首页> 外文期刊>Journal of Asian earth sciences >Emplacement and metamorphism of the mafic rocks from the Chencai terrane within the Cathaysia Block: Implications for the Paleozoic orogenesis of the South China Block
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Emplacement and metamorphism of the mafic rocks from the Chencai terrane within the Cathaysia Block: Implications for the Paleozoic orogenesis of the South China Block

机译:华夏地块内陈财地块的镁铁质岩的沉积和变质作用:对华南地块古生代造山的意义

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摘要

Understanding the Early Paleozoic tectonic evolution of the South China Block (SCB) is critical in constraining its relationship with (super-) continent configurations, such as the Rodinia and Gondwana. High-grade mafic and supracrustal rocks occurring in the Chencai terrane of the Cathaysia Block are the uplifted lower crustal components of the Kwangsian (Early Paleozoic) Orogen which extensively reshaped many parts of the SCB. Two amphibolites, three biotite-bearing amphibolites, one norite and one mafic granulite were collected from the Chencai terrane. In previous studies, these rocks (or their protoliths) have been suggested to belong to the same cumulate series and the mafic granulite records metamorphic P-T conditions of a high-geothermal-gradient environment (similar to 30 degrees C/km). Our SIMS zircon U-Pb results indicate that protoliths of these meta-mafic rocks were emplaced at similar to 434-445 Ma and most of them have experienced subsequent (almost synchronous) metamorphism at 428-439 Ma. The norite sample (434 Ma), which experienced the least crustal contamination and the least metamorphic alteration, has the lowest zircon delta O-18 values of similar to+ 6.7 parts per thousand (V-SMOW), whereas the mafic granulite which experienced the highest grade metamorphism has the highest zircon delta O-18 values of similar to+9.4 parts per thousand (V-SMOW). Zircon delta O-18 values of other samples mostly scatter between them. Most metamorphic zircons have younger U-Pb ages and higher delta O-18 values than magmatic zircons. High delta O-18 crustal materials (e.g. sedimentary rocks) have possibly been involved during the metamorphism which resulted in the contrasting delta O-18 values of magmatic and metamorphic zircons. The large variations in delta O-18 values shown by magmatic zircons of each sample (like the amphibolite and biotite-bearing amphibolite) indicate that the high-delta O-18-value crustal materials (sedimentary rocks) must have started to affect these mafic rocks since the magmatic stage. Zircon 178 (Hf)/177(Hf) values of each of these samples scatter within small ranges. Initial epsilon(Hf)(t) values of most zircons fall in between the CHUR line and the DM linear model line, indicating that these mafic rocks were derived from an enriched mantle source. Combined with previous geochronological, metamorphic and geochemical data, we propose that these Paleozoic mafic magmatism might have contributed thermal energy to the later thermal relaxation of the orogeny. This episode of mafic magmatism may represent a transition of the Kwangsian Orogen from early compression to post-orogenic extension. Metamorphism of these mafic rocks and the synchronous anatexis indicated by the high grade supracrustal rocks from Chencai terrane, might be related with extension rather than orogenic compression.
机译:了解华南地块(SCB)的早期古生代构造演化对于限制其与(超级)大陆构造(如Rodinia和Gondwana)的关系至关重要。在华夏地块的Chencai地层中出现的高级镁铁质和地壳上岩石是广生造山带(早古生代)隆升的下地壳成分,广泛地重塑了SCB的许多部分。从Chencai地层中收集了2个闪石,3个含黑云母的闪石,1个黑土和1个镁铁质花岗石。在以前的研究中,这些岩石(或它们的原生石)被认为属于相同的堆积系列,而镁铁质花岗石记录了高地热梯度环境(类似于30摄氏度/公里)的变质P-T条件。我们的SIMS锆石U-Pb结果表明,这些准镁铁质岩石的原岩在大约434-445 Ma处就位,并且大多数在428-439 Ma处经历了随后的(几乎同步的)变质作用。地壳污染最少,变质变化最少的Norite样品(434 Ma)具有最低的锆石δO-18值,约为+ 6.7千分之一(V-SMOW),而镁铁质粒岩的样品最高等级变质具有最高的锆石δO-18值,接近+9.4千分之多(V-SMOW)。其他样品的锆石δO-18值大多分散在它们之间。与岩浆锆石相比,大多数变质锆石具有更年轻的U-Pb年龄和更高的δO-18值。高变质O-18地壳物质(例如沉积岩)可能与变质作用有关,这导致了岩浆和变质锆石的相对变质O-18值。每个样品的岩浆锆石(如角闪石和含黑云母的角闪石)显示的O-18值变化很大,表明高δO-18值地壳物质(沉积岩)必定已经开始影响这些镁铁质岩体。岩浆阶段以来的岩石。这些样品中每一个的锆石178(Hf)/ 177(Hf)值均在较小范围内散布。大多数锆石的初始epsilon(Hf)(t)值介于CHUR线和DM线性模型线之间,这表明这些镁铁质岩石均来自丰富的地幔源。结合以前的地质年代,变质和地球化学数据,我们认为这些古生代铁镁质岩浆作用可能为造山带的后期热弛豫贡献了热能。镁铁质岩浆作用的这一事件可能代表了Kwangsian造山带从早期压缩到造山后扩展的过渡。这些岩质岩的变质作用和陈财地层中的高级表壳岩所指示的同步麻醉作用可能与伸展而不是造山压缩有关。

著录项

  • 来源
    《Journal of Asian earth sciences》 |2019年第15期|11-28|共18页
  • 作者单位

    Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, 19 Beituchengxi Rd, Beijing 100029, Peoples R China|Univ Wollongong, Sch Earth Atmospher & Life Sci, GeoQuEST Res Ctr, Wollongong, NSW 2522, Australia;

    Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, 19 Beituchengxi Rd, Beijing 100029, Peoples R China|Hebei GEO Univ, Shijiazhuang 050031, Hebei, Peoples R China;

    Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, 19 Beituchengxi Rd, Beijing 100029, Peoples R China|Univ Chinese Acad Sci, Key Lab Computat Geodynam, Beijing 100049, Peoples R China;

    Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China;

    Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, 19 Beituchengxi Rd, Beijing 100029, Peoples R China;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    SIMS zircon U-Pb geochronology; Zircon Lu-Hf and O isotopes; Lower-crustal components; South China Paleozoic orogen; Cathaysia Block;

    机译:SIMS锆石U-Pb年代学;Zrcon Lu-Hf和O同位素;下地壳组分;华南古生代造山带;Cathaysia区块;
  • 入库时间 2022-08-18 04:13:06

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