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
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Bibliographic record
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 87 Sr/ 86 Sr i (0.702990–0.703060) and 187 Os/ 188 Os i (0.1220–0.1247) and high 143 Nd/ 144 Nd i (0.512989–0.512999) and are depleted in incompatible elements relative to primitive mantle. Enriched (E‐type) lavas have higher 87 Sr/ 86 Sr i (0.703306–0.703851) and 187 Os/ 188 Os i (0.1261–0.1303), lower 143 Nd/ 144 Nd i (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 δ 18 O olivine 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 187 Os/ 188 Os i 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 3 He‐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.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it