Geochronological and geochemical evidence for a Late Ordovician to Silurian arc-back-arc system in the northern Great Xing'an Range,NE China  

作　　者：Bo Liu Jia-Fu Chen Bao-Fu Han Jun-Lai Liu Jia-Wei Li 

机构地区：[1]Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines,Department of Geology,School of Resources and Civil Engineering,Northeastern University,Shenyang 110819,China [2]Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources,Changchun 130061,China [3]State Key Laboratory of Geological Process and Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China [4]Ministry of Education,Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China

出　　处：《Geoscience Frontiers》2021年第1期131-145,共15页地学前缘（英文版）

基　　金：supported by National Natural Science Foundation of China(41802236);“the Fundamental Research Funds for the Central universities”(N170103013,N2001004 and N170104022);Opening Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources(DBY-KF-18-05)。

摘　　要：The early Paleozoic tectonic evolution of the Xing'an-Mongolian Orogenic Belt is dominated by two oceanic basins on the northwestern and southeastern sides of the Xing'an Block,i.e.,the Xinlin-Xiguitu Ocean and the Nenjiang Ocean.However,the early development of the Nenjiang Ocean remains unclear.Here,we present zircon U-Pb geochronology and whole-rock elemental and Sr-Nd isotopic data on the gabbros in the Xinglong area together with andesitic tuffs and basalts in the Duobaoshan area.LA-ICP-MS zircon U-Pb dating of gabbros and andesitic tuffs yielded crystallization ages of 443-436 Ma and 452-451 Ma,respectively.The Early Silurian Xinglong gabbros show calc-alkaline and E-MORB affinities but they are enriched in LILEs,and depleted in HFSEs,with relatively low U/Th ratios of 0.18-0.36 andεNd(t)values of-1.6 to+0.5.These geochemical features suggest that the gabbros might originate from a mantle wedge modified by pelagic sediment-derived melts,consistent with a back-arc basin setting.By contrast,the andesitic tuffs are characterized by high MgO(>5 wt.%),Cr(138-200 ppm),and Ni(65-110 ppm)contents,and can be termed as high-Mg andesites.Their low Sr/Y ratios of 15.98-17.15 and U/Th values of 0.24-0.25 and moderate(La/Sm)_n values of 3.07-3.26 are similar to those from the Setouchi Volcanic Belt(SW Japan),and are thought to be derived from partial melting of subducted sediments,and subsequent melt-mantle interaction.The Duobaoshan basalts have high Nb(8.44-10.30 ppm)and TiO2 contents(1.17-1.60 wt.%),typical of Nb-enriched basalts.They are slightly younger than regional adakitic rocks and have positiveεNd(t)values of+5.2 to+5.7 and are interpreted to be generated by partial melting of a depleted mantle source metasomatized by earlier adakitic melts.Synthesized with coeval arc-related igneous rocks from the southeastern Xing'an Block,we propose that the Duobaoshan high-Mg andesitic tuffs and Nbenriched basalts are parts of the Late Ordovician and Silurian Sonid Zuoqi-Duobaoshan arc belt,and they were formed by the nor

关 键 词：Nenjiang ocean Arc-back-arc system Xing'an-Mongolian orogenic belt GABBROS Nb-enriched basalts 

分 类 号：P59[天文地球—地球化学] P534.4[天文地球—地质学]