Mantle

Most volatile elements have very low solubilities in magmas at atmospheric pressure, so virtually all erupted lavas are degassed and do not retain their primary volatile signatures.

Evidence support: Supported by the cited evidence · one source

Evidence: Saal 2002 · Peer-reviewed

The mantle contains more iron, magnesium and calcium than the crust, and is hotter and denser because temperature and pressure increase with depth.

Evidence support: Supported by the cited evidence · 2 sources, multiple sources, independence unknown

Evidence: Kious 1996 · Primary authority; U.S. Geological Survey n.d. · Primary authority

How many convection cells exist in the mantle, where and how they originate, and what their structure is remain open questions.

Evidence support: Supported by the cited evidence · one source

Evidence: Kious 1996 · Primary authority

Below the lithospheric plates, at some depth, the mantle is partially molten and can flow slowly in response to steady forces applied over long periods.

• precision note: "Partially molten" means a small melt fraction distributed through solid rock, not a liquid layer.
• locality: Beneath the lithospheric plates.

Evidence support: Supported by the cited evidence · one source

Evidence: Kious 1996 · Primary authority

The mantle is solid rock that nonetheless flows: subjected to heat and pressure over millions of years, solid rock softens and changes shape, exactly as a solid metal such as steel does.

• precision note: The source describes the mantle as semi-solid and notes that at some depth beneath the plates it is partially molten; "flows" here means solid-state creep over millions of years, not liquid motion.

Evidence support: Supported by the cited evidence · one source

Evidence: Kious 1996 · Primary authority

The mantle is a dense, hot layer of semi-solid rock approximately 2,900 kilometres thick.

• precision note: Approximately, as stated by the source.

Evidence support: Supported by the cited evidence · one source

Evidence: Kious 1996 · Primary authority

Undersaturated pre-eruptive volatile contents in mid-ocean-ridge basalts from the Siqueiros intra-transform spreading centre give improved limits on the abundances of carbon dioxide, water, fluorine, sulfur and chlorine in the source of normal mid-ocean-ridge basalt.

• method: Measurement of pre-eruptive volatile contents in undersaturated melt inclusions, from which source abundances are derived.
• precision note: Source abundances are derived from erupted material, not measured in the mantle. The authors note that most volatile elements have very low solubilities in magmas at atmospheric pressure, so that virtually all erupted lavas are degassed and do not retain their primary volatile signatures; the value of the undersaturated inclusions is precisely that they escaped this.
• locality: Siqueiros intra-transform spreading centre, eastern Pacific.

Evidence support: Supported by the cited evidence · one source

Evidence: Saal 2002 · Peer-reviewed