Transcript lecture37
Magnetic field including all terms Hulot et al., 2002 Magnetic minerals: Ferromagnetism Ternary diagram of the irontitanium oxide solid solution magnetic minerals Two most useful natural rock magnetizations (NRM, Jr) 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 thermo-remanent magnetization, TRM Detrital remanent magnetization DRM Paleomagnetic measurements Collect many suitable samples (e.g. basalt) with in situ orientation determined 2001 Paleomag trip to Grand Canyon We drilled the Tapeats sandstone from the Cambrian; involved lots of water to cool the drill (me at top, Dave Evans, Yale below) In August, 2001 I was one of about 12 student slaves on a 2 week rafting trip down the Grand canyon to collect paleomag samples. Led by Joe Kirschvink, Caltech Because we were in a national park, we had to patch the drill holes once the samples were removed. Here I am mixing some concete with local rocks Good result Bad result thermal demag (°C) AC demag (mT) Isolation from environmental and geomagnetic fields cage Mu metal encased room corrections for structure corrections for structure Blocks rotated during Neogene Mojave extension (Miocene) Paleomagnetic declinations Declination vrs age for the western Transverse Block Samples from this area Closing the North Atlantic Ordovician to Jurassic (500-200 Ma) “Apparent polar wander” (APW) paths for North America and Europe Europe rotated by 38 degrees about rotation pole at 88.5N, 27.7E Errors (a95 cones of confidence)