Thegeology ofItaly includes mountain ranges such as theAlps and theApennines formed from the uplift of igneous and primarily marine sedimentary rocks all formed since thePaleozoic.[1] Some active volcanoes are located inInsular Italy.
The oldest rocks in Italy may include oceanic crust subducted during theCaledonian orogeny and 440 million year oldOrdovician granites. Only detritalzircons in the Alps dates to thePrecambrian.[2]
These granites are located offshore ofVenice, found in the Agip Assunta well and deformed, transforming intoorthogneiss during theHercynian orogeny. Overall, ItalianPaleozoic rocks commonly show evidence of the Hercynian orogeny in the Alps,Sardinia, theApuan Alps of Tuscany, and thePeloritani mountains of Sicily and Calabria.
The Hercynian orogeny produced a large thrust belt, thickened the crust and led to polyphaser metamorphism yielding rocks such asgneiss,phyllite andamphibolite.Metamorphic facies range from high-pressurekyanite to low-pressureandalusite.[3]
The Western Alps atMont Blanc andMonte Rosa, theSouthern Alps at Braveno,Brixen,Cima d'Asta, Doss del Sabion and theBarbagia andGallura granites in Sardinia are all examples ofCarboniferous andPermian granitepluton andbatholith intrusions.Ignimbrite eruptions had an important role at the same time in forming parts of the central Southern Alps. Sedimentary rocks from before the Permian have remained intact and unmetamorphosed (or only having experienced low-grade metamorphism) in the Paleocarniancharn of the eastern Southern Alps. Themetamorphic grade increases to the west, reachingamphibolite grade in the Orobic Alps andgranulite grade in theIvrea-Verbano Zone. Most of the basement rocks in theDolomites arephyllite or gneiss atgreenschist grade. Within the Dioritic-Kinzigitic unit,biotite andsillimanite-rich gneiss outcrop in Calabria.
At the same time in the Permian and Carboniferous, the opening of the west branch of theTethys Ocean reoriented sections of Italy atop theAdriatic Plate and created the Ligure-Piemontese ocean basin, leading to widespread deposition of carbonates, evaporites andred beds.[4] Units such as the Valgardena Sandstone emplaced during a westward marine transgression in areas later uplifted as the Alps. These sandstones were succeeded bysabkha, the lagoonal Bellerophon Formation, volcanic rocks, theWerfen Formation and Servino Formation.[5]
Even in the 19th century, geologists recognizedLadinian andCarnian agecarbonate platforms in theDolomites that likely formed ascoralatolls. Throughout the earlyTriassic, theZorzino Limestone, Rhaetian Choncodon Dolomite,Riva di Solto Shale and Zu Limestone filled the Lombard Basin. Up to two kilometers of carbonates assembled in the late Triassic as theDolomia Principale. Meanwhile, the Lagonegro Basin accumulated limestone, chert and marl into theJurassic. Complex tectonics producedhorst and graben features and some lowlands deposited evaporites, such as the Burano Anhydrite—now a significant unit in theApennine Mountains.
Jurassic tectonic conditions differed somewhat from the Triassic, resulting in new basin formation and a carbonate depositional environment akin to the current day Florida-Bahamas platform. Southern Alps basins such as the Lombard Basin and the Belluno Basin gathered marl and limestone, whileturbidite and nodular limestone was more common in the Vajont Limestone, Fonzaso Formation and Selcifero Lombardo. In addition to wide shelf environments like the Bahamas, seamounts like the Trento Swell or the Sicilian Iblean and Saccense zones, some basins such as the Piemontese Basin, the Lagonegro Basin and the Ligurian-western Tuscan Ligure Basin were situated aboveophiolite and ended up with abundantradiolarite fossils in limestone.
During theCretaceous, global high sea levels and local tectonic conditions produced a greater share of basins than platform environments (although the Campano-Lucana,Friuli,Apulia and Latium-Abruzzi platforms persisted). Morepelagic, open water sediments like marl joinedbreccia and underwater debris flows. Triassic conditions persisted in only one location in Sardinia where up to one kilometer of carbonates finished depositing in the Cretaceous, atop deformed Cambrian-Carboniferousmetamorphic basement rock.
