Nanograins form carbonate fault mirrors

Shalev Siman-Tov, Einat Aharonov, Amir Sagy, Simon Emmanuel

Research output: Contribution to journalArticlepeer-review


Many faults are characterized by naturally polished, reflective, glossy surfaces, termed fault mirrors (FMs), that form during slip. Recent experiments also find that FMs form during rapid sliding between rock surfaces, and that FM formation coincides with pronounced friction reduction. The structure of FMs and the mechanism of their formation are thus important for understanding the mechanics of frictional sliding, particularly during earthquakes. Here we characterize the small-scale structure of natural carbonate FMs from three different faults along a tectonically active region of the Dead Sea transform. Atomic force microscopy measurements indicate that the FMs have extremely smooth surface topography, accounting for their mirror-like appearance. Electron microscope characterization revealed a thin (<1 μm) layer of tightly packed nanoscale grains coating a rougher layer comprising micron-size calcite crystals. The crystals contain closely spaced, plastically formed twins that define new subgrain boundaries. The narrow subgrains are observed to break into submicron pieces near the sheared surface. This observation suggests a new brittle-ductile mechanism for nanograin formation. The role of ductility during frictional sliding, both in forming the nanograin layer, and in the deformation process of the powder, may be critical for understanding shear on geological faults.

Original languageAmerican English
Pages (from-to)703-706
Number of pages4
Issue number6
StatePublished - Jun 2013

All Science Journal Classification (ASJC) codes

  • Geology


Dive into the research topics of 'Nanograins form carbonate fault mirrors'. Together they form a unique fingerprint.

Cite this