Scientific Meeting Report of the Field Workshop in Cuba, March 2003 During the period March 18-28, 2003, a field workshop of the IGCP Project 433 "Caribbean Plate Tectonics" was celebrated in Cuba, as part of the V Geological and Mining Congress of the Cuban Geological Society. The Field Workshop was attended by project members from Costa Rica (2), Cuba (6), Germany (2), Italy (1), Jamaica (1), Mexico (1), Spain (1), USA (2), and New Zealand (1). Additionally, non-members of the project, around 15 persons (from Cuba and USA), actively participated in the debates during the scientific meeting. The field workshop was subdivided into a field trip (March 18-23), a scientific meeting (March 27, with posters, oral presentations, and a round table), and the Project’s Bussiness Meeting. In the following paragraphs the most important moments of the field workshop are briefly explained. SCIENTIFIC MEETING
PROJECT’S BUSINESS MEETING Forthcoming meetings for 2003 and 2004. It was announced that the field meeting planned for Venezuela (2002) and Haiti (2003) were cancelled. The next meetings in the present year will be in Germany (Latinamerican Geological Colloqium, Freiberg, April 2-5), in Spain (Meeting of the Iberoamerican group for Petrology and Geochronology, Granada, October 2003) and for 2004 will celebrate a field meeting in Costa Rica and the final meeting in Italy (Florence). The IGCP 433 Final Volume. It was also announced that some autghors are already working in the preparation of chapters for the final volume of the project, to be compiled during 2004. More information on this issue will be available soon.
FIELD TRIP TO EASTERN CUBA
In order to explain the origin of the Caribbean area, two major conceptions are in dispute regarding the evolution of the volcanic activity. One is the concept of a single "Great Arc" evolving at the leading edge of the Caribbean Plate from Lower Cretaceous to the Present. An alternative conception is the Multiple Arc hypothesis, which sustain that during the evolution of the Caribbean realm several independent volcanic arcs have been active. The multiple arcs being identified taking into account several criteria, as: 1. Change in the trend of the axial part (volcano-plutonic core) of one arc with respect to the other; 2. Major unconformities, magmatic quiescence, and tectonic events separating one arc from the other; 3. A particular geochemistry of each arc’s igneous suite; and 4. Simultaneous evolution of two or more independent arcs in distinct geographic areas. During the field trip exposures were visited in support of the Multiple Arc hypothesis. The region of Eastern Cuba, eastward of the Cauto-Nipe Fault Zone, is very distinct with repect to other areas of the island. It is the only place of Cuba where the Bahamian (North American) borderland suite occur as metamorphic rocks (Asunción massive); and the only one where Cretaceous volcanic arc rocks are partially metamorphosed up to HP/LT (Purial massive). Is one of the few places where Cretaceous amphibolites occur as representatives of oceanic crustal elements (Guira de Jauco and Sierra del Convento amphibolites). Specially, is the only place of Cuba where ophiolites bodies (the so called Mayarí-Moa-Baracoa allochthon) are almost horizontally lying, and furthermore, where there is evidence to show that the emplacement of this body took place in the Maastrichtian due to a gravitational mechanism. Is the only place in Cuba where the Paleocene-Eocene volcanic arc rocks occur slightly deformed in two main environments, a back arc basin (North of Sierra Maestra-Cayman rise) and an axial arc system (Sierra Maestra-Cayman ridge). During this field trip will not be visited the Asunción, Güira de Jauco and Sierra de Convento, but all the other elements will be evaluated from the scope of its tectonic position and relationship with the evolution of the Caribbean plate.
THE EASTERN CUBA MICROPLATE
Probably the lowest structural elements in the tectonic pile of Eastern Cuba are the Late Jurassic-Lower Cretaceous low degree HP/LT metasedimentary rocks (marbles and shales) of the Asunción massive. Tectonically emplaced above this unit are found the Güira de Jauco amphibolites, represented by deformed serpentinites and coarse to fine grained layered or massive amphibolites of low degree HP/LT metamorphism. The Purial massive is represented by Cretaceous metavolcanic rocks, including volcano-sedimentary, sedimentary and igneous protoliths. The sections located southwestward yield a higher degree of HP/LT metamorphism (blueshists), while those to the North varies from green shists to a very low regional metamorphism. The relationships of the Purial metavolcanics are complex, as these rocks are found tectonically overlying the Güira de Jauco amphibolites, overlying or intermingled with non-metamorphosed Cretaceous volcanic rocks; and also overlaid by the Sierra de Convento amphibolites and the Mayarí-Moa-Baracoa allochthon. Sedimentary rocks of Lower to Middle Eocene overlie the Purial massive. Above the area of the Purial metavolcanics are reported blocks of Maastrichtian limestones of the Cañas Formation, which may be not in situ. The Maastrichtian La Picota olistostrome and the Lower-Middle Eocene San Ignacio slope breccia with fragments of Purial’s marbles and shists do occur above the Purial rocks. This relationships suggest that the metamorphism is pre-Maastrichtian, and that by Lower Eocene Purial was already uplifted. The origin of the Purial metamorphic massive is a real puzzle, because there is not any reasonable explanation for the HP/LT, maybe the emplacement of the ophiolites can be the cause, but such an idea is contradictory with present understanding of the origin of blue shist.
