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Paleomagnetism, Geochemistry, and Potassium-Argon Ages of the Rio Grande de Santiago Volcanics, Central Mexico

1971; Geological Society of America; Volume: 82; Issue: 7 Linguagem: Inglês

10.1130/0016-7606(1971)82[1955

1943-2674

Norman D. Watkins, Bernard M. Gunn, Ajoy K. Baksi, Derek York, J. M. Ade‐Hall,

Geology and Paleoclimatology Research

Research Article| July 01, 1971 Paleomagnetism, Geochemistry, and Potassium-Argon Ages of the Rio Grande de Santiago Volcanics, Central Mexico NORMAN D WATKINS; NORMAN D WATKINS Graduate School of Oceanography, Narragansett Marine Laboratory, University of Rhode Island. Kingston, Rhode Island 02881 Search for other works by this author on: GSW Google Scholar BERNARD M GUNN; BERNARD M GUNN Department of Geology, University of Montreal, Montreal, Quebec, Canada Search for other works by this author on: GSW Google Scholar AJOY K BAKSI; AJOY K BAKSI Department of Geological Sciences, Queens University, Kingston, Ontario, Canada Search for other works by this author on: GSW Google Scholar DEREK YORK; DEREK YORK Geophysics Division, Department of Physics, University of Toronto, Toronto 5, Ontario. Canada Search for other works by this author on: GSW Google Scholar JAMES ADE-HALL JAMES ADE-HALL Department of Geology, Dalhousie University, Halifax, Nova Scotia, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information NORMAN D WATKINS Graduate School of Oceanography, Narragansett Marine Laboratory, University of Rhode Island. Kingston, Rhode Island 02881 BERNARD M GUNN Department of Geology, University of Montreal, Montreal, Quebec, Canada AJOY K BAKSI Department of Geological Sciences, Queens University, Kingston, Ontario, Canada DEREK YORK Geophysics Division, Department of Physics, University of Toronto, Toronto 5, Ontario. Canada JAMES ADE-HALL Department of Geology, Dalhousie University, Halifax, Nova Scotia, Canada Publisher: Geological Society of America Received: 06 Jul 1970 Revision Received: 04 Feb 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (7): 1955–1968. https://doi.org/10.1130/0016-7606(1971)82[1955:PGAPAO]2.0.CO;2 Article history Received: 06 Jul 1970 Revision Received: 04 Feb 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation NORMAN D WATKINS, BERNARD M GUNN, AJOY K BAKSI, DEREK YORK, JAMES ADE-HALL; Paleomagnetism, Geochemistry, and Potassium-Argon Ages of the Rio Grande de Santiago Volcanics, Central Mexico. GSA Bulletin 1971;; 82 (7): 1955–1968. doi: https://doi.org/10.1130/0016-7606(1971)82[1955:PGAPAO]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Seventy-two oriented cores of 2.5 cm diameter have been drilled from seven bodies comprising part of a sequence of ignimbrite sheets interdigitated with basalts and basaltic andesites, in the Grand Canyon of the Rio Grande de Santiago of the Mexican Cordilleran Volcanic Province. Field observations and whole-rock analyses reveal two groups: an olivine basalt-high alumina basalt-basaltic andesite series, and a sequence of rhyolitic ignimbrite sheets, with some rhyolitic and obsidian lava flows. Crystal separation, partial melting of oceanic tholeiite, and simple mixing of basalt and oceanic sediments or granodiorite cannot acceptably explain the observed fractionation trends. The favored origin is a partial melting of a second or third stage product, such as a basalt or amphibolite enriched in K, Rb, Th, and Pb, relative to oceanic tholeiite. The observed fractionation trends are parallel to those of the andesite-dacites of the Mexico City region, but the Rio Grande de Santiago rocks have a systematically higher K2O/SiO2 ratio, which can be explained by a greater magma generation depth.The paleomagnetic polarity sequence with decreasing age is R,R,N,R,R,N,N, providing easily measurable markers of high potential stratigraphic value. The mean virtual geomagnetic pole is not significantly different from the present spin axis. The potassium-argon analyses show that the sampled section contains two distinct volcanic episodes, from approximately t = 4.6 to 5.5. m.y. and from approximately t = 8.7 to 9.5 m.y. The polarities recorded by the youngest volcanic cycle are consistent with the predicted polarity time scale of Heirtzler and others (1968), while the older cycle polarities can be explained by minor modification of the predicted polarity scale, to include a short period of reversed polarity between 9.0 and 9.5 m.y., within the normal polarity anomaly 5 (t = 8.79 to 9.94 m.y.) of the time scale. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.