华北陆块岩石圈减薄作用:热薄化与机械拉伸的数值模拟研究

针对华北陆块岩石圈减薄作用的动力学机制开展了一系列二维定量数值模拟研究。其模拟结果表明,在给定的岩石圈热传导和放射性生热条件下,岩石圈底部地幔热流(mantlethermalflux)的增加能导致岩石圈内热状态的明显改变,导致早古生代以来华北岩石圈厚度的巨大变化,当地幔热流达到35～40mWm-2,华北陆块的岩石圈厚度将减薄至100km以内。单纯的机械拉张同样能导致岩石圈厚度的薄化,但岩石圈厚度的减薄相对有限。即使拉张伸展率达25%,其岩石圈厚度最大减薄至150km。因此通过数值模拟的研究揭示了这样的事实,即华北陆块岩石圈厚度的减薄主要受制于岩石圈内热状态的变化,以热侵蚀的减薄方式为主,机械拉张作用可能对华北陆块岩石圈厚度的减薄作用有一定贡献。

LITHOSPHERIC THINNING IN THE NORTH CHINA BLOCK:A NUMERICAL APPROACH ON THERMAL PERTURBATION AND TECTONIC EXTENSION

In an attempt to understand the dynamics of lithospheric thinning in the North China Block, we have conducted a series of 2D quantitative numerical simulations. The results indicate that for a given thermal conductive rate and t he radioactive heating condition, the increase of the mantle thermal flux at the base of the lithosphere can trigger a great deal of changes in the thermal stat e and in the lithospheric thickness of the lithosphere. The lithospheric thickne ss in the North China Block could be thinned to a magnitude <100 km when the man tle thermal flux was increased to 35-40 mWm-2. The effect of tectonic extensio n on lithosphere thickness has been explored by incorporating a constant extensi onal displacement rate at the lateral edges of the model. But the results show t hat the thinning of the lithosphere is still quite limited after a 25%extension (with no increase in thermal flux), since in this case the lithospheric thickne ss can only be thinned to about 150 km. Therefore, thermal perturbation in the f orm of elevated mantle thermal flux seems to be the predominant mechanism respon sible for the significant lithospheric thinning in the North China block, while tectonic extension may possibly play a more profound role on lithospheric thinni ng at a later stage when the lithosphere had already been inhomogeneously thinne d.