DETRITAL SHOCKED ZIRCON PROVIDES FIRST RADIOMETRIC AGE CONSTRAINT OF <1472 MA FOR THE SANTA FE IMPACT STRUCTURE, NEW MEXICO, USA
Bibliographic record
Abstract
Impact structures are prone to erosion, burial and tectonic deformation. The Santa Fe impact structure in New Mexico contains shatter cones and shocked quartz, but is highly tectonized and eroded; estimates of the impact age (1200-300 Ma) and size (6-13 km) are poorly constrained. Here we report the first occurrence of shock-twinned zircon identified both in modern sediments and bedrock at the Santa Fe impact structure. Zircon {112} twin lamellae are considered diagnostic evidence of shock deformation and have been identified at several impact structures including Vredefort, Sudbury, Ries, Rock Elm, and in lunar impact breccia. A total of 6619 grains from fifteen sediment samples and two rock samples were surveyed; seven shocked grains were identified (7/6619 = 0.1%). One shocked zircon was identified in a biotite schist shatter cone. Five of seven shocked zircon grains were EBSD mapped; three were analyzed with multiple SIMS spots. EBSD mapping revealed {112} deformation twin lamellae in each of the five zircon grains. U-Pb geochronology for three of the shocked zircon grains yield crystallization ages from 1715+/-22 to 1472+/-35 Ma. LA-ICPMS U-Th-Pb analysis of detrital zircon grains from five samples yielded Paleoproterozoic (1800-1600 Ma) and Mesoproterozoic (1500-1300 Ma) ages. We reveal the first confirmed shocked zircon at the Santa Fe structure. Zircon is the third shocked mineral identified at this site, in addition to xenotime and quartz]; the {112} twin lamellae indicate that exposed bedrock may have experienced shock pressures up to ~20 GPa. The 1472+/-35 Ma age determined from a shock-twinned zircon is the first reliable maximum impact age constraint based on analysis of shocked material and extends the window for the Santa Fe impact event into the Mesoproterozoic.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.002 |
| 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".