Formation of multistage garnet grains by fragmentation and overgrowth constrained by microchemical and microstructural mapping

IF 3.5 2区 地球科学 Q1 GEOLOGY Journal of Metamorphic Geology Pub Date : 2024-02-01 DOI:10.1111/jmg.12761
Paola Manzotti, Daniele Regis, Duane C. Petts, Riccardo Graziani, Matthew Polivchuk
{"title":"Formation of multistage garnet grains by fragmentation and overgrowth constrained by microchemical and microstructural mapping","authors":"Paola Manzotti,&nbsp;Daniele Regis,&nbsp;Duane C. Petts,&nbsp;Riccardo Graziani,&nbsp;Matthew Polivchuk","doi":"10.1111/jmg.12761","DOIUrl":null,"url":null,"abstract":"<p>Garnet is an exceptionally useful mineral for reconstructing the evolution of metamorphic rocks that have experienced multiple tectonic or thermal events. Understanding how garnet crystallizes and its mechanical behaviour is important for establishing a petrological and temporal record of metamorphism and deformation and for recognizing multiple geologic stages within the growth history of an individual crystal. Here, we integrate fine-scale microstructural (electron backscatter diffraction [EBSD]) and microchemical (Laser Ablation Inductively Coupled Plasma Mass Spectrometry [LA-ICP-MS] mapping) data obtained on a polycyclic garnet-bearing micaschist from the Alpine belt. Results suggest that fragmentation of pre-Alpine garnet porphyroblasts occurred during the late pre-Alpine exhumation and/or the onset of the Alpine burial, such that the older pre-Alpine garnet fragments were transported/redistributed during Alpine deformation and acted as nucleation sites for Alpine garnet growth. These processes produced a bimodal garnet size distribution (millimetre- and micrometre-sized grains). Thermodynamic modelling indicates that Alpine garnet grew during the final stage of burial (from 1.9 GPa 480°C to 2.0 GPa 520°C) and early exhumation (down to 1.6 GPa 540°C) forming continuous idioblastic rims on and sealing fractures in pre-Alpine garnet grains. We propose that fragmentation–overgrowth processes in polycyclic rocks, coupled with ductile deformation, may produce a bimodal garnet size distribution in response to fragmentation and re-distribution of pre-existing grains; these clasts can act as new nucleation sites during a subsequent orogenic cycle.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"42 4","pages":"471-496"},"PeriodicalIF":3.5000,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.12761","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Metamorphic Geology","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1111/jmg.12761","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOLOGY","Score":null,"Total":0}
引用次数: 0

Abstract

Garnet is an exceptionally useful mineral for reconstructing the evolution of metamorphic rocks that have experienced multiple tectonic or thermal events. Understanding how garnet crystallizes and its mechanical behaviour is important for establishing a petrological and temporal record of metamorphism and deformation and for recognizing multiple geologic stages within the growth history of an individual crystal. Here, we integrate fine-scale microstructural (electron backscatter diffraction [EBSD]) and microchemical (Laser Ablation Inductively Coupled Plasma Mass Spectrometry [LA-ICP-MS] mapping) data obtained on a polycyclic garnet-bearing micaschist from the Alpine belt. Results suggest that fragmentation of pre-Alpine garnet porphyroblasts occurred during the late pre-Alpine exhumation and/or the onset of the Alpine burial, such that the older pre-Alpine garnet fragments were transported/redistributed during Alpine deformation and acted as nucleation sites for Alpine garnet growth. These processes produced a bimodal garnet size distribution (millimetre- and micrometre-sized grains). Thermodynamic modelling indicates that Alpine garnet grew during the final stage of burial (from 1.9 GPa 480°C to 2.0 GPa 520°C) and early exhumation (down to 1.6 GPa 540°C) forming continuous idioblastic rims on and sealing fractures in pre-Alpine garnet grains. We propose that fragmentation–overgrowth processes in polycyclic rocks, coupled with ductile deformation, may produce a bimodal garnet size distribution in response to fragmentation and re-distribution of pre-existing grains; these clasts can act as new nucleation sites during a subsequent orogenic cycle.

Abstract Image

查看原文
分享 分享
微信好友 朋友圈 QQ好友 复制链接
本刊更多论文
以微观化学和微观结构绘图为依据,通过碎裂和过度生长形成多级石榴石晶粒
石榴石是一种非常有用的矿物,可用于重建经历过多次构造或热事件的变质岩的演变过程。了解石榴石的结晶方式及其机械行为对于建立变质和变形的岩石学和时间记录以及识别单个晶体生长历史中的多个地质阶段非常重要。在这里,我们整合了从阿尔卑斯山带的多环石榴石微晶岩上获得的精细微结构(电子反向散射衍射[EBSD])和微化学(激光烧蚀电感耦合等离子体质谱[LA-ICP-MS]绘图)数据。结果表明,前阿尔卑斯山石榴石斑岩的碎裂发生在前阿尔卑斯山晚期的掘起过程中和/或阿尔卑斯山埋藏的开始阶段,因此较早的前阿尔卑斯山石榴石碎片在阿尔卑斯山变形过程中被搬运/重新分布,并成为阿尔卑斯山石榴石生长的成核点。这些过程产生了双峰石榴石大小分布(毫米和微米大小的颗粒)。热力学建模表明,阿尔卑斯石榴石在埋藏的最后阶段(从 1.9 GPa 480°C 到 2.0 GPa 520°C)和早期掘出阶段(低至 1.6 GPa 540°C)生长,在前阿尔卑斯石榴石晶粒上形成连续的特质边缘,并封住了裂缝。我们提出,多环岩石中的碎裂-增生过程与韧性变形相结合,可能会在原有颗粒的碎裂和再分布过程中产生双峰石榴石粒度分布;这些碎屑可在随后的造山周期中充当新的成核点。
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 去求助
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.
期刊最新文献
Issue Information Zircon Coupled Dissolution–Precipitation Replacement During Melt–Rock Interaction Modifies Chemical Signatures Resulting in Misleading Ages Pressure–Temperature–Time Evolution of a Polymetamorphic Paragneiss With Pseudomorphs After Jadeite From the HP–UHP Gneiss-Eclogite Unit of the Variscan Erzgebirge Crystalline Complex, Germany Issue Information Experimental Replacement of Zircon by Melt-Mediated Coupled Dissolution-Precipitation Causes Dispersion in U–Pb Ages
×
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
现在去查看 取消
×
提示
确定
0
微信
客服QQ
Book学术公众号 扫码关注我们
反馈
×
意见反馈
请填写您的意见或建议
请填写您的手机或邮箱
已复制链接
已复制链接
快去分享给好友吧!
我知道了
×
扫码分享
扫码分享
Book学术官方微信
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术
文献互助 智能选刊 最新文献 互助须知 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 Book学术 All rights reserved.
ghs 京公网安备 11010802042870号 京ICP备2023020795号-1