1. Hi guys!

I got this question to solve and it makes me pretty confused. ( I wonder if any of you could help. Thanks a lot in advance.

Question:

The Sala y Gomez Seamount chain is a row of submarine volcanoes (seamounts) in the Pacific Ocean, on the Nazca Plate. The seamounts form a roughly E-W trending line, which changes to an ENE-WSW trending line closer to the South American continent, in which the submarine volcanoes become progressively younger to the west. Table 1(below) list a subset of seamounts from the Sala y Gomez Seamount chain, showing the age of each seamount and the distance from the youngest ( Umu) to each successive seamount moving towards South America. The change in direction of the chain occurs between seamounts 8 and 9 ( at 21 Ma).

Seamount-Seamount name- approximate age/Ma- Distance from Umu/km

1.)Umu-5Ma-0km
2.)Pukao-6Ma-75km
3.)No name-8Ma-315km
4.)No name-12Ma-750km
5.)Rock-14Ma-1050km
6.)Cupole-16Ma-1370km
7.)No name-17Ma-1490km
8.)No name-21Ma- 2000km
9.)Amber Guyot-24Ma-2250km
10.)Baral Guyot-27Ma-2430km
11.)Shoal-29Ma-2550km
12.)No name-30Ma-2690km
13.)No name-31Ma-2760km
14.)No name-33Ma-2900km

(i) Plot the data in Table 1 by hand on a graph of the age (Ma) versus distance (km) for the Sala y Gomez Seamount chain, and draw two best fit lines, one through seamounts 1-8 and one through seamounts 8-14.

[B]I ploted the data on the graph, and have done the following calculationsB]

(ii) Use the best-fit lines to calculate teh average speed of the Nazca plate before and after 21 Ma.

Before 21 Ma

Gradient of the line through seamounts 8-14:

Gradient = y2 – y1 / x2- x1
= 32-25 / 2800- 2320
= 7/ 480
= 0.014583333

Average speed = 1/ 0.014583333
= 68.57 km Ma-1

After 21 Ma

Gradient of the line through seamounts 1-8:

Gradient = y2- y1/ x2- x1
= 16.5- 8/ 1400- 300
= 8.5/ 1100
= 7.72 x 10-3

Average speed = 1/ 7.72 x 10-3
= 129.53 km Ma-1

(iii)

Using your graph to help you, briefly describe how the average speeds calculated in (ii) have changed and explain the significance of change in orientation of the Sala y Gomez Seamount chain at 21 Ma.

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2.

3. It looks like an interesting homework assignment and I'm sure there are several of us that might like to help you discover the answer (we won't do it for you, however).

Which part has you confused?

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