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Sample records for bohemian massif se

  1. Horizontal Strain Field for the Bohemian Massif, Central Europe

    NASA Astrophysics Data System (ADS)

    Schenk, V.; Pichl, R.; Schenkova, Z.; Marek, T.

    2010-12-01

    The horizontal strain field of the Bohemian Massif, central Europe, was assessed from GNSS data monitored on permanent stations of the Geodynamic Network of the Academy of Science of the Czech Republic (GEONAS) and of the Czech Office for Surveying, Mapping and Cadastre (CZEPOS). For every area a representative motion velocity was determined. Their comparison with general motions of the Eurasian plate ascertained by the NNR-NUVEL-1A model gave deviations characterizing recent influence of the Alps to the northern geological units, in our case the Bohemian Massif. From these motions a regional pattern of the horizontal strain field for the Bohemian Massif had been calculated. It was found that (i) the northern part of the Massif is under dominant E-W extensions and (ii) slight contractions were detected for the NNE-SSW direction in eastern regions of the Massif. Obtained results will be presented and discussed from a viewpoint of the Alpine structural unit actions to surrounding geological units.

  2. Petrogenesis of Variscan lamproites of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Krmíček, Lukáš; Romer, Rolf L.; Glodny, Johannes

    2015-04-01

    Paleozoic convergence of Laurussia and Gondwana-derived terranes with subduction of oceanic and continental crust of various compositions metasomatized the local mantle, a process which eventually led to a highly heterogeneous lithospheric mantle beneath the European Variscides. The eastern termination of the European Variscides (Moldanubian and Saxo-Thuringian zones of the Bohemian Massif in the Czech Republic, Austria, Germany, and Poland) is unusual as within a small area, the mantle had been modified by material from several subduction zones. Along the eastern border of the Bohemian Massif, mantle-derived dyke intrusions of peralkaline, perpotassic, and ultrapotassic compositions occur. The rocks are distinguished by mineral associations with K-amphibole and Fe-microcline and correspond mineralogically to a new variety of silica-rich lamproites. Lamproites from the Moldanubian Zone contain characteristic Ba-Ti-Zr accessory minerals (e.g., baotite, benitoite, hollandite), whereas lamproites from the Saxo-Thuringian Zone lack these minerals. Variscan lamproites from the Bohemian Massif sampled lithospheric mantle, whose chemical signature reflects extreme depletion (low CaO and Al2O3 contents) followed by strong metasomatic enrichment by material released from the subducted rocks, giving rise to crust-like trace element pattern, variably radiogenic Sr and unradiogenic Nd isotopic compositions, crustal Pb isotopic compositions, and a wide range of δ7Li ratios ranging from markedly positive to highly negative values. The metasomatic component is variably prominent in the lamproites, depending on the extent of partial melting, and the nature of the source of the metasomatic component. Preferential melting of the metasomatically enriched lithospheric mantle with stable K-amphibole resulted in lamproitic melts with very negative δ7Li values, which correlate positively with the peralkalinity, HFSE contents, and lower ɛNd of these rocks. Both, higher degree of

  3. Low pressure granulites from the Bohemian Massif, Upper Austria

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Daghighi, Donia; Simic, Katica; Pichler, Ruth; Schwaiger, Christian; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph

    2014-05-01

    Low pressure granulite facies rocks are commonly found in the Bohemian Massif in Upper Austria. They belong to the Moldanubian Unit and were metamorphosed during the last stage of the Variscan orogeny. The investigated granulites from the Donau valley (west of Linz), Lichtenberg (northwest of Linz), Sauwald (south of the river Danube) and Bad Leonfelden zone comprise mainly migmatic paragneisses. Most of these rocks underwent high degrees of melting forming meta- and diatexites (''Perlgneise)''. Al-rich metapelites with partly cm-sized garnet porphyroblasts, which are suitable for precise PT and PT-path determinations, can be found in some localities of this unit. In this study samples taken along the Danube valley between Linz and Wilhering, from Lichtenberg and from Bad Leonfelden (north of Linz) were sampled and investigated petrographically in detail. Since garnets are rare and usually consumed by cordierite, a sample with large garnets was investigated in detail. A chemical zoning profile across the c. 1cm large garnet displayed elevated Ca contents (Xgrs=0.06) in the central part which decreased discontinuously towards the rim to Xgrs=0.02. Almandine, pyrope and spessartine components do not show any pronounced zoning pattern. Most of the smaller garnet grains in other samples are also homogeneous in composition with a slight Xalm increase and Xprp decrease at the rims, typical for retrograde diffusional zoning. The cordierite-garnet-sillimanite-granulites as well as some mafic granulites were used for geothermobarometry. Metamorphic conditions of around 770°C to 850°C and 0.5-0.6 GPa could be obtained, which are similar to the values obtained by Tropper et al. (2006). P. Tropper I. Deibl F. Finger R. Kaindl (2006). P-T-t evolution of spinel-cordierite-garnet gneisses from the Sauwald Zone (Southern Bohemian Massif, Upper Austria): is there evidence for two independent late-Variscan low-P / high-T events in the Moldanubian Unit? Int J Earth Sci (Geol

  4. A Treasure Chest of Nanogranites: the Bohemian Massif (Central Europe)

    NASA Astrophysics Data System (ADS)

    Ferrero, S.; O'Brien, P. J.; Walczak, K.; Wunder, B.; Ziemann, M. A.; Hecht, L.

    2014-12-01

    Despite 150 years of investigation of the Bohemian Massif (Central Europe), it is only recently that the investigation of old and new samples displayed the occurrence of tiny portions of crystallized anatectic melt in regional migmatites. These vestiges of magma, called "nanogranites", are natural probes of the partial melting processes in the crust. Original melt composition and water content can be directly analyzed after piston cylinder re-homogenization. When compared to classic re-melting experiments, nanogranites are ideal "natural" experimental charges of anatectic melt. They are encapsulated in peritectic garnet immediately after production - both phases are products of the same partial melting reaction. Sheltered inside garnet, they remain unaffected by the physico-chemical changes which affected the host migmatites during their slow cooling, unlike leucosomes and anatexis-related plutons. Five different case studies of nanogranite-bearing high-grade rocks have been identified so far: three in metapelites from the Moldanubian Zone, and two in metagranitoids from the Granulitgebirge and Orlica-Śnieżnik Dome. Their characterization provides insights into how the continental crust melts at different depths, from shallow levels to mantle depths, during different moments of its metamorphic history (prograde vs. decompressional melting). For example, the investigation and experimental re-melting of nanogranites from Grt+Ky leucogranulites (Orlica-Śnieżnik Dome) recently provided evidence of prograde melting of metagranitoids under eclogite-facies conditions (T≥875°C and P~2.7 GPa), close to the stability field of coesite. The melt generated is granitic, hydrous (6 wt% H2O) and metaluminous (ASI=1.03), and is at the moment the "deepest" glass obtained through re-homogenization of primary polycrystalline inclusions in natural rocks. This work confirms that nanogranites in migmatites 1) are a powerful tool to constrain anatexis in natural rocks, and 2) can

  5. Horizontal strain field of the Bohemian Massif determined from GPS measurements

    NASA Astrophysics Data System (ADS)

    Schenkova, Z.; Talich, M.; Schenk, V.

    2011-12-01

    Permanent GNSS and campaign GPS data monitored on several geodynamic networks located in the territory of the Bohemian Massif, Central Europe, allowed site movements to be determined. To constrain the first image of regional strain field for this territory a 2-D numerical modeling based on the theory of continuum mechanics under an assumption of homogeneity of the area was applied and site movements, i.e. displacement vectors, were taken as calculation inputs. This approach represents a purely geometric solution. Further attention was paid to influences of regional geological discontinuities of the Massif, by means of an evaluation of their mechanical decoupling along major faults and/or fault zones that play an important role in the distribution of the regional and local motions and stress patterns. The particular analysis of the behavior of tectonic zones in the Bohemian Massif was performed. Fundamental source of the mobility of these zones depends directly on sizes and directions of existing northward movements of structural blocks of the Alpine orogenic system. It was found that common horizontal strain field of the Bohemian Massif displays significant E-W extensions in the eastern and western parts of the Massif and mild N-S compressions in its central part. Additional analyses of the strain field pattern and its numerical uncertainties will be discussed from the viewpoint of data processing and knowledge of geological structures.

  6. Significance of Geological Units of the Bohemian Massif, Czech Republic, as Seen by Ambient Noise Interferometry

    NASA Astrophysics Data System (ADS)

    Růžek, Bohuslav; Valentová, Lubica; Gallovič, František

    2016-05-01

    Broadband recordings of 88 seismic stations distributed in the Bohemian Massif, Czech Republic, and covering the time period of up to 12 years were processed by a cross-correlation technique. All correlograms were analyzed by a novel approach to get both group and phase dispersion of Rayleigh and Love waves. Individual dispersion curves were averaged in five distinct geological units which constitute the Bohemian Massif (Saxothuringian, Teplá-Barrandean, Sudetes, Moravo-Silesian, and Moldanubian). Estimated error of the averaged dispersion curves are by an order smaller than the inherent variability due to the 3D distribution of seismic velocities within the units. The averaged dispersion data were inverted for 1D layered velocity models including their uncertainty, which are characteristic for each of the geological unit. We found that, overall, the differences between the inverted velocity models are of similar order as the variability inside the geological units, suggesting that the geological specification of the units is not fully reflected into the S-wave propagation velocities on a regional scale. Nevertheless, careful treatment of the dispersion data allowed us to identify some robust characteristics of the area. The vp to vs ratio is anomalously low (~1.6) for all the units. The Moldanubian is the most rigid and most homogeneous part of the Bohemian Massif. Middle crust in the depth range of ~3-15 km is relatively homogeneous across the investigated region, while both uppermost horizon (0-3 km) and lower crust (>15 km) exhibit lower degree of homogeneity.

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

    NASA Astrophysics Data System (ADS)

    Schnabl, P.; Cajz, V.; Tietz, O.; Buechner, J.; Suhr, P.; Pecskay, Z.; Cizkova, K.

    2013-05-01

    Lusatia is situated in the NE continuation of the Ohre Rift (OR) behind Lusatian Overtrust. Compared to the neighbouring volcanic complex of the České stredohorí Mts. (CS) inside the OR. The scattered occurrences of basaltic bodies in Lusatia are spread on wider area. This can be caused by different tectonic development of the regions and from derived erosional conditions. The Lusatian Overtrust, high-order tectonic structure running across the course of the OR, separates Lusatian region into two different geological areas where Cretaceous sediments or granodiorites of Lusatian Massif represent the country rock of the Cenozoic volcanism, respectively. The age of volcanic activity ranges from 19 to 33 Ma, it's proved by newly obtained Ar-Ar data from Freiberg and K-Ar data from Debrecen. Forty two scattered remnants of Cenozoic volcanic products were sampled to get paleomagnetic data. The superficial volcanics with detectable geological position and volcanology were chosen preferentially, several dykes and separate vents were sampled as well. Paleomagnetic research was processed on more than 500 samples which were demagnetized using alternate field in the range 0-80 mT. Q-ratio was counted to prevent the lightning influence - solitary volcanic occurrences build positive morphology and thus, they are prone to be targeted by lightnings. The values of Q-ratio predominantly span from 0.1 to 7.0; those samples having the value over 10, were excluded for evaluation. The mean paleomagnetic direction (MPD) was acquired from several samples on each sampling site. Declination and Inclination show values of 11.8 deg and 62.7 deg (α95 = 9.3 deg) for normal polarity, or 182.1 deg and -59.2 deg (α95 = 6.1 deg) for reverse polarity, respectively,The corresponding paleolatitude of 41.9 deg was counted from the Inclination. This is 1000 km to the South, compared to recent position. The dispersions of the MPD are relatively wide. This coincides well with the idea of long

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

    PubMed

    Przylibski, Tadeusz A; Gorecka, Joanna

    2014-08-01

    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. PMID:24657989

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

    PubMed

    Przylibski, Tadeusz A; Gorecka, Joanna

    2014-08-01

    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.

  10. 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

    NASA Astrophysics Data System (ADS)

    Sláma, Jiří; Dunkley, Daniel J.; Kachlík, Václav; Kusiak, Monika A.

    2008-12-01

    Sedimentological, petrological and geochemical data combined with SHRIMP and LA ICP-MS U-Pb ages of pebbles of granitic rocks and detrital zircons from Neoproterozoic Vletice metaconglomerates of the SE margin of the Teplá-Barrandian Unit were used to characterize the regional geotectonic setting at the Proterozoic/Paleozoic boundary. The metaconglomerates form several-metres thick intercalations in metasediments of the Svrchnice Formation (roof pendants of Central Bohemian Plutonic Complex), which is considered to have been deposited in Neoproterozoic/Cambrian times. A sedimentological study indicates that the metaconglomerates are products of debris flows deposited in submarine canyons or proximal parts of submarine fans. Geochemistry of metaconglomerate matrix and petrography of pebbles revealed an obvious difference from the western and central part of the Teplá-Barrandian Unit Proterozoic where pebbles eroded from uplifted parts of the basin and island arc sources are most common. The abundance of quartz, quartzite, granite and crystalline limestone in pebbles together with the more mature composition of host metagreywackes indicate the presence of relatively evolved continental crust in the source area for the Vletice metaconglomerates, and shallowing of the Neoproterozoic basin to the SE (in the present geographic co-ordinate system). The Neoproterozoic to lowermost Cambrian age of the Svrchnice Formation, suggested by its comparison with similar rocks in the central part of the Teplá-Barrandian Unit, was confirmed by U-Pb dating. Ages of detrital zircons from the metaconglomerate matrix cluster around two values: Archaean to Paleoproterozoic U/Pb ages between ca. 2580 and 1780 Ma and Neoproterozoic to early Cambrian ages between 660 and 520 Ma with a significant peaks at 600 and 544 Ma suggesting local volcanic activity extending shortly beyond the Proterozoic/Paleozoic boundary. Zircons separated from two trondhjemite pebbles from the metaconglomerate

  11. Exotic crustal components at the northern margin of the Bohemian Massif-Implications from Usbnd Thsbnd Pb and Hf isotopes of zircon from the Saxonian Granulite Massif

    NASA Astrophysics Data System (ADS)

    Sagawe, Anja; Gärtner, Andreas; Linnemann, Ulf; Hofmann, Mandy; Gerdes, Axel

    2016-06-01

    The Saxonian Granulite Massif is located at the northern margin of the Saxo-Thuringian Zone of the peri-Gondwana Bohemian Massif. Eight felsic and mafic granulites were studied with respect to their geochemistry and Usbnd Pb zircon geochronology. The felsic granulites are interpreted to be derived from continental crust of possible granitoid composition. An origin from depleted mantle sources with IAT to MORB composition can be assumed for the mafic granulites. The peak of metamorphism is thought to be timed at about 340 Ma, while several earlier metamorphic events are supposed to have occurred at about 355-360, 370-375, 405, and 450 Ma. They reveal a complex and polyphased geologic evolution of the Saxonian Granulite Massif. Protolith emplacement likely took place at c. 450 and 494 Ma. Hf isotopic data suggest Mesoproterozoic crustal ages at least for parts of the massif. As these crustal ages are exotic for the Bohemian Massif, their origin has to be searched elsewhere. Potential source areas could be Amazonia and Baltica, of which the latter is the one preferred. Furthermore, a composite architecture with at least two components-the felsic granulites with Mesoproterozoic crustal model ages, and the mafic granulites of potential island arc origin-is hypothesised. Their amalgamation to the recent appearance of the Saxonian Granulite Massif is likely bracketed between 375 and 340 Ma.

  12. Forearc deformation and strain partitioning during growth of a continental magmatic arc: The northwestern margin of the Central Bohemian Plutonic Complex, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Žák, Jiří; Dragoun, František; Verner, Kryštof; Chlupáčová, Marta; Holub, František V.; Kachlík, Václav

    2009-04-01

    The Late Devonian subduction followed by the Early Carboniferous continental collision of the Saxothuringian and overriding upper-crustal Teplá-Barrandian units led to the growth of a large magmatic arc (the ˜ 354-337 Ma Central Bohemian Plutonic Complex) in the central part of the Bohemian Massif. Far-field tectonic forces resulting from the collision produced ˜WNW-ESE to ˜NW-SE regional shortening across the forearc upper crust above the subduction zone; the shortening was accommodated by predominantly top-to-the-ESE tectonic transport along the southeastern flank of the Teplá-Barrandian unit. Approaching the magmatic arc margin, the regional structural pattern changes and exhibits significant across- and along-strike variations interpreted as a result of strain partitioning, where the Saxothuringian/Teplá-Barrandian convergence interacted in different ways with the intruding magma pulses. Around the voluminous, northeasterly ˜ 354 Ma Sázava pluton the principal shortening was at high angle to the forearc-facing intrusive contact and the host rocks were significantly thermally softened. The regional top-to-the-ESE tectonic transport converted here into arc-parallel ductile flow within the structural aureole around and above the pluton. In contrast, a narrow to nonexistent ductile strain aureole is preserved in the host rocks around discordant sheet-like plutons (the southwesterly pre-354 (?) Ma Marginal granite and the Milín granodiorite of unknown radiometric age). Our AMS study of the Marginal granite and Milín granodiorite, and mapping of mesoscopic magmatic foliations and lineations in another neighboring sheet-like pluton (the ˜ 346 Ma Kozárovice granodiorite), reveals sigmoidal map-scale fabric patterns consistent with dextral transpression. We thus suggest that the thin sheet-like plutons were oriented obliquely to the principal shortening and were rheologically weaker than the host rocks prior to final crystallization, producing dextral

  13. Mantle anisotropy of the Bohemian Massif as seen by SKS-wave splitting

    NASA Astrophysics Data System (ADS)

    Vecsey, Ludek; Plomerova, Jaroslava; Babuska, Vladislav

    2014-05-01

    The Bohemian Massif (BM) assembled during the collision of Laurasia (Laurentia-Baltica) and Gondwana as a part of the Armorican Terrane Assemblage. It represents the estern-most outcrop of the European Variscan belt. The detailed tomographic and seismic anisotropy research of the deep structure of the BM has proceeded in several passive seismic experiments: BOHEMA I (2001-2003), BOHEMA II (2004-2005), BOHEMA III (2005-2006), PASSEQ (2006-2008) and Eger Rift (2007-2011). During these periods, the whole massif was stepwise covered by networks of temporal short-period and broad-band stations that recorded large amount of data from teleseismic events. The inferences from seismic anisotropy image the Bohemian Massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric. The mantle domains can be associated with the tectonic units recognized by geological studies: Saxothuringian (ST), Teplá-Barrandian (TB), Moldanubian (MB) and finally Moravian (M) and Silesian (S) parts of the MS Zone, overlying the Brunovistulian mantle lithosphere. In this contribution, we concetrate on the large-scale mantle anisotropy modelled from splitting of SKS waves and their particle motion (PM). An advantage of using PM analysis is its ability to employ even events with lower signal-to-noise ratio (SNR) that are otherwise not usable for splitting analysis. To improve results of splitting analysis of signals distorted by noise, we use stacking of individual splitting measurements from waves closely propagating through the mantle. Another way of improving our analysis is a stacking of individual splittings of a single event measured at nearby stations. On average, the fast shear waves are polarized in the E-W direction in the ST, MD, TB units, but exhibit different regional variations of the splitting parameters in dependence on back-azimuths. Thus, different lithosphere mantle fabrics in the ST, MD and TB units were modelled. Moreover, the ST unit can

  14. Experimental constraints on ultrapotassic magmatism from the Bohemian Massif (durbachite series, Czech Republic)

    NASA Astrophysics Data System (ADS)

    Parat, Fleurice; Holtz, François; René, Miloš; Almeev, Renat

    2010-03-01

    The equilibrium phase relations of a mafic durbachite (53 wt.% SiO2) from the Třebíč pluton, representative of the Variscan ultrapotassic magmatism of the Bohemian Massif (338-335 Ma), have been determined as a function of temperature (900-1,100°C), pressure (100-200 MPa), and H2O activity (1.1-6.1 wt.% H2O in the melt). Two oxygen fugacity ranges were investigated: close to the Ni-NiO (NNO) buffer and 2.6 log unit above NNO buffer (∆NNO + 2.6). At 1,100°C, olivine is the liquidus phase and co-crystallized with phlogopite and augite at 1,000°C for the whole range of investigated pressure and water content in the melt. At 900°C, the mineral assemblage consists of augite and phlogopite, whereas olivine is not stable. The stability field of both alkali feldspar and plagioclase is restricted to low pressure (100 MPa) at nearly water-saturated conditions (<3-4 wt.% H2O) and T < 900°C. A comparison between experimental products and natural minerals indicates that mafic durbachites have a near-liquidus assemblage of olivine, augite, Ti-rich phlogopite, apatite and zircon, followed by alkali feldspar and plagioclase, similar to the mineral assemblage of minette magma. Natural amphibole, diopside and orthopyroxene were not reproduced experimentally and probably result from sub-solidus reactions, whereas biotite re-equilibrated at low temperature. The crystallization sequence olivine followed by phlogopite and augite reproduces the sequence inferred in many mica-lamprophyre rocks. The similar fractionation trends observed for durbachites and minettes indicate that mafic durbachites are probably the plutonic equivalents of minettes and that K- and Mg-rich magmas in the Bohemian Massif may have been generated from partial melting of a phlogopite-clinopyroxene-bearing metasomatized peridotite. Experimental melt compositions also suggest that felsic durbachites can be generated by simple fractionation of a more mafic parent and mixing with mantle-derived components at

  15. Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

    USGS Publications Warehouse

    Davis, J.C.; Hausberger, G.; Schermann, O.; Bohling, G.

    1995-01-01

    The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik O??sterreich, and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types. ?? 1995 International Association for Mathematical Geology.

  16. Magmatic to solid state fabrics in syntectonic granitoids recording early Carboniferous orogenic collapse in the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Žák, Jiří; Verner, Kryštof; Holub, František V.; Kabele, Petr; Chlupáčová, Marta; Halodová, Patricie

    2012-03-01

    The ˜354-336 Ma Central Bohemian Plutonic Complex is a Variscan magmatic arc that developed in the central Bohemian Massif in response to subduction of the Saxothuringian lithosphere beneath the Teplá-Barrandian microplate. Magmatic to solid state fabrics in the most voluminous portion of this arc (the ˜346 Ma Blatná pluton) record two superposed orogenic events: dextral transpression associated with arc-parallel stretching and arc-perpendicular shortening, and normal shearing associated with exhumation of the high-grade core of the orogen (Moldanubian unit). This kinematic switch is an important landmark in the evolution of this segment of the Variscan belt for it marks the cessation of subduction-related compressive forces in the upper crust giving way to gravity-driven normal movements of the Teplá-Barrandian hanging wall block relative to the high-grade Moldanubian footwall. We use thermal modeling to demonstrate that the emplacement of huge volumes of arc magmas and their slow cooling produced a thermally softened domain in the upper crust and that the magmatic arc granitoids may have played a major role in initiating the orogenic collapse in the Bohemian Massif through lubrication and reactivation of a pre-existing lithospheric boundary and decreasing the overall strength of the rigid orogenic lid.

  17. The rare earth element potential of kaolin deposits in the Bohemian Massif (Czech Republic, Austria)

    NASA Astrophysics Data System (ADS)

    Höhn, S.; Frimmel, H. E.; Pašava, J.

    2014-12-01

    Four kaolin deposits in the Bohemian Massif were studied in order to assess the potential for the recovery of rare earth elements (REE) as by-products from the residue after extraction and refining of the raw kaolin. The behaviour of REE + Y during kaolinitization was found to be largely a function of pre-alteration mineralogy. In the examples studied, i.e. granite-derived deposits of Kriechbaum (Austria) and Božičany, and arkose-derived deposits of Kaznějov and Podbořany (all Czech Republic), the REE + Y are predominantly hosted by monazite which has remained unaffected by kaolinitization. The overall REE + Y content of the variably kaolinitized rocks is strongly dependent on their genesis. While ion adsorption plays only a minor role in the concentration of REE + Y in the studied kaolinitized rocks, the processing and refining of the raw kaolin leads to residues that are enriched in REE + Y by a factor of up to 40. The use of a magnetic separator and a hydrocyclone in the processing of the raw material can yield REE + Y contents of as much as 0.77 wt%. Although this value compares well with the REE + Y concentration in some potentially economic REE + Y projects elsewhere, the overall tonnage of the (REE + Y)-enriched residue is by far not sufficient to consider economic extraction of REE + Y as by-product. Our results are most probably applicable also to other kaolin deposits derived from the weathering of Hercynian basement granites elsewhere (e.g. in Saxonia and Bavaria, Germany). Overall, the potential for REE + Y production as by-product from kaolin mining has to be regarded as minimal.

  18. Tectonometamorphic evolution of the Bohemian Massif: evidence from high pressure metamorphic rocks

    NASA Astrophysics Data System (ADS)

    O'Brien, P. J.; Carswell, D. A.

    1993-09-01

    The Variscan orogenic belt, of which the Bohemian Massif is a part, is typically recognized for its characteristic low pressure, high temperature metamorphism and a large volume of granites. However, there are also bodies of high pressure rocks (eclogites, garnet peridotites and high pressure granulites) which are small in size but widely distributed throughtout the Massif. Initially the high pressure rocks were considered to be relicts of a much older orogenic event, but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have Palaeozoic protoliths. Metamorphic ages from the high pressure rocks define no single event. Instead, a number of discrete clusters of ages are found between about 430 Ma and the time of the dominant low pressure event at around 320 330 Ma. Most of the eclogite and granulite facies rocks are assigned to allochthonous nappes that arrived close to the end of the low pressure event, but before final granite intrusion. The nappes contain a mixture of different units and the relationship between rocks with high pressure relicts and host gneisses with no apparent signs of deep burial is still problematic. Some of the high pressure rocks retain evidence of multiple stages of partial re-equilibration during uplift. Moreover, it can be shown in certain instances that host gneisses also endured a multistage metamorphic development but with a peak event convergent with one of the breakdown stages in the enclosed rocks with high pressure relicts. It thus appears that the nappe units are composite bodies probably formed during episodic intracrustal thrusting. Fluids derived from prograde dehydration reactions in the newly under thrusting slab are taken to be the catalysts that drove the partial re-equilibrations. On the scale of the whole Massif it can be seen within the units with high pressure relicts that the temperature at the peak recorded pressure and that during the breakdown are variable in

  19. Dating granulite-facies structures and the exhumation of lower crust in the Moldanubian Zone of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Svojtka, M.; Košler, J.; Venera, Z.

    2002-05-01

    Deformation of granulite-facies rocks in the Moldanubian Zone of the southern Bohemian Massif is expressed in two intersecting planar fabrics - steeply disposed (S1) and flat-laying (S2) - which correspond to two deformation stages (D1) and (D2). The existing Sm-Nd garnet ages from banded granulite gneisses, new U-Pb zircon data from deformed granite intrusions within the granulite gneisses, and the P-T and field structural relations constrain the ages and P-T conditions of the two deformation phases. The early deformation (D1) was associated with a HP-HT metamorphic stage with a minimum age of ca. 354 Ma which was followed by a near-isothermal decompression. A concordant U-Pb zircon age of 318±1 Ma dates the emplacement of intrusions of deformed granite into the granulite gneisses and constrains deformation phase (D2). This phase was associated with an LP-HT metamorphism dated in the region at ca. 340-330 Ma. The available structural and isotopic data indicate that granulites in the southern Bohemian Massif were exhumed from lower to middle crust during compression. The structural relations and P-T-t data for the studied granulites are consistent with their exhumation by near-vertical extrusion of the softened orogenic root.

  20. Cross-border radon index map 1:100 000 Lausitz - Jizera - Karkonosze - Region (northern part of the Bohemian Massif).

    PubMed

    Barnet, Ivan; Pacherová, Petra; Preusse, Werner; Stec, Bartosz

    2010-10-01

    The first cross-border map describing the radon (Rn) risk from bedrock was assembled in the northern part of the Bohemian Massif at a scale 1:100 000. The map covers the area of Lausitz (Germany), Karkonosze (Czech Republic and Poland) and Jizera (Czech Republic). The map is based on 818 measurements of soil gas Rn in rock types of Precambrian to Mesozoic age with variable geology. Geographic information system (GIS) processing enabled a good coincidence of soil gas Rn concentrations between data from all three countries in lithologically adjacent rock types as well as the direct correlation to georeferenced indoor Rn values, which was tested using the Czech indoor Rn data. The method of data processing can contribute to assembling the European Geogenic Radon Map. PMID:20022148

  1. Two types of ultrapotassic plutonic rocks in the Bohemian Massif — Coeval intrusions at different crustal levels

    NASA Astrophysics Data System (ADS)

    Kotková, Jana; Schaltegger, Urs; Leichmann, Jaromír

    2010-03-01

    We present U-Pb zircon age determinations of two Variscan ultrapotassic plutonic rocks from the Moldanubian Zone (Bohemian Massif). Equant, multifaceted zircons without inherited cores from a two-pyroxene-biotite quartz monzonite of the Jihlava Pluton yielded a precise age of 335.12 ± 0.57 Ma, interpreted as dating magma crystallization. The majority of both tabular and prismatic grains from the amphibole-biotite melagranite ("durbachite") from the Třebíč Pluton plot along a discordia intersecting the concordia at 334.8 ± 3.2 Ma; prismatic zircon grains commonly contain inherited cores and yield an upper intercept age of 2.2 Ga, indicating early Proterozoic inheritance. We therefore suggest that both types of the ultrapotassic plutonic rocks from the Bohemian Massif crystallized at ca 335 Ma, and the previously published ages higher than ca 340 Ma for "durbachites" were biased by a small amount of unresolved inheritance. The ultrapotassic magma emplacement in the middle crust was related to rapid exhumation of a deep crustal segment, considered as isothermal decompression between high-pressure (˜ 340 Ma) and medium-pressure (˜ 333 Ma) stages recorded in granulites. Mineral assemblages as well as external and internal zircon morphology suggest that the Jihlava intrusion was deep and dry, whereas the Třebíč intrusion was shallow and wet. Low ɛHf values of zircons (- 4.4 to - 7.5) in both rock types suggest a similar source with a predominant crustal component. However, inherited grains in the Třebíč melagranite indicate its contamination with crustal material during emplacement, and thus possibly a slower rate of exhumation and/or of magma ascent through the crust.

  2. Multistage evolution of UHT granulites from the southernmost part of the Gföhl Nappe, Bohemian Massif, Lower Austria

    NASA Astrophysics Data System (ADS)

    Schantl, Philip; Hauzenberger, Christoph; Linner, Manfred

    2016-04-01

    A detailed petrological investigation has been undertaken in leucocratic kyanite-garnet bearing and mesocratic orthopyroxene bearing granulites from the Dunkelsteiner Wald, Pöchlarn-Wieselburg and Zöbing granulite bodies from the Moldanubian Zone in the Bohemian Massif (Austria). A combination of textural observations, conventional geothermobarometry, phase equilibrium modelling as well as major and trace element analyses in garnet enables us to confirm a multistage Variscan metamorphic history. Chemically homogenous garnet cores with near constant grossular-rich plateaus are considered to reflect garnet growth during an early HP/UHP metamorphic evolution. Crystallographically oriented rutile exsolutions restricted to those grossular-rich garnet cores point to a subsequent isothermal decompression of the HP/UHP rocks. Overgrowing garnet rims show a pronounced zonation and are interpreted as the result of dehydration melting reactions during an isobaric heating phase which could have taken place near the base of an overthickened continental crust, where the previously deeply subducted rocks were exhumed to. For this HP granulite facies event maximum PT conditions of ~1050 °C and 1.6 GPa have been estimated from leucocratic granulites comprising the peak mineral assemblage quartz, ternary feldspar, garnet, kyanite and rutile. The pronounced zoning of garnet rims indicates that the HP granulite facies event must have been short lived since diffusion in this temperature region is usually sufficient fast to homogenize a zoning pattern in garnet. A retrogressive metamorphic stage is documented in these rocks by the replacement of kyanite to sillimanite and the growth of biotite. This retrograde event took place within the granulite facies but at significantly lower pressures and temperatures with ~0.8 GPa and ~760 °C. This final stage of re-equilibration is thought to be linked with a second exhumation phase into middle crustal levels accompanied by intensive

  3. The systematics and paleobiogeographic significance of Sub-Boreal and Boreal ammonites (Aulacostephanidae and Cardioceratidae) from the Upper Jurassic of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Hrbek, Jan

    2014-10-01

    Upper Jurassic marine deposits are either rarely preserved due to erosion or buried under younger sediments in the Bohemian Massif. However, fossil assemblages from a few successions exposed in northern Bohemia and Saxony and preserved in museum collections document the regional composition of macro-invertebrate assemblages and thus provide unique insights into broad-scale distribution and migration pathways of ammonites during the Late Jurassic. In this paper, we focus on the systematic revision of ammonites from the Upper Oxfordian and Lower Kimmeridgian deposits of northern Bohemia and Saxony. The ammonites belong to two families (Aulacostephanidae and Cardioceratidae) of high paleobiogeographic and stratigraphic significance. Six genera belong to the family Aulacostephanidae (Prorasenia, Rasenia, Eurasenia, Rasenioides, Aulacostephanus, Aulacostephanoides) and one genus belongs to the family Cardioceratidae (Amoeboceras). They show that the Upper Jurassic deposits of the northern Bohemian Massif belong to the Upper Oxfordian and Lower Kimmeridgian and paleobiogeographically correspond to the German-Polish ammonite branch with the geographical extent from the Polish Jura Chain to the Swabian and Franconian Alb. Therefore, the occurrences of ammonites described here imply that migration pathway connecting the Polish Jura Chain with habitats in southern Germany was located during the Late Oxfordian and Early Kimmeridgian in the Bohemian Massif.

  4. Cenozoic volcanism in the Bohemian Massif in the context of P- and S-velocity high-resolution teleseismic tomography of the upper mantle

    NASA Astrophysics Data System (ADS)

    Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk.; Kissling, Eduard; Achauer, Ulrich; Babuška, Vladislav

    2016-08-01

    New high-resolution tomographic models of P- and S-wave isotropic-velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel-time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30-50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity-perturbations of the P- and S-wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low-velocity anomaly, which would validate the "baby-plume" concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low-velocity perturbations beneath the Eger Rift, observed in about 200km-broad zone, agree with shear-velocity models from full-waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.

  5. Petrochronological and structural arguments for upper plate thickening and relamination of the lower plate buoyant material in the Variscan Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Peřestý, Vít; Holder, Robert; Lexa, Ondrej; Racek, Martin; Jeřábek, Petr

    2014-05-01

    Recent tectonic models for the Variscan evolution of the Bohemian Massif emphasize the role of Rayleigh-Taylor instability for the 355-340 Ma evolution of the Moldanubian domain. This model is based on the presence of weak, low-density felsic material tectonically underplating a high-density mafic layer and its subsequent gravity-driven overturn. However, earlier phases of the Variscan orogeny concerning the emplacement of felsic low-density material to the base of the upper plate are so far poorly documented. We contribute to this problem by deciphering of polyphase early-Variscan (~375 Ma) deformation and metamorphism close to the main Variscan suture. Detailed structural, pseudosection and microstructural analyses combined with LASS monazite dating were carried out in metapelites along the western margin of the upper plate represented by the Teplá Crystalline Complex (TCC). This region is represented by a ~25 km wide deformation zone with E-W metamorphic gradients associated with two distinct early-Variscan events (~380-375 and ~375-370 Ma). The first compressional event produced a vertical NNE-SSW trending fabric and a continuous and prograde Barrovian metamorphic sequence ranging from biotite to kyanite zones at a field geotherm of 20 to 25 °C/km. Subsequently, a gently SE dipping normal shear-zone associated with retrogression develops along the base of the TCC. This sub-horizontal fabric shows normal metamorphic zonation ranging from sillimanite, biotite to chlorite zones and indicates vertical shortening related to unroofing of high pressure metabasites of the underlying Mariánské-Lázně Complex. The first metamorphic fabric is interpreted to result from early thickening of the upper plate during continental underthrusting of Saxothuringian continent (380 to 375 Ma) while the second deformation and metamorphism (~370 Ma) reflects vertical shortening produced by buoyant uplift of accreted Saxothuringian felsic crust. This event is the unique yet

  6. Palaeomagnetism and geochemistry of Early Palaeozoic rocks of the Barrandian (Teplé-Barrandian Unit, Bohemian Massif): palaeotectonic implications

    NASA Astrophysics Data System (ADS)

    Patočka, F.; Pruner, P.; Štorch, P.

    The Barrandian area (the Teplá-Barrandian unit, Bohemian Massif) provided palaeomagnetic results on Early Palaeozoic rocks and chemical data on siliciclastic sediments of both Middle Cambrian and Early Ordovician to Middle Devonian sedimentary sequences; an outcoming interpretation defined source areas of clastic material and palaeotectonic settings of the siliciclastic rock deposition. The siliciclastic rocks of the earliest Palaeozoic sedimentation cycle, deposited in the Cambrian Přı´bram-Jince Basin of the Barrandian, were derived from an early Cadomian volcanic island arc developed on Neoproterozoic oceanic lithosphere and accreted to a Cadomian active margin of northwestern Gondwana. Inversion of relief terminated the Cambrian sedimentation, and a successory Prague Basin subsided nearby since Tremadocian. Source area of the Ordovician and Early Silurian shallow-marine siliciclastic sediments corresponded to progressively dissected crust of continental arc/active continental margin type of Cadomian age. Since Late Ordovician onwards both synsedimentary within-plate basic volcanics and older sediments had been contributing in recognizable proportions to the siliciclastic rocks. The siliciclastic sedimentation was replaced by deposition of carbonate rocks throughout late Early Silurian to Early Devonian period of withdrawal of the Cadomian clastic material source. Above the carbonates an early Givetian flysch-like siliciclastic suite completed sedimentation in the Barrandian. In times between Middle Cambrian and Early/Middle Devonian boundary interval an extensional tectonic setting prevailed in the Teplá-Barrandian unit. The extensional regime was related to Early Palaeozoic large-scale fragmentation of the Cadomian belt of northwestern Gondwana and origin of Armorican microcontinent assemblage. The Teplá-Barrandian unit was also engaged in a peri-equatorially oriented drift of Armorican microcontinent assemblage throughout the Early Palaeozoic

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    An analysis of fault-slip data from the Lusatian Fault Belt, limiting the Lusatian Block of the Bohemian Massif in the SW, yielded parameters of eight successive paleostress patterns, Late Cretaceous to Plio-Pleistocene in age. These patterns were linked with specific stages in fault kinematics and fault-belt deformation. They include (1) α1, NE- to NNE-directed compression in a reverse fault regime (σ3 vertical) associated with major thrusting and drag zone formation in the latest Cretaceous, preceded by pre-drag origin of deformation bands α0; (2) αβ1-2, WNW-directed extension associated with emplacement of polzenite-group volcanics (≈80-61 Ma) and influx of hydrothermal fluids, overlapping in time with α1; (3) α2, N-directed compression in a reverse fault regime, probably Paleocene in age, associated with thrusting and intensive shear faulting in adjacent parts of blocks; (4) αβ3, Early Oligocene W- to WNW-directed extension in a regime of strike-slip faulting (σ2 vertical), probably connected with an emplacement of phonolitic magmas and influx of hydrothermal fluids; (5) α3, NNW-directed compression associated with activation of transverse/oblique faults of the fault belt, close in age to αβ3 with unclear mutual superposition; (6) β, Late Oligocene-Early Miocene multi-stage N- to NE-directed extension in a normal fault regime, specific to the Bohemian Massif, responsible for downfaulting of the hangingwall block; (7) γ, Mid to Late Miocene NE-directed compression in a reverse fault regime associated with thrusting; (8) δ, Pliocene (to Pleistocene?) NW- to NNW-directed compression in a strike-slip regime, associated with transverse faulting in the fault belt. The identified paleostress patterns show a good correlation with the hitherto identified paleostress fields transmitted to the Alpine foreland and refine the temporal sequence of paleostress states, especially in the post-Lower Miocene period.

  8. Mantle lithosphere transition from the East European Craton to the Variscan Bohemian Massif imaged by shear-wave splitting

    NASA Astrophysics Data System (ADS)

    Vecsey, L.; Plomerová, J.; Babuška, V.

    2014-08-01

    We analyse splitting of teleseismic shear waves recorded during the PASSEQ passive experiment (2006-2008) focused on the upper mantle structure across and around the Trans-European Suture Zone (TESZ). Altogether 1009 pairs of the delay times of the slow split shear waves and orientations of the polarized fast shear waves exhibit lateral variations across the array, as well as back-azimuth dependences of measurements at individual stations. Variable components of the splitting parameters can be associated with fabrics of the mantle lithosphere of tectonic units. In comparison with a distinct regionalization of the splitting parameters in the Phanerozoic part of Europe that particularly in the Bohemian Massif (BM) correlate with the large-scale tectonics, variations of anisotropic parameters around the TESZ and in the East European Craton (EEC) are smooth and of a transitional character. No general and abrupt change in the splitting parameters (anisotropic structure) can be related to the Teisseyre-Tornquist Zone (TTZ), marking the edge of the Precambrian province on the surface. Instead, regional variations of anisotropic structure were found along the TESZ/TTZ. The coherence of anisotropic signals evaluated beneath the northern part of the Brunovistulian in the eastern rim of the BM and the pattern continuation to the NE towards the TTZ, support the idea of a common origin of the lithosphere micro-plates, most probably related to Baltica. Smooth changes in polarizations of the core-mantle boundary refracted shear waves (SKS), polarizations, or even a large number of null splits northward of the BM and further across the TESZ towards the EEC indicate less coherent fabrics and a transitional character of structural changes in the mantle beneath the surface trace of the TESZ/TTZ. The narrow and near-vertical TTZ in the crust does not seem to have a steep continuation in the mantle lithosphere. The mantle part of the TESZ, whose crust was formed by an assemblage of

  9. Southeastern slope of the Bohemian Massif: Paleogene submarine fill of the Nesvacilka depression and its importance for petroleum exploration

    SciTech Connect

    Benada, S.; Berka, J.; Brzobohaty, J.; Rehanek, J. )

    1993-09-01

    The Nesvacilka depression is a trough-like paleovalley, about 2000 m deep, that was cut at the transition from the Cretaceous to the Paleocene by fluvial erosion into Jurassic and Carboniferous strata. This morphological feature, which is superimposed on an ancient tectonic zone, trends to the present southeast boundary of the Bohemian massif and is, from a hydrocarbon exploration point of view, the most important structure in the Czech Republic. During the Paleogene, marine transgressions gradually flooded this paleovalley. In the resulting relatively closed water body, more than 1500 m of thick deeper water clastics accumulated. These clastics display features similar to those described from submarine fan lobes in other hydrocarbon-producing basins. Following the discovery of two oil and gas accumulations contained in Jurassic and Paleogene clastic rocks, exploration was focused on the central parts of the Nesvacilka depression. The depositional pattern of its Paleogene fill was worked out on the basis of well data and the results of two-dimensional and three-dimensional seismic surveys. From this, it was concluded that accumulation of the Paleogene clastic series was significantly influenced by sea level changes. The depositional concepts developed may be applied to the deeper parts of the Nesvacilka Canyon, where exploration for hydrocarbons is still at an early stage. Results obtained so far indicate that the Nesvacilka depression can be ranked as the most prospective oil play in the Czech Republic. Play concepts developed may be extrapolated to similar morphological features occurring elsewhere in the Carpathian foreland.

  10. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2016-09-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

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

    NASA Astrophysics Data System (ADS)

    Breiter, Karel

    2016-06-01

    The chemical compositions of zircon and monazite and the relationships between the contents of Th, U, Y, and REE in both minerals and in the bulk samples of their parental rocks were studied in three Variscan composite peraluminous granite plutons in the Bohemian Massif. It was established that granites of similar bulk composition contain zircon and monazite of significantly different chemistry. Monazite typically contains 5-13 wt% (rarely up to 28 wt%) ThO2, 0.4-2 wt% (up to 8.2 wt%) UO2, and 0.5-2 wt% (up to 5 wt%) Y2O3, whereas zircon typically contains less than 0.1 wt% (rarely up to 1.7 wt%) ThO2, less than 1 wt% UO2 (in the Plechý/Plockenstein granite, commonly, 1-2 wt% and scarcely up to 4.8 wt% UO2), and less than 1 wt% Y2O3 (in the Nejdek pluton often 2-5, maximally 7 wt% Y2O3). Monazite is an essential carrier of thorium, hosting more than 80 % of Th in all studied granites. Monazite also appears to be an important carrier of Y (typically 14-16 %, and in the Melechov pluton, up to 81 % of the total rock content) and U (typically 18-35 % and occasionally 6-60 % of the total rock budget). The importance of zircon for the rock budget of all the investigated elements in granites is lower: 4-26 % U, 5-17 % Y, and less than 5 % Th.

  12. The Blaník Gneiss in the southern Bohemian Massif (Czech Republic): a rare rock composition among the early palaeozoic granites of Variscan Central Europe

    NASA Astrophysics Data System (ADS)

    René, Miloš; Finger, Fritz

    2016-08-01

    Metamorphosed and deformed tourmaline-bearing leucogranites with a Cambro-Ordovician formation age are widespread in the Monotonous Group of the Variscan southern Bohemian Massif, Czech Republic. The rocks, known locally as Blaník gneiss, are strongly peraluminous and classify as phosphorus-rich low-T, S-type granite. The magma formed from a metapelitic source, most likely through muscovite dehydration melting. With respect to its low-T origin and the abundance of tourmaline, the Blaník gneiss is exotic within the spectrum of Early Palaeozoic granites of the Variscan fold belt of Central Europe. Coeval granitic gneisses in the neighbouring Gföhl unit of the Bohemian Massif can be classified as higher T S-type granites and were probably generated through biotite dehydration melting. The geochemical differences between the Early Palaeozoic granitic magmatism in the Gföhl unit and the Monotonous Group support models claiming that these two geological units belonged to independent peri-Gondwana terranes before the Variscan collision. It is suggested here, that the Gföhl unit and the Monotonous Group represent zones of higher and lower heat flow within the Early Palaeozoic northern Gondwana margin, respectively. The geochemical data presented in this study could be helpful for terrane correlations and palaeogeographic reconstructions.

  13. Major and trace elements in pyrope almandine garnets as sediment provenance indicators of the Lower Carboniferous Culm sediments, Drahany Uplands, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Čopjaková, Renata; Sulovský, Petr; Paterson, Bruce A.

    2005-05-01

    The Lower Carboniferous Culm Basin is part of the European Variscan foreland basin. Garnet is an abundant heavy mineral at all stratigraphic levels of the Culm sediments (the Protivanov, Rozstání and Myslejovice Formation from base to top). This paper compares the major element (electron microprobe) and trace element (LA-ICP-MS) compositions of garnet for the purpose of studying the provenance of the Culm sediments. The polymict garnet assemblages ranging from the Protivanov to lower part of the Myslejovice Formation (Goniatite zones Pe γ-Go α) pass into oligomict ones dominated by pyrope-almandine garnets (uppermost part of the Myslejovice Formation; Goniatite zones Go β-Go γ). As the predominant low-grossular pyrope-almandines from oligomict garnet assemblages are very uniform and homogeneous in major element composition, we studied their trace element composition and zoning. Pyrope-almandine garnets are poor in LREE and show enrichment in HREE; the chondrite-normalized patterns are almost flat from Dy to Lu and show a significant negative Eu anomaly, typical for granulite-grade garnets. Major element compositions of detrital low-grossular pyrope-almandines can only be matched with some granulites and garnetiferous felsic gneisses of the Bohemian Massif. Garnets from granulites cropping out at the present-day erosion level of the Bohemian Massif have usually higher Ca and/or lower Mg contents. The major and trace element compositions and zoning patterns of pyrope-almandine garnets from the upper part of the Myslejovice Formation compare well with garnets from the Miroslav granulites and small Moldanubian granulite bodies west of the Třebíč Massif. The Moldanubian granulites are commonly associated with mantle-derived peridotites and eclogites. The presence of detrital Cr-spinels with high Cr# and low Mg# (single grains of Cr-spinels and fine-grained kelyphitic intergrowths of Cr-spinel with chlorite) comparable with spinel types from Moldanubian

  14. Evidence of unadulterated mantle-depth, granitic melt inclusions: kumdykolite and kokchetavite crystallized from melt in Bohemian Massif granulites.

    NASA Astrophysics Data System (ADS)

    O´Brien, Patrick J.; Ferrero, Silvio; Ziemann, Martin A.; Walczak, Katarzyna; Wunder, Bernd; Hecht, Lutz; Wälle, Markus

    2016-04-01

    Partial melting under near-UHP conditions of metagranitoids (now HP felsic granulites) at mantle depth in the Orlica-Śnieżnik Dome (Bohemian Massif, Poland) is recorded in small volumes of hydrous melt trapped as primary melt inclusions (MI) in peritectic garnets. When free of cracks connecting the inclusion with the leucocratic matrix, these "nanogranites" (≤ 50μm inclusion diameter) contain a unique assemblage including kumdykolite, kokchetavite and cristobalite - polymorphs of albite, K-feldspar and quartz, respectively. These usually metastable phases crystallized from the melt (glass?) during rapid exhumation (cm/a) at high T but the crack-free state strongly suggests over-pressuring of the inclusion with respect to the pressure-time path followed by the matrix. Reports of both kumdykolite and kokchetavite have been mainly from natural rocks equilibrated in the diamond stability field. The precise calculation of the PT path of the MI on cooling and the comparison with previous studies suggests, however, that pressure is not influential to their formation, ruling out the possible interpretation of kumdykolite and kokchetavite as indicators of ultra-high pressure conditions. Experimental re-homogenization of these crack-free nanogranites was achieved using a piston cylinder apparatus at 2.7 GPa and 875°C. These conditions are consistent with the results of geothermobarometric calculations on the host rock, suggesting that no H2O loss occurred during exhumation as this would have caused a shift of the inclusion melting T toward higher values. Coupled with the absence of H2O-loss microstructural evidence, e.g. decrepitation cracks and/or vesciculation in re-homogenized nanogranites, this evidence suggests that the nanogranites still preserve the original H2O content of the melt. Both experimental and microstructural evidence support the hypothesis that the presence of these polymorphs should be regarded as direct mineralogical criterion to identify former

  15. Underground electromagnetic activity in two regions with contrasting seismicity: a case study from the Eastern Alps and Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Baroň, Ivo; Koktavý, Pavel; Stemberk, Josef; Macků, Robert; Trčka, Tomáš; Škarvada, Pavel; Lenhardt, Wolfgang; Meurers, Bruno; Rowberry, Mattew; Marti, Xavi; Plan, Lukas; Grasemann, Berhnard; Mitrovic, Ivanka

    2016-04-01

    Electromagnetic emissions (EME) occur during the fracturing of solid materials under laboratory conditions and may represent potential earthquake precursors. We recorded EME from May 2015 to October 2015 in two caves situated in contrasting seismotectonic settings. Zbrašov Aragonite Caves are located close to the seismically quiescent contact between the Bohemian Massif and the Outer Western Carpathians while Obir Caves are located near the seismically active Periadriatic Fault on the southern margin of the Eastern Alps. The specific monitoring points are located at depths of tens of metres below the ground surface as such places are assumed to represent favourably shielded environments. The EME signals were continuously monitored by two custom-made Emission Data Loggers (EDLOG), comprising both analogue and digital parts. The crucial analogue component within the EDLOG is a wideband shielded magnetic loop antenna. To be able to observe EME related rock deformation and microfracturing we recorded signals between 10 and 200 kHz with a sampling frequency of 500 kHz. An ultralow noise preamplifier placed close to the antenna increases the signal-to-noise ratio. Further signal processing consisted of filtering, such as antialiasing and interference rejection, and additional amplification to fit the signal to the full scale range of the AD convertor. The digital part of the EDLOG comprises a range of PC components such as high-capacity replaceable data storage and unbuffered RAM, high-speed multichannel DAQ cards, and custom made control software in the programming environment LabVIEW. During our EME monitoring all the raw data were stored. This has allowed us to perform advanced data processing and detailed analysis. During the study period some artificial EME signals were observed in Zbrašov Aragonite Caves. This artificial noise may have overprinted any natural signals and is most likely to relate to the pumping of CO2. In contrast, markedly different signals were

  16. Grain-scale processes in actively deforming magma mushes: New insights from electron backscatter diffraction (EBSD) analysis of biotite schlieren in the Jizera granite, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Žák, Jiří; Verner, Kryštof; Týcová, Patricie

    2008-12-01

    In the porphyritic Jizera granite, Bohemian Massif, three distinct types of lattice-preferred orientations of biotite grains were revealed in schlieren-delineated magmatic structures using the electron backscatter diffraction (EBSD) method. (1) Biotite basal planes (001) reorient from schlieren-subparallel near the schlieren base to schlieren-perpendicular in the upper part of the schlieren. Both orientations share subhorizontal ˜N-S to ˜NNE-SSW-trending a axes. (2) In some domains, the a axes are steep and at a high angle to the schlieren plane while the c axes plunge shallowly and rotate around an ill-defined a axis. (3) In other domains, the EBSD coincides with background magnetic fabric of the host granite revealed using the anisotropy of magnetic susceptibility (AMS) method: that is, the a axes plunge shallowly to the SE or NW while the c axes are subhorizontal and cluster around the ˜NE-SW trend. These multiple biotite orientations in the schlieren are interpreted to reflect (1) velocity-gradient in laminar magma flow along channel-like conduits, localized within the high-strength host phenocryst framework, (2) grain-scale gravity-driven constrictional deformation of the magma mush, and (3) overprinting background (tectonic?) deformation transmitted across large parts of the magma chamber prior to its final crystallization. The grain-scale mechanisms of biotite fabric acquisition in the schlieren presumably involved rotation of biotite crystals during flow, with the biotite alignment reflecting the flow geometry and kinematics, replaced after flow cessation by melt-aided grain-boundary sliding of those biotite crystals still enclosed in melt pockets within otherwise static, highly crystallized magma mush. The latter process was sufficient to reorient biotite grains but not to cause destruction of the schlieren. Using the Jizera granite as a case example, we argue that the lattice-preferred orientation of mineral grains in mafic schlieren is highly

  17. Gallium and germanium geochemistry during magmatic fractionation and post-magmatic alteration in different types of granitoids: a case study from the Bohemian Massif (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Gardenová, Nina; Kanický, Viktor; Vaculovič, Tomáš

    2013-06-01

    Contents of Ga and Ge in granites, rhyolites, orthogneisses and greisens of different geochemical types from the Bohemian Massif were studied using inductively coupled plasma mass spectrometry analysis of typical whole-rock samples. The contents of both elements generally increase during fractionation of granitic melts: Ga from 16 to 77 ppm and Ge from 1 to 5 ppm. The differences in Ge and Ga contents between strongly peraluminous (S-type) and slightly peraluminous (A-type) granites were negligible. The elemental ratios of Si/1000Ge and Al/1000Ga significantly decreased during magmatic fraction: from ca. 320 to 62 and from 4.6 to 1.2, respectively. During greisenization, Ge is enriched and hosted in newly formed hydrothermal topaz, while Ga is dispersed into fluid. The graph Al/Ga vs. Y/Ho seems to be useful tool for geochemical interpretation of highly evolved granitoids.

  18. Constraining long-term denudation and faulting history in intraplate regions by multisystem thermochronology: An example of the Sudetic Marginal Fault (Bohemian Massif, central Europe)

    NASA Astrophysics Data System (ADS)

    DanišíK, Martin; Å TěPančíKová, Petra; Evans, Noreen J.

    2012-04-01

    The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th)/He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous-Permian basement in the Late Cretaceous (˜95-80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85-70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of ˜300 m/Ma as evidenced by Late Cretaceous-Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene-Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than ˜1.5 km in the study area.

  19. Two-stage exhumation of subducted Saxothuringian continental crust records underplating in the subduction channel and collisional forced folding (Krkonoše-Jizera Mts., Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Jeřábek, Petr; Konopásek, Jiří; Žáčková, Eliška

    2016-08-01

    The Krkonoše-Jizera Massif in the northern part of the Variscan Bohemian Massif provides insight into the exhumation mechanisms for subducted continental crust. The studied region exposes a relatively large portion of a flat-lying subduction-related complex that extends approximately 50 km away from the paleosuture. wide extent of HP-LT metamorphism has been confirmed by new P-T estimates indicating temperatures of 400-450 °C at 14-16 kbar and 450-520 °C at 14-18 kbar for the easternmost and westernmost parts of the studied area, respectively. A detailed study of metamorphic assemblages associated with individual deformation fabrics together with analysis of quartz deformation microstructures and textures allowed characterisation of the observed deformation structures in terms of their subduction-exhumation memory. An integration of the lithostratigraphic, metamorphic and structural data documents a subduction of distal and proximal parts of the Saxothuringian passive margin to high-pressure conditions and their subsequent exhumation during two distinct stages. The initial stage of exhumation has an adiabatic character interpreted as the buoyancy driven return of continental material from the subduction channel resulting in underplating and progressive nappe stacking at the base of the Teplá-Barrandian upper plate. With the transition from continental subduction to continental collision during later stages of the convergence, the underplated high-pressure rocks were further exhumed due to shortening in the accretionary wedge. This shortening is associated with the formation of large-scale recumbent forced folds extending across the entire studied area.

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

    NASA Astrophysics Data System (ADS)

    Tomek, Filip; Žák, Jiří; Chadima, Martin

    2015-07-01

    The Late Devonian Staré Sedlo complex, Bohemian Massif, was emplaced as a subhorizontal sheeted sill pluton into a transtension zone. The transtensional setting is documented by strong constrictional fabric, corroborated by the anisotropy of magnetic susceptibility (AMS), with variably developed subhorizontal magmatic to solid-state foliation suggesting vertical shortening. Intrusive contacts of the granitoids with metapelitic screens and tapered sill tips indicate that magma wedging was the dominant process of sill propagation. The sills exhibit two intrusive styles, ranging from thin lit-par-lit injections to widely spaced meter-thick sills. These two styles are interpreted as reflecting variable viscosities of intruding magma where low-viscosity magma percolated along foliation planes whereas high-viscosity magma produced more localized thicker sills. We propose that the magma/host rock system in transtension must have evolved from initial crack tip propagation and vertical expansion due to new magma additions through conduit flow to ductile thinning after the magma input had ceased. The sill emplacement and their subsequent deformation are then interpreted as recording early-orogenic syn-convergent sinistral transtension along the rear side of an upper-crustal wedge, which was extruded both upward and laterally in response to subduction and continental underthrusting.

  1. Kumdykolite, kokchetavite, and cristobalite crystallized in nanogranites from felsic granulites, Orlica-Snieznik Dome (Bohemian Massif): not an evidence for ultrahigh-pressure conditions

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; Ziemann, Martin A.; Angel, Ross J.; O'Brien, Patrick J.; Wunder, Bernd

    2016-01-01

    A unique assemblage including kumdykolite and kokchetavite, polymorphs of albite and K-feldspar, respectively, together with cristobalite, micas, and calcite has been identified in high-pressure granulites of the Orlica-Snieznik dome (Bohemian Massif) as the product of partial melt crystallization in preserved nanogranites. Previous reports of both kumdykolite and kokchetavite in natural rocks are mainly from samples that passed through the diamond stability field. However, because the maximum pressure recorded in these host rocks is <3 GPa, our observations indicate that high pressure is not required for the formation of kumdykolite and kokchetavite, and their presence is not therefore an indicator of ultrahigh-pressure conditions. Detailed microstructural and microchemical investigation of these inclusions indicates that such phases should instead be regarded as (1) a direct mineralogical criteria to identify former melt inclusions with preserved original compositions, including H2O and CO2 contents and (2) indicators of rapid cooling of the host rocks. Thus, the present study provides novel criteria for the interpretation of melt inclusions in natural rocks and allows a more rigorous characterization of partial melts during deep subduction to mantle depth as well as their behavior on exhumation.

  2. Crustal melting during subduction at mantle depth: anatomy of near-UHP nanogranites (Orlica-Śnieżnik Dome, Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; Ziemann, Martin; Walczak, Katarzyna; Wunder, Bernd; O'Brien, Patrick J.; Hecht, Lutz

    2015-04-01

    Small volumes (≤ 50µm) of hydrous melt were trapped as primary inclusions in peritectic garnets during partial melting of metagranitoids from the Orlica-Śnieżnik Dome (Bohemian Massif) at mantle depth [1]. Detailed microstructural/microchemical investigation confirmed the occurrence of a granitic assemblage (biotite+feldspars+quartz) in every investigated inclusion, i.e they are nanogranites [2]. MicroRaman mapping of unexposed inclusions showed the occurrence of residual, H2O-rich glass in interstitial position. Despite the oddity of this finding within a classic regional HP/HT terrain, an incomplete crystallization of the melt inclusions (MI) is consistent with the (relatively) rapid exhumation of the Orlica-Śnieżnik Dome proposed by some authors [e.g. 3]. Moreover glassy and partially crystallized MI have been already reported in lower-P (<1 GPa) migmatites [4]. MicroRaman investigation also showed the possible presence of kumdykolite, a high-temperature polymorph of albite reported in UHP rocks from the Kokchetav Massif as well as the Bohemian massif ([5] and references therein). Experimental re-homogenization of nanogranites was achieved using a piston cylinder apparatus at 2.7 GPa and 875°C under dry conditions, in order to investigate melt composition and H2O content with in situ techniques. The trapped melt is granitic, hydrous (6 wt% H2O) and metaluminous (ASI=1.03), and it is similar to those produced experimentally from crustal lithologies at mantle conditions. Re-homogenization conditions are consistent with the results of geothermobarometric calculations on the host rock, suggesting that no H2O loss occurred during exhumation - this would have caused a shift of the inclusion melting T toward higher values. Coupled with the absence of H2O-loss microstructural evidence, e.g. decrepitation cracks and/or vesciculation [4] in re-homogenized nanogranites, this evidence suggests that the nanogranites still preserves the original H2O content of the

  3. Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria)

    NASA Astrophysics Data System (ADS)

    Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin

    2016-06-01

    Dykes in the Strudengau area (SW Moldanubian Zone, Austria) can be mineralogically divided into lamprophyres (spessartites and kersantites) and felsic dykes (granite porphyries, granitic dykes and pegmatoid dykes). Geochemical analyses of 11 lamprophyres and 7 felsic dykes show evidence of fractional crystallization. The lamprophyres are characterized by metaluminous compositions, intermediate SiO2 contents and high amounts of MgO and K2O; these rocks have high Ba (800-3000 ppm) and Sr (250-1000 ppm) contents as well as an enrichment of large-ion lithophile elements over high field strength elements, typical for enriched mantle sources with variable modifications due to fractionation and crustal contamination. This geochemical signature has been reported from durbachites (biotite- and K feldspar-rich mela-syenites particularly characteristic of the Variscan orogen in Central Europe). For most major elements, calculated fractionation trends from crystallization experiments of durbachites give an excellent match with the data from the Strudengau dykes. This suggests that the lamprophyres and felsic dykes were both products of fractional crystallization and subsequent magma mixing of durbachitic and leucogranitic melts. Rb-Sr geochronological data on biotite from five undeformed kersantites and a locally deformed granite porphyry gave cooling ages of c. 334-318 Ma, indicating synchronous intrusion of the dykes with the nearby outcropping Weinsberger granite (part of the South Bohemian Batholith, c. 330-310 Ma). Oriented matrix biotite separated from the locally deformed granite porphyry gave an Rb-Sr age of c. 318 Ma, interpreted as a deformation age during extensional tectonics. We propose a large-scale extensional regime at c. 320 Ma in the Strudengau area, accompanied by plutonism of fractionated magmas of syncollisional mantle-derived sources, mixed with crustal components. This geodynamic setting is comparable to other areas in the Variscan belt documenting an

  4. Variscan granitoids related to shear zones and faults: examples from the Central Sudetes (Bohemian Massif) and the Middle Odra Fault Zone

    NASA Astrophysics Data System (ADS)

    Oberc-Dziedzic, T.; Kryza, R.; Pin, C.

    2015-07-01

    The granitoid intrusions of the Central Sudetes (CS) and of the Middle Odra Fault Zone (MOFZ), NE part of the Bohemian Massif, are both spatially and temporally related to large-scale shear zones and faults (including possible terrane boundaries) that provided effective channels for melt migration. Summarizing common features of the CS and MOFZ granitoids, we have delineated a set of characteristics of the fault-related and shear zone-related granitoids: (1) they are mainly generated by partial melting of crustal sources, with variable contribution (or no contribution) of mantle materials; (2) the sheet-like, steeply inclined, narrow and rather small granitoid intrusions are emplaced within shear zones at mid-crustal level (c. 20 km depth), whereas the larger, flat-lying plutons intrude into the upper crust, outside or above these shear zones; (3) the magmatic foliation and lineation in granitoids of the deeper, sheet-like intrusions are concordant with those in the surrounding metamorphic rocks, suggesting that the solidification of granitoids was coeval with the deformation in the shear zones; instead, the magmatic foliation in the shallower and larger dome-like plutons reflects magma flow; (4) ductile, transcurrent movements along the shear zones postdate medium-pressure regional metamorphism and are accompanied by an increase in the local thermal gradient, as documented by the crystallization of cordierite, andalusite and sillimanite; (5) the increase in the thermal gradient precedes the emplacement of granitoids and their concomitant thermal influence on the country rocks. The granitoids related to the final stages of tectonothermal activity of the shear zones are good-time markers of their evolutionary path.

  5. Fluid evolution of the Hub Stock, Horní Slavkov-Krásno Sn-W ore district, Bohemian Massif, Czech Republic

    NASA Astrophysics Data System (ADS)

    Dolníček, Zdeněk; René, Miloš; Prochaska, Walter; Kovář, Michal

    2012-10-01

    The Horní Slavkov-Krásno Sn-W ore district is hosted by strongly altered Variscan topaz-albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ˜500 to <50°C. Rarely observed highest-temperature (˜500°C) highest-salinity (˜30 wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0-7 wt.% NaCl eq.) aqueous fluids with low amount of CO2, CH4, and N2 (≤10 mol% in total) at temperatures of ˜350-400°C and pressures of 300-530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ˜50-100 bar), and mostly also decreasing salinity.

  6. Origin of the Zálesí U-Ni-Co-As-Ag/Bi deposit, Bohemian Massif, Czech Republic: fluid inclusion and stable isotope constraints

    NASA Astrophysics Data System (ADS)

    Dolníček, Zdeněk; Fojt, Bohuslav; Prochaska, Walter; Kučera, Jan; Sulovský, Petr

    2009-01-01

    The Zálesí vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the northern margin of the Bohemian Massif. The mineralization is composed of three main stages: uraninite, arsenide, and sulfide. The mineral assemblages formed at low temperatures (~80 to 130°C, locally even lower) and low pressures (<100 bars). The salinity of the aqueous hydrothermal fluids (0 to 27 wt.% salts) and their chemical composition vary significantly. Early fluids of the oldest uraninite stage contain a small admixture of a clathrate-forming gas, possibly CO2. Salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines [ δ 18O around +2‰ relative to standard mean ocean water (SMOW)] with meteoric waters ( δ 18O around -4‰ SMOW). The fluid is characterized by highly variable halogen ratios (molar Br/Cl = 0.8 × 10-3 to 5.3 × 10-3; molar I/Cl = 5.7 × 10-6 to 891 × 10-6) indicating a dominantly external origin for the brines, i.e., from evaporated seawater, which mixed with iodine-enriched halite dissolution brine. The cationic composition of these fluids indicates extensive interaction of the initial brines with their country rocks, likely associated with leaching of sulfur, carbon, and metals. The brines possibly originated from Permian-Triassic evaporites in the neighboring Polish Basin, infiltrated into the basement during post-Variscan extension and were finally expelled along faults giving rise to the vein-type mineralization. Cenozoic reactivation by low-salinity, low- δ 18O (around -10‰ SMOW) fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite-like mineral aggregates.

  7. Thermochronological record of long term faulting, burial and exhumation history in the Sudetes (Bohemian Massif, Central Europe): a multi-system thermochronological approach

    NASA Astrophysics Data System (ADS)

    Štěpančíková, P..; Danišík, M.; Evans, N. J.

    2012-04-01

    Reconstructing erosional and faulting history in the old crystalline basement terrains, with lacking or sparse post-tectonic geological records, is a challenging task where even radiometric data on the basement rocks need not to provide ultimate answers. NE part of the Bohemian Massif (known as the Sudetes) represents a classic example where numerous attempts to constrain denudation, faulting and relief formation on the Variscan basement, often based on incomplete lines of evidence, led to formulation of controversial models. In this study we aim to reconstruct the post-orogenic exhumation history of the Rychlebské hory Mts. in the eastern Sudetes and constrain paleo-activity along the Sudetic Marginal Fault (SMF) - one of the morphologically most prominent, but poorly understood features of Central Europe, forming a >140 km long escarpment separating the Sudetic Mountains from the foreland in the northeast. We do so by applying zircon (U-Th)/He (ZHe), apatite fission track (AFT) and apatite (U-Th)/He (AHe) dating methods to the basement samples from different fault-bounded blocks and sparsely preserved post-orogenic sedimentary samples. New thermochronological data reveals that in the Late Cretaceous at ~95-80 Ma, the Carboniferous-Permian basement blocks SW and NE of the SMF were buried to ~4-7 km and >6.5 km depths, respectively, by sediments of the Bohemian Cretaceous Basin System. This finding contradicts the traditional paleogeographic reconstructions suggesting exposure of large portions of the Sudetes for most of the Mesozoic-Cenozoic. During the burial, the SMF acted as a normal fault as documented by offset in ZHe ages across the fault. At 85-70 Ma, the basin was inverted, Cretaceous strata eroded and basement blocks were exhumed to the near-surface at exhumation rate of ~300 m/Ma as evidenced by Late Cretaceous-Paleocene AFT ages and thermal modelling results. There is no appreciable difference in AFT and AHe ages across the fault suggesting that the

  8. Structural style, deformation mechanisms and paleodifferential stress along an exposed crustal section: constraints on the rheology of quartzofeldspathic rocks at supra- and infrastructural levels (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Zulauf, G.

