花岗岩拓扑学的反思

花岗岩成因与大地构造环境相结合的研究是壳、幔动力学研究中的重要组成部分。文中以花岗岩热力学体系的某一拓扑学处理为基础 ,把地质环境、花岗岩侵位和岩石、矿物、化学元素的共生组合相结合 ,形成“三位一体” ,建立起了花岗岩拓扑学的观点 ,用以说明一个地区的大地构造旋回各个阶段的花岗岩系的属性 ,并以此反映出大地构造中的某些基本问题。在拓扑学处理中以代表花岗岩体系主要组分的KNCASH为基础 ,建立了一系列不同层次的元素判据 ,描绘出花岗岩系的演化痕迹。其中TAS图解居于首位 ,用以说明演化的主要趋向 ;Al及Alk饱和度图解说明在各个主要趋向中Al及Alk的变化以及它们与源岩和演化过程的关系 ;K2 O在整个体系中是一个灵敏指示计 ,KS、K/N以及岩石中的K2 O含量对评价陆壳的参与程度以及岩浆作用过程中的变化是有效的。在上述前提下 ,以中国的主要花岗岩为准提出了一个花岗岩岩系分类 ,待进一步修正。

MEDITATION ON GRANITE TOPOLOGY

Granite Topology is a theme of the granite petrogenesis linking up with the tectonic setting, and is considered as one of the important topics of the crustal-mantle interaction within the regime of crustal geodynamics. Based on the topological treatment of the granite thermodynamic system, we closely combined the geological environment, the granite emplacement, and the paragenetic associations of rocks, minerals and chemical elements of granitic rocks to form a "trinity" to be the main line of granite topology for the purpose of linking up with its tectonic environment in revealing the characteristic features of granite series within a tectonic cycle. During the topological treatment, several diagnostic concentration diagrams within the granite system expressed as (KNCASH) are used in establishing different ranks of elemental criteria to demonstrate the evolutional trend of the granite-forming process. As the first rank, the TAS diagram behaves as major coordinates to depict the main trend of evolution process. The saturation degree of Al and alkalis rank as second order to illustrate the degree of saturation of Al and alkalis which are available for deciphering the behavior of sources and alkali changes within each trend. The amounts of K_2O are considered as a sensitive indicator throughout the whole stages of process. The diagrams of K_2O vs. SiO_2 and K_2O/Na_2O together with its amounts in bulk compositions are useful in assessing the nature of continental crust and the change of magmatic process during its initiation and ascent. According to the treatment of the granite topology, an interim classification of granite series based on some granite terranes of China is proposed, and is to be subjected to further improvement.