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The AAPG International Meeting, 2003, Barcelona, Spain, included a session on Caribbean tectonics.
Proposed by K. H. James
Chaired by F. Audemard, K. H. James and J. Pindell

The session was intended to highlight differences between Pacific and in-situ models for the origin of the Caribbean Plate. This summary, by Keith James (keith@hjames.u-net.com), is presented as a contribution to IGCP 433.

The session opened with a tribute to Bob Speed, who passed away September 18th, 2003. Bob made significant contributions to Caribbean geology, notably in Barbados and in the SE Caribbean.

The session comprised seven papers, abstracted below. They include regional papers on the Caribbean and Gulf of Mexico and progress to local focus on hydrocarbon aspects of Cuba and Trinidad.

The oral session was complemented by a poster session with nine contributions. Extended abstracts of papers and posters are available on the conference CD, issued by theAAPG.

In the opening address James noted that geologically the Caribbean remains one of the world's most highly debated areas. There are abundant models of plate migrations, hotspot and mantle plume activity, island arc development and disappearance, subduction reversals, opening of young oceanic basins, major block rotations and major plate migration.

Why so much discussion?
-The plate forms part of a region of great geographic diversity extending from southern N America to northern S. America, including Central America, several thousand islands and the oceanic areas in between.
-Parts of the region are well known. Others, because of tectonic complexity, poor accessibility, poor exposure and tropical weathering are poorly known.
-The Caribbean Plate is largely oceanic, although it carries large continental fragments in the west. However, there are no spreading anomalies (except central Cayman Trough) to tell how and when the plate formed.
-The initial oceanic crust (unsampled in place) was thinned by extensional faulting to 3-5 km and then locally thickened to as much as 15 km by basalt outpouring. Thickening occurred on at least two occasions, at 120 and 90 Ma, both episodes lasting only a few million years. Hotspot and/or mantle plume activity is held responsible.
-Few people make comprehensive synthesis of all this geology. Most works simple quote "the generally accepted model" or state "It is well known that".

James emphasized that the two models have significantly different implications for the explanation of known and the prediction of remaining hydrocarbon reserves in the area. Audience response expressed enthusiastic appreciation of this forum where the Pacific and in-situ models were presented side by side. There was strong encouragement for a formal public debate of these models.

ABSTRACTS

• Giunta, G., L. Beccaluva, M. Coltorti and S. Franca
  The Peri-Caribbean Ophiolites and Implications for the Caribbean Plate Evolution

  Ophiolitic terranes deformed and dismembered along both the northern and southern peri-Caribbean margins represent fundamental markers for the origin and evolution of the Caribbean Plate.

  The proto-Caribbean oceanic crust was generated in a "near Mid-America" location since Late Jurassic. Its accretion was initially related to multiple spreading centres (LREE-depleted MORB, in Venezuela, Costa Rica, Cuba, Guatemala, Hispaniola), evolving during the Cretaceous to a thickened oceanic plateau in its westernmost end (REE-flat MORG locally associated with picrites, in Costa Rica, Hispaniola, Venezuela, Dutch and Venezuelan Islands).

  Sub-continental and intra-oceanic east-dipping subduction zones initiated within the proto-Caribbean domain since the early Cretaceous with generation of HP metamorphic subduction complexes and island arc tholeiitic to calcalkaline volcano-plutonic sequences (1° eo-Caribbean phase: in Guatemala, Cuba, Puerto Rico and Venezuela). Since the Late Cretaceous a second intra-oceanic subduction, with reverse polarity, took place, recorded by unmetamorphosed tonalitic intrusives, and related to the onset of the Aves-Lesser Antilles arc system (2° eo-Caribbean phase). During Late Cretaceous-Tertiary large-scale tear faulting along the northern and southern margins of the Caribbean Plate favoured eastward dispersion and uplifting of the subduction-accretion systems. The present Caribbean Plate is mainly represented by the Cretaceous plateau crust trapped in the Colombia and Venezuela basins by the intervening Pacific subduction, which built the Central American isthmus.

  The recent data allow to better define some important constraints which lead the kinematic evolution of the Caribbean Plate's deformed margins.

