Mesozoic crustal melting and metamorphism in the U.S. Cordilleran hinterland: Insights from the Sawtooth metamorphic complex, central Idaho
Bibliographic record
Abstract
In this study, we present whole-rock geochemistry and Sm-Nd data; zircon trace element, U-Pb, and Lu-Hf data; titanite U-Pb dating; and structural analysis of igneous and metasedimentary rocks of the Sawtooth metamorphic complex that provide insight into regional metamorphism, partial melting, and crustal thickening in the Idaho batholith segment of the Cordilleran orogen. Four magmatic events are revealed: (1) pre-tectonic felsic magmatism at ca. 156 Ma, (2) syn-tectonic mafic and felsic magmatism between ca. 100 Ma and ca. 92 Ma, (3) felsic magmatism concurrent with late-stage deformation at ca. 89−84 Ma, and (4) post-tectonic felsic magmatism at ca. 77 Ma. The multiple generations of felsic magmatism include a variety of sedimentary- and igneous-derived granitoids distinguished by zircon trace element compositions (e.g., U/Ce versus Th and Ce/Sm versus Yb/Gd) and were sourced from progressively more evolved crustal components as shown by Lu-Hf and Sm-Nd isotopic data. U-Pb data of metamorphic zircons and titanites from high-grade metasedimentary rocks suggest that regional metamorphism occurred from ca. 100−93 Ma, which was characterized by granulite-facies partial melting and concurrent growth of metamorphic zircons and garnets. The episodic magmatism in the Sawtooth metamorphic complex records pervasive melt migration in a hot, mid-crustal setting at ca. 100‒92 Ma and additional magma ascent in a cool, upper-crustal setting at ca. 77 Ma. The uplift of the Sawtooth metamorphic complex from mid- to upper-crust was likely caused by underthrusting at lower crustal levels coupled with erosion and thinning of the upper crust. This work suggests that the crust of the Cordilleran hinterland in the Idaho batholith region underwent significant thickening from ca. 100‒84 Ma, and a crust of Andean-like thickness was probably achieved by ca. 84 Ma. By ca. 77 Ma, the central Idaho crust started to thin likely due to mid-crustal flow and surface erosion. The new data from the Sawtooth metamorphic complex are consistent with the two major magmatic flare-ups in the Late Jurassic and Late Cretaceous in the U.S. Cordilleran orogen.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 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".