Geology and geochemistry of Nuku Hiva, Marquesas: Temporal trends in a large Polynesian shield volcano

Nuku Hiva, one of the largest shield volcanoes in French Polynesia, was built up largely between 4.8 and 3.7 Ma We present a geological sketch map of the island showing three nested calderas opened southward, the origin of which is attributed to submarine gravity landslide collapses. The emergent part of the Tekao shield is made up of thin tholeiitic flows mostly emplaced between 4.8 and 4.5 Ma, overlain by transitional basalts, alkali basalts and hawaiites. The main caldera collapse event is dated at 4.05 +/- 0.10 Ma. It was immediately followed by the construction of the Taiohae volcano which exposes an alkalic suite ranging from basalts to trachytes. Major and trace element data document a rapid transition from tholeiites to alkali basalts, which we relate to time-decreasing degrees of melting of a garnet Iherzolite source. The isotopic Sr, Nd, Pb variability of Nuku Hiva basalts, and especially of the Tekao shield tholeiites, may reflect small-scale heterogeneities in a plume of dominantly EMII-HIMU composition.