东准噶尔巴塔玛依内山组火成岩锆石U-Pb年龄及其地质意义

以东准噶尔双井子地区巴塔玛依内山组和石钱滩组剖面为研究对象,通过岩矿鉴定、地球化学分析、锆石U-Pb定年和牙形刺挑选等方法,对巴塔玛依内山组和石钱滩组的年代学特征进行了研究。结果表明,巴塔玛依内山组火山岩的形成时间始于348. 7±2. 9Ma,318. 7±4. 2Ma之后结束,侵入岩的形成时间为255. 9±3. 5Ma,这些样品中普遍含有捕获锆石,这些锆石具有岩浆锆石的特征,年龄介于早石炭世杜内期和前寒武纪之间(354. 7～971. 2Ma),与盆地周边发育的岛弧火成岩和蛇绿岩年龄相仿,此外在石钱滩组灰岩内得到4颗牙形刺化石,分属于2个属,分别为Idiognathodus和Streptognathodus。以此为基础,通过搜集整理前人数据,得到如下结论:(1)巴塔玛依内山组火山岩地层是穿时的,从早石炭世到晚石炭世连续发育,形成时间介于348. 7±2. 9Ma～300. 4±1. 3Ma之间;(2)巴塔玛依内山组上部的石钱滩组形成于318. 7±4. 2Ma之后的晚石炭世;(3)卡拉麦里蛇绿岩所代表的准噶尔洋盆闭合时间在晚泥盆世法门期和348. 7Ma之间;(4)准噶尔盆地基底可能由岛弧和洋壳组成,且存在前寒武纪基底。本研究旨在确定巴塔玛依内山组和石钱滩组地层时代,并为卡拉麦里洋闭合时限以及盆地基底性质等问题的解决提供依据。

Zircon U-Pb age and its geological significance of the igneous rocks from Batamayineishan Formation in East Junggar

The Batamayineishan Formation and Shiqiantan Formation that range in Shuangjingzi area (within East Junggar) have been studied through thin section authentication, geochemical analysis, zircon U-Pb dating and conodonts selection. The results show that the formation time of Batamayineishan volcanic rocks began at 348.7±2.9Ma and ended after 318.7±4.2Ma, the only intrusive rock formed at 255.9±3.5Ma. The rocks commonly have captured zircons which have the characteristics of magmatic zircon and whose ages range from Carboniferous Tournaisian to Precambrian (354.7~971.2Ma). The ages of these captured zircons are similar to the ages of the island arc igneous rocks and ophiolites developed around the basin. Besides, four complete conodonts that belong to Idiognathodus and Streptognathodus have been found in the limestone of Shiqiantan Formation. On the basis of this, we get the following understanding by collecting and sorting out the previous data:(1) The volcanic rocks of the Batamayineishan Formation are diachronous, whose ages range from the Early Carboniferous (348.7±2.9Ma) to the Late Carboniferous (300.4±1.3Ma); (2) The Shiqiantan Formation which is located on the Batamayineishan Formation formed at Late Carboniferous after 318.7±4.2Ma; (3) The closure time of Junggar ocean which is represented by Kalamaili suture belt was between Famennian of Late Devonian and 348.7Ma; (4) The basement of the Junggar basin may be composed of island arc and oceanic crust, and there is a Precambrian basement. This study aims to determine the formation time of Batamayineishan Formation and Shiqiantan Formation and provide evidences for solving the scientific problems such as closing time of Kalamaili Ocean and basement features of Junggar Basin.