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Kinematics and dynamics of the Mesozoic orogeny and late-orogenic extensional collapse in the Sino-Mongolian border areas

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Science china Earth Sciences 2005年第7期48卷 849-862页

作者： zheng yadong 1.& wang tao2.1. key laboratory of orogenic belts and crustal evolution (Peking University), ministry of education, beijing 1.0871. china 2. Institute of Geology, Chinese Academy of Geological Sciences, beijing 100037, china key laboratory of orogenic belts and crustal evolution (Peking University) Ministry of Education Beijing 100871 China Institute of Geology Chinese Academy of Geological Sciences Beijinq 100037 China

The Sino-Mongolian border areas underwent two important tectonic events during Mesozoic time after late Paleozoic orogeny: a late Triassic to earlier Jurassic contractional event that resulted in a large-scale south-vergent thrust during the orogeny and a late Jurassic-earlier Cretaceous extensional event in a north-south direction that formed a metamorphic core complex. The kinematic and dynamic analyses show that the thrust sheet moved southwards with a kinematic vorticity number of ca. -0.10 and sub-horizontal maximum compressive stress axis that belongs to a contraction-thickening shear. The upper plate of the late-orogenic detachment relatively moved in a 165°direction. The average kinematic vorticity in its earlier stage was 0.74 that belongs to simple shear dominated shearing and related to the maximum compressive stress axes dipping at ～66°, while the later average kinematic vorticity was ～0.55°that belongs to pure shear dominated shearing with sub-vertical maximum compressive stress axes. This suggests that the thrusting led to the crust thickened and the lower plate rocks that were originally located in the upper crust depressed through a brittle-ductile transition zone into the lower crust and became warmer. The heated rocks trended to uplift since their increasing volume and decreasing density while the loading of the upper-plate rocks increased due to the structural thickening. Under the combined effect of the loading and the thermal-uplifting, the ductile shear zone in between increased in its component of vertical pure shear. Once its pure-shear component exceeded its simple-shear one the ductile shear zone became an extension-thinned shear zone. This progressive transitional process reflects internal and essential temporal and spatial relationships: the extensional factor nucleated during the crust thickening by thrusting and increase of the extensional factor finally led to late-orogenic collapse.

关键词： Mesozoic thrusting,late-orogenic collapse,kinematic vorticity number,stress state.

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A challenge to the concept of slip-lines in extrusion tectonics

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Geoscience Frontiers 2011年第1期2卷 23-34页

作者： yadong zheng~(a,*),Erchie wang~b,Jinjiang Zhang~a,tao wang~c a key laboratory of orogenic belts and crustal evolution,ministry of education,School of Earth and Space Sciences, Peking University,beijing 1.0871.china b Institute of Geology and Geophysics,Chinese Academy of Sciences,beijing 100029,china c Institute of Geology,Chinese Academy of Geological Sciences,beijing 100037,china [a] key laboratory of orogenic belts crustal evolution Ministry of Education School of Earth Space Sciences Peking University Beijing 100871 China [b] Institute of Geology Geophysics Chinese Academy of Sciences Beijing 100029 China [c] Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

Wide-open V-shaped conjugate strike-slip faults in Asia are typically related to extrusion ***,the tectonic model based on the slip-line theory of plasticity has some critical problems associated with *** conjugate sets of slip-lines in plane deformation,according to the theory of plasticity should be normal to each another but,in reality,the angles between the conjugate strike-slip faults,which are regarded as slip-lines in extrusion tectonics in the eastern Mediterranean,Tibet-middle Asia,china and the Indochina Peninsular regions,are always more than 90°(on average～110°) in the direction of contraction. Another problem is that the slip-line theory fails to explain how,in some cases,e.g.,in the Anatolian area in the eastern Mediterranean,the extrusion rate is much higher than the indent *** two major problems are easy to solve in terms of the Maximum-Effective-Moment(MEM) Criterion that predicts that orientations of the shear zones are theoretically at an angle of 54.7°and practically at angles of 55°±10°with theσ- or contractional *** orientations of the strike-slip faults that accommodate extrusion tectonics are,therefore, fundamentally controlled by the MEM *** extrusion is along the MEM-orientations,the extruding rate is normally higher than the indenting rate.

