|
 The
Aeolian archipelago, with its seven islands, is the tip of the
iceberg of a large volcanic complex, mainly submarine, which
stretches for about 200 kilometres and which is a curved
structure trending revolt, with its concave towards the middle
of the Tyrrhenian Sea.
The
emerged parties of the eruptive complex (the islands), were
formed in the last million years, while the submerged parties
reached age slightly more: the oldest age - about 1.3 million
years - is that of the undersea volcano Sisyphus, north-west of
Alicudi. From the date of the earliest products of each island
you can deduct the age of birth. In the Tyrrhenian Sea the
southern African plate slips under the European one, giving rise
to the volcanic arc of the Aeolian islands forming an inclined
seismic zone, which reaches under the Tyrrhenian the depth of
about 450 kilometres. In Lipari, Vulcano and Stromboli the
volcanism is still active
 while
in the other islands the activity ceased between 5,000 and
20,000 years ago.
Lipari last eruption occurred in 729 AD, in Vulcano in
1889-90 while Stromboli activity lasts uninterrupted for at
least 2,000 years. The magmas of Aeolian Islands are similar to
those of volcanoes that make up the circumpacific "belt of
fire". They show, over time, an evolution towards ever more
basic compositions (lower content of silica, which is the main
constituent of magmas) and more rich in
potassium (andesites and basalt andesitic, with daciti and
rhyolities,
 until the shoshoniti of Vulcano and Stromboli). Magmas of
this kind
are typical of subduction zones: where a lithospheric
oceanic plate slides under a continental, giving origin to
magmas that are forming strings of islands (ex. Japan,
Indonesia) or volcanic cordilleras, as the chain of the Andes,
and giving rise to the generation of
earthquakes that usually settle along a tilted plane
(Benioff plan). |
