Abstract and Scientific Objectives
The Hawaiian hotspot model has become the standard hotspot model almost by default, as no other hotspot has received nearly as much study. Controversy continues unabated as to whether or not hotspots are driven by mantle plumes, whether indeed plumes even exist, whether all hotspots have similar underlying dynamics and melting regimes, and whether the Hawaiian hotspot has enough generality on which to base a standard model. The Samoan hotspot chain bears many similarities to the Hawaiian hotspot, though intriguing differences are also manifest. Based on our recent detailed studies of the eastern Samoan province, and key reconnaissance in the western province, we have designed a tightly focused 22-day dredging cruise that will illuminate and test the generality of existing models for hotspot chains. Our studies in Samoa began with a NSF-supported dredging cruise in 1999, and continued with two U.S. Coast Guard-supported cruises in 2000 and 2001. We have studied Samoan volcanism from the active leading-edge volcano Vailulu’u in the east, to long-extinct seamounts 1,400 km west of Savai’i Island. We have shown that basalts with an unambiguous Samoan isotopic “pedigree” occur all along the chain, that radiometric and morphological evidence supports a plate-motion age progression but with unexplained exceptions, that volcanism locates along distinct en echelon trends, and that there is a striking linear increase in Pb isotope ratio going east along the chain. Based on this wealth of new information, we are able to articulate a set of inter-related dredging goals that will fully-define the Samoan chain, and allow us to compare with, and test, the Hawaiian/Standard hotspot model. Specifically, we propose to dredge 15 volcanic edifices spaced along 1,040 km of the chain, to elucidate the age progression model, to expand and fill in the Pb-isotope correlation, to explore the limits of the globally extreme enriched Sr isotope signature found at many of the volcanoes, and to map and characterize the en echelon lineaments that knit Samoan volcanoes together.