cordier, Stéphane; Harmand, Dominique; May, Simon Matthias; Kelterbaum, Daniel; Dunai, Tibor; Binnie, Steven; Brückner, Helmut

    2014-05-01

    Throughout the whole river network of the Rhenish Massif, the terrace complex of the so-called Main Terrace forms the morphological transition between a wide upper palaeovalley (plateau valley) and a deeply incised lower valley. The youngest level of this Main Terrace complex (YMT), directly located at the edge of the incised valley, represents a dominant geomorphic feature in the terrace flight; it is often used as a reference level to identify the start of the main middle Pleistocene incision episode (Demoulin & Hallot, 2009). The latter probably reflects the major tectonic pulse that affected the whole Massif and was related to an acceleration of the uplift rates (Demoulin & Hallot, 2009). The Main terraces are particularly well preserved in the lower Moselle valley and are characterized by a constant absolute elevation of their base along a 150 km-long reach. Despite that various hypotheses have been proposed to explain this horizontality (updoming, faulting...), all studies assumed an age of ca. 800 ka for the YMT, mainly based on the questionable extrapolation of palaeomagnetic data obtained in the Rhine valley. Therefore, a reliable chronological framework is still required to unravel the spatio-temporal characteristics of the Pleistocene evolution of the Moselle valley. In this study, we apply cosmogenic nuclide dating (10Be/26Al) to fluvial sediments pertaining to the Main Terrace complex or to the upper Middle Terraces. Several sites along the lower Moselle were sampled following two distinct sampling strategies: (i) depth profiles where the original terrace (palaeo-)surface is well preserved and did not experience much postdepositional burial (e.g., loess cover); and (ii) the isochron technique where the sediment thickness exceeds 3 m. Cosmogenic nuclide ages recently obtained for three rivers in the Meuse catchment in the western Rhenish Massif demonstrated that the Main Terraces were younger than expected and their abandonment was diachronic along the

  6. Petrological, Geochemical and Sr–Nd–O Isotopic Constraints on the Origin of Garnet and Spinel Pyroxenites from the Moldanubian Zone of the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Svojtka, Martin; Ackerman, Lukáš; Medaris Jr., G.; Hegner, E.; Valley, J. W.; Hirajima, T.; Jelínek, E.; Hrstka, Tomáš

    2016-01-01

    Roč. 57, č. 5 (2016), s. 897-920 ISSN 0022-3530 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100131203 Program:Program interní podpory projektů mezinárodní spolupráce AV ČR Institutional support: RVO:67985831 Keywords : garnet and spinel pyroxenites * Bohemian Massif * Sr, Nd, and oxygen isotopes * trace elements * subduction Subject RIV: DD - Geochemistry Impact factor: 3.280, year: 2016

  7. IODP Expedition 340T: Borehole Logging at Atlantis Massif Oceanic Core Complex

    Directory of Open Access Journals (Sweden)

    Donna Blackman

    2013-03-01

    Full Text Available Integrated Ocean Drilling Program (IODP Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP. Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800–1400 meters below seafloor (mbsf portionof the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offsetnow extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution.

  8. The Taavinunnanen gabbro massif. A compilation of results from geological, geophysical and hydrogeological investigations

    International Nuclear Information System (INIS)

    Gentzschein, B.; Tullborg, E.L.

    1985-01-01

    The gabbro massif at Taavinunnanen, northern Sweden, is one of the study sites which has been investigated by the Swedish Nuclear Fuel and Waste Management Co (SKB) in order to study different geological environments within the scope of the long-range program for final disposal of spent nuclear fuel. A 700 metres long borehole was drilled within the gabbro. Regional geophysics, geological mapping, petrographical studies, mineralogical studies of rock-forming materials and of fracture fillings as well as hydrogeological tests were carried out. The gabbro shows primary differentiation. Thus, the composition varies from gabbroic to ultrabasic. The gabbro body is intersected by severeal granite dikes. These dikes exhibit a higher hydraulic conductivity and a higher fracture frequency than the gabbro. Comparison of hydraulic conductivity and fracture frequency in the gabbro itself indicates a high degree of sealing of the fractures mainly caused by smectites. Calcite is almost lacking down to a depth of 75 metres, indicating a relatively rapid transport of surface waters down to this depth. With 27 refs. (author)

  9. K-Ar ages of the low-grade metamorphic rocks in the Altar massif, Northwest Sonora, Mexico

    International Nuclear Information System (INIS)

    Hayama, Yoshikazu; Shibata, Ken; Takeda, Hideo.

    1984-01-01

    The K-Ar ages of low-grade regional metamorphism, granodiorite intrusion and its contact metamorphism were studied in the Altar massif of Northwest Sonora, Mexico. The results gave the ages of 55 Ma for metamorphic hornblende and 15 to 17 Ma for mica of metamorphic rocks and granodiorite. About the meaning of these discordant ages and the too young ages of 15 to 17 Ma against the previously presented data, we pointed out the following two possibilities; 1) the contact effect of the Miocene granodiorite on the regional metamorphic rocks of the Laramide phase, 2) both regional metamorphism and granodiorite intrusion took place during the Laramide phase, whereas the young ages, 15 to 17 Ma, show the time of temperature release after the low-angle thrust movement, which is well known in the hinterland of the Sevier orogenic belt in Nevada and Utah. (author)

  10. Sr isotope stratigraphy of some Rupelian carbonated laminites from the Limagne Basin: influence of seawater in the rift of the French Massif central?

    International Nuclear Information System (INIS)

    Briot, D.; Poidevin, J.L.

    1998-01-01

    87 Sr/ 86 Sr ratios of biogenic and abiotic calcites Upper Rupelian sediments in the Limagne rift (French Massif Central) define a smooth and regular negative correlation with time interrupted by repetitive sharp peaks; the progressive drop in isotopic ratio can be explained by the geological evolution of the river basin through time. Negative peaks are explained by synsedimentary volcanism, repeated marine incursions, or leaching of ancient evaporites. Comparison with available paleontologic data does not favour the volcanic explanation, but rather the influence of Rupelian marine waters. (authors)

  11. The rockfall observatory in the Reintal, Wetterstein Massif, German Alps

    Science.gov (United States)

    Schöpa, Anne; Turowski, Jens M.; Hovius, Niels

    2017-04-01

    The Reintal is an Alpine valley in the Wetterstein Massif close to the Zugspitze, Germany's highest mountain. Due to the variety of active geomorphic processes, including rockfalls off the steep limestone cliffs, debris flows, and snow avalanches, and the river Partnach, the Reintal has been the field area of many geomorphological and hydrological research campaigns over the last few decades. In 2014, the Geomorphology Section of the GFZ Potsdam started to install a monitoring network to detect and classify rockfalls in the Reintal. The network includes six seismic stations, optical and infrared cameras, and two weather stations measuring air and rock temperature, air pressure and relative humidity, precipitation, wind speed and direction, and solar radiation. The continuous observations of the network are supplemented by repeated field campaigns including terrestrial laser scans of a prominent rockfall niche at the Hochwanner mountain. The about 1,500 m high north face of the Hochwanner experienced the detachment of a 2.8 Mio m3 rockfall about 500 years ago that created the so-called Steingerümpel (German for rock debris deposit) and dammed the river Partnach. The cliff still shows high rockfall activity, and an 80,000 m3 block can be expected to fall in the near future. In this contribution, the layout of the observatory and details of the seismic network centered around the Hochwanner north face are described. Furthermore, the network data of a severe thunderstorm event in June 2016, that triggered many rockfalls and debris flows in the Reintal, is presented.

  12. Palladium, platinum, rhodium, iridium and ruthenium in chromite- rich rocks from the Samail ophiolite, Oman.

    Science.gov (United States)

    Page, N.J.; Pallister, J.S.; Brown, M.A.; Smewing, J.D.; Haffty, J.

    1982-01-01

    30 samples of chromitite and chromite-rich rocks from two stratigraphic sections, 250 km apart, through the basal ultramafic member of the Samail ophiolite were spectrographically analysed for platinum-group elements (PGE) and for Co, Cu, Ni and V. These data are reported as are Cr/(Cr + Al), Mg/(Mg + Fe) and wt.% TiO2 for most samples. The chromitite occurs as pods or lenses in rocks of mantle origin or as discontinuous layers at the base of the overlying cumulus sequence. PGE abundances in both sections are similar, with average contents in chromite-rich rocks: Pd 8 ppb, Pt 14 ppb, Rh 6 ppb, Ir 48 ppb and Ru 135 ppb. The PGE data, combined with major-element and petrographic data on the chromitite, suggest: 1) relatively larger Ir and Ru contents and highest total PGE in the middle part of each section; 2) PGE concentrations and ratios do not correlate with coexisting silicate and chromite abundances or chromite compositions; 3) Pd/PGE, on average, increases upward in each section; 4) Samail PGE concentrations, particularly Rh, Pt and Pd, are lower than the average values for chromite-rich rocks in stratiform intrusions. 2) suggests that PGEs occur in discrete alloy or sulphide phases rather than in the major oxides or silicates, and 4) suggests that chromite-rich rocks from the oceanic upper mantle are depleted in PGE with respect to chondrites. L.C.C.

  13. Lower Brioverian formations (Upper Proterozoic) of the Armorican Massif (France): geodynamic evolution of source areas revealed by sandstone petrography and geochemistry

    Science.gov (United States)

    Dabard, Marie Pierre

    1990-11-01

    Formations with interbedded cherts constitute an important part of the Lower Brioverian succession (Upper Proterozoic age) in the Armorican Massif (northwest France). These formations are composed of shale-sandstone alternations with interbedded siliceous carbonaceous members. Petrographic and geochemical study of the detrital facies shows that these rocks are compositionally immature. The wackes are rich in lithic fragments (volcanic fragments: 3-20% modal; sedimentary and metamorphic fragments: 0-7% modal) and in feldspar (5-16%). From the geochemical point of view, they are relatively enriched in Fe 2+MgO (about 5.5%) and in alkalis with {Na 2O }/{K 2O } ratios greater than 1. The CaO contents are low (about 0.3%). Slightly negative Eu anomalies are observed ( {Eu}/{Eu ∗} = 0.8 ). Their chemical compositions are in agreement with a dominantly acidic source area with deposition in a continental active margin setting. Compared with other Upper Proterozoic deposits of the Armorican Massif, the interbedded-chert formations appear rather similar to other deposits in North Brittany which accumulated in an intra-arc or back-arc basin environment. The formations with interbedded cherts are interpreted as having been deposited during an early stage of magmatic arc activity (around 640-630 Ma ago) in an immature marginal basin. The clastic supply to these formations is derived in part from early volcanic products (acidic to intermediate) which are linked to subduction beneath the North Armorican Domain. Another component is inherited from the reworking of 2000 Ma old basement relics. The opening of the back-arc domain, with associated basaltic volcanism, would bring about a progressive displacement of the interbedded-chert depositional basin towards the continental margin.

  14. Migration of 137Cs artificial radionuclide in the valley of the Takhtakushuk river of the Degelen massif

    International Nuclear Information System (INIS)

    Panitskij, A.V.

    2005-01-01

    Study of horizontal and vertical radionuclide distribution in the valley of the Takhtakushuk River of the 'Degelen' Massif is carried out in the framework of ecological and biological investigations of soil and plant cover within radioactive contaminated areas, and radionuclide migration in biological chain 'soil - plant - animal'. For the first time, the pool-type method was used in the studies of soil of the valley that allows tracing solid and liquid substances migrating by means of surface and soil drainage from its head to final part. This paper presents some physical and chemical properties of the study landscape's soils, radionuclide content in soil genetic horizons of the valley. The study results showed that major mass of 137 Cs radionuclide is sorbed by soil humus and fine-dispersed clay particles of grass soils within the valley. (author)

  15. The Alleret Maar lacustrine sequence (French Massif Central): a 150 ka long early-middle Pleistocene continental paleoenvironmental record.

    Science.gov (United States)

    Nomade, S.; Pastre, J.; Guillou, H.; Gauthier, A.; Scaillet, S.

