Estimates suggest an approximately 40 km thick layer of moderately serpentinized mantle would be sufficient to explain the observed seismic P-wave attenuations associated to events occurring at depths of around 5 35 km below the Wadati Benioff zone.
22.
Subsequently, renewed melt generation modified the overlying crust until major volcanism, associated with a " flare up " of ignimbritic volcanism occurred 10 mya . beneath the local volcanic zone lies the Benioff zone of the subducting Nazca plate.
23.
The mechanism behind the lower zone of seismicity, located in the upper-mantle portion of the down-going lithosphere, is still debated; the global ubiquity of double Benioff zones indicates that it must be a process that commonly occurs in subduction zones.
24.
In the Eolian Arc in the southern Tyrrhenian Sea ( between the Eurasian and African tectonic plates ), volcanism has changed between calc-alkaline to high-K calc-alkaline to shoshonitic with the last one million years, possibly due to the progressive steepening of the Benioff zone, with is inclined at 50-60?
25.
Similar to other back-arc basins, the Tyrrhenian basin displays a shallowing of the Moho discontinuity towards the central part of the basin, a Wadati Benioff zone, abnormally high heat flow ( exceeding 200 mW / m?in some places ), and an active volcanic belt on the arc-ward edge of the basin.
26.
Simultaneous advances in early seismic imaging techniques in and around Wadati-Benioff zones along the trenches bounding many continental margins, together with many other geophysical ( e . g . gravimetric ) and geological observations, showed how the oceanic crust could disappear into the mantle, providing the mechanism to balance the extension of the ocean basins with shortening along its margins.
