Flat slab subduction
A broader definition of flat slab subduction includes any shallowly dipping lower plate, as in western Mexico.
[2][3] The flat slab also may hydrate the lower continental lithosphere[2] and be involved in the formation of economically important ore deposits.
The Cornell-Carnegie debate between Cornell University geophysicists and workers at the Carnegie Institute of Washington centered on whether local deployments of seismometers would yield better results than looking at global (teleseismic) data.
[9] The idea was taken up to explain the Laramide orogeny, as the flat slab subduction zones on the Andean margin are associated with more inboard surface deformation and magmatic gaps.
The overriding plate is often equipped with a cratonic keel of thick continental lithosphere which, if close enough to the trench, can impinge upon the flow in the mantle wedge.
Flat slabs are thought to result in zones of broad, diffuse deformation in the upper plate located far landward from the trench.
Crustal shortening is observed to extend farther inland than in normally dipping subduction zones; the Sierra Pampeanas are over 650 km east of the trench axis.
[22] Another interesting feature that may be associated with the flat slab subduction of the Nazca Ridge is the Fitzcarrald arch located in the Amazonian Basin.
The Fitzcarrald arch is a long-wavelength, linear topographic feature extending from eastern Peru to western Brazil beyond the Subandean thrust front into an undeformed area and rising ~600 masl.
[26] Although the lower lithosphere of the upper deforms plastically, numerical modeling has shown stress can be transmitted to crustal regions which behave in a brittle fashion.
Thick crust that is not as deeply fractured by trench rise normal faulting may not dehydrate rapidly enough to induce intermediate-depth earthquakes.
[1] The Peruvian flat slab lacks significant intermediate-depth earthquakes and is associated with the subduction of the ~17 km thick Nazca Ridge.
[1] In the late 1970s early research recognized the unique nature of the two large flat slab subduction zones along the Andean margin of South America.
[28][29] Two large and one smaller current flat slab subduction segments exist along the Andean margin: the Peruvian, Pampean, and the Bucaramanga.
The subducting plate starts at a dip of 30 degrees then flattens out at a depth of 100 km under the Eastern Cordillera and Subandean zone.
The second highest zone in the Andes, Cordillera Blanca, is associated with the Peruvian flat slab segment and uplift of basement-cored blocks.
There are several other flat slab segments that warrant a mention:[3] Subduction of thick oceanic crust could be linked with the metallogenesis of copper and gold deposits.
[4] The failure of the putative flat slab under western North America may have been vital in producing Carlin-type gold deposits.
