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Wan Bo Wu Fuyuan Chen Ling Zhao Liang Liang Xiaofeng Xiao Wenjiao Zhu Rixiang 《中国科学:地球科学(英文版)》2019,62(12):2005-2016
Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past-500 millionyears.These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two.Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethy an Realm.After reappraisal of geological records of the rift,collision and subduction initiation from the surface and various geophysical observations from depth,we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic.The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards,giving birth to new oceans since the Paleozoic.The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions,which would have induced the initiation of oceanic subduction in the Tethyan Realm.Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia.The final disappearance of Neo-Tethy s would have induced collision of the Gondwana-derived continents with the Eurasian continent,giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system.Therefore,the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south,into the terminal in the north.In this regard,the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs. 相似文献
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The subduction of the west Pacific plate and the destruction of the North China Craton 总被引：5，自引：0，他引：5
While a general concensus has recently been reached as to the causal relationship between the subduction of the west Pacific plate and the destruction of the North China Craton, a number of important questions remain to answer, including the initial subduction of west Pacific plate beneath the eastern Asian continent, the position of west Pacific subduction zone during the peak period of decratonization(i.e., Early Cretaceous), the formation age of the big mantle wedge under eastern Asia, and the fate of the subducted Pacific slab. Integration of available data suggests that the subduction of the western Pacific plate was initiated as early as Early Jurrasic and the subduction zone was situated to 2,200 km west of the present-day trench in the Early Creataceous, as a result of eastward migration of the Asian continent over a distance of ca. 900 km since the Early Cretaceous.The retreat of the subducting west Pacific plate started ～145 Ma ago, corresponding to the initial formation of the big mantle wedge system in the Early Cretaceous. The subduction of the Pacific slab excerted severe influence on the North China Craton most likely through material and energy echange between the big mantle wedge and overlying cratonic lithosphere. The evolution history of the west Pacific plate was reconstructed based on tectonic events. This allows to propose that the causes of phases A and B for the Yanshanian orogeny were respectively related to rapid low-angle subduction and to lowering subduction angle of the west Pacific plate. At ca. 130–120 Ma, the subduction of the west Pacific plate was characterized by increasing subducting angle, slab rollback and rapid trench retreat, leading to the final stagnation of the subducting slab within the mantle transition zone. This process may have significantly affected the physical property and viscosity of the mantle wedge above the stagnant slab, resulting in non-steady mantle flows. The ingression of slab-released melts/fluids would significantly lower the viscosity of the mantle wedge and overlying lithosphere, inducing decratonization. This study yields important bearings on the relationship between the subduction of the west Pacific plate and the evolution of the lithospheric mantle beneath the North China Craton. 相似文献
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The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean. 相似文献
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Timing of the Nihewan formation and faunas 总被引：2，自引：0，他引：2
