Characterizing some major Archean faults at depth in the Superior craton, North America
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Bibliographic record
Abstract
Abstract. The geometry of ancient (2.75–2.65 Ga) faults at depth can only be mapped in detail by high-resolution geophysical surveys such as seismic reflection profiling. Recent deep (35–48 km) reflection profiles acquired throughout the Archean southern Superior craton of North America provided such data with which to map some major shear zones in 3D, many of which are associated with significant orogenic gold or volcanogenic massive sulfide (VMS) deposits. Most faults are (re-)interpreted as low-angle (<35°) thrusts; a few appear as sub-vertically (>75°) aligned truncations of prominent reflectors. Asymmetry of reflectors suggests that the sub-vertical faults may have originated as 2.75–2.70 Ga syn-volcanic leaky transform faults. We relate thrust structures primarily to the dominant phase of folding and horizontal shortening strain that occurred at 2.72–2.66 Ga during regional crustal deformation, mineralization, and peak metamorphism, associated with terrane accretion. Palinspastic restoration near Timmins, Ontario, indicates 40 km of horizontal shortening. Previous mapping indicates that deformation after this orogenic shortening event resulted in modest lateral movement. Coincident magnetotelluric (MT) surveys indicate that pervasive conductive minerals, such as graphite/carbon and sulfide, exist within the mid-crust and in near-vertical channels within the more brittle and resistive upper crust. Many such channels, but not all, coincide with fault zones and mineral deposits. Palinspastic and paleomagnetic-based reconstructions suggest many faults had multiple periods of activity with evolving vertical to horizontal offsets. Some prominent faults appear paired, partitioning normal and oblique strains on vertical shear zones and dipping thrust zones, respectively.
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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 | 0.001 |
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 it