Geochemical dating of a Swiss freshwater limestone cave using 230 Th/ - - PowerPoint PPT Presentation

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Geochemical dating of a Swiss freshwater limestone cave using 230 Th/ - - PowerPoint PPT Presentation

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PAUL SCHERRER INSTITUT Geochemical dating of a Swiss freshwater limestone cave using 230 Th/ 234 U ingrow and 226 Ra-excess decay chronometry Jost Eikenberg, Maya Jggi Division for Radiation Protection and Safety Paul Scherrer Institute,

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Geochemical dating of a Swiss freshwater limestone cave using 230Th/234U ingrow and 226Ra-excess decay chronometry

Jost Eikenberg, Maya Jäggi Division for Radiation Protection and Safety Paul Scherrer Institute, CH-5232 Villigen

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Overview / Topics

  • Presentation of a radiochemical method for

simultaneous determination of 226Ra+228Ra followed by TDCR-measurement and optimized alpha/beta-separation

  • Application of the chronometers 230Th/234U and

226Ra for dating sedimentary systems

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

relevant isotopes for quaternary limestone dating

radionuclide analytical technique

234U, (235U), 238U, 230Th, 232Th

U/TEVA separation, electro- deposition, α-spectrometry

226Ra, 228Ra

filtration (RadDisc), OptiPhase Hisafe3 cocktail, LSC

210Po

spontaneous deposition on silver disc, α-spectrometry

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Method implementation: low level determination

  • f 226Ra in sediments (limestone)
  • Sample dissolution CaCO3 in 1 mol/liter HCl,

evaporation, dilution with distilled water

  • Filtration of the sample through 3 Empore RadDisc

(Mn-oxide impregnated) membrane

  • Elution of Ra with alkaline Na-EDTA solution
  • Measuring via LSC with optimized α/β-

discrimination

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

The triple coincidence to double coincidence ratio (TDCR) counting technique

SAM PLE PM R

PM S

PM T

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Pulse Length Index (PLI) discrimination with HIDEX SL 300

27 38 52 72 99 135 185 252 343 466 634 861 1169 1588 2156 2927 3973 5393 7319 9934 13481 18296 4 8 12 16 20 24 28

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

α-spectrum of 226Ra with ingrowing daughters 2 h and 8 h after separation using HIDEX 300 SL LSC

Alpha

20 40 60 80 100 120 140 10 100 1000 10000

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

α-spectrum of 226Ra with ingrowing daughters

  • btained 6 days after separation

Alpha

20 40 60 80 100 120 140 160 10 100 1000 10000

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

β-spectrum of 228Ra with ingrowing 228Ac 1 h and 8 h after separation using HIDEX 300 SL LSC

Beta

5 10 15 20 25 30 35 40 45 50 1 10 100 1000

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

TDCR vs. Efficiency using high purity radionuclide standard solutions

0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.4 0.5 0.6 0.7 0.8 0.9 1.0

TDCR = efficiency

226Ra 210Pb 228Ra

TDCR efficiency

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Comparison of measured 226Ra and the progeny isotopes

222Rn, 218Po and 214Po with calculated decay/ingrowth curves

5 10 15 20 25 30 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

222Rn+ 218Po+ 214Po: measured data 226Ra decay curve 226Ra: measured data 222Rn+ 218Po+ 214Po ingrowth curve

relative activity time after separation [d]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

238U 234U 230Th 234Pa 234Th 226Ra 222Rn 218Po 214Po 210Po 210Bi 210Pb 206Pb 235U 231Pa 231Th 227Th 227Ac 223Ra 219Rn 232Th 228Th 228Ac 224Ra 228Ra 220Rn 215Po 211Pb 207Pb 211Bi 212Bi 216Po 212Po 212Pb 208Pb 207Tl 208Tl 214Bi 214Pb

