Preliminary Evidence on the Nature and Composition of Carbonatite Magma

Abstract

CARBONATITES are igneous rocks¹ but the exact nature of carbonatite magma has not been established. Silicate magmas, both extrusive and intrusive, are molten and normally carry a low-pressure gas phase. Carbonatite magmas appear also to be molten when extrusive² but there is evidence, in the form of brecciation and fenitization, that a gaseous phase plays a dominant role in carbonatite intrusions (see also ref. 3). We now report that a fluid medium capable of transporting carbonatitic material can exist, not as a molten liquid but as a gaseous and mobile supercritical fluid from which carbonatites can crystallize directly. Such a system is a strong contrast with the usual notion of an igneous magma.