Continuing the Carbonatite Controversy Preface

Extract

Carbonatites have always been controversial (Mitchell, 2005). Their magmatic origin was disputed in the early days of the last century, regardless of the fact that experiments clearly demonstrated the crystallization of magmatic calcite (Wyllie and Tuttle, 1960). The observation of the eruption of natrocarbonatite lava in Oldoinyo Lengai (Dawson 1962) finally convinced petrologists that they were dealing with the products of magmatic carbonate liquids. Since that time, further controversies have emerged, especially regarding the ultimate origin of carbonatite magmas, for which there are two ‘endmember’ hypotheses. The generally accepted hypothesis is based on isotopic evidence and suggests that carbonatites are from deep asthenospheric sources, such as mantle plumes (Bell, 2001; Bell et al., 2004). This fails to explain why carbonatites are essentially confined to the continental lithosphere and are extremely rare in the ocean basins (Woolley and Kjarsgaard, 2008; Woolley and Bailey, this issue), and leads to the alternative hypothesis of lithosphere-generated carbonatitic magmatism. It may be that this is simply because we have not yet understood how to identify carbonatites in oceanic regions (Bailey and Kearns, this volume), or there may be some more profound reason why carbonatites cannot form within or erupt through oceanic lithosphere.