Reactive transport and the genesis of kimberlites
Bibliographic record
Abstract
When studying the bulk rock analysis of kimberlites a <br/>significant correction for visible xenocrysts must be made <br/>[1,2]. Such studies concluded that olivine in kimberlite has a <br/>xenocrystic core and cognate margin. Previously, material <br/>entrained by the melt and dissolved during transport has only <br/>been qualitatively discussed [3]. We find bulk rock and <br/>electron microprobe data strongly support dissolution of <br/>orthopyroxene coupled with crystallization of cognate olivine <br/>rims in the Majuagaa kimberlite sensu stricto dyke. This <br/>reaction was suggested by the topography of phase diagrams <br/>for systems containing Enstatite, Forsterite and CO2. The <br/>‘parental’ melt for Majuagaa kimberlite was magnesiocarbonatite <br/>which entrained 50wt% harzburgite, consistent with <br/>melting experiments. The melt processed ~20wt% SiO2 but at <br/>any given time had no more than ~5wt% SiO2. We explain <br/>geochemical variations across the southern West Greenland <br/>kimberlites sensu lato using similar processes. We may also <br/>account for the intercraton variety in kimberlite composition <br/>and mineralogy. <br/>Mg# and Ni composition was obtained for transects across <br/>olivine grains. Pure Rayleigh fractionation did not explain the <br/>shape of the nickel transects. Diffusion between <br/>homogeneous olivine grains and melt was also eliminated. <br/>The data was replicated using a combination of growth and <br/>minor later diffusion. Growth was modeled using AFC <br/>equations [4]. Later diffusive equilibration between core and <br/>margin was minor. Since kimberlite transport time was short <br/>magmatic temperatures of ~900oC were supported. <br/>! <br/>[1] Nielsen & Sand (2008), Canadian Mineralogist 46, 1043- <br/>1061 [2] Ardnt, Guitreau, Boullier, Le Roex, Tommasi, <br/>Cordier & Sobolev (2010), Journal of Petrology 51, 573-602 <br/>[3] Mitchell (2008), Journal of Volcanology and Geothermal <br/>Research 174, 1-8 [4] De Paulo (1981), Earth and Planetary <br/>Science Letters 53, 189-202
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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 | 0.002 | 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 | 0.001 | 0.003 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.245 | 0.005 |
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; both teacher heads agree on what is shown here.
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".