摘要
古纬度演化可以为地质历史时期古气候变化以及构造变形过程等提供宏观的构造位置背景。加强青藏高原中北部可可西里盆地的古纬度研究,对于理解青藏高原中北部的构造抬升过程历史以及机制、阐明东亚季风起源和演化与高原隆升变形的耦合关系、探讨可可西里盆地晚始新世孢粉所指示的干旱气候的动力机制等具有重要的意义。笔者等选取青藏高原腹地研究相对薄弱的可可西里盆地的一个次级沱沱河盆地(TTHC剖面)作为研究对象开展了古地磁研究,重建其在新生代的古纬度演化历史。岩石磁学研究表明TTHC剖面的主要载磁矿物是磁铁矿和赤铁矿,但以赤铁矿为主。与同期(约35 Ma)欧亚极期望磁倾角以及研究区西边乌兰乌拉湖地区的火山岩磁倾角对比,TTHC剖面所记录的磁倾角存在明显的浅化现象,经E/I方法校正后,得到在约35 Ma的古地磁方向为Dec=358.5°,Inc=44.4°,a95=5.7°。综合已发表的贡觉盆地、改则盆地、尼玛盆地、囊谦盆地、下拉秀盆地和乌兰乌拉湖火山岩等古纬度数据以及本文的研究结果,得到沱沱河盆地新生代古纬度演化历史(以TTHC剖面坐标为参考点),沱沱河盆地在约35 Ma古纬度为26.1°N,处于副热带高气压气候带内,可以解释孢粉和岩性所指示的暖干气候。在约24 Ma沱沱河盆地到达现在的纬度位置,盆地上地壳缩短在约24 Ma减小或者停止。
Objectives:Paleolatitude evolution could provide a general paleo location framework for explaining the paleoclimate change and tectonic deformation in geological time.Strengthening the paleolatitude study of the Hoh Xil Basin in the north—central Qinghai-Xizang(Tibetan) Plateau is important for understanding the history and mechanism of the tectonic uplift process in the north—central Qinghai-Xizang(Tibetan) Plateau,elucidating the coupling relationship between the origin and evolution of the East Asian monsoon and the uplift and deformation of the plateau,and exploring the dynamics of the arid climate indicated by the Late Eocene sporulation in the Hoh Xil Basin.In this paper,we choose a sub-basin of the Hoh Xil Basin,Tuotuohe Basin( TTHC) as the target for paleomagnetic research and reconstructing its paleolatitude evolution history during the Cenozoic.Methods:Samples from the TTHC are got every 1 meter.Typical samples are selected for rock magnetic experiments,and carriying out stepwise thermal demagnetization experiments on the paleomagnetic specimens collected in TTHC.The inclination of data is corrected by the E—I test.Results:Rock magnetism indicates that the carrier minerals are magnetite and hematite,while hematite is the main carrier mineral.The paleomagnetic result indicates that there is an evident shallowness in inclination in TTHC when comparing with the expected inclination of the Eurasian pole at ~ 35 Ma and the volcanic inclination in Wulanwula Lake,which locates at the western of our section.After E/I adjustment,the paleomagnetic direction at~35 Ma in TTHC is Dec=358.5°,Inc=44.4°,a 95=5.7° and the paleolatitude is 26.1°N.Conclusions:After synthesizing the paleolatitude results from Gongjue Basin,Gaize Basin,Nima Basin,Nangqiang Basin,Xialaxiu Basin and Wulanwula Lake and this study,we get the paleolatitude evolution history of the Tuotuohe Basin during the Cenozoic( the reference point is TTHC).Paleolatitude results indicate that the Tuotuohe Basin located at 26.1° at 35 Ma and the climate is controlled by the sub-tropical high pressure belt,which could explain the arid climate suggested by the pollen and lithology.At 24 Ma,Tuotuohe Basin gets to present latitude and the surface crustal shortening ceased or reduced.
作者
李乐意
常宏
关冲
LI Leyi;CHANG Hong;GUAN Chong(State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an,710061;Xi’an Institute for Innovative Earth Environment Research,Xi’an,710061;CAS Center for Excellence in Quaternary Science and Global Change,Xi’an,710061;Xi’an Center of Geological Survey(Northwest China Center of Geoscience),China Geological Survey,Xi’an,710054)
出处
《地质论评》
CAS
CSCD
北大核心
2022年第5期1801-1817,共17页
Geological Review
基金
国家自然科学基金资助项目(编号:42102023)
第二次青藏高原科考项目(编号:2019QZKK0707和2019QZKK0704)
中国科学院战略先导B项目(编号:XDB40010100)
黄土与第四纪地质国家重点实验室开放基金项目(编号:SKLLQGPY1804,SKLLQG2030和SKLLQG2121)的成果。
关键词
青藏高原
沱沱河盆地
新生代
古纬度
气候
地壳缩短
Qinghai—Xizang(Tibetan)Plateau
Tuotuohe basin
Cenozoic
paleolatitude
climate
crustal shortening
