Broadband Seismological Imaging of Flat-Slab Subduction and its Long-Term Impact on Lithospheric Structure and Processes

Persistent Link:
http://hdl.handle.net/10150/205469
Title:
Broadband Seismological Imaging of Flat-Slab Subduction and its Long-Term Impact on Lithospheric Structure and Processes
Author:
Porter, Ryan Charles
Issue Date:
2011
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.
Embargo:
Embargo: Release after 11/28/2012
Abstract:
In subduction zones, the dip of the downgoing oceanic lithosphere has a profound impact on the nature and extent of deformation as well as the generation of melt. In ~10% of subduction zones, the downgoing slab assumes a low-angle, or horizontal geometry, referred to as flat-slab subduction. The focus of this work is to better understand both the driving forces and impacts of flat-slab subduction on the Earth's lithosphere and asthenosphere. This is accomplished by focusing on three areas impacted by flat-slab subduction. The first area is the Pampean region of central Argentina and Chile, a modern flat-slab subduction zone. In this region, we invert Rayleigh-wave-dispersion data to produce a 3D shear velocity model. The flat slab is visible within the upper mantle as a high-velocity body containing low-velocity pockets that dissipate inboard from the trench. We interpret these velocities in the context of slab hydration and argue that the subducting Nazca plate is initially hydrated at the trench and dewaters as it subducts. The second area is southern California, which was impacted by Laramide flat-slab subduction. In this area, we use receiver functions to locate and parameterize anisotropy within the crust. Results show a persistent NE-SW oriented layer of lower crustal anisotropy. We conclude that this layer consists of schists that were emplaced during Laramide flat-slab subduction and have remained largely intact since. The final component of this work is a study of the Colorado Plateau in which we use ambient-noise tomography and receiver functions to study lithospheric structure. Results show fast crust, a complicated Moho and intact Laramide features throughout the crust beneath the Colorado Plateau while slower crust with a sharp Moho is observed along its margins. Based on these observations, published tomographic data and the volcanic and uplift history of the region, we argue that delamination of the lower crust has occurred beneath the Marysvale volcanic field. This process was driven by the gravitational instability of a dense mafic root that formed during mid-Tertiary magmatism related to the rollback of the Farallon flat slab.
Type:
text; Electronic Dissertation
Keywords:
Geosciences
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Zandt, George

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleBroadband Seismological Imaging of Flat-Slab Subduction and its Long-Term Impact on Lithospheric Structure and Processesen_US
dc.creatorPorter, Ryan Charlesen_US
dc.contributor.authorPorter, Ryan Charlesen_US
dc.date.issued2011-
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.releaseEmbargo: Release after 11/28/2012en_US
dc.description.abstractIn subduction zones, the dip of the downgoing oceanic lithosphere has a profound impact on the nature and extent of deformation as well as the generation of melt. In ~10% of subduction zones, the downgoing slab assumes a low-angle, or horizontal geometry, referred to as flat-slab subduction. The focus of this work is to better understand both the driving forces and impacts of flat-slab subduction on the Earth's lithosphere and asthenosphere. This is accomplished by focusing on three areas impacted by flat-slab subduction. The first area is the Pampean region of central Argentina and Chile, a modern flat-slab subduction zone. In this region, we invert Rayleigh-wave-dispersion data to produce a 3D shear velocity model. The flat slab is visible within the upper mantle as a high-velocity body containing low-velocity pockets that dissipate inboard from the trench. We interpret these velocities in the context of slab hydration and argue that the subducting Nazca plate is initially hydrated at the trench and dewaters as it subducts. The second area is southern California, which was impacted by Laramide flat-slab subduction. In this area, we use receiver functions to locate and parameterize anisotropy within the crust. Results show a persistent NE-SW oriented layer of lower crustal anisotropy. We conclude that this layer consists of schists that were emplaced during Laramide flat-slab subduction and have remained largely intact since. The final component of this work is a study of the Colorado Plateau in which we use ambient-noise tomography and receiver functions to study lithospheric structure. Results show fast crust, a complicated Moho and intact Laramide features throughout the crust beneath the Colorado Plateau while slower crust with a sharp Moho is observed along its margins. Based on these observations, published tomographic data and the volcanic and uplift history of the region, we argue that delamination of the lower crust has occurred beneath the Marysvale volcanic field. This process was driven by the gravitational instability of a dense mafic root that formed during mid-Tertiary magmatism related to the rollback of the Farallon flat slab.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectGeosciencesen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorZandt, Georgeen_US
dc.contributor.committeememberBeck, Susanen_US
dc.contributor.committeememberBennett, Ricken_US
dc.contributor.committeememberDucea, Mihaien_US
dc.contributor.committeememberJohnson, Royen_US
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