The petrographic and geochemical analysis of lamprophyre dikes in Williston, Vermont
Bibliographic record
Abstract
Lamprophyres are relatively uncommon alkaline, silica-undersaturated, small volume ultrapotassic igneous rocks often found as dikes or small intrusions. In New England, lamprophyres are most abundant in the New England-Quebec magma series found in parts of northern Vermont and southern Quebec. Here, they are relatively uncommon mafic to ultramafic magmas that are thought to have intruded sometime during the Cretaceous period during the Mesozoic era. This study focuses on the lamprophyre dikes found in Williston, Vermont. Thirty-seven samples were collected, seventeen were made into thin sections to understand mineralogical and petrographic characteristics, and twenty-nine samples were analyzed for major and trace element using ICAP. A subset of ten samples was analyzed for rare earth elements. Radiometric argon-argon ages were determined on two samples. Lamprophyres are strongly porphyritic, with abundant phenocrysts of biotite, amphiboles and pyroxene. Feldspar usually occurs in small amounts and is confined to the ground mass. The chemistries of the lamprophyres ranged between 42% to 60% silica by weight. From petrographic and chemical analysis, the samples are characterized into one of four types based on the minerals present and the silica content of the lamprophyres. The lamprophyre rock types found in Williston include: camptonites, monchiquites, spessarites and diabases. Argon-argon age dates for the whole rock was found to be 113 +/- 3.3 Ma with the total fusion age of the biotite flakes as 134 +/- 0.7 Ma. Linear decreasing trends of CaO, MgO, Fe2O3, Ni, Sc and Cr with decreasing Mg number show fractionation of plagioclase, amphibole, biotite, pyroxene and olivine. Ti-Zr-Y variations indicate that the dikes were formed from within plate environments resembling basalts that have possibly formed as a result of partial melting of a garnet-peridotite mantle. Enriched trends in LREE, LIL and HFS incompatible elements determine that the source rock is located either in the mantle lithosphere or in the deeper mantle. The lack of negative anomalies in Nb, Ta, P and Ti in the spider diagrams suggest that partial melting occurred in the deeper mantle. The different varieties of lamprophyres could be the result of different degrees of fractional crystallization of a parent magma or partial melting of different areas within the heterogeneous deeper mantle. After their formation, magmas moved along the weaknesses in the crust where they finally crystallized forming intrusive dikes. The Williston lamprophyres seem to be part of a suite of dikes that has been formed from the partial melting of deeper mantle as a result of a hotspot plume.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".