Magnesium metasomatism in dolomite from Lucerne Valley, California

Abstract

A small, isolated, rock-knob forms a prominence above the detritus-strewn desert surface of Lucerne Valley, California. It exposes a series of metamorphic rocks intruded by biotite-tonalite and by minor garnet-aplite dikes. The dominant formation in the metamorphic series is a brucite-marble. Thermal metamorphism seems inadequate to account for the relatively high ratio of MgO to CaO found in some facies of this rock. Formation of brucite by hydrothermal processes appears likely. Additional evidence favouring a hypogene source of magnesia is provided by veins of magnesite, possibly pseudomorphous after nematolite, which cut the brucite-marble.

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