Abstract The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens in the world. The mechanism of continental growth and tectonic evolution of the CAOB remain debated. Here we present an overview of Early Paleozoic ophiolitic melanges, calc-alkaline intrusions, and metamorphic rocks in West Junggar with an aim to provide constraints on the time and mechanism of subduction initiation in the Junggar Ocean, a branch of the southern Paleo-Asian Ocean (PAO). The Early Paleozoic ophiolitic melanges are composed of ultramafic-mafic rocks, cherts, pelagic limestones, basaltic breccias and tuffs. The mafic rocks from these ophiolitic melanges are divided into MORB-like and OIB-like types. The MORB-like rocks were formed in a fore-arc setting, but the OIB-like mafic rocks were formed by the intra-plate magmatism related to mantle plume activities. The Early Paleozoic intrusions are occurred as small stocks with a dominant composition of diorite, trondhjemite, and granodiorite. These granitoids display (high-K) calc-alkaline affinities, and have high and positive eNd(t) and eHf(t) values, formed in an arc-related setting. The metamorphic complex is mainly composed of blueschist and amphibolite blocks with metamorphism ages ranging from ~500 Ma to ~460 Ma. Their protoliths are calc-alkaline andesite and tholeiitic and alkaline basalts, formed in an arc related and seamount setting, respectively. It is clearly show that the West Junggar was under an intra-oceanic subduction regime during the Early Paleozoic, and the initial subduction of the southern PAO might have occurred in the Early Cambrian. Based on our observations, and in combination with previous work, we propose the plume-induced subduction initiation model for the Early-Middle Cambrian tectonic evolutionary of the Junggar Ocean. Our new model not only shed light on subduction initiation dynamics of the southern PAO, but also contribute to tectonic evolution of the CAOB.

中文翻译：

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准噶尔洋内早寒武世羽流诱发的俯冲起始事件：蛇绿混杂岩、弧岩浆作用和变质岩的见解

摘要 中亚造山带（CAOB）是世界上最大的增生造山带之一。CAOB 的大陆生长和构造演化的机制仍然存在争议。在这里，我们概述了西准噶尔早古生代蛇绿岩混杂岩、钙碱性侵入岩和变质岩，旨在为古亚洲南部的一个分支准噶尔洋的俯冲开始时间和机制提供限制。 (PAO)。早古生代蛇绿混杂岩由超镁铁质-镁铁质岩石、燧石、远洋灰岩、玄武角砾岩和凝灰岩组成。这些蛇绿混杂岩中的基性岩分为类 MORB 和类 OIB 类型。类似 MORB 的岩石形成于前弧环境中，但类 OIB 基性岩是由与地幔柱活动相关的板内岩浆作用形成的。早古生代侵入岩以闪长岩、长闪长岩和花岗闪长岩为主成分的小岩体出现。这些花岗岩显示出（高 K）钙碱性亲和力，并具有高且正的 eNd(t) 和 eHf(t) 值，形成于与弧相关的环境中。变质杂岩主要由蓝片岩和角闪岩块体组成，变质年龄从~500 Ma到~460 Ma。它们的原岩是钙碱性安山岩和拉斑玄武岩和碱性玄武岩，分别形成于弧相关和海山环境中。清楚地表明西准噶尔在早古生代处于洋内俯冲状态，PAO 南部的最初俯冲可能发生在早寒武世。基于我们的观察，并结合前人的工作，我们提出了准噶尔洋早-中寒武世构造演化的羽流诱发俯冲起始模型。我们的新模型不仅揭示了南部 PAO 的俯冲起始动力学，而且还有助于 CAOB 的构造演化。