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Petrologic, Geochemical and Isotopic Characteristics of Potassic and Ultrapotassic Magmatism in Central-Southern Italy

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Petrologic, Geochemical and Isotopic Characteristics of Potassic and Ultrapotassic Magmatism in Central-Southern Italy Per. Mineral. (2004), 73, 135-164 http://go.to/permin SPECIAL ISSUE 1 : A showcase of the Italian research in petrology: magmatism in Italy An International Journal of MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY, ORE DEPOSITS, PETROLOGY, VOLCANOLOGY and applied topics on Environment, Archaeometry and Cultural Heritage Petrologic, geochemical and isotopic characteristics of potassic and ultrapotassic magmatism in central-southern Italy: inferences on its genesis and on the nature of mantle sources SANDRO CONTICELLI1,2*, LEONE MELLUSO3, GIULIA PERINI1, RICCARDO AVANZINELLI1 and ELENA BOARI1 1 Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira, 4, 50121 Firenze, Italy 2 Istituto di Geoscienze e Georisorse, Sezione di Firenze, Consiglio Nazionale delle Ricerche, Via Giorgio La Pira, 4, 50121 Firenze, Italy 3 Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Via Mezzocannone 8, 80100 Napoli, Italy ABSTRACT. — Miocene to Quaternary magmatic Latian area (i.e., Vulsinian, Vico, Sabatinian, Alban, rocks, found along the Tyrrhenian border of Hernican, Auruncan) whereas in the southernmost peninsular Italy, mostly belong to potassic and portion of the province, the Neapolitan district, ultrapotassic suites. They can be divided into three shoshonitic and ultrapotassic magmatism are different petrographic provinces, where magmatism consistently younger than the Latian ones, ranging is confined in terms of space, time and petrographic from 0.3 Ma to present. Historical eruptions in the characteristics. Neapolitan district are indeed recorded at Phlegrean The Tuscan Magmatic Province is the Fields, Procida, Ischia and Vesuvius volcanoes. northernmost province, in which mantle-derived The Lucanian Magmatic Province is the potassic and ultrapotassic, leucite-free volcanic easternmost volcanic region characterized by rocks rocks occur, prevailing over high potassium calc- rich in both Na and K. Most of the rocks are haüyne- alkaline rocks, and covering a time span of activity and leucite-bearing, and were erupted at Monte between 14.2 and 0.19 Ma. These rocks are silica- Vulture volcano between 0.6 and 0.1 Ma. saturated to silica-oversaturated and range from Carbonatites have been described in the last phase of high-potassium calc-alkaline to ultrapotassic activity. lamproite, through potassic and ultrapotassic Minor amounts of K-rich rocks are also found in shoshonitic series. the Aeolian Arc, in the southern Tyrrhenian Sea. The Roman Magmatic Province extends from These rocks are intimately associated with calc- Northern Latium to the Umbrian and Campanian alkaline rocks at Vulcano, Vulcanello, and Stromboli. areas, arranged in a volcanic belt along the Enrichment in K2O and related incompatible trace Tyrrhenian border of the Apennine chain. It is made elements is accompanied by strong to mildly up of rare shoshonitic rocks (KS) and leucite-bearing fractionation of high field strength elements with rocks (HKS). Some HKS may contain melilite, and respect to large ion lithophile elements. This can be therefore belong to the kamafugitic group (KAM). attributed to the input of a crustal component into Minor high potassium calc-alkaline rocks are also the mantle source of the magma prior to partial found in the Pontine archipelago and in drill in the melting. Variations in trace element enrichment and Campanian plain. Volcanism has been active from isotope characteristics of the three magmatic 0.7 Ma to 0.1 Ma in the northern districts of the provinces are thought to be the result of different metasomatic events and complex processes of partial melting of the mantle sources. Peculiar geochemical * Corresponding author, E-mail: [email protected] and isotopic characteristics of the Lucanian and 136 S. CONTICELLI, L. MELLUSO, G. PERINI, R. AVANZINELLI and E. BOARI Neapolitan regions are the result of different state messe in posto al Monte Vulture tra 0,6 e 0,1 channelling of withinplate material through lateral Ma. Recentemente è stata suggerita la presenza di inflow from foreland, during the roll-back of the magmi ad affinità carbonatitica durante le fasi finali Ionian subduction. Metasomatism affected di attività dei vulcani di Monticchio. lithospheric mantle sources characterised by variable Quantità subordinate di prodotti potassici e degrees of depletion. shoshonitici sono stati emessi in tempi recenti The peculiar petrologic, geochemical and isotopic nell’arco eoliano, nel Tirreno meridionale, a features of the mafic magmas are consistent with a Vulcano, Vulcanello, e Stromboli. post-orogenic subduction-related geodynamic setting Tutti