特提斯地球动力学

特提斯是地球显生宙期间位于北方劳亚大陆和南方冈瓦纳大陆之间的巨型海洋,它在新生代期间的闭合形成现今东西向展布的欧洲阿尔卑斯山、土耳其-伊朗高原、喜马拉雅山和青藏高原。根据演化历史,特提斯可划分为原特提斯、古特提斯和新特提斯三个阶段,分别代表早古生代、晚古生代和中生代期间的大洋。大约在500Ma左右,冈瓦纳大陆北缘发生张裂,裂解的块体向北漂移,并使其与塔里木-华北之间的原特提斯洋在420～440Ma左右关闭,产生原特提斯造山作用,与北美-西欧地区Avalonia地体与劳伦大陆之间的阿巴拉契亚-加里东造山作用基本相当。原特提斯造山带之南、早古生代即已存在的龙木错-双湖-昌宁-孟连古特提斯洋在380Ma向北俯冲,使早期闭合的康西瓦-阿尼玛卿洋重新张开,并由于弧后扩张形成金沙江-哀牢山洋。330～360Ma左右,特提斯西部大洋由于南侧非洲板块和北侧欧洲板块的碰撞而关闭,形成欧洲华力西造山带。而特提斯东段的上述三条古特提斯洋在250Ma左右基本同时关闭,华北、华南、印支等块体聚合形成华夏大陆。该大陆与冈瓦纳大陆、劳亚大陆和华力西造山带一起围限形成封闭的古特提斯残留洋,并一直到晚三叠世-早侏罗世海水才全部退出。此后,南侧冈瓦纳大陆在三叠纪晚期重新裂解形成新特提斯洋,该洋盆在新生代初期由于印度和亚洲的碰撞而关闭。原、古、新特提斯三次造山作用基本代表了中国大陆显生宙期间的地质演化历史,并在此过程中形成了特色的特提斯域金属成矿作用。广布的被动陆缘和赤道附近的古地理位置,以及后期的造山作用同时也成就了特提斯域内巨量油气资源的形成;塑就的地貌与海陆分布格局,也对当时的古气候与古环境产生了重要影响。特别是,与原、古、新特提斯洋消亡相关的三次弧岩浆活动与显生宙地球历史上三次温室地球向冰室地球的转变,在时间上高度吻合。上述演化历史同时还表明,特提斯地质演化以南侧冈瓦纳大陆不断裂解、块体向北漂移并与劳亚大陆持续聚合为特征,其动力机制主要来自俯冲板片的拖拽力,而地幔柱是否对大陆的裂解与漂移有所贡献,则有待进一步评价。

Tethyan geodynamics

Tethys is a giant and long-lived oceanic system between what once was Gondwana in the south and what has become Laurasia in the north. Its evolution can be broadly represented by the Proto-, Paleo-, and Neo-Tethys oceans, formed in the Early Paleozoic, Late Paleozoic, and Mesozoic, respectively. The final oceanic closure in the Cenozoic resulted in formation of the Alps, the Turkish-Iranian Plateau, and the Himalayan-Tibetan Plateau, representing the development of elevated topography within the tropical-to-subtropical climate belts. The Proto-Tethys formed by the first rifting of the northern Gondwana margin at ca. 500Ma, and the blocks drifted northward and collided with Tarim and North China, and formed the Proto-Tethyan orogeny at ca. 440~420Ma, with a wide Longmucuo-Shuanghu ocean located to the south. This scenario is comparable with the Appalachian-Caledonian orogeny between the Gondwana-derived Avalonian terrane and Laurentia and Baltic. Northward subduction of the Paleo-Tethys along the Longmucuo-Shuanghu trench made opening of the previously closed Kuangxiwa-Anemaqen Ocean at ca. 380Ma and spreading of the Jingshajiang-Ailaoshan Ocean as a back-arc basin. During the Late Paleozoic, the western Paleo-Tethys (Rheic Ocean) was manifested by collision of Africa with Europe along the Variscan orogenic belt at 360~330Ma; whereas in the east, the Paleo-Tethyan oceans among the North China, South China, and Indochina closed simultaneously at ca. 250Ma, with formation of the Cathaysian continent. Together with Laurasia to the north, Gondwana to the south, and the Variscan orogen to the west, a residual Paleo-Tethys ocean was trapped, and the final eustatic regression took place in the Late Triassic-Early Jurassic. Meanwhile, the northern Gondwanan margin resumed rifting with a series of blocks to form the Neo-Tethyan Ocean, which was subsequently closed in the Cenozoic. The formation of the Chinese continent is variably contributed by the Proto-, Paleo-, and Neo-Tethyan orogenies, and formed the world well-known Tethyan metallogenic province. The extensive and long-lived passive margin sedimentation in tropical-to-subtropical climates helped form tremendous reserves of oil and gas. Tethyan paleogeography and paleotopography have influenced global climate and environmental change from deep time to the present. Especially, the oceanic subductions of the Proto-Tethy, Paleo-Tethys and Neo-Tethys match well with the transition of the Earth climate from the greenhouse to the icehouse in the Phanerozoic. The above synthesis indicates that the Tethyan evolution is characterized by northward drift of the rifted continental blocks from Gondwana, and subsequently collision with Eurasia continuously throughout Phanerozoic time. Such northward drifting and subduction strongly suggests that the slab pull is a dominant geodynamic force of plate movement, and the role of mantle plume as a driving force needs further investigation.