The Tuscany Province

The Tuscany Magmatic Province (Fig. 2.1) comprises several mafic to silicic intrusive and extrusive centres scattered through southern Tuscany and the Tuscan archipelago. The silicic rocks of the Tolfa-Manziana-Cerite area, north-west of Rome, and a mafic ultrapotassic dyke from Sisco (Corsica) are also traditionally included into the Tuscany Province (Poli et al. 2003). 

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Table 2.1. Petrological characteristics and ages (in Ma) of magmatism in the Tuscany Province.

The igneous rocks of the Tuscany Province consist of an association of mafic to silicic rocks (Fig. 2.2a) exhibiting contrasting compositions and genesis. Silicic rocks (here defined as those with SiCL > 65 wt %) consist of a large number of intrusive and extrusive bodies having a peraluminous character (Alumina Saturation Index, ASI >1), and moderate variations of major and trace elements at a given silica level. 

Fig. 2.2. A) TAS classification diagram of Tuscany magmatic rocks. Note that TAS nomenclature applies to volcanic rocks only. The dashed line divides the subalkaline and alkaline fields (Irvine and Baragar 1971). B) AQ vs. K20/Na20 diagram for mafic rocks (MgO > 3 wt%) of the Tuscany Province. For definition of AQ see Chap. 1.

Fig. 2.3. Variation diagrams of MgO vs. selected major and trace elements and 87Sr/86Sr for magmatic rocks of the Tuscany Province. Symbols as in Fig. 2.2.

Hf-isotope ratios also fall close or within the field of crustal rocks (Fig. 2.4 Table 2.2). This has been interpreted as evidence that metasomatic modification of lamproitic mantle sources in Tuscany was provided by addition of crustal material (e.g. metapelites). Interestingly, the mantle-normalised incompatible element patterns of Tuscany lamproites are similar to those of gneisses and schists in almost eveiy detail. This has been interpreted as evidence for addition of bulk upper crustal material to the mantle, with little element fractionation during metasomatism and the subsequent partial melting (Peccerillo 2002). This makes the Tuscany Province a zone where the upper mantle magmas look very much like the upper crust in terms of trace element and radiogenic isotope compositions. 

The Sabatini Volcanic District developed between about 0.8-0.6 Ma and 40 ka over a wide area located just to the north of Rome. Volcanism was predominantly explosive and generated widespread pyroclastic deposits with only minor lava flows, which were emitted from a large number of centres including several calderas (e.g. De Rita et al. 1983, 1993). The vol-canism occurred along a zone of crosscutting NW-SE and NE-SW faults (Di Filippo 1993). The Sabatini rocks rest over the same type of sedimentary bedrocks as at Vico, as well over the acid volcanics of Tolfa-Manziana-Cerite complex of the Tuscany Province. 

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