Oceanic spreading center–generated basaltic crust and associated sulfidic and carbonate-rich hydrothermal deposits in the Archean (ca. 3 Ga), North Spirit Lake greenstone belt, Ontario, Canada
Bibliographic record
Abstract
Research Article| November 01, 2009 Oceanic spreading center–generated basaltic crust and associated sulfidic and carbonate-rich hydrothermal deposits in the Archean (ca. 3 Ga), North Spirit Lake greenstone belt, Ontario, Canada H.W. Nesbitt; H.W. Nesbitt † 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada †E-mail: hwn@uwo.ca Search for other works by this author on: GSW Google Scholar G.M. Young; G.M. Young 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar S.A. Bosman; S.A. Bosman 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar F.J. Longstaffe F.J. Longstaffe 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information H.W. Nesbitt † 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada G.M. Young 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada S.A. Bosman 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada F.J. Longstaffe 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada †E-mail: hwn@uwo.ca Publisher: Geological Society of America Received: 23 Jun 2008 Revision Received: 05 Nov 2008 Accepted: 05 Nov 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2009 Geological Society of America GSA Bulletin (2009) 121 (11-12): 1562–1569. https://doi.org/10.1130/B26496.1 Article history Received: 23 Jun 2008 Revision Received: 05 Nov 2008 Accepted: 05 Nov 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation H.W. Nesbitt, G.M. Young, S.A. Bosman, F.J. Longstaffe; Oceanic spreading center–generated basaltic crust and associated sulfidic and carbonate-rich hydrothermal deposits in the Archean (ca. 3 Ga), North Spirit Lake greenstone belt, Ontario, Canada. GSA Bulletin 2009;; 121 (11-12): 1562–1569. doi: https://doi.org/10.1130/B26496.1 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 Detailed mapping of a portion of the North Spirit Lake greenstone belt reveals a basal basaltic volcanic unit (ca. 3 Ga) with a komatiitic component and strong major and trace element geochemical affinity with typical mid-ocean ridge basalts (e.g., N-MORB). The overlying transitional unit includes basaltic tuffs, which have close geochemical affinity to the underlying basalts, and to N-MORB. Interbedded with and overlying the tuffs is a thin, laterally continuous sulfide-rich unit with chert interbeds, which is in turn overlain by interbedded carbonate, chert, and iron-rich sedimentary rocks. The chemical sedimentary rocks of the transitional unit display rare-earth element (REE) patterns and positive Eu anomalies consistent with derivation from fluids associated with submarine hydrothermal vent fields. The sulfide unit is interpreted to represent proximal hydrothermal vent deposits derived from black smoker activity near a spreading center. The overlying carbonate and chert mounds and beds are interpreted as hydrothermal deposits formed at lower temperatures in a more distal setting relative to the spreading center. The carbonate deposits may have formed in an environment analogous to that of the Lost City hydrothermal field (Kelley et al., 2001), where abundant chimneys, dendrites, and beds of carbonate are produced ~15 km from the mid-Atlantic rift axis. The basal volcanic unit consequently is interpreted as oceanfloor basalts formed at an Archean spreading center, with the basaltic tuffs representing the last volcanic emanations, and with the chemical sediments representing hydrothermal-vents deposits both proximal and distal to the spreading center. The capping siliciclastic unit likely is part of an accretionary wedge, possibly representing ocean closure after a protracted seafloor spreading episode. The sedimentary rocks were derived, in part, from a weathered tonalite-trondhjemite-granodiorite source. The supracrustal rocks of the North Spirit Lake greenstone belt provide an unusually clear window into some tectonic activity on the primitive Earth, including evidence for the existence of ocean-floor basalts, proximal and distal hydrothermal activity, and possibly a protracted cycle of ocean opening and destruction. 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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 | 0.003 | 0.006 |
| 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) | 0.008 | 0.001 |
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".