The Sierra del Convento massive is represented by deformed serpentinites with a variety of HP/LT metamorphic inclusions. This tectonic unit, yet to be properly characterized, may be an important element to understand the process of tectonic emplacement and metamorphism of the metamorphic terranes and the ophiolites. The Mayarí-Moa-Baracoa allochthon have been described in several papers. Its uniqueness with respect to other such bodies in Cuba, is its nearly horizontal position and the fact that it is intermingled with the Maastrichtian La Picota olistostrome and with the Maastrichtian-early Danian Mícara greywakes. Another exclusivity of the Mayarí-Moa-Baracoa allochthon is that is overlying Cretaceous volcano-sedimentary rocks (Santo Domingo Formation), while the allochthonous ophiolites west of the Cauto-Nipe Fault Zone usually rest above parts of the Bahamian continental margin units. The implication is that the mechanism of emplacement of this allochthon is probably different from those of the Northern ophiolites in central Cuba. Furthermore, as central Cuba was strongly deformed by the Paleocene-Eocene tectonic events, probably the Mayari-Moa-Baracoa allochthon is a clue to understand the history of collision in central Cuba.
The fact is that in west-central Cuba there are olistostromic deposits in the latest Campanian-Maastrihctian rocks (Jibacoa olistostrome in Havana-Matanzas), suggesting the occurrence of some --and yet poorly understood-- early thrust event within the Cretaceous volcanic arc-northern ophiolites, at the end of the Cretaceous, as in eastern Cuba. Every data from central and western Cuba suggest that just south of the Bahamian borderland there was an oceanic crustal basin that was the first element detached from the Caribbean crust (Northern ophiolites) and emplaced above the Bahamian borderland, and only later, segments of the Cretaceous volcanic arc suites. In Eastern Cuba seems to be that the first element detached from the Caribbean crust and emplaced above the Bahamian borderland was also a slice of ocean crust (Güira de Jauco amphibolites). Above that one took place the emplacement of volcano-sedimentary rocks (Santo Domingo Formation and Purial massive), and just at the end of the accresionary process, a slice of ophiolites (Mayarí-Moa-Baracoa). Evidently the case for Eastern Cuba is different from that of central Cuba so the whole process needs to be more fully investigated.
SAGUA DE TÁNAMO BASIN.
Three main sources of clastic material are recognized for the Sagua de Tánamo basin. One source was probably the uplifted Cretaceous volcanic arc suites, which provided detritus composed of fragments of tuffs, tuffites, and basic to acid types of Cretaceous igneous rocks. This source may have been located South of the sedimentary pile. The second source were the ophiolites, probably located south of the sedimentary basin. These two sources are present, in different amounts, in the Latest Cretaceous to Lower Eocene formations (Mícara, La Picota, Gran Tierra, and Sabaneta). The third source were contemporaneous explosive subaereal volcanoes, generally located to the South, which is represented by volcanic ash and volcanogenic rocks and minerals. This source first occur as fine layers in the lower Danian (upper Mícara Fm.), later as some isolated beds in the middle-late Danian (Gran Tierra Formation), and became dominant since late Danian and until the end of the Lower Eocene (Sabaneta Formation). From South to North the pyroclastic material becomes of thinner grain and less abundant with respect to the sedimentary component of the rock sections. After the demise of the volcanic activity, carbonate rocks deposited all over the basin in distinct shallow to deep marine environments. Above the carbonate level occur conglomerates and clastic rocks in general, derived from the exhumation of the Paleogene volcanic arc in the south (Camarones conglomerate and San Luis Formation).
The present-day relationships of the latest Cretaceous-Middle Eocene litostratigraphic units are illustrated in the following drawing (Figure 3). It provides a mechanism as how the Mayarí-Moa-Baracoa allochton (ophiolites and Cretaceous volcanic arc rocks) was emplaced during the Maastrichtian as a gravitational body (Cobiella, 1976). This conclusion is based in the following observations: 1. Sedimentation in the Sagua de Tánamo basin was continuous since Latest Cretaceous till Latest Eocene-Oligocene, 2. During the Maastrichtian there was a large input of detritus (both in amount and size) of ophiolite composition, along with syn-sedimentary deformations, 3. The Paleocene and younger rocks in the basin are slightly deformed and deposited directly above allochthonous deformed bodies of ophiolites and Cretaceous arc rocks (both metamorphosed and non-metamorphosed), but also without interruption above some non-deformed Latest Cretaceous sedimentary sections. These facts strongly suggest that after Maastrichtian there were not more strong tectonic deformations in Easternmost Cuba until the Oligocene.
THE PALEOGENE ARC
SIERRA MAESTRA.
ABSTRACTS OF PRESENTATIONS
MAPAS GENERALIZADOS DE LAS ANOMALÍAS GRAVIMÉTRICAS DEL CARIBE OCCIDENTAL Y AMÉRICA
CENTRAL PDF of paper This result is the amplification of the methodological generalization of the calculation of the gravity Bouguer anomalies map in the area western Caribbean, where they are most of the islands belonging to the Greater Antilles, including central America, and the part northern Westerner of America of the South, what will allow in the frame the Project "Contribution to the Model of Geological Evolution of the Western Caribbean according to Geophysical Data", to carry out geological and geophysical interpretations with new information. PALEOMAGNETISMO DE FORMACIONES DEL CRETÁCICO SUPERIOR Y EL TERCIARIO INFERIOR EN LAS
GRANDES ANTILLAS. PDF of paper The goals of this investigation were: There were also obtained the RCM and their for ten geological formations, being established their probable primary origin. The rotations and latitudinal displacements underground by the different blocks under study were calculated, which allowed to impose quantitative restrictions to the numerous models of tectonic evolution developed by different authors. Finally the relative positions of the three islands respect to the North American Craton for the Upper Jurassic-Lower Cretaceous? times to Eocene times are shown.
