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

Oleg Yakovlev Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS, Moscow, Russia

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

vapor

melt

ejecta

isobars

tp

Schematic cratering process

target melt

projectile meltprojectile melt

target melttarget melt

projectile melt

Projectile/target mixing proportions?

Computational issues:

v imp < 25 km/sm 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 %

What happens to chemical composition of colliding materials?

Projectilematerial

Targetmaterial

mixing +

volatilization

Impactites

+

Nd-glass laser

Calorimeter

Focussing lens

Filter

Sample chamber

Inflow ofpurging gas

Outflow

Foil

Sample

Quartz window

Dust trap Foils with grid system

SampleProjectile trajectoryLIGHT-GAS-GUN (LGG) EXPERIMENTS.

A SCHEME OF THE SAMPLE CHAMBER

SIMULATION EXPERIMENTS WITHLASER PULSE (LP) HEATING

Starting Droplets augite Volatilization sequence

SiO2 49.29 50.05 37.68 34.16 23.29 15.64TiO2 1.13 1.19 1.73 2.38 3.38 4.47Al2O3 9.98 11.05 17.56 24.41 31.39 43.20FeO 8.22 6.28 4.20 2.63 1.51 1.76MgO 13.09 14.79 16.90 7.89 3.91 4.79CaO 15.46 15.13 20.54 26.94 35.58 28.43MnO 0.07 0.13 0.17 0.10 0.12 0.30Na2O 2.75 1.28 1.15 1.28 0.71 1.39

Al0 10 20 30 40 50 60 70 80 90 100

Si

0

10

20

30

40

50

60

70

80

90

100

Ca

0

10

20

30

40

50

60

70

80

90

100

Droplets

Cratermelt

Starting augiteLP experiment with augite.

Chemical composition of crater melt and ejected droplets.

SiO2

MgO+FeONa2O+K2O+Al2O3

ultramaficrocks

mafic rocks

acidic rocks

alkali rocks

0 15 30 45 6040

55

70

85

1000

15

30

45

60

Transformation of silicates chemical composition fromstarting sample (filled symbols) to condensed material (open symbols) in LGG experiments

LGG experimentFe-Ni meteorite (5.6 km/s) granite

granite condensateSiO2 70.2 50.7Al2O3 16.0 19.2FeO 2.3 1.1CaO 1.1 3.5Na2O 3.8 22.7K2O 6.6 2.7

No Sample K Na Al Si O

BE Al 2s73.3 ev

Phase NBE Si 2p102.1 ev

Phase QBE Si 2p103.6 ev

1 Ab96Ort4 - 3.9 4.3 4.3 23.0 64.52 Ab80Ort20 1.3 5.3 5.1 4.0 21.8 62.5

3 Ab80Ort20 1.0 5.2 4.9 4.6 21.7 62.6

4 Ab56Ort44 2.7 5.5 4.9 4.9 20.2 61.8

5 Ab56Ort44 2.2 5.0 4.9 5.1 20.3 62.5

Bulk compositions of condensed films (mol. %) obtained in LP experiments for target samples composed of some Ab-Ort proportions.

NaAlSi3O8 melt NaAlSiO4 vapor + 2 SiO2 vapor/melt

2.0

1.5

1.0

0.5

0 20 40 60 80 100Ab in Ab-Ort mixtures (mol %)

Al/Si (phase N)

KAl

Na

Si

Surface 20 6040 80 Bottom

5

10

15

25

30

20

conc

entr

atio

n, m

ol %

Depth inside condensed film, %

Depth-profiles of main elements through the thickness of condensed film obtained in LP experiments with Ab56Ort44 mixture

“Netheline” cluster Na : Al : Si = 1 : 1 : 1

Augite

Depth from the surface, %

Surface 20 40 60 80 Bottom

Co

nce

ntr

atio

n, a

t. %

1

2

3

4

5

Al

Na

Startingsamplevalues

Indarch EH4

Depth from the surface, %

Surface 20 40 60 80 Bottom

Co

nce

ntr

atio

n, a

t.%

0

1

2

3

Na

Al

Etter L5

Depth from the surface, %

Surface 20 40 60 80 BottomC

on

cen

trat

ion

, a

t.%

0

1

2

3

4

Na

Al

Tsarev L5

Depth from the surface, %

Surface 20 40 60 80 Bottom

Co

nce

ntr

atio

n, a

t. %

0

1

2

3

4

Na

Al

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.

Profiles of Mg/Si ratios through the thickness of condensed films in LP experiments with enstatite, olivine, and serpentine. Simbols on the ordinate indicate initial values.

