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.
The Block's 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 the Isthmus of Tehuantepec, along the Gulf of Mexico, and into Louisiana.

Geography

Physical

Mountains

A broad arching fold belt of 'morphologically 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, and five southeasterly states of Mexico. 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 Yucatán Peninsula to in the Peninsula's south. The crust, 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, this being considered impossible on an unstretched basement at isostatic equilibrium.

Morphology

Provinces

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

Basins

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

Faults

Several 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, gradually lowering the northern portion of the Yucatán Platform, and 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 1900–1993, the epicentres of at least two of these were located the Block, though a further nine were located it.

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 complex movement of crustal blocks and terranes between the two pre-existing continental masses .' Details of the pre-Cenozoic portion of this process, 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, is 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. 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 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 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 extensive than their present-day counterparts, are thought to have reached their 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

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; 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

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

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

Date	Location	Lat. ºN	Lon. ºW	Depth mi	M_s
	SW Guatemala	14.9	91.5	0–25	7.5
	S Chiapas	16.5	92.5	N	7.6
	S Chiapas	15.0	93.0	N	7.6
	SW Guatemala	15.0	91.0	75	7.2
	S Chiapas	15.5	92.5	N	7.1
	S Chiapas	14.8	92.5	N	7.3
	SW Guatemala	14.8	91.3	25	7.9
	S Chiapas	14.3	92.6	N+	7.2
	SW Guatemala	14.3	91.8	19	7.3
	S Chiapas	14.6	92.6	N	7.3
	SE Guatemala	15.2	89.2	S	7.6