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首页> 外文期刊>Contributions to Mineralogy and Petrology >Recycling of sediment into the mantle source of K-rich mafic rocks: Sr-Nd-Hf-O isotopic evidence from the Fushui complex in the Qinling orogen
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Recycling of sediment into the mantle source of K-rich mafic rocks: Sr-Nd-Hf-O isotopic evidence from the Fushui complex in the Qinling orogen

机译：沉积物再循环到富钾镁铁质岩的地幔源中：秦岭造山带富水联合体的Sr-Nd-Hf-O同位素证据

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摘要

Potassium (K)-rich mafic rocks are viewed as being derived from partial melting of an enriched mantle source, but it is controversial about which processes cause the mantle enrichment. The Fushui intrusive complex is the largest early Paleozoic K-rich intrusive complex in the eastern Qinling orogen. Therefore, detailed studies on the Fushui complex can contribute not only to understanding of the petrogenesis of K-rich mafic rocks, but also to unraveling the Paleozoic evolution of the Qinling orogen. In this study, we provide an integrated investigation of in situ zircon U-Pb dating and Hf-0 isotopes, in combination with whole-rock major and trace elements, as well as Sr-Nd-Hf isotopes, for the Fushui intrusive complex. In situ zircon secondary ion mass spectrometry (SIMS) / laser ablation induction coupled plasma mass spectrometry (LA-ICPMS) U-Pb dating reveals that different rock types of the Fushui complex have identical formation ages of 488-484 Ma. The Fushui complex belongs to the shoshonitic series, and is characterized by extreme large ion lilhophile element (LILE, e.g., Ba, U. Th and Sr) and Pb enrichment and depletion of high field-strength elements (HFSHs. e.g. Nb, Ta, Zr, Hf, P and Ti). It shows high initial Sr isotopic ratios (0.7100-0.7151), negative whole-rock ε_(Nd)(t) (-3.97 to -5.68) and negative to slight positive whole-rock (-2.24 to 2.38) and zircon (-2.85 to 0.34) ε_(Hf){t) values, as well as high zircon δ~(18)O values (6.86 ± 0.13 ‰). The HI'-Nd isotopic systems are decoupled with positive Δε_(Hf) values (3.85-5.37). These geochemical features indicate that the mantle source has incorporated subducted zircon-barren oceanic sediments. A simple two-end-members mixing model constrains the amount of subducted sediments in the Fushui mantle source to 5-8 %. The Fushui complex originated from 1 to 6 % equilibrium melting of a phlogopite-bearing garnet lherzolite by non-modal melting. As shoshonitic magmas have been discovered in modern nascent arcs, we suggest that the generation of the Fushui complex was induced by the subduction of the Paleotethyan Ocean, when it jumped from the northern to the southern boundary of the North Qinling microcontinent.
机译：富含钾（K）的镁铁质岩被认为是来自富集地幔源的部分熔融，但关于哪个过程引起地幔富集存在争议。抚水侵入复合体是东秦岭造山带中最大的早古生代富钾侵入复合体。因此，对Fu水复合体的详细研究不仅有助于了解富含钾的镁铁质岩石的岩石成因，而且有助于揭示秦岭造山带的古生代演化。在这项研究中，我们提供了对the水侵入性配合物的原位锆石U-Pb测年和Hf-0同位素以及全岩石主要和微量元素以及Sr-Nd-Hf同位素的综合研究。原位锆石二次离子质谱（SIMS）/激光烧蚀诱导耦合等离子体质谱（LA-ICPMS）的U-Pb测年表明，抚水矿床的不同岩石类型具有相同的形成年龄488-484 Ma。 Fu水配合物属于肖氏铁酸系列，其特征是具有超大离子的亲锂元素（LILE，例如Ba，U。Th和Sr）以及高场强元素（HFSHs，例如Nb，Ta， Zr，Hf，P和Ti）。它显示出较高的初始Sr同位素比（0.7100-0.7151），负全岩ε_（Nd）（t）（-3.97至-5.68）和负至轻度正全岩（-2.24至2.38）和锆石（-2.85）到0.34）ε_（Hf）{t）值，以及高锆石δ〜（18）O值（6.86±0.13‰）。 HI'-Nd同位素系统与正Δε_（Hf）值（3.85-5.37）分离。这些地球化学特征表明，地幔源已包含俯冲的锆石-贫瘠的海洋沉积物。一个简单的两端混合模型将阜水地幔源中俯冲沉积物的量限制在5-8％。抚水复合物是通过非模态熔融，使含金云母的石榴石绿铁矿的平衡熔融达到1％至6％。由于在现代新生弧中发现了尖晶岩岩浆，我们认为，阜水复合体的产生是由古埃及的俯冲作用引起的，当它从北秦岭微大陆的北部边界跳到南部边界时。

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