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Age and stratigraphic relationships of pre- and syn-rift volcanic deposits in the northern Puertecitos Volcanic Province, Baja California, Mexico

Nagy, Elizabeth A. and Grove, Marty and Stock, Joann M. (1999) Age and stratigraphic relationships of pre- and syn-rift volcanic deposits in the northern Puertecitos Volcanic Province, Baja California, Mexico. Journal of Volcanology and Geothermal Research, 93 (1-2). pp. 1-30. ISSN 0377-0273. doi:10.1016/S0377-0273(99)00080-3.

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Geologic mapping of volcanic strata of the northern Puertecitos Volcanic Province (PVP) in northeastern Baja California, Mexico, performed in conjunction with ^(40)Ar/^(39)Ar analysis and petrochemical study, documents the Miocene geologic history of a well-preserved volcanic succession within the northern Sierra Santa Isabel and its relationship to the evolving Pacific–North America plate boundary. Subduction-related volcanic deposits, well-exposed in profile along the northern margin of the PVP in the informally named Santa Isabel Wash region, span pre-17 to 15 Ma. Minor rift-related volcanism occurred at ∼12.5 and ∼9 Ma, prior to voluminous PVP-forming volcanism at ∼6–6.5 Ma. Isochron ages typically exhibit precision (1σ) for plagioclase of ±2–7% and for anorthoclase and sanidine of ±2–5%, and replicate analysis of an internal anorthoclase standard indicate ∼1–2% reproducibility within a given irradiation and ∼2.5% for samples irradiated separately. Improved local correlations made possible by the rich stratigraphic section preserved in Santa Isabel Wash help constrain the relationships of several widespread pyroclastic flow deposits in northeastern Baja California. These correlations are important for both paleomagnetic studies within the region and for establishing geologic ties across the Gulf of California. The combined mapping and age results imply that most extensional deformation in the study area is post-6 Ma, although some earlier faulting and the development of the pre-6 Ma Matomı́ accommodation zone are also documented. Results support a transitional plate boundary model which implies that much of the Pacific–North America relative plate motion north of Delfı́n basin (i.e., the northernmost Gulf of California) is accommodated on N- to NNW-striking faults developed during Late Miocene ENE-directed extension. The model predicts a zone of divergence east of the PVP which provides a structural mechanism for the positions and jumps of nearby Gulf of California spreading centers (Upper and Lower Tiburón and Delfı́n basins) since 6 Ma, and relates major pulses of PVP volcanism at ∼6 and ∼3 Ma to these offshore spreading center adjustments. Results also imply that most extensional deformation in Santa Isabel Wash is the result of incorporation of the PVP into the Gulf Extensional Province ∼2–3 Ma due to northwestward propagation of the Guaymas fracture zone. Rotational deformation north of the PVP may have begun contemporaneously with this adjustment along the Gulf Extensional Province rift margin.

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Stock, Joann M.0000-0003-4816-7865
Additional Information:© 1999 Elsevier Science B.V. Received 6 October 1997; accepted 20 August 1998. E.A.N. thanks M.A. House, A.J.R. Kent, C.J. Lewis, and X.Y. Quidelleur for helpful discussions and reviews of early versions of this manuscript. K. Holt, K. Rostedt, T. Tyndall, and K. Wertz are thanked for invaluable field assistance, and P. Kokelaar and M. Howells are thanked for their enlightening visit to the field area. X.Y. Quidelleur and K.D. Mahon are also acknowledged for providing software employed to analyze the ^(40)Ar/^(39)Ar results. G. Axen is thanked for providing a preprint (Axen and Fletcher, 1998) and C.J. Lewis is thanked for providing assistance with Fig. 1. We appreciate helpful reviews by G. Axen, C. Devey, and M. Heizler. This work was supported by NSF grants EAR-9218381, -9296102, and -9614674. This is contribution 6220 from the Division of Geological and Planetary Sciences of the California Institute of Technology.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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Subject Keywords:Puertecitos Volcanic Province; 40Ar/39Ar geochronology; Gulf Extensional Province; volcaniclastic deposit; lava flow; pyroclastic flow deposit
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Caltech Division of Geological and Planetary Sciences6220
Issue or Number:1-2
Record Number:CaltechAUTHORS:20140414-080523933
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Official Citation:Elizabeth A Nagy, Marty Grove, Joann M Stock, Age and stratigraphic relationships of pre- and syn-rift volcanic deposits in the northern Puertecitos Volcanic Province, Baja California, Mexico, Journal of Volcanology and Geothermal Research, Volume 93, Issues 1–2, 15 November 1999, Pages 1-30, ISSN 0377-0273, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44906
Deposited By: Ruth Sustaita
Deposited On:14 Apr 2014 15:30
Last Modified:10 Nov 2021 16:57

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