EVOLUTION OF LAMPROITES SUGGESTED BY MELT INCLUSIONS IN MINERALS

Diverse lamproites have been investigated by thermobarogeochemical met hods. Study of inclusion glasses in minerals has shown that there is a common compositional trend in olivine and leucite lamproites from dif ferent occurrences (W.Kimberley, Leucite Hills, etc.): initial melt ev olution during crystallization had an agpaitic trend and was towards g radual depletion in Al2O3, CaO, MgO, P2O5 and enrichment in SiO2, FeO , BaO, TiO2, ZrO2, alkalies. This resulted in the formation of K-rich Al-undersaturated or Al-free silicates and K-Ba-titanates during the l ate stages of rock crystallization. According to cryometric and Raman studies, volatile components such as F (or HF), CO2, N-2, and H2O play ed a significant role in the evolution of primary lamproitic magmas. I n some cases, aqueous-saline fluid (or melt) may separated from silica te liquid during the latest stages of lamproite magma evolution. Only lamproitic rocks from SE Spain (verite, fortunite) contain inclusion g lasses different in composition to those in lamproites from other loca lities. They are not agpaitic and have shoshonitic affinity. In genera l, the evolution of lamproitic magma during crystallization differs gr eatly from that of other potassic liquids (in particular, shoshonite a nd K-basaltoid) in its peralkaline trend. Melt evolution during crysta llization in these other rock types has a strong miaskitic trend and i s directed toward a gradual increase in SiO2, Al2O3, alkalis and deple tion in FeO, MgO, CaO, TiO2 and P2O5.