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Huang X.,Chinese Academy of Geological Sciences | Shi W.,Chinese Academy of Geological Sciences | Shi W.,Key Laboratory Neotectonic Movement and Geohazard | Shi W.,Wuhan University | And 2 more authors.
Journal of Asian Earth Sciences | Year: 2015

The North China Plate (NCP) underwent multi-phase intracontinental deformation during the Mesozoic, which is a much-debated research subject. Here we present a case study of this deformation inferred from regional-scale Helanshan superposed folds in the west of the NCP. New structural analyses and fault kinematic analyses in the Helanshan Structural Belt (HSB) indicate a two-stage syn-folding paleo-stress field, comprising early NNE-SSW compression, with mean orientations 190°/01° (plunge direction/plunge) for σ1, 283°/26° for σ2, and 100°/63° for σ3, and later WNW-ESE compression with mean orientations of σ1, σ2, and σ3 at 124°/07°, 213°/04°, and 001°/75°, respectively. These results, combined with geochronological analysis, indicate two episodes of shortening in this belt during the Mesozoic. Late Triassic-Early Jurassic NNE-SSW shortening, which produced ~8.1km of horizontal shortening, led to the development of open WNW-trending fold structures. Subsequent Late Jurassic-Early Cretaceous WNW-ESE shortening, which produced ~18.7km of horizontal shortening, reshaped the early WNW-trending structures and generated close, overprinting NNE-trending folds that resulted in the development of the regional-scale superposed folds in this area. In terms of geodynamics, the early NNE-SSW shortening is likely to be related to Indosinian intercontinental convergence between the North China Plate and the Yangtze Plate, and the later WNW-ESE shortening is likely to have been related to subduction of the Paleo-Pacific Plate. The regional structural analysis indicates that the whole of the western North China Plate experienced two-phase contractional deformation during the Mesozoic, as manifest by the early NNE-SSW and the late WNW-ESE shortening that characterized Mesozoic intracontinental deformation in the western NCP. © 2015 Elsevier Ltd.


Shi W.,Chinese Academy of Geological Sciences | Shi W.,Key Laboratory Neotectonic Movement and Geohazard | Shi W.,Wuhan University | Cen M.,Chinese Academy of Geological Sciences | And 6 more authors.
Journal of Asian Earth Sciences | Year: 2015

The Shanxi Rift, an intracontinental belt along the eastern margin of the Ordos Block, North China Plate, has undergone multi-stage extensional deformation during the late Cenozoic. In this study, new fault kinematic analysis of boundary faults in the Shanxi Rift, constrained by geochronological data, defines a three-stage tectonic stress regime since the late Miocene, providing new structural evidence for deciphering the northeastward growth of the Tibetan Plateau. The earliest stage involved a transtensional stress regime of NW-SE extension and NE-SW compression in the late Miocene-early Pleistocene (ca. 10-1.8Ma) and characterized by mean principal stress axes of σ1 at 344.7°/87.2°, σ2 at 217.6°/01.1°, and σ3 at 128.1°/01.0°. The early transtensional stress regime was responsible for the opening of the Shanxi Rift and was very likely associated with intensive right-lateral pull-apart activity in the eastern Ordos Block due to the northeastward growth of the Tibetan Plateau. During the second stage, the stress regime changed to less intense NE-SW extension, with mean stress orientations of 323.3°/85.2° for σ1, 127.5°/02.9° for σ2, and 214.9°/02.6° for σ3 in the early late Pleistocene (ca. 1.8-0.11Ma). This stage is marked by a distinct shift from fluvio-lacustrine to fluvio-piedmont sedimentary facies at the end of the early Pleistocene, and the widespread eruption of basalt in the Datong Basin north of the Shanxi Rift. This short-lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the Tibetan Plateau. The third stage was transtensional, characterized by NNW-SSE extension and WNW-ESE compression (σ1 at 060°/88.9°, σ2 at 074.9°/03.9°, and σ3 at 164°/00°) since the late Pleistocene (ca. 0.11Ma), causing dextral shear deformation in the Shanxi Rift and the disappearance of its paleo-lake. This stage resulted from regional ENE-WSW shortening due to northeastward growth of the Tibetan Plateau. © 2015 Elsevier Ltd.

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