Metasomatism of oceanic gabbros by late stage melts and hydrothermal fluids: Evidence from the rare earth element composition of amphiboles
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
We report new compositional and textural observations on amphiboles hosted in oceanic gabbros recovered from the slow spreading Mid‐Atlantic (MARK area) and Southwest Indian (Hole 735B) ridges and the fast spreading East Pacific Rise (Hess Deep) in an effort to find a set of reliable criteria that unequivocally distinguishes magmatic from hydrothermal amphibole. We find that there is no simple set of criteria that may be applied to distinguish between these parageneses. Rather, it is necessary to assess both a magmatic and hydrothermal origin for all amphibole grains in order to establish appropriate criteria for a particular sample suite. The rare earth element (REE) content of ∼75% of our amphibole grains may be accounted for by crystallization from residual melts; some of these melts were enriched in the light rare earth elements by the crystallization of apatite and/or amphibole. Of significance, only a small subset of these grains crystallized at magmatic temperatures (>825°C). We conclude that the grains that equilibrated at lower temperatures were initially magmatic but that their major elements were reset during subsolidus, hydrothermal alteration, and deformation. This decoupling of the major and rare earth elements was most prevalent in the Hess Deep and MARK suites, both of which were tectonically exhumed at amphibolite to greenschist facies conditions. The remaining REE data identify hydrothermal amphibole that formed by mineral‐scale reactions involving clinopyroxene, fluids, and ± plagioclase at subsolidus conditions. Evaluation of fluids in equilibrium with amphibole shows that deep hydrothermal fluids are unlike those venting at the seafloor in terms of REE contents and/or patterns.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 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) | 0.002 | 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 it