青藏高原晚三叠世构造-古地理综述

Summary of the Late Triassic tectonic paleogeography in the Qinghai-Tibetan Plateau， China

关键词:  晚三叠世  沉积相  构造-古地理  青藏高原

Key words:  late Triassic  sedimentary facies  tectonic paleogeography  Qinghai-Tibetan Plateau  China

摘要:

遵循刘宝珺院士提出的“构造控盆、盆地控相”指导思想，在系统厘定地层格架和构造单元划分基础上，确定青藏高原巨型造山带晚三叠世构造-古地理从北往南依次发育：羌塘-三江多岛海、班公湖-双湖-怒江洋、冈底斯-喜马拉雅多岛海和若干次级构造-古地理单元。班公湖-双湖-怒江洋是分隔冈瓦纳大陆和欧亚大陆的特提斯大洋，南羌塘地块是漂浮在特提斯大洋中的块体。本次重点对北羌塘前陆盆地和北喜马拉雅被动大陆边缘盆地的沉积相带展布和古地理进行了研究。造成两个盆地沉积序列及古气候差别的主要因素是构造地质事件。构造事件决定了盆地性质，盆地性质又控制了沉积相带的空间展布。北喜马拉雅盆地位于冈瓦纳构造域，晚三叠世盆地基底南浅北深，继承了古生代构造离散型被动大陆边缘沉积，印支造山作用不发育；北羌塘盆地位于泛华夏构造域，晚三叠世发育印支挤压造山作用及其前陆盆地沉积记录。盆地分析研究表明，北羌塘南部江爱达日那和热觉茶卡等地下三叠统康鲁组底部均发现灰紫色中厚层复成分砾岩、含砾粗砂岩、细砂岩组成向上变细的海侵型地层结构，沉积相为滨岸三角洲；上三叠统土门格拉群沉积相为含煤盆地边缘三角洲。从沉积相展布型式和北东向古水流方向分析，三叠纪北羌塘沉积盆地的物源主要来自羌塘中部双湖造山剥蚀区或“中央隆起带”。

Abstract:

Based on the systematic analytical stratigraphic framework and tectonic unit division, following the guiding ideology of "tectonic controlled basin and basin controlled sedimentary facies" suggested by Liu Baojun academician, it is determined that the late Triassic tectonic paleogeography of the Qinghai-Tibetan Plateau giant orogenic belt developed the Qiangtang-Sanjiang multi-island sea, the Bangonghu-Shuanghu-Nujiang ocean, the Gangdis-Himalaya multi-island sea and several secondary tectonic-paleogeographic units from the north to the south. The Bangonghu -Shuanghu-Nujiang ocean is the Tethys ocean separating the Gondwana and the Eurasia continents, and the southern Qiangtang is a floating block in the Tethys ocean. This paper focuses on the sedimentary facies distribution and paleogeography of the northern Qiangtang foreland basin and the northern Himalayan passive continental margin basin. Tectonic events determined the nature of the basin, which in turn controls the spatial distribution of sedimentary facies belts. The northern Himalayan basin was located in the Gangwana tectonic domain, and the basement of the late Triassic basin deepened from the south to the north, inheriting the Paleozoic tectonic discrete passive continental margin deposits, and the Indosinian orogeny didn't develop at that time. The northern Qiangtang basin located in the Cathaysian tectonic domain, developed the Indosinian extrusion orogeny and foreland basin sedimentary records during the late Triassic. The basinal analysis shows that the bottom of the lower Triassic Kanglu formation in Jiangaidarina Mt. and Rejuechaka lake in the southern part of North Qiangtang Basin, occurred upward thinning and finning transgressive stratigraphic structures composed of gray-purple medium-thick bedding polymictic conglomerates, gravel-bearing coarse sandstones and fine sandstones, and the sedimentary facies was shore-delta. The sedimentary facies of the upper Triassic Tumengera Group were coal-bearing basin marginal delta. Analysis of NE direction paleocurrent and sedimentary facies distribution pattern indicates the material sources of the Triassic northern Qiangtang basin were mainly from the Shuanghu orogenic denuded zone at the middle of Qiangtang or "Qiangtang central uplift belt".