P23B-2146
O-triple Isotopes of Primary and Secondary Minerals Provide Clues to the Past and Present Hydrosphere of Mars: New Experimental Evidence
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Robina Shaheen1, Mark H Thiemens1, Ani Khachatryan2,3, Vera Smirnova4, Teresa Lou Jackson1 and Mars Simulation Platinum Team, (1)University of California San Diego, Department of Chemistry and Biochemistry, La Jolla, CA, United States, (2)University of California San Diego, Physics, La Jolla, CA, United States, (3)University of California San Diego, Department of Physics, La Jolla, CA, United States, (4)University of California San Diego, Chemical Engineering, La Jolla, CA, United States
Abstract:
Oxygen, the most abundant element in terrestrial planets link their lithospheres, hydrospheres and atmospheres, thus providing a powerful tool to fingerprint the physical and chemical processes involved in the exchange of material between these reservoirs (
1). The oxygen triple isotopic composition of SNC Martian meteorites minerals provided a record of this unique interaction. Martian silicates showed an O-isotope anomaly (Δ
17O = 0.4 ‰) unlike earth's silicate (Δ
17O = 0‰). Additionally, there is a signficant variation in the oxygen isotopic composition of primary and secondary minerals both in the oldest (ALH84001: Δ
17O
CO3 = 0.7‰, Δ
17O
silicates = 0.3‰)(
2) and younger martian rocks (NWA7034: Δ
17O
CO3 = 0.0‰, Δ
17O
silicates = 0.6‰)(
3) indicating substantial changes in the global aqueous chemistry of Mars and its formation. These variations in oxygen isotope anomalies are important, but puzzling due to the lack of knoweldege of the intial conditions and relevant experiments. To understand the origin and nature of heterogeneity in the oxygen triple isotopes of various minerals, laboratory experiments were conducted by simulating current Martian conditions. Ozone, a martian atmospheric constituent, was used as a tracer to identify molecular reactions occurring on the mineral surfaces. The oxygen isotopic composition of decomposed ozone and water was measured following reaction over extended time under defined conditions . The decomposed O
2 defines an array with a slope δ
17O = 0.87 x δ
18O + 5 (r
2 = 0.99). The left over ozone after 18hours showed a decrease in slope (δ
17O = 0.7 x δ
18O + 5 (r
2 = 0.97) and significant variations in Δ
17O= 20 - 31‰ depending on the mineral used in the experiment. The slope did not pass through the initial ozone and water suggesting the formation of an intermediate species and its reaction and removal that is responsible for the exchange of O-isotopes between water-ozone and mineral oxides. These results coupled with the UV photochemical transformation of minerals as a function of water content adsorbed on minerals and in the vapor phase will be used to unlock the mystery of oxygen isotope anomaly in the martian rocks.
1. M. H. Thiemens, .PNAS 110, 17631 (Oct 29, 2013).
2. R. Shaheen, et al.,, PNAS 112, 336 (January 13, 2015, 2015).
3. C. B. Agee et al., Science 339, 780 (Feb 15, 2013).
