Timescales of faulting through calcite geochronology: a review

Calcite is a common mineral precipitated within upper crustal fault zones and associated fractures, forming veins, mineral cements and fault coatings. It has the potential to be dated using several radioisotopic systems if parent/daughter isotope abundances are suitable for the currently available analytical techniques. U-Pb dating can be most readily achieved using the in-situ laser ablation technique, which has led to a rapid growth area in the U-Pb dating of calcite. The ability to constrain the timing of fault slip hinges critically on the ability to confidently link calcite precipitation to fault movement and/or spatially and temporally associated fracture opening which requires careful microstructural and petrographic documentation. We discuss the varying reliability of different fracture fill types to make these links, and demonstrate that crack-seal-slip fills associated with faults are the most suitable for unambiguously linking calcite growth to phases of fault slip. Previous applications of the U-Pb and U-Th methods to natural examples at a range of temporal and spatial scales are reviewed, in particular their implications for the timescales of faulting and for the rates of fracture-filling. We then highlight the main limitations of the method, and provide a brief commentary on future directions.