Thermal History of the Bandelier Magmatic System: Evidence for Magmatic Injection and Recharge at 1.61 Ma as Revealed by Cathodoluminescence and Titanium Geothermometry
Bibliographic record
Abstract
The rhyolitic Valles Caldera complex, New Mexico, is one of the type examples of resurgent calderas, and has experienced two well-studied caldera-forming eruptions.The first formed the Lower Bandelier Tuff (LBT) at 1.608 ± 0.010 Ma, and the second emplaced the Upper Bandelier Tuff (UBT) at 1.225 ± 0.008 Ma.During the time between the LBT and UBT, the much smaller-scale Cerro Toledo Rhyolite (CTR) was sporadically erupted.Quartz crystals from these stages of activity were imaged using cathodoluminescence (CL) microscopy, and growth zones in certain quartzes, due to varying Ti content, were revealed.Using a titanium-in-quartz geothermometer, crystallization temperatures were obtained.LBT quartzes are unzoned, with temperatures clustering between 660-715oC when a calculated aTi of 0.4 is applied to the system.These near-solidus temperatures imply that the LBT magma chamber was highly crystalline at one point.However, the low crystal content and the widespread presence of resorption features on LBT crystals require that pervasive melting affected the LBT magma chamber at some point prior to eruption.This melting is hypothesized to result from a hot magmatic injection into the system, with the injection also being a likely trigger of the cataclysmic LBT volcanism.The earliest erupted CTR units contain many zoned quartz crystals.Inner zones are usually rounded and invariably reveal cold (~660-700oC) cores and hot (~750-825oC) rims.We interpret these results as thermal evidence of magmatic recharge, where new magma mixed vigorously with leftover magma, and high-temperature rims crystallized around low-temperature restitic quartz cores.Thermal results for the rest of the CTR record the continuing cooling and evolution of this mixture of magma.These results present an unprecedented glimpse into the thermal history of the Bandelier magma system, as well as strong evidence for the timing and overall importance of magmatic injections in silicic magma systems.
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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) | 0.002 | 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".