Age and evolution of the lithospheric mantle beneath the Grib kimberlite (NW Russia)
Bibliographic record
Abstract
Abstract The Grib kimberlite in NW Russia erupted into a poorly defined cratonic region along the White Sea coast. This region is part of the East European (or Baltica) Super-Craton that is comprised of several cratonic nuclei, including the Kola, Karelian and Murmansk. The eastern extent of the Kola-Karelian-Murmansk cratonic regions is uncertain due to a lack of exposed basement crust. We analysed olivine from a suite of 17 peridotite xenoliths from the Grib kimberlite in NW Russia for their Re-Os isotopic compositions and platinum-group elements (PGE) contents. Os isotopic compositions range from unradiogenic (below the present-day 187 Os/ 188 Os of the primitive upper mantle, i.e., < 0.1296) to values more radiogenic than any estimate of the primitive upper mantle (PUM). We observed no correlation between the amount of melt depletion reflected by olivine Mg# [100 × molar Mg/(Mg + Fe)] and the most unradiogenic Os isotopic composition measured in the inclusions within olivine. Samples with unradiogenic 187 Os/ 188 Os have similar PGE N patterns (where the subscript N indicates normalisation to CI chondrite), that are typical for depleted cratonic peridotites, with depletion in Pd N and Re N compared to the iridium-group (I)-PGE N (Os, Ir, Ru). Only one Grib peridotite xenolith has an Archaean T RD age of 3.27 ± 0.37 Ga. The majority of Grib peridotite xenoliths have Proterozoic T RD ages between 2.5 and 1.2 Ga. Three olivines have 187 Os/ 188 Os between 0.136 and 0.316, more radiogenic than present-day PUM. Geothermobarometry of Grib peridotite xenoliths show that the local lithospheric mantle is between 210 and 240 km thick, with diamond stability below 130 km. Overall, the majority of mantle lithosphere beneath this portion of the East European (or Baltica) Super-Craton has a minimum age between 2.5 and 1.2 Ga suggesting significant lithosphere modification during Proterozoic rifting and subduction/accretion events.
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How this classification was reachedexpand
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) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".