Geology, geochronology, and geochemistry of the Miocene–Pliocene Ancestral Cascades arc, northern Sierra Nevada, California and Nevada: The roles of the upper mantle, subducting slab, and the Sierra Nevada lithosphere
Bibliographic record
Abstract
The assemblage of ca. 28-3 Ma volcanic rocks exposed in the Lake Tahoe-Reno region of the northern Sierra Nevada, United States, is interpreted to be part of the Ancestral Cascades volcanic arc. The volcanic rocks are commonly highly porphyritic, including abundant plagioclase with clinopyroxene, amphibole, and rare biotite, and range from basaltic andesite to dacite in composition. Less common are poorly phyric, olivine- and clinopyroxene-bearing basalts and basaltic andesites. Porphyritic lavas dominate composite volcanic centers, whereas the poorly phyric lavas form isolated cinder cone and lava flow complexes. Tahoe-Reno arc lavas are calc-alkaline, enriched in the large ion lithophile elements but depleted in Nb and Ta relative to the light rare earth elements, and have highly variable radiogenic isotopic compositions. Compared to the modern south Cascade arc, Tahoe-Reno region basalts are enriched in the light rare earth and large ion lithophile elements and have higher 87Sr/86Sr and lower 143Nd/144Nd that are consistent with an old, subduction-modified lithospheric mantle source, such as that proposed for lavas of the Western Great Basin. Melting of the lithospheric mantle may be enhanced by fluid flux from the subducting slab if the Juan de Fuca slab dip is shallow. Andesites and dacites evolved from basaltic magmas by a combination of fractional crystallization and assimilation of lower crustal melts. Available geochronological data indicate that the westward sweep of Cenozoic volcanism through Nevada was associated with steepening of the slab dip, but the dip angle was lower during Miocene-Pliocene arc volcanism than it is today beneath the modern south Cascades. © 2008 Geological Society of America.
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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 | 0.001 | 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) | 0.001 | 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".