SO461, Geological Oceanography

Magnetic Anomalies Lab, Fall 2008

You may complete question #1 in groups.  Question #2 will be turned in for a grade, and will be individual work.

1.  This diagram shows three marine magnetic anomaly profiles.  The distance scale is given at the top and bottom, and marine magnetic anomaly scale for the past 10 Ma (black normal) is on the bottom.

Explain, by referring to the diagram:

• How we can determine the location of ridges.
• How we can determine the spreading rates.
• How we can match anomalies from one profile to another.

2.  This diagram shows three east-west magnetic profiles across a suspected ridge that runs north-south.  All have the same scale.  A magnetic anomaly scale at the bottom shows the times of the anomalies for the past 13 Ma.
• Pick five anomalies and show how you would correlate the three profiles.

• Name those anomalies using the picks in Table 1.

• Show the locations of 5, 10,  and 15 Ma crust on each profile.

• If it is present, show the location of the ridge crest on each diagram.

• Which profile has the fastest spreading rate, how can you tell, and what would you estimate the rate to be?  Compare this with the rate for the other two profiles.

• Which profile is closest to the Euler pole about which the two plates are moving, and how do you know?

• Which location on the three profiles has the oldest crust, and what would you estimate to be the age of that crust?

Table 1.  Cande and Kent Geomagnetic Time Scale

 Top (Ma) Base (Ma) NORMAL interval NAME 0.000 0.780 1n Brunhes/Matuyama 0.990 1.070 1r.1n Jaramillo 1.770 1.950 2n Olduvai 2.140 2.150 2r.1n 2.581 3.040 2An.1n Matuyama/Gauss 3.110 3.220 2An.2n 3.330 3.580 2An.3n Gauss/Gilbert 4.180 4.290 3n.1n Cochiti 4.480 4.620 3n.2n Nunivak 4.800 4.890 3n.3n Sidufjall 4.980 5.230 3n.4n Thvera 5.894 6.137 3An.1n 6.269 6.567 3An.2n 6.935 7.091 3Bn 7.135 7.170 3Br.1n 7.341 7.375 3Br.2n 7.432 7.562 4n.1n 7.650 8.072 4n.2n 8.225 8.257 4r.1n 8.699 9.025 4An 9.230 9.308 4Ar.1n 9.580 9.642 4Ar.2n 9.740 9.880 5n.1n 9.920 10.949 5n.2n 11.052 11.099 5r.1n 11.476 11.531 5r.2n 11.935 12.078 5An.1n 12.184 12.401 5An.2n 12.678 12.708 5Ar.1n 12.775 12.819 5Ar.2n 12.991 13.139 5AAn 13.302 13.510 5ABn 13.703 14.076 5ACn 14.178 14.612 5ADn 14.800 14.888 5Bn.1n 15.034 15.155 5Bn.2n 16.014 16.293 5Cn.1n 16.327 16.488 5Cn.2n 16.556 16.726 5Cn.3n 17.277 17.615 5Dn 18.281 18.781 5En 19.048 20.131 6n