ThePampean flat-slab is thelow angle subduction ofoceanic lithosphere beneath NorthernArgentina. The Pampean flat-slab is one of three flat slabs in South America, the other being thePeruvian flat-slab and theBucaramanga flat-slab.[1]
It is thought that the subduction of theJuan Fernández Ridge, a chain of extinct volcanoes on theNazca Plate, is the underlying cause of the Pampean flat-slab.[2][3]
The shallowing of subducted slab beneath north-central Chile and Argentina is linked to a series of changes in volcanism and tectonics.
The flat-slab has caused anuplift ofSierras Pampeanas which begun first in the north and then moved southwards over millions of years.[2] The oldest noted uplift episode associated with Pampean flat-slab is that ofSierra de Aconquija (27 °S) from 7.6 to 6 million years ago (Ma) in theLate Miocene epoch.[2] This was followed by the uplift of massifs further south such asSierra de Famatina (29 °S) that rose 4.5 to 4.19 Ma ago.[2] Next to rise wasSierra de Pocho (31 °S) 5.5 to 4.7 Ma ago followed bySierra de San Luis (33 °S) 2.6 Ma ago.[2]
At latitude 33 °S deformation of the Andes proper has changed as the slab underneath has gradually shallowed.Thrust front propagation of thePrincipal Cordillera has increased five-fold in from 15-9 Ma ago to thePliocene andEarly Quaternary.[2] Slightly east theFrontal Cordillera was greatly uplifted 9 million years ago.[2]
The Pampean flat-slab has also caused a lull in thevolcanism in the Andes seen in the lack of modern volcanoes between the Central Andean Volcanic Zone and the Southern Andean Volcanic Zone.[3] As the flat slab migrated from west to east under South America, so did volcanic activity, until it vanished 1.9 Ma ago, about 750 kilometres (470 mi) from the Pacific, far to the east ofordinary subduction volcanism.[2] Migration of the volcanic activity to the east meant that in thePrincipal Cordillera magmatic activity ended as early as 8.6 Ma ago.[2]