    2001-03-01

    Investigations of Variscan shortening of quartzofeldspathic rocks have been carried out along an exposed crustal section located in the western part of the Teplá Barrandian unit (Bohemian Massif). The study focuses on determining differential stress, deformation mechanisms and geometry of Cadomian metagreywackes and Cambrian granitoids which show different grade of Variscan Barrovian-type metamorphism ranging from the greenschist-/subgreenschist-facies boundary (semibrittle deformation regime) to the high-grade amphibolite facies. The semibrittle deformation regime ( T=ca. 300°C) is characterized by large-scale thrusting within a folding environment and by similar intensities of cataclasis, diffusive mass transfer, and crystal plasticity of quartz, the latter including low-temperature migration recrystallization. Within Cadomian quartz veins of the greenschist-facies part, dislocation creep of quartz operated at differential stresses ranging from ca. 70 MPa in the lowermost greenschist-facies to ca. 20 MPa in the uppermost greenschist-facies. These values have been derived by paleopiezometry using the grain size of recrystallized quartz. They are interpreted as upper bounds for the bulk stress because of intense diffusive mass transfer within the adjacent metagreywackes. A marking increase in recrystallized grain size of quartz occurs within the lower greenschist-facies, where low-temperature grain boundary migration is replaced by subgrain rotation. Thus, causion is needed when applying the recrystallized grain size paleopiezometer to this crustal level. Pressure solution of quartz and development of discrete crenulation cleavage was common in fine-grained metagreywackes of the lower greenschist-facies, whereas the upper greenschist-facies ( T=ca. 500-570°C) is characterized by increasing intensity of metamorphic reactions, grain coarsening and development of a schistosity. The entire greenschist-facies level forms a suprastructure where viscosity contrasts

  9. Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Bizimis, Michael; Haluzová, Eva; Sláma, Jiří; Svojtka, Martin; Hirajima, Takao; Erban, Vojtěch

    2016-07-01

    We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial εHf values ranging from - 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and εHf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial εHf of + 66 for a given εNd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Bečváry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial γOs. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor

  10. The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization

    NASA Astrophysics Data System (ADS)

    Kříbek, Bohdan; Žák, Karel; Dobeš, Petr; Leichmann, Jaromír; Pudilová, Marta; René, Miloš; Scharm, Bohdan; Scharmová, Marta; Hájek, Antonín; Holeczy, Daniel; Hein, Ulrich F.; Lehmann, Bernd

    2009-01-01

    Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K-Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K-Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K-Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to

  11. UHP-UHT peak conditions and near-adiabatic exhumation path of diamond-bearing garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Haifler, Jakub; Kotková, Jana

    2016-04-01

    Intermediate garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif, contain microdiamonds enclosed in garnet and zircon. The variable mineral assemblage of these rocks allows for an evaluation of the P-T evolution using numerous univariant equilibria and thermodynamic modelling, in addition to the ternary feldspar solvus, Ti-in-garnet, Zr-in-rutile and Ti-in-zircon thermometry. Zircon mantle domains with diamond inclusions contain 111-189 ppm Ti, reflecting temperatures of 1037-1117 °C. The peak pressure consistent with diamond stability corresponds to c. 4.5-5.0 GPa. Ti-in-garnet thermometry using the Ti content of diamond-bearing garnet core yielded temperatures of 993-1039 °C at c. 5.0 GPa. An omphacite inclusion in garnet (reflecting c. 2.3-2.4 GPa at c. 1050 °C) and metastably preserved kyanite represent relics of eclogite-facies conditions. The dominant high-pressure granulite-facies mineral assemblage of low-Ca garnet, diopsidic clinopyroxene, antiperthitic feldspar and quartz equilibrated at 1.8-2.1 GPa and c. 1050 °C, based on the XGrs isopleth of the garnet mantle, garnet-feldspar-kyanite-quartz univariant equilibria and ternary feldspar solvus. Our thermodynamic modelling shows that a steep decrease of XGrs from a maximum core value of 0.32 to 0.17 at the rim as well as a rimward XMg increase (from 0.42 to 0.50) are consistent with significant decompression without heating. The latter is related to omphacite and kyanite breakdown reactions producing garnet and plagioclase. The Ti content in the rim zone of zircon (13-42 ppm), exsolved plagioclase and K-feldspar associated with matrix diopside and garnet rim, and late biotite reflect temperatures of c. 830-900 °C at c. 1.4 GPa. A similar temperature is recorded by matrix rutile grains, containing 2028-4390 ppm Zr and representing a relatively homogeneous population in contrast to rutile enclosed in garnet with variable Zr content. Our results show that the garnet

  12. Partial melting of granitoids under eclogite-facies conditions: nanogranites from felsic granulites from Orlica-Śnieżnik Dome (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O'Brien, Patrick; Walczak, Katarzyna; Wunder, Bernd; Hecht, Lutz

    2014-05-01

    Melt inclusions (MI) study in migmatites is a powerful tool to retrieve the original composition of the anatectic melt, both as major elements (Ferrero et al., 2012) and fluid contents (Bartoli et al., 2013). Crystallized MI, or "nanogranites" (Cesare et al., 2009), were identified within HP felsic granulites from Orlica-Śnieżnik Dome, NE Bohemian Massif (Walczak, 2011). The investigated samples are Grt+Ky leucogranulites originated from a granitic protolith, with assemblage Qtz+Pl+Kfs+Grt+Ky+Ttn+Rt+Ilm. Nanogranites occur in garnet as primary inclusions, and consist of Qtz+Ab+Bt+Kfs±Ep±Ap. Such assemblage results from the crystallization of a melt generated during a partial melting reaction; the same reaction is also responsible for the production of the host garnet, interpreted therefore as a peritectic phase. Besides nanogranites, former presence of melt is supported by the occurrence of tiny pseudomorphs of melt-filled pores (Holness & Sawyer, 2008) and euhedral faces in garnet. Garnet composition, with Grs =0.28-0.31, phase assemblage (kyanite, ternary feldspar) and classic thermobarometry suggest that partial melting took place at T≥875°C and P~2.2-2.6 GPa, under eclogite-facies conditions. Although other authors reported palisade quartz after coesite in this area (see e.g. Bakun-Czubarow, 1992), no clear evidence of UHP conditions have been identified during this study. Piston cylinder re-homogenization experiments were performed on MI-bearing garnet chips to obtain the composition of the pristine anatectic melt. The first data from experiments in the range 850-950°C and 2-2.2 GPa show that nanogranites can be re-melted at T≥875°. However, homogenization has not been reached yet since new Grt, with lower CaO and higher MgO, crystallizes on the walls of the inclusion. As P increases, the modal amount of new phase decreases, while its composition evolves closer to those of the host garnet. Further experiments at higher pressure are in underway, with

  13. Continental crust subducted deeply into lithospheric mantle: the driving force of Early Carboniferous magmatism in the Variscan collisional orogen (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Janoušek, Vojtěch; Schulmann, Karel; Lexa, Ondrej; Holub, František; Franěk, Jan; Vrána, Stanislav

    2014-05-01

    The vigorous Late Devonian-Early Carboniferous plutonic activity in the core of the Bohemian Massif was marked by a transition from normal-K calc-alkaline, arc-related (~375-355 Ma), through high-K calc-alkaline (~346 Ma) to (ultra-)potassic (343-335 Ma) suites, the latter associated with mainly felsic HP granulites enclosing Grt/Spl mantle peridotite bodies. The changing chemistry, especially an increase in K2O/Na2O and 87Sr/86Sri with decrease in 143Nd/144Ndi in the basic end-members, cannot be reconciled by contamination during ascent. Instead it has to reflect the character of the mantle sources, changing over time. The tectonic model invokes an oceanic subduction passing to subduction of the attenuated Saxothuringian crust under the rifted Gondwana margin (Teplá-Barrandian and Moldanubian domains). The deep burial of this mostly refractory felsic metaigneous material is evidenced by the presence of coesite/diamond (Massonne 2001; Kotková et al. 2011) in the detached UHP slices exhumed through the subduction channel and thrusted over the Saxothuringian basement, and by the abundance of felsic HP granulites (> 2.3 GPa), some bearing evidence for small-scale HP melt separation, in the orogen's core (Vrána et al. 2013). The subduction channel was most likely formed by 'dirty' serpentinites contaminated by the melts/fluids derived from the underlying continental-crust slab (Zheng 2012). Upon the passage through the orogenic mantle, the continental crust-slab derived material not only contaminated the adjacent mantle forming small bodies/veins of pyroxenites (Becker 1996), glimmerites (Becker et al. 1999) or even phlogopite- and apatite-bearing peridotites (Naemura et al. 2009) but the felsic HP-HT granulites also sampled the individual peridotite types at various levels. Eventually the subducted felsic material would form an (U)HP continental wedge under the forearc/arc region, to be later redistributed under the Moldanubian crust by channel flow and crustal

  14. Quantitative geomorphologic data of the reactivated variscan Hluboká fault system (Budĕjovice Basin, southern Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Popotnig, Angelika; Tschegg, Dana; Decker, Kurt

    2015-04-01

    The NW-SE and NNE-SSW striking Hluboká-Rudolfov-Fault System in southern Bohemia is a potentially active late Variscan fault. It was repeatedly activated in Mesozoic, Miocene and Pliocene times and forms a "disputed seismic source" in the vicinity of the nuclear power plant of Temelin. The Fault System at the NE and SE margin of the Budĕjovice Basin with its up to 340 m thick Cretaceous to Neogene sediments overlaying the hanging wall of the Fault System is partly characterized by a prominent linear morphological scarp. Geomorpholigic analysis mainly focus on mountain fronts at the basin margin crossing the Hluboká and Rudolfov fault as well as on the NE facing slope of the Racice Mountain which is not crossing the fault. Analyses use morphological parameters of small ephemeric tributaries of the Vltava River, which are all similar with respect to their catchments, hydrological conditions and location in crystalline basement rocks. Morphological differences in valley shapes are therefore likely to result from different amounts of uplift of the catchments with respect to the Vltava River. All parameters were measured from a 10 m resolution DEM and digital topographic maps 1:10,000. Additional field measurements were made at locations where the resolution of the digital data is insufficient. Data show extremely low mountain-front-sinuosity of the hillslope forming the footwall of the Hluboká Fault characterizing a very straight mountain front at the fault and an uplift influenced morphology. Almost all values differ significantly from those observed at the other mountain slopes. The results are in line with the evidence obtained from mountain sinuosity. The mountain slope at the faults show deep and narrow V-shaped valleys with streams that are actively incising probably responding to continuous uplift. Vf (Valley-Floor-Width-to-Height) and SL (Stream Length) values are generally lower than those from drainages not crossing the fault. Convex-up thalweg sections

  15. High-pressure granulites of the Podolsko complex, Bohemian Massif: An example of crustal rocks that were subducted to mantle depths and survived a pervasive mid-crustal high-temperature overprint

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Žák, Jiří

    2016-03-01

    The Podolsko complex, Bohemian Massif, is a mid-crustal migmatite-granite dome exposed along a tectonic boundary separating the upper crust from the deeply eroded interior of the Variscan orogen, referred to as the Moldanubian Zone. This study examines metamorphic history of mafic and felsic granulites that occur in this complex as minor lenses or layers hosted in pervasively anatectic rocks. The mafic granulite contains garnet with preserved high-Ca cores, which based on pseudosection modelling indicates pressure conditions near the coesite stability field at temperatures of ca. 550-600 °C. The relicts of an earlier eclogite-facies stage have been overprinted by a later granulite-facies assemblage consisting of ternary feldspar, orthopyroxene, and spinel in the mafic granulite and sillimanite and spinel in the felsic granulite. Composition of younger garnet (in rims and as smaller grains) in both granulites suggests that a near isothermal decompression of these rocks was followed by heating that reached temperature of ca. 900 °C at pressure of ca. 0.5 GPa. It is thus concluded that the granulites underwent at least two temporally separate tectonometamorphic events: they were first subducted to mantle depths and exhumed rapidly at relatively low temperatures and then near isobarically heated at mid-crustal levels. The preservation of earlier eclogite-facies garnet in the mafic granulite indicates that the latter event was short-lived and was followed by near isobaric cooling. The geologically brief granulite-facies metamorphism was previously explained as a result of slab break-off and mantle upwelling after the main phase of microplate convergence in the Bohemian Massif. To put the Podolsko complex into a broader tectonic context, we synthesize the available petrologic and structural data from the correlative (U)HP assemblages of the Moldanubian Zone to suggest that they typically do not preserve structural record of the subduction stage, only rarely preserve an

  16. Monitoring and validating the temporal dynamics of interday streamflow from two upland head micro-watersheds with different vegetative conditions during dry periods of the growing season in the Bohemian Massif, Czech Republic.

    PubMed

    Deutscher, Jan; Kupec, Petr

    2014-06-01

    At present, dynamic land use, climate change, and growing needs for fresh water are increasing the demand on the ecosystem effects of forest vegetation. Mountainous areas are at the forefront of scientific interest in European forest ecology and forest hydrology. Although uplands cover a significant area of the Czech Republic and other countries and are often covered with forest formations, they do not receive an appropriate amount of attention. Therefore, two experimental upland head micro-watersheds in the Bohemian Massif were selected for study because they display similar natural conditions, but different vegetative conditions (forest versus meadow). During the 2011 growing season, short-term streamflow measurements were carried out at the discharge profiles of both catchments and were evaluated in relation to climatic data (rainfall and temperature). The basic premise was that the streamflow in a forested catchment must exhibit different temporal dynamics compared to that in treeless areas and that these differences can be attributed to the effects of woody vegetation. These conclusions were drawn from measurements performed during dry periods lasting several days. A decreasing streamflow trend during the day part of the day (0900-1900 hours) was observed in both localities. The decrease reached approx. 44 % of the initial morning streamflow (0.24 dm(3) s(-1) day(-1)) in the treeless catchment and approx. 20 % (0.19 dm(3) s(-1) day(-1)) in the forested catchment. At night (1900-0900 hours), the streamflow in the forested catchment increased back to its initial level, whereas the streamflow in the treeless catchment stagnated or slowly decreased. We attribute these differences to the ecosystem effects of woody vegetation and its capacity to control water loss during the day. This type of vegetation can also function as a water source for the hydrographic network during the night.

  17. The Cadomian Orogeny and the opening of the Rheic Ocean: The diacrony of geotectonic processes constrained by LA-ICP-MS U Pb zircon dating (Ossa-Morena and Saxo-Thuringian Zones, Iberian and Bohemian Massifs)

    NASA Astrophysics Data System (ADS)

    Linnemann, Ulf; Pereira, Francisco; Jeffries, Teresa E.; Drost, Kerstin; Gerdes, Axel

    2008-12-01

    Cadomian orogenic processes and their continuum to the opening of the Rheic Ocean were modeled by making use of new LA-ICP-MS U-Pb ages from detrital zircons of sedimentary rocks of Late Neoproterozoic (Ediacaran) and Cambro-Ordovician sediments of the Ossa-Morena Zone (Iberian Massif) compared with those from the Saxo-Thuringian Zones (Bohemian Massif). Presented data constrain a diachrony of Cadomian and related geotectonic processes along the northern realm of the Gondwana Supercontinent. Early stage of Cadomian evolution is characterized by a continental magmatic arc at the periphery of the West African Craton and a related back-arc basin opened at c. 590 to 570 Ma. Diacronic arc-continent collision was caused by oblique vector of subduction and started first in the East of Peri-Gondwana at c. 560-570 Ma and resulted at c. 543 Ma in the formation of a short-lived Cadomian retro-arc basin in the Saxo-Thuringian Zone. In contrast, more to the West in the Ossa-Morena Zone, the Cadomian back-arc basin was longer active, at least until c. 545 Ma. In that region, final magmatic pulse of the Cadomian magmatic arc at c. 550 Ma is documented by new zircon data. Closure of the Cadomian back-arc basin and arc-continent collision in the Ossa-Morena Zone occurred between c. 545 Ma and the overall onset of Cambrian plutonism at c. 540 Ma. A mid-oceanic ridge was subducted underneath the Cadomian orogen accompanied by slab break-off of the subducted oceanic plate. Oblique incision of the oceanic ridge into the continent caused the formation of rift basins during the Lower to Middle Cambrian (c. 530-500 Ma). This process continued and finally caused the opening of the Rheic Ocean documented by thick Lower Ordovician siliciclastic sediments and a final magmatic event at c. 490-485 Ma. Opening of the Cambrian rift basin and of the Rheic Ocean again was diachronic and started from the West of Peri-Gondwana and expanded eastward.

  18. Melt-melt immiscibility as result of synchronous melting of metapelites and impure marbles at crustal depth in the Moldanubian Zone, Bohemian Massif.

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O´Brien, Patrick J.; Ziemann, Martin A.; Wunder, Bernd; Hecht, Lutz; Wälle, Markus

    2016-04-01

    Investigation of melt and fluid inclusions in migmatites grants access to the unadultered products of crustal melting, shedding light on the processes driving crustal differentiation. Stromatic migmatites from the Oberpfalz (Moldanubian Zone, Bohemain Massif) present a unique occurrence of calcite-rich inclusions (CRI), crystallized inclusions of anatectic melt (nanogranites) and CO2-rich inclusions, all hosted in peritectic garnet. Their distribution as clusters in the host suggests a primary nature, i.e. that they formed during garnet growth, thus testifying for the coexistence of different melts and fluid during partial melting in the middle-lower crust. CRI are generally small (≤10 μm in diameter) and, from a microstructural point of view, strikingly resemble the coexistent nanogranites, i.e. they show a well-developed negative crystal shape and have a cryptocrystalline nature. Their phase assemblage, identified via Raman spectroscopy and EDS mapping, consists of calcite, white mica and chlorite, with quartz as accessory mineral. Moreover, calcite crystals locally develop euhedral faces, further supporting the hypothesis that this phase crystallized from an originally homogeneous calcite-rich melt. Piston-cylinder re-homogenization experiments achieved nanogranites re-melting at pressure-temperature conditions consistent with geothermobarometric estimates, 800-850°C and 0.7-0.9 GPa. After having been re-heated at these conditions, the coexistent calcite-rich inclusions appear modified, with formation of internal porosity and re-crystallization of calcite in microcrystalline aggregates, suggesting that during the experimental run calcite melting was achieved. LA-ICPMS analyses show that CRIs are generally highly enriched in LILE (particularly Sr, Ba) and LREE (up to LaN ≈500, with moderate to low fractionation among LREE, La/Sm=1-9) with respect both to the host garnet and the coexistent nanogranites. The higher abundance of LREE in CRIs is consistent with

  19. First finding of microdiamond, coesite and other UHP phases in felsic granulites in the Moldanubian Zone: Implications for deep subduction and a revised geodynamic model for Variscan Orogeny in the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Perraki, Maria; Faryad, Shah Wali

    2014-08-01

    Heavy mineral fractions and polished thin sections from felsic granulites from the Moldanubian Zone of the Bohemian Massif were thoroughly studied by means of Raman microspectroscopy combined with optical microscopy and scanning electron microscopy. The following phases were identified, among others, as inclusions in robust minerals such as garnet and zircon: Diamond, characterized by an intense narrow peak at 1332 cm- 1, was found in two inclusions in zircon. They have a size of ~ 5 μm. Coesite, identified by its very characteristic peak at ~ 520 cm- 1, was found in an inclusion in garnet together with quartz. Coesite has been almost completely transformed into quartz; only minor coesite nano-domains remain. Kumdykolite, the orthorhombic polymorph of NaAlSi3O8, characterized by strong peaks at 220, 456 and 492 cm- 1, occurs either as single crystals or as a part of multiphase inclusions in garnet and in zircon along with other mineral phases such as K-feldspar, phengite, rutile. Moissanite, SiC, exhibiting the characteristic Raman bands at ~ 767, 788 and 969 cm- 1, occurs as inclusions in garnet. Diamond and coesite are considered to have formed at the peak ultrahigh-pressure metamorphic (UHPM) conditions. Kumdykolite has been proposed to be a metastable phase formed during rapid cooling from high temperature. Moissanite points to extremely reduced conditions during subduction to great depths. The finding of UHP phases in felsic granulites in the Moldanubian Zone is clear evidence for subduction of crustal materials to mantle depths. The garnet hosting the UHP phase inclusions usually preserves prograde compositional zoning; this in combination with the UHPM mineral inclusions suggests that the felsic material should have passed UHP metamorphism at a low-temperature gradient. Isothermal decompression (the commonly accepted model) at temperatures of 850-950 °C would have substantially modified and homogenized the garnet composition eliminating any compositional

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

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Ulrych, Jaromír; Řanda, Zdeněk; Erban, Vojtěch; Hegner, Ernst; Magna, Tomáš; Balogh, Kadosa; Frána, Jaroslav; Lang, Miloš; Novák, Jiří K.

    2015-05-01

    distinct fluids are implicated from the Li-Cs correlations. The derivation of these melts/liquids from sedimentary and/or meta-sedimentary crustal sources is underscored by variable but overall light Li isotopic compositions. Some phonolites exhibit enrichments in high-field-strength elements coupled with increased Zr/Nb ratios. In contrast to previous studies, we show that this feature, apparent in many volcanic rocks from the Bohemian Massif, can be explained with progressive melt fractionation of parental magmas involving amphibole and plagioclase.

  1. Cancrinite from nepheline syenite (mariupolite) of the Oktiabrski massif, SE Ukraine, and its growth history.

    PubMed

    Dumańska-Słowik, Magdalena; Pieczka, Adam; Heflik, Wiesław; Sikorska, Magdalena

    2016-03-15

    Secondary cancrinite, (Na5.88K<0.01)∑5.88(Ca0.62 Fe0.01Mn0.01Zn<0.01 Mg<0.01)∑0.64[Si6.44Al 5.56O24](CO3)0.67(OH)0.26(F<0.01,Cl<0.01)·2.04H2O), was found as accessory component of mariupolite (albite-aegirine nepheline syenite) from the Oktiabrski massif in the Donbass (SE Ukraine). It probably crystallized from a subsolidus reaction involving nepheline (and sodalite?) and calcite dissolved in the aqueous-carbonic fluid at the maximum temperature of 930 °C, decreasing to hydrothermal conditions. It is depleted in sodium, calcium and carbon, what results in the occurrence of vacant positions at both cationic and anionic sites. Ca-deficient cancrinite crystallized from the same hydrothermal Si-undersaturated fluids enriched in the ions such as Na(+), Ca(2+), Cl(-), F(-), HCO3(-), which formed calcite, sodalite, natrolite and fluorite. It has dark-red CL colours with patchy zoning, what indicates the variable/diverse fluid composition during its formation. In the CL spectrum of cancrinite only one broad emission band at 410 nm is observed, which can be attributed to O* center (the recombination of a free electron with an O(-) hole center). The formation of secondary CO3-rich species, i.e. cancrinite and calcite in mariupolite suggests that redox conditions in the Oktiabrski massif were oxidizing at the postmagmatic stage. PMID:26773267

  2. Cancrinite from nepheline syenite (mariupolite) of the Oktiabrski massif, SE Ukraine, and its growth history.

    PubMed

    Dumańska-Słowik, Magdalena; Pieczka, Adam; Heflik, Wiesław; Sikorska, Magdalena

    2016-03-15

    Secondary cancrinite, (Na5.88K<0.01)∑5.88(Ca0.62 Fe0.01Mn0.01Zn<0.01 Mg<0.01)∑0.64[Si6.44Al 5.56O24](CO3)0.67(OH)0.26(F<0.01,Cl<0.01)·2.04H2O), was found as accessory component of mariupolite (albite-aegirine nepheline syenite) from the Oktiabrski massif in the Donbass (SE Ukraine). It probably crystallized from a subsolidus reaction involving nepheline (and sodalite?) and calcite dissolved in the aqueous-carbonic fluid at the maximum temperature of 930 °C, decreasing to hydrothermal conditions. It is depleted in sodium, calcium and carbon, what results in the occurrence of vacant positions at both cationic and anionic sites. Ca-deficient cancrinite crystallized from the same hydrothermal Si-undersaturated fluids enriched in the ions such as Na(+), Ca(2+), Cl(-), F(-), HCO3(-), which formed calcite, sodalite, natrolite and fluorite. It has dark-red CL colours with patchy zoning, what indicates the variable/diverse fluid composition during its formation. In the CL spectrum of cancrinite only one broad emission band at 410 nm is observed, which can be attributed to O* center (the recombination of a free electron with an O(-) hole center). The formation of secondary CO3-rich species, i.e. cancrinite and calcite in mariupolite suggests that redox conditions in the Oktiabrski massif were oxidizing at the postmagmatic stage.

  3. Cancrinite from nepheline syenite (mariupolite) of the Oktiabrski massif, SE Ukraine, and its growth history

    NASA Astrophysics Data System (ADS)

    Dumańska-Słowik, Magdalena; Pieczka, Adam; Heflik, Wiesław; Sikorska, Magdalena

    2016-03-01

    Secondary cancrinite, (Na5.88K< 0.01)∑ 5.88(Ca0.62 Fe0.01Mn0.01Zn< 0.01 Mg< 0.01)∑ 0.64[Si6.44Al 5.56O24](CO3)0.67(OH)0.26(F< 0.01,Cl< 0.01)·2.04H2O), was found as accessory component of mariupolite (albite-aegirine nepheline syenite) from the Oktiabrski massif in the Donbass (SE Ukraine). It probably crystallized from a subsolidus reaction involving nepheline (and sodalite?) and calcite dissolved in the aqueous-carbonic fluid at the maximum temperature of 930 °C, decreasing to hydrothermal conditions. It is depleted in sodium, calcium and carbon, what results in the occurrence of vacant positions at both cationic and anionic sites. Ca-deficient cancrinite crystallized from the same hydrothermal Si-undersaturated fluids enriched in the ions such as Na+, Ca2 +, Cl-, F-, HCO3-, which formed calcite, sodalite, natrolite and fluorite. It has dark-red CL colours with patchy zoning, what indicates the variable/diverse fluid composition during its formation. In the CL spectrum of cancrinite only one broad emission band at 410 nm is observed, which can be attributed to O* center (the recombination of a free electron with an O- hole center). The formation of secondary CO3-rich species, i.e. cancrinite and calcite in mariupolite suggests that redox conditions in the Oktiabrski massif were oxidizing at the postmagmatic stage.

  4. Late Devonian - Early Carboniferous polyphase metamorphic evolution of the Orlica-Śnieżnik Dome (NE Bohemian Massif, Poland): evidence from Th-U-total Pb monazite dating

    NASA Astrophysics Data System (ADS)

    Budzyń, Bartosz; Jastrzębski, Mirosław; Stawikowski, Wojciech

    2014-05-01

    The Orlica-Śnieżnik Dome, located in the NE part of the Bohemian Massif, mainly consists of Cambro-Ordovician orthogneisses and the metavolcano-sedimentary Młynowiec and Stronie Formations. This study constrains electron microprobe Th-U-total Pb ages of monazite in (1) orthogneisses, (2) paragneisses of the Młynowiec Formation (MF), (3) mica schists of the Stronie Formation (SF) and (4) light quartzites. The latter light quartzites form a continuous 'horizon' between two metavolcano-sedimentary formations, however, they are traditionally treated as the lowest member of the Stronie Formation (SF). Our field and structural studies conducted along the transects crossing the boundaries between the above-mentioned rocks indicate that there is a stratigraphic and structural continuity between the Młynowiec and Stronie Formations. Samples for the monazite dating were collected at different distances from the contact between orthogneisses and metasediments. The aim of this study was to provide a new data to verify a hypothesis of Cambro-Ordovician contact or regional metamorphism of the Młynowiec-Stronie Group and to constrain age of the Variscan metamorphic events in the Orlica-Śnieżnik Dome. Monazite from medium-grained orthogneiss yield dates ranging from 546 to 322 Ma, while three age domains of ca. 481 Ma, ca. 421 Ma and ca. 370 Ma are defined in fine-grained orthogneiss. Monazite in two porphyroblastic paragneisses (MF) yields two age domains of 369-361 Ma and 340-336 Ma. It should be noted that the older ages are recorded by inclusions of monazite in staurolite and plagioclase, as well as by matrix monazite. Monazite in leucosome of the migmatized paragneiss (MF) yields ca. 337 Ma age, while matrix monazite in melanosome yields ages of ca. 331 Ma age and a faint record of ca. 355 Ma. In two K-feldspar bearing light quartzites (SF), older spectrum of ages within 524-463 Ma, as well as younger ages of ca. 358 Ma and 347 Ma are obtained. On the other hand, only

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

    NASA Astrophysics Data System (ADS)

    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

  6. New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

    USGS Publications Warehouse

    Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

    2007-01-01

    The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

  7. Bohemian circular structure, Czechoslovakia: Search for the impact evidence

    NASA Technical Reports Server (NTRS)

    Rajlich, Petr

    1992-01-01

    Test of the impact hypothesis for the origin of the circular, 260-km-diameter structure of the Bohemian Massif led to the discovery of glasses and breccias in the Upper Proterozoic sequence that can be compared to autogeneous breccias of larger craters. The black recrystallized glass contains small exsolution crystals of albite-oligoclase and biotite, regularly dispersed in the matrix recrystallized to quartz. The occurrence of these rocks is limited to a 1-sq-km area. It is directly underlain by the breccia of the pelitic and silty rocks cemented by the melted matrix, found on several tens of square kilometers. The melt has the same chemistry as rock fragments in major and in trace elements. It is slightly impoverished in water. The proportion of melted rocks to fragments varies from 1:5 to 10:1. The mineralogy of melt viens is the function of later, mostly contact metamorphism. On the contact of granitic plutons it abounds on sillimanite, cordierite, and small bullets of ilmenite. Immediately on the contact with syenodiorites it contains garnets. The metamorphism of the impact rock melt seems the most probable explanation of the mineralogy and the dry total fusion of rocks accompanied by the strong fragmentation. Other aspects of this investigation are discussed.

  8. Triclinic Transpression in brittle shear zones evaluated via combined numerical and analogue modeling: the case of The Torcal de Antequera Massif, SE Spain.

    NASA Astrophysics Data System (ADS)

    Barcos, Leticia; Díaz-Azpiroz, Manuel; Faccenna, Claudio; Balanyá, Juan Carlos; Expósito, Inmaculada; Giménez-Bonilla, Alejandro

    2013-04-01

    Numerical kinematic models have been widely used to understand the parameters controlling the generation and evolution of ductile transpression zones. However, these models are based on continuum mechanics and therefore, are not as useful to analyse deformation partitioning and strain within brittle-ductile transpression zones. The combination of numerical and analogue models will potentially provide an effective approach for a better understanding of these processes and, to a broader extent, of high strain zones in general. In the present work, we follow a combined numerical and analogue approach to analyse a brittle dextral transpressive shear zone. The Torcal de Antequera Massif (TAM) is part of a roughly E-W oriented shear zone at the NE end of the Western Gibraltar Arc (Betic Cordillera). This shear zone presents, according to their structural and kinematic features, two types of domains i) Domain type 1 is located at both TAM margins, and is characterized by strike-slip structures subparallel to the main TAM boundaries (E-W). ii) Domain type 2 corresponds to the TAM inner part, and it presents SE-vergent open folds and reverse shear zones, as well as normal faults accommodating fold axis parallel extension. Both domains have been studied separately applying a model of triclinic transpression with inclined extrusion. The kinematic parameters obtained in this study (?, ? and Wk) allows us to constrain geometrical transpression parameters. As such, the angle of oblique convergence (α, the horizontal angle between the displacement vector and the strike of the shear zone) ranges between 10-17° (simple shear dominated) for domain type 1 and between 31-35° (coaxial dominated) for domain type 2. According to the results obtained from the numerical model and in order to validate its possible utility in brittle shear zones we develop two analogue models with α values representative of both domains defined in the TAM: 15° for type 1 and 30° for type 2. In the

  9. The Freyenstein Shear Zone - Implications for exhumation of the South Bohemian Batholith (Moldanubian Superunit, Strudengau, Austria)

    NASA Astrophysics Data System (ADS)

    Griesmeier, Gerit; Iglseder, Christoph; Konstantin, Petrakakis

    2016-04-01

    The Moldanubian superunit is part of the internal zone of the Variscan Orogen in Europe and borders on the Saxothuringian and Sudetes zones in the north. In the south, it is blanketed by the Alpine foreland molasse. Tectonically it is subdivided into the Moldanubian Nappes (MN), the South Bohemian Batholith (SBB) and the Bavarian Nappes. This work describes the ~ 500 m thick Freyenstein shear zone, which is located at the southern border of the Bohemian Massif north and south of the Danube near Freyenstein (Strudengau, Lower Austria). The area is built up by granites of Weinsberg-type, which are interlayered by numerous dikes and paragneisses of the Ostrong nappe system. These dikes include medium grained granites and finegrained granites (Mauthausen-type granites), which form huge intrusions. In addition, smaller intrusions of dark, finegrained diorites und aplitic dikes are observed. These rocks are affected by the Freyenstein shear zone und ductily deformed. Highly deformed pegmatoides containing white mica crystals up to one cm cut through the deformed rocks and form the last dike generation. The Freyenstein shear zone is a NE-SW striking shear zone at the eastern edge of the SBB. The mylonitic foliation is dipping to the SE with angles around 60°. Shear-sense criteria like clast geometries, SĆ structures as well as microstructures show normal faulting top to S/SW with steep (ca. 50°) angles. The Freyenstein shear zone records a polyphase history of deformation and crystallization: In a first phase, mylonitized mineral assemblages in deformed granitoides can be observed, which consist of pre- to syntectonic muscovite-porphyroclasts and biotite as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. The muscovite porphyroclasts often form mica fishes and show top to S/SW directed shear-sense. The lack of syntectonic chlorite crystals points to metamorphic conditions of lower amphibolite-facies > than 450° C. In a later stage fluid

  10. Geochemistry and detrital zircon U-Pb and Hf isotopes of the paragneiss suite from the Quanji massif, SE Tarim Craton: Implications for Paleoproterozoic tectonics in NW China

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Wang, Qinyan; Chen, Nengsong; Sun, Min; Santosh, M.; Ba, Jin

    2014-12-01

    The Delingha paragneiss suite in the Quanji massif, southeastern Tarim Craton, is composed of mica schist, paragneiss, leptynite and quartzite, similar to the 'khondalite suites' described from elsewhere in the world. The mica schist is rich in Al2O3 (up to ∼26 wt%) and contains graphite and diagnostic minerals including sillimanite and garnet, with metamorphism under amphibolite-facies to locally granulite-facies conditions as manifested by association with amphibolite and granulite. The detrital zircon U-Pb ages and geochemical data indicate that the protolith materials of the Delingha paragneiss suite were mainly sourced from 2.20 to 2.45 Ga granites, felsic volcanic rocks and TTG, and were deposited at 2.17-1.92 Ga. The detrital zircon Hf and whole-rock Nd isotopes document important crustal growth at ∼2.5-2.7 Ga. The detrital zircon age spectra, the whole rock Nd and zircon Hf model ages, the low-maturity of the protolith, and short-distance transportation suggest that the detritus were derived from the underlying Delingha Complex and the lower Dakendaban sub-Group. The timing of magmatic activities in the source region, the depositional age and metamorphic histories of the Delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the Ordos Block in the North China Craton. Our study shows that the 2.2-2.45 Ga magmatic rocks were generated in arc or active continental margin settings, suggesting a prolonged subduction and accretion history prior to final amalgamation (∼2.5-1.8 Ga) to form the unified North China Craton and the assembly of the Tarim Craton in NW China.

  11. An early extensional event of the South China Block during the Late Mesozoic recorded by the emplacement of the Late Jurassic syntectonic Hengshan Composite Granitic Massif (Hunan, SE China)

    NASA Astrophysics Data System (ADS)

    Wei, Wei; Chen, Yan; Faure, Michel; Martelet, Guillaume; Lin, Wei; Wang, Qingchen; Yan, Quanren; Hou, Quanlin

    2016-03-01

    Continental scaled extension is the major Late Mesozoic (Jurassic and Cretaceous) tectonic event in East Asia, characterized by faulting, magmatic intrusions and half-grabens in an area with a length of > 5000 km and a width of > 1000 km. Numerous studies have been conducted on this topic in the South China Block (SCB), However, the space and time ranges of the compressional or extensional regimes of the SCB during the Jurassic are still unclear, partly due to the lack of structural data. The emplacement fabrics of granitic plutons can help determine the regional tectonic background. In this study, a multidisciplinary approach, including Anisotropy of Magnetic Susceptibility (AMS), macro and microstructural analyses, quartz c-axis preferred orientation, gravity modeling and monazite EPMA dating, was conducted on the Hengshan composite granitic massif in SCB that consists of the Triassic Nanyue biotite granitic pluton and the Late Jurassic Baishifeng two-mica granitic pluton. The magnetic fabrics are characterized by a consistent NW-SE oriented lineation and weakly inclined foliation. A dominant high temperature deformation with a top-to-the-NW shear sense is identified for both plutons. The deformation increasing from the center of the Baishifeng pluton to its western border is associated to the development of the West Hengshan Boundary Fault (WHBF). The gravity modeling shows a "saw tooth-shaped" NE-SW oriented structure of the Baishifeng pluton, which may be considered as NE-SW oriented tension-gashes formed due to the NW-SE extension. All results show that the Triassic Nanyue pluton was deformed under post-solidus conditions by the WHBF coeval with the emplacement of the Late Jurassic Baishifeng pluton. All these observations comply with the NW-SE extensional tectonics coeval with the emplacement of the Baishifeng pluton, which argues that the NW-SE crustal stretching started since the Late Jurassic, at least in this part of the SCB.

  12. Craddock Massif and Vinson Massif remeasured

    USGS Publications Warehouse

    Gildea, Damien; Splettstoesser, John F.

    2007-01-01

    The highest peak in Antarctica, the Vinson Massif (78º35’S, 85º25’W), is at an elevation of 4892 m (16,046 ft), as determined in 2004. Measurements of the elevation have fluctuated over the years, from its earliest surveyed elevation of 5140 m (16,859 ft), to its present height. Vinson Massif and three of its near neighbors in the Sentinel Range of the Ellsworth Mountains are the highest peaks in Antarctica, making them a favorite objective of mountaineers. Well over 1,100 people have climbed Vinson since the first ascent by a team in the 1966-67 austral summer. The range is composed of Crashsite quartzite, making the Sentinel’s very resistant to erosion. Very accurate elevations have been achieved annually by GPS mapping done by a climbing team sponsored by the Omega Foundation, active in Antarctica since 1998. The Craddock Massif now includes Mt. Craddock, the ninth highest peak in Antarctica, at 4368 m (14,327 ft). Both are named for Campbell Craddock*, a U.S. geologist active in Antarctic research beginning in 1959-60.

  13. Metamorphic history of LP/HT migmatites from the Bavarian Unit (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph

    2016-04-01

    Granulite facies migmatites are commonly observed in the Bavarian Unit which were formed during a late Variscan (post 330 Ma) LP-HT overprint. This event is related to a delamination of mantle lithosphere and subsequent asthenospheric upwelling. Most of these rocks underwent high degrees of melting forming meta- and diatexites. Former work in the Sauwald area, Upper Austria, by Tropper et al. (2006) determined metamorphic conditions of 700-800°C and 0.4-0.5 Gpa. In this study samples were taken along the (1) Danube valley (west of Linz), from the (2) Lichtenberg area (north of Linz), the (3) Bad Leonfelden area (west of the Rodl Fault) and the (4) Sauwald area (south of the river Danube). Biotite and plagioclase bearing migmatite is very common and occurs all over the investigated area. These rocks are the product of intensive melting (anatexite) and formed at conditions of ~650-700°C and 0.25-0.45 Gpa. Scarce outcrops of garnet bearing Al-rich migmatitic metapelites occur along the Danube valley. The formation of the migmatitc texture with well-developed leucosomes (K-feldspar, plagioclase, quartz) and melanosomes (garnet, cordierite, sillimanite, spinel, ilmenite, ± biotite) indicate high temperature metamorphism. Most of the garnet grains show a homogenous iron-rich composition and form generally an almandine-pyrope (Xalm=0.78-0.80, Xprp=0.16-0.18) solid solution with minor contents of grossular and spessartine (Xgrs=0.028-0.032, Xsps=0.020-0.024). Large garnet porphyroblasts (up to 1cm in size) display a distinct chemical zoning, especially in grossular component. Elevated homogeneous grossular content in the core is followed discontinously by low grossular content at the rim indicating a two stage growth. Garnet core and rim also display different mineral inclusions. Thermobarometric calculations using garnet core compositions with inclusions and garnet rim compositions with matrix phases as well as pseudosection calculations allow the reconstruction of a P-T path. A first HP-HT stage (740-825°C and 1.1-1.3 Gpa) is indicated by the garnet core which is followed by decompression and cooling to 580- 610°C and 0.44-0.54 GPa. The main LP-HT metamorphic event gives 830-910°C and 0.60-0.66 GPa using the garnet rims and matrix minerals. TROPPER, P., DEIBL, I., FINGER, F., KAINDL, R. (2006): International Journal of Earth Sciences: Geologische Rundschau 95.6, 1019-1037.

  14. Garnet-bearing granite from the Třebíč pluton, Bohemian Massif (Czech Republic)

    NASA Astrophysics Data System (ADS)

    René, M.; Stelling, J.

    2007-09-01

    Garnet occurs as a significant mineral constituent of felsic garnet-biotite granite in the southern edge of the Třebíč pluton. Two textural groups of garnet were recognized on the basis of their shape and relationship to biotite. Group I garnets are 1.5-2.5 mm, euhedral grains which have no reaction relationship with biotite. They are zoned having high XMn at the rims and are considered as magmatic. Group II garnets form grain aggregates up to 2.5 cm in size, with anhedral shape of individual grains. The individual garnet II grains are usually rimmed by biotite and have no compositional zoning. The core of group I garnets and group II garnets contains 67-80 mol% of almandine, 5-19 mol% of pyrope, 7-17 mol% of spessartine and 2-4 mol% of grossular. Biotite occurs in two generations; both are magnesian siderophyllites with Fe/(Fe + Mg) = 0.50-0.69. The matrix biotite in granites (biotite I) has high Ti content (0.09-0.31 apfu) and Fe/(Fe + Mg) ratio between 0.50 and 0.59. Biotite II forms reaction rims around garnet, is poor in Ti (0.00-0.06 apfu) and has a Fe/(Fe + Mg) ratio between 0.61 and 0.69. The textural relationship between biotite and garnet indicates that garnet reacted with granitic melt to form Ti-poor biotite and a new granitic melt, depleted in Ti and Mg and enriched in Fe and Al. In contrast to the host durbachites (hornblende-biotite melagranites), which originated by mixing of crustal melts and upper mantle melts, the origin of garnet-bearing granites is related to partial melting of the aluminium-rich metamorphic series of the Moldanubian Zone.

  15. Tectonic rotations south of the Bohemian Massif from palaeomagnetic directions of Permian red beds in Hungary

    USGS Publications Warehouse

    Marton, E.; Elston, D.P.

    1987-01-01

    Palaeomagnetic studies were carried out in Permian red beds of the Balaton Highlands, the Mecsek Mountains and the Bu??kk Mountains of Hungary. Statistically well defined directions were obtained from six localities in the Balaton Highlands and two localities in the Mecsek Mountains. No meaningful results were obtained from the Bu??kk Mountains. Three magnetic components were identified from red beds of the Balaton Highlands: (1) in haematite with a very high unblocking temperature (700??C), interpreted as a Permian magnetization (Dc= 79??, Ic=-11??, k = 24, ??95 = 13.6 ??), in six samples from three beds in a single locality (2) a secondary but ancient component residing mainly inmaghemite (D = 314??, I = 49??, k = 48, ??95 = 10.0??), in 84 samples from six localities with a within-locality scatter increasing on unfolding; and (3) a direction parallel to the present field (D = 7??, I = 62??, k = 46, ??95 = 7.7 ??), in nine samples from a single locality. For the Balaton Highlands, the component 1 direction agrees with directions obtained from Permian red beds and volcanics in the eastern part of the Southern and Eastern Alps and the Inner West Carpathians. All show large, apparent rotations relative to stable Europe since the Permian. Component 2 is of post-folding (post-Aptian) age. Its direction agrees with known Late Cretaceous directions from the Transdanubian Central Mountains, which also show significant counterclockwise rotation relative to stable Europe. The characteristic magnetization for the Mecsek Mountains resides in haematite and may be primary. The directions indicate only a slight net counterclockwise rotation of the Mecsek Mountains with respect to stable Europe since the Permian. ?? 1987.

  16. Precambrian reservoirs sealed by Western Carpathian nappes, southeast slope of the Bohemian Massif, Moravia, Czechoslovakia

    SciTech Connect

    Krejci, J.J. )

    1991-08-01

    The West Carpathian overthrust in Moravia, Czechoslovakia, overlies Proterozoic crystalline basement productive from buried topographic ridges and hills. The Neogene thrust belt forms the seal for oil and gas trapped in the Precambrian crystalline rocks which have been disaggregated by joint, fractures, and weathering. The reservoir rocks include granite, granodiorite, and quartz diorite. Five oil and gas fields have been discovered in this unusual setting. Zdanice-Krystalinikum field is the largest of this type of field in Czechoslovakia (its cumulative production is 66,000 tons of oil), and the ultimate potential is unknown as development is still in process. Three separate pools have been discovered in this field, with differing oil/water contacts and sometimes different oil gravities. These pools appear to be separated by fault zones that have sealed and become impermeable. Other Precambrian reservoir production in Moravia includes East and West Kostelany, West Zdanice, and Korycany fields. Zdanice-Krystalinikum field was discovered using refraction and reflection seismic lines and correlations with previously drilled dry holes which had encouraging shows.

  17. High-temperature microstructures and rheology of deformed granite, Erzgebirge, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Schulmann, Karel; Mlčoch, Bedřich; Melka, Radek

    1996-06-01

    Three stages of granite deformation were recognized in porphyric granitoids sheared under amphibolite facies conditions in the Erzgebirge Mts: (1) weakly deformed granite in lozenge-shaped pods, (2) S—C orthogneiss, and (3) thin zones of banded mylonites. Weakly deformed granite forms a load-bearing framework (LBF) structure in which quartz and feldspar aggregates exhibit similar strain intensities and shapes. K-feldspar deforms by fracturing and onset of dynamic recrystallization along clast margins, plagioclase recrystallizes completely and quartz shows effects of grain boundary migration recrystallization and activity of basal (a) slip. S—C orthogneiss is interpreted as an interconnected weak layer (IWL) structure with high viscosity contrast between quartz and both feldspars. Concentration of deformation into thin quartz layers is indicated by intense strain of quartz, grain size variations of recrystallized quartz and dominant prism (a) slip. Feldspars show well annealed structures and slip on (010)(001). Banded mylonite is marked by similar strain intensity of quartz and feldspar aggregates and low viscosity contrast between constituent phases. Quartz shows evidence for grain size increase and rhomb (a + c) slip. Fully recrystallized feldspars show evidence for (010)(100) slip. The whole microstructural sequence and the transitions from LBF structure to IWL structures show the dependence of microstructural evolution of different materials on the bulk strain intensity.

  18. Kondyor Massif, Russia

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This is neither an impact crater nor a volcano. It is a perfect circular intrusion, about 10 km in diameter with a topographic ridge up to 600 m high. The Kondyor Massif is located in Eastern Siberia, Russia, north of the city of Khabarovsk. It is a rare form of igneous intrusion called alkaline-ultrabasic massif and it is full of rare minerals. The river flowing out of it forms placer mineral deposits. Last year 4 tons of platinum were mined there. A remarkable and very unusual mineralogical feature of the deposit is the presence of coarse crystals of Pt-Fe alloy, coated with gold. This 3-D perspective view was created by draping a simulated natural color ASTER composite over an ASTER-derived digital elevation model.

    The image was acquired on June 10, 2006, and is located at 57.6 degrees north latitude, 134.6 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  19. Documentation and evaluation of slope instabilities and other geological phenomena in the Geopark Bohemian Paradise (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Krejčí, Oldřich; Krejčí, Vladimíra; Švábenická, Lilian; Hartvich, Filip

    2016-04-01

    Geographically, the area is part of the Bohemian Cretaceous Basin, the unit Jičín Hilly land. Since October 2005, the area belongs to the European Geopark UNESCO Bohemian Paradise. The reason of the protection is a major complex of rocks, natural forest communities and geomorphological valuable territory. The territory has been newly geologically mapped in a scale of 1 : 25,000. Sediments of the Czech Cretaceous Basin covers an area of 181 km2 and were deposited transgressively on the Permian - Carboniferous and crystalline basement of the Bohemian Massif. Except for locally developed basal sediments of fluvial origin they are mostly shallow marine sediments. Middle Turonian to Lower Coniacian rocks of the Jizera lithofacies are dominant by calcareous sandstones deposited under extremely dynamic conditions. Scattered alkaline volcanics penetrate the older formations as small intrusions and form locally preserved bodies at the surface. Area is strongly predisposed to the development of various types of landforms by structural segmentation of the Cretaceous sandstones and claystones and by Plio-Pleistocene inverse erosion. Numerous archival manuscripts are available from this area together with published geological, engineering-geological, geomorphological and historical papers. This is due to the fact that in 1926 a large landslide destroyed a substantial part of the village Dneboh, situated on the slope below a rock castle Drabske Svetnicky. Drabske Svetnicky is a ruin of a 13th century castle. It is located on the ragged edge of a sandstone cliff high above surrounding landscape. The castle covers a group of seven sandstone rocks, connected with wooden bridges. In the 50ies of the 20th century, an increased attention was paid to Drabske Svetnicky by experts on medieval architecture and a restoration of the original state of the castle rock was accomplished. Remnants of pottery and other findings suggest that the plateau region of the castle was first inhabited

  20. Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

    NASA Astrophysics Data System (ADS)

    Maierova, Petra; Lexa, Ondrej; Jeřábek, Petr; Franěk, Jan; Schulmann, Karel

    2015-04-01

    A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 μm) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 μm grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 μm grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most

  1. Radiometric dating of granitic rocks from the Central Bohemian Plutonic Complex (Czech Republic): constraints on the chronology of thermal and tectonic events along the Moldanubian-Barrandian boundary

    NASA Astrophysics Data System (ADS)

    Holub, František V.; Cocherie, Alain; Rossi, Philippe

    1997-07-01

    ingle-zircon dating by step-wise evaporation has established that successive granitic intrusions were emplaced in the Central Bohemian Plutonic Complex (CBPC) during a short time span of about 10 Ma. In agreement with field data, the Požáry trondhjemite, emplaced early at 351 ±11 Ma and subcontemporaneously with the Sázava granodiorite dated at 349 ±12 Ma, was followed by the Blatná granodiorite at 346 ±10 Ma. The magnesium-potassium-rich units (durbachites) indicate younger ages both for the Čertovo Břemeno melagranite at 343 ±6 Ma (within the CPBC) and for durbachite from the Třebíč Massif (south-east of the CPBC) at 340 ±8 Ma. These data provide evidence that the sequence of intrusion and the age of the emplacement of the CBPC are comparable with those of other western Variscan batholiths (i.e. the Vosges or the French Massif Central) in similar structural environment.

  2. An early Palaeozoic supra-subduction lithosphere in the Variscides: new evidence from the Maures massif

    NASA Astrophysics Data System (ADS)

    Bellot, Jean-Philippe; Laverne, Christine; Bronner, Georges

    2010-04-01

    Petrographic and geochemical studies of peridotites and melagabbros from the Maures massif (SE France) provide new constraints on the Early Palaeozoic evolution of the continental lithosphere in Western Europe. Peridotites occur as lenses along a unit rooted in the main Variscan suture zone. They are dominantly spinel peridotites and minor garnet-spinel peridotites. Spinel peridotites represent both residual mantle and ultramafic cumulates. Mantle-related dunites and harzburgites display high temperature textures, with olivine (Mg#0.90), orthopyroxene (Mg#0.90) and spinel (TiO2 < 0.2%; Cr#0.64-0.83) compositions typical of fore-arc upper mantle. Ultramafic cumulates are dunite adcumulates, harzburgite heteradcumulates and mesocumulates, melagabbro heteradcumulates and amphibole peridotites, with olivine (Mg#0.85-0.89), orthopyroxene (Mg#0.86-0.89) and Cr-spinel (TiO2 = 0.5-3.3%; Cr#0.7-0.98) compositions typical of ultramafic cumulates. Cr-spinel compositions of both spinel peridotite types suggest their genesis in a supra-subduction zone lithosphere. Core to rim zoning in spinel is related to the incomplete influence of regional metamorphism and serpentinisation. The covariation of major and minor elements with Al2O3 for cumulates is consistent with igneous processes involving crystal accumulation. Both mantle and cumulate dunites and harzburgites have U-shaped REE patterns and extremely low trace element contents, similar to peridotites from modern fore-arc peridotites (South Atlantic) and from ophiolites related to supra-subduction zones (Semail, Cyclops, Pindos, Troodos). Melagabbros also have U-shaped REE patterns similar to xenoliths from the Philippine island arc, but also similar to intrusive ultramafic cumulates from the Semail nappe of Oman related to a proto-subduction setting. A wehrlite has a REE pattern similar to that of amphibole peridotites reflecting metasomatism of clinopyroxene-bearing peridotites due to subduction-related fluids. The Maures

  3. The tectonics of anorthosite massifs

    NASA Technical Reports Server (NTRS)

    Seyfert, C. K.

    1981-01-01

    Anorthosite massifs developed approximately 1.4 to 1.5 billion years ago along an arch which developed parallel to a zone of continental separation as a block which included North America, Europe, and probably Asia separated from a block which included parts of South America, Africa, India, and Australia. Anorthosite massifs also developed at the same time along a belt which runs through the continents which comprise Gondwanaland (South America), Africa, India, Australia, and Antarctica. This was a zone of continental separation which subsequently became a zone of continental collision about 1.2 billion years ago. The northern anorthosite belt also parallels an orogenic belt which was active between 1.8 and 1.7 billion years ago. Heat generated during this mountain building period helped in the formation of the anorthosites.

  4. A key extensional metamorphic complex reviewed and restored: The Menderes Massif of western Turkey

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, Douwe J. J.

    2010-09-01

    have been previously shown to thrust to the SE between 23 and 15 Ma over at least 75 km. This is contemporaneous with, and orthogonal to stretching along the Simav detachment. I here argue that the amount of SE-wards displacement of the Lycian Nappes was twice the minimum amount of 75 km, which would restore them back on top of most of the Menderes Massif, apart from the ˜ 50 km unroofed along the Simav detachment. A decollement was likely formed by a high-pressure, low-temperature metamorphosed nappe immediately underlying the Lycian Nappes in the north — the Ören unit. Latest Oligocene to early Miocene fission track ages of the Menderes Massif, as well as NE-SW trending lower Miocene grabens on the Massif are in line with this hypothesis. The main implications of this restoration are that 1) the eastern part of the Aegean back-arc accommodated not more than 50 km of NE-SW extension in the early Miocene, and 2) any pre-Miocene exhumation of the Menderes Massif cannot be attributed to the known extensional detachments. The restoration in this paper suggests that most of the Menderes Massif already resided at upper crustal levels at the inception of extensional detachment faulting, a situation reminiscent of the role of extensional detachments on the island of Crete.

  5. Crustal structure of the northern Menderes Massif, western Turkey, imaged by joint gravity and magnetic inversion

    NASA Astrophysics Data System (ADS)

    Gessner, Klaus; Gallardo, Luis A.; Wedin, Francis; Sener, Kerim

    2016-05-01

    In western Anatolia, the Anatolide domain of the Tethyan orogen is exposed in one of the Earth's largest metamorphic core complexes, the Menderes Massif. The Menderes Massif experienced a two-stage exhumation: tectonic denudation in the footwall of a north-directed Miocene extensional detachment, followed by fragmentation by E-W and NW-SE-trending graben systems. Along the northern boundary of the core complex, the tectonic units of the Vardar-Izmir-Ankara suture zone overly the stage one footwall of the core complex, the northern Menderes Massif. In this study, we explore the structure of the upper crust in the northern Menderes Massif with cross-gradient joint inversion of gravity and aeromagnetic data along a series of 10-km-deep profiles. Our inversions, which are based on gravity and aeromagnetic measurements and require no geological and petrophysical constraints, reveal the salient features of the Earth's upper crust. We image the northern Menderes Massif as a relatively homogenous domain of low magnetization and medium to high density, with local anomalies related to the effect of interspersed igneous bodies and shallow basins. In contrast, both the northern and western boundaries of the northern Menderes Massif stand out as domains where dense mafic, metasedimentary and ultramafic domains with a weak magnetic signature alternate with low-density igneous complexes with high magnetization. With our technique, we are able to delineate Miocene basins and igneous complexes, and map the boundary between intermediate to mafic-dominated subduction-accretion units of the suture zone and the underlying felsic crust of the Menderes Massif. We demonstrate that joint gravity and magnetic inversion are not only capable of imaging local and regional changes in crustal composition, but can also be used to map discontinuities of geodynamic significance such as the Vardar-Izmir-Ankara suture and the West Anatolia Transfer Zone.

  6. Crustal structure of the northern Menderes Massif, western Turkey, imaged by joint gravity and magnetic inversion

    NASA Astrophysics Data System (ADS)

    Gessner, Klaus; Gallardo, Luis A.; Wedin, Francis; Sener, Kerim

    2016-10-01

    In western Anatolia, the Anatolide domain of the Tethyan orogen is exposed in one of the Earth's largest metamorphic core complexes, the Menderes Massif. The Menderes Massif experienced a two-stage exhumation: tectonic denudation in the footwall of a north-directed Miocene extensional detachment, followed by fragmentation by E-W and NW-SE-trending graben systems. Along the northern boundary of the core complex, the tectonic units of the Vardar-Izmir-Ankara suture zone overly the stage one footwall of the core complex, the northern Menderes Massif. In this study, we explore the structure of the upper crust in the northern Menderes Massif with cross-gradient joint inversion of gravity and aeromagnetic data along a series of 10-km-deep profiles. Our inversions, which are based on gravity and aeromagnetic measurements and require no geological and petrophysical constraints, reveal the salient features of the Earth's upper crust. We image the northern Menderes Massif as a relatively homogenous domain of low magnetization and medium to high density, with local anomalies related to the effect of interspersed igneous bodies and shallow basins. In contrast, both the northern and western boundaries of the northern Menderes Massif stand out as domains where dense mafic, metasedimentary and ultramafic domains with a weak magnetic signature alternate with low-density igneous complexes with high magnetization. With our technique, we are able to delineate Miocene basins and igneous complexes, and map the boundary between intermediate to mafic-dominated subduction-accretion units of the suture zone and the underlying felsic crust of the Menderes Massif. We demonstrate that joint gravity and magnetic inversion are not only capable of imaging local and regional changes in crustal composition, but can also be used to map discontinuities of geodynamic significance such as the Vardar-Izmir-Ankara suture and the West Anatolia Transfer Zone.

  7. The Lassell Massif - a Silicic Lunar Volcano

    NASA Astrophysics Data System (ADS)

    Ashley, J.; Robinson, M. S.; Stopar, J. D.; Glotch, T. D.; Hawke, B. R.; Lawrence, S. J.; Jolliff, B. L.; Greenhagen, B. T.; Paige, D. A.

    2013-12-01

    Lunar volcanic processes were dominated by mare-producing basaltic extrusions. However, limited occurrences of non-mare, geochemically evolved (Si-enriched) volcanic deposits have long been suspected on the basis of spectral anomalies (red spots), landform morphologies, and the occurrence of minor granitic components in Apollo sample suites [e.g., 1-5]. The LRO Diviner Lunar Radiometer Experiment (Diviner) measured thermal emission signatures considered diagnostic of highly silicic rocks in several red spot areas [6,7], within the Marius domes [8], and from the Compton-Belkovich feature on the lunar farside [9]. The present study focuses on the Lassell massif red spot (14.73°S, 350.97°E) located in northeastern Mare Nubium near the center of Alphonsus A crater. Here we use Diviner coverage co-projected with Lunar Reconnaissance Orbiter Camera (LROC) images [10] and digital elevation models to characterize the Lassell massif geomorphology and composition. Localized Diviner signatures indicating relatively high silica contents correlate with spatially distinct morphologic features across the Lassell massif. These features include sub-kilometer scale deposits with clear superposing relationships between units of different silica concentrations. The zone with the strongest signal corresponds to the southern half of the massif and the Lassell G and K depressions (formerly thought to be impact craters [11]). These steep-walled pits lack any obvious raised rims or ejecta blankets that would identify them as impact craters; they are likely explosive volcanic vents or collapse calderas. This silica-rich area is contained within the historic red spot area [4], but does not appear to fully overlap with it, implying compositionally distinct deposits originating from the same source region. Low-reflectance deposits, exposed by impact craters and mass wasting across the massif, suggest either basaltic pyroclastics or minor late-stage extrusion of basaltic lavas through vents

  8. Geochemistry of carbonatites of the Tomtor massif

    USGS Publications Warehouse

    Kravchenko, S.M.; Czamanske, G.; Fedorenko, V.A.

    2003-01-01

    Carbonatites compose sheet bodies in a 300-m sequence of volcanic lamproites, as well as separate large bodies at depths of >250-300 m. An analysis of new high-precision data on concentrations of major, rare, and rare earth elements in carbonatites shows that these rocks were formed during crystallization differentiation of a carbonatite magma, which resulted in enrichment of the later melt fractions in rare elements and was followed by autometasomatic and allometasomatic hydrothermal processes. Some independent data indicate that the main factor of ore accumulation in the weathered rock zone (also known as the "lower ore horizon" comprising metasomatized volcanics with interbedded carbonatites) was hydrothermal addition of Nb and REEs. The giant size of the Tomtor carbonatite-nepheline syenite massif caused advanced magma differentiation, extensive postmagmatic metasomatism and recrystallization of host rocks, and strong enrichment of carbonatites in incompatible rare and rare earth elements (except for Ta, Zr, Ti, K, and Rb) compared to the rocks of many other carbonatite massifs. We suggest that a wide range of iron contents in carbonatites-2 can be related to extensive magnetite fractionation at the magmatic stage in different parts of the huge massif. Copyright ?? 2003 by MAIK "Nauka/Interperiodica" (Russia).

  9. Reactivity of North Bohemian coals in coprocessing of coal/oil mixtures

    SciTech Connect

    Sebor, G.; Cerny, J.; Maxa, D.; Blazek, J.; Sykorova, I.

    1995-12-01

    Autoclave experiments with North Bohemian coal were done in order to evaluate their reactivity in coprocessing with petroleum vacuum residue, Selected coals were comprehensively characterized by using a number of analytical methods. While the coals were of similar geological origin, some of their characteristics differed largely from one coal to another. Despite the differences in physical and chemical structure, the coals provided very similar yields of desired reaction products. The yields of a heavy non- distillable fraction and/or an insoluble solid residue were, under experimental conditions, largely affected by retrogressive reactions (coking). The insoluble solid fractions were examined microscopically under polarized light.

  10. Sulfur and selenium systematics of the subcontinental lithospheric mantle: Inferences from the Massif Central xenolith suite (France)

    NASA Astrophysics Data System (ADS)

    Lorand, Jean-Pierre; Alard, Olivier; Luguet, Ambre; Keays, Reid R.

    2003-11-01

    Selenium has been analyzed in addition to S in 58 spinel peridotite xenoliths collected in Cenozoic alkali basalts from the Massif Central (France). The S concentration range now available for this suite, calculated from 123 samples, is the largest ever reported for alkali basalt-hosted xenoliths (<3-592 ppm). Likewise, the Se concentrations range between 0.2 and 67 ppb. No partial melting signature can be identified from the S and Se systematic. Half of the analyzed xenoliths have lost S during supergene weathering. By contrast, neither surficial alteration, nor loss of chalcophile elements during eruption can explain the regional-scale variations of S and Se concentrations. A first group of lherzolite xenoliths sampled in Southern Massif Central, from volcanic centers older and spatially unrelated to the Massif Central plume that triggered the Cenozoic volcanism, contains between 20 and 250 ppm S (with occasional S concentrations up to 592 ppm) and 12-67 ppb Se. It is clear that the highest S values, originally interpreted as representing S abundances in the primitive mantle, were in fact enriched by metasomatism. Highly variable S and Se contents (<5-360 ppm; 9-52 ppb) have also been observed in peridotite xenoliths collected in the Northern Massif Central, from volcanic centers mostly older than the plume. Like Group I xenoliths, these Group II xenoliths were strongly metasomatized by volatile-rich carbonated/silicated melts which precipitated Cu-rich sulfides. A third group of xenoliths from Plio-Quaternary basalts spatially related to the Massif Central Plume are uniformly poor in S (10-60 ppm) and Se (9-29 ppb). In this Group III, poikiloblastic textured xenoliths have lost most of their S and Se budget by peridotite-melt interactions at high melt/rock ratios. Taken as a whole, the Massif Central xenolith suite provides further evidence for strong heterogeneities in the S and Se budget of the sub-continental lithospheric mantle. However, the few LREE

  11. Œdème vulvaire massif pendant la grossesse: à propos d'un cas

    PubMed Central

    El Hassani, Moulay Elmehdi; Kassidi, Farid; Benabdejlil, Youssef; Kouach, Jaouad; Moussaoui, Driss Rahali; Dehayni, Mohammed

    2014-01-01

    L’œdème vulvaire massif est rare pendant la grossesse, mais requiert une attention particulière car il peut se greffer de complications maternelles et fœtales. Il peut être associé à plusieurs pathologies spécifiques ou non spécifiques à la grossesse dont le diagnostic fait appel obligatoirement à un interrogatoire et un examen clinique minutieux, puis à un bilan biologique standard. Le traitement doit être étiologique chaque fois que possible à coté du traitement symptomatique. Cette situation peut nécessiter un accouchement par césarienne. En dehors du risque potentiel de nécrose tissulaire et du risque exceptionnel de décès maternel associé à l’œdème vulvaire massif du post-partum l’évolution est favorable sous traitement bien conduit. PMID:25922627

  12. Tertiary carbonate development on the Shenhu Massif, South China Sea

    SciTech Connect

    Turner, N.L. ); Siemann-Gartmann, S. )

    1994-07-01

    The Shenhu Massif lies between the Zhu III Depression to the northwest, the Kaiping/Baiyun depressions to the northeast, and the Xisha Basin to the south. Major faulting began in the Paleocene, and initial basins formed on and around the Shenhu Massif during this time. Continental coarse clastics, derived from the massif area, filled the basins prior to the middle Oligocene though larger, deeper basins may have contained lacustrine environments. During the marine incursion from the middle Oligocene and until the early Miocene, coarse clastics were deposited adjacent to exposed basement areas, fine marine clastics were deposited on the massif, carbonate buildups formed along the massif rim, and carbonate platforms developed from the massif edge back into the shallow-water high-massif interior. In mid-lower Miocene, the carbonate areas were reduced in size and replaced by shales. Carbonate deposition as layers and mounds was reestablished over much of the Shenhu Massif in the early and middle Miocene. Prodelta shales in the east Shenhu Massif area and coarser clastics present in clinoforms in the Baiyun Depression are the distal components of a southerly prograding delta system located to the north. Carbonates continued to develop along the southeast side of the west Shenhu Massif during the latter part of the middle Miocene, but fine clastics dominated the rest of the area except in the Kaiping/Baiyun Depression where coarser clastics from the delta were deposited. Amoco and its partners, Nanhai West Oil Co. and Kerr-McGee Co., have begun evaluation of the Shenhu Massif area with the drilling of a Miocene carbonate buildup, the Amoco 23-1 Baodao prospect.

  13. Lower crust exhumation and ongoing continental convergence in the Variscan Maures-Tanneron Massif, France, geological synthesis and numerical models

    NASA Astrophysics Data System (ADS)

    Gerbault, Muriel; Schneider, Julie; Corsini, Michel; Reverso-Peila, Alexandre

    2015-04-01

    internal volume forces rose and exceeded far-field boundary forces, linked with the balancing of masses in all three directions. The original location of this portion of the Variscan belt remains unclear but it presents consistent transitional characteristics between the Massif Central and the Bohemian massif.

  14. The timing of eclogite facies metamorphism and migmatization in the Orlica–Śnieżnik complex, Bohemian Massif: Constraints from a multimethod geochronological study

    USGS Publications Warehouse

    Brocker, M.; Klemd, R.; Cosca, M.; Brock, W.; Larionov, A.N.; Rodionov, N.

    2009-01-01

    The Orlica–Śnieżnik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic conditions. A multimethod geochronological approach (40Ar–39Ar, Rb–Sr, Sm–Nd, U–Pb) has been used to gain further insights into the polymetamorphic evolution of eclogites and associated country rocks. Special attention was given to the unresolved significance of a 370- to 360 Ma age group that was repeatedly described in previous studies. Efforts to verify the accuracy of c.370 Ma K–Ar phengite and biotite dates reported for an eclogite and associated country-rock gneiss from the location Nowa Wieś suggest that these dates are meaningless, due to contamination with extraneous Ar. Extraneous Ar is also considered to be responsible for a significantly older 40Ar–39Ar phengite date of c. 455 Ma for an eclogite from the location Wojtowka. Attempts to further substantiate the importance of 370–360 Ma zircon dates as an indicator for a melt-forming high-temperature (HT) episode did not provide evidence in support of anatectic processes at this time. Instead, SHRIMP U–Pb zircon dating of leucosomes and leucocratic veins within both orthogneisses and (U)HP granulites revealed two age populations (490–450 and 345–330 Ma respectively) that correspond to protolith ages of the magmatic precursors and late Variscan anatexis. The results of this study further underline the importance of Late Carboniferous metamorphic processes for the evolution of the OSC that comprise the waning stages of HP metamorphism and lower pressure HT overprinting with partial melting. Eclogites and their country rocks provided no chronometric evidence for an UHP and ultrahigh-temperature episode at 387–360 Ma, as recently suggested for granulites from the OSC, based on Lu–Hf garnet ages (Anczkiewicz et al., 2007).

  15. Durbachites from the Eastern Moldanubicum (Bohemian Massif): erosional relics of large, flat tabular intrusions of ultrapotassic melts—geophysical and petrological record

    NASA Astrophysics Data System (ADS)

    Leichmann, J.; Gnojek, I.; Novák, M.; Sedlák, J.; Houzar, S.

    2016-01-01

    The results of the airborne survey comprising gamma-ray spectrometry and proton magnetometry, ground gravity survey, and field geological observations (e.g., deep borehole profiles, contact aureole in dolomite marbles, distribution of granitic pegmatites within the Třebíč pluton) suggest that the ultrapotassic Třebíč and Jihlava plutons are flat intrusions. They intruded distinct deep levels of the crust, 2-4 kbar for Třebíč pluton, and 5-7 kbar for Jihlava-pluton. Current thickness of the intrusions is generally less than 2 km, with two exceptions: (1) central part of the Jihlava pluton and (2) a small body near Věžnice, where the estimated depth of tube-shaped stocks of shoshonitic and ultrapotassic gabbros or monzogabbros is around 2.5 km. These stocks could represent feeding pipes of basic and alkaline and dry magmas protruding to the upper crust level. The NE part of the Třebíč pluton is a bottom part of this body, whereas the NW corner and the southern promontory of the pluton could represent an upper (roof) part of the intrusion. Small isolated durbachite bodies located within the Moldanubian gneisses and migmatites of the Strážek Unit represent rootless remnants of a former large and flat durbachite body initially extending significantly more to N and NE and eroded since Lower Carboniferous. Discrepancy between the long-wave magnetic and gravity anomalies, and surface geological structure of the eastern part of the Moldanubian Zone indicates a crucial role of the thrust tectonics.

  16. Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian, Gzhelian, Pennsylvanian, Bohemian Massif), their timing, and possible trigger mechanism

    NASA Astrophysics Data System (ADS)

    Stárková, Marcela; Martínek, Karel; Mikuláš, Radek; Rosenau, Nicholas

    2015-07-01

    The succession of Stephanian C lacustrine and fluvial facies of the Ploužnice member (Semily Formation) paleolake in the Krkonoše Piedmont Basin (northern Czech Republic) preserved in borehole Sm-1 shows five types of soft-sediment deformation structures (SSDS): (1) sediment injections (clastic dikes), (2) load structures and ball-and-pillow structures, (3) water-escape structures (discontinuous laminations, deformed wavy bedding, recumbent folding, and dish or pillar structures), (4) deformations by growth of carbonate and silica minerals during diagenesis, and (5) bioturbation. Bioturbations disturbing mechanical SSDS suggest that soft-sediment deformations may occur syndepositionally or soon after deposition. The discussed mechanical SSDS are developed in a lacustrine environment, most being in lower shoreface and offshore facies. The mechanical SSDS found in the Ploužnice lake deposits occur in all lacustrine facies associations (290 SSDS horizons in a 67-m-thick succession). The cumulative thickness in cm of mechanical SSDS horizons per meter of thickness (ratio cm SSDS/m) is the highest in lower shoreface facies where it reaches from 50 up to 59.7 cm SSDS/m. Offshore facies association reaches 44 cm SSDS/m. Upper shoreface facies associations have 25.9 and 26.0 cm SSDS/m, while nearshore/mudflat facies associations preserve from 22.5 to 20.5 cm SSDS/m, and in palustrine carbonate, 13.5 cm mechanical SSDS/m was found. SSDS in fluvial facies are rare (2.9 cm SSDS/m). The distribution of SSDS in the Sm-1 borehole shows clear relationships to sedimentary facies and processes such as density flows or fluctuation of water level. The relationships of particular structures indicate a relative timing of formation which is as follows: sediment deposition was followed by the formation of mechanical SSDS, then by bioturbation, and finally by deformations due to early diagenetic growth of carbonates and silica. The distribution of SSDS in vertical sections and their direct relationship to sedimentary facies point to endogenic rather than external trigger mechanisms such as seismic activity. The main endogenic trigger mechanisms responsible for the origin of SSDS included a Stephanian semi-humid seasonal climate, basin morphology with relatively steep gradients, and elevated source areas, which created a conducive environment for rapid and repeated deposition of sheetfloods and hyperconcentrated flows and turbidites causing syndepositional loading.

  17. Coincidence of gabbro and granulite formation and their implication for Variscan HT metamorphism in the Moldanubian Zone (Bohemian Massif), example from the Kutná Hora Complex

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Kachlík, Václav; Sláma, Jiří; Jedlicka, Radim

    2016-11-01

    Leucocratic metagabbro and amphibolite from a mafic-ultramafic body within migmatite and granulite in the Kutná Hora Complex were investigated. The mafic-ultramafic rocks show amphibolite facies metamorphism, but in the central part of the body some metagabbro preserves cumulus and intercumulus plagioclase, clinopyroxene and spinel. Spinel forms inclusions in both clinopyroxene and plagioclase and shows various degree of embayment structure, that was probably a result of reaction with melt during magmatic crystallization. In the metagabbro, garnet forms coronae around clinopyroxene at the contacts with plagioclase. Amphibolite contains garnet with prograde zoning and plagioclase. Phase relations of igneous and metamorphic minerals indicate that magmatic crystallization and subsequent metamorphism occurred as a result of isobaric cooling at a depth of 30-35 km. U-Pb dating on zircon from leucogabbro yielded a Variscan age (337.7 ± 2 Ma) that is similar or close to the age of granulite facies metamorphism (ca 340 Ma) in the Moldanubian Zone. Based on the calculated PT conditions and age data, both the mafic-ultramafic body and surrounding granulite shared the same exhumation path from their middle-lower crustal position at the end of Variscan orogeny. The coincidence of mafic-ultramafic intrusives and granulite-amphibolite facies metamorphism is explained by lithospheric upwelling beneath the Moldanubian Zone that occurred due to slab break-off during the final stages of subduction of the Moldanubian plate beneath the Teplá Barrandian Block. The model also addresses questions about the preservation of minerals and/or their compositions from the early metamorphic history of the rocks subjected to ultradeep subduction and subsequent granulite facies metamorphism.

  18. Experimental and Modeling Studies of Massif Anorthosites

    NASA Technical Reports Server (NTRS)

    Longhi, John

    1999-01-01

    This termination report covers the latter part of a single research effort spanning several grant cycles. During this time there was a single title, "Experimental and Modeling Studies of Massif Anorthosites", but there were several contract numbers as the mode and location of NASA contract administration changed. Initially, the project was funded as an increment to the PI's other grant, "Early Differentiation of the Moon: Experimental and Modeling Studies", but subsequently it became an independent grant. Table 1 contains a brief summary of the dates and contract numbers.

  19. Long lasting paleolandscapes stability of the French Massif Central during the Mesozoic

    NASA Astrophysics Data System (ADS)

    Ricordel-Prognon, C.; Thiry, M.; Theveniaut, H.; Lagroix, F.

    2009-04-01

    wander path of the European plate in Upper Triassic-Lower Jurassic times and the Liassic intraplate fracturing of the Pangea : New palaeomagnetic constraints from NW France and SW Germany. Geophysical Journal International 128 (2), 331-344. Parcerisa D., Thiry M., Schmitt J.-M., 2009, Albitization related to the Triassic unconformity in igneous rocks of the Morvan Massif (France), International Journal of Earth Sciences, DOI: 10.1007/s00531-008-0405-1 Ricordel C, Parcerisa D, Thiry M, Moreau M-G, Gómez-Gras D (2007) Triassic magnetic overprints related to albitization in granites from the Morvan massif (France). Palaeogeogr Palaeoclimatol Palaeoecol 251: 268-282 Ricordel C. (2007) - Datations par paléomagnétisme des paléoaltérations du Massif central et de ses bordures : implications géodynamiques. Thèse Ecole Nat. Sup. Des Mines de Paris, Paris, 172 p. Ricordel C., Thiry M., Moreau M.-G., Théveniaut H. (2005) Paleomagnetic datings on "Siderolithic" paleoweathering profiles along French Massif Central. European Geosciences Union, Vienne, Autriche, 24-29 avril, Geophysical Research Abstracts, vol. 7, 06631, 6 p. Schmitt J.M. (1992) Triassic albitization in southern France: an unusual mineralogical record from a major continental paleosurface In: Schmitt JM, Gall Q (eds). Mineralogical and geochemical records of paleoweathering. Paris, ENSMP, Mem Sci Terre 18, pp 115-131

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Spatial thermal radiometry contribution to the Massif armoricain and the Massif central (France) litho-structural study

    NASA Technical Reports Server (NTRS)

    Scanvic, J. Y. (Principal Investigator)

    1980-01-01

    The author has identified the following significant results. Although the limited number of images received did not permit construction of a thermal inertia map, important geological details were obtained in the areas of lithology and tectonics. Interpretation of day, night, and seasonal imagery resulted in differentiating broad calcareous and dolomitic units in the Causse Plateau. In the Massif amoricain, some granite massifs were delineated which were not observed by LANDSAT. Neotectonic faults were also revealed.

  2. Garzon Massif basement tectonics: A geopyhysical study, Upper Magdalena Valley, Colombia

    NASA Astrophysics Data System (ADS)

    Bakioglu, Kadir Baris

    basement rocks throughout the Garzon Massif and asymmetric loading (sedimentary basin is much deeper on NW flank -- Upper Magdalena Valley). Crust thickens to the NW toward the Central Cordillera. Euler deconvolution of the magnetic field shows pronounced NE-SW trending features under the Massif which are interpreted as faults bounding a possible pre-Cambrian sedimentary rift graben. Retrodeformed 2D regional models indicate 13 km of shortening on the Garzon basement thrust in the last 12 Ma. Approximately 9 km of shortening occurred on the SE marginal basement thrust fault, probably also in the last 12 Ma. This was preceded by approximately 43 km of shortening by thin-skinned imbricate thrusting to the southeast (12 - 25 Ma). This study provides a well-documented example of an active basement uplift on low angle thrust faults.

  3. On the occurrence of Ctenocheles (Decapoda, Axiidea, Ctenochelidae) in the Bohemian Cretaceous Basin

    PubMed Central

    HYŽNÝ, MATÚŠ; VESELSKÁ, MARTINA KOČOVÁ; DVOŘÁK, PAVEL

    2015-01-01

    Because of close morphological affinities, fossil cheliped fragments of the ghost shrimp Ctenocheles (Decapoda, Axiidea, Ctenochelidae) can be easily misidentified as remains of different decapod crustacean taxa. Re-examination of the Cretaceous decapods deposited in the National Museum in Prague revealed that all supposed specimens of the lobster genus Oncopareia found in the Middle Coniacian calcareous claystones of the Březno Formation, including one of the Fritsch’s original specimens of Stenocheles parvulus, actually belong to Ctenocheles. This material together with newly collected specimens from the same locality, allowed for erection of a new species, Ctenocheles fritschi. Its major chela possesses a serrated ischium and ovoid, unarmed merus; therefore, it is considered a close relative of the extant C. collini and C. maorianus. Ctenocheles fritschi sp. nov. represents the first report on the occurrence of the genus from the Bohemian Cretaceous Basin. It is one of the oldest records of Ctenocheles and simultaneously one of the best preserved fossils of the genus reported to date. Confusing taxonomy of S. parvulus is reviewed and shortly discussed. PMID:25983568

  4. Seismic tomography of the Massif Central - The plume story revisited

    NASA Astrophysics Data System (ADS)

    Granet, Michel; Achauer, Ulrich; Barruol, Guilhem

    2010-05-01

    Picking up on the earlier ideas from the 70', that there might be a mantle plume beneath the Massif Central, and following extensive seismological and petrological field work in the French Massif Central in the beginning of the 1990's a small-scale plume beneath the volcanic zone in the central part of the Massif Central, ascending from asthenospheric depths was postulated (Granet et al., 1995 a, b). Including Bouguer gravity and petrophysical modelling arguments this fascinating idea was further established and the name "baby-plume" was created for this kind of phenomena (Sobolev et al., 1997). However, the southeastern end and the depth extension of this plume structure could not be properly established, due to the limited aperture of the seismic arrays used at the time. This triggered a new research program, called TRACK, with the aim of tracking the traces of supposed small-scale continental mantle plume structures by integrated seismological methods. Part of Track was a new seismological field experiment carried out in central-southern part of the Massif Central in 1998/99, with seismic tomography and the study of seismic anisotropy at its core. The joint analysis of both data-sets suggests that the plume deflects to the South-East with depth, in accordance with the flow pattern suggested from SKS-splitting (Barruol and Granet,2002). In this paper we will present the new results (size and depth extent) of the mantle plume beneath the Massif Central and discuss the geodynamic implications.

