DISSOLUTION OF TONALITIC ENCLAVES IN ASCENDING HYDROUS GRANITIC MAGMAS: AN EXPERIMENTAL STUDY

Abstract

Dissolution of natural mafic magmatic enclaves in a hydrous leucogranitic synthetic melt has been tested experimentally. Results suggest that the mechanism of enclave dissolution is a potential hybridization process in granitic systems. Experiments performed in decompression, simulating ascending magmas, show interesting results: from 10 kbar to 4 kbar, for a given temperature, enhanced dissolution of the tonalitic enclave into the melt has been observed, compared with experiments at constant pressure. Furthermore, the composition of the melt changed to higher CaO, FeO and MgO contents. Dissolution textures on relict crystals from the tonalitic enclave were monitored. These results have implications for the generation of peraluminous monzogranites and granodiorites and an example for the Cabeza de Araya (Cáceres, Spain) from the "serie mixta" of the Iberian Massif is given. The tonalitic enclaves that are partially dissolved may be early or coeval intrusions into the granite magma or even into the source migmatitic area. Many mineralogical, geochemical and isotopic features of monzogranites (e.g.: reverse zoning in plagioclase, low Sr isotopic ratios) are accounted for by this mechanism of enclave dissolution during ascent and emplacement. © 2006 Elsevier B.V. All rights reserved.