Three-dimensional geometry of axial magma chamber roof and faults at Lucky Strike volcano on the Mid-Atlantic Ridge

Abstract : We present results from three-dimensional (3-D) processing of seismic reflection data, acquired in June 2005 over the Lucky Strike volcano on the Mid-Atlantic Ridge as a part of the Seismic Study for Monitoring of the Mid-Atlantic Ridge survey. We use a 3-D tomographic velocity model derived from a coincident ocean bottom seismometer experiment to depth convert the poststack time-migrated seismic volume and provide 3-D geometry of the axial magma chamber roof, fault reflectors, and layer 2A gradient marker. We also generate a high-resolution bathymetric map using the seismic reflection data. The magma chamber roof is imaged at 3.4 ± 0.4 km depth beneath the volcano, and major faults are imaged with dips ranging between 33° and 50°. The magma chamber roof geometry is consistent with a focused melt supply at the segment center and steep across-axis thermal gradients as indicated by the proximity between the magma chamber and nearby faults. Fault scarps on the seafloor and fault dip at depth indicate that tectonic extension accounts for at least 10% of the total plate separation. Shallow dipping reflectors imaged in the upper crust beneath the volcano flanks are interpreted as buried lava flow surfaces.