Tectonic
evolution of the Colombian Andes
Victor
A. Ramos, Manuel Moreno
Journal of South American Earth Sciences
Volume 21, Issue 4, September
2006, Pages 319-321
https://doi.org/10.1016/j.jsames.2006.07.008
Tectonic evolution of the Colombian Andes
This issue represents the major contribution of the Andean Committee of the International Program of the Lithosphere, resulting from selected papers presented at the IX Colombian Geological Congress held in Medellı´n and the VIII Simposio Bolivariano of Petroleum Explora tion in the Subandean Basins held in Cartagena, both in 2003.
These articles were chosen to provide a complete review of the Colombian Andes, including the Precambrian base ment inliers of the Eastern and Central cordilleras and other isolated blocks, such as the Guajira and Sierra Nevada de Santa Marta. The early Mesozoic rift processes, evolution of some Cretaceous oceanic basins, and tectonic inversion of the Andes are discussed in different sections to offer a comprehensive update of the geology of Colombia. The authors of these articles are Colombian natives, which demonstrates the advances in knowledge of the geology of Colombia and recent research, rarely reflected in current international literature in the earth sciences. The Garzo´n Massif, one of the most prominent pieces of the Eastern Cordillera basement (Fig. 1), is examined with petrological and geochronological data by Jime´nez Mejı´a and colleagues, who establish a clockwise, nearly isother mal decompression path for the Las Margaritas migma tites. These processes took place between 1148 and 1000 Ma and provide new insights into the complex Mesoproterozoic orogen associated with the Grenville orogeny that assembled the Rodinia supercontinent. The Guajira and Sierra Nevada de Santa Marta base ments (Fig. 1) are analyzed with new U–Pb SHRIMP, Ar–Ar, and Sm–Nd geochronology by Cardona Molina and colleagues. These basement blocks, now dispersed by Cenozoic displacement, record a common Grenvillian history with other pieces of the Colombian basement. However, their complex evolution, in addition to their affiliation with Rodinia in Grenville times, includes impor tant metamorphism related to the late Paleozoic assembly of Pangea. Thermal effects related to Jurassic igneous activity, as well as Ar–Ar ages associated with deformation during Cenozoic times, reflect the multifaceted evolution of these regions of Colombia. 0895-9811/$- see front matter 2006 Published by Elsevier Ltd. The basement of the Central Cordillera (Fig. 1) is inves tigated by Vinasco and colleagues, who present new U–Pb SHRIMP ages in zircons, Ar–Ar ages in micas and amphi bole, Nd-Sr isotopes, and REE geochemical analyses. They envisage the collisional orogen produced by the docking of several blocks together with Laurentia against this margin of Gondwana by the end of the Paleozoic, which built the Pangea supercontinent. A metamorphic age of 280 Ma is proposed for the main episode of collision, and an age of approximately 228 Ma is associated with the collapse of Pangea and the beginning of the supercontinent break up at these latitudes. The pre-Devonian history of Colombia is reviewed by Ordon˜ez and colleagues, who integrate the previously described basements blocks with other pieces of the Central and Eastern cordilleras, Serranı´a de Perija´, and Santander Massif. A comprehensive tectonic evolution of the Precambrian and early Paleozoic basement offers a common history for the basement of Colombia. The rift history of Colombia is presented by Sarmiento Rojas and colleagues, who integrate data from more than 160 stratigraphic columns and wells (Fig. 1) through high-resolution backstripping and forward modeling. These techniques show a many-sided rift history for the Eastern Cordillera that includes five pulses of extension from Triassic to Early Cretaceous times. Some of these normal faults have not been reactivated through Andean contraction, as the present basement shortcut blocks, which transported these faults passively during the Ceno zoic deformation, show. The Bucaramanga fault termination exhibits the deep structure of two Early Jurassic rift depocenters in the northern sector of the Eastern Cordillera (Fig. 1). The re search performed by Kammer and Sa´nchez shows the wedge geometry of these synrift deposits and depositional history of the two subbasins. The reconstruction of these rifts provides new constraints on the kinematics of the Bucaramanga fault. Volcanic and sedimentary sequences with oceanic affin ities exposed along the western margin of the Central Cordillera (Fig. 1) were studied by Nivia and colleagues. The petrological analyses of these rocks, together with doi:10.1016/j.jsames.2006.07.008 320 Editorial / Journal of South American Earth Sciences 21 (2006) 319–321 Fig. 1. Location map with indication of the authors of the different contributions. Base map after Ordon˜ez et al. (2005). the geochemical characteristics of Quebradagrande Com plex, indicate the existence of a calcalkaline magmatic arc and an ensialic to quasi-oceanic backarc basin during the Early Cretaceous. These mafic rocks differ from the Late Cretaceous oceanic plateau preserved in the Western Cordillera and thereby suggest a different setting for these rocks. The Andean structure of the Eastern Cordillera is ana lyzed in the study by Corte´s and colleagues (Fig. 1) on the basis of field data, reflection seismic sections, and bio stratigraphic controls. They construct a series of structural ly balanced cross-sections that indicate two different structural styles. A positive flower structure is recognized on the western flank of the Eastern Cordillera for rocks Editorial / Journal of South American Earth Sciences 21 (2006) 319–321 321 older than Eocene, and a more orthogonal compressional structure appears for the Miocene to recent deformation. The model implies a total shortening of 70 km for the East ern Cordillera. The analysis of the Albian–Santonian interval, corre sponding to the Villeta Group, enables the documentation of an important regional unconformity by Jaimes and Fre itas in the Upper Magdalena Valley and the Eastern Cor dillera of Colombia (Fig. 1). On the basis of a large database of 2D/3D seismic, well, surface geology, and bio stratigraphic data, they constrain the unconformity to the Albian–Cenomanian. This unconformity is regionally cor related with unconformities known in other areas of Colombia and Peru. According to the authors, it relates to the opening of the south Atlantic Ocean at equatorial latitudes. The unconformity provides new insights into the understanding of the petroleum system of the Upper Magdalena Valley. The structure of the Girardot Basin in the Upper Mag dalena Valley is analyzed by Ramon and Rosero, using structural sections and seismic data. Field photos display singular breaks and unconformities in the sequence, as a result of multiphase deformation of the Central and Eastern cordilleras. In the last article, Martı´nez presents a novel description of the eastern foothills of the Eastern Cordillera with a sys tematic classification of the different structures developed along the western border of Los Llanos Basin. This review of the different structural styles proposed for the foothills culminates with an interpretation of new seismic data that offers a better understanding of the complex structures. The structural setting of important oil fields found in the Piedemonte Llanero is scrutinized, with an analysis of the tectonic evolution of the foothills. These articles present a complete review of the Colombi an Andes, including the basement history, rift controls on the Andean evolution, and the structure of the intermoun tain basins and foothills. These papers represent an impor tant step for understanding the complex evolution of the Northern Andes of South America.
We are indebted to the following reviewers : R.D. Mar tino, J.E. Otamendi, P. Alvarez, R. Seggiaro, T. Zapata, F. Bettini, O. Lo´pez-Gamundı´, J. Franzese, G. Vujovich, I. Petrinovic, R. Pankhurst, J.A. Dahlquist, M. Lo´pez de Lu chi, A. Steenken, and E. Cristallini. We thank all the authors who presented their unpublished work in the two meetings, which helped make this issue an important con tribution of the Andean Committee of the International Program of the Lithosphere. Victor A. Ramos * Universidad de Buenos Aires, Laboratorio de Tecto´nica Andina, Argentina Manuel Moreno Universidad Nacional de Colombia, Bogota´, Colombia
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