Three suites of volcanic rocks from Radicofani, Mts. Cimini and Mt. Amiata (south Tuscany, Italy) were analyzed for major- and trace-element contents and Sr isotopic composition. All samples are silica saturated, hypersthene normative and some are peraluminous. Samples from Radicofani and the less evolved Mts. Cimini samples have high Mg numbers (74.5–66.3), consistent with the fosteritic-rich nature of their olivine phenocrysts and high bulk-rock abundances of ferromagnesian trace elements. All samples are highly enriched in light REE (150–315 × chondrites) compared to heavy REE (9–15 × chondrites) and have negative Eu anomalies (). ratios are high and variable: Radicofani = 0.7137-0.7150; Mts. Cimini = 0.7128-0.7138; Mt. Amiata = 0.7119-0.7131. A distinctive feature of the Radicofani samples is that with decreasing age, the rocks increase in K2O content but decrease in La/Ce. These south Tuscany rocks have geochemical characteristics of the calc-alkaline and alkaline series: namely, in addition to the high K, Rb, Cs, Ba and LREE contents, they have high ratios of incompatible elements relative to the high-field-strength ions such as Ti, Zr, Hf, Nb and HREE when compared to an estimated primitive mantle composition. In general, the geochemical characteristics of south Tuscany volcanics are consistent with mixing between crustal-derived material and mantle-derived magma. The mantle-derived component was unusually rich in radiogenic Sr and incompatible elements and had geochemical features similar to basic lavas of the high-K series in the Roman Province.
Geochemical characteristics of the south Tuscany (Italy) volcanic province: Constraints on lava petrogenesis
POLI, Giampiero;
1984
Abstract
Three suites of volcanic rocks from Radicofani, Mts. Cimini and Mt. Amiata (south Tuscany, Italy) were analyzed for major- and trace-element contents and Sr isotopic composition. All samples are silica saturated, hypersthene normative and some are peraluminous. Samples from Radicofani and the less evolved Mts. Cimini samples have high Mg numbers (74.5–66.3), consistent with the fosteritic-rich nature of their olivine phenocrysts and high bulk-rock abundances of ferromagnesian trace elements. All samples are highly enriched in light REE (150–315 × chondrites) compared to heavy REE (9–15 × chondrites) and have negative Eu anomalies (). ratios are high and variable: Radicofani = 0.7137-0.7150; Mts. Cimini = 0.7128-0.7138; Mt. Amiata = 0.7119-0.7131. A distinctive feature of the Radicofani samples is that with decreasing age, the rocks increase in K2O content but decrease in La/Ce. These south Tuscany rocks have geochemical characteristics of the calc-alkaline and alkaline series: namely, in addition to the high K, Rb, Cs, Ba and LREE contents, they have high ratios of incompatible elements relative to the high-field-strength ions such as Ti, Zr, Hf, Nb and HREE when compared to an estimated primitive mantle composition. In general, the geochemical characteristics of south Tuscany volcanics are consistent with mixing between crustal-derived material and mantle-derived magma. The mantle-derived component was unusually rich in radiogenic Sr and incompatible elements and had geochemical features similar to basic lavas of the high-K series in the Roman Province.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
