天山东段尾亚地区白尖山超单元特征

早石炭世白尖山超单元横亘于尾亚站东西两侧，沙泉子断裂以南的狭长地带（研究区长５０余千米，宽３～６ｋｍ）。它是北部觉洛塔格早石炭世火山型被动陆缘与其南（以沙泉子断裂为界）卡瓦布拉克古陆块汇聚事件的产物。这次事件导致沿卡瓦布拉克地块北缘成线状分布的巨大岩基链的形成，即该带事实上成为一个活动陆缘弧──白尖山岩浆弧（白尖山超单元）。根据各岩石单元的接触关系，白尖山超单元由早至晚为辉长岩—石英闪长岩—花岗闪长岩—二长花岗岩—钾长花岗岩—碱长花岗岩。从沙泉子断裂向南，大体上反映出偏基性的石英闪长岩单元偏北侧分布，钾长花岗岩及碱长花岗岩单元偏南分布，表现出当时碰撞带的特性。由于晚石炭世末受到韧性剪切作用，大部分产生塑性变形，成为初糜棱岩—超糜棱岩的花岗质岩石，宏观上似具片麻状构造。无论从岩石学、岩石化学及地球化学特征方面来看，均具同源岩浆演化的特征。白尖山超单元侵入于含早石炭世动物化石的卡拉火大山组中，被二叠纪尾亚超单元组合（原尾亚岩体）侵入，测定Ｕ—Ｐｂ同位素年龄为３３８．４Ｍａ及３２５．２４Ｍａ，从而确定白尖山超单元形成时代为早石炭世。

BAIJIANSHAN SUPREUNIT IN THE WEIYA AREA OF EASTERN TIANSHAN

Baijianshan superunit of Early Carboniferous goes along the narrow zone north of Weiya station and south of Shaquanzi fault, of over 50 km in length and 3-6 km in width. It's a product of the convergence between Qoltag volcanic passive continental margin in the north and Kawabulake paleo-land in the south bounded by Shaquanzi fault. Along the northern margin formed a large linear chain of batholith which is in fact an active continental margin arc called Baijianshan magmatic arc (Baijianshan superunit). Baijianshan superunit consists of gabbro-quartz diorite-granodiorite - monzonitic granite-K-feldspar granite-akalifeldspar granite from early unit to late unit according to their contact relation. To the south of Shaquanzi fault quartz diorite unit occurs in the relatively northern part, and K-feldspar granite and alkali-feldspar unit occur in the relatively southern part. Due to the ductile shearing at the end of Late Carboniferous most rocks are deformed to be granitic mylonites and super-mylonites macroscopically in a gneissic-like structure.The petrology,lithochemistry and geochemistry show syn-genetic magmatic evolution of rocks. Baijianshan superunit which was intruded into Karahuojianshan Formation with Early Carboniferous fauna fossils was intruded by Permian Weiya superunit (previously called Weiya rock body). The U-Pb isotopic dating of 338. 4Ma and 325. 24 Ma shows the age of Baijianshan superunit to be Early Carboniferous.