Sample records for facies metamorphic conditions

  1. Granulites by name but eclogite facies by formation conditions: extreme metamorphism recorded by Saxony-type granulites (United States)

    O Brien, P. J.


    The type locality `granulite' from the Saxonian Granulitgebirge is a felsic, granitic to granodioritic rock, composed predominantly of feldspars and quartz along with minor garnet, kyanite and rutile, and exhibiting a strong mylonitic fabric. In such rocks abundant mesoperthitic K-feldspar testifies to the former presence of high temperature (>900^oC) ternary feldspar. In intermediate to mafic layers the common antiperthite, when reconstituted to its single phase precursor, yields unequivocal ultrahigh-temperature (>1000^oC) conditions by feldspar solvus thermometry. The presence of kyanite together with such feldspar requires pressures (>15 kbar) equivalent to mantle depths. In addition, orthopyroxene, where present, is demonstrably of secondary origin. Importantly, experimental results show that the position of the orthopyroxene-out reaction curve for granitic/granodioritic compositions coincides with that of the plagioclase-out reaction in rocks of quartz-tholeiite composition. This means that the orthopyroxene-free felsic `granulites' formed at conditions above those generally taken as defining the start of the eclogite facies. It has long been known that rare mafic lenses contain clinopyroxene with jadeite content approaching or even exceeding that of omphacite. The presence or absence of plagioclase in these omphacite-bearing rocks is purely a function of bulk composition: more quartz tholeiitic rocks are plagioclase-free and are thus eclogites. Likewise, tectonic lenses of garnet peridotites in the granulite massifs are a clear indicator of metamorphism at mantle depths. Recent discoveries have extended the formation depths of some of these rocks even further as coesite (in eclogite) and microdiamond (in granulites) have been discovered in the nearby Erzgebirge. Even more remarkable are consistent ca. 340 Ma zircon ages which, along with other evidence, point to exhumation rates of several mm/a. The presence of garnet peridotites, combined with the

  2. Mineral deformation mechanisms in granulite facies, Sierra de Valle Fértil, San Juan province: evelopment conditions constrained by the P-T metamorphic path

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    Sergio Delpino


    Full Text Available In the Sierra de Valle Fértil, evidence of granulite facies metamorphism have been preserved either in the constitutive associations as in deformation mechanisms in minerals from biotite-garnet and cordierite-sillimanite gneisses, cordierite and garnet-cordierite migmatites, metagabbros, metatonalites-metadiorites and mafic dikes. The main recognized deformation mechanisms are: 1 quartz: a dynamic recrystallisation of quartz-feldspar boundaries, b combination of basal and prism [c] slip; 2 K-feldspar: grain boundary migration recrystallisation; 3 plagioclase: combination of grain boundary migration recrystallisation and subgrain rotation recrystallisation; 4 cordierite: subgrain rotation recrystallisation; 5 hornblende: grain boundary migration recrystallisation. Preliminary geothermometry on gabbroic rocks and the construction of an appropriated petrogenetic grid, allow us to establish temperatures in the range 800-850 C and pressures under 5 Kb for the metamorphic climax. Estimated metamorphic peak conditions, preliminary geothermobarometry on specific lithologic types and textural relationships, together indicate an counter-clockwise P-T path for the metamorphic evolution of the rocks of the area. Ductile deformation of phases resulting from anatexis linked to the metamorphic climax indicates that the higher-temperature ductile event recognized in the study area took place after the metamorphic peak. Evidence of ductile deformation of cordierite within its stability field and presence of chessboard extinction in quartz (only possible above the Qtzα/Qtzß transformation curve, both indicate temperatures above 700 C considering pressures greater than 5 Kb. Based on the established P-T trajectory and the characteristics described above, it can be concluded that deformation mechanisms affecting the Sierra de Valle Fértil rocks were developed entirely within the granulite facies field.

  3. Timing and conditions of regional metamorphism and crustal shearing in the granulite facies basement of south Namibia: Implications for the crustal evolution of the Namaqualand metamorphic basement in the Mesoproterozoic (United States)

    Bial, Julia; Büttner, Steffen; Appel, Peter


    Granulite facies basement gneisses from the Grünau area in the Kakamas Domain of the Namaqua-Natal Metamorphic Province in south Namibia show high-grade mineral assemblages, most commonly consisting of garnet, cordierite, sillimanite, alkali feldspar and quartz. Cordierite + hercynitic spinel, and in some places quartz + hercynitic spinel, indicate granulite facies P-T conditions. The peak assemblage equilibrated at 800-850 °C at 4.0-4.5 kbar. Sillimanite pseudomorphs after kyanite1 and late-stage staurolite and kyanite2 indicate that the metamorphic record started and ended within the stability field of kyanite. Monazite in the metamorphic basement gneisses shows a single-phase growth history dated as 1210-1180 Ma, which we interpret as the most likely age of the regional metamorphic peak. This time coincides with the emplacement of granitic plutons in the Grünau region. The ∼10 km wide, NW-SE striking Grünau shear zone crosscuts the metamorphic basement and overprints high-temperature fabrics. In sheared metapelites, the regional metamorphic peak assemblage is largely obliterated, and is replaced by synkinematic biotite2, quartz, alkali feldspar, sillimanite and cordierite or muscovite. In places, gedrite, staurolite, sillimanite and green biotite3 may have formed late- or post-kinematically. The mylonitic mineral assemblage equilibrated at 590-650 °C at 3.5-5.0 kbar, which is similar to a retrograde metamorphic stage in the basement away from the shear zone. Monazite cores in two mylonite samples are similar in texture and age (∼1200 Ma) to monazite in metapelites away from the shear zone. Chemically distinct monazite rims indicate a second growth episode at ∼1130-1120 Ma. This age is interpreted to date the main deformation episode along the Grünau shear zone and the retrograde metamorphic stage seen in the basement. The main episode of ductile shearing along the Grünau shear zone took place 70-80 million years after the thermal peak metamorphism

  4. Petrology of blueschist facies metamorphic rocks of the Meliata Unit

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    Faryad Shah Wali


    Full Text Available Meliata blueschists originated from basalts, limestones, pelites, psammitic and amphibolite facies basement rocks. Compositionally, the metabasalts have a geochemical signature mostly indicative of a transitional arc-MORB origin, but some mafic rocks having affinity with within plate basalts also present. The mafic blueschists consist of blue amphibole, epidote and albite, rarely also garnet, Na-pyroxene and chloritoid. Apart from phengite and quartz the metapelites and metapsammites contain one or more of the minerals: chloritoid, paragonite, glaucophane, albite, chlorite, occasionally also Na-pyroxene and garnet. Amphibolite facies rocks contain relic garnet, plagioclase and hornblende, the latter two replaced by albite and blue amphibole, respectively. The zoning patterns of blue amphibole, garnet and chloritoid suggest their formation during prograde stage of metamorphism. P-T conditions of meta-morphism are estimated to be about 350-460 oC and 10-12 kbar.

  5. Uranium, rare metals, and granulite-facies metamorphism

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    Michel Cuney


    The Tranomaro metasomatized marbles recrystallizing under granulite-facies conditions represent a demonstrative example of fluid transfer from granulite-facies supracrustals to traps represented by regional scale skarns. Such fluids may be at the origin of the incompatible element enrichment detected in leucosomes of migmatites from St Malo in Brittany (France and Black Hills in South Dakota. The northern French Massif Central provides us with an example of a potential association between incompatible element enrichment of granitic melts and granulite-facies metamorphism. U- and F-enriched fine-grained granites are emplaced along a crustal scale shear zone active during the emplacement within the St Sylvestre peraluminous leucogranitic complex. We propose that during granulite-facies metamorphism dominated by carbonic waves in a deep segment of the continental crust, these shear zones control: (i the percolation of F-, LILE-, rare metal-rich fluids liberated primarily by the breakdown of biotite; (ii the enhancement of partial melting by F-rich fluids at intermediate crustal levels with the generation of F-, LILE-, rare metal-rich granitic melts; (iii their transfer through the crust with protracted fractionation facilitated by their low viscosity due to high F-Li contents; and finally (iv their emplacement as rare metal intrusions at shallow crust levels.

  6. Nature and origin of fluids in granulite facies metamorphism (United States)

    Newton, R. C.


    The various models for the nature and origin of fluids in granulite facies metamorphism were summarized. Field and petrologic evidence exists for both fluid-absent and fluid-present deep crustal metamorphism. The South Indian granulite province is often cited as a fluid-rich example. The fluids must have been low in H2O and thus high in CO2. Deep crustal and subcrustal sources of CO2 are as yet unproven possibilities. There is much recent discussion of the possible ways in which deep crustal melts and fluids could have interacted in granulite metamorphism. Possible explanations for the characteristically low activity of H2O associated with granulite terranes were discussed. Granulites of the Adirondacks, New York, show evidence for vapor-absent conditions, and thus appear different from those of South India, for which CO2 streaming was proposed. Several features, such as the presence of high-density CO2 fluid inclusions, that may be misleading as evidence for CO2-saturated conditions during metamorphism, were discussed.

  7. Age and duration of eclogite-facies metamorphism, North Qaidam HP/UHP terrane, Western China (United States)

    Mattinson, C.G.; Wooden, J.L.; Liou, J.G.; Bird, D.K.; Wu, C.L.


    Amphibolite-facies para-and orthogneisses near Dulan, at the southeast end of the North Qaidam terrane, enclose minor eclogite and peridotite which record ultra-high pressure (UHP) metamorphism associated with the Early Paleozoic continental collision of the Qilian and Qaidam microplates. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449 to 422 Ma, and REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate these ages record eclogite-facies metamorphism. The coherent field relations of these samples, and the similar range of individual ages in each sample suggests that the ???25 m.y. age range reflects the duration of eclogite-facies conditions in the studied samples. Analyses from zircon cores in one sample yield scattered 433 to 474 Ma ages, reflecting partial overlap on rims, and constrain the minimum age of eclogite protolith crystallization. Inclusions of Th + REE-rich epidote, and zircon REE patterns are consistent with prograde metamorphic growth. In the Lu??liang Shan, approximately 350 km northwest in the North Qaidam terrane, ages interpreted to record eclogite-facies metamorphism of eclogite and garnet peridotite are as old as 495 Ma and as young as 414 Ma, which suggests that processes responsible for extended high-pressure residence are not restricted to the Dulan region. Evidence of prolonged eclogite-facies metamorphism in HP/UHP localities in the Northeast Greenland eclogite province, the Western Gneiss Region of Norway, and the western Alps suggests that long eclogite-facies residence may be globally significant in continental subduction/collision zones.

  8. Low-grade Prehnite-Pumpellyite facies metamorphism in the Bamble sector, SE-Norway


    Velo, Mari Roen


    Low-grade metamorphic minerals have been found within the high-grade terrain in the Bamble sector, SE-Norway. The minerals prehnite and pumpellyite indicative of prehnite-pumpellyite facies conditions have been confirmed around the Kragerø area. The formation of analcime, thomsonite, hydrogarnet, albite and clay minerals is also a part of the low-grade metamorphism. The occurrence of these low-grade minerals is constricted to pseudomorph replacement of earlier mineral phases, hydrothermal vei...

  9. Episodic subgreenschist facies metamorphism in the Andes of Chile - is it a valid model? (United States)

    Bevins, R. E.; Robinson, D.; Aguirre, L.; Vergara, M.


    The Central Andes of Chile are characterized by subgreenschist facies burial metamorphism that is reported as having developed in up to seven episodic cycles of some 40Myr duration. The main evidence in support of the model is reported as mineralogical breaks at major stratigraphic boundaries that are interpreted as documenting sharp breaks in metamorphic grade. Here we test this model by examination of the progressive secondary mineral development, reaction progress in mafic phyllosilicates, and topological variations of the low-grade assemblages in metabasites for Jurassic to Miocene sequences east of Santiago. The mafic phyllosilicates (smectite - mixed-layer chlorite/smectite - chlorite) show increasing reaction progress with stratigraphic age and there is a continuum across the main stratigraphic boundaries, such there is no offset or gap in the reaction progress at these boundaries. There are some differences in mineral assemblages between the various stratigraphic units, such as between prehnite+pumpellyite+/-laumonite or amphibole-bearing and non amphibole bearing rocks, from which contrasting subgreenschist facies can be recognised. However, consideration of the controls on mineral parageneses at subgreenschist facies conditions demonstrates that these different facies cannot be used solely as evidence of sharp breaks in metamorphic grade at unconformities, as has been reported in many previous publications for the Andes. The presently accepted model for the Central Andes, involving repeated cycles of episodic metamorphism developing in extensional basins, is, therefore, partly unfounded. Consideration of the overall tectonic evolution of this part of the Andes concurs that the burial metamorphism developed in extensional settings, but in only two events, namely in mid-late Cretaceous and Late Miocene times respectively. The results from this work suggest that the record of sharp metamorphic breaks and the episodic model of metamorphism reported for many

  10. UHT granulite-facies metamorphism in Rogaland, S Norway, is polyphase in nature (United States)

    Laurent, Antonin; Duchene, Stéphanie; Bingen, Bernard; Seydoux-Guillaume, Anne-Magali; Bosse, Valérie


    Propensity of metamorphic assemblages to remain metastable after melt extraction complicates singularly the petrologist's task to discriminate between a single granulite-facies P-T path and a polyphase one. Using an integrated petrological and in-situ geochronological approach in key rock-samples, we reconstruct the pressure-temperature-time path of Sveconorwegian metamorphism across a 30 km-wide metamorphic gradient ranging from upper amphibolite facies to ultra-high temperature (UHT) granulite-facies in Rogaland, S. Norway. Thermodynamic modelling of phase equilibria in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Ti2O-O2 chemical system (PerpleX code) are carried out with an emphasis on moderately oxidized, spinel-bearing assemblages resulting from either garnet or sapphirine breakdown. Geochronological U-(Th)-Pb data acquired on both monazite (LA-ICP-MS) and zircon (SIMS) are complemented by minor- and trace-elements signatures of both minerals, to monitor REE distribution through time and to evaluate garnet apparition or demise. Coupling field, petrological and geochronological data lead to a polyphase metamorphic history, lasting about 100 My. The onset of regional granulite facies metamorphism at 1035 Ma is associated with the emplacement of large volumes of granitic magmas in the amphibolite to granulite facies transition zone. In the deeper part of the crustal section, localized sapphirine-bearing restitic lithologies testify to UHT temperatures (900-920 °C). These conditions were reached at ca. 1010 Ma following a tight clockwise P-T path associated with minor exhumation (7 to 5.5 kbar) and subsequent cooling to 700 °C. A distinct thermal episode, initiated at ca. 950 Ma, reached UHT granulite-facies conditions with the intrusion of massif-type anorthosite plutons at ca. 930 Ma producing a 5-km wide aureole. The aureole is delimited by the presence of osumilite in high Fe-Al rocks yielding quantitative estimates of 900-950 °C at a maximum pressure of 5 kbar

  11. Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence (United States)

    Valley, J.W.; O'Neil, J.R.


    The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their

  12. Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history? (United States)

    Jedlicka, Radim; Faryad, Shah Wali


    High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite

  13. Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks (United States)

    Bernard, Sylvain; Benzerara, Karim; Beyssac, Olivier; Brown, Gordon E., Jr.


    Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.

  14. Partial melting of metavolcanics in amphibolite facies regional metamorphism

    Indian Academy of Sciences (India)

    Alan Bruce Thompson


    Metavolcanic rocks containing low-Ca amphiboles (gedrite, cummingtonite) and biotite can undergo substantial dehydration-melting. This is likely to be most prominent in Barrovian Facies Series (kyanite-sillimanite) and occurs at the same time as widespread metapelite dehydration- melting. In lower pressure facies series, metavolcanics will be represented by granulites rich in orthopyroxene when dehydration occurs at much lower temperatures than melting. In higher pressure facies series it is not well known whether metavolcanic rocks dehydrate or melt at temperatures lower or similar to that of metapelites.

  15. Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet (United States)

    Zhang, Zeming; Xiang, Hua; Dong, Xin; Ding, Huixia; He, Zhenyu


    The Namche Barwa Complex exposed in the Eastern Himalayan Syntaxis, south Tibet, underwent high-pressure (HP) and high-temperature (HT) granulite-facies metamorphism and associated anatexis. The HP pelitic granulites contain garnet, kyanite, sillimanite, cordierite, biotite, quartz, plagioclase, K-feldspar, spinel, ilmenite and graphite. These minerals show composite reaction texture and varying chemical compositions and form four successive mineral assemblages. Phase equilibrium modeling constrains the P-T conditions of 10-12 kbar and 550-700 °C for the prograde stage, 13-16 kbar and 840-880 °C for the peak-metamorphic stage, and 5-6 kbar and 830-870 °C for the late retrograde stage, indicating that the HP granulites recorded a clockwise P-T path involving the early heating burial and anatexis through dehydration melting of both muscovite and biotite, and the late isothermal decompression and gradual melt crystallization under HT granulite-facies conditions. The zircon U-Pb dating reveals that the HT granulite-facies metamorphism probably initiated at ca. 40 Ma, and lasted to ca. 8 Ma. Therefore, the present study provides robust evidence for a long-lived HT metamorphism and associated anatexis in the deeply buried Indian continent and important constraints on the leucogranite generation and tectonic evolution of the Himalayan orogen.

  16. Mineral deformation mechanisms in granulite facies, Sierra de Valle Fértil, San Juan province: evelopment conditions constrained by the P-T metamorphic path Mecanismos de deformación en minerales en facies granulita, Sierra de Valle Fértil, provincia de San Juan: condiciones de desarrollo acotadas por la trayectoria P-T

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    Sergio Delpino


    Full Text Available In the Sierra de Valle Fértil, evidence of granulite facies metamorphism have been preserved either in the constitutive associations as in deformation mechanisms in minerals from biotite-garnet and cordierite-sillimanite gneisses, cordierite and garnet-cordierite migmatites, metagabbros, metatonalites-metadiorites and mafic dikes. The main recognized deformation mechanisms are: 1 quartz: a dynamic recrystallisation of quartz-feldspar boundaries, b combination of basal and prism [c] slip; 2 K-feldspar: grain boundary migration recrystallisation; 3 plagioclase: combination of grain boundary migration recrystallisation and subgrain rotation recrystallisation; 4 cordierite: subgrain rotation recrystallisation; 5 hornblende: grain boundary migration recrystallisation. Preliminary geothermometry on gabbroic rocks and the construction of an appropriated petrogenetic grid, allow us to establish temperatures in the range 800-850 C and pressures under 5 Kb for the metamorphic climax. Estimated metamorphic peak conditions, preliminary geothermobarometry on specific lithologic types and textural relationships, together indicate an counter-clockwise P-T path for the metamorphic evolution of the rocks of the area. Ductile deformation of phases resulting from anatexis linked to the metamorphic climax indicates that the higher-temperature ductile event recognized in the study area took place after the metamorphic peak. Evidence of ductile deformation of cordierite within its stability field and presence of chessboard extinction in quartz (only possible above the Qtzα/Qtzß transformation curve, both indicate temperatures above 700 C considering pressures greater than 5 Kb. Based on the established P-T trajectory and the characteristics described above, it can be concluded that deformation mechanisms affecting the Sierra de Valle Fértil rocks were developed entirely within the granulite facies field.En la sierra de Valle Fértil han quedado preservadas

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

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

  18. Active metasomatism in the Cerro Prieto geothermal system, Baja California, Mexico: a telescoped low pressure/temperature metamorphic facies series

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    Schiffman, P.; Elders, W.A.; Williams, A.E.; McDowell, S.D.; Bird, D.K.


    In the Cerro Prieto geothermal field, carbonate-cemented, quartzofeldspathic sediments of the Colorado River delta are being actively metasomatized into calc-silicate metamorphic rocks by reaction with alkali chloride brines between 200/sup 0/ and 370/sup 0/C, low fluid and lithostatic pressures, and low oxygen fugacities. Petrologic investigations of drill cores and cutting from over 50 wells in this field identified a prograde series of calc-silicate mineral zones which include as index minerals: wairakite, epidote, prehnite, and clinopyroxene. Associated divariant mineral assemblages are indicative of a very low pressure/temperature metamorphic facies series which encompasses the clay-carbonate, zeolite, greenschist, and amphibolite facies. This hydrothermal metamorphic facies series, which is becoming increasingly recognized in other active geothermal systems, is characterized by temperature-telescoped dehydration and decarbonation mineral equilibria. Its equivalent should now be sought in fossil hydrothermal systems.

  19. Coupling of Oceanic and Continental Crust During Eocene Eclogite-Facies Metamorphism: Evidence From the Monte Rosa Nappe, Western Alps, Italy (United States)

    Lapen, T. J.; Johnson, C. M.; Baumgartner, L. P.; Skora, S.; Mahlen, N. J.; Beard, B. L.


    Subduction of continental crust to HP-UHP metamorphic conditions requires overcoming density contrasts that are unfavorable to deep burial, whereas exhumation of these rocks can be reasonably explained through buoyancy-assisted transport in the subduction channel to more shallow depths. In the western Alps, both continental and oceanic lithosphere has been subducted to eclogite-facies metamorphic conditions. The burial and exhumation histories of these sections of lithosphere bear directly on the dynamics of subduction and the stacking of units within the subduction channel. We address the burial history of the continental crust with high precision U-Pb rutile and Lu-Hf garnet geochronology of the eclogite-facies Monte Rosa nappe (MR), western Alps, Italy. U-Pb rutile ages from quartz-carbonate-white mica-rutile veins that are hosted within eclogite and schist of the MR, Gressoney Valley, Italy, indicate that it was at eclogite-facies metamorphic conditions at 42.6 +/- 0.6 Ma. The sample area (Indren glacier, Furgg zone; Dal Piaz, 2001) consists of eclogite boudins that are surrounded by micaceous schist. Associated with the eclogite and schist are quartz-carbonate-white mica-rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins occurred at eclogite-facies metamorphic conditions (480-570°C, >1.3-1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. Lu-Hf geochronology of garnet from a chloritoid-talc-garnet-phengite-quartz-calcite-pyrite - chalcopyrite bearing boudin within talc-chloritoid whiteschists of the MR, Val d'Ayas, Italy (Chopin and Monie, 1984; Pawlig, 2001) yields an age of 40.54 +/- 0.36 Ma. The talc-chloritoid whiteschists from the area record pressures and temperatures of 1.6-2.4 GPa and 500-530°C (Chopin and Monie, 1984; Le Bayon et al., 2006) indicating near UHP metamorphic conditions. Based on the age, P-T, and textural

  20. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins (United States)

    Zheng, Yong-Fei; Chen, Ren-Xu


    Regional metamorphism at extreme conditions refers either to Alpine-type metamorphism at low geothermal gradients of 30 °C/km. Extreme pressures refer to those above the polymorphic transition of quartz to coesite, so that ultrahigh-pressure (UHP) eclogite-facies metamorphism occurs at mantle depths of >80 km. Extreme temperatures refer to those higher than 900 °C at crustal depths of ≤80 km, so that ultrahigh-temperature (UHT) granulite-facies metamorphism occurs at medium to high pressures. While crustal subduction at the low geothermal gradients results in blueschist-eclogite facies series without arc volcanism, heating of the thinned orogenic lithosphere brings about the high geothermal gradients for amphibolite-granulite facies series with abundant magmatism. Therefore, UHP metamorphic rocks result from cold lithospheric subduction to the mantle depths, whereas UHT metamorphic rocks are produced by hot underplating of the asthenospheric mantle at the crustal depths. Active continental rifting is developed on the thinned lithosphere in response to asthenospheric upwelling, and this tectonism is suggested as a feasible mechanism for regional granulite-facies metamorphism, with the maximum temperature depending on the extent to which the mantle lithosphere is thinned prior to the rifting. While lithospheric compression is associated with subduction metamorphism in accretionary and collisional orogens, the thinned orogenic lithosphere undergoes extension due to the asthenospheric upwelling to result in orogen-parallel rifting metamorphism and magmatism. Thus, the rifting metamorphism provides a complement to the subduction metamorphism and its operation marks the asthenospheric heating of the orogenic lithosphere. Because of the partial melting and melt extraction of the lower continental crust, contemporaneous granite-migmatite-granulite associations may serve as a petrological indicator of rifting orogeny that is superimposed on precedingly accretionary and

  1. Syn-metamorphic interconnected porosity during blueschist facies reactive fluid fluxes at the slab-mantle interface (United States)

    Konrad-Schmolke, Matthias; Klitscher, Nicolai; Halama, Ralf; Wirth, Richard; Morales, Luiz


    At the slab-mantle interface in subdution zones fluids released from the downgoing plate infiltrate into a mechanical mixture of rocks with different chemical compositions, different hydration states and different rheological behaviour resulting in a highly reactive mélange within a steep temperature gradient. Fluid pathways, reaction mechanisms and reaction rates of such fluxes, however, are poorly known, although these parameters are thought to be crucial for several seismic phenomena, such as those commonly referred to as slow earthquakes (e.g., episodic tremor and slip (ETS)). We discovered syn-metamorphic fluid-pathways in the form of interconnected metamorphic porosity in eclogite and blueschist facies mélange rocks from the Franciscan Complex near Jenner, CA. The sampled rocks occur as rigid mafic blocks of different sizes (cm to decametre) in a weak chlorite-serpentine matrix interpreted to be an exhumed slab-mantle interface. Some of these mafic blocks record reactive fluid infiltration that transforms dry eclogite into hydrous blueschist with a sharp reaction front clearly preserved and visible from outcrop- down to µm-scale. We can show that a number of interconnected fluid pathways, such as interconnected metamorphic porosity between reacting omphacite and newly formed sodic amphibole enabled fluid infiltration and interface coupled solution-reprecipitation reactions at blueschist facies conditions. We investigated the different types of fluid pathways with TEM and visualized their interconnectivity with 3D focused ion beam (FIB) sections. The eclogitic parts of the samples preserve porous primary omphacite as a product of amphibole and epidote breakdown during subduction. This primary porosity in omphacite I results from a negative volume change in the solids during amphibole and epidote dehydration. The resulting pores appear as (fluid filled) elongated inclusions the orientations of which are controlled by the omphacite lattice. During

  2. Chemical modifications accompanying blueschist facies metamorphism of Franciscan conglomerates, Diablo Range, California (United States)

    Moore, Diane E.; Liou, J.G.; King, B.-S.


    As part of an investigation of blueschist-facies mineral parageneses in pebbles and matrix of some Franciscan metaconglomerates of the Diablo Range, California, textural and major-element chemical analyses were conducted on a number of igneous pebbles that comprise a range of rock types from granite and dacite to gabbro and basalt. Compositions of the igneous pebbles differ significantly from common igneous rocks, particularly with respect to Ca, K, Na, Si and H2O. The SiO2 and H2O contents are characteristically high and the K2O contents low. The CaO and Na2O contents may be relatively enriched or reduced in different pebbles. The igneous pebbles show little evidence of alteration prior to their incorporation into the Franciscan conglomerates, and the chemical modifications are considered to have been produced during metamorphism of the conglomerates to (lawsonite + albite + aragonite ?? jadeite)-bearing assemblages. The observed variations in the pebbles are shown to be functions of: (1) bulk chemistry; (2) the igneous mineral assemblage; (3) the stable metamorphic mineral assemblage; and (4) the composition of pore fluids in the conglomerates. The relative proportions of Mg and Fe in most of the pebbles apparently have been unaffected by the metamorphism, and these parameters, along with other textural and chemical factors, were used to determine the petrogenetic affinities of the igneous pebbles. The plutonic and most of the volcanic pebbles correspond to calc-alkaline rock series, whereas a few volcanic pebbles show apparent Fe-enrichment characteristic of tholeiitic rocks. A continental margin arc-batholith complex would be the best source for these igneous detrital assemblages. Conglomerates in local areas differ in igneous lithologies from conglomerates in other areas and probably differ somewhat in age, perhaps reflecting varying degrees of unroofing of such a complex during deposition of Franciscan sediments. ?? 1981.

  3. Neoproterozoic eclogite- to high-pressure granulite-facies metamorphism in the Mozambique belt of east-central Tanzania: A petrological, geochemical and geochronological approach (United States)

    Sommer, H.; Kröner, A.; Lowry, J.


    This study investigated Neoproterozoic (Pan-African) eclogite- and high-pressure-granulite (E-HPG) facies rocks from the Mozambique belt of east-central Tanzania, collected close to the town of Ifakara and the adjacent Furua area from different tectonic settings, the Palaeoproterozoic Usagaran and the Neoproterozoic Mozambique belt. The studied rocks are E-HPG facies granite- and diorite-gneisses and a meta-gabbroic rock, which are retrogressed to amphibolite- and greenschist-facies conditions. Four different clockwise P-T paths were constructed. The first P-T path for a granodioritic gneiss displays peak metamorphic conditions at 830 °C and 13.0 kbar. The second P-T path for a quartz dioritic gneiss shows peak metamorphic conditions of 920 °C and 14.9 kbar. The third P-T path for a mafic granulite shows peak metamorphic conditions of 820 °C and 13.2 kbar. A fourth P-T path for a monzodioritic gneiss also displays peak metamorphic conditions of up to 810 °C and 14.9 kbar. Evidence for all four P-T paths is provided by mineral chemical and modal abundance calculations in combination with textural observations in thin sections. Zircon ages indicate that the east-central part of the Mozambique belt in Tanzania consists of granite-, granodiorite- and monzodiorite gneisses with Mesoarchaean ( 2915 Ma), Neoarchaean ( 2637-2676 Ma) and Palaeoproterozoic ( 1873-1926 Ma) protolith ages. Early Neoproterozoic (Tonian) igneous zircons were found in the mafic granulite with an age of 989 Ma. Late Neoproterozoic (Cyrogenian) igneous zircons were found in a dioritic and monzodiorite gneiss with ages of 748 Ma and 718 Ma, respectively. Metamorphic zircons extracted from Qtz-monzodiorite and granodiorite gneisses yielded ages of 640 Ma and are considered to approximate the peak of regional E-HPG metamorphism. We suggest that this high-grade metamorphic event was caused by the collision of fragments of East and West Gondwana during the Pan-African orogeny, associated with ocean

  4. Flux rates for water and carbon during greenschist facies metamorphism: implications for the role of orogenic belts as a source/sink for atmospheric CO2 (United States)

    Skelton, A.


    The time-averaged flux rate for a CO2-bearing hydrous fluid during greenschist facies regional metamorphism was estimated to 10-10.2 ± 0.4 m3.m-2.s-1. This was evaluated by combining 1) Peclet numbers obtained by chromatographic analysis of the propagation of reaction fronts in 33 metamorphosed basaltic sills in the SW Scottish Highlands, 2) empirical diffusion rates for CO2 in water obtained by Wark & Watson (2003), and 3) calculated time-averaged metamorphic porosities. The latter were calculated using an expression obtained by combining estimated Peclet numbers with the empirical porosity - permeability relationships obtained by Wark and Watson (1998) and Price et al. (2006) and Darcy’s law. This approach yielded a time-averaged metamorphic porosity of 10-2.6 ± 0.2 for greenschist facies conditions. The corresponding timescale for metamorphic fluid flow was 103.6 ± 0.1 years. By using mineral assemblages to constrain fluid compositions, I further obtained a time-averaged annual flux rate for carbon of 0.5-7 mol-C.m-2.yr-1. This matches measured emission rates for metamorphic CO2 from orogenic hot springs. These fluxes significantly exceed estimated rates of CO2 drawdown by orogenic silicate weathering and therefore indicate that orogenic belts are a source rather than a sink of atmospheric CO2. Thin section in XPL showing replacement of amphibole by calcite recording syn-metamorphic carbonation of a metamorphosed basaltic sill in the SW Scottish Highlands.

  5. Timing of the granulite facies metamorphism in the Sanggan area, North China craton: zircon U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)


    Zircon U-Pb ages are reported for three samples of intrusive rocks in Khondalite series in the Sanggan area, North China craton. The age of meta-granite is dated as 2005±9 Ma, implying that the sedimentary sequences in Khondalites series formed before 2.0Ga. The age of 1921 ±1Ma for the meta-diorite constrain the age of granulite facies metamorphism younger than this date. The age of 1892±10 Ma for garnet granite is obtained, but the granite crystallization age seems a little younger than the date considering the morphology of zircons. On the basis of these dates and of a concise review of previous age data, it is inferred that the Khondalite series was subjected to granulite facies metamorphism at about 1.87Ga together with tonalitic granulites and HP basic granulites in the Sanggan area.

  6. Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China (United States)

    Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang


    An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel

  7. New age data and geothermobarometric estimates from the Apuseni Mountains (Romania); evidence for Cretaceous amphibolite-facies metamorphism (United States)

    Reiser, Martin; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard


    New Ar-Ar ms, Rb-Sr bt and Sm-Nd grt age data in combination with microprobe analyses and structural data from the Apuseni Mountains provide new constraints for the tectonic evolution of the Tisza and Dacia Mega-Units during the Late Jurassic-Late Cretaceous time interval, which is of special importance for the present day arrangement of tectonic units in the Alpine-Carpathian-Dinaridic region. Late Jurassic obduction of Transylvanian Ophiolites (155 Ma) partially reset Ar-Ar ms ages at the top of the Biharia Nappe System in the Dacia Mega-Unit. New Sm-Nd grt ages and P-T estimates yielded amphibolite-facies conditions of 500°C and about 0.8 GPa during the Early Cretaceous (125 Ma Sm-Nd age) for the Dacia Mega-Unit and during late Early Cretaceous times (104 Ma Sm-Nd age) for the Tisza Mega-Unit. This implies that not only the Dacia Mega-Unit, but also the Tisza Mega-Unit experienced a strong regional metamorphic overprint accompanying Alpine deformation. New 95 Ma Ar-Ar ms and 81 Ma Rb-Sr bt ages from the Bihor Nappe (Tisza Mega-Unit), in combination with fission track ages constrain rapid cooling of more than 20°C/Ma after the thermal maximum. The amplitude of cooling corresponds to data from the Dacia Mega-Unit, which started cooling 20 Ma earlier, but at a rate of only about 12°C/Ma. Kinematic indicators and stretching lineations show NE-directed, in-sequence nappe stacking for the Tisza and Dacia Mega-Units during "Austrian Phase" deformation (125-100 Ma). Following the Austrian Phase, the Dacia Mega-Unit was thrust over the Tisza Mega-Unit during the Turonian Phase (93-89 Ma). Constrained through NW-directed kinematic indicators and 94-80 Ma Rb-Sr bt ages, this tectonic phase is responsible for a pervasive retrograde greenschist-facies overprint and the geometry of the present-day nappe stack in the Apuseni Mountains.

  8. High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy) (United States)

    Fassmer, Kathrin; Obermüller, Gerrit; Nagel, Thorsten J.; Kirst, Frederik; Froitzheim, Nikolaus; Sandmann, Sascha; Miladinova, Irena; Fonseca, Raúl O. C.; Münker, Carsten


    The Etirol-Levaz Slice in the Penninic Alps (Valtournenche, Italy) is a piece of eclogite-facies continental basement sandwiched between two oceanic units, the blueschist-facies Combin Zone in the hanging wall and the eclogite-facies Zermatt-Saas Zone in the footwall. It has been interpreted as an extensional allochthon from the continental margin of Adria, emplaced onto ultramafic and mafic basement of the future Zermatt-Saas Zone by Jurassic, rifting-related detachment faulting, and later subducted together with the future Zermatt-Saas Zone. Alternatively, the Etirol-Levaz Slice could be derived from a different paleogeographic domain and be separated from the Zermatt-Saas Zone by an Alpine shear zone. We present Lu-Hf whole rock-garnet ages of two eclogite samples, one from the center of the unit and one from the border to the Zermatt-Saas Zone below. These data are accompanied by a new geological map of the Etirol-Levaz Slice and the surrounding area, as well as detailed petrology of these two samples. Assemblages, mineral compositions and garnet zoning in both samples indicate a clockwise PT-path and peak-metamorphic conditions of about 550-600 °C/20-25 kbar, similar to conditions proposed for the underlying Zermatt-Saas Zone. Prograde garnet ages of the two samples are 61.8 ± 1.8 Ma and 52.4 ± 2.1 Ma and reflect different timing of subduction. One of these is significantly older than published ages of eclogite-facies metamorphism in the Zermatt-Saas Zone and thus contradicts the hypothesis of Mesozoic emplacement. The occurrence of serpentinite and metagabbro bodies possibly derived from the Zermatt-Saas Zone inside the Etirol-Levaz Slice suggests that the latter is a tectonic composite. The basement slivers forming the Etirol-Levaz Slice and other continental fragments were subducted earlier than the Zermatt-Saas Zone, but nonetheless experienced similar pressure-temperature histories. Our results support the hypothesis that the Zermatt-Saas Zone and the

  9. Formation history and protolith characteristics of granulite facies metamorphic rock in Central Cathaysia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

    Institute of Scientific and Technical Information of China (English)

    YU Jinhai; ZHOU Xinmin; Y. S. O'Reilly; ZHAO Lei; W. L. Griffin; WANG Rucheng; WANG Lijuan; CHEN Xiaomin


    The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (~736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their -Hf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

  10. Active metasomatism in the Cerro Prieto geothermal system, Baja California, Mexico: a telescoped low-pressure, low-temperature metamorphic facies series

    Energy Technology Data Exchange (ETDEWEB)

    Schiffman, P.; Elders, W.A.; Williams, A.E.; McDowell, S.D.; Bird, D.K.


    In the Cerro Prieto geothermal field, carbonate-cemented, quartzofeldspathic sediments of the Colorado River delta are being actively metasomatized into calc-silicate metamorphic rocks by reaction with alkali chloride brines between 200 and 370 C, at low fluid and lithostatic pressures and low oxygen fugacities. Their petrologic investigations of drill cores and cuttings from more than 50 wells in this field identified a prograde series of zones that include as index minerals wairakite, epidote, prehnite, and clinopyroxene. Associated divariant mineral assemblages are indicate of a very low pressure, low-temperature metamorphic facies series spanning the clay-carbonate, zeolite, greenschist, and amphibolite facies. This hydrothermal facies series, which is now recognized in other active geothermal systems, is characterized by temperature-telescoped dehydration and decarbonation. Its equivalent can now be sought in fossil hydrothermal systems.

  11. Active metasomatism in the Cerro Prieto geothermal system, Baja California, Mexico: A telescoped low-pressure, low-temperature metamorphic facies series (United States)

    Schiffman, P.; Elders, W. A.; Williams, A. E.; McDowell, S. D.; Bird, D. K.


    In the Cerro Prieto geothermal field, carbonate-cemented, quartzofeldspathic sediments of the Colorado River delta are being actively metasomatized into calc-silicate metamorphic rocks by reaction with alkali chloride brines between 200 and 370 °C, at low fluid and lithostatic pressures and low oxygen fugacities. Our petrologic investigations of drill cores and cuttings from more than 50 wells in this field identified a prograde series of zones that include as index minerals wairakite, epidote, prehnite, and clinopyroxene. Associated divariant mineral assemblages are indicative of a very low pressure, low-temperature metamorphic facies series spanning the clay-carbonate, zeolite, greenschist, and amphibolite facies. This hydro-thermal facies series, which is now recognized in other active geothermal systems, is characterized by temperature-telescoped dehydration and decarbonation. Its equivalent can now be sought in fossil hydrothermal systems.

  12. Timing of the granulite facies metamorphism in the Sanggan area, North China craton: zircon U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    GUO; Jinghui


    [1]Lu, L. Z., Jin, S. Q., P-T-t paths and tectonic history of an early Precambrian granulite facies terrane, Jining District, south-eastern Inner Mongolia, China, J. Metamorphic Geol., 1993, 11: 483-498.[2]Liu, F. L., Shen, Q. H., Retrogressive textures and metamorphic reaction features of Al-rich gneisses in the granulite facies belt from northwestern Hebei province, Acta Petrologia Sinica (in Chinese with English abstract), 1999, 15(4): 505-517.[3]Zhai, M. G., Guo, J. H., Yan, Y. H. et al., Discovery of high-pressure basic granulite terrain in North China Archaean craton and preliminary study, Science in China, Ser. B, 1993, 36(11): 1402-1408.[4]Guo, J. H., Zhai, M. G., Zhang, Y. G. et al., Early Precambrian Manjinggou high-pressure granulite melange belt on the south edge of the Huaian complex, North China craton: geological features, petrology and isotopic geochronology, Acta Petrologica Sinica (in Chinese with English abstract), 1993, 9(4): 329-341.[5]Liu, S. W., Shen, Q. H., Geng, Y. S., Metamorphic evolution of two types of garnet-granulites in Northwestern Hebei province and analyses by Gibbs method, Acta Petrologica Sinica (in Chinese with English abstract), 1996, 12(2): 261-275.[6]Wang, R. M., Some evidence of the late Archaean collision zone in the northwestern Hebei Province, in Geological Evolution of the Granulite Terrane in North Part of the North China Craton (eds. Qian, X., Wang, R.), Beijing: Seismolgical Press. 1994, 7-20.[7]Liu, D. Y., Geng, Y. S., Song, B., Late Archean crustal accretion and reworking in northwest Hebei Province: geochronological evidence, Acta Geoscientia Sinica (in Chinese with English abstract), 1997, 18(3): 226-232.[8]Geng, Y. S., Liu, D. Y., Song, B., Chronological framework of the early Precambrian important events of the north-western Hebei granulite terrain, Acta Geologica Sinica (in Chinese with English abstract), 1997, 71:316-327.[9]Guo, J. H., Zhai, M. G., Sm-Nd age dating of high

  13. Omphacite microstructures as time-temperature indicators of blueschist- and eclogite-facies metamorphism (United States)

    Carpenter, Michael A.


    Omphacites from a wide range of geological environments have been examined by transmission electron-microscopy. Their microstructures are sufficiently variable as to be potential indicators of thermal history for blueschist and eclogite metamorphism. In particular, the average size of equiaxed antiphase domains (APD's) arising from cation ordering appears to be a characteristic feature of each environment and increases in the sequence: Franciscan, blueschist (1) ≈ Turkey, blueschist (2) Wine Complex, Canada, amphibolite (1) behaviour in other systems where: (APD size)n 410_2004_Article_BF00375206_TeX2GIFE1.gif ({text{APD size)}}^{text{n}} ∝ {text{e}}^{{text{(}} - {text{Q/RT)}}} \\cdot {text{ }}time{text{.}} . Most omphacites fit into a self-consistent scheme with n=8±2 if the activation energy ( Q) is assumed to be that of cation disordering (75 kcal mole-1), available estimates of peak metamorphic temperature ( T) are used, and a reasonable geological time-scale is taken as 104 108 years. According to this model, APD sizes are set in a relatively short interval of the total history of a rock when its temperature is close to its peak value. APD sizes are much more sensitive to temperature than to time and may be used as a geothermometer which has the advantage of not being reset by re-equilibration at low temperatures. Petrological implications arising from the model are that Allalin metagabbros were metamorphosed at a similar peak temperature to Zermatt-Saas blueschists, Franciscan eclogites reached higher temperatures than has been previously supposed and that the microstructures in some Sesia-Lanzo omphacites are consistent with a high temperature, pre-blueschist origin. Deviation from an ideal coarsening law with n=2 implies that the APD's are not simply stacking mistakes but have some associated structural or compositional modification locally. Excess titanium concentrated at APD's in Red Wine Complex omphacites may account for their anomalously low

  14. Accessories after the facts: Constraining the timing, duration and conditions of high-temperature metamorphic processes (United States)

    Taylor, Richard J. M.; Kirkland, Christopher L.; Clark, Chris


    High-temperature metamorphic rocks are the result of numerous chemical and physical processes that occur during a potentially long-lived thermal evolution. These rocks chart the sequence of events during an orogenic episode including heating, cooling, exhumation and melt interaction, all of which may be interpreted through the elemental and isotopic characteristics of accessory minerals such as zircon, monazite and rutile. Developments in imaging and in situ chemical analysis have resulted in an increasing amount of information being extracted from these accessory phases. The refractory nature of these minerals, combined with both their use as geochronometers and tracers of metamorphic mineral reactions, has made them the focus of many studies of granulite-facies terrains. In such studies the primary aim is often to determine the timing and conditions of the peak of metamorphism, and high-temperature metasedimentary rocks may seem ideal for this purpose. For example pelites typically contain an abundance of accessory minerals in a variety of bulk compositions, are melt-bearing, and may have endured extreme conditions that facilitate diffusion and chemical equilibrium. However complexities arise due to the heterogeneous nature of these rocks on all scales, driven by both the composition of the protolith and metamorphic differentiation. In additional to lithological heterogeneity, the closure temperatures for both radiogenic isotopes and chemical thermometers vary between different accessory minerals. This apparent complexity can be useful as it permits a wide range of temperature and time (T-t) information to be recovered from a single rock sample. In this review we cover: 1) characteristic internal textures of accessory minerals in high temperature rocks; 2) the interpretation of zircon and monazite age data in relation to high temperature processes; 3) rare earth element partitioning; 4) trace element thermometry; 5) the incorporation of accessory mineral growth

  15. Initiation of continental accretion: metamorphic conditions (United States)

    Clement, Conand; Frederic, Mouthereau; Gianreto, Manatschal; Adbeltif, Lahfid


    The physical processes involved at the beginning of the continental collision are largely unknown because they are transient and therefore hardly identifiable from the rock record. Despite the importance of key parameters for understanding mountain building processes, especially the formation of deep mountain roots and their impacts on earthquakes nucleation, rock/fluid transfers and oil/gas resources in the continental crust, observations from the earliest collision stages remain fragmentary. Here, we focus on the example of Taiwan, a young and active mountain belt where the transition from oceanic subduction, accretion of the first continental margin to mature collision can be followed in space and time. We present preliminary results and provide key questions regarding the reconstruction of time-pressure-temperature paths of rocks & fluids to allow discriminating between rift-related thermal/rheological inheritance and burial/heating phases during convergence. Previous studies have focused on peak temperatures analyzed by Raman Spectrometry of Carbonaceous Matter from the deeper structural layers exposed in the Central Range of Taiwan. In the pre-rift sediments, these studies reported a positive gradient from West to Est, and values from units. Cross sections and maps with high resolution peak temperatures are in process as well as pressure estimations to determine how the sediments were metamorphosed. In addition to this work, we report a few inherited temperatures in the 390-570 °C range, indicating recycling of organic matter from metasediments that recorded HT events, likely originated from higher grade metamorphic units of mainland China, which have been eroded and deposited in the post-rift sediments.

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

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


    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

  17. The metamorphic evolution from ultrahigh-temperature to amphibolite facies metamorphism in the Odaesan area after the collision between the North and South China Cratons in the Korean Peninsula (United States)

    Lee, Byung Choon; Oh, Chang Whan; Kim, Tae Sung; Yi, Keewook


    The Odaesan Gneiss Complex (Odesan Gneiss Complex) is the eastern end of the Hongseong-Odaesan collision belt in the Korean Peninsula, which is an extension of the Dabie-Sulu collision belt between the North and South China cratons. The Odaesan Gneiss Complex mainly consists of banded and migmatitic gneisses with porphyritic granitoids and amphibolites. The garnet-bearing banded gneisses can be subdivided into garnet-biotite and garnet-orthopyroxene banded gneisses. At the beginning of the post-collision stage, the banded gneisses underwent regional ultrahigh-temperature metamorphism (902-950 °C/8.8-9.4 kbar) at ca. 247-245 Ma due to the heat supplied from underplated basic magma, which was generated by the partial melting of the lithospheric mantle caused by the heat supplied from the asthenospheric mantle. As a result of the continuous extensional force, the study area (lower crust) uplifted onto the middle crust depths, and then the study area underwent prograde granulite facies metamorphism from 660 °C and 8.7 kbar to 750-760 °C and 6.3-6.5 kbar at ca. 227 Ma, causing migmatization, which erased the ultrahigh-temperature metamorphism in most of the study area. The ultrahigh-temperature metamorphism was preserved only in the garnet-orthopyroxene banded gneisses due to their very low water contents. During migmatization, the garnet-biotite banded gneisses were retrograded into upper granulite facies due to the relatively abundant water compared with the garnet-orthopyroxene gneisses. Finally, the study area was uplifted to a shallow depth and locally underwent amphibolite facies retrograde metamorphism (575-680 °C and 3.1-4.5 kbar). In addition, Paleoproterozoic metamorphic (ca. 1930-1886 Ma) and post-collisional magmatic events (ca. 1847 Ma) are identified based on SHRIMP age dating. These ages agree well with the regional Paleoproterozoic metamorphic and post-collisional magmatic activities reported from other areas of the Gyeonggi Massif.

  18. Cl-rich minerals in Archean granulite facies ironstones from the Beartooth Mountains, Montana, USA: Implications for fluids involved in granulite metamorphism (United States)

    Henry, D. J.


    The implications of Cl-rich minerals in granulite facies rocks are discussed. Results from ironstones of the Beartooth Mountains, Montana are discussed. It is suggested that CO2-brine immiscibility might be applicable to granulite facies conditions, and if so, then aqueous brines might be preferentially adsorbed onto mineral surfaces relative to CO2.

  19. Short-lived brine infiltration during upper amphibolite facies metamorphism in the continental collision zone (United States)

    Higashino, Fumiko; Kawakami, Tetsuo; Tsuchiya, Noriyoshi; Satish-Kumar, Madhusoodhan; Ishikawa, Masahiro; Grantham, Geoffrey; Sakata, Shuhei; Hirata, Takafumi


    The importance of brine is increasingly recognized because of its role on mass transportation at the mid- to lower-crustal pressure-temperature (P-T) conditions (e.g., Newton & Manning, 2010). However, the passage and residence times of brine are not well understood. This study deals with garnet-hornblende (Grt-Hbl) veins, discordantly cutting the gneissose structure of garnet-orthopyroxene-hornblende gneiss from the central Sør Rondane Mountains (SRM), East Antarctica. The Cl contents of hornblende and biotite, K content of hornblende, and the thickness of Na-richer rims of plagioclase decreased with distance from the Grt-Hbl vein. The P-T conditions of the vein formation were estimated to be 680 °C, 0.69 GPa (Higashino et al., under review). In the wall rock in the vicinity of the vein, addition of Li, Cu, Rb, Ba, Pb, and U, which tend to be mobile in brines rather than in melts is observed, using Zr as an immobile element (Higashino et al., 2015). This indicates that the Grt-Hbl vein was formed by the infiltration of NaCl-KCl brine. Trace element concentrations in the wall rock minerals decrease with distance from the vein, and in most cases show concave up/down profiles. Distances where these concentrations in each mineral species become constant are dependent on elements, and not on mineral species. These profiles can be best modelled by diffusion equations, suggesting that the diffusion is the major process transferring the trace elements perpendicular to the vein. Although plagioclase does not show significant trace element zoning within each single grain, the discontinuous drop of anorthite content at rims is preserved. Thin brine films in grain boundaries presumably caused dissolution-reprecipitation (e.g., Ruiz-Agudo et al., 2014), and lattice diffusion in plagioclase would have followed this to form homogeneous trace element zonings. Therefore, the main process of brine infiltration into the wall rock is possibly grain boundary diffusion in wet

  20. Zircon U-Pb Age, Trace Element, and Hf Isotope Evidence for Paleoproterozoic Granulite-Facies Metamorphism and Archean Crustal Remnant in the Dabie Orogen

    Institute of Scientific and Technical Information of China (English)

    Lei Nengzhong; Wu Yuanbao


    Zircon U-Pb age, trace elements, and Hf isotopes were determined for granulite and gneiss at Huaugtuling (黄土岭), which is hosted by ultrahigh-pressure metamorphic rocks in the Dabie(大别) orogen, east-central China. Cathodolumineseence (CL) images reveal core-rim structure for most zircons in the granulite. The cores show oscillatory zoning, relatively high Th/U and 176 Lu/177 Hf ratios, and high rare earth element (HREE)-enriched pattern, consistent with magmatic origin. They gave a weighted mean 207 Pb/206 Pb age of (2 766±9) Ma, dating magma emplacement of protolith. The rims are characterized by sector ur planar zoning, low Th/U and 176 Lu/177 Hf ratios, negative Euanomalies and flat HREE patterns, consistent with their formation under granulite-facies metamorphicconditions. Zircon U-Pb dating yields an age of (2 029±13) Ma, which is interpreted as a record ofmetamorphic event during the assembly of the supercontinent Columbia. The gneiss has a protolith ageof (1982±14) Ma, which is similar to the zircon U-Pb age for the granulite-facies metamorphism,suggesting complementary processes to granulite-facies metamorphism and partial melting. A fewinherited cores with igneous characteristics have 207 pb/206 Pb ages of approximately 3.53, 3.24, and 2.90Ga, respectively, suggesting the presence of Mesoarchean to Paleoarchean crustal remnants. A fewTriassic and Cretaceous metamorphic ages were obtained, suggesting the influences by the Triassiccontinental collision and postcollisional collapse in response to the Cretaceous extension. Comparingwith abundant occurrence of Triassic metamorphic zircons in ultrahigh-pressure eclogite and granitehydrous melt is evident for zircon growth in theHuangtuling granulite and gneiss during thecontinental collision. The magmatic protolithzircons from the granulite show a large variationin 176 Hf/177 Hf ratios from 0.280 809 to 0.281 289,corresponding to era(t) values of-7.3 to 6.3 andHf model ages of 2.74 to 3.34 Ga. The 2

  1. Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar (United States)

    Maw Maw Win; Enami, Masaki; Kato, Takenori


    The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.


    Quirico, E.; Montagnac, G.; Rouzaud, J.; Bonal, L.; Bourot-Denise, M.; Duber, S.; Reynard, B.


    Unravelling the origin of carbonaceous matter in pristine chondrites requires the understanding of the effect of post-accretion processes. In chondrites of petrologic type 3, thermal metamorphism modified to various extents the composition and structure of carbonaceous matter. Interestingly, this process controls the degree of structural order of carbonaceous matter, and clues on the thermal history of the parent body may be recovered from the physico-chemical study of carbonaceous matter. Following this framework, geothermometers based on Raman spectrometry of carbonaceous matter and covering a wide range of temperatures (100-650 °C) have been developed over recent years, both on terrestrial rocks and chondrites. While Raman data have been largely interpreted in terms of temperature, they are also the fingerprint of certain metamorphic conditions, especially in the low temperature range relevant to poorly ordered carbonaceous matter. This study investigates the Raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions. The Raman spectra of Polyaromatic Carbonaceous Matter (PCM) from 42 chondrites and 27 coal samples, measured with visible (514 nm) and ultra-violet (244 nm) excitation wavelengths, are analyzed. The Raman spectra of low rank coals and chondrites of petrologic types 1 and 2, which contain the more disordered PCM, reflect the distinct carbon structures of their precursors. The 514 nm Raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event. They result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups, or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms, due

  3. How High Are the P-T Conditions for Paleoproterozoic Metamorphism of the Huangtuling Felsic Granulite, North Dabieshan, Central China?

    Institute of Scientific and Technical Information of China (English)


    The 2.34 cm-wide garnet porphyroblast in the Paleoproterozoic felsic granulite from the Huangtuling area, North Dabieshan, has been reinvestigated for compositional variation in light of Cacomposition X-ray mapping to obtain peak P-T conditions of granulite-facies metamorphism.A new core-rim traverse was conducted through where there is little influence on Ca-profile and slight modification in Mn-, Mg- and Fe-profiles with the highest Mg/(Mg+Fe) value of 0.467.Reasonable peak P-T conditions were estimated to be 1.50- 1.70 GPa and 1 100- 1 150 ℃ according to TWQ-based garnetAl-orthopyroxene thermobarometry.These estimations suggest that the Huangtuling granulite once was subjected to ultrahigh-temperature (UHT) granulite-facies metamorphism following a high-pressure granulite-faices metamorphic stage, implying that a deep subduction and collision process relevant to the Yangtze block occurred in the Paleoproterozoic time, probably as a response to the global assembly event of the Columbia supercontinent.

  4. Active hydrothermal metamorphism in the Cerro Prieto geothermal system, Baja California, Mexico: a telescoped low P/T facies series. [Abstract only

    Energy Technology Data Exchange (ETDEWEB)

    Schiffman, P. (Univ. of California, Riverside); Elders, W.A.; Williams, A.E.; McDowell, S.D.; Bird, D.K.


    In the Cerro Prieto geothermal system, carbonate-cemented, quartzo-feldspathic sediments of the Colorado River delta are being actively recrystallized into calc-silicate metamorphic rocks through intense fluid/rock interaction with alkali chloride brine (1.5 x 10/sup 4/ ppM TDS) at temperatures between 200/sup 0/ and 370/sup 0/C, fluid pressures <0.25 Kb, lithostatic pressures <1.0 Kb, and oxygen fugacities close to the QFM buffer. Petrologic investigations of cuttings and core from more than 50 wells in this field reveal a prograde series of calc-silicate mineral zones with index metamorphic minerals: wairakite (wr), epidote (ep), prehnite (pr), and calcic clinopyrosene (cpx). The compositions of these and other key phases: wr (Ca/Ca + Na + K + 0.97), ep (Fe/Fe + Al/sup vi/ = 0.11 to 0.31), pr (Fe/Fe + Al/sup vi/ = 0.01 to 0.28), cps (close to Wo/sub 50/ and Mg/Mg + Fe + Mn = 0.23 to 0.90), actinolite (0.20 Al/sup iv//15 cations and Mg/Mg + Fe + Mn = 0.67 to 0.82), biotite (Mg/Mg + Fe + Mn = 0.58 to 0.87) and microcline (Or/sub 96 to 100/) reflect recrystallization under low fluid pressures, relatively low f/sub O/sub 2//, and varying brine compositions. Divariant mineral assemblages in this system comprise a very low P/T facies series encompassing the clay-carbonate, zeolite, greenschist, and amphibolite facies and reflect equilibrium occurring in response to both increasing temperature and decreasing CO/sub 2/ pressure. Similar facies series, characterized by telescoped devolatization mineral reactions, are becoming increasingly recognized in other active geothermal systems above 300/sup 0/C. However, close analogues in the fossil geologic record are as yet unidentified.

  5. Prograde, peak and retrograde metamorphic fluids and associated metasomatism in upper amphibolite to granulite facies transition zones

    NARCIS (Netherlands)

    Nijland, T.G.; Touret, J.L.R.


    Abstract Granulites constitute a major part of the (lower) continental crust, occurring on a regional scale in many metamorphic belts. Their origin is generally discussed in terms of vapour-absent melting and fluid-assisted dehydration. This last model is notably supported by the occurrence of two i

  6. Facies metamórficas y edades relativas de las rocas del extremo oriental del Brazo Huemul, provincia de Neuquén Metamorphic facies and relative ages of rocks on the eastern part of Brazo Huemul, Neuquén province

    Directory of Open Access Journals (Sweden)

    M.F. Gargiulo


    exposed in the study area are mainly of tonalitic composition and have been correlated with the Subcordilleran Patagonian Batholith because they are crosscut by two different types of dikes. One group of dikes shows an albite - chlorite - epidote - cummingtonite/ grunerite - hornblende mineral assemblage as a consequence of a thermal metamorphic event transitional between albite - epidote hornfels facies and hornblende hornfels conditions. This process has been attributed to the emplacement of the Cordilleran Patagonian Batholith of Cretaceous age. Because of this, the hornfels dikes were correlated with Montes de Oca Formation. The other group of dikes shows a chlorite + pumpellyite + laumontite + chlorite/esmectite + iron oxides assemblage indicating metamorphism in zeolite facies of high temperature or, sometimes shows propilitic alteration and these dikes have been correlated with the Ventana Formation. The differences between these two types of dikes allow the discussion of the relative age of the tonalitic rocks that host them. In this paper it is proposed that this tonalitic body is of Low to Middle Jurassic age.

  7. Regional variation in the Amitsoq gneisses related to crustal levels during late Archean granulite facies metamorphism: Southern west Greenland (United States)

    Nutman, A. P.; Bridgwater, D.; Mcgregor, V. R.


    The dominant lithology at Kangimut sangmissoq is described as nebulitic tonalitic gneiss containing highly distended plagioclase phyric amphibolites. The gneiss amphibolite complex was intruded by Nuk gneiss between 3.05 and 2.90 Ga and later (2.6 to 2.7 Ga) by post granulite facies granitoid sheets. The amphibolites are though to be Ameralik dikes and the older gray gneiss are then Amitsoq by definition. The problem arises when the isotopic data are considered, none of which indicate rocks older that about 3.0 Ga.

  8. Zircon U-Pb ages of olivine pyroxenite xenolith from Hannuoba:Links between the 97-158 Ma basaltic under-plating and granulite-facies metamorphism

    Institute of Scientific and Technical Information of China (English)

    LIU Yongsheng; YUAN Honglin; GAO Shan; HU Zhaochu; WANG Xuance; LIU Xiaoming; LIN Wenli


    U-Pb zircon dating by LA-ICP-MS and SHRIMP for one olivine pyroxenite yields complex age populations including Mesozoic ages of 97-158 Ma and 228 ±8.7 Ma, Early Paleozoic ages of 418-427 Ma, Paleoproterozoic age of 1844±13 Ma, Neoarchean age of 2541 ± 54 Ma and middle Archean age of 3123 ± 4.4 Ma. The 97-158 Ma and 228 ± 8.7 Ma zircons show typical igneous oscillatory zonation in CL images, suggesting two episodes of magmatic events. Overlapping of the 97-158 Ma ages with that of granulite xenoliths indicates that the Mesozoic granulite-facies metamorphism was induced by heating from the basaltic underplating at the base of the lower crust. Both processes lasted at least from about 158 to 97 Ma. Ages of 418-427 Ma could be records of the subduction of Mongolia oceanic crust under the North China craton. Ages of 1.84 Ga,2.54 Ga and 3.12 Ga correspond to the three important crust-mantle evolutionary events in the North China craton,and imply preservation of Precambrian lower crust in the present-day lower crust.

  9. Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India (United States)

    Belkin, H.E.; Macdonald, R.; Grew, E.S.


    Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (49.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios. ?? 2009 The Mineralogical Society.

  10. Episodic burial metamorphism in the Andes—A viable model? (United States)

    Bevins, R. E.; Robinson, D.; Aguirre, L.; Vergara, M.


    Burial metamorphism of regional extent throughout Mesozoic to Cenozoic sequences in the Andean Mountain belt has been attributed previously to a unique model of metamorphic development, involving episodic ˜40 m.y. cycles of extensional basin formation, burial, metamorphism, and then exhumation. A main premise of this model is that breaks in metamorphic grade occur at major stratigraphic unconformities, so marking successive metamorphic cycles. This model is tested in a Mesozoic Cenozoic sequence east of Santiago, where three metamorphic episodes have been reported on the basis of sharp breaks in metamorphic grade at two main unconformities. In metabasites from this area, reaction progress in mafic phyllosilicates shows a continuum across the sequence without breaks at the unconformities. There are differences in mineral assemblages between the various stratigraphic units, from which contrasting subgreenschist facies can be recognized. However, consideration of the controls on mineral paragenesis at subgreenschist facies conditions demonstrates that these different facies cannot be used as evidence of sharp breaks in metamorphic grade at unconformities, as has been reported in many previous publications. Thus, metamorphic breaks within this Andean section cannot be confirmed. Accordingly, models of Andean burial metamorphism linked to episodic tectonic cycles throughout the Mesozoic and Cenozoic appear unfounded.

  11. Experimental simulation of the condensation and metamorphism of seasonal CO2 condensates under martian conditions. (United States)

    Grisolle, F.; Schmitt, B.; Beck, P.; Philippe, S.; Brissaud, O.


    An experimental set-up, CARBON-IR, has been developed in order to perform the condensation and metamorphism of CO2 condensates in various controlled martian conditions at, or out of, equilibrium. The sample texture is monitored and near-infrared reflectance spectra are recorded. We present a first set of experiments aimed to simulate the formation of compact translucent slabs by condensation of CO2 gas, the metamorphism of CO2 snow, as well as their sublimation.

  12. LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite,Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

    Institute of Scientific and Technical Information of China (English)

    Chen Nengsong; Liu Rong; Sun Min; Li Huimin; He Lei; Wang Qinyan; Zhang Hongfei


    Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207Pb/206Pb age in the range of (2 493±54) -(2 500±180) Ma. The magmatic genesis-derived detrital zircon domain gives a 207Pb/206Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206Pb/238U age of (2 790±150) Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a dicsordia with an upper intercept age of (2 044.7±29.3) Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. ~2.8 Ga magmatism and ~2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at (2.04±0.03) Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT (ultrahigh temperature) metamorphosed slab.

  13. Seismic facies; Facies sismicas

    Energy Technology Data Exchange (ETDEWEB)

    Johann, Paulo Roberto Schroeder [PETROBRAS, Rio de Janeiro, RJ (Brazil). Exploracao e Producao Corporativo. Gerencia de Reservas e Reservatorios]. E-mail:


    The method presented herein describes the seismic facies as representations of curves and vertical matrixes of the lithotypes proportions. The seismic facies are greatly interested in capturing the spatial distributions (3D) of regionalized variables, as for example, lithotypes, sedimentary facies groups and/ or porosity and/or other properties of the reservoirs and integrate them into the 3D geological modeling (Johann, 1997). Thus when interpreted as curves or vertical matrixes of proportions, seismic facies allow us to build a very important tool for structural analysis of regionalized variables. The matrixes have an important application in geostatistical modeling. In addition, this approach provides results about the depth and scale of the wells profiles, that is, seismic data is integrated to the characterization of reservoirs in depth maps and in high resolution maps. The link between the different necessary technical phases involved in the classification of the segments of seismic traces is described herein in groups of predefined traces of two approaches: a) not supervised and b) supervised by the geological knowledge available on the studied reservoir. The multivariate statistical methods used to obtain the maps of the seismic facies units are interesting tools to be used to provide a lithostratigraphic and petrophysical understanding of a petroleum reservoir. In the case studied these seismic facies units are interpreted as representative of the depositional system as a part of the Namorado Turbiditic System, Namorado Field, Campos Basin.Within the scope of PRAVAP 19 (Programa Estrategico de Recuperacao Avancada de Petroleo - Strategic Program of Advanced Petroleum Recovery) some research work on algorithms is underway to select new optimized attributes to apply seismic facies. One example is the extraction of attributes based on the wavelet transformation and on the time-frequency analysis methodology. PRAVAP is also carrying out research work on an

  14. 40Ar/ 39Ar mineral ages from the Oki metamorphic complex, Oki-Dogo, southwest Japan: implications for regional correlations (United States)

    Dallmeyer, R. D.; Takasu, A.


    The Oki metamorphic complex exposed in the Oki-Dogo islands consists predominantly of psammitic and pelitic gneisses with subordinate amphibolite and rare calcareous gneiss. The Oki gneisses were regionally metamorphosed to general amphibolite facies conditions, with local development of granulite facies assemblages. Peak metamorphic conditions of c. 800°C have been suggested. Hornblende concentrates from amphibolites collected within the Oki metamorphic complex record 40Ar/ 39Ar isotope correlation ages of 199-192 Ma. These are interpreted to date the post metamorphic cooling through temperatures required for intracrystalline retention of argon (c. 500°C). Muscovite concentrates record 40Ar/ 39Ar plateau ages of 167-168 Ma. These are interpreted to date post metamorphic cooling through appropriate closure temperature of muscovite (c. 400-375°C). Combined with the previously reported geochronological data, the Oki metamorphic complex appears to have experienced peak metamorphic conditions at c. 250 Ma. Subsequently, it cooled and was exhumed at the earth's surface at c. 90 Ma with cooling rate of c. 5°C/Ma. The Oki metamorphic complex records a similar prograde metamorphic event as the Hida metamorphic complex exposed in central Japan. The cooling and exhumation rates of the Hida metamorphic complex were significantly more rapid compared with the Oki metamorphic complex, and they were exhumed with extensively intruded Jurassic granites (Funatsu granites).

  15. The effect of CO2 and N2 on phase relations, fluid composition, and quartz solubility in amphibolite facies metamorphic rocks (United States)

    Artimenko, Margaret V.


    Phase equilibria in the system SiO2-TiO2-Al2O3-Fe2O3-MnO-MgO-CaO-Na2O-K2O-P2O5-H2O-CO2-N2 are calculated to illustrate phase relations in amphibolite facies metasediments over a wide range of X[H2O-CO2-N2] conditions at 600 °C and 4.4 kb. Calculations are performed using the Gibbs free energy minimization technique. Results are presented in plots showing stable mineral assemblages as a function of total carbon in the system at varying water (a_{{{{H}}2 {{O}}}} = 1) content in the presence/absence of N2 in the fluid. The calculations indicate that the typical assemblage plagioclase—quartz—biotite—ilmenite—garnet—apatite is restricted to the rocks with CO2 saturation and X_{{{{H}}_{ 2} {{O}}}} higher than 60% in the fluid. Significant decrease in X_{{{{CO}}2 }} favors the stability of muscovite rather than garnet, whereas the decrease in X_{{{{H}}_{ 2} {{O}}}} leads to the stability of microcline over all range of X_{{{{CO}}2 }}. This paper also presents the composition and parameters (pH, Eh) of the fluid equilibrated with mineral assemblage. It is shown that the presence of low concentrations of N2 causes the fluid to consist of two phases when an aqueous supercritical solution (AS) coexists with a supercritical fluid with gas-like properties (SF). At high concentration of N2, the fluid consists of SF alone; in the absence of nitrogen, the fluid consists of AS alone. The solubility of monomer SiO 2 0 and dimer Si2O 4 0 decreases with increasing CO2 and after CO2 saturation point is held constant. The magnitude of the silica solubility at CO2 saturation depends upon the water content in AS. The effect of nitrogen on quartz solubility has been demonstrated to be negligible.

