IGCP Project short title: Caribbean Plate Tectonics Duration and ...

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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. 26 EVOLUTION OF THE CRETACEOUS TO RECENT OROGENIC BELT OF NORTHERN VENEZUELA SISSON, Virginia B. and AVÉ LALLEMANT, H. G 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. 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 southvergent 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. 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 26
27 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 THEPUERTORICOTRENCH MARTIN, Jennifer L., TEN BRINK, Uri S., DILLON, William P., and NEALON, Jefferey W. 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., LIDIAK, Edward G and JOLLY, Wayne T. The northern margin of the Caribbean plate is distinguished by the southeastward curving Greater Antillean (GA) arc. Volcanism above the south-facing 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. 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 27
Page 1 and 2: *The information in this report wil
Page 3 and 4: 3 arc at about 120 Ma. However, sev
Page 5 and 6: 5 geometry of the arcs are no longe
Page 7 and 8: ABSTRACTS AND PRESENTATIONS 7 Ander
Page 9 and 10: Pindell, J., Higgs, R., and Kennan,
Page 11 and 12: Coast Ranges) and the Josephine oph
Page 13 and 14: to the meeting from Cuba, Jamaica,
Page 15 and 16: 6.2 SCIENTIFIC MEETINGS AND WORKSHO
Page 17 and 18: 17 west of both of them, and, conse
Page 19 and 20: 19 geology of Cuba were the subject
Page 21 and 22: 21 The aim of the Workshop was for
Page 23 and 24: 23 5. Does the plume source contain
Page 25: less deformed sedimentary sections,
Page 29 and 30: 29 PREMA (Primitive fertile mantle)
Page 31: 31 Lawver, L.A., M.F. Coffin, I.W.D

IGCP Project short title: Caribbean Plate Tectonics Duration and ...

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