Shoshonite to latite lavas, showing high MgO, Ni and Cr, and different degrees of enrichment in potassium, incompatible elements and radiogenic Sr, occur at Radicofani Volcano, Tuscany Magmatic Province (Central Italy). Compositional variation reflects mixing between two distinct magma types. One end-member has a latitic composition and resembles high-silica lamproites from the same area. Another end-member is less enriched in incompatible elements and radiogenic Sr and resembles Roman-type shoshonites. The occurrence of two distinct magma types at a single small volcano testifies to the occurrence of a zoned mantle source, which experienced two different metasomatic events. An early metasomatism took place by addition to the mantle of metapelitic material during the Eocene-Oligocene subduction of the European plate beneath the northern margin of the African plate. The second metasomatic event occurred by addition of marly sediments to the upper mantle, during Oligocene to present subduction of the Adriatic plate beneath Central Italy. Melting of the mantle rocks contaminated by metapelites gave magmas akin to Tuscany lamproites, whereas melting of mantle peridotite contaminated by marly sediments gave Roman-type shoshonitic melts. Lamproitic-like and Roman-type magmas underwent mixing within the volcanic conduit giving the range of compositions observed at Radicofani.
THE RADICOFANI VOLCANO:A WINDOW ON A COMPLEXLY ZONED UPPER MANTLE BENEATH SOUTHERN TUSCANY (CENTRAL ITALY)
PECCERILLO, Angelo;DONATI, Carmelita
2008
Abstract
Shoshonite to latite lavas, showing high MgO, Ni and Cr, and different degrees of enrichment in potassium, incompatible elements and radiogenic Sr, occur at Radicofani Volcano, Tuscany Magmatic Province (Central Italy). Compositional variation reflects mixing between two distinct magma types. One end-member has a latitic composition and resembles high-silica lamproites from the same area. Another end-member is less enriched in incompatible elements and radiogenic Sr and resembles Roman-type shoshonites. The occurrence of two distinct magma types at a single small volcano testifies to the occurrence of a zoned mantle source, which experienced two different metasomatic events. An early metasomatism took place by addition to the mantle of metapelitic material during the Eocene-Oligocene subduction of the European plate beneath the northern margin of the African plate. The second metasomatic event occurred by addition of marly sediments to the upper mantle, during Oligocene to present subduction of the Adriatic plate beneath Central Italy. Melting of the mantle rocks contaminated by metapelites gave magmas akin to Tuscany lamproites, whereas melting of mantle peridotite contaminated by marly sediments gave Roman-type shoshonitic melts. Lamproitic-like and Roman-type magmas underwent mixing within the volcanic conduit giving the range of compositions observed at Radicofani.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