  5. Ordovician magmatism in the Lévézou massif (French Massif Central): tectonic and geodynamic implications

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    New U-Pb dating on zircon yielded ca. 470 Ma ages for the granitoids from the Lévézou massif in the southern French Massif Central. These new ages do not support the previous interpretation of these granitoids as syn-tectonic intrusions emplaced during the Late Devonian-Early Carboniferous thrusting. The geochemical and isotopic nature of this magmatism is linked to a major magmatic Ordovician event recorded throughout the European Variscan belt and related to extreme thinning of continental margins during a rifting event or a back-arc extension. The comparable isotopic signatures of these granitoids on each side of the eclogite-bearing leptyno-amphibolitic complex in the Lévézou massif, together with the fact that they were emplaced at the same time, strongly suggest that these granitoids were originally part of a single unit, tectonically duplicated by either isoclinal folding or thrusting during the Variscan tectonics.

  6. Flash flood in 1714 in the Bohemian-Moravian Highlands - Reconstructing a Catastrophe.

    NASA Astrophysics Data System (ADS)

    Elleder, Libor; Krejčí, Jakub; Šírová, Jolana

    2015-04-01

    Read against the backdrop of the past twenty years with their exceptional frequency of summer floods, records of historical flood events have become highly topical. Aside from the May flood of 1872, the flash flood that occurred at the turn of July and August 1714 in the Bohemian-Moravian Highlands is probably the most important case of its kind in the Czech lands, and may likely be ranked among the most notable occurrences of extreme weather even within the larger Central European context. Within the catchment basin of the Sázava River, the headwater level rose about three meters above the highest floods on the hydrological record and 1.5m above the highest historical flood-mark. Taking into account the time period - i.e., the beginning of the 18th century - some of the concurrent accounts of the flood are uncommonly detailed, containing not only a specification of the damage caused, but also high water mark figures and, at least in broad strokes, a record of the changing water levels over time. The flood caused tremendous material damage at the time, breaching e.g. about 70 fish ponds and destroying essentially all bridges; over 230 people were killed. It was revealed that the area of Žďárské vrchy (Žďár Hills) at the divide of the rivers Loučná, Chrudimka, Sázava, and Svratka which was impacted by the causative extreme precipitation may have measured 800 to 1000 square kilometers. Rough estimates of the headwater flow rate equal about four times current Q100 values. We therefore used the hydrological model Aqualog in order to determine whether an event of this scope was at all realistic. The goal was to assess whether it was realistically possible that precipitation may have been of such scope as to trigger a hydrological response of this intensity.

  7. The seismotectonic significance of the 2008-2010 seismic swarm in the Brabant Massif (Belgium)

    NASA Astrophysics Data System (ADS)

    Van Noten, Koen; Lecocq, Thomas; Shah, Anjana K.; Camelbeeck, Thierry

    2015-04-01

    Structural interpretations of the tectonic grain of orogenic mountain belts have often been based on the study of potential field data. The steep architecture of mountain belts can be highlighted by the inclination of the magnetic field and by the persistence of aeromagnetic lineaments with depth. With respect to seismology, matched filtering has proven to be very useful for linking seismicity with deep-seated tectonic structures by separating short-wavelength anomalies, that originate from shallow depths, from long-wavelength anomalies that generally originate at greater depths. Between 2008 and 2010 more than 300 low-magnitude earthquakes occurred 20 km SE of Brussels (Belgium). Thanks to a locally deployed temporary seismic network covering the epicentral area, very small events could be detected (magnitude variation between ML -0.7 and ML 3.2). The spatial distribution of the hypocenter locations show a dense spatial cluster displaying a narrow, 1.5-km long, NW-SE oriented fault zone at a depth range between 5 and 7 km, located in the Cambrian basement rocks of the Lower Palaeozoic Anglo-Brabant Massif. Its NW-SE orientation is in agreement with the structural grain in this part of the Brabant Massif. In order to find a relevant tectonic structure that could correspond to the 2008-2010 seismic swarm, we present a full seismotectonic analysis linking local geology to the seismic swarm. A systematic filtering approach was applied in which the magnetic field was carefully bandpass filtered to generate different aeromagnetic maps that highlight sources near the hypocenter depths. Filtering demonstrates that the structure responsible for the seismic swarm is limited in length as it is bordered at both ends by magnetic lineaments with different orientations than the seismic swarm. These observations explain the rather limited spatial distribution of the swarm, both in a vertical and horizontal direction. Although few of the largest historical seismic events in

  8. Massification in Higher Education: Large Classes and Student Learning

    ERIC Educational Resources Information Center

    Hornsby, David J.; Osman, Ruksana

    2014-01-01

    In introducing the special issue on "Large Class Pedagogy: Opportunities and Challenges of Massification" the present editorial takes stock of the emerging literature on this subject. We seek to contribute to the massificaiton debate by considering one result of it: large class teaching in higher education. Here we look to large classes…

  9. Entrepreneurship and Image Management in Higher Education: Pillars of Massification

    ERIC Educational Resources Information Center

    Mount, Joan; Belanger, Charles H.

    2004-01-01

    Mass higher education has taken hold in the developed nations, and a widely held belief exists that higher education is a "right." With massification have emerged two notable trends: an entrepreneurial emphasis fuelled by the revenue-cost squeeze ensuing from reduced and realigned government funding; and a quest for differentiation through "Image…

  10. Occurrence of springs in massifs of crystalline rocks, northern Portugal

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando António Leal; Alencoão, Ana Maria Pires

    2002-02-01

    An inventory of artesian springs emerging from fractures (fracture springs) was conducted in the Pinhão River Basin and Morais Massif, northern Portugal, comprising an area of approximately 650 km2. Over 1,500 springs were identified and associated with geological domains and fracture sets. Using cross-tabulation analysis, spring distributions by fracture sets were compared among geological environments, and the deviations related to differences in rock structure and, presumably, to differences in deformational histories. The relation between spring frequencies and rock structures was further investigated by spectral determination, the model introduced in this study. Input data are the spring frequencies and fracture lengths in each geological domain, in addition to the angles between fracture strikes and present-day stress-field orientation (θ). The model's output includes the so-called intrinsic densities, a parameter indexing spring occurrence to factors such as fracture type and associated deformational regime and age. The highest densities (12.2 springs/km of lineament) were associated with young shear fractures produced by brittle deformation, and the lowest (0.1) with old tensional and ductile fractures. Spectral determination also relates each orientation class to a dominant structural parameter: where spring occurrence is controlled by θ, the class is parallel to the present-day stress-field orientation; where the control is attributed to the length of fractures, the spring occurrence follows the strike of large-scale normal faults crossing the region. Résumé. Un inventaire des sources artésiennes émergeant de fractures (sources de fractures) a été réalisé dans le bassin de la rivière Pinhão et dans le massif de Morais, dans le nord du Portugal, dans une région couvrant environ 650 km2. Plus de 1,500 sources ont été identifiées et associées à des domaines géologiques et à des ensembles de fractures. Grâce à une analyse de tableaux

  11. Occurrence of springs in massifs of crystalline rocks, northern Portugal

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando António Leal; Alencoão, Ana Maria Pires

    2002-02-01

    An inventory of artesian springs emerging from fractures (fracture springs) was conducted in the Pinhão River Basin and Morais Massif, northern Portugal, comprising an area of approximately 650 km2. Over 1,500 springs were identified and associated with geological domains and fracture sets. Using cross-tabulation analysis, spring distributions by fracture sets were compared among geological environments, and the deviations related to differences in rock structure and, presumably, to differences in deformational histories. The relation between spring frequencies and rock structures was further investigated by spectral determination, the model introduced in this study. Input data are the spring frequencies and fracture lengths in each geological domain, in addition to the angles between fracture strikes and present-day stress-field orientation (θ). The model's output includes the so-called intrinsic densities, a parameter indexing spring occurrence to factors such as fracture type and associated deformational regime and age. The highest densities (12.2 springs/km of lineament) were associated with young shear fractures produced by brittle deformation, and the lowest (0.1) with old tensional and ductile fractures. Spectral determination also relates each orientation class to a dominant structural parameter: where spring occurrence is controlled by θ, the class is parallel to the present-day stress-field orientation; where the control is attributed to the length of fractures, the spring occurrence follows the strike of large-scale normal faults crossing the region. Résumé. Un inventaire des sources artésiennes émergeant de fractures (sources de fractures) a été réalisé dans le bassin de la rivière Pinhão et dans le massif de Morais, dans le nord du Portugal, dans une région couvrant environ 650 km2. Plus de 1,500 sources ont été identifiées et associées à des domaines géologiques et à des ensembles de fractures. Grâce à une analyse de tableaux

  12. The Apollo 17 samples: The Massifs and landslide

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1992-01-01

    More than 50 kg of rock and regolith samples, a little less than half the total Apollo 17 sample mass, was collected from the highland stations at Taurus-Littrow. Twice as much material was collected from the North Massif as from the South Massif and its landslide (the apparent disproportionate collecting at the mare sites is mainly a reflection of the large size of a few individual basalt samples). Descriptions of the collection, documentation, and nature of the samples are given. A comprehensive catalog is currently being produced. Many of the samples have been intensely studied over the last 20 years and some of the rocks have become very familiar and depicted in popular works, particularly the dunite clast (72415), the troctolite sample (76535), and the station 6 boulder samples. Most of the boulder samples have been studied in Consortium mode, and many of the rake samples have received a basic petrological/geochemical characterization.

  13. K-alkaline rocks and lamproites of Tomtor massif

    NASA Astrophysics Data System (ADS)

    Vladykin, Nikolai

    2015-04-01

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

  14. Miocene mass-transport sediments, Troodos Massif, Cyprus

    USGS Publications Warehouse

    Lord, A.R.; Harrison, R.W.; BouDagher-Fadel, M.; Stone, B.D.; Varol, O.

    2009-01-01

    Sediment mass-transport layers of submarine origin on the northern and southern flanks of the Troodos ophiolitic massif are dated biostratigraphically as early Miocene and late Miocene, respectively and therefore represent different seismogenic events in the uplift and erosional history of the Troodos terrane. Analysis of such events has potential for documenting Miocene seismic and uplift events regionally in the context of changing stress field directions and plate vectors through time. ?? 2009 The Geologists' Association.

  15. The Lassell massif-A silicic lunar volcano

    NASA Astrophysics Data System (ADS)

    Ashley, J. W.; Robinson, M. S.; Stopar, J. D.; Glotch, T. D.; Hawke, B. Ray; van der Bogert, C. H.; Hiesinger, H.; Lawrence, S. J.; Jolliff, B. L.; Greenhagen, B. T.; Giguere, T. A.; Paige, D. A.

    2016-07-01

    Lunar surface volcanic processes are dominated by mare-producing basaltic extrusions. However, spectral anomalies, landform morphology, and granitic or rhyolitic components found in the Apollo sample suites indicate limited occurrences of non-mare, geochemically evolved (Si-enriched) volcanic deposits. Recent thermal infrared spectroscopy, high-resolution imagery, and topographic data from the Lunar Reconnaissance Orbiter (LRO) show that most of the historic "red spots" and other, less well-known locations on the Moon, are indeed silica rich (relative to basalt). Here we present a geologic investigation of the Lassell massif (14.65°S, 350.96°E) near the center of Alphonsus A basin in Mare Nubium, where high-silica thermal emission signals correspond with morphological indications of viscous (possibly also explosive) extrusion, and small-scale, low-reflectance deposits occur in a variety of stratigraphic relationships. Multiple layers with stair-step lobate forms suggest different eruption events or pulsing within a single eruption. Absolute model ages derived from crater size-frequency distributions (CSFDs) indicate that the northern parts of the massif were emplaced at ∼4 Ga, before the surrounding mare. However, CSFDs also indicate the possibility of more recent resurfacing events. The complex resurfacing history might be explained by either continuous resurfacing due to mass wasting and/or the emplacement of pyroclastics. Relatively low-reflectance deposits are visible at meter-scale resolutions (below detection limits for compositional analysis) at multiple locations across the massif, suggestive of pyroclastic activity, a quenched flow surface, or late-stage mafic materials. Compositional evidence from 7-band UV/VIS spectral data at the kilometer-scale and morphologic evidence for possible caldera collapse and/or explosive venting support the interpretation of a complex volcanic history for the Lassell massif.

  16. The French Atlantic littoral and the Massif Armoricain, part 3

    NASA Technical Reports Server (NTRS)

    Verger, F. (Principal Investigator); Scanvic, J. Y.; Monget, J. M.

    1977-01-01

    The author has identified the following significant results: (1) An original map of lineaments of the Armorican Massif and the Vendean platform was prepared. (2) Validity of spatial information through comparison with maps of various kinds, such as geological, geophysical, morphological, etc., was verified. (3) It was confirmed that LANDSAT images, in many cases, reflect data on deep phenomena which were only accessible geophysically and by means of borings. Tectonic domains were outlined, and known lineaments were extended.

  17. Complete Alpine reworking of the northern Menderes Massif, western Turkey

    NASA Astrophysics Data System (ADS)

    Cenki-Tok, B.; Expert, M.; Işık, V.; Candan, O.; Monié, P.; Bruguier, O.

    2016-07-01

    This study focuses on the petrology, geochronology and thermochronology of metamorphic rocks within the northern Menderes Massif in western Turkey. Metasediments belonging to the cover series of the Massif record pervasive amphibolite-facies metamorphism culminating at ca. 625-670 °C and 7-9 kbars. U-Th-Pb in situ ages on monazite and allanite from these metapelites record crustal thickening and nappe stacking associated with the internal imbrication of the Anatolide-Taurides platform during the Eocene. In addition, new 39Ar/40Ar single muscovite grain analyses on deformed rocks were performed in three localities within the northern Menderes Massif and ages range from 19.8 to 25.5 Ma. These mylonites may be related to both well-known detachments, Simav to the north and Alaşehir to the south, which accommodate Oligo-Miocene exhumation of the Menderes core complex. U-Th-Pb data on monazite grains (22.2 ± 0.2 Ma) from migmatites emplaced within the Simav detachment confirm these ages.

  18. The Front of the Aar Massif: A Crustal-Scale Ramp Anticline?

    NASA Astrophysics Data System (ADS)

    Herwegh, Marco; Mock, Samuel; Wehrens, Philip; Baumberger, Roland; Berger, Alfons; Wangenheim, Cornelia; Glotzbach, Christoph; Kissling, Edi

    2015-04-01

    The front of the Aar Massif (Swiss Central Alps) is characterized by Paleozoic basement rocks exposed at altitudes of more than 4600m above sea level, followed by a steeply north dipping Mesozoic sedimentary cover and overlying Helvetic nappes. The sediments turn into subhorizontal orientations just few kilometers to the N, where the top of the basement is situated at depths of about 7000m below sea level. What is the origin of this vertical jump of about 12000m of the basement rocks over such short horizontal distances? Recent structural investigations at the Basement-Cover contact indicate a complex structural evolution involving reactivation of extensional faults and inversion of half-grabens during early compressional stages. In the internal parts of the Aar Massif a general steepening of the faults resulted with progressive compression. In the northern frontal part, however, a new spaced cleavage evolved, which is dipping with 20-30° to the SE. In places, the new cleavage in the basement rocks is intense and pervasive and correlates with a steepening of the basement-cover contact and its offsets of several tens to hundreds of meters. Hence strain is strongly partitioned in a large number of high strain zones, which cover a cumulative thickness of at least 2000m, eventually even much more considering subsurface continuation. The Mesozoic sediments affected by this large-scale deformation zone are either intensely ductile folded in the case of limestones or faulted and imbricated in the case of dolomites. These differences in deformation style result from the deformation conditions of about < 250-300°C, where calcite still deforms in a ductile manner, while dolomite and crystalline basement preferentially undergo brittle deformation in combination of dissolution-precipitation processes. In a large-scale point of view, we suggest that the high strain domain in the crystalline basement in fact represents a crustal-scale several kilometers wide shear zone, which

  19. Soil Collembola communities within Plešné Lake and Čertovo Lake catchments, the Bohemian Forest

    NASA Astrophysics Data System (ADS)

    Čuchta, Peter

    2016-04-01

    The soil Collembola communities were studied for three years in disturbed spruce forest stands in the catchments areas of Čertovo and Plešné Lakes in the Bohemian Forest, Czech Republic. The study was focused on the impact of the windthrow, bark beetle outbreak damage and consecutive changes in the forest stands including soil environment. Four different treatments were selected for the study on both study areas: undamaged (control) forest stands, "dead" forest stands damaged by bark beetle, slightly managed windthrown forest stands left for the natural succession, and freshly harvested windthrown stands. After two years of research a total of 7,294 Collembola specimens were recorded belonging to 93 species. We recorded the highest collembolan abundance and species richness in the reference stands within catchments of both lakes, while both given parameters were considerably lower in harmed forest stands. To summarize, the disturbance led to a general decrease of Collembola communities.

  20. Evaluation of Water Use Efficiency of Short Rotation Poplar Coppice at Bohemian-Moravian Highlands

    NASA Astrophysics Data System (ADS)

    Hlaváčová, Marcela; Fischer, Milan; Mani Tripathi, Abhishek; Orság, Matěj; Trnka, Miroslav

    2015-04-01

    The water availability of the locality constitutes one of the main constraint for short rotation coppices grown on arable land. As a convenient characteristic assessing how the water use is coupled with the biomass yields, so called water use efficiency (WUE) is proposed. One method of water use efficiency determination is presented within this study. The study was carried out at short rotation poplar coppice (poplar clone J-105) at the Test Station Domanínek, Ltd. at Bohemian-Moravian Highlands during the growing season 2013. Diameters at breast height (DBH) were measured for 16 sample trees where sap flow measuring systems (Granier's Thermal Dissipation Probe, TDP) were installed. TDP outputs are expressed as temperature differences (ΔT) between the heated and non-heated probes. Estimation of sap flux density (Fd) by the Granier method relies on the measurement of temperature difference (ΔT). Determination of maximum temperature difference (ΔTmax) is fundamental for sap flux density (Fd) calculation. Although ΔTmax can be theoretically defined as ΔT at Fd = 0, many factors may prevent the occurrence of the zero flow state, such as night-time water movement for new growth (vegetative or reproductive) or water loss from the canopy due to high vapour pressure deficit (VPD). Therefore, the VPD condition was established for determination of ΔTmax. VPD condition was established as follows: VPD reaching values 0.2 at least 6 hours during night (from 21 p. m. to 3 a. m. and when the condition was fullfilled, the value at 3 a. m. was taken) because it is a supposed time after that the tree has no transpiration. The programmable part of Mini 32 software (www.emsbrno.cz) was used for application of the script establishing ΔTmax values under this VPD condition. Nevertheless, another script was applied on ΔT data set to determination of ΔTmax values for every night at 3 a. m. (as this is when ΔT should be at its daily maximum) without VPD condition restriction for

  1. Cenozoic denudation of the Menderes Massif and its geodynamic framework: slab tear or not?

    NASA Astrophysics Data System (ADS)

    Gessner, Klaus; Gallardo, Luis; Markwitz, Vanessa; Ring, Uwe; Thomson, Stuart

    2014-05-01

    Despite having experienced similar rates of convergence during the Alpine Orogeny, the Hellenides and Anatolides display fundamental differences in crust and mantle structure across a region that broadly coincides with the Aegean coastline of the Anatolian peninsula. The Menderes Massif experienced early Miocene tectonic denudation and surface uplift in the footwall of a north-directed extensional detachment system, followed by late Miocene to recent fragmentation by E-W and NW-SE trending graben systems, resulting in one of Earth's largest metamorphic core complexes. Based on the interpretation of geological and geophysical data we propose that the tectonic denudation of the Menderes Massif was caused by late Oligocene/early Miocene lithosphere scale transtension along the boundary of the Adriatic and Anatolian lithospheric domains, when rollback of the Aegean slab affected the Aegean-Menderes section of the Tethyan Orogen. In addition to previously hypothesized crustal discontinuities, gravity data, earthquake locations and seismic velocity anomalies highlight a north-south oriented boundary in the upper mantle between a fast slab below the Aegean and a slow asthenospheric region below western Turkey. As an alternative to the common interpretation of this discontinuity representing the western edge of a slab tear, we propose that the change in lithospheric structure is the result of how different lithosphere domains responded to roll-back: relatively slow removal of lithospheric mantle below western Anatolia versus trench retreat in the rapidly extending Aegean Sea region. Our findings highlight the significance of lateral variations in subduction-collision systems for the formation of continental plateaux and metamorphic core complexes.

  2. Timing and Kinematics of Cretaceous to Paleogene inversion at the SE margin of the Central European Basin System: Part 2, Thermochronology

    NASA Astrophysics Data System (ADS)

    Hoffmann, V.-E.; Dunkl, I.; von Eynatten, H.; Jähne, F.; Voigt, T.; Kley, J.

    2009-04-01

    mixed age information two different age groups can be recognized. A major group that is similar to the one reported above points to a short but intense pulse of exhumation and inversion in Coniacian to Campanian time. A younger, less significant age cluster yields information on a second phase of cooling and exhumation in the Paleocene-Eocene. The length distribution of AFT data leads to the assumption of rapid, partially multi-phase, exhumation events. In addition, the data of this study provides indications for thick Jurassic burial that likely reflect phases of Mesozoic extensional tectonics in at least parts of the CEBS. Jacobs, J., Breitkreuz, C. (2003): Zircon and apatite fission-track thermochronology of Late Carboniferous volcanic rocks of the NE German Basin. International Journal of Earth Sciences (Geologische Rundschau), 92, 165-172. Thomson, S., Brix, M., Carter, A. (1997): Late Cretaceous denudation of the Harz Massif assessed by apatite fission track analysis. In: G. Büchel and H. Lützner (Editors), Regionale Geologie von Mitteleuropa, 149. Hauptversammlung Deutsche Geologische Gesellschaft, Jena. Schriftenreihe der Deutschen Geologischen Gesellschaft, 3, 115. Thomson, S.N., Zeh, A. (2000): Fission-track thermochronology of the Ruhla Crystalline Complex:. New constraints on the post-Variscan thermal evolution of the NW Saxo-Bohemian Massif. Tectonophysics, 324, 17-35. Ventura, B., Lisker, F., Kopp, J. (2003): Apatite fission track data from the dill-core Züllsdorf 1/63: implications for the reconstruction of the post Variscan exhumation of the Mid German Crystalline High. Zeitschrift für Geologische Wissenschaften, 31, 251-261. Voigt, T., Wiese, F., von Eynatten, H., Franzke, H.-J. & Gaupp, R. (2006): Facies evolution of syntectonic Upper Cretaceous deposits in the Subhercynian Cretaceous Basin and adjoining areas (Germany). Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 157/2, 203-244.

  3. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    NASA Astrophysics Data System (ADS)

    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. Higher Education, Changing Labour Market and Social Mobility in the Era of Massification in China

    ERIC Educational Resources Information Center

    Mok, Ka Ho; Wu, Alfred M.

    2016-01-01

    This article attempts to investigate the relationship between the massification of higher education, labour market and social mobility in contemporary China. Though only a short period of time has elapsed from elite to mass education, China's higher education has been characterised as a wide, pervasive massification process. Similar to other East…

  5. Massification without Equalisation: The Politics of Higher Education, Graduate Employment and Social Mobility in Hong Kong

    ERIC Educational Resources Information Center

    Lee, Siu-yau

    2016-01-01

    This article explains why the massification of higher education in Hong Kong has, contrary to the predictions of received wisdom, failed to enhance the upward social mobility of the youth in the city. Building upon recent literature in political science, it argues that massification can take different forms, which in turn determine the effects of…

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

    ERIC Educational Resources Information Center

    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…

  7. Zirconology of ultrabasic rocks of the Karabash massif (Southern Urals)

    NASA Astrophysics Data System (ADS)

    Krasnobaev, A. A.; Valizer, P. M.; Anfilogov, V. N.; Sergeev, S. A.; Rusin, A. I.; Busharina, S. V.; Medvedeva, E. V.

    2016-07-01

    Dating of zircon (SHRIMP) from dunite and harzburgite of the Karabash massif was carried out for the first time. Relics of ancient crystals (1940 ± 30 Ma in harzburgite, 1860 ± 16 Ma in dunite) provide evidence for the Paleoproterozoic age of the protolith. The morphological peculiarities of zircon crystals allow us to assume differentiation of the magmatic source 1720 m. y. ago. The major variety of zircons indicates stages of metamorphic evolution in the Neoproterozoic (530-560 Ma) and Early-Late Ordovician (440-480 Ma).

  8. Petrogenetic characteristics of mafic-ultramafic massifs in Nizhne-Derbinsk complex (East Sayan Mountains)

    NASA Astrophysics Data System (ADS)

    Cherkasova, T.; Chernishov, A.; Goltsova, Yu; Timkin, T.; Abramova, R.

    2015-11-01

    The article describes the results of petrographic, petrochemical, petrofabric, mineralogical and geochemical studies of the major rock groups potentially Cu, Ni, Pt ore- bearing mafic-ultramafic massifs in the Nizhne- Derbinsk complex (Eastern Sayan Mountains). Based on the data interpretation the investigated massifs can be classified as peridotite- pyroxenite-gabbronorite formation of geosynclinal regime in Altai-Sayan folding area. Significant massif deformation occurred during the final post-consolidation formation stage. The petrographic features of gabbro and petrofabric patterns of the rock-forming minerals in the Burlakski and Nizhne-Derbinsk massifs indicated the fact that massifs were involved in the accretion-collisional development stage of the Central Asian folding belt during the final formation stages the Nizhne-Derbinsk complex.

  9. Thermal history and extensional exhumation of a high-temperature crystalline complex (Hırkadağ Massif, Central Anatolia)

    NASA Astrophysics Data System (ADS)

    Lefebvre, Côme; Kalijn Peters, M.; Wehrens, Philip C.; Brouwer, Fraukje M.; van Roermund, Herman L. M.

    2015-12-01

    The Central Anatolian Crystalline Complex (CACC) is a large continental domain exposed in central Turkey that was affected by high temperature metamorphism during the Late Cretaceous. As a result of this event, Paleozoic sediments became metamorphosed, initially under Barrovian conditions, then overprinted locally by high temperature-low pressure metamorphism, and intruded by widespread batholiths. In this study we focus on the crystalline Hırkadağ Massif located in the central part of the CACC, where we applied an integrated approach involving metamorphic, structural and geochronological analysis in order to elucidate its tectonic history from burial to exhumation. Our metamorphic study reveals that conditions of metamorphism reached ~ 7-8 kbar/700 °C and were relatively homogeneous at the scale of the Hırkadağ Massif. Coeval with the regional metamorphism, the rocks were intensely deformed as reflected by isoclinal folding, the development of a pervasive foliation and top-to-the-SE shearing. This was followed by decompression to pressures of ~ 3-4 kbar at 800 °C, which may be linked to the emplacement of local granodioritic intrusions at ~ 77 Ma. Subsequent cooling of the Hırkadağ high-grade metamorphic and intrusive rocks is indicated by 40Ar/39Ar cooling ages of 68.8 ± 0.9 Ma (biotite) and 67.0 ± 1.2 Ma (potassium feldspar). Evidence for tectonic exhumation has been identified within the marbles at the NE margin of the Hırkadağ Massif, in the form of discrete protomylonitic and mylonitic shear bands showing a consistent N40-60 top-to-NE sense of shear. Further east, the contact between brecciated mylonitic marbles and non-metamorphic conglomerates preserves the typical structural features of an upper-crustal detachment fault. Restoration of the Hırkadağ Massif and the CACC to their late Cretaceous configuration suggests that the LP-HT metamorphism, magmatism and extensional structures evolved as a result of the development and exhumation of a ~ N

  10. August, 2002 - floods events, affected areas revitalisation and prevention for the future in the central Bohemian region, Czech Republic

    NASA Astrophysics Data System (ADS)

    Bina, L.; Vacha, F.; Vodova, J.

    2003-04-01

    Central Bohemian Region is located in a shape of a ring surrounding the capitol of Prague. Its total territorial area is 11.014 sq.km and population of 1 130.000 inhabitants. According to EU nomenclature of regional statistical units, the Central Bohemian Region is classified as an independent NUTS II. Bohemia's biggest rivers, Vltava and Labe form the region's backbone dividing it along a north-south line, besides that there are Sazava and Berounka, the two big headwaters of Vltava, which flow through the region and there also are some cascade man made lakes and 2 important big dams - Orlik and Slapy on the Vltava River in the area of the region. Overflowing of these rivers and their feeders including cracking of high-water dams during the floods in August 2002 caused total or partial destruction or damage of more than 200 towns and villages and total losses to the extend of 450 mil. EUR. The worst impact was on damaged or destroyed human dwellings, social infrastructure (schools, kindergartens, humanitarian facilities) and technical infrastructure (roads, waterworks, power distribution). Also businesses were considerably damaged including transport terminals in the area of river ports. Flowage of Spolana Neratovice chemical works caused critical environmental havoc. Regional crisis staff with regional Governor in the lead worked continuously during the floods and a regional integrated rescue system was subordinated to it. Due to the huge extent of the floods the crisis staff coordinated its work with central bodies of state including the Government and single "power" resorts (army, interior, transport). Immediately after floods a regional - controlled management was set up including an executive body for regional revitalisation which is connected to state coordinating resort - Ministry for Local Development, EU sources and humanitarian aid. In addition to a program of regional revitalisation additional preventive flood control programs are being developed

  11. Mesoscopic faults in the Bregaglia (Bergell) massif, Central Alps

    NASA Astrophysics Data System (ADS)

    Passerini, P.; Sguazzoni, G.; Marcucci, M.

    1991-11-01

    The strike, direction of dip and pitch of the striae along mesoscopic faults in the Oligocene granodiorite-tonalite of Val Masino-Val Bregaglia (Bergell) are analysed. Most fault planes are steeply dipping, and show strike-slip or oblique-slip motion. Dominant strikes are NNW or NNE. A relative chronology of fault sets is suggested based on the presence of different minerals (chlorite and epidote) on fault planes. The pattern of mesoscopic faults in the Val Masino-Val Bregaglia massif does not follow the earlier tectonic trends of the Pennidic nappe edifice, nor even the trend of the nearby section of the Insubric Line considered at both regional and mesoscopic scales. The mesoscopic analysis of the Val Masino-Val Bregaglia massif thus reveals a fault system largely oblique to the major Alpine lineaments. The observed fault pattern does not reveal traces of thrusting referable to late Alpine orogenic phases, and can be related to subsequent deformation, dominated by strike-slip movements; this pattern does not match the traditional schemes of extensional dip-slip faulting following orogenesis. It records a stage of tectonic evolution which follows nappe emplacement, yet it precedes vertical or extensional post-orogenic tectonics.

  12. Long-term studies (1871-2000) on acidification and recovery of lakes in the Bohemian Forest (central Europe).

    PubMed

    Vrba, Jaroslav; Kopácek, Jirí; Fott, Jan; Kohout, Leos; Nedbalová, Linda; Prazáková, Miroslava; Soldán, Tomás; Schaumburg, Jochen

    2003-07-01

    This paper evaluates long-term changes in the atmospheric depositions of S and N compounds, lake water quality, and biodiversity at eight glacial lakes in the Bohemian Forest over the past 130 years. This time interval covers (i) the 'background' pre-acidification status of the lakes, (ii) a period of changes in the communities that can be partly explained by introduction of fish, (iii) a period of strong lake acidification with its adverse impacts on the communities, (iv) the lake reversal from acidity, which includes the recent status of the lakes. The lake water chemistry has followed-with a characteristic hysteresis-both the sharp increase and decline in the deposition trends of strong anions. Remarkable changes in biota have mirrored the changing water quality. Fish became extinct and most species of zooplankton (Crustacea) and benthos (Ephemeroptera and Plecoptera) retreated due to the lake water acidification. Independent of ongoing chemical reversal, microorganisms remain dominant in the recent plankton biomass as well as in controlling the pelagic food webs. The first signs of the forthcoming biological recovery have already been evidenced in some lakes, such as the population of Ceriodaphnia quadrangula (Cladocera) returning into the pelagial of one lake or the increase in both phytoplankton biomass and rotifer numbers in another lake.

  13. Cross-borehole flow analysis to characterize fracture connections in the Melechov Granite, Bohemian-Moravian Highland, Czech Republic

    USGS Publications Warehouse

    Paillet, Frederick L.; Williams, John H.; Urik, Joseph; Lukes, Joseph; Kobr, Miroslav; Mares, Stanislav

    2012-01-01

    Application of the cross-borehole flow method, in which short pumping cycles in one borehole are used to induce time-transient flow in another borehole, demonstrated that a simple hydraulic model can characterize the fracture connections in the bedrock mass between the two boreholes. The analysis determines the properties of fracture connections rather than those of individual fractures intersecting a single borehole; the model contains a limited number of adjustable parameters so that any correlation between measured and simulated flow test data is significant. The test was conducted in two 200-m deep boreholes spaced 21 m apart in the Melechov Granite in the Bohemian-Moravian Highland, Czech Republic. Transient flow was measured at depth stations between the identified transmissive fractures in one of the boreholes during short-term pumping and recovery periods in the other borehole. Simulated flows, based on simple model geometries, closely matched the measured flows. The relative transmissivity and storage of the inferred fracture connections were corroborated by tracer testing. The results demonstrate that it is possible to assess the properties of a fracture flow network despite being restricted to making measurements in boreholes in which a local population of discrete fractures regulates the hydraulic communication with the larger-scale aquifer system.

  14. Structural investigations in the Massif-Central, France

    NASA Technical Reports Server (NTRS)

    Scanvic, J. Y.

    1974-01-01

    This survey covered the French Massif-Central (where crystalline and volcanic rocks outcrop) and its surrounding sedimentaries, Bassin de Paris, Bassin d'Aquitaine and Rhodanian valley. One objective was the mapping of fracturing and the surveying of its relationship with known ore deposits. During this survey it was found that ERTS imagery outlines lithology in some sedimentary basins. On the other hand, in a basement area, under temperature climate conditions, lithology is rarely expressed. These observations can be related to the fact that band 5 gives excellent results above sedimentary basins in France and generally band 7 is the most useful in a basement area. Several examples show clearly the value of ERTS imagery for mapping linear features and circular structures. All the main fractures are identified with the exception of new ones found both in sedimentaries and basement areas. Other interesting findings concern sun elevation which, stereoscopic effect not being possible, simulates relief in a better way under certain conditions.

  15. Structural geology investigation on Massif Central and Parisian Basin (France)

    NASA Technical Reports Server (NTRS)

    Weecksteen, G. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Band 5 gives the most information concerning the fracturing in the Massif Central and Parisian Basins. Band 6 and 7 show the fractures emphasized by forest boundaries and by the linear trace of water courses. The most remarkable information drawn from the preliminary investigation of two ERTS-1 images covering two different landscapes, a regular relief of shelving plateau bounded by cuestas having a sedimentary origin and a mountainous region built in crystalline and volcanic rocks, is that the deep structural elements under a thick sedimentary cover can be translated on the surface by indirect criteria. MSS imagery has permitted the Metz fault to be extended towards the west and shows clearly, through land use on the Rhone Valley fluvial deposit, the continuation towards the east of the carboniferous basin of St. Etienne.

  16. Petrogenesis of massif anorthosites: a perspective from St. Urbain, Quebec

    SciTech Connect

    Gromet, L.P.; Dymek, R.F.

    1985-01-01

    The St. Urbain massif is a post-orogenic anorthosite pluton (approx. 500 km/sup 2/) emplaced within the central high-grade granulite terrain of the Grenville structural province. In contrast to other Grenville anorthosites, primary magmatic features are largely preserved. The massif consists predominantly of andesine anorthosite (AA) of remarkable purity containing abundant plagioclase megacrysts. AA has high K/sub 2/O (approx. 2 wgt.%), very high Sr contents (approx. 1200 ppm) and highly fractionated, low REE contents. Features of AA provide the following insights into anorthosite origins: (1) Crystallization from anorthositic magmas, as evidenced by early crystallization of abundant antiperthitic plag, and igneous emplacement of AA dikes and veins into older, unrelated labradorite anorthosite; (2) in situ crystallization of pyroxene after plag, with no direct evidence of earlier crystallization of mafic minerals from a basaltic parent magma; (3) limited differentiation during crystallization, indicated by small variation in plag and opx and limited variations in plag Sr and REE contents; (4) the involvement of water, suggested by the late igneous crystallization of biotite and the localized grain-boundary replacement of plag by calcic myrmekite (An/sub 80/ + qtz). (5) high temperature, relatively oxidizing conditions, indicated by magmatic hemoilmenite +/- rutile and rare ferropseudobrookite in AA and associated ores. AA crystallized from highly feldspathic, relatively oxidized, somewhat hydrous parent magma with little trapped melt. The development of a hyperfeldspathic parent magma with the requisite geochemical features can be ascribed to hydrous partial melting of mafic (to intermediate) rocks at deep crustal or greater depths, leaving a garnetiferous residue.

  17. Serpentinization and Life: Motivations for Drilling the Atlantis Massif

    NASA Astrophysics Data System (ADS)

    Frueh-Green, G. L.; Lang, S. Q.; Brazelton, W. J.; Schrenk, M. O.

    2014-12-01

    The Atlantis Massif, located at the intersection of the Atlantis transform fault and the Mid-Atlantic Ridge at 30°N, is one of the best-studied oceanic core complexes (OCCs) and is the target of IODP Expedition 357 late 2015. Drilling will address two exciting discoveries in ridge research: off-axis, serpentinite-hosted hydrothermal activity and carbonate precipitation, exemplified by the Lost City hydrothermal field, and the significance of tectono-magmatic processes in forming heterogeneous and variably serpentinized lithosphere as key components of slow spreading ridges. Serpentinization reactions at moderate- to low-temperatures result in alkaline fluids, characterized by elevated concentrations of abiotic hydrogen, methane and low molecular weight hydrocarbons, and which lead to precipitation of carbonate and brucite upon mixing with seawater. These highly reactive systems have major consequences for lithospheric cooling, global geochemical cycles, carbon sequestration and microbial activity. However, little is known about the nature and distribution of microbial communities in subsurface ultramafic environments and the potential for a hydrogen-based deep biosphere in areas of active serpentinization and fluid circulation. The continuous flux of reduced compounds provides abundant thermodynamic energy to drive chemolithoautotrophy, however, carbon availability may be limited in these high pH environments and represent a challenge for microbial growth. Here we review serpentinization processes as fundamental to understanding the evolution of oceanic lithosphere and discuss open questions related to the impact of serpentinization on the subsurface biosphere. Motivations for drilling the shallow subseafloor of the Atlantis Massif include: (1) exploring the extent and activity of the subsurface biosphere in young ultramafic and mafic seafloor; (2) quantifying the role of serpentinization in driving hydrothermal systems, in sustaining microbiological communities

  18. Late Carboniferous remagnetisation of Palaeozoic rocks in the NE Rhenish Massif, Germany

    NASA Astrophysics Data System (ADS)

    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

  19. Taconic collision in SE Penna and Delaware

    SciTech Connect

    Crawford, M.L.; Crawford, W.A.; Hoersch, A.L.; Srogi, L.A.; Wagner, M.E.

    1985-01-01

    Taconic metamorphism and tectonism in SE Pennsylvania and northern Delaware were a result of the collision of a volcanic arc with North America. The Wilmington Complex, the infrastructure of the arc, is presently the highest structural unit. It consists of granulite facies volcanogenic sediments intruded by gabbro and a ca. 500 Ma gabbronorite-charnockite suite. Latest Precambrian-earliest Paleozoic sediments of the Glenarm series were metamorphosed to conditions above the second sillimanite isograd beneath the overthrust hot (700-800/sup 0/C) Wilmington Complex. As the edge of the continent was depressed and heated under the advancing thrust complex, basement-involved nappes of Grenville age rocks (Avondale anticline, Woodville dome) with the Glenarm sedimentary cover were thrust over still rigid autochthonous basement (West Chester Prong). On the NW flank of the orogen, Grenville age gneiss-cored massifs (Honey Brook Upland, Mine Ridge, Trenton Prong), unconformably overlain by lower Paleozoic continental shelf sediments, were involved in the thrusting but metamorphosed only to the greenschist facies. Steep anticlines developed later in the Paleozoic, contributing to the present pattern of northeast trending Grenville basement massifs mantled by overlying units.

  20. Cenozoic rejuvenation events of Massif Central topography (France): Insights from cosmogenic denudation rates and river profiles

    NASA Astrophysics Data System (ADS)

    Olivetti, Valerio; Godard, Vincent; Bellier, Olivier

    2016-06-01

    The French Massif Central is a part of the Hercynian orogenic belt that currently exhibits anomalously high topography. The Alpine orogenesis, which deeply marked Western European topography, involved only marginally the Massif Central, where Cenozoic faulting and short-wavelength crustal deformation is limited to the Oligocene rifting. For this reason the French Massif Central is a key site to study short- and long-term topographic response in a framework of slow tectonic activity. In particular the origin of the Massif Central topography is a topical issue still debated, where the role of mantle upwelling is invoked by different authors. Here we present a landscape analysis using denudation rates derived from basin-averaged cosmogenic nuclide concentrations coupled with longitudinal river profile analysis. This analysis allows us to recognize that the topography of the French Massif Central is not fully equilibrated with the present base level and in transient state. Our data highlight the coexistence of out-of-equilibrium river profiles, incised valleys, and low cosmogenically derived denudation rates ranging between 40 mm/kyr and 80 mm/kyr. Addressing this apparent inconsistency requires investigating the parameters that may govern erosion processes under conditions of reduced active tectonics. The spatial distribution of denudation rates coupled with topography analysis enabled us to trace the signal of the long-term uplift history and to propose a chronology for the uplift evolution of the French Massif Central.

  1. Country, cover or protection: what shapes the distribution of red deer and roe deer in the Bohemian Forest Ecosystem?

    PubMed

    Heurich, Marco; Brand, Tom T G; Kaandorp, Manon Y; Šustr, Pavel; Müller, Jörg; Reineking, Björn

    2015-01-01

    The Bohemian Forest Ecosystem encompasses various wildlife management systems. Two large, contiguous national parks (one in Germany and one in the Czech Republic) form the centre of the area, are surrounded by private hunting grounds, and hunting regulations in each country differ. Here we aimed at unravelling the influence of management-related and environmental factors on the distribution of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) in this ecosystem. We used the standing crop method based on counts of pellet groups, with point counts every 100 m along 218 randomly distributed transects. Our analysis, which accounted for overdispersion as well as zero inflation and spatial autocorrelation, corroborated the view that both human management and the physical and biological environment drive ungulate distribution in mountainous areas in Central Europe. In contrast to our expectations, protection by national parks was the least important variable for red deer and the third important out of four variables for roe deer; protection negatively influenced roe deer distribution in both parks and positively influenced red deer distribution in Germany. Country was the most influential variable for both red and roe deer, with higher counts of pellet groups in the Czech Republic than in Germany. Elevation, which indicates increasing environmental harshness, was the second most important variable for both species. Forest cover was the least important variable for roe deer and the third important variable for red deer; the relationship for roe deer was positive and linear, and optimal forest cover for red deer was about 70% within a 500 m radius. Our results have direct implications for the future conservation management of deer in protected areas in Central Europe and show in particular that large non-intervention zones may not cause agglomerations of deer that could lead to conflicts along the border of protected, mountainous areas.

  2. Country, Cover or Protection: What Shapes the Distribution of Red Deer and Roe Deer in the Bohemian Forest Ecosystem?

    PubMed Central

    Heurich, Marco; Brand, Tom T. G.; Kaandorp, Manon Y.; Šustr, Pavel; Müller, Jörg; Reineking, Björn

    2015-01-01

    The Bohemian Forest Ecosystem encompasses various wildlife management systems. Two large, contiguous national parks (one in Germany and one in the Czech Republic) form the centre of the area, are surrounded by private hunting grounds, and hunting regulations in each country differ. Here we aimed at unravelling the influence of management-related and environmental factors on the distribution of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) in this ecosystem. We used the standing crop method based on counts of pellet groups, with point counts every 100 m along 218 randomly distributed transects. Our analysis, which accounted for overdispersion as well as zero inflation and spatial autocorrelation, corroborated the view that both human management and the physical and biological environment drive ungulate distribution in mountainous areas in Central Europe. In contrast to our expectations, protection by national parks was the least important variable for red deer and the third important out of four variables for roe deer; protection negatively influenced roe deer distribution in both parks and positively influenced red deer distribution in Germany. Country was the most influential variable for both red and roe deer, with higher counts of pellet groups in the Czech Republic than in Germany. Elevation, which indicates increasing environmental harshness, was the second most important variable for both species. Forest cover was the least important variable for roe deer and the third important variable for red deer; the relationship for roe deer was positive and linear, and optimal forest cover for red deer was about 70% within a 500 m radius. Our results have direct implications for the future conservation management of deer in protected areas in Central Europe and show in particular that large non-intervention zones may not cause agglomerations of deer that could lead to conflicts along the border of protected, mountainous areas. PMID:25781942

  3. Silvibacterium bohemicum gen. nov. sp. nov., an acidobacterium isolated from coniferous soil in the Bohemian Forest National Park.

    PubMed

    Lladó, Salvador; Benada, Oldrich; Cajthaml, Tomáš; Baldrian, Petr; García-Fraile, Paula

    2016-02-01

    During the course of a study assessing the bacterial diversity of a coniferous forest soil (pH 3.8) in the Bohemian Forest National Park (Czech Republic), we isolated strain S15(T) which corresponded to one of the most abundant soil OTUs. Strain S15(T) is represented by Gram-negative, motile, rod-like cells that are 0.3-0.5μm in diameter and 0.9-1.1μm in length. Its pH range for growth was 3-6, with optimal conditions found at approximately 4-5. It can grow at temperatures between 20°C and 28°C, with optimum growth at 22-24°C. Its respiratory quinone is MK-8, and its main fatty acid is iso-C15:0 (73.7%). The G+C DNA content was 58.2mol%. According to the 16S rRNA gene sequence analysis, strain S15(T) belongs to subdivision 1 of the phylum Acidobacteria, being affiliated to the cluster of Acidipila rosea AP8(T) and Acidobacterium capsulatum ATCC 51196(T). Analysis of the S15(T) genome revealed the presence of 404 genes that are involved in carbohydrate metabolism, which indicates the metabolic potential to degrade polysaccharides of plant and fungal origin. Based on genotypic and phenotypic characteristics, the strain S15(T) represents a new genus and species within the family Acidobacteriaceae, for which the name Silvibacterium bohemicum gen. nov., sp. nov. is proposed (type strain S15(T)=LMG 28607(T)=CECT 8790(T)).

  4. Character, Distribution and Significance of Coarse Sedimentary Material in Mid-Mountain Valleys: Case Studies from Bohemian Forest Mts.

    NASA Astrophysics Data System (ADS)

    Hartvich, F.; Langhammer, J.; Taborik, P.

    2014-12-01

    The aim of this study is to collect information on the distribution, character and parameters of the coarse fluvial sediments in order to reconstruct the formation and significant changes in development of mid-mountain streams and their valleys. The studied area is situated to two small catchments in the Bohemian Forest Mts. Roklanský/Javoří brooks are observed in a 10 km long segment on the flat area of the Šumava Plateau, the Losenice R. was followed on a 7 km segment in a deeply incised, steep-sloped valley. First, the hydromorphological mapping of the floodplain and channel landforms took place to collect information on position of the fluvial landforms. The mapping was performed using the HEM methodics, developed by the authors. The Electric Resistivity Tomography was used in 20 profiles across the valleys. These cross-sections formed a backbone of the research aiming to observe the depth and distribution of the coarse sediment valley fill (above bedrock) both across the valleys and along. Next we employed digital optical granulometry using Sedimetrics software on the mapped gravel bodies, classic sieve granulometry on sandy accumulations, and on-site, in-channel boulder granulometry. Finally, magnetic susceptibility measurements were performed on suitable sediment profiles along the courses to assess the provenience of the material. There are several notions, indicated by the results of the abovementioned analyses. First, the valley floor sedimentary infill is surprisingly shallow (10-15 m), notably in the case of Javoří and Roklanský brook where the valley floor often exceeds 200 - 300 m. Also, the MS points to rather fast changes in the main sediment sources. Observations of the sediment character in the Losenice valley indicate significant role of the slope/channel coupling, namely persisting influence of large, slope-based sources of angular material (rockslides, debris flows), as well as strong impact of flood events on the valley floor morphology.

  5. Pyroxenites - Melting or Migration?: Evidence from the Balmuccia massif

    NASA Astrophysics Data System (ADS)

    Sossi, Paolo; O'Neill, Hugh

    2014-05-01

    The recognition of pyroxenites in the mantle, combined with their lower solidus temperatures than peridotite, have been proposed as contributors to melting (Pertermann and Hirschmann, 2003; Sobolev et al, 2005; 2007). Geochemical fingerprints of this process invoke an unspecified 'pyroxenite' as the putative source. In reality, mantle pyroxenites are diverse (Downes, 2007), requiring that their mode of origin and compositional variability be addressed. Due to the excellent preservation and exposure of the Balmuccia massif, it has become an archetype for orogenic peridotites, providing information on their composition, field relationships and metamorphic history (Shervais and Mukasa, 1991; Hartmann and Wedepohl, 1993; Rivalenti et al., 1995; Mazzucchelli et al., 2009). The Balmuccia massif consists of fertile lherzolite with subordinate harzburgite and dunite and is riddled with pyroxenite bands, which fall into two suites - Chrome-Diopside (Cr-Di) and Aluminous-Augite (Al-Aug), a pairing present in most massif peridotites. Two-pyroxene thermometry gives temperatures of 850±25°C at 1-1.5 GPa, 500°C lower than asthenospheric mantle at that pressure, meaning they do not preserve their original, high temperature mineralogy. Decimetre-sized Cr-Di bands (≡75% CPX, 25% OPX) occur as initially Ol-free and bound by refractory dunite, but, as the bands are rotated into the plane of foliation, they mechanically incorporate olivine. Al-Aug veins (60% CPX, 25% OPX, 15% Sp) discordantly cut the body, intruding lherzolites which show enrichments in Fe, Al and Ti adjacent to the dykes. Both the Cr-Di suite and the Al-Aug series have indistinguishable Sr-, Nd-isotopic compositions to the host peridotite (Mukasa and Shervais, 1999). The major element compositions of pyroxenes in the Cr-Di bands and those in the surrounding peridotites are identical. Together with isotopic evidence, this suggests a local source, not only chemically but spatially, where a very low degree melt (

  6. Distribution patterns, properties and ages of Pleistocene periglacial slope deposits in the eastern Rhenish Massif

    NASA Astrophysics Data System (ADS)

    Sauer, Daniela; Scholten, Thomas; Felix-Henningsen, Peter; Kadereit, Annette

    2010-05-01

    Pleistocene periglacial slope deposits (PPSD) cover almost continuously the low mountain areas of Germany. They are interpreted as the result of frost weathering, gelisolifluction, cryoturbation, meltwater outwash processes and loess incorporation. Four types of PPSD are distinguished in the German classification system: A Basal Layer consists entirely of debris of the underlying rock, which it usually directly overlies. It occurs in almost every relief position, and several Basal Layers may have formed on top of each other. An Intermediate Layer contains varying proportions of loess. It is only found in relief positions favourable for loess accumulation and preservation. Its position within a vertical sequence of PPSD is usually on top of a Basal Layer. An Upper Layer consists of a mixture of rock debris and loess, and contains generally a lower amount of loess than a possibly underlying Intermediate Layer. It has a remarkably steady thickness of around 50 cm, as confirmed in many studies. The Top Layer is mostly restricted to the surroundings of outcrops of particularly resistant rock in higher regions and mainly consists of rock debris. PPSD were investigated in the eastern Westerwald area, at the eastern edge of the Rhenish Massif, Germany. Parent rock, exposition, position and shape of slope were expected to be factors influencing the occurrence, thickness and properties of the different types of PPSD. Therefore, profiles were excavated on the main rock types in the area, which are shale, quartzite and diabase. On each rock type, profiles were studied along catenas in NW, SW, SE and NE exposition, each catena including a profile in upper, middle and footslope position. In upper slope positions on shale an Upper Layer covers directly the rock, independent of exposition. In downslope direction, still above the mid slope profiles, a Basal Layer appears between the Upper Layer and the rock. In upper slope positions on quartzite, a Basal Layer is already present

  7. New insights from U Pb zircon dating of Early Ordovician magmatism on the northern Gondwana margin: The Urra Formation (SW Iberian Massif, Portugal)

    NASA Astrophysics Data System (ADS)

    Solá, A. R.; Pereira, M. F.; Williams, I. S.; Ribeiro, M. L.; Neiva, A. M. R.; Montero, P.; Bea, F.; Zinger, T.

    2008-12-01

    .85). The geochemical data are compatible with an orogenic geodynamic environment. However, the "orogenic" signature can be considered to represent, in part, an inherited feature caused by melting of the Cadomian basement which also has calc-alkaline affinities. The Early Ordovician crustal growth and associated magmatism, represented by the Urra felsic volcaniclastic rocks and associated calc-alkaline granitoids, diorites and gabbros, can be interpreted in terms of the underplating and temporal storage of mantle-derived magmas as the potential source for the "orogenic melts" that were intruded during Early Paleozoic extension. This record of Early Ordovician magmatism has striking similarities with other correlatives from the Iberian, Bohemian and Armorican massifs that are discussed in this paper. This comparison reinforces the probable existence of a large-scale crustal melting process linked to a significant episode of extension on the northern Gondwana margin that probably resulted in the birth of the Rheic Ocean.

  8. Deforestation Along the Maya Mountain Massif Belize-Guatemala Border

    NASA Astrophysics Data System (ADS)

    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.

  9. Preliminary hydrochemical study of Ronda ultramafic massif (South Spain)

    NASA Astrophysics Data System (ADS)

    Vadillo, Iñaki; Urresti, Begoña; Jiménez, Pablo; Martos, Sergio; José Durán, Juan; Benavente, José; Carrasco, Francisco; Pedrera, Antonio

    2016-04-01

    During 2015 more than 70 springs related to the peridotite outcrops of the Ronda mountainous massif, South Spain, have been identified. The field work included "in situ" measurements of physical-chemical parameters (T, EC, pH), and water sampling for major components and stable isotopes of water and DIC. The hydrogeochemical study allowed us to characterize different flow systems: (1) springs with very low to medium electrical conductivities (200-700 μS/cm) and pH below 9.0, and (2) springs with EC above 700 μS/cm and pH above 9.0. The first group of springs are supposed to be linked with surface and subsurface flows. The hydrogeochemical reactions that determine their composition are characterized by the low solubility of minerals, atmospheric CO2 (open system) and active serpentinization reactions that supplies hundreds of ppm of Mg2+. All of them are waters of HCO3-Mg or HCO3-Mg-Na type. The second group of springs drains water with EC above 700 μS/cm and pH over 9. In general, these springs are associated to deep flows connected to regional faults or major tectonic features. Deeper flow enhances water-rock interaction and time of contact, so this system evolves towards a closed system to O2 and CO2. All these waters are old or older than the first group and show reducing features and are of Na-Cl or OH-Ca type.

  10. Organic matter in rocks of certain alkalic massifs of Siberia

    SciTech Connect

    Petersil'e, I.A.; Andreeva, E.D.; Sveshnikova, E.V.

    1983-01-01

    Parts of certain alkalic intrusive massifs contain up to 63 cc methane per kilogram of rock, with smaller amounts of heavier hydrocarbon gases, bitumen, hydrogen, carbon monoxide and carbon dioxide. The authors argue that the hydrocarbons cannot have come from assimilated limestone, because the igneous rocks contain much more of these gases than do the enclosing limestones. Likewise, the hydrocarbons cannot have been introduced by late solutions because they are much lower in hydrothermal and metasomatic facies than in primary minerals of the high temperature intrusive facies. Hydrocarbons are not stable at magmatic temperatures; the authors conclude that these must have formed in the presence of natural catalysts during slow cooling below 500/sup 0/C, in accordance with industrial synthesis of hydrocarbons. The C/sup 12//C/sup 13/ ratio of the bitumens is in the range for ordinary petroleum, suggesting that they formed at relatively low temperature, but the carbon of the gaseous hydrocarbons is lighter, which may indicate that they formed at somewhat higher temperatures.

  11. 40Ar- 39Ar geochronology of the charnockites and granulites of the Kan Nack complex, Kon Tum Massif, Vietnam

    NASA Astrophysics Data System (ADS)

    Maluski, Henri; Lepvrier, Claude; Leyreloup, André; Tich, Vu Van; Thi, Phan Truong

    2005-07-01

    The Truong Son Belt forms the eastern rim of the Indochina Block in Southeast Asia. The age of the metamorphism, mainly along NW-SE mylonitic shear zones that affects this belt, has been formerly determined at about 240-250 Ma. This age corresponds to the Indosinian tectonometamorphic episode. The Kon Tum Massif, situated to the south of this belt, comprises high-temperature rocks, the Kan Nack Complex, including charnockites and granulites. The main charnockitic outcrops, restricted to the Song Ba Valley, establish the intrusive nature of these magmatic rocks within granulite facies material. Basic charnockitic rocks are mainly quartz enderbites to norites and hornblende-pyroxene granulite facies rocks. The 40Ar- 39Ar age of intrusion-cooling of charnockitic magmas is determined from primary magmatic biotites at about 245 Ma. In the east of the Kan Nack Complex some granulite facies rocks exhibit relicts of primary granulite facies parageneses, whereas others show evidence of overprinting by a retrogressive low-grade metamorphism. Ar-Ar dating confirm this evolution, giving ages of 400 Ma for primary relict granulite facies phases and 260-270 Ma from the most retrogressed samples establishing the youngest limit for the granulite facies metamorphism. Granulites intruded by charnockites in the Song Ba Valley yield ages of about 250 Ma, equivalent to the ages of the charnockites, and have evidently been completely reset by these high temperature intrusions. Therefore, the Kan Nack Complex of the Kon Tum Massif is not an independent unit with respect to the Indosinian orogen, but represents the deep-crustal part of this belt.

  12. Tephrochronology of the Mont-Dore volcanic Massif (Massif Central, France): new 40Ar/39Ar constraints on the Late Pliocene and Early Pleistocene activity

    NASA Astrophysics Data System (ADS)

    Nomade, Sébastien; Pastre, Jean-François; Nehlig, Pierre; Guillou, Hervé; Scao, Vincent; Scaillet, Stéphane

    2014-03-01

    The Mont-Dore Massif (500 km2), the youngest stratovolcano of the French Massif Central, consists of two volcanic edifices: the Guéry and the Sancy. To improve our knowledge of the oldest explosive stages of the Mont-Dore Massif, we studied 40Ar/39Ar-dated (through single-grain laser and step-heating experiments) 11 pyroclastic units from the Guéry stratovolcano. We demonstrate that the explosive history of the Guéry can be divided into four cycles of explosive eruption activity between 3.09 and 1.46 Ma (G.I to G.IV). We have also ascertained that deposits associated with the 3.1-3.0-Ma rhyolitic activity, which includes the 5-km3 "Grande Nappe" ignimbrite, are not recorded in the central part of the Mont-Dore Massif. All the pyroclastites found in the left bank of the Dordogne River belong to a later explosive phase (2.86-2.58 Ma, G.II) and were channelled down into valleys or topographic lows where they are currently nested. This later activity also gave rise to most of the volcanic products in the Perrier Plateau (30 km east of the Mont-Dore Massif); three quarters of the volcano-sedimentary sequence (up to 100 m thick) was emplaced within less than 20 ky, associated with several flank collapses in the northeastern part of the Guéry. The age of the "Fournet flora" (2.69 ± 0.01 Ma) found within an ash bed belonging to G.II suggests that temperate forests already existed in the French Massif Central before the Pliocene/Pleistocene boundary. The Guéry's third explosive eruption activity cycle (G.III) lasted between 2.36 and 1.91 Ma. It encompassed the Guéry Lake and Morangie pumice and ash deposits, as well as seven other important events recorded as centimetric ash beds some 60 to 100 km southeast of the Massif in the Velay region. We propose a general tephrochronology for the Mont-Dore stratovolcano covering the last 3.1 My. This chronology is based on 44 40Ar/39Ar-dated events belonging to eight explosive eruption cycles each lasting between 100 and 200

  13. Unraveling polyphase brittle tectonics through fault-slip analysis in the Voltri Massif, Western Alps (Italy)

    NASA Astrophysics Data System (ADS)

    Federico, Laura; Crispini, Laura; Vigo, Andrea; Malatesta, Cristina; Capponi, Giovanni

    2014-05-01

    We investigated a system of faults in the northwestern Voltri Massif (Ligurian Alps, northern Italy) usually mapped as a km-scale fault, but actually made up of different fault segments. The Ligurian Alps represent the evolving linkage area between the Western Alps and Northern Apennines: here the two orogenic systems interfered since Oligocene times. Our aim is to characterise kinematics and evolution of this fault system, coupling structural analysis with photointerpretation and paleo-stress/strain determinations, through inversion of fault-slip data. The high-pressure Voltri Massif belongs to the Internal Pennine Units of the Alps; it is composed mainly of metaophiolites and slices of subcontinental lithospheric mantle. The bedrock is overlain by upper Eocene-lower Oligocene clastic sediments of the Tertiary Piemontese Basin. The late-orogenic structural evolution (i.e. since Oligocene) of the area is complex, with superposition of several tectonic events, in the framework of the Adria-Europe convergence and the opening of the Liguro-Provençal basin (with associated rotation of the Corsica-Sardinia block). On the basis of both fieldwork and photointerpretation, we selected 13 structural stations divided into two groups (north-eastern and western): we have measured more than 500 faults in the field and identified more than 400 lineaments from photointerpretation. Both low-angle thrust faults and high-angle (dominantly strike-slip) faults occur. In the NE sector high-angle faults show a clear NE-SW maximum in strike, whereas in the western sector main sets are WNW-ESE and ENE-WSW striking. Among the collected faults, more than 100 are complete fault-slip data to be analysed by inversion techniques with two different open-source programs (F.s.a. by B. Célérier, 1999 and Tensor by D. Delvaux, 2011). We detected several incompatible stress/strain fields in each structural station, thus implying that the fault population was heterogeneous. On the basis of

  14. Evidence for polymetamorphic garnet growth in the Çine (southern Menderes) Massif, Western Turkey

    NASA Astrophysics Data System (ADS)

    Baker, C. B.; Catlos, E. J.; Sorensen, S. S.; Çemen, I.; Hancer, M.

    2008-07-01

    Garnet-based thermobarometry is often used to develop models for the evolution of the Menderes Massif, a key Aegean metamorphic core complex. Here we present X-ray element maps and high-contrast backscattered electron (BSE) and cathodoluminescence (CL) images from a garnet-bearing rock from the Çine (southern Menderes) Massif. The images document a polymetamorphic history as plagioclase and garnet grains show distinct cores and rims. The sample contains matrix monazite in reaction with allanite. The garnet in the sample is likely not in equilibrium with its matrix minerals. This is evidenced by BSE images that document compositional variability in both core and rim zoning and tracks of bright streaks extending from rim to core. We propose that some garnet that is now present in the Menderes Massif formed due to collision during Cambro-Ordovician and may have recrystallized during subsequent collisional and extensional events. These processes led to non-equilibrium compositions and can result in spurious pressure-temperature (P-T) calculations. To establish the feasibility of the P-T estimates of rocks from the Çine Massif for input into tectonic models for the region, more than one sample from single outcrops should be analyzed. Rocks within the Çine Massif have been suggested to display inverted metamorphism, an increase in T towards structurally higher levels. Based on the garnet documented here, we propose that the inverted metamorphism may be a consequence of apparent P-T rather than a real phenomenon.

  15. Paleoproterozoic anorogenic granitoids of the Zheltav sialic massif (Southern Kazakhstan): Structural position and geochronology

    NASA Astrophysics Data System (ADS)

    Tretyakov, A. A.; Degtyarev, K. E.; Sal'nikova, E. B.; Shatagin, K. N.; Kotov, A. B.; Ryazantsev, A. V.; Pilitsyna, A. V.; Yakovleva, S. Z.; Tolmacheva, E. V.; Plotkina, Yu. V.

    2016-01-01

    The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U-Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural-geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm-Nd isotopic—geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan.

  16. The promotion of geotourism in protected areas: a proposal of itinerary through the Matese Massif (Campania and Molise regions, Italy).

    NASA Astrophysics Data System (ADS)

    Rosskopf, Carmen Maria; Filocamo, Francesca; Amato, Vincenzo; Cesarano, Massimo

    2016-04-01

    The Matese Massif is a ca. 1000 km2 wide and NW-SE elongated carbonate relief, located in the inner sector of the Southern Apennine chain. It has a tabular setting with steep structural slopes bordering the central high mountain sector including its major peaks and is crossed from approximately west to east by the border between Campania and Molise regions. The Matese Mountains represent a key area for the comprehension of the geological and tectonic evolution of the Southern Apennines since Mesozoic times. Its long-term geomorphological evolution has been controlled by Quaternary tectonics and climate variations that have allowed the temporary or permanent establishment of various environments and morphodynamics. Deposits and landforms originated by glacial, periglacial, karst and fluvial processes, along with a rich assemblage of tectonic-structural features and landforms of complex origin have given origin to a geological heritage of exceptional value. The geosites actually censured within the Campanian sector of Matese are reported in the Geosites Map of Campania, available at the website of Campania Region and partly included in the Italian Geosites Inventory of ISPRA. The geosites of the Molise sector have been recently assessed within the geosite inventory carried out by Molise University. They are reported in the Geosites Map of Molise, available at the website of Molise Region, and partly included in the ISPRA's National Inventory of Geosites. The Matese area is largely included in protected areas: the Campania portion falls within the Matese Regional Park, established in 2002, while most of the Molise sector falls in the extensive ZPS/SIC IT72222287. To better protect and exploit the unique natural and geological heritage of the Matese Massif, numerous initiatives aimed at the establishment of the National Park of Matese have continued for several years and very recent attempts to promote the Matese Geopark have been made, but unfortunately without any

  17. A Library Response to the Massification of Higher Education: The Case of the University of Zambia Library

    ERIC Educational Resources Information Center

    Kanyengo, Christine Wamunyima

    2009-01-01

    This paper looks at the challenges that libraries in Africa face in responding to massification of higher education by discussing the University of Zambia library's response in library and information resources provision. As a result of massification of higher education, libraries have been forced not only to employ new and different strategies to…

  18. Critical Reflection on the Massification of Higher Education in Korea: Consequences for Graduate Employment and Policy Issues

    ERIC Educational Resources Information Center

    Yeom, Min-ho

    2016-01-01

    The paper critically reviews the results of Korean massification in higher education (HE) and focuses on the consequences related to graduate employment. By analysing statistical data and reviewing related articles, this study explores the process of the massification of HE, investigates major factors influencing the expansion, and analyses and…

  19. Geomorphological and sedimentological evidences in the Western Massif of Picos de Europa since the Last Glaciation

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesus; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Conceição Freitas, Maria; García-Hernández, Cristina; Nieuwendam, Alexandre; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2015-04-01

    The Western Massif of Picos de Europa includes some of the highest peaks of the Cantabrian Mountains. However, the environmental evolution in this massif since the Last Glaciation is still poorly understood. This research provides a new geochronological approach to the sequence of environmental events occurred here since the maximum expansion of glaciers during the last Pleistocene glaciation. The distribution of the glacial landforms suggests four main stages regarding the environmental evolution in the massif: maximum glacial advance, phase of second maximum glacial expansion, Late Glacial and Little Ice Age. A 5.4-m long sedimentological section retrieved from the kame terrace of Belbín, in a mid-height area of the massif, complements the geomorphological interpretation and provides a continuous paleoenvironmental sequence from this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, a new glacial expansion occurred around 18.7-22.5 ka cal BP. The melting of the glaciers after this phase generated a shallow lake in the Belbín depression. Lake sediments do not reveal the occurrence of a cold stage during the Late Glacial, whilst, at higher locations, moraine complexes were formed suggesting a glacier readvance. The terrestrification of this lake started at 8 ka cal BP, when Belbín changed to a peaty environment. At 5 ka cal BP human occupation started at the high lands of the massif according to the existence of charcoal particles in the section. The presence of moraines in the highest northern cirques evidences the last phase with formation of small glaciers in the Western Massif of Picos de Europa, corresponding to the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers.

  20. Geochemistry of alkali syenites from the Budun massif and their petrogenetic properties (Ol'khon Island)

    NASA Astrophysics Data System (ADS)

    Makrygina, V. A.; Suvorova, L. F.; Zarubina, O. V.; Bryanskii, N. V.

    2016-07-01

    The first data on the geochemistry of the alkali syenite massif in Cape Budun of Ol'khon Island, where it makes contact in the south with the Khuzir gabbroid massif, are presented. Syenites occur among granite gneisses of the Sharanur dome and, like its granites, are enriched with Zr and REEs, but depleted in other trace elements. They contain anorthoclase, corundum, rare nepheline, zircon, and hercynite and are accompanied by desilicified pegmatites. Their unusual geochemical properties allow the assumption that alkaline magmas resulted from the interaction between basic and granitoid melts.

  1. Subduction petrofabrics of lawsonite eclogite and blueschist facies rocks, Sivrihisar massif, Turkey

    NASA Astrophysics Data System (ADS)

    Seaton, N. C.; Whitney, D. L.; Teyssier, C.; Toraman, E.

    2011-12-01

    The Sivrihisar Massif, west-central Turkey, is an exhumed subduction complex consisting of metasedimentary and metabasaltic rocks that record lawsonite blueschist and eclogite facies conditions of metamorphism and deformation. Layers of marble, quartzite, calc-schist, and blueschist contain m-scale pods of lawsonite eclogite in the NW part of the massif. All rock types preserve textures and/or mineral assemblages that provide clues to metamorphic and deformation conditions at P > 2 GPa. To the SE, lawsonite has been replaced by epidote in metabasalt, indicating higher T conditions of metamorphism; EBSD analyses of quartz in quartzite and calcite in marble also show a progressive overprinting of HP microstructures. In the region most affected by overprinting, a progressive recrystallization front is observed in a change in calcite texture in marble, a change in white mica composition in quartzite, and transformation of eclogite and blueschist to greenschist and amphibolite. In this region, HP marble is characterized by rod-shaped calcite with long axes parallel to each other and oblique to foliation; most rods have a high angle to the foliation plane but some are sub-horizontal. Calcite rods are pseudomorphs after aragonite and have a strong CPO with the c-axis close to the long axis of the rods, irrespective of the orientation of the rod long axis relative to foliation. A narrow zone of partial recrystallization exists where the calcite rods are partially replaced by chains of small equant grains that maintain the CPO of the rods. This is succeeded by a narrow zone of recrystallized, equant calcite: rods are absent but CPO remains. At higher T (amphibolite facies), calcite grains are large and equant and have no CPO. In the lawsonite eclogite-bearing unit, quartzite is characterized by a single girdle c-axis fabric with some asymmetry, and some samples show a prism point maximum. All show top-to-E (NE) shear sense, which is consistent with kinematic criteria in

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

    NASA Astrophysics Data System (ADS)

    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

  3. Structural geology and sedimentology of the Sermat Quartzites, Strandja Massif, NW Turkey

    NASA Astrophysics Data System (ADS)

    Yazıcı, Müge; Natal'in, Boris A.

    2015-04-01

    The Strandja Massif, NW Turkey, is the eastern continuation of the Rhodope Massif in Bulgaria. The massif is generally correlated with the Hercynian orogenic belt that was later modified by the Cimmerian orogeny. The basement of the massif is composed by various kinds of gneisses and schists, which are intruded by the metagranites. In the studied area, the Cambrian K-feldspar metagranites are unconformably overlain by metaclastics, where both units have fault contacts with volcano-sedimentary rocks. The metagranite intrusions yield Carboniferous U-Pb zircon ages (Natal'in et al., 2012a). All of them constitute the basement of the Strandja Massif. Cambrian age of metagranites and their subduction related nature as well as the subduction related nature of the Carboniferous igneous rocks suggest a prolong evolution of the Strandja Massif (Natal'in et al., 2012a). The Cambrian metagranites are unconformably overlain by a metasedimetary cover unit, which is known in the literature as the Şermat Quartzite of presumably Permo-Triassic age (Çağlayan and Yurtsever, 1998). In the studied region, detrital zircons extracted from quartzites show that their depositional age is not younger than the Ordovician (Natal'in et al., 2012a). The basement of the Strandja Massif is subjected to the epidote-amphibolite-greenschist facies of metamorphism and high strain deformation in the late Jurassic - early Cretaceous times. The Şermat Quartzite forms a transgressive sequence, which starts with metaconglomerates, metasandstones and grades up to quartz-sericite schists. The thickness of bedding changes from thin to medium with parallel bedding planes, containing lens-shaped bodies of massive quartzites. The late Jurassic - early Cretaceous foliation (S1) is generally parallel to the primary bedding plane. Foliations and lineations consistently dip to the northeast and kinematic indicators suggest a tectonic transport in the same direction. High strain in the Şermat Quartzite

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

    ERIC Educational Resources Information Center

    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…

  5. Unique paragenesis of cerium and yttrium allanites in tourmalinite of the Severny massif (Chukotka)

    NASA Astrophysics Data System (ADS)

    Alekseev, V. I.; Marin, Yu. B.

    2016-07-01

    A description of hydrothermal allanite-(Y) and its unique association with allanite-(Ce) from tourmaline metasomatic rock of the Severny granite massif in Chukotka is presented in the article. Examination of the composition of metasomatic rims in allanite-(Y) allowed us to estimate the limit of isomorphic replacement in allanite of Y and heavy lanthanides by LREE, reaching 25%.

  6. Structure, age, and ore potential of the Burpala rare-metal alkaline massif, northern Baikal region

    NASA Astrophysics Data System (ADS)

    Vladykin, N. V.; Sotnikova, I. A.; Kotov, A. B.; Yarmolyuk, V. V.; Sal'nikova, E. B.; Yakovleva, S. Z.

    2014-07-01

    The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.

  7. Time of formation and genesis of yttrium-zirconium mineralization in the Sakharjok massif, Kola Peninsula

    NASA Astrophysics Data System (ADS)

    Vetrin, V. R.; Skublov, S. G.; Balashov, Yu. A.; Lyalina, L. M.; Rodionov, N. V.

    2014-12-01

    The Kola geotectonic province in the northeastern Fennoscandian Shield accommodates a significant number of alkaline rock massifs differing in age. They are of mantle and mantle-crustal origin (alkali and nepheline syenites, carbonatites) and related to crustal sources (Neoarchean alkali granites). Among them, the Neoarchean Sakharjok nepheline syenite massif is related to the oldest intrusions of this kind bearing yttrium-zirconium mineralization. The crystallization of alkali syenite pertaining to the first intrusive phase of the intrusive Sakharjok massif is dated to 2645 ± 7 Ma, and this implies that this syenite postdated alkali granites (2.66-2.67 Ga). To date the yttrium-zirconium ore, we applied the local U-Pb method to zircon crystals occurring in the mineralized block hosted in nepheline syenite. The earliest fragments of zircon crystallized 1832 ± 7 Ma ago; the age of metamorphism is estimated at 1784 ± 13 Ma. These dates indicate the Paleoproterozoic age of the yttrium-zirconium mineralization, which was formed as a product of fluid reworking of the Neoarchean nepheline syenite of the Sakharjok massif.

  8. Massification of University Education in Nigeria: Private Participation and Cost Challenges

    ERIC Educational Resources Information Center

    Ahunanya, S.; Chineze, U.; Nnennaya, I.

    2013-01-01

    This study investigated the massification of university education in Nigeria as a result of the reforms in the education subsector that led to private participation in the provision of university education from 1999. The question of the study hinges on the percentage of access and if the increased number of universities has led to increased…

  9. Niklas - a Hitherto Unknown Deep Magmatic Massif in the Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Rybakov, M.; Voznesensky, V.; Ben-Avraham, Z.

