Can dolomitic marble be weaker than calcitic marble at lower greenschist-facies conditions? Microstructural analyses of coexisting greenschist-facies calcitic and dolomitic mylonites

Author(s)
Mark J. Coleman, Anna Rogowitz, Bernhard Grasemann, Riccardo Graziani, David A. Schneider
Abstract

The bedrock of Mt Hymittos, Greece, exposes two parallel Miocene low-angle extensional faults. Strain along the upper detachment is localized in calcitic marble and schist; deformation associated with the lower detachment is accommodated in a >100 m thick package of dolomitic mylonite exhibiting consistent top-to-SW kinematic indicators and pronounced L–S fabrics. Field and geochronometric evidence indicates that both detachments deformed under middle to lower greenschist-facies conditions, where dolomite is predicted to be stronger than calcite. Evidence of preferential strain localization in dolomitic marble under these conditions conflicts with generally expected predictions of mineral and rock strength; microstructural analysis and electron backscatter diffraction were applied to investigate this anomaly. Microstructures in both dolomitic and calcitic marbles record dislocation creep of dolomite and calcite leading to subgrain rotation recrystallization and grain-size reduction of coarse domains (>50 (Formula presented.) m). Grain-size reduction initiated a switch in the dominant deformation mechanism from dislocation creep to diffusion creep in fine-grained dolomite domains. Zener pinning and limited recovery controlled dolomite grain sizes. The crystallographic preferred orientation in calcitic marble indicates that deformation by dislocation creep accommodated grain boundary sliding. Our work suggests that polydeformed dolomitic marble can be weaker than calcitic marble at relatively low temperatures.

Organisation(s)
Department of Geology
External organisation(s)
University of Ottawa, Leopold-Franzens-Universität Innsbruck, University of British Columbia (UBC)
Journal
Journal of the Geological Society
Volume
182
ISSN
0016-7649
DOI
https://doi.org/10.1144/jgs2024-205
Publication date
05-2025
Peer reviewed
Yes
Austrian Fields of Science 2012
105124 Tectonics
ASJC Scopus subject areas
Geology
Portal url
https://ucrisportal.univie.ac.at/en/publications/5ef18efb-d10f-41e1-8723-cbeb8e859482