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by M. Iturralde-Vinent

It is my opinion that the GSA annual meeting in Boston was a great success and a unique opportunity to update ourselves on the state of the art of American geology. Those particularly interested in the Caribbean participated in the IGCP-433 presentations distributed in three different sessions (T3, Tectonics and Igneous Petrology). The papers presented show the different points of view that color the Caribbean plate tectonic canvas today. As the abstracts included here are self-explanatory, so I will not comment on this matter in depth. I would only like to underline that as we gather more information about the Caribbean and more agreement is focused into the allochthonous origin of the Caribbean Plate, many contradictions arise as how to develop this model. For this reason, during informal conversations during the meeting, we have agreed that the IGCP-433 annual session to be celebrated during the forthcomming Caribbean Geological Congress in Barbados (June, 2002), must focus in three main issues:

1. The Early Mesozoic evolution of the Caribbean
2. The Early Tertiaty Evolution of the Caribbean
3. The interactions between the Caribbean Plate and South America.

Please submitt your abstracts - the sooner the better.

GSA Abstracts from the IGCP Project 433-Caribbean Plate Tectonics

EVOLUTION OF THE NORTHERN PORTION OF THE CARIBBEAN PLATE: PACIFIC ORIGIN TO BAHAMIAN COLLISION
PINDELL, James¹, DRAPER, Grenville², KENNAN, Lorcan¹, STANEK, Klaus P.³, and MARESCH, Walter V.
¹Tectonic Anaysis Ltd, Cokes Barn, West Burton, Pulborough, RH20 1HD, United Kingdom, jim@tectonicanalysis.com
²Earth Sciences, Florida International University, Miami, FL 33199, United Kingdom, draper@fiu.edu
³Inst. für Geologie, TU Bergakademie Freiberg, Bernhard von Cotta Str. 2, Freiberg, D 09596, Germany

Pacific origin models of Caribbean are more compatible with regional Caribbean geology than Intra-American models because (1) the Greater Antilles Arc (GAA) is older than the Central American Arc, which is predicted by Pacific, but not by Intra-American models; and (2) Caribbean tectonic interaction with northern Colombia and southern Yucatan began in the Campanian, which requires a more southwestward (Pacific) position of the Caribbean Plate before that time. We have refined earlier Pacific-derived Caribbean evolutionary models to new levels of precision and conclude: 1) the Galapagos Hotspot did not form the Caribbean plateau; 2) Early Cretaceous subduction dipped NE; 3) Panama-Costa Rica arc formed at equatorial latitudes; 4) Caribbean HP/LT metamorphic assemblages (except those of Jamaica) pertain to initiation and subsequent development of SW-dipping subduction beneath the GAA that followed an Aptian-early Albian subduction polarity reversal event; the new polarity then allowed the Caribbean Plate to enter the inter-American realm during Upper Cretaceous-Cenozoic; 5) the central Cuban Arc comprises mainly forearc elements of the GAA, and Sierra Maestra is more representative of the GAA axis; 6) Campanian cessation of magmatism in central Cuba resulted from shallowing of subduction as the GAA approached southern Yucatan, 7) the Yucatan intra-arc basin formed in two phases: Maastrichtian -Paleocene NW-SE extension driven by slab rollback of Jurassic Proto-Caribbean lithosphere along eastern Yucatan, and Early and Middle Eocene NNE extension driven by rollback of Proto-Caribbean crust toward the Bahamas, controlled by N-ward propagation of a NNE-trending east-Yucatan tear fault, during which western and northern Cuban terranes were accreted to the front of the central Cuban fore-arc; 8) Middle Eocene collision of all Cuban terranes with the Bahamas, and rapid uplift of the orogen after the detachment of the SW-dipping; 9) Eocene onset of Cayman Trough pull-apart as the Caribbean Plate began its well-known subsequent migration to its present position ;10) Oligocene transpression in Hispaniola and Puerto Rico which led to the ?Late Oligocene separation onset of separation of the Hispaniola arc assemblages from Oriente, Cuba.

