Middle Cambrian convergence at the southwestern Baltica margin, Holy Cross Mts., Poland, and its significance for reconstructions of early Gondwana
Bibliographic record
Abstract
• U-Pb detrital zircon geochronology and Lu-Hf zircon isotopes. • 40 Ar/ 39 Ar single grain fusion white mica geochronology. • Ediacaran-Cambrian paleogeography of the south-west Baltica margin. The western periphery of Baltica has traditionally been viewed as a passive continental margin formed during the fragmentation of Rodinia and the opening of the Iapetus and Tornquist Oceans. This view is supported by the Volyn Large Igneous Province (VLIP) of Ediacaran age in Eastern Europe, which may be associated with break-up and evolution of the Tornquist Ocean. However, in western Ukraine, the sedimentary succession overlying the VLIP contains latest Ediacaran to early Cambrian detrital zircon with mixed ε Hf ( t ) values that can be interpreted to reflect deposition in a convergent margin setting with input from a continental volcanic arc. To investigate the potential convergent tectonic setting along SW Baltica during the Ediacaran to Cambrian transition, we conducted research in the Holy Cross Mts. (HCM), Poland. Here, tightly folded, and low-grade metamorphosed slates are unconformably overlain by Lower Ordovician (Tremadocian) sedimentary rocks. We applied 40 Ar/ 39 Ar geochronology on white mica defining cleavage in lower Cambrian rocks and U-Pb geochronology on detrital zircons to constrain the timing of the deformation. Our samples show similar populations of detrital zircons, with affinities to regions within or on the outskirts of Baltica. For all Cambrian samples, the calculated maximum depositional age is close to their stratigraphic age, suggesting rapid deposition in an active tectonic setting. The ε Hf ( t ) values range from −18 to +12, indicating significant mixing of mantle-derived magmas with mature crustal material typical of continental magmatic arc systems. Single-grain fusion 40 Ar/ 39 Ar geochronology on white mica yielded two populations of weighted average ages of 537 ± 1 Ma and 510 ± 4.4 Ma, interpreted as a detrital white mica population and the maximum approximation of the age of post-depositional early to middle Cambrian deformation, respectively. The similarities in zircon populations and isotopic compositions between Cambrian sediments of the HCM and those from Ukraine, suggest that both areas were sourced from a continental arc on the Baltica margin, above a subduction zone consuming Neoproterozoic Mirovoi Ocean crust. This arc is likely an equivalent to the Cadomian Arc on the opposite side of the ocean.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".