引用本文：邵鹏程,陈世悦,孙娇鹏,马帅,刘金,汪峰.2018.柴达木盆地北缘西段嗷唠山辉长闪长岩锆石SHRIMP U-Pb定年及岩石地球化学特征[J].地质学报,92(9):1888-1903. SHAO Pengcheng,CHEN Shiyue,SUN Jiaopeng,MA Shuai,LIU Jin,WANG Feng.2018.SHRIMP Zircon U-Pb Dating and Petro-Geochemistry of Aolaoshan Gabbro-Diorite in the Western North Margin of Qaidam Basin[J].Acta Geologica Sinica,92(9):1888-1903.
Abstract:Systemic chronology and petro-geochemistry analysis of Aolaoshan gabbro-diorite was conducted to analyze its genesis, which makes up understanding of tectonic attributes of the northern Qaidam in Late Paleozoic time. Our study shows that the Aolaoshan gabbro diorite is characterized by high SiO2 and K2O contents, low Na and Al contents, and high Mg#. The primitive mantle normalized spider diagram shows that the rock is enriched in large ion lithophile elements (Rb, Ba, K) and depleted in high field strength elements (Ta, Nb, Ti and P). The chondrite normalized REE distribution pattern shows a relatively flat, low differentiation curve of LREE and HREE, with low ∑LREE/∑HREE and (La/Yb)N ratios and weak negative to positive Eu anomalies, compared with that of contemporary intermediate-felsic intrusive rocks. SHRIMP U-Pb zircon dating yields an average weighted age of 370.4±3.4 Ma for the gabbro-diorite samples from the Aolaoshan area, which corresponds to Lae Paleozoic magmatic activity. The major and trace element geochemistry analysis illustrates that the rock is of attributes of magmatic rocks formed in island arc or active continental margin, suggesting that it probably originated from lithosphere mantle contaminated by crust material and metasomatized by fluid in subduction belt. Based on the previous studies on the Neoproterozoic Late Paleozoic oceanic crust subduction and collision between continents tectonic setting, and combined with geochemical tectonic environment discrimination in this study, it can be concluded that the Aolaoshan gabbro-diorite formed in a lithosphere thinning and crustal extension environment resulted from post-orogenic lithosphere delamination, which marks the end of Caledonian orogenesis in the northern margin of Qaidam region.