Magnetite Chemistry As A Provenance Indicator In Archean Metamorphosed Sedimentary Rocks
Bibliographic record
Abstract
Abstract: Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone are limited due to intense recrystallization, destruction of original minerals, and growth of new minerals. Magnetite is a heavy mineral common in a wide range of sedimentary rocks. It can originate from a wide range of rock sources from high-temperature to low-temperature magmatic, metamorphic, or hydrothermal environments. Laser ablation (LA)-ICP-MS and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two Archean sedimentary formations in Eeyou Istchee Baie-James, Québec, Canada. Results were plotted on multi-element diagrams. The most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the Magin Formation. Overlap between the spectra of the Magin and Keyano formations substantiate the existence of a common source. Interbedded conglomerate magnetite-bearing clasts were examined to determine potential source-rocks. Mafic clasts apparently do not contain magnetite. Detrital magnetites analyzed have low Ti values that would support either felsic (to intermediate) plutonic or a hydrothermal source. The trace-element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks. Only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone. To further substantiate a felsic plutonic source, a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in Ni and Cr. From this data base, four individual plutons were identified as potential sources for the Magin Formation. Recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance. However, our database shows the importance of identifying low-Ti magnetite from felsic rocks since these could be misidentified as low-Ti magnetite from hydrothermal mineral deposits. Thus, we propose improvement to these diagrams by differentiating magnetite from felsic magmatic (low Ni/Cr) and hydrothermal (high Ni/Cr) sources before applying the mineral-deposit discrimination diagrams.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.026 | 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".