摘要
羌塘盆地是中国海相中一上侏罗统最为发育的地区.本文对采自北羌塘盆地雁石坪地区侏罗系雁石坪群的沉积岩样品开展了系统热退磁和岩石磁学研究,其结果表明,中侏罗统雀莫错组(上、下段)主要载磁矿物为磁铁矿和赤铁矿;布曲组的主要磁性矿物是细颗粒磁铁矿;夏里组磁性矿物以磁铁矿为主;上侏罗统索瓦组以磁铁矿为主要载磁矿物.布曲组NRM远远高于其余各组(平均值为2.2×10^(-4)A/m)、索瓦组NRM次之(平均值为4.4×10^(-5)A/m)、雀莫错组和夏里组样品的NRM基本相当(平均值为2.2~2.4×10^(-5)A/m).本文认为细颗粒磁铁矿含量的增加可能是布曲组的NRM平均值远远高于索瓦组的主要原因,并且自生磁性矿(如针铁矿、铁的硫化物等)可能是引起布曲组、索瓦组NRM大于的雀莫错组和夏里组的原因之一.通过本研究与古水深和沉积相变化的对比分析,认为雁石坪地区中-上侏罗统磁性矿物组合变化主要受该区沉积环境变化的控制.本研究首次系统报道了羌塘盆地侏罗系雁石坪群各组的磁性矿物组成和组合规律,这将为羌塘盆地侏罗纪高精度磁性地层年代序列的建立以及特提斯沉积一构造演化等研究提供重要的依据.
Qiangtang Basin is the most developed regions for middle - Late Jurassic marine strata in China. In this study, we have developed the system thermal demagnetization and the rock magnetism research for the sedimentary rock samples of Jurassic Yanshiping Group which collected from Yanshiping area, Northern Qiangtang Basin. The results show that： The main magnetic minerals of Quemocuo Formation （lower member, upper member） performed as coexistence of magnetite and hematite. And it is expressed as mainly to small particles magnetite in Buqu Formation. In Xiali Formation, the magnetic minerals showed mainly to magnetite. In Suowa Formation, the magnetic minerals showed as magnetite^based. In addition, the average value of NRM in Buqu Formation （ 2. 2 X 10-4 A/ m, ） was significantly higher than it in Quemocuo Formation, Xiali Formation and Suowa Formation （an average value of 2.2 ~2. 4 X 10-s A/m, 4. 4 X 10-5 A/m）, and we believe that the increase in the content of small particles magnetite may be the main reason which caused that the average value of NRM in Buqu Formation is much higher than Suowa Formation, and the authigenic magnetic mineral （such as goethite, iron sulfide, etc. ） may be one of the reasons which caused the NRM of Buqu Formation and Suowa Formation is higher than Quemocuo Formation and Xiali Formation. By analysis of the magnetic mineral assemblages Changes and the ancient water depth and sedimentary faces changes for the Middle-Late Jurassic Yanshiping Group in Yanshiping area, we found a good correspondence between the two of them, and indicating that the magnetic mineral changes in Yanshiping Group is mainly controlled by the sedimentary environment changes of Yanshiping area. Among them, there is a good correspondence between the magnetite＇s and maghemite＇s cycle changes and the secondary ancient water depth changes in Xiali Formation. And in the upper member of Xiali Formation, the arid paleoclimate changes directly affect the changes of magnetite and maghemite. The result
出处
《地球物理学进展》
CSCD
北大核心
2015年第2期571-580,共10页
Progress in Geophysics
基金
国家973重点基础研究发展计划项目(2011CB403000
2013CB956400)
中国科学院战略性先导科技专项(XDB03020402)的联合资助
关键词
岩石磁学
雁石坪群
侏罗系
沉积环境
北羌塘盆地
rock magnetic
Yanshiping group
Jurassic
sedimentary environment~ northern Qiangtang Basin
