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Gong W.,Chinese Academy of Geological Sciences | Gong W.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | Hu J.,Chinese Academy of Geological Sciences | Hu J.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | And 10 more authors.
Precambrian Research | Year: 2014

The Paleoproterozoic is a pivotal period of the tectonic evolution of the North China Craton (NCC). Various models have been postulated by previous researchers through the study of petrology and metamorphism, but the lack of structural analyses has hampered further understanding of the tectonic evolution of the NCC. A series of well-exposed ductile shear zones developed on the northern, northwestern and eastern edges of the Ordos Block in the western part of the NCC. We carried out detailed field studies along with isotopic dating focused on the kinematics and geochronology of the ductile shear zones. On the north margin of the Ordos block, the Wulashan-Daqingshan ductile shear zone is characterized by an E-W trending shearing foliation that steeply dips 75-80° to the north or south, with subhorizontal stretching lineation plunging 10-15° toward the east or west and dextral strike-slip shearing kinematics. On the west margin of the Ordos block is the Zongbieli ductile shear zone with top-to-the-NW thrusting kinematics. On the east margin of the Ordos block is the Xueling ductile shear zone with top-to-the-SE thrusting accompanied by sinistral strike-slip shearing kinematics. The 40Ar-39Ar ages of deformed minerals from mylonitic high-grade metamorphic rocks and LA-ICP-MS U-Pb dating results of zircons from syn-tectonic anatectic granites reflect that the ductile shear zones surrounding the Ordos block deformed between 1.85 and 1.81Ga. The similar deformation ages indicate that the ductile shear zones might be genetically correlated. The geometry, kinematics and geochronology characteristics of the Wulashan-Daqingshan ductile shear zone on the north margin, the Zongbieli ductile shear zone on the west margin, and the Xueling ductile shear zone combined with the Zhujiafang sinistral ductile shear zone on the east margin defined the possible southwestward extrusion of the Ordos block in the late Paleoproterozoic, which might have resulted from the westward subduction-collision of the Eastern Block under the Western Block at approximately 1.85Ga and which is correlated with the amalgamation of the Columbia supercontinent. © 2014 Elsevier B.V.

Wu S.,Chinese Academy of Geological Sciences | Wu S.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | Hu J.,Chinese Academy of Geological Sciences | Hu J.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | And 5 more authors.
Journal of Asian Earth Sciences | Year: 2014

The Bayanwulashan Metamorphic Complex (BMC) exposes along the eastern margin of the Alxa Block, the westernmost part of the North China Craton (NCC). BMC is principally composed of metamorphic rocks with amphibole plagiogneiss, biotite plagioclase gneiss and granitic gneiss. Our research has been focused on the petrography and zircon U-Pb geochronology of the BMC to better understand the evolution of the Alxa Block and its relationship with the NCC. Evidences from field geology, petrography, and mineral chemistry indicate that two distinct metamorphic assemblages, the amphibolite and greenschist facies, had overprinted the preexisting granitic gneiss and suggest that the BMC experienced retrograde metamorphic episodes. The LA-ICP-MS zircon U-Pb ages reveal that the primary magmatic activities of BMC were at ca. 2.30-2.24. Ga and the two metamorphic events were at ca. 1.95-1.91. Ga and ca. 1.88-1.85. Ga respectively. These ages indicate that BMC initially intruded during Paleoproterozoic, not as previously suggested at Archean period. The Early Paleoproterozoic metamorphic records and the magmatic thermochronological data in BMC exhibit different evolution paths between the Alxa Block and the NCC. The Alxa Block was most likely an independent Early Paleoproterozoic terrain. Following different amalgamation processes, The Alxa Block combined with Western Block at ca. 1.95. Ga and then united with NCC at ca. 1.85. Ga. © 2014 Elsevier Ltd.

Hu J.,Chinese Academy of Geosciences | Hu J.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | Ren M.,University of Nevada, Las Vegas | Zhao Y.,Chinese Academy of Geosciences | And 5 more authors.
Gondwana Research | Year: 2015

The Grove Mountains are the inland exposures of the Prydz Belt in East Antarctica. Although the 550-500. Ma orogenic event was recognized as the latest major magmatic-metamorphic activity in the Prydz Belt, its subduction-collision origin was not confirmed until the discovery of high-pressure (HP) mafic granulite erratic boulders in the glacial moraines from the Grove Mountains. Because no HP metamorphic bedrock is exposed in this area, an understanding the regional geology required a thorough study of the morainal debris mineralogy and detrital zircon U-Pb chronology. Detrital zircon U-Pb age histograms show 550-450. Ma, 900-800. Ma, and 1100-1000. Ma modes from three morainal deposits and one paleosol samples. The oldest ages were 2300 to 2420. Ma. Detailed electron probe microanalyses (EPMA) for the detrital mineral grains were compared with the minerals from the nearby exposed bedrock. The mineral chemistry indicates that the exposed bedrock in the Grove Mountains was not the sole source for morainal materials. This new U-Pb zircon geochronology and microprobe mineral data support the previous interpretation that the 550-500. Ma tectonic activity was the final collisional event that formed the Prydz Belt and amalgamated East Antarctica. © 2015 International Association for Gondwana Research.

