Evolution of Middle America and the in situ Caribbean Plate model

KEITH H. JAMES

Institute of Geography and Earth Sciences, Aberystwyth, Wales, UK and

Consultant Geologist, Plaza de la Cebada 3, 09346 Covarrubias, Burgos, Spain

(e-mail: khj@aber.ac.uk)

Abstract: Regional geological data and global analogues suggest Caribbean Plate geology con-tinues that seen along the margin of eastern North America in a more extensional setting,between the diverging Americas. From west to east there are continental masses with Triassicrifts, proximal continental blocks with kilometres-thick Mesozoic carbonates, more distal areasof Palaeozoic horsts flanked by Triassic–Jurassic dipping wedges of sediments, including saltand overlain by Cretaceous basalts, and most distal areas of serpentinized upper mantle. Platehistory began along with the Late Triassic formation of the Central Atlantic Magmatic Provinceand involved Triassic–Jurassic rifting, Jurassic–Early Cenozoic extension and Oligocene–Recent strike–slip. Great extension promoted volcanism, foundering, eastward growth of theplate by backarc spreading and distribution of continental fragments on the plate interior andalong its margins. Hydrocarbons probably are present. Caribbean geology has important implica-tions for understanding of oceanic plateaus, intra-oceanic volcanic arcs, the ‘andesite problem’ andgenesis of ‘subduction’ HP/LT metamorphic rocks. The model can be tested by re-examination ofexisting samples and seismic data and by deep sea drilling.

Middle America – crustal makeup

Based upon data discussed in a sister article thispaper suggests an in situ evolution of the CaribbeanPlate between North and South America. The dataindicate that Middle America is built mainly ofextended/distributed continental crust and smallerareas of pseudo-oceanic crust (serpentinized mantle)(the only recognized spreading crust, with magneticanomalies, lies in the centre of the Cayman Trough;Fig. 1). The geology continues that along the easternmargin of North America but in a more extensionalsetting between the diverging Americas. Rifted andextended continent with thick Mesozoic carbonatecover recording subsidence surrounds the Gulfof Mexico and Yucatan basins and underpins theFlorida–Bahamas platform and the submergedextension, as far as Jamaica, of continental Chortısalong the Nicaragua Rise. The internal Gulf ofMexico, Yucatan, Colombian, Venezuelan andGrenada basins carry extended continental blocksflanked by half-grabens with wedge-shape fill,bounded by areas of thin (c. 3 km) pseudo oceaniccrust of serpentinized mantle.

Tectonic fabric

Middle America manifests a regional tectonicfabric (Fig. 2) that demonstrates regional geologicalcoherence and shows that no major block rotationsor plate migration occurred. The stress–strainellipse (inset) for sinistral movement of NorthAmerica away from South America along N608Wfractures (a) reactivated N358E Palaeozoic sutures

as Triassic–Jurassic rifts with dextral componentof movement; (b) generated N608E extensionalfaults such as the Hess and NW Campeche escarp-ments; and (c) generated the Florida Arch. Curvedfaults in northern Central America reflect oroclinalbending and shortening during Cenozoic sinistralreactivation of N358E trends (James 2007).

The following sketches suggest a Pangaean recon-struction and the evolution of Middle America.They do not pretend to be quantitative.

Pangaean reconstruction

Pre-drift restoration of Middle America (Fig. 3a)requires removal of sinistral offset and extensionbetween North and South America and removal ofvolcanic-arc crust and serpentinized mantle (Fig. 1).The Gulf of Mexico (NAm) is closed up around theMaya Block. Maya and Chortıs are united (removalof c. 900 km of Jurassic–Cretaceous, early Caymanoffset and 300 km of Oligocene–Recent Caymanoffset) by aligning their faulted eastern marginsand Jurassic rifts associated with the Rıo Hondoand Guayape faults (Fig. 2). This also restoresCuba north of Hispaniola and Puerto Rico, them-selves closed up by removal of Cenozoic pull-apart.Thick crust of the Caribbean ‘Plateau’, westernVenezuela Basin, lies close to South America.Similar crust seems to be present in the Yucatanand Colombian basins. Cenozoic oroclinalbending of the Motagua and Agalta areas andwestern Cuba (James 2007) is removed. The HessEscarpment/southern limit of the Nicaragua Riserestores against the Merida trend of NW Venezuela.

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, 127–138.DOI: 10.1144/SP328.4 0305-8719/09/$15.00 # The Geological Society of London 2009.

Northwestern South America – the ‘Bolivar Block’is restored several hundred kilometres to the SWalong the Merida Andes – Eastern Cordillera ofVenezuela–Colombia. The Aruba–Blanquilla islandchain does not exist at this time. Southern CentralAmerica (Chorotega–Choco) restores to the SWof Chortıs (present day Gulf of Tehuantepec,James 2007).

This schematic reconstruction suggests continu-ity of major faults crossing Maya and Chortıs withsouthern Florida and the eastern seaboard of NorthAmerica and its continuation into NW SouthAmerica, possibly through the Sierra Nevada deSanta Marta in Colombia.

Geological evolution

Triassic–Early Jurassic rifting (Fig. 3b) reactivatedPalaeozoic continental sutures as rifts, accommo-dating red beds and basalts (Manspeizer 1988; fora more regional vision of the Central Atlantic Mag-matic Province and continental margin wedgessee McHone et al. 2005, Fig. 1). Inboard basinswere then abandoned as extension moved to the

continental margin. Here, asymmetric basinsaccommodated red beds, carbonates and evaporitesas seaward-dipping wedges along the eastern sea-board of North America to Caribbean latitudes.Major N608E trending features such as the Hessand NW Campeche escarpments and the LaTrocha F. formed as the extensional strain withinthe regional N608W sinistral system of offsetbetween North and South America (Fig. 2). Theresultant new basins accommodated salt deposition.Since salt diapirs and ultramafic rocks are seenalong northern Honduras (Pinet 1971, 1972) andsince serpentinites occur in the Motagua fault zonein the Cretaceous (Harlow et al. 2004), this papersuggests that the early Cayman Trough extendedbetween Maya and Chortıs as a salt basin at thistime (Figs 4 & 5).

Late Jurassic–Early Cretaceous spreading inthe Central Atlantic resulted in WNW drift of NorthAmerica from Gondwana (South America–Africa)and great extension in Middle America (Fig. 4a,James 2009, fig. 4). Slip along major NW transferfaults within southern North America continued, off-setting the formerly linear Appalachian–Ouachita

Fig. 1. Middle America crustal types/distribution. Continental blocks, indicated by crustal thickness (gravity, seismic),high silica rocks and dredge samples, beneath southern Central America (SCA) and the Greater Antilles–northernLesser Antilles (NLA) are hidden beneath obducted volcanic arc/oceanic crust. Thick crustal areas on the LowerNicaragua Rise (LNR), eastern Yucatan Basin (EYB), Caribbean ‘Plateau’ (CP) and west Colombia Basin (WCB) areunderpinned by extended continent and locally overlain by Upper Cretaceous basalts. Serpentinized mantle possiblyincludes extremely attenuated continental crust. The Oligocene–Recent area in the Cayman Trough (red) is the onlyarea with spreading magnetic anomalies.

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trend and opening the Gulf of Mexico as the conti-nent interior pulled away from the Maya Blockand the NW Campeche Escarpment.

Maya moved west relative to Chortıs by some900 km (early Cayman displacement). Chortısmoved around 900 km NW relative to SouthAmerica and 400 km NW relative to Chorotega/Choco. Marginal areas subsided to accommodateplatform carbonates several kilometres thick(Florida–Bahamas platform–Greater Antilles,Limestone Caribbees, Campeche–Yucatan–Nicaragua Rise). Further outboard, NE-trendingnormal faults (Triassic–Jurassic rifts) becamelistric as continental crust thinned into horstsflanked by wedges of sediments.

