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首页> 外文学位 >Tectonic implications of para- and orthogneiss geochronology and geochemistry from the southern Appalachian crystalline core.
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Tectonic implications of para- and orthogneiss geochronology and geochemistry from the southern Appalachian crystalline core.

机译：来自阿巴拉契亚南部结晶岩心的准和正斜纪的年代学和地球化学的构造意义。

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摘要

Sedimentary and metasedimentary rocks the southern Appalachian Blue Ridge and Inner Piedmont contain a valuable record of Late Proterozoic Laurentian margin evolution following the breakup of Rodinia. These paragneisses contain rift-and-drift facies cover rocks deposited unconformably on Grenville basement in the western and eastern Blue Ridge. Paleogeographic reconstructions and increasing amounts of geochronologic and isotopic data limit the derivation of most southern Appalachian crystalline core cover sequences to the Laurentian and/or west Gondwanan craton(s). Southern Appalachian crystalline core paragneiss samples have &egr;Nd values between -8.5 and -2.0 at the time of deposition and contain abundant 1.1--1.25 Ga zircon cores with Grenville 1.0--1.1 Ga metamorphic rims. Less abundant detrital zircon core ages include pre-Grenvillian Middle Proterozoic 1.25--1.6 Ga, Early Proterozoic 1.6--2.1 Ga, and Late Archean 2.7--2.9 Ga sources. Blue Ridge Grenvillian basement has almost identical &egr;Nd values and displays the same dominant magmatic core and metamorphic rim zircon ages. Based on these data, nonconformable basement-cover relationships, and crustal ages in eastern North America, we suggest that the extensive sedimentary packages in the southern Appalachian Blue Ridge and western Inner Piedmont are derived from Laurentia. Relatively high initial 87Sr/86Sr values between 0.707 and 0.723, Middle to Upper Proterozoic TDM ages, high SiO2 content, LREE enrichment, low chemical index of alteration values mostly between 41 and 66, and restricted Th/Sc and Zr/Sc values for Laurentian sedimentary and metasedimentary samples further support derivation from Grenvillian rocks like those exposed in the western Blue Ridge. &egr; Nd values from Carolina terrane volcanic, plutonic, and volcaniclastic rocks are isotopically less evolved than southern Appalachian paragneisses and Blue Ridge Grenvillian basement easily separating this composite terrane from the mostly Laurentian terranes to the west. Neoproterozoic (∼590 Ma), Ordovician (peaks at ∼500 and ∼485 Ma), and Silurian (peak at ∼435 Ma), as well as Grenvillian and older, zircons in eastern Inner Piedmont paragneisses indicate that these rocks were deposited much later (late Silurian to Devonian) and could be entirely derived from a Panafrican source or possibly a mixture of Panafrican and recycled Laurentian margin assemblages. (Abstract shortened by UMI.)
机译：阿巴拉契亚山脉南部南部的沉积和准沉积沉积岩石和罗丹尼亚解体后的晚元古代劳伦式边缘演化具有重要的记录。这些石碑包含裂谷和漂移相覆盖的岩石，这些岩石不均匀地沉积在蓝岭西部和东部的格伦维尔地下室。古地理的重建以及不断增加的地质年代学和同位素数据限制了大多数南阿巴拉契亚山脉的岩心覆盖层序列向劳伦系和/或西贡多瓦南克拉通的推导。南部阿巴拉契亚结晶岩心石矿样品在沉积时的Nd值在-8.5至-2.0之间，并且含有丰富的1.1--1.25 Ga锆石核和Grenville 1.0--1.1 Ga变质边沿。较少的碎屑锆石核心年龄包括格伦维利亚前元古代1.25--1.6 Ga，元古代早期1.6--2.1 Ga和太古代2.7--2.9 Ga。 Blue Ridge Grenvillian地下室具有几乎相同的＆Nd值，并显示出相同的主要岩浆核心和变质缘锆石年龄。基于这些数据，不整合的基底-盖关系以及北美东部的地壳年龄，我们建议南部阿巴拉契亚蓝岭和内山麓西部的大量沉积物包来自劳伦西亚。相对较高的初始87Sr / 86Sr值介于0.707至0.723之间，中元古代至上元古代TDM年龄，较高的SiO2含量，LREE富集，较低的化学变化指数值通常在41至66之间，以及Laurentian的Th / Sc和Zr / Sc值受到限制沉积和变质沉积的样品进一步支持了格林维尔岩石的衍生，例如暴露在蓝岭西部的岩石。 ＆egr;与南阿巴拉契亚Paragneisses和Blue Ridge Grenvillian地下室相比，卡罗来纳州地层火山岩，深成岩和火山碎屑岩中的Nd同位素演化较少，从而很容易将这种复合地层与西部的大部分Laurentian地层分开。新元古代（〜590 Ma），奥陶纪（峰值在〜500和〜485 Ma）和志留纪（峰值在〜435 Ma），以及内格林斯山脉和早老的锆石，在内皮德蒙特教区东部的锆石表明这些岩石沉积得较晚。 （志留纪晚期至泥盆纪），可能完全来自Panafrican来源，也可能是Panafrican和回收的Laurentian边缘组合的混合物。 （摘要由UMI缩短。）

著录项

  • 作者

    Bream, Brendan R.;

  • 作者单位

    The University of Tennessee.;

  • 授予单位 The University of Tennessee.;
  • 学科 Geology.; Geochemistry.
  • 学位 Ph.D.
  • 年度 2003
  • 页码 310 p.
  • 总页数 310
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;地质学;
  • 关键词

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