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CU-Boulder GEOL 5700 - Tectonic Assembly of the Northern Andean Block

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Tectonic Assembly of theNorthern Andean BlockFabio CedielGeotec Ltda., Bogota´, ColombiaRobert P. ShawGeotec Ltda., Bogota´, ColombiaCarlos Ca´ceresGeotec Ltda., Bogota´, ColombiaABSTRACTBased primarily on geologic field observations as recorded by numerousgeoscientists over the last three decades, backed by more recent geo-chemical, seismic, gravity, magnetic, tomographic, and satellite-basedtechniques, an integrated synthesis and interpretation of the tectonic assembly ofthe entire Northern Andean Block (the Andes of Ecuador, Colombia, and Ven-ezuela) is presented. Tectonic reconstruction is based on the identification andcharacterization of more than 30 distinct lithotectonic and morphostructuralunits (including terranes, terrane assemblages, physiographic domains, etc.) andtheir bounding suture and fault systems, which, based on geologic, geophysical,and dynamo-tectonic considerations, define four distinct tectonic realmsrepresenting the entire Northern Andean region. These include the GuianaShield Realm (GSR), the Maracaibo subplate Realm (MSP), the Central Continentalsubplate Realm (CCSP), and the Western Tectonic Realm (WTR). The GSR pro-vided the backstop for the progressive, accretionary continental growth ofnorthwestern South America in the middle–late Proterozoic, in the middlePaleozoic, and finally during the Mesozoic-Cenozoic Northern Andean orogeny.Middle Cretaceous through Miocene time slices illustrate how, beginning in theAptian, the sequential dextral-oblique accretion of the allochthonous oceanicWTR along the Pacific margin acted simultaneously with the northwestmigration of the MSP (a detached segment of the Guiana Shield) into and overthe Caribbean plate, exerting enormous transpression upon the CCSP trappedbetween them. Each tectonic realm contributed distinct tectonic mechanismsduring Northern Andean ‘‘cause and response’’ orogenesis, and each realm re-cords a unique internal deformational style, which in large part provides the basisfor realm definition. Additionally, based on lithologic, geochemical, and pa-leomagnetic data and paleogeographic reconstructions, the intimate andcomplementary Mesozoic-Cenozoic history of the Northern Andean Block andthe Caribbean plate are recognized. The migratory path of the Caribbean plate37Cediel, F., R. P. Shaw, and C. Ca´ceres, 2003, Tectonic assembly of theNorthern Andean Block, in C. Bartolini, R. T. Buffler, and J. Blickwede,eds., The Circum-Gulf of Mexico and the Caribbean: Hydrocarbonhabitats, basin formation, and plate tectonics: AAPG Memoir 79,p. 815 – 848.815HOMECONTENTSSEARCHalong the western and northern margin of the South American craton, as recordedby the accretionary history of the allochthonous WTR, has been instrumental inthe modern-day configuration of the Northern Andean Block.Throughout this paper, the importance and contribution of underlyingProterozoic through middle Mesozoic geostructural elements in the developmentof Mesozoic-Cenozoic Northern Andean orogeny-phase tectonic configuration(structural style, uplift mechanisms, basin development, magmatism, etc.) arestressed. Additionally, the complex reality of Northern Andean Block assembly iscontrasted with ‘‘classical’’ Central Andean ‘‘Cordilleran-type’’ orogenic models,and numerous differences are illustrated that render the application of typicalCordilleran-type models unacceptable. These differences are exemplified by thehighly oblique collision/accretion/subduction tectonics of allochthonous oce-anic terranes in the WTR, the detachment, migration and plis de fond–style ofdeformation in the MSP and the unique, transpressive pop-up of the EasternCordillera in the CCSP, all of which have no geologic analog in the Central Andes.INTRODUCTIONThe present-day tectonic mosaic occupying thenorthwestern corner of South America is dominatedby three principal lithospheric plates: the Pacific(Nazca) and Caribbean plates of oceanic affinity, andthe South American plate, cored in this region by thecontinental Guiana Shield, and including the North-ern Andean Block (Figure 1). In this domain, variousauthors (e.g., Gansser, 1973a, b; Shagam, 1975; Mei-jer, 1995) have recognized the Northern AndeanBlock as a distinct geologic segment of the AndeanCordillera, as illustrated by the application of litho-spheric modeling, stress field analyses, and tomo-graphic images (Van der Hilst, 1990; Van der Hilstand Mann, 1994). Regardless, integrated attempts tointerpret the geotectonic history of the entire North-ern Andean Block are temporally and/or regionallyfragmented and have become dated somewhat withrespect to the currently available database (e.g., Gan-sser, 1973a, b; Shagam, 1975; Burke et al., 1984; Fei-ninger, 1987; Aspden et al., 1987).In parallel with recent developments in theunderstanding of the Northern Andes, increasinglyhigh-quality geophysical and geochemical defini-tions of the Caribbean and Pacific oceanic domainshas led to the generation of various models thatattempt to explain the origin and evolution of theCaribbean plate. These models were summarized byMann (1995, figure 13 and p. xxx), who synthesizedthe following (mutually exclusive) ‘‘end-member’’hypotheses for Caribbean plate origin:1) ‘‘The Caribbean oceanic plateau forms by theseparation of North and South America duringthe period 130 to 80 Ma’’, or2) ‘‘The Caribbean oceanic plateau forms as normalPacific oceanic crust, drifts over the GalapagosFigure 1. Tectonic framework of northwestern SouthAmerica. NAB = Northern Andean Block; Car = Caribbeanplate; Nzc = Nazca plate; Coc = Cocos plate; Nam = NorthAmerican plate; Afr = African plate; GS = Guiana Shield;Ec, Col, Ve = geographic limits of Ecuador, Colombia andVenezuela, respectively.816 / Cediel et al.HOMECONTENTSSEARCHhot spot, thickened in the middle to late Cre-taceous, and passes into the gap between Northand South America’’ (see figure 13 of Mann, 1995).Given these proposed models, in conjunctionwith the modern-day tectonic configuration of north-western South America, it is apparent that the North-ern Andes and Caribbean plate must share an inti-mate and complementary geotectonic evolution. Itfollows that integrated analysis of the evolution ofthe Northern Andean Block (the Andes sensu lato ofEcuador, Colombia, and Venezuela) is an indispens-able process in the construction or evaluation of anytectonic model involving the plate mosaic compris-ing northwestern South America


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CU-Boulder GEOL 5700 - Tectonic Assembly of the Northern Andean Block

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