Characteristics of Large-Scale Thermal Structure in the Lithosphere beneath Junggar Basin and Surroundings
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摘要: 岩石圈热结构是生热元素及深部热状态和构造-热活动的综合反映,同时又会对岩石圈的演化过程产生重大影响.利用S2.9EA地幔三维横波速度模型,基于深部岩石温度与地震波速度之间的关系,反演得到准噶尔盆地及邻区上地幔顶部75~250 km深度范围内的温度分布与“热学”岩石圈厚度分布;将反演得到的75 km深度处的温度分布作为底面约束、地表温度作为顶面约束,利用一维稳态热传导方程推算了地壳温度场与地表热流分布;预测与实测地表热流分布具有较好的一致性,从而验证了反演方法与计算结果的可靠性.结果显示:研究区岩石圈热结构具有明显的横向与垂向不均匀分布特征;浅层温度分布与盆山构造特征一致,且与150 km 深度以下温度分布呈现立交特征.基于岩石圈上地幔高、低温异常体的空间分布特征,综合分析了研究区的盆地热结构性质、盆山接触关系、天山造山带的岩石圈拆沉、盆山的构造-热演化过程以及印度-青藏高原碰撞对研究区岩石圈上地幔温度结构的远程影响,为研究区的大地构造与深部动力学分析提供了有益的参考与资料.Abstract: Lithospheric thermal structure is an integrated reflection of heat producing elements, deep thermal state and tectonic-thermal activities, and it also has a significant impact on the evolution of the lithosphere. Based on the correlativity between temperature and seismic wave velocity of deep rocks, we derived the uppermost mantle temperature distributions and thermal lithosphere thickness beneath the Junggar basin and its surroundings at the depths ranging from 75 to 250 km by the seismic tomography imaging model S2.9EA in this study. Utilizing the inverted temperature distribution at 75 km depth as the bottom boundary constraint and the surface temperature as the top boundary constraint, we calculated the crustal temperature structure and surface heat flow variations according to the one-dimensional steady heat conduction equation. A good agreement is found between the surface heat flow variations by the model prediction and the field measurements, which shows the reliability of the method and the calculated results in this study. The results show that lithospheric thermal structure in Junggar basin and its surroundings presents obvious lateral and vertical inhomogeneity, and the thermal structure distribution in shallow layer is consistent with the basin-mountain tectonic features and it has the trait of interchange with the temperature distribution below 150 km depth. Based on the spatial distribution characteristics of high and low temperature abnormal bodies in the upper mantle of study area, the thermal structure features of basins, contact relationships between basins and mountains, lithospheric delamination of Tianshan orogenic belt, tectonic thermal evolution process of basins and mountains, and the remote influence of India-Tibetan plateau collision on the lithospheric upper mantle thermal structure are synthetically analyzed, respectively, which further provide useful reference and information for the geotectonic and deep dynamic analysis of the study area.
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