Dikes Intrusions and the Formation of MidOcean Ridge Faults
Abstract
The first numerical model that treats faulting and dike intrusions in a mechanically consistent way is used to simulate midocean ridge topography, fault patterns and extrusive thicknesses. The observed range of these features are reproduced by varying three variables: the effective radius of the axial partial melt or mush zone, R; the time interval between diking episodes , T; and the axial lithosphere thickness, D. The mush zone radius R controls the amount of magma that can be supplied to fill dikes and erupt for a given driving pressure. For reasonable values of the diking time interval it is the ratio of R to D that controls the height to which dikes may build topography. For R/D > ~1 an axial high can result. If the diking time interval T is greater than the time to develop lithosphere scale faults, Tf, then a valley will result if R/D < ~1. The observed spreading rate dependence of axial relief is reproduced if the axial lithospheric thickness is inversely related to spreading rate and the effective magma mush region is directly related to spreading rate. The maximum depth of an axial valley with little or no magma input is limited by the value of D. Fault offsets, similar to those seen in association with axial valleys, result when T>Tf. Fault offset increases with increasing dike time interval. Oceanic core complex style, unlimited fault offset for a restricted range of parameters: the dike time interval, T must be close to twice the time for stresses to build the level of faulting Tf; the effective magma source dimension R must be less than the axial lithospheric thickness D.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.T53B1294Q
 Keywords:

 8120 Dynamics of lithosphere and mantle: general (1213);
 8145 Physics of magma and magma bodies;
 8164 Stresses: crust and lithosphere;
 8178 Tectonics and magmatism;
 8416 Midoceanic ridge processes (1032;
 3614)