Geoscientist Online

Iain Neill* believes that while no single model to date fully explains the Caribbean Plate, this is no reason to forsake well-established and fundamental tectonic laws.

Geoscientist Online 18 December 2009

A cursory glance at the literature shows that the Caribbean is a hot topic. The kerfuffle over the Origin of the Caribbean Plate (Geoscientist v.19.9), however, bears little relationship to the fervent debate that occasionally erupts at workshops, conferences, or on paper, in part around the many facets of my own supervisors’ (Andrew Kerr and James Pindell) models of how the Caribbean has evolved! I wrote in November (Geoscientist v.19.11) that the Origin debate should have finished years ago. That debate is being re-stoked by those who do not even believe in the existence of Plate Tectonics. Can this mess be put in the garbage can for once and for all?

In defence of Plate Tectonics

The present understanding states that oceanic crust is generated at mid-ocean ridges, and returns to the depths of the Earth at subduction zones, in tune to the beat of mantle convection. Rock will partially melt in the mantle or lower crust under the right circumstances when decompressed or hydrated. Continental crust has built up over time by addition of magmas and the accretion of oceanic material, seamounts, plateaux, arcs und so weiter at collisional margins. Plumes may be generated by the rise of material from disturbances within the mantle. The crust shall twist, shear, fold and fault, thicken and thin in response to the movement of plates and the fiery Play-doh beneath. Numerous processes leave their imprint upon the geochemistry of the rocks involved. Collectively we have the mix of events whose sum total is tectonic geology as we know it – and the existence of these events can be tested scientifically. Thus satisfied, every rock that we pick up, scan, image, blast or zap can then be investigated alongside its neighbours and put into a tectonic context. And so we build up a pattern of local, regional or global Earth history. Thus it has been for over fifty years of intense study. The Caribbean region is not exempt.

The very few remaining in-situ followers would admit our comprehension is not aided by poor exposure; limited access; weathered rocks and incomplete, misused and often inaccurate data. Through time this lack of detailed information has led to the debates we see and ultimately the doubters of the Pacific Origin Paradigm continuing, albeit in my opinion falsely, to have a voice. However, the inability of Pacific Origin workers to produce a self-agreeable explanation of Caribbean geology simply does not reflect a problem with Plate Tectonic theory. Disagreement is eminently resolvable by tweaking the current models as new data is generated, old reviewed and new understandings reached.

In November, I laid out some of the key problems I saw with Keith James’ interpretation of the Caribbean; one that shows unwillingness to see the gamut of facts and interpret them with the eyes of a tectonic geologist, geophysicist or geochemist. I now see in Karsten Storetvedt’s descriptions of the Caribbean a similar problem. His arguments come straight off the back of a reading of the commentary of James and Lorente. He states: “as a wide range of regional and larger scale geophysical and geological information is omitted from their re-evaluation, the arena is open for alternative non-plate tectonic solutions.” The arena would be well and truly shut had he a full appreciation of the available facts about the Caribbean region at the level of detail required. Not once does Professor Storetvedt talk specifically about the ages of rocks, of their chemistry, their inferred tectonic setting and actually challenge what is wrong with the current interpretations. He has not seen beyond his own model of wrench tectonics and ridden roughshod over what we know. Indeed, what of all the other proofs, aside from his bugbear, palaeomagnetism, that show Plate Tectonic theory to be rather sound? What is wrong with what radiometric dating or geochemistry tells us? Or the stories trapped in the sedimentary record, in faunal associations, ophiolites, high-pressure belts and suture zones, even in geophysical surveys?

Such tales are closer to fact than fiction so let us not break convention and instead turn to resolving the history of the Caribbean using plate tectonic means.

To return to the real debate

The posturing today in the peer-reviewed community relates to what Jim Pindell calls the ‘how’ of transporting the Caribbean Plate from the Pacific to the inter-American realm, rather than the ‘if’ it did or did not start life out west. The ‘how’ question is being answered by detailed investigation of the island arc systems that have developed at the leading edge of the Caribbean Plate. Resolving their number, ages, polarity and interaction with the Caribbean Oceanic Plateau is the key to unlocking the tectonic truth behind the Caribbean. This of course goes completely against the hypothesis of James et al., namely that Pacific Origin models are simply too complex to be true. They see debate and take that to mean that we are all fundamentally wrong. I would take the opposing view, that we are all partially right and that another model can be developed which satisfies the most rigorous geological tests. Truth will out, given time. I’m going to try and explain in broad terms some of the ideas and variations on the Pacific Ocean Paradigm that are getting us hot under the collar at the moment, if only to show that they are entirely reasonable!

Three models - but it all hinges upon the Great Arc

As I noted, chief among the challenges in Caribbean geology is to explain the precise mechanism of wrapping the Americas around the Caribbean Plate to attain today’s configuration. It is clear that much of Caribbean eastward motion is only apparent. The formation of an arc at the trailing edge of the plate, coupled with the west-dipping ‘Great Arc’ subduction zone in the east, anchored the Caribbean in the mantle reference frame (Pindell and Barrett, 1990). This allowed the plate’s relative motion into the proto-Caribbean realm as the Atlantic widened and the Americas pushed west. Our problem then is to explain where and when the Great Arc itself originated and when it became west-dipping to allow the Americas to begin their slide-past. Over the past few decades, many hypotheses have arisen but I will focus upon grossly summarising three models that all have their particular enthusiasts. Which is right?

The Caribbean crust, upon thickening by the starting Galapagos mantle plume (e.g. Duncan and Hargraves, 1984) at ca.90 Ma was rendered unsubductable at a west-facing Great Arc which lay at the western edge of the proto-Caribbean sea which split the Americas. This thick plateau crust forced a ~85-80 Ma subduction polarity reversal and the generation of a west-dipping subduction zone for the remainder of Caribbean history (for example, Burke et al. 1988; Kerr et al. 2003 and several other models).

The plateau collision model I believe holds sway until the history and polarity of the forearc-arc-backarc assemblages in Cuba and Hispaniola are investigated in detail. Pindell et al. (2005; 2006) argued the case for a polarity reversal prior to the formation of the Oceanic Plateau, based on a number of key points, not all of which have stood the test of time, but including importantly the Aptian-Albian onset of high-pressure metamorphism in the eastern (forearc) of the Great Arc – concurrent with Model 2.

Pacific crust subducted beneath the splitting Americas forming a precursor Great Arc until the Aptian-Albian interval, such a time as the Americas took flight westwards. The Great Arc itself was forced into a reversal of polarity, possibly after a phase of transform motion due to the greater motion of North America versus South America (see Pindell and Dewey, 1982 (original hypothesis); Pindell and Barrett 1990; Pindell et al. 2005; 2006).

The Aptian-Albian reversal model has stood up for debate alongside the plateau collision model for nearly three decades, but the model remains to my mind somewhat vague about the exact timing of events from one location to another and furthermore predicts the subduction of the proto-Caribbean spreading centre resulting in a ‘slab gap’ or slab-free zone which might act as a helping conduit through which the Galapagos plume head might rise (Pindell and Kennan, 2009). Hastie and Kerr (2009) make it very clear that the appearance of a plume head even vaguely close to the Great Arc subduction zone would result in contamination of the plume head by supra-subduction zone fluids. Contamination is simply not witnessed in the studied sections.

Regardless of this problem, Pindell and his co-workers have now set upon the possibility that all of the island arc rocks of the Greater Antilles are part of a singular arc system with a singular west-dipping polarity. The idea stems from the realisation that there is a very long-lived west-dipping subduction history recorded in the Cuban high-pressure rocks (Maresch et al., 2009; Stanek et al., 2009; Pindell and Kennan, 2009).

At the beginnings of the westward flight of North America, the proto-Caribbean – Pacific boundary was a simple transform which took on a strong sinistral transpressive motion and became the locus for a west-dipping Great Arc subduction zone at ~135 Ma, a state that has continued in general terms until the present day (Pindell and Kennan, 2009).

Some other ideas

Which is right? Time will tell but I do not believe that any of the models fit the bill in totality. This does not mean we should ditch tectonics as our framework! Joint investigations suggest east-dipping subduction during the latest Jurassic. I favour that the earliest parts of the current Caribbean arc crust including the North Coast Schist, Tobago, La Désirade and perhaps some older parts of Cuba (Kerr et al., 1999; Snoke et al., 2001; Neill et al., unpublished data), developed on this west-facing arc system which lay further to the north of the Caribbean region and were brought southwards along the sinistral transform to meet the newly-developing east-facing Great Arc components to be found on Cuba and Jamaica today (Stanek et al., 2009; Pindell and Kennan, 2009). I think one might get around the problem of emplacing a pristine plateau close to an active arc by breaking that convention and having the plateau erupt at a considerable distance from the Great Arc, away from any subduction fluid influence (see reconstructions in Pindell and Kennan, 2009). To reconcile arc and plateau, a second and third arc, now the Dutch Antilles (thanks to Jim Wright!) and parts of Jamaica; would transiently form and thus remove the crustal gap between the plateau and the Great Arc so they are together today.