  16. Fluid inclusions evidence for differential exhumation of ultrahigh pressure metamorphic rocks in the Sulu terrane

    Institute of Scientific and Technical Information of China (English)

    FAN Hongrui; GUO Jinghui; HU Fangfang; CHU Xuelei; CHEN Fukun; JIN Chengwei


    Differential exhumation was petrologically recognized in ultrahigh pressure metamorphic rocks from the southern and northern parts of the Sulu terrane. While a normal exhumation occurred for eclogites and gneisses in south Sulu, granulite-facies overprinting of ultrahigh pressure metamorphic rocks took place with high retrograde temperatures in north Sulu. A study of fluid inclusions reveals trapping of five type fluid inclusions in high and ultrahigh pressure eclogite minerals and vein quartz in the Sulu terrane. These are A-type N2±CO2 inclusion trapped at high and ultra-high pressure eclogite-facies metamorphic condition, B-type pure-CO2 liquid phase inclusion with higher density trapped during granulite-facies overprinting metamorphism of eclogites, C-type CO2-H2O inclusion and D-type hypersaline inclusion trapped in high pressure eclogite-facies re-crystallization stage, and E-type low salinity H2O inclusion trapped in the latest stage of ultrahigh pressure exhumation (amphibolite-facies retrogression). Identification of crowded-distributing pure-CO2 liquid inclusions with higher density trapped in garnet of eclogites provides an evidence for granulite-facies overprinting metamorphism in the north Sulu terrane.

  17. Generation of trondhjemite from partial melting of dacite under granulite facies conditions: an example from the New Jersey Highlands, USA (United States)

    Puffer, J.H.; Volkert, R.A.


    New field and geochemical data place the Losee Metamorphic Suite (a tonalite/trondhjemite complex) of northern New Jersey into the context of a major Proterozoic continental are represented by a discontinuous belt of northern Appalachian metadacite. Samples of Losee rock range from extremely leucocratic trondhjemite locally associated with amphibolite, to banded biotite, hornblende, pyroxene, and garnet-bearing tonalites. The major element and REE composition of the tonalite closely resembles dacite from continental are settings and model melts extracted from an eclogite residue by partial melting at 15 kbar. The REE composition of most Losee trondhjemite is enriched in REE, particularly HREE, compared with Losee tonalite, and is interpreted as the product of local anatectic melting of Losee tonalite (metadacite) that occurred in a granulite facies environment during the Grenville orogeny. ?? 1991.

  18. Facies conditions of the 2. Lusatian seam horizon in the area East of Peitz

    Energy Technology Data Exchange (ETDEWEB)

    Boenisch, R.; Liskow, C.


    Characterizes the Miocene brown coal deposit in the area Peitz, Jaenschwalde and Guben (GDR) by methods of paleobotany and paleogeography. Results of macropetrographic facies analysis and geophysical borehole measurements were employed in the study. Geologic profiles of the region as well as maps of seam distribution were drawn up. The analysis proves that prehistoric river meanders divide the brown coal moor into a northern and a southern section. A description of the paleoenvironment and the sedimentation process is given. A correlation between coal facies and technological coal quality is pointed out. The study is being used to develop a geologic seam model for this brown coal mining area. 9 refs.

  19. Brittle–viscous deformation of vein quartz under fluid-rich low greenschist facies conditions

    Directory of Open Access Journals (Sweden)

    H. J. Kjøll


    Full Text Available A coarse grained, statically crystallized quartz vein, embedded in a phyllonitic matrix, was studied by EBSD and optical microscopy to gain insights into the processes of strain localization in quartz deformed under low-grade conditions, broadly coincident with the frictional–viscous transition. The vein is from a high strain zone at the front of the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The vein was deformed under lower greenschist facies conditions during deformation along a large out-of-sequence phyllonitic thrust of Caledonian age. The host phyllonite formed at the expense of metabasalt wherein feldspar broke down to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the studied quartz vein acted as a relatively rigid body deforming mainly by coaxial strain. Viscous deformation was initially accommodated by basal ⟨a⟩ slip of quartz during the development of a mesoscopic pervasive extensional crenulation cleavage. Under the prevailing boundary conditions, however, dislocation glide-accommodated deformation of quartz resulted inefficient and led to dislocation tangling and strain hardening of the vein. In response to hardening, to the progressive increase of fluid pressure and the increasing competence contrast between the vein and the weak foliated host phyllonite, quartz crystals began to deform frictionally along specific, optimally oriented lattice planes, creating microgouges along microfractures. These were, however, rapidly sealed by nucleation of new grains as transiently over pressured fluids penetrated the deforming system. The new nucleated grains grew initially by solution-precipitation and later by grain boundary migration. Due to the random initial orientation of the vein crystals, strain was accommodated differently in the individual crystals, leading to the development of remarkably different

  20. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan (United States)

    Collett, Stephen; Faryad, Shah Wali


    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  1. FBC desulfurization process using coal with low sulfur content, high oxidizing conditions and metamorphic limestones

    Directory of Open Access Journals (Sweden)

    S. R. Bragança


    Full Text Available A metamorphic limestone and a dolomite were employed as SO2 sorbents in the desulfurization of gas from coal combustion. The tests were performed in a fluidized bed reactor on a bench and pilot scale. Several parameters such as bed temperature, sorbent type, and sorbent particle size at different Ca/S molar ratios were analyzed. These parameters were evaluated for the combustion of coal with low-sulfur/high-ash content, experimental conditions of high air excess and high O2 level in fluidization air. Under these conditions, typical of furnaces, few published data can be found. In this work, a medium level of desulfurization efficiency (~60% for Ca/S = 2 was obtained.

  2. FBC desulfurization process using coal with low sulfur content, high oxidizing conditions and metamorphic limestones

    Energy Technology Data Exchange (ETDEWEB)

    Braganca, S.R.; Castellan, J.L. [Universidade Federal do Rio Grande do Sul, Porto Alegre (Brazil)


    A metamorphic limestone and a dolomite were employed as SO{sub 2} sorbents in the desulfurization of gas from coal combustion. The tests were performed in a fluidized bed reactor on a bench and pilot scale. Several parameters such as bed temperature, sorbent type, and sorbent particle size at different Ca/S molar ratios were analyzed. These parameters were evaluated for the combustion of coal with low-sulfur/high-ash content, experimental conditions of high air excess and high O{sub 2} level in fluidization air. Under these conditions, typical of furnaces, few published data can be found. In this work, a medium level of desulfurization efficiency (similar to 60%) for Ca/S = 2 was obtained.

  3. FBC desulfurization process using coal with low sulfur content, high oxidizing conditions and metamorphic limestones

    Energy Technology Data Exchange (ETDEWEB)

    S.R. Braganca; J.L. Castellan [Federal University of Rio Grande do Sul, Porto Alegre (Brazil)


    A metamorphic limestone and a dolomite were employed as SO{sub 2} sorbents in the desulfurization of gas from coal combustion. The tests were performed in a fluidised bed reactor on a bench and pilot scale. Several parameters such as bed temperature, sorbent type, and sorbent particle size at different Ca/S molar ratios were analyzed. These parameters were evaluated for the combustion of coal with low-sulfur/high-ash content, experimental conditions of high air excess and high O{sub 2} level in fluidization air. Under these conditions, typical of furnaces, few published data can be found. In this work, a medium level of desulfurization efficiency (about 60%) for Ca/S = 2 was obtained. 25 refs., 5 figs.

  4. Brittle-viscous deformation of vein quartz under fluid-rich low greenschist facies conditions (United States)

    Jørgen Kjøll, Hans; Viola, Giulio; Menegon, Luca; Sørensen, Bjørn


    A coarse grained, statically crystallized quartz vein with a random CPO, embedded in a phyllonitic matrix, was studied by optical microscopy, SEM imaging and EBSD to gain insights into the processes of strain localization in quartz deformed under low greenschist facies conditions at the frictional-viscous transition. The vein is located in a high strain zone at the front of an imbricate stack of Caledonian age along the northwesternmost edge of the Repparfjord Tectonic Window in northern Norway. The vein was deformed within the Nussirjavrri Fault Zone (NFZ), an out-of-sequence thrust with a phyllonitic core characterized by a ramp-flat-ramp geometry, NNW plunging stretching lineations and top-to-the SSE thrusting kinematics. Deformation conditions are typical of the frictional-viscous transition. The phyllonitic core formed at the expense of metabasalt wherein feldspar broke down to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the studied quartz vein acted as a relatively rigid body deforming mainly by coaxial strain. Viscous deformation, related to the development of a mesoscopic pervasive extensional crenulation cleavage, was accommodated within the vein initially by basal slip of suitably oriented quartz crystals, which produced e.g. undulose extinction, extinction bands and bulging grain boundaries. In the case of misoriented quartz crystals, however, glide-accommodated dislocation creep resulted soon inefficient and led to localized dislocation tangling and strain hardening. In response to 1) hardening, 2) progressive increase of fluid pressure within the actively deforming vein and 3) increasing competence contrast between the vein and the surrounding weak, foliated phyllonitic fault core, quartz crystals began to deform frictionally along specific lattice planes oriented optimally with respect to the imposed stress field. Microfaulting generated small volumes of gouge along

  5. Metamorphic P-T-t path retrieved from metapelites in the southeastern Taihua metamorphic complex, and the Paleoproterozoic tectonic evolution of the southern North China Craton (United States)

    Lu, Jun-Sheng; Zhai, Ming-Guo; Lu, Lin-Sheng; Wang, Hao Y. C.; Chen, Hong-Xu; Peng, Tao; Wu, Chun-Ming; Zhao, Tai-Ping


    The Taihua metamorphic complex in the southern part of the North China Craton is composed of tonalite-trondhjemite-granodiorite (TTG) gneisses, amphibolites, metapelitic gneisses, marbles, quartzites, and banded iron formations (BIFs). The protoliths of the complex have ages ranging from ∼2.1 to ∼2.9 Ga and was metamorphosed under the upper amphibolite to granulite facies conditions with NWW-SEE-striking gneissosity. Metapelitites from the Wugang area have three stages of metamorphic mineral assemblages. The prograde metamorphic mineral assemblage (M1) includes biotite + plagioclase + quartz + ilmenite preserved as inclusions in garnet porphyroblasts. The peak mineral assemblage (M2) consists of garnet porphyroblasts and matrix minerals of sillimanite + biotite + plagioclase + quartz + K-feldspar + ilmenite + rutile + pyrite. The retrograde mineral assemblage (M3), biotite + plagioclase + quartz, occurs as symplectic assemblages surrounding embayed garnet porphyroblasts. Garnet porphyroblasts are chemically zoned. Pseudosection calculated in the NCKFMASHTO model system suggests that mantles of garnet porphyroblasts define high-pressure granulites facies P-T conditions of 12.2 kbar and 830 °C, whereas garnet rims record P-T conditions of 10.2 kbar and 840 °C. Integrating the prograde mineral assemblages, zoning of garnet porphyroblasts with symplectic assemblages, a clockwise metamorphic P-T path can be retrieved. High resolution SIMS U-Pb dating and LA-ICP-MS trace element measurements of the metamorphic zircons demonstrate that metapelites in Wugang possibly record the peak or near peak metamorphic ages of ∼1.92 Ga. Furthermore, 40Ar/39Ar dating of biotite in metapelites suggests that the cooling of the Taihua complex may have lasted until ∼1.83 Ga. Therefore, a long-lived Palaeoproterozoic metamorphic event may define a slow exhumation process. Field relationship and new metamorphic data for the Taihua metamorphic complex does not support the previous

  6. Charnockite microstructures: From magmatic to metamorphic

    Directory of Open Access Journals (Sweden)

    Jacques L.R. Touret


    Full Text Available Charnockites sensu lato (charnockite-enderbite series are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry (H2O-poor felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post-magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstructures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at intergrain boundaries during retrogradation are documented by microstructures including K-feldspar microveins and myrmekites. They indicate that a large quantity of low-H2O activity salt-rich brines, were present (together with CO2 under immiscible conditions in the lower crust.

  7. Tomography-based monitoring of isothermal snow metamorphism under advective conditions

    Directory of Open Access Journals (Sweden)

    P. P. Ebner


    Full Text Available Time-lapse X-ray micro-tomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. Diffusion and advection across the snow pores were analysed in controlled laboratory experiments. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective transport properties. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Diffusion originating in the Kelvin effect between snow structures dominates and is the main transport process in isothermal snow packs.

  8. Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif,China

    Institute of Scientific and Technical Information of China (English)

    索书田; 钟增球; 游振东


    A detailed tectonic analysis demonstrates that the present ob served regional tectonic configuration of the ultrahigh-pressure metamorphic terrane in the Da bie massif was mainly formed by the extension processes of the post-lndosinian continent-continent oblique collision between the Sino-Korean and V’angtze cratons and ultrahigh-pressure metamorphism (UHPM). The configuration is characterized by a regional tectonic pattern similar to metamorphic core complexes and by the development of multi-layered detachment zones. On the basis of the identification of compressional and extensional fabrics, it is indicated that the exhumation and uplift of ultrahigh-pressure (UHP) metamorphic rocks from the mantle depth to the surface can be divided into at least three different decompression retrogressive metamo rphism and tectonic deformation stages, in which the subhorizontal crustal-scale extensional flow in the middle-lower crust under amphibolite facies conditions is an important geodynamic process in the exhu

  9. Paleogeographic and litho-facies formation conditions of MidUpper Jurassic sediments in S-E Western Siberia (Tomsk Oblast) (United States)

    Shaminova, M.; Rychkova, I.; Sterzhanova, Ju


    This paper describes the criteria to identify Tumen (lower Bathonian) and Naunak (upper Bathonian-Callovian- Oxfordian) suites within S-E Western Siberia (Tomsk Oblast). The specific paleogeographic and litho-facies formation conditions of sediments and numerous vegetable remains and ichnofossils indicated the fact that this territory was the location of sedimentogenesis transition during Tumen and Naunak suite formation. Based on integrated survey oil-gas potential litho-facies groups were defined in Mid-Upper Jurassic sediments within S-E Western Siberia.

  10. Tomography-based monitoring of isothermal snow metamorphism under advective conditions


    P. P. Ebner; M. Schneebeli; A. Steinfeld


    Time-lapse X-ray micro-tomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. Diffusion and advection across the snow pores were analysed in controlled laboratory experiments. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective transport properties. The results showed that isothermal advection with saturated air have no influence...

  11. Tomography-based monitoring of isothermal snow metamorphism under advective conditions


    P. P. Ebner; M. Schneebeli; A. Steinfeld


    Time-lapse X-ray microtomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. The effect of diffusion and advection across the snow pores on the snow microstructure were analysed in controlled laboratory experiments and possible effects on natural snowpacks discussed. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective permeabi...

  12. Chemical and mineralogical data and processing methods management system prototype with application to study of the North Caucasus Blybsky Metamorphic Complexes metamorphism PT-condition (United States)

    Ivanov, Stanislav; Kamzolkin, Vladimir; Konilov, Aleksandr; Aleshin, Igor


    There are many various methods of assessing the conditions of rocks formation based on determining the composition of the constituent minerals. Our objective was to create a universal tool for processing mineral's chemical analysis results and solving geothermobarometry problems by creating a database of existing sensors and providing a user-friendly standard interface. Similar computer assisted tools are based upon large collection of sensors (geothermometers and geobarometers) are known, for example, the project TPF (Konilov A.N., 1999) - text-based sensor collection tool written in PASCAL. The application contained more than 350 different sensors and has been used widely in petrochemical studies (see A.N. Konilov , A.A. Grafchikov, V.I. Fonarev 2010 for review). Our prototype uses the TPF project concept and is designed with modern application development techniques, which allows better flexibility. Main components of the designed system are 3 connected datasets: sensors collection (geothermometers, geobarometers, oxygen geobarometers, etc.), petrochemical data and modeling results. All data is maintained by special management and visualization tools and resides in sql database. System utilities allow user to import and export data in various file formats, edit records and plot graphs. Sensors database contains up to date collections of known methods. New sensors may be added by user. Measured database should be filled in by researcher. User friendly interface allows access to all available data and sensors, automates routine work, reduces the risk of common user mistakes and simplifies information exchange between research groups. We use prototype to evaluate peak pressure during the formation of garnet-amphibolite apoeclogites, gneisses and schists Blybsky metamorphic complex of the Front Range of the Northern Caucasus. In particular, our estimation of formation pressure range (18 ± 4 kbar) agrees on independent research results. The reported study was

  13. Experiments to constrain the garnet-talc join for metapelitic material at eclogite-facies conditions (United States)

    Chmielowski, Reia M.; Poli, Stefano; Fumagalli, Patrizia


    Increasing pressure due to the subduction of mica-dominated sediments results in a loss of biotite as garnet-talc becomes a stable assemblage. While this transition is observed in natural samples, it has not yet been well constrained experimentally. Previous experimental investigations into metapelitic compositions at the University of Milan (Poli and Schmidt 2002, Ferri et al., 2009) indicated that further work in the range of 600-700° C, 2-3 GPa was required to elucidate this tie-line transition. The assemblages leading to garnet-talc stability through tie-line flip reactions include biotite-chlorite, biotite-chloritoid, and biotite-kyanite. Furthermore the mutual stability of garnet-chlorite and chloritoid-biotite at relatively high pressure conditions below the garnet-talc field is reevaluated. Current investigations on two synthetic compositions (NM, NP) in the model metapelitic system CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O are carried out in a piston cylinder apparatus at pressures and temperatures up to 2.7 GPa and to 740°C. Experiments are buffered with graphite, and are generally run under fluid saturated conditions. Two capsules, one of each composition, are included within the pressure chamber for each experiment. The NM composition is representative of metapelites and the NP composition is representative of metagreywackes. Experiments are characterized by XRD, BSE images and EMPA. The following summary includes both current investigations and the above mentioned previous work, undertaken on the same chemical compositions. All assemblages also contain quartz, white mica, fluid ± zoisite or lawsonite. The assemblage garnet-chlorite-chloritoid ± staurolite is present at 500° C at pressures of 1.4 and 1.6 GPa. The assemblage biotite-staurolite-chlorite is present at 600° C, 1.2 GPa and at 625° C, 1.4 GPa. The assemblage biotite-chloritoid-chlorite is present at 600° C for pressures ≥ 1.3 GPa and ≤ 1.7 GPa. The assemblage garnet-chloritoid-biotite is

  14. Mechanical behaviour of the Oman metamorphic sole: rheology of amphibolites at lower crustal conditions during subduction initiation (United States)

    Soret, Mathieu; Agard, Philippe; Ildefonse, Benoît; Dubacq, Benoît; Prigent, Cécile; Yamato, Philippe


    Amphibolites are commonly found in the middle to lower continental crust and along oceanic transform faults and detachments. Amphibolites are also the main component of metamorphic soles beneath highly strained peridotites at the base of large-scale ophiolites as exemplified in Oman. Metamorphic soles are crustal slivers stripped from the slab during early subduction and underplated below the upper plate (future ophiolite) mantle when the subduction interface is still young and warm (i.e. during the first million years -My- of intra-oceanic subduction). Understanding the rheological behaviour of amphibolitic rocks is therefore of major interest to model and quantify deformation and strain localisation in varied geodynamical environments. This contribution focuses on the deformation mechanisms of amphibole through a microstructural and petrological study of garnet-bearing and garnet-free clinopyroxene-bearing amphibolites, using EBSD analysis. The first aim is to test the influence of progres- sive changes in PT conditions during deformation and of the appearance/disappearance of anhydrous minerals (plagioclase, clinopyroxene and garnet) on the mechanical behaviour of mafic amphibolites. The second aim is to track deformation mechanisms during early subduction, through the study of these metamorphosed oceanic rocks, commonly 10-100 m thick, which range from high- to low-grade away from the contact with the peridotites (i.e. from 800 ± 100˚C - 0.9 ± 0.2 GPa to 500 ± 100˚C - 0.5 ± 0.1 GPa) and are essentially mafic at the top). Our study points out the existence of two major steps of deformation in the high-temperature amphibolite slices of the metamorphic soles during the early subdduction dynamics. These two steps witness important mechanical coupling and progressive strain localization at plate interface under cooling and hydrated conditions after subduction initiation. During the accretion of the first slice of metamorphic sole at 850 ± 50˚C (the garnet


    Institute of Scientific and Technical Information of China (English)


    <正>20070226 Chen Nengsong (Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China); Liu Rong LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance (Journal of China University of Geosciences, ISSN1002-0705, CN42-1279/P, 16(4), 2005, p.317-323, 4 illus., 2 tables, 32 refs.) Key words: granulites, Dabie Mountains

  16. High-pressure subduction-related serpentinites and metarodingites from East Thessaly (Greece): Implications for their metamorphic, geochemical and geodynamic evolution in the Hellenic-Dinaric ophiolite context (United States)

    Koutsovitis, Petros


    Metaophiolites that consist mainly of serpentinites or metabasites outcrop in the East Thessaly region, Central Greece. These formations, along with some ophiolite outcrops, have been variably emplaced onto the Pelagonian tectonostratigraphic zone as dispersed and deformed thrust sheets. Based upon their estimated metamorphic degree, serpentinites from the metaophiolites and ophiolitic units of East Thessaly have been divided into three groups: Group-1 serpentinites from East Othris, include lizardite and antigorite in balanced amounts, defining greenschist facies metamorphic conditions ( 320-340 °C, P ≈ 6-7 kbar). Group-2 serpentinites are marked by further prevalence of antigorite over lizardite, suggesting upper-greenschist to lower-blueschist facies metamorphism ( 340-370 °C, P ≈ 8-10 kbar). Group-3 serpentinites are mainly characterized by the predominance of antigorite corresponding to blueschist facies metamorphism ( 360-400 °C, P ≈ 11-12 kbar). The chemical composition and mineral chemistry of the East Thessaly serpentinites suggest that their protoliths were highly depleted harzburgites. Group-1 serpentinites exhibit higher Mg/Si ratio values and LOI compared to serpentinite Groups-2 and -3, due to increasing metamorphic conditions of the latter groups. The prominent Cs, U, Pb, As and Sb enrichments point to subduction-related serpentinites that were subjected to fluid/rock interactions. The East Thessaly serpentinites also seem to have undergone deserpentinization retrograde metamorphism (estimated at P processes.

  17. Variscan terrane of deep-crustal granulite facies in Yushugou area, southern Tianshan

    Institute of Scientific and Technical Information of China (English)

    王润三; 周鼎武; 王居里; 王焰; 刘养杰


    The Yushugou terrane of deep-crustal granulite facies in southern Tianshan consists of two parts, granulite and metaperidotite. The whole terrane is a metamorphism of (high-pressure) granulite facies, and typical mineral associations are: Gt-Cpx-Pl-Tit-Ilm (±Qz) (silica-saturated and oversaturated mafic rocks), Gt-Ky (pseudomorph)-Pl-Ru-Ilm±Qz (metapelitic rocks) and Spi-Opx-Cpx-Ol (meta-ultramafic rocks). The peak-stage P-T conditions are 795—964℃, 0.97—1.42 GPa, which are obtained with mineral chemistry, assemblage analyses and P-T estimation. The Sm-Nd isochron age of peak-stage metamorphic minerals is (315±3.62) Ma. All of these indicate that the terrane is a deep-crustal body, which subduets to the depth of 40—50 km in the middle late-Paleozoic, undergoing metamorphism of (high-pressure) granulite facies, and exhumed again to the surface by tectonic uplifting.

  18. Metamorphic Evolution of Garnet-bearing Epidote-Barroisite Schist from the Meratus Complex in South Kalimantan, Indonesia

    Directory of Open Access Journals (Sweden)

    Nugroho Imam Setiawan


    Full Text Available DOI:10.17014/ijog.2.3.139-156This paper presents metamorphic evolution of metamorphic rocks from the Meratus Complex in South Kalimantan, Indonesia. Eight varieties of metamorphic rocks samples from this location, which are garnet-bearing epidote-barroisite schist, epidote-barroisite schist, glaucophane-quartz schist, garnet-muscovite schist, actinolite-talc schist, epidote schist, muscovite schist, and serpentinite, were investigated in detail its petrological and mineralogical characteristics by using polarization microscope and electron probe micro analyzer (EPMA. Furthermore, the pressure-temperature path of garnet-bearing epidote-barroisite schist was estimated by using mineral parageneses, reaction textures, and mineral chemistries to assess the metamorphic history. The primary stage of this rock might be represented by the assemblage of glaucophane + epidote + titanite ± paragonite. The assemblage yields 1.7 - 1.0 GPa in assumed temperature of 300 - 550 °C, which is interpreted as maximum pressure limit of prograde stage. The peak P-T condition estimated on the basis of the equilibrium of garnet rim, barroisite, phengite, epidote, and quartz, yields 547 - 690 °C and 1.1 - 1.5 GPa on the albite epidote amphibolite-facies that correspond to the depth of 38 - 50 km. The retrograde stage was presented by changing mineral compositions of amphiboles from the Si-rich barroisite to the actinolite, which lies near 0.5 GPa at 350 °C. It could be concluded that metamorphic rocks from the Meratus Complex experienced low-temperature and high-pressure conditions (blueschist-facies prior to the peak metamorphism of the epidote amphibolite-facies. The subduction environments in Meratus Complex during Cretaceous should be responsible for this metamorphic condition.

  19. Metamorphic Evolution of Garnet-bearing Epidote-Barroisite Schist from the Meratus Complex in South Kalimantan, Indonesia

    Directory of Open Access Journals (Sweden)

    Nugroho Imam Setiawan


    Full Text Available This paper presents metamorphic evolution of metamorphic rocks from the Meratus Complex in South Kalimantan, Indonesia. Eight varieties of metamorphic rocks samples from this location, which are garnet-bearing epidote-barroisite schist, epidote-barroisite schist, glaucophane-quartz schist, garnet-muscovite schist, actinolite-talc schist, epidote schist, muscovite schist, and serpentinite, were investigated in detail its petrological and mineralogical characteristics by using polarization microscope and electron probe micro analyzer (EPMA. Furthermore, the pressure-temperature path of garnet-bearing epidote-barroisite schist was estimated by using mineral parageneses, reaction textures, and mineral chemistries to assess the metamorphic history. The primary stage of this rock might be represented by the assemblage of glaucophane + epidote + titanite ± paragonite. The assemblage yields 1.7 - 1.0 GPa in assumed temperature of 300 - 550 °C, which is interpreted as maximum pressure limit of prograde stage. The peak P-T condition estimated on the basis of the equilibrium of garnet rim, barroisite, phengite, epidote, and quartz, yields 547 - 690 °C and 1.1 - 1.5 GPa on the albite epidote amphibolite-facies that correspond to the depth of 38 - 50 km. The retrograde stage was presented by changing mineral compositions of amphiboles from the Si-rich barroisite to the actinolite, which lies near 0.5 GPa at 350 °C. It could be concluded that metamorphic rocks from the Meratus Complex experienced low-temperature and high-pressure conditions (blueschist-facies prior to the peak metamorphism of the epidote amphibolite-facies. The subduction environments in Meratus Complex during Cretaceous should be responsible for this metamorphic condition.

  20. Tomography-based characterization of ice-air interface dynamics of temperature gradient snow metamorphism under advective conditions (United States)

    Ebner, Pirmin Philipp; Andreoli, Christian; Schneebeli, Martin; Steinfeld, Aldo


    Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. A functional understanding of this process is essential for many disciplines, from modeling the effects of snow on regional and global climate to assessing avalanche formation. Time-lapse X-ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Experiments specifically analyzed sublimation and deposition of water vapor on the ice structure. In addition, an analysis of the ice-air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer. The results indicate that sublimation of the ice matrix dominated for flow rates surface area and thus suggest a change of the physical and optical properties of the snow. The estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values.

  1. Metamorphism, Plate Tectonics, and the Supercontinent Cycle (United States)

    Brown, Michael

    Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G-UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite, high-pressure granulite metamorphism (E-HPGM), is also first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E-HPGM belts are complementary to G-UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts—reflecting a duality of thermal regimes—appears in the record only since the Neoarchean Era. A

  2. High grade metamorphism in the Bundelkhand massif and its implications on Mesoarchean crustal evolution in central India

    Indian Academy of Sciences (India)

    S P Singh; S B Dwivedi


    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 retro-grade 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.

  3. Applicability of the RSCM geothermometry approach in a complex tectono-metamorphic context: The Jebilet massif case study (Variscan Belt, Morocco) (United States)

    Delchini, Sylvain; Lahfid, Abdeltif; Plunder, Alexis; Michard, André


    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

  4. Chlorine isotope behavior during prograde metamorphism of sedimentary rocks (United States)

    Selverstone, Jane; Sharp, Zachary D.


    )sedimentary layers except within the Urseren shear zone. These data contribute to a relatively closed-system view of metamorphic devolatilization from anchizone through mid-amphibolite facies conditions.

  5. Time interval between volcanism and burial metamorphism and rate of basin subsidence in a Cretaceous Andean extensional setting (United States)

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


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

  6. Cause Analysis on the Phase Transition of the Tectonic Facies of the Metamorphic Rock Series in the Wutai Mountain-Heng Mountain Areas%五台山—恒山地区变质岩系构造相相变成因分析

    Institute of Scientific and Technical Information of China (English)

    郭景林; 米广尧; 范林森


    Areas in the Wutai mountain-Heng mountain are considered to be one of the most popular places for the tectonic facies researches owing to the various structural characters at different crust levels. In the present study, the structural characteristics of the Early Precambrian were analyzed. On the basis of the different geological characters of fold, fracture, pudding of the rock and syntectonic crystallization, some references were provided for analyzing the tectonic facies and the structural phase transition in the areas. Combined with the information of the geological characteristics, petrology, deformation,and metamorphic characteristics,and isotope chronology of the geological unit,the preliminary studies were conducted on the tectonic environment of the the Early Precambrian in the areas, and discussions were made on the crustal evolution andthe cause of the tectonic facies phase transition. The phenomena occurring commonly in the Metamorphic rock areas was explained reasonably,that is, the alienation between the same rocks and the convergence between the different rocks,or the same thing with different phases and the same phase with different faces. All of these provided the new research thinking and the working methods for the metamorphic rock areas.The high-grade regions of the Hornblende granulite phase in the Heng mountain areas represent the mid-lower crust's transitional zone and detachment zone. Their and it's typical structural styles, material composition, metamorphism and the effects of the deep melting have important significance on the researches of the mid-lower crust's rheological behavior, crustal differentiation and the cracking events for early continent.%五台山—恒山地区出露有不同层次的地壳,是研究构造相最理想的地区之一.作者对该区早前寒武纪构造特征进行了分析.根据不同层次的褶皱、断裂、布丁化岩石及同构造分泌结晶脉的宏观地质特征和与其相关的微组构特

  7. Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif, China

    Institute of Scientific and Technical Information of China (English)


    A detailed tectonic analysis demonstrates that the present observed regional tectonic configuration of the ultrahigh-pressure metamorphic terrane in the Dabie massif was mainly formed by the extension processes of the post-Indosinian continent-continent oblique collision between the Sino-Korean and Yangtze cratons and ultrahigh-pressure metamorphism (UHPM). The configuration is characterized by a regional tectonic pattern similar to metamorphic core complexes and by the development of multi-layered detachment zones. On the basis of the identification of compressional and extensional fabrics, it is indicated that the exhumation and uplift of ultrahigh-pressure (UHP) metamorphic rocks from the mantle depth to the surface can be divided into at least three different decompression retrogressive metamorphism and tectonic deformation stages, in which the subhorizontal crustal-scale extensional flow in the middle-lower crust under amphibolite facies conditions is an important geodynamic process in the exhumation of UHP metamorphic rocks. Moreover, the extensional flow is probably driven by delamination and magmatic underplating of thickened lithospheric mantle following the continental oblique collision.

  8. Metamorphic sole formation, emplacement and blueschist overprint: early obduction dynamics witnessed by W. Turkey ophiolites (United States)

    Plunder, Alexis; Agard, Philippe; Chopin, Christian; Soret, Mathieu; Okay, Aral; Whitechurch, Hubert


    Western Turkey, with a >200 km long-belt of unmetamorphosed ophiolite overlying continental lithosphere is one or even the largest obducted ophiolite on Earth and therefore a key example to study obduction and early subduction dynamics. All Western Turkish ophiolite fragments are considered as part of the same Neotethyan branch resulting of a long-lived continental subduction (or underthrusting). Synchronous (ca. ~ 93 Ma) metamorphic sole formation and preservation at the base of most of the Turkish ophiolite fragments support this single event and place a strong constraint on the age of subduction initiation. Metamorphic soles are indeed generally considered to have formed during the early and hot subduction zone at 25 ± 10 km depths and welded to the overriding oceanic lithosphere. In Western Turkey however (as for most places worldwide) a systematic study of the pressure-temperature conditions with modern thermobarometric tools is generally lacking, and fundamental mechanisms of formation or accretion to the upper plate are poorly (if at all) constrained. We herein reappraise Western Turkish metamorphic soles focusing on the following points and issues: (i) detailed structures of metamorphic sole and other subduction derived units, petrological evolution and refined pressure-temperature conditions; peak pressure-temperature conditions of metamorphic sole were estimated using garnet, clinopyroxene, amphibole and plagioclase as the peak paragenesis at 10.5 ± 2 kbar and 800 ± 50°C based on pseudosections using the Theriak/Domino package (ii) the rather unique (and enigmatic) blueschist facies overprint found in places was investigated in terms of structural position and pressure-temperature conditions. Conditions of overprint were estimated around 12 kbar and 425 °C from the presence of glaucophane, lawsonite, jadeite and garnet overgrowing the amphibolite-facies assemblage. This field-based study provides clues to mechanisms of metamorphic sole underplating

  9. 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 (United States)

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


    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.

  10. Temperature micro-mapping and redox conditions of a chlorite zoning pattern in green-schist facies fault zone (United States)

    Trincal, Vincent; Lanari, Pierre; Lacroix, Brice; Buatier, Martine D.; Charpentier, Delphine; Labaume, Pierre; Muñoz, Manuel


    Faults are major discontinuities driving fluid flows and playing a major role in precipitation of ore deposits. Mineral paragenesis and crystal chemistry depend on Temperature (T) condition, fluid composition but also on the redox environment of precipitation. The studied samples come from the Pic de Port Vieux thrust sheet, a minor thrust sheet associated to Gavarnie thrust fault zone (Central Pyrenees). The Pic de Port Vieux Thrust sheet comprises a 1-20 meter thick layer of Triassic red beds and mylonitized Cretaceous limestone. The thrust sheet is affected by faults and cleavage; the other important deformation product is a set of veins filled by quartz and chlorite. Microstructural and mineralogical investigations were performed based on the previous work of Grant (1992). The crystallization of chlorite is syn-tectonic and strongly controlled by the fluid circulation during the Gavarnie thrust sheet emplacement. Chlorite precipitated in extension veins, crack-seal shear veins or in open cavities. The chlorite filling the open cavities occurs as pseudo-uniaxial plates arranged in rosette-shaped aggregates. These aggregates appear to have developed as a result of radial growth of the chlorite platelets. According to point and microprobe X-ray images, these chlorites display oscillatory chemical zoning patterns with alternating iron rich and magnesium rich bands. The chlorite composition ranges from Fe rich pole (Si2.62Al1.38O10(Al1.47Fe1.87Mg2.61)6(OH)8) to Mg rich pole (Si2.68Al1.31O10(Al1.45Fe1.41Mg3.06)6(OH)8). In metamorphic rocks, zoning pattern or rimmed minerals results for varying P or T conditions and can be used to unravel the P-T history of the sample. In the present study, temperature maps are derived from standardized microprobe X-ray images using the program XMapTools (Lanari et al 2014). The (Fe3+/Fetot) value in chlorite was directly measured using μXANES spot analyses collected at the Fe-K edge. The results indicate a homogeneous temperature of

  11. Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu (United States)

    Narayana, B. L.; Natarajan, R.; Govil, P. K.


    Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

  12. Diagenesis, low-grade and contact metamorphism in the Triassic-Jurassic of the Vichuquen-Tilicura and Hualane-Gualleco Basins, Coastal Range of Chile

    Energy Technology Data Exchange (ETDEWEB)

    Belmar, M.; Schmidt, S.T.; Mahlmann, R.F.; Mullis, J.; Stern, W.B.; Frey, M. [University of Chile, Santiago (Chile). Dept. of Geology


    Diagenetic and low-grade metamorphic conditions have been determined (pressure and temperature) for Late Triassic to Early Jurassic sedimentary rocks from the Vichuquen-Tilicura and the Hualane-Gualleco basins in Central Chile using Kubler index (KI), coal rank data, K-white mica b cell dimension, characteristic mineral assemblages and fluid inclusion data. A burial-related diagenetic to low-grade metamorphic event, which is recorded in both basins, is partly overprinted in the Hualane-Gualleco basin by contact metamorphism around Jurassic dioritic to granodioritic intrusions. Diagenetic conditions prevailed in the northern Vichuquen-Tilicura basin, whereas in the southern Hualane-Gualleco basin low-grade metamorphism is observed with an increase in metamorphic grade from north to south. Epizonal conditions are locally reached in the very south of the Hualane-Gualleco basin. Low-pressure conditions were determined using the K-white mica b cell dimension. A numerical maturity model corroborates with the regional low-grade metamorphism. Evidence of contact metamorphism in the immediate proximity of some Jurassic intrusions includes: (1) hornfels facies assemblages such as ferrosilite (XFe0.6)-magnesiohornblende-ferroactinolite-biotite together with chlorite, plagioclase, stilpnomelane and (2) natural coke and pyrolitic bituminite in some sedimentary samples. Epizonal KI and high coal rank values are probably a result of this locally occurring contact metamorphism.

  13. Contrasting geochemistry and metamorphism of pillow basalts in metamorphic complexes from Aysén, S. Chile (United States)

    Hervé, F.; Aguirre, L.; Sepúlveda, V.; Morata, D.


    The geochemistry of pillow basalts from the Chonos Metamorphic Complex (CMC) and the Eastern Andes Metamorphic Complex of Aysén (EAMC) indicates contrasting tectonic environments for these basic lavas. They have E-MORB and continental alkaline affinities, respectively. The MORB-like basalts are metamorphosed in the pumpellyite-actinolite metamorphic facies, with mineral associations indicative of relatively high P/T metamorphism. The continental alkali basalts exhibit pumpellyite-chlorite assemblages developed in a low to intermediate P/T regime. These contrasting eruptive and metamorphic settings agree with recently established age differences between the complexes, and invalidate direct correlation between them.

  14. HP metamorphic belt of the western Alps

    Institute of Scientific and Technical Information of China (English)



    The understanding of the subduction-related processes benefited by the studies of the high-pressure (HP) meta-morphic rocks from the western Alps. The most stimu-lating information was obtained from the inner part of the western Alpine belt, where most tectonic units show an early Alpine eclogite-facies recrystallisation. This is especially true for the Austroalpine Sesia Zone and the Penninic Dora-Maira massif. From the Sesia zone,which consists of a wide spectrum of continental crust lithologies recrystallised to quartz-eclogite-facies min-eral assemblages, the first finding of a jadeite-bearingmeta-granitoid has been described, supporting evidencethat even continental crust may subduct into the mantle.From the Dora-Maira massif the first occurrence of regional metamorphic coesite has been reported, open-ing the new fertile field of the ultrahigh-pressure meta-morphism (UHPM), which is now becoming the rule in the collisional orogenic belts.

  15. Preservation of Blueschist Facies Minerals Along a Shear Zone By Fast Flowing CO2-Bearing Fluids - a Field Study from the Cycladic Blueschist Unit on Syros, Greece (United States)

    Kleine, B. I.; Skelton, A.; Huet, B.; Pitcairn, I.


    Our study was undertaken at Fabrika Beach on the southeastern shore of Syros which belongs to the Greek Cycladic archipelago in the Aegean Sea. The island is situated within the Attic-Cycladic metamorphic core complex belt and is now located in the back-arc of the active Hellenic subduction zone. At Fabrika Beach, blueschist facies minerals are observed in haloes fringing a shear zone within greenschist facies rocks. The approximately vertical shear zone cuts a near horizontal layer of greenschist facies rocks. The blue haloes are ca. 1 m wide, and are seen on both sides of the shear zone. The haloes consist of a carbonated blueschist facies mineral assemblage. Based on petrological, geochemical and thermodynamic evidence we show that these haloes were preserved at greenschist facies conditions in response to fast flowing CO2-bearing fluid. Furthermore, we use a simple mass balance to calculate the fluid flux within the shear zone which would be required to cause the observed preservation of blueschist facies minerals. We constructed a simplified P-T vs. XCO2 pseudosection using PerPlex 6.6.6 to confirm that preservation of carbonated blueschist can occur at greenschist facies conditions in the presence of CO2-bearing fluid. The flux of CO2-bearing fluid along the shear zone was rapid with respect to the fluid flux in the surrounding rocks. Mass balance calculations reveal that the fluid flux within the shear zone was at least 100 - 2000 times larger than the fluid flux within the surrounding rocks. Mineral textures show greenschist facies minerals partially replacing blueschist minerals in the haloes supporting our interpretation that blueschist facies minerals were preserved during greenschist facies retrogression.

  16. Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India (United States)

    Sachan, Himanshu K.; Santosh, M.; Prakash, Divya; Kharya, Aditya; Chandra Singh, P.; Rai, Santosh K.


    The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.


    Institute of Scientific and Technical Information of China (English)


    20160203 Ji Genyuan(Cores and Samples Center of Land Resources,Sanhe 065201,China);Dai Tagen Petrological Characteristics and Original Rocks for Metamorphic Rocks from the Jinmo Sb Deposit,in Quang Ninh Province,Vietnam(Acta Geologica Sichuan,ISSN1006-0995,CN51-1273/P,35(1),2015,p.43-46,6illus.,1table,6refs.)

  18. Telescoping metamorphic isograds: Evidence from 40Ar/39A dating in the Orange-Milford belt, southern Connecticut (United States)

    Kunk, Michael J.; Walsh, Gregory J.; Growdon, Martha L.; Wintsch, Robert P.


    New 40Ar/39Ar ages for hornblende and muscovite from the Orange-Milford belt in southern Connecticut reflect cooling from Acadian amphibolite facies metamorphism between ∼380 to 360 Ma followed by retrograde recrystallization of fabric-forming muscovite and chlorite during lower greenschist facies Alleghanian transpression at ∼280 Ma. Reported field temperature and pressure gradients are improbably high for these rocks and a NW metamorphic field gradient climbing from chlorite-grade to staurolite-grade occurs over less than 5 km. Simple tilting cannot account for this compressed isograd spacing given the geothermal gradient of ∼20 °C/km present at the time of regional metamorphism. However, post-metamorphic transpression could effectively telescope the isograds by stretching the belt at an oblique angle to the isograd traces. Textures in the field and in thin section reveal several older prograde schistosities overprinted by lower greenschist facies fabrics. The late cleavages commonly occur at the scale of ∼100 μm and these samples contain multiple age populations of white mica. 40Ar/39Ar analysis of these poly-metamorphic samples with mixed muscovite populations yield climbing or U-shaped age spectra. The ages of the low temperature steps are late Paleozoic, while the ages of the older steps are late Devonian. These results support our petrologic interpretation that the younger cleavage developed under metamorphic conditions below the closure temperature for Ar diffusion in muscovite, that is, in the lower greenschist facies. The correlation of a younger regionally reproducible age population with a pervasive retrograde muscovite ± chlorite cleavage reveals an Alleghanian (∼280 Ma) overprint on the Acadian metamorphic gradient (∼380 Ma). Outcrop-scale structures including drag folds and imbricate boudins suggest that Alleghanian deformation and cleavage development occurred in response to dextral transpression along a northeast striking boundary

  19. Geochronology of accessory allanite and monazite in the Barrovian metamorphic sequence of the Central Alps, Switzerland (United States)

    Boston, Kate R.; Rubatto, Daniela; Hermann, Jörg; Engi, Martin; Amelin, Yuri


    The formation of accessory allanite, monazite and rutile in amphibolite-facies rocks across the Barrovian sequence of the Central Alps (Switzerland) was investigated with a combination of petrography and geochemistry and related to the known structural and metamorphic evolution of the Lepontine dome. For each of these minerals a specific approach was adopted for geochronology, taking into account internal zoning and U-Th-Pb systematics. In-situ U-Th-Pb dating of allanite and monazite by ion microprobe revealed systematic trends for the ages of main deformation and temperature in the Lepontine dome. Isotope dilution TIMS dating of rutile returns dates in line with this picture, but is complicated by inheritance of pre-Alpine rutile and possible Pb loss during Alpine metamorphism. Allanite is generally a prograde mineral that is aligned along the main foliation of the samples and found also as inclusions in garnet. Prograde allanite formation is further documented by rutile inclusions with formation temperatures significantly lower than the maximum T recorded by the rock mineral assemblage. Allanite ages vary from 31.3 ± 1.1 Ma in orthogneisses in the East to 31.7 ± 1.1 Ma for a Bündnerschiefer and 28.5 ± 1.3 Ma for a metaquartzite in the central area, to 26.8 ± 1.1 Ma in the western part of the Lepontine dome. These ages are interpreted to date the main deformation events (nappe stacking and isoclinal deformation of the nappe stack), close to peak pressure conditions. The timing of the thermal peak in the Lepontine dome is recorded in monazite that grew at the expense of allanite and after a main episode of garnet growth at temperatures of 620 °C. Monazite in the central area yields an age of 22.0 ± 0.3 Ma, which is indistinguishable from the age of 21.7 ± 0.4 Ma from a metapelite in the western part of the Lepontine dome. In the central area some of the classical kyanite-staurolite-garnet schists directly underlying the metamorphosed Mesozoic sediments

  20. Oman metamorphic sole formation reveals early subduction dynamics (United States)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Plunder, Alexis; Ildefonse, Benoît; Yamato, Philippe; Prigent, Cécile


    Metamorphic soles correspond to m to ~500m thick tectonic slices welded beneath most of the large-scale ophiolites. They typically show a steep inverted metamorphic structure where the pressure and temperature conditions of crystallization increase upward (from 500±100°C at 0.5±0.2 GPa to 800±100°C at 1.0±0.2 GPa), with isograds subparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphic soles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). These soles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associated with large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction (as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subduction dynamics (i.e., thermal structure, fluid migration and rheology along the nascent slab interface). We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections along the Oman ophiolite. We show precise pressure-temperature estimates obtained by pseudosection modelling and EBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantification of the micro-scale deformation and highlight differences in pressure-temperature-deformation conditions between the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuous in all locations. Based on these new constraints, we suggest a new tectonic-petrological model for the formation of metamorphic soles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leading to the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between the sole and the peridotite as the plate interface progressively cools down

  1. Burial metamorphism in rocks of the Western Andes of Peru (United States)

    Offler, R.; Aguirre, L.; Levi, B.; Child, S.


    An unconformity bound, episodic pattern of burial metamorphism is preserved in marine and terrestrial volcanic and sedimentary rocks which were deposited in the West Peruvian Trough during the Mesozoic and Cenozoic Eras. A particular metamorphic facies series is developed in each of the stratigraphic-structural units bounded by unconformities. In each unit, grade increases with stratigraphic depth and covers part or all of the range from zeolite to greenschist facies. At every unconformity a mineralogic break occurs where higher grade assemblages on top of the unconformity plane overlie lower grade assemblages. The presence of wairakite and the development of a wide range of metamorphic facies in thin sequences suggest high geothermal gradients, possibly related to generation of magma at depth.

  2. Fe-Ni metal in primitive chondrites: Indicators of classification and metamorphic conditions for ordinary and CO chondrites (United States)

    Kimura, M.; Grossman, J.N.; Weisberg, M.K.


    We report the results of our petrological and mineralogical study of Fe-Ni metal in type 3 ordinary and CO chondrites, and the ungrouped carbonaceous chondrite Acfer 094. Fe-Ni metal in ordinary and CO chondrites occurs in chondrule interiors, on chondrule surfaces, and as isolated grains in the matrix. Isolated Ni-rich metal in chondrites of petrologic type lower than type 3.10 is enriched in Co relative to the kamacite in chondrules. However, Ni-rich metal in type 3.15-3.9 chondrites always contains less Co than does kamacite. Fe-Ni metal grains in chondrules in Semarkona typically show plessitic intergrowths consisting of submicrometer kamacite and Ni-rich regions. Metal in other type 3 chondrites is composed of fine- to coarse-grained aggregates of kamacite and Ni-rich metal, resulting from metamorphism in the parent body. We found that the number density of Ni-rich grains in metal (number of Ni-rich grains per unit area of metal) in chondrules systematically decreases with increasing petrologic type. Thus, Fe-Ni metal is a highly sensitive recorder of metamorphism in ordinary and carbonaceous chondrites, and can be used to distinguish petrologic type and identify the least thermally metamorphosed chondrites. Among the known ordinary and CO chondrites, Semarkona is the most primitive. The range of metamorphic temperatures were similar for type 3 ordinary and CO chondrites, despite them having different parent bodies. Most Fe-Ni metal in Acfer 094 is martensite, and it preserves primary features. The degree of metamorphism is lower in Acfer 094, a true type 3.00 chondrite, than in Semarkona, which should be reclassified as type 3.01. ?? The Meteoritical Society, 2008.

  3. Late-Stage Ductile Deformation in Xiongdian-Suhe HP Metamorphic Unit, North-Western Dabie Shan, Central China

    Institute of Scientific and Technical Information of China (English)

    Suo Shutian; Zhong Zengqiu; Zhou Hanwen; You Zhendong


    New structural and petrological data unveil a very complicated ductile deformation history of the Xiongdian-Suhe HP metamorphic unit, north-western Dabie Shan, central China. The fine-grained symplectic amphibolite-facies assemblage and coronal structure enveloping eclogite-facies garnet, omphacite and phengite etc., representing strain-free decompression and retrogressive metamorphism, are considered as the main criteria to distinguish between the early-stage deformation under HP metamorphic conditions related to the continental deep subduction and collision, and the late-stage deformation under amphibolite to greenschist-facies conditions occurred in the post-eclogite exhumation processes. Two late-stages of widely developed, sequential ductile deformations D3 and D4, are recognized on the basis of penetrative fabrics and mineral aggregates in the Xiongdian-Suhe HP metamorphic unit, which shows clear, regionally, consistent overprinting relationships. D3 fabrics are best preserved in the Suhe tract of low post-D3 deformation intensity and characterized by steeply dipping layered mylonitic amphibolites associated with doubly vergent folds. They are attributed to a phase of tectonism linked to the initial exhumation of the HP rocks and involved crustal shortening with the development of upright structures and the widespread emplacement of garnet-bearing granites and felsic dikes. D4 structures are attributed to the main episode of ductile extension (D14) with a gently dipping foliation to the north and common intrafolial, recumbent folds in the Xiongdian tract, followed by normal sense top-to-the north ductile shearing (D24) along an important tectonic boundary, the so-called Majiawa-Hexiwan fault (MHF), the westward continuation of the Balifan-Mozitan-Xiaotian fault (BMXF) of the northern Dabie Shan. It is indicated that the two stages of ductile deformation observed in the Xiongdian-Suhe HP metamorphic unit, reflecting the post-eclogite compressional or extrusion

  4. Links between fluid circulation, temperature, and metamorphism in subducting slabs (United States)

    Spinelli, G.A.; Wang, K.


    The location and timing of metamorphic reactions in subducting lithosph??re are influenced by thermal effects of fluid circulation in the ocean crust aquifer. Fluid circulation in subducting crust extracts heat from the Nankai subduction zone, causing the crust to pass through cooler metamorphic faci??s than if no fluid circulation occurs. This fluid circulation shifts the basalt-to-eclogite transition and the associated slab dehydration 14 km deeper (35 km farther landward) than would be predicted with no fluid flow. For most subduction zones, hydrothermal cooling of the subducting slab will delay eclogitization relative to estimates made without considering fluid circulation. Copyright 2009 by the American Geophysical Union.

  5. Genesis of the Hongzhen metamorphic core complex and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    ZHU Guang; XIE ChengLong; XIANG BiWei; HU ZhaoQi; WANG YongSheng; LI Xing


    The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie orogenic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magmatism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.

  6. Genesis of the Hongzhen metamorphic core complex and its tectonic implications

    Institute of Scientific and Technical Information of China (English)


    The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.

  7. Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey (United States)

    Gücer, Mehmet Ali; Arslan, Mehmet; Sherlock, Sarah; Heaman, Larry M.


    In the northern part of the Central Pontides (N Turkey) there are different metamorphic rocks exposed, notably the Devrekani metamorphic rocks. Here, upper amphibolite-lower granulite facies metamorphic rocks contain predominantly paragneiss, orthogneiss and metacarbonate, and to a lesser extent, amphibolite and quartzite, with cross-cutting aplite, pegmatite and granite veins. This is the first report of these rocks and includes new data on the petrochemistry, geochronology and metamorphic evolution of the Devrekani orthogneisses from the Central Pontides. The orthogneisses show five different mineral parageneses with the characteristic mineral assemblage quartz + K-feldspar + plagioclase + biotite ± hornblende ± opaque (± ilmenite and ± magnetite), and accessory minerals (zircon, sphene and apatite). These metamorphic rocks exhibit generally granoblastic, lepidogranoblastic and nematolepidogranoblastic with locally migmatitic and relic micrographic textures. They have well-developed centimeter-spaced gneissic banding and display gneissose structure with symmetric, asymmetric and irregular folds. The petrographic features, mineralogical assemblages and weak migmatization reflect high temperature conditions. Thermometric calculations in the orthogneisses indicate metamorphic temperatures reached 744 ± 33 °C. Field relations, petrography and petrochemistry suggest that the orthogneisses have predominantly granodioritic and some granitic protoliths, that show features of I-type, medium to high-potassic calc-alkaline volcanic arc granitoids. The orthogneisses have high contents of LILEs and low contents of HFSEs with negative Nb and Ti anomalies, which are typical of subduction-related magmas. The orthogneisses also show significant LREE enrichment relative to HREE with negative Eu anomalies (EuN/Eu* = 0.33-1.07) with LaN/LuN = 6.98-20.47 values. Based on U-Pb zircon dating data, the protoliths are related to Permo-Carboniferous (316-252 Ma) magmatism. It is

  8. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil) (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas


    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  9. Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment (United States)

    Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.


    bulk δ13C and δ18O dolomite-calcite thermometry. These isotopic exchange thermometers are largely consistent with peak temperatures in all samples within 4 km of the contact, indicating that metamorphic recrystallization can occur even in samples too low-grade to produce growth of conventional metamorphic index minerals (i.e., talc and tremolite). Altogether, this work demonstrates the potential of these methods to quantify the conditions of metamorphism at sub-greenschist facies.

  10. Can the Metamorphic Basement of Northwestern Guatemala be Correlated with the Chuacús Complex? (United States)

    Cacao, N.; Martens, U.


    The Chuacús complex constitutes a northward concave metamorphic belt that stretches ca. 150 km south of the Cuilco-Chixoy-Polochic (CCP) fault system in central and central-eastern Guatemala. It represents the basement of the southern edge of the Maya block, being well exposed in the sierra de Chuacús and the sierra de Las Minas. It is composed of high-Al metapelites, amphibolites, quartzofeldspathic gneisses, and migmatites. In central Guatemala the Chuacús complex contains ubiquitous epidote-amphibolite mineral associations, and local relics of eclogite reveal a previous high-pressure metamorphic event. North of the CCP, in the Sierra de Los Cuchumatanes area of western Guatemala, metamorphic rocks have been considered the equivalent of the Chuacús complex and hence been given the name Western Chuacús group, These rocks, which were intruded by granitic rocks and later mylonitized, include chloritic schist and gneiss, biotite-garnet schist, migmatites, and amphibolites. No eclogitic relics have been found within metamorphic rocks in northwestern Guatemala. Petrographic analyses of garnet-biotite schist reveal abundant retrogression and the formation of abundant zeolite-bearing veins associated with intrusion. Although metamorphic conditions in the greenschist and amphibolite facies are similar to those in the sierra de Chuacús, the association with deformed intrusive granites is unique for western Guatemala. Hence a correlation with metasediments intruded by the Rabinal granite in the San Gabriel area of Baja Verapaz seems more feasible than a correlation with the Chuacús complex. This idea is supported by reintegration of the Cenozoic left-lateral displacement along the CCP, which would place the metamorphic basement of western Guatemala north of Baja Verapaz, adjacent to metasediments intruded by granites in the San Gabriel-Rabinal area.

  11. Low grade metamorphism of mafic rocks (United States)

    Schiffman, Peter


    Through most of this past century, metamorphic petrologists in the United States have paid their greatest attention to high grade rocks, especially those which constitute the core zones of exhumed, mountain belts. The pioneering studies of the 50's through the 80's, those which applied the principles of thermodynamics to metamorphic rocks, focused almost exclusively on high temperature systems, for which equilibrium processes could be demonstrated. By the 1980's, metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks. Of course, low grade metamorphic rocks - here defined as those which form at pressures and temperatures up to and including the greenschist facies - had been well known and described as well, initially through the efforts of Alpine and Circum-Pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts, and that they underlay large portions of accreted terranes, many of oceanic origins. But until the mid 80's, much of the effort in studying low grade rocks - for a comprehensive review of the literature to that point see Frey (1987) - had been concentrated on mudstones, volcanoclastic rocks, and associated lithologies common to continental mountain belts and arcs. In the mid 80's, results of the Deep Sea Drilling Project (DSDP) rather dramatically mitigated a shift in the study of low grade metamorphic rocks.

  12. The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

    Directory of Open Access Journals (Sweden)

    Yuri de Melo Portella


    Full Text Available The Cedrolina chromitite body (Goiás-Brazil is concordantly emplaced within talc-chlorite schists that correspond to the poly-metamorphic product of ultramafic rocks inserted in the Pilar de Goiás Greenstone Belt (Central Brazil. The chromite ore displays a nodular structure consisting of rounded and ellipsoidal orbs (up to 1.5 cm in size, often strongly deformed and fractured, immersed in a matrix of silicates (mainly chlorite and talc. Chromite is characterized by high Cr# (0.80–0.86, high Fe2+# (0.70–0.94, and low TiO2 (av. = 0.18 wt % consistent with variation trends of spinels from metamorphic rocks. The chromitite contains a large suite of accessory phases, but only irarsite and laurite are believed to be relicts of the original igneous assemblage, whereas most accessory minerals are thought to be related to hydrothermal fluids that emanated from a nearby felsic intrusion, metamorphism and weathering. Rutile is one of the most abundant accessory minerals described, showing an unusually high Cr2O3 content (up to 39,200 ppm of Cr and commonly forming large anhedral grains (>100 µm that fill fractures (within chromite nodules and in the matrix or contain micro-inclusions of chromite. Using a trace element geothermometer, the rutile crystallization temperature is estimated at 550–600 °C (at 0.4–0.6 GPa, which is in agreement with P and T conditions proposed for the regional greenschist to low amphibolite facies metamorphic peak of the area. Textural, morphological, and compositional evidence confirm that rutile did not crystallize at high temperatures simultaneously with the host chromitite, but as a secondary metamorphic mineral. Rutile may have been formed as a metamorphic overgrowth product following deformation and regional metamorphic events, filling fractures and incorporating chromite fragments. High Cr contents in rutile very likely are due to Cr remobilization from Cr-spinel during metamorphism and suggest that Ti was

  13. Record of high-pressure overprint in metamorphic soles of the Tavşanli zone, Western Anatolia (United States)

    Plunder, Alexis; Agard, Philippe; Chopin, Christian; Okay, Aral


    Large obducted ophiolites correspond to the emplacement of dense oceanic lithosphere on top of a continent and thereby provide insights into rheological and thermal coupling between plates or fluid budgets. Obducted ophiolites thrust onto the continental margin of the Anatolide-Tauride block (Western Anatolia, south of the Izmir-Ankara suture zone) are dated through their metamorphic sole at ca. 90-95Ma and derive from the same intra-oceanic Neotethyan subduction. We herein focus on the metamorphic soles of the Tavşanlı zone, which show a variable high-pressure low-temperature (HP-LT) overprint of the initial amphibolitic metamorphic conditions (Önen & Hall, 1993; Dilek & Whitney, 1997; Okay et al, 1998). Systematic sampling was done in both the already studied areas as well as new locations. PT conditions were estimated at 8 kbar and 700°C for the amphibolitic stage with the assemblage hornblende + plagioclase ± garnet ± epidote. The HP-LT metamorphic overprint reached incipient blueschist to blueschist facies PT conditions. Development of the characteristic assemblage glaucophane + lawsonite yields PT estimates of >6-7 kbar and 300°C. The high-pressure stage is similar to the one observed for the underlying accretionary-complex unit of the Tavşanlı zone (Plunder et al, this meeting). This HP overprint was not observed in other obduction contexts such as Oman or New Caledonia but was documented in Fransciscan Complex amphibolites (Wakayabashi, 1990). The record of two metamorphic events can be understood as: (1) rapid cooling of the subduction zone after initiation and the exhumation of the metamorphic sole; (2) reburial after or during exhumation of the amphibolite initially welded at the base of the ophiolite. Several observations (i.e., lack of tectonic contact between the ophiolitic body and the metamorphic sole, PT estimates,...) point to cooling as the most likely hypothesis. Metamorphic soles allow to highlight: (1) the dynamics of obducted

  14. Ce anomaly in minerals of eclogite and garnet pyroxenite from Dabie-Sulu ultrahigh pressure metamorphic belt:Tacking subducted sediment formed under oxidizing conditions

    Institute of Scientific and Technical Information of China (English)

    LUO Yan; GAO Shan; YUAN Honglin; LIU Xiaomin; Deltlef Günther; JIN Zhenmin; SUN Min


    In-situ excimer laser ICP-MS analysis of minerals of eclogites and garnet pyroxenites from type localities (Shuanghe, Maowu, Bixiling, and Yangkou) in the Dabie-Sulu ultrahigh-pressure metamorphic belt reveals highly variable Ce anomalies from negative to positive in garnet. Similar Ce anomalies are also present in omphacite or clinopyroxene but to a much lesser extent. Such mixed negative and positive Ce anomalies mimic those found in severe weathering profiles developed under oxidizing conditions. They suggest the presence of subducted sediment components in the eclogites and garnet pyroxenites, which in turn points to the potential importance of the recycled sediments in modification of the mantle composition during the deep subduction of the continental crust.

  15. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros Junior, Edgar Batista; Marques, Rodson Abreu, E-mail:, E-mail: [Universidade Federal do Espirito Santo (UFES), Alegre, ES (Brazil). Departamento de Geologia; Jordt-Evangelista, Hanna; Queiroga, Glaucia Nascimento, E-mail:, E-mail: [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Schulz, Bernhard, E-mail: [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)


    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  16. Restoration of the Western Himalaya:implications for metamorphic protoliths,thrust and normal faulting,and channel flow models

    Institute of Scientific and Technical Information of China (English)

    Michael P.Searle; Ben Stephenson; James Walker; Christian Walker


    @@ The Greater Himalayan Sequence(GHS)is composed of a sequence of Barrovian facies metamorphic rocks up to kyanite or sillimanite+K-feldspar grade,migrmatites,layered stromatic migmatites and leucogranite sheets.

  17. Structural analysis and metamorphism of Palaeoproterozoic metapelites in the Seinäjoki-Ilmajoki area, western Finland

    Directory of Open Access Journals (Sweden)

    Mäkitie, H.


    Full Text Available The Palaeoproterozoic Svecofennian bedrock of the Seinäjoki-Ilmajoki area, western Finland, is largely composed of porphyroblastic metapelites. In the area, the regional metamorphic grade increases towards the southwest. Over a distance of 15 km, andalusite mica schists gradually grade into migmatitic garnet cordierite-sillimanite mica gneisses with a facies-series of the andalusite-sillimanite type. Five regional metamorphic zones are present: andalusite, sillimanite-muscovite, sillimanite-K-feldspar, cordierite-K-feldspar and garnet-cordierite-K-feldspar. The primary layering (S0 of the mica schists is deformed by an isoclinal fold phase (F2, which is synchronous with the main metamorphic phase and the growth of micas. S1 is very weak and subject to interpretation. The S2 schistosity is deformed by intense late-metamorphic F3 and F3b folds, which have formed under slightly different metamorphic conditions: practically no metamorphic micas have grown parallel to axial planes while within F3b folds there are a few granitic veins parallel to these planes. The F3 and F3b folds probably belong to one phase. S2 dominates in the mica schists while S3 and S3b dominate in the mica gneisses. The metapelites are also deformed by younger minor fold phases (F4 and F5. A composite schistosity (S0±S1±S2±S3, or S3b commonly occurs in the metapelites. The peak of regional metamorphism has been associated with the intrusion of 1.89-1.88 Ga old tonalite plutons. Geothermometric estimates for regional metamorphism are c. 730 °C at an assumed pressure of 5 kbar. Neosomes in the high-grade mica gneisses occur as patches rather than as elongated, narrow veins. Garnet coexists with cordierite, but the minerals are rarely in equilibrium. Muscovitization and the formation of retrogressive andalusite did not occur in the high-grade mica gneisses, but there is minor kyanite indicating that the crust probably underwent near-isobaric cooling. The area of highest

  18. Conditions for the formation and atmospheric dispersion of a toxic, heavy gas layer during thermal metamorphism of coal and evaporite deposits by sill intrusion (United States)

    Storey, Michael; Hankin, Robin K. S.


    There is compelling evidence for massive discharge of volatiles, including toxic species, into the atmosphere at the end of the Permian. It has been argued that most of the gases were produced during thermal metamorphism of coal and evaporite deposits in the East Siberia Tunguska basin following sill intrusion (Retallack and Jahren, 2008; Svensen et al., 2009). The release of the volatiles has been proposed as a major cause of environmental and extinction events at the end of the Permian, with venting of carbon gases and halocarbons to the atmosphere leading to global warming and atmospheric ozone depletion (Svensen et al., 2009) Here we consider the conditions required for the formation and dispersion of toxic, heavier than air, gas plumes, made up of a mixture of CO2, CH4, H2S and SO2 and formed during the thermal metamorphism of C- and S- rich sediments. Dispersion models and density considerations within a range of CO2/CH4 ratios and volatile fluxes and temperatures, for gas discharge by both seepage and from vents, allow the possibility that following sill emplacement much of the vast East Siberia Tunguska basin was - at least intermittently - covered by a heavy, toxic gas layer that was unfavorable for life. Dispersion scenarios for a heavy gas layer beyond the Siberian region during end-Permian times will be presented. REFERENCES G. J. Retallack and A. H. Jahren, Methane release from igneous intrusion of coal during Late Permian extinction events, Journal of Geology, volume 116, 1-20, 2008 H. Svensen et al., Siberian gas venting and the end-Permian environmental crisis, Earth and Planetary Science Letters, volume 277, 490-500, 2009

  19. Post-Collisional Ductile Extensional Tectonic Framework in the UHP and HP Metamorphic Belts in the Dabie-Sulu Region, China

    Institute of Scientific and Technical Information of China (English)

    索书田; 钟增球; 游振东; 张泽明


    The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.

  20. Strain localization in shear zones during exhumation: a graphical approach to facies interpretation (United States)

    Cardello, Giovanni Luca; Augier, Romain; Laurent, Valentin; Roche, Vincent; Jolivet, Laurent


    Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shear zones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailed characterization and processes comprehension are far to be fully addressed. In this work, a graphic approach to tectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), which is mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite. Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, from syn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphic reactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frame of smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5 tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved within large boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetric boudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed by chlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture is progressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequence of stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage. In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formed glaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tension gashes that gradually evolve to blueschist shear bands. This process determinates the

  1. The timing of the tectono-metamorphic evolution at the Neoproterozoic-Phanerozoic boundary in central southern Madagascar

    DEFF Research Database (Denmark)

    Giese, Jörg; Berger, Alfons; Schreurs, Guido;


    emplaced. HT/HP granulite facies metamorphism (M1), including migmatisation and anatexis of the crust started at~585Maand lasted until at least~500 Ma. Monazite growth between 480 and 450Mapostdates major ductile deformation and might be related to a second, HT/MP metamorphism (M2), indicating...

  2. Deciphering the tectonometamorphis history of the Anarak Metamorphic Complex, Central Iran (United States)

    Zanchetta, Stefano; Malaspina, Nadia; Zanchi, Andrea; Martin, Silvana; Benciolini, Luca; Berra, Fabrizio; Javadi, Hamid Reza; Koohpeyma, Meysam; Ghasemi, Mohammad R.; Sheikholeslami, Mohammad Reza


    most of the "ophiolites" within the AMC. Structural analyses show that the Chah Gorbeh, Morghab units and the "ophiolites" have been tectonically coupled during at least two deformational phases that occurred at greenschist facies conditions and predate the LT-HP metamorphic overprint. Available geochronological data loosely constraints the subduction event in the Late Permian - Early Triassic times. Subsequent deformation events that occurred during the whole Mesozoic and the Cenozoic up to the Miocene and possibly later, resulted in folding, thrusting and faulting that dismembered the original tectonic contacts. Therefore, the correlations among deformation structures and metamorphic events in the different units are not straightforward. The other units of the AMC lack evidence of HP metamorphism, especially the Lakh Marble a large thrust sheet that occupies the uppermost structural position in the AMC. The contact with the underlying units is invariably tectonic, thus no original relationships have been preserved. So, if structural and petrographic data point out an accretionary wedge setting for the evolution of the Chah Gorbeh, Morghab and the "ophiolites", geodynamic significance and paleogeographic attribution of other units still remain controversial. In progress U-Pb dating of undeformed intrusive bodies and metamorphic minerals in the LT-HP rocks will soon help to better constrain the evolution of the ACM.

  3. Mineral inclusions in zircons of S-type granite: implications for high pressure metamorphism history of meta-sedimentary rocks in the Huai'an terrain, North China Craton (United States)

    Wang, Haozheng; Zhang, Huafeng; Zhai, Mingguo; Cui, Xiahong


    The Paleoproterozoic evolution of North China Craton (NCC) arises many argument as geologists have different viewpoints on the distribution and metamorphic history of mafic granulites and granulite facies meta-sedimentary rocks. To provide more evidence of constraining the metamorphic history of granulite facies meta-sedimentary rocks, we select granulite facies meta-sedimentary rocks and co-existing S-type granite in the Huai'an terrain to make a deep research. Magmatic zircons derived from the S-type granite reveal the magmatic age of ˜1.95 Ga and metamorphic age of ˜1.85 Ga with ɛHf(t) value of -4.5 - -0.5. The ɛHf(t) value of S-type granite and relict of garnet-sillimanite gneiss suggest that the S-type granite is generated by melting of meta-sedimentary rocks. Zircons with ages of ˜1.95 Ga and ˜1.85 Ga have the mineral inclusions of Ky + Qz + Ru + Pl and these mineral inclusions are determined by method of Laser-Raman. The ˜1.95 Ga magmatic zircons with inclusions of Ky + Qz + Ru + Pl suggest that meta-sedimentary rocks have mineral assemblages Ky + Qz + Ru + Pl. However, previous studies in the Huai'an terrain showed that almost granulite facies metamorphic condition of meta-sedimentary rocks were regarded as medium pressure by considering the Sill + Grt + Bt + Pl + Qz + Ru + Kf. Presence of kyanite instructs that meta-sedimentary rocks may experience high pressure granulite facies metamorphism. According to pseudosection calculation by using effective bulk composition of garnet-sillimanite gneiss, mineral assemblage of Grt + Ky + Pl + Bt + Qz + Ru + Kf is regarded as the peak stage of high pressure metamorphism. This mineral assemblage is occurred at field of 1033 - 1123 K and 9 - 15 Kbar and the peak pressure is around 11 - 13 Kbar, determined by the XMg and XCa isopleths of garnet. This P-T result is consistent with peak condition of high pressure mafic granulite. Considering the ˜1.95 Ga magmatic age of S-type granite generated by decompression

  4. Facies studies of bituminous coals in Poland

    Energy Technology Data Exchange (ETDEWEB)

    Nowak, Grzegorz J. [Polish Geological Institute, Lower Silesian Branch, al. Jaworowa 19, 53-122, Wroclaw (Poland)


    Polish bituminous coal basins are associated exclusively with Carboniferous deposits, differing in origin and geological structure. This paper presents only short review of papers of Polish authors on coal facies studies of Carboniferous coals occurring in the Lower Silesian Coal Basin (LSCB), Upper Silesian Coal Basin (USCB) and Lublin Coal Basin (LCB) of Poland. Facies investigations of Carboniferous coals of Poland have been in progress over 20 years. The results of these studies have provided new information on such subjects as: (1) recognition of main depositional conditions in paleomires, (2) determine prevailing paleoplant communities, (3) appraisal of peat-forming environment reconstruction-types and characteristics of paleomires. These facies analyses are connected to results of such studies as: pure coal petrology, using maceral and microlithotype composition as parameters of the environment of coal deposition, combined results of petrological, palynological and sedimentological studies.

  5. Fluid inclusions hidden in coesite-bearing zircons in ultrahigh-pressure metamorphic rocks from southwestern Sulu terrane in eastern China

    Institute of Scientific and Technical Information of China (English)

    LIU Fulai; XU Zhiqin


    Primary fluid inclusions, together with coesite mineral inclusions, are identified in the same zircon domains by laser Raman spectroscopy, cathodoluminescence (CL) image and micro-texture analysis in paragneiss and eclogite from the main drilling hole of Chinese Continental Scientific Drilling Project in southwestern Sulu terrane. Most fluid inclusions are characterized by CO2 (gas)-H2O (liquid) two-phase, a few by H2O one-phase liquid inclusions. These features indicate that the eclogite and its country-rocks may be located in the "wet system" rather than in the "dry system" during UHP metamorphism. SHRIMP U-Pb dating indicates that the timing of trapping the fluid and coesite inclusions in metamorphic zircon domains is about 233.7 ± 4.3 Ma, which may represent the age of zircon growth in the stage of pressure decrease but temperature increase during the retrograde period of UHP metamorphism thus indicating the fluid activity still under the UHP conditions. The zircons further overgrew at about 213.2 ± 5.2 Ma in response to amphibolite-facies retrogression. Therefore, fluid activity in the Sulu UHP metamorphic rocks principally occurred during the exhumation of UHP slab in the Middle to Late Triassic. The present results not only provide insight into the fluid property and fluid-rock interaction mechanism in the Sulu-Dabie UHP terrane, but also present a new means to exactly identify the primary fluid inclusions preserved in zircons from the UHP metamorphic rocks.

  6. Combustion metamorphic events as age markers of orogenic movements, in Central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Novikov, I.S.; Sokol, E.V. [Russian Academy of Science, Novosibirsk (Russian Federation)


    Combustion metamorphic (pyrometamorphic) complexes produced by prehistoric natural coal fires are widespread in Central Asia, namely at the interfaces between mountain systems and the flanking sedimentary basins. Large-scale and prolonged fires accompanied the initial orogenic stages as unweathered coal-bearing formations became exposed into the aeration zone. Pyrometamorphic rocks are comparable to sanidinite facies rocks in formation conditions and in alteration of sedimentary material but, unlike these, their protolith underwent different melting degrees to produce either ferrous basic paralavas or glazed clinkers. The phase composition of the newly-formed melted rocks are favorable for Ar-40/Ar-39 dating of combustion metamorphic events which are coeval to the onset of the main stage of recent orogenic events. We suggest a new algorithm providing correct Ar-40/Ar-39 dating of pyrometamorphic rocks followed by well-grounded geological interpretation. We applied it to pyrometamorphic rocks in the western Salair zone of the Kuznetsk coal basin where combustion metamorphism under temperatures above 1000 degrees C acted upon large volumes of coal-bearing sediments.

  7. Metamorphism of the Oddanchatram anorthosite, Tamil Nadu, South India (United States)

    Wiebe, R. A.; Janardhan, A. S.


    The Oddanchatram anorthosite is located in the Madurai District of Tamil Nadu, near the town of Palni. It is emplaced into a granulite facies terrain commonly presumed to have undergone its last regional metamorphism in the late Archean about 2600 m.y. The surrounding country rock consists of basic granulites, charnockites and metasedimentary rocks including quartzites, pelites and calc-silicates. The anorthosite is clearly intrusive into the country rock and contains many large inclusions of previously deformed basic granulite and quartzite within 100 meters of its contact. Both this intrusion and the nearby Kaduvar anorthosite show evidence of having been affected by later metamorphism and deformation.

  8. Eclogite-high-pressure granulite metamorphism records early collision in West Gondwana: new data from the Southern Brasilia Belt, Brazil

    DEFF Research Database (Denmark)

    Reno II, Barry Len; Brown, Michael; Kobayashi, Katsura


    constrain the age of. (1) retrograded eclogite from a block along the tectonic contact beneath the uppermost nappe in a stack of passive margin-derived nappes; (2) high-pressure granulite-facies metamorphism in the uppermost passive margin-derived nappe; (3) high-pressure granulite-facies metamorphism...... in the overlying arc-derived nappe. Rare zircons from a retrograded eclogite yield a Pb-206/U-238 age of 678 +/- 29 Ma. which we interpret as most likely to (late close-to-peak-P metamorphism and to provide a minimum age for detachment of the overlying passive margin-derived nappe from the subducting plate. Zircon...

  9. Strain partitioning into dry and wet zones and the formation of Ca-rich myrmekite in syntectonic syenites: A case for melt-assisted dissolution-replacement creep under granulite facies conditions (United States)

    De Toni, G. B.; Bitencourt, M. F.; Nardi, L. V. S.


    The formation of Ca-rich myrmekites is described in syntectonic syenites crystallized and progressively deformed under granulite facies conditions. The syenites are found in high- and low-strain zones where microstructure and mineral composition are compared. Heterogeneously distributed water-rich, late-magmatic liquids were responsible for strain partitioning into dry and wet high-strain zones at outcrop scale, where contrasting deformation mechanisms are reported. In dry high-strain zones K-feldspar and clinopyroxene are recrystallized under high-T conditions. In wet high-strain zones, the de-stabilization of clinopyroxene and pervasive replacement of relatively undeformed K-feldspar porphyroclasts by myrmekite and subordinate micrographic intergrowths indicate dissolution-replacement creep as the main deformation mechanism. The reworking of these intergrowths is observed and is considered to contribute significantly to the development of the mylonitic foliation and banding. A model is proposed for strain partitioning relating a positive feedback between myrmekite-forming reaction, continuous inflow of late-magmatic liquids and dissolution-replacement creep in the wet zone at the expenses of original mineralogy preserved in the dry zones. Melt-assisted dissolution-replacement creep in syntectonic environments under granulite-facies conditions may extend the field of operation of dissolution-replacement creep, changing significantly the rheology of the lower continental crust.

  10. Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides (United States)

    McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.


    Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in

  11. Petrology, geochemistry, and metamorphic evolution of meta-sedimentary rocks in the Diancang Shan-Ailao Shan metamorphic complex, Southeastern Tibetan Plateau (United States)

    Wang, Fang; Liu, Fulai; Liu, Pinghua; Shi, Jianrong; Cai, Jia


    Meta-sedimentary rocks are widely distributed within the Diancang Shan-Ailao Shan metamorphic complex in the Southeastern Tibetan Plateau. Detailed geochemical analyses show that all of them have similar geochemical features. They are enriched in light rare-earth elements (LREEs) and depleted in heavy rare-earth elements (HREEs), with moderately negative Eu anomalies (Eu/Eu∗ = 0.55-0.75). Major and trace element compositions for the meta-sedimentary rocks suggest that the protoliths were probably claystone, siltstone, and greywacke and deposited in an active continental margin. Garnet porphyroblasts in meta-sedimentary rocks have distinct compositional zonation from core to rim. The zonation of garnet in St-Ky-Grt-Bt-Ms schist indicates an increasing P-T trend during garnet growth. In contrast, garnets from (Sil)-Grt-Bt paragneiss show diffusion zoning, implying a decreasing P-T trend. Based on mineral transformations and P-T estimates using conventional geothermobarometers and pseudosection calculations, four metamorphic stages have been determined, including an early prograde metamorphic stage (M1), a peak amphibolite-granulite facies metamorphic stage (M2), a near-isothermal decompression stage (M3), and a late amphibolites-facies retrograde stage (M4). The relic assemblage of Ms + St ± Ky ± Bt ± Kfs + Qz preserved as inclusions in garnet porphyroblasts of the meta-sedimentary rocks belongs to prograde (M1) stage and records P-T conditions of 560-590 °C and 5.5-6.3 kb. Matrix mineral assemblages of Grt + Bt + Ky/Sil + Pl + Qz and Grt + Bt ± Sil + Pl ± Kfs + Qz formed at peak (M2) stage yield P-T conditions of 720-760 °C and 8.0-9.3 kb. M3 is characterized by decompression reactions, dehydration melting of assemblages that include hydrous minerals (e.g., biotite), and partial melting of felsic minerals. The retrograde assemblages is Grt + Bt + Sil + Pl + Qz formed at 650-760 °C and 5.0-7.3 kb. At the amphibolites-facies retrograde (M4) stage, fine

  12. Geochemistry, provenance, and metamorphic evolution of Gabal Samra Neoproterozoic metapelites, Sinai, Egypt (United States)

    Abu El-Enen, Mahrous M.


    Metapelites are exposed at Wadi Ba'ba, east of Abu Zenima city; represent the northwestern extension of the Fieran-Solaf Metamorphic Complex, Sinai Peninsula, Egypt. The metapelites are characterized by qtz + pl (An 24-28) + bt + grt ± crd ± sil mineral assemblage, indicating upper amphibolite facies with peak metamorphic conditions of 700 °C and pressures of 7 kbar, as determined by conventional geothermobarometeric methods. This resulted in incipient migmatization, forms patches of leucosomes and melanosomes. Geochemical investigation indicates that the precursor sediments of the metapelites had been deposited as immature Fe-rich shales from source materials of dominantly intermediate composition. Source area exhibited weak to moderate chemical weathering in a tectonically active continental marginal basin within a continental-arc system. A strong shallow-dipping foliation, characterizing the metapelites, was folded around an open antiform with sub-horizontal south plunging hinge. Phase equilibria calculations in the KFMASH system indicate that the peak metamorphic conditions formed at 730-750 °C and 6.8-7.9 kbar. This was followed by a retrogression formed at 770-785 °C and 3.9-4.5 kbar. Hence, this implies an isothermal decompression and rapid exhumation of the metapelites from depth (25-29 km) in the lower crustal level at peak conditions, continuous to include shallow to middle crustal level (14-17 km), at overprint retrograde conditions. Subsequent isobaric cooling took place at 720-750 °C and 3.6-4.5 kbar. The resulting isothermal decompression followed by isobaric cooling clockwise P-T path of the metapelites is more likely, in which the high-temperatures attained maximum conditions during isothermal decompression were enhanced by heat flux, due to the presence of an active magmatic arc that formed on top of subducting young lithosphere. This is supported by a moderate geothermal gradient of 27-43 °C/km and dating compatibility of the Sinai

  13. Metamorphic sole formation and early plate interface rheology: Insights from Griggs apparatus experiments (United States)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Hirth, Greg; Yamato, Philippe; Ildefonse, Benoît; Prigent, Cécile


    Metamorphic soles correspond to m to ~500 m thick highly strained metamorphic rock units found beneath mylonitic banded peridotites at the base of large-scale ophiolites, as exemplified in Oman. Metamorphic soles are mainly composed of metabasalts deriving from the downgoing oceanic lithosphere and metamorphosed up to granulite-facies conditions by heat transfer from the mantle wedge. Pressure-temperature peak conditions are usually estimated at 1.0±0.2 GPa and 800±100°C. The absence of HP-LT metamorphism overprint implies that metamorphic soles have been formed and exhumed during subduction infancy. In this view, metamorphic soles were strongly deformed during their accretion to the mantle wedge (corresponding, now, to the base of the ophiolite). Therefore, metamorphic soles and banded peridotites are direct witnesses of the dynamics of early subduction zones, in terms of thermal structure, fluid migration and rheology evolution across the nascent slab interface. Based on fieldwork and EBSD analyses, we present a detailed (micro-) structural study performed on samples coming from the Sumeini window, the better-preserved cross-section of the metamorphic sole of Oman. Large differences are found in the deformation (CPO, grain size, aspect ratio) of clinopyroxene, amphibole and plagioclase, related to mineralogical changes linked with the distance to the peridotite contact (e.g., hardening due to the appearance of garnet and clinopyroxene). To model the incipient slab interface in laboratory, we carried out 5 hydrostatic annealing and simple-shear experiments on Griggs solid-medium apparatus. Deformation experiments were conducted at axial strain rates of 10-6 s-1. Fine-grained amphibolite was synthetized by adding 1 wt.% water to a (Mid-Ocean Ridge) basalt powder as a proxy for the metamorphic sole (amphibole + plagioclase + clinopyroxene ± garnet assemblage). To synthetize garnet, 2 experiments were carried out in hydrostatic conditions and with deformation at

  14. SEM observation of grain boundary structures in quartz-iron oxide rocks deformed at intermediate metamorphic conditions

    Directory of Open Access Journals (Sweden)

    Leonardo Lagoeiro


    Full Text Available Several studies have demonstrated the effect of a second phase on the distribution of fluid phase and dissolution of quartz grains. However, as most observations came from aggregates deformed under hydrostatic stress conditions and mica-bearing quartz rocks, 3-D distribution of pores on quartz-quartz (QQB and quartz-hematite boundaries (QHB has been studied. Several fracture surfaces oriented according to finite strain ellipsoid were analyzed. The pore distribution characterizes the porosity and grain shape as highly anisotropic, which results from the nature and orientation of boundaries. QHB have physical/chemical properties very different from QQB, once the hematite plates have strong effect on wetting behavior of fluid, likewise micas in quartzites. They are pore-free flat surfaces, normal to compression direction, suggesting that they were once wetted with a continuous fluid film acting as faster diffusion pathway. At QQB, the pores are faceted, isolated, close to its edges reflecting the crystallographic control and an interconnected network of fluid along grain junctions. The QQB facing the extension direction are sites of fluid concentration. As consequence, the anisotropic dissolution and grain growth were responsible for the formation of hematite plates and tabular quartz grains significantly contributing for the generation of the foliation observed in the studied rocks.Muitos estudos têm demonstrado o efeito de uma segunda fase sobre a distribuição de fase fluida e dissolução de grãos de quartzo. Entretanto, como a maioria das observações vêm de agregados deformados sob condições de tensão hidrostática e em rochas quartzosas ricas em mica, a distribuição 3D de poros e bordas quartzo-quartzo (BQQ e quartzo-hematita (BQH tem sido estudada. Várias superfícies de fraturas orientadas segundo o elipsóide de deformação finita foram analisadas. A distribuição dos poros caracteriza a porosidade e a forma dos grãos como

  15. Correlation of metabasic rocks from metamorphic soles of the Dinaridic and the Western Vardar zone ophiolites (Serbia: Three contrasting pressure-temperature-time paths

    Directory of Open Access Journals (Sweden)

    Srećković-Batoćanin Danica


    Full Text Available The field, petrological-mineralogical, geochemical and geochronological data of the metamorphic sole rocks recorded beneath the Fruška Gora, Povlen (Tejići, Stolovi and Banjska ophiolites in the Western Vardar Zone (WVZ and beneath the Zlatibor, Bistrica, Sjenički Ozren and Brezovica ophiolites in the Dinaridic ophiolite belt (DOB in Serbia are compared. The focus has been made on metabasic rocks formed in contact with the oceanic crust members: cumulate gabbro and basalts of SSZ-type with E-MORB and OIB-signature and more evolved tholeiitic basalts of MOR-affinity. Amphibole, the major phase formed from the mafic sole components, depending on pressure-temperature conditions exhibits compositional variations. According to mineral assemblages, estimated P-T conditions and ages, the potential P-T paths are given: high pressure - low temperature blueschist facies assemblage (7-9 kbar and ~400°C and <300-350°C and 4-8 kbar, recorded only in the metamorphic sole at the Fruška Gora (WVZ; high pressure - high temperature amphibolite to granulite facies (8-10 kbar and >700-850°C, recorded in both domains, the WVZ (Banjska and the DOB (Bistrica, Sjenički Ozren, Brezovica and medium pressure - medium temperature amphibolite facies assemblages (~3.5-7 kbar and >350-650°C recognized in the WZV (Tejići, Devovići and the DOB (Zlatibor. The peak metamorphic conditions point to depths of the oceanic lithosphere detachment and its initial cooling at 10-30 km, but the ages and tectonic setting of ophiolites remain poorly constrained. The summarized data may be used as an important key in geodynamic evolution of the Mesozoic Tethyan ophiolites. [Projekat Ministarstva nauke Republike Srbije, br. 176019 and br. 176016

  16. Prograde and retrograde metamorphic processes in high-pressure subduction zone serpentinites from East Thessaly, Greece (United States)

    Koutsovitis, Petros


    The East Thessaly region, Central Greece, includes metaophiolitic mélange formations which extend from the eastern foothills of Mt. Olympus and Ossa, throughout the Agia basin, Mt. Mavrovouni (Sklithro region), South Pelion and reaching up to northeast Othris (regions of Aerino and Velestino). They appear in the form of dispersed and deformed thrust sheets having been variably emplaced onto Mesozoic platform series rocks of the Pelagonian tectonostratigraphic zone[1]. These formations consist mainly of serpentinites, as well as metasediments, metagabbros, metadolerites, rodingites, ophicalcites, talc-schists and chromitites. Based upon petrographic observations, mineral chemistry data and XRD patterns, the subduction zone-related serpentinites from the regions of Potamia, Anavra, Aetolofos and Kalochori-Chasanbali (Agia basin), as well as from the regions of Aerino and Velestino, are characterized by the progressive transformation of lizardite to antigorite and are distinguished into two groups. The first group includes serpentinites from the metaophiolitic formations of Potamia, Anavra, Aerino and Velestino, which are marked by destibillization of lizardite to antigorite, mostly along the grain boundaries of the lizardite mesh textured relics. The presence of lizardite and antigorite in almost equal amounts indicates medium-temperature blueschist facies metamorphic conditions (˜340-370 ° C; P≈10-11 kbar)[2,3,4]. The second serpentinite group appears in the regions of Aetolofos and Kalochori, characterized by the predominance of antigorite, the minor occurrence of lizardite and the complete replacement of spinel by Cr-magnetite. The absence of metamorphic olivine suggests that these serpentinites were most likely formed at slightly higher temperature and pressure conditions compared to the first serpentinite group, corresponding to medium or high temperature blueschist facies metamorphism (˜360-380 ° C; P≈12 kbar)[2,3,4]. These metamorphic conditions are

  17. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland

    Directory of Open Access Journals (Sweden)

    Korstgård, John A.


    Full Text Available Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolites facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E–W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E–W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite–granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.

  18. Hydrothermal alteration of a seamount complex on La Palma, Canary Islands: Implications for metamorphism in accreted terranes (United States)

    Schiffman, P.; Staudigel, H.


    The hydrothermal metamorphism of a sequence of Pliocene-age seamount extrusive and volcaniclastic rocks on La Palma, Canary Islands, is characterized by a relatively complete low-pressure-high-temperature facies series encompassing the zeolite, prehnite-pumpellyite, and greenschist facies. The observed mineral zonations imply metamorphic gradients of 200-300 °C/km. The metamorphism of the seamount, at least in its core region, is distinct from ocean-floor metamorphism: the former is characterized by a serially continuous facies series encompassing zeolite, prehnite-pumpellyite, and greenschist assemblages, and the latter by a discontinuous metamorphic gradient in which prehnite-pumpellyite assemblages are absent. These metamorphic features, presumably reflecting fundamental thermal-tectonic differences between extending oceanic crust at mid- oceanic ridges vs. the more static crust underlying seamount volcanoes, should aid in the recognition of incoherent fragments of seamount metamorphic rocks within accreted terranes which typically have undergone subsequent higher pressure-temperature regional metamorphism, albeit to comparable grades.

  19. 3-D assessment of peak-metamorphic conditions by Raman spectroscopy of carbonaceous material: an example from the margin of the Lepontine dome (Swiss Central Alps)

    DEFF Research Database (Denmark)

    Wiederkehr, Michael; Bousquet, Romain; Ziemann, Martin;


    within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across...

  20. Indicators of coal metamorphism

    Energy Technology Data Exchange (ETDEWEB)

    Proskuryakov, A.E.


    Important in determining metamorphism of coal is the reliability of indicators of coalification. Both the reflection of vitrinite and emission of volatile matter have been used for this purpose. To determine which indicator more accurately characterizes metamorphism of coal, their conformity to the following demands was established: 1. uniformity in direction of change of parameters with degree of metamorphism; 2. independence of the indicator of the genetic characteristics of coal (petrographic composition, reduction and oxidation of coal); 3. sensitivity of indicator. Both indicators conform to the first requirement. Emission of volatile substance decreases and reflective capacity of vitrinite increases uniformly with degree of metamorphism. However, the reflectivity of vitrinite is not influenced by petrographic composition of coals and is less dependent on the oxidation and reduction of coal than emission of volatile matter. It is also a more sensitive indicator distinguishing more degrees of metamorphism than emission of volatile matter. Reflectivity of vitrinite is a more reliable indicator of metamorphism than emission of volatile matter. However, in many laboratories this indicator is not measured with sufficient accuracy. To correct this, measuring equipment must be standardized.

  1. Geochemical, Metamorphic and Geodynamic Evolution implications from subduction-related serpentinites and metarodingites at East Thessaly (Central Greece) (United States)

    Koutsovitis, Petros


    In Central Greece, the East Thessaly region encompasses ophiolitic and metaophiolitic formations emplaced onto Mesozoic platform series rocks. Metaophiolitic thrust sheets are characterized either by the predominance of serpentinites or metabasites. Serpentinites have been distinguished into three groups, representing distinct metamorphic degrees. Group-1 serpentinites (East Othris region) are characterized by the progressive transformation of lizardite to antigorite, estimated to have been formed under greenschist facies conditions (˜320-340 ˚ C, P≈6-8 kbar) [1]. Group-2 serpentinites (NE Othris and Agia-Agiokampos region) are marked by the further prevalence of antigorite over lizardite, suggesting upper-greenschist to low-blueschist facies metamorphism (˜340-370 ˚ C, P≈9-11 kbar) [1]. Group-3 serpentinites (Agia-Agiokampos region) are characterized by the predominance of antigorite and Cr-magnetite, as well as by their relatively low LOI (10.9-12.6 wt.%), corresponding to blueschist facies metamorphism (˜360-400 ˚ C, P≈12 kbar) [1]. These metamorphic conditions are highly comparable with the P-T estimates from the Easternmost Thessaly metabasic rocks, strongly indicating that the entire metaophiolitic formation (excluding East Othris) underwent blueschist facies metamorphism. Serpentinites from East Thessaly were formed from serpentinization of highly depleted harzburgitic protoliths under extensive partial melting processes (>15%), pointing to a hydrous subduction-related environment. Group-1 serpentinites exhibit higher Mg/Si ratio values and LOI compared to serpentinite Groups-2 and -3. Differences in the trace element behavior amongst the three serpentinite groups are also consistent with increasing metamorphic conditions (e.g. Pb, La enrichments, Ti, Y, Yb depletions) [1]. The East Thessaly serpentinites reflect highly oxidizing conditions (-0.4processes (Pprocesses upon the rodingite intrusions hosted within the serpentinites. Late

  2. Rheologic Transitions During Exhumation of High-Pressure Metamorphic Rocks (United States)

    Whitney, D. L.; Teyssier, C. P.; Rey, P. F.


    The exhumation of deeply buried rocks typically involves dynamic feedbacks between deformation and metamorphic reactions (+ fluid and/or melt) that influence rheology and facilitate or drive large-magnitude exhumation. The evolution of grain-scale to terrane-scale processes during decompression can be seen in rocks exhumed from oceanic and continental subduction and from orogenic crust. In the Sivrihisar (Turkey) high-P/low-T (oceanic subduction) complex, microstructures record deformation and syn-kinematic reactions during decompression from eclogite to blueschist facies conditions; this transformation resulted in dramatic strength reduction that promoted strain localization along the subduction interface. In quartz-rich rocks, qz was deformed in the dislocation creep regime and records transitions in microstructure and slip systems during near-isothermal decompression from 2.5 to 1.5 GPa; these transitions may be related to decreasing water fugacity over tens of km of decompression. High-to ultrahigh-P eclogite in exhumed continental subduction zones such as the Western Gneiss Region (Norway) record decompression from >2.5 GPa to crust, upper crustal extension/transtension drives rapid ascent of the deep crust to form migmatite-cored domes. The exhuming deep crust entrains HP relics such as eclogite (e.g. Montagne Noire dome, France) as it traverses much of the orogenic crust, from >1.2 GPa to (in some cases) crust reaches the near-surface. In summary, decompression of subducted or deeply buried crust systematically leads to rheologic transitions and feedbacks between deformation and metamorphism in the presence of aqueous fluid and/or melt.

  3. Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand (United States)

    Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.


    Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern Fiordland, must have occurred prior to 126. Ma, that loading occurred at a rate of ca. 0.06. GPa/m.y., and that garnet granulite metamorphism lasted 3-7m.y. Locally-derived partial melts formed and crystallized in considerably less than 10 and perhaps as little as 3m.y. ?? 2010 Elsevier B.V.

  4. Micro-facies of Dead Sea sediments (United States)

    Neugebauer, Ina; Schwab, Markus J.; Brauer, Achim; Frank, Ute; Dulski, Peter; Kitagawa, Hiroyuki; Enzel, Yehouda; Waldmann, Nicolas; Ariztegui, Daniel; Drilling Party, Dsddp


    Lacustrine sediments infilling the Dead Sea basin (DSB) provide a rare opportunity to trace changing climates in the eastern Mediterranean-Levant region throughout the Pleistocene and Holocene. In this context, high-resolution investigation of changes in sediment micro- facies allow deciphering short-term climatic fluctuations and changing environmental conditions in the Levant. The Dead Sea is a terminal lake with one of the largest drainage areas in the Levant, located in the Mediterranean climate zone and influenced also by the Saharo-Arabian deserts. Due to drastic climatic changes in this region, an exceptionally large variety of lacustrine sediments has been deposited in the DSB. These sediments, partially the results of changing lake levels, primarily represent changes in precipitation (e.g. Enzel et al., 2008). Evaporites (halite and gypsum) reflect dry climatic conditions during interglacials, while alternated aragonite-detritus (AAD) is deposited during glacial lake level high-stands. Here we present the first micro-facies inventory of a ~450 m long sediment profile from the deepest part of the northern DSB (ICDP site 5017-1, ~300 m water depth). The sediment record comprises the last two glacial-interglacial cycles, with mainly AAD facies in the upper part of the Amora Formation (penultimate glacial) and the last glacial Lisan Formation. The last interglacial Samra and the Holocene Zeelim Formations are predominantly characterized by thick bedded halite deposits, intercalated by partly laminated detrital marl sequences. Representative sections of the different facies types have been analyzed for micro-facies on petrographic thin sections, supported by high-resolution µXRF element scanning, magnetic susceptibility measurements and microscopic fluorescence analysis. Furthermore, Holocene sediments retrieved at the deep basin core site have been compared to their shallow-water counterpart at the western margin of the lake (core DSEn; Migowski et al., 2004

  5. Petrology, phase equilibria and monazite geochronology of granulite-facies metapelites from deep drill cores in the Ordos Block of the North China Craton (United States)

    He, Xiao-Fang; Santosh, M.; Bockmann, Kiara; Kelsey, David E.; Hand, Martin; Hu, Jianmin; Wan, Yusheng


    Among the various Precambrian crustal blocks in the North China Craton (NCC), the geology and evolution of the Ordos Block remain largely enigmatic due to paucity of outcrop. Here we investigate granulite-facies metapelites obtained from deep-penetrating drill holes in the Ordos Block and report petrology, calculated phase equilibria and in-situ monazite LA-ICP-MS geochronology. The rocks we studied are two samples of cordierite-bearing garnet-sillimanite-biotite metapelitic gneisses and one graphite-bearing, two-mica granitic gneiss. The peak metamorphic age from LA-ICP-MS dating of monazite in all three samples is in the range of 1930-1940 Ma. The (U + Pb)-Th chemical ages through EPMA dating reveals that monazite occurring as inclusions in garnet are older than those in the matrix. Calculated metamorphic phase diagrams for the cordierite-bearing metapelite suggest peak P-T conditions ca. 7-9 kbar and 775-825 °C, followed by decompression and evolution along a clockwise P-T path. Our petrologic and age data are consistent with those reported from the Khondalite Belt in the Inner Mongolia Suture Zone in the northern part of the Ordos Block, suggesting that these granulite-facies metasediments represent the largest Paleoproterozoic accretionary belt in the NCC.

  6. Hornblende-rich, high grade metamorphic terranes in the southernmost Sierra Nevada, California, and implications for crustal depths and batholith roots (United States)

    Ross, Donald Clarence


    The southernmost Sierra Nevaaa widely exposes hornblende-rich, gneissic to granoblastic, amphibolite- to granulite-grade, metamorphic rocks and associated magmatic rocks, all of mid-Cretaceous age. Locally, red garnet, in part in euhedral crystals as large as 10 cm, as well as strongly pleochroic hyperstnene, characterize these rocks. These hornblende-rich rocks dominate the north slopes of the southern tail of the Sierra Nevada, but are also present as inclusion masses of various sizes in the dominantly granitic terrane to She northeast. The mafic, hornblende-rich rocks reflect a deeper crustal level than the dominantly granitic terrane to the northeast based on: 1) 'index' minerals (presence of hypersthene, coarse garnet, and brown hornblende; 2) textures (considerable ambivalence of whether individual samples are metamorphic or magmatic, 3) metamorphic grade (at least local granulite facies); and 4) the presence of migmatite, and the eviaence of local melting and mobilization. These rocks may be exposures of the upper part of the root zone and metamorphic substrate of the Sierra Nevada batholith. Xenoliths of gneiss, amphibolite, and granulite from sub-batholithic levels, that have been transported upward and preserved in volcanic rocks in the central Sierra Nevada, are similar to some exposed rocks of the southernmost Sierra Nevada. Hypersthene-bearing granulite and tonalite, as well as distinctive granofels of mid-Cretaceous age, are exposed in the western part of the Santa Lucia Range (some 300 km to the northwest across the San Andreas fault). These rocks have much in common with some of the metamorphic and magmatic rocks in the southernmost Sierra Nevada, suggesting that the two areas record similar metamorphic conditions and crustal depth. Mid-Cretaceous hypersthene granulite is rare, which makes correlation of the Santa Lucia Range and the southernmost Sierra Nevada seem attractive. Nevertheless, possibly significant petrographic anm rock distribution

  7. Metamorphism, argon depletion, heat flow and stress on the Alpine fault (United States)

    Scholz, C. H.; Beavan, J.; Hanks, T. C.


    The Alpine fault of New Zealand is a major continental transform fault which was uplifted on its southeast side 4 to 11 km within the last 5 m.y. This uplift has exposed the Haast schists, which were metamorphosed from the adjacent Torlesse graywackes. The Haast schists increase in metamorphic grade from prehnite-pumpellyite facies 9-12 km from the fault through the chlorite and biotite zones of the greenschist facies to the garnet-oligoclase zone amphibolite facies within 4 km of the fault. These metamorphic zone boundaries are subparallel to the fault for 350 km along the strike. The K-Ar and Rb-Sr ages of the schists increase with distance from the fault: from 4 m.y. within 3 km of the fault to approximately 110 m.y. 20 km from the fault. Field relations show that the source of heat that produced the argon depletion aureole was the fault itself.

  8. Low-grade metamorphism in the eastern Southern Alps: Distribution, conditions, timing and implications for the tectonics of the Alps and NW Dinarides (United States)

    Neubauer, Franz; Heberer, Bianca; Genser, Johann; Friedl, Getrude


    Based on 40Ar/39Ar dating of newly-grown syntectonic metamorphic white mica (sericite), we recognize for the first time the timing of Alpine low-grade metamorphism in the eastern part of the Southalpine unit: (1) A Silurian phyllite of Seeberg inlier located to the south of the Periadriatic fault yields a plateau age at c. 75 Ma suggesting a Late Cretaceous age of previously recognized low-grade (Rantitsch & Rainer, 2003) metamorphism. (2) Within the Tolmin nappe, four sericite plateau ages of mainly Middle Triassic volcanics are at c. 51 Ma (Early Eocene). The Late Cretaceous age in the Seeberg inlier is considered to record ductile deformation during formation of a retro-wedge related to the Eo-Alpine orogeny in the Austroalpine units in the Eastern Alps exposed north of the future Periadriatic fault. The Eocene age at the boundary of very low-grade to low-grade metamorphism in the Tolmin nappe (Rainer et al., 2009) relates to the emplacement of the Southalpine nappe complex onto the Dinarides and is contemporaneous with the initial ductile deformation in the Dinarides during Adria-directed shortening and formation of a siliciclastic flysch belt in front of the SW-directed growing fold-thrust belt (Placer, 2008). Similar rare Late Cretaceous and dominant Eocene ages within post-Variscan units are virtually more widespread in the Southalpine unit and Dinarides as considered before. These regions include the Collio basin (Feijth, 2002) and the Eder unit (Läufer et al., 1996) in the western and central Southern Alps, in the internal NW Dinarides (Borojević Šoštarić et al., 2012) and the Mid Bosnian Schist Mountains (Pamić et al., 2004) and Lim Paleozoic unit in the central Dinarides (Ilic et al., submitted). Consequently, the Southalpine unit and Dinarides were affected by two stages of metamorphism, Late Cretaceous (ca. 80 to 75 Ma) and Eocene (ca. 51 - 40 Ma), both stages are related to back-thrusting. The ages of metamorphism are different from those in the

  9. The timing of metamorphism in the Odenwald-Spessart basement, Mid-German Crystalline Zone (United States)

    Will, T. M.; Schulz, B.; Schmädicke, E.


    New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald-Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 Ma. Granulite-facies metamorphism occurred in the western Odenwald at c. 430 and 349 Ma, and amphibolite-facies metamorphism affected the eastern Odenwald and the central Spessart basements between c. 324 and 316 Ma. We interpret these data to indicate that the Otzberg-Michelbach Fault Zone, which separates the eastern Odenwald-Spessart basement from the Western Odenwald basement, is part of the Rheic Suture, which marks the position of a major Variscan plate boundary separating Gondwana- and Avalonia-derived crustal terranes. The age of the Carboniferous granulite-facies event in the western Odenwald overlaps with the minimum age of eclogite-facies metamorphism in the adjacent eastern Odenwald. The granulite- and eclogite-facies rocks experienced contrasting pressure-temperature paths but occur in close spatial proximity, being separated by the Rheic Suture. As high-pressure and high-temperature metamorphisms are of similar age, we interpret the Odenwald-Spessart basement as a paired metamorphic belt and propose that the adjacent high-pressure and high-temperature rocks were metamorphosed in the same subduction zone system. Juxtaposition of these rocks occurred during the final stages of the Variscan orogeny along the Rheic Suture.

  10. The timing of metamorphism in the Odenwald-Spessart basement, Mid-German Crystalline Zone (United States)

    Will, T. M.; Schulz, B.; Schmädicke, E.


    New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald-Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 Ma. Granulite-facies metamorphism occurred in the western Odenwald at c. 430 and 349 Ma, and amphibolite-facies metamorphism affected the eastern Odenwald and the central Spessart basements between c. 324 and 316 Ma. We interpret these data to indicate that the Otzberg-Michelbach Fault Zone, which separates the eastern Odenwald-Spessart basement from the Western Odenwald basement, is part of the Rheic Suture, which marks the position of a major Variscan plate boundary separating Gondwana- and Avalonia-derived crustal terranes. The age of the Carboniferous granulite-facies event in the western Odenwald overlaps with the minimum age of eclogite-facies metamorphism in the adjacent eastern Odenwald. The granulite- and eclogite-facies rocks experienced contrasting pressure-temperature paths but occur in close spatial proximity, being separated by the Rheic Suture. As high-pressure and high-temperature metamorphisms are of similar age, we interpret the Odenwald-Spessart basement as a paired metamorphic belt and propose that the adjacent high-pressure and high-temperature rocks were metamorphosed in the same subduction zone system. Juxtaposition of these rocks occurred during the final stages of the Variscan orogeny along the Rheic Suture.

  11. 榴辉岩相高压-超高压变质岩的He同位素地球化学研究现状与问题%Helium isotopic geochemistry of HP-UHP eclogite facies metamorphic rocks: a review

    Institute of Scientific and Technical Information of China (English)

    李兆丽; 李天福


    The helium isotopic composition of each sphere of the Earth has its characteristic isotopic ratios. These ratios show significant differences. Therefore, helium isotopes, as a tracer, are more sensitive than other isotopes to distinguishing crust from mantle materials. Up till now, geochemical behaviors of helium isotopes during the HP-UHP metamorphism have not been well studied, it led to the limited application of helium isotope in eclogites. Many HP-UHP eclogite belts have been discovered in China. These eclogites can be genetically classified into two types: one is associated with subduction of the continental slab, and the other is formed by the subduction of the oceanic slab. This paper reviewed the progresses therefore of HP-UHP eclogite fades metamorphic rocks well studied and some problems and future work of the application of helium isotope in eclogites are also discussed.%He同位素是区分地壳、地幔物质,研究壳-幔相互作用最灵敏的示踪剂之一,但其在高压-超高压变质作用过程中的地球化学行为目前仍不清楚,因而制约其在榴辉岩研究中的应用.中国作为高压-超高压榴辉岩带分布的重要地区,榴辉岩产出得天独厚,大洋、大陆两种俯冲成因榴辉岩均有分布.本文在归纳榴辉岩相高压-超高压变质岩研究进展的基础上,分析了He同位素示踪在榴辉岩研究中的应用现状.

  12. Garnet-bearing Granulite Facies Rock Xenoliths from Late Mesozoic Volcaniclastic Breccia, Xinyang, Henan Province

    Institute of Scientific and Technical Information of China (English)


    This paper presents the primary results of petrologic,mineralogical and petrochemical studies of garnet beating granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13-3.30 g/cm3) and high seismic velocity (Vp = 7.04-7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.


    Institute of Scientific and Technical Information of China (English)


    The concept of metamorphic mechanism is put forward according to the change of configurations from one state to another. Different configurations of metamorphic mechanism are described through the method of Huston lower body arrays. Kinematics analyses for metamorphic mechanism with generalized topological structure, including the velocity, angular velocity, acceleration and angular acceleration, are given. Dynamic equations for an arbitrary configuration, including close-loop constraints, are formed by using Kane's equations. For an arbitrary metamorphic mechanism, the transformation matrix of generalized speeds between configuration (*)and(*)+1 is obtained for the first time. Furthermore, configuration-complete dynamic modeling of metamorphic mechanism including all configurations is completely established.

  14. Stenian - Tonian and Ediacaran metamorphic imprints in the southern Paleoproterozoic Ubendian Belt, Tanzania: Constraints from in situ monazite ages (United States)

    Boniface, Nelson; Appel, Peter


    In situ monazite geochronological data yield the timing of migmatitic metamorphism in southern Ubendian Belt. The mineral assemblage of garnet-biotite- sillimanite- K-feldspar- plagioclase-quartz- ilmenite, in migmatitic metapelitic gneisses was achieved during the Ediacaran metamorphic episode between 565 ± 4 Ma and 559 ± 8 Ma as manifested by dating of monazite grains that include garnet. The Ediacaran metamorphic event in the southern Ubendian Belt overprinted the Paleoproterozoic metamorphic event established at 1808 ± 9 Ma and the Mesoproterozoic metamorphic event at 944 ± 4 Ma (Tonian Period). The Stenian - Tonian and Ediacaran metamorphic imprints in the southern Ubendian Belt fall within the time window of metamorphism and deformation of the neighboring Irumide, southern Irumide, and Unango/Marrupa Complexes. The ca. 560 Ma old granulite facies imprinting in the southern Ubendian Belt is coeval with shear zone patterns in the neighboring Nyika Terrane in NE Malawi the event that was followed by eclogite facies metamorphism during the last stage of Gondwana amalgamation.

  15. On Continent-Continent Point-Collision and Ultrahigh-Pressure Metamorphism

    Institute of Scientific and Technical Information of China (English)

    董树文; 武红岭; 刘晓春; 薛怀民


    Up to now it is known that almost all ultrahigh-pressure (UHP) metamorphism of non-impact origin occurred in continent-continent collisional orogenic belt, as has been evidenced by many outcrops in the eastern hemisphere. UHP metamorphic rocks are represented by coesite- and diamond-bearing eclogites and eclogite facies metamorphic rocks formed at 650–800°C and 2.6–3.5 Gpa, and most of the protoliths of UHP rocks are volcanic-sedimentary sequences of continental crust. From these it may be deduced that deep subduction of continental crust may have occurred. However, UHP rocks are exposed on the surface or occur near the surface now, which implies that they have been exhumed from great depths. The mechanism of deep subduction of continental crust and subsequent exhumation has been a hot topic of the research on continental dynamics, but there are divergent views. The focus of the dispute is how deep continental crust is subducted so that UHP rocks can be formed and what mechanism causes it to be subducted to great depths and again exhumed to the shallow surface. Through an analysis of the continental process and mechanical boundary conditions of the Dabie collisional belt—an UHP metamorphic belt where the largest area of UHP rocks in the world is exposed, this paper discusses the variations of viscous stresses and average pressure in the viscous fluid caused by tectonism with rock physical properties and the contribution of the tectonic stresses to production of UHP. Calculation indicates that the anomalous stress state on the irregular boundary of a continental block may give rise to stress concentration and accumulation at local places (where the compressional stress may be 5–9 times higher than those in their surroundings). The tectonic stresses may account for 20–35% of the total UHP. So we may infer that the HP (high-pressure)-UHP rocks in the Dabie Mountains were formed at depths of 60–80 km. Thus the authors propose a new genetic model of UHP

  16. "High-grade burial metamorphism of sedimentary mélange, Shoo Fly Complex, central Sierra Nevada, California" (United States)

    Mendoza, Y.; Wakabayashi, J.


    The Shoo Fly Complex, California is a subduction complex metamorphosed at lower greenschist facies in much of the northern Sierra Nevada. Central Sierra Nevada exposures include higher grade assemblages. Previous studies have interpreted the higher grade rocks as gneissic granitoids representing the roots of a Paleozoic arc. Recent field work in the North Fork Mokelumne River drainage, shows that high-grade and low-grade metamorphic rocks were derived from similar subduction complex protoliths. The Shoo Fly in this region consists of mostly phyllite (metasiltstone, metasandstone, metachert), with some metabasite, and metaultramafic blocks. There is a metamorphic gradient from west to east in the field area, transitioning from sub to lower greenschist facies (white mica only) to middle and upper green schist facies (biotite) within the phyllites to amphibolite/upper amphibolite/granulite grade mica schists, gneisses, and amphibolites This gradient occurs across a zone about 1.5 km wide and this gradient is about 5 km west of the contact between the Shoo Fly Complex and plutons of the Sierra Nevada batholith. The higher-grade rocks do not have an apparent west-east metamorphic gradient. Accordingly the high-grade metamorphism does not appear to be a consequence of either contact metamorphism or raised regional geothermal gradients connected with the batholith. This conclusion is consistent with the fact that published metamorphic ages from probable correlative rocks within the central Sierra are much older than the Sierra Nevada batholith. Protoliths for the higher grade rocks appear identical to the lower grade rocks, for metaclastic rocks dominate with subordinate metacherts, metabasites, and metaultramafic rocks. The latter are represented by tremolite-talc schists. In the lower grade rocks some of the metabasite and metaultramafic blocks exhibit a higher grade of metamorphism than the surrounding metaclastic rocks and metacherts. Amphibolite and tremolite schist

  17. Early Cretaceous Shallow-Water Platform Carbonates of the Bolkar Mountains, Central Taurides - South Turkey: Facies Analysis and Depositional Environments (United States)

    Solak, Cemile; Taslı, Kemal; Koç, Hayati


    The study area comprises southern non-metamorphic part of the Bolkar Mountains which are situated in southern Turkey, eastern part of the Central Taurides. The studied five outcrops form geologically parts of the tectonostratigraphic units called as allochthonous Aladag Unit and autochthonous Geyikdagi Unit. The aim of this study is to describe microfacies and depositional environments of the Bolkar Mountains Early Cretaceous shallow- water platform carbonates. The Lower Cretaceous is represented by continuous thick- bedded to massive dolomite sequence ranging from 100 to 150 meters thick, which only contains locally laminated limestone intercalations in the Yüğlük section and thick to very thick-bedded uniform limestones ranging from approximately 50 to 120 meters, consist of mainly laminated- fenestral mudstone, peloidal-intraclastic grainstone-packstone, bioclastic packstone- wackestone, benthic foraminiferal-intraclastic grainstone-packstone, ostracod-fenestral wackestone-mudstone, dasycladacean algal packstone-wackestone and ooidal grainstone microfacies. Based on a combination sedimantological data, facies/microfacies and micropaleontological (predominantly dasycladacean algae and diverse benthic foraminifera) analysis, it is concluded that Early Cretaceous platform carbonates of the Bolkar Mountains reflect a tidally affected tidal-flat and restricted lagoon settings. During the Berriasian- Valanginian unfavourable facies for benthic foraminifera and dolomitization were predominate. In the Hauterivian-early Aptian, the effect of dolomitization largely disappeared and inner platform conditions still prevailed showing alternations of peritidal and lagoon facies, going from peritidal plains (representing various sub-environments including supratidal, intertidal area, tidal-intertidal ponds and ooid bars) dominated by ostracod and miliolids, to dasycladacean algae-rich restricted lagoons-subtidal. These environments show a transition in the vertical and

  18. Tectono-metamorphic evolution of high-P/T and low-P/T metamorphic rocks in the Tia Complex, southern New England Fold Belt, eastern Australia: Insights from K-Ar chronology (United States)

    Fukui, Shiro; Tsujimori, Tatsuki; Watanabe, Teruo; Itaya, Tetsumaru


    The Tia Complex in the southern New England Fold Belt is a poly-metamorphosed Late Paleozoic accretionary complex. It consists mainly of high-P/low-T type pumpellyite-actinolite facies (rare blueschist facies) schists, phyllite and serpentinite (T = 300 °C and P = 5 kbar), and low-P/high-T type amphibolite facies schist and gneiss (T = 600 °C and P high-Mg andesite and adakite might explain formation of S-type granitoids (Hillgrove suite) and coeval low-P/high-T type metamorphism in the Tia Complex.

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

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


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

  20. Post-peak metamorphic evolution of the Sumdo eclogite from the Lhasa terrane of southeast Tibet (United States)

    Cao, Dadi; Cheng, Hao; Zhang, Lingmin; Wang, Ke


    A reconstruction of the pressure-temperature-time (P-T-t) path of high-pressure eclogite-facies rocks in subduction zones may reveal important information about the tectono-metamorphic processes that occur at great depths along the plate interface. The majority of studies have focused on prograde to peak metamorphism of these rocks, whereas after-peak metamorphism has received less attention. Herein, we present a detailed petrological, pseudosection modeling and radiometric dating study of a retrograded eclogite sample from the Sumdo ultrahigh pressure belt of the Lhasa terrane, Tibet. Mineral chemical variations, textural discontinuities and thermodynamic modeling suggest that the eclogite underwent an exhumation-heating period. Petrographic observations and phase equilibria modeling suggest that the garnet cores formed at the pressure peak (∼2.5 GPa and ∼520 °C) within the lawsonite eclogite-facies and garnet rims (∼1.5 GPa and growth of garnet spans an interval of ∼7 million years, which is a minimum estimate of the duration of the eclogite-facies metamorphism of the Sumdo eclogite.

  1. Genesis of the metamorphic rock from southeastern Lhasa terrane and the Mesozoic-Cenozoic orogenesis%拉萨地体东南部变质岩的成因与中-新生代造山作用

    Institute of Scientific and Technical Information of China (English)

    董昕; 张泽明; 刘峰; 王伟; 于飞; 林彦蒿; 姜洪颖; 贺振宇


    temperature (HT) and medium pressure (MP) granulite-facics metamorphism, then amphibolite-facies retrograde metamorphism. The temperature and pressure conditions of the peak granulite-facies metamorphism are 830 ~900t and 0. 9 - 1. 3GPa. And the time of metamorphism is the Late Cretaceous of 89 -81 Ma. Secondly, Bayi belt generally experienced 1ow pressure (LP) amphibolite-faaes metamorphism, of which the time is Eocene of 55 ~49Ma. And the temperature and pressure conditions are 625 ~ 679℃ and 0. 4 ~ 0. 55GPa. Thirdly, Bujiu belt experienced MP amphibolite-facies metamorphism, of which the time is Oligocene of 36 ~26Ma. And the temperature and pressure conditions are 615 ~ 663t and 0. 5 - 0. 8GPa. This study demonstrates that the prctoliths of these metamorphic rocks is mainly composed of the Late Paleozoic sedimentary rocks and the Paleozoic to Cenozoie magmatic rocks. Moreover, the material sources of the metasedimentary rocks have the records of the tectono-thermal events related to the Grenville and Pan-African orogenesis, indicating a tectonic affinity to Gondwana supercontinent. We consider that the Late Cretaceous HT and MP metamorphism related to the Andean-type orogeny derived from the subduction of Neo-Tethyan oceanic lithosphere, the Eocene LP amphibolite-facies metamorphism formed during the collision orogeny between Indian and Eurasian continents and then the deep-subduction slab' s break-off of Neo-Tethyan, and the Oligocene MP amphibolite-facies metamorphism resulted from the crustal thickening caused by the subduction between India and Eurasia continents. Therefore, the high-grade metamorphic rocks located on the southeastern segment of Lhasa terrane not only reveals the middle and lower crust composition, but also the tectonic evolution for the hanging wall of the subduction/collision compound orogenic belt.

  2. Metamorphic Testing for Cybersecurity. (United States)

    Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey; Zhou, Zhi Quan


    Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity.

  3. Geochronological review of Sambagawa metamorphic belt in Southwest Japan

    Institute of Scientific and Technical Information of China (English)


    Based on almost all available published age data, the protolith ages, peak metamorphic ages and cooling rate of the Sambagawa metamorphic belt have been discussed and the latest constraints on the ages of the Sambagawa metamorphism and subduction-related accretionary evolutions were summarized. Peak metamorphic conditions attained within the Kuma nappe complex at ca. 145~185 Ma, and uplift through ca. 500℃ at ca. 150 Ma and 350~400℃ at ca. 110~ 115 Ma. The protolith sediments of the Besshi nappe complex were accumulated and subsequently progressively subducted and suffered high P-T prograde metamorphism during the Kuma nappe complex uplifting. The Besshi nappe complex arrived maximum metamorphic conditions at ca. 110 ~ 120 Ma and subsequently started rapid uplift with the cooling rate of ca. 14.2℃/Ma at ca. 75 ~85 Ma, followed with the cooling rate of ca. 6.0 ~8.9℃/Ma. The Oboke nappe complex started subduction later than other tectonic units and arrived the peak metamorphic conditions at ca. 75 Ma, which followed by the uplift with a cooling rate of ca. 8℃/Ma.

  4. Origin of eclogite-bearing, domed, layered metamorphic complexes ("core complexes") in the D'entrecasteaux Islands, Papua New Guinea (United States)

    Davies, Hugh L.; Warren, R. G.


    Compositionally layered metamorphic rocks of the D'Entrecasteaux Islands, Papua New Guinea, are folded into domes and antiforms bounded by faults parallel to metamorphic layering and foliation. The structures are broadly similar to the metamorphic "core complexes" of western North America. Lenses of ultramafic rock lie on the bounding faults, and the same faults have served as loci for Quaternary andesitic volcanic activity. Metamorphic grade in the northern islands (Goodenough and Fergusson) is amphibolite facies, with pockets of eclogite (Fergusson Island only) and granulite, and is greenschist facies in the southern island (Normanby). In all three islands there is a characteristic tectonostratigraphic sequence (FMU sequence) from felsic metamorphic rocks at base, or internally, through mafic metamorphic rocks to ultramafic rocks at top, or externally. The association of metamorphic and ultramafic rocks apparently developed in a north dipping Paleogene subduction system and was exhumed to upper crustal level in the Oligocene--Early Miocene, possibly by reversal of movement on faults in the former subduction system. Vigorous uplift and development of domes and antiforms in the Pliocene was triggered by westward propagation of the Woodlark Basin spreading ridge and was accompanied by rifting, rift-related magmatism, rapid erosion, and deposition of coarse sediment in the adjacent Trobriand Basin.

  5. Late Cretaceous extension and exhumation of the Stong and Taku magmatic and metamorphic complexes, NE Peninsular Malaysia (United States)

    François, T.; Md Ali, M. A.; Matenco, L.; Willingshofer, E.; Ng, T. F.; Taib, N. I.; Shuib, M. K.


    Fragmentation of large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts, as exemplified by the Stong and Taku magmatic and metamorphic complexes of northern Peninsular Malaysia. For this case, we have employed a field and microstructural kinematic study combined with low temperature thermo-chronology to analyse the tectonic and exhumation history. The results show that the Late Palaeozoic - Triassic Indosinian orogeny created successive phases of burial related metamorphism, shearing and contractional deformation. This orogenic structure was subsequently dismembered during a Cretaceous thermal event that culminated in the formation of a large scale Late Santonian - Early Maastrichtian extensional detachment, genetically associated with crustal melting, the emplacement of syn-kinematic plutons and widespread migmatisation. The emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range, represented by amphibolite- and greenschist- facies mylonites and as well as brittle structures, such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment. The formation of this detachment and a first phase of Late Cretaceous cooling was followed by renewed Eocene - Oligocene exhumation, as evidenced from our fission track ages. We infer that an initial Cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults. These Cretaceous processes played a critical role in the establishment of the presently observed crustal structure of Peninsular Malaysia.

  6. Near-isothermal conditions in the middle and lower crust induced by melt migration. (United States)

    Depine, Gabriela V; Andronicos, Christopher L; Phipps-Morgan, Jason


    The thermal structure of the crust strongly influences deformation, metamorphism and plutonism. Models for the geothermal gradient in stable crust predict a steady increase of temperature with depth. This thermal structure, however, is incompatible with observations from high-temperature metamorphic terranes exhumed in orogens. Global compilations of peak conditions in high-temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure, for both isothermal decompression and isobaric cooling paths. Here we develop simple one-dimensional thermal models that include the effects of melt migration. These models show that long-lived plutonism results in a quasi-steady-state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust. The models also predict that the upward advection of heat by melt generates granulite facies metamorphism, and widespread andalusite-sillimanite metamorphism in the upper crust. Once the quasi-steady-state thermal profile is reached, the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions, thus setting the stage for gravitational collapse, exhumation and isothermal decompression after the onset of plutonism. Near-isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that, in part, control the shape of the geotherm.

  7. Coal facies studies in Spain

    Energy Technology Data Exchange (ETDEWEB)

    Suarez-Ruiz, Isabel [INCAR (CSIC), Ap. Co., 73, 33080, Oviedo (Spain); Jimenez, Amalia [Geology, University of Oviedo, 33005, Oviedo (Spain)


    This work is a synthesis of the distribution of the main coal basins and sub-basins in Spain as well as the research carried out on their coal facies. The coal fields are distributed through the Paleozoic (mainly Pennsylvanian), Mesozoic (Cretaceous) and Cenozoic times. Peats also exist in the southeast Spain (Granada area), although these types of deposits are not included in this review. Spanish coal basins are both of a paralic and intramontane type and the coal rank is highly variable, from lignite in the case of the younger coal seams to anthracite for those of Carboniferous age.

  8. Coal facies studies in Australia

    Energy Technology Data Exchange (ETDEWEB)

    Crosdale, Peter J. [Coalseam Gas Research Institute, School of Earth Sciences, James Cook University, Townsville, Qld 4814 (Australia)


    Despite the economic importance of coal to the Australian economy, detailed studies of controls on variation in coal type are remarkably few. However, important contributions have been made in the understanding of coal facies development. Tertiary lignite deposits of the Gippsland Basin provide key insights into the development of lithotype cyclicity and its relationship to relative sea-level changes, with individual paling-up cycles being correlated to parasequences. Studies of Permian hard coals have identified relationships between coal type and surrounding sediments. Unfortunately, these relationships have been widely over-interpreted in a manner that has diminished their real value.

  9. Scientific results from the deepened Lopra-1 borehole, Faroe Islands: Mineralogical and thermodynamic constraints on Palaeogene palaeotemperature conditions during low-grade metamorphism of basaltic lavas recovered from the Lopra-1/1A deep hole, Faroe Islands

    Directory of Open Access Journals (Sweden)

    Glassley, William E.


    Full Text Available The sequene of secondary minerals that are reported for the Lopra-1/1A well records progressive zeolite facies to prehnite–pumpellyite-facies mineral progressions consistent with those of other wellstudied hydrothermally altered rock sequences. Detailed comparison of the calc–silicate (zeolites and prehnite mineral distributions of the Lopra-1/1A sequence with those from other regions indicates that this sequence exhibits consistently longer down-hole intervals for secondary mineral species than reported elsewhere. When compared to measured down-hole temperatures reported in other hydrothermally altered regions, the results suggest that the Lopra-1/1A mineral progression formed under conditions typical of low temperature hydrothermal systems that form shortly after eruption of thick basaltic piles. Maximum temperatures achieved at the 3500 m level of the well were at or below 200°C. The implied geothermal gradient was less than 50°C/km. An analysis of prehnite – fluid composition relationships was also conducted in order to determine if results compatible with the paragenetic sequence study could be obtained from thermodynamic constraints. In this case, thelimiting temperature for prehnite formation in equilibrium with albite–quartz–calcite–laumontite (the mineral assemblage at the bottom of the hole was determined for a range of fluid compositions.The resulting calculations suggest temperatures of formation of prehnite in the range of 140°C to 205°C, a conclusion which is broadly consistent with those reached from study of the parageneticrelationships. Comparison of these results with other studies of palaeogeothermal gradients of the North Atlantic margins suggests a consistent pattern in which relatively low geothermal gradientspersisted in the Palaeogene rift basin.

  10. Organic facies applied to petroleum exploration; Facies organica: conceitos, metodos e estudos de casos na industria do petroleo

    Energy Technology Data Exchange (ETDEWEB)

    Menezes, Taissa Rego; Araujo, Carla Viviane; Souza, Igor Viegas Alves F. de [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES). Gerencia de Geoquimica,]. E-mail:; Mendonca Filho, Joao Graciano; Mendonca, Joalice de Oliveira [Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, RJ (Brazil). Dept. de Geologia


    The concept of organic facies, as well as the definitions and means of the different facies became a very important tool to petroleum exploration. The application of this concept is the best way to integrate microscopy and geochemical techniques to study kerogen contained in sedimentary rocks. Thus, palynofacies analysis and bulk geochemical methods are used to characterize the total particulate organic matter. Palynofacies analysis involves the integrated study of all aspects of the kerogen assemblage: identification of the individual particulate components, assessment of their absolute and relative proportions and preservation states. The correlation between palynofacies and geochemical data provides the organic facies models that point out the depositional environmental conditions and hydrocarbon source rock potential. (author)

  11. Ployphase Early Paleozoic metamorphism in the northern Qinling orogenic belt%北秦岭造山带的早古生代多期变质作用

    Institute of Scientific and Technical Information of China (English)

    张建新; 于胜尧; 孟繁聪


    北秦岭造山带的秦岭岩群以高级变质岩石为特征,主要包括少量榴辉岩、高压麻粒岩和区域上广泛分布的麻粒岩-角闪岩相变质岩石.年代学研究显示秦岭岩群中不同岩石记录了多期变质作用.已有的定年资料给出北秦岭官坡地区的榴辉岩的年龄为500Ma左右,代表榴辉岩相的变质时代.结合岩相学资料,对两个高压麻粒岩样品的SHRIMP和LA-ICPMS U-Pb测定分别获得504±7Ma和506±3Ma的年龄,应代表高压麻粒岩相变质时代.这表明高压麻粒岩和相邻的榴辉岩有相近的变质时代,但形成在造山带中不同的构热造环境中.西峡地区的角闪二辉麻粒岩的U-Pb定年给出两组早古生代年龄,一组为440±2Ma,可能代表了中低压麻粒岩相的变质时代,另一组为426±1Ma,应代表区域角闪岩相的变质时代.桐柏山北部的石榴二辉麻粒岩的U-Pb定年数据给出436±lMa的年铃,为中压麻粒岩相的变质时代.这些资料表明北秦岭造山带经历了早奥陶世的俯冲和地壳增厚作用,并在晚志留世遭受了广泛的巴罗式区城变质作用.%High-grade metamorphic rocks in North Qinling orogen, traditionally regarded as the Qinling Croup, consist of minor eclogites, high pressure granutlite and widely distributed medium-low P/T granulite-amphibolite facies metamorphic rocks. Radiometric data indicate that ployphase Early Paleozoic metamorphisms are recorded in different rocks. The previous U-Pb datings of eclogites and associated rocks in the Cuanpo area of the North Qinling orogen gave an age of ca. 500Ma, interpreted as the time of eclogite facies metamorphism. In combination with petrological data, SHRIMP and LA-ICPMS U-Pb geochronology on two HP granulite samples in the Songshugou area of the North Qinling orogen yield ages of 504 ± 7Ma and 506 ± 3Ma, respectively, representing the time of high pressure granulite metamorphism. This implies that HP granulite-facies conditions in

  12. Coupling thermodynamic modeling and high-resolution in situ LA-ICP-MS monazite geochronology: evidence for Barrovian metamorphism late in the Grenvillian history of southeastern Ontario (United States)

    McCarron, Travis; Gaidies, Fred; McFarlane, Christopher R. M.; Easton, R. Michael; Jones, Peter


    The Flinton Group is a greenschist to upper amphibolite facies package of metasediments in southeastern Ontario that was metamorphosed during the Ottawan Orogeny. Thermodynamic modeling of metapelitic mineral assemblages suggests an increase in peak conditions of metamorphism across the 40 km wide study area from 3.5 to 7.9 kbar and 540 to 715 °C. Garnet isopleth thermobarometry applied to the cores of compositionally zoned porphyroblasts reveals remarkably similar P-T conditions of initial crystallization at approximately 3.7-4.0 kbar and 512-520 °C, corresponding to a relatively high geothermal gradient of ca. 34-45 °C km-1. It is inferred from modeling and reaction textures that metamorphism was along Barrovian P-T paths. Major and trace element zoning in garnet from one sample records a complex growth history as evidenced by major and trace element zoning and the distribution of xenotime, allanite and monazite inclusions. High-resolution (6 μm) LA-ICP-MS U-Pb geochronology performed on monazite in the rock matrix and included in the outer 150 μm of garnet rim-ward of a Y annulus revealed an age of 976 ± 4 Ma. The age is interpreted to reflect monazite growth at the expense of allanite and apatite late in garnet's growth history over the P-T interval 4.5-6.8 kbar and 540-640 °C. This new age estimate for near peak metamorphism fits well into the regional framework but is significantly younger than previously reported ages for Ottawan metamorphism. Based on microstructures this new age suggests that compressional tectonics were operating much later in the history of the Grenville of southeastern Ontario than previously thought.

  13. High-pressure/low-temperature metamorphism in the collision zone between the Chilenia and Cuyania microcontinents (western Precordillera, Argentina) (United States)

    Boedo, F. L.; Willner, A. P.; Vujovich, G. I.; Massonne, H.-J.


    In central-western Argentina, an Early Paleozoic belt including mafic-ultramafic bodies, marine metasedimentary rocks and high-pressure rocks occur along the western margin of the Precordillera and in the Frontal Cordillera. First pressure-temperature estimates are presented here for low-grade rocks of the southern sector of this belt based on two metasedimentary and one metabasaltic sample from the Peñasco Formation. Peak metamorphic conditions resulted within the range of 345-395 °C and 7.0-9.3 kbar within the high-pressure greenschist facies. The corresponding low metamorphic gradient of 13 °C/km is comparable with subduction related geothermal gradients. Comparison between these results and data from other localities of the same collision zone (Guarguaraz and Colohuincul complexes) confirms a collision between Chilenia and the composite margin of western Gondwana and suggests a stronger crustal thickening in the south of the belt, causing exhumation of more deeply buried sequences. During the Early Paleozoic a long-lived marine sedimentation coupled with the intrusion of MORB-like basalts occurred along a stable margin before the collision event. This contrasts with the almost contemporaneous sedimentation registered during accretion in accretionary prism settings and additionally proves the development of a collision zone along western Precordillera and the eastern Frontal Cordillera as well as the existence of Chilenia as a separate microcontinent.

  14. Structural analysis and deformation characteristics of the Yingba metamorphic core complex, northwestern margin of the North China craton, NE Asia (United States)

    Yin, Congyuan; Zhang, Bo; Han, Bao-Fu; Zhang, Jinjiang; Wang, Yang; Ai, Sheng


    The presence of the Yingba (Yinggete-Bagemaode) metamorphic core complex (MCC) is confirmed near the Sino-Mongolian border in China. We report its structural evolution and the rheological features of ductile shear zones within this complex. Three deformations (Ds, Dm, and Db) since the Late Jurassic are identified. Ds is characterized by ductile structures that resulted from early NW-oriented, low-angle, extensional ductile shearing. Dm is associated with partial melting and magmatic diapirism, which accelerated the formation of the dome-like geometry of the Yingba MCC. Synchronously with or slightly subsequently to Ds and Dm, the Yingba MCC was subjected to brittle, extensional faulting (Db), which was accompanied by the exhumation of the lower crust and the formation of supracrustal basins. The ductile shearing (Ds) developed under greenschist-to amphibolite-facies metamorphic conditions (400-650 °C), as indicated by microstructures in quartz and feldspar, quartz [c] axis fabrics, and two-feldspar geothermometry. The mean kinematic vorticity estimates of 48-62% show a pure shear-preferred flow during Ds. The Yingba MCC provides an excellent sample that recorded an intermediate to high temperature shearing, which also implies the widely extensional regime in northeastern Asia at that time.

  15. Characteristics of Telemagmatic Metamorphism of the Ceshui Formation Coal in Lianyuan Coal Basin

    Institute of Scientific and Technical Information of China (English)

    毕华; 彭格林


    The Ceshui Formation coal is mostly anthracite and its metamorphism has been less documented.By analyzing systematically the reflectance of vitrinite and the results of X-ray diffraction of the Ceshui Formation cola in the Lianyuan coal basin,the spatial variation characteristics of coal ranks,coal metamorphic regions,the extension of coal metamorphic belts.coal metamorphic gradients,coal chemical structure and the effect on the degree of metamorphism of heat-production and -storge conditions,buried depth of the Indosinian-Yenshanian granites at the margins of the Lianyuan coal basin are discussed.The research results in conjunction of the features of regional hydrothermal alterations,endogenetic deposits with the Ceshui Formation coal measures,and the development of secondary vesicles indicate that the telemagmatic metamorphism is the main factor leading to the metamorphism of the Ceshui Formation coal in the region studied.

  16. The Lopu Kangri High-Pressure Metamorphic Complex: A Tso Morari Analog in Southern Tibet (United States)

    Laskowski, A. K.; Kapp, P. A.


    The Lopu Range, located along the Yarlung-Tsangpo suture ~600 km west of Lhasa city in southern Tibet, exposes a high-pressure metamorphic complex composed of Indian passive margin (Tethyan) rocks. An integrated approach involving geologic mapping, kinematic analysis, phengite geobarometry, Zr-in-rutile geothermometry, garnet-phengite Fe-Mg exchange geothermometry and pseudosection modeling reveals that Lopu Range meta-Tethyan rocks reached peak pressures of 20-25 kbar (2.0-2.5 GPa) at temperatures <550-630 ºC along a clockwise P-T path. These data indicate subduction to mantle depths (~75 km) at eclogite facies conditions followed by exhumation to mid-crustal depths and retrogression at upper greenschist to amphibolite facies conditions. The structural geometry and interpreted P-T-t history of Lopu Kangri rocks is similar to the Tso Morari complex, located ~700 km along-strike to the northwest. Therefore, we interpret that these two localities formed in a similar manner following the onset of Tethyan Himalaya—Eurasia collision ca. 58-52 Ma. A previously published Ar-Ar date from Lopu Kangri suggests that exhumation to mid-crustal levels occurred by ~41 Ma. Two key differences exist between the Lopu Kangri and Tso-Morari complexes. 1) the high-grade nappe in the Lopu Kangri complex is composed entirely of Cambrian-Ordovician metasedimentary rocks whereas the high-grade nappe in the Tso Morari complex is composed of the Tso Morari orthogneiss, eclogite boudins (meta-mafic enclaves) and Cambrian-Ordovician metasediments. We interpret that the lack of eclogite boudins at Lopu Kangri resulted from the absence of a basic protolith. 2) Lopu Kangri is located along the Yarlung-Tsangpo segment of the Indus-Yarlung (India-Asia) suture whereas Tso Morari and nearby Kaghan Valley are located along the Indus suture. Prior to this study, no continental high-pressure metamorphic complexes were known along the Yarlung-Tsangpo suture. Previously formulated tectonic models

  17. Eclogites of the Dabie Region: Retrograde Metamorphism and Fluid Evolution

    Institute of Scientific and Technical Information of China (English)

    顾连兴; 杜建国; 翟建平; 赵成浩; 范建国; 张文兰


    Based upon fluid effects, retrograde metamorphism of eclogites in the Dabie region can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stage is marked by polymorphic inversion, recrystallization and exsolution of solid solutions, and is thought to represent eclogite-facies retrograde environments. The fluid-bearing stage is likely to have occurred at the late stage of ecologite-facies diaphthorosis and is represented by kyanite porphyroblasts, rutile, and sodic pyroxene in association with high-pressure hydrous minerals such as phengite and zoisite (clinozoisite) without significant amount of hydrous minerals such as amphibole, epidote and biotite. The fluid-rich stage might have commenced concomitantly with lower amphibolite-facies diaphthoresis and persisted all the way towards the near-surface environment. The product of this stage is characterized by plentiful hydrous and volatile-bearing phases.The dissemination-type rutile mineralizations in eclogites might have formed by preferential shearing-induced pressure solution of gangue minerals at the fluid-bearing stage. The accompanying vein rutile was precipitated from fluids of this stage after local transport and concentration, and may hence represent proximal mobilization of titanium from the eclogite. Therefore, rutile veins can be used as an exploration indicator for dissemination-type rutile deposits.

  18. Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian Zone (United States)

    Henriques, S. B. A.; Neiva, A. M. R.; Ribeiro, M. L.; Dunning, G. R.; Tajčmanová, L.


    A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 °C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and

  19. Weakening and strain localization during metamorphic overprint: The example of Arnøya, Scandinavian Caledonides, Northern Norway (United States)

    Faber, Carly; Stünitz, Holger; Jeřábek, Petr


    Metamorphic processes such as new mineral growth, changes in mineral composition, and infiltration of water are thought to play an important role in rheological weakening and strain localization in the lower crust. However, the exact mechanisms and extent to which these processes have an effect, are not well understood. The Scandinavian Caledonides in northern Norway offer a unique field laboratory to study pervasively deformed and metamorphosed lower crustal nappes and allow for the comparison of deformation and metamorphic conditions between nappe cores, nappe boundaries, and the transition between the two. The island of Arnøya provides a 20 km-long cross section through the Vaddas, Kåfjord and Nordmannvik nappes, with metamorphic grade increasing upwards from amphibolite to granulite facies, respectively. The nappes display a pervasive foliation associated with a strong NW-SE lineation and top-to-SE shear sense consistent with Caledonian thrust deformation. Nappe boundaries occur as wide (10's of metres) ultramylonite-, mylonite- and schist-bearing shear zones, and have a different mineralogy to internal parts of the nappes. Metapelites and migmatites of the Nordmannvik nappe are kyanite-bearing (high T, high P), and the Kåfjord nappe is composed mainly of homogenous semi-pelite (medium T and P). The Vaddas nappe is more variable and contains interlayered metapsammites, amphibolites and local marbles. A comparison of metapelitic samples from the nappes and the two nappe boundary shear zones show that grain size decreases and degree of mixing of phases increases towards shear zone cores. Also grain size becomes homogeneous towards shear zone cores. All samples show evidence of high temperature dynamic recrystallization of quartz. Quartz within aggregates in nappe rocks have a crystallographic preferred orientation (CPO), while quartz in shear zone rocks shows no CPO, indicating deformation mainly by dislocation creep in the nappes and a switch to diffusion

  20. Coal facies studies in Canada

    Energy Technology Data Exchange (ETDEWEB)

    Kalkreuth, Wolfgang D. [Laboratorio de Carvao e de Petrologia Organica, Instituto de Geociencias, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Goncalves, 9500, 91501-970 Porto Alegre, RS (Brazil)


    The present study is a compilation of published data on coal facies studies in Canada based on coal petrological and other methods. The geological age of the coals range from the Devonian coal deposits in Arctic Canada to coals of Tertiary age in the Western Canada Sedimentary Basin, intermontane British Columbia and Arctic Canada. In terms of rank, the coal deposits studied range from lignite to low volatile bituminous. Coal petrological methods include maceral and microlithotype analyses, frequently integrated with data from palynological and geochemical analyses. Most recently, a number of studies have applied sequence stratigraphic concepts to the coal-bearing strata including the interpretation of coal petrological data in the context of this concept.

  1. Contact metamorphism in Middle Ordovician arc rocks (SW Sardinia, Italy): New paleogeographic constraints (United States)

    Costamagna, Luca Giacomo; Elter, Franco Marco; Gaggero, Laura; Mantovani, Federico


    In the early Cambrian Bithia Formation in the Variscan foreland of Sardinia, a Middle Ordovician granitic intrusion (478-457 Ma) is hosted by marly metasedimentary rocks that were affected by high-temperature (HT) metamorphism. A detailed structural-petrographical transect was conducted through the granitic intrusion and its host rocks. Field data and relationships between HT/low-pressure (LP) mineral assemblages in the metasedimentary rocks (Grt + Wo + Ves in carbonate lenses and And in pelite) demonstrate that the study area was affected by a polyphase HT overprint (I: T = 520-620 °C at XCO2 = 0.1, P: 0.2-0.4 GPa; and II: T = 600-670 °C at XCO2 = 0.1, P = 0.2-0.4 GPa) that pre-dates the Variscan tectonic, metamorphic, and igneous phases. In the Canigò or Canigou Massif (Eastern Pyrenees), the Somail Massif (Montagne Noire), and the Ruitor Massif (Internal Massifs, NW Alps), Middle Ordovician orthogneiss with relict igneous textures are deciphered despite being overprinted by Variscan amphibolite-to-granulite-facies metamorphism and subsequent Alpine low-grade metamorphism. Comparisons of associated igneous and metasedimentary rocks in the Sardinia foreland with the High-Grade Metamorphic Complex in the Variscan Axial Zone and the Canigou Massif indicate a convergent Middle Ordovician evolution that was overprinted by HT Variscan metamorphism.

  2. High-temperature metamorphism of the Yushugou ophiolitic slice: Late Devonian subduction of seamount and mid-oceanic ridge in the South Tianshan orogen (United States)

    Zhang, Li; Jin, Zhenmin


    The South Tianshan Orogenic Belt (STOB), representing the southern segment of the Central Asian Orogenic Belt (CAOB), underwent a long-lived and subduction-related accretionary orogenic process. Revealing the petrogenesis of high-pressure (HP) metamorphic ophiolitic slices within this orogen is of crucial importance to understanding the geodynamic evolution of the STOB. In this study, we carry out a petrological, geochemical and geochronological study of HP mafic granulites from the Yushugou ophiolitic slice within the South Tianshan Accretionary Complex. Our results combined with previously published data suggest that the Yushugou mafic granulites, including garnet-clinopyroxene granulite, garnet two-pyroxene granulite and garnet-orthopyroxene granulite, are generally subalkaline to alkaline basalts, and show geochemical characteristics of MORB and OIB. The nominally anhydrous minerals of the mafic granulites contain certain but trace amounts of water in the manner of structural OH and sub-microscopic fluid inclusions. The granulites have a possible protolith age of ca. 400 Ma and metamorphic age of 390-360 Ma, and underwent HP and high-temperature (HT) granulite-facies metamorphism under conditions of 12-14 kbar and 840-950 °C and low H2O activity. Our study indicates that the Yushugou ophiolitic slice was probably derived from seamount that formed at mid-oceanic ridge closing to the oceanic trench and subduction zone during the Early Devonian, and then underwent metamorphism and deformation as a result of the subduction of the seamount and associated spreading ridge during the Middle to Late Devonian. Therefore, the Yushugou HP ophiolitic slice provides an important information of the Paleozoic tectonic evolutionary of the STOB.

  3. P-T-time evolution of the Mejillones Metamorphic Complex: Insights into Late Triassic to Early Jurassic orogenic processes in northern Chile (United States)

    Calderón, M.; Massonne, H.-J.; Hervé, F.; Theye, T.


    Better constrained pressure-temperature (P-T) histories of metamorphic complexes along the Andean continental margin are important for understanding the late Paleozoic and Mesozoic tectonic evolution of the southwestern margin of Gondwana. The Mejillones Metamorphic Complex of the northern Chilean Coastal Cordillera is composed of two tectonic units, the Morro Mejillones and Morro Jorgiño blocks. These units are bound by the NW-trending Caleta Herradura fault and show distinctly metamorphic ages and thermal evolution. The Morro Mejillones block was metamorphosed at low pressure conditions (andalusite-sillimanite series) during the intrusion of tonalitic plutons at ca. 208 Ma, as indicated by available geochronological data. In contrast, the Morro Jorgiño block comprises amphibolite-facies schists, gneisses and foliated metabasites with characteristic garnet-bearing mineral assemblages. For garnet-bearing pelitic gneisses, a clockwise P-T path has been determined from pseudosection modelling in the MnNCKFMASHTO system. The proposed evolution is characterized by a pressure increase from 7.5 to 8.5 kbar at increasing temperatures from 585 to 615 °C. Decompression to 6 kbar followed, accompanied by heating to 630-640 °C. Electron microprobe Th-U-Pb in-situ dating of high-Y monazite grains yielded a weighted average age of ca. 190 ± 4 Ma, which is interpreted as the age of tectonic burial of metamorphic rocks of the Morro Jorgiño tectonic unit. We infer that the block was buried to 25 km depth through contractional deformation of the continental edge in a subduction zone, likely linked to the docking of the Mejillonia terrane. Rapid exhumation followed and the ensuing juxtaposition of both tectonic units was controlled by Jurassic transtensional activity of the Atacama Fault System.

  4. The role of boron and fluids in high temperature, shallow level metamorphism of the Chugach Metamorphic Complex, Alaska (United States)

    Sisson, V. B.; Leeman, W. P.


    The possible role of boron (B) involvement in granite equilibria and generation of melts during crustal metamorphism has been a focus of speculation in recent literature. Most of the evidence for such involvement derives from experimental data which implies that the addition of B will lower the temperature of the granite solidus. Also the presence of tourmaline has a minor effect on the temperature of the solidus. Further indirect evidence that B may be involved in partial melting processes is the observation that granulites are commonly depleted in B, whereas the B content of low grade metapelites can be high (up to 2000 ppm). Researchers' measurements of the whole-rock B contents of granulites from the Madras region, India are low, ranging from 0.4 to 2.6 ppm. Ahmad and Wilson suggest that B was mobilized in the fluid phase during granulite facies metamorphism of the Broken Hill Complex, Australia. Thus, it appears that during the amphibolite to granulite transition, B is systematically lost from metasediments. The B that is released will probably partition into the vapor phase and/or melt phase. Preliminary measurements imply that the boron content of rocks in the Chugach Metamorphic Complex is not sufficient to influence the processes of partial melting at low pressures.

  5. High-grade metamorphism during Archean-Paleoproterozoic transition associated with microblock amalgamation in the North China Craton: Mineral phase equilibria and zircon geochronology (United States)

    Yang, Qiong-Yan; Santosh, M.; Tsunogae, Toshiaki


    Metamorphic regimes in Archean terranes provide important keys to the plate tectonic processes in early Earth. The North China Craton (NCC) is one of the ancient continental nuclei in Asia and recent models propose that the cratonic architecture was built through the assembly of several Archean microcontinental blocks into larger crustal blocks. Here we investigate garnet- and pyroxene-bearing granulite facies rocks along the periphery of the Jiaoliao microcontinental block in the NCC. The garnet-bearing granulites contain peak mineral assemblage of garnet + clinopyroxene + orthopyroxene + magnetite + plagioclase + quartz ± biotite ± ilmenite. Mineral phase equilibria computations using pseudosection and geothermobarometry suggest peak P-T condition of 800-830 °C and 7-8 kbar for metamorphism. Isopleths using XMg of orthopyroxene and XCa of garnet in another sample containing the peak mineral assemblage of garnet + orthopyroxene + quartz + magnetite ± fluid yield peak P-T conditions of 860-920 °C and 11-14 kbar. Geochemical data show tonalitic to granodioritic composition and arc-related tectonic setting for the magmatic protoliths of these rocks. Zircon LA-ICP-MS analyses yield well-defined discordia with upper intercept ages of 2562 ± 20 Ma (MSWD = 0.94) and 2539 ± 21 Ma (MSWD = 0.59) which is correlated with the timing of emplacement of the magmatic protolith. A younger group of zircons with upper intercept ages of 2449 ± 41 Ma (MSWD = 0.83); N = 6 as 2449 ± 41 Ma (MSWD = 0.83; N = 6) and 2480 ± 44 Ma (MSWD = 1.2; N = 9) constrains the timing of metamorphism. Zircon Lu-Hf data show dominantly positive εHf(t) values (up to 8.5), and yield crustal residence ages (TDMC) in the range of 2529 to 2884 Ma, suggesting magma sources from Meso-Neoarchean juvenile components. The high temperature and medium to high pressure metamorphism is considered to have resulted from the subduction-collision tectonics associated with microblock amalgamation in the NCC at

  6. Thermal structure of pumpellyite-actinolite facies regions in the Sanbagawa belt, Shikoku, SW Japan (United States)

    Sakaguchi, M.


    On the basis of the mineral assemblages of pelitic rocks, the Sanbagawa belt in Shikoku, SW Japan, has been divided, from low- to high-grade parts, into the chlorite, garnet, albite-biotite and oligoclase-biotite zones (Higashino, 1990). Also, the mineral assemblage of pumpellyite + actinolite + epidote + chlorite or epidote + actinolite + hematite + chlorite, which defines the pumpellyite-actinolite (PA) facies (e.g., Banno, 1998), is widely recognized in metabasites in the chlorite zone (e.g. Banno & Sakai, 1989). However, the detailed study on the PA facies regions has been done only in the Omoiji-Nagasawa area (Nakajima et al., 1977) and Asemigawa-Shirataki area (Nakajima, 1982) in central Shikoku, and thus, it is still hard to solve the regional thermal structure of the PA facies region. This study is aimed to reveal the thermal structure of the PA facies region of the Sanbagawa belt in Shikoku by analyzing the mineral assemblages and mineral chemistries of metabasites from the nine newly studied areas. The studied areas studied belong to the chlorite zone in the Oboke and Besshi units; the Oboke unit structurally underlay the Besshi unit. The mineral assemblages include pumpellyite + epidote + actinolite, epidote + actinolite _ hematite and epidote + Na-amphibole + actinolite + hematite. The metabasites from some areas involve Na-pyroxene-bearing assemblages, but the analyses of the Schreinemakers bundle of Tagiri et al. (1992) show that these assemblages do not define the Na-pyroxene-chlorite subfacies. As the low-grade metamorphic rocks do not have the hematite + pumpellyite paragenesis, its metamorphic temperature is estimated to be higher than the discontinuous reaction temperature of pumpellyite + hematite + quartz = epidote + actinolite + H2O, as shown by Nakajima et al. (1977). It is difficult to detect the difference in temperature in the PA facies regions by analyzing mineral assemblages. To detect the difference in temperature, and then to reveal

  7. On the compositional variability of metamorphic chlorites as an effect of the micro-site chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Sassi, Raffaele; Zane, Antonella [Padua, Univ. (Italy). Dipt. di Mineralogia e Petrologia


    Chlorite is a widespread mineral in all metamorphic rock sequence with the exception of the upper part of the amphibolite facies and granulite. Its stability field is well known but the petrologic meaning of its compositional variability is still poorly understood. In this paper, the chemical variability of low grade metamorphic chlorites as an effect of the micro-site chemistry has been tested by means of 2169 microprobe analyses of selected chlorite flakes. The chemistry of studied chlorites turns out to be significantly scattered, as a function of the micro-site chemistry. As a general conclusion, the possible existence in the same thin section, of chlorite flakes having different composition is a serious drawback for geothermobarometry, at least in low grade metamorphic rocks.

  8. Comparison of geostatistical kriging algorithms for intertidal surface sediment facies mapping with grain size data. (United States)

    Park, No-Wook; Jang, Dong-Ho


    This paper compares the predictive performance of different geostatistical kriging algorithms for intertidal surface sediment facies mapping using grain size data. Indicator kriging, which maps facies types from conditional probabilities of predefined facies types, is first considered. In the second approach, grain size fractions are first predicted using cokriging and the facies types are then mapped. As grain size fractions are compositional data, their characteristics should be considered during spatial prediction. For efficient prediction of compositional data, additive log-ratio transformation is applied before cokriging analysis. The predictive performance of cokriging of the transformed variables is compared with that of cokriging of raw fractions in terms of both prediction errors of fractions and facies mapping accuracy. From a case study of the Baramarae tidal flat, Korea, the mapping method based on cokriging of log-ratio transformation of fractions outperformed the one based on cokriging of untransformed fractions in the prediction of fractions and produced the best facies mapping accuracy. Indicator kriging that could not account for the variation of fractions within each facies type showed the worst mapping accuracy. These case study results indicate that the proper processing of grain size fractions as compositional data is important for reliable facies mapping.

  9. Comparison of Geostatistical Kriging Algorithms for Intertidal Surface Sediment Facies Mapping with Grain Size Data

    Directory of Open Access Journals (Sweden)

    No-Wook Park


    Full Text Available This paper compares the predictive performance of different geostatistical kriging algorithms for intertidal surface sediment facies mapping using grain size data. Indicator kriging, which maps facies types from conditional probabilities of predefined facies types, is first considered. In the second approach, grain size fractions are first predicted using cokriging and the facies types are then mapped. As grain size fractions are compositional data, their characteristics should be considered during spatial prediction. For efficient prediction of compositional data, additive log-ratio transformation is applied before cokriging analysis. The predictive performance of cokriging of the transformed variables is compared with that of cokriging of raw fractions in terms of both prediction errors of fractions and facies mapping accuracy. From a case study of the Baramarae tidal flat, Korea, the mapping method based on cokriging of log-ratio transformation of fractions outperformed the one based on cokriging of untransformed fractions in the prediction of fractions and produced the best facies mapping accuracy. Indicator kriging that could not account for the variation of fractions within each facies type showed the worst mapping accuracy. These case study results indicate that the proper processing of grain size fractions as compositional data is important for reliable facies mapping.

  10. Facies del subfondo del canal Beagle, Tierra del Fuego Sub-bottom facies of the Beagle Channel, Tierra del Fuego

    Directory of Open Access Journals (Sweden)

    Gustavo Bujalesky


    Full Text Available El canal Beagle conecta los océanos Pacífico y Atlántico en el extremo meridional de Sudamérica y se ubica en el ambiente subantártico. Conforma una cuenca de unos 300 m de profundidad máxima y está separada del océano Atlántico por un umbral de 30 m de profundidad. El canal es un valle tectónico que fue completamente cubierto por el hielo glacial durante la última glaciación. Posteriormente, el canal fue ocupado por un lago glacial desde los 12.000 a los 8.000 años A.P., cuando fue invadido por el mar que alcanzó un nivel máximo entre los 6.000 y 5.000 años A.P. Con el objetivo de analizar las facies sedimentarias superficiales y del subfondo del canal se realizó un relevamiento geofísico con sonar de barrido lateral y un perfilador de 3,5 kHz. Sobre un basamento constituido por rocas metamórficas del Mesozoico, se identificaron depósitos de till y secuencias granodecrecientes que representan distintos estadios del retroceso glaciar, evidenciando hacia la sección superior facies lacustres y por encima depósitos de la transgresión marina del Holoceno. Además, se han identificado paleocauces y secuencias fluviales cubiertas por sedimentos marinos transgresivos.The Beagle Channel connects the Pacific and Atlantic oceans in the southernmost part of South America, and has a subantarctic environment. It is a deep basin (300 m depth separated from the Atlantic Ocean by a shallow sill (30 m depth. The Beagle Channel is a tectonic valley that was completely covered by ice during the Last Glaciation. Later, it was occupied by a glacial lake from 12,000 to 8,000 years B.P. and then flooded by the sea, reaching a maximum sea level between 6,000 and 5,000 years B.P. A geophysical survey (side scan sonar and 3.5 kHz profiler was carried out in the channel to analyze the sea-bed and sub-bottom sedimentary facies. Metamorphic Mesozoic basement rocks are overlain by glacial deposits (till and fining upwards sequences. These sequences

  11. Measured versus calculated thermal conductivity of high-grade metamorphic rocks – inferences on the thermal properties of the lower crust at ambient and in-situ conditions

    DEFF Research Database (Denmark)

    Ray, Labani; Förster, Hans-Jürgen; Förster, Andrea

    The bulk thermal conductivity (TC) of 26 rock samples representing felsic, intermediate and mafic granulites, from the Southern Granulite Province, India, is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity is also calculated from modal mineralogy (d...

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

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


    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

  13. Disjunctive Grade Variation from Greenschist to Granulite Facies, Siyom Valley, Eastern Arunachal Pradesh, India (United States)

    Clarke, G. L.; Bhowmik, S. K.; Aitchison, J. C.; Ireland, T. R.


    The Siyom Valley section in eastern Arunachal Pradesh exposes an inverted metamorphic succession (Nandini & Thakur, 2011), metapelitic assemblages increasing in grade northwards from chlorite, through biotite, garnet-staurolite and kyanite-bearing schist to kyanite-sillimanite migmatite. Grade changes are mostly controlled by shallowly north, and northwest-dipping fault structures. Two textural stages of garnet growth can be identified in the ilmenite-bearing amphibolite facies rocks, staurolite having formed late in, or after, deformation responsible for the main penetrative foliation (S2). Kyanite and rutile inclusions in garnet indicate that their growth in migmatite preceded that of matrix sillimanite, ilmenite and cordierite, though unrecrystallized kyanite is also common in the feldspathic matrix. Preliminary data indicate the pronounced tectonic thinning of metasedimentary protoliths during exhumation, and the probability of a pronounced step in grade in the middle part of the river section. Similarities with sections in the Sikkim (Dasgupta et al., 2004) and western Arunachal Pradesh (Goswami et al., 2009) Himalaya reflect the lateral continuity of the south-vergent thrusts that controlled the exhumation of the high-grade rocks, with debate concerning the location and significance of the Main Central Thrust zone begging protolith and metamorphic age data. Dasgupta, S.,Ganguly, J. & Neogi, S., 2004. Inverted metamorphic sequence in the Sikkim Himalayas: crystallization history, P-T gradient and implications. Journal of Metamorphic Geology, 22, 395-412. Goswami, S., Bhowmik, S.K. & Dasgupta, S., 2009. Petrology of a non-classical Barrovian inverted metamorphic sequence from the western Arunachal Himalaya, India. Journal of Asian Earth Sciences, 36, 390-406. Nandini, P. & Thakur, S.S., 2011. Metamorphic evolution of the Lesser Himalayan Crystalline Sequence, Siyom Valley, NE Himalaya, India. Journal of Asian Earth Sciences, 40, 1089-1100

  14. Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

    Directory of Open Access Journals (Sweden)

    Mirijam Vrabec


    Full Text Available Ultrahigh-pressure (UHP metamorphism has been recorded in Eo-Alpine garnet peridotites from the PohorjeMts., Slovenia, belonging to the Eastern Alps. The garnet peridotite bodies are found within serpentinized metaultrabasitesin the SE edge of Pohorje and are closely associated with UHP kyanite eclogites. These rocks belongto the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriaticfault system.Garnet peridotites show signs of a complex four-stage metamorphic history. The protolith stage is represented bya low-P high-T assemblage of olivine + Al-rich orthopyroxene + Al-rich clinopyroxene + Cr-spinel. Due to metamorphism,primary clinopyroxene shows exsolutions of garnet, orthopyroxene, amphibole, Cr-spinel and ilmenite. TheUHP metamorphic stage is defined by the assemblage garnet + olivine + Al-poor orthopyroxene + clinopyroxene +Cr-spinel. Subsequent decompression and final retrogression stage resulted in formation of kelyphitic rims aroundgarnet and crystallization of tremolite, chlorite, serpentine and talc.Pressure and temperature estimates indicate that garnet peridotites reached the peak of metamorphism at 4 GPaand 900 °C, that is well within the UHP stability field. Garnet peridotites in the Pohorje Mountains experiencedUHP metamorphism during the Cretaceous orogeny and thus record the highest-pressure conditions of all Eo-Alpinemetamorphism in the Alps.

  15. Submarine-fan facies associations of the Eocene Butano Sandstone, Santa Cruz mountains, California (United States)

    Nilsen, Tor H.


    The Eocene Butano Sandstone was deposited as a submarine fan in a relatively small, partly restricted basin in a borderland setting. It is possibly as thick as 3000 m and was derived from erosion of nearly Mesozoic granitic and older metamorphic rocks located to the south. Deposition was at lower bathyal to abyssal water depths. The original fan may have been 120-to 160-km long and 80-km wide. Outcrops of submarine-canyon, innerfan, middle-fan, and outer-fan facies associations indicate that the depositional model of Mutti and Ricci Lucchi can be used to describe the Butano Sandstone.

  16. P-T-t conditions, Nd and Pb isotopic compositions and detrital zircon geochronology of the Massabesic Gneiss Complex, New Hampshire: isotopic and metamorphic evidence for the identification of Gander basement, central New England (United States)

    Dorais, Michael J.; Wintsch, Robert P.; Kunk, Michael J.; Aleinikoff, John; Burton, William; Underdown, Christine; Kerwin, Charles M.


    We present new evidence for the assignment of the Neoproterozoic Massabesic Gneiss Complex of New Hampshire to the Gander terrane rather than the Avalon terrane. The majority of Avalonian (sensu stricto) igneous and meta-igneous rocks as defined in Maritime Canada have positive whole-rock ɛNd compared to more negative values for Gander rocks, although there is a region of overlap in ɛNd between the two terranes. Our samples from areas in Connecticut previously thought to be Avalonian and samples from the Willimantic dome have the same isotopic signatures as Maritime Canada Avalon. In contrast, samples from the Clinton dome of southern Connecticut plots exclusively in the Gander field. The majority of the orthogneiss samples from Lyme dome (coastal Connecticut), Pelham dome (central Massachusetts) and Massabesic Gneiss Complex also plot in the Gander field, with a few samples plotting in the overlap zone between Gander and Avalon. U-Pb age distributions of detrital zircon populations from quartzites from the Massabesic Gneiss Complex more closely approximate the data from the Lyme Dome rather than Avalon. Additionally, the similarity of the P-T-t path for the rocks of the Massabesic Gneiss Complex (established by thermobarometry and 40Ar/39Ar dating of amphibole, muscovite, biotite and K-feldspar) with that established in the Ganderian Lyme dome of southern Connecticut strengthens the assignment of these rocks to a single Gander block that docked to Laurentia during the Salinic Orogeny. The identification of Ganderian isotopic signatures for these rocks all of which show evidence for Alleghanian metamorphism, supports the hypothesis that Neoproterozoic Gander lower crustal rocks underlie southern New Hampshire, Massachusetts, and Connecticut, and that all rocks of the overlying Central Maine trough that largely escaped high-grade Alleghanian metamorphism are allochthonous. We suggest that during the Alleghanian, the docking of Gondwana caused Avalon to wedge into

  17. Geology of crystalline rocks of northern Fiordland: details of the granulite facies Western Fiordland Orthogneiss and associated rock units (United States)

    Bradshaw, J.Y.


    A c. 700 km2 area of northern Fiordland (South Island, New Zealand) is described in which Early Cretaceous high-pressure metamorphic rocks and virtually unmetamorphosed plutonic rocks occur. The dominant rocks are orthogneisses developed from synmetamorphic basic-intermediate intrusive complexes, the youngest and most widespread of which is the Early Cretaceous Western Fiordland Orthogneiss (WFO). The latter has undergone granulite facies metamorphism and occurs throughout much of western Fiordland. WFO was emplaced synkinematically in a subduction-related magmatic arc. A collisional event during or immediately following magma emplacement resulted in crustal thickening equivalent to onloading of a 20 km thick section over rocks already buried at mid-crustal depths. This event was responsible for peak load pressures of c. 12-13 kbar. The steeply dipping Surprise Creek Fault juxtaposes high-pressure metamorphic rocks of western and central Fiordland against virtually unmetamorphosed gabbroic rocks of the Early Cretaceous Darran Complex. -from Author

  18. P-T path and timing of crustal thickening during amalgamation of East and West Gondwana: A case study from the Hafafit Metamorphic Complex, Eastern Desert of Egypt (United States)

    Abu El-Enen, Mahrous M.; Abu-Alam, Tamer S.; Whitehouse, Martin J.; Ali, Kamal A.; Okrusch, Martin


    The southeastern sector of the Hafafit Metamorphic Complex, southern Eastern Desert of Egypt comprises infrastructural orthogneisses of tonalite and syenogranite parentage, amphibolites, and a volcano-sedimentary association. These are overthrust by an obducted suprastructural ophiolite nappes via the Nugrus thrust. The protolith of the biotite-hornblende-gneisses was formed during island-arc accretion, while that of the garnet-biotite gneisses were formed in a within-plate regime, consistent with a transition to a post-collisional setting. The volcano-sedimentary association comprises interbedded and intercalated highly foliated metapelitic schists, metabasites, and leucocratic gneisses, deposited in a back-arc basin. The metapelites and the leucocratic gneisses originated from immature Fe-shales and arkoses derived from intermediate-mafic and acidic igneous rocks, respectively, via weak chemical weathering in a tectonically active island arc terrane. The intercalated amphibolites were derived from tholeiitic basalts generated in a back-arc setting. The volcano-sedimentary association was metamorphosed under upper-amphibolite facies conditions with pressures of 9-13 kbar and temperatures of 570-675 °C, as derived from conventional geothermobarometry and pseudosection calculation. A steep, tight clockwise P-T path is constrained and a geothermal gradient around 20 °C/km is estimated for the peak metamorphism. We assume that deformation and metamorphism are due to crustal thickening during the collision of East and West Gondwana, where peak metamorphism took place in the middle to lower crust at 33 km average crustal depth. This was followed by a subsequent quasi-isothermal decompression due to rapid exhumation during wrench tectonics. Sinistral transcurrent shearing with extensional denudation resulted in vertical ductile thinning that was accompanied by heat input from magmatism, as indicated by a higher geothermal gradient during retrograde metamorphism and

  19. Protolith ages and timing of peak and retrograde metamorphism of the high-pressure granulites in the Shandong Peninsula, eastern North China Craton

    Directory of Open Access Journals (Sweden)

    Pinghua Liu


    Full Text Available High-pressure (HP granulites widely occur as enclaves within tonalite-trondhjemite-granodiorite (TTG gneisses of the Early Precambrian metamorphic basement in the Shandong Peninsula, southeast part of the North China Craton (NCC. Based on cathodoluminescence (CL, laser Raman spectroscopy and in-situ U-Pb dating, we characterize the zircons from the HP granulites and group them into three main types: inherited (magmatic zircon, HP metamorphic zircon and retrograde zircon. The inherited zircons with clear or weakly defined magmatic zoning contain inclusions of apatites, and 207Pb/206Pb ages of 2915–2890 Ma and 2763–2510 Ma, correlating with two magmatic events in the Archaean basement. The homogeneous HP metamorphic zircons contain index minerals of high-pressure metamorphism including garnet, clinopyroxene, plagioclase, quartz, rutile and apatite, and yield 207Pb/206Pb ages between 1900 and 1850 Ma, marking the timing of peak HP granulite facies metamorphism. The retrograde zircons contain inclusions of orthopyroxene, plagioclase, quartz, apatite and amphibole, and yield the youngest 207Pb/206Pb ages of 1840–1820 Ma among the three groups, which we correlate to the medium to low-pressure granulite facies retrograde metamorphism. The data presented in this study suggest subduction of Meso- and Neoarchean magmatic protoliths to lower crust depths where they were subjected to HP granulite facies metamorphism during Palaeoproterozoic (1900–1850 Ma. Subsequently, the HP granulites were exhumated to upper crust levels, and were overprinted by medium to low-pressure granulite and amphibolite facies retrograde event at ca. 1840–820 Ma.

  20. Metamorphic and age constraints on tectono-thermal reworking in the western H.U. Sverdrupfjella: A new crustal evolution model for Western Dronning Maud Land, Antarctica (United States)

    Grosch, Eugene; Frimmel, Hartwig; Abu-Alam, Tamer; Košler, Jan


    Western Dronning Maud Land (WDML) of East Antarctica is argued to consist of two major crustal domains, namely the low-grade Archaean Kalahari-Grunehogna Craton and the high-grade Maud belt (e.g. Grantham et al., 1995; Jacobs et al. 2008). The geodynamic and tectono-thermal crustal evolution histories of these two proposed domains remain a debated topic in Rodinia and Gondwana reconstructions. In this study we conducted a petrological and metamorphic comparison of Mesoproterozoic metabasic rocks on the eastern margin of the Archaean Grunehogna Craton and the adjacent westernmost Maud Belt, across a major structural discontinuity known as the Pencksökket-Jutulstraumen Discontinuity (PJD). As such we evaluate to what extent the two domains of WDML represent independent crustal growth and metamorphic histories. Metamorphic constraints on low-grade rocks on the eastern Grunehogna craton record greenschist facies conditions of T = 340 ± 25oC and P = 2.9 ± 0.8 kbar. The high-grade PT-constraint of T =700 ± 30oC and P = 9.0 ± 2 kbar for the western extreme of the Maud Belt, derived from garnet-hornblende-plagioclase-quartz geothermobarometry and phase diagram modeling in PERPLEX, is very similar to that reported for the eastern Maud Belt and thus, does not support the concept of a westward decreasing metamorphic field gradient within the Maud Belt as previously proposed. Laser-ablation-ICP-MS U-Pb dating of titanite in a hornblende-plagioclase-quartz symplectite (after garnet breakdown), yielded a Pan-African age for high-grade metamorphism in the westernmost Maud belt, which overlaps with the age of tectonic decompression in the eastern Maud Belt. The new U-Pb age data argues against previous models that invoke only late-Mesoproterozoic high-grade metamorphism in the western Maud Belt. The new petrological data indicate that the inferred sub-glacial boundary (PJD) between the Grunehogna Craton and the Maud Belt, represents a major metamorphic hiatus as a Pan

  1. Feldspathic granulite 79215 - Limitations on T-fo2 conditions and time of metamorphism. [temperature-oxygen fugacity relationship in annealed lunar polymict beccia (United States)

    Mcgee, J. J.; Bence, A. E.; Eichhorn, G.; Schaeffer, O. A.


    Feldspathic granulite 79215, an annealed polymict breccia which has a bulk composition between anorthositic gabbro and gabbroic anorthosite, contains numerous oxide complexes in the matrix. An Ar-39-Ar-40 stepwise heating experiment gives a well-defined plateau corresponding to an age of 4.03 + or - 0.02 AE. The polmict character of this breccia and the variability of the complexes suggest that they formed as a consequence of reactions between spinel-rich clasts and matrix under the high-T low-P conditions of an ejecta blanket. The duration of annealing is estimated to have been less than 10 million yr; the absence of a KREEP component may indicate an inhomogeneous distribution of this component at the lunar surface at 4.0 AE.

  2. 湘中坳陷二叠系海陆过渡相页岩气地质条件%Geological conditions of Permian sea-land transitional facies shale gas in the Xiangzhong depression

    Institute of Scientific and Technical Information of China (English)

    顾志翔; 彭勇民; 何幼斌; 胡宗全; 翟羽佳


    Based on such analytical methods as outcrop core observation, gas content, geochemical and physical property data and isothermal adsorption as well as argon ion polishing plus scanning electron microscopy of Permian black shale in the center of Hunan depression, the authors investigated the geological conditions of shale gas. The results show that the geological conditions of shale in Permian Longtan Formation and Dalong Formation of sea-land transitional facies are beneficial to gas accumulation. The organic carbon content is high than 2%, the grade of maturity distribution is between 1.2%and 1.6%, the main reservoir types are mineral holes with minor organic holes such as residual intergranular pores, intragranular pores and corrosion holes. The porosity is between 0.54% and 5.15%,the average gas content capacity of isothermal adsorption test is between 5.488 and 6.905 m3/t. The thermal evolution analysis shows that Permian shale experienced two times of uplift and denudation, and the second denudation didn’t reach the maximum depth of the first time and there was no secondary hydrocarbon. This might have been the reason which led to the low gas content in the study area. Structural analysis shows that the modification effect of Indo-Chinese epoch and Yanshanian period resulted in the poor preservation conditions that damaged the oil gas obviously and increased the risk of exploration. Using the method of superposition to predict the areas, the authors reveal that Lianyuan-Loudi-Shuangfeng area and Shaoyang-Shaodong area are favorable shale gas areas. The volume method was used to calculate the total quantity of shale gas resource, which yielded (127-425)×108 m3, (the medium value being 254×108 m3),suggesting a certain potential of shale gas resources. The comprehensive analysis shows that the preservation condition is the key factor for shale gas accumulation in this area, and is also the principal factor for successful exploration.%提根据湘中坳陷二

  3. Mesozoic metamorphism and its tectonic implication along the Solonker suture zone in central Inner Mongolia, China (United States)

    Zhang, Jinrui; Wei, Chunjing; Chu, Hang; Chen, Yaping


    The Xing'an-Inner Mongolia Orogenic Belt (XIMOB) exposed in the eastern section of the Central Asian Orogenic Belt (CAOB) is generally thought to have resulted from closure of the Paleo-Asian Ocean. However, disputations still exist on the age and detailed tectonic processes involved in its final amalgamation. The Solonker suture zone in the central Inner Mongolia, once recognized as the major paleo-plate boundary recording the terminal collision of the XIMOB, is characterized by extensive regional low-temperature metamorphism of greenschist to epidote-amphibolite facies with local presence of blueschists, which lacks systematic study. Four metabasite and garnet-mica schist samples were studied for determination of metamorphic P-T evolution using pseudosection and conventional thermobarometry. The two metabasite samples from Wulangou and Daqing Pasture contain actinolite, albite, epidote, chlorite and hornblende (in Daqing Pasture) and are estimated to have peak P-T conditions of 5.2-5.9 kbar/415-450 °C in Wulangou and 7.0-7.9 kbar/470-475 °C in Daqing Pasture. Two garnet-mica schist samples from Shuangjing (or Shuangjing schist) contain garnet porphyroblasts, muscovite, quartz, plagioclase, chlorite with or without potassium feldspar, biotite, and calcite, and are modeled to record prograde P-T vectors respectively of 3.0 kbar/482 °C-3.3 kbar/495 °C and 4.2 kbar/478 °C-4.8 kbar/483 °C, followed by near-isothermal decompression. The zircon U-Pb dating analyses suggest that the metamorphism probably occurred soon afterwards in the Early Mesozoic. The peak P-T conditions for the metabasite and garnet-mica schist samples yield thermal gradients respectively of 18-22 °C/km and 26-33 °C/km, being intermediate and low P/T series, and the metamorphic evolution in these rocks characteristic of clockwise P-T paths may correspond to tectonic thickening and thinning processes. The extensive low-temperature metamorphism of intermediate to low P/T types along the

  4. Metamorphic pattern of the Cretaceous Celica Formation, SW Ecuador, and its geodynamic implications (United States)

    Aguirre, Luis


    The volcanic rocks of the Cretaceous Celica Formation of southern Ecuador are affected by a weak although widespread alteration. The chemical study of the secondary chemical phases present in andesitic and basaltic lava flows reveals that this alteration corresponds to very low-grade metamorphism comprising the zeolite and the prehnite-pumpellyite facies. Main features of this metamorphism are: weak lithostatic pressure, moderate to steep thermal gradient, high ƒ O2, low value of the seawater/rock ratio and total absence of deformation. These characteristics are typically present in other volcanic suites of similar age and composition along the Andes and correspond to the pattern of metamorphism developed in extensional settings (diastathermal metamorphism) linked to various degrees of thinning of the continental crust. Based on this metamorphic pattern, a geodynamic model is proposed in which the Celica Formation is interpreted as an ensialic, aborted, marginal basin developed on strongly attenuated continental crust at the border of the South American plate. The relationship between the Ecuadorian and Colombian volcanic suites of Cretaceous age present along the Western Cordillera is discussed in the light of the model suggested.

  5. Metamorphic Rocks in West Irian

    NARCIS (Netherlands)

    Wegen, van der G.


    Low-grade metamorphics of West Irian occur to the east of Geelvink Bay associated with two narrow belts of basic and ultrabasic igneous rocks which represent ophiolitic suites of an eugeosynclinical development beginning in Early Mesozoic time. In both of these belts there are indications of regiona

  6. Cretaceous high-pressure metamorphism and low pressure overprint in the Sistan Suture Zone, eastern Iran: Additional temperature estimates for eclogites, geological significance of U-Pb zircon ages and Rb-Sr constraints on the timing of exhumation (United States)

    Kurzawa, Timon; Bröcker, Michael; Fotoohi Rad, Gholamreza; Berndt, Jasper; Lisker, Frank


    The Sistan Suture Zone, eastern Iran, includes blocks and lenses of eclogite-, blueschist- and/or epidote amphibolite-facies rocks that provide an excellent opportunity to examine the exhumation history of oceanic HP/LT rocks and their retrograde derivatives. Zr-in-rutile thermometry of eclogites corroborates previous interpretations suggesting metamorphic temperatures of ca. 550-600 °C during the HP stage in the Sistan area. Flat HREE distribution patterns and Ti-in-zircon temperatures of ca. 500-600 °C document that zircon in eclogite is of metamorphic origin. REE patterns of zircon from felsic meta-igneous rocks do not allow to distinguish between a magmatic or metamorphic origin, but relatively low temperatures indicated by Ti-in-zircon thermometry (ca. 500-600 °C) and the close similarity of zircon (U-Pb) and white mica (Rb-Sr, Ar-Ar) ages favor a metamorphic zircon origin. Previously published isotopic ages of the felsic rocks cannot unambiguously be linked to the eclogite- and/or blueschist-facies P-T conditions due to the absence of unequivocal mineralogical and petrological evidence. Instead, these rocks may record contemporaneous metamorphic processes that took place at a different depth within the subduction complex, or may indicate active ridge subduction and/or melt formation in the subduction zone at relatively low pressures. Biotite-based internal Rb-Sr isochrons of newly dated epidote amphibolite and biotite-albite gneisses indicate ages of ca. 74-80 Ma, either dating fluid-infiltration-induced formation of biotite during relatively fast uplift, or the time of final passage through the effective biotite closure temperature. Rb-Sr ages of phengite from both an epidote amphibolite and a biotite-albite gneiss yield ages that correspond to the HP/LT stage. This outcome, combined with textural evidence for derivation from eclogitic precursors documents that white mica ages of some strongly overprinted Sistan rocks are compromised by inheritance and do

  7. Trace element signature and U-Pb geochronology of eclogite-facies zircon, Bergen Arcs, Caledonides of W Norway (United States)

    Bingen, Bernard; Austrheim, Håkon; Whitehouse, Martin J.; Davis, William J.

    Secondary-ion mass spectrometry (SIMS) U-Pb and trace element data are reported for zircon to address the controversial geochronology of eclogite-facies metamorphism in the Lindås nappe, Bergen Arcs, Caledonides of W Norway. Caledonian eclogite-facies overprint in the nappe was controlled by fracturing and introduction of fluid in the Proterozoic-Sveconorwegian-granulite-facies meta-anorthosite-norite protolith. Zircon grains in one massive eclogite display a core-rim structure. Sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith, i.e. 0.31<=Th/U<=0.89, heavy rare earth element (HREE) enrichment, and negative Eu anomaly. Weakly-zoned to euhedral oscillatory-zoned Caledonian rims are characterized by Th/U<=0.13, low LREE content (minimum normalized abundance for Pr or Nd), variable enrichment in HREE, and no Eu anomaly. A decrease of REE towards the outermost rim, especially HREE, is documented. This signature reflects co-precipitation of zircon with garnet and clinozoisite in a feldspar-absent assemblage, and consequently links zircon to the eclogite-facies overprint. The rims provide a mean 206Pb/238U crystallization age of 423+/-4 Ma. This age reflects eclogite-forming reactions and fluid-rock interaction. This age indicates that eclogite-facies overprint in the Lindås nappe took place at the onset of the Scandian (Silurian) collision between Laurentia and Baltica.

  8. Geologic and Geochronologic Studies of the Early Proterozoic Kanektok Metamorphic Complex of Southwestern Alaska (United States)

    Turner, Donald L.; Forbes, Robert B.; Aleinikoff, John N.; McDougall, Ian; Hedge, Carl E.; Wilson, Frederic H.; Layer, Paul W.; Hults, Chad P.


    The Kanektok complex of southwestern Alaska appears to be a rootless terrane of early Proterozoic sedimentary, volcanic, and intrusive rocks which were metamorphosed to amphibolite and granulite facies and later underwent a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism of overlying sediments. The terrane is structurally complex and exhibits characteristics generally attributed to mantled gneiss domes. U-Th-Pb analyses of zircon and sphene from a core zone granitic orthogneiss indicate that the orthogneiss protolith crystallized about 2.05 b.y. ago and that the protolithic sedimentary, volcanic and granitic intrusive rocks of the core zone were metamorphosed to granulite and amphibolite facies about 1.77 b.y. ago. A Rb-Sr study of 13 whole-rock samples also suggests metamorphism of an early Proterozoic [Paleoproterozoic] protolith at 1.77 Ga, although the data are scattered and difficult to interpret. Seventy-seven conventional 40K/40Ar mineral ages were determined for 58 rocks distributed throughout the outcrop area of the complex. Analysis of the K-Ar data indicate that nearly all of these ages have been totally or partially reset by a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism. Several biotites gave apparent K-Ar ages over 2 Ga. These ages appear to be controlled by excess radiogenic 40Ar produced by the degassing protolith during the 1.77 Ga metamorphism and incorporated by the biotites when they were at temperatures at which Ar could diffuse through the lattice. Five amphibolites yielded apparent Precambrian 40K/40Ar hornblende ages. There is no evidence that these hornblende ages have been increased by excess argon. The oldest 40K/40Ar hornblende age of 1.77 Ga is identical to the sphene 207Pb/206Pb orthogneiss age and to the Rb-Sr 'isochron' age for six of the 13 whole-rock samples. The younger hornblende ages are interpreted as

  9. Unusual high-density and saline aqueous inclusions in ultrahigh pressure metamor-phic rocks from Sulu terrane in eastern China

    Institute of Scientific and Technical Information of China (English)

    SHEN Kun; ZHANG Zeming; A. M. van den Kerkhof; XIAO Yilin; XU Zhiqin; J. Hoefs


    Primary high-density fluid inclusions were identified in garnet from ultrahigh pressure eclogite in the southern part of the Sulu terrane. They occur isolatedly or in cluster together with relatively low-density two-phase inclusions. The eutectic temperature of the inclusions is as low as ≤ -52℃. A bubble was nucleated in a liquid inclusion during the specific stage of cyclic cooling-heating runs, and the liquid-gas homogenization temperature was measured to be ≤-12.5℃. The composition of the inclusions modeled by the system CaCl2-NaCl-H2O, yields the fluid density of 1.27 g/cm3 that corresponds to a pressure of ca. 2.4 Gpa at the temperature of peak eclogite-facies metamorphism, close to the ultrahigh pressure metamorphic conditions. During the exhumation of the eclogite the inclusions reacted with the host mineral, forming hydrous silicate minerals that resulted in lowering of the fluid density and its transformation to multi-phase inclusions.

  10. Petrology of HP metamorphic veins in coesite-bearing eclogite from western Tianshan, China: Fluid processes and elemental mobility during exhumation in a cold subduction zone (United States)

    Lü, Zeng; Zhang, Lifei; Du, Jinxue; Yang, Xin; Tian, Zuolin; Xia, Bin


    A petrological study was carried out for high pressure (HP) veins which cut through the host coesite-bearing eclogites at Habutengsu-Kebuerte in western Tianshan, China. The results place constraints on the origin and property of metamorphic fluids during subduction-zone metamorphism. Omphacite-, clinozoisite- and quartz-dominated veins occur on centimeter to meter scales within lens-shaped and layered eclogites, or cutting into the country rocks of garnet phengite schists. Coesite-bearing eclogites mainly consist of fibrous fine-grained omphacite and porphyroblastic garnet, with minor amounts of amphibole (mainly barroisite), clinozoisite, white mica (mainly paragonite) and rutile. The veins are pronouncedly coarse-grained compared to the host eclogites and commonly consist of quartz, clinozosite, rutile, white mica (phengite and paragonite) and garnet, with or without omphacite, titanite, apatite, carbonate (mainly dolomite) and glaucophane. Fluid inclusions are abundant in vein omphacite, titanite and apatite, but are rare in the equivalent minerals of host eclogites. Rounded vein garnets usually occur close to the sharp interface of vein and host eclogite. Omphacite in the veins is characterized by its euhedral form surrounded by quartz, or coarse bladed aggregates in contrast to the fibrous or patchy one, suggesting dynamic recrystallization in the host rocks. Omphacite in both veins and host eclogites has similar jadeite contents (Jd40-50), indicating formation at eclogite-facies metamorphic conditions. Vein phengite uniformly contains certain amounts of Ba with maximum BaO content of 3.16-4.25 wt.%, suggesting that Ba was mobilized during the exhumation of UHP rocks. Specific textures of vein minerals, such as the enclosure of magnesite (or calcite) in dolomite, rutile in titanite, and the occurrence of zoned Ba-rich phengite, indicate the chemical variability of channelized fluids over time. Based on Zr content in rutile and the presence of paragonite

  11. Multiparameter Elastic Full Waveform Inversion With Facies Constraints

    KAUST Repository

    Zhang, Zhendong


    Full waveform inversion (FWI) aims fully benefit from all the data characteristics to estimate the parameters describing the assumed physics of the subsurface. However, current efforts to utilize full waveform inversion as a tool beyond acoustic imaging applications, for example in reservoir analysis, faces inherent challenges related to the limited resolution and the potential trade-off between the elastic model parameters. Adding rock physics constraints does help to mitigate these issues, but current approaches to add such constraints are based on including them as a priori knowledge mostly valid around the well or as a boundary condition for the whole area. Since certain rock formations inside the Earth admit consistent elastic properties and relative values of elastic and anisotropic parameters (facies), utilizing such localized facies information in FWI can improve the resolution of inverted parameters. We propose a novel confidence map based approach to utilize the facies-based constraints in both isotropic and anisotropic elastic FWI. We invert for such a confidence map using Bayesian theory, in which the confidence map is updated at each iteration of the inversion using both the inverted models and a prior information. The numerical examples show that the proposed method can reduce the trade-offs and also can improve the resolution of the inverted elastic and anisotropic properties.

  12. 40Ar/39Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai,East China

    Institute of Scientific and Technical Information of China (English)

    LI Jinyi; YANG Tiannan; CHEN Wen; ZHANG Sihong


    Recent investigations reveal that the ultrahigh-pressure metamorphic (UHPM) rocks in the Donghai regionof East China underwent ductile and transitional ductile-brittle structural events during their exhumation. The earlierductile deformation took place under the condition of amphibolite facies and the later transitional ductile-brittledeformation under the condition of greenschist facies. The hanging walls moved southeastward during both of these twoevents. The 40Ar/39Ar dating of muscovites from muscovite-plagioclase schists in the Haizhou phosphorous mine, whichare structurally overlain by UHPM rocks, yields a plateau age of 218.0±2.9 Ma and isochron age of 219.8Ma, indicatingthat the earlier event of the ampibolite-facies deformation probably took place about 220 Ma ago. The 40Ar/39Ar dating oforiented amphiboles parallel to the movement direction of the hanging wall on a decollement plane yields a plateau age of213.1 ±0.3 Ma and isochron age of 213.4±4.1 Ma, probably representing the age of the later event. The dating of pegmatiticbiotites and K-feldspars near the decollement plane from the eastern Fangshan area yield plateau ages of 203.4±0.3 Ma,203.6±0.4 Ma and 204.8±2.2 Ma, and isochron ages of 204.0±2.0 Ma, 200.6±3.1 Ma and 204.0±5.0 Ma, respectively,implying that the rocks in the studied area had not been cooled down to closing temperature of the dated biotites and K-feldspars until the beginning of the Jurassic (about 204 Ma). The integration of these data with previous chronological ageson the ultrahigh-pressure metamorphism lead to a new inference on the exhumation of the UHPM rocks. The UHPM rocksin the area were exhumed at the rate of 3-4 km/Ma from the mantle (about 80-100 km below the earth's surface at about240 Ma) to the lower crust (at the depth of about 20-30km at 220 Ma), and at the rate of 1-2 km/Ma to the middle crust (atthe depth of about 15 km at 213 Ma), and then at the rate of less than 1 km/Ma to the upper crust about 10 km deep

  13. Facies Constrained Elastic Full Waveform Inversion

    KAUST Repository

    Zhang, Z.


    Current efforts to utilize full waveform inversion (FWI) as a tool beyond acoustic imaging applications, for example for reservoir analysis, face inherent limitations on resolution and also on the potential trade-off between elastic model parameters. Adding rock physics constraints does help to mitigate these issues. However, current approaches to add such constraints are based on averaged type rock physics regularization terms. Since the true earth model consists of different facies, averaging over those facies naturally leads to smoothed models. To overcome this, we propose a novel way to utilize facies based constraints in elastic FWI. A so-called confidence map is calculated and updated at each iteration of the inversion using both the inverted models and the prior information. The numerical example shows that the proposed method can reduce the cross-talks and also can improve the resolution of inverted elastic properties.

  14. Identification of hydrochemical facies in the Roswell Artesian Basin, New Mexico (USA), using graphical and statistical methods (United States)

    Newman, Brent D.; Havenor, Kay C.; Longmire, Patrick


    Analysis of groundwater chemistry can yield important insights about subsurface conditions, and provide an alternative and complementary method for characterizing basin hydrogeology, especially in areas where hydraulic data are limited. More specifically, hydrochemical facies have been used for decades to help understand basin flow and transport, and a set of facies were developed for the Roswell Artesian Basin (RAB) in a semi-arid part of New Mexico, USA. The RAB is an important agricultural water source, and is an excellent example of a rechargeable artesian system. However, substantial uncertainties about the RAB hydrogeology and groundwater chemistry exist. The RAB was a great opportunity to explore hydrochemcial facies definition. A set of facies, derived from fingerprint diagrams (graphical approach), existed as a basis for testing and for comparison to principal components, factor analysis, and cluster analyses (statistical approaches). Geochemical data from over 300 RAB wells in the central basin were examined. The statistical testing of fingerprint-diagram-based facies was useful in terms of quantitatively evaluating differences between facies, and for understanding potential controls on basin groundwater chemistry. This study suggests the presence of three hydrochemical facies in the shallower part of the RAB (mostly unconfined conditions) and three in the deeper artesian system of the RAB. These facies reflect significant spatial differences in chemistry in the basin that are associated with specific stratigraphic intervals as well as structural features. Substantial chemical variability across faults and within fault blocks was also observed.

  15. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes (United States)

    Bustamante, Andres; Juliani, Caetano


    In the surroundings of Caldas and El Retiro cities (Colombia) metamorphic rocks derived from basic and pelitic protoliths comprise the Caldas amphibole schist and the Ancón schist respectively. Subordinated metamorphosed granite bodies (La Miel gneiss) are associated to these units, and The El Retiro amphibolites, migmatites and granulites crops out eastwards of these units, separated by shear zones. The Caldas amphibole schist and the Ancón schist protoliths could have been formed in a distal marine reduced environment and amalgamated to the South American continent in an apparent Triassic subduction event. The El Retiro rocks are akin to a continental basement and possible include impure metasediments of continental margin, whose metamorphism originated granulite facies rocks and migmatites as a result of the anatexis of quartz-feldspathic rocks. The metamorphism was accompanied by intense deformation, which has juxtaposed both migmatites and granulite blocks. Afterward, heat and fluid circulation associated with the emplacement of minor igneous intrusions resulted in intense fluid-rock interaction, variations in the grain size of the minerals and, especially, intense retrograde metamorphic re-equilibrium. Thermobarometric estimations for the Caldas amphibole schist indicate metamorphism in the Barrovian amphibolite facies. The metamorphic path is counter-clockwise, but retrograde evolution could not be precisely defined. The pressures of the metamorphism in these rocks range from 6.3 to 13.5 kbar, with narrow temperature ranging from 550 to 630 °C. For the Ancón schist metapelites the P- T path is also counter-clockwise, with a temperature increase evidenced by the occurrence of sillimanite and the cooling by later kyanite. The progressive metamorphism event occurred at pressures of 7.6-7.2 kbar and temperatures of 645-635 °C for one sample and temperature between 500 and 600 °C under constant pressure of 6 kbar. The temperature estimated for these rocks

  16. "Fossil" bright layer recorded in the low-P/T metamorphic rocks (United States)

    Terabayashi, M.; Yamamoto, H.; Kitajima, K.


    The "fossil" (geological time) bright layer was recognized in the Cretaceous low-P/T Ryoke metamorphic rocks in the Iwakuni-Yanai area, southwest Japan. Silicified pelitic schists distribute as layers or lenticular bodies several to fifteen meters in thickness, and they are restricted in the greenschist facies conditions within structurally vertical thickness about one kilometer. Silicified pelitic schist is mainly composed of fine-grained quartz and minor muscovite and biotite, and some of colored minerals are decolored by alteration more or less. The boundary between silicified layer and underlying pelitic schist is fairly distinct but that between the overlying pelitic schist is rather gradual. Quartz veins crossing high angles with schistosity were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent ductile flow, were observed in the pelitic schist. En echelon quartz vein and fishnet-like quartz veins are characteristic of silicified rocks. The mode of occurrences of quartz veins indicates that silicified rocks are competent relative to underlying pelitic schist. Fluid inclusion studies were conducted from two kinds of quartz-filled veins: crosscutting foliation in silicified pelitic schist and foliation-parallel in pelitic schist. Fluid inclusions in quartz from a vein crosscutting foliation in silicidied pelitic schist occur as isolated individual inclusions or clusters with preferred spatial arrangement. The isolated inclusions display negative crystal geometries, and are generally range in size from 5 to 10 μ m, with some inclusions up to 20 μ m across. Fluid inclusions in quartz from a foliation-parallel vein are rounded and usually small about a few μ m. Homogenization of the vapour and liquid phases to a single liquid phase occurred at temperatures (Th) between 275 and 330 ° C except in rare instances. The value is considered to be close to the condition of vein formation. Importantly, the

  17. Peak metamorphic temperature and thermal history of the Southern Alps (New Zealand) (United States)

    Beyssac, O.; Cox, S. C.; Vry, J.; Herman, F.


    The Southern Alps orogen of New Zealand results from late Cenozoic convergence between the Indo-Australian and Pacific plates and is one of the most active mountain belts in the world. Metamorphic rocks carrying a polymetamorphic legacy, ranging from low-greenschist to high-grade amphibolites, are exhumed in the hanging wall of the Alpine Fault. On a regional scale, the metamorphic grade has previously been described in terms of metamorphic zones and mineral isograds; application of quantitative petrology being severely limited owing to unfavorable quartzofeldspathic lithologies. This study quantifies peak metamorphic temperatures (T) in a 300 × 20 km area, based on samples forming 13 transects along-strike from Haast in the south to Hokitika in the north, using thermometry based on Raman spectroscopy of carbonaceous material (RSCM). Peak metamorphic T decreases across each transect from ≥ 640 °C locally in the direct vicinity of the Alpine Fault to less than 330 °C at the drainage divide 15-20 km southeast of the fault. Thermal field gradients exhibit a degree of similarity from the southernmost to the northernmost transects, are greater in low-grade semischist than high-grade schist, are affected by folding or discontinuous juxtaposition of metamorphic zones, and contain limited information on crustal-scale geothermal gradients. Temperatures derived by RSCM thermometry are slightly (≤ 50 °C) higher than those derived by traditional quantitative petrology using garnet-biotite thermometry and THERMOCALC modeling. The age of RSCM T appears to be mostly pre-Cenozoic over most of the area except in central Southern Alps (Franz Josef-Fox area), where the amphibolite facies schists have T of likely Cenozoic age. The RSCM T data place some constraints on the mode of exhumation along the Alpine Fault and have implications for models of Southern Alps tectonics.

  18. Coal facies studies in Greece

    Energy Technology Data Exchange (ETDEWEB)

    Christanis, Kimon [Department of Geology, University of Patras, GR-265.00 Rio-Patras (Greece)


    In Greece, coal-forming conditions prevailed mainly during Neogene and Quaternary times in several intermontane and paralic basins and resulted in the formation of significant peat and lignite deposits. The economically recoverable lignite reserves are 3.9 Gt and the annual production, mainly for power generation, exceeds 65 Mt.

  19. MetPetDB: New Directions for Metamorphic Studies (United States)

    Spear, F. S.; Adali, S.; Szymanski, B. K.; Hallett, B. K.; Waters, A. J.; Linder, Z. J.; Fyffe, M. E.; Goldfarb, D.; Barlett, K.


    It is estimated that less than 1% of the data collected on metamorphic rocks is published, and MetPetDB (database for metamorphic geochemistry) is being developed and populated to preserve these data and to foster new and innovative directions for scientific research and education. The data model is based on a sample of metamorphic rock and includes information about location, rock type, mineral assemblage, fabric, plus images of all types and mineral composition data. Mineral analyses are linked to locations on appropriate images so the spatial integrity of the data is preserved. Tools will be available for mineral recalculation, plotting, and thermobarometric applications. Derivative data such as peak P-T conditions, metamorphic P-T path, and cooling rate will also be stored. The database will be searchable based on any number of data fields, permitting rapid location of samples that can be used to test hypotheses and discover new relationships. For example: A student is designing a thesis project and MetPetDB will be a first resource to determine the types of rocks present in a region, the work that has been done on them, and links to the published findings. The Fe/Mg zoning in migmatitic garnets has been used to infer cooling rates. What is the range of cooling rates recorded by migmatitic garnets, and is there a correlation between peak metamorphic temperature and cooling rate? Is it possible that melting triggers rapid thrusting that causes the rapid cooling? A search on: rock type = migmatite plus Fe and Mg X-ray maps of garnet would reveal all samples that could be used in this study. A new geobarometer based on a specific mineral assemblage is proposed that permits pressures to be estimated to within 50 MPa. A search of the database for all samples with this assemblage plus analyses of the necessary minerals would provide a set of samples to which this new barometer can be applied. Recalculating pressures and temperatures for an entire region using new

  20. Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: A non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane (United States)

    Liou, J.G.; Tsujimori, T.; Chu, W.; Zhang, R.Y.; Wooden, J.L.


    The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes over an area of about 15 km2. The U-Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ???1730 Ma, and the formation of amphibolite-facies assemblages in both metagabbro and granulite occurred at ???340-460 Ma. Petrologic and geochronological data indicate that these various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies metamorphism at ???1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. ?? Springer-Verlag 2006.

  1. Stratigraphy and Facies Analysis of a 122 M Long Lacustrine Sequence from Chalco Lake, Central Mexico (United States)

    Herrera, D. A.; Ortega, B.; Caballero, M.; Lozano, S.; Pi, T.; Brown, E. T.


    Chalco lake is located SE of the outskirts of Mexico City, at the central part of the Trans Mexican Volcanic Belt. Previous studies show the importance of this lacustrine sequence as an archive of paleoenvironmental and paleoclimatic changes. A set of five cores up to 122 m depth were drilled in the basin, in order to analyze the sedimentary record and to extent the previous knowledge of past environmental changes in central Mexico. As an initial step, in this work we present the identification and classification of sedimentary facies. Preliminary paleomagnetism analyses recognize the possible record of the Blake Event (ca. 120 kyr BP), and suggest that the sequence might span the last 240 kyr. In this case, variations in sedimentary facies could reflect the conditions of the MIS 1-7. The facies are mostly diatom ooze, carbonate mud, organic rich silt and volcaniclastic, both massive and laminated, and massive dark gray to reddish brown silt. From 1 to 8 m depth dominates the organic rich silt facies, which correlates with the MIS 1. Intercalations of reddish brown and grayish brown silt facies, between 8 to 60 m depth, indicate changes occurred during MIS 2 to 5d. Between 60-75 m depth the sequence is characterized by dark grayish silty clay facies, which possibly coincide with the MIS 5e. At 79 m depth (ca. 130 kyr BP) we found struvite (MgNH4PO4.6H2O), which may be related to dry conditions. The laminated diatom ooze facies dominates between 90 to 122 m depth and indicates rhythmic changes in the sediment deposition of the basin. The volcaniclastic facies is represented by lapilli and ash deposits in more than 100 individual tephra layers of both mafic and felsic composition. Some of them correspond to main volcanic eruptions, as the Upper Toluca Pumice (13,500 cal yr BP), from the Nevado de Toluca volcano and the Pómez con Andesita (17,700 cal yr BP) from the Popocatépetl volcano. The carbonate mud facies is composed of calcite and siderite, with frequent

  2. Blueschist-facies high-Si phengites record the timing of greenschist-facies overprinting: a Rb-Sr and Ar-ar study of marbles from the Cyclades, Greece (United States)

    Bieling, D.; Bröcker, M.; Hacker, B.; Gans, P.


    In the Attic-Cycladic crystalline belt (Greece), white mica geochronology (Rb-Sr, K-Ar, Ar-Ar) has established time constraints for at least two metamorphic events: well-preserved high-pressure/low-temperature rocks yielded Eocene ages (c. 50-40 Ma); their greenschist-facies counterparts provided Oligocene-Miocene dates (c. 25-20 Ma). Previous studies indicated that the ages recorded by high-Si phengites may not correspond to the high-pressure stage but to the subsequent greenschist-facies overprint. This hypothesis is based on the observation that the range in Si-contents and the modal proportion of phengites with a specific Si-value are not significantly different between Eocene HP rocks and Oligocene-Miocene greenschists. The possibility that the barometric information and the geochronological record might be decoupled is of general importance for interpretation of phengite ages from polymetamorphic rocks. In order to look in more detail into this problem, we have studied marbles from Tinos and Sifnos. On both islands, HP rocks are best preserved in the upper parts of the metamorphic succession. Towards the base, the degree of greenschist overprinting increases. Phengite populations of blueschist- and greenschist facies rocks mostly show a considerable range in Si-values. However, in marbles which are either associated with HP or strongly retrogressed rocks, homogeneous high-Si phengite populations (>3.5 pfu) were recognized. On Tinos, Rb-Sr and Ar-Ar white mica dating of such samples yielded ages between 40 to 24 Ma. Of special interest are samples which yielded ages of c. 24 Ma. If the earlier metamorphic history is not taken into account, such datasets may suggest the erroneous conclusion of Miocene HP metamorphism. Recent studies [1] have reported large displacements (> 100km) for detachment faults in the Aegean. The critical parameter for such models is the age of HP metamorphism as deduced from white mica dating [1,2]. In the light of the complexities

  3. Igneous and metamorphic petrology in the field: a problem-based, writing-intensive alternative to traditional classroom petrology (United States)

    DeBari, S. M.


    The Geology Department at Western Washington University (~100 geology majors) offers field and classroom versions of its undergraduate petrology course. This is a one-quarter course (igneous and metamorphic petrology) with mineralogy as a prerequisite. The field version of the course is offered during the three weeks prior to fall quarter and the classroom version is offered in spring quarter. We take 15-20 students around the state of Washington, camping at different outcrop sites where students integrate observational skills, petrologic knowledge, and writing. Petrogenetic associations in various tectonic settings provide the theme of the course. We compare ophiolites vs. arc sequences (volcanic, plutonic, and metamorphic rocks), S- vs. I-type granitoids (plutonic rocks and associated metamorphic rocks), Barrovian vs. Buchan vs. subduction zone metamorphism of different protoliths, and flood-basalt vs. active-arc volcanism. Some basics are covered in the first day at WWU, followed by 17 days of field instruction. Lecture is integrated with outcrop study in the field. For example, students will listen to a lecture about magma differentiation processes as they examine cumulate rocks in the Mt. Stuart batholith, and a lecture about metamorphic facies as they study blueschist facies rocks in the San Juan Islands. Students study multiple outcrops around a site for 1-4 days. They then use their observations (sketches and written descriptions of mineral assemblages, rock types, rock textures, etc.) and analysis techniques (e.g. geochemical data plotting, metamorphic protolith analysis) to write papers in which the data are interpreted in terms of a larger tectonic problem. In advance of the writing process, students use group discussion techniques such as whiteboarding to share their observational evidence and explore interpretations. Student evaluations indicate that despite the intense pace of the course, they enjoy it more. Students also feel that they retain more

  4. Structural and alteration controls on gold mineralization the of the amphibolite facies Detour Lake Deposit, Canada (United States)

    Dubosq, Renelle; Schneider, David


    The 15M oz Detour Lake deposit is a Neoarchean orogenic gold ore body located in the northern most region of the Abitibi district within the Superior Province. The mine is an open pit design in the high strain zone of the Sunday Lake Deformation Zone (SLDZ). The ductile-brittle SLDZ parallels the broadly E-W Abitibi greenstone belt and the deposit is situated in a dilation zone between volcanoclastic rocks of the Caopatina Assemblage and Lower Detour Lake Formation, consisting of ultramafic talc-chlorite-sericite schist. The Upper Detour Lake Formation consists of pillowed and massive flows and hyloclastic units crosscut by minor felsic to intermediate dykes. All of the formations are sub-vertical, north-dipping units with stretching lineations indicating dip-slip motion. The Detour deposit differs from other classic ore deposits in the dominantly greenschist facies Abitibi Subprovince by possessing an amphibolite facies metamorphic assemblage of actinolite-biotite-plagioclase-almandine. Consequently, the typical indicator minerals used to identify alteration and mineralization, such as secondary biotite, may not be useful. Petrological and geochemical analyses have revealed at least four populations of biotite: 1) large euhedral crystals located within quartz-carbonate veins, 2) small, euhedral zoned crystals present as alteration haloes, 3) very small, anhedral to subhedral indistinct crystal present in mafic volcanic host rock, and 4) large euhedral crystals defining the main metamorphic foliation in the metasediments. Extensive examination of mineral assemblages, alteration products, and vein structure in rock core across barren and mineralized zones has documented over a dozen vein types which can be grouped into two main categories: 1) sulfidized quartz-carbonate veins associated with biotite alteration and 2) late carbonate veins. Gold grades do not prove to be dependent on vein type but rather on the host rock composition: the highest ore grades are present

  5. Ultrahigh Pressure Metamorphic Terrane Evolution; Norwegian Caledonides (United States)

    Rodda, C. I.; Koons, P. O.; Terry, M.; Robinson, P.


    Rocks in Norway's Western Gneiss Region (WGR) experienced high pressure and ultrahigh pressure (UHPM) (4GPa., 800C) peak metamorphic conditions during the Scandian orogeny at 410Ma. Thermobarometric studies of exhumed ultramafic eclogite pods from the Nordfjord, Soroyane and Nordoyane areas place tight time constraints on subduction, UHP metamorphism and exhumation, with all but the final phase of exhumation occurring in ca. 12 million years. However, few structures apparently related to the descent phase of terrane evolution were observed during field studies. Rather, ubiquitous quartz-rod lineation and pervasive minor folding indicate top-to-the-west, relatively shallow unroofing of the subducted margin as indicated in a new bedrock map of a portion of the Norwegian coast. Many of the mapped units have been redescribed, with emphasis put on those features that are of interest to the geophysical community.. To address the ambiguous kinematics of UHPM evolution, numerical models are employed in this study to consider the trajectory of crustal materials during continental collision that concentrate on the delicate balance of forces driving and resisting the subduction of buoyant continental materials as a function of kinetically-controlled equilibration.. In the WGR, past stability of coesite and rarely, of diamond, is preserved in robust mafic eclogites as inclusions within zircon and garnet grains. However, the extent of UHPM equilibration of the volumetrically dominant quartzo-feldspathic gneisses and consequently the contribution of these lithologies to the overall subduction suystemare unclear. . As such, simple equilibrium- defined strength and density parameters are insufficient to define natural model behavior. (Meaning of this next sentence escapes me. How does the following sound?) Rather, numerical solutions involving end member and intermediate states between equilibrium and non-equilibrium assemblages are explored While UHP metamorphic reactions in the

  6. Assessing Biogenecity of Stromatolites: Return to the Facies (United States)

    Shapiro, R. S.; Jameson, S.; Rutter, A.; McCarthy, K.; Planavsky, N. J.; Severson, M.


    not occur, the interval is autobrecciated with many clasts containing syneresis cracks. Flow-banded iron oxides in these layers are not stromatolitic but likely formed from fluid flow at the boundary between well- and poorly-cemented lithofacies. Mesostructure is similar between collection sites that are essentially unaltered, low-grade diagenetic, and amphibolite-grade metamorphic. Furthermore, mesostructure is consistent in most stromatolites throughout both layers in the Biwabik as well as the Gunflint. These new results provide a much broader context then previous studies and demonstrate that the upper and lower stromatolite horizons in the Biwabik and Gunflint iron ranges are formed in similar facies. Complexity in stromatolite forms occurs on the sub-meter scale, as would be expected for a nearshore, microbially mediated system. However, there appears to be a gradient in the degree of microbial control of stromatolite morphology, with both ';biogenic' and ';abiogenic' forms present. More broadly, this work highlights the importance of field and regional context when deciphering the significance of microbialites.

  7. Metamorphism of bauxites on Naxos, Greece

    NARCIS (Netherlands)

    Feenstra, A.


    This thesis presents the results of a petrological-mineralogical and geochemical study of the metamorphosed karstbauxites on the island of Naxos, Greece. The bauxites have been subject to an Eocene highpressure metamorphism (M1), followed by a Late Oligocene-Miocene medium-pressure metamorphism (M2)

  8. Metamorphic geology: Why should we care? (United States)

    Tajcmanova, Lucie; Moulas, Evangelos; Vrijmoed, Johannes


    Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data then often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. Obtaining high-quality analytical data from metamorphic rocks has become a standard part of geology studies. The numerical tools for geodynamic reconstructions have evolved to a great extend as well. Furthermore, the increasing demand on using the Earth's interior for sustainable energy or nuclear waste disposal requires a better understanding of the physical processes involved in fluid-rock interaction. However, nowadays, metamorphic data have apparently lost their importance in the "bigger picture" of the Earth sciences. Interestingly, the suppression of the metamorphic geology discipline limits the potential for understanding the aforementioned physical processes that could have been exploited. In fact, those phenomena must be considered in the development of new generations of fully coupled numerical codes that involve reacting materials with changing porosity while obeying conservation of mass, momentum and energy. In our contribution, we would like to discuss the current role of metamorphic geology. We will bring food for thoughts and specifically touch upon the following questions: How can we revitalize metamorphic geology? How can we increase the importance of it? How can metamorphic geology contribute to societal issues?

  9. Timing and conditions of metamorphism and melt crystallization in Greater Himalayan rocks, eastern and central Bhutan: insight from U-Pb zircon and monazite geochronology and trace-element analyses (United States)

    Zeiger, K.; Gordon, S. M.; Long, S. P.; Kylander-Clark, A. R. C.; Agustsson, K.; Penfold, M.


    Within the eastern Himalaya in central and eastern Bhutan, Greater Himalayan (GH) rocks are interpreted to have been thickened by the Kakhtang thrust (KT). In order to understand the metamorphic and exhumation history of the GH and to evaluate the structural significance of the KT, zircon and monazite from twenty samples were analyzed by laser-ablation split-stream ICPMS. In eastern Bhutan, zircon and monazite from samples collected in the KT hanging wall revealed ca. 36-28 Ma metamorphism. Subsequently, the initiation of melt crystallization shows a trend with structural distance above the KT, with early melt crystallization (ca. 27 Ma) in the structurally highest samples and younger melt crystallization (ca. 16 Ma) for leucosomes within the KT zone. Melt crystallization was protracted and continued until ca. 14-13 Ma in both the KT hanging wall and the footwall. In comparison, in central Bhutan, two leucosomes revealed extended melt crystallization from ca. 31 to 19 Ma. The youngest zircon dates from samples exposed structurally above and below the KT are similar, indicating that the KT was not as significant of a structure as other fault systems to which it has been correlated. However, the younging trend in the initiation of melt crystallization with decreasing structural distance above the KT argues that progressive underplating of ductile material assisted in the initial emplacement of the GH unit in central and eastern Bhutan. The KT likely represents a minor shear zone that aided in this underplating process.

  10. Thermal effects of metamorphic reactions in a three-component slab

    DEFF Research Database (Denmark)

    Chemia, Zurab; Dolejš, David; Steinle-Neumann, Gerd


    or consumption can occur due to metamorphic reactions, including endothermic devolatilization. We investigate enthalpy budget in a subducting slab using a self-consistent thermodynamic model. Petrological model of a subducting slab consists of three layers: oceanic subducting sediment (GLOSS), oceanic basalt (OB......), and moderately serpentinized harzburgite (SHB). These layers are examined over the range of pressure-temperature conditions of interest by computing metamorphic phase diagrams and retrieving whole-rock thermodynamic properties. Our results suggest that metamorphic reactions consume a significant amount of slab...

  11. Thermal effects of metamorphic reactions in a three-component slab

    DEFF Research Database (Denmark)

    Chemia, Zurab; Dolejš, David; Steinle-Neumann, Gerd


    or consumption can occur due to metamorphic reactions, including endothermic devolatilization. We investigate enthalpy budget in a subducting slab using a self-consistent thermodynamic model. Petrological model of a subducting slab consists of three layers: oceanic subducting sediment (GLOSS), oceanic basalt (OB......), and moderately serpentinized harzburgite (SHB). These layers are examined over the range of pressure-temperature conditions of interest by computing metamorphic phase diagrams and retrieving whole-rock thermodynamic properties. Our results suggest that metamorphic reactions consume a significant amount of slab...

  12. Syn-collapse eclogite metamorphism and exhumation of deep crust in a migmatite dome: The P-T-t record of the youngest Variscan eclogite (Montagne Noire, French Massif Central) (United States)

    Whitney, Donna L.; Roger, Françoise; Teyssier, Christian; Rey, Patrice F.; Respaut, J.-P.


    In many orogens, high-pressure (HP) metamorphic rocks such as eclogite occur as lenses in quartzofeldspathic gneiss that equilibrated at much lower pressures. The pressure-temperature-time (P-T-t) history of eclogite relative to host gneiss provides information about mechanisms and timescales of exhumation of orogenic crust. The Montagne Noire of the southern Massif Central, France, is an eclogite-bearing gneiss (migmatite) dome located at the orogen-foreland transition of the Variscan belt. Results of our study show that it contains the youngest eclogite in the orogen, similar in age to migmatite and granite that crystallized under low-pressure conditions. P-T conditions for an exceptionally unaltered eclogite from the central Montagne Noire were estimated using a pseudosection supplemented by garnet-clinopyroxene and Zr-in-rutile thermometry. Results indicate peak P ∼ 1.4 GPa and T ∼ 725°C for Mg-rich garnet rim (50 mol% pyrope) + omphacite (36 mol% jadeite) + rutile + quartz. U-Pb geochronology (LA-ICP-MS) of 16 zoned zircon grains yielded ∼360 Ma (4 cores) and ∼315 Ma (12 rims and cores). Rare earth element abundances determined by LA-ICP-MS for dated zircon are consistent with crystallization of ∼315 Ma zircon under garnet-stable, plagioclase-unstable conditions that we interpret to indicate high pressure; in contrast, the ∼360 Ma zircon core corresponds to crystallization under lower pressure plagioclase-stable conditions. Based on garnet zoning and inclusion suites, rutile textures and Zr zoning, P-T results, and zircon petrochronology, we interpret the ∼315 Ma date as the age of eclogite-facies metamorphism that only slightly preceded dome formation and crystallization at 315-300 Ma. This age relation indicates that eclogite formation at high pressure and migmatite dome emplacement at low pressure were closely spaced in time. We propose that collapse-driven material transfer from the hot orogen to the cool foreland resulted in thickening of

  13. Submarine-fan facies associations of the Upper Cretaceous and Paleocene Gottero Sandstone, Ligurian Apennines, Italy (United States)

    Nilsen, Tor H.; Abbate, Ernesto


    The Upper Cretaceous and Paleocene Gottero Sandstone was deposited as a small deep-sea fan on ophiolitic crust in a trench-slope basin. It was thrust northeastward as an allochthonous sheet in Early and Middle Cenozoic time. The Gottero, as thick as 1500 m, was probably derived from erosion of Hercynian granites and associated metamorphic rocks in northern Corsica. Outcrops of inner-fan channel, middle-fan channel and interchannel, outer-fan lobe, fan-fringe, and basin-plain facies associations indicate that the depositional model of Mutti and Ricci Lucchi for mixed-sediment deep-sea fans can be used. The original fan had a radius of 30 to 50 km.

  14. Alisitos Formation, calcareous facies: Early Cretaceous episode of tectonic calm

    Energy Technology Data Exchange (ETDEWEB)

    Suarez-Vidal, F.


    The Alisitos Formation (Aptian-Albian), shaped as a marine volcanic arc, crops out along the western side of the peninsula of Baja California bounding the Peninsular Range batholith. Lithologically, this formation is formed by volcanic-breccias, porphyritic flows, biohermal limestones, and tuffaceous and pyroclastic sediments. The distribution of the different facies depends on the nature of volcanism and the distance from a volcanic center, although the presence of massive biohermal limestone indicates that in the Early Cretaceous (during the tectonic episodes), the volcanic activity decreased to the level that the environmental conditions were favorable for the development of an organic reef barrier, behind an island arc. Such conditions existed south of the Agua Blanca fault and extended to El Arco, Baja California. Based upon field observations and petrological analysis of the Alisitos limestone, an attempt is made to recreate the environmental condition in the Punta China and San Fernando, Baja California, sites.

  15. Age of metamorphic events : petrochronology and hygrochronology (United States)

    Bosse, Valerie; Villa, Igor M.


    Geodynamic models of the lithosphere require quantitative data from natural samples. Time is a key parameter: it allows to calculate rates and duration of geological processes and provides informations about the involved physical processes (Vance et al. 2003). Large-scale orogenic models require linking geochronological data with other parameters: structures, kinematics, magmatic and metamorphic petrology (P-T-A-X conditions), thermobarometric evolution of the lithosphere, chemical dynamics (Muller, 2003). This requires geochronometers that are both powerful chemical and petrological tracers. In-situ techniques allow dating a mineral in its petrological-microstructural environment. Getting a "date" has become quite easy... But what do we date in the end ? What is the link between the numbers obtained from the mass spectrometer and the age of the metamorphic event we are trying to date ? How can we transform the date into a geological meaningful age ? What do we learn about the behavior of the geochronometer minerals? Now that we can perform precise dating on very small samples directly in the studied rock, it is important to improve the way we interpret the ages to give them more pertinence in the geodynamic context. We propose to discuss the Th/U/Pb system isotopic closure in various metamorphic contexts using our published examples of in situ dating on monazite and zircon (Bosse et al. 2009; Didier et al. 2014, 2015). The studied examples show that (i) fluid assisted dissolution-precipitation processes rather than temperature-dependent solid diffusion predominantly govern the closure of the Th/U/Pb system (ii) monazite and zircon are sensitive to the interaction with fluids of specific composition (F, CO2, K ...), even at low temperature (iii) in the absence of fluids, monazite is able to record HT events and to retain this information in poly-orogenic contexts or during partial melting events (iv) complex chemical and isotopic zonations, well known in monazite

  16. Electron microprobe monazite Th-Pb dating and its constraints on multi-stage metamorphism of low-pressure pelitic granulite from the Jingshan Group in the Jiaobei terrane

    Institute of Scientific and Technical Information of China (English)

    ZHOU Xiwen; WEI Chunjing; GENG Yuansheng; ZHANG Lifei


    Monazites from low-pressure pelitic granulite of the Jingshan Group in the Jiaobei terrane were dated by the electron microprobe method. Three stages of metamorphic age at 1720±15 Ma, 1687±16 Ma and 1568±15 Ma were yielded by constructing age mapping for zoned monazites and PbO-ThO2* isochron diagram for unzoned monazites, respectively. The first age was interpreted as the age of an early amphibolite-facies metamorphism, the second age as the peak granulite-facies, and the last age as uplifting of the granulite unit. These ages are the first geochronologic data for the low-pressure pelitic granulites in the Jingshan Group, and thus are of important significance when discussing the tectono-metamorphic evolution of the Jiaobei terrane.

  17. Different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks (United States)

    Xia, Qiong-Xia; Zhou, Li-Gang


    Garnet in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions, which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction-zone conditions. It provides an important target to retrieve physicochemical changes in subduction-zone processes, including those not only in pressure and temperature but also in the durations of metamorphism and anatexis. Garnet from different compositions of HP to UHP metamorphic rocks may show different types of major and trace element zonation, as well as mineral inclusions. Discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the HP to UHP metamorphic rocks. Magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction-zone conditions, with spessartine-increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim. Metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation, with spessartine-decreasing from core to rim if the intracrystalline diffusion is not too fast. The compositional profiles of metamorphic garnet in the abundances of grossular, almandine and pyrope are variable depending on the composition of host rocks and co-existing minerals. Peritectic garnet grows through peritectic reactions during partial melting of HP to UHP rocks, with the composition of major elements to be controlled by anatectic P-T conditions and the compositions of parental rocks and anatectic melts. Trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages, the garnet

  18. Late miocene/pliocene origin of the inverted metamorphism of the Central Himalaya

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, T.M.; Ryerson, F.J.; LeFort, P.; Yin, A. Lovera, O.M.


    The spatial association of intracontinental thrusting and inverted metamorphism, recognized in the Himalaya more than a century ago, has inspired continuing efforts to identify their causal relationship. Perhaps the best known sequence of inverted metamorphism is that found immediately beneath the Himalayan Main Central Thrust (MCT), generally thought to have been active during the Early Miocene. It has been widely assumed that the pattern of inverted metamorphism also developed at that time. Using a new approach, in situ Th-Pb dating of monazite included in garnet, we have discovered that the peak metamorphic recrystallization recorded in the footwall of the MCT fault occurred at ca. 5 Ma. The apparent inverted metamorphism resulted from activation of a broad shear zone beneath the MCT zone which juxtaposed two right-way-up metamorphic sequences. Recognition of this remarkably youthful phase of metamorphism resolves outstanding problems in Himalayan tectonics, such as why the MCT (and not the more recently initiated thrusts) marks the break in slope of the present day mountain range, and transcends others, such as the need for exceptional conditions to explain Himalayan anatexis.

  19. Neoarchean arc magmatism followed by high-temperature, high-pressure metamorphism in the Nilgiri Block, southern India (United States)

    Samuel, Vinod O.; Sajeev, K.; Hokada, T.; Horie, K.; Itaya, T.


    The Nilgiri Block, southern India is an exhumed lower crust formed through arc magmatic processes in the Neoarchean. The main lithologies in this terrane include charnockites, gneisses, volcanic tuff, metasediments, banded iron formation and mafic-ultramafic bodies. Mafic-ultramafic rocks are present towards the northern and central part of the Nilgiri Block. We examine the evolution of these mafic granulites/metagabbros by phase diagram modeling and U-Pb sensitive high resolution ion microprobe (SHRIMP) dating. They consist of a garnet-clinopyroxene-plagioclase-hornblende-ilmenite ± orthopyroxene ± rutile assemblage. Garnet and clinopyroxene form major constituents with labradorite and orthopyroxene as the main mineral inclusions. Labradorite, identified using Raman analysis, shows typical peaks at 508 cm- 1, 479 cm- 1, 287 cm- 1 and 177 cm- 1. It is stable along with orthopyroxene towards the low-pressure high-temperature region of the granulite facies (M1 stage). Subsequently, orthopyroxene reacted with plagioclase to form the peak garnet + clinopyroxene + rutile assemblage (M2 stage). The final stage is represented by amphibolite facies-hornblende and plagioclase-rim around the garnet-clinopyroxene assemblage (M3 stage). Phase diagram modeling shows that these mafic granulites followed an anticlockwise P-T-t path during their evolution. The initial high-temperature metamorphism (M1 stage) was at 850-900 °C and ~ 9 kbar followed by high-pressure granulite facies metamorphism (M2 stage) at 850-900 °C and 14-15 kbar. U-Pb isotope studies of zircons using SHRIMP revealed late Neoarchean to early paleoproterozoic ages of crystallization and metamorphism respectively. The age data shows that these mafic granulites have undergone arc magmatism at ca. 2539.2 ± 3 Ma and high-temperature, high-pressure metamorphism at ca. 2458.9 ± 8.6 Ma. Thus our results suggests a late Neoarchean arc magmatism followed by early paleoproterozoic high-temperature, high

  20. Dating sub-20 micron zircons in granulite-facies mafic dikes from SW Montana: a new approach using automated mineralogy and SIMS U-Pb geochronology (United States)

    Ault, A. K.; Mahan, K. H.; Flowers, R. M.; Chamberlain, K.; Appleby, S. K.; Schmitt, A. K.


    Geochronological data is fundamental to all tectonic studies, but a major limitation for many lithologies is a paucity of sizeable zircons suitable for conventional U-Pb techniques. In particular, mafic dike swarms provide important time markers for tectonometamorphic activity in Precambrian terranes, but commonly yield little or no zircon or baddeleyite sufficient for TIMS or standard ion-probe analysis of crystal separates. We apply a new approach involving in-situ automated mineralogy and high spatial resolution Secondary Ion Mass Spectrometry (SIMS) geochronology to a mafic dike swarm exposed in the Northern Madison Range of SW Montana. The dikes cross-cut early fabrics but are also variably deformed and metamorphosed to P-T conditions as high as 1.2 GPa and 850 C. The swarm emplacement age is inferred to be ca. 2.1 Ga based on similarities to dated dikes in the adjacent Tobacco Root Mountains. Resolving the timing of dike emplacement and high-grade metamorphism in the study area is important for understanding the extent of post-Archean modification to the northwest margin of the Wyoming craton. Identification and textural characterization of zircons were facilitated by in-situ automated mineralogical analysis, in contrast to a standard elemental X-ray mapping approach. Our technique uses an SEM-based platform coupling calibrated BSE data with X-ray data collected by multiple energy dispersive spectrometers to rapidly identify target accessory phases at high spatial resolution. Whole thin section search maps were generated in ~30 minutes at 4 µm pixel resolution. Our dike thin sections commonly contained >300 zircons in a variety of textural settings, with 80% having a short dimension 95% for 206Pb. SIMS data for 22 zircons from a granulite-facies mafic dike thin section define a chord with upper and lower intercepts of 1753.1 ± 9.5 Ma and 63.2 ± 7.9 Ma, respectively (2 sigma error, MSWD = 1.6). A positive correlation between U concentration and degree of

  1. Facies development and paleoenvironment of the Hajajah Limestone Member, Aruma Formation, central Saudi Arabia (United States)

    El-Sorogy, Abdelbaset S.; Ismail, Abdelmoneim; Youssef, Mohamed; Nour, Hamdy


    The Campanian Hajajah Limestone Member of the Aruma Formation was formed during two regressive episodes. Each of them formed of three depositional facies, from base to top: 1) intra-shelf basin facies, made up of fossiliferous green shale and mudstone with ostracods and badly preserved foraminifers. 2) fore-reef facies, consists of hard, massive, marly coralline limestone. The upper part is rich with low divers, badly to moderate preserved, solitary and colonial corals, and, 3) back reef and near-shore facies, consists of fossiliferous sandy dolomitized, bioturbated limestone with abundant reworked corals, bivalves, gastropods, and aggregate grains. On the basis of field observations, micro-and macrofossils and microfacies analysis, the Hajajah Limestone Member was deposited in distal marine settings below storm wave base in a low-energy environment changed upward to fore-reef framework in an open marine environment with moderate to high energy conditions and terminated with shallow marine facies with accumulation of skeletal grains by storms during regression.

  2. The potential role of fluids during regional granulite-facies dehydration in the lower crust

    Directory of Open Access Journals (Sweden)

    Daniel E. Harlov


    Full Text Available High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting, fluid-aided solid-state dehydration, or varying degrees of both. On the localized meter scale, solid-state dehydration, due to CO2-rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock, normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur. Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which, along with accompanying amphibolite-facies rocks, form traverses of lower crust. This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale. The more prominent of these fluid-induced textures in the granulite-facies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite. The fluids believed responsible take the form of concentrated NaCl- and KCl- brines from a basement ultramafic magma heat source traveling upwards along grain boundaries. Additional experimental work involving CaSO4 dissolution in NaCl-brines, coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks, have demonstrated the possibility that NaCl-brines, with a CaSO4 component, could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths. These results, taken together, lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it. Their presence allows for rapid mass and

  3. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizario ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Hartmann, Leo A.; Porcher, Carla C. [Rio Grande do Sul Univ., Porto Alegre (Brazil). Inst. de Geociencias]. E-mail:; Santos, Joao O.S. [Centro de Pesquisas de Recursos Minerais (CPRM), Porto Alegre, RS (Brazil). Brazilian Geological Survey; Leite, Jayme A.D. [Mato Grosso Univ., Cuiaba (Brazil). Dept. de Recursos Minerais; McNaughton, Neal J. [Western Australia Univ., Nedlands, WA (Australia). Centre for Global Metallogeny


    The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizario ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 {+-} 12 Ma. Amphibolite facies metamorphism M{sub 1} formed voluminous hornblende in the investigated rock possibly at 1989 {+-} 21 Ma. This ultramafic rock was re-metamorphosed at 702+- 21 Ma during a greenschist facies event M{sub 2}; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257 {+-} 12 Ma) and Camboriu Orogeny ({approx}1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702 {+-} 21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton. (author)

  4. Sequence associations of sedimentary facies in continental basins and their applications to palaeogeographic mapping

    Institute of Scientific and Technical Information of China (English)

    TANG Hua-feng; CHENG Ri-hui; KONG Qing-ying; BAI Yun-feng; YU Ming-feng


    According to the characteristics of sedimentary facies and their vertical associations, sequence association of sedimentary facies can be divided into 2 types and 28 subtypes. The first type (type A) is a sedimentary sequence without volcanic rocks, including 18 subtypes. The second type (type B) is a volcanogenic succession including 10 subtypes.Each subtype may reflect certain filling condition under certain sedimentary environment. Time and space distribution of different types of sequence associations can reflect tectonics that controlled the basin evolution, sedimentary environments and palaeogeography.

  5. The influence of facies heterogeneity on the doublet performance in low-enthalpy geothermal sedimentary reservoirs

    DEFF Research Database (Denmark)

    Crooijmans, R. A.; Willems, C. J L; Nick, Hamid


    A three-dimensional model is used to study the influence of facies heterogeneity on energy production under different operational conditions of low-enthalpy geothermal doublet systems. Process-based facies modelling is utilised for the Nieuwerkerk sedimentary formation in the West Netherlands Basin...... and the energy recovery rate for different discharge rates and the production temperature (Tmin) above which the doublet is working. With respect to the results, we propose a design model to estimate the life time and energy recovery rate of the geothermal doublet. The life time is estimated as a function of N....../G, Tmin and discharge rate, while the design model for the energy recovery rate is only a function of N/G and Tmin. Both life time and recovery show a positive relation with an increasing N/G. Further our results suggest that neglecting details of process-based facies modelling may lead to significant...

  6. Protolith age of Santa Maria Chico granulites dated on zircons from an associated amphibolite-facies granodiorite in southernmost Brazil. (United States)

    Hartmann, Léo A; Liu, Dunyi; Wang, Yenbin; Massonne, Hans-Joachim; Santos, João O S


    U-Pb dating of zircon was undertaken with the Beijing SHRIMP II (sensitive high resolution ion microprobe) on anamphibolite facies granodiorite and an almandine-albite granulite from the Santa Maria Chico Granulitic Complex, southern Brazilian Shield. This work was also done to unravel protolith ages which are often hidden in the array of partly reset data. The obtained metamorphic ages of the granodiorite gneiss and the granulite are 2035 +/- 9 Ma and 2006 +/- 3 Ma, respectively. These data are within the range of metamorphic ages determined in previous studies (2022 +/- 18 Ma and 2031 +/- 40 Ma). However, protolith ages for the granodiorite (2366 +/- 8 Ma) and the granulite (2489 +/- 6 Ma) were obtained which are outside the previously recognized range (> 2510-2555 Ma). The magmatic protolith age of the granodiorite refers to a previously little known magmatic event in the shield. Further investigations may demonstrate that amphibolite facies zircon crystals are useful as a window into geological events in associated granulites, because zircon ages are blurred in the studied granulites.

  7. Protolith age of Santa Maria Chico granulites dated on zircons from an associated amphibolite-facies granodiorite in southernmost Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Hartmann, Leo A. [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Geociencias; Liu, Dunyi; Wang, Yenbin [Chinese Academy of Geological Sciences, Beijing (China); Massonne, Hans-Joachim [Universitaet Stuttgart (Germany). Inst. fuer Mineralogie und Kristallchemie; Santos, Joao O.S. [University of Western Australia, Perth, WA (Australia). Centre for Global Targeting


    U-Pb dating of zircon was undertaken with the Beijing SHRIMP II (sensitive high resolution ion microprobe) on an amphibolite facies granodiorite and an almandine-albite granulite from the Santa Maria Chico Granulitic Complex, southern Brazilian Shield. This work was also done to unravel protolith ages which are often hidden in the array of partly reset data. The obtained metamorphic ages of the granodiorite gneiss and the granulite are 2035 {+-} 9 Ma and 2006 {+-} 3 Ma, respectively. These data are within the range of metamorphic ages determined in previous studies (2022 {+-} 18 Ma and 2031 {+-} 40 Ma). However, protolith ages for the granodiorite (2366 {+-} 8 Ma) and the granulite (2489 {+-} 6 Ma) were obtained which are outside the previously recognized range (> 2510-2555 Ma). The magmatic protolith age of the granodiorite refers to a previously little known magmatic event in the shield. Further investigations may demonstrate that amphibolite facies zircon crystals are useful as a window into geological events in associated granulites, because zircon ages are blurred in the studied granulites. (author)

  8. Prima Facie Questions in Quantum Gravity

    CERN Document Server

    Isham, C J


    The long history of the study of quantum gravity has thrown up a complex web of ideas and approaches. The aim of this article is to unravel this web a little by analysing some of the {\\em prima facie\\/} questions that can be asked of almost any approach to quantum gravity and whose answers assist in classifying the different schemes. Particular emphasis is placed on (i) the role of background conceptual and technical structure; (ii) the role of spacetime diffeomorphisms; and (iii) the problem of time.

  9. Effects of Metamorphism on the Valence and Coordination of Titanium in Ordinary Chondrites

    Energy Technology Data Exchange (ETDEWEB)

    Simon, S.B.; Sutton, S.R.; Grossman, L. (UC)


    Despite years of study, the conditions under which ordinary chondrites were metamorphosed from grade 3 to grade 6 are not well defined. Wide ranges of peak temperature are inferred for each grade. The long-popular 'onion shell' model, in which higher metamorphic grade is attributed to greater depths of origin, implies a corresponding decrease in cooling rate with increasing grade, and there is disagreement as to whether or not this is observed. Redox conditions during chondrite metamorphism are also not well understood. Some workers have reported evidence for reduction, presumably by carbon, with increase in grade from 3-4, followed by oxidation during metamorphism to higher grades, but other work indicates little variation in fO{sub 2} as a function of metamorphic grade. During our investigation of the valence of Ti in planetary materials, we found high proportions of Ti{sup 3+} in olivine and pyroxene in chondrules in Semarkona (LL3.0) and low proportions in New Concord (L6) olivine, suggesting that Ti was oxidized during ordinary chondrite metamorphism. We have undertaken a study of L and LL chondrites of grades 3-6 to see how Ti valence and coordination vary with grade and to see if the variations can be used to constrain conditions of chondrite metamorphism.

  10. Multi-waveform classification for seismic facies analysis (United States)

    Song, Chengyun; Liu, Zhining; Wang, Yaojun; Li, Xingming; Hu, Guangmin


    Seismic facies analysis provides an effective way to delineate the heterogeneity and compartments within a reservoir. Traditional method is using the single waveform to classify the seismic facies, which does not consider the stratigraphy continuity, and the final facies map may affect by noise. Therefore, by defining waveforms in a 3D window as multi-waveform, we developed a new seismic facies analysis algorithm represented as multi-waveform classification (MWFC) that combines the multilinear subspace learning with self-organizing map (SOM) clustering techniques. In addition, we utilize multi-window dip search algorithm to extract multi-waveform, which reduce the uncertainty of facies maps in the boundaries. Testing the proposed method on synthetic data with different S/N, we confirm that our MWFC approach is more robust to noise than the conventional waveform classification (WFC) method. The real seismic data application on F3 block in Netherlands proves our approach is an effective tool for seismic facies analysis.

  11. A Specialized Lightweight Metamorphic Function for KASUMI Metamorphic Cipher and Its FPGA Implementation

    Directory of Open Access Journals (Sweden)

    Rabie A. Mahmoud


    Full Text Available To enhance the performance of the KASUMI Metamorphic Cipher, we apply a lightweight Metamorphic Structure. The proposed structure uses four lightweight bit-balanced operations in the function Meta-FO of the KASUMI Metamorphic Cipher. These operations are: XOR, INV, XNOR, and NOP for bitwise XOR, invert, XNOR, and no operation respectively building blocks of the Specialized Crypto Logic Unit (SCLU. In this work, we present a lightweight KASUMI Specialized-Metamorphic Cipher. In addition, we provide a Field Programmable Gate Array (FPGA implementation of the proposed algorithm modification.

  12. Metamorphic manipulating mechanism design for MCCB using index reduced iteration (United States)

    Xu, Jinghua; Zhang, Shuyou; Zhao, Zhen; Lin, Xiaoxia


    The present research on moulded case circuit breaker(MCCB) focuses on the enhancement of current-limiting interrupting performance during short circuit, overload, under voltage and phase failure, involving electrics, magnetic, mechanics, thermal, material, friction, arc extinguishing, impact vibration, skin effect, etc. The rigid-flexible coupling of the parts and components of the metamorphic manipulating mechanism in multi-fields leads to the non-rigid, high frequency, high damping, singularity of the Euler-Lagrange equations which represents the multi-body dynamics. The small step iteration which is used for obtaining the instantaneous and short time critical interrupting performance of metamorphic mechanism appears inaccuracy. It is difficult to realize top-down design by existing CAD systems. Therefore, a metamorphic manipulating mechanism design method for MCCB using index reduced iteration(IRI) is put forward. The metamorphic manipulating mechanism of MCCB is decomposed into three mechanisms: main switch connector mechanism, electromagnet-drawbar-jump buckle mechanism, and bimetallic strip-drawbar mechanism, which is respectively described by electro-dynamic force, electromagnet force, and bimetallic strip force. The dummy part(virtual rigid) without moment of inertia and mass is employed as intermediate to join the flexible body and rigid body. The model of rigid-flexible coupling metamorphic mechanism multi-body dynamics is built. The differential algebraic equations(DAEs) of the multibody dynamics model are converted to pure ordinary differential equations(ODEs) by coordinate partition. Order reduced integration with multi-step and variable step-size is preceded based on IRI. The non-linear algebraic equations are solved in each integration step by Newton-Rapson iteration. There is no ill-condition and singularity of Jacobian matrix when step size reduces to zero. The independent prototype design system using ACIS R13, HOOPS V11.0 and Visual C++.NET 2003

  13. A Method for Determining Sedimentary Micro-Facies Belts Automatically

    Institute of Scientific and Technical Information of China (English)

    Linfu Xue; Qitai Mei; Quan Sun


    It is important to understand the distribution of sedimentary facies, especially the distribution of sand body that is the key for oil production and exploration. The secondary oil recovery requires analyzing a great deal of data accumulated within decades of oil field development. At many cases sedimentary micro-facies maps need to be reconstructed and redrawn frequently, which is time-consuming and heavy. This paper presents an integrated approach for determining the distribution of sedimentary micro-facies, tracing the micro-facies boundary, and drawing the map of sedimentary micro-facies belts automatically by computer technique. The approach is based on the division and correlation of strata of multiple wells as well as analysis of sedimentary facies. The approach includes transform, gridding, interpolation, superposing, searching boundary and drawing the map of sedimentary facies belts, and employs the spatial interpolation method and "worm" interpolation method to determine the distribution of sedimentary micro-facies including sand ribbon and/or sand blanket. The computer software developed on the basis of the above principle provides a tool for quick visualization and understanding the distribution of sedimentary micro-facies and reservoir. Satisfied results have been achieveed by applying the technique to the Putaohua Oil Field in Songliao Basin, China.

  14. Metamorphic and tectonic evolution of Ceuta peninsula (Internal Rif): new interpretation in the framework of arc and back arc evolution (United States)

    Homonnay, Emmanuelle; Lardeaux, Jean-Marc; Corsini, Michel; Cenki-Tok, Bénédicte; Bosch, Delphine; Munch, Philippe; Romagny, Adrien; Ouazzani-Touhami, Mohamed


    In the last twenty years, various geophysical investigations have established that the Western Mediterranean opened in a subduction context as a back arc domain. In the Alboran basin the dip of the subduction plane is eastwards or southeastwards depending of considered models. If the geological records of back-arc opening are well-known, the arc-related tectonic and petrologic evolutions are still poorly documented. In order to decipher these markers, we focalised structural, petrological and thermo-chronological studies on the Ceuta peninsula located in the Rif belt, on the western part of the Gibraltar arc to the North of Morocco. The present-day tectonic pile is constituted by: (1) the upper Ceuta unit, composed of High Pressure and High Temperature metapelites retromorphosed under Amphibolite-facies condition, with Ultra-High Pressure relicts, and pyrigarnite and spinel bearing peridotites boudins at its base, (2) the lower Monte Hacho unit, with orthogneisses metamorphosed under Amphibolite-facies conditions. Structural analysis indicates a polyphase tectonic evolution: (1) an earlier deformation phase only observed in the UHP metapelites and characterized by a steep S1 foliation plane, (2) a main deformation phase associated to a pervasive gently dipping S2 foliation plane bearing a L2 stretching lineation and synschistose folds whose axes are parallel to L2 and (3) a late deformation phase which developed S3 foliation plane and L3 stretching lineation coeval with development of narrow normal ductile shear zones. A zone of increasing deformation, several dozen meters wide, is identified as a major ductile shear zone involving the peridotitic lenses at the base of the metapelites of the Ceuta unit and overlaying this upper unit on top of the orthogneisses of the Monte Hacho lower unit. The attitude of mylonitic foliation and stretching and mineral lineations as well as the numerous shear sense indicators observed in the shear zone are consistent with a

  15. The Garzón Massif, Colombia-a new ultrahigh-temperature metamorphic complex in the Early Neoproterozoic of northern South America (United States)

    Altenberger, U.; Mejia Jimenez, D. M.; Günter, C.; Sierra Rodriguez, G. I.; Scheffler, F.; Oberhänsli, R.


    The Garzón Complex of the Garzón Massif in SW Colombia is composed of the Vergel Granulite Unit (VG) and the Las Margaritas Migmatite Unit (LMM). Previous studies reveal peak temperature conditions for the VG of about 740 °C. The present study considers the remarkable exsolution phenomena in feldspars and pyroxenes and titanium-in-quartz thermometry. Recalculated ternary feldspar compositions indicate temperatures around 900-1,000 °C just at or above the ultra-high temperature-metamorphism (UHTM) boundary of granulites. The calculated temperatures range of exsolved ortho- and clinopyroxenes also supports the existence of an UHTM event. In addition, titanium-in-quartz thermometry points towards ultra-high temperatures. It is the first known UHTM crustal segment in the northern part of South America. Although a mean geothermal gradient of ca 38 °C km-1 could imply additional heat supply in the lower crust controlling this extreme of peak metamorphism, an alternative model is suggested. The formation of the Vergel Granulite Unit is supposed to be formed in a continental back-arc environment with a thinned and weakened crust behind a magmatic arc (Guapotón-Mancagua Gneiss) followed by collision. In contrast, rocks of the adjacent Las Margaritas Migmatite Unit display "normal" granulite facies temperatures and are formed in a colder lower crust outside the arc, preserved by the Guapotón-Mancagu Gneiss. Back-arc formation was followed by inversion and thickening of the basin. The three units that form the modern-day Garzón Massif, were juxtaposed upon each other during collision (at ca. 1,000 Ma) and exhumation. The collision leading to the deformation of the studied area is part of the Grenville orogeny leading to the amalgamation of Rodinia.

  16. P- T- t constraints on the development of the Doi Inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt, northern Thailand (United States)

    Macdonald, A. S.; Barr, S. M.; Miller, B. V.; Reynolds, P. H.; Rhodes, B. P.; Yokart, B.


    The western gneiss belt in northern Thailand is exposed within two overlapping Cenozoic structural domains: the extensional Doi Inthanon metamorphic core complex domain located west of the Chiang Mai basin, and the Mae Ping strike-slip fault domain located west of the Tak batholith. New P- T estimates and U-Pb and 40Ar/ 39Ar age determinations from the Doi Inthanon domain show that the gneiss there records a complex multi-stage history that can be represented by a clockwise P- T- t path. U-Pb zircon and titanite dating of mylonitic calc-silicate gneiss from the Mae Wang area of the complex indicates that the paragneissic sequence experienced high-grade, medium-pressure metamorphism (M1) in the Late Triassic - Early Jurassic (ca. 210 Ma), in good agreement with previously determined zircon ages from the underlying core orthogneiss exposed on Doi Inthanon. Late Cretaceous monazite ages of 84 and 72 Ma reported previously from the core orthogneiss are attributed to a thermal overprint (M2) to upper-amphibolite facies in the sillimanite field. U-Pb zircon and monazite dating of granitic mylonite from the Doi Suthep area of the complex provides an upper age limit of 40 Ma (Late Eocene) for the early stage(s) of development of the actual core complex, by initially ductile, low-angle extensional shearing under lower amphibolite-facies conditions (M3), accompanied by near-isothermal diapiric rise and decompression melting. 40Ar/ 39Ar laserprobe dating of muscovite from both Doi Suthep and Doi Inthanon provided Miocene ages of ca. 26-15 Ma, representing cooling through the ca. 350 °C isotherm and marking late-stage development of the core complex by detachment faulting of the cover rocks and isostatic uplift of the sheared core zone and mantling gneisses in the footwall. Similarities in the thermochronology of high-grade gneisses exposed in the core complex and shear zone domains in the western gneiss belt of northern Thailand (and also in northern Vietnam, Laos, Yunnan

  17. Campo Belo Metamorphic Complex: tectonic evolution of an Archean sialic crust of the southern São Francisco Craton in Minas Gerais (Brazil

    Directory of Open Access Journals (Sweden)



    Full Text Available Systematic geological studies performed in the study area allowed the characterization of six lithodemic units: three gneissic, one amphibolitic, one supracrustal and one fissure mafic. The mineral assemblage and the structural record of these lithodemic units indicate that the study area was affected by five tectonothermal events. The structural pattern of the first and oldest event occurred under granulite facies conditions and reveals essentially a sinistral kinematic pattern. The second event, showing dominant extensional characteristics, is related to the generation of an ensialic basin filled by the volcano-sedimentary sequence of the supracrustal lithodemic unit. The third event, which is the most expressive in the study region, is characterized by a vigorous regional migmatization process and by the generation of the Claudio Shear Zone, presenting dextral kinematic movement. The fourth event is represented by a fissure mafic magmatism (probably two different mafic dike swarms and finally, the fifth event is a regional metamorphic re-equilibration that reached the greenschist facies, closing the main processes of the tectonic evolution of the Campo Belo Metamorphic Complex.Estudos geológicos sistemáticos permitiram a caracterização de seis unidades litodêmicas na área estudada: três gnáissicas, uma anfibolítica, uma supracrustal e uma máfica fissural. A assembléia mineral e os registros estruturais dessas unidades litodêmicas mostraram que a área estudada foi afetada por cinco eventos tectonotermais. O padrão estrutural do primeiro e último evento ocorreu em condições de fácies granulito e revelaram uma cinemática essencialmente sinistral. O segundo evento mostrou uma tectônica extensional relacionado à abertura da bacia ensiálica onde se alojou a seqüência vulcanosedimentar da unidade supracrustal. O terceiro evento, que é o mais expressivo na região estudada, é o responsável por um intenso processo de

  18. Petrology and phase equilibrium modeling of sapphirine + quartz assemblage from the Napier Complex, East Antarctica: Diagnostic evidence for Neoarchean ultrahigh-temperature metamorphism

    Directory of Open Access Journals (Sweden)

    Hisako Shimizu


    Full Text Available A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine + quartz assemblage from two localities (Tonagh Island (TI and Priestley Peak (PP in the Napier Complex, East Antarctica, provides unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during Neoarchean. The reaction microstructures associated with sapphirine + quartz vary among the samples, probably suggesting different tectonic conditions during the metamorphic evolution. Sapphirine and quartz in TI sample were probably in equilibrium at the peak stage, but now separated by corona of Grt + Sil + Opx suggesting near isobaric cooling after the peak metamorphism, whereas the Spr + Qtz + Sil + Crd + Spl assemblage replaces garnet in PP sample suggesting post-peak decompression. The application of mineral equilibrium modeling in NCKFMASHTO system demonstrated that Spr + Qtz stability is lowered down to 930 °C due to small Fe3+ contents in the rocks (mole Fe2O3/(FeO + Fe2O3 = 0.02. The TI sample yields a peak p-T range of 950–1100 °C and 7.5–11 kbar, followed by cooling toward a retrograde stage of 800–950 °C and 8–10 kbar, possibly along a counterclockwise p-T path. In contrast, the peak condition of the PP sample shows 1000–1050 °C and >12 kbar, which was followed by the formation of Spr + Qtz corona around garnet at 930–970 °C and 6.7–7.7 kbar, suggesting decompression possibly along a clockwise p-T trajectory. Such contrasting p-T paths are consistent with a recent model on the structural framework of the Napier Complex that correlates the two areas to different crustal blocks. The different p-T paths obtained from the two localities might reflect the difference in the tectonic framework of these rocks within a complex Neoarchean subduction/collision belt.

  19. Age, temperature and pressure of metamorphism in the Tasriwine Ophiolite Complex, Sirwa, Morocco (United States)

    Samson, S. D.; Inglis, J.; Hefferan, K. P.; Admou, H.; Saquaque, A.


    Sm-Nd garnet-whole rock geochronology and phase equilbria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex,Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ~0.72GPa and ~615°C and ended at ~0.8GPa and ~640°C. A bulk garnet Sm-Nd age of 645.6 × 1.6 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is nearly 20 million years younger than a previous age estimate of regional metamorphism of 663 × 14 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Irri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm- Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  20. Field Observations of Crustal Seismic Anisotropy: Implications for Mapping Tectonic Structure in Metamorphic Terranes (United States)

    Christensen, N. I.; Okaya, D.; Meltzer, A.; Brocher, T.; Holbrook, W. S.


    The study of seismic anisotropy within continental tectonic provinces provides earth scientists with a powerful tool for measuring and quantifying deformation within the crust. Preferred mineral alignment observed in metamorphic terranes produced by recrystallization during metamorphism is associated with planar structures such as slaty cleavage, schistosity, and gneissic layering. These structures are often pervasive for tens to hundreds of kilometers and produce significant compressional wave seismic anisotropy as well as shear wave splitting. Observations of crustal anisotropy within (1) slates of the chlorite subzone of the Haast schist terrane of South Island, New Zealand, (2) lower greenschist facies phyllites and metagraywackes of the Valdez Group Chugach terrane in southern Alaska, (3) amphibolite facies mica schists within the Yukon-Tanana terrane in the eastern Alaska range and (4) amphibolite facies quartzofeldspathic gneisses, approaching granulite grade, within the Nanga Parbat-Haramosh massif demonstrate that crustal anisotropy is not limited to rocks of any particular metamorphic grade and thus can be present at all crustal levels. Two refraction lines at approximately right angles shown up to 10% compressional wave anisotropy in relatively low grade metapelites of the Haast schist terrane. Fast velocities parallel the strike of the upturned slaty cleavage. Measured field velocities in the Chugach terrane, obtained from observed first arrival travel times, demonstrate significant compressional wave anisotropy (~9%) with fastest directions oriented approximately east-west and parallel to foliations observed in outcrops. Within the Alaskan Yukon-Tanana terrane variations in seismic velocities of the first arrivals correlate with field observations of regional dips of foliated schists. A northward shallowing of foliation dips produces an observed northward increasing seismic velocity. The core of the Nanga-Parbat massif forms a large-scale antiformal

  1. In search of early life: Carbonate veins in Archean metamorphic rocks as potential hosts of biomarkers (United States)

    Peters, Carl A.; Piazolo, Sandra; Webb, Gregory E.; Dutkiewicz, Adriana; George, Simon C.


    The detection of early life signatures using hydrocarbon biomarkers in Precambrian rocks struggles with contamination issues, unspecific biomarkers and the lack of suitable sedimentary rocks due to extensive thermal overprints. Importantly, host rocks must not have been exposed to temperatures above 250 °C as at these temperatures biomarkers are destroyed. Here we show that Archean sedimentary rocks from the Jeerinah Formation (2.63 billion yrs) and Carawine Dolomite (2.55 billion yrs) of the Pilbara Craton (Western Australia) drilled by the Agouron Institute in 2012, which previously were suggested to be suitable for biomarker studies, were metamorphosed to the greenschist facies. This is higher than previously reported. Both the mineral assemblages (carbonate, quartz, Fe-chlorite, muscovite, microcline, rutile, and pyrite with absence of illite) and chlorite geothermometry suggest that the rocks were exposed to temperatures higher than 300 °C and probably ∼400 °C, consistent with greenschist-facies metamorphism. This facies leads to the destruction of any biomarkers and explains why the extraction of hydrocarbon biomarkers from pristine drill cores has not been successful. However, we show that the rocks are cut by younger formation-specific carbonate veins containing primary oil-bearing fluid inclusions and solid bitumens. Type 1 veins in the Carawine Dolomite consist of dolomite, quartz and solid bitumen, whereas type 2 veins in the Jeerinah Formation consist of calcite. Within the veins fluid inclusion homogenisation temperatures and calcite twinning geothermometry indicate maximum temperatures of ∼200 °C for type 1 veins and ∼180 °C for type 2 veins. Type 1 veins have typical isotopic values for reprecipitated Archean sea-water carbonates, with δ13CVPDB ranging from - 3 ‰ to 0‰ and δ18OVPDB ranging from - 13 ‰ to - 7 ‰, while type 2 veins have isotopic values that are similar to hydrothermal carbonates, with δ13CVPDB ranging from - 18

  2. Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: New constraints on the tectonic evolution during ophiolite formation from high-precision U-Pb zircon geochronology (United States)

    Rioux, Matthew; Garber, Joshua; Bauer, Ann; Bowring, Samuel; Searle, Michael; Kelemen, Peter; Hacker, Bradley


    The Semail (Oman-United Arab Emirates) and other Tethyan-type ophiolites are underlain by a sole consisting of greenschist- to granulite-facies metamorphic rocks. As preserved remnants of the underthrust plate, sole exposures can be used to better understand the formation and obduction of ophiolites. Early models envisioned that the metamorphic sole of the Semail ophiolite formed as a result of thrusting of the hot ophiolite lithosphere over adjacent oceanic crust during initial emplacement; however, calculated pressures from granulite-facies mineral assemblages in the sole suggest the metamorphic rocks formed at >35 km depth, and are too high to be explained by the currently preserved thickness of ophiolite crust and mantle (up to 15-20 km). We have used high-precision U-Pb zircon dating to study the formation and evolution of the metamorphic sole at two well-studied localities. Our previous research and new results show that the ophiolite crust formed from 96.12-95.50 Ma. Our new dates from the Sumeini and Wadi Tayin sole localities indicate peak metamorphism at 96.16 and 94.82 Ma (±0.022 to 0.035 Ma), respectively. The dates from the Sumeini sole locality show for the first time that the metamorphic rocks formed either prior to or during formation of the ophiolite crust, and were later juxtaposed with the base of the ophiolite. These data, combined with existing geochemical constraints, are best explained by formation of the ophiolite in a supra-subduction zone setting, with metamorphism of the sole rocks occurring in a subducted slab. The 1.3 Ma difference between the Wadi Tayin and Sumeini dates indicates that, in contrast to current models, the highest-grade rocks at different sole localities underwent metamorphism, and may have returned up the subduction channel, at different times.

  3. Metamorphism history and dynamics of high-pressure granulites in the Dulan area of the North Qaidam Mountains, northwest China%柴北缘都兰高压麻粒岩的变质演化及形成的动力学背景

    Institute of Scientific and Technical Information of China (English)

    于胜尧; 张建新; 李金平


    A high-pressure granulite unit was recognized in the Dulan area, the eastern end of the North Qaidam-South Altyn HP-UHP metamorphism belt, Northwest China. High-pressure granulites are mainly mafic in composition although small amounts of acid-intermediate varieties also exist. Mineral assemblages in equilibrium in mafic granulites contain mainly garnet, clinopyroxene, plagioclase, with different amounts of kyanite, amphibole, rutile, quartz, zoisite/clinozoisite, scapolite and ilmenite, whereas acid-intermediate granulites contain garnet, kyanite, K-feldspar, plagioclase and quartz, with small amounts of clinopyroxene and amphibole. Petrologic and mineralogical data indicate these HP rocks experienced multistage metamorphism history. Thermobarometry of the peak mineral assemblages yields P-T conditions of 1.40 ~ 1. 85GPa and 800 ~ 925℃ . Retrogression began under high amphibolite-facies conditions estimated at 0. 8 ~ 1. 05GPa and 580 ~ 695℃ , and is followed by subsequent retrogression under low amphibolite-facies/greenschist-facies conditions ( <0. 8GPa and < 550℃ ). This study suggests that the Dulan high-pressure granulites experienced a single metamorphic history, and not associated with the effects of thermal relaxation after eclogite-facies metamorphism recorded in adjacent eclogites. The high-pressure granulites probably formed at the bottom of thickening continental crust related to continental subduction corresponding to the depth of about 50 ~ 70 km.%在柴北缘-阿尔金HP/UHP变质带东端,新识别出一个高压麻粒岩单元.高压基性麻粒岩是高压麻粒岩单元的主体,还包括少量高压中酸性麻粒岩.高压基性麻粒岩主要由平衡共生的石榴子石、单斜辉石、斜长石组成,还含有不等量的蓝晶石、角闪石、石英、金红石、黝帘石/斜黝帘石、钛铁矿、方柱石等矿物.高压长英质麻粒岩主要包括石榴子石、蓝晶石、钾长石、斜长石

  4. Prolonged episodic Paleoproterozoic metamorphism in the Thelon Tectonic Zone, Canada: an in-situ SHRIMP/EPMA monazite geochronology study (United States)

    Mitchell, Rhea; William, Davis; Robert, Berman; Sharon, Carr; Michael, Jercinovic


    The Thelon Tectonic zone (TTZ), Nunavut, Canada, is a >500km long geophysically, lithologically and structurally distinct N-NNE striking Paleoproterozoic boundary zone between the Slave and Rae Archean provinces. The TTZ has been interpreted as a ca. 2.0 Ga continental arc on the western edge of the Rae craton, that was deformed during collision with the Slave craton ca. 1.97 Ga. Alternatively, the Slave-Rae collision is interpreted as occurring during the 2.35 Ga Arrowsmith orogeny while the 1.9-2.0 Ga TTZ represents an intra-continental orogenic belt formed in previously thinned continental crust, postdating the Slave-Rae collision. The central part of the TTZ comprises three >100 km long, 10-20 km wide belts of ca. 2.0 Ga, mainly charnockitic plutonic rocks, and a ca. 1910 Ma garnet-leucogranite belt. Metamorphism throughout these domains is upper-amphibolite to granulite-facies, with metasedimentary rocks occurring as volumetrically minor enclaves and strands of migmatites. The Ellice River domain occurs between the western and central plutonic belts. It contains ca. 1950 Ma ultramafic to dacitic volcanic rocks and foliated Paleoproterozoic psammitic metasedimentary rocks at relatively lower grade with lower to middle amphibolite-facies metamorphic assemblages. In-situ U-Pb analyses of monazite using a combination of Sensitive High-Resolution Ion Microprobe (SHRIMP) and Electron Probe Microanalyzer (EPMA) were carried out on high-grade metasedimentary rocks from seventeen samples representing the eastern margin of the Slave Province and all major lithological domains of the TTZ. 207Pb/206Pb monazite ages from SHRIMP analysis form the foundation of this dataset, while EPMA ages are supplementary. The smaller <6µm spot size of EPMA allowed for further constraint on ages of micro-scale intra-crystalline domains in some samples. Monazite ages define four distinct Paleoproterozoic metamorphic events and one Archean metamorphic event at ca. 2580 Ma. The latter is

  5. 越南西北部大象山超高温变质岩的发现及其区域构造意义%The discovery and tectonic implication of ultrahigh-temperature metamorphic rocks in the Day Nui Con Voi, northwestern Vietnam

    Institute of Scientific and Technical Information of China (English)

    吴虎峻; 刘俊来; TRANMy Dung; NGUYEN QuangLuat; PHAMBinh; 吴文彬; 陈文; 张招崇


    . 90 ~0. 94GPa, respectively. The early stage metamorphism is featured by the occurrence of corundum + fibrolite assemblage, which marks a shift of metamorphic conditions from upper amphibolite facies to granulite facies. Meanwhile, the peak metamorphism is characterized by the spinel + quartz assemblage, which indicates an ultrahigh-temperature metamorphic condition (temperature higher than 900℃ ). On the other hand, the formation of ilmenite during retrogressive metamorphism suggests that the rocks experienced a drastic decrease in pressure after the peak metamorphic conditions. The metamorphic P-T path shows that there is an early coeval increase in temperature and pressure and a subsequent rapid increase in temperature before reaching the peak conditions. In addition, a fast isothermal decrease in pressure characterizes temperature and pressure evolution after the peak metamorphism. Such a P-T path is in accordance with the temperature and pressure evolution of anomalously heated slab due to upwelling the asthenosphere by the break-off of subducting oceanic plate during plate convergence. SIMS U-Pb dating of zircons from the ultrahigh-temperature metamorphic rocks gave a minimum age of 58Ma Therefore, it is suggested that the ultrahigh-temperature metamorphism along the Day Nui Con Voi is related to the convergence between the Indian and the Eurasian plates.

  6. Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China (United States)

    Xiao, Yuanyuan; Niu, Yaoling; Wang, Kuo-Lung; Iizuka, Yoshiyuki; Lin, Jinyan; Wang, Dong; Tan, Yulong; Wang, Guodong


    To understand the geochemistry of subduction zone metamorphism, especially the large-scale mass transfer at forearc to subarc depths, we carried out a detailed study of a ∼1.5 m size metabasaltic block with well-preserved pillow structures from the Chinese Western Tianshan high- to ultrahigh-pressure metamorphic belt. This metabasaltic block is characterized by omphacite-rich interiors gradually surrounded by abundant channelized (veins) glaucophane-rich patches toward the rims. The glaucophane-rich rims share the same peak metamorphic conditions with omphacite-rich interiors, but have experienced stronger blueschist-facies overprinting during exhumation. Representative samples from the glaucophane-rich rims and omphacite-rich interiors yield a well-defined Rb-Sr isochron age of 307 ± 23 Ma, likely representing this overprinting event. Both glaucophane-rich rims and omphacite-rich interiors show elevated K-Rb-Cs-Ba-Pb-Sr contents relative to their protolith, reflecting a large-scale enrichment of these elements and formation of abundant phengite during subduction. Compared with the omphacite-rich interiors, the glaucophane-rich rims have gained rare earth elements (REEs, >25%), U-Th (∼75%), Pb-Sr (>100%) and some transition metals like Co and Ni (25-50%), but lost P (∼75%), Na (>25%), Li and Be (∼50%); K-Rb-Cs-Ba show only 10% loss. These chemical changes would be caused by serpentinite-derived fluids during the exhumation in the subduction channel. Therefore, there are two stages of fluid action in the subduction channel. As the formation of phengite stabilizes K-Rb-Cs-Ba at the first stage, the residual fluids released from the phengite-rich metabasaltic rocks would be depleted in these elements, which are unlikely to contribute to elevated contents of these elements in arc magmas if phengite remains stable at subarc depths. In addition, the decrease of U/Pb ratios as the preferred enrichment of Pb over U in the eclogitic rocks during the first stage

  7. The petrological evidence for the uplift of ultrahigh-pressure met-amorphic rocks in root zone of the Qinling-Dabie orogenic belt

    Institute of Scientific and Technical Information of China (English)

    游振东; 韩郁菁; 张泽明


    Petrographic evidence indicates that some of the ultrahigh-pressure (UHP) eclogites in Dabie Mountains area may be evolved from epidote amphibolite fades rocks recrystallized under ultrahigh pressure conditions. The evolution of the erogenic belt had eventually resulted in the uplift of the metamorphic terrane soon after the peak metamorphic ultrahigh pressure stage of collision. During the uplift the ultrahigh-pressure metamorphic rocks were superimposed by nearly isothermal decompressive retrograde metamorphism through high-pressure (HP) edogite fades to amphibolite fades. Some of them were followed by epidote amphibolite fades and greenschist fades of metamorphism, while others were followed by epidote blueschist fades and then lowered to greenschist fades. Accompanying the retrogressive metamorphism. the rocks underwent at least 6 stages of deformation ranging from plastic to brittle character. The decompressive P-T path is also shown in the evolution of fluid inclusions: the entrapment pressure is

  8. Metamorphic evolution of the contact aureole of the Jhirgadandi pluton, Sonbhadra district,Mahakoshal mobile belt, central India

    Indian Academy of Sciences (India)

    S P Singh; Anand K Srivastava; Gopendra Kumar; S B Dwivedi


    The metamorphic evolution of the contact aureole around the Late Paleoproterozoic Jhirgadandi pluton in the eastern part of Parsoi Formation of Mahakoshal terrain, central India represents three distinct metamorphic zones, characterized by definite mineral assemblages. The contact-metamorphic event produced the peak-metamorphic mineral assemblages Bt + Qtz + Alb + Sil ± Cd ± Grt ± Mus ± Kfs in the metapelites of inner aureole, Bt + Qtz + And + Mus + Kfs + Plag ± Cd ± Chl in middle aureole and Chl + Mus + Bt ± And + Alb + Qtz ± Ep + Mt ± tourmaline in the outer aureole. The estimated P–T conditions based on detailed geothermobarometric calculations in the thermal metamorphosed rocks are 690°C/3.4 kbar, 580 ± 15°C and 487 ± 30°C in inner aureole, middle aureole and outer aureole, respectively. The variation in metamorphic condition suggests that the shallow crustal level emplacement of Jhirgadandi pluton is responsible for the overprinting of contact metamorphic assemblages (M2) in the low grade metapelites (regional metamorphism M1) of Mahakoshal Group.

  9. Assessment of fire-damaged concrete. Combining metamorphic petrology and concrete petrography

    NARCIS (Netherlands)

    Larbi, J.A.; Nijland, T.G.


    Metamorphic petrology is a branch of geology that deals with the study of changes in rocks due changing physio-chemical conditions. As conditions shift in or out of the thermodynamic stability field of phases, new phases may appear whereas others disappear. A basic approach is mapping of so-called

  10. Las facies Keuper al SW de la provincia de Soria

    Directory of Open Access Journals (Sweden)

    Hernando, S.


    Full Text Available This paper deals with the sedimentological analysis of the materials that correspond to the Keuper facies in the area situated between the Iberian Ranges and the Central System. Acording to the obtained data, two main aspects are emphasized: - During the Upper Triassic, a c1ear retreat of the roast line towards the East took place, since this area constituted the litoral zone during the sedimentation of the Rot and Muschelkalk. - Facies change lateraly from West to East as proximal alluvial Can sediments pass into facies interpreted as distal alluvial fans and continental sabkha environment.Se analizan, desde el punto de vista sedimentológico, unos materiales correspondientes a las facies Keuper entre la Cordillera Ibérica y el Sistema Central. Dos aspectos resaltan tras este análisis: - Desplazamiento de la línea de costa (que durante la sedimentación del Rot y del Muschelkalk estaba situada en esta zona hacia el Este. - Marcado cambio lateral de facies desde el Oeste hacia el Este, pasando de unas facies proximales-medias de abanico aluvial a unas facies distales y ambiente de sabkha continental.

  11. Coupling among Microbial Communities, Biogeochemistry, and Mineralogy across Biogeochemical Facies

    Energy Technology Data Exchange (ETDEWEB)

    Stegen, James C.; Konopka, Allan; McKinely, Jim; Murray, Christopher J.; Lin, Xueju; Miller, Micah D.; Kennedy, David W.; Miller, Erin A.; Resch, Charles T.; Fredrickson, Jim K.


    Physical properties of sediments are commonly used to define subsurface lithofacies and these same physical properties influence subsurface microbial communities. This suggests an (unexploited) opportunity to use the spatial distribution of facies to predict spatial variation in biogeochemically relevant microbial attributes. Here, we characterize three biogeochemical facies—oxidized, reduced, and transition—within one lithofacies and elucidate relationships among facies features and microbial community biomass, diversity, and community composition. Consistent with previous observations of biogeochemical hotspots at environmental transition zones, we find elevated biomass within a biogeochemical facies that occurred at the transition between oxidized and reduced biogeochemical facies. Microbial diversity—the number of microbial taxa—was lower within the reduced facies and was well-explained by a combination of pH and mineralogy. Null modeling revealed that microbial community composition was influenced by ecological selection imposed by redox state and mineralogy, possibly due to effects on nutrient availability or transport. As an illustrative case, we predict microbial biomass concentration across a three-dimensional spatial domain by coupling the spatial distribution of subsurface biogeochemical facies with biomass-facies relationships revealed here. We expect that merging such an approach with hydro-biogeochemical models will provide important constraints on simulated dynamics, thereby reducing uncertainty in model predictions.

  12. Plagioclase deformation in upper-greenschist facies meta-pegmatite mylonites from the Austroalpine Matsch Unit (Eastern Alps, Italy) (United States)

    Eberlei, Tobias; Habler, Gerlinde; Abart, Rainer; Grasemann, Bernhard


    Feldspars are common rock forming minerals as they are stable over a wide range of bulk rock compositions and metamorphic conditions within the Earth's crust. The deformation mechanisms of feldspar play an important role in rheological models for the crust and therefore have received considerable attention in studies on natural rocks and in experimental studies. The interaction of frictional and viscous deformation mechanisms and the onset of crystal plastic deformation in feldspars occur over a broad range of pressures and temperatures. In this work, we present new microstructural, textural and mineral chemical data of plagioclase from Permian metapegmatites within the Austroalpine Matsch Unit in Southern Tyrol (Italy). These crystalline basement rocks were deformed and metamorphosed at conditions close to the greenschist/amphibolites facies transition at 480±26°C during the Cretaceous (Habler et al., 2009). The investigated samples have been collected from meter-scale shear zones which typically occur at boundaries of lithological subunits. The southern tectonic boundary of this unit is commonly referred to as the "Vinschgau Shear Zone" (Schmid & Haas, 1989). We applied the Electron Backscatter Diffraction method to investigate the grain- and subgrain-boundaries and the nature of effective deformation mechanisms in plagioclase. Large albite porphyroclasts in the mylonitic Permian metapegmatites show grain internal traces of dissolution surfaces and the formation of new, strain-free grains with straight grain boundary segments and partly 120° grain boundary triple junctions in dilatant sites. The aggregates of new grains neither have a lattice preferred orientation nor a crystallographic orientation relation with the adjacent clast, and are characterized by the lack of grain internal deformation, suggesting that these are new precipitates rather than clast-fragments or recrystallized subgrains. Furthermore, the porphyroclasts show cracks and kinks, associated

  13. Over 400 m.y. metamorphic history of the Fennoscandian lithospheric segment in the Proterozoic (the East European Craton) (United States)

    Skridlaite, G.; Bogdanova, S.; Taran, L.; Baginski, B.; Krzeminska, E.; Wiszniewska, J.; Whitehouse, M.


    Several Palaeoproterozoic terranes in the Fennoscandian lithospheric segment of the East European Craton (EEC) evolved differently prior to their final amalgamation at c. 1.8 Ga. South-westward younging of the major tectono-thermal events characterizes the Baltic -Belarus region between the Baltic and Ukrainian Shields of the EEC. While at c.1.89-1.87 Ga and 1.85-1.84 Ga rocks of some northern and eastern terranes (Estonia, Belarus and eastern Lithuania) experienced syncollisional, moderate P metamorphism, subduction-related volcanic island arc magmatism still dominated southwestern terranes in Lithuania and Poland. The available age determinations of metamorphic zircon (SIMS/NORDSIM and TIMS methods, Stockholm, SHRIMP method, RSES, ANU, Canberra) and metamorphic monazite (TIMS, Stockholm and EPMA method, Warsaw University) allow to distinguish several metamorphic events related to major orogenic processes: - 1.90-1.87 Ga amphibolite-facies H/MP metamorphism occurred along with emplacements of juvenile TTG-type granitoids in the North Estonian and Lithuanian-Belarus terranes. They are coeval with the main accretionary growth of the crust in the Svecofennian Domain in the Baltic Shield (e.g. Lahtinen et al., 2005). - 1.84-1.79 Ga high-grade metamorphism affected sedimentary and igneous rocks in almost all the terranes and is assumed to have been related to the major aggregation of the EEC (Bogdanova et al, 2006, 2008). In the metasedimentary granulites of western Lithuania, a prograde metamorphism commenced with monazite growth prior garnet at 1.84-1.83 Ga. The sediments and mafic igneous rocks in Lithuania, felsic igneous rocks in NE Poland underwent peak metamorphism and deformation at 1.81-1.79 Ga (zircon and monazite ages). The 1.83-1.79 Ga metamorphism has the same age as a metamorphic imprint and strong shearing of the crust in central Sweden (Andersson et al., 2004). The postcollisional granulite metamorphism of mafic intrusions at 1.80-1.79 Ga in Belarus

  14. Thermal contraints on high-pressure granulite metamorphism of supracrustal rocks (United States)

    Ashwal, L. D.; Morgan, P.; Leslie, W. W.


    The circumstances leading to the formation and exposure at the Earth's surface of supracrustal granulites are examined. These are defined as sediments, volcanics, and other rock units which originally formed at the surface of the Earth, were metamorphosed to high-pressure granulite facies (T = 700-900 C, P = 5-10 kbar), and reexposed at the Earth's surface, in many cases underlain by normal thicknesses of continental crust (30-40 km). Five possible heating mechanisms to account for granulite metamorphism of supracrustal rocks are discussed: magnetic heating, thermal relaxation of perturbed temperature profiles following underthrusting of the continental crust, thermal relaxation after underthrusting of thin slivers of supracrustal rocks below continental crust of normal thickness, major preheating of the upper plate, and shear heating caused by frictional stress along the thrust plane.

  15. 华北克拉通的组成及其变质演化%Constituents and Evolution of the Metamorphic Basement of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    沈其韩; 耿元生; 宋会侠


    Precambrian metamorphic basement of North China Craton (NCC) is composed of five sets of different types of metamorphic rocks. In the formation process, the NCC experienced multiple tectonic activities, multiple magma emplacement, multiple metamorphism, different degrees of migmatization and anatexis. The rocks suffered multiple superposition of different geological processes and, therefore, the NCC has a complicated evolution history. From Archean to Late Paleoproterozoic, the NCC mainly underwent five stages of regional metamorphism. Anshan area experienced amphibolite facies metamorphism in Paleo/Meso-Archean. However, no metamorphic ages have been obtained except 3560 Ma and 3000~3300 Ma metamorphic ages obtained from TTG series. In Lushan Taihua complex of Henan, 2776~2792 Ma and 2671~2651 Ma metamorphic ages are obtained from Mesoarchean amphibolites, which represent metamorphism in early Neoarchean. Granulites-TTG series and granite-greenstone belt of Neoarchean both experienced metamorphic transformation in late Neoarchean and early Paleoproterozoic. In Paleoproterozoic, on the northern margin of the NCC, L-MP/HP granulite facies metamorphism occurred between 1965~1900 Ma and UHT metamorphism appeared locally. This metamorphism is considered to be related to the continental collision and subsequent mantle upwelling. In Late Paleoproterozoic (1890~1800 Ma), in the central and eastern NCC, high-pressure granulite facies to amphibolite facies metamorphism occurred in Jiao–Liao–Ji belt, which indicates the collision and collage of continental blocks. Different types of metamorphic rock series experienced different kinds of metamorphism, which reflect different tectonic settings. A large number of late Archean TTG rock series and planar distribution M-LP granulites are mainly located in the central-northern part of NCC. They generally have counterclockwisep-T paths, which reflect mantle plume underplating tectonic setting. Granite-greenstone series of

  16. Coal facies studies in the eastern United States

    Energy Technology Data Exchange (ETDEWEB)

    Hower, James C. [Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511-8433 (United States); Eble, Cortland F. [Kentucky Geological Survey, University of Kentucky, Lexington, KY 40506 (United States)


    Coals in the eastern United States (east of the Mississippi River) have been the subject of a number of coal facies studies, going back to the 19th century. Such studies would not necessarily fall within a strict modern classification of coal facies studies, but if a study encompassed some aspects of paleobotany, palynology, petrology, geochemistry, or sedimentology, we assumed that some data and interpretations may be of use in evaluations of the facies. References are presented, as a guide for further research, with annotation in the tables.

  17. Granulitic metamorphism in the Laouni terrane (Central Hoggar, Tuareg Shield, Algeria) (United States)

    Bendaoud, Abderrahmane; Derridj, Amel; Ouzegane, Khadidja; Kienast, Jean-Robert


    In the Laouni terrane, which belongs to the polycyclic Central Hoggar domain, various areas contain outcrops of formations showing granulite-facies parageneses. This high-temperature metamorphism was accompanied by migmatization and the emplacement of two types of magmatic suite, one of continental affinity (garnet pyroxenites and granulites with orthoferrossilite-fayalite-quartz), and the other of arc affinity (layered metanorites). Paragenetic, thermobarometric and fluid-inclusion studies of the migmatitic metapelites and metabasites make it possible to reconstruct the P- T- aH 2O path undergone by these formations. This path is clockwise in the three studied areas, being characterized by a major decompression (Tamanrasset: 10.5 kbar at 825 °C to 6 kbar at 700 °C; Tidjenouine: 7.5 kbar at 875 °C; to 3.5 kbar at 700 °C; Tin Begane: 13.5 kbar at 850 °C; to 5 kbar at 720 °C), followed by amphibolitization that corresponds to a fall of temperature (from 700 to 600 °C) and an increase in water activity (from 0.2-0.4 to almost 1). The main observed features are in favour of petrogenesis and exhumation related to the Eburnean orogeny. However, the lacks of good-quality dating work and a comparison with juvenile Pan-African formations having undergone high-pressure metamorphism, in some cases reaching the eclogite facies, do not rule out the possibility that high-temperature parageneses are locally due to Pan-African events.

  18. Using informative priors in facies inversion: The case of C-ISR method (United States)

    Valakas, G.; Modis, K.


    Inverse problems involving the characterization of hydraulic properties of groundwater flow systems by conditioning on observations of the state variables are mathematically ill-posed because they have multiple solutions and are sensitive to small changes in the data. In the framework of McMC methods for nonlinear optimization and under an iterative spatial resampling transition kernel, we present an algorithm for narrowing the prior and thus producing improved proposal realizations. To achieve this goal, we cosimulate the facies distribution conditionally to facies observations and normal scores transformed hydrologic response measurements, assuming a linear coregionalization model. The approach works by creating an importance sampling effect that steers the process to selected areas of the prior. The effectiveness of our approach is demonstrated by an example application on a synthetic underdetermined inverse problem in aquifer characterization.

  19. Metamorphism of the Basement of the Qilian Fold Belt in the Minhe-Ledu Area, Qinghai Province, NW China

    Institute of Scientific and Technical Information of China (English)

    蔡金郎; 魏光华; 王庆树


    The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammiticschists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist andmetabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz + tourmaline ±titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ±garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consistsof muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist orthose of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivinewas subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed promi-nently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experiencedmetamorphism up to temperature 606-778C and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities alongthe studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, duringwhich biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.

  20. Quantifying the impact of metamorphic reactions on strain localization in the mantle (United States)

    Huet, Benjamin; Yamato, Philippe


    Metamorphic reactions are most often considered as a passive record of changes in pressure, temperature and fluid conditions that rocks experience. In that way, they provide key constraints on the tectonic evolution of the crust and the mantle. However, natural examples show that metamorphism can also modify the strength of rocks and affect the strain localization in ductile shear zones. Hence, metamorphic reactions have an active role in tectonics by inducing softening and/or hardening depending on the involved reactions. Quantifying the mechanical effect of such metamorphic reactions is, therefore, a crucial task for determining both the strength distribution in the lithosphere and its evolution. However, the estimate of the effective strength of such polyphase rocks remains still an open issue. Some flow laws (determined experimentally) already exist for monophase aggregates and polyphase rocks for rheologically important materials. They provide good constraints on lithology-controlled lithospheric strength variations. Unfortunately, since the whole range of mineralogical and chemical rock compositions cannot be experimentally tested, the variations of strength due to in metamorphism reaction cannot be systematically and fully characterized. In order to tackle this issue, we here present the results of a study coupling thermodynamical and mechanical modeling that allows us to predict the mechanical impact of metamorphic reactions on the strength of the mantle. Thermodynamic modeling (using Theriak-Domino) is used for calculating the mineralogical composition of a typical peridotite as a function of pressure, temperature and water content. The calculated modes and flow laws parameters for monophase aggregates are then used as input of the Minimized Power Geometric model for predicting the polyphase aggregate strength. Our results are then used to quantify the strength evolution of the mantle as a function of pressure, temperature and water content in two

  1. Tectonic evolvement of metamorphic complexes at Jilin paleocontinental margin during the transition from late Archaean to early Proterozoic

    Institute of Scientific and Technical Information of China (English)

    SUN Zhongshi; DENG Jun; JIANG Yanguo; WANG Jianping; WANG Qingfei; WEI Yanguang


    The kinematics and dynamical process of tectonic evolvement of metamorphic complexes at the interim from late Archaean to early Proterozoic is one of the key problems in geosciences. For the disputation on the genesis of metamorphic complexes at the margin of Jilin palaeocontinent, this paper takes the example of Banshigou region, Jilin Province to discuss the dynamical evolution of palaeocontinent during the transition from late Archaean to early Proterozoic (2600-2000 Ma). On the time sequence, from center to palaeocontinental margin, it shows a series of dynamical movements including underplating, horizontal movement, subduction, intraplate extension and separation. And its corresponding sequence of kinematical modes is as follows: vertical movement, horizontal movement, extension and shearing in contact zone,uplift-sliding movement in paleocontinental margin and interformational sliding, resulting in such tectonite sequence, tectonic gneiss, gneissic complex, gneissic complex-mylonite, mylonite and fracture cleavage-mylonite, which consist of the main body of metamorphic complexes. Their palaeostresses are: < 20, 20.40, 21.72, 28.80 and 30.8-69.8 MPa respectively. The deformational metamorphic temperature is between hornblende and low-grade greenschist facies. The general deformational characters of Jilin palaeocontinent reflect a complete dynamic system of crust evolution, which indicates that the formation of the metamorphic complexes and the tectonic evolution are altered from vertical movement to compression to extension. It also indicates a continuous tectonic transformation from deep to shallow, and from ductile to brittle. The transformation between different dynamic mechanisms not only forms tectonic rocks, but also benefits the linking up, exchange and enrichment with rock-forming minerals and ore-forming elements.This research is helpful to classifying regional tectonic events and making further study on the evolution of palaeocontinental dynamics.

  2. A metamorphic mineral source for tungsten in the turbidite-hosted orogenic gold deposits of the Otago Schist, New Zealand (United States)

    Cave, Ben J.; Pitcairn, Iain K.; Craw, Dave; Large, Ross R.; Thompson, Jay M.; Johnson, Sean C.


    The orogenic gold deposits of the Otago Schist, New Zealand, are enriched in a variety of trace elements including Au, As, Ag, Hg, W and Sb. We combine laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) traverses and images to show that detrital rutile is the most important host mineral for W in the subgreenschist facies rocks. Furthermore, the prograde metamorphic recrystallisation of detrital rutile to titanite releases significant amounts of W (potentially 0.41 g/tonne of rock). Scheelite development closely follows the progression of this W-liberating reaction. Scheelite micrograins form early within the fabric of the rock evolving to locally and regionally sourced scheelite-bearing veins. Scheelite from syn-metamorphic veins at Fiddlers Flat and Lake Hāwea shows distinct differences in composition compared with scheelite from late-metamorphic veins at the Macraes Mine, the latter of which is enriched in REEs, Y and Sr. We suggest that the scheelite at Macraes became enriched due to the liberation of these elements during alteration of the Ca-silicate minerals epidote and titanite by the ore-forming fluid. These results are supportive of recent models for orogenic gold mineralisation in the Otago Schist, whereby prograde metamorphic recrystallisation of diagenetic or detrital metal-rich mineral phases (pyrite to pyrrhotite: Au, As, Ag, Hg and Sb; rutile to titanite: W) releases significant amounts of metals into the concurrently developing metamorphic fluids that can be subsequently focussed into regional structures and form significant tungsten-bearing orogenic gold deposits.

  3. P-T-t path of metamorphism for the Julin Group and its geodynamical implications in Yuanmou, Yunnan

    Institute of Scientific and Technical Information of China (English)


    The metamorphic complex of the Julin Group occurs in the Yuanmou area of Yunnan Province on the western margin of the Yangtze Platform, and connects with the Kangdian metamorphic complex to the north. Based on the detailed petrographic observations and studies of garnet growth zoning, a P-T-t path has been reconstructed for the staurolite-kyanite zone in the Julin Group. This path is characterized by (1) a counter-clockwise evolutional trend, (2) a quicker increase of temperature than that of pressure in the initial prograde metamorphism, but slower near the peak, then temperature and pressure simultaneously reaching the peak metamorphic conditions, and (3) a slow near-isobaric cooling during the retrograde process. The P-T-t path for prograde metamorphism is closely related to magmatic accretion in the arc setting. The magmatic accretion model, metamorphism type and tectonic setting may be compared with the global Grenville tectono-metamorphic events, and related to the assembly of the Rodinia at the late Meso-proterozoic-early Neoproterozoic (~1.0 Ga). The retrograde P-T-t path shows a slow near-isobaric cooling, indicating sustained heat supplies from the upper mantle and no rapid erosion. This heat source may be originated from the Neoproterozoic (~0.82 Ga) breakup of the Rodinia.

  4. Mineralogy and geochemistry of the main glauconite bed in the Middle Eocene of Texas: paleoenvironmental implications for the verdine facies.

    Directory of Open Access Journals (Sweden)

    Sherie C Harding

    Full Text Available The Main Glauconite Bed (MGB is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14Å diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA from the average of 31 data points from clay pellets accompanied with Mössbauer analyses were used to calculate the structural formula which is that of odinite: Fe(3+ 0.89 Mg0.45 Al0.67 Fe(2+ 0.30 Ti0.01 Mn0.01 Σ = 2.33 (Si1.77 Al0.23 O5.00 (OH4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions.

  5. Mineralogy and geochemistry of the main glauconite bed in the Middle Eocene of Texas: paleoenvironmental implications for the verdine facies. (United States)

    Harding, Sherie C; Nash, Barbara P; Petersen, Erich U; Ekdale, A A; Bradbury, Christopher D; Dyar, M Darby


    The Main Glauconite Bed (MGB) is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14Å diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA) from the average of 31 data points from clay pellets accompanied with Mössbauer analyses were used to calculate the structural formula which is that of odinite: Fe(3+) 0.89 Mg0.45 Al0.67 Fe(2+) 0.30 Ti0.01 Mn0.01) Σ = 2.33 (Si1.77 Al0.23) O5.00 (OH)4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions.

  6. Mineralogy and Geochemistry of the Main Glauconite Bed in the Middle Eocene of Texas: Paleoenvironmental Implications for the Verdine Facies (United States)

    Harding, Sherie C.; Nash, Barbara P.; Petersen, Erich U.; Ekdale, A. A.; Bradbury, Christopher D.; Dyar, M. Darby


    The Main Glauconite Bed (MGB) is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14Å diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA) from the average of 31 data points from clay pellets accompanied with Mössbauer analyses were used to calculate the structural formula which is that of odinite: Fe3+0.89 Mg0.45 Al0.67 Fe2+0.30 Ti0.01 Mn0.01) Σ = 2.33 (Si1.77 Al0.23) O5.00 (OH)4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions. PMID:24503875

  7. Structural and metamorphic evolution of the Turku migmatite complex, southwestern Finland

    Directory of Open Access Journals (Sweden)

    Väisänen, M.


    Full Text Available The Turku migmatite complex in southwestern Finland is a representative area for the type of tectonic and metamorphic evolution seen within the Palaeoproterozoic Svecofennian Orogen in southern Finland. The orogeny can be divided into early, late and postorogenic stages. The early orogenic structural evolution of the crust is expressed by a D1/D2 deformation recorded as bedding-parallel S1 mica foliation deformed by tight to isoclinal D2 folds with subhorizontal axial planes and a penetrative S2 axial plane foliation. Syntectonic ca. 1890-1870 Ma tonalites were emplaced during D2 as sheet intrusions. This deformation is attributed to thrust tectonics and thickening of the crust. The late orogenic structural evolution produced the main D3 folding, which transposed previous structures into a NE-SW trend. The doubly plunging fold axis produced dome-and-basin structures. The attitude of the F3 folds varies from upright or slightly overturned to locally recumbent towards the NW. Granite dikes were intruded along S3 axial planes. Large D3 fold limbs are often strongly deformed, intensively migmatized and intruded by garnet- and cordierite-bearing granites. These observations suggest that these potassium-rich granites, dated at 1840-1830 Ma, were emplaced during D3. This late orogenic NW-SE crustal shortening further contributed to crustal thickening. Subvertical D4 shear zones that cut all previous rock types possibly controlled the emplacement of postorogenic granitoids. Steeply plunging lineations on D4 shear planes suggest vertical displacements during a regional uplift stage. Metamorphic grade increases from cordierite-sillimanite-K-feldspar gneisses in the northwest and from muscovite-quartz±andalusite rocks in the southeast to high-temperature granulite facies migmatites in the middle of the study area. Block movements during D4 caused the observed differences in metamorphic grade. Garnet and cordierite are mostly breakdown products of biotite

  8. Geochronological evidence of Indosinian(high-pressure) metamorphic event and its tectonic significance in Taxkorgan area of the Western Kunlun Mountains,NW China

    Institute of Scientific and Technical Information of China (English)


    The CL images,LA-ICP-MS in situ trace elements analysis,and U-Pb dating for zircons indicate that the metamorphic ages of the sillimanite-garnet-biotite gneiss and the garnet-amphibole gneiss from eastern Taxkorgan of the Western Kunlun Mountains are 220±2 and 220±3 Ma respectively,and their protolith ages are younger than 253±2 and 480±8 Ma respectively.Two samples were collected at the same outcrops with HP mafic granulite and HP pelitic granulite.Mineral assemblage of the sillimanite-garnet-biotite gneiss(Grt+Sill+Per+Q) is consistent with that of HP pelitic granulite at early high amphibolite-granulite facies stage.Mineral assemblage of the garnet-amphibole gneiss(Grt+Amp+Pl+Q) is consistent with retro-metamorphic assemblage of HP mafic granulite at amphibolite facies stage.The dating results suggest that these HP granulites underwent peak metamorphism at 220±2 to 253±2 Ma.Thus,the Kangxiwar tectonic zone was probably formed by subduction and collision of the Paleo-Tethys Ocean during Indosinian.Protolith ages of the two samples,together with previously published U-Pb zircon dating age,suggest that the sillimanite-garnet schist-quartzite unit is a late Paleozoic unit,not a part of the Paleoproterozoic Bulunkuole Group.

  9. P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications

    Institute of Scientific and Technical Information of China (English)

    HU Daogong; WU Zhenhan; JIANG Wan; YE Peisheng


    Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (Mi) is preserved only in the granulites and represented by plagioclase+homblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of gamet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of horublende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of homblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of gamet+clinopyroxene+plagioclase+homblende were estimated at 769-905°C and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800°C and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708°C and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.

  10. Sedimentary Facies Models on Carbonatite in the Upper Shuaiba Member of Lower Cretaceous in Daleel Field, Oman

    Institute of Scientific and Technical Information of China (English)

    Wang Feng; Jiang Zaixing; Zhou Liqing; Zhao Guoliang; Wang Lin; Zheng Ning; Xiang Shu'an


    The Upper Shuaiba Member (USH) is the main force pay bed in the Daleel field in northern Oman; 5 layers including A, B, C, D, and E were divided in profile, and layer D and layer E are the main beds. With the development of exploration in the Daieel oil field, studying the sedimentary systems about their inner composition and the collocation in dimension, and setting up the sedimentary models in the USH are becoming more and more necessary and important to meet the further exploration requirement. Based on the data of geology, seism, and paleo-biology, according to the analysis method on carbonatite depositional system, the litho-facies assemblage and sedimentary environment in the USH were studied. Intershoal low-lying sub-facies (where the water depth is 10-50 m) and shallow shoal sub-facies (where the water depth is not more than 10 m) were extinguished in the layer D, and storm deposit was found in layer E1, in which intershoal low-lying sub-facies also developed. The feature of the sedimentary sub-facies and the sedimentary condition were analyzed, and the sedimentary model was set up in the article: the carbonatite intershoal low-lying developed under the background of open land in shallow sea, where storm events usually occurred in the Lower Cretaceous in the area.

  11. Evolución metamórfica de los gabros coroníticos de El Arenal, faja máfica-ultramáfica El Destino-Las Águilas, sierra de San Luis Metamorphic evolution of the coronitic gabbrons of the El Arenal, El Destino-Las Aguilas, mafic-ultramafic belt, Sierra de San Luis

    Directory of Open Access Journals (Sweden)

    N. Brogioni


    Sierra de San Luis. They are fine-grained rocks with corona microstructures around Mg-rich olivine and An-rich plagioclase which record three metamorphic stages of mineral crystallization developed under granulite, amphibolite and greenschist P-T conditions. The coronitic meta-melagabbros represent early, high Cr-Ni fractions, with [Mg++/Mg+++FeT++] comprised between 0.72 and 0.75, derived from a low-Ti olivine tholeiitic magma which emplaced before the penetrative Famatinian deformation and the widespread coeval metamorphism. The subsequent uplift and the slow cooling of the deep-seated magma was possible because of the high P-T conditions of the crustal level, ca. amphibolite facies, and result in the development of the coronas after an early slightly deuteric alteration of the primary, now preserved as relics, igneous minerals. When granulite facies conditions were reached Mg-rich olivine and Ca-rich plagioclase became unstable and reacted to form orthopyroxene and symplectitic clinopyroxene + spinel around olivine. H2O-rich fluids necessary for the amphibole crystallization, which formed symplectite intergrowths with spinel and also replaced relic orthopyroxene during the amphibolite stage, were provided by dehydration of the adjacent country rocks caused by the development of metamorphic reactions. Minerals formed under greenschist P-T conditions were probably related with the final exhumation of the rocks, and are thought to represent the last part of the counterclockwise evolutionary path followed by the melagabbronites during the early Palaeozoic times.

  12. Fine-Grained Turbidites: Facies, Attributes and Process Implications (United States)

    Stow, Dorrik; Omoniyi, Bayonle


    Within turbidite systems, fine-grained sediments are still the poor relation and sport several contrasting facies models linked to process of deposition. These are volumetrically the dominant facies in deepwater and, from a resource perspective, they form important marginal and tight reservoirs, and have great potential for unconventional shale gas, source rocks and seals. They are also significant hosts of metals and rare earth elements. Based on a large number of studies of modern, ancient and subsurface systems, including 1000s of metres of section logging, we define the principal genetic elements of fine-grained deepwater facies, present a new synthesis of facies models and their sedimentary attributes. The principal architectural elements include: non-channelised slope-aprons, channel-fill, channel levee and overbank, turbidite lobes, mass-transport deposits, contourite drifts, basin sheets and drapes. These comprise a variable intercalation of fine-grained facies - thin-bedded and very thin-bedded turbidites, contourites, hemipelagites and pelagites - and associated coarse-grained facies. Characteristic attributes used to discriminate between these different elements are: facies and facies associations; sand-shale ratio, sand and shale geometry and dimensions, sand connectivity; sediment texture and small-scale sedimentary structures; sediment fabric and microfabric; and small-scale vertical sequences of bed thickness. To some extent, we can relate facies and attribute characteristics to different depositional environments. We identify four distinct facies models: (a) silt-laminated mud turbidites, (b) siliciclastic mud turbidites, (c) carbonate mud turbidites, (d) disorganized silty-mud turbidites, and (e) hemiturbidites. Within the grainsize-velocity matrix turbidite plot, these all fall within the region of mean size < 0.063mm, maximum grainsize (one percentile) <0.2mm, and depositional velocity 0.1-0.5 m/s. Silt-laminated turbidites and many mud

  13. Early Tertiary subsidence and sedimentary facies - northern Sirte Basin, Libya

    Energy Technology Data Exchange (ETDEWEB)

    Gumati, Y.D.; Kanes, W.H.


    The subsidence curves and subsidence rate curves for the Sirte basin, constructed from the stratigraphic record, show that subsidence was continuous throughout Late Cretaceous and Tertiary times, reaching a maximum during the Paleocene and Eocene, when a major reactivation of faults occurred. Shales and carbonates were deposited during all of the Late Cretaceous and Tertiary. Abrupt lateral facies changes occur from the platform areas toward the deeper troughs along with steep downdip thickening. These conditions were probably assisted by contemporaneous faulting along structurally weak hinge lines where the dominant structural elements are normal step faults. The absence of upper Paleozoic and lower Mesozoic sediments suggests that the area was domed, faulted, and eroded during the late Mesozoic. As a result of crustal extension during the Paleocene, a marked lithologic and structural change occurred. The Heira Shale succeeded the Kalash Limestone in the Marada trough. Reactivation of the earlier faults, accompanied by an increase in the sediment supply from the south, caused these lower Paleocene shales to cover the entire area, with the exception of the old highs where carbonate deposition continued. An intercalation of shales and carbonates provides a sensitive indicator of change of depth and sediment type.

  14. Middle Eocene seagrass facies from Apennine carbonate platforms (Italy) (United States)

    Tomassetti, Laura; Benedetti, Andrea; Brandano, Marco


    Two stratigraphic sections located in the Latium-Abruzzi (Monte Porchio, Central Apennines, Central Italy) and in the Apulian carbonate platform (S. Cesarea-Torre Tiggiano, Salento, Southern Italy) were measured and sampled to document the sedimentological characteristic and the faunistic assemblages of Middle Eocene seagrass deposits. The faunistic assemblages are dominated by porcellaneous foraminifera Orbitolites, Alveolina, Idalina, Spiroloculina, Quinqueloculina, Triloculina and abundant hooked-shaped gypsinids, associated with hooked red algae and green algae Halimeda. Fabiania, rotaliids and textulariids as well as nummulitids are subordinated. The samples were assigned to Lutetian (SBZ13-16) according to the occurrence of Nummulites cf. lehneri, Alveolina ex. gr. elliptica, Idalina berthelini, Orbitolites complanatus, Slovenites decastroi and Medocia blayensis. At Santa Cesarea reticulate nummulites occur in association with Alveolina spp. and Halkyardia minima marking the lower Bartonian (SBZ17). Three main facies associations have been recognised: I) larger porcellaneous foraminiferal grainstones with orbitolitids and alveolinids deposited into high-energy shallow-water settings influenced by wave processes that reworked the sediments associated with a seagrass; II) grainstone to packstone with small porcellaneous foraminifera and abundant permanently-attached gypsinids deposited in a more protected (e.g., small embayment) in situ vegetated environment; III) bioclastic packstone with parautochthonous material reworked from the seagrass by rip currents and accumulated into rip channels in a slightly deeper environment. The biotic assemblages suggest that the depositional environment is consistent with tropical to subtropical vegetated environments within oligotrophic conditions.

  15. Mid-crustal shear zone development under retrograde conditions: pressure-temperature-fluid constraints from the Kuckaus Mylonite Zone, Namibia (United States)

    Diener, Johann F. A.; Fagereng, Åke; Thomas, Sukey A. J.


    The Kuckaus Mylonite Zone (KMZ) forms part of the larger Marshall Rocks-Pofadder shear zone system, a 550 km-long, crustal-scale strike-slip shear zone system that is localized in high-grade granitoid gneisses and migmatites of the Namaqua Metamorphic Complex. Shearing along the KMZ occurred ca. 40 Ma after peak granulite-facies metamorphism during a discrete tectonic event and affected the granulites that had remained at depth since peak metamorphism. Isolated lenses of metamafic rocks within the shear zone allow the P-T-fluid conditions under which shearing occurred to be quantified. These lenses consist of an unsheared core that preserves relict granulite-facies textures and is mantled by a schistose collar and mylonitic envelope that formed during shearing. All three metamafic textural varieties contain the same amphibolite-facies mineral assemblage, from which calculated pseudosections constrain the P-T conditions of deformation at 2.7-4.2 kbar and 450-480 °C, indicating that deformation occurred at mid-crustal depths through predominantly viscous flow. Calculated T-MH2O diagrams show that the mineral assemblages were fluid saturated and that lithologies within the KMZ must have been rehydrated from an external source and retrogressed during shearing. Given that the KMZ is localized in strongly dehydrated granulites, the fluid must have been derived from an external source, with fluid flow allowed by local dilation and increased permeability within the shear zone. The absence of pervasive hydrothermal fractures or precipitates indicates that, even though the KMZ was fluid bearing, the fluid/rock ratio and fluid pressure remained low. In addition, the fluid could not have contributed to shear zone initiation, as an existing zone of enhanced permeability is required for fluid infiltration. We propose that, following initiation, fluid infiltration caused a positive feedback that allowed weakening and continued strain localization. Therefore, the main

  16. Reaction induced nucleation and growth v. grain coarsening in contact metamorphic, impure carbonates

    DEFF Research Database (Denmark)

    Berger, Alfons; Brodhag, Sabine; Herwegh, Marco


    aureole of the Adamello pluton (N-Italy). As a function of increasing distance from the pluton contact, the investigated samples have peak metamorphic temperatures ranging from the stability field of diopside/tremolite down to diagenetic conditions. All samples consist of calcite as the dominant matrix...

  17. Heat transfer by fluids in granulite metamorphism (United States)

    Morgan, Paul; Ashwal, Lewis D.


    The thermal role of fluids in granulite metamorphism was presented. It was shown that for granulites to be formed in the middle crust, heat must be advected by either magma or by volatile fluids, such as water or CO2. Models of channelized fluid flow indicate that there is little thermal difference between channelized and pervasive fluid flow, for the same total fluid flux, unless the channel spacing is of the same order or greater than the thickness of the layer through which the fluids flow. The volumes of volatile fluids required are very large and are only likely to be found associated with dehydration of a subducting slab, if volatile fluids are the sole heat source for granulite metamorphism.

  18. Shape Metamorphism Using p-Laplacian Equation

    Energy Technology Data Exchange (ETDEWEB)

    Cong, Ge; Esser, Mehmet; Parvin, Bahram; Bebis, George


    We present a new approach for shape metamorphism, which is a process of gradually changing a source shape (known) through intermediate shapes (unknown) into a target shape (known). The problem, when represented with implicit scalar function, is under-constrained, and regularization is needed. Using the p-Laplacian equation (PLE), we generalize a series of regularization terms based on the gradient of the implicit function, and we show that the present methods lack additional constraints for a more stable solution. The novelty of our approach is in the deployment of a new regularization term when p --> infinity which leads to the infinite Laplacian equation (ILE). We show that ILE minimizes the supremum of the gradient and prove that it is optimal for metamorphism since intermediate solutions are equally distributed along their normal direction. Applications of the proposed algorithm for 2D and 3D objects are demonstrated.

  19. Re-equilibration history and P- T path of eclogites from Variscan Sardinia, Italy: a case study from the medium-grade metamorphic complex (United States)

    Cruciani, Gabriele; Franceschelli, Marcello; Groppo, Chiara; Oggiano, Giacomo; Spano, Maria Elena


    Retrogressed eclogites are hosted within the Variscan low- to medium-grade metamorphic complex near Giuncana, north-central Sardinia. These rocks are medium to fine grained with garnet and amphibole as the most abundant mineral phases along with clinopyroxene, plagioclase, quartz, biotite, chlorite, epidote, ilmenite, rutile and titanite. Four stages of mineralogical re-equilibration have been distinguished. The stage I is characterized by the occurrence of omphacite, epidote, quartz, amphibole, rutile and ilmenite in garnet poikiloblasts. The stage II is characterized by two types of symplectitic microstructures: (1) amphibole + quartz symplectite and (2) clinopyroxene + plagioclase ± amphibole symplectite. The first symplectite type replaces omphacite included in garnet, whereas the second one is widespread in the matrix. Biotite droplets and/or lamellae intimately growing with fine-grained plagioclase resemble biotite + plagioclase symplectite after phengite. The stage III is characterized by the widespread formation of amphibole: (1) as zoned porphyroblasts in the matrix, (2) as corona-type microstructure replacing garnet. Subordinate plagioclase (oligoclase) is also present in the amphibole corona. The stage IV is characterized by the local formation of biotite replacing garnet, actinolite, chlorite, albite and titanite. P- T pseudosections calculated with Perple_X give P- T conditions 580 < T < 660 °C, 1.3 < P < 1.8 GPa for the stage I. After the stage I, pressure decrease and temperature increase led to the breakdown of omphacite with the formation of clinopyroxene + plagioclase ± amphibole symplectite at ~1.25-1.40 GPa and 650-710 °C (stage II). P- T conditions of the amphibolite-facies stage III have been defined at 600-670 °C, P = 0.65-0.95 GPa. P- T conditions of the latest stage IV are in the range of greenschist facies. The P- T path of the retrogressed eclogite hosted in the medium-grade micaschist and paragneiss of Giuncana recalls the P- T

  20. Genetic Types of Meter-Scale Cyclic Sequences and Fabric Natures of Facies Succession

    Institute of Scientific and Technical Information of China (English)


    Different genetic types of meter-scale cyclic sequences in stratigraphic records result from episodic accumulation of strata related to Milankovitch cycles. The distinctive fabric natures of facies succession result from the sedimentation governed by different sediment sources and sedimentary dynamic conditions in different paleogeographical backgrounds, corresponding to high-frequency sea-level changes. Naturally, this is the fundamental criterion for the classification of genetic types of meter-scale cyclic sequences. The widespread development in stratigraphic records and the regular vertical stacking patterns in long-term sequences, the evolution characters of earth history and the genetic types reflected by specific fabric natures of facies successions in different paleogeographical settings, all that show meterscale cyclic sequences are not only the elementary working units in stratigraphy and sedimentology, but also the replenishment and extension of parasequence of sequence stratigraphy. Two genetic kinds of facies succession for meter-scale cyclic sequence in neritic-facies strata of carbonate and clastic rocks, are normal grading succession mainly formed by tidal sedimentation and inverse grading succession chiefly made by wave sedimentation, and both of them constitute generally shallowing upward succession, the thickness of which ranges from several tens of centimeters to several meters. The classification of genetic types of meter-scale cyclic sequence could be made in terms of the fabric natures of facies succession, and carbonate meter-scale cyclic sequences could be divided into four types: L-M type, deep-water asymmetrical type, subtidal type and peritidal type. Clastic meter-scale cyclic sequences could be grouped into two types: tidal-dynamic type and wave-dynamic type. The boundaries of meter-scale cyclic sequences are marked by instantaneous punctuated surface formed by non-deposition resulting from high-frequency level changes, which include


    Institute of Scientific and Technical Information of China (English)


    The concept of metamorphic mechanisms is presented, configuration models and configuration transformations relating to a set of new matrix operations are discussed and proposed. The configuration of a m etamorphic mechanism reflects the connectivity change in the mechanism during motions which r esults in mobility change and presents the characteristics of the mechanism which is discussed in various applications particularly in decorative artifacts. The characteristics is further investigated with mobility analysis.

  2. Recent Advances in Characterizing Depositional Facies and Pore Network Modeling in Context of Carbon Capture Storage: An Example from the Cambrian Mt. Simon Sandstone in the Illinois Basin (United States)

    Freiburg, J. T.; Nathan, W.; Best, J.; Reesink, A.; Ritzi, R. W., Jr.; Pendleton, J.; Dominic, D. F.; Tudek, J.; Kohanpur, A. H.


    In order to understand subsurface flow dynamics, including CO2 plume migration and capillary trapping, a diverse set of geologic properties within the reservoir, from the pore scale to the basin scale, must be understood and quantified. The uncertainty about site-specific geology stems from the inherent variation in rock types, depositional environments, and diagenesis. In collaboration with geocellular and multiphase modeling, detailed characterization of the Lower Mt. Simon Sandstone (LMSS), a reservoir utilized for carbon capture storage, is supporting data-driven conceptual models to better understand reservoir heterogeneity and its relationship to reservoir properties. This includes characterization of sedimentary facies and pore scale modeling of the reservoir The Cambrian-age Lower Mt. Simon Sandstone (LMSS) is a reservoir utilized for two-different carbon capture storage projects in the Illinois Basin, USA. The LMSS is interpreted to have formed in a braided river environment comprising a hierarchy of stratification, with larger scale depositional facies comprising assemblages of smaller scale facies. The proportions, geometries, length scales, and petrophysical attributes of the depositional facies, and of the textural facies they comprise, are being quantified. Based on examination of core and analog outcrop in adjacent areas, the LMSS is comprised of five dominant depositional facies, the most abundant facies being planar to trough cross-bedded sandstones produced by subaqueous sand dunes. This facies has the best reservoir conditions with porosity up to 27% and permeability up to 470 mD. Three-dimensional pore network modeling via micro computed tomography of this facies shows well-connected and unobstructed pore throats and pore space. This presentation will outline the depositional heterogeneity of the LMSS, its relationship to diagenetic fabrics, and its influence on fluid movement within the reservoir.

  3. Giants, dwarfs and the environment - metamorphic trait plasticity in the common frog.

    Directory of Open Access Journals (Sweden)

    Franziska Grözinger

    Full Text Available In order to understand adaptation processes and population dynamics, it is central to know how environmental parameters influence performance of organisms within populations, including their phenotypes. The impact of single or few particular parameters in concert was often assessed in laboratory and mesocosm experiments. However, under natural conditions, with many biotic and abiotic factors potentially interacting, outcomes on phenotypic changes may be different. To study the potential environmental impact on realized phenotypic plasticity within a natural population, we assessed metamorphic traits (developmental time, size and body mass in an amphibian species, the European common frog Rana temporaria, since a larval amphibians are known to exhibit high levels of phenotypic plasticity of these traits in response to habitat parameters and, b the traits' features may strongly influence individuals' future performance and fitness. In 2007 we studied these metamorphic traits in 18 ponds spread over an area of 28 km2. A subset of six ponds was reinvestigated in 2009 and 2010. This study revealed locally high variances in metamorphic traits in this presumed generalist species. We detected profound differences between metamorphing froglets (up to factor ten; both between and within ponds, on a very small geographic scale. Parameters such as predation and competition as well as many other pond characteristics, generally expected to have high impact on development, could not be related to the trait differences. We observed high divergence of patterns of mass at metamorphosis between ponds, but no detectable pattern when metamorphic traits were compared between ponds and years. Our results indicate that environment alone, i.e. as experienced by tadpoles sharing the same breeding pond, can only partly explain the variability of metamorphic traits observed. This emphasizes the importance to assess variability of reaction norms on the individual level to

  4. Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan resion

    Institute of Scientific and Technical Information of China (English)

    LIU ZhengHong; XU ZhongYuan; WANG KeYong


    Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typical microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz ribbons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are obviously different from inclusions captured at granulite facies, in both fluid compositions and T-P estimations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.


    Institute of Scientific and Technical Information of China (English)

    Michael; Brown


    Granulite facies ultrahigh temperature metamorphism (G - UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G - UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G - UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G - UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite-high-pressure granulite metamorphism (E - HPGM) also is first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E - HPGM belts are complementary to G - UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM - UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM - UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts-reflecting a duality of thermal regimes-appears in the record only since the Neoarchean

  6. Zircon U-Pb Dating of Yushugou Terrain of High-Pressure Granulite Facies in Southern Tianshan Mountain and Its Geological SIgnificance

    Institute of Scientific and Technical Information of China (English)


    The Yushugou terrain of high-pressure granulite facies in southern Tianshan Mountain is composed mainly of an ophiolite suite.Most selected zirocons are round or elliptical in shape,and some are of tetragonal prism with round edges.The granulometric analyses show that they are well sorted in sedimentation.ZrO2/HfO2 ratios in zircons range from 45 to 57.these characters,together with the petrologic and geochemical characters of plagioclase-garnet-orthopyroxenite bearing zircons,indicate that the protolith of plagioclase-garnet-orthopyroxenite may be derived mainly from volcanic base surge sedimentary debris in oceanic islands and from clays formed by seafloor weathering.Zircons are simply of pyroclastic debris.The ophiolite formation age of (440±18)Ma and the first-stage metamorphic age(amphibolite or granulite facies) of (364±5) Ma were obtained with a method of multiple grains in different groups and a method of concordia plot.These ages provide important information on the temporal and spatial occurrence of southern Paleoxoic Tianshan Ocean,The subduction rate of the oceanic crust and the formation mechanism of ophiolite of granulite facies.

  7. High-grade contact metamorphism in the Reykjanes geothermal system: Implications for fluid-rock interactions at mid-oceanic ridge spreading centers (United States)

    Marks, Naomi; Schiffman, Peter; Zierenberg, Robert A.


    Granoblastic hornfels identified in cuttings from the Reykjanes seawater-dominated hydrothermal system contains secondary pyroxene, anorthite, and hornblendic amphibole in locally equilibrated assemblages. Granoblastic assemblages containing secondary orthopyroxene, olivine, and, locally, cordierite and spinel occur within groups of cuttings that show dominantly greenschist facies hydrothermal alteration. Granoblastic plagioclase ranges continuously in composition from An54 to An96, in contrast with relict igneous plagioclase that ranges from An42 to An80. Typical hydrothermal clinopyroxene compositions range from Wo49En3Fs48 to Wo53En30Fo17; clinopyroxene from the granoblastic grains is less calcic with an average composition of Wo48En27Fs25. The hornfels is interpreted to form during contact metamorphism in response to dike emplacement, resulting in local recrystallization of previously hydrothermally altered basalts. Temperatures of granoblastic recrystallization estimated from the 2-pyroxene geothermometer range from 927°C to 967°C. Redox estimates based on the 2-oxide oxybarometer range from log fO2 of -13.4 to -15.9. Granoblastic hornfels comprised of clinopyroxene, orthopyroxene, and calcic plagioclase have been described in a number of ancient hydrothermal systems from the conductive boundary layer between the hydrothermal system and the underlying magma source, most notably in Integrated Ocean Drilling Program Hole 1256D, Ocean Drilling Program Hole 504B, and in the Troodos and Oman ophiolites. To our knowledge, this is the first evidence of high-grade contact metamorphism from an active geothermal system and the first description of equilibrated amphibole-absent pyroxene hornfels facies contact metamorphism in any mid-ocean ridge (MOR) hydrothermal system. This contribution describes how these assemblages develop through metamorphic reactions and allows us to predict that higher-temperature assemblages may also be present in MOR systems.

  8. Potential links between porphyry copper deposits and exhumed metamorphic basement complexes in northern Chile (United States)

    Cooper, Frances; Docherty, Alistair; Perkins, Rebecca


    Porphyry copper deposits (PCDs) are typically associated with magmatic arcs in compressional subduction zone settings where thickened crust and fractionated calc-alkaline magmas produce favourable conditions for copper mineralisation. A classic example is the Eocene-Oligocene PCD belt of Chile, the world's leading copper producing country. In other parts of the world, older late Cretaceous to early Tertiary PCDs are found in regions of former subduction-related magmatism that have undergone subsequent post-orogenic crustal extension, such as the Basin and Range province of western North America, and the Eurasian Balkan-Carpathian-Dinaride belt. In the Basin and Range there is a striking correlation between the location of many PCDs and exhumed metamorphic core complexes (isolated remnants of the middle to lower crust exhumed during extensional normal faulting). This close spatial relationship raises questions about the links between the two. For example, are their exhumation histories related? Could the presence of impermeable metamorphic rocks at depth affect and localise mineralising fluids? In Chile there appears to be a similar spatial relationship between PCDs and isolated outcrops of exhumed metamorphic basement. In northern Chile, isolated exposures of high-grade metamorphic gneisses and amphibolites are thought to be exhumed remnants of the pre-subduction Proterozoic-Paleozoic continental margin of Gondwana [2], although little is known about when they were exhumed and by what mechanism. For example, the Limón Verde metamorphic complex, exhumed from a depth of ca. 50 km, is situated adjacent to Chuquicamata, the largest open pit copper mine in the world. In northernmost Chile, another metamorphic exposure, the Belén complex, sits close to the Dos Hermanos PCD, a small deposit that is not actively mined. Comprising garnet-bearing gneisses and amphibolites, the Belén is thought to have been exhumed from a depth of ca. 25 km, but when and how is unclear [3

  9. Unraveling eclogite-facies fluid-rock interaction using thermodynamic modelling and whole-rock experiments: the in-situ eclogitization of metapelites from Val Savenca (Sesia Zone, Western Alps) (United States)

    Jentsch, Marie; Tropper, Peter


    A common feature of HP and UHP terranes is the subduction of crustal rocks to great depths. Previous investigations have shown that this process is triggered by fluids present during an eclogite-facies metamorphic overprint. An examples is exposed in the metapelites at Val Savenca in the Sesia-Lanzo Zone, Italy where Alpine eclogite-facies metamorphism and fluid flow led to partial transformation of Variscan amphibolite-eclogite facies metapelites (garnet + biotite + sillimanite + K-feldspar + plagioclase + quartz) to zoisite ± jadeite + kyanite + phengite + quartz. This transformation took place under P-T conditions of 1.7 - 2.1 GPa at 600°C and low a(H2O) of 0.3-0.6. The replacement of plagioclase by jadeite + zoisite + kyanite + quartz takes place also along former fractures. Biotite is replaced by the assemblage phengite + omphacite ± kyanite adjacent to former plagioclase, otherwise by phengite + rutile/titanite. Garnet and clinopyroxene show variable compositions depending in which micro-domain (plagioclase or biotite) they grew. The extreme development of microdomains can best be studied by thermodynamic pseudosection modelling of individual microdomains using stoichiometric mixtures of protolith minerals from this domain and the program DOMINO (De Capitani & Petrakakis, 2010). The aim of these calculations was: 1.) to reproduce the observed mineral assemblage and 2.) to provide constraints on the amount of fluid present in the transformation. The results so far indicate that the amount of fluid was very low, otherwise paragonite would have formed instead of jadeite and reproduction of the observed mineral assemblage has only been partly successful so far since biotite is still stable in the calculations. In addition to understand the role of fluids in the mineralogical and textural transformation piston-cylinder experiments with a fresh, natural orthogneiss granulite from the Moldanubic Unit in upper Austria with the assemblage garnet + biotite + K

  10. X-ray color maps of the zoned garnets from Silgará Formation metamorphic rocks,SantanderMassif, Eastern Cordillera (Colombia

    Directory of Open Access Journals (Sweden)

    Takasu Akira


    Full Text Available

    The metamorphic rocks of the Lower Paleozoic Silgará Formation of the Santander Massif, Eastern Cordillera (Colombia, were affected by a Barrovian-type metamorphism under low to high temperature and medium pressure conditions. These rocks contain garnet porphyroblasts, which show several kinds of chemical zoning patterns. The garnet grains behave as closed systems with respect to the rock matrix. Most of the observed zoning patterns are due to gradual changes in physicochemical conditions during growth. However, some garnet grains show complex zoning patterns during multiple deformation and metamorphic events.

  11. Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite (United States)

    Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.


    High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

  12. Plate tectonics. Seismological detection of slab metamorphism. (United States)

    Julian, Bruce


    The occurrence of more or less continuous ground vibrations ("volcanic tremor") is an important indicator of volcanic activity. But results from the "Hi-net" seismic network in Japan reported by Obara show that continuous ground vibrations can occur far away from any volcanic activity. In his Perspective, Julian discusses the idea that this tremor is excited by flow of metamorphic fluids. He also identifies other possible locations where such a tremor may be detected and explains what may be learnt from measuring it.

  13. Measuring metamorphic history of unequilibrated ordinary chondrites (United States)

    Sears, D. W.; Grossman, J. N.; Melcher, C. L.; Ross, L. M.; Mills, A. A.


    Measurements performed by a thermoluminescence sensitivity technique of the degree of metamorphism experienced by unequilibrated ordinary chondrites are reported. Samples of type 3 chondrites were ground and heated to 500 C to remove their natural thermoluminescence, then irradiated with either 50 krad from a Co-60 gamma ray source or 25 krad from a Sr-90 beta source. The resulting thermoluminescence measured as a function of temperature is found to differ as much among some type 3 chondrites as between type 3 and other types, leading to the proposal of scheme for subdividing type 3 ordinary chondrites based on their thermoluminescence sensitivity.

  14. Chemical mobility during low-grade metamorphism of a Jurassic lava flow: Río Grande Formation, Peru (United States)

    Aguirre, L.

    Chemical and mineralogical changes produced by very low-grade metamorphism in a 40 meter thick, K-rich, calc-alkaline andesite flow of the marine Jurassic Río Grande Formation of southern coastal Peru are discussed. This metamorphism (=spilitization) was non-deformational and generated spilitic domains at (and near) both vesicular margins of the flow, whereas the massive central zone remained relatively unaltered. The metadomains are characterized by mineral associations of the zeolite facies. Primary minerals are Ca-plagioclase, augitic pyroxene, iron-titanium oxides, and (pseudomorphs after) olivine. Metamorphic minerals are: albite (three generations), K-feldspar, pumpellyite, chlorite, interlayered chlorite-celadonite, celadonite, various mixed-layer Si- and Fe-rich phyllosilicates, "iddingsite," calcite, analcime, titanite, and white mica. The effect of the metamorphism on the rock chemistry is reflected in changes especially observed at the marginal zones of the flow which affect major, trace, and RE elements: 1) strong increase of the iron oxidation ratio (Fe 2O 3/FeO); 2) enrichment in Na 2O accompanied by a concomitant depletion of CaO in non-amygdaloidal domains; 3) depletion of SiO 2; 4) strong enrichment in H 2O and CO 2; 5) marked depletion of Sr and Rb; 6) enrichment in Cl and S; and 7) slight depletion in RE elements, notably in the top zone of the flow. Conversely, elements such as Ti, P, Nb, and Y were fairly immobile, whereas Zr and K were only slightly mobilized. The effect of the metamorphism on the mineral chemistry is expressed by the predominance of metastable equilibrium evidenced by the existence of wide compositional ranges in the phyllosilicates, the incomplete albitization of the Ca-plagioclase, and the Al-rich character of the pumpellyites. The metamorphism is considered to be of hydrothermal-burial type, which takes place at low temperature and pressure — probably about 125-230°C and less than 3 kb, and is produced mainly through

  15. Predicted seafloor facies of Central Santa Monica Bay, California (United States)

    Dartnell, Peter; Gardner, James V.


    Summary -- Mapping surficial seafloor facies (sand, silt, muddy sand, rock, etc.) should be the first step in marine geological studies and is crucial when modeling sediment processes, pollution transport, deciphering tectonics, and defining benthic habitats. This report outlines an empirical technique that predicts the distribution of seafloor facies for a large area offshore Los Angeles, CA using high-resolution bathymetry and co-registered, calibrated backscatter from multibeam echosounders (MBES) correlated to ground-truth sediment samples. The technique uses a series of procedures that involve supervised classification and a hierarchical decision tree classification that are now available in advanced image-analysis software packages. Derivative variance images of both bathymetry and acoustic backscatter are calculated from the MBES data and then used in a hierarchical decision-tree framework to classify the MBES data into areas of rock, gravelly muddy sand, muddy sand, and mud. A quantitative accuracy assessment on the classification results is performed using ground-truth sediment samples. The predicted facies map is also ground-truthed using seafloor photographs and high-resolution sub-bottom seismic-reflection profiles. This Open-File Report contains the predicted seafloor facies map as a georeferenced TIFF image along with the multibeam bathymetry and acoustic backscatter data used in the study as well as an explanation of the empirical classification process.

  16. [Vaginal ecology, climate, landscapes and populations (xenoecies and facies)]. (United States)

    Nicoli, J M; Nourrit, J; Michel-Nguyen, A; Sempe, M; Nicoli, R M


    Brief study of vaginal populations, the human vagina being considered as a biotopic cavity. Allusion to dynamic aspects ("vaginal climate", "landscapes") and to various bacterial populations. Introduction of the concept of xenoecies and of facies. This study is preceded by essential definitions of terms widely used in ecology.

  17. Metamorphic and thermal evolution of large contact aureoles - lessons from the Bushveld Igneous Complex (United States)

    Waters, D.


    . The sequence is grossly inconsistent with the predictions of equilibrium calculations; its formation requires the simultaneous operation of metastable as well as stable reactions at conditions significantly removed from equilibrium, the large overstepping governed largely by delayed nucleation of refractory porphyroblasts such as andalusite (Waters & Lovegrove, 2002). The dramatic conversion of chloritoid-chlorite slate into porphyroblastic andalusite hornfels is compressed into a short interval after the nucleation of the critical phases cordierite (metastable) and andalusite (stable), so that most of the prograde fluid release and endothermic heat drawdown in a given rock volume is predicted to occur in a relatively brief pulse. Since the metamorphic zonation is inverted, the released fluid will pass up into higher-temperature metamorphic zones that have already experienced peak temperature, where it may cause retrograde mineral growth. Reaction "cascades" of this kind can give rise to a more episodic pattern of metamorphic effects than predicted by equilibrium models, and contribute to a view of metamorphism in which long periods of relative quiescence are punctuated by bursts of fluid-present mineral transformation and mass transfer. Waters, D.J. & Lovegrove, D.P. (2002). J metamorphic Geol., 20, 135-149.

  18. Ultrahigh-temperature metamorphism under isobaric heating: New evidence from the North China Craton (United States)

    Yang, Qiong-Yan; Santosh, M.; Tsunogae, Toshiaki


    The Khondalite Belt within Inner Mongolia Suture Zone (IMSZ) in the North China Craton (NCC) preserves evidence for extreme crustal metamorphism under ultra-high temperature (UHT) conditions at ca. 1.92 Ga, associated with the subduction-collision tectonics between the Yinshan and Ordos Blocks. Here we report a new locality in Hongsigou where cordierite- and spinel-bearing granulites record UHT metamorphism. The prograde, peak, and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as: Bt1 + Grt1 + Sil1 + Kfs1 + Pl1 + Ilm + Qtz1, Grt1 + Sil2 + Kfs2 + Pl2 + Spl + Ilm + Qtz2 + Liq, and Crd + Grt2 + Sil3 + Kfs2 + Pl2 + Ilm + Qtz2 respectively. The peak metamorphic conditions of the pelitic granulite were estimated as 930-1050 °C and 6.5-7.5 kbar based on pseudosection analysis in the system NCKFMASHTO, suggesting extreme thermal metamorphism. We report LA-ICPMS zircon U-Pb data from the granulite which show weighted mean 207Pb/206Pb age of 1881 ± 6.6 Ma, marking the timing of UHT metamorphism. Lu-Hf analyses of the zircons show εHf(t) values within a restricted range of -4.2 to 0.3 and together with Hf model ages, a Paleoproterozoic arc magmatic source is inferred for the detrital zircons. The estimated P-T path for the UHT granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory, different from the anti-clockwise P-T paths defined in earlier studies for the 1.92 Ga UHT rocks from the IMSZ. The younger age and the isobaric heating trajectory suggest that the Hongsigou UHT rocks are related to heat input from underplated mafic magmas following continental collision.

  19. Mapping contact metamorphic aureoles in Extremadura, Spain, using Landsat thematic mapper images (United States)

    Rowan, L.C.; Anton-Pacheco, C.; Brickey, D.W.; Kingston, M.J.; Payas, A.


    In the Extremadura region of western Spain, Ag, Pb, Zn, and Sn deposits occur in the pieces of late Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke that have been regionally metamorphosed to the green schist facies. The plutons generally are well exposed and have distinctive geomorphological expression and vegetation; poor exposures of the metasedimentary host rocks and extensive cultivation, however, make delineation of the contact aureoles difficult. Landsat Thematic Mapper (TM) images have been used to distinguish soil developed on the contact metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are similar, except that muscovite is more common in the contact metamorphic soil; carbonaceous material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 1.6-micrometers wavelength region (TM 5), and weaker Al-OH, Mg-OH, and Fe3+ absorption features than do spectra of the slate-metagraywacke soil. The low-reflectance and subdued absorption features exhibited by the contact metamorphic soil spectra are attributed to the high absorption coefficient f the carbonaceous material caused by heating during emplacement of the granitic plutons. These spectral differences are evident in a TM 4/3, 4/5, 3/1 color-composite image. Initially, this image was used to outline the contact aureoles, but digital classification of the TM data was necessary for generating internally consistent maps of the distribution of the exposed contact metamorphic soil. In an August 1984, TM scene of the Caceras area, the plowed, vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of TM 4/5 and 3/1 values were determine for selected plower fields within and outside the contact aureoles; TM 5 produced results similar to TM 4/5. Field evaluation, supported by X-ray diffraction and petrographic

  20. Facies analysis and paleoenvironmental interpretation of Piacenzian carbonate deposits from the Guitar Formation of Car Nicobar Island, India

    Directory of Open Access Journals (Sweden)

    Amit K. Ghosh


    Full Text Available Facies characterization of Piacenzian (late Pliocene carbonate sediments of the Guitar Formation in Car Nicobar Island, India and the subsequent integration of paleoecological data have been applied to interpret the paleoenvironment of the coralline algal-reef deposits. Thin-section analysis reveals that Amphiroa, Corallina and Jania are the dominant geniculate corallines, while Lithothamnion, Mesophyllum, Phymatolithon, Lithophyllum, Spongites and Lithoporella are the major non-geniculate corallines contributing to the sedimentary facies. Numerous small and larger benthic foraminifera also dominate the biogenic assemblages. Corals, barnacle shells, echinoid spines, fragments of bryozoans, mollusks and ostracodes are the subordinate constituents. Grainstones dominate the studied facies while packstones and boundstones (with wackestone elements are the sub-lithofacies showing a fair representation. Six carbonate facies presenting a complete reef complex have been distinguished that were deposited in shallow intertidal, back-reef shelf/lagoon, reef and deeper fore-reef shelf settings. Evidences of coralline algal and benthic foraminiferal assemblages, taphonomic signatures of abrasion and fragmentation, grain size, angularity and encrustation indicate a shallow to relatively deeper bathymetric horizon of approximately 10–60 m that corresponds to a regime of high to moderate hydrodynamic conditions.

  1. Structural and metamorphic evolution of serpentinites and rodingites recycled in the Alpine subduction wedge (United States)

    Zanoni, D.; Rebay, G.; Spalla, M. I.


    Hydration-dehydration of mantle rocks affects the viscosity of the mantle wedge and plays a prominent role in subduction zone tectonics, facilitating marble cake-type instead of large-slice dynamics. An accurate structural and petrologic investigation of serpentinites from orogenic belts, supported by their long-lived structural memory, can help to recognize pressure-sensitive mineral assemblages for deciphering their P-prograde and -retrograde tectonic trajectories. The European Alps preserve large volumes of the hydrated upper part of the oceanic lithosphere that represents the main water carrier into the Alpine subduction zone. Therefore, it is important to understand what happens during subduction when these rocks reach P-T conditions proximal to those that trigger the break-down of serpentine, formed during oceanic metamorphism, to produce olivine and clinopyroxene. Rodingites associated with serpentinites are usually derived from metasomatic ocean floor processes but rodingitization can also happen in subduction environments. Multiscale structural and petrologic analyses of serpentinites and enclosed rodingites have been combined to define the HP mineral assemblages in the Zermatt-Saas ophiolites. They record 3 syn-metamorphic stages of ductile deformation during the Alpine cycle, following the ocean floor history that is testified by structural and metamorphic relics in both rock types. D1 and D2 developed under HP to UHP conditions and D3 under lower P conditions. Syn-D2 assemblages in serpentinites and rodingites indicate conditions of 2.5 ± 0.3 GPa and 600 ± 20°C. This interdisciplinary approach shows that the dominant structural and metamorphic imprint of the Zermatt-Saas eclogitized serpentinites and rodingites developed during the Alpine subduction and that subduction-related serpentinite de-hydration occurred exclusively at Pmax conditions, during D2 deformation. In contrast, in the favourable rodingite bulk composition (Ca-rich), hydrated minerals

  2. Surficial Sediment Facies features near Shorty's Island on the Kootenai River near Bonners Ferry, ID (United States)

    U.S. Geological Survey, Department of the Interior — The surficial bed-sediment facies, herein after referred to as the sediment facies, quantitatively describes the dominant sediment substrate on the surface of the...

  3. Alkali control of high-grade metamorphism and granitization

    Directory of Open Access Journals (Sweden)

    Oleg G. Safonov


    Full Text Available We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is implemented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes: rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s.

  4. Facies composition and scaling relationships of extensional faults in carbonates (United States)

    Bastesen, Eivind; Braathen, Alvar


    Fault seal evaluations in carbonates are challenged by limited input data. Our analysis of 100 extensional faults in shallow-buried layered carbonate rocks aims to improve forecasting of fault core characteristics in these rocks. We have analyzed the spatial distribution of fault core elements described using a Fault Facies classification scheme; a method specifically developed for 3D fault description and quantification, with application in reservoir modelling. In modelling, the fault envelope is populated with fault facies originating from the host rock, the properties of which (e.g. dimensions, geometry, internal structure, petrophysical properties, and spatial distribution of structural elements) are defined by outcrop data. Empirical data sets were collected from outcrops of extensional faults in fine grained, micro-porosity carbonates from western Sinai (Egypt), Central Spitsbergen (Arctic Norway), and Central Oman (Adam Foothills) which all have experienced maximum burial of 2-3 kilometres and exhibit displacements ranging from 4 centimetres to 400 meters. Key observations include fault core thickness, intrinsic composition and geometry. The studied fault cores display several distinct fault facies and facies associations. Based on geometry, fault cores can be categorised as distributed or localized. Each can be further sub-divided according to the presence of shale smear, carbonate fault rocks and cement/secondary calcite layers. Fault core thickness in carbonate rocks may be controlled by several mechanisms: (1) Mechanical breakdown: Irregularities such as breached relays and asperities are broken down by progressive faulting and fracturing to eventually form a thicker fault rock layer. (2) Layer shearing: Accumulations of shale smear along the fault core. (3) Diagenesis; pressure solution, karstification and precipitation of secondary calcite in the core. Observed fault core thicknesses scatter over three orders of magnitude, with a D/T range of 1:1 to 1

  5. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite (United States)

    Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.


    In order to understand the age and tectonic framework of Eastern to Peninsular Thailand from the viewpoint of basement (metamorphic and plutonic) geology, the LA-ICP-MS U-Pb zircon dating and the chemical Th-U-total Pb isochron method (CHIME) monazite dating were performed in the Khao Chao, Hub-Kapong to Pran Buri, and Khanom areas in Eastern to Peninsular Thailand. The LA-ICP-MS U-Pb zircon dating of the garnet-hornblende gneiss from the Khao Chao area gave 229 ± 3 Ma representing the crystallization age of the gabbro, and that of the garnet-biotite gneisses gave 193 ± 4 Ma representing the timing of an upper amphibolite facies metamorphism. The CHIME monazite dating of pelitic gneiss from the Khao Chao gneiss gave scattered result of 68 ± 22 Ma, due to low PbO content and rejuvenation of older monazite grains during another metamorphism in the Late Cretaceous to Tertiary time. The U-Pb ages of zircon from the Hua Hin gneissic granite in the Hub-Kapong to Pran Buri area scatter from 250 Ma to 170 Ma on the concordia. Granite crystallization was at 219 ± 2 Ma, followed by the sillimanite-grade regional metamorphism at 185 ± 2 Ma. Monazite in the pelitic gneiss from this area also preserves Early to Middle Jurassic metamorphism and rejuvenation by later contact metamorphism by non-foliated granite or by another fluid infiltration event in the Late Cretaceous to Tertiary time. The Khao Dat Fa granite from the Khanom area of Peninsular Thailand gave a U-Pb zircon age of 477 ± 7 Ma. This is the second oldest granite pluton ever reported from Thailand, and is a clear evidence for the Sibumasu block having a crystalline basement that was formed during the Pan-African Orogeny. The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses. Metamorphic rocks in the Doi Inthanon area

  6. Hereditary gingival fibromatosis with distinctive facies. (United States)

    Prasad, Sunkara Shree Ramalinga; Radharani, Chitturi; Sinha, Soumya; Kumar, Sv Kiran


    Hereditary gingival enlargement also known as gingivitis or familial elephantiasis is a rare type of gingival enlargement. It appears as an isolated autosomal dominant disorder or maybe associated with other conditions. Oral manifestations may vary from minimal involvement of only tuberosity area and the buccal gingiva around the lower molars to a generalized enlargement inhibiting eruption of the teeth. This paper discusses the case of a 13-year-old female patient with distinctive facial characteristics who presented to the department with a chief complaint of swollen gums since 1 year. She had severe diffuse gingival enlargement of the maxilla and mandible. Diagnosis was made based upon clinical examination and family history. Quadrant wise internal bevel gingivectomy procedure was done for the patient to restore her functional and esthetic needs.

  7. Tertiary plate tectonics and high-pressure metamorphism in New Caledonia (United States)

    Brothers, R.N.; Blake, M.C.


