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A new concordia age for the Forearc Bay of Islands Ophiolite Complex, Western Newfoundland utilizing spatially-resolved LA-ICP-MS U-Pb analyses of zircon
Gondwana Research ( IF 6.1 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.gr.2020.05.007
Weiyao Yan , John F. Casey

Abstract Advancements of zircon U-Pb dating techniques using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) provide an opportunity to precisely constrain the age of the Bay of Islands Ophiolite Complex (BOIC) in the Newfoundland Appalachians. New LA-ICP-MS U-Pb dates are presented for a large population of relatively simple magmatic zircon grains from trondhjemites using selective domain analyses and a 3% discordance filter in five samples collected from a single ophiolite massif, with four of the samples from a single pluton. All samples were derived from plagiogranite plutons intruded just below the gabbro-sheeted dike contact of the Blow Me Down Mountain massif, the massif sampled for three of the four prior single sample ID-TIMS age studies of the ophiolite. A highly consistent series of LA-ICP-MS concordant ages from the five samples collected yield a composite concordia age of 488.3 ± 1.5 Ma, which we propose for the revised igneous age of the ophiolite massif. This new age for the BOIC is based on 127 individual LA-ICP-MS zircon analyses and is slightly older and with lower uncertainty than the previous consensus age. We review previous pioneering ID-TIMS U-Pb dates, ages, intercept assumptions, and uncertainties for the BOIC in light of this new formation age. Legacy ages and uncertainties differ somewhat when data are reduced with modern recommended techniques and without geological interpretations that fix lower intercepts. The ca. 488.3 Ma BOIC age indicates its formation along a younger supra-subduction forearc trench-orthogonal spreading center that rifted the older Coastal Complex forearc ophiolitic assemblages reported to be formed at ca. 500-508 Ma. This rifted forearc is analogous to many modern ophiolitic forearcs. The BOIC age is highly correlated with similar ages of the peri-Laurentian Notre Dame arc-proximal Betts Cove and Point Rousse ophiolites, indicating temporal BOIC spreading center linkages within the Baie Verte Oceanic Tract.

中文翻译:

利用空间分辨的 LA-ICP-MS U-Pb 分析锆石,获得 Forearc Bay of Islands 蛇绿岩复合体的新协和时代,纽芬兰西部

摘要 使用激光烧蚀电感耦合等离子体质谱 (LA-ICP-MS) 的锆石 U-Pb 测年技术的进步为精确限制纽芬兰阿巴拉契亚群岛湾蛇绿岩复合体 (BOIC) 的年龄提供了机会。新的 LA-ICP-MS U-Pb 日期显示了从单一蛇绿岩地块中收集的五个样品中使用选择性域分析和 3% 不一致过滤器的大量相对简单的长岩岩浆锆石颗粒,其中四个样品来自一个单一的岩体。所有样品均来自斜长花岗岩岩体,这些岩体侵入 Blow Me Down Mountain 地块的辉长岩片状堤防接触点下方,该地块为蛇绿岩的四个先前单个样品 ID-TIMS 年龄研究中的三个采样。来自收集的五个样品的一系列高度一致的 LA-ICP-MS 一致年龄产生 488.3 ± 1.5 Ma 的复合协和年龄,我们建议修改蛇绿岩地块的火成岩年龄。BOIC 的这个新年龄基于 127 次单独的 LA-ICP-MS 锆石分析,与之前的共识年龄相比,年龄稍大,不确定性更低。我们回顾了之前开创性的 ID-TIMS U-Pb 日期、年龄、截距假设和 BOIC 的不确定性,以适应这个新的形成时代。当使用现代推荐技术减少数据并且没有固定较低截距的地质解释时,遗留的年龄和不确定性会有所不同。约。488. 3 Ma BOIC 年龄表明它沿着一个较年轻的超俯冲前弧沟-正交扩展中心形成,该中心将较旧的沿海复合体前弧蛇绿岩组合裂开,据报道在大约 10 年形成。500-508 马。这种裂隙前弧类似于许多现代蛇绿岩前弧。BOIC 年龄与 Laurentian Notre Dame 弧近端 Betts Cove 和 Point Rousse 蛇绿岩的相似年龄高度相关,表明 Baie Verte 洋道内的时间 BOIC 扩张中心联系。
更新日期:2020-10-01
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