Internal Structure of Oceanic Lithosphere: A Perspective from Tectonic Windows

Composition of the Oceanic Crust

“…If the dike pierces the surface, magma erupts on the ocean floor as lava, forming the eruptive layer. Below the crust lie mantle rocks that are the residues of a previous melting event that provided the melt that formed the ocean crust above, but may also locally include melt-rock reaction products, intrusive bodies, and cumulate ultramafic rocks (Dick et al, 1984Johnson and Dick, 1992;Karson, 1998;Kelemen et al, 1997;Michael and Bonatti, 1985).…”

Deep crustal structure of the Adare and Northern Basins, Ross Sea, Antarctica, from sonobuoy data

“…5e and S3c), where fast crustal velocities (up to 7400 m/s) are detected at relatively shallow depths in the crust. Adare Basin crust appears to be similar to that of oceanic core complexes observed and modeled at ultraslow spreading ridges (e.g., Karson, 1998).…”

“…The traditional view of oceanic crustal structure was determined from studies of ophiolite suites on land and marine seismic data, both of which indicated subhorizonal layering beneath the sediment-basement contact of 1) basaltic pillow lavas (v p ∼ 5000 m/s), 2) sheeted dikes, 3) gabbro (v p ∼ 7000 m/s), and 4) peridotite mantle (v p ∼ 8000 m/s), with mean oceanic crust (composed of basalt and gabbro) being ∼7 km thick (e.g., Christensen, 1978). However, in situ studies of these layers reveal that the oceanic crustal structure is complex and variable (Karson, 1998;Dick et al, 2003). Fault scarps on the seafloor reveal deviations from mean oceanic crustal structure on the scale of tens of meters to tens of kilometers, particularly along slow spreading ridges and in magma-poor locations, where stretching and thinning of the lithosphere often results in crust <7 km thick and the presence of oceanic core complexes (exposed along low-angle detachment faults, where rock units are missing, and contacts between units that are neither horizontal or continuous) (Karson, 1998).…”

“…However, in situ studies of these layers reveal that the oceanic crustal structure is complex and variable (Karson, 1998;Dick et al, 2003). Fault scarps on the seafloor reveal deviations from mean oceanic crustal structure on the scale of tens of meters to tens of kilometers, particularly along slow spreading ridges and in magma-poor locations, where stretching and thinning of the lithosphere often results in crust <7 km thick and the presence of oceanic core complexes (exposed along low-angle detachment faults, where rock units are missing, and contacts between units that are neither horizontal or continuous) (Karson, 1998).…”

Relating Crustal Structure and Stress Indicators in the Azores Islands

“…Figure 2 displays the best (minimum) 1-D model obtained for the area between the islands of Faial, Pico and São Jorge, labelled FAIAL98 . Considering the P and S velocities and the Vp/Vs ratio of the model, and comparing with values associated with typical oceanic crusts (Tanimoto, 1995;Karson, 1998) it is possible to make a generic interpretation in petrological terms of the crustal structure of the area under study. The results indicate a basaltic composition for the layer located between 1 and 3 km in depth (Layer 2), with the velocities values suggesting a succession from lava flows to pillow lava and basaltic dikes.…”