北山造山带南缘一条山北闪长岩地球化学、年代学特征及其构造意义

一条山北闪长岩地处北山造山带与敦煌地块的接触部位，对其研究可以更深入地了解北山造山带南缘古生代的构造演化及其地球动力学意义。笔者对一条山北闪长岩系统开展了锆石U-Pb同位素和全岩主量、微量元素分析。LA-ICP-MS 锆石U-Pb分析显示，一条山北闪长岩侵位时代为早二叠世(274.6±1.6)Ma。全岩地球化学分析显示，其为准铝质钙碱性系列岩石，富集大离子亲石元素Rb、Pb、Th、U等元素，尤其是强不相容元素Rb、Th、K富集程度较高，强烈亏损Ba、Nb、Ta、P、Ti等高场强元素，富集Zr、Hf。岩石成因分析表明，一条山北早二叠世闪长岩岩浆源区为岩石圈地幔岩浆作用导致下地壳岩石部分熔融，并与少量幔源玄武质岩浆混合。根据相关判别图解并结合区域地质资料分析，一条山北早二叠世闪长岩形成于后碰撞伸展拉张环境，指示北山南带在早二叠世进入了后碰撞演化阶段或者局部进入后碰撞演化阶段。

Geochemistry,Geochronology Characteristics and Tectonic Significance of Yitiaoshan Diorite in the Southern Margin of Beishan Orogenic Belt

The Yitiaoshanbei diorites are located between the Beishan orogenic belt and Dunhuang terrane. The study of these diorites has important geological implications for the Paleozoic tectonic evolution and geodynamic processes of the Beishan orogenic belt. In this study, we present zircon U-Pb ages, and whole-rock major and trace element compositions for diorites from the Yitiaoshanbei area. LA-ICP-MS zircon U-Pb dating suggests that Yitiaoshanbei diorites were emplaced at the Early Permian(ca. 274.6 Ma). Geochemical characteristics imply that these diorites belong to the metaluminous and calc-alkaline series rocks. These diorites are enriched in large ion lithophile elements(LILEs; e.g., Rb, Th, K, U and Pb), and depleted high field strength elements(HFSEs; e.g., Ba，Nb, Ta, Ti, P, Zr and Hf). The Early Permian Yitiaoshanbei diorites were derived by partial melting of lower crustal materials, induced by lithospheric mantle magmatism and mixed with a small amount of mantle derived basaltic magma.Along with related discriminant diagrams and regional geological data, we suggest that the Yitiaoshanbei diorites were generated in a post-collisional extensional setting. These results also indicate that the southern belt of the Beishan has been underwent post-collisional stage or partially entered the post collisional evolution stage during the Early Permian.