Year: 2019
Type: conference-paper
Abstract: Isotopic studies indicate that some examples of potassic magmatism are derived from ancient, highly enriched (radiogenic ^'^Sr/^'^Sr, unradiogenic ^'^^Nd/^'^'^Nd) sources, and in an attempt to investigate the origins of these enriched components, we have undertaken a comparative Sr, Nd and Pb isotopic and geochemical examination of potassic magmatism from a number of localities.Diamond-bearing lamproites from Western Australia, leucitites from Gaussberg, high-K alkaline dykes from MacRobertson Land, Enderby Land and Queen Mary Land regions of east Antarctica and madupites, wyomingites and orendites from Leucite Hills, Wyoming, have remarkably similar geochemical characteristics (Fig. 1).All have high Ni and Cr contents and high Mg numbers (each locality averaging Mg/(Mg+total Fe)>0.65 with the exception of Maiming Massif, Mt Bayliss and Bunger Hills samples, which have Mg numbers of 0.58, 0.58 and 0.50 respectively) as well as high to extreme abundances of K2O, Ti02, F, Cl, SO-,, H2O, P2O5, Ba, LREE, high K20/Na20, Fe^VFe^'*', Th/U, La/Nb and Ba/La ratios, low K/Rb and K/Ba ratios and relatively low abundances of AI2O3, CaO and Na20.On a Sr-Nd isotope diagram (Fig. 2), these magmas lie within the "enriched" quadrant, indicating that their sources have had long histories (>1 byrs) of high Rb/Sr and low Sm/Nd (ie; LREE enrichment).Pb isotopic compositions (Fig. 3) indicate multistage histories of U/Pb fractionation, requiring an earlier high U/Pb stage to generate the high ^^^Pb/^'^Pb, followed by a low U/Pb stage during which the evolution of 206pj3/204pjj retarded.
DOI: 10.29173/ikc1116
Authors: D. R. Nelson, M. T. McCulloch, A. E. Ringwood
Institution: Australian National University
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4250394001