Formation of wide-blocky calcite veins by extreme growth competition

Spruzeniece, L. , Späth, M., Urai, J. L., Ukar, E., Selzer, M., Nestler, B. and Schwedt, A. (2020) Formation of wide-blocky calcite veins by extreme growth competition. Journal of the Geological Society, 178(2), jgs2020-10. (doi: 10.1144/jgs2020-104)

Abstract

Liassic limestones on the coast of Somerset in the UK contain dense arrays of calcite microveins with a common, but poorly understood microstructure, characterized by laterally wide crystals that form bridges across the vein. We investigated the mechanisms of formation and evolution of these ‘wide-blocky’ vein microstructures using a combination of high-resolution analytical methods, including virtual petrography, optical cathodoluminescence and scanning electron microscopy techniques (e.g. energy-dispersive X-ray spectrometry, back-scattered electron imaging, cathodoluminescence and electron back-scattered diffraction), laboratory experiments and multiphase field modelling. Our results indicate that the studied veins formed in open, fluid-filled fractures, each in a single opening and sealing episode. As shown by the optical and electron back-scattered diffraction images, the vein crystals grew epitaxially on grains of the wall rock and we hypothesize that their growth rates differed depending on whether the crystals were on a wall rock grain substrate that fractured intergranularly (slow growth rates) or transgranularly (rapid growth rates). Our multiphase field models support this hypothesis, showing that wide, blocky crystals only form where there are significant differences in the growth rate and are dependent on the type of seed grain. These results provide strong evidence for extreme growth competition, a process that we propose controls vein-filling in many micritic carbonate reservoirs, as well as demonstrate that the characteristics of the fracture wall can affect the filling processes in syntaxial veins.

• Item Type: Articles
• Additional Information: Funding: Deutsche Forschungsgemeinschaft (NE 822/34-1, UR 64/17-1). U.S. Department of Energy (DE-FG02-03ER15430).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Spruzeniece, Dr Liene
• Authors: Spruzeniece, L., Späth, M., Urai, J. L., Ukar, E., Selzer, M., Nestler, B., and Schwedt, A.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Journal of the Geological Society
• Publisher: Geological Society
• ISSN: 0016-7649
• ISSN (Online): 2041-479X
• Published Online: 15 October 2020