拉萨-羌塘地体碰撞时间新认识-来自羌塘盆地古地磁年代学的证据  

Magnetostratigraphy and Biostratigraphy of the Jurassic sedimentary sequences,Qiangtang Basin,revealed the initial time of the Lhasa–Qiangtang collision

作　　者：曾永耀 郭东宝 Zeng Yong-Yao;Sun Chong-Hui(Lanzhou Resources&Environment Voc-Tech University,Lanzhou 730000,China;Key Laboratory of Western China’s Mineral Resources(Gansu Province),Lanzhou University,Lanzhou 730000,China)

机构地区：[1]兰州资源环境职业技术大学,兰州730000 [2]甘肃省黄河上游战略性矿产资源重点实验室,兰州730000

出　　处：《Applied Geophysics》2023年第4期572-591,673,共21页应用地球物理（英文版）

基　　金：supported by National 973 Basic Research Program of China(No.2011CB403003).

摘　　要：青藏高原从北到南由松潘甘孜可可西里地体、羌塘地体和拉萨地体组成,上述地体的碰撞过程涉及到特提斯洋的开合演化和陆陆碰撞等科学问题。例如,班公湖-怒江特提斯洋的闭合以及青藏高原从洋盆抬升为陆地等的时间和过程,其中拉萨-羌塘地体的碰撞时间和过程尤为关键。在羌塘盆地北部,拉萨-羌塘地体的碰撞过程被雁石坪群上段的夏里组和索瓦组地层所记录,此前虽然我们建立了羌塘盆地雁石坪剖面夏里组和索瓦组的磁性地层,由于在上述两组地层中没有发现标准化石,故而不能通过古生物年代来约束其古地磁年代,这就限制了对上述科学问题的理解。最近,Yin(2016)根据菊石化石,给出了索瓦组较为可靠的古生物年代,也结束了索瓦组古生物年代的长期争议。这一成果,为我们给出夏里组和索瓦组的古地磁年代,提供了重要的古生物年代约束。鉴于此,本次研究重新梳理了夏里组和索瓦组的菊石、双壳、孢粉等古生物地层,重新厘定了夏里组和索瓦组的古生物年代,在此基础上约束出夏里组和索瓦组的古地磁年代,其年代分别为~164.0-160.2 Ma和160.2-156.8 Ma。除此之外,结合前人对上覆地层的U-Pb定年,揭示拉萨地体与羌塘地体的碰撞时间约为~156.8-154.9 Ma。The Qiangtang Basin,located in the Tibetan Plateau,is an appropriate area to verify the Lhasa–Qiangtang collision,which was recorded by the middle-upper part of the Yanshiping Group(the Xiali and Suowa Fms)in the basin.However,the chronology of the Xiali and Suowa Fms is HYPERLINK"javascript:;"controversial,which limits comprehending the timing of the Lhasa–Qiangtang collision.More importantly,HYPERLINK"javascript:;"oil HYPERLINK"javascript:;"shale and salt springs were exposed in the Xiali and Suowa Fms in the basin.544 paleomagnetic samples were collected from the Yanshiping section in the basin in order to reveal the timing of the Lhasa–Qiangtang collision from the view of paleomagnetic ages of the two formations.However,we did not give credible magnetostratigraphic ages of the two formations because of ammonite fossils,a global primary standard for the Jurassic strata correlation,without being found in the last study.Yin(2016)revised the longterm HYPERLINK"javascript:;"controversial paleontological age of the Suowa Fm.from a Tithonian age of the Late Jurassic or a Berriasian age of the Early Cretaceous,to a Middle Bathonian–Middle Callovian age of the Middle Jurassic based on new ammonite fossils.Considering ammonite fossils as a powerful tool and a global primary standard for the Jurassic strata correlation,we attempted to correlate the last magnetostratigraphy with the GPTS 2012 again.Magnetostratigraphic ages of 164.0–160.2 Ma and 160.2–156.8 Ma for the Xiali and Suowa Fms are suggested,respectively.The timing of the Lhasa–Qiangtang collision(156.8–154.9 Ma)is revealed from the magnetostratigraphic ages and the zircon U–Pb age of the Xueshan Fm,154.9(+6.8/−1.6)Ma,overlying the Suowa Fm in the Yanshiping section.

关 键 词：古地磁年代 古生物地层 羌塘盆地 拉萨-羌塘地体 碰撞 

分 类 号：P318.44[天文地球—固体地球物理学] P597.3[天文地球—地球物理学] P542