Mantle Plume - The Plate Hypothesis

The Plate Hypothesis

The plate hypothesis suggests that "anomalous" volcanism results from lithospheric extension that permits melt to rise passively from the asthenosphere beneath. It is thus the conceptual inverse of the plume hypothesis, attributing volcanism to shallow, near-surface processes associated with plate tectonics, rather than active processes arising at the core-mantle boundary. The Plate hypothesis embodies the concept that deep mantle plumes causing surface, time-progressive volcanism do not exist.

Lithospheric extension is attributed to processes related to plate tectonics. These processes are well understood at mid-ocean ridges, where most of Earth's volcanism occurs. It is less commonly recognised that the plates themselves deform internally, and can permit volcanism in those regions where the deformation is extensional. Well-known examples are the Basin and Range Province in the western USA, the East African rift valley, and the Rhine graben. Variable fertility in the source region, usually the mantle, results in variable volumes of magma being produced. The ocean-island basalt (OIB) geochemistry of lavas found at many places, and attributed to plumes, is, in fact, a geochemical signature of enhanced fertility in the melt source.

The Plate hypothesis thus attributes all of Earth's volcanism to a single process – plate tectonics – rather than to two independent processes (plumes and plate tectonics), but does not address issues of core–mantle heat and/or material transfer.

Under the umbrella of the Plate hypothesis, the following sub-processes, all of which can contribute to permitting surface volcanism, are recognised:

• Continental break-up;
• Fertility at mid-ocean ridges;
• Enhanced volcanism at plate boundary junctions;
• Small-scale sublithospheric convection;
• Oceanic intraplate extension;
• Slab tearing and break-off;
• Shallow mantle convection;
• Abrupt lateral changes in stress at structural discontinuities;
• Continental intraplate extension;
• Catastrophic lithospheric thinning;
• Sublithospheric melt ponding and draining.