• Miranda, E., J. Pindell, J. Patino, I. Alor, A. Alvarado, H. Alzaga, A. Cerón, R. Dario, M. Espinosa, J. Granath, L. Hernandez, J. Hernandez, J. Jacobo, L. Kennan, M. Maldonado, A. Marin, A. Marino, J. Mendez, E. Pliego, A. Ramirez, G. Reyes, J. Rosenfeld and A. Vera
  Mesozoic Tectonic Evolution of Mexico and Southern Gulf of Mexico: Framework for Basin Evaluation in Mexico

  Gravity, magnetics, seismic, wells, paleogeography, facies, structure, subsidence histories and plate kinematic data were appraised to test and refine existing models for the evolution of Mexico and southern Gulf of Mexico (GoM). Closure of Atlantic oceans, restoration of Yucatán Block between Texas and Venezuela, and NW retraction of central and southern Mexican territories allows an entirely continental, internally consistent Pangean (Permian) reconstruction in which Yucatán was thrust onto USA. The Gulf then opened in two stages. Stage 1: Triassic-Oxfordian NW-SE asymmetric continental stretching (Yucatán was hanging wall), with minor CCW rotation of Yucatán, during which sinistral motion occurred along "Texas", "Burgos" and Trans-Mexican Volcanic Belt lineaments. Motion on an E-ward projection of Mojave-Sonora Megashear was unlikely. Stage 2: Oxfordian-Valanginian CCW rotation of Yucatán as seafloor crust formed in the central GoM. The Yucatán-NoAm pole of rotation migrated SE from the SE GoM to Isle of Youth during rotation. During Stage 2, the "East Mexican Shear Zone" at the base of the Tuxpan margin initially defined the trace of Yucatán/Mexico relative motion, but by Tithonian transform motion jumped into Veracruz Basin, which became a dextral pull-apart basin adjacent to the western GoM. Syn-rift subsidence (Stage 1) exceeded post-rift thermal subsidence (Stage 2) in the northern margin, whereas post-rift thermal subsidence was more significant into the Cretaceous for Yucatán. The model provides a kinematically robust paleogeographic and crustal- and basin-dynamic framework in which Pemex can assess existing exploration opportunities and also develop future strategic exploration programs and efforts.

• Pindell, J. L.
  Pacific Origin of Caribbean Oceanic Lithosphere and Circum-Caribbean Hydrocarbon Systems

  Circumstantial evidence overwhelmingly favours a Pacific origin for Caribbean oceanic lithosphere with respect to North and South America, as opposed to and "intra-American" origin whereby Caribbean lithosphere formed by spreading between North and South America. Direct implications of intra-American models are examined and found to violate dynamics of arc systems and significant aspects of Caribbean geology. Therefore, the kinematic, geometric, and geologic basis for Pacific origin models is presented, including a range of primary aspects requiring a Pacific origin model. For example, continent-verging arc-continent collisions between various portions of the Great Caribbean Arc with the Atlantic-type Proto-Caribbean margins are documented as younging east, from Chortis and Ecuador to Puerto Rico Trench and Trinidad, from Albian to Plio-Pleistocene, in accord with Caribbean-American relative displacements exceeding 1,500 km during that interval. This relative migration is outlined as a function of progressive westward drift of the Americas in a hotspot reference frames as the Atlantic opened, "engulfing" a piece of Pacific crust that is now Caribbean lithosphere. A "non-Caribbean" Paleogene tectonic event is proposed in NE South America that explains the only known relationships contrary to this model. An animation shows the relative migration and origin of larger circum-Caribbean tectonic features. Primary circum-Caribbean hydrocarbon systems are summarized in light of the model, making predictions for deposition of reservoir units, timing and magnitudes of source rock burial, and timing and direction of oil migration in the four circum-Caribbean foreland basins created by Caribbean loading as Caribbean Plate progressed relatively eastwards.

• James, K. H.
  A Simple Synthesis of Caribbean Geology

  Most modern syntheses of Caribbean geology derive the Caribbean Plate from the Pacific. They invoke changes of subduction direction, major rotation of island-arcs (90°) and continental blocks (up to 50°), plate thickening over a Pacific hotspot or mantle plume and major migration of the Caribbean Plate with a 45° change in direction. The models are complex and geometrically unlikely. This paper suggests a simple Pangean reconstruction and in-situ evolution that involves none of these complications and accounts for all Caribbean geology. Jurassic-Late Cretaceous, WNW oriented sinistral transtension produced N-S offset of around 950 km and sinistral offset of at least 1,000 km between N and S America. Cretaceous plate thickening resulted from extension over triple junctions heralding abandonment of spreading between the Americas and from N-S extension associated with 600-km growth of the Mid-Atlantic Ridge. A circum-Caribbean Palaeocene - Middle Eocene compressional event preceded Oligocene - Present, E - W strike-slip between the Caribbean and the American Plates. The contrast between the simple in-situ model and complex Pacific models argues for the former (Occam's razor).

