由白云母变形和应变局部化控制的40Ar/39Ar日期:通过比较原位激光烧蚀和单晶粒融合技术的见解

IF 3.5 2区 地球科学 Q1 GEOLOGY
Christopher J. Barnes, David A. Schneider, Jarosław Majka, Alfredo Camacho, Michał Bukała, Adam Włodek
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引用次数: 0

摘要

利用斯堪的纳维亚Caledonides中Seve推覆杂岩(SNC) Vaimok Lens的9块变质沉积岩中的白色云母,对原位激光消融和单粒熔融40Ar/39Ar年代学技术进行了直接比较。其中7块岩石来自透镜体内含榴辉岩的Grapesvare推覆体,属于D2构造(S2和F2),是在晚寒武世/早奥陶世超高压变质作用下出土形成的。另外两块岩石来自“加拿大”剪切带,该剪切带划分了透镜体内的推覆体。在志留纪至泥盆纪波罗的海与劳伦提亚碰撞末期,剪切带活跃。岩石表现出不同的变形强度和应变局部化程度,特别是白云母。原位激光烧蚀和单粒熔融40Ar/39Ar的时间跨度均为晚寒武世至中泥盆世。这两种技术的结果通常表明,随着体变形强度的增加和连续的结构世代(即D2然后是Scandian结构),日期逐渐减少。此外,当比较两种技术对同一块岩石的结果时,一些差异是明显的,这表明40Ar/39Ar日期不仅仅是由体积变形强度和构造世代决定的。相反,这些差异表明了白云母菌株定位的额外影响,这是由不同的分析量的技术所阐明的。因此,40Ar/39Ar数据集被全部解读为影响整体白色云母体积的体变形强度和应变局部化程度的函数。前者控制总体体积的总40Ar损失,后者决定体积内40Ar损失的可变性。利用原位激光烧蚀法对Vaimok Lens岩石进行这两种现象的相互作用,可以将40Ar/39Ar的大跨度日期背景化到一系列构造事件中:(1)474±3 Ma的冷却,(2)447±2 Ma的碰撞前变形,以及(3)SNC中与431±3 Ma和411±3 Ma的大陆碰撞相关的地壳尺度剪切带的激活。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
40Ar/39Ar dates controlled by white mica deformation and strain localization: Insights from comparing in situ laser ablation and single-grain fusion techniques

In situ laser ablation and single-grain fusion 40Ar/39Ar geochronological techniques were directly compared using white mica from nine metasedimentary rocks from the Vaimok Lens of the Seve Nappe Complex (SNC) in the Scandinavian Caledonides. Seven of the rocks are from the eclogite-bearing Grapesvare nappe within the lens that is defined by D2 structures (S2 and F2), which were formed during exhumation following late Cambrian/Early Ordovician ultra-high pressure metamorphism. Two other rocks were obtained from ‘Scandian’ shear zones that delimit the nappes within the lens. The shear zones were active during terminal collision of Baltica and Laurentia in the Silurian to Devonian. The rocks exhibit variable deformation intensities and degrees of strain localization, expressed in particular by white mica. The in situ laser ablation and single-grain fusion 40Ar/39Ar dates both span from the late Cambrian to Middle Devonian. Results of both techniques generally show decreasing dates with increasing bulk deformation intensity and successive structural generations (i.e., D2 then Scandian structures). Furthermore, several discrepancies are evident when comparing the results of the two techniques for the same rocks, indicating the 40Ar/39Ar dates are not solely governed by bulk deformation intensities and structural generations. Instead, the discrepancies demonstrate the additional influence of white mica strain localization, which is illuminated by the different analytical volumes of the techniques. Thus, the 40Ar/39Ar datasets are altogether deciphered as a function of bulk deformation intensity and degree of strain localization that affected the overall white mica volume. The former controls the gross 40Ar loss from the overall volume and the latter dictates the variability of 40Ar loss within the volume. Exploiting the interplay of these two phenomena for the Vaimok Lens rocks with in situ laser ablation allows for the broad span of 40Ar/39Ar dates to be contextualized into a sequence of tectonic events: (1) cooling at 474 ± 3 Ma, (2) pre-collision deformation at 447 ± 2 Ma and (3) activation of crustal-scale shear zones in the SNC related to continental collision at 431 ± 3 Ma and 411 ± 3 Ma.

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来源期刊
CiteScore
6.60
自引率
11.80%
发文量
57
审稿时长
6-12 weeks
期刊介绍: The journal, which is published nine times a year, encompasses the entire range of metamorphic studies, from the scale of the individual crystal to that of lithospheric plates, including regional studies of metamorphic terranes, modelling of metamorphic processes, microstructural and deformation studies in relation to metamorphism, geochronology and geochemistry in metamorphic systems, the experimental study of metamorphic reactions, properties of metamorphic minerals and rocks and the economic aspects of metamorphic terranes.
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