Medellín, Colombia29 de agosto al 2 de septiembre de 2011

XIV CONGRESO LATINOAMERICANO DE GEOLOGÍAXIII CONGRESO COLOMBIANO DE GEOLOGÍA

“LAS GEOCIENCIAS PARA EL DESARROLLO DE LATINOAMÉRICA”

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XIV Congreso Latinoamericano de Geología y XIII Congreso Colombiano de Geología

Crecimiento y modificación de la corteza en los 1. bordes de la Placa Caribe

CoordinadoresAgustín CARDONA – Smithsonian Tropical Research Institute (STRI)CardonaA@si.eduPanamáMarion WEBER – Universidad Nacional de Colombia, Sede Medellínmweber@unal.edu.coColombiaAntonio GARCÍA CASCO – Universidad de Granadaagcasco@ugr.esEspaña

El margen noroccidental de Suramérica se ha caracterizado por la interacción de las placas Suramérica, Caribe y Pacífico. Esta interacción incluye, desde el Cretácico Temprano, múltiples episodios de acreción de terrenos oceánicos diversos (tipo MORB, arcos de islas y plateaus) al margen continental pre – Mesozoico y resultó en la formación de complejos de subducción – acreción, los cuales sufrieron la transición compleja de corteza primitiva a más evolucionada, a través de diferenciación y génesis magmática.

La obtención de nuevos datos de campo, radiométricos y geoquímicos ha permitido la revisión de los modelos geodinámicos vigentes para los Andes del norte y el Caribe, además de aportar a algunas de las preguntas actuales sobre los modelos de subducción – acreción tales como la naturaleza de los terrenos acrecionados, la formación de batolitos en las placas oceánicas y continentales, la importancia de las zonas de falla responsables para la redistribución de la margen y la formación de diferentes cuencas oceánicas.

La sesión especial Crecimiento y modificación de la corteza en las márgenes de la placa Caribe hará énfasis en la interacción compleja de la placa Caribe con las placas de Norteamérica y Suramérica. Se recibirán contribuciones relacionadas con la identificación de los terrenos acrecionados, las suturas y las zonas de cizalla, la evolución tectonomagmática de los complejos de subducción – acreción, el análisis de cuencas, la formación de corteza continental granítica y las reconstrucciones paleogeográficas.Keynote speakers

Walter MARESCH – Ruhr Univeristaet, BochumNombre de la charla:

Margarita Island: the 120 Myr logbook of its journey from Colombia to the Oriente of Venezuela

GermanyJames PINDELL – Tectonic Analysis Ltd.Nombre de la charla: The Colombia – Caribbean confrontation;

Plate responses at a continental promontoryEngland

Geodesia espacial y dinámica terrestre2. CoordinadorHéctor MORA – Instituto Colombiano de Geología y Minería (INGEOMINAS)hmora@ingeominas.gov.coColombia

Simposio diseñado para poner en consideración y promover la discusión de un grupo diverso de la comunidad científica orientado hacia la aplicación de métodos de geodesia espacial en el entendimiento de la dinámica de la Tierra. Estas discusiones abarcarán diversas áreas incluyendo pero no restringidas a deformación, deformación tectónica, rotación de bloques, deformación volcánica, geodesia de imágenes, cambio climático global, nivel absoluto del nivel del mar, estudios ionosféricos, predicción de tsunamis, carga atmosférica, variaciones de mareas terrestres, carga oceánica, predicción geoidal, dinámica de corteza profunda y estudios de la criosfera.

Isótopos estables tradicionales y no 3. tradicionales como nuevos proxies en paleoceanografía, paleoclimatología y paleobiología

CoordinadoresJuan Carlos SILVA – Universidad de Caldasjsilvatamayo@yahoo.comColombiaAlcides Nóbrega SIAL – Universidad Federal de Pernambucosial@ufpe.brBrasilValdrez P. FERREIRA – Universidad Federal de Pernambucovalderez@ufpe.brBrasil

Within only a few years, the development of novel mass spectrometric analytical techniques has allowed using new non – traditional stable isotopes as promising tools to complement

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nos permiten reconocer las litologías contenidas en las Formaciones geológicas que se encuentran en profundidad mediante el estudio de un parámetro físico, p.e. la aplicación de Sondeos Eléctricos Verticales.

Basal stratigraphy of a NW – trending Jurassic rift in Honduras (Chortis Block)Robert ROGERS1

1California State Univeristy – StanislausPalabras claves: Chortis, proto – Caribbean, Jurassic, Honduras, rift.

North of Danli in SW Honduras 1300–1500 meters of Jurassic nonmarine and 1300 meters of marine clastic

strata exposed on limbs of large NW–verging asymmetric folds reveal a depositional architecture consistent with continental rifting.

The lowest member (Unit 1) consists of 200–300 meters of fluvial overbank shale, siltstone and coal unconformably above basement gneiss. Above the shale (Unit 2) are about 250 meters of alternating very coarse pebble – cobble quartz and metamorphic clast conglomerates with scoured bases and overbank shale facies containing plant fragments. This unit contains at least one 20–meter thick silicic ash – fall tuff. The coarse conglomerate and shale unit grades upward into Unit 3, comprised of a 200–meters–thick fine quartz pebble conglomerate and medium – grained quartz sandstone with unidirectional crossbeds, channels with scoured bases and shale from the overbank environments. This is overlain by Unit 4, approximately 400 meters of fine grained well–sorted and rounded quartz sandstone in 20–40 meter–thick units displaying lateral accretion surfaces of a mixed–load fluvial system. Sand bodies are embedded in shale sequences representing overbank deposition. Within this unit the steeply dipping north limb of the Cerro San Cristobal anticline is comprised of an amalgamated sand body at least 350 to 400 meters thick that represents the location of the axis of the valley in the Jurassic. This individual sand body was tracked 30 km to NW through a series of folds. Above (Unit 5) is an abrupt transition to dark dominantly shale section at least 1300 meters thick and containing ammonites. There are a number of beds that coarsen upward to fine–grained sandstone in the shale. A marine transgressive surface at the top of the fluvial sandstone is interpreted between Units 4 and 5. Deposition of Unit 5 appears to have been dominated by marine shelf conditions, and several lower shoreface sand bodies are recognized.

The depositional architecture, thickness and geographic positions of the strata are consistent with deposition on a south– or southeast – facing passive margin that resulted from the breakup of North and South America. The NW trend of the axial fluvial facies (Unit 4) indicates a large river system draining from the NW and is consistent with a rift extending into North America that subsequently failed as the proto – Caribbean seaway opened between the Americas. This

NW–trending rift intersects the larger NNE–trending Agua Fria rift of eastern Honduras near Danli. Deposition along this and other NW–trending depocenters in central Honduras continued through the Cretaceous before being inverted in the Late Cretaceous.

Procedencia de los sedimentos jurásicos – cretácicos del flanco occidental de la Serranía del PerijáPaola Catalina MONTAÑO CORTÉS1, Giovanny NOVA RODRÍGUEZ1, Uwe MARTENS2, José María JARAMILLO3

1 Universidad Nacional de Colombia – Sede Bogotá2 Tectonic Analysis Ldt.3 Gmas Ltda.Palabras claves: Serranía del Perijá, geocronología U/Pb, procedencia.

En el Mesozoico la tectónica para el límite norte de la placa suramericana es de gran actividad. Durante el Triásico

cuando Pangea comienza a romperse, se inicia un periodo de formación de fosas, que se extiende hasta el Cretácico temprano, durante este periodo se depositan secuencias clásticas continentales, capas rojas y depósitos salinos; en la esquina noroccidental de Suramérica uno de los lugares donde afloran estas secuencias es la Serranía del Perijá, representadas por las Formaciones La Quinta y Río Negro.

En este trabajo las lodolitas calcáreas hacia el tope de la Formación La Quinta se interpretan como depósitos lacustres mientras que las secuencias de areniscas conglomeráticas grano – decrecientes e intercalaciones de lodolitas rojas de la Formación Río Negro se interpretan como depositadas en ambientes fluviales de ríos trenzados y meandriformes.

Para determinar la fuente de los sedimentos detríticos se realizaron análisis de geocronología por el método U/Pb en granos de circones detríticos extraídos de muestras de ambas Formaciones. En la Formación La Quinta se encontró circones cuyas edades oscilan entre el Proterozoico y Jurasico Medio mientras que en la Formación Río Negro se encontraron circones con edades correspondientes al Meso Proterozoico, Cámbro –Ordovícico y Triásico – Jurásico.

Finalmente basados en esta información se sugiere que el área de mayor aporte está localizada en los Andes de Mérida y el Macizo de Santander; al Este y Sureste de la Serranía del Perijá.

