Zircon xenocrysts from Easter Island (Rapa Nui) reveal hotspot activity since the middle Jurassic

Abstract

The 0–2.5 Ma volcanism in Easter Island (Rapa Nui) emerges just east of the East Pacific Rise on young (Pliocene, 3–4.8 Ma) ocean floor. Here, we report the finding of mantle-derived zircon grains retrieved from Easter Island beach sands and red soils that are much older than the Easter Island volcanism and its underlying lithosphere. A large population of 0–165 Myr old zircons have coherent oxygen (δ18O(zircon) 3.8– 5.9‰) and hafnium mantle isotopic signatures (εHf(t) +3.5–+12.5). These results are consistent with the crystallization of zircon from plume-related melts. In addition, a chemically diverse population with ages as old as Precambrian was also found. We thus suggest that the Easter hotspot started at least ~165 Ma ago. A large population of ~160-164 Ma zircons could signal an intense initial massive melting phase associated with the formation of a Large Igneous Province (LIP) upon the first arrival of the plume. We use plate reconstructions to show that such a LIP would have formed on the Phoenix Plate. It would have subducted below the Antarctic Peninsula around 100-105 Ma, offering a solution for the enigmatic Palmer Land deformation event, previously proposed to result from a collision with an unknown indenter. Our findings show that asthenospheric mantle-derived xenocryst zircon cargo, as recently reported from Galápagos, may not be an exception. The here-reported “ghost” of a prolonged hotspot activity suggests that the Easter hotspot and the sub-lithospheric mantle in which it is entrained remained mantle-stationary for at least 165 Ma.