Distribution of admixture elements in sulfides and norites of the Elan intrusive body (Voronezh Crystalline Massif) and genesis of boninite-like magmas

Using ICP mass spectrometry, we have first determined the contents of trace and rare-earth elements in sulfide ores and the host norites of the Ni-bea ring Elan Massif, which occurs in the Early Proterozoic structures of the V oronezh Crystalline Massif. For the system sulfide-basalt the calculated Ne rnst partition coefficients for lanthanides correlate well with the experim ental ones, but for Ni and Cu they differ by almost an order of magnitude f rom earlier established K-D. Sulfide ores considered in this paper differ s ignificantly in contents of major and, particularly, admixture elements. In concentrations of Fe, Ni, Cu, Zn, and Sn the Elan sulfides are similar to those from inclusions in diamonds of eclogite paragenesis. The obtained geochemical data suggest that most sulfides of the norites of the Elan intrusive body crystallized from a sulfide melt immiscible with a silicate melt. A sulfide liquid was segregated into an individual phase bot h at the superliquidus (drop-like impregnations and bunch segregations) and at the subsolidus (matrix ores) stages of crystallization of the norite in trusion. Another source of sulfide liquid was a deep-seated magma chamber. At all stages of intrusion solidification, the sulfide melt was in equilibr ium with a silicate melt of baste composition. We propose a new model for t he genesis of boninite-like intrusions, which implies partial melting of th e basite crust layer under the effect of mantle diapir.