    2004-12-01

    A Niklas massif was discovered recompiling the gravity and magnetic maps and interpreting in 3-D mode all the available data in the area around Eratosthenes Seamount (ESM). The updated datasets clearly show two partially superimposed magnetic dipoles, which also correspond well to disturbances in the gravity field. The pronounced Eratosthenes magnetic anomaly (EMA) is only the positive part of the southeastern dipole. There is no large gravity anomaly here, however the specific gravity pattern corresponds to the magnetic body. The northwestern `magnetic dipole coincides with a prominent (about of 100mGal) gravity high that was recently delineated by Russian geophysicists. Such grav/mag combination allowed us to interpret the anomalies as being caused by a hitherto unknown dense and magnetic body which we have named the Niklas massif. The parameters and depth of causative bodies were calculated by inverse programs and forward modeling using the seismic refraction and reflection constraints. The reliability of the final model was verified using forward modeling. The magnetic data were interpreted by assuming an induced magnetization as the main magnetizing factor. The final model consists of two large compact features oriented NE-SW and located south of the Cyprian arc,as the Eratosthenes and Niklas bodies. The gravity and magnetic pattern of the Niklas is typical for the ophiolite massifs of the Eastern Mediterranean and Southern Turkey (Troodos, Hatay, Antalya). Based on this likeness we assume the Niklas composed by dense and magnetic ophyolites. This large (~100*75km) deep-seated (~7km) thick (~7km) massif is located ~95km southwest of Cyprus. We consider the Niklas as the south-most fragment of the large allochthonous ophiolite thrust slab including the Troodos massif. The tectonic situations of the Niklas area and the central segment of the Cyprian Arc are similar to that of the Eastern Taurus, Bayer-Bassit and Hatay areas. Interaction of the large Late

  10. Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico

    SciTech Connect

    Seni, S.J. )

    1991-03-01

    Salt structures in a 4000-km{sup 2} region of the continental slope, the northeast Green Canyon area, include stocks, massifs, remnant structures, and an allochthonous sheet. Salt-withdrawal basins include typical semicircular basins and an extensive linear trough that is largely salt-free. Counterregional growth faults truncate the landward margin of salt sheets that extend 30-50 km to the Sigsbee Escarpment. The withdrawal basins, stocks, and massifs occur within a large graben between an east-northeast-trending landward zone of shelf-margin growth faults and a parallel trend of counterregional growth faults located 48-64 km basinward. The graben formed by extension and subsidence as burial of the updip portion of a thick salt sheet produced massifs and stocks by downbuilding. Differential loading segmented the updip margin of the salt sheet into stocks and massifs separated by salt-withdrawal basins. Initially, low-relief structures evolved by trap-door growth as half-graben basins buried the salt sheet. Remnant-salt structures and a turtle-structure anticline overlay a salt-weld disconformity in sediments formerly separated by a salt sheet. Age of sediments below the weld is inferred to be be late Miocene to early Pliocene (4.6-5.3 Ma); age of sediments above the weld is late Pliocene (2.8-3.5 Ma). The missing interval of time (1-2.5 Ma) is the duration between emplacement of the salt sheet and burial of the sheet. Sheet extrusion began in the late Miocene to early Pliocene, and sheet burial began in the late Pliocene in the area of the submarine trough to early Pleistocene in the area of the massifs.

  11. PGE mineralization of dunite-wehrlite massifs at the Gutara-Uda interfluve, Eastern Sayan

    NASA Astrophysics Data System (ADS)

    Mekhonoshin, A. S.; Tolstykh, N. D.; Podlipsky, M. Yu.; Kolotilina, T. B.; Vishnevsky, A. V.; Benedyuk, Yu. P.

    2013-05-01

    The Pt-Pd and Au-Ag mineralization hosted in both wehrlite without visible links to sulfide mineralization (dispersed assemblage of the Tartai massif) and disseminated Cu-Ni sulfide ore (ore assemblage of the Ognit massif) was found in dunite-wehrlite massifs localized in the fold framework of the Siberian Craton. The Pt minerals in both assemblages comprise sperrylite (PtAs2) and secondary Pt-Fe-Ni alloys in the Ognit massif and Pt-Fe-Cu and Pt-Cu alloys in the Tartai massif. The Pd minerals are widespread in the ore assemblages as compounds with Te, Sb, and Bi, whereas in the dispersed assemblage Pd is concentrated primarily in Pd-Cu-Sb compounds. Both assemblages are characterized by similar substitution of sperrylite with orcelite (Ni5 - xAs2) and then with secondary Pt-Fe-Ni or Pt-Fe-Cu and Pt-Cu alloys; the occurrence of Au-Ag alloys with prevalence of Ag over Au; and replacement of them with auricupride (Cu3Au) at the late stage. Sperrylite in both assemblages contains Ir impurities, while the Pd minerals contain Cu and Ni admixtures, which are typical of mineral assemblages related to the ultramafic intrusions with nickel specialization. PGM were formed under a low sulfur fugacity and high As, Bi, and Sb activities. The postmagmatic fluids affected the primary mineral assemblages under reductive conditions, and this effect resulted in replacement of sperrylite with Ni arsenide (orcelite) and Pt-Fe-Ni and Pt-Fe-Cu alloys; Ni and Cu sulfides were replaced with awaruite and native copper.

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

    NASA Astrophysics Data System (ADS)

    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

  13. Long lasting paleolandscapes stability of the French Massif Central during the Mesozoic

    NASA Astrophysics Data System (ADS)

    Ricordel-Prognon, C.; Thiry, M.; Theveniaut, H.; Lagroix, F.

    2009-04-01

    Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Usually, little is known about geodynamics of the peripheral areas and even less on the evolution of the basement areas. Continental unconformities are essential to estimate erosion rates of basement and to model the crustal dynamics that control subsidence of surrounding sedimentary basins but also uplift and erosion on their edges. Dating such unconformities has always been the stumbling block while it is a prerequisite to constrain geodynamical models. Paleomagnetism has been proven as a suitable tool to date ferrugineous paleoweathering features. The method has been applied to paleoweathering occurrences resting on the Massif Central crystalline basement as well as to paleoweathering features affecting the crystalline basement itself. The remanence measurements were obtained at the Paleomagnetic Laboratory of the Institut Physique du Globe de Paris and data analyses were carried out using PaleoMac 5 software (Cogné, 2003). Relative dating of the paleoweathering profiles have been acquired by comparing the recorded paleomagnetic poles from the analysed samples to the apparent polar wandering path of the Eurasian plate (Edel et Duringer, 1997 ; Besse and Courtillot, 2003). Thick red kaolinitic formations rest locally on the Massif Central basement. They are generally bounded by the Tertiary grabens and buried by the Oligocene formations. Thus these azoic red formations have classically been ascribed to the "Siderolithic" formations of Eocene-Oligocene age. They show many pedogenic features (termites burrows, illuviation and hydromorphic features and nodules) and strong relationships with paleolandscape organisation (leaned against fault scarps, infilling paleovalleys, etc.). Macro and micromorphological arrangements show that these formations are in situ paleosols. Paleomagnetic ages range from 160 Ma (Late Jurassic) in the centre of the Massif Central to 140 Ma (Early

  14. Petrological and geochemical evolution of the Tolbachik volcanic massif, Kamchatka, Russia

    NASA Astrophysics Data System (ADS)

    Churikova, Tatiana G.; Gordeychik, Boris N.; Iwamori, Hikaru; Nakamura, Hitomi; Ishizuka, Osamu; Nishizawa, Tatsuji; Haraguchi, Satoru; Miyazaki, Takashi; Vaglarov, Bogdan S.

    2015-12-01

    Data on the geology, petrography, and geochemistry of Middle-Late-Pleistocene rocks from the Tolbachik volcanic massif (Kamchatka, Klyuchevskaya group of volcanoes) are presented and compared with rocks from the neighboring Mount Povorotnaya, Klyuchevskaya group basement, and Holocene-historical Tolbachik monogenetic cones. Two volcanic series of lavas, middle-K and high-K, are found in the Tolbachik massif. The results of our data analysis and computer modeling of crystallization at different P-T-H2O-fO2 conditions allow us to reconstruct the geochemical history of the massif. The Tolbachik volcanic massif started to form earlier than 86 ka based on K-Ar dating. During the formation of the pedestal and the lower parts of the stratovolcanoes, the middle-K melts, depleted relative to NMORB, fractionated in water-rich conditions (about 3% of H2O). At the Late Pleistocene-Holocene boundary, a large fissure zone was initiated and the geodynamical regime changed. Upwelling associated with intra-arc rifting generated melting from the same mantle source that produced magmas more enriched in incompatible trace elements and subduction components; these magmas are high-K, not depleted relative to N-MORB melts with island arc signatures and rift-like characteristics. The fissure opening caused degassing during magma ascent, and the high-K melts fractionated at anhydrous conditions. These high-K rocks contributed to the formation of the upper parts of stratovolcanoes. At the beginning of Holocene, the high-K rocks became prevalent and formed cinder cones and associated lava fields along the fissure zone. However, some features, including 1975-1976 Northern Breakthrough, are represented by middle-K high-Mg rocks, suggesting that both middle-K and high-K melts still exist in the Tolbachik system. Our results show that fractional crystallization at different water conditions and a variably depleted upper mantle source are responsible for all observed variations in rocks within

  15. Scorpions from the Mitaraka Massif in French Guiana. II. Description of a new species of Ananteris Thorell, 1891 (Scorpiones: Buthidae).

    PubMed

    Lourenço, Wilson R

    2016-01-01

    A new remarkable species belonging to the genus Ananteris Thorell, 1891 (Buthidae) is described from the Mitaraka Massif in French Guiana, a site located near the borders of French Guiana, Brazil, and Suriname. The description of this new species brings further evidence about the biogeographic patterns of distribution presented by most species of the genus Ananteris, which are highly endemic in most biogeographic realms of South America, including the Tepuys and Inselberg Massifs. PMID:27156170

  16. Scorpions from the Mitaraka Massif in French Guiana. II. Description of a new species of Ananteris Thorell, 1891 (Scorpiones: Buthidae).

    PubMed

    Lourenço, Wilson R

    2016-01-01

    A new remarkable species belonging to the genus Ananteris Thorell, 1891 (Buthidae) is described from the Mitaraka Massif in French Guiana, a site located near the borders of French Guiana, Brazil, and Suriname. The description of this new species brings further evidence about the biogeographic patterns of distribution presented by most species of the genus Ananteris, which are highly endemic in most biogeographic realms of South America, including the Tepuys and Inselberg Massifs.

  17. North Massif lithologies and chemical compositions viewed from 2-4 mm particles of soil sample 76503

    NASA Technical Reports Server (NTRS)

    Bishop, Kaylynn M.; Jolliff, Bradley L.; Korotev, Randy L.; Haskin, Larry A.

    1992-01-01

    We identify the lithologic and compositional components of soil 76503 based on INAA of 243 2-4-mm particles and 72 thin sections from these and associated 1-2-mm particles (76502). We present a statistical distribution of the major compositional types as the first step of a detailed comparative study of the North and South Massifs. The soil sample was collected well away from any boulder and is more representative of typical North Massif material than any single large rock or boulder sample. So far, our examination of the 76503 particles has provided a better definition of precursor igneous lithologies and their petrogenetic relationships. It has enabled us to refine the nature of mixing components for the North Massif less than 1-mm fines. It has confirmed the differences in lithologies and their proportions between materials of the North and South Massifs; e.g., the North Massif is distinguished by the absence of a 72275-type KREEP component, the abundance of a highly magnesian igneous component, and the absence of certain types of melt compositions found in the South Massif samples.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  19. Significance of the Early Jurassic Garamilla formation in the western Nordpatagonian Massif

    NASA Astrophysics Data System (ADS)

    Benedini, Leonardo; Gregori, Daniel

    2013-08-01

    By means of facial, stratigraphic, petrographic, geochemical and geochronological studies we characterize the Garamilla Formation, cropping out in the western Nordpatagonian Massif. The studies of these volcanic rocks reveal an Early Jurassic volcanic episode formed by three volcanic units that change from normal calc-alkaline to high-K calc-alkaline series. Other geochemical features reveal a progressive change from an initial subduction-related volcanism to one intraplate-related volcanism. This volcanic episode is temporally and geochemically equivalent to those volcanic units located in half-grabens in several areas of the Neuquén Basin. The volcanic units were erupted into different structural designs. A portion of its depocenter was interpreted as a transtensional half-graben, whereas the other exhibits a trapdoor structure. The lineament trends that bound the volcanic system were also recognized in western Nordpatagonian Massif, and were assigned to the Gondwanide Orogeny.

  20. Two types of noble metal mineralization in the Kaalamo massif (Karelia)

    NASA Astrophysics Data System (ADS)

    Ivashchenko, V. I.; Ruchyev, A. M.; Golubev, A. I.

    2016-05-01

    Noble metal mineralization of the syngenetic (Southern Kaalamo) and epigenetic (Surisuo) types are defined in the Kaalamo massif. The ƩPt, Pd, Au content is as high as 0.9-1.1 g/t. Syngenetic mineralization started at the late magmatic stage (at around 800°C) gradually evolving to cease during the hydrothermal-metasomatic stage (<271°C). Epigenetic mineralization was formed at temperatures ranging from 500 to <230°C in zones of intense shear deformations and low-temperature metasomatosis during the collisional stage of the Svecofennian tectono-magmatic cycle (approximately 1.85 Ga ago). Taking into consideration the geological position of the Kaalamo massif in the Raakhe-Ladoga metallogenic zone with widely developed intense shear dislocations, the epigenetic mineralization type seems to be more promising with respect to noble metals.

  1. Petrology of a stratified boulder from South Massif, Taurus-Littrow. [Apollo 17 lunar rock sample

    NASA Technical Reports Server (NTRS)

    Stoeser, D. B.; Marvin, U. B.; Wood, J. A.; Wolfe, R. W.; Bower, J. F.

    1974-01-01

    Boulder 1 from Station 2 at the foot of South Massif is unique in being the only stratified boulder sampled by the Apollo 17 astronauts. Our studies of two of the four specimens that were collected from separate layers show that the boulder is composed of glass-poor, fragment-rich breccias which are aggregates of differentially annealed terra material, mainly ANT, but including basaltic troctolite, pigeonite basalt, granitic particles, dark breccia-rimmed anorthositic clasts, and a KREEPless norite that has not been recognized elsewhere at the Apollo 17 site. The boulder appears to derive from the uppermost blue-gray layer on South Massif, which we believe consists of ejecta deposited from a single large impact event (possibly the one which excavated the Serenitatis Basin).

  2. Parameters determining the portion of energy radiated during dynamic unloading of a section of rock massif

    NASA Astrophysics Data System (ADS)

    Adushkin, V. V.; Kocharyan, G. G.; Ostapchuk, A. A.

    2016-03-01

    Presented are the main results of laboratory experiments aimed at studing the regularities of transition of the cumulated deformation energy to the kinetic one when a block exhibits stick-slip along model fracture filled with geomaterials with different properties. It was shown that even a small variation of material composition of the fault principal slip zone may result in a significant variation of the portion of seismic energy radiated during dynamic unloading of the enclosing rock massif.

  3. Crustal Structure at the vicinity of Nigde Massif and Central Anatolian Fault Zone from Magnetotelluric Data

    NASA Astrophysics Data System (ADS)

    Tank, B.; Sandvol, E. A.; Karas, M.; Ozaydin, S.

    2015-12-01

    Three magnetotelluric (MT) profiles were constructed to examine the electrical resistivity strucuture of a metamorphic core complex renown as Niğde massif and a northeast - southwest aligned fault zone (Central Anatolian Fault Zone, CAFZ) bounding this massif on the east in Central Anatolia. Nigde massif is a crystalline dome close to Inner-Tauride suture at the southern part of Central Anatolian Crystalline Complex. The sinistral CAFZ (in the south it is called Ecemis fault) is a ~700 km long, 2 to 80 km wide zone with an offset of 60 to 80 km. Northwest-southeast aligned Tuz Gölü (Salt Lake) and Derinkuyu faults are other major features that shape up the study area. A three-dimensional numerical modeling routine based on data-space modeling (WSINV3DMT) was used to invert the MT data collected at 85 high quality soundings. A mesh with 76 x 74 x 40 (7 layers for air) cells was used during the inversions. The resulting models suggest that (i) there is a low conductivity dome-like anomaly that coincides with the Nigde massif (presumably matches with Uckapili granite). (ii) Beneath this low conductivity anomaly there is a deeper (>20 km) high conductivity zone caused by partial melting (iii) Ecemis fault near Pozanti appears as a low to high conductivity interface. (iv) Likewise, Tuz Gölü and Derinkuyu faults appear as a low to high conductivity interfaces representing barriers for fluid flow (v) Adana basin sediments show high conductivity values (vi) Mt. Hasan and Mt. Karaca and the volcanic complexes in between them show highly conductive features in their roots, but (vi) older Mt. Erciyes lacks such a deep conductor.

  4. The deformation of the Egersund Ogna anorthosite massif, south Norway: finite-element modelling of diapirism

    NASA Astrophysics Data System (ADS)

    Barnichon, J. D.; Havenith, H.; Hoffer, B.; Charlier, R.; Jongmans, D.; Duchesne, J. C.

    1999-03-01

    This paper aims at testing the mechanical relevance of the petrological model of anorthosite massif diapiric emplacement. The Egersund-Ogna massif (S. Norway) is of particular interest because recent petrological and geochronological data constrain the initial geometry, emplacement conditions and timing (about 2 m.y.). The formation of this anorthosite massif is in agreement with the classical petrological model, in which accumulation of plagioclase takes place in a deep-seated magma chamber at the crust-mantle limit, from which masses of plagioclase separate and rise through the lower crust up to the final level of emplacement at mid-crustal depths. The Egersund-Ogna massif also displays a foliated inner margin, in which strain ellipsoids have been reconstructed by investigating at 51 sites the deformation of megacrysts of high-alumina orthopyroxene. Based on these petrological data, a model made up of one rigid layer (upper granitic crust) and three viscous layers (lower part of the granitic crust, noritic lower crust and anorthosite) has been built up. The upper crust behaviour is represented by an elastoplastic law and the viscous layers obey elastic-viscoplastic laws with Newtonian viscosity. An inverse density gradient is considered between the lower crust ( d=3.00) and the anorthosite ( d=2.75), the loading consisting only in gravity. The modelling is carried out under axisymmetrical conditions, using the LAGAMINE finite-element code coupled with an automatic re-meshing algorithm designed to deal with large strains in complex structures. The results show that, from a mechanical point of view, the diapirism model is a robust and consistent assumption for the emplacement of anorthosites, because realistic diapir and rim-syncline shapes are obtained. Moreover, the numerically obtained emplacement time (about 2.5 m.y.) is in agreement with the available geochronological data, and the computed strain field is coherent with field measurements, especially regarding

  5. Post-orogenic Extension in NW Anatolia as Indicated by Neogene Exhumation of the Kazdag Massif

    NASA Astrophysics Data System (ADS)

    Cavazza, W.; Okay, A. I.; Zattin, M.

    2006-12-01

    The Kazdag massif is an amphibolite facies metamorphic core complex in NW Anatolia. Apatite fission-track analyses indicate that exhumation of the basement rocks of Kazdag covers a time span between 22 and 11 Ma (i.e. early-middle Miocene), with a cluster of ages at 17-14 Ma. Structural analysis of remnants of low- angle shear zones, high-angle normal faults and strike-slip faults, as well as stratigraphic analysis of upper- plate sedimentary successions, point to a two-stage structural evolution of the massif. The first stage comprised a continuum of chronologically overlapping mechanisms, from late Oligocene-early Miocene low- angle detachment faulting to early Miocene development of small supradetachment grabens filled with a mixture of epiclastic, volcaniclastic and volcanic rocks (Kucukkuyu Fm.). This phase encompassed much of the rapid thermal evolution of the massif, including the emplacement of a suite of granitoid stocks with cooling ages around 21 Ma. Younger fission-track ages are aligned along the borders of the massif, substantiating the notion of a progressive, bivergent denudation along opposing detachment faults whose remnants are still visible. The second stage (Plio-Quaternary) was dominated by strike-slip faulting related to the westward propagation of the North Anatolian fault system and seemingly reactivated Miocene normal faults. This later stage did not have a components of vertical (normal) movement large enough to affect the distribution of fission-track ages, although along the southern flank of Kazdag such vertical component is responsible for the development of the Edremit Gulf, with extensional structural offset in the order of 4,000+ meters. The thermochronological data presented here confirm that widespread extensional tectonism in westernmost Anatolia occurred during early-middle Miocene time.

  6. Timing and Style of Deformation in the Floresta Massif, Axial Eastern Cordillera, Colombia

    NASA Astrophysics Data System (ADS)

    Saylor, J.; Stockli, D. F.; Mora, A.

    2009-12-01

    The Floresta Massif is one of the largest exposures of Paleozoic and Pre-Cambrian rocks in the Eastern Cordillera. Estimates for the age of onset of shortening-related deformation in the Eastern Cordillera range from late Cretaceous to late Miocene (e.g., Hoorn et al., 1995; Bayona et al., 2008; Parra et al., 2009). The massif is typically interpreted as being exhumed along a high-angle reverse fault (the Soapaga fault) that reactivated Mesozoic extensional structures (e.g., Kammer and Sanchez, 2006). We examined these dual linked issued with new zircon U/Th-He (ZHe) data, new geological mapping and previously published apatite fission track (AFT) data from the Floresta Massif and the associated footwall strata. Previously, an overturned Paleozoic - Cretaceous sequence was mapped emplaced on Tertiary strata along the Soapaga fault. However, new geologic mapping identifies two previously unrecognized thrusts which place, from west to east, Paleozoic strata on Jurassic strata (Fault 3), Jurassic strata on Cretaceous strata (Fault 2) and Cretaceous strata on Tertiary strata (along the previously identified Fault 1). These results are confirmed by AFT and ZHe data. ZHe ages show no resetting in the Tertiary footwall strata, but show partial resetting in the Cretaceous strata and full resetting in the Jurassic and Paleozoic strata. Similarly, AFT data show older ages in the Cretaceous strata than in the Jurassic or Paleozoic strata. Fully reset ZHe ages from Jurassic strata show that exhumation of the Floresta Massif was ongoing by at least the early Oligocene (~ 30 Ma). However, this deformation post-dates an older episode of deformation associated with partially reset ZHe ages in the Cretaceous strata. Based on a decrease in lag time in detrital ZHe data, we infer that the earlier episode of deformation occurred in the mid - late Eocene (45 - 35 Ma).

  7. Mineralogy and geochemistry of the Tartai massif, East Siberian metallogenic province

    NASA Astrophysics Data System (ADS)

    Podlipsky, M. Yu.; Mekhonoshin, A. S.; Tolstykh, N. D.; Vishnevskiy, A. V.; Polyakov, G. V.

    2015-05-01

    The Tartai ultramafic-mafic massif is located in the central part of the East Siberian metallogenic (PGE-Cu-Ni) province (728-712 Ma), which constitutes part of the southern margin of the Siberian craton. This dunite-peridotite-pyroxenite-gabbro massif is the host to low-sulfide PGE-Cu-Ni mineralization. The massif was formed by fractional crystallization of picritic magmas and is composed of wehrlite, dunite, plagiowehrlite, and olivine melanogabbro. The composition of olivine varies from Fo89.9 in dunite to Fo83 in melanocratic olivine gabbro; clinopyroxene is esentially augite. Chrome-spinels crystallized at a low degree of oxidation and have a high iron content. Disseminated sulfide mineralization (pentlandite and heazlewoodite) with high PGE concentrations was identified in wehrlites. Pentlandite is enriched in Fe and Co and depleted in S. These features and the association pentlandite with heazlewoodite suggest that the sulfide mineralization was formed over a wide temperature range (600-400°C) at low sulfur activity (log fS2 from -16 to -9). PGM are represented by Ir-bearing sperrylite, Pd-Cu-Sb panning compounds of variable compositions, Pt-Fe-Cu and Pt-Cu alloys. The evolutionary trend of the ore system was from essentially Ni compositions at the early magmatic stage during formation of disseminated mineralization toward Cu-rich composition at the post-magmatic stage. The PGM assemblage from heavy concentrate haloes differs from bedrock-hosted mineralization in its wider variety of mineral species and the presence of refractory platinoids. Sperrylite from heavy concentrate haloes of the Tartai massif serves as a reliable prospecting guide for bedrock-hosted sulfide Cu-Ni deposits.

  8. Re-Os isotopic evidence for a lower crustal origin of massif-type anorthosites

    PubMed

    Schiellerup; Lambert; Prestvik; Robins; McBride; Larsen

    2000-06-15

    Massif-type anorthosites are large igneous complexes of Proterozoic age. They are almost monomineralic, representing vast accumulations of plagioclase with subordinate pyroxene or olivine and Fe-Ti oxides--the 930-Myr-old Rogaland anorthosite province in southwest Norway represents one of the youngest known expressions of such magmatism. The source of the magma and geodynamic setting of massif-type anorthosites remain long-standing controversies in Precambrian geology, with no consensus existing as to the nature of the parental magmas or whether these magmas primarily originate in the Earth's mantle or crust. At present, massif-type anorthosites are believed to have crystallized from either crustally contaminated mantle-derived melts that have fractionated olivine and pyroxenes at depth or primary aluminous gabbroic to jotunitic melts derived from the lower continental crust. Here we report rhenium and osmium isotopic data from the Rogaland anorthosite province that strongly support a lower crustal source for the parental magmas. There is no evidence of significantly older crust in southwest Scandinavia and models invoking crustal contamination of mantle-derived magmas fail to account for the isotopic data from the Rogaland province. Initial osmium and neodymium isotopic values testify to the melting of mafic source rocks in the lower crust with an age of 1,400-1,550 Myr. PMID:10866196

  9. Chain Lakes massif, west central Maine: northern Appalachian basement or suspect terrane

    SciTech Connect

    Cheatham, M.M.; Olszewski, W.J. Jr.; Gaudette, H.E.

    1985-01-01

    The Chain Lakes massif of west-central Main is a 3 km thick sequence of diamictite and aquagene metavolcanics and metasediments, which contrasts strikingly with its surrounding Paleozoic rocks in lithology, structural style and metamorphic grade. The rocks of the massif are characterized by mineral assemblages developed during two separate metamorphic events. The first, of second sillimanite grade, is reflected by qtz-oligoclase-Kspar-sillimanite-biotite and muscovite. The second metamorphism is a retrograde event of greenschist facies, and chlorite grade. Isotopic Rb-Sr and Sm-Nd whole rock, and Rb-Sr mineral analyses of samples of the diamictite members, now gneiss and granofels, indicate that the first prograde metamorphism occurred at 770 Ma. with the retrograde event at approximately 405 Ma. Due to the restricted range of /sup 147/Sm//sup 144/Nd, no Sm-Nd isochron age could be determined. However, model ages for both Sr and Nd are approximately 1500 Ma for derivation of the Chain Lakes protolith material from depleted mantle. Lithology, bounding formations, complexes and plutons, and the isotopic data support previous contentions that the Chain Lakes massif is a suspect terrane. However, similarities with Proterozoic rocks along the Eastern Margin, as well as recent suggestions of similar rocks underlying the Kearsarge-Central Main synclinorium may suggest the possible widespread occurrence of dismembered masses of a perhaps once coherent, Precambrian terrane underlying the Northern Appalachians.

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

    NASA Astrophysics Data System (ADS)

    Rozenberg, K. A.; Rastsvetaeva, R. K.; Aksenov, S. M.

    2016-09-01

    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 Na37Ca10Mn2FeZr6Si50(Ti, Nb)2O144(OH)5Cl3 · H2O. 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.

  11. Re-Os isotopic evidence for a lower crustal origin of massif-type anorthosites

    PubMed

    Schiellerup; Lambert; Prestvik; Robins; McBride; Larsen

    2000-06-15

    Massif-type anorthosites are large igneous complexes of Proterozoic age. They are almost monomineralic, representing vast accumulations of plagioclase with subordinate pyroxene or olivine and Fe-Ti oxides--the 930-Myr-old Rogaland anorthosite province in southwest Norway represents one of the youngest known expressions of such magmatism. The source of the magma and geodynamic setting of massif-type anorthosites remain long-standing controversies in Precambrian geology, with no consensus existing as to the nature of the parental magmas or whether these magmas primarily originate in the Earth's mantle or crust. At present, massif-type anorthosites are believed to have crystallized from either crustally contaminated mantle-derived melts that have fractionated olivine and pyroxenes at depth or primary aluminous gabbroic to jotunitic melts derived from the lower continental crust. Here we report rhenium and osmium isotopic data from the Rogaland anorthosite province that strongly support a lower crustal source for the parental magmas. There is no evidence of significantly older crust in southwest Scandinavia and models invoking crustal contamination of mantle-derived magmas fail to account for the isotopic data from the Rogaland province. Initial osmium and neodymium isotopic values testify to the melting of mafic source rocks in the lower crust with an age of 1,400-1,550 Myr.

  12. Crystallization and emplacement of the Lac St-Jean anorthosite massif (Quebec, Canada)

    NASA Astrophysics Data System (ADS)

    Woussen, G.; Dimroth, E.; Corriveau, L.; Archer, P.

    1981-05-01

    The Lac St-Jean anorthosite massif underlies an area of over 20,000 km2 and has been emplaced into migmatitic gneisses of the central granulite terrain of the Grenville Province of the Canadian shield. Field data and petrography in an area straddling the anorthosite-gneiss contact, close to Chicoutimi (Quebec) permits an outline of its tecto-magmatic evolution. Depositional magmatic textures in the massif reveals that it crystallized from a magma in a relatively calm tectonic environment. The absence of fusion in pelitic gneisses at the contact proves that the crystallization did not take place at the level presently exposed. The parallelism of subvertical foliation in the enveloping gneisses and the anorthosite indicates that both were deformed together. It is suggested that the deformation results from a diapiric ascent of the anorthosite massif after its consolidation at depth. The depth of consolidation of the anorthosite is estimated at ˜ 25 30 km from subsolidus reaction between plagioclase and olivine. The diapiric ascent is further substantiated by the fact that three sets of mafic dykes of different ages, intrusive into the anorthosite, have a mineralogy which indicates successively decreasing P, T conditions of emplacement from granulite fades to amphibolite facies. An evolution of the basement gneisses and the anorthosite is proposed as a working hypothesis; it relies on the fact that metabasite dyke swarms in the basement gneisses represent a period of major crustal extension and could be used as a stratigraphic subdivision of the Grenville Province.

  13. Origin and significance of tourmalinites and tourmaline-bearing rocks of Menderes Massif, western Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Yücel-Öztürk, Yeşim; Helvacı, Cahit; Palmer, Martin R.; Ersoy, E. Yalçın; Freslon, Nicolas

    2015-03-01

    In the western central portion of Anatolia lies the Menderes Massif - a large metamorphic crystalline complex made of Neoproterozoic to Precambrian basement rocks overlain by Palaeozoic to early Tertiary metasedimentary rocks, and with a multistage metamorphic evolution developed from the late Neo-Proterozoic to Eocene. We have undertaken a study of the petrology, geochemistry and boron isotope composition of these tourmaline occurrences aiming to constrain the processes responsible for the enrichment of boron and other fluid mobile elements in the Menderes Massif. The dispersed tourmaline has chemical and boron isotope compositions typical of a continental crust setting, but while some of the tourmalinites display similar signatures, others have heavier boron isotope compositions (up to + 7.5‰). We suggest that the tourmalinites with continental characteristics formed part of the original Pan African basement rocks, whereas those with heavier δ11B signatures formed by later metamorphism during the Alpine orogeny, possibly through interaction with subduction-like fluids. This proposed process may also have been coincident with metasomatism of the lithospheric mantle beneath the massif, which is known to have experienced multistage metasomatism and enrichment history up to Neogene time.

  14. Soil mesofauna in disturbed spruce forest stands near Čertovo and Plešné Lakes, the Bohemian Forest: preliminary results

    NASA Astrophysics Data System (ADS)

    Čuchta, Peter; Starý, Jozef

    2016-04-01

    The soil microarthropod communities were studied in disturbed spruce forest stands in the catchments areas of Čertovo (CT) and Plešné (PL) Lakes in the Bohemian Forest, Czech Republic. The study is focused on the impact of the windthrow, bark beetle outbreak damage and consecutive changes in the forest stands including soil environment. Within the soil microarthropods, two main groups, Collembola (Hexapoda) and Oribatida (Acari) are analysed. Four different treatments were selected for the study on both study areas: CT1 and PL1 stands - undamaged control forest stands, CT2 and PL2 stands - "dead" forest stands damaged by bark beetle, CT3 and PL3 stands - slightly managed windthrown forest stands left for the natural succession, and CT4 and PL4 stands - harvested windthrown stands. Soil samples were taken in June (CT1/PL1 - CT3/PL3), July and October (CT1/PL1 - CT4/PL4) 2012 from each treatment. Microarthropods were subsequently extracted in a modified high-gradient apparatus in the laboratory for seven days. Finally, the comparison of the microarthropod assemblages found at different treatment stands was performed. The most abundant groups in both study areas (Čertovo and Plešné Lakes) were Collembola and Oribatida with considerable diferences within particular treatments and in time as well.

  15. Geophysical Constraints on the Nature of Atlantis Massif, 30°N MAR

    NASA Astrophysics Data System (ADS)

    Blackman, D.

    2005-12-01

    Recent drilling at Atlantis Massif, Mid-Atlantic Ridge 30°N, provides new insights into oceanic core complex (OCC) development. IODP Expeditions 304/305 had high recovery in the footwall of the detachment capping the central dome of the massif: Hole U1309B, 100 m deep; Hole U1309D, 1415 m. Recovery of a dominantly gabbroic sequence challenges prior interpretations that this OCC was mainly ultramafic, geophysical data having suggested much of the uplifted core was mantle peridotite, with Moho less than 1 km deep. Although models based on prior analysis fit the data well and were consistent with outcrops of serpentinized peridotite on the south face of Atlantis Massif, it is now clear that additional complexity needs to be incorporated in the geophysical analysis. The southern ridge is morphologically distinct from the central dome. Does this indicate that the south and central parts of this OCC are fundamentally different? Or, is the serpentinized peridotite exposed on the south wall (and found in a few loose fragments on top of the central dome) a thin veneer of mantle rock that has deformed around a dominantly gabbroic core? The occurrence of many gabbroic samples from the southern ridge could support the latter but models of serpentinization that drives the Lost City hydrothermal system near the peak of the massif might favor the former. New analysis of geophysical data provide further constraints on the scale of possible variability. Prior seismic analysis suggested fresh mantle might shoal by a couple hundred meters 1-2 km north of Site U1309. In contrast, gravity data suggest the highest density rocks occur at and to the south of the site. These observations will be combined in a 3D model of Atlantis Massif and we expect to report initial results. Downhole logging indicates that bulk density increases steadily from 2.8 to 2.9 g/cc downhole. Log and core sample seismic velocity are variable within a 5.5-6.8 km/s range, lower values where degree of alteration

  16. Jurassic hot spring deposits of the Deseado Massif (Patagonia, Argentina): Characteristics and controls on regional distribution

    NASA Astrophysics Data System (ADS)

    Guido, Diego M.; Campbell, Kathleen A.

    2011-06-01

    The Deseado Massif, Santa Cruz Province, Argentinean Patagonia, hosts numerous Middle to Late Jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs (sinters and travertines, respectively), hydrothermal breccias, quartz veins, and widespread hydrothermal silicification. They indicate pauses in explosive volcanic activity, marking the final stages in the evolution of an extensive Jurassic (ca. 178-151 Ma) volcanic complex set in a diffuse extensional back-arc setting heralding the opening of the Atlantic Ocean. Published paleo-hot spring sites for the Deseado Massif, plus additional sites identified during our recent field studies, reveal a total of 23 locations, five of which were studied in detail to determine their geologic and facies associations. They show structural, lithologic, textural and biotic similarities with Miocene to Recent hot spring systems from the Taupo and Coromandel volcanic zones, New Zealand, as well as with modern examples from Yellowstone National Park, U.S.A. These comparisons aid in the definition of facies assemblages for Deseado Massif deposits - proximal, middle apron and distal siliceous sinter and travertine terraces and mounds, with preservation of many types of stromatolitic fabrics - that likely were controlled by formation temperature, pH, hydrodynamics and fluid compositions. Locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and/or fluvial sediments, silicic to intermediate lava domes, and hydrothermal mineralization, all of which are related to local and regional structural lineaments. Moreover, the numerous geothermal and significant epithermal (those with published minable resources) deposits of the Deseado Massif geological province mostly occur in four regional NNW and WNW hydrothermal-structural belts (Northwestern, Northern, Central, and Southern), defined here by alignment of five or more hot

  17. Mapping of the Ronda peridotite massif (Spain) from AVIRIS spectro-imaging survey: A first attempt

    NASA Technical Reports Server (NTRS)

    Pinet, P. C.; Chabrillat, S.; Ceuleneer, G.

    1993-01-01

    In both AVIRIS and ISM data, through the use of mixing models, geological boundaries of the Ronda massif are identified with respect to the surrounding rocks. We can also yield first-order vegetation maps. ISM and AVIRIS instruments give consistent results. On the basis of endmember fraction images, it is then possible to discard areas highly vegetated or not belonging to the peridotite massif. Within the remaining part of the mosaic, spectro-mixing analysis reveals spectral variations in the peridotite massif between the well-exposed areas. Spatially organized units are depicted, related to differences in the relative depth of the absorption band at 1 micron, and it may be due to a different pyroxene content. At this stage, it is worth noting that, although mineralogical variations observed in the rocks are at a sub-pixel scale for the airborne analysis, we see an emerging spatial pattern in the distribution of spectral variations across the massif which might be prevailingly related to mineralogy. Although it is known from fieldwork that the Ronda peridotite massif exhibits mineralogical variations at local scale in the content of pyroxene, and at regional scale in different mineral facies, ranging from garnet-, to spinel- to plagioclase-lherzolites, no attempt has been done yet to produce a synoptic map relating the two scales of analysis. The present work is a first attempt to reach this objective, though a lot more work is still required. In particular, for the purpose of mineralogical interpretation, it is critical to relate the airborne observation to field work and laboratory spectra of Ronda rocks already obtained, with the use of image endmembers and associated reference endmembers. Also, the pretty rough linear mixing model used here is taken as a 'black-box' process which does not necessarily apply correctly to the physical situation at the sub-pixel level. One may think of using the ground-truth observations bearing on the sub-pixel statistical

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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. New Isotopic age data for understanding the resetting radioactive clock of the Kazdaǧı Massif (Western Anatolia, Turkey)

    NASA Astrophysics Data System (ADS)

    Hasözbek, Altug; Akay, Erhan; Sherlock, Sarah Christine

    2016-04-01

    The Kazdaǧı Massif comprises one of the well-known high-grade metamorphic complexes in the western Anatolia (Turkey). This high-grade succession is subdivided into two units, which is separated by regionally defined unconformity. The lower unit defines a typical oceanic crust package including ultramafic rocks and cumulate gabbros (Tozlu metaophiolite unit). The upper unit comprises of a thick platform succession of detritals and carbonates with mafic volcanic intercalations. Carbonates of this succession are now found as white coarse-crystalline marbles, detritals are schists, metagranites and migmatites and mafic volcanic intercalations are as amphibolites (Sarikiz unit). The whole sequence is cut by shallow-seated Late Oligocene-Early Miocene non-metamorphic granites (Evciler, Eybek granites). New 40Ar-39Ar amphibole ages of 22-19.7 Ma state that both associations of the Tozlu metaophiolite and Sarıkız units experienced almost the same age era as the youngest granites (Evciler, Eybek granites) in the study area. In addition to that, previous U-Pb zircon age results indicate a peak metamorphism age of the Kazdaǧı Massif is around 30-35 Ma. Such young Ar-Ar ages from the Kazdaǧı Massif, which gather close to the granite intrusion crystallization ages, are likely indicators of the resetting radioactive clock of the Kazdaǧı Massif. This data is also in agreement of a single stage migmatization of the massif during the Alpine Orogeny.

  1. Amphibole genesis in pyroxenites from the Beni Bousera peridotite massif (Rif, Morocco): Evidence for two different metasomatic episodes

    NASA Astrophysics Data System (ADS)

    El Atrassi, Fatima; Chazot, Gilles; Brunet, Fabrice; Chopin, Christian; Bouybaouene, Mohamed

    2014-11-01

    The presence of variable amounts of amphibole ± phlogopite in a garnet websterite and a garnet clinopyroxenite from the Beni Bousera peridotite massif provides evidence for post-formation metasomatism. Textural observations associated with major- and trace-element mineral compositions allowed us to distinguish two metasomatic episodes, which occurred at different stages of the Beni Bousera massif evolution. The garnet websterite has recorded interaction with LREE-rich silicate melts before the uplift of the massif. Amphibole/clinopyroxene and amphibole/garnet trace-element ratios closely approach partition coefficient values, indicating that chemical equilibrium was attained between amphibole and pyroxenite matrix minerals. The geochemical signatures of the putative alkaline interacting melts are similar to those of recent basaltic magmas erupted in Morocco, suggesting a common peridotite mantle source. In contrast, amphibole from the garnet clinopyroxenite is in chemical disequilibrium with the pyroxenite matrix minerals. In this clinopyroxenite the crystallization of amphibole and plagioclase occurred at lower T (and P) conditions, most probably during the ascent of the Beni Bousera massif and its emplacement into the crust. The melt responsible for this later metasomatic episode was LREE-depleted and HREE-enriched, suggesting that it resulted from decompression melting of a garnet-bearing source (with garnet as a melting phase), similar to the garnet-bearing pyroxenites outcropping in the Beni Bousera massif.

  2. Diverse subaerial and sublacustrine hot spring settings of the Cerro Negro epithermal system (Jurassic, Deseado Massif), Patagonia, Argentina

    NASA Astrophysics Data System (ADS)

    Guido, Diego M.; Campbell, Kathleen A.

    2012-06-01

    The Late Jurassic (~ 150 Ma) Cerro Negro volcanic-epithermal-geothermal system (~ 15 km2 area), Deseado Massif, Patagonia, Argentina, includes two inferred volcanic emission centers characterized by rhyolitic domes linked along NW-SE regional faults that are associated with deeper level Au/Ag mineralization to the NW, and with shallow epithermal quartz veins and mainly travertine surface hot spring manifestations to the SE. Some travertines are silica-replaced, and siliceous and mixed silica-carbonate geothermal deposits also are found. Five hot spring-related facies associations were mapped in detail, which show morphological and textural similarities to Pleistocene-Recent geothermal deposits at Yellowstone National Park (U.S.A.), the Kenya Rift Valley, and elsewhere. They are interpreted to represent subaerial travertine fissure ridge/mound deposits (low-flow spring discharge) and apron terraces (high-flow spring discharge), as well as mixed silica-carbonate lake margin and shallow lake terrace vent-conduit tubes, stromatolitic mounds, and volcano-shaped cones. The nearly 200 mapped fossil vent-associated deposits at Cerro Negro are on a geographical and numerical scale comparable with subaerial and sublacustrine hydrothermal vents at Mammoth Hot Springs, and affiliated with Yellowstone Lake, respectively. Overall, the Cerro Negro geothermal system yields paleoenvironmentally significant textural details of variable quality, owing to both the differential preservation potential of particular subaerial versus subaqueous facies, as well as to the timing and extent of carbonate diagenesis and silica replacement of some deposits. For example, the western fault associated with the Eureka epithermal quartz vein facilitated early silicification of the travertine deposits in the SE volcanic emission center, thereby preserving high-quality, microbial macro- and micro-textures of this silica-replaced "pseudosinter." Cerro Negro provides an opportunity to reconstruct

  3. Genesis of platinum-bearing ultrabasic massifs in the plutonic chambers: evidence from melt inclusions

    NASA Astrophysics Data System (ADS)

    Simonov, V.; Prikhod'ko, V.

    2012-04-01

    Platinum-bearing ultramafic massifs occur as bodies of concentrically zonal inner structures due to the successive replacement of dunite with pyroxenite and gabbro from their cores to margins. A most important peculiarity of such massifs is their dunite cores, to which commercial Pt deposits are related. There are a different opinions about genesis of these massifs and geological, petrological, geochemical methods not always can solve this question. We found melt inclusions in Cr-spinel from dunites of the platinum-bearing Konder and Inagli massifs (Siberian Platform) and this provides direct evidence of the participation of magmatic systems in the crystallization of ultrabasic rocks. Contents of most major chemical components in the heated and quenched melt inclusions are close to those in biotite-pyroxene picrite and this testifies dunite crystallization from ultrabasic alkaline magma. Ion probe analyses of melt inclusions in Cr-spinel yielded relatively high water concentration in ultrabasic melts of the Konder (0.45-0.53 wt %) and Inagli (up to 0.63 wt %) massifs. These data are generally close to the water contents in magma that produced dunites of ophiolites (0.58-0.65 wt %) (Simonov et al., 2009). The REE patterns of inclusions in Cr-spinel from the Konder and Inagli dunites show a pronounced negative slope with strong enrichment of LREE relative to HREE, as is typical of plume-related magmatic systems of oceanic islands and continental hotspots. The values of such indicator ratios as Nb/U (23.4), Zr/Nb (7.20), and Th/U (3.0) of inclusions practically exactly coincide with those of glasses from areas of continental hotspots (Naumov et al., 2010). At the Nb/Y-Zr/Y diagram the data points of the inclusions plot within the field of melts with a plume source. As a whole the patterns of trace elements and REE in melt inclusions in the Cr-spinel provide evidence that mantle plumes affected the magmatic events, that produced dunites of the studied platinum

  4. Thermal and structural evolution of the external Western Alps: Insights from (U-Th-Sm)/He thermochronology and RSCM thermometry in the Aiguilles Rouges/Mont Blanc massifs

    NASA Astrophysics Data System (ADS)

    Boutoux, A.; Bellahsen, N.; Nanni, U.; Pik, R.; Verlaguet, A.; Rolland, Y.; Lacombe, O.

    2016-06-01

    In the Western Alps, the External Crystalline Massifs (ECM) are key places to investigate the kinematics and thermal structure of a collisional crustal wedge, as their paleo-brittle/ductile transition is now exhumed at the surface. New (U-Th-Sm)/He data on zircon and new Raman Spectroscopy on Carbonaceous Material (RSCM) data from the Aiguilles Rouges and the Mont Blanc massifs, coupled to HeFTy thermal modeling, constrain the thermal evolution and exhumation of the massifs. In the cover of the Aiguilles Rouges massif, we found that the maximal temperature was about 320 °C (+/- 25 °C), close to the maximal temperature reached in the cover of the Mont Blanc massif (~ 350 °C +/- 25 °C). We show that, after a fast heating period, the thermal peak lasted 10-15 Myrs in the Mont Blanc massif, and probably 5-10 Myrs in the Aiguilles Rouges massif. This thermal peak is synchronous with crustal shortening documented in the basement. (U-Th-Sm)/He data and thermal modeling point toward a coeval cooling of both massifs, like other ECM, at around 18 Ma +/- 1 Ma. This cooling was related to an exhumation due to the initiation of frontal crustal ramps below the ECM, quite synchronously along the Western Alps arc.

  5. Mantle refertilization by garnet pyroxenite melts: Evidence from the Ronda peridotite massif, southern Spain

    NASA Astrophysics Data System (ADS)

    Marchesi, C.; Garrido, C.; Bosch, D.; Bodinier, J.; Gervilla, F.

    2011-12-01

    Lherzolite at the recrystallization front of the Ronda peridotite massif, a mantle region that experienced pervasive melt migration and melt/rock reaction, hosts pyroxenite composite layers that show an inner transition from Al- to Cr-rich compositions. These particular pyroxenite-peridotite associations record intense processes of pyroxenite melting/replacement and related peridotite refertilization. Al-rich spinel websterite in a composite layer close to the front was generated by melting of former garnet pyroxenite with an evident imprint of primary plagioclase and reaction of this protolith with incoming peridotite melt. These events produced more refractory major element compositions of whole-rock and higher REE contents in clinopyroxene but preserved the characteristic MREE/HREE fractionation and positive Eu anomaly of the garnet pyroxenite protolith. In the waning stages of melt porous flow at the recrystallization front, the parental melts of Cr-rich pyroxenite progressively replaced residual Al-rich spinel websterite partially conserving their original subduction-related affinity. Lherzolite hosting the composite layer was intensely refertilized by melt resulted from garnet pyroxenite replacement. The presence in the refertilizing agent of an important component extracted from garnet pyroxenite induced Eu and Sr positive anomalies, higher FeO* at similar SiO2 and higher Sm/Yb in these mantle rocks compared to common peridotite from the Ronda massif. Some peculiar geochemical signatures of garnet pyroxenite were thus imparted to highly fertile lherzolite hosting the pyroxenite composite layer by partial melting, melt migration and melt/rock reaction in the Ronda massif. These mechanisms may explain the presence of a garnet pyroxenite component in the source of different types of melt generated in the mantle. However, the efficiency of these processes in transferring the geochemical imprint of garnet pyroxenite to extruded lavas depends on the reactivity of

  6. Formation of the Red Hills Ultramafic Massif during Subduction Initiation along an Oceanic Transform Fault

    NASA Astrophysics Data System (ADS)

    Tikoff, B.; Stewart, E. D.; Newman, J.; Lamb, W. M.

    2015-12-01

    The Red Hills ultramafic massif in the South Island, New Zealand, is part of the Dun Mountain Ophiolite Belt (DMOB). The DMOB was created at the onset of subduction in a forearc setting in the Middle Permian, and it likely formed immediately prior to the establishment of a magmatic arc along the New Zealand and Australian portions of the Gondwanan margin. The Red Hills ultramafic massif records a two-stage history of high temperature mantle flow during subduction initiation along the Gondwanan margin. Initial deformation was homogeneous and fabrics are constrictional. Kilometer-scale deformation zones, part of the second stage of deformation, overprinted the early homogeneous fabric throughout the western portion of the massif. Timing of all high-temperature mantle deformation in the Red Hills was between 285 and 274 Ma during subduction initiation based on the earliest ages of igneous activity in adjacent volcanic rocks, and a new U-Pb zircon age of 274.55±0.43 Ma from a cross-cutting dike. We present a kinematic model to explain the occurrence of the constructional fabrics during subduction initiation, and find that the three-dimensional boundary conditions for deformation in the incipient mantle wedge must have been transtensional, with a dominant trench-parallel component of motion. Such a scenario indicates subduction likely initiated along an active oceanic transform fault. We test this model by kinematically restoring the Red Hills ultramafics to their Permian orientation, and find the consistent elongation direction of the constructional fabrics was oriented nearly parallel to the trench. Stage 2 deformation zones were variably oriented, but all accommodated normal motion. These results support a model where the incipient mantle wedge was undergoing highly oblique transtension, and the lack of evidence for contraction suggests the onset of subduction along the Permian margin of New Zealand occurred along a transform fault due to spontaneous, density driven

  7. Subsurface Implications of Spatially Variable Seafloor Character on the Atlantis Massif

    NASA Astrophysics Data System (ADS)

    Greene, J. A.; Tominaga, M.; Blackman, D. K.

    2014-12-01

    We documented and mapped the characteristics of the seafloor on the Atlantis Massif, an ocean core complex located at 30°N on the Mid-Atlantic Ridge. Our goal is to investigate the implications of these surficial features, particularly whether their spatial variations might reflect subsurface lithology and geological processes. We utilized data collected during the MARVEL 2000 cruise AT3-60, specifically Alvin videos and rock samples, Argo II digital still photos, and TOBI/DSL-120 side-scan sonar mosaic. The Alvin dives studied occurred over the Central Dome and Eastern Block, which is interpreted as the hanging wall to the detachment that unroofed the dome. We also studied two Argo II dives located over the Central Dome, one over the Eastern Block, and one over the Western Shoulder of the southern dome. The TOBI/DSL-120 side-scan sonar followed a widespread, looped track providing near total coverage of the massif. We classified the character of the seafloor based on imagery, the acoustic reflectivity, and the basic composition of rock samples. To aid in our classification, we merged Argo II still images to produce photo-mosaics displaying tens of meters long transects. We then classified the seafloor as unconsolidated sediment, lithified sediment (a carbonate crust or cap), exposed bedrock, or rubble. To obtain a broader understanding of the Atlantis Massif, we analyzed the distribution of these classes of seafloor. Over the Central Dome and Western Shoulder, we found most seafloor classes present in notable amounts, with many individual areas dominated by a particular type.

  8. Metamorphic evolution of pelitic-semipelitic granulites in the Kon Tum massif (south-central Vietnam)

    NASA Astrophysics Data System (ADS)

    Tích, Vu Van; Leyreloup, Andrey; Maluski, Henry; Lepvrier, Claude; Lo, Chinh-hua; Vượng, Nguyễn V.

    2013-09-01

    Pelitic and semipelitic anatectic granulites form one of the major lithological units in Kan Nack complex of the Kon Tum massif (in south-central Vietnam), which comprises HT metamorphic and magmatic rocks including granulites and charnockites is classically regarded as the older part of the Gondwana-derived Indosinia terrain. Metamorphic evolution study of pelitic granulite, the most abundant among granulites exposed in this massif, facilitates to understand that tectonic setting take place during the Indosinian time. The paragenetic assemblages, mineral chemistry, thermobarometry and P-T evolution path of pelitic-semipelitic granulites from Kon Tum massif has been studied in detail. Petrographic feature demonstrates that the pelitic granulite experienced prograde history, from pregranulitic conditions in the amphibolite facies up to the peak granulitic assemblages. Successive prograde reactions led to the temperature-climax giving rise to assemblages with cordierite-hercynite and cordierite-hercynite-K-feldspar. Then, as attested by the mineralogic association occurring in cordieritic coronas, these rocks have been affected by retrograde conditions coeval with a decrease of the pressure. Thermobarometic results show that the highest temperature obtained by ksp/pl thermometry is 850 °C and the highest pressure obtained by GASP (Garnet Alumino-Silicate Plagioclase) is 7.8 kbar. The obtained clockwise P-T evolution path involving heating decompression, then nearly isothermal decompression and nearly isobar cooling conditions shows that high temperature-low pressure metamorphism of the studied pelitic anatectic granulites of Kan Nack complex occurred possibly in extensional setting during the Indosinian orogeny of 260-240 Ma in age.

  9. Catalog of Apollo 17 rocks. Volume 1: Stations 2 and 3 (South Massif)

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1993-01-01

    The Catalog of Apollo 17 Rocks is a set of volumes that characterize each of 334 individually numbered rock samples (79 larger than 100 g) in the Apollo 17 collection, showing what each sample is and what is known about it. Unconsolidated regolith samples are not included. The catalog is intended to be used by both researchers requiring sample allocations and a broad audience interested in Apollo 17 rocks. The volumes are arranged geographically, with separate volumes for the South Massif and Light Mantle, the North Massif, and two volumes for the mare plains. Within each volume, the samples are arranged in numerical order, closely corresponding with the sample collection stations. The present volume, for the South Massif and Light Mantle, describes the 55 individual rock fragments collected at Stations two, two-A, three, and LRV-five. Some were chipped from boulders, others collected as individual rocks, some by raking, and a few by picking from the soil in the processing laboratory. Information on sample collection, petrography, chemistry, stable and radiogenic isotopes, rock surface characteristics, physical properties, and curatorial processing is summarized and referenced as far as it is known up to early 1992. The intention has been to be comprehensive: to include all published studies of any kind that provide information on the sample, as well as some unpublished information. References which are primarily bulk interpretations of existing data or mere lists of samples are not generally included. Foreign language journals were not scrutinized, but little data appears to have been published only in such journals. We have attempted to be consistent in format across all of the volumes, and have used a common reference list that appears in all volumes. Where possible, ages based on Sr and Ar isotopes have been recalculated using the 'new' decay constants recommended by Steiger and Jager; however, in many of the reproduced diagrams the ages correspond with the

  10. Accelerated glacier shrinkage in the Ak-Shyirak massif, Inner Tien Shan, during 2003-2013.

    PubMed

    Petrakov, Dmitry; Shpuntova, Alyona; Aleinikov, Alexandr; Kääb, Andreas; Kutuzov, Stanislav; Lavrentiev, Ivan; Stoffel, Markus; Tutubalina, Olga; Usubaliev, Ryskul

    2016-08-15

    The observed increase in summer temperatures and the related glacier downwasting has led to a noticeable decrease of frozen water resources in Central Asia, with possible future impacts on the economy of all downstream countries in the region. Glaciers in the Ak-Shyirak massif, located in the Inner Tien Shan, are not only affected by climate change, but also impacted by the open pit gold mining of the Kumtor Gold Company. In this study, glacier inventories referring to the years 2003 and 2013 were created for the Ak-Shyirak massif based on satellite imagery. The 193 glaciers had a total area of 351.2±5.6km(2) in 2013. Compared to 2003, the total glacier area decreased by 5.9±3.4%. During 2003-2013, the shrinkage rate of Ak-Shyirak glaciers was twice than that in 1977-2003 and similar to shrinkage rates in Tien Shan frontier ranges. We assessed glacier volume in 2013 using volume-area (VA) scaling and GlabTop modelling approaches. Resulting values for the whole massif differ strongly, the VA scaling derived volume is 30.0-26.4km(3) whereas the GlabTop derived volume accounts for 18.8-13.2km(3). Ice losses obtained from both approaches were compared to geodetically-derived volume change. VA scaling underestimates ice losses between 1943 and 2003 whereas GlabTop reveals a good match for eight glaciers for the period 2003-2012. In comparison to radio-echo soundings from three glaciers, the GlabTop model reveals a systematic underestimation of glacier thickness with a mean deviation of 16%. GlabTop tends to significantly underestimate ice thickness in accumulation areas, but tends to overestimate ice thickness in the lowermost parts of glacier snouts. Direct technogenic impact is responsible for about 7% of area and 5% of mass loss for glaciers in the Ak-Shyirak massif during 2003-2013. Therefore the increase of summer temperature seems to be the main driver of accelerated glacier shrinkage in the area. PMID:27100016

  11. The Geological ve Geochemical Evaluation of Albite Deposits in Menderes Massif (SW Turkey)

    NASA Astrophysics Data System (ADS)

    Cansu, Zeynep; Emre, Hasan

    2013-04-01

    Menderes Massif which is one of the main rock association in southwestern Turkey consists of a Pan-African basement considered as the core and the overlying Lower Paleozoic - Paleocene age cover series. Albite deposits take place not only in the center but also around the Menderes Massif, with the increase amount of quartz from center to rim. The main rock units of the massif consist highly metamorphosed gneiss and mica schist hosting the albite deposits which situated in the tectonic lines has direction of N-NE. Nearly 250 feldspar quarries are being operated in the region. Albites are generally contaminated by minerals containing iron and titanium (rutile, sphene, mica etc.). The origin of the undesired elements in the albite deposits are aimed to obtain whether they originated from primary formation conditions or late alternations (metamorphism and/or deformation). Preliminary studies were done on 75 samples of Armutludüzü albite deposit (Milas - Turkey) and geochemical composition of these samples are evaluated in point of undesired elements for albite's quality. Compared to pure albite which has %11,8 Na2O in composition, the Armutludüzü albite deposit has a mean value of % 10,18 Na2O and % 0,28 K2O with undesired % 0,06 Fe2O3 and % 0,18 TiO2 composition. By correlation of the geochemical data with geologic unit boundaries, it is obtained that Ti concentration becomes intense in the N40-45oE gneiss boundary and Fe concentration increases in the mica schist boundary. Titanium is the most important component of albite quality because of its negative effects on burning color and iron which is the other important component of albite quality is restrictive for albite usage in the glass industry. Samples which are taken from core rocks and albites are being prepared for U- Pb and K-Ar/Ar-Ar dating methods to compare K-Ar/Ar-Ar ages measured from the micas which gives the latest deformation age and U-Pb ages of gneiss and albites which gives the actual age of

  12. Recycled gabbro signature in Upper Cretaceous Magma within Strandja Massif: NW Turkey

    NASA Astrophysics Data System (ADS)

    Ulusoy, Ezgi; Kagan Kadioglu, Yusuf

    2016-04-01

    Basic magma intrusions within plate interiors upwelling mantle plumes have chemical signatures that are distinct from mid-ocean ridge magmas. When a basic magma interact with continental crust or with the felsic magma, the compositions of both magma changes, but there is no consensus as to how this interaction occurs. Here we analyse the mineral behavior and trace element signature of gabbroic rocks of the samples collected from the Strandja Massif. Srednogorie magmatic arc is a part of Apuseni- Banat-Timok-Srednogorie magmatic belt and formed by subduction and closure of the Tethys Ocean during Upper Cretaceous times. Upper Cretaceous magmatic rocks cutting Strandja Massif in NW Turkey belong to eastern edge of Srednogorie Magmatic arc. Upper Cretacous magmatic rocks divided into four subgroup in Turkey part of Strandja massif: (I) granitic rocks, (II) monzonitic rock, (III) syenitic rocks and (IV) gabbroic rocks. Gabbroic rocks outcropped around study area in phaneritic - equigranular texture. According to mineralogic - petrographic studies gabbros have mainly holocrystalline texture and ophitic to subophitic texture composed of plagioclase, amphibole, pyroxene, and rarely olivine and opaque minerals. Also because of special conditions there have been pegmatitic texture on mafic minerals with euhedral form up to 3 cm in size and orbicular texture which reach 15cm in size and rounded - elliptical form. Confocal Raman Spectroscopy studies reveals that plagioclase are ranging in composition from labradorite to bytownite, the pyroxene are ranging in composition from diopside to augite acting with uralitization processes and the olivine are generally in the composition of forsterite. Petrographic and mineralogical determination reveals some metasomatic magmatic epidote presence. Confocal Raman Spectroscopy studies on anhydrous minerals within gabbroic rocks shows affect of hydrous process because of magma mixing. The gabbroic rocks have tholeiitic and changed towards

  13. Isotopic age and heterogeneous sources of gabbro‒anorthosites from the Patchemvarek massif, Kola Peninsula

    NASA Astrophysics Data System (ADS)

    Vrevsky, A. B.; Lvov, A. P.

    2016-07-01

    New U‒Pb (SHRIMP II) data on the age (2661.8 ± 7.1 Ma) and isotopic (Sm‒Nd) composition of the Patchemvarek gabbro‒anorthosite massif located in the junction zone between the Neoarchean Kolmozero-Voron'ya greenstone belt and Keivy paragneiss structure are discussed. The established age and geological‒tectonic position of gabbro‒anorthosites allow the prognostic metallogenic estimate of Ti‒V‒Fe mineralization to be extended to the entire Kolmozero-Voron'ya‒Keivy infrastructural zone of the Kola‒Norwegian province of the Fennoscandian shield.

  14. Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2014-05-01

    This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz

  15. MASSIF-1: a beamline dedicated to the fully automatic characterization and data collection from crystals of biological macromolecules

    PubMed Central

    Bowler, Matthew W.; Nurizzo, Didier; Barrett, Ray; Beteva, Antonia; Bodin, Marjolaine; Caserotto, Hugo; Delagenière, Solange; Dobias, Fabian; Flot, David; Giraud, Thierry; Guichard, Nicolas; Guijarro, Mattias; Lentini, Mario; Leonard, Gordon A.; McSweeney, Sean; Oskarsson, Marcus; Schmidt, Werner; Snigirev, Anatoli; von Stetten, David; Surr, John; Svensson, Olof; Theveneau, Pascal; Mueller-Dieckmann, Christoph

    2015-01-01

    MASSIF-1 (ID30A-1) is an ESRF undulator beamline operating at a fixed wavelength of 0.969 Å (12.8 keV) that is dedicated to the completely automatic characterization of and data collection from crystals of biological macromolecules. The first of the ESRF Upgrade MASSIF beamlines to be commissioned, it has been open since September 2014, providing a unique automated data collection service to academic and industrial users. Here, the beamline characteristics and details of the new service are outlined. PMID:26524320

  16. Utilization of digital LANDSAT imagery for the study of granitoid bodies in Rondonia: Case example of the Pedra Branca massif

    NASA Technical Reports Server (NTRS)

    Parada, N. D. J. (Principal Investigator); Almeidafilho, R.; Payolla, B. L.; Depinho, O. G.; Bettencourt, J. S.

    1984-01-01

    Analysis of digital multispectral MSS-LANDSAT images enhanced through computer techniques and enlarged to a video scale of 1:100.000, show the main geological and structura features of the Pedra Branca granitic massif in Rondonia. These are not observed in aerial photographs or adar images. Field work shows that LANDSAT photogeological units correspond to different facies of granitic rocks in the Pedra Branca massif. Even under the particular characteristics of Amazonia (Tropical Forest, deep weathering, and Quaternary sedimentary covers), an adequate utilization of orbital remote sensing images can be important tools for the orientation of field works.

  17. New species from the Galoka and Kalabenono massifs: two unknown and severely threatened mountainous areas in NW Madagascar

    PubMed Central

    Callmander, Martin W.; Rakotovao, Charles; Razafitsalama, Jeremi; Phillipson, Peter B.; Buerki, Sven; Hong-Wa, Cynthia; Rakotoarivelo, Nivo; Andriambololonera, Sylvie; Koopman, Margaret M.; Johnson, David M.; Deroin, Thierry; Ravoahangy, Andriamandranto; Solo, Serge; Labat, Jean-Noël; Lowry, Porter P.

    2011-01-01

    The Galoka mountain chain, comprising principally the Galoka and Kalabenono massifs, situated at the northern edge of the Sambirano Region in NW Madagascar is an area that was virtually unknown botanically. It was visited three times between 2005 and 2007 as part of a floristic inventory. Both massifs contain the last remaining primary forests in the Galoka chain, which extends parallel to the coastline from South of Ambilobe to North of Ambanja. Several new species have been discovered amongst the collections, eight of which are described here. PMID:21857767

  18. MASSIF-1: a beamline dedicated to the fully automatic characterization and data collection from crystals of biological macromolecules.

    PubMed

    Bowler, Matthew W; Nurizzo, Didier; Barrett, Ray; Beteva, Antonia; Bodin, Marjolaine; Caserotto, Hugo; Delagenière, Solange; Dobias, Fabian; Flot, David; Giraud, Thierry; Guichard, Nicolas; Guijarro, Mattias; Lentini, Mario; Leonard, Gordon A; McSweeney, Sean; Oskarsson, Marcus; Schmidt, Werner; Snigirev, Anatoli; von Stetten, David; Surr, John; Svensson, Olof; Theveneau, Pascal; Mueller-Dieckmann, Christoph

    2015-11-01

    MASSIF-1 (ID30A-1) is an ESRF undulator beamline operating at a fixed wavelength of 0.969 Å (12.8 keV) that is dedicated to the completely automatic characterization of and data collection from crystals of biological macromolecules. The first of the ESRF Upgrade MASSIF beamlines to be commissioned, it has been open since September 2014, providing a unique automated data collection service to academic and industrial users. Here, the beamline characteristics and details of the new service are outlined. PMID:26524320

  19. MASSIF-1: a beamline dedicated to the fully automatic characterization and data collection from crystals of biological macromolecules.

    PubMed

    Bowler, Matthew W; Nurizzo, Didier; Barrett, Ray; Beteva, Antonia; Bodin, Marjolaine; Caserotto, Hugo; Delagenière, Solange; Dobias, Fabian; Flot, David; Giraud, Thierry; Guichard, Nicolas; Guijarro, Mattias; Lentini, Mario; Leonard, Gordon A; McSweeney, Sean; Oskarsson, Marcus; Schmidt, Werner; Snigirev, Anatoli; von Stetten, David; Surr, John; Svensson, Olof; Theveneau, Pascal; Mueller-Dieckmann, Christoph

    2015-11-01

    MASSIF-1 (ID30A-1) is an ESRF undulator beamline operating at a fixed wavelength of 0.969 Å (12.8 keV) that is dedicated to the completely automatic characterization of and data collection from crystals of biological macromolecules. The first of the ESRF Upgrade MASSIF beamlines to be commissioned, it has been open since September 2014, providing a unique automated data collection service to academic and industrial users. Here, the beamline characteristics and details of the new service are outlined.

  20. Petrogenesis and P-T Conditions of Metamorphic Rocks From the Chiapas Massif Complex in the Custepec Area, Chiapas, Mexico

    NASA Astrophysics Data System (ADS)

    Estrada-Carmona, J.; Weber, B.; Hecht, L.; Martens, U.

    2007-05-01

    The Chiapas Massif Complex (CMC), located in the southern Maya block, is primarily composed of igneous and metaigneous rocks of late Permian age. Within the CMC, two metasedimentary basement units have been described: (1) The `La Sepultura Unit' is located in the NW part of the CMC and is composed of metapsammites, metapelites and calcsilicate rocks metamorphosed under high-T/low-P conditions and (2) the `Custepec Unit' located in the SE part of the CMC. The Custepec Unit is mainly composed of anatectic amphibolites with or without garnet, intercalated with quartz-feldspar and pelitic gneisses, marbles, and calcsilicates. The main foliation trend in the Custepec area is E-W to NW-SE mostly dipping to the north. Stretching lineations and fold axes of varied orientations indicate that the D1 deformation was folded by a subsequent D2 event. We applied the garnet-biotite geothermometer, the GASP, and GRAIL geobarometers in metapelites and the garnet-plagioclase-hornblende-quartz geobarometer in amphibolites. The results are consistent, yielding peak metamorphic conditions above 800°C and 9 Kbar. These data, along with petrographic observations place the metamorphic peak in the high amphibolite facies to granulite facies transition at 25-30 km depth. Relics of bluish-green (low-T) amphiboles yielded similar pressures than the high-T brownish hornblende, indicating a clockwise P-T path with isobaric heating at the metamorphic pressure peak. The high-grade event was followed by greenschist facies retrogression, which is probably contemporaneous with the formation of E-W trending dextral mylonite zones. On the basis of our field observations, chemical composition, and the presence of detritic zircons in the amphibolites, we interpret the Custepec Unit as a volcanosedimentary sequence. Our data favor a model in which peak metamorphism in the CMC during the late Permian is the result of stacking in an orogenic wedge with the Sepultura Unit as the upper plate thrusted over

  1. Geologic and tectonic setting of Deseado Massif epithermal deposits, Argentina, based on El Dorado-Monserrat

    NASA Astrophysics Data System (ADS)

    Echavarría, Leandro E.; Schalamuk, Isidoro B.; Etcheverry, Ricardo O.

    2005-09-01

    Middle-Late Jurassic bimodal volcanism, typical of a retroarc setting, developed during widespread extensional tectonism within the Deseado Massif, southern Argentina. This geologic environment led to the formation of numerous low-sulfidation epithermal deposits that are spatially and temporally related to the volcanic activity. The lack of significant high-sulfidation epithermal deposits may be because the tectonic and volcanic settings do not favor the formation of these types of deposits. El Dorado-Monserrat is a low-sulfidation epithermal prospect located near the southern boundary of the Deseado Massif. Mineralization is genetically linked to the Late Jurassic Chon Aike Formation and hosted by volcanic rocks of the middle Late Jurassic Bajo Pobre Formation. Two different mineralization areas have been identified. The Monserrat area is the most important, with veins hosted in a north-striking, left-lateral shear zone. The average thickness is 0.85 m, and the average metal content is 6.2 ppm gold and 153 ppm silver. The El Dorado area has discontinuous echelon veins within a right-lateral shear zone with low gold and silver grades. Hydrothermal alteration of the host rocks includes an inner zone of quartz-adularia and illite alteration and an outer zone of propylitic alteration. The main gangue mineral is quartz, which formed in successive pulses, plus adularia, pyrite, hematite, magnetite, and barite. Precious metals occur as zoned electrum. Ore mineral precipitation took place between 200 and 280 °C from low salinity fluids due to boiling.

  2. New radiocarbon chronology of a late Holocene landslide event in the Mont Blanc massif, Italy

    NASA Astrophysics Data System (ADS)

    Hajdas, Irka; Sojc, Ursula; Ivy-Ochs, Susan; Akçar, Naki; Deline, Philip

    2016-04-01

    The Ferret valley Arp Nouva peat bog located in the Mont Blanc massif was critically evaluated since previously published radiocarbon dates have led to controversial conclusions on the formation of the swamp. Radiocarbon dating of roots from three pits of up to 1 m depth was applied to discuss the question whether the historical documented rock avalanche occurring in AD 1717 overran the peat bog or formed it at a later stage. Our results indicate that the rock avalanche formed the Arp Nouva peat bog by downstream blockage of the Bellecombe torrent. Furthermore, careful sample preparation with consequent separation of roots from the bulk peat sample provides possible explanation for the too old 14C ages of bulk peat samples dated previously (Deline and Kirkbride, 2009 and references therein). This work demonstrates that a combined geomorphological and geochronological approach is the most reliable way to reconstruct landscape evolution, especially in light of apparent chronological problems. The key to successful 14C dating is a careful sample selection and the identification of material that might be not ideal for chronological reconstructions. References Deline, Philip, and Martin P. Kirkbride. "Rock avalanches on a glacier and morainic complex in Haut Val Ferret (Mont Blanc Massif, Italy)".Geomorphology 103 (2009): 80-92.

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

    PubMed

    de Mello, William Z; de Almeida, Marcelo D

    2004-05-01

    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.

  4. Thermochronology and tectonics of the Mérida Andes and the Santander Massif, NW South America

    NASA Astrophysics Data System (ADS)

    van der Lelij, Roelant; Spikings, Richard; Mora, Andrés

    2016-04-01

    New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature (~ 500 °C-~ 300 °C) thermal histories of igneous and metamorphic rocks exposed in the Mérida Andes of Venezuela, and new apatite and zircon fission track data constrain the ~ 500 °C-~ 60 °C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Mérida Andes suggest that it cooled from > 500 °C to < 350 °C between ~ 266 Ma and ~ 225 Ma. Late Permian to Triassic cooling is also recorded in Early Palaeozoic granitoids and metasedimentary rocks in the Mérida Andes by numerous new muscovite and biotite 40Ar/39Ar plateau dates spanning 257.1 ± 1.0 Ma to 205.1 ± 0.8 Ma. This episode of cooling is not recognised in the Santander Massif, where 40Ar/39Ar data suggest that some Early Palaeozoic rocks cooled below ~ 320 °C in the Early Palaeozoic. However, most data from pre-Jurassic rocks reveal a regional heat pulse at ~ 200 Ma during the intrusion of numerous shallow granitoids, resulting in temperatures in excess of ~ 520 °C, obscuring late Palaeozoic histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Mérida Andes by > 30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Mérida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at ~ 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Mérida Andes in the Late Permian. The coeval onset of exhumation in the Mérida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of

  5. Géométrie et cinématique des chevauchements varisques du Nord-Est du Massif armoricain (France)Geometry and kinematics of Variscan thrusts in the northeastern Armorican Massif (France)

    NASA Astrophysics Data System (ADS)

    Butaeye, Damien; Laville, Edgard; Le Gall, Jean

    2001-02-01

    Variscan structures of the northeastern Armorican massif consist of folds induced by south-verging thrust faults. This thin-skinned process is controlled by a major décollement that would be expected at the base of the Brioverian flysch. So, the northeastern Armorican domain can be integrated to the tectonic model admitted at the Variscan Orogenesis scale.

  6. A Paleozoic anorthosite massif related to rutile-bearing ilmenite ore deposits, south of the Polochic fault, Chiapas Massif Complex, Mexico

    NASA Astrophysics Data System (ADS)

    Cisneros, A.; Ortega-Gutiérrez, F.; Weber, B.; Solari, L.; Schaaf, P. E.; Maldonado, R.

