Geochemical study of the magmatic rocks from the FAMOUS area and the islands of Azores

Trace elements have been determined in samples of the mid-atlantic ridge which were taken during FAMOUS and MIDLANTE missions of the CNEXO and in samples of the volcanic islands of Azores taken for the INAG programme studies. A quantitative interpretation of the results is made, using hydromagmatophile elements properties (Th, U, Zr, Hf, Nb, Ta, rare earths). The following points are discussed: different differentiated volcanic rock series are distinguable in Azores and on the mid-atlantic ridge, showing important fractional crystallization process with different proportions of olivines, plagioclases, pyroxenes, magnetites phases; the different series correspond to different primary magmas which are generated by a partial melting process of the mantle; the partial melting curve drawn for the mid-atlantic ridge samples allow us to calculate the mantle composition wich is characterized by a flat chondritic rare earths distribution curve in Masuda-Coryell-Winchester plot