ESTRUCTURA DEL ÁREA DE MERCEDITAS Y CONSIDERACIONES ACERCA DE LA PROCEDENCIA DE LAS OFIOLITAS DEL MACIZO MOA-BARACOA PDF of paper At the first stage it is associated a distension, that faulting the rocks and dike systems appear. At the second stage it is associated generally brittle deformation, overthrust faults, inverse shear zones and dike deformation. To the third stage are associated generaly brittle deformations with predominance of horizontal movements and some distension faults filled with carbonates and reverse faults. The lineation structures on the overthrust faults planes, as well as reverse shear zone, which occurr in the second deformation stage, clearly indicate the sense of tectonic transport (vergence) towards the NNE, it can be interpreted as the Moa Baracoa ophiollite were emplaced over the cretaceous metavolcanic complex from the south.
METABASITES FROM THE NORTHERN SERPENTINITE BELT (CUBA) AND A METAMORPHIC PERSPECTIVE
OF THE PLATE TECTONIC MODELS FOR THE CARIBBEAN REGION PDF of paper
NICOYA COMPLEX SENSU STRICTU, CRETACEOUS STRATIGRAPHY AND TERRANES OF THE NICOYA
PENINSULA, COSTA RICA The Nicoya Complex s.st. was originally defined at the NW of Nicoya Peninsula. The Ar/Ar-dates and bio-stratigraphic data do not confirm either one of the current hypotheses, in which an oceanic basement and its Jurassic-Cretacecous sediment cover is overlaid by Upper Cretaceous plateau basalts. The Nicoya Complex s. str. is a fragment of the Late Cretaceous Caribbean Plateau created by uplift and southward tilting during an early Campanian collisional event. The deepest levels of the Plateau are exposed in NW-Nicoya, where over 50 % of the igneous rocks are intrusives (gabbros and plagiogranites). Ar/Ar-dates of igneous rocks (83-92 Ma) are consistently younger than most of the radiolarian cherts (Early Jurassic-Late Cretaceous). No Jurassic oceanic basement has been identified. Therefore, the Jurassic-Cretaceous rediolarites became disrupted and detached from its original basement by multiple intrusions during the formation of the Caribbean Plateau (Baumgartner and Denyer, in prep). The origin of the Cretaceous series of the Nicoya Peninsula has been described in different ways and by many authors. However, only Di Marco and others (1995), based on paleomagnetism and stratigraphy, proposed the existence of two teranes. The Nicoya terrane comprises the Santa Elena Peninsula and the outer Nicoya Peninsula, constituted by mafic and ultramafic oceanic basement and associated deep water sediments. The Chorotega Terrane constitutes most of the southern Middle American land bridge and probablyformed the western edge of the Caribbean Plate during Late Cretaceous. Using the stratigraphic criteria, we have recognized two different terranes, subdividing the Chorotega terrane proposed by Di Marco and others (1984). The Chorotega terrane sensu stricto is constituted by oceanic basalts and bitouminous shales interbedded with siliceous and tuff sediments (Albian-Santonian). We propose a new terrane constituted by basalts and breccias overlaid by pre-Campanian (probably Santonian) green siliceous volcaniclastic shales, green very fine grain ignimbrites and occasionally bitouminous sediments. Microscopically these rocks show hornblende, piroxene, plagioclases, shards and collapsed pumice. The pelagic-hemipelagic Sabana Grande Formation (Late Santonian-Early Campanian) is overlapping both terranes. * Baumgartner, P. O and Denyer, P., (in prep.), The Nicoya Complex s. str. (Middle
Jurassic-Late Cretaceous) Age and origin of basalts, intrusives and associated
radiolarites, Nicoya Peninsula (Costa Rica) HISTORY OF TECTONIC INTERACTIONS BETWEEN THE CUBAN FOREARC TERRANE AND MEXICO -
CENTRAL AMERICA. North-vergent, Paleogene collision between the Cuban "arc" terrane with the passive Bahamas carbonate bank of the Proto-Caribbean Seaway is widely accepted among workers. In contrast to the "passiveness" of the Atlantic-type Proto-Caribbean margins, the Cuban arc terrane holds a wealth of information that tells of a complex tectonic, metamorphic and magmatic history that dates back to the Jurassic. Despite the fact that Cuba has been geographically isolated from the Caribbean Plate since the Eocene by the Yucatán Basin and Cayman Ridge, the geology of the Cuban arc terrane is so similar to that of numerous Caribbean terranes that it was clearly part of the Caribbean Plate prior to the Paleogene. And because the Caribbean Plate is of Pacific origin, then parts of the Cuban arc terrane may also be of Pacific origin, or perhaps the Neocomian inter-American arc that spanned the gap from Chortis to Ecuador. Accepting that a Pacific/inter-American arc origin is viable, the geology of Cuba may be interpreted as part of the far-travelled Caribbean Plate, rather than in terms of more local modes of evolution. Thus, regional integrated models of Gulf of Mexico/Caribbean evolution potentially provide a geometric and kinematic framework in which to interpret that history. Further, considering Cuba's position at the northwesternmost part of the Caribbean Plate, then Caribbean-Mexico/Central American plate interactions are likely recorded in the geology of Cuba. Using the Caribbean evolutionary model of Pindell and Kennan (2001) as a guide, cause-and-effect geological relationships between the Cuban arc terrane and Mexico-Central America are proposed. It is argued that the Cuban arc terrane derives from the inter-American Arc between Chortis (when Chortis lay adjacent to Guerrero, Mexico) and Ecuador, was involved in the Aptian Caribbean arc-polarity reversal during which west-dipping subduction beneath Caribbean Plate began, underwent arc-parallel extension during middle and Late Cretaceous time, converged obliquely with southern Yucatán in the Maastrichtian, and migrated ahead of the Yucatán intra-arc basin during the Paleogene on its way to collision with the Bahamas. Finally, it is proposed that the Cuban "arc" terrane represents a forearc piece of the Great Caribbean Arc only, and should not be considered as an arc in itself.
