Midocean trenches which form arcs of a circle

There are certain arcs which should attract special attention, because they usually satisfy one or more of four attributes (1) they define an almost exact circular arc (2) they are relatively small features, with a radius of 250-625 km (3) subduction takes place at the outward bow of the arc, i.e. the arc points into the direction of plate motion and (4) they usually exhibit 'ocean ocean' lithospheric contact. This latter point is very important for, as may be inferred from our earlier...

The splitting of continents

One may readily infer from the known geology that more than one mechanism must be involved in the break-up of continents. For example, from movement patterns of the San Andreas and associated faults of this plate boundary complex, it can be inferred that slices of continent can be cut away from the main continental unit by means of major strike-slip faults. Similarly, the strike-slip Baykal structure of Central Asia also appears to have the potential to split that continent. The break-up of...

Summary conclusions and inference

Bombardment of the Earth by large meteorites is not a thing of the distant past, to be relegated to the early Archean. There is ample evidence, to be seen on the Moon, that our satellite has an approximately linear accumulation curve of craters over at least the past 2000 Ma. The Earth's atmosphere has guarded our planet against the host of minor events which are so evident on the Moon. The frictional resistance generated by the atmosphere, as small bodies enter at high speeds, consumes...

Info

Elastic shortening of oceanic lithosphere It can be inferred from Figure 3.18a, that the horizontal stresses in a plate will increase in magnitude from the spreading-ridge. For a 7500 km long plate length L , the average value of the nett compressive stress Sh in the direction of movement will be dependent upon the plate velocity. Let us assume that the average nett horizontal differential stress is 3 108 Pa 3 kb . This will give rise to elastic shortening of the plate by a total distance l....

The world stress map WSM

This project is a cooperative effort to compile and interpret data on the orientation and relative magnitudes of in situ tectonic stress in the Earth's lithosphere. Zoback 1992b reports that over 30 scientists from more than 18 different countries have been involved in this project. Doubtless, these numbers have increased since 1992. At that time, over 7300 data points had been compiled. The techniques used to establish the stress orientation and sometimes magnitude of the stress have been...

Conclusions

By using simple models to represent a plate moving in a specific direction for long periods, it may be inferred that such a plate must be pushed, pulled, or moves as the result of both pushing and pulling. Whether the dominant force, or pressure, results from pushing or pulling, it should give rise to a dominant strain and, therefore, a dominant stress pattern within the plate. If the dominant force is one generated by some pulling mechanism, the least horizontal stress S3 should generally be...

Clew

South 46 46 Figure 6.3 Generalised geological cross-section through Rattlesnake Hills and Horse Heaven Hills in the central Columbia Plateau after Reidel et al., 1989 . South 46 46 Figure 6.3 Generalised geological cross-section through Rattlesnake Hills and Horse Heaven Hills in the central Columbia Plateau after Reidel et al., 1989 . can be found related to the plateau basalts to which White and McKenzie 1989 applied their model, Anderson et al. suggest, renders their application to the...

Conventional development of arcuate oceanic trenches

It is now understood that oceanic lithosphere may eventually become subducted at a trench, and that a belt of volcanoes forms above the site where the subducted oceanic plate reaches a depth of about 150 km Figure 7.2 . The simple geometry represented in this section can develop, whether the over-riding lithosphere is a continental, b oceanic or c transitional between a and b . The position of the subducting slab is inferred from geophysical data. However, these data do not generally permit one...

Characteristics of oceanic lithosphere

It is apposite here to outline some of the dominant and important characteristics of oceanic lithosphere and note their apparent simplicity and limited age-range. In Chapter 3, it will be argued that the generation of forces which cause plate motion is mainly related to the oceanic lithosphere, while the continental lithospheres are mainly passive, driven elements. Indeed, in its simplest form, plate tectonics fails to describe processes in the continental crust. As noted in Chapter 1, simple...