    2008-12-01

    Lacustrine maar sequences of the French Massif Central are of great interest for paleoclimatic and paleoenvironmental reconstructions of mid-latitudes Quaternary continental environments. In particular, the western Velay region yields exceptional sequences spanning the last 450 ka (Reille et al., J. Quat. Sci. 2000). However, older sequences remain largely unknown despite the presence of interbedded alkaline tephras allowing precise absolute radiochronological control of many lacustrine squences. The Alleret maar is a 1500 m wide phreatomagmatic crater that provides a long lacustrine sequence (41 m). The upper part of this sequence (AL2 core, 14.6 m) was studied between 2005 and 2006 (Pastre et al., C. R. Acad Sci, 2007). A 39Ar/40Ar date (557 ± 5ka) obtained from an interbedded tephra layer located at 7m as well as the associated pollen data attribute the beginning of this sequence to the MIS 15. Thanks to the AL3 core recovered in 2005 (40.6 m, CNRS Meudon) several new tephra layers were discovered in the bottom part of this lacustrine sequence. Three new 39Ar/40Ar ages (single crystal analyses) from trachytic tephra layers were obtained at the LSCE Argon Laboratory (France). These layers are located at -30.2, -36.2 and -39.2m. Ages obtained relative to the ACR-2 flux standard (1,201Ma, Kuiper et al., Science, 2008) range from 692 ± 6 ka (MSWD: 2.3, n=18) for the youngest (-30.2m) to 726 ± 9Ka Ka (MSWD: 2.2, n=12) for the lowest tephra located at -39.2m. These new dates indicate a relatively homogeneous deposition rate of 3.5cm/ka and that the last 10 meters cover the MIS 17-MIS18 period. According to these current radiochronological data the complete lacustrine sequence last more than 150ka. Ongoing sedimentary and pollen studies will allow to extend the paleoenvironmental and paleoclimatic records of the French Massif Central towards the beginning of the early middle Pleistocene.

  16. Geochemical and petrological constraints on mantle composition of the Ohře(Eger) rift, Bohemian Massif: peridotite xenoliths from the České Středohoří Volcanic complex and northern Bohemia

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Medaris Jr., G.; Špaček, P.; Ulrych, Jaromír

    2015-01-01

    Roč. 104, č. 8 (2015), s. 1957-1979 ISSN 1437-3254 R&D Projects: GA ČR GA205/09/1170 Institutional support: RVO:67985831 Keywords : Bohemian Massif * mantle * metasomatism * Ohře(Eger) rift * xenolith Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.133, year: 2015

  17. Geochemical aspects of alkaline massif of Banhadao, PR, Brazil

    International Nuclear Information System (INIS)

    Ruberti, E.; Gomes, C.B.; Dutra, C.V.

    1987-01-01

    The alkaline massif of Banhadao, located near Cerro Azul, State of Parana, southern Brazil, occupies an area of about 8 Km 2 and is constituted by three magnetic associations: a group of mesocratic to leucocratic coarse nepheline syenites (NeS) (melanite NeS, NeS I, and light reddish and grey varieties of NeS II); a second group of medium to fine-grained ultrabasic to basic rocks (phlogopite melteigites and petrologically related malignites and feldspar-melanite ijolites); and a group of fine-grained to aphanitic phonolotic dikes, cutting NeS. The rocks of the complex are miaskitic, showing low concentrations of trace elements (V, Th and mainly REE), lack of rare metal silicates, and relative abundance of apatite and sphene. NeS are distinguished by a differentiation trend in which highly differentiated end members are enriched in alkalis and Al 2 O 3 , with decrease in MgO, FeO (total), CaO and TiO 2 . The less differentiated melanite-rich rocks show higher concentrations in Zr, Nb, Y and V. Phlogopite melteigites and associated rocks show the highest contents of MgO, FeO (total), CaO and TiO 2 , and the lowest concentration of alkalis and Al 2 O 3 ; they are significantly enriched in Ba and are the only rocks with detectable amounts of Ni, Cu and Cr. The phonolites are chemically similar to NeS. The Banhadao rocks were probably formed during successive intrusions of two different magmas types. The source of NeS and phonolites was probably a nephelinitic magma, while phlogopite melteigites and related rocks were probably derived from an alkali-enriched ferromagnesian magna. Both parent magmas probably derived by melting of rocks of the lower crust or upper mantle. (author) [pt

  18. Seawater Circulation and Thermal Sink at OCEAN Ridges - FIELD Evidence in Oman Ophiolite

    Science.gov (United States)

    Nicolas, A. A.; Boudier, F. I.; Cathles, L. M.; Buck, W. R.; Celerier, B. P.

    2014-12-01

    Exceptionally, the lowermost gabbros in the Oman ophiolite are black and totally fresh, except for minute traces of impregnation by seawater fluids at very high temperature (~1000°C). These black gabbros sharply contrast with normal, whitish gabbros altered down to Low-T~500-350°C. These hydrous alterations are ascribed to an unconventional model of seawater circulation and cooling of the permanent magma chambers of fast spreading ocean ridges. In this model, gabbros issued from the magma chamber cross a ~100 m thick thermal boundary layer (TBL) before reaching a narrow, Low-T high permeability channel where the heated return seawater is flowing towards black smokers and the local gabbros are altered. Uprising mantle diapirs in Oman diverge at ~5 km on each side of the palaeo-ridge axis and feed an overlying magma chamber that closes at this distance from axis. Preservation of black gabbros along the Moho implies that the loop of seawater alteration locally does not reach Moho beyond this ~5km distance (otherwise black gabbros would be altered in whitish gabbros). This defines an internal "thermal sink" within ~5 km to the ridge axis. There, the sink is efficiently cooled by the active hydrothermal convection that is ridge transverse. This has been documented near the Galapagos ridge by marine geophysical data, within the same distance. Beyond this critical distance, the cooling system becomes dominantly conductive and ridge-parallel. The TBL and attached return flow channels must be rising into the overcooled, accreted crust. Beyond the thermal sink, the 500°C isotherm rebounds into the crust. It is only after ~ 1My of crustal drift that this isotherm penetrates into the uppermost mantle in a sustained fashion, developing serpentinites at the expense of peridotites.

  19. Short Term vs Long Term Environmental Reconstruction from Carbonated Deposits of the Limagne Area (Massif Central, France)

    Energy Technology Data Exchange (ETDEWEB)

    Barbecot, F.; Gibert, E.; Amokrane, Y.; Massault, M.; Noret, A. [Centre National de la Recherche Scientifique Interaction et Dynamique des Environnements de Surface, Universite Paris (France); Ghaleb, B. [Geotop, Universite du Quebec a Montreal, Montreal (Canada)

    2013-07-15

    A 80 cm sequence has been cored from carbonated travertine in the limagne area (French Massif Central, France) in order to document recent environmental fluctuations (0-100 a) of gaseous springs, in relation to the environmental and geochemical parameters that control the isotopic signatures of modern carbonate deposits. The chronology of these finely laminated deposits that are ideal for reconstructing hydrological conditions at very narrow time steps is determined through AMS-{sup 14}C and {sup 210}Pb/{sup 226}Ra radiometric methods. Preliminary results highlight a high enrichment in stable isotopes (eg up to +8 per mille vs VPDB for {delta}{sup 13}C), likely linked to both recharge temperature and degassing processes. Moreover, two general trends are superimposed: the first one, cyclic, may be correlated to the hydrologic annual/biannual budget while the second one, linear, implies a long term environmental trend. (author)

  20. Petrology of forearc basalt-related isotropic gabbros from the Bonin Ridge, Izu-Bonin forearc

    Science.gov (United States)

    Garcia, S. E.; Loocke, M. P.; Snow, J. E.

    2017-12-01

    The early arc volcanic rocks exposed on the Bonin Ridge (BR), a large forearc massif in the Izu-Bonin arc, have provided us with a natural laboratory for the study of subduction initiation and early arc development. The BR has been the subject of focused sampling by way of dredging, diving, and drilling (IODP EXP352) expeditions which have revealed a composite stratigraphy consisting, from bottom to top, of intercalated peridotites and gabbros, isotropic gabbros, sheeted dykes, and a lava sequence which transitions from forearc basalt (FAB) to more arc-like volcanics up section. Although little has been published regarding the moho-transition zone rocks of the BR in comparison to the volcanic rocks, even less work has been published regarding the isotropic gabbros recovered in close association with FABs. Ishizuka et al. (2011) determined that the isotropic gabbros are compositionally and temporally related to the FABs. We provide the first petrologic characterization, including petrography and electron probe microanalysis, of a suite of FAB-related gabbros recovered by dredge D42 of the 2007 R/V Hakuho Maru KH07-02 dredging cruise. Preliminary petrographic observations of the fourteen thin sections reveal that all of the samples contain variable amounts of relict orthopyroxene and consist of five disseminated oxide gabbros, 5 oxide gabbros, and 2 gabbros. We note that all of the D42 gabbros exhibit strong textural variability akin to the varitextured gabbros described in the dyke-gabbro transition of ophiolites (e.g., MacLeod and Yaouancq, 2000). Geochemical data from this critically understudied horizon have the potential to inform regarding the nature of crustal accretion during subduction initiation and the formation, migration, and evolution of FABs. Further, with many authors comparing the volcanic record and crustal stratigraphy of the BR to ophiolites (e.g., Ishizuka et al., 2014), these data would provide another in situ analogue for comparison with the

  1. Lu-Hf geochronology on cm-sized garnets using microsampling: New constraints on garnet growth rates and duration of metamorphism during continental collision (Menderes Massif, Turkey)

    Science.gov (United States)

    Schmidt, Alexander; Pourteau, Amaury; Candan, Osman; Oberhänsli, Roland

    2015-12-01

    This study shows Lu-Hf geochronology of zoned garnet crystals contained in mica schists from the southern Menderes Massif, Turkey. Selected samples are four 3-5 cm large garnet megacrysts of which several consecutive garnet shells have been sampled with a micro-saw and analyzed for dating. The results are used to extract growth rates of garnet, and also to improve the time constraint for Alpine-aged overprint of the Pan-African basement in the Menderes Massif. Lu-Hf ages of the sampled garnet shells are determined by two-point garnet-only isochrons using the garnets' Lu-depleted rim compositions. This yields a consistent decrease of age information from core to rim segments of individual garnet crystals and the calculated isochron ages propose a time frame of growth between 42.6 ± 1.9 and 34.8 ± 3.1 Ma. Major element profiles in the investigated garnets characterize zoning patterns indicative of prograde conditions: Rayleigh fractionated bell-shaped Mn and decreasing Fe/(Fe + Mg) are recorded by the garnets' core to rim compositions. Therefore the obtained Lu-Hf ages record timing of early prograde growth for the cores of the garnets. Two of the large garnet crystals also yield isochron ages of 58.83 ± 0.69 and 50.16 ± 0.84 Ma in their innermost cores, which appear to record an early nucleation event. This view, however, is not in concordance with the observed major element profiles of these garnets, and therefore is interpreted with caution. Termination of the garnet growth period is determined through the calculation of radial growth rates based on the size of the garnets and the Lu-Hf ages obtained for consecutive shells. Extrapolation of these rates potentially constrains the total duration for garnet growth terminating at 31 ± 6 Ma. Comparison of the growth rates calculated for individual crystals shows a variety of slow and fast growing garnets, and similar results have been previously obtained with the Rb-Sr and Sm-Nd isotope systems. The new data

  2. Geophysical Characterization of Serpentinite Hosted Hydrogeology at the McLaughlin Natural Reserve, Coast Range Ophiolite

    Science.gov (United States)

    Ortiz, Estefania; Tominaga, Masako; Cardace, Dawn; Schrenk, Matthew O.; Hoehler, Tori M.; Kubo, Michael D.; Rucker, Dale F.

    2018-01-01

    Geophysical remote sensing both on land and at sea has emerged as a powerful approach to characterize in situ water-rock interaction processes in time and space. We conducted 2-D Electrical Resistivity Tomography (ERT) surveys to investigate in situ hydrogeological architecture within the Jurassic age tectonic mélange portion of the Coast Range Ophiolite Microbial Observatory (CROMO) during wet and dry seasons, where water-rock interactive processes are thought to facilitate a subsurface biosphere. Integrating survey tracks traversing two previously drilled wells, QV1,1 and CSW1,1 at the CROMO site with wireline and core data, and the Serpentine Valley site, we successfully documented changes in hydrogeologic properties in the CROMO formation, i.e., lateral and vertical distribution of conductive zones and their temporal behavior that are dependent upon seasonal hydrology. Based on the core-log-ERT integration, we propose a hydrogeological architectural model, in which the formation is composed of three distinct aquifer systems: perched serpentinite aquifer without seasonal dependency (shallow system), well-cemented serpentine confining beds with seasonal dependency (intermediate system), serpentinite aquifer (deep system), and the ultramafic basement that acts as a quasi-aquiclude (below the deep system). The stunning contrast between the seasonality in the surface water availability and groundwater storativity in the formation allowed us to locate zones where serpentinite weathering and possibly deeper serpentinization processes might have taken place. We based our findings primarily on lithological composition and the distribution of the conductive formation, our work highlights the link between serpentinite weathering processes and possible sources of water in time and space.

  3. Significance of Zr-in-Rutile Thermometry for Deducing the Decompression P–T Path of a Garnet–Clinopyroxene Granulite in the Moldanubian Zone of the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Usuki, T.; Iizuka, Y.; Hirajima, T.; Svojtka, Martin; Lee, H.-Y.

