Return to Reports Return to Caribbean Plate Origin Revised August 26, 2002

The 16 Caribbean Geological Conference took place in Barbados, British West Indies, between June 16 and 23, and included field trips, workshops and scientific meetings. As part of the Conference, IGCP Project 433 organized a Field Workshop and Business Meeting, which will be briefly described in the following paragraphs. We all agreed that the conference in Barbados was a great opportunity for exchange and debate, we learned from the field trips and scientific presentations, and especially enjoyed the hospitality and wonderful landscape of the island.

The Permanent Standing Committee for the Caribbean Geological Conferences announced at the meeting that the next Caribbean Geological Conference is scheduled to be held on the Island of Margarita (Venezuela) and will be organized by the Geological and Geophysical Societies of Venezuela. Serving as a backup is the University of Puerto Rico at Mayag uez. Also announced at the meeting is the good news that the Proceedings of the 15th Conference will soon be available re: Caribbean Geology into the Third Millennium. Transactions of the Fifteenth Caribbean Geological Conference, edited by Trevor Jackson, University of West Indies, Jamaica. Orders from sales@uwimona.edu.jm

The purpose of this report is to describe briefly the scientific results and progress made at this conference with respect to the following topics: (A) The Field Trip to an accretionary prism, (B) the scientific presentations and debate, and (C) the business meeting.

Field trip to the Scotland District: Exposed example of an accretionary prism.
Field trip leader Robert C. Speed, Northwestern University, Department of Geological Sciences, Evanston, Illinois 60208, USA.

The island of Barbados is the only emergent peak of the Barbados ridge complex. It lies above the active subduction zone between the Caribbean and South American plates. In the Scotland District is exposed two fault bounded deformed units: 1) the mid-middle Eocene to late Oligocene oceanic allochthon and, 2) the Early to Late Eocene terrigenous unit. The oceanic allochthon was emplaced from west to east above the western (inner) front of the accretionary prism in the Middle Miocene. It is composed of well-bedded yellowish pelagic marls with gray intercalations of volcanic ash that do not contain terrigenous sediments. The sole of this tectonic section is a distinctive zone of deformed rocks. The terrigenous unit is interpreted to be an entirely submarine turbidite fan deposit, composed of non-amalgamated sandstones, amalgamated sandstones and multi-layers of mudstone and sandstones. The section is quartz rich, with conglomerates containing a wide collection of rocks eroded from the South American continent, but there is no volcanic ash in this unit. Inactive mud volcanoes cut through previous units, and are mainly represented by a mass of poorly sorted fragments of older rocks.

Members of IGCP Project 433 participated in this very interesting field trip which started at Chalky Mount, a hill 175 meters above sea level, and ended at the sea shore, after an exercise of walking and climbing along a poorly forested and rugged landscape. One of the many interesting features observed was that most of the accretionary section consists of terrigenous and pelagic sediments and that only the oceanic unit contains some distal volcanic material, even though it was deposited in a fore arc environment. In comparison, all of the Cretaceous volcanic arc deposits of Cuba contain a large amount of volcanic material, whereas in the Cuban Paleocene-Early Eocene arc sections volcanic material occurs as far away as 200 km from the volcanoes, and only in those sections located more than 300 km away, do pure sedimentary rocks dominate and with only isolated horizons of volcanic ash. This trip was a unique opportunity to see an exposure of a true accretionary prism, with the guidance of a person who knows this area in great detail. The excellent field guide to this and others areas of the Lesser Antilles is available from the organizers of the Conference.

Some members of the IGCP Project also visited St. Vincent Island after the meeting, to see a volcanic island and its active volcano.

The status of the debate about the Caribbean Plate Tectonic Interpretation
Conveners: Manuel A. Iturralde-Vinent and Edward Lidiak

This meeting was well attended by active participants from Barbados (3), Puerto Rico (5), Cuba (4), Jamaica (5), Venezuela (3), United States of America (10), United Kingdom (1), Germany (2), Spain (2), France (2), and more than 20 other interested scientists who attended the presentations and discussions. There were two kinds of oral and poster presentations: theoretical ones about the plate tectonic modeling of the Caribbean, and those providing new data and interpretations from different parts of the region. A third and very important part of the scientific meeting was a very active Open Debate about the latest version of the plate tectonic model of J. Pindell and his collaborators.

In the introductory words to the meeting, M. Iturralde-Vinent presented an evaluation of the status of the Project, based on an updated version of the 2000-2001 Project Report (www.ig.utexas.edu/CaribPlate/CaribPlate.html). In the following presentations and debate, most of these issues were revisited and discussed in greater details.

