Chronology, chemistry, and origin of trachytes from Hualalai Volcano, Hawaii
Bibliographic record
Abstract
Hualalai Volcano is unique among Hawaiian volcanoes in that it possesses a relatively high proportion of evolved, trachytic lavas that were erupted at the beginning of the alkalic, postshield phase of volcanism. These evolved lavas yield insights into magma sources, magma supply rates, and the evolution of the subvolcanic magmatic plumbing system at this time. Trachyte lavas are exposed at the Puu Waawaa pumice dome and Puu Anahulu flow, as blocks in maars on the south flank of the volcano, and as flows in water wells drilled on the west flank of Hualalai. New 40Ar/39Ar dates show that the Puu Waawaa and Puu Anahulu complex is 114 ka, a block from the Waha Pele maar is 103 ka, and water well trachytes range from 107 to 92 ka in age, indicating a range for trachyte volcanism of 20 ka. Nd and Pb isotopic compositions overlap with younger alkalic basalts from Hualalai but are distinct from Hualalai tholeiitic basalts and Pacific mid‐ocean ridge basalts, linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas. Both Sr and O isotopic ratios are higher in the trachytes than in Hualalai alkalic lavas, which is best explained by reaction with, or assimilation of, altered Hualalai shield basalts at shallow depth. Major, trace element, and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a Puu Anahulu parent. The short time gap between the end of tholeiitic volcanism (<133 ka) and the onset of trachytic, alkalic volcanism and the lack of deep‐origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow (<7 km) depth. Whereas Mauna Kea and Kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage, postshield magma intrusion rates at Hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions. Subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular, allowing some trachytes to evolve independently from others.
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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 | 0.003 | 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) | 0.002 | 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".