Abstract

Info

Title:: Genesis of Early Devonian Granitoid in East Segment of East Kunlun: Evidences from Longmoka Pluton

Author(s):: WANG Xin; DONG Guo-chen; DONG Liang-qiong; School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China

Keywords:: petrogenesis; granodiorite; zircon U-Pb age; geochemistry; Hf isotope; Early Devonian; North Kunlun tectonic belt

Abstract:: Longmoka pluton is located in Dulan-Gouli area of the east segment of North Kunlun tectonic belt, East Kunlun orogen. The zircon U-Pb dating, geochemistry of whole rocks and zircon Hf isotope of Longmoka pluton were studied, and the genesis and dynamic background of pluton were discussed. The results show that Longmoka pluton is mainly composed of granodiorites, the zircon dating yields an weighted average ²⁰⁶Pb/²³⁸U age of (409±2)Ma, belonging to the early Early Devonian; the SiO₂ contents (mass fractions) of whole rocks vary from 66.25% to 69.61%, and the granodiorites are characterized by relatively high Al₂O₃ and Na₂O contents, and low K₂O, MgO and CaO contents, and they are relatively rich in Na and have high A/CNK of 1.04-1.19, showing an Ⅰ-type granite affinity with peraluminous; the granodiorites have low REE and poor fractionation between LREE and HREE, and they are enriched in LILE (Rb, Ba, Pb, Sr) and depleted in HFSE (Th, Ta, Nb, Ti), the granodiorites show similar geochemical characteristics to adakites with high Sr/Y (56.9-80.8) and positive Eu anomalies; the ε_Hf(t) of granodiorites ranges from 5.6 to 11.7 with T_DMC of 659-867 Ma, indicating the magma are probably produced by partial melting of juvenile basaltic lower crust caused by the upper mantle uplift; East Kunlun orogen may be under a tectonic setting of post-collision extensional stage in Early Devonian.