HR: 1340h
AN: V33A-1459    [Abstracts]
TI: Numerical Modelling of Formation of Sheeted-Dyke Complex at Different Types of Mid-Ocean Ridges
AU: * Kuehn, D
EM: daniela.kuehn@dkrz.de
AF: Institute of Geophysics, University of Hamburg, Bundesstr. 55, Hamburg, 20146 Germany
AU: Dahm, T
EM: dahm@dkrz.de
AF: Institute of Geophysics, University of Hamburg, Bundesstr. 55, Hamburg, 20146 Germany
AB: Magma dykes are the most important structural elements of oceanic crust. In this work, attention is concentrated on the origin of the sheeted-dyke complex. Generally, it is formed by solidification of episodic intrusions from magma reservoirs. Up to now, most models are qualitative and tend to neglect stress fields arising from dyke openings. In this model, heterogeneities of the stress field are calculated quantitatively and are taken into account. A modified boundary element code capable of simulating quasi-static finite-volume fluid-filled fracture growth and movement in an elastic lithosphere under inhomogeneous stress loading is used. Numerical models for slow to fast spreading ridges are presented. Slow spreading ridges, possessing magma reservoirs at the crust-mantle boundary with large extension perpendicular to the ridge, demand broad dyke injection zones with continuous magma supply, whereas melt ascent from crustal magma chambers at fast spreading ridges generates only narrow dyke injection zones. Despite the different origins of magma at slow and fast spreading ridges, the sheeted-dyke complex looks similar. Finally, ridges spreading at intermediate rates provide discontinuous magma supply for crust formation either by unstable crustal magma chambers or by feeding of the sheeted-dyke complex by underlying sills. Results of modelling are that stress fields caused by dyke emplacement cannot be neglected in any models for the formation of oceanic crust, since self-induced stress fields can locally surmount the effect of regional stress fields. For example, crossing and focussing of dykes may either lead to the development of volcanic centres with different spacing or to pooling of sills building up a whole layer, the behaviour being dependent e.g. on dyke lenghts. Moreover, the focussing of dykes may generate a cumulative stress field similar to that of an elliptical magma chamber in a kind of self-organising way. If a regional, extensional stress field is introduced additionally, both narrow and broad dyke injection zones result in parallelism of ascending dykes and thus favour the construction of a sheeted-dyke complex. Acknowledgments: The project is supported by the German Research Foundation (DFG).
DE: 8434 Magma migration
DE: 7220 Oceanic crust
DE: 8164 Stresses--crust and lithosphere
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting