Thrust Kinematics Of The Tangara/Mundo Nuevo Area: New Insight From Apatite Fission Track Analysis

Tangara & Mundo Nuevo blocks are located in the Llanos Foothills northeast of Bogota which are mainly structured by thrust related folds. New seismic, new structural field data, and new burial computation allowed us to revise the tectono-sedimentary history of the area and to propose a new sequential deformation modeling based on balanced cross sections. Burial history of the area has been interpreted using new AFTA and new maturity data. Thicknesses of Carbonera and Guayabo Fms computed as well as measured in seismic and wells show significant E-W variations. Seismic evidences of progressive unconformities within the Carbonera Fm. underline a Pre-Guayabo structuration. This pre Midddle-Miocene deformation stage could have controlled the formation of a slightly folded belt involving Cretaceous and younger series and probably linked with an early inversion of the Lower Cretaceous rift basin. Guayabo foreland basin system appears to have been controlled by an active thrust wedge represented by the internal structures now outcropping in the Mundo Nuevo block which are consistent with a minor burial (<300 m) below the molasse sequence. Thicknesses of Guayabo Fm. (2400-1700 m.) computed in Tangara block indicate a more distal foreland environment but remain lesser that the Guayabo Fm. thickness measured in the present day Llanos foreland (3100m) which is completely overthrusted by the external fault. Because of lack of high resolution ages within the Guayabo Fm., we used the sedimentation rate to propose that this significant difference of burial indicates that the external structures were also active before the Pleistocene.