Seismic constraints on shallow crustal processes at the East Pacific Rise

Abstract

Abstract : This thesis is concerned with understanding bow oceanic crust is emplaced at mid-ocean ridges. Nine on-bottom seismic refraction experiments are analyzed in an effort to resolve the structure of the emplacement zone of lavas and dikes at the fast-spreading East Pacific Rise. The results suggest that the volcanic section doubles in thickness within approx. 1 km of the axial summit caldera (ASC) due to the emplacement of lava that either overflows the ASC or is emplaced through eruptions outside of the ASC, and the depth to the top of the sheeted dike complex increases from approx. 130-180 m within the ASC to approx. 300-350 m a kilometer away on the flank. It is suggested that the process of dike subsidence is controlled by the axial magma chamber, which is defined as the melt lens and underlying mush zone. In addition, the results of MCS (multi-channel seismic) and wide-angle experiments over plausible velocity structures are predicted quantitatively. It is concluded that the accuracy of correlating the prominent shallow reflector observed in MCS and wide-angle data with the layer 2A/2B boundary is strongly dependent on the structure within layer 2A.