Kinematic Model for Evolution of a "Transtensional" Basin from Transform Fault Whose Initial Displacement is Purely Strike-Slip

Vincent S. Cronin

The instantaneous motion of one plate as observed from another plate can be described as a simple rotation around a pole of relative motion. In contrast, relative motion generally cannot be described as a single rotation throughout an extended (finite) time interval. Consequently, a transform plate-boundary fault will generally have a component of convergence (transpression) or divergence (transtension) during finite displacements. The cycloid model for finite relative plate motion provides a way to describe the systematic variation in the direction and magnitude of relative plate motion through time, permitting the kinematic modeling of transtensional basins.

In this study, a synthetic transform fault between the Pacific and North American plates was modeled. The fault trace coincided with a small circle around the North American-Pacific relative pole at the time the Gulf of California began to open, about 6 Ma. Displacement along the fault from 6 Ma to today was simulated with the cycloid model. A transtesional gap developed along the southern reach of the fault, and the northern segment of the fault was transpressional. The gap simulated by the model is similar in shape and magnitude to the gap represented by the observed Gulf of California and Salton Trough. In contrast, neither transpression nor transtension would occur along this fault if finite relative plate motion had occurred around a fixed pole of rotation throughout the past 6 m y.

The cycloid model provides an improved method of kinematic modeling for basins whose evolution is closely linked to the finite relative motion of plates.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.