Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone, Tibet and its tectonic implications
Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone, Tibet and its tectonic implications
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DOI：
10.1007/s11430-006-0348-y
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发表时间：
2006-03
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通讯作者：
Jie Zhu;Yuansheng Du;Zaoxue Liu;Q. Feng;Wangxue Tian;Jin-Ping Li;Chang-Liang Wang
中科院分区：
文献类型：
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作者：
Jie Zhu;Yuansheng Du;Zaoxue Liu;Q. Feng;Wangxue Tian;Jin-Ping Li;Chang-Liang Wang
中晚三叠世和晚侏罗世—早白垩世放射虫岩中sio2的平均含量分别为90.24%和92.58%，其中Al/(Al+Fe+Mn)的平均比值分别为0.75和0.74，MnO/TiO2as的平均比值为0.36和1.24，Ce/Ce*的平均比值为1.15和1.03，LaN/CeNas的平均比值为0.85和0.93。这些地球化学特征表明两者均为生物成因，沉积于大陆边缘盆地。早白垩世放射虫燧石的sio2含量为94.12%,Al/(Al+Fe+Mn)比值为0.59，MnO/TiO2as比值为4.30，Ce/Ce*比值为0.60，LaN/CeNas比值为1.59，表明该燧石为生物成因，沉积于深海盆地。中晚三叠世放射虫质燧石岩与浊积岩的组合及其地球化学特征表明当时雅鲁藏布江带存在强烈的裂谷边缘盆地。蛇绿岩套顶部的早白垩世放射虫燧石与枕状玄武岩共存，代表了海洋特提斯盆地的沉积物。
Three radiolarian fauna, aged as the Middle-Late Triassic, Late Jurassic-Early Cretaceous 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 SiO2in 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/TiO2as 0.36 and 1.24, the average ratios of Ce/Ce* as 1.15 and 1.03, and the average ratios of LaN/CeNas 0.85 and 0.93. These geochemical features indicate that both of them are biogenic, deposited in a continental margin basin. The SiO2content of the Early Cretaceous radiolarian chert is 94.12%, with the ratio of Al/(Al+Fe+Mn) as 0.59, ratio of MnO/TiO2as 4.30, ratio of Ce/Ce* as 0.60, ratio of LaN/CeNas 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.