塔里木盆地西北缘柯坪逆冲推覆带构造-热演化的低温热年代学约束

The Kalpin fold-and-thrust belt in the northwestern margin of Tarim Basin is favorable for the hydrocarbon generation and accumulation based on the oil and gas exploration results. But now it is still hard to understand the time and periods of the hydrocarbon generation correctly in the Kalpin area due to the existence of massive problems on the thermal history reconstruction and structural deformation explanation, which restricts the further oil and gas exploration in this area. At present, the low-temperature thermochronometer parameters (including apatite fission track (AFT) and (U-Th)/He) are the most effective tool to study the tectono-thermal evolution and structural deformation process of the subsurface. In this project, both the low-temperature thermochronometer parameters and the traditional paleothermal indicators are planned to be used to study the thermal history, deformation time and dynamic process of the Kalpin fold-and-thrust belt. Furthermore, this study will analyze the tectonic evolution relationship among the Kalpin area, Tarim Basin and Tianshan and discuss how the tectono-thermal evolution affect the hydrocarbon generation and accumulation in the Kalpin area. This project will be of theoretical and practical significance to not only provide a new insight for the oil and gas exploration based on enriching the tectono-thermal evolution research and determining the time and periods of the hydrocarbon generation in the Kalpin area, but also promote the application of the low-temperature thermochronometer in the fold-and-thrust belts.

油气勘探成果表明塔里木盆地西北缘柯坪逆冲推覆带是一个重要的油气富集有利区，但由于其热历史恢复及构造变形研究还存在许多问题，导致人们无法正确认识该地区的烃源岩生烃时间及期次，制约了下一步的油气勘探。低温热年代学参数(磷灰石裂变径迹和(U-Th)/He)是目前研究近地表构造-热演化和构造变形机制最有效的方法。本项目拟采用多种低温热年代学参数结合传统古温标恢复柯坪逆冲推覆带的热历史，研究柯坪逆冲推覆带的逆冲变形时间和变形动力学机制，分析其与天山及塔里木盆地的构造演化关系，并探讨构造-热演化对烃源岩生烃及成藏的影响。本项目的研究成果不仅可以丰富研究区的构造-热演化研究，确定生烃时间及期次，从而为油气勘探提供新依据，而且可推动低温热年代学参数在逆冲推覆带的研究应用，具有重要的理论与实际意义。

塔里木盆地北缘柯坪逆冲推覆带和库车坳陷是我国重要的油气富集有利区，但薄弱的热史研究导致人们无法正确认识研究区烃源岩的生烃时间及期次，制约了进一步油气勘探。本项目借助磷灰石裂变径迹、磷灰石(U-Th)/He及镜质体反射率等多种古温标参数对柯坪逆冲推覆带、库车坳陷北缘及塔里木盆地内部的构造-热演化史进行了系统研究。取得的主要认识包括：（1）柯坪逆冲推覆带磷灰石裂变径迹年龄介于50~70Ma，而磷灰石(U-Th)/He年龄介于15.2~45.6Ma。进一步分析认为柯坪逆冲推覆带北部快速变形始于渐新世，到中新世时期才推进到南部的柯坪塔格地区，甚至可能影响到巴楚隆起；（2）库车坳陷北缘露头样品的实测磷灰石(U-Th)/He年龄介于4~32Ma，其年龄分散性主要是由eU含量造成的。通过正演模拟揭示出库车坳陷北缘曾经历过10-20Ma一期快速隆升事件，在此基础上，构建了南天山与塔里木盆地北缘中新世以来的构造-沉积耦合模式；（3）塔里木盆地现今地温梯度为20.7±2.9℃/km，大地热流为42.5±7.7 mW/m2。早古生代时期，塔里木盆地中部和东部古地温梯度为35-39℃/km，而西部地温梯度偏低，为28-34℃/km。塔里木盆地大部分地区热岩石圈厚度为164-205km。除东南隆起的热流变学结构表现为布丁模式，其他地区均表现为典型的三明治模式；（4）塔中隆起早中生代的地温梯度为24.8℃/km，当时的剥蚀量高达2700-3900m；磷灰石裂变径迹实测数据和热史模拟结果揭示出塔中隆起自中生代以来曾经历过190-140 Ma和80-45Ma两期快速隆升事件，分别是由羌塘-拉萨地体和大印度板块与欧亚板块南缘碰撞造成的。本次研究不仅丰富了塔里木盆地及周缘的热史成果，而且为柯坪逆冲推覆带和库车坳陷的油气成藏和勘探提供了重要理论依据。