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Timing and mechanism of opening the Neo-Tethys Ocean:Constraints from mélanges in the Yarlung Zangbo suture zone

Science China Earth Sciences 2023年第12期66卷 2807-2826页

作者： Tong LIU Chuanzhou LIU Fuyuan WU Wenbin JI Chang ZHANG Weiqi ZHANG Zhenyu ZHANG State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 10029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China Department of Geology Northwest UniversityXi'an 710069China

The evolution and final closure of the Neo-Tethys Ocean are one of the most important geological events that have occurred on Earth since the mesozoic.However,the evolution of the Neo-Tethys is not well constrained,in particular whether its opening occurred in the Permian or the Triassic and whether a plume was involved with its opening or not.In this study,we present geochronological and geochemical data for mafic igneous rocks in mélanges along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet to constrain the timing and mechanism of opening the Neo-Tethys Ocean.Based on field observations,the YZSZ mélanges can be divided into three segments.The western(west of Zhongba)and eastern(Sangsang-Renbu)segments are composed of ocean plate stratigraphy representing accretionary complexes that formed during subduction of Neo-Tethyan oceanic lithosphere beneath the southern margin of the Asian continent.mélanges in the central segment(Zhongba-eastern Saga)typically have a siliciclastic matrix,and represent Tethyan Himalayan strata that were structurally mixed with the southern margin of the Asian continent.Based on our and previously published geochemical data,the mafic rocks in the YZSZ mélanges are ocean island basalt(OIB)-like,with ages in the Late Permian-middle Triassic,the middle-Late Jurassic,and the Early Cretaceous,respectively.An OIB-like block with an age of ca.253 ma is identified from the Zhongba mélanges in the western segment,and it is the oldest OIB lithology yet identified in the YZSZ mélanges related to the evolution of the Neo-Tethys Ocean.Geochemical features indicate that this OIB-like block is distinct from typical OIBs and would be formed during continental rifting to incipient seafloor spreading.In the framework of plate divergent-convergent coupling systems and based on literature data for early middle Triassic seamounts,radiolarian cherts,and normal mid-ocean ridge basalt-like oceanic crust,we conclude that opening of the Yarlung Zangbo Neo-Tethys Ocean would mainly occur at~250–243 ma in th

关键词： Neo-Tethys Ocean Wilson Cycle Yarlung Zangbo suture zone mélange Ocean island basalt Tethyan geodynamics

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The study of subduction channels:Progress,controversies,and challenges

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Science China Earth Sciences 2020年第12期63卷 1831-1851页

作者： Jianxin Zhang Key Laboratory of Deep-Earth Dynamics of the ministry of Land and Resources Institute of GeologyChinese Academy of Geological SciencesBeijing100037China

The subduction channel is defined as a relatively thin and weak zone with coherent kinematics between the descending and overriding plates during subduction.The materials in the channel,showing the characteristics of mélange,consist of low-density,low-viscosity,highly sheared metasediments and/or serpentinite-rich matrix with relatively rigid blocks.The channel materials flow downwards and upwards,forming a kind of channel convection.Based on geophysical and geological observations on active oceanic subduction zones,combined with numerical simulations,the subduction channel model was initially set to shallow depthsm.With the development of numerical simulation technology and fossil subduction zone investigations,the subduction channel model was extended to depths of 80-100 km to describe deeper geodynamic environments of oceanic subduction zones and explore the exhumation of high to ultrahigh pressure metamorphic rocks.It is also extended to continental subduction zones in order to explain the exhumation of metamorphic rocks in different grades as well as fluid activity and crust-mantle interaction during continental subduction.Although there are a series of differences in material composition and slab/mantle interface property between the upper and lower plates,continental subduction channels exhibit many similarities in structure and dynamics to oceanic subduction channels.Existing studies have provided a fundamental understanding of the structural and dynamic characteristics of subduction channels,but many problems still need to be solved and clarified.In particular,the fundamental characteristics of subduction channels obtained by numerical simulation need to be confirmed and modified through geological investigations of fossil subduction channels.