4.47x109y 2.45x105y 24.1d 7.54x104y 1.17min

α 4.196 MeV α 4.776 MeV α 4.688 MeV α 4.784 MeV α 5.490 MeV α 6.003 MeV

1600y 3.825d 3.11min 19.9min 26.8min 22.3y 7.04x108y

α 6.038 MeV α 4.395 MeV β α 5.013 MeV

3.28x104y

β

18.7d 21.8y 11.4d

α 4.010 MeV

1.41x1010y 1.91y 5.75y

α 5.423 MeV

6.13h

β

3.66d

α 5.686 MeV

55.6s

α 6.288 MeV β β β β

1.6x10-4s 5.01d

α 7.687 MeV α 5.304 MeV

stable 138.4d

β β

1.06d

β α 5.716 MeV α 6.819 MeV

3.96s 1.8x10-3s 2.14min 36.1min stable

α 7.386 MeV α 6.623 MeV

4.77min

β

66.3% 0.15s

β β α 6.779 MeV

1.01h 33.7%

α 6.051 MeV

10.6h 3.05min

β

stable

β α 8.784 MeV

3x10-7s

238U-Series 235U-Series 232Th-Series

U Pa Th Ac Ra Fr Rn At Po Bi Pb Tl

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Challange for the isotope geochemist: closing the gap between the established210Pb and 230Th/234U chronometers

10-1 100 101 102 103 104 105 106

0.0 0.5 1.0 1.5 2.0

210Po/210Pb 210Po/210Pb 210Pb/226Ra

210Pb/226Ra

226Ra/230Th

226Ra/230Th 230Th/234U

230Th/234U

daughter / parent time after formation [y]

( ) ( )

Po Pb Rn Ra Th U U

210 210 222 226 230 234 238

→ → → →

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Principles of U series dating: 1. 230Th/234U/238U

( )

t

e U t Th

230

1 ) ( ) (

234 230 λ −

− ⋅ =

) ( ) ( ) (

230 234

234 230 t t

e e U t Th

λ λ − −

− ⋅ =

) ( ) ( ) ( ) (

230 234 230

234 230 230 t t t

e e U e Th t Th

λ λ λ − − −

− ⋅ + ⋅ =

t

e U t U

238

) ( ) (

234 234 λ −

⋅ =

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Principles of U series dating: 1. 230Th/234U/238U

U U U

238 238 234

) ( ) ( = =

( )

t

e U t Th

230

1 ) ( ) (

234 230 λ −

− ⋅ =

50 100 150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0

238U, 234U 230Th

relative activity (not to scale) time after separation [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Problem 1: inherited 230Th, wrong age calculation

( )

t t

e Th e U t Th

230 230

) ( 1 ) ( ) (

230 234 230 λ λ − −

⋅ + − ⋅ =

50 100 150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0

230Th ingrowth + decay, with initial 230Th(0)/ 234U = 0.2

230Th/ 234U = 1

230Th ingrowth, without inherited 230Th 230Th ingrowth + decay, with initial 230Th(0)/ 234U = 0.1 U-Th-evolution

230Th(t)/ 234U activity ratio

time after formation [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

U-series application with U-Th isochrones in sedimentology

0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0

Sedimentary Systems

mixed (authigenic + detritus) phases:

230Th

ingrowth dating T equipoint = U/Th ratio of detritus component T

1

U/Th mixing line at T0: authigenic phases with detritus contamination isochrone

equiline: T > 0.3 My

230Th / 232Th activity ratio (relative scale) 234U / 232Th activity ratio (relative scale)

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Geological section of the aquifer / recharge area of hell grottoes springs

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Travertine dating via 226Raex/234U and 230Th/234U

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

View into the cave system

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Travertine precipitation: thermodynamic background

O H CO O CO H

2 2 2 2

+ → +  

− + +

→ → +

3 3 2 2 2

HCO H CO H O H CO

− + − +

+ ↔ + +

3 2 3 3

2HCO Ca HCO H CaCO

HCO CO OH

3 2 − −

↔ + HCO CO H

3 3 2 − − +

↔ +

Ca CO CaCO

2 3 2 3 + −

+ ↔

2

3 2 3 2 2

HCO Ca CaCO CO H O

− +

+ ↔ ↓ + ↑ +

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Ingrowth of 230Th without an inherited component, why that ?

3 4 5 6 7 8 9 1E-16 1E-14 1E-12 1E-10 1E-8 1E-6 1E-4 detection limit for

232Th, 230Th and 228Th

uraninite solubility (mildly reducing: Eh = 0.5 - 0.059pH)

thorianite solubility

concentration [mol/l]

