Temporal geochemical evolution in oceanic intra-plate volcanics: a case study from the Marquesas (French Polynesia) and comparison with other hotspots

Sr-, Nd-isotopic and trace element data are reported for a suite of Marquesan volcanic rocks. These data complement earlier work on the island of Ua Pou and reveal that the marked shifts in source composition between shield-building and post-shield eruptives noted there are common to most islands in the archipelago. In addition, there appears to be a relationship between the magnitude of these shifts and the repose period between shield-building and post-shield activity such that, the longer the period of volcanic inactivity, the larger the isotopic and trace element differences between the two phases of volcanism. This, coupled with the compositional uniformity of the shield-building phase, and its close geochemical similarity to depleted mantle reservoirs, implies a strong lithosperic control on magmatic evolution: models invoking entrainment of asthenospheric material during plume ascent are not readily compatible with the observed time-compositional paths. Comparisons with other oceanic islands reveal two end member styles of temporal evolution, herein termed Marquesan and Hawaiian, and attributed to the interaction between the oceanic lithosphere and respectively weak and strong plumes, terms used to denote penetrative capacity and not necessarily size or buoyancy flux. Many other plumes may display characteristics intermediate between these extremes. The state of stress and temperature within the oceanic lithosphere in the region of an ascending diapir is also likely to exert a strong control on the geochemical evolution of OIB suites.