The Romeral Fault Sytem as a kilometric scale shear zone in NW Colombian AndesCesar Javier VINASCO VALLEJO1, Marion WEBER1, Vicente RODRÍGUEZ1, Daniel GARCÍA1, María Isabel GIRALDO1 & Carlos ARCHANJO2

1 Universidad Nacional de Colombia 2 Universidade de Sao PauloPalabras claves: Romeral Shear zone, Arquía Complex, Diorita de Pueblito, Caribbean Plate.

Physiographically speaking the westernmost segment of the Colombian Andes encompasses the Central and Western

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Cordillera as well as the Atrato basin and the Baudo Ranges. The Central and western Cordilleras are separated by the Cauca River depression. The geological configuration closely follows the physiographic trend whereby the two cordilleras belong to two contrasting domains separated by the Romeral Fault System (RFS). The RFS encloses a series of rocks (including the Arquia Complex), which is here interpreted as an extensive shear zone (kilometric – scale) composed of multiple lithological units of varying ages, diverse origins, polydeformed, and in faulted contact. The Pre – Mesozoic continental margin worked as a Meso – Cenozoic back stop, which is defined by the actual Central Cordillera. The accreted terranes are in turn represented by the Western Cordillera, some of the components of the Arquia Complex and rocks of the Baudo Range. Despite the complex distribution of reported ages for the Central Cordillera block, which suggest the presence of pre – Mesozoic constituents, an Upper Paleozoic – Lower Mesozoic event is perhaps the most important orogenic event recorded for the block. This event could be associated with the build up of Pangea driven by the collision between Laurentia and Gondwana during the Alleghenian orogeny and responsible for the subsequent closure of the proto Atlantic Ocean. Triassic tectonic regime recorded for the Pueblito diorite suggests a dominant left lateral regime by this time, in contrast to the dextral dominant regime for the Cretaceous. The easternmost trace of the RFS is defined by the San Jeronimo fault. This fault defines the beginning of a broad boundary that separates the Central Cordillera in the east from the accreted terranes to the west. Regionally, this broad boundary corresponds to a kilometric shear zone hosting a series of rocks including: (1) the Cretaceous sedimentary – volcanic sequence of the Quebradagrande Complex; (2) low grade devonian(?) metasediementary rocks of Sinifaná Schists; (3) mafic and ultramafic Triassic supra subduction intrusives and finally (4) Permian (?) and/or (?) Cretaceous (?) low to medium grade meta vulcano–sedimentary N–MORB type sequences of the Arquia Complex. The Amaga Formation, a coal – bearing, Oligo – Miocene sedimentary sequence unconformably covers the older lithological units. Mio–Pliocene volcanic and subvolcanic rocks of the Combia Formation covered and intruded the Amaga Formation and other older rocks. Geometrically, the RFS shear zone is characterized by an anastomosed arrange of faults yielding a block tectonics configuration. Different authors agree that the Late Cretaceous to early Cenozoic tectonic evolution of the northern South American margin was controlled by its interaction with the margins of an allochthonous (Pacific – derived), anomalously thick Caribbean oceanic plate and its associated arc. Subsequent Palaeogene orogenic phases seem to be related to variations in plate convergence or to accretionary phenomena (Pindell et al., 1998; Restrepo – Moreno et al., 2009; Vallejo et al., 2009; Jaillard et al., 2010). Cardona et al (2011), suggest that the Caribbean oceanic plate influenced the Late Cretaceous–Eocene orogeny of the northern Andes by the collision of the

Caribbean arc with the continental margin about 90 Ma with subsequent installation of the subduction regime possibly since about 65 Ma. This situation seems to be different from that of the Central Antioquia segment of the Central Cordillera where subduction regime is recorded at least since 90 Ma. Finally, they suggest magmatic quiescence and block uplift after 50 Ma as product of shallow subduction and oblique convergence. Regional reconstructions given by Pindell (in prep) since Jurassic times involves the eastward subduction of Farallon plate under the continental margin represented by the Central Cordillera. The result of this subduction is represented by the Quebradagrande belt containing the arc and back arc rocks while the Arquia belt contains HP–LT subduction related rocks. In the model depicted above, the Quebradagrande belt corresponds to an autochthonous arc contemporaneous to the Arquia belt produced by eastward subduction of the Farallon plate. Alternatives hypothesis suggest that Arquia Complex is a composite collection of rocks including pre–mesozoic and upper cretaceous fragments. Some of these fragments would be remobilized pieces from both Central and Western Cordillera in a long lasting shear zone, developed to the continental margin since Triassic times, as suggested by ASM studies in the Pueblito diorite.

Geochemistry of the Santa Fe Batholith in NW Colombia – Remnant of an accreted Cretaceous arcMarion WEBER1, Jorge GÓMEZ TAPIAS2, Edison DUARTE1, Agustín CARDONA3 & César Javier VINASCO VALLEJO1

1 Universidad Nacional de Colombia – Sede Medellín2 Instituto Colombiano de Geología y Minería – INGEOMINAS3 Smithsonian Tropical Research Institute – STRIPalabras clave: Santa Fe Batholith, Colombian Caribbean Oceanic Plateau, island arc, Cretaceous.

The Santa Fe Batholith in northern Colombia comprises gabbros, tonalities to quartzdiorites that intruded the

Cretaceous plateau related basalts of the Barroso Formation, which are linked to the allochtonous Colombian – Caribbean plateau.

The tonalitic and quartzodioritic rocks share some similarities with Archean TTG suites (high Sr and Ba, low Nb and Y). The primordial mantle – normalized spidergrams are characterized by negative Nb–Ta and Ti anomalies, suggesting a subduction related signature. Sr and Nd isotopic data are strongly homogenous (87Sr/86Sr – 0.70366, eNdi – + 6.7) and are compatible with melt generation from a mafic source.

Sm–Nd isotopic ages are 98 ± 9.1 Ma, whereas new incremental heating 40Ar/39Ar date indicates that cooling of the Batholith occurred around 92 Ma.

The geochemical characteristics and field relations are similar to those described for the Aruba Batholith (White et al., 1999) and the Buga Batholith (Villagómez et al., 2008),

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and therefore a similar tectonic setting is probable for the three units.

It is therefore envisioned that during the late Cretaceous west dipping subduction zone initiated along the eastern margin of the Turonian Colombian Caribbean plateau, enabling the emplacement of the Santa Fe Batholith into basaltic rocks or the Barroso Formation. During the Maastrichtian these two units were accreted onto the South American margin, prior to the formation of a post – collisional continental arc at 65–55 Ma.

References. White, R.V., Tarney, J., Kerr, A.C., Saunders, A.D.,

Kempton, P.D., Pringle, M.S. & Klaver, G.T., 1999, Modification of an oceanic plateau, Aruba, Dutch Caribbean: Implications for the generation of continental crust: Lithos, v. 46, p. 43–68.

Villagómez, D., Spikings, R.A., Seward, D., Magna, T. & Winkler, W., 2008, New thermochronological constraints on the tectonic history of western Colombia, in 11th International Conference on Thermochronometry, Alaska, p. 253–255.

Thermobarometry of amphibolites from the Arquía Complex (Central Colombia): Geodynamic implications Antonio GARCÍA CASCO1, Idael F. BLANCO QUINTERO1, Elvira Cristina RUIZ2, Mario MORENO2, Luz Mary TORO2, Arley De Jesús GÓMEZ2 & Cesar VINASCO3

1 Universidad de Granada2 Universidad de Caldas3 Universidad Nacional de Colombia – Sede MedellínPalabras claves: Arquía complex, geodynamic implications, magnesiohornblende, the Caribbean–Colombian Oceanic Plateau.

Epidote – garnet amphibolite rocks from the Arquía complex (central Colombia) are composed of magnesiohornblende

+ garnet + epidote + quartz + plagioclase + calcite, plus rutile + titanite + apatite as accessory phases. The rocks are fine – to medium – grained, with grains up to 1 mm in size, though grain size reduction is related to foliation development during an intense and retrograde deformation stage overprinting an earlier higher–T foliation. Locally, fine veins of leucocratic materials appear parallel to the main foliation, suggesting partial melting of amphibolite. The cores of magnesiohornblende are relatively rich in AlVI, NaBand Ti (1.01, 0.49 and 0.06 apfu, atoms per formula units, respectively), approaching barroisite composition, while retrograde amphibole is actinolite (AlVI<0.26, NaB<0.15 and Ti<0.02 apfu). Garnet porphyroblasts are euhedral, partly replaced by chlorite, and rich in almandine (Xalm= 0.46–0.60) and grossular (Xgrs= 0.25–0.32). Plagioclase is mostly albitic, locally reaching oligioclase composition (max. Xan= 0.18). Epidote is clinozoisite with Xpistacite up to 0.27. Thermobarometric calculations indicate peak metamorphic conditions of ca. 630 ± 30 ºC and 10.5 ± 1.2 kbar, close to the wet solidus for basaltic rocks and in agreement with melting

at peak conditions. The apparent geothermal gradient at peak conditions suggests a collision–related metamorphic event, probably related to collision and obduction of the Caribbean – Colombian Oceanic Plateau during the late Cretaceous.

