Evidence for mantle metasomatism: an oxygen and strontium isotope study of the Vulsinian District, Central Italy

Paul Holm, Niels Munksgaard

Research output: Contribution to journalArticle

Abstract

This paper presents new O and Sr isotope data for lavas from the northern part of the Roman perpotassic province. The samples comprise the tephritic leucititic to leucite phonolitic lavas and the saturated lavas from the Vulsinian District, the olivine leucite melilitite of San Venanzo, and the kalsilite diopside melilitite of Cupaello. Previous oxygen isotope work on the lavas of the Vulsinian District suggested crustal contamination of "normal" mantle-derived magmas. The new data cover the ranges previously found. O and Sr isotope ratios of evolved lavas of the undersaturated suite indicate assimilation in variable amounts of up to ca. 10% of continental crustal material. The saturated lavas probably assimilated large amounts (up to ca. 50%) of crust. Lavas chemically identified as corresponding to little modified mantle-derived liquids are high in both 87Sr/86Sr and d180: 0.7103-0.7107, +7.8 to +9.4 (Vulsini), 0.7104,
+ 12.3 (San Venanzo) and 0.7112, + 14.4 (Cupaello). These high values are interpreted to have been inherited from a metasomatized parental mantle. Hydrous fluids enriched in large-ion lithophile elements and high in d18O and
87Sr/86Sr are thought to have mixed with mantle of "'normal" d18O and 87Sr/86Sr. The fluids probably originated by dehydration of continent-derived sediments, which were subducted beneath a mantle wedge in the continent-continent collision of the Corsica-Sardinia block and the Adriatic (Italian) plate. This hypothesis is supported by Pb and Nd isotopic evidence and is probably valid for the entire Roman Province.
Original languageEnglish
Pages (from-to)376-388
Number of pages13
JournalEarth and Planetary Science Letters
Volume60
Issue number3
DOIs
Publication statusPublished - 1982
Externally publishedYes

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