Magmatic evolution of the Borzago Valley calc-alkaline basic satellite body (Southern Adamello batholith - Northern Italy) and role of xenocrystic phases in its geochemistry
Bellieni, Giuliano; Cavazzini, Giancarlo; Fioretti, Anna M.; Visentin, Ester Justin; Zanettin, Bruno; Zantedeschi, Paolo
European Journal of Mineralogy Volume 7 Number 4 (1995), p. 967 - 988
published: Aug 1, 1995
manuscript accepted: Feb 27, 1995
manuscript received: Dec 23, 1994
ArtNo. ESP147050704022, Price: 29.00 €
Abstract The Borzago Valley magmatic rocks constitute a satellite intrusive body inside the metamorphic aureole close to the north-eastern edge of the Re di Castello Superunit (Adamello batholith). The outcropping body mainly consists of gabbro-diorite and diorite with minor hornblende-gabbro, and sporadic granodiorite and granite. Field relationships between mafic and acidic rock-types are extremely complex. Geological, petrographic, geochemical and Sr isotope data suggest a separate origin for basic and acidic magmas. The former display evolution consistent with a two-stage crystallization process (at high and low pressures, respectively) in a mafic parental magma. The thermal anomaly due to crystallizing and rising mafic magma probably induced melting at a deep crustal level, producing acidic magma which was emplaced subcontemporaneously with basic magma. The geochemistry and serial characters shown by basic rocks reflect the presence of xenocrystic phases (An-rich plagioclase and Al -rich amphibole) partially retained during the high-pressure crystallization stage. Subsequent re-equilibration processes hinder precise evaluation of the xenocrystic fraction and quantitative petrogenetic modelling.