Controls on fluid movement in crustal lithologies: evidence from zircon in metaconglomerates from Shetland

Abstract

An investigation of the morphology of zircon in clasts and matrix of a greenschist facies metaconglomerate from Shetland has revealed a history of alteration of radiation‐damaged grains, partial dissolution and growth of new zircon. These processes are linked to the generation of chemically modified dark backscattered electron (BSE) zircon that is spatially related to fractures generated during radiation damage; embayments and rounding of zircon margins; and late overgrowths of original grains. These late modifications of zircon are all linked to the presence of fluids and so zircon morphology is used to track fluid behaviour in different lithologies in the metaconglomerate. Alteration is unrelated to clast margins and radically different in various clast types. This reflects a difference in permeability and suggests that deformation strongly controls fluid influx into quartzite, whereas zircon alteration in granite is associated with a restricted permeability reflecting the more limited response to deformation events.

Dating shear zones with plastically deformed titanite: New insights into the orogenic evolution of the Sudbury impact structure (Ontario, Canada)

“…In an experimental study, Lucassen et al, (2010) Similar micro-textural relationships between different REE-bearing accessory phases are attributed to the process of dissolution-reprecipitation in accessory phases from natural metasomatic settings (Pan et al, 1993, Dempster et al, 2006, Dempster and Macdonald, 2016. Experimental studies have also shown that permeating metasomatic fluids can exploit micro and nano-scale intragranular porosity paths (e.g.…”

Petrochronology and mineral chemistry of mid-crustal shear zones

“…The nucleation of fluorapatite and allanite grains (LREE-enriched epidote) as inclusions in the LREE-depleted titanite grains is another textural line of evidence that can be related to the fluid-mediated petrogenesis of titanite in the Six Shaft Shear Zone. Similar micro-textural relationships between different REE-bearing accessory phases are attributed to the process of dissolution-reprecipitation in accessory phases from natural metasomatic settings (Pan et al, 1993, Dempster et al, 2006, Dempster and Macdonald, 2016. Experimental studies have also shown that permeating metasomatic fluids can exploit micro and nano-scale intragranular porosity paths (e.g.…”