ESR studies for absolute dating of fault movements

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Abstract
The principle of absolute dating of fault movements is based on the initialization or resetting of some ‘clock’ system by faulting. In the case of ESR dating, heating is more effective in resetting ESR signals than fracturing. According to a computer simulation of resetting by shear heating during faulting, the ESR signals can never be completely reset at depths of less than 100–200 m below the surface of the earth. Therefore, ESR samples must be collected from depth by coring or tunnelling, or from outcrop, with consideration of the rate of exhumation of the fault outcrop. In general, unpaired electrons trapped at lattice defects in crystals can diffuse much more easily than atoms, hence samples for other dating methods, which are based on the diffusion of atoms, should be collected at even greater depth. On the other hand, if no ESR signal is observed from unfractured quartz in the wall rocks, one may directly determine the age of the fault movement using ESR signals in the fractured quartz whose precursors were formed by faulting. The age obtained ( T ) should then satisfy the following relationship: T b ≥ T ≥ T e , where T b and T e are the ages of the beginning and end of the fault movements, and it may show the time of a fault movement.

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