    2017-01-01

    Roč. 58, č. 6 (2017), s. 1173-1198 ISSN 0022-3530 Grant - others:Program interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100131203 Program:Program interní podpory projektů mezinárodní spolupráce AV ČR Institutional support: RVO:67985831 Keywords : Bohemian Massif * P–T path * Zr-in-rutile thermometry * high-pressure granulite * continental collision * garnet–clinopyroxene barometry Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 3.280, year: 2016

  4. A critique of massification of higher education in Poland and the United States: Mass-media discourse analysis

    Directory of Open Access Journals (Sweden)

    Łukasz Stankiewicz

    2017-01-01

    Full Text Available The nearly universal access to higher education (HE in developed countries was once praised as a great democratic achievement, and a basis for both economic development and social mobility. After the onset of the 2008 recession, the narratives changed considerably. The most radical critics of HE propose a partial “deschooling” of society by reversing the process of massification. This paper aims to present a critical discourse analysis (CAD of the “don’t go to college” discourse that became popular in Poland and the United States. I trace the differences in the way the decision to go to college is conceptualized in Poland and the U.S to the differences in dominant political ideologies – democratic and egalitarian in the U.S., paternalistic and conservative in Poland. I also show how recent changes in the actual HE systems put those ideologies at odds with the educational realities of both countries.

  5. A preliminary spatial-temporal study of some soil characteristics in the calcareous massif of Sicó, Portugal.

    Science.gov (United States)

    Torres, Maria Odete; Neves, Maria Manuela

    2016-04-18

    The mountainous massif of Sicó, in the centre of Portugal, is an extensive area composed of calcareous Jurassic formations. Hillside calcareous soils, with high pH, present chemical restrictions to support plant growth and are subjected to important erosion processes leading to their degradation if not protected by vegetation. In a first year of study some soil physicochemical characteristics have been measured in some geo-referenced locations of a larger design experiment and an exploratory spatial analysis has been performed. The objective of this study was to present some suggestions in order to give sustainable phosphorus fertiliser recommendations aiming to establish pastures in these soils and thus support traditional livestock activity. Ten years apart, those soil characteristics have been measured again in the same locations and comparisions have been made. The objective was to understand the variability of the soil properties under study in order to better adequate the fertiliser soil management regarding the area restoration.

  6. The Alto Moxoto Terrain in Eastern Paraiba ('Caldas Brandao Massif')

    International Nuclear Information System (INIS)

    Neves, Benjamim Bley de Brito; Campos Neto, Mario da Costa; Souza, Solange Lucena de; Schmus, William Randall Van; Fernandes, Tania Maria Gomes

    2001-01-01

    The Alto Moxoto Terrane (TAM), at the east of Paraiba State is mostly composed of sheared ortho gneisses, porphyritic granodioritic gneisses and it bears an imbricated sheet of Al-rich (garnet-biotite-sillimanite) gneisses, deeply affected by migmatization phenomena. This litho-structural assemblage is drawing a regional asymmetric anti formal structure, with its axial zone running parallel to the B R-230 highway (E-W trending). It is limited in both, north (Alto Pajeu terrane) and south (Rio Capibaribe terrane) sides by important shear zones, which are feather faults connected with the development of the Pernambuco lineament, to the southwest. The adopted designation of 'terrane' is based upon its singular geological features, in terms of lithological and structural characteristics, Paleoproterozoic in age and sharp limits with the different confining terranes. TAM is here considered as a mega-fragment of the Atlantica Super continent, that was built up by the Paleoproterozoic Collage ('Transamazonian') and that was preserved in the framework of West Gondwana (Brasiliano/Pan African Collage) as a 'terrane'. This terrane shows conspicuous continuity to the far interior of the province, to the southwestern part of Pernambuco State, and so doing, it demonstrates that the former designation of 'Caldas Brandao Massif must be ruled out, as obsolete for many reasons. Geochronological determinations using Rb-Sr, Sm-Nd and U-Pb methods confirm the Paleoproterozoic age of this terrane, with the presence of some Archean protoliths as well as the various degrees of structural reworking and isotopic reseting promoted by the Brasiliano Cycle. This cycle was responsible for some intrusive granites, for most of the general geological features, like usual informal limits and even the present shape of the TAM, a typical reworked 'basement inlier'. (author)

  7. Lichen flora particular features of Degelen mountain massif in location of underground nuclear explosion carrying out

    International Nuclear Information System (INIS)

    Ajdarkhanova, G.S.; Andreeva, E.I.; Tuleubaev, B.A.

    1998-01-01

    The 25 kinds of dominant lichens of the Degelen mountain massif of the former Semipalatinsk test site are studied. It is defined, that complex of ecological factors have influence on spreading of lichen flora ceno-population. Lichens heterogeneousness in ability to radionuclides accumulation is determining of variety its anatomic-morphologic structure and physiological activity as well as physico-chemical properties of soils in places of its inhabited place. It is determined, that lichens are able to exist within limits of exposure dose capacity 18-3000 μR/h and under radioactivity by α-radiation 233-426 Bq/kg, by β-radiation 7000-15000 Bq/kg and Cs 137 150-620 Bq/kg. The largest accumulating ability have Parmelia scortea (570 Bq/kg), Parmelia fraudans (620 Bq/kg), Parmelia cetrata (470 Bq/kg), Parmelia conspersa (340 Bq/kg). Cesium-137 in lichens in 2-8 times higher than maximum permissible dose. Complete relation is showed between lichens and inhabitated substrates created conditions for determination of radiation situation by precise characteristics of lichen flora

  8. Stimulation Of The Methane Production With The Use Of Changing Of The Rock Massif Physical Conditions

    Directory of Open Access Journals (Sweden)

    Baev Mikhail

    2017-01-01

    Full Text Available The commercial coalbed methane production success is majorly defined by the effectiveness of the use of special gas inflow stimulation methods. The necessity of using of such methods issubject to the aspects of searching and displacement of methane within the coal compound. Theanalysis of the ways of methane production stimulation from virgin coal formations is given. The description of the process of hydraulic fracturing (fracturing as the most common stimulation method during the commercial coalbed methane production as well as its major advantages are presented. The present work provides data about the initiated laboratory research of sands collected from Kemerovo region deposits for the purpose of finding of the most prospective samples by means of anchoring of fractures. The prospectivity and ability to implement the hydraulic fracturing with the use of locally available sands acting as proppants are shown. The influence of the strain-stress state of the rock massif on the alteration of permeability and the necessity of its extension study with respect to different technological features of hydraulic fracturing is shown

  9. VOSGES, a long and rich geologic history

    Science.gov (United States)

    Dominique, Carteaux; Cyrille, Delangle; Sophie, Demangel

    2015-04-01

    The study of geology in scientific classes is often too theoretical and abstract for the pupils. How can teachers make the link between some samples of rocks observed in a practical class and the geologic story of the region? There's nothing better than outdoor education to establish a relationship between the rock observed in macroscopic and microscopic scale in the classroom,with the outcrop scale and the landscape scale in the field: all of them are the result of a fascinating geologic history.Our pupils are lucky enough to live at the heart of a modest mountain massif that has a very rich geologic story: the massif from Vosges situated in the east of France. During two expeditions we show the students all the following tectonic processes: Accretion at the scale of the landscape with the Rhenish Ditch (tectonic and volcanic markers) Obductionis observed due to ophiolites found in the massive of Thalhorn (peridotite, gabbro and sedimentary marine rocks of great depth). Collisionis illuminated with numerous sites like the schists of Steige, the phyllite of Villé, the gneisses of Climont. Subductionis captured bystudying the outcrops of magmatic rocks within the continental crust (andesite, diorite, granodiorite). At each of the stops we have the students, from a hand sample, to findits story in a more global context. So the theory becomes reality. A study of thin slides of rocks observed on the ground finishes these exits and so various scales of understanding are approached. The long and rich geologic history of Vosges maybe reconstituted on hundreds of million years, allowing certainly giving another aspect to the living environment of our pupils.

  10. First insights on the molybdenum-copper Bled M'Dena complex (Eglab massif, Algeria)

    Science.gov (United States)

    Lagraa, Karima; Salvi, Stefano; Béziat, Didier; Debat, Pierre; Kolli, Omar

    2017-03-01

    Molybdenum-Copper showings in the Eglab massif (eastern part of the Reguibat rise of Algeria), are found in quartz-monzodiorite and granodiorite of the Bled M'Dena complex, a Paleoproterozoic circular structure of ∼5 km in diameter, comprising volcanic and intrusive suites. The latter consist of quartz-diorite, quartz-monzodiorite and granodiorite with a metaluminous normative composition. They display an "adakitic character" with moderate light rare-earth element (LREE) enrichment, minor Eu anomalies, high Sr/Y ratio and low Yb concentration, suggestive of a hydrous, arc magma of volcanic-arc affinity. The mineralization occurs mostly in quartz + molybdenite + chalcopyrite stockwork veins marked by widespread propylitic alteration along the selvages. Molybdenite and chalcopyrite are commonly associated with calcite, which precipitated at relatively late stages of the hydrothermal alteration. Fluid inclusions related to the mineralization stage, range from aqueous to aqueous-carbonic to solid bearing. The latter inclusions have the highest homogenization temperature (up to ∼400 °C), are salt saturated, and commonly contain molybdenite and/or chalcopyrite crystals. The petrology and geochemistry of the host rocks, the style of the hydrothermal alteration, the ore mineral associations, and the characteristics of the fluid inclusions, are all coherent in indicating that the Bled M'Dena represents a Paleoproterozoic porphyry style Mo mineralization, which is far unreported in the African continent.

  11. An alkaline spring system within the Del Puerto ophiolite (California USA): A Mars analog site

    Energy Technology Data Exchange (ETDEWEB)

    Blank, J.G.; Green, S.; Blake, D.; Valley, J.; Kita, N.; Treiman, A.; Dobson, P.F.

    2008-10-01

    Mars appears to have experienced little compositional differentiation of primitive lithosphere, and thus much of the surface of Mars is covered by mafic lavas. On Earth, mafic and ultramafic rocks present in ophiolites, oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of cold-water alkaline springs associated with these mafic and ultramafic rocks represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene, yields fluids with unusual chemistry (Mg-OH and Ca-OH waters with pH values up to {approx}12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rockhosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial alkaline springs associated with mafic and ultramafic rocks are particularly timely. This study focuses on the alkaline Adobe Springs, emanating from mafic and ultramafic rocks of the California Coast Range, where a community of novel bacteria is associated with the precipitation of Mg-Ca carbonate cements. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.

  12. Methane Dynamics in a Tropical Serpentinizing Environment: The Santa Elena Ophiolite, Costa Rica

    Directory of Open Access Journals (Sweden)

    Melitza Crespo-Medina

    2017-05-01

    Full Text Available Uplifted ultramafic rocks represent an important vector for the transfer of carbon and reducing power from the deep subsurface into the biosphere and potentially support microbial life through serpentinization. This process has a strong influence upon the production of hydrogen and methane, which can be subsequently consumed by microbial communities. The Santa Elena Ophiolite (SEO on the northwestern Pacific coast of Costa Rica comprises ~250 km2 of ultramafic rocks and mafic associations. The climatic conditions, consisting of strongly contrasting wet and dry seasons, make the SEO a unique hydrogeological setting, where water-rock reactions are enhanced by large storm events (up to 200 mm in a single storm. Previous work on hyperalkaline spring fluids collected within the SEO has identified the presence of microorganisms potentially involved in hydrogen, methane, and methanol oxidation (such as Hydrogenophaga, Methylobacterium, and Methylibium spp., respectively, as well as the presence of methanogenic Archaea (such as Methanobacterium. Similar organisms have also been documented at other serpentinizing sites, however their functions have not been confirmed. SEO's hyperalkaline springs have elevated methane concentrations, ranging from 145 to 900 μM, in comparison to the background concentrations (<0.3 μM. The presence and potential activity of microorganisms involved in methane cycling in serpentinization-influenced fluids from different sites within the SEO were investigated using molecular, geochemical, and modeling approaches. These results were combined to elucidate the bioenergetically favorable methane production and/or oxidation reactions in this tropical serpentinizing environment. The hyperalkaline springs at SEO contain a greater proportion of Archaea and methanogens than has been detected in any terrestrial serpentinizing system. Archaea involved in methanogenesis and anaerobic methane oxidation accounted from 40 to 90% of total

  13. Geochemical study of water-rock interaction processes on geothermal systems of alkaline water in granitic massif; Estudio geoquimico de los procesos de interaccion agua-roca sobre sistemas goetermales de aguas alcalinas en granitoides

    Energy Technology Data Exchange (ETDEWEB)

    Buil gutierrez, B; Garcia Sanz, S; Lago San Jose, M; Arranz Uague, E; Auque Sanz, L [Universidad de Zaragoza (Spain)

