Liquid Immiscibility in the Join NaAlSi3O8-CaCO3 to 2 Liquid Immiscibility in the Join NaAlSi3O8-CaCO3 to 2.5 GPa and the Origin of Calciocarbonatite Magmas W.J. Lee and P.J. Wyllie Presented by RD Bartman

What is a Carbonatite? Alkaline Intrusive/extrusive igneous rocks >20% volume carbonates Dykes, sills, breccia, plugs, veins Continental rift related settings Proterozoic/Phanerozoic Carbonate lava flows – unstable Ol Doinyo Lengai – erupt, lowest T lava

How does it form? Magmatic or Metasomatic origin Fractional crystallization REE

Experiments & Samples

Isobaric phase fields intersected by the join albite-calcite at 2.5GPa

Silicate-Carbonate liquid miscibility gaps projected onto the CO2-saturated, Hamilton projection. The tie line, C‘, connects coexisting silicate-rich liquid and carbonate-rich liquid. Results are seen at A, B and C. The size of the miscibilty gap increases with pressure. Liquid miscibily = calcite liquidus divides into Lc and Ls.

Petrogenesis Petrology allows development by fractional crystallization SiO2 and Carbonate magma Liquid immiscibility of a silica magma Partial melting Metasomatism

Other carbonatite occurences Brazil Italy Telemark, Norway Gardar Province, SW Greenland Ol Doinyo Lengai, Tanzania Barberton Greenstone Belt Loolekop, Phalaborwa Salpeterkop Complex, Sutherland Bulhoek Complex, NW province

2 Questions to be debated - liquidus paths to calciocarbonatite magmas Conclusion 2 Questions to be debated - liquidus paths to calciocarbonatite magmas Do calciocarbonatite magmas, which are extremely CaCO3 enriched, exist? If so, how are they derived from the parent rocks or parent magmas? 2 Theories

References The Paper Wikipedia Turner and Verhoogen; Igneous and Metamorphic Petrology, 2nd Edition; Mcgraw Hill Book Company Inc.; pp 398-401 Carmicheal, Turner, Verhoogen; Igneous and Metamorphic Petrology; Mcgraw Hill Book Company; pp 517-522. Bell, Kjarsgaard, Simonetti; Carbonatites into the 21st Century; Journal of Petrology; pp 1839-1845 J. Gittins, and R. E. Harmer; Dawson's Oldoinyo Lengai calciocarbonatite; a magmatic sovite or an extremely altered natrocarbonatite?; South African Journal of Geology. 1999; pp 109-121