Plio-Quatemary Volcanism

Plio-Quatemary volcanism in Sardinia consists of a wide variety of rock types, ranging from mafic to silicic and from subalkaline to alkaline (Fig. 9.3), which cover an area of about 2200 km2. Mafic rocks are the most abundant and range from compositions that are oversaturated to strongly undersaturated in silica (Fig. 9.4). 

The Sardinian Plio-Quatemary rocks define at least three main evolutionary series that are clearly defined on several major and trace element diagrams (Figs. 9.3, 9.5, 9.6)  

The alkaline mafic volcanics are less enriched in silica and more enriched in incompatible trace elements than oversaturated tholeiitic rocks with similar MgO contents. REE show smooth and fractionated patterns (Fig. 9.7). Mantle normalised incompatible element patterns of mafic rocks generally display a small upward convexity with moderate enrichments in Ta and Nb. The large majority of the mafic volcanic rocks exhibit positive spikes of Ba and Pb, which are small or absent in the southern outcrops of Capo Ferrato, Guspini and Rio Girone (Fig. 9.7). Silicic volcanics exhibit a large range of incompatible element concentrations. Sr- and Nd-isotopic 

Radiogenic isotopic variations for Sardinia Plio-Quaternary volcanics are accompanied by systematic modifications of trace element ratios (Lustrino et al. 2004a). For instance, Ba/Nb is higher in the northern than in the southern outcrops, whereas Ce/Pb is lower (Fig. 9.9). In general terms, the rocks from the southern occurrences have incompatible element ratios close to typical anorogenic magmas such as those of the Sicily Province, 

Genesis of Mafic Melts and Composition of Mantle Sources 

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Table 1.1. Petrological characteristics and ages of Plio-Quatemary volcanic provinces in Italy. ...

Fig. 1.2. Total alkali vs. silica (TAS) classification diagram of Le Maitre (1989) for representative Italian Plio-Quatemary volcanic rocks. The thick dashed line is the divide between the subalkaline and the alkaline fields of Irvine and Baragar (1971).

Fig. 1.3. AQ vs. K20/Na20 classification diagram for mafic Plio-Quatemary volcanic rocks (MgO > 4 wt %) from Italy. For explanation see text.

Fig. 1.6. Variation diagrams of incompatible trace element ratios and 87Sr/86Sr for mafic (MgO > 4 wt %) Plio-Quatemary volcanic rocks from Italy.

The strong regionality for major, trace element and isotopic compositions of Italian Plio-Quatemary volcanism allows subdivision into several com-positionally different magmatic provinces. For the purpose of this review, a magmatic province is defined as a relatively restricted zone within... 

Fig. 8.7. TAS diagram for Iblei Plio-Quatemary volcanic rocks. The dashed line is the boundary between subalkaline and alkaline fields (Irvine and Baragar 1971).

Fig. 8.9. REE (A) and incompatible element patterns (B restricted to mafic rocks) of Iblei Plio-Quatemary volcanic rocks.

Fig. 9.1. Distribution of Plio-Quatemary volcanism in the southern Tyrrhenian Sea and Sardinia. The Oligo-Miocene arc-type magmatism of Sardinia is also reported.

Fig. 9.2. Schematic distribution of Oligo-Miocene and Plio-Quatemary volcanism in Sardinia.

Fig. 9.3. TAS classification diagram for the Sardinia Plio-Quatemary volcanic rocks.

Fig. 9.4. Normative compositions of mafic Plio-Quatemary volcanic rocks (MgO > 4%) from Sardinia. Symbols as in Fig. 9.3.

Fig. 9.7. REE patterns and mantle-normalised incompatible element patterns (restricted to mafic rocks for most centres) for Plio-Quatemary volcanic rocks from Sardinia.

Fig. 9.9. Ba/Nb vs. Ce/Pb variation diagram for Sardinian Plio-Quatemary volcanic rocks (MgO >4 wt %). The composition of the Sardinian Oligo-Miocene orogenic volcanism and of the anorogenic rocks from Sicily are shown for comparison. Symbols as in Fig. 9.3.

Etruschi Seamount Quaternary hawaiite (Etruschi) similar to Sardinia Plio-Quatemary volcanics. 

The Sardinia Province contains a wide variety of rocks, ranging from subalkaline to Na alkaline and nephelinitic, and from mafic to felsic. Most rocks have relatively unradiogenic Sr and Pb isotopic signatures, resembling EMI mantle compositions. A few outcrops from southern Sardinia have isotopic and trace element signatures very close to the rocks of the Sicily Province. Plio-Quatemary volcanism in Sardinia overlies Oligo-cene-Miocene arc-type tholeiitic to calc-alkaline volcanism. 

Lustrino M, Melluso L, Morra V, Secchi F (1996) Petrology of Plio-Quatemary volcanic rocks from central Sardinia. Per Mineral 65 275-287 Lustrino M, Melluso L, Morra V (2000) The role of lower continental crust and lithospheric mantle in the genesis of Plio-Pleistocene volcanic rocks from Sardinia (Italy). Earth Planet Sci Lett 180 259-270 Lustrino M, Melluso L, Morra V (2002) The transition from alkaline to tholeiitic magmas a case study from the Orosei-Dorgali Pliocene volcanic district (NE Sardinia, Italy). Lithos 63 83-113... 

Peccerillo A, Turco E (2004) Petrological and geochemical variations of Plio-Quatemary volcanism in the Tyrrhenian Sea area regional distribution of magma types, petrogenesis and geodynamic implications. Per Mineral 73 231-251... 

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