Igneous Rock Associations 7. Arc Magmatism I: Relationship Between Subduction and Magma Genesis
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Bibliographic record
Abstract
Dehydration of subducted oceanic lithosphere releases fluid into the overlying mantle wedge and initiates a chain of events culminating in the generation of magma that rises to form volcanic arcs. Arc magmas are distinct from magmas in other settings because of the different geothermal regimes at destructive plate margins, the presence of fluids/volatiles derived from dehydration of the subducted slab and the generally compressive tectonic regime that inhibits the ascent of magma, thereby promoting extensive interaction with the adjacent wall rocks. As a result, most arc magmas solidify as intrusive bodies, ranging from sills and dykes to large plutonic complexes. Several mechanisms facilitate the rise of arc magmas. Diapirs rising from a larger pool of buoyant magma are important in the ductile lower crust. The rapid rise and the expansion of magma results in the propagation of fractures, that facilitate stoping and assimilation in the brittle upper crust. Fracture zones are repeatedly exploited, and the net result may be formation of a composite batholith. Water plays an important role in all stages of arc-magma evolution. Water lowers the temperatures that are required for the partial melting in the mantle wedge, which produces mafic magma, and in the crust, produces felsic magma. Arc magmatism is intimately related to metamorphism, although this relationship is complicated largely because maximum pressures and temperatures are attained at different times. Arcs under compression undergo rapid thickening, followed by erosional or tectonic exhumation. Crustal melting is triggered by a variety of processes, including relaxation following crustal thickening. Melting initiates at the base of the crust, but eventually occurs at shallower crustal levels. Arcs under extension have a steep geo-thermal gradient and underplating of the crust by mafic magma may transfer sufficient heat to induce anatexis. During a prolonged history of subduction, the dip and location of the subduction zone may vary causing the locus of arc magmatism to migrate and causing intermittent switching from compressional to extensional environments. SOMMAIRE Le phenomene de deshydratation qui accompagnent la subduction de la lithosphere oceanique relâche des fluides dans le prisme mantelique susjacent et initie une suite d’evenements qui conduit a la generation de magmas qui forment des structures d’iles en arc. Les magmas d’iles en arc different des magmas d’autres contextes parce que les regimes geothermaux aux lieux de destruction de marges tectoniques sont differents, etant donne la presence de fluides et/ou de volatiles issus de la deshydratation de la plaque en subduction, et du regime tectonique generalement compressif qui inhibe l’ascension du magma, d’ou l’importance de l’interaction avec la roche encaissante. En consequence, la plupart des magmas d’iles en arc forment des intrusifs, variant des filons-couches, aux dykes aux complexes plutoniques. Plusieurs mecanismes favorisent l’ascension des magmas d’iles en arc. Ainsi, l’ascension de diapirs a partir d’une grande accumulation de magma moins dense que l’encaissant est-il un phenomene important dans la croute inferieure ductile. Cette ascension rapide jointe a l’expansion du magma provoque la propagation de fractures, ce qui facilite l’agregation et l’assimilation de l’encaissant dans la portion superieure cassante de la croute. Frequemment, le magma injecte ces zones de fractures, ce qui conduit parfois a la formation d’un batholite composite. L’eau joue un role important a toutes les etapes de l’evolution des magmas d’iles en arc. La presence d’eau abaisse les temperatures de fusion partielle dans le prisme mantelique, ce qui conduit a la formation de magmas mafiques, et de magmas felsiques dans la croute. Le magmatisme d’ile en arc est intimement lie au metamorphisme, bien que cette relation soit compliquee, surtout parce que les pressions et les temperatures maximales sont atteintes a des moments differents. Les magmas d’iles en arc en situation de compression s’epaississent rapidement, puis sont erodes ou exhumes tectoniquement. La fusion de la croute est declenchee par une variete de processus, dont la detente accompagnant l’epaississement crustal. La fusion se produit d’abord a la base de la croute, mais elle atteint eventuellement des niveaux moins profonds de la croute. Les magmas d’ile en arc en situation d’extension ont un gradient geothermal tres pentu, et le placage de la croute par un magma mafique peut y apporter assez de chaleur pour provoquer l’anatexie. Si l’histoire de la subduction se prolonge, le contexte d’un systeme d’iles en arc peut alterner episodiquement d’un regime en compression a un regime en extension.
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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 | 0.000 | 0.000 |
| 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 it