• Audemard, F.
  The "Orogenic Float" of Northern South America

  A set of three parallel regional seismic transects allow to present the northern margin of Venezuela from Colombia to Trinidad as an "Orogenic Float" developed by the interaction between oceanic crusts and the South-America's passive margin during late Cretaceous to Neogene times from west to east. These two distinct subduction zones play important roles in the geodynamic context: the "B" subduction of the Lesser Antilles (west polarity) and the coeval "B" Colombo-Venezuelan subduction (south polarity).

  Additional examples of the structural styles formed in domains are also presented: - The Barbados Accretionary Prism evolves over oceanic crust to the west and progressively rides continental crust towards the south. The prism is currently being disrupted by gravitational tectonics associated with the Orinoco Delta edifice. - The south vergent Mid-Miocene Serrania del Interior shows differential uplift due to remobilization of Miocene shales along its leading edge. -Orogenic collapse of the igneous-metamorphic "Caribbean allochthonous belt" and transpression superimposed to the Neogene sequence are caused by a transfer system between two "B" subduction zones. -The Falcón anticlinorium resulted from partial inversion of a Neogene flexural basin, as opposed to the prevalent pull-apart model. It is actually overthrusted to the north, following the Present-day Colombo-Venezuelan Accretionary Prism. -Comments will be addressed on both the geodynamic setting of wrench tectonic models, e.g. the Boconó and Oca lineaments and "opposing" northwest vergence of the Mérida and Perijá folded belts. Implications for exploration will be discussed for all these structural styles.

• Chambers, A. F., P. Lukito, C. Solla Hach, S. Torrescusa Villaverde, C. Riaza Molina and H. Bachmann
  Structural controls on the Hydrocarbon Prospectivity of Blocks 25-29 and 36, Offshore Northern Cuba

  Integration of new 3D seismic interpretations with a regional 2D seismic dataset has revealed the main structural controls upon hydrocarbon prospectivity in the deepwater north Cuban basin. The plate tectonic evolution of the region can be simplified into three main phases. Firstly the carbonate-dominated Florida-Bahama passive margin developed during Jurassic-Cretaceous times. Secondly, during the late Cretaceous-Eocene, the Cuban volcanic arc converged and collided with the Florida-Bahama passive margin. Finally the infilling Cuban foredeep basin was subjected to late compression and erosion. The evolution of the western and southern Florida-Bahama platform margin since mid-Cretaceous times has been defined using a regional 2D seismic dataset. This regional interpretation indicates that the platform margin to the west of Florida has remained static form Mid-Cretaceous Unconformity (MCU) to Neogene times forming a pronounced bathymetric escarpment. In the north Cuban offshore area, however, the platform margin has retreated northwards since Mid-Cretaceous times in response to loading by the Cuban thrust. It is observed that the well-defined MCU platform margin is consumed by the Cuban thrust belt in northern Cuba.

  3D seismic data have been acquired over two zones in the study area. In one area the structural style is dominated by Mesozoic fault trends that have been extensionally reactivated during platform margin collapse. In the other, this pre-existing extensional framework has been strongly overprinted by oblique sinistral compression. Despite the large scale compressional regime, the majority of the small-scale, seismically-observed faults are extensional in nature and may potentially enhance reservoir performance.

• Mullin, P. and D. Truempy
  Exploration at the Plate Margin: Trinidad Block 25(a)

  Deepwater hydrocarbon exploration dominantly focuses on passive margin settings. In Trinidad, however, ongoing and future exploration is taking place at a plate boundary: the southeastern suture between the Caribbean and Atlantic/South American plates. Drilling results by BHP in shallow water Block 2(c) have demonstrated that significant hydrocarbons can be discovered in such a setting.

  Most workers believe that the Caribbean plate is stationary with respect to the mantle, while the Atlantic/American plate is moving westwards at two centimetres per year, being subducted underneath the Caribbean plate to the northwest of Trinidad, generating the Barbados accretionary prism, and is currently sliding past the Caribbean plate within and adjacent to Trinidad itself. The extent to which this motion has been purely strike-slip, or has included a significant transpressional element, is a matter of some dispute.

  A Shell-led partnership (Shell 55%, Agip 40%, Petrotrin 5%) acquired deepwater acreage along this margin in 1998 (Block 25 (a)). Early evaluation had suggested that shale diapirism has generated most of the highs in the Block, which were therefore seen as non-prospective for hydrocarbons. Thus first exploration efforts were concentrated on the intervening Plio-Pleistocene depotroughs. Recent re-evaluation of the NW portion of the Block suggests that WSW-ENE trending strike-slip movements, rather than diapirism, have been the dominant structure forming mechanism from Miocene times to the present, and that the main highs are cored with older Pliocene and possibly Oligo-Miocene strata. This paper will review the structural development of the Block, in the light of recent drilling activity.

  

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  Last revised: October 31, 2003