Geochemistry of garnets from a tonalite and granitic aplite-pegmatite veins from Ciborro-Aldeia da Serra, Ossa-Morena Zone, Southern Portugal

Lima, S. S. M.; Neiva, A.M.R.; Ramos, João Farinha

http://hdl.handle.net/10400.9/754

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Authors

Lima, S. S. M.

Neiva, A.M.R.

Ramos, João Farinha

Abstract(s)

Electron-microprobe analysis of garnet from a tonalite and aplite-pegmatite and pegmatite veins cutting different lithologies from an area located in the Ossa-Morena Zone, southern Portugal, show distinct compositions, mainly andradite with a subordinate grossular component in tonalite, and predominantly spessartine with a subordinate almandine component [and rarely, of mainly almandine with a subordinate spessartine component] in the veins. In general, single crystals of garnet are unzoned in tonalite, but commonly show a Mn-enriched core in veins, as the ratio Mn/(Mn + Fe) in the melt is controlled by garnet. However, reverse zoning also occurs owing to resorption of garnet at lower temperatures. A fractionation trend involving a decrease of Mn/(Mn + Fe) occurs in garnet from a complex aplite-pegmatite vein with 22 alternating layers cutting schists; values decrease toward the hanging wall because garnet is the sole host of Mn, which is depleted in the granitic magma.

Keywords

Geoquímica Garnet Tonalite Aplitos Pegmatito granítico Ciborro-Aldeia da Serra (Concelho de Montemor-o-Novo, Portugal) Zona de Ossa-Morena (Portugal)

URI

http://hdl.handle.net/10400.9/754

Citation

Lima, S. S. M.; Neiva, Ana Margarida R.; Ramos, João Farinha - Geochemistry of garnets from a tonalite and granitic aplite-pegmatite veins from Ciborro-Aldeia da Serra, Ossa-Morena Zone, Southern Portugal. In: Estudos Geológicos, v. 19 (2), 2009, p. 193-197