1. Manuel Iturralde-Vinent
   Introductory words: Status of the Debate about the Caribbean Plate Tectonic Interpretations

2. JAMES, Keith
   A simple Synthesis model for the Evolution of the Caribbean

3. PINDELL, J., KENNAN, L., MARESCH, W., STANEK, K., DRAPER, G.
   Evolution of the Northern Portion of the Caribbean Plate: Pacific to Bahamian Collision

4. STANEK, K., MARESCH, W., GRAFE, F., GREVEL, C., MILLAN, G.
   Tectonics, Petrology and Geochronology of Escambray Complex, Central Cuba

5. PINDELL, J., KENNAN, L.
   A critical assessment of Caribbean tomography in light of Caribbean kimematic evolution.

6. GARCIA CASCO, A., ROLDAN TORRES, R., MILLAN, G., ITURRALDE-VINENT, M., NUÑEZ, K., PEREZ de ARCE, C., FONSECA, E., MORATO, D., QUINTANA, O.
   Diversity of Tectonic Settings of Formations and Metamorphism of Basic Rocks From the Northern Serpentinite Belt of Cuba: A Preliminary Statement and Consequence

7. MARESCH, W., GERYA, T., KREBS, M., SCHERTL, H-P., DRAPER, G.
   The Serpentinite Melanges of the Rio San Juan Complex Dominican Republic and the Dynamics of Subduction Zones

8. LIDIAK, E.
   The Role of Radiogenic Isotopes in Deciphering the Evolution of the Plate Tectonic Interpretation

9. LEWIS, J.
   Is there a Regional Albian Unconformity in the Greater Antilles?

10. PINDELL, J., ROSENFELD, J.
    Key Moments in the Evolution of the Gulf of Mexico

11. CRUZ, L., TEYSSIER, Ch., WEBER, J.
    Structural Styles, Deformation and Exhumation of Ductile Crust in Convergence: The Eastern Caribbean Plate Boundary

12. ROJAS, R.
    Stratigraphic distribution of rudists genera in the American province

13. ITURRALDE-VINENT, M.
    Early evolution of the Gulf of Mexico and the Caribbean

14. LIDIAK, E., JOLLY, W.
    Water Island Formation, US Virgin Islands: A New Look at the Original Primitive Island Arc (PIA) Suite of the Caribbean

15. SUKAR, K., PEREZ, M., LLANES, A., ULLOA, M., RODRIGUEZ, R.
    Oceanic Plagiogranites of Cuba

The position in favor of an in situ origin for the Caribbean Plate was championed by K. James, with the presentation of a "Simple synthesis model..." and a discussion of arguments for and against the far-field origin of the Caribbean Plate (his model will be available at the project's web page). His interpretation uses as a present day analog the North Atlantic Ocean around Iceland. Some of the points against the allochthonous model raised by J. Keith are the following:

- Jurassic rift directions on the Maya Block conform with regional extensional strain in North and South America and in the intervening area. They show that the Block has not rotated.

- The ocean crust in the Gulf of Mexico follows the same extensional trend and broadens somewhat to the east. If the Maya Block had rotated, it this crust would broaden markedly to the west, which it does not.- It is geometrically impossible for a 3,000 kilometre long, straight arc to enter the Caribbean and assume its strongly curved configuration without intense compression of the Caribbean Plate, on which it sits. In fact the Caribbean Plate is highly extended.

- It is geometrically impossible for the Chortis Block to migrate southeastwards into the Central American location at the same time as the Caribbean Plate is supposed to be migrating northeastwards.

- Northward transport of the (South America derived) Middle Eocene Scotland Group sands of Barbados was stopped by the Tiburón Rise, on top of which coeval sands occur (DSDP drilling results; drilling 19 km to the north did not find these sands). The Rise lies on the Atlantic Plate. The relationship shows that the Scotland Group accumulated close to its present location and not north of the Maracaibo area.

- Coeval Maastrichtian - Middle Eocene clastics throughout Middle America record a regional convergence event that cannot be explained by the allochthonous model, which attributes diachronous flysch deposition to entry and passage of the plate.

During two later talks, most of James’ arguments were debated by J. Pindell, who opposed the autochthonous interpretation. The discussion concerning an in situ vs allochthonous origin of the Caribbean continued for about two hours in the "Open Debate" session where J. Pindell was asked to made a detailed presentation of his model, and it was the subject of many critical comments and questions. During this debate, it became clear, at least to some of us, that the allochthonous origin for the Caribbean Plate explains more aspects of the evolution of the Caribbean, but at the same time, as Iturralde-Vinent indicated in the introductory words to the session, this type of model still contains many unsolved problems and issues that need to be properly addressed.

