Geochemistry of early Late Cretaceous Gaerqiong high-Mg# diorite porphyry in midnorthern Lhasa terrane: Partial melting of delaminated lower continental crust?

The Gaerqiong diorite porphyry developed in the mid-northern Lhasa terrane shows some adakite affinities. The geochemical features, combined with high MgO (＞3.56%), Cr (＞150×10-6) and Ni (＞70×10-6) concentrations, and Mg# values (＞61), suggest that the Gaerqiong diorite porphyry can be classified as high Mg# adakitic rocks. Previous studies have indicated that the granodiorites and diorite porphyries in the Gaerqiong area were developed during 90~86Ma. The high Mg# adakitic rocks in this study have a close spatial relationship with these rocks, which suggests that all of them were formed by the same tectonic event. The geochemical characteristics of the Gaerqiong high-Mg# adakitic rocks are consistent with a derivation from partial melting of delaminated lower continental crust. The results achieved by the authors suggest that the major crustal thickening of mid-northern Lhasa terrane occurred prior to the Indo-Asian collision.