珠江三角洲与周边典型地区岩石热物性及其地热效应的比较研究

A comparative study on thermal properties of rocks and their geothermal effects in the Pearl River Delta and surrounding typical areas

珠江三角洲位于华夏板块南部,虽然已发现多个水热型地热田,但地热研究仍然较为薄弱.岩石热物性研究是地热研究中最为基础和重要的工作之一.本研究采集并测量了珠江三角洲与周边典型地区100块地表岩石的密度、热导率、热扩散率,以及50块岩浆岩的U、Th、K_(2)O含量,并分别计算了体积热容和放射性生热率.实测结果表明,碎屑岩中细砂岩的热导率最高(3.94±0.92 W·(m·K)^(-1)),页岩的热导率最低(2.68±0.55 W·(m·K)^(-1)).岩石热导率和热扩散率具有明显的正相关性.结合地层厚度建立了地层热物性柱,其中古近系的热导率最低,地层热物性与沉积环境有关.岩浆岩中玄武岩的热导率最低(2.17±0.13 W·(m·K)^(-1)),花岗岩平均热导率为3.87±0.59 W·(m·K)^(-1).花岗岩放射性生热率在0.36~14.23μW·m^(-3)之间,平均值为5.23±3.03μW·m^(-3),属于高产热花岗岩.结合前人对研究区岩石放射性元素含量的测试结果,我们发现,相对于K_(2)O,U、Th与生热率具有更强的相关性,并对产热的贡献更高.相对于花岗岩,玄武岩的生热率较低,K_(2)O对产热的贡献较高.新的资料为区域热流的确定和地热资源评价提供了新的视角.模拟和计算结果表明,三水盆地沉积层能对深部热量起到聚集和保存的作用,并在基底附近形成高温区(>150℃);上地壳中花岗岩体产生的热流超过45 mW·m^(-2),占地表热流的一半以上.盆地和花岗岩体均具有形成高温地热资源的地质条件.此外,酸性岩浆岩放射性生热率随时间逐渐降低的特征与幔源基性岩浆的混合作用有关.

The Pearl River Delta is located in the south of the Cathaysia Block. Although several hydrothermal geothermal fields have been found, the geothermal aspect is poorly researched. The study of thermal properties is one of the most fundamental and important tasks in geothermal research. In this study, we measured the density, thermal conductivity, thermal diffusivity of 100 surface rocks, and tested the U, Th, K2O content of 50 magmatic rocks in the Pearl River Delta and its surrounding areas, and calculated the volume heat capacity and radioactive heat production rate (RHPR) respectively. The results indicate that the thermal conductivity of fine sandstone in clastic rocks is the highest (3.94±0.92 W·(m·K)^(-1)), while the shale is the lowest (2.68±0.55 W·(m·K)^(-1)). There is a significant positive correlation between the thermal conductivity and thermal diffusivity. Based on the thickness of strata, a stratigraphic thermal properties column is established, with the Paleogene having the lowest thermal conductivity. The stratigraphic thermal properties are related to the sedimentary environment. The thermal conductivity of basalt in magmatic rocks is the lowest (2.17±0.13 W·(m·K)^(-1)), while the average thermal conductivity of granite is 3.87±0.59 W·(m·K)^(-1). The RHPR of granite ranges from 0.36 to 14.23 μW·m^(-3), with an average value of 5.23±3.03 μW·m^(-3), indicating a high heat production granite. Based on the radioactive element content measurement of previous researchers in this region, it is found that, compared to K2O, U and Th have stronger correlations with RHPR and contributes more to heat production. Compared to granite, basalt has a lower RHPR and its K2O contribution to heat production is higher. The new data provides a new perspective for determining regional heat flow and evaluating geothermal resources. The simulation and calculation results indicate that the sedimentary layers of the Sanshui Basin can accumulate and preserve deep heat, and form high-temperature (> 150 ℃) zones near the basement. The heat flow generated by granite bodies in the upper crust exceeds 45 mW·m^(-2), accounting for more than half of the average surface heat flow. Both basins and granite bodies have geological conditions for the formation of high-temperature geothermal resources. In addition, the RHPR of felsic magmatic rocks gradually decreases with time, which is related to the mixing effect of basaltic magma from the mantle.