The Chortis Block is a -wide

continental fragment 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. Cau ...

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

( Honduras,

Nicaragua Nicaragua (; ), officially the Republic of Nicaragua (), is the largest country in Central America, bordered by Honduras to the north, the Caribbean to the east, Costa Rica to the south, and the Pacific Ocean to the west. Managua is the countr ...

, El Salvador, Guatemala, and the off-shore Nicaragua Rise) located in the northwest corner of the

oceanic Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places * Oceanic, British Columbia, a settlement on Smith Island, ...

Caribbean Plate The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America. Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean Plate borders ...

Extent

The northern margin of the Chortis Block is the Motagua- Polochic fault of the

North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

- Caribbean strike-slip boundary. The Cocos/

Farallon Plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...

subducts beneath its western margin resulting in the Middle America Trench and the

Central America Volcanic Arc The Central American Volcanic Arc (often abbreviated to CAVA) is a chain of volcanoes which extends parallel to the Pacific coastline of the Central American Isthmus, from Mexico to Panama. This volcanic arc, which has a length of 1,100 kilometer ...

. Miocene-Holocene-aged rifts in the northern and western Chortis Block is the result of slow internal deformation. The southern and eastern extent is roughly the Nicaragua- Costa Rica border and the offshore Hess Escarpment. The Chortis Block can be subdivided into several

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 ...

s, the names and extents of which varies considerably between different authors.

Tectonic history

Gondwanan origin

During the Late Neoproterozoic-Early Palaeozoic the Chortis Block was probably located on the northern shores of what is now Colombia, then the northern margin of the

Amazonian Craton The Amazonian Craton is a geologic province located in South America. It occupies a large portion of the central, north and eastern part of the continent and represents one of Earth's largest cratonic regions. The Guiana Shield and Central Braz ...

, with an ocean separating it and the other blocks from core North America or

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 ...

. Before the Early Carboniferous formation of

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

the Chortis Block thus formed part of the northern margin of Gondwana, located south of other Peri-Gondwanan terranes such as

Oaxaca Oaxaca ( , also , , from nci, Huāxyacac ), officially the Free and Sovereign State of Oaxaca ( es, Estado Libre y Soberano de Oaxaca), is one of the 32 states that compose the political divisions of Mexico, Federative Entities of Mexico. It is ...

, Carolina,

Yucatán Yucatán (, also , , ; yua, Yúukatan ), officially the Free and Sovereign State of Yucatán,; yua, link=no, Xóot' Noj Lu'umil Yúukatan. is one of the 31 states which comprise the federal entities of Mexico. It comprises 106 separate mun ...

, and

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

. These blocks either escaped the Laurussia-Gondwana collision and were broken off Gondwana later, or were accreted to Laurentia during the collision.

Laurentian origin

Located in a largely unpopulated, mountainous region, the geology of which is poorly known, the Chortis Block is the only Precambrian-Palaeozoic

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial'' be ...

on the Caribbean Plate and even its origin within North America has remained enigmatic and disputed for decades. Three models have been proposed for the origin of the Chortis Block: * According to the first, most widely accepted model, the Chortis Block moved eastward and rotated counterclockwise 30-40° along the Cayman- Motagua- Polochic fault system from its Middle Eocene location off the southwestern coast of Mexico. This model is supported by matching lineations in the Chortis Block and Mexico. * A second model proposes that the Chortis Block originated in the eastern Pacific Ocean south of the Cayman-Motagua-Polochic fault. From this remote location it has moved while rotating 40° clockwise. This rotation is, however, not supported by geological observations. * A third, ''in situ'' model suggests that the Chortis Block has been located more or less just south of Mexico since

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...

and

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 ...

separated in the Late Jurassic.See for example This model is based on matching lineaments in the Chortis Block and the areas surrounding it.

References

Notes

Sources

* * * * * * * {{Refend Geology of the Caribbean Geology of Central America Geology of El Salvador Geology of Guatemala Geology of Honduras Geology of Mexico Geology of Nicaragua