对新元古代湘桂海盆及邻区构造属性的探讨

Probe into the Tectonic Nature of Neoproterozoic Southern Hunan-Northern Guangxi Marine Basin

新元古代的湘桂海盆夹持在中上扬子陆块的东南缘与华夏地块群之间,是古华南洋与下扬子陆块俯冲碰撞后在西南方向的残留海。东段古华南洋俯冲的地质记录发生在860～1034Ma间,为绍兴-江山-萍乡碰撞带,形成江南岛弧造山带;西段古华南洋与上扬子陆块俯冲的构造地质记录,推测在湖南的新化-城步至广西的三江一带,时间为850～820Ma,形成雪峰-四堡岛弧造山带,但无陆陆碰撞的记录。东、西两段构造活动有近1亿年至数十百万年的时间差,为湘桂海盆在停止扩张的洋底上提供了发育的空间,并转为弧前-深海盆地。由萍乡向南西方向至湖南茶陵-郴州为一结合带,西侧的沉积物属扬子沉积构造域和湘桂海盆,沉积了细屑浊积岩和硅泥质岩;东侧为华夏沉积构造域,包括赣、闽和粤北,充填了与热活动有关细碧岩、含铁石英岩和火山碎屑沉积岩;郴州至贺县间,有一东-西向的古南岭裂陷海与之相连,是分隔云开地块、粤东南地块与罗霄-武夷地块的深海槽。在早古生代构造旋回中,湘桂海盆、古南岭海槽以及华夏沉积构造域,分别转为不同构造走向的湘桂加里东褶皱带和华南加里东造山带。

Neoproterozoic Hunan-Guangxi Marine Basin （Southern Hunan-Northern Guangxi, NHGMB）, a remnant oceanic basin after that Paleo-South-China Ocean （PSCO） subducted to Lower Yangtze Block, was located between the South-East marginal of Middle-Upper Yangtze Block and Cathaysian Massif Group. The east segment of PSCO subduction had taken place from 1034Ma to 860Ma, the geological record was the Shaoxing-Jiangshan-Pingxiang collision zone, and so Jiangnan Island-arc Orgenic Belt had come into being. The record of PSCO west segment subducting and colliding with Upper Yangtze Block during 850 ~ 820Ma, could be distributed in the zone from Xinhua-Chengbu in Hunan to Sanjiang in Guangxi, and established Xuefeng-Sibao Island-arc Orogenic Belt, but without collision of continent to continent. The stepout of tectonic activity between the east part and the west part, therefore, was about 100Ma which had presented the space and time for NHGMB development upon the oceanic floor stopping subduction. From Pingxiang, via Chaling, to Chenzhou was a tectonic combination belt, the west side of this belt was belong to Yangtze sedimentary tectonic domain and NHGMB, deposited fine turbidite and siliceous argillite. The east side was Cathaysian sedimentary tectonic domain, including Jiangxi, Fujian and Guangdong, deposited spilite and ferriferous quartzite related to hydrothermal activity, and volcanoclastic rock. Between Chenzhou and Hexian, there was Paleo-Nanling Rift Trough （PNRT） in east-west strike, which separated Yunkai Massif, Southeast Guangdong Massif and Luoxiao-Wuyi Massif. During the Caledonian tectonic cycle, NHGMB, PNRT and Cathyasian Sedimentary-Tectonic Domain turned into Hunan-Guangxi Caledonian Fold Belt and South China Caledonian Orogenic Belt with different strike respectively.