论汉南古陆及大巴山隆起

On the Hannan Old Land and Dabashan Uplift

一、前言 大巴山和米仓山位于扬子碳酸盐台地北缘,是研究扬子地区和秦岭早古生代地层的关键地区之一。从早古生代地层的发育来看,镇巴以西和以东有所不同,在地质上常称为大巴山西段和东段,而大巴山的主要山脉均集中在镇巴以东的大巴山东段。米仓山虽位于大巴山的西北,但在早古生代地层特征上与大巴山东段颇为近似,因此常为人们笼统地包括在大巴山地区之内。中外地质学家们早就注目于这一地区(Richthofen,1882;

The Mountain range of Dabashan (Tapa Mountains) and Micangshan (Mechang Mountains) situated in the border area between Shaanxi and Sichuan provinces are one of the key areas for studying the Paleozoic rocks in both Qin Lin (Chinling Mountains) and Yangtze Region.Based upon a series of Early Paleozoic sections measured by the writers during the last decade, the Early Paleozoic geological history can be reconstructed.As far as we know, the most important events during the Early Paleozoic in this region are three uplifts, namely, Nanzheng Uplift, Xixiang Uplift and the first episode of Yangtze Uplift.The Nanzheng Uplift was the largest one in wide distribution and the longest in time interval.The absence of the middle Cambrian (except the earliest middle Cambrian in some areas) to early Ordo-vician (at least for Tremadocian, but whole early Ordovician in some areas) rocks indicates a 20 m.y.to 72 m.y.uplift around the Hannan Old Land.It caused the most wide expansion of the Hannan Old-land.The maximum of the eustatic sea level rising in Caradoc caused flooding of the whole area and therefore the Pagoda limestone was widely accumulated.The following episode, the Xixiang Uplift was relatively short in time and rather small on scale.It only covered three local areas, south, side of the Hannan Oldland, Wangcan-Nanjiang area, and Ningqiang area forming an archipelagic framework.The Xixiang Uplift was proposed by Prof.Mu En-zhi in the year before he died.It demonstrates a short break during Aeronian, since turriculatus Zone overlies on vesiculosus Zone immediately.In Nanjiang, Wangcan, and Ningqiang counties, turriculatus Zone deposits onlapped on the Kuanyinchiao beds (with Hirnantia fauna) or Pagoda limestone respectively, forming a 9 m.y.or longer break.The Yangtze platform uplifted as a whole during late Telychian to early Wenlock.It corresponds the expansion of the Cathayian Land from southeastern of the South China paleoplate.However, it is interesting that the process was not developed step by step from southeast to northwest, but originated from the Dabashan, the northern edge of the Yangtze carbonate platform.The highest marine deposit (onlapped by early Permian rocks) in the west part of Dabashan, including Liangshan, Nanzheng County to Sanlangpu, Xixiang County, is the lower part of the turriculatus Zone.The latest Telychian marine beds getting higher southwards, the upper turricualtus Zone in Xingzishan, Zhenba County, and may attain crispus Zone more southwards in Chengkou County, N.E.Sichuan.Most area of the Upper Yangtze platform uplifted after the crispus Zone.