Changing interaction between theEuropean Plate and the Adriatic Plate resulted in tectonic compression along the Adriatic Plate's northern margin, kicking off the formation of the Alps and the Apennines. In the late Cretaceous, foredeeps filled withflysch andmolasse sediments shed off the rising mountains. Examples include the Bergamo Flysch within the Lombard Basin of the Southern Alps.[6]
The Mesozoic was largely quiescent in terms ofmagmatism, but some igneous activity did take place. Pietra Verde sandstones from theLadinian in the Southern Alps containcalc-alkaline rock while granite,shoshonite andmonzonite intruded the Dolomites region into theCarnian. In fact, subsurface rocks in thePo Valley, the Lagonegro Basin, westTrentino, the Venetian foothills, Sicily, Lombary and the northern Apennines show signs ofvolcaniclastic sediments andpillow lava from the time period.
Although the oceanic crust of the Tethys Ocean has been recycled into the mantle, sections of it remain as ophiolite withperidotite,gabbro,prasinite,serpentinite and pillow lava of Jurassic to Cretaceous age inLiguria,Tuscany,Val d'Aosta andPiemonte.[7] Petrological research indicates thatophiolites in the Alps are metamorphosed, while those in the Apennines are not. The Ragusa Basin in the Iblean Plateau of Sicily had magmatism in the Jurassic, together with the Trapanese Basin, followed by Cretaceous activity in theSyracuse area.[8]
During thePaleocene, the Eurasia-Africa convergent margin driving the Alpine orogeny accompanied the closure of Alpine Tethys ocean basin. As a result, magmatism emplaced in the Periadriatic region lasting into theOligocene:Basalt dyke intrusions (Dolomites) and volcaniclastic rocks (Lessini Mountains), alongside variousbatholiths (acid rocks liketrachyte,tonalite,syenite,...) can be found. The Alpine tectonics affected the magmatic bodies during the uplift: the Insubric Lineament dividing the Southern Alps, for example, sheared the Bregaglia batholith.
Sedimentary processes were affected from the orogeny in form of turbiditic deposits accumulating in nearby basins. In the North-east, Eocene age flysch shed off theDinaric Alps can be found in the present-day foothills of Friuli region, while shallow water deposition (shale and carbonates) persisted in areas further away from the thrust belt. Paleontological evidences include the fish fossils ofBolca quarry ( close toVerona).
In theEocene, the Apennine orogeny started evolving independently from the Alps as a result of a new west-dipping subduction and continental collision between Corsica-Sardinia block and Adria microplate.Following the eastward migrating subduction zone, sediments of the Adriatic margin and Ionian Basin accreted onto the Apennine area as a tectonic nappe stacking from the west. As the Adria microplate migrated to the northeast with an anti-clockwise rotation, Apennine foredeeps migrated to the east with continued flysch deposition in younging basins from west to east (Macigno, Cervarola, Marnoso-Arenacea...).In the Northern Apennines, the Liguride units (oceanic sediments and ophiolites) were deformed and later (Oligo-Miocene) thrusted upon Tuscan and Umbria-Marche Units (passive margin pelagic basins). In Central-Southern Italy, carbonate platforms (Lazio-Abruzzi, Apulia...) persisted alongside turbiditic basins (Lagonegro...) up until late Miocene. In the Southern Apennines, like the Liguride Units, flysch units withophiolite were incorporated in the orogenic arc (Cilento Flysch, Flysch Rosso and Frido Flysch). The deformational history of these units is recorded by the alternating shale, sandstone and conglomerate. In Sicily the Maghreb-related Numidian Flysch from Miocene contains quartz andarenite sands likely deposited by a river delta from Africa and overlain by the coarser Goroglione Flysch.
