Melting of the continental crust during orogenesis: the thermal, rheological, and compositional consequences of melt transport from lower to upper continental crustThis article is one of a selection of papers published in this Special Issue on the the theme<i>Lithoprobe—parameters, processes, and the evolution of a continent</i>.
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
The formation and differentiation of the continental crust occurs at convergent plate margins in accretionary and collisional orogenic belts where sufficient heat is generated to achieve high-grade metamorphism and anatexis. Volumetrically significant H 2 O-present melting requires an influx of aqueous fluid along zones of high-strain deformation or via fracture networks, or recycling of the fluid dissolved in melt via melt migration and fluid exsolution during crystallization. In contrast, in “dry” crust, melting occurs via hydrate-breakdown melting reactions at higher temperatures than H 2 O-present melting; volumetrically significant melt production requires temperatures above ∼800 °C. Melting wets residual grains, and anatectic crust becomes porous at a few vol.% melt. Feedback between deformation and melting creates a dynamic rheological environment; as melt volume increases to the melt connectivity transition, which varies but is around 7 vol.% (see discussion later in the text), melt may escape from the source in the first of several melt-loss events with increasing temperature. Major and accessory phase controls on melt production and melt composition for different pressure–temperature–time paths are evaluated using calculated phase equilibria for average pelite. The pristine to slightly retrogressed condition of peritectic minerals in residual crust requires significant loss of melt from the system. The consequences of melt loss are evaluated here. In residual crust, evidence of melt at the grain scale may be preserved in microstructures, whereas evidence of melt extraction pathways at outcrop scale is recorded by leucosome networks. Strain and anisotropy of permeability control the form of mesoscale melt channels with strong anisotropy promoting high-melt focusing. The sequence of structures observed in nature records a transition from storage to drainage; focused melt flow occurs by dilatant shear failure of low-melt-fraction rocks, leading to the formation of networks of channels that allow accumulation and storage of melt and that form the link for melt flow from grain boundaries to ascent conduits. Melt ascent is via ductile-to-brittle fracture; ductile fractures may propagate along foliation as sills or from dilation or shear bands as dikes. Emplacement of horizontal tabular and wedge-shaped plutons occurs around the brittle–ductile transition zone, whereas vertical lozenge-shaped plutons represent crystallization of magma in the ascent conduit. Blobby plutons form by lateral expansion in the ascent conduit localized by thermal or mechanical instabilities.
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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 | 0.001 | 0.000 |
| 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 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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