Geochemistry of Ultramafic to Mafic Rocks in the Norwegian Lapland: Inferences on Mantle Sources and Implications for Diamond Exploration
Why this work is in the frame
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Bibliographic record
Abstract
Geology of the Norwegian Lapland is dominated by diverse Archean crystalline basement complexes superimposed with Proterozoic greenstone belts. Isotopic dating of detrital zircons from basement gneisses in the Kirkenes area establishes presence of Early Archean (3.69 Ga) crustal component as well as three major episodes of crustal growth at 3.2 Ga, 2.7-2.9 Ga and 2.5 Ga. Precambrian terranes are intruded by ultramafic-mafic dikes and sills that range in composition from komatiites and ultramafic-mafic lamprophyres to high-Mg basalts and low-Ti subalkaline basalts. Geochemical characteristics of these rocks fall into three principal groups: 1) enriched compositions with high Nd, Nb, Hf, Zr and Th concentrations and elevated La/Th and Nb/Th coupled with low La/Nb, Ba/Nb and U/Nb ratios; 2) compositions depleted in Th, Hf and Nb together with low LREE/HFSE (such as La/Nb) and LILE/HFSE (such as Ba/Nb and U/Nb) ratios; 3) transitional group clearly identified by marked depletions in Ti, Nb and Ta contents coupled with enrichment in Th and U and other large-ion lithophile elements (LILE). These geochemical characteristics are interpreted within the framework of two principal source models: 1) derivation of parental ultramafic-mafic melts from multiple mantle sources (depleted to enriched) inherited from Archaean lithospheric tectonics and 2) a single primitive mantle source which underwent several depletion and enrichment episodes, at least partially associated with subduction zone processes. Subduction modification of depleted lithospheric mantle was assisted by accretion of subducted sediment to depleted mantle source at Archean, Proterozoic or Early Paleozoic convergent margin. Alkaline ultramafic rocks such as lamprophyres and mica picrites display geochemical characteristics supportive of their origin within stability field of diamond in a deep mantle beneath Norwegian Arctic margin which, together with other lithospheric characteristics, suggests its high potential for hosting economic diamond mineralization.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it