印度-亚洲碰撞:从挤压到走滑的构造转换

印度-亚洲板块碰撞导致喜马拉雅山脉的崛起、青藏高原的生长、两倍于正常地壳厚度的巨厚陆壳体，以及大量青藏高原腹地的物质沿着大型走滑断裂朝东、东南、西的方向逃逸。印度-亚洲碰撞如何造成板块汇聚边界由挤压到走滑的构造转换对认识大陆岩石圈的变形机制具有重要意义。本文通过总结喜马拉雅造山带及青藏东南缘～55Ma以来的构造、变质、岩浆记录，发现高喜马拉雅的挤出起始于始新世加厚的喜马拉雅造山带中-下地壳的部分熔融，受控于渐新世以来同期发育的向南逆冲和平行造山带的韧性伸展，并建立了高喜马拉雅“三维挤出”构造模式。晚始新世以来，羌塘地块和拉萨地块的物质通过“岩石圈横弯褶皱和壳内解耦”的运动学机制，围绕东构造结发生顺时针旋转并向青藏高原东南缘逃逸。结合东南亚板块重建的资料，我们认为：印度-亚洲的“陆-陆碰撞”到印度洋板块一亚洲东南大陆的“洋-陆俯冲”的转换是导致从印度-亚洲主碰撞带的挤压到青戚东南缘走滑转换的根本原因。

Advances in numerical simulation of demolition blasting

The applications of numerical simulation in demolition blasting were reviewed.Several methods of numerical simulation in demolition blasting were introduced.The strength and weakness of the numerical methods mentioned in this paper were also indicated,respectively.Furthermore,the solid lattice model in the frame of discrete element method(DEM),which was developed by the author and his team,was detailedly described.The existed problems in the current numerical simulation methods of demolition blasting were presented and the future trend of the numerical simulation is finally prospected.

Early Cretaceous extensional structures in the Liaodong Peninsula:Structural associations,geochronological constraints and regional tectonic implications

Various extensional structures,e.g.,half grabens,detachment faults,and metamorphic core complexes,were formed in the Liaodong Peninsula.There are two metamorphic core complexes (mcc's) in the western part of the Peninsula,i.e.the Liaonan mcc and the Wanfu mcc.They share the same lower plate and constitute a conjugate mcc pair.The Dayingzi detachment fault system and the three half grabens are exposed in the central and eastern parts,respectively.U-Pb dating of zircons from syntectonic plutons in the lower plates of the detachment faults and volcanic rocks from half graben basins indicates that their formation spans from 135 to 106 Ma,although the individual structure may be formed at a particular stage.Despite the differences in age of formation,in the regional attitudes,and in rooting depths,the extensional structures have great similarities in their kinematics,geometrical asymmetry,and coeval tectono-magmatic activities etc.Macroscopically,the extensional structures constitute conjugate associations,but a particular one generally has asymmetric patterns.Early Cretaceous extensional structures extend from the Liaodong Peninsula to North China,Northeast China,South China,and eastern Mongolia and Transbaikal area in Russia.The extensional structures from different areas share many common features.The Liaodong Peninsula is the miniature of the East Asia with respect to the formation of extensional structures in Early Cretaceous.It is suggested that the interaction of the Izanagi Plate with Eurasia Plate is responsible for the extension of crust.The structural mobility of the lithosphere,partly attributed to the fluid flow at the depth,and detachment faulting in both the crustal and mantle lithosphere provide important constraints on the development of Early Cretaceous extensional structures in the East Asia.

Tectonic contrast between the conjugate margins of the South China Sea and the implication for the differential extensional model