AGE SYSTEMATICS OF HIGH-PRESSURE METAMORPHISM IN THE CARIBBEAN: CONFRONTING EXISTING
MODELS WITH NEW DATA The development of plate-tectonic models in the Caribbean has been traditionally based mainly on a two-dimensional perspective centred on terrane analyses and studies of relative movements between terranes and plates, augmented by geochemical and geochronological data on volcanic activity. However, the importance of the information recorded in the pressure(depth)-temperature-deformation-time development of crystalline rocks has recently become more widely acknowledged. Such data require a modern and diverse, yet highly correlated multidisciplinary methodology. As more, and more detailed P-T-d-t-paths become available around the Caribbean, a systematic picture is beginning to emerge. The extent of this new level of perception is due to the increasing quantity and above all better quality of geochronological control on the pressure-temperature evolution of metamorphic rocks. Although early petrological studies were able to relate the high-pressure metamorphic rocks exposed along the northern and southern borders of the Caribbean to collisional geodynamic environments, it was detailed geochronological work that showed that the subduction environments responsible for the formation of these rocks were actually located far to the west of a nascent Caribbean gap. The available data set - both old and new - is consistent with the fact that peak high-pressure conditions of high-pressure suites around the Caribbean were uniformly reached between 120 to 100 Ma, i.e. before diachronous emplacement along the northern and southern margins commenced. By contrast, new data on the cooling, i.e. exhumation history of high-pressure suites as well as metamorphic rocks from the lower levels of associated volcanic arcs show that specific sections around the margins of the Caribbean exhibit characteristic and variable exhumation histories. Such data therefore faithfully record the particular timing and geodynamic setting of each area around the Caribbean perimeter and provide local stringent detailed constraints on plate tectonic models. Although we are just beginning to "see through" the chronology of high-pressure metamorphic events and exhumation evolution to determine details on the timing of prior events, new data are providing enigmatic and intriguing prospects. Conventional multi-grain analysis as well as corroborating detailed SHRIMP investigations have revealed that zircons in certain eclogites from the Escambray massif in Cuba point to a 140-160 Ma event. Even if discussions on the significance of this age are in full progress (crystallization of the precursor gabbro? a second earlier, pre-Caribbean high-pressure event?), it is clear that studies of P-T-d-t histories are indispensable in our quest to better understand the plate-tectonic history of the Caribbean region. EVIDENCIAS MINERALÓGICAS DE MAGMATISMO ALCALINO EN LOS NIVELES MANTÉLICOS DE LA FAJA
OFIOLÍTICA MAYARÍ-BARACOA (CUBA ORIENTAL) Los niveles mantélicos de la Faja Ofiolítica Mayarí-Baracoa (FOMB) encajan abundantes depósitos de cromita, los cuales han sido formados en un manto litosférico suboceánico en una zona de suprasubducción. Entre estos depósitos destaca el yacimiento Potosí, en el cual se pueden reconocer dos eventos de intrusiones magmáticas que cortan y/o "impregnan" los cuerpos de cromititas. El primer evento ha dado lugar a la cristalización de noritas olivínicas pegmatíticas, las cuales han reaccionado con las cromititas preexistentes. La zona de contacto entre las cromititas y las noritas olivínicas se caracteriza por presentar una atípica asociación mineral formada por cromita (#Cr = 0.51-0.64, #Fe3+ = 0.14-0.29), ilmenita (con alta proporción de componente geikielita, hasta 12.7 % en peso de MgO), rutilo, magnetita, sulfuros de Fe-Ni-Cu, ortopiroxeno (En83-86Wo1.4-4.9Fs12-15; TiO2 =0.42-0.58 % en peso), plagioclasa alterada, olivino (Fo = 86-87), kaersutita (#Mg = 82-87; TiO2 = 4.42-5.78 % en peso; Cr2O3 = 1.28-1.71 % en peso) apatito (Cl/F = 0.33-0.48), baddeleyita (HfO2 = 1.5-2.0 % en peso) y zirconolita (CaZrTi2O7). La zirconolita es un óxido raro de Ca-Zr-Ti, que ha sido descrito mayoritariamente en relación con magmatismo alcalino. La zirconolita de Potosí representa la primera descripción de zirconolita en niveles mantélicos ofiolíticos. En el diagrama triangular Zr-Ti-Ca, la zirconolita presente en las cromititas de Potosí se localiza en la parte correspondiente a bajos contenidos de Ca y altos de Zr. La zirconolita de Potosí presenta los contenidos más altos de Y descritos en zirconolitas terrestres (Y2O3 = 10.13-11.06 % en peso). Los contenidos de REE2O3 varían entre 9.25 y 10.7 % en peso, y los de HfO2 alcanzan valores de hasta de un 