Helium isotope variations in seafloor basalts from the Northwest Lau Backarc Basin: Mapping the influence of the Samoan hotspot

Abstract

New helium isotope results for seafloor basalts from the northern Lau Basin indicate that the signature of the Samoan hotpot has penetrated beneath the Rochambeau Rifts (RR) and the Northwest Lau Spreading Center (NWLSC) all the way to the Peggy Ridge (PR). Helium isotope ratios in 29 samples from the NWLSC - RR range from 10.9 to 28.1 Ra, all clearly higher than typical depleted mantle or MOR-type values. Comparison with other helium results from the northern Lau Basin show the Samoan hotspot influence is confined to the NWLSC - RR extensional zone, and is absent in the northeast Lau Basin and along the PR. The absence of high 3He/4He ratios in the northeast Lau Basin may delimit the eastward extent of the Pacific Plate tear which allowed southward intrusion of the Samoan plume, or indicate deep mantle flow carrying the Samoan plume signal westward from the Samoan Islands.