THE STRUCTURAL GEOLOGY OF A SURGE-TYPE GLACIER

The range of deformation structures found in surge-type Variegated Gla cier, Alaska, is similar to that found in many thin-skinned thrust bel ts, and includes foliations, folds, dip-slip and strike-slip faults, t hrust faults and fractures. The development of structural relationship s and the overall structural assemblage can be related to the deformat ion histories of quiescent and surge phases of motion. The surge phase dominates the formation of brittle structures because of the large st resses and strain rates associated with it. The relationship between d ownglacier-verging overturned folds with hinge lines transverse to flo w, and a family of transverse arcuate thrust faults is characteristic of structural development in the lower part of the glacier during the surge. Longitudinal foliation develops mainly from sedimentary stratif ication in the upper part of the glacier in a marginal transpressive d eformation regime during quiescent phase flow from broad accumulation basins. The structural relationships in this surge-type glacier may ai d in the interpretation of structures in other gravity-driven tectonic settings.