Tobífera Formation () is a volcano-sedimentary formation of

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

age. The formation is crops out in the

Magallanes Region The Magallanes Region (), officially the Magallanes y la Antártica Chilena Region () or Magallanes and the Chilean Antarctica Region in English, is one of Chile's 16 first order administrative divisions. It is the southernmost, largest, and sec ...

in southern

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

and

Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan. The archipelago consists of the main is ...

of Chile, the Santa Cruz Province of southern Argentina, and in the subsurface of the Malvinas Basin offshore Argentina and the

Falkland Islands The Falkland Islands (; ), commonly referred to as The Falklands, is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and from Cape Dub ...

Description

The bulk of the formation originates from

silicic Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. Granite and rhyolite are the most common silicic rocks. Silicic is the g ...

pyroclastic material during a period of bimodal volcanism in Rocas Verdes Basin, a

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

basin.Fildani, Andrea, Romans, B.W., Fosdick, J.C., Crane, W.H., and Hubbard, S.M. (2008)
Orogenesis of the Patagonian Andes as reflected by basin evolution in southernmost South America
in Spencer, J.E., and Titley, S.R., eds., Ores and orogenesis: Circum-Pacific tectonics, geologic evolution, and ore deposits: ''Arizona Geological Society Digest'' 22: 259-268. The Tobífera Formation is grouped together with other formations of similar age in Patagonia in the Chon Aike Province an extraordinarily large province of silicic volcanism. Except for some western and southern exposures most of the formation is buried and known only from

borehole A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petr ...

s in the Magallanes and Malvinas Basins. The formation is equivalent to El Quemado and Ibañez Formations. Tobífera Formation has an up to thick Basal Clastic Complex, a sub-unit made up of conglomerate and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

. Tobífera Formation unconformably overlies

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

and

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

complexes of Cambrian age.

Deformation and metamorphism

Much of the formation is folded and faulted as consequence of the

Andean orogeny The Andean orogeny () is an ongoing process of orogeny that began in the Early Jurassic and is responsible for the rise of the Andes mountains. The orogeny is driven by a reactivation of a long-lived subduction system along the western margin o ...

. At

Última Esperanza Province Última Esperanza (, meaning "Province of the Last Hope") is one of four provinces in the southern Chilean region of Magallanes and Antártica Chilena. The capital is Puerto Natales and it is named after Última Esperanza Sound. A section of it ...

the formation

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

first under

greenschist facies Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, ...

and then under prehnite-pumpellyite facies conditions. Some

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

s of Tobífera Formation were incorporated into Cordillera Darwin Metamorphic Complex. The incorporation of part of Tobífera Formation in the metamorphic complex was accompanied by deformation and metamorphism and occurred in the context of the Andean orogeny in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

References

{{DEFAULTSORT:Tobifera Formation Geologic formations of Chile Geologic formations of Argentina Jurassic System of South America Jurassic Argentina Jurassic Chile Jurassic volcanism Tuff formations of Argentina Formations Geology of Magallanes Region Geology of Santa Cruz Province, Argentina Geology of Patagonia Geology of the Atlantic Ocean Tuff formations of Chile