DEFORMATION PRODUCED BY OBLIQUE RIFTING
	WITHJACK, Martha Oliver 
		Mobil Technology Corporation, P. O. Box 650232, 
		Dallas, TX 75265-0232, USA
	JAMISON, William R. 
		Department of Earth Sciences, Memorial University, St. 
		Johns, Newfoundland A1B 3X5, Canada
We have used a series of analytical and experimental (clay) models to 
simulate the deformation patterns associated with oblique rifting.  
With oblique rifting, both extension perpendicular to the rift trend and 
shear parallel to the rift trend contribute to rift development.  The 
relative amounts of extension and shear depend on a, the acute angle 
betweeen the rift trend and the relative displacement direction 
between opposite sides of the rift.  In models with combined extension 
and left-lateral shear, conjugate sets of steeply dipping strike-slip 
faults develop if a is less than 30¡.  If a is 30¡, strike-slip, oblique-
slip, and normal faults form.  The strike-slip faults with left-lateral 
and right-lateral displacement trend at small and large angles to the 
rift trend, respectively.  The normal faults strike about 30¡ 
counterclockwise from the rift trend.  If a exceeds 30¡, only normal 
faults form develop.  They have moderate dips and generally strike 
obliquely to the rift trend and to the relative displacement direction 
between opposite sides of the rift.  If a equals 90¡, the normal faults 
strike parallel to the rift trend and orthogonally to the displacement 
direction.  
Our modeling results apply to the gulfs of California and Aden, 
two Tertiary continental rifts systems produced by combined 
extension and shear.  The modeling results explain the presence and 
trends of oblique-slip and strike-slip faults along the margins of the 
Gulf of California and the oblique trend (relative to the rift trend) of 
many normal faults along the margins of both the gulfs of California 
and Aden.