Zhou Z.-Z.,Chinese Academy of Geological Sciences | Zhou Z.-Z.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | Zhou Z.-Z.,China University of Geosciences | Pei J.-L.,Chinese Academy of Geological Sciences | And 6 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2016

The Pamir-western Himalayan syntaxis lies at the western end of the India-Asia collision zone and is bounded by the Main Pamir Thrust to the north, and the Main Boundary Thrust and Main Frontal Thrust to the south. To facilitate the study on the deformation history of the northeastern Pamir in response to the India-Asia collision, paleomagnetic samples were collected from 11 sites in the Pliocene sedimentary rock adjacent to the western Kunlun mountains. A stable magnetic component was isolated by stepwise thermal demagnetization of 111 samples from this section, which is characterized by a positive C-class reversal test. The mean direction of residual magnetism is Dg=342.4°, Ig=59.2°, κg=32.3,α 95=8.6°; Ds=352.4°, Is=49.9°, κs=59.1,α95=6.3°,corresponding to a paleopole at λp=79.7°N, φp=295.9°E, dp=5.6°, dm=8.4°, α95=6.9°. The paleomagnetic study on sedimentary rock developed in the Tarim basin offers a useful method for researching tectonic evolution. Combining with geomorphology and GPS data, our results suggest that the Yengisar anticline has undergone significant counterclockwise rotation since Pliocene. Comparisons of this paleomagnetic pole with adjacent regions imply the tectonic rotation in Kashi depression is associated with Northeastern Pamir evolution during the late Cenozoic. © 2016, Science Press. All right reserved.

Chen H.,Chinese Academy of Geological Sciences | Chen H.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | Hu J.,Chinese Academy of Geological Sciences | Hu J.,Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Land and Resources | And 6 more authors.
Journal of Asian Earth Sciences | Year: 2015

The Qinling Orogen of central China was formed by intracontinental collision between the North and South China Blocks. The orogen comprises several micro-blocks bounded by sutures and faults, and has undergone long-term intracontinental deformation since the Late Triassic. The micro-blocks include the southern margin of the North China Block (S-NCB), the Northern Qinling Belt (NQB), the Southern Qinling Belt (SQB), and the northern margin of the South China Block (N-SCB). Under a uniform tectonic setting in late Mesozoic-Cenozoic, these micro-blocks have been subjected to a range of deformation styles, as demonstrated by their structural deformation, history of magmatism, and the development of sedimentary basins. To investigate the differences among the micro-blocks and to quantify their uplift and exhumation, we obtained 45 rock samples from eight Mesozoic granites in these micro-blocks, and conducted apatite fission-track (AFT) thermochronological modeling. The results reveal that the Qinling Orogen underwent four distinct stages of rapid cooling histories during the late Mesozoic-Cenozoic, and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south (the N-SCB) and propagated to the north (S-NCB). In the first stage, during the Late Jurassic-Early Cretaceous (ca. 160-120. Ma), rock cooling occurred mainly in the N-SCB, attributed to the clockwise rotation and northward subduction of the South China Block beneath the Qinling Orogen. In the second stage, compression- and extension-related uplift was initiated during the late Early Cretaceous-early Late Cretaceous (ca. 120-90. Ma) in the SQB, consistent with the southward subduction of the North China Block and broadly extensional deformation in the eastern China continent. In the third stage, a gentle regional-scale cooling event that occurred during the latest Cretaceous-Paleocene (ca. 90-50. Ma) started in the NQB and became widespread in the Qinling Orogen. This regional-scale uplift and exhumation event was probably a response to the opposite polarity subduction beneath the Qinling Orogen combined with the effects of subduction of the Pacific Plate from the southeast. The fourth stage (Eocene-Oligocene, ca. 50-20. Ma) was marked by another phase of rapid cooling in the S-NCB, the NQB, and the NW-SQB, and is interpreted as being cause by the eastward tectonic escape of Tibetan Plateau related to India-Asia collision. Furthermore, the record of variable timings and rates of cooling of these micro-blocks, together with regional structural analysis, indicates that the late Mesozoic-Cenozoic intracontinental deformation in the Qinling Orogen was characterized by a spatiotemporally variable and propagating-style uplift and exhumation of the micro-blocks, and the predominant deformation was through displacement across various boundary sutures and faults. © 2014 Elsevier Ltd.

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