Fluid Regime in Southern Norway: The Record of Fluid Inclusions
Fluid Regime in Southern Norway: The Record of Fluid Inclusions
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挪威南部的流体状况：流体包裹体的记录
DOI：
10.1007/978-94-009-5450-2_30
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发表时间：
1985
影响因子：
5
通讯作者：
J. Touret
中科院分区：
文献类型：
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作者：
J. Touret
流体包裹体在挪威南部有代表性的岩石中被研究过，特别是在班布尔麻粒岩中。根据最早捕获在造岩矿物(主要是石英)中的流体包裹体，已识别出五种主要的流体分布类型：两相水相(H20为主，不含固体)，碳酸盐(主要是纯CO2，可能存在N_2和/或CH_4)，混合1(水和碳质包裹体数量相当，但在不同的空腔中)，混合2(水和碳酸盐流体在同一空腔中，捕获在H20-CO_2体系的混溶状态)，卤水(H_20+固体，NaC_1为主)。只有卤水显示出主要包裹体类型与给定原岩之间的关系；它们在3个明确的环境中尤其丰富：富铝变泥质岩、夕卡岩和酸性火山岩。其他类型包裹体的分布与变质程度密切相关：麻粒岩相区以高密度碳质包裹体为主，早期两相水包裹体几乎全部产于麻粒岩西北部和台勒马克片麻岩-花岗岩中，斜方辉石等轴线以北的角闪岩相域和麻粒岩相域之间的复杂过渡带以混合(1和2)包裹体为特征。流体包裹体的P-T估计对于Bamble(变质峰期的最大二氧化碳浓度)和Rogaland(变质峰期后的最大CO2浓度)明显不同。大多数二氧化碳来自碳酸盐熔体(碳酸盐岩)的分解，这些熔体以不混溶液滴的形式侵位在深部同变质侵入岩中。挪威南部是元古界角闪岩-麻粒岩相转变的典型例子。尽管变质作用的年代仍然存在争议(见本卷中的各种条目，特别是R.H.Verschure，D.Demaiffe和J.Michot.D.菲尔德等人)，压力和温度条件开始被相对较好地理解(Jansen等人，本卷)。最近的所有研究都强调了流体的关键重要性，特别是水，其逸度在麻粒岩相边界突然减小。许多信息来自对特征矿物组合的实验和理论分析；然而，自从首次在许多麻粒岩中发现特殊的、高密度的二氧化碳包裹体(Touret，1971)以来，对岩石矿物(特别是石英、斜长石、辉石等)中流体的直接观察已变得明显。可以提供大量的信息。后来在世界上几乎所有的麻粒岩中都观察到了富含二氧化碳的流体，有时还混合了其他物种(氮气、甲烷)(Hollister和Crawford 1981，Roedder 1984)，这导致了“碳质变质作用”的概念，这为下大陆地壳的地质提供了新的见解(例如牛顿等人)。1980年，牛顿，这本书)。关于挪威南部的各种研究已经在许多出版物上发表(例如，见Roedder 1984年的评论)，但流体包裹体技术的快速发展，特别是利用显微拉曼光谱进行原位、非破坏性分析的可能性，需要对先前的数据进行批判性的重新评估。本文试图对过去15年来在挪威南部进行的所有研究进行综述。它将完善早期的合成(特别是Touret 1981,1984)，并解决高级变质岩中流体研究的三个基本方面：
i)
角闪岩和麻粒岩相岩石中流体包裹体的分布以及岩性成分(原岩)和变质程度的相对重要性。
Ii)
来自流体包裹体的压力和温度估计及其与固体矿物组合数据的比较。
Iii)
二氧化碳流体的来源。
Fluid inclusions have been studied in representative rocks from Southern Norway, notably in the Bamble granulites. On the basis of the earliest fluid inclusions trapped in rock-forming minerals (mainly quartz), five major types of fluid distribution have been recognized: 2-phase aqueous (H20 dominant, without solid), carbonic (mostly pure CO2, possiDle occurrence of N2 and/or CH4), mixed 1 (aqueous and carbonic inclusions in comparable amounts, but in separate cavities), mixed 2 (aqueous and carbonic fluids in the same cavity, trapped in the miscible state of the H20-C02 system), brines (H20 + solids, NaC1 dominant). Only brines show a relation between a dominant inclusion type and a given protolith; these are especially abundant in 3 well-defined environments: Al-rich metasediments (meta-pelites), skarns and acid volcanics. The distribution of other types is more related to metamorphic grade: high- density carbonic inclusions are typical for the granulite- -facies domain, early 2-phase aqueous inclusions occur almost exclusively in the north-western part of the Bamble and in the Telemark gneiss-granites, mixed (1 and 2) inclusions characterize the complicated transition zone between the amphibolite- and granulite-facies domains north of the orthopyroxene-in isograd. P-T estimates from fluid inclusions are apparently very different for Bamble (maximum C02 density during peak metamorphism) and Rogaland (maximum CO2 density after the peak of metamorphism). Most of the C02 originates from the breakdown of carbonate melts (carbonatites) emplaced as immiscible droplets in deep-seated synmetamorphic intrusives. Southern Norway is a classical example of amphibolite — granulite facies transition in a Proterozoic terrain. Although the age of metamorphism remains controversial (see various entries in this volume, notably by R.H. Verschure, D. Demaiffe and J. Michot. D. Field et al.), the pressure and temperature conditions start to be relatively well understood (Jansen et al., this volume). All recent studies emphazise the key importance of fluids, notably H2O, the fugacity of which decreases suddenly at the granulite — facies boundary. Much information has been derived from the analysis, both experimental and theoretical, of characteristic mineral assemblages; however, since the first discovery of specific, high density CO2 inclusions in many granulites (Touret, 1971), it has become evident that the direct observation of fluids trapped in rock-forming minerals (notably quartz, plagioclase, pyroxene etc.) can provide a great deal of information. CO2-rich fluids, sometimes mixed with other species (N2, CH4) have later been observed in virtually all granulites in the world (Hollister and Crawford 1981, Roedder 1984), leading to the notion of “carbonic metamorphism”, which has provided a new insight into the geology of the lower continental crust (e.g Newton et al. 1980, Newton, this volume). Various studies dealing with Southern Norway have been issued in a number of publications (see e.g. review in Roedder 1984), but the rapid development of fluid-inclusion techniques, notably the possibility of in-situ, non-destructive analysis by micro-Raman spectroscopy, necessitates a critical reevaluation of earlier data. In this paper, a review of all studies performed in Soutern Norway during the last 15 years will be attempted. It will refine earlier syntheses (notably Touret 1981, 1984) and address three fundamental aspects of fluid investigations in high-grade metamorphic rocks:
i)
The distribution of fluid inclusions in amphibolite- and granulite-facies rocks and the relative importance of lithological composition (protolith) and metamorphic grade.
ii)
The pressure and temperature estimates derived from fluid inclusions and their comparison with data from solid mineral assemblages.
iii)
The origin of the CO2 fluids.