EXTENDED ABSTRACT The sheets 587 “Milazzo” and 600 “Barcellona Pozzo di Gotto” of the Geological Map of Italy, at 1:50.000 scale, is realized on the base of a convention between the APAT – Geological Survey of Italy (Servizio Geologico d’Italia), the Autonomous Region of Sicily (Regione Siciliana) and the Department of Geological Sciences of the Catania University. Both sheets, which interest the central-northern and central Peloritani Mts., respectively, lie entirely within the Messina Province (NE Sicily). The geological map has been investigated and surveyed on a former map at the scale 1:10.000 (CTR – Carta Tecnica Regionale). The field survey has been coordinated by F. Lentini, directed by S. Carbone; the crystalline basement units have been investigated by A. Messina and E. Macaione. 1. - GEOLOGICAL SETTING In the Africa-Adria-verging Mediterranean orogenic system, Sicily exhibits a complicate geological architecture involving the Orogenic Domains of the Calabria-Peloritani Arc, the Apenninic-Maghrebian Chain, the Pelagian-Sicilian Thrust System, and the Hyblean-Sciacca Foreland Domain. The Calabria-Peloritani Arc (CPA) is part of an orogenic belt that extends from North Africa to southern Apennines named Kabilo-Calabride Chain. The CPA is an arc-shaped belt interpreted as the effect of migration toward the southeast of an arc-trench system. It is represented by crustal fragments overriding the Apenninic-Maghrebian chain along the submerged margin of the Ionian Sea. The CPA consists of a stack of continental and oceanic crust tectonic units. The former involve Pre-Variscan or Variscan basements, locally intruded by Late-Variscan plutonics, and remnants of their original Meso-Cenozoic cover. The latter, derived from Tethys Ocean branches, are composed by a Jurassic volcanic sequence and a Jurassic-Early Cretaceous sedimentary cover, both affected by an Alpine metamorphism. The Peloritani Mts. correspond to the highest structural layer and the innermost allochthonous orogenic domain of Sicily. Their geological setting involves nine Africa-verging continental tectonic units, named, from uppermost to lowermost: Aspromonte, Mela, Piraino, Mandanici, Alì, Fondachelli, S. Marco d’Alunzio, Longi-Taormina, Capo S. Andrea Units. The Alì, Longi-Taormina and Capo S. Andrea Units don’t crop out in the studied area. Units involve Pan-African and Variscan crystalline basements, and also remnants of Meso-Cenozoic sedimentary covers. The Pan-African basement, recognized in the Aspromonte Unit, corresponds to a Proterozoic crystalline lower crust, whereas the Variscan basements, reconstructed in the remained units, derived from Paleozoic sedimentary-volcanic sequences. Since Late Oligocene the tectonic phases gave rise to the present stacking of Alpine units, implying cataclastic effects to localized, metamorphic re-equilibrations, recorded both in the Aspromonte Unit basement and in the Alì Unit basement and cover. Late Oligocene-Early Miocene siliciclastic turbidites of the Capo d’Orlando flysch unconformably covered and sealed Peloritani crystalline units. Since Early Miocene tectonic activity affected the Peloritani edifice, during the orogenic transport onto the Apenninic-Maghrebian Chain, and since Middle Miocene, as consequence of the Tyrrhenian back-arc basin development. Middle Miocene to Recent sedimentary deposits unconformably cover both crystalline and terrigenous units, further affected by Plio-Pleistocene and Recent fault systems. 2. – TECTONIC AND STRATIGRAPHIC UNITS Basements On the basis of the evolutional history of each Peloritani unit, have been recognized: - a Proterozoic and Paleozoic crystalline basement in the Aspromonte Unit, lacking of Meso-Cenozoic cover; - Paleozoic sedimentary-volcanic sequences in the remaining units, some of them preserving slices of originary Meso-Cenozoic covers. The Aspromonte Unit (PMA and PMP) in Sicily represents the uppermost tectonic element. It consists of a Paleo-Proterozoic crystalline (plutonics and metamorphics) basement, affected by a Pan-African H-T granulite facies metamorphism, intruded by a Late-Pan-African orogenic peraluminous plutonic series, followed by a Variscan