[Eoas-seminar] Geology Thesis Prospectus Defense - Brandon Fish - May 5, 10:00a - B333 MagLab

eoas-seminar at lists.fsu.edu eoas-seminar at lists.fsu.edu
Fri May 5 07:30:18 EDT 2017


> Please attend Brandon Fish’s prospectus defense this morning:

> Title: Compositional Evolution of the IIAB Iron Meteorites
> Major Professor: Munir Humayun
> 
> 
> Abstract:
> Until the past decade, IIAB irons were thought to have formed by fractional crystallization in low pressure environments in an asteroidal (<200 km) body, but newer models have now suggested that IIAB irons may have originally formed in a planetesimal sized (>1000 km) parent body under higher pressures. In order to test models of fractional crystallization, 21 IIAB iron meteorites were analyzed by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for their elemental compositions that provided new abundance data for Mo, Ru, Rh, Pd, Sn, Sb, and Os. Highly incompatible elements are useful tools for studying fractional crystallization in irons, so a primary objective was obtaining abundances for Sb, which has been experimentally shown to be one of the most incompatible elements present in irons. This data in conjunction with literature data are used to model fractional crystallization of IIAB irons as a function of the pressure and sulfur content in the melt fraction. Existing low pressure (0.1 MPa) models are in agreement for  a number of elements (Ge, Pd, Sb, W, Ir, etc.), but not for other elements known to be sensitive to high pressure (Ru, Rh, As, etc.). High pressure (9 GPa)  models are tested for the first time in IIAB irons at varying S contents, and As vs. Au crystallization pathways could partially be explained by high pressure. However, Ga, Ge, Ru, Rh, Pd, W, etc. do not support the case for a high pressure environment during fractional crystallization. The failure of the high pressure model led to a closer examination of D(As) vs. S content. A new formalism was developed for a limited range of S contents (18-30 wt.%) pertinent to IIAB evolution. The new formalism for As is consistent with a low pressure environment and 18 wt.% S content in the IIAB core.
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Munir Humayun
Professor
Department of Earth, Ocean, and Atmospheric Science
	& National High Magnetic Field Laboratory
Florida State University
1800 E. Paul Dirac Drive
Tallahassee, FL32310
(850) 644-1908
(850) 644-0827 (FAX)




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