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 lower levels of the layered Kohistan Island Arc, in Pakistan. We provide petro‐structural evidence for melt‐consuming reactions between mantle rocks and infiltrated, volatile‐rich magmas in both complexes. Precipitated minerals in Jijal and Chilas suggest that melt‐rock reaction occurred at higher pressure in Jijal than in Chilas. The early appearance of orthopyroxene in Chilas 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‐arc crust/mantle boundary and that ultramafic associations of the Chilas Complex are apices of possibly younger, intra‐arc mantle diapirs.