Geochemistry, tectonic setting, and petrogenesis of the Coldbrook Group and associated plutons, southern New Brunswick, Canada: a unique Late Ediacaran magmatic episode in Avalonia

Alicia P. Escribano, S. Barr
{"title":"Geochemistry, tectonic setting, and petrogenesis of the Coldbrook Group and associated plutons, southern New Brunswick, Canada: a unique Late Ediacaran magmatic episode in Avalonia","authors":"Alicia P. Escribano, S. Barr","doi":"10.4138/atlgeo.2023.010","DOIUrl":null,"url":null,"abstract":"The Coldbrook Group is a unique suite of late Ediacaran volcanic and epiclastic rocks deposited in an extensional setting in the Avalonian Caledonia terrane of southern New Brunswick. It is informally divided into a lower part composed of mainly andesitic to dacitic tuffs and epiclastic sedimentary rocks intruded by bimodal plutons, and an upper part composed mainly of mafic flows and tuffs interlayered with but mainly overlain by rhyolitic flows and tuffs and minor epiclastic sedimentary rocks. Recent U–Pb (zircon) dating of four formations in the Coldbrook Group and a subvolcanic granitic dome led to the proposal that the lower and most of the upper Coldbrook Group and associated plutons were formed within <760 kyr at about 551.5 Ma whereas the uppermost rhyolite (Fundy Trail Parkway rhyolite) and underlying basalt of the Hosford Brook Formation formed in a younger event at about 549.5 Ma. Overlapping dates and chemical data also suggest that the subvolcanic granitic domes are the plutonic counterparts of the ca. 551.5 Ma felsic volcanic rocks whereas the other granitic plutons represent extracted melts that evolved separately. Whole-rock geochemical and isotopic data combined with previous field work and map information and integrated with the geochronological data provide new insights into the genesis of these magmas and their change from intermediate to bimodal magmatism. The data indicate that the volcanic and plutonic rocks are mainly tholeiitic and were derived from varying proportions of juvenile melts and recycled older arc lithosphere. The mafic rocks have chemical similarities to flood basalts which inherited some calc-alkalic signatures from older arc-like rocks. Intermediate magmas that formed much of the lower Coldbrook Group had larger lithospheric inputs and thus have mainly calc-alkalic signatures. The Vernon Mountain, Blackall Lake and Silver Hill area rhyolites represent evolved melts derived from the lower Coldbrook Group magmas, and their chemical differences are interpreted to result from melt extraction and solid-liquid dripping magmatic processes. Enhanced extension and thinning led to formation of less lithosphere-contaminated melts that formed the ca. 549.5 Ma bimodal units of the upper Coldbrook Group.","PeriodicalId":142525,"journal":{"name":"Atlantic Geoscience","volume":"19 2","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2023-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Atlantic Geoscience","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.4138/atlgeo.2023.010","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0

Abstract

The Coldbrook Group is a unique suite of late Ediacaran volcanic and epiclastic rocks deposited in an extensional setting in the Avalonian Caledonia terrane of southern New Brunswick. It is informally divided into a lower part composed of mainly andesitic to dacitic tuffs and epiclastic sedimentary rocks intruded by bimodal plutons, and an upper part composed mainly of mafic flows and tuffs interlayered with but mainly overlain by rhyolitic flows and tuffs and minor epiclastic sedimentary rocks. Recent U–Pb (zircon) dating of four formations in the Coldbrook Group and a subvolcanic granitic dome led to the proposal that the lower and most of the upper Coldbrook Group and associated plutons were formed within <760 kyr at about 551.5 Ma whereas the uppermost rhyolite (Fundy Trail Parkway rhyolite) and underlying basalt of the Hosford Brook Formation formed in a younger event at about 549.5 Ma. Overlapping dates and chemical data also suggest that the subvolcanic granitic domes are the plutonic counterparts of the ca. 551.5 Ma felsic volcanic rocks whereas the other granitic plutons represent extracted melts that evolved separately. Whole-rock geochemical and isotopic data combined with previous field work and map information and integrated with the geochronological data provide new insights into the genesis of these magmas and their change from intermediate to bimodal magmatism. The data indicate that the volcanic and plutonic rocks are mainly tholeiitic and were derived from varying proportions of juvenile melts and recycled older arc lithosphere. The mafic rocks have chemical similarities to flood basalts which inherited some calc-alkalic signatures from older arc-like rocks. Intermediate magmas that formed much of the lower Coldbrook Group had larger lithospheric inputs and thus have mainly calc-alkalic signatures. The Vernon Mountain, Blackall Lake and Silver Hill area rhyolites represent evolved melts derived from the lower Coldbrook Group magmas, and their chemical differences are interpreted to result from melt extraction and solid-liquid dripping magmatic processes. Enhanced extension and thinning led to formation of less lithosphere-contaminated melts that formed the ca. 549.5 Ma bimodal units of the upper Coldbrook Group.
加拿大新不伦瑞克省南部冷溪岩群及相关岩浆岩的地球化学、构造环境和岩石成因:阿瓦鲁尼亚独特的晚埃迪卡拉岩浆事件
冷溪组是一套独特的埃迪卡拉纪晚期火山岩和震旦岩,沉积于新不伦瑞克省南部阿瓦隆喀里多尼亚地层的伸展环境中。它被非正式地划分为下部和上部,下部主要由安山质至达赤质凝灰岩和由双峰柱状侵入的震旦系沉积岩组成,上部主要由黑云母流和凝灰岩组成,与流纹岩流和凝灰岩及少量震旦系沉积岩相互交错,但主要被流纹岩流和凝灰岩及少量震旦系沉积岩所覆盖。最近对冷溪组的四个地层和一个亚火山花岗岩穹丘进行的 U-Pb(锆石)年代测定结果表明,冷溪组下部和上部的大部分地层及相关柱状岩是在小于 760 千年(约 551.5 千兆年)内形成的,而最上部的流纹岩(Fundy Trail Parkway 流纹岩)和霍斯福德布鲁克地层下部的玄武岩则形成于更年轻的时期,约 549.5 千兆年。重叠的日期和化学数据还表明,亚火山花岗岩穹丘是约 551.5 Ma 长英岩的对应岩体。551.5 Ma 长岩火山岩的对应岩体,而其他花岗岩柱状岩体则是单独演化的提取熔体。全岩地球化学和同位素数据与先前的野外工作和地图信息相结合,并与地质年代数据相结合,为了解这些岩浆的成因及其从中间岩浆活动到双峰岩浆活动的变化提供了新的视角。数据表明,火山岩和柱状岩主要为透辉岩,由不同比例的幼年熔体和再循环的老弧岩圈形成。黑云母岩的化学成分与洪积玄武岩相似,而洪积玄武岩则继承了老弧状岩石的一些钙碱性特征。形成下冷溪组大部分地区的中间岩浆有较大的岩石圈输入,因此主要具有钙碱性特征。弗农山、黑尔湖和银山地区的流纹岩代表了从下冷溪岩群岩浆中衍生出来的演化熔体,其化学差异被解释为熔体萃取和固液滴落岩浆过程的结果。延伸和减薄的加强导致岩石圈污染较少的熔体形成,形成了约 549.5 Ma 的双峰岩。上冷溪组的双峰单位。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
求助全文
约1分钟内获得全文 求助全文
来源期刊
自引率
0.00%
发文量
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
copy
已复制链接
快去分享给好友吧!
我知道了
右上角分享
点击右上角分享
0
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信