Reaction‐Induced Mantle Weakening at High‐Pressure Conditions: An Example From Garnet Pyroxenites of Ulten Zone (Eastern Alps, N Italy)

Abstract

The deformational behavior of the upper mantle in response to the forces in the Earth's interior depends on several factors, including pressure, temperature, deviatoric stress, mineralogy, presence of fluids and/or melts, and the grain size of the deforming mantle rocks (e.g., Bürgmann & Dresen, 2008 and reference therein). Studies on both naturally and experimentally deformed mantle rocks indicate that most of the plastic deformation of the upper mantle is accommodated by grain size insensitive (GSI) deformation mechanisms, e.g., dislocation creep

Probing the deep mantle wedge in an active subduction zone: Xenoliths from the Mercaderes Volcanic District, Southern Colombia

“…The (re)crystallization associated to this deformation largely erased the microstructures produced at precursor evolutionary stages. Consequently, these rocks have different microstructures from other supra subduction garnet-bearing mantle peridotites and pyroxenites, which still preserve petrological and textural evidence of a polyphase and colder evolution within the lithosphere of the overriding plate or associated with the subduction-induced flow (e.g., Malaspina et al, 2009;Pellegrino et al, 2021). The present xenoliths were also equilibrated at higher temperatures.…”

“…High-pressure orogenic peridotites are metasomatized spinel and garnet peridotites derived from cold domains of the supra-subduction mantle in contact with, or in proximity of, the subducting slab (Bodinier and Godard, 2003), which became tectonically scraped off their original supra-subduction domains and were exhumed to the surface in subduction channels (Brueckner and Medaris, 2000;Scambelluri et al, 2010). Known examples are mostly garnet peridotites, among which those from the Alpine Ulten Zone (Godard et al, 1996;Gudelius et al, 2019;Ionov et al, 2017;Pellegrino et al, 2021;Rampone and Morten, 2001;Sapienza et al, 2009;Scambelluri et al, 2006;Tumiati et al, 2003), Sulu in China (Malaspina et al, 2009(Malaspina et al, , 2012Zheng et al, 2005Zheng et al, , 2008, and from Bardane, Fjørtoft island, Western Norway (Scambelluri et al, 2008;Drury, 1998, Van Roermund et al, 2002). These rocks commonly contain hydrated minerals (amphibole, phlogopite) coexisting with garnet as the result of reactions with metasomatic slab fluids or melts at temperatures around 800-850 • C, as shown by thermobarometry of the above rock occurrences.…”