HR: 11:50h
AN: T11E-07 INVITED     [PDF]
TI: The Formation of Non-Volcanic Rifted Margins by the Progressive Extension of the Continental Lithosphere
AU: * Reston, T J
EM: treston@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, D24226 Germany
AU: Perez-Gussinye, M
EM: martap@earth.ox.ac.uk
AF: Dept Earth Sciences, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Gaw, V
EM: vgaw@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, D24226 Germany
AU: Phipps Morgan, J
EM: jmorgan@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, D24226 Germany
AB: Rifted margins include two main end-members: those termed "Volcanic Rifted Margins - VRMs" where magmatism is much more voluminous than predicted by passive asthenospheric upwelling (e.g. White et al., 1989), and those where magmatism is consistent or even less than the same predictions. The latter are termed "Non-Volcanic Rifted Margins - NVRMs" to emphasise the contrast with the VRMs: the name does not exclude the presence of minor amounts of magmatic activity. The NVRMs are typified by the North Biscay, south Australian, SW Greenland, and the West Iberian margins, which share a number of common characteristics: - extreme crustal thinning, increasing towards the ocean; - presence of well-defined rotated fault blocks. However at the feather edge of the continent there is an extension discrepancy: the amount that can be inferred from the geometry of these faults is far less than that indicated by the crustal thinning observed; - presence in places of a detachment fault at the base of the fault blocks; - little evidence for synrift magmatism; - the presence of a broad zone of partially serpentinised mantle (Boillot et al., 1988; Whitmarsh et al., 1996; Krawczyk et al., 1996; Pickup et al., 1996), both occurring beneath the highly thinned and faulted continental crust, and as a zone of exhumed continental mantle, now largely buried by postrift sediments. We show that such margins are the logical result of progressive extension of continental lithosphere above cool sub-lithospheric mantle. The key factors controlling the development of the margin are the rheological evolution of the crust (explaining the serpentinisation of the mantle), the occurrence of multiple phases of faulting (explaining the apparent extension discrepancy), and the temperature structure of the sub-continental mantle (explaining the lack of magmatism).
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting