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The Wuhe complex is located at the southeastern margin of the North China Block and belongs to the Precambrian metamorphic basement. It is exposed in the Bengbu area and its neighbourhood. The Wuhe complex consists of the metamorphosed igneous mafic and felsic rocks and supracrustal rocks associated with the Paleoproterozoic foliated K-feldspar granites and Mesozoic granitoids, constituting the "Bengbu uplift". Its main rock types comprise a variety of lithologies, including garnet amphibolite, garnet granulite, rodingile, garnet-plagioclase-amphibolite gneiss, granitoid gneiss, micaschist, marble, quartzite and meta-sandstone. These rocks contain similar peak metamorphic minerals such as garnet, clinopyroxene, plagioclase, rutile and quartz. As a result, combined with their zircon U-Pb ages, it is suggested that they suffer from a common high pressure granulite facies metamorphism in Palaeoprotcrozoic. The multiphase solid inclusions within garnet porphyroblasts are discovered from the garnet amphibolite. Some multiphase solid inclusions consist of quartz, calcite, hornblende and chlorite, with quartz and calcite showing a secondary rim of hornblende and chlorite. The intergrowths of quartz, K-feldspar, plagioclase and biotite, and related MS inclusions in garnet show that the Wuhe complex experiences the high pressure granulite facies metamorphism, accompanying close-to-coeval partial melting and heterogeneous carbonate metasomatism. In addition, there are late altered minerals such as calcite, epidote and chlorite, and K-feldspar, plagioclase, quartz, biotite and amphibole distribute along fractures of garnets in the meta-basites. It is suggested that the Wuhe complex experiences the high pressure granulite fades metamorphism, accompanying close-lo-coeval partial melting and heterogeneous carbonate metasomatism. In addition, there are late altered minerals such as calcite, epidote and chlorite, and K-feldspar, plagioclase, quartz, biotite and amphibole distribute along fractures of garnets in the meta-basites. It is suggested that the rocks undergo heterogeneously carbonate-hearing hydrous melt/fluid metasomatism, and epidotization and chloritization. The carbonate metasomatism at the Palaeoproterozoic is likely responsible for the exceptionally high Pb-isotopic compositions registered by some of the meta basic rocks in the metamorphic basement in the area, quite different from those of typical Precambrian granulite terrains or of lower crustal xenoliths in the North China Block. [ABSTRACT FROM AUTHOR]

The type and kinetics of metamorphic CO 2-producing processes in metacarbonate rocks is of importance to understand the nature and magnitude of orogenic CO 2 cycle. This paper focuses on CO 2 production by garnet-forming reactions occurring in calc-silicate rocks. Phase equilibria in the CaO–FeO–Al 2O 3–SiO 2–CO 2–H 2O (CFAS–CO 2–H 2O) system are investigated using P– T phase diagrams at fixed fluid composition, isobaric T– X(CO 2) phase diagram sections and phase diagram projections in which fluid composition is unconstrained. The relevance of the CFAS–CO 2–H 2O garnet-bearing equilibria during metamorphic evolution of calc-silicate rocks is discussed in the light of the observed microstructures and measured mineral compositions in two representative samples of calc-silicate rocks from eastern Nepal Himalaya. The results of this study demonstrate that calc-silicate rocks may act as a significant CO 2 source during prograde heating and/or early decompression. However, if the system remains closed, fluid–rock interactions may induce hydration of the calc-silicate assemblages and the in situ precipitation of graphite. The interplay between these two contrasting processes (production of CO 2-rich fluids vs. carbon sequestration through graphite precipitation) must be considered when dealing with a global estimate of the role exerted by decarbonation processes on the orogenic CO 2 cycle. [ABSTRACT FROM AUTHOR]

A combined study of detailed petrographic observation, mineral chemistry analysis and phase equilibrium modeling indicates that the high-temperature eclogites from the Dabie orogen, central China, experienced two episodes of anatexis: the first is phengite dehydration melting during the exhumation of deeply subducted slices, and the second is heating melting related to the postorogenic collapse. Petrographic evidence and clues of the anatectic events include biotite + plagioclase + garnet ± amphibole intergrowth in matrix and biotite + plagioclase intergrowth within amphibole porphyroblast. Pressure--temperature (P--T) pseudosection and modal variation diagram indicate that the biotite + plagioclase + garnet ± amphibole in matrix was formed by the reactions phengite + clinopyroxene + quartz = melt + sanidine + garnet + plagioclase and later melt + sanidine + garnet = biotite + plagioclase, while the biotite + plagioclase intergrowths within poikiloblastic amphibole were formed by the reaction amphibole + muscovite + epidote = biotite + plagioclase + melt. In addition, the combination of petrological observations and P--T estimates suggests that the first melting event occurred at the late Triassic, while the second is related to the early Cretaceous mountain-root removal and subsequent asthenospheric upwelling and heat input. As the P--T paths of high-temperature/ultrahighpressure rocks have high probabilities to cross-cut phengite-melting curves, phengite melting during decompression may be a common process in these rocks. Moreover, the coexistence of multiple episodes of anatexis in a single tectonic slice suggests caution when identifying and dating partial melting in high-temperature/(ultra)high-pressure rocks. [ABSTRACT FROM AUTHOR]

Fluid-earthquake interplay, as evidenced by aftershock distributions or earthquake-induced effects on near-surface aquifers, has suggested that earthquakes dynamically affect permeability of the Earth’s crust. The connection between the mid-crust and the surface was further supported by instances of carbon dioxide (CO2) emissions associated with seismic activity, so far only observed in magmatic context. Here we report spectacular non-volcanic CO2 emissions and hydrothermal disturbances at the front of the Nepal Himalayas following the deadly 25 April 2015 Gorkha earthquake (moment magnitude Mw = 7.8). The data show unambiguously the appearance, after the earthquake, sometimes with a delay of several months, of CO2 emissions at several sites separated by > 10 kilometres, associated with persistent changes in hydrothermal discharges, including a complete cessation. These observations reveal that Himalayan hydrothermal systems are sensitive to co- and post- seismic deformation, leading to non-stationary release of metamorphic CO2 from active orogens. Possible pre-seismic effects need further confirmation. Earthquakes rarely affect hydrothermal systems in non-magmatic context. Here the authors report outbursts of CO2 and hydrothermal disturbances triggered by the 2015 Nepal earthquake, revealing high sensitivity of Himalayan hydrothermal systems to co-, post- and possibly pre- seismic deformation. [ABSTRACT FROM AUTHOR]

Fluid-earthquake interplay, as evidenced by aftershock distributions or earthquake-induced effects on near-surface aquifers, has suggested that earthquakes dynamically affect permeability of the Earth's crust. The connection between the mid-crust and the surface was further supported by instances of carbon dioxide (CO 2 ) emissions associated with seismic activity, so far only observed in magmatic context. Here we report spectacular non-volcanic CO 2 emissions and hydrothermal disturbances at the front of the Nepal Himalayas following the deadly 25 April 2015 Gorkha earthquake (moment magnitude M w  = 7.8). The data show unambiguously the appearance, after the earthquake, sometimes with a delay of several months, of CO 2 emissions at several sites separated by > 10 kilometres, associated with persistent changes in hydrothermal discharges, including a complete cessation. These observations reveal that Himalayan hydrothermal systems are sensitive to co- and post- seismic deformation, leading to non-stationary release of metamorphic CO 2 from active orogens. Possible pre-seismic effects need further confirmation.