Structural changes caused by dips in lateral ramps of fold and thrust belts

Abstract Transverse zones are tectonic structures parallel or oblique to the shortening direction. Lateral ramps are inherited tectonic structures and are comprised in a transverse zone. During shortening transverse zones are usually confused with simple strike-slip faults. We evaluated 36 analogue models under brittle conditions using two frontal ramps connected by a lateral ramp at different inclinations (30°, 45°, and 60°) to identify lateral ramps characteristics in the fold and thrust belts. The experiments were conducted in a subduction-type sandbox, using dry sand and a rigid block, representing a brittle crust and the backstop. During shortening, faults and folds related grow parallel to frontal ramps. Significative plunges correlate with the inclination of the lateral ramp. The oblique faults dipped along the direction opposite to the lateral ramp, while the normal faults parallel to the lateral ramp only occurred when linked to lateral ramps with high inclinations. The inclination of the lateral ramp controls the plunge and rotation of the folds and thrust structures. Regardless of the lateral ramp inclinations, in map view, the main characteristics used to identify lateral ramps are i) disrupted structures along the strike in the lateral ramp area and ii) oblique faults related to frontal ramp structures.