Albian commencement of westward drift ofSouth America from Africa at Caribbean latitudes

introduced strike–slip along the southern CaribbeanPlate boundary, possibly provoking HP/LTmetamorphism in rapidly subsiding/filling deeps,enhanced Caribbean extension and resulted in afirst phase of basalt extrusion (120 Ma). Atlantic–Caribbean convergence resulted in subductionbelow dispersed continental fragments along theLesser Antilles with resultant volcanism. Uplift towave base, formation of an unconformity cappedby shallow marine limestones and change ofarc chemistry from primitive to calc-alkaline(continental input) occurred plate-wide, possiblyreflecting intra-plate expansion due to decompres-sion melting. A further plate-wide unconformityformed in the Cenomanian. Extrusion occurredagain in the Turonian (90–88 Ma), forming theprobably subaerial smooth seismic Horizon B00,

Fig. 2. Interpretation of Middle America tectonic fabric as the result of (1) reactivation of ancient lineaments (N358E),(2) extension (N608E) and strike–slip (east–west) strain within the sinistral offset (N608W) of North from SouthAmerica. AI, Aklins–Inagua–Caicos; BF, Beata F; BR, Beata Ridge; BRR, Blue Ridge Rift; CE, CampecheEscarpment; CT, Catoche Tongue; EG, Espino Graben; GF, Guayape FM; HE, Hess Escarpment; LT, La TrochaFM; MG, Merida Graben; MiG, Mississippi Graben; M-SF, Motagua–Swan FM; OR, Oachita Rift; PF, Patuca FM; PG,Perija Graben – Urdaneta; RBFZ, Rıo Bravo fault zone; RGR, Rıo Grande Rift; RHF, Rıo Hondo FM; SAL, San AndresLineament; TF, Ticul FM; TG, Takutu Graben; TT, Texas Transform; TSZ, Tenochtitlan Shear Zone; TZR, Tepic–Zacoalco Rift; VF, Veracruz FM; YC, Yucatan Channel. Red line, SE limit of Caribbean Plateau, the Central VenezuelaFZ. Green lines, magnetic anomalies. Compiled from many sources.

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Fig. 3. (a) Schematic Pangaean restoration of middle America, modern coastlines shown for reference. Cayman offsetbetween Maya and Chortıs removed. Chorotega/Choco restored to SW Chortıs. NW South America (Bolivar Block, B)restored S608W along Merida Andes–Eastern Cordillera. Lesser Antilles basement represented by a single block, laterdispersed by radial spreading. Extension of Bahamas Plateau, Nicaragua Rise and oroclinal bending of western Cubaremoved. B, Bolivar Block; BP, Bahamas Platform; C, Chortıs; Ch, Chorotega/Choco; Cu, Cuba; Hi, Hispaniola;J, Jamaica; LA, Lesser Antilles; M, Maya; NAm, North America; NR, Nicaragua Rise; SAm, South America; YB,Yucatan Basin. (b) Triassic–Early Jurassic rifting accommodated intracontinental Triassic red beds (Jurassic in SouthAmerica) and continent margin red beds and salt (Callovian? in Gulf of Mexico). Rifts reactivated N358E Palaeozoicsutures. Offset along major transforms in southern North America pulled the Maya Block from the Gulf of Mexico andthe Nicaragua Rise away from NW South America – the parallel Campeche and Hess Escarpments are the extensionalstrain of N608E sinistral movement of North relative to South America (inset Fig. 2). Early Cayman offset (east–westsinistral synthetic to N608W movement) began to separate Maya from Chortıs along the northern Caribbean. C, ChortısBlock; CB, Colombia Basin; CE, Campeche Escarpment; HE, Hess Escarpment; LT, La Trocha F; M, Maya Block;VB, Venezuela Basin; YB, Yucatan Basin.

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Fig. 4. (a) Late Jurassic–Early Cretaceous. Severe extension and subsidence of continental margin crustaccommodated kilometres-thick carbonate platforms (Florida–Bahamas–Greater Antilles–Limestone Caribees,Yucatan–Campeche, Nicaragua Rise). Early ‘Cayman’ offset of Maya and Chortıs continued. Chortıs was offset NWfrom Chorotega/Choco. NW trending grabens formed in SW Mexico–West Central America. Subduction volcanismbegan in Central America and the Lesser Antilles. C, Chortıs; Ch, Chorotega/Choco; F-B, Florida–Bahamas Platform;GA, Greater Antilles; LC, Limestone Caribbees; NR, Nicaragua Rise; Y-C, Yucatan Campeche Platform. (b) Middle–Late Cretaceous. Basaltic intrusion/extrusion occurred over highly extended continental crust, forming the ‘CaribbeanPlateau’ in the Venezuela Basin. Similar seismic signature is seen in Colombia, north Grenada and Yucatan basins.Severe extension resulted in serpentinization of upper mantle (pink areas). Back-arc spreading at the Aves Ridge (AR)drove the Lesser Antilles eastwards over Atlantic crust. Peripheral volcanic arc rock chemistry shows continental inputsince the Albian and rocks contain ancient zircons.

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capping the horsts and half grabens of extended con-tinental crust in the Caribbean Plate interior. Thepresence of basalt flows dated 120 and 90 Ma inareas such as Ontong Java suggests episodes ofglobal activity. This paper suggests that thethick areas of crust in the Venezuelan, Yucatanand Colombian basins include thick carbonate

sections sandwiched between the 120 and90 Ma basalts.

Middle Eocene

Flysch deposition became common in the LateCretaceous. It culminated violently with Middle

Fig. 5. (a) Middle Eocene. Allochthons of ‘oceanic’, volcanic arc and continental margin rocks emplaced around theCaribbean, covered by erosional unconformity and shallow marine limestones (uplift to wave base). Volcanism ceasedalong northern and southern Caribbean Plate boundaries. Beginning NE movement of NW South America along theMerida Andes/Eastern Cordillera. (b) Oligocene–Recent. East Pacific Rise spreading drives the Cocos Plateorthogonally against Central America, reactivating Jurassic rifts as sinistral faults, resulting in oroclinal bending ofMotagua (Mo), Agalta (Ag) and western Cuba (James 2007, figs 11 & 12). It also drives the Caribbean Plate eastwards,triggering central Cayman Trough spreading and strike–slip (300 km) along the northern and southern boundaries.Transtensional extension disperses the Greater (GA) and Leeward (LA) Antilles. Southern Choco sutures to NW SouthAmerica (SB, Serranıa de Baudo); northward extrusion of the Panama arc (PA) and the Bolivar Block (BB) drives thePanama (PDF) and South Caribbean (SCDB) Deformed Belts.

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Eocene emplacement of extremely large olistolithsof ‘oceanic’, volcanic arc and continental marginrocks in the Greater Antilles and along northernSouth America, where arc volcanism ceased (Fig. 5a,James 2005a). Uplift raised allochthons throughwave base where a regional Middle Eocene uncon-formity developed, overlain by regional MiddleEocene shallow-water carbonates (James 2005a).Allochthons included the 250 km long Villa deCura Nappe (Venezuela), with its former westernextension, the Aruba–Blanquilla island chain, the1000 km long ophiolite belt of Cuba and theDuarte and Bermeja complexes of Hispaniola andPuerto Rico. Horizontal movement was as muchas 140 km in Cuba (Cobiella-Reguera 2009). Atthe same time thrust slices in Mexico’s VeracruzBasin stacked 6 km high and moved eastward atleast 30 km (Mossman & Viniegra-O 1976, fig. 2).

Rapid (204 + 80 mm/annum, Daly 1989) LateEocene convergence between the Nazca Plate andnorthwestern South America began to drive theBolivar Block (Fig. 5a) of northwestern SouthAmerica (James 2000) NE.

