Question

4. On the following pages are three maps showing bathymetry and earthquakes from 1965-2005 (green < 50 km, yellow 50-250 km, red > 250 km deep). For each, [1] describe kind of plate tectonic setting it is and give 2-3 lines of evidence for how you know, (2) Give the geographic names of two places/features that exemplify that type of plate boundary, [3] produce a cartoon cross-section sketch showing the topography, sub-surface geology showing the main layers of the oceanic crust (hint: there's 4) including a quantitative depth scale, any other types of crust not "normal oceanic crust,” shape of the base of the crust, any magma reservoirs that you would expect to exist, and label any plate boundaries by name an type` on your cross-section. Nb. Cross-section shouldn't be along any particular line but rather be cartoon representation of the typical crustal structure of the main plate tectonic setting that is depicted in the map overall. *coast, shelf, slope, rise, abyssal plain, seamount, oceanic ridge, ocean island, oceanic plateau, trench, etc. Areview of plate tectonic concepts from lecture 5 tectonics.ppt on Blackboard. Some choices of plate tectonic setting: Slow-spreading ridge, intermediate spreading ridge, fast-spreading ridge, continental-arc subduction zone, island-arc subduction zone, back-arc basin, continental collision zone, continental rift zone, hotspot island chain

Answer 1

Figure 1:

In this figure, there are two linear features, one of which is offset across the other. The earthquakes in this zone are also shallow (less than 50km), indicating that the tectonic perturbation is shallow. The line that has been offset is a divergent boundary, while the line causing the offset is a transform fault. Transform faults are commonly present across mid-ocean ridges, which is a divergent boundary between two oceanic plates. The Mid-Atlantic Ridge in the Atlantic Ocean and the East Pacific rise

Figure 2:

In this figure, earthquakes increase in depth from east to west, and then decrease in depth in isolated regions to the west. The earthquakes in these isolated regions can be associated with volcanism. The progressive reduction of depth from the west to east, combined with the trench of sudden lower elevation (shown in purple) is a clear indicator of subduction i.e. the eastern plate is subducting below the western plate. The series of islands to the west of this oceanic trench are island arcs formed by melting of the sinking rock which rises up as melt. Famous examples of island arc subductions are the Java trench the Indian ocean as well as the Mariana trench in the Pacific ocean.

Figure 3:

Shallow earthquakes within this region are present only within regions of high elevations. These high elevations also show linear trends.Such linear mountains are formed when two continents collide, forming an orogenic zone. Thus, this is a convergent zone where the two plates on opposite sides of the mountains move towards each other. Two famous examples of continental convergences are Alps and Himalayas.

The diagram below shows cross sections of all three:

RHYOLITE RAYOPACITE I BACITE, ANDESITE CONTINENTAL ARC 1 OCEN | Riape NITE CONTINENTAL | CRUST OCEANK Crust MANTLE BASALT 4. Didrite, granite, → Bilsin & gabbro MEST