Twinning and partial melting as early weakening processes in plagioclase at high pressure: insights from Holsnøy (Scandinavian Caledonides, Norway)

Abstract

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Eclogitisation of dry and impermeable granulite by fluid flow with reaction-induced porosity: Insights from hydro-chemical modelling

“…Austrheim, 1987;Bras et al, 2021), and (2) eclogite fingers that undergo static eclogitisation without associated macroscopic deformation (e.g. Jamtveit et al, 2000;Zertani et al, 2019;Baïsset et al, 2023). In our model we attribute overpressure only to a short-lived fluid pressure pulse, but additional causes of overpressure may be at play, in both eclogite fingers and shear zones.…”

“…Consistent with our work, Putnis (2021) inferred a pressure gradient from the host-rock granulite to an eclogite finger, deducing that the eclogite finger experienced a higher pressure. It was also shown (Jamtveit et al, 2000;Baïsset et al, 2023) that static eclogitisation of granulite causes perturbation in the local stress field, and could accelerate the propagation of fluids. Yamato et al (2022) recently proposed that eclogitisation-induced densification of reacting granulite can generate sufficient shear stress to fail the rocks, and self-propagates eclogitisation in a finger-like structure.…”

“…Shear zones. Sustained high pressure in eclogite shear zones can be achieved by weakeninginduced overpressure (Jamtveit et al, 2018b), and numerous studies showed that eclogitisation me-chanically weakens the granulite (Jolivet et al, 2005;Bras et al, 2021;Baïsset et al, 2023). This weakening can have crucial effects: Mancktelow (1993) showed that in deforming rocks, weak and strong layers can experience pressure differences of several kbar.…”

“…in the Himalaya, Hetényi et al, 2007), high pressure laboratory rock deformation experiments (Incel et al, 2017;Shi et al, 2018) and mathematical modelling based on the concepts of continuum mechanics and thermodynamics (Malvoisin et al, 2020;Schmalholz et al, 2020;Moulas et al, 2022;Yamato et al, 2022). However, investigating this interplay with direct petrological and structural observations from exhumed crustal rocks in the field is essential to understand how metamorphic reactions control the properties of the deep crust (Jackson et al, 2004;Labrousse et al, 2010;Baïsset et al, 2023).…”

Petrological study of an eclogite-facies metagranite from the Champtoceaux Complex (La Picherais, Armorican Massif, France)

“…The transformation of continental material modifies its density, rheology, and chemistry, which can have a significant impact on subduction dynamics, the exhumation mechanisms of HP terranes, and melt fertility (e.g. Young and Kylander-Clark, 2015;Baïsset et al, 2023). However, while HP quartzofeldspathic rocks (e.g.…”