GEOCHEMISTRY OF UA-HUKA BASALTS (MARQUESA S) - PARTIAL MELTING VARIATIONS AND MANTLE SOURCE HETEROGENEITY

The main shield volcano of Ua Huka Island (Marquesas Archipelago) was emplaced between 2.2 and 2.4 Ma, and then affected by two caldera coll apse events. After a 0.9 Ma-long gap, volcanic activity resumed with t he emplacement of two smaller volcanoes in the southwest part of the i sland, between 2.5 and 0.75 Ma. The geochemical characteristics of Ua Huka mafic lavas, which range from olivine tholeiites to alkali basalt s and basanites, are consistent with a temporal decrease in partial me lting degrees of a heterogeneous mantle source. The associated tempora l variation of the isotopic signatures of Ua Huka basalts implies a mo re important contribution of a Depleted MORB Mantle (DMM) end-member d uring the genesis of the youngest basanitic lavas. Such a variation wa s not previously documented in the Marquesas Archipelago.