PHANEROZOIC TECTONIC EVOLUTION OF THE NORTH AMERICAN PLATE BOUNDARY IN CUBA
ITURRALDE-VINENT, Manuel A.
Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana 10100 Cuba, iturralde@mnhnc.inf.cu

In the Cuban territory crops out Phanerozoic rocks that contain stratigraphic sections of both the Bahamas and Yucatan borderlands of the North American continental margin. These sections can be subdivided into three tectonic stages as follow: 1. The Jurassic to latest Cretaceous passive margin stage, represented by siliciclastic and carbonate rocks sections that characterize the formation and early evolution of the Caribbean sea and its northern continental margin. This was a stage of extensional stress and evolution from intracontinental to open marine facies. 2. The Paleocene to latest Eocene collisional margin stage, represented by foreland sediments with large amount of allochthonous materials (ophiolite and volcanic arc elements). During these stage took place strong compressional deformations. 3. The latest Eocene to Recent stage, characterized by less deformed sedimentary sections, mostly along the trend of wrench faults. In general represent post-collisional tectonics associated with transpresional and transtensional stress.

ASYMMETRIC SEAFLOOR SPREADING, CRUSTAL THICKNESS VARIATIONS AND TRANSITIONAL CRUST IN CAYMAN TROUGH FROM GRAVITY
TEN BRINK, Uri S.¹, COLEMAN, Dwight F.², and DILLON, William P.^1
1US Geol Survey, 384 Woods Hole Rd, Woods Hole, MA 02543-1598, tenbrink@usgs.gov
²Institute for Exploration, 55 Coogan Blvd, Mystic, CT 06355-1927

With a few exceptions, oceanic crust, which forms at divergent plate boundaries (and away from the influence of mantle plumes near hot spots), has nearly constant thickness regardless of age, geographic location, water depth, and spreading velocity. Using free-air gravity anomaly data, we model the crustal structure of the Cayman Trough to analyze the processes occurring at this slow-spreading mid-ocean ridge. Our model indicates considerable and abrupt crustal thickness variations along the trough axis, which parallels the direction of ocean opening. The proximal part to the spreading ridge extends ~170 km east of the spreading ridge and 250 km west of it. Sea floor in the proximal part is slightly deeper (by ~500 m) east of the ridge than west of the ridge, and crustal thickness east of the ridge is considerably thicker than the crust to the west. The distal part of Cayman Trough extends to a distance of ~300 km on both sides of the proximal part to the spreading ridge. It has a greater water depth and a thinner crust than the proximal part and it does not increase in depth away from the ridge. By tying our model to published seismic refraction data, we estimate the crustal thickness of the distal part to be 5.5 km and of the west and east sides of the proximal part as ~7 and ~9.5 km, respectively. To our knowledge, this is the largest crustal thickness contrast inferred across any spreading ridge, and it augments recent similar results from the SW Indian Ocean. We interpret the thin crust in the distal part as transitional crust formed by extreme attenuation without organized sea floor spreading, and the proximal part by crustal accretion at a slow spreading mid-ocean ridge. In the proximal part, there is an inverse relationship between the ratio of crustal thicknesses and the ratio of spreading rates east and west of the spreading center. We interpret this relationship to indicate that new material is accreted preferentially to an existing crust on the slow moving east side of this spreading system. Off-axis crustal accretion can take place either by lava flowing from the axis or by off-axis intrusions.

CENOZOIC ROTATION OF THE YUCATAN (MAYA) BLOCK ALONG THE ORIZABA FAULT ZONE OF SOUTHERN MEXICO AND THE FAULTS OF CENTRAL AMERICA
BURKART, Burke¹ and SCOTESE, Christopher R.^2
1Geology, Univ Texas - Arlington, Box 19049, Arlington, TX 76019-0049, burkart@uta.edu
²Geological Sciences, Univ of Texas at Arlington, 500 Yates, Arlington, TX 76019

