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.