Bibliographic record
Abstract
Komatiites are ultramafic volcanic rocks that occur mainly in Archean and Paleoproterozoic greenstone belts. These olivine-rich rocks are assumed to have crystallized from magmas that have about 28–30 wt% MgO. They are characterized by spinifex texture - platy or skeletal crystals of olivine set in a glassy matrix. Chemically, komatiites resemble peridotites and have high MgO but low SiO2, TiO2 (<1 wt%), K2O (<0.5 wt%) and incompatible trace element contents. Most of their compositional variations can be accounted for by olivine fractionation. Komatiites are conventionally considered to be derived from high temperature melts that have eruption temperatures of about 1600EC and are produced by high degrees of anhydrous melting of mantle plumes. The abundance of Archean komatiites, their decrease through the Proterozoic and extreme rarity in the Phanerozoic have been taken as evidence for secular cooling of the mantle. However, the plume model has recently been challenged. In marked contrast, it has been proposed that komatiites originate via hydrous melting at a shallow depth in subduction environments at significantly lower melting temperatures than those invoked by the plume hypothesis. This new model thus challenges traditional views of the early evolution of the Earth. Nevertheless, it appears that many komatiites are plume-related. In addition to the information they provide about the tectonics and the thermal evolution of Archean Earth, komatiites are economically important because they host locally significant magmatic Ni-sulfide (Ni-Cu-PGE) mineralization. SOMMAIRE Les komatiites sont des roches volcaniques ultramafiques que l’on retrouve principalement dans des bandes de roches vertes archeennes et paleoproterozoiques. On suppose que ces roches a fort contenu en olivine ont cristallise a partir de magmas ayant des teneurs de 28 a 30% en poids de MgO. Typiquement, elles presentent une texture spinifex; c’est-a-dire en cristaux lamellaires ou squelettiques d’olivine dans une matrice vitreuse. Chimiquement, les komatiites ressemblent aux peridotites et presentent des teneurs elevees en MgO mais basses en SiO2, TiO2 (<1% en poids), K2O (<0.5% en poids) ainsi qu’en elements traces incompatibles. La plupart de leurs variations compositionnelles peuvent s’expliquer par le fractionnement de l’olivine. Par convention, on considere que les komatiites proviennent de magmas de hautes temperatures qui ont des temperatures d’eruption d’environ 1600°C, et qui proviennent d0un haut degre De fusion de panaches manteliques anhydres. L’abondance des komatiites archeennes, leur moindre abondance au Paleozoique et leur extreme rarete au Phanerozoique ont ete interpretes comme etant l’effet d’un refroidissement seculaire du manteau. Par-centre, recemment, le modele des panaches manteliques a ete remis en question. On a propose qui au contraire les komatiites proviendraient de fusions hydratees de faibles profondeurs en milieux de subduction, et a des temperatures de fusion significativement plus basses que celles supposees par l’hypothese des panaches. Ce nouveau modele remet donc en question la perspective traditionnelle sur les premiers stades de l’evolution de la Terre. Ceci dit, il semble que nombre de komatiites soit relie a des panaches. Au-dela des informations qu’elles fournissent sur la tectonique et l’evolution thermique de la Terre archeenne, les komatiites sont importantes economiquement, etant les roches hotes de mineralisations magmatiques de sulfures de nickel (Ni-Cu-EGP) en certains endroits.
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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 | 0.001 |
| 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) | 0.021 | 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".