Geology, Structure, and Radiometric Age Determination of the Murowa Kimberlites, Zimbabwe
Bibliographic record
Abstract
Abstract The Murowa kimberlite field includes three diamondiferous kimberlite pipes (K1, K2, and K3) and multiple kimberlite dikes that have been emplaced into the Archean Chibi granite batholith north of the Limpopo belt in south-central Zimbabwe. Here we summarize the key aspects of the geology of the Murowa kimberlites from previous studies and integrate these findings with new structural data to interpret a structural model governing the locations, relative positions, and orientations of emplaced kimberlite. Key observations of drill core, thin section petrography, geochemistry, and mapping of exposed rocks at the Murowa diamond mine are summarized from previous work, and these data collectively form the basis for emplacement interpretations and threedimensional (3-D) geologic models of each body. Structural observations are used to interpret the presence of a km-scale tensile bridge hosting the Murowa kimberlites and suggest Murowa is an example of kimberlite emplacement into multiple, reactivated, preexisting near-surface structures at different orientations. We propose that the physical state of the ascending magma (% of gas, extent of phase separation) can dictate whether kimberlite is emplaced along preexisting structures or creates and intrudes new fracture networks in planes of weak horizontal stress. A reproducible age of ~526 Ma is determined for two coherent kimberlite dikes at K1, while an older Rb-Sr model age of ~543 Ma is calculated for a single dike from K2, though this result is of limited reliability due to potential disturbance of the Rb-Sr system due to phlogopite alteration. These results highlight potential problems with reported ages from kimberlite pipes.
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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 | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".