The Pampean flat-slab is the low angle subduction of

oceanic lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time sc ...

beneath Northern

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. The Pampean flat-slab is one of three flat slabs in South America, the other being the Peruvian flat-slab and the Bucaramanga flat-slab. It is thought that the subduction of the

Juan Fernández Ridge The Juan Fernández Ridge is a volcanic island and seamount chain on the Nazca plate. It runs for about in a west–east direction from the Juan Fernández hotspot to the Peru–Chile Trench between the latitudes of 32-34° S before subducting ...

, a chain of extinct volcanoes on the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

, is the underlying cause of the Pampean flat-slab.

Effects

The shallowing of subducted slab beneath north-central Chile and Argentina is linked to a series of changes in volcanism and tectonics.

Deformation of crust

The flat-slab has caused an uplift of

Sierras Pampeanas The Sierras Pampeanas (also called Central Sierras or Pampas Sierras) (English: Pampas Mountains) is a geographical region of Argentina. The Sierras Pampeanas are a chain of mountains that rise sharply from the surrounding pampa region of N ...

which begun first in the north and then moved southwards over millions of years. The oldest noted uplift episode associated with Pampean flat-slab is that of

Sierra de Aconquija Sierra (Spanish for "mountain range" or "mountain chain" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Nieves ...

(27 °S) from 7.6 to 6 million years ago (Ma) in the Late Miocene epoch. This was followed by the uplift of massifs further south such as

Sierra de Famatina image:Coat of arms of the La Rioja Province.svg, 200px, Coat of arms of La Rioja featuring ''Cerro General Belgrano'' The Sierra de Famatina is a mountain range and massif in the Sierras Pampeanas of the Argentine province of La Rioja Province (Arge ...

(29 °S) that rose 4.5 to 4.19 Ma ago. Next to rise was Sierra de Pocho (31 °S) 5.5 to 4.7 Ma ago followed by

Sierra de San Luis Sierra (Spanish for "mountain range" or "mountain chain" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Nieves ...

(33 °S) 2.6 Ma ago. At latitude 33 °S deformation of the Andes proper has changed as the slab underneath has gradually shallowed. Thrust front propagation of the

Principal Cordillera Principal Cordillera () is the Andean mountain range that makes up the boundary between Central Chile and neighbouring areas of Argentina. It is also a continental divide between the Atlantic and the Pacific watersheds. It extends in a north–s ...

has increased five-fold in from 15-9 Ma ago to the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Early Quaternary. Slightly east the Frontal Cordillera was greatly uplifted 9 million years ago.

Volcanic gap

The Pampean flat-slab has also caused a lull in the volcanism in the Andes seen in the lack of modern volcanoes between the Central Andean Volcanic Zone and the Southern Andean Volcanic Zone. As the flat slab migrated from west to east under South America, so did volcanic activity, until it vanished 1.9 Ma ago, about from the Pacific, far to the east of ordinary subduction volcanism. Migration of the volcanic activity to the east meant that in the

magmatic activity ended as early as 8.6 Ma ago.

References

{{reflist Andean Volcanic Belt Geology of Atacama Region Geology of Catamarca Province Geology of Córdoba Province, Argentina Geology of Coquimbo Region Geology of La Rioja Province, Argentina Geology of San Juan Province, Argentina Geology of San Luis Province Geology of Valparaíso Region Geology of the Andes Subduction