Ocean/ESS 410

Lab 1. Plate Tectonic Summary Map

In this class we are going to work with a set of maps of global elevation and earthquakes in order to understand plate tectonics. We will first use these maps to get a basic understanding of the surface features created by plate tectonics. Later in the class and perhaps for your term paper, we will look at some features in more detail.

There are four maps each of which shows a quarter of the Earth’s surface. The elevation is shown by color and by contours spaced 1000 m apart. To give them a three-dimensional appearance, the maps are illuminated from the North, so that steep south facing slopes appear in shadows. The maps show earthquakes with a magnitude greater than 5 that were detected over a 20 year period with the Global Seismic Network. Earthquakes are shown by colored dots and color-coded for depth as follows:

red = 0 to 70 km green = 70 to 300 km blue = 300 to 700 km.

Your goal is to generate a tectonic summary of one map but you should take time to look at all the maps (quite useful when you are trying to understand features on the edge of your map). The goals of the exercise are to learn to read the maps, use them to create a summary map of plate boundaries; and identify any interesting plate tectonic features.

Outside the class period, we will leave the maps in the map case – please do not remove them from the class.

Making a map of plate boundaries

For this exercise you will use a sheet of gridded paper to make a carefully drawn summary map of the plate boundaries and interesting tectonic features on the map. The maps you are working from use a Mercator projection in which the map scale increases at high latitudes – this produces a lot of distortion but has the advantage that at any given position the scale is the same in the horizontal and vertical directions For the map you draw, use the same constant scale for 1 degree of latitude and longitude. Tape 2 pieces of 8 ½ x 11” graph paper together lengthwise and choose a scale so that your map covers as much of the page as possible.

You should include the following on your map

• Plate boundaries The symbols for the different plate boundaries are shown on the next page:

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Spreading Center

Transform Fault Overriding plate

Spreading Center

Subduction Zone

o You can identify spreading centers (also known as mid-ocean ridges) from the bathymetry (they are linear shallow features). o Ocean transforms offset the ridges and are usually delineated by shallow earthquakes (what is the sense of motion on these transforms?). o Subduction zones are usually (but not always) characterized by deep earthquakes and you can infer the direction the slab dips from how the depths change and hence infer the overriding plate. o In some instances plate boundaries may be diffuse in which case you should indicate so by labeling

• Coastlines • Arrows to show the relative directions of plate movements. • Dotted lines to show seamount chains • Dashed lines to show fracture zones (the inactive parts of oceanic transforms). • With help from the instructor, the TA and your fellow students try identify other interesting features on the bathymetry map (see list on the next page) and add them to your plot.

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Interesting Features

The following is a list of some interesting global tectonic features.

Southeast Quadrant (Australia) • Australian-Antarctic Discordance on the South-East Indian Mid-Ocean Ridge (50°S, 125°E) • Ridge Triple Junctions - central Indian Ridge, Southeast Indian Ridge and Southwest Indian Ridge all meet at a triple junction (25°S, 70°E) • Macquarie ridge (53°S, 160°E) • Diffuse plate boundaries that subdivide the Indo-Australian plates (not something you can see on the map but a very interesting topic) • Super-slow spreading ridges - Southwest Indian Ridge (also Gakkel ridge in the Arctic) • Large Igneous Provinces - Kerguelen Plateau (50°S, 70°E) and Ontong Java Plateau (5°N, 160°E).

Southwest Quadrant (South America) • Scotia Plate (55°S, 70°W) • Pacific Microplates (25°S, 125°W) • Lau Back Arc Basin (21°S, 176°W) • Eltanin Transform Fault (54°S, 123°W) • South Shetland Subduction Zone and the Bransfield Basin (63°S, 60°W)

Northwest Quadrant (North America) • Caribbean Plate (20°N, 70°W) • Ridge-Hotspot Interactions - Iceland and the Reykjanes Ridge (60°N, 30°W) -also see the Azores on this map and the Galapagos Island and Ridge near the equator on the western quadrant maps • Hawaii hotspot (157°W, 20°N) - also numerous other oceanic hotspots such as Reunion Island in the Indian Ocean • Aleutian Islands (170°W, 50°N) • Farallon Plate and the west coast of North America

Northeast Quadrant (Eurasia) • Himalayas (35°N 70E) • Aegean Sea (35°N, 25°E) • Red Sea (20°N 40°E) and East African Rift • Large Igneous Provinces - Ontong Java Plateau (5°N, 160°E) and Kerguelen Plateau (50°S, 70°E). • Sumatra Subduction Zone and the 2004 earthquake (15°N, 95°E)

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