...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Contributions to Mineralogy and Petrology >Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonic setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems
【24h】

Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonic setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems

机译：含霞石片麻岩的锆石大晶体的地质年代学对构造环境的限制：对U-Pb和Lu-Hf同位素系统复位的影响

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

Nepheline-bearing gneisses from the 75 km2 Tambani body in the Mozambique Belt of southern Malawi, are miaskitic biotite-nepheline monzodiorites, reflecting an absence of K-feldspar, alkali amphiboles or pyroxenes, and contain euhedral zircon megacrysts up to 5 cm across. The zircons contain U = 1–1,860 ppm, Th = 0–2,170 ppm and Y = 400–1,100 ppm, and very low concentrations of all other measured trace elements except Hf (HfO2 = 0.53–0.92 wt. %). Cathodoluminescence images reveal oscillatory sector growth zoning and no evidence for xenocrystic cores, indicating that the zircons represent primary magmatic crystallization products that have survived amphibolite grade metamorphism. U-Pb isotopic analyses (by TIMS) yield an upper intercept age of 730 ± 4 Ma (MSWD = 1.7), which we interpret as the time of magmatic crystallization of the zircons. This is coincident with 11 SHRIMP spot analyses, which yield a mean age of 729 ± 7 Ma (MSWD = 0.37). Metamorphism, at 522 ± 17 Ma as suggested by monazite, caused partial Pb-loss during local recrystallization of zircon. Lu-Hf isotopic data for three whole-rock samples of nepheline-bearing gneiss are collinear with those for zircon megacrysts, and correspond to an age of 584 ± 17 Ma (MSWD = 0.37. We interpret the Lu-Hf array to represent a mixing line defined by the Hf isotopic signature of primary zircon and that of the rock-forming minerals reset during metamorphic (re-)crystallization; hence the 584 Ma age is likely geologically meaningless. Given the well-defined association of nepheline syenites (and phonolitic volcanic equivalents) with continental rifting, we suggest that the Tambani body represents a magmatic product formed at 730 Ma during the break-up of the Rodinia supercontinent. The 522 Ma age is akin to other Pan-African metamorphic ages that record collisional suturing events during the final assembly of Gondwana. Zircon-bearing nepheline gneisses thus preserve a record of intra-continental rifting and of continental collision in southern Malawi.
机译：来自马拉维南部莫桑比克地带75 km2 Tambani体中的含霞石片麻岩为含镁长石，黑云母辉闪石，反映出不含钾长石，碱性闪石或辉石，并且含有正电子锆石大晶体，最多5个厘米。锆石中的U含量为1–1,860 ppm，Th = 0–2,170 ppm，Y = 400–1,100 ppm，除Hf外，其他所有痕量元素的浓度都非常低（HfO2 = 0.53-0.92 wt。％） 。阴极发光图像显示出振荡的扇形区增长带，并且没有异晶核的证据，表明锆石代表了主要的岩浆结晶产物，它们在角闪石级变质中幸存了下来。 U-Pb同位素分析（通过TIMS）得出的最高截距年龄为730±4 Ma（MSWD = 1.7），我们将其解释为锆石的岩浆结晶时间。这与11个SHRIMP点分析相吻合，平均年龄为729±7 Ma（MSWD = 0.37）。独居石表明，在522±17 Ma的变质作用在锆石的局部重结晶过程中造成了部分Pb损失。三个含霞石的片麻岩全岩样品的Lu-Hf同位素数据与锆石大晶岩的Lu-Hf同位素数据共线，对应的年龄为584±17 Ma（MSWD = 0.37）。我们解释了Lu-Hf阵列以表示混合由初级锆石的Hf同位素特征和成岩矿物的特征线确定的线，在变质（再）结晶过程中复位；因此584 Ma年龄在地质上可能是无意义的。鉴于霞石正长岩（和晚火山岩火山岩）的定义明确等价物）的大陆裂谷作用，我们认为Tambani体代表了在Rodinia超大陆分裂过程中在730 Ma形成的岩浆产品。522 Ma的年龄类似于记录了在该过程中发生碰撞缝合事件的其他泛非变质年龄。含锆石的霞石片麻岩因此保留了马拉维南部大陆内裂谷和大陆碰撞的记录。

著录项

  • 来源
    《Contributions to Mineralogy and Petrology》 |2007年第4期|389-403|共15页
  • 作者

    L. D. Ashwal; R. A. Armstrong; R. J. Roberts; M. D. Schmitz; F. Corfu; C. J. Hetherington; K. Burke; M. Gerber;

  • 作者单位

    School of Geosciences University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa;

    Research School of Earth Sciences The Australian National University Mills Road Canberra 0200 ACT Australia;

    School of Geosciences University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa;

    Department of Terrestrial Magnetism Carnegie Institution of Washington 5241 Broad Branch Road Washington DC 20015 USA;

    Department of Geosciences University of Oslo P.O. Box 1047 Blindern 0316 Oslo Norway;

    Department of Geosciences University of Massachusetts 611 North Pleasant Street Amherst MA 01003-9297 USA;

    School of Geosciences University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa;

    School of Geosciences University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa;

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

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