The Maya Block, also known as the Maya Terrane, Yucatan Block, or YucatanChiapas Block, is a physiographic or geomorphic region and tectonic or crustal block in the southernmost portion of the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacifi ...

Extent

The Block is commonly delimited by the

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

in the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...

to the north, in the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

to the east, and in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

to the southwest, and further, by the MotaguaPolochic Faults to the south-southeast, and by the

Isthmus of Tehuantepec The Isthmus of Tehuantepec () is an isthmus in Mexico. It represents the shortest distance between the Gulf of Mexico and the Pacific Ocean. Before the opening of the Panama Canal, it was a major overland transport route known simply as t ...

to the west. The MotaguaPolochic Faults divide the Maya Block from the

Chortis Block The Chortis Block is a -wide continental fragment in Central America ( Honduras, Nicaragua, El Salvador, Guatemala, and the off-shore Nicaragua Rise) located in the northwest corner of the oceanic Caribbean Plate. Extent The northern margin of t ...

, while the Isthmus of Tehuantepec divides it from the Oaxaquia Block (ie the Juarez, Cuicateco, or Oaxaquia Block, Terrane, or microcontinent). The Block's ''precise'' subaerial limits are not widely agreed upon, in contrast to its relatively exact submarine borders. Furthermore, it has been recently suggested that the Block's western extreme may rather extend ''past'' the Isthmus of Tehuantepec, along the Gulf of Mexico, and into Louisiana.

Geography

Physical

Mountains

A broad arching fold belt of 'morphological distinct mountain ranges separated by deep fault-controlled canyons and occasional broad alluvial valleys' extends along the south-southeasterly limit of the Block. The most prominent of said mountain ranges are the Northern Chiapas Mountains and the Sierra Madre de Chiapas in Mexico, the Cuchumatanes, Chama, Santa Cruz, and Lacandon Ranges in Guatemala, and the Maya Mountains in Belize.

Karstlands

The 'most extensive karstlands of the North American continent' extend northwards from the Block's southern extreme. The Block's most prominent karstic landform is the Yucatan Platform to its north. Relatively less prominent karstic formations occur in the Block's southern portion, including an unnamed formation in northwestern Petennortheastern Belize, the Belize Barrier Reef, the Lacandon Range, the Cuchumatanes Range, and various formations to the north and south of the Maya Mountains.

Coasts

The most prominent topographic features of the Block's Caribbean coast are extensive seagrass beds and coral reefs, with the Belize Barrier Reef forming a notable example of the latter. Its Pacific coast, in contrast, is predominated by extensive mangrove forests.

Human

The terrestrial portion of the Block encompasses all six

districts of Belize Belize is divided into six districts. __NOTOC__ List See also * Constituencies of Belize *List of municipalities in Belize *List of West Indian First-level Subdivisions This is a list of first-level country subdivisions within the Caribbean ...

, five northerly

departments of Guatemala Guatemala is divided into 22 departments ( Spanish: ''departamentos'') which are in turn divided into 340 municipalities. In addition, Guatemala has claimed that all or part of the nation of Belize Belize (; bzj, Bileez) is a Caribbean a ...

(ie Huehuetenango, Quiche, Alta Verapaz, Izabal, Peten), and five southeasterly states of Mexico (ie Chiapas, Tabasco, Campeche, Yucatan, and Quintana Roo). Its submarine portion encompasses the continental shelf which abuts the coastal districts.

Geology

Stratigraphy

Crust

Mean thickness of the continental crust constituting the Block increases southwards, ranging from in the northern Yucatan Peninsula to in the Peninsula's south. The crust's ie Block's crystalline basement is composed mainly of SilurianTriassic metamorphic and igneous rocks, and is exposed in at least five formations, ie the Mixtequita Massif, Chiapas Massif, Cuchumatanes Dome, TucuruTeleman, and the

Maya Mountains The Maya Mountains are a mountain range located in Belize and eastern Guatemala, in Central America. Etymology The Maya Mountains were known as the ''Cockscomb'' or ''Coxcomb Mountains'' to Baymen and later Belizeans at least until the mid-2 ...

. Elsewhere, the basement is overlain by a thick sedimentary cover of Upper Palaeozoic clasts and carbonates, Upper Jurassic continental redbeds, and Cretaceous–Eocene carbonates and evaporites. It has been suggested that the Block's continental basement is stretched, since its sedimentary cover reaches a thickness of up to , this being considered impossible on an unstretched basement at isostatic equilibrium.

Morphology

Provinces

The Block is thought to fully or partially incorporate between two and thirteen geologic provinces.

Basins

The Block is believed to fully or partially comprehend some four or five sedimentary basins.

Faults

A number of faults or fault zones have been identified within the Block, the most prominent of which include various boundary faults abutting the Maya Mountains, various offshore faults east of the Yucatan PeninsulaBelize, the Ticul Fault, the Malpaso Faults, and the Rio Hondo Faults.

Tectonics

The Block is thought to experience significant counterclockwise rotation and a north-northwest down tilt, which gradually lowers the northern portion of the Yucatan Platform, thereby lifting its southern extreme in the Maya Mountains. It is nonetheless tectonically rigid or stable, experiencing an absolute west-southwest motion of per annum. Central America, including the southern portion of the Maya Block, 'is very well-known and characterised by numerous, medium size earthquakes preceded and followed by damaging shocks,' with the Middle America Trench in the Pacific deemed the main source of such quakes. Of thirty-three earthquakes of M_s ≥ 7.0 in Central America during 19001993, the epicentres of at least two of these were located ''within'' the Block (in its southwestern quadrant), though a further nine were located ''near'' it (in the MotaguaPolochic Faults or the portion of the Middle America Trench bordering the Block).

History

Pre-Cenozoic

Middle America, including the Maya Block, is thought to have taken shape sometime after 170 million years ago. Its formation is thought to have 'involved hecomplex movement of ariouscrustal blocks and terrains between the two pre-existing continental masses e North and South America' Details of the pre-Cenozoic portion of this process (ie 17067 million years ago), however, are not widely agreed upon. Nonetheless, it has been proposed that the Block formed before or during the opening of the

Iapetus Ocean The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleoc ...

. It, together with the Oaxaquia, Suwannee, and Carolina Blocks, are thought to have constituted a peri-Gondwanan terrane on that continent's western, northwestern, or eastern edge during the AppalachianCaledonian or OuachitaMarathonAppalachian orogeny (ie during the 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 millio ...

from the collision of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

and

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 ...

). It is thought to have been displaced away from the Laurentian craton by clockwise rotation, translation, or anticlockwise rotation, during the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations ...

opening of the

and subsequent northwesterly drift of North America away from Pangaea.

Cenozoic

Details of the Cenozoic (ie 660 million years ago) geologic history of Middle America, including that of the Maya Block, are relatively more widely agreed upon. In broad strokes, the Chortis Block is thought to have reached its present-day position by at least 20 million years ago. The northern and eastern coasts of the Block are not thought to have been fully subaerially exposed until some 52 million years ago. The Block's coastlines, which were initially more expansive than its present-day ones, are thought to have reached modern dimensions due to rising sea levels some 118 thousand years ago.

Timeline

Scholarship

The Block was discovered in 1969 by Gabriel Dengo, a Guatemalan geographer. It was quickly adopted in scholarship, and remains 'accepted by many as a valid subdivision of Central America's geology, especially of its crystalline basement.'

Notes and references

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# # {{authority control Geology of North America Geology of the Atlantic Ocean Geology of Belize Geology of Guatemala Geology of Mexico Geomorphology#Physiographic divisions Physiographic divisions