Regional Deformation of the Southern Puna Plateau, Central Andes, Recorded by Basin Evolution and Bedrock Exhumation History
Bibliographic record
Abstract
The regional deformation history of the southern Puna Plateau remains poorly constrained but is key to understanding the growth and dynamics of the central Andes, an important example of orogeny along a non-collisional plate boundary. Several lines of evidence lead us to propose that the southern Puna Plateau was occupied by an uninterrupted sedimentary basin during the late Eocene to early Oligocene (~38-28 Ma). First, oldest strata in the Antofagasta de la Sierra region (SW Puna) and the Pasto Ventura region (SE Puna) both contain little volcanic material, suggesting they predate the most recent arc activity at ~28 Ma. Second, detrital zircons from the Antofagasta de la Sierra region yield youngest U-Pb ages of ~39 Ma and detrital apatites from the Pasto Ventura region yield youngest fission-track ages of ~38 Ma, giving a maximum depositional age. Third, provenance analysis reveals a single, western source for the Antofagasta de la Sierra region (SW Puna) and dual, eastern and western sources for the Pasto Ventura region (SE Puna), supporting the presence of a regional basin. This regional basin was disrupted and compartmentalized by uplift of ~N-S trending bedrock ranges starting as early as in late Oligocene time. Bedrock samples from the eastern foot of the Sierra de Calalaste (SW Puna) yield an apatite (U-Th-Sm)/He age of 19.92.0 Ma, consistent with modeled apatite fission-track data that show onset of exhumation at ~25-20 Ma. Modeling of apatite fission-track and (U-Th-Sm)/He data shows that the Sierra Laguna Blanca (SE Puna) experienced exhumation at ~15-10 Ma, the youngest bedrock exhumation documented in the plateau region, implying that deformation and erosion of basement-bounding structures continued into the middle Miocene. We suggest that the post-late Eocene regional deformation history of the southern Puna Plateau documents an important dynamic shift from flexure-controlled foreland dynamics to flexure-limited broken foreland dynamics during the Oligocene.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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".