Physical Sciences and Mathematics Commons^™

Early Solar System Chronology And Isotopic Linkage Of Non-Carbonaceous Chondrules, Clasts And Achondrites, Philip M. Reger

Electronic Thesis and Dissertation Repository

Chondrules are ubiquitous igneous spherules, the main constituents of ordinary chondrites, and are considered to be critical building blocks of planetesimals, yet their age and formation mechanism(s) remain debated. Differences between ages determined from the long-lived Pb-Pb and the short-lived ²⁶Al-²⁶Mg chronometers have been attributed to the heterogeneous distribution of ²⁶Al in the solar nebula, a radionuclide that was responsible for early differentiation of planetesimals.

To evaluate this hypothesis, the ²⁶Al-²⁶Mg and the ²⁰⁷Pb-²⁰⁶Pb isotopic compositions were both measured by multi-collector ICP-MS in individual chondrules and igneous clasts in unequilibrated …

Aluminum-26: A Canonized Cosmochemical Conundrum, John Anton

Dissertations, Theses, and Capstone Projects

This study focuses on the challenges associated with the historical development of the interpretative role of ²⁶Al as both a thermodynamic contributor to planetesimal formation processes and an acutely precise chronometer of protoplanetary disk events. Conventional thought asserts that ²⁶Mg concentrations can occur as isotopic excesses in meteorites and represent the daughter product of ²⁶Al, a radioactive form of aluminum (t_½ = ~0.73 ka). The greatest ²⁶Mg concentrations generally occur in calcium aluminum inclusions (CAIs), meteoric constituents considered among the oldest known materials in the Solar System whose formation appear to predate the less refractory …

The Formation Of Fine-Grained Chondrule Rims In Unequilibrated Ordinary Chondrites, John Bigolski

Dissertations, Theses, and Capstone Projects

Fine-grained rims are ubiquitous, non-igneous, features that completely or partially envelope the majority of chondrules within the least equilibrated of the unequilibrated ordinary chondrites (UOCs). A detailed examination of such rims in 4 UOC samples less than petrologic type 3.2 was conducted in order to 1) characterize the relative distribution of rims within chondrite samples, 2) inspect differences between fine-grained rims and adjacent matrix material, 3) petrologically analyze the rims and their relationships with chondrule cores, 4) characterize an ungrouped UOC, Northwest Africa 5717, 5) conduct a microanalytical investigation of rim / matrix boundaries to discern relative chronologies of fine-grained …