花岗岩与地壳厚度关系探讨

Granitic Rocks and their Formation Depth in the Crust

文中首先从板块构造与大陆构造的对比出发,指出板块构造主要研究洋壳,洋壳主要研究玄武岩,玄武岩主要研究构造环境。大陆构造主要研究陆壳,陆壳玄武岩少花岗岩多,因此,花岗岩在大陆构造研究中具有特殊的地位。由于花岗岩比玄武岩复杂得多,其中尤以源岩和深度对花岗岩的影响最大,是大陆花岗岩研究最重要的课题。文中接着讨论了Sr和Yb的变化对于花岗岩的意义,指出它们可以作为花岗岩新的分类的标志,主要与其形成的深度有关。由于花岗岩大多形成于下地壳底部,于是,形成于不同深度的不同类型的花岗岩即与地壳厚度存在一定的关系,可以用来研究大陆垂直运动的变化,识别地质历史上曾经存在过但现在已经消失的古高原和古山脉。大陆构造主要研究块体的水平运动和垂直运动。由于垂直运动研究的难度大,而且花岗岩在垂直运动研究中具有的优越性,因此,花岗岩研究最重要的地球动力学意义即在于地壳厚度问题。文中还讨论了花岗岩地壳厚度研究与其他方面研究的关系,指出了花岗岩与地壳厚度关系研究存在的问题,认为花岗岩与地壳厚度的研究具有极大的前景,将推进大陆构造学的研究,将推进花岗岩迈入新时代,将开辟花岗岩研究的新纪元,将创立花岗岩堪与玄武岩媲美的新的理论体系。

Granitic rocks as the major component in the continental crust are particularly helpful to decipher the evolution of continental tectonics, which is quite similar in the way that basaltic rocks, being the major component of the oceanic crust, can be used to trace the tectonic settings in plate tectonics. Diversity of source rock composition and formation depth are two crucial factors controlling the compositions of resultant granitic rocks. It is proposed in this study that the variation of Sr and Yb contents of the granitic rocks a new classification criteria for granitic rocks. Provided is related to their formation depth, which can be further used as most of granitic rocks are derived from the lowest part of the lower crust, the depth from which the granitic rocks formed may indicate the thickness of the crust, therefore, the variation of the formation depth can be used to trace the evolution of vertical movement of the continental crust, i. e. , to indentify ancient plateaus and mountain ranges which ever existed in the history of the earth. Major concerns about the relationship of the composition of granitic rocks and formation depth are also discussed in the paper.