The Geology of Colombia Volume 1 Proterozoic - Paleozoic

This work marks a fundamental milestone in the geological knowledge of Colombia. This work is the result of four years of intense work by the editors Jorge GÓMEZ TAPIAS and Daniela MATEUS ZABALA and a small group of collaborators who, through the Servicio Geológico Colombiano, present the work The Geology of Colombia. These four volumes would not have been completed without the firm support of Dr. Oscar PAREDES ZAPATA, who, as director of the Servicio Geológico Colombiano, provided the material and human resources that made this work a success. Previous attempts to compile the vast knowledge of fascinating Colombian geology have been incomplete. The Evolución geológica de Colombia carried out by Jean– François TOUSSAINT between 1993 and 1999 was a great and highly commendable effort by a single author. The partial syntheses made by Fabio CEDIEL and collaborators in 2003 and the most recent version edited by CEDIEL and SHAW (2019) Geology and Tectonics of Northwestern South America were outstanding efforts. The 2006 publication Tectonic Evolution of the Colombian Andes in a special issue of the Journal of South American Earth Sciences, which we edited with Manuel MORENO, was another important intent written almost entirely by Colombian geologists. This work is more significant compared to previous geologic summaries. The present legion of geologists and geophysicists contributed their regional expertise and specialties to thoroughly represent the current geological knowledge of the country. Participation from academia and industry shows that Colombian geology is vigorous and active. The editorial treatment of the chapters and their peer evaluation, the professional presentation of figures and maps, the style corrections, and the final layout of each chapter further enhance the already important scientific value of all the contributions. At times like these, we should remember the observations and work of those who laid the foundations of our present knowledge. As a scholar and observer of the Andes who is located more than 6000 km away, I consider myself privileged to have been able to follow the evolution of that knowledge through the decades. First, I would like to remember Paul GANSSER (1910–2012), who after his successful investigations in the Himalayas, landed in Colombia and performed fundamental studies during the 1930s and 1940s, leaving us his Facts and Theories on the Andes of 1973. In this work, he first divided the Andes based on plate tectonics, a division that is still used by Andean geologists. In the following decade, we participated in a nearly month–long field trip to Antarctica, where we and Paul GANSSER discussed his explanations of the complex structure of the Colombian Andes. These talks were in correct Spanish and full of incredible stories and anecdotes. I also would like to recall the works of Jacques BOURGOIS and collaborators, who unraveled the complex structure of ophiolites in a sector of the Western Cordillera. We shared discussions during several Andean symposia with François MÉGARD, another great promoter of Colombian tectonic evolution with his models of the Mesozoic – Cenozoic island arc accretion by reverse subduction and collision. Another person who introduced me to this fascinating geology was Professor Manuel JULIVERT, who in his visits to Buenos Aires, described the structural geology of the Eastern Cordillera fold belts. His experience was obtained through several years of teaching and research at the Universidad Industrial de Santander and the Universidad Nacional Sede Bogotá between 1957 and 1963. His work on Cover and Basement Tectonics in the Cordillera Oriental of Colombia, South America, and a Comparison with Some Other Folded Chains pre–dated by several years the acceptance of tectonic inversion as a structural style. This group of colleagues, and others, introduced me to exciting Colombian geology. However, the person most responsible for me being here today is Dr. Umberto CORDANI, a great promoter of the geochronology of Colombia and editor of the Tectonic Evolution of South America, on the occasion of the International Geological Congress held in Rio de Janeiro in 2000. CORDANI telephoned me to tell me that he had to send this book to the printer but the Northern Andes chapter was missing; the invited authors had not provided their work. We met with my colleague and friend Antenor ALEMÁN in Houston, and in a few days, we prepared the chapter that awakened my curiosity about the geology of the Colombian Andes. I learned from the pioneering studies of Darío BARRERO to recognize oceanic rocks in the Western Cordillera and about their accretion in the Late Cretaceous. From Alberto FORERO SUÁREZ I learned about the North American affinities of the Eastern Cordilleran basement terrane and the Laurentian influence of the associated Paleozoic basins. While sharing a room at a symposium in Medellín, Hermann DUQUE CARO and I had long conversations about the collision of the Chocó terrane and the determination of its age through precise micropaleontological analyses. Jorge RESTREPO and Jean– François TOUSSAINT taught me the complex accretion history of Colombia during the Magmatic Evolution of the Andes (IGCP–Unesco) symposia, and on a visit to Arizona, I learned about the isotopic interactions between Colombia and southern México blocks from Joaquín RUIZ. These initial encounters showed me the complex problems of Colombian geology, and our new work The Geology of Colombia shows how much our knowledge has increased. Numerous novelties are presented as reviews or original works in different chapters. One example is the precise geochronological determinations of the Putumayo Orogen, which changed our vision of the ancient Orinoquensis Orogeny by showing different ages and orogenic belts on the western margin of the Guiana Shield. Another example is the new ages of the Andean Proterozoic basement, which suggest a complex paleogeographic history. The analysis of Paleozoic terranes and their paleogeographic distribution reaffirms the previously defined limits of these allochthonous blocks. However, new geochronological data allow us to re–evaluate Famatinian tectogenesis. Successive chapters show the dynamics of the Eopaleozoic accretion of Chibcha in the Late Ordovician and its influence on the distribution of Devonian and Neopaleozoic faunas with clear Laurentic affinities. The increasing identification of a Permian magmatic arc in the Central Cordillera deserves to be mentioned since its obliteration by deformation and superimposed metamorphism makes it hard to identify. This destruction prevents an assessment of the vergence of deformation or metamorphism that could associate the magmatic arc with the Alleghanides Orogeny. Later anathectic processes culminated in a Triassic extension, which is widely distributed along the Paleozoic continental proto–margin, with a strong presence in the Central Cordillera. Jurassic evolution shows a complex paleogeography driven by the interaction between different Caribbean and Pacific Plates. The combination of paleomagnetic data, detrital zircon provenance studies, structural analysis, and the evolution of the Jurassic and Early Cretaceous magmatic arcs show different episodes controlled by the subduction kinematics along the Pacific margin. Special mention should be made of the analyses showing the transition from an early Mesozoic extensional subduction regime to a compressive regime. For the first time, this important change is associated with the dynamics of the continental margin. Provenance studies in developed basins, the characteristics of their magmatic arcs, and the associated deformation allow us to explain the distribution of their deposits. New dates, petrological analysis, and geochemical characterization of the accreted ocean terranes on the Pacific margin, highlight the processes that constructed the new margin. The characterization of areas with significant high–pressure metamorphism sheds light on their common characteristics and differences. Studies on the source and provenance of the synorogenic deposits in the Eastern Cordillera and interpretation of their uplift history through fission track analysis allow different chapters to reconstruct the tectonic evolution of this Andean region. Analysis of Pacific margin basins and Caribbean margin Cenozoic belts shows interaction mechanics in the accretionary prisms of the Farallón and Nazca Plates as well as the deformation from the passage of the Caribbean Plate through northern South America. The interaction of the Isthmus of Panamá and the South American continent deserves special attention because it shows connections prior to the collision of the Chocó Block and before the great faunal exchange. Sedimentological studies and assessment of oleogenetic potential of the sedimentary sequences provide essential information to enhance the hydrocarbon value of these basins. Analyses of the Cenozoic volcanic arc and presentation of the active Western and Central Cordilleran volcanic centers show the recent evolution of knowledge and the influence of Caldas Tear on the development. Geophysical and geothermal studies in the northern region of Eastern Cordillera show the hydrothermal processes associated with acidic volcanism and the remnants of the foreland migrated late Cenozoic arc. Analyses of Quaternary sedimentation, neotectonic structures, and the evolution of the tropical biome are presented in an interrelated way, allowing them to be linked to global events that affected the entire continent. A detailed reading of this work demonstrates the rapid advance of geological knowledge in recent years, the dynamic evolution of concepts with the application of new technologies and the degree of specialization obtained in different disciplines. The different presentations through successive chapters show us that old problems and questions have been solved, while the information provided illuminates new unknowns and opens up new challenges. I would like to again congratulate the editors, editorial group, and numerous authors for their effort, which will undoubtedly be a difficult milestone to surpass in the advancement Colombian geologic knowledge. Victor A. RAMOS Buenos Aires, 3 November 2020