Abstract The chemical composition of a basalt is a critical indicator of mantle thermal condition and tectonic setting. The Yangtze Block, which is a part of the Rodinia supercontinent, formed during the Neoproterozoic era presents an enigmatic thermal state of the mantle and tectonic evolution. We compiled a large database of petrogeochemical data on the Middle Tonian volcanic rocks covering the entire Jiangnan Orogen with a view to evaluate the evolution of the magma compute the composition of the primary magma, estimate the mantle potential temperature (Tp), and distinguish the tectonic setting. Calc-Alkaline picrites, basalts, and basaltic andesites (type A) from ca. 845–825 Ma and tholeiitic basalts (Type B) from ca. 860–830 Ma were both identified as interbedded layers accompanied with the Middle Tonian sedimentary sequences (the Fanjingshan Group and its equivalents) and geographically intersecting with each other along the Jiangnan Orogen. Geochemical and isotopic features of type A volcanic rocks indicate that they originated from an enriched mantle source. Both slab-derived fluids and fractionation of olivine and clinopyroxene played important roles during magma generation and evolution. The calculated composition of the primary magma is picritic and the estimated average Tp is 1404 °C. This temperature is consistent with the melting of a mantle wedge due to a rapid slab roll-back process, but it is lower by 166 °C than that produced by a hot mantle plume. Considering the occurrence of the arc-like type A volcanic rocks and the back-arc basin basalts (BABB)-like type B basalts along with contemporaneous sedimentary sequences with the bidirectional detritus sources in the Jiangnan Orogen, we hereby speculate a rear-arc setting for type A volcanic rocks and a back-arc setting for Type B basalts.

中文翻译：

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江南造山带中托尼阶钙碱性苦英岩、玄武岩和玄武安山岩：弧后岩浆作用的证据

摘要 玄武岩的化学成分是地幔热条件和构造环境的重要指标。扬子地块是罗迪尼亚超大陆的一部分，形成于新元古代，呈现出地幔和构造演化的神秘热状态。我们编制了覆盖整个江南造山带的中托期火山岩岩石地球化学数据的大型数据库，以评估岩浆演化，计算原生岩浆成分，估算地幔位温（Tp），区分构造构造。环境。钙碱性苦味岩、玄武岩和玄武质安山岩（A 型）来自约 约 845-825 Ma 和拉斑玄武岩（B 型）。860-830 Ma 均被确定为伴随中托期沉积层序（梵净山群及其等价物）的互层，并且沿江南造山带在地理上相互交叉。A型火山岩的地球化学和同位素特征表明它们起源于富集的地幔源。板片衍生流体以及橄榄石和斜辉石的分馏在岩浆生成和演化过程中都发挥了重要作用。计算出的原生岩浆成分为苦味酸盐，估计平均 Tp 为 1404 °C。由于板坯快速回滚过程，该温度与地幔楔的熔化温度一致，但比热地幔柱产生的温度低 166 °C。