1 % en peso. La "exótica" asociación mineralógica presente en las cromititas de Potosí es el resultado de la intrusión de un fundido silicatado alcalino (rico en volátiles, Ti, Zr, Y, REE) que reacciona con las cromititas provocando la disolución parcial y la recristalización de la cromita. Los altos contenidos en volátiles quedan reflejados en la cristalización de apatito rico en F y Cl, y la alta actividad de Ti en el fundido queda registrada en los altos contenidos de TiO2 presentes en la kaersutita (4.42-5.78 % en peso) y en los ortopiroxenos (0.42-0.58 % en peso). Los fundidos a partir del cual cristalizaron las noritas olvínicas y que reaccionaron con las cromititas de Potosí eran ricos en Na+K (ej: kaersutitas con valores de Na2O+K2O > 3.5 % en peso), favoreciendo el transporte de Zr. Trabajos experimentales sugieren que la solubilidad del Zr se incrementa hasta 4 % en peso en fundidos con alta relación álcali/alúmina. La presencia de fundidos alcalinos en los niveles mantélicos de la FOMB puede estar relacionada con la evolución de una cuenca trasera de arco. En un ambiente de este tipo la adición de sectores mantélicos "fértiles" a la cuña de suprasubducción, favorecida por subduction roll-back, provoca características geoquímicas muy heterogéneas (desde típicas signaturas tholeiíticas hasta alcalinas). LA FAJA OFIOLÍTICA MAYARÍ-BARACOA (CUBA ORIENTAL): UN NUEVO RECONOCIMIENTO
PETROLÓGICO Y ESTRUCTURAL La Faja Ofiolítica Mayarí-Baracoa (FOMB), de edad Jurásico-Cretácico, se puede dividir en 2 macizos: Mayarí-Cristal (parte occidental) y Moa-Baracoa (parte oriental). En este trabajo presentamos nuevos datos petrológicos y estructurales de la parte más occidental del Macizo de Mayarí-Cristal (zona de Mayarí) y de la zona de transición manto-corteza del macizo de Moa-Baracoa. El Macizo de Mayarí-Cristal, en la zona de Mayarí, está constituido mayoritariamente por peridotitas mantélicas con un espesor no inferior a los 5 km, diferenciándose dos dominios principales: 1) Un dominio inferior que ocupa la parte S y central del macizo. Este dominio esta formado principalmente por harzburgitas porfiroclásticas, mostrando una foliación penetrativa de dirección NE-SW con buzamiento de 50-60º NW. También es frecuente la presencia de harzburgitas con parches centimétricos de dunita. Además, se reconocen capas (normalmente < 1m de espesor) subcordantentes e irregulares de dunitas (N75º 70ºNW), así como cuerpos concordantes de cromititas con una envolvente dunítica variable. Todas estas litologías están cortadas por, al menos, tres generaciones de diques de piroxenitas de espesores centimétricos. 2) Un dominio superior que aparece bien expuesto en la parte norte del macizo (cuya área tipo se encuentra en la Loma de la Bandera). Este dominio está constituido por harzburgitas porfiroclásticas (localmente muy ricas en piroxenos) que muestran una foliación de dirección NE-SW, con buzamiento de ~ 55ºNW. Las harzburgitas están cortadas por diques máficos que muestran una marcada zonación textural desde los bordes (diabasa) al centro (microgabro). Estos diques presentan un espesor variable, desde pocos centímetros hasta espesores superiores a los 10 m, y cortan a la foliación de las peridotitas con ángulos variables entre ~ 10º y ~ 60º. El macizo de Moa-Baracoa se caracteriza por presentar: niveles mantélicos, niveles de gabros bandeados inferiores y niveles volcánicos discordantes. Sin embargo, los niveles de gabros isotrópicos superiores y de diques de diabasas de una secuencia ofiolítica clásica, no afloran. La secuencia mantélica tiene un espesor de "paleomanto" superior a 2.2 km y los niveles de gabros bandeados de ~ 300 m. La unidad mantélica expuesta del macizo Moa-Baracoa está compuesta por una zona de transición manto-corteza inusual, constituida predominantemente por harzburgitas, mostrando una foliación predominante de dirección NE-SW. En esta unidad existen varios niveles de impregnación magmática representados por peridotitas residuales impregnadas con plagioclasa y, en menor medida con clinopiroxeno, que llegan a formar zonas de lherzolitas con plagioclasa y de troctolitas, encajadas en harzburgitas. Además, es frecuente la presencia de cuerpos concordantes de dunitas, de gabros (sills) de cromititas con una envolvente dunítica. Los cuerpos de dunitas, normalmente de pequeño espesor, se restringen principalmente a la cercanía de los cuerpos de cromititas. También están presente numerosos diques de gabros y de gabros pegmatitas, y en menor medida de diabasas. Asimismo hemos observado algunos diques de noritas olivínicas y de piroxenitas. Los niveles basales de gabros bandeados se componen de gabros olivínicos y gabronoritas, y presentan un bandeado modal bien desarrollado de orientación N 30ºE, buzando ~30º al NW.
