Preservation of mantle heterogeneities and serpentinization signature during antigorite dehydration: The example of the Bergell contact aureole

IF 3.5 2区 地球科学 Q1 GEOLOGY
Romain Lafay, Lukas P. Baumgartner, Adélie Delacour
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引用次数: 1

Abstract

Major, minor, and trace element geochemistry as well as iron oxidation state and isotopes were investigated in serpentinites and olivine-talc fels present along a metamorphic gradient in the Bergell contact aureole (Central European Alps) to evaluate element mobility during serpentine. This aureole is an ideal target to study dehydration of mantle rocks due to the increase in temperature from greenschist facies conditions (350°C) to amphibolite facies conditions (750°C) at low pressures of 0.4 GPa. Petrography and geochemistry document several events of fluid–rock interaction and metamorphism. Serpentinization of the mantle rocks started on the ocean floor. Subsequent Alpine regional metamorphism led to the formation of antigorite-serpentinites containing olivine and diopside. These antigorite-serpentinites were transformed into olivine-talc fels in a large part of the contact-aureole. Bulk-rock major and trace element compositions maintain the geochemical signature of the precursor antigorite-serpentinites. No apparent changes are indeed observed despite the fact that major dehydration reactions occurred. In addition, changes neither in Fe3+/Fetot ratio nor in δ56Fe values were observed. Local composition variations of antigorite-serpentinites and olivine-talc fels reflect chemical heterogeneities related to protolith composition and serpentinization processes on the ocean floor prior to contact metamorphism. Hence, prograde dehydration reactions occurring during contact metamorphism did not induce substantial element mobility, change in redox state, or isotopic fractionation in these contact metamorphic rocks.

Abstract Image

反Gorite脱水过程中地幔非均质性和蛇纹石化特征的保存:以Bergell接触Aurele为例
主要、次要和微量元素地球化学以及铁氧化态和同位素在沿着Bergell接触Aurele(中欧阿尔卑斯山)变质梯度存在的蛇纹岩和橄榄石滑石中进行了研究,以评估蛇纹岩期间的元素迁移率。由于温度在0.4 GPa的低压下从绿片岩相条件(350°C)上升到角闪岩相条件(750°C),该金黄色带是研究地幔脱水的理想目标。岩石学和地球化学记录了几个流体-岩石相互作用和变质作用的事件。地幔岩石的蛇形作用始于海底。随后的阿尔卑斯区域变质作用导致了含有橄榄石和透辉石的反gorite蛇纹岩的形成。这些反gorite蛇纹岩在接触Aurele的大部分转化为橄榄石滑石毡。大块岩石的主要元素和微量元素组成保持了前体反gorite蛇纹岩的地球化学特征。尽管发生了主要的脱水反应,但确实没有观察到明显的变化。此外,既没有观察到Fe3+/Fetot比值的变化,也没有观察到δ56Fe值的变化。反gorite蛇纹岩和橄榄石滑石毡的局部成分变化反映了与接触变质作用前的原岩成分和海底蛇纹石化过程有关的化学不均匀性。因此,在这些接触变质岩中,接触变质过程中发生的进变质脱水反应没有引起实质性的元素迁移、氧化还原状态的变化或同位素分馏。
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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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