GL101 Lecture Notes - Lecture 24: Geomagnetic Reversal, Continental Crust, Continental Shelf
Document Summary
Chapter 12: plate tectonics: the framework for modern geology. Included fit of continents (continental shelves), matching fossils and mountain chains now separated by oceans. Magnetized iron-rich minerals capture the direction to earth"s magnetic. Rocks retain original magnetism poles at formation. 1950s poles had migrated through time (polar wandering theory) or. Poles remained relatively stationary (apparent movement) and continents moved. Magnetic poles more-or-less correspond to geographic poles, thus continents must move. 1950s 1960s: extensive ocean floor mapping. Ocean floor rocks not older than 180 million years. Proposed by harry hess in early 1960s. Seafloor moves away from ocean ridges, newly formed oceanic crust replaces it. At deep-ocean trenches older oceanic crust is consumed. Stripes of high intensity magnetism are regions of normal polarity. Ocean ridge lava magnetized with current polarity. Crust records alternating stripes of normal and reversed polarity as seafloor spreads. Transform faults discovered by j. tuzo wilson in the mid 1960s.
