Figure 3.11a Development of stresses in 12,500 km plate, using successive triangular sections.

down-going slab, results in a quite significant change in sign (i.e. from compression to extension and possibly back to compression) as well as in the rate of strain.

In the 'flat-lying' portion of the oceanic lithosphere, variations in strain-rates may be induced as the result of vertical loading caused by basaltic extrusions. The importance of the flexure brought about by such loading will be related to the periphery of the intrusion, so that even in the W Pacific, where large and small oceanic flood basalts abound, anomalous strain-rates will be experienced in only a small percentage of the total area of the oceanic plate.

As regards mature oceanic lithospheres (i.e. those that have attained a depth of about 100 km) the maximum potential stress is constant at about 16.5 kb, so it can be inferred that the strain-rate will be related to the length of the 'horizontal' oceanic lithosphere, and hence to the average rate of absolute plate motion.

As may be inferred from Figure 3.11a, the rate at which the potential horizontal stress develops, decreases with distance from the spreading-ridge. However, for all parts of flatlying, mature oceanic lithospheres, the range of strain-rates is unlikely to exceed an order of magnitude. Hence, as may be inferred from Bodine et al. (1981), the change of magnitude of the potential, maximum horizontal stress owing to this factor is not likely to be large.

Was this article helpful?

0 0

Post a comment