新疆阿尔金山喀腊大湾地区玄武岩的地球化学特征及地质意义

对新疆阿尔金山东段喀腊大湾地区玄武岩进行了系统的岩石地球化学分析, 结果表明, 喀腊大湾地区的玄武岩具有低的Mg#值(Mg#=Mg/(Mg+Fe)×100)。稀土元素的含量变化范围较大, 轻重稀土分异不明显, 具有轻微的轻稀土富集, 弱的Eu负异常。微量元素Ni、Co、Cr与MgO呈正相关, 微量元素多元素标准化图解中, 普遍具有Nb、Ta的负异常, 部分样品具有Ti的负异常。在Th/Yb-Ta/Yb和Th/Hf-Ta/Hf构造环境判别图解中, 分别落入活动大陆边缘环境和大陆拉张(或初始裂谷)环境, 结合本区双峰式火山岩中玄武岩的地球化学特征, 以及与北阿尔金蛇绿混杂岩带其它地区玄武岩的对比, 认为喀腊大湾地区的玄武岩可能形成于紧邻北阿尔金地区古洋盆的活动大陆边缘环境。

Geochemical Characteristics of Basalts from Kaladawan in East Altun Mountains of Xinjiang and Their Implications

Kaladawan area in the eastern part of the Altun Mountains is tectonically situated between the NE-trending Altun strike-slip fault and the WE-trending northern Altun marginal fault. In this area, there appears a set of volcanic-sedimentary rocks. A geochemical study was made for the basalts. The result shows that the basalts have low Mg#, the content of REE changes greatly, the LREE is moderately enriched, but the Eu anomaly is not obvious. Co, Cr and Ni are positively correlated with MgO. In the chondrite-normalized spidergrams, some samples have Nb and Ta anomalies, whereas some other samples show Ti anomalies. In the Th/Yb-Ta/Yb diagram, the basalts belong to active continental margins. In the Th/Hf-Ta/Hf diagram, the basalts belong to continental breakup setting or early rift. Combined with geochemical characteristics of basalts of bimodal volcanic rocks in Kaladawan area and basalts in other areas of the north Altun ophiolite belt, the authors hold that the basalts from the Kaladawan area might have erupted in the active continental margins.