Infra-arc mantle-crust transition and intra-arc mantle diapirs in the Kohistan Complex (Pakistani Himalaya): petro-structural evidence

The Jijal and Chilas Complexes have been interpreted previously as the lowe r levels of the layered Kohistan Island Are, in Pakistan, We provide petro- structural evidence for melt-consuming reactions between mantle rocks and i nfiltrated, volatile-rich magmas in both complexes, precipitated minerals i n Jijal and Chilas suggest that melt-rode reaction occurred at higher press ure in Jijal than in Chilas. The early appearance of orthopyroxene in Chila s and the spatial relationship of the ultramafic rocks with quartz-bearing norites indicate that the reactant melt was more silicic, We argue that the Jijal Complex includes the infra-are crust/mantle boundary and that ultram afic associations of the Chilas Complex are apices of possibly younger, int ra-arc mantle diapirs.