Geoinformatic approach to global nepheline syenite and carbonatite distribution: Testing a Wilson cycle model

The association of alkaline igneous rocks and carbonatites (ARCs) with intracontinental rifts has long been recognized. Deformed alkaline rocks (such as nepheline syenites) and carbonatites (DARCs), which form a small subset (<10%) of ARCs and carbonatites, have become a focus of attention since it was recognized that in some places they are associated with suture zones marking locations where oceans have closed. The association of DARCs with sutures can be readily understood in terms of the operation of the Wilson cycle in the opening and the closing of ocean basins. The Wilson cycle hypothesis for the origin of DARCs has been tested for the Proterozoic of both Africa and India. For Africa, an additional hypothesis that we have also tested is that ARCs in intracontinental rifts represent magmas made by partial melting of DARC material in the underlying mantle lithosphere. A limitation of the African and Indian studies is that they are local and regional. Only a worldwide geoinformatic study can fully test the two hypotheses. If one of the hypothesis can be invalidated that will have profound petrogenetic signifi cance. In this study, we describe our ongoing geoinformatic work on the worldwide distribution of ARCs and DARCs, including the databases, techniques, and operating procedures. To illustrate our approach, we report on a local analysis that we have carried out on the ARCs and DARCs of the Kola Peninsula in Arctic Russia.