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Published August 1998 | public
Journal Article

Late Miocene to Recent transtensional tectonics in the Sierra San Fermín, northeastern Baja California, Mexico

Abstract

Basins and ranges within part of the Gulf of California Extensional Province (Mexico) have experienced complex distributed deformation, including normal and strike-slip faulting and block rotations, linked to dextral shear at the Pacific–North America plate boundary. In the Sierra San Fermı́n and southern Sierra San Felipe (northeastern Baja California), normal faulting began between 12.5 and 6 Ma, although most extension occurred between about 6 and 3 Ma, strongly influencing thickness and distribution of ash-flow tuffs and sedimentary deposits. Extension is generally <10% in 6 Ma rocks and somewhat more in 12.5 Ma rocks. Inversion of kinematic data, interpreted together with published paleomagnetic data, suggests that the axis of least principal stress was oriented between W–E and SW–NE in late Miocene time. Our data indicate an important change in the amount of dextral shear, but not necessarily the least principal stress direction (WSW–ENE), at about 3 Ma. Structural constraints limit significant sinistral strike-slip faulting, conjugate to the dextral plate boundary, to the last ∼3 My. Progressive changes in the geometry of faulting through time are consistent with regional strain partitioning within the Pacific–North America plate boundary zone, and are predicted by physical and analytical models of oblique divergence as the orientation of the stretching vector α changes to lower and lower values.

Additional Information

© 1998 Elsevier Science Ltd. Received 4 March 1997; accepted in revised form 31 March 1998. This research was partially supported by National Science Foundation grants EAR-89-04022 and EAR-92-18381 and a Presidential Young Investigator Award (EAR-90-58217/EAR-92-96102) to Joann M. Stock. Additional support was provided to Claudia Lewis by the Harvard University Department of Earth and Planetary Sciences Grants-in-Aid for Fieldwork. We thank John Gephart for his generosity in allowing us to use his computer program FMSI for inverting fault/slickenline data, Rick Allmendinger and Randy Marrett for use of FaultKin, and the Division of Earth and Planetary Sciences at the California Institute of Technology for many resources necessary for completion of this project. We are grateful to Josephine Burns, Cheryl Contopulos, Tim Johnson, Dan Reilly, Chris Small, and Susan Turbek for assistance in the field and to Mark Abolins, Gary Axen, Jeff Lee, Arturo Martín Barajas, Tim Melbourne, Elizabeth Nagy, Zeke Snow, and Leslie Sonder for many helpful discussions. We thank Richard Norris and two anonymous referees for constructive reviews which greatly improved the manuscript.

Additional details

Created:
August 19, 2023
Modified:
October 26, 2023