i prodotti, sia mafici che evoluti, delle tre for the production of their parental magmas. regioni magmatiche sono caratterizzati dal notevole seppur variabile arricchimento in K2O ed elementi RIASSUNTO. — Le rocce magmatiche Mio- affini, ed appare quindi evidente il forte Quaternarie affioranti lungo il margine Tirrenico frazionamento che ha favorito gli elementi in traccia dell’Italia peninsulare appartengono ad associazioni a largo raggio ionico (LILE) rispetto a quelli ad alta alcaline potassiche ed ultrapotassiche, e possono forza di campo (HFSE), sebbene si noti una essere suddivise in tre grandi province petrografiche, diminuzione di tale frazionamento spostandosi verso definibili attraverso parametri temporali, areali e sud. L’arricchimento in LILE rispetto agli HFSE è petrografici. interpretato come dovuto alla presenza di una forte La Provincia Magmatica Toscana è la provincia componente di crosta continentale aggiunta, petrografica alcalino potassica ed ultrapotassica più attraverso metasomatismo, alla sorgente dei magmi settentrionale, dove i magmi di derivazione prima della fusione. L’arricchimento differenziale mantellica non hanno portato alla cristallizzazione di negli elementi incompatibili rispetto a quello di leucite e sono stati messi in posto in un’arco di potassio, osservabile nelle rocce mafiche delle tre tempo compreso tra 14,2 e 0,19 Ma. Le rocce regioni magmatiche è stato ricondotto sia a fenomeni mafiche di questa provincia variano da sature a di metasomatismo intervenuti su sorgenti sovrasature in silice, ed appartengono a tre gruppi mantelliche variabilmente residuali, che ad ingresso petrologici distinti: i) serie calco-alcalina alta in di mantello dell’avampaese lateralmente alla potassio; ii) serie shoshonitica; iii) lamproiti. subduzione della placca ionica in seguito al suo La Provincia Magmatica Romana si estende dal arretramento. Le peculiari caratteristiche Lazio settentrionale, attraverso l’Umbria, fino alla petrologiche, geochimiche ed isotopiche osservate Campania, ed è caratterizzata prevalentemente da nei prodotti mafici potassici ed ultrapotassici rocce alcalino potassiche ed ultrapotassiche, da dell’intera area italiana sono compatibili con una debolmente a fortemente sottosature in silice, genesi dei magmi in un ambiente geodinamico post- contenenti leucite e, nei casi di maggiore orogenico. sottosaturazione, melilite e kalsilite (kamafugiti). Le rocce mafiche di questa regione appartengono alla serie shoshonitica (KS), alla Serie alta in Potassio KEY WORDS: potassic and ultrapotassic alkaline (HKS), o in maniera più limitata alla famiglia delle rocks, lamproite, kamafugite, Roman type rocks, kamafugiti (KAM). Quantità subordinate di rocce leucite-bearing rocks, Italy, Roman Magmatic calco-alcaline alte in potassio sono state trovate nelle Province, Tuscan Magmatic Province, Lucanian isole Pontine ed in perforazione nella Piana Magmatic Province. Campana. Il vulcanismo in questa regione ha avuto inizio a circa 0,7 Ma e si è protratto fino a 0,1 Ma, nei distretti più settentrionali della provincia (area INTRODUCTION laziale), mentre è significativamente più giovane nell’area Napoletana, sviluppandosi tra 0,3 Ma ed il presente. Attività vulcanica storica è infatti segnalata Potassic and ultrapotassic volcanic rocks ai Campi Flegrei, Ischia, Procida e Vesuvio. Le occur in different tectonic settings, from rocce variano da tipologie a leucite, a tipologie within-plate (Alto Paranaíba and Serra do Mar, shoshonitiche prive di leucite (KS), con la presenza, Brazil; Toro-Ankole, Western African Rift; seppur rara, di rocce calco-alcaline. Eifel, Germany; Leucite Hills, Wyoming; West La Provincia Magmatica Lucana è la più orientale Kimberley, Australia; etc.) to destructive plate tra le province petrografiche potassiche ed ultrapotassiche dell’Italia centro-meridionale, e boundaries (Western Mexico, Indonesia, mostra prodotti fortemente sottosaturi in silice, Central-Southern Italy, Perù, etc.), and have ricchi anche in Na oltrechè in K. Queste rocce sono fascinated and attracted scientists for decades Petrologic, geochemical and isotopic characteristics of potassic and ultrapotassic magmatism ... 137 in inverse proportion to their abundance. Daly in the Aeolian Arc (i.e., Vulcano and (1910) made the first attempt to explain their Stromboli) (Fig. 1). The main volcanic centres peculiar mineralogical and chemical occur in a narrow chain along the western characteristics. Since then, papers dealing with margin of the Apennine chain, from the alkaline rocks have become very abundant. Florence-Pisa area (Central Tuscany) down to Despite more than a century of intense the Neapolitan area, and a few are found either scientific interest, the processes responsible for inside (San Venanzo, Cupaello, Polino) or the genesis of alkaline rocks are still debated. close to the thrust fronts of the Apennine
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