雄安新区地热地质模型探究：来自地球物理的证据

雄安新区内地热资源丰富,区内有牛驼镇地热田、容城地热田和高阳地热田,地热资源开发利用较早,但是对其深部热源机制仍未形成统一观点。为了研究雄安新区内地热田深部热源机制,在新区及外围进行了深反射地震和长周期大地电磁探测,对取得的同剖面的深反射地震和大地电磁数据进行处理和综合解释,探明了研究区从地表至莫霍面范围内地质构造和电性结构。下地壳结构在深反射地震剖面与大地电磁剖面上有很好的对应关系。电阻率低值区对应着在深反射地震剖面上存在一系列反射同相轴,且同相轴可以延续到莫霍面,电阻率高值区对应着在深反射地震剖面上无明显连续反射同相轴,尤其是在莫霍面之上呈现地震反射近似"空白区"。结合区域地热资料构建了研究区深部地热地质模型,对新区内深部地热机制进行了解释。该模型为"二元"生热模型,其热源包含两个部分,深部地幔热源和地壳放射性元素衰变生热。放射性元素衰变生热占地表热流的接近30%,而幔源热流在地表热流中的占比可达约70%。在牛驼镇下方,莫霍面以上,由于地幔热物质上涌造成下地壳上隆,幔源岩浆底侵作用于下地壳形成了局部热异常,该热异常具有低速高导的地球物理特征,认为是牛驼镇地热田和容城地热田的深部热源;以区域断裂为热通道,大地热流由深部向上传导、扩散到牛驼镇凸起和容城凸起顶部,对碳酸盐岩储水层进行加热,形成地热储层;上覆新近系沉积地层是良好的热盖层。

Geothermal-geological model of Xiong'an New Area: Evidence from geophysics

Geothermal resources are abundant in the Xiong''an New Area, including Niutuozhen geothermal field, Rongcheng geothermal field and Gaoyang geothermal field. The geothermal resources in this area were developed and utilized earlier, but there is still no unified view on its deep heat source mechanism. In order to study the deep heat source mechanism, deep reflection seismic and long-period magnetotelluric survey were carried out in Xiong''an New Area and its periphery. The deep reflection seismic data and magnetotelluric data of the same section were processed and jointly interpreted. The geological structure and electrical structure in the study area from the surface to the Moho surface were explored. The lower crustal structure has a good corresponding relationship between the deep reflection seismic profile and the magnetotelluric profile. The area of low resistivity corresponds to the existence of a series of reflection events on the deep reflection seismic profile, and the event axis can continue to the Moho surface. The areas of high resistivity correspond to the absence of obvious continuous reflection events on the deep reflection seismic profile. Especially above the Moho surface, there is an approximate "blank area" of seismic reflection. Combined with regional geothermal data, a deep geothermal geological model of the study area was constructed, and the deep geothermal mechanism in the new area was explained. This model is a "dual" heat generation model, and its heat source consists of two parts, the deep mantle heat source and the heat generated by the decay of radioactive elements in the crust. The decay heat of radioactive elements accounts for nearly 30% of the surface heat flow, and the mantle-derived heat flow accounts for about 70% of the surface heat flow. Below Niutuo Town and above the Moho, the lower crust was uplifted due to the upwelling of hot mantle material, and the undercut of mantle-derived magma formed a local thermal anomaly in the lower crust. This thermal anomaly has low-speed and high-conductivity geophysical characteristics. It is considered to be the deep heat source of the Niutuozhen geothermal field and the Rongcheng geothermal field. With regional faults as the heat channel, the terrestrial heat flow is conducted upward from depth and diffused to the top of the Niutuozhen and Rongcheng bulges, which is a source of carbonate reservoirs. The water layer is heated to form a geothermal reservoir; the overlying Neogene sedimentary stratum is a good thermal cap layer.