基于主微量元素与风化指标的砂岩物源构造演化研究——以平山湖盆地为例

Study on the Evolution of Sandstone Source Structure Based on Major Element Contents and Weathering Indicators—A Case Study of Pingshanhu Basin

摘要: 以河西走廊北缘平山湖盆地早白垩世庙沟群砂岩为研究对象，通过主量元素、微量元素及稀土元素地球化学测试，结合化学风化指标、构造环境与物源区判别图解，系统分析沉积物化学风化程度、物源属性及构造背景。结果显示：研究区砂岩CIA值集中于50~78，整体为弱–中等化学风化，风化过程受钾长石分解控制，指示沉积期气候温和、沉积速率较快；物源以中酸性长英质火成岩为主，含少量再旋回石英质沉积岩组分，排除基性火山岩为主要物源；构造环境以活动大陆边缘与大陆岛弧为核心，兼具被动大陆边缘特征，无大洋岛弧物源输入。研究结果为平山湖盆地早白垩世沉积–构造演化及西北陆相盆地对比研究提供关键地球化学依据。

Abstract: Taking the Early Cretaceous Miaogou Group sandstones in the Pingshanhu Basin on the northern margin of the Hexi Corridor as the research object, systematic analyses of chemical weathering intensity, provenance properties and tectonic setting were carried out based on major, trace and rare earth element geochemical data, combined with weathering indices and tectonic-provenance discrimination diagrams. The results show that the CIA values of the sandstones range mainly from 50 to 78, indicating weak to moderate chemical weathering controlled by K-feldspar decomposition, which reflects a warm climate and rapid sedimentation rate during the deposition period. The provenance is dominated by intermediate-felsic igneous rocks with minor recycled quartzose sedimentary components, and basic volcanic rocks are excluded as the main source. The tectonic setting is characterized by active continental margin and continental island arc with some passive continental margin affinity, and no oceanic island arc source is identified. This study provides key geochemical evidence for the Early Cretaceous sedimentary-tectonic evolution of the Pingshanhu Basin and the correlation of continental basins in Northwest China.