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Resolving the Routine Presence of Kyanite, Andalusite and Sillimanite across a Region using Foliation Intersection/Inflection Axes Preserved in Porphyroblasts, Petrographic Observations and Thermobarometry
Author(s) -
ALI Asghar
Publication year - 2012
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2012.00744.x
Subject(s) - andalusite , sillimanite , kyanite , geology , schist , geochemistry , metamorphic rock , petrography , foliation (geology) , staurolite , devonian , overprinting , petrology , paleontology , biotite , quartz
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 Al 2 SiO 5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al 2 SiO 5 triple point. All three Al 2 SiO 5 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.