Anisotropy in the mechanical strength of the lithosphere and its tectonic implications

The mechanical strength of the lithosphere is a fundamental geophysical parameter that modulates geological processes ranging from plate tectonics to landscape evolution. Anisotropy in lithospheric strength has implications for the long-term evolution of the continental lithosphere and how it may inherit a directional strength signature from previous tectonic events, thus impacting on future rifting and orogenic events. In this paper, we present a new, robust analysis of anisotropy in continental effective elastic thickness (T_e), a proxy for the long-term strength of the lithosphere. Based on a moving window technique analysing Bouguer coherence, our technique restricts analysis to regions where firstly, the anisotropy detected in the coherence is statistically significant and has a well-defined orientation and secondly, the effect on T_e is not within error. Under these strict criteria, many continental regions show no convincing mechanical anisotropy; amongst those that do, we examine their correlation with a range of other proxies, including anisotropy indicated by stress measurements and seismic data. We also examine the correlation with anisotropy in the gravity anomaly or topography data and with specific tectonic provinces and boundaries.