GOLDSCHMIDT CONFERENCE TOULOUSE 1998 The genesis of natrocarbonatites: Constraints from experimental petrology and trace element partition coefficients

Despite the widespread studies on natrocarbonatites from Oldoinyo Lengai, their petrogenesis remains controversial. The two most common hypotheses which are used to explain their origin are: (1) closed system crystal fractionation of a primary mantle-derived sodic, dolomitic carbonatite magma (Sweeney et al., 1995); or (2) products of liquid immiscibility at crustal pressures from a wollastonite nephelinite magma (Kjarsgaard et al., 1995). An important observation relevant o the natrocarbona-tite petrogenesis problem is recognition that both silicate-free and silicate-bearing atrocarbonatites are present at Oldoinyo Lengai (Petibon et al., 1998). Here we present he trace element data obtained on experimental charges using mixtures of natura