Michael C. Puchalski¹, Paul J. Umhoefer¹, Larry Mayer²

(1) Northern Arizona University, Flagstaff, AZ
(2) University of Arizona

ABSTRACT: Evidence for Regional Strain Partitioning in the Southern Gulf of California: A Modern Analogue for Ancient Petroleum Provinces

The southern Baja California peninsula, Mexico, lies along an oblique-divergent plate boundary, which occupies the Gulf of California. Strain partitioning has been recognized as an important process in many oblique plate margins but is still poorly understood in oblique-divergent settings. Patterns of active faulting and modern seismicity along the southern portion of the Baja California plate boundary suggest strain partitioning on a regional scale. Fault plane solutions for earthquakes along transform faults in the deep gulf indicate strike-slip motion. Conversely, large earthquakes within the plate margin indicate normal motion. Numerous late Quaternary faults also suggest dominantly normal, dip-slip offset. Therefore, east-west extensional faulting is located in the margin along Baja California, while northwest-directed transform motion occurs along the main plate boundary.

Based on the above criteria, the southern Baja California peninsula may be divided into two domains. The first domain, from ~25° latitude to the southern tip of the peninsula includes multiple normal faults that cut across the narrow marine shelf and peninsula and have facilitated several moderate to large earthquakes this century. The second domain, from ~25° to ~30° shows late Quaternary normal faults, but significantly less modern seismicity. Therefore, the entire southern Baja California peninsula shows a similar style of strain partitioning, but the extensional component along the margin is much more significant in the southern domain.

Studying the strain partitioning patterns of this active plate boundary may provide a modern analogue to the development of ancient petroleum provinces that have developed in such plate tectonic settings.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado