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Tong Y.-B.,Chinese Academy of Geological Sciences | Tong Y.-B.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.,Capital Normal University | Wang H.,Chinese Academy of Geological Sciences | And 4 more authors.
Tectonophysics | Year: 2015

Paleomagnetic studies were conducted on the Eocene and Oligocene strata at the western part of the Chuan Dian Fragment in order to describe the crustal deformation induced by continuous penetration of the Indian plate into Eurasia during the late Cenozoic. High-temperature magnetic components with unblocking temperatures of ~680°C were isolated, and positive fold and/or reversal tests reveal the primary nature of the magnetization. The tilt-corrected site-mean directions obtained from the Oligocene and middle-early Eocene strata are, respectively, Ds =200.9°, Is =-31.3°, k =52.8, α 95 =7.7° and Ds =29.7°, Is =32.0°, k =44.9, α 95 =5.6°. Comparison of these results with previous paleomagnetic data from the Chuan Dian Fragment shows that the western and central parts of the Chuan Dian Fragment experienced ~20° integral clockwise rotation relative to East Asia since the middle Miocene. However, the eastern part of the Chuan Dian Fragment has experienced different rotational deformation relative to East Asia since the Pliocene, because of the intense regional crustal deformation and activity on fault systems. The eastern boundary of the Chuan Dian Fragment was bounded by the Yuanmou-Luezhijiang left lateral strike-slip fault prior to the Pliocene, and then substituted by the Xiaojiang left lateral strike-slip fault since the Pliocene, due to the eastwards spreading of the clockwise rotational movement of the Chuan Dian Fragment. The evolutionary characteristics of the Ailaoshan-Red River and Xianshuihe-Xiaojiang strike-slip faults were controlled by the difference between the clockwise rotational extrusion velocities of the Chuan Dian Fragment and the Indochina Block. © 2015 Elsevier B.V.

Yuan W.,Nanjing University | Yuan W.,Sinopec | Yang Z.,Nanjing University | Yang Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.,Chinese Academy of Geological Sciences
Gondwana Research | Year: 2015

The relationship between the Alashan Terrane and North China is a contentious issue given the discovery of allochthonous detrital zircons in Middle Ordovician flysch sandstones from the southwestern Ordos Margin and the large differences in palaeolatitudes between the North China and Tarim cratons. We have collected a suite of Middle to Late Devonian sedimentary rocks from the Niushoushan Mountains at the southeastern margin of the Alashan Terrane, adjacent to the western margin of the Ordos Basin of the North China Craton (NCC). U-Pb dating and Lu-Hf isotopic studies were carried out on detrital zircons from these rocks. The zircon U-Pb ages define five age populations: 0.4-0.7Ga (peak at 488Ma), 1.0-1.3Ga (peaks at 1001 and 1152Ma), 1.5-1.8Ga, 2.4-2.8Ga (prominent peak at 2506Ma and secondary peaks at 2668 and 2796Ma) and >3.0Ga (peak at 3332Ma). One detrital zircon yielded a Hadean age of 4022±17Ma. Zircons with U-Pb age spectra of 2.4-2.7 and >3.0Ga and their corresponding εHf(t) values are significantly different from those in the NCC, indicating that these detrital zircons are not from the NCC, which implies that the Alashan Terrane was not part of North China until the Middle to Late Devonian. U-Pb age spectra of zircons dated at 1.0-1.3Ga, 2.4-2.7Ga, and >3.0Ga, and their corresponding Hf isotope data, have a strong similarity with zircons from East Gondwana and the South China Craton. © 2013 International Association for Gondwana Research.

Jing X.-Q.,Nanjing University | Yang Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.,Chinese Academy of Geological Sciences | Tong Y.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | And 2 more authors.
Precambrian Research | Year: 2015

The paleogeographic relationship between South China and Australia during the Neoproterozoic is still hotly debated. Although a series of propositions for the close proximity between South China and Australia are suggested, their relative positions are varied. To better constrain the paleoposition of South China, we have carried out a new paleomagnetic study from the Neoproterozoic Liantuo Formation in two localities, Yichang and Changyang, in Hubei province, China. Stepwise thermal demagnetization reveals that a late Cretaceous remagnetization (component 'L', 350-500°C) was removed from most of the samples. A medium component ('M') isolated mainly between 350°C and 600°C, but in some cases with an upper limit of 640°C, yields a mean direction of Dg=59.5°, Ig=64.6°, α95=3.7° in situ; and Ds=81.6°, Is=61.5°, α95=4.1° after tilt correction. A steeper medium-high temperature component, 'B', was separated from 71 specimens with almost the same temperature range of 'M' (Dg=341.3°, Ig=78°, α95=5.6° in situ; and Ds=78.3°, Is=83.8°, α95=6.9° after tilt correction) and is similar to the 'B' component obtained by Evans et al. (2000). In addition, a high temperature component 'H' (Ds=102.5°, Is=62.4°, α95=3.7° after tilt correction) with both reversed and normal polarity was revealed up to 690°C, yielding a pole at 12.7°N, 157.4°E, with dp/dm=4.5°/5.8°. A change of magnetic polarity, with 5 magnetozones defined, is revealed in our sampling section, in which a reversed-normal polarity succession in the upper part of the section may be correlative with that obtained in a section 6.5km away by Evans et al. (2000), demonstrating the primary nature of the 'H' component. Combining our results with those of Evans et al. (2000) yields a grand mean pole from the upper Liantuo Formation at 13.2°N and 155.2°E with A95=5.3°. Considering the distribution of our sampling sites, and together with the results of a detailed recent SIMS U-Pb zircon study on the Liantuo Formation in the Three Gorges area (Lan et al., 2015), an age of 720Ma was assigned to component 'H' and its corresponding pole. After carefully reevaluating the Neoproterozoic apparent polar wander paths (APWP) from Australia and South China, we suggest that the South China block was located to the northwest of Northern Australia during the Ediacaran period. Subsequently, the South China block moved to the northwest of Western Australia through counter-clockwise rotation of the Northern Australian craton at the later time of 550Ma, or in the middle Cambrian. © 2015 Elsevier B.V.

Gao L.,Chinese Academy of Geological Sciences | Yang Z.,Chinese Academy of Geological Sciences | Yang Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Tong Y.,Chinese Academy of Geological Sciences | And 3 more authors.
Journal of Geodynamics | Year: 2015

Cretaceous, Paleogene, and Miocene sandstones were sampled in the Jinggu area to constrain the internal deformation of the Lanping-Simao Terrane of the Indochina Block. The tilt-corrected overall site-mean direction of the middle Cretaceous strata recorded in the Jinggu area is Ds/Is=77.0°/43.0°, with α95=2.9° (N=47), with a positive fold test indicating a primary remanence acquisition. The site-mean direction recorded for the high-temperature component of the Miocene strata is Ds/Is=13.7°/36.0°, with α95=3.3° (n=38). The best-fit linear regressions between regional tectonic lines and rotation degree from each sampled area in the Lanping-Simao Terrane indicate a direct relationship between tectonic rotation and formation of the sinusoidal shape of the Lanping-Simao arcuate structural zone. The large clockwise rotation in the Jinggu area can be subdivided into three periods. During the formation of the sinusoidal shape of the Lanping-Simao Arc, the Jinggu area and the Indochina Block experienced approximately 20° of clockwise rotation. An additional ~40° of clockwise rotation in the Jinggu area was caused by bending of the Chongshan-Lancang-Chiang Mai belt between 27 and 20Ma. After the early Miocene, a significant small-scale internal rotation (8.2±3.2°) adjustment occurred in the Jinggu area. Quantitative comparison between the paleomagnetically determined clockwise rotation and tectonic-metamorphic events suggests that the Lanping-Simao Arc was formed by the west-to-east compression and southeastward extrusion of the Shan-Thai Terrane since 36Ma in southeast Tibet. © 2015 Elsevier Ltd.

Tong Y.-B.,Chinese Academy of Geological Sciences | Tong Y.-B.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.-Y.,Chinese Academy of Geological Sciences | Yang Z.-Y.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | And 6 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

Detailed paleomagnetic and rock magnetic studies were carried out on the Cretaceous red beds at the Weishan and Wuyin area in the middle part of Simao Tarrane . High-temperature magnetic components were isolated from the two study areas and the positive fold test shows its primary nature of magnetization. The tilt corrected site-mean direction of the Upper Cretaceous from the Weishan section and the Lower Cretaceous from the Wuyin section is Ds=64.3°, Is=48.5°, k=54.6, α95=4.7° and Ds=15.4°, Is=44.8°, k=212.0, α95=4.6°, respectively. The correlation analysis between the declination changing and the tectonic line changing of Simao Terrane shows that the different rotational deformation of Simao Terrane was controlled by the formation of arcuate structure zone of Simao terrane. According to the active history of the huge strike-slip fault zones in the southeast edge of Tibet plateau, the wasp waist structure of the middle part of Simao Terrane was formed in two tectonic deformation stages. The early stage was related to the NNE stress between the Indian Plate and the Eurasia Plate. The later stage was induced by the southward rotational extrusion movement of Chuandian Terrane. The Weishan and Wuyin area moved about 10.5°±6.0° and 3.8°±4.9° southward respectively relative to the stable area of South China Block. The analysis of the inclination shows that the Wuyin sampling area displaced about 3.4°±5.0° and 3.1°±5.4° northward relative to the Weishan area and Pu'er area, respectively, indicating large crustal shorting occurred between the Wuyin area and the the Weishan area since the collision of India/Eurasia.

