Question

The features of active and passive continental margins and the characteristics of ocean basins are evidence for the existence or absence of a plate boundary.
Read the sentences below, and fill in the blanks to make them complete and correct. Make certain each sentence is complete. Note that some terms will remain unused.

deep-ocean trenches, volcanic island arcs, Ring of Fire, turbidity currents, mid-ocean ridges, volcanic island arcs, submarine canyons

1. Oceanic crust spreads at ________, creating new crust and slowly enlarging the ocean basin.
2. ________ are deep valleys at passive continental boundaries. They are likely carved out by continental ________, which occur when sediment-laden water rapidly moves down slope.
3. Melt from the subducting plate rises to the surface, erupts through the crust on the overriding plate and forms ________ on continents, or ________ in the ocean.
4. Subduction zones surrounding the Pacific Ocean give rise to volcanoes. This area surrounding the Pacific Ocean is called the ________.

Answer 1

Answer:

1. Mid-ocean ridges.

2. Submarine canyons.

3. Turbidity currents.

4. Continental volcanic arcs.

5. Volcanic island arcs.

6. Ring of fire

Explanation:

When two oceanic plates collide one oceanic plate is eventually subducted under the other. Where one plate slides under the other is referred to as the 'subduction zone'. As the subducting plate descends into the mantle where it is being gradually heated a benioff zone is formed. This benioff zone is a zone of shallow,intermediate and deep focused earthquakes. Some deep focused earthquakes that occur at ocean ocean- collision boundaries can be as deep as 670 kilometres. As the subducted plate descends into the mantle it is gradually heated allowing the formation of magma. The magma that forms is andesitic in composition and begins to form when the subducted plate reaches a depth of 100 kilometres. This andesitic magma is formed from the partial melting of the asthenosphere just above the subduction zone. This partial melting of the subducting plate is due to the loss of water as it descends into the mantle. The andesitic magma is now less dense than the surrounding material so it rises through the crust and erupts to form an arc of volcanoes called an island arc