Geoscientist Online

Geoscientist 19.9 September 2009

Caribbean Plate understanding is hampered by geology spread over many geographic elements, absence of ocean fracture patterns, magnetic anomalies and recognized spreading ridges (except the Cayman Trough centre) and by presumed oceanic origins – the Pacific paradigm. Unquestioning acceptance of this creates two problems: ¹) many projects are premised (and funded) upon it, ²) all data are interpreted in an oceanic context. There is strong resistance to alternative models that could provide important possibilities for new resource exploration and improved seismic risk control.

Geologic Setting

The Caribbean Plate forms part of Middle America where four marine areas, the Gulf of Mexico, the Yucatán Basin, the Cayman Trough and the Caribbean Sea (Colombian and Venezuelan basins), large continental blocks (Maya and Chortis) and many islands are dispersed between North and South America (Figure 1).

The Pacific Origin Paradigm (POP)

The Caribbean Plate was originally thought to have formed in place but in 1966, Wilson suggested that the Caribbean and Scotia plates were tongues of lithosphere intruding between North and South America, South America and Antarctica, like inter fingering ice sheets1. The Pacific origin of the Caribbean Plate has since become paradigm ^2,3,4 (Fig. 2).

The POP model holds that the Plate formed in the Pacific during the Jurassic, thickened into an oceanic plateau in the Cretaceous above a mantle plume/hotspot or above a "slab gap" in subducting "proto-Caribbean" crust and moved between the Americas. It collided with west-facing volcanic arc, blocking subduction and reversing polarity. The arc collided with Yucatán and Colombia, subducting continent to 70 – 80 km and HP/LT metamorphism. Volcanic activity ceased during Eocene to Oligocene oblique and diachronous arc collision with the Florida-Bahamas platform and northern South America. HP/LT rocks resurfaced in Cuba and along northern Venezuela. Slab roll-back in two different directions opened the Yucatán Basin south of Cuba. These elements joined North America as the plate boundary transferred to the Cayman Trough, where spreading accompanied 1100 km of eastward plate movement. Cenozoic Grenada Basin inter- or back-arc spreading separated the Aves Ridge from the Lesser Antilles, the active remains of the arc. Chorotega and Chocó are seen to be intra-oceanic volcanic arcs with accreted oceanic rocks on the trailing edge of the Caribbean Plate.

This model regards the Caribbean Plate as comprising mainly oceanic crust surrounded by volcanic arc rocks. It requires subduction of large areas of the plate below South America and rotation of the large continental blocks of Maya (135° counter clockwise or 100° clockwise) and Chortis (180 counter clockwise or 80° clockwise).

An in situ “antiparadigm”

The in-situ model 5-8 suggests that Caribbean Plate formed in place between the diverging Americas, just as the remarkably similar Scotia Plate is known to have formed by spreading and dispersal of continental fragments between South America and Antarctica ⁹.

Diverse geological data show that geology between North and South America shows regional harmony and a shared history among the many geographic components. Regional tectonic fabric (Fig. 3) reflects reactivation of ancient lineaments and shows that no major block rotations occurred. Crustal thicknesses up to 45 km, gravity data and high silica content of igneous rocks indicate that continental fragments lie beneath the whole of Central America ¹⁰ and the Greater and Lesser Antilles. Seismic data (Fig. 4) suggest that they underpin the thick "plateau" of the Venezuelan Basin ¹¹ and parts of the Colombian, Yucatán and Grenada basins. Salt diapirs are present.

Plate history involved Late Triassic formation of the Central Atlantic Magmatic Province, Triassic-Jurassic rifting, Jurassic – early Cenozoic extension and Oligocene – Recent strike-slip. The geology continues that of the eastern seaboard of North America but in a more extensional setting that promoted volcanism, foundering, eastward plate growth by backarc spreading and distribution of continental fragments on the plate interior and margins.

Subsidence of proximal areas (Bahamas and Yucatán-Campeche platforms, Nicaragua Rise) accommodated kilometres-thick carbonate sections. Horsts of continental crust flanked by wedges of Jurassic-Cretaceous sediments, flows and salt formed in more distal areas along the eastern margin of North America and within Middle America (Yucatán, Colombian and Venezuelan thick crust). Shallow/subaerial flows of smooth seismic Horizon B" capped thick crust in the late Cretaceous. Extreme extension serpentinized upper mantle, forming rough Horizon B" (thin Caribbean crust).

Figure 1: Middle America. The Gulf of Mexico is intracontinental, surrounded by southern North America and the Florida-Bahamas, Tehuantepec (T) and Campeche (Maya) platforms. Cuba (C), with basement and Mesozoic carbonate cover intimately related to Florida – Bahamas, bounds the Yucatán Basin to the north; the Cayman Ridge separates it from the Cayman Trough. The Chortis Block (CB), with its marine extension, the Nicaragua Rise (NR), forms about a third of the Caribbean Plate and is the only place where continental crust is currently recognized. Chorotega and Chocó (Chr, Chc) link Chortis to South America as Central America. The Greater Antillean islands of Jamaica (J), Hispaniola (H), Puerto Rico (PR) and the northern Virgin Islands, large, mostly submerged blocks separated by narrow deeps, lie along the northern Caribbean Plate boundary. The southern plate boundary runs along northern S America. On the plate interior the Beata and Aves Ridges (BR, AR) separate the Colombian Basin - Venezuelan and the Venezuelan - Grenada basins. Sinistral and dextral strike slip on the northern and southern plate boundaries and the Lesser Antilles volcanic arc mark westward movement of North and South America relative to the Caribbean. The Pacific Cocos Plate converges NE with Central America, where volcanism also occurs.

Figure 2: Caribbean Plate (CP) migration from the Pacific (Central America, outlined, not present at that time). Arrows show rotations of Maya, out of the Gulf of Mexico, and Chortis, from SW Mexico, which followed the plate and accreted to its NW corner. Chorotega and Chocó (Fig. 1) are intra-oceanic arc + accreted oceanic rocks on the western tail of the plate. Note impossible bending of a linear arc, which must be rooted in crust, into an extreme curve.

Fig. 3. Tectonic fabric of Middle America. Sinistral offset of North from South America along N60°W fractures/intracontinental faults reactivated N35°E palaeolineaments as dextral faults, generated N60°E normal faults (e.g. Hess Escarpment HE), E-W sinistral slip along the northern plate boundary (early Cayman offset CT) and the Florida Arch (FA).

While the Gulf of Mexico remained largely intra-continental, the Caribbean, west of diverging fractures in the Central Atlantic and a lengthening Mid Atlantic Ridge, suffered greater extension. Middle and Late Cretaceous and Middle Eocene convergence led to pause or cessation of volcanic activity, uplift to wavebase/subaerial erosion and development of regional unconformities and shallow marine carbonates. Cretaceous change of volcanic arc rock chemistry from primitive to calc-alkaline recorded continental input. Restricted marine, organic-rich sediments formed along with Late Cretaceous subaerial flood basalts. The Middle Eocene event resulted in emplacement of enormous olistoliths (up to 5km thick and 1000 km long) onto plate boundaries and terminated most volcanic activity along the northern and southern Caribbean plate boundaries (coeval, not diachronous) ¹³. Oligocene – Recent strike-slip followed, corresponding to 300 km of central Cayman Trough spreading - the only identified spreading and magnetic anomalies in Middle America. The Caribbean Plate extended eastwards over Atlantic crust. Scotia Plate analogy suggests back-arc spreading along the Aves Ridge.

Indications of continental fragments below the Caribbean "Plateau" and the Greater and Lesser Antillean and Central American volcanic arcs advise caution in assuming purely intra-oceanic origins for oceanic plateaux and volcanic arcs ¹⁴. Accepted discriminatory chemical/isotope data for such areas need to be statistically qualified and examined independent of presumed origins to see what messages they carry. Caribbean volcanic arcs suggest answers to the "andesite problem" - it is not a case of understanding how subducting basalt gives rise to such silica-rich rocks ¹⁵ but rather of recognizing that arc roots, related by seismic velocities to continental rocks ¹⁶ involve original continental fragments. HP/LT metamorphic rocks are not necessarily signals of subduction. No such rocks are associated with the Lesser Antilles or Central America arcs, active since at least the early Cretaceous. Such rocks (Cretaceous) occur close to major plate boundary faults, along with sedimentary equivalents. The Columbus – Maturin Basin of southern Trinidad – eastern Venezuela, foredeep to the El Pilar Fault, contains up to 25km of Tertiary sediments above Mesozoic section perhaps equally thick and heat flow is low to moderate - conditions capable of generating blueschists.

Concluding Remarks

Models for the Pacific origin of the Caribbean Plate models are complicated, with many processes difficult to explain or test. The in-situ model incorporates data in a regionally coherent, simple evolution that conforms to the wider geology of eastern North America and the Gulf of Mexico. It can be tested by re-examination of existing samples, seismic data and deep sea drilling ⁸.