SUPRASUBDUCTION VERSUS POLARITY REVERSAL - A CASE STUDY FROM ORIENTE, EASTERN
CUBA In the light of new tectonic and geochronological data from Central Cuba the structure of easternmost Cuba will be discussed. The mostly accepted model for the origin of the Caribbean plate proceeds from a Protopacific oceanic plate indenting the rifted space between North and South America in the Late Jurassic / Early Cretaceous. At this time a primitive island arc has been developed along the evolving subduction zone. Subduction of the young hot Protocaribbean oceanic crust below the indenting Pacific plate led to a strong mechanical coupling between downgoing and overriding crustal slabs resulting in a tectonic offscraping (erosion) of large parts of the fore arc region. Beginning in the Upper Cretaceous the evolving Greater Antillean island arc collided with the southern margin of the Yucatan and Florida Straits blocks. The suture zone between the Great Antillean arc and the Bahamas platform at the Cuban island can be subdivided into three structural domains, a pop up structure of continental margin sediments in western Cuba and the Cretaceous island arc thrusted onto the Bahamas margin in Central Cuba. Eastern Cuba consists of three main structural domains, in the south the Paleogene island arc (Sierra Maestra), the Paleogene Guatanamo basin and the Oriente complex. The Oriente complex represents an assemblage of metasedimentary, metavolcanic and serpentinic nappes. The metavolcanic rocks contain Hp-minerals like lawsonite and glaukophan. The uppermost nappe comprise the largest ophiolite massifs in the northern Caribbean. The strongly reduced ophiolitic section is restricted to ultramafic and rare diabasic to gabbroic rocks, the upper section of the ophiolite sequence is mostly absent. The age of trusting can be estimated by stratigrafic data between uppermost Cretaceous und Paleogene. The thrusting of the ophiolite massifs has been accompanied and followed by the development of the short lived Paleogene island arc of the Sierra Maestra, resting on a basement of Cretaceous volcano-sedimentary sequences. Due to the association of metamorphic nappes, igneous rocks and synorogenic sediments Eastern Cuba looks like a key area for understanding of collision tectonics in the Northern Caribbean. Questions under discussion are the origin of the Oriente ophiolite (suprasubduction related basement of the Cretaceous arc or back arc-opening in the Paleogene); the polarity of the Paleogene arc (shifting of the Cretaceous magmatic front or polarity reversal of the subduction zone); age of HP-metamorphism in the Cretaceous island arc and what represents the Yucatan basin (new oceanic crust originated by fore-arc extension or trapped Pacific oceanic crust. THE PUZZLE OF LOMA CARIBE CHROMITITES (HISPANIOLA)
J.F. Lewis1, J.A. Proenza2, J.C. Melgarejo2, F. Gervilla3 The Loma Caribe peridotite (mantle peridotites and associated chromitites) is exposed in
the Cordillera Central, Dominican Republic. The peridotite body is about 4-5 km wide and
extends for 95 km from La Vega to Cerro Prieta north of Santo Domingo, but the southeastern
part of the peridotite is exposed as thin fault slices only. These mantle rocks are
considered to have been exposed because of the collision of an oceanic plateau (Duarte
plateau terrane) with the primitive Caribbean island-arc (Maimon-Amina terrane) at Aptian
time. The Loma Caribe peridotite is composed of lherzolite, Cpx-rich harzburgite,
harzburgite and dunite. In addition, pyroxenite and small bodies of podiform chromitites
(Loma Caribe chromitites) also occur. The peridotites typically show porphyroclastic and
coarse-grained granoblastic textures. Orthopyroxene phenocrysts are strongly deformed,
showing kink bands deformation, suggesting that the peridotites could represent remnants of
depleted upper mantle. The #Cr [(Cr/(Cr+Al)] in Cr-spinel (an indicator of melt depletion
in the peridotites) from Loma Caribe peridotites vary from (0.30 to 0.88). These large
compositional variations indicate the occurrence of peridotites with very different melting
histories. Relatively fertile peridotites as found in Loma Caribe (e.g. #Cr ~ 0.3) have not
reported in eastern Cuba ophiolites where they exhibit mostly #Cr > 0.5). The equilibration
temperature estimates (according to three thermometric formulations using pyroxenes) give
large ranges of equilibration temperatures, between 980 and 1260 oC. The upper mantle rocks
present in Loma Caribe peridotite probably include rocks from suboceanic mantle, including
mantle underneath oceanic ridge, oceanic plateau and island arc. The chromitite bodies
associated with Loma Caribe peridotites have small size, and show massive textures. No
primary silicate minerals are preserved in the matrix of the chromitite in any of the
samples studied. The intergranular minerals mainly consist of chlorite, and minor
serpentine. The Loma Caribe chromitite is Cr-rich chromite, the Cr# varies from 0.75 to
0.78 (corresponding to Cr2O3 contents between 49.42 and 51.66 wt%, and Al2O3 between 9.93
and 11.13 wt% ), the Mg# from 0.47 to 0.50. These values are typical of ophiolitic
chromitites elsewhere. However, Loma Caribe chromite exhibits systematically high TiO2
(0.79-0.93 wt%) and Fe2O3 (7.23-8.46 wt%) contents. Chromite with the chemical composition
of the Loma Caribe chromitite, to our knowledge, never has been reported in ophiolitic
chromitites. In general, the chromite from Loma Caribe chromitite differs from Cr-spinel
reported in bonitites, high-magnesian andesites, MORB, BABB and Alaskan-type plutonic
complexes (arc magma chambers or arc-root complexes). Chromite in small podiform deposits,
with relatively high #Cr (62-85) and ferric iron contents (up to 8.95 wt% of Fe2O3), have
been described in ultrabasic rocks form the Bragança massif (Portugal), and are interpreted