Sometime in the Late Cretaceous, possibly EarlyCenozoic, back arc spreading in the eastern Carib-bean extended the plate eastwards over Atlanticcrust and dispersed continental blocks below theLesser Antilles.

The most recent phase of Caribbean history(Fig. 5b) involved some 300 km of Oligocene–Recent strike–slip, sinistral and dextral respect-ively, along the northern and southern plateboundaries, driven by convergence of the CocosPlate with the western Caribbean. Along bothmargins uplift occurred earlier and is greater in thewest. The size of Greater Antillean islands and theheight and depth of erosion in the Coastal Range–Northern Range of Venezuela and Trinidad dimin-ish eastwards. Erosion has exposed the strata lyingbelow allochthons in the west (continental basementin Cuba and the Venezuelan Coastal Range as far asthe Gulf of Paria). In the east these rocks remainocculted. From Hispaniola to the Virgin Islandsonly uplifted oceanic and volcanic arc rocks cropout; however, gravity and chemical data indicatethick and siliceous basement.

The episode began with a pulse of block faultingand pull-apart extension, possibly triggered by theMiddle Eocene event. Once again, highly extendedareas subsided. Middle Eocene, shallow marinecarbonates on the Beata and Aves Ridges now liein thousands of metres water depths. It was followedby eastward-migrating thrusting over complemen-tary foredeep basins in Venezuela–Trinidad(Guarico Basin–Oligocene; Maturın Basin–Miocene; Gulf of Paria–Pliocene; ColumbusBasin–Pleistocene–Recent). Earth’s largest nega-tive gravity anomaly at sea level over the Maturın

Basin and great thickness of young Cenozoic sedi-ments in the Columbus Basin testify to the highlydynamic nature of the strike–slip system, capableof driving rocks quickly to depths where HP meta-morphism can occur at low temperatures.

Along the northern plate boundary a secondphase of Cayman offset was accompanied by spread-ing in the Trough and separation of the easternGreater Antilles along the Mona, Windward andAnegada Passages (Fig. 5b). North–south faultsdivided the Hess Escarpment into three c. 200 kmlong elements and the Nicaragua Rise becamesegmented (Muttia et al. 2005).

Convergence of the Farallon/Nazca plate withNW South America, low (44 + 26 mm/annum)during the Oligocene–Early Miocene and high(125 + 33 mm/annum) from Middle Miocene–Recent (Daly 1989), continued to drive the BonaireBlock NE. The northern part of the block trans-gressed the South America–Caribbean dextralboundary, driving the South Caribbean DeformedBelt ahead of it. Extrusion occurred along theNNW Santa Marta–Bucarramanga Fault and NEfaults in the Colombian Eastern Cordillera–Venezuelan Merida Andes. A large positivegravity anomaly associated with the 5800 m highSierra Nevada de Santa Marta, Colombia, indicatesthe absence of isostatic equilibrium and witnessesthe dynamism of this system.

Pull-apart extended the northern Bonaire Block,formerly the western continuation of the Villa deCura nappe, as it crossed the plate boundary. TheAruba–Blanquilla islands, highs of 5.4 km s21

material separated by basins with thick Oligo-cene–Recent sediments, exhibit the same structuralperiodicity as the nappe (Edgar et al. 1971; Curet1992; James 2005b, c, fig. 14).

Northern Choco separated from Chorotega alongthe Panama F., moving northwards to form thePanama arc and driving the Panama Deformed Belt.

NE convergence of the Cocos Plate alongCentral America drives a regional system of NEtrending sinistral faults in the western Caribbean(James 2007). They transform in the north andsouth into oroclines and fold and thrust-belts andaccommodate shortening between the boundingfracture zones of North Cuba and CentralAmerica. The most impressive system runs alongeastern Maya, linking the Motagua ‘orocline’ withwestern Cuba. An estimated 350 km of shortening(Rosencrantz 1990; James 2007) here closed thewestern extension of the Cayman Trough byNE-moving Chortıs.

