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3-D Structure of the Lithosphere and Its Dynamic Implications of Central Orogenic System and Vicinity, in the Chinese Mainland

Author: ChengShunYou
Tutor: ZhangGuoWei
School: Northwestern University
Course: Structural Geology
Keywords: Global gravity field model Central Orogenic System East-Asian continent 3-D structure of the lithosphere Qinghai-Tibetan plateau Isostatic residual geoidal anomaly Horizontal stress of the lithosphere
CLC: P542
Type: PhD thesis
Year: 2006
Downloads: 441
Quote: 5
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Abstract


Anisotropism and dynamics for continental lithospheric structure and composition is one of major realms for studying continental dynamics. Based on the summary of newest progresses of global gravity field models, isostatic models and flexural theory of Hthosphere and making used of global gravity model (UTCSR GRACE/GFZ EIGEN-GRACE), First, I calculate geoidal anomalies with different degrees and orders, isostatic residual geoidal anomalies of Hthosphere and horizontal stress distribution in Chinese mainland and vicinity and make an interpretation with multi-levels isostatic equilibrium. Secondly, combination with surface geology and others geophysical data, I analyze detailed structure of lithosphere within various segments of the central orogenic system (COS), respectively. Then, On the basis of making a comparative analysis with among East-Asian tomography, anomalies of geoid and satellite magnetic field for lithosphere and gravity and aeromagnetic, I propose a the lithospheric structural framework model for the Chinese mainland and adjacent area, specially the COS. Finally, I probe its present stress regime, deformation and dynamics. Some progresses are as following:1. In view of an analysis from lithospheric geoid, horizontal stress and existing seismic tomographic data and so on, they show that Chinese mainland and adjacent area is controlled by mantle dynamics of interaction, mutual influence and constraint by western Pacific ocean plate, Indian plate and circum-Siberian arc tectonics that formed after Paleo-Asian ocean closed, which consist of three tectonic areas, with on the base of the Tethyan tectonic realm. Overall tectonic framework of the Chinese mainland is outwards obduction along main tectonic borders within shallow crust and inwards subduction and convergence within deep lithospheric mantle from south-western, south-eastern and northern parts, respectively. The lithospheric mantle of the Chinese continent, as a whole, is in compressive tectonic regime.2. The lithosphere of eastern portion of the Chinese continent, being in extensional regime for level-shallow and motion eastward but westward dipping imbricated subduction that formed by high- and lower velocity slabs within lithosphere, suggests that it is in compressional regime in deep levels as a whole. Accommodations among different depth levels are accomplished by decoupling. The geoid of lithosphere, horizontal stress and P velocity tomography suggest that southern part of the Chinese mainland overall shows matching features of multi-lithospheric slabs during from Indo-Chinese to Yanshan ages.3. Deep lithospheric mantle in the Qinghai-Tibetan plateau and adjacent area, which consists of imbricated dipping-northward multi-lithospheric terrains, is in convergent-subduction regime for sinking of cold lithospheric material. Geoidal anomalies and P/S velocity tomographies show that subduction into beneath Euro-Asian continent by Indian lithosphere not only causes intensive crustal upwelling, thickening and shorting deformation along S-N, but also affects depth of~600km in the plateau and eastern part of the Chinese continent and southern margin of the Siberian block. A great geoidal low in the Euro-Asian continent is just an indication of the large-scale tectonic process in satellite global gravity field.4. The Yangtze and ORDOS cratons with thickened lithospheric roots become as a transitional zone or a firm rock in midstream between the eastern and western parts with different structural characteristics in Chinese continent and obstruct mutual material exchange and migration between the both. Not only is the present Yangtze craton constrained by regional compressional stress field but also its cold and dense lithospheric root is descended into the deep mantle by negative buoyancy, Which further strengthens inward obduction of orogenic belts surrounding it. For examples, Longmen shan mountain, Huaying shan and Bamian shan mountains override onto western margin and eastern part of Sichuan basin, respectively.5. Being on the setting of the above-mentioned three tectonic dynamic systems, the western Qinling and Songpan tectonic node takes the Mianlue-Animaqin suture, Ganzi-Litang suture and Longmen shan mountain as its boundary faults, and forms a material-sinking triangular prism area, which is surrounded, converged and superimposed by the North China block, Yangtze block and Qinghai-Tibetan plateau with different times, structural orientations and properties, also at the same time following delamination of the deep lithosphere. Studies for geology, geochemistry and geophysics indicate that Songpan-Ganzi block is attributed to a portion of the Gondwana old continent, being similar to the Yangtze block. A wholesale detachment interface had existed between its upper- and lower crust (depths from 18 to 21km). The western Qinling orogenic belt, along with the surface Mianlue-Animaqin suture and the detachment interface, had obducted southward onto the Songpan-Ganzi block, in turn, the Songpan-Ganzi block had thrusted southward along with Danba arc-shaped fault. As a whole, a crustal-scale double thrust tectonic system is formed. This structural framework had formed during Indo-Chinese and early Yanshan ages.6. Newest geoidal anomalies, satellite lithospheric magnetic field and seismic tomography indicate that lithosphere and mantle for the Euro-Asian continent, specially the Chinese mainland, is divided by EW,NW,NE and SN structures and formed type-chessboard structural framework.. NE and NW structures stride over surface tectonic units and form conjugate-like tectonics. It suggests that they are intra-plate tectonics after the Chinese mainland formation and mainly originate from the upper mantle. The EW structure, which originated from collision and match by North China and Yangtze plates during and past Indo-Chinese epoch, is further reactivated and superimposed by continuing intra-continent subduction since Mesozoic-Cenozoic. The structure, as an indicator of sub-dynamic system, is controlled and modified from the mantle by regional three dynamic systems that mentioned so that it is gradually decomposed and even vanishes. The SN structure is superimposed and compounded by Paleozoic relict structure of the lithosphere and new production from the mantle or the core-mantle interface.7. The lithospheric structure of the central orogenic system has distinct segmentation. At present the Tongbai-Dabie orogenic belt is controlled by SN and NW-SE compressive stresses and more thoroughly modified from deep mantle but the base of crust and within crust manifest EW structural traces that originated from plates subduction and match during Indo-Chinese times and/or later subduction of intra-continent. By which the high- and ultrahigh pressure metamorphic terrains (UHP) was extruded. The eastern Qinling orogenic belt, due to be affected by intensive convergence between the Yangtze and ORDOS high velocity lithospheres along SN trending, shows obviously EW structural character. Although the western Qinling orogenic belt is superposed and reformed by NE, NW and SN structures to cause complex lithospheric structures, vestige of the Mianlue paleo suture within lithosphere can be traced by geophysical data and linked to Animaqing structural belt.

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CLC: > Astronomy,Earth Sciences > Geology > Structural Geology > Tectonic movement
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