Fig. 4. In-situ interpretation (James, 2007b) of seismic line 1293 over the Venezuela Basin (line location Fig. 3). Line and original interpretation, showing 40 km wide highs of vertical dykes flanked by volcanic flows, with local seamounts, in Diebold et al. 1999 (Figs. 2, 15)^9.

References

1. Wilson, J. T., 1966, Are the structures of the Caribbean and Scotia arcs analogous to ice rafting?: Earth and Planetary Science Letters, v. 1, p. 335-338.
2. Pindell, J. L., 1991, Geological arguments suggesting a Pacific origin for the Caribbean Plate: Transactions 12th Caribbean Geological Conference, St. Croix.
3. Pindell, J., L. Kennan, K-P. Stanek, W. V. Maresch and G. Draper, 2006, Foundations of Gulf of Mexico and Caribbean evolution: eight controversies resolved: In: Iturralde-Vinent, M. A. and E. G. Lidiak (eds.), Caribbean Plate Tectonics, Geologica Acta, v. 4, no. 1-2, p. 303-341.
4. Pindell, L. J. and L. Kennan, 2009, Tectonic evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference frame: an update: In: James, K. H., Lorente, M. A. & Pindell, J. L. (eds.), The Origin and Evolution of the Caribbean Plate. Geological Society, London, Special Publications, v. 328, p. 1–55.
5. James, K. H., 2005, A simple synthesis of Caribbean geology: Transactions, 16th Caribbean Geological Conference, Barbados, Caribbean J. of Earth Sciences, v. 39, p. 71-84.
6. James, K. H., 2006, Arguments for and against the Pacific origin of the Caribbean Plate: discussion, finding for an inter-American origin: In: Iturralde-Vinent, M. A. and E. G. Lidiak (eds.), Caribbean Plate Tectonics, Geologica Acta, v. 4, no. 1-2, p. 279-302.
7. James, K. H. In situ origin of the Caribbean: discussion of data: In: James, K. H., Lorente, M. A. & Pindell, J. L. (eds), The Origin and Evolution of the Caribbean Plate. GSL, Special Publications, v. 328, p. 77-126
8. James, K. H., 2009, Evolution of Middle America and the in situ Caribbean Plate model: In: James, K. H., Lorente, M. A. & Pindell, J. L. (eds.), The Origin and Evolution of the Caribbean Plate. GSL, Special Publications, v. 328, p. 127-138.
9. Barker, P. F., 2001, Scotia Sea tectonic evolution: implications for mantle flow and palaeocirculation: Earth-Science Reviews, v. 55, p. 1-39.
10. James, K. H., 2007, Structural Geology: from local elements to regional synthesis: In: Bundschuh, J. and G. E. Alvarado (eds.), Central America: Geology, Resources and Hazards, Ed. Balkema, Chapter 11, p. 277-321.
11. James, K. H., 2007, Geology of the Caribbean Plateau: http://www.mantleplumes.org/PPPs.html
12. Diebold, J., N. Driscoll and the EW-9501 Science Team, 1999, New insights on the formation of the Caribbean basalt province revealed by multichannel seismic images of volcanic structures in the Venezuelan Basin: In: Mann, P. (ed.), Caribbean Sedimentary Basins, Sedimentary Basins of the World, Elsevier, p. 561-589.
13. James, K. H., 2005, Palaeocene to middle Eocene flysch-wildflysch deposits of the Caribbean area: a chronological compilation of literature reports, implications for tectonic history and recommendations for further investigation: Transactions, 16th Caribbean Geological Conference, Barbados, Caribbean J. of Earth Sciences, v. 39, p. 29 - 46.
14. Leat, P. T. and R. D. Larter, 2003, Intra-oceanic subduction systems: introduction: In: Larter, R. D. and P. T. Leat (eds.), Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes: GSL Spec. Pub. 219, p. 1 - 17.
15. Takahashi, N., S. Kodaira, S. L. Klemperer, Y. Tatsumi, Y. Kaneda and K. Suyehiro, 2007, Crustal Evolution of the Mariana intra-oceanic island arc: Geology, v. 35, p. 203-206.
16. Tatsumi, Y. and T. Kosigo, 2003, The subduction factory: its role in the evolution of the Earth's crust and mantle: In: Larter, R. D. and P. T. Leat (eds.), Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes: GSL Spec. Pub. 219, p. 55-80

Author affiliations

* Institute of Geography and Earth Sciences, University of Wales, Aberystwyth; Professor of Advanced Stratigraphy, Central University of Venezuela, Caracas, resp.