南沙海槽岩石圈热-流变结构与动力学演化分析

发布时间：2018-06-26 22:57

  本文选题：南沙海槽 + 陆壳结构　； 参考：《地学前缘》2017年03期

【摘要】：南沙海槽前陆盆地是我国南海南缘陆架区重要的含油气盆地,海槽之下陆壳减薄的原因、前陆区逆冲推覆构造的变形机制是南海地球动力学研究的重要科学问题。利用地震、重磁、地热观测资料,依据地震沉积地层分析、重磁反演分析、地幔流应力场分析、热-流变学分析方法,文中计算了南沙海区地壳结构特征、南沙海槽逆冲推覆热-流变学结构。结果表明:南沙海区Moho面深度在18~26km,其中海槽区Moho面最浅,由海槽中心向东南至陆坡,Moho面由20km快速下降到26km深度,说明南沙海区陆壳结构曾发生过强烈的构造变动。南沙海区地壳累积流变强度FC与岩石圈累积流变强度FL之比小于80%,显示为一个整体陆壳地块,岛礁区大部分地段地壳热流QC与海底热流Q0之比大于60%,为"热壳冷幔"型热结构,而海槽区情况正相反,QC/Q0小于40%,为"冷壳热幔"型热结构。南沙海槽Moho面温度在300~700℃,地壳整体温度较低,地温梯度在垂向上高、低相间成层分布,地壳浅层地温梯度在15~30℃/km,深层地温梯度大于45℃/km。南沙海槽南北两侧应力分布特征不同,北侧挤压,南侧伸展。北侧挤压区,地层挤压收缩量由深向浅减小,南侧伸展区,地层伸展量由深向浅增大,类似手风琴风箱结构。北侧黏滞系数高、流变强度大,南侧黏滞系数低、流变强度小。南侧的黏滞系数、流变强度大约比北侧低2~3个数量级,因此南沙海槽南侧比北侧更容易发生构造变形。由计算结果推测,南沙Moho面起伏或陆壳减薄与"地壳重力均衡作用"和"地幔热隆升作用"有关,海槽东南缘逆冲推覆体构造变形机制主要是"地壳缩短"作用,其次是"重力滑脱"作用。文中没有涉及南沙陆块不同地质时期Moho面、"地壳均衡"、"地幔热隆升"之间的演化关系,也没有涉及南沙海槽基底变形中"弹性挠曲"和"逆冲推覆"之间的关系。
[Abstract]:Nansha trough Foreland basin is an important oil and gas bearing basin in the continental shelf area of the South China Sea. The reason of continental crust thinning under the trough and the deformation mechanism of the thrust nappe structure in the Foreland region are important scientific problems in the study of the South China Sea geodynamics. Based on seismic, gravity, magnetic and geothermal observation data, according to seismic sedimentary stratigraphic analysis, gravity and magnetic inversion analysis, mantle flow stress field analysis, thermo rheological analysis method, the crustal structure characteristics in Nansha sea area are calculated in this paper. Thermal rheological structure of thrust nappe in Nansha trough. The results show that the depth of Moho surface in Nansha sea area is at 18 ~ 26km, among which the Moho surface is the shallowest in the trough area, from the center of trough to southeast to the continental slope Moho surface decreases rapidly from 20km to 26km depth, indicating that the continental crust structure in Nansha sea area has experienced strong tectonic changes. The ratio of crustal cumulative rheological strength FC to lithospheric accumulative rheological strength FL is less than 80, which shows that it is a whole continental crust block, and the ratio of crustal heat flow QC to submarine heat flow Q _ 0 is greater than 60 in most parts of island and reef area, which is a "hot crust cold mantle" type thermal structure. On the contrary, QC / Q _ 0 is less than 40, which is a "cold crust and hot mantle" type heat structure. The temperature of Moho surface in Nansha trough is 300 ~ 700 鈩，

本文编号：2071708