Some of the problems that remain to be solved, or at least require further discussion and agreement, are:
(A) Is there one or several plateau basalts events in the Caribbean?
(B) If the Galapagos Hot Spot is unrelated to the origin of these plateau basalts, then how did the plateau basalts form?
(C) Is the thick Caribbean crust a result of a mantle plume, the result of plate superposition by subduction, or are there other causes?
(D) Is there a section of Lower Cretaceous volcanic arc rocks in southern Central America?
(E) What and where are the relicts of the original ProtoCaribbean crust?
(F) Are these relicts present within or adjacent to the ophiolite belts along the plate boundaries?
(G) Are the Aptian-Albian, Santonian-Campanian, Campanian-Maastrichtian, Lower Paleocene and Middle-Late Eocene unconformities in the volcanic arc sections of a single or of different origins?
(H) Is the prominent unconformity in the Aptian-Albian volcanic arc sections of regional extent and is it related to a change in arc polarity?
(I) Is there a single volcanic "Great Arc" since the Aptian-Albian to the Present, or there were several arcs evolving as in circum Pacific region?
(J) Are the Cuban Cretaceous and Paleogene volcanic arcs a single back arc (main Cuba)-axial arc (Sierra Maestra) couple?
(K) Are they instead two distinct arcs, as suggested by geochemistry, petrology and classic regional geology?
(L) Is there any true axial arc section in the Paleogene rock suites of Hispaniola and Puerto Rico-Virgin Islands?
(M) Are the Paleogene igneous rock suites in Hispaniola and Puerto Rico-Virgin Islands of back arc or front arc instead of axial arc?
(N) Did the Yucatan basin actually open during the Paleogene?
(O) Did this proposed Paleogene event fracture and subdivide the Cuban volcanic arc igneous suites into two branches so that now one suite is the main Cuban island arc (back arc setting) and the other Sierra Maestra-Cayman ridge arc (axial arc setting)?
(P) Are the Cuban Southwestern allochthonous terranes (Guaniguanico, Pinos and Escambray) deformed crustal sections of the ancient margin of North America?
(Q) If so, where were their original locations and do they actually represent ancient basins that are now deformed and superimposed as a stack of thrust units?
(R) Why do some models show these terranes as being of the same size in both the Mesozoic and the Present?
(S) How and when were these terranes emplaced to their present position?
(T) Where they just dragged, according to the allochthonous model, as crustal fragments in front of the leading edge of the Caribbean Plate?

In fact, it is possible to add many more questions, but this can be a never ending exercise. We need, in future years, to start discussing some of these issues within the egroup, and by this method, bring our debate to a new level and to reasonable conclusions.

The abstracts of papers related to the general modeling of the Caribbean are the following:

A SIMPLE PLATE TECTONIC MODEL OF THE CARIBBEAN, A DISCUSSION OF ARGUMENTS FOR AND AGAINST THE FAR-FIELD ORIGIN OF THE CARIBBEAN PLATE
Keith H. James

Literature continues to favor a far-field (Pacific) origin for the Caribbean Plate, with few papers arguing for an in-situ origin. This paper takes a critical look at arguments for the far-field model, considers others that support the in-situ origin, and finds in favor of the latter.

The complex area between the continental masses of North and South America comprises numerous continental, stretched continental, island arc and oceanic elements, described by numerous works. Some are poorly exposed and not well known. Others are intensely explored and well documented.

Syntheses of this geology popularly derive the Caribbean Plate from the Pacific area and require major rotation of island arc elements and continental blocks. Such models are complex. This paper suggests a simple evolution from a Pangean configuration principally via regional (N - S America), Jurassic-Middle Eocene, WNW oriented sinistral transtension, followed by Oligocene-Recent, E-W strike-slip between the Caribbean and the American Plates.

CRITICAL ASSESSMENT OF CARIBBEAN SEISMIC TOMOGRAPHY (HILST, 1990) IN LIGHT OF CARIBBEAN KINEMATIC EVOLUTION
James Pindell and Lorcan Kennan
TectonicAnalysis, Ltd ~also at: Dept. Earth Science, Rice University, Houston, Tx USA

Careful integration of Caribbean seismic tomography (Hilst, 1990) with Caribbean kinematic and tectonic history allows plausible interpretations of nearly all the imaged high velocity zones in the upper mantle and the apparent breaks between them. The analysis generates several testable models for the Cenozoic subduction of various parts of Proto-Caribbean lithosphere beneath the migrating Caribbean Plate. These models of former subduction geometry carry implications for Caribbean evolution, which have been incorporated with caution as refinements in the Pacific-origin Caribbean tectonic model.

Hilst and Mann (1993) used tomography to show Caribbean lithosphere dipping shallowly beneath the Maracaibo Block, and Pindell et al. (1991) used it to map a torn Atlantic slab comprising the Lesser Antilles subduction zone, and to propose Paleogene south-dipping subduction of Proto-Caribbean crust beneath South America. Here, we add (1) that the Proto-Caribbean slab can be seen tearing from the Bahamas beneath Hispaniola, which we infer occurred beneath Cuba in the Eocene which in turn led to strong isostatic rebound of the Cuban Orogen; (2) that Proto-Caribbean subduction beneath South America caused orogeny there BEFORE the arrival of the Caribbean Plate, the understanding of which is essential to correctly interpreting the Paleogene evolution of Trinidad and Eastern Venezuela, and the tectonic grain for Neogene structural development.

The analysis shows that tomography is a useful tool in deciphering former plate boundary histories, and that the fate of subducted slabs can often be related to geological developments at the surface, such as helping to understand the region of very high heat flow in the Guarico Basin of central Venezuela.

