This paper presents zircon U–Pb dating and Hf isotopic, and whole-rock geochemical and Sr–Nd isotopic data for early Paleozoic igneous rocks as well as zircon U–Pb dating for the sedimentary rocks of the Songnen Massif within the eastern Central Asian Orogenic Belt (CAOB), aiming to reveal arc magma evolution process. The zircon U–Pb dating results of the siltstone of the Xiaojingou Formation yielded 450 Ma, 471 Ma, 502 Ma, 773 Ma, 818 Ma and 949 Ma age peaks, as well as multi-episodic Paleo-proterozoic ages (2486-1612 Ma), implying its deposition time is younger than ∼ 450 Ma. The zircon U–Pb dating results reveal that the Songnen Massif exists three episodes of volcanic rocks of the middle Cambrian (502 Ma), Middle Ordovician (453-449 Ma) and the Silurian (435-420 Ma). The middle Cambrian basalts are low-K tholeiitic to calc-alkaline series, weakly depleted ε(t) and ε(t) values. They were derived from the weakly depleted mantle metasomatized by slab fluid in an immature island arc setting. The Middle Ordovician to Silurian volcanic rocks show SiO of 49.4–58.1 wt%, plotting into high-K calc-alkaline series, which are also featured by higher Th/Nd and (Hf/Sm) ratios, together with moderate depleted ε(t) values, suggesting their derivation of the depleted mantle wedge metasomatized by sediment-derived melt. In contrast, coeval early Paleozoic volcanic rocks in the eastern Xing’an Massif with the MORB-like ε(t) values are characterized by an origin of the depleted mantle wedge and the distinct interaction of oceanic crust melt and mantle peridotite. Combined with the variation of calculated crust thickness, we suggested that there was a continental arc in the eastern Songnen Massif, which developed from immaturity to maturity during middle Cambrian to Silurian, while the early Paleozoic island arc in the eastern Xing’an Massif is characterized by ocean ridge subduction process.

中文翻译：

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中亚造山带东部两个不同的早古生代俯冲带：俯冲再循环和弧演化的证据


本文介绍了早古生代火成岩的锆石 U-Pb 定年和 Hf 同位素、全岩地球化学和 Sr-Nd 同位素数据，以及中亚造山带东部松嫩地块沉积岩的锆石 U-Pb 定年数据。带（CAOB），旨在揭示岛弧岩浆演化过程。小金沟组粉砂岩锆石U-Pb定年结果显示450 Ma、471 Ma、502 Ma、773 Ma、818 Ma和949 Ma年龄峰值，以及多幕式古元古代年龄（2486-1612 Ma） ），表明其沉积时间小于~ 450 Ma。锆石U-Pb测年结果​​表明，松嫩地块存在中寒武世（502Ma）、中奥陶世（453-449Ma）和志留世（435-420Ma）3期火山岩。中寒武统玄武岩为低钾拉斑玄武岩至钙碱性系列，ε(t)和ε(t)值弱贫化。它们源自未成熟岛弧环境中由板片流体交代的弱贫化地幔。中奥陶统至志留纪火山岩的 SiO 含量为 49.4%~58.1%，属于高钾钙碱性系列，具有较高的 Th/Nd 和 (Hf/Sm) 比值，以及中等贫化的 ε(t) 特征。 ）值，表明它们源自由沉积物熔融交代的贫化地幔楔。相比之下，兴安地块东部同期早古生代火山岩具有类MORB ε(t)值，其特征是贫乏地幔楔的起源以及洋壳熔体与地幔橄榄岩的明显相互作用。 结合计算地壳厚度的变化，认为松嫩地块东部存在大陆弧，在中寒武世至志留世由未成熟期发育到成熟期，而兴安地块东部则以早古生代岛弧为特征。受洋脊俯冲过程影响。