Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone,Tibet and its tectonic implications  

作　　者：ZHU Jie1,2, DU Yuansheng1, LIU Zaoxue2, FENG Qinglai1, TIAN Wangxue2, LI Jinping2 & WANG Changping2 1. Faculty of Earth Sciences,China University of Geology, Wuhan 430074, China 2. Hubei Institute of Regional Geology Survey, Wuhan 430034, China 

出　　处：《Science China Earth Sciences》2006年第4期348-357,共10页中国科学（地球科学英文版）

基　　金：sponsored by Regional Geology Survey of Lhaze County Sheet(1:250000)(Grant No.19991300009221);the National Natural Science Foundation of China(Grant No.40372061).

摘　　要：Three radiolarian fauna, aged as the Middle-Late Triassic, Late Jurassic-Early Creta- ceous and Cretaceous radiolarian fauna, have been recognised in the radiolarian cherts from the middle sector of the Yarlung Zangbo suture zone, southern Tibet, China. The average contents of SiO2 in the radiolarian cherts of the Middle-Late Triassic and Late Jurassic-Early Cretaceous are 90.24% and 92.58% respectively, with average ratios of Al/(Al+Fe+Mn) as 0.75 and 0.74 respectively, the average ratios of MnO/TiO2 as 0.36 and 1.24, the average ratios of Ce/Ce* as 1.15 and 1.03, and the average ratios of LaN/CeN as 0.85 and 0.93. These geochemical features indicate that both of them are biogenic, deposited in a continental margin basin. The SiO2 content of the Early Cretaceous radiolarian chert is 94.12%, with the ratio of Al/(Al+Fe+Mn) as 0.59, ratio of MnO/TiO2 as 4.30, ratio of Ce/Ce* as 0.60, ratio of LaN/CeN as 1.59, which imply that the chert is biogenic and was deposited in a pelagic basin. The Middle-Late Triassic association of the radiolarian chert and turbidites as well as their geochemical characteristics indicates the existence of a strong rifting marginal basin in the belt of the Yarlung Zangbo River then. The association of radiolarian chert and bedded basalt indicate an initial Tethyan ocean basin in southern Tibet during the Late Jurassic-Early Cretaceous. The early Cretaceous radiolarian chert coexisting with pillow basalt in top of the ophiolite suite represents sediments from the oceanic Tethyan basin.Three radiolarian fauna, aged as the Middle-Late Triassic, LateJurassic-Early Cretaceous and Cretaceous radiolarian fauna, have been recognised in the radiolariancherts from the middle sector of the Yarlung Zangbo suture zone, southern Tibet, China. The averagecontents of SiO_2 in the radiolarian cherts of the Middle-Late Triassic and Late Jurassic-EarlyCretaceous are 90.24% and 92.58% respectively, with average ratios of Al/(Al+Fe+Mn) as 0.75 and 0.74respectively, the average ratios of MnO/TiO_2 as 0.36 and 1.24, the average ratios of Ce/Ce~* as1.15 and 1.03, and the average ratios of La_N/Ce_N as 0.85 and 0.93. These geochemical featuresindicate that both of them are biogenic, deposited in a continental margin basin. The SiO_2 contentof the Early Cretaceous radiolarian chert is 94.12%, with the ratio of Al/(Al+Fe+Mn) as 0.59, ratioof MnO/TiO_2 as 4.30, ratio of Ce/Ce~* as 0.60, ratio of La_N/Ce_N as 1.59, which imply that thechert is biogenic and was deposited in a pelagic basin. The Middle-Late Triassic association of theradiolarian chert and turbidites as well as their geochemical characteristics indicates theexistence of a strong rifting marginal basin in the belt of the Yarlung Zangbo River then. Theassociation of radiolarian chert and bedded basalt indicate an initial Tethyan ocean basin insouthern Tibet during the Late Jurassic-Early Cretaceous. The early Cretaceous radiolarian chertcoexisting with pillow basalt in top of the ophiolite suite represents sediments from the oceanicTethyan basin.

关 键 词：RADIOLARIAN chert  SEDIMENTARY geochemistry  Mesozoic  Yarlung Zangbo SUTURE zone  Tibet. 

分 类 号：Q915[天文地球—古生物学与地层学]