Magnetostratigraphic dating of the fluvio-lacustrine sequence in the Nihewan Basin, North China, has permitted the precise timing of the basin infilling and associated Nihewan mammalian faunas. The combined evidence of new paleomagnetic findings from the Hongya and Huabaogou sections of the eastern Nihewan Basin and previously published magnetochronological data suggests that the Nihewan Formation records the tectono-sedimentary processes of the Plio-Pleistocene Nihewan Basin and that the Nihewan faunas can be placed between the Matuyama-Brunhes geomagnetic reversal and the onset of the Olduvai subchron (0.78-1.95 Ma). The onset and termination of the basin deposition occurred just prior to the Gauss-Matuyama geomagnetic reversal and during the period from the last interglaciation to the late last glaciation, respectively, suggesting that the Nihewan Formation is of Late Pliocene to late Pleistocene age. The Nihewan faunas, comprising a series of mammalian faunas (such as Maliang, Donggutuo, Xiaochangliang, Banshan, Majuangou, Huabaogou, Xiashagou, Danangou and Dongyaozitou), are suggested to span a time range of about 0.8-2.0 Ma. The combination of our new and previously published magnetostratigraphy has significantly refined the chronology of the terrestrial Nihewan Formation and faunas. 相似文献
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主要评述了近年来泥河湾盆地磁性地层学的研究进展,包括建立泥河湾组的磁性地层年代格架、厘定泥河湾动物群的时代和确定华北地区早期人类活动年代序列.研究表明:第一,泥河湾组河湖相沉积序列记录了高斯正极性时末期以来的地磁极性特征(松山和布容极性时),即沉积时代始于约2.6Ma.早期人类至少在1.66～0.78Ma期间的大约90万年的时间内长期持续地占据高纬度的泥河湾盆地.泥河湾动物群(包括广义和狭义)的时代为2.0～0.8 Ma.第二,华北地区早期人类已经能够适应东亚高纬度地区冬季风增强、夏季风减弱和干旱化趋势增强的复杂环境变化,尤其能适应中更新世气候转型前后中国北方多变而且不稳定气候条件和生态环境.因此,气候和生态环境的多变性与不稳定性是促进人类进化的重要因素.第三,早期人类走出非洲以后,可能沿不同的路径并以较快的速度扩散到东亚地区.向南越过印度尼西亚的赤道地区,向北至少扩散到40°N的泥河湾盆地. 相似文献
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No apparent lock-in depth of the Laschamp geomagnetic excursion: Evidence from the Malan loess 总被引：2，自引：1，他引：2
ZHU Rixiang LIU Qingsong PAN Yongxin DENG Chenglong ZHANG Rui & WANG Xianfeng . Paleomagnetism Geochronology Laboratory 《中国科学D辑(英文版)》2006,49(9):960-967
Developing an accurate chronological framework is always a key issue in paleoclimatic studies. Magneto- stratigraphy has been a routine tool for such purposes. However, complexities arise for inter-profile correla- tions of magnetostratigraphy due to effects of the lock-in process. One good example is the “mystery” of the mismatching of stratigraphic locations of the Matuyama/Brunhes boundary (MBB) (occurred at ~780 ka) recorded in Chinese loess and marine sedi- ments. Tauxe et al.[1] con… 相似文献
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40Ar/39Ar method is a high precision dating means, of which the age is obtained by contrasting the un- known sample with those of standards. Usually the age of standard is determined by K-Ar method in which the 38Ar spike should be added for measurement. However, the absolute concentration of 38Ar spike is measured through the calibrated standards in turn, al- though occasionally the concentration of 38Ar spike is determined by other dating methods, such as Rb-Sr, U-Pb methods, which is kn… 相似文献
10.
Wang Fei He Huaiyu Zhu Rixiang Sang Haiqing Wang Yinglan Yang Liekun 《中国科学D辑(英文版)》2006,49(5):461-470
Four international standards, Ga1550, MMhb-1, Lp-6, Bem 4M, and one domestic standard BT-1 have been intercalibrated. The
repeated measurements on MMhb-1 with different mass demonstrate that MMhb-1 is inhomogeneous in age and its average age is
519.8 Ma. The results of Bern 4M and Lp-6 reflect that they have an invariable value of 40Ar*/39Ark (F) and the ages we obtained are consensus with their K-Ar age: Lp-6=127.7Ma; Bern 4M=18.2 Ma. Analyses of BT-1 age spectra,
Ca/K and Cl/K spectra as well as inverse isochrons indicate that the sample is homogeneous and invariable and keeps close
chemically, with its trapped argon isotope composition close to the atmosphere. The dating results show that age values are
reproducible and steady, total fusion age, step-heating age, plateau age and isochron age are in accord with each other within
the error range (2σ). Therefore, we recommend 28.7 Ma as the calibrated age of BT-1.
We also discuss the variation in neutron flux gradients of Beijing 49-2 reactor. It was found that the neutron flux gradient
varies considerably, and more monitors (standard samples) are needed to fix the trend of variation. The coefficient of the
49-2 reactor that transfers the ratio of production rate of 37ArCa/39ArK into Ca/K ratio is 1.78. This is different from that reported earlier, 2.0, which may be caused by the reconstruction of
the reactor. 相似文献