QQ登录
微博登录
微信登录
新科学想法 › 学术文库 › 学术文献 › 浏览文献

有读书笔记U–Pb baddeleyite ages, distribution and geochemistry of 925Ma mafic dykes and 900Ma sills in the North China craton: Evidence for a Neoproterozoic mantle plume

唐唐 添加于 2011-11-8 05:37 | 2133 次阅读 | 0 个评论

  •  作 者

    Peng P, Bleeker W, Ernst RE, Söderlund U, McNicoll V

  •  摘 要

    Numerous Neoproterozoic mafic dykes, referred to as the Dashigou swarm, are identified in the central and southeastern parts of the North China craton (NCC). They are 305–010° trending dykes, with widths of ~ 10–100 m and exposed lengths of several to > 10 km. Precise U–Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS) measurements on baddeleyite grains separated from three dykes yield 207Pb/206Pb average ages of 924.0 ± 3.7 Ma (Dashigou dyke), 921.8 ± 2.6 Ma (Yangjiaogou dyke) and 925.8 ± 1.7 Ma (Taohuagou dyke). Baddeleyite grains from a late-stage pegmatite vein in the Dashigou dyke were analyzed by secondary ion mass spectrometry (SIMS) methods. These yield a207Pb/206Pb average age of 920.4 ± 5.7 Ma. The Dashigou dyke swarm exhibits an overall radiating geometry (the overall fan angle is about 60°), with a focal point located along the southern margin of the eastern NCC, where a large ca. 900 Ma sill swarm was previously recognized. The rift system hosting these slightly younger sills, named the Xu–Huai Rift System, could represent two breakup-parallel arms of a rift–rift–rift triple junction related to the initiation of the magma center that produced the Dashigou dykes. The sills have similar characteristics and could be cogenetic with the Dashigou dykes. The Dashigou dykes are coarse-grained, composed mainly of clinopyroxene and plagioclase feldspar, with or without olivine. One of the most primitive dykes has 47.79 wt.% SiO2, 6.41 wt.% MgO, 1.38 wt.% TiO2, 17.77 wt.% Al2O3, 10.47 wt.% CaO and 0.62 wt.% K2O. It shows slight enrichment in light rare earth elements and a slightly positive Eu/Eu* anomaly (1.1), and is slightly depleted in high field-strength elements compared to neighboring elements on a primitive mantle-normalized spidergram. The Dashigou dykes show some similarities with enriched-mid ocean ridge basalts (E-MORB) or ocean island basalts (OIB) and have εNdt values of + 1.8 to + 3.1 and 87Sr/86Srt values of 0.7019–0.7047 (t = 920 Ma). All these characteristics indicate that they are not likely derived from the ancient lithospheric mantle under the NCC, but rather from amantle source below, in the asthenosphere. This 925–900 Ma magmatism represents a second sub-lithospheric mantle upwelling event following the 1780–1730 Ma event that occurred shortly (~ 70 Ma) after the formation of the subcontinental lithospheric mantle (SCLM). Therefore the SCLM of the NCC was multiply metasomatized during asthenospheric upwellings (at least at 1780–1730 and 925–900 Ma), before most of its eastern part was finally removed during the Mesozoic. Collectively, these ~ 925 Ma dykes and ~ 900 Ma sills constitute a large igneous province (LIP) with an areal extent of about 0.5 Mkm2 and a diameter of about 1000 km. This LIP probably resulted from aNeoproterozoicmantleplume centered along the present southern margin of the eastern NCC, and probably resulted in the break-off and rifting away of a separate crustal block. We speculate that this conjugate block could have been the combined São Francisco–Congo craton on the basis of precisely matched ages for the Bahia dykes (São Francisco craton) and Gangila–Mayumbian volcanic associations (western part of the Congo craton).

  •  详细资料

    • 文献种类: Journal Article
    • 期刊名称: Lithos
    • 期刊缩写: Lithos
    • 期卷页: 2011年  第127卷 第1-2期 210-221页
    • ISBN: 0024-4937

  • 学科领域 自然科学 » 地球科学

  •  所属群组

    环境科学  

  • 相关链接 DOI URL 

  •  唐唐 的文献笔记  订阅

    华北克拉古大陆重建研究获进展

    华北克拉通新元古代大石沟基性岩墙群与裂谷系分布及9亿年前大陆格局假想图
     
    岩浆地质记录不仅是人们认识地球早期演化和古大陆重建的主要依据之一，也是矿产资源探查的重点关注对象。目前，华北克拉通报道的新元古代（5.4-10亿年之前）岩浆记录非常少，因此对其古大陆重建和矿产资源潜力的认识存在争议。
     
    中科院地质与地球物理研究所岩石圈演化国家重点实验室彭澎副研究员与合作者在国家自然科学 基金资助下，于华北克拉通内部发现了一些新元古代大型基性岩墙（大石沟岩墙群），同位素稀释等离子质谱法获得其斜锆石U-Pb年龄为9.26-9.20亿 年。这些岩墙分布于华北克拉通中-北和东部，宽10-100 m，出露长度达10 km，分布范围可能达到上千公里，构成了一个大岩浆岩省。它们组成一个发散状的几何形态，几何中心位于华北克拉通东南缘；该区域分布着一些时代稍晚（～9 亿年）、性质相近的岩床杂岩（参考链接）；这些岩床所在的裂谷，可能构成了一个三叉裂谷系，代表华北克拉通与相邻古陆裂离的部位。基性岩墙群的含义明确， 是地质演化的构造标志和时间标尺，是古大陆重建的关键地质记录（参考链接）。在全球主要基性岩墙群数据库中，圣弗朗西斯科-刚果（São Francisco-Congo）克拉通有同时代的相关记录，推测华北克拉通该时期有可能与其相连。与17.8亿年前的大型基性岩墙群（参考链接）一样， 这一岩浆活动可能有软流圈或者地幔柱物质贡献，推测华北克拉通的大陆岩石圈地幔在中生代克拉通破坏之前，受到过至少两次（17.8和9.2亿年）改造和弱 化，活动中心位于克拉通东部的～9.2亿年的岩浆活动影响可能更大。
     
    大岩浆岩省和三叉裂谷系对探查硫化物和氧化物矿藏非常重要，而古大陆重建为矿产资源的分布预测提供了可供对比的对象，这一研究为在华北克拉通进行新元古代找矿探查工作提供了新的重要地质依据。
     
    该研究成果近期发表在国际知名的岩石学领域期刊《国际矿物学、岩石学与地球化学期刊》（Lithos） 上（Peng et al., U-Pb baddeleyite ages, distribution and geochemistry of 925 Ma mafic dykes and 900 Ma sills in the North China craton: Evidence for a Neoproterozoic mantle plume. Lithos，2011, 127: 210-221）。（来源：中科院地质与地球物理研究所）
管理选项： 导出文献|

评论(0 人)

facelist doodle 涂鸦板

求全文 推荐 收藏

1 人收藏

该用户的其他文献

Copyright;  © 新科学想法 2016-2017   浙公网安备 33010202000686号   ( 浙ICP备09035230号-1 )