Intrusion and Crystallization of a Spinifex-Textured Komatiite Sill in Dundonald Township, Ontario
Bibliographic record
Abstract
Although komatiite has been defined as an ultramafic volcanic rock characterized by spinifex texture, there is a growing recognition that similar textures can also form in high-level dykes and sills. Here, we report the results of a petrological and geochemical investigation of a $5 m thick komatiite sill in Dundonald Township, Ontario, Canada. This unit forms part of a series of komatiites and komatiitic basalts, some of which clearly intruded unconsolidated sediments. The komatiite sill is differentiated into a spinifex-textured upper part and an olivine cumulate lower part. Features characteristic of the upper sections of lava flows, such as volcanic breccia and a thick glassy chilled margin, are absent and, instead, the upper margin of the sill is marked by a layer of relatively large (1-5 mm) solid, polyhedral olivine grains that grades downwards over a distance of only 2 cm into unusually large, centimetre-sized, skeletal hopper olivine grains. This is underlain by a $1 m thick zone of platy spinifex-textured olivine and coarse, complex, dendritic, spinifextextured olivine. The texture of the olivine cumulate zone in the overlying unit is uniform right down to the contact and a lower chilled margin, present at the base of all lava flows, is absent. The textures in the sill and the overlying unit are interpreted to indicate that the sill intruded the olivine cumulate zone of the overlying unit. Thermal modelling suggests that soon after intrusion, a narrow interval of the overlying cumulate partially melted and that the liquid in the upper part of the sill became undercooled. The range of olivine morphologies in the spinifex-textured part of the sill was controlled by nucleation and crystallization of olivine in these variably undercooled liquids.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".