新疆东准噶尔纸房地区早古生代花岗岩的确定及其地质意义

DETERMINATION OF THE EARLY PALEOZOIC GRANITE IN ZHIFANG AREA,EAST JUNGGAR,XINJIANG AND ITS GEOLOGICAL IMPLICATIONS

纸房花岗岩体位于新疆东准噶尔卡拉麦里构造带北侧。该岩体侵入的最新地层为中—上奥陶统荒草坡群,并被晚志留世及早泥盆世地层不整合覆盖。对纸房花岗岩进行锆石SHRIMP U-Pb定年,获得的206Pb/238U加权平均年龄为(463±7)^(436±4)Ma,表明该岩体形成于晚奥陶世—早志留世,是早古生代岩浆活动的产物。对已有的区域地质资料、岩体侵位时代及其与围岩接触关系进行综合分析后认为,纸房花岗岩体的形成时代大致对应于卡拉麦里构造带内区域性角度不整合的形成时间,推测该岩体为早古生代造山过程中形成的花岗质岩石。高Sr、低Yb、弱的Eu负异常等地球化学特征也显示其为埃达克型同造山花岗岩。纸房地区早古生代同造山花岗岩的存在为东准噶尔卡拉麦里构造带早古生代造山作用的确认提供了证据。

Zhifang granite pluton outcrops in the northern part of Kalamaili tectonic belt, East Junggar Xinjiang. The latest strata intruded by the granite pluton are the Middle-Upper Ordovieian Huangeaopo formation and it is unconformably covered by the Upper Silurian and Lower Devonian strata. Zircon SHRIMP U-Pb data showed that the weighted mean 2-6pb/238U age was （463 ± 7） （436 ＋_4） Ma, which indicated that the granite pluton was emplaced during Late Ordovieian and Early Silurian and it was the product of the early Paleozoic magmatic activity. Combining the existing regional geological data, the emplacement age of the granite pluton and the contact relation with the country rocks, it is speculated that the forming time of the granite pluton roughly corresponds to that of the regional angular unconformity in the Kalamaili tectonic belt and the Zhifang granite pluton might be formed during the early Paleozoic orogenic stage. The geochemical characteristics of high Sr, low Yb and weak negative Eu anomalies also suggests that it is the Adak-type syn-orogenic granite. Therefore determination of the syn-orogenic granite in Zhifang defines the presence of early Paleozoic orogenesis in Kalamaili tectonic belt, East Junggar.