Reconstruction of magma chamber processes preserved in olivine-phlogopite micro-ijolites from the Oldoinyo Lengai, Tanzania
نویسندگان
چکیده
A detailed petrographic and mineralogical investigation of olivine-phlogopite micro-ijolite xenoliths from Oldoinyo Lengai, Tanzania indicates a complex evolutional history. These consist diverse textural subdomains characterized by minerals ranging early-formed olivine, through diopside-hosted perovskite phlogopite, to evolved aegirine-augite titanite. Thermometry mineral compositions in the suggest crystallization temperatures 1070–970 °C 850–700 at plutonic pressures SiO2-activities controlled perovskite-titanite equilibria. Double coronas are characteristic feature micro-ijolite, consisting olivine cores surrounded an inner clinopyroxene corona outer phlogopite corona. double might have formed during early magma chamber processes, including movement subsequent resulting dissolution with accumulation diopside phlogopite. Diopside−aegirine-augite compositional zonation several injections followed cooling periods, formation groundmass. Mg# (80–83) Ca (0.1–0.3 wt%) contents together presence primary melt inclusions clinopyroxene, nepheline indicate magmatic origin possible parental olivine-nephelinite melt. There is evidence for subsolidus, or near-solidus, re-equilibration processes as indicated reaction titanite forming symplectitic textures ilmenite minor zirconolite. Ti-exchange between phenocrysts other Ti-bearing (perovskite, titanite, magnetite) resulted ∼750 equilibrium which much lower than mafic (>900 °C) conditions. Calculated subsolidus micro-ijolites over 10–20 km depth interval.
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ژورنال
عنوان ژورنال: Journal of African Earth Sciences
سال: 2023
ISSN: ['1464-343X', '1879-1956']
DOI: https://doi.org/10.1016/j.jafrearsci.2022.104738