Rock magnetizations that are most useful for paleomagnetism Detrital Remanent Magnetization (DRM) formed during or soon after deposition of sediments locked in by compaction and lithification to sedimentary rock relatively weak Thermo-remanent Magnetization (TRM) formed in basic igneous rocks (e.g., basalt) upon cooling through Curie temperature locked in upon further cooling very strong

Ternary diagram of the iron- titanium oxide solid solution magnetic minerals “ferromagnetic” minerals:

Paleomagnetic measurements  Collect many suitable samples (e.g. basalt) with in situ orientation determined

Paleomagnetic measurements  Collect many suitable samples (e.g. basalt) with in situ orientation determined  For each sample measure stable component of magnetization intensity and direction (declination, D, and inclination, I) in laboratory (“cleaning” samples by removing unstable superimposed magnetizations.  alternating current (AC) demagnetization  thermal demagnetization

Paleomagnetic measurements  Collect many suitable samples (e.g. basalt) with in situ orientation determined  For each sample measure stable component of magnetization intensity and direction (declination, D, and inclination, I) in laboratory (“cleaning” samples by removing unstable superimposed magnetizations. alternating current (AC) demagnetization thermal demagnetization  Determine VGP locations, average VGP for specified time in past, and error

Paleomagnetic measurements  Collect many suitable samples (e.g. basalt) with in situ orientation determined  For each sample measure stable component of magnetization intensity and direction (declination, D, and inclination, I) in laboratory (“cleaning” samples by removing unstable superimposed magnetizations. alternating current (AC) demagnetization thermal demagnetization  Determine VGP locations, average VGP for specified time in past, and error  Plot time sequence of VGP locations on equal area projection of earth

Fisher statistics for VGP’s Consider each VGP as the intersection of a unit vector at the center of the earth with the earth’s surface. The latitude and longitude of the VGP can be transformed into a cartesian coordinate system at the earth’s center, with the x axis pointing to 0N, 0W, the y axis pointing to 0N, 90E, and the z axis pointing to the North Pole. For a set of N VGP’s., one can add up the unit vectors and find the resultant direction. The intersection of this resultant vector with the earth’s surface is the best estimate of the average VGP for the N data. The magnitude of the resultant vector, say, is L. If all the data pointed in the same direction (same VGP location), then L = N. Otherwise, L is less than N, and is the key measure of the clustering of the data about the average. Precision parameter K = (N-1)/(N-L) angular standard deviation S = 81°/sqrt(K) 95% cone of confidence about the mean vector is a small circle centered on the mean vector with angle (measured from the mean vector) given approximately by  95 = 140°/sqrt(KN)

VGP’s average Earth’s rotation axis! Polar projection showing VGP’s for igneous rocks at many sites, all dated at less than 20 million years old (too young to be significantly affected by plate motions). North Pole W 90 E 15 N 30 N

Apparent polar wander paths for North America and Europe

T 0 to T 4 Re-assembling continental fragments

T 0 to T 4 Re-assembling continental fragments

T 0 to T 4 T 4 to T 8 Re-assembling continental fragments

A T 0 to T 4 T 4 to T 8 Re-assembling continental fragments Note that the VGP’s are rigidly connected to the continental fragments, and are rotated along with the fragments

A T 0 to T 4 T 4 to T 8 Re-assembling continental fragments Note that the VGP’s are rigidly connected to the continental fragments, and are rotated along with the fragments

Apparent polar wander paths for North America and Europe

Europe rotated by 38 degrees about rotation pole at 88.5N, 27.7E Closing the North Atlantic Ordovician to Jurassic ( Ma) “Apparent polar wander” (APW) paths for North America and Europe

Errors (  95 cones of confidence)

Geologic time scale My 600 My 65 My

Geologic time scale My 600 My 65 My

seafloor tape recorder

Geologic time scale My 600 My 65 My

Paleozoic Continental Drift Paleomagnetic VGP’s and APW’s Geological structures Paleo-environments and paleo climatic zones See continental reconstructions from PLATES project of the University of Texascontinental reconstructions