从特提斯到青藏高原形成:构造-岩浆事件的约束

From the Tethys to the formation of the Qinghai-Tibet Plateau:constrained by tectono-magmatic events

青藏高原被誉为“世界第三极”。然而，从特提斯的形成演化到青藏高原的形成，经历了一个漫长的复杂过程。这一过程分为三个明显的演化阶段：古特提斯阶段、新特提斯阶段、印度-欧亚大陆碰撞与青藏高原形成阶段。古特提斯洋自早石炭世开始打开，形成三个主支（修沟-玛沁洋、金沙江-哀牢山洋、澜沧江-昌宁孟连洋），至早二叠世扩张到最大规模后开始俯冲消减，逐渐缩小，至晚三叠世末-早侏罗世初洋盆闭合，冈瓦纳古陆的前缘与劳亚古陆的前缘碰撞拼合。这大约经历了150Ma的时间。大致与此同时或略早，古特提斯以南的新特提斯洋两支同时打开，并大致于早-中侏罗世之交扩张到最大规模，然后开始消减、缩小。北支班公湖-怒江洋在晚侏罗世初到早白垩世末（大致在160～100Ma的时间间隔内）闭合，完成拉萨地块与羌塘地块的碰撞拼合过程。南支雅鲁藏布洋闭合较晚，在白垩纪／古近纪之交（65／70Ma左右）印度大陆开始与拉萨地块（即欧亚大陆南缘）碰撞。新特提斯洋从打开到闭合，经历了约140Ma。印度-欧亚大陆碰撞是青藏高原形成的直接原因，从开始到完成，整个碰撞过程用了约20Ma（大致在65-40／45Ma时间间隔内）；然后转入后碰撞阶段至今。很显然，几亿年时间尺度和几万公里空间尺度的特提斯的开合、演化、特别是印度-欧亚大陆碰撞和青藏高原隆升，必定对应着地球各圈层间巨大的物质与能量的调整和交换。而正是这种巨大的物质、能量交换，才是形成青藏高原及其资源环境效应的基本动力。

The Qinghai-Tibet plateau is known as ＂the third pole of the Earth＂. The process from the evolution of Tethys to the formation of the Qinghai-Tibet plateau, however, is a complex long-term period. This process consists of three stages： the Paleo-Tethys, the Neo-Tethys and the India-Eurasia collision and formation of the plateau. The Paleo-Tethys opened since the early Carboniferous, formed three branches including the Xiugou- Maqing, the Jinshajiang-Ailaoshan and the Lancangjiang-Changning-Menglian oceanic basins. It reached the maximum width in the early Permian and then started with plate subduction. All the Paleo-Tethyan oceanic basins were closed at the end of the Triassic/the beginning of Jurassic, resulting in collision between the fronts of the Gondwana and Laurasia paleo-continents. This whole process for the evolution of the Paleo-Tethys took about 150 Mys period of time. Almost at the same time as the closure of the Paleo-Tethys or earlier, the Neo- Tethys opened and subsequently reached its maximum width in early/middle Jurassic, and then started with plate subduction and consumption. The Bangongco-Nujiang oceanic basin, i. e. , the northern branch of the Neo-Tethys, was closed up in the period from the late Jurassic to the early Cretaceous （about 160-100 Ma）, given rise to collision between the Lhasa and the Qiangtang blocks. Later on, southern branch of the Neo-Te- thys, the Yarlung Tsangbo oceanic basin started to close at the boundary between the late Cretaceous and the early Paleogene and caused the initiation of India-Eurasia continental collision, the real staring point of formation of the Tibetan plateau. The entire process of this collision took about 20 Mys （65-40/45 Ma or so）to be completed, and subsequently transformed into post-collisional time. Obviously, such a huge crustal and lithospheric movement mentioned above, with hundreds of million years in time scale and tens of thousand kilometers in space scale, must have corresponded to a huge mass-energy exchange among various geospheres of the Earth＇s interior. It was this huge mass-energy exchange that eventually caused the formation of the Qinghai-Tibet plateau and the influence on resources and environments.