EVOLUTION OF THE NORTHERN PORTION OF THE CARIBBEAN PLATE, PACIFIC ORIGIN TO BAHAMIAN COLLISION James Pindell¹, Grenville Draper², Lorcan Kennan¹, Walter V. Maresch³, Klaus P. Stanek^4
1TectonicAnalysis, Ltd., CokesBarn, WestBurton, Pulborough RH20IHDEngland and Dept. Geology, Rice University, Houston, TX
²Dept of Earth Sciences, FIU, Miami, Florida 33199 USA
³Inst. fur Geologie, Minerealogie und Geophysik, Ruhr-UniversitoetBochum, 44780 Bochum, Germany
⁴Inst. fur Geologie, TUBergakademie Freigerg, Bernhard con Cotta Str. 2, D 09596, Freiberg, Germany

Pacific origin models of Caribbean geologic evolution are more compatible with regional geology than Inter-American origin models because (a) the Greater Antilles Arc (GAA) is older than the Central American Arc, and (b) Caribbean tectonic interaction with northern Colombia/southern Yucatan began in the Campanian, which requires a Pacific position of the Caribbean Plate before that time (c) recent paleomagnetic studies show the Caribbean Plateau 5° south of its present position in the late Cretaceous, requiring it to be in the same place as South America in an Inter-American model.

We refine earlier Pacific-derived 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)the Panama-Costa Rica arc formed at equatorial latitudes, (4) Caribbean HP/LT metamorphic terranes (except Jamaica) pertain to development of SW-dipping subduction beneath the GAA that followed an Aptian subduction polarity reversal event - the new polarity then allowed the Caribbean Plate to enter the interAmerican realm during Upper Cretaceous, (5) the central Cuban Arc comprises mainly forearc elements of the GAA, (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: a. Maastrichtian -Paleocene NW extension driven by slab rollback of Proto-Caribbean lithosphere along eastern Yucatan, during which the western and central Cuban metamorphic terranes were uplifted as core complexes, and b. Early-Middle Eocene NNE extension driven by rollback of ProtoCaribbean crust toward the Bahamas, (8) Middle Eocene collision of Cuba with the Bahamas, (9) Eocene onset of Cayman Trough pull-apart as the Caribbean Plate began its eastward migration to its present position (10) Oligocene transpression in Hispaniola and Puerto Rico which led to the separation of the Hispaniola from Oriente.

PALINSPASTIC PALEOGEOGRAPHIC EVOLUTION OF EASTERN VENEZUELA AND TRINIDAD
James Pindelll and Lorcan Kennan
TectonicAnalysis, Ltd 'also at: Dept. Earth Science, Rice University, Houston, Tx USA

We have completed an intensive examination of the geology and crustal setting o the Trinidad/Tobago region using plate motion data, surgical field studies, core observations, 5,000 km of seismic data, dozens of wells, gravity, seismicity and structural analysis, seismic tomography, and integration with Eastern Venezuelan geology. These data have been integrated to produce sequential palinspastic paleogeographic maps at 2, 4, 6, 8, 10, 12, 18, 33, 49, 56, 72, 84, 119, 140, 156, and 180 Ma, which incorporate known and interpreted plate motions and deformations. The palinspastic approach restores observed deformations through time, allowing clarification of origins of terranes, former relationships of blocks, sources of clastic sediments, and reconstruction o regional paleo-environments. Kinematic development was dominated by 240 km of E-W shear (toward 085°) back to 12 Ma. About 100 km of this has occurred south of the Northern Range since about 6Ma, with the other 140 km occurring offshore to the north along North Coast Fault Zone, mainly between 5 and 12 Ma. The 12 Ma reconstruction reconstructs the Middle Miocene "Serrania-Nariva" thrust front. A partitioned, NE?-directed minor extension occurred along the toe of the Middle Miocene thrust front during this 12 to 5 Ma interval. In the Paleogene, Proto-Caribbean lithosphere underthrust northern South America prior to arrival of Caribbean Plate from the west, establishing the tectonic grain for the Neogene events, and causing minor basement involved deformation with associated areas of erosion and deposition of Paleogene clastic units. Restoration of these deformations allows portrayal of Cretaceous paleogeography upon a basement configuration related to Jurassic rifting from Yucatan and the Bahamas. The study provides a three-dimensional understanding of tectonics and deposition at this economically important region, and will help to guide future exploration efforts.

KEY MOMENTS IN THE EVOLUTION OF THE GULF OF MEXICO
James Pindell¹ and Joshua Rosenfeld^2
1Tectonic Analysis Ltd., Cokes Barn, West Burton, West Sussex RH20 1HD, England
²Veritas Services, Houston Texas

The Gulf of Mexico developed in two stages, an Early Jurassic to Oxfordian, NW-SE directed, asymmetric rift stage, followed by an Oxfordian-earliest Cretaceous drift stage of seafloor spreading involving strong counterclockwise rotation of Yucatan _ about a pole near western Cuba. Because evaporite deposition matched rift-stage subsidence, the flanks of the Gulf remained shallow for a time as seafloor spreading began in the central Gulf. Upper Jurassic source rocks are rumored to be of shallow water nature. But these rocks are now found at depths far too deep to be explained by known subsidence mechanisms, and I speculate that large magnitudes of "subsidence" of these Upper Jurassic sediments to much deeper marine settings in the US was caused by latest Jurassic or earliest Cretaceous halokinetic mass slumping of the Louann and Campeche salt wedges flanking the deep zone of oceanic crust as it formed in the central Gulf.

