HR: 09:15h
AN: V41F-06    [Abstracts]
TI: Magmatic Genesis Versus Evolution: the Tale of the Miocene - Pliocene Tuscan Magmatic Province
AU: * Poli, G
EM: polig@unipg.it
AF: Department of Earth Sciences, University of Perugia, Piazza Università, Perugia, 06100, Italy
AU: Perugini, D
EM: diegop@unipg.it
AF: Department of Earth Sciences, University of Perugia, Piazza Università, Perugia, 06100, Italy
AB: Miocene-Pliocene Tuscan Magmatic Province (TMP, Central Italy) reveals a complex magmatic setting with a large variety of volcanic and plutonic rock types closely associated in space and time (8-1 Ma). The main rock associations are represented by three group of rocks with different degree of evolution: i) mafic rocks with lamproitic, high-potassium calc-alkaline, and shoshonitic affinity; ii) intermediate rocks showing strong field, petrographic, and geochemical evidence of magma interaction processes; iii) felsic volcanics and intrusives showing petrological and geochemical characteristics of both extreme evolved and pure anatectic melts. Geochemical and thermodynamical characteristics of volcanic and plutonic rocks of TMP suggest a complex petrological evolution in which interaction between mafic and felsic magmas played a major role. The development of interaction processes between mafic and felsic magmas involves several evolutionary stages including the evolution of mafic magmas by Contamination and Fractional Crystallization (CFC) processes, once injected into the felsic reservoirs, followed by widespread mixing processes in magma chambers. Petrologic data indicate that felsic end-members are crustal anatectic melts derived by partial melting at ca 4-6 Kbar of a metasedimentary protolith constituting the Tuscan basement. Residual assemblages of the partial melting process, calculated by geochemical models, are consistent with experimental petrology data, and constraint the levels of emplacement for intrusive complexes, and the paths of extrusion for the effusive ones. Mafic end-members are compositionally akin to basic-intermediate magmas cropping out on the island of Capraia and to lamproites; such a variety of mafic magmas are found associated even in a single volcanic or plutonic complex, testifying for an extremely heterogeneous mantle source. The petrological model proposed in this work fits well with geophysical data. Starting from Middle Pliocene, western Tuscany underwent a strong regional uplift caused by an asthenospheric intrusion that thinned the crustal stack and completely restructured the crust-mantle boundary with possible intercalation of stack of high- level crust even in the lower crust. In response to the increasing heat flow both asthenosphere and heterogeneously metasomatized lithosphere melted to give basaltic magmas that either extruded or intruded and mixed with anatectic melts, the latter generated in the interlayered metasedimentary crustal stacks.
DE: 1065 Major and trace element geochemistry
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3618 Magma chamber processes (1036)
DE: 3619 Magma genesis and partial melting (1037)
DE: 8104 Continental margins: convergent
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting