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Microstructures,Deformation Mechanisms and Seismic Properties of Synkinematic migmatite from Southeastern Tibet:Insights from the Migmatitic Core of the Ailao Shan-Red River Shear Zone,Western Yunnan,China

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Journal of Earth Science 2024年第4期35卷 1149-1169页

作者： Weiwei Ma Bo Zhang Fulong Cai Baoyou Huang Lei Zhang Key Laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space SciencesPeking UniversityBeijing100871China Institute of Tibetan Plateau Research Chinese Academy of SciencesBeijing100085China

Seismic anisotropy originating within the continental crust is commonly used to determine the deformation and kinematic flow within active orogens and is attributed to regionally oriented mica or hornblende ***,naturally deformed rocks usually contain compositional layers(e.g.,parallel compositional banding).It is necessary to understand how both varying mineral contents and differing intensities of compositional layering influence the seismic properties of the deep *** this study,we analyzed the seismic response of migmatitic amphibolite with compositional banding *** present the microstructures,fabrics,calculated seismic velocities,and seismic anisotropies of mylonitic amphibolite from a horizontal shear layer preserved within the Ailao Shan-Red River shear zone,southwestern Yunnan,*** investigated sample is characterized by pronounced centimeter-scale compositional *** microstructures and fabrics suggest that migmatitic amphibolite rocks within deep crust may delineate regions of deformation-assisted,channelized,reactive,porous melt *** origin of compositional banding in the studied migmatitic amphibolite is attributed primarily to partial melting together with some horizontal shearing *** microfabrics and structures investigated in this study are considered to be typical for the base of active horizontal shear layers in the deep crust of southeastern *** responses are modeled by using crystal preferred orientations for minerals of the migmatitic amphibolite by applying the Voigt-Reuss-Hill homogenization *** P-wave and S-wave velocities are largely consistent in the various layers of the ***,seismic anisotropies of P-wave(AV_(p))and S-wave(AVs)are higher in the melanosomes(AV_(p)=5.6%,AV_(s)=6.83%)than those in the leucosomes and the whole rock(AV_(p)=4.2%–4.6%,AV_(s)=3.1%–3.2%).In addition,there is pronounced,S-wave splitting oblique to the foliation plane in the migm

关键词： deformation-assisted melt flow seismic anisotropy microstructure compositional banding migmatite deep crust southeastern Tibet

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Zircon Geochronological Evidence for Participation of the North China Craton in the Protolith of migmatite of the North Dabie Terrane

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Journal of Earth Science 2018年第1期29卷 30-42页

作者： Haijin Xu Junfeng Zhang State Key Laboratory of Geological Processes and Mineral Resources School of Earth SciencesChina University of Geosciences

The plate affiliation of the North Dabie terrane （NDT） has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zircons and field investigation for migmatite in the NDT was carried out, which reveals par- ticipation of crustal rocks of the North China Craton （NCC） in the protolith in addition to the more common crustal rocks of the Yangtze Craton （YC）. The evidence of an NCC affinity for protolith of migmatite in the NDT is the -2.5 Ga （2 486±14 and 2 406±26 Ma） magamtic age and -1.8 Ga （1 717±79 Ma） metamorphic age in the relict zircon domains because these two age groups are characteristic for the evolution of the NCC. The evidence of a YC affinity for protolith of migmatite in the NDT is the more common 0.7-0.8 Ga （e.g., 787±12 Ma） magamtic zircon age. Mid-Neoproterozoic magmatic age （0.7-0.8 Ga） is a symbol of YC basement rocks. In view of the widely exposed YC crustal components in the NDT, we suggest that the protolith of the NDT is mainly crustal rocks from the YC with minor crustal components from the NCC. The zircon rim domains and new growth grains from all the migmatite sam- ples are characterized by anatectic zircons and have a widely concordant ages ranging from 112.2±2.8 to 159.6±4.3 Ma with several peak values, suggesting a long lasting multistage anatexis. In conclusion, the NDT has a mixed protolith origin of both the YC and the NCC crustal rocks were strongly remoulded by anatexis during orogenic collapse.

关键词： North Dabie terrane migmatite zircon U-Pb age protolith tectonic affinity.

