Abstract
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/188Osi) 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.
Highlights
A fundamental question concerns the origin of the hundreds of thousands of solitary seamounts and small isolated clusters of such seamounts on the seafloor of the world’s ocean basins (>20,000 at least 1 km high; [1])
Petit-spot volcanism is a newly recognized form of intraplate volcanic phenomena occurring out board of oceanic trenches at the fore-bulge of the down-going subducting oceanic plate [24,27,27,63,113–116]
Petit-spot volcanism is believed to be the result of plate-flexure allowing the direct sampling of an underlying asthenosphere melt lying at the lithosphere-asthenosphere boundary (LAB) [117]
Summary
A fundamental question concerns the origin of the hundreds of thousands of solitary seamounts and small isolated clusters of such seamounts on the seafloor of the world’s ocean basins (>20,000 at least 1 km high; [1]). Most of them are not directly associated with age-progressive hotspot tracks and are difficult to explain within the classic mantle plume model [2–7]. They could be the result of shallow tectonically driven processes, and several models have been proposed (e.g., [8–14]), or alternatively the result of smaller scale mantle plumes (e.g., [15,16]). Christmas Island located in the northeast Indian Ocean (10◦29 S 105◦38 E; Figure 1) is an ideal subject for investigation as it belongs to the extensive but diffuse Christmas Island Seamount Province (CHRISP, Figures 1 and S1; [10]), which shows no relationship to any mantle plume but instead shows complex, irregular age–distance relationships (Figure S1; [10]).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
