The early magmatic and tectonic history of the Carolina terrane and its possible affinities with other Neoproterozoic circum‐Atlantic arc terranes have been poorly understood, in large part because of a lack of reliable geochronological data. Precise U‐Pb zircon dates for the Virgilina sequence, the oldest exposed part, constrain the timing of the earliest known stage of magmatism in the terrane and of the Virgilina orogeny. A flow‐banded rhyolite sampled from a metavolcanic sequence near Chapel Hill, North Carolina, yielded a U‐Pb zircon date of 632.9 +2.6/−1.9 Ma. A granitic unit of the Chapel Hill pluton, which intrudes the metavolcanic sequence, yielded a nearly identical U‐Pb zircon date of 633 +2/−1.5 Ma, interpreted as its crystallization age. A felsic gneiss and a dacitic tuff from the Hyco Formation yielded U‐Pb zircon dates of 619.9 +4.5/−3 Ma and 615.7 +3.7/−1.9 Ma, respectively. Diorite and granite of the Flat River complex have indistinguishable U‐Pb upper‐intercept dates of 613.9 +1.6/−1.5 Ma and 613.4 +2.8/−2 Ma. The Osmond biotite‐granite gneiss, which intruded the Hyco Formation before the Virgilina orogeny, crystallized at 612.4 +5.2/−1.7 Ma. Granite of the Roxboro pluton, an intrusion that postdated the Virgilina orogeny, yielded a U‐Pb upper intercept date of 546.5 +3.0/−2.4 Ma, interpreted as the time of its crystallization. These new dates both provide the first reliable estimates of the age of the Virgilina sequence and document that the earliest known stage of magmatism in the Carolina terrane had begun by 633 +2/−1.5 Ma and continued at least until 612.4 +5.2/−1.7 Ma, an interval of ∼25 m.yr. Timing of the Virgilina orogeny is bracketed between 612.4 +5.2/−1.7 Ma and \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$586\pm 10$$ \end{document} Ma (reported age of the upper Uwharrie Formation). The U‐Pb systematics of all units studied in the Virgilina sequence are simple and lack any evidence of an older xenocrystic zircon component, which would indicate the presence of a continental‐type basement. This observation, together with the juvenile Nd isotopic character of the Virgilina volcanic arc sequence, suggests that the oldest part of the Carolina terrane was built on oceanic crust away from a continental crustal influence.

中文翻译：

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卡罗莱纳地体最早岩浆历史上的精确 U-Pb 锆石约束

卡罗莱纳地体的早期岩浆和构造历史及其与其他新元古代环大西洋弧地体的可能亲缘关系知之甚少，这在很大程度上是因为缺乏可靠的地质年代学数据。Virgilina 序列（最古老的暴露部分）的精确 U-Pb 锆石日期限制了地体中已知最早的岩浆活动阶段和 Virgilina 造山运动的时间。从北卡罗来纳州教堂山附近的变质火山序列中采样的流动带状流纹岩产生了 632.9 +2.6/−1.9 Ma 的 U-Pb 锆石日期。Chapel Hill 岩体的一个花岗岩单元侵入变质火山序列，产生了几乎相同的 U-Pb 锆石日期 633 +2/-1.5 Ma，被解释为它的结晶年龄。来自 Hyco 组的长英质片麻岩和英安质凝灰岩产生了 619.9 +4 的 U-Pb 锆石日期。分别为 5/−3 Ma 和 615.7 +3.7/−1.9 Ma。Flat River 杂岩体的闪长岩和花岗岩具有难以区分的 U-Pb 上截距日期 613.9 +1.6/-1.5 Ma 和 613.4 +2.8/-2 Ma。在 Virgilina 造山运动之前侵入 Hyco 组的 Osmond 黑云母-花岗岩片麻岩在 612.4 +5.2/-1.7 Ma 结晶。Roxboro 岩体的花岗岩是 Virgilina 造山运动之后的侵入体，其 U-Pb 上截距日期为 546.5 +3.0/-2.4 Ma，解释为其结晶时间。这些新日期既提供了对 Virgilina 层序年龄的首次可靠估计，也证明了卡罗莱纳地体中已知最早的岩浆活动阶段始于 633 +2/-1.5 Ma 并至少持续到 612.4 +5.2/-1.7 Ma，间隔约 25 m.yr。Virgilina 造山运动的时间在 612.4 +5.2/-1 之间。7 Ma 和 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage {portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$586\pm 10$$ \end{document } Ma（Uwharrie 组上部的报告年龄）。在 Virgilina 层序中研究的所有单元的 U-Pb 系统学很简单，并且缺乏任何更古老的异晶锆石成分的证据，这表明存在大陆型基底。这个观察，