At the link below there is an interesting discussion about the validity of current thinking about plate tectonics
CardiffEarthSciences
Speaker: Professor Christopher MacLeod
Have we got plate tectonics wrong?
https://www.youtube.com/watch?v=nKAGVY6fDac
Among other things he discusses the discovery of detachment faults (aka core complexes) at slow spreading mid ocean ridges. These are very large displacement (usually about 10 km but can be more than 100 km) low angle convex foot wall exposures that feature surface striations in the direction of movement. He speculates that up to 25% of the ocean floor may be sepentinite that has been exhumed in this way. Serpentinite is a metamorphic rock which is thought to form at great depth.
Spreading ridges are not the only regions that feature extensional detachment faults. They have also been found close to subduction trenches (these are currently thought to be an artefact of slab rollback where the leading edge of the subducting slab begins to retreat as the slab temporarily stops subducting and sinks in situ) and on continents. e.g.
Oceanic trenches, which are the deepest chasms in the ocean, are formed during the subduction of two tectonic plates – basically, when they collide and one slides under the other. However, the Weber Deep is a forearc basin, which is basically a depression located in front of the Banda arc, a curved chain of volcanic islands. So how did this basin end up becoming like a trench? …
Further analysis of high-resolution maps of the Banda Sea floor shows hundreds of straight parallel scars marring the rocks on the seabed. These wounds point to the likelihood that the abyss was formed when a piece of crust bigger than Belgium or Tasmania was ripped apart by 120 km (75 mi) of extension along a low-angle crack, or detachment fault.
According to the researchers, the fault, which they dubbed the Banda Detachment, represents a rip in the ocean floor exposed over 60,000 sq km (23,166 sq m). So extreme was the amount of extension that in some spots there was no longer any trace of oceanic crust. …
https://newatlas.com/banda-detachment-f … eep/46660/
… In the Western Alps, ultra high pressure rocks were exhumed from the greatest depth … during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients …
https://www.academia.edu/resource/work/22734586
Oceanic core complexes were first noted along the mid-Atlantic Ridge based on their corrugated, domal bathymetry. Analogies were made with continental core complexes and their associated detachment fault systems. … Both continental and oceanic detachment fault systems are characterized by corrugated, domal topography … Oceanic detachment fault systems are likely influenced by a serpentine, olivine and/or plagioclase dominated rheology compared to a quartz and feldspar rheology in continental settings. Oceanic detachment faults are `new’ faults, which do not interact with pre-existing weaknesses/older faults …
https://www.researchgate.net/publicatio … Continents
This implies that seafloor spreading may not be restricted to mid ocean ridges (MOR’s), rather that it is more of a distributed seafloor wide phenomenon.
Low angle faults have generally been attributed to thrust faulting but re-examination of some of these faults has shown they are more likely, at least in their latest activity, detachment structures. Detachment faults are extensional features whereas thrust faults are the result of compressional forces. Both of these fault types can also have a horizontal strike/slip component. Many so called thrust faults require kilometres of vertical erosion (often over a fairly localized region) to obtain their current form. How this differential erosion occurs is poorly explained. For example in the Himalayas it is suggested that the differential erosion is the result of high rainfall in the regions that are said to be eroding faster than the surrounding region.
moonkoon 