Origin of the mafic dykes in Nagarparker area of Pakistan

Abstract

The Nagarparker area of Pakistan comprises igneous and metamorphic rocks dissected by coarse-grained gabbro dykes and medium- to fine-grained dolerites at Karai, Dhedvero, and the central part of the area. The gabbro dykes contain plagioclase (An79), diopside, diopsidic-augite, and olivine with minor biotite, magnetite, ilmenite, titanite, and ilmenite-titanite composite grains. The dolerites consist of plagioclase, titaniferous augite, augite, hornblende, biotite, titanite, apatite, zircon, titanomagnetite, rutile, and ilmenite. Based on geochemistry, the gabbro dykes (group I) and dolerites (group II) are classified as subalkaline whereas group III dolerites as alkaline. In spidergram, Nb troughs and Sr crests are depicted in the group I and group II dykes whereas the group III dykes illustrate positive Nb and negative Sr with relatively smooth trace element pattern. The mineralogical composition, discriminant quadratic analysis, and trace element variations distinguish the mafic dykes of the study area into two magmatic groups. The first group comprises group I and group II dykes which depict island-arc type whereas the group III dykes resemble OIB-type compositions similar to Seychelles islands and the Tavidar region of Indian Rajasthan. The tentative timing of their emplacement may be Neoproterozoic and Cretaceous (?), respectively.