The Mount Gharib A-type granite, Nubian Shield: petrogenesis and role of metasomatism at the source

摘要: The Mount Gharib peralkaline A-type complex (476±2 Ma), located in the Nubian Shield of Egypt, contains sodic-calcic to sodic amphiboles, accessory astrophyllite, zircon, fluorite, apatite, allanite, aenigmatite, elpidite(?) and ilmenite. This “within plate” hypersolvus suite is enriched large-ion lithophile (LIL) high field-strength (HFS) elements, characterized by a fractionated REE pattern (Ce/Yb=49) significant negative Eu anomaly. A fine-grained acicular-amphibole-bearing roof facies shows further enrichment LIL HFS elements. was emplaced Pan-African granodiorite-adamellite host, which it locally metasomatized. affected rocks contain hydrothermal albite, end-member arfvedsonite, levels elements intermediate between those granite facies. Trace element isotopic modeling this granite, with its initial 87Sr/86Sr value (0.7110), documents an active role lithosphere magma generation. Lithospheric extension, expressed regional dyke-swarms, caused cooling, fracturing relaxation thin, newly formed crust. Localized partial melting took place open system, possibly as result influx alkali-rich fluid derived from sublithospheric source. Metasomatic reactions similar observed metasomatized wallrocks are considered have played important just prior onset anatexis generation melt.