Edad y contexto geodinámico del magmatismo básico Ordovícico del Sistema Central Español

Résumé

New geochemical (major, trace and isotopic) and geochronological data obtained on metabasites intrusive into pre-Arenig metasedimentary and metaigneous rocks of the Spanish Central System confirm their heterogeneous composition. They exhibit a tholeiitic affinity, but show relatively high incompatible element contents, contrary to NMORB magmas. Two groups can be distinguished: 1) one isotopically depleted and more evolved and 2) one isotopically enriched, representing more primitive liquids with higher metal (Cr, Ni) and LILE contents. These data point to the involvement of several mantle sources, including lithospheric sections with a crustal imprint. Two samples have provided U-Pb zircon ages in the range 473- 453 Ma, thus related to the rifting context associated with the Rheic ocean opening. The absence of basic magmatism in the Central-Iberian Zone prior to that described in this work, might indicate that rifting was a late event in this region when compared to other terranes from the Iberian Massif.