The Tsavorite (Gem Quality Vanadium Grossularite) Minerogenetic System in East Africa
When Supercontinent Rodinia began to break up at ~800 Ma, wide rifts formed evolving into a passive margin of the Mozambique Ocean. At one stage, organic-rich pelites with gypsum (the later host rock of tsavorites) were interbedded with siliciclastics, carbonates, and bimodal volcanic rocks. Ocean closure, subduction, collision and welding of various microcontinents and volcanic arcs formed the Mozambique Belt and at ~550 Ma, ended with the assembly of Supercontinent Gondwana. In East Africa, deformation and metamorphism climaxed at 615–600 Ma Fritz et al. (J. Afr. Earth Sci. 86:65–106, 2013 ). At peak metamorphic conditions, anatexis of siliciclastic metasediments produced abundant metamorphic mobilizates such as pegmatites and quartz veins. In the black schist hosting tsavorites, however, partial melting only produced small fractions of a supercritical hydrous liquid. Most of this liquid remained within the host but migrated over short distances into structural traps of different origin; turbid green grossular crystallized from the melt and transparent tsavorite from exsolved fluids.
KeywordsEast Africa Mozambique belt Metasediments Anhydrite Graphite Supercritical hydrous melt Lateral secretion
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