In the Eocene, the existence of several deeply incised and filled paleo-canyons in -a Paleocene shelf strata around the Gulf of Mexico leads us to speculate that water level was drawn down by evaporation by as much as 3,000 ft while the Gulf was temporarily isolated from the world ocean. Isolation of the Gulf was caused by choking of the southeastern Gulf/Florida Straits during collision of the Cuban forearc terrane with Yucatan and Bahamas platforms. Deeply incised unconformities of Paleocene-Eocene age in the Yucatan and Nicholas channels and the Straits of Florida north of Cuba suggest that breaching and refilling (catastrophic?) of the Gulf occurred here, possibly more than once. We find no evidence for early Paleogene structural or tectonic uplift in the western and northern Gulf margins. In contrast, the canyons in the Mexican portion of this trend -a were situated in the tectonically loaded Sierra Madre foredeep basin and thus were actively subsiding at this time.

THE EARLY EVOLUTION OF THE CARIBBEAN AND GULF OF MEXICO
M. Iturralde-Vinent
Museo Nacional de Historia Natural, Cuba, iturralde@mnhnc.inf.cu

This paper presents a set of paleogeographic maps that illustrate the formation and evolution of the Caribbean from latest Triassic to latest Jurassic. Stratigraphic data and plate tectonic models indicate that the breakup of Pangae first took place along a system of latest Triassic-Middle Jurassic rift valleys within west-central Pangaea. This system aborted and the new breakup jump into the present mid Atlantic rift and its extinct prolongation along the Caribbean. Probably since the Bajocian, but certainly since the Oxfordian, this area became a marine seaway connecting western Tethys with the eastern Pacific. In contrast, abundant paleontological data strongly suggest that the seaway across west-central Pangaea opened during the Early Jurassic (Hettangian-Pliensbachian), which conflict with the stratigraphic data. This contradiction between paleontology (biogeographic interpretations) and stratigraphy (paleogeographic interpretation) reveals our insufficient knowledge about the Mesozoic geology of west-central Pangaea.

Presentations about the geology of local areas contributing to the knowledge of the Plate Tectonics of the Caribbean
A group of presentations dealing with the petrology, geochronology, geological mapping, tectonic analysis, stratigraphy and paleontology of local areas have strong bearing on our understanding of the Caribbean Plate Tectonics.

In general, it was clear that the best we know some area or some rocks suite, the more complex the picture arose, and usually conflict with previous simple interpretation of the area or subject. Also it was clear, at least for some of us, that even in areas where we agree on basic data, conflict arose when this data is incorporated into some plate models. Reading of the following abstracts will help understanding these points.

THE ROLE OF RADIOGENIC ISOTOPES IN DECIPHERING THE EVOLUTION OF THE PLATE TECTONIC INTERPRETATION
Edward G. Lidiak, Dept. of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, U. S. A.

Isotopes of Pb, Nd, and Sr may be used to distinguish among igneous rocks, which comprise three major rock associations within the Caribbean region. Geochemically distinct igneous rocks may be grouped within the Caribbean plateau province (CPP), the primitive island arc (PIA) series, and the island arc tholeiite (IAT)-calcalkaline (CA)-shoshonitic (SHO) rock association.

Rocks of the CPP include the Curacao Lava Formation, the Aruba Lava Formation, the Dumisseau Formation of Haiti, the Duarte Complex of the Dominican Republic, the Nicoya Complex of Costa Rica, and basalts from the Venezuelan Basin. Pb, Nd, and Sr isotopes indicate that all of these rocks were derived from a depleted to enriched plume-like mantle. The Aruba, Curacao and Nicoya sequences show evidence of containing an additional high-Sr altered oceanic crustal component.

Rocks of the PIA association have been identified in the Virgin Islands (Water Island Formation), in the Dominican Republic (Maimon and Los Ranchos formations), on Bonaire (Washikemba Formation), and in Cuba (Los Pasos Formation). Except for detailed Pb isotope studies of the Maimon and Los Ranchos formations, detailed isotopic studies have not yet been carried out on these PIA rocks. Los Ranchos contains elevated ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb and thus shows distinct evidence of having incorporated a considerable pelagic sediment component during the melting and generation of its magmas. Similarly, some of the Maimon contains slightly enriched ²⁰⁸Pb/²⁰⁴Pb. In contrast, rocks of the Water Island Formation have the most primitive Pb isotope ratios of any Caribbean igneous rocks, and in 206Pb/204Pb ratio are comparable to Indian Ocean MORB.

Rocks of the IAT-CA-SHO series have been studied in most detail in Puerto Rico and in the Dominican Republic. In Puerto Rico, the volcanics display a temporal progression from IAT to CA to SHO series. Pb, Nd, and Sr isotopes in these rocks become progressively enriched in radiogenic component from Aptian-Lower Albian (phase 1) through Upper Albian (phase II) to Cenomanian-Santonian (phase III) time. These enriched Pb, Nd, and Sr isotopic signatures reflect the assimilation of an increased pelagic sediment component in the younger lavas. In contrast, preliminary results on Campanian-Maastrichtian lavas (phase IV) indicate that they coincide with the MORB array. Paleocene-Eocene lavas (phase V) have Nd and Sr isotopic ratios that are similar to phase IV rocks, but have distinctly higher ²⁰⁷Pb/²⁰⁴Pb than the underlying Puerto Rican sequence. The Pb isotopic ratios of the Paleocene-Eocene sequences in both Puerto Rico and Cuba are closely similar.

