How does lithospheric extension cause passive mantle melting?

Lithospheric extension allows pre-existing melt in the crust and mantle to escape to the surface. When extension becomes severe enough to thin the lithosphere and cause the asthenosphere to rise, decompression upwelling produces additional melt. This mechanism explains how volcanic activity can be driven by lithospheric stress fields and plate tectonics during processes like continental rifting.

What we know

• Extension of the lithosphere enables pre-existing melt located in the crust and mantle to escape to the surface. [5]
• If lithospheric extension is severe and thins the lithosphere enough for the asthenosphere to rise, additional melt is produced by decompression upwelling. [5]
• The extension of the lithosphere is driven by the lithospheric stress field, which governs the global distribution and evolution of volcanic activity. [5]
• Continental rifting transitions from rifting to seafloor spreading and thermal subsidence, creating extensive sedimentary wedges above transitional crust. [2]

Still open

• Geologists debate whether specific historical events like the opening of the North Atlantic Ocean were caused primarily by mantle plumes such as Iceland or by secondary plate tectonic extension.

Where to go next

• the bigger pictureWhat is a passive margin?
• how it workedHow does plate theory explain volcanism?
• compared withWhat causes intraplate volcanism away from plate boundaries?
• a case in pointHow did the North Atlantic Ocean open?
• what followedWhat role does thermal subsidence play after rifting?
• an unexpected connectionWhy might plate tectonics explain anomalous volcanism?Plate theory attributes even superficially anomalous volcanic activity entirely to the operation of plate tectonics and lithospheric stress fields rather than isolated mantle anomalies.

Sources

• [1]passive margin (Wikidata Q1918464) · CC0 1.0
• [2]Passive margin · CC BY-SA 4.0
• [3]Intraplate volcanism · CC BY-SA 4.0
• [4]Opening of the North Atlantic Ocean · CC BY-SA 4.0
• [5]Plate theory (volcanism) · CC BY-SA 4.0