2019


Teodora Mitroi

Teodora Mitroi


Years participated in RESESS:
2019, 2018


Poster
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An Overview

Major: Applied Mathematics
Academic Affiliation: Georgia State University
Research Mentor(s): Dr. Cailey Condit
Communications Mentor: Mikaela Algren


Biography

As a 2nd year intern, Teodora is keen on learning new subjects and skills that revolve around geoscience. This year, she will be analyzing seismic anisotropy data from an experimentally deformed mineral to better understand the mechanisms and processes that deform the deep crust and the geophysical signals they preserve. She has recently graduated with her B.S. in Applied Mathematics and is searching for a PhD program that combines her passion for numerical simulations and field work, such as machine learning in seismology or other areas of geophysics. Being an immigrant woman, Teodora is interested in diversifying the STEM field by becoming a professor and creating an environment of inclusion at her future university.


Abstract

Deep-crustal Deformation: An Experimental and EBSD-based Study of Amphibole’s Seismic Anisotropy

Seismic anisotropy is a powerful tool for imaging the deep crust and identifying deformation structures at depth. However, interpreting these geophysical signals remains difficult due to a lack of geologic and mechanistic constraints on their formation. Strong lattice preferred orientations (LPOs) of anisotropic minerals create significant seismic anisotropy, and the formation of these LPOs is intimately related to the style and conditions of deformation. We investigate anisotropy and LPO formation in amphibole, a common anisotropic deep crustal mineral, using deformation experiments and EBSD analysis. Two fine-grained, pure amphibole samples were experimentally hot-pressed for 16 hours at deep crustal conditions (1.5GPa, 750 C). Subsequently, one sample was deformed using a Griggs-type apparatus at strain rates of 106-10-3 s-1 while the other was recovered undeformed.

Microstructural observations show that both the undeformed and deformed samples exhibit strong LPOs. The undeformed sample shows minimal intragranular misorientations, suggesting that grains underwent rigid body rotation during-hot pressing, where elongated grained oriented themselves with the long [001] axis along the shear plane which developed a moderate LPO (J-Index: 2.39). However, the deformed sample has an even stronger LPO (J-Index: 2.75), and exhibited significant intragranular misorientations and subgrain formation, indicative of dislocation activity. Hence, it appears that the initial, rigid- body rotation induced LPO is subsequently modified by creep. The resultant calculated P-wave seismic anisotropy (AVp) for the deformed sample is 9.9%, while the undeformed sample’s AVp is 10.4%. In the deformed sample, LPO variation with grain size was also investigated. Large grains (>2µm) exhibit a stronger LPO and 10.6% AVp, while the fine grains have a moderate LPO and 8.1% AVp. This work demonstrates that amphibole is susceptive to rigid- body rotation induced LPO formation due to its crystal habit, with deformation modifying LPO only mildly under the explored conditions. In all, hot pressing and deformation of amphibole at deep crustal conditions lead to strong LPOs and seismic anisotropy, suggesting that deformed amphibole may be a significant contributor to deep crustal seismic anisotropy.


Presentation