    2002-07-01

    The study of geothermal systems developed within granitic massifs (with alkaline waters and reducing ORP values) is a topic of increasing scientific interest. These systems are a perfect natural laboratory for studying the water-rock interaction processes as they are defined by three main features: 1) long residence time of water within the system, 2) temperature in the reservoir high enough to favour reaction kinetics and finally, 3) the comparison of the chemistry of the incoming and outgoing waters of the system allows for the evaluation of the processes that have modified the water chemistry and its signature, The four geothermal systems considered in this paper are developed within granitic massifs of the Spanish Central Pyrenes; these systems were studied from a geochemical point of view, defining the major, trace and REE chemistry of both waters and host rocks and then characterizing the composition and geochemical evolution of the different waters. Bicarbonate-chloride-sodic and bicarbonate-sodic compositions are the most representative of the water chemistry in the deep geothermal system, as they are not affected by secondary processes (mixing, conductive cooling, etc). (Author)

  14. Petrology and geochemistry of mafic magmatic rocks from the Sarve-Abad ophiolites (Kurdistan region, Iran): Evidence for interaction between MORB-type asthenosphere and OIB-type components in the southern Neo-Tethys Ocean

    Science.gov (United States)

    Saccani, Emilio; Allahyari, Khalil; Rahimzadeh, Bahman

    2014-05-01

    The Sarve-Abad (Sawlava) ophiolites crop out in the Main Zagros Thrust Zone and represent remnants of the Mesozoic southern Neo-Tethys Ocean that was located between the Arabian shield and Sanandaj-Sirjan continental block. They consist of several incomplete ophiolitic sequences including gabbroic bodies, a dyke complex, and pillow lava sequences. These rocks generally range from sub-alkaline to transitional character. Mineral chemistry and whole-rock geochemistry indicate that they have compositions akin to enriched-type mid-ocean ridge basalts (E-MORB) and plume-type MORB (P-MORB). Nonetheless, the different depletion degrees in heavy rare earth elements (HREE), which can be observed in both E-MORB like and P-MORB like rocks enable two main basic chemical types of rocks to be distinguished as Type-I and Type-II. Type-I rocks are strongly depleted in HREE (YbN 9.0). Petrogenetic modeling shows that Type-I rocks originated from 7 to 16% polybaric partial melting of a MORB-type mantle source, which was significantly enriched by plume-type components. These rocks resulted from the mixing of variable fractions of melts generated in garnet-facies and the spinel-facies mantle. In contrast, Type-II rocks originated from 5 to 8% partial melting in the spinel-facies of a MORB-type source, which was moderately enriched by plume-type components. A possible tectono-magmatic model for the generation of the southern Neo-Tethys oceanic crust implies that the continental rift and subsequent oceanic spreading were associated with uprising of MORB-type asthenospheric mantle featuring plume-type component influences decreasing from deep to shallow mantle levels. These deep plume-type components were most likely inherited from Carboniferous mantle plume activity that was associated with the opening of Paleo-Tethys in the same area.

  15. Geology of the epithermal Ag-Au Huevos Verdes vein system and San José district, Deseado massif, Patagonia, Argentina

    Science.gov (United States)

    Dietrich, Andreas; Gutierrez, Ronald; Nelson, Eric P.; Layer, Paul W.

    2012-03-01

    The San José district is located in the northwest part of the Deseado massif and hosts a number of epithermal Ag-Au quartz veins of intermediate sulfidation style, including the Huevos Verdes vein system. Veins are hosted by andesitic rocks of the Bajo Pobre Formation and locally by rhyodacitic pyroclastic rocks of the Chon Aike Formation. New 40Ar/39Ar constraints on the age of host rocks and mineralization define Late Jurassic ages of 151.3 ± 0.7 Ma to 144.7 ± 0.1 Ma for volcanic rocks of the Bajo Pobre Formation and of 147.6 ± 1.1 Ma for the Chon Aike Formation. Illite ages of the Huevos Verdes vein system of 140.8 ± 0.2 and 140.5 ± 0.3 Ma are 4 m.y. younger than the volcanic host rock unit. These age dates are among the youngest reported for Jurassic volcanism in the Deseado massif and correlate well with the regional context of magmatic and hydrothermal activity. The Huevos Verdes vein system has a strike length of 2,000 m, with several ore shoots along strike. The vein consists of a pre-ore stage and three main ore stages. Early barren quartz and chalcedony are followed by a mottled quartz stage of coarse saccharoidal quartz with irregular streaks and discontinuous bands of sulfide-rich material. The banded quartz-sulfide stage consists of sulfide-rich bands alternating with bands of quartz and bands of chlorite ± illite. Late-stage sulfide-rich veinlets are associated with kaolinite gangue. Ore minerals are argentite and electrum, together with pyrite, sphalerite, galena, chalcopyrite, minor bornite, covellite, and ruby silver. Wall rock alteration is characterized by narrow (propylitic alteration. Gangue minerals are dominantly massive quartz intergrown with minor to accessory adularia. Epidote, illite, illite/smectite, and, preferentially at deeper levels, Fe-chlorite gangue indicate near-neutral pH hydrothermal fluids at temperatures of >220°C. Kaolinite occurring with the late sulfide-rich veinlet stage indicates pH 315°, whereas strike

  16. Pb-Pb Dating mono zircon from Gloria Norte Massif, Sergipano belt; Datacao de Pb-Pb em monozircao do Macico Gloria Norte, faixa Sergipana

    Energy Technology Data Exchange (ETDEWEB)

    Lisboa, V.A.C.; Rosa, M.L.S.; Conceicao, H., E-mail: viniciuslisboa1@hotmail.com [Pós-Graduacão em Geociências e Análise de Bacias/Universidade Federal de Sergipe, São Cristóvão, SE (Brazil); Macambira, M.J.B.; Galarza, M.A. [Pós-Graduacão em Geociências/Universidade Federal do Pará, Belem, PA (Brazil); Rios, D.C. [Departamento de Geologia/Universidade Federal da Bahia, Salvador, BA (Brazil)

    2014-11-01

    The Gloria Norte Massif (MGN) has about 50 km{sup 2} in area, lies between the cities of Nossa Senhora da Gloria and Monte Alegre, northeastern Sergipe state, is composed of monzonitic rocks, being intrusive in metasediments Domain Macurure, in the Sergipano Belt. In this study Pb-Pb geochronological determinations were performed using the evaporation technique single crystals of zircon in MGN. Two samples were analyzed (03A and 12A) and the results were ages of 646 ± 2.5 Ma and 650 ± 4.5 Ma, place this magmatism in the Cryogenian period. These data may imply that around 645-655 Ma, there was an active magmatic arc in this region of the Sergipano Belt. (author)

  17. New petrographic, geochemical and geochronological data for the Reguengos de Monsaraz pluton (Ossa Morena Zone, SW Iberian Massif, Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, A.; Santos, J. F.; Azevedo, M. R.; Mendez, M. H.; Ribeiro, S.

    2010-07-01

    The Reguengos de Monsaraz pluton is a late to post-tectonic Variscan intrusion occurring in the Ossa Morena Zone (Iberian Variscan Chain). The dominant lithological types are tonalites and granodiorites, but the internal area of the massif is composed of gabbro-dioritic rocks. Field evidence shows that the intrusion is heterogeneous at mesoscopic scale suggesting that the emplacement of mafic and felsic magmas was contemporaneous. Petrographic and geochemical studies reveal that the different lithologic types define a continuous sequence with compositions varying from metaluminous to slightly peraluminous and a typical calc-alkaline signature. In Harker variation diagrams, it is possible to observe systematic rectilinear correlations pointing to the involvement of magma mingling/mixing processes in the petrogenesis of this sequence. Rb-Sr isotopic data, using a mineral-mineral pair from a granodiorite sample, yielded an age of 298 Ma, interpreted as a cooling age after igneous crystallization. (Author) 13 refs.

  18. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    Science.gov (United States)

    Soejono, Igor; Janoušek, Vojtěch; Žáčková, Eliška; Sláma, Jiří; Konopásek, Jiří; Machek, Matěj; Hanžl, Pavel

    2017-09-01

    Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U-Pb data (601 ± 3 Ma, Brno Massif; 634 ± 6 Ma, paraautochtonous core of the Svratka Dome; 568 ± 3 Ma, Bíteš orthogneiss) from the allochtonous Moravicum indicate the prolonged magmatic activity within the Brunovistulian Domain during the Ediacaran. The major- and trace-element and Sr-Nd isotopic signatures show heterogeneous geochemical characteristics of the granitic rocks and suggest a magmatic-arc geotectonic setting. The two-stage Depleted Mantle Nd model ages ( c. 1.3-2.0 Ga) indicate derivation of the granitic rocks from a relatively primitive crustal source, as well as from an ancient and evolved continental crust of the Brunovistulian Domain. These results constrain the magmatic-arc activity to c. 635-570 Ma and provide a further evidence for a long-lived (at least c. 65 Myr) and likely episodic subduction-related magmatism at the northern margin of Gondwana. The presence of granitic intrusions derived from variously mature crustal sources at different times suggests heterogeneous crustal segments to having been involved in the magmatic-arc system during its multistage evolution.

  19. Les granites sodiques et les roches associées de l'ophiolite de Chamrousse-Tabor et du groupe de Rioupéroux-Livet ( Isère-France) - Pétrochimie et géochimie .

    OpenAIRE

    Scarenzi , Denis

    1984-01-01

    Les roches leucocrates du massif UB-B de Chamrousse - Tabor sont intrusives au sommet de la séquence ophiolitique et y sont associées à des gabbros cumulats, des ferrogabbros, des basaltes et des dolérites. Ces roches correspondent à des cumulats plagioclastiques (albitites et anorthosites), des diorites quartziques, des tonalltes et des leucotonalites. . Des diorites quartziques, tonalites et leucotonalites sont également présentes dans le groupe de Séchilienne. Elles y sont accompagnées par...

  20. Tephras in lacustrine sediments of the Sarliève marsh (French Massif Central): age and preservation

    Science.gov (United States)

    Fourmont, Agathe; Macaire, Jean-Jacques; Bréhéret, Jean-Gabriel; Argant, Jacqueline; Prat, Béatrice; Vernet, Gérard

    2006-12-01

    The Sarliève marsh sediments (Massif Central, France) contain two tephras. The first tephra [ 13.7±0.4ka(2δ), ca. 12 000 BP], regionally well known, enables to date the beginning of lacustrine infill to the Lateglacial. The second tephra, the 'tephra de Sarliève', the emitting volcano of which is unknown, would be dated to around the Early Subboreal from pollen data. This occurrence, after the discovery of the 'tephra de Beaunit', emphasizes that volcanic eruption(s) occurred in the 'Chaîne des Puys' or in the volcanic Cézallier more than 1000 years after the last known eruption (Pavin) in the 'Chaîne des Puys' at around 6.6/6.7 ka (5800/5900 BP). In the Sarliève piles, these tephras, well preserved in thick and more silicated deposits of deltas, were not observed in carbonated basin sediments where they were altered. The abundance of authigenic zeolites formed during the Lateglacial in restricted depocentre lacustrine waters allows us to detect initial CF1 tephra occurrence. To cite this article: A. Fourmont et al., C. R. Geoscience 338 (2006).

  1. Lithological Classification Using Sentinel-2A Data in the Shibanjing Ophiolite Complex in Inner Mongolia, China

    Directory of Open Access Journals (Sweden)

    Wenyan Ge

    2018-04-01

    Full Text Available As a source of data continuity between Landsat and SPOT, Sentinel-2 is an Earth observation mission developed by the European Space Agency (ESA, which acquires 13 bands in the visible and near-infrared (VNIR to shortwave infrared (SWIR range. In this study, a Sentinel-2A imager was utilized to assess its ability to perform lithological classification in the Shibanjing ophiolite complex in Inner Mongolia, China. Five conventional machine learning methods, including artificial neural network (ANN, k-nearest neighbor (k-NN, maximum likelihood classification (MLC, random forest classifier (RFC, and support vector machine (SVM, were compared in order to find an optimal classifier for lithological mapping. The experiment revealed that the MLC method offered the highest overall accuracy. After that, Sentinel-2A image was compared with common multispectral data ASTER and Landsat-8 OLI (operational land imager for lithological mapping using the MLC method. The comparison results showed that the Sentinel-2A imagery yielded a classification accuracy of 74.5%, which was 2.5% and 5.08% higher than those of the ASTER and OLI imagery, respectively, indicating that Sentinel-2A imagery is adequate for lithological discrimination, due to its high spectral resolution in the VNIR to SWIR range. Moreover, different data combinations of Sentinel-2A + ASTER + DEM (digital elevation model and OLI + ASTER + DEM data were tested on lithological mapping using the MLC method. The best mapping result was obtained from Sentinel-2A + ASTER + DEM dataset, demonstrating that OLI can be replaced by Sentinel-2A, which, when combined with ASTER, can achieve sufficient bandpasses for lithological classification.

