Nomarski study of zoned plagioclases from granitoids of the Seville Range batholith, SW Spain. Petrogenetic implications
Castro, Antonio; De La Rosa, Jesús D.
European Journal of Mineralogy Volume 6 Number 5 (1994), p. 647 - 656
published: Sep 28, 1994
manuscript accepted: May 24, 1994
manuscript received: Dec 6, 1993
ArtNo. ESP147050605001, Price: 29.00 €
Abstract The application of Nomarski imagery to the study of etched plagioclases from intermediate plutonic rocks, reveals many features not observable through conventional polarizing microscopy. The most salient features are resorption surfaces indicative of dramatic changes in conditions during magma consolidation. The distribution of these resorption surfaces across the crystals is related to changes in the anorthite content of the melt in an open system induced by magma mixing. These features are typical of hybrid granitoids, such as the granodiorites and tonalites of the Seville Range batholith, Spain. In these rocks, previous geochemical and isotopic studies indicate mixing between a felsic end-member and a fractionated mantle-derived magma at a shallow depth in the crust. The cyclicity of resorption processes, repeated several times during plagioclase growth, is consistent with some kind of self-organized process related to convection induced by mafic-magma input in the composite magma chamber. Alternatively, cyclicity may be related to repeated pulses of mafic magma