Ultradeep Kimberlite/Carbonatite Petrogenesis: Melting of Model Carbonated Lherzolite in the System CaO-MgO-Al2O3-SiO2-CO2 at 7-14 GPa

University Of Texas At Dallas, Richardson TX

Investigators

Abstract

EAR-0106645 Presnall Kimberlite is the magma type that is the carrier of most diamonds from the deep interior (mantle) of the Earth. These magmas generally erupt at the Earth's surface, form a pipe-like throat near the surface where the diamonds are found, and are commonly associated with another magma type called carbonatite. Kimberlites are generally understood to represent the greatest depth of origin of any magma type and therefore tell us something about the Earth's interior at depths not generally sampled. Traditionally, the depth of origin has been thought to be about 220 km., but the recent discovery of exotic mineral inclusions in a very few diamonds indicates an origin much deeper in some cases, possibly even to the core-mantle boundary. Experimental data on the chemistry of melting processes at depths in excess of about 200 km are very sparse. This project is designed to examine melting relations for compositions that model the Earth's deep interior at depths up to about 430 km. The apparatus used for this study is called a multianvil press and is capable of duplicating temperatures and pressures thought to be relevant to possible melting process at these great depths. The purpose is to determine the temperature of melting as pressure increases and the compositions of the melts generated. These data will provide quantitative data that will help resolve the issue of whether melting at these depths is reasonable or if the diamonds are transported slowly from extreme depths by solid-state convective processes in the mantle, to be sampled by kimberlites generated at more traditionally accepted depths of about 220 km.