Structural analysis of the Tabaco anticline, Cerrejon mine, Northern Colombia (South America)

Abstract

The Tabaco anticline is located in the Cesar-Ranchería basin of northern Colombia, South America, close to the transpressional collision between the Caribbean and South American plates. The anticline is bounded by the Cerrejón thrust to the east, the right lateral strike slip Oca fault to the north, and the left lateral strike slip Ranchería fault to the south. The anticline is asymmetric and verges to the SE, with a NW limb dipping in average 26°W, a SE limb dipping 41°E, and a fold axis 217°/7° (trend and plunge). The fold’s vergence is opposite to that of the Cerrejón thrust. In this thesis, I make a 3D structural model of the Tabaco anticline using a high resolution dataset from the Cerrejón open coal mine in an area of about 10 km2. This 3D model contains 17 coal seams and 67 faults. The thesis is divided in three main parts: Construction of a 3D structural model, fault displacement analysis, and restoration of the anticline. Four different patterns in the contours of fault throw were observed: 1) Low throw in the middle of the fault and high throw in the areas around, 2) Highest throw at one corner of the fault and not in the center, 3) Highest throw in the middle of the fault, and 4) In conjugated faults, highest value of throw at the intersection of the two fault planes. Most of the faults show pattern 3. Patterns 1 and 2 are mostly due to lack of sampling of the entire fault surfaces. Faults show a consistent pattern of slip in the area. 3D restoration of the anticline using a flexural slip technique suggests a total shortening of 18%. Fault-related strain (from the analysis of fault displacement) and fold-related strain (from the restoration of the coal seams) are related, with the highest values of fold-related strain associated with a fault in the core of the anticline, and the faults located in the SW anticlinal limb. Fold-related strains are also high in the SE, steeply dipping anticlinal limb. The results of this study show that the anticline was affected by uplift of the Santa Marta massif, Perijá range deformation, and strike-slip movement of the Oca , Samán and Ranchería faults.