# Maya Block

The Maya Block, also known as the Maya Terrane, Yucatan Block, or Yucatan–Chiapas Block, is a physiographic or geomorphic region and tectonic or crustal block in the southernmost portion of the North American Plate.

## Extent

The Block is commonly delimited by the continental margin in the Gulf of Mexico to the north, in the Caribbean Sea to the east, and in the Pacific Ocean to the southwest, and further, by the Motagua–Polochic Faults to the south-southeast, and by the Isthmus of Tehuantepec to the west. The Motagua–Polochic Faults divide the Maya Block from the Chortis Block, while the Isthmus of Tehuantepec divides it from the Oaxaquia Block (i.e. 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 Yucatán Platform to its north. Relatively less prominent karstic formations occur in the Block's southern portion, including an unnamed formation in northwestern Peten to northeastern 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, five northerly departments of Guatemala (Huehuetenango, Quiche, Alta Verapaz, Izabal, Peten), and five southeasterly states of Mexico (Chiapas, Tabasco, Campeche, Yucatán, 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 20–25 kilometres (12–16 mi) in the northern Yucatán Peninsula to 30–40 kilometres (19–25 mi) in the Peninsula's south. The crust's i.e. Block's crystalline basement is composed mainly of Silurian–Triassic metamorphic and igneous rocks, and is exposed in at least five formations, namely, the Mixtequita Massif, Chiapas Massif, Cuchumatanes Dome, Tucuru–Teleman, and the Maya Mountains. 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 6 kilometres (3.7 mi), 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 Yucatán Peninsula–Belize, 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 Yucatán Platform, thereby lifting its southern extreme in the Maya Mountains. It is nonetheless tectonically rigid or stable, experiencing an absolute west-southwest motion of 1.8 centimetres (0.71 in) 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 1900–1993, 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 Motagua–Polochic 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 [the] complex movement of [various] crustal blocks and terranes between the two pre-existing continental masses [ie North and South America].' Details of the pre-Cenozoic portion of this process (170–67 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. It, together with the Oaxaquia, Suwannee, and Carolina Blocks, are thought to have constituted a peri-Gondwanan terrane on that continent's western, northwestern, northern, or eastern edge during the Appalachian–Caledonian or Ouachita–Marathon–Appalachian orogeny (that is, during the formation of Pangaea from the collision of Gondwana and Laurentia). It is thought to have been displaced away from the Laurentian craton by clockwise rotation, translation, or anticlockwise rotation, during the Middle Jurassic opening of the Gulf of Mexico and subsequent northwesterly drift of North America away from Pangaea.

#### Cenozoic

Details of the Cenozoic (66–0 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 5–2 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 11–8 thousand years ago.

## 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.'

## Tables
### Karstlands

Topographic characterisations of karstland in the northern portion of the Maya Block. :
| Description | Location | Notes |
| Block-faulted coastal plain | east | incl broad lagoons, mangrove swamps, and seasonal marshlands; incl north-northeast fault-bounded ridges and depressions; incl coral reefs and cayes |
| Pitted peninsular plain | north, west | incl dense network of cenotes; incl extensive, contiguous system of flooded caverns; not incl any surface streams |
| Hilly peninsular plain | west | incl La Sierrita de Ticul hills; incl ephemeral surface streams |
| Varied inland plain | south, west | incl steep, irregular hills and depressions; incl extensive fractures and caverns; incl vast alluvial plain with various large swamps and lakes; incl various surface streams |

### Provinces

Geologic provinces in the Maya Block per 21st century literature. :
| USGS No. | Name | Location | Notes |
| 5308 | Yucatán Platform | north | cf |
| 6117 | Greater Antilles Deformed Belt | east | cf |
| 6125 | Maya Mountains | south | cf |
| 5310 | Sierra Madre de Chiapas–Peten Foldbelt | south, west | cf |
| 6122 | Chiapas Massif–Nuclear Central America | south, west | – |
| 6088 | Pacific Offshore Basin | south, west | cf |
| 5311 | Chiapas Massif | west | – |
| 5302 | Veracruz Basin | west | – |
| 5303 | Tuxla Uplift | west | – |
| 5307 | Campeche–Sigsbee Salt Basin | north, west | – |
| 5304 | Saline–Comalcalco Basin | north, west | – |
| 5305 | Villahermosa Uplift | north, west | – |
| 5306 | Macuspana Basin | north, west | – |

