Accretion and subduction mass transfer processes: Zircon SHRIMP and geochemical insights from the Carboniferous Western Series, Central Chile
Metadatos
Afficher la notice complèteEditorial
Taylor & Francis
Materia
Western Series Zircon geochronology Basal accretion Subduction Sedimentary recycling Seamounts
Date
2023-03-07Referencia bibliográfica
Jesus Munoz-Montecinos, Aitor Cambeses & Samuel Angiboust (2023): Accretion and subduction mass transfer processes: Zircon SHRIMP and geochemical insights from the Carboniferous Western Series, Central Chile, International Geology Review, [https://doi.org/10.1080/00206814.2023.2185822]
Patrocinador
IDEX [6CR538]Résumé
In the region of Pichilemu (Central Chile), the exhumed roots of the Carboniferous paleo-accretionary
wedge developed during subduction of an oceanic realm underneath the western Gondwana margin
are exposed. We focus on the areas of Infiernillo beach and Punta de Lobos: the former representing a
well-characterized transitional blueschist-facies coherent stack of metabasitic lithologies interlayered
at the centimetre- to metre-scale within metasedimentary rocks and glaucophanites, whereas the
latter corresponds to a massive, up to hundreds of metres thick, strained metapillow lavas edifice
surrounded (not interlayered) by metasedimentary rocks. We provide new field, geochemical, Raman
thermometry and zircon SHRIMP U-Th-Pb geochronology on the lithologies forming the Infiernillo-
Punta de Lobos complex aiming at characterizing the sedimentary sources and the extent of
mechanical mixing. Field observations suggest that the Infiernillo-Punta de Lobos complex can be
considered as part of the same successions, subducted and basally accreted almost coherently at
high pressure-low temperature (HP-LT) conditions. The geochemistry signal in metasedimentary
rocks and maximum deposition ages point to a marked forearc source for all the metasedimentary
and glaucophanite lithologies, whereas massive metapillow lavas and greenschists might represent
volcanic products and oceanic roughnesses erupted near the trench when the oceanic material
approached the Gondwana margin at c. 329 Ma. It is suggested that the interlayering now observed
in the field is mostly the consequence of sedimentary and/or volcanic processes close to the trench
environment, with minor tectonic reworking of the pre-subduction structures (e.g. lithological
contacts). Our results suggest that the Punta de Lobos edifice is closely related to the subduction
of large volumes of continent-derived, trench-filling sediments towards HP-LT conditions. Thus, in
line with previous experimental and numerical simulations, we emphasize the potential role of
oceanic roughness as stress perturbations that could contribute to the subduction of thick sedimen-
tary sequences, and discuss their implications for seismogenesis.