The isotopic ratios displayed by the three main rock associations discussed here are clear indication that the Caribbean plate underwent significant change during plate evolution. The absence of a subduction-related isotopic component in the CPP indicates that arc development did not occur until PIA time and then continued to evolve during the generation of the IAT-CA-SHO association.

STRATIGRAPHIC DISTRIBUTION OF RUDISTS’S GENERA IN THE AMERICAN PROVINCE
Rojas Consuegra, R.
Museo Nacional de Historia Natural, Obispo 61, Plaza de Armas 10100, Cuba

Rudist are a common group of fossil mollusk in the American paleofaunal province. They occur in calcareous rocks of both carbonate platforms and volcano-sedimentary sections which belong to volcanic arcs. The Rudist’s Biozones, identified according to the associations of several genera, are a very useful tool for regional and trans-tethyan stratigraphic correlations. In the Cuban territory, specific biozones can be identified both in the continental margin (Bahamas Platform) and the volcanic arc sections of the Pacific-Caribbean arcs. Both types of sections are correlated with their isochronous in other terrains of the Caribbean and surroundings. According to the list of rudist taxa present in each area, I have identified the relationships between the faunal association found in those tectonic terranes. Correlation of the limestone intercalations in the Cretaceous Volcanic Arc in the Greater Antilles with rudists bearing-levels within the carbonate platfoms sections in the North American continental margins (underlined) can be illustrated as follows:

Age	North America	Cuba	Hispaniola	Puerto Rico	Jamaica
Hauterivian-Aptian	Sligo-Cupido fms.	Remedios group. Gibara	¿?	¿?	Jubilee Limestn.
Lower Albian	Rosse-Sunniland fm.	‘Pre-provincial’(deduced)	Hatillo and Guamira fms.	¿?	¿?
Middle Albian	Edwards-Estuard City fms.	¿?	Las Canas fm.	Barranquitas fm.	¿?
Upper Albian	El Abra, Delvis River fms.	Provincial, Guaos, Guaimaro fms.	¿?	¿?	¿?
Santonian	Mexico (present)	Loma Yucatán,Moscas	¿?	Cotuí fm.	Peter’s Hill Limestn.
Lower-Middle Campanian	Mexico (present)	Piragua, Hilario	Reworked rudists in the San Juan Conglomerate	Botijitas fm.	Grange inlier
Maastrichtian	MexicoChiapas	Jimaguayú,Isabel fms.	Resedimented rudists in the San Juan Conglomerate	El Rayo Limestone	Guinea Corn fm.

Some of these rudist limestones in the Volcanic Arc sections are associated with unconfoirmities, as those of Albian, Santonian, Campanian and Maastrichtian age.

THE BONAO FAULT, CENTRAL HISPANIOLA, DOMINICAN REPUBLIC Grenville Draper¹ and Pedro P. Hernaiz^2
1Dept. of Earth Sciences, Florida International University, Miami, FL 33186, U.S.A. (draper@fiu.edu)
²Informes y Proyectos, S. A. General Diaz Porlier 49, 28001 Madrid, Spain

The trace of Bonao Fault of the central Hispaniola is clearly visible on satellite imagery where it appears to have the form of a distorted interrogation mark. The northwestern segment extension of the trace is straight and trends WNW. The central part of the fault trace runs due S along the Bonao Valley's western edge. South of the Bonao valley the southeastern segment of the fault trace curves concave to the east.

Recent geologic mapping along with structural and geomorphic observations has enabled us to develop a model to explain this perplexing structure. The south eastern segment is a west-verging ohlique thrust fault that thrusts the (Jurassic)Duarte Complex over the Maastrichtian and older volcanic rocks of the Tireo Fo-rmation. The northwestern segment is a transpressional sinistral fault. We suggest that these two segments formed at the same time during and episode of Oligocene tectonic transpression.

The central, S-trending part of the fault is marked by a clear straight trace. The geomorphology of the mountain front is marked by triangular facets that strongly suggest that segment of the fault is a recent, east-dipping normal fault. We suggest that this normal fault was formed by the reactivation of the older thrust fault. Moreover, this fault marks the western most fault of a zone of extension caused by the recent eastward motion of Puerto Rico relative to Hispaniola.

WATER ISLAND FORMATION, U. S. VIRGIN ISLANDS: A NEW LOOK AT THE ORIGINAL PRIMITIVE ISLAND ARC (PIA) SUITE OF THE CARIBBEAN
Edward G. Lidiak¹ and Wayne T. Jolly^2
1Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA, 15260, USA
²Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada, L2S 3AI

