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Title Mineralogy and geochemistry of Eocene intrusive rocks and their enclaves, El Paso area, Texas and New Mexico
Creator/Author Barnes, C.G. ; Ensenat, S.E. (Texas Tech Univ., Lubbock (United States)) ; Hoover, J.D. (Westinghouse Hanford Co., Richland, WA (United States))
Publication Date1991 Jul 01
OSTI IdentifierOSTI ID: 5676156
Other Number(s)ISSN0003-004X; CODEN: AMMIA
Resource TypeJournal Article
Resource RelationAmerican Mineralogist ; Vol/Issue: 76:7-8
Subject580000 -- Geosciences; NEW MEXICO-- MAGMATISM;PLUTONIC ROCKS-- GEOCHEMISTRY;PLUTONIC ROCKS-- MINERALOGY;TEXAS-- MAGMATISM; EOCENE EPOCH;GEOLOGIC HISTORY;GEOLOGIC MODELS;MAGMA SYSTEMS;ORIGIN;PRECAMBRIAN ERA;RESERVOIR TEMPERATURE
Related SubjectCENOZOIC ERA;CHEMISTRY;DEVELOPED COUNTRIES;FEDERAL REGION VI;GEOLOGIC AGES;GEOTHERMAL SYSTEMS;IGNEOUS ROCKS;NORTH AMERICA;ROCKS;TERTIARY PERIOD;USA
Description/Abstract Trans-Pecos magmatism in the El Paso, Texas, area was characterized by numerous shallow trachyandesitic intrusions of Eocene age.^Cognate enclaves in the intrusions consist of monzodiorite and porphyritic trachyandesite.^The compositions of these enclaves indicate that they are cumulates formed near the margins of a crustal (possibly midcrustal) magma chamber.^The mineral assemblages of the trachyandesitic and monzodioritic enclaves (tschermakitic amphibole + biotite + oxides + plagioclase {plus minus} titanite {plus minus} quartz) constrain preemplacement temperature to less than 850C and f{sub o{sub 2}} to 1 or 2 log units above NNO.^H{sub 2}O contents were probably in the range of 3.0 to 3.5 wt% and the confining pressure of the crustal chamber as much as 5.5 kbar (based on Al content of amphibole).^Xenolithic enclaves include dioritic and anorthositic compositions.^These are interpreted to be the wall rocks of the crustal chamber and are probably Precambrian in age.^Incompatible element contents of the trachyandesitic magmas are interpreted to be the product of fractional crystallization of a subduction-related basaltic magma.^Disequilibrium among phenocrysts in the trachyandesitic magmas and local enrichment of compatible elements can be explained by minor contamination by anorthositic and dioritic xenoliths.
Country of PublicationUnited States
LanguageEnglish
FormatPages: 1306-1318
System Entry Date2001 May 13

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