The Kaapvaal craton seismic anisotropy: petrophysical analyses of upper mantle kimberlite nodules

A dense network of seismic stations has been deployed on the Kaapvaal crato n (South Africa) to investigate the upper mantle seismic structures. In ord er to bring independent petrophysical constraints, we analyze a direct samp ling of the cratonic upper mantle and determine the seismic properties of 4 8 mantle nodules brought up to the Earth's surface by kimberlite eruptions. Seismic properties of these nodules are calculated from the olivine and py roxene crystal preferred orientations and the single crystal elastic consta nts. Despite variations in the nodules compositions, microstructures and cr ystallographic preferred orientations, seismic anisotropy is rather homogen eous throughout the craton. Mean S-wave anisotropy is weak (2.64 %), which is compatible with the small measured SKS wave splitting (mean delay time o f 0.62 s).