The Cambrian volcanic arc terrane: a peri-East European Craton assemblage in the heart of the European Variscan Belt
Bibliographic record
Abstract
Cambrian age volcanic arc-related rocks crop-out in high-grade metamorphic complexes marking the principal Devonian age suture zone in the Bohemian Massif. The age and tectonic setting of these rocks are established from whole-rock geochemical and isotopic data from basic-intermediate rocks transformed to eclogite and granulite, and U-Pb and Lu-Hf isotopic data of detrital zircon in associated meta-sediments. Recent works have established that these rocks can be correlated on the basis of their age and tectonic setting as well as their Variscan metamorphic evolution with allochthonous complexes in NW Iberia, and potentially, the whole European Variscan Belt (Martínez Catalán et al., 2020). Detrital zircon spectra from the high-grade metasediments associated with the Cambrian volcanic arc are superficially similar to the classically interpreted ‘West African signature’ with Neoarchean, Paleoproterozoic and late Neoproterozoic maxima. Nonetheless, limited Cryogenian input and shifting of the late Neoproterozoic maxima into the early Cambrian is in contrast to Variscan autochthonous complexes. Moreover, Lu-Hf isotopic data show important contrasts in the source of the Paleoproterozoic detritus. The Variscan autochthon is charecterised by Paleoproterozoic detritus with negative ɛHfi values indicating reworking of an Archean crust. However, the Paleoproterozoic detritus in the Cambrian arc terrane exhibits mostly positive ɛHfi values indicating a juvenile Paleoproterozoic source. In fact, the data from the Cambrian arc terrane show remarkable similarity to detrital zircon data from early Cambrian sediments on the southern margin of the East European Craton (Paszkowski et al., 2021). These sediments incorporate significant juvenile late Neoproterozoic-early Cambrian detritus from an as yet unidentified volcanic arc and their whole-rock geochemical composition is consistent with immature sediments sourced from intermediate igneous rocks. If true, this correlation suggests that the Cambrian arc terrane is a peri-East European Craton assemblage and necessitates a re-evaluation of the role of the East European Craton within the Variscan Orogeny. Catalán, J. R. M., Collett, S., Schulmann, K., Aleksandrowski, P., and Mazur, S., 2020. Correlation of allochthonous terranes and major tectonostratigraphic domains between NW Iberia and the Bohemian Massif, European Variscan belt. International Journal of Earth Sciences, 109, 1105-1131. Paszkowski, M., Budzyń, B., Mazur, S., Sláma, J., Środoń, J., Millar, I.L., Shumlyanskyy, L., Kędzior, A. and Liivamägi, S., 2021. Detrital zircon U-Pb and Hf constraints on provenance and timing of deposition of the Mesoproterozoic to Cambrian sedimentary cover of the East European Craton, part II: Ukraine. Precambrian Research, 362, 106282.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".