Abstract:

We discuss the zircon U-Pb dating, whole-rock geochemical and zircon Hf isotope data of the dioritic intrusion (stocks) in the southeast of Xiarihamu ore district. The rock assembles of the intrusion include diorites and quartz diorites. Zircon U-Pb dating demonstrates that the concordant age of the zircon in the quartz diorite is (243±1) Ma (MSWD＝0.013), i.e., the late Early Triassic. Geochemically, the diorite and quartzdiorite are metaluminous and belong to the high-K calc-alkaline series. The diorite is enriched in LREE and relatively depleted in HREE ((La/Yb)_N=8.7-12.7), and no obvious Eu anomaly (δEu=0.84-1.01). Both the diorite and the quartz diorite are enriched in Rb, Ba, and K, and depleted in Nb, Ta, P, and Ti, with a variable ε_Hf(T) values (from -1.0 to -0.9) and ancient T^C_DM ages (from 1.34 to 1.84 Ga). Combined with the discrimination diagram of experimental petrology studies, the authors suggest that their primary magma maybe derived from dehydration melting from a Meso-Proterozoic metabasaltic low crust source. Moreover, some contributions from enriched mantle materials maybe the main reason of a variable ε_Hf(T) values and T^C_DM ages. Trace elements and their characteristic ratio values display that the dioritic intrusion was generated within an Andean-type active continental margin setting. Taken together, in the late period of Early Triassic, the middle uplifted basement in eastern Kunlun was in the late-stage of Andean-type active continental margin setting.

Key words: diorite, zircon U-Pb age, geochemistry, tectonic setting, east Kunlun, Xiarihamu