A rapid transition from subduction to Barrovian metamorphism: geochronology of mafic-ultramafic relicts of oceanic crust in the Central Alps, Switzerland.

IF 1.8 2区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Swiss Journal of Geosciences Pub Date : 2024-01-01 Epub Date: 2024-08-30 DOI:10.1186/s00015-024-00462-7
Kim Lemke, Daniela Rubatto, Jörg Hermann
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引用次数: 0

Abstract

Relicts of subducted oceanic lithosphere provide key information for the tectonic reconstructions of convergent margins. In the Central Alps, such relicts occur as isolated mafic-ultramafic lenses within the migmatites of the southern Adula nappe and Cima-Lunga unit. Analysis of the major-, minor-, and accessory minerals of these ophiolitic relicts, combined with zircon and rutile U-Pb ages and zircon oxygen isotopes, allows the reconstruction of different stages of their complex evolution. The mafic-ultramafic suite in Valle di Moleno consists of chlorite-harzburgites associated with metarodingites and retrogressed eclogites. Relic omphacite and kyanite in retrogressed eclogites provide evidence for subduction-related metamorphism. Increasing XPrp in the garnet mantle towards the rim documents heating during high-pressure metamorphism up to 800-850 °C. Polyphase inclusions and chemical zoning in garnet suggest fluid-assisted melting during high-pressure metamorphism dated at 31.0 ± 0.9 Ma. In Val Cama, chlorite-harzburgites, metarodingites and calcsilicate-metasediments occur. Detrital zircon ages in the metasediment suggest a Mesozoic deposition. The metarodingite-metaperidotite-metasediment association and the low δ18O signatures of zircon (δ18O 3.0-3.7‰), inherited from seafloor metasomatism of the protoliths, show that the rocks are derived from former altered oceanic crust. Amphibolite facies metamorphism related to the Central Alps Barrovian evolution in Val Cama occurred at 28.8 ± 1.5 Ma. The combined data from Moleno and Cama indicate a rapid transition (~ 2 Ma) from subduction to collisional metamorphism with corresponding exhumation rates of 3-6 cm/year. Fast exhumation tectonics may have been favored by slab break-off or slab extraction. U-Pb dating of rutile from both localities yields ages of ~ 20 Ma, suggesting that these rocks remained at amphibolite-facies conditions for about 10 Ma and underwent a second fast exhumation of 3 cm/year associated with vertical movements along the Insubric line.

Supplementary information: The online version contains supplementary material available at 10.1186/s00015-024-00462-7.

从俯冲到巴罗维变质作用的快速过渡:瑞士阿尔卑斯山中部大洋地壳岩浆-超岩浆遗迹的地质年代学。
俯冲的海洋岩石圈遗迹为汇聚边缘的构造重建提供了关键信息。在中阿尔卑斯山,此类遗迹以孤立的黑云母-超黑云母透镜体形式出现在南部阿杜拉岩脉和西马-隆加单元的伟晶岩中。通过对这些蛇绿岩遗迹的主要矿物、次要矿物和附属矿物进行分析,并结合锆石和金红石的 U-Pb 年龄和锆石氧同位素,可以重建其复杂演化的不同阶段。Valle di Moleno 的黑云母-超黑云母岩套由绿泥石-哈兹堡垒岩组成,与变质岩和后退蚀变岩伴生。逆冲闪长岩中的残余闪长岩和闪长岩为与俯冲有关的变质作用提供了证据。榴辉岩地幔中的XPrp向边缘增加,证明了高压变质过程中的加热温度高达800-850 °C。石榴石中的多相包裹体和化学分带表明,高压变质作用期间的流体辅助熔融作用发生在 31.0 ± 0.9 Ma。在 Val Cama,出现了绿泥石-哈兹堡垒岩、元丁岩和钙硅酸盐-基岩。变质岩中的锆石年龄表明是中生代沉积。变质岩-方镁石-变质岩的关联和锆石的低δ18O特征(δ18O 3.0-3.7‰)(由原岩的海底变质作用继承)表明,这些岩石来自以前的蚀变洋壳。与瓦尔卡马的中阿尔卑斯山巴罗维演化有关的闪长岩变质作用发生在 28.8±1.5 Ma。莫莱诺和卡马的综合数据表明,从俯冲变质作用到碰撞变质作用的过渡十分迅速(约 2 Ma),相应的掘起速度为 3-6 厘米/年。板块断裂或板块萃取可能有利于快速掘出构造。这两个地点的金红石的U-Pb年代测定结果显示,这些岩石的年龄约为20Ma,表明这些岩石在闪长岩成因条件下保持了约10Ma,并经历了与沿Insubric线垂直运动相关的第二次快速隆升,隆升速度为3厘米/年:在线版本包含补充材料,可查阅 10.1186/s00015-024-00462-7。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Swiss Journal of Geosciences
Swiss Journal of Geosciences 地学-地质学
CiteScore
4.50
自引率
12.90%
发文量
21
审稿时长
>12 weeks
期刊介绍: The Swiss Journal of Geosciences publishes original research and review articles, with a particular focus on the evolution of the Tethys realm and the Alpine/Himalayan orogen. By consolidating the former Eclogae Geologicae Helvetiae and Swiss Bulletin of Mineralogy and Petrology, this international journal covers all disciplines of the solid Earth Sciences, including their practical applications. The journal gives preference to articles that are of wide interest to the international research community, while at the same time recognising the importance of documenting high-quality geoscientific data in a regional context, including the occasional publication of maps.
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