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

Details

Serval ID
serval:BIB_168D34F09EB0
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
A rapid transition from subduction to Barrovian metamorphism: geochronology of mafic–ultramafic relicts of oceanic crust in the Central Alps, Switzerland
Journal
Swiss Journal of Geosciences
Author(s)
Lemke Kim, Rubatto Daniela, Hermann Jörg
ISSN
1661-8726
1661-8734
ISSN-L
1661-8726
Publication state
Published
Issued date
12/2024
Peer-reviewed
Oui
Volume
117
Number
1
Language
english
Notes
FNS: 2000021_191959
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 X <sub>Prp</sub> 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 δ <sup>18</sup> O signatures of zircon (δ <sup>18</sup> O 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.
The online version contains supplementary material available at 10.1186/s00015-024-00462-7.
Pubmed
Web of science
Open Access
Yes
Funding(s)
Swiss National Science Foundation / 200020_196927
Swiss National Science Foundation
University of Lausanne
Create date
13/09/2024 13:50
Last modification date
21/09/2024 6:09
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