Compositional and geochronological signatures of metamafic dykes from the Sangsang peridotites, South Tibet: Evidence for magma-starved forearc rifting during Neo-Tethyan subduction re-initiation  

作　　者：Chi Xu Hao Zheng Argyrios Kapsiotis Yang Xiao Zhifeng Wan 

机构地区：[1]School of Marine Sciences,Sun Yat-sen University,Zhuhai 519000,China [2]Southern Laboratory of Ocean Science and Engineering(Guangdong,Zhuhai),Zhuhai 519000,China

出　　处：《Geoscience Frontiers》2020年第6期2271-2286,共16页地学前缘（英文版）

基　　金：funded by the Fundamental Research Funds for the Central Universities in China(Grant No.19lgpy99);the National Natural Science Foundation of China(Grant Nos.41776056,41706055,41602231);the Natural Science Foundation of Guangdong Province(Grant Nos.2020A1515010501,2018B030311030)。

摘　　要：In this study we present new mineral chemistry,whole-rock geochemical and zircon U-Pb geochronological data for 12 metamafic dykes in the mantle sequence of the Sangsang ophiolite in South Tibet(China).Modal analyses of these dykes gave averages of^40%-65%plagioclase and^35%-60%amphibole and small amounts of(igneous)clinopyroxene,epidote and opaque minerals.This mineral assemblage resembles that of typical orthoamphibolites.Nevertheless,due to the absence of foliation the investigated rocks are described as metamafic lithologies.These rocks have primitive mantle(PM)-normalized multi-element patterns with negative Nb and Ta anomalies as well as weak,negative Ti anomalies.In addition,they have initial 87Sr/86Sr ratios[(87Sr/86Sr)1]of0.702844-0.703581,initial 143Nd/144Nd ratios[(143Nd/144Nd)i]of 0.512891-0.512959 and high εNd(t)values(+7.9 to+9.3).Uranium-Pb ages of magmatic zircons separated from the investigated metamafic dykes indicate that the parental melts of their protoliths intruded the Sangsang mantle at^119.0-118.5 Ma.The metamorphic mineral assemblages recognized in the investigated dykes are suggestive of a retrograde metamorphic process,from(epidote-)amphibolite facies(~470-610℃,-1.9-4.3 kbar)and to prehnitepumpellyite facies(≤280℃,<3 kbar),active within a rift-produced oceanic lithosphere.Microtextural and geochemical data suggest that the protoliths of the dykes were most likely massive gabbros.Compositional data show that the parental magmas of the gabbroic protoliths were generated by melting of a depleted mantle(DM)source that had been weakly modified by fluids emanating from a subducted oceanic lithospheric slab.The age of the gabbroic protoliths is slightly younger than the existing ages for ophiolites from the central Yarlung-Zangbo Suture Zone(YZSZ)in the literature(~129-123 Ma).We,therefore,suggest that the gabbroic protoliths of the Sangsang metamafic dykes were formed in an incipient forearc setting during Neo-Tethyan subduction reinitiation(Aptian).Our tectonomagmatic model provides

关 键 词：Zircon Dyke Ophiolite Sangsang Tibet NEO-TETHYS 

分 类 号：P588.3[天文地球—岩石学] P542[天文地球—地质学]