Yucatan (Maya)has been an independent block since early Cenozoic when counter-clockwise rotation began that continues today. It is bounded in Mexico by the Orizaba fault zone (OFZ), which begins near the Gulf of Mexico at the Santa Ana massif, runs along the western Isthmus of Tehuantepec, crosses the northern Gulf of Tehuantepec W of the Chiapas massif, and connects with the major faults of Guatemala and the Cayman trough. Faults of Guatemala and adjacent Honduras are boundaries to wedges whose eastward rotation has been away from the Cuicateco terrane of Oaxaca, Mexico. Dextral slip of about 340 km across the OFZ is measured by offset of Laramide structures and Mesozoic and Tertiary contacts of the northern Chiapas massif from those in the fold and thrust belt of the Sierra Madre Oriental. Reversing the Cenozoic counter-clockwise rotation and simultaneously restoring previously-known sinistral offset across the Polochic fault of 130 km, moves the westernmost part of the tapered block between the Polochic and Jocotan faults (Chuacus-Tambor block) of Guatemala to a position between the Yucatan and Guerrero blocks about 160 km NW of the Pacific coast. Very little offset occurred across the Motagua fault zone. The northernmost part of the Chiapas massif is moved NW across the Isthmus to near the Santa Ana uplift near the Gulf of Mexico. Ophiolites, granitoids, metasedimentary rocks and volcaniclastics related to Cretaceous arc magmatism found in the Cuicateco terrane of Oaxaca and Tambor of Guatemala are juxtaposed with this restoration model. Obduction during strike-slip movement may account for wider distribution of ophiolites of Guatemala, which were obducted during strike-slip movement. The eastern Veracruz basin opened during rotation of the Yucatan block. Sinistral offset across the Chiapas Strike-Slip fault zone may reflect partial decoupling from the rest of the Yucatan block. The western basin (Cordoba platform) was dropped downward at an early stage of rotation.

EVOLUTION OF THE CRETACEOUS TO RECENT OROGENIC BELT OF NORTHERN VENEZUELA
SISSON, Virginia B. and AVÉ LALLEMANT, H. G.
Dept. of Earth Science, Rice Univ, MS-126, Houston, TX 77005-1892, jinnys@rice.edu

The Caribbean Mountain system (Venezuela) is both a Modern and Ancient Plate Boundary and Orogen. At first glance, this mountain range appears to be a classical orogenic belt with a metamorphic "Hinterland" and a non-metamorphic "Foreland" fold and thrust belt. However, extensive dating (mostly 40Ar/39Ar) indicates that metamorphism of the hinterland belt took place in mid-Cretaceous time, whereas the non-metamorphic foreland rocks were deformed in Cenozoic time. This situation resulted from marked right-oblique convergence of the Caribbean and South American plates along their mutual EW-trending plate boundary zone. The metamorphic rocks contain blueschists and eclogites and have formed in the Leeward Antilles subduction zone along which the Atlantic plate was subducted. Blueschists and eclogites were partially exhumed by arc-parallel stretching resulting from displacement partitioning along an oblique plate margin. The collision of the Leeward Antilles arc with South America resulted in obduction of the accretionary wedge onto the South American margin and change of subduction polarity. This obduction took place in Paleocene time in the west and is still occurring in the east. The development of foreland basins and the foreland fold and thrust belt was diachronous as well and young from west to east. The oblique convergence rate vector was strongly partitioned into a plate-boundary normal component that resulted into the south-vergent fold and thrust belt and a plate-boundary parallel component resulting in boundary parallel right-lateral strike slip faults along which the metamorphic belts were displaced toward the east. In addition, subduction related processes vary along strike. In the west, two high-pressure belts (Cordillera de la Costa and Villa de Cura belts) occur whereas in the east, (Margarita Island) only one exists. The Cordillera de la Costa belt contains eclogites that were formed at ~70 km depth. Eclogites on Margarita formed at ~45 km depth. The Villa de Cura belt blueschist formed at ~30 km depth. The age of exhumation varies from mid-Cretaceous (Villa de Cura and Margarita) to Eocene (Cordillera de la Costa). The dependence of depth of metamorphism and timing of exhumation of these high-P rocks on plate tectonic configuration is complicated, because of Tertiary overprint.

