新疆东准噶尔野马泉花岗岩体的年龄和地球化学特征

Geochronology and geochemical characteristics of the Yemaquan granitic pluton in East Junggar,Xinjiang

新疆东准噶尔野马泉花岗岩体是一个主要由花岗闪长岩、二长花岗岩和碱长花岗岩组成的复式花岗岩体。三种岩石的锆石U-Pb年龄在误差范围内有很好的一致性(～300Ma),指示野马泉岩体是在晚石炭世侵位的,也属于东准噶尔地区后碰撞阶段的岩浆作用产物。元素地球化学组成表明,花岗闪长岩、二长花岗岩和碱长花岗岩均属于准铝质,其主量元素和微量元素如CaO、Al2O3、Na2O、K2O、Rb、Sr与SiO2之间有明显的线性关系,三种岩石在不相容元素蛛网图和稀土元素配分模式上均表现出相似的特征,Eu负异常程度也随着SiO2含量的增加而提高。此外,野马泉岩体不同岩石有非常近似的Hf同位素组成,其εHf(t)值为+11.8～+12.7。因此,年龄结果和地球化学特征说明,野马泉复式花岗岩体很可能是由同源岩浆通过一定的岩浆演化形成的。

Yemaquan granitic pluton in East Junggar of Xinjiang is a granitic complex,which dominantly consists of granodiorite, monzogranite,and alkali-feldspar granite. These rocks have nearly coincident zircon U-Pb ages ( ～ 300Ma) within errors,suggesting that this pluton was emplaced in Late Carboniferous by the post-collisional magmatic activity in East Junggar. The geochemical compositions show that all of these rocks are metaluminous,and their major elements and trace elements,such as CaO,Al2O3,Na2O, K2O,Rb,Sr have obviously linear relationship with SiO2. All these rocks display similar characteristics in incompatible-element spidergrams and REE patterns,and with SiO2content increasing,their negative Eu anomalies become stronger. In addition,in situ Hf isotope analysis of zircons reveal that the rocks in the Yemaquan pluton have much close Hf isotopic compositions,their εHf( t) values ranging from + 11. 8 to + 12. 7. According to the age and geochemical characteristics,we argue that the Yemaquan granitic complex was probably formed by the same magma which experienced some evolution.