The post-collision intracontinental rifting and olistostrome on the southern slope of Bogda Mountains, Xinjiang.
Résumé
A regional-scale tectonic event of closure of ocean and collision-orogeny took place in the interval from Late Devonian to Late Carboniferous in the Xinjiang area. At the late stage of collision, some tectonic changes occurred in the piedmont area. The preliminary framework of mountains-basins of northern Xinijiang was composed of both Late Carboniferous-Early Permian orogenic belt and piedmont basins. In the direction toward continent, post-collision intracontinental rifting and olistostrome developed well. The bedded diabase and bimodal volcanic rocks were distributed in the Early Permian strata in the piedmont area. The most typical area is located on the southern slope of Bogda Mountains, namely the Qijiaojing-Cheguluquan segment of Harm city and the Baiyanggou section of Urumgi. This paper studied the geometrical, petrological and geochemical features of intracontinent bimodal volcanic rocks and olistostrome. Of them, post-collision olistostrome is the first time discovery by us. In the Qijiaojing-Cheguluquan segment, basalt and rhyolite are ranged alternately that overlie the Early Permian red molasses. This post-collision bimodal volcanic series with a big thickness is distributed in parallel with the sub-E-W mountain extension. In the Baiyanggou section, post-collision underwater olistostrome co-exists with underwater eruption and is composed of olistostrome zone, pillow lava and pore basalt zone, and siliceous shale and siltstone zone; the bottom plane is contacted with Late Carboniferous limestone and sandstone series by a NEE-trending detachment fault.