The Ivrea-Verbano Zone (IVZ, Southern Alps), in northern Italy, is part of the pre-Alpine basement characterized by the exposure of a well-preserved lower crustal section. The middle-lower crustal rocks of the IVZ have commonly been subdivided in three major units, from bottom to top: i) different ultramafic mantle bodies; ii) the Mafic Complex (MC), which represents an intrusive complex (gabbros, norites and diorites); iii) the Kinzigite Formation (KF), consisting of amphibolite- to granulite-facies metapelites with subordinate metabasites, marbles and calc-silicate gneisses. U-Pb zircon data on the MC indicate an emplacement at 295-280 Ma in the central sector of the IVZ (Peressini et al., 2007, and references therein) and at about 232 Ma in the north-eastern sector (External Gabbro, Finero Complex; Zanetti et al., 2013). The Permian intrusion was coeval with granite intrusions in the middle-upper crust and rhyolitic volcanism, while the Triassic intrusion was concurrent with the activity of (low-/high-temperature) shear zones. In order to shed light on the observed diachronism of the MC and to provide useful insights on the tectonic evolution, new P-T-t data from the KF exposed in the Val Cannobina (Cursolo-Orasso area) were carried out. Here, the KF shows the narrowest thickness and is partially affected by mylonitic deformation. It mainly consists of micaschists and migmatitic paragneisses, dominant at the higher structural levels (SE), and amphibolites, prevailing at the contact with the MC (lower structural levels; NW; Boriani & Burlini, 1995). Septa, both mafic and metapelitic in composition, occur within the MC and show granulite-facies metamorphism. Metapelites are mainly composed of Pl, Qtz, Bt, Grt and Sil. With increasing the metamorphic grade (towards NW), the abundance of Bt decreases, that of Grt increases andfibrolitic Sil is progressively replaced by prismatic Sil. Preliminary P-T estimates on metapelites indicate P of about 0.4 GPa and T ranging from 620 to 700°C. The septa show T higher than 800°C. Preliminary U-Pb dates on monazite fromthe migmatitic paragneisses zone indicate that an HT metamorphic event occurred at about 277 Ma, coherently with other areas of the IVZ. A single age at 225±7 Ma obtained from a narrow rim suggests a later perturbation of the U-Pb system. Boriani A. & Burlini L. 1995. Carta Geologica della Valle Cannobina. Scala 1:25000. Centro di Studio per la Geodinamica Alpina e Quaternaria del CNR-Milano. Grafica Diodoro, Milano. Peressini G., Quick J.E., Sinigoi S., Hofmann A.W. & Fanning M. 2007. Duration of a large mafic intrusion and heat transfer in the lower crust: a SHRIMP U/Pb zircon study in the Ivrea-Verbano Zone. J. Petrol. 48, 1185-1218. Zanetti A., Mazzucchelli M., Sinigoi S., Giovanardi T., Peressini G. & Fanning M. 2013. SHRIMP U-Pb zircon Triassic intrusion age of the Finero Mafic Complex (Ivrea-Verbano Zone, Western Alps) and its geodynamic implications. J. Petrol., 54, 2235-2265.

Is the Ivrea-Verbano Zone subdivided in two sectors? New insights from the Kinzigite Formation exposed in the Val Cannobina (northern Italy) / A., Langone; M., Tiepolo; A., Zanetti; Mazzucchelli, Maurizio; C., Bergamaschi. - In: RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA. - ISSN 2035-8008. - ELETTRONICO. - 31, Suppl. 1:(2014), pp. 473-473. (Intervento presentato al convegno The Future of the Italian Geosciences - The Italian Geosciences of the Future tenutosi a Milano nel 10-12/09/2014).

