Trace Element Composition of Apatite from Intrusive Rocks in Northeastern Nevada, USA

Persistent Link:
http://hdl.handle.net/10150/620842
Title:
Trace Element Composition of Apatite from Intrusive Rocks in Northeastern Nevada, USA
Author:
Dabbs, Jennifer Marie
Issue Date:
2016
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The apatite crystal structure-A5(TO4)3X-allows for complex substitutions of various minor and trace elements including volatile constituents, rare earth elements, and redox sensitive elements (e.g., As, Mn, Fe, S) (Piccoli and Candela, 1994; Piccoli and Candela, 2002; Pan and Fleet, 2002; Teiber et al., 2015; Harlov, 2015). In this study, apatite grains from 19 intrusions across northeastern Nevada with varied petrogenetic and metallogenic properties were analyzed by electron probe microanalysis (EPMA) to obtain major and trace element abundances. Systematic variations in Sr and REE concentrations in apatite grains from granitic host rocks are the result of competition with pre-existing and coexisting minerals in silicate melts. The presence of zoning in cathodoluminescence colors combined with high Sr concentrations in apatite from many of the Eocene granodiorite rocks suggest magma mixing affected the geochemical evolution in many of the Eocene igneous systems. In addition, high Sr concentrations in apatite grains from Late Cretaceous two-mica granites may reflect significant magmatic input from lower crustal and/or mantle sources despite the felsic nature of these intrusive rocks.A new EPMA analytical routine to measure arsenic down to detection limits of approximately 20 ppm allowed a more extensive characterization of As concentration in igneous apatite than has previously been published. Still, correlations between As and other trace-element concentrations are not evident, which may reflect the simple substitution of As5+ for P5+ in the apatite structure. Petrologic controls on As content include redox state, indicated by the high Asapat/Asbulk-rock in relatively oxidized intrusive rocks. An additional control is competition among other magmatic phases, exsolving aqueous fluids, or sulfide melts, indicated by enrichment of As in apatite cores relative to apatite rims. Past studies on redox-sensitive elements in igneous apatite have focused on Mn and S, but with further investigation, As may also prove to be a key redox-sensitive trace element in apatite for interpreting igneous and hydrothermal processes.
Type:
text; Electronic Thesis
Keywords:
Arsenic; Great Basin; Mineral Deposits; Geosciences; Apatite
Degree Name:
M.S.
Degree Level:
masters
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Barton, Mark D.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleTrace Element Composition of Apatite from Intrusive Rocks in Northeastern Nevada, USAen_US
dc.creatorDabbs, Jennifer Marieen
dc.contributor.authorDabbs, Jennifer Marieen
dc.date.issued2016-
dc.publisherThe University of Arizona.en
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en
dc.description.abstractThe apatite crystal structure-A5(TO4)3X-allows for complex substitutions of various minor and trace elements including volatile constituents, rare earth elements, and redox sensitive elements (e.g., As, Mn, Fe, S) (Piccoli and Candela, 1994; Piccoli and Candela, 2002; Pan and Fleet, 2002; Teiber et al., 2015; Harlov, 2015). In this study, apatite grains from 19 intrusions across northeastern Nevada with varied petrogenetic and metallogenic properties were analyzed by electron probe microanalysis (EPMA) to obtain major and trace element abundances. Systematic variations in Sr and REE concentrations in apatite grains from granitic host rocks are the result of competition with pre-existing and coexisting minerals in silicate melts. The presence of zoning in cathodoluminescence colors combined with high Sr concentrations in apatite from many of the Eocene granodiorite rocks suggest magma mixing affected the geochemical evolution in many of the Eocene igneous systems. In addition, high Sr concentrations in apatite grains from Late Cretaceous two-mica granites may reflect significant magmatic input from lower crustal and/or mantle sources despite the felsic nature of these intrusive rocks.A new EPMA analytical routine to measure arsenic down to detection limits of approximately 20 ppm allowed a more extensive characterization of As concentration in igneous apatite than has previously been published. Still, correlations between As and other trace-element concentrations are not evident, which may reflect the simple substitution of As5+ for P5+ in the apatite structure. Petrologic controls on As content include redox state, indicated by the high Asapat/Asbulk-rock in relatively oxidized intrusive rocks. An additional control is competition among other magmatic phases, exsolving aqueous fluids, or sulfide melts, indicated by enrichment of As in apatite cores relative to apatite rims. Past studies on redox-sensitive elements in igneous apatite have focused on Mn and S, but with further investigation, As may also prove to be a key redox-sensitive trace element in apatite for interpreting igneous and hydrothermal processes.en
dc.typetexten
dc.typeElectronic Thesisen
dc.subjectArsenicen
dc.subjectGreat Basinen
dc.subjectMineral Depositsen
dc.subjectGeosciencesen
dc.subjectApatiteen
thesis.degree.nameM.S.en
thesis.degree.levelmastersen
thesis.degree.disciplineGraduate Collegeen
thesis.degree.disciplineGeosciencesen
thesis.degree.grantorUniversity of Arizonaen
dc.contributor.advisorBarton, Mark D.en
dc.contributor.committeememberMazdab, Frank K.en
dc.contributor.committeememberSteele-MacInnis, Matthewen
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