DESCRIPTION AND KINEMATICS OF THE SE LORETO BASIN FAULT ARRAY, BAJA-CALIFORNIA-SUR, MEXICO - A POSITIVE FIELD-TEST OF OBLIQUE-RIFT MODELS

We present the results of mapping and kinematic analysis on an similar to 18 km2 array of normal and oblique-slip faults in the SE Loreto ba sin, near Loreto, Baja California Sur, Mexico. The fault array develop ed on the western margin of the Gulf of California in late Pliocene ti me, during the early part of the modern stage of oblique rifting of th e gulf. The SE Loreto fault array is an antithetic transfer zone betwe en two large, E-dipping normal faults. The fault array is coherent and formed in one episode. The dominant N- to NNE-striking faults primari ly dip W and display nearly pure normal slip. More NE-striking faults show normal-sinistral slip and NW-striking faults have dextral-normal to dextral slip. N- to NW-striking faults have steeper dips and a grea ter component of dextral slip with more northwesterly strike. Bulk ext ension, based on strain analysis of faults with striae, is oriented ne arly E-W with little plunge and consistent throughout the fault array. The kinematic analysis of the SE Loreto fault array provides a well-c onstrained test of oblique-rift models. Our results support previous m odeling of homogeneous extension in oblique-rifted margins when both i nstantaneous and finite strain are considered. Positive field tests of analytical and experimental models, such as this one, indicate that s uch models may be robust predictors of the obliquity of rifting in anc ient mountain belts where brittle fault arrays are preserved. but plat e motions are unknown. (C) 1996 Published by Elsevier Science Ltd