Publication Date:
2023-10-26
Description:
Numerous studies exist on exhumed tectonic mélanges along subduction channels whereas, in accretionary
wedge interiors, deformation mechanisms and related fluid circulation in tectonic mélanges are still underexplored.
We combine structural and microstructural observations with geochemical (stable and clumped isotopes
and isotope composition of noble gases in fluid inclusions of calcite veins) and U-Pb geochronological data to
define deformation mechanisms and syn-tectonic fluid circulation within the Mt. Massico intra-wedge tectonic
mélange, located in the inner part of the central-southern Apennines accretionary wedge, Italy. This mélange
developed by shear deformation at the base of a clastic succession. Deformation was characterized by disruption
of the primary bedding, mixing, and deformation of relicts of competent olistoliths and strata within a weak
matrix of deformed clayey and marly interbeds. Recurrent cycles of mutually overprinting fracturing/veining
and pressure-solution processes generated a block-in-matrix texture. The geochemical signatures of syntectonic
calcite veins suggest calcite precipitation in a closed system from warm (108°-147 °C) paleofluids, with δ18O
vlaues between þ9‰ and 14‰, such as trapped pore waters after extensive 18O exchange with the local limestone
host rock and/or derived by clay dehydration processes at T 〉 120 °C. The 3He/4He ratios in fluid inclusions
are lower than 0.1 Ra, indicating that He was exclusively sourced from the crust. We conclude that: (1)
intraformational rheological contrasts, inherited trapped fluids, and low-permeability barriers such as marlyshaly
matrix, can promote the generation of intra-wedge tectonic mélanges and the development of transient
fluid overpressure; (2) clay-rich tectonic mélanges, developed along intra-wedge décollement layers, may
generate low-permeability barriers hindering the fluid redistribution within accretionary wedges.
Description:
Published
Description:
104086
Description:
1T. Struttura della Terra
Description:
2T. Deformazione crostale attiva
Description:
JCR Journal
Keywords:
Tectonic mélange
;
Fluid-rock interaction
;
Stable and clumped isotopes
;
Noble gases
;
Fold and thrust belt
;
04.04. Geology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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