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 Mg O(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.