Geology Reference
In-Depth Information
14.1.2 Structure and Tectonic History Associated with
Potassic Volcanism in Italy
Ninkovitch and Hess (1972) considered that intermediate depth earthquakes in the
Mediterranean are distributed beneath the two arcs at the Tyrrhenian and southern
margin of the Aegean sea. The active volcanoes in both the areas are located above
these intermediate depth earthquakes. They thought that shallow focus earthquakes
are associated with axis of orogenic belt passing through Sicily and the Apennine
peninsula.
According to Ellam et al. (1989), the Benioff zone is continuous to a depth of
500 km dipping at an angle of 70
°
to around 250 km depth, and then
flattening to
around 45
. The regions of active volcanoes in Italy are Tyrrhenian Sea, Sicily and
the Eolian islands and the Neopolitan regions. Ellam et al. (1989) considered that
the subduction zone in the southern part of Italy, and is probably in the late stage of
its evolution and the arc is located on a thin continental basement of about 16 km
thickness. There is no oceanic crust remaining in the fore-arc i.e. in the southern
part of the archipelago. Anderson and Jackson (1987) suggested that the process of
subduction has ceased. Ellam et al. (1989) considered that the subduction beneath
the Roman Province is highly speculative. They thought that the deep seismicity
beneath the Aeolian and Naples area was associated with different portions of a
bifurcating slab.
Alverez (1972) thought that the subduction beneath the Roman Province is not
directly related to Benioff zone associated with the Aeolian arc, but an earlier
episode of subduction. He presented palaeomagnetic evidence that the Corsica
°
-
Sardinia microplate was rotated anticlockwise between 11.5 and 6 Ma ago by
tectonic activities. According to him the rotation was accompanied by Eastward
subduction in the Tyrrhenian Sea, located close to the modern west coast of main
land Italy. He thus believed that both Roman and Aeolian magmatism may be
related to subduction processes and the timing of subduction was probably different
in the two areas. According to Elam et al. (1989) the magmatic activities of the
Roman Province and Aeolian region might have been coeval. The age of eruption
range from 0.9 to 0.15 Ma (Ferrara et al. 1986) and the age of K-rich volcanic rocks
of the Roman province is 1 Ma. The oldest volcanic rock in the Aeolian arc lavas
are 0.5 Ma old, The dredged samples from the seamounts related to Aeolian vol-
canism to the west of the exposed arc is 1.3
+
0.2 Ma old (Beccaluva et al. 1982).
The Aeolian arc and Roman Province magmatism was essentially contemporaneous
but mostly post date the activity of the Tuscan province (0.7
0.43 Ma) and Mt. Etna
-
has been active during the past 0.1 Ma.
Generation of potassic volcanism in the Roman province evoked a question
whether it could be linked to present day subduction beneath the Calabrian Arc or
whether it was related to a continental rift system very similar to those in East Africa
(Cundari 1980); resolution of the problem is ambiguous (Beccaluva et al. 1991).
While most of the Italian volcanoes erupting K-rich silica-undersaturated rocks
(except for Somma
Vesuvius and Ischia
—
Phlegraean Fields), lie on the lithospheric
segments not associated with the present day active Calabrian
-
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