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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.,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.

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.,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.

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.

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