Coronites from the Chilas and Jijal-Patan Complexes of Kohistan
Abstract
This paper describes coronites from the Jijal-Patan and Chilas complexes of northern Pakistan. In Jijal, plagioclase and ortho pyroxene reacted under high P-high T metamorphic conditions (830oC, 12-1 4 kbar) to produce garnet +clinopyroxene coronas. These rocks occur along the MMT suture zone and were metamorphosed at > 40 km depth due to subduction/sinking, In the Chilas complex, orthopyroxene/clinopyroxene/hornblende+spinel coronas developed due to reactions between highly calcic plagioclase and mafic minerals under medium P-high T conditions (730-850 oC, 3-7 kbar). These coronas may have formed due to slow cooling, either during uplift or pyroxene granulite facies metamorphism of feldspathic peridotites, troctolites, olivine gabbros, and related rocks. At higher levels during uplift, when the Chilas complex had access to water labradorite-andesine reacted with mafic minerals to produce thin amphibole and epidote+-quartz coronas in noritic granulite. These medium to low P-low T epidote amphibolite facies coronas are mostly very thin but quite common. In rare cases the rocks aye more severely affected, thus bridging the gap to epidote amphibolites.
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