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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; ~4.4 Ma), and four samples from the earlier, Eocene (Lower Volcanic Series, LVS; ~40 Ma) shield building phase of Christmas Island. Osmium concentrations are low (5–82 ppt) with initial Os isotopic values (¹⁸⁷Os/¹⁸⁸Os_i) ranging from (0.1230–0.1679). Along with additional new geochemical data (major and trace elements, Sr-Nd-Pb isotopes, olivine δ¹⁸O 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 (γOs –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.

Item Type:	Refereed Article
Keywords:	osmium isotopes, petit-spot volcanism, olivine oxygen isotopes, intraplate volcanism, Christmas Island, Indian Ocean, CHRISP, crust recycling, lithosphere recycling, DUPAL
Research Division:	Earth Sciences
Research Group:	Geochemistry
Research Field:	Isotope geochemistry
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the earth sciences
UTAS Author:	Falloon, TJ (Dr Trevor Falloon)
ID Code:	149128
Year Published:	2022
Deposited By:	Earth Sciences
Deposited On:	2022-03-11
Last Modified:	2022-05-16
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