Resolving the Routine Presence of Kyanite,Andalusite and Sillimanite across a Region using Foliation Intersection/Inflection Axes Preserved in Porphyroblasts,Petrographic Observations and Thermobarometry |
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| Authors: | Asghar ALI |
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| Institution: | 1. School of Earth and Environmental Science, James Cook University, Townsville, Queensland 4811, Australia;2. Department of Geology, University of Peshawar, Peshawar, Khyber Pakhtunkhwa 25120, Pakistan |
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| Abstract: | Constraints from P‐T pseudosections (MnNCKFMASH system), foliation intersection/inflection axes preserved in porphyroblasts (FIAs), mineral assemblages and textural relationships for rocks containing all three Al2SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P‐T‐t‐D path that swaps from clockwise to anticlockwise in the tectono‐metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation. |
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| Keywords: | Al2SiO5 triple point microtextures foliation intersection/inflection axes Barrovian sequence episodic porphyroblast growth |
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