A Jurassic oceanic core complex in the high-pressure Monviso ophiolite (western Alps, NW Italy)

Abstract

The eclogite-facies Monviso ophiolite in the western Alps displays a complex record of Jurassic rift-drift, subduction zone, and Cenozoic collision tectonics in its evolutionary history. Serpentinized lherzolites intruded by 163 ± 2 Ma gabbros are exposed in the footwall of a thick shear zone (Baracun shear zone) and are overlain by basaltic lava flows and synextensional sedimentary rocks in the hanging wall. Mylonitic serpentinites with sheared ophicarbonate veins and talc-and-chlorite schist rocks within the Baracun shear zone represent a rock assemblage that formed from seawater-derived hydrothermal fluids percolating through it during intra-oceanic extensional exhumation. A Lower Cretaceous calc-schist, marble, and quartz-schist metasedimentary assemblage unconformably overlies the footwall and hangingwall units, representing a postextensional sequence. The Monviso ophiolite, Baracun shear zone, and the associated structures and mineral phases represent core complex formation in an embryonic ocean (i.e., the Ligurian-Piedmont Ocean). The heterogeneous lithostratigraphy and the structural architecture of the Monviso ophiolite documented here are the products of rift-drift processes that were subsequently overprinted by subduction zone tectonics, and they may also be recognized in other (ultra)high-pressure belts worldwide. LITHOSPHERE

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

“…This study focuses mainly on the LSU (Figures 1b-1e), which comprises, from bottom to top: a serpentinized lherzolite sole, intruded and/or capped by late Jurassic Mg-Al metagabbros and minor Fe-Ti gabbros mostly at their top (or as centimeter-to meter-thick boudins intruding the primary oceanic lithostratigraphic sequence; e.g., Locatelli et al, 2019Locatelli et al, , 2018Lombardo, 1978), banded tholeiitic basalts, and diabases and mixed calcareous/pelitic Cretaceous metasediments (Balestro et al, 2014(Balestro et al, , 2013Castelli et al, 2002;Festa et al, 2015;Locatelli et al, 2019;Lombardo, 1978).…”

“…The original stratigraphic sequence of the LSU is partly disrupted by two regional shear zones (Angiboust et al, 2011;Angiboust, Langdon, et al, 2012;Festa et al, 2015;Lombardo, 1978;Philippot & Kienast, 1989b): the ISZ localized between the metagabbros and the overlying metabasalts and the LSZ between the serpentinized sole and the metagabbros (Figures 1b and 1e). The omphacite-and garnet-rich veins emplaced in metagabbros at the base of the ISZ (Lago Superiore area; Figures 1b and 1c) have been the subject of structural and petrological (Philippot, 1987;Philippot & Kienast, 1989a;Philippot & van Roermund, 1992), fluid inclusion (Nadeau et al, 1993;Philippot & Selverstone, 1991), stable isotope (Nadeau et al, 1993), geochronological (Rubatto & Hermann, 2003), and geochemical studies (Philippot & Selverstone, 1991;Rubatto & Hermann, 2003;Spandler et al, 2011).…”

The life of a marginal basin depicted in a structural map of the South China Sea

“…The structure of the margin by the end of the rifting is dominated by a severe boudinage of a thin crust , on which the low-angle normal faults are either the granitoids boundaries or the short limbs of Cretaceous folds. Reactivation of early structures is common during rifting or basin inversion (Festa et al, 2015;Balestro et al, 2018). Because the thinned margin was sustained at shallow depth, platform and reef carbonates occupy some of the bathymetric highs.…”

Ocean floor and subduction record in the Zermatt‐Saas rodingites, Valtournanche, Western Alps

“…Dal Piaz & Ernst, 1978;Dal Piaz et al, 1981). Recently, some ophiolitic complexes of the Western Alps have been interpreted as oceanic core complexes characteristic of slow-spreading oceanic ridges (Festa et al, 2015;Lagabrielle et al, 2015).…”