Drainage of subduction interface fluids into the forearc mantle evidenced by a pristine jadeitite network (Polar Urals)

Abstract

The physical and mechanical processes rooted in the hydrated, serpentinized mantle above subduction zones remain insufficiently explored despite fundamental implications for our understanding of rheology and fluid recycling along subduction interfaces. Through a field-based investigation, serpentinized peridotites and jadeitite samples from a fossil forearc mantle in the Polar Urals (Russia) are studied here to document fluid-rock interaction processes in the high-P field, as well as the long-term evolution of the base of the mantle wedge. Petrographic, geochemical and microstructural observations reveal a complex, protracted evolution of the jadeitite-forming fluid pathway throughout the gradual cooling of the forearc mantle and increasing serpentinization of the host. It is shown that the jadeitite lenses in the studied locality (a) derive for a large part from a trondhjemitic dyke earlier emplaced in a warm subduction environment, and (b) record the cooling of the subduction hangingwall under high-P conditions associated with increasing host serpentinization. In the studied locality, the majority of the jadeitites formed at relatively high temperatures (>600°C) by the influx of Na-Al-rich, slab-derived metamorphic fluids that were drained along the base of the mantle wedge, parallel to the subduction interface. Changes in bulk-rock geochemical signatures and in paragenetic sequences also constrain the compositional evolution of the fluid channelized along this drainage, with an increasing sedimentary component. The phlogopite-bearing walls of the dyke exhibit Rb-Sr and Ar-Ar ages ranging between c. 405 and c. 390 Ma, a range partly overlapping within uncertainty with the previously dated zircons from the jadeitite core (410-400 Ma; U-Pb). This study opens a unique window on the pristine structures formed above the plate interface by melting and fluid-rock interaction in the early subduction stages, as well as their evolution during secular cooling of the base of the mantle wedge.

The Subducting Slab as a Chromatographic Column: Regimes of Sub‐Solidus Mass Transport as a Function of Lithospheric Hydration State, With Special Reference to the Fate of Carbonate

“…For example, shifting the fore-arc/subarc threshold to 90 km depth doubles the predicted forearc H 2 O flux (Figure S13 in Supporting Information S1). This could typically account for interface-parallel upward fluid transfer, in which a fraction of the fluid pulse released from the basaltic layer between 80 and 90 km would be channelized to the fore-arc by migration within the slab, or along the subduction interface (Angiboust, Glodny, et al, 2021;John et al, 2012;Kawano et al, 2011). Only our IHS and LHS models (Table 1) yield sub-solidus H 2 O releases to sub-arc depth that match observational constraints on global H 2 O degassing at volcanic arcs, that is, ∼650 Mt H 2 O/yr (Fischer, 2008).…”

Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

“…The fluid flow mechanisms may have different dynamics in the downgoing slab, at the slab-mantle interface or in the hanging-wall mantle wedge (e.g. Konrad-Schmolke et al 2011;Angiboust et al 2020). A better understanding of the dynamics of fluid-rock interaction and the associated permeability is crucial to quantify fluid-driven mass transfer processes in subduction zones (Ingebritsen and Manning 1999, 2003, 2010Manning and Ingebritsen 1999;Konrad-Schmolke et al 2011;Ganzhorn et al 2019).…”

Episodic hydrofracturing and large-scale flushing along deep subduction interfaces: Implications for fluid transfer and carbon recycling (Zagros Orogen, southeastern Iran)

“…The most obvious evidence for COH-bearing fluid-rock interactions in subduction zones is the occurrence of complex vein systems in both the subducting interface-channel and the overlying forearc (e.g., Philippot and Selverstone, 1991;Bebout and Barton, 1993;Spandler et al, 2011;Angiboust et al, 2020), which provide valuable information regarding fluid-rock interactions (e.g., Molina et al, 2004;Zack and John, 2007;Spandler et al, 2008;van der Straaten et al, 2012;Taetz et al, 2016), fluid pathways and chemistry (e.g., Scambelluri and Philippot 2001;Spandler et al, 2003;Angiboust et al, 2017), and pressure-temperature (P-T) conditions of fluid circulation (Vrolijk et al 1988;Raimbourg et al, 2018). Understanding whether fluids are locally derived or far-travelled has long been a matter of debate (Philippot and Kienast, 1989;Widmer and Thompson, 2001;Piccoli et al, 2018).…”