Is the Ivrea-Verbano Zone subdivided in two sectors? New insights from the Kinzigite Formation exposed in the Val Cannobina (northern Italy)

MAZZUCCHELLI, Maurizio;
2014

Abstract

The Ivrea-Verbano Zone (IVZ, Southern Alps), in northern Italy, is part of the pre-Alpine basement characterized by the exposure of a well-preserved lower crustal section. The middle-lower crustal rocks of the IVZ have commonly been subdivided in three major units, from bottom to top: i) different ultramafic mantle bodies; ii) the Mafic Complex (MC), which represents an intrusive complex (gabbros, norites and diorites); iii) the Kinzigite Formation (KF), consisting of amphibolite- to granulite-facies metapelites with subordinate metabasites, marbles and calc-silicate gneisses. U-Pb zircon data on the MC indicate an emplacement at 295-280 Ma in the central sector of the IVZ (Peressini et al., 2007, and references therein) and at about 232 Ma in the north-eastern sector (External Gabbro, Finero Complex; Zanetti et al., 2013). The Permian intrusion was coeval with granite intrusions in the middle-upper crust and rhyolitic volcanism, while the Triassic intrusion was concurrent with the activity of (low-/high-temperature) shear zones. In order to shed light on the observed diachronism of the MC and to provide useful insights on the tectonic evolution, new P-T-t data from the KF exposed in the Val Cannobina (Cursolo-Orasso area) were carried out. Here, the KF shows the narrowest thickness and is partially affected by mylonitic deformation. It mainly consists of micaschists and migmatitic paragneisses, dominant at the higher structural levels (SE), and amphibolites, prevailing at the contact with the MC (lower structural levels; NW; Boriani & Burlini, 1995). Septa, both mafic and metapelitic in composition, occur within the MC and show granulite-facies metamorphism. Metapelites are mainly composed of Pl, Qtz, Bt, Grt and Sil. With increasing the metamorphic grade (towards NW), the abundance of Bt decreases, that of Grt increases andfibrolitic Sil is progressively replaced by prismatic Sil. Preliminary P-T estimates on metapelites indicate P of about 0.4 GPa and T ranging from 620 to 700°C. The septa show T higher than 800°C. Preliminary U-Pb dates on monazite fromthe migmatitic paragneisses zone indicate that an HT metamorphic event occurred at about 277 Ma, coherently with other areas of the IVZ. A single age at 225±7 Ma obtained from a narrow rim suggests a later perturbation of the U-Pb system. Boriani A. & Burlini L. 1995. Carta Geologica della Valle Cannobina. Scala 1:25000. Centro di Studio per la Geodinamica Alpina e Quaternaria del CNR-Milano. Grafica Diodoro, Milano. Peressini G., Quick J.E., Sinigoi S., Hofmann A.W. & Fanning M. 2007. Duration of a large mafic intrusion and heat transfer in the lower crust: a SHRIMP U/Pb zircon study in the Ivrea-Verbano Zone. J. Petrol. 48, 1185-1218. Zanetti A., Mazzucchelli M., Sinigoi S., Giovanardi T., Peressini G. & Fanning M. 2013. SHRIMP U-Pb zircon Triassic intrusion age of the Finero Mafic Complex (Ivrea-Verbano Zone, Western Alps) and its geodynamic implications. J. Petrol., 54, 2235-2265.
2014
31, Suppl. 1
473
473
A., Langone; M., Tiepolo; A., Zanetti; Mazzucchelli, Maurizio; C., Bergamaschi
Is the Ivrea-Verbano Zone subdivided in two sectors? New insights from the Kinzigite Formation exposed in the Val Cannobina (northern Italy) / A., Langone; M., Tiepolo; A., Zanetti; Mazzucchelli, Maurizio; C., Bergamaschi. - In: RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA. - ISSN 2035-8008. - ELETTRONICO. - 31, Suppl. 1:(2014), pp. 473-473. (Intervento presentato al convegno The Future of the Italian Geosciences - The Italian Geosciences of the Future tenutosi a Milano nel 10-12/09/2014).
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