共和盆地干热岩地热资源的成因机制:来自岩石放射性生热率的约束

共和盆地位于青藏高原东北缘，是我国重要的干热岩地热资源赋存区之一．成因机制研究是干热岩地热资源研究中最为基础与核心的工作之一，也是干热岩地热资源潜力精细评价和合理开发利用的重要依据．本文基于98块采自共和—贵德盆地岩石样品的放射性生热率数据，分析了盆地主要岩性岩石的放射性生热率分布特征，讨论了共和盆地干热岩地热资源的成因机制，并初步建立了干热岩地热资源的成因模式．研究表明，共和盆地恰卜恰地热区沉积岩（以泥岩和粉砂质泥岩为主）放射性生热率为1.21～2.02μW·m~(-3)，平均值为1.67±0.29μW·m~(-3)；以花岗岩和花岗岩闪长岩等为主的基底岩石的放射性生热率介于1.17～5.81μW·m~(-3)之间，平均值为3.20±1.07μW·m~(-3)．贵德盆地扎仓寺地热区沉积岩（以砂岩和泥质砂岩为主）放射性生热率为1.83～2.40μW·m~(-3)，平均值为2.13±0.23μW·m~(-3)；基底花岗质岩石的放射性生热率介于0.92～6.49μW·m~(-3)之间，平均值为2.81±1.40μW·m~(-3)．测试数据显示共和—贵德盆地基底花岗岩不存在高放射性生热率异常．但是，新生代以来印度—欧亚板块持续性陆-陆碰撞作用造成的壳内放射性生热元素富集层增厚，导致了花岗岩放射性生热率的热贡献量同步增大（30.3～40.5mW·m~(-2)），因此，花岗岩放射性生热可为共和盆地干热岩地热资源提供稳定的壳内热源基础．基于放射性生热率数据和热流配分研究，结合研究区已有地质-地球物理研究资料，本文认为壳内部分熔融层作为附加热源为共和盆地干热岩地热资源提供了重要的附加热流贡献．在此基础上，本文初步构建了共和盆地干热岩地热资源成因模式：加厚地壳花岗岩放射性生热与壳内部分熔融层供热．

Genesis of the hot dry rock geothermal resources in the Gonghe basin: constraints from the radiogenic heat production rate of rocks

The Gonghe Basin, located in the northeastern margin of the Tibetan Plateau, is one of the important hot dry rock (HDR) geothermal resources occurrence area in China. Among the researches of the HDR geothermal resources, the study of the genesis mechanism is one of the most basic and core works and it is also the important basis for the precise potential evaluation and rational development and utilization of the HDR geothermal resources. Based on the radiogenic heat production rate (RHPR) data measured on the 98 core samples gathered from the Gonghe-Guide basin, the characteristics of the RHPR of the main lithology rock in the basin are analyzed, the genesis mechanism of the HDR geothermal resources in the Qabqa geothermal area of the Gonghe basin is discussed, and the corresponding genesis model of HDR geothermal resources is constructed in this study. The results show that the RHPR of the sedimentary rocks (mainly mudstone and silty mudstone) of the Qabqa geothermal area in the Gonghe basin ranges from 1.21 to 2.02 μW·m^-3, with an arithmetic average of 1.67±0.29 μW·m^-3, while the RHPR of the basal granites, which are mainly composed of granite and granodiorite, ranges from 1.17 to 5.81μW·m^-3, with an arithmetic average of 3.20±1.07μW·m^-3. For the Zhacangsi geothermal area in the Guide basin, the RHPR of the sedimentary rocks (sandstone and muddy sandstone) ranges from 1.83 to 2.40 μW·m^-3, 2.13±0.23 μW·m^-3 on average, while it varies from 0.92 to 6.49 μW·m^-3(the average of which is 2.81±1.40μW·m^-3) for the basal granitic rocks. The tests show that there is no high RHPR anomaly of the basal granites in the Gonghe-Guide basin. However, the thickening of the radioactively enriched layer caused by the continuous collision between the Indian and Eurasian plates since Cenozoic leads to the synchronous increase of the heat contribution of the RHPR of granites, which is about 30.3~40.5 mW·m^-2, and therefore it can serve as a stable heat source for the HDR geothermal resources in the Gonghe basin. Based on the RHPR data and the heat flow partition analysis, as well as the existing geological-geophysical research data in this area, this work suggests that the partial melting layer in the crust beneath the study area may be an additional heat source, providing important additional heat flow contribution to the HDR geothermal resources in the study area. On the basis above, the genesis model of the HDR geothermal resources in the Gonghe basin is preliminarily constructed in this study: the joint effect of the radiogenic heat contribution of the granite in the thickened crust and the heat contribution of the partial melting layer within the crust.