Persistent Link:
http://hdl.handle.net/10150/289045
Title:
Lithospheric-scale structure across the Bolivian Andes
Author:
Myers, Stephen Christopher
Issue Date:
1997
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:
I have developed a three-dimensional, lithospheric-scale model of the Bolivian Andes at ∼20°S. The model is based on tomographic images of velocity and attenuation for both P- and S-waves. Observations of travel-time and attenuation for this study are from regional, mantle earthquakes in the subducted Nazca plate recorded on a portable, broadband seismic array in Bolivia. The shallow mantle under the Altiplano from ∼18°S to ∼20°S is high velocity, but seismic Q is relatively low (Vp∼8.3, Vs∼4.9, Qp∼150, Qs∼100). These seismic properties suggest lithospheric mantle, approaching solidus conditions. High velocity material in the Altiplano extends to a depth of ∼150 km at 18.5°S, shallowing to ∼100 km at 20.5°S. Anomalously low velocity and Q anomalies are imaged in the mantle beneath the Eastern (fold and thrust) and Western (volcanic arc) Cordilleras of Bolivia. In the Western Cordillera, velocity and attenuation anomalies are locally strong (Vp∼7.8, Vs∼4.25, Qp∼80, Qs∼20), consistent with partial melt conditions. However, there is a segment of higher velocity and Q between 19°S and 20°S, that is correlated with reduced Quaternary arc volcanism. In the Eastern Cordillera, shallow mantle velocity and Q generally decrease from Altiplano values, but there is a localized low velocity and Q anomaly (Vp∼7.8, Vs∼4.1, Qp∼50, Qs∼10) underneath the Los Frailes volcanic center. The strong velocity and attenuation anomalies and the spatial correlation with the volcanic complex favor an interpretation of partial melt. From the subduction trench into parts of the Western Cordillera, processes associated with Nazca Plate subduction dominate shallow mantle structure. Structural constrains from the tomographic results and the geologic history of the Bolivian Andes favor a model of lithospheric shortening for the development of shallow-mantle structure in the Eastern Cordillera and Altiplano. A delamination/partial-continental-subduction process is favored for the production of both shallow mantle structure and volcanism in the Eastern Cordillera. This process may remove mafic components in thickened lower crust, refining the crust towards a more felsic composition.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geophysics.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Beck, Susan L.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleLithospheric-scale structure across the Bolivian Andesen_US
dc.creatorMyers, Stephen Christopheren_US
dc.contributor.authorMyers, Stephen Christopheren_US
dc.date.issued1997en_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.abstractI have developed a three-dimensional, lithospheric-scale model of the Bolivian Andes at ∼20°S. The model is based on tomographic images of velocity and attenuation for both P- and S-waves. Observations of travel-time and attenuation for this study are from regional, mantle earthquakes in the subducted Nazca plate recorded on a portable, broadband seismic array in Bolivia. The shallow mantle under the Altiplano from ∼18°S to ∼20°S is high velocity, but seismic Q is relatively low (Vp∼8.3, Vs∼4.9, Qp∼150, Qs∼100). These seismic properties suggest lithospheric mantle, approaching solidus conditions. High velocity material in the Altiplano extends to a depth of ∼150 km at 18.5°S, shallowing to ∼100 km at 20.5°S. Anomalously low velocity and Q anomalies are imaged in the mantle beneath the Eastern (fold and thrust) and Western (volcanic arc) Cordilleras of Bolivia. In the Western Cordillera, velocity and attenuation anomalies are locally strong (Vp∼7.8, Vs∼4.25, Qp∼80, Qs∼20), consistent with partial melt conditions. However, there is a segment of higher velocity and Q between 19°S and 20°S, that is correlated with reduced Quaternary arc volcanism. In the Eastern Cordillera, shallow mantle velocity and Q generally decrease from Altiplano values, but there is a localized low velocity and Q anomaly (Vp∼7.8, Vs∼4.1, Qp∼50, Qs∼10) underneath the Los Frailes volcanic center. The strong velocity and attenuation anomalies and the spatial correlation with the volcanic complex favor an interpretation of partial melt. From the subduction trench into parts of the Western Cordillera, processes associated with Nazca Plate subduction dominate shallow mantle structure. Structural constrains from the tomographic results and the geologic history of the Bolivian Andes favor a model of lithospheric shortening for the development of shallow-mantle structure in the Eastern Cordillera and Altiplano. A delamination/partial-continental-subduction process is favored for the production of both shallow mantle structure and volcanism in the Eastern Cordillera. This process may remove mafic components in thickened lower crust, refining the crust towards a more felsic composition.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeophysics.en_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.advisorBeck, Susan L.en_US
dc.identifier.proquest9729482en_US
dc.identifier.bibrecord.b34811928en_US
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