Hf and Pb Isotopic Constraints on the Origin of a Well-Studied Suite of Icelandic Picrites.

• Main Authors: Niklas, Robert W., Brandon, A.D., Waight, Tod
• Format: Conference Object
• Language: English
• Published: 2019
• Subjects: Iceland
• Online Access: https://curis.ku.dk/portal/da/publications/hf-and-pb-isotopic-constraints-on-the-origin-of-a-wellstudied-suite-of-icelandic-picrites(e76ff372-6f86-4029-91bc-5502305877b2).html

The Iceland plume is one of the best geochemically studied plume in the literature. Isotopically enriched Icelandic lavas likely contained significant recycled components in their mantle source regions [1]. Although up to four endmembers have been proposed to explain the isotopic range sampled by the plume [2], principle component analysis (PCA) has shown that >99% of the variation is the result of mixing between two endmembers [3]. A suite of modern Icelandic picrites have been previously analyzed for 186-187Os, He, Nd, Sr and Tl isotopic systematics and major and trace elements [4-6]. These data show mixing between a high 3He/4He enriched component and a low 3He/4He depleted component in the picrite mantle source. Both components contained negligable subducted sediment [5]. In order to provide context for these end-members, we have determined the Hf and double-spike Pb isotopic compositions of these picrites. Measured 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios varied between 0.28310-0.28336, 18.04818.967, 15.432-15.572 and 37.711-38.526, respectively. 207Pb and 208Pb values are almost uniformly negative and positive, respectively, consistent with the bulk of Icelandic lavas [2]. All lithophile element isotopic systematics show broad correlation with 187Os/188Os consistent with mixing. These correlations allow calculation of the lithophile isotopic systematics of the two mantle endmembers, which are consistent with the hybrid recycled crust-primitive mantle and depleted mantle end members proposed in [4]. This hybrid endmember shows that recycled crust is likely mixed with primordial undegassed material in the deep mantle, and that this mixture has recently been sampled by mantle plumes.