藏东北构造古地理特征及冈瓦纳北界的时空转换

Tectono-paleogeographic characteristics in northeastern Tibet, China and spatial-temporal transition of the northern boundary of Gondwana

研究区位于南北向三江构造带与东西向羌塘构造带的衔接处,是特提斯构造域的重要组成部分。研究区包含金沙江、澜沧江、双湖-昌宁、班公湖-怒江4条古特提斯洋壳带及昌都-芒康、羌北、索县-左贡、多玛-安多4个微陆块的相关部位。4条缝合带时分时合,其间的微陆块则"藕断丝连"。前奥陶纪金沙江带属于泛冈瓦纳"泛非软基底"的北界,早古生代它还是"泛非"混合生物群与扬子区系的界线。泥盆纪—石炭纪,古特提斯形成南北2支,即金沙江带和双湖-昌宁带,与其间亲扬子的中间岛块群(昌都-芒康、羌北、索县-左贡)形成"多岛海"格局,此间,双湖-昌宁转换为冈瓦纳的北界,多玛-安多微陆块为亲冈瓦纳相。早、中二叠世,中间岛块(群)裂解为亲扬子的昌都-芒康和亲冈瓦纳的羌北、索县-左贡三岛块,形成多岛洋,冈瓦纳北界转换到澜沧江带。晚二叠世,古特提斯消亡,形成Pangaea联合古陆,研究区为陆间多岛海。晚三叠世印支运动阶段,金沙江、澜沧江和双湖-昌宁带相继转换为陆内造山带;与此同时,班公湖-怒江带与雅鲁藏布江带形成中特提斯北、南2支,其间为中间陆块群(基墨里),班公湖-怒江带是晚侏罗世—早白垩世消亡的,"基墨里"岛块群是晚白垩世增生在亚洲大陆之上的。喜马拉雅地块是喜马拉雅运动阶段才最后俯冲到亚洲大陆之下,转换为亚洲大陆。

The study region is located in the junction between the N-S-trending Sanjiang tectonic belt and E-W-trending Qiangtang tectonic belt. It is an important component part of the Tethys tectorfic domain, including the Jinshajiang, Lancang River, Shuanghu-Changning and Bangong Co-Nujiang Paleo-Tethyan oceanic crustal belts and related parts of the Qamdo- Markam, Qiangbei, Sog-Zogang and Doima-Amdo microblocks. Four sutures sometimes were separated and sometimes converged and the microblocks between them were apparently separated but actually joined. The pre-Ordovician Jinshajiang belt is the northern boundary of the Pan-African soft basement of Pan-Gondwana, and in the early Paleozoic it was still the boundary of the Pan-African mixed biota and the Yangtze realm. In the Devorfian to Carboniferous, the Paleo-Tethys diverged into the north and south branches, i.e. the Jinshajiang belt and Shuanghu-Changning belt, which, together with the median island block swarm of Yangtze affinity （Qamdo-Markam, Qiangbei and Sog-Zogang） between them, formed the framework of the ＂archipelagic sea＂. Then the Shuanghu-Changning belt was transformed in the northern boundary of Gond-wana and the Doima-Amdo microblock was of Gondwana affinity. In the Early-Mid Permian, the median island blocks （block swarm） broke up into three island blocks： the Qamdo-Markam block of Yangtze affinity and the Qiangbei and Sog-Zogang blocks of Gondwana affinity, forrmng an archipelagic sea. The northern boundary of Gondwanaland was converted into the Langcangjiang belt. In the Late Permian, the Paleo-Tethya died out, forming Pangaea with an archipelagic sea in the study region. During the Late Triassic Indosinian orogeny, the Jinshajiang, Langcangjiang and Shuanghu-Qamdo belts were transformed into intracontinental orogenic belts. Meanwhile, the Bangong Co-Nujiang and Yarlung Zangbo belts formed the north and south branches of the Meso-Tethys, with a median microblock swarm named ＂Cimmerides＂ between them. In Late Jurassic to Early Cretaceous the Bangong Co-Nujiang belt was extinguished and the ＂Cimmerides＂ was accreted to the Eurasian continent in the Late Cretaceous. The Himalayan block was finally subducted beneath the Asian continent in the stage of the Himalayan movement.