Electrical Properties of amphiboles from the Kola super deep borehole, Russia, at mantle pressure and temperature conditions

Abstract

We present here for the first time, the temperature and pressure dependence of the electrical resistivity of ferro-actinolite amphibole from the World's deepest borehole, the Kola super-deep borehole (KSDB) up to the depth of 12.84 km. High-pressure and high-temperature measurements were carried out by using an opposed anvil system up to 700 K and 4 GPa. Ten samples from different depths (from the surface to the deepest 12,890 m) were investigated for their compositional, structural and electrical behaviour. Ferro-actinolite sample exhibits a thermally induced phase transformation to cummingtonite-clinopyroxene—quartz assemblages at 780 K and 0.5 GPa. The transformation temperature is found to be decreasing with the increase of pressure and reaches a value of 680 K at 6.0 GPa. The conductivity activation energy, (determined from the temperature dependence of conductivity) of the ferroactinolite is found to be decreasing from 0.8 eV at 0.5 GPa to 0.30 eV at 6 GPa. The present study indicates that the amphiboles at deeper crustal level is more conducting and bears significance in understanding the physical properties of rocks at the deep continental crust.