<scp><scp>U–Pb</scp></scp> Ages for Zircon Grains from <scp>N</scp>sanaragati Alluvial Gem Placers: Its Correlation to the Source Rocks
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Bibliographic record
Abstract
Abstract The M amfe B asin is located in the SW of C ameroon and is an extension of the much bigger B enue T rough in the SE of N igeria. Along the A senem R iver and its tributaries in the western part of the M amfe B asin (close to the border with N igeria) gem placers yielding big zircon grains were found in recent river sediments close to N sanaragati. In order to determine the source area and to establish a possible correlation between the zircons found in the N sanaragati placers and rocks surrounding the M amfe B asin 56 detrital zircon grains were analysed regarding their U – P b ages and selected trace element contents by LA‐ICP – MS techniques. Possible source areas are rocks from the B enue T rough in the W est and from the C ameroon V olcanic L ine ( CVL ) in the SE of the study area. Based on microscopic analyses it was possible to distinguish two groups of zircons: reddish and non‐reddish ones, where the latter group comprises color variations from brown to orange, yellow to even colorless. In general, the detrital zircons show high hafnium values (4576 to 12565 ppm) and very variable thorium (7.8 to 1565 ppm) and uranium values (13.4 to 687 ppm). The T h/ U ratios vary from 0.4 to 2.3, allowing correlations for some zircon grains to kimberlitic, granitic or syenitic affinities. It was also possible to distinguish zircon grains crystallised in mafic mantle‐derived melts from those crystallised in felsic melts, e.g. from continental rift‐related magmatic systems. In general, the U – Pb zircon ages obtained range from 11.7 to 1949 Ma. All zircons of the reddish group yielded almost similar ages resulting in a C oncordia age of 12.4 Ma (Serravallian), an age unknown from the M amfe B asin so far. The group of non‐reddish zircons showed various ages ranging from Serravallian to Orosirian. It was possible to correlate the youngest ages with rocks known from intrusions along the CVL , dated with K / A r or A r/ A r methods. The most probable sources were M ount B amenda and M ount B ambouto in the east of the M amfe B asin. Cretaceous ages are interpreted as re‐recycled clastic sediments whose original source had been rocks in the south and the north of the B enue T rough and who had been eroded and deposited within the catchment area of the A senem river system in the M amfe B asin in post‐ C retaceous times. The oldest ages are assumed to represent the pan‐ A frican and pre‐pan‐ A frican basement of the M amfe basin.
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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 | 0.001 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.002 |
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 it