A Sr, Nd, Hf, and Pb isotope perspective on the genesis and long-term evolution of alkaline magmas from Erebus volcano, Antarctica
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We report new Nd, Hf, Sr, and high-precision Pb isotopic data for 44 lava and tephra samples from Erebus volcano. The samples cover the entire compositional range from basanite to phonolite and trachyte, and represent all three phases of the volcanic evolution from 1.3 Ma to the present. isotopic analyses of 7 samples from Mr. Morning and the Dry Valley Drilling Project (DVDP) are given for comparison. The Erebus volcano samples have radiogenic Pb-206/Pb-204, unradiogenic Sr-87/Sr-86, and intermediate Nd-143/Nd-144 and Hf-176/Hf-177, and lie along a mixing trajectory between the two end-member mantle components DMM and HIMU. The Erebus time series data show a marked distinction between the early-phase basanites and phonotephrites, whose Nd, Hf, Sr, and Pb isotope compositions are variable (particularly Pb), and the current ‘phase-three’ evolved phonolitic lavas and bombs, whose Nd, Hf, Sr, and Pb isotope compositions are essentially invariant. Magma mixing is inferred to play a fundamental role in establishing the isotopic and compositional uniformity in the evolved phase-three phonolites. In-situ analyses of Pb isotopes in melt inclusions hosted in an anorthoclase crystal from a 1984 Erebus phonolite bomb and in an olivine from a DVDP basanite are uniform and identical to the host lavas within analytical uncertainties. We suggest that, in both cases, the magma was well mixed at the time melt inclusions were incorporated into the different mineral phases. (c) 2007 Elsevier B.V. All rights reserved.