Choiyoi Group

{{Short description|Group of volcano-sedimentary formations in Argentina and Chile}}

{{Infobox rockunit

| name = Choiyoi Group

| image =

| caption =

| type = Group

| period = Permian

| age = Permian-Triassic

| prilithology = Basaltic lava flow, breccia, andesite, rhyolitic ignimbrite

| otherlithology = Dacite

| namedfor =

| namedby = Stipanicic et al.

| year_ts = 1968

| region =

| country = Argentina
Chile

| coordinates =

| unitof = Frontal Cordillera, San Rafael Massif, Principal Cordillera

| subunits = El Palque Fm., Horcajos Fm., Portezuelo del Cenizo Fm., Tambillos Fm., Vega de Los Machos Fm.

| underlies = Mendoza & Cuyo Groups

| overlies = Carapacha Formation (Sierra de Calencó)

| thickness = {{convert|2|–|4|km|ft|abbr=on}}

| extent =

| area = >{{convert|200000|km2|sqmi|abbr=on}}

| map =

| map_caption =

}}

Choiyoi Group ({{langx|es|Grupo Choiyoi}}{{refn|name=note 1|group=note|Pablo Groeber described the group as early as in 1918. Subsequently the Choiyoi Group became known by a variety of names. The current name dates to the 1968 work of Stipanicic and co-workers where the group was described in a locality in Somún Cura Massif, Río Negro Province.}}) is a Permian and Triassic-aged group of volcano-sedimentary formations in Argentina and Chile. The group bears evidence of bimodal-style volcanism related to an ancient subduction zone that existed along the western margin of the supercontinent Gondwana.

The Choiyoi Group has a large areal extent through western Argentina and parts of Chile, covering at least {{convert|200000|km2|sqmi}}, but probably around {{convert|500000|km2|sqmi}}. While the subsurface extent of the group is large, exposures in Argentina are most common in the Frontal Cordillera, the San Rafael Massif and the Principal Cordillera of southern Mendoza and northern Neuquén.{{cite journal |last=Llambías |first=Eduardo J. |last2=Quenardelle |first2=Sonia |last3=Montenegro |first3=Teresita |date=2003 |title=The Choiyoi Group from central Argentina: a subalkaline transitional to alkaline association in the craton adjacent to the active margin of the Gondwana continent |url=https://www.researchgate.net/publication/235452239 |journal=Journal of South American Earth Sciences |publisher=Elsevier |volume=16 |issue= 4|pages=243–257 |doi=10.1016/S0895-9811(03)00070-1 |bibcode=2003JSAES..16..243L |hdl=11336/83501 |hdl-access=free }} In parts the group reaches thicknesses of 2 to 4 km.{{cite journal |last=Martinez |first=A. |last2=Giambiagi |first2=L. |date=2010 |title=Evolución petrológica y geoquímica del magmatismo bimodal Permo-Triásico del Grupo Choiyoi en el cordón del Portillo, Mendoza, Argentina |url=http://www.unioviedo.es/reunido/index.php/TDG/article/view/214 |journal=Trabajos de Geología |publisher=Universidad de Oviedo |volume=30 |pages=432–451 |language=es |access-date=5 January 2016}}

File:Pangaea physical map.jpg, 237 million years ago. The Choiyoi Group was deposited immediately east of the Proto-Andes.]]

The plutonic equivalent of the Choiyoi Group volcanic material are mostly granitoids. The remnants of the magmatic arc that produced much of volcanic material is now preserved as a series of batholiths, including the Coastal Batholith of central Chile in the Chilean Coast Range. During the Permian, the zone of arc magmatism moved {{convert|350|km|mi}} inland from the Chilean Coast Range, reaching San Rafael about 280 million years ago.

Many Triassic basins in southern South America, including Cuyo Basin, have their lowermost sections made up of Choiyoi Group formations.{{cite journal |last=Spalletti |first=L.A. |last2=Fanning |first2=C.M. |last3=Rapela |first3=C.W. |date=2008 |title=Dating the Triassic continental rift in the southern Andes: the Potrerillos Formation, Cuyo Basin, Argentina |journal=Geologica Acta |volume=6 |issue=3 |pages=267–283 }}