CATACLASTIC FLOW DURING DEFORMATION IN A FOLD-THRUST BELT

Cataclastic flow (CF) can be broadly defined as a deformation in which fracturing forms clasts that frictionally slide past each other and possibly rotate, resulting in a ductile deformation within the elastico-frictional (EF) regime. In detail there are two distinct types of CF, both of which occur over a wide range of scales and often develop a co-dependent relationship across different scales.

Type 1 CF typically forms within discrete zones, such as fault zones. Larger clasts are supported within a matrix of smaller fragments. The clasts progressively decrease in size as cataclasis continues and a foliation may develop in the matrix. The grain size of the larger clasts primarily controls the activity/inactivity and growth of these cataclasite zones.

Type 2 CF is not matrix supported and is typically a more distributed deformation. The clasts are bound by a stable network of fractures and deformation zones (DZs). The deformation involves collective movement on a population of fractures and DZs. Clast solid body rotation is very limited. The shape and position of the clasts, rather than clast size, controls the activity/inactivity and size of the area deforming by cataclastic flow. As deformation continues, the clasts begin to define a fabric, similar to a foliation.

The Canyon Range syncline, central Utah, Sevier orogenic belt, underwent fold tightening within he EF regime. Several generations of fracture populations and DZs developed from the micro- to the outcrop-scale to accommodate fold tightening. A cooperative relationship exists between the two types of cataclastic flow at two distinct scales: matrix supported at the micro-scale and clast supported at the outcrop-scale. The collective character of the fracture and DZ networks at all scales allows for an overall ductile deformation at the largest scale.