Early to Middle Ordovician back-arc basin in the southern Appalachian Blue Ridge: characteristics, extent, and tectonic significance
Early to Middle Ordovician back-arc basin in the southern Appalachian Blue Ridge: characteristics, extent, and tectonic significance
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DOI：
10.1130/b30967.1
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发表时间：
2014-07
影响因子：
4.9
通讯作者：
J. Tull;C. Holm-Denoma;Clinton I. Barineau
中科院分区：
文献类型：
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作者：
J. Tull;C. Holm-Denoma;Clinton I. Barineau
一个独特的、广泛的、高度异源的、具有重要构造意义的奥陶纪（约 480-460 Ma）盆地的断层破碎部分，包含成套双峰变火山岩、相关的贱金属矿床和厚的未成熟深水（浊积）变沉积岩，出现在阿巴拉契亚塔拉迪加带南部、蓝岭东部和内皮埃蒙特的部分地区。 阿拉巴马州、乔治亚州、北卡罗来纳州和南卡罗来纳州。该盆地的主要变沉积地层显示出混合物源的地球化学和同位素证据，包括邻近的活动火山弧和富含云母（粘土）的沉积岩和长英质深成岩的物源，与劳伦（格伦维尔）上地壳大陆岩及其被动边缘覆盖序列一致。次级夹层双峰变质火山岩的地球化学特征表明形成于超俯冲环境，很可能是弧后盆地，而变沉积岩单元的特征表明沉积物位于新元古代裂谷和外缘下古生代斜坡之上，并在沿奥陶系劳伦蒂亚土卫八边缘的边缘盆地内隆起沉积物。这种构造环境表明，最南端的阿巴拉契亚奥陶纪造山运动（塔科尼造山运动）始于沿劳伦蒂亚外缘的伸展增生造山带，而不是在奇异（非劳伦蒂亚）弧碰撞环境中。 B型俯冲极性要求相关的弧沟系统形成于弧后盆地回痉位置的东南部。这种情况可以解释南阿巴拉契亚塔科造山带的几个独特特征，包括：关键构造要素（即弧后、弧等）的古痉挛地理排序，以及缺乏（1）劳伦山脉边缘上的逆冲弧，（2）广泛的奥陶纪区域变质作用，以及（3）塔科山脉的供应 碎屑进入塔科尼克前陆盆地。
Fault-dismembered segments of a distinctive, extensive, highly allochthonous, and tectonically significant Ordovician (ca. 480–460 Ma) basin, which contains suites of bimodal metavolcanic rocks, associated base metal deposits, and thick immature deep-water (turbiditic) metasediments, occur in parts of the southern Appalachian Talladega belt, eastern Blue Ridge, and Inner Piedmont of Alabama, Georgia, and North and South Carolina. The basin’s predominantly metasedimentary strata display geochemical and isotopic evidence of a mixed provenance, including an adjacent active volcanic arc and a provenance of mica (clay)-rich sedimentary and felsic plutonic rocks consistent with Laurentian (Grenvillian) upper-crustal continental rocks and their passive-margin cover sequences. Geochemical characteristics of the subordinate intercalated bimodal metavolcanic rocks indicate formation in a suprasubduction environment, most likely a back-arc basin, whereas characteristics of metasedimentary units suggest deposition above Neoproterozoic rift and outer-margin lower Paleozoic slope and rise sediments within a marginal basin along Ordovician Laurentia’s Iapetus margin. This tectonic setting indicates that southernmost Appalachian Ordovician orogenesis (Taconic orogeny) began as an extensional accretionary orogen along the outer margin of Laurentia, rather than in an exotic (non-Laurentian) arc collisional setting. B-type subduction polarity requires that the associated arc-trench system formed southeast of the palinspastic position of the back-arc basin. This scenario can explain several unique features of the southern Appalachian Taconic orogen, including: the palinspastic geographic ordering of key tectonic elements (i.e., back-arc, arc, etc.), and a lack of (1) an obducted arc sensu stricto on the Laurentian margin, (2) widespread Ordovician regional metamorphism, and (3) Taconic klippen to supply detritus to the Taconic foreland basin.