Ridge Crest Processes

Further insight into the link between ocean ridge magmatism and the tectonic processes that combine to form oceanic crust at ocean ridge spreading centers has been gained by direct observation of processes occurring along active ridge crests. Detailed observations of spatial and temporal variations in ocean ridge crest magmatic processes at the EPR were provided by Haymon et al. [1991] at 910N, by Haymon et al. [1993] at 945N, and by Perfit et al. [1994] at 931N. Studies of the occurrence and location of magma chambers at axial spreading centers primarily utilized seismic constraints [ Detrick et al., 1993; Kong et al., [1992]; Caress et al., [1992]; and Kent et al., 1993a,b]. Additional insights into the distribution of melt within the oceanic crust were provided by study of variations in distributions of hydrothermal venting sites [ Baker and Hammond, 1992], in the cross-sectional area of the axial ridge [ Scheirer and Macdondald, 1993], and in the extent of Fe-enrichment observed in MORB [ Sempere, 1991]. A synthesis discussion was presented by Sinton and Detrick [1992] which integrated seismic and petrologic views of the nature of the magma chambers that exist at ocean ridges. This study described the composite magma chamber model which involves a thin (10-100 m), narrow (<1-2 km) melt lens overlying a zone of crystal mush, in contrast to earlier models of large, mainly molten magma chambers that were thought to exist beneath fast spreading ridges.