Paleocene‐Eocene High‐Pressure Carbonation of Western Alps Serpentinites: Positive Feedback Between Deformation and CO₂‐CH₄ Fluid Ingression Responsible for Slab Slicing?

Abstract

Large amounts of fluids are released in subduction zones by progressive dehydration of the downgoing lithosphere (Hacker, 2008;Schmidt & Poli, 2014). The release and migration of fluids at depth strongly impact rheology (as they contribute to fracturing and earthquake nucleation; e.g., Hacker et al., 2003) and control the generation and geochemical signature of arc magmas (e.g., Stern, 2002). Characterization of the sources, amounts, and pathways of fluids in subduction zones is therefore a prerequisite to assess their impact on subduction dynamics and global element cycling (e.g., Bebout & Penniston-Dorland, 2016).In subduction zones, boundaries between dissimilar lithologies (i.e., sediments, mafic and ultramafic rocks) with contrasting mechanical behaviors appear to localize deformation and act as important fluid pathways (Piccoli et al., 2018;Vitale Brovarone et al., 2014). In the presence of fluids, their contrasting chemical compositions enhance the formation of metasomatic "hybrid" rocks enriched in fluid-mobile elements (Bebout &

Fractal Distribution of Subduction‐Related Crack‐Seal Veins (Schistes Lustrés, W. Alps): Implications for Fluid Flow and Rupture Processes at the Downdip End of the Seismogenic Zone

“…Moreover, the mean D c of 0.67 for all studied outcrops indicate a weak clustering of veins, in agreement with pervasive fluid flow. Fluid channelization, if any, must therefore be looked for at a scale greater than single outcrops and possibly along major tectonic contacts (Herviou & Bonnet, 2023; Jaeckel et al., 2018; Figure 13a): the observed higher vein densities in the studied outcrops might represent zones of more localized deformation and channelized fluid flow that could only be statistically detected on hm‐ to km‐scale transects across the complex. The feasibility of this larger scale approach seems however limited by the characteristic length scale and discontinuity of rock exposures (Figures 2c and 2d).…”

“…This may indicate in turn that slow slip events were localized along larger‐scale shear structures, for example, 100 m‐long shear bands wrapping around the sections investigated for vein patterns. Highly sheared talcschist horizons found along the contacts between tectonic slices (Herviou & Bonnet, 2023) correspond to potential candidates as the stress amplification observed in talc‐bearing rocks has been proposed to record former slow slip events (Hoover et al., 2022).…”

“…These rocks were buried between ∼30 and 80 km depth (Agard et al., 2001, 2002, 2009; Herviou et al., 2022) and form a HP‐LT nappe‐stack known as the Liguro‐Piemont domain (e.g., Agard, 2021) or the Schistes Lustrés complex (owing to their characteristic sediments; Agard et al., 2001; Caron, 1977; Deville et al., 1992; Tricart & Schwartz, 2006). After peak burial between ∼60 and ∼40 Ma, these rocks were scrapped off as tectonic slices from the downgoing plate, and exhumed from the Late Eocene to the Miocene (Agard et al., 2002; Angiboust & Glodny, 2020; Gyomlai et al., 2023; Herviou & Bonnet, 2023; Schwartz et al., 2007, 2020).…”