Multiple mantle sources during island arc magmatism: U–Pb and Hf isotopic evidence from the Kohistan arc complex, Pakistan

Abstract

ABSTRACT This paper presents high‐precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB‐type isotopic characteristics generated 99–92‐Ma‐old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a >600‐Ma‐old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82‐Ma‐old felsic peraluminous dykes have MORB‐type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex.