喀喇昆仑河尾滩地区中三叠统上河尾滩组下段细碎屑岩地球化学特征及意义

Geochemical Characteristics and Signatures of Microclasitcrocks from the Lower Member of Upper Heweitan Formation at Heweitan Area of Karakoram

中三叠统上河尾滩组出露于西昆仑河尾滩地区,为一套碎屑岩夹灰岩、硅质岩沉积地层。为明确该地层源区风化强度、物源性质、沉积环境、大地构造背景及沉积环境,对其开展岩石主量及微量元素分析测试。依据其主量元素特征,绝大多数粉砂岩样品归为砂屑砂岩;样品具有高的ΣREE含量(166. 29×10-6~216. 68×10-6,平均176. 45×10-6),PAAS标准化后显示:相对亏损LREE,富集HREE,Eu正异常,Ce弱负异常;与UCC对比,样品弱富集大离子亲石元素,弱富集高场强元素,亏损过渡族元素。样品具有高的ICV值、低的CIA值及PIA值,指示其为初次循环沉积,且源区风化强度低;物源判别图解显示样品的物源主要为长英质物质,包含少量中性及基性物质;构造背景判别图解指示构造背景为弧环境。沉积环境为海相还原环境,该时期气候为半干旱气候。

The lower member of Upper Heweitan Formation of Middle Triassic,cropping out in Heweitan Area of Karakoram consists of a set of clasitc rock interbedding with limestone and silicite.Major and trace elements analysis were employed to identify the weathering intensity of the provenance,sources nature,geotectonic setting and depositional environment.The majority of the samples were classified as arenite according to the characteristics of major elements.ΣREE contents of the samples are 166.29×10-6-216.68×10-6(avg.200.10×10-6),the pattern of REE are characterized by LREE depletion,HREE enrichment,positive Eu abnormity and weakly negative Ce abnormity with respect to PAAS.Compared with UCC,samples are enriched in LILEs,weakly enriched in HFSEs and depleted in transitional elements.ICV values of microclastirocks are high,which imply the source materials are mainly first recycled sediments,CIA values and PIA values are relatively low,which suggest that the weathering intensity of provenance is low.Element analysis indicates that felsic rocks serve as the main source rocks,including small amounts of intermediate and basic materials;geotectonic setting belongs to arc;sedimentary environment is reducing marine environment and paleo-climate is semiarid.