The Water Island Formation consists of a thick Albian (.~) bi-modal submarine sequence of albite basalt (spilite) and albite rhyolite (keratophyre) flows, pyroclastic rocks, and hypabyssal intrusives. Approximately 87% of the mapped sequence is composed of rhyolitic rocks. Original rock textures are preserved except for small patches of the matrix that have been replaced by low-grade metamorphic minerals. New major and trace element data along with new lead isotopic ratios confirm that the rocks are part of a geochemically primitive subduction sequence. Low abundances of rare earth elements (REE), flat REE patterns, and low contents of Th, U, and the high field strength elements (HFSE), particularly Nb and Ta and to a lesser extent Hf and Zr, characterize both the basalts and rhyolites. Lead isotope ratios are among the lowest on any igneous rock in the Caribbean plate. Among major and minor elements, Water Island basalts are generally distinct from MORB in containing lower TiO2 and P205 and greater K20 and Rb. Compared to basalts from the Caribbean Plateau Province of Curacao and Aruba, Water Island basalts are higher in Al2O3, lower in MgO, Cr2O3, Ga, and Nb, and particularly low in Nb/Y and Nb/Yb ratios. The low HFSE concentrations and the prominent negative spikes for both Nb and Ta on chondrite-normalized diagrams are especially indicative of a convergent magmatic arc tectonic setting. These Water Island magmas help characterize the early stages of magmatic arc development along the northeastern margin of the developing Caribbean plate.

OCEANIC PLAGIOGRANITES OF CUBA
Kustrini Sukar¹, Mireya Perez², Angelica I. Llanes¹, Miriela Ulloa¹ y Ramona Rodríguez^3
1Instituto de Geologia y Paleontologia Via Blanca y Carretera Central, San Miguel de Padron, C. Habana 11000, Cuba, nini@lacemi.cu
²Centro de Estudio de Tecnologias Avanzadas. Calle 22 entre 1-ra y Mar, Playa, C. Habana, Cuba, ceta@ceniai.inf.cu
³Empresa Geominera de Oriente. Carretera de Siboney Km 21/2 Alturas de San Juan, Santiaga de Cuba 90800, Cuba

Ophiolite leucocratic rocks called oceanic plagiogranites (Coleman and Donato, 1979) occur in different regions of Cuba: from Habana (west) to Moa-Baracoa region (east).

These rocks range from diorite (SiO2: 59%) to albite and plagiogranite (SiO2: from 60 to 72%). They are found mainly in the upper parts gabbros and sheeted complexes of ophiolites, and rarely they intrude the serpentinized peridotites or form tectonic blocks within the latter. The rocks are characterized by low K2O (< 1%), total iron (< 3%) and high Na2O (> 4%) contents.

Plots of K2O - SiO2, modal Q - A - P and normative An - Ab - Or diagrams show the similarity of Cuban rocks to plagiogranites of well known supra-subduction zone (SSZ) ophiolites from Semail (Oman) and Troodos (Cyprus). On AFM diagram they fall, as the most of Semail and Troodos plagiogranites, within CA f~eld, untypical of MORB-type magma.

The Cuban rocks display LREE enriched patterns, untypical of MORB-type magma, with flat HREE patterns similar to those of oceanic plagiogranites (Coleman and Donato, 1979). Their geochemical feature consists of selective enrichment in Sr, K, Rb, Ba, Th, Ce and Sm relative to Nb, Hf, Zr, Ti, Y and Yb, which is considered as a distinctive feature for many of SSZ-type ophiolites (Pearce et al., 1984).

Their similarity to Semail and Troodos plagiogranites, as well as their geochemical feature, suggest that the Cuban oceanic plagiogranite formed in supra-subduction zone.

INDICATION OF UHP METAMORPHISM IN GARNET PERIDOTITE, CUABA UNIT, RIO SAN JUAN COMPLEX, DOMINICAN REPUBLIC
Grenville DRAPER¹, Richard N. ABBOTT. Jr.², Shantanu KESHAV^1
1Department of Geology, Florida International University, Miami, FL 33199, U.S.A.
²Department of Geology, Appalachian State University, Boone, NC 28608, U.S.A.

Spinel-bearing garnet peridotite (olivine + diopside + enstatite + garnet + spinel late magnesiohornblende + late serpentine) is associated with hornblende gneiss and schist (hornblende + plagioclase + quartz + rutile +/- garnet +/- biotite +/- epidote) and retrograded eclogite (hornblende + symplectic diopside-plagioclase + garnet + quartz +/epidote) in the Cuaba amphibolite unit of the Cretaceous Rio San Juan complex. The occurrence is unusual because the garnet peridotite was educted at an ocean-ocean convergent plate boundary.

Four attributes suggest low-P/T (UHT) conditions: (1) Sequence of mineral assemblages, (2) nature of associated rocks, (3) Cr-in-clinopyroxene, Mg2Si206-inclinopyroxene thermobarometry (>1.8 Gpa, >900 °C), and (4) tectonic setting. However, the thermobarometry is questionable because of low Cr in clinopyroxene. On the other hand, CFMAS equilibria involving components in olivine, garnet, clinopyroxene, and spinel suggest pressures from 2.5 Gpa (600 °C) to 3.7 Gpa (800 °C), depending on the activity models used for the mineral components. These high-P/T (UHP3 conditions are at odds with other indications (1, 2, 4, above) for low-P/T conditions. The contradiction highlights the unusual character of the rocks, but may be consistent with eduction at an ocean-ocean convergent plate boundary.

