东准噶尔红柳峡辉长岩锆石U-Pb年龄及地质意义

U- Pb Zircon ages of the gabbro in Hongliuxia area of the eastern Junggar and its geological implications

准噶尔盆地基底性质及形成时期问题对研究新疆地壳演化、油气资源的勘探与评价均有重要意义,但长期以来一直存在很大争议.准噶尔盆地东部红柳峡地区是探讨准噶尔盆地是否存在前寒武纪基底的代表性地区之一,因此对该区进行同位素定年分析,以期获得古老锆石年龄的同位素证据.选取原定为中元古界札曼苏岩群中的大量发育的变质辉长岩进行了LA-ICP-MS锆石U-Pb定年研究.发现U-Pb表面年龄值分布的范围很宽,从385±7 Ma至2 322±45Ma.岩浆锆石^206 Pb/^238U加权平均年龄为（396±5）Ma（MSWD=1.15,n=7）,代表辉长岩的结晶年龄为旱泥盆世晚期.此外辉长岩中尚有4粒年龄为（842 ～2 322） Ma捕获锆石,代表了岩浆上升溢流路经区围岩中的锆石形成时代.札曼苏岩群被划分为中元古代是不准确的,综合该区的变质砂岩和玄武岩锆石同位素定年数据,认为札曼苏岩群形成时期的下限不早于早泥盆世.结合区域地质综合分析认为,准噶尔盆地东部可能存在前寒武纪的古老结晶基底.

Textural features and ages of the basement of Junggar basin iv very important for studying of the assessment and exploration of oil and gas resources, also important for evolutionary history of Xin- jiang, China. However, there has been a big-debated issue for a long time. The Hongliuxia exposed in the eastern Junggar Basin is considered one of the representative regions for demonstrating whether Precam- brian basement was existed in the Junggar Basin. So, LA - ICP MS U - Pb dating of zircons from the gabbro in the Zhamansu rocks, can obtain the information on the old age of the zircons. In this paper, Metamorphic gabbro in the Zhamansu rocks was geochronologically analyzed using LA -ICP -MS U -Pb dating of its zircons. Zircons apparent ^206PB/^238 U or^206PB/^207PB ages between （385± 7 ）Ma and （2 322±45） Ma,Magmatic zircons from gabbro were dated to be 407.2 ±4.3 Ma（ MSWD = 1.15 ,n =7） ,it re- present the magma intrusion time of the Hongliuxia mafic magma during the Late stage of the Early De- vonian epoch. In addition, four age points are between 842 and 2 322 Ma, it represent the time of the zir- con in surrounding rock of Magma rising overflow path zone. Data suggest it is inaccurate that the Zha- mansu rock suite which previously suggested to have formed in the Mesoproterozoicare are of the Devoni- an in age. The result together with regional geology, indicating that early Precambrian crystalline base- ment may exist in the eastern Junggar Basin.