The petrogenetic interrelationship of Wajilitag complex components in the early Permian Tarim large igneous province, NW China

The Permian Tarim large igneous province (TLIP) is located in the Tarim basin, NW China. Although the flood basalt of the TLIP has been intensively studied, other igneous components within TLIP have not yet been sufficiently investigated. The Wajilitag igneous complex is outcropped with a rather limited exposure by regional tectonic uplift. However, various igneous rocks, both mafic–ultramafic and syenitic, can be observed as either intrusions or extrusions in this area. It is an ideal location for studying the magmatic evolution of different components within the TLIP. We systematically examine the geological, geochronological, and geochemical characteristics of the Wajilitag complex, to further constrain the petrogenesis of each component and their interrelationships, as well as the implications to the petrogenetic model of TLIP. The igneous rocks in Wajilitag complex can be classified into two series based on their geochemical features: Series A and Series B. Series A are more alkalic, more trace element enriched and more isotopically depleted than Series B. Series A includes nephelinite, aegirine–nepheline syenite (ANS), and syenite porphyry (SP), whereas the Series B consists of clinopyroxenite, gabbro, diorite, hornblende-bearing syenite (HS), and quartz syenite (QSN). Dolerites can either belong to Series A or Series B depend on its geochemistry. Kimberlitic rocks are independent of the Wajilitag complex geologically, geochemically, and geochronogically. The temporal sequences of Wajilitag complex would be clinopyroxenite→gabbro→ diorite/syenite→nephelinite. The dolerite can be emplaced later than the syenite but can extend to an earlier period. In contrast to the Tarim basalts, the Wajilitag complex belongs to the second stage of magmatism in the TLIP. The mantle source for the Tarim basalts, the Series B and Series A gradually changed from SCLM-dominated to plume-dominated component.

二叠纪塔里木大火成岩省（Permian Tarim large igneous province, TLIP）位于中国西北部塔里木盆地。尽管学界已对TLIP的溢流玄武岩开展了深入研究，但该火成省内部的其他火成组分尚未得到充分探究。受区域构造隆升影响，瓦吉里塔格火成杂岩（Wajilitag igneous complex）的出露范围相对有限，但该区域可见多种镁铁质-超镁铁质及正长质火成岩，它们既可呈侵入体产出，也可作为喷出体出露，是研究TLIP内部不同组分岩浆演化的理想场所。本研究系统分析了瓦吉里塔格杂岩的地质、年代学与地球化学特征，旨在进一步约束各组分的岩石成因及其相互联系，以及其对TLIP岩石成因模型的启示意义。依据地球化学特征，瓦吉里塔格杂岩内的火成岩可划分为A系列与B系列。相较于B系列，A系列具有更强的碱质特征、更显著的微量元素富集程度以及更明显的同位素亏损。A系列包括霞石岩、霓石霞石正长岩（ANS）以及正长斑岩（SP）；而B系列则由辉石岩、辉长岩、闪长岩、含角闪石正长岩（HS）以及石英正长岩（QSN）组成。辉绿岩的归属需依据其地球化学特征确定，可隶属于A系列或B系列。金伯利岩类在地质、地球化学及年代学层面均独立于瓦吉里塔格杂岩。瓦吉里塔格杂岩的岩浆作用时序依次为辉石岩→辉长岩→闪长岩/正长岩→霞石岩。辉绿岩的侵位时间可晚于正长岩，也可早于该阶段。与塔里木溢流玄武岩不同，瓦吉里塔格杂岩属于TLIP岩浆作用的第二阶段。塔里木玄武岩、A系列与B系列的幔源组分，逐渐从以大陆岩石圈地幔（SCLM）为主转变为以地幔柱主导的组分。