Seismic Modeling of Lower and Mid-Crustal Structure as Exemplified by the Massiccio dei Laghi (Ivrea-Verbano Zone and Serie dei Laghi) Crustal Section, Northwestern Italy

Abstract

An aim of seismic reflection profiling of the present-day deep continental crust is to infer the geologic structure and hence to infer the tectonic processes that led to the formation of that structure. An important test of the validity of such interpretations lies in comparison with exposed geologic sections that once lay at deep crustal levels. The Massiccio dei Laghi (Lakes Massif) of Northern Italy provides such a section, on a scale comparable with that of contemporary deep seismic profiles, yet illustrates heterogeneity on a wide range of scales. On account of its importance as providing a substantial composite cross section through continental crustal rocks, coupled with its relative accessibility in the inner arc of the Western Alps, the region has been subjected to an extraordinary degree of structural, petrological, geochemical and petrophysical study by geoscientists during the past few decades. The rocks of the region record Paleozoic accretion, metamorphic and magmatic processes, the effects of the Hercynian orogeny,post-orogenic magmatic underplating and associated lithospheric stretching and thinning, Mesozoic extension and effects associated with the position of the region in Alpine tectonism (see review by Handy et al., 1999). The assembly of the rock units probably dates from Permo-Triassic time onwards.Their relative positions in outcrop are likely close to how they that might be taken as a model for a magmatically underplated and extended crustal section. Such a section can be compared with interpretations drawn from present-day seismic reflection profiles taken from regions of extended lithosphere that have not had the misfortune(good fortune?) to be upended and exposed during a subsequent phase of collisional orogeny.