Late Miocene magmatic activity in the Attic-Cycladic Belt of the Aegean (Lavrion, SE Attica, Greece): implications for the geodynamic evolution and timing of ore deposition
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Bibliographic record
Abstract
Abstract Numerous post-metamorphic Miocene granitoids occur in the area of Lavrion, SE Attica, at the western end of the Attic-Cycladic Belt of the Aegean. U–Pb ion microprobe-dating (SHRIMP) of zircon from a granitoid sill in the hanging-wall of a regional detachment fault reveals two distinct ages: (1) 11.93 ± 0.41 Ma, obtained from inherited zircon cores with metamorphic characteristics (homogeneous cathodoluminescence, low Th/U ratios) and granulite-type (round/resorbed) morphology. This age is interpreted as the time of a likely granulite-facies metamorphism of the precursor rock. (2) 8.34 ± 0.20 Ma, obtained by oscillatory zoned zircon domains with cathodoluminescence and Th/U characteristics typical for magmatic origin. This age is interpreted as the crystallization time of the granitoid sills. Although a granulite-facies metamorphic event has not been recognized so far for rocks of the Attic-Cycladic Belt, it seems to be the most plausible hypothesis to explain both the zircon systematics and age results. This hypothesis is consistent with an extensional regime predominating in the Aegean from Late Miocene times onwards. A possible granulite-facies metamorphism can be related to magmatic underplating at the initial stages of extension, setting an upper age of c. 12 Ma for the operation of the detachment fault. The 8.34 ± 0.20 Ma zircon crystallization age is, statistically, marginally different to a previous K–Ar feldspar date of hornblende-bearing dykes (9.4 ± 0.3 Ma) and identical to a 8.27 ± 0.11 Ma K–Ar biotite date of the main granitoid stock in the area, thus being generally consistent with prior age constraints from the region. Operation of the detachment fault in the Lavrion area is therefore bracketed between c. 11.9 Ma and at least 8.3 Ma. This time range is in line with the time of operation of detachment faults suggested previously for the Cycladic islands. Carbonate-hosted replacement-type massive sulphide Pb–Zn–Ag ores are spatially associated with the detachment fault and related extensional structures in the Basal Unit. Therefore, these Pb–Zn–Ag ores probably also formed within the above time span of c. 11.9 to at least 8.3 Ma. U–Pb ion microprobe (SHRIMP) dating of zircon from an orthogneiss within the metaclastic subunit of the Basal Unit in Lavrion yielded a protolith age of 240 ±4 Ma, consistent with ages of Triassic volcanism elsewhere in Greece.
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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) | 0.000 | 0.000 |
Machine scores (provisional)
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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