Penecontemporary tectonic forms in basement areas: evidence derived from quarry exposures on northwestern Eyre Peninsula, South Australia

Abstract

Monitoring of quarry exposures on northwestern Eyre Peninsula, South Australia has shown that the granite domes of that region are structurally complex features, commonly with several structural domes within each topographic form. The rock masses are in horizontal compression so that few steeply inclined fractures have been penetrated by water and hence are not weathered, though sheet fractures, which are tectonic features, are arched, dilated, and thus readily infiltrated by water. Neotectonic forms, such as fault scarps, A-tents, or pop-ups, and disturbed blocks are still developing. These observations provide further evidence of neotectonism, even in cratonic lands.

Lineage As a Factor in Landscape Analysis

“…Each major block defined by orthogonal fractures and affected by subsurface weathering has become a bornhardt, though many granitic bornhardts comprise several minor structural domes (Twidale and Bourne, 2003;Bourne and Twidale, 2005). They may also have given rise to sheet fractures, which are arcuate subhorizontal partings.…”

Active dislocations in granitic terrains of the Gawler and Yilgarn cratons, Australia, and some implications

“…One large, and innumerable small, A-tents (the latter involving thin flakes of rock) formed on Minnipa Hill during the January 1999 tremor and another, with the crestal fracture oriented 140º and associated with further dislocation along low-angle reverse faults, formed between mid 1999 and mid 2001 (Twidale and Bourne, 2000;Bourne and Twidale, 2003). A blister, or arched slab lacking a crestal fracture, developed in the floor of the larger quarry excavated in the northeastern flank of the dome.…”