Award Date

May 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Arya Udry

Second Committee Member

Shichun Huang

Third Committee Member

Elisabeth M. Hausrath

Fourth Committee Member

Jason H. Steffen

Number of Pages

109

Abstract

The martian meteorite Northwest Africa (NWA) 10169 is classified as a new member of the geochemically enriched poikilitic shergottites, based on mineral composition, Lu-Hf isotope systematics, and rare earth element (REE) composition. Akin to other poikilitic shergottites, it shows a similar bimodal texture to other enriched and intermediate poikilitic shergottites. In addition, olivine and pyroxene in the poikilitic zone have higher Mg#’s (Mg/Mg+Fe) than those in the interstitial areas, suggesting that the poikilitic texture represents early-stage crystallization, opposed to late-stage non-poikilitic crystallization. Calculated fO2 values are reduced (FMQ -2.3 ± 0.23) within the poikilitic texture, and more oxidized (FMQ -1.07 ± 0.14) within the interstitial areas likely representing auto-oxidation and degassing during magma crystallization. Melt inclusions within olivine crystals provide snapshots of magma composition throughout parent melt evolution. The calculated parental melt compositions share evolution trends with the enriched olivine-phyric shergottite Larkman Nunatuk (LAR) 06319, and suggest that two melts (K-poor and K-rich) were involved in the formation of NWA 10169, likely representing interaction with a metasomatized melt during the entrapment of the K-rich melt inclusions. The Lu-Hf crystallization age for NWA 10169 is 167 ± 31 Ma, consistent with the other enriched shergottites. Based on the isochron initial 176Hf/177Hf value, the modeled the source 176Lu/177Hf composition for NWA 10169 is 0.02748 ± 0.00037, identical within error to the source compositions of the enriched shergottites Shergotty, Zagami, LAR 06319, NWA 4468, and Roberts Massif (RBT) 04262, suggesting a shared, long-lived geochemical source, distinct from the source tapped by Los Angeles, NWA 856, and NWA 7320. This study reveals that at least two sources are responsible for the enriched shergottites, and a more heterogeneous martian mantle than previously thought. Additionally, the shared source with NWA 10169, coupled with consistent crystallization ages and magmatic histories indicates that a common magmatic system on Mars is likely responsible for the formation of this group of shergottites.

Keywords

Heterogeneous; NWA 10169; Polybaric; Shergottite

Disciplines

Geochemistry | Geology

Language

English


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