Fluid Evidence of the Formation and Evolution of Daqingshan Thrust-nappe

Fluid veins, which can be divided into filled veins and edged veins according to occurrences, extensively developed in the Daqingshan thrust-nappe. On the basis of their relative age, the forming of the fluid veins can be chronologically classified into three phases: the early-phase quartz veins, the middle-phase quartz veins, and the late-phase calcite veins. The types of fluid inclusions in the first-phase quartz veins are relatively complex, which contain two-phase aqueous, three-phase CO2-bearing, pure CO2, and single-phase aqueous fluid inclusions, respectively, analytical data revealed that their forming solutions come from lower crust or upper mantle. The second-phase quartz veins contain only two-phase aqueous and single-phase aqueous fluid inclusions, fluids come from meteoric water, which interfused with magmatic water. The late calcite veins contain two-phase aqueous and a few single-phase aqueous fluid inclusions, fluids come from interlayer solutions. The evolution history of Daqingshan thrust-nappe system is concluded according to deformation phases, time, and the depth data of those different kinds of veins. The thrusting of Indo-Chinese occurred at the 7–8 km in the crust, the middle Yanshan thrusting occurred at 3–6 km in the crust, and the late Yanshan thrusting within 2 km in the crust.