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bearing, and were erupted at Monte Vulture volcano between 0.6 and 0.1 Ma.
Carbonatites have been described in the last phase of activity.
Minor amounts of K-rich rocks are also found in the Aeolian Arc, in the southern
Tyrrhenian Sea. These rocks are intimately associated with calc-alkaline rocks at
Vulcano,Vulcanello, and Stromboli.
According to them enrichment in K
2
O and related incompatible trace elements is
accompanied by strong to mildly fractionation of high
field strength elements with
respect to large ion lithophile elements. This can be attributed to the input of a
crustal component into the mantle source of the magma prior to partial melting.
Variations in trace element enrichment and isotope characteristics of the three
magmatic provinces are thought to be the result of different metasomatic events and
complex processes of partial melting of the mantle sources. Peculiar geochemical
and isotopic characteristics of the Lucanian and Neapolitan regions are the result of
different channelling of in-plate materials through lateral in
ow from the foreland
during the roll-back of the Ionian subduction. Metasomatism affected lithospheric
mantle sources characterized by variable degrees of depletion.
They suggest that peculiar petrologic, geochemical and isotopic features of the
ma
c magmas are however consistent with a post-orogenic subduction-related
geodynamic setting for the production of their parental magmas.
4.8.4.1 South Tuscany
The intrusion of igneous bodies of Orciatico (10
°
44
′
22
″
E, 43
°
26
′
10
″
N; Fig.
4.21
a)
and Montecatini Val di Cecina (10
N; Fig.
4.21
b) are exposed a
few km northwest of Volterra town (Conticelli et al. 1992; Poli et al. 1984). These
two bodies are located on the western edge of vol d
°
46
′
08
″
E, 43
°
23
′
30
″
Era graben. According to
Conticelli et al. the emplacement of these two igneous bodies was controlled by the
north
'
southeast-trending fault formed during post-tectonic
extensional regime. The emplacement age of these two took place 4.1 Ma ago.
The Orciatico igneous body intruded into Pliocene-sediment in the form of a sill
and laccolith fed by a narrow northwest
northwest
south
-
-
-
southeast-trending dyke (Fig.
4.21
a). The
outer part of the body has chilled margins. Mineralogically the rocks are charac-
terized by the presence of abundant olivine and clinopyroxene with phlogopite, K-
feldspar and oxides of microlites (An olivine-bearing minette). The inner part of the
body has a holocrystalline texture with abundant olivine phenocrysts, phlogopite
plates, minor amount of clinopyroxenes and rare K-richterites. Oxides and K-
feldspar are the most abundant phases in the groundmass.
The igneous body at Montecatini Val di Cecina was intruded in the form of a
shallow level plug. It is not only bordered but dissected by recent normal faults.
According to Conticelli et al. the Orciatico complex crystallized from mantle-
derived magmas, and the most primitive rock types of this complex might not have
gone through any differentiated process. These petrologists think that volcanics at
Montecatini Val di Cecina were derived from the Orciatio magma by a process
involving assimilation and fractional crystallization.
-
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