Whatever eventually wins out, at no point in this debate have we felt the need to knowingly break the laws of geology. Long live tectonics!

*PhD student in SE Caribbean tectonics at the School of Earth and Ocean Sciences, Cardiff University

References

• Burke, K. 1988. Tectonic evolution of the Caribbean. Annual Reviews in Earth and Planetary Sciences, 16, 210-230.
• Duncan, R. A. & Hargraves, R. B. 1984. Plate tectonic evolution of the Caribbean region in the mantle
• reference frame. In: Bonini, W. E., Hargraves, R. B. & Shagam, R. (eds) The Caribbean–South American Plate Boundary and Regional Tectonics. Geological Society of America, Memoirs, 162, 81–93.
• Hastie, A.R. & Kerr, A.C. 2009. Mantle plume or slab window? Physical and geochemical constraints on the origin of the Caribbean oceanic plateau. Earth-Science Reviews in press.
• Kerr, A. C., Iturralde Vinent, M. A., Saunders, A. D., Babbs, T. L. & Tarney, J. 1999. A new plate tectonic model of the Caribbean: implications from a geochemical reconnaissance of Cuban Mesozoic volcanic rocks. Geological Society of America Bulletin, 111, 1581–1599.
• Kerr, A.C., White, R.V., Thompson, P.M.E., Tarney, J. & Saunders, A.D. 2003. No oceanic plateau, no Caribbean Plate? The seminal role of an oceanic plateau in Caribbean plate evolution. In:  Bartonlini, C., Buffler, R. T. & Blickwede, J. F. (eds) The Circum-Gulf of Mexico and the Caribbean; Hydrocarbon Habitats, Basin Formation, and Plate Tectonics. American Association of Petroleum Geologists, Memoirs, 79, 126–168.
• Maresch, W.V., Pindell, J.L. and Stanek, K.P. 2009. Migration of the Great Caribbean Arc relative to the Americas (2): History of subduction and collision along the arc. Caribbean and North Andean tectonomagmatic evolution, workshop, Cardiff University, 2-4th September, 2009.
• Pindell, J. L. & Dewey, J. F. 1982. Permo-Triassic reconstruction of western Pangaea and the evolution of the Gulf of Mexico/Caribbean region. Tectonics, 1, 179–211.
• Pindell, J. L. & Barrett, S. F. 1990. Geological evolution of the Caribbean region: a Plate tectonic perspective. In: Dengo, G. & Case, J. E. (eds) The Caribbean Region. The Geology of North America, H. Geological Society of America, 405–432.
• Pindell, J. L., Kennan, L., Maresch,W. V., Stanek, K. P., Draper, G. & Higgs, R. 2005. Plate kinematics and crustal dynamics of circum-Caribbean arc-continent interactions, and tectonic controls on basin development in proto-Caribbean margins. In: Avé -Lallemant, H. G. & Sisson, V. B. (eds) Caribbean–South American Plate Interactions, Venezuela. Geological Society of America, Special Papers, 394, 7–52.
• Pindell, J. L., Kennan, L., Stanek, K. P., Maresch, W. V. & Draper, G. 2006. Foundations of Gulf of Mexico and Caribbean evolution: eight controversies resolved. Geologica Acta, 4, 89–128.
• Pindell, J.L. & Kennan, L. 2009. Tectonic evolution of the Gulf of Mexico, Caribbean and northern
• South America in the mantle reference frame: an update. From: James, K. H., Lorente, M. A. & Pindell, J. L. (eds) The Origin and Evolution of the Caribbean Plate. Geological Society, London, Special Publications, 328, 1–55.
• Snoke, A. W., Rowe, D. W., Yule, J.D. & Wadge, G. 2001. Petrologic and Structural History of Tobago, West Indies: a Fragment of the Accreted Mesozoic Oceanic-arc of the Southern Caribbean. Geological Society of America, Special Papers, 354.
• Stanek, K. P., Maresch, W. V. & Pindell, J.L. 2009. The geotectonic story of the northwestern branch of the Caribbean arc: implications from structural and geochronological data of Cuba. From: James, K. H., Lorente, M. A. & Pindell, J. L. (eds) The Origin and Evolution of the Caribbean Plate. Geological Society, London, Special Publications, 328, 1–55.