The Mesoproterozoic to Paleozoic history of the southeastern Laurentian margin involved repeated collisional and accretionary tectonomagmatic events that reworked and recycled older continental crust of preceding events. The Great Smoky Mountains Basement Complex (GSMBC) within the southern Appalachian Blue Ridge exposes complexly deformed orthogneiss and paragneiss that preserve a record of Laurentian margin evolution from ca. 1.9 Ga to 450 Ma. The GSMBC consists primarily of: (1) 1.34 to 1.31 Ga (pre-Elzevirian) granodioritic orthogneiss and entrained mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (correlated with pre-Elzevirian crustal components in the Adirondack, Green Mountains, New Jersey Highlands, and French Broad massifs), (2) ca. l.15 to 1.05 Ga augen and granitic orthogneiss produced during Shawinigan and Ottawan phases of Grenville-age magmatism and metamorphism, respectively, and (3) paragneiss derived from protoliths with either Grenville-age (1.1–1.0 Ga) or post-Grenville (Neoproterozoic) depositional ages based on presence/absence of ca. 1.0 Ga metamorphic zircon and 1.9 to 1.1 Ga detrital zircon. All lithologies experienced Taconian metamorphism and variable migmatization. Pre-Ottawan paragneiss exhibits major detrital zircon ages modes at 2.0 to 1.6 and 1.4 to 1.3 Ga that require a component of older Proterozoic crust in the sediment source region. Detrital zircon grains in post-Ottawan paragneiss exhibits the full spectrum of Grenville-age modes that correlate with the five phases of Grenville magmatic/metamorphic events in eastern Laurentia. These paragneiss samples also contain scattered 750 to 600 Ma detrital zircon grains that constrain their maximum depositional age to late Neoproterozoic. The sedimentary protoliths of the latter paragneiss consist largely of detritus from exhumation of all Grenville crustal age components during post-orogenic exhumation and crustal extension leading up to Late Neoproterozoic breakup of Rodinia. Most zircon U-Pb age systematics exhibit variable discordance that can be attributed to disturbance of the U-Pb system and/or new zircon growth during either high-grade Ottawan (ca. 1.04 Ga) or Taconian (ca. 0.46 Ga) regional metamorphism and migmatization. Neodymium TDM model ages for granodioritic orthogneiss and paragneiss range from 1.8 to 1.6 Ga, indicating that the rocks were derived from recycling of Proterozoic crust (that is, they are not juvenile), consistent with the 1.9 to 1.6 Ga detrital zircon grains in pre-Ottawan paragneiss and with 1.8 to 1.7 Ga inherited zircon in some 1.33 Ga orthogneisses and a 1.35 Ga xenolith. Whole rock Pb isotope compositions of GSMBC rocks overlap the field of compositions characteristic of Amazonian crust and of other basement rocks from the south-central Appalachians. The Pb isotopes and geochronology in orthogneiss, mafic xenoliths, and pre-Ottawan paragneiss are consistent with a correlation of the GSMBC with the Mars Hill terrane within the French Broad massif and with the greater Grenvillian south-central Appalachian basement (SCAB) that is considered exotic to Laurentia, and transferred during Rodinian collision prior to ca. 1.2 Ga. Similarities in protolith ages and Pb isotopes point to the Paraguá terrane of Amazonia (southwestern Brazil and eastern Bolivia) as a likely match for SCAB. Initial Amazonia-Laurentia collision occurred at ca. 1.35 to 1.32 Ga with final transfer of SCAB to Laurentia occurring after 1.20 Ga within the sinistral oblique collision zone between Laurentia and Amazonia defined by previous workers.

中文翻译：

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美国大雾山东部蓝岭基底的锆石 U-Pb 年代学和 Nd-Pb 同位素地球化学：对劳伦大陆东南部元古代构造演化的意义

Laurentian 边缘东南部的中元古代至古生代历史涉及重复的碰撞和增生构造岩浆事件，这些事件对先前事件的旧大陆地壳进行了改造和再循环。位于阿巴拉契亚蓝岭南部的大烟山基底复合体 (GSMBC) 暴露了复杂变形的正方麻岩和副片麻岩，它们保留了约 10 年代以来劳伦边缘演化的记录。1.9 Ga 至 450 Ma。GSMBC 主要包括： (1) 1.34 至 1.31 Ga（前 Elzevirian）花岗闪长岩正片麻岩和夹带的镁铁质包体，代表阿巴拉契亚 Grenville 地块中一些最古老的地壳（与阿迪朗达克、绿山、新泽西高地和法国布罗德地块），（2）约。l.15 比 1。05 Ga augen 和花岗质正片麻岩分别产生于 Grenville 时代岩浆作用和变质作用的 Shawinigan 和 Ottawan 阶段，以及 (3) 源自 Grenville 时代 (1.1-1.0 Ga) 或后 Grenville（新元古代）沉积时代的原岩的副片麻岩基于 ca 的存在/不存在。1.0 Ga 变质锆石和 1.9 至 1.1 Ga 碎屑锆石。所有岩性都经历了塔科阶变质作用和可变混杂作用。前渥太华副片麻岩表现出 2.0 至 1.6 和 1.4 至 1.3 Ga 的主要碎屑锆石年龄模式，这需要沉积物源区中较旧的元古代地壳的组成部分。后渥太华副片麻岩中的碎屑锆石颗粒显示出与劳伦西亚东部格伦维尔岩浆/变质事件的五个阶段相关的格伦维尔时代模式的全谱。这些副片麻岩样品还包含分散的 750 至 600 Ma 碎屑锆石颗粒，将其最大沉积年龄限制在新元古代晚期。后者的副片麻岩的沉积原岩主要由造山后剥露和地壳伸展过程中所有 Grenville 地壳时代成分剥落的碎屑组成，导致罗迪尼亚晚新元古代分裂。大多数锆石 U-Pb 年龄系统表现出不同的不一致，这可归因于 U-Pb 系统的干扰和/或在高品位 Ottawan（约 1.04 Ga）或 Taconian（约 0.46 Ga）区域变质作用期间新锆石的生长和迁移。花岗闪长岩和副片麻岩的钕 TDM 模型年龄范围为 1.8 至 1.6 Ga，表明这些岩石来自元古代地壳的再循环（即，它们不是幼年），与渥太华前平行片麻岩中的 1.9 至 1.6 Ga 碎屑锆石颗粒以及一些 1.33 Ga 正片麻岩和 1.35 Ga 捕虏体中的 1.8 至 1.7 Ga 继承锆石一致。GSMBC 岩石的全岩 Pb 同位素组成与亚马逊地壳和阿巴拉契亚中南部其他基底岩石的组成特征领域重叠。正片麻岩、镁铁质包体和前渥太华平行片麻岩中的 Pb 同位素和年代学与 GSMBC 与法国布罗德地块内的火星山地体和更大的 Grenvillian 阿巴拉契亚中南部基底 (SCAB) 的相关性一致劳伦西亚的异国情调，并在罗迪尼亚碰撞期间转移。1.2 嘎。原岩年龄和铅同位素的相似性表明亚马逊（巴西西南部和玻利维亚东部）的巴拉瓜地体可能与 SCAB 相匹配。最初的 Amazonia-Laurentia 碰撞发生在大约。1.35 到 1.32 Ga，SCAB 最终转移到 Laurentia 发生在 1.20 Ga 之后，位于 Laurentia 和 Amazonia 之间由以前的工人定义的左旋斜碰撞区。