L-T granulite to L-T amphibolite facies re-equilibration, and intruded by a Late-Variscan orogenic metaluminous to peraluminous plutonic series. Pre-Variscan and Variscan rocks were also, locally, interested by an Alpine MH-P greenschist to amphibolite facies metamorphic overprint. The Paleo-Proterozoic plutonic event is dated on titanite of Variscan metahornblendites after Pre-Variscan meta-ultramafics. Pre-Variscan relics of Grt-metapyroxenites and of metaperidotites, partly re-equilibrated in the Variscan event, are considered coeval and more preserved. All these rocks derived from within plate Tholeiitic mantle magmas. The Neo-Proterozoic metamorphic event, dated on amphibole cores of the above defined metahornblendites, is ascribed to the Pan-African Orogenesis and developed under H-T granulite facies conditions (T=700°C, P=1.0 GPa). The Neo-Proterozoic-Cambrian plutonic event is testified by the presence of calc-alkaline intermediate to acidic Variscan metaplutonic series. The augengneisses, which are the dated types, are prevailing. The Late Carboniferous metamorphic event, dated on amphibole rims from Peloritani Variscan amphibolites and on micas from Aspromonte Massif Variscan paragneisses, is related to the Variscan Orogenesis. It affected Pre-Variscan metamorphics and plutonics, originating a polyphasic (Dv1 - Dv2) and plurifacial Bosost-type metamorphism, responsible for a ML-P retrograde zoning. The highest in grade zone realized under the granulite-amphibolite facies transition (P=0.5 GPa, T=680°C), the lowest was typical of the beginning of the amphibolite facies conditions (P<0.3 GPa, T=550°C). The Late Carboniferous–Permian plutonic event is testified by several Late-Variscan metaluminous (only in Calabria) to peraluminous (dated) plutonic bodies, cropping out in different small stocks. An intersected network of felsic and rare mafic dykes constitutes the latest intrusions. The Late Oligocene metamorphic event is ascribed to the Alpine Orogenesis. It developed along shear zones, and was responsible for a polyphasic (Da1 to Da4) and plurifacial Barrovian in type re-equilibration, realized in two different stages. In the pervasive overprinted zone, the first (syn- to post-Da1) stage originated under H-T greenschist facies conditions (T=500±20°C, P=0.8–0.7 GPa), the second (syn-Da2 to post-Da3), was typical of L-T amphibolite facies conditions(P= 0.4-0.5 GP, T>550°C). Further late sub-horizontal shear zones, cutting also the Fa2m foliation, are present at the bottom of the Unit, along the overthrusts on the underlying units. The Variscan metamorphic basement (PMA) consists of layers of paragneisses passing to gneissic micaschists (PMAa) showing the Fv1 main foliation. They include lenses of metamafics (amphibolites and gneissic amphibolites) and Pre-Variscan meta-ultramafic relics (metahornblendites, Grt-metapyroxenites and metaperidotites), interlayered by silicate marbles, Ca-silicate fels, quartzites; and of several bodies of intermediate to acidic orthogneisses, with augengneisses (PMAb) prevailing. Localized migmatitic phenomena are also present. The Late-Variscan plutonic basement (PMP) involves bodies of peraluminous leucotonalites to leucomonzogranites, and acidic to very rare basic dykes (PMPa). In the studied areas bodies are small, whereas aplo-pegmatitic dykes are very widespread, cutting both metamorphic basement and plutonic bodies. The pervasive Alpine overprinted rocks are both fine-grained Alpine white mica-garnet-rich (at the mesoscale) gneissic micaschists, schists, marbles, amphibolites (s.l.), and amphibole/garnet -rich ultramafics, after Variscan and Pre-Variscan metamorphics, and Alpine white mica-garnet-rich leuco- and orthogneisses after Late-Variscan plutonites. These rocks show a crenulated Fa2 main foliation, and in the rich-mica types also the Fa3 foliation. The Mela Unit (MLE), lacking of Meso-Cenozoic cover, consists of a basement made up of a Paleozoic sedimentary-volcanic sequence interested by an Eo-Variscan eclogite facies metamorphism, and by a Variscan Barrovian-type retrograde L-T amphibolite to H-T greenschist facies re-equilibration. The Paleozoic sedimentary sequence is