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doi:10.2204/iodp.sp.330.2010

Abstract

The Louisville Seamount Trail is a 4300 km long volcanic chain that is inferred to have been built in the past 80 m.y. as the Pacific plate moved over a persistent mantle-melting anomaly or hotspot. Because of its linear morphology and its long-lived age-progressive volcanism, Louisville is the South Pacific counterpart of the much more extensively studied Hawaiian–Emperor Seamount Trail. Together, the Louisville and Hawaiian–Emperor seamount trails are textbook examples of two primary hotspots that have been keystones in deciphering the motion of the Pacific plate relative to a set of fixed deep-mantle plumes. However, drilling the Emperor Seamount Trail during Ocean Drilling Program (ODP) Leg 197 revealed a substantial ~15° southward motion of the Hawaiian hotspot prior to 50 Ma, calling into question whether the primary Pacific hotspots constitute such a fixed frame of reference. Is it possible that the Hawaiian and Louisville hotspots have moved in concert and therefore constitute a moving reference frame for modeling plate motion in the Pacific? Alternatively, is it possible that they have moved independently, as predicted by modeled mantle flow patterns that reproduce the observed latitudinal motion of the Hawaiian hotspot but predict essentially no latitudinal shift (but rather a longitudinal shift) for the Louisville hotspot? These two end-member geodynamic models will be tested during Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamount Trail.

In addition, existing data from dredged lavas suggest that the mantle plume source of the Louisville hotspot has been remarkably homogeneous for as long as 80 m.y. These lavas are predominantly alkali basalts and likely represent a mostly alkalic shield-building stage that differs distinctly from the massive tholeiitic shield-building stage of Hawaiian volcanoes. Geochemical and isotopic data for the recovered lavas will consequently provide key insights into the magmatic evolution and melting processes of Louisville volcanoes between 80 and 50 Ma. These measurements will yield new information about the fundamental homogeneity of the Louisville mantle plume, the progression from shield-building to postshield and (perhaps) posterosional volcanic stages during the construction of these volcanoes, and the temperature and depths of partial melting in the mantle plume source. Collectively, this will enable us to characterize the Louisville Seamount Trail as a product of one of the few primary Pacific hotspots and constrain its interaction with the lithosphere on which it formed.

During Expedition 330 we will replicate the drilling strategy of Leg 197, which provided compelling evidence for the motion of the Hawaiian mantle plume between 80 and 50 Ma (Tarduno et al., 2003; Duncan et al., 2006). For this reason, we will target four Louisville seamounts that have ages similar to the Detroit, Suiko, Nintoku, and Koko seamounts of the Emperor Seamount Trail. Our principal drilling goal is to drill 350 m (or deeper) into the igneous basement of these Louisville seamounts in order to core and recover as many individual lava flows as possible. By analyzing these lava flows using modern paleomagnetic, ⁴⁰Ar/³⁹Ar geochronological, and geochemical techniques, we will be able to directly compare paleolatitude estimates and geochemical signatures between seamounts in the two longest-lived hotspot systems in the Pacific. Using data from Expedition 330 we hope to resolve whether the Hawaiian and Louisville mantle plumes have moved in concert or independently, constrain the magmatic evolution of the Louisville Seamount Trail and its possible plume–lithosphere interactions, and more definitively test the hypothesis that the Ontong Java Plateau formed from the plume head of the Louisville mantle plume at ~120 Ma. Finally, the thin sediment cover on these guyots may provide additional information about the subsidence history of the Louisville seamounts and guyots and may be a valuable contribution to the southern hemisphere paleoclimate record.

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