Page 112 - Handbook of Gold Exploration and Evaluation

92 Handbook of gold exploration and evaluation

2.15 Diagrammatic sketch of a transform fault.

Transform plate margins
Two lithospheric plates in contact with one another along a common boundary
provide conditions for the formation of a transform fault when one plate slides
past the other with no motion that would cause plates to separate or converge.
The plane along which a transform fault (Fig. 2.15) occurs is a nearly vertical
fracture extending down through the entire lithosphere. The transcurrent motion
may consist of two plates sliding past one another or pieces of the same plate
moving at different speeds. They may be moving at different speeds in opposite
directions or in the same direction. The boundaries are sites of intense seismic
activity, with moderate to strong earthquakes. Most transform faults are found in
the ocean basins, but important examples such as the San Andreas Fault in
California and Mexico are found on land. The San Andreas Fault forms the
boundary between the American plate and the Pacific Island plate in California.
A huge rift zone, of which the Great Artesian Basin is now part, was formed
along the eastern edge of Australia some 1,800 million years ago. Eyre
Peninsular, Broken Hill, and Mt Morgan are all typical rift sequences.

2.2.3 Marine and continental volcanic settings
The foregoing sets the stage for examining the types and direction of the forces
responsible for building large folded mountain belts, movement and growth of
continents, global climatic change and the associated processes of metamorphism
and plutonism. Differences in the concepts of orogeny and epeirogeny are
explained as they apply to the evolution of landscapes and large-scale development