Publication Date:
2020-10-15
Description:
Liassic limestones at the Somerset coast (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. This paper investigates the formation mechanisms and evolution of these wide-blocky vein microstructures by a combination of high-resolution analytical methods (ViP microscopy, optical CL and SEM techniques (EDS, BSE, CL and EBSD)), laboratory experiments and phase-field modelling.Results indicate that the studied veins formed in open, fluid-filled fractures, each in a single opening and sealing episode. As shown by optical and EBSD images, vein crystals grow epitaxially on wall-rock grains and we hypothesize that their growth rates differ depending on whether crystals are substrated on wall-rock grains that are fractured intergranularly (slow) or transgranularly (fast). Phase-field models support this hypothesis, showing that wide-blocky crystals only form in cases with significant growth rate differences that are dependent on the type of seed grain.This provides strong evidence for “extreme growth competition”, a process, which we propose controls vein filling in many micritic carbonate reservoirs, as well as demonstrating that the characteristics of the fracture wall can affect filling processes in syntaxial veins.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5172371
Print ISSN:
0016-7649
Topics:
Geosciences
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