Elsewhere, Alpine-type garnet peridotite is associated with deep subducted continental rock. Presumably, eduction was driven by the buoyancy of the continental material. This is not possible in the present example. We therefore offer a model in which eduction is driven by upwelling asthenosphere. The process may be a natural consequence of isostatic disequilibrium accompanying subduction of an ocean ridge or mantle plume.

THE SERPENTINITE MELANGES OF THE RIO SAN JUAN COMPLEX, DOMINICAN REPUBLIC AND THE DYNAMICS OF SUBDUCTION ZONES
W.V. Maresch¹, T.V. Geryal², M. Krebst, H-P. Schertl, G. Draper^3
1Institutfur Geologie, Mineralogie und Geophysik, Ruhr-Universitat Bochum, D-44786 Bochum, Germany
²Institute of Experimental Mineralogy RAS, Chernogolovia Moscow district, 142432, Russia
³Dept of Geology, Florida Int'l University, University Park Miami FL 33199, USA

Serpentinite melanges associated with Cretaceous subduction at the leading edge of the eastward-drifting Caribbean plate now decorate the trace of the Caribbean/ NorthAmerican suture zone exposed in Cuba and Hispaniola. The diapir-like occurrences found in the Rio San Juan Complex of the northern Dominican Republic very likely represent deeper levels of the "serpentinite-mud" volcanoes and seamounts now observed on the sea floor in the trenches of several present-day subduction zones. The blocks of metamorphic rocks entrained in the Rio San Juan melanges exhibit distinctive arrays of interrelated P-T-t-paths that yield information on the dynamics of mass flow in oceanic subduction zones. Maximum pressures of 8-25 kbar and peak temperatures of 350-800°C are indicated.

Two-dimensional numerical experiments have been carried out to simulate the circulation of rocks in subduction-zone complexes in general and to simulate the distinctive P-T-patterns found in the Rio San Juan melanges in particular. The shapes of the derived P-T-paths at a given subduction rate are greatly dependent on the actual shape of the wedge in which massflow takes place. The distinctive array of PT-paths for the northern Caribbean melanges can only be explained when blocks circulate in a funnel-shaped setting that is narrow at depth and widens abruptly towards the surface. Such widening can be related to hydration and weakening of the lithospheric mantle such that the hanging wall becomes involved in mass circulation of the subduction channel. Complex patterns of PTtrajectories are possible. No single PT-trajectory by itsej will suffce to characterize the particular dynamics of such a collision zone.

TUESDAY 18th
The business meeting in Barbados was scheduled as the Annual Meeting for this year 2002. During the meeting three major issues were evaluated.
The first subject was the need to start working on the preparation of the final memoir of the Project. In this regards, potential contributors are requested to start thinking about their papers in three lines:

1. Historical evaluation of Plate Tectonics in the Caribbean,
   
2. Caribbean Plate Tectonic Models,
   
3. Papers contributing with hard data bearing on the understandiong of the Caribbean geological evolution.

1. AUSTIN, TEXAS, USA. September 20, 2002.
   IGCP P433: Contributions of the University of Texas to the understanding of the Caribbean Plate Tectonics. IGCP Project 433 Scientific Meeting at Institute for Geophysics, University of Texas at Austin. Lisa Gahagan (lisa@ig.utexas.edu) will be coordinating this meeting of the project. For more information visit www.ig.utexas.edu/CaribPlate/CaribPlate.html.

2. CARACAS, VENEZUELA. November 15-17.
   IGCP P433: The Caribbean-South American Plate Tectonic Interactions. Annual Meeting of the Geological Society of Venezuela. Workshop of IGCP Project 433. Dr. Jose A. Martínez (martinezja@pdvsa.com) will be coordinating this meeting of the project.

3. PORT-AU-PRINCE, HAITI. January 10-19, 2003.
   IGCP P433: Field workshop to the Caribbean oceanic crust exposure in Haiti. Drs. M. Iturralde-Vinent (iturralde@mnhnc.inf.cu) and Edward Lidiak (egl+@pitt.edu) will be coordinating this meeting of the project.

4. LA HABANA, CUBA. March 24-28 , 2003.
   IGCP P433: A single vs multiple arc interpretation of the Caribbean. Field trip to th e Ophiolites and Cretaceous and Paleogene arc terranes in eastern Cuba. Field workshop of IGCP Project 433. Dr. M. Iturralde-Vinent (iturralde@mnhnc.inf.cu) will be coordinating this meeting of the project. For more information visit www.scg.cu.

5. MAYAGUEZ, P. Rico. April 29-May 3, 2003.
   IGCP P433: Caribbean Seismology and Plate Tectonics. IGCP Project 433 Field workshop as part of the 98th Annual Meeting of the Seismological Society of America. Dr. Hans Schellekens (j_schellekens@rumac.upr.clu.edu) will be coordinating this meeting of the project.

6. FREIBERG, DE. May , 2003.
   IGCP P433: Contribution of Petrology and Geochronology to the Plate Tectonic Interpretation of the Caribbean. IGCP Scientific meeting. Dr. Klaus P. Stanek (stanek@geo.tu-freiberg.de) will be coordinating this meeting of the project. For more information about the Colloquium visit www.geo.tu-freiberg.de/dynamo/lak2003.