新疆大黑山地区双庆铜矿北岩体地球化学特征及其构造环境

新疆哈密大黑山地区双庆铜矿北岩体的岩石类型主要为花岗闪长岩,少数为英云闪长岩,SiO2含量平均为74.18%,K2O/Na2O值平均为1.52,相对富钾,岩石属高钾钙碱性系列,岩石酸、碱度与同类岩石平均值相当,而镁铁组分低于平均值,显示岩石偏酸性,与碰撞构造环境形成的花岗岩特征类似。Al2O3含量较高,平均为12.83%,A/CNK平均为1.05,呈轻微铝过饱和。岩石总体上相对富集大离子亲石元素,亏损高场强元素。稀土元素总量较高,平均为202.12×10^-6,（La/Yb）N=6.32-19.57 1,（La/Sm）N=3.54-4.88 1,为轻稀土富集型。δEu=0.29~0.5,为明显的铕负异常。经多种相关图解判别,岩石属S型花岗岩,其构造环境相当于碰撞挤压环境花岗岩类。锆石颗粒U-Pb测年结果显示,源岩的岩浆成因锆石形成年龄为1058 Ma,相当于中元古代。本文指出该岩体为南天山地块与中天山地块碰撞后期长城系变质岩部分熔融的产物,是Rodinia超大陆的形成在该区的反映。

Geological Characteristics and Tectonic Environment of Rocks in the North Shuangqing Copper Mine of Daheishan, Xinjiang

Hosting rock in the north Shuangqing copper mine comprises mainly diorite granite. This hosting rock contains 74.18% of SiO_2 and has a K_2O/Na_2O ratio of 1.52 on average, it can be classified into potassium-rich calc-alkali rock series. The acidity and alkalinity of this hosting rock are consistent with the average values of similar rocks while its mafic content is lower than the average value, suggesting that the rock is similar to the post-collision type granite. This rock is peraluminous, containing 12.83% of Al_2O_3 and having an A/CNK ratio of 1.05 on average. In general, the rocks are relatively rich in LILE but poor in HFSE and show moderate negative Eu anomalies, δEu values are from 0.29 to 0.5, ∑REE value is 202.12×10~(-6), (La/Yb)_N values are from 6.32 to 19.57, and (La/Sm)N values are from 3.54 to 4.88. Geochemical characteristics and related dis-crimination diagrams analyses suggested that the rock is S type granite and its tectonic structure is VAG+Syn-COLG (a post-collision structure). U-Pb dating of zircon show that the forming period of the source rock is Mesoproterozoic(1058 Ma). In summary, we believes that this hosting rock is the product of partial melting of Changcheng Period metamorphic rock, which happened in the post-collision of southern Tianshan block and the middle Tianshan block, and reflects the formation of Rodinia supercontinent in this area.