Abstract
Pb isotopic composition and concentrations were determined for whole-rock samples from the Pliocene-Pleistocene, acid, Tuscan Igneous Province, Italy, in order to clarify their relation to the Cenozoic alkaline volcanism of Central Italy. The Pb of the Tuscan rocks is fairly uniform in its isotopic composition, despite variable and high 87Sr/86Sr ratios (0.711–0.725; Barberi et al, 1971).
A comparison of the Pb isotopic composition in the Tuscan and the potassic alkaline rocks strongly suggests a continuous mixing relation between both rock series, with partial melts of mantle material and argillaceous sedimentary rocks as likely end-members. Such an interrelation could also provide a simple explanation for the range in the Sr isotopic ratio within the Tuscan rocks. The favoured model envisages a similar history for both rock-series; it is suggested that their main petrographic differences result from a lower portion of mantle-derived material in the parental material for the Tuscan rocks, and from the mineral phases present in the residue during partial melting of the source region.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Appleton, J.D.: Petrogenesis of potassium-rich lavas from the Roccamonfina volcano, Roman Region, Italy. J. Petrol. 13, 425–456 (1972)
Barberi, F., Innocenti, F., Mazzuoli, F.: Contribute alla conoscenza chimico-petrografica e magmatologica delle rocce intrusive, vulcaniche e filoniane del Campigliese (Toscana). Mem. Soc. Geol. Ital. 6, 643–681 (1967)
Barberi, F., Innocenti, F., Ricci, C.A.: Il magmatismo nell'Appennino Centre Settentrionale (“La Toscana Meridionale”). Spec. Issue Rend. Soc. Ital. Mineral. Petrol. 27, 1–45 (1971)
Bell, K., Powell, J.L.: Strontium isotopic studies of alkalic rocks: the potassium-rich lavas of the Birunga and Toro-Ankole regions, East and Central Equatorial Africa. J. Petrol. 10, 536–572 (1969)
Capaldi, G., Gasparini, P., Moauro, A., Salvia, E., Travaglione, O.: Rare earth abundances in the alkaline volcanic rocks from Campania, south Italy. Earth Planet. Sci. Lett. 17, 247–257 (1972)
Catanzaro, E.J., Murphy, T.J., Shields, W.R., Garner, E.L.: Absolute isotopic abundance ratios of common, equal-atom, and radiogenic lead isotopic standards. J. Res. Nat. Bur. Stand. (U.S.) 72A, 261–267 (1968)
Cox, K.G., Hawkesworth, C.J., O'Nions, R.K., Appleton, J.D.: Isotopic evidence for the derivation of some Roman Region volcanics from anomalously enriched mantle. Contrib. Mineral. Petrol. 56, 173–180 (1976)
Dupuy, C., Allègre, C.J.: Fractionnement K/Rb dans les suites ignimbriteques de Toscane. Un example de rejuvenation crustale. Geochim. Cosmochim. Acta 36, 437–458 (1972)
Ferrara, G., Macera, P.: Contenuti di U, Th e K nelle rocce della provincia magmatica Toscana. Parte seconda. Soc. Ital. Mineral. Petrol. 32, 171–178 (1976)
Ferrara, G., Macera, P., Valentinetti, R.: Contenuti di U e Th nelle rocce della provincia magmatica Toscana. Parte prima. Soc. Ital. Mineral. Petrol. 31, 209–219 (1975)
Holmes, A., Harwood, H.F.: The volcanic area of Bufumbira: the petrology of the volcanic area of Bufumbira. Uganda Geol. Survey Mem. 3, Part 2, 1–300 (1937)
Hurley, P.M., Fairbairn, H.W., Pinson, W.H.: Rb-Sr isotopic evidence in the origin of potash-rich lavas of western Italy. Earth Planet. Sci. Lett. 1, 301–306 (1966)
Kay, R.W., Gast, P.W.: The rare earth content and origin of alkali-rich basalts. J. Geol. 81, 653–682 (1973)
Marinelli, G., Mittempergher, M.: On the genesis of some magmas of typical Mediterranean (potassic) suite. Bull. Volcanol. 29, 113–140 (1966)
Stacey, J.S., Kramers, J.D.: Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet. Sci. Lett. 26, 207–221 (1975)
Sun, S.S., Hanson, G.N.: Origin of Ross Island basanitoids and limitations upon the heterogeneity of mantle sources for alkali basalts and nephelinites. Contrib. Mineral. Petrol. 52, 77–106 (1975)
Taylor, H.P., Jr., Turi, B.: High-18O igneous rocks from the Tuscan magmatic province, Italy. Contrib. Mineral. Petrol. 55, 33–54 (1976)
Turi, B., Taylor, H.P., Jr.: Oxygen isotope studies of potassic volcanic rocks of the Roman Province, Central Italy. Contrib. Mineral. Petrol. 55, 1–31 (1976)
Vollmer, R.: Rb-Sr and U-Th-Pb systematics of alkaline rocks: the alkaline rocks from Italy. Geochim. Cosmochim. Acta 40, 283–295 (1976)
Wedepohl, K.H.: Pb abundances in volcanic rocks. In: Handbook of Geochemistry (K.H. Wedepohl, ed.). Berlin-Heidelberg-New York: Springer 1974
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Vollmer, R. Isotopic evidence for genetic relations between acid and alkaline rocks in Italy. Contr. Mineral. and Petrol. 60, 109–118 (1977). https://doi.org/10.1007/BF00372277
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00372277