关键词： Extrusion tectonics Slip-line Wide-open V-shaped strike-slip faults MEM-Criterion Strain rate

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On the material invariant of 110°-conjugate angle of shear bands——Reply to Gomez-Rivas and Griera(2.15)

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Science china Earth Sciences 2015年第12期58卷 2363-2368,1-3页

作者： zheng yadong ZHANG JinJiang wang tao The key laboratory of orogenic belts and crustal evolution Ministry of Education School of Earth and Space SciencesPeking University Institute of Geology Chinese Academy of Geological Sciences

After their experimental data were re-explained in terms of the maximum-effective-moment （MEM） criterion, Gomez-Rivas and Griera （2.15） challenge the validity of the MEM-Criterion in terms of shear fractures, which have mixed up with shear fractures and shear bands. The two features are similar in appearance but different in deformation mechanism （s）. The MEM-criterion proves that ±55° to σ1era are the maximum effective moment directions and the shear bands that formed by mate- rial-line （beddings or fabrics） rotation mechanism have a constant conjugate angle of 110°. Theoretically, the 55° or 110° is a material-invariant, and practically, a statistic-invariant or preferred direction with average deviation of -10°. By this angle, shear bands can be easily recognized from shear fractures with conjugate angle never over 90°. The High-strain deformation in the lozenges usually predates the surrounding shear bands. Two stress states can not coexisted simultaneously in the same place and the resolving cr1＇ normal to the related shear zone represents 0-100% deformation partitioning, depending on the original kinematic vorticity of the shear zones.

关键词： kink-bands/shear bands deformation localization MEM-criterion deformation partitioning

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Interpretation of the experimental data provided by Gómez-Rivas and Griera(2.12) in terms of the MEM-criterion

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Science china Earth Sciences 2014年第11期57卷 2819-2824页

The systematical experiments carried out by G6mez-Rivas and Griera （2.12） demonstrate that the ductile shear zones initiate at 55° to 0-1 just as predicted by the MEM-criterion. However, the data are explained in terms of dilatancy, which requires many prerequisites and implies that the ±55° angle is only valid for the used material. In contrast, the -55°predicted by the MEM-criterion is material independent, which makes it widely applicable to explaining the development of ductile shear zones in nature.

关键词： MEM-criterion initiate conjugate angle deformation localization

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The Maximum Effective Moment Criterion (MEMC) and Its Implications in Structural Geology

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Acta Geologica Sinica(English Edition) 2006年第1期80卷 70-78页

作者： zheng yadong wang tao wang Xinshe The key laboratory of orogenic belts and crustal evolution School of Earth and Space Sciences Peking University Beijing 100871 Institute of Geology Chinese Academy of Geological Sciences Beijing 100037

The MohroCoulomb criterion has been widely used to explain formation of fractures. However, it fails to explain large strain deformation that widely occurs in nature. There is presently a new theory, the MEMC, which is mathematically expressed as Meff = （（σ1-σ3） *** 2α sin α）/2, where σ1-σ3 represents the yield strength of the related rock, L is a unit length and a is the angle between σ1 and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to σ1 and there is a slight difference in the moment in the range of 55°±10°. The range covers the whole observations available from nature and experiments. Its major implications include：（1） it can be used to determine the stress state when the related deformation features formed; （2） it provides a new approach to determine the Wk of the related ductile shear zone if only the ratio of the vorticity and strain rate remains fixed; （3） It can be used to explain （a） the obtuse angle in the contraction direction of conjugate kink-bands and extensional crenulation cleavages, （b） formation of low-angle normal faults and high-angle reverse faults, （c） lozenge ductile shear zones in basement terranes, （d） some crocodile structures in seismic profiles and （e） detachment folds in foreland basins.

关键词： maximum effective moment criterion crenulation cleavage low-angle normal fault high-angle reverse fault crocodile structure lozenge structure detachment fold

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Diagenesis and Metamorphism of Triassic Flysch Along Profile Zoige-Lushan,Northwest Sichuan,china

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Acta Geologica Sinica(English Edition) 2008年第4期82卷 917-926页

作者： wang Hejing M. RAHN tao Xiaofeng zheng Nan XU Tingjing key laboratory of orogenic belts and crustal evolution Ministry of Education China School of Earth and Space Sciences Peking University Beijing 100871 China Hauptabteilung fiir die Sicherheit der Kernanlagen 5232 Villigen-HSK Switzerland College of Earth Sciences Chengdu University of Technology Chengdu 610059 China

We used illite and chlorite crystaHinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis （EMPA）, b0 geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan-Garze orogen along profile Zoige-Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in-between them are defined on the basis of the obtained data. lllite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2.1 white mica polytype are observed within the epizone whilst 2.1 and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370℃±21℃ at low-to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint： on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.

关键词： diagenesis metamorphism Songpan-Garze orogen Triassic flysch illite crystallinity,Longmenshan fault

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