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A STUDY ON THE Nd-Sr ISOTOPE OF THE WUGONGSHAN migmatite

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Chinese Science Bulletin 1991年第24期36卷 2069-2072页

作者：徐士进沈渭洲王银喜杨杰东李惠民 Department of Earth Sciences Nanjing University Nanjing 210008 PRC Center of Modem Analysis Nanjing University Nanjing 210008 PRC

Ⅰ. GEOLOGICAL BACKGROUND Covering an area of 1200 km^2, the Wugongshan migmatite-granite batholith is located on the northwestern margin of South China Caledonian folded region and the southern flank of Pingxiang-Gua... 详细信息

关键词： Wugongshan migmatite Nd-Sr isotope

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Zircon Zr isotope fractionation during crustal anatexis

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Science China Earth Sciences 2024年第8期67卷 2495-2506页

作者： Erlin ZHU Qiongxia XIA Zhaoya LI Renxu CHEN James VAN ORMAN School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China State Key Laboratory of Lithospheric and Environmental Coevolution Hefei 230026China Frontiers Science Center for Planetary Exploration and Emerging Technologies University of Science and Technology of ChinaHefei 230026China Department of Earth Environmental and Planetary SciencesCase Western Reserve UniversityCleveland OH 44106USA

Zirconium is one of high field strength elements but its isotope behavior during geochemical processes is still uncertain because of the limited *** Zr isotopes in magmatic rocks are often used to trace the evolution of magmas through fractional crystallization,it is intriguing how highly heterogeneous Zr isotopes were produced by the growth of zircon during crustal *** address this issue by in-situ zircon Zr isotope analyses of migmatites from two high-temperature metamorphic terranes in the South Lhasa zone and the North Dabie zone,respectively,in *** results show highly variable δ^(94)Zr values from-0.30‰ to +0.81‰ and from-0.58‰ to +0.49‰,*** addition to the relict zircon of magmatic origin,two types of newly-grown zircons were identified in terms of their occurrences,trace elements and δ^(94)Zr *** peritectic zircon,mainly occurring in the in-situ leucosomes,exhibits the highest Nb-Ta-Hf-U contents and variably higher δ^(94)Zr values than those of the relict *** anatectic zircon,mainly occurring in the leucocratic veins,shows higher Nb-Ta-Hf-U contents than and similar δ^(94)Zr values to those of the relict *** calculations demonstrate that the variable Zr isotope compositions of newly-grown zircons would result from decoupled release of Zr from zircon and non-zircon *** Zr supply of the peritectic zircon is mainly derived from the decomposition of Zr-bearing minerals in the in-situ anatectic melt(the non-zircon effect),whereas the Zr supply of the anatectic zircon is mainly from the dissolution of pre-existing zircons in the evolved melt(the zircon effect).The significant Zr isotope variations in the migmatites well illustrate the generation,migration and accumulation of the anatectic melts during the partial ***,Zr isotopes can be used as a powerful means for distinguishing between the peritectic and anatectic zircons during crustal anatexis.

关键词： Zr isotopes Zircon effect Non-zircon effect migmatite Crustal anatexis

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Structural characteristics and geochronology of migmatites in the North Dabie Complex unit: Timing of post-collisional deformation

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Science China Earth Sciences 2018年第7期61卷 887-902页

作者： Yongsheng WANG Qiao BAI Bingfei YANG School of Resources and Environmental Engineering Hefei University of Technology

Extensive migmatization and large-scale post-collisional intrusions occurred in the Dabie orogen, east-central China,during the Early Cretaceous, characterized by distinct deformation preserved in migmatites in the North Dabie Complex *** North Dabie Complex unit can be subdivided into three areas based on detailed field observations： the north of the Tiantangzhai pluton, the Luotian area and the Yuexi area. Banded migmatites crop out in the north of the Tiantangzhai pluton while anisotropically deformed migmatites occur in the Luotian area, and both types coexist in the Yuexi area. Microscopy reveals similar micro-structures are in migmatites from the north of the Tiantangzhai pluton, the Yuexi area and border of the Luotian area, while static recrystallization appears in migmatites from the core of the Luotian area. The Lattice-Preferred Orientation of dynamically recrystallized quartz grains in the migmatites are measured using electron backscattered diffraction,revealing prism slip or slip in migmatite from the north of the Tiantangzhai pluton and the Yuexi area and in one sample from the Luotian area. A Type I crossed girdle is developed in another sample from the Luotian area, indicating top-to-the-SE shearing that developed under greenschist facies conditions. Zircon U-Pb dates from four migmatites reveal that mainly Early Cretaceous ages are from the north of the Tiantangzhai pluton, only four Early Cretaceous ages are from the Luotian area, and all zircons from the Yuexi area record Indosinian metamorphic ages. Although zircon U-Pb results show multiple migmatization events, all samples record a migmatization age of about 132 Ma, suggesting an orogen-scale event at that time. The subsolidus deformation in migmatites indicates that deformation were soon after migmatization. Overall, this study shows that deformation in migmatites of the North Dabie Complex unit occurred somewhat later than the migmatization（132 Ma） at about 131 Ma. The most likely mecha