关键词： Plate interface Subduction channel mélange Numerical modeling High-ultrahigh pressure metamorphism Exhumation mechanism

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Shear strength of extremely altered serpentinites based on degree of saturation(Ankara, Turkey)

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Journal of mountain Science 2019年第4期16卷 944-954页

作者： Koray ULAmI? Department of Geological Engineering Ankara University

The term "mélange" has several definitions due to the origin, tectonic and petrographical features. The geotechnical engineering behaviors of mélanges are either dominated by different kinds of intact rock blocks or matrix material. Landslides were encountered within the serpentinite matrix of Ankara mélange, which is a typical bimrock mass. The residual sections of the extremely altered serpentinites are sandy soils. Such soils undergo rapid change of saturation, leading to shear strength reduction. Undisturbed and disturbed samples were obtained from the outcrops for shear box tests. Geochemical and petrographical composition of the serpentinites were determined by XRF(X Ray Fluorescence), XRD(X-ray diffraction) and thin section inspections, in order to outline the alteration process. Based on field observations, physically decomposed core stones exist beneath 40-120 cm thick residual green and grey-dark grey residual sandy soil. Physical and mechanical properties of the soils were tested with particular emphasis on residual shear strength parameters. Disturbed samples were remolded by standard compaction. The field work was completed during both rainy and summer seasons. Disturbed samples were prepared using phase diagrams in order to attain varying saturation degree. Two distinct sandy soil groups were determined through classification tests. The volumetric compression and/or expansion of the loose and dense samples were also considered based on the angle of dilatancy. A series of consolidated and drained shear box tests were conducted with ascending degree of saturation. The reduction of effective apparent cohesion, internal friction angle and dilatancy angle were determined to obtain a threshold of the degree of saturation. All the sand samples had zero residual internal friction angle and/or apparent cohesion after reaching 70% degree of saturation.

关键词： mélange Serpentinite Shear strength Saturation Dilatancy Ankara

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Discovery of Paleogene palynological assemblages from the Wanbaogou Group-complex in western part of the Eastern Kunlun orogenic belt and its geological significance

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Science China Earth Sciences 2006年第4期49卷 358-367页

作者： GUO Xianpu WANG Naiwen DING Xiaozhong ZHAO min WANG Daning Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

The Wanbaogou Group-complex is a suit of mélange aggregation of the Eastern Kunlun orogenic belt, which is divided into two parts, i.e. the exotic blocks and the matrix strata. Based on stromatolite fossils yielded in the exotic blocks, the age of this group-complex was once defined to the Precambrian. Recently, two Paleogene palynological assemblages have been found in samples from the matrix strata of the Upper Part in this group-complex by the authors: in ascending order, the Al- nipollenites-Quercoidites assemblage of Late Eocene and the Caryapollenites-Pinuspollenites as- semblage of Early Oligocene. Those results show that the matrix strata of this mélange were mainly formed in Paleogene, and the event causing mixture should be a Himalayan movement Phase. This paper is designed to provide some detailed evidence for determining the age of the matrix strata in this group-complex based upon study at the Kunlunqiao Section, which would be of important geo- logical significance for further understanding this group-complex as a suit of mélange aggregation and establishing or improving the stratigraphic framework of the studied region. The new finding will cer- tainly benefit from now on the investigation on geotectonic and sedimentary evolution of Eastern Kunlun.

关键词： Wanbaogou Group-complex, Paleogene, palynological assemblages, mélange aggregation, the Eastern Kunlun orogenic belt.

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PRELImINARY STUDY ON THE OPHIOLITIC mElange IN THE YALU TSANGPU GRAND CANYON AREA

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地学前缘 2000年第S1期7卷 53-54页

作者： Geng Quanru,Pan Guitang,Liu Yuping,Zheng Lailing,Liu Chaoji [WT5,5”BX](Chengdu Institute of Geology and mineral Resources,Chengdu 610082,China)