    The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs. ?? 1973.

  8. On ultrahigh temperature crustal metamorphism:Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

    Institute of Scientific and Technical Information of China (English)

    David E. Kelsey; Martin Hand


    Ultrahigh temperature (UHT) metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 ?C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as‘normal’ in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine þ quartz, orthopyroxene þ sillimanite ? quartz and osumilite in MgeAl-rich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar ther-mobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1) development of a ferric iron activityecomposition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions;(2) quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3) more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4) recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions;(5) more strongly linking UePb geochronological data from zircon and monazite to PeT points or path segments through using Y þ REE partitioning between accessory and major phases, as well as phase diagrams incorporating Zr and REE

  9. On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

    Directory of Open Access Journals (Sweden)

    David E. Kelsey


    Full Text Available Ultrahigh temperature (UHT metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 °C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as ‘normal’ in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine + quartz, orthopyroxene + sillimanite ± quartz and osumilite in Mg–Al-rich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar thermobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1 development of a ferric iron activity–composition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions; (2 quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3 more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4 recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions; (5 more strongly linking U–Pb geochronological data from zircon and monazite to P–T points or path segments through using Y + REE partitioning between accessory and major phases, as well as phase

  10. In situ oxygen isotope analysis of garnet from high pressure metamorphic veins of the Italian Western Alps and New Caledonia: Resolving fluid flow regimes in subducted crust (United States)

    Groflin, S. A.; Spandler, C.; Cliff, J.


    Metamorphic veins cutting eclogite-facies rocks represent products of fluid-rock interaction under the high pressure (HP) conditions typical of suduction zones. We present new chemical and oxygen isotope data on minerals in HP veins and their mafic host rocks from paleo-subducted slabs of the Lago Superiore Unit (Monviso Massif, Italian Western Alps), Eclogitic Micaschist Complex (Sesia Zone, Italian Western Alps) and Pouébo Eclogite Melange (New Caledonia). X-ray mapping and analysis of garnets from these veins show complex zoning features indicative of complex history of vein evolution. These garnet zones which were targeted for δ18O measurements by ion microprobe help fingerprint the origin of the vein-forming fluids. Isotopic analyses were carried out on a Cameca IMS 1280 and corrected for instrumental mass fractionation due to varying cation chemistry in garnet by using a newly developed correction scheme (Page et al., 2010). The intragranular δ18O heterogeneities in all garnets from each sample are relatively small (≤1.5‰) which suggest that similar fluids were present during garnet formation. The oxygen isotope data for all zones of garnet from vein and metabasaltic host rock from the New Caledonian (6.1-6.5‰ relative to VSMOW) and Sesia Zone (3.8-4.9‰) samples are very homogeneous. This result does not support the involvement of external fluids during vein formation, despite previous suggestions that metasedimentary components may have been added to the New Caledonian veins (Spandler and Hermann, 2006). The mafic rocks from New Caledonia experienced low-temperature seafloor alteration prior to subduction, thus the veins must have formed by internal fluids produced during transition from blueschist to eclogite facies. The Monviso vein garnets have distinctly different oxygen isotope compositions (3.2-3.7‰) than garnets in their mylonitic Fe-Ti eclogite host rocks (2.1-2.3‰). The low δ18O values of garnet in these metagabbros are consistent

  11. Thermal durations and heating behaviour for the Barrovian metamorphism, Scotland (United States)

    Viete, D. R.; Lister, G. S.; Hermann, J.; Forster, M. A.; Oliver, G. J.


    Published U/Pb ages for the syn-metamorphic gabbros and granites of the Grampian Terrane, Scotland, that provided heat for the classical Barrovian metamorphism, suggests that they were emplaced between 473.5 and 470 Ma. New SHRIMP U/Pb ages of 472.2 ± 5.8 Ma and 470.4 ± 6.1 Ma for peak metamorphism in the highest-grade units of the Barrovian metamorphic series are consistent with a 473.5 to 470 Ma heating episode in the highest-grade units. U/Pb-calibrated 40Ar/39Ar ages for white mica from the Barrovian metamorphic series vary from c. 465 Ma for the biotite zone to c. 461 Ma for the sillimanite zone and suggest that the Barrovian thermal episode lasted less than 8.5 million years in the biotite zone and less than 12.5 million years in the sillimanite zone. The lowest-grade units of the Barrovian metamorphic series retain detrital ages in white mica 40Ar/39Ar step-heating spectra, while units metamorphosed to temperatures of 475°C or more yield Grampian 40Ar/39Ar plateau ages. Forward modelling of Ar diffusion from white mica grains was carried out for different grain sizes and thermal histories to match the position of the across-metamorphic-grade transition from detrital 40Ar/39Ar patterns to Grampian 40Ar/39Ar plateau ages. The results of Ar diffusion modelling are consistent with thermal durations of between one and 4.5 million years for the Barrovian metamorphism of the biotite zone. Microstructural observations suggest that peak metamorphism and cooling occurred earliest in the lowest-grade units of the Barrovian metamorphic series and metamorphism in the higher-grade units continued for longer. We propose metamorphic durations of between 3.5 and eight million years for the Barrovian metamorphism of the sillimanite zone. Geochemical textures preserved within high-grade garnets from the Barrovian metamorphic series record evidence of Mn diffusion over c. 1000 μm lengthscales during the Barrovian metamorphism. In addition, sillimanite-grade garnets from the

  12. A tale of two eras: Pliocene-Pleistocene unroofing of Cenozoic and late Archean zircons from active metamorphic core complexes, Solomon Sea, Papua New Guinea (United States)

    Baldwin, Suzanne L.; Ireland, Trevor R.


    U/Pb ion microprobe analyses of zircons from gneisses and granodiorites exposed in the D'Entrecasteaux Islands, and from conglomerate sections of the Goodenough No. 1 well in the adjacent Trobriand Basin, provide constraints on the age of magmatism, peak metamorphism, and nature of rocks unroofed during initial stages of metamorphic core complex formation in the Solomon Sea. The youngest populations of zircons from felsic gneisses and granodiorites indicate late Pliocene 206Pb*/238U ages. No inherited zircons were identified in the granodiorites, and the 206Pb*/238U ages (1.65 ± 0.18 Ma; 1.98 ± 0.08 Ma [2σ]) are interpreted as crystallization ages. These synkinematically emplaced granodiorites, intruded into actively extending continental crust, are some of the youngest known granitoids currently exposed at the Earth' surface. Zircon ages from felsic gneisses (2.63 ± 0.16 Ma; 2.72 ± 0.28 Ma [2σ]) are interpreted to date zircon growth subsequent to eclogite facies metamorphism. Felsic gneiss samples also contained zircon xenocrysts from Cretaceous-Miocene protoliths. In striking contrast, zircons from igneous and metamorphic clasts from the Goodenough No. 1 well indicate a single population with a 207Pb*/206/Pb* age of 2781 ± 9 Ma (2σ). We speculate that they are derived from basement rocks unroofed during initial stages of development of the D&Entrecasteaux metamorphic core complexes. These results provide the first direct evidence for the existence of Archean protoliths in the basement rocks of southeastern Papua New Guinea.

  13. Granitoid magmatism of Alarmaut granite-metamorphic dome, West Chukotka, NE Russia (United States)

    Luchitskaya, M. V.; Sokolov, S. D.; Bondarenko, G. E.; Katkov, S. M.


    Main tectonic elements of West Chukotka are Alazey-Oloy, South-Anyui and Anyui-Chukotka fold systems, formed as a result of collision between structures of North-Asian continent active margin and Chukotka microcontinent [1-3]. South-Anyui fold system, separating Alazey-Oloy and Anyui-Chukotka systems, is considered as suture zon, formed as a result of oceanic basin closing [4-6]. Continent-microcontinent collision resulted in formation of large orogen with of northern and southern vergent structures, complicated by strike-slip deformations [7, 8]. Within Anyui-Chukotka fold system several rises, where most ancient deposits (crystalline basement and Paleozoic cover of Chukotka microcontinent) are exposed, were distinguished [2, 9-11]. Later they were considered as granite-metamorphic domes [12-14]. Alarmaut dome is located at West Chukotka to the north from Bilibino city and is traced from south to north in more than 120 km. General direction of structure is discordant to prevailing NW extensions of tectonic elements of the region. Paleozoic-Triassic deposits are exposed within the Alarmaut dome: 1) D3-C1 - crystalline schists, quartz-feldspar metasandstones, quartzites, marbles (700 m) [11]; 2) C1 - marblized limestones, quartz-feldspar metasandstones, quartzites, amphibole-pyroxene crystalline schists. Limestones contain corals, indicating Visean age of deposits [11]. Metamorphism reaches amphibolite facies, maximum P-T conditions are 660°С and 5 kbar. Migmatites, indicating in situ partial melting, are observed. Intensity of deformations of Paleozoic rocks increases at the boundary with Triassic deposits [11]; in the western part of dome slices of Pz rocks are separated by blastomylonite horizons [14]. Within Alramaut dome granitoids of Lupveem batholith (central part of dome), Bystrinsky pluton (southeastern part), and small Koyvel' and Kelil'vun plutons were studied. New U-Pb SHRIMP zircon data indicate Early Cretaceous (117-112 m.a.) age of granitoids [15

  14. Significance of the late Archaean granulite facies terrain boundaries, Southern West Greenland (United States)

    Friend, C. R. L.; Nutman, A. P.; Mcgregor, V. R.


    Three distinct episodes and occurrences of granulite metamorphism in West Greenland are described: (1) the oldest fragmentary granulites occur within the 3.6-Ga Amitsoq gneisses and appear to have formed 200 Ma after the continental crust in which they lie (Spatially associated rapakivi granites have zircon cores as old as 3.8 Ga, but Rb-Sr, whole-rock Pb-Pb, and all other systems give 3.6 Ga, so these granulites apparently represent a later metamorphic event); (2) 3.0-Ga granulites of the Nordlandet Peninsula NW of Godthaab, developed immediately after crustal formation in hot, dry conditions, are carbonate-free, associated with voluminous tonalite, and formed at peak metamorphic conditions of 800 C and 7 to 8 kbar (Synmetamorphic trondhjemite abounds and the activity of H2O has been indicated by Pilar to have varied greatly); and (3) 2.8-Ga granulites south of Godthaab, lie to the south of retrogressed amphibolite terranes. Prograde amphibolite-granulite transitions are clearly preserved only locally at the southern end of this block, near Bjornesund, south of Fiskenaesset. Progressively deeper parts of the crust are exposed from south to north as a major thrust fault is approached. Characteristic big hornblende pegmatites, which outcrop close to the thrust in the east, have been formed by replacement of orthopyroxene. Comparable features were not seen in South Indian granulites. It was concluded that no one mechanism accounts for the origin of all granulites in West Greenland. Various processes have interacted in different ways, and what happened in individual areas must be worked out by considering all possible processes.

  15. Metamorphic and tectonic evolution of the Greater Himalayan Crystalline Complex in Nyalam region, south Tibet (United States)

    Wang, Jia-Min; Zhang, Jin-Jiang; Rubatto, Daniela


    Recent studies evoke dispute whether the Himalayan metamorphic core - Greater Himalayan Crystalline Complex (GHC) - was exhumed as a lateral crustal flow or a critical taper wedge during the India-Asia collision. This contribution investigated the evolution of the GHC in the Nyalam region, south Tibet, with comprehensive studies on structural kinematics, metamorphic petrology and geochronology. The GHC in the Nyalam region can be divided into the lower and upper GHC. Phase equilibria modelling and conventional thermobarometric results show that peak temperature conditions are lower in the lower GHC (~660-700°C) and higher in the upper GHC (~740-780°C), whereas corresponding pressure conditions at peak-T decrease from ~9-13 kbar to ~4 kbar northward. Monazite, zircon and rutile U-Pb dating results reveal two distinct blocks within the GHC of the Nyalam region. The upper GHC underwent higher degree of partial melting (15-25%, via muscovite dehydration melting) that initiated at ~32 Ma, peaked at ~29 Ma to 25 Ma, possibly ended at ~20 Ma. The lower GHC underwent lower degree of melting (0-10%) that lasted from 19 to 16 Ma, which was produced mainly via H2O-saturated melting. At different times, both the upper and lower blocks underwent initial slow cooling (35 ± 8 and 10 ± 5°C/Myr, respectively) and subsequent rapid cooling (120 ± 40°C/Myr). The established timescale of metamorphism suggests that high-temperature metamorphism within the GHC lasted a long duration (~15 Myr), whereas duration of partial melting lasted for ~3 Myr in the lower GHC and lasted for 7-12 Myr in the upper GHC. The documented diachronous metamorphism and discontinuity of peak P-T conditions implies the presence of the Nyalam Thrust in the study area. This thrust is probably connected to the other thrusts in Nepal and Sikkim Himalaya, which extends over ~800 km and is named the "High Himalayan Thrust". Timing of activity along this thrust is at ~25-16 Ma, which is coeval with active

  16. Protolith age of Santa Maria Chico granulites dated on zircons from an associated amphibolite-facies granodiorite in southernmost Brazil

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    Léo A. Hartmann


    Full Text Available U-Pb dating of zircon was undertaken with the Beijing SHRIMP II (sensitive high resolution ion microprobe on anamphibolite facies granodiorite and an almandine-albite granulite from the Santa Maria Chico Granulitic Complex, southern Brazilian Shield. This work was also done to unravel protolith ages which are often hidden in the array of partly reset data. The obtained metamorphic ages of the granodiorite gneiss and the granulite are 2035 ± 9 Ma and 2006 ± 3 Ma, respectively. These data are within the range of metamorphic ages determined in previous studies (2022 ± 18 Ma and 2031 ± 40 Ma. However, protolith ages for the granodiorite (2366 ± 8 Ma and the granulite (2489 ± 6 Ma were obtained which are outside the previously recognized range (> 2510-2555 Ma. The magmatic protolith age of the granodiorite refers to a previously little known magmatic event in the shield. Further investigations may demonstrate that amphibolite facies zircon crystals are useful as a window into geological events in associated granulites, because zircon ages are blurred in the studied granulites.Um granodiorito de fácies anfibolito e um almandina-albita granulito do Complexo Granulítico Santa Maria Chico, porção sul do Escudo Brasileiro, foram datados pelo método U-Pb em zircão por Beijing SHRIMP II (sensitive high resolution ion microprobe. Esta investigação inclui a determinação das idades de protólitos que estão ocultas no conjunto de dados parcialmente re-equilibrados. As idades metamórficas obtidas no gnaisse granodiorítico e no granulito são 2035 ±9 Ma e 2006 ±3 Ma, respectivamente. Esses dados estão dentro da variação das idades metamórficas determinadas em estudos anteriores (2022 ±18 Ma e 2031 ±40 Ma. No entanto, as idades do protólito do granodiorito (2366 ±8 Ma e do granulito (2489 ±6 Ma estão fora da variação de idades ( > 2510-2555 Ma reconhecidas anteriormente. A idade magmática do protólito do granodiorito corresponde

  17. Late Jurassic blueschist facies pebbles from the Western Carpathian orogenic wedge and paleostructural implications for Western Tethys evolution (United States)

    Dal Piaz, Giorgio V.; Martin, Silvana; Villa, Igor M.; Gosso, Guido; Marschalko, Robert


    In spite of the absence of ophiolitic slices at the surface, some traces of the lost Tethys ocean are recorded along the Pieniny Klippen Belt (PKB), a narrow décollement thrust system sutured at the transpressive boundary between the Outer and Inner Carpathians. The enigmatic precollisional evolution of Western Carpathians can be deciphered from some late Albian to Campanian flysch conglomerates which display chrome spinel grains, ophiolitic detritus and pebbles of blueschist facies tholeiitic metabasalts yielding a 40Ar/39Ar plateau age of 155.4+/-0.6 Ma. Other detrital components are represented by extrabasinal pebbles of limestones, arc volcanics, and igneous to metamorphic basement rocks from southern sources. Our results suggest a markedly northward extension of the sublongitudinal Triassic Vardar (Meliata) Ocean and its subduction since the late Middle Jurassic, supposedly balanced westward by coeval spreading in the Ligurian-Piedmont basin of the Apennine-Western Alpine Tethys. A lateral kinematic connection between these diachronous and roughly parallel Tethys branches was provided on the north by a left-lateral east-west trending shear zone running from the Swiss-Austrian Penninic domain to the Northern Carpathians. This reconstruction replaces the classic model of two paired North Penninic and South Penninic oceanic basins and eastern homologues with the Briançonnais-Hochstegen and Czorstin microcontinents in between. The Late Jurassic-Early Cretaceous evolution of the Carpathian active margin was characterized by subduction metamorphism and accretion of a wide orogenic wedge; in this time, the shallowing to deeply subsiding basins inferred from facies analyses on the sedimentary units of the PKB were likely floored by individual sections of the growing wedge. Later, some exhuming blueschist ophiolitic units of the wedge were uplifted to the surface and functioned in the Albian-Campanian as an ``exotic ridge'' supplying clasts to the forearc basin

  18. Bayesian inversion for facies detection: An extensible level set framework (United States)

    Cardiff, M.; Kitanidis, P. K.


    In many cases, it has been assumed that the variability in hydrologic parameters can be adequately described through a simple geostatistical model with a given variogram. In other cases, variability may be best described as a series of "jumps" in parameter behavior, e.g., those that occur at geologic facies contacts. When using indirect measurements such as pump tests to try to map such heterogeneity (during inverse modeling), the resulting images of the subsurface are always affected by the assumptions invoked. In this paper, we discuss inversion for parameter fields where prior information has suggested that major variability can be described by boundaries between geologic units or facies. In order to identify such parameter fields, we propose a Bayesian level set inversion protocol framework, which allows for flexible zones of any shape, size, and number. We review formulas for defining facies locations using the level set method and for moving the boundaries between zones using a gradient-based technique that improves fit through iterative deformation of the boundaries. We describe the optimization algorithm employed when multiple level set functions are used to represent a field with more than two facies. We extend these formulas to the investigation of the inverse problem in a Bayesian context in which prior information is taken into account and through which measures of uncertainty can be derived. We also demonstrate that the level set method is well suited for joint inversion problems and present a strategy for integrating different data types (such as hydrologic and geophysical) without assuming strict petrophysical relations. Our framework for joint inversion also contrasts with many previous methods in that all data sources (e.g., both hydrologic and geophysical) contribute to boundary delineation at once.

  19. Paleoproterozoic high-pressure metamorphism in the northern North China Craton and implications for the Nuna supercontinent. (United States)

    Wan, Bo; Windley, Brian F; Xiao, Wenjiao; Feng, Jianyun; Zhang, Ji'en


    The connection between the North China Craton (NCC) and contiguous cratons is important for the configuration of the Nuna supercontinent. Here we document a new Paleoproterozoic high-pressure (HP) complex dominated by garnet websterite on the northern margin of the NCC. The peak metamorphism of the garnet websterite was after ∼1.90 Ga when it was subducted to eclogite facies at ∼2.4 GPa, then exhumed back to granulite facies at ∼0.9 GPa before ∼1.82 Ga. The rock associations with their structural relationships and geochemical affinities are comparable to those of supra-subduction zone ophiolites, and supported by subduction-related signatures of gabbros and basalts. We propose that a ∼1.90 Ga oceanic fragment was subducted and exhumed into an accretionary complex along the northern margin of the NCC. Presence of the coeval Sharyzhalgai complex with comparable HP garnet websterites in the southern Siberian active margin favours juxtaposition against the NCC in the Paleoproterozoic.


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    Full Text Available Este artículo presenta los resultados de una simulación de flujo de agua subterránea en rocas fracturadas. Se emplea un enfoque estocástico (modelo estocástico equivalente en medio poroso fracturado para construir el modelo conceptual y para usar este último en la roca de baja permeabilidad encontrada en el sitio elegido como caso de estudio (Olkiluoto, Finlandia. La roca que se investiga se encuentra localizada alrededor de un grupo de pozos de sondeo y cubre un área de algunas hectáreas. Las mediciones de campo de pruebas de interferencia hidráulica se utilizan para calibrar el modelo de flujo de agua subterránea. Múltiples combinaciones de facies estocásticos se consideran para evaluar el impacto de la distribución y del número de facies en las cargas hidráulicas y en los caudales. Este estudio cuantifica la variabilidad de los resultados numéricos, lo cual es importante para el análisis de la incertidumbre en los sistemas hidrogeológicos. Por otra parte, este estudio muestra que el modelo conceptual de facies estocásticos es una alternativa adecuada a los modelos conceptuales de redes de fracturas discretas.

  1. The history of crustal uplift and metamorphic evolution of Panzhihua-Xichang micro-palaeoland, SW China:Constraints on Sm-Nd, 40Ar/39Ar and FT ages of granulites

    Institute of Scientific and Technical Information of China (English)

    XU Shijin; LIU Wenzhong; WANG Rucheng; YU Hangbo; LI Daming; WAN Jinglin; FANG Zhong


    Panzhihua-Xichang (Panxi) micro-palaeoland is the oldest terrane on the western margin of the Yangtze Block. Some intermediate-basic granulites are considered to be the crystalline basement of lower crust in the terrane. Granulite-facies metamorphism of the granulites was developed in the period from 1186 Ma to 1128 Ma. The origin of granulites was related to the collision orogenic process occurring when the micro-palaeolands merged to form the Rodinia Supercontinent. Amphibolite-facies retrogressive metamorphism of granulites took place in the period from 877 Ma to 825 Ma. This period was consistent with the breakup time of the Rodinia Supercontinent. 40Ar/39Ar ages and fission track (FT) ages of granulites in the Panxi micro-palaeoland show that the vertical movement history of crustal rocks was a slow uplift process of the rigid terrane in the time from Neoproterozoic to Mesozoic. The subduction of India Plate towards Euroasia Plate resulted in the rapid uplift of the Qinghai-Tibetan Block in Cenozoic.Meanwhile, the Qinghai-Tibetan Block moved towards east. Consequently the Panxi terrane was uplifted rapidly. As a result of the collision orogeny between the Qinghai-Tibetan Block and the Panxi terrane, the granulite-facies crystalline basement in this region was exhumed and exposed to the surface.

  2. Dating of Mesoproterozoic metamorphism in the Mount Isa and George Fisher Zn-Pb-Cu-Ag deposits, Australia, by paleomagnetism (United States)

    Kawasaki, K.; Symons, D. T.


    The Mount Isa Zn-Pb-Cu-Ag and George Fisher Zn-Pb-Ag black-shale-hosted deposits in Queensland, Australia, are in carbonaceous and dolomitic shales of the ~1655 Ma Urquhart Formation of the Mount Isa Group that exhibit greenschist facies metamorphism. Both deposits give lead model ages of ~1655 Ma. Ar-Ar biotite and Re-Os ages for the Mount Isa copper ore are 1523±3 and 1372±4 Ma, respectively. Excluding modern hematite, paleomagnetic and rock magnetic analyses of 333 specimens (28 sites) isolate a stable characteristic remanent magnetization (ChRM) in single- and pseudosingle-domain pyrrhotite for the Zn-Pb-Ag ore specimens and in pyrrhotite and/or titanomagnetite for the Cu ore. A negative paleomagnetic fold test shows that the ChRM postdates D3 deformation of the ~1595 to 1500 Ma Isan orogeny, yielding a Mesoproterozoic paleopole at ~1505 Ma on the northern Australian apparent polar wander path. The ~1505 Ma age is similar to the ~1523 Ma Ar-Ar age and it provides a minimum age for ore genesis of both deposits, as well as the age for peak greenschist metamorphism during the Isan orogeny in the surrounding Mount Isa inlier.

  3. 拉萨地块松多超高压变质带含石榴石云母石英片岩的变质演化相平衡模拟%Phase equilibrium modeling for metamorphic evolution of garnet-bearing mica-quartz schist in Sumdo UHP metamorphic belt, Lhasa Block

    Institute of Scientific and Technical Information of China (English)

    陈梅; 田作林; 张聪; 杨经绥; 黄杰


    岩与榴辉岩经历了相同或者相似的俯冲折返过程。%The garnet-bearing mica-quartz schist of Sumdo UHP belt in Lhasa block occurs as country rocks of eclogite, and is mainly composed of garnet, muscovite, albite, chlorite, quartz and minor rutile and sphene. Garnet displays an obvious compositional zonation where Xprp increases from the core to the mantle and then decreases in the rim, whereas Xsps decreases gradually from the core to mantle, with the trend of declining following rising in the rim, indicating that garnet composition profiles from core to mantle have preserved the prograde growth zoning and were partially reset during retrogression. The model system MnNCKFMASHO was chosen to calculate P-T and P-M(H2O) pseudosections of the garnet-bearing mica-quartz schist. Garnet isopleth thermobarometry involved plotting compositional isopleths of garnet as contours on a P-T pseudosection, with the combination of contours of saturated H2O content, thus obtaining estimated peak P-T conditions of 27 kbar, 523/580℃and peak mineral assemblages of g-jd-cr-law (+phn +q/coe+H2O). The compositional profile of garnet from the core to the mantle and contouring of the H2O content saturated indicate that prograde metamorphic evolution represents a cold subduction stage with heating with the increasing pressure, and the rocks experienced blueschist-facies to eclogite-facies metamorphism during this stage. P-M(H2O) pseudosections and isopleth of saturated H2O content could be used to assess evolution of mineral assemblages in terms of changes in water content during decompression, which shows that garnet-bearing mica quartz schist experienced an early isothermal decompression process and was then followed by a cooling with decompression evolution during the late stage. Amphibolite-facies to epidote-amphibolite-facies metamorphism occurred during early stage and was followed by greenschist-facies metamorphism. The isothermal decompression of garnet-bearing mica-quartz schist probably

  4. Facies y ambientes del grupo Salta (cretácico-paleógeno en Tumbaya, Quebrada de Humahuaca, provincia de Jujuy Facies and environments of the Salta Group (Cretaceous-Paleogene in Tumbaya, Quebrada de Humahuaca, JujuyProvince

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    María Cristina Sánchez


    Full Text Available Los depósitos rojos del Grupo Salta (Cretácico-Paleógeno que afloran en la quebrada de Tumbaya, margen derecha de la quebrada de Humahuaca (provincia de Jujuy, se caracterizan por presentar facies distintas a las típicas de otros lugares de la cuenca. Son facies proximales de ambiente general árido a semiárido cuya acumulación avanzó sobre el extremo N-NO del alto constituido por la dorsal Salto-Jujeña. La relación de base y de techo del depósito es de discordancia erosiva con el Grupo Mesón (Cámbrico y angular con acumulaciones cuaternarias de bajada respectivamente. En el afloramiento están representadas las principales unidades del Grupo Salta tanto del synrift como del postrift. El reconocimiento y estudio de las facies permitió identificar y caracterizar de base a techo los Subgrupos Pirgua, Balbuena y Santa Bárbara, y las distintas formaciones de cada subgrupo. En el Subgrupo Pirgua (arenas eólicas no es posible diferenciar sus tres unidades formacionales, por lo tanto se lo menciona como Formación Pirgua. En el Subgrupo Balbuena se reconocen las Formaciones Lecho, que consta de facies fluviales de tipo mantos de crecida, y Yacoraite que muestra condiciones ambientales transicionales, continentales y marino litoral-sublitoral carbonático influenciado por mareas y tormentas. El Subgrupo Santa Bárbara está presente con sus Formaciones Mealla, Maíz Gordo y Lumbrera que representan una sucesión fluvial granodecreciente con desarrollo de paleosuelos múltiples; se reconocen mantos de crecida asociadas a planicies fangosas.The red deposits of Salta Group (Cretaceous-Paleogene which outcrops in the quebrada de Tumbaya, right margin of Quebrada de Humahuaca (province of Jujuy, they are characterized by facies that differs from the typical ones in their places of the Salta Group basin. They are proximal facies, characterized by arid and semi-arid conditions whose accumulation advanced on the N-NW side of the Salto-Jujuy high

  5. Structural and metamorphic analysis of the Sucuru-Paraba region: implications for evolution of the Alto Moxotó Terrane, Borborema Province

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    Lauro Cézar Montefalco de Lira Santos


    Full Text Available Inserted on the Alto Moxot Terrane of the Borborema Province, the Sucuru region (Paraba state, Brazil includes two dominantly pre-Ediacaran tectono-stratigraphic domains, bounded by an expressive thrust shear zone (Carmo SZ. The first domain has a metaplutonic nature, being formed by granodioritic to migmatitic orthogneisses (Floresta Complex cut by several intrusive suites. These suites comprise a unit of mafic-ultramafic nature (Malhada Vermelha, a second one mainly of granitic-granodioritic composition (Pedra d'gua and a last suite whose composition ranges from syenitic to syenogranitic (Serra da Barra. On the second domain predominate migmatitic paragneisses from of the Sertnia Complex. All these units were cut by Cambrian-Ediacaran felsic dykes and A-type granites. Three tectonic events were recognized. The first Dn episode represents a thrusting with tectonic transport to NW-NNW, being important the Sucuru and Carmo shear zones. The Dn+1 episode is a transcurrent event of Ediacaran age, being important in regional context the Coxixola and Congo shear zones. The final progressive late Ediacaran-Cambrian Dn+2 episode, culminated with the emplacement of the Sucuru dyke swarm and the Prata and Serra da Engabelada A-type granites. Petrographic evidences show that the Dn episode reached its metamoprhic peak on the granulitic or eclogitic facies, whose paragenesis was after re-equilibrated to the amphibolite during the Dn+1 event. The Dn+1 episode developed mylonitic corridors on the amphibolite facies with associated migmatization, while the Dn+2, event reached a greenschist facies restrict to influence of the late and post-tectonic intrusives. The occurrence of garnet amphibolites with symplectite texture along the metamorphic path Mn-Mn+1 suggests that the thrust event represented a high pressure metamorphic episode, indicating a probable Paleoproterozoic suture.

  6. Metamorphic gradients in burial metamorphosed vesicular lavas: Comparison of basalt and spilite in Cretaceous basic flows from central Chile (United States)

    Levi, Beatriz; Aguirre, Luis; Nyström, Jan Olov


    Partial spilitization of a 9 km thick pile of flood basalts with highly vesicular flow tops gave rise to patterns of secondary mineralogy at different scales: (a) a local pattern of mineralogical variation from the almost unaltered bottom towards the altered top of each flow, and (b) an overall pattern, comparing flow tops throughout the pile, with changes in mineralogical composition within a sequence of metamorphic zones and facies. The local patterns mimic the trend of the overall pattern, but are of opposite direction and telescoped. Thus, a gradual ordering and Andepletion of the secondary “albite” and increases in the Fe*/Al ratio of epidote and pumpellyite upwards within individual flows are comparable in range to corresponding overall changes downwards throughout several kilometres. The mineralogical changes within the flows diminish in range towards the more altered deeper part of the pile. The local and overall patterns cannot be interpreted in terms of grade. They represent trends from metastable towards stable equilibrium, this latter only approached in the flow tops of the lower part of the pile. The patterns of secondary mineralogy were formed by an interplay of metamorphic gradients at different scales at any given time, and as burial proceeded. The overall pattern was caused by depth-controlled gradients: increasing P fluid, temperature and temperature-induced increase of reaction rates, and decreasing fO2 (downwards in the pile). The local patterns resulted from permeability-controlled gradients: increasing reaction rates, fO2 and contrast in chemical activity between different domains, and decreasing P fluid (upwards in each flow). The mineralogical observations reported in this paper fall into line if the overall temperature-induced increase of reaction rates and the local permeability-controlled rate factors played the leading role during burial metamorphism of the pile.

  7. LASS U-Th-Pb monazite and rutile geochronology of felsic high-pressure granulites (Rhodope, N Greece): Effects of fluid, deformation and metamorphic reactions in local subsystems (United States)

    Wawrzenitz, Nicole; Krohe, Alexander; Baziotis, Ioannis; Mposkos, Evripidis; Kylander-Clark, Andrew R. C.; Romer, Rolf L.


    altered monazite of the three pre-mylonitic domains by having a significantly more pronounced negative Eu anomaly, a flatter HREE pattern, and high Th content. These compositional characteristics are linked with syn-mylonitic formation of plagioclase and resorption of garnet in the shear bands under amphibolite facies conditions. The absence of pre-mylonitic monazite in the shear zones, in contrast to the other domains, suggests complete dissolution of old and formation of new monazite. This probably results from an increased alkalinity and reactivity of the fluid that again is controlled by syn-mylonitic interaction with feldspar and apatite in the shear zones. There, the deformation was accommodated by dissolution precipitation creep at ca. 690 ± 50 °C and 6-7.5 kbar. Growth of monazite at 55 ± 1 Ma dates this deformation, which precedes the regional migmatization of the Sidironero Complex, whereas rutile and biotite ages reflect these later stages. This new pressure-temperature-time constraint for a relictic deformation structure provides insight into the still missing parts of the overall metamorphic, deformation and exhumation processes of the UHP units in the Rhodope.

  8. Northernmost Known Outcrop in North America of Lower Cretaceous Porphyritic Ocoite Facies (Ocoa, Chile) at Western Mexico: the Talpa Ocoite (United States)

    Zárate-del Valle, P. F.; Demant, A.


    At Talpa de Allende region in Western Mexico is located the northernmost known outcrop of ocoite facies (andesite): the Talpa ocoite (TO). The ocoite facies consists of an calk-alkaline andesitic rock rich in K and characterized by the presence of megacrysts of plagioclase (An48-65). TO belongs to the so-called Guerrero Terrane composed of plutono-volcanic and volcano-sedimentary sequences of the Alisitos-Teloloapan arc that was accreted to the North American craton at the end of the early Cretaceous (Lapierre et al., 1992, Can. J. Earth Sci. 29. 2478--2489). Geodynamically TO belongs to lithological sequence number IV or "Tecoman" of Tardy et al. (1994, Tectonophysics 230, 49--73). TO in hand-sample shows typical megacrysts (>1 cm) of plagioclase and clinopyroxene in a dark green aphanitic matrix. This andesitic lava has a shoshonitic character as evidenced by chemical composition: SiO_2 TiO_2 Al_2O_3 Fe_2O_3 MnO MgO CaO Na_2O K_2O P_2O_5 LOI % Ba Sr (ppm) 55.64 0.73 16.61 8.39 0.13 3.59 6.40 3.55 2.85 0.36 1.84% 1093 880 Under microscope TO is characterized by a porphyritic texture made of large labradorite phenocrysts (up to 3 cm) and clinopyroxene with a matrix made of plagioclase microlites; TO has been affected by a low grade metamorphism process belonging to the prehnite-pumpellite facies as it happens in Chile (Levi, 1969, Contr. Mineral. and Petrol. 24-1, p. 30--49). Electron microprobe analysis shows that plagioclase (An55-57) is partly transformed into albite (An7-9); clinopyroxene shows a variation in composition from Wo33En41Fs17 to Wo40En44Fs24 and it is transformed towards the margin first into amphibole and then into biotite. TO outcrops located at East of Talpa river are affected by a deep rubefaction process. TO is not characterized by the presence of bitumen as it occurs in Northern Chile (Nova-Muñoz et al., 2001, EUG XI Meeting, OS09 Supo09 PO, 606); TO is related in time with albian-cenomanian volcanogenic massive sulphides of Western Mexico

  9. Pb-Pb zircon ages of the Porto Nacional high-grade metamorphic terrain, northern portion of the Goias Massif, central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Gorayeb, Paulo Sergio de Sousa; Moura, Candido Augusto Veloso [Para Univ., Belem, PA (Brazil). Centro de Geociencias]. E-mail:;; Barros, Gisele Ribeiro de [Para Univ., Belem, PA (Brazil). Programa Institucional de Bolsas de Iniciacao Cientifica (PIBIC)]. E-mail:


    Single zircon Pb-evaporation ages were determined for a mafic granulite, two enderbites and a kinzigite of the Porto Nacional High-Grade Metamorphic Terrain (PNHGT) in the Goias massif. Zircons from mafic granulites and one of the enderbites of yielded average {sup 207} Pb/{sup 206} Pb ages of 2125{+-}3 Ma and 2153{+-}1 Ma, respectively, being interpreted as minimum ages of the igneous protoliths. The other enderbite, whose zircons presented round terminations, yielded an average {sup 207} Pb/{sup 206} Pb age of 2097 {+-} 2 Ma. Zircons from the kinzigite, displaying cores and rims overgrowth, presented {sup 207} Pb/{sup 206} Pb ages ranging between 2027 and 2115 Ma. However, a very homogeneous zircon crystal without overgrowth yielded age of 2100 {+-} 2 Ma, with a distinctive low Th/U value (0.02). This zircon is interpreted as a metamorphic crystal and its age probably sets the age of the granulite facies metamorphism, indicating that the PNHGT is a result of the Transamazonian thermotectonic event. (author)

  10. Late Cretaceous extension and exhumation of the Stong and Taku magmatic and metamorphic complexes, NE Peninsular Malaysia

    NARCIS (Netherlands)

    François, T.; Md Ali, M.A.; Matenco, L.; Willingshofer, E.; Ng, T.F.; Taib, N.I.; Shuib, M.K.


    Fragmentation of large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts, as exemplified by the Stong and Taku magmatic and metamorphic complexes of northern Peninsular Malaysia. For this cas

  11. Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample (United States)

    Ebner, Pirmin Philipp; Schneebeli, Martin; Steinfeld, Aldo


    Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m-1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

  12. Growth, destruction and volcanic facies architecture of three volcanic centres in the Miocene Uşak-Güre basin, western Turkey: Subaqueous-subaerial volcanism in a lacustrine setting (United States)

    Karaoğlu, Özgür; Helvacı, Cahit


    Early to Mid-Miocene extension in western Anatolia, related to plate tectonic motions, resulted in the development of a number of normal fault-bounded sedimentary basins as well as different styles and compositions of volcanic activity. The Uşak and Güre basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadağ, İtecektepe and Beydağı) and their deposits can overlap with each other and with the sediments produced by the background sedimentation. In addition, complete facies architectures of small-volume (monogenetic) volcanoes have been recognised in association with the three large complex (polygenetic) volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place. All three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits, with abundant evidences of magma-water interaction such as peperites for non-explosive magma-water interaction with the lacustrine water-saturated sediment and standing water body in a large alkaline lake. During the constructive phase, proximal successions of pyroclastic flows, pyroclastic falls, and rarely surge deposits are associated with distally-emplaced debris flow deposits, sometimes of mixed volcanogenic and terrestrial origins, and are interbedded with lacustrine sediments of the Inay Group. All three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15 Ma ago, most likely related to a combination of tectonic movements on NE-SW-trending basement faults, which triggered multiple flank collapses and volcanic debris avalanches (Elmadağ), and voluminous ignimbrite eruptions that triggered caldera formation (İtecektepe and Beydağı volcanic centres). Lacustrine conditions persisted during the destruction and post-destruction stages of the volcano's evolution, as evidenced by indications of magma-water interactions


    Directory of Open Access Journals (Sweden)

    E. G. Kolomyts


    Full Text Available The paper presents a novel approach to the study of development of microstructures in snowpack based on the crystal-morphology and on the fundamental laws of natural symmetry. An empirical deterministic model describing the sublimation-metamorphic cycle in seasonal snow cover and the polymorphic variants of this cycle is suggested. Staging in the formation of crystal shapes and self-development of snow microstructure in snow layers is revealed. The crystal shapes are the result of successive process of superposition of ice crystal-chemical symmetry and dissymmetry of the soil – snow cover – atmosphere system, according to the known P. Curie principle. Morphological classification of snow crystals in seasonal snow cover is developed on the base of evolutionary model. Evolution of snow microstructure is conditioned by a marked degree by probabilistic conformity to natural laws, manifesting itself in the processes of auto-regulation of metamorphism. These processes include two types of regulation: the self-regulation of snow layers, on the one hand, and the regulation related to external conditions – under the influence of atmospheric perturbations, on the other hand. The accounting the processes of auto-regulation of snow metamorphism for allows development of new methods in short- and long-term avalanche forecast.

  14. High Radiation Resistance Inverted Metamorphic Solar Cell Project (United States)

    National Aeronautics and Space Administration — The innovation in the proposed SBIR Phase I project is the development of a unique triple unction inverted metamorphic technology (IMM), which will enable the...

  15. High Radiation Resistance Inverted Metamorphic Solar Cell Project (United States)

    National Aeronautics and Space Administration — The innovation in this SBIR Phase II project is the development of a unique triple junction inverted metamorphic technology (IMM), which will enable the...

  16. The contribution of metamorphic petrology to understanding lithosphere evolution and geodynamics

    Institute of Scientific and Technical Information of China (English)

    Michael Brown


    In the early 1980s, evidence that crustal rocks had reached temperatures >1000℃at normal lower crustal pressures while others had followed low thermal gradients to record pressures characteristic of mantle conditions began to appear in the literature, and the importance of melting in the tectonic evolution of orogens and metamorphicemetasomatic reworking of the lithospheric mantle was realized. In parallel, new developments in instrumentation, the expansion of in situ analysis of geological ma-terials and increases in computing power opened up new fields of investigation. The robust quantifi-cation of pressure (P), temperature (T) and time (t) that followed these advances has provided reliable data to benchmark geodynamic models and to investigate secular change in the thermal state of the lithosphere as registered by metamorphism through time. As a result, the last 30 years have seen sig-nificant progress in our understanding of lithospheric evolution, particularly as it relates to Precambrian geodynamics. EoarcheaneMesoarchean crust registers uniformly high T/P metamorphism that may reflect a stagnant lid regime. In contrast, two contrasting types of metamorphism, eclogiteehigh-pressure granulite metamorphism, with apparent thermal gradients of 350e750℃/GPa, and granulite eultrahigh temperature metamorphism, with apparent thermal gradients of 750e1500℃/GPa, appeared in the Neoarchean rock record. The emergence of paired metamorphism is interpreted to register the onset of one-sided subduction, which introduced an asymmetric thermal structure at these developing convergent plate margins characterized by lower T/P in the subduction channel and higher T/P in the overriding plate. During the Paleoarchean to Paleoproterozoic the ambient mantle temperature was warmer than at present by w300e150℃. Although the thermal history of Earth is only poorly constrained, it is likely that prior to ca. 3.0 Ga heating from radioactive decay would have exceeded surface heat

  17. Application of Metamorphic Testing to Supervised Classifiers (United States)

    Xie, Xiaoyuan; Ho, Joshua; Kaiser, Gail; Xu, Baowen; Chen, Tsong Yueh


    Many applications in the field of scientific computing - such as computational biology, computational linguistics, and others - depend on Machine Learning algorithms to provide important core functionality to support solutions in the particular problem domains. However, it is difficult to test such applications because often there is no “test oracle” to indicate what the correct output should be for arbitrary input. To help address the quality of such software, in this paper we present a technique for testing the implementations of supervised machine learning classification algorithms on which such scientific computing software depends. Our technique is based on an approach called “metamorphic testing”, which has been shown to be effective in such cases. More importantly, we demonstrate that our technique not only serves the purpose of verification, but also can be applied in validation. In addition to presenting our technique, we describe a case study we performed on a real-world machine learning application framework, and discuss how programmers implementing machine learning algorithms can avoid the common pitfalls discovered in our study. We also discuss how our findings can be of use to other areas outside scientific computing, as well. PMID:21243103

  18. Inverted Metamorphic Multijunction (IMM) Cell Processing Instructions

    Energy Technology Data Exchange (ETDEWEB)

    Duda, A.; Ward, S.; Young, M.


    This technical report details the processing schedule used to fabricate Inverted Metamorphic Multijunction (IMM) concentrator solar cells at The National Renewable Energy Laboratory (NREL). These devices are used as experimental test structures to support the research at NREL that is focused on increasing the efficiency of photovoltaic power conversion. They are not intended to be devices suitable for deployment in working concentrator systems primarily because of heat sinking issues. The process schedule was developed to be compatible with small sample sizes and to afford relatively rapid turn-around times, in support of research efforts. The report describes the use of electro deposition of gold for both the back and front contacts. Electro-deposition is used because of its rapid turn around time and because it is a benign metallization technique that is seldom responsible for damage to the semiconductors. The layer transfer technique is detailed including the use of a commercially available adhesive and the etching away of the parent gallium arsenide substrate. Photolithography is used to define front contact grids as well as the mesa area of the cell. Finally, the selective wet chemical etchant system is introduced and its use to reveal the back contact is described.

  19. Thermal history of a metamorphic core complex (United States)

    Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.


    Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

  20. A fluid inclusion study of blueschist-facies lithologies from the Indus suture zone, Ladakh (India): Implications for the exhumation of the subduction related Sapi-Shergol ophiolitic mélange (United States)

    Sachan, Himanshu Kumar; Kharya, Aditya; Singh, P. Chandra; Rolfo, Franco; Groppo, Chiara; Tiwari, Sameer K.


    The best occurrence of blueschist-facies lithologies in Himalaya is that of the Shergol Ophiolitic Mélange along the Indus suture zone in Ladakh region of north-western India. These lithologies are characterized by well preserved lawsonite-glaucophane-garnet-quartz assemblages. This paper presents for the first time the results of a detailed fluid inclusion study on these lithologies, in order to understand the fluid P-T evolution and its tectonic implications. The blueschist rocks from Shergol Ophiolitic Mélange record metamorphic peak conditions at ∼19 kbar, 470 °C. Several types of fluid inclusions are trapped in quartz and garnet, most of them being two-phase at room temperature. Three types of fluid inclusions have been recognised, basing on microtextures and fluid composition: Type-I are primary two-phase carbonic-aqueous fluid inclusions (VCO2 - LH2O); Type-II are two-phase (LH2O - VH2O) aqueous fluid inclusions, either primary (Type-IIa) or secondary (Type-IIb); Type-III are re-equilibrated fluid inclusions. In the Type-I primary carbonic-aqueous inclusions, H2O is strongly predominant with respect to CO2; the homogenization temperature of CO2 range from -7 to -2 °C. The clathrate melting temperature in such inclusions varies in between +7.1 and +8.6 °C. Type-II two-phase aqueous fluid inclusions show a wide range of salinity, from 7.8-14 wt.% NaCleq (Type-IIa) to 1.65-6.37 wt.% NaCleq (Type-IIb) with accuracy ±0.4 wt.% NaCleq. Type-I and Type-IIa primary fluid inclusions are hosted in peak minerals (garnet and quartz included in garnet), therefore they were likely entrapped at, or near to, peak P-T conditions. The dominantly aqueous fluid of both Type-I and Type-IIa inclusions was most likely produced through metamorphic devolatilization reactions occurring in the subducting slab. Despite their primary nature, the isochores of Type-I and Type-IIa inclusions do not intersect the peak metamorphic conditions of the blueschist mineral assemblage

  1. Global dominance of coralline red-algal facies: A response to Miocene oceanographic events (United States)

    Halfar, Jochen; Mutti, Maria


    Rhodoliths (free-living coralline red algae) can thrive under a wide range of temperatures, reduced light, and increased nutrient levels, and often form a distinct so-called rhodalgal lithofacies that is an important component of Cenozoic shallow-water carbonates. Global distributions illustrate that from the late-early to early-late Miocene (Burdigalian early Tortonian), rhodalgal facies reached peak abundances and commonly replaced coral-reef environments, accompanied by a decline in other carbonate-producing phototrophs. We argue that the dominance of red algae over coral reefs was triggered in the Burdigalian by enhanced trophic resources associated with a global increase in productivity, as evidenced by a long-term shift toward higher carbon isotope values. Rhodalgal lithofacies expanded further in the middle Miocene when strengthened thermal gradients associated with the establishment of the East Antarctic Ice Sheet led to enhanced upwelling while climate change generated increased weathering rates, introducing land-derived nutrients into the oceans. Globally cooler temperatures following a climatic optimum in the early-middle Miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs. The global shift in nearshore shallow-water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow-water carbonate facies as indicators of past oceanographic conditions.

  2. Permian Mengkarang coal facies and environment, based on organic petrology study

    Directory of Open Access Journals (Sweden)

    Nana Suwarna


    Full Text Available Permian Mengkarang Coal Measures is situated in the middle part of Sumatera Island. Some fresh outcrop samples of the Permian Mengkarang coals have been analyzed both macroscopically and microscopically, to asses their depositional environment. On the basis of organic-petrological analysis, the coal seams show variation in the predominance of some macerals, indicating successions of environmental changes. The dominant maceral group is vitrinite, present in very low to very high values; whilst the minor one is inertinite showing low amount. Environmental information derived from the organic facies study shows that the coals were deposited in wet zone of mire, ranges from wet limnic-telmatic zone to telmatic wet forest swamp under rapid burial condition, due to rapid basin subsidence. The organic facies concept is thus applicable in basin studies context and has potential to become an additional tool for interpretation of depositional environment.    

  3. Facies patterns and depositional environments of Palaeozoic cephalopod limestones (United States)

    Wendt, J.; Aigner, T.


    In the eastern Anti-Atlas (Morocco) a platform and basin topography was established during the late Devonian, probably as a result of early Variscan tensional tectonics. Cephalopod limestones were deposited on shallow pelagic platforms, platform slopes and shallow, slowly subsiding basins. On the platform a transition from land areas into nearshore quartzose brachiopod coquinas, crinoidal limestones, condensed cephalopod limestones and finally into nodular limestones is observed. The latter often become disintegrated into incipient debris flows which pass into nodular limestone/marl alternations of a shallow basin. Deeper basins with shale sedimentation lack cephalopod limestones. Similar facies types also occur in the late Devonian of the Montagne Noire (France), Rheinisches Schiefergebirge (West Germany), Moravian Karst (Czechoslovakia), Holy Cross Mountains (Poland) and in the early Carboniferous of the Cantabrian Mountains (Spain). Due to strong late Variscan compressional tectonics and limited outcrops, detailed facies patterns could not be mapped in these regions, but the same facies types as in the eastern Anti-Atlas suggest similar coast/platform, slope and shallow basin topographies. During cephalopod limestone deposition water depth on the platforms was in the order of several tens to about one hundred metres, as is inferred from repeated subaerial exposures and distinctive depositional and faunal/floral features. Water depth in the adjacent shallow basins might have reached several hundreds of metres. Cephalopod limestones represent a typical stage in the evolution of geosynclines, characterized by extremely low sedimentation rates (1-5 m m.y. -1). This stage is preceded by deposition of thick neritic clastics and/or carbonates and is succeeded by deposition of deep-water clastics or flysch.

  4. Coal facies studies in Brazil. A short review

    Energy Technology Data Exchange (ETDEWEB)

    Correa da Silva, Zuleika Carretta [Rua Eca de Queiroz, 682/402, 90670-020, Porto Alegre RS (Brazil)


    Coal facies studies in Brazil have been done for south Brazilian coal measures over the last 20 years using different methods for reconstructing paleoenvironments of peat formation and deposition. The first studies were based on Teichmuller's concept of macerals; from 1984 to 1993, microlithotypes and palynomorphs were used according to the methodology described by Hacquebard and Donaldson. In the 1990s, a new method of interpreting paleoenvironments implementing organic geochemistry, sequence stratigraphy and the use of biomarkers has become more common in the literature, as well as the use of Diessel's Gelification Index (GI) and Tissue Preservation Index (TPI)

  5. SHRIMP U–Pb and REE data pertaining to the origins of xenotime in Belt Supergroup rocks: evidence for ages of deposition, hydrothermal alteration, and metamorphism (United States)

    Aleinikoff, John N.; Lund, Karen; Fanning, C. Mark


    The Belt–Purcell Supergroup, northern Idaho, western Montana, and southern British Columbia, is a thick succession of Mesoproterozoic sedimentary rocks with an age range of about 1470–1400 Ma. Stratigraphic layers within several sedimentary units were sampled to apply the new technique of U–Pb dating of xenotime that sometimes forms as rims on detrital zircon during burial diagenesis; xenotime also can form epitaxial overgrowths on zircon during hydrothermal and metamorphic events. Belt Supergroup units sampled are the Prichard and Revett Formations in the lower Belt, and the McNamara and Garnet Range Formations and Pilcher Quartzite in the upper Belt. Additionally, all samples that yielded xenotime were also processed for detrital zircon to provide maximum age constraints for the time of deposition and information about provenances; the sample of Prichard Formation yielded monazite that was also analyzed. Ten xenotime overgrowths from the Prichard Formation yielded a U–Pb age of 1458 ± 4 Ma. However, because scanning electron microscope – backscattered electrons (SEM–BSE) imagery suggests complications due to possible analysis of multiple age zones, we prefer a slightly older age of 1462 ± 6 Ma derived from the three oldest samples, within error of a previous U–Pb zircon age on the syn-sedimentary Plains sill. We interpret the Prichard xenotime as diagenetic in origin. Monazite from the Prichard Formation, originally thought to be detrital, yielded Cretaceous metamorphic ages. Xenotime from the McNamara and Garnet Range Formations and Pilcher Quartzite formed at about 1160– 1050 Ma, several hundred million years after deposition, and probably also experienced Early Cretaceous growth. These xenotime overgrowths are interpreted as metamorphic–diagenetic in origin (i.e., derived during greenschist facies metamorphism elsewhere in the basin, but deposited in sub-greenschist facies rocks). Several xenotime grains are older detrital grains of igneous

  6. Evolution of Migmatitic Granulite Complexes: implications from Lapland Granulite Belt, Part I: metamorphic geology

    Directory of Open Access Journals (Sweden)

    Pekka Tuisku


    Full Text Available The Palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Proterozoic terrains in the NE part of the Fennoscandian Shield concurrently with the accretion of Svecofennian arc complexes at ~1.9 Ga. The belt consists mainly of aluminous migmatiticmetagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly into the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas. This is supported by structural and contact relations of metasediments and igneous rocks, and by the lack progressive metamorphic reaction textures in the igneous rock series. The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quartz assemblageat 750−850°C and 5−8.5 kbar which lead to formation of a restitic palaeosome and peraluminous granitic melt in metapelites. Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pelitic rocks (650°C under the stability field of andalusite coexisting with potassium feldspar (2−3 kbar. Cooling was accompanied by the crystallization of the neosomes, often carrying aluminium-rich phases. Postmetamorphic duplexing of the LGB is clearly seen in the distribution of calculated PT conditions.

  7. Salt facies and budgets as environmental indicators in the Dead Sea (United States)

    Kiro, Yael; Goldstein, Steven L.; Stein, Mordechai; Garcia-Veigas, Javier; Levy, Elan J.; Lazar, Boaz


    Deep drilling in the Dead Sea reveals thick sections of halite that precipitated during the last three interglacials, when lake levels were low. Pore water and halite fluid inclusions show an increase in Mg concentration and a decrease in Na/Cl ratio during precipitation of halite, both during the last interglacial and the beginning of the Holocene. A mass balance based on the thickness of the halite layers and the changes in the chemical composition of the brine has been developed in order to calculate the change in the lake levels. Results indicate a drastic decrease in fresh water input, with the average discharge at 30% and 50% of the modern over thousands of years during the last interglacial and early Holocene, respectively. However, packages of detritus alternating with the halite indicate wetter episodes over intervals of centuries to a few millennia with conditions similar to the present-day, as well as more severe conditions with ~10% of the modern discharge over periods of decades to a few centuries. The different facies of halite in the core are well preserved. The lake level calculation based on the salt budget shows that although the lake level decreased drastically, the lake was always >100 m depth, and the absence of significant halite dissolution supports this conclusion. Thus, the halite reflects deep-water facies. There are two main halite crystal types. Small cumulate crystals that are formed on the lake surface, which alternate with bottom-growth crystals with relatively scarce fluid inclusion bands. The frequency of the crystal alternation varies between seasonal and multi-year changes and reflects the hydrological and limnological regime. The small cumulate crystals require that the lake surface was supersaturated with respect to halite, indicating high evaporation and possibly a thermally stratified water column. The bottom-growth crystals are formed only when it is not disturbed by the "rain" of cumulate crystals, with a lower degree of

  8. Neoarchean metamorphism recorded in high-precision Sm-Nd isotope systematics of garnets from the Jack Hills (Western Australia) (United States)

    Eccles, K. A.; Baxter, E. F.; Mojzsis, S. J.; Marschall, H.; Williams, M. L.; Jercinovic, M. J.


    .0Ma, 2612.4×6.0Ma, 2605.0×5.5Ma, and 2567.3×8.3Ma, while the second sample yielded a date of 2579.6×4.6 Ma (2σ). Compositional and geochronologic data indicate likely in situ garnet growth during a late Archean greenschist facies metamorphic event. These dates are generally consistent with published monazite ages placing a metamorphic event at ~ca.2.65Ga [4,5]. It remains possible that an as yet unidentified detrital garnet component is present and may explain some of the scatter in absolute age. [1] Baxter EF, Jordan MK & Inglis JD, 2010, Goldschmidt [2] Baxter EF, Eccles KA & Sullivan N, 2012, Goldschmidt [3] Harvey J & Baxter EF, 2009, Chem Geol, 258, 251-257 [4] Rasmussen B, et al, 2010, Precambrian Res, 180, 26-46 [5] Iizuka T, et al, 2010, Contrib Mineral Petr, 160, 803-823

  9. Design and accuracy analysis of a metamorphic CNC flame cutting machine for ship manufacturing (United States)

    Hu, Shenghai; Zhang, Manhui; Zhang, Baoping; Chen, Xi; Yu, Wei


    The current research of processing large size fabrication holes on complex spatial curved surface mainly focuses on the CNC flame cutting machines design for ship hull of ship manufacturing. However, the existing machines cannot meet the continuous cutting requirements with variable pass conditions through their fixed configuration, and cannot realize high-precision processing as the accuracy theory is not studied adequately. This paper deals with structure design and accuracy prediction technology of novel machine tools for solving the problem of continuous and high-precision cutting. The needed variable trajectory and variable pose kinematic characteristics of non-contact cutting tool are figured out and a metamorphic CNC flame cutting machine designed through metamorphic principle is presented. To analyze kinematic accuracy of the machine, models of joint clearances, manufacturing tolerances and errors in the input variables and error models considering the combined effects are derived based on screw theory after establishing ideal kinematic models. Numerical simulations, processing experiment and trajectory tracking experiment are conducted relative to an eccentric hole with bevels on cylindrical surface respectively. The results of cutting pass contour and kinematic error interval which the position error is from-0.975 mm to +0.628 mm and orientation error is from-0.01 rad to +0.01 rad indicate that the developed machine can complete cutting process continuously and effectively, and the established kinematic error models are effective although the interval is within a `large' range. It also shows the matching property between metamorphic principle and variable working tasks, and the mapping correlation between original designing parameters and kinematic errors of machines. This research develops a metamorphic CNC flame cutting machine and establishes kinematic error models for accuracy analysis of machine tools.

  10. A combined study of SHRIMP U-Pb dating, trace element and mineral inclusions on high-pressure metamorphic overgrowth zircon in eclogite from Qinglongshan in the Sulu terrane

    Institute of Scientific and Technical Information of China (English)

    LI Qiuli; LI Shuguang; HOU Zhenhui1; HONG Jian; YANG Wei1


    Methods recently advanced for discrimination on the genesis of metamorphic zircon, such as analysis of mineral inclusions and trace elements, provide us powerful means to distinguish zircon overgrowth during high-pressure metamorphism. Zircons in ultrahigh-pressure eclogite from Qinglongshan in the Sulu terrane were studied by the SHRIMP U-Pb method in combining with trace element and mineral inclusion analyses. No inherited core was identified in the analyzed zircons by means of cathodoluminescence images. The occurrence of high-pressure metamorphic mineral inclusions in zircon, such as garnet, omphacite, rutile, and the flat HREE pattern in zircon indicate that the zircon formed at high-pressure metamorphic conditions. Therefore, a weighted average U-Pb age of 227.4 ± 3.5 Ma obtained from such a kind of zircon is interpreted to represent the timing of peak metamorphism for the Qinglongshan eclogite.

  11. Simulating the metamorphic evolution of rocks in the laboratory: experimental modelling of orogenic metamorphism of metapelites using a piston cylinder apparatus (United States)

    Tropper, Peter; Mair, Philipp


    Metamorphic rocks contain a more or less complex mineral assemblage reflecting their metamorphic evolution. If the complex mineral assemblage is of multi-stage origin how do we know which mineral grew at which stage during the P-T evolution? To answer this question one needs to put constraints on the geological evolution of a given rock. The metamorphic evolution of a rock can be deciphered using three approaches: 1.) the practical geothermobarometric approach (inverse modelling), 2.) the theoretical pseudosection approach (forward modelling) and 3.) the experimental approach. Whereas with the first two approaches it is possible to constrain several stages of the P-T-X evolution but how do we know what assemblage is actually present at the desired P-T conditions? This question leads to the experimental approach, which allows a detailed mineralogical investigation of a given rock at distinct P-T conditions. Therefore, experimental investigations should be viewed as a forward modelling technique, which allow putting additional constraints on the evolution of a rock under defined P and T conditions and hence represents a snap-shot of a P-T point of the evolution of a given rock! For this purpose, simple experiments using natural rocks as starting materials can easily be conducted. The disadvantage of this method lies in the complex chemical composition of natural rocks and the deviation from chemical end-member systems. Therefore these experiments need to be evaluated not only 1.) in terms of their ability to reproduce the natural observations but also 2.) in their ability to reproduce theoretical calculations. In this study experimental investigations of orogenic metamorphism of metapelites (quartzphyllites with Grt1 + Ms1 + Ch1 + Bt1 + Rt) was investigated. Four different P-T conditions were chosen to represent an orogenic clockwise P-T loop: 400°C, 0.8 GPa, 600°C, 1.2 GPa, 700°C, 1 GPa and 500°C, 0.4 GPa. Two experiments with a duration of 16 and 33 days were

  12. Is the turbidite facies association scheme valid for interpreting ancient submarine fan environments? (United States)

    Shanmugam, G.; Damuth, J. E.; Moiola, R. J.


    Although turbidite facies reflect only processes of deposition, turbidite facies associations are routinely used to identify ancient submarine-fan subenvironments (e.g., upper fan, channel, lobe, etc.). The assumption that process of deposition also reflects environment of deposition may not be valid for the following reasons: (1) Mutti and Ricci Lucchi's facies association scheme for submarine fans has been developed exclusively from ancient turbidite sequences; however, the true relationship between such turbidite facies associations and related fan subenvironments has not been confirmed from modern fans; (2) individual channel-levee systems of many modern submarine fans are in many cases large enough to contain the entire ancient fan systems on which these facies associations are based; (3) large channel-levee systems comparable to those of modern fans have not been recognized in outcrops. Consequently, the validity of turbidite facies associations for interpreting ancient submarine-fan subenvironments must be considered tenuous until confirmed in modern fans.

  13. A review of 35 cases of asymmetric crying facies. (United States)

    Caksen, H; Odabaş, D; Tuncer, O; Kirimi, E; Tombul, T; Ikbal, M; Ataş, B; Ari Yuca, S


    A review of 35 cases of asymmetric crying facies: Congenital asymmetric crying facies (ACF) is caused by congenital hypoplasia or agenesis of the depressor anguli oris muscle (DAOM) on one side of the mouth. It is well known that this anomaly is frequently associated with cardiovascular, head and neck, musculoskeletal, respiratory, gastrointestinal, central nervous system, and genitourinary anomalies. In this article we report 35 ACF patients (28 children and 7 adults) and found additional abnormalities in 16 of them (i.e. 45%). The abnormalities were cerebral and cerebellar atrophy, mega-cisterna magna, mental motor retardation, convulsions, corpus callosum dysgenesis, cranial bone defect, dermoid cyst, spina bifida occulta, hypertelorism, micrognatia, retrognatia, hemangioma on the lower lip, short frenulum, cleft palate, low-set ears, preauricular tag, mild facial hypoplasia, sternal cleft, congenital heart defect, renal hypoplasia, vesicoureteral reflux, hypertrophic osteoarthropathy, congenital joint contractures, congenital hip dislocation, polydactyly, and umbilical and inguinal hernia. Besides these, one infant was born to a diabetic mother, and had atrial septal defect and the four other children had 4p deletion, Klinefelter syndrome, isolated CD4 deficiency and Treacher-Collins like facial appearance, respectively Although many of these abnormalities were reported in association with ACF, cerebellar atrophy, sternal cleft, cranial bone defect, infant of diabetic mother, 4p deletion, Klinefelter syndrome, isolated CD4 deficiency and Treacher-Collins like facial appearance were not previously published.

  14. Mid-Neoproterozoic (ca. 830-800 Ma) metamorphic P-T paths link Tarim to the circum-Rodinia subduction-accretion system (United States)

    Ge, Rongfeng; Zhu, Wenbin; Wilde, Simon A.


    Long-lived exterior accretionary orogeny shapes tectonothermal evolution of the peripheral building blocks of supercontinents and leads to considerable crustal growth. However, such accretionary orogeny has only been locally recognized for the Rodinia supercontinent. Here a suite of newly discovered mid-Neoproterozoic high-grade metamorphic rocks in the northern Tarim Craton, NW China, are used to test the exterior accretion hypothesis for Rodinia. These rocks occur as dark-colored mafic and calc-silicate boudins in impure marbles and mica schists. Geochemical data suggest a protolith of arc-related basalts metasomatized by Ca-rich fluids. Mineral assemblages, phase diagram modeling, and mineral compositions for a garnet pyroxenite and a garnet clinopyroxene gneiss reveal upper amphibolite to high-pressure granulite facies peak metamorphism (660-700°C, 11-12 kbar) following a counterclockwise P-T path, which is characterized by prograde burial and heating, followed by near-isothermal burial and retrograde exhumation and cooling. This P-T path is interpreted to have recorded crustal thickening of an earlier magmatic arc transformed to a fore arc by subduction erosion and subsequent burial along bent isotherms near the subduction channel. All studied samples record ca. 830-800 Ma metamorphic zircon U-Pb ages, which probably date the early exhumation and cooling according to Ti-in-zircon temperatures, zircon rare earth element patterns, and Hf isotopes. This is the first mid-Neoproterozoic P-T-t path in Tarim, and it provides metamorphic evidence for a mid-Neoproterozoic advancing-type accretionary orogeny, which is coeval with the initial breakup events of Rodinia and thus links Tarim to the circum-Rodinia accretion system, supporting the peripheral subduction model.

  15. Elemental geochemistry and Nd isotopic characteristics of the metasedimentary rocks from the metamorphic belt in central Jiangxi: Provenance and tectonically environmental constraints

    Institute of Scientific and Technical Information of China (English)

    HU Gongren; LIU Congqiang; ZHANG Bangtong; TANG Hongfeng; YU Ruilian


    The metamorphic belt in central Jiangxi, located in the compound terrain within the Cathaysia, Yangtze Block and Caledonian fold zone of South China, is composed dominantly of meta-argillo-arenaceous rocks, with minor amphibolite. These rocks underwent amphibolite-facies metamorphism. The meta-argillo-arenaceous rocks show large variations in major element composition, but have similar REE patterns and trace element composition, incompatible element and LIE enrichments [ high Th/Sc (0.57-3.59) , La/Sc ( 1.46 - 12.4), La/Yb (5.84 - 19.0) ] and variable Th/U ratios, with ∑REE = 129-296μg/g, δEu =0.51 -0.86, and (La/Yb)N = 3.95 -12.9. The Nd isotopic model ages tDM of these rocks vary from 1597 to 2124 Ma. Their 143 Nd/144 Nd values are low [εNd (0) = - 11.4 to -- 15.8]. Some conclusions have been drawn as follows: (1) The metamorphic rocks in central Jiangxi Province are likely formed in a tectonic environment at the passive continental margin of the Cathaysia massif. (2) The metamorphosed argillo-arenaceous rocks are composed dominantly of upper crustal-source rocks (Al- and Krich granitic or/and sedimentary rocks of Early Proterozoic), which experienced good sorting, slow deposition and more intense chemical weathering. (3) According to the whole-rock Sm-Nd isochron ages (1113±49 to 1199 ± 26 Ma) of plagioclase-amphibole (schist) and Nd isotopic model age tDM ( 1597 - 2124Ma) of meta-argillo-arenaceous rocks, the metamorphic belt in central Jiangxi Province was formed during the Middle Proterozoic ( 1100 - 1600 Ma).