pH

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

226Ra/230Th/234U dating principle

230 230 230 234 230

1 Th t Th e U e

t t

( ) ( ) ( ) = ⋅ + ⋅ −

− − λ λ

230 232 230 232 230 234 232 230

1 Th t Th Th Th e U Th e

t t

( ) ( ) ( ) = ⋅ + ⋅ −

− − λ λ

234 234 232

U U k Th

aut m m

= − ⋅

100 200 300 400 500 10 20 30 40

  • Fig. 8-3a

magnification in Fig. 8-3b 3 8 y e a r c

  • n

s t r u c t i

  • n

l i n e 6500 year isochron present day U/Th mixing line equiline

230Th / 232Th activity ratio 234U / 232Th activity ratio

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

226Ra/230Th/234U dating principle

230 230 230 234 230

1 Th t Th e U e

t t

( ) ( ) ( ) = ⋅ + ⋅ −

− − λ λ

230 232 230 232 230 234 232 230

1 Th t Th Th Th e U Th e

t t

( ) ( ) ( ) = ⋅ + ⋅ −

− − λ λ

234 234 232

U U k Th

aut m m

= − ⋅

10 20 30 40 50 1 2 3 4

  • Fig. 8-3b

3800 year construction line 6500 year isochron present day U/Th mixing line e q u i l i n e

230Th / 232Th activity ratio 234U / 232Th activity ratio

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

226Ra/230Th/234U dating principle

230 230 230 234 230

1 Th t Th e U e

t t

( ) ( ) ( ) = ⋅ + ⋅ −

− − λ λ

Let‘s find an analytical (not numerical) solution for the propagation of the 226Ra activity with time

5 10 15 20

0.0 0.2 0.4 0.6 0.8 1.0

226Ra(0)/ 234U = 0.2 226Ra(0)/ 234U = 0.5 226Ra(0)/ 234U = 1.0

230Th(t=0) = 0 234U(t) = 234U(0) 230Th /234U, 226Ra /234U activity ratio

time after formation [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

226Ra/230Th/234U dating principle

226 226 226 234 226 230 230 226 226 230

1 1 Ra t Ra e U e e

t t t

( ) ( ) ( ) ( ) = ⋅ + ⋅ ⋅ − − ⋅ − −

− − − λ λ λ

λ λ λ λ

226 226 226

Ra t Ra Ra t

ex aut

( ) ( )

sup

= −

226 226 232

Ra Ra k Th

aut m m

= − ⋅

226 226 226 226 226

226

Ra t Ra Ra Ra t Ra e

ex aut t

( ) ( ) ( ) ( )

sup

= − =

−λ

t Ra Ra t Ra

age aut

= − ⋅ −         1

226 226 226 226

λ ln ( ) ( )

sup

F t Ra Ra t Ra e

aut t

( ) ( ) ( )

sup

= − −

− 226 226 226

226

λ

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Validating the model with the sample data

2 4 6 8 10

10

  • 2

10

  • 1

10

regression fit: λ = (0.444 + 0.041)10

  • 3 y
  • 1

T1/2 = 1560 + 150 years

17

19

6 14 12 9 15 16 10 8 1 11 2 18 13 5 4

excess

226Ra decay curve 226Raex(t)/ 226Ra(0) = e

  • λ

226t

226Raex / 226Ra(0)

time after formation [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Calculating 226Raex-ages analytically with the assumption of constant Raex/234U ratios

2 4 6 8 10 0.00 0.05 0.10 0.15 0.20

19 11 6 10 15 18 17 2 5

4

8 12 16 14 9 13 1

226Ra(0)/ 234U initial value 230Th ingrowth 226Raex decay 230Th supported 226Ra ingrowth 226Ra(t)/ 234U decay + ingrowth curve

226Ra(t)/ 234U activity ratio

time after formation [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Reasons for a stable aqueous chemistry, i.e. constant initial 226Ra(0)

2 4 6 8 10 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0

mean 234U/238U ratio in travertine = 1.28 + 0.06 mean Ba/Ca ratio in travertine = (0.49 + 0.02)10-3 present day 234U/238U groundwater ratio

Ba/Ca weight ratio (*10

  • 3)

234U/ 238U activity ratio 230Th/234U sample age [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Comparing 226Raex/ 226Ra(0) with 230Th/234U ages

2 4 6 8 2 4 6 8

17

19

6 12 9 15 10 8 11 2 18 5 4

226Raex/ 226Ra(0) age = 230Th/ 234U age

226Raex/ 226Ra(0) age [ky] 230Th/ 234U age [ky]

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Conclusions

  • 230Th/234U and 226Raex/234U two chronometer

dating yields consistent results (agreeing ages)

  • Inherited 230Th at sample formation is negligible
  • The chemical groundwater composition seems to

be highly uniform, obviously there is almost no change of the 226Ra-initial with time

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Understanding the dynamics of active volcanic systems: Can we determine melt uplift velocities, melt chamber residence times

  • r eruption events by use of natural