西准噶尔包古图地区石炭系希贝库拉斯组碎屑锆石LA-ICP-MSU-Pb年代学及其地质意义

DETRITAL ZIRCON LA-ICP-MS U-Pb DATING OF THE CARBONIFEROUS XIBEIKULASI FORMATION SANDSTONE IN THE BAOGUTU AREA, WEASTERN JUNGGAR,AND ITS GEOLOGICAL SIGNIFICANCE

碎屑岩锆石研究是探讨碎屑岩沉积时代、源区特征和形成环境的一种有效途径。通过对西准噶尔包古图地区希贝库拉斯组砂岩样品进行碎屑锆石LA—ICP—MSU—Pb的年代学研究，获得了34粒锆石U—Pb年龄数据，分布在322～359Ma，4个峰值年龄分别为324．3Ma、334．0Ma、344．oMa和355．oMa；结合前人关于包古图组328．4～345．6Ma以及成吉思汗山组312Ma的年龄，认为本区三组地层的自下而上顺序是包古图组→希贝库拉斯组→成吉思汗山组，这与前人通过野外地质接触关系获得的认识是一致的。西准噶尔地区石炭系包古图组、希贝库拉斯组和成吉思汗山组之间的关系对揭示本区晚古生代地层格架和地质历史具有重要意义。

The nature of the contacts between the Baogutu, Xibeikulasi, and Chengjisihanshan formations is important in understanding the regional stratigraphic sequence and Late Paleozoic geologic history in the Baogutu area of the weastern Junggar Basin, and the depositional ages of these stratigraphic units have attracted some attention of geologists. Analysis of detrital zircons is an effective approach to constrain the provenance and deposit ages of these units. LA-ICP-MS U-Pb dating was performed on 34 detrital zircons from the Xibeikulasi Formation sandstone and yielded four peaks at 324.3 Ma, 334.0 Ma, 344.0 Ma, and 355.0 Ma, with a range of 322--359 Ma; Combined with the reported ages of the Baogutu Formation （345.6--328.4 Ma） and Chengjisihanshan Formation （312 Ma）, the new data show that the Xibeikulasi Formation is younger than the Baogutu Formation and older than the Chengjisihanshan Formation, consistent with results from previous field geological study.