Evidence for an enriched asthenospheric source for coronitic metagabbros in the Adirondack Highlands
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Bibliographic record
Abstract
Coronitic metagabbros (CMGs) in the Adirondack Highlands display chemical and isotopic features consistent with derivation from an enriched asthenospheric mantle source and are samples of the parental magma of Adirondack anorthosite. Primary ophitic textures in the CMGs are overprinted by mineral coronas developed during granulite-facies metamorphism of anhydrous olivine gabbronorites during the Ottawan orogeny. Restricted in silica content (45–48 wt%) and olivine normative, the CMGs are predominantly tholeiitic in composition, although a minority display some calc-alkaline features. Unlike older Adirondack mafic and felsic suites, the CMG rocks lack or have greatly reduced, incompatible element patterns (NPM) generally associated with subduction processes. Rare-earth elements (NCH) have minor light rare-earth element (LREE) enrichment with La/Sm values from 1.42 to 1.98, compatible with a transitional to enriched mantle source. When CMGs are plotted on various major (TiO2 versus P2O5) and trace-element (Sm versus Cr) diagrams, the CMGs form a continuous field between that of oxide- and apatite-rich gabbros (OGNs and OAGNs) and anorthosites and leucogabbros within the Adirondacks. Initial epsilon Nd (εNd) values are +3.13 to +3.69, generally higher than Adirondack anorthosite values, but significantly less than contemporaneous depleted mantle. Neodymium TDM model ages that are ∼400 million years older than their crystallization age and enriched compositional trends indicate that they were not derived from depleted mantle. These data indicate Adirondack CMGs were derived from a previously untapped and enriched asthenospheric source. Asthenospheric upwelling was triggered by lithospheric delamination following Shawinigan orogenesis at ca. 1160 Ma and provides a link between tectonism, mantle geodynamics, and massif anorthosite petrogenesis in the Grenville allochthonous monocyclic belt.
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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 | 0.000 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.009 | 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