Martian near-surface materials in shergottite meteorites: Searching for evidence from Tissint shock-melt pockets

• Author / Creator

  Kuchka, Cody R.

• Three thin sections of the Tissint Martian meteorite were examined by an array of in situ techniques in order to assess the possibility that a geochemical signature characteristic of the Martian near-surface has been preserved within the meteorite. Tissint is a recent basaltic Martian fall that contains an abundance of shock-generated melt glass that formed by a variety of mechanisms including grain-boundary frictional melting, concentration of shockwaves along boundaries of minerals with contrasting shock-impedance, and void collapse. Tissint is special amongst the suite of Martian meteorites in that it is only the fifth witnessed Martian fall, and its short residence time in a hot desert precluded significant terrestrial weathering. Shock melt pockets form in situ by local melting of igneous phases. Major element compositions and rare earth element patterns do not suggest a contribution from Martian soil or minerals derived from the Martian surface (e.g. jarosite) to the shock melt. Shock-metamorphic sulfides (iron-sulfide spherules within shock melt pockets) exhibit elevated Fe/S ratios compared to groundmass sulfides that were not incorporated into shock melt pockets or veins. Additionally, Raman spectra collected for shock-metamorphic sulfides exhibit Raman peaks characteristic of hematite. These Raman peaks are not present for groundmass sulfides; sulfides were altered (oxidized) as a consequence of the shock event. Thermal modelling results show that cooling times for individual regions of shock melt are controlled by their size, geometry, proximity to other regions of shock melt, and the presence or absence of vesicles. Volatile abundances determined by SIMS revealed that H2O and Cl concentrations are correlated in shock melt glass. Water, chlorine, and fluorine concentrations are not correlated with phosphorus; water in Tissint shock melt glass cannot be attributed to igneous apatite. Hydrogen isotopes demonstrate that the water within Tissint shock melt glass has experienced mixing between two reservoirs: the Martian mantle and the Martian near-surface. For shock melt glass containing vesicles, the shock melt may partially devolatilize to the vesicle before quenching was complete. A geochemical signature derived from the Martian near-surface is preserved in Tissint shock melt pockets, observed primarily in H2O and Cl concentrations and hydrogen isotopes. This signature is very minor and is only detectable by sensitive techniques. Shock melt pockets with the greatest potential to preserve such a signature are isolated from other regions of shock melt, vesicle-free, and glassy.

• Subjects / Keywords

  • Tissint
  • Volatiles
  • Martian meteorite
  • Shock metamorphism
  • Hydrogen isotopes

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3MK65H1V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.