Buckle folding in accretionary wedges: an example from the Tripura-Mizoram fold belt of NE India
Abstract
Tripura Mizoram fold belt (TMFB) belongs to the outer wedge of the Indo-Burma wedge (IBW), resulting from the accretion of a thick pile of Neogene sediments lying over the subducting Indian Plate foundering below the Burmese Plate in the east. TMFB covers an east-west stretch of around 270 km width (along 23.5 N latitude), lying over a decollement at shallow crustal depth (3.5 - 4 km). The Tripura Mizoram fold belt shows the development of a series of N-S trending anticlines-synclines with varying tightness both along and across the strike. Based on a popular concept of accretionary wedge growth, several studies have invoked the dominance of brittle faulting for explaining the evolution of anticlines-synclines in the entire TMFB. However, deformation in the mechanically stratified layers of Neogene sediments provides evidence of distributed ductile deformation by forming a series of N-S trending buckle folds in response to east-west India-Burma convergence. The general strike of the N-S trending upright folds in outcrops mimics the strike of map scale anticlinal ridges, implying the influence of ductile deformation in the overall structures of TMFB. In addition, our field investigation reveals inference of two different fold geometries, giving rise to hook-shaped fold (Type 3 of Ramsay) and development of pressure solution cleavages. Our present study provides a detailed analysis of the evolution of the first-order structure of the outer wedge of IBW. We show that the style of folding becomes progressively complex towards the hinterland direction of the wedge. The complexity of the fold structure is defined by the development of different geometries of folds, including refolding of earlier structures. In contrast, simple symmetric anticlines and synclines characterize the frontal part of the wedge. However, different geometries of folds towards the hinterland show uniform orientation of folds axes, implying pure shear deformation. Based on field investigations in TMFB and available tectonic profiles across the IBW, we interpret that the weak Neogene sediments of the outer wedge have played a crucial role in shifting the decollement lying at a greater depth below the inner wedge to localize at a shallow crustal depth below the outer wedge of IBW.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.T55C0088D