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Paleomagnetic evidence of localized vertical axis rotation during Neogene extension, Sierra San Fermín, northeastern Baja California, Mexico

Lewis, Claudia J. and Stock, Joann M. (1998) Paleomagnetic evidence of localized vertical axis rotation during Neogene extension, Sierra San Fermín, northeastern Baja California, Mexico. Journal of Geophysical Research B, 103 (B2). pp. 2455-2470. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20140415-123711983

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Abstract

Paleomagnetic data from Sierra San Fermín in the Gulf of California Extensional Province indicate that localized clockwise rotations about vertical axes occurred during Pliocene through Recent extension and dextral shear. Relative declination discordances in upper Miocene and Pliocene ash flow tuffs indicate a net clockwise rotation of 30° ± 16°. Clockwise rotation between 12.5 and 6 Ma is statistically insignificant (11° ± 17°). Structural observations and geochronological data suggest that rotations in this area began post-6 Ma, comprising uniform-sense block rotations (oblique divergence) associated with extension and dextral slip in the northwest striking boundary between the Pacific and North American plates. Northeast striking sinistral-slip faults and north striking normal faults accommodate distributed dextral shear in this area, allowing fault blocks to rotate in a clockwise sense. A model for oblique divergence predicts ∼21 km of shear in the direction of relative plate motion and ∼20% (∼7 km) ENE directed extension, perpendicular to the Main Gulf Escarpment. A broad region of northeastern Baja California may have undergone similar distributed shear. Two possible dynamic models may explain this shear. In one model, rotation accumulates above a deep, subhorizontal, basal shear zone. Rotating blocks may extend downward to a detachment beneath the extensional province, either a low-angle eastward continuation of the San Pedro Mártir fault or to a basal shear surface on top of a subducted remnant of the Farallon plate. Alternatively, distributed dextral shear may be the surface manifestation of a deep vertical shear zone linking transform faults in the northern gulf with dextral transpeninsular faults. In either case, shear may have transferred northward onto faults west of the San Andreas fault, contributing to late Miocene to Recent clockwise rotation of the Western Transverse Ranges. This shear is not accounted for in the 300 km of dextral slip computed from cross-gulf geologic tie points.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/97JB02673DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/97JB02673/abstractPublisherArticle
ORCID:
AuthorORCID
Stock, Joann M.0000-0003-4816-7865
Additional Information:© 1998 American Geophysical Union. Manuscript Accepted: 18 Sep 1997; Manuscript Received: 10 Mar 1997. This research was partially supported by a National Science Foundation grant (EAR-92-18381) and a Presidential Young Investigator Award (EAR-92-96102) to Joann M. Stock. Additional support was provided by the Harvard University Department of Earth and Planetary Sciences Grants-in-Aid for Fieldwork. We thank Joe Kirschvink for the use of his paleomagnetics laboratory and sampling equipment, John Holt for patient guidance in the field and the lab, and the Division of Geological and Planetary Sciences at the California Institute of Technology for many resources necessary for completion of this project. We are grateful to Mario Rebolledo Vieyra and Liz Warner Holt for assistance in the field and to John Holt, Tim Melbourne, Elizabeth Nagy, and Leslie Sonder for many helpful discussions. Revisions were done at the Universitat de Barcelona, funded in part by a Fulbright Fellowship to Lewis. We thank John Geissman, Jonathan Hagstrum, Mark Hudson, Bruce Luyendyk, Steve Sheriff, and Paul Umhoefer for careful reviews. This is California Institute of Technology Division of Geological and Planetary Sciences contribution 5615.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-92-18381
NSF Presidential Young Investigator AwardEAR-92-96102
Harvard University Department of Earth and Planetary Sciences Grants-in-Aid for FieldworkUNSPECIFIED
Fulbright FellowshipUNSPECIFIED
Subject Keywords:Continental neotectonics; Paleomagnetism applied to tectonics: regional, global; Structural Geology; Tectonophysics: Continental tectonics—extensional
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5615
Issue or Number:B2
Record Number:CaltechAUTHORS:20140415-123711983
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140415-123711983
Official Citation:Lewis, C. J., and J. M. Stock (1998), Paleomagnetic evidence of localized vertical axis rotation during Neogene extension, Sierra San Fermín, northeastern Baja California, Mexico, J. Geophys. Res., 103(B2), 2455–2470, doi:10.1029/97JB02673.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44958
Collection:CaltechAUTHORS
Deposited By: Aucoeur Ngo
Deposited On:17 Apr 2014 16:46
Last Modified:03 Oct 2019 06:24

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