International Geologiical Congress - Oslo 2008


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MPI-06 Layered intrusions and the evolution of magma chambers: A tribute to J. Richard Wilson


New results from the mafic complex in the Finero area


Ferdinand Hingerl, University of Cologne (Germany)
Urs Kloetzli, University of Vienna (Austria)
Claudia Steuber , University of Cologne (Germany)
Reiner Kleinschrodt, University of Cologne (Germany)


The magmatic suite surrounding the Finero peridotite complex (Ivrea Zone, N-Italy) was re-examined in regard to its petrography and structure. The dominance of Triassic U-Pb zircon ages (240 - 210 Ma) found in this northern part of the Ivrea Zone (Stähle et al. 1990, Opizzi and Schaltegger 1999, Peressini et al. 2004, Klötzli et al., 2007) suggests a significantly different magmatic and metamorphic evolution compared to the central part of the Ivrea Zone in the Val Sesia - Val Sesserra transsects. There, mapping (Quick et al. 2003) and geochronological studies argue for a major Permian intrusive event at 288+/-4Ma after the onset of magmatic underplating in the deeper parts at about 310Ma (Peressini et al. 2007).
In the Finero area most of the contacts between the major units (Finero peridotite - internal gabbro - hornblende peridotite - external gabbro) are tectonic, only few could be identified as primary magmatic. A sapphirine-bearing contact zone of the internal gabbro/ hornblende peridotite interface documenting such a primary contact could be mapped in a much larger extend than previously known. A detailed profile though the external gabbro along the Cannobino Valley with a thickness of ca 900m reveals more than 10 metapelite septa, suggesting that magmatic activity consisted of numerous pulses of melts. Partial melts can be found in the contact zones, but in general only minor crustal assimilation can be derived from the chemistry of the basic intrusions (Lu et al. (1997). Contact melting of the metapelitic septa decreases towards the top of the complex in accordance with deacreasing temperatures documented in garnet-bearing parageneses from about 800°C in the lower part to 650°C at the upper boundary of the external gabbro approaching the granulite facies/amphibolite facies transition in its upper part. The magmatic/metapelitic rock association is strongly deformed. Under high-T deformation polygonal grain fabrics and a distinct metamorphic foliation, mostly parallel to compositional layering formed, which is successively overprinted by amphibolite to greenschist facies deformation increments documenting the ongoing crustal thinning leading to the strongly telescoped lower crustal succession. U-Pb ages from zircons separated from different dikes crosscutting these fabrics will be presented.
Klötzli et al. 2007, Mitt. Österr. Min. Ges., 153, 65
Lu et al. 1997, Chem. Geol. 140, 223-235
Opizzi and Schaltegger 1999, SMPM 79, 330-331
Peressini et al. 2004, Geophys. Res. Abstr. 6, 05072
Peressini et al. 2007, Jour. Petrol. 48, 1185-1218
Quick et al. 2003,US-Geol. Surv. I-Map 2776
Stähle et al. 1990, EPSL, 1001, 196-205


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