Age of the Eastern Kaapvaal mantle: Re-Os isotope data for peridotite xenoliths from the Monastery kimberlite
Bibliographic record
Abstract
Research Article| June 01, 2004 Age of the Eastern Kaapvaal mantle: Re-Os isotope data for peridotite xenoliths from the Monastery kimberlite Richard W. Carlson; Richard W. Carlson Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC, 20015 USA, Phone 202 478-8474, Fax 202 478-8821, e-mail: carlson@dtm.ciw.edu Search for other works by this author on: GSW Google Scholar Rory O. Moore Rory O. Moore Mineral Services Canada, #1300 - 409 Granville Street, Vancouver, B. C. V6C 1T2, Canada, e-mail: rory.moore@mineralservices.com Search for other works by this author on: GSW Google Scholar Author and Article Information Richard W. Carlson Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC, 20015 USA, Phone 202 478-8474, Fax 202 478-8821, e-mail: carlson@dtm.ciw.edu Rory O. Moore Mineral Services Canada, #1300 - 409 Granville Street, Vancouver, B. C. V6C 1T2, Canada, e-mail: rory.moore@mineralservices.com Publisher: Geological Society of South Africa First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2003 Geological Society of South Africa South African Journal of Geology (2004) 107 (1-2): 81–90. https://doi.org/10.2113/107.1-2.81 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard W. Carlson, Rory O. Moore; Age of the Eastern Kaapvaal mantle: Re-Os isotope data for peridotite xenoliths from the Monastery kimberlite. South African Journal of Geology 2004;; 107 (1-2): 81–90. doi: https://doi.org/10.2113/107.1-2.81 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 SocietySouth African Journal of Geology Search Advanced Search Abstract New whole rock chemical and Re-Os isotopic analyses of peridotite xenoliths from the Monastery kimberlite show the majority of the samples to have the low Fe, Al and Ca, and high MgO contents typical of magmaphile-element depleted cratonic lithospheric mantle. Two out of nine samples have elevated Al and lower Mg contents. Re-Os results show these two samples to be mid-Proterozoic in age indicating that additions of compositionally distinct material to this mantle section took place well after its initial assembly in the Archean. The remainder of the samples have the low Re/Os and 187Os/188Os characteristic of old cratonic peridotites, overlapping extensively with most other peridotite xenoliths contained in kimberlites erupted through the Kaapvaal craton. Excluding the two Proterozoic samples and two samples with anomalously old Re-Os model ages, the Monastery results give a mean Re-depletion model age (TRD) of 2.76 ± 0.41 Ga and mantle model age (TMA) of 3.25 ± 0.28 Ga. The oldest TRD observed at Monastery is 3.02 Ga. Compared to two well-studied localities from west of the Colesberg lineament that may mark a 2.9 Ga suture between the western and eastern blocks of the Kaapvaal craton, the Monastery mean TMA is older, but within uncertainty of, the mean TMA observed for Kimberley (2.93 Ga) and Newlands (3.18 Ga) peridotites. Similarly, the maximum TRD obtained at Kimberley (2.95 Ga) and Newlands (3.22 Ga) span the maximum TRD observed at Monastery. These results show conclusively that the most significant geochemical differentiation event affecting the Kaapvaal mantle occurred in the Archean. Compared to the results for peridotite xenoliths in kimberlites that penetrate the western Kaapvaal, the older mean TMA observed for Monastery peridotites is suggestive of older mantle beneath the older crust of the eastern Kaapvaal. However, the combination of the scatter observed in the TMA ages for samples from each locality and the uncertainty in the interpretation of Re-Os mantle model ages caused by the multistage, e.g. metasomatic, history of the samples does not allow conclusive resolution of this possible age difference. 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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 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".