20 May 2022
20 May 2022
Status: this preprint is open for discussion.

Epidote dissolution–precipitation during viscous granular flow: a micro-chemical and isotope study

Veronica Peverelli1, Alfons Berger1, Martin Wille1, Thomas Pettke1, Pierre Lanari1, Igor M. Villa1,2, and Marco Herwegh1 Veronica Peverelli et al.
  • 1Department of Geological Sciences, University of Bern, Bern, 3012, Switzerland
  • 2Dipartimento di Scienze dell’Ambiente e della Terra, University of Milano-Bicocca, Milan, 20126, Italy

Abstract. Deformation of polymineralic aggregates can be accommodated by viscous granular flow, a process mediated by the interplay among intracrystalline plasticity and dissolution–precipitation, each active in specific minerals at given P–T conditions. Common rock-forming minerals like quartz, feldspars and sheet silicates have been intensively studied in terms of deformation processes. Instead, the deformation behavior of epidote and its role during viscous granular flow is not well investigated, although this mineral is ubiquitous in granitic rocks deforming at greenschist-facies conditions. In this contribution, we provide microstructural and geochemical evidence for the occurrence of dissolution–precipitation of epidote during deformation of an epidote-quartz vein. The main part of the vein is deformed producing a fold, which is visible due to relicts of primary-growth layering inside the vein. The deformation mechanisms active during deformation include dynamic recrystallization of quartz by subgrain rotation recrystallization, producing grain-size reduction of the primary vein quartz. This occurs contemporaneously with dissolution and (re)precipitation of epidote, and grain-boundary sliding, leading to a combined process described as viscous granular flow. The combination of intracrystalline plasticity, grain boundary sliding and dissolution locally and repeatedly produce creep cavities. These represent not only loci for nucleation of new epidote grains at the expenses of dissolved one, but they also allow fluid-mediated transport of elements. The same trace element patterns between old epidote relicts and newly formed grains, with much narrower variability, indicate a process of chemical homogenization. The nature of the fluid mediating deformation is investigated using Pb–Sr isotope data of epidote, which suggest that deformation is assisted by internally recycled fluids with the addition of a syn-kinematic external fluid component.

Veronica Peverelli et al.

Status: open (until 15 Jul 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-311', Anonymous Referee #1, 23 Jun 2022 reply
  • CC1: 'Comment on egusphere-2022-311', Matthias Konrad-Schmolke, 23 Jun 2022 reply
  • CC2: 'Comment on egusphere-2022-311', Matthias Konrad-Schmolke, 23 Jun 2022 reply

Veronica Peverelli et al.

Veronica Peverelli et al.


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Short summary
This work studies the interplay of epidote dissolution-precipitation and quartz dynamic recrystallization during viscous granular flow in a deforming epidote-quartz vein. Pb and Sr isotope data indicate that epidote dissolution-precipitation is mediated by internal/recycled fluids with an additional external fluid component. Microstructures and geochemical data show that the epidote material is redistributed and chemically homogenized within the deforming vein via dynamic granular fluid pump.