HR: 11:35h
AN: T32A-06    [Abstracts]
TI: On the Geodynamics of Oblique Spreading
AU: * Montesi, L
EM: montesi@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Geology and Geophysics WHOI MS 24, Woods Hole, MA 02543 United States
AU: Behn, M D
EM: mbehn@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Geology and Geophysics WHOI MS 24, Woods Hole, MA 02543 United States
AU: Barry, J
EM: jbarry1@swarthmore.edu
AF: Woods Hole Oceanographic Summer Student Fellowship Program, Dept. Geology and Geophysics, Woods Hole, MA 02543 United States
AB: Oblique spreading segments are more common at ultraslow spreading ridges than at any other type of mid-ocean ridge. Obliquity is particularly important at slow spreading ridges like the Southwest Indian Ridge as it causes their melting regime to approach that of an ultraslow spreading center. To explain this phenomenon, Dick et al. [2003] observed that the area of crust accreted per unit ridge length decreases with increasing obliquity. For a more thorough understanding of this phenomenon, we solve for the flow field and temperature structure of the mantle in the context of oblique spreading. Considering an infinitely long oblique segment, a natural reference frame has one axis oriented along the ridge. The solution is then invariant in that direction. Assuming that the mantle behaves as a Newtonian fluid, the flow field can be decomposed into a ridge-parallel component and a component in the plane perpendicular to the ridge (cross-axis component). Both components can be solved analytically. The along-strike component obeys Laplace's equation while the cross-ridge component follows the classical corner flow solution, but with a reduced driving velocity corresponding to the effective spreading rate. Therefore, the upwelling velocity decreases with the cosine of the obliquity angle. Ignoring conductive cooling, the melt produced per unit length of the ridge should decrease in the same manner. However, the area accreted per unit length of the ridge also decreases with the cosine of the obliquity angle. Therefore, obliquity does not influence crustal thickness directly. On the other hand, conduction in the plane perpendicular to the ridge is more important for oblique spreading because of the reduced corner flow velocity. This enhanced cooling reduces melt generation by truncating the summit of the melt column and total crustal thickness is shown to scale with the effective spreading rate. The flow solution also leads to the prediction of the principal stress directions in the lithospheric plates. Ridge obliquity rotates the stresses with the resulting principal stress directions oriented at an intermediate angle between the ridge-perpendicular and spreading-parallel directions. This implies that if a ridge-parallel fabric is present an additional set of faults should be expected.
DE: 3035 Midocean ridge processes
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8164 Stresses: crust and lithosphere
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: Fall Meeting 2005