Abstract Type: Topical Sessions

Description:

Calcite-rich rocks such as limestone, chalk, and marble offer a natural laboratory for investigating the coupled chemical and mechanical processes that control deformation in sedimentary basins and fault zones. Calcite’s high chemical reactivity and capacity for crystal plasticity across a wide range of temperature, pressure, and stress conditions make it a model mineral for examining interactions among brittle, ductile, and fluid-assisted deformation mechanisms. This study integrates controlled laboratory deformation experiments with detailed microstructural analyses of naturally deformed fault-related samples to better constrain these coupled processes.

We employ Electron Backscatter Diffraction (EBSD) and Laue X-ray microdiffraction to characterize grain-scale deformation, residual strain, crystallographic misorientation, and lattice rotation. Complementary deformation experiments using nitratine, a structural analog to calcite, allow simulation of higher-temperature and lower strain-rate conditions that are difficult to achieve experimentally in calcite. Experimental results are directly compared with naturally deformed calcite samples collected from a range of tectonic settings.

Preliminary results indicate a strong influence of fluid chemistry on deformation mechanisms and strain accommodation. Manganese-doped experiments show enhanced dislocation creep behavior relative to control samples, as demonstrated by (1) elevated proportions of low-angle neighbors in disorientation angle distribution histograms, (2) qualitative microstructural observations, and (3) the development of a well-defined Crystallographic Vorticity Axis (CVA) fabric. In addition, manganese-doped samples exhibit a marked decrease in twin density relative to undoped samples, which instead show a significant increase in deformation twinning.

New analyses using geometrically necessary dislocation (GND) density mapping further clarify the mechanical behavior of these materials. GND maps enable visualization and quantification of force chain networks, expressed as connected regions of elevated dislocation density that highlight preferential pathways for stress transmission and the onset of strain localization.

By bridging experimental and natural observations through advanced microstructural techniques, this work provides new constraints on fault mechanics and deformation processes in carbonate systems. These results have broader implications for understanding subsurface deformation, seismic hazard development, and the mechanical evolution of sedimentary basins.

Categories: Structural Geology

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