Mantle metasomatism is currently recognised to be a first order process responsible for governing mineralogical, chemical and isotopic heterogeneity within the lithospheric mantle, but many questions are still unresolved with respect to the composition of the metasomatic agents, the related exchange reactions with the peridotite matrix, and the mode and scale of the processes. The geochemical characteristics and Sr-Nd-Pb isotopic compositions of alkaline mafic lavas and entrained spinel-peridotite xenoliths from various Cenozoic anorogenic volcanic districts of the peri-Mediterranean area suggest that fluidinduced metasomatic enrichment of the lithosphere is widespread. However, whilst 87Sr/86Sr - 143Nd/144Nd isotopic compositions characterised by an EM signature are observed in both lavas and mantle xenoliths (e.g.: Sardinia; Massif Central; Tallante, south Spain) and in alpine-type peridotites (e.g.: Lherz, Lanzo) from the European plate, they have never been recorded in alkaline lavas or mantle xenoliths of “African lithosphere” derivation. This is evident both in the African lithosphere s.s. (Iblean district, Sicily; Sicily Channel; Hoggar; Jebel Marra; Cameroon volcanic Line; Canary Islands) and its northern promontory of the Adria microplate (Pietre Nere, SE Italy; Veneto Volcanic District). On the other hand, HIMU-type metasomatism seems to be ubiquitous in both mantle domains at least from the Cretaceous.
Distinct metasomatic processes in the European and African lithospheric mantle: evidence from alkaline lavas and entrained peridotite xenoliths
BECCALUVA, Luigi;BIANCHINI, Gianluca;COLTORTI, Massimo;SIENA, Franca;VACCARO, Carmela;
2001
Abstract
Mantle metasomatism is currently recognised to be a first order process responsible for governing mineralogical, chemical and isotopic heterogeneity within the lithospheric mantle, but many questions are still unresolved with respect to the composition of the metasomatic agents, the related exchange reactions with the peridotite matrix, and the mode and scale of the processes. The geochemical characteristics and Sr-Nd-Pb isotopic compositions of alkaline mafic lavas and entrained spinel-peridotite xenoliths from various Cenozoic anorogenic volcanic districts of the peri-Mediterranean area suggest that fluidinduced metasomatic enrichment of the lithosphere is widespread. However, whilst 87Sr/86Sr - 143Nd/144Nd isotopic compositions characterised by an EM signature are observed in both lavas and mantle xenoliths (e.g.: Sardinia; Massif Central; Tallante, south Spain) and in alpine-type peridotites (e.g.: Lherz, Lanzo) from the European plate, they have never been recorded in alkaline lavas or mantle xenoliths of “African lithosphere” derivation. This is evident both in the African lithosphere s.s. (Iblean district, Sicily; Sicily Channel; Hoggar; Jebel Marra; Cameroon volcanic Line; Canary Islands) and its northern promontory of the Adria microplate (Pietre Nere, SE Italy; Veneto Volcanic District). On the other hand, HIMU-type metasomatism seems to be ubiquitous in both mantle domains at least from the Cretaceous.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
