This thesis presents a detailed chemical and isotopic study of picritic and basaltic lava flows and dykes from Baffin Island, the most westerly and least studied part of the North Atlantic Igneous Province (NAIP). Most of the Baffin Island olivine phenocrysts are not in equilibrium with their host-rock compositions (MgO = 8-28 wt. %), and lava flows with > 14 wt.% MgO contain accumulated olivines. The wide range of calculated liquid compositions (9-20 wt. % MgO) indicates a complex magmatic system, in which several batches of magmas have been mixed and of which only a small proportion has reached the surface. The Baffin Island rocks were generated over a wide range of depths with estimated liquidus temperatures of 1211-1430°C and segregation pressures of 1.7-3.1 Gpa. trace element and isotope ratios show that two distinct mantle sources were available: (1) a relatively depleted source with (La/Sm)<sub>n</sub> <1, Nb/Zr<0.04, negative ΔNb, <sup>87</sup>Sr/<sup>86</sup>sr: 0.7030-0.7034 and <sup>143</sup>Nd/<sup>144</sup>Nd ~0.5130m, and (2) a relatively enriched source with (La/Sm)<sub>n</sub> >1, positive ΔNb, <sup>87</sup>Sr/<sup>86</sup>Sr: 0.7039-0.7042 and <sup>143</sup>Nd/<sup>144</sup>Nd: 0.51280-0.51284. with the exception of Pb-isotope ratios, which show evidence for some interaction with Precambrian basement rocks, isotope and trace element ratios are not significantly affected by crustal material. Therefore, the high-<sup>87</sup>Sr/<sup>86</sup>Sr, low-<sup>41</sup>Nd/<sup>144</sup>Nd samples represent the most enriched endmember of the ancestral Iceland plume which was present at ca. 61 Ma but not evident today. The highest <sup>3</sup>He/<sup>4</sup>He (up to 50 <i>R</i><sub>a</sub>) yet recorded from any terrestrial rocks are found in the low-<sup>87</sup>Sr/<sup>86</sup>Sr, high-<sup>43</sup>Nd/<sup>144</sup>Nd rocks. Mixing, at the 670-km thermal boundary, of depleted mantle material with primordial helium form the lower mantle may account for the association of high <sup>3</sup>He/<sup>4</sup>He with depleted Sr- and Nd-isotope ratios.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653690 |
| Date | January 2004 |
| Creators | Lass-Evans, Solveigh |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11034 |
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