Petrology and geochemistry of dolerite and lamprophyre sills in Mesozoic successions of Khanozai–Muslim Bagh area, northwestern Pakistan

In Khanozai–Muslim Bagh area, NW Pakistan, the sills are intruded into mainly Triassic–Jurassic successions of Indian platform sediments. They are petrographically identified as dolerite and lamprophyre. The dolerite is a normal dolerite and olivine dolerite and is altered compared with lamprophyre. Lamprophyre is classified as sannaite, camptonite, minette, and damtjernite. The geochemical signature of dolerite, olivine dolerite, and lamprophyre suggests that these rocks belong to alkali series by classification and may be alkaline in nature. Normal mid-oceanic ridge basalts (NMORB)–normalized plots of dolerite, olivine dolerite, and lamprophyre show higher enrichment of large ion lithophile elements (LILEs) relative to high field strength elements (HFSEs) and marked positive anomalies on Nb which confirm their origin from an enriched mantle source. The ocean island basalt (OIB)–normalized plots of these rocks exhibit patterns almost alike to those of OIB suggesting a source similar to OIB. The tectono-magmatic discrimination plots of dolerite, olivine dolerite, and lamprophyres plot them in the OIB field and indicate that they are alkaline rocks in nature. The petrogenesis and tectonic setting of these rocks suggest that they are OIB in nature and may represent a Late Cretaceous magmatic activity that erupted as hotspot fluid through the crust of Indian Plate during the Late Cretaceous. It is much similar to the other hotspot-related rocks that intruded into the Parh Group and Bela ophiolite melange. Much like the magmatism of Deccan Traps and the Chagos-Laccadive Ridge, these rocks may be the melt of a hotspot possibly Reunion that intruded into the Indian Plate margin when it had passed over it during the Late Cretaceous.