Part l: Plate Tectonics OBJECTIVE-To do a simple calculation of the rate of plat

Question

Part l: Plate Tectonics OBJECTIVE-To do a simple calculation of the rate of plate motion. You will need a ruler that has mm. Rulers will be available in Study Groups Determine seafloor spreading rate over the past 30 million years for the Southeast Indian Rise. In this exercise, you will use ages of oceanic crust in the southeast Indian Ocean to determine the rate of spreading at the Southeast Indian Rise, which separates Australia from Antarctica. The map on the last page shows ages of oceanic crust for the Australian-Indian and Antarctic plates in the southeast Indian Ocean. The position of the Southeast Indian Rise is indicated by the dark line. Oceanic crust that is less than 30 million years old is white, while older crust is shaded in gray. 1. Use the scale on the map on the last page to determine the width of oceanic crust that is younger than 30 million years old (white) on the Australian-Indian Plate measured from the Southeast Indian Rise. Write that distance below with units shown (look at scale to determine units). Remember to measure from the ridge (bold line in the middle of the white) to the edge of the white 2. Divide the measured distance by 30 million years to calculate the rate in km/m.y at which the Australian-Indian Plate is being created at the Southeast Indian Rise. SHOW YOUR WORK, INCLUDING UNITS. 3. An approximately equal amount of Antarctic plate is generated on the opposite side of the Southeast Indian Rise. Now determine the total rate of seafloor spreading at the Southeast Indian Rise (hint: multiply by what?). 4. Using the conversion 1 km/m.y. 1 mm/yr, convert the seafloor spreading rate to mm /yr. Write what the spreading rate is in mm/yr below.

Explanation / Answer

1. Width of oceanic crust from south-east indian rise to australian

   1 mm=100 km

   20*100=2000km

   widht of oceanic crust = 2000km.

2. Rate of plate spreading = 2000/30=66.67 km/m.y

3. Total rate of plate spreading (from south-east indian rise to austalia & antatica)=2*66.67=133.34 km/m.y

4.Sea floor spreading rate 133.34 mm/y (because 1km/m.y=1mm/y, given in question)

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