鄂尔多斯盆地西缘羊虎沟组物源区分析

Provenance Analysis of Yanghugou Formation in the Western Margin of Ordos Basin, China

鄂尔多斯盆地西缘羊虎沟组物源特征对天然气勘探尤为重要。通过砂岩的碎屑组分、岩屑组分、重矿物组合以及石英阴极发光等研究,认为研究区羊虎沟组受到北部、西南部、南部物源控制,各个方位物源在研究区中部吴忠—马家滩地区汇合。通过砂岩轻、重矿物组合和碎屑组分的Dickinson三角图解,以及泥岩的稀土元素特征等分析,认为研究区羊虎沟组源岩以大陆上地壳岩石为主。研究区北部砂岩物源区为再旋回造山带物源区,泥岩球粒陨石标准化稀土元素配分模式与阿拉善古陆浅变质岩相似,具有亲缘性;西南部及南部砂岩物源区为稳定陆块区和再旋回造山带物源区,泥岩球粒陨石标准化稀土元素配分模式与祁连—北秦岭造山带中浅变质岩相似。综上所述,研究区北部母岩主要为阿拉善古陆的浅变质岩夹少许火山岩,西南部及南部母岩主要为祁连—北秦岭造山带的中浅变质岩,其次为碳酸盐岩和火山岩。

The provenance characteristics of Yanghugou Formation in the western margin of Ordos Basin is particularly important for natural gas exploration. Through the studies on clastic components, lithic components, heavy mineral combination and quartz cathodoluminescence (CL) of sandstones, it is believed that Yanghugou Formation is controlled by the provenances in the north, southwest and south of the study area, which meet at Wuzhong-Majiatan area in the middle of the study area. Through the analysis on light and heavy mineral combination, Dickinson triangle diagram of debris components of sandstones, and rare earth element (REE) characteristics of mudstones, it is believed that the source rocks of Yanghugou Formation in the study area are dominated by continental crust rocks. The north sandstone provenance is a recyclic orogenic belt, the chondrite-normalized REE pattern of mudstone is similar to that of Alashan paleocontinental metamorphic rock;the southwest and south provenances are stable land masses and recyclic orogenic belts, the chondrite-normalized REE pattern of mudstone is similar to that of the shallow metamorphic rocks in Qilian-North Qinling orogenic belt. In conclusion, the parent rock in the north of the study area is mainly a shallow metamorphic rock with a small volcanic rock in Alashan paleocontinent, and the parent rocks in the southwest and south are mainly the medium-shallow metamorphic rocks in Qilian-North Qinling orogenic belt, followed by carbonate and volcanic rocks.