TY - ABST

T1 - Hf and Pb Isotopic Constraints on the Origin of a Well-Studied Suite of Icelandic Picrites.

AU - Niklas, Robert W.

AU - Brandon, A.D.

AU - Waight, Tod

PY - 2019

Y1 - 2019

N2 - 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.

AB - 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.

M3 - Conference abstract for conference

T2 - Goldschmidt Conference

Y2 - 18 August 2019 through 23 August 2019

ER -