...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >U-Pb geochronology and Hf-Nd isotope compositions of the oldest Neoproterozoic crust within the Cadomian orogen: new evidence for a unique juvenile terrane
【24h】

U-Pb geochronology and Hf-Nd isotope compositions of the oldest Neoproterozoic crust within the Cadomian orogen: new evidence for a unique juvenile terrane

机译：Cadomian造山带中最古老的新元古代地壳的U-Pb年代学和Hf-Nd同位素组成：独特的幼年地层的新证据

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

New U-Pb dates, combined with Nd and Hf isotopic data, from rocks within the Port Morvan area of the Baie de St Brieuc region of Brittany identify a unique portion of the Neoproterozoic Cadomia terrane. Two gneisses near Port Morvan yielded U-Pb dates of 754.6 ± 0.8 Ma and 746.0 ± 0.9 Ma, ages that are more than 130 Myr older than the oldest units formed during the main phase of early Cadomian magmatism. Two trondhjemite boulders from the monogenetic facies of the Cesson conglomerate yielded identical ages of 665.2 ± 0.5 Ma and 665.5 ± 0.7 Ma, and a cobble from the polygenetic facies yields a ~(207)Pb-~(206)Pb date of 637 ± 2 Ma. Individual detrital zircons from a sandstone associated with the Cesson conglomerates yield concordant U-Pb dates ranging from 650 ± 3 Ma to 624.1 ± 0.6 Ma. Initial ε_(Nd) values for the rocks in this region range from +5.0 to +6.6, indicative of a substantial input from depleted mantle. Initial ε_(Hf) values determined on zircons from these Neoproterozoic rocks, including the detrital zircons, range from +6.7 to +14.5, consistent with the Nd isotopic results. Maximum initial ε_(Hf) values for two 2 Ga Icartian gneisses, considered basement to Cadomia, average +8.4 and +8.7. In contrast to the results of the Port Morvan rocks, 616-608 Ma syn-tectonic intrusions from Normandy and the British Channel Islands all have negative initial ε_(Nd) values (-10.4 to -8.3) consistent with significant contamination by ancient crust such as the 2 Ga gneisses. The oldest arc-related magmas should have interacted most extensively with Cadomian basement, buffering younger mantle-derived magmas that were generated in subsequent magmatic episodes. The rocks within the Port Morvan region are thus inconsistent as examples of the earliest Cadomian intrusions as they show no evidence of interaction with 2 Ga basement. Instead, the older ages and mantle-like isotopic composition of these rocks suggest they are part of an independent terrane that formed prior to, and independently from, the Cadomian arc. Possible terrane-scale structural boundaries have recently been identified, including the newly recognized Port Morvan thrust fault and the NW-dipping Main Cadomian thrust.
机译：来自布列塔尼Baie de St Brieuc地区Port Morvan区域内岩石的新的U-Pb日期与Nd和Hf同位素数据相结合，确定了新元古代Cadomia地层的独特部分。莫凡港附近的两个片麻岩的U-Pb年代分别为754.6±0.8 Ma和746.0±0.9 Ma，年龄比早期Cadomian岩浆作用主要阶段形成的最古老的单元年龄大了130 Myr。来自Cesson砾岩单相岩相的两个长白云母巨石的年龄相同，分别为665.2±0.5 Ma和665.5±0.7 Ma，而来自多岩相的卵石产生的〜（207）Pb-〜（206）Pb日期为637±2嘛。来自与Cesson砾岩相关的砂岩的单个碎屑锆石产生一致的U-Pb日期，范围从650±3 Ma到624.1±0.6 Ma。该区域岩石的初始ε_（Nd）值在+5.0至+6.6范围内，表明来自地幔耗尽。这些新元古代岩石（包括碎屑锆石）的锆石上确定的初始ε_（Hf）值在+6.7至+14.5之间，与Nd同位素结果一致。被认为是卡多米亚基底的两个2 Ga伊卡斯蒂安片麻岩的最大初始ε_（Hf）平均值为+8.4和+8.7。与Port Morvan岩石的结果相反，来自诺曼底和英吉利海峡群岛的616-608 Ma同构造侵入均具有负的初始ε_（Nd）值（-10.4至-8.3），这与古代地壳的大量污染相吻合。作为2个Ga片麻岩。最古老的与弧有关的岩浆应该与Cadomian基底发生最广泛的相互作用，以缓冲在随后的岩浆事件中产生的年轻的地幔衍生岩浆。因此，Port Morvan地区内的岩石与最早的Cadomian侵入岩不一致，因为它们没有证据表明与2 Ga地下岩相互作用。取而代之的是，这些岩石的年代久远和地幔状同位素组成表明它们是独立的地层的一部分，该地层是在卡多米弧之前形成的，并且独立于该弧。最近已经确定了可能的地表尺度结构边界，包括新近认识到的莫凡港逆冲断层和西北倾角的主要卡多夫逆冲断层。

著录项

相似文献

  • 外文文献
  • 中文文献
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号