represented by pelitic-arenaceous and carbonate levels. The last are the most important, for thickness and extension, of the entire CPA. The volcanic sequence is in part ascribed to Cambrian or Middle-Late Devonian and documented by the presence of Eo-Variscan Na-alkaline picritic metabasalts of distensive tectonic environment. Variscan intermediate to acidic metavolcanics belong to a different magmatic cycle. The Variscan metamorphic event realized in two stages. The first one, Early Carboniferous in age, is Eo-Varisican. It was prograde, from epidote amphibolite facies to eclogite facies (P=1.6 GPa, T=600°C) conditions. The second stage, Late Carboniferous in age, is Variscan. It was responsible for a polyphasic (Dv1 to Dv4) and plurifacial retrograde Barrovian-type process, realized under amphibolite (P<0.6 GPa, T<600°C) to greenschist (P<0.4 GPa,T=500°C) facies conditions. Late Oligocene shear zones, which cut the Fv3 main foliation, were responsible for an Alpine mylonitic deformation, accompanied by grain-size reduction and pseudomorphosis of Variscan minerals, up to localized very-low P and T re-crystallization. Further sub-horizontal shear zones originated meter-thick cataclastic to mylonitic bands, with retromorphosis and metallic deposits remobilization along tectonic overthrusts. The Variscan metamorphic basement (MLE) consists of kilometer in extension fine-grained garnet-relic paragneisses passing to micaschists (MLEa) showing the strongly crenulated Fv3 main foliation, intercalated by bodies of K-feldspar-relic two mica orthogneisses and andesine-relic amphibolitic gneisses, and including concordant meter-thick K-feldspar leuco-orthogneisses. In the high portion of the unit very-thick layers of grey-whitish fine-grained two mica marbles (MLEc), interlayered by several hectometer sub-horizontal levels of garnet-relic metahornblendites after Eo-Variscan eclogites (MLEb) and rare quartzites, also crop out. The Piraino Unit (FIP) consists of a basement defined by a Paleozoic sedimentary-volcanic sequence, affected by a Variscan metamorphic process responsible for a prograde greenschist to amphibolite facies zoning, and by a Mesozoic cover. The Paleozoic sedimentary sequence is made up of pelitic-arenaceous levels, with intercalations of small carbonate bodies. The volcanic sequence is testified by several lenses of not characterized amphibolite schists. The Variscan metamorphic event, Late Carboniferous in age as in the other units, developed a polyphasic (Dv1-Dv4) and plurifacial Abukuma-type process, responsible for a prograde zoning, from L-T greenschist facies (P about 0.3 GPa, T=400°C) to L-T amphibolite facies (P about 0.4 GPa, T=550°C). The sedimentary cover, Late Triassic(?)–Middle Jurassic in age, prevalently constituted by continental clastic deposits don’t crops out in the studied area. Late Oligocene shear zones, widespread in the unit, was accompanied by Alpine mylonitic effects. Further late sub-horizontal shear zones, cutting the Fv2 main and the thin spaced Fv3 foliations, characterize the Unit, along the meter-thick cataclastic bands related to the tectonic overthrusts. The Variscan metamorphic basement (FIP) consists of hectometer in extension layers of dark grey graphite-garnet phyllites passing to metarenites, with intercalation of meter-thick lenses of amphibolite schists, metric bodies of quartzites and rare marbles. The last lithotypes don’t crop out in the studied area. The Mandanici Unit (FDN) is constituted by a Paleozoic sedimentary-volcanic sequence affected by a Variscan metamorphic process responsible for a greenschist to beginning of amphibolite facies prograde zoning, and by a Mesozoic cover. The Paleozoic sedimentary sequence consists of pelitic-arenaceous and carbonate levels. The volcanic sequence is Cambrian to Early Carboniferous in age; an Ordovician cycle is testified by the calc-alkaline dacite-rhyolite metavolcanic series of collisional environment. The Late Carboniferous metamorphic event, related to the Variscan Orogenesis, developed a polyphasic (Dv1-Dv3) and plurifacial process, responsible for a L-T greenschist (P<0.3 GPa, T=400°C), to greenschist-amphibolite facies