The Diverse Habitats of Eclogite Formation: Insights From the Mesoproterozoic Glenelg Inlier, Scotland

IF 3.5 2区 地球科学 Q1 GEOLOGY
Nicholas A. Lucas, Owen M. Weller, Alex Copley, Catherine M. Mottram, Glenn Chapman, William J. McMahon
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Abstract

Eclogite-facies rocks provide important constraints on the behaviour of convergent plate boundaries and the geometries of tectonic reconstructions due to the high to ultrahigh pressure conditions at which they form. Many eclogite occurrences are documented near the suture zone of active collisional settings where they are interpreted to mark the approximate location of former ocean basin subduction. Such observations influence tectonic interpretations for older eclogites within more deeply eroded and/or less well-exposed terranes. The eclogitic Glenelg inlier in northwest Scotland is one such example, with c. 1 Ga eclogites having previously been interpreted as marking the trace of a Grenville-aged collisional suture zone that defines a third ‘arm’ to the Grenville orogen alongside well-defined sutures in North America and Scandinavia. Here we use a combination of geochronology, phase equilibrium modelling and accessory-phase thermometry to show that the eclogite-facies assemblages were produced at $$ \sim $$ 18–19 kbar and 700°C–750°C from c. 1.1 to 1.0 Ga. Accounting for the foreland basin setting of equivalent-aged sedimentary rocks in the region and demonstrating the thermal viability of this setting, we show that eclogite formation occurred in deforming foreland crust adjacent to the Grenville orogen, in a setting broadly analogous to fault-bounded basement uplifts in the forelands of active deformation belts, such as the Himalayas and Andes. Our results demonstrate that eclogite-facies rocks can form in a greater range of tectonic settings than are sometimes considered, with implications for tectonic reconstructions of collisional zones. In this instance, our results remove the need for a third ‘arm’ of the Grenville orogen by placing Glenelg in a foreland setting, reconciling the absence of plentiful Grenville-aged metamorphic rocks in northwest Scotland, the sedimentological record and paleomagnetic data in the wider region.

Abstract Image

榴辉岩形成的不同生境:来自苏格兰Glenelg Inlier中元古代的启示
榴辉岩相岩石由于其形成的高压至超高压条件,对收敛板块边界的行为和构造重建的几何形状提供了重要的限制。在活跃碰撞环境的缝合带附近记录了许多榴辉岩的产状,在那里它们被解释为标志着前洋盆俯冲的大致位置。这些观测影响了对侵蚀更深和/或暴露程度较低的地层中较老榴辉岩的构造解释。苏格兰西北部的榴辉岩Glenelg inlier就是一个这样的例子,早前就有1c Ga榴辉岩被解释为标志着格伦维尔时代的碰撞缝合带的痕迹,该缝合带与北美和斯堪的纳维亚明确的缝合带一起定义了格伦维尔造山带的第三条“臂”。在这里,我们结合了地质年代学、相平衡建模和辅助相测温,表明榴辉岩相组合产生于- $$ \sim $$ 18-19 kbar和700°C - 750°C,从C . 1.1到1.0 Ga。考虑到该地区等年龄沉积岩的前陆盆地背景,并证明了该背景的热活力,我们表明,榴辉岩形成于格伦维尔造山带附近的变形前陆地壳中,其背景与喜马拉雅山脉和安第斯山脉等活动变形带前陆的断界基底隆起大致相似。我们的研究结果表明,榴辉岩相岩石可以在比有时考虑的更大范围的构造环境中形成,这对碰撞带的构造重建具有重要意义。在这种情况下,我们的结果消除了对格伦维尔造山带的第三个“分支”的需要,将格伦维尔置于前陆环境中,调和了苏格兰西北部缺乏丰富的格伦维尔时代的变质岩,更广泛地区的沉积学记录和古地磁数据。
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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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