Tectonic evolution of the Leeward Antilles: Late Cretaceous to Eocene Caribbean – South American interactions and amalgamation of the Bonaire BlockRoelant VAN DER LELIJ1, Richard SPIKINGS1, Andrew KERR2, Alexandre KOUNOV3, Michael COSCA4, David CHEW5 & Diego VILLAGOMEZ2

1 University of Geneva2 Cardiff University 3 University of Basel 4 United States Geological Survey 5 Trinity College Dublin Palabras claves: Caribbean, thermochronology, Antilles, Bonaire Block, accretion.

Any tectonic reconstruction of the evolution of the Caribbean Plate must account for the timing of accretion

of allochthonous terranes which are currently exposed in the South Caribbean Plate Boundary Zone (SCPBZ). This 300 km wide, diffuse plate boundary comprises parts of the Northern Andes of Ecuador and Colombia, the Coastal Cordillera of Venezuela, and the mainly submerged Bonaire Block, whose emergent part forms the Leeward Antilles islands of Aruba, Curacao, Bonaire and Gran Roque. New zircon U/Pb, 40Ar/39Ar, apatite fission track and apatite (U–Th)/He data from the Leeward Antilles constrains quantitative thermal and exhumation histories, which have been used to propose a new model for the tectonic evolution of the emergent parts of the Bonaire Block and the SCPBZ. An east–facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma, and crops out on Aruba. Early interactions between the Caribbean and South American Plates resulted in cooling of the basement rocks exposed on Aruba, by >80°C at 70–60 Ma. Cooling was driven by exhumation during island arc and plateau accretion, to the western margin of Northern South America. Burial metamorphism of ~95 Ma volcanic arc rocks exposed on Bonaire was rapidly followed by a major exhumation phase at 90–80 Ma, forming a major angular unconformity with the overlying Campanian sedimentary rocks. Exhumation may have been driven by the collision of a west–facing island arc with the Caribbean Plate. A second phase of exhumation at ~50 Ma resulted in an angular unconformity with an overlying fluvial conglomerate hosting Mesoproterozoic gneiss clasts derived from granulite belts currently exposed in the Colombian Andes. Island–arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian – Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate, resulting in the amalgamation of

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the Bonaire Block. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene – early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ~1 km. Late Miocene – recent transpression caused inversion and ~1 km of exhumation, possibly as a result of the northwards escape of the Maracaibo Block following collision of the Panama Arc with allochthonous Cretaceous rocks exposed in the Western Cordillera of Colombia.

Margarita Island: The 120 Ma logbook of its journey from Colombia to the Oriente of VenezuelaWalter V. MARESCH1

1Ruhr–UPalabras claves: Margarita Island, high–pressure metamorphism, arc–continent collision, exhumation history.

Details of the interaction between the Caribbean plate (CP) and South America (SA) have been modified and

in part obliterated by continuous later tectonic modification. Much work is still required to summarize and link individual histories of the dispersed crustal fragments into a coherent scenario. Rocks exposed on Margarita Island (MAR) not only record evidence of some of the earliest CP/SA interaction but also document a particularly far – travelled journey along northern SA. The core of MAR comprises rocks of both continental and oceanic affinity that were brought together, subducted to depths of at least 50 km and metamorphosed at HP/LT–MT conditions in a subduction zone that must already have been active at 116–106 Ma, when trondhjemitic/adakitic anatectic melts intruded rocks of both origins. Zircon – based ages of ~ 315 Ma (multi–grain), 287 Ma (SHRIMP) and 271 Ma (LA–ICPMS) Ma on various granitic orthogneisses indicate that Permo – Carboniferous continental basement was involved. Quartzofeldspathic schists and gneisses, metaconglomerates, lenticular and massive marbles as well as graphitic garnet – mica schists predominate. Detrital zircons indicate Lower Cretaceous ages for these metasediments (J. Wright, pers. comm., 2010). Rocks of oceanic origin include MORB–type metabasalts with IAT tendencies. Abundant ultramafic rocks are predominantly serpentinized spinel peridotites with common clinopyroxenite/wehrlite. Correlated primary spinel/olivine compositions suggest a supra–subduction–zone setting with 40% melt extraction. The intrusion of potassium–rich granitic rocks between 86 and 82 Ma followed exhumation into middle crustal levels and signaled a radical change from a HP/LT subduction zone environment to a MP continental–margin sub – arc setting. K–Ar, Ar–Ar and Rb–Sr results on rocks and minerals that were spared later deformation cluster at 90–80 Ma and substantiate rapid cooling/exhumation at this time. This pulse of calcalkaline magmatism was immediately followed by a ~ 30 Myr interval of penetrative dextral shearing at ductile greenschist – facies conditions and relatively constant crustal

depth. Widespread recrystallization, especially in quartz – rich lithologies, occurred. Another major event at ~ 50 Ma triggered exhumation of the HP complex into brittle upper crustal levels. Rb–Sr thin slab techniques on mylonitized Kfeldspar– rich orthogneiss confirm 50 Ma as the age of the last major isotopic equilibration. Nine K–Ar results from phengite in strongly recrystallized HP schists and sheared orthogneiss yield ages from 56 to 50 Ma. Ar–Ar studies on magmatic amphibole from unmetamorphosed dykes cross – cutting the HP core indicate 56 to 43 Ma (Kaiser, Ph.D. thesis Bochum, 1996). Zircon fission – track analyses range from 53 to 37 Ma and indicate dissection into individual blocks during exhumation into the brittle crust. The HP core of MAR is now tectonically overlain by LP greenschist – facies sequences with a conspicuously different P–T history. These are various metasediments including thick sequences of marbles and intermediate to basic metavolcanic deposits. Historically, ages of mid(?)– to Upper Cretaceous have been assumed from poorly preserved fossils. However, zircons from a metadacitic “porphyroid” yield a Triassic eruption age (225 Ma: LA–ICPMS), suggesting that the protolith for the greenschist – facies tectonic cover was as heterogeneous as that of the HP core. This LP periphery also contains trondhjemitic intrusions analogous in composition and zircon – based age (two at 114: multi – grain; 104,103 Ma: LA–ICPMS) to the widespread trondhjemitic/adakitic orthogneisses of the HP core. Associated ultramafic rocks are mainly harzburgite. Periphery and HP core were juxtaposed before the coeval brittle – ductile transition, as indicated by analogous cross – cutting dykes and 49 Ma K–Ar phengite ages on sheared orthogneiss.

The geological history recorded on MAR requires (see also Pindell, this volume) a collisional event along NW South America that involved subduction of continental margin material. Collision must have begun before ~ 120 Ma, in line with the existence of a west – dipping Caribbean subduction zone already at this time (Pindell et al., Int. Geology Rev., 2011). A first major reorganization is indicated by rapid exhumation at 90–80 Ma, and by calcalkaline intrusions perforating the HP complex, which was then transported northeastward at depth in a ductile strike–slip milieu. Final uplift into the brittle crust occurred at ~ 50 Ma, probably triggered by intra – arc rifting in the advancing Caribbean Arc, en–route to a Middle Miocene collision with central and eastern Venezuela.

Acknowledgements: I am indebted to my colleagues A. Baumann, M. Brix, R. Kluge, F. Koller, J. Pindell, H. P. Schertl, K.P. Stanek and S. Thomson for allowing me free use of unpublished data and ideas in this summary.

An alternative to plume for the building of the Caribbean–Colombian oceanic plateau: insights from new geologic and chronologic data from Gorgona islandLuca FERRARI1, Lina SERRANO DURÁN2, Margarita LÓPEZ MARTÍNEZ3, Chiara María PETRONE4 & Carlos

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JARAMILLO5

1 Universidad Nacional Autónoma de México – UNAM2 Universidad de Padua3 Centro de Investigación Científica y Educación Superior de

Ensenada4 University of Cambridge5 Smithsonian Tropical Research Institute

Palabras claves: Caribbean plateau, Gorgona, Slab window.

