塔里木板块上元古界火山岩SHRIMP定年及其对新元古代冰期时代的制约

新疆库鲁克塔格地区贝义西组顶部火山岩锆石的SHRIMP定年结果为732±7Ma,它表明贝义西冰期的上限。考虑该组杂砾岩之下火山岩已有的定年结果,贝义西冰期的时限为740~732Ma。综合上元古界三层火山岩SHRIMP定年结果,可以明确地将库鲁克塔格地区上元古界四个含杂砾岩的组限定在三个时间段内,即740Ma到732Ma的贝义西组,732Ma到615Ma之间的阿勒通沟组和特瑞爱肯组,以及615Ma到542Ma之间的汉格尔乔克组,这些年龄段代表了库鲁克塔格地区新元古代各冰期的时代范围。与冰期有关的同位素年代学资料分析表明,贝义西冰期可与Kaigas冰期对比; 阿勒通沟冰期和特瑞爱肯冰期可能与Sturtian冰期和Elatina冰期对比; 而汉格尔乔克冰期和Gaskiers冰期可以对比。

SHRIMP dating of the upper Proterozoic volcanic rocks in the Tarim plate and constraints on the Neoproterozoic glaciation

The SHRIMP analyses of zircons from the volcanic rocks at the top of the Beiyisi Formation, in Quruqtagh area, Xinjiang, yield a weighted mean ²⁰⁶Pb/²³⁸U age of 732±7Ma, which gives the upper limit for the Beiyixi glaciation. Considering a previous age from volcanic rocks below the Beiyisi diamictites, the Beiyisi glaciation has been constrained between 740Ma and 732Ma. Combining with previous SHRIMP data from other three volcanic rock levels of the Neoproterozoic in study area, four tillite-contained formations of the Neoproterozoic can be divided into three durations from 740 to 732Ma of the Beiyixi Formation, from 732 to 615Ma of the Altungal and Tereeken formations and from 615 to 542Ma of the Hangelchaok Formation, respectively, which suggests that isolated glaciations occur during the Neoproterozoic in Quruqtagh. Data analyses related with glaciation indicate that the Beiyixi, Altungol and Tereekan and Hangelchaok glaciations could be correlated with the Kaigas, Sturtian and Elatina, and Gaskiers glaciations, respectively.