Advanced Geophysical Studies of Accretion of Oceanic Lithosphere in Mid-Ocean Ridges Characterized by Contrasting Tectono-Magmatic Settings

Min Xu, Ph.D., 2012
Juan Pablo Canales, Advisor

The structure of the oceanic lithosphere is represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This thesis uses advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography, and near-bottom magnetics) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00’N, and the Kane Oceanic Core Complex (KOCC, MAR 23°20’-23°38’N) formed by detachment faulting. At the EPR study area, the axial magma chamber (AMC) is segmented into four prominent 2-4-km-long sections characterized by very high melt content. The total magma volume extracted from the AMC was estimated of ~46 x 10⁶ m³ during the 2005-06 eruption. At the KOCC, streamer tomography was used to constrain the shallow seismic velocity structure. Lithological interpretation provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved.