Famatinian orogeny

The Famatinian orogeny (Spanish: Orogenia de Famatina) is a process that made mountains and changed the land a very long time ago. It happened in what is now western South America during a time called the Paleozoic. This event started in the Late Cambrian and went on until at least the Late Devonian, maybe even later. The most activity was about 490 to 460 million years ago.

During the Famatinian orogeny, the Earth's crust was changed by strong heat and pressure, called metamorphism and deformation. Hot liquid from deep inside the Earth, called magma, erupted and pushed up into the crust along a line called a Famatinian magmatic arc. This made a chain of volcanoes.

The rocks formed from this magma are special. They are called igneous rocks and have a calc-alkaline character. Some of these rocks include gabbros, tonalites, granodiorites, and trondhjemites. The youngest rocks from this time are granites. Some of the pegmatite dykes in a place called the Pampean Pegmatite Province also formed during this time, and they might have come from special kinds of melted rock called S-type granitic melts.

Outcrops and sediments

The Famatinian orogen’s main visible parts are in the Sierras Pampeanas in northwestern Argentina. Only the western part of this area shows signs of the Famatinian orogeny. The eastern parts seem mostly unchanged. In northern Chile, the Belén Metamorphic Complex is thought to have experienced similar changes during the early Paleozoic. It can be considered part of the orogen in a broader sense. In La Pampa Province to the south, there are few visible parts of the orogeny because newer layers cover most of the area.

In Peru’s Cordillera Oriental, a “Famatinian” orogeny happened around the same time as the main one further south. Between 480 million and 435 million years ago, rocks in this area were bent and a chain of volcanoes formed.

To the east of the Famatinian volcanic chain, an old area of sediments turned into a special basin during the Ordovician period. This basin stretched from Peru through Bolivia to northwestern Argentina. It collected sediments from the Famatinian orogen and volcanoes. It was a sea basin, though it did not contain ocean floor.

Hard rocks that appear in Cordón de Lila and Sierra de Almeida south of Salar de Atacama in Chile formed during the Cambrian and Ordovician periods because of the orogeny. These rocks are types of granodiorite and monzogranite. They are either metaluminous or peraluminous. They are leftovers from the volcanic activity along the western edge of the Famatinian orogeny.

Plate tectonic setting

The Famatinian arc formed when the Iapetus Ocean moved under Gondwana. The main event happened when the Cuyania terrane crashed into Pampia during the Ordovician period.

Some think the Appalachian Taconic orogeny might be part of the Famatinian orogeny. They believe this because Laurentia and Gondwana may have collided when the Iapetus Ocean closed. Both areas have similar carbonate platform sediments and Olenellid trilobite faunas. However, there are different ideas about where Cuyania came from and how it moved.