Sourcing of Miocene accretionary lapilli on ‘Eua, Tonga; atypical dispersal distances and tectonic implications for the central Tonga Ridge

Volcaniclastics hosting accretionary lapilli on the Tonga Ridge were sourced from the remnant Lau Ridge, prior to Lau back-arc basin opening. For the Eua occurrences, an atypical dispersal distance of not less than 70km is estimated, partly arising from the anomalous easterly position of Eua. Dispersal within ocean-surface pyroclastic density currents is supported but strike-slip movement in a fault zone south of Eua, post-middle Miocene but pre-ridge-splitting, can account for part of the dispersal distance by vertical axis block rotation, a tectonic process common on the southern Tonga-Kermadec-Hikurangi trend. In this model, the volcano which sourced the Eua tephra was on a subjacent block, rather than the block which hosts Eua. After deposition but prior to the opening of the Lau Basin, the accretionary lapilli on Eua became displaced by block rotation c. 40km towards the Tonga trench and away from source.