Age and origin of authigenic K-feldspar in uppermost Precambrian rocks in the North American Midcontinent
Bibliographic record
Abstract
Research Article| April 01, 2003 Age and origin of authigenic K-feldspar in uppermost Precambrian rocks in the North American Midcontinent Junzhe Liu; Junzhe Liu 1Publication Division, American Chemical Society, 1155 16 Street N.W., Washington, D.C. 20036, USA Search for other works by this author on: GSW Google Scholar Richard L. Hay; Richard L. Hay 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Alan Deino; Alan Deino 3Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA Search for other works by this author on: GSW Google Scholar T.K. Kyser T.K. Kyser 4Department of Geological Sciences, Queens University, KL7 3N6 Ontario, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (2003) 115 (4): 422–433. https://doi.org/10.1130/0016-7606(2003)115<0422:AAOOAK>2.0.CO;2 Article history received: 05 Mar 2001 rev-recd: 30 Jul 2002 accepted: 01 Oct 2002 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Junzhe Liu, Richard L. Hay, Alan Deino, T.K. Kyser; Age and origin of authigenic K-feldspar in uppermost Precambrian rocks in the North American Midcontinent. GSA Bulletin 2003;; 115 (4): 422–433. doi: https://doi.org/10.1130/0016-7606(2003)115<0422:AAOOAK>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 Authigenic K-feldspar occurs widely in the North American Midcontinent in an alteration profile developed on uppermost Precambrian rocks. In the study areas of west-central Wisconsin and southeast Missouri, the alteration profiles are kaolinitic and interpreted as former saprolite formed by weathering prior to deposition of Upper Cambrian sandstone. K-feldspar in granitic alteration profiles of west-central Wisconsin occurs either as coarse-grained red crystals and veins replacing kaolinite or as overgrowths and fine-grained crystals in pore space of partly altered granite. In a granitic profile of southeast Missouri, K-feldspar replaces primary feldspar and probably kaolinite. In a diabasic profile, K-feldspar is disseminated and forms veins in saprolite, and it replaces the outer 3–5 cm of core-stones.Dating was conducted with the 40Ar/39Ar method using incremental heating. Observed spectral types are plateaus (6), near plateaus (3), undulatory (14), and stair-step (5). Undulatory patterns are attributed chiefly to recoil, and integrated ages of these are usually within the error of plateau ages where present, indicating a balanced enrichment/depletion of 39Ar due to recoil. Stair-step spectra are attributed to severe recoil.Plateau 40Ar/39Ar ages of 446–427 Ma (Late Ordovician and Silurian) were obtained from coarse-grained K-feldspar replacing kaolinite in Wisconsin, suggesting a duration of the alteration episode of ∼19 m.y. However, potentially accurate nonplateau age measurements (integrated and near-plateau ages) suggest that alteration continued for a considerable time thereafter, possibly to ca. 399–395 Ma (Early Devonian). Integrated 40Ar/39Ar ages of ca. 362 Ma (Late Devonian and/or Early Mississippian) were obtained from fine-grained K-feldspar. Plateau ages of ca. 450 (Late Ordovician) were obtained from K-feldspar of the diabase profile in Missouri; duration of K-feldspar alteration in this region was at least ∼16 m.y. and may have been as long as ∼52 m.y.The Late Devonian–Early Mississippian K-feldspar formed at temperatures of ∼100 °C from saline fluid averaging ∼10% NaCl equivalent and having a δ18O value of ∼3.5‰. This brine may have originated from the Michigan Basin, East-Central Iowa Basin, and/or the Illinois Basin, coincident with the Acadian orogeny.The Middle Ordovician to Early Devonian dates of K-feldspar do not generally correspond in time with orogenic activity at the continental margin, and the mechanism(s) for forming the K-feldspar are uncertain. Fluid sources proposed for some or all of the K-feldspar include the Michigan Basin, Taconic mountains, Reelfoot Rift, Illinois Basin, and Midcontinent epeiric seas. Middle Ordovician K-feldspar of Missouri very likely formed at elevated temperatures, but evidence of fluid temperature is lacking for other pre–Late Devonian K-feldspar. 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 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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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 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".