Implications

Data (James 2005c, 2006, 2009) and the interpret-ation of this paper suggest learnings for aspects

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of global geology. Indications of continentalfragments below the Caribbean ‘Plateau’ and theGreater and Lesser Antillean and Central Americanvolcanic arcs imply that it is perilous to assumepurely intra-oceanic origins for oceanic plateausand volcanic arcs (Leat & Larter 2003; Kerr et al.2009). Accepted discriminatory chemical/isotopedata for such areas need to be statistically qualifiedand examined independently of presumed origins tosee what messages they carry. Geology of the Carib-bean volcanic arcs suggests answers to the ‘andesiteproblem’ – it is not a case of understanding howsubducting basalt gives rise to such silica-richrocks (Takahashi et al. 2007) but rather of recogniz-ing that arc roots, related by seismic velocities tocontinental rocks (Tatsumi & Kosigo 2003),involve original continental fragments.

HP/LT metamorphic rocks are not necessarilysignals of subduction. Transcurrent faulting iscapable of generating rapid, deep burial and exhu-mation of such rocks.

The Caribbean Plate lies between the giant oilprovinces of the Gulf of Mexico and northernSouth America. Oil is seen on Puerto Rico, Hispa-niola, Jamaica, Belize, Guatemala, Honduras,Nicaragua, Costa Rica, Panama, Colombia, Vene-zuela, Trinidad and Barbados, circumscribingpractically the whole of the plate. This signals over-looked potential on the Caribbean Plate. Some oil isthought to come from Cenozoic sources but oils ofGuatemala, Belize, Jamaica, Costa Rica and Barba-dos have Jurassic or Cretaceous chemical signatures(Larue & Warner 1991; Babaie et al. 1992; Burggrafet al. 2002; Cameron 2004; Emmet 2002; Lawrenceet al. 2002).

Source rocks are likely in Jurassic and Creta-ceous sections on the Caribbean Plate interior. Theformer developed in narrow marine basins; thelatter in seas restricted by subaerial basalt extrusionover extended continental crust, since subsidedbelow thousands of metres of water. A risk is thatthey were overmatured by igneous activity. Gasmight be expected.

Questions

Juxtaposition of continental, volcanic arc and ophio-litic rocks in locations such as the supposed suturebetween Maya and Chortıs and along northernVenezuela is problematic (Giunta & Oliveri 2009).Ophiolites, once attributed to mid-ocean spreading,today are seen to form in several different environ-ments, including pull-apart intra-arc basins,back-arc basins and extensional zones in forearcsduring development of island arcs (Moores 2003).All these settings can be envisaged in MiddleAmerica as extension occurred during theJurassic–Cenozoic. Ophiolite thicknesses up to

5 km, common around the Caribbean, testify to sig-nificant extension, presumably close to thinned con-tinental crust.

What caused repeated episodes of convergence,metamorphism, uplift, erosion and unconformitiescovered by shallow marine limestones? Trans-pression? Vigorous plate expansion, driven bydecompression melting? Pulses of Pacific Plateconvergence?

The Middle Eocene event was remarkable forits suddenness and violence (Stainforth 1969). Itabruptly emplaced sections of serpentinite up to5 km thick and up to 1000 km long by as much as140 km onto continental margins in Cuba andVenezuela – outward moving in response to aplate interior compressional stress or sudden conver-gence of North and South America. Coeval depositsin Peru and Ecuador and an eastward verging stackof thrusts 6 km high in the Veracruz Basin ofMexico rule out the latter. Conventional wisdomsuggests convergence of such material should leadto subduction, not obduction. Did salt and/or ser-pentinite assist decollement? Did hydro-pressuredue to hydrocarbon generation play a role? What-ever the cause, the regional and coeval occurrenceof these deposits correlates continental marginwith Caribbean Plate boundary and internal geology.

What is the age and nature of thin crust in theHaiti Basin, the SW Colombian and Venezuelanbasins? Jurassic, Cretaceous, Cenozoic?

Did high standing blocks in the Caribbean and/or shallow/subaerial basalt outpouring causerestriction and supply nutrients for Albian andTuronian organic rocks?

Why are there no return path metamorphic rocksassociated with the Lesser Antilles or CentralAmerican subduction arcs?

Why is there no major difference in chemistrybetween the northern (descent of oceanic crustclose to the arc) and southern (descent of oceancrust east of the Barbados Accretionary Prism andTobago Trough) parts of this arc?

Are there hydrocarbons on the Caribbean Plateinterior?

Predictions

The model described by this paper suggests thefollowing.

El Tambor rocks of the Motagua ‘suture’ are theexhumed western continuation of the CaymanTrough.

Thin, ‘oceanic’ crust in the southeastern Colom-bian and Venezuela Basins and in the Grenada Basinis serpentinized mantle, Cretaceous or Cenozoicin age.

Dispersed continental blocks underpin theCayman Ridge, the Upper Nicaragua Rise, Costa

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Rica, Hispaniola, Puerto Rico, the Virgin Islands,the northern Lesser Antilles, Chorotega/Choco.

Thick crust of the Venezuela, Colombia,Yucatan and Grenada basins is underlain by blocksof continental rocks flanked by wedges of Triassic–Jurassic–Cretaceous rift sediments, evaporites andcarbonates, overlain by subaerial basalt flows.

The Lower Nicaragua Rise is underpinned byhighly extended/transitional crust – there arelocal continental blocks.

The N608E Hess Escarpment is the outer marginallimit of the Nicaragua Rise/Chortıs continental block.It formed as a major extension in the Jurassic–Cretaceous sinistral N608W offset of North fromSouth America. It became segmented by north–south trending faults during Cenozoic extension.

Pull-apart extension along the Nicaragua Rise/Hess Escarpment, the Greater Antilles and Aruba–Blanquilla sums to around 300 km, equal toCentral Cayman spreading in the north and exten-sion of the Falcon Basin and separation of theLeeward Antilles in the south.

The Greater Antilles mirror-image northern SouthAmerica. They are built of north verging thrust sheets,some inverting stratigraphy, and mixed blocks ofallocthonous, mainly Jurassic–Cretaceous, oceanicand volcanic arc rocks deposited as Middle Eocenewildflysch above continental blocks.

The Beata and Aves Ridges were the focus ofback-arc spreading in the Mid–Late Cretaceousand Late Cretaceous–Early Cenozoic, respectively.

There are salt diapirs in the Caribbean, predictedsalt age Jurassic.

Hydrocarbons are present on the Caribbeaninterior.

Tests

The understanding of this paper suggests thefollowing tests.

Many data are easily obtainable. Dredge samplesof the Cayman Trough walls, walls of the PuertoRico Trough and the Aves Ridge and core samplesof the deeper Venezuelan and Colombian basinscould be re-investigated for lithology, age andzircon content. Existing seismic data could berevisited and new data gathered that would dis-tinguish between in situ and allochthonousmodels. It should be possible to distinguish defini-tively between seamounts and salt diapirs, to see ifthickened parts of the Colombian, Grenada andYucatan basins have the same architecture as thewestern Venezuelan Basin and to see if combinedvelocity/magnetic/gravity data can distinguishbetween igneous/volcanic and extended continentalorigins. Much could be learned by systematic repro-cessing/reinterpretation of existing seismic data.

† Age date zircon in volcanic/oceanic rocks inCentral America, Hispaniola, Puerto Rico,Lesser Antilles and Aves Ridge.

† Age date zircon in volcanic rocks from DSDPsamples of the Caribbean Plateau.

† Age date zircon in dredge samples from theCaribbean.

† Age date clasts in rocks dredged from theCayman Trough.

† Palynological study of salt/cap rock at Salinas,Puerto Rico, Cerro Sal, Dominican Republicand Salt Pond Pen, Jamaica.

† Gravity and heat flow investigation of seamountsv. diapirs.

Fig. 6. Suggested drill sites to test ideas of this paper.