Depth of the condensed film, %

Surface 20 40 60 80 Bottom

Mg

/Si,

ato

mic

ra

tio

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

- enstatite- olivine-serpentine

“Enstatite” cluster

Mg : Si = 1 : 1

Na

0

2000

4000

6000

8000

10000

initial melt cond

Na

initial melt cond0

2000

4000

6000

8000

K

initial melt cond0

400

800

1200

1600

K

initial melt cond0

400

800

Sc

initial melt cond0

4

8

12

Sc

initial melt cond048

12

162024

Co

initial melt cond0

300

600

900

Co

initial melt cond0

30

60

90

La

initial melt cond0

10

20

30

40

50

La

initial melt cond 0

0.3

0.6

0.9

1.2

1.5

Sm

initial melt cond 0

0.1

0.2

0.3

0.4

Sm

initial melt cond0

1

2

3

Eu

initial melt cond 0

0.03

0.06

0.09

0.12

Eu

initial melt cond 0

0.1

0.2

0.3

0.4

Ce

initial melt cond0

30

60

90

Ir

initial melt cond 0

0.2

0.4

0.6

0.8

Hf

initial melt cond0

1

2

3

4

Hf

initial melt cond0

2

4

6

8

U

initial melt cond 0

0.5

1.0

1.5

2.0

U

initial melt cond0

1

2

3

4

5

Dy

initial melt cond 0

0.3

0.6

0.9

1.2

Ga

initial melt cond0

2

4

6

8

Ga

initial melt cond0

5

10

15

20

Th

initial melt cond0

3

6

9

12

Tsarev (L5) Amphibole Tsarev (L5) Amphibole

Con

cent

rati

on, p

pm

INAA analysis of trace elements compositions in starting Tsarev (L5)

and amphibole samples and in their melts and condensates obtained in LP experiments

Sc

Sc

Sm

Eu

Eu

Th

Th YbYb

Sm

La

Ce

U

Ce

La

Rb

10-5 10-4 10-3 10-2 10-1

10-4

10-3

10-2

10-1

Target

Con

dens

ate

Ci/CNa

Ci/CNa

basalt target

granite target

Comparative composition of trace-elements in starting basalt and granite samplesand in their condensates formed during LGG experiments.

Concentrations of elements Ci are given relative to concentration of sodium, CNa.

LP experiment with olivine

LP experiment with olivine

Ni0 20 40 60 80 100

Si

0

20

40

60

80

100

Mg

0

20

40

60

80

100

condensate

starting kerolite

melt spherules

Ni0 20 40 60 80 100

Si

0

20

40

60

80

100

Mg

0

20

40

60

80

100

melt spherules

starting garnierite

condensate

Chemical composition (mol %) of starting kerolite (left) and garnierite (right) and of their experimentally produced condensates and melt spherules.

KeroliteSiO2 – 53,44 wt.%NiO – 11.32MgO – 22.59Fe2O3 – 0.24Al2O3 – 0.05H2O –12.58

GarnieriteSiO2 – 33,00 wt.% NiO – 44.50MgO – 4.52Fe2O3 – 1.08Al2O3 – 0.62CaO – 0.33H2O –16.42

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

Al/Si

0 1 2

P/S

i

0

0.5

1

- silicate droplets- Pt-rich droplets

Al/Si

0 1 2

S/S

i

0

1

2

3

4

5

6

7

- silicate droplets- Pt-rich droplets

Al/Si

0 1 2

Ni/S

i

0

1

2

3

4

5

- silicate droplets- Pt-rich droplets

Al/Si

0 1 2

Fe

/Si

0

5

10

15

20

25

30

- silicate droplets- Pt-rich droplets

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.

- LP spherules- "pristine" glasses- average target- Murchison - Ti - basalt

Mg+Fe0 10 20 30 40 50 60 70 80 90 100

Si+Ti

0

10

20

30

40

50

60

70

80

90

100

Al+Ca

0

10

20

30

40

50

60

70

80

90

100

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

Mg/Al, wt. ratio

0 1 2 3 4 5

Al,

wt.

%

0

4

8

12

16 - LP spherules- "pristine" glasses- average target- Murchison - Ti - basalt

10.57

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

SiO2, wt. %

30 35 40 45 50 55

TiO

2,

wt.

%

0

5

10

15

20

- "pristine" glasses- lunar basalts

Chemical trend for Ti during an impact of a chondritic projectile into lunar basalts

basaltsvolatilization

mixing

trend

SiO2, wt. %

30 35 40 45 50 55

Al 2

O3,

wt.

%

0

5

10

15

- 'pristine" glasses- lunar basalts

SiO2, wt. %

30 35 40 45 50 55

CaO

, w

t. %

0

5

10

15

- "pristine" glasses- lunar basalts

basaltsvolatilization

mixing

trend

Chemical trends for Al and Ca during an impact of a chondritic projectile into lunar basalts

basalts

volatilization

mixing trend

Chemical trends for Mg and Fe during an impact of a chondritic projectile into lunar basalts

SiO2, wt. %

30 35 40 45 50 55

Mg

O,

wt.

%

0

5

10

15

20

25

30

- "pristine" glasses- lunar basalts

SiO2, wt. %

30 35 40 45 50 55

Fe

O,

wt.

%

0

5

10

15

20

25

30

- "pristine" glasses- lunar basalts

basalts

volatiliza

tion

mixing

trend

SiO2, wt.%

30 40 50

Ca/

Al,

wt.

rat

io

0

1

2

3

- "pristine" glasses- lunar basalts

Ca/Al ratios vs. SiO2 in lunar «pristine» glasses (Delano, 1986) and in lunar basalts (Papike et al., 1998)

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.