Middle Miocene thermal metamorphism due to the infiltration of high-temperature fluid in the Sanbagawa metamorphic belt, southwest Japan

Article Abstract:

The concentration of high-temperature fluids in areas of high-fracture permeability and a large fluid flux over a metamorphic period of < 100 years produced the Middle Miocene hornfelses of the Sanbagawa metamorphic belt, Shikoku, southwest Japan. The hornfelses contain plagioclase, hornblende and orthopyroxene metamorphic areas that formed at 300-475 degrees celsius (C), 475-680 degrees C and 680-730 degrees C, respectively. The hornfelses have a temperature gradient of five degrees C/m, which is much higher than that of hornfelses formed by igneous intrusion.

Natural history, Geology, Stratigraphic, Stratigraphy, Miocene Epoch, Shikoku Island

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Simple models of coupled fluid infiltration and redox reactions in the crust

Article Abstract:

Research was undertaken to determine the interaction between fluid fluxes, fluid compositions and mass transfer during medium crustal metamorphic conditions through the development of one-dimensional numerical models of coupled porous media flow and oxidation-reduction reactions. The redox state has a basic control on mineral assemblages, mineral composition and fluid compositions evolving during crustal metamorphism. Results revealed that reaction times primarily influenced spatial and temporal patterns of mineralogic evolution.

Models, Analysis, Fluid dynamics, Oxidation-reduction reaction, Oxidation-reduction reactions, Rocks, Metamorphic, Metamorphic rocks, Mass transfer

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Mid-crustal contact metamorphism around the Chimakurthy mafic-ultramafic complex, Eastern Ghats Belt, India

Article Abstract:

Pelitic rocks at the contact of the Chimarkurthy mafic-ultramafic igneous complex in India were thermally metamorphosed. Progressive changes in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar to garnet-spinel-cordierite-K-feldspar-sillimanite have been observed. Down-temperature mineral reactions were mainly diffusion controlled.

Observations, Composition, Rocks

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