关键词： The North Dabie Complex unit migmatite Structural evidence Zircon U-Pb dating

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On the Origin of migmatites in Yunlu, Western Guangdong

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Acta Geologica Sinica(English Edition) 1995年第1期69卷 41-52,118页

作者： Chen Bin and Huang Fusheng Department of Geology, Peking University, Beijing Jiang M inxi Department of Geology Peking University Beijing

Partially migmatized rocks, banded migmatites, augen-banded migmatites and gneissic migmatites are developed successively from Xindong to Yunlu, Gaozhou, Guangdong Province in the Yunkai Caledonian orogenic belt at the border between Guangdong and Guangxi. Mass-balance calculations, statistical analysis of the textural relations and mineralogical and geochemical studies of the migmatites and the study of the metamorphlc setting of the Yunlu area indicate that the migmatites in the study area were primarily formed by anatexis without remarkable introduction of foreign components such as K, Na and Si and removal of Ca, Fe, Mg, etc.

关键词： migmatite anatexis leucosome Yunlu

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Deciphering the presence of axial-planar veins in tectonites

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Geoscience Frontiers 2019年第6期10卷 2101-2115页

作者： Elena Druguet Departament de Geologia Universitat Autonoma de Barcelona

Veins and dikes are often oriented subparallel to the axial surfaces of folds in the adjacent layered or foliated *** implies an awkward situation,since veins would lay in planes close-to-parallel to the maximum stretching axis.A series of geometric models have been conceived in order to gain insight into the possible mechanisms for their *** models are based on the analysis of a varied selection of field structures and on the review of similar structures in the existing literature.A first categorization consists on distinguishing between axial-planar veins achieved by either progressive or polyphase *** models of axial-planar veins resulting from progressive deformation are described and discussed:(1) fold-related veins associated with the standard folding mechanisms,(2) fracture arrays localized along the short limbs of folds(asymmetric fold-related veins),(3) folds associated with rotation of extension veins(vein-related folds),(4) high strain and transposition of early veins,and(5) high strain and late veins parallel to axial planar foliations(axial planar foliation-related veins).The axial planar geometry is achieved through variable amounts of progressive rotational strain,except in model 5,in which the co-planarity is acquired at the time of vein *** possibility for axial-planar veins to have developed in two distinct phases in the context of polyphase or polyorogenic tectonics has also been explored and *** study contributes to a better understanding of the intriguing interplays between deformation,metamorphic and magmatic processes in orogenic belts.

关键词： Dike Fold Fracture Metamorphic rock migmatite Shear

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Kabbaldurga charnockites revisited: Incipient growth or anatectic melt?

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Natural Science 2013年第3期5卷 419-436页

作者： Samarendra Bhattacharya Aswini K. Chaudhary Indian Institute of Technology Roorkee India Indian Statistical Institute Kolkata India

A popular hypothesis of in situ transformation of amphibolite facies gneisses to patchy charnockites by CO2 influx from mantle was proposed primarily from the Kabbaldurga quarries in South Karnataka and subsequently reported from several south Indian localities. However, presence of abundant mafic granulite enclaves in Kabbaldurga and its neighborhood and its implications in relation to patchy charnockite genesis were not discussed. In these quarries patchy charnockites occur in various modes and associations. Some of these patches do occupy structural weak zones, such as shear bands and fold noses in the migmatitic gneisses, but many of the patchy charnockite bodies occur as branching veins transecting the gneissic foliation and hence do not account for fluid pathways. Most importantly, charnockitic leucosomes at margins of mafic granulite enclaves and charnockitic veins within some mafic granulite enclaves indicate a close genetic link between them via dehydration partial melting. This is further corroborated by trace element distribution between them. Dehydration partial melting in mafic rocks in a migmatite terrain such as Kabbaldurga, can explain all the different modes of the patchy charnockites as various stages of segregation and mobility relative to deformation. Abundant mafic granulite enclaves and field features suggesting a relatively late origin of the patchy charnockites, are compelling evidence against the notion of a transition zone. Mantle derivation age of the mafic source rocks (protoliths of mafic granulites) at Kabbaldurga at 3.08 ± 0.08 Ga with small positive ? values is virtually identical to the source of the massive charnockite of Karnataka craton at 3.08 Ga. This could imply a widespread mafic magmatism in South India around 3.0 Ga.

关键词： migmatite Zone Crustal Anatexis Mafic Magmatism

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