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

Miguel Ángel Orjuela,Giovanny Jiménez,Dilan Arturo Martínez-Sánchez

doi:10.18273/revbol.v43n2-2021002

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.

Highlights

Methods and assumptionsTransverse zones comprise tectonic structures parallel or oblique to the shortening trend (Butler, 1982); they are located transversely to the fold and thrust belt and connect strike-parallel frontal ramps
Once the shortening reached 5 cm, the first thrust fault in each frontal ramp and several related back-thrust faults were generated, which led to the formation of pop-up structures and anticlines parallel to the frontal ramps
With an increase in the shortening, new back-thrust faults were generated in each frontal ramp, following a direction opposite to that of motion; the first thrust fault became convex (Figures 3C-2E)

Summary

Introduction

Methods and assumptionsTransverse zones comprise tectonic structures parallel or oblique to the shortening trend (Butler, 1982); they are located transversely to the fold and thrust belt and connect strike-parallel frontal ramps. Transverse zones include lateral ramps, transverse faults, and transfer zones (Thomas, 1990) These zones generate several sets of thrusts, and the extent of shortening of these thrusts is comparable to the displacement of the detachment (Kwon and Mitra, 2006). The origin and evolution of transverse structures include (i) basement faults, (ii) mechanical and stratigraphic differences along the strike, and (iii) a decrease in the displacement along the strike of the primary structure (Dixon and Spratt, 2004; McClay, 1992; Pohn, 2000; Thomas, 1990)

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