as having crystallized in the upper few kilometres of the magmatic arc mantle (Bridges et
al., 1995). Nevertheless, the Bragança chromitites show low TiO2 content (< 0.24 wt%). The
high TiO2 content in chromite from podiform deposits is associated with Al-rich chromite,
never with Cr-rich chromite as in the Loma Caribe chromitite. The composition of chromite
from Loma Caribe chromitite, is relatively close to that reported for Cr-spinel from
oceoanic plateau.basalts. For example, Cr-spinels from Hole 462A (Nauru Basin Oceanic 44
Fe2O3 from 6 to 9 wt% (Tokuyama and Batiza, 1981). In general, Cr-spinels in the oceanic
plateau basalts differ from MORB Cr-spinel in their higher #Cr and #Fe3+, and are slightly
higher in TiO2 content than arc magma Cr-spinel (Arai, 1992). Also, the oceanic plateau
Cr-spinels have sightly lower #Cr values than arc-magma Cr-spinel. The most recent
interpretation on the genesis of ophiolitic chromitites suggests a suprasubduction zone
setting for the precipitation of chromitite bodies. In contrast, no ophiolitic chromitite
would be expected in mature spreading centers, such as midocean ridges. The genesis of Loma
Caribe chromitite is still subject of debate. Here, tentatively, we suggest two
possibilities to explain their "exotic" composition: References: OXFORDIAN REPTILES IN THE CARIBBEAN CORRIDOR Phylogenetic affinities between the middle Jurassic marine reptiles of Europe and western South America suggest a connection through central-western Pangea. However, it is not until the Oxfordian when reptiles are first recorded in the Caribbean, and their taxonomic diversity is in agreement with a corridor related to a great oceanographicevent. So far, all the Caribbean Jurassic reptiles were found at western Cuba (Guaniguanico terrane). The bearing levels belong mostly to the Jagua Vieja Member of the Jagua Formation (middle reptiles are particularly important because of their geographic location and because of their age, since middleupper Oxfordian records are not frequent worldwide.Among the Cuban marine reptiles prevail the pelagic forms that frequently rambled in near shore environments. This was the case of long-necked plesiosaurs (Cryptoclididae: Vinialesaurus caroli), crocodiles (Metriorhynchidae: Geosausus sp.), and turtles (Pleurodira: Caribemys oxfordiensis). The relative vicinity of the shore, of the marine environments in which these reptiles are recorded, is supported also by the presence of pterosaurs (Rhamphorhynchidae: Nesodactylus and a new taxon), isolated post-cranial fragments of sauropod dinosaurs, and abundant plant remains, particularly logs. The Caribbean Corridor was also the way for other pelagic off-shore reptiles such as ophthamosarian ichthyosaurs and pliosaurs. The close taxonomic relationships between the Oxfordian reptiles -and fishes- of Cuba and western Tethys - eastern Pacific presupposes that the Caribbean Corridor played a main role in the association of the pelagic fauna from both regions. ENSAYO SOBRE LA PALEOGEOGRAFÍA DEL CUATERNARIO DE CUBA PDF of paper MESOZOIC TERRESTRIAL VOLCANISM VS. COEVAL REDBED DEPOSITION IN
THE RIM OF THE GULF OF MEXICO: WHERE IS THE BOUNDARY? Volcanic, sedimentary and granitic plutonic rocks that are part of the early Mesozoic Cordilleran continental magmatic arc are exposed in a belt from the southwestern United States to Guatemala. In north-central Mexico, these volcanic arc suites are grouped into the Nazas Formation, which record volcanic activity, crustal extension, and erosion of volcanic edifices in a subaerial volcanic arc that developed from Late Triassic to Middle Jurassic time along the México western continental margin. The Nazas arc consists of more than 3 km of volcanic flows, pyroclastic rocks and clastic sedimentary strata that were formed in extensional intra-arc basins within the upper arc structure. These sequences are characterized by drastic facies changes over short distances, highly variable thicknesses of basin-fill, mixed sediment composition, heterogeneous lithologic associations, and poorly known fluvial and alluvial facies distribution, reflect the complexity of the arc environment. The size, original orientation and geometry of individual basins within the arc are unknown in detail due to younger tectonic events and erosion. Early Mesozoic extension along the arc was contemporaneous with rifting along the western Gulf of México to the east. Rift basins along the Gulf were filled with Late Triassic and Early-Middle Jurassic redbeds, evaporite deposits and occasional intercalations of pyroclastic rocks that may have erupted from the arc and probably traveled east reaching the zone of rifting that created the Gulf of México. In this scenario, two distinct extensional provinces overlapped within the Nazas arc, one with volcanic and pyroclastic rocks dominant in the west (Nazas Formation) and redbeds (Huizachal Group) in the east and offshore in the western part of the Gulf of Mexico. The complex interaction of geologic processes related to two distinct but coeval tectonic settings (subduction beneath the arc and rifting along the Gulf of Mexico rim) rule out previously proposed simple rift system models. Whether extension along the Nazas magmatic arc is the result of westward propagation of Gulf-related rifting or extension along the Gulf of Mexico coastal region is related to back-arc extension is an issue to be resolved. The evolution of these two tectonic domains is critical in understanding the structural framework and the Late Jurassic source rock distribution of the prolific petroleum basins in Mexico. SOME REMARKS ON THE CARIBBEAN SUPRASUBDUCTION OPHIOLITES AND RELATIONSHIPS WITH THE MODE OF