  2. Sylvicultural procedures in catchment areas of the mountain streams as exemplified by the Skrzyczne massif in Poland

    Directory of Open Access Journals (Sweden)

    Małek Stanisław

    2014-03-01

    Full Text Available Extensive disintegration of spruce forests in the Beskidy Mts. in South Poland generates a need to regenerate sizeable areas as well as to rebuild forest stands which have defended themselves against breakdown. In practice, the magnitude of relevant management tasks does not allow for keeping up with the progressive destruction of forest, especially at higher altitudes, where natural regeneration does not occur as much as necessary. In addition, the species composition is limited to spruce, sometimes accompanied by beech and fir, whereas other species have a negligible share. What may be helpful in solving this problem is the method of regeneration of such areas and of establishment of under-canopy cultures, consisting of patchwork, multi-stage regeneration task performance, starting from the areas with the best chance of reforestation success and using the existing self-sown trees. Such areas undoubtedly include habitats with better water balance, i.e. humid habitats (in the case of larger areas, distinguished in the forest management plan as humid forest site types. The aim of the present study was to propose management of watercourses and headwater areas in the region of the Skrzyczne massif where the selected catchments are situated on the southern (the Malinowski Stream and the northern (the Roztoka Czyrna stream slopes of this massif. The research was carried out in August 2012 and included juxtaposition of available hydrological maps with actual field conditions along with identification of springs and streams and the course of their beds in order to update the existing data. The updating of the forest numerical maps in the existing databases of the State Forests IT System (SILP included verification of the course of streams and determination of their nature (permanent or periodic with a division into the existing ones and the added ones. The data was recorded against the background of the division of the forest surface, contour lines

  3. Heavy Metal Resistant, Alkalitolerant Bacteria Isolated From Serpentinizing Springs in the Zambales Ophiolite, Philippines

    Science.gov (United States)

    Vallalar, B.; Meyer-Dombard, D. R.; Cardace, D.; Arcilla, C. A.

    2016-12-01

    Serpentinization involves hydrologic alteration of ultramafic mantle rocks containing olivine and pyroxene to produce serpentine minerals. The fluids resulting from this reaction are reduced, extremely depleted in dissolved inorganic carbon, and are highly alkaline with pH values typically exceeding 10. Major byproducts of the serpentinizing reaction include iron oxides, hydrogen, methane, and small amounts of organic molecules that provide chemosynthetic energy for subsurface microbial communities. In addition, weathering of serpentine rocks often produces fluids and sediments that have elevated concentrations of various toxic heavy metals such as chromium, nickel, cobalt, copper, and zinc. Thus, microorganisms inhabiting these unique ecological niches must be adapted to a variety of physicochemical extremes. The purpose of this study is to isolate bacteria that are capable of withstanding extremely high concentrations of multiple heavy metals from serpentine fluid-associated sediments. Fluid and sediment samples for microbial culturing were collected from Manleluag Spring National Park located on the island of Luzon, Philippines. The area is part of the Zambales ophiolite range, and hosts several serpentinizing fluid seeps. Fluid emanating from the source pool of the spring, designated Manleluag 2 (ML2), has a pH of 10.83 and temperature of 34.4 °C. Luria-Bertani agar medium was supplemented with varying concentrations of five trace elements - Cu, Cr, Co, Ni, and Zn. Environmental samples were spread on each of these media and colony forming units were subsequently chosen for isolation. In all, over 20 isolates were obtained from media with concentrations ranging from 25 mg/L - 400 mg/L of each metal. Taxonomic identity of each isolate was determined using 16S rRNA gene sequences. The isolates were then tested for tolerance to alkaline conditions by altering LB medium to pH values of 8, 9, 10, 11, and 12. The majority of strains exhibit growth at the highest p

  4. Debris flows of the mountain massif of Hjorthfjellet and Adventtoppen, Svalbard: Implications for gullies on mountains in the Argyre basin, Mars

    Science.gov (United States)

    Reiss, D.; Hiesinger, H.; Zanetti, M.; Hauber, E.; Johnsson, A.; Carlsson, E.; Raack, J.; Olvmo, M.; Johansson, H. A. B.; Johansson, L.; Fredriksson, S.; Schmidt, H. T.; McDaniel, S.; Heldmann, J. L.; McKay, C. P.

    2008-09-01

    will focus on the regional distribution of gullies on the Hjorthfjellet and Adventtoppen mountain massif (Fig. 1, inset and Fig. 2), and detailed local studies of individual gullies on the same mountain massif are carried out as described by [8] and [9]. The Hjorthfjellet and Adventtoppen mountain massif consists of four stratigraphic units of sandstone and shales from the Tertiary and Mesozoic [10]. Several studies concerning talus slopes and debris flows on Svalbard have been performed in the last decades [e.g., 11, 12, 13, 14]. Regional studies of [14] using airborne imagery revealed that there are differences in the frequency and activity of debris flows on Svalbard between east- and west-facing slopes. Åkerman [14] suggested that differences in the solar radiation, the depth of the active layer and the amount of precipitation cause variances in the morphology and morphometry of the debris slopes as well as variances in the frequency and age of debris flows between east- and west-facing slopes. Studies and direct observations imply that debris flows on Svalbard are triggered by high intensity rainfall [e.g., 14, 15]. Gullies on mountains in Argyre basin, Mars For a comparative study on Mars we chose the Argyre region. Several isolated mountain massifs occur in the Nereidum and Charitum Montes (Fig. 3) with similar morphologies as the studied massif in Svalbard. A first data analysis with High Resolution Stereo Camera (HRSC) data revealed that gullies occur on the mountain slopes only at specific orientations. Fig. 4 shows an example of an isolated mountain, on which gullies only occur on west-facing slopes. Project Description The formation of gullies on Earth depends on several parameters, including rainfall and/or melting of snow, the presence of steep slopes, and sufficient amounts of fines/debris [e.g., 16]. As on Earth, the differences of slope angles and variabilities in bedrock and grain sizes influence the regional occurrence of gullies [17]. The main

  5. Upper crustal structure of the northern part of the Bohemian ­Massif in ­rel­ation­ t­o geological, potential field data and new deep seismic data (Eger/Ohře Rift, Central Europe)

    Czech Academy of Sciences Publication Activity Database

    Skácelová, Z.; Mlčoch, B.; Novotný, Miroslav; Mrlina, Jan

    2011-01-01

    Roč. 39, č. 1 (2011), s. 1-18 ISSN 0303-4534 R&D Projects: GA AV ČR IAA300460602; GA MŽP SB/630/3/02 Institutional research plan: CEZ:AV0Z30120515 Keywords : upper crustal structure * Bohemian Massif * Eger/Ohře Rift * Saxothuringian Zone * Teplá-Barrandian Unit * Moldanubian Zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure

  6. A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites: Chapter K in Mineral Deposit Models for Resource Assessment

    Science.gov (United States)

    Woodruff, Laurel G.; Nicholson, Suzanne W.; Fey, David L.

    2013-01-01

    This descriptive model for magmatic iron-titanium-oxide (Fe-Ti-oxide) deposits hosted by Proterozoic age massif-type anorthosite and related rock types presents their geological, mineralogical, geochemical, and geoenvironmental attributes. Although these Proterozoic rocks are found worldwide, the majority of known deposits are found within exposed rocks of the Grenville Province, stretching from southwestern United States through eastern Canada; its extension into Norway is termed the Rogaland Anorthosite Province. This type of Fe-Ti-oxide deposit dominated by ilmenite rarely contains more than 300 million tons of ore, with between 10- to 45-percent titanium dioxide (TiO2), 32- to 45-percent iron oxide (FeO), and less than 0.2-percent vanadium (V).

  7. The "Escarot" gas seep, French Massif Central: CO2 discharge from a quiescent volcanic system - Characterization and quantification of gas emissions

    Science.gov (United States)

    Gal, F.; Leconte, S.; Gadalia, A.

    2018-03-01

    Natural CO2 emissions from the volcanic rocks of the French Massif Central are poorly constrained. It is of interest better to assess the emission of such non-anthropogenic gases that may significantly contribute to the global carbon budget. We quantified the CO2 emissions to the atmosphere in a small area (0.052 km2) located in the Massif Central close to Lake Pavin, the most recent volcanic edifice in metropolitan France. The specific character of this area, known as the Escarot mofette, was earlier studied for soil-gas concentrations only. In June 2017, we used the accumulation chamber method for measuring CO2 flux and related O2 depletion in the gases emitted at the soil/atmosphere interface, resulting in 176 data acquisitions over four days. In addition, 44 soil-gas concentration measurements were made at selected locations. CO2 emission rates are estimated at 8100 ± 1800 tons/year of deep-seated CO2 and at 660 ± 440 tons/year of biologically produced CO2. The uncertainty on these evaluations comes from the high-frequency variability of CO2 efflux in the more emissive areas and from the occurrence of heavy precipitation events. Though unexpected, these events were used for quantifying the decreases in CO2 efflux, which were as high as 500% over a few hours or even days in some locations. However, repeat acquisitions performed under more favourable weather conditions showed errors of commonly accepted amplitude (±15%). The area showed several degassing centres aligned along a NNW-SSE direction that correlates well with known geological structures, proving the ability of soil-gas methods to map hidden faults. The whole area is characterized by strong CO2 enrichment and related O2 depletion, but it is nonetheless possible to detect areas influenced by the rise of deep-seated gases and a few peripheral areas where biological processes dominate (CO2 up to 10% vol.). This study of gas emissions in a non-urban area also provides complementary information that is

  8. Pb-Pb zircon ages of the Porto Nacional high-grade metamorphic terrain, northern portion of the Goias Massif, central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Gorayeb, Paulo Sergio de Sousa; Moura, Candido Augusto Veloso [Para Univ., Belem, PA (Brazil). Centro de Geociencias]. E-mail: gorayebp@ufpa.br; c_moura@ufpa.br; Barros, Gisele Ribeiro de [Para Univ., Belem, PA (Brazil). Programa Institucional de Bolsas de Iniciacao Cientifica (PIBIC)]. E-mail: agbarros@amazon.com.br

    2000-03-01

    Single zircon Pb-evaporation ages were determined for a mafic granulite, two enderbites and a kinzigite of the Porto Nacional High-Grade Metamorphic Terrain (PNHGT) in the Goias massif. Zircons from mafic granulites and one of the enderbites of yielded average {sup 207} Pb/{sup 206} Pb ages of 2125{+-}3 Ma and 2153{+-}1 Ma, respectively, being interpreted as minimum ages of the igneous protoliths. The other enderbite, whose zircons presented round terminations, yielded an average {sup 207} Pb/{sup 206} Pb age of 2097 {+-} 2 Ma. Zircons from the kinzigite, displaying cores and rims overgrowth, presented {sup 207} Pb/{sup 206} Pb ages ranging between 2027 and 2115 Ma. However, a very homogeneous zircon crystal without overgrowth yielded age of 2100 {+-} 2 Ma, with a distinctive low Th/U value (0.02). This zircon is interpreted as a metamorphic crystal and its age probably sets the age of the granulite facies metamorphism, indicating that the PNHGT is a result of the Transamazonian thermotectonic event. (author)

  9. An Archaean Tonalite-Trondhjemite-Granodiorite Association of the Kursk Block (Voronezh Massif): Composition, Age, and Correlation with the Ukrainian Shield

    Science.gov (United States)

    Savko, K. A.; Samsonov, A. V.; Larionov, A. N.; Korish, E. Kh.; Bazikov, N. S.

    2018-01-01

    Framing of the Archaean greenstone belts of the Kursk Block (KB) of the East Sarmatia preserves rocks of the TTG association: those do not form massifs with distinct boundaries, but occur as fields gradually transiting into gneisses and migmatites. According to Sm-Nd isotope-geochemical data, the TTG are characterized by positive values of ɛNd(2960) = +0.3…+1.6 and protolith model ages of T Nd( DM) = 3100-3200 Ma. Magmatic protoliths of the Kursk Block TTG were formed about 2960 Ma by melting from a juvenile basite source. These age estimates are significantly younger than heterochronous (3.19, 3.13 and 3.07 Ga) TTGs of the Middle Dnieper granite-greenstone terrane. On the other hand, the similarity of ɛNd(T) implies a single source of their protoliths. Consequently, the KB TTGs, apparently, are a result of transformation of an older sial crust preserved within the Middle Dnieper Block.

  10. Characterizing the nature of melt-rock reaction in peridotites from the Santa Elena Ophiolite, NW Costa Rica

    Science.gov (United States)

    Carr, D.; Loocke, M. P.; Snow, J. E.; Gazel, E.