transition (P>0.3 GPa, T=550°C) prograde zoning. The Late Triassic-Creataceous? sedimentary cover is commonly composed by evaporitic and siliciclastic carbonate deposits. Late Oligocene shear zones are present in the unit, originating Alpine mylonites with retrocession of Variscan minerals to, localized, very-low grade re-crystallizations, accompanied by remobilization of metallic deposits. Further sub-horizontal shear zones, responsible for meter cataclastic to mylonitic bands, with new carbonate, Fe-oxide and hydroxide deposits, are present along tectonic overthrusts. The Variscan metamorphic basement (FDN) consists of kilometer in extension layers of green chlorite-, silvery muscovite- and leaden biotite-phyllites passing to metarenites, with intercalation of meter-thick lenses of actinolitic schists, metric bodies of porphyroids and quartzites, and of hectometer-thick bodies of marbles. In the studied area, marbles have not been observed. The sedimentary cover (M. Ficherelle formation - FIH) consists of localized small slices of limestones, dolostones and cargneules (Late Triassic-Early Jurassic). The Fondachelli Unit (FND) is characterized by a Paleozoic sedimentary-volcanic sequence, interested by a Variscan greenschist facies metamorphic process, and by a Mesozoic–Cenozoic cover. The Paleozoic sedimentary sequence consists of pelitic-arenaceous levels with thin carbonate intercalations. The volcanic sequence, ascribed to Cambrian or Middle-Late Devonian, is documented by Na-alkaline metabasalts of extensional tectonic environment. The metamorphic event, Late Carboniferous in age and related to the Variscan Orogenesis, developed a polyphasic (Dv1-Dv4) L-T greenschist facies process (P<0.3 GPa, T<420°C). The sedimentary cover, Upper Jurassic (Tithonian)–Oligocene? in age, consists of the Rocca di Novara stratigraphic succession. Late Oligocene shear zones affected all the unit, originating widespread Alpine mylonites and localized very-low grade re-crystallizations and remobilization of metallic deposits. Further sub-horizontal shear zones, marked by meter-thick cataclastic bands, were accompanied by widespread hydrothermal processes, with remobilization of metallic and carbonate deposits, in addition to Fe-oxides and Fe-hydroxides. The Variscan metamorphic basement (FND) is composed by kilometer in extension layers of dark graphite phyllites passing to metarenites and quartzites, exhibiting the crenulated Fv2 main foliation and the thin spaced Fv3 foliations, they are intercalated by meter-thick lenses of metadiabases and very rare metalimestones. The last lithotypes have not been observed in the studied areas. The Rocca di Novara sedimentary cover is characterized by a sequence beginning with a platform facies of the Malm, then passing into Aptian pelagic facies and Scaglia Fm. (NOV). The proximal character of this sequence is confirmed by the extension of the carbonate platform facies into the Malm, which had been “drowned” elsewhere already during the Middle Lias. The Scaglia Fm. grading up and laterally into turbiditic coarse grained sandstones grading up to a red conglomerate (GLO) (Late Eocene-Oligocene?). The sequence is entirely exposed, overturned, only along the southern slope of the Rocca di Novara. The S. Marco d’Alunzio Unit (ESM) consists of a basement defined by a Paleozoic volcanic-sedimentary sequence, affected by a Variscan greenschist facies metamorphic process, and by a thin Meso-Cenozoic cover. The Paleozoic pelitic-arenaceous-carbonate sequence is Cambrian to Early Carboniferous in age. Volcanic cycles typify the sequence, also dated Cambrian to Early Carboniferous in age The Late Carboniferous metamorphic event, ascribed to the Variscan Orogenesis, affected the Paleozoic sequence, originating a polyphasic (Dv1-Dv4) process, typical of L-T greenschist facies conditions (P<0.3 GPa, T about 350°C). The sedimentary cover, Early Lias-Eocene in age, consists of basal continental clastic deposits, grading up to both platform and basinal successions. The cover don’t crops out in the studied area. Late Oligocene shear zones were responsible for widespread Alpine mylonitic effects. Further sub-horizontal