Evidence for crustal removal, tectonic erosion and flare-ups from the Japanese evolving forearc sediment provenance
Bibliographic record
Abstract
Forearc basins preserve the geologic record relating strictly to arc magmatism. The provenance of forearc sediment can be used to differentiate periods of crustal growth, accretion, and destruction, enhanced magmatism, advancing and retreating subduction slabs, delamination, etc. All these tectonic events systems predict differing degrees of sedimentary reworking of the older forearc units. Additionally, Hf isotopes of zircon can be used to evaluate the degree of continental reworking that occurs in the arc system. In this paper, we evaluate the changes in a long-lived subduction system using detrital zircon U-Pb and Hf data from forearc units in northern Honshu, Japan that span in age from the Silurian Period to the present from the forearc provenance of the Japanese subduction system. Our data demonstrate a series of dominant age peaks (430 ± 20, 360 ± 10, 270 ± 20, 184 ± 12, 112 ± 22, and 7 ± 7 Ma) and a progressive loss of the older zircon populations. Zircon Hf data reveal three discrete shifts that correspond to differing degrees of isotopic enrichment and correlate with changes in the dominant zircon age peaks. Additionally, each temporal isotopic shift is associated with isolation of the older sedimentary packages wherein no detrital zircon from the previous stages are observed in subsequent stages. We propose these shifts provide evidence for rapid shifts in arc tectonics including: magmatic flare-ups, producing the dominant peaks; protracted tectonic erosion progressively removing older sources of zircons reveals; a late Carboniferous event triggering the complete removal of the Precambrian crust; and the Cretaceous melting of the entire Permian arc crust, likely related with the subduction of the mid-oceanic ridge separating the Izanagi and Pacific plates.
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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 | 0.001 | 0.001 |
| 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) | 0.001 | 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 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".