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Style tectonique et contexte géodynamique au Paléoprotérozoïque.
Exemple du Craton de Chine du Nord

Abstract : This thesis is essentially devoted to the study of the tectonic style and the geodynamic evolution of the "Trans-North China Belt", a collisional orogen that marks the amalgamation of the North China Craton during Paleoproterozoic. We carried a detailed field study in the five main massifs, with emphasis on geometry of structures and kinematics that allows the distinction of several lithotectonic units showing distinct metamorphic features. The time constraints of magmatism, metamorphism and deformation were obtained by U-Th-Pb dating on monazite with the electron microprobe, 40Ar/39Ar dating on amphibole, muscovite and biotite and U-Pb LA-ICP-MS dating on zircon. Two domains are distinguished. The first one is characterized by a horizontal style tectonics. The unit "LGMU" (Low-Grade Mafic Unit) is interpreted as an ophiolitic nappe that is rooted along the «Trans-North China Suture", located in the western part of the belt. This nappe thrusts toward the SE over the "OVU" (Orthogneiss-and-Volcanites Unit), that comprises a series of volcano-sedimentary rocks and orthogneiss metamorphosed at amphibolite facies. These rocks have protolithe ages at ~2.5 Ga and ~2.1 Ga and are involved in the collision characterized by a polyphase history between 1900 and 1800 Ma. In addition to the U-Th-Pb and U-Pb dating results, a thermobarometrical study conducted on a kyanite and staurolite bearing micaschist led to the construction of a prograde Pressure- Temperature-Deformation-time path that confirms the age of the nappe stacking and the crustal thickening around 1880 Ma. The second area is the para-autochtonous domain upon which the OVU nappe is thrust over. This area is characterized by a "domeand- basin" structure, interpreted as the result of an interplay between diapirism and regional deformation characterized by an E-W directed stretching and a N-S directed shortening. This "archaic" tectonics is estimated to have taken place around 2.1 Ga. Finally, the preliminary study of the Zanhuang massif, east of the para-autochtonous domain, can highlight a second suture zone along which a stack of east verging slices of ophiolitic and passive continental margin rocks formed. The synthesis of all results led to the reconstruction of the overall structure of the considered part of the belt, from inner zones to external ones. In addition, we propose a geodynamic model involving three Neoarcheans blocks, the Western Block, the Fuping Block and the Eastern Block, separated by two oceans, the Lüliang Ocean and the Taihang Ocean. The opening of oceanic basins occurred around 2175 Ma. The collision occurred at 1880 Ma, in response to the closing of ocean basins and is responsible for the main architecture of the "Trans-North China Belt". This work shows that during Paleoproterozoic, a collisional orogen such as modern ones can form, including the development of Alpine type thrusts, suggesting rheological continental lithosphere behaviour almost similar to the current one.
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https://tel.archives-ouvertes.fr/tel-00267150
Contributor : Nathalie Pothier <>
Submitted on : Wednesday, March 26, 2008 - 3:36:45 PM
Last modification on : Thursday, March 5, 2020 - 6:48:59 PM
Long-term archiving on: : Thursday, May 20, 2010 - 10:32:13 PM

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  • HAL Id : tel-00267150, version 1

Citation

Pierre Trap. Style tectonique et contexte géodynamique au Paléoprotérozoïque.
Exemple du Craton de Chine du Nord. Tectonique. Université d'Orléans, 2007. Français. ⟨tel-00267150⟩

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