Linear and nonlinear Thellier paleointensity behavior of natural minerals
Bibliographic record
Abstract
We tested single‐domain (SD) and multidomain (MD) theories of the acquisition and thermal demagnetization of thermoremanent magnetization (TRM) and partial TRM (pTRM) in Thellier paleointensity determination, using as samples plagioclase and mafic minerals extracted from Matachewan diabase dikes. Susceptibility, hysteresis, and coercivity data indicate that the plagioclase contains mainly SD grains of magnetite while the mafic minerals (clinopyroxene, biotite, and actinolite) contain mainly MD magnetite. The extracted minerals were used in simulated Thellier experiments with laboratory TRM as a proxy for natural remanent magnetization (NRM). The plagioclase behaved ideally, as predicted by Néel SD theory, giving a linear NRM‐pTRM (Arai) plot with positive pTRM checks. The mafic minerals behaved nonideally, with strongly curved Arai plots sagging below the ideal SD line, in accord with observations for MD magnetites and with predictions that in heating to moderate temperatures T , more TRM is lost than can be regained as pTRM, causing convex‐down Arai plots. In experiments with pTRM parallel to NRM, all pTRM tail checks were zero, but pTRM checks increasingly deviated from the Arai curve toward the SD line as T increased. However, in repeat Thellier experiments, pTRMs at all T agreed with the original pTRMs. The negative pTRM checks were therefore not due to physicochemical alteration but rather to departure from initial states with different magnetic histories than those of the original pTRMs. The inability of pTRM checks to reliably distinguish between MD behavior and irreversible alteration could lead to overestimates of paleointensity from straight‐line fits to the low‐ T “unaltered” part of the Arai curve or underestimates from fits to high‐ T data. Alternating field cleaning to 15 mT before each Thellier step made the Arai plot only marginally less curved. Low‐temperature demagnetization (LTD, zero‐field cycling through the 120 K Verwey transition) hardly changed the curvature of the Arai plot for pTRM parallel to NRM. For pTRM perpendicular to NRM, LTD led to an inflected Arai curve straddling the ideal SD line. Data of either form would not give reliable paleointensity values. No presently available pretreatment renders the paleointensity data of MD grains usable. SD and nearly SD grains which behave ideally in the Thellier experiment remain the only useful recorders of absolute paleointensity.
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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) | 0.000 | 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".