Occurrence of a large variety of rock types, intrusive and effusive, closely associated in space and time reveal a complex magmatic setting for the Tuscan Magmatic Province. Extensive petrological and geochemical investigations carried out over the later years indicate that main rock associations are represented by three groups of rocks at different degrees of evolution: i) mafic ultrapotassic rocks with lamproitic affinity, and high-potassium calc-alkaline and shoshonitic rocks; ii) intermediate-acid rocks bearing strong petrographic and geochemical evidence of magma interaction processes; iii) acid volcanics and intrusives showing petrological and geochemical characteristics of both extremely evolved and pure anatectic melts. Literature and new data suggest that a process of interaction between basic and acid end-members is responsible for the evolution of the Tuscan Magmatic Province magmatism. Major and trace elements and isotopic systematic help to recognize the basic end-members as compositionally akin to three basic-intermediate magmas belonging to Capraia shoshonites, Capraia high potassium calc-alkaline rocks rich in Sr, and lamproites from Tuscan area that acted together even in a single intrusive or effusive complex. The acid end-members in the interaction process are crustal anatectic melts derived by partial melting at ca 4-6 kbar of gneiss and garnet micaschists of the Tuscany basement having a sedimentary protolith. Residual assemblages of the partial melting process calculated by geochemical models agree with experimental petrological data, and help to reconstruct levels of melting and emplacement for intrusive complexes, and level of crystallization of phenocrysts for the effusive ones. The petrological model reported in this work fits well with geophysical data indicating a superposition of upper crust of both the European and Adriatic plates in westernmost Tuscany.
Genesis and evolution of Miocene-Quaternary intermediate-acid rocks from the Tuscan Magmatic Province
POLI, Giampiero
2004
Abstract
Occurrence of a large variety of rock types, intrusive and effusive, closely associated in space and time reveal a complex magmatic setting for the Tuscan Magmatic Province. Extensive petrological and geochemical investigations carried out over the later years indicate that main rock associations are represented by three groups of rocks at different degrees of evolution: i) mafic ultrapotassic rocks with lamproitic affinity, and high-potassium calc-alkaline and shoshonitic rocks; ii) intermediate-acid rocks bearing strong petrographic and geochemical evidence of magma interaction processes; iii) acid volcanics and intrusives showing petrological and geochemical characteristics of both extremely evolved and pure anatectic melts. Literature and new data suggest that a process of interaction between basic and acid end-members is responsible for the evolution of the Tuscan Magmatic Province magmatism. Major and trace elements and isotopic systematic help to recognize the basic end-members as compositionally akin to three basic-intermediate magmas belonging to Capraia shoshonites, Capraia high potassium calc-alkaline rocks rich in Sr, and lamproites from Tuscan area that acted together even in a single intrusive or effusive complex. The acid end-members in the interaction process are crustal anatectic melts derived by partial melting at ca 4-6 kbar of gneiss and garnet micaschists of the Tuscany basement having a sedimentary protolith. Residual assemblages of the partial melting process calculated by geochemical models agree with experimental petrological data, and help to reconstruct levels of melting and emplacement for intrusive complexes, and level of crystallization of phenocrysts for the effusive ones. The petrological model reported in this work fits well with geophysical data indicating a superposition of upper crust of both the European and Adriatic plates in westernmost Tuscany.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
