1. What lines of evidence confirm that seafloor spreading has been taking place?

Question

1. What lines of evidence confirm that seafloor spreading has been taking place? You should be able to explain both paleomagnetic evidence and that of ocean floor core samples.

2. What is the general relationship between global earthquake activity and plate boundaries?

3. Describe the fundamental differences among divergent, convergent, and transform plate boundaries.

4. Describe and explain the tectonic activity, volcanic activity, and general topographic features associated with the three kinds of convergent plate boundary: oceanic–continental plate subduction, oceanic–oceanic plate subduction, and continental plate collision. Mention at least one present-day example of each of these kinds of convergent boundary.

5.Why is there such a concentration of volcanoes and earthquakes around the margin of the Pacific Ocean (the region referred to as the Pacific Ring of Fire)?

Explanation / Answer

1) new oceanic crust is continuely creating at the ridge axis, magma from the mantle upwell and push the plates apart and then solidify, also this ridge axis is elevated from the mean ocean floor height due to its higher gravitational potential it start to slide down or moves apart. there are evidences of marine magnetic anomalies fromed in this ocean floor, when the magnetic minerals in the magma cools they align with the earths magnetic field, so from this data we can found out the position the plates in the past. and the age of the ocean floor can also be determine by the core sampling for the dating.

2) most of the earthquakes are associated with the plate boundaries such as convergent, divergent and transform plate boundaries. in the convergent plateboundary zones there are deep earthquakes across the subducting plate or in the wadati-benioff zone, and shallow earthquakes in the divergent plate boundaries and transform plate boundaries. the rate of stress accumulation along these boundries are much more due to its motional nature, so the frequency of earthquakes in this regions will be higher.

3) in the convergent plate boundary denser plate subduct beneath the other towards the mantle and melt, so it is also known as destructive plate boundary. but in the case of divergent plate boundary two plates are moving apart and new oceanic crust is form at the ridge axis so it is known as constructive plate margin. two plates are just sliding each other in the transform plate boundary, there is no construction or destruction of plate across the boundary.

4)oceanic continental : in this case denser oceanic plate subduct beneath the continental plate and start melting in the mantle, this molten material rises towards the overriding plate and form volcanos. eg: the Andes mountain range of western South America

oceanic -oceanic: when two ocanic plates converges the denser plate will subduct beneath the other and eventually the melting of subducted plate will causes volcanic activity in the over riding plate, and form volcanic island arc. eg: Aleutian islands

continental plate collision: when two continental plates collide they start to rise and form mountain ranges, because both the plates has nearly same density so they will not subduct. eg: Himalayan mountain ranges(Everest)

5) in the ring of fire, the ocanic plates are subducting beneath the continental plate and the melting of this subducted plate causes the volcanic activity and hence it is known as ring of fire.

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