Dating metamorphic processes and identifying 87Sr/86Sr inheritance using volume-coupled Rb/Sr geochronology and geochemistry of in situ white mica: A demonstration with HP/LT rocks from Syros, Greece
Bibliographic record
Abstract
High-pressure/low-temperature rocks from two well-studied outcrops of the Cycladic Blueschist Unit on Syros are used to demonstrate the advantages of volume-coupled 87 Rb/ 87 Sr geochronology and geochemistry of in situ white mica. Single-spot Rb/Sr dates are interpreted based on the microstructural position of white mica combined with its chemical information, and the results are discussed within the tectonic framework of the island. The first outcrop on Katerghaki cape exposes rigid blocks of foliated eclogite within well-foliated blueschist, whereas the second outcrop on Delfini peninsula comprises massive eclogitic blocks, likely of metasomatic origin, hosted within blueschist that are interlayered with white mica schists. The rheological contrasts exhibited in both outcrops preserve (near-)peak HP/LT metamorphism/metasomatism (eclogites) followed by retrogression and deformation in lower P-T conditions (blueschist, micaschist). The white mica in eclogite from both outcrops are in equilibrium with the HP/LT mineral assemblages, do not show chemical zoning nor systematic chemical variations, and yield uniform single-spot Rb/Sr dates. Weighted averages of the Rb/Sr dates are 48.2 ± 3.7 Ma (MSWD: 0.9, n: 34; Katerghaki) and 44.5 ± 3.1 Ma (MSWD: 0.7, n: 28; Delfini), interpreted as (near-)peak HP/LT metamorphism and metasomatism , respectively, overlapping with published garnet Lu Hf and Sm Nd geochronology of the corresponding outcrops. White mica in the Katerghaki blueschist and the Delfini micaschist exhibit significant chemical zoning and correlations of Ti with major and trace elements (Al, Fe , Mg, Rb, Sr, Zn, Ba, Nb). Weighted age averages were calculated from Rb/Sr dates corresponding to high-Ti and low-Ti white mica compositions. The blueschist yields ages of 56.0 ± 10.6 Ma (MSWD: 2.2, n: 20/80) and 36.3 ± 2.1 Ma (MSWD: 0.9, n: 20/80), whereas the micaschist produced ages of 43.7 ± 3.5 Ma (MSWD: 0.5, n: 14/53) and 31.9 ± 2.7 Ma (MSWD: 1.0, n: 13/53), respectively. These results are interpreted to resolve the timing of fluid-mediated isotopic re-equilibration of white mica during deformation and retrogression (low-Ti), and reflect 87 Sr/ 86 Sr inheritance from the earlier HP/LT history (high-Ti). Overall, the results demonstrate that coupling 87 Rb/ 87 Sr geochronology with geochemistry of white mica in situ is advantageous for evaluating Rb/Sr datasets that may possess a single mica population (eclogites) or are affected by 87 Sr/ 86 Sr inheritance (blueschist, micaschist) in order to interpret geologically meaningful ages.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".