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† Examination of Middle Eocene sections forevidence of impact (tektites, iridium).

† IODP drilling of Cayman Trough basement,predicted to be Early Cretaceous serpentinite(Site 1, Fig. 6).

† IODP drilling of ‘seamounts’ – predicted to besalt diapirs, north of Honduras, Yucatan Basin,Beata Ridge, seismic line 1293 (Sites 2–5).

† IODP drilling with greater penetration of theCaribbean Plateau (Sites 5 and 8).

† IODP drilling to ‘oceanic crust’ Haiti and Vene-zuela basins (Sites 5 and 10).

† IODP drilling to test a circular bathymetric lowin the Venezuela Basin (Site 8), a possibleimpact crater (James 1997).

† IODP drilling to date early sediments exposed inthe Guajira Canyon (Site 9).

† IODP drilling to test deep section on the southernwall of the Puerto Rico Trough, predicted conti-nental crust (Site 11).

Conclusions

The geology of the area between North and SouthAmerica shows regional harmony and a sharedhistory among the various geographic components,all of which are autochthonous. FollowingTriassic/Jurassic extrusion of the Central AtlanticMagmatic Province North America separated fromSouth America/Africa. Triassic–Jurassic riftingreactivated ancient NE-trending basement linea-ments. This structural grain is regionally preservedtoday in Middle America, including the CaribbeanPlate interior. No major block rotations haveoccurred.

Volcanism accompanied extension but com-pressional events in the Middle and Late Creta-ceous and Middle Eocene led to pause or cessationof activity, uplift to wavebase and subaerialerosion, development of unconformities andshallow marine carbonates, karstification. Abundantextrusion accompanied the Middle and LateCretaceous events in the Colombia and Vene-zuela basins. Coeval high organic productivityresulted from restriction and formed hydrocarbonsource rocks.

Subsidence of proximal areas (Bahamas andYucatan–Campeche platforms, Nicaragua Rise)accommodated kilometres-thick carbonate sections.Horsts of continental crust flanked by wedges ofJurassic–Cretaceous sediments, flows and saltformed in more distal areas along the easternmargin of North America and within MiddleAmerica (Yucatan, Colombian and VenezuelanBasins). Shallow/subaerial flows of smoothseismic Horizon B00 capped the Caribbean areas inthe Late Cretaceous. Areas of extreme extension

suffered serpentinization of upper mantle, formingrough Horizon B00.

The Middle Eocene regional, convergent eventterminated most volcanic activity along the northernand southern Caribbean Plate boundaries, whereOligocene–Recent strike–slip followed. The onlyspreading crust in Middle America, with recogniz-able spreading ridges and magnetic anomalies,formed in the central 300 km of the CaymanTrough during this latest tectonic phase.

Continued divergence of North and SouthAmerica, shown by diverging fractures in theAtlantic ocean east of North and South Americaand by a wedge of fractures east of Caribbeanlatitudes recording 650 km of north–south growthof the Mid-Atlantic Ridge, created space forback-arc growth of the Caribbean Plate. Analogywith the Scotia Plate, which occupies as similartectonic setting, suggests that this occurred firstlyalong the Beata Ridge and later along the AvesRidge.

Many unrecognized fragments of continentalcrust are dispersed around and on the CaribbeanPlate. They underlie the whole of Central Americaand the Greater and Lesser Antilles and at leastthe northern and southern Lesser Antilles.

The strength of the in situ model is that it incor-porates data in a regionally coherent, simple evol-ution that conforms to the wider geology ofeastern North America and the Gulf of Mexico. Itcompares with the well-calibrated geology of theanalogous Scotia Plate. It is a model that can betested. In contrast, models deriving the CaribbeanPlate from the Pacific models are complicated.Required processes such as slab-rollback beneathan overriding plate and below the Yucatan Basinare not recorded by data and are not testable.

I pay tribute to those geologists of the past who, with farless data than I have, also saw Caribbean geology insimple terms.

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