青藏高原生长的三维地球动力学数值模拟

The margins surrounding the Tibetan Plateau show some diversity in topographic gradient. To date, it is still controversial that why the topographic gradient across some margin is steep while other is rather smooth，and how the plateau grew to its present height and size. Recently, results revealed by deep seismic investigation conducted at the plateau and its surrounding region show that there are significant differences in the lithospheric structure and rheological properties between the plateau and its adjacent region, especially the surrounding cratonic basin. Petrological studies indicate that such differences probably existed even before the uplift of the Tibetan plateau. However, previous studies paid little attention to the inherent lateral differences between the proto-plateau and its surrounding regions, except a few recent 2D numerical modeling studies, which totally ignored the along-strike variation of the mountain building process. To investigate the roles of the preexisting lateral contrast in lithospheric structures and properties between the proto-plateau and its surrounding blocks, including cratonic basins, in the outward growth of the Tibetan Plateau, this project will conduct 3D geodynamic numerical modeling based on the observations from the plateau and its margins. The project will concentrate on the interaction between the proto-plateau and its surrounding blocks, especially the cratonic basins. The insights gained from this project are supposed to improve our understanding to the process and style of the outward growth of the Tibetan Plateau and mountain building process due to continent-continent collision. The conclusion will be broadly applicable to other orogenies also.

青藏高原的周缘展现出多样性的地形坡度特征。目前，对造成青藏高原不同边缘地形梯度有陡有缓的原因以及高原的生长方式与过程仍然存在着争议。近年来在青藏高原及其周边开展的深部地震探测结果表明：高原与周边岩石圈在结构以及流变物性上存在着重大差异，岩石地球化学研究表明这种差异在高原隆升之前就已经存在。然而，以往的研究对这种固有的横向差异未给予足够的重视，而且有限几项的研究局限于二维数值模拟，忽略了造山带沿走向的变化。为此，本项目拟开展三维岩石-热力学数值模拟研究，从青藏高原与周边块体包括克拉通盆地之间的相互作用来考察高原的向往生长过程与机制，探讨陆内会聚带岩石圈在结构和物性上的横向差异以及克拉通阻挡对高原生长样式的影响，所获得的结论与认识将深化人们对青藏高原侧向生长过程与方式、大陆碰撞造山等科学问题的理解，同时对于我们理解其他地区同类型边缘或高原的成因机制与过程也具有广泛的借鉴意义。

青藏高原及其周缘下方的地壳/岩石圈在结构和物性上均存在显著的横向差异。这种横向非均一性可能继承于碰撞前亚洲大陆南缘经历的多期微陆块拼贴事件。 然而，已有的有关青藏高原形成的模型大多建立在假设大陆岩石圈是横向均匀的前提之下，对碰撞前亚洲板块的构造继承性未予以足够重视。在本研究中，我们将亚洲板块的构造继承性与青藏高原的构造演化联系起来思考，利用高分辨三维热-力学模拟方法，对地壳/岩石圈非均一性在青藏高原的生长方式、中地壳部分熔融以及东西差异等方面的作用开展了系统性的研究。模拟结果显示：碰撞前亚洲大陆的构造继承性导致了青藏高原的幕式生长以及高原后期深部地壳的熔融，深部地壳熔融及其向外流动是高原演化后期的产物，地壳流并非是驱动高原演化的主要机制。此外，模拟结果还表明岩石圈强度横向非均一性控制了青藏高原岩石圈变形与深部结构的东西差异性，为认识造山带的复杂性和多样性提供了新的视角。由于大陆地壳/岩石圈横向非均一性在大陆中普遍存在，因此本研究取得的成果对认识其他造山带的地质过程具有重要的启示意义。