地球的节律与大陆动力学的思考

SPECULATIONS ON EARTH′S RHYTHMS AND CONTINENTAL DYNAMICS

地球的节律可能是地质作用在地球发展中普遍存在的规律，既有不同的类别，又有时限不同的级别。节律具有突发性和旋回性或周期性，总的构成不同的发展阶段。地球节律可能最终受到天文因素背景的控制。节律现象因受到地区性因素以及一些非线性因素的叠加和干扰，形成不同程度的耦合和偏离，表现十分复杂。文中讨论了较长周期的沉积旋回周期和构造岩浆旋回周期。大陆地质是地球动力学的信息库。文中讨论了陆壳形成、大陆在地史中的聚散演变；讨论了联合古陆和超级大陆的周期，也涉及板块运动、大陆聚散及其受深部过程的控制和驱动力问题；最后论述了地球阶段性有限膨胀的可能性及其初步检验情况。

Rhythms in earth history are probably a common feature and are recognizable in various geological processes, often with different ranks of time duration. Rhythms are generally characterized by episodicity, cyclicity or periodicity, and make up synthetically differtent development stages. They might be ultimately controlled by astronomic factors and backgrounds. Owing to the effect of superposition and disturbance through local conditions and possibly some non linear factors in geology, the rhythmic phenomenon may be complicated and shows in various degrees coupling and divergence. Long term cycles in sedimentation and tectono magmatism are emphasized, especially the Precambrian tectonic and magmatic stages, which are correlatable with each other and comparable with the major stratigraphic sequences. Stratigraphic sequences longer than the Mesosequence (30～40 Ma) on the platforms in China are briefly discussed. The controversial time limit of the Orthosequence (3rd order sequence) is reviewed on the basis of new results obtained in China. Continental geology is the main data source for earth dynamic studies. The formation of the continental crust and the assembling and dispersal of continents in earth′s history are discussed, including the possible driving force connected with different scaled mantle convections. Pangaea cycles with a time interval of 550～600 Ma forming the five pangaeas with alternating longitudinal hemisphere pattern and circum equater pattern are outlined. Possible earth expansion is addressed on the basis of increased length of solar days, recognition of ever more extensional structures on the earth, and the discrepancy between the global reconstruction of palaeocontinents and the pattern required by palaeobiogeographical interpretation. A proposal of limited earth expansion with radius reduction of no more than 25% since 2.5 Ga is presented. Expansion may have occurred through each Pangaea disintegration at ca 5% radius increase. Reconstruction of palaeocontinents on the reduced earth surface was designed and effected, and a test of the supposed earth expansion rates is provided by the method of the least dispersal of the palaeopoles of the same continent in the same period.