shear zones along the tectonic overthrusts are marked by meter-thick cataclastic bands. The Variscan metamorphic basement (ESM) is made up of hectometric bodies of pinkish metavolcanics, porphyroids prevailing, with alternances of layers of grey-violet slates and metarenites, grey-pinkish quartzites and rare metalimestones, and of lenses of grey-bluish metabasalts. Sedimentary cover Tertiary terrigenous and carbonatic covers The Capo d’Orlando flysch (COD) can be interpreted as a thrust top basin deposit, posterior to the CPA Southern Sector tectonic units emplacement, also involved in further tectonic phases. The COD consists of molasse-type sediments, evolving into flysch-type deposits. The Early Chattian conglomeratic interval grades upward into an arenaceous-argillaceous facies, ascribed to the Chattian-Lower Burdigalian. This deposit, characterized by variable thickness and facies distribution, unconformably rests on the CPA Southern Sector units, and was furthermore deformed by ramps, which breach the defined edifice, progressively involving younger flysch horizons from south to north. These deposits underthrust the Antisicilide Units. The present COD distribution is a result of the activation, from the Tortonian onward, of impressive systems of transcurrent dextral faults of the South Tyrrhenian System, that have profoundly deformed the geometry of the Early Miocene thrust system. Antisicilide Tectonic Unit. On the top of the Calabride Units in northeastern Sicily the Sicilide nappes, constituted of the Cretaceous Argille Scagliose dei Monti Peloritani (ASI) rest tectonically upon the Capo d’Orlando flysch (COD), and, locally, on the basement. The ASI have the aspect of polychromic clays with sliced texture, often with a chaotic habit, and intercalations of bituminous clayey schists alternating with variegated radiolarites, thin clayey-arenaceous strata. The Floresta calcarenites (CFL), Late Burdigalian-Early Langhian in age, consist of mostly shallow-water coralgal biostromes, bioclastic calcarenites and arkose glauconitic sandstones with carbonate cement, unconformably overlie the Antisicilide Unit and sometimes seal the tectonic contact with the Capo d’Orlando flysch. The deposits are scattered over central and northern areas of the Peloritani Mts., but they were originally widely distributed before undergoing deep erosion, as their distribution in some structural depression suggests. The Floresta calcarenites deposited during the last overthrusting of the Calabride Chain onto the Apenninic-Maghrebian Chain, preceeding the initial opening of the Tyrrhenian Sea. Middle Miocene-Pleistocene deposits The M. Pitò marly (PIO). Prevalently along the Tyrrhenian side of Peloritani Mts., marls and marly clays with thin lenses of sandstones overlie in a top-lapping arrangement the south-dipping foresets of the Floresta calcarenites or unconformably rest on a Langhian erosional surface. They are mostly pelagic fine-grained sediments and indicate a sudden change in the tectono-sedimentary regime, that lead to the demise of source areas that fed the clastic horizons of Floresta calcarenites, followed by an overall marine transgression over the previously emerged areas. There was a northward migration of clastic fans within newly created hinterland basins. This inversion was related to onset of the Tyrrhenian Basin and the progressive collapse of its southern margin. The areas feeding the Middle Serravallian–Early Messinian deposits, as suggested by the foreset geometry, were probably located in the modern eastern (Messina Straits and Calabria) and southern areas of the mountain belt, which did not suffer faulting and subsidence. The S. Pier Niceto fm. (PCT). These Middle Serravallian-Early Messinian deposits are preserved within down-faulted areas bordering the Peloritani Ridge, along both Tyrrhenian and Ionian slopes, separated by a modern NE-SW oriented horst structure, upon which a few depositional remnants are scattered. They consist of repeated conglomeratic horizons interbedded with an arenaceous-argillaceous alternation, arranged in NW-dipping foresets and downlapping onto the substratum. The upper portion of the sequence