科研之友
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摘要
The area around Darjeeling consists of medium grade metamorphic rocks and provides a classic example of inverted Himalayan metamorphism. The area under investigation shows upper amphibolite facies metamorphism (sillimanite-muscovite subfacies), rocks are intimately associated with the migmatites and granites. The presence of quartzite, calc-silicate rocks, graphitic schist and abundance of aluminous minerals like kyanite or sillimanite in these rocks indicate their metasedimentary character. Granet-sillimanite bearing gneisses occupy most of the area of Darjeeling but not persistent throughout. Textural relationship suggests sequential growth of progressively higher-grade metamorphic minerals during D (1) and D (2) deformation. The relative X (Mg) in the minerals varies in the order: biotite > staurolite > garnet, and the X (Mn) decreases in the order: garnet > staurolite > biotite. The P-T evolution of these garnet-sillimanite gneiss has been constrained through the use of conventional geothermobarometry, internally consistent TWEEQU programme and Perple_X software in the KFMASH model system, the combination of these three approaches demonstrates that the Darjeeling gneisses experienced peak pressure and temperature at 7.0 +/- 0.3 kbar and 700 +/- 30(a similar to)C. The observation in this study has important bearing on the inverted metamorphism in the Himalayan metamorphic belt.
- 出版日期2015-8
