Positions of ancient continents, 550 million years ago

The Famatinian orogeny ( es, Orogenia de Famatina) is an orogeny that predates the rise of the Andes and that took place in what is now western

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

, leading to the formation of the Famatinian orogen also known as the Famatinian belt. The Famatinian orogeny lasted from the

Late Cambrian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

to at least the Late Devonian and possibly the

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * ...

, with orogenic activity peaking about 490 to 460

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

. The orogeny involved

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...

and

deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defor ...

in the crust and the

eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...

and intrusion of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

along a Famatinian

magmatic arc Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

that formed a chain of

volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...

es. The

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

s of the Famatinian magmatic arc are of

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

character and include

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

tonalite Tonalite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total ...

s and

granodiorite Granodiorite () is a coarse-grained ( phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gr ...

s. The youngest igneous rocks of the arc are

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

s. The relationship of the orogeny with the Achala and Cerro Aspero batholiths of central Argentina is not fully understood. These Devonian batholiths are possibly of post-orogenic character.

Outcrops and sediments

The Famatinian orogen's main

outcrops An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial ...

lie in

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 ...

in northwestern Argentina. Only the western part of Sierras Pampeanas bears evidence of the Famatinian orogeny; the eastern parts appear to have been largely unaffected. In northern Chile the Belén Metamorphic Complex is believed to be part of the orogen as it was subject to metamorphism in the early Paleozoic. To the south in La Pampa Province, outcrops associated with the orogeny are scarce since most of that region has become blanketed by much more recent Quaternary

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s. In Peru's Cordillera Oriental a "Famatinian" orogeny exists which is coeval with the classical Famatinian orogeny found further south. In the time-span from 480 Ma to 435 Ma (Late Cambrian to Silurian) rocks of Cordillera Oriental were deformed and a magmatic arc developed. Towards what is now the east of the Famatinian magmatic arc a Precambrian

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subside ...

developed into a back-arc basin during the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

. This basin went from Peru, through Bolivia to northwestern Argentina. The basin collected sediments from the Famatinian orogen and arc and while it did not contain

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic ...

it was a marine basin.

Plutonic rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...

s cropping out in

Cordón de Lila Cordón de Lila is a mountain range of the Andes located in northern Chile, south of Salar de Atacama. Geologically it is made up of a batholith of Cambrian and Ordovician age. The rocks of Cordón de Lila are the result of pre-Andean magmatism ...

and Sierra de Almeida south of

Salar de Atacama Salar de Atacama is the largest salt flat in Chile. It is located south of San Pedro de Atacama, is surrounded by mountains, and has no drainage outlets. In the east it is enclosed by the main chain of the Andes, while to the west lies a secondar ...

in Chile formed in the Cambrian and Ordovician in association with the orogeny. The compositions of the plutonic rocks are

and

monzogranite Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly metaluminous or

peraluminous Peraluminous rocks are igneous rocks that have a molecular proportion of aluminium oxide higher than the combination of sodium oxide, potassium oxide and calcium oxide.Blatt, Harvey and Robert J. Tracy, ''Petrology,'' Freeman, 2nd ed., 1995, p. ...

. These rocks are remnants of the magmatism along the western rim of the Famatinian orogeny.

Plate tectonic setting

Famatinian arc

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

was caused by the subduction of Iapetus Ocean lithosphere beneath Gondwana. As subduction went on, the peak of the orogeny resulted from the

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

of the

Cuyania The Precordillera Terrane or Cuyania was an ancient microcontinent or terrane whose history affected many of the older rocks of Cuyo in Argentina. It was separated by oceanic crust from the Chilenia terrane which accreted into it at ~420-390 Ma w ...

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a tectonic plate (or broken off from it) and Accretion (geology), accreted or "Suture (geology), sutured" to crust lying on another pla ...

with

Pampia Pampia was an ancient microcontinent or terrane that collided with Río de la Plata Craton and Río Apas Craton during the Pampean orogeny of late Proterozoic and early Cambrian. It was one of the first terranes to be amalgamated to the old ...

in the Ordovician. It has been suggested that the coeval Appalachian

Taconic orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...

is the "northward" continuation of the Famatinian orogeny. This has been explained by adding that the continent

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

could have collided with Gondwana (at what is today western South America) in early Paleozoic times due to the closure of the Iapetus Ocean. Supporting this hypothesis is the suggestion that the orogens have "truncated ends" that can be matched and that both share the commonality of having

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

platform Platform may refer to: Technology * Computing platform, a framework on which applications may be run * Platform game, a genre of video games * Car platform, a set of components shared by several vehicle models * Weapons platform, a system or ...

s at what is today their western side. Further, in the mentioned sediments both orogens host similar Olenellid trilobite faunas, something that is not expected to be unless both orogens had some sort of contact. This is because trilobites are unable to cross deep ocean basins. According to this view the

would be an

allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary out ...

ous block of Laurentian origin that was left in Gondwana after the continents went apart. But such views are not unchallenged since Cuyania is alternatively suggested to have drifted across Iapetus Ocean as a

microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

starting in Laurentia and accreting then to Gondwana. Further a third model claims Cuyania is para-autochthonous and arrived at its current place by strike-slip fault movements starting not from Laurentia but from another region of Gondwana. The fact that Precordillera terrane has many trilobite genera in common with Laurentia but many species are endemic have led to some differing interpretations on what paleogeographic and tectonic history conditions are plausible explanations for this biogeography.

Notes

References

{{Major South American geological formations

External links

Animation of world plate tectonics
note Cuyania's (red) trajectory from 0:20 onwards. Orogenies of South America Geology of Argentina Geology of Bolivia Geology of Chile Geology of Peru Cambrian orogenies Ordovician orogenies Silurian orogenies Devonian orogenies Carboniferous orogenies Cambrian South America Ordovician South America Silurian South America Devonian South America Carboniferous South America Sierras Pampeanas