Highly aluminous hornblende-cummingtonite coronas in gabbronorites of the southern amphibolite belt, Kohistan
Abstract
The gabbronorites of the Chilas complex and southern amphibolite belt locally contain thin 0.2 mm) amphibole coronas around pyroxene. These consist of an inner shell offibrous, colourless to pate cummingtonite, and an outer shell of bluish green alumino-tschermakite, with or without a discrete growth of epidote + vermicular quartz on the edges of the plagioclase. The coronas represent the initial stage of amphibolite facies metamorphism which prevailed in the southern part of the Kohistan arc during mid Cretaceous. The tschermakite, with 19.2% Al2O3, is one of the most aluminous calcic amphiboles thus far reported. The primary amphibole in the gabbronorites is brown ferroan pargasile containing much higher Ti and K than the coronitic tschermakite.
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