Magma Recharge and Crystal Mush Rejuvenation Associated with Early Post-collapse Upper Basin Member Rhyolites, Yellowstone Caldera, Wyoming
Bibliographic record
Abstract
The Upper Basin Member rhyolites are the oldest known post-collapse rhyolites of the third Yellowstone caldera. They were erupted near the caldera's resurgent domes between 516 ± 7 and 473 ± 9 ka and at 257 ± 13 ka. An unusual characteristic is their low δ18O signature. Few data are available on their mineralogy and glass geochemistry, and this study fills an important gap in understanding their petrogenesis. We report new mineralogical observations and plagioclase, whole-rock and glass compositional data. Based on our observations, we describe a new lava flow for which we propose the name East Biscuit Basin flow. This unit is a quartz- and sanidine-free low-silica rhyolite (71–72% SiO2 in the whole-rock) in which the dominant mineral, plagioclase, comprises two populations: (1) small fresh euhedral crystals of An20–48 (average of An31) composition, commonly part of aggregates with pyroxenes and Fe–Ti oxides; (2) large sieve-textured isolated crystals, which are slightly more sodic in composition (An19–34, average of An27). Plagioclase compositions in most other Upper Basin Member rhyolites are similar. The range of compositions for trace elements such as Rb, Th, Y and the rare earth elements is small (e.g. 158–189 ppm Rb, 20–25 ppm Th, 52–63 ppm Y, 60–82 ppm La in the whole-rock), and there is no systematic variation of these elements as a function of SiO2 content or mineralogy. Certain trace element signatures and ratios are specific to each of these rhyolites, allowing us to propose that the Upper Basin Member rhyolites originate from six independent magma batches. The coexistence of the two types of plagioclase and their progressive disappearance in the more evolved rhyolites suggest the following petrogenetic model for each magma batch. A low-δ18O rhyolitic protolith is heated by replenishing magmas, which initiate melting, forming a crystal mush. Replenishment by buoyant silicic magma may enhance melting and cause mixing with the mush material. As a consequence, crystal-poor eruptible magma batches are formed, which contain small, more calcic plagioclase crystals (aggregates) formed during cooling and mixing of the replenishing silicic melt, and larger, lower temperature crystals exhibiting dissolution features inherited from the protolith.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.003 | 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".