摘要
对贺兰山北段三叠纪构造背景的理解具有重要的理论和实践意义,本文通过对该地区周边同期构造事件的分析,结合最近的研究成果,认为贺兰山北部三叠纪沉积的构造背景类似于新生代早、中期莺歌海拉分盆地形成的环境。晚三叠世—早侏罗世由于巴彦乌拉山—狼山韧性剪切带的左行走滑,致使巴彦乌拉山崛起,它类似于目前的红河—哀牢山剪切带中的哀牢山,而在贺兰山北部由于该断层的左行走滑形成了走滑拉分盆地,堆积了巨厚的上三叠统延长组和侏罗系碎屑岩。虽然在三叠纪地理上贺兰山地区与鄂尔多斯盆地可能相连,但两者的沉降机制并不相同,它们的关系可能类似于目前的莺歌海盆地与南海盆地的关系。在晚侏罗世,该地区的拉分盆地由于受到阿拉善地块的东向挤压而反转。造成巴彦乌拉山—狼山韧性剪切带左行活动的原因是晚三叠世—早侏罗世鄂尔多斯盆地相对于阿拉善地块的左行压扭运动,其动力则可能来自中朝板块与扬子板块的碰撞。该模型不仅可以解释贺兰山北段三叠纪区别于鄂尔多斯盆地本部的强烈伸展,还能解释该地区分布局限的板内拉斑玄武岩的原因,而且也能够将晚三叠世巴彦乌拉山的隆起与该地区同时期的沉积以及阿拉善地块南缘的变形联系起来,而从区域上也可以解释同时期南蒙古地区发育的左行走滑构造及其相关沉积。
Based on the latest studies and the analysis on the tectonic events occurring around the Helanshan region, it is concluded that the tectonic setting of the northern Helanshan in the Late Triassic-Early Jurassic may be similar to that of the Yinggehai pull apart basin in the Early-Middle Cenozoic. During the Late Triassic-Early Jurassic, the left lateral strike-slipping of the Bayan-UI Shan-Langshan shearing zone resulted in the uplift of Bayan-UI Shan, whereas the left lateral strike-slipping resulted in the formation of a pull apart basin in the northern Helanshan as well as deposition of thick Upper Triassic Yanchang Formation and Jurassic strata. Although the northern Helanshan and the Ordos basin may connect with each other geographically, their depositional mechanisms were different; their relationship may be similar to that between the Yinggehai basin and the South China Sea basin. During the Late Jurassic, this pull- apart basin was reversed due to the eastward compression of the Alxa Block. The reason for the left-lateral strike-slipping of the Bayan-U1 Shan-Langshan ductile shear zone was the left-lateral transprssion of the Alxa Block relative to the Ordos Block in the Late Triassic-Early Jurassic. Its dynamics may result from the collision between the Sino-Korean Plate and the Yangtze Plate. This model could explain the strong extension of the northern Helanshan, which was very different from the Ordos basin itself in the Late Triassic-Early Jurassic; provide the reason for the limited distribution of the intraplate tholeiite; and also interpret the relationships between the uplift of the Bayan-U1 Shan and deposition in the northern Helanshan, as well as the deformation along the southern Alxa block during the same time. Regionally, this model can also explain the evolution and related sediments of left-lateral strike-slipping in southern Mongolia in the same time.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2009年第9期1233-1246,共14页
Acta Geologica Sinica
基金
国家重点基础研究发展计划(编号2007CB411306
2001CB409810)
国家青年自然科学基金(编号484562145986)
中国地质调查局(编号1212010611806)等项目共同资助的成果
