Tectonics of the Caribbean Richard Robertson Seismic Research

Tectonics of the Caribbean Richard Robertson Seismic Research Unit, U. W. I. St. Augustine, Trinidad www. uwiseismic. com

Outline • • • Definitions: Tectonics, Caribbean Plate Tectonics Evolution of the Caribbean Physiographic/Tectonic Provinces Tectonics of the Caribbean Summary

Tectonics • The processes responsible for tectonic activity • Field of study concerned with structures within the crust and with forces and movements that operate to create these • Concerned with mountain building & with the development of cratons and tectonic terranes => earthquakes, volcanoes & tsunamis

The Earth’s layered structure • • • Melting of the more fusible constituents of the upper mantle produces magma Inner core: 1216 km thick and consists of solid rock at very high temperature and pressure Outer core: extends up to 2270 km from the centre of the earth and consists mainly of molten iron with about 10% nickel and traces of other materials Mantle: extends to ~ 2900 km and consists of silicate rocks; due to high temperature and pressure the rocks are able to flow extremely slowly like a thick & stick liquid The Mantle accounts for 83 % of the Earth’s volume & 67% of its mass The Upper and lower mantle separated by the 670 km seismic discontinuity

Lithospheric Plates

Plate boundary settings

The Caribbean Plate • A lithospheric plate consisting mainly of a unusually thick, oceanic plateau situated between two major continental regions • A geologically complex region that displays a variety of plate boundary interactions including subduction (Lesser Antilles), transcurrent/strike-slip (north & south) and sea-floor spreading (Cayman Trough)

The Caribbean

Evolution of Caribbean • • Allochthonous/Mobilist vs. In Situ/Fixist models for origin of Caribbean In-situ evolution • Gulf of Mexico & Caribbean region existed in the past i. e. during Triassic, Jurassic & early Cretaceous Allocthonous evolution: • All accept significant amounts of eastward Caribbean migration relative to the Americas • A Great Arc vs Multi-arc evolution of the region Interpretation of the facts => A single geology and too many points of view

Evolution of the Caribbean Plate

The Caribbean IGCP Project 433 • • • Is the Caribbean Plate allochthonous or developed in situ? There is a single Great Arc or the compressive margins evolved as multiarcs? Why can not be reconcile local geology with the general models?

Physiographic regions

Geologic Provinces

Tectonics of the Caribbean - I • • Result primarily from the interaction of one relatively small plate of lithosphere with surrounding plates The Caribbean – geologically complex region; variety of plate boundary interactions including: • Subduction (Lesser Antilles & Central America) • Transcurrent (strike-slip) on northern and southern boundaries • Sea floor spreading in

Tectonics of the Caribbean - II • Caribbean – a lithospheric plate that consists mainly of anomalously thick, oceanic plateau located between 2 major continental regions => tectonic interactions between thick oceanic crust and continental crust

Caribbean Seismicity • • Caribbean Earthquakes: 1964 to 2002 • First motion studies indicate left-lateral strike slip at northern & right-lateral strike slip at southern boundary => left lateral and right lateral transform boundaries Thrust fault solutions, typical of upper parts of convergent plate boundaries occur at western and eastern margins of plate Depth of hypocentres and their positions relative to island arc volcanoes indicates Wadati-Benioff

Summary • • • The Caribbean is a geologically complex region which exhibits a variety of plate boundary interactions and by extension tectonic features It is a lithospheric plate that consists mainly of anomalously thick, oceanic plateau located between 2 major continental regions Despite recent advances in knowledge there is still disagreement over its

References • • Mattson, Peter, H. ed. (1977): West Indies island arcs. Benchmark Papers in Geology V. 33. Dowden, Hutchinson & Ross, Inc. , p. 361. (see Chapters 2, 3235 b) Jackson, Trevor, A. ed. (2002): Caribbean Geology into the Third Millennium – transactions of the Fifteenth Caribbean Geological Conference. University of the West Indies Press, 279 p. Donovan, Stephen K. and Jackson, Trevor, A. (1994): Caribbean Geology – An Introduction. The University of the West Indies Publishers Association, Jamaica, 289 p. http: //www. ig. utexas. edu/Carib. Plate. html

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