INTERCRATONIC OROGENS: THE CARIBBEAN AND SCOTIA ARCS
DALZIEL, Ian W.D., LAWVER, Lawrence A., GAHAGAN, Lisa M., and MANN, Paul
Institute for Geophysics, Univ of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500, ian@utig.ig.utexas.edu

The Caribbean and Scotia arcs are two striking features of any tectonic map of the Earth and are in fact nearly identical in size. They are respectively located between North and South America, and South America and Antarctica, joining the North American Cordillera to the Andes, and the Andes to the West Antarctic continental margin orogen. Their tectonic evolutions can be related to the relative motion between the two pairs of cratons. Their evolving physiography produced critical controls, varying with time, on the movement of biota between the cratons, and between the Pacific and Atlantic Oceans. The Caribbean arc differs from the Scotia arc with the presence of the Central American land bridge. Yet differential motion along the Shackleton Fracture Zone between Cape Horn and the tip of the Antarctic Peninsula has produced a ridge as shallow as 700 meters. This ridge with only minor changes in plate motions could develop into a subduction zone and generate an island arc. Absence of a South America-Antarctica land bridge permits a complete and vigorous wind-driven circum-Antarctic current and intense sediment scour in Drake Passage. Cenozoic magnetic anomalies have been identified in Drake Passage and the eastern Scotia Sea where oceanic crust was formed as Antarctica separated from South America. High sedimentation rates, possible formation during the Cretaceous Normal Superchron, and a large igneous province obscure the equivalent history of the older Caribbean arc and seafloor. The nature and tectonic history of these 'fusible orogenic links' between the continental margin cordilleras of the western Americas and Antarctica are considered as are their evolutions in terms of possible 'mantle return flow' from the Pacific Ocean basin to the Atlantic Ocean basin. Possible analogs to the ancient geologic record such as a link between the Ordovician Taconic and Famatinian arcs of North and South America are also considered.

3-D GRAVITY ANALYSIS OF THE N.E. CARIBBEAN AND THE DEVELOPMENT OF THE PUERTO RICO TRENCH
MARTIN, Jennifer L., TEN BRINK, Uri S., DILLON, William P., and NEALON, Jefferey W.
Woods Hole Field Center, U.S. Geological Survey, 384 Woods Hole Rd, Woods Hole, MA 02543, jlmartin@usgs.gov

A 500-km long section of the carbonate platform north of Puerto Rico and the Virgin Islands collapsed simultaneously sometime after 3.4 Ma to a maximum depth of 4.5 km. This sudden subsidence, which may be associated with the formation of the Puerto Rico Trench, is puzzling given that the direction (ENE) and the rate (~20 mm/y) of North American (NOAM)-Caribbean plate motion in this area has remained constant during the past 45 Ma. The collapse has been attributed to subduction erosion, to a tear in the downgoing NOAM plate in the area of maximum curvature, and to an interaction at depth between the flaps of the Caribbean and NOAM plates. We modeled the gravity field in the NE Caribbean in 3-D with the simplifying assumption that the sources of the anomaly are only due to the water-crust and crust-mantle interfaces. Consistent results were obtained by modeling in the space domain (CordellÕs method) and in the wave number domain (ParkerÕs method). A 2-D model along a 350-km-long seismic profile across this plate boundary was also compared with the 3-D model results. The gravity model indicates that a 25±5 km thick crust extends from Puerto Rico northward under the collapsed area to just south of the Puerto Rico Trench. The thick crust is not an artifact of excluding low-density sedimentary rocks from the model, because there is no evidence in seismic reflection data for an appreciable accretionary prism south of the trench. Moreover, dredging has recovered arc-related metamorphic rocks and limestone, similar to those found in Puerto Rico, at a depth of 7100 m south of the trench. The gravity model suggests that the entire crust north of Puerto Rico has been tilted northward. A whole-crustal tilt requires space to be created by a sudden removal of the foundation. One possibility is that the NOAM plate flap, which underlies Puerto Rico and the Virgin Islands has suddenly increased its dip or rolled back. Either of these options will pull down the overlying crust if the interface between them has high friction, which allows shear stresses to build up. The existence of a large negative gravity anomaly (-355 mGal), more negative than in typical trenches is consistent with this interpretation. Large magnitude earthquakes may occur at the interface between the Caribbean and the NOAM plate if the interface can support high shear stresses.

