Info Wkn
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....
Info Mbs
Figure 8.1 Histogram of craters plotted against age and diameter for the Upper Phanerozoic. The various points relate the centre of 10 Ma bins after Shaw, 1994 Seyfert and Sirkin, 1979 . Figure 8.1 Histogram of craters plotted against age and diameter for the Upper Phanerozoic. The various points relate the centre of 10 Ma bins after Shaw, 1994 Seyfert and Sirkin, 1979 . force which acted on the Solar System. This force is considered to be of particular importance in disrupting the tracks of...
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 1
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...
Info Ion
Oceanic plateau basalts are broad features with, as their name implies, a relatively flat top. They have an elevation above the surrounding sea-floor sometimes in excess of 2 km. These plateaus are sometimes supported by anomalously thick crust. Obviously, their age must be younger than the surrounding sea-floor. However, the age difference may sometimes be surprisingly small. The volume of erupted rock that forms OPBs extends over more than two orders of magnitude. The largest of these...
The Mariana Trench
We have noted that the west Pacific rim exhibits a variety of arcuate subduction zones with very large radii of curvature, which are adjacent to the Asiatic landmass. In this section, we shall only be concerned with the development of the Mariana arcuate feature. However, before we discuss this feature, it is apposite to comment briefly on the tracks of a point in Figure 7.34 which relates to the movement of a point, currently at the most eastern point of the Mariana Trench. The current...
Info Nun
Source Reproduced from Coffin and Eldholm 1992 , by permission of the Geological Society Publishing House. Notes a At 15-30 per cent partial melting. b Assumes crustal thickness from seismic refraction experiments. c Minimum and maximum volumes assume off- and on-ridge emplacement, resp. d Timescale of Harland et al. 1982 . e Timescale of Harland et al. 1990 . Large igneous Area 106 km2 Volume 106 km3 Age range Ma Emplacement Spherical province rate km3 yr-1 diameter km f First range, minimum...
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...
Gz 1
Figure 5.34 a Radiating compressive pulse giving rise to concentric folds and deep thrusts. Hoop-stresses coupled with high fluid pressure that results in the development of vertical radiating fractures. b Rebound phase, possibly coupled with a tensile pulse that results in the development of the concentric graben. The thrusts were only revealed when, subsequently, deep cuts were made through the crater and outlying area. These structures developed when the maximum principal stress SI acted...
Info Tcw
When one looks at the Moon through even a low-powered telescope, one cannot but be impressed by the evidence of intense bombardment recorded on the surface of our satellite. The higher the degree of magnification used, the smaller are the diameters of craters that can be seen. Astronauts, from 'fly-by' and Moon landings, have recorded myriads of small craters with diameters of only a few metres. As the Moon is devoid of a significant atmosphere, erosion or covering of small craters will only...
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...