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 cale-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 (Sr-87/Sr-86 = 0.706326-0.706654; Nd-143/Nd-144 = 0.5 12388-0.512361; Pb-206/Pb-204 = 18.944-18.940). The delta O-18 values are variable delta O-18(cpx) from +5.75 to +7.08 parts per thousand; and delta O-18(ol) from +5.50 to +6.23 parts per thousand), 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 (Sr-87/Sr-86 = 0.709679-0.711102; delta O-18(cpx) from +6.27 to +7.08 parts per thousand). 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.
Coexisting calc-alkaline and ultrapotassic magmatism at Monti Ernici, Mid Latina Valley (Latium, central Italy) / Frezzotti, Ml; De Astis, G; Dallai, L; Ghezzo, C. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 0935-1221. - 19:4(2007), pp. 479-497. [10.1127/0935-1221/2007/0019-1754]
Coexisting calc-alkaline and ultrapotassic magmatism at Monti Ernici, Mid Latina Valley (Latium, central Italy)
Dallai L;
2007
Abstract
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 cale-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 (Sr-87/Sr-86 = 0.706326-0.706654; Nd-143/Nd-144 = 0.5 12388-0.512361; Pb-206/Pb-204 = 18.944-18.940). The delta O-18 values are variable delta O-18(cpx) from +5.75 to +7.08 parts per thousand; and delta O-18(ol) from +5.50 to +6.23 parts per thousand), 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 (Sr-87/Sr-86 = 0.709679-0.711102; delta O-18(cpx) from +6.27 to +7.08 parts per thousand). 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
