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Giglio Island, Isola del Giglio, Grosseto Province, Tuscany, Italyi

Regional Level Types
Giglio Island	Island
Isola del Giglio	Commune
Grosseto Province	Province
Tuscany	Region
Italy	Country

The Island of Giglio (23.8 km²), one of the seven islands that constitute the Tuscan Archipelago, is separated by a 16-kilometre stretch of sea from the nearest point of the mainland, the promontory of Monte Argentario. Mainly mountainous, it culminates in the Poggio della Pagana (496 m a.s.l.). The island belongs to a municipality of the province of Grosseto, whose official name is Isola del Giglio, composed of the islands of Giglio and Giannutri.

The larger part of Giglio Island consists of Pliocene monzogranite intrusions. Metamorphic and sedimentary rocks of Jurassic to Triassic age form the small Franco Promontory on the western side (Lazzarotto et al., 1964).

The island is a unique site to study the link between the syn- and the post-orogenic processes that affected the internal portions of the northern Apennine orogenic wedge in the Tyrrhenian region. Ferrocarpholite-bearing rocks representing the exhumed deep root of the orogenic wedge are in fact in tectonic contact with Pliocene intrusives, which in turn are products of thermal relaxation processes that accompanied the late extensional attenuation of the previously thickened orogenic crust (Rossetti et al., 1999).

The Giglio Monzogranite Intrusion (GMI) comprises two different monzogranitic intrusions of an overall S-type peraluminous and sub-alkaline composition, with an average Rb/Sr radiometric cooling age of 5.0 Ma (Westerman et al., 1993). The main intrusive body is characterised by an outer zone that is strongly foliated and locally layered (Pietrabona Facies) and an inner zone that is porphyritic and homogeneously textured (Arenella Facies). All the GMI rocks consist of the same primary mineral assemblage, namely dominant K-feldspar, albitic plagioclase, quartz, and biotite with minor muscovite, tourmaline, apatite, and zircon. The presence of strongly pinitised cordierite is ubiquitous; garnet, andalusite, monazite, rutile, and titanite occur sporadically (Faggioni et al., 1998).
A small leucocratic pluton, the Scole monzogranite intrusion, also intruded the GMI along the mid-point of the eastern shore of the island (Westerman et al., 1993). It crops out at Le Scole, a group of rocks located less than 100 meters from shore (Le Scole have gained notoriety in recent times because one of these rocks caused the shipwreck of the Costa Concordia cruise liner).

At the Franco Promontory, similar to the nearby Monte Argentario [see: http://www.mindat.org/loc-12330.html], the stacking of three different tectonostratigraphic units has been observed. The rock assemblage mainly consisting of ferrocarpholite-bearing metasediments (predominately quartz-rich phyllites and schists belonging to the Tuscan Verrucano sequence) crops out extensively along the western part of the promontory and constitutes the lowermost unit of the whole nappe complex. The other two units are made of metaophiolitic rocks and Calcare Cavernoso (grey limestones, dolostones, and breccias).

Note: the island derives its name from the goats, in fact, it was called "Aigylion (Αιγύλιον) mikros" by the Ancient Greeks (while Capraia Island was "Aigylion megas"). The Greek name was later transformed into Aegilium or Igilium by the Romans and Gilio during the Middle Ages.

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Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Isola_del_Giglio
Wikidata ID:	Q204152
GeoNames ID:	6542742

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