During theMiocene, the ongoing uplift affected Alps as well as the Paleo-Apenninic chain and backarc to foredeep basins continued developing. In the Southern Alps, Gonfolite Lombarda and Molassa Bellunese flysch started filling the Po basin. Around the Apennines and Sicily, late Miocene evaporites were left by theMessinian salinity crisis (for example, Gessosso-Solfifera Formation).[9]The opening of backarc basins like the Thyrrenian Sea caused the Calabro-Peloritan block to be separated from Sardinia, moving further south-east and finally included in the southern apenninic arc.Uplift continues today and since the Pleistocene, Calabrian sedimentary rocks have uplifted more than one kilometre (0.62 mi).[10]
Pliocene-Quaternary volcanism in Italy occurred with the onset ofextensional tectonics of backarc basins like theTyrrhenian Sea: seamounts and island arc volcanism developed as well as on-land magmatism in Tuscany, Lazio and Campania, often aligned with NE-SW trend followed by the main normal faults of the Apenninic chain. For example, the islands ofElba is an exhumed granitic batholith over thinned continental crust, whileStromboli is a stratovolcano originated atop newly formed oceanic crust. The most recent volcanic island isFerdinandea near Sicily, once emerged with the 1891 offshore eruption but quickly eroded below the water, remaining as theGraham Bank. Historically active volcanoes are sometimes very explosive likeVesuvius, while others likeMount Etna tend toward less explosive basaltic eruptions.[11]
Petroleum exploration in Italy began in the late 19th century and resulted in the discovery of the Caviaga gas field close to Milan in 1944. Apennine folding has created structural traps in Pliocene sand reservoirs in the Bradanic Trough, Adriatic Sea and beneath the Po Plain. In between Brescia and Milan, the stratigraphic traps are formed at the base of Pliocene transgressive rocks and then migrated into Neogene clastic rocks that were experiencing more intense tectonic activity. In some places, organic matter in Miocene flysch may have been the original source of hydrocarbon. Off of eastern Calabria (Crotone), offshore of Trapani in western Sicily and inGagliano, northeast Sicily are flysch-derived gas condensate reservoirs.
Liassic and Triassic age carbonates and reservoirs offshore in the south Adriatic or onshore atIrpinia are hosted in Triassic dolomites. Extremely deep production more than five kilometers deep takes place east of Milan in the Malossa Field. The eastern Sicilian Gela and Ragusa oil fields are also particularly deep.
In spite of extensive extraction after World War II, Italy still retains oil and gas resources. Production rose from 13.8 million cubic metres (490 million cubic feet) of gas in 1984 and 2.2 million tonnes (2.4 million short tons) of oil to 17.4 billion cubic metres (610 billion cubic feet) and 4.3 million tonnes (4.7 million short tons) of oil by 1991, and new reserves were sound in Italy between 1992 and 1993.
Italy has extensivelignite coal from the Eocene, concentrated in Sardinia. However, extraction is limited by thin seams and complicated tectonics. Graphiteanthracite is known in Carboniferous Val d'Aosta rocks and the Permian rocks of Sardinia. Both Calabria and central Italy have peat deposits from the Paleogene.
Because of the extent of mining throughout Italy's history, from Roman times to the present, many of the country's generally small mineral deposits have already been depleted. The country has small deposits oflead,sulfur,copper,zinc,silver,fluorite,barite,strontium,aluminum,gold,beryl,molybdenum,tin,uranium,iron,cobalt,chromium,titanium,mercury andastatine.Quartz,salt,feldspar,asbestos,talc,magnesite,graphite,leucite,bentonite andperlite are all extracted for industrial purposes. Historically, Italy had silver-zinc-lead mines in Monte Neve, Raibl (in the Eastern Alps), and Sardinia, mercury in north Amiata, Tuscany, fluorite and antimony in Sardinia andpyrite in Tuscany. Elba, Cogne in the Val d'Aosta valley and the Nurra Province of Sardinia all had historical iron mining. Sardinia also producedbauxite, the Western Alps asbestos and talc, Liguria and Sardiniamanganese,nickel in Piemonte and copper in Val d'Aosta.
Sicily remains active as a producer of sulfur and potassium salts and aluminum production has shifted into leucitic lavas in the center of the country.[12]
