Abstract, Institute of Lake Superior Geology Conference in Thunder Bay, 2012 Anatomy of a Mesoarchean Batholith
Bibliographic record
Abstract
The North Caribou greenstone belt (NCGB) lies in the North Caribou Terrane (NCT) of the Superior Province at the northeastern boundary of the North Caribou Core and the Island Lake Domain (Stott et al. 2010). The NCGB hosts the Musselwhite gold mine, a banded-ironformation-hosted orogenic load gold deposit, and structural controls on the deposit have been linked to intrusions along the margins of the NCGB (Stott and Biczok 2010). The most prominent of these intrusions is the North Caribou Batholith (NCB), which forms the southern and western boundaries of the west-central half of the NCGB. The contact of the NCB with the greenstone belt is marked by a crescent of low magnetic susceptibility relative to the centre of the NCB, and this has been interpreted by Stott and Biczok (2010) as a “crescent pluton,” like those found elsewhere in the Superior Province. These crescent plutons intrude along the contact of greenstone belts and older gneissic terranes and impose a strain aureole on the less-competent greenstone belts, causing them to form arcuate shapes. Since the margin of the NCB conforms to the structural and geometric constraints of crescent plutons, this area has been dubbed the North Caribou Pluton (NCP). This interpretation prompted an investigation of the NCP to determine if this pluton is a discrete, younger intrusion. New U-Pb ages from zircon and titanite, along with whole rock and zircon geochemistry, and amphibole and plagioclase thermobarometry illuminate the evolution and relationship between the NCP and the rest of the NCB. Rocks in the NCB range from tonalites to granites and have a wide variety of textures and compositions. Textures throughout the NCB include enclaves of isotropic, equigranular, weaklydeformed granitoids, strongly foliated and lineated gniesses, and migmatites. Some of the migmatites are partially-melted amphibolites, which occur near the northern margin of the intrusive complex, but there are also granitoids with schlieren and other textures suggesting either partial melting, melt segregation, or magma mixing. Late K-feldspar-rich pegmatites occur around the margins of the NCB, in both the NCP and the central batholith. U-Pb geochronology on zircon and titanite was conducted using LA-ICP-MS methods at the University of New Brunswick. Single zircon ages range from 3132-2693 Ma, with a majority of rock ages falling between 2870 Ma and 2830 Ma. These ages are consistent with those reported by previous workers in the NCB and elsewhere in the NCT (e.g. Biczok et al. 2012). Ages from titanite are similar to the younger zircon populations. In the central NCB, titanite ages from 2798-2791 Ma are found in rocks with zircon ages of 2834-2833 Ma. This 30 My difference could represent cooing through the different closure temperatures of titanite and zircon (500 and 900 oC, respectively). The titanite in the NCP, however, record ages between 2766 Ma and 2748 Ma, with a ~100 My difference between the zircon and titanite ages. As the titanites from these rocks are roughly aligned with the foliation, and the ages match zircon ages in younger intrusions surrounding the NCGB, these ages likely reflect later tectonism. To further assess the relationship between the rocks in the NCP and those in the central NCB, depth and temperature of emplacement was estimated using the plagioclase-amphibole thermobarometer and the Ti-in-zircon thermometer. Titanium concentrations in zircon were
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.000 | 0.003 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.159 | 0.026 |
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".