5. Ares is a planet with just two plates, A and B (Fig. 2.24). Plate B comprises

Question

5. Ares is a planet with just two plates, A and B (Fig. 2.24). Plate B comprises the lower hemisphere and plate A the upper, as shown. Points a, b and c lie on the equator, and point d is diametrically opposite b. The zero meridian passes through point a. The pole of rotation of plate A relative to plate B is at 45 degree N, 0 degree E. The amplitude of the angular velocity vector is 10^-10 radians per terrestrial year. The radius of Ares is 3400 km. (a) What is the nature of the plate boundary between plates A and B? (b) State where magnetic lineations might be found and sketch the pattern that would he observed. (e) Calculate the relative velocity between plates A and B at locations a, b, c and d. (d) Sketch possible fault-plane solutions for earthquakes occurring at locations a, b, c and d. (e) Discuss the possible existence of such a two-plate planet. (f) Discuss briefly how the stability or instability of a two-plate tectonic system depends upon the pole position and/or relative size of the two plates.

Explanation / Answer

Ans. a) Transform boundaries. Transform boundaries (Conservative) occur where two lithospheric plates slide, or perhaps more accurately, grind past each other along transform faults, where plates are neither created nor destroyed. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). Transform faults occur across a spreading center.

b) Magnetic lineations may be found parallel to plane abcd. abMagnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility.

c) Relative velocity will be the same (10^-10 radians per terrestrial year but in opposite direction) at locations a,b, c and d.

d) Fault plane solution for earthquakes occuring at locations a, b, c, d

e) There is a possibility of existance of two-plate system as we have been able to identify only the two plates on Mars planet.They are the Valles Marineris North and the Valles Marineris South.

F) The two plates divided by Mars' Valles Marineris have moved approximately 93 miles horizontally relative to each other. California's San Andreas Fault, which is over the intersection of two plates, has moved about twice as much. Hence, there is instabilty of a two plate tectonic system.

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