Oceanic plateaus are considered the result of short – lived (few Ma) periods of intense submarine volcanism marking

the arrival of mantle plumes at the base of the lithosphere. This major pulse of volcanism should be followed by a volcanic chain with ages decreasing away from the site of the plume head impact. One such an event is postulated to have formed the Caribbean – Colombian Oceanic Plateau (CCOP) at ~90 Ma, when the Galapagos plume head would have impacted the Farallon plate. At present, the remnants of the CCOP form the irregularly thickened and locally deformed oceanic crust of the Caribbean Sea as well as several highly deformed fragments obducted in the northern Andes, Central America and the Antilles. Gorgona island, offshore western Colombia, is one of the less deformed and last accreted pieces of the CCOP and its highly heterogeneous igneous suite, ranging from enriched basalts to depleted komatiites and picrites, was assumed to have formed at ~89 Ma from different parts of the plume. Based on our new geologic and geochronologic data we question this simple mechanism and propose an alternative scenario for the origin of the CCOP. The island of Gorgona represents the top of a faulted anticlyne which is part of a series of NNE trending axial basement bulges formed in Eocene times during the accretion of a sliver of the CCOP to the continental margin. These structures were partly disrupted by Miocene to recent right lateral transtensional and extensional faulting associated to the post–accretion deformation. Gorgona and the other submerged basement structures formed the Gorgona terrane, a >400 km long strike–slip horse bounded by the NE striking Garrapatas and Buenaventura reverse and oblique fault zones, which is located between the Western Cordillera and the Serranía del Baudó. Gorgona mafic lavas and gabbros were thoroughly sampled and the freshest fragments were dated by the 40Ar–39Ar method through multiple step–heating experiments using a laser with the VG5400 mass spectrometer and a Ta–furnace with the MS–10 mass spectrometer. The experiments show good reproducibility and document a ~30 Ma long magmatic activity, spanning the whole Late Cretaceous and part of Paleocene. A late, shallower, picritic pyroclastic eruption is constrained to the Paleocene based on stratigraphic and paleontological data. We obtained a similar age range for the Bolivar Ultramafic Complex (BUC) of the Western Cordillera of Colombia, which represent the largest and more mafic continental exposure of the intrusive complexes of the CCOP. The time and space distribution of the available CCOP ages, including our new Gorgona and BUC ages, show a long period

of igneous activity spanning the whole Late Cretaceous. The prolonged period of igneous activity spanning over ~30 Ma is not consistent with a short, voluminous outburst of magmatism from a plume head at ~91–89 Ma, as suggested by previous authors (e.g. Sinton et al., 1998, EPSL; Kerr, 2005, Lithos). On the other hand, the geographic distribution of ages does not point to a definite pattern of migration as it would be expected if magmatism would be the result of the passage of the Farallon plate over a stationary, or slowly moving, hotspot. Particularly, the persistence of magmatic activity at the restricted location of Gorgona Island is at odds with the model of a volcanic chain with ages decreasing away from the initial impact site of a plume head. The distribution of ages rather suggests a long period of pulsing magmatism in areas up to 1500 km apart. The data point to a diffuse and irregular magmatism, consistent with the crustal structure of the Caribbean plateau seen in seismic profiles. Compared with other classic oceanic plateau (e.g. Ontong – Java, Kerguelen) the CCOP is thinner and with a more irregular crustal thickness (between 6 and 15 km), a feature that allowed the subduction of some of its parts under South America as well as its internal deformation. The long period of diffuse magmatism that formed the CCOP is broadly concurrent with the existence of the Caribbean slab window (~100 to 66 Ma), which must be considered into any model of the plateau formation. Decompression melting of a heterogeneous, partly wet, mantle within such a tectonic setting may explain the observed space–time pattern of magmatism. We thus speculate that the CCOP melting anomaly may have resulted from westward flow of Atlantic asthenosphere through the Caribbean slab window.

Regional provenance of the late Paleocene to Miocene San Jacinto belt (Northern Colombia): A record of Late Cretaceous to Cenozoic continuous convergence in the Southern margin of the Caribbean plateAgustín CARDONA1, Camilo MONTES1, Carolina AYALA1, Camilo BUSTAMANTE1, Camilo MONTENEGRO1, Carolina OJEDA1, Natalia HOYOS1, Helga NIÑO2, Víctor RAMIREZ2 Daniel RINCÓN3, Víctor VALENCIA4 & Jeff VERVOORT4

1 Smithsonian Tropical Research Institute – STRI2 ECOPETROL S.A.3 Instituto Colombiano del Petróleo – ICP4 Washington State UniversityPalabras claves: Provenance, Caribbean Plate, Arc – Continent Collision.

The San Jacinto belt in northernmost Colombia represents a long and narrow Late Paleocene to Oligocene sedimentary

wedge formed at the southern margin of the Caribbean plate (Duque Caro, 1984). Understanding its filling history provides major insights on the Early Cenozoic Caribbean – South American plate tectonic interactions and the unroofing of the Northern Andes. A regional provenance analysis including conglomerate clast counting and whole rock

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geochemistry, U–Pb and Hf isotopic granitoid clast analysis, together with petrographic, heavy minerals and detrital zircon geochronology was carried on Late Paleocene to Oligocene conglomerates and associated sandstones. Provenance results reveal a bi – modal source which can be related to the erosion of an allochthonous Late Cretaceous arc and the Late Paleozoic to Triassic continental margin signature. This compositional signature was followed by a significant increase in compositional maturity although detrital ages are preserved. The provenance features can be related to the erosion of the Late Maastrichtian to Early Paleocene Caribbean – South America arc–continent collision, whereas the preservation of the major Late Cretaceous magmatic source and the quartz increased are related to partial vanishing of the allochthonous arc source and the major denudation of the Central Cordillera of the Colombian Andes. It´s also suggested that this changes record orogen submergence following arc continent collision and the northeastern lateral displacement of this wedge before final accretion.

The paucity of Cretaceous detrital ages older than ca. 90 Ma recognized within this belt and other tectonostratigraphic elements from northern Colombia suggest that the Caribbean – Americas arc continent collision is more akin to a multiple arc than the single great Caribbean arc type (Wright and Wylde, 2011; Neill et al., 2011).

ReferencesDuque Caro, H.,1984. Structural Style, diapirism and

accretionary episodes of the Sinu – San Jacinto terrane, southwestern Caribbean borderland. in Bonini, W.E., Hargraves, R.B., and Shagam, R., (eds.), The Caribbean–South American plate boundary and regional tectonics. Geological Society of America Memoir, 162, 303–316.

Wright, J. E. & Wyld, S. J. 2011. Late Cretaceous subduction initiation on the eastern margin of the Caribbean – Colombian Oceanic Plateau: One Great Arc of the Caribbean (?). Geosphere, 7, 468–493; DOI: 10.1130/GES00577.1

Neill, I., Kerr, A., Hastie, A., Stanek, K–P. & Milllar, I., 2011. Origin of the Aves Ridge and Dutch–Venezuelan Antilles: interaction of the Cretaceous ‚Great Arc‘ and Caribbean – Colombian Oceanic Plateau?. Journal of the Geological Society, London, Vol. 168, 2011, pp. 333–347. doi: 10.1144/0016–76492010–067.

Las Sedimentitas de Tripogadi y las Brechas de Triganá: Un registro de volcanismo de arco, corrientes de turbidez y levantamiento rápido Eoceno en el noroccidente de Sur AméricaMaría Isabel SIERRA ROJAS1 & Gabriel RODRÍGUEZ GARCÍA2

1Universidad Nacional Autónoma de México – UNAM2Instituto Colombiano de Geología y Minería –

INGEOMINAS Palabras claves: Sedimentitas de Tripogadí, Brechas de Triganá, turbiditas, arco volcánico.

Entre la Cuenca de Colombia y las serranía de San Blas–Darién al sur, limitado al sur occidente por la Falla

Atrato – Urabá, correspondiente a la sutura colisional entre Centro América y Sur América al oriente afloran una serie de rocas volcánicas, volcano – sedimentarias, sedimentarias e intrusivas con edades que van desde el Cretácico Tardío hasta el Cenozoico. El Complejo Santa Cecilia – La Equis hace parte de esta secuencia y está constituido por derrames lávicos y secuencias piroclásticas de composición basáltica a andesítica de edad Cretácico Superior–Paleoceno, el cual es intruído por el Batolito de Acandí y demás cuerpos hipoabisales todos con afinidad de arco volcánico en una suite que varía desde rocas toleíticas a calco alcalinas. En la zona se describen de manera informal tres unidades nuevas que corresponden a las Sedimentitas de Tripogadí, las Brechas de Triganá y las Sedimentitas del río Cutí, de edades desde el Eoceno inferior a probablemente el Oligoceno. Las Sedimentitas de Tripogadí corresponden a una secuencia de aproximadamente 3000 m de espesor que aflora en la Serranía de Tripogadí, descansa de manera discordante sobre tobas y aglomerados del Complejo Santa Cecilia – La Equis, pero tiene influencia del vulcanismo que dio lugar este complejo. Las sedimentitas de Tripogadi se caracterizan por presentar hacia la base un fuerte aporte volcánico, desarrollando brechas sedimentarias, aglomerados volcánicos, intercalados con tobas de ceniza y lapilli, asociación litológica que marca una influencia volcánica la cual domina los procesos de sedimentación en un ambiente marino profundo. En una posición estratigráfica superior y marcando una posible somerización de la cuenca, se encuentran areniscas finas a medias con presencia de cuarzo fino y plagioclasa y hornblenda, intercalado con limolitas, arcillolitas silíceas y calcáreas, mostrando un carácter bimodal en composición y una posible sedimentación en ambientes con aporte volcánico primario o por retrabajamiento de unidades preexistentes (epiclastitas). La presencia de foraminíferos y radiolaritas de ambientes pelágicos en las calizas permite inferir una depositación en ambiente de talud continental con aportes de detritos cuya fuente es un arco volcánico activo. Las relaciones de campo y los fechamientos paleontológicos permiten ubicar dicha formación entre el Paleoceno superior – Eoceno inferior. Hacia la línea de costa afloran la unidad denominada Brechas de Triganá, la cual constan de gruesos paquetes de brechas oligomícticas en la base y polimícticas hacia el techo, interestratificadas con bancos gruesos de arcosas, subarcosas, litoarenitas y areniscas conglomeráticas con estratificación plano paralela. Se considera que esta unidad corresponde a depósitos de abanicos submarinos y slumps producto de procesos de levantamiento rápido y altas tasas de denudación con un área fuente cercana. esta unidad marca el levantamiento rápido del área, puesto que la fuente de aporte de las Brechas de Triganá en la base es el arco volcánico (Complejo Santa Cecilia La Equis) y hacia la parte superior lo que aflora corresponde a un orógeno levantado. El origen de las Brechas de Triganá es la respuesta al proceso de levantamiento tectónico en el Eoceno o ligeramente posterior al Eoceno, del arco magmático representado por Complejo Santa Cecilia – La

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Equis y el Batolito de Acandí. Ambas formaciones registran la evolución de un margen continental con procesos volcano tectónicos activos y depositación de abanicos submarinos y turbiditas (Sedimentitas de Tripogadí), registrando en la unidad de Brechas de Triganá un levantamiento rápido del arco, acompañada de una erosión de grandes dimensiones o catastrófica, que erosionó parte del arco volcánico y alcanzó a erosionar las rocas plutónicas y subvolcanicas (Cuerpos de pórfidos y Batolito de Acandi).

Source area lithology controlling the composition of the siliciclastic fill in intra – mountain Cenozoic basins: Implication for the Paleogeography of NW South AmericaJuan Carlos SILVA TAMAYO1,2, Andrés PARDO1, Agustín CARDONA2, Germán BAYONA3, Carlos BORRERO1 & Sergio RESTREPO2

1 Universidad de Caldas2 Smithsonian Tropical Research Institute – STRI3 Corporacion Geologica ARESPalabras claves: NW South America paleogeography, Intra mountain basins, Amaga Formation, Tectonic evolution, Colombia.

The tectonic evolution of NW South America since the late Cretaceous to the present has been closely related to the

evolution of the Caribbean Plate and its interaction with the South American Block. Changes in tectonic regime along NW South America and major variations in the neotropical climate seem to have likely affected the sedimentologic, stratigraphic and compositional characteristics of siliciclastic successions cropping out along some of the Oligocene – Miocene basins of NW South America (i.e. the Amaga and Santa Fe de Antioquia – San Jeronimo basins, Van der Hammen, 1958, Pons 1984; Silva Tamayo et al., 2008).

The Oligocene – Miocene Amaga Formation crops out along of the Cauca depression in NW Colombia. Previous studies have suggested that the Amaga Formation was deposited in several confined intramountain basins occurring along the Cauca depression (Silva Tamayo et al., 2008). Here we present new sedimentologic and stratigraphic, along with new detrital compositional modes of the Amaga Formation (along the Santa Fe de Antioquia – San Jerónimo Basin) that further account for deposition of the Amaga Formation silicilastics along intra – mountain basins. Local compositional similarities between the siliciclastic record and the underlying basements and regoliths suggest a provincialism in the sediment provenances. Such provincialism and the preferential south – north paleocurrent directions further account for a fluvial system functioning similarly to the modern Cauca River (Silva et al., 2008).

The sedimentologic, stratigraphic and sandstone compositional characterisitics of the Amaga Formation contrast with those displayed by other Oligocene – Miocene siliciclastic successions cropping along the Cauca depression, but to the south of the Garrapatas Fault (i.e. the Cinta de Piedra, Mosquera and Esmita formations). While continental

sedimentation occurred along the Cauca depression to the north of the Garrapatas Fault, mixed marine – siliciclastic sedimentation occurred to the South of this tectonic feature.

The Garrapatas Fault is the main tectonic feature separating the Cretaceous Choco Block from the Ancestral Western Cordillera of Colombia. We suggest that a possible geographic barrier developed along the Cauca depression. Such geographic and hydrographic barrier would have been related to tectonic up–lift of the ancestral Western and Central Cordillera, north of the Garrapatas Fault. Such uplift (ca 23 Ma) may have ultimately been related to the initial interaction of the Pamana – Choco block with northern South America. This scenario is in agreement with our interpretation that the Oligocene – Miocene siliciclastics cropping out along the Cauca depression, north of the Garrapatas Fault, were deposited along intra–mountain basins confined between the Western and Central Cordilleras of Colombia, while those cropping out to the south of the Garrapatas would have been deposited along coastal plains draining towards the south. The occurrence of siliciclastic Paleocene – Eocene mixed continental – marine sedimentary successions and early Oligocene coral reef successions (Vijes Formation) overlying the basement of the Western Cordillera of Colombia, south of the Garrapatas Fault, further support this interpretation and may suggest an interaction between the Choco Block and NW South America dating back to early Cenozoic times.

The transpressive left – lateral Chiapas Mountain Chain and its buried front in The Tabasco Plain (South Mexico) Cesar Augusto WITT OLIVO1, Stephanie BRICHAU2, Andrew CARTER3 & Claude RANGIN4

1GEOAZUR2Institute of research for development – IRD3Birkbeck College – London4Collège de FrancePalabras claves: Chiapas, Polochic – Motagua, Punto triple, Placa Caribe.

The Chiapas mountain chain (CMC) evolved in the vicinity of the triple junction between the Cocos, North America

and Caribbean plates. Major exhumation and topographic growth occurred during the middle – late Miocene (16–10 Ma). This deformational event is evidenced by fault activity, major stratigraphic unconformities along the CMC and the Tabasco coastal plain (i.e. southern Gulf of Mexico), major salt–related motion and northward progradation of sediments and by the northward migration of the buried deformational front. During Neogene, strike slip deformation and related exhumation has migrated landwards from the western edge of the Chiapas massif to the Chiapas Sierra. Horizontal displacement along the main strike – slip faults on the Sierra may be comprised between 30 and 43 km during the last 6–5 Ma involving 0.5–0.8 cm/a of lateral accommodation. These values suggest that a significant amount of the motion

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transferred from the Caribbean and North American plates is currently accommodated along the Chiapas area. The CMC tectonics reflects positive topographic growth along its main core and a northwards – directed collapse trough a free–border related to the Gulf of Mexico. In this scenario, the CMC formation enhances earlier pervasive deformation mainly triggered by earlier periods of salt motion along the Tabasco coastal plain. Sediment provenance and low temperature thermochronology (apatite fission track and (U–Th)/He) study on igneous and terrigenous samples of the Chiapas mountain chainyielded important constraints for the chain evolution and its relationships with the Caribbean, North America and Cocos triple–junction. Results show that Palaeocene – Eocene terrigenous units (outcropping at the northern section of the Sierra) were derived from Grenville (~1Ga) basement whereas internal section of the chain display Chiapas massif–derived (270–250 Ma) components. Grenville–sourced sediments are probably derived from a Laramide deformation front and deposited in an open marine to continental environment north of the Sierra. Sediment input related to this process seems important due to the high degree of resetting of AFT and (U–Th)/He systems at site. Batholith – related input increases with the onset of major tectonic deformation at 16–9 Ma. Apatite fission track and (U–Th)/He data combined with previously published results define three main exhumation periods: 1) A slow 40–25 Ma exhumation affecting the massif and relatively unexpressed along the Chiapas Sierra; 2) A fast 16–9 Ma exhumation period related to the onset of major strike slip deformation related to the Caribbean – North American plates limit and affecting both Chiapas massif and Chiapas Sierra; and 3) A 6 – 5 Ma period affecting the Sierra and coincident with the landward migration of the plate limit. Stratigraphic, cinematic and termochronologic evidence suggests that the left – lateral strike – slip faults bounding the Chiapas Sierra to the west accommodates most of the current displacement between the North American and Caribbean plates.

Subduction in the Southern CaribbeanAlan LEVANDER1, Michael SCHMITZ2, Maximiliana BEZADA3, Meghan S. MILLER4, Jeniffer MASY1, Fenglin NIU1 & James PINDELL1

1 Rice University2 Fundación Venezolana de Investigaciones Sismológicas –

FUNVISIS3 University of Oregon4 University of Southern CaliforniaKeywords: Southern Caribbean plate boundary, subduction, mountain building.

The southern Caribbean is bounded at either end by subduction zones: In the east at the Lesser Antilles

subduction zone the Atlantic part of the South American plate subducts beneath the Caribbean. In the north and west under

the Southern Caribbean Deformed Belt accretionary prism, the Caribbean subducts under South America. In a manner of speaking the two plate subduct beneath each other. Finite – frequency teleseismic P–wave tomography confirms this, imaging the Atlantic and the Caribbean subducting steeply in opposite directions to transition zone depths under northern South America (Bezada et al, 2010).

The two subduction zones are connected by the El Pilar–San Sebastian strike–slip fault system, a San Andreas scale system. A variety of seismic probes identify where the two plates tear as they begin to subduct (Niu et al, 2007; Clark et al., 2008; Miller et al. 2009; Masy et al, 2009). The El Pilar system forms at the southeastern corner of the Antilles subduction zone by the Atlantic tearing from South America. The deforming plate edges control mountain building and basin formation at the eastern end of the strike–slip system.

In northwestern South America the Caribbean plate tears, its southernmost element subducting at shallow angles under northernmost Colombia and then rapidly descending to transition zone depths under Lake Maracaibo (Bezada et al., 2010). We believe that the flat slab produces the Merida Andes, the Perija, and the Santa Marta ranges. The southern edge of the nonsubducting Caribbean plate underthrusts northern Venezuela to about the width of the coastal mountains (Miller et al., 2009). We infer that the underthrust Caribbean plate supports the coastal mountains, and controls continuing deformation.

The Colombia – Caribbean tectonic confrontation; plate responses at a continental promontoryJames PINDELL1

1 Rice University and Tectonic Analysis Ltd.Palabras claves: Subduction accretion, arc, rifting, plate motions.

Evolving concepts of Caribbean evolution since 1970 show advantages of considering regional evolution in the mantle

reference frame, because subducted slabs in the mantle can only migrate forward/backward at a fraction of plate motion rates and thus the “room” for error is much less (Pindell and Kennan, 2009). From Triassic to Early Cretaceous, northern South America remained attached to Africa, both moving little relative to the mantle in contrast to North America’s NW–ward migration, leading to Jurassic rifting and drifting between the Americas. By Aptian (125Ma), opening of the Equatorial Atlantic had begun, and northern South America has migrated westward across the mantle ever since, thereby throwing subduction systems and intra–arc basins along the NW Andes into E–W compression sensu Dewey (1980), with variable strike slip components. This long – lived compressive period comprises unique phases of convergent tectonic style between the NW corner of South America (Colombian continental promontory) and lithosphere that was either driven by, or belonged to, the Caribbean Plate.

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In Early to Middle Jurassic, granitic intrusives were produced and cooled in a “Central Cordilleran” belt from Guajira into Ecuador, usually presumed to be arc magmas from E–dipping subduction. However, they may relate to rifting within a zone of crustal anatexis caused by Alleghanian – Gondwanan crustal thickening of Late Paleozoic arc – related terrane. Following the arc model, I have proposed the opening of an intra – arc basin as a means of terminating this “arc” by 140–150 Ma (Pindell, 1993), but the anatexis model can pertain only to Jurassic rifting, without subduction, of Mexico/Chortis from Colombia (Pindell and Dewey, 1982). Redbed deposition on phaneritic intrusive rock (eg, Saldaña Fm on Ibague pluton) attests to syn – magmatic extension and exhumation of deep terrane, fitting either model. But the arc model predicts evolution of an offshore active arc from 145–125 Ma; such ages on arc rocks are rare/absent in Colombia/southern Caribbean, making this an issue for investigation.

The NW–ward flight of North America probably created an archipelago of stretched arc and continental blocks from Mexico and Chortis along a SE – trending and lengthening sinistral shear zone/transform to the Andean intra–arc basin (Pindell et al. 2011), which can be called Quebradagrande Basin. 125Ma opening of the Equatorial Atlantic and onset of Andean compression caused this basin and its outlying Quebradagrande Arc to collapse, achieved by dextral and W–dipping subduction such that the Central Cordilleran margin choked the trench during arc collision, as shown by Margarita which hosts a far–travelled remnant of this event (Maresch, this volume). The collision involved propagation of transpressive faults into the continental margin, parts of which were uplifted and cooled (Villagomez, 2010), and probably carried northward along orogen–parallel shears. However, E–dipping subduction of Farallon Plate outside Quebradagrande Arc, marked by the Arquila HP–LT complex, probably continued throughout closure of the weak backarc basin, and after arc accretion.

The Caribbean – Colombian intra – oceanic oceanic plateau (CCOP) then formed on Farallon/Caribbean crust at about 110–88Ma and progressively converged with Colombia, accreting slices of the plateau into a wide subduction prism as it encountered the E–dipping trench outboard from the Quebradagrande/Arquila belts. Subduction – related magmas intruded inner parts of the prism (Buga Batholith) and adjacent continental margin (eg, Antioquia and other batholiths) from about 100–75Ma. Margarita was situated beyond the northern end of this setting, where a lengthening NE–trending dextral shear zone connected the Colombian trench to the eastern, W–dipping, Caribbean trench. The CCOP followed Margarita and, like Margarita, began to receive Caribbean arc magmas by 89Ma as the Caribbean arc lengthened due to the shear, to include the Aves Ridge, Margarita and the Leeward Antilles (Wright and Wyld, 2010).

The Late Cretaceous Andean setting of plateau subduction/accretion prevailed until Maastrichtian, when Andean

“Laramide” orogenesis was initiated by 1, CCOP buoyancy; 2, acceleration of CCOP orthogonal subduction (Pindell and Kennan, 2009); and 3, westward acceleration of South America across the mantle (Pindell and Tabbutt, 1995). By Middle Eocene, much of Colombia had become subaerial with multi–kilometric uplift and erosion of material from the Colombian hanging wall as it telescoped across the Caribbean Benioff Zone, thereby effecting flat slab subduction. Cenozoic Caribbean arc magmas are limited to Early Paleogene partial melts of downgoing slab in the Santa Marta region (Cardona et al., 2010). Late Eocene reduction of plate convergence allowed deposition to resume in Colombia, but by Oligocene, the Caribbean’s west–facing arc (Panama) began to enter and choke the trench. This, combined with rejuvenated plate compression at 25 Ma, initiated the “Andean” Orogeny that persists today.

Análisis de vulnerabilidad aplicando herramientas SIG en la cuenca del arroyo de la Quebrada de Los Filtros, Jujuy – ArgentinaLlanos VALERA PRIETO1, Susana A. CHALABE2 & Reinhold Siegfried WEIGERT2

1Universidad Nacional de La Plata – UNLP2Universidad Nacional de JujuyPalabras claves: Vulnerabilidad, SIG, Cuencas.

La presente investigación se realizó en el marco de la Maestría en “Manejo Integral de Cuencas Hidrográficas” de la Facultad

de Ciencias Agrarias y Forestales de la Universidad Nacional de La Plata (Argentina), en virtud de una ayuda económica otorgada por la Agencia Española de Cooperación Internacional (AECID). Tiene como objetivo evaluar la vulnerabilidad de una población ante eventos extremos y por ello se seleccionó la cuenca de la Quebrada de Los Filtros, Jujuy, Argentina, que por sus particulares características geológicas, tectónicas y climáticas se distingue por ser un ambiente muy inestable que facilita el desarrollo de procesos geodinámicos intensos; estos producen movimientos de masa entre los que se encuentran deslizamientos, derrumbes y flujos densos que se constituyen en amenazas naturales recurrentes para esta cuenca. Gran parte de la ciudad de Volcán se localiza en este ámbito, situación que ha provocado que en numerosas ocasiones esta se vea inundada por coladas de barro y flujos densos. Los incidentes ocurridos movilizaron a la comunidad quienes plantearon la necesidad de analizar la vulnerabilidad para establecer pautas y protocolos de actuación en caso de que ocurra un desastre. El análisis de la vulnerabilidad implicó realizar un estudio detallado a nivel de parcelas, desagregando la vulnerabilidad en física, ambiental y ecológica, social, política e institucional, educativa, económica, cultural e ideológica y científica y tecnológica. Para la recolección de los datos necesarios que la investigación requería, se combinaron fuentes de información primaria y secundaria aplicando el método inductivo–deductivo a través de la observación directa, la técnica de encuestas y se realizaron entrevistas y cuestionarios. Por otra

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de las curvas de SEV en diferentes condiciones geológicas estudiadas, las cuales pueden ser tomadas como referencia en cualquier proyecto relacionado con la búsqueda de aguas subterráneas.

Interpretación de registros de voladuras por medio de softwares, Boyacá, ColombiaMaría Del Carmen FUENTES FUENTES1

1 Universidad Pedagógica y Tecnológica de Colombia – UPTC

Palabras claves: Geofísica, Voladuras, Geociencias, acelerógrafos, INGEOFISICA

El control de vibraciones implica la medición de estas perturbaciones en una voladura de producción. Si el

nivel de vibraciones registrado fuera menor que el criterio de prevención, podrá incrementarse progresivamente la carga operante hasta que las intensidades de vibración fueran iguales al valor máximo admisible, de tal forma que los análisis realizados en éste articulo sirvan como estudios preliminares para establecer una tabla patrón de cargas máximas por microretardo contra la distancia a las estructuras a proteger en función de la velocidad ó aceleración de la partícula.

Investigación geofísica compleja, análisis geoestadístico y modelación 3D, con métodos eléctricos y nucleares en Macanal y Chinavita, Boyacá, ColombiaFreddy Alexander FONSECA BENÍTEZ1

1 Universidad Pedagógica y Tecnológica de Colombia – UPTC

Palabras claves: Geofísica, Geoélectrica y radiometría, Geociencias, acelerógrafos, INGEOFISICA.

La implementación de los métodos geofísicos en el departamento de Boyacá es vital en la realización de proyectos que nos permitan evaluar geológico–geofísicamente las formaciones geológicas y específicamente las unidades litologías presentes en ellas. A continuación se presenta el marco geológico de la zona de estudio en la cual se realizo la exploración geofísica así como los fundamentos físico – geológicos, la metodología de los trabajos de campo y los resultados obtenidos a partir de la implementación de métodos eléctricos y el método de radiometría. De igual forma se realizo un análisis geoestadístico de los datos y comparación entre poblaciones por medio de histogramas de frecuencias de los parámetros físicos medidos.

Evolución cenozoica de la subcuenca de Plato, Valle Inferior del Magdalena, ColombiaLorena SUÁREZ BERMÚDEZ1 & Crelia PADRÓN DE CARRILLO2

1 Pacific Rubiales Energy2 Universidad Simón Bolívar

Palabras claves: Subcuenca de Plato, Interpretación Sísmica, Gravimetría.

A través de la interpretación de un transecto sísmico regional y varias líneas auxiliares y la correlación con

información de registros de pozo y bioestratigrafía, se propone un modelo tectonoestratigráfico en la subcuenca de Plato, en el Valle Inferior del Magdalena. Se identificaron las principales discordancias estratigráficas y se definieron cinco unidades tectonoestratigráficas que registran la evolución de la subcuenca desde su activación como cuenca transtensional en el Oligoceno hasta el Reciente. Las unidades U1 y U2 se depositaron en el Oligoceno al Mioceno Temprano durante una etapa de transtensión y colapso tectónico asociado a la colisión oblicua entre las placas Caribe y Suramérica. La unidad U1 constituye la secuencia basal transgresiva, principal roca reservorio en la cuenca y probable roca generadora. Las unidades U3 y U4 corresponden a una fase de subsidencia pronunciada durante el Mioceno medio – tardío. La unidad U5 se deposita durante el pulso más pronunciado de la orogenia Andina en el Plioceno, etapa en la que se interpreta un basculamiento de la cuenca e inversión del principal depocentro. Se establece una correlación entre la interpretación sísmica y gravimétrica mediante la integración de ambos métodos geofísicos, confirmándose de esta manera conceptos geológicos en el área de estudio. En el mapa de Anomalía Residual se delinean rasgos tectónicos como los altos El Difícil, Cicuco, Apure, Ayhombe y la Plataforma de Chimichagua, las depresiones de Plato, Sucre y Bálsamo, así como el Sistema Romeral. En la subcuenca de Plato se revelan dos depocentros bien definidos separados por un alto de basamento. El modelo gravimétrico confirma la presencia de un basamento de afinidad continental en la subcuenca, presentando una densidad de 2,67 g/cm3. El espesor de la corteza disminuye de noreste a suroeste de 29 km a 22 km, resultado que concuerda con estudios corticales realizados en la región

Geochemical and geochronological tests for the Caribbean tectonic setting of early Paleocene partial melting in the Sierra Nevada de Santa Marta (Colombia)Jakeline VANEGAS ARROYAVE1, Agustín CARDONA2, José Fernando DUQUE TRUJILLO3, Antonio GARCÍA CASCO4, Víctor VALENCIA5, Jeff VERVOORT5, Samuel JARAMILLO2 & Marion WEBER1

1 Universidad Nacional de Colombia, Sede Medellín2 Smithsonian Tropical Research Institute – STRI3 Universidad Autónoma de México – UNAM4 Universidad de Granada5 Washington State University Palabras claves: Partial melting, Caribbean, geochemical modelling, tectonics.

Recent geochronological and geochemical constraints from plutonic rocks in the northwestern segment of the

Sierra Nevada de Santa Marta have reveal the existing of two

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highly contrasting magmatic suites (Duque, 2010; Cardona et al., 2011). The older magmatism (ca. 63–65 Ma) includes micaceous granites and dykes which are spatially associated with amphibolitic rocks. This magmatism is temporally unrelated with a broader and apparently more standard tonalite to granodiorite arc plutonism formed between 58–50 Ma. Geochemical characteristics from the older granites includes low Y and HREE that reseambles both high silica adakites and TTG and have been interpret to the melt of basaltic rocks. To model the origin of this magmatism and its tectonic context additional field work on the granitic rocks and the associated amphibolites, geochemical modelling and geochronological constrains from the Cretaceous metamorphic rock of Santa Marta are in progress. Field relations near Playa Salguero (near the town of Santa Marta) highly interspersed leucratic veins and dikes and more extensively widespread granitic bodies that intrude de metamorphic host rocks. This feature suggest that this crustal is probabbly more link to an area of melt accumulation within a migmatitic terrane. Whereas new in published geochemical data from the host metamorphic rocks suggest a basaltic protolith formed in MORB to arc tectonic setting. Preliminary hypothesis for the tectonic setting of this partial melting event preceeding the a shor duration arc setting include: 1) closure a thickening of the accreted intra – oceanic back – arc, 2) slab brek off after arc–continent collision, 3) melting of the upper crust thickened during subduction initiation.

Análisis de la distribución del tamaño de cristales (CSD) en los stocks eocenos del Hatillo (Cordillera Central) y Parashi (Península de La Guajira): Implicaciones petrotectónicasCamilo BUSTAMANTE1, Agustín CARDONA2, Carlos ARCHANJO1 & Camilo MONTES2

1 Univerdidade de Sao Paulo2 Smithsonian Tropical Research Institute – STRIPalabras claves: Crystal Size Distribution, Stock del Hatillo, Stock de Parashi.

Las características texturales de las rocas graníticas están controladas en parte por la competencia entre los procesos

de nucleación y crecimiento. Variaciones en las condiciones fisicoquímicas del magma (contenidos de agua, mezcla de magmas) o modificaciones en el nivel de emplazamiento pueden causar cambios significativos en el tamaño de los cristales y la distribución de los minerales. Los stocks del Hatillo en la Cordillera Central y Parashi en la Península de la Guajira son rocas plutónica de Edad Eocena cuya historia de generación magmática y emplazamiento se encuentran aparentemente relacionada con el reinicio de una nueva subducción que siguió a la colisión entre el arco del Caribe y Suramérica y por lo tanto en términos tectónicos y de generación de magmas representa un escenario propicio a condiciones cambiantes. El stock del Hatillo presenta importantes variaciones en los

tamaños de la biotita: en el sector sureste los cristales son ehuedrales a subhedrales con textura poikilitica y alcanzan hasta 1 cm. En el noroccidente el tamaño de grano alcanza hasta 0,5 cm. El Stock de Parashi se caracteriza por presentar una masa granodiorítica principal cortada por abundantes diques de andesita y dacita porfirítica. Las edades de cristalización definidad por el método U–Pb en ambas litologías son relativamente próximas entre sí, sobreponiéndose en error y por lo tanto sugiriendo que las variaciones texturales son parte de un proceso magmático continuo. Las variaciones en el tamaños de los cristales observadas en estos dos cuerpos sugiere claramente la existencia de una inestabilidad en la historia de cristalización de los magmas. Estas variaciones podrían estar relacionadas con el crecimiento y cristalización de estos cuerpos en un ambiente de tectónica activa donde existiría una exhumación contemporánea con la cristalización, así como niveles de exposición variables (caso Hatillo), o simplemente reflejarían variaciones en los contenidos de agua en el sistema.

Middle Miocene volcanism within the south Caribbean deformed belt in northern Colombia: Petrotectonic implicationsMario Enrique LARA OCAMPO1, Agustín CARDONA2,3, Víctor VALENCIA4, Marion WEBER5, John CERON6, Felipe DE LA PARRA7, Diana ESPITIA7 & Margarita MARTÍNEZ8

1 Universidad Nacional de Colombia 2 Smithsonian Tropical Research Institute – STRI3 Corporación Geológica Ares4 Washington State University, Pullman5 Universidad Nacional de Colombia, sede Medellín7 ECOPETROL S.A.6 Instituto Colombiano del Petróleo8 CICESE; MéxicoPalabras claves: Slab roll back, Volcanism, South Caribbean deformed belt.

New field, petrological, geochemical and Ar–Ar geochronological results reveals the existence of a

Middle Miocene basaltic volcanism within the Oligo–Pliocene continuation of the South Caribbean deformed belt in onshore Colombia (Sinu belt after Duque–Caro, 1984). Geochemical characteristics of this volcanism including LILE enrichment and Nb and Ti negative anomalies suggest that this magmatism was formed by the melting of a subduction modified mantle, formed by relatively shallow melting as suggested by their 1.1 to 1.3 Ce/Y ratios (Mantle & Collins, 2008). Available geophysical models and geodetic constraints from the northern margin of South America have shown the existence of a flat slab subduction configuration and slow plate convergence relations (van der Hilst & Mann, 1994; Toto & Kellogg, 1992, Weber et al., 2001). We suggest that this volcanism formed within a commonly considered amagmatic margin is link to a slab roll back event formed as the upper plate (Northern Anden

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block) accelerates to the northwest due to the Panama–South America plate convergence.

Procedencia de las formaciones neógenas Pavo y Arenas Monas, Cuenca de Urabá, Caribe colombiano: Relación con la colisión del Bloque Chocó – PanamáSandra Catalina MÉNDEZ ESPINOSA1, Pedro PATARROYO GAMMA2, Agustín CARDONA3, Camilo MONTES4, Juan Manuel MORENO MURILLO2 & Pedro Pablo VILLEGAS5

1 Centro de investigación GMAS Ltda. 2 Universidad Nacional de Colombia, Sede Bogotá3 Instituto Smithsoniano de Investigaciones Tropicales –

STRI4 Corporación Geológica ARES5 CORPOURABÁPalabras claves: Neógeno, Análisis de procedencia, Sutura Uramita, Apartadó, Urabá.

En zonas de colisión y acreción de terrenos, la edad de las suturas y los niveles corticales asociados a la colisión

están comúnmente registrados en las secuencias sedimentarias que se depositan sobre la sutura y los bloques suturados. En el Urabá Antioqueño, a lo largo de los ríos Apartadó y la quebrada Cuchillo se encuentran expuestas las formaciones Pavo de edad Mioceno Inferior a Medio y Arenas Monas de edad Mioceno Superior a Plioceno Superior. Estas unidades sedimentarias se depositaron sobre la sutura entre el arco intraoceánico Chocó – Panamá (BCP) y los Andes del Norte. La Formación Pavo incluye areniscas subangulares, composicionalmente corresponde a arcosas líticas, litoarenitas feldespáticas y litoarenitas con importantes porcentajes de cuarz con 27,6% – 49,5 %. Los feldespatos más abundantes son los potásicos, generalmente están sericitizados y es más evidente cuando la roca presenta matriz arcillosa. Las plagioclasas son de composición cálcica. Los fragmentos líticos más abundantes son los sedimentarios que incluyen chert y en menor proporción de cuarzoareniscas y lodolitas laminadas. Los fragmentos volcánicos son principalmente de tipo andesítico, consisten en cristales de plagioclasa embebidos en una matriz vítrea. En menor proporción se presentan fragmentos de esquistos y filitas. La Formación Arenas Monas incluye litoarenitas volcánicas con cuarzo y fragmentos líticos. Estos últimos incluyen material tobaceo con textura de tipo shard, además lodolitas y cuarzoareniscas. Las inmadurez composicional y textural marcada por la presencia de feldespatos y líticos altamente inestables (material volcánico), así como por el carácter angular sugiere que las fuentes de aporte son relativamente proximales y estarían relacionadas a la erosión de un terreno volcano–plutónico y sedimentario. Este bloque aportante podría corresponder al Complejo Santa Cecilia–La Equis y el Batolito de Mande que constituyen el armazón del BCP, mientras que el abundante aporte sedimentario estaría relacionado con el Grupo Cañasgordas asociado a la Cordillera Occidental. La presencia de líticos metamórficos

esquistosos estaría asociado con el material derivado de la Cordillera Central o al retrabajemiento de este mismo material en secuencias sedimentarias más antiguas depositadas sobre la Cordillera Occidental. Estos resultados sugieren que para el Mioceno Inferior a Medio la colisión entre del BCP y la margen continental de Suramérica ya estaría en proceso, lo que indica un carácter más temprana para este evento (Farris et al., 2009, Montes et al., 2010) que contrasta con la edad Miocena Superior–Pliocena previamente sugerida con datos paleontológicos (Duque Caro et al., 1990). Adicionalmente la presencia de feldespatos y plagioclasa sugiere que el BCP habría experimentado una exhumación significativa hasta exponer niveles corticales superiores a medios del arco volcánico. REFERENCIAS Farris, D., Cardona, A., Montes, C., Jaramillo, C., 2009. Demise of arc magmatism along the Panama Canal. Geological Society of America, Annual meeting. Paper 79–1 Montes, C., Cardona, A., Bayona, G., Silva, C., Farris, D., Moron, S., Wilson, J., Valencia, V., 2009. Structural transects across the isthmus of Panama: Orocline or subduction–related. Geological Society of America, Annual meeting. Paper 79–2 Duque–Caro et al., 1990. Neogene stratigraphy, paleoceanography and paleobiogeography in northwest Sout america and the evolution of the Panama Seaway., vol 77, p 203–234

Mapeamento de cursos d’água do parque Fernão Dias, Contagem, MGMargarete PEREIRA1, Madrith STHEL COSTA DUARTE1, Adriel ANDRADE PALHARES1, Alexandre OLIVEIRA1, Marcus Gustavo DELLA LUCIA1, Thiago MONTALVÃO1, Tawan LACRISIO1 & Arthur BARBOSA DE PAULA1 1 Centro Universitario UnaPalabras claves: mapeamento, qualidade de águas, parque Fernão Dias.

O Parque Fernão Dias, localizado na divisa dos municípios de Contagem e Betim possui uma considerável área de

vegetação com várias nascentes. Trata–se de uma área de 1,2 milhão de metros quadrados, coberta por vegetação nativa secundária caracterizada como floresta estacional semidecidual com vestígios de um antigo plantio de eucaliptus.sp com mais de 30 anos de idade com sub–bosque nativo e espécies invasoras. Não existe nenhum estudo sobre a área e visto a importância ambiental que esta representa, objetivou–se neste trabalho, a localização mapeamento e verificação da qualidade da água de algumas nascentes do parque. O presente trabalho foi realizado como atividade complementar na disciplina Projeto Aplicado Qualidadade de Águas do Centro Universitário Una. Inicialmente, foi realizado um modelo produzido com mapas topográficos 1:25 000 e posterior sobreposição das curvas de nível a imagens da vegetação obtidas pelo Google Earth e em ortofoto do ano de 1982. O modelo foi testado em campo, alguns dos cursos d’água não encontrados foram retirados. Forma realizados ainda análise de amostras de água para análise de