The continental lithosphere - The Solid Earth - page 569

Figure 10.43. A schematic model of the development of a non-volcanic rifted
margin, based on the Iberian margin and the Tethyan margin as exposed in the Alps.
(a) The initial lithosphere has four layers - strong upper crust, weak lower crust,
strong upper mantle and weak underlying mantle. (b) Lithosphere 'necks' beneath
an underplated gabbro; ductile lower crust controls rift basins. (c) Rising
asthenosphere has a major influence on the style and location of rifting; extensive
thinning of continental crust; subcontinental mantle exposed. (d) Mid-ocean-ridge
basalts intruded into and onto exposed subcontinental mantle, seafloor spreading
begins; margin has a very wide transition zone between oceanic crust and
continental crust. The conjugate margin need not be symmetrical. Shown to true
scale. Reprinted with permission from Nature (Whitmarsh et al ., Nature , 413 , 150-4.
Copyright 2001 Macmillan Magazines Ltd.)

the start of seafloor spreading, coupling between the flow at the margin and that
at the ridge axis may be possible.
In contrast, further to the south in the Atlantic off the Iberian penninsula
(the conjugate margin to Newfoundland formed at 130 Ma) is a non-volcanic

margin. It lacks any associated volcanic province and seaward-dipping reflectors

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