SUBDUCTION Supra-Subduction Zone (SSZ) ophiolites may be classified in two main types based on their structure, tectonics and magmatic features: 1) "Tethyan complexes" (such as those of the Albanide-Hellenide belt) which mostly consist of complete and extensive volcanic, dyke, plutonic, and mantle sections with prevalent Island Arc Tholeiitic (IAT) magmatic affinity and the significant presence of Boninites, obducted as relatively intact lithospheric slabs onto collisional continental margins; 2) "Cordilleran complexes' (including the circum-Caribbean ophiolites of Guatemala, Cuba and Venezuela), mostly represented by dismembered sections of arc volcanic, plutonic and subordinate mantle sequences with tholeiitic to calc-alkaline (IAC) magmatic affinity and acidic differentiates, commonly associated with metamorphic "subduction complexes" and tectonically emplaced onto or juxtaposed against the continental margin within polygenetic terranes. These two types appear to be related to significantly different subduction modes and intra-oceanic plate dynamics whereby SSZ ophiolites were generated. The Tethyan complexes can be best accounted for by west Pacific-type subductions with accentuated steepening and retreat of the subducted slab, accompanied by progressive decoupling of the converging plates, intense mantle diapirism and tensional events in the upper plate; in fact, the presence of large sheeted dike complexes testify for continuous injection of basaltic magmas in "open" oceanic spreading systems. Continuous slab sinking and roll back allow increasing asthenospheric diapirism from the arc axis to the forearc region, which may trigger: a) shallow partial melting of the sub-arc mantle with generation of boninites and/or very low-Ti tholeiites, and b) opening of a backarc basin with transitional MORB/IAT, up to pure MORB magmatism when mantle diapirs do not interfere anymore with the subduction zone. By contrast, the genesis of the Cordilleran complexes requires a subduction mode characterized by a steady-state regime, with moderate and constant dip of the subducted slab and limited extension in the backarc region. The magmatic evolution of these ophiolites from IAT to IAC and the significant presence of rhyodacite (and tonalite) differentiates coherently indicate a more mature stage of arc magmatism, as well as the occurrence of efficient differentiation processes developing under nearly 'closed-system" conditions in independent magma chambers. During convergence processes, Tethyan complexes are in a favourable condition to be obducted as large and relatively intact slabs onto the continental margins through the interposition of metamorphic soles, which represent relics of the MORB lithosphere underplating the SSZ ophiolites since the inception of the intra-oceanic subduction. On the other hand, the common emplacement of Cordilleran complexes within polygenetic terranes appears to be controlled by prolonged accretionary mechanisms which trap, against the continental margin, parts of the arc structure, subduction complexes, melanges, and volcanoclastic products. These features represent an important constraint for the kinematics of both the northern and southern Caribbean margins, even if with significant differences in the tectonic evolution of each margin. TIMING AND TECTONIC EPISODES BASED ON A NEW LATE CRETACEOUS CARIBBEAN RUDIST
BIOSTRATIGRAPHY The integration of Late Cretaceous rudist biostratigraphic schemes with the international chronostratigraphy is essential in order to correlate shallow-water carbonate successions, radiometric dates from igneous rock units, and relate these to the tectonostratigraphic events that occurred on the northern margin of the Caribbean Plate. Jamaica is key to understanding the rudist successions because of the low degree of deformation of the late Cretaceous shallow-water sediments and the presence of inter-bedded shallow-water and deep-water successions. Using a combination of macrofossils (rare ammonites and inoceramids), planktonic foraminifera and calcareous nannofossils, the different species of the rudist Barrettia can be correlated with late Cretaceous substages. Barrettia coatesi is of mid Santonian age, B. ruseae of late Santonian age, B. multilirata of late Middle Campanian age and B. gigas of late Middle to earliest Late Campanian age. B. monilifera is more difficult to date, but is probably of Middle Campanian age. Previous dating of the Titanosarcolites assemblages has been based on the last occurrence of certain calcareous nannofossils, which are now known to be reworked. New strontium isotope dating of well-preserved skeletal calcite suggests that the Titanosarcolites limestones range throughout the Upper Maastrichtian. Different species, previously incorporated within T. giganteus, can be distinguished and allow a zonal scheme to be developed for the Upper Maastrichtian. Sections in the Central Inlier of Jamaica show a major unconformity between the Titanosarcolites limestones and the Barrettia beds, with preserved evidence of thrusting prior to the deposition of the Titanosarcolites limestones. This indicates a major tectonic event of late Late Campanian or Early Maastrichtian age. This event is linked to the collision of the Caribbean Plate with the Yucatan Peninsula. An extrapolation of this new scheme elsewhere in the northern Caribbean and Mexico will undoubtedly yield important results. PAPERS MAPAS GENERALIZADOS DE LAS ANOMALÍAS GRAVIMÉTRICAS DEL CARIBE OCCIDENTAL Y AMÉRICA
CENTRAL PALEOMAGNETISMO DE FORMACIONES DEL CRETÁCICO SUPERIOR Y EL TERCIARIO INFERIOR EN LAS
GRANDES ANTILLAS. ESTRUCTURA DEL ÁREA DE MERCEDITAS Y CONSIDERACIONES ACERCA DE LA PROCEDENCIA DE LAS OFIOLITAS DEL MACIZO MOA-BARACOA METABASITES FROM THE NORTHERN SERPENTINITE BELT (CUBA) AND A METAMORPHIC PERSPECTIVE
OF THE PLATE TECTONIC MODELS FOR THE CARIBBEAN REGION
ENSAYO SOBRE LA PALEOGEOGRAFÍA DEL CUATERNARIO DE CUBA IGCP 433 home page Last revised: April 17, 2003 |
