地壳滑脱层对大陆裂谷发育演化的影响——基于数值模拟方法  

Controls of crustal detachment layer on the development and evolution of continental rifts——Based on numerical simulations

作　　者：范庆凯 郭金瑞[1] 王炎阳 FAN QingKai;GUO JinRui;WANG YanYang(Sinopec Petroleum Exploration and Production Research Institute,Beijing 100083,China)

机构地区：[1]中国石化石油勘探开发研究院,北京100083

出　　处：《地球物理学报》2023年第3期1025-1035,共11页Chinese Journal of Geophysics

基　　金：中国石化基础前瞻项目(P22214-2)资助。

摘　　要：裂谷型大陆边缘是重要的离散型板块边界,其发育演化受控于地壳滑脱层的厚度变化.岩石圈流变性质、温度结构、物质组成等因素决定了地壳滑脱层的厚度.通过地球动力学数值模拟探究地壳滑脱层厚度与裂谷形态间的关系,结果表明,对于强下地壳(湿钙长石)模型来说,滑脱层厚度与裂谷上盘断块(H-block)规模呈反相关关系.且当滑脱层总厚度偏小时,以壳-幔滑脱层对上盘断块规模的影响为主;反之,壳间滑脱层的影响更大.岩石圈,尤其是下地壳强度的减弱使地壳滑脱层厚度不断增加,裂谷形态也随之产生由上盘断块缩小到裂谷轴横向跃迁的转变.弱下地壳(湿石英)模型发育明显更厚的地壳滑脱层,直接导致了裂谷轴的离轴跃迁,且迁移距离随滑脱层厚度的增加而不断增大,指示弱岩石圈更容易产生大尺度变形.基于数值模拟结果,对比位于南大西洋中段的刚果盆地和坎波斯盆地可知,二者下地壳流变性质相似,且强度较大,但上盘断块的规模表现出显著差异,揭示出坎波斯盆地下伏滑脱层的厚度显著大于刚果盆地.由于裂谷期两个盆地距其南侧热点、地幔柱活动的距离不同,可能导致岩石圈温度结构的变化,从而产生地壳滑脱层厚度的差异.Rift continental margins are an important divergence plate boundary, whose evolution are affected by the variation in crustal detachment thickness. Factors like rheology, thermal structure and composition in lithosphere control the detachment thickness. We carried out geodynamic modelling to investigate the quantitative relationship between crustal detachment thickness and rift morphology. The results show that, for cases with strong lower crust(wet anorthite), there is an inverse correlation between the thickness of detachment layers and the size of hanging wall block(H-block). In addition, when detachment layers have a limited overall thickness, the crust-mantle detachment layer plays a dominant role in controlling the size of H-block;on the contrary, the inter-crustal detachment layer will have greater influence. Lithosphere, especially lower crust weakening thickens crustal detachment layers, creating a shift from H-block shrinking to rift jumping. Cases with weak lower crust(wet quartzite) develop thicker detachment layers, resulting in the off-axis jump of rift axis. The migration distance increases with the thickening of detachment layers, indicating that the weak lithosphere is more prone to large-scale deformation. Based on simulation results, we compare Congo basin and Campos Basin located in the central segment of South Atlantic. Comparative results indicate similar lower-crustal rheological properties between them, and they both develop a relatively strong lower crust. However, they show a significant contrast in the size of H-blocks, indicating that Campos Basin has greater underlying detachment layers than Congo basin. Because of the different distance between these two basins and the hot spot, mantle plume during rifting stage, a change of lithospheric thermal structure may be caused, which will finally result in the discrepancy detachment thickness between them.

关 键 词：滑脱层 大陆裂谷 数值模拟 温度 流变性质 

分 类 号：P541[天文地球—构造地质学]