    2013-12-01

    The Chiapas Massif Complex in the southern Maya terrane is mostly composed of late Permian igneous and meta-igneous rocks. Within this complex in southern Mexico and in the adjacent San Marcos Department of Guatemala, south of the Polochic fault, several small outcrops (~10 km2) of a Phanerozoic andesine anorthosite massif were found following an E-W trend similar to the Polochic-Motagua Fault System. Such anorthosites are related to rutile-bearing ilmenite ore deposits and hornblendite-amphibolite bands (0.1-3 meters thick). The anorthosites show recrystallization and metamorphic retrogression (rutile with titanite rims), but no relicts of high-grade metamorphic minerals such as pyroxene or garnet have been found. In Acacoyagua, Chiapas, anorthosites are spatially related to oxide-apatite rich mafic rocks; in contrast, further to the west in Motozintla, they are related to monzonites. Zircons from these monzonites yield a Permian U-Pb age (271.2×1.4 Ma) by LA-MC-ICPMS. Primary mineral assemblage of the anorthosites include mostly medium to fine-grained plagioclase (>90%) with rutile and apatite as accessory minerals, occasionally with very low amounts of quartz. Massive Fe-Ti oxide lenses up to tens of meters in length and few meters thick are an ubiquitous constituent of these anorthosites and their mineralogy include ilmenite (with exsolution lamellae of Ti-magnetite), rutile, magnetite, clinochlore, ×spinel, ×apatite, ×zircon and srilankite (Ti2ZrO6, first finding of this phase in Mexico). Rutile occurs within the massive ilmenite in two morphological types: (1) fine-grained (5-40 μm) rutile along ilmenite grain boundaries or fractures, and (2) coarse-grained rutile (<5 mm) as discrete grains, whereas magnetite and srilankite only appear as small grains along ilmenite boundaries. Zircon is present as discontinuously aligned small grains (10-40 μm) forming rims around many rutile and ilmenite grains. Attempts to date zircon rims by U-Pb using LA

  7. Human impacts of hydrometeorological extremes in the Bohemian-Moravian Highlands derived from documentary sources in the 18th-19th centuries

    NASA Astrophysics Data System (ADS)

    Dolák, Lukáš; Brázdil, Rudolf; Valášek, Hubert

    2014-05-01

    The extent of damage caused by hydrometeorological events or extremes (HME) has risen up in the entire world in the last few years. Especially the floods, flash floods, torrential rains and hailstorms are the most typical and one of the most frequent kind of natural disasters in the central Europe. Catastrophes are a part of human history and people were forced to cope with their consequences (e. g. material damage, economical losses, impacts on agriculture and society or losses of human lives). This paper analyses the human impacts of HME in the Bohemian-Moravian Highlands (central part of the Czech Republic) on the basis of documentary sources from the 18th-19th centuries. The paper presents various negative impacts of natural disasters on lives and property and subsequent inconveniences of Czech peasants. The preserved archival documents of estates or domains became the primary sources of data (e. g. taxation reliefs, damaged records, reports of afflicted farmers, administrative correspondence etc.). Particularly taxation reliefs relate to taxation system in the Czech lands during the 17th-19th centuries allowing to farmers to ask for tax alleviation when their crops were significantly damaged by any HME. These archival documents are a highly valuable source for the study of human impacts of natural disasters. Devastating consequences of these extremes affected individual farmers much more than the aristocracy. Floods caused inundations of farmer's fields, meadows, houses and farm buildings, washed away the arable land with crops, caused losses of cattle, clogged the land with gravel and mud and destroyed roads, bridges or agricultural equipment. Afflicted fields became worthless and it took them many years to become became fertile again. Crop was also damaged by hailstorms, droughts or late/early frosts. All these events led to lack of food and seeds in the following year and it meant the decrease of living standard, misery and poverty of farmers. Acquired

  8. Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif.

    PubMed

    Nardi, Lauro V S; Plá-Cid, Jorge; Bitencourt, Maria de Fátima; Stabel, Larissa Z

    2008-06-01

    The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism. PMID:18506262

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

    SciTech Connect

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

    2002-12-27

    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 sufficient information to make an estimate of the suitability of locating a radioactive waste (R W) underground isolation facility at the Nizhnekansky granitoid massif

  10. Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif.

    PubMed

    Nardi, Lauro V S; Plá-Cid, Jorge; Bitencourt, Maria de Fátima; Stabel, Larissa Z

    2008-06-01

    The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

  11. Possible petrogenetic associations among igneous components in North Massif soils: Evidence in 2-4 mm soil particles from 76503

    NASA Technical Reports Server (NTRS)

    Jolliff, Bradley L.; Bishop, Kaylynn M.; Haskin, Larry A.

    1992-01-01

    Studies of Apollo 17 highland igneous rocks and clasts in breccias from the North and South Massifs have described magnesian troctolite, norite, anorthositic gabbro, dunite, spinel cataclasites, and granulitic lithologies that may have noritic anothosite or anorthositic norite/gabbro as igneous precursors, and have speculated on possible petrogenetic relationships among these rock types. Mineral compositions and relative proportions of plagioclase and plagioclase-olivine particles in samples 76503 indicate that the precursor lithology of those particles were troctolitic anorthosite, not troctolite. Mineral and chemical compositions of more pyroxene-rich, magnesian breccias and granulites in 76503 indicate that their precursor lithology was anorthositic norite/gabbro. The combination of mineral compositions and whole-rock trace-element compositional trends supports a genetic relationship among these two groups as would result from differentiation of a single pluton. Although highland igneous lithologies in Apollo 17 materials have been described previously, the proportions of different igneous lithologies present in the massifs, their frequency of association, and how they are related are not well known. We consider the proportions of, and associations among, the igneous lithologies found in a North Massif soil, which may represent those of the North Massif or a major part of it.

  12. Cenozoic remagnetization of the Paleozoic rocks in the Kitakami massif of northeast Japan, and its tectonic implications

    NASA Astrophysics Data System (ADS)

    Otofuji, Yo-ichiro; Takemoto, Kazuhiro; Zaman, Haider; Nishimitsu, Yoshitomo; Wada, Yutaka

    2003-05-01

    Secondary remanent magnetization is identified in the Paleozoic igneous and sedimentary rocks of the Kitakami massif. The secondary nature is shown by a negative fold test for the Permo-Carboniferous sedimentary rocks. The northwesterly paleomagnetic declination with moderate inclination ( D=321.2°, I=56.5°, α95=5.2°, N=18) of this secondary remanent magnetization is almost parallel to the primary magnetization reported for the Cenozoic welded tuffs of northeast Japan, indicating that the Paleozoic rocks were subjected to remagnetization at any period between 62 and 16 Ma. The secondary magnetization of the serpentinized ultramafic rocks is carried by magnetite, which grew in veins and mesh rims of serpentine, whereas the carrier of the magnetization in limestones is fine-grained pyrrhotite. Combining this with the previously reported remagnetization of the Kitakami granitic rocks, it is suggested that rocks in the Kitakami massif were subjected to crystallization remanent magnetization at low-temperature conditions. Since serpentinization requires fluid migration, one of the most likely events is the eastward lateral migration of water into the Kitakami massif. We postulate a Cenozoic suturing of the Kitakami massif with the Asian continent as a plausible tectonic event for this fluid migration.

  13. Has Massification of Higher Education Led to More Equity? Clues to a Reflection on Portuguese Education Arena

    ERIC Educational Resources Information Center

    Dias, Diana

    2015-01-01

    Massification is an undeniable phenomenon in the higher education arena. However, there have been questions raised regarding the extent to which a mass system really corresponds to an effective democratisation not only of access, but also of success. With regards to access, this article intends, through a brief analysis of the expansion of higher…

  14. The Vercors and Chartreuse Massifs at the leading edge of the alpine thrust belt: Tetonic history and petroleum assessment

    SciTech Connect

    Deville, E.; Mascle, A.; Philippe, Y.

    1995-08-01

    The Vercors and Chartreuse Massifs are located at the leading edge of the Western Alps Thrust Belt. They developed in late Miocene-Pliocene times above a major decollement hosted in late Triassic evaporites and/or Liassic marls. The uplift of both massifs led to the oblique and partial inversion of the previous Mesozoic margin of the Southeastern Basin, the thickest onshore sedimentary basin in France. Both massifs are unexplored. The regional geology of eastern France and the results of ten wells located in the near foreland suggest that source rocks are present in late Paleozoic and late Liassic strata, and that fractured sandstones and/or limestones of Triassic/Jurassic age could act as reservoirs. A nonexclusive seismic survey has been shot in 1991 by CGG allowing the first well constrained balanced sections to be drawn across both massifs. They have been used inturn to model the forward kinematics of thrust propagation, and the source rock maturation history, using the {open_quotes}Thrustpack{close_quotes} software developed by IFP and partners.

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

    ERIC Educational Resources Information Center

    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…

  16. Crustal segments in the North Patagonian Massif, Patagonia: An integrated perspective based on Sm-Nd isotope systematics

    NASA Astrophysics Data System (ADS)

    Martínez Dopico, Carmen I.; López de Luchi, Mónica G.; Rapalini, Augusto E.; Kleinhanns, Ilka C.

    2011-03-01

    New insights on the Paleozoic evolution of the continental crust in the North Patagonian Massif are presented based on the analysis of Sm-Nd systematics. New evidence is presented to constrain tectonic models for the origin of Patagonia and its relations with the South American crustal blocks. Geologic, isotopic and tectonic characterization of the North Patagonian Massif and comparison of the Nd parameters lead us to conclude that: (1) The North Patagonian Massif is a crustal block with bulk crustal average ages between 2.1 and 1.6 Ga TDM (Nd) and (2) At least three metamorphic episodes could be identified in the Paleozoic rocks of the North Patagonian Massif. In the northeastern corner, Famatinian metamorphism is widely identified. However field and petrographic evidence indicate a Middle to Late Cambrian metamorphism pre-dating the emplacement of the ca. 475 Ma granitoids. In the southwestern area, are apparent 425-420 Ma (?) and 380-360 Ma metamorphic peaks. The latter episode might have resulted from the collision of the Antonia terrane; and (3) Early Paleozoic magmatism in the northeastern area is coeval with the Famatinian arc. Nd isotopic compositions reveal that Ordovician magmatism was associated with attenuated crust. On the southwestern border, the first magmatic recycling record is Devonian. Nd data shows a step by step melting of different levels of the continental crust in the Late Palaeozoic. Between 330 and 295 Ma magmatism was likely the product of a crustal source with an average 1.5 Ga TDM (Nd). Widespread magmatism represented by the 295-260 Ma granitoids involved a lower crustal mafic source, and continued with massive shallower-acid plutono volcanic complexes which might have recycled an upper crustal segment of the Proterozoic continental basement, resulting in a more felsic crust until the Triassic. (4) Sm-Nd parameters and detrital zircon age patterns of Early Paleozoic (meta)-sedimentary rocks from the North Patagonian Massif and those

  17. Depleted subcontinental lithospheric mantle and its tholeiitic melt metasomatism beneath NE termination of the Eger Rift (Europe): the case study of the Steinberg (Upper Lusatia, SE Germany) xenoliths

    NASA Astrophysics Data System (ADS)

    Kukuła, Anna; Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Büchner, Jörg; Tietz, Olaf

    2015-12-01

    The ca. 30 Ma Steinberg basanite occurs at the NE termination of the Eger (Ohře) Rift in the NW Bohemian Massif, Central Europe, and belongs to the Cenozoic alkaline Central European Volcanic Province. The basanite hosts a suite of mantle xenoliths, most of which are harzburgites containing relatively magnesian olivine (Fo 90.5-91.6) and Al-poor (0.04-0.13 a pfu) orthopyroxene (mg# 0.90-0.92). Some of these harzburgites also contain volumetrically minor clinopyroxene (mg# 0.92-0.95, Al 0.03-0.13 a pfu) and have U-shaped LREE-enriched REE patterns. The Steinberg harzburgites are typical for the Lower Silesian - Upper Lusatian domain of the European subcontinental lithospheric mantle. They represent residual mantle that has undergone extensive partial melting and was subsequently affected by mantle metasomatism by mixed carbonatite-silicate melts. The Steinberg xenolith suite comprises also dunitic xenoliths affected by metasomatism by melt similar to the host basanite, which lowered the Fo content in olivine to 87.6 %. This metasomatism happened shortly before xenolith entrainment in the erupting lava. One of the xenoliths is a wehrlite (olivine Fo 73 %, clinopyroxene mg# 0.83-0.85, subordinate orthopyroxene mg# 0.76-0.77). Its clinopyroxene REE pattern is flat and slightly LREE-depleted. This wehrlite is considered to be a tholeiitic cumulate. One of the studied harzburgites contains clinopyroxene with similar trace element contents to those in wehrlite. This type of clinopyroxene records percolation of tholeiitic melt through harzburgite. The tholeiitic melt might be similar to Cenozoic continental tholeiites occurring in the Central European Volcanic Province (e.g., Vogelsberg, Germany).

  18. Cambrian to Lower Ordovician complexes of the Kokchetav Massif and its fringing (Northern Kazakhstan): Structure, age, and tectonic settings

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.; Tolmacheva, T. Yu.; Tretyakov, A. A.; Kotov, A. B.; Shatagin, K. N.

    2016-01-01

    A comprehensive study of the Lower Palaeozoic complexes of the Kokchetav Massif and its fringing has been carried out. It has allowed for the first time to discover and investigate in detail the stratified and intrusive complexes of the Cambrian-Early Ordovician. Fossil findings and isotope geochronology permitted the determination of their ages. The tectonic position and internal structures of those complexes have also been defined and their chemical features have been analyzed as well. The obtained data allowed us to put forward a model of the geodynamic evolution of Northern Kazakhstan in the Late Ediacaran-Earliest Ordovician. The accumulation of the oldest Ediacaran to Earliest Cambrian siliciclastics and carbonates confined to the Kokchetav Massif and its fringing occurred in a shallow shelf environment prior to its collision with the Neoproterozoic Daut island arc: complexes of the latter have been found in the northeast of the studied area. The Early Cambrian subduction of the Kokchetav Massif under the Daut island arc, their following collision and exhumation of HP complexes led to the formation of rugged ground topography, promoting deposition of siliceous-clastic and coarse clastic units during the Middle to early Late Cambrian. Those sediments were mainly sourced from eroded metamorphic complexes of the Kokchetav Massif basement. At the end of the Late Cambrian to the Early Ordovician within the boundaries of the massif with the Precambrian crust, volcanogenic and volcano-sedimentary units along with gabbros and granites with intraplate affinities were formed. Simultaneously in the surrounding zones, which represent relics of basins with oceanic crust, N-MORB- and E-MORB-type ophiolites were developed. These complexes originated under extensional settings occurred in the majority of the Caledonides of Kazakhstan and Northern Tian Shan. In the Early Floian Stage (Early Ordovician) older heterogeneous complexes were overlain by relatively monotonous

  19. Additional Constraints on the Shallow Seismic Velocity Structure of the Atlantis Massif Oceanic Core Complex

    NASA Astrophysics Data System (ADS)

    Henig, A. S.; Blackman, D. K.; Harding, A. J.; Kent, G. M.; Canales, J. P.

    2008-12-01

    We investigate the detailed structure of the uppermost ~km of Atlantis Massif, an oceanic core complex at 30°N on the Mid Atlantic Ridge, using pre-existing multichannel seismic data. The Synthetic On- Bottom Experiment (SOBE) method that we employ downward continues both the shots and receivers to a depth just above the seafloor. This allows us to pick refracted arrivals recorded on the streamer at very-near offset, providing constraints from rays that are received within the 300-2000 m range that was unavailable to earlier studies where standard shot gathers had been analyzed. Thus, we can better model the upper few hundred meters of the section which, in turn, adds confidence for determining the deeper (400-1500 m) structure. New work on a ridge-parallel line has been added to last year's work on a cross-axis line over the Central Dome of the massif. Tomographic results are similar for these crossing lines: a thin (100-150 m) low velocity (< 3 km/s) layer caps the dome; high horizontal gradients (>1.25 s-1) occur in local (1-2 km wide) regions within these 6-8 km long subsections of the MCS lines analyzed to date; and very high vertical velocity gradients, greater than 3.75 s-1, occur within the km just below the exposed detachment in these areas. We obtain general agreement with Canales et al., 2008, results over the Central Dome but our models suggest a finer scale lateral heterogeneity. We have begun analysis of additional and extended MCS lines over the domal core of the massif and our priority for this presentation is to assess the detailed structure of the Southern Ridge. In at least some areas the thin, low velocity layer contrasts sufficiently with underlying material that a clear refracted arrival is visible in supergathers. We will determine whether the low velocity layer persists over the whole dome or if it is restricted to the Central Dome. An important question is whether its thickness on the Southern Ridge, if it exists there, differs from that

  20. SE-FIT

    NASA Technical Reports Server (NTRS)

    Chen, Yongkang; Weislogel, Mark; Schaeffer, Ben; Semerjian, Ben; Yang, Lihong; Zimmerli, Gregory

    2012-01-01

    The mathematical theory of capillary surfaces has developed steadily over the centuries, but it was not until the last few decades that new technologies have put a more urgent demand on a substantially more qualitative and quantitative understanding of phenomena relating to capillarity in general. So far, the new theory development successfully predicts the behavior of capillary surfaces for special cases. However, an efficient quantitative mathematical prediction of capillary phenomena related to the shape and stability of geometrically complex equilibrium capillary surfaces remains a significant challenge. As one of many numerical tools, the open-source Surface Evolver (SE) algorithm has played an important role over the last two decades. The current effort was undertaken to provide a front-end to enhance the accessibility of SE for the purposes of design and analysis. Like SE, the new code is open-source and will remain under development for the foreseeable future. The ultimate goal of the current Surface Evolver Fluid Interface Tool (SEFIT) development is to build a fully integrated front-end with a set of graphical user interface (GUI) elements. Such a front-end enables the access to functionalities that are developed along with the GUIs to deal with pre-processing, convergence computation operation, and post-processing. In other words, SE-FIT is not just a GUI front-end, but an integrated environment that can perform sophisticated computational tasks, e.g. importing industry standard file formats and employing parameter sweep functions, which are both lacking in SE, and require minimal interaction by the user. These functions are created using a mixture of Visual Basic and the SE script language. These form the foundation for a high-performance front-end that substantially simplifies use without sacrificing the proven capabilities of SE. The real power of SE-FIT lies in its automated pre-processing, pre-defined geometries, convergence computation operation

  1. Thematic mapping of likely target areas for the occurence of cassiterite in the Serra do Mocambo (GO) granitic massifs using LANDSAT 2 digital imaging

    NASA Technical Reports Server (NTRS)

    Almeidofilho, R. (Principal Investigator)

    1984-01-01

    The applicability of LANDSAT/MSS images, enhanced by computer derived techniques, as essential tools in mineral research was investigated and the Serra do Mocambo granitic massif was used as illustration. Given the peculiar factors founded in this area, orbital imagery permitted the delineation of potential target areas of mineralization occurrences, associated to albitized/greisenized types. Follow up prospection for primary tin deposits in this granitic massif should be restricted to the delineated areas which are less than 5% of the total superficial area of the massif.

  2. First geochronological study of the volcanic plateau of aubrac (French Massif Central) - tectonic and regional implications

    NASA Astrophysics Data System (ADS)

    Baubron, J. C.; Demange, J.

    1982-10-01

    The volcanism of the Aubrac fissural basaltic plateau is located between Cantal a large stratovolcano to the north, and the Causse of Séverac-le-Château - a limestone plateau on which crop out some basaltic intrusions - to the south. The first K/Ar age determinations show that this volcanism mainly took place between 8 and 7.5 m.y. preceded and followed by short episodes around 9.2 and 5.8 m.y. The occurrence of differentiated products is discussed and correlated with substratum geology of these volcanic centres. The episode of activity (i.e. 8 to 7.5 m.y.) discovered in Aubrac and Causse of Séveracle-Château, is not a localized event, but part of a regional activity in the central area of the Massif Central. The occurrence of magmatic activity correlates with the old Hercynian tectonic.

  3. Crystal structure of hydrogen-bearing vuonnemite from the Lovozero alkaline massif

    SciTech Connect

    Rastsvetaeva, R. K. Aksenov, S. M.; Verin, I. A.; Lykova, I. S.

    2011-05-15

    Hydrogen-bearing vuonnemite from the Shkatulka hyperagpaitic pegmatite (the Lovozero alkaline massif, Kola Peninsula) was studied by single-crystal X-ray diffraction. The triclinic unit-cell parameters are as follows: a = 5.4712(1) Angstrom-Sign , b = 7.1626(1) Angstrom-Sign , c = 14.3702(3) Angstrom-Sign , {alpha} = 92.623(2) Degree-Sign , {beta} = 95.135(1) Degree-Sign , {gamma} = 90.440(1) Degree-Sign , sp. gr. P1, R = 3.4%. The Na{sup +} cations and H{sub 2}O molecules are ordered in sites between the packets. The water molecules are hydrogen bonded to the PO{sub 4} tetrahedra.

  4. Oxidation state of the lithospheric mantle beneath the Massif Central,France

    NASA Astrophysics Data System (ADS)

    Uenver-Thiele, L.; Woodland, A. B.; Downes, H.; Altherr, R.

    2012-04-01

    The Tertiary and Quaternary volcanism of the French Massif Central sampled the underlying subcontinental lithospheric mantle (SCLM) in the form of xenoliths over a wide geographic area of ~20.000km2. Such an extensive distribution of xenoliths provides an unique opportunity to investigate regional variations in mantle structure and composition. On the basis of textural and geochemical differences, Lenoir et al. (2000) and later Downes et al. (2003) identified two distinct domains in the SCLM lying north and south of latitude 45° 30' N, respectively. The northern domain is relatively refractory, but has experienced pervasive enrichment of LREE. The southern domain is generally more fertile, exhibiting depletion in LREE. A metasomatic overprint has developed to variable extents in many xenolith suites. The different histories of these two juxtaposed blocks of SCLM should also be reflected in their oxidation state, with local variations also to be expected due to metasomatic interactions. For example, if carbonate-melt metasomatism played a role in the LREE enrichment of the northern domain (Lenoir et al. 2000; Downes et al. 2003), then such mantle should be relatively oxidised. Since surprisingly little redox data are currently available, we are undertaking a study to determine the oxidation state of the SCLM beneath the Massif Central over the largest geographical area possible. All xenoliths investigated are spinel peridotites, mostly with protogranular textures (although some samples are porphyroclastic or equigranular). Most samples are nominally anhydrous although minor amphibole is present in some xenolith suites. Major element compositions of the individual minerals were determined by microprobe. Two-pyroxene temperatures (BKN) range from 750° to ~1200° C. Ferric iron contents of spinel were determined by Mössbauer spectroscopy and gave a range of Fe3+/ Fetot from 0.191 to 0.418, with a conservative uncertainty of ±0.02. These data were used to calculate

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

    NASA Technical Reports Server (NTRS)

    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.

  6. Application of GIS technologies to monitor secondary radioactive contamination in the Delegen mountain massif

    NASA Astrophysics Data System (ADS)

    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.

  7. Sm-Nd dating of fluorite from the worldclass Montroc fluorite deposit, southern Massif Central, France

    USGS Publications Warehouse

    Munoz, M.; Premo, W.R.; Courjault-Rade, P.

    2005-01-01

    A three-point Sm-Nd isotope isochron on fluorite from the very large Montroc fluorite vein deposit (southern Massif Central, France) defines an age of 111??13 Ma. Initial ??Nd of -8.6 and initial 87Sr/86Sr of ???0.71245 suggest an upper crustal source of the hydrothermal system, in agreement with earlier work on fluid inclusions which indicated a basinal brine origin. The mid-Cretaceous age of ???111 Ma suggests the Albian/Aptian transition as the most likely period for large-scale fluid circulation during a regional extensional tectonic event, related to the opening of the North Atlantic ocean. ?? Springer-Verlag 2004.

  8. Permafrost detection in the headwalls of receding glaciers at the Dachstein Massif, Northern Calcareous Alps, Austria

    NASA Astrophysics Data System (ADS)

    Rode, Matthias; Gitschthaler, Christoph; Schnepfleitner, Harald; Kellerer-Pirklbauer, Andreas; Sass, Oliver

    2014-05-01

    The Northern Calcareous Alps cover a large area of the Austrian Alps forming a boundary zone between the Alpine Foreland to the north and the crystalline Central Alps to the south. Generally, climate in this area is more maritime compared to the mountain ranges further south. Few small glaciers are to be found mostly on north-facing slopes. The Northern Calcareous Alps reach maximum elevations of about 3000 m asl. Some of highest summits are to be found are located in the Dachstein Massif reaching 2995 m asl (47° 28' 32″ N, 13° 36' 23″ E). Occurrence, thickness and thermal regime of permafrost at this mountain massif are widely unknown and knowledge is based on simulations only. In contrast, the glaciation changes at this mountain massif (e.g. Schladminger and Hallstätter glaciers) have been well documented for decades. Within the framework of the research project ROCKING ALPS - dealing with frost weathering and rockfall in alpine regions - knowledge of permafrost distribution in the headwalls surrounding the receding glaciers is substantial to understand rock decay. For this reason, several techniques have been applied in order to detect bedrock permafrost. During the winter of 2012 22 i-buttons (temperature sensors) were attached to rock walls with different orientations but at similar elevations (2600-2700 m asl). Most of these sites were later covered by an insulating winter snow cover therefore allowing the calculation of the base temperature of the winter snow cover (BTS). These BTS data have been used as a first indicator of permafrost presence. In selected rock walls of several mountains in the massif - Koppenkarstein (2863 m asl), Dirndln (2829 m asl) and Gjaidstein (2794 m asl) - additional 2D-geoelectric surveys (five ERT profiles with a length of 100 m and 2 m electrode spacing) were measured in summer 2013. The high resistivities (> 50.000 ohm.m) at about 1.5 m depth and deeper strongly suggest permafrost existence inside the bedrock at all

  9. Physical-Chemical Factors Affecting the Low Quality of Natural Water in the Khibiny Massif

    NASA Astrophysics Data System (ADS)

    Mazukhina, Svetlana; Masloboev, Vladimir; Chudnenko, Konstantin; Maksimova, Viktoriia; Belkina, Natalia

    2014-05-01

    One peculiarity of the Khibiny Massif is its spatial location. Rising over 1000 m above the surrounding hilly land and thus obstructing the passage of air masses, it promotes condensation and accumulation of surface and underground water. Annual precipitation here amounts to 600-700 mm in the valleys and up to 1600 mm on mountainous plateaus. Using this water for drinking and household purposes is problematic due to excess Al and F concentrations and high pH values. Now it is known that in its profile, the Massif is represented by three hydrogeological subzones: the upper (aerated), medium and lower ones. The upper subzone spreads throughout the Massif and is affected by the local drainage network and climatic conditions. The medium subzone is permanently saturated with underground water flowing horizontally to sites of discharge at the level of local river valleys and lakes. The fissure-vein water in the lower subzone is confined to tectonic fractures and faults in the so far underexplored, deeper parts of the Massif. Being abundant, this water ascends under high pressure. At places, water has been observed spurting from as deep as 700 m, and even 960 m. In the latter case, the temperature of ascending water was higher than 18 centigrade (Hydrogeology of the USSR, V. 27, 1971). This work was undertaken to reveal the nature of the low quality of water in the Khibiny by using physical-chemical modeling (software package Selector, Chudnenko, 2010). Processes of surface and underground water formation in the Khibiny were examined within a physical-chemical model (PCM) of the "water-rock-atmosphere-hydrogen" system. In a multi-vessel model used, each vessel represented a geochemical level of the process interpreted as spatiotemporal data - ξ (Karpov, 1981). The flow reactor consisted of 4 tanks. In the first tank, water of the Kuniok River (1000 L) interacted with atmosphere and an organic substance. The resulting solution proceeded to tanks 2-4 containing with

  10. Remains of early Ordovician mantle-derived magmatism in the Santander Massif (Colombian Eastern Cordillera)

    NASA Astrophysics Data System (ADS)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Cottle, John M.; Hart, Craig J. R.

    2012-10-01

    An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛHft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth's mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure.

  11. Geochemistry of a Triassic dyke swarm in the North Patagonian Massif, Argentina. Implications for a postorogenic event of the Permian Gondwanide orogeny

    NASA Astrophysics Data System (ADS)

    González, Santiago N.; Greco, Gerson A.; González, Pablo D.; Sato, Ana M.; Llambías, Eduardo J.; Varela, Ricardo

    2016-10-01

    Permo-Triassic magmatism is widespread in the eastern North Patagonian Massif and has been related to the Gondwanide orogeny. Although a magmatic arc setting is widely accepted for the Permian plutonic rocks, the origin and geotectonic setting for the Triassic plutonic and volcanic rocks are still unknown. A NW-SE Triassic dyke swarm composed of andesites and latites with minor rhyolites was previously described in the Sierra Grande - Rincon de Paileman area. The dyke swarm was associated with extensional tectonics which was linked to a postorogenic process. In this paper we present new geochemical data of the rocks that form the swarm. Trachyandesites and rhyolites were separated based on their geochemical characteristics. Both groups may be considered originated from different sources. On the other hand, the content of incompatible elements (LILE and HFSE) indicates a strong relation between the swarm and an active continental margin. The samples also show a transitional signature between continental-arc and postcollisional or anorogenic settings. The new geochemical data on the dyke swarm support the idea of a magmatism that was linked to a postorogenic extensional tectonic regime related to a continental magmatic arc. Such an extension started in the Paleopacific margin of Pangea during the Anisian and might indicate the beginning of the Pangea break-up.

  12. Fluid flow and polymetallic sulfide mineralization in the Kettara shear zone (Jebilet Massif, Variscan Belt, Morocco)

    NASA Astrophysics Data System (ADS)

    N'diaye, I.; Essaifi, A.; Dubois, M.; Lacroix, B.; Goodenough, K. M.; Maacha, L.

    2016-07-01

    The Kettara shear zone is a regional wrench shear zone within the Jebilet massif of Western Morocco, part of the Variscan orogenic belt. This massif is characterized by bimodal magmatism, largely intrusive, and by a number of polymetallic massive sulfide deposits. A syntectonic mafic-ultramafic intrusion and an adjacent, deformed pyrrhotite-rich massive sulfide deposit are located within a 'compressional jog' of the shear zone. Hydrothermal alteration in both the intrusion and the wall rocks adjacent to the deposit is characterized by syntectonic replacement processes leading to formation of chlorite-schists and quartz ± calcite veins. Fluid inclusions in mineralized (pyrrhotite-bearing) quartz veins from the wall rocks adjacent to the deposit and in veins associated with chlorite-schists within the intrusion indicate a prevalence of H2O-CO2-CH4-N2 and H2O-salt fluid systems. In the mineralized veins the fluid shows reducing conditions, with gas dominated by CH4 and N2 and salinities around 7.5 wt% NaCl, whereas in the chlorite shear zones fluid is CO2 dominated and salinities are higher than 23 wt% NaCl. Hydrogen and oxygen isotopic compositions of chlorite and quartz are similar and demonstrate involvement of metamorphic water in both the deposit and the intrusion. The data are consistent with a regional metamorphic fluid flow through the Kettara shear zone. The migrating metamorphic fluids were reduced in the organic matter-rich host rocks leading to deposition of sulfides in the mineralized veins. There are two possible hypotheses for the origin of these mineralized veins: either they were formed during deformation and remobilization of a syn-sedimentary massive sulfide deposit, or they were formed synchronously with the sulfide deposit during development of the Kettara shear zone.

  13. Proterozoic massif anorthosites and related rocks in Labrador: the anorthosite-charnockite connection

    SciTech Connect

    Emslie, R.F.

    1985-01-01

    Massif anorthosites of Labrador are closely associated in space and time with voluminous, felsic, fayalite- and ferrous pyroxene-bearing igneous rocks. These include charnockites, monzonites, biotite-hornblende granites, and locally syenites. Igneous charnockites form major parts of some of the granitic complexes. In Mistastin batholith for example, charnockitic assemblages comprise about 35% of a total area of 6500 sq. km. Feldspar pairs and coexisting fayalite-opx-qtz in these rocks indicate P and T near 3.5 kb, 750/sup 0/C, assumed to represent near solidus equilibration. Diorites and monzonites intruded by charnockite have mesoperthites implying crystallization T>900/sup 0/C presumably recording earlier stages of crystallization. Oxide and silicate assemblages indicate redox conditions between FMQ and WM oxygen buffers and water pressures well below Ptotal. Younger biotite-hornblende granites and quartz syenites lack Ti-mt. but retain fayalite suggesting that magmatic crystallization was largely closed to water and oxygen. Initial Sr isotope ratios in charnockite-granite suites of central labrador support derivation of the magmas largely or entirely from crustal source rocks. Compositions of mafic silicates and plagioclase, associated Fe-Ti oxide concentrations, trace elements and Sr isotopes in massif anorthosites are in accord with the rocks being crystallization products of substantially fractionated, originally more mafic, mantle magmas. Close association of high temperature, water-poor, reduced crustal melts is consistent with a fusion process in which heat supply and oxygen buffering were controlled by fractional crystallization of a substantial body of mafic magma subjacent to continental crust.

  14. Homogeneous /sup 18/O enrichment of the Marcy Anorthosite Massif, Adirondack Mountains, New York

    SciTech Connect

    Morrison, J.; Valley, J.W.

    1985-01-01

    The Marcy Anorthosite Massif in the Adirondack Mountains, New York, is a composite intrusion that was metamorphosed to granulite facies at approx. 1.1 Ga. The massif is dominantly anorthosite but ranges from anorthosite (1-10% mafics) to oxide-rich pyroxenite layers (up to 98% mafics). In the St Regis Quad (SRQ) systematic variations in the percentage of mafics (POM) roughly parallel the foliation and increase toward the contacts (Davis, 1971). In 47 SRQ samples studied the POM varies from 2-25%; garnet ranges from 0-11%, pyroxene from <1-16% and oxides from <1-8%. Percent phenocrysts varies between 1-80. The Port Kent-Westport Unit (PKW) and an associated hybrid unit show significantly greater textural variability. The POM Varies from 1-50%; garnet ranges from 0-18%, pyroxene from 0-15%, oxides from 0-3% and phenocrysts vary from 0-80%. A total of 28 unaltered plagioclase phenocrysts have been analyzed for delta/sup 18/O: in 13 SRQ samples delta/sup 18/O = 9.0-9.8 (x=9.4. sigma=0.2) and in 15 samples from the PKW and hybrid units values of delta/sup 18/O=8.5-10.5 (x=9.5.sigma0.5). No correlations exist between the modal parameters and delta/sup 18/O. The results from SRQ demonstrate an extreme homogeneity suggesting for the first time a pristine magmatic character which is supported by the virtual absence of metasedimentary inclusions. This contrasts with PKW where inclusions are common and delta/sup 18/O values are more heterogeneous. Further analyses will evaluate the possibility of an anomalous source region as a cause of the /sup 18/O enrichment in the anorthosite.

  15. Fluid flow and polymetallic sulfide mineralization in the Kettara shear zone (Jebilet Massif, Variscan Belt, Morocco)

    NASA Astrophysics Data System (ADS)

    N'diaye, I.; Essaifi, A.; Dubois, M.; Lacroix, B.; Goodenough, K. M.; Maacha, L.

    2016-07-01

    The Kettara shear zone is a regional wrench shear zone within the Jebilet massif of Western Morocco, part of the Variscan orogenic belt. This massif is characterized by bimodal magmatism, largely intrusive, and by a number of polymetallic massive sulfide deposits. A syntectonic mafic-ultramafic intrusion and an adjacent, deformed pyrrhotite-rich massive sulfide deposit are located within a 'compressional jog' of the shear zone. Hydrothermal alteration in both the intrusion and the wall rocks adjacent to the deposit is characterized by syntectonic replacement processes leading to formation of chlorite-schists and quartz ± calcite veins. Fluid inclusions in mineralized (pyrrhotite-bearing) quartz veins from the wall rocks adjacent to the deposit and in veins associated with chlorite-schists within the intrusion indicate a prevalence of H2O-CO2-CH4-N2 and H2O-salt fluid systems. In the mineralized veins the fluid shows reducing conditions, with gas dominated by CH4 and N2 and salinities around 7.5 wt% NaCl, whereas in the chlorite shear zones fluid is CO2 dominated and salinities are higher than 23 wt% NaCl. Hydrogen and oxygen isotopic compositions of chlorite and quartz are similar and demonstrate involvement of metamorphic water in both the deposit and the intrusion. The data are consistent with a regional metamorphic fluid flow through the Kettara shear zone. The migrating metamorphic fluids were reduced in the organic matter-rich host rocks leading to deposition of sulfides in the mineralized veins. There are two possible hypotheses for the origin of these mineralized veins: either they were formed during deformation and remobilization of a syn-sedimentary massive sulfide deposit, or they were formed synchronously with the sulfide deposit during development of the Kettara shear zone.

  16. Investigating K-feldspar Luminescence Thermochronometry for Application in the Mont Blanc Massif

    NASA Astrophysics Data System (ADS)

    Lambert, R.; King, G. E.; Herman, F.; Valla, P.

    2015-12-01

    Luminescence dating has the potential to quantify the recent exhumation history of mountain ranges as a low-temperature thermochronometer. During rock exhumation, electrons get trapped through exposure to ionizing radiation whilst elevated temperatures cause thermally stimulated detrapping. The resulting luminescence signals measured in the laboratory can be used to constrain rock thermal histories through modelling of the kinetic parameters of electron trapping and detrapping. Here, we investigate and model laboratory kinetic processes of the luminescence of K-feldspar and assess their extrapolation over geological timescales. Samples were taken from the actively eroding Mont Blanc massif in the European Alps, along a 12 km long tunnel with ambient temperatures of 10-35 °C. In this setting rapid exhumation rates have been found during the last 2 million years (up to ~2 km/Myr), however, we intend to increase the temporal resolution to sub-Quaternary timescales using luminescence thermochronometry. Infra-red stimulated luminescence signals at 50 °C (IR50) and at 225 °C (post-IR IRSL225) of K-feldspar extracted from Mont Blanc tunnel samples were measured and our first results reveal a thermal signature from which rock cooling rates can be derived. Isothermal decay experiments show non-exponential decay, but interestingly, experiments with a range of regenerative doses reveal first-order kinetics. The observed thermal decay pattern is well-described by a model based on a physically plausible distribution of the density of states. Ultimately, we intend to use the IR50 and post-IR IRSL225 signals of K-feldspar as dual thermochronometers to determine the late-Quaternary cooling history of the Mont Blanc massif. Moreover, the luminescence signals may give insights into local thermal field evolution, before the influence of postglacial hydrothermal flow.

  17. Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

    NASA Astrophysics Data System (ADS)

    Pál-Molnár, Elemér; Batki, Anikó; Almási, Enikő; Kiss, Balázs; Upton, Brian G. J.; Markl, Gregor; Odling, Nicholas; Harangi, Szabolcs

    2015-12-01

    Mafic-ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75-73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~ 1000-1050 °C and ~ 0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting.

  18. Structural analysis and evolution of the Hadong-Sancheong-Hwagae area in the Yeongnam massif, Korea: a NS-trend tectonic frame in the Korean Peninsula

    NASA Astrophysics Data System (ADS)

    Deok-Seon, Lee; Ji-Hoon, Kang

    2016-04-01

    The Hadong-Sancheong-Hwagae area in the Jirisan province of the Yeongnam massif, Korea, is mainly composed of Precambrian Hadong anorthosite complex (HAC), Precambrian Jirisan metamorphic rock complex (JMRC), Jurassic˜Triassic granitoids which intrude them, and Cretaceous sedimentary rocks which unconformably cover them. Lithofacies distribution and tectonic frame of the Precambrian constituent rocks mainly show a NS trend, unlike a general NE trend of those in the Korean Peninsula. To unravel the geological structures associated with the NS-trend tectonic frame which was built in the HAC and JMRC, we researched the structural characteristics of each deformation phase based on the geometric and kinematic features and the forming sequence of rock structures of the multi-deformed HAC and JMRC. The results indicate that the pre-Late Paleozoic geological structures of this area were formed at least through the following three times of ductile deformation phases. The D1 deformation happened due to the large-scale top-to-the SE shearing, and formed sheath or A-type folds and a regional NE trend of tectonic frame in the HAC and JMRC. The D2 deformation occurred under the EW-directed tectonic compression, and formed a regional NS trend of active and passive folds and Hadong ductile shear zone over 2.3˜1.4 km width, and transposed most of D1 tectonic frame into D1-2 composite tectonic frame. The extensive Hadong shear zone, which was formed in the mylonitization process accompanying the passive folding, was persistently developed along the eastern boundary of HAC and JMRC which corresponds to a limb of passive fold on a geological map scale. It produced a very strong mylonitic structure and stretching lineation. The NE-trend D1 structural elements were mainly reoriented into NS trend by the powerful active and passive folding. The D3 deformation occurred under the NS-trend tectonic compression environment, and formed EW-trend kink or open folds, and partially rearranged

  19. Carboniferous magmatism in the Evora Massif (southwest Portugal, Ossa-Morena Zone): from typical arc calc-alkaline to adakitic-like magmatism

    NASA Astrophysics Data System (ADS)

    Lima, Selma M.; Neiva, Ana M. R.; Ramos, Joao M. F.

    2014-05-01

    The Evora Massif is one of the subdivisions of western Ossa-Morena Zone. It is a dome-like structure mainly composed of Ediacaran, Cambrian and Ordovician country rocks, affected by medium- and high-grade metamorphism coeval with the emplacement of several mafic to felsic intrusive bodies. The last magmatic event recorded in this area (Carboniferous) consists of calc-alkaline volcanism and voluminous plutonism (mainly composed by tonalites, gabbros, diorites and late-orogenic granodiorites and granites) [1]. Detailed chemical and isotopic studies from Evora Massif plutons were performed in the last few years. Whole-rock chemical and isotopic data suggest that the Hospitais tonalite (HT), Alto de Sao Bento area (ASB) and Reguengos de Monsaraz pluton (RM) resulted from fractional crystallization of mantle-derived magmas followed by mixing with variable proportions of crustal melts [2-4]. U-Pb ID-TIMS data indicate an age of 337-335 for the RM [4]. The Pavia pluton is a multiphase granitic body constructed incrementally by the episodic emplacement of several batches of magma (at 328 Ma, ca. 324 Ma and 319-317 Ma) [5]. The main granitic phases range from tonalite to two-mica granite that contain rare surmicaceous and fine-grained enclaves, and granitic and amphibolitic xenoliths. On the other hand, they are cut by abundant rhyodacite porphyries, microgranites (s.l.) and pegmatite dikes, predominantly oriented NE-SW and NW-SE. Although each phase seems to represent a distinct batch of magma, whole-rock Sr-Nd isotopic data suggest a similar and fairly homogenous source for all the constituent phases. Initial 87Sr/86Sr varies between 0.70428 and 0.7058 and ɛ Ndt ranges from -3.4 to +0.4, pointing towards a mantle or juvenile crust origin. A higher variation is observed in whole-rock δ18O (5.6-9.6 o), consistent with assimilation of crust. The PP was interpreted as the result of assimilation-fractional crystallization of a basaltic magma. Substantial differences between

  20. Instability of a highly vulnerable high alpine rock ridge: the lower Arête des Cosmiques (Mont Blanc massif, France)

    NASA Astrophysics Data System (ADS)

    Ravanel, L.; Deline, P.; Lambiel, C.; Vincent, C.

    2012-04-01

    Glacier retreat and permafrost degradation are actually more and more thought to explain the increasing instability of rock slopes and rock ridges in high mountain environments. Hot summers with numerous rockfalls we experienced over the last two decades in the Alps have indeed contributed to test/strengthen the hypothesis of a strong correlation between rockfalls and global warming through these two cryospheric factors. Rockfalls from recently deglaciated and/or thawing areas may have very important economic and social implications for high mountain infrastructures and be a fatal hazard for mountaineers. At high mountain sites characterized by infrastructures that can be affected by rockfalls, the monitoring of rock slopes, permafrost and glaciers is thus an essential element for the sustainability of the infrastructure and for the knowledge/management of risks. Our study focuses on a particularly active area of the Mont Blanc massif (France), the lower Arête des Cosmiques, on which is located the very popular Refuge des Cosmiques (3613 m a.s.l.). Since 1998, when a rockfall threatened a part of the refuge and forced to major stabilizing works, observations allowed to identify 10 detachments (20 m3 to > 1000 m3), especially on the SE face of the ridge. Since 2009, this face is yearly surveyed by terrestrial laser scanning to obtain high-resolution 3D models. Their diachronic comparison gives precise measurements of the evolution of the rock slope. Eight rock detachments have thus been documented (0.7 m3 to 256.2 m3). Rock temperature measurements at the ridge and the close Aiguille du Midi (3842 m a.s.l.), and observations of the evolution of the underlying Glacier du Géant have enable to better understand the origin of the strong dynamics of this highly vulnerable area: (i) rock temperature data suggest the presence of warm permafrost (i.e. close to 0°C) from the first meters to depth in the SE face, and cold permafrost in the NW face; (ii) as suggested by the

  1. Volcanic evolution of the submarine super volcano, Tamu Massif of Shatsky Rise: New insights from Formation MicroScanner logging imagery

    NASA Astrophysics Data System (ADS)

    Tominaga, Masako; Iturrino, Gerardo; Evans, Helen F.

    2015-01-01

    Massif, the southernmost plateau of Shatsky Rise, is recently reported as the largest single volcano known on Earth. This work seeks to understand the type of volcanism necessary to form such an anomalously large single volcano by integrating core and high-resolution wireline logging data. In particular, resistivity imagery obtained by the Formation MicroScanner, in Integrated Ocean Drilling Program Hole U1347A, located on the eastern flank of Tamu Massif, was used to construct a logging-based volcanostratigraphy. This model revealed two different volcanic stages formed Tamu Massif: (i) the core part of the massif's basaltic basement was formed by a "construction phase" of volcanism with cyclic eruption events from a steady state magma supply and (ii) the very topmost basaltic section was formed by a "depositional phase" of volcanism during which long-traveling lava flows were deposited from a distant eruption center.

  2. Subcontinental rift initiation and ocean-continent transitional setting of the Dinarides and Vardar zone: Evidence from the Krivaja-Konjuh Massif, Bosnia and Herzegovina

    NASA Astrophysics Data System (ADS)

    Faul, Ulrich H.; Garapić, Gordana; Lugović, Boško

    2014-08-01

    The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to the Albanian and Greek ophiolites. Detailed sampling of the Krivaja-Konjuh massif, one of the largest massifs in the Dinaride belt, reveals fertile compositions and an extensive record of deformation at spinel peridotite facies conditions. High Na2O clinopyroxene and spinel-orthopyroxene symplectites after garnet indicate a relatively high pressure, subcontinental origin of the southern and western part of Krivaja, similar to orogenic massifs such as Lherz, Ronda and the Eastern Central Alpine peridotites. Clinopyroxene and spinel compositions from Konjuh show similarities with fertile abyssal peridotite. In the central parts of the massif the spinel lherzolites contain locally abundant patches of plagioclase, indicating impregnation by melt. The migrating melt was orthopyroxene undersaturated, locally converting the peridotites to massive olivine-rich troctolites. Massive gabbros and more evolved gabbro veins cross-cutting peridotites indicate continued melt production at depth. Overall we infer that the massif represents the onset of rifting and early stages of formation of a new ocean basin. In the south of Krivaja very localized chromitite occurrences indicate that much more depleted melts with supra-subduction affinity traversed the massif that have no genetic relationship with the peridotites. This indicates that volcanics with supra-subduction affinity at the margins of the Krivaja-Konjuh massif record separate processes during closure of the ocean basin. Comparison with published compositional data from other Balkan massifs shows that the range of compositions within the Krivaja-Konjuh massif is similar to the compositional range of the western massifs of the Dinarides. The compositions of the Balkan massifs show a west to east gradient, ranging from subcontinental on the western side of the Dinarides to depleted mid-ocean ridge/arc compositions in the Vardar

  3. The Carboniferous volcano-sedimentary depocentre of Tazekka Massif (Middle-Atlas, Morocco): new observations and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Bennouna, Azzeddine; Abbou, Mohamed Ben; Hoepffner, Christian; Kharbouch, Fatima; Youbi, Nasrrddine

    2004-06-01

    The integrated analysis of thrust structures and facies allows us to interpret the Carboniferous volcano-sedimentary complex of Tazekka massif as a compressive sub-basin controlled mainly by the Hajra Sbaa-Merja Caï'd northwest-verging thrust-propagation fold. The tectono-sedimentary sequence (conglomerates, greywacke and shale) is associated with an extrusive magmatism comprising basalts, andesites and rhyolites, under effusive and volcanoclastic facies (or rhyolites with exotic blocks), of orogenic calk-alkaline nature, which is consistent with a context of continental subduction. These results, and the comparison of regional contraction ages in the Moroccan Meseta, integrate the Carboniferous volcano-sedimentary depocentre of Tazekka massif in the wedgetop depozone of a foreland basin system generated by two north-west thrusted piggy-back sequences (aged from Fameno-Tournaisian to upper Visean-lower Westphalian) from the eastern Meseta to the western Meseta of Morocco.

  4. A MASSIF Effort To Determine The Mass-Luminosity Relation for Stars of Various Ages, Metallicities, and Evolution States

    NASA Technical Reports Server (NTRS)

    Henry, Todd J.; Beedict, G. Fritz; Gies, Douglas R.; Golimowski, David A.; Ianna, Philip A.; Mason, Brian; McArthur, Barbara; Nelan, Edmund; Torres, Guillermo

    2004-01-01

    The MASSIF (Masses and Stellar Systems with Interferometry) Team will use SIM to investigate the mass content of the Galaxy - from huge stars to barely glimmering brown dwarfs, and from hot white dwarfs to exotic black holes. We will target various samples of the Galactic population to determine and relate the fundamental characteristics of mass, luminosity, age, composition, and multiplicity - attributes that together yield an extensive understanding of the stars. Our samples will include distant clusters that span a factor of 5000 in age, and commonplace stars and substellar objects that lurk near the Sun. The principal goals of the MASSIF Key Project are to (1) define the mass-luminosity relation for main sequence stars in five fundamental clusters so that effects of age and metallicity can be mapped (Trapezium, TW Hydrae, Pleiades, Hyades, and M67), and (2) determine accurate masses for representative examples of nearly every type of star, stellar descendant or brown dwarf in the Galaxy.

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

    NASA Astrophysics Data System (ADS)

    Dvorani, Sami N.

    2016-04-01

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

  6. The Galicia-Ossa-Morena Zone: Proposal for a new zone of the Iberian Massif. Variscan implications

    NASA Astrophysics Data System (ADS)

    Arenas, Ricardo; Díez Fernández, Rubén; Rubio Pascual, Francisco J.; Sánchez Martínez, Sonia; Martín Parra, Luis Miguel; Matas, Jerónimo; González del Tánago, José; Jiménez-Díaz, Alberto; Fuenlabrada, Jose M.; Andonaegui, Pilar; Garcia-Casco, Antonio

    2016-06-01

    Correlation of a group of allochthonous terranes (referred to as basal, ophiolitic and upper units) exposed in the NW and SW of the Iberian Massif, is used to propose a new geotectonic zone in the southern branch of the Variscan Orogen: the Galicia-Ossa-Morena Zone. Recent advances in SW Iberia identify most of the former Ossa-Morena Zone as another allochthonous complex of the Iberian Massif, the Ossa-Morena Complex, equivalent to the Cabo Ortegal, Órdenes, Malpica-Tui, Bragança and Morais complexes described in NW Iberia. The new geotectonic zone and its counterparts along the rest of the Variscan Orogen constitute an Internal Variscan Zone with ophiolites and units affected by high-P metamorphism. The Galicia-Ossa-Morena Zone includes a Variscan suture and pieces of continental crust bearing the imprint of Ediacaran-Cambrian events related to the activity of peri-Gondwanan magmatic arcs (Cadomian orogenesis). In the Iberian Massif, the general structure of this geotectonic zone represents a duplication of the Gondwanan platform, the outboard sections being juxtaposed on top of domains located closer to the mainland before amalgamation. This interpretation offers an explanation that overcomes some issues regarding the differences between the stratigraphic and paleontological record of the central and southern sections of the Iberian Massif. Also, equivalent structural relationships between other major geotectonic domains of the rest of the Variscan Orogen are consistent with our interpretation and allow suspecting similar configurations along strike of the orogen. A number of issues may be put forward in this respect that potentially open new lines of thinking about the architecture of the Variscan Orogen.

  7. Scorpions from the Mitaraka Massif in French Guiana: Description of one new genus and species (Scorpiones: Chactidae).

    PubMed

    Lourenço, Wilson R

    2016-01-01

    A new genus and species, Spinochactas mitaraka gen. n., sp. n. (Chactidae) are described from the Mitaraka Massif in French Guiana, a site located near the borders of French Guiana, Brazil, and Suriname. The description of the new genus and species brings further evidence of the biogeographic pattern of distribution presented by some elements of the family Chactidae endemic to the Tepuys or to the Inselberg formations of South America.

  8. The western limits of the Seattle and Tacoma faults and their interaction with faults of the Olympic Massif, Washington (Invited)

    NASA Astrophysics Data System (ADS)

    Lamb, A.; Blakely, R. J.; Liberty, L. M.; Pratt, T. L.; Sherrod, B. L.

    2013-12-01

    Recently acquired high-resolution seismic-reflection and magnetic data show that the Seattle fault of Washington State extends 24-km west of its previously mapped extent and thus comprises a >100-km-long active fault zone. These same data reveal largely concealed faults and folds that kinematically link the Seattle fault with active faults in the Olympic Massif. Linkage between the Seattle fault and the north-northeast-striking Saddle Mountain fault in the Olympic Massif may explain the synchroneity of M7 earthquakes occurring on both these faults approximately 1,100 years ago. The western limits of the 20-km-long east-striking Tacoma fault, a backthrust in the hanging wall of the Seattle fault zone, forms the southern margin of the Seattle uplift in contact with the Tacoma basin to the south. A ~20-km-long potential-field lineament extends from the western limits of the Tacoma fault northward to the Seattle fault and may reflect a structure linking these active faults. A geologic model based on magnetic, gravity, and seismic data shows that this potential-field lineament is likely caused by a low-angle, west-verging thrust fault, that we refer to as the Dewatto fault. We suggest that the Dewatto fault was initiated during exhumation of the Olympic Massif but, because of changes in principal strain direction, today largely accommodates north-directed, strike-slip motion along the west margin of the Seattle uplift. Thus, the Dewatto and Saddle Mountain faults and the western parts of the Seattle and Tacoma faults kinematically interact to accommodate north-directed horizontal displacement of the Seattle uplift relative to the Olympic Massif.

  9. The Tolbachik volcanic massif: A review of the petrology, volcanology and eruption history prior to the 2012-2013 eruption

    NASA Astrophysics Data System (ADS)

    Churikova, T. G.; Gordeychik, B. N.; Edwards, B. R.; Ponomareva, V. V.; Zelenin, E. A.

    2015-12-01

    The primary goal of this paper is to summarize all of the published data on the Tolbachik volcanic massif in order to provide a clear framework for the geochronologic, petrologic, geochemical and to a lesser extent the geophysical and tectonic characteristics of the Tolbachik system established prior to the 2012-2013 eruption. The Tolbachik massif forms the southwestern part of the voluminous Klyuchevskoy volcanic group in Kamchatka. The massif includes two large stratovolcanoes, Ostry ("Sharp") Tolbachik and Plosky ("Flat") Tolbachik, and a 70 km long zone of the basaltic monogenetic cones that form an arcuate rift-like structure running across the Plosky Tolbachik summit. The Tolbachik massif gained international attention after the 1975-1976 Great Tolbachik Fissure Eruption (GTFE), which was one of the largest eruptions of the 20th century and one of the six largest basaltic fissure eruptions in historical time. By the end of the GTFE, 2.2 km3 of volcanic products of variable basaltic compositions with MORB-like isotopic characteristics covered an area of > 1000 km2. During the following three decades more than 700 papers on various aspects of this eruption have been published both in national and international journals. Although the recent 2012-2013 eruption, which is the main topic of this volume, was not as long as the GTFE in duration or as large in area and volume of the erupted deposits, it brought to the surface a unique volcanic material never found before. In order to understand the data from new eruptions and make significant progress towards a better understanding of the Tolbachik magmatic system it is important to be able to put the new results into the historic context of previous research.

  10. Behaviour of Sr, Ca, Nd and Li Isotopes During Granite Weathering: the Margeride Massif, France

    NASA Astrophysics Data System (ADS)

    Negrel, P.; Bullen, T. D.; Millot, R.

    2008-12-01

    The Massif Central region of France contains numerous mineral water springs with salinities up to 6 g/L. These high salinities develop due to water-rock interaction processes accompanying weathering of granitic rocks such as the Margeride massif, a 5 km-deep laccolith having an age of 323 ± 12 Ma and consisting mainly of granitoid and gneiss. In order to better constrain weathering processes, we have determined the Sr, Nd, Ca and Li-isotope compositions of the Margeride granite, weathered granite (arene) and saprolite, sediment and soil overlying the granite, and groundwater samples (e.g., mineral water springs) associated with the massif. 87Sr/86Sr ratios increase in the order apatite-plagioclase-K-feldspar-arene- sediments and soils-biotite, and are well correlated with Rb/Sr ratios. Mineral waters have 87Sr/86Sr ratios similar to that of plagioclase, but have higher Rb/Sr ratios. 44Ca/40Ca ratios of plagioclase and apatite are similar to that of the whole rock, while those of K-feldspar and biotite are significantly less. 44Ca/40Ca ratios of arene, soil and sediment are similar to or less than that of K- feldspar, reflecting complete loss of Ca from plagioclase and apatite during weathering. In contrast, 44Ca/40Ca ratios for the mineral waters are similar to or substantially greater than that of plagioclase, reflecting extensive calcium carbonate precipitation during ascent of the waters along the rock fracture network. 44Ca/40Ca ratios of the waters are as much as 3.5 per mil greater than that of seawater, and thus contain the heaviest Ca yet reported for terrestrial materials. 7Li/6Li ratios differ by a few per mil among the granite minerals; of the weathering products, arene and soils have the least 7Li/6Li ratios, while river bank sediment and arene surface sediment have progressively greater ratios. 7Li/6Li ratios of the mineral waters have the greatest values, reflecting preferential retention of 6Li in the weathering products. 143Nd/144Nd ratios are

  11. The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

    NASA Astrophysics Data System (ADS)

    Martínez Catalán, José R.

    2012-07-01

    An arcuate structure, comparable in size with the Ibero-Armorican arc, is delineated by Variscan folds and magnetic anomalies in the Central Iberian Zone of the Iberian Massif. Called the Central Iberian arc, its sense of curvature is opposite to that of the Ibero-Armorican arc, and its core is occupied by the Galicia-Trás-os-Montes Zone of NW Iberia, which includes the Rheic suture. Other zones of the Iberian Massif are bent by the arc, but the Ossa-Morena and South Portuguese zones are not involved. The arc formed during the Late Carboniferous, at final stages of thermal relaxation and collapse, and an origin related with right-lateral ductile transpression at the scale of the Variscan belt is proposed. The Central Iberian arc explains the width of the Central Iberian Zone, clarifies the position of the allochthonous terranes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central zone represents the continuation of the southwest branch of the arc detached by strike-slip tectonics.

  12. Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

    NASA Astrophysics Data System (ADS)

    Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.

    2014-12-01

    In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.

  13. Geology and Tectonic Evolution of the Kazdaǧ Massif (NW Anatolia)

    NASA Astrophysics Data System (ADS)

    Erdoğan, B.; Akay, E.; Hasözbek, A.; Satır, M.; Siebel, W.

    2009-04-01

    In the northwestern part of Anatolia along the Izmir-Ankara Suture Zone, the Kazdağ and Uludağ metamorphic massifs form an E-W trending belt between the Sakarya Continent in the north and the Menderes Massif in the south. Internal succession of these two massifs have been described as metamorphic complexes consisting of various kinds of micaschists, quartz mica schist, gneisses, amphibolites and marbles. In the Kazdağ metamorphics, metaophiolites have been described additionally (Okay et al., 1991; Yaltırak and Okay, 1994; Okay et al., 1996; Duru et al., 2004). These metamorphic complexes were considered to form the basement of the Sakarya Continent tectonically overlain by the Early Permian (Topuz et al., 2004) to Late Triassic (Okay and Monie, 1997; Okay et al., 2002) Karakaya Complex. This old basement and the Karakaya Complex were suggested to be unconformably overlain by Liassic and younger platform limestones and detritals (Altıner et al., 1991). In the literature, it has also been suggested that the Kazdağ Massif had experienced polyphase metamorphism, first during Carboniferous time, second during Early Triassic and third during Tertiary (Bingöl, 1971; Okay et al., 1996; Okay and Satır, 2000). In this study we mapped the Kazdağ Massif on 1/25000 scale, studied its internal stratigraphy and structures and performed some petrologic analyses and radiogenic age determinations. Stratigraphically in the lower part of the Kazdağ metamorphic sequence, there is a part of an oceanic crust represented by metaultramafic rocks and gabbroic metacumulates. Geochemistry of these banded metagabbros show a mid-oceanic affinity. This oceanic crust is overlain, along an unconformity, by a platform type marble succession. At the base of the marbles, there is a basal conglomerate, clasts of which derived from the underlying ultramafic sequence. Thick white marble sequence is overlain along a gradational boundary with a metadetrital succession consisting of quartz mica

  14. Lithospheric Structure Along the Wide-Angle Seismic Reflection Transect of the Central Iberian Massif

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Cembrowski, Marcel; Marti, David; Gil, Alba; Marzan, Ignacio; Ayarza, Puy; Martinez-Poyatos, David; Simancas, Jose Fernando; Azor, Antonio

    2014-05-01

    The Iberian Massif is the largest outcrop of the Late Paleozoic Variscan Orogen in western Europe. In May 2012, a spatially dense high resolution wide-angle seismic reflection profile ALCUDIA was acquired across the Central Iberian Massif. The ALCUDIA wide-angle profile investigates lithospheric structure of the Central Iberian Zone and a suture zone (the Central Unit). The experiment consisted in a main SW-NE line of receivers, c. 300 km long, and a supplementary transect, c. 35 km long, that sampled the crust beneath the Central Iberian System. The acoustic energy generated by 5 shots, c. 70 km apart, was recorded by over 900 TEXANS (single component, digital recording stations) from the IRIS-PASSCAL Instrument Center. Each shot consisted in 1 TM of explosives fired in a single 55-65 m deep borehole. Approximately, 100 stations were deployed across the Central Iberian System in an effort to map the topography of the crust mantle boundary beneath this mountain range. This design generated enough energy to be able to identify Pn and even mantle reflections. The preliminary analysis of the shot gathers reveals that the recorded events features relatively low frequencies (4-30 Hz). The processing of the shot gathers resulted into high amplitude reflective events within the upper crust and strong PmP phases. From the southwest to northeast, the interpreted PmP arrivals are located at c. 11 s and c. 12 s (normal incidence traveltime) respectively. The ALCUDIA wide-angle profile provided a detailed P-wave velocity structural model and complemented the previously acquired normal incidence deep seismic profile ALCUDIA. The velocity model obtained by forward modelling constraints the composition of the crust and upper mantle. The upper crust is located at c. 13 km and the Moho is in the 32-36 km range, equates to normal incidence reflection profile ALCUDIA. Existing knowledge indicates that the mid-lower crust along the southern part of the CIZ is characterized by

  15. Holocene collapse of a mountain summit in the Belledonne massif (France): evidence from geomorphological mapping

    NASA Astrophysics Data System (ADS)

    Ravanel, L.; Allignol, F.; Deline, P.

    2009-04-01

    Rock avalanching is a high magnitude / low frequency process in mountain environment. It is an extremely rapid flow of fragmenting rock particles, with a volume > 1 M m3, involving a large amount of energy and travelling farther than expected with a normal sliding friction law. Rock avalanches are not uncommon in the Alps, in particular because of debuttressing of rock slopes due to glacier retreat and downwasting since the last Glacial maximum. The upper Vorz catchment basin is one of the few still glaciarized basins in the Belledonne massif (French external crystalline massif, peaking at 2977 m a.s.l.). A deposit related to a rock avalanche lies at the Habert du Mousset (1680 m a.s.l.), covering an area of 95 000 m2, tens of meters-thick and with a volume exceeding 1 M of m3. A geomorphological study suggests that the deposit should result from the collapse of the palaeo-summit of Roche Rousse (2753 m a.s.l. at present). The main part of the collapsed volume fell on the east side of the mountain ridge, but a smaller part probably travelled along the west side to form the deposit of the Habert du Mousset. Vertical and horizontal travel distances would have been 1100 m and 2750 m, respectively. The apparent coefficient of friction (height-over-length H/L ratio) is 0.4, indicating a highly mobile rock avalanche (H/L ratio is 0.62 with a ‘normal' coefficient of friction). Two elements support the hypothesis of a Holocene collapse: (i) glacial striations, rat tails, chattermarks and grooves are present on roches moutonnées up to 20 m to the crest. Those inherited glacial forms required a glacier thick enough to erode the bedrock. Because the surface of the Last Glacial Maximum glacier was standing well below this site (> 1000 m), only a local glacier could have form, which would have been impossible with the present topography. Thus, the palaeo-summit of Roche Rousse collapsed not before the Lateglacial. As suggested by (ii) the very steep, sometimes overhanging

  16. Methane Seepage at Hyperalkaline Springs in the Ronda Peridotite Massif (Spain)

    NASA Astrophysics Data System (ADS)

    Etiope, G.; Vadillo, I.; Whiticar, M. J.; Marques, J. M.; Carreira, P. M.; Tiago, I.; Benavente, J.; Jimenez, P.; Urresti, B.

    2014-12-01

    Methane-rich, hyperalkaline spring waters and bubbling pools have been sampled in the Ronda peridotite massif in southern Spain. Water chemistry (T: 17.1-21.5 ºC; pH: 10.7-11.7; DO: <2 mg/L; Ca-OH facies) is characteristic of present-day serpentinization. Dissolved CH4 concentrations range from 0.1 to 3.2 mg/L. CH4 stable C and H isotope ratios suggest a dominant abiotic origin in two natural spring sites (delta13C: -13 to -29 ‰ VPDB; delta2H: -309 to -333 ‰ VSMOW) and a mixed biotic-abiotic origin in springs with artificial water delivery systems (i.e., pipes or fountains; delta13C: -44 to -69 ‰; delta2H: -180 to -319 ‰). At the natural springs, gas is mainly released through bubbles close to the water outlet (CH4 flux ~1 kg/day by individual bubble trains), and subordinately by microseepage from the ground, even at distances of ~100 m from the bubble-spring site (flux of 10's, up to 97, mg CH4 m-2day-1). Gas seepage is strictly controlled by faults. Under-saturation of CH4 in water, bubbling and seepage location suggest that CH4 is not exclusively transported to the surface by hyperalkaline water, but it follows autonomous migration pathways along faults. Similar 'dry' seepage of abiotic gas was observed in the Philippines, New Zealand, Turkey and Italy. Like other land-based serpentinization systems, the Ronda peridotite massif is characterized by low heat flow (<40 mW/m2), with temperatures <60°C at depths of 1.5 km. At these low T and high pH conditions, CO32- is the only available carbon source dissolved in the water, and unlikely contributes to catalysed Fischer-Tropsch Type reactions. Methane production from CO2 hydrogenation in a gas phase system (unsaturated fractured rocks) cannot be excluded. The presence of ruthenium-enriched chromitites in the Ronda peridotites may support the hypothesis that CH4 is produced by CO2 hydrogenation catalyzed by Ru minerals, even at temperatures below 100°C, as demonstrated in recent laboratory experiments

  17. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

    NASA Astrophysics Data System (ADS)

    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).

  18. Crustal Structure in the Vicinity of IODP Hole U1309D, Atlantis Massif

    NASA Astrophysics Data System (ADS)

    Harding, A. J.; Arnulf, A. F.

    2012-12-01

    The Atlantis Massif oceanic core complex (OCC) was formed initially by faulting within the axial zone of the Mid-Atlantic Ridge at 30°N, followed by strain localization and unroofing along a detachment surface between 0.5-1.5 Ma. IODP Hole U1309D extends approximately 1.4 km into the Central dome of the Massif and sampled primarily gabbroic rocks. As a relatively deep hole, U1309D is an attractive target for addressing one of the long-term goals of ocean drilling: better integration of borehole geophysical and geologic sampling with surface seismic results. In addition, a number of high quality multichannel seismic (MCS) profiles pass close to the hole. In winter 2012, IODP Expedition 340T reentered U1309D and collected a vertical seismic profile (VSP) as well as high-quality sonic, resistivity, and temperature logs over the entire extent of the Hole. We will present a synthesis, comparing the seismic results from the reprocessing and waveform inversion of all MCS lines passing near Hole U1309D with the results from the new VSP and sonic logs. The waveform inversion results build upon earlier tomographic inversion of downward continued data (Henig et al, 2012) but exhibit significantly improved vertical and horizontal resolution, allowing better integration with the borehole data. Waveform inversion of the nearest flowline MCS profiles that crosses the Central dome just to the north indicates that the original upper surface of the gabbroic body drilled at Hole 1309D now lies just to the west of the hole. Imaging reveals a sharp, almost planar contact, that dips steeply at about 30°. Based upon seismic velocities and seafloor sampling and observations, the rocks on other side of the contact are most likely serpentinized peridotite but other lithologies cannot be ruled out (Henig et al,2012). Reprocessing of the reflection image contains few, if any, coherent reflections from within the core of the gabbroic body but there are reflections adjacent to the western

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

    NASA Astrophysics Data System (ADS)

    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

  20. Isotope Sm-Nd age of the paleoproterozoic PGE-bearing Monchetundra massif trachytoid gabbronorites (Fennoscandian shield)

    NASA Astrophysics Data System (ADS)

    Kunakkuzin, Evgeniy; Bayanova, Tamara; Serov, Pavel; Borisenko, Elena

    2015-04-01

    Monchetundra massif is located in the central part of the Kola Peninsula (Russia) and it is the south-eastern part of the Main Ridge Intrusion. Monchetundra massif together with well-known layered mafic-ultramafic PGE-bearing intrusions in the Fennoscandian shield such as the Fedorovo-Pansky complex, the mt. Generalskaya, the Monchepluton is of interest as a target for the PGE prospecting (Mitrofanov et al. 2006; Nerovich et al., 2009; Grokhovskaya et al., 2003). According to some previously researchers (Nazimova, Rayan, 2008, Nerovich et al., 2009, Layered intrusions…p.1, 2004) rocks of the Monchetundra massif is subdivided into two to five syngenetic zones. Hence the last isotope-geochronological and isotope-geochemical data revealed that the massif includes at least four groups of mafic rocks distinguished by formation ages (Bayanova et al., 2010). The aim of this work is to present Sm-Nd dating results of trachytoid gabbronorites, which are the second mafic rocks group in the Monchetundra massif. The Sm-Nd investigations for these rocks were carried out for the first time. The second group of mafic rocks comprises of medium-grained and coarse-grained mesocratic gabbronorites of trachytoid texture, with they characterized by well-preserved primary magmatic minerals and gabbro-ophitic texture. The U-Pb ages on single zircon-baddeleyite for these rocks recently obtained (2505 ± 6 Ma, 2501 ± 8 Ma, 2504.4±2.7 Ma and 2507.5±7.7 Ma (Layered intrusions…p.1., 2004, Borisenko et al., 2013)). Two samples of trachytoid gabbronorites were selected to study these rocks by Sm-Nd isotopic method. Mineral isochrons plotted from plagioclase, ortho- and clinopyroxene and whole-rock minerals gave ages of 2496±27 (MSWD = 0.9; ɛNd = -1.6±0.5) and 2492±55 Ma (MSWD = 0.5; ɛNd = -1.7±0.5). The new Sm-Nd ages obtained are close to the U-Pb data on zircons and baddeleyites for this rocks group and consider as oridin of second mafic rocks group. All investigations are

  1. Absorption and optical conduction in InSe/ZnSe/InSe thin film transistors

    NASA Astrophysics Data System (ADS)

    Al Garni, S. E.; Qasrawi, A. F.

    2016-01-01

    In this work, (n)InSe/(p)ZnSe and (n)InSe/(p)ZnSe/(n)InSe heterojunction thin film transistor (TFT) devices are produced by the thermal evaporation technique. They are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy and optical spectroscopy techniques. While the InSe films are found to be amorphous, the ZnSe and InSe/ZnSe films exhibited polycrystalline nature of crystallization. The optical analysis has shown that these devices exhibit a conduction band offsets of 0.47 and valence band offsets of 0.67 and 0.74eV, respectively. In addition, while the dielectric spectra of the InSe and ZnSe displayed resonance peaks at 416 and 528THz, the dielectric spectra of InSe/ZnSe and InSe/ZnSe/InSe layers indicated two additional peaks at 305 and 350THz, respectively. On the other hand, the optical conductivity analysis and modeling in the light of free carrier absorption theory reflected low values of drift mobilities associated with incident alternating electric fields at terahertz frequencies. The drift mobility of the charge carrier particles at femtoseconds scattering times increased as a result of the ZnSe sandwiching between two InSe layers. The valence band offsets, the dielectric resonance at 305 and 350THz and the optical conductivity values nominate TFT devices for use in optoelectronics.

  2. A large and complete Jurassic geothermal field at Claudia, Deseado Massif, Santa Cruz, Argentina

    NASA Astrophysics Data System (ADS)

    Guido, Diego M.; Campbell, Kathleen A.

    2014-04-01

    Late Jurassic geothermal deposits at Claudia, Argentinean Patagonia, are among the largest (40 km2) and most varied in the Deseado Massif, a 60,000 km2 volcanic province hosting precious metals (Au, Ag) mineralization generated during diffuse back arc spreading and opening of the South Atlantic Ocean. Both siliceous sinter and travertine occur in the same stratigraphic sequence. Deposits range from those interpreted as fluvially reworked hydrothermal silica gels, to extensive apron terraces, to a clustering of high-temperature subaerial vent mounds. Paleoenvironmentally diagnostic textures of sinters include wavy laminated, bubble mat and nodular fabrics, and for travertines comprise fossil terracette rims, wavy laminated, bubble mat, spherulitic, oncoidal, and peloidal fabrics. Of special note is the presence of relatively large (to 25 cm high), inferred subaqueous "Conophyton" structures in travertines, which serve as analogs for some Precambrian stromatolites and imply the presence of relatively deep pools maintained by voluminous spring discharges. The Claudia geothermal field is geographically and geologically linked to the Cerro Vanguardia epithermal project (total resource of ~ 7.8 million ounces Au equivalent) via proximity, similar veins, and structural linkages, making it an especially large and relevant prospect for the region. The combined Claudia-Cerro Vanguardia hydrothermal system likely represents a fortuitous alignment of focused fluid flow and structure conducive to forming a giant epithermal ore deposit, with respect to size, ore concentration and potentially duration, in the Late Jurassic of Patagonia.

  3. Raman mapping of coesite inclusions in garnet from the Kokchetav Massif (Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Hutsebaut, Didier; Theunissen, Karel; Vandenabeele, Peter; Stepanov, Alexander S

    2007-12-15

    Coesite inclusions occur in a wide range of lithologies and coesite is therefore a powerful ultrahigh-pressure (UHP) indicator. The transformation of coesite to quartz is evidenced by three optically well identifiable characteristics (e.g. palisade textures, radial crack patterns, polycrystalline quartz pseudomorphs). Under overpressure monomineralic coesite (on an optical basis), lacking the above transformation characteristics may survive. Raman micro-spectroscopy was applied on monomineralic coesite inclusions in garnet porphyroblasts from diamond-bearing garnet-clinozoisite-biotite gneisses of the Barchi-Kol area (Kokchetav Massif, Northern Kazakhstan). These coesite inclusions are euhedral and display a characteristic anisotropic hallo. However, Raman maps and separate spectra of these inclusions display shifted bands for coesite and quartz. Microscopically undetectable, quartz shows on the Raman map as a thin shell around coesite inclusion. Shift of the main coesite band allows to estimate their overpressure: coesite inclusions record 0-2.4 GPa in garnet and zircon. The quartz shell remains under lower pressure 0-1.6 GPa. The possible application of coesite and quartz Raman geobarometers for UHP metamorphic rocks is discussed. PMID:17553735

  4. Raman imaging of fluid inclusions in garnet from UHPM rocks (Kokchetav massif, Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Dieing, Thomas; Golovin, Aleksandr V; Toporski, Jan

    2011-10-01

    Confocal Raman imaging of fluid inclusions in garnet porphyroblasts from diamond-grade metamorphic calc-silicate rocks from the Kumdy-Kol microdiamond deposit (Kokchetav Massif, Northern Kazakhstan) reveals that these fluid inclusions consist of almost pure water with different step-daughter phases (e.g., calcite, mica and rare quartz). These fluid inclusions are characterized by negative crystal shape of the host-garnet and they exclusively occur within the core of garnet porphyroblasts. These observations are consistent with their primary origin, most likely at ultrahigh-pressure (UHP) metamorphic conditions. The euhedral newly formed garnet, different in color and composition, was found to be associated with these fluid inclusions. It is proposed that newly formed garnet and water fluid inclusions appear by reaction between the hydrous fluid and the garnet-host. These fluid inclusions provide an unequivocal record of almost pure H(2)O fluids, indicating water-saturated conditions within subducted continental crust during prograde stage and/or ultrahigh-P metamorphism.

