The Ophiolitic Peridotites
In the frame of the palaeogeographic reconstruction of the Jurassic Ligure-Piemontese basin (Fig. 3), the various Alpine-Apennine ophiolitic peridotite bodies have been ascribed to different palaeogeographic settings of the basin, marginal and distal, with respect to the paired Jurassic Europe and Adria continental margins. The marginal peridotite massifs from the Eastern Central Alps (Malenco, Upper Platta, Totalp) and the Northern Apennines (External Ligurides) pertain to structural units originally located at pericontinental settings of the basin along the Adria margin. The distal peridotite massifs of the Eastern Central Alps (Lower Platta) and Western Alps (Chenaillet) and of the Northern Apennines (Internal Ligurides) pertain to structural units originally located at more internal settings of the basin (e.g. Marroni et al., 1998; Schaltegger et al., 2002; and references therein). The Lanzo peridotite massif (Western Alps) is composed of a marginal sector (the North Lanzo body), likely located close to the Adria margin, and a distal sector (the South Lanzo body), likely located at a more internal sector of the basin (Bodinier et al., 1991; Piccardo, 2010b). The Erro-Tobbio massif (Ligurian Alps) is composed by marginal-type peridotites (north-east sector) and distal-type peridotites (south-western sector) (Piccardo and Vissers, 2007; Piccardo and Guarnieri, 2010a). The Monte Maggiore massif (Northern Corsica) is composed by distal peridotites from an internal setting of the basin (Rampone et al., 2008; Piccardo and Guarnieri, 2010b).
Figure 3. Schematic palaeogeographic reconstruction of the Ligure-Piemontese basin during Late Jurassic
Schematic palaeogeographic reconstruction of the Ligure-Piemontese basin during Late Jurassic, with location of the main ophiolite sequences at marginal OCT settings [North Lanzo (LA), External Ligurides (EL), part of Erro-Tobbio(ET)] and at distal intra-oceanic settings [South Lanzo (LA), part of Erro-Tobbio (ET), Internal Ligurides (IL), Mt. Maggiore (MM)]. The position of the future subduction zone is also schematically reported (redrawn and modified after Piccardo et al., 2009). Two major transects across the Adria margin, i.e. Lanzo and the Ligurides, are characterized by exhumed sub-continental peridotites at the marginal settings (i.e., North Lanzo and External Ligurides) and melt-modified peridotites at the more distal settings (i.e., South Lanzo and Internal Ligurides) (see text for explanation).
Accordingly, in the following we refer to the ophiolitic peridotite massifs of Malenco, Upper Platta, Totalp (in the Eastern Central Alps), North Lanzo (in the Western Alps), Erro-Tobbio (north-eastern part) (in the Ligurian Alps) and External Ligurides (in the Northern Apennines) as marginal peridotites, derived from the ocean-continent transition (OCT) zones of the Ligure-Piemontese basin, and we refer to the ophiolitic peridotite massifs of Lower Platta (in the Eastern Central Alps), South Lanzo (in the Western Alps), Erro-Tobbio (south-western part) (in the Ligurian Alps), Internal Ligurides and Tuscany (in the Northern Apennines) and Mt. Maggiore (in Northern Corsica) as distal peridotites, deriving from more internal oceanic settings of the basin.