Temporal evolution of a deeply eroded orogen: the Nagssugtoqidian Orogen, West Greenland
Bibliographic record
Abstract
The east-northeast-trending Paleoproterozoic Nagssugtoqidian Orogen of West Greenland records the response of deep crust to collision of the North Atlantic craton and a lesser known cratonic mass to the north. This paper presents conventional UPb ages of documented magmatic and thermotectonic events within this orogen, thus providing a precise time frame for its development and offering a test of previous spatial and temporal correlations with segments of the Trans-Hudson Orogen of northern Labrador and Quebec. Convergence of the two cratons culminated in a collision that commenced after 1873 +7 4 Ma, the crystallization age of the youngest known pre-Nagssugtoqidian, subduction-related intrusion. Earliest collisional deformation was thrust dominated (west-northwest vergent) and caused thickening and consequent heating to peak temperatures by ca. 1850 Ma. Subsequent north-south shortening at elevated temperatures was accommodated by a fold-dominated style of deformation dated at 1825 ± 1 Ma. Between 1821 and 1778 Ma, temperatures remained sufficiently high to generate pegmatites, metamorphic zircon, and titanite, but no major, penetrative structures are known to have formed in this interval. Further shortening between 1779 ± 6 and 1774 ± 6 Ma exploited preexisting fabrics in steep F 3 fold limbs to form discrete, east-northeast west-southwest-oriented, sinistral steep belts that are not important crustal boundaries. One of these late, steep belts is cut by 17721761 Ma pegmatites, indicating that deformation was waning by this time. Slow cooling followed the late shearing, with rutile closing in the central Nagssugtoqidian Orogen as late as 1676 ± 10 Ma. The timing of tectonic events in the Nagssugtoqidian Orogen is indistinguishable from that of the QuebecBaffin and Torngat segments of the Trans-Hudson Orogen of northeastern Laurentia. Accepting an intercratonic setting for the Nagssugtoqidian Orogen, this new data require that the QuebecBaffin, Torngat, and Nagssugtoqidian orogens meet in a triple junction offshore. This geometry implies a genetic link between the Rinkian and Nagssugtoqidian belts of West Greenland, thereby defining a middle- to deep-crustal collisional belt more than 900 km wide.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.026 | 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".