The paleomagnetism and rock magnetism of oceanic basalts: From remanence acquisition to the motion of hot spots and plates.

摘要

Magnetic signatures of oceanic basalts are of critical importance for accessing the reliability of paleomagnetic data from oceanic plates, constraining plate motions and understanding convective flow of the mantle. This thesis presents rock-magnetic, paleomagnetic and plate tectonic investigations of submarine basalts relevant to these topics.;Rock magnetic analyses of pillow lavas from Detroit Seamount of the Hawaiian-Emperor seamount chain (Ocean Drilling Program Site 883) led to the recognition of pervasive self-reversed magnetization components formed in situ by extreme low-temperature oxidation of titanomagnetite. However, further study of tholeiitic basalts from eleven drilling sites in the Pacific Ocean suggests that such self-reversals are not a common feature of oceanic basalts. A refined 34°N paleolatitude for the Hawaiian hot spot in the Late Cretaceous (76--80 Ma) obtained from the Site 883 data (and other high-quality data sets from Detroit Seamount) is consistent with earlier estimates and predicts rapid (∼50 mm/yr) southward migration of the hot spot from Late Cretaceous to Paleogene time (80--47 Ma).;Direct paleolatitude estimates from Detroit and other Pacific seamounts were compared to the non-Pacific reference paleomagnetic poles through the use of global plate circuit reconstructions. Agreement between Late Cretaceous data attests to the accuracy of both plate circuit reconstructions and paleomagnetic estimates. It is argued that discrepancies observed in some comparisons of Paleogene data point to deficiencies in non-Pacific reference poles. Revised kinematic parameters for the motion of oceanic plates of the paleo-Pacific basin relative to North America that consider hot spot motion suggest smaller Kula and Farallon plates. More oblique convergence with North America is suggested for Late Cretaceous to Middle Eocene (73--46 Ma) times, potentially providing more efficient driving for coastwise transport of tectonostratigraphic terranes.