The earth's interior from both a seismological and petrological perspective

Shear-wave splitting measurements of teleseismic shear waves, such as SKS, have been used to estimate the amount and direction of upper-mantle anisotropy worldwide. One of the basic assumptions in making these measurements is that the anisotropy is confined to a single, homogeneous layer. In this thesis, I use both numerical and analytical modeling to examine the validity of this assumption. I find that variability in the orientation of anisotropy with depth causes observable effects, such as frequency dependence in the apparent splitting parameters, and that the measured fast-axis direction is consistently different than the average of the medium. A separate focus of this thesis is how spatial associations between minerals in a thin-section can be used to infer the evolutionary pressure-temperature history of a rock. I present a new method for textural analysis that uses digital images obtained with the electron microprobe. This method is used to characterize nine mantle xenoliths erupted from kimberlite pipes in South Africa and to test whether the pyroxenes are spatially correlated with the garnets. The observed associations can be explained by a model in which harzburgitic residues are produced by large extents of partial melting at shallow depths (-60-90 km) and high temperatures (1300-1400ʻ C) and are then subsequently dragged down to greater depths where garnet and clinopyroxene exsolve, perhaps in an Archean subduction zone. The third focus of this thesis is on the seismological evidence for compositional heterogeneity in the lower mantle. Using reprocessed ISC data, I compare P and S wave tomographic models and find systematic differences between regions that have undergone subduction in the last 120 million years and those that have not below -1500 km.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Saltzer, Rebecca Lee

Advisor dc:contributor.advisor

• Robert D. van der Hilst.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/16815
• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Identifier URI

http://dspace.mit.edu/handle/1721.1/16815

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16815