Chen H.,Chinese Academy of Geological Sciences | Chen H.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Hu J.,Chinese Academy of Geological Sciences | Hu J.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2014

Southern Qinling belt is located in the south part of the Qinling orogen, which experienced the complex intra-continental deformation in Mesozoic. In the Late Mesozoic period, there were a series of strike-slip faults developed along the orogen in the southern Qinling belt. At present, the understanding of the deformation features, superposition relationship and dynamic mechanism for these strike-slip faults on different location is not sufficient. Structural studies show that the Ningshan fault and the Ankang fault are characterized by the A type fold and sub-horizontal stretching lineation, which indicated the southern Qinling belt underwent a tectonic stage dominated with the strike-slip shear deformation. Kinematic studies revealed the Ningshan fault was characterized by a sinistral shear deformation, while the Ankang fault by dextral characteristics. We chose the typical rock samples for isotopic dating to limit the fault activity time. The zircon SHRIMP U-Pb age of the syn-tectonic granite vein in the Ningshan fault was (186.0±4.0) Ma, and the mica 40Ar-39Ar dating results in the Ankang fault are 161.2-173.5 Ma. Although the kinematic features are opposite between the Ningshan fault and the Ankang fault, the geochronological results defined that the deformation time of these two faults is the same, e.g. Early-Middle Jurassic, both of which constitute a eastward extrusion for the central block of southern Qinling belt. This tectonic characteristic also indicated that the deformation of the orogen was soon transformed into the intra-continental deformation stage, which was dominant with the lateral extrusion and strike-slip displacement along the orogen. ©, 2014, Jilin University Press. All right reserved.

Xu H.,CAS Institute of Geology and Geophysics | Xu H.,University of Chinese Academy of Sciences | Yang Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.,Chinese Academy of Geological Sciences | And 3 more authors.
Precambrian Research | Year: 2014

Several new paleomagnetic and geological studies focused on the reconstruction of the North China Craton (NCC) within the Paleo-Mesoproterozoic Columbia supercontinent. In spite of these new data, there are still widely divergent opinions regarding supercontinental reconstructions. In addition to qualitative correlations of orogenic belts, rift basin ages, stratigraphy and distribution of igneous provinces, paleomagnetic data can provide key constraints on the positioning of individual cratons on the globe. In this paper, we report a detailed paleomagnetic study on the coeval ~1780Ma mafic dyke swarm and Xiong'er volcanic province, which extended for more than one thousand kilometers in the central NCC. Rock magnetic studies, including thermomagnetic curves, hysteresis loops and the progressive acquisition of isothermal remanence conducted in selected samples, indicate that the dominant magnetic carriers are PSD magnetite. Stepwise thermal demagnetization isolated higher-temperature components directed to NNE/SSW with shallow inclinations from 37 sampling sites (16 sites in Yinshan area, 13 sites in Taihang area and 8 sites in Xiaoshan area). A baked contact test conducted on two Yinshan dykes intruded by a younger dyke demonstrates the magnetization in the Yinshan dykes pre-dates 1320Ma. The existence of dual-polarity magnetizations in both Taihang and Xiong'er areas support our contention that the ChRM was acquired during the cooling of the magma. The primary origin of the ChRM is also supported by a positive fold test on the Xiong'er data, and a coherent regional test between the results from the Taihang and Xiong'er areas. Two different site-mean directions were compiled from these new results along with previous publications. The first direction, from the Taihang and Xiong'er areas, yields Declination (D)/Inclination (I)=12.4°/-3.7° (κ=20.5, α95=4.3°, N=57 sites). The second, from the Yinshan area is at (D) 36.7°/(I)-12.4° (κ=86.8, α95=2.7°, N=32 sites). We argue that the difference is due to Mesozoic and/or Cenozoic vertical-axis rotation of the Taihang and Xiong'er areas with respect to the fixed Yinshan-Ordos basin. The corresponding paleopoles for the Yinshan dykes falls at 245.2°E/35.5°N (A95=2.4°). A comparison between the NCC, Laurentia, Siberia and Baltica is consistent with possible links between these four blocks in a perhaps, even larger, continent. The proximity of Australia and India to the NCC is also evaluated. © 2014 Elsevier B.V.

