Rapid kimberlite ascent and the significance of Ar-Ar ages in xenolith phlogopites

Kimberlite eruptions bring exotic rock fragments and minerals, including di amonds, from deep within the mantle up to the surface. Such fragments are r apidly absorbed into the kimberlite magma so their appearance at the surfac e implies rapid transport from depth. High spatial resolution Ar-Ar age dat a on phlogopite grains in xenoliths from Malaita in the Solomon Islands, so uthwest Pacific, and Elovy Island in the Kola Peninsula, Russia, indicate t ransport times of hours to days depending upon the magma temperature. In ad dition, the data show that the phlogopite grains preserve Ar-Ar ages record ed at high temperature in the mantle, 700 degrees C above the conventional closure temperature.