Experimental Constraint of the Volatility of Germanium, Zinc, and Lithium in Martian Basalts and the Role of Degassing in Alteration of Surface Lithologies
Abstract
Recently, the MSL Curiosity rover reported elevated levels of Ge, Li, and Zn in Gale Crater with local measurements of Ge upwards of 850 ppm. Since such excesses of Ge are far larger than any chondritic input to the Martian surface, a volcanic source origin has been assumed. This has raised questions regarding how the presence of Cl and S effects the partitioning of these trace elements between a silicate melt and vapor phase during magmatic ascent and eruption.
To constrain the role of Cl and S on the loss of Ge, Li, and Zn from these lavas, we conducted a series of degassing experiments that simulate magmatic ascent to the Martian surface. Our first set of experiments focused on the individual effects of Cl and S on the volatility of alkalis, Fe, Ge, Li, and Zn from the Gusev basalt, Irvine after 6 hours of degassing. During the initial experiments, Cl-bearing runs lost larger fractions of Na, K, and Fe, than the S-free and volatile-free runs. The loss of alkalis favored K2O over Na2O, consistent with the lower vaporization temperature of K2O. Zn and Ge were lost almost completely after 6 hours from both volatile-free and volatile-bearing runs. The greatest loss of Zn occurs in the Cl-bearing system, implying the volatility of Zn in the form of Zn chlorides. Li concentrations remain nearly constant between initial and final melts. Volatility of Ge was lower in S-bearing runs (94%) compared to the loss in Cl-bearing (100%) and volatile-free systems (99%). These experiments resulted in significant losses of major and volatile trace elements and only showed the individual effects of Cl and S after 6 hours of degassing. Here, we will report on a second set of experiments that focused on constraining the individual effects of Cl and S on the volatility of alkalis, Fe, Ge, Li, and Zn from two Martian basalt (Irvine and Backstay) compositions after 10 min, 30 min, and 1 hr of degassing. Preliminary results for Cl+S-bearing mixes show that Zn degasses from the melt at a rate independent of the Fe-content of the melt, whereas the volatility of Ge is enhanced in the Fe-rich Irvine composition. For both compositions, over 93% of Ge and Zn was lost after only 30min of degassing. Final results from these experiments will serve to confirm these observations and constrain the relationship between volatiles in the melt and the volatility of these trace metals.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR23B0094R
- Keywords:
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- 1038 Mantle processes;
- GEOCHEMISTRYDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3630 Experimental mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 5199 General or miscellaneous;
- PHYSICAL PROPERTIES OF ROCKS