The extensional model of the South China Sea(SCS)has been widely studied,but remains under debate.Based on the latest high-quality multi-channel seismic data,bathymetric data,and other obtained seismic profiles,the asymmetric characteristics between the conjugate margins of the SCS are revealed and extensional model of the SCS margin is discussed further.Spatial variation of morphology,basement structure,and marginal faults are discovered among the SCS margin profiles.As for the NS-trending variation,the basement of northern margin displays in the shape of step downwards to the sea,while the basement of southern margin is composed of wide rotated and tilted blocks,without any obvious bathymetric change.The variation also exists in the development of marginal faults between the conjugate margins,and detachment fault system is identified on the southern margin.Along the southern margin from east to west,the Eastern and Southwestern Basins developed different structural units.Based on the tectonic contrast of the conjugate margins,differential extensional model is proposed to explain the spatial variation of the SCS structure,which introduces detachment faults controlling the evolution of the SCS.The upper crust above the detachment fault was deformed by simple shear,while the lower crust and upper mantle below the detachment fault was deformed by pure shear.Because of the different lateral transfer between the upper brittle faulting and the lower ductile extensional regions,there developed marginal plateau(Liyue basin)and outer rise(Zhenghe massif)on the lower plate margin of the Eastern Basin and the Southwestern Basin,respectively.The evolution of the present SCS may be influenced by the diachronous close of the paleo-SCS.

The Dayingzi detachment fault system in Liaodong Peninsula and its regional tectonic significance

Large scale lithosphere thinning is an important characteristic of the destruction of the North China Craton （NCC） during the late Mesozoic. A series of extensional structures were developed under extensional setting, among which is the Dayingzi detachment fault system （DFS）. The DFS is constituted by three parts, volcano-sedimentary basins at the hanging wall, the Dayingzi-Huanghuadian detachment fault zone, and Paleoproterozoic metamorphic rock series and Mesozoic plutons at the footwall. In the section across the detachment fault zone, there is a sequence of tectonites including fault gouge, microbreccia, cataclastic-mylonites, mylonites, and gneissic biotite monzonite granite. Microstructural characteristics of tectonites and electron backscatter diffraction （EBSD） patterns of quartz indicate that the rocks from the footwall experienced a process from upper greenschist facies to lower greenschist facies. SHRIMP and LA-ICP MS U-Pb dating of zircons from the volcanic rocks in the basins, the tectonic evolution of the DFS is summarized as follows： 1） regional extension started at 135.0±1.2 Ma ago, when the detachment fault cut through the middle crust. Faulting induced the upwelling of magma and eruption of volcanic rocks and deformed a series of medium-acid volcanic rocks; 2） after 135.0±1.2 Ma, a large scale detachment faulting was active cross-cutting the mid-upper crust. The western margin of Jurassic and Triassic granite was ductilly and brittly sheared; besides, the Cretaceous volcanoedimentary rocks were tilted when the master fault approached the surface; 3） at around 127±1 Ma, the detachment fault stopped its activity and was intruded by the unsheared Cretaceous granite near Chaoyang. Comparison with the Liaonan metamorphic core complex （MCC） and other extensional structures in Liaodong Peninsula led to a general trend of including three zones in the Peninsula： MCC zone, detachment fault systems （DFS） zone, and half graben zone. MCC commonly cuts through the mid-lower crust, DFS through the mid-upper crust, and half graben through the upper crust. Therefore, development of the extensional structures in Liaodong Peninsula indicates that they are the results of crustal extension and thinning at different crustal levels. They may provide a deep insight into the dynamic mechanism, history of destruction and lithosphere thinning of the North China Craton （NCC）. Liaodong Peninsula, detachment fault system, Cretaceous extension, lithosphere thinning, North China Craton

Determining the key conditions for the formation of metamorphic core complexes by geodynamic modeling and insights into the destruction of North China Craton

Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Craton(NCC), which have been intensively studied on their structural and geological characteristics. Yet, the condition for the formation of MCCs and their link with NCC destruction are still in debate. In this study, we perform numerical simulations to investigate MCC formation under extension, with a focus on the effect of crustal rheologies. Results indicate that three end-member modes of deformation may occur: the metamorphic core complex mode, the detachment fault-uplifting mode and the pure shear mode. Weaker lower crust and stronger upper crust may promote the formation of MCC. In contrast, stronger lower crust(>1.3×1021 Pa s) may prohibit the exhumation of lower crust(detachment fault-uplifting mode), while weaker upper crust(<7.8×1021 Pa s) may fail to develop detachment faults(pure shear mode). Given that cratons typically have a strong crust, we suggest that the lower crust of NCC was weakened prior to extension, which promoted the formation of MCC in a later stage under the back-arc extension.