Characterising the extent of volcanism at the Galapagos Spreading Centre using Deep Tow sediment profiler records


Neil C. Mitchell

Volcanism at the Galapagos Spreading Centre consists of sheet flows and other distributed extrusives. The surficial volcanics in the axial region should therefore be generally young over a finite area and those on the ridge flanks should be younger, on average, than would be predicted from simple seafloor spreading. A method for determining an upper bound on the mean age anomaly of the flanks, which is interpreted as equivalent to the mean extent of volcanism, is demonstrated using sediment thicknesses digitised from Deep Tow profiler records of the Galapagos Spreading Centre. As found previously, the sediments thicken linearly with distance from the ridge, reflecting simple seafloor spreading up to ~1 Ma. Deviations from the linear trend are due to sediment redistribution (short wavelength fluctuations) and the age distribution of extrusives, in particular due to large volcanic flows revealed by regions of uniform thickness. The full width of the extrusion zone is obtained by regressing sediment thickness on across-axis distance for both flanks and observing the separation of the two regression lines where they cross zero thickness. Since the method is quantitative and provides an average value for the length of the profile, it is more representative than estimating the width from morphological observations of the spreading axis. Due to scattering from the basement, which obscures sediment in depressions, sediment thickness is generally under-estimated and the measured axial width is an upper bound (10-12 km for the Galapagos Spreading Centre). The mean sediment thickness bias is calculated from high-resolution topography data of lava flows and is ~1.5 m, suggesting that the true mean width of the extrusion zone is 8-10 km. Using this corrected value, the surface of the crust is younger than predicted by seafloor spreading by ~120-150 kyr, on average. This large value implies that the flanks of the Galapagos Spreading Centre are covered with a series of large overlapping volcanic flows.

Mitchell, N. C., "Characterising the extent of volcanism at the Galapagos spreading centre using Deep Tow sediment profiler records", Earth Planet. Sci. Lett., 134, 459-472, 1995.


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