泛华夏大陆群与东特提斯构造域演化

EVOLUTION OF THE PAN-CATHAYSIAN LANDMASS GROUP AND EASTERN TETHYAN TECTONIC DOMAIN

关键词:  东特提斯构造域  泛华夏大陆群  软流层水平涡旋

Key words:  Eastern Tethyan tectonic domain  Pan-Cathaysian landmass group  horizontal eddy motion in the asthenosphere

摘要:

本文以板块构造理论为基础,根据全球各大陆陆块和微陆块的相对亲缘性、统一性和独立性,提出晚前寒武纪末一早古生代初泛大陆解体后,整个古生代期间,全球大陆可划分为三大陆块群,即冈瓦纳大陆群、劳亚大陆群,和泛华夏大陆群。论述了三大陆块群,特别是泛华夏大陆群的形成演化及其作为独立大陆群存在的统一性。指出泛华夏大陆群的独立性和统一性表现在:①早古生代末,扬子、华夏(包括黄海一东海一南海古陆)、中朝、柴达木、塔里木、昆仑一北羌塘一昌都一印支等陆块曾一度拼贴在一起,形成统一的大陆;②晚古生代中晚期形成独立的华夏植物群区系;③晚古生代末一早中生代,泛华夏大陆群主体部分的扬子一华夏和中朝陆块向西运移楔入,导致其南北两侧古特提斯洋的同步消亡和全球泛大陆的最终形成。泛华夏大陆群的形成演化历经了晚前寒武纪末一早古生代初各陆块的裂离、割据;早古生代末的拼贴、统一;晚古生代的再次分裂和晚古生代末一早中生代与南北大陆群拼贴4个发展阶段。同时指出在东特提斯构造域内,古特提斯既表现出对原特提斯的继承性,又有新生性;中特提斯不是古特提斯的延续和发展,它是标志泛大陆裂一聚巨旋回演化中另一旋回的开始。最后讨论了显生宙地球上大陆由南聚北散到北聚南散,陆块在总体上向北漂移中旋转、裂、聚和泛大陆重组和立即又解体的可能的动力学机制,即地球内部物质向南半球运移,南半球膨胀,促使泛大陆解体。地球内部物质的南移又迫使软流层物质向北运动,驱动大陆碎块北上。蠕动的软流层中,除具有垂向环流的对流环外,还具有大小不等的水平涡旋运动。正是巨大的水平涡旋运动导致了陆块的旋转、会聚(泛大陆形成)和很快脱离涡旋体面离散(泛大陆解体)。

Abstract:

Based on the theory of plate tectonics,the present paper separates,according to the affinity,unity and independence of the global palaeocontinents,landmasses and microland-masses,the global palaeocontinents during the whole time of the Palaeozoic into three landmass groups,i.e.the Gondwana,Laurasis and Pan-Cathaysian landmass groups,all of which are described with the emphasis on the formation and evolution of the Pan-Cathaysian landmass group.The independence and unity of the Pan-Cathaysian landmass group are manifested in:(1)the united continent consisting of the Yangtze,Cathaysia(in-cluding the Yellow Sea-East China Sea-South China Sea oldland),Sino-Korean,Qaidam, Tarim,Kunlun-North Qangtang-Qamdo-Indosinian landmasses during the latest Early Palaeozoic;(2)the independent Cathaysia flora during the middle-late Late Palaeozoic,and (3)the westward migration of the Yangtze-Cathaysia and Sino-Korean landmasses as the bulk of the Pan-Cathaysian landmass group,resulting in the simultaneous obliteration of the Palaeo-Tethyan Ocean on the northern and southern sides of the landmass group,and the final formation of the global Pangea during the latest Late Palaeozoic and Early Meso-zoic.Four stages are recognized for the formation and evolution of the Pan-Cathaysian landmass group;(l)The divergence stage of all the global landmasses at the end of the Late Precambrian to Early Palaeozoic;(2)the partly Convergence stage of the landmasses and the formation of the initial Pan-Cathaysian landmass group during the latest Early Palaeozoic;(3)the divergence and rifting stage of the southwestern margin of the Pan-Cathaysian landmass group during the Late Palaeozoic,and (4)the collision and conver-gence of the Pan-Cathaysian landmass group with the Laurasis landmass group during the latest Late Palaeozoic to Early Mesozoic.In the eastern Tethyan tectonic domain,the Palaeo-Tethys not only has inherited the features of the Proto-Tethys,but also possesses the newly emerging features.The Mid-Tethys marks the beginning of a new tectonic cycle in the divergence-convergence megacycle of the Pangea rather than the continuation and development of the Palaeo-Tethys.This paper deals finally with the geodynamic mecha-nisms for the divergence and convergence of various landmasses,and reorganization and disintegration of the Pangea.In other words,the internal material of the earth migrated to-ward the southern semisphere,giving rise to the expansion of the southern semisphere and disintegration of the Pangea.The southward migration of the internal material of the earth also caused the northward movement of the material in the asthenosphere,leading to the northward movement of the microlandmasses.In addition to the vertical circulation and convection,the horizontal eddy motion of varying sizes also occurred in the creeping as-thenosphere,resulting in the rotation,convergence (the formation of the Pangea) and rapid divergence (the disintegration of the Pangea) of the landmasses.