Stock, Joann M. and Lewis, Claudia J. and Nagy, Elizabeth A. (1999) The Tuff of San Felipe: an extensive middle Miocene pyroclastic flow deposit in Baja California, Mexico. Journal of Volcanology and Geothermal Research, 93 (1-2). pp. 53-74. ISSN 0377-0273. doi:10.1016/S0377-0273(99)00079-7. https://resolver.caltech.edu/CaltechAUTHORS:20140414-073556126
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Abstract
We document the existence of a widespread Miocene ash-flow tuff sheet in northeastern Baja California, Mexico. The Tuff of San Felipe (new name) was erupted from a vent east of the Sierra San Felipe of NE Baja California at ca. 12.6 Ma. This is the only widespread middle Miocene pyroclastic flow deposit identified in northeastern Baja California. Its distinctive age and widespread distribution make it an important marker horizon for structural reconstruction of this part of the Gulf Extensional Province, which is on the Pacific plate. The vent position, near the modern Gulf of California coast, allows the possibility that exposures of the Tuff of San Felipe may be preserved east of the Gulf on the North America plate in Sonora, yielding a tie point for the past relative position of the two plates. This paper summarizes all known information including petrography, geochemistry, geochronology, paleomagnetics, geographic distribution, and field appearance of this important tuff. It is a densely welded, crystal-rich, lithic-lapilli pyroclastic flow deposit, with 5–15% alkali feldspar, and can be 180 m thick in some locations near the vent. The Tuff of San Felipe is >40 m thick up to 40 km SW of the vent and >10 m thick at least 25 km NNW of the vent. A minimum volume estimate for the deposit is 54 km^3. Some recent ^(40)Ar/^(39)Ar age determinations suggest that the tuff is about 12.6 Ma in age. In all locations studied, the Tuff of San Felipe has a unique, low-inclination, reversed magnetization, which may record a field transition or a geomagnetic excursion within reversed polarity subchron C5Ar.2r (12.401 to 12.678 Ma). This low-inclination magnetization, as well as the mineralogy and age, is key to correlating the tuff across the region, because deposits are highly disrupted by subsequent normal faulting and outcrops are sparse and discontinuous away from the vent. The documentation of these characteristics is important because the Tuff of San Felipe is a key structural marker for the subsequent development of the Pacific–North America plate boundary in the Gulf of California, and it will be important to identify this tuff in outcrops elsewhere on the Baja California Peninsula and on the North America plate in Sonora.
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| Additional Information: | © 1999 Elsevier Science B.V. Received 6 October 1997; received in revised form 12 March 1999; accepted 3 May 1999. This work was supported by NSF grants EAR-92-18381 and EAR-96-14674. California Institute of Technology, Division of Geological and Planetary Sciences, contribution 6219. We thank Kip Hodges for access to the MIT CLAIR facility for the argon analyses. XRF analyses were performed at the University of Massachusetts, Amherst. We thank Fred McDowell, Luca Ferrari, and Kozo Uto for very helpful reviews of an earlier version of the manuscript. | |||||||||
| Group: | Seismological Laboratory, Division of Geological and Planetary Sciences | |||||||||
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| Subject Keywords: | Gulf of California; Baja California, Mexico; ignimbrite; 40Ar/39Ar | |||||||||
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| Issue or Number: | 1-2 | |||||||||
| DOI: | 10.1016/S0377-0273(99)00079-7 | |||||||||
| Record Number: | CaltechAUTHORS:20140414-073556126 | |||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20140414-073556126 | |||||||||
| Official Citation: | Joann M Stock, Claudia J Lewis, Elizabeth A Nagy, The Tuff of San Felipe: an extensive middle Miocene pyroclastic flow deposit in Baja California, Mexico, Journal of Volcanology and Geothermal Research, Volume 93, Issues 1–2, 15 November 1999, Pages 53-74, ISSN 0377-0273, http://dx.doi.org/10.1016/S0377-0273(99)00079-7. (http://www.sciencedirect.com/science/article/pii/S0377027399000797) | |||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | |||||||||
| ID Code: | 44905 | |||||||||
| Collection: | CaltechAUTHORS | |||||||||
| Deposited By: | Ruth Sustaita | |||||||||
| Deposited On: | 14 Apr 2014 15:27 | |||||||||
| Last Modified: | 10 Nov 2021 16:57 |
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