CARIBBEAN PLATE BOUNDARIES - EOCENE SUBDUCTION, COLLISION AND SUTURING IN PUERTO RICO: SIGNIFICANCE OF THE GREAT SOUTHERN PUERTO RICO FAULT ZONE
ANDERSON, Thomas H.¹ and LIDIAK, Edward G.^2
1Univ Pittsburgh - Pittsburgh, 321 Old Engineering Hall, Pittsburgh, PA 15260-3303, taco@pop.pitt.edu
²Dept. of Geology & Planetary Science, Univ of Pittsburgh, Pittsburgh, PA 15260
JOLLY, Wayne T., Dept. of Earth Sciences, Brock Univ, St. Catherines, ON L2S 3A1, Canada

The northern margin of the Caribbean plate is distinguished by the southeastward curving Greater Antillean (GA) arc. Volcanism above the south-facing subduction zone ceased after the western Cuba segment of the arc collided with the Bahamas platform between 66 and 44 Ma. In eastern Cuba, Hispaniola and attached islands to the south collisional structures are less prominent because of the southeastward curvature of the GA arc away from the Bahamas Platform. South of the Cauto fault in Oriente Province, Eocene igneous rocks crop out as they do in Hispaniola and Puerto Rico. In Puerto Rico, Eocene lavas and plutons are most common among northwesterly striking faults that distinguish the Great Southern Puerto Rico fault zone (GSPRFZ). Tertiary strata include lavas, volcaniclastic and other sedimentary units some of which are fine-grained and cherty and may be pelagic. Well layered strata may contain olistoliths and commonly record faults and folds some of which may be penecontemporaneous. Older, Late Cretaceous rocks covering the oceanic crust southwest of the GSPRFZ may have been offscraped and deformed as they were carried toward the trench. Subduction related Eocene volcanism was areally limited and short-lived. Convergence waned during Oligocene time perhaps in response to the arrival and collision of thick oceanic terrains (eg. Cayman Ridge, Nicaraguan Rise, Beata Ridge) with the overriding plate. During collision, volcanic units at the edge of the overriding crust were uplifted and destabilized sufficiently so that masses calved off and collapsed southwestward forming an apron of debris (Sabana Grande Formation). We propose that the Eocene volcanic rocks record renewed subduction, although the subduction was north-facing and involved the consumption of the Caribbean plate along a zone roughly coincident with the back arc of the Cretaceous belt.

STRUCTURAL STYLES ALONG OBLIQUELY CONVERGENT OROGENS: THE EASTERN CARIBBEAN-SOUTH AMERICA PLATE BOUNDARY
CRUZ, Leonardo¹, TEYSSIER, Christian¹, and WEBER, John²
Geology and Geophysics, Univ of Minnesota, Minneapolis, MN 55455, cruz0031@umn.edu
²Geology, Grand Valley State Univ, Allendale, MI

The Caribbean-South America plate boundary in NE Venezuela and northern Trinidad exposes an E-W oriented mountain belt of deformed and metamorphosed sediments deposited on the northern South America passive margin in early Mesozoic time. Northern Trinidad and NE Venezuela display contrasting styles of deformation developed during oblique collision and wrenching between the Caribbean and South American plates in the past 50 million years. In northern Trinidad, metamorphic conditions increase from east to west with structures evolving from upright in the east to recumbent in the west, across the brittle-ductile transition. In ductilely deformed rocks, foliation is subhorizontal and lineation is ~E-W, parallel to the belt. Sense of shear is ambiguous. In NE Venezuela, metamorphic grade is similar to the western part of northern Trinidad; foliation dips moderately to steeply to the S and lineation plunges moderately to the SW. In general, sense of shear criteria parallel to lineation show top (down) to SW relations, indicating increased exhumation of the northern part of the belt. Oblique collision and wrenching in the Caribbean-South American plate boundary may have generated a complex deformation history, which evolved diachronously from west to east to produce the two styles of deformation displayed in northern Trinidad and NE Venezuela. Two models have been proposed to account for the generation and exhumation of this belt. In the first model, deformation is concentrated in a retro-wedge developed in front of the rigid Caribbean plate indenter, which deformed the softer South American continental crust. Vertical stretch decreases southward, exhumation rate increases to the north and deformation ages are younger to the east due to diachronous collision. The second model implies a midcrustal coupling zone that deforms ductilely due to translation of upper crustal blocks and transpression of the system. Subhorizontal fabrics develop contemporaneously parallel to the rheological layering of the lithosphere. For both models, spatial and kinematic variations of fabric orientation, cooling ages, and exhumation rates, are key elements to understand the overall deformation history of this region and are currently being studied.

