Compositional Analysis of the Martian Meteorites Northwest Africa 6342 and Northwest Africa 10961

The most abundant type of meteorite that we have from Mars is the shergottite. This makes the study of shergottite samples invaluable to understanding the geological evolution of that planet. Electron microprobe analyses, bulk elemental composition calculation, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were used to analyze the composition and petrology of two distinct but related shergottites. The Martian meteorite Northwest Africa (NWA) 6342 recovered from Algeria in 2010 and the Martian meteorite NWA 10961 recovered from Morocco in 2016 are both classified as members of the geochemically intermediate family of poikilitic shergottites based on their mineral composition, Lu-Hf and Sm-Nd isotope systematics, and rare earth element (REE) concentrations. These shergottites are cumulate rocks that exhibit bimodal texture characterized by large pyroxene oikocrysts (poikilitic texture) surrounded by olivine-rich interstitial material (non-poikilitic texture) like other intermediate and enriched poikilitic shergottites. Chadacrysts are minerals that are fully enveloped within another mineral. The surrounding mineral is the oikocryst. Olivine chadacrysts and pyroxene oikocrysts have higher Mg#s (molar Mg/Mg + Fe) than those in the interstitial areas suggesting that the poikilitic texture represents early-stage crystallization and accumulation as opposed to latestage non-poikilitic (i.e., interstitial material) crystallization. Calculated oxygen fugacity values for NWA 6342 are more reduced (FMQ -3.0) within the poikilitic regions and more oxidized (FMQ -2.2) within the interstitial areas, likely representing auto-oxidation and degassing during crystallization. Calculated average oxygen fugacity values for NWA 10961 are FMQ -1.35 at a subsolidus temperature of 904 °C with possible auto-oxidation and degassing during magma crystallization. Spinel-group minerals are observed as chadacrysts in both pyroxene and olivine and at the edge of melt pockets and veins within both of these meteorites. Poikilitic zones have Cr-rich spinels in the form of chromite while the nonpoikilitic areas exhibit Ti-rich spinels. NWA 6342 and NWA 10961 have experienced high levels of shock metamorphism as demonstrated by substantially fractured minerals, melting and subsequent crystallization of plagioclase into maskelynite, and the fine-grained texture of recrystallized olivine. The recrystallization of plagioclase required an extended period of postshock thermal metamorphism, most likely from the launch of these shergottites from Mars. The significant differences in textures and mineral element compositions observed across the bimodal textures of these meteorites provide the basis for defining their crystallization history. These data collected can be further used to potentially constrain the evolution of Mars’ crust.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Geology

Grantor

University of Houston

Year dc:date.issued

2024

Author dc:creator

• Richards, Brent Collin

Advisor dc:contributor.advisor

• Copeland, Peter

Committee members dc:contributor.committeemember

• Stewart, Robert
• Loocke, Matthew

• Mars
• Martian
• meteorite
• shergottite
• poikilitic
• intermediate
• ultramafic

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10657/17648

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/17648