Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

Bovay, Thomas; Rubatto, Daniela; Lanari, Pierre (2021). Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet. Contributions to mineralogy and petrology, 176(7) Springer-Verlag 10.1007/s00410-021-01806-4

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Dehydration reactions in the subducting slab liberate fluids causing major changes in rock density, volume and permeability. Although it is well known that the fluids can migrate and interact with the surrounding rocks, fluid pathways remain challenging to track and the consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive fluid-rock interaction in a sequence of schists and mafic felses exposed in the Theodul Glacier Unit (TGU), Western Alps. This unit is embedded within metaophiolites of the Zermatt-Saas Zone and reached eclogite-facies conditions during Alpine convergence. Chemical mapping and in situ oxygen isotope analyses of garnet from the schists reveal a sharp chemical zoning between a xenomorphic core and a euhedral rim, associated to a drop of ~ 8‰ in δ18O. Thermodynamic and δ18O models show that the large amount of low δ18O H2O required to change the reactive bulk δ18O composition cannot be produced by dehydration of the mafic fels from the TGU only, and requires a large contribution of the surrounding serpentinites. The calculated time-integrated fluid flux across the TGU rocks is 1.1 × 105 cm3/cm2, which is above the open-system behaviour threshold and argues for pervasive fluid flow at kilometre-scale under high-pressure conditions. The transient rock volume variations caused by lawsonite breakdown is identified as a possible trigger for the pervasive fluid influx. The calculated schist permeability at eclogite-facies conditions (~ 2 × 10–20 m2) is comparable to the permeability determined experimentally for blueschist and serpentinites.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Bovay, Thomas; Rubatto, Daniela and Lanari, Pierre

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0010-7999

Publisher:

Springer-Verlag

Funders:

[4] Swiss National Science Foundation ; [18] European Research Council

Language:

English

Submitter:

Pierre Lanari

Date Deposited:

14 Jul 2021 16:47

Last Modified:

14 Jul 2021 16:47

Publisher DOI:

10.1007/s00410-021-01806-4

BORIS DOI:

10.48350/157532

URI:

https://boris.unibe.ch/id/eprint/157532

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