Rocks collected on the coast of northern Greenland, at a latitude of 76.5 degrees North are...

Rocks collected on the coast of northern Greenland, at a latitude of 76.5 degrees North are brought into the paleomagnetic lab for study. You collect a number of samples and find that the magnetic field preserved within them varies slightly, but that the group has an average inclination of -75 degrees and a declination of 135 degrees. Geochemical dating show that all the rocks are 60 My old.

2) describe how these rocks have moved since forming (Be as specific as possible) and determine at what speed must these rocks have traveled since their formation? is this a minimum or maximum estimate of their velocity?

Expert Solution

The average inclination of the rocks indicate that the rocks formed in the Southern hemisphere 60 million years ago (based on the negative sign). The formula that relates inclination to latitude is

tanI = 2tanL

L = tan^-1(tan75/2) = 61.8 degrees.

Thus, the latitude of formation is 61.8^oS.

The distance between 1 degree of latitude is approximately 111km. Thus, the distance between the latitude of formation and the current latitude is (76.5 - (-61.8))x111 = 15351.3km.

Thus, since the formation of these rocks, the continent of Greenland has moved from the southern hemisphere at a latitude of 61.8S to 76.5N. The main reason for this motion is continental drift, and plate tectonics, which causes continetal lithospheric plates to move over the surface of the Earth with time.

The average speed of motion can be calculated by dividing the distance travelled over the time in which the travel has taken place. Thus, speed of plate motion is:

15351.3/60 = 255.855km/My = 25.585mm/yr.

This is the minimum rate of motion, since we have assumed that the plate has traveled in a straight line from the position of formation of the rock to the current position. In reality, the continent may have deviated from this straight line, thus increasing the distance which it has traveled. However, the time period in which it as traveled this distance is the same i.e. 60 My, and thus, the speed of motion will have to be greater if it has to travel a greater distance in the same time

Amanda K answered 1 year ago

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