My research focuses on the crustal and upper mantle structure beneath western Tibet. In order to understand the geodynamic conditions beneath this region I performed tomographic inversions to determine 3D velocity structure. Also, I used Ps receiver functions (RFs) to investigate seismic discontinuities. I found laterally uniform low seismic velocity in the crust of Tibet, and a clear change in seismic properties at the India-Asia boundary. Crustal thickness varies from 43 km beneath the Himalayas to 88 km in the northern part of the Lhasa block. The Vp/Vs ratio also varies systematically, with lower values in the Lhasa block and higher values beneath the India - Asia boundary, and south of it. In many locations RFs show evidence for a mid-crustal boundary where speed decreases with depth. However, no evidence of a continuous low velocity zone in the crust is found in tomographic images, suggesting that low velocity bodies detected by RFs are relatively thin. Additional boundaries where speed increases with depth are seen 15 - 25 km above the crust-mantle transition. Again, tomography does not detect a continuous fast layer in the lower crust of western Tibet, suggesting thin discontinuous features. A narrow very fast feature in the uppermost mantle beneath part of the study region is consistent with formerly Indian crustal rock that has converted to eclogite when Indian lithosphere was underthrust beneath the Tibetan Plateau. Patterns of velocity variation in the upper mantle show close similarity for P and S waves, and thus likely represent differences in mantle rock temperature. A key finding is the absence of a continuous fast anomaly expected if Indian lithosphere was subducting into the mantle beneath Asia. Instead, I found two separate fast anomalies beneath western Tibet. One is nearly vertical, ~100 km across, and circular in cross-section, and is positioned beneath the present day India – Asia boundary. It may be interpreted as a viscous drip formed by Indian lithosphere material. Another is thin and slab-like in shape, and is present further north. Coexistence of these features suggests there was a recent change in the mode of emplacement of Indian mantle lithosphere beneath Tibet.
Subject (authority = RUETD)
Topic
Geological Sciences
Subject (authority = ETD-LCSH)
Topic
Tibet, Plateau of
Subject (authority = ETD-LCSH)
Topic
Seismology
RelatedItem (type = host)
TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
Identifier (type = RULIB)
ETD
Identifier
ETD_7210
PhysicalDescription
Form (authority = gmd)
electronic resource
InternetMediaType
application/pdf
InternetMediaType
text/xml
Extent
1 online resource (xviii, 180 p. : ill.)
Note (type = degree)
Ph.D.
Note (type = bibliography)
Includes bibliographical references
Note (type = statement of responsibility)
by Ayda Shokoohi Razi
RelatedItem (type = host)
TitleInfo
Title
Graduate School - New Brunswick Electronic Theses and Dissertations
Identifier (type = local)
rucore19991600001
Location
PhysicalLocation (authority = marcorg); (displayLabel = Rutgers, The State University of New Jersey)
Rutgers University. Graduate School - New Brunswick
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Type
License
Name
Author Agreement License
Detail
I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.