High-precision Pb and Hf isotope and highly siderophile element abundance systematics of high-MgO Icelandic lavas

• Published in: Chemical Geology
• Main Authors: Nicklas, Robert W., Brandon, Alan D., Waight, Tod E., Puchtel, Igor S., Day, James M.D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Hf Isotopes; Highly siderophile elements; Iceland; Mantle geochemistry; Ocean Island Basalts; Pb isotopes; Ocean Island
• Online Access: https://curis.ku.dk/portal/da/publications/highprecision-pb-and-hf-isotope-and-highly-siderophile-element-abundance-systematics-of-highmgo-icelandic-lavas(42bbcf83-da7d-4f8e-8e85-5c9b8310fdd1).html; https://doi.org/10.1016/j.chemgeo.2021.120436

Ocean island basalts (OIB) exhibit significant variations in their 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, 176 Hf/ 177 Hf, 186,187 Os/ 188 Os, and 206,207,208 Pb/ 204 Pb compositions that indicate contributions from multiple mantle sources. To further constrain the relationships between diverse long-lived isotopic systems in OIB, new double-spike Pb and Hf isotope data, as well as isotope dilution highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundances are reported for nineteen Icelandic picrites and basalts for which 3 He/ 4 He, 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, and 186,187 Os/ 188 Os data have been reported previously (Brandon et al., 2007. GCA). Hafnium-Nd-He isotope systematics for the sample set reveal the presence of an ancient refractory source with low- 3 He/ 4 He, while He-Pb isotope correlations indicate that recycled oceanic crustal components with high- 3 He/ 4 He added from a less degassed mantle source are present in the Iceland plume. The highly depleted, low- 3 He/ 4 He signature is sampled in the Northern and Western Volcanic Zones, likely due to higher degrees of partial melting at those localities enabling sampling of this refractory endmember. The 187 Os/ 188 Os ratios show correlations with Pb, Hf, and Nd isotope ratios indicating binary mixing between depleted and enriched sources, with no evidence for decoupling due to sulfide metasomatism. The spread of 187 Os/ 188 Os- 206,207,208 Pb/ 204 Pb data can be explained by addition of 1–11% young recycled oceanic crust to a depleted mantle source distinct from the source of Atlantic MORB. Abundances of the HSE in Northern and Western Volcanic Zone lavas overlap with those from other OIB with similar MgO contents, showing fractionated patterns that are enriched in the more incompatible Re, Pd, and Pt over the compatible Ru, Ir, and Os. Calculated parental melt HSE abundances of those lavas also overlap with those of other OIB. Eastern Volcanic Zone lavas are highly depleted in Pt and Pd relative to other Icelandic lavas. Abundances of Pt and Pd ...