HR: 0800h
AN: T11C-0399    [Abstracts]
TI: The Significance of Sheeted Dyke Complexes in Ophiolites For Spreading Dynamics in SSZ Environments
AU: * Robinson, P T
EM: p.robinson@ns.sympatico.ca
AF: Department of Earth Sciences, Dalhousie University, Halifax, NS B3H3J5 Canada
AU: Malpas, J
EM: jgmalpas@hku.hk
AF: Department of Earth Sciences, The University of Hong Kong Pokfulam Road, Hong Kong, 100000 Hong Kong
AU: Zhou, M
EM: mfzhou@hku.hk
AF: Department of Earth Sciences, The University of Hong Kong Pokfulam Road, Hong Kong, 100000 Hong Kong
AU: Dilek, Y
EM: dileky@muohio.edu
AF: Department of Geology, Miami University, Oxford, OH 45056 United States
AB: Sheeted dike complexes form a crucial part of the ophiolite definition and are commonly interpreted as evidence of seafloor spreading similar to that occurring at mid-ocean ridges. By analogy with mid-ocean ridges, well-developed sheeted complexes in ophiolites are generally considered to have formed in fast-spreading environments, whereas poorly developed complexes are taken as evidence of formation at slow-spreading ridges. However, ophiolites form in suprasubduction zone (SSZ) environments where the relationship between spreading rate and magma supply is entirely different from that at mid-ocean ridges. At most mid-ocean spreading centers, the spreading rate and magma supply are linked by convection such that there is an approximate balance between the two, as indicated by the relatively uniform thickness of oceanic crust (approximately 6 km), whether formed at fast- or slow-spreading ridges. In contrast, spreading in suprasubduction zone environments is controlled by the rate of subduction rollback, which may be linked to rates of mantle extrusion, the age of the subducting lithosphere, and/or the angle of subduction. Magma supply rates in suprasubduction zones reflect local temperature gradients, the mode of asthenospheric upwelling, the volume of subducted fluids, and the nature of the subducted slab, and thus may be independent of the spreading rate. In a SSZ environment rapid slab rollback would produce a fast-spreading regime in which the magma supply could be low. This would lead to extensive tectonic disruption similar to that seen along slow-spreading mid-ocean ridges such as MAR and SWIR, and the formation of thinner crustal sections than found in modern ocean basins. Well-developed sheeted dyke complexes, such as those of Troodos and Semail, represent a fortuitous balance between spreading and magma supply rates in a suprasubduction zone environment. In most ophiolites, however, such a balance is not maintained, leading to significant tectonic dismemberment of their crustal sections prior to emplacement on continental margins.
DE: 8140 Ophiolites (3042)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: Fall Meeting 2005