Anglona, Sassari Province, Sardinia, Italyi

Regional Level Types
Anglona	Historic County
Sassari Province	Province
Sardinia	Autonomous Region
Italy	Country

Anglona is a geographical and historical area in the north of Sardinia and also a volcanic district (Miocene volcanism, ~ 21-18 Ma) that roughly encompasses the same territory.

From a geographical and historical point of view, the Anglona territory is delimited in the broad sense to the north by the sea (Asinara Gulf), to the east by River Coghinas, to the south by Monte Sassu, and to the west by River Silis and Monte Pilosu. It belongs to the municipalities of Bulzi, Castelsardo, Chiaromonti, Erula, Laerru, Martis, Nulvi, Perfugas, Santa Maria Coghinas, Sedini, Tergu, and Valledoria.

From a geological point of view, if compared with the territory defined above, the Anglona volcanic district is less extended towards the east and more extended towards the west and the south. It is delimited by the Gallura Hercynian granites and Palaeozoic metamorphites (lower valley of River Coghinas) to the east and by the sedimentary rocks of the Sardinian Rift (also known as Fossa Sarda rift system) to the south (Logudoro Basin) and to the west (Porto Torres Basin). Therefore, according to this last definition, it also includes practically all municipal territory of Osilo and part of those of Sennori, Ploaghe, and Chilivani.
Some authors (e.g. Ghiara et al., 1999) attributed to the Anglona volcanic district also occurrences located in proximity of the southern margin of the Logudoro sedimentary basin (e.g. the Stazzo Silimbru [Istazzu Silimbru] rhyolite, Migaleddu dacite, and Monte Corvos rhyolite in the municipal territory of Ozieri; the Nuraghe Brundette rhyodacite in the municipal territory of Ittiri).

The main lithologies of the Anglona volcanic district are represented by andesitic lava flows, welded and unwelded ignimbrites (dacitic to rhyolitic in composition). Andesitic lava domes with interbedded small ignimbritic horizons, overlain by volcaniclastic and pillow lavas of andesitic composition, occur at various sites. Secondarily, welded ignimbrites, small andesitic lava flows, and ash/pumice deposits are present. The Miocene origin of this rocks was already recognised by La Marmora (1857 and 1860).
Basaltic andesites are porphyritic to glomeroporhyritic, with plagioclase being the predominant phenocryst. Clinopyroxene (augitic in composition) generally occurs as pheno- to microphenocrysts with rounded rims, sometimes completely altered. Olivine crystals are rare, often altered to hematite or iddingsite. Orthopyroxene (enstatite-ferrosilite) is represented by rare euhedral and quite fractured crystals. Opaque oxides occur as inclusions within mafic minerals or in the groundmass. The groundmass is microcrystalline to intersertal, more rarely hypocrystalline, with microlites of plagioclase, clinopyroxene, and opaque oxides.
Unwelded ignimbrites are made up of glassy shards, pumices, and scoria fragments. The observed mineral assemblages include rounded and zoned plagioclase, euhedral brown phlogopite-annite microcrysts, corroded clinopyroxene, quartz, rare subhedral green-brown amphibole, and orthopyroxene, plus K-feldspar and opaque oxides. Common accessories are apatite and zircon. Occasionally, secondary minerals such as zeolites, glauconite, and chlorite are present.
Welded ignimbrites show textures varying from eutaxitic to spherulitic, more rarely vitrophyric. The observed minerals are euhedral to subhedral plagioclase, subhedral clinopyroxene, rare rounded orthopyroxene, apatite, and opaque oxides. Subordinate K-feldspar and quartz are also observed. The welded ignimbrites are characterised by the presence of volcanic fragments of microcrystalline plagioclase, scorias, and deeply altered subhedral minerals.

Clinoptilolite and mordenite occur as diagenetic products of medium-grained, moderately welded and poorly sorted pyroclastic flows. Most ignimbrites contain zeolites associated with clay minerals; opal-CT and euhedral crystals of quartz occur as newly-formed minerals; clinoptilolite is the most widespread zeolite found, followed by mordenite. Textural features indicate that zeolites, as commonly observed elsewhere, are products of glass alteration (Ghiara et al., 1999).

In the Osilo territory, andesitic horizons are associated with epithermal gold mineralisation.

Furthermore, Anglona is famous for the petrified forests, which crop out at various sites distributed over an area of about 300 km² in the municipal territories of Martis, Perfugas, Laerru, Bulzi, and Santa Maria Coghinas. The most well-known sites are Carrucana (Martis) and Rio Altena (Perfugas).

Fossils

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Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Anglona
Wikidata ID:	Q2572110

Localities in this Region

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References