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Experimental modeling of impact-induced high-temperature processing of silicates .

Experimental modeling of impact-induced high-temperature processing of silicates. Mikhail Gerasimov Space Research Institute, RAS, Moscow, Russia Yurii Dikov Institute of Ore Deposits, Petrography, Mineralogy and Geochemistry, RAS, Moscow, Russia

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Experimental modeling of impact-induced high-temperature processing of silicates .

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  1. Experimental modeling of impact-induced high-temperature processing of silicates. Mikhail Gerasimov Space Research Institute, RAS, Moscow, Russia Yurii Dikov Institute of Ore Deposits, Petrography, Mineralogy and Geochemistry, RAS, Moscow, Russia Oleg Yakovlev Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS, Moscow, Russia

  2. t p Schematic cratering process

  3. Projectile/target mixing proportions? Computational issues: v imp < 25 km/s m target melt < 10 m projectile  vap < 50 % melt projectile/melt target > 5 % Geochemical observations: (PGEs, Ni, Co, Cr, etc.) individual samples of melt ~ 1 % integral melt sheets « 1 %

  4. What happens to chemical composition of colliding materials?

  5. LIGHT-GAS-GUN (LGG) EXPERIMENTS. A SCHEME OF THE SAMPLE CHAMBER SIMULATION EXPERIMENTS WITH LASER PULSE (LP) HEATING

  6. Starting augite Crater melt Droplets LP experiment with augite. Chemical composition of crater melt and ejected droplets. Starting Droplets augite  Volatilization sequence   SiO249.29 50.05 37.68 34.16 23.29 15.64 TiO21.13 1.19 1.73 2.38 3.38 4.47 Al2O39.98 11.05 17.56 24.41 31.39 43.20 FeO 8.22 6.28 4.20 2.63 1.51 1.76 MgO 13.09 14.79 16.90 7.89 3.91 4.79 CaO 15.46 15.13 20.54 26.94 35.58 28.43 MnO 0.07 0.13 0.17 0.10 0.12 0.30 Na2O 2.75 1.28 1.15 1.28 0.71 1.39

  7. Transformation of silicates chemical composition from starting sample (filled symbols) to condensed material (open symbols) in LGG experiments LGG experiment Fe-Ni meteorite (5.6 km/s)  granite granite condensate SiO2 70.2  50.7 Al2O3 16.0  19.2 FeO 2.3  1.1 CaO 1.1  3.5 Na2O 3.8  22.7 K2O 6.6  2.7

  8. “Netheline” cluster Na : Al : Si = 1 : 1 : 1 Bulk compositions of condensed films (mol. %) obtained in LP experiments for target samples composed of some Ab-Ort proportions. Depth-profiles of main elements through the thickness ofcondensed film obtained in LP experiments with Ab56Ort44 mixture NaAlSi3O8melt NaAlSiO4vapor + 2 SiO2vapor/melt

  9. Depth-profiles of concentrations of Na and Al through the thickness of condensed films produced in LP experiments with augite and meteorites: Indarch, Tsarev, and Etter.

  10. “Enstatite” cluster Mg : Si = 1 : 1

  11. INAA analysis of trace elements compositions in starting Tsarev (L5) and amphibole samples andin their melts and condensates obtained in LP experiments

  12. Comparative composition of trace-elements in starting basalt and granite samples and in their condensates formed during LGG experiments. Concentrations of elements Ci are given relative to concentration of sodium, CNa.

  13. LP experiment with olivine

  14. LP experiment with olivine

  15. Chemical composition (mol %) of starting kerolite (left) and garnierite (right) and of their experimentally produced condensates and melt spherules. Kerolite SiO2 – 53,44 wt.% NiO – 11.32 MgO – 22.59 Fe2O3 – 0.24 Al2O3 – 0.05 H2O –12.58 Garnierite SiO2 – 33,00 wt.% NiO – 44.50 MgO – 4.52 Fe2O3 – 1.08 Al2O3 – 0.62 CaO – 0.33 H2O –16.42

  16. Concentrations of Fe, S, P, and Ni in Pt-rich and in silicate droplets

  17. Volatilization during an impact is a “non linear” process: - volatilization of elements is dominated by formation of clusters which assemble elements having different “classic” volatility (“enstatite”, “netheline”, “wollastonite”, … clusters); - thermal and chemical reduction of iron with subsequent agglomeration of iron droplets and their dispersion from silicate melts; - scavenging of siderophile elements from silicate melts into forming and dispersing metallic droplets; - observed high volatility of “classically” refractory elements such as REE, U, Th, Hf, Zr, etc.

  18. Chemical composition of glass spherules obtained in LP experiment with target mixture of Murchison +Ti-basalt (1:1) in comparison with the composition of «pristine» glasses

  19. Al vs. Mg/Al in starting sample and in glass spherules in LP experiment with a mixture sample (Murchison+Ti-basalt (1:1))

  20. Chemical trend for Ti during an impact of a chondritic projectile into lunar basalts volatilization basalts mixing trend

  21. Chemical trends for Al and Ca during an impact of a chondritic projectile into lunar basalts volatilization basalts mixing trend

  22. Chemical trends for Mg and Fe during an impact of a chondritic projectile into lunar basalts trend trend basalts mixing mixing volatilization volatilization basalts

  23. 3 - "pristine" glasses - lunar basalts 2 Ca/Al, wt. ratio 1 0 30 40 50 SiO , wt.% 2 Ca/Al ratios vs. SiO2 in lunar «pristine» glasses (Delano, 1986) and in lunar basalts (Papike et al., 1998)

  24. Conclusions: - the usage of siderophile elements is a powerful tool as an indicator of the presence of meteoritic material but it can provide an underestimation of proportion of the projectile in the impact melt; - we need an involvement of computational methods into the problem of projectile/target mixing.

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