荥经-峨眉地区上三叠统物源变化及对扬子板块西缘构造活动的启示  

The provenance change within the Upper Triassic in Yingjing and Emei region and its implications for the tectonic activities of the western margin of the Yangtze Block

作　　者：田亚杰 魏国齐[1] 杨威[1] 金惠[1] 周国晓 白壮壮 TIAN YaJie;WEI GuoQi;YANG Wei;JIN Hui;ZHOU GuoXiao;BAI ZhuangZhuang(Research Institute of Petroleum Exploration and Development,PetroChina,Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《岩石学报》2024年第8期2538-2556,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(U22B6002);中国石油天然气股份有限公司项目(2021DJ0605)联合资助。

摘　　要：碎屑岩物源研究是当今地质学研究的热点,利用多种物源研究方法可以全面揭示碎屑岩的源岩信息,揭示源区构造古地理格局的变化。三叠纪期间,扬子板块西缘由被动大陆边缘转变为挤压构造带,引起了显著的古地理格局和沉积体系的变化,但目前对这一转变过程仍缺乏研究。本文综合利用砂岩颗粒成分统计、电子探针测试重矿物成分和碎屑锆石U-Pb年龄方法,研究了荥经-峨眉地区上三叠统碎屑岩物源转变时间,并结合其他地区物源研究探讨了扬子板块西南缘的物源变化过程。结果显示,上三叠统马鞍塘组的砂岩主要由石英和长石组成;电气石主要来自贫锂的花岗岩类和相关伟晶岩、细晶岩,其次来自富铝贫钙变质碎屑岩;铬尖晶石来自具有洋岛和大火成岩省背景的基性-超基性火山岩;碎屑锆石U-Pb年龄的主要分布在730~850Ma范围内。上三叠统须家河组的砂岩由石英、岩屑和长石组成,具有再旋回造山带物源;电气石大部分来自富铝贫钙、贫铝贫钙的变质碎屑岩,小部分来自贫锂的花岗岩类和相关伟晶岩、细晶岩;铬尖晶石主要来自具岛弧背景的橄榄岩;碎屑锆石U-Pb年龄主要分布在200~300Ma、400~500Ma、650~850Ma、1750~1950Ma和2400~2600Ma年龄段。综合分析表明,马鞍塘组的物源为康滇构造带的新元古代花岗质结晶基底,并包含少量新元古代中酸性火山岩、变质碎屑岩和二叠纪基性-超基性火山岩;须家河组的物源包括松潘-甘孜褶皱带的三叠系浊积岩、花岗岩类以及龙门山断裂带的上古生界碎屑岩与新元古界基底。马鞍塘组与须家河组之间的物源转变,表明扬子板块西缘的松潘-甘孜褶皱带和龙门山断裂带取代康滇构造带成为新的地貌高部位和主要剥蚀区,这一古地理格局的转变发生于马鞍塘组沉积之后,即晚三叠世的卡尼期与诺利期之间或诺利期期间。Sandstone provenance analysis is a hot topic in Geosciences today.Combined multiple provenance analysis methods could reveal abundant information of the source rocks and reflect regional tectonic and paleogeographic changes of the source region.The western margin of the Yangtze Block transferred from a passive margin to a compressional structural boundary during the Triassic,resulting in significant change of regional paleogeography and depositional system.The process of this transition is not well studied by current research.In this paper,sandstone modal petrography,electron microprobe analysis of heavy mineral composition and detrital zircon U-Pb geochronology are utilized to study the provenance change time of the Upper Triassic clastic sedimentary rocks in Yingjing and Emei sections and the provenance change time of the Upper Triassic rocks in southwestern margin of the Yangtze Block is discussed combined with earlier provenance studies of this region.The result shows that for Upper Triassic Maantang Formation,the sandstones are mainly composed of quartz and feldspar;the tourmalines are dominantly derived from Li-poor granitoids,pegmatites and aplites and subordinately from aluminous metapelites and metapsammites;the source rocks for the chromian spinels are mafic-ultramafic extrusive rocks in large volcanic province and oceanic island;the U-Pb ages of detrital zircons are confined in a narrow range of 730~850Ma.For the Upper Triassic Xujiahe Formation,the sandstones are composed of quartz,rock fragment and feldspar,with recycled orogen sources;the compositions of tourmaline indicate derivation mainly from metapelites,metapsammites and subordinately from Li-poor granitoids,pegmatites and aplites;the chromian spinels are from peridotites in island arc and middle oceanic ridge,with a few grains from basic-ultrabasic extrusive rocks in oceanic island and large volcanic province;detrital zircon U-Pb ages are clustered within ranges of 200~300Ma,400~500Ma,650~850Ma,1750~1950Ma and 2400~2600Ma.Comprehensive provena

关 键 词：扬子板块西南缘 晚三叠世 物源变化 龙门山断裂带 松潘-甘孜褶皱带 康滇构造带 

分 类 号：P575.1[天文地球—矿物学] P588.212[天文地球—地质学] P597.3