Quartz grain boundaries as fluid pathways in metamorphic rocks

Jörn H. Kruhl, Richard Wirth, Luiz F.G. Morales

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

TEM and SEM/FIB sequential imaging of quartz grain boundaries from contact and regional metamorphic rocks show that most of the grain boundaries are open on the nanometer scale. Three types of voids occur. (i) Roughly 40-500 nm wide open zones parallel to the grain boundaries. They are suggested to be caused by general volume reduction as a result of anisotropic cooling contraction at temperatures decreasing below ca. 300°C, the threshold temperature of diffusion in quartz and of decompression expansion at pressures decreasing below several hundred MPa. (ii) Cavities of variable shape and up to micrometer size along the open grain boundaries and (iii) cone-shaped, nanometer-sized depressions at sites where dislocation lines meet the open grain boundaries. The latter two types are generated by dissolution-precipitation processes. Open grain boundaries, cavities, and depressions form a connected network of porosity, which allows fluid circulation and may affect physical properties of the rocks. The same process is suggested to occur along grain and phase boundaries in other rocks as exemplified in this study, and it should be expected along intracrystalline cracks or cleavage planes. Key Points TEM and SEM/FIB sequential imaging show voids along quartz grain boundariesThermal contraction probably leads to up to 500 nm wide open grain boundariesA network of cavities allows fluid circulation and affects rock properties

Original languageEnglish
Pages (from-to)1957-1967
Number of pages11
JournalJournal of Geophysical Research: Solid Earth
Volume118
Issue number5
DOIs
StatePublished - 1 May 2013

Keywords

  • fluid pathway
  • focused ion beam technique
  • grain boundary cavity
  • quartz cell reduction
  • quartz grain boundary
  • transmission electron microscopy

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