Geometry, kinematics, and timing of Proterozoic shear zones in New Mexico and northwestern Arizona: a record of multiple orogenic pulses?
Bibliographic record
Abstract
Proterozoic shear zones are key features of southwestern North America's orogenic belts that extend over 1,000 km along strike from Mexico to eastern Canada. The dominant fabric of these shear zones is a subvertical, northeast-trending foliation expressed in a wide range of temperature regimes, from migmatites to mylonites to pseudotachylytes, that have previously been envisioned to have formed during the Paleoproterozoic (1.7-1.6 Ga Yavapai and Mazatzal orogenies). An emerging addendum is that the lower temperature shearing possibly represents reactivation of earlier shear zones during the later deformation such as the ~1.45 Ga Picuris and ~1.1 Ga Grenville orogenies. The research plan for this project is to use 40 Ar/ 39 Ar thermochronology to date fine-grained mica found in the grain-reduced shear zones as well as coarse-grained mica from the coarser grained shear zones to attempt to parse 1.65 versus ~1.45 Ga, or younger, tectonites. Previous studies have found that Paleoproterozoic shear zones in the Manzano Mountains of New Mexico may have been reactivates. Other ultramylonites in areas, away from the center of Picuris-age deformation in the Picuris Mountains, such as in the Cimmaron Range, remain undated. This study will date in-hand samples from shear zones in the Cimmaron Range and Manzano Mountains at the New Mexico Geochronology Lab to test the sensitivity of this methodology. This methodology will also be applied more regionally to an important tectonic boundary between the Mojave and Yavapai provinces that is present in the Lower Granite Gorge of the Western Grand Canyon where discrete myloniteultramylonite zones, some with pseudotachylyte, are embedded within the ~13-km-wide higher temperature Gneiss Canyon shear zone. For the Lower Granite Gorge shear zones, we plan to integrate U-Th-Pb monazite and xenotime in-situ geochronology to help parse out high temperature versus low temperature deformation. Using these combined field laboratories, the nature and timing of regional shear zone reactivation and this 40 Ar/ 39 Ar methodology will be tested.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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 source (direct Gemma or distilled Codex), 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".