Henig A. S.

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Henig
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A. S.
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  • Article
    Downward continued multichannel seismic refraction analysis of Atlantis Massif oceanic core complex, 30°N, Mid-Atlantic Ridge
    (American Geophysical Union, 2012-05-19) Henig, A. S. ; Blackman, Donna K. ; Harding, Alistair J. ; Canales, J. Pablo ; Kent, Graham M.
    Detailed seismic refraction results show striking lateral and vertical variability of velocity structure within the Atlantis Massif oceanic core complex (OCC), contrasting notably with its conjugate ridge flank. Multichannel seismic (MCS) data are downward continued using the Synthetic On Bottom Experiment (SOBE) method, providing unprecedented detail in tomographic models of the P-wave velocity structure to subseafloor depths of up to 1.5 km. Velocities can vary up to 3 km/s over several hundred meters and unusually high velocities (~5 km/s) are found immediately beneath the seafloor in key regions. Correlation with in situ and dredged rock samples, video and records from submersible dives, and a 1.415 km drill core, allow us to infer dominant lithologies. A high velocity body(ies) found to shoal near to the seafloor in multiple locations is interpreted as gabbro and is displaced along isochrons within the OCC, indicating a propagating magmatic source as the origin for this pluton(s). The western two-thirds of the Southern Ridge is capped in serpentinite that may extend nearly to the base of our ray coverage. The distribution of inferred serpentinite indicates that the gabbroic pluton(s) was emplaced into a dominantly peridotitic host rock. Presumably the mantle host rock was later altered via seawater penetration along the detachment zone, which controlled development of the OCC. The asymmetric distribution of seismic velocities and morphology of Atlantis Massif are consistent with a detachment fault with a component of dip to the southeast. The lowest velocities observed atop the eastern Central Dome and conjugate crust are most likely volcanics. Here, an updated model of the magmatic and extensional faulting processes at Atlantis Massif is deduced from the seismic results, contributing more generally to understanding the processes controlling the formation of heterogeneous lithosphere at slow-rate spreading centers.
  • Preprint
    Axial morphology along the Southern Chile Rise
    ( 2012-06) Blackman, Donna K. ; Appelgate, B. ; German, Christopher R. ; Thurber, Andrew R. ; Henig, A. S.
    Morphology of four spreading segments on the southern Chile Rise is described based on multi-beam bathymetric data collected along the axial zones. The distribution of axial volcanoes, the character of rift valley scarps, and the average depths vary between Segment 1 in the south, terminating at the Chile Triple Junction, and Segment 4 in the north, which are separated by three intervening transform faults. Despite this general variability, there is a consistent pattern of clockwise rotation of the southern-most axial volcanic ridge within each of Segments 2, 3, and 4, relative to the overall trend of the rift valley. A combination of local ridge-transform intersection stresses and regional tectonics may influence spreading axis evolution in this sense.