四川盆地周缘盆-山系统热体制耦合研究

Basin and range, two basic structural units in tectonic and geodynamic research, they not only depend on each other for existence in spatial position, but also have a close coupling relationship on multifarious geological processes which take place in both the surface and deep of the earth. Geotherm, which is the power and thermal background that have to be involved in the dynamics process, while it also is a response or record of the result of the process, hence, the geothermal regime and its evolution could be helpful to reveal the geological process in the regions. The Sichuan basin and its adjacent ranges are chose to be the research area, in which the geothermal coupling process will be studied. In details, based on the temperature logging data, the thermal propriety measurement and also the different kinds of paleo-geothermal indicators, multi-thermal indicates reversion method and structure-thermal evolution modelling will be used to recognize the thermal evolution of the Sichuan basin and the surrounding areas. Furthermore, the coupling process and its dynamic mechanism of the Basin and Range geothermal system will be concluded after the analysis of the geo-thermal histories of the evolution stages of the different units in the Basin and Range system. The result of the thermal evolution and the geothermal coupling in the Basin and Range system, will not only reveal the disputed understanding of the geological evolution in the collision belts between Tibet Plateau and Yangtze plate, but also be significant for the petroleum and geothermic resources, and even the earthquake activities in the research area.

盆、山是板块构造和大陆动力学研究中的重要地质单元，两者不仅在地貌上互相依存，在构造、沉积演化等种地质过程中也存在耦合关系，且这种耦合存在于地表，也存在于地球深部。地热既作为动力与热背景参与着地球动力学过程，同时又对该过程的结果予以响应，因此，区域热体制及其变迁，可以揭示该地区经历的地质演化过程。本研究选择四川盆地及其周缘典型的盆山系统，对盆山热体制的耦合过程进行研究。以稳态地温、岩石热物性以及多种古温标数据为基础，通过综合热史恢复手段，辅以构造-热演化模拟，系统研究四川盆地及周缘地区的热体制变迁。分析盆山系统演化过程中不同构造单元的热状态差异，总结盆-山热体制耦合规律并分析其动力学机制。对研究区盆山热体制耦合机制的认识，不仅可以进一步揭示青藏高原与扬子板块碰撞带的地质演化过程，对于认识研究区油气、地热资源的分布规律以及地震活动性等亦有一定的参考价值。

针对四川盆地及周缘地区盆山系统的古、今热体制开展研究，在盆地岩石热物性、大地热流与盆山构造的关系、盆山在剥蚀过程方面的耦合过程、深部岩石热导率原位校正、四川盆地深部地温场分布等方面取得一定认识。四川盆地砂岩样品的生热率为0.83±0.36μW/m3，粉砂岩为1.09±0.38μW/m3，泥岩为1.07±0.39μW/m3，灰岩和白云岩的生热率分别为0.40±0.39μW/m3和0.35±0.27 μW/m3。四川盆地灰岩热导率平均值为2.526±0.437 W/m•K，白云岩的热导率均值为3.550±0.713 W/m•K，泥岩热导率平均值为2.669±0.414 W/m•K，砂岩热导率平均值为3.113±0.777 W/m•K。四川盆地大地热流介于35.4-68.8mW/m2，平均53.2 mW/m2。在区域分布上，四川盆地基底隆起区的大地热流较高，坳陷区的比较低。川中和川西南的大地热流达到60 mW/m2以上，川西北的大地热流为50-60W/m2，川东地区的热流较低，大巴山褶皱带前缘的大地热流低至40 mW/m2左右。大地热流影响因素主要受控于大地构造背景和岩石圈热结构。四川盆地白垩纪以来的前陆盆地发展和抬升剥蚀过程的差异和内在联系反映出盆地各构造单元在晚中生代-新生代共处于统一的、递进的挤压变形动力学体制下。前陆盆地演化和抬升剥蚀造成热流降低的主要因素有：挤压坳陷作用下的岩石圈挠曲增厚并逐渐冷却、前陆盆地快速沉积对地表热流的压制、抬升剥蚀造成的地表热流降低。此外，沉积层与结晶之间的热导率差异也是造成热流再分配的因素之一。在沉积盆地中，相对低热传导的沉积岩覆盖在高热传导的结晶岩石之上，上部沉积层构成为一相对的隔温盖层。热导率差异造成的“热折射”效应也会使热量向高热导率基底隆起区汇聚。