Analogue modelling study reveals how detachment layer viscosity and backstop position govern structural vergence in fold-and-thrust belts, explaining anomalous landward-vergent wedges.
Key Points
To investigate the influence of basal detachment viscosity and backstop configuration on along-strike structural vergence variations and anomalous landward thrust wedges in fold-and-thrust belts.
Conducted physical analogue experiments using six different configurations varying basal layer viscosities and piston backstop positions.
Evaluated brittle-ductile shear stress ratios, fault angles, and fold geometries to reproduce structural features observed in the Cascadia margin and Eastern Sichuan Basin.
Low detachment layer viscosity and reduced basal friction produced wider deformation zones characterized by low-amplitude folds and low-angle faults.
The shear stress ratio between brittle and ductile layers governed transitions between symmetrical pop-up structures and forward or backward thrust faults.
Pure backward thrusting observed in Cascadia wedges was driven by low detachment viscosity, while Sichuan Basin along-strike vergence variations were controlled by basal detachment weakness and differential shear stress.