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. Caus ...

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

(

Honduras Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...

Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...

El Salvador El Salvador, officially the Republic of El Salvador, is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south by the Pacific Ocean. El Salvador's capital and largest city is S ...

Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...

, and the off-shore Nicaragua Rise) located in the northwest corner of the oceanic Caribbean Plate.

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 and Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Caribbean Sea, and to the sou ...

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

strike-slip boundary. The Cocos/ Farallon Plate subducts beneath its western margin resulting in the

Middle America Trench The Middle America Trench is a major subduction zone, an oceanic trench in the eastern Pacific Ocean off the southwestern coast of Middle America, stretching from central Mexico to Costa Rica. The trench is 1,700 miles (2,750 km) long an ...

and the Central America Volcanic Arc. 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 Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...

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 fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...

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 Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

, then the northern margin of the Amazonian Craton, 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 Geology of North America, 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 ...

. 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 period approximately 335 mi ...

the Chortis Block thus formed part of the northern margin of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

, located south of other Peri-Gondwanan terranes such as

Oaxaca Oaxaca, officially the Free and Sovereign State of Oaxaca, is one of the 32 states that compose the political divisions of Mexico, Federative Entities of the Mexico, United Mexican States. It is divided into municipalities of Oaxaca, 570 munici ...

, Carolina,

Yucatán Yucatán, officially the Free and Sovereign State of Yucatán, is one of the 31 states which, along with Mexico City, constitute the 32 federal entities of Mexico. It comprises 106 separate municipalities, and its capital city is Mérida. ...

, and

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

. 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, metamorphic, and sedimentary 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 '' si ...

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 (geometry), direction or geography. Etymology T ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

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