大青山逆冲推覆构造形成演化过程的流体证据

Fluid evidence of the formation and evolution of Daqingshan thrust-nappe

大青山逆冲断层带内热液脉体十分发育,按其产状可划分为充填脉和边缘脉。根据形成时间主要划分为3期:早期石英脉、中期石英脉和晚期方解石脉。早期石英脉中流体包裹体类型较为复杂,见有气液两相、含CO2三相、纯CO2及少量单液相等4种类型原生包裹体,分析表明流体主要来源于地壳深部或上地幔。中期石英脉中主要发育气液两相包裹体和少量单液相包裹体,流体主要来源于大气降水,并且有少量岩浆热液混入。晚期方解石脉内仅含有气液两相包裹体及少量的单液相包体,流体主要来源于层间建造水。根据逆冲变形事件期次、时间,结合热液脉体形成深度数据,确定了大青山逆冲推覆体系变形演化历史:印支期逆冲推覆事件发生在地壳7～8km深度,燕山中期逆冲推覆事件发生在3～6km范围内,而燕山晚期逆冲推覆事件发生近地表2km范围内。

Fluid veins widely developed in the Daqingshan thrust-nappe, and can be divided into filled veins and edged veins according to their occurrences. According to their age, the formation of the fluid veins can be classified into three phases： the first phase quartz veins, the second phase quartz veins and the late phase calcite veins. The types of fluid inclusions in the first phase quartz veins is relatively complex, which contain twophase aqueous, three-phase CO2-bearing, pure CO2 and single phase aqueous fluid inclusions, respectively; analytical data revealed that their forming solutions came from lower crust or upper mantle. The second phase quartz veins contain only two-phase aqueous and single phase aqueous fluid inclusions; fluids came from mete- oric water which interfused With magmatic water. The late calcite veins contain two-phase aqueous and a few single phase aqueous fluid inclusions; fluids came from interlayer solutions. The evolution history of Daqingsban thrust-nappe system is determined according to the deformation phases, time and the depth data of those different kinds of veins. The thrusting of Indo-Chinese occurred at 7-8 km in the crust, the thrusting of middle Yanshanian occurred at 3-6 km in the crust and the thrusting of late Yanshanian within 2 km in the crust.