The origin of tectonic mélanges and implication for the subduction interface processes

• Main Authors: Rajič, Kristijan, Raimbourg, Hugues, Famin, Vincent, Moris-Muttoni, Benjamin
• Other Authors: Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Magma & Déformation, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université de La Réunion (UR), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2024
• Subjects: [SDU]Sciences of the Universe [physics]; Kodiak; Alaska
• Online Access: https://insu.hal.science/insu-04647682; https://doi.org/10.5194/egusphere-egu24-8453

International audience Tectonic mélanges, penetrative mixes of sediments and basalts, are often interpreted as fossil subduction plate interfaces. These formations, marked by intense deformation, contain witnesses of past earthquakes and commonly include remnants of the oceanic crust of the subducting plate. The original process that led to penetrative mixing of sediments and basalts is often controversial, and classically relies either on tectonic slicing of the downgoing plateduring subduction, or on pre-subduction, olistostrome-forming sedimentary mixing. In addition, magma emplacement in sediments of the downgoing plate may also explain the mixed lithologies of mélanges. This latter case should leave an aureole of contact metamorphism in sediments near basalts. In this work, we applied Raman Spectroscopy of Carbonaceous Material in the modern seafloor sediments where magmatism is reported, in order to evaluate the thermal influence from basalts onto carbonaceous material in the contacting sediments. Then, to check the potential contact metamorphism in mélanges, we employed the same methodology in several examples of sediment-basalt mélanges at (sub)-greenschist-facies conditions (Kodiak complex, Alaska; Shimanto Belt, Japan).In modern ocean-floor settings, magmas intruding, and to a lesser extent, flowing onto sediments, resulted in higher crystallinity of carbonaceous material in a cm- to dm-thick contact aureole. In four of five studied mélanges, the crystallinity of carbonaceous material in metasediments increases toward basalts, indicating a ~1 cm-thick contact metamorphism aureole. Thus, we propose that for the studied mélanges the mixing likely occurred prior to subduction, with the preservation of contact metamorphism despite syn-subduction, low-temperature metamorphism.As a consequence, the block-in-matrix structure observed in mélanges, as well as the occurrence of mafic bodies at seismogenic depths in accretionary prisms, is in many instances the result of pre-subduction structure, rather than ...