ROCKS from 700 kilometres beneath the Earth’s surface have been found by
Australian geochemists. The deepest-ever rocks come from volcanic pipes on
Malaita Island in the Solomon Islands. Magma rising from the Earth’s lower
mantle broke off chunks of mantle rock and carried them to the surface. These
xenoliths contain mineral crystals such as diamonds that are formed at high
pressure.
Ken Collerson of the University of Queensland in Brisbane told the American
Geophysical Union in San Francisco last month that some crystals were only
formed at pressures of more than 22 gigapascals, corresponding to a depth of up
to…