  5. Raman mapping of coesite inclusions in garnet from the Kokchetav Massif (Northern Kazakhstan)

    NASA Astrophysics Data System (ADS)

    Korsakov, Andrey V.; Hutsebaut, Didier; Theunissen, Karel; Vandenabeele, Peter; Stepanov, Alexander S.

    2007-12-01

    Coesite inclusions occur in a wide range of lithologies and coesite is therefore a powerful ultrahigh-pressure (UHP) indicator. The transformation of coesite to quartz is evidenced by three optically well identifiable characteristics (e.g. palisade textures, radial crack patterns, polycrystalline quartz pseudomorphs). Under overpressure monomineralic coesite (on an optical basis), lacking the above transformation characteristics may survive. Raman micro-spectroscopy was applied on monomineralic coesite inclusions in garnet porphyroblasts from diamond-bearing garnet-clinozoisite-biotite gneisses of the Barchi-Kol area (Kokchetav Massif, Northern Kazakhstan). These coesite inclusions are euhedral and display a characteristic anisotropic hallo. However, Raman maps and separate spectra of these inclusions display shifted bands for coesite and quartz. Microscopically undetectable, quartz shows on the Raman map as a thin shell around coesite inclusion. Shift of the main coesite band allows to estimate their overpressure: coesite inclusions record 0-2.4 GPa in garnet and zircon. The quartz shell remains under lower pressure 0-1.6 GPa. The possible application of coesite and quartz Raman geobarometers for UHP metamorphic rocks is discussed.

  6. The limnology and biology of the Dufek Massif, Transantarctic Mountains 82° South

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Convey, Peter; Verleyen, Elie; Vyverman, Wim; McInnes, Sandra J.; Sands, Chester J.; Fernández-Carazo, Rafael; Wilmotte, Annick; De Wever, Aaike; Peeters, Karolien; Tavernier, Ines; Willems, Anne

    2010-08-01

    Very little is known about the higher latitude inland biology of continental Antarctica. In this paper we describe the limnology and biology of the Dufek Massif, using a range of observational, microscopic and molecular methods. Here two dry valleys are home to some of the southernmost biota on Earth. Cyanobacteria were the dominant life forms, being found in lakes and ponds, in hypersaline brines, summer melt water, relict pond beds and in exposed terrestrial habitats. Their species diversity was the lowest yet observed in Antarctic lakes. Green algae, cercozoa and bacteria were present, but diatoms were absent except for a single valve; likely windblown. Mosses were absent and only one lichen specimen was found. The Metazoa included three microbivorous tardigrades ( Acutuncus antarcticus, Diphascon sanae and Echiniscus (cf) pseudowendti) and bdelloid rotifer species, but no arthropods or nematodes. These simple faunal and floral communities are missing most of the elements normally present at lower latitudes in the Antarctic which is probably a result of the very harsh environmental conditions in the area.

  7. Vorticity analysis in calcite tectonites: An example from the Attico-Cycladic massif (Attica, Greece)

    NASA Astrophysics Data System (ADS)

    Spanos, D.; Xypolias, P.; Koukouvelas, I.

    2015-11-01

    Although calcite tectonites are widespread in nature their use to quantify flow vorticity is limited. We use new (micro-)structural, petrofabric and vorticity data to analyse the kinematics of flow in outcrop-scale calcite mylonite zones. These zones are genetically related to a crustal-scale NE-directed ductile thrust (Basal Thrust) that emplaced the Blueschist over the Basal unit during the exhumation of the Attico-Cycladic Massif. Calcite microstructures reveal that the last stage of deformation occurred at temperatures 200-300 °C achieved by mild heating, which is possibly related with the reburial of the Basal Thrust's footwall. Vorticity analyses were based on the degree of asymmetry of calcite c-axis fabrics as well as on the assumption that the orientation of the long axes of calcite neoblasts within an oblique foliation delineates the direction of instantaneous stretching axis. Both methodological approaches provide consistent estimates with a simple shear component between 55% and 82% (Wn = 0.76-0.96). The use of the stress axis (σ1) orientation recorded by twin-c-axis-pairs to quantify vorticity generally gives significantly lower simple shear component. Comparison of our vorticity estimates with previous estimates inferred from quartz fabrics and rigid porphyroclasts reveals that exhumation-related deformation in the nappe pile was steady state.

  8. Raman imaging of fluid inclusions in garnet from UHPM rocks (Kokchetav massif, Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Dieing, Thomas; Golovin, Aleksandr V; Toporski, Jan

    2011-10-01

    Confocal Raman imaging of fluid inclusions in garnet porphyroblasts from diamond-grade metamorphic calc-silicate rocks from the Kumdy-Kol microdiamond deposit (Kokchetav Massif, Northern Kazakhstan) reveals that these fluid inclusions consist of almost pure water with different step-daughter phases (e.g., calcite, mica and rare quartz). These fluid inclusions are characterized by negative crystal shape of the host-garnet and they exclusively occur within the core of garnet porphyroblasts. These observations are consistent with their primary origin, most likely at ultrahigh-pressure (UHP) metamorphic conditions. The euhedral newly formed garnet, different in color and composition, was found to be associated with these fluid inclusions. It is proposed that newly formed garnet and water fluid inclusions appear by reaction between the hydrous fluid and the garnet-host. These fluid inclusions provide an unequivocal record of almost pure H(2)O fluids, indicating water-saturated conditions within subducted continental crust during prograde stage and/or ultrahigh-P metamorphism. PMID:21377920

  9. AMS 14C Dates for Extinct Lemurs from Caves in the Ankarana Massif, Northern Madagascar

    NASA Astrophysics Data System (ADS)

    Simons, Elwyn L.; Burney, David A.; Chatrath, Prithijit S.; Godfrey, Laurie R.; Jungers, William L.; Rakotosamimanana, Berthe

    1995-03-01

    An extensive late Quaternary fauna, including many extinct giant lemurs, has been collected recently in a 110+-km system of caves in the Ankarana Massif of northern Madagascar. AMS 14C dates for the acid-insoluble (collagen/gelatin) fraction of bones of the giant lemur Megaladapis (26,150 ± 400 and 12,760 ± 70 yr B.P.) confirm its presence in the area during the late Pleistocene and provide the first Pleistocene 14 C ages from bones of the extinct megafauna of the island. The first date from bones of the recently described extinct Babakotia radofilai (4400 ± 60 yr B.P.) shows that it was present in northern Madagascar in mid-Holocene times. A comparatively recent age of 1020 ± 50 yr B.P. for the extinct Archaeolemur indicates survival of this genus for at least a millennium after the first direct evidence for humans in Madagascar. This suggests that the island's "extinction window" may have represented a longer time span than would have been expected under the Blitzkrieg model of late Quaternary extinctions. A mid-Holocene age (4560 ± 70 yr B.P.) for a bone sample of the small extant lemur Hapalemur simus indicates that the disappearance of this now-restricted species from the Ankarana occurred after this date. New data from the Ankarana and other sites on the island add to the consensus that major biotic changes occurred on Madagascar in the late Holocene.

  10. Raman mapping of coesite inclusions in garnet from the Kokchetav Massif (Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Hutsebaut, Didier; Theunissen, Karel; Vandenabeele, Peter; Stepanov, Alexander S

    2007-12-15

    Coesite inclusions occur in a wide range of lithologies and coesite is therefore a powerful ultrahigh-pressure (UHP) indicator. The transformation of coesite to quartz is evidenced by three optically well identifiable characteristics (e.g. palisade textures, radial crack patterns, polycrystalline quartz pseudomorphs). Under overpressure monomineralic coesite (on an optical basis), lacking the above transformation characteristics may survive. Raman micro-spectroscopy was applied on monomineralic coesite inclusions in garnet porphyroblasts from diamond-bearing garnet-clinozoisite-biotite gneisses of the Barchi-Kol area (Kokchetav Massif, Northern Kazakhstan). These coesite inclusions are euhedral and display a characteristic anisotropic hallo. However, Raman maps and separate spectra of these inclusions display shifted bands for coesite and quartz. Microscopically undetectable, quartz shows on the Raman map as a thin shell around coesite inclusion. Shift of the main coesite band allows to estimate their overpressure: coesite inclusions record 0-2.4 GPa in garnet and zircon. The quartz shell remains under lower pressure 0-1.6 GPa. The possible application of coesite and quartz Raman geobarometers for UHP metamorphic rocks is discussed.

  11. Using several monitoring techniques to measure the rock mass deformation in the Montserrat Massif

    NASA Astrophysics Data System (ADS)

    Janeras, M.; Jara, J. A.; López, F.; Marturià, J.; Royán, M. J.; Vilaplana, J. M.; Aguasca, A.; Fàbregas, X.; Cabranes, F.; Gili, J. A.

    2015-09-01

    Montserrat Mountain is located near Barcelona in Catalonia, at the north-east corner of Spain, and its massif is formed by conglomerate interleaved by siltstone/sandstone with steep slopes very prone to rock falls. The increasing visitor's number in the monastery area, reaching 2.4 million per year, has pointed out the risk derived from rock falls for this building area and also for the terrestrial accesses, both roads and rack railway. A risk mitigation plan is currently been applied for 2014-2016 that contains monitoring testing and implementation as a key point. The preliminary results of the pilot tests carried out during 2014 are presented, also profiting from previous sparse experiences and data, and combining 4 monitoring techniques under different conditions of continuity in space and time domains, which are: displacement monitoring with Ground-based Synthetic Aperture Radar and characterization at slope scale, with an extremely non uniform atmospheric phase screen because of the stepped topography and atmosphere stratification; Terrestrial Laser Scanner surveys quantifying frequency for unnoticed activity of small rock falls, and monitoring rock block displacements over 1cm; monitoring of rock joints with a wireless net of sensors; and tentative surveying for singular rocky needles with Total Station.

  12. Constraints on strain rate and fabric partitioning in ductilely deformed black quartzites (Badajoz-Córdoba Shear Zone, Iberian Massif)

    NASA Astrophysics Data System (ADS)

    Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio

    2013-04-01

    The Badajoz-Córdoba Shear Zone is a is 30-40 km wide and 400 km long, NW-SE trending structure located at the boundary between the Ossa-Morena and Central-Iberian Zones of the Iberian Massif. Two elongated domains can be differentiated inside: the Obejo-Valsequillo domain to the NE and the Ductile Shear Belt (DSB) to the SW. The former exhibits Precambrian to Cambrian volcano-sedimentary rocks unconformably overlaying a Neoproterozoic basement formed by the "Serie Negra". The latter, 5-15 km wide, is composed mainly of metamorphic tectonites including the "Serie Negra" and other units located structurally under it. The petrofabric of "Serie Negra" black quartzites from the DSB is analyzed in this study with the Electron Back-Scattered Diffraction technique (EBSD). Black quartzites represent originally siliceous, chemical-biochemical shallow-water marine deposits, currently composed almost exclusively of quartz and graphite. Macroscopically they exhibit an outstanding planolinear tectonic fabric. Petrographically, coarse- and fine-grained dynamically recrystallized quartz bands alternate. The former contain quartz grains with irregular shapes, mica inclusions and "pinning" grain boundaries. Oriented mica grains and graphite particles constrain irregular quartz grain shapes. Quartz ribbons with chessboard microstructures also occur, indicating recrystallization under elevated temperatures coeval with extreme stretching. Fine-grained recrystallized quartz bands are dominated by quartz grains with straight boundaries, triple junctions, a scarcer evidence of bulging, and a higher concentration of dispersed, minute graphite grains. Quartz lattice-preferred orientation (LPO) patterns permit to identify two well-developed maxima for [c] axes: one close to the Y structural direction and the other one around Z, and -axes girdles normal to Y and Z. Although both [c] axis maxima appear in the coarse- and fine-grained bands, subsets can be isolated with grain cluster

  13. Lithologic Distribution and Geologic History of the Apollo 17 Site: The Record in Soils and Small Rock Particles from the Highland Massifs

    NASA Technical Reports Server (NTRS)

    Jolliff, Bradley L.; Rockow, Kaylynn M.; Korotev, Randy L.; Haskin, Larry A.

    1996-01-01

    Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm-4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm-4 mm fragments provide a bridge between compositions of less than 1 mm fines and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm-4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% Incompatible-Trace-Element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm - 4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31 % agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass- weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their

  14. Prise en charge d’un afflux massif de brûles lors d’une situation de catastrophe par incendie au Maroc

    PubMed Central

    Siah, S.; Hatimi, E.M.; Ihrai, H.; Drissi Kamili, N.

    2012-01-01

    Summary La brûlure est l’une des lésions les plus fréquemment rencontrées lors de catastrophes naturelles ou lors de catastrophes d’origine humaine (incendies de lieux publics d’origine accidentelle, ou en temps de guerre ou encore lors d’attentats terroristes). La prise en charge et le triage de brûlés en nombre reste un problème difficile; ceci souligne la nécessité d’une réflexion et de prévisions de ces crises en insistant sur la formation des médecins et des soignants. Les défis à relever sont multiples: les soins aux brûlés requièrent un nombre important de personnel qualifié; les évacuations doivent être planifiées en fonction de la gravité de la brûlure et des lésions associées; les stocks et lots de dotation (en particulier en topiques anti-infectieux et en cristalloïdes) doivent être suffisants et adéquats. Les services hospitaliers de l’Hôpital Militaire d’Instruction Mohammed V de Rabat doivent pouvoir être rapidement adaptés pour accueillir et surtout isoler ces patients. L’hypothèse d’une catastrophe par incendie avec afflux massif de brûlés à l’hôpital militaire d’instruction Mohammed V de Rabat ne doit laisser place à aucune improvisation. PMID:23467075

  15. Properties of Se/InSe Thin-Film Interface

    NASA Astrophysics Data System (ADS)

    Qasrawi, A. F.; Kayed, T. S.; Elsayed, Khaled A.

    2016-06-01

    Se, InSe, and Se/InSe thin films have been prepared by the physical vapor deposition technique at pressure of ˜10-5 torr. The structural, optical, and electrical properties of the films and Se/InSe interface were investigated by means of x-ray diffraction (XRD) analysis, ultraviolet-visible spectroscopy, and current-voltage ( I- V) characteristics. XRD analysis indicated that the prepared InSe films were amorphous while the Se films were polycrystalline having hexagonal structure with unit cell parameters of a = 4.3544 Å and c = 4.9494 Å. Spectral reflectance and transmittance analysis showed that both Se and InSe films exhibited indirect allowed transitions with energy bandgaps of 1.92 eV and 1.34 eV, respectively. The Se/InSe interface exhibited two energy bandgaps of 0.98 eV and 1.73 eV above and below 2.2 eV, respectively. Dielectric constant values were also calculated from reflectance spectra for the three layers in the frequency range of 500 THz to 272 THz. The dielectric constant exhibited a promising feature suggesting use of the Se/InSe interface as an optical resonator. Moreover, the Au/Se/InSe/Ag heterojunction showed some rectifying properties that could be used in standard optoelectronic devices. The ideality factor and height of the energy barrier to charge carrier motion in this device were found to be 1.72 and 0.66 eV, respectively.

  16. The Laschamp Excursion in Lava Flows From the Massif Central (France): New Data and Synthesis

    NASA Astrophysics Data System (ADS)

    Laj, C. E.; Guillou, H.; Kissel, C.; Wandres, C.

    2011-12-01

    The Laschamp excursion, originally identified by N. Bonhommet in the French Massif Central, has been intensively investigated worldwide. Based on its short duration, this excursion has been very often used as a chronostratigraphic tiepoint by different communities. Recently, however, Plenier et al., (2007) have proposed a duration of about 6000 years for this excursion, in sharp contrast with previous estimates based on sedimentary and volcanic studies, as well as on analysis of the 10Be and 36Cl records in ice cores (Laj et al., 2000; 2004; Wagner et al., 2000; Guillou et al., 2004; Svensson et al., 2006; Singer et al., 2009). If correct this new evaluation would make this chronostratigraphic tie point largely less interesting, and would also have an impact of geodynamo mechanisms proposed to explain differences between excursions and reversals of the geomagnetic field (Gubbins, 1999). To further investigate this point, we have conducted a new study in the Massif Central. In addition to the three original lavas exposed at La Louchadière, Laschamp and Olby, recently dated by Guillou et al. (2004) and by Singer et al. (2009), we have intensively investigated several other outcrops characterized by transitional paleomagnetic directions, including different outcrops of the same lava flows at different localities separated by up to a few km, using a coupled paleomagnetic/ K/Ar and 40Ar/39Ar approach. All the obtained 40Ar/39Ar and K/Ar ages are tightly grouped and very consistent with the previous estimates of the Laschamp excursion of Guillou et al (2004) and Singer et al. (2009) around 41 ka. Geomagnetic field intensities (Thellier & Thellier) also show transitional values around 16 μT, however slightly higher than those obtained at the Laschamp and Olby outcrops (Roperch et al., 1988).The paleomagnetic directions, while all transitional, are sometimes significantly different from each other, indicating that the different outcrops have recorded different

  17. Thermochronological Constraints on the Exhumation of the Lys Caillaouas Massif, West-Central Pyrenees

    NASA Astrophysics Data System (ADS)

    Metcalf, J. R.; Fitzgerald, P. G.; Baldwin, S.; Muñoz, J.; Perry, S. E.; Feinberg, E. B.

    2009-12-01

    The Pyrenees Mountains of Spain and France are a collisional orogen cored by a south-vergent antiformal stack of Paleozoic basement thrust sheets (the Axial Zone). Thrusting accommodated shortening due to convergence between Iberia and Europe during the Alpine orogeny. In the central Pyrenees, the Axial Zone is divided structurally into the Nogueres, Orri, and Rialp thrust sheets. The Orri thrust sheet is in the footwall of the Gavarnie thrust, a folded south-vergent thrust fault that separates the Orri thrust sheet from the hanging-wall Nogueres thrust sheet. In the central Pyrenees, integrated 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He thermochronologic studies of the Maladeta pluton, lying within the Orri thrust sheet, constrains Late Cretaceous onset of heating due to thrust burial in the footwall of the Gavarnie thrust, followed by Cenozoic cooling due to erosional exhumation. To examine along-strike variations in the tectonic evolution of the Pyrenean orogen, we apply the same approach to the Lys Caillaouas massif (LCM) in the west-central Pyrenees. This massif occupies a similar structural position as the Maladeta but lies ~30 km to the WNW. The LCM is a ~60 km2 Hercynian igneous complex intruded into the Early Paleozoic metasediments of the Orri thrust sheet, five kilometers south of the present exposure of the Gavarnie thrust and bounded to the south by the south-vergent Alpine-age Estos Thrust, a fault within the Orri thrust sheet. In thin section, muscovite from the highest elevation sample (3221 m) from the LCM is often rimmed with neo-crystallized mica, yet >95% of the 39Ar yields an 40Ar/39Ar plateau age of 299.7 ± 1.4 Ma, similar to the crystallization age. Mica from the lowest elevation sample (2060 m) yields an apparent age gradient, with a minimum age of 125 Ma that increases steadily and reaches a maximum apparent age of 295 Ma. This sample has experienced significant chloritization, and the age spectra is interpreted to reflect the

  18. Dirty or Tidy ? Contrasting peraluminous granites in a collapsing Orogen: Examples from the French Massif Central

    NASA Astrophysics Data System (ADS)

    Villaros, Arnaud; Pichavant, Michel; Moyen, Jean-François; Cuney, Michel; Deveaud, Sarah; Gloaguen, Eric; Melleton, Jérémie

    2013-04-01

    Post collisional collapse commonly enhances crustal melting. Such melting typically produces peraluminous granitic magmas. In the French Massif Central, a mid-crustal segment of the western Variscan belt, two large granitic bodies were produced during the collapse of the Variscan Belt. The St Sylvestre Leucogranitic Complex (SSyL) in the western part of the Massif Central and the Velay Migmatitic Complex (VMC) in the Eastern part. Although these two complexes are formed in similar geodynamic context they present meaningful petrological and geochemical differences. The VMC (~305 Ma) is clearly intrusive in migmatitic terranes. The migmatitic host recorded two successive melting events M3 (720 °C and 5kb) dated between 335 and 315 Ma and M4 (850°C and 4 kb) dated at 305 Ma. The compositions of the VMC are strictly H2O-undersaturated and ranges from leucogranitic to granodioritic. Three main successive granite types have been distinguished (1) A heterogeneous banded biotite granite, (2) A main biotite-cordierite granite, where cordierite can be prismatic, as cockade or pseudomorphic (3) a late magmatic with large K-feldspar phenocryst and prismatic cordierite. The compositions of the VMC granites are quite similar to typical Australian S-type granites in the sense that they also show a positive correlation between ferromagnesian abundance and aluminosity. The SSyL (~320 Ma) is intrusive in upper greenschist facies to upper amphibolite migmatitic metasediment and orthogneiss (~3kb). The compositional variety observed in the SSyL suggests a continuous trend from a moderately mafic, peraluminous magma (cd- and sill- granite) to a H2O saturated granite ("two-mica" granite) facies and finally to an extremely felsic, H2O-saturated magma. Three granitic units have been recognized in the SSyL: (1) the western "Brame Unit" composed of the less evolved cd- and sill- granite facies (2) the central "St Sylvestre Unit", composed mainly by U-rich two-mica granite, intruded by two

  19. Serpentinite Carbonation in the Pollino Massif (southern Italy) for CO2 Sequestration

    NASA Astrophysics Data System (ADS)

    Carmela Dichicco, Maria; Mongelli, Giovanni; Paternoster, Michele; Rizzo, Giovanna

    2015-04-01

    Anthropogenic gas emissions are projected to change future climates with potentially nontrivial impacts (Keller et al., 2008 and references therein) and the impacts of the increased CO2 concentration are, among others, the greenhouse effect, the acidification of the surface of the ocean and the fertilization of ecosystems (e.g. Huijgen and Comans, 2003). Geologic Sequestration into subsurface rock formations for long-term storage is part of a process frequently referred to as "carbon capture and storage" or CCS. A major strategy for the in situ geological sequestration of CO2 involves the reaction of CO2 with Mg-silicates, especially in the form of serpentinites, which are rocks: i) relatively abundant and widely distributed in the Earth's crust, and ii) thermodynamically convenient for the formation of Mg-carbonates (e.g., Brown et al., 2011). In nature, carbonate minerals can form during serpentinization or during hydrothermal carbonation and weathering of serpentinites whereas industrial mineral carbonation processes are commonly represented by the reaction of olivine or serpentine with CO2 to form magnesite + quartz ± H2O (Power et al., 2013). Mineral carbonation occurs naturally in the subsurface as a result of fluid-rock interactions within serpentinite, which occur during serpentinization and carbonate alteration. In situ carbonation aims to promote these reactions by injecting CO2 into porous, subsurface geological formations, such as serpentinite-hosted aquifers. In the northern sector of the Pollino Massif (southern Italy) extensively occur serpentinites (Sansone et. al., 2012) and serpentinite-hosted aquifers (Margiotta et al., 2012); both serpentinites and serpentinite-hosted aquifers are the subject of a comprehensive project devoted to their possible use for in situ geological sequestration of CO2. The serpentinites derived from a lherzolitic and subordinately harzburgitic mantle, and are within tectonic slices in association with metadolerite dykes

  20. Rockfall hazard assessment by means of the magnitude-frequency curves in the Montserrat Massif (central Catalonia, Spain): first insights

    NASA Astrophysics Data System (ADS)

    Janeras, Marc; Domènech, Guillem; Pons, Judit; Prat, Elisabet; Buxó, Pere

    2016-04-01

    Montserrat Massif is located about 50 km North-West of Barcelona (Catalonia, North-Eastern Spain). The rock massif is constituted by an intercalation of conglomerate and fine layers of siltstones due to the Montserrat fan-delta sedimentation within the Eocene age. The current relief is consequence of the several depositional episodes and the later tectonic uplift, leading to stepped slopes up to 250 m high, and a total height difference close to 1000 m. Montserrat Mountain has been a pilgrimage place since the settlement of the monastery, around the year 1025, and a spot of touristic interest, mostly within the last 150 years, when the first rack railway was inaugurated to reach the sanctuary. The amount of 2.4 M visitors in 2014 reveals the potential risk derived from rockfalls. To assess and mitigate this risk, a plan funded by the Catalan government is currently under development. Three rockfall mechanisms and magnitude ranges have been identified (Janeras et al. 2011): 1) physicochemical weathering causing the detachment of pebbles and aggregates (0.0001 - 0.1 m3); 2) thermic-induced tensions responsible for the generation of slabs and plates (0.1 - 10 m3); and 3) intersection of structural joints within the rock mass resulting in blocks of 10 - 10,000 m3. In order to quantify the rockfall hazard, a magnitude-frequency analysis has been performed starting from an event-based inventory gathered from field surveillance and historical research. A methodology has been applied to take the maximum profit of only 30 registers with information on volume and date. The massif has been split into several domains with sampling homogeneity. For each one, there have been defined several periods of time during which, all the rockfall events of a given volume have been recorded. Thus, the magnitude-frequency relationship, for each domain, has been calculated. Results show that the curves are well fitted by a power law with exponents ranging from -0.59 to -0.68 for magnitudes

  1. Geometry and thermal structure of the Menderes Massif Core Complex (Western Turkey), implications for thermal evolution of Hellenic subduction zone

    NASA Astrophysics Data System (ADS)

    Roche, Vincent; Jolivet, Laurent; Guillou-Frottier, Laurent; Tuduri, Johann; Bouchot, Vincent; Beccaletto, Laurent; Lahfid, Abdeltif

    2016-04-01

    The eastern Mediterranean region is one of the most promising geothermal areas, with more than 250 geothermal fields discovered in Turkey (Parlaktuna, 2013), in a region of active tectonics and volcanism. Although the potential of these deep geothermal resources has not been systematically investigated yet, the geothermal activity of the western Turkey area is the most recent signature of the high heat flow (120-140 mW/m²; Aydin, 2005, from Teczan, 1995). Based on Turkish data, 2084 MWt are being utilized for direct applications and most of the energy originates from the Menderes Massif (Baba et al., 2015). This large-scale thermal anomaly at the surface is correlated to a long wavelength east-west increase of surface heat flow that could reflect the thermal state of Aegean subduction zone at depth. In order to better understand and characterize the possible connections between large-scale mantle dynamics and surface processes in space and time, we study the structure and thermal evolution of the Menderes Massif. Both the acceleration of the Aegean extension in the Middle Miocene and the recent escape of Anatolia have been proposed to result from several slab tearing events, the first one being located below western Turkey and the Eastern Aegean Sea. These events have triggered the formation of metamorphic complexes with contrasted exhumation P-T paths. While the extension in the Aegean domain is well-characterized with high-temperature domes in the center and east, the succession of several metamorphic events in the Menderes Massif and their significance in terms of geodynamics is still debated. Hence, the exhumation history is key to understanding the temporal and spatial distribution of the thermal signature of the Hellenic slab and its tearing/detachment. The Menderes Massif displays a large variety of metamorphic facies, from the Barrovian type metamorphism in the Eocene (the Main Menderes Metamorphism) to the coeval (?) HP-LT metamorphism on the southernmost

  2. Variable viral and grazer control of prokaryotic growth efficiency in temperate freshwater lakes (French Massif Central).

    PubMed

    Ram, A S Pradeep; Palesse, S; Colombet, J; Sabart, M; Perriere, F; Sime-Ngando, T

    2013-11-01

    The effects of viral lysis and heterotrophic nanoflagellate grazing (top down forces) on prokaryotic mortality and their subsequent impact on their metabolism were estimated in the upper euphotic and deeper aphotic depth of 11 freshwater lakes located in the French Massif Central. The standing stocks of viruses (VA) and heterotrophic nanoflagellate (HNF) varied significantly (p < 0.05) with sampled depth. VA was substantially (twofold on an average) and significantly higher (p < 0.03) at the aphotic compared to euphotic depth, whereas the reverse was true (p < 0.02) for HNF. Among the prokaryote subgroup, high nucleic acid content prokaryotes explained for significant variability in the total VA and served as principle host target for viral proliferation. Like standing stocks, flagellate grazing and viral infection rates also followed similar patterns. In the investigated lakes, the mechanism for regulating prokaryotic production varied with sampled depth from grazing control in the euphotic to control due to viral lysis in the aphotic. We also tested the hypothesis of top down control on prokaryotic growth efficiency (PGE, which we used as an index of prokaryotic physiological and energetic status at the community level) at both depths. Overall, among the studied lakes, PGE varied widely (4-51 %) with significantly (p < 0.05) lower values in the aphotic (mean = 18 ± 4 %) than euphotic depth (mean = 32 ± 9 %). Contrasting observations on the top down control of PGE between sampled depths were observed. The presence of grazers was found to stimulate PGE at the euphotic, whereas viruses through their lytic infection had a strong negative impact on PGE at the aphotic depth. Such observed differences in PGE and the mechanism controlling prokaryotic production with depth could eventually have strong implication on carbon and nutrient flux patterns in the studied lakes.

  3. Alpine thermal events in the central Serbo-Macedonian Massif (southeastern Serbia)

    NASA Astrophysics Data System (ADS)

    Antić, Milorad D.; Kounov, Alexandre; Trivić, Branislav; Wetzel, Andreas; Peytcheva, Irena; von Quadt, Albrecht

    2016-07-01

    The Serbo-Macedonian Massif (SMM) represents a crystalline belt situated between the two diverging branches of the Eastern Mediterranean Alpine orogenic system, the northeast-vergent Carpatho-Balkanides and the southwest-vergent Dinarides and the Hellenides. We have applied fission-track analysis on apatites and zircons, coupled with structural field observations in order to reveal the low-temperature evolution of the SMM. Additionally, the age and geochemistry of the Palaeogene igneous rocks (i.e. Surdulica granodiorite and dacitic volcanic rocks) were determined by the LA-ICPMS U-Pb geochronology of zircons and geochemical analysis of main and trace elements in whole-rock samples. Three major cooling stages have been distinguished from the late Early Cretaceous to the Oligocene. The first stage represents rapid cooling through the partial annealing zones of zircon and apatite (300-60 °C) during the late Early to early Late Cretaceous (ca. 110-ca. 90 Ma). It is related to a post-orogenic extension following the regional nappe-stacking event in the Early Cretaceous. Middle to late Eocene (ca. 48-ca. 39 Ma) cooling is related to the formation of the Crnook-Osogovo-Lisets extensional dome and its exhumation along low-angle normal faults. The third event is related to regional cooling following the late Eocene magmatic pulse. During this pulse, the areas surrounding the Surdulica granodiorite (36 ± 1 Ma) and the slightly younger volcanic bodies (ca. 35 Ma) have reached temperatures higher than the apatite closure temperature (120 °C) but lower than ca. 250 °C. The geochemistry of the igneous samples reveals late- to post-orogenic tectonic setting during magma generation.

  4. High-pressure metamorphism in the Early Variscan subduction complex of the SW Iberian Massif

    NASA Astrophysics Data System (ADS)

    Rubio Pascual, Francisco J.; Matas, Jerónimo; Martín Parra, Luis M.

    2013-04-01

    Several units exposed in the boundary area of the Ossa Morena Zone (OMZ) and the South Portuguese Zone (SPZ) preserve petrographic and thermobarometric evidence for an early metamorphic episode (M1), developed under a high-P, low to intermediate-T gradient, related to Early Variscan subduction in the SW Iberian Massif. In the OMZ, these are the Cubito-Moura Unit (Pmin ~ 9.2 kbar and T = 395 ± 45 °C), blueschists from its basal mélange (Pmin ~ 12.4 kbar and T = 310 ± 11 °C), and the underlying Fuenteheridos Group (P = 10.9 ± 0.4 kbar and T = 449 ± 31 °C). The equivalent units in the SPZ are the La Minilla Formation (P = 8.7 ± 0.4 kbar and T = 388 ± 16 °C) and the lawsonite pseudomorphs-bearing Pulo do Lobo Formation. All these units formed part of an approximately NE verging orogenic wedge (present coordinates) developed by the accretion of subducted slabs of the outermost margin of Gondwana and other elements of the Rheic Ocean realm, from at least the Middle Devonian to the lowermost Tournaisian. High-pressure rocks were subsequently emplaced on more internal zones of the OMZ that only experienced a younger high-T, low to intermediate-P metamorphism (M2). This high-T event was coeval with magmatic activity from the uppermost Devonian to the Middle Mississippian, probably as a consequence of transtensional lithospheric thinning and/or delamination of the lower crust and mantle lithosphere of the Gondwana margin. Pre-Late Devonian synorogenic sedimentation in forearc and back-arc basins of the subduction complex evolved to a Late Devonian-Middle Mississippian foreland basin system in early collisional stages. Finally, a new Middle-Late Mississippian fold-and-thrust belt with opposite (SW) vergence and new foreland basins developed during late collisional stages.

  5. The structural evolution of dunite and chromite ore from the Kharcheruz Massif, the Polar Urals

    NASA Astrophysics Data System (ADS)

    Chernyshov, A. I.; Yurichev, A. N.

    2016-03-01

    The Kharcheruz block of the Syumkeu ultramafic massif is a southern fragment of the Khadata ophiolitic belt, which closes the ophiolites of the Polar Urals in the north. The block, striking in the latitudinal direction, is sheetlike in shape and primarily composed of dunite with nearly latitudinal zones of chromite mineralization. The dunites are subject to ductile deformation various in intensity, and this variability is displayed in their heterogeneous structure and texture. The following microstructural types are distinguished by the variety and intensity of their deformation: protogranular → mesogranular → porphyroclastic → porphyrolath → mosaic. The petrostructural patterns of olivines pertaining to the above types reflect conditions of ductile deformation. Protogranular dunite is formed as a product of pyroxene decomposition in mantle harzburgite accompanied by annealing recrystallization at a temperature above 1000°C. Mesogranular dunite is formed as a product of high-temperature plastic flow by means of translation sliding in olivine and diffuse creep at a temperature dropping from 1000 to 650°C and at a low rate (<10-6 s-1). Cr-spinel segregates into linear zones of disseminated chromite mineralization within zones of bedding-plane plastic flow. Porphyroclastic and mosaic dunites are formed under conditions of intense deformation at a temperature of 500-750°C and at a significant rate (>10-6 s-1). Dunite is deformed by means of syntectonic recrystallization and subordinate translation gliding. Linear zones of disseminated mineralization undergo destruction thereby, with the formation of lenticular chromitite bodies from which ductile olivine is squeezed out with the formation of densely impregnated and massive ores.

  6. Microstructural evolution of the Yugu peridotites in the Gyeonggi Massif, Korea

    NASA Astrophysics Data System (ADS)

    Park, M.; Jung, H.

    2015-12-01

    The Yugu peridotite is the largest and freshest ultramafic body in the Gyeonggi Massif, Korean Peninsula, which potentially has a tectonic affinity to the eastward extension of the Qinling-Dabie-Sulu collision belt in China. In spite of its tectonic and rheological importance, only few mineralogical and petrological studies have been reported from Yugu peridotite. In order to understand the microstructural evolution of the Yugu peridotites, we conducted a detailed analysis of the microstructures and petro-fabrics. The majority of Yugu peridotite body is significantly serpentinized, and it consists predominantly of spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We collected peridotites from mainly two areas (northwestern and southwestern parts) of the Yugu ultramafic body, and all samples are spinel harzburgites consisting of olivine, orthopyroxene, clinopyroxene, spinel, and amphibole. These samples have similar mineralogy except for the varied amount of clinopyroxene and amphibole. These mineral contents are generally increasing from proto-mylonite peridotites to mylonite peridotites. Based on microstructural characteristics of highly deformed peridotites (especially grain-size of olivine), we classified the samples into four textural types, which are proto-mylonite, proto-mylonite to mylonite transition, mylonite, and ultra-mylonite. Depending on the texture of specimen, it is found that the lattice-preferred orientation (LPO) of olivine varies from A-type (proto-mylonite) via D-type like (mylonite) to E-type (ultra-mylonite). The fabric strength of olivine (M-index and J-index) systematically decreases with decreasing grain-size of olivine from proto-mylonite via mylonite to ultra-mylonite. The cause of fabric evolution in the Yugu peridotites will be discussed.

  7. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    USGS Publications Warehouse

    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.

  8. The magmatic history of the Vetas-California mining district, Santander Massif, Eastern Cordillera, Colombia

    NASA Astrophysics Data System (ADS)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Valencia, Víctor; Hart, Craig J. R.

    2013-08-01

    The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U-Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ˜1240 and 957 Ma; (2) early Ordovician calc-alkalic magmatism, which was synchronous with the Caparonensis-Famatinian Orogeny (˜477 Ma); (3) middle to late Ordovician post-collisional calc-alkalic magmatism (˜466-436 Ma); (4) late Triassic to early Jurassic magmatism between ˜204 and 196 Ma, characterized by both S- and I-type calc-alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc-alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic-hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic-early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204-199 Ma), Intermediate rocks (199-198 Ma), and late leucogranites, herein referred to as Alaskites-II (198-196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins.

  9. Partial re-equilibration of highly siderophile elements and the chalcogens in the mantle: A case study on the Baldissero and Balmuccia peridotite massifs (Ivrea Zone, Italian Alps)

    NASA Astrophysics Data System (ADS)

    Wang, Zaicong; Becker, Harry; Gawronski, Timo

    2013-05-01

    primitive mantle values, whereas Au, Re and S are somewhat depleted. The good linear correlation of S with Al2O3 in both suites reflects sulfide removal controlled by sulfur solubility in silicate melt, or co-precipitation with pyroxenes and spinel, and indicates very similar bulk partition coefficients for S and Al. S/Se and Se/Te in the lherzolites change little with decreasing Al2O3. Results for BM lherzolites are consistent with sulfide-silicate melt partitioning as the dominant control on abundances of the HSE, S, Se and Te during low to moderate degrees of melt extraction (DPt > DPd > DTe ⩾ DSe ⩾ DS ≈ DRe). Replacive dunites at Balmuccia have low abundances of Re, Au, Pd and chalcogens, but variable and higher abundances of Os, Ir and Ru, high S/Se and Se/Te, yet 187Os/188Os similar to BM lherzolites. The residual HSE and chalcogen compositions differ from those in dunites of subduction-related ophiolites. The composition and contact relations of the BM dunites with the host rocks likely reflect focused flow of sulfur-undersaturated melt after open system melting and re-equilibration of the lherzolites. The compositional record of the Balmuccia massif thus reflects the composition of different types of melts and their interaction with the peridotites at different P-T conditions.

  10. Relationship between Bajo Pobre and Chon Aike formations (Deseado Massif, Patagonia, Argentina):a melt inclusions study

    NASA Astrophysics Data System (ADS)

    Busà, T.; Bellieni, G.; Fernandez, R.; Hecheveste, H.; Piccirillo, E. M.

    2003-04-01

    The Deseado Massif covers the centre-east of the Santa Cruz Province, in the extra-Andean Patagonia. Although the Deseado Massif is mainly composed of silicic volcanic rocks (Chon Aike Formation, CA; 151.5 ±0.5 - 177.8 ±0.4 Ma), mafic and intermediate volcanites (Bajo Pobre Formation, BP; 152.7 ±0.5 and 164 ±0.3 Ma) outcrop largely in the central part of the Massif. In this paper quarz-trapped melt inclusions (rhyolitic in composition) from selected samples of the BP and the CA are analysed. On the basis of major elements content, for BP the sequence from andesite (BP whole rock) to ryholite (trapped as inclusions in quartz) can be modelled by simple fractional crystallisation of ortho- and clinopyroxene, plagioclase, quartz and apatite. As regards trace elements, a good calculated/measured ratio (around 1 ±0.2) is obtained assuming only a relatively high apatite fractionation. Since the apatite fractionation amount is not acceptable for major elements, the evolution of BP Formation cannot be modelled by a simple process of fractional crystallisation, and a contamination process probably occurred. The sequence from BP to CA cannot be modelled by fractional crystallisation. 30% batch melting of BP andesite (BP whole rock) produces a magma from which the CA ryholites (trapped as inclusions in quartz) can be obtained by Rayleigh fractional crystallisation of ortho- and clinopyroxene, plagioclase, magnetite, quartz, apatite and small amounts of zircon and minor allanite. Since the latter one was not observed in the analysed sample, a contamination process during magma evolution cannot be completely excluded. Finally, on the basis of the different trace elements concentration (Nb anomaly, different content in LILE, B/Be and B/Nb), it is possible to suppose that, at the time of the BP and CA emplacement, a changing in the tectonic setting, from subduction to a lithospheric extension, was active.

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

    PubMed

    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.

  12. New insights into serpentinization at Atlantis Massif, 30° N Mid-Atlantic Ridge, using wide-angle seismic method

    NASA Astrophysics Data System (ADS)

    Singh, S. C.; Collins, J. A.; Canales, J. P.; Tucholke, B. E.; Detrick, R. S.

    2004-12-01

    The Atlantis Massif is an ultramafic core complex that was formed in the last 1.5-2.0 Myr at the intersection of the Atlantis Fracture Zone and the Mid-Atlantic Ridge near 30° N by tectonic extension along a long-lived oceanic detachment fault. The exhumation of deep crustal and upper mantle rocks in the footwall of the fault provides an excellent tectonic window into the oceanic lithosphere. The Atlantis Massif will be the subject of a deep-drilling investigation for upcoming IODP Legs 304 and 305 (November 2004 - February 2005). Near-offset seismic reflection data (offset up to 3 km) across the core complex imaged a reflection at 0.2-0.25 s below the seafloor, which has been interpreted as an older detachment fault [Canales et al., Earth Planet. Sci. Lett., 222, 543-560, 2004]. The application of a non-conventional multichannel seismic (MCS) imaging technique allows us to include wide-angle seismic reflection data (offset up to 6 km) in the imaging process. We find that this reflection is continuous along most of the profiles and is present beneath the exposed detachment surface over an area larger than previously estimated from the near-offset MCS sections. Complementary data from on-bottom shots and ocean bottom seismometers constrain both P and S-wave velocities down to 0.5-0.6 km below the seafloor, at approximately the depth of the widespread reflection. The combined seismic data suggest that the interval between the seafloor and the reflection contains serpentinized peridotite. We quantify the amount and distribution of alteration in this layer by using an effective medium theory, and we interpret the results to shed new light on serpentinization processes at Atlantis Massif. IODP drilling results this winter will allow us to compare our interpretation to ground-truth measurements.

  13. Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif, France.

    PubMed

    Baron, S; Lavoie, M; Ploquin, A; Carignan, J; Pulido, M; De Beaulieu, J L

    2005-07-15

    This study aims to document the history of the metallurgical activities on the Mont Lozère massif in the Cévennes Mountains in Southern France. Many medieval sites of metallurgical wastes (slags) have been reported on the massif. These sites are thought to represent ancient lead workshops. The impact of past metallurgical activity on the environment was studied using geochemical and palynological techniques on a core collected in the Narses Mortes peatland near medieval smelting area. Two main periods of smelting activities during the last 2200 years were revealed bythe lead concentration and isotopic composition along the core profile: the first period corresponds to the Gallic period (approximately ca. 300 B.C. to ca. 20 A.D.) and the second one to the Medieval period (approximately ca. 1000-1300 A.D.). Forest disturbances are associated with lead anomalies for the two metallurgical activities described. The impact of the first metallurgy was moderate during the Gallic period, during which beech and birch were the tree species most affected. The second period corresponds to the observed slag present in the field. Along with agropastoral activities, the medieval smelting activities led to the definitive disappearance of all tree species on the summit zones of Mont Lozère. The abundance of ore resources and the earlier presence of wood on the massif justify the presence of workshops at this place. The relationship between mines and ores has been documented for the Medieval period. There is no archaeological proof concerning the Gallic activity. Nevertheless, 2500-2100 years ago, the borders of the Gallic Tribe territory, named the Gabales, were the same as the present-day borders of the Lozère department. Julius Caesar reported the existence of this tribe in 58 B.C. in "De Bello Gallico", and in Strabon (Book IV, 2.2) the "Gabales silver" and a "treasure of Gabales" are mentioned, but to this day, they have not been found.

  14. Geological and geochemical reconnaissance in the central Santander Massif, Departments of Santander and Norte de Santander, Colombia

    USGS Publications Warehouse

    Evans, James George

    1976-01-01

    The central Santander Massif is composed of Precambrian Bucaramanga Gneiss and pre-Devonian Silgara Formation intruded by Mesozoic quartz diorite, quartz monzonite, and alaskite and Cretaceous or younger porphyry. Triassic (Bocas Formation), Jurassic (Jordan and Giron Formations).and Cretaceous (Tambor, Rosa Blanca, Paja, Tablazo, Simiti, La Luna, and Umir Formations) sedimentary rocks overlie the metamorphic rocks and are younger than most of the intrusions. A geological and geochemical reconnaissance of part of the central Santander Massif included the Vetas and California gold districts. At Vetas the gold is generally in brecciated aphanitic quartz and phyllonite. Dark-gray material in the ore may be graphite. The ore veins follow steep west-northwest- and north-northeast-striking fracture zones. No new gold deposits were found. Additional geochemical studies should concentrate on western Loma Pozo del Rey and on improvement of the gold extraction process. At California the gold is in pyritiferous quartz veins and quartz breccia. Ore containing black sooty material (graphite?) is highly radioactive. Some of the mineralization is post-Lower Cretaceous. Soil samples indicate that gold deposits lie under the thick blanket of soil on the ridges above the zone of mining. Three principal gold targets are outlined by gold and associated minerals in pan concentrates. The close relation of gold and copper anomalies suggests that copper may be useful as a pathfinder for gold elsewhere in the region. Based on occurrences of gold or high concentrations of pyrite or chalcopyrite in pan concentrates and on analytical data, eight potential gold targets are outlined in the central massif. Reconnaissance of the surrounding region is warranted.

  15. 10Be exposure dating of onset and timing of Neoglacial glacier advances in the Ecrins massif, French Alps

    NASA Astrophysics Data System (ADS)

    Le Roy, Melaine; Deline, Philip; Carcaillet, Julien

    2013-04-01

    Alpine glaciers are known to be highly sensitive to change in temperature and precipitation on decadal to centennial time scales. For two decades, numerous studies on Holocene climate revealed a period marked by abrupt cold reversals (e.g. 8.2 ka event) with increasing frequency and magnitude after the Holocene Climatic Optimum, during the so-called Neoglacial period (roughly the last 4 ka). State-of-the-art studies indicate that largest alpine glaciers failed to exceed their Little Ice Age (LIA) extent during these LIA Type-Events, unlike certain smaller glaciers. In the French Alps, very few investigations were conducted to date on Holocene glacier variability. Almost all studies focused on the most glacierized area: the Mont Blanc massif, where suitable organic remains to apply radiocarbon dating and dendrochronology are available. Other glacierized massifs are poorly studied, without any Holocene/Neoglacial glacier chronology up to now. Here, we present the results of a study focusing on six glacier forefields distributed in the Ecrins massif. Detailed geomorphological mapping and in-situ produced 10Be dating were carried on multi-crested so-called "LIA composite moraines". The targeted ridges are located in distal position with respect to late LIA drift in order to identify Holocene cold pulses that have led to (or slightly exceeded) LIA-like glacier extent. The 35 10Be ages obtained revealed that the onset of Neoglacial occurred at ~4.2 ka, and that at least two other advances were recorded at ~3.3 ka and ~0.85 ka. One site has yielded a nearly complete Neoglacial record as four discrete events have been dated. These results highlight the potential of lateral moraine ridge stratigraphy which could yield accurate record when sufficiently preserved, but also the different preservation of landforms along the glacier margin which could censor the record.

  16. U-Pb dating and composition of inclusions in zircon from ophiolitic gabbro of the Klyuchevsk massif (Middle Urals): Results and geological interpretation

    NASA Astrophysics Data System (ADS)

    Smirnov, V. N.; Ivanov, K. S.; Koroteev, V. A.; Erokhin, Yu. V.; Khiller, V. V.

    2016-06-01

    The U-Pb (SHRIMP) dating of zircon from the layered complex of ophiolitic gabbro in the Klyuchevsk massif yielded an age of 456 ± 6 Ma corresponding within the limits of error to zircon dates obtained for other petrographic varieties from this massif. The investigation of the composition of silicate inclusions in dated zircon grains revealed that they are represented by typical metamorphic minerals: albite, zoisite, and secondary amphiboles. The data indicate that zircon was crystallized during metamorphic transformations of gabbroids and its U-Pb age (Late Ordovician-Silurian) is characteristic of all rocks in the ophiolite association of the Klyuchevsk massif indicating the age of metamorphism, not their formation time.

  17. The migmatite-gneiss complex of the Chuya-Kendyktas sialic massif (Southern Kazakhstan): Structure and age

    NASA Astrophysics Data System (ADS)

    Tretyakov, A. A.; Degtyarev, K. E.; Kovach, V. P.; Kotov, A. B.; Salnikova, E. B.; Pilitsyna, A. V.; Yakovleva, S. Z.

    2016-03-01

    A migmatite-gneiss complex made up of paraand orthogneisses and crystalline schists with bodies of ultrametagenic tonalites is distinguished in the basement of the northwestern part of the Chuya-Kendyktas Massif. ID-TIMS dating of accessory zircon from orthogneisses and ultrametagenic tonalites in combination with LA-ICP-MS analyses of detrital zircons from garnet-biotite paragneisses showed that the migmatite-gneiss complex was formed after protoliths with an age within 800-770 Ma and completed its evolution in the first half of the Neoproterozoic.

  18. Quantification of low elevation relief vertical movements from global sea level curves and scattered marine deposits (Armorican Massif, France)

    NASA Astrophysics Data System (ADS)

    Bessin, Paul; Guillocheau, François; Robin, Cécile; Bauer, Hugues; Schroëtter, Jean-Michel

    2016-04-01

    Amplitudes of vertical movements, amount of burial or of denudation are often too low or too old to be quantified from thermochronological or cosmogenic isotopes methods. This is the case for the vertical movements experienced by European Variscan basements of low relief during Cenozoic times. Some of these basements bear scattered thin Cenozoic marine sediments. Thus, we proposed to quantify Cenozoic vertical movements from i) current elevation of well dated marine sediments scattered on these basements, corrected from their bathymetry of deposition provided by their sedimentary facies and ii) elevation of global sea level at time of sediment deposition from a new compilation of available curves. This compilation highlights that i) curve which takes into account ocean basin volume change are consistent for the ca. 100 to 40 Ma "greenhouse" period whereas ii) curves based on coreholes backstripping methods better reflect global sea level changes since ca. 40 Ma. For their respective time intervals, both are in accordance with curves which together take into account ocean water volume and ocean basin volume changes. We quantify Cenozoic vertical movements of the Armorican Massif showcase. This massif is French Variscan basement of low relief (elevation < 420 m), two times buried then exhumed during Jurassic to Paleocene times, which bears numerous Cenozoic remnants of marine sediments of four periods: Bartonian, Rupelian, Langhian-Serravalian and Piacezian-Gelasian. We evidence a tree-step history of Cenozoic vertical movements and deformation: i) 38-34 Ma: a phase of near stability of the massif related to no to low deformation period for the Western Europe; ii) 30-16 Ma: a phase of low subsidence which coeval to a long wavelength subsidence of Western Europe which is proposed to be mantle-driven (dynamic topography); iii) 3.5-0 Ma: an overall bulging phase of the massif related to Apulia-Eurasia convergences due to Africa-Apulia and Iberia plates convergence which

  19. Research the dynamical characteristics of slow deformation waves as a rock massif response to explosions during its outworking

    NASA Astrophysics Data System (ADS)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2015-04-01

    As a result of long-term natural geomechanics and geophysical observation data on mines of complex ore rocks, generalization of the non-linear reaction of rock massif to heavy dynamic influences have been established. In addition, pendulum type waves have been observed and the sources of them have been located inside geoblocks of different hierarchic levels (Oparin et al., 2010). At the same time, these waves propagate with wide low (compared with seismic waves) velocity values (Kurlenja et al., 1993; Oparin et al., 2006). Research into the massif state with the use of the dynamic systems theory approach (Naimark et al., 2009; Chulichkov, 2003; Hachay et al., 2010) has been developed to ascertain the criteria of dissipative regimes changing for real rock massifs, which are under heavy man-caused influence. To realize such research we used the data from the seismic record of the Tashtagol mine for the two-year period from June 2006 up to June 2008. We used the space-time coordinates for all dynamic massif event responses, which occurred during that period inside the mine space and for the explosions - values fixed by seismic station energy (Hachay et al., 2010). The phase diagrams of the massif state for the northern and southern parts of the mine space were plotted in coordinates Ev(t) and d(Ev(t))/dt, t - time - in parts of 24 hours, Ev - the dissipated massive seismic energy - in joules. Hachay et al., (2010) analysed the morphology of seismic response phase trajectories on the explosion influences during different serial intervals in the southern part of the mine. In that period, according to data for different explosions in the mine, the majority of the total energy had been injected into the southern part of the mine. Moreover, at the end of 2007, just in the southern part, the strongest rock burst during the whole history of the working mine happened. We developed a new processing method of seismological information in real, which we can use directly in the

  20. Recharge areas and hydrochemistry of carbonate springs issuing from Semmering Massif, Austria, based on long-term oxygen-18 and hydrochemical data evidence

    NASA Astrophysics Data System (ADS)

    Yehdegho, Beyene; Reichl, Peter

    2002-10-01

    Résumé. Les teneurs en oxygène-18 et l'hydrochimie des sources émergeant du massif de Semmering ont été suivies de manière intensive dans le but de caractériser les zones de recharge et l'évolution hydrochimique. L'effet d'altitude sur le δ18O a été déterminé grâce aux données isotopiques et hydrogéologiques de petites sources de référence, principalement en terrains cristallins; cet effet est d'environ -0,27 et -0,21‰ par 100 m pour les versants respectivement nord et sud du massif. En appliquant ces valeurs, l'altitude moyenne de recharge des sources a été calculée. Pour les sources à fort débit issues des carbonates, elle est comprise entre 1,100 et 1,400 m, compatible avec le cadre topographique et hydrogéologique des calcaires et des dolomies de l'Austro-alpin inférieur alimentant ces sources. La composition chimique des sources des carbonates est dominée par les ions Ca2+, Mg2+, HCO3- et SO42-. Les sources sont presque toutes proches de la saturation par rapport à la calcite, mais sont sous-saturées en dolomite (sauf quelques sources proches de la saturation). Comme cela est habituel en ce qui concerne le dioxyde de carbone fourni par les sols en régions montagneuses, la pCO2 équilibrante moyenne est faible, comprise entre 10-3.0 et 10-2.5 atm (0,1 à 0,3% en volume). En ce qui concerne les variations à long terme, le pH, SIc, Sid et la pCO2 équilibrante sont soumis à des variations saisonnières, alors que les concentrations en Ca2+, Mg2+ et HCO3- ne varient pratiquement pas. En intégrant les résultats de δ18O et les données hydrochimiques, la variabilité altitudinale du chimisme des eaux souterraines des carbonates est démontrée. Reflétant les variations d'activité biologique et des conditions de recharge dans les zones d'alimentation, une covariation négative résulte de l'altitude de recharge et de la pCO2 et la concentration en HCO3- n'est pas modifiée par aucun des termes source ou puits, ce qui fait varier

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

    NASA Astrophysics Data System (ADS)

    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. Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

    NASA Astrophysics Data System (ADS)

    Javier Álvaro, J.; Colmenar, Jorge; Monceret, Eric; Pouclet, André; Vizcaïno, Daniel

    2016-06-01

    Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing. The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances.

  3. Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

    NASA Astrophysics Data System (ADS)

    Harding, Alistair J.; Arnulf, Adrien F.; Blackman, Donna K.

    2016-06-01

    Seismic full waveform inversion (FWI) is a promising method for determining the detailed velocity structure of the igneous oceanic crust, especially for locations such as the Mid-Atlantic Ridge with significant lateral heterogeneity and seafloor topography. We examine the accuracy of FWI by inverting, after downward continuation to datum just above the seafloor, a multichannel seismic (MCS) profile from Atlantis Massif oceanic core complex at 30°N that passes close to Integrated Ocean Drilling Program (IODP) Hole U1309D and comparing the results against borehole measurements and existing on-bottom refraction data. The comparisons include the results of IODP Expedition 340T, which extended the sonic logging and vertical seismic profiling to the bottom of the borehole at 1400 m below seafloor. Compared to travel time tomography, the refinement in velocity and velocity gradient produced by FWI significantly improves the overall match to the borehole measurements, and allows the multilevel pattern of deformation and alteration of the detachment footwall seen in Hole U1309D to be extrapolated across the Central Dome. Prestack depth migration of the profile using the FWI velocities reveals the top and edges of the high-velocity, gabbroic core of the massif. It also indicates that the comparatively uniform gabbroic rocks drilled at Hole U1309D extend to ˜2.5 km below seafloor but overlie an extended, ˜2 km thick, mantle transition zone.

  4. Neutron porosity logging and core porosity measurements in the Beauvoir granite, Massif Central Range, France

    NASA Astrophysics Data System (ADS)

    Gallé, C.

    1994-08-01

    A large suite of geophysical logs have been run in the Beauvoir granite. The drillhole (900 m deep), first target of the French Deep Geology programme, is located in the Hercynian bedrock of Echassières in central France (Massif Central Range). After geochemical and petrological studies, the batholith was used for experiments pertaining to the storage of radioactive wastes. With its low porosity, its weak fracturing and its high homogeneity, the Beauvoir granite was chosen for the analysis of the relationship between logged data and the properties measured in the core. The study focused on neutron porosity and core water porosity. The Beauvoir granite has a total free water porosity of around 2% (average value of 54 core samples of rock mass) and an average neutron porosity of around 10%. We show that the origin of this significant difference is related to the neutron matrix effect of the granite. This phenomenon is partly due to the slowing-down effect of the combined water of clays and micas but also to the neutronic capture effect linked with the relatively high lepidolite (lithium mica) content of the granite. The Li 2O content controls 85% of the granite macroscopic capture cross-section. These two factors represent around 75% of the global neutron porosity of the Beauvoir granite. They have to be taken into consideration to get representative water contents of a low-porosity igneous rock from a neutron porosity log. Further investigations also demonstrated the necessity of choosing a better adapted neutron tool calibration for crystalline rocks. Instead of a standard calibration with limestone blocks, a calibration in granite blocks was simulated in order to obtain a better evaluation of the global neutron response of the granite. Then, by correcting this new neutron porosity for the matrix effect, it has been possible to determine water contents in accordance with laboratory water porosity values measured on core samples (2% average porosity). This

  5. Hydrothermal alterations in the Echassières granitic cupola (Massif central, france)

    NASA Astrophysics Data System (ADS)

    Merceron, Thierry; Vieillard, Philippe; Fouillac, Anne-Marie; Meunier, Alain

    1992-11-01

    Detailed petrographic and mineralogic investigations of an albite-lepidolite granite at Echassières (Massif Central, France; scientific deep drill program) shows the existence of hydrothermal stages which are closely related to the magmatic and structural history. According to fluid inclusion data, K-Ar datations and 18O/16O-D/H compositions of secondary minerals, two successive hydrothermal periods have been recognized. The early one (273 268 million years) produced a series of aluminous phyllosilicates: muscovite, pyrophyllite, donbassite, tosudite, kaolinite which are observed as vein deposits (<10 mm wide) and alteration products of primary minerals in wall-rocks. The vein system was sealed by monomineralic assemblages during a cooling period (400 150°C). This early hydrothermal alteration stage was controlled by interactions of rock with low salinity (1 10 wt% NaCl equivalent) fluids expelled from the granitic body during the cooling processes. The chemical properties of these fluids were the following: low pH, very low Mg and Fe and high Li, Na and K contents. Thermodynamic calculations show that the sequence pyrophyllite, Li-bearing donbassite, tosudite is mostly temperature dependent. From the chemical composition of secondary minerals and isotopic data it can be deduced that these fluids, which have a meteoric origin, have been expelled from the granite body during its cooling period and after interaction with it at high temperature. The late hydrothermal stage corresponds to deposits of fluorite and Fe-Mg rich illite (151 million years) in subvertical fractures. Temperature conditions did not exceed 250° C and fluids came through the surrounding metamorphic rocks into the granitic body. IIlite/smectite mixed-layer minerals have been identified in subvertical fractures which were opened during Tertiary periods. In the host micaschists, successive hydrothermal alterations took place during the cooling of the Beauvoir granite. Early magmatic fluids

  6. Ssismic Methodologies Applied To The Characterization Of Fractured Rock Massifs: Case Studies

    NASA Astrophysics Data System (ADS)

    Marti, D.; Carbonell, R.; Flecha, I.; Palomeras, I.; Font-Capo, J.; Vazquez-Sune, E.; Perez-Estaun, A.

    2007-05-01

    The detailed characterization of fractured media in the shallow subsurface is becoming important. The detailed knowledge of the fracture network is mandatory in any hydrogeological model to constrain the potential pathways for water circulation. The geophysical methodolgies can provide a detailed image of the fractured rock and also the 3D distribution of physical properties. Two case studies are discussed in this work. The characterization of fractures in a waste disposal site and, the design and construction of a subway tunnel. In the first case, a multiseismic experiment was carried out in an old abandoned uranium mine. 2D and 3D seismic experiments including VSP, surface seismic reflection and travel time seismic tomography provided a 3D image of the internal structure of a granitic massif for hydrogeological studies of the preferred paths for the migration of contaminants. The tectonic stability of the site was also addressed by means of seismic measurements. The joint interpretation of all the available data enabled the interpretation of the low velocity anomalies in the 3D seismic tomography image as the fragile fractures and the alteration associated to them. A 3D image of the geometry of the heterogeneous weathered surface layer was also obtained. This surface is controlled by the complex network of faults and dykes observed in the area. The second case study involves 2D and 3D seismic experiments to aid the horizontal drilling of tunnels for a new subway line in Barcelona (Spain). Seismic data acquisition in a densely populated city is very difficult. The street layout determines the geometry of the acquisition experiments. The instrumentation can not always be located on the surface projection of the tunnel trace, therefore, pseudo 3D acquisition is required, deploying the instrumentation were it is possible. Furthermore, the shallow subsurface features extremely heterogeneous "weathered" layer of variable thickness (building fundations, sewage system

  7. Generation and evolution processes of Paleoproterozoic massive-type Sancheong anorthosite complex, Yeongnam massif, Korea

    NASA Astrophysics Data System (ADS)

    Kang, Ji-Hoon; Lee, Deok-Seon

    2016-04-01

    The Paleoproterozoic (˜1.87-1.79 Ga) Sancheong anorthosite complex in the Jirisan province of the Yeongnam massif, Korea, consists of massive-type and foliation-type Sancheong anorthosite (SA), Fe-Ti ore body (FTO), and mafic granulite (MG). We report their characteristics and interrelation on foliations, occurrences, lithofacies, composition minerals, suggesting the generation and evolution processes of the Sancheong anorthosite complex with the origin of their foliations. The main characteristics and interrelation are as follows: multilayer structures of FTO, straight-, anastomosing-, uneven-types FTO and MG veins derived from blocking associate with size reduction of SA, gradual or irregular boundaries of SA blocks, FTO and MG showing bulbous lobate margins and comb structures between SA blocks, flow foliations and linear arrangements of FTO and MG, discontinuous shear zone of SA, orientation of FTO and MG foliations parallel to the boundaries of SA blocks, predominance of FTO and MG foliations toward the boundaries of SA blocks, flow folding structures of FTO and MG foliation, lithfacies change of MG into FTO by the injection of MG into SA, and very similar assemblage of mafic minerals and chemical composition of ilmenite and almost equal occurrence and foliation features between FTO and MG. Such evidences indicate that the SA, FTO, MG foliations are magmatic foliations which were formed in a not fully congealed state of SA from the results of the fracturing of partly congealed SA, the injection and flow of FTO and MG melts into the fractured SA, the dynamic intercompaction between them. It also implies that the SA, FTO, MG were not formed from the intrusion and differentiation of magmas which were different from each other in genesis and age but from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma. Our new model suggests that the Sancheong anorthosite complex was generated and evolved as following sequence: the

  8. Lithospheric transition from the Variscan Iberian Massif to the Jurassic oceanic crust of the Central Atlantic

    NASA Astrophysics Data System (ADS)

    Fernàndez, M.; Marzán, I.; Torne, M.

    2004-08-01

    A 1000-km-long lithospheric transect running from the Variscan Iberian Massif (VIM) to the oceanic domain of the Northwest African margin is investigated. The main goal of the study is to image the lateral changes in crustal and lithospheric structure from a complete section of an old and stable orogenic belt—the Variscan Iberian Massif—to the adjacent Jurassic passive margin of SW Iberia, and across the transpressive and seismically active Africa-Eurasia plate boundary. The modelling approach incorporates available seismic data and integrates elevation, gravity, geoid and heat flow data under the assumptions of thermal steady state and local isostasy. The results show that the Variscan Iberian crust has a roughly constant thickness of ˜30 km, in opposition to previous works that propose a prominent thickening beneath the South Portuguese Zone (SPZ). The three layers forming the Variscan crust show noticeable thickness variations along the profile. The upper crust thins from central Iberia (about 20 km thick) to the Ossa Morena Zone (OMZ) and the NE region of the South Portuguese Zone where locally the thickness of the upper crust is <8 km. Conversely, there is a clear thickening of the middle crust (up to 17 km thick) under the Ossa Morena Zone, whereas the thickness of the lower crust remains quite constant (˜6 km). Under the margin, the thinning of the continental crust is quite gentle and occurs over distances of ˜200 km, resembling the crustal attitude observed further north along the West Iberian margins. In the oceanic domain, there is a 160-km-wide Ocean Transition Zone located between the thinned continental crust of the continental shelf and slope and the true oceanic crust of the Seine Abyssal Plain. The total lithospheric thickness varies from about 120 km at the ends of the model profile to less than 100 km below the Ossa Morena and the South Portuguese zones. An outstanding result is the mass deficit at deep lithospheric mantle levels required

  9. Seismicity without a fault ? Structural evidence from pseudotachylites in the UHP Dora Maira Massif

    NASA Astrophysics Data System (ADS)

    Zechmeister, M.; Ferre, E. C.; Geissman, J. W.; Cosca, M.; Caby, R.; Frima, C.; Ward, C.

    2004-12-01

    The Dora Maira massif, in the Italian Alps, is a world famous example of ultra-high pressure (UHP) metamorphism of crustal rocks with peak pressure of ca 3 GPa (depth ≈ 100 km) at about 35 My. Exhumation began shortly after the peak of metamorphism. The UHP rocks had equilibrated at a temperature of 250° C around 30 My. Pseudotachylite veins (1 to 20 mm thick) formed parallel to the syn-exhumation mylonitic foliation and were dated at 20.1 ± 0.5 Ma by Ar/Ar method. The geochronologic data suggests that the pseudotachylite veins formed at depths shallower than ≈ 10 km. These veins are found mainly in gently dipping medium grained phengite/coesite bearing orthogneiss. The generation veins are parallel to the foliation, constant in thickness and up to several tens of meters in length. Injection veins are less common and generally only a few cm in length. Structural mapping of UHP mylonitic gneisses and surrounding rocks reveals the dominance of high ductile strain, a puzzling lack of localized cataclastic deformation and the absence of fault associated with the pseudotachylite veins. The pseudotachylite veins are concentrated along a 50 m wide, foliation-parallel corridor. Conversely, the two major faults along which the UHP rocks were exhumed are > 500 m away from the pseudotachylite-bearing rocks and do not contain pseudotachylite veins. The formation of these pseudotachylite veins is clearly related to exhumation history of UHP rocks. The formation of pseudotachylite results from frictional melting as shown by microstructural criteria including corroded quartz grains and spherulitic microstructures. The localized heat source required for melting the UHP orthogneisses along narrow bands is attributed to frictional heat produced along the foliation plane. Fault-related pseudotachylite studies and friction experiments have shown that seismic strain rates (in the order of s-1) are required to maintain heat along the fault plane. At slower strain rates, heat would

  10. Recharge areas and hydrochemistry of carbonate springs issuing from Semmering Massif, Austria, based on long-term oxygen-18 and hydrochemical data evidence

    NASA Astrophysics Data System (ADS)

    Yehdegho, Beyene; Reichl, Peter

    2002-10-01

    Résumé. Les teneurs en oxygène-18 et l'hydrochimie des sources émergeant du massif de Semmering ont été suivies de manière intensive dans le but de caractériser les zones de recharge et l'évolution hydrochimique. L'effet d'altitude sur le δ18O a été déterminé grâce aux données isotopiques et hydrogéologiques de petites sources de référence, principalement en terrains cristallins; cet effet est d'environ -0,27 et -0,21‰ par 100 m pour les versants respectivement nord et sud du massif. En appliquant ces valeurs, l'altitude moyenne de recharge des sources a été calculée. Pour les sources à fort débit issues des carbonates, elle est comprise entre 1,100 et 1,400 m, compatible avec le cadre topographique et hydrogéologique des calcaires et des dolomies de l'Austro-alpin inférieur alimentant ces sources. La composition chimique des sources des carbonates est dominée par les ions Ca2+, Mg2+, HCO3- et SO42-. Les sources sont presque toutes proches de la saturation par rapport à la calcite, mais sont sous-saturées en dolomite (sauf quelques sources proches de la saturation). Comme cela est habituel en ce qui concerne le dioxyde de carbone fourni par les sols en régions montagneuses, la pCO2 équilibrante moyenne est faible, comprise entre 10-3.0 et 10-2.5 atm (0,1 à 0,3% en volume). En ce qui concerne les variations à long terme, le pH, SIc, Sid et la pCO2 équilibrante sont soumis à des variations saisonnières, alors que les concentrations en Ca2+, Mg2+ et HCO3- ne varient pratiquement pas. En intégrant les résultats de δ18O et les données hydrochimiques, la variabilité altitudinale du chimisme des eaux souterraines des carbonates est démontrée. Reflétant les variations d'activité biologique et des conditions de recharge dans les zones d'alimentation, une covariation négative résulte de l'altitude de recharge et de la pCO2 et la concentration en HCO3- n'est pas modifiée par aucun des termes source ou puits, ce qui fait varier

  11. Fractionation of highly siderophile and chalcogen elements during magma transport in the mantle: Constraints from pyroxenites of the Balmuccia peridotite massif

    NASA Astrophysics Data System (ADS)

    Wang, Zaicong; Becker, Harry

    2015-06-01

    Sulfide segregation from sulfur saturated basic magmas affects the compositions of chalcophile elements such as the highly siderophile elements (HSE) and the chalcogens S, Se, Te to variable extent. Whether this process predominantly occurs in the lower crust or in the mantle and how segregation of liquid sulfide and accumulation affects concentrations and ratios of these elements at different mantle depths and in presumed primitive basic magmas remains uncertain. Abundances of the HSE, S, Se and Te and Os isotopes in websterites and spinel clinopyroxenites of the Balmuccia peridotite massif (Ivrea-Verbano Zone, Italian Alps) provide new insight on sulfide segregation and the compositional change of melt and peridotite during magma transport in the mantle. Balmuccia websterites and clinopyroxenites formed from late Paleozoic and Mesozoic melt influx into stretched continental lithospheric mantle of the Ivrea-Verbano Zone, respectively. The HSE and chalcogen element compositions of websterites and clinopyroxenites reflect the segregation and accumulation of sulfide melt from S saturated silicate melts with different abundances and ratios of chalcogens and the HSE. The pyroxenites display large variations in abundances of the platinum group elements (PGE) and Te whereas abundances of less chalcophile elements S, Se and Re are much less variable. The fractionation between the PGE and fractionation of Re/Os, S/Se and Se/Te in the mantle pyroxenites are consistent with sulfide melt-silicate melt partitioning with a sequence of apparent coefficients of DPGE > DAu ⩾ DTe > DSe ⩾ DS ≈ DRe. Concentrations in ocean ridge basalts and in gabbros of the lower oceanic crust are also consistent with such fractionation. Websterites which have formed during refertilization of depleted peridotites display ratios of the HSE and moderately suprachondritic initial 187Os/188Os similar to interstitial sulfides of refertilized peridotites. These compositions are different from

  12. Tectonic control on the late stage exhumation of the Aar Massif (Switzerland): Constraints from apatite fission track and (U-Th)/He data

    NASA Astrophysics Data System (ADS)

    Reinecker, John; DanišíK, Martin; Schmid, Claudia; Glotzbach, Christoph; Rahn, Meinert; Frisch, Wolfgang; Spiegel, Cornelia

    2008-12-01

    We examine the hypothesis that Pliocene exhumation of the external massifs in the central Alps is controlled by climatic change. New thermochronological data from the western Gastern-Aar massif are used to investigate the timing, extent, and reasons for Neogene exhumation. Our data reveal that exhumation was constant with 0.5 km/Ma over the last 10 Ma in the north. In the southern part, exhumation was of the same order until ˜3.5 Ma but then increased gradually toward the south to values of up to 1.2 km/Ma, resulting in overall northward tilting of the western Aar massif. We explain this accelerated exhumation in the south after ˜3.5 Ma mainly by tectonic denudation in the footwall of the Rhône-Simplon fault and discuss changes in deep crustal configuration, which may have triggered south directed normal faulting. We propose that the Rhône river was structurally trapped by the Rhône-Simplon normal fault zone, which additionally enhanced erosion in the southern section of the Aar massif. Climatic forcing may have an impact in the very late stage of exhumation due to Alpine glaciation in the late Pliocene.

  13. Determination of Granite Rock Massif Weathering and Cracking of Surface Layers in the Oldest Parts of Medieval Mine Depending on Used Mining Method

    NASA Astrophysics Data System (ADS)

    Lednická, Markéta; Kaláb, Zdeněk

    2016-06-01

    The paper presents the use of selected non-destructive testing methods for the purpose of specifying information on weathering and cracking of surface layers of granite rock massif in the medieval Jeroným Mine (the Czech Republic). This mine has been declared the National Heritage Site of the Czech Republic and its opening as a mining museum to the public is gradually prepared. Geological and geomechanical evaluation documents the possibility to find all kinds of weathering grades of rock massif in this mine. Two non-destructive methods have been tested, namely the measurement of ultrasonic pulse velocity and the measurement of Schmidt hammer rebound value. Field measurements were performed in two selected galleries to verify the application of such methods in specific conditions of underground spaces. Used mining method is one of the parameters later influencing cracking of rock massif. In selected galleries, two different mining methods were used which means that a part of a gallery profile was mined out by hand tools in the Middle Ages and another part of the profile was later mined out by blasting. Measurements in these galleries have enabled to analyse the influence of used mining methods on cracking of rock massif in the impaired zone, and, consequently, on ongoing weathering processes in those zones.

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

    NASA Astrophysics Data System (ADS)

    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

  15. Pressure stabilized Se-Se dimer formation in PbSe 2

    NASA Astrophysics Data System (ADS)

    Bremholm, M.; Hor, Y. S.; Cava, R. J.

    2011-01-01

    The preparation of PbSe 2 through the reaction of PbSe with excess Se at 4.5 GPa and 650 °C is reported. The crystal structure, determined from X-ray powder diffraction data (CuAl 2 structure type, I4/mcm (#140), a = 6.42695(11) Å, c = 7.70254(13) Å, Z = 4), consists of layers of [Se 2] 2- dimers with Pb 2+ in square antiprismatic coordination with Se. This is a rare crystal structure for divalent metal chalcogenides, previously only identified for SrS 2 and BaTe 2. Undoped PbSe 2 as well as Bi 3+- and Ag +-doped samples (10% Pb substitution) show semi-metallic resistivity down to 0.4 K. Magnetic susceptibility measurement of PbSe 2 shows no magnetic ordering above 1.8 K. The Seebeck coefficients show nearly linear behavior from 35 to 400 K and the largest numerical values are found in the case of undoped PbSe 2, + 99 μVK -1, and Bi 3+-doped PbSe 2, - 146 μVK -1, at the highest temperature measured, 400 K.

