巴里坤塔格晚古生代侵入岩岩石地球化学与SrNdPb同位素特征

巴里坤塔格地区晚石炭世—早二叠世侵入岩主要包括闪长岩、花岗闪长岩、花岗岩和辉绿岩, 相互呈侵入接触关系, 形成时代在误差范围内一致。在地球化学上, 均属过铝质钙碱性和高钾钙碱性系列,富集轻稀土元素、大离子亲石元素以及不相容元素, 亏损高场强元素, 显示火山弧花岗岩的特征,低Sr、低Pb、高Nd的同位素组成特征表明该区侵入岩起源于亏损地幔。通过对综合区域地质演化分析, 认为巴里坤塔格地区在晚石炭世—早二叠世为后碰撞拉张环境, 其侵入岩的岛弧特征可能是由于岩浆源区受过早期俯冲作用的影响。TDM =1 076～806 Ma, 指示中酸性侵入岩类的来源可能是古亚洲洋俯冲形成的新生陆壳, 该陆壳起源于亏损地幔。因此, 认为晚石炭世—早二叠世晚期巴里坤塔格与邻区博格达、哈尔里克地区自晚石炭世全面进入板内构造演化阶段。

Geochemistry and Sr-Nd-Pb Isotopes of Late Paleozoic Intrusive Rocks in Balikuntage,Xinjiang

The intrusive rocks of late Carboniferous and early Permian in the Balikuntage area mainly include diorite, granodiorite, granite and diabase.They show intrusive contact relationships and their ages are similar within the error range. All the intrusive rocks belong to peraluminous calc-alkaline and high-K calc-alkaline series. They are rich in LREE, LILE and incompatible elements, but deficient in HFSE, which are characteristics of the volcanic arc granite. Besides, isotopic composition characteristics of high Nd, low Sr and Pb content suggest that the intrusive rocks come from the depleted mantle.Based on the analysis of the regional geological evolution, the tectonic environment of Balikuntage region is the intercontinental rift valley between late Carboniferous and early Permian, and its island arc characteristics may be induced by the early subduction in magma source. The TDM value(1076—806 Ma) reflects that the intermediate-acid intrusive rocks have same source area which is given priority to the partial melting of the juvenile crust, and the source of the young crust is derived from the depleted mantle. It can be deduced that Balikuntage and its adjacent area Bogda and Haerlike fully entered into the intraplate environment in late Carboniferous and early Permian.