Temperature derivatives of compressional and shear wave velocities in crustal and mantle rocks at 6 kbar confining pressure

Measurements of compressional and shear wave velocities, VP and VS, were made in a cubic anvil apparatus up to 700° C at 6 kbar in igneous and metamorphic rocks typical of the crust and mantle. Samples range in composition from acidic to ultramafic, with bulk density of 2.67–3.46 g/cm3 at 6 kbar. Mean atomic weights of the rocks vary between 20.37 and 23.03. A rough dependence of wave velocity on bulk density is apparent. However, there is considerable scatter, and the velocities do not generally follow lines of constant mean atomic weight. Both VP and VS increase with increasing amphibole, garnet, pyroxene and olivine content. High quartz content produces relatively low P-wave and high S-wave velocities, giving significantly low Poisson's ratios. In contrast, a high feldspar content is related to relatively high P-wave and low S-wave velocities and consequent high Poisson's ratios. The calculated temperature derivatives of VP and VS for the range 20-500° C at 6 kbar confining pressure, using best-fit solutions, cover the range –1.60 to –4.94 x 10–4 km/s° C and –1.39 to –3.93 x 10–4 km/s° C, respectively. The results compare fairly well with the few data published so far. For the dunite and peridotite rocks the (dVP/dT)p-values are in excellent agreement with published Voigt-Reuss-Hill values calculated from single crystal data. Using the experimental results, P-velocity profiles were calculated along a geotherm of a cold Precambrian shield crust and a warm continental crust. The temperature gradients for the latter cause velocity inversion in numerous rocks, rich in olivine or quartz.           ARK: https://n2t.net/ark:/88439/y069600 Permalink: https://geophysicsjournal.com/article/145 &nbsp