Sarmiento 2006

Journal of South American Earth Sciences 21 (2006) 383–411 www.elsevier.com/locate/jsames

Mesozoic transtensional basin history of the Eastern Cordillera, Colombian Andes: Inferences from tectonic models
L.F. Sarmiento-Rojas
b

a,*

, J.D. Van Wess b, S. Cloetingh

c

a Ecopetrol-Empresa Colombiana de Petroleos, P.O. Box 5938-6813-Bogota, Colombia Netherlands Institute of AppliedGeoscience TNO National Geological Survey, Prins Hendriklaan 105 P.O. Box 80015 3508 TA Utretch, The Netherlands c Tectonics Group, Faculty of Earth Sciences, Free University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands

Received 1 October 2004; accepted 1 March 2006

Abstract Backstripping analysis and forward modeling of 162 stratigraphic columns and wells of the Eastern Cordillera(EC), Llanos, and Magdalena Valley shows the Mesozoic Colombian Basin is marked by five lithosphere stretching pulses. Three stretching events are suggested during the Triassic–Jurassic, but additional biostratigraphical data are needed to identify them precisely. The spatial distribution of lithosphere stretching values suggests that small, narrow (180 km) wide, asymmetrical, transtensionalhalf-rift basin existed, divided by the Santander Floresta horst or high. The location of small mafic intrusions coincides with areas of thin crust (crustal stretching factors >1.4) and maximum stretching of the subcrustal lithosphere. During the Aptian–early Albian, the basin extended toward the south in the Upper Magdalena Valley. Differences between crustal and subcrustal stretching values suggest somelowermost crustal decoupling between the crust and subcrustal lithosphere or that increased thermal thinning affected the mantle lithosphere. Late Cretaceous subsidence was mainly driven by lithospheric cooling, water loading, and horizontal compressional stresses generated by collision of oceanic terranes in western Colombia. Triassic transtensional basins were narrow and increased in width duringthe Triassic and Jurassic. Cretaceous transtensional basins were wider than Triassic–Jurassic basins. During the Mesozoic, the strike-slip component gradually decreased at the expense of the increase of the extensional component, as suggested by paleomagnetic data and lithosphere stretching values. During the Berriasian–Hauterivian, the eastern side of the extensional basin may have ´ developed byreactivation of an older Paleozoic rift system associated with the Guaicaramo fault system. The western side probably developed through reactivation of an earlier normal fault system developed during Triassic–Jurassic transtension. Alternatively, the eastern and western margins of the graben may have developed along older strike-slip faults, which were the boundaries of the accre´ tion ofterranes west of the Guaicaramo fault during the Late Triassic and Jurassic. The increasing width of the graben system likely was the result of progressive tensional reactivation of preexisting upper crustal weakness zones. Lateral changes in Mesozoic sediment thickness suggest the reverse or thrust faults that now define the eastern and western borders of the EC were originally normal faults ´ ´ with astrike-slip component that inverted during the Cenozoic Andean orogeny. Thus, the Guaicaramo, La Salina, Bituima, ´ Magdalena, and Boyaca originally were transtensional faults. Their oblique orientation relative to the Mesozoic magmatic arc of

*

Corresponding author. Tel: +2345657. E-mail address: luis.sarmiento@ecopetrol.com.co (L.F. Sarmiento-Rojas).

0895-9811/$ - see front matter Ó 2006Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2006.07.003

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L.F. Sarmiento-Rojas et al. / Journal of South American Earth Sciences 21 (2006) 383–411

the Central Cordillera may be the result of oblique slip extension during the Cretaceous or inherited from the pre-Mesozoic structural grains. However, not all Mesozoic transtensional faults were inverted. Ó 2006 Elsevier Ltd....