Two isotopic mixing lines in Martinique Island: The effect of ridge subduction
Bibliographic record
Abstract
The Lesser Antilles arc presents an unusually wide range of chemical and isotopic compositions compared to other arcs. Due to the subduction of a buoyant ridge the northern part of the arc displays two branches with distinct ages. In contrast, both periods of volcanic activity are superimposed in the southern part. With its central position, Martinique, where both northern branches merge, is the island with the most complete history of the arc. Old and recent arc volcanics, together with intermediate arc products, outcrop in this Island. In addition, Martinique lavas cover most of the isotopic variability of the arc. The aim of this study is (1) to constrain the source of volcanics in Martinique, (2) to explain the large chemical and isotopic variability in the island itself and along the arc. We measured major and trace elements on ~ 100 dated samples carefully chosen to cover all volcanic phases of Martinique, and Pb and Sr isotopic ratios on a selection of 30 samples. Our isotopic results cover most of the range of Lesser Antilles volcanics from fairly unradiogenic rocks (Pb/Pb ~ 19 and Sr/Sr ~ 0.7037) to highly radiogenic rocks with Pb/Pb ~ 20 or Sr/Sr over 0.710. Samples define two mixing lines in Pb and Sr isotopic spaces: one for the old and intermediate arcs (25Ma to 7Ma) and the other for the recent arc volcanics (5.5Ma to present). The two lines have different unradiogenic (mantle) and enriched (subducted sediments) end-members. The old arc results of the contamination of a mantle with high Sr/Sr (~ 0.7037) and relatively low Pb/Pb (37.95) by less than 0.1% of sediments (Pb/Pb > 39.87). The intermediate arc is produced by the same end-members but with a sediment contribution of 0.1 to 6%. In contrast, the recent arc is produced by contamination of a different mantle (higher Pb/Pb ≈ 38.1 but Sr/Sr similar to the older volcanics) by 0.1 to 5% sediments with less radiogenic Pb isotopic compositions (Pb/Pb ~ 39.52). The origin of the isotopic range in lavas can be found in variable sediment input but more importantly in a sudden switch in the composition of both the mantle source and the subducted sediments. We suggest that the switch is related to the ridge subduction event that shifted the northern part of the arc to the west and changed the slab dip. Coupled cation and O isotope exchange in alkali feldspar T. LABOTKA*, D. COLE AND M. FAYEK Dept. of Earth and Planetary Sciences, University of Tennessee, Knoxville TN 37996 (*correspondence: tlabotka@utk.edu) Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 (coledr@ornl.gov) Department of Geological Sciences, University of Manitoba, Winnipeg MB (fayek@cc.umanitoba.ca)
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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) | 0.006 | 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".