太行山中生代板内造山作用与华北大陆岩石圈巨大减薄

近年来,华北大陆岩石圈巨大减薄成为国际地学界关注的焦点之一,但对其减薄的时间、机制仍然知之甚少。约束条件的多解性和表面上相互矛盾的证据导致了对区域构造发展史的模糊认识。笔者认为,华北板内造山过程是理解岩石圈巨大减薄机制的关键,因为华北岩石圈是在造山带而不是在克拉通基础上开始减薄过程的。岩石圈减薄过程可以划分为拆沉减薄、伸展减薄、热减薄和化学侵蚀减薄4种类型。前者依赖于岩石圈重力不稳定性,是一种突变过程;后三者取决于软流圈挤出构造,属于渐变过程。减薄过程主要始于120~110Ma的拆沉减薄,其标志是造山后脉岩组合的形成。亚洲大陆软流圈的多阶段汇聚过程造成软流圈向东挤出,是中国东部中新生代以来岩石圈持续减薄的重要基础。因此,大陆动力学与大洋最重要的区别之一就是大陆岩石圈经常发生减薄作用,特别是拆沉作用,并由此将软流圈系统区分为浅部混染系统和深部纯净系统,火成岩的地球化学属性主要取决于岩浆起源的深度。

The Mesozoic intraplate orogeny of the Taihang Mountains and the thinning of the continental lithosphere in North China

Recently, the thinning of the continental lithosphere in the North China has become one of the main topics in modern geoscience. However, the timing and mechanism of lithosphere thinning are still poorly understood. The ambiguity of the known constraints and the apparent contradiction of the evidences used to explain the thinning processes has resulted in a somewhat poor understanding of the regional tectonic history. In this paper, the recognition of intraplate orogeny in North China is considered as a key for understanding the thinning of lithosphere, because the thinning process is initiated at the base of the lithosphere, and not the craton. Lithosphere thinning can be divided into four types: 1)delamination, 2)extension, 3)thermal thinning and 4)chemical erosion. The former is dependent on gravitational instability of the lithosphere and display a sudden change of the lithosphere thickness. The other three processes are continuous and influenced by asthenospheric upwelling. The thinning process in North China began at about 120~110 Ma and is marked by the emplacement of the post-orogenic dike swarms. The multistage convergence of the asthenosphere beneath the Asian continent induces asthenospheric extrusion eastward. These processes are the important bases of the continuous lithosphere thinning beneath Eastern China since the Meso-Cenozoic era. Therefore, one of the most important differences between the continental and oceanic geodynamics is that commonly lithosphere thinning, especially delamination is a character of subcontinental lithosphere. Based on this, the subcontinental asthenosphere can be subdivided into two subsystems: shallow contaminated and deep undepleted. The geochemical features of igneous rocks reflect the level of magma generation.