【作者】 何建坤； 刘福田； 刘建华； 孙若昧；

【Author】 He Jiankun Liu Futian Liu Jianhua Sun Ruomei (Institute of Geophysics,Chinese Academy of Science,Beijing,100101)

【机构】 中国科学院地球物理研究所；

【摘要】 本文根据地震层析成像的结果,对华北东部中新生代盆地构造特征与大陆动力学过程进行了地球物理、地质、地球化学的综合研究,认为自中新生代以来,华北地块东部区发生岩石层厚度减薄和地壳构造伸展主要受两种不同性态的大陆动力学过程制约。在新乡-商丘断裂以北,地壳伸展可能与该区在中生代晚期的岩石层水平撤压使岩石层上地幔不同深度发生局部减压熔融、之后自源区抽提的玄武岩浆强烈底辟上升的大陆内部裂谷作用动力学体制有关。在裂谷型伸展过程中,受印-藏碰撞的远程效应影响地壳变形又叠加了明显的右旋剪切拉伸。伸展变形时间主要在早第三纪。岩石层厚度的减薄除了与软流层的上隆、还与部分原属岩石层上地幔的组分经减压熔融和玄武岩浆的抽提后使其转变成上地幔高速异常尔后又向软流层中下沉有关。在新乡-商丘断裂南到东秦岭造山带间,伸展构造的发育与俯冲于原华北地块南缘的古秦岭洋冷板片在碰撞造山结束后,因上地幔热结构的调整和负浮力的增加而发生板片拉断下沉(Slab Breakoff)的大陆动力学体制有关。由于冷板片的拉断下沉,它诱发了上地幔楔在造山带后陆区的上隆和地壳强烈伸展。由此,造成变质核杂岩在后陆区的抬升和后陆盆地自中生代晚期不断向板内扩展。这两类伸展盆地在深部过程上,前者主要受控于周边板块运动的影响使其地块内不同地球层圈间物质和能量稳定性的破坏效应、后者则主要受俯冲和碰撞造山期所破坏的地球不同层圈间物质和能量的稳定性在碰撞造山结束后再度向稳定状态转变时所诱发的盆-山体系在能量和动力学上的耦合效应。更多还原

【Abstract】 Based on the results of seismic tomography,the author makes integrative researches of geology,geophysics and geochemisty on the problem of basin tectonics and its geodynamic processes in the eastern domain of north China block.The results imply that the crustal extension and the lithospheric thinning in the researched areas are controlled mainly by two types of continental geodynamic processes. In the north of Xinxiang-shangqiu fault,initiation of Cenozoic crustal extension can be attributed to result of upper-mantle partial melting caused by the regional lithospheric depression horizontally.Owing to the magma diapir toward the crust which was extracted from the partial melting magma chamber,the tectonic affinity had transformed to the continental rifting system.Late the long-distance effect of India-Tibet collision had probably intensified the crustal dextral transtension.The lithospheric thinning is related to the combined action of asthenosphere-upsurge metasomatism and the sinking of high-velocity upper mantle anomaly which was formed by the accumulation of high-density minerals in its origin belong to the lithospheric mantle. Between the Xinxiang-shangqiu fault and the eastern Qinling orogenic belt,the crustal extension and lithospheric thinning is induced by the post-collision geodynamics of Qinling-Dabie orogenic belt.After the cessation of the Qinling collision processes,the cold slab preserved below the mantle triangle zone will be broken off from the mountain root because of the asthenospheric thermal reboundance and the increasing of negative buoyancy.With the break-off of the cold slab,the asthenosphere had upheld from the slab window toward hinterland.For this process,the lithospheric thinning and crustal extension had formed in the hinterland. Furthermore the continuous sinking of detached slab had caused the hinterland basin to propagate forward the north China block. Conclusively,the interior processes controlling the development of two-type basins can be outlined as follows.The former is mainly characterized by the destruction of energy-and-material balance in earth’s interior which was initiated by action of the peripheral plates.The latter is characterized by the reconstruction of the energy-and-material balance system which was destroyed owing to the early-stage subduction and collision. Thus the mountain-and-basin system in the latter case has been coupled in a unique geodynamic system.更多还原