Yuan W.,Nanjing University | Yang Z.-Y.,Nanjing University | Yang Z.-Y.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction
Geological Bulletin of China | Year: 2012

U-Pb geochronology and Lu-Hf isotopic studies of detrital zircons from middle Cambrian sediments of Niushoushan area, eastern Hexi Corridor, show three major groups of U-Pb age: 0.6-0.8Ga (peak at 669Ma), 1.0-1.3Ga (peak at 1173Ma), and 1.6-1.8Ga (peak at 1710Ma), which are significantly different from the detrital zircons U-Pb age spectrum of the upper strata in the Hexi Corridor belt. The characteristics of the detrital zircon U-Pb age spectra and Hf isotopes indicate that the detrital zircons 1.0-1.3Ga and 1.7-1.75Ga in age might have originated from southwest Australia, which is consistent with the evidence of paleontological and paleomagnetic studies in the Hexi Corridor. The Jinning-age (0.8-1.0Ga) detrital zircons that appear in the middle Ordovician strata in Hexi Corridor may indicate the changes of the source area of detrital materials, which resulted from the expansion of the North Qilian Ocean. The detrital zircons 0.4-0.5Ga in age extracted from post Ordovician strata were probably produced by the uplift of Qilian orogenic belt as well as the erosion and weathering processes in the Hexi Corridor.

Yuan W.,Nanjing University | Yuan W.,Sinopec | Yang Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction | Yang Z.,Chinese Academy of Geological Sciences
Journal of Asian Earth Sciences | Year: 2014

Rock magnetic and paleomagnetic studies have been carried out on the early Carboniferous limestones and the Late Permian purple sandstones sampled in the eastern Alashan Terrane (ALT), northwest of China. Two components were isolated from the Early Carboniferous limestone by thermal progressive demagnetisation: a low unblocking temperature component (LTC) of recent origin; a pre-folding medium temperature component (MTC) (the paleomagnetic pole is λ = 13.1°N, F{cyrillic} = 11.0°E, A95 = 7.0°) that is probably the result of the hydrothermal fluids from the Qilian Orgenic Belt acquired during the Late Carboniferous-Early Permian. Also, two components were separated from the Late Permian purple sandstone by thermal progressive demagnetisation: the LTC with the recent viscous remanent magnetisation, and the higher temperature component (HTC) revealed from three sections which has passed a regional fold test at the 95% probability level and reversal test, suggesting a primary characteristic magnetisation. The corresponding paleomagnetic pole is λ = 27.2° N, F{cyrillic} = 18.8° E, A95 = 12.0°. The apparent polar wander path (including early Carboniferous, late Carboniferous-Early Permian, Late Permian and Early-middle Triassic poles) of the ALT is significantly different with those of the NCB. Comparison of the APWPs between the ALT and NCB shows a strong similarity. If the APWP of Hexi Corridor-Alashan rotated counterclockwise around an Euler pole at 44°N, 84°E by 32°, then the coeval APW path of the ALT overlaps to that of the NCB. This result indicates that the ALT migrated to the NCB after the Early-Middle Triassic along a tectonic boundary located between Helanshan Mountain and Zhuozishan Mountain, and finally amalgamated to the NCB before the Early Cretaceous. © 2014 Elsevier Ltd. All rights reserved.

Yuan W.,Tongji University | Yuan W.,Sinopec | Xu X.-H.,Sinopec | Lu J.-L.,Sinopec | And 3 more authors.
Geological Bulletin of China | Year: 2014

SHRIMP U-Pb geochronology and in situ Lu-Hf isotope have been measured to constrain the timing of the two late-Mesozoic volcanic rock samples from the southern Changling fault depression, Northeast China. The Huoshiling Formation volcanic rock yielded a U-Pb age of 125.3Ma±1.1Ma, younger than the previous K-Ar system ages, suggesting that the volcanic rocks erupted simultaneously in the southern and northern Songliao Basin. The analyzed zircons from Huoshiling volcanic rocks yielded the εHf(t) values between 2.0 and 8.1, which demonstrates that their parent magmas were derived from juvenile crust. The basement volcanic rocks yielded a U-Pb age of 173.6Ma±1.7Ma and the εHf(t) values between -8.8 and +1.5, which indicates the mixing of the juvenile and the pre-existent ancient crust. The εHf(t) values in this study are obviously similar to those of the coeval zircons from the eastern Xing-Meng orogenic belt, suggesting that they might have originated from a common source. In the detrital zircons age spectrum, the ca. 171~176Ma peaks were recorded in the Late-Mesozoic sedimentary strata both from Taiwan and Northeast China, which can be interpreted as the start of the subduction of the Paleo-Pacific Block to the Eurasia Block. It is also inferred that the magmatism was widely distributed at the eastern edge of Eurasia, including coastal areas of Southeast China, southern Korean Peninsula and Northeast China. ©, 2014, Science Press. All right reserved.

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