consists of arenaceous-argillaceous alternations, forming a top-set geometry, and dates to the Upper Tortonian–Lower Messinian. The analysis of facies distribution and tectonics demonstrates that the overall geometry of the Middle Serravallian–Early Messinian sequence is that of an original fan-delta controlled by tectonics and eustasy. The conglomerate distribution reflects the arrangement of structural palaeodepressions, originated from Serravallian faulting, connected to the initial phases of Tyrrhenian opening.Along the north-facing slopes of the Nebrodi-Peloritani ridge there are a number of exposures of Upper Tortonian-Lower Messinian reefal carbonates and calcareous breccias (PCTd). Pliocene and Pleistocene sediments are preserved in downfaulted areas, adjacent to the modern coastline. They were deposited within structural depressions and then successively modified by Recent tectonics. The Early Pliocene sediments are composed of white marls (Trubi - TRB), deposited during rising sea-level, following the Messinian salinity crisis (Gessoso-Solfifera Group - GS, Upper Messinian). The Plio-Pleistocene deposits consist of shallow-water calcarenites, sands and clays, and form distinct cycles, unconformably covering the substratum and filling depocentres originated during the Messinian. In chronological order, the following formations are recognized in the studied area: Biodetrital calcarenites, fossiliferous sands, clays and sandy clays (Rometta fm. – ROE; Upper Pliocene-Middle Pleistocene). The Middle Pleistocene-Olocene succession consists of marine terraced deposits (gn) and active (g2) strandlines (beaches); transitional to continental deposits represented by conglomerates, sands and gravels (ghiaie e sabbie di Messina - MSS, Middle Pleistocene); inactive alluvial terraced deposits (bn), undergoing pedogenesis or terracing developed during different pulses of the glacial-eustatic activity; alluvial and litoral deposits (bb) constitute the widely plain of Milazzo-Barcellona P.G.; active alluvial deposits (b) grade laterally into slope detritus and alluvial fan deposits; eluvium and colluvium (b2); gravity deposits and some large and active mass-movements (a1); slope debris (a). Numerous active quarries are localized in the area. 3. – TYRRHENIAN PHASE TECTONIC EVOLUTION The present structural setting of the CPA Southern Sector derives from the collision tectonics affecting the area since the Serravallian, which deeply modified the pre-existing outlines. They originated from the combination of the Tyrrhenian Sea opening coupled with the Calabrian Peloritanian Arc SE-ward migration, which resulted in the activation of the South Tyrrhenian System along the northern coast of Sicily. It consists of NW-SE trending dextral faults, which drove the SE migration of the allochthonous units, and ENE-WSW oriented normal faults, which caused the progressive collapse of the orogenic units along the Tyrrhenian coast. Middle Miocene to Recent sedimentary deposits unconformably cover both crystalline and terrigenous units. These are preserved within down-faulted areas bordering the Peloritani Mts., along the modern coasts and also extend within the mountain belt, within Recent structural depression (i.e. Furnari and Castroreale depressions). They were deposited on downfaulted blocks, mainly bordered by normal faults, which originally affected the southern margin of the Tyrrhenian Sea, and were later largely obliterated by Recent tectonics. The studied area is characterized by a wide palaeo-erosional surface involving both crystalline basements and their terrigenous-carbonate cover; This surfacee correlates with the top of the mid-Pleistocene deposits. Several wave-cut terraces are recognized in the uppermost part of the mid-Pleistocene sediments. They are marine deposits referable to the Late Pleistocene period. Such terraces are located at different altitude above present level and are locally cut by Recent faults.
|Titolo:||Note Illustrative della Carta Geologica d’Italia alla scala 1:50.000 - Fogli 587 “Milazzo” e 601 “Barcellona P.G.”.|
|Data di pubblicazione:||2011|
|Appare nelle tipologie:||3.1 Monografia o trattato scientifico|