鄂尔多斯盆地本溪组沉积物物源探讨及其构造意义

Sediment Provenance Analysis and Tectonic Implication of the Benxi Formation, Ordos Basin

鄂尔多斯盆地在经历了古生代抬升剥蚀之后,在晚古生代晚期开始沉降并沉积了海陆过渡相本溪组碎屑岩.为阐明该套碎屑岩的物源体系特征,基于露头、岩芯、分析化验等多种分析测试手段,分析了本溪组砾岩分布、轻矿物碎屑组分、石英阴极发光、重矿物特征及碎屑锆石U-Pb年龄分布特征,识别了本溪组平面上不同物源体系,继而确定了不同物源体系的母岩类型及本溪组沉积时期盆地南部构造演化特征;研究表明本溪组沉积时期,鄂尔多斯盆地整体南北双向供源,其中北部物源供给相对较强,进一步划分为四个子物源体系,西北物源母岩主要为变质岩和少量火山岩,东北部地区母岩主要为酸性侵入岩,西南部地区物源主要为高级变质岩、部分岩浆岩和少量沉积岩,东南部地区主要为高级变质岩.同时在本溪组沉积时期,南部物源影响范围可达盆地中部地区,北秦岭陆块该时期已与华北板块南缘发生碰撞是南部物源体系重要组成部分.

The Ordos Basin experienced uplift and bending in the Paleozoic,then started to subside and deposit the sea-land transition phase clastics of the Benxi Formation.Data from outcrops,cores and various analytical testing tools were used to clarify the provenance of the Benxi Formation,including conglomerate distribution,light mineraldebris component,quartz cathodoluminescence,heavy mineral suites,stability coefficient and zircon ages.Differentprovenance systems were recognized from consistent source-rock types from different sources,as well as the tectonic evolutionary history of the southern part of the basin.The study revealed two main provenance systems,which were further subdivided into four systems,two in the northern basin and two in the south.The northern provenance supply ability was found to be greater than in the south.The source rocks of the NW provenance were metamorphics,together with a small amount of volcanic rocks.The NE source rocks were acidic intrusives.The SW source rocks were highgrade metamorphics,with some magmatic rocks and a small proportion of sedimentary rocks.The SE source rocks were high-grade metamorphics.During deposition of the Benxi formation,the southern provenance extended as far as the center of the basin.A main component of the southern provenance system at that time was the collision of the North Qinling terrace and the North China Block.