Geological reconnaissance of Rencontre East: stratigraphic context and petrochemical evolution of volcanic rocks from the Long Harbour Group and Rencontre Formation, Avalon Zone, Newfoundland
Bibliographic record
Abstract
Bimodal volcanic and cogenetic volcano-sedimentary rocks of the Long Harbour Group and Rencontre Formation (Fortune Group), northern Fortune Bay, are among the youngest Precambrian rocks of the Avalon Zone in Newfoundland. Previous U–Pb dating of rhyolites from the base and top of the Long Harbour Group indicate an age spanning ca. 570–550 Ma. The lowermost Belle Bay Formation is conformably overlain by the Andersons Cove and Mooring Cove formations, each of which is locally unconformably overlain by the Rencontre Formation. Microspherulitic, flow-banded rhyolite from the upper Belle Bay Formation is rare-earth-element (REE) enriched, and is an A-type, alkali rhyolite. Mafic volcanic flows, bombs and breccias in the overlying Mooring Cove and Rencontre formations are subdivided into four petrochemical suites. Basalts of the stratigraphically lowest, suite 1, have plagioclase phenocrysts with honeycomb-textured cores and sieve-textured rims, reflecting complex petrogenetic histories related to repeated magmatic replenishment. They have low Mg#’s, Ni, Co and V, and high SiO2 and Zr contents, negatively sloped multi-element patterns and prominent negative Nb anomalies. They are similar to mature magmatic arc rocks but are more heavy-REE-enriched and lack Zr and Hf troughs characteristic of calc-alkaline basalts. Suites 2 and 3 are tholeiitic basalts, have iron-enrichment trends, and flatter multi-element patterns relative to suite 1 basalts. Suite 2 rocks contain primary clinopyroxene, have the flattest multi-element patterns (lowest La/Yb and La/Sm ratios), and contain higher Mg#, Ni, Cr, V and Co and lower SiO2, Zr and Th than suite 3 rocks. Suite 2 rocks are the most primitive and originated from a more NMORB-like, albeit enriched source. Suite 3 basalts, intermediate between those of suites 1 and 2, have higher light-REE contents, higher La/Yb ratios, more variable Th and Nb, and originated from a more EMORB-like source than suite 2. Suite 4 basalts have relatively smooth negative multi-element patterns, and high TiO2 and P2O5 relative to the other three suites. They are alkali, OIB-like basalts, and originated from low-degree partial melting of a deeper source than the other basalt suites. Petrochemical investigation of the basalts indicates a progression from calc-alkaline, through transitional basaltic compositions ranging from NMORB-like to EMORB-like, to alkaline. This temporal change reflects progressive deepening of the magmatic source, resulting from late Ediacaran extension of an inherited lower Ediacaran volcanic arc. The decreasing lithospheric input and increasing source depths through time reflect the waning of this extensional pulse. Subsequent extension continued episodically, possibly evolving to rifting by Terreneuvian to Miaolingian times.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.005 | 0.017 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".