Geology and petrography of the Nagar Parkar igneous complex, southeastern Sindh: the Dinsi body

Abstract

Geological mapping and detailed petrography suggest that the Dinsi area is principally occupied by medium-grained porphyritic granite, and quartz monzonite which covers the western part of the outcrop area. The granite is composed of perthite, quartz, some plagioclase, opaque oxide, biotite and/or amphibole, and titanite, whereas the quartz monzonite comprises perthite, calcic oligoclase/andesine, quartz, and minor amount of mafic minerals similar to those of the granite. The two granitoids contain local bodies of the basement consisting of fine-grained doleritic to medium-grained dioritic rocks. The basement shows brittle deformation and low-grade metamorphic overprint that resulted in development of epidote, chlorite, albitic plagioclase, and actinolite before the emplacement of the granitoids. These rocks were cut by small dykes of granitic and aplitic rocks showing a range of texture and composition. They are of more than one generation and at places show complex relations, but many are related to the two main intrusions of the granitic rocks. The final phases of magmatism are represented by mafic and rhyolite dykes and their contemporaneous, rare microgranite dykes. The mafic dykes, reaching 500x3 m in size, can be divided into two broader groups one of which contains hornblende and the other augite as the characteristic primary mafic phase.