Each claim states how it is known and cites its evidence.
DisputedSlab melting, overlying-lithosphere melting, or both — the balance is debated.
The source of arc magma is contested: eruptive activity above subduction zones is clearly associated with subduction, but whether the magma is generated by partial melting of the subducted oceanic slab, of the overlying lithosphere, or of both, is vigorously debated.
- precision note: The association between arc volcanism and subduction is not in dispute; only the melting mechanism is.
Evidence support: Supported by the cited evidence · 2 sources, multiple sources, independence unknown
Evidence: Kious 1996 · Primary authority; French 2015 · Peer-reviewed
EstablishedOceanic–oceanic convergence builds trench-parallel volcanic island arcs.
Where two oceanic plates converge one is usually subducted and a trench forms; erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level, producing curved chains called volcanic island arcs that closely parallel the trenches.
Evidence support: Supported by the cited evidence · one source
Evidence: Kious 1996 · Primary authority
MeasuredDehydration and melting are distinguishable at 120 km; by 180 km a single supercritical liquid mobilises most trace elements.
Experiments on basaltic eclogite show a dichotomy between dehydration and melting at conditions equivalent to 120 kilometres depth, expressed in the contrasting behaviour of many trace elements including uranium and thorium, strontium, barium, beryllium and the light rare-earth elements. At conditions equivalent to 180 kilometres a supercritical liquid with melt-like solubilities appears even at low temperatures, mobilising most of the key trace elements.
- method: Laser-ablation ICP-MS analysis of fluids and melts equilibrated with basaltic eclogite at pressures equivalent to 120 to 180 kilometres depth and temperatures of 700 to 1,200 degrees Celsius.
- precision note: These are experimental conditions, not observations of a subduction zone. The depths are the depths the experimental pressures correspond to.
Evidence support: Supported by the cited evidence · one source
Evidence: Kessel 2005 · Peer-reviewed
EstablishedConvergent-boundary recycling of crust: one plate sinks beneath another at a subduction zone.
At convergent boundaries, crust is destroyed as one plate sinks beneath another; the location where sinking occurs is a subduction zone, and subduction creates the deepest parts of the ocean floor.
Evidence support: Supported by the cited evidence · one source
Evidence: Kious 1996 · Primary authority