摘要
南羌塘坳陷三叠系与侏罗系地层之间存在广泛的沉积间断,针对这一时期地层的研究对于南羌塘盆地在该时期的沉积环境以及构造演化具有重要意义。笔者等以南羌塘坳陷内上三叠统—下侏罗统索布查组碳酸盐岩的地球化学元素为对象进行相关分析。剔除陆源组分影响之后利用微量元素对碳酸盐岩进行沉积环境分析显示索布查组碳酸盐岩沉积时处于氧化环境,且地层由下往上水体逐渐变深,盐度逐渐增加,且研究区在当时处于炎热干燥的气候环境下。碳酸盐岩中的REE含量主要受陆源组分的影响,Ce与Eu主要反映的是陆源碎屑的特征。Ce的负异常反映陆源碎屑源岩沉积时为氧化环境,Eu的正异常主要来自含长石碎屑岩的风化淋滤导致。根据样品中与陆源碎屑相关的稳定元素特征结合区域地质调查推断陆源碎屑源岩为研究区北部中央隆起带附近的上三叠统土门格拉组地层。土门格拉组地层由于南、北羌塘地块汇聚隆升而成为索布查组碳酸盐岩中陆源碎屑的来源,之后南羌塘坳陷开始拉伸,索布查组碳酸盐岩开始沉积,其形成表示南羌塘坳陷开始进入被动大陆边缘沉积的演化阶段。
Objective:Sedimentary discontinuities exist between almost all of the Triassic and Jurassic stratas in the South Qiangtang Depression.The research on the stratas in this period has great significance to the sedimentary environment and its evolution.In this paper,the sedimentary environment and evolution characteristics of the study area are discussed by the analysis of the geochemical elements of the carbonate rocks of Upper Triassic—Lower Jurassic.Methods:The sedimentary environment of the rock was analyzed by the ratio value of V/Cr,Ni/Co,Sr/Ba,1000×Sr/Ca,Sr/Cu et al.The source of REEs was analyzed by using the correlation betweenΣREE and the content of Al_(2)O_(3),Ti,Zr,CaO,Na_(2)O and Sr;the tectonic background of the provenance area were analyzed by using La—Th—Sc and Th—Sc—Zr/10 diagrams;the source of carbonate terrigenous clastic material were analyzed by using chondrite standardized pattern map of REE andΣREE—La/Yb diagrams.Results:Through the elemental analysis of Sobucha carbonate rocks in the Upper Triassic—Lower Jurassic.After removing the influence of terrestrial components,the V/Cr value is distributed in 0.04~0.47,the Ni/Co value is distributed in 0.16~5.38,the Sr/Ba value is distributed in 101.33~277.45,and the 1000×Sr/Ca value is distributed in 1.30~1.82,the Sr/Cu averate value is more than 10.TheΣREEs have positive correlation with Al_(2)O_(3),Ti and Zr,but have no correlation with CaO,Na_(2)O and Sr.The Ce andδCe have positive correlation with Al,the correlation coefficients are 0.98 and 0.77 but have no correlation with Ca.The Eu also have positive correlation with Al,K,the correlation coefficients are 0.93 and 0.88.Conclusion:The Suobucha carbonate rocks were deposited in an oxidative environment,the paleo-salinity of the sedimentary water gradually increased,and the paleo-water depth also gradually increased.Rare earth elements are mainly derived from feldspar-bearing terrigenous clastic components.The Ce negative anomaly is related to the oxidative environment during the deposition of terrigenous clastic source rocks,and the Eu positive anomaly may be caused by the weathering and leaching of feldspar-bearing source rocks.The La—Th—Sc and Th—Sc—Zr/10 diagrams show that the terrigenous detrital components have the tectonic setting of continental island arcs.The chondrite normalized model of REE and theΣREE—La/Yb diagrams show that the terrigenous detrital components were mainly from the same sedimentary rocks.Combining the tectonic evolution and regional stratigraphic characteristics of the Qiangtang Basin,it is inferred that the source area of terrigenous clasts in the carbonate rocks is the Upper Triassic Tumengla Formation near the Central Uplift Belt,and the continental island arc structural background characteristics of terrigenous clasts are inherited in the clastic rocks of the Tumengla Formation.The Sobucha carbonate rock should be a sign of the expansion of the Bangong Lake—Nujiang ocean basin,and its formation indicates that the South Qiangtang Depression has entered the evolutionary stage of passive continental margin deposition.
作者
谭梅
季长军
周冰洋
康少伟
TAN Mei;JI Changjun;ZHOU Bingyang;KANG Shaowei(Chongqing Natural History Museum,Chongqing,400700;Chinese Academy of Geological Sciences,Beijing,100081;Hubei Institute of Geosciences,Wuhan,430000;Shaanxi Coal Geology Group Co.Ltd.,Xi’an,710021)
出处
《地质论评》
CAS
CSCD
北大核心
2023年第3期943-958,共16页
Geological Review
基金
中国地质调查局二级项目“羌塘盆地阿木错凹陷油气地质调查项目”(编号:DD20221855)
中国地质调查局二级项目“羌塘北部龙尾错地区油气地质调查”(编号:DD20211343)
陕西省煤田地质集团有限公司科研项目“羌塘重点区块油气地质选区评价”(编号:SCG20211201)
中国地质科学院基本科研业务费项目“羌塘盆地古油藏调查及成藏机理研究”(编号:JKY202209)的成果。
关键词
南羌塘坳陷
晚三叠世—早侏罗世
碳酸盐岩
元素分析
south Qiangtang depression
Late Triassic—Early Jurassic
carbonate rocks
elements analysis
