Petrogenesis of Lava from Christmas Island, Northeast Indian Ocean: Implications for the Nature of Recycled Components in Non-Plume Intraplate Settings

Lava samples from the Christmas Island Seamount Province (CHRISP) record an extreme range in enriched mantle (EM) type Sr-Nd-Pb-Hf isotope signatures. Here we report osmium isotope data obtained on four samples from the youngest, Pliocene petit-spot phase (Upper Volcanic Series, UVS; similar to 4.4 Ma), and four samples from the earlier, Eocene (Lower Volcanic Series, LVS; similar to 40 Ma) shield building phase of Christmas Island. Osmium concentrations are low (5-82 ppt) with initial Os isotopic values (Os-187/Os-188(i)) ranging from (0.1230-0.1679). Along with additional new geochemical data (major and trace elements, Sr-Nd-Pb isotopes, olivine delta O-18 values), we demonstrate the following: (1) The UVS is consistent with melting of shallow Indian mid-ocean ridge basalt (MORB) mantle enriched with both lower continental crust (LCC) and subcontinental lithospheric mantle (SCLM) components; and (2) The LVS is consistent with recycling of SCLM components related to Gondwana break-up. The SCLM component has FOZO or HIMU like characteristics. One of the LVS samples has less radiogenic Os (gamma Os-3.4) and provides evidence for the presence of ancient SCLM in the source. The geochemistry of the Christmas Island lava series supports the idea that continental breakup causes shallow recycling of lithospheric and lower crustal components into the ambient MORB mantle.

Automated summary

Lava samples from Christmas Island show a wide range of isotopic signatures, indicating different sources including enriched mantle, lower continental crust, and subcontinental lithospheric mantle. The study suggests that these components may come from shallow melting of the Indian mid-ocean ridge and recycling during the breakup of Gondwana, with evidence of the presence of ancient components.