Rapid kimberlite ascent and the significance of Ar-Ar ages in xenolith phlogopites
Kimberlite eruptions bring exotic rock fragments and minerals, including diamonds, from deep within the mantle up to the surface. Such fragments are rapidly absorbed into the kimberlite magma so their appearance at the surface implies rapid transport from depth. High spatial resolution Ar-Ar age data on phlogopite grains in xenoliths from Malaita in the Solomon Islands, southwest Pacific, and Elovy Island in the Kola Peninsula, Russia, indicate transport times of hours to days depending upon the magma temperature. In addition, the data show that the phlogopite grains preserve Ar-Ar ages recorded at high temperature in the mantle, 700 degrees C above the conventional closure temperature.
Kelley
SP
Department of Earth Sciences, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
Wartho
JA