Silicification of peridotites at the stalemate fracture zone (Northwestern Pacific): Reconstruction of the conditions of low-temperature weathering and tectonic interpretation

Abstract

During cruise SO201 1b of the joint Russian-German expedition on the R/V Sonne in 2009, mantle peridotites affected by varying secondary alteration were dredged on the eastern slope of the north western segment of the Stalemate transverse ridge adjacent to the eponymous fracture zone. The collection discussed in this paper included four samples of silicified serpentinites after dunites and 11 lherzolite samples serpentinized to a varying degree. The abundance of amorphous silica and quartz, very high SiO 2 content (up to 88.7 wt %), and unusually low MgO (up to 1.4 wt %) in the serpentinized dunites strongly distinguish these rocks from the known products of hydrothermal alteration and low temperature (seafloor) weathering of peridotites in the oceanic crust. In order to determine the conditions and processes resulting in the silicifica tion of peridotites at the Stalemate Fracture Zone, thermodynamic modeling accounting for the kinetics of mineral dissolution implemented in the GEOCHEQ program package was used in this study. The results of modeling allowed us to suppose that the geochemical and mineralogical effects observed in the silicified ser pentinized dunites of the Stalemate Fracture Zone are consequences of low temperature deserpentinization of oceanic materials under subaerial conditions.

A Triassic to Cretaceous Sundaland–Pacific subduction margin in West Sarawak, Borneo

“…Sample TB10 is a chlorite-albite-(orthoclase)-quartz-mica schist ( Fig. 4e and been reported from many areas including the Semail nappe of Oman (Stanger, 1985), the United Arab Emirates (Lacinska and Styles, 2013) and the Stalemate Fracture Zone in the NW Pacific (Silantyev et al, 2012). Magnetite occurs along cracks as commonly found in serpentinised olivine.…”

Weathering crusts on peridotite

“…Hence, SI Qtz = 1.2 appears to be below critical supersaturation with respect to quartz at surface conditions. The absence of any form of silica phase in the pores of the rinds or sinter in the riverbeds suggests that silicification, observed elsewhere (Silantyev et al 2012), is not an active process in the Ronda peridotite.…”

Tracking Subsurface Active Weathering Processes in Serpentinite

“…Serpentinite, as an end‐member resulting from water‐rock interactions within mantle peridotite formations, has been recognized as a key rock type to document the role of volumetrically significant components of the solid Earth (Beinlich et al., 2018). Quantifying and documenting weathering process in serpentinite enable us to not only understand the mechanisms that drive this component of global geochemical cycle (Beard & Hopkinson, 2000; Guillot & Hattori, 2013; Hattori & Guillot, 2007; Kelemen & Matter, 2008; Kelemen et al., 2011; Silantyev et al., 2012), but also provide insights on local soil ecosystem (Baumeister et al., 2015), and impact water quality (McClain et al., 2017; Oze et al., 2004). Despite of these important implications and numerous studies on kinetics and dissolution of serpentinite‐forming minerals, our knowledge on how weathering progresses within in situ serpentine formations has been rather limited (Baumeister et al., 2015; Caillaud et al., 2006; Ducloux et al., 1976).…”