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
• 来源期刊: 地学前缘（英文版）
• 年，卷（期）: 2021,（1）
• 所属期刊栏目: Research Paper
• 页码范围: 131-145
• 页数: 15页
• 语种: 英文

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 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 TiC2 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.