Abstract:

Naij Tal Group mainly consists of metamorphic volcanic-sedimentary series, which is the important material records of Early Paleozoic tectonic evolution in East Kunlun. Petrologic and geochemical characteristics indicate that the meta-sedimentary rocks from Naij Tal Group are mainly composed of mica-quartz schist, chlorite sericite schist, feldspar quartz schist, sericite quartz schist. Additionally, marble, gneiss and quartzite were occasionally outcropped in some area. The geochemical characteristics are very similar to upper continental crust, with high SiO₂ (average 69.82%), Sr (average 559.60×10^-6) and Ba (average 194.68×10^-6). The meta-sedimentary rocks have high quantity of LREE ((La/Yb)_N=7.18) with obvious negative Eu anomalies (δEu=0.44-0.66), which is similar to active continental margin. The upper continental crust-normalized trace elements diagram shows that their protoliths are dominatly felsic rocks (e.g., sandstone, greywacke, and pelite) from upper continental crust. Tectonic discrimination based on geochemical data of meta-sedimentary rocks, as well as the CIA (49.70-75.95，Chemical Index of Alteration) and ICV (1.32-2.01, Index of Compositional Variation) reveal that the provenance of meta-sedimentary rocks are characterized by low degree weathering, and lied in the cold or semiarid zone. Based on the previous regional data, we conclude that the Naij Tal Group formed in the backarc basin relating to the Proto-Tethys northward subduction, and that the southern tectonic belt of East Kunlun was in the avtive continental margin in Early Paleozoic.

Key words: East Kunlun, south tectonic belt of East Kunlun, Naij Tal Group, meta-sedimentary rock, geochemistry, tectonic significance