南海海盆IODP349钻井岩心的生热元素测试与应用研究

放射性生热率是岩石热物性参数之一,也是研究岩石圈热结构和构造热演化的重要参数。针对南海海盆区缺少岩石生热率资料的实际情况,本文通过整理和分析IODP349航次中的测井资料,测试钻井岩心样品的主要放射性生热元素,通过计算得出:玄武岩样品的生热率平均值为0.28±0.07μW/m~3,沉积碎屑岩样品的生热率为1.21±0.34μW/m~3,以及3个钻井的地热流值。获得以下认识:(1)本次研究的沉积碎屑岩样品生热率与中国东南沿海的同类岩石样品的生热率值相近,而洋壳中的基性火山岩生热率明显低于大陆碱性玄武岩。(2)用新资料计算南海西南次海盆段的岩石圈热结构得出其热岩石圈厚度约为39~42 km,平均壳幔热流比值为2.4%,说明西南次海盆岩石圈薄,海底热流主要受深部的地幔热源控制。(3)U1431D和U1433A钻井的热流密度值与附近探针热流密度值相近;而U1431C的热流密度值明显偏小,属于受地下水热循环影响所致。

Contents of Heat Producing Elements in Drilling Cores from IODP Expedition 349 in South China Sea Basin and Geological Implications

Radioactive heat production rate, as one of the thermal physical parameters of rocks, is an important parameter to constrain the thermal structure and tectonic thermal evolution of the lithosphere. To offset the lack of data about the heat production rate of rocks in South China Sea basin, we calculated the radioactive heat production rate of different kinds of rocks based on the analyses of the main radioactive elements of dill core samples and well logging data obtained from the International Ocean Discovery Program (IODP) Expedition 349. The heat production rates for the basalt and sedimentary clastic rocks are 0.28±0.07μW/m3 and 1.21±0.34μW/m3, respectively. The results demonstrated that the heat production rate of sedimentary clastic rock is identical to that for the counterpart in the coastal areas of the Southeast China. However, the value of the oceanic basic volcanic rocks is significantly lower than that of mainland alkaline basalt. Calculation by using the new dataset shows that the thickness of thermal lithosphere in southwest sub-basin of South China Sea is about 39?42 km. Crust-mantle heat flow value proportion distribution calculation suggests that the average of crust-mantle heat flow ratio is 2.4%, which implies that the lithospheric thickness of southwest sub-basin of South China Sea is thin and the submarine heat flow is mainly controlled by the deep mantle heat source. The heat flow measured from U1431D and U1433A are close to the value measured from nearby probe. The heat flow measured from U1431C is apparently smaller. The low heat flow value is the result of hydrothermal circulation.