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1 Dipartimento di Scienze Della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy
2 IGAG – C.N.R., P.le A. Moro 5, 00185 Roma, Italy
3 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Via Diocleziano, 328, 80124 Napoli, Italy
4 Istituto di Geoscienze e Georisorse – C.N.R, Via G. Moruzzi, 1, 56124 Pisa, Italy
* Corresponding author, e-mail: frezzottiml{at}unisi.it
New major and trace element data, and Sr-Nd-Pb-O isotopic ratios for volcanic mafic rocks outcropping at Monti Ernici in the Mid Latina Valley (southern Latium) are reported, with the aim of investigating the nature and evolution of Plio-Quaternary K-rich volcanism in Central Italy. Petrographical and geochemical studies allow us to identify mafic rocks ranging from ultrapotassic (HKS) to shoshonitic (SHO), and calc-alkaline (CA), these last ones being identified for the first time. The CA rocks exhibit the most primitive signatures for Sr, Nd, and Pb isotopes (87Sr/86Sr =0.706326–0.706654; 143Nd/144Nd = 0.512388–0.512361; 206Pb/204Pb = 18.944–18.940). The 
18O values are variable (18Ocpx from +5.75 to +7.08 
; and 18Ool from +5.50 to +6.23 ), suggesting interaction with carbonate wall rocks. Radiogenic isotope ratios and incompatible elements distribution have several characteristic in common with equivalent rocks from Pontine Islands (Ventotene), Campania and Aeolian arc volcanoes. Conversely, the HKS rocks closely resemble the ultrapotassic rocks from the Roman Province (87Sr/86Sr = 0.709679–0.711102; 18Ocpx from +6.27 to +7.08 ). The high ratios of LILE (Large Ion Lithophile Elements: Rb, Cs, Th, U, K, LREE) and HFSE (High Field Strength Elements: Ta, Nb, Zr, Hf, Ti), and radiogenic isotope compositions of CA to HKS rocks indicate that all suites contain subduction-related components, and suggest a N-MORB-type mantle source variably contaminated by hydrous fluids and/or melts released by undergoing slabs, possibly during two distinct stages of metasomatism. The coexistence of ultra-alkaline and sub-alkaline orogenic magmatism, combined with tectonic, geophysical and geological evidence, support the possibility that the mantle beneath central-southern Italy (Ernici-Roccamonfina Province) was vertically zoned and produced different magma suites during time.
Key-words: Monti Ernici, Latium magmatic Province, calcalkaline rocks, ultrapotassic rocks, geochemistry, igneous petrology.
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