Motion and development of the Pacific Plate from the Middle Jurassic to the Late Cretaceous

Brian Paul Wallick, Purdue University

Abstract

Aspects of the early history of the Pacific plate have been studied using the techniques of rock magnetism and paleomagnetism on samples retrieved from the presumed oldest portion of the Pacific plate. The magnetic properties of 51 basalt samples from Hole 801C were analyzed to study the reason for the magnetic quiescence in the presumed oldest portion of the Pacific plate. The results indicate magnetizations which are not atypical of other younger sites and which are very similar in several respects to Jurassic basalts from the Atlantic. The identification of five inclination zones within the basalt pile are interpreted to be the result of rapid change in polarity of the Earth's magnetic field and suggest a possible reason for the apparent magnetic quiescence. Paleomagnetic analysis of 25 Cretaceous basalts recovered from the Jurassic Quiet Zone region (ODP Site 802) yielded a useful paleolatitude approximation of approximately 19$\sp\circ$ S. Similarities between this estimate and that calculated for the basalts of Site 462, in addition to age similarities and geochemical data, suggest that these may be related as part of an episode of mid-Cretaceous spreading. Finally, the paleomagnetic analysis of sediments from five sites produced reliable paleolatitude estimates from the Bathonian-Callovian to the Campanian-Maestrichtian. The principal results from these paleolatitude estimates outline a general northward migration of the plate for much of its history; however, a period of anomalous south motion was observed for the period of time from approximately 150 to 125 Ma. A period of counter-clockwise rotation of 41$\sp\circ$ calculated from a combination of sediment structural data and FMS images is thought to be responsible for the apparent south motion.

Degree

Ph.D.

Advisors

Ogg, Purdue University.

Subject Area

Geophysics|Geology

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