    2017-12-01

    The Santa Elena Ophiolite (SEO), located on the northwestern coast of Costa Rica, consists primarily of preserved oceanic mantle and crustal rocks thrust above an accretionary complex. The SEO is predominantly characterized by mantle peridotites (i.e., primarily spinel lherzolite with minor amounts of harzburgite and dunite) cut and intruded by minor pegmatitic gabbros, layered gabbros, plagiogranites, and doleritic and basaltic dykes. Previous studies have concluded that the complex formed in a suprasubduction zone (SSZ) setting based on the geochemical nature of the layered gabbros and plagiogranites (i.e., depleted LREE and HFSE and enriched LILE and Pb), as well, as the peridotites (i.e., low-TiO2, Zr, and V, and high MgO, Cr, and Ni)(Denyer and Gazel, 2009). Eighteen ultramafic samples collected during the winter 2010/2011 field season (SECR11) exhibit abundant evidence for melt-rock reaction (e.g., disseminated plagioclase and plagioclase-spinel, clinopyroxene-spinel, and plagioclase-clinopyroxene symplectites) and provide a unique opportunity to characterize the textural and chemical nature of melt-rock reaction in the SEO. We present the results of a petrologic investigation (i.e., petrography and electron probe microanalysis) of 28 thin sections (19 spinel lherzolites, of which 14 are plagioclase-bearing, 4 pyroxenite veins, and 5 harzburgites) derived from the SECR11 sample set. The results of this investigation have the potential to better our understanding of the nature of melt generation and migration and melt-rock interaction in the SEO mantle section and shed further light on the complex petrogenetic history of the SEO. Denyer, P., Gazel, E., 2009, Journal of South American Earth Sciences, 28:429-442.

  11. Subsurface geometry of the San Andreas-Calaveras fault junction: influence of serpentinite and the Coast Range Ophiolite

    Science.gov (United States)

    Watt, Janet Tilden; Ponce, David A.; Graymer, Russell W.; Jachens, Robert C.; Simpson, Robert W.

    2014-01-01

    While an enormous amount of research has been focused on trying to understand the geologic history and neotectonics of the San Andreas-Calaveras fault (SAF-CF) junction, fundamental questions concerning fault geometry and mechanisms for slip transfer through the junction remain. We use potential-field, geologic, geodetic, and seismicity data to investigate the 3-D geologic framework of the SAF-CF junction and identify potential slip-transferring structures within the junction. Geophysical evidence suggests that the San Andreas and Calaveras fault zones dip away from each other within the northern portion of the junction, bounding a triangular-shaped wedge of crust in cross section. This wedge changes shape to the south as fault geometries change and fault activity shifts between fault strands, particularly along the Calaveras fault zone (CFZ). Potential-field modeling and relocated seismicity suggest that the Paicines and San Benito strands of the CFZ dip 65° to 70° NE and form the southwest boundary of a folded 1 to 3 km thick tabular body of Coast Range Ophiolite (CRO) within the Vallecitos syncline. We identify and characterize two steeply dipping, seismically active cross structures within the junction that are associated with serpentinite in the subsurface. The architecture of the SAF-CF junction presented in this study may help explain fault-normal motions currently observed in geodetic data and help constrain the seismic hazard. The abundance of serpentinite and related CRO in the subsurface is a significant discovery that not only helps constrain the geometry of structures but may also help explain fault behavior and the tectonic evolution of the SAF-CF junction.

  12. Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge

    Science.gov (United States)

    Falcon-Suarez, Ismael; Bayrakci, Gaye; Minshull, Tim A.; North, Laurence J.; Best, Angus I.; Rouméjon, Stéphane

    2017-11-01

    Serpentinized peridotites co-exist with mafic rocks in a variety of marine environments including subduction zones, continental rifts and mid-ocean ridges. Remote geophysical methods are crucial to distinguish between them and improve the understanding of the tectonic, magmatic and metamorphic history of the oceanic crust. But, serpentinite peridotites exhibit a wide range of physical properties that complicate such a distinction. We analysed the ultrasonic P- and S-wave velocities (Vp, Vs) and their respective attenuation (Qp-1, Qs-1), electrical resistivity and permeability of four serpentinized peridotite samples from the southern wall of the Atlantis Massif, Mid-Atlantic Ridge, collected during International Ocean Discovery Program Expedition 357. The measurements were taken over a range of loading-unloading stress paths (5-45 MPa), using ∼1.7 cm length, 5 cm diameter samples horizontally extracted from the original cores drilled on the seafloor. The measured parameters showed variable degrees of stress dependence, but followed similar trends. Vp, Vs, resistivity and permeability show good inter-correlations, while relationships that included Qp-1 and Qs-1 are less clear. Resistivity showed high contrast between highly serpentinized ultramafic matrix (>50 Ω m) and mechanically/geochemically altered (magmatic/hydrothermal-driven alteration) domains (serpentinization and the alteration state of the rock, contrasted by petrographic analysis. This study shows the potential of combining seismic techniques and controlled source electromagnetic surveys for understanding tectonomagmatic processes and fluid pathways in hydrothermal systems.

  13. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    Science.gov (United States)

    Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

    2002-01-01

    The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

  14. Characterization of Serpentine Samples from the Coast Range Ophiolite Microbial Observatory with μ-FTIR and XRD. ­­

    Science.gov (United States)

    Sousa, A.; Cardace, D.

    2017-12-01

    Serpentinizing systems hold much promise as potentially habitable environments in diverse planetary settings. They involve abundant and simple ingredients (i.e., the mineral olivine, liquid water), support subsurface microbial communities on Earth (Crespo-Medina et al. 2014; Suzuki et al. 2014; Kelley et al. 2005) and are thought to occur elsewhere in our solar system such as Mars (Schulte et al. 2006; Ehlmann et al. 2010)and possibly ocean worlds (Waite et al. 2017; Vance 2009). Although geochemical and microbial data collection continues in serpentinizing systems, the identification and resolution of potential biosignatures in serpentinites are not yet clear. Specifically, the micro-scale mineralogical contexts in which cell fragments or biofilm residues may be formed and preserved is lacking. Here we report preliminary transmission and reflection mode μ-FTIR spectral maps and XRD diffractograms, obtained with instruments relevant to robotic exploration missions (Blake et al. 2012; Igisu et al. 2009; Leroi et al. 2009). Samples analyzed include ultramafic rock and constituent mineral standards (e.g., olivine) and rocks collected from near surface sites associated with the NASA Astrobiology Institute-funded initiative, the Coast Range Ophiolite Microbial Observatory (CROMO), in Lower Lake, CA (Cardace et al. 2013). These new results provide co-registered, complementary data on astrobiologically important rock and mineral phases related to serpentinization (Crespo-Medina et al. 2014; Twing et al. 2017). Future work will leverage this data set in microbial colonization experiments aimed at parsing background organic loads in serpentinites from surficial/fracture-localized modern biofilm signatures.

  15. Age and geochemistry of Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

    Science.gov (United States)

    Luan, Jin-Peng; Xu, Wen-Liang; Wang, Feng; Wang, Zhi-Wei; Guo, Peng

    2017-10-01

    This study presents new zircon U-Pb ages and geochemical data for Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif (SZRM) of NE China. This dataset provides insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent. The zircon U-Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages: (1) a ∼917-911 Ma suite of syenogranites and monzogranites, and (2) an ∼841 Ma suite of granodiorites. The 917-911 Ma granitoids contain high concentrations of SiO2 (67.89-71.18 wt.%), K2O (4.24-6.91 wt.%), and Al2O3 (14.89-16.14 wt.%), and low concentrations of TFe2O3 (1.63-3.70 wt.%) and MgO (0.53-0.88 wt.%). They are enriched in the light rare earth elements (LREE) and the large ion lithophile elements (LILE), are depleted in the heavy REE (HREE) and the high field strength elements (HFSE; e.g., Nb, Ta, and Ti), and have slightly positive Eu anomalies, indicating that they are geochemically similar to high-K adakitic rocks. They have zircon εHf (t) values and TDM2 ages from -4.4 to +1.5 and 1915 Ma to 1592 Ma, respectively, suggesting that they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material. In comparison, the 841 Ma granodiorites contain relatively low concentrations of Al2O3 (14.50-14.58 wt.%) and K2O (3.27-3.29 wt.%), relatively high concentrations of TFe2O3 (3.78-3.81 wt.%) and the HREE, have negative Eu anomalies, and have zircon εHf (t) values and TDM2 ages from -4.7 to +1.0 and 1875 to 1559 Ma, respectively. These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material. The ∼917-911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting, whereas the ∼841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic

  16. Hydrothermal alterations and O, H, C isotopic characterization of fluids and minerals in uraniferous massif of Saint Sylvestre (France). Extension to other French intragranitic uranium deposits

    International Nuclear Information System (INIS)

    Turpin, L.

    1984-05-01

    Petrographical, mineralogical, geochemical and stable isotope ( 18 O/ 16 O, D/H, 13 C/ 12 C) studies have been performed on the leucogranitic massif of St Sylvestre (Limousin, Massif Central francais), particularly on the different hydrothermal alterations. The oxygen isotope geochemistry of granites confirms the unicity of the different facies and their sialic origin (delta 18 O whole rocks = +11.0 +- 0.5 per mill), with a major contribution of detritic sediments rich in organic matter and poor in carbonate (delta 13 C magm. CO 2 = -10.6 per mill). Late lamprophyres have a deep-seated origin (delta 18 O = + 6 per mill). The pervasive chloritization of granitic biotites occurs during the convective circulation of a fluid of meteoric origin, at temperatures around 350-450 0 C. The chemical composition of chlorite which is buffered by that of biotite and the large 18 O-shift of fluid towards high delta values indicate that water-rock ratio was not very high. Chloritization takes place in high permeability zones. In regions where porosity is generally low, fluids are ''canalised'' in localised micro-fissured zones. Very high water/rock ratios lead to the dissolution of quartz, and the formation of the ''feldspathic episyenite'' alteration facies. The isotopic features of this fluid (delta 18 O approximately - 8 per mill, deltaD approximately - 50 per mill) indicate an elevated altitude. An isotopically similar fluid is responsible for the later ''micaceous episyenite'' alteration facies, found in fractured zones. Mixing of this fluid with a sedimentary fluid (delta 18 O approximately + 10 per mill, deltaD approximately - 30 per mill, delta 13 C approximately - 18 per mill) yielded the conditions necessary for the deposit of primary economic ore. Such fluids, sedimentary or metamorphic in origin, have been recognized in most hercynian intragranitic U and Sn-W deposits [fr

  17. Isotopic characteristic of meteoric water and groundwater in Ahaggar massif (central Sahara)

    International Nuclear Information System (INIS)

    Saighi, O.; Michelot, J.L.; Filly, A.

    2001-01-01

    The mean contents of both oxygen-18 and deuterium in precipitation from the Ahaggar massif (central Sahara) are: δ 18 O = -3 per mille and 2 H = -15 per mille. The heterogeneity in meteoric events and the great scattering of these isotopic contents can be ascribed to the origins and the histories of air masses. The main contribution comes from the inflow of the Guinean monsoon during summer months. During winter, the N/W winds, arriving in the area from the Moroccan coast, provide some rains. The deuterium excess of these precipitation are up to +10 per mille, indicating that the air masses generating these rains are supplied by the recycling of the continental air moisture. Groundwater resources are produced in some little phreatic aquifers, which are recharged by sporadic wadi floods. Aquifer zones that are the most favourable are located in the valleys and occur as three overlying levels of unequal importance: the alluvial aquifer, the weathered zone of the underlying substratum and the deep aquifer of fissured basement. The alluvial aquifer contain weakly mineralised water (0.3 g/l). Their stable isotopes contents (δ 18 O∼ -2.7 per mille) and 14 C activity of them (> 100 pmc) are comparable to present meteoric water, allowing modern meteoric waters to be identified. The weathered zone groundwater's are more mineralised (0.8 g/l) and its isotopic contents (δ 18 O∼ -4.2 per mille) and intermediate radiocarbon activity, prove their old water component. The basement's groundwater are more mineralised (> 1 g/l) and their very depleted isotopic contents (δ 18 O∼ -9 per mille) diverge clearly from the present precipitation. Furthermore, the absence of 3 H and 14 C activity of them, prove an old heritage, resulting from recharge during the last humid episode of the Holocene. (author)

  18. Ophiolite Emplacement and the Effects of the Subduction of the Active Chile Ridge System: Heterogeneous Paleostress Regimes Recorded in the Taitao Ophiolite (Southern Chile Emplazamiento de ofiolitas y los efectos de la subducción de la dorsal activa de Chile: Regímenes heterogéneos de paleostress registrados en la Oflolita Taitao (Sur de Chile

    Directory of Open Access Journals (Sweden)

    Eugenio E Veloso

    2009-01-01

    Full Text Available The repeated north and southward migration of the Chile Triple junction, offshore the Península de Taitao, is expected to have imposed contrasting stress fields in the forearc for the last 6 Ma because of changes in convergence direction and rate of subducting plates. NNW-SSE to E-W and minor NE-SW striking brittle faults developed in the plutonic units of the Mio-Pliocene Taitao Ophiolite, whereas NNE-SSW and minor NW-SE trending faults developed in its eastern border (Bahía Barrientes fault-zone. These brittle faults are studied to elucídate the style of ophiolite emplacement and the tectonic effects resulting from the alternated migration of the Chile Triple junction in the área. Analyses of heterogeneous fault-slip data on both áreas suggest that faults were activated by different stress fields. Two different compressional stress fields were identified in the plutomc units (A and B, whereas three different stress fields, ranging from compressional to strike-slip, were identified in the BahíaBarrientos fault-zone (C, D and E. Calculated directions of Oj axes for A, C, D and E solutions are mostly E-W trending, roughly similar to the convergence direction of subducting plates, whereas that for B solution is counterclockwise rotated ca. 60° with respect to the previous E-W trend. Brittle structures related to solution B were attributed to an early deformation of the ophiolite, most probably developed shortly after its emplacement {ca. 6 Ma. These structures were further counterclockwise rotated, while new structures (related to solution A developed in the plutomc units in order to absorb the continuous deformation. In the eastern margin of the ophiolite, the stress field divided inte compressional and strike-slip components. During periods of relatively strong compression (fast subduction of the Nazca píate, the fault-zone experienced well defined compressional and strike-slip movements (solutions C and D. In contrast, during periods of

  19. Characterizing Dissolved Organic Matter and Metabolites in an Actively Serpentinizing Ophiolite Using Global Metabolomics Techniques

    Science.gov (United States)

    Seyler, L. M.; Rempfert, K. R.; Kraus, E. A.; Spear, J. R.; Templeton, A. S.; Schrenk, M. O.

