Fluid-absent Melting of High-grade Semi-pelites: P-T Constraints on Orthopyroxene Formation and Implications for Granulite Genesis |
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Authors: | NAIR RAJEEV; CHACKO THOMAS |
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Institution: | DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES, UNIVERSITY OF ALBERTA, EDMONTON, ALBERTA, CANADA T6G 2E3 |
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Abstract: | Rocks of semi-pelitic composition are common in high-grade terranes.The first appearance of orthopyroxene in these rocks marks thetransition from amphibolite- to granulite-facies conditions,and is commonly attributed to the process of fluid-absent partialmelting. We have conducted fluid-absent melting experimentson two natural semi-pelitic rocks (quartz, plagioclase, alkalifeldspar, biotite and garnet) with the specific objective ofdetermining the pressuretemperature conditions necessaryto produce orthopyroxene. In contrast to previous experimentalstudies, our starting materials were obtained from a transitionalamphibolitegranulite terrane. Importantly, the high TiO2(>5 wt %) and F (>1 wt %) contents of biotite in our experimentsare more representative of biotite found in rocks on the vergeof granulite-facies conditions than those used in earlier studies.Experiments were conducted in a piston-cylinder apparatus at8001050°C and 715 kbar. We reversed the firstappearance of orthopyroxene in two-stage experiments at 7 and10 kbar. Fluid-absent melting of biotite began at |
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