| Popis: |
On the island of Lesvos in the north-eastern Aegean Sea, thrust sheets of mantle peridotite override a tectonic melange containing metasediments, metabasalts and a few metagabbros. Previous workers have collectively called the above rock types the “Lesvos ophiolite” and suggested it represents Neotethyan (Jurassic) oceanic crust of N-MORB and IAT affinities. However, the complete absence of a sheeted dyke complex and of a layered cumulate sequence, in turn overlain by isotropic gabbros does not support the ophiolite description. The basalts of the melange define two distinct groups on the basis of Nb/Y values: the Vatera (low Nb/Y) and the Melange (high Nb/Y) groups. The Vatera basalts show multi-element profiles and REE patterns lying well within the field of N-MORB with the exception of Y and HREE abundances that are lower than those of N-MORB and match those of E-MORB. They originated by similar to 10% melting of depleted MORB mantle that carried a small amount (similar to 3%) of an enriched (OIB-like) components corroborated by moderate initial epsilon Nd values (+4.6-+6.2). The Melange basalts, in contrast, have multi-element profiles and REE patterns typical of within-plate compositions, transitional between E-MORB and OIB. They originated by |
