塔里木克拉通形成以来的背景热史研究

塔里木盆地是一个典型大型叠合盆地,发育在太古代-早中元古代的结晶基底之上,具有稳定克拉通性质.现今地表热流为43mW·m^-2,平均地温梯度为21℃·km-1,莫霍面温度为550℃,较低的热流背景值指示塔里木盆地经历了一个长期冷却加厚的过程.然而对于这样一个长期冷却过程,之前的研究都只停留在显生宙阶段,并未获得塔里木显生宙以前的热史.本文以塔里木地区已有的地热数据作为约束,依据地幔动力学模型设置底部边界条件,利用正演拟合的方法,反演出塔里木的背景热史,填补了该区域古生代以前热史研究的空白.结果表明,塔里木克拉通自形成以来背景热流不断降低(由85mW·m^-2降至43mW·m^-2),岩石圈持续加厚(由130km加厚到190km),在长时间尺度下,塔里木克拉通总体的热演化模式为长期冷却加厚,这与世界上其他典型克拉通的热演化规律类似.显生宙以来受到短期局部的构造-热事件影响,塔里木克拉通在长期冷却的趋势下叠加了约20～40mW·m^-2的热扰动.

Inversion of background thermal history since the formation of the Tarim Craton

The Tarim basin is a typical large-scale superimposed structure which developed on a Archean-Early Proterozoic crystalline basement, with stable craton properties. Its present-day surface heat flux is only 43 mW·m^-2, with average geothermal gradient 21℃·km^-1 and Moho temperature 550℃. The low heat flow background value indicates that this basin experienced a process of secular cooling and thickening. However, for such a secular cooling process, previous studies only concentrated on Phanerozoic stage and did not cover the entire thermal history of Tarim. In this paper, we use the thermal data of the Tarim area as a constraint, and set up the bottom boundary conditions according to different mantle dynamic models. Then, the background thermal history of Tarim is reconstructed by forward modeling, which fills the gap in the study of thermal history before the Palaeozoic in this region. The results show that the background heat flow of Tarim was decreasing (reduced from 85 mW·m^-2 to 43 mW·m^-2) and the lithosphere was thickening (increased from 130 km to 190 km) continuously since the basin's formation. On a long time scale, the thermal evolution model of the Tarim craton is secular cooling and thickening, which is similar to that of other typical cratons in the world. While, under the influence of short-term local tectono-thermal events, the thermal history of the Tarim craton was superposed by about 20~40 mW·m^-2 thermal disturbance on the trend of secular cooling.