U-Pb geochronology and origin of granitoid rocks in the Thetford Mines ophiolite, Canadian Appalachians
Bibliographic record
Abstract
Research Article| June 01, 2000 U-Pb geochronology and origin of granitoid rocks in the Thetford Mines ophiolite, Canadian Appalachians J. Whitehead; J. Whitehead 1Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada Search for other works by this author on: GSW Google Scholar G.R. Dunning; G.R. Dunning 2Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X5, Canada Search for other works by this author on: GSW Google Scholar J.G. Spray J.G. Spray 1Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information J. Whitehead 1Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada G.R. Dunning 2Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X5, Canada J.G. Spray 1Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada Publisher: Geological Society of America Received: 05 Feb 1999 Revision Received: 10 Aug 1999 Accepted: 05 Oct 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (6): 915–928. https://doi.org/10.1130/0016-7606(2000)112<915:UGAOOG>2.0.CO;2 Article history Received: 05 Feb 1999 Revision Received: 10 Aug 1999 Accepted: 05 Oct 1999 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation J. Whitehead, G.R. Dunning, J.G. Spray; U-Pb geochronology and origin of granitoid rocks in the Thetford Mines ophiolite, Canadian Appalachians. GSA Bulletin 2000;; 112 (6): 915–928. doi: https://doi.org/10.1130/0016-7606(2000)112<915:UGAOOG>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We integrate new and existing age data from ophiolite and subophiolite rocks in the Thetford Mines region, Québec Appalachians, to determine the timing of: (1) oceanic crust formation; (2) oceanic decoupling; (3) ophiolite emplacement onto the continent, and; (4) postemplacement Taconic orogenesis. Few ophiolites possess high-precision temporal data for all these events. This allows us to develop models to explain the origin of emplacement-related granitoids that have intruded the ophiolite.U-Pb zircon ages have been determined for four samples from the Thetford Mines ophiolite. Oceanic plagiogranite from the Lac de l'Est region of the Thetford massif yields an age of 480 ± 2 Ma. This age is identical to that of the adjacent Mont Ham massif thrust sheet (478 +3/−2 Ma), suggesting a close temporal and spatial association of these two units in the source oceanic domain.Two peridotite-hosted granitoid samples yield crystallization ages of 470 +5/−3 Ma and 469 ± 4 Ma. A Precambrian inherited zircon component is also present in one sample. These granitoids are strongly peraluminous, contain abundant inherited zircon, exhibit variable but high 87Sr/86Sr initial ratios, and low 208Pb/206Pb ratios in igneous zircon, which suggest that they were derived by partial melting of Laurentian margin sedimentary rocks. The ages indicate that the ophiolite was thrust over the Laurentian margin within 1–17 m.y. of oceanic crustal crystallization and that these obduction-related granites were generated during a period of <10 m.y.Shear heating calculations indicate that shearing can generate the peridotite-hosted granitoid melts and their observed contact-zone mineralogies under specific conditions, although margin sedimentary rock melting in response to west-dipping subduction-related arc magmatism cannot be excluded. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.005 | 0.006 |
| Science and technology studies | 0.004 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 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".