| Geochronological and geochemical evidence for a Late Ordovician to Silurian arc-back-arc system in the northern Great Xing'an Range,NE China |
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| 作者姓名： | Bo Liu Jia-Fu Chen Bao-Fu Han Jun-Lai Liu Jia-Wei Li |
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| 作者单位： | Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines;Key Laboratory of Mineral Resources Evaluation in Northeast Asia;State Key Laboratory of Geological Process and Mineral Resources;Ministry of Education |
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| 基金项目： | 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)。 |
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| 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 northwestern subduction of the Nenjiang Ocean.Such a subduction beneath the integrated Xing'an-Erguna Block also gave rise to the East Ujimqin-Xinglong igneous belt in a continental back-arc basin setting.Our new data support an early Paleozoic arc-back-arc model in the northern Great Xing'an Range.
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| 关 键 词： | Nenjiang ocean Arc-back-arc system Xing'an-Mongolian orogenic belt GABBROS Nb-enriched basalts |
| 收稿时间： | 23 October 2019 |
Geochronological and geochemical evidence for a Late Ordovician to Silurian arc–back-arc system in the northern Great Xing’an Range,NE China |
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| Bo Liu,Jia-Fu Chen,Bao-Fu Han,Jun-Lai Liu,Jia-Wei Li.Geochronological and geochemical evidence for a Late Ordovician to Silurian arc-back-arc system in the northern Great Xing'an Range,NE China[J].Geoscience Frontiers,2021,12(1):131-145. |
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| Authors: | Bo Liu Jia-Fu Chen Bao-Fu Han Jun-Lai Liu Jia-Wei Li |
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| Institution: | 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;Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources, Changchun 130061, China;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;State Key Laboratory of Geological Process and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;Ministry of Education, Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;State Key Laboratory of Geological Process and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;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 |
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| Abstract: | 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 and εNd(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 positive εNd(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 Nb-enriched basalts are parts of the Late Ordovician and Silurian Sonid Zuoqi–Duobaoshan arc belt, and they were formed by the northwestern subduction of the Nenjiang Ocean. Such a subduction beneath the integrated Xing’an–Erguna Block also gave rise to the East Ujimqin–Xinglong igneous belt in a continental back-arc basin setting. Our new data support an early Paleozoic arc–back-arc model in the northern Great Xing’an Range. |
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| Keywords: | Nenjiang ocean Arc–back-arc system Xing’an–Mongolian orogenic belt Tectonic evolution Gabbros Nb-enriched basalts |
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