Mesozoic igneous activity in the southern Cordillera of North America: Implications for tectonics and magma genesis.

Persistent Link:
http://hdl.handle.net/10150/184421
Title:
Mesozoic igneous activity in the southern Cordillera of North America: Implications for tectonics and magma genesis.
Author:
Asmerom, Yemane.
Issue Date:
1988
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 first part of this dissertation deals with the timing of Mesozoic igneous activity in southern Cordillera of North America and its tectonic implications. A representative section in Santa Rita Mountains is dated using the zircon U-Th-Pb isotopic method. The oldest unit, the lower member of the Mt. Wrightson Formation, is concordantly dated at 210 ± 3 Ma. Initial basaltic andesite to andesite volcanism was followed by deposition of redbeds and associated volcanic rocks that are dated at 200 Ma. Felsic volcanism and eolian sand deposition may have spanned from 190 to 170 Ma. The Piper Gulch Granodiorite, representing the earliest Mesozoic intrusive equivalent, gives concordant dates of 188 ± 2 Ma. A second cycle of andesite and rhyolitic volcanism and sedimentation is dated at 151 ± 5 Ma using the whole-rock Rb-Sr isotopic method. The Hovatter Volcanics in the Little Harquahala Mountains, southwestern Arizona is dated at 165 Ma. Whole-rock Rb-Sr isotopic method on the same rocks gives a coherent reset isochron of 70 ± 3 Ma (Appendix III). A new stratigraphic correlation is proposed based on the dating data. Tectonic models proposed by previous workers to account for what seemed to be the lack of Triassic volcanic rocks are not necessary. This part of the Cordillera was an uplifted arc terrane during the Early Mesozoic (Appendix II) and may have provided volcanic detritus to the Late Triassic Chinle Formation in the Colorado Plateau. The second part of the dissertation deals with magma evolution and crust modification during arc magmatism. Rocks in southeastern Arizona have ƭ(N)(d) values of -3.4 to -6.4, while rocks to the west have ƭ(N)(d) values ranging from -8.5 to -9.2. An ƭ(N)(d) value of +2 for a Jurassic basalt indicates the presence of depleted mantle under the arc. Using lower crust and mantle end-members, 20 to 40% mantle input is estimated. This seems to argue for continuous growth model of the continental crust. Combined REE and isotopic data indicate that assimilation of lower crust by mantle melts followed by fractional crystallization took place. Detailed study indicates that the lower crust along sites of arc magmatism gets progressively hybridized by the mantle, becoming more mantle-like with time.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Igneous rocks -- Arizona.; Geology, Stratigraphic -- Mesozoic.; Magmatism -- Arizona.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Damons, Paul E.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleMesozoic igneous activity in the southern Cordillera of North America: Implications for tectonics and magma genesis.en_US
dc.creatorAsmerom, Yemane.en_US
dc.contributor.authorAsmerom, Yemane.en_US
dc.date.issued1988en_US
dc.publisherThe University of Arizona.en_US
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_US
dc.description.abstractThe first part of this dissertation deals with the timing of Mesozoic igneous activity in southern Cordillera of North America and its tectonic implications. A representative section in Santa Rita Mountains is dated using the zircon U-Th-Pb isotopic method. The oldest unit, the lower member of the Mt. Wrightson Formation, is concordantly dated at 210 ± 3 Ma. Initial basaltic andesite to andesite volcanism was followed by deposition of redbeds and associated volcanic rocks that are dated at 200 Ma. Felsic volcanism and eolian sand deposition may have spanned from 190 to 170 Ma. The Piper Gulch Granodiorite, representing the earliest Mesozoic intrusive equivalent, gives concordant dates of 188 ± 2 Ma. A second cycle of andesite and rhyolitic volcanism and sedimentation is dated at 151 ± 5 Ma using the whole-rock Rb-Sr isotopic method. The Hovatter Volcanics in the Little Harquahala Mountains, southwestern Arizona is dated at 165 Ma. Whole-rock Rb-Sr isotopic method on the same rocks gives a coherent reset isochron of 70 ± 3 Ma (Appendix III). A new stratigraphic correlation is proposed based on the dating data. Tectonic models proposed by previous workers to account for what seemed to be the lack of Triassic volcanic rocks are not necessary. This part of the Cordillera was an uplifted arc terrane during the Early Mesozoic (Appendix II) and may have provided volcanic detritus to the Late Triassic Chinle Formation in the Colorado Plateau. The second part of the dissertation deals with magma evolution and crust modification during arc magmatism. Rocks in southeastern Arizona have ƭ(N)(d) values of -3.4 to -6.4, while rocks to the west have ƭ(N)(d) values ranging from -8.5 to -9.2. An ƭ(N)(d) value of +2 for a Jurassic basalt indicates the presence of depleted mantle under the arc. Using lower crust and mantle end-members, 20 to 40% mantle input is estimated. This seems to argue for continuous growth model of the continental crust. Combined REE and isotopic data indicate that assimilation of lower crust by mantle melts followed by fractional crystallization took place. Detailed study indicates that the lower crust along sites of arc magmatism gets progressively hybridized by the mantle, becoming more mantle-like with time.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectIgneous rocks -- Arizona.en_US
dc.subjectGeology, Stratigraphic -- Mesozoic.en_US
dc.subjectMagmatism -- Arizona.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorDamons, Paul E.en_US
dc.contributor.committeememberRuiz, Joaquinen_US
dc.contributor.committeememberPatchett, Jonathanen_US
dc.contributor.committeememberDickinson, William R.en_US
dc.contributor.committeememberReynolds, Stephen J.en_US
dc.identifier.proquest8816307en_US
dc.identifier.oclc701248135en_US
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