LEAD ISOTOPE STUDY OF THE PALEOGENE IGNEOUS ROCKS OF THE SIERRA MAESTRA, SOUTHEASTERN CUBA
KYSAR MATTIETTI, Giuseppina¹, LEWIS, John F.¹, and WYSOCZANSKI, Richard^2
1Dept. Earth and Environmental Sciences, The George Washington University, Washington, DC, jlewis@gwu.edu
²Mineral Sciences, National Museum of Nat History, Smithsonian Institution, Washington, DC

The Sierra Maestra of southeastern Cuba occupies a key position between the remnants of the Greater Antilles arc accreted terranes and the Cayman strike-slip belt that constitutes the present day northern Caribbean plate boundary. An isotopic study has been undertaken to constrain the paleotectonic setting and the source of the Sierra Maestra structure. Lead isotope ratios were determined for a set of lithologies representative of each major magmatic complex of the Sierra Maestra. Both 207Pb/204Pb and 208Pb/204Pb ratios are restricted to a narrow, well-defined array of values in a band parallel to the North Atlantic Reference Line NHRL The slight enrichment in 207Pb/204Pb ratios represent the selective mobilization U with respect to Th, (U/Th ratios ranges from 0.8 to 1). Overall Pb isotope ratios for the Sierra Maestra are homogeneous, indicating the existence of a single magma source. This observation correlates with the low Ce/Yb values that characterize primitive arcs with varying degrees of the PREMA (Primitive fertile mantle) component. There is a significant overlap between the isotopic ratios of the Sierra Maestra and the Cretaceous island arc tholeiites of Puerto Rico indicating that the Paleogene arc rocks have a similar mantle source.

Related abstracts

ANIMATION OF PLATE MOTIONS AND GLOBAL PLATE BOUNDARY EVOLUTION SINCE THE LATE PRECAMBRIAN
SCOTESE, Christopher R., Geological Sciences, Univ of Texas at Arlington, 500 Yates, Arlington, TX 76019, chris@scotese.com

A computer animation will be presented that illustrates both plate motions and the evolution of plate boundaries since the Late Precambrian. Plate motions during the Jurassic, Cretaceous and Cenozoic plate motions are based on linear magnetic anomalies and the tectonic fabric of the ocean floor revealed by satellite altimetry, in combination with "absolute" motion trajectories determined by the Indian and Atlantic hotspot tracks and paleomagnetism. Early Mesozoic, Paleozoic and Late Precambrian plate tectonic reconstructions, however, are less well constrained and are based on less precise paleomagnetic data, lithologic indicators of climate, biogeographic inferences, and the timing of continental rifts and collisions. In addition to the motion of the plates, the animation shows the continuous evolution of global plate boundaries. Though the rifts and subduction zones associated with the breakup of Pangea are well known, the pre-Mesozoic plate boundaries shown here are speculative. Their location is based on the timing of rifts and continental collisions inferred from the geologic record, and the fundamental assumption that plates move as a result of slab pull and ridge push. For example, fast moving plates must be attached to old, cold subducting slabs. Large continental plates (Eurasia), on the other hand, tend to move slowly because of deep lithospheric keels. The evolving geometry of plate boundaries controls the tempo and mode of plate evolution. The history of plate motions might be best described as "long periods of boredom, interrupted by short intervals of terror (rapid change)". Episodes of global plate reorganization punctuate long periods of steady-state plate motion. As shown by the animation, these global reorganizations are due to catastrophic changes in plate boundary geometry that result in new lithospheric stress regimes. One of the most important plate boundary events is the subduction of a spreading center. The subduction of the Tethyan Ridge in the early Jurassic may have been responsible for the breakup of Pangea.