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Sequence and geochronology of Miocene rocks adjacent to the main gulf escarpment: southern Valle Chico, Baja California Norte, Mexico

Stock, J. M. (1989) Sequence and geochronology of Miocene rocks adjacent to the main gulf escarpment: southern Valle Chico, Baja California Norte, Mexico. Geofisica Internacional, 28 (5). pp. 851-896. ISSN 0016-7169.

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Geologic mapping and K/Ar dating of Tertiary rocks in NE Baja California, at latitude 30° 30' N, reveal a history of volcanism from 20 Ma to at least 6 Ma. From 20 to 15 Ma, basalt, andesite and pyroclastic flows locally covered the Cretaceous and older batholithic and prebatholithic rocks. These deposits were followed by up to 300 m of additional pyroclastic flows, reworked tuff, basalt, sandstone and conglomerate. Subsequent eruptions between 11 and 6 Ma produced andesite to rhyolite flows and breccias. Eruptions at about 6 Ma covered the region with up to an additional 300 m of pyroclastic flows, ash fall deposits and welded vitric tuff. These units cap the high plateaus of the northwestern corner of the Puertecitos volcanic province. Local undated volcanic units may be younger than 6 Ma. The tilting, faulting and topographic relief associated with the Main Gulf Escarpment began developing sometime between 11 and 6 Ma; variations in thickness of the pre- I I Ma units arc not generally fault-related, although variations in thickness of the 6 Ma deposits arc. The alignment of four prc-6 Ma volcanic vents along a NNW trend parallel to the present escarpment suggests that ascent of the magmas may have been structurally controlled by Late Miocene extensional faults.

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Stock, J. M.0000-0003-4816-7865
Additional Information:© 1989. Universidad Nacional Autónoma de México. Received: July 27, 1988. Accepted: January 5, 1989. Francisco Suárez Vidal, head of the Geologic Division of the Centro de Investigaciόn Científica y Educaciόn Superior de Ensenada (CICESE), provided valuable assistance with logistical aspects of the field work. Robert Fleck provided access to the argon geochronology laboratory at the U. S. Geological Survey in Menlo Park, and Malcolm Pringle, James Saburomaru, and Jerry von Essen provided patient teaching and assistance there. Kurt Sternlof performed argon spectrometry for the 87-I experiments. R. Gordon Gastil and Clarence Allen lent aerial photos of parts of the map area. Holly Ryan, Lee Clark, Kelly McCloskey, and Kate Whidden assisted in the field. Acknowledgement is made to the Petroleum Research Fund, administered by the American Chemical Society, for the partial support of this research. Additional support was obtained from the Society of Sigma Xi and from the Geological Society of America. J. M. Stock's graduate studies at M. I. T. were supported by a Fannie and John Hertz Foundation fellowship. Comments by T. Byrne, K. Hodges, T. Grove, and an anonymous referee are gratefully acknowledged. Spec. Vol.: Dynamics and Evolution of the Lithosphere, Part 2.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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American Chemical Society Petroleum Research FundUNSPECIFIED
Society of Sigma XiUNSPECIFIED
Geological Society of AmericaUNSPECIFIED
Fannie and John Hertz Foundation FellowshipUNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20140924-074741801
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Official Citation:Sequence and geochronology of Miocene rocks adjacent to the main gulf escarpment: southern Valle Chico, Baja California Norte, Mexico pp.851-896 J. M. Stock
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49965
Deposited By: Ruth Sustaita
Deposited On:09 Oct 2014 21:39
Last Modified:03 Oct 2019 07:18

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