晚三叠世早期义敦前陆盆地的沉积特征与形成演化模式

Sedimentary Characteristics and Evolution of the Yidun Foreland Basin,Western Sichuan During the Early Late Triassic

义敦盆地是三叠纪时期金沙江洋闭合而由俯冲板块边缘沉积环境演化而来。90年代初,通常把义敦盆地称为弧后盆地,因为晚三叠世晚期甘孜-理塘洋壳向西俯冲而在盆地东边形成一系列火山弧。但是从盆地内的沉积特征、相变化、形成时间和演化过程来看,更具有“前陆”盆地的性质。...

The Yidun foreland basin,western Sichuan was developed on the underthrusting plate near the suture zone during the continent continent collision triggered by the subduction and closure of the Jinshajiang oceanic crust on the basis of sedimentary characteristics and basin evolution.The sedimentary associations are mostly made up of flysch,and the material was derived mainly from the recycled orogens.For example,the Qugasi Formation is characterized by the alternating fan delta and platform carbonate sediments;the material on fan deltas,in turn,was derived from the recycled orogens in the upwarping area on the passive continental margins.The Tumugou Formation is well represented by a number of submarine fans;the material was derived dominantly from the active margins of the recycled orogens.Three stages of evolution have been distinguished,including:(1) the closure of the Jinshajiang oceanic basin,when the Early and Middle Triassic passive marginal sediments in the Yidun foreland basin evolved into the basin basement sediments;(2)the collision and mountain building phase of the Jinshajiang suture zone,when the margin of the basin(e.g.the Lanashan region)was subjected to erosion due to compression giving rise to the upwarping,while the centre of the basin began to descend to receive the denuded sediments,and (3)the formation of the basin thanks to the input of abundant material from the collisional orogenic zones into the basin.