阿尔金山南缘清水泉地区斜长角闪岩锆石LA-ICP-MS U-Pb测年及其地质意义

Zircon LA-ICP-MS U-Pb dating of amphibolite in the southern margin of Altyn Tagh,China and its geological implication

阿尔金群为阿尔金构造带的古老变质基底,由于缺乏精确的同位素测年数据,对其形成时代尚存争议。运用LA-ICP-MS锆石U-Pb定年分析方法,对阿尔金山南缘清水泉地区阿尔金群中的斜长角闪岩进行了年代学测定,并初步探讨其地质意义。锆石CL图像具有多晶面面状结构,无岩浆锆石具有的震荡环带和核边结构,Th/U比值大多都较低(<0.1),显示变质锆石的特点。18个锆石颗粒的19个测点给出的207Pb/206Pb年龄介于(1786±16)～(1877±12)Ma之间,加权平均值为(1827±13)Ma(MSWD=4.4,1σ)。区域地质与同位素年代学新资料表明,阿尔金山南缘清水泉地区在古元古代晚期存在一期构造-热事件,本期事件与吕梁运动的时限相吻合,在全球尺度上可能是古元古代哥伦比亚超大陆汇聚-裂解事件在该地区的响应,也证明阿尔金山存在新太古代—古元古代的变质基底,并且为探讨阿尔金构造带前寒武纪构造-热事件和演化历史提供了新证据。

Altyn Tagh Group is the oldest metamorphosed strata in the Altyn Tagh area.Because of lack of precise isotopic dating,some researchers porposed that this Group formed in Neoproterozoic and there were not existence of Neoarchean to Paleoproterozoic metamorphosed basement in Altyn Tagh area.This paper provides the zircon LA-ICP-MS U-Pb isotopic dating result of the amphibolite from Altyn Tagh Group in the southern margin of Altyn Tagh and discusses its geological significance.The CL images of zircons from the amphibolite show that most of the zircons present the typical characteristics of metamorphic zircons with multi-faceted shape structure and without girdle structure and core-rim structure of magmatic zircons and with lower Th/U ratios.Zircon LA-ICP-MS U-Pb isotopic dating give a weighted mean 207Pb/ 206Pb age of 1827±13Ma（MSWD=4.4）,with 207Pb/206Pb ages ranging from（1786±10） Ma to（1877±12） Ma of 19 analysing plots and suggest that the epoch of metamorphism of the amphibolite is Later Paleoproterozoic.The new data of isotopic chronology indicated that there existed a tectothermal event which corresponds to Lüliang orogenic movement in China and maybe related to the converging or breakup event of global Columbia suppercontinent in Paleoproterozoic.The result also indicate that there are Neoarchean-Paleoproterozoic metamorphosed basement in the Altyn Tagh area and provide a new data for research Precambrian teotothermal events and the evolution of Altyn Tagh belt.