Selective ingress of a Samoan plume component into the northern Lau backarc basin.

Oliver Nebel,Richard J Arculus

doi:10.1038/ncomms7554

Oliver Nebel, Richard J Arculus

Open Access

https://doi.org/10.1038/ncomms7554

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Abstract

Intra-plate basalt isotopic trends require mixing between enriched mantle components (EM1, EM2, HIMU) and a primordial component with high (3)He/(4)He termed FOZO. However, proportions of components, geometric distributions within individual plumes, relative proportions of melting components and loci of mixing of melts and residues remain poorly understood. Here we present new Hf-Nd isotopic data of dredged sea floor basalts from the northern Lau backarc basin, ~250 km south of the subaerial and submerged Samoan chain, with high (3)He/(4)He, (20)Ne/(22)Ne and primordial (129)Xe/(130)Xe, characteristic of the FOZO component. Combined Hf-Nd-noble gas isotope systematics require mixing of refractory, sub-northwestern Lau backarc mantle only with a spatially restricted FOZO component, most plausibly sourced from part of the Samoan plume. Other geographically restricted and possibly volumetrically minor enriched Samoan plume components are not detectable in northern Lau backarc samples, consistent with selective plume ingress of the FOZO component beneath the basin.

Highlights

Intra-plate basalt isotopic trends require mixing between enriched mantle components (EM1, enriched mantle-2-type (EM2), HIMU) and a primordial component with high 3He/4He termed FOZO
Samples from the Northwest Lau Spreading Centre (NWLSC) have a narrower spread from eHf 1⁄4 þ 16.3 to þ 13.8 and eNd 1⁄4 þ 10.2 to þ 6.7, respectively
We conclude that neither the Vitiaz arc, nor the current plate tectonic setting has modified or is modifying the supra-subducted Pacific Plate mantle wedge currently serving as a magma source below the northwestern Lau Basin

Summary

Introduction

Intra-plate basalt isotopic trends require mixing between enriched mantle components (EM1, EM2, HIMU) and a primordial component with high 3He/4He termed FOZO. We present new Hf-Nd isotopic data of dredged sea floor basalts from the northern Lau backarc basin, B250 km south of the subaerial and submerged Samoan chain, with high 3He/4He, 20Ne/22Ne and primordial 129Xe/130Xe, characteristic of the FOZO component. Combined Hf-Nd-noble gas isotope systematics require mixing of refractory, sub-northwestern Lau backarc mantle only with a spatially restricted FOZO component, most plausibly sourced from part of the Samoan plume. Some OIBs, including Samoa, have elevated 3He/ 4He and other distinct noble gas isotopic systematics compared with MORB19–21, requiring a distinctive source reservoir characterized either by relatively low U/He and/or lesser extents of outgassing[19,20]. On the basis of distinction of FOZO and DMM, in terms of noble gases, mantle plumes with OIB as their likely surface expression, have been postulated to originate in the deeper (relatively undegassed) mantle[19]

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