    2017-12-01

    Environmental metabolomics is an emerging approach used to study ecosystem properties. Through bioinformatic comparisons to metagenomic data sets, metabolomics can be used to study microbial adaptations and responses to varying environmental conditions. Since the techniques are highly parallel to organic geochemistry approaches, metabolomics can also provide insight into biogeochemical processes. These analyses are a reflection of metabolic potential and intersection with other organisms and environmental components. Here, we used an untargeted metabolomics approach to characterize dissolved organic carbon and aqueous metabolites from groundwater obtained from an actively serpentinizing habitat. Serpentinites are known to support microbial communities that feed off of the products of serpentinization (such as methane and H2 gas), while adapted to harsh environmental conditions such as high pH and low DIC availability. However, the biochemistry of microbial populations that inhabit these environments are understudied and are complicated by overlapping biotic and abiotic processes. The aim of this study was to identify potential sources of carbon in an environment that is depleted of soluble inorganic carbon, and to characterize the flow of metabolites and describe overlapping biogenic and abiogenic processes impacting carbon cycling in serpentinizing rocks. We applied untargeted metabolomics techniques to groundwater taken from a series of wells drilled into the Semail Ophiolite in Oman.. Samples were analyzed via quadrupole time-of-flight liquid chromatography tandem mass spectrometry (QToF-LC/MS/MS). Metabolomes and metagenomic data were imported into Progenesis QI software for statistical analysis and correlation, and metabolic networks constructed using the Genome-Linked Application for Metabolic Maps (GLAMM), a web interface tool. Further multivariate statistical analyses and quality control was performed using EZinfo. Pools of dissolved organic carbon could

  20. Polymineralic inclusions in mantle chromitites from the Oman ophiolite indicate a highly magnesian parental melt

    Science.gov (United States)

    Rollinson, Hugh; Mameri, Lucan; Barry, Tiffany

    2018-06-01

    Polymineralic inclusions interpreted as melt inclusions in chromite from the dunitic Moho Transition Zone in the Maqsad area of the Oman ophiolite have been analysed and compositions integrated using a rastering technique on the scanning electron microscope. The inclusions now comprise a range of inter-grown hydrous phases including pargasite, aspidolite, phlogopite and chlorite, indicating that the parental melts were hydrous. Average inclusion compositions for seven samples contain between 23.1 and 26.8 wt% MgO and 1.7-3.6 wt% FeO. Compositions were corrected to allow for the low FeO concentrations using coexisting olivine compositions. These suggest that the primary melt has between 20 and 22 wt% MgO and 7-9.7 wt% FeO and has an affinity with boninitic melts, although the melts have a higher Ti content than most boninites. Average rare earth element concentrations suggest that the melts were derived from a REE depleted mantle source although fluid-mobile trace elements indicate a more enriched source. Given the hydrous nature of the inclusions this enrichment could be fluid driven. An estimate of the melt temperature can be made from the results of homogenisation experiments on these inclusions and suggests 1300 °C, which implies for a harzburgite solidus, relatively shallow melting at depths of <50 km and is consistent with a boninitic origin. The current "basaltic" nature of the chromite host to highly magnesian melt inclusions suggests that the dunitic Moho Transition Zone operated as a reaction filter in which magnesian melts were transformed into basalts by the removal of high magnesian olivines, particularly in areas where the Moho Transition Zone is unusually thick. We propose therefore that podiform mantle chromitites, even those with an apparent MORB-like chemical signature, have crystallised from a highly magnesian parental melt. The data presented here strongly support the view that this took place in a subduction initiation setting.

  1. Fluid properties control degassing or storage of abiogenic CH4 during slab exhumation: the fluid inclusion record from the Western Alps.

    Science.gov (United States)

    Ferrando, S.; Castelli, D.; Frezzotti, M. L.

    2017-12-01

    Abiogenic CH4 can be produced by interaction between carbonates and reducing fluids derived from the hydration of ultramafics (e.g., mantle peridotite or HP Ol-serpentinite). This process occurs during slab exhumation because cooling promotes serpentinization of olivine in presence of water (Fo + H2O = Atg + Brc and the linked reactions: Fa + H2O = Fe-Atg + Mag + H2 and Atg + CaCO3 + H2 = Di + Brc + CH4 + H2O) at ca. 500-375°C (P=2.0-0.2 GPa). Experiments in the CH4-H2O-NaCl system indicate that, at these conditions, fluids are immiscible even for very low salinity (ca. 3 wt%) and that the NaCl content in the aqueous part of the fluid increases with temperature whereas the CH4 content in the gaseous part shows an opposite trend (Lamb et al., 2002; Li, 2017).In HP rodingite from the Piemonte ophiolite Zone (W Alps), primary fluid inclusions consisting of a brine (6 wt% CaCl2 + 6 wt% NaCl) with H2 + CH4 ≤ 1 mol % [CH4/(H2+CH4) = 0.37-10] occur in vesuvianite veins that formed at P=0.2 GPa and T=375°C. We interpret them as the aqueous part of an immiscible reducing fluid produced during late Alpine serpentinization of the surrounding ultramafics. Interestingly, CH4-H2 gaseous fluids are never reported in rodingite, whereas early CH4-H2O-H2±graphite and CH4-H2±graphite fluid inclusions, with variable gas-water proportions, trapped in calcite at P≤1.0 GPa and T≤450°C, are recently reported from HP "graphitized" ophicarbonate from the Lanzo peridotite Massif (W Alps; Vitale Brovarone et al., 2017).Both HP ophiolites and partially-serpentinized peridotite massifs are, thus, efficient lithologies to produce CH4 during exhumation. The amount of released CH4 depends on the amount of water available during exhumation. However, when fluids immiscibility occurs, the gaseous-rich part (CH4-H2) of the immiscible fluid produced in ultramafics likely remains confined in the slab because it is less mobile with respect to the aqueous-rich part due to its high dihedral

  2. Old inherited zircons in two synkinematic variscan granitoids: the 'granite du Pinet' and the 'Orthogneiss de Marvejols' (Southern French Massif Central)

    International Nuclear Information System (INIS)

    Pin, C.

    1981-01-01

    Two granitic bodies outcropping in the metamorphic basement of the Southern French Massif Central have been studied with the zircon U-Pb method: the Pinet granite (Rouergue area) and the Marvejols orthogneisses (Serie du Lot). It is shown that neither of them are pre-Variscan intrusions but that they were emplaced synkinematically, during the early stages of the Hercynian tectonometamorphic event. As numerous other S-type granitoids, both formations are characterized by an important inherited zircon component, whose apparent age is 1800 +- 200 m.y. Lower intersections with the Concordia curve allow to settle an emplacement age around 350-360 m.y., although the Pinet zircons display a complex pattern, owing both to heterogeneity of the inherited component and to late isotopic disturbances. Regional consequences of the synkinematic character of these S-type granitoids are outlined. It is shown that inherited zircons occurences often hinder accurate dating and the possible petrogenetic significance of the old proterozoic component is discussed. (orig.)

  3. Weathering and transport of chromium and nickel from serpentinite in the Coast Range ophiolite to the Sacramento Valley, California, USA

    Science.gov (United States)

    Morrison, Jean M.; Goldhaber, Martin B.; Mills, Christopher T.; Breit, George N.; Hooper, Robert L.; Holloway, JoAnn M.; Diehl, Sharon F.; Ranville, James F.

    2015-01-01

    A soil geochemical study in northern California was done to investigate the role that weathering and transport play in the regional distribution and mobility of geogenic Cr and Ni, which are both potentially toxic and carcinogenic. These elements are enriched in ultramafic rocks (primarily serpentinite) and the soils derived from them (1700–10,000 mg Cr per kg soil and 1300–3900 mg Ni per kg soil) in the Coast Range ophiolite. Chromium and Ni have been transported eastward from the Coast Range into the western Sacramento Valley and as a result, valley soil is enriched in Cr (80–1420 mg kg−1) and Ni (65–224 mg kg−1) compared to median values of U.S. soils of 50 and 15 mg kg−1, respectively. Nickel in ultramafic source rocks and soils is present in serpentine minerals (lizardite, antigorite, and chrysotile) and is more easily weathered compared to Cr, which primarily resides in highly refractory chromite ([Mg,Fe2+][Cr3+,Al,Fe3+]2O4). Although the majority of Cr and Ni in soils are in refractory chromite and serpentine minerals, the etching and dissolution of these minerals, presence of Cr- and Ni-enriched clay minerals and development of nanocrystalline Fe (hydr)oxides is evidence that a significant fractions of these elements have been transferred to potentially more labile phases.

  4. Compositional and isotopic heterogeneities in the Neo-Tethyan upper mantle recorded by coexisting Al-rich and Cr-rich chromitites in the Purang peridotite massif, SW Tibet (China)

    Science.gov (United States)

    Xiong, Fahui; Yang, Jingsui; Xu, Xiangzhen; Kapsiotis, Argyrios; Hao, Xiaolin; Liu, Zhao

    2018-06-01

    The Purang harzburgite massif in SW Tibet (China) hosts abundant chrome ore deposits. Ores consist of 20 to >95% modal chromian spinel (Cr-spinel) with mylonitic fabric in imbricate shaped pods. The composition of Cr-spinel in these ores ranges from Al-rich [Cr#Sp or Cr/(Cr + Al) × 100 = 47.60-57.56] to Cr-rich (Cr#Sp: 62.55-79.57). Bulk platinum-group element (PGE) contents of chromitites are also highly variable ranging from 17.5 ppb to ∼2.5 ppm. Both metallurgical and refractory chromitites show a general enrichment in the IPGE (Os, Ir and Ru) with respect to the PPGE (Rh, Pt and Pd), resulting mostly in right-sloping primitive mantle (PM)-normalized PGE profiles. The platinum-group mineral (PGM) assemblages of both chromitite types are dominated by heterogeneously distributed, euhedral Os-bearing laurite inclusions in Cr-spinel. The Purang chromitites have quite inhomogeneous 187Os/188Os ratios (0.12289-0.13194) that are within the range of those reported for mantle-hosted chromitites from other peridotite massifs. Geochemical calculations demonstrate that the parental melts of high-Cr chromitites were boninitic, whereas those of high-Al chromitites had an arc-type tholeiitic affinity. Chromite crystallization was most likely stimulated by changes in magma compositions due to melt-peridotite interaction, leading to the establishment of a heterogeneous physicochemical environment during the early crystallization of the PGM. The highly variable PGE contents, inhomogeneous Os-isotopic compositions and varying Cr#Sp ratios of these chromitites imply a polygenetic origin for them from spatially distinct melt inputs. The generally low γOs values (different sections of a heterogeneously depleted mantle source region. These melts were most likely produced in the mantle wedge above a downgoing lithospheric slab.

  5. Active Microbial Sulfate Reduction in Serpentinization Fluids of the Semail Ophiolite in Oman

    Science.gov (United States)

    Glombitza, C.; Rempfert, K. R.; Templeton, A. S.; Hoehler, T. M.

