Electronic Resource
Oxford, UK
:
Blackwell Publishing Ltd
Geophysical journal international
98 (1989), S. 0
ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
In two recent papers, normal incidence and expanding spread profiles (ESPs) shot across the Hatton Bank passive continental margin showed seaward dipping reflectors in the upper crust and elevated velocities in the lower crust. The reflectors were interpreted as subaerial basalt flows and the high velocities as underplated or intruded igneous material in the lower crust. A recent gravity model shows high densities in the lower crust supporting the velocity model. In this study we present the forward modelling of two wide-angle seismic refraction datasets shot perpendicular to strike and through the ESP midpoints. The final velocity model across the margin is consistent with all the seismic datasets but differs in some important respects from the ESP-based model: a high velocity volcanic pile is outlined mid-way up the continental slope and the inferred velocities in the lower crust are slightly lower. The differences between the two models can be explained by the three-dimensional nature of the margin: the ESPs were modelled assuming that the sub-sediment structure was invariant along strike. The final velocity model is used to obtain an estimate of the total thickness of melt accreted across the margin, which is calculated to thicken from zero at Hatton Bank to about 12km mid-way down the continental slope. At the bottom of the continental slope the adjacent igneous section forming the oceanic crust is about 18 km thick and thins rapidly northwestwards to 11 km. As the oceanic crust thins its seismic velocity decreases; this suggests that it is less mafic and that there is a post-rift decrease in the percentage of mantle melting. This decrease may be explained by a decrease in asthenospheric temperature and/or by a reduction in volatile content.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1989.tb03358.x
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