Mantle heterogeneity during the formation of the North Atlantic Igneous Province: Constraints from trace element and Sr‐Nd‐Os‐O isotope systematics of Baffin Island picrites

Abstract

Sr‐Nd‐Os‐O isotope and major and trace element data from ∼62 Ma picrites from Baffin Island constrain the composition of mantle sources sampled at the inception of North Atlantic Igneous Province (NAIP) magmatism. We recognize two compositional types. Depleted (N‐type) lavas have low 87Sr/86Sri (0.702990–0.703060) and 187Os/188Osi (0.1220–0.1247) and high 143Nd/144Ndi (0.512989–0.512999) and are depleted in incompatible elements relative to primitive mantle. Enriched (E‐type) lavas have higher 87Sr/86Sri (0.703306–0.703851) and 187Os/188Osi (0.1261–0.1303), lower 143Nd/144Ndi (0.512825–0.512906), and incompatible element concentrations similar to, or more enriched than, primitive mantle. There is also a subtle difference in oxygen isotope composition; E‐type lavas are marginally lower in δ18Oolivine value (5.16–4.84‰) than N‐type lavas (5.15–5.22‰). Chemical and isotopic variations between E‐ and N‐type lavas are inconsistent with assimilation of crust and/or subcontinental lithospheric mantle and appear to instead reflect mixing between melts derived from two distinct mantle sources. Strontium‐Nd‐O isotope compositions and incompatible trace element abundances of N‐type lavas suggest these are largely derived from the depleted upper mantle. The 187Os/188Osi ratios of N‐type lavas can also be explained by such a model but require that the depleted upper mantle had γOs of approximately −5 to −7 at 62 Ma. This range overlaps the lowest γOs values measured in abyssal peridotites. Baffin Island lava compositions are also permissive of a model involving recharging of depleted upper mantle with 3He‐rich material from the lower mantle (Stuart et al., Nature, 424, 57–59, 2003), with the proviso that recharge had no recognizable effect on the lithophile trace element and Sr‐Nd‐Os‐O isotope composition. The origin of the enriched mantle component sampled by Baffin Island lavas is less clear but may be metasomatized and high‐temperature‐altered recycled oceanic lithosphere transported within the proto Iceland plume. Differences between Baffin Island lavas and modern Icelandic basalts suggest that a range of enriched and depleted mantle sources have been tapped since the inception of magmatism in the province. Similarities between Baffin Island lavas erupted and those of similar age from East and West Greenland also suggest that the enriched component in Baffin Island lavas may have been sampled by lavas erupted over a wide geographic range.

Heterogeneous pumice populations in the 2.08-Ma Cerro Galán Ignimbrite: implications for magma recharge and ascent preceding a large-volume silicic eruption

“…Trace element concentrations in individual minerals were analyzed by LA-ICP-MS (laser ablation ICP-MS) in the W.M. Keck Collaboratory for Plasma Spectrometry, Oregon State University using a NewWave DUV 193-mm ArF Excimer laser and VG PQ ExCell Quadrupole ICP-MS. Plagioclase and biotite crystals were ablated for 45 s using a 40-μm spot size and 4-Hz pulse rate, following the methods of Kent et al (2004). Care was taken to avoid intersecting inclusions in the analyses by visual inspection, although we cannot entirely eliminate this possibility in all cases.…”

Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galán caldera, NW Argentina

“…Keck Collaboratory for Plasma Spectrometry, Oregon State University using a NewWave DUV 193 mm ArF Excimer laser and VG PQ ExCell Quadrupole ICP-MS. Analyses were performed following the methods of Kent et al (2004).…”

Processes controlling the 2010 Eyjafjallajökull explosive eruption

“…The radiogenic Pb isotopic composition of the Eyjafjallajökull samples requires a contribution of enriched mantle components to the magma, such as IE1 (high-206 Pb/ 204 Pb Icelandic enriched component dominant at Torfajökull and Hekla) [e.g., Thirlwall et al, 2004]. This component could be hydrothermally altered Icelandic crust or a component of the mantle plume [Chauvel and Hémond, 2000;Kent et al, 2004;Thirlwall et al, 2004]. The Sr-Nd-Pb isotopic characteristics of the 2010 Eyjafjallajökull volcanic products are similar to those of the southeastern volcanic zone of Iceland (e.g., Hekla) (Figure 4), a similarity which may indicate that a mantle plume component (e.g., IE1) enriched in volatiles (B, F, Cl, and As) can play a key role in the saturation of differentiated magmas with aqueous fluid.…”

“…Thus, our data for the 2010 Eyjafjallajökull event, combined with data from other sources, suggest that pre-eruptive aqueous fluids may have originated through the intensive differentiation of primitive Icelandic basalts derived from an enriched mantle plume. Given that recycling of hydrothermally altered lithosphere is common in Icelandic plume magmas [Chauvel and Hémond, 2000;Kent et al, 2004;Thirlwall et al, 2004], the enriched plume can be the Figure 7. Modeling of Rayleigh fractionation of primitive ocean-island basalt (OIB) melts for (a) H 2 O, in wt%; (b) CO 2 , in ppm; (c) Cl, in ppm; and (d) S, in ppm.…”