Oceanic Lithosphere Magnetization: Marine Magnetic Investigations of Crustal Accretion and Tectonic Processes in Mid-Ocean Ridges

Clare M. Williams, Ph.D., 2007
Maurice Tivey, Advisor

The origin of symmetric alternating magnetic polarity stripes on the seafloor is investigated along East Pacific Rise (EPR) (9º 25’-9º 55’N) and Kane Megamullion (KMM) (23º 40’N) in the Atlantic. At the EPR, along-axis variations in the axial magnetic anomaly result from changing source layer thickness, consistent with observed changes in seismic Layer 2a. The extrusive basalts therefore constitute the magnetic source layer along the ridge axis and long term crustal accretion patterns are reflected in the axial anomaly appearance. At KMM the C2r.2r/C2An.1n (~2.581 Ma) polarity reversal boundary is recorded by lower crust (gabbro) and upper mantle (serpentinized peridotites) rocks exposed on the seafloor by detachment faulting. Both lithologies have stable remanent magnetization, capable of contributing to the magnetic source layer. The geometry of the polarity boundary in the northern KMM region, interpreted to be a gabbro pluton, dips away from the ridge axis and is consistent with a rotated conductively cooled isotherm. In the central region the boundary in the serpentinized peridotites dips towards the ridge axis and is thought to represent an alteration front. The linear appearance of the polarity boundary across the two regions suggests that both lithologies acquired their remanence at approximately the same time.