距今40~30Ma时期青藏高原北缘酒西盆地沉积物重矿物分析和构造意义

活动造山带地区形成的沉积物包含极其丰富的构造信息。位于青藏高原北缘阿尔金断裂和北祁连断裂交汇处的酒西盆地在早新生代时期受到强烈的构造活动,于盆地内形成了巨厚的早新生代沉积物,全面记录了盆地周边的构造运动和隆升过程。对酒西盆地火烧沟剖面和红柳峡剖面早新生代沉积物重矿物分析表明,40~30Ma沉积物中重矿物组合、形态和特征指数ATi、GZi及ZTR具明显的规律性变化,自下而上划分为4个不同阶段:①不稳定矿物阶段(骟马城段,40.2~37.9Ma),②较稳定矿物阶段(乔家段,37.9~35.3Ma),③不稳定矿物阶段(红柳峡段,35.3~33.4Ma),④极不稳定矿物阶段(白杨河组,33.4~30Ma)。结合大量沉积学特征可清楚表明,酒西盆地在40~30Ma期间经历了4个阶段:①构造活动阶段(40.2~37.9Ma),②构造稳定阶段(37.9~35.3Ma),③逆冲走滑阶段(35.3~33.4Ma),④强烈逆冲阶段(33.4~30Ma)。

Analysis of heavy minerals in sediments of Jiuxi basin in north margin of the Tibet plateau in 40-30 Ma and its tectonic implication

The sediments in an orogen contain very rich tectonic information.The Jiuxi basin,located in the triangular belt between Altyn Tagh Fault(ATF)and North Qilian Fault(NQF),was affected by strong active tectonics in the early Cenozoic;therefore,it was covered by mass sediments which could reflect the tectonic actions and uplift process nearby.The assemblage,texture and sensitive index(ATi,GZi and ZTR)of the sedimental heavy minerals show regular variations in the Huoshaogou and Hongliuxia sections of Jiuxi basin in 40-30 Ma.The detailed study of the heavy mineral has revealed four different stages:①the unstable mineral stage(Shanmacheng segment,40.2-37.9 Ma);②the stable mineral stage(Qiaojia segment,37.9-35.3 Ma);③the unstable mineral stage(Hongliuxia segment,35.3-33.4 Ma);④the extra unstable mineral stage(Baiyanghe Formation,33.4-30 Ma).In addition,the detailed analysis of heavy mineral characteristics and sedimentary characteristics shows that there should be four different tectonic stages in the Jiuxi basin between 40 and 30 Ma:①the strong tectonic stage(40.2-37.9 Ma);②the stable tectonic stage(37.9-35.3 Ma);③the thrusting and striking stage(35.3-33.4 Ma);④the strong thrusting stage(33.4-30 Ma).