Portland State University. Department of Geology
Date of Award
Master of Science (M.S.) in Geology
1 online resource (vi, 141 pages)
Chondrites (Meteorites), Chondrules, Olivine, Accretion (Astrophysics), Rock deformation
This thesis studies ordinary chondrites with cluster chondrite lithologies using electron backscatter diffraction so as to measure the temperatures of their olivine grains during deformation, for the purpose of constraining the accretion temperatures of cluster chondrites and creating new constraints on chondrule formation models. Samples analyzed with the technique are shock classified in this thesis as S1 and are type 3, so the deformation analyzed is interpreted to represent the temperatures of the chondrules during accretional deformation. It is found that the studied samples are primarily composed of chondrules at hot temperatures (>850°C) during deformation, mixed with a questionable minority at cold (<850°C) temperatures. This is interpreted to represent a primarily hot or possibly heterogeneous temperature of accretion; the objects accreting were mostly hot chondrules with a possible addition of cold chondrules. This interpretation establishes two new possible constraints for chondrule formation models, requiring that they must allow for chondrule accretion shortly after the heating event and that they might require the mixing of hot and cold chondrules in the short time period prior to that accretion. The former of these new constraints has much stronger evidence for it than the latter. These new constraints are most compatible with established protoplanetary bow shock and impact formation models, though if the mixing constraint can be dismissed density shockwave models are also viable. Other models are either wholly incompatible with the new constraints or require modification to be consistent with them.
Goudy, Secana Portia, "Assessment of Cluster Chondrite Accretion Temperature Using Electron Backscatter Diffraction and Implications for Chondrule Formation Models" (2019). Dissertations and Theses. Paper 5268.