Potassic Magmas Derived from Metasomatized Lithospheric Mantle: Nomenclature and Relevance to Exploration for Diamond-Bearing Rocks
Bibliographic record
Abstract
Abstract Kimberlites, orangeites and lamproites are rocks derived by the differentiation and crystallization of genetically diverse mantle-derived magmas Currently, nomenclatural distinctions between these rock types are made on the basis of mineralogical-genetic classifications and not simple modal classification schemes The principle followed in such classification schemes is that the groundmass minerals reflect the fundamental characteristics of the melt from which they crystallized Classification of most of these rocks cannot be made using bulk rock geochemistry as many contain significant and variable amounts of xenocrystal and xenolith mateual It is now well-known that kimberlites are mineralogically and geochemically-distinct from orangeites and lamproites and are probably derived from depleted asthenosphenc mantle sources In contrast, isotopic and experimental petrological data indicate clearly that orangeites, lamproites and other potassic rocks are piobably derived from ancient veined metasomatized (enriched) lithospheric mantle Petrological studies have shown that each lamproite province has unique mineralogical and geochemical characteristics These differences result from the differing metasomatic histories of the source rocks within individual cratons and accreted mobile belts Orangeites are considered to represent the expression of potassic magmatism in the Kaapvaal craton and to have similar sources and origins to lamproites The unique cratonic metasomatic history, perhaps coupled with distinct asthenospheric contributions as the impetus for magma genesis, of each potassic province explains why it is difficult to classify some potassic rocks occurring in the Sao Francisco, Aldan and Dharwar cratons as lamproites, orangeites or kamafugites As the magmas from which these rocks crystallized are the unique expression of potassic magmatism in a particular craton they cannot, by definition, be classified according to schemes devised for potassic magmas in other provinces Inter-provincial similarities arise because of the common physicochemical character of the metasomatic process in the lithospheuc mantle The differences reflect variations in the ages and modes of the metasomatic veins coupled with differing degrees of partial melting and/or asthenosphenc contributions to the magmas Any given craton can contain both kimberlites and potassic rocks Rocks in each potassic province could in theory be given its own terminology, which taken to an extreme could lead to a proliferation of cratonic type-locality names Alternatively, all of these diverse magmas might be collectively termed the metasomatized lithospheric mantle magma group (or MLM magmas) The mineralogical-genetic approach to classification implies that none of the MLM magmas are transitional to kimberlite magmas and that use of the portmanteau term “kimberlite clan rocks” for diverse diamondiferous rocks of different genesis is inappropriate for both scientific and economic purposes The diamond potential of each province of potassic rocks must assessed independently as this will also reflect the unique geological history of the parental lithospheric mantle Correct classification of potentially diamondiferous rocks is essential as this has implications with respect to exploration for, and evaluation of, particular intrusions using heavy mineral indicator suites and/or geophysical methods
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| 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 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".