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

摘要: Abstract The early Paleozoic tectonic evolution of the Xing’an–Mongolian Orogenic Belt is dominated by two oceanic basins on northwestern and southeastern sides Xing’an Block, i.e., Xinlin–Xiguitu Ocean Nenjiang Ocean. However, development remains unclear. Here, we present zircon U–Pb geochronology whole-rock elemental Sr–Nd isotopic data gabbros in Xinglong area together with andesitic tuffs basalts Duobaoshan area. LA-ICP-MS dating yielded crystallization ages 443–436 ​Ma 452–451 ​Ma, respectively. Early Silurian show calc-alkaline E-MORB affinities but they are enriched LILEs, depleted HFSEs, relatively low U/Th ratios 0.18–0.36 eNd(t) values −1.6 to +0.5. These geochemical features suggest that might originate from a mantle wedge modified pelagic sediment-derived melts, consistent back-arc basin setting. By contrast, characterized high MgO (>5 ​wt.%), Cr (138–200 ​ppm), Ni (65–110 ​ppm) contents, can be termed as high-Mg andesites. Their Sr/Y 15.98–17.15 0.24–0.25 moderate (La/Sm)n 3.07–3.26 similar those Setouchi Volcanic (SW Japan), thought derived partial melting subducted sediments, subsequent melt-mantle interaction. have Nb (8.44–10.30 ​ppm) TiO2 contents (1.17–1.60 ​wt.%), typical Nb-enriched basalts. They slightly younger than regional adakitic rocks positive +5.2 +5.7 interpreted generated source metasomatized earlier melts. Synthesized coeval arc-related igneous propose parts Late Ordovician Sonid Zuoqi–Duobaoshan arc belt, were formed subduction Such beneath integrated Xing’an–Erguna Block also gave rise East Ujimqin–Xinglong belt continental Our new support an arc–back-arc model northern Great Range.