### Basins

Sedimentary basins in the Maya Block per 21st century literature. :
| Evenick ID | Name | Location | Notes |
| 119 | Campeche | north, west | cf |
| 757 | Yucatán | east | cf |
| 519 | Peten–Corozal | south | cf |
| – | Limon–Bocas del Toro | south | cf |
| 647 | Sureste | west | cf |

### Tectonics

Earthquakes of M$_s$ ≥ 7.0 during 1900–1993 with epicentres located in or near the Maya Block. :
| Date | Location | Lat. ºN | Lon. ºW | Depth mi | M$_s$ |
| 19 Apr 1902 | SW Guatemala | 14.9 | 91.5 | 0–25 | 7.5 |
| 3 Sep 1902 | S Chiapas | 16.5 | 92.5 | N | 7.6 |
| 14 May 1903 | S Chiapas | 15.0 | 93.0 | N | 7.6 |
| 4 Feb 1921 | SW Guatemala | 15.0 | 91.0 | 75 | 7.2 |
| 10 Dec 1925 | S Chiapas | 15.5 | 92.5 | N | 7.1 |
| 14 Dec 1935 | S Chiapas | 14.8 | 92.5 | N | 7.3 |
| 6 Aug 1942 | SW Guatemala | 14.8 | 91.3 | 25 | 7.9 |
| 28 Jun 1944 | S Chiapas | 14.3 | 92.6 | N+ | 7.2 |
| 23 Oct 1950 | SW Guatemala | 14.3 | 91.8 | 19 | 7.3 |
| 29 Apr 1970 | S Chiapas | 14.6 | 92.6 | N | 7.3 |
| 4 Feb 1976 | SE Guatemala | 15.2 | 89.2 | S | 7.6 |

### Timeline

Prominent events related to the geologic history of the Maya Block. :
| Start | End | Unit | Epoch | Event | Notes |
| 1600 | 910 | Ma | Calymmian–Tonian | Maya Block basement formation starts | partially during Grenville orogeny; cf |
| 240 | 200 | Ma | Middle Triassic–Early Jurassic | Pangaean rifting starts | cf |
| 165 | 165 | Ma | Middle Jurassic | Gulf of Mexico seafloor spreading starts | incl exposed northern Yucatán Peninsula; cf |
| 144 | 144 | Ma | Early Cretaceous | Caribbean Sea seafloor spreading starts | cf |
| 120 | 120 | Ma | Early Cretaceous | Chortis Block subduction into southwestern Mexico stops | cf |
| 78 | 72 | Ma | Late Cretaceous | Greater Antilles Arc collision into Maya Block starts | cf |
| 78 | 63 | Ma | Late Cretaceous–Palaeocene | Chortis Block collision into Maya Block starts | cf |
| 66 | 66 | Ma | Palaeocene | Chicxulub asteroid impact on Maya Block occurs | cf |
| 49 | 49 | Ma | Eocene | Cayman Trough rifting starts | cf |
| 26 | 20 | Ma | Oligocene–Miocene | Cayman Trough rifting slows down | cf |
| 23 | 22 | Ma | Miocene | Farallon Plate rifting starts | cf |
| 22 | 22 | Ma | Miocene | Cocos Plate subduction into Chortis Block starts | incl end of eastwards migration of Chortis Block; incl possible uplift of Chortis Block; incl formation of Bay of Honduras i.e. initial linking of Maya and Chortis Blocks; cf |
| 19 | 10 | Ma | Miocene | Super-fast spreading of East Pacific Rise starts and stops | cf |
| 15 | 3 | Ma | Miocene–Pliocene | Panamanian isthmus closure starts and stops | cf |