Petrology of the Southern Amphibolite Belt Rocks from Mahak and Surrounding Area, Kohistan Arc, North Pakistan
Abstract
The various rock types at Mahak are medium to coarse-grained amphibolites, hornblendites, hornblende pegmatite, diorite, meta-gabbro, metapyroxenite and quartzo-feldpathic veins and dykes. Amphibolites are the most abundant rocks of the area. These are distinguished into epidote amphibolite and plagioclase amphibolite. The major element chemistry of the amphibolites suggests their derivation from a basic igneous parent of tholeiitic character, but field data also indicate some of them to be hybrids having been developed as a result of reaction between hornblendites and the granitic magma. The true amphibolites contain mineral assemblages indicating amphibolite grade metamorphism followed by the prevailance of epidote amphibolite facies and a minor phase of green schist facies environments. Hornblendites are usually monomineralic. Two types of hornblendite occur, i.e. (a) pre-granitic and the common ones and b) sys-granitic. Field and laboratory data show that the former types may be representing early cumulate for the basic amphibolites or rocks having been formed in the loci of fluid phases during the amphibolite grade metamorphism. However, field evidence show that the sys-granitic hornblendites are the product of reaction between amphibolites and the granitic magma.
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