    2017-12-01

    Dissimilatory sulfate reduction (SR) is among the oldest known microbial processes on Earth. It is the predominant anaerobic microbial process in sulfur-rich marine sediments but it also occurs in subsurface lithoautotrophic ecosystems, where it is driven by radiolytically produced H2 and sulfate [1]. Serpentinization is a process by which H2 is generated in a reaction of water with peridotite rock. This abiotic generation of H2 suggests its potential to power life in rocks as a stand-alone process, independent of the photosynthetic biosphere, because the generated H2 is a key energy source for microbial metabolism. This is of particular interest in understanding the role of water-rock reactions in generating habitable conditions on and beyond Earth. Sulfate is plausibly available in several of the water-bearing environments now known beyond Earth, making SR a potentially important metabolism in those systems. Sulfate minerals are abundant on the surface of Mars [2], suggesting that Martian groundwaters may be sulfate-rich. Sulfate is also postulated to be a component of the oceans of Europa and Enceladus [3, 4]. The inferred presence of both sulfate and peridotite rocks in these environments points toward a potential niche for sulfate reducers and highlights the need to understand how and where SR occurs in serpentinizing systems on Earth. We incubated formation fluids sampled from in the Semail Ophiolite in Oman with a 35-S labelled sulfate tracer and determined the rates of in-situ microbial sulfate reduction. The selected fluids represent different environmental conditions, in particular varying substrate concentrations (sulfate, H2 and CH4) and pH (pH 8.4 to pH 11.2). We found active microbial SR at very low rates in almost all fluids, ranging from 2 fmol mL-1 d-1 to 2 pmol mL-1 d-2. Lowest rates were associated with the hyperalkaline fluids (pH > 10), that had also the lowest sulfate concentration (50-90 µmol L-1). In line with previously determined species

  6. Hydrochemical characteristics and spatial analysis of groundwater quality in parts of Bundelkhand Massif, India

    Science.gov (United States)

    Ali, Syed Ahmad; Ali, Umair

    2018-03-01

    The tribulations of water quality have become more serious than the quantity, as the environmental evils are getting more severe day by day in different parts of the world. Large number of components like soil, geology, sewage disposal, effluents and other environmental conditions in which the water tends to reside or move and interact with ground and biological characteristics, greatly persuade the groundwater quality. Therefore, hydrochemical study has been carried out graphically and spatially in GIS environment in part of Bundelkhand Massif. The hydrochemical study exposes the water quality by measuring the concentration of parameters and comparing them with the drinking water and irrigation standards. Groundwater samples have been collected and analysed for physiochemical characteristics in order to understand the hydrochemistry of the water. The results revealed that ground water is alkaline in nature and total hardness observed in all samples falls under moderately hard to very hard category. At some places higher concentration of Cl- could be dangerous from health point of view. Major hydrochemical facies were identified using Piper Trilinear diagram and Durov diagrams, etc. Analysis of different determinations such as sodium adsorption ratio, residual sodium carbonate and per cent sodium revealed that most of the samples are unsuitable for irrigation. It was also observed that the quality of groundwater was not suitable for drinking purpose in industrial and irrigation area. In the area, few sampling sites showed unsuitability because of influences of urban and industrial waste discharge, aquifer material mineralogy, other anthropogenic activities and increased human interventions.

  7. Sr and Nd isotope geochemistry of coexisting alkaline magma series, Cantal, Massif Central, France

    International Nuclear Information System (INIS)

    Downes, H.

    1984-01-01

    Sr and Nd isotope analyses are presented for Tertiary continental alkaline volcanics from Cantal, Massif Central, France. The volcanics belong to two main magma series, silica-saturated and silica-undersaturated (with rare nephelinites). Trace element and isotopic data indicate a common source for the basic parental magmas of both major series; the nephelinites in contrast must have been derived from a mantle source which is isotopically and chemically distinct from that which gave rise to the basalts and basanites. 87 Sr/ 86 Sr initial ratios range from 0.7034 to 0.7056 in the main magma series (excluding rhyolites) and 143 Nd/ 144 Nd ratios vary between 0.512927 and 0.512669; both are correlated with increasing SiO 2 in the lavas. The data can be explained by a model of crustal contamination linked with fractional crystallisation. This indicates that crustal magma chambers are the sites of differentiation since only rarely do evolved magmas not show a crustal isotopic signature and conversely basic magmas have primitive isotopic ratios unless they contain obviuos crustal-derived xenocrysts. Potential contaminants include lower crustal granulites or partial melts of upper crustal units. Equal amounts of contamination are required for both magma series, refuting hypotheses of selective contamination of the silica-saturated series. The isotopic characteristics of the apparently primary nephelinite lavas demonstrates widespread heterogeneity in the mantle beneath Cantal. Some rhyolites, previously thought to be extremely contaminated or to be crustally derived, are shown to have undergone post-emplacement hydrothermal alteration. (orig.)

  8. Formation of pyroxenite layers in the Totalp ultramafic massif (Swiss Alps) - Insights from highly siderophile elements and Os isotopes

    Science.gov (United States)

    van Acken, David; Becker, Harry; Walker, Richard J.; McDonough, William F.; Wombacher, Frank; Ash, Richard D.; Piccoli, Phil M.

    2010-01-01

    Pyroxenitic layers are a minor constituent of ultramafic mantle massifs, but are considered important for basalt generation and mantle refertilization. Mafic spinel websterite and garnet-spinel clinopyroxenite layers within Jurassic ocean floor peridotites from the Totalp ultramafic massif (eastern Swiss Alps) were analyzed for their highly siderophile element (HSE) and Os isotope composition. Aluminum-poor pyroxenites (websterites) display chondritic to suprachondritic initial γOs (160 Ma) of -2 to +27. Osmium, Ir and Ru abundances are depleted in websterites relative to the associated peridotites and to mantle lherzolites worldwide, but relative abundances (Os/Ir, Ru/Ir) are similar. Conversely, Pt/Ir, Pd/Ir and Re/Ir are elevated. Aluminum-rich pyroxenites (clinopyroxenites) are characterized by highly radiogenic 187Os/ 188Os with initial γOs (160 Ma) between +20 and +1700. Their HSE composition is similar to that of basalts, as they are more depleted in Os, Ir and Ru compared to Totalp websterites, along with even higher Pt/Ir, Pd/Ir and Re/Ir. The data are most consistent with multiple episodes of reaction of mafic pyroxenite precursor melts with surrounding peridotites, with the highest degree of interaction recorded in the websterites, which typically occur in direct contact to peridotites. Clinopyroxenites, in contrast, represent melt-dominated systems, which retained the precursor melt characteristics to a large extent. The melts may have been derived from a sublithospheric mantle source with high Pd/Ir, Pt/Ir and Re/Os, coupled with highly radiogenic 187Os/ 188Os compositions. Modeling indicates that partial melting of subducted, old oceanic crust in the asthenosphere could be a possible source for such melts. Pentlandite and godlevskite are identified in both types of pyroxenites as the predominant sulfide minerals and HSE carriers. Heterogeneous HSE abundances within these sulfide grains likely reflect subsolidus processes. In contrast, large grain

  9. Derivation of P-T paths from high-pressure metagranites - Examples from the Gran Paradiso Massif, western Alps

    Science.gov (United States)

    Massonne, Hans-Joachim

    2015-06-01

    Metamorphosed granites (SiO2 ≥ 70 wt.%) are, in fact, a common rock type in high pressure (HP) and ultrahigh pressure (UHP) terrains, but these rocks were rarely used to derive metamorphic P-T paths. To test the suitability of HP metagranites for such derivations, two metagranites from the Gran Paradiso Massif were studied applying elemental mapping of phengite and garnet and calculated P-T pseudosections contoured by various chemical and modal parameters. Both rocks contain phengite with maximum Si contents of about 3.42 Si per formula unit (pfu) and 3.55 Si pfu in cores, and accessory garnet which is compositionally zoned. Garnet core compositions are rich in grossular component (XCa up to 0.72). Only a rough P-T path could be derived with peak pressures below 2 GPa because, for instance, Si contents in phengite become geobarometrically insensitive at HP conditions, when biotite is not anymore stable. A test of the pseudosection approach to a metagranite from the North Qaidam UHP metamorphic belt resulted in an ambiguous finding. In fact, compositions of garnet and phengite in this rock are indicative of both UHP and specific HP conditions ( 1.3 GPa, 530 °C), but the latter conditions fit the entire mineralogical observations better.

  10. U-Th-Pb dating of the Brossasco ultrahigh-pressure metagranite, Dora-Maira massif, western Alps

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, J.L.; Montel, J.M. [Centre National de la Recherche Scientifique, 63 - Clermont-Ferrand (France); Chopin, C. [Ecole Normale Superieure, 75 - Paris (France). Lab. de Geologie

    1999-01-01

    The Brossasco metagranite is part of the coherent ultrahigh-pressure metamorphic terrane in the Dora-Maira massif and, although it has reached Alpine peak metamorphic conditions of about 725 C/30 kbar, still locally preserves an undeformed magmatic texture. In order to obtain new chronological constraints on this key area of the western Alps, we studied the behaviour of the U-Th-Pb system in zircons and monazites from such an undeformed facies. Only zircon fractions containing very small needle-shaped inclusions are concordant at 304{+-}3 Ma. This result is interpreted as the emplacement age of the granite. All other zircons show an old inherited memory and the more U-rich of these crystals were affected by an episodic Pb loss with a poorly defined lower intercept at 60{+-}45 Ma. Both TIMS (thermo-ionisation mass spectrometry) and electron-microprobe analysis of monazites show that this last event has also disturbed their U-Pb and Th-Pb isotopic systems, without resetting them completely. Comparison with cofacial rock-types which have been completely reworked under these extreme P-T conditions shows that deformation and mass transfer as well as the nature of the protoliths and the characteristics of their zircons have a much more pronounced influence on the behaviour of isotopic systems than the temperature and/or pressure parameters. This evidence is an obvious limitation to the use of the blocking-temperature concept. (orig.)

  11. U-Th-Pb dating of the Brossasco ultrahigh-pressure metagranite, Dora-Maira massif, western Alps

    International Nuclear Information System (INIS)

    Paquette, J.L.; Montel, J.M.; Chopin, C.

    1999-01-01

    The Brossasco metagranite is part of the coherent ultrahigh-pressure metamorphic terrane in the Dora-Maira massif and, although it has reached Alpine peak metamorphic conditions of about 725 C/30 kbar, still locally preserves an undeformed magmatic texture. In order to obtain new chronological constraints on this key area of the western Alps, we studied the behaviour of the U-Th-Pb system in zircons and monazites from such an undeformed facies. Only zircon fractions containing very small needle-shaped inclusions are concordant at 304±3 Ma. This result is interpreted as the emplacement age of the granite. All other zircons show an old inherited memory and the more U-rich of these crystals were affected by an episodic Pb loss with a poorly defined lower intercept at 60±45 Ma. Both TIMS (thermo-ionisation mass spectrometry) and electron-microprobe analysis of monazites show that this last event has also disturbed their U-Pb and Th-Pb isotopic systems, without resetting them completely. Comparison with cofacial rock-types which have been completely reworked under these extreme P-T conditions shows that deformation and mass transfer as well as the nature of the protoliths and the characteristics of their zircons have a much more pronounced influence on the behaviour of isotopic systems than the temperature and/or pressure parameters. This evidence is an obvious limitation to the use of the blocking-temperature concept. (orig.)

  12. Methane- and Hydrogen-Influenced Microbial Communities in Hydrothermal Plumes above the Atlantis Massif, Mid Atlantic Ridge

    Science.gov (United States)

    Stewart, C. L.; Schrenk, M.

    2017-12-01

    Ultramafic-hosted hydrothermal systems associated with slow-spreading mid ocean ridges emit copious amounts of hydrogen and methane into the deep-sea, generated through a process known as serpentinization. Hydrothermal plumes carrying the reduced products of water-rock interaction dissipate and mix with deep seawater, and potentially harbor microbial communities adapted to these conditions. Methane and hydrogen enriched hydrothermal plumes were sampled from 3 sites near the Atlantis Massif (30°N, Mid Atlantic Ridge) during IODP Expedition 357 and used to initiate cultivation experiments targeting methanotrophic and hydrogenotrophic microorganisms. One set of experiments incubated the cultures at in situ hydrostatic pressures and gas concentrations resulting in the enrichment of gammaproteobacterial assemblages, including Marinobacter spp. That may be involved in hydrocarbon degradation. A second set of experiments pursued the anaerobic enrichment of microbial communities on solid media, resulting in the enrichment of alphaproteobacteria related to Ruegeria. The most prodigious growth in both case occurred in methane-enriched media, which may play a role as both an energy and carbon source. Ongoing work is evaluating the physiological characteristics of these isolates, including their metabolic outputs under different physical-chemical conditions. In addition to providing novel isolates from hydrothermal habitats near the Lost City Hydrothermal Field, these experiments will provide insight into the ecology of microbial communities from serpentinization influenced hydrothermal systems that may aid in future exploration of these sites.

  13. The Krásná Hora, Milešov, and Příčovy Sb-Au ore deposits, Bohemian Massif: mineralogy, fluid inclusions, and stable isotope constraints on the deposit formation

    Science.gov (United States)

    Němec, Matěj; Zachariáš, Jiří

    2018-02-01

    The Krásná Hora-Milešov and Příčovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks. Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krásná Hora-Milešov) or are associated with local strike-slip faults (Příčovy). Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 °C and gold at 200 to 130 °C from low-salinity aqueous fluids. The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 °C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature ( 250 MPa, 400 °C). The estimated oxygen isotope composition of the or