Infra-arc mantle–crust transition and intra-arc mantle diapirs in the Kohistan Complex (Pakistani Himalaya): petro-structural evidence |
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| Authors: | Burg Bodinier Chaudhry Hussain & Dawood |
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| Institution: | Geologisches Institut, ETH-Zentrum, Sonneggstrasse 5, CH-8092 Zürich, Switzerland.; UMR C5569, ISTEEM, UniversitéMontpellier 2, Place E. Bataillon, Cc 57, 34095 Montpellier Cédex 05, France.; Institute of Geology, Punjab University, Quaid-e-Azam Campus, 54590 Lahore, Pakistan.; Pakistan Museum of Natural History, Garden Avenue, Shakarparian, Islamabad 44000, Pakistan.; Pakistan Museum of Natural History, Garden Avenue, Shakarparian, Islamabad 44000, Pakistan. |
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| Abstract: | 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. |
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