The Tarava Seamounts: a newly characterized hotspot chain on the South Pacific Superswell

The Tarava Seamount chain, also known as the Savannah seamounts on some previous marine charts, is located 200 km south of the Society Islands and was surveyed in 1996. It is 700 km long and comprises 18 seamounts, two of which have been dredged and dated. This chain exhibits two main branches: a western branch parallel to Pacific plate motion before 43 Ma and an eastern one parallel to plate motion since 43 Ma. To first order, K–Ar ages obtained on two dredged samples (43.5±0.6 Ma and 35.9±0.5 Ma), morphology and alignments are compatible with a hotspot origin but a large discontinuity exists in the track at 43 Ma, where the chain splits into two distinct alignments. Several volcanic sources could be responsible for these features but a more convincing solution is proposed that involves the influence of the lithospheric stress field on the track of a single hotspot. Considering that the stress field can be separated into a field due to the deflection of the lithosphere under new volcanic load and a pre-existing regional field, we show that volcanoes appear within the width of the hotspot track only where the less compressive component of the horizontal stress field is minimal. This analysis highlights the key role of the lithosphere and of its pre-existing state of stress on the path of the hotspot tracks.