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Southern Cordilleran Basaltic Andesite suite, southern Chihuahua, Mexico: A link between Tertiary continental arc and flood basalt magmatism in the North America

Journal Article · · J. Geophys. Res.; (United States)
; ; ; ;
Mid-Cenozoic orogenic andesites and ignimbrites of western Mexico, southwestern New Mexico, and Arizona are commonly capped by basaltic andesites, most from 29--20 Ma. We refer to these mafic lavas as the Southern Cordilleran Basaltic Andesite (SCORBA) suite, and they may constitute the most extensive Cenozoic basaltic suite in North America. The SCORBA suite has trace element and isotopic characteristics of orogenic (arc) rocks (i.g., Ba/Nb/gt/40), and silica content (53--56% SiO/sub 2/) like the Grande Ronde Basalt, which represents about 80% of the volume of the Columbia River Group. Geochemical and isotopic data are presented on SCORBA lavas and rare mafic lavas (PRE-SCORBA) interlayered with older ignimbrites from a 700-km-long NE-SW transect of southern Chihuahua, Mexico. SCORBA and PRE-SCORBA lavas with relatively low K/P (/lt/7) and differing Ba/Nd (50 versus 18) have similar isotopic compositions, arguing against their isotopic signatures being controlled by crustal assimilation. Along the entire length of the transect, the basaltic rocks have /var epsilon//sub Nd/ and /sup 87/Sr//sup 86/Sr near bulk Earth and /sup 206/Pb//sup 204/Pb and /sup 207/Pb//sup 204/Pb ratios that lie along a 1.7 Ga pseudoisochron. The Pb isotopic variation is geographically controlled, becoming more radiogenic from east to west, reflecting mixing in mantle source regions. The eastern mantle source has low/sup 206/Pb//sup 204/Pb and is a mixture of an enriched, enriched-mantle-like (EMI) component with one or more depleted components, which could include an intraplate component with relatively high Nb/Y (/gt/0.8).
Research Organization:
Earth Sciences, University of California, Santa Cruz(US); Nuclear Chemistry, Lawrence Livermore National Laboratory, Livermore, California; Earth Sciences, University of California, Santa Cruz
OSTI ID:
5875939
Journal Information:
J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 94:B6; ISSN JGREA
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580202* -- Geophysics-- Volcanology-- (1980-1989)
ALKALINE EARTH ISOTOPES
BASALT
CENOZOIC ERA
CONTINENTAL CRUST
DEVELOPING COUNTRIES
EARTH CRUST
ERUPTION
GEOLOGIC AGES
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
LATIN AMERICA
LAVA
LEAD ISOTOPES
MAGMATISM
MEXICO
NORTH AMERICA
PETROCHEMISTRY
ROCKS
STRONTIUM ISOTOPES
TECTONICS
TERTIARY PERIOD
VOLCANIC ROCKS
VOLCANISM