变质和矿化过程中氮和氮同位素的行为:来自新西兰奥塔哥和阿尔卑斯片岩的证据

IF 4.8 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Iain K. Pitcairn , Damon A.H. Teagle , Robert Kerrich , Dave Craw , Tim S. Brewer
{"title":"变质和矿化过程中氮和氮同位素的行为:来自新西兰奥塔哥和阿尔卑斯片岩的证据","authors":"Iain K. Pitcairn ,&nbsp;Damon A.H. Teagle ,&nbsp;Robert Kerrich ,&nbsp;Dave Craw ,&nbsp;Tim S. Brewer","doi":"10.1016/j.epsl.2005.01.029","DOIUrl":null,"url":null,"abstract":"<div><p><span><span>Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust<span>, with these processes most prominently highlighted by the occurrence of major gold resources within these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and </span></span>isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (&lt;</span> <!-->190 Ma), metasedimentary belt with multiple generations of quartz<!--> <!-->±<!--> <span>carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith<span><span> to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen </span>isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust.</span></span></p><p>The range of δ<sup>15</sup>N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ<sup>15</sup>N or N concentration in micas, suggesting that there has been little discernible loss of <sup>15</sup><span>N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies<span> significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ</span></span><sup>15</sup><span>N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.</span></p></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"233 1","pages":"Pages 229-246"},"PeriodicalIF":4.8000,"publicationDate":"2005-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.epsl.2005.01.029","citationCount":"50","resultStr":"{\"title\":\"The behavior of nitrogen and nitrogen isotopes during metamorphism and mineralization: Evidence from the Otago and Alpine Schists, New Zealand\",\"authors\":\"Iain K. Pitcairn ,&nbsp;Damon A.H. Teagle ,&nbsp;Robert Kerrich ,&nbsp;Dave Craw ,&nbsp;Tim S. Brewer\",\"doi\":\"10.1016/j.epsl.2005.01.029\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p><span><span>Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust<span>, with these processes most prominently highlighted by the occurrence of major gold resources within these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and </span></span>isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (&lt;</span> <!-->190 Ma), metasedimentary belt with multiple generations of quartz<!--> <!-->±<!--> <span>carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith<span><span> to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen </span>isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust.</span></span></p><p>The range of δ<sup>15</sup>N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ<sup>15</sup>N or N concentration in micas, suggesting that there has been little discernible loss of <sup>15</sup><span>N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies<span> significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ</span></span><sup>15</sup><span>N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.</span></p></div>\",\"PeriodicalId\":11481,\"journal\":{\"name\":\"Earth and Planetary Science Letters\",\"volume\":\"233 1\",\"pages\":\"Pages 229-246\"},\"PeriodicalIF\":4.8000,\"publicationDate\":\"2005-04-30\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://sci-hub-pdf.com/10.1016/j.epsl.2005.01.029\",\"citationCount\":\"50\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Earth and Planetary Science Letters\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0012821X05000786\",\"RegionNum\":1,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Earth and Planetary Science Letters","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0012821X05000786","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 50

摘要

变质作用是地壳中流体和物质重新分配的主要机制,这些过程最突出的是这些地体中主要金矿资源的出现。然而,尽管造山带金矿占全球黄金产量的20%以上,但它们的起源仍然存在争议。岩石和矿物的氮浓度和同位素组成是地壳变质作用和成矿作用的潜在强有力的示踪剂,但迄今为止,这种方法的详细应用很少。虽然氮同位素最近被用于阐明一些新太古代造山带金矿床和元古代至古生代山带的流体来源,但由于这些地体的年龄和地质复杂性,氮的行为仍然存在主要的不确定性。新西兰南岛的奥塔哥片岩和阿尔卑斯片岩包括一个较大的、相对年轻的(<190ma),变质沉积带多代石英±碳酸盐脉体,部分脉体金矿化。从未变质的原岩到高档角闪岩,暴露出一系列原始成分变化不大的岩石,因此它们提供了一个理想的实验室来研究变质和成矿过程中氮的流动性和潜在的氮同位素分馏。在这里,我们提出了氮浓度和同位素分析的整个岩石样品和云母分离的一些地壳样带通过奥塔哥地壳。片岩中云母和全岩样品的δ15N值在0.2 ~ 7.0‰之间,氮浓度在23 ~ 3483 ppm之间。样品物源和岩石类型对氮浓度和同位素值的影响较小,似乎是由原始沉积干酪根继承而来。变质温度与云母中δ15N或N浓度之间没有系统的变化,表明随着变质温度的升高,硅酸盐中15n贫流体的损失很少。流体流动碱元素(K、Rb和Cs)、全岩碳氮浓度对比表明,奥塔哥和阿尔卑斯片岩上至绿片岩相的岩石中,除云母相外,还存在大量的氮,极有可能是未成熟的碳质物质。Macraes Flat金矿样品的δ15N值范围与成矿地体相似,但由于矿化热液中氮的掺入,其氮浓度明显高于未矿化样品。这表明,在成矿过程中,尽管同位素分馏作用很小,但氮的变质再分布并不明显。至少在氮的情况下,矿化岩石的同位素特征支持变质流体来源,并且与地幔或大气流体储层不一致。然而,由于沉积岩中氮的相对丰度高于其他潜在储层,除非流体通量非常大且通道良好,否则氮特征不能灵敏地记录来自地幔、岩浆或大气储层的流体输入。相反,如果没有类似于造山矿床中寄主岩石的“沉积”源氮同位素特征,则非常有力地表明矿化流体存在外部、外来来源。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The behavior of nitrogen and nitrogen isotopes during metamorphism and mineralization: Evidence from the Otago and Alpine Schists, New Zealand

Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust, with these processes most prominently highlighted by the occurrence of major gold resources within these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (< 190 Ma), metasedimentary belt with multiple generations of quartz ± carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust.

The range of δ15N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ15N or N concentration in micas, suggesting that there has been little discernible loss of 15N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ15N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.

求助全文
通过发布文献求助,成功后即可免费获取论文全文。 去求助
来源期刊
Earth and Planetary Science Letters
Earth and Planetary Science Letters 地学-地球化学与地球物理
CiteScore
10.30
自引率
5.70%
发文量
475
审稿时长
2.8 months
期刊介绍: Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.
×
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