  16. Use of Digital Elevation Models to understand map landforms and history of the magmatism Khibiny Massif (Kola Peninsula, Russia)

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Middle Jurassic syn-kinematic magmatism, anatexis and metamorphism in the Zheduo-Gonggar massif, implication for the deformation of the Xianshuihe fault zone, East Tibet

    NASA Astrophysics Data System (ADS)

    Li, Hailong; Zhang, Yueqiao; Zhang, Changhou; Dong, Shuwen; Zhu, Fusheng

    2015-08-01

    The Xianshuihe fault (XSHF) zone is an important lithospheric structure in east Tibetan Plateau. The Zheduo-Gonggar massif, about 120 km long and 13-18 km wide, developed along its eastern segment. Based on geological mapping, meso- and micro-structure studying and geochronology testing, the massif is divided into 5 units: (1) Intrusions of 216-204 Ma, (2) Intrusions of ∼170 Ma, (3) mid-Jurassic sillmanite-grade metasediments, (4) Oligo-Miocene migmatite zone, (5) Intrusions less than 20 Ma ago. Intrusions of 216-204 Ma related to the Songpan-Garze folding and distributes on the southern segment of the massif. The middle Jurassic intrusions which were found for the first time in the region, includes the syn-kinematic Zheduoshan granite and a suit of leucogranite. The former constrained by the youngest U-Pb age of 171 Ma which provides a minimum shear age of the XSH fault. The latter, U-Pb age of 170 Ma, is a common feature of convergent orogens or intracontinental subduction. The Oligo-Miocene migmatite zone, about 80 km long and 1-3 km wide, developed on the eastern edge of the massif. Intrusions less than 20 Ma ago is located on the northern segment of the massif. It had been widely researched that the latter two units are associated to the Cenozoic deformation of the XSH fault. While the mid-Jurassic syn-kinematic magmatism, anatexis and metamorphism along the XSH fault suggests a more strong Mesozoic tectono-thermal event in the fault zone. The discoveries provide us with a new perspective on understanding the Mesozoic and Cenozoic deformation of the XSH fault zone, southeastern Tibet.

  19. Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain

    NASA Astrophysics Data System (ADS)

    Marchesi, Claudio; Garrido, Carlos J.; Bosch, Delphine; Bodinier, Jean-Louis; Gervilla, Fernando; Hidas, Károly

    2013-01-01

    Geochemical studies of primitive basalts have documented the presence of crustal-derived garnet pyroxenite in their mantle sources. The processes whereby melts with the signature of garnet pyroxenite are produced in the mantle are, however, poorly understood and somewhat controversial. Here we investigate a natural example of the interaction between melts of garnet pyroxenite derived from recycled plagioclase-rich crust and surrounding mantle in the Ronda peridotite massif. Melting of garnet pyroxenite at ˜1.5 GPa generated spinel websterite residues with MREE/HREE fractionation and preserved the positive Eu anomaly of their garnet pyroxenite precursor in whole-rock and clinopyroxene. Reaction of melts from garnet pyroxenite with depleted surrounding peridotite generated secondary fertile spinel lherzolite. These secondary lherzolites differ from common spinel lherzolite from Ronda and elsewhere by their lower-Mg# in clinopyroxene, orthopyroxene and olivine, lower-Cr# in spinel and higher whole-rock Al2O3, CaO, Sm/Yb and FeO* at a given SiO2. Remarkably, secondary spinel lherzolite shows the geochemical signature of ghost plagioclase in the form of positive Eu and Sr anomalies in whole-rock and clinopyroxene, reflecting the transfer of a low-pressure crustal imprint from recycled pyroxenite to hybridized peridotite. Garnet pyroxenite melting and melt-peridotite interaction, as shown in the Ronda massif, may explain how the signature of subducted or delaminated crust is transferred to the mantle and how a garnet pyroxenite component is introduced into the source region of basalts. The efficiency of these processes in conveying the geochemical imprint of crustal-derived garnet pyroxenite to extruded lavas depends on the reactivity of pyroxenite melt with peridotite and the mantle permeability, which may be controlled by prior refertilization reactions similar to those documented in the Ronda massif. Highly fertile heterogeneities produced by pyroxenite

  20. Zircon typology combined with SmNd whole-rock isotope analysis to study Brioverian sediments from the Armorican Massif

    NASA Astrophysics Data System (ADS)

    Dabard, M. P.; Loi, A.; Peucat, J. J.

    1996-02-01

    The identification of source materials contributing to mature terrigenous clastic deposits is made difficult due to a lack of useful discriminant criteria. SmNd isotope analysis can provide some indication of the present of mantle-derived constituents in clastic rocks. However, since this method is based on whole-rock samples, it is only possible to obtain the averaged composition of the different source materials involved. Moreover, SmNd isotope systematics can be strongly influenced by the presence of heavy minerals rich in rare earth elements and/or displaying isotopic ratios very different to the sedimentary host. In this manner, 0.1% of zircon or 0.01% of monazite from an extraneous source is sufficient to modify significatively the SmNd signature of the whole-rock. The typological study of zircon populations is an extremely valuable tool, especially since this mineral is highly resistant and exhibits a morphology controlled by the physical and chemical conditions under which it crystallized. Zircons that have been reworked in a sedimentary deposit display typologies that make it possible to identify the different igneous rock-types present in the source region. Moreover the typological study can be associated with a single-grain PbPb dating. This twofold approach was applied to Brioverian sedimentary rocks (Neoproterozoic III to Early Palaeozoic in age) from the Central Brittany Domain (Armorican Massif, NW France). It is proposed that these deposits inherited a major component from juvenile crustal materials ( ɛND(540) = - 1.4 to - 6.3), reflecting the presence of igneous precursors with a dominantly mantle-derived origin (zircon sub-types S19, S20, S24, S25 etc.), to which was added another component of crustal anatectic affinity (zircon sub-types S2, S6, S7 etc.). Two igneous source regions are identified on the basis of the present study: the anatectic granitic massifs of the Mancellian Batholith (540 Ma), along with a coeval ignimbritic

  1. Apatite Fission Track Thermochronology of Khibina Massif (Kola Peninsula, Russia): Implications for post-Devonian Tectonics of the NE Fennoscandia

    NASA Astrophysics Data System (ADS)

    Veselovskiy, R. V.; Thomson, S. N.; Arzamastsev, A.

    2015-12-01

    The thermal history of the Kola Peninsula area of NE Fennoscandia remains almost fully unknown because of absence of any thermochronological data such as apatite and/or zircon fission track or (U-Th)/He ages. In order to fill this gap and to constrain the post-Devonian erosion and exhumation history of this region, we present the results of apatite fission track (AFT) dating of eleven samples selected from the cores taken from different depths of the northern part of the Khibina intrusive massif. This alkaline magmatic complex is located at the center of Kola Peninsula and formed at about 370 Ma (Kramm and Kogarko, 1994). Samples were analyzed from depths between +520 to -950 meters and yielded AFT ages between 290-268 Ma with an average age uncertainty (1σ) of ±30 Ma. Mean track lengths (MTL) lie between 12.5-14.4 μm. We used the most reliable AFT ages and distribution of MTL in two samples, corresponding to depths of +280 and -920 m, to conduct inverse time-temperature modelling of the Khibina massif. Thermal histories that best predict the measured data show three stages: (1) 290-250 Ma - rapid cooling from >110°C to 70°C/50°C for lower/upper sample correspondingly; (2) 250-50 Ma - a stable temperature stage; (3) 50-0 Ma - slightly increased cooling rates down to modern temperatures. We propose that the first cooling stage is related to late-Hercynian orogenesis; the second cooling stage may be associated with tectonics accompanying with opening of Arctic oceanic basin. The obtained data show that geothermal gradient at the center of Kola Peninsula has remained close to the modern value of 20°C/km for at least the last 250 Myr. AFT data show that the Khibina massif has been exhumed not more then 5-6 km in the last 290 Myr. This study was funded by grants 15-35-20599, 15-05-02116, 15-05-01860 and 13-05-01033 from the Russian Foundation of Basic Research, grant 3.38.224.2015 from the St. Petersburg State University, grant 14.Z50.31.0017 from the Government

  2. Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif, France.

    PubMed

    Baron, S; Lavoie, M; Ploquin, A; Carignan, J; Pulido, M; De Beaulieu, J L

    2005-07-15

    This study aims to document the history of the metallurgical activities on the Mont Lozère massif in the Cévennes Mountains in Southern France. Many medieval sites of metallurgical wastes (slags) have been reported on the massif. These sites are thought to represent ancient lead workshops. The impact of past metallurgical activity on the environment was studied using geochemical and palynological techniques on a core collected in the Narses Mortes peatland near medieval smelting area. Two main periods of smelting activities during the last 2200 years were revealed bythe lead concentration and isotopic composition along the core profile: the first period corresponds to the Gallic period (approximately ca. 300 B.C. to ca. 20 A.D.) and the second one to the Medieval period (approximately ca. 1000-1300 A.D.). Forest disturbances are associated with lead anomalies for the two metallurgical activities described. The impact of the first metallurgy was moderate during the Gallic period, during which beech and birch were the tree species most affected. The second period corresponds to the observed slag present in the field. Along with agropastoral activities, the medieval smelting activities led to the definitive disappearance of all tree species on the summit zones of Mont Lozère. The abundance of ore resources and the earlier presence of wood on the massif justify the presence of workshops at this place. The relationship between mines and ores has been documented for the Medieval period. There is no archaeological proof concerning the Gallic activity. Nevertheless, 2500-2100 years ago, the borders of the Gallic Tribe territory, named the Gabales, were the same as the present-day borders of the Lozère department. Julius Caesar reported the existence of this tribe in 58 B.C. in "De Bello Gallico", and in Strabon (Book IV, 2.2) the "Gabales silver" and a "treasure of Gabales" are mentioned, but to this day, they have not been found. PMID:16082940

  3. Melt extraction and metasomatism recorded in basal peridotites above the metamorphic sole of the northern Fizh massif, Oman ophiolite

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Masako; Python, Marie; Tamura, Akihiro; Arai, Shoji; Takazawa, Eiichi; Shibata, Tomoyuki; Ueda, Akira; Sato, Tsutomu

    2015-05-01

    The Oman ophiolite is one of the best preserved sections of oceanic crust and upper mantle worldwide, and consists of multiple massifs that lie along more than 400 km of the Arabian coast. In the northernmost massifs, the oceanic crust preserves a record of polygenetic magmatism from mid-ocean ridge to subduction-related stages. The lherzolites and clinopyroxene (Cpx)-rich harzburgites of the Fizh block are located a few tens to a hundred meters above the metamorphic sole of the ophiolite and the geochemistry of these Cpx-rich peridotites provides evidence of a genetic link between oceanic crust and mantle. These Cpx-rich peridotites contain olivine with a restricted range of forsterite contents (90-91), but variable Cr-spinel Cr# (Cr/(Cr + Al) atomic ratio) values (0.12-0.33), suggesting that these Cpx-rich peridotites have undergone variable degrees of melt extraction. Cpxs within the Cpx-rich peridotites have chondrite-normalised trace element variation patterns that slope either gently or steeply between the heavy rare earth elements (REEs) and the middle REEs ((Sm/Yb)N = 0.08-0.55, where N chondrite-normalised) and are enriched in highly incompatible elements such as Rb, Ba and Nb. This Cpx chemistry can be explained by a polygenetic evolution whereby an initial 4-12% of melt was extracted from the depleted mantle source before this mantle was metasomatised by interaction with fluids derived from dehydration of the metamorphic sole during subduction initiation and obduction. A comparison between 143Nd/144Nd versus 147Sm/144Nd for Cpx in the Fizh basal Cpx-rich peridotites and a mineral-whole rock Sm-Nd isochron for a gabbro from the same massif suggests a genetic link between crustal and mantle rocks in this area. In addition, Cpxs within the basal Cpx-rich peridotites have highly variable Sr isotopic compositions that are indicative of a significant contribution of seawater from the metamorphic sole, originally derived from subducted oceanic crustal material.

  4. Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)

    NASA Astrophysics Data System (ADS)

    Cosmidis, Julie; Benzerara, Karim; Morin, Guillaume; Busigny, Vincent; Lebeau, Oanez; Jézéquel, Didier; Noël, Vincent; Dublet, Gabrielle; Othmane, Guillaume

    2014-02-01

    The availabilities of iron and phosphorus have considerably impacted biological productivity in past and present natural aquatic environments, and therefore have been key regulators of climate changes over geological time scales. Microbial organisms are known to play important roles in reactions that drive Fe and P cycling at redox interfaces in Earth's surface environments. Here we study the depth variations of Fe and P speciation in Lake Pavin (Massif Central, France), a deep (bottom depth ˜92 m) and permanently stratified lake with anoxic and ferruginous conditions in the water column below ˜60 m depth. We particularly focus on the potential roles of microbes on Fe and P transformations and traces left by these processes in the sedimenting particular matter. Bulk chemical analyses, powder X-ray diffraction and X-ray absorption spectroscopy (XAS) at the Fe K-edge were performed to characterize the mineralogy and Fe oxidation state of solid particles at different depths in the water column and in sediments deposited at the bottom of the lake. Fe is mainly hosted by Fe(III)-(oxyhydr)oxides and phyllosilicates in the shallower oxygenated water column of the lake (25 m). The amount of Fe in suspended matter increases with depth, and an additional amorphous Fe(II)-Fe(III)-phosphate phase is detected close to the chemocline (at 56 m depth), while vivianite (an Fe(II)-phosphate with a formula of Fe(II)3(PO4)2·8(H2O)) becomes dominant in the deeper anoxic water (67 m and 86 m depths). Fe-(oxyhydr)oxides are preserved down to these depths in the water column suggesting that Fe-reduction has little impact on the particulate Fe budget over the monimolimnion. These Fe-(oxyhydr)oxides undergo reductive dissolution at the surface of the sediments, where vivianite is the main Fe-bearing phase. These results are confirmed by imaging at the micrometer and nano-scales using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and synchrotron-based scanning

  5. Carbonates in mantle xenoliths from French Massif Central: inference for carbonatite-related metasomatism.

    NASA Astrophysics Data System (ADS)

    Wagner, Christiane; Deloule, Etienne

    2016-04-01

    Mantle xenoliths from the sub-continental lithospheric mantle (SCLM) frequently display evidence of metasomatism by melts or fluids of variable composition, e.g. alkali-basaltic, alkali-carbonate or carbonate melts. Carbonate-bearing mantle xenoliths are particularly interesting as highly mobile carbonate melts are likely prominent metasomatic agents of the mantle. This study presents detailed petrographic descriptions and major and trace element compositions of minerals in protogranular spinel lherzolites from the Mont Coupet occurrence (Devès province, French Massif Central), with focus on the carbonate phases to discuss their possible link to carbonatite melt. Two representative samples are described here. MC9 shows no evidence for infiltration of the host basanitic magma. Carbonates occur (1) as large (100 μm - 200 μm) anhedral crystals in interstitial pockets at triple point of primary olivine grains, (2) in a few cross-cutting veins (up to 200 μm width), (3) along grain boundaries and (4) in composite carbonate-silicate pockets from well-developed reaction zones, in which carbonates fill globular vesicles. The reaction zone contains secondary subhedral to euhedral phases: Al- and Ti-rich clinopyroxene, Ca-rich olivine, Cr-rich spinel and quenched plagioclase and relict sieved-textured primary spinel. MC2 shows carbonate-bearing thin (< 50 μm width) interconnected veinlets and only a few poorly-developed reaction zones around primary spinel. Large carbonate crystals (1), as in sample MC9, occur associated with (2) fibrous carbonate with a well-formed meniscus at the boundary between the two carbonate types. In some reaction zones the carbonate patches (3) show well-developed concentric carbonate structures, similar to those observed in the globular vesicles from the host basanite. In sample MC9, the carbonate is an alkali-free Mg-poor calcite (XCa = 0.95 - 0.98; with 0.5 - 1.8 wt. % MgO) whatever the occurrence. In sample MC2, carbonates are Mg

  6. Soil thermal regime and geomorphogenesis at Fuentes Carrionas massif (Cantabrian Range, NW Iberian Peninsula).

    NASA Astrophysics Data System (ADS)

    Pellitero, Ramon; Serrano Cañadas, Enrique

    2015-04-01

    Fuentes Carrionas is a massif within the Cantabrian Range, in NW Iberian Peninsula. Its altitude ranges between 1400 and 2500 meters and its climate is an oceanic/Mediterranean transition one, with cold temperatures and heavy snowfall in the winter/early spring season, and a warm and dry summer season. Due to its outstanding altitude and lithological variety in the Cantabrian Range context, Fuentes Carrionas holds some periglacial activity (gelifluction, frost shattering) which is absent elsewhere in NW Iberian Peninsula. This work is relates the soil thermal regime across the mountain gradient to landforms formation. 14 thermometers (11 i-button, protected in a plastic can, and three UTL data loggers) were buried at a shallow depth (10 cm.) between autumn 2009 and summer 2012. 12 thermometers were placed between 1900 and 2400 m.a.s.l. at 250 meters altitude interval at the four main aspects. Two additional thermometers were place in the Curavacas N face for permafrost identification. Thermometers were calibrated to yield a measurement every 6 hours starting from 8 AM during one year's time. Data was collected annually in the summer season. Some additional soil temperature data was obtained from an external project in the same area for the 2007-2009 interval. In this case thermometers were "Hobbo" model, and they were also buried to a shallow depth. Results show a permafrost free mountain range. Annual average soil temperatures range between 1 and 8 degrees Celsius. Snow pack appears as a decisive factor in winter temperatures, as the zero curtain effect can be tracked in many cases. Snow cover patterns show a distinctive behavior between S and N aspects, with a 3 months snow cover on the southern faces and between 6 and 9 at the northern analogues. This cover has a relevant impact on geomorphological processes. There is a clear relation between spring snow melt and solifluction or channelized erosion. Also, snow cover prevents the occurrence of freeze/thaw cycles

  7. The Kokchetav Massif, Kazakhstan: "Type locality" of diamond-bearing UHP metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Schertl, H.; Sobolev, N. V.

    2012-12-01

    Since the first discovery of in situ metamorphic diamond in the Kokchetav Massif in 1990, numerous scientists from different disciplines paid special attention to petrological and geochemical features, geodynamics and the mechanism of deep subduction and exhumation of UHP rocks. This discovery was a trigger for an intense search of further possible diamondiferous UHP terranes worldwide, successfully documented by numerous new findings. Thus far, more than 350 papers have been published on various aspects of the Kokchetav UHP rocks. A compilation of the most important and far-reaching implications are outlined here. PT-estimates yield peak metamorphic conditions of at least 43 kbar at temperatures of about 950-1000°C. Zircon separates show inherited Proterozoic cores and mantle with the peak of UHP metamorphism at about 537-530 Ma. Several Ar-Ar-ages on micas scatter around 529-528 and 521-517 Ma and reflect different stages of the exhumation history. Migmatization occurred during exhumation at about 526-520 Ma. Microdiamonds which reach a grain size of 300 micrometers, contain highly potassic fluid inclusions as well as solid inclusions like carbonates, different silicates and metal sulfides, which favours the idea of a diamond formation from a C-O-H bearing fluid. Nitrogen isotope data and negative δ13C values of Kokchetav diamonds indicate a metasedimentary origin. δ18O studies on garnet and clinopyroxene of a layered calcsilicate are ruling out a primitive mantle protolith; similar studies on eclogite indicate their basaltic protolith to have experienced water-rock interaction prior to UHP metamorphism. A number of unique mineralogical findings have been made. K-feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the clinopyroxene structure under upper mantle pressures. Other significant observations are coesite exsolutions in titanite, quartz-rods in clinopyroxene, the discovery of K-tourmaline as well as new minerals

  8. Syntectonic Variscan magmatism in the Aguiar da Beira region (Iberian Massif, Portugal)

    NASA Astrophysics Data System (ADS)

    Mafalda Costa, Maria; Margarida Neiva, Ana; do Rosario Azevedo, Maria; Corfu, Fernando

    2014-05-01

    The Aguiar da Beira region (Portugal) is located in the core of the Iberian Massif, more precisely in the Central-Iberian Zone, which is dominantly composed by abundant volumes of plutonic rocks, emplaced into Late Proterozoic - Early Cambrian and Palaeozoic metasediments, mainly during or slightly after the third deformation phase of the Variscan Orogeny (D3). A considerable amount of these granites are syntectonic, intruded during the peak of this deformation event (D3). In particular, at the Aguiar da Beira region, two suites of syntectonic granitoids represent distinct magmatic series: a medium- to coarse-grained porphyritic biotite granodiorite-granite (322 Ma), which belongs to the early granodiorite series, and a medium-grained muscovite-biotite granite (317 Ma) that is part of the two-mica peraluminous leucogranites suite. The petrographic, geochemical (whole-rock and mineral compositions) and isotopic (Sr-Nd, δ18O-wr and δ18O-zr) study of the two intrusions reveals their remarkably different character. It is concluded that they correspond to two independent magma pulses, derived from distinct sources and/or petrogenetic processes. The biotite granodiorite-granite is a weakly peraluminous intrusion, characterized by intermediate to felsic SiO2 contents (66 - 68 %), high Ba, Sr and REE, and biotite with high Al and Mg contents, typical of the calc-alkaline associations. The Sr-Nd initial ratios are homogeneous (87Sr-86Sr322: 0.7070 - 0.7074; ɛNd322: -3.9 to -4.6) and overlap the isotopic signatures of lower crustal felsic metaigneous granulites (Villaseca et al. 1999). This similarity, which is further supported by δ18O-wr and δ18O-zr data, may indicate an origin by anatexis of lower felsic metaigneous rocks. Alternatively, the same data, allied to the presence of microgranular enclaves seen in this intrusion, can also be explained by the mixing of lower crustal derived magmas and mantle melts. By contrast, the muscovite-biotite granite has an entirely

  9. Significance of Diamond-free Heterogeneous UHP Dolomitic Marble From the Kokchetav Massif

    NASA Astrophysics Data System (ADS)

    Aoki, K.; Ogasawara, Y.

    2003-12-01

    Local heterogeneity of fluid conditions during UHP metamorphism has been well demonstrated in a cm-scaled continuous sample of UHP marble (sample no. Y665) from the Kumdy-kol in the Kokchetav Massif. This banded carbonate rock sample consists of three zones; zone-A: dolomitic marble with abundant Ti-clinohumite, zone-B: dolomite marble, zone-C: dolomitic marble without forsterite and Ti-clinohumite. All three zones lack diamond. Zone-A consists of Ti-clinohumite, forsterite, diopside, Mg-calcite, dolomite, symplectite, and is characterized by the presence of Ti-clinohumite and by Ti-clinohumite-aragonite tie-line at the peak metamorphic condition. Diopside lacks lamella. Garnet is completely retrograded to symplectite (Di + Spl + Mg-Cal). Large-grained Ti-clinohumite shows clear compositional zoning of TiO2 between core (1.5-1.8 wt.%) and rim (2.2-3.4 wt.%). Some Ti-clinohumite grains contain very thin needles with preferred orientations. Zone-B consists mainly of dolomite, diopside, phlogopite, symplectite (Di + Spl + Mg-Cal) with minor amount of Mg-calcite, and is characterized by the stability of dolomite-diopside tie-line and by lack of Ti-clinohumite and forsterite. No lamella was observed in diopside. Garnet is rarely preserved. Zone-C consists mainly of Mg-calcite, dolomite, diopside, garnet and phlogopite and is characterized by phlogopite lamellae in diopside that indicate high pressure conditions. Phlogopite lamellae in diopside were confirmed by the laser Raman spectroscopy (Raman bands: 681.3 cm-1 and 357.9 cm-1 ) and by microprobe analysis. Lack of Ti-clinohumite and forsterite also characterizes this zone. Garnet has been well preserved from the retrograde reaction. High MgCO3 calcite (originally aragonite + dolomite) with large-grained exsolved dolomite lamellae occurs. All three zones have different bulk compositions each other; however, the tie-line relations cannot be explained by their bulk compositions. In zones C and B, diopside-dolomite tie

  10. Stability relations of Ti-bearing assemblages in UHP marbles from the Kokchetav Massif

    NASA Astrophysics Data System (ADS)

    Kikuchi, M.; Ogasawara, Y.

    2003-12-01

    Stability relations of Ti-bearing phases (rutile, titanite, Ti-clinohumite) in UHP marbles from the Kokchetav Massif, northern Kazakhstan were well analyzed by the phase relations in the model system CaO-MgO-SiO2-TiO2-CO2-H2O. Three types of UHP marbles have been described in the Kumdy-kol area: diamond-bearing dolomite marble (type-A), diamond-free Ti-clinohumite-bearing dolomitic marble (type-B), and diamond-free calcite marble (type-C) (Ogasawara et al., 2000; 2002), and they contain a distinct Ti-bearing phase, rutile, Ti-clinohumite, and titanite, respectively. The characteristics of these three marbles are as in the followings. Type-A: Dominant carbonate is dolomite. Abundant microdiamonds are included in garnet and diopside. Diopside-dolomite tie-line was stable. Diopside contains K-bearing silicate lamellar. The peak assemblage was dolomite + diopside + aragonite + garnet + rutile + diamond. Type-B: High MgCO3-calcite (originally aragonite + dolomite) is distinct. No diamond occurs. Diopside lacks lamellar texture. The peak assemblage was aragonite + dolomite + garnet + Ti-clinohumite or forsterite. Type-C: Only carbonate phase is calcite (originally aragonite). No diamond occurs. Titanite contains coesite exsolution lamellae and indicated supersilicic compositions stable at UHP conditions (P > 6GPa). Diopside contains phengite and K-feldspar lamellae. The peak assemblage was aragonite + diopside + K-feldspar + garnet + titanite. The solid-solid reaction, CaTiSiO5 (titanite) + CaMg(CO3)2 (dolomite) = CaCO3 (aragonite) + CaMgSi2O6 (diopside) + TiO2 (rutile), controlled the stability of Ti-bearing phases in calcite marble and dolomite marble. At UHP conditions, aragonite + diopside + rutile assemblage is stable compared with titanite + dolomite, and divides the compositional space into dolomite-free and dolomite-bearing tetrahedrons in the model system CaO-MgO-SiO2-TiO2. The presence of titanite in calcite marble indicates that the P-T condition was located

  11. The Mirdita Eastern Ophiolite, Albania: petrological evidence for MORB Mantle in the Tropoje peridotite massif?

    NASA Astrophysics Data System (ADS)

    Ntaflos, Theodoros; Onuzi, Kujtim; Hauzenberger, Christoph; Rice, A. Hugh N.; Proßegger, Peter; Mekshiqi, Nazir; Kaza, Gjon

    2016-04-01

    The Mirdita ophiolites in northern Albania are divided into the Western Mirdita Ophiolite (WMO), with MORB geochemical affinities, and the Eastern Mirdita Ophiolite (EMO), for which suprasubduction geochemical affinities have been reported. Ultramafic massifs in the WMO are often plagioclase bearing lherzolites/harzburgites whereas those in the EMO are strongly depleted spinel harzburgites. The Tropoje ultramafic-mafic complex, which forms the northernmost part of the EMO, consists of spinel harzburgites, wherlites, orthopyroxenites and gabbros. The spinel harzburgites, which experienced variable degrees of serpentinization, are coarse- to medium-grained. One of the most striking features of the Tropoje ultramafic rocks is an outcrop of exceptionally fresh coarse- to medium-grained spinel harzburgites. While occasionally the peridotites exhibit a weak foliation, the prevalent texture is protogranular. Olivine is mainly coarse-grained (up to 6 mm size), typically showing kink-bands that frequently contain submicron-sized spinel exsolution lamellae. Both orthopyroxene and clinopyroxene, with grain size up to 3 mm and 1.5 mm, respectively, carry very thin exsolution lamellae of the other pyroxene. Spinel, up to 1 mm in size, is interstitial between boundaries of the associated silicates. The mineral compositions of the spinel harzburgites indicate that they are strongly depleted in basaltic components. The rock-forming minerals (olivine, orthopyroxene and clinopyroxene) are all highly magnesian and chemically homogenous. The magnesium numbers (Mg#=100xMg/[Mg+Fe]) for olivine and orthopyroxene are fairly homogeneous and vary within the narrow range of 90.9-91.6 and 91.5-91.7, respectively. The clinopyroxene is exceptionally highly magnesian, with Mg# ranging between 93.6 and 95.4. In both orthopyroxene and clinopyroxene, the Al2O3 contents range from 0.95 to 1.75 and from 0.62 to 2.27 wt%, respectively. Spinel shows a considerable variation in Al2O3 and Cr2O3. The

  12. The internal deformation of the Peridotite Nappe of New Caledonia: A structural study of serpentine-bearing faults and shear zones in the Koniambo Massif

    NASA Astrophysics Data System (ADS)

    Quesnel, Benoît; Gautier, Pierre; Cathelineau, Michel; Boulvais, Philippe; Couteau, Clément; Drouillet, Maxime

    2016-04-01

    We present a structural analysis of serpentine-bearing faults and shear zones in the Koniambo Massif, one of the klippes of the Peridotite Nappe of New Caledonia. Three structural levels are recognized. The upper level is characterized by a dense network of fractures. Antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics. As a result, the upper level keeps the record of at least two deformation events, the first associated with the growth of antigorite (WNW-ESE extension), the second with the growth of polygonal serpentine (NW-SE compression). The lower level coincides with the 'serpentine sole' of the nappe, which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites. The sole records pervasive tangential shear with top-to-SW kinematics and represents a décollement at the base of the nappe. The intermediate level is characterized by the presence of several meters-thick conjugate shear zones accommodating NE-SW shortening. Like the sole, these shear zones involve polygonal serpentine and magnesite as the main syn-kinematic mineral phases. The shear zones likely root into the basal décollement, either along its roof or, occasionally, around its base. Compared to top-to-SW shearing along the sole, the two deformation events recorded in the upper level are older. The three structural levels correlate well with previously recognized spatial variations in the degree of serpentinization. It is therefore tempting to consider that the intensity of serpentinization played a major role in the way deformation has been distributed across the Peridotite Nappe. However, even the least altered peridotites, in the upper level, contain so much serpentine that, according to theoretical and experimental work, they should be nearly as weak as pure serpentinite. Hence, no strong vertical gradient in strength due to variations in the degree of serpentinization is expected within the exposed part of the nappe

  13. First findings of monocrystalline aragonite inclusions in garnet from diamond-grade UHPM rocks (Kokchetav Massif, Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Vandenabeele, Peter; Perraki, Maria; Moens, Luc

    2011-10-01

    The presence of aragonite inclusions in garnet from diamond-grade metamorphic rocks from the Kokchetav Massif, Northern Kazakhstan was identified for the first time by means of Raman analyses and mapping. Aragonite appears within the inclusions up to 50 μm in size as a single crystal. These inclusions have rounded shape. The grain boundary between the host-garnet is smooth. No cracks occur around the aragonite inclusions. No significant shift in the main aragonite Raman band was measured. These observations indicate that residual pressure within the inclusion is minor. These findings imply either non-UHPM origin of the host garnet or significant plastic deformation of host minerals during retrograde stage. These features should be taken into account for recovery peak metamorphic conditions and modeling of exhumation processes of UHPM complexes. PMID:21247793

  14. Multiple Feldspar replacement in Hercynian granites of the Montseny-Guilleries Massif (Catalan Coastal Ranges, NE Spain)

    NASA Astrophysics Data System (ADS)

    Fàbrega, Carles; Parcerisa, David; Gómez-Gras, David

    2013-04-01

    The core of the Montseny-Guilleries Massif (Catalan Coastal Ranges) is mainly composed by late-Hercynian granitoids (leucogranites and granodiorites) intruded within Cambrian to Carnoniferous metasediments. The granites are unconformably covered by Triassic (Buntsandstein) and Paleocene red beds at the western boundary, preserving a continuous outcrop of the Permo-Triassic unconformity for about 20 km. In the southwestern Montseny-Guilleries Massif the granites are covered by the Buntsandstein red sandstones that overlain a peneplain paleorelief called the Permo-Triassic palaeosurface. Beneath the palaeosurface the granite displays a characteristic pink colouration. This pink alteration is characterized by precipitation of minute heamatite crystals and albitization of pristine plagioclases (mostly labradorite). The secondary albite is pseudomorphic (mono- or polycrystalline), optically continuous, non-luminiscent, contains widespread microporosity and displays compositions about Ab98. These features are typical of low temperature replacive feldspars (Kastner and Siever, 1979). Albitization of plagioclases is almost total close to the Permo-Triassic palaeosurface and progressively decreases towards depth, displaying a 150-200 m thick alteration profile. The formation of this profile was controlled by fluid circulation along macro- and microfractures and crystal boundaries. Inside the plagioclase crystals fluid pathways were microfractures, twinning and cleavage planes and crystalline defects. The secondary albite holds widespread unconnected micron-size porosity often filled by Fe-oxides. The reaction front is sharp and displays an abrupt composicional change (Ab65 to Ab98) at micron scale. Porosity only appears to be connected at this reaction front surface. The geometrical arrangement of this alterations suggest that albitization was a shallow process related with Na-rich descending fluids linked to the Permo-Triassic palaeosurface, in a similar way to

  15. First findings of monocrystalline aragonite inclusions in garnet from diamond-grade UHPM rocks (Kokchetav Massif, Northern Kazakhstan).

    PubMed

    Korsakov, Andrey V; Vandenabeele, Peter; Perraki, Maria; Moens, Luc

    2011-10-01

    The presence of aragonite inclusions in garnet from diamond-grade metamorphic rocks from the Kokchetav Massif, Northern Kazakhstan was identified for the first time by means of Raman analyses and mapping. Aragonite appears within the inclusions up to 50 μm in size as a single crystal. These inclusions have rounded shape. The grain boundary between the host-garnet is smooth. No cracks occur around the aragonite inclusions. No significant shift in the main aragonite Raman band was measured. These observations indicate that residual pressure within the inclusion is minor. These findings imply either non-UHPM origin of the host garnet or significant plastic deformation of host minerals during retrograde stage. These features should be taken into account for recovery peak metamorphic conditions and modeling of exhumation processes of UHPM complexes.

  16. 190Pt-4He age of PGE ores in the Alkaline-Ultramafic Kondyor Massif (Khabarovsk District, Russia)

    NASA Astrophysics Data System (ADS)

    Mochalov, A. G.; Yakubovich, O. V.; Bortnikov, N. S.

    2016-08-01

    A new 190Pt-4He method for dating isoferroplatinum has been developed at the Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences. Here we publish the first results of dating of isoferroplatinum from the main mineralogical and geochemical types of PGE mineralization in dunite. The obtained 190Pt-4He age of isoferroplatinum is 129 ± 6 Ma. The gained 190Pt-4He age of isoferroplatinum specimens of different genesis (magmatic, fluid-metamorphogenic, and metasomatic) from the Kondyor Massif indicates that the PGM mineralization took place synchronously and successively with evolution of primarily picrite, followed by subalkaline and alkaline melts of the Mesozoic tectonic-magmatic activation of the Aldan Shield.

  17. High grade metamorphism in the Bundelkhand massif and its implications on Mesoarchean crustal evolution in central India

    NASA Astrophysics Data System (ADS)

    Singh, S. P.; Dwivedi, S. B.

    2015-02-01

    The Bundelkhand Gneissic Complex (BnGC) in the central part of the Bundelkhand massif preserves a supracrustal unit which includes pelitic (garnet-cordierite-sillimanite gneiss, garnet-sillimanite gneiss, biotite gneiss and garnet-biotite gneiss) and mafic (hornblende-biotite gneiss and garnetiferous amphibolite) rocks. Granulite facies metamorphism of the complex initiated with breaking down of biotite to produce garnet and cordierite in the pelitic gneisses. Geothermobarometric calculations indicate metamorphic conditions of 720°C/6.2 kbar, followed by a retrograde (687°C/4.9 kbar) to very late retrograde stages of metamorphism (579°C/4.4 kbar) which is supported by the formation of late cordierite around garnet. The P-T conditions and textural relations of the garnet-cordierite-bearing gneiss suggest a retrograde cooling path of metamorphism.

  18. Platinum potential of mafic-ultramafic massifs in the western part of the Dambuka ore district (Upper Amur Region, Russia)

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Stepanov, V. A.; Moiseenko, V. G.

    2016-02-01

    New data on the Pt potential of mafic-ultramafic massifs of the Khani-Maya, Uldegit, and Dzhalta complexes in the western part of the Dambuka ore district are discussed. The Khani-Maya Complex is represented by metamorphosed gabbro, gabbronorites, gabbro anorthosites, subordinate pyroxenites, hornblendites, and peridotites. The Uldegit Complex is composed of pyroxenites, hornblendites, gabbro, gabbronorites, norites, troctolites, peridotites, dunites, actinolite-tremolites, serpentinites, anthophyllites, and tremolite-plagioclase rocks. The Dzhalta Complex is formed of peridotites, gabbro, eclogitized gabbro, hornblendites, cortlandites, and pyroxenites. All these complexes differ from each other by the concentrations of Ni, Cu, Co, Au, and platinoids depending on the composition of the constituting rocks and the presence of sulfide minerals.

  19. Strain partitioning in the Belledonne and Pelvoux massifs. Some clues to understand the Variscan tectono-thermal evolution.

    NASA Astrophysics Data System (ADS)

    Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jeremie; Blein, Olivier

    2016-04-01

    This contribution presents new structural, petrological, geochemical and geochronological data obtained in the Variscan basement of the Alpine Belledonne and Pelvoux External Crystalline massifs. The Belledonne-Pelvoux area is a stack of four litho-tectonic units. The uppermost unit is the early Ordovician Chamrousse ophiolite. It overthrusts a volcanic-sedimentary unit (VSU) made of an alternation of volcanoclastic rocks, plagiogranites and metapelites. The VSU crops out in the eastern Belledonne and western Pelvoux massifs. It is unconformably overlain by a Visean sandstone-conglomerate series with felsic lava (keratophyres). The lowermost litho-tectonic unit is made of felsic and mafic migmatites and granitoids that form the major part of the Pelvoux massif. The western boundary of this tectonic pile is the "synclinal median" strike-slip fault, on the western side of which crops out the Belledonne micaschist unit made of Cambro-ordovician turbiditic series. The structural analysis revealed four main tectono-thermal events: Dx, D1, D2, and D3. Dx is only recorded in relictual metamorphic assemblage in Ky-Grt-Ab bearing micaschist from the VSU holding an obduction metamorphic gradient (3kbar, 370°C up to 7kbar, 430°C). The age of the Dx event remains unknown. The D1 event, characterized by westward low-angle dipping foliation (S1) and a NE-SW striking stretching lineation (L1), is responsible for the crustal thickening resulting of the Eastward emplacement of the Chamrousse ophiolite upon the VSU. D1 is coeval with a barrovian metamorphism with P-T conditions of 6kbar, 600°C recorded in metapelites, and partial melting developed at the base of the VSU. Monazite LA-ICP-MS U-Pb dating revealed that D1 crustal thickening occurred at 337±7 Ma. D2 is a sinistral transpressional deformation responsible for the folding of S1 and L1, and the development of a NE-SW trending pervasive sub-vertical foliation S2. In the lower structural domain, i.e. the partially molten

  20. Surprisingly young Rb/Sr ages from the Simav extensional detachment fault zone, northern Menderes Massif, Turkey

    NASA Astrophysics Data System (ADS)

    Bozkurt, Erdin; Satır, Muharrem; Buğdaycıoğlu, Çağrı

    2011-12-01

    The present paper demonstrates that exposed semi-brittle-brittle detachment fault zones, in addition to footwall mylonites and syn-extensional granitoids, can be used to date the timing of faulting and constrain the history and evolution of metamorphic core complexes. We employed Rb-Sr geochronology on micas, sampled directly from a part of the Simav detachment fault (SDF) zone in the northern Menderes Massif (western Turkey). The exposed part of the fault zone is marked by ˜3-m thick zone of low-grade mylonites/foliated cataclasites, in which mylonitic fabrics in orthogneisses are overprinted by fabrics of semi-brittle deformation. The low-grade mylonites/foliated cataclasites are characterized by coexistence of brown and green biotites. Rb-Sr ages on muscovite and brown and green biotite from the low-grade mylonites/foliated cataclasites are ca. 30 Ma, 17-13 Ma and 12-10 Ma, respectively; green biotite ages are interpreted as dating fluid-assisted deformation-induced dynamic recrystallization and suggest that a part of the SDF was active during a 12-10 Ma interval. The ca. 30 Ma muscovite ages date dynamic crystallization and probably beginning of extensional exhumation of the northern Menderes Massif. The coexistence of brown and green biotites in the same sample indicates retrogressive processes associated within a detachment faulting during which green biotites have recrystallized from primary brown biotites with an age of 19 ± 2 Ma in this area. This further means that the isotopic system became opened during faulting and that the green biotite ages therefore record the activity of the SDF. We have also dated an orthogneiss sample exposed well away from the detachment fault zone (devoid of any retrogressive processes); muscovites and biotites from this sample yield Rb-Sr ages of 45.7 ± 0.6 and 18.17 ± 0.18 Ma, respectively. The biotite age is in accord with regional biotite ages (19 ± 2 Ma) and record cooling of the footwall rocks of the detachment fault

  1. The origin of summit basins on the Aleutian Ridge: implications for block rotation of an arc massif ( Pacific).

    USGS Publications Warehouse

    Geist, E.L.; Childs, J. R.; Scholl, D. W.

    1988-01-01

    It is proposed that many summit basins along the Aleutian Arc form from the clockwise rotation of blocks of the arc massic. Summit basins are arc-parallel grabens or half-grabens formed within the arc massif and are commonly located near or along the axis of late Cenozoic volcanism. Geomorphically, the Aleutian Arc appears to consist of contiguous rhombic blocks of varying size, 10's to 100's of km in length. Presents a model for block rotation that involves translation of blocks parallel to an arc. It is suggested that block rotation, which appears to have accelerated in late Cenozoic time, is linked to: 1) a shift in the Euler pole for the Pacific plate; 2) the consequential start-up of late Cenozoic volcanism; 3) improved interplate coupling instigated by sediment flooding of the Aleutian Trench; and 4) westward subduction of NE striking segments of the inactive Kula-Pacific Ridge.-from Authors

  2. The Cenozoic history of the Armorican Massif: New insights from the deep CDB1 borehole (Rennes Basin, France)

    NASA Astrophysics Data System (ADS)

    Bauer, Hugues; Bessin, Paul; Saint-Marc, Pierre; Châteauneuf, Jean-Jacques; Bourdillon, Chantal; Wyns, Robert; Guillocheau, François

    2016-05-01

    Borehole CDB1 (675.05 m) crosses the deepest Cenozoic sedimentary basin of the Armorican Massif, the Rennes Basin, to reach the underlying basement at a depth of 404.92 m, made up of the Late Neoproterozoic to Early Cambrian Brioverian Group, weathered down to 520 m depth. The basin's Cenozoic deposits are divided into seven formations, ranging from Early-Middle Bartonian to Late Pliocene in age. Coastal sediments at the very base, along with a thick Priabonian lacustrine episode, imply a major revision of the regional palaeogeography, whilst a very steady and low-energy lacustrine-palustrine environment throughout the Priabonian and Early Rupelian argue for an aggradational system associated with uniform subsidence. Palynological assemblages attest to environmental and climatic changes through the Eocene and Early Oligocene, in accordance with regional and global trends (Eocene-Oligocene Transition).

  3. A preliminary spatial-temporal study of some soil characteristics in the calcareous massif of Sicó, Portugal.

    PubMed

    Torres, Maria Odete; Neves, Maria Manuela

    2016-01-01

    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. PMID:27087036

  4. Statistical adaptation of ALADIN RCM outputs over the French alpine massifs - application to future climate and snow cover

    NASA Astrophysics Data System (ADS)

    Rousselot, M.; Durand, Y.; Giraud, G.; Mérindol, L.; Dombrowski-Etchevers, I.; Déqué, M.

    2012-01-01

    In this study, snowpack scenarios are modelled across the French Alps using dynamically downscaled variables from the ALADIN Regional Climate Model (RCM) for the control period (1961-1990) and three emission scenarios (SRES B1, A1B and A2) by the mid- and late of the 21st century (2021-2050 and 2071-2100). These variables are statistically adapted to the different elevations, aspects and slopes of the alpine massifs. For this purpose, we use a simple analogue criterion with ERA40 series as well as an existing detailed climatology of the French Alps (Durand et al., 2009a) that provides complete meteorological fields from the SAFRAN analysis model. The resulting scenarios of precipitation, temperature, wind, cloudiness, longwave and shortwave radiation, and humidity are used to run the physical snow model CROCUS and simulate snowpack evolution over the massifs studied. The seasonal and regional characteristics of the simulated climate and snow cover changes are explored, as is the influence of the scenarios on these changes. Preliminary results suggest that the Snow Water Equivalent (SWE) of the snowpack will decrease dramatically in the next century, especially in the Southern and Extreme Southern part of the Alps. This decrease seems to result primarily from a general warming throughout the year, and possibly a deficit of precipitation in the autumn. The magnitude of the snow cover decline follows a marked altitudinal gradient, with the highest altitudes being less exposed to climate change. Scenario A2, with its high concentrations of greenhouse gases, results in a SWE reduction roughly twice as large as in the low-emission scenario B1 by the end of the century. This study needs to be completed using simulations from other RCMs, since a multi-model approach is essential for uncertainty analysis.

  5. Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. PMID:25874424

  7. Structure and modeling of disorder in miserite from the Murun (Russia) and Dara-i-Pioz (Tajikistan) massifs

    NASA Astrophysics Data System (ADS)

    Kaneva, Ekaterina; Lacalamita, Maria; Mesto, Ernesto; Schingaro, Emanuela; Scordari, Fernando; Vladykin, Nikolay

    2014-01-01

    The structure, structural disorder and chemistry of miserite from the charoite-bearing rocks of the Murun massif (Russia) and from alkaline-syenite pegmatitic rocks of the Dara-i-Pioz massif (Tajikistan) were investigated employing a combination of electron microprobe, single crystal diffraction and micro-Fourier transform infrared spectroscopy analysis. Chemical analysis of the sample investigated by X-ray diffraction evidenced that Dara-i-Pioz miserite has a greater REE concentration than Murun miserite (~0.22 vs. 0.05 apfu, respectively) and also contains Y (0.14 apfu), which is absent in Murun miserite. The occurrence of a band at about 1,600 cm-1 testified to the presence of H2O in miserite at hand. Structural analyses yielded average cell parameters of a = 10.092, b = 16.016, c = 7.356 Å, α = 96.60°, β = 111.27° and γ = 76.34°. Anisotropic structural refinement in space group P converged at similar values for the analyzed samples ( R ~3.4, R w ~3.8 %). An interesting feature shown by both the miserite specimen is the presence, revealed by difference Fourier analysis, of a disordered part of the structure. This turned out to be due to the flipping of the tetrahedra belonging to the isolated [Si2O7]6- diorthogroups, one of the two radicals (the other is [Si12O30]12-) characterizing the miserite structure. The sixfold and seven-vertex Ca polyhedra linked to the inverted diorthogroups show variation in coordination number with respect to those of the ordered structure.

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

    PubMed

    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.

  9. Middle Proterozoic emplacement and deformation of metanorthosite and related rocks in the northeastern Marcy massif, Adirondack Mountains, New York

    SciTech Connect

    Fakundiny, R.H. ); Muller, P.D. . Dept. of Earth Sciences)

    1993-03-01

    Geologic mapping in the Elizabethtown and Mount Marcy 15 foot quadrangles in the northeastern Adirondack Mountains has shown that Middle Proterozoic anorthosite suite rocks of the Marcy massif were intruded in at least two temporally distinguishable episodes separated by a period of localized ductile shearing. Strain was concentrated in a 100 m to > 1 km thick zone consisting mainly of metamorphosed gabbroic anorthosite, ferrodiorite, and ferrosyenite gneiss with subordinate granite gneiss, calc-silicate gneiss, amphibolite, and marble. This zone of flat to steeply-dipping layered gneisses, designated the Elizabethtown ductile deformation zone (EDDZ) for exposures along Rt 9 south of Elizabethtown, appears to extend from Lake Champlain on the east to at least Lake Placid on the west. Its upper boundary is most clearly evident where it occurs in olivine metagabbro bodies of Jay and Iron Mountain. Massive metagabbro is sheared and recrystallized into amphibolite gneiss. The lower boundary of the zone is more difficult to map, but commonly lies within contaminated metamorphosed gabbroic anorthosite and ferrodiorite gneiss that characterize the margins of the massif in the area. Rocks of the EDDZ display pervasive mesoscopic S and LS fabrics, but exhibit totally recrystallized microtextures. Kinematic indicators such as winged porphyroclasts and S-C fabrics are sporadically developed and provide a regionally ambiguous sense of shear. The authors favor a regional extension origin for the fabrics. Mineral assemblages defining the EDDZ fabrics are consistent with granulite facies conditions during shear-zone development and suggest a lower crustal position. Mapping suggests that the younger anorthosite intrusions were mainly domical and generated a chaotic contact zone typified by block structure and dikes of ferrodiorite, ferromonzonite, and ferrosyenite.

  10. Magmatic/metasomatic amphibole in the mantle: evidence from the Balmuccia lherzolite massif, Ivrea zone, western Italian Alps

    SciTech Connect

    Shervais, J.W.

    1985-01-01

    Amphibole and mica are the most important alkali-rich phases stable under mantle P-T conditions, and constitute the primary source of the alkalis needed to form basaltic magmas. Yet, the origin and distribution of these phases in the upper mantle is poorly understood. The Balmuccia lherzolite massif is a small slice of subcontinental mantle in the western Alps that intruded granulite facies lower crust 250 m.y. ago, and was exposed during the Alpine orogeny. Amphibole (HB) ranging in composition from Ti-pargasite to kaersutite in a minor but widespread accessory phase in the lherzolite, in websterite and bronzite dikes of the Cr-Di suite, and in pyroxenite and gabbro dikes of the Al-Aug suite. Textural and compositional relations show that HB in the Cr-Di and Al-Aug suite dikes formed by crystallization of residual magma, or by reaction between this magma and earlier formed phases (primarily spinel). Hb also occurs in thin (1-2 cm) veins of hornblendite and pyroxene hornblendite, and in the HB-enriched wallrock adjacent to these veins. Similar Hb veins in the Lherz massif have been shown to form from an alkali and water-enriched residual magma derived by filter pressing of Al-Aug pyroxenites. This origin is not possible at Balmuccia because the Hb veins have higher Ti, Cr, K/Na and Mgnumbers than any accessory Hb in Al-Aug suite dikes. Fractionation trends in the veins are controlled by HB. This requires that the HB veins formed from a separate and distinct parent magma that metasomatically enriched the lherzolite on a local scale. However, remelting of the widespread pyroxenite dikes may constitute a more important source of alkalis than the rare HB-rich veins.

  11. The Brabant Massif as part of Armorica/Gondwana: UPb isotopic evidence from detrital zircons

    NASA Astrophysics Data System (ADS)

    Von Hoegen, J.; Kramm, U.; Walter, R.

    1990-12-01

    UPb isotopic ratios of zircons are used as time-dependent geochemical tracers for the formation of the zircons and for the sum of processes and their intensities effective for the disturbance of the UPb systems during the history of the zircons. By comparison detrital zircons can thus serve as indicators for the provenance of clastic sediments. The UPb systematics of 57 carefully selected fractions of detrital zircons from four Cambrian sandstones of the Ardennes and the Brabant Massif have been investigated. According to the UPb data features of color and shape of these zircons are suited for distinguishing to major groups: (1) colourless, mainly rounded, subordinately subhedral or euhedral zircons which are characterized by U contents below 300 ppm and by apparent 207Pb/ 235U ages between 0.53 Ga and 1.65 Ga. (2) reddish, generally subrounded to very well rounded zircons with U contents from 240 ppm to more than 800 ppm and apparent 207Pb/ 235U ages between 1.75 Ga and 2.4 Ga. From the group of colourless zircons only one fraction yields concordant UPb data and documents a Cadomian/PanAfrican crystal growth at 545 Ma. UPb data of the other colourless zircons arrange in a fan-shaped area in the Concordia diagram below Concordia and from 530 Ma to 600 Ma. Zircons with such UPb characteristics are well-known from Central and Southern Europe. They suggest a strong Cadomian/Pan-African influence. The reddish zircons are dominantly derived from Archean to Early Proterozoic crystalline rocks. Based on these results and on comparison with U-Pb data of other detrital zircons the Ardennes and the Brabant Massif must be regarded to be coherent to the Gondwana continental plate before the Caledonian orogeny.

  12. Physico-chemical conditions of crystallization of the Guli ulrabasic massif (North Part of the Siberian Platform): evidence from melt inclusions

    NASA Astrophysics Data System (ADS)

    Simonov, Vladimir; Vasiliev, Yuri; Kotlyarov, Alexey; Stupakov, Sergey

    2014-05-01

    Conditions of formation of the Guli ultrabasic massif (Maimecha Kotui Province in the North Part of the Siberian Platform) attract attention of numerous researchers. For the solution of genetic problems of various rocks from this ultramafic complex the data on melt inclusions in minerals has been earlier used (Sokolov et al., 1999; Rass, Plechov, 2000; Sokolov, 2003; Panina, 2006). At the same time, formation of dunites, occupying the main volume of the Guli massif, remain almost not considered by means of thermobarogeochemical methods and the role of magmatic processes in this case is not ascertained. As a result of melt inclusions study in the Cr-spinel the new data on physical and chemical parameters of dunite crystallization in the Guli ulrabasic massif was obtained. On the ratio (Na2O + K2O) - SiO2 the majority of analyses of glasses and calculated compositions of inclusions settle down in the field of subalkaline series. On the diagram MgO - SiO2 bulk chemical compositions of inclusions (with the magnesium content of 19-28 wt. %) correspond to picrites and picrite-basalts. They are in close association with the data on inclusions in the Cr-spinel from dunites of Konder (Siberian Platform) and Nizhnii Tagil (Ural Mountains) platinum-bearing ultrabasic massifs and also are situated near to the field of inclusions in the olivine phenocrysts from meimechites (Maimecha Kotui Province in the North Part of the Siberian Platform). Similarity of melt inclusions in the Cr-spinel from the dunite of the Guli massif and in the olivine from meimechites is established on the variety of petrochemical components - Al2O3, CaO, Na2O, K2O. The calculated compositions of inclusions from dunites coincide mostly with the data on inclusions from meimechites, while glasses of inclusions from Cr-spinel contain less titan and magnesium. As a whole for the melts of the Maimecha Kotui Province (that form both dunites of the Guli massif and meimechites) much higher contents of TiO2 (from

  13. Lithologic distribution and geologic history of the Apollo 17 site: The record in soils and small rock particles from the highland massifs

    NASA Astrophysics Data System (ADS)

    Jolliff, Bradley L.; Rockow, Kaylynn M.; Korotev, Randy L.; Haskin, Larry A.

    1996-01-01

    Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm-4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm-4 mm fragments provide a bridge between compositions of <1 mm fines, and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm-4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% incompatible-trace-element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm-4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31% agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass-weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their compositions

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

    NASA Astrophysics Data System (ADS)

    Kochemasov, G.

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

  15. Use of Digital Elevation Models to understand map landforms and history of the magmatism Khibiny Massif (Kola Peninsula, Russia)

    NASA Astrophysics Data System (ADS)

    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. Reply to Comment on "The Late Devonian Variscan suture of the Iberian Massif: A correlation of high-pressure belts in NW and SW Iberia"

    NASA Astrophysics Data System (ADS)

    Fernández, Rubén Díez; Arenas, Ricardo

    2016-02-01

    The existence of a large allochthonous nappe pile emplaced onto the hinterland of the Iberian Massif and covering most of the basement of NW and SW Iberia proposed by Díez Fernández and Arenas has been called into question on the basis of structural, geophysical, and regional data from SW Iberia. The discussion provided here is based on a revision of the fundamentals of the Variscan geology of NW Iberia and on a more detailed presentation of the geology of SW Iberia. Our counterarguments reveal the reasoning of Simancas et al. against the verisimilitude of the large allochthonous pile as inconclusive, incomplete, or erroneous in some cases. Therefore, we maintain that our structural correlation and its implications remain fully valid for the case of the Iberian Massif.

  17. The fluid phase evolution during the formation of carbonatite of the Guli massif: Evidence from the isotope (C, N, Ar) data

    NASA Astrophysics Data System (ADS)

    Buikin, A. I.; Verchovsky, A. B.; Kogarko, L. N.; Grinenko, V. A.; Kuznetsova, O. V.

    2016-02-01

    The first data on variations of the isotope composition and element ratios of carbon, nitrogen, and argon in carbonatites of different generations and ultrabasic rocks of the Guli massif obtained by the method of step crushing are reported. It is shown that early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotope compositions of carbon (CO2), argon, and hydrogen (H2O). The data obtained allow us to conclude that the mantle component predominated in the fluid at the early stages of formation of rocks of the Guli massif, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon, and most likely a high portion of carbon dioxide with isotopically heavy carbon.

  18. The Armorican Massif (Western France) - A buried relief two times exhumed in response to Iberia-Eurasia movements (Early Cretaceous, base of Cenozoic)

    NASA Astrophysics Data System (ADS)

    Bessin, Paul; Guillocheau, François; Robin, Cécile; Bauer, Hugues; Schroëtter, Jean-Michel

    2014-05-01

    The Armorican Massif is an outcropping Variscan basement located in Western France. The age of its exhumation is debated, as most of the outcropping European basements: Is this relief a remnant of the planation of the Variscan Belt or a buried and then exhumed relief at time of the North-Atlantic (Biscay Bay) opening during Early Cretaceous or/and during the Africa-Eurasia convergence? We performed a geomorphological study (based on DEM analysis and field controls) of the different landforms of the Armorican Massif. The dating of those relief forms is based on their geometrical relationships with the weatherings and dated preserved sediments. Our results allow to propose a model of evolution of the Armorican Massif and of its relief for the Mesozoic to Cenozoic period and underscore four main points: (1) The Armorican relief preserved old landforms - planation surfaces (mainly pediments and pediplains) - of Triassic (?) to Early Cretaceous age buried by Jurassic and Upper Cretaceous (chalk) carbonate platforms. (2) Those paleo-landforms were exhumed at two periods (i) Early Cretaceous in response to the opening of the Biscay Bay and (ii) Upermost Cretaceous-Paleocene at time of the Iberia-Eurasia increasing of convergence. (3) A major planation surface - called the Armorican Surface - result from the Early Cretaceous physical and chemical (laterite) erosion when the Armorican Massif was the North rift shoulder of the Biscay Bay. This planation surface is later deformed (buckling?) and eroded during Uppermost Cretaceous and Paleocene. (4) During Paleogene times, a last generation of pediments is shaped and then flooded by the Mid-Miocene eustatic sea-level rise. (5) The Armorican relief and landforms is later incised by rivers, (i) during Upper Miocene to Pliocene and (ii) at the Early to Middle Pleistocene transition with the incision of the present-day valleys in both response to uplift (Apulia-Eurasia convergence) and climate (precipitation) change.

  19. Mass flux into the Nanga Parbat-Haramosh massif: Orogen-parallel transport, lower crustal flow, or both?

    NASA Astrophysics Data System (ADS)

    Whipp, D. M.; Beaumont, C.; Braun, J.

    2011-12-01

    Relative to most of the Himalaya, the Nanga Parbat-Haramosh massif requires an additional mass flux into its base to balance extreme rates of surface denudation (>10 mm/a) over the last ~2-3 Ma. One proposed source is middle to lower crustal flow into the massif (e.g., Zeitler et al., 2001), which while likely inactive elsewhere along strike, may be sustainable by very rapid surface denudation, a high geothermal gradient, and thermal weakening of rocks beneath the syntaxes. An alternative source is orogen-parallel (OP) transport due to oblique convergence and strain partitioning along the Himalayan arc (e.g., Seeber and Pêcher, 1998). Several observations including (1) predominantly orogen-normal slip on the frontal thrusts deduced from seismic events, (2) OP extension accommodated on orogen-normal structures, and (3) distributed and segmented strike-slip faulting trending parallel to the arc are consistent with strain partitioning and OP mass transport. A key question is can this mechanism supply sufficient mass to the Nanga Parbat syntaxis, or is local channel flow required? We explore mass transport into the western Himalayan syntaxis region using lithospheric-scale 3D mechanical and coupled thermo-mechanical models of an arcuate orogen. The crust is either frictional plastic or power-law viscous, with a constant low viscosity lower crust present in some experiments. Applied velocity boundary conditions are transmitted to the base of the crust by a strong frictional plastic mantle lithosphere, and mantle detachment/subduction drives formation of a bivergent, arcuate orogen. To assess the magnitude of mass transport from strain partitioning, we first explore purely mechanical experiments featuring a 5-km-high Tibet-like plateau above a weak lower crust and with a frictional plastic decollement that dips at 10° beneath the incipient orogen, similar to the Himalayan basal detachment. Preliminary results show gravitational feedback from the plateau drives

  20. Chronology and evolution of glacio-nival systems of Mongun-Taiga mountain massif in Late Pleistocene and Holocene

    NASA Astrophysics Data System (ADS)

    Ganushkin, Dmitry; Chistyakov, Kirill

    2013-04-01

    The main glacial complex of western Tuva - Mongun-Taiga mountain massif (3970.5 m) is situated in the center of Altai-Sayan mountain system. Modern glaciation of the massif has area about 20 km2, average firn line altitude is about 3400 m. Average summer temperatures at the firn line is 0.5°C, precipitation about 270 mm. We studied glacial fluctuations of the past on base of geomorphologic methods and radiocarbon dating of peat, soils and wood samples. Moraines of the Early Stage of the Last Glaciation (MIS 4) extend from cirques and troughs to the flat piedmonts forming lobes reaching the level of 1830 m in the south of the massif and 2200 ° in the north. There are traces of 4 glacial advances, during the maximal the area of glaciation reached 513 km2 with 800 m of depression of firn line. We reconstructed that average summer temperatures were 2.5°C below present with precipitation 2.3 times more than now. During MIS 3 the area of glaciation reduced to less than 0.5 km2 with 450-490 m of elevation of firn line. Samples of moraine-buried wood with with radiocarbon age about 58-39 and 27-25 kBP found 600 m higher than present upper limit of growth of trees give evidence of climatic conditions at least 1.5°C warmer than present (with a correction for tectonics). In the Late Stage of the Last Glaciation glaciers mostly remained inside troughs reaching during the maximum the level of 2200 m in the south and 2400 m in the north, the area of glaciation about 320 km2, firn line depression about 690 m. We estimate cooling in the maximum -3.6 °C with precipitation 65% of present. There are moraine complexes of 4 postglacial advances, in the latest of them, presumably Younger Drias, firn line depression reached 500 m. In the Early Holocene glaciers reduced rapidly, evidence of this reduction are samples of wood with age 9120±110 cal. B.P. that were found about 350 m over the present forest line. According to our reconstruction in the Boreal Holocene optimum (about 9000

  1. GPS Velocity Field in Bangladesh: Delta Subsidence, Seasonal Water Loading and Shortening Across the Burma Accretionary Prism and Shillong Massif

    NASA Astrophysics Data System (ADS)

    Steckler, M. S.; Mondal, D. R.; Nooner, S. L.; Akhter, S. H.; Seeber, L.; Bettadpur, S. V.; Sazedul Karim, C.; Howe, M.; Masson, F.; Maurin, T.; Rangin, C.

    2013-12-01

    We installed a suite of 25 GPS receivers between 2003 to 2012 covering the deltaic country of Bangladesh, which lies near the junction of the Indian Shield, the Himayalan collision belt and the Indo-Burman wedge. The crust of the Indian Shield thins southeastward in Bengal Basin across the hinge zone of an Early Cretaceous continental margin. The thin continental and/or oceanic crust of the Bengal Basin beyond the hinge zone is overlain by the southwest prograding Ganges-Brahmaputra Delta (GBD) creating a total sediment thickness of ≥16 km. The GBD is formed by the convergence of these great rivers which together supply >1GT/y of sediment. Their flow, the second largest on earth, is strongly seasonal and causes widespread flooding during the summer monsoon. The heavily-sedimented GBD is being overridden from the north by the Shillong Massif, a 2-km high basement-cored anticlinorium exposing Indian Shield, and from the east by the accretionary prism of the Indo-Burma wedge. The soft, oblique collision of the Burma platelet with the Bengal Basin and the GBD has built a large accretionary prism that widens northwards to 250-300 km. The prism extends westward up to half way across the GBD. The outer folds and thrust front are blind due to burial by the rapid sedimentation of the GBD. The GPS data in Bangladesh cover the frontal region of this unusual subaerial accretionary prism, while observations from India and Myanmar provide velocities for more internal parts of the system. The GPS velocities provide data on multiple processes taking place in the region. The vertical component shows both long-term and seasonal signals. The horizontal components quantify the shortening and lateral motion between the GBD and both the Indo-Burman wedge and Shillong Massif. The Indo-Burman convergence is oblique and partitioned into multiple strike-slip faults and a large number of thrust folds, presumably rooted into a basal megathrust.. The velocity gradients across the

  2. A Warning System For Catastrophic Man-made Hazards Using Electromagnetic Induction Monitoring Verified In Rock Burst Massif

    NASA Astrophysics Data System (ADS)

    Hachay, Olga; Khachay, Oleg

    2010-05-01

    By providing mining works in high stressed rock massif the man-made seismicity become evident, therefore the problem of its forecasting and prevention attracts much attention in all countries with developed mining industry. The near-term forecasting plays a significant role, but till now the developing of a method which allows to define quantitative criterions for the warning system is a large problem as in mining and in seismology [1]. Using the idea of physical mesomechanics, which includes the synergetic approach for analyzing the state changing of rock massif of different matter content, that problem can be solved by monitoring methods, which can research a medium with hierarchic structure. [2-3]. The medium changing, which lead to near-term precursors of dynamical events can be explained in a frame of a conception of self organized criticality [4-5], for which the main factors are heterogeneity and nonlinearity. In the frame of the Siberian Mining Institute a new direction of massive state research develops, which is named as nonlinear geomechanics [6]. But in our opinion we can achieve more success using together geomechanical and geophysical methods, which are based on a medium model as a model of a stratified block structure with hierarchic inclusions. More over if we are interested also in the evolution of that structure we are needed to use complex geophysical methods, which have sufficient resolution of revealing of the origin and decay of the self organized structures [3]. For the first time by using the planshet electromagnetic method, which was elaborated in the Institute of geophysics UD RAS we could in the frame of natural investigations realize the idea of revealing of disintegration zones in the rock massif and organize the monitoring of their morphology [7-8]. That method covers to geophysical methods of non destroying control. It differs from other tomography methods by a system of observation and methods of processing and interpretation, which

  3. Incidence of mass movement processes after an historical episode of heavy snowfall in the Asturian Massif (Northern Spain)

    NASA Astrophysics Data System (ADS)

    Garcia-Hernandez, Cristina; Ruiz-Fernández, Jesús; Gallinar, David

    2015-04-01

    This research examines a mass movement event caused in the context of the Great Blizzard of 1888, one of the most severe recorded blizzards in the history of Europe, whose implications go far beyond. In the Asturian Massif the episode consisted in four linked and consecutive snowstorms that took place between the 14th of February 1888 and the 8th of April 1888, creating snow covers with a depth ranging between 5 and 7 m, snow avalanches and flooding, causing dozens of deaths and large material damage. The Asturian Massif belongs to the Atlantic-climate area and is composed mainly by sedimentary and metamorphic paleozoic rocks. Many sectors of the Massif are between 1.000 and 2.000 m a.s.l., and its topography is characterized by a great height difference and steep slopes. Because of the lack of deep soils suitable for farming, the main traditional activity has been livestock keeping, and goods traffic. We have devised a method that enables the reconstruction of this event on the basis of nivo-meteorogical conditions, geographical location and socio-economic impact. The mass movement episode has been studied through the issues of 6 newspapers published in Asturias between the 20th of January and 30th of May 1888, the ancient meteorological station data of the University of Oviedo, and field work. A logical database structure has been designed with the aim to store and cross the information for statistical analysis. Thirty six mass movement worthy of consideration were documented, 28 of them causing material damage (six homes destroyed and at least 22 interruptions with the traffic flow on roads, highways and railways). Ten high- and mid-elevation mountain municipalities were affected by mass movement. We must consider that only the most important events, or those that happened in crowded places, have been considered by the newspapers, so the total number of mass movements should be considered as a minimum figure. We have got to identify and classify 27 of them; 16

  4. Genesis and significance of the silico-aluminous nodules in the Ordovician of the Montagne Noire and the Massif Armoricain (France)

    NASA Astrophysics Data System (ADS)

    Becq-Giraudon, Jean-François; Bouillé, Suzanne; Chauvel, Jean-Jacques

    1992-04-01

    Siliceous nodules of the Arenigian of the Montagne Noire (southern France) and the Massif Armoricain (western France) are made up of quartz, illite and chlorite with secondary apatite and, less frequently, dolomite. Diffractometrical and geochemical data indicate that the chlorite is a chamosite (trioctahedral 2:1 chlorite), whose development may be accompanied by that of apatite and diminution of illite. Three types of nodules are defined: Type 1, siliceous nodules, with more than 85% of SiO 2, very frequent in the Montagne Noire; Type II, nodules made of a micaceous siltstone with chlorite matrix, abundant in the Massif Armoricain but present also in the Montagne Noire; Type III, chloritic nodules with a finely globular structure, especially developed in the Massif armoricain but observed in the Montagne Noire as well. The nodules are always poorer in illite than their host sediments and often show traces of the initial sediments. Their formation occurs after the deposition and prior to the development of foliation. The frequent presence of undistorted fossil remains suggests an early formation linked to the physico-chemical modifications occurring in an unconsolidated sediment around a decaying organism. The post-depositional mineralogical evolution should have started with an illite/dolomite assemblage and end up with a chamosite-dominant one, under cold climatic conditions. The simultaneous presence of the three types of nodules in the same formation, or even in the same beds, shows that this mineralogical differentiation is not strictly related to the diagenetic and metamorphic transformation of this material.

  5. The last stages of the Avalonian-Cadomian arc in NW Iberian Massif: isotopic and igneous record for a long-lived peri-Gondwanan magmatic arc

    NASA Astrophysics Data System (ADS)

    Andonaegui, Pilar; Arenas, Ricardo; Albert, Richard; Sánchez Martínez, Sonia; Díez Fernández, Rubén; Gerdes, Axel

    2016-06-01

    The upper allochthonous units of NW Iberian Massif contain an extensive Cambrian magmatism (c. 500 Ma), covering felsic to mafic compositions. The magmatic activity generated large massifs of granitoids and gabbros, with calc-alkaline and tholeiitic compositions respectively. Petrological and geochemical features of these massifs are characteristic of volcanic arc. The plutons intruded siliciclastic sedimentary series deposited in the periphery of the West Africa Craton. U-Pb/Hf isotopic compositions of detrital zircon in the siliciclastic host series, indicate continental arc activity between c. 750 Ma and c. 500 Ma. It was characterized by a large variety of isotopic sources, including from very old continental input, even Archean, to the addition of a significant amount of juvenile mafic material. These isotopic sources experienced an extensive mixing that explains the composition and isotopic features (εHft from - 50 until + 15) of the represented Cambrian plutons. The Cambrian igneous rocks of the upper units of NW Iberia are related to the latest activity of the Avalonian-Cadomian arc. From the Middle Cambrian arc activity in the periphery of Gondwana was replaced by pronounced extension associated with the development of continental rifting, which finally led to separation of the microcontinent Avalonia. Subsequent drifting of Avalonia to the North caused progressive opening one of the main Paleozoic ocean, the Rheic Ocean.

  6. U-Pb dating of granodiorite and granite units of the Los Pedroches batholith. Implications for geodynamic models of the southern Central Iberian Zone (Iberian Massif)

    NASA Astrophysics Data System (ADS)

    Carracedo, M.; Paquette, J. L.; Alonso Olazabal, A.; Santos Zalduegui, J. F.; García de Madinabeitia, S.; Tiepolo, M.; Gil Ibarguchi, J. I.

    2009-10-01

    The first U-Pb geochronological results on the magmatic alignment of the Los Pedroches batholith are presented. The batholith is composed of a main granodioritic unit, several granite plutons and an important acid to basic dyke complex, all of them intrusive after the main Variscan regional deformation phase, D1, along the boundary between the Ossa-Morena and Central Iberian zones (SW Iberian Massif). Zircons from samples on both extremes of the granodiorite massif record nearly simultaneous magmatic crystallization at ca. 308 Ma, while the emplacement of granite plutons was diachronic between 314 and 304 Ma. The U-Pb results combined with new field and textural observations allow to better constrain the age of Variscan deformations D2 and D3 across the region, while the age of D1 remains imprecise. Transcurrent D2 shearing-tightening of D1 folds occurred around 314 Ma (lower Westphalian) in relation to the emplacement of the first granitic magmas. D3 faults and shear bands bearing a strong extensional component developed at ca. 308 Ma (upper Westphalian), associated to the intrusion of the main granodiorite pluton (granodiorite) of the batholith. Together with available geochemical and geophysical information, these results point to the Variscan reactivation of lithospheric fractures at the origin and subsequent emplacement of hybrid magmas within this sector of the Massif.

  7. The sequence and origin of mineralization in the tectonic zones in the Suwalki Anorthosite Massif, NE Poland

    NASA Astrophysics Data System (ADS)

    Wiszniewska, J.; Cymerman, Z.; Gaweda, A.

    2003-04-01

    The Suwalki Anorthosite Massif (SAM) is emplaced within the Mesoproterozoic rapakivi-type Mazury Complex (ca. 1.56 Ga) of the AMCG affinity. This massif has been subjected by several tectono-hydrothermal events resulted in extensive mineralization. A comprehensive structural study of the SAM requires investigation of numerous (99) boreholes because each well displays several structural components and the combination of these data can be used to summarize SAM evolution. The style of deformation in the SAM area ranges from localised ductile flow, producing shear zones (from a few cm to tens of metre wide) with a mylonitic foliation and a stretching lineation, to brittle fracturing and accompanying brecciation. The SAM features alternating zones of high- and low-strain, both in ductile and brittle conditions. Dip-parallel stretching lineations are inferred to be remnants of the Gothian shortening and ductile thrusting. Almost all shear sense indicators indicate reverse sense of movements. Younger planar fabrics in the fault zones include a well-developed pressure-solution cleavage and or fracture cleavage. Locally, the cleavage become parallel to the fault direction, suggesting rotation of a passive marker during shearing and shortening. The fault zones commonly exhibit newly formed subhorizontal stretching lineations that overprint the former dip-parallel stretching lineations. The kaolinization was the first brittle process, restricted to the close vicinity of the mylonitic structures. The syntectonic C_1 carbonate (calcite or Fe-dolomite) precipitated on the C planes of the S-C composite fabric. C_1 (calcite) carbonate is accompanied by the Fe-Mg chlorite. The further faulting process was accompanied by the crushing, brecciation and pseudotachylite formation. The cracks and fissures are filed by fine grained quartz and C_2 calcite, forming the cement of the tectonic breccias. The following relaxation event caused the opening of the earlier formed cracks and the

  8. Collapse in a rock massif induced by lateral confinement loss: the case of Montegolf (Málaga, Spain)

    NASA Astrophysics Data System (ADS)

    Azañón, J. M.; Puertas, E.; Ureña, C.; Gallego, R.; Romero-Gómez, F.

    2012-04-01

    The use of computing codes allowing finite elements analysis is a very useful tool in detecting variations of the tensional state of rock massifs. Most of the codes used for ground modelling only allow 2D analysis. However, in the case of complex slope instabilities, it is necessary to consider the variation of resistant properties in a 3D model. This work presents an example in which 3D analysis carried out by finite elements methods becomes essential to understand the surface processes occurred in a urbanized rock massif (Montegolf, Malaga). The studied area is a small hill of elliptical shaped plan (300x200m plan). As a main peculiarity of this hill, it was intensively undergone to human activity in recent years. On September 11th, 2000, the collapse of an inner cavity (100m3 in volume) took place. The cavity proceeded from a mining abandoned 30 years before. The application of a 3D finite elements model showed that the highway slope digged in the Eastern face of the mount produced a change in the tensional state inside the mount. Vertical stresses shifted from compression to tension eliminating the vault effect. To define the geometry of the model, a survey of the existing contour map was carried out and conveniently transformed into ACIS format to be processed by ABAQUS (finite elements program). In the two-dimensional case an E-W section involving houses, highway and cavity was chosen. Mining hole was considered in the model, using a 10m-diameter sphere to represent the cavity. The performance of the natural materials was supposed to be elastic so Young modulus and Poisson's ratio were required. The ground strains due to collapse of the cavity and obtained by the finite elements model were accurately related to the mapping of cracks on the surface, the sinking of topographical landmarks (located on the top of the mountain) and the photographic analysis (captures before and after the collapse). Thus it is confirmed that the surface sliding which affected the

  9. High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement

    NASA Astrophysics Data System (ADS)

    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

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

    SciTech Connect

    Jardine, L J

    2005-06-15

    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

  11. Inclusions in topaz from miarolitic pegmatites of the Volodarsk-Volynski Massif (Ukraine)--a Raman spectroscopic study.

