DefinePK

Abstract

The pyroxene granulites of Swat and Kohistan, formerly called norites, form a part of an extensive belt stretching between Nanga Parbat and central Dir. They are relatively uniform in composition and usually represented by leucocratic rocks essentially composed of plagioclase, orthopyroxene and clinopyroxene, with subordinate amounts of quartz, opaque mineral(s), apatite, amphibole, biotite and, locally, garnet; but some' of the rocks contain a higher proportion of amphibole and biotite. The proportion of quartz increases towards the intermediate members which may also have essential K-feldspar. The rocks are gneissose (foliated) and layered/banded, with some of the layers being pyroxenitic or anorthositic. Some of the bands are due to metamorphic segregation whilst others are relict igneous layers modified by metamorphism.
This paper presents a detailed account of the petrography of the rocks together with a discussion on the nature of the foliation, layering, and other aspects (xenoliths, hornblende-pegmatites, etc.), and details of the plagioclase in the granulite. Many of the features can be better explained by invoking metamorphism. It appears that the rocks crystalized plutonically from an andesitic basalt magma in an island arc or a continental margin, were metamorphosed (800oC, 7-5 kb) and finally intruded, as crystalline material capable of plastic flow, in the country rocks which were passing through amphibolite facies metamorphism.