Since 1980’s Chinese geologists have organized several scientific expeditions with foreign colleagues to enter the Canyon to study its geology and geography.1\ major petrologic units\;There are three major petrologic units in this region: (1)Namche barwa formation(Pt nj ). It is situated in the center of great bend area ,representing the lower part of Indian plate wedged into Eurasia plate, which is composed of plagioclase gneiss, amphibole\|containing high\|pressure granulite lenses. (2)Gandise formation(Pt gd ).It is exposed in the outside of Namche barwa edge(Pt nj ), and is considered to be the lower part of Eurasia plate which is composed of plagioclase\|gneiss, amphibolite, marble, quartzite, etc., and were intruded by large granite batholiths (γ 2 5 to γ 6). (3)Great bend formation(mz). It stretches along Yarlung Zangbo river and is constrained between Pt nj and Pt gd . It is composed of metamorphic basic igneous rocks , ultramafic rocks and quartzite. The whole rock assemblage is characterized by ophiolite suite. Nice ophiolitic mélange exposures exist in Pangxin, Jiaresa and between Pailong and Zhaqu.2\ Basic rock assemblage\;The present ophiolitic components are mostly metamorphic rocks after structural movements and metamorphism for long period. (1) meta\|intermediate rocks. Amphibolite is a dominant component of ophiolitic mélange in this region . Chemical analysis and protolith recognition shows that amphibolite originated from basalt, diabase and gabbro. (2) Ultramafic rocks. This kind of rocks distributes along the northeast edge of the wedge from Pangxin to Jiaresa. Original pyroxene\|olivinite and serpentine exposures have been found . Electronic\|probe and bulk\|rock analysis suggest that original olivinite is strongly mgO\|enriched and can be named magnesian olivinite. (3) Quartzite. It is exposed along the northeast and southeast margin of the wedge forming steep cliffs and high peaks . In some places it consists of pure fine\|grained quartz and may contain muscovite, biotite, plagioclase or e

关键词： Yarlung Zangbo grand canyon ophiolitic mélange eastern syntaxis wedge uplift

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Lithological Analysis of Nain Ophiolitic Zone Using ASTER Data

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Open Journal of Geology 2017年第8期7卷 1200-1214页

作者： Ali Reza Nasiri Khaneghah Ramin Arfania Department of Geology Isfahan (Khorasgan) Branch Islamic Azad University Isfahan Iran

The mesozoic ophiolitic mélange, north of Nain in the Central-East Iran microplate (CEIm) comprises serpentinized ultramafic rocks, harzburgites, dunite, gabbro, peridotite, pelagic limestone and other carbonate rocks. The excellent and vast exposure of this desert region is well suited for geologic mapping of this rock suite using remote sensing, especially using data from the satellite-borne advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) imaging system which was designed for mapping mineral information. In this study, data processing methods like method minimum noise fraction (mNF), Feature Oriented Principal Components Selection (FPCS), Band Ratios (BR) and Optimum Index Factor (OIF) were used to process ASTER data to optimize the mapping of ophiolite rock types. For example, a simple color composites of OIF (Red: B3, Green: B4, and Blue: B8) and Band ratios (e.g. Red: (B2 + B4)/B3, Green: (B5 + B7)/B6, Blue: (B7 + B9)/B8) were useful for discriminating serpentinite, meta-basalt and granite rock types. It is concluded here that proposed ASTER data has the potential for mapping similar ophiolites elsewhere using the global archive of ASTER imagery.

关键词： Ophiolitic mélange Ultramafic Rocks Advanced Space Borne Thermal Emission and Reflection Radiometer (ASTER) Optimum Index Factor (OIF) Feature Oriented Principal Components Selection (FPCS) Band Ratio (BR)

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泰国北部Inthanon带外来硅质岩块的中、晚二叠世放射虫:对与古特提斯消减有关的混杂岩形成时代的约束(英文)

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地球学报 2012年第S1期33卷 36-37页

作者： Yoshihito KAmATA Hidetoshi HARA Katsumi UENO Apsorn SARDSUD Thasinee CHAROENTITIRAT Punya CHARUSIRI Ken-ichiro HISADA Graduate School of Life and Environmental Sciences University of TsukubaIbarakiJapan Geological Survey of Japan AIST1-1-1 HigashiTsukubaIbaraki 305-8567Japan Department of Earth System Science Faculty of ScienceFukuoka UniversityFukuoka 814-0180Japan Bureau of Geological Survey DMRBangkok 10400Thailand Department of Geology Faculty of ScienceChulalongkorn UniversityBangkok 10330Thailand

The Inthanon Zone of Northern Thailand,originally proposed by Barr and macdonald(1991),is characterized by the occurrence of Paleo-Tethyan pelagic sediments including Carboniferous-Permian seamount-type carbonate asso... 详细信息

关键词： Northern Thailand mélange Radiolarian Permo-Carboniferous

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