热造山运动地壳近等温剥蚀过程中低压反应纹理的形成(奥地利波希米亚山丘)

IF 3.5 2区 地球科学 Q1 GEOLOGY Journal of Metamorphic Geology Pub Date : 2023-09-14 DOI:10.1111/jmg.12744
Dominik Sorger, Christoph A. Hauzenberger, Fritz Finger, Manfred Linner, Etienne Skrzypek, Simon Schorn
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引用次数: 0

摘要

来自 Loosdorf 复合地层(奥地利东北部波希米亚山丘)的两种类型的铝质辉长岩含有粗粒花岗岩集合体和逆冲反应纹理,通过研究这些集合体和纹理,可以确定波希米亚山丘南部 Gföhl 单元的峰后历史。这两种类型都具有石榴石-生物陶瓷-菱镁矿-斜长石-K长石-石英-花岗岩熔体±黝帘石±钛铁矿±金红石的峰值组合,记录了等化学相平衡模型估计的峰值变质条件:0.9-1.1 GPa 和 780-820°C 。第一类样品(Ysper副玢岩)在石榴石周围形成了(i)堇青石冠状体,(ii)在原石榴石-矽线石界面形成了堇青石-尖晶石和堇青石-石英反应纹理。计算的化学势关系表明,这些纹理是在达到 ∼0.4 GPa 的峰后近等温减压过程中形成的。纹理的形成有两个步骤。最初,堇青石冠层在石榴石和矽线石之间生长。随着这些冠层的增厚,它们促进了局部成分域的发展,从而形成了堇青石-尖晶石和堇青石-石英共辉石。第二种样品类型(Pielach片麻岩)仅在石榴石斑岩周围表现出不连续的堇青石冠脉,但缺乏共辉石。那里的堇青石的形成也表明,在 0.4-0.5 GPa 和 750-800°C 的温度下发生了近等温减压。这种相对较热的减压路径可以用现在位于卢斯多夫复合地层下的大型 HP-UHT 花岗岩体的同期出露来解释。花岗岩和整个波希米亚山丘南部的区域变质作用的时间得到了很好的确定,其峰值在 ∼340 Ma。从洛斯多夫(Loosdorf)片麻岩样本中提取的独居石的年龄略小,为 ∼335 Ma。虽然这些年龄在误差范围内重叠,但它们被解释为反映了近等温减压和剥蚀作用,从而形成了所观察到的反应纹理。
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Formation of low-pressure reaction textures during near-isothermal exhumation of hot orogenic crust (Bohemian Massif, Austria)

Two types of aluminous paragneiss from the Loosdorf complex (Bohemian Massif, NE Austria) contain coarse-grained granulite assemblages and retrograde reaction textures that are investigated to constrain the post-peak history of the Gföhl unit in the southern Bohemian Massif. Both types have a peak assemblage garnet–biotite–sillimanite–plagioclase–K-feldspar–quartz–granitic melt ± kyanite ± ilmenite ± rutile, recording peak metamorphic conditions of 0.9–1.1 GPa and 780–820°C estimated by isochemical phase equilibrium modelling. The first sample type (Ysper paragneiss) developed (i) cordierite coronae around garnet and (ii) cordierite–spinel and cordierite–quartz reaction textures at former garnet–sillimanite interfaces. Calculated chemical potential relationships indicate that the textures formed in the course of a post-peak near-isothermal decompression path reaching 0.4 GPa. Texture formation follows a two-step process. Initially, cordierite coronae grow between garnet and sillimanite. As these coronae thicken, they facilitate the development of local compositional domains, leading to the formation of cordierite–spinel and cordierite–quartz symplectites. The second sample type (Pielach paragneiss) exhibits only discontinuous cordierite coronae around garnet porphyroblasts but lacks symplectites. The formation of cordierite there also indicates near-isothermal decompression to 0.4–0.5 GPa and 750–800°C. This relatively hot decompression path is explained by the contemporaneous exhumation of a large HP–UHT granulite body now underlying the Loosdorf complex. The timing of regional metamorphism in the granulites and the southern Bohemian Massif in general is well constrained and has its peak at 340 Ma. Monazite from Loosdorf paragneiss samples yield a slightly younger age of 335 Ma. Although the ages overlap within error, they are interpreted to reflect near-isothermal decompression and exhumation resulting in the formation of the observed reaction textures.

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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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