Crustal reworking and hydration: insights from element zoning and oxygen isotopes of garnet in high-pressure rocks (Sesia Zone, Western Alps)

Details

Ressource 1Request a copy Sous embargo indéterminé.
State: Public
Version: Final published version
License: CC BY 4.0
Serval ID
serval:BIB_F16624618402
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Crustal reworking and hydration: insights from element zoning and oxygen isotopes of garnet in high-pressure rocks (Sesia Zone, Western Alps)
Journal
Contributions to Mineralogy and Petrology
Author(s)
Alice Vho, Daniela Rubatto, Pierre Lanari, Francesco Giuntoli, Daniele Regis, Jörg Hermann
ISSN
0010-7999
1432-0967
Publication state
Published
Issued date
11/2020
Volume
175
Number
11
Language
english
Abstract
Subduction zones represent one of the most critical settings for fluid recycling as a consequence of dehydration of the subducting
lithosphere. A better understanding of fluid flows within and out of the subducting slab is fundamental to unravel
the role of fluids during burial. In this study, major and trace element geochemistry combined with oxygen isotopes were
used to investigate metasediments and eclogites from the Sesia Zone in order to reconstruct the effect of internal and external
fluid pulses in a subducted continental margin. Garnet shows a variety of textures requiring dissolution–precipitation
processes in presence of fluids. In polycyclic metasediments, garnet preserves a partly resorbed core, related to pre-Alpine
high-temperature/low-pressure metamorphism, and one or multiple rim generations, associated with Alpine subduction
metamorphism. In eclogites, garnet chemical zoning indicates monocyclic growth with no shift in oxygen isotopes from
core to rim. In metasediments, pre-Alpine garnet relics show δ18O values up to 5.3 ‰ higher than the Alpine rims, while
no significant variation is observed among different Alpine garnet generations within each sample. This suggests that an
extensive re-equilibration with an externally-derived fluid of distinct lower δ18O occurred before, or in correspondence
to, the first Alpine garnet growth, while subsequent influxes of fluid had δ18O close to equilibrium. The observed shift in
garnet δ18O is attributed to a possible combination of (1) interaction with sea-water derived fluids during pre-Alpine crustal
extension and (2) fluids from dehydration reactions occurring during subduction of previously hydrated rocks, such as the
serpentinised lithospheric mantle or hydrated portions of the basement.
Keywords
Geochemistry and Petrology, Geophysics
Web of science
Open Access
Yes
Funding(s)
Swiss National Science Foundation / 200021_169062
Swiss National Science Foundation / 200021_166280
Create date
30/11/2020 10:20
Last modification date
11/12/2020 7:26
Usage data