Provenance of Late Neoproterozoic and Cambrian Sediments in Avalonia: Constraints from Detrital Zircon Ages and Sm‐Nd Isotopic Compositions in Southern New Brunswick, Canada
Provenance of Late Neoproterozoic and Cambrian Sediments in Avalonia: Constraints from Detrital Zircon Ages and Sm‐Nd Isotopic Compositions in Southern New Brunswick, Canada
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阿瓦隆尼亚新元古代晚期和寒武纪沉积物的来源：加拿大新不伦瑞克省南部碎屑锆石年龄和 Sm-Nd 同位素组成的限制
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发表时间：
2010
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通讯作者：
S. Samson
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作者：
A. Satkoski;S. Barr;S. Samson
新元古代至寒武纪的碎屑沉积岩和/或变质沉积岩产于Hammondvale变质岩套（HMS; ca. 680-620 Ma）和布罗德河（约680 - 620 Ma）620 Ma），Coldbrook（ca. 560-550马），和圣约翰（约。540-490 Ma）群，位于新玩法南部的阿瓦隆喀里多尼亚高地。演化的Nd同位素值表明，宽河群的HMS和变质沉积岩部分来自较老的岩浆物质。HMS中存在中元古代的锆石，而没有古元古代的锆石，这表明这种较古老的古元古代物质的来源是亚马逊克拉通。相比之下，Coldbrook群的沉积岩显示出普遍的正钕值，可能来自当地的阿瓦隆源。圣约翰群下部更演化的同位素特征表明，它们又回到了更古老的白垩纪源区。来自圣约翰群最低部分的碎屑锆石具有与HMS相似的中元古代年龄，但也具有2000 - 800-Ma的年龄。中元古代的颗粒可能来自亚马逊河流域，但额外的2000-800-Ma颗粒表明一个新的源区，可能是西非克拉通。不断演化的Nd同位素值、中元古界锆石的缺失以及早寒武世沉积物中2000 - 800-Ma锆石的增加表明，早寒武世阿瓦隆尼亚完全来自西非克拉通。这种物源的转变显然是在冷溪群的火山岩和沉积岩记录的张扭裂谷之后开始的，并在阿瓦隆尼亚从其位置沿着靠近西非边缘的亚马逊边缘沿着走滑断层移动到劳伦西亚之前，继续穿过寒武纪。
Neoproterozoic though Cambrian clastic sedimentary and/or metasedimentary rocks occur in the Hammondvale Metamorphic Suite (HMS; ca. 680–620 Ma) and the Broad River (ca. 620 Ma), Coldbrook (ca. 560–550 Ma), and Saint John (ca. 540–490 Ma) groups in the Avalonian Caledonia terrane of southern New Brunswick. Evolved Nd isotopic values show that the HMS and the metasedimentary rocks of the Broad River Group were in part derived from older cratonic material. The presence of Mesoproterozoic and the absence of Paleoproterozoic zircon in the HMS suggest that the source of this older cratonic material was the Amazonian craton. In contrast, sedimentary rocks of the Coldbrook Group show generally positive ϵNd values and likely were derived from local Avalonian sources. More evolved isotopic signatures in the lower Saint John Group indicate a return to older cratonic source areas. Detrital zircon from the lowest part of the Saint John Group has Mesoproterozoic ages like those of the HMS but also has 2000‐ and 800‐Ma ages. The Mesoproterozoic grains are likely from Amazonia, but the additional 2000–800‐Ma grains suggest a new source area, likely the West African craton. The increasingly evolved Nd isotopic values, the absence of Mesoproterozoic zircon, and the addition of 2000‐ and 800‐Ma zircon in Early Cambrian sediments suggest that by the Early Cambrian Avalonia was deriving detritus exclusively from the West African craton. This transition in provenance apparently started after transtensional rifting recorded by volcanic and sedimentary rocks in the Coldbrook Group and continued through the Cambrian as Avalonia moved along strike‐slip faults from its location along the Amazonian margin closer to the West African margin before starting its journey to Laurentia.