    PubMed

    Dumańska-Słowik, Magdalena; Wesełucha-Birczyńska, Aleksandra; Natkaniec-Nowak, Lucyna

    2013-05-15

    The differently coloured (colourless, brown-pinkish and blue-pinkish) crystals of topaz from granitic pegmatites of Volodarsk-Volynsky Massif (VVM) have been investigated by scanning electron microscopy (SEM) and Raman microspectroscopy (RS) methods. Topaz (287, 522, 855, 929 cm(-1)), goethite (390 cm(-1)), pyrite (377-379 cm(-1)), marcasite (397 and 331 cm(-1)) and monazite (460 and 970-1070 cm(-1)) were identified as mineral inclusions in analysed crystals. On the basis of RS spectra some of this inclusions contain also organic matter, represented by carbonaceous matter (D-band at ca. 1320-1340 cm(-1) and G-band at ca. 1590-1600 cm(-1)) and liquid simple hydrocarbons consisting of aliphatic and aromatic groups (1240, 1325 and 1420 cm(-1)). Other solid phases found the host topaz, i.e. quartz, orthoclase, very rare minerals (micas) as lepidolite, zinnwaldite and also beryl and rutile, were identified with SEM-EDS analyses. All these mineral inclusions have been formed by post-magmatic, fluid-induced processes, extended from pegmatite to hydrothermal stages of magma crystallization.

  12. Characteristics of Polycrystalline Garnets in Micaschists From the Southern Menderes Massif (Turkey) and the Solitude Range (BC, Canada)

    NASA Astrophysics Data System (ADS)

    Anderson, C.; Whitney, D. L.; Seaton, N.

    2008-12-01

    Electron backscatter diffraction (EBSD) analysis of garnets in metamorphic rocks has revealed the presence of grain boundaries within what appear, based on morphology, to be single crystals. There have only been a few previous studies that have described these types of polycrystals in nature. In this study we analyzed garnets from two suites of metamorphic rocks: kyanite-staurolite schist from the Solitude Range, SW Rocky Mountains (BC, Canada), and mica schist from the southern Menderes Massif (western Turkey). Garnets from both sites are growth zoned and formed during a single metamorphic event, although the Solitude Range garnets record in their zoning and inclusion textures a change from chloritoid-present to staurolite- present (chloritoid-out) reaction history. The garnet-bearing rocks from these sites formed at P-T conditions of 430-550 C, 7-8 kbar (Menderes) and 550-600 C, 6-7 kbar (BC). Less than 10% of the garnets analyzed are polycrystals, but all polycrystals detected have similar characteristics: high-angle misorientation boundaries that crosscut inclusions and inclusion trails. Most polycrystals have 2-3 domains (crystals), but one complex polycrystal was comprised of 16 distinct lattice domains. In most cases, misorientation boundaries crosscut growth zoning, but one Menderes polycrystal exhibited distinct zoning in each domain. Most polycrystals likely formed early in the garnet growth history as closely-spaced nuclei coalesced, but clustering (coalescence) continued throughout the history of garnet crystallization in these rocks.

  13. The cyclic carbonates of the Latemar Massif: Evidence for the orbital forcing of a carbonate platform during the Middle Triassic

    NASA Technical Reports Server (NTRS)

    Hinnov, Linda

    1992-01-01

    The Latemar Massif is an exhumed carbonate platform in the Dolomites of Northern Italy that was deposited during the Ladinian stage of the Middle Triassic. The platform interior is comprised of hundreds of vertically stacked, meter scale, subtidal limestone/vadose cap carbonate cycles ('Latemar couplets') arranged into upward thinning bundles of 5. The individual couplets are interpreted as the products of sea level oscillations occurring with an approximately 20,000 year periodicity; the 5:1 bundling is indicative of a lower order approximately 100,000 year modulating component. This combination of cycling is interpreted as a platform response to precession forcing with the 5:1 bundling an expression of modulation by the eccentricity. Spectral analysis confirms the significance of the 5:1 bundling, and identifies other significant bundling components related to other components of the eccentricity. The results show that the Latemar bundling spectrum is complex, with a splitting of components around the 1 percent bundling frequency, suggestive of the multiple component eccentricity in the 100,000 year range. On the other hand, there is no direct evidence for the major 400,000 year eccentricity component, although there is a dominant approximately 700,000 year cycling in the buildup (a 35:1 bundling period). Other higher frequency bundling components may be related to obliquity forcing. Simple models are presented to argue for and against an astronomical origin of these cyclic platform carbonates.

  14. The carbon-isotopic composition of Proterozoic carbonates: Riphean successions from northwestern Siberia (Anabar Massif, Turukhansk Uplift)

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Kaufman, A. J.; Semikhatov, M. A.

    1995-01-01

    Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks.

  15. Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards

    NASA Astrophysics Data System (ADS)

    Chapron, E.; Albéric, P.; Jézéquel, D.; Versteeg, W.; Bourdier, J.-L.; Sitbon, J.

    2010-09-01

    Sedimentation processes occurring in the most recent maar lake of the French Massif Central (Lake Pavin) are documented for the first time based on high resolution seismic reflection and multibeam bathymetric surveys and by piston coring and radiocarbon dating on a sediment depocentre developed on a narrow sub aquatic plateau. This new data set confirms the mid Holocene age of maar lake Pavin formation at 6970±60 yrs cal BP and highlights a wide range of gravity reworking phenomena affecting the basin. In particular, a slump deposit dated between AD 580-640 remoulded both mid-Holocene lacustrine sediments, terrestrial plant debris and some volcanic material from the northern crater inner walls. Between AD 1200 and AD 1300, a large slide scar mapped at 50 m depth also affected the southern edge of the sub aquatic plateau, suggesting that these gas-rich biogenic sediments (laminated diatomite) are poorly stable. Although several triggering mechanisms can be proposed for these prehistoric sub-aquatic mass wasting deposits in Lake Pavin, we argue that such large remobilisation of gas-rich sediments may affect the gas stability in deep waters of meromictic maar lakes. This study highlights the need to further document mass wasting processes in maar lakes and their impacts on the generation of waves, favouring the development of dangerous (and potentially deadly) limnic eruptions.

  16. High-yielding aquifers in crystalline basement: insights about the role of fault zones, exemplified by Armorican Massif, France

    NASA Astrophysics Data System (ADS)

    Roques, Clément; Bour, Olivier; Aquilina, Luc; Dewandel, Benoît

    2016-08-01

    While groundwater constitutes a crucial resource in many crystalline-rock regions worldwide, well-yield conditions are highly variable and barely understood. Nevertheless, it is well known that fault zones may have the capacity to ensure sustainable yield in crystalline media, but there are only a few and disparate examples in the literature that describe high-yield conditions related to fault zones in crystalline rock basements. By investigating structural and hydraulic properties of remarkable yielding sites identified in the Armorican Massif, western France, this study discusses the main factors that may explain such exceptional hydrogeological properties. Twenty-three sites, identified through analysis of databases available for the region, are investigated. Results show that: (1) the highly transmissive fractures are related to fault zones which ensure the main water inflow in the pumped wells; (2) the probability of intersecting such transmissive fault zones does not vary significantly with depth, at least within the range investigated in this study (0-200 m); and (3) high yield is mainly controlled by the structural features of the fault zones, in particular the fault dip and the presence of a connected storage reservoir. Conceptual models that summarize the hydrological properties of high-yield groundwater resources related to fault zones in crystalline basement are shown and discussed.

  17. Inclusions in topaz from miarolitic pegmatites of the Volodarsk-Volynski Massif (Ukraine) - A Raman spectroscopic study

    NASA Astrophysics Data System (ADS)

    Dumańska-Słowik, Magdalena; Wesełucha-Birczyńska, Aleksandra; Natkaniec-Nowak, Lucyna

    2013-05-01

    The differently coloured (colourless, brown-pinkish and blue-pinkish) crystals of topaz from granitic pegmatites of Volodarsk-Volynsky Massif (VVM) have been investigated by scanning electron microscopy (SEM) and Raman microspectroscopy (RS) methods. Topaz (287, 522, 855, 929 cm-1), goethite (390 cm-1), pyrite (377-379 cm-1), marcasite (397 and 331 cm-1) and monazite (460 and 970-1070 cm-1) were identified as mineral inclusions in analysed crystals. On the basis of RS spectra some of this inclusions contain also organic matter, represented by carbonaceous matter (D-band at ca. 1320-1340 cm-1 and G-band at ca. 1590-1600 cm-1) and liquid simple hydrocarbons consisting of aliphatic and aromatic groups (1240, 1325 and 1420 cm-1). Other solid phases found the host topaz, i.e. quartz, orthoclase, very rare minerals (micas) as lepidolite, zinnwaldite and also beryl and rutile, were identified with SEM-EDS analyses. All these mineral inclusions have been formed by post-magmatic, fluid-induced processes, extended from pegmatite to hydrothermal stages of magma crystallization.

  18. Inclusions in topaz from miarolitic pegmatites of the Volodarsk-Volynski Massif (Ukraine)--a Raman spectroscopic study.

    PubMed

    Dumańska-Słowik, Magdalena; Wesełucha-Birczyńska, Aleksandra; Natkaniec-Nowak, Lucyna

    2013-05-15

    The differently coloured (colourless, brown-pinkish and blue-pinkish) crystals of topaz from granitic pegmatites of Volodarsk-Volynsky Massif (VVM) have been investigated by scanning electron microscopy (SEM) and Raman microspectroscopy (RS) methods. Topaz (287, 522, 855, 929 cm(-1)), goethite (390 cm(-1)), pyrite (377-379 cm(-1)), marcasite (397 and 331 cm(-1)) and monazite (460 and 970-1070 cm(-1)) were identified as mineral inclusions in analysed crystals. On the basis of RS spectra some of this inclusions contain also organic matter, represented by carbonaceous matter (D-band at ca. 1320-1340 cm(-1) and G-band at ca. 1590-1600 cm(-1)) and liquid simple hydrocarbons consisting of aliphatic and aromatic groups (1240, 1325 and 1420 cm(-1)). Other solid phases found the host topaz, i.e. quartz, orthoclase, very rare minerals (micas) as lepidolite, zinnwaldite and also beryl and rutile, were identified with SEM-EDS analyses. All these mineral inclusions have been formed by post-magmatic, fluid-induced processes, extended from pegmatite to hydrothermal stages of magma crystallization. PMID:23501722

  19. Fabric evidence for granodiorite emplacement with extensional shear zones in the Variscan Gredos massif (Spanish Central System)

    NASA Astrophysics Data System (ADS)

    Díaz-Alvarado, Juan; Fernández, Carlos; Díaz-Azpiroz, Manuel; Castro, Antonio; Moreno-Ventas, Ignacio

    2012-09-01

    Three granitoid bodies in the central part of the Gredos massif (Spanish Central System batholith) are tabular, around 1 km in thickness, and intruded into a migmatitic middle crust during the D3 deformation phase of the Variscan Orogeny. Petrologically, they are composed of Bt-granodiorite and Crd-monzogranite, and they show varying abundance of large (cm-scale) feldspar megacrysts. A detailed study of the shape preferred orientation (SPO) magmatic fabric defined by these megacrysts, together with a kinematic analysis of the structures due to interactions between them, and the measurement of quartz c-axis fabrics in migmatites and granitoids, suggests that granitic magma and country rocks were mechanically coupled during deformation. The emplacement took place along large-scale, extensional shear zones active during the first stages of the D3 phase. The shape of the SPO ellipsoids varies from constrictional at the centre of the granitic bodies, to flattening or even oblate at their external contacts with the migmatitic host rocks. The favoured interpretation of this spatial fabric variation is the overprinting of the emplacement fabrics by a constrictional tectonic regime associated with the growth of tabular magma chambers along extensional detachments, followed by shear zone development commonly at the top of the granitic bodies. The entire structure was later folded during the last stages of the D3 phase.

  20. A new species of the genus Calotes (Squamata: Agamidae) from high elevations of the Knuckles massif of Sri Lanka.

    PubMed

    Amarasinghe, A A Thasun; Karunarathna, D M S Suranjan; Hallermann, Jakob; Fujinuma, Junichi; Grillitsch, Heinz; Campbell, Patrick D

    2014-01-01

    A new species of agamid lizard, of the genus Calotes, is described based on morphological evidence. This species is restricted to the Knuckles massif (>900 m elevation) of Sri Lanka. The genus Calotes consists of seven species in Sri Lanka, five of which appear to form an endemic radiation. The new species most closely resembles C. liocephalus Günther, 1872 which has an isolated population in the central highlands and is only known from Pundaluoya (~1000m), Dickoya (~1200m), Upcot (~1400m), Agrapatanas (1665m) and Peak Wilderness (Sri Pada) (>1400m). The populations from Pundaluoya and Dickoya appear to be locally extinct from the wild and are known only from museum specimens collected over 120 years ago. Males of the new species are different from males of C. liocephalus because of the absence of a gular pouch; by having mid gular scales smaller in size than those of its counterpart; scales on the snout which are larger in size than those on the occipital and forehead; pectoral scales which are not enlarged; elongated subcaudal scales; slightly carinate and acuminate abdominal scales; and scales on venter which are somewhat larger in size than those on dorsum at the same level. Finally, we also redescribe Calotes liocephalus, and provide a key to the Sri Lankan species of genus Calotes. PMID:24872171

  1. Evolution of hut access facing glacier shrinkage in the Mer de Glace basin (Mont Blanc massif, France)

    NASA Astrophysics Data System (ADS)

    Mourey, Jacques; Ravanel, Ludovic

    2016-04-01

    Given the evolution of high mountain environment due to global warming, mountaineering routes and huts accesses are more and more strongly affected by glacial shrinkage and concomitant gravity processes, but almost no studies have been conducted on this relationship. The aim of this research is to describe and explain the evolution over the last century of the access to the five alpine huts around the Mer de Glace glacier (Mont Blanc massif), the larger French glacier (length = 11.5 km, area = 30 km²), a major place for Alpine tourism since 1741 and the birthplace of mountaineering, by using several methods (comparing photographs, surveying, collecting historical documents). While most of the 20th century shows no marked changes, loss of ice thickness and associated erosion of lateral moraines generate numerous and significant changes since the 1990s. Boulder falls, rockfalls and landslides are the main geomorphological processes that affect the access, while the glacier surface lowering makes access much longer and more unstable. The danger is then greatly increased and the access must be relocated and/or equipped more and more frequently (e.g. a total of 520 m of ladders has been added). This questions the future accessibility to the huts, jeopardizing an important part of mountaineering and its linked economy in the Mer de Glace area.

  2. A new species of the genus Pristimantis (Amphibia, Craugastoridae) associated with the moderately elevated massifs of French Guiana.

    PubMed

    Fouquet, Antoine; Martinez, Quentin; Courtois, Elodie A; Dewynter, Maël; Pineau, Kévin; Gaucher, Philippe; Blanc, Michel; Marty, Christian; Kok, Philippe J R

    2013-12-23

    We describe a new Pristimantis from French Guiana, northern South America, which is mainly distinguished from known phenotypically related congeners (i.e. species from the polyphyletic unistrigatus species group) occurring at low and middle elevations in the Guiana Shield by the combination of a distinct tympanum, a lower ratio of tibia vs. hand length, a reddish groin region, and a distinct advertisement call consisting of clusters of generally four short notes. The new species inhabits pristine primary forests on the slopes of isolated massifs reaching more than 400 m elevation, and seems not to occur below ca. 200 m above sea level. Such a sharp altitudinal limit suggests a strong influence of thermal variation on the distribution of the species, and therefore a potential sensitivity to climate change. With only nine isolated populations documented so far, the new species should be prioritized for conservation. Historical climate fluctuations during the Quaternary are likely responsible for the distribution pattern of the new species. 

  3. Sinfonevada: Dataset of Floristic diversity in Sierra Nevada forests (SE Spain).

    PubMed

    Pérez-Luque, Antonio Jesús; Bonet, Francisco Javier; Pérez-Pérez, Ramón; Rut Aspizua; Lorite, Juan; Zamora, Regino

    2014-01-01

    The Sinfonevada database is a forest inventory that contains information on the forest ecosystem in the Sierra Nevada mountains (SE Spain). The Sinfonevada dataset contains more than 7,500 occurrence records belonging to 270 taxa (24 of these threatened) from floristic inventories of the Sinfonevada Forest inventory. Expert field workers collected the information. The whole dataset underwent a quality control by botanists with broad expertise in Sierra Nevada flora. This floristic inventory was created to gather useful information for the proper management of Pinus plantations in Sierra Nevada. This is the only dataset that shows a comprehensive view of the forest flora in Sierra Nevada. This is the reason why it is being used to assess the biodiversity in the very dense pine plantations on this massif. With this dataset, managers have improved their ability to decide where to apply forest treatments in order to avoid biodiversity loss. The dataset forms part of the Sierra Nevada Global Change Observatory (OBSNEV), a long-term research project designed to compile socio-ecological information on the major ecosystem types in order to identify the impacts of global change in this area. PMID:24843285

  4. Sinfonevada: Dataset of Floristic diversity in Sierra Nevada forests (SE Spain).

    PubMed

    Pérez-Luque, Antonio Jesús; Bonet, Francisco Javier; Pérez-Pérez, Ramón; Rut Aspizua; Lorite, Juan; Zamora, Regino

    2014-01-01

    The Sinfonevada database is a forest inventory that contains information on the forest ecosystem in the Sierra Nevada mountains (SE Spain). The Sinfonevada dataset contains more than 7,500 occurrence records belonging to 270 taxa (24 of these threatened) from floristic inventories of the Sinfonevada Forest inventory. Expert field workers collected the information. The whole dataset underwent a quality control by botanists with broad expertise in Sierra Nevada flora. This floristic inventory was created to gather useful information for the proper management of Pinus plantations in Sierra Nevada. This is the only dataset that shows a comprehensive view of the forest flora in Sierra Nevada. This is the reason why it is being used to assess the biodiversity in the very dense pine plantations on this massif. With this dataset, managers have improved their ability to decide where to apply forest treatments in order to avoid biodiversity loss. The dataset forms part of the Sierra Nevada Global Change Observatory (OBSNEV), a long-term research project designed to compile socio-ecological information on the major ecosystem types in order to identify the impacts of global change in this area.

  5. Sinfonevada: Dataset of Floristic diversity in Sierra Nevada forests (SE Spain)

    PubMed Central

    Pérez-Luque, Antonio Jesús; Bonet, Francisco Javier; Pérez-Pérez, Ramón; Rut Aspizua; Lorite, Juan; Zamora, Regino

    2014-01-01

    Abstract The Sinfonevada database is a forest inventory that contains information on the forest ecosystem in the Sierra Nevada mountains (SE Spain). The Sinfonevada dataset contains more than 7,500 occurrence records belonging to 270 taxa (24 of these threatened) from floristic inventories of the Sinfonevada Forest inventory. Expert field workers collected the information. The whole dataset underwent a quality control by botanists with broad expertise in Sierra Nevada flora. This floristic inventory was created to gather useful information for the proper management of Pinus plantations in Sierra Nevada. This is the only dataset that shows a comprehensive view of the forest flora in Sierra Nevada. This is the reason why it is being used to assess the biodiversity in the very dense pine plantations on this massif. With this dataset, managers have improved their ability to decide where to apply forest treatments in order to avoid biodiversity loss. The dataset forms part of the Sierra Nevada Global Change Observatory (OBSNEV), a long-term research project designed to compile socio-ecological information on the major ecosystem types in order to identify the impacts of global change in this area. PMID:24843285

  6. Geological setting and petrogenesis of symmetrically zoned, miarolitic granitic pegmatites at Stak Nala, Nanga Parbat - Haramosh Massif, northern Pakistan

    USGS Publications Warehouse

    Laurs, B.M.; Dilles, J.H.; Wairrach, Y.; Kausar, A.B.; Snee, L.W.

    1998-01-01

    Miarolitic granitic pegmatites in the Stak valley in the northeast part of the Nanga Parbat - Haramosh Massif, in northern Pakistan, locally contain economic quantities of bi- and tricolored tourmaline. The pegmatites form flat-lying sills that range from less than 1 m to more than 3 m thick and show symmetrical internal zonation. A narrow outer or border zone of medium-to coarse-grained oligoclase - K-feldspar - quartz grades inward to a very coarse-grained wall zone characterized by K-feldspar - oligoclase - quartz - schorl tourmaline. Radiating sprays of schorl and flaring megacrysts of K-feldspar (intermediate microcline) point inward, indicating progressive crystallization toward the core. The core zone consists of variable mixtures of blocky K-feldspar (intermediate microcline), oligoclase, quartz, and sparse schorl or elbaite, with local bodies of sodic aplite and miarolitic cavities or "pockets". Minor spessartine-almandine garnet and lo??llingite are disseminated throughout the pegmatite, but were not observed in the pockets. The pockets contain well-formed crystals of albite, quartz, K-feldspar (maximum microcline ?? orthoclase overgrowths), schorl-elbaite tourmaline, muscovite or lepidolite, topaz, and small amounts of other minerals. Elbaite is color-zoned from core to rim: green (Fe2+- and Mn2+-bearing), colorless (Mn2+-bearing), and light pink (trace Mn3+). Within ???10 cm of the pegmatites, the granitic gneiss wallrock is bleached owing to conversion of biotite to muscovite, with local quartz and albite added. Schorl is disseminated through the altered gneiss, and veins of schorl with bleached selvages locally traverse the wallrock up to 1 m from the pegmatite contact. The schorl veins can be traced into the outer part of the wall zone, which suggests that they formed from aqueous fluids derived during early saturation of the pegmatite-forming leucogranitic magma rich in H2O, F, B, and Li. Progressive crystallization resulted in a late-stage sodic

  7. A Sb-As-W-Te-rich manganese-quartzite from the UHP-metamorphic Kimi Complex, Rhodope Massif, Greece

    NASA Astrophysics Data System (ADS)

    Konzett, Jürgen

    2010-05-01

    A Mn-quartzite was found as a layer of ~0.5 m in diameter within a sequence of garnet-kyanite metapelites intercalated with amphibolites and marbles in the UHP-metamorphic Kimi Complex, Rhodope Massif, Northern Greece. This rock shows an oxidized assemblage quartz + piemontite + garnet + phengite + biotite + K-feldspar + clinopyroxene + calcic amphibole + tourmaline + hematite + titanite + rutile + calcite + apatite + zircon. Zr-in-rutile thermometry yields 690-730° C for cores and ~600° C for discontinuous Zr-poor rims of rutiles. Phengite barometry in the limiting assemblage with K-feldspar + phlogopite + quartz yields ~9-10 kbar for phengite cores (Si = 2.25-3.32 apfu) and ~6 kbar for rims (Si = 3.15 apfu). These low pressures are consistent with the diopside-rich (90-95 mol%) composition of clinopyroxene in spite of bulk Na-contents of 1.1-1.7 wt% Na2O. The Mn-quartzite is rich in Sb, As, W, Te and Ba. This results in the local formation of Sb-Nb-Fe3+-W-rich rutile with up to 13.2 wt% Sb2O5, 1.8 wt% Nb2O5, 7.6 wt% Fe2O3 and 1.1 wt% WO3 which is equivalent to ~14 mol% squawcreekite [Fe3+Sb5+O4]-component. Textures indicate a late and locally confined Sb-W-Nb-Fe3+-enrichment along narrow and irregular veins. Rutiles may contain numerous tiny (≥1-2 μm) inclusions of a Cu-Te phase which is most likely weissite [Cu5Te3]. Secondary titanite replacing rutile shows up to 4.5 wt% As2O5 and 2.0 wt% Sb2O5, respectively. Element correlations are consistent with an exchange Si4+ + Ti4+ = As5+ + M3+. Both phengite and K-feldspar contain significant Ba with up to 0.4 and 5.4 wt% BaO, respectively. Garnets are mostly spessartite-rich solid solutions with up to 10 mol% calderite-[Mn3Fe23+Si3O12] component. The mineralogy and geochemistry of the Mn-quartzite is consistent with an origin as a siliceous deep-sea sediment mixed with polymetallic/ferromanganese crusts. Metamorphosed Fe-Mn rich metasediments with very similar geochemistry have been described from the Penninic

  8. Thermomechanical constraints for the buoyancy-driven exhumation of the ultrahigh-pressure unit of the Dora-Maira Massif (Western Alps)

    NASA Astrophysics Data System (ADS)

    Schmalholz, Stefan M.; Schenker, Filippo L.

    2015-04-01

    The exhumation of UltraHigh-Pressure (UHP) rock units and their incorporation into orogenic wedges exhibiting significantly smaller peak pressures is still incompletely understood. The Dora-Maira Massif in the Western Alps includes the Brosassco-Isasca unit (BIU) whose metamorphic conditions peak at ~40 kbar and ~730 ˚C. Current estimates suggest decompression from the peak conditions to ~10 kbar within ~2 Ma. The BIU has a thickness of ~1 km and a width between 10 and 20 km. The BIU is sandwiched between the San Schiaffredo unit (below) and the Rocca-Soleil unit (above) which both exhibit significantly lower peak metamorphic conditions of ~15 kbar and ~530 ˚C. All three units are usually considered to be from the same pre-alpine paleogeographic domain (i.e. Briançonnais domain). Assuming that metamorphic peak pressures were close to the lithostatic pressure, the San Schiaffredo and Rocca Solei units were buried to ~50 km and the BIU to ~130 km. The exhumation of UHP units is usually explained by buoyancy-driven flow, and two models are frequently considered: 1) Overall return flow of rocks within a distinct subduction channel and 2) upward flow of individual, lighter rock units within a heavier material (termed Stokes flow). However, both models fail to explain the formation of the Dora-Maira Massif and the BIU because model 1) predicts considerably larger volumes of UHP rocks than observed in the Dora-Maira Massif, and model 2) usually incorporates the UHP unit in the overriding plate and not within the orogenic wedge. Here, we present simple two-dimensional thermomechanical numerical models of exhumation by Stokes flow. We performed systematic simulations for linear viscous flow without temperature to constrain the general conditions for which exhumation by Stokes flow is applicable to the Dora-Maira Massif and the BIU. We assumed a dip of the subduction zone of 45 degrees. This requires that the UHP rocks not only exhume vertically by 80 km but also move

  9. Glacial history of a mid-altitude mountain massif: cartography and dating in the Chablais area (France, Switzerland)

    NASA Astrophysics Data System (ADS)

    Perret, A.; Reynard, E.; Delannoy, J.-J.

    2012-04-01

    The Chablais area, considered as one of the cradles of glaciology (de Charpentier, 1841; Morlot, 1859), has been studied for a long time but several questions still remain unresolved. This study aims to reconstruct the glacial history of the massif, in order to explain the glacial landforms, which constitute an important part of the local geomorphology. The study focuses on the last glacial cycle (OIS 5 - OIS 2). The area is primarily associated with the the Valais glacier, by several local glacial flows and, to a lesser extent, by the Giffre glacier. Its position at the interface of the important Valais glacial flow and less powerful local flows is a specificity of the study area, which implies several bifurcations, penetration of the main glacier into laterals valleys, damming situations, and different responses of the various ice bodies to climatic changes. The study is divided in four steps. (1) The first step was to carry out a wide bibliographic survey to identify the state of knowledge, especially in relation to areas previously poorly studied and areas that needed to be reconsidered given developments in dating methods. (2) Field surveys allowed us to complete observations and prepare local geomorphological maps (of glacial landforms and associated phenomena). (3) The third step was to assemble heterogeneous data (old and new maps, Digital Terrain Models, aerial photographies) in a GIS to establish maps of glacial stages. (4) Finally, the absolute and relative chronology of deglaciation (Guitter, 2003) was completed by cosmogenic nuclide dating. Results have allowed us to address the conditions of glacial landform deposition and evolution in a mid-altitude mountain range, and show the need to be prudent in comparing results of different dating methods. Our results suggest that the ages obtained are overall too young in regard to 10Be ages on the northern alpine foreland (Ivy-Ochs et al., 2004) and are in conflict with 14C dates obtained in the area

  10. A Search for Amino Acids and Nucleobases in the Martian Meteorite Roberts Massif 04262 Using Liquid Chromatography-Mass Spectrometry

    NASA Technical Reports Server (NTRS)

    Callahan, Michael P.; Burton, Aaron S.; Elsila, Jamie E.; Baker, Eleni M.; Smith, Karen E.; Glavin, Daniel P.; Dworkin, Jason P.

    2013-01-01

    The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of beta-alanine and gamma-amino-eta-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal eta-omega-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites. A carbon isotope ratio of -24(0/00) +/- 6(0/00) for beta-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of eta-omega-amino acids may be due to a high temperature Fischer-Tropschtype synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.

  11. A search for amino acids and nucleobases in the Martian meteorite Roberts Massif 04262 using liquid chromatography-mass spectrometry

    NASA Astrophysics Data System (ADS)

    Callahan, Michael P.; Burton, Aaron S.; Elsila, Jamie E.; Baker, Eleni M.; Smith, Karen E.; Glavin, Daniel P.; Dworkin, Jason P.

    2013-05-01

    The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of β-alanine and γ-amino-n-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal n-ω-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites (Burton et al. 2012; Chan et al. 2012). A carbon isotope ratio of -24‰ ± 6‰ for β-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of n-ω-amino acids may be due to a high temperature Fischer-Tropsch-type synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.

  12. Structural, mineralogical, and paleoflow velocity constraints on Hercynian tin mineralization: the Achmmach prospect of the Moroccan Central Massif

    NASA Astrophysics Data System (ADS)

    Mahjoubi, El Mahjoub; Chauvet, Alain; Badra, Lakhlifi; Sizaret, Stanislas; Barbanson, Luc; El Maz, Abdelkader; Chen, Yan; Amann, Méderic

    2016-03-01

    The Achmmach tin mineralization (NE of the Moroccan Central Massif) is associated with tourmaline-rich alteration halos, veins, and faults hosted in sandstones and metapelites of the Upper Visean-Namurian. These deposits are reported to be late Hercynian in age and related to the emplacement of late-orogenic granite not outcropping in the studied area. Structural and paragenetic studies of the Achmmach tin deposit were conducted in order to establish a general model of the mineralization. From field constraints, the late Hercynian phase is marked by a transition from transpression to extension with deformation conditions evolving from ductile to brittle environments. The transpression (horizontal shortening direction roughly trending E-W) is coeval with the emplacement of the first tourmaline halos along several conjugated trends (N070, N020, and N120). Thereafter, a tourmaline-rich breccia formed in response to the fracturing of early tourmaline-altered rocks. Subsequently, during the extensional phase, these structures were reactivated as normal faults and breccias, allowing the formation of the main tin mineralization (cassiterite) associated with a wide variety of sulfides (arsenopyrite, chalcopyrite, sphalerite, galena, pyrrhotite, bismuthinite, pyrite, and stannite). This evolution ends with fluorite and carbonate deposition. The hydrothermal fluid flow velocity, calculated by applying statistical measures on the tourmaline growth bands, varies with the lithology. Values are lower in metapelites and higher in breccia. In the general evolution model proposed here, tourmaline alteration makes the rock more competent, allowing for brittle fracturing and generation of open space where the main Sn mineralization was precipitated.

  13. Characterization of wrench tectonics from dating of syn- to post-magmatism in the north-western French Massif Central

    NASA Astrophysics Data System (ADS)

    Cartannaz, C.; Rolin, P.; Cocherie, A.; Marquer, D.; Legendre, O.; Fanning, C. M.; Rossi, P.

    2007-04-01

    This work establishes the relative timing of pluton emplacement and regional deformation from new dating and structural data. (1) Monazite and (2) zircon dating show Tournaisian ages for the Guéret granites [Aulon granite 352 ± 5 Ma (1), 351 ± 5 Ma (2) and Villatange tonalite 353 ± 6 Ma (1)] and Viseo-Namurian ages for the north Millevaches granites [Chavanat granite 336 ± 4 Ma (1), Goutelle granite 336 ± 3 Ma (1), Royère granite 323 ± 2 Ma (1) and 328 ± 6 Ma (2), Courcelles granite 318 ± 3 Ma (1)]. The Guéret and Millevaches granites are separated by the N110 Arrènes-la Courtine Shear Zone (ACSZ), composed from West to East by the Arrènes Fault (AF), the North Millevaches Shear Zone (NMSZ) and the la Courtine Shear Zone (CSZ), respectively. Tournaisian Guéret granites experienced a non-coaxial dextral shearing (NMSZ) recorded by the Villatange granite while the Aulon granite (Guéret granite) cuts across this dextral shear zone which thus stopped shearing during Tournaisian time. Visean to Namurian Millevaches granites experienced a coaxial deformation. Therefore, low displacements along the NMSZ and the CSZ occurred at the emplacement time of Chavanat and Pontarion-Royère granites (336-323 Ma). The structural analyses of Goutelle granite emphasizes a deformation related to the dextral Creuse Fault System (CFS) oriented N150-N160. From 360 to 300 Ma, the Z strain axis is always horizontal inferring a wrench setting for these granite emplacements. During this tectonic evolution, the Argentat zone acted as a minor normal fault and is related with a local Middle Visean (340-335 Ma) syn-orogenic extension on the western border of the Millevaches massif.

  14. Se metallomics during lactic fermentation of Se-enriched yogurt.

    PubMed

    Palomo, María; Gutiérrez, Ana M; Pérez-Conde, M Concepción; Cámara, Carmen; Madrid, Yolanda

    2014-12-01

    Selenium biotransformation by lactic acid bacteria during the preparation of Se-enriched yogurt was evaluated. The study focused on the distribution of selenium in the aqueous soluble protein fraction and the detection of selenoamino acids. Screening of selenium in Tris-buffer-urea soluble fraction was carried out by sodium dodecyl sulphate polyacrylamide gel electrophoresis after pre-fractionating with asymmetric field flow fractionation using inductively coupled plasma-mass spectrometry as the detector. Selenium-containing fractions were identified by peptide mapping using nano LC-ESI/LTQMS. Proteins such as thioredoxin, glutaredoxin, albumin, β-lactoglobulin, and lactoperoxidase were identified in the selenium-containing fraction. All these proteins were detected in both the control and the selenium-enriched yogurt except chaperones, which were only detected in the control samples. Chaperones are heat-shock proteins expressed in response to elevated temperature or other cellular stresses. Selenium may have an effect on chaperones expression in Lactobacillus. For the amino acids analysis, selenocysteine was the primary seleno-containing species.

  15. Geological structure and ore mineralization of the South Sopchinsky and Gabbro-10 massifs and the Moroshkovoe Lake target, Monchegorsk area, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Pripachkin, Pavel V.; Rundkvist, Tatyana V.; Miroshnikova, Yana A.; Chernyavsky, Alexey V.; Borisenko, Elena S.

    2015-08-01

    The South Sopchinsky massif (SSM), Gabbro-10 (G-10) massif, and Moroshkovoe Lake (ML) target Monchegorsk area, Kola Peninsula, are located at the junction of the Monchepluton and Monchetundra layered intrusions. The intrusions were studied in detail as they are targets for platinum-group element (PGE) mineralization. The rocks in these targets comprise medium- to coarse-grained mesocratic to leucocratic gabbronorites, medium-grained mesocratic to melanocratic norites and pyroxenites, and various veins mainly comprising norite, plagioclase-amphibole-magnetite rocks, and quartz-magnetite rocks. The veins contain Ni-Cu-PGE mineralization associated with magnetite and chromite. In all targets, the contacts between gabbronorite and norite-pyroxenite are undulating, and the presence of magmatic (intrusive) breccias suggests that these rocks formed through mingling of two distinct magmatic pulses. In places, the gabbronorites clearly crosscut the modal layering of the norites and pyroxenites. Trace element data indicate that the gabbronorites have similar compositions to rocks of the upper part of the Monchetundra intrusion, whereas the norites and pyroxenites resemble rocks from the lower to intermediate stratigraphic levels of the Monchepluton, such as in the Nude-Poaz and Sopcha massifs. Sulfide mineralization in the studied targets principally consists of secondary bornite, millerite, and chalcopyrite. In contrast, the primary sulfide assemblage within the layered sequence of the adjacent Monchepluton is characterized by pentlandite, chalcopyrite, and pyrrhotite. Therefore, the mineralization in the studied targets is interpreted to be of a contact style. We argue that the studied area represents the contact zone between gabbronorites of the Monchetundra intrusion and norites and pyroxenites of the Monchepluton. In addition, the rocks were overprinted by postmagmatic veining and remobilization of contact style sulfide and PGE mineralization.

  16. Magnetic fabric and microstructures of Late Paleozoic granitoids from the North Patagonian Massif: Evidence of a collision between Patagonia and Gondwana?

    NASA Astrophysics Data System (ADS)

    López de Luchi, Mónica G.; Rapalini, Augusto E.; Tomezzoli, Renata N.

    2010-10-01

    Widespread Late Paleozoic magmatism in northern Patagonia is a target to test hypotheses on the long standing question over the origin of Patagonia. In recent years, a dispute over whether it is an accreted crustal block that collided with Gondwana in Paleozoic times or an autochthonous part of South America has taken place. As part of a multidisciplinary study, an integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex and the Early Permian Navarrete Plutonic Complex, both exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W). Other investigated units are the Late Carboniferous Tardugno Granodiorite, the newly defined Cabeza de Vaca Granite and the Late Permian San Martin pluton. Over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility (AMS) measurements. A systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units. Microstructures in the Yaminué Complex are indicative of a transition from magmatic to solid-state deformation. Microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex. The Cabeza de Vaca Granite, intrusive in Yaminué Complex, is the most evolved unit and records less intense high-temperature solid-state deformation which suggests that the stress field that controlled the emplacement of the Yaminué Complex outlasted it. According to petrologic and structural considerations, the Navarrete Plutonic Complex has been subdivided into three facies, i.e. Robaina, Guanacos and Aranda, respectively. Microstructures of the Navarrete Plutonic Complex are mostly magmatic to submagmatic, versus the solid-state fabric that characterizes the Robaina facies at the contact with the Yaminué Complex. Combined analyses of AMS and microstructural data lead us to suggest that the Yaminué Complex

  17. A re-analysis of 533 rockfalls occurred since 2003 in the Mont Blanc massif for the study of their relationship with permafrost

    NASA Astrophysics Data System (ADS)

    Ravanel, Ludovic; Magnin, Florence; Deline, Philip

    2015-04-01

    Rockfall is one of the main natural hazards in high mountain regions and its frequency is growing, especially since two decades. Collapses at high elevation are with an increasing certainty assumed to be a consequence of the climate change through the warming permafrost. In the Mont Blanc massif, data on present rockfalls (occurrence time when possible, accurate location, topographical and geological settings, volume, weather and snow conditions) were acquired for 2003 and for the period 2007-2014 thanks to a satellite image of the massif and a network of observers in the central part of the massif, respectively. The study of the 533 so-documented rockfalls shows a strong correlation at the year scale between air temperature and rockfall. Along with this data acquisition, a statistical model of the Mean Annual Rock Surface Temperature (MARST) for the 1961-1990 period has been implemented on a 4-m-resolution DEM of the Mont Blanc massif. The model runs with Potential Incoming Solar radiation (PISR) calculated with GIS tools and air temperature parameters computed from Chamonix Météo France records. We cross here the data on rockfalls with the permafrost distribution model to show that: (i) rockfall occurs mainly over modeled negative MARST (context of permafrost); (ii) simulated warm permafrost areas (> -2°C) are the most affected by instabilities; (iii) as the 1961-1990 period is supposed to be representative of the conditions at depth that are not affected by the climate warming during the two last decades, the latest results are mainly valuable for rockfalls related to pluri-decadal signal; and (iv) the higher (close to 0°C) the MARST, the deeper the detachment (possibly related to the deepening of the permafrost active layer). These results and field observations confirm that warming permafrost corresponds to the main required configuration for rockfall triggering at high elevation. In addition, we show that rockfalls for which ice observed in their scar

  18. Applicability of the RSCM geothermometry approach in a complex tectono-metamorphic context: The Jebilet massif case study (Variscan Belt, Morocco)

    NASA Astrophysics Data System (ADS)

    Delchini, Sylvain; Lahfid, Abdeltif; Plunder, Alexis; Michard, André

    2016-07-01

    The Raman Spectroscopy of Carbonaceous Materials (RSCM) geothermometry approach allows determining the peak temperature recorded by metasediments through their metamorphic history. This technique, however, has been calibrated using Meso-Cenozoic metapelitic rocks that underwent a single metamorphic cycle. Until now, the reliability of the RSCM method has never been demonstrated for contexts with superposition of regional and contact metamorphism, such as many Variscan contexts. The present study aims at testing the applicability of the RSCM method to these polyphased metamorphism terrains and at investigating the cumulative molecular transformations of carbonaceous materials related to metamorphic superposition. To address the above issues, samples were collected in the Variscan Jebilet massif of the Moroccan Meseta. This massif was first affected by a regional, greenschist facies metamorphic event (D1 phase), and then by a higher-T, regional and contact metamorphism that reached the hornfels/amphibolite facies conditions (D2 and D2/D3 phases). Mineralogical, thermobarometric and RSCM methods have been used in this study to determine the peak T recorded by the studied rocks. The results obtained for greenschist facies metapelitic rocks show a good agreement between the mineralogical assemblage Chlorite-Phengite-Felspar-Quartz and the Raman temperatures ranging from 330 to 394 ± 50 °C. In the metapelitic rocks that underwent higher metamorphism grades (hornfels/amphibolite facies), four dominant mineral assemblages were observed: (1) Chlorite-Biotite, (2) Cordierite-Biotite, (3) Andalusite-Garnet-Bt, and (4) Andalusite-Cordierite-Biotite. The corresponding Raman temperatures vary respectively between 474 ± 50 °C and 628 ± 50 °C. The pseudo-sections generated for samples from the hornfels/amphibolite facies confirmed the peak temperatures measured by the RSCM method. Our results do not support clear evidence of potential molecular cumulative effect on CM

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

    USGS Publications Warehouse

    Amelin, Y.V.; Ritsk, E. Yu; Neymark, L.A.

    1997-01-01

    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 with ??Nd = +6.6 to +7.1 and ??Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit: ??Nd = + 4.6 to + 6.1 and ??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 basaltic

  20. Liquidus Projections of Bi-Se-Ga and Bi-Se-Te Ternary Systems

    NASA Astrophysics Data System (ADS)

    Lin, Po-han; Chen, Sinn-wen; Hwang, Jenn-dong; Chu, Hsu-shen

    2016-06-01

    This study determines the liquidus projections of both Bi-Se-Ga and Bi-Se-Te ternary systems which are constituent ternary systems of promising Bi-Se-Te-Ga thermoelectric materials. Ternary Bi-Se-Ga and Bi-Se-Te alloys are prepared. Their primary solidification phases are experimentally determined, and thermal analysis experiments are carried out. The liquidus projections are determined based on the ternary experimental results and phase diagrams of constituent binary systems. The Bi-Se-Ga system includes seven primary solidification phases, Bi, Ga, GaSe, Ga2Se3, Se, Bi2Se3, and (Bi2)n(Bi2Se3)m. In the Bi-Se-Te system, there are five primary solidification phases, Bi, (Bi2)n(Bi2Te3)m, Bi2(Se,Te)3, (Se,Te), and (Bi2)n(Bi2Se3)m. Both the (Bi2)n(Bi2Te3)m and (Bi2)n(Bi2Se3)m phases are not a single phase, but a collection of series undetermined phases. Large miscibility gaps are observed in the Bi-Se-Ga system. The temperatures of the invariant reactions, Liquid + Bi + GaSe = Ga and Liquid + Ga2Se3 = Bi + GaSe, are at 495 K (222 °C) and 533 K (260 °C), respectively.

  1. Establishing the geometry and nature of sediments trapped in either natural or artificial dam lakes in contrasted drainage basins from Western Europe (French Massif Central and Pyrenees)

    NASA Astrophysics Data System (ADS)

    Chapron, Emmanuel; Chassiot, Léo; Zouzou, Claude; Simonneau, Anaelle; Galop, Didier; Di Giovanni, Christian

    2016-04-01

    Lacustrine sedimentary archives from artificial dam lakes are poorly documented both in terms of basin fill geometries and dominating sedimentary processes. In order to better understand their sensitivities to regional environmental changes, we performed a similar multidisciplinary study of French natural and artificial dam lakes in contrasted drainage basins from the volcanic Massif Central (lakes Aydat and Crégut) and two granitic sectors of the northern Pyrenees (lakes Fourcat and Orédon). Our approach combined high-resolution sub bottom profiling (14 kHz and 4 kHz chirp) and a detailed study of sediment cores based on qualitative and quantitative analysis (radiographies, sediment physical and chemical properties) together with radionuclide and radiocarbon dates. In all cases either changes in land uses within the drainage basin or the flooding of natural lakes by dams and the production of hydroelectricity induced changes in sedimentation rates and modes. Human activities affecting either the catchment or the lake itself favored enhanced clastic sediment supply in the lake basins and/or higher and fluctuating lake levels. Subaquatic slopes failures are also identified in Lake Aydat formed by a lava flow 8.5 kYrs ago and in glacial lakes Crégut (Massif Central) and Orédon (Pyrenees) now used to produce hydroelectricity and suggest that lake level changes and ground accelerations during earthquakes can remobilize distinct sectors of the basin fills and not only deltaic environments.

  2. Interaction between tectonic and erosion processes on the morphogenesis of an Alpine valley: geological and geophysical investigations in the lower Romanche valley (Belledonne massif, western Alps)

    NASA Astrophysics Data System (ADS)

    Le Roux, Olivier; Schwartz, Stéphane; Gamond, Jean François; Jongmans, Denis; Tricart, Pierre; Sebrier, Michel

    2010-03-01

    In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides, from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone (SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited structures, the BMF and the SFZ.

  3. ZnSe/CdSe Superlattice Nanowires by Catalyst-assisted Molecular Beam Epitaxy

    SciTech Connect

    Karczewski, G.; Dluzewski, P.; Kret, S.; Klopotowski, L.; Wojtowicz, T.

    2007-04-10

    We report on Au catalyst-assisted molecular beam epitaxy growth and properties of pure ZnSe and ZnSe/CdSe superlattice nanowires. In particular, we concentrate our attention on the morphological characterization by transmission and scanning electron microscopy of pure ZnSe NWs and we compare their optical properties with those of ZnSe/CdSe superlattice NWs fabricated at the same technological conditions.

  4. Tectonic record, magmatic history and hydrothermal alteration in the Hercynian Guérande leucogranite, Armorican Massif, France

    NASA Astrophysics Data System (ADS)

    Ballouard, C.; Boulvais, P.; Poujol, M.; Gapais, D.; Yamato, P.; Tartèse, R.; Cuney, M.

    2015-04-01

    The Guérande peraluminous leucogranite was emplaced at the end of the Carboniferous in the southern part of the Armorican Massif. At the scale of the intrusion, this granite displays structural heterogeneities with a weak deformation in the southwestern part, whereas the northwestern part is marked by the occurrence of S/C and mylonitic extensional fabrics. Quartz veins and pegmatite dykes orientations as well as lineations directions in the granite and its country rocks demonstrate both E-W and N-S stretching. Therefore, during its emplacement in an extensional tectonic regime, the syntectonic Guérande granite has probably experienced some partitioning of the deformation. The southwestern part is characterized by a muscovite-biotite assemblage, the presence of restites and migmatitic enclaves, and a low abundance of quartz veins compared to pegmatite dykes. In contrast, the northwestern part is characterized by a muscovite-tourmaline assemblage, evidence of albitization and gresenization and a larger amount of quartz veins. The southwestern part is thus interpreted as the feeding zone of the intrusion whereas the northwestern part corresponds to its apical zone. The granite samples display continuous compositional evolutions in the range of 69.8-75.3 wt.% SiO2. High initial 87Sr/86Sr ratios and low εNd(T) values suggest that the peraluminous Guérande granite (A/CNK > 1.1) was formed by partial melting of metasedimentary formations. Magmatic evolution was controlled primarily by fractional crystallization of K-feldspar, biotite and plagioclase (An20). The samples from the apical zone show evidence of secondary muscovitization. They are also characterized by a high content in incompatible elements such as Cs and Sn, as well as low Nb/Ta and K/Rb ratios. The apical zone of the Guérande granite underwent a pervasive hydrothermal alteration during or soon after its emplacement. U-Th-Pb dating on zircon and monazite revealed that the Guérande granite was emplaced

  5. Origin of Au-bearing rodingite in the Karabash massif of alpine-type ultramafic rocks in the southern Urals

    NASA Astrophysics Data System (ADS)

    Murzin, V. V.; Varlamov, D. A.; Ronkin, Yu. L.; Shanina, S. N.

    2013-07-01

    The rodingite belt in the Karabash massif situated 40 km north of Miass is continuously traced for 2.5 km along its central part. Rodingites bear up to 1% sulfide disseminations and gold particles with high Cu content (up to 40 wt %) throughout the belt. The central part of the rodingite belt is especially rich in gold, which was mined at the Zolotaya Gora (Gold Mountain) deposit. The Au-bearing rodingite belt is zonal and was formed during three stages. The inner zone is composed of chlorite-andradite-diopside rock of the first stage, which is crosscut by diopside veinlets of the second stage and calcite veinlets of the third stage. The intermediate zone consists of fine-grained chloritolite of the first stage and coarse-grained chlorite veinlets of the second stage. The outer zone of the metasomatic column is occupied by antigorite and chrysotile-lizardite serpentinites. No relict rocks or minerals of the replaced protolith have been established except sporadic Cr-spinel grains. Native gold was being deposited during all periods of rodingite formation. In terms of the currently adopted concept of evolution of the Ural Foldbelt, the Sm-Nd isochron age of rodingite estimated at 369.4 ± 8.8 Ma corresponds to the period of collisional compression of Silurian-Devonian oceanic and island-arc complexes and upward pushing out of a block of the melanocratic basement underlying these complexes. A proposed model of rodingite formation is based on ore mineralogy, REE geochemistry, and thermobarogeochemical and isotopic study of minerals. It is suggested that in contrast to the barren bimetasomatic rodingite replacing dikes, the studied rodingite are considered to be fissure veins accompanied by metasomatic alteration of host serpentinite. The estimation of initial isotopic composition of fluid components indicates that the ore-bearing fluid is of metamorphic origin (δDfl = -4 to -13‰ and δ18Ofl = 5.9 to 8.3‰). The fluid was formed as a product of dehydration of

  6. Stable isotopic evidence for large-scale seawater infiltration in a regional metamorphic terrane; the Trois Seigneurs Massif, Pyrenees, France

    NASA Astrophysics Data System (ADS)

    Wickham, Stephen M.; Taylor, Hugh P.

    1985-10-01

    Oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a Hercynian metamorphic sequence in the Trois Seigneurs Massif, Pyrenees, France, indicate that all lithologies at higher metamorphic grades than the “andalusite in” isograd have relatively homogeneous δ 18O values. The extent of homogenization is shown by the similarity of δ 18O values in metacarbonates, metapelites and granitic rocks (+11 to +13), and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies. These values contrast with the δ 18O values of metapelites of lower metamorphic grade ( δ 18O about +15). Homogenization was caused by a pervasive influx of hydrous fluid. Mass-balance calculations imply that the fluid influx was so large that its source was probably high-level groundwaters or connate formation water. Hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at δD=-25 to -30, suggesting a seawater origin. Many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water-rich fluid, the composition of which was externally buffered. Deep penetration of surface waters in such environments has been hitherto unrecognized, and may be a key factor in promoting major anatexis of the continental crust at shallow depth. Three types of granitoid are exposed in the area. The leucogranites and the biotite granite-quartz diorite are both mainly derived from fusion of local Paleozoic pelitic metasediment, because all these rocks have similar whole-rock δ 18O values (+11 to +13). The post-metamorphic biotite granodiorite has a distinctly different δ 18O (+9.5 to +10.0) and was probably derived from a deeper level in the crust. Rare mafic xenoliths within the deeper parts of the biotite granite-quartz diorite also have different δ 18O (+8.0 to +8.5) and possibly represent

  7. 3D Detection, Quantification and Correlation of Slope Failures with Geologic Structure in the Mont Blanc massif

    NASA Astrophysics Data System (ADS)

    Allan, Mark; Dunning, Stuart; Lim, Michael; Woodward, John

    2016-04-01

    A thorough understanding of supply from landslides and knowledge of their spatial distribution is of fundamental importance to high-mountain sediment budgets. Advances in 3D data acquisition techniques are heralding new opportunities to create high-resolution topographic models to aid our understanding of landscape change through time. In this study, we use a Structure-from-Motion Multi-View Stereo (SfM-MVS) approach to detect and quantify slope failures at selected sites in the Mont Blanc massif. Past and present glaciations along with its topographical characteristics have resulted in a high rate of geomorphological activity within the range. Data for SfM-MVS processing were captured across variable temporal scales to examine short-term (daily), seasonal and annual change from terrestrial, Unmanned Aerial Vehicle (UAV) and helicopter perspectives. Variable spatial scales were also examined ranging from small focussed slopes (~0.01 km2) to large valley-scale surveys (~3 km2). Alignment and registration were conducted using a series of Ground Control Points (GCPs) across the surveyed slope at various heights and slope aspects. GCPs were also used to optimise data and reduce non-linear distortions. 3D differencing was performed using a multiscale model-to-model comparison algorithm (M3C2) which uses variable thresholding across each slope based on local surface roughness and model alignment quality. Detected change was correlated with local slope structure and 3D discontinuity analysis was undertaken using a plane-detection and clustering approach (DSE). Computation of joint spacing was performed using the classified data and normal distances. Structural analysis allowed us to assign a Slope Mass Rating (SMR) and assess the stability of each slope relative to the detected change and determine likely failure modes. We demonstrate an entirely 3D workflow which preserves the complexity of alpine slope topography to compute volumetric loss using a variable threshold. A

  8. Water content and hydrogen behaviour during metasomatism in the uppermost mantle beneath Ray Pic volcano (Massif Central, France)

    NASA Astrophysics Data System (ADS)

    Denis, Carole M. M.; Alard, Olivier; Demouchy, Sylvie

    2015-11-01

    To understand the deep cycle of water, upper mantle water content and distribution between nominally anhydrous minerals (NAMs) and hydrous minerals (e.g., amphibole) must be constrained. We need then to understand H behaviour during mantle melting and metasomatism. Major, minor and trace element compositions including water contents were obtained on ten xenoliths of spinel-bearing peridotites from the Ray Pic locality, in the Southern part of the Massif Central (France). The sample suite investigated here is composed of rather fertile lherzolites (89.4 ≤ Fo ≤ 90.8%; 11.3 ≤ cr# in spinel ≤ 21.1%; 0.942 ≤ [Yb]cpx ≤ 1.90 ppm; cpx: clinopyroxene), which can be best explained by batch melting, with degree of melting between 3 and 10%. These xenoliths contain up to 8% modal amphibole. Three groups are defined as a function of the amphibole modal abundance (above or below 1%) and equilibrium temperature (above or below 1000 °C). Results show no clear positive correlation between modal metasomatism (amphibole) and incompatible element enrichment in cpx. Trace element compositions in cpx show strong enrichments of the most incompatible elements (e.g., (La/Sm)PM as high as 15.7; PM: normalised to primitive mantle values), but strong negative anomalies of the high field strength elements (e.g., (Th/Nb)PM as high as ~ 680). Such trace element fractionations are usually ascribed to the so-called carbonatitic metasomatism involving the percolation of small volume melts which are enriched in volatiles. The hydrogen concentrations in cpx range from 203 to 330 ppm wt. H2O, in orthopyroxene from 66 to 160 ppm wt. H2O and in olivine from 2 to 6 ppm wt. H2O. These values are within the common concentration range of other spinel-bearing peridotites. Amphiboles contain 1.9 ± 0.5 wt.% of H2O. The effect of metasomatism on water abundances in NAMs is not straightforward. Hydrous metasomatism (i.e., leading to the crystallisation of OH-bearing amphibole) has no effect on the

  9. Contribution of the RSCM geothermometry to understanding the thermal history of the Hajjar deposit (Guemassa massif, Morocco).

    NASA Astrophysics Data System (ADS)

    Delchini, S.; Lahfid, A.; Ramboz, C.; Branquet, Y.; Maacha, L.

    2015-12-01

    The knowledge of the thermal history of rocks is a key point for reconstructing the history of basins or mountain belts for mining or petroleum industries. Conventional techniques such as mineralogy, isotopic analysis, provide basic data concerning the maturity degree of organic matter. Recent new geothermometric approach based on the Raman Spectroscopy of Carbonaceous Materials (RSCM) has been developed. This approach allows successfully estimating peak temperatures of advanced diagenesis to high-grade metamorphic rocks. The aim of this study is mainly to apply the RSCM geothermometry for 3D paleotemperatures cartography in the Guemessa area, a Hercynian massif located at 35 Km SW of Marrakech, Morocco. This area composed of the carboniferous metasediments, underwent tectonic, metamorphic and hydrothermal events that explain the presence of several base metal deposits like Zn-Pb-Cu Hajjar mine. Combining RSCM data and classical methods of thermometry like fluid inclusions and chlorite thermometry will allow a good understanding of thermal history of Hajjar deposits. The samples used in this study were collected around the Hajjar mine and from different depths in the Hajjar body collected in the footwall and hangingwall of the massive ore. Our peak temperature estimates show values superior to 500°C. These temperatures differ from the ones obtained by other classical methods, which are not higher than 450°C. Nevertheless, fluid inclusion homogenization temperatures of 450°C represent minimum trapping temperature conditions, since the fluids were trapped above boiling conditions. Also, 450°C represents minimum thermic condition for the biotite isograd. Higher Raman temperatures obtained in this work confirm the hypothesis of a late heat flow related to a deep granitic intrusion. This intrusion could be closer to the Hajjar deposit which would explain the higher Raman temperature around the mineralization. It is important to properly evaluate the consequences of

  10. A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites

    USGS Publications Warehouse

    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). The origin of these typically discordant ore deposits remains as enigmatic as the magmatic evolution of their host rocks. The deposits clearly have a magmatic origin, hosted by an age-constrained unique suite of rocks that likely are the consequence of a particular combination of tectonic circumstances, rather than any a priori temporal control. Principal ore minerals are ilmenite and hemo-ilmenite (ilmenite with extensive hematite exsolution lamellae); occurrences of titanomagnetite, magnetite, and apatite that are related to this deposit type are currently of less economic importance. Ore-mineral paragenesis is somewhat obscured by complicated solid solution and oxidation behavior within the Fe-Ti-oxide system. Anorthosite suites hosting these deposits require an extensive history of voluminous plagioclase crystallization to develop plagioclase-melt diapirs with entrained Fe-Ti-rich melt rising from the base of the lithosphere to mid- and upper-crustal levels. Timing and style of oxide mineralization are related to magmatic and dynamic evolution of these diapiric systems and to development and movement of oxide cumulates and related melts. Active mines have developed large open pits with extensive waste-rock piles, but

  11. Early differentiation of the Moon: Experimental and modeling studies and experimental and modeling studies of massif anorthosites

    NASA Technical Reports Server (NTRS)

    Longhi, John

    1994-01-01

    NASA grant NAG9-329 was in effect from 3/1/89 to 8/31/94, the last 18 months being a no-cost extension. While the grant was in effect, the P.I., coworkers, and students gave 22 talks and poster sessions at professional meetings, published 12 articles in referred journals (one more is in press, and another is in review), and edited 2 workshop reports relevant to this project. Copies of all the publications are appended to this report. The major accomplishments during the grant period have derived from three quarters: 1) the application of quantitative models of fractional crystallization and partial melting to various problems in planetary science, such as the petrogenesis of picritic glasses and mare basalts and the implications of the SNC meteorites for martian evolution; 2) an experimental study of silicate liquid immiscibility relevant to early lunar differentiation and the petrogenesis of evolved highlands rocks; and 3) experimental studies of massif anorthosites and related rocks that provide terrestrial analogs for the proposed origin of lunar anorthosites by multistage processes. The low-pressure aspects of the quantitative models were developed by the P.I. in the 1980s with NASA support and culminated with a paper comparing the crystallization of terrestrial and lunar lavas. The basis for the high-pressure modifications to the quantitative models is a data set gleaned from high pressure melting experiments done at Lamont and is supplemented by published data from other labs that constrain the baric and compositional dependences of various liquidus phase boundaries such as olivine/orthopyroxene, relevant to the melting of the mantles of the terrestrial planets. With these models it is possible to predict not only the thermal and compositional evolution of magmatic liquids ranging in composition from lumar mare basalt to terrestrial calc-alkaline basalts, but also the small increments of fractional melting that are produced when mantle rises adiabatically

  12. The destabilization of the Pilatte hut (2577 m a.s.l. - Ecrins massif, France), a paraglacial process?

    NASA Astrophysics Data System (ADS)

    Ravanel, Ludovic; Dubois, Laurent; Fabre, Sébastien; Duvillard, Pierre-Allain; Deline, Philip

    2015-04-01

    The Pilatte hut is located at 2572 m a.s.l. at Saint-Christophe-en-Oisans (south of the Ecrins Massif, France), at a 3-hours-walk from La Bérarde hamlet. Its capacity is 120 beds for hikers and climbers who are engaged in the ascent of Les Bans (3669 m a.s.l.). Built on a rocky ledge on the right side of the Pilatte Glacier (A = 2.64 km2; L = 2.6 km), it currently dominates the glacier by about 150 m. This relief results from the retreat of the glacier since the end of the Little Ice Age, as the till around the hut was deposited during this stage. The glacier has lost about 1.8 km in length during the same period. A first wooden hut was built in 1925 and presently serves as a winter refuge. In 1954, the growth of mountain activities led to the construction of a larger hut made of cemented stones. An extension to the west made of reinforced concrete was built in 1994. But in the late 1980s, severe damages to the 1954 part of the building were already recognized: vertical cracks lining the north and south facades, ,subsidence (c. 10 cm downstream) of the ground floor, cracked interior walls. Currently, the evolution of the instability is monitored by several methods: - since 2003, cracks in the building are surveyed by 25 Saugnac gauges, while an outside fracture in the rock is surveyed by a simple extensometer; - since 2009, 8 strain gauges allow to annually measure displacements along the main fractures that delimit the unstable rock mass; - a high-resolution topographic data set acquired by terrestrial laser scanning from the surface of the glacier in July 2014 has completed the monitoring. The acting process is a translational slide of a rock mass with a volume of about 300 000 m3, initiated by the glacier shrinkage. Therefore, it has to be considered as a paraglacial process. Even if the slide velocity is presently decreasing, a demolition project of the hut is under consideration in favor of a new building on the right side of the valley, 800 m downstream the

  13. Fluid-present disequilibrium melting in Neoarchean arc-related migmatites of Daeijak Island, western Gyeonggi Massif, Korea

    NASA Astrophysics Data System (ADS)

    Lee, Yuyoung; Cho, Moonsup

    2013-10-01

    The melting process of meta-igneous rocks was investigated via field, petrographic and geochemical analyses of the Neoarchean (~ 2.51 Ga) migmatite complex in Daeijak Island, western Gyeonggi Massif. This complex consists primarily of garnet-free amphibolites and tonalitic migmatites, both of which contain hornblende, plagioclase and quartz as major constituents. Neosomes and leucosomes in the migmatite have dioritic-tonalitic and tonalitic-trondhjemitic compositions, respectively. Compositions of hornblende (XFe = 0.39-0.42) and plagioclase (An24-27) vary little between the neosomes and leucosomes. The amphibolites show distinct depletions in Nb, Ta, Zr, and Ti relative to large ion lithophile elements, suggesting an arc-related origin for their basaltic protolith. Leucosomes have lower contents of K2O, MgO, FeO*, TiO2, Zr, Rb, and rare earth elements (REE) than amphibolites and neosomes, but are higher in SiO2, Na2O, and Sr contents. Leucosomes and neosomes have positive [(Eu/Eu*)N = 1.32-7.26] and negative (0.71-0.97) Eu anomalies, respectively, which are attributed to the variable degree of plagioclase fractionation during the partial melting. The P-T condition for the migmatite formation was estimated to be ~ 700-730 °C and 4.7-5.5 kbar, primarily based on the hornblende-plagioclase thermobarometry and phase equilibria. Various lines of textural evidence, such as the channel flow of melt along migmatitic layers and the segregation of melt into shear bands or boudin necks suggest a syn-deformation crystallization of melt. Chemical disequilibrium in migmatites is documented not only by petrographic and geochemical data but also by the REE modeling between melt product and source rock. Disequilibrium process is most likely attributed to the rapidity of melt extraction or migration, compared to chemical diffusion rate. In summary, the fluid-present disequilibrium melting of dioritic-tonalitic protoliths has produced tonalitic-trondhjemitic leucosomes in a dynamic

  14. The quartz-dioritic Hospitais intrusion (SW Iberian Massif) and its mafic microgranular enclaves - Evidence for mineral clustering

    NASA Astrophysics Data System (ADS)

    Moita, P.; Santos, J. F.; Pereira, M. F.; Costa, M. M.; Corfu, F.

    2015-05-01

    The Hospitais pluton is an elliptical body, with its long axis oriented WNW-ESE, that belongs to the Évora Massif (Iberian Variscan belt). This intrusion has a quartz-dioritic composition, with plagioclase, quartz, amphibole (hornblende, but locally also cummingtonite) and biotite as the main mineral phases. Mafic microgranular enclaves in the quartz-diorite show the same minerals as the host, but with a greater abundance of amphibole and lower proportions of felsic minerals, especially quartz. U-Pb zircon ages obtained in one sample of the quartz-diorite and one sample of a mafic microgranular enclave gave identical ages, within error, of ca. 337 Ma. Geochemical data show that the quartz-diorite has a calc-alkaline signature with moderate enrichment in LILE/HFSE ratio (ThN/YN: 2.71-11.43) and clear negative Ti and Nb-Ta anomalies (ThN/NbN: 1.33-6.22). The composition of the enclaves shows that they do not represent direct melt compositions. Instead, their geochemical features (namely the abundances of Fe and Mn in variation diagrams and REE patterns in primitive mantle normalized diagrams) suggest that they correspond to mineral clustering formed during the previous crystallization stage of quartz-dioritic magma. Overlapping of mineral chemistry and Sr-Nd isotope compositions in the quartz-diorite and the enclaves provides further support to that conclusion. The values for [87Sr/86Sr]i and εNdi (calculated for 337 Ma) in the quartz-diorite vary from 0.706147 to 0.706491 and from - 1.87 to - 3.22, respectively. This isotope composition may be explained either by differentiation of a mafic magma extracted from a mantle wedge enriched by long lasting subduction processes, or by mixing between a mafic magma from a depleted mantle source and a crustal melt. In the second case, the most likely source for the felsic component should be meta-igneous rocks, like the Lower Cambrian Alcáçovas orthogneisses that outcrop in neighbouring areas.

  15. Characteristics and origin of organic matter and basal respiration of soils from Majella massif (Central Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Basili, M.; Cioci, C.; Cocco, S.; Agnelli, A.; di Peco, D.; Ferraris, P.; Corti, G.

    2009-04-01

    The effects of the global climate change on the soil organic matter (SOM) are still open to debate. Many studies hypothesize an increase of the CO2 fluxes from the soil following the rise of air temperature, especially for the high latitude soils where the low temperatures have a protective effect on the SOM, holding the mineralization reactions back. We studied the feedback between soil and climate change in the Mediterranean environments, on patterned ground soils and soils developed from glacial lacustrine sediments found in the high-elevated areas (2500 m a.s.l.) of Majella massif (Central Apennines, Italy). Here, several profiles were opened and the soil described and sampled according to the recognized horizons. The samples were characterised according to the routine analyses and the SOM extracted according to the International Humic Substances Society protocol. The obtained humic and fulvic acids were characterised for elemental composition and by Fourier-transform infrared (FT-IR) spectroscopy. Further, the basal respiration at 5°C, 20°C and 30°C for 20 days was determined on the samples collected from the superficial horizon of each soil. The extracted humic substances showed a particular composition, being mostly comprised of proteinaceous residues (amides II and III), polysaccarides, and esters and aliphatic compounds. This unusual chemical structure and the paucity of vegetation in the study area could support the hypothesis of a mainly soil animal origin of the SOM, probably due to residues of insects, arachnids and arthropods. In fact, the species belonging to these Orders are abundant in these ecosystems and, further, are often characterised by the presence of compounds, such as glycerine and glycoproteins, in their organic fluids that act as antifreezing systems. The basal respiration experiments indicated that the soil microbial community was active at 5°C, while at 20°C or 30°C rather no respiration occurred; further, after 20 days at both

  16. Phase relations in trachytes: implication for magma storage conditions in the Chaîne des Puys (French Massif Central)

    NASA Astrophysics Data System (ADS)

    Martel, C.; Champallier, R.; Prouteau, G.; Pichavant, M.; Arbaret, L.; Balcone-Boissard, H.; Boudon, G.; Boivin, P.; Bourdier, J. L.; Scaillet, B.

    2012-04-01

    Trachytes from the Chaîne des Puys, French Massif Central, have been studied by performing phase equilibria in order to (i) constrain the storage conditions of the trachytic magmas that lead to explosive eruptions (either dome destructions as concentrated or diluted pyroclastic density currents or highly explosive events) and (ii) provide phase relationships and compositions for differentiated alkaline magmas. Phase assemblage, proportion, and compositions have been determined on six trachytes (62-69 wt % SiO2 and 10.5-12.0 wt % alkali) mostly coming from the actual domes dated from 9.2 to 15 Ka and aligned along a 10-km distance in the Chaîne des Puys. All samples contain ~23-30 % of phenocrysts, mainly consisting of plagioclase (15-17 % and K-feldspars for the two SiO2-richest samples), biotites (2-6 % except in the SiO2-poorest sample, where it is absent), and Fe-Ti oxides (1-3 %). The three SiO2-poorest samples also contain ~2 % of amphibole and the SiO2-richest one has 1 % of clinopyroxene. All samples have apatite and zircon as minor phases and sphene for the SiO2-richest one. Glasses (melt inclusions and residual glasses) analysed in pumices resulting from highly explosive events, show trachytic to rhyolitic compositions (65-73 wt % SiO2 and 10.5-13.0 wt % alkali). Analyses of melt inclusions (EMP by-difference method) and the biotite+K-feldspar+magnetite hygrobarometer both suggest pre-eruptive H2O contents up to 7-8 wt %, which are so far the highest contents ever reported for alkaline liquids. The melt inclusions also contain ~3400 ppm chlorine, ~700 ppm fluorine, and ~300 ppm sulphur (EMP analyses). Phase equilibria of six representative trachytes have been performed between 200 and 400 MPa, 700-900°C, H2O saturation, and oxygen fugacity from NNO-1 to NNO+1. The comparison between the natural and experimental products suggests magma storage conditions at pressures of 300-350 MPa, temperatures increasing from 700 to 825°C with decreasing bulk SiO2

  17. Paleoproterozoic pge-bearing Monchetundra massif (Fennoscandian shield): isotope-geochemical Nd-Sr features of the mafic rocks

    NASA Astrophysics Data System (ADS)

    Kunakkuzin, Evgeniy; Borisenko, Elena; Bayanova, Tamara; Nerovich, Lydmila; Serov, Pavel; Elizarov, Dmitry

    2016-04-01

    The Monchetundra massif (MM) is situated in the central part of the Kola Peninsula (northwest of Russia) and belongs to the Paleoproterozoic East-Scandinavian Large Igneous province (ESCLIP) enclosing Cr, Ni, Cu, Co, Ti, V and PGM-bearing deposits (Mitrofanov, 2009). There are two belts of Paleoproterozoic layered intrusions in the Baltic (Fennoscandian) Shield: the Northern (Kola) Belt and the Southern (Fenno-Karelian) Belt. The last includes mafic-ultramafic intrusions of Finland (the Tornio-Näränkävaara Belt), Sweden (Tornio intrusion) and Russia (Olanga complex). The Northern Belt includes intrusions of the Kola Peninsula, the most famous of them are Mt Generalskaya, Monchegorsk Layered Complex, Fedorovo-Pansky. The MM is traditionally attributed to the Main Range Complex and together with Monchegorsk Layered Complex occurs in the central part of the Kola Belt. According to the new isotopic Nd-Sr data, the MM mafic rock groups of different ages are characterized by various isotopic and geochemical characteristics. These new Sm-Nd isotopic data obtained for the main types of the MM mafic rocks indicate that most of the rocks with negative ɛNd values have older TDM values from 3.4 to 3.1 Ga, and most of the rocks with positive ɛNd values have younger TDM values from 3.0 to 2.7 Ga. A special type of gabbronorites with high positive ɛNd values and TDM of ca. 2.7 Ga were found among the MM mafic rocks. According to isotopic Nd data, these rocks were formed from a depleted mantle source, but at present there are no enough geological and geochemical data to determine a mantle source for them. Thus, the isotope-geochemical Nd-Sr data indicate that the MM mafic rocks were formed from a mantle source enriched in lithophile elements. The variations of isotopic values in different groups of rocks are likely to cause by the evolution of the long life mantle reservoir during the plume-lithospheric interaction. The studies were supported by the Russian Foundation of

  18. Pollen rain and subfossil pollen spectra of the Mongun-Taiga mountain massif (South-Eastern Altai)

    NASA Astrophysics Data System (ADS)

    Kolunchukova, M.; Savelieva, L. A.

    2011-12-01

    Palynological analysis is commonly used for the vegetation and climatic reconstructions. It is known that there are many factors influenced on pollen spectra formation and it is necessary to study in detail the modern spectra from the investigated area which form interpretation base of fossil samples. In July 2010, during the expedition to the Mongun-Taiga mountain massif (South-Western Tuva, the Altai Mountains) the collections of modern surface samples from diverse plant communities were made to depict the present-day pollen rain. For this purpose a longitudinal profile at the altitudes of 2300-3100 m was laid. The detailed geobotanical descriptions on each sampling site were made. Soil samples were taken from 1.5 cm depth and catching of pollen rain was carrying out on glass plates in an area of 108 cm2. A total of 9 samples were treated for pollen analysis, pollen residues mounted in glycerin were analyzed under the microscope. The interpretation of the pollen and spores was performed using pollen atlases and pollen diagrams were made. All samples are distorted by strange pollen of arboreal. The Pinus pollen content varies between 20% and 80%. Single grains of Piceae, Alnus, Alnuster are found. Some non-arboreal pollen like Artemisia and Chenopodiaceae is presented in all spectra, their abundance varies between 1-20 %. Although this species grow within researching area, they are found not in all described vegetative associations. Connection between projective cover of local species and strange pollen's participation in spectra formation is found: low projective cover causes less pollen production and amount of strange pollen (generally arboreal) increases. Domination of some local species is not reflected by their pollen assemblages. For example abundance of Larix pollen (the main arboreal species within researching area) reaches only 2%, and grains of Dryas are not found at all. It can be explained by bad safety and volatility of their grains. So even single

  19. Gypsum, jarosite, and hydrous iron-phosphate in Martian meteorite Roberts Massif 04262: Implications for sulfate geochemistry on Mars.

    NASA Astrophysics Data System (ADS)

    Greenwood, J. P.

    2008-12-01

    Gypsum has been identified on Mars by MEX OMEGA [1] and jarosite identified via MER-B lander [2] and both minerals are examples of the importance of calcium and iron sulfates in Martian weathering processes. The weathering of Martian basalt to form Ca and iron sulfates should be an important process on Mars. Martian jarosite has been identified in MIL 03346 [3] and Ca-sulfate has been identified in EETA 79001 [4], but both phases have yet to be identified in the same Martian sample