拉萨地体中部上白垩统达雄组的建立及构造隆升意义

发布时间：2018-08-04 08:51

【摘要】：拉萨地体中部措勤盆地内,呈东西向发育一套厚度巨大(~1800m)的晚白垩世陆相磨拉石沉积建造。通过对研究区内达雄村附近出露较好的虾格子剖面开展详细的测制工作,并将该套地层自底到顶分为5段,依次为中-粗粒砂岩层段、大套砾岩层段、中粒砂岩夹粉砂岩-泥岩层段、大套紫红色与绿色粉砂岩/泥页岩层段以及均质中粒砂岩层段。地层底部与下伏郎山组含圆笠虫灰岩呈沉积不整合关系,顶部被新生代沉积物覆盖。通过岩相组合与沉积结构构造分析研究,认为该套地层形成于冲积扇-辫状河沉积体系。通过地层顶部火山灰夹层和下伏郎山灰岩的圆笠虫化石显示其形成年龄约为98~91 Ma,这与获得的砂岩碎屑最年轻锆石年龄较为一致。砾岩砾石统计结果显示火山岩砾石为其主要成分。砂岩碎屑成分显示以大量火山岩岩屑为主。这些碎屑成分特征表明其主要来自岩浆弧的物源区。结合碎屑锆石U-Pb年代学和Hf同位素数据表明,中拉萨地体上广泛分布的则弄群火山岩可能为其主要的物源区。本文综合该套晚白垩世沉积的时空分布、岩性组合以及物源区特征,将其新命名为"达雄组",并将其与中拉萨地体北侧的竟柱山组对比表明,两者可能共同代表了中拉萨地体在晚白垩世早期(约98~91 Ma)所经历构造隆升,为青藏高原腹地在印度-亚洲大陆碰撞之前隆升提供了地质证据。
[Abstract]:In the Cuoqin basin in the central part of Lhasa, a set of late Cretaceous continental Moralite sedimentary formations with a large thickness of 1800m were developed in the east-west direction. Through the detailed survey of the shrimp lattice section near Daxion Village in the study area, this set of strata is divided from bottom to top into 5 sections, in order of medium coarse sand formation and large conglomerate formation. Medium-grained sandstone intercalated siltstone and mudstone formation, large fuchsia and green siltstone / shale-shale formation and homogeneous medium-grained sandstone formation. There is a sedimentary unconformity relationship between the bottom of the strata and the calcareous limestone of the Lower Volang formation, the top of which is covered by Cenozoic sediments. Based on the analysis of lithofacies assemblage and sedimentary structure, it is considered that this set of strata was formed in alluvial fan-braided stream sedimentary system. The calcareous fossils from the volcanic ash intercalation at the top of the strata and the lower Volang limestone show that the age of formation is about 98 ~ 91 Ma, which is consistent with the youngest zircon age obtained from the sandstone clastic. The statistical results of gravel show that volcanic gravel is the main component. The clastic composition of sandstone shows that a large number of volcanic lithoclasts are dominant. The characteristics of these clastic compositions indicate that they are mainly derived from the provenance of magmatic arcs. Combined with the U-Pb chronology of clastic zircon and HF isotopic data, the volcanic rocks of Zelong Group, which are widely distributed in the Middle Lhasa terrane, may be its main provenance. Based on the space-time distribution, lithologic assemblage and provenance characteristics of the late Cretaceous sediments, this paper has named it "Daxion formation" and compared it with the Jingzhushan formation on the north side of the central Lhasa terrane. The two may jointly represent the tectonic uplift experienced by the Central Lhasa terrane in the early late Cretaceous (about 9891 Ma) and provide geological evidence for the uplift in the hinterland of the Qinghai-Tibet Plateau before the Indo-Asian continental collision.
【作者单位】：河海大学海洋学院;南京大学地球科学与工程学院;
【基金】：国家自然科学基金(批准号41602104,41472081) 江苏省自然科学青年基金(批准号BK20160858) 中央高校业务费(2015B11414)项目共同资助的成果
【分类号】：P534.53;P542

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