Mid–Late Ordovician magmatism and metamorphism along the Gander margin in central Newfoundland
Mid–Late Ordovician magmatism and metamorphism along the Gander margin in central Newfoundland
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纽芬兰中部甘德边缘的中晚奥陶世岩浆作用和变质作用
DOI：
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发表时间：
2006
影响因子：
2.7
通讯作者：
G. Dunning
中科院分区：
文献类型：
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作者：
P. Valverde;C. V. van Staal;V. Mcnicoll;G. Dunning
现场工作与 U-Pb 测年相结合，阐明了 Exploits 弧后盆地中奥陶世开放期间纽芬兰中部的 Exploits 与甘德衍生岩石之间的关系，加强了阿巴拉契亚-喀里多尼亚造山带近冈瓦南段的相关性。我们将一个新的与弧后相关的单位——红十字会小组，从与弧线相关的维多利亚湖超级小组中分离出来。该组包括 466 ± 3 Ma 长英质火山岩，夹有富含碱性玄武岩的洋中脊玄武岩、457 ± 6 Ma 辉长岩、Llanvirn-Caradoc 正常洋中脊玄武岩-岛弧拉斑岩、石灰岩、黑色页岩和混杂岩。当地红十字会正在与低品位的甘德沙粒进行非本土接触。在泥盆纪期间，该接触面被梅尔帕格变质推覆体所淹没。推覆面含有 Gander 变英质岩（Meelpaeg 亚带）和含有小叶的 Howley Waters 杂岩（Exploits），其中含有 467 ± 3 Ma 长英质斑岩。推覆体中的 Gander 和 Exploits 变沉积岩由 Arenig-Llanvirn 花岗岩（467 ± 6 Ma 和 468 +3.5/−3 Ma）和 Caradoc 侵入体（458 ± 3 Ma 和 454 ± 2 Ma）缝合。来自附近科马克山次带（甘德）的变质独居石（462 ± 1 Ma）和钛铁矿（460 ± 3 Ma）表明低压-高温变质穹顶的同时形成。卡拉多克岩浆活动的广泛存在表明弧后盆地的宽度仍然相对狭窄。
Fieldwork coupled with U–Pb dating has clarified the relationships between the Exploits and Gander-derived rocks in central Newfoundland during the Mid-Ordovician opening of the Exploits back-arc basin, reinforcing correlation across the peri-Gondwanan segments of the Appalachian–Caledonian orogen. We have separated a new back-arc-related unit, the Red Cross Group, from the arc-related Victoria Lake Supergroup. This group includes 466 ± 3 Ma felsic volcanic rock interlayered with alkali basalt–enriched mid-ocean ridge basalt, 457 ± 6 Ma gabbro, Llanvirn–Caradoc normal mid-ocean ridge basalt–island arc tholeite, limestone, black shale and mélange. Locally the Red Cross Group is in parautochthonous contact with low-grade Gander psammite. This contact was overrun by the Meelpaeg Metamorphic Nappe during the Devonian. The nappe contains Gander metapsammite (Meelpaeg Subzone) and the coticule-bearing Howley Waters Complex (Exploits), which hosts 467 ± 3 Ma felsic porphyry. The Gander and Exploits metasediments in the nappe are stitched by Arenig–Llanvirn granite (467 ± 6 Ma and 468 +3.5/−3 Ma) and Caradoc intrusions (458 ± 3 Ma and 454 ± 2 Ma). Metamorphic monazite (462 ± 1 Ma) and titanite (460 ± 3 Ma) from the nearby Mount Cormack Subzone (Gander) indicate the coeval formation of a low-pressure–high-temperature metamorphic dome. The widespread presence of Caradoc magmatism suggests that the width of the back-arc basin remained relatively narrow.