东昆仑东段清水泉辉长岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

摘要

Located in central Eastern Kunlun suture zone on the northern side of Qingshuiquan ophiolite, the Qingshuiquan gabbro consists mainly of hornblende gabbros. The LA-ICP-MS zircon U-Pb age is 452.1 ± 5Ma, suggesting the formation of gabbro in Late Ordovician. The gabbro samples have 43.89%~45.99%SiO2, 1.30%~2.32%Na2O, 0.68%~1.39%K2O, and 5.72%~6.54%MgO, with low P2O5 (0.26%~0.40%), TiO2(0.74%~0.95%) and Mg#(53~54). The geochemical characteristics indicate that the gabbro be⁃longs to tholeiitic rocks;REE patterns show that the rocks are enriched in LREE and depleted in HREE;the trace elements are char⁃acterized by enrichment of LILE (Cs,Rb,Ba,especially positive anomaly of Ba) and obvious depletion of HFSE (Nb,Ta,Ti,Zr and Hf). Tectonic discrimination diagrams indicate that the gabbro formed in an island arc setting of active continental margin. Combined with regional studies, the authors hold that Qingshuiquan gabbro rocks might have formed at the initial stage of the northward sub⁃duction of Central Eastern Kunlun back-arc limited ocean, represented by the Qingshuiquan ophiolite.%清水泉辉长岩体位于东昆仑中缝合带清水泉蛇绿岩北侧，主要岩性为角闪辉长岩。该岩体的LA-ICP-MS锆石U-Pb测年结果为452.1±5Ma，形成时代为晚奥陶世。辉长岩体样品SiO2含量为43.89%～45.99%，Na2O含量为1.30%~2.32%，K2O含量为0.68%~1.39%，P2O5含量为0.26%~0.40%，TiO2含量较低，为0.74%~0.95%，MgO含量为5.72%~6.54%，Mg#值较低，为53~54。岩石地球化学特征显示，该岩体属于拉斑玄武岩系列，稀土元素表现出轻稀土元素富集、重稀土元素亏损的特点，微量元素以富集大离子亲石元素（Cs、Rb、Ba等，尤其以Ba的正异常最为突出）、亏损高场强元素（Nb、Ta、Ti、Zr、Hf）为特征。微量元素构造判别显示，其形成于活动陆缘岛弧构造环境。结合区域地质资料研究表明，清水泉辉长岩体可能形成于以清水泉蛇绿岩为代表的东昆仑中弧后有限洋盆向北俯冲的初始阶段。