新疆准噶尔盆地侏罗系齐古组凝灰岩SHRIMP锆石U-Pb年龄

摘要

There is an unconformity between Jurassic and Cretaceous. The authors obtained a SHRIMP U-Pb zircon age of 164.6 Ma ± 1.4Ma (MSWD=1.3) for tuff from so-called upper series of Jurassic Qigu Fromation, and die age is almost the same as the bottom age of the Callovian (164.7 Ma ±4.0 Ma) in the International Geological Time Scale. According to the depositional rate of the formation, the upper boundary age should be 161.8 Ma, which is close to the upper boundary age of the Callovian (161.2 Ma + 4.0 Ma). However, the upper boundary age of die Kalaza Formation is about 160.0Ma, which should be assigned to the lower part of the Oxfordian. The age of the lower Lower Cretaceous Qingshuihe Formation of should be early Early Cretaceous Berriasian period. So, the main age of the Qigu Fromation is Middle Jurassic Callovian period. The lower part of the formation might have entered late Late Bathonian period. The age of the Kalaza Formation is probably early Early Oxfordian period. In fact, between the Jurassic and the Cretaceous the whole Upper Jurassic is absent, suggesting diat a relatively strong tectonic movement occurred in Late Jurassic period.%报道了准噶尔盆地获得侏罗纪齐古组凝灰岩精确的SHRIMP锆石U-Pb年龄164.6 Ma±1.4 Ma(MSWD=1.3).该年龄值几乎相当于国际地质年表中Callovian阶的底界年龄(164.7 Ma±4.0Ma).根据地层沉积速率推算,齐古组上界年龄值应为161.8Ma,接近Callovian阶的上界(161.2Ma±4.0Ma);其上的喀拉扎组上界年龄大致在160.0 Ma左右,此年龄值应位于牛津阶(Oxfordian)的下部.另外,下白垩统下部清水河组的时代为早白垩世早期(Berriasian).由此得出:齐古组的主体时代为中侏罗世卡洛期(Callovian),其下部跨入了巴通期最晚期(late Late Bathonian);喀拉扎组的时代可能仅为牛津期最早期(early Early Oxfordian),反映白垩系与侏罗系之间的不整合几乎缺失了整个上侏罗统,由此推断晚侏罗世曾发生过一次较强烈的构造运动.