Seminari di Scienze della Terra
Universita’ di Genova
30 Gennaio 2007

 Multidisciplinar Approach to Natural Triggers of Lithosphere Evolution

In this frame, the high Pb- isotopic ratios (HIMU-like) of the rocks of the central and western branch of the arc are explained with the high 206Pb/204Pb carried from a fluid component which is derived from the dehydration of the ancient subducting Ionian oceanic crust. On the contrary, the low Pb isotope signature of Stromboli magmas is dictated by the sediment input, as for Sr and Nd isotopes. Parental Vulcano-SHO magmas are generated by low melting degrees of a MORB-like mantle wedge, metasomatised by crustal contaminant with high fluids/sediment values, whereas Vulcano-KS magmas are interpreted as derived by RTFA-like evolutionary processes from the SHO magmas. At Stromboli, potassic to calc-alkaline magmas are generated by increasing melting degrees of a heterogeneous veined mantle. The involvement of K-micas in the genesis of KS magmas (during partial melting of mantle wedge and/or subducted sediments) is also suggested. U-Th disequilibria confirm the higher fluid vs. melt proportion in the central than in the western islands. At Stromboli, the 238U-excesses measured in CA suggest a consistent addition of slab derived fluids in the source, promoting also higher degrees of melting. The shift to the consistent 230Th-excesses in SHO and KS rocks requires dynamic melting processes capable to produce the in-growth of 230Th. Quantitative modelling suggests lower melting rates for SHO and KS rocks which are consistent with the lower melting degree proposed for these magmas.

<< Program