Date: of California, Oregon, Washington, and southwest bands are rocks with a 2.

Question

Date: of California, Oregon, Washington, and southwest bands are rocks with a 2.4 Paleomagnetic Stripes and Seafloor S ACTIVITY positive (o) ma ke anomaly, so they have Course/Section Canada. The colored bands are seafloor magnet polariy. Df ommal polariny, like now. The whise bands ane rocks with a ngative G-) ial time scale prowided polarity. Different colors Name A. Analyne the scafloor part of the map below, just off the Pacific Coast, west of yeas kraw a linc on the sea floor so show where new occan crust and lithosphere is form ing FIGURE 2.2 as a guide, label the segments of your line that are Juan now (zero millions indicate the ages of the rocks, in millions of years as shown in the polar de Fuca Ridge and Gorda Ridge the old). Using FIGURE 2.2 as a guide half-arros to hel the sgmens of your pencil line thar are transform faule plate bhou half arrows to the transform fault boundaries to show the relative motion of the rocks Mdnt Meager time scale: ages are in millions of years ago Glacier Colors indicate rocks 4 The needle Mt. Hood would have pointed in 0 ML Jefferson Juan de Fuca Ridge the geographic North

Explanation / Answer

Here in the figure given below the dashed line marks the crest, or axis, of the ridge.

The peaks of the magnetic profiles are positive and show where the rocks are magnetized. It points to magnetic north in direction same as magnetic north is today.

The valleys of the magnetic profiles are negative and shows where the rocks are magnetized. It points to magnetic north in the opposite to the direction as magnetic north is today.

The theory of seafloor spreading suggests that the profiles should be mirror images of each other on either side of the ridge and each and every magnetic anomaly should form a line or stripe parallel to the ridge.

Find the same for B to A. Label anomalies 1, 2, 3, 4 and 1', 2', 3', 4' in each of four profiles. The ages of the magnetic anomalies is measured in this way. Now the rate the plates have been spreading away from the ridge at profile D since 7 Ma is calculated.

This is calculated by dividing the distance from peak (measured in km) by the age (in Ma) to get the average rate of late motion away from the ridge.

The units of plate motion will be in kilometers per million years (km/Ma).

Conversion of kilometers per million years (km/Ma) to centimeters per year (cm/yr), is done afterwards and divide the km/Ma number by 10, or multiply by 0.1.

For a map scale, one cm (centimeter) equals 50 km.

The coloured areas are those where the ocean floor has normal magnetism, with north in about the same direction as it is now.

The white stripes between the coloured stripes are those areas where the ocean floor has reversed magnetism in opposite direction as it is now.

First measure distances from the center of the Juan de Fuca Ridge to the magnetic reversals that appear on the map as the edges of the coloured zones.

the scale of 1 cm = 50 km.. Once you measure a distance in cm on the map, multiply it by 50 to get km.

Measure the distances out from the center of the ridge, at right angles from the ridge. Measure anomalies on both sides of the ridge, east and west.

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