  16. Fluid evolution in H2O-CO2-NaCl system and metallogenic analysis of the Surian metamorphic complex, Bavanat Cu deposit, Southwest Iran (United States)

    Asadi, Sina; Moore, Farid


    The Bavanat Cu deposit occurs as veins controlled by a NE-trending structure within the Permo-Triassic Surian metamorphic complex (SMC), southwest of Iran. The SMC rocks exposed in the area have undergone greenschist-facies metamorphism. The ore-forming process can be divided into early, middle, and late stages, represented by, respectively, pyrite-quartz, polymetallic sulfide-quartz, and late-stage barren quartz veins. Systematic studies of fluid inclusions (FIs) in the quartz veins found four types: aqueous, mixed aqueous-carbonic, carbonic, and multiphase-bearing inclusions. The FIs of early, middle and late-stages are mainly homogenized at temperatures of 335-417 °C, 230-380 °C, and 190-227 °C, with salinities of 1.1-6.7, 2.9-36.6, and 0.8-2.6 wt.% NaCl equivalent, respectively. The main stage of Cu mineralization is related to the middle-stage, where FIs show evidence of fluid immiscibility. The metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility, cooling, crystallization of multiphase-bearing inclusions, and a small increase in pH. Laser Raman spectroscopy and FIs evidences indicate that the metallogenic system evolved from metamorphic CO2 (+CH4)-rich, relatively high fO2 (10-25 to 10-29 bars) to CO2-poor and relatively low fO2 (10-31 to 10-34 bars). Muscovite from the middle-stage veins yields 40Ar/39Ar plateau age of 195.2 ± 1.0 Ma, suggesting that the Cu mineralization at Bavanat formed in the Early Jurassic coeval with the retrograde metamorphic events during the post-early Cimmerian orogeny.

  17. Fluid evolution in H2O-CO2-NaCl system and metallogenic analysis of the Surian metamorphic complex, Bavanat Cu deposit, Southwest Iran (United States)

    Asadi, Sina; Moore, Farid


    The Bavanat Cu deposit occurs as veins controlled by a NE-trending structure within the Permo-Triassic Surian metamorphic complex (SMC), southwest of Iran. The SMC rocks exposed in the area have undergone greenschist-facies metamorphism. The ore-forming process can be divided into early, middle, and late stages, represented by, respectively, pyrite-quartz, polymetallic sulfide-quartz, and late-stage barren quartz veins. Systematic studies of fluid inclusions (FIs) in the quartz veins found four types: aqueous, mixed aqueous-carbonic, carbonic, and multiphase-bearing inclusions. The FIs of early, middle and late-stages are mainly homogenized at temperatures of 335-417 °C, 230-380 °C, and 190-227 °C, with salinities of 1.1-6.7, 2.9-36.6, and 0.8-2.6 wt.% NaCl equivalent, respectively. The main stage of Cu mineralization is related to the middle-stage, where FIs show evidence of fluid immiscibility. The metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility, cooling, crystallization of multiphase-bearing inclusions, and a small increase in pH. Laser Raman spectroscopy and FIs evidences indicate that the metallogenic system evolved from metamorphic CO2 (+CH4)-rich, relatively high fO2 (10-25 to 10-29 bars) to CO2-poor and relatively low fO2 (10-31 to 10-34 bars). Muscovite from the middle-stage veins yields 40Ar/39Ar plateau age of 195.2 ± 1.0 Ma, suggesting that the Cu mineralization at Bavanat formed in the Early Jurassic coeval with the retrograde metamorphic events during the post-early Cimmerian orogeny.

  18. Determining age of Pan African metamorphism using Sm-Nd garnet-whole rock geochronology and phase equilibria modeling in the Tasriwine ophiolite, Sirwa, Anti-Atlas Morocco (United States)

    Inglis, Jeremy D.; Hefferan, Kevin; Samson, Scott D.; Admou, Hassan; Saquaque, Ali


    Sm-Nd garnet-whole rock geochronology and phase equilibria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex, Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ∼0.72 GPa and ∼615 °C and ended at ∼0.8 GPa and ∼640 °C. A bulk garnet Sm-Nd age of 647.2 ± 1.7 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is over 15 million years younger than a previous age estimate of regional metamorphism of 663 ± 13 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Iriri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm-Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  19. Sedimentology and clast fabric of subaerial debris flow facies in a glacially-influenced alluvial fan (United States)

    Eyles, N.; Kocsis, S.


    A large alluvial fan (2 km 2), constructed between 11,000 and 7000 years B.P. at the mouth of Cinquefoil Creek in interior British Columbia, Canada, is identified as "glacially-influenced, debris flow-dominated". The fan was rapidly constructed during and immediately after deglaciation when large volumes of glacial debris were resedimented downslope; fans of this type are widespread in the glaciated portion of the North American Cordillera. Diamict facies, deposited as debris flows, account for 48% of the fan volume, sheetflodd gravels 37%, and other facies 15%. Diamicts show three facies types; crudely-bedded facies containing rafts of soft sediment that are attributed to downslope collapse and mixing of heterogeneous glacial deposits. These occur within the core of the fan. Massive and weakly graded (inverse to normal) diamict facies, derived from the downslope flow of weathered volcanic bedrock, occur within a well-defined bed that can be traced across the entire fan. The occurrence of weakly graded facies as lateral equivalents to massive facies within the same bed, implies the partial development of turbulent, high-velocity "streams" within a viscous debris flow moving over a slope of 6°. Clast fabrics in these facies show weakly-clustered a-axes dipping up and downslope comparable to other debris flows and lahars. The Cinquefoil fan, its internal structure and facies, provides a good "modern" analogue for ancient diamictite sequences deposited in areas of active uplift, rifting and glaciation.

  20. Organic matter and metamorphic history of CO chondrites (United States)

    Bonal, Lydie; Bourot-Denise, Michèle; Quirico, Eric; Montagnac, Gilles; Lewin, Eric


    The metamorphic grades of a series of eight CO3 chondrites (ALHA77307, Colony, Kainsaz, Felix, Lancé, Ornans, Warrenton and Isna) have been quantified. The method used was based on the structural grade of the organic matter trapped in the matrix, which is irreversibly transformed by thermal metamorphism. The maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration. This metamorphic tracer is thus valid whatever the chemical class of chondrites. Moreover, it is sensitive to the peak metamorphic temperature. The structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals, Fa and Fs silicate composition in type I chondrules, presolar grains and noble gas (P3 component) abundance. The deduced metamorphic hierarchy and the attributed petrographic types are the following: ALHA77307 (3.03) Chopin C., and Rouzaud J. N. (2002) Raman spectrum of carbonaceous material in metasediments: a new geothermometer. J. Metamorph. Geol., 20, 859-871]. A value of 330 °C was obtained for Allende (CV chondrite), Warrenton and Isna, consistent with temperatures estimated from Fe diffusion [Weinbruch S., Armstrong J., and Palme H. (1994). Constraints on the thermal history of the Allende parent body as derive from olivine-spinel thermometry and Fe/Mg interdiffusion in olivine. Geochim. Cosmochim. Acta58(2), 1019-1030.], from the Ni content in sulfide-metal assemblages [Zanda B., Bourot-Denise M., and Hewins R. (1995) Condensate sulfide and its metamorphic transformations in primitive chondrites. Meteorit. Planet. Sci.30, A605.] and from the d002 interlayer spacing in poorly graphitized carbon [Rietmeijer, F., and MacKinnon, I. (1985) Poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials. Nature, 315, 733-736]. The trapped noble gas and C content appear to be sensitive but not precise metamorphic tracers, indicating that the "Ornans

  1. Pennsylvanian coniferopsid forests in sabkha facies reveal the nature of seasonal tropical biome (United States)

    Falcon-Lang, H. J.; Jud, N.A.; John, Nelson W.; DiMichele, W.A.; Chaney, D.S.; Lucas, S.G.


    Pennsylvanian fossil forests are known from hundreds of sites across tropical Pangea, but nearly all comprise remains of humid Coal Forests. Here we report a unique occurrence of seasonally dry vegetation, preserved in growth position along >5 km of strike, in the Pennsylvanian (early Kasimovian, Missourian) of New Mexico (United States). Analyses of stump anatomy, diameter, and spatial density, coupled with observations of vascular traces and associated megaflora, show that this was a deciduous, mixed-age, coniferopsid woodland (~100 trees per hectare) with an open canopy. The coniferopsids colonized coastal sabkha facies and show tree rings, confirming growth under seasonally dry conditions. Such woodlands probably served as the source of coniferopsids that replaced Coal Forests farther east in central Pangea during drier climate phases. Thus, the newly discovered woodland helps unravel biome-scale vegetation dynamics and allows calibration of climate models. ?? 2011 Geological Society of America.

  2. Formation of metamorphic core complexes in non-over-thickened continental crust: A case study of Liaodong Peninsula (East Asia)


    Wang, Kun; Burov, Evgueni; Gumiaux, Charles; Chen, Yan; Lu, Gang; Mezri, Leila; Zhao, Liang


    International audience; Pre-thickened hot orogenic crust is often considered a necessary condition for the formation of continental metamorphic core complexes (MCCs). However, the discovery of MCCs in the Liaodong Peninsula, where the crust has a normal thickness (~ 35 km), challenges the universality of this scenario. Therefore, we implement a series of 2-D numerical thermo-mechanical modeling experiments in which we investigate the conditions of MCC formation in normal crusts, as well as th...

  3. Fluid-related modifications of Cr-spinel and olivine from ophiolitic peridotites by contact metamorphism of granitic intrusions in the Ablah area, Saudi Arabia (United States)

    Ahmed, Ahmed Hassan; Surour, Adel Abdullah


    heterogeneous modification in which the alteration starts from the cores outwards forming a very characteristic "atoll" textured SiO2- and Cr-rich porous spinel. This type is characterized by core-to-rim increase in Cr, Fe3+, Si, Mn, Ni and Ti, and decrease in Mg, Al and Fe2+. The mineral assemblage in equilibrium with this pattern is chlorite + carbonates + lizardite/chrysotile ± antigorite. The first modification pattern is suggested to form under nearly solid-state conditions in the distal part from the granitic intrusion. The second pattern could be formed under reducing conditions with high temperature and fluid/rock ratio near the contact zone. The peak metamorphic temperature of this stage ranges from 500 to 650 °C that indicate upper amphibolite facies conditions. During retrograde metamorphism, the hydrothermal fluids are cooler and oxidizing which lead to the precipitation of thick marble-like carbonate veins within the serpentinized peridotites. In such a case, the aqueous fluids attack the Al- and Mg-rich cores, which are less resistant and replicable than the Fe-rich rims, and form the third chemical modification pattern of porous SiO2-rich spinel. The high SiO2 content in Cr-spinel is most probably attributed to the formation of Mg- and Al-rich silicates within the sub-microscopic pores of altered Cr-spinel.

  4. Ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites (United States)

    Scott, E. R. D.; Lusby, D.; Keil, K.


    Ten objects with aberrant Fe/(Fe + Mg) ratios have been found in apparently unbrecciated types 4-6 H and L chondrites. Since the Fe/(Fe + Mg) ratios of these objects are incompatible with the metamorphic history of the host chondrites, it is concluded that a high proportion of ordinary chondrites are breccias that were lithified after peak metamorphism. This is consistent with the results of Scott (1984), who concluded that most type three ordinary chondrites are breccias of materials with diverse thermal histories, even though they do not show prominent brecciation. It is found that the classification scheme of Van Schmus and Wood (1967) does not identify chondrites with similar thermal histories; the petrologic type of a chondrite is only a measure of the average thermal history of its ingredients. Chondrite and achondrite breccias are also compared in order to understand how brecciation of chondrites after metamorphism is so well camouflaged.

  5. Submarine hydrothermal metamorphism of the Del Puerto ophiolite, California. (United States)

    Evarts, R.C.; Schiffman, P.


    Metamorphic zonation overprinted on the volcanic member and overlying volcanogenic sediments of the ophiolite complex increases downward in grade and is characterized by the sequential appearance with depth of zeolites, ferric pumpellyite and pistacitic epidote. Metamorphic assemblages of the plutonic member of the complex are characterized by the presence of calcic amphibole. The overprinting represents the effects of hydrothermal metamorphism resulting from the massive interaction between hot igneous rocks and convecting sea-water in a submarine environment. A thermal gradient of 100oC/km is postulated to account for the zonal recrystallization effects in the volcanic member. The diversity and sporadic distribution of mineral assemblages in the amphibole zone are considered due to the limited availability of H2O in the deeper part of the complex. Details of the zonation and representative microprobe analyses are tabulated.-M.S.

  6. Post-inversion stage of regional metamorphism of coals

    Energy Technology Data Exchange (ETDEWEB)

    Proskuryakov, A.Ye.


    A study is made of the metamorphism of coals in Kuznetsk Basin. To interpret the stages of coalification, measurements were used of the indicators of vitrinite along the hinges of folds, graphic plottings of isometamorphism of coals, analysis of interrelationships of the isolines of coal metamorphism with isopachites covering their deposits. The elevation of the coal mass of Kuzbass in the post-inversion time was accompanied by the formation of steep linear folds and longitudinal bending of their hinges. As a consequence of this, the hinges of the folds in beds of the same name occurred at different depths from the modern surface, however coal metamorphism along the hinges has not changed. In the Kuznetsk Basin there are no traces of post-inversion coalification.

  7. Metamorphic Algorithm of Self-reconfigurable Modular Robotic System

    Institute of Scientific and Technical Information of China (English)

    徐威; 王高中; 李倩; 王石刚


    A self-reconfigurable robot is a non-linear complex system composed of a large number of modules. The complexity caused by non-linearity makes it difficult to solve the problem of module motion planning and shape-changing control with the traditional algorithm. In this paper, a full-discrete metamorphic algorithm is proposed. The modules concurrently process the local sensing information, update their eigenvector, and act by the same predetermined logical rules. Then a reasonable motion sequence for modules and the global metamorphosis can be obtained. Therefore, the complexity of metamorphic algorithm is reduced, the metamorphic procedure is simplified, and the self-organizing metamorphosis can be obtained. The algorithm cases of several typical systems are studied and evaluated through simulation program of 2-D planar homogeneous modular systems.

  8. Metamorphic Virus Detection in Portable Executables Using Opcodes Statistical Feature

    CERN Document Server

    Rad, Babak Bashari


    Metamorphic viruses engage different mutation techniques to escape from string signature based scanning. They try to change their code in new offspring so that the variants appear non-similar and have no common sequences of string as signature. However, all versions of a metamorphic virus have similar task and performance. This obfuscation process helps to keep them safe from the string based signature detection. In this study, we make use of instructions statistical features to compare the similarity of two hosted files probably occupied by two mutated forms of a specific metamorphic virus. The introduced solution in this paper is relied on static analysis and employs the frequency histogram of machine opcodes in different instances of obfuscated viruses. We use Minkowski-form histogram distance measurements in order to check the likeness of portable executables (PE). The purpose of this research is to present an idea that for a number of special obfuscation approaches the presented solution can be used to i...

  9. Mid-Eocene alluvial-lacustrine succession at Gebel El-Goza El-Hamra (Shabrawet area, NE Eastern Desert, Egypt): Facies analysis, sequence stratigraphy and paleoclimatic implications (United States)

    Wanas, H. A.; Sallam, E.; Zobaa, M. K.; Li, X.


    This study aims to provide the depositional facies, sequence stratigraphic and paleoclimatic characteristics of the Mid-Eocene (Bartonian) continental succession exposed at Gebel El-Goza El-Hamra (Shabrawet Area, NE Eastern Desert, Egypt). The studied succession consists of siliciclastic rocks followed upward by carbonate rocks. Detailed field observation and petrographic investigation indicate accumulation in floodplain-dominated alluvial and shallow lacustrine systems. The floodplain-dominated alluvial facies (45 m thick) is composed mainly of carbonate nodules-bearing, mottled mudrock with subordinate sandstone and conglomerate beds. The conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits. The massive, laminated, planner cross-bedded, fine- to medium-grained sandstone bodies interlayered within mudstone reflect sheet flood deposits. The mudrocks associated with paleosols represent distal floodplain deposits. The shallow lacustrine facies (15 m thick) is made up of an alternation of marlstone, micritic limestone, dolostone and mudrock beds with charophytes and small gastropods. Both the alluvial and lacustrine facies show evidence of macro-and micro-pedogenic features. Pollen assemblages, stable δ18O and δ13C isotopes, and paleopedogenic features reflect prevalence of arid to semi-arid climatic conditions during the Bartonian. The sequence stratigraphic framework shows an overall fining-upward depositional sequence, consisting of Low- and High-accommodation Systems Tracts (LAST, HAST), and is bounded by two sequence boundaries (SB-1, SB-2). Conglomerate and pebbly sandstone deposits (braided channel and sheet flood deposits) of the lower part of the alluvial facies reflect a LAST. Mudrock and silty claystone facies (distal floodplain deposits) of the upper part of alluvial facies and its overlying lacustrine facies correspond to a HAST. The LAST, HAST and SB were formed during different accommodation-to-sediment supply (A

  10. Pseudo- and real-inverted metamorphism caused by the superposition and extrusion of a stack of nappes: a case study of the Southern Brasília Orogen, Brazil (United States)

    da Motta, Rafael Gonçalves; Moraes, Renato


    The Southern Brasília Orogen is a Neoproterozoic belt that occurs along the southernmost border of the São Francisco Craton where the Andrelândia Nappe System represents the subducted sedimentary domain and is divided into three allochthonous groups, of which the ages and P-T conditions of metamorphism are studied here. The basal unit, the Andrelândia Nappe, exhibits an inverted metamorphic pattern. The base of the structure, composed of staurolite, garnet, biotite, kyanite, quartz, and muscovite, marks the metamorphic peak, whereas at the top, the association of the metamorphic peak does not contain staurolite. The Liberdade Nappe, the middle unit, presents a normal metamorphic pattern; its base, close to the Andrelândia Nappe, shows paragneiss with evidence of in situ partial melting, and towards the top, coarse-grained staurolite schist is found. The staurolite-out and melt-in isograds are coincident and parallel to the main foliation. Thus, the shear zone that limits the nappes is syn-metamorphic, reheating the underlying Andrelândia Nappe and influencing the establishment of metamorphic inversion. This suggestion is supported by the monazite chemical ages, which indicates that the Andrelândia Nappe metamorphic peak (586 ± 15 Ma) is younger than that of the Liberdade Nappe (622.3 ± 7.6 Ma). The upper unit, the Serra da Natureza Klippe, bears a typical high-pressure granulite mineral assemblage that is composed of kyanite, garnet, K-feldspar, rutile, and leucosome, as well as a metamorphic peak at 604.5 ± 6.1 Ma. This tectonic assembly, with inverted and non-inverted metamorphic patterns and generation of klippen structures, is consistent with exhumation models and a strong indentor located in the lower continental crust.

  11. Latest Jurassic-early Cretaceous regressive facies, northeast Africa craton

    Energy Technology Data Exchange (ETDEWEB)

    van Houten, F.B.


    Nonmarine to paralic detrital deposits accumulated in six large basins between Algeria and the Arabo-Nubian shield during major regression in latest Jurassic and Early Cretaceous time. The Ghadames Sirte (north-central Libya), and Northern (Egypt) basins lay along the cratonic margin of northeastern Africa. The Murzuk, Kufra, and Southern (Egypt) basins lay in the south within the craton. Data for reconstructing distribution, facies, and thickness of relevant sequences are adequate for the three northern basins only. High detrital influx near the end of Jurassic time and in mid-Cretaceous time produced regressive nubian facies composed largely of low-sinuosity stream and fahdelta deposits. In the west and southwest the Ghadames, Murzuk, and Kufra basins were filled with a few hundred meters of detritus after long-continued earlier Mesozoic aggradation. In northern Egypt the regressive sequence succeeded earlier Mesozoic marine sedimentation; in the Sirte and Southern basins correlative deposits accumulated on Precambrian and Variscan terranes after earlier Mesozoic uplift and erosion. Waning of detrital influx into southern Tunisia and adjacent Libya in the west and into Israel in the east initiated an Albian to early Cenomanian transgression of Tethys. By late Cenomanian time it had flooded the entire cratonic margin, and spread southward into the Murzuk and Southern basins, as well as onto the Arabo-Nubian shield. Latest Jurassic-earliest Cretaceous, mid-Cretaceous, and Late Cretaceous transgressions across northeastern Africa recorded in these sequences may reflect worldwide eustatic sea-level rises. In contrast, renewed large supply of detritus during each regression and a comparable subsidence history of intracratonic and marginal basins imply regional tectonic control. 6 figures.

  12. Facies del subfondo del canal Beagle, Tierra del Fuego

    Directory of Open Access Journals (Sweden)

    Gustavo Bujalesky


    Full Text Available El canal Beagle conecta los océanos Pacífico y Atlántico en el extremo meridional de Sudamérica y se ubica en el ambiente subantártico. Conforma una cuenca de unos 300 m de profundidad máxima y está separada del océano Atlántico por un umbral de 30 m de profundidad. El canal es un valle tectónico que fue completamente cubierto por el hielo glacial durante la última glaciación. Posteriormente, el canal fue ocupado por un lago glacial desde los 12.000 a los 8.000 años A.P., cuando fue invadido por el mar que alcanzó un nivel máximo entre los 6.000 y 5.000 años A.P. Con el objetivo de analizar las facies sedimentarias superficiales y del subfondo del canal se realizó un relevamiento geofísico con sonar de barrido lateral y un perfilador de 3,5 kHz. Sobre un basamento constituido por rocas metamórficas del Mesozoico, se identificaron depósitos de till y secuencias granodecrecientes que representan distintos estadios del retroceso glaciar, evidenciando hacia la sección superior facies lacustres y por encima depósitos de la transgresión marina del Holoceno. Además, se han identificado paleocauces y secuencias fluviales cubiertas por sedimentos marinos transgresivos.

  13. The onset of metamorphism in ordinary and carbonaceous chondrites (United States)

    Grossman, J.N.; Brearley, A.J.


    Ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by X-ray mapping techniques. A variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) methods. The distribution of Cr in FeO-rich olivine systematically changes as metamorphism increases between type 3.0 and type 3.2. Igneous zoning patterns are replaced by complex ones and Cr-rich coatings develop on all grains. Cr distributions in olivine are controlled by the exsolution of a Cr-rich phase, probably chromite. Cr in olivine may have been partly present as tetrahedrally coordinated Cr3+. Separation of chromite is nearly complete by petrologic type 3.2. The abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type. TEM shows this to be the result of crystallization of albite. Residual glass compositions systematically change during metamorphism, becoming increasingly rich in K. Glass in type I chondrules also gains alkalis during metamorphism. Both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules. The matrix in the least metamorphosed chondrites is rich in S and Na. The S is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains. Progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules. Alkalis initially leave the matrix and enter chondrules during early metamorphism. Feldspar subsequently nucleates in the matrix and Na re-enters from chondrules. These metamorphic trends can be used to refine classification schemes for chondrites. Cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to

  14. The effect of thermal resetting and recrystallisation on white mica 40Ar/39Ar ages during retrograde metamorphism on Syros, Greece (United States)

    Uunk, Bertram; Wijbrans, Jan; Brouwer, Fraukje


    White mica 40Ar/39Ar dating is a proven powerful tool for constraining timing of metamorphism, deformation and exhumation. However, in high-pressure metamorphic rocks, dating often results in wide age ranges which are not in agreement with constraints from other isotopic systems, indicating that geological and chemical processes complicate straightforward 40Ar/39Ar dating. In this research project, white mica ages from rocks of the Cycladic Blueschist Unit on Syros, Greece with contrasting rheology and strain mechanisms are compared, in order to better understand the role of deformation, recrystallization and fluid flow on 40Ar/39Ar ages of white mica during retrograde metamorphism. Resulting ages vary along different sections on the island, inconsistent with other isotopic constraints on eclogite-blueschist metamorphism (55-50 Ma) and greenschist overprinting (41-30 Ma). Two end-member models are possible: 1) Results represent continuous crystallization of white mica while moving from blueschist to greenschist conditions in the metamorphic P-T loop, or 2) white mica equilibrated in eclogite-blueschist conditions and their diffusion systematics were progressively perturbed during greenschist overprinting. The single grain fusion analyses yielded contrasting age distributions, which indicate contrasts in degree of re-equilibration during retrograde metamorphism. Step wise heating of larger grain populations resulted in flat plateau shapes, providing no evidence for partial resetting. Electron microprobe measurements of Si per formula unit, as a proxy for pressure during crystallisation, do not explain age variation within sections or on the island scale. The previously unreported north-south age trend and age ranges per sample, as shown only in the 40Ar/39Ar system of the metapelitic and marble lithologies, contains key information that will allow us to test between different scenarios for age formation. Excess argon infiltration at this stage seems to have been of

  15. An integrated tectonothermal model for the evolution of the High Himalaya in western Zanskar with constraints from thermobarometry and metamorphic modeling (United States)

    Walker, C. B.; Searle, M. P.; Waters, D. J.


    We present an integrated model for the tectonothermal evolution of the High Himalaya in NW Zanskar based on detailed field mapping, petrographic and microstructural analysis, thermobarometric techniques, and metamorphic modeling. Metasedimentary lithologies in the Suru valley can be correlated with the Palaeozoic-Mesozoic Tethyan shelf sediments along the north Indian continental margin in Kashmir and Ladakh, and metaigneous amphibolites correlate with Permian rift-related igneous units. Subsequent to India-Asia collision at ca. 54 Ma, crustal thickening of Indian plate rocks resulted in a polyphase deformational and metamorphic history. The large-scale structure of the area is that of kilometer-scale, SW vergent recumbent folds that have been folded by structurally lower, later domes such as the Suru Dome. Prograde M1 metamorphism reached a maximum of kyanite grade and is believed to be synkinematic to postkinematic with respect to the formation of the large folds. Thermobarometric analysis indicates that peak conditions relating to this Harrovian event between 33 and 28 Ma were 9.5-10.5 kbar and 620°-650°C. A later metamorphic event (M2) associated with doming throughout the Zanskar Himalaya and crustal anatexis in the sillimanite + K-feldspar-grade core of the High Himalaya caused reequilibration of deeper Suru Dome rocks to slightly lower pressures (4.5-7 kbar). Metamorphic modeling, involving phase diagram construction and pressure-temperature (P-T) path determination, suggests that metamorphic garnets grew under conditions of heating and burial along moderate slopes in P-T space. Rapid exhumation of the High Himalayan Crystallines between the Main Central Thrust and the Zanskar Shear Zone occurred during or immediately after peak M2 metamorphism (21.5-19.5 Ma).

  16. Metamorphic crystallization kinetics quantified through space and time (United States)

    Kelly, E. D.; Carlson, W. D.; Ketcham, R. A.


    Numerical simulations of diffusion-controlled nucleation and growth of garnet porphyroblasts in regionally metamorphosed rocks constrain values for interfacial energy and rates of nucleation and Al intergranular diffusion, quantities that exert a strong control on the sizes and disposition of porphyroblasts in most metamorphic rocks. During simulation of a reaction, product crystals consume a rate-limiting component (Al) and gradients in Al concentration in the intergranular fluid develop between the product and reactant crystals. Low Al concentrations surrounding product crystals (low reaction affinity) reduce nucleation probability, creating a tendency toward spatial ordering of crystal centers in homogeneous portions of a rock. Also, as Al depletion zones impinge, crystals compete for Al, resulting in a tendency toward smaller sizes for neighboring crystals and larger sizes for those that grow in isolation. These phenomena produce distinctive textural effects that allow the simulations to be constrained by measurements of the sizes and locations of porphyroblasts in natural samples. The 13 rocks analyzed in this study were collected from 7 localities exhibiting a diverse range of crystallization conditions. In the simulations, unknown kinetic parameters governing nucleation and intergranular diffusion were adjusted iteratively to achieve fits between simulated and natural porphyroblastic textures. Model fits were assessed primarily from textural characteristics precisely measured by high-resolution X-ray computed tomography. The range of interfacial energies obtained for heterogeneous nucleation is 0.007-0.118 J/m2 for the sample suite, assuming shape factors in the range 0.1-1.0. Nucleation rates change through space and time due to growth and impingement of Al depletion zones. In some modeled rocks, the actual (whole-rock) rate rises steeply, achieves a steady state, and then falls rapidly as reactants are consumed; in others, the steady-state is not achieved

  17. conditions

    Directory of Open Access Journals (Sweden)

    M. Venkatesulu


    Full Text Available Solutions of initial value problems associated with a pair of ordinary differential systems (L1,L2 defined on two adjacent intervals I1 and I2 and satisfying certain interface-spatial conditions at the common end (interface point are studied.

  18. Research on Diageneses of Cambrian Shoal Facies Carbonate Rocks in the Xiadong Area, Hubei Province

    Institute of Scientific and Technical Information of China (English)

    张秀莲; 蒋凌志


    With continuous outcrops, developed shoal facies rocks, complete types of diagenesis and changeable diagenetic environments, Cambrian strata are well developed in the Xiadong area, Yichang, Hubei Province. Under the combined influence of numerous diageneses, secondary pores can be formed, which result in better reservoir properties of the rock strata. The Cambrian rocks in this area consist of mainly carbonate rocks and secondarily detrital rocks. The carbonate rocks are dominated by grainstones including wormkalk, calcirudite-calcarenite, oolitic limestone and oncolitic limestone. Graded bedding and cross bedding are well developed in the strata, which indicates that the formation environment is of a high-energy shoal facies. In this area, there has developed a sequence of stable Cambrian platform carbonate deposition. The evolution trend is as follows: open sea shelf facies? intertidal low-energy restricted sea facies? intertidal high-energy shoal facies? coastal shoal facies? evaporite tidal-flat facies. The diageneses that the strata have experienced mainly include dolomitization, dedolomitization and dissolution, which are constructive diageneses for the formation of secondary pores, such as intercrystal pores, intercrystal solution pores, gypsum mold pores and caverns of dolomite. The diagenetic facies intervals can be divided into the unitary and the compound ones, totalling 22 in the area. In the early atmospheric fresh-water diagenetic environment and the late epidiagenetic environment, Cambrian rocks, especially dolomite of the Middle and Upper Cambrian, experienced extensive and profound fresh water corrosion, forming pore intervals with a porosity ranging from 5% to 15%.

  19. Facies discrimination in a mixed fluvio-eolian setting using elemental whole rock geochemistry

    DEFF Research Database (Denmark)

    Svendsen, Johan; Friis, Henrik; Stollhofen, Harald


    performed on the geochemical data has enabled discrimination of seven of the eight facies types. Furthermore, the facies discrimination method allowed a quantitative estimate of the degree of fluvial reworking of eolian sand. We believe that the method presented here, when calibrated to a reference well...

  20. Tectono-metamorphic evolution and timing of the melting processes in the Svecofennian Tonalite-Trondhjemite Migmatite Belt: An example from Luopioinen, Tampere area, southern Finland

    Directory of Open Access Journals (Sweden)

    Mouri, H.


    Ma, which is marginally younger than the age of the adjacent mesosome and the concordant leucosome (1877+18 and 1880±23 Ma, respectively and the age of monazite. Zircons from the studied migmatites display complex zoning structures using SEM-based CL-imaging. Most grains have distinct cores, clearly remnants of original grains. The cores display various types of zoning but oscillatory zoning dominates. The cores are overgrown by one or two thin outer rims that are of two types: i unzoned outer rim, considered as overgrowth of new zircon during a metamorphic event, and ii weakly oscillatory zoned rim, considered as typical of magmatic recrystallization. Ion probe dating of cores yielded slightly discordant 207Pb/206Pb ages of between 2866-2002 Ma, which are interpreted as protolith age. Rims yielded two major age groups: the unzoned rims gave ages of 1872-1886 Ma, whereas the rims with oscillatory zoning yielded ages of 1951—1959 Ma. The youngest age group is consistent with the conventional Sm-Nd dating on garnet and U-Pb dating on monazite and we suggest that the migmatites were metamorphosed at granulite facies conditions at ca. 1880 Ma. The 1951-1959 Ma age group yielded by magmatic zircon rims remains difficult to interpret, but may reflect a magmatic event prior to the metamorphic one. This magmatic event might be related to the rifting of a Svecofennian protocontinent.

  1. The Wuluma granite, Arunta Block, central Australia: An example of in situ, near-isochemical granite formation in a granulite-facies terrane (United States)

    Collins, W. J.; Flood, R. H.; Vernon, R. H.; Shaw, S. E.


    The Wuluma granite is a small, elongate, relatively undeformed pluton in the Proterozoic Strangways Metamorphic Complex, central Australia. The complex constitutes a supracrustal assemblage that underwent granulite-facies metamorphism 1800 Ma ago. Metamorphism was associated with at least three phases of folding that ultimately produced upright, regional, doubly plunging F 3 folds and isobaric cooling ensued. Generation of the Wuluma granite occurred at ˜ 1750 Ma, based on RbSr isotopic data, during syn-D 3 regional retrogression and rehydration of the terrane. Contacts between the granite and gneisses are invariably gradational. At the pluton margin, banded gneisses grade along strike into granite containing abundant biotite schlieren that parallel regional structures. Granite and pegmatite dykes cut these rocks. Inwards from the contact, the granite is more homogeneous, containing diffuse parallel schlieren and small aligned rectangular feldspar crystals, indicating flow of magma. Rafts of unmelted granofels form a ghost layering; they mimic macroscopic F 3 folds and show only minor retrogressive metamorphic effects. At the pluton core, the granite is homogeneous and structurally isotropic, containing some subrounded granofelsic inclusions, very diffuse schlieren and disaggregated pegmatite dykes. Thus, it appears that an isoclinally folded, vertical body of quartzofeldspathic gneiss was melted "in situ" to form the pluton, which did not break away from the source. The body resembles a tapered diapir and we term this type of pluton a regional migmatite terrane granite. Geochemical data are consistent with the granite forming by anatexis of quartzofeldspathic migmatitic gneisses with appropriate composition. The chemical similarity of both rock types implies derivation of the granite by either partial melting and retention of residual material in the magma or more complete melting, followed by solidification virtually in situ. The latter interpretation is

  2. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia (United States)

    Nesheim, T.O.; Vervoort, J.D.; McClelland, W.C.; Gilotti, J.A.; Lang, H.M.


    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085??2. Ma, 1198??79. Ma, 1207??8. Ma, 1255??28. Ma, and 1314??2. Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347??10. Ma and 1102??47. Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~. 1330. Ma (M1) and ~. 1080. Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~. 1080. Ma, which overlaps in time with the Grenville Orogeny. The older ~. 1330. Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia. ?? 2011 Elsevier B.V.

  3. A short report of the investigations made on the facies of German coal deposits

    Energy Technology Data Exchange (ETDEWEB)

    Dehmer, Janet [An den Rothen 96, D-97080 Wurzburg (Germany)


    In 1996, Commission II of the ICCP set up a coal facies working group. The first step was to collate literature on coal facies analysis for different countries. This report provides an overview on the investigations made on the facies interpretations of German coal deposits over the last 50 years with an emphasis on Tertiary coals. It outlines the major deposits present in Germany and gives the main facies interpretations of coals of lignite and bituminous rank. Furthermore, it points out that there lies a certain ambiguity in the interpretation of specific maceral associations, which could confuse facies analyses without the support of interdisciplinary studies and thus suggests that the working group should address this point for future work.

  4. Contact metamorphism, partial melting and fluid flow in the granitic footwall of the South Kawishiwi Intrusion, Duluth Complex, USA (United States)

    Benko, Z.; Mogessie, A.; Molnar, F.; Severson, M.; Hauck, S.; Lechler, P.; Arehart, G.


    The footwall of the South Kawishiwi Intrusion (SKI) a part of the Mesoproterozoic (1.1 Ga) Duluth Complex consists of Archean granite-gneiss, diorite, granodiorite (Giant Range Batholith), thin condensed sequences of Paleoproterozoic shale (Virginia Fm.), as well as banded iron formation (Biwabik Iron Fm). Detailed (re)logging and petrographic analysis of granitic footwall rocks in the NM-57 drillhole from the Dunka Pit area has been performed to understand metamorphic processes, partial melting, deformation and geochemical characteristics of de-volatilization or influx of fluids. In the studied drillhole the footwall consists of foliated metagranite that is intersected by mafic (dioritic) dykes of older age than the SKI. In the proximal contact zones, in the mafic dykes, the orthopyroxene+clinopyroxene+plagioclase+quartz+Fe-Ti-oxide+hornblende±biotite porphyroblasts embedded in a plagioclase+K-feldspar+orthopyroxene+apatite matrix indicate pyroxene-hornfels facies conditions. Migmatitization is revealed by the euhedral crystal faces of plagioclase and pyroxene against anhedral quartz crystals in the in-situ leucosome and by the presence of abundant in-source plagioclase±biotite leucosome veinlets. Amphibole in the melanosome of mafic dykes was formed with breakdown of biotite and implies addition of H2O to the system during partial melting. Towards the deeper zones, the partially melted metatexite-granite can be characterized by K-feldspar+plagioclase+quartz+ortho/clinopyroxene+biotite+Fe-Ti-oxide+apatite mineral assemblage. The felsic veins with either pegmatitic or aplititic textures display sharp contact both to the granite and the mafic veins. They are characterized by K-feldspar+quartz±plagioclase±muscovite mineral assemblage. Sporadic occurrence of muscovite suggest local fluid saturated conditions. Emplacement of gabbroic rocks of the SKI generated intense shear in some zones of the granitic footwall resulting in formation of biotite-rich mylonites with

  5. Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution

    Energy Technology Data Exchange (ETDEWEB)

    Sitzman, S.D.; Banfield, J.F.; Valley, J.W.


    The microstructures of magnetite crystals in three samples from a single outcrop of granulite-facies marble were characterized by transmission electron microscopy (TEM) to determine how exsolution history can affect physical properties and mineral reactivity during retrograde metamorphism. The microstructure of sample 90LP9 consists of dislocation, dislocation arrays (with dislocation spacings of 100 to 500 nm), and linear channels filled with layer silicates. Acid etching and ion milling of polished 90LP9 magnetite grains show dislocation arrays clustered near grain boundaries with rheologically hard magnetite, diopside, and monticellite, but rarely near grain boundaries with softer calcite. Samples LP204-1 magnetite grains contain coherent {l{underscore}brace}100{r{underscore}brace} Al-Mn-Fe-spinel precipitates ({approximately}40 nm diameter, {approximately}1--3 nm thick, {approximately}10{sup 4} platelets/{micro}m{sup 3}) and very few dislocations. Larger, more widely spaced spinel precipitates are present in a third sample, 94AK3. Extremely low dislocation densities in powders of LP204-1 and intermediate dislocation densities in powders of 94AK3, compared with extremely high dislocation densities in powders of 90LP9, are related to strong dislocation pinning effects by precipitates. The different exsolution behavior of the three magnetite samples is attributed to small, but important, differences in Al content. Because dislocations can provide fast pathways for exchange that enhance diffusion, especially in very slowly cooled rocks, these microstructural results may explain previously reported subgrain-scale oxygen isotopic heterogeneity in 90LP9 magnetite compared with relative isotopic homogeneity in LP204-1 magnetite.

  6. High temperatures and inverted metamorphism in the schist of Sierra de Salinas, California (United States)

    Kidder, Steven; Ducea, Mihai N.


    New field and thermobarometric work in the Californian Salinian block clarifies current and pre-Tertiary relationships between the schist of Sierra de Salinas and Cretaceous arc-related granitic rocks. The contact is variably preserved as a brittle fault and high-temperature mylonite zone, the Salinas shear zone, which represents the contact between North America and sediments accreted above the Farallon slab between ˜ 76 Ma and ˜ 70 Ma. Near granulite facies, prograde replacement of hornblende with clinopyroxene is associated with deformation of plutonic rocks at the base of the upper plate. In the lower plate, the schist of Sierra de Salinas, garnet-biotite thermometry indicates decreasing temperatures down-section from at least 714 °C to ˜ 575 °C over an exposed thickness of ˜ 2.5 km, consistent with petrologic evidence of an inverted metamorphic gradient. The measured temperatures are significantly higher than observed at shallow levels above subducting slabs or predicted by 2D computational models assuming low shear stresses. Previous workers have called upon shear heating to explain similar observations in the correlative Pelona schist, an unlikely scenario given the results of recent rock deformation experiments which predict that feldspar-quartz-mica aggregates are far too weak to withstand stresses of ˜ 70 MPa required by the shear heating hypothesis. As an alternative, we propose that high temperatures resulted from conductive heating while the leading edge of the schist traveled ˜ 150 km beneath the recently active Salinian continental arc during the initiation of shallow subduction. Weakening of the schist due to high temperatures helped facilitate the collapse of the Salinian arc as the schist was emplaced. Schist emplacement coincided with loss of lower, mafic portions of the arc, and therefore evolution of the Southern California crust towards a more felsic composition.

  7. Formation conditions of the Rudny Altai metallogenic province (United States)

    Kozlov, M. S.


    The results of previous geological, petrochemical, and metallogenic surveys conducted from the 1960s to the 1990s provide the geological and tectonic basis of this study. The unique mineral deposits of the Rudny Altai metallogenic province were formed in the Middle Paleozoic (S2-C1) at the junction between different structures of the Altai-Mongolian terrane: the Alei-Charysh-Tigirek rift (in the north) with the Korgon-Markakol' island arc and Belaya Uba-Maimyr intra-arc trough (in the southwest). The Rudny Altai structural-formational zone that formed at the junction between these structures evolved as a magmatic arc and was characterized by the formation of granite-greenschist arches, volcanoplutonic magmatism and high heat and fluid flow (greenschist-facies metamorphism of Upper Silurian-Upper Devonian rocks and deposition of pyrite-bearing hydrothermal-sedimentary horizons, VMS and copper-VMS deposits and isolated base-metal ore bodies). The tectonomagmatic history of the Rudny Altai zone can be subdivided into several stages: Ludlow-Emsian, Late Emsian-Givetian, Frasnian-Early Famennian, Middle Famennian-Early Visean, and Late Visean-Serpukhovian. The island arc is represented by volcanic rocks of the andesite-dacite-rhyolite (early stage), basalt-rhyolite (Late Emsian-Eifelian), and basalt-andesite-rhyolite series (Late Visean). Volcanosedimentary strata (until the Givetian age) and turbidites up to 3-5 km thick were deposited in the interarc trough. Because of their metastable behavior, the volcanic rocks became actively involved in ion-exchange reactions with the formational waters, whereas the differences in hydraulic head between arches and troughs created favorable conditions for the transport of the metamorphic fluids, and the thermal gradient promoted thermodiffusion of divalent species of Mg, Pb, Zn, Cu, etc. toward the high-temperature zone and development of the high-Mg metamorphic-metasomatic alteration with a VMS-base-metal mineralization. As a

  8. Control of facies/potential on hydrocarbon accumulation:a geological model for Iacustrine rift basins

    Institute of Scientific and Technical Information of China (English)

    Chen Dongxia; Pang Xiongqi; Zhang Shanwen; Wang Yongshi; Zhang Jun


    The formation and distribution of hydrocarbon accumulations are jointly controlled by"stratigraphic facies"and"fluid potential",which can be abbreviated in"control of facies/potential on hydrocarbon accumulation".Facies and potential control the time-space distribution of hydrocarbon accumulation macroscopically and the petroliferous characteristics of hydrocarbon accumulation microscopically.Tectonic facies and sedimentary facies control the time-space distribution.Lithofacies and petrophysical facies control the petroliferous characteristics.Favorable facies and high porosity and permeability control hydrocarbon accumulation in the lacustrine rift basins in China.Fluid potential is represented by the work required,which comprises the work against gravity,pressure,interfacial energy and kinetic energy.Hydrocarbon migration and accumulation are controlled by the joint action of multiple driving forces,and are characterized by accumulation in the area of low potential.At the structural high,low geopotential energy caused by buoyancy control anticlinal reservoir.The formation of lithological oil pool is controlled by low interfacial energy caused by capillary force.Low compressive energy caused by overpressure and faulting activity control the formation of the faulted block reservoir.Low geopotential energy of the basin margin caused by buoyancy control stratigraphic reservoir.The statistics of a large number of oil reservoirs show that favorable facies and low potential control hydrocarbon accumulation in the rift basin.where over 85% of the discovered hydrocarbon accumulations are distributed in the trap with favorable facies and lOW potentials.The case study showed that the prediction of favorable areas by application of the near source-favorable facies-low potential accumulation model correlated well with over 90% of the discovered oil pools' distribution of the middle section of the third member of the Shahejie Formation in the Dongying Depression,Bohai Bay

  9. Marine habitat mapping of the Milford Haven Waterway, Wales, UK: Comparison of facies mapping and EUNIS classification for monitoring sediment habitats in an industrialized estuary (United States)

    Carey, Drew A.; Hayn, Melanie; Germano, Joseph D.; Little, David I.; Bullimore, Blaise


    A detailed map and dataset of sedimentary habitats of the Milford Haven Waterway (MHW) was compiled for the Milford Haven Waterway Environmental Surveillance Group (MHWESG) from seafloor images collected in May, 2012 using sediment-profile and plan-view imaging (SPI/PV) survey techniques. This is the most comprehensive synoptic assessment of sediment distribution and benthic habitat composition available for the MHW, with 559 stations covering over 40 km2 of subtidal habitats. In the context of the MHW, an interpretative framework was developed that classified each station within a 'facies' that included information on the location within the waterway and inferred sedimentary and biological processes. The facies approach provides critical information on landscape-scale habitats including relative location and inferred sediment transport processes and can be used to direct future monitoring activities within the MHW and to predict areas of greatest potential risk from contaminant transport. Intertidal sediment 'facies' maps have been compiled in the past for MHW; this approach was expanded to map the subtidal portions of the waterway. Because sediment facies can be projected over larger areas than individual samples (due to assumptions based on physiography, or landforms) they represent an observational model of the distribution of sediments in an estuary. This model can be tested over time and space through comparison with additional past or future sample results. This approach provides a means to evaluate stability or change in the physical and biological conditions of the estuarine system. Initial comparison with past results for intertidal facies mapping and grain size analysis from grab samples showed remarkable stability over time for the MHW. The results of the SPI/PV mapping effort were cross-walked to the European Nature Information System (EUNIS) classification to provide a comparison of locally derived habitat mapping with European-standard habitat

  10. Sulfate incorporation in monazite lattice: potential for dating the cycle of sulfur in metamorphic belts (United States)

    Laurent, Antonin; Seydoux-Guillaume, Anne-Magali; Duchene, Stéphanie; Bingen, Bernard; Bosse, Valérie


    Monazite is a common accessory mineral in magmatic and metamorphic rocks that often shows complex chemical zoning at the μm- to nm-scale. The large number of cations that may be accommodated in its lattice, makes monazite particularly responsive to changes in the rock-forming minerals and fluid composition. Chemical zoning resulting from replacement or overgrowth may coincide, or not, with age zoning derived from U-Th-Pb isotopes. In this study, we focus on the potential for monazite to record both the redox condition of its crystalizing medium and an absolute U-Th-Pb isotopic age, during polyphase metamorphism in the Proterozoic province of Rogaland, S. Norway. The metamorphic evolution of several samples is derived from phase diagrams and the oxygen fugacity estimated from the FeO/Fe2O3 ratio measured by titration. Monazite grains were mapped at high spatial resolution for minor elements with electron microprobe, revealing convolute chemical zoning. Some of these zones yield appreciable content of S (up to 7000 ppm), accommodated following the Ca2+ + S6+ = REE3+ + P5+ substitution vector. The incorporation of sulfate in monazite has been subsequently investigated by TEM thanks to site specific FIB preparations. Besides, LA-ICP-MS U-Pb isotopic ages of monazite grains show a remarkable correlation with the sulfate content. It is therefore possible to distinguish different generations of monazite based on their S-content. From our petrological study we conclude that sulfate-bearing monazite reflects incongruent melting of Fe-Cu-As sulfides under oxidizing conditions, coeval with biotite dehydration melting. Monazite may therefore be used to probe the presence of sulfur in anatectic melts from high-grade terrains at a specific point in time. This property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework.

  11. Tectono-metamorphic evolution of the Paleoproterozoic ultra-high temperatures Khondalite Belt, North China Craton. (United States)

    Lobjoie, Cyril; Trap, Pierre; Lin, Wei; Goncalves, Philippe; Marquer, Didier


    In the North China Craton, the Khondalite belt is a famous Paleoproterozoic domain where ultra-high temperatures (UHT) metamorphism was extensively documented over an area of 1000 square kilometers. Numerous petrological analyses argue for P-T conditions around 0.6-0.8GPa for temperature above 900°C for peak metamorphism. Unfortunately, the scarcity of available structural data prevents any discussion about thermo-mechanical behavior of the orogenic crust suffering high thermal regime. In this contribution, we present a detail structural analysis of the Khondalite belt that allowed to distinguish two main deformation events, named D1 and D2. The deformation D1 led to the formation of the S1 foliation that dips weakly toward the South-East. S1 holds a N70°E trending mineral and stretching L1 lineation that is sub-horizontal or plunges weakly to the East. The D1 fabrics is reworked by the dextral transpressional D2 deformation responsible for the development of km-scale S2-C2-C'2 system. The N30°E trending S2 foliation is sub-vertical to highly dipping toward the East. Kilometer-scale C2 and C'2 shear zones are sub-vertical and trend N70°E and N90-100°E, respectively. Petrological study and phase diagram modeling suggest that both D1 and D2 developed at UHT conditions. Garnet and spinel-bearing migmatites recording D1 fabric yield 0.7GPa for ca. 950-1015°C P-T conditions. Within D2 shear zones, numerous granitoids and mafic bodies are injected. Mafic intrusions are responsible for UHT contact metamorphism that can occur at low pressure as recorded in an olivine-bearing migmatite. This may suggest that the D2 S-C-C' system form an interconnected network of kilometer scale shear zones that act as pathways for percolation of mafic magmas from the mantle up to the base of the upper crust. Our results allow to discuss the role of localized heat advection along crustal-scale shear zones as a possible mechanism responsible for UHT metamorphism at regional scale, with

  12. Contrasting metamorphism across Cauvery Shear Zone, south India

    Indian Academy of Sciences (India)

    Manish M John; S Balakrishnan; B K Bhadra


    The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating the metamorphic history of the southern granulite terrane (SGT). In the mafic granulites occurring to the south of CSZ, evidence of garnet breaking down during near isothermal decompression (ITD) is indicated by the development of orthopyroxene + plagioclase moats in between quartz and garnet. The presence of comparatively small elongated second generation garnet embedded in pyroxenes from the mafic granulites occurring to the north of CSZ is indicative of the garnet formation via reaction between pyroxenes and plagioclase, which occurred during isobaric cooling (IBC). Rocks occurring to the south of CSZ have recorded comparatively higher temperature and pressure (849°C and 9.6 kbar) than those occurring to the north of the CSZ (731°C and 8.6 kbar) using conventional geothermobarometry. The rocks occurring to the north of CSZ have suffered more complex metamorphic histories in comparison to the southern part. Integrating the results of the present field and metamorphic studies with the earlier investigations and available geochronological data we suggest that the CSZ could represent a suture zone between two different continental blocks that underwent distinct metamorphic evolution.

  13. Metamorphic Virus Detection in Portable Executables Using Opcodes Statistical Feature

    Directory of Open Access Journals (Sweden)

    Babak Bashari Rad


    Full Text Available Metamorphic viruses  engage different mutation techniques to escape from string signature based scanning. They try to change their code in new offspring so that the variants appear non-similar and have no common sequences of string as signature. However, all versions of a metamorphic virus have similar task and performance. This obfuscation process helps to keep them safe from the string based signature detection. In this study, we make use of instructions statistical features to compare the similarity of two hosted files probably occupied by two mutated forms of a specific metamorphic virus. The introduced solution in this paper is relied on static analysis and employs the frequency histogram of machine opcodes in different instances of obfuscated viruses. We use Minkowski-form histogram distance measurements in order to check the likeness of portable executables (PE. The purpose of this research is to  present an idea that for  a number of special  obfuscation approaches the presented solution can be  used to identify morphed copies of a file. Thus, it can be applied by antivirus scanner to recognize different versions of a metamorphic virus.

  14. Surficial Sediment Facies features near the Myrtle Bend Confluence with the Kootenai River near Bonners Ferry, ID (United States)

    U.S. Geological Survey, Department of the Interior — The surficial bed-sediment facies, herein after referred to as the sediment facies, quantitatively describes the dominant sediment substrate on the surface of the...

  15. Distribution and composition of verdine and glaucony facies from the sediments of the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.

    Investigations on green grains from sediments of the western continental margin of India, between Ratnagiri and Cape Comorin, (water depth 37-330 m) indicate the presence of verdine and glaucony facies. Verdine facies occurs over an area of about...

  16. Distinguishing fluvio-deltaic facies by bulk geochemistry and heavy minerals: an example from the Miocene of Denmark

    DEFF Research Database (Denmark)

    Olivarius, Mette; Rasmussen, Erik S.; Siersma, Volkert Dirk


    Interpretations of seismic profiles, gamma-ray logs and sediment descriptions were used to classify seven facies in Miocene fluvio-deltaic deposits ofDenmark. An impartial approach was adopted by not including analytical data in the facies definition. This approach allowed identification...... is found from the delta slope facies offshore to the delta toe and shelf facies. This trend is interpreted as a result of sorting by turbidity currents. The mixed origin of the transgressive lag facies is shown by the poorer sorting in this facies. By indicating the amount of alteration the sediments have...... been exposed to, the Ti-mineral maturity has proven useful in characterizing the facies. This systematic approach of tying depositional environments to a well-calibrated sequence stratigraphic model has generated analytical results which are valid as reference levels for future facies identifications....

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

    Directory of Open Access Journals (Sweden)

    Morovvat Faridazad


    Full Text Available Introduction Khoy ophiolite at the global scale is in the middle part of the Alp-Himalaya orogenic belt and it is extended over 3900 Km2 which indicates remnant Neotethys oceanic lithosphere in the Mesozoic era (Kananian et al., 2010. In this paper, in addition to a review of previous investigations about Khoy ophiolite, we will try to determine the nature and kind of minerals, origin and partial melting rate as well as the equilibrium pressure and temperature of harzburgites from the Eastern Metamorphic Complex of Khoy ophiolite. Materials and methods Thin sections microscopy studies were carried out following field investigations. EPMA analysis was carried out with using a Superprobe JEOL, JXA 8200 Microprobe unit at the state of WDS and under condition of 15kv accelerating voltage, 10nA current beam, 1µm beam diameter and collection of natural and synthetic standards for calibration. Results The study area is located at the NW of Iran and north of the Khoy city in the west Azarbaijan province. This area is part of the ophiolitic complex of NW Iran and belongs to its Eastern Metamorphic Complex. This metamorphic zone has large tectonically segments of the metamorphic ophiolites which mainly include serpentinized peridotites with associated metagabbros. There are three types of peridotitic rocks in this area which are: Lherzolites, harzburgites and dunites. Lherzolites are composed of olivine (60-70%, orthopyroxene (10-30% and clinopyroxene (~10-20% with minor amounts (~2% of Cr-spinel mineral. Harzburgites are composed of olivine (70-80%, orthopyroxene (10-20% and clinopyroxene (~5% with minor amounts (~2% of Cr-spinel mineral. Dunites are composed of olivine (90-95%, orthopyroxene (5-10% with minor amounts (~1-2% of Cr-spinel mineral. Composition range of olivines is between Fo89.46 Fa10.37 to Fo89.86 Fa10.0 as well as NiO content range is 018-046 (wt %. The calculated Mg# of olivines is 0.90 and the composition of olivines in Fo-Fa diagram

  18. Constraint Force Analysis of Metamorphic Joints Basedon the Augmented Assur Groups

    Institute of Scientific and Technical Information of China (English)

    LI Shujun; WANG Hongguang; YANG Qiang


    In order to obtain a simple way for the force analysis of metamorphic mechanisms, the systematic method to unify the force analysis approach of metamorphic mechanisms as that of conventional planar mechanisms is proposed. A force analysis method of metamorphic mechanisms is developed by transforming the augmented Assur groups into Assur groups, so that the force analysis problem of metamorphic mechanisms is converted into the force analysis problems of conventional planar mechanisms. The constraint force change rules and values of metamorphic joints are obtained by the proposed method, and the constraint force analysis equations of revolute metamorphic joints in augmented Assur group RRRR and prismatic metamorphic joints in augmented Assur group RRPR are deduced. The constraint force analysis is illustrated by the constrained spring force design of paper folding metamorphic mechanism, and its metamorphic working process is controlled by the spring force and geometric constraints of metamorphic joints. The results of spring force show that developped design method and approach are feasible and practical. By transforming augmented Assur groups into Assur groups, a new method for the constraint force analysis of metamorphic joints is proposed firstly to provide the basis for dynamic analysis of metamorphic mechanism.

  19. A study on the relationships between metamorphic anatexis and petrogenesis and mineralization

    Institute of Scientific and Technical Information of China (English)


    Metamorphic processes are closely associated with the formation and evolution of the crust and highly related to petrogenesis and mineralization processes. Dynamic systematic analysis indicates that regional metamorphism-migmatization-metamorphic anatexis process is a temperature-pressure progressive process. Metamorphic anatexis process is a critical part with its unique pressure/temperature and thermodynamic, dynamic and geochemical characteristics. The concept of metamorphic anatexis system (MAS) introduced by the author includes the essential factors of material resources, energy resources, process format, material transportation and concentration, occurring time and location. Based on the essential factors of MAS, metamorphic anatexis process-related granitic rocks and deposit cases are discussed on their petrogenesis and/or mineralizaion mechanisms. The discussion points out that granites in the Ailaoshan and Yunkai metamorphic zones are of metamorphic anatexis origin. The genesis of pegmatite ore deposits in metamorphic zones and shear zone gold deposits in shear zones are highly related to metamorphic anatexis process. The study of metamorphism process involved in ore formation and material transport is a hot subject concerned by the international geological circles. Thorough investigations into the relationships between metamorphic anatexis and petrogenesis-meneralization processes are of great importance not only in geological theory, but also in industrial practice.

  20. The structural evolution of carbonaceous material during metamorphism : a geothermometer (United States)

    Beyssac, O.; Goffe, B.; Brunet, F.; Bollinger, L.; Avouac, J.; Rouzaud, J.


    With increasing metamorphic temperature, the organic matter present in sedimentary rocks is progressively transformed into graphite (graphitization). The degree of organization of this carbonaceous material (CM) as characterized by Raman spectroscopy (RSCM), can be used as a geothermometer which yields the maximum temperature reached during the metamorphic cycle (Beyssac et al., 2002). We used this RSCM geothermometer to map the maximum metamorphic temperatures through the Lesser Himalaya (LH) in Nepal. This study provides a large dataset (80 samples) to estimate uncertainty of this method and to ascertain its reliability by comparison with conventional petrological investigations. We show that the RSCM geothermometer might be used to detect inter-samples temperature variations as small as 10° C or so, but absolute temperatures are only loosely determined to +/- 50° C due to the uncertainty on the calibration. This successful application of the RSCM geothermometer confirms that, at the timescale of regional metamorphism (several My), the transformation of CM is mainly controlled by temperature. However, laboratory investigations suggest that, in addition to temperature, pressure should also play a role (Beyssac et al. 2003). As a matter of fact, high degree of organizations encountered in natural CM cannot be reproduced in laboratory without pressure, even at temperatures as high as 3000° C. In addition to the data acquired on natural CM, we will discuss laboratory experiments performed up to 8 GPa which show that (1) a few kbar of hydrostatic pressure are required to initiate microtextural and subsequent structural transformations within CM and (2) the overall effect of increasing pressure is to speed up graphitization process. Beyssac, O., Goffe, B., Chopin, C., and Rouzaud, J.N., 2002, Raman spectra of carbonaceous material in metasediments: a new geothermometer. Journal of Metamorphic Geology, 20, 859-871. Beyssac, O., Brunet, F., Petitet, J.P., Goffe, B

  1. Geochemistry, Nd Isotopic Characteristics of Metamorphic Complexes in Northern Hebei: Implications for Crustal Accretion

    Institute of Scientific and Technical Information of China (English)

    LIU Shuwen; TIAN Wei; L(U) Yongjun; LI Qiugen; FENG Yonggang; K. H. PARK; Y. S. SONG


    The middle segment of the northern margin of the North China Craton (NCC) consists mainly of metamorphosed Archean Dantazi Complex, Paleoproterozoic Hongqiyingzi Complex and unmetamorphosed gabbro-anorthosite-meta-alkaline granite, as well as metamorphosed Late Paleozoic mafic to granitoid rocks in the Damiao-Changshaoying area. The ~2.49 Ga Dantazi Complex comprises dioritic-trondhjemitic-granodoritic-monzogranitic gneisses metamorphosed in amphibolite to granulite facies. Petrochemical characteristics reveal that most of the rocks belong to a medium- to high-potassium calc-alkaline series, and display Mg# less than 40, right-declined REE patterns with no to obviously positive Eu anomalies, evidently negative Th, Nb, Ta and Ti anomalies in primitive mantlenormalized spider diagrams, εNd(t)=+0.65 to -0.03, and depleted mantle model ages TDM=2.78-2.71 Ga.Study in petrogenesis indicates that the rocks were formed from magmatic mixing between mafic magma from the depleted mantle and granitoid magma from partial melting of recycled crustal mafic rocks in a continental margin setting. The 2.44-2.41 Ga Hongqiyingzi Complex is dominated by metamorphic mafic-granodioritic-monzogranitic gneisses, displaying similar petrochemical features to the Dantazi Complex, namely medium to high potassium callc-alkaline series, and the mafic rocks show evident change in LILEs, negative Th, Nb, Ta, Zr anomalies and positive P anomalies. And the other granitiod samples also exhibit negative Th, Nb, Ta, P and Ti anomalies. All rocks in the Hongqiyingzi Complex show right-declined REE patterns without Eu anomaly. The metamorphic mafic rocks with εNd(t) = -1.64 may not be an identical magmatic evolution series with granitoids that have εNd(t) values of +3.19 to +1.94 and TDM ages of 2.55-2.52 Ga. These granitic rocks originated from hybrid between mafic magma from the depleted mantle and magma from partial melting of juvenile crustal mafic rocks in an island arc setting. All the ~311

  2. Facies discrimination in a mixed fluvio-eolian setting using elemental whole rock geochemistry

    DEFF Research Database (Denmark)

    Svendsen, Johan; Friis, Henrik; Stollhofen, Harald


    Fluvio-eolian successions are generally characterized by a high degree of complexity and internal heterogeneity. Quantifying the rapid facies changes in time and space is a major challenge to hydrocarbon reservoir characterisation.We present a method for facies discrimination in fluvio-eolian suc......Fluvio-eolian successions are generally characterized by a high degree of complexity and internal heterogeneity. Quantifying the rapid facies changes in time and space is a major challenge to hydrocarbon reservoir characterisation.We present a method for facies discrimination in fluvio......-eolian successions. The method is developed on the modern fluvio-eolian sediments from the Skeleton Coast dune field, Namibia. The examined sediments comprise eight different facies types; eolian dune sands, inter dune fluvial channel sands, intra erg mass flow deposits, intra erg hyperconcentrated flow deposits...... performed on the geochemical data has enabled discrimination of seven of the eight facies types. Furthermore, the facies discrimination method allowed a quantitative estimate of the degree of fluvial reworking of eolian sand. We believe that the method presented here, when calibrated to a reference well...


    Directory of Open Access Journals (Sweden)



    Full Text Available The only occurrence of Tertiary (Oligocene sediments in the Dolomites at Monte Parei results from a complex tectonic and sedimentary history. The Tertiary marine clastic succession is sealing the Dinaric (Late Cretaceous to Paleogene deformed basement. The basin-fill can be differentiated into four lithofacies which show extensive lateral interfingering: ,local scarp breccias with giant blocks (facies A, chaotic breccias of debris flow origin (facies B, balanid and shell coquina beds (facies C and conglomeratic grain and debris flows with sandstone intercalations (facies D. Transport directions (imbricate clasts and cross bedding and petrographic composition indicate two different source areas. Sediments of facies B were shed from a structural high in the SW, while carbonate-siliciclastic debris of facies C and D originated from a pebbly or rocky shore in the N. Lithofacies and facies interrelationships clearly indicate the control by synsedimentary tectonic activity. Neoalpine closure of the basin by overthrusting lead to the preservation of the sediments. 

  4. Sedimentary facies of Maastrichtian to Danian deposits in Amur River area, Russian Far East

    Institute of Scientific and Technical Information of China (English)

    Shigeyuki Suzuki; Abdul R. Ashraf; Hakuyu Okada


    Sedimentary facies of the Tsagayan Formation is distributed in the eastern Zeya-Bureya Basin has been analyzed. The formation is of the Maastrichtian to Danian in age and characterized by the cyclicity of the fining-upwards successions. Analysis of environmental changes during the K/T boundary is the focus of this study. Five facies have been identified: Facies A, thick and laterally extensive coarse-grained to medium-grained sandstone units, interpreted as channelfill deposits; Facies B, parallel-laminated to massive mudstone units interpreted as interchannel lakes and flood plain deposits; Facies C, sheet-like medium-grained to fine-grained sandstones interpreted as crevasse splay deposits;Facies D, coal to coaly mudstone beds interpreted as deposits ofpeatlands; Facies E, very poorly sorted sandy mudstone beds interpreted as debris flow deposits. Fluvial environments with the low-relief flat topography was inferred. A channel transported large volumes of clasts, and a flood basin with interchannel lakes and peatlands was deciphered. Any distinct change of sedimentary environments has not been identified throughout the Tsagayan Formation (including the K/T boundary). However, two beds of debris flow deposits were identified. The one occurs at the uppermost part of the lower Tsagayan Subformation and contains dinosaur fossils. The other is intercalated in the upper Tsagayan Subformation.

  5. Early Tertiary subsidence and sedimentary facies - Northern Sirte Basin, Libya

    Energy Technology Data Exchange (ETDEWEB)

    Gumati, Y.D.; Kanes, W.H.


    The subsidence curves and subsidence rate curves for the Sirte basin, constructed from the stratigraphic record, show that subsidence was continuous throughout Late Cretaceous and Tertiary times, reaching a maximum during the Paleocene and Eocene, when a major reactivation of faults occurred. Shales and carbonates were deposited during all of the Late Cretaceous and Tertiary. Abrupt lateral facies changes occur from the platform areas toward the deeper troughs along with steep downdip thickening. The absence of upper Paleozoic and lower Mesozoic sediments suggests that the area was domed, faulted, and eroded during the late Mesozoic. As a result of crustal extension during the Paleocene, a marked lithologic and structural change occurred. The Heira Shale succeeded the Kalash Limestone in the Marada trough. Reactivation of the earlier faults, accompanied by an increase in the sediment supply from the south, caused these lower Paleocene shales to cover the entire area, with the exception of the old highs where carbonate deposition continued. An intercalation of shales and carbonates provides a sensitive indicator of change of depth and sediment type. 14 figures.

  6. Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan region

    Institute of Scientific and Technical Information of China (English)


    Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typi- cal microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz rib- bons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are ob- viously different from inclusions captured at granulite facies, in both fluid compositions and T-P esti- mations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.

  7. 大别-苏鲁超高压变质带内部的浅变质岩%On low-grade metamorphic rock within Dabie-Sulu ultrahigh pressure metamorphic belt.

    Institute of Scientific and Technical Information of China (English)

    周建波; 郑永飞; 李龙; 谢智


    There are sparotic occurrences of low-grade metamorphic rocks as tectonic relict flakes within the Dabie-Sulu ultrahigh pressure (UHP) orogen. They are mainly composed of metaclastics, phyllites and marbles. They having, suffered from dynamic metamorphism at low greenschist-facies and fold-and-fault deformation, are in tectonic contacts with the surrounding UHP rocks. Micro-paleontologic fossils from the low-grade metamorphic rocks suggest that their sedimentary protoliths were deposited in a shallow marine environment at Sinian in the northern margin of Yangze plate. Isotopic datings indicate that their igneous protoliths are of Late Proterozoic ages and experienced tectonic events at Caledonian and Indosinian like the surrounding UHP eclogites and gneisses. Oxygen isotope analysis shows that the low-grade metamorphic rocks within the Dabie orogen are depleted in 18O like the surrounding UHP rocks and thus their protoliths underwent hydrothermal alteration by ancient meteoric water at high temperatures. It appears that the low-grade metamorphic rocks were originally the Sinian sedimentary rocks and enclosed volcaniclastic rocks in the northern margin of the Yangtze plate, and have the geological occurrence and formation mechanism similar to accretionary wedge that was scraped from the subducting Yangtze plate and accumulated in the subduction zone. Therefore, they may be a part of the tectonic accretionary wedge of continental plate subduction.%大别苏鲁超高压变质带内部零星出露有若干呈构造残片状产出的浅变质岩,主要以变质碎屑岩-千枚岩-大理岩组合为代表,遭受过低绿片岩相变质和脆-韧性变形作用的改造,与围岩均为构造接触(断层或韧性剪切带)。微古生物化石研究表明,其原岩为震旦纪前后扬子板块北缘的浅海相沉积。同位素年代学研究指示,它们经历过加里东期和印支期构造热事件的影响,与区域超高压岩石经受

  8. Kanfenggou UHP Metamorphic Fragment in Eastern Qinling Orogen and Its Relationship to Dabie-Sulu UHP and HP Metamorphic Belts, Central China

    Institute of Scientific and Technical Information of China (English)

    Suo Shutian; Zhong Zengqiu; Zhou Hanwen; You Zhendong


    In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun-North QaidamNorth Qinling UHP metamorphic belt. The other is the Dabie-Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite- and microdiamond-bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and col