南岭地区与东南沿海地区中生代花岗岩放射性地球化学特征及岩石圈热结构对比研究

Radioactive geochemical characteristics of Mesozoic granites from Nanling region and southeast coastal region and their constraints on lithospheric thermal structure

华南地区广泛发育中生代花岗岩,主要出露于南岭地区和东南沿海地区。受大地构造作用影响,自西向东,莫霍面深度逐渐变薄,深部温度逐渐升高,软流圈顶部上升,花岗岩形成时代也随之逐渐年轻化。南岭和东南沿海地区的地表和钻孔花岗岩放射性生热元素含量测试结果表明,南岭地区放射性生热率平均值为5.18μW/m^3,东南沿海地区为3.01μW/m^3,最高生热率为南岭佛冈岩体7.56μW/m^3;热贡献率主要来自Th和U的放射性衰变热,K的热贡献率一般不超过10%。通过本文研究结果,结合前人地质学、地球物理学和地热学研究成果,发现南岭地区和东南沿海地区地壳热流对地表热流值的贡献率分别为60%~65%和40%~45%,指示两者分别为"热壳冷幔"和"冷壳热幔"型岩石圈热结构。

Mesozoic granite is widely distributed in southeast China, which can be divided into Nanling and southeast coastal granitic belts. Due to the effect of tectonism, the depth of Moho and the thickness of lithosphere together with the emplacement age of granite bodies decrease eastward, but the temperature at the depth increases eastward. Radioactive heat-producing element content determinations of granites from surface and drill holes within Nanling region and Southeast coastal region show that the average radioactive heat generation ratios are 5.18 and 3.01 μW/m3, respectively, and that the Fogang granitic body exhibits the highest value of 7.56 μW/m3. In addition, the thermal contribution rate mainly comes from the radioactive decay heat of Th and U with 40K thermal contribution being less than 10%. The new data obtained by the authors, in combination with previous geological, geophysical and geothermal data, indicate that the contribution rate from the crust to the surface heat flow in Nanling region and Southeast coastal region is about 60%~65% and 40%~45%, respectively. The result suggests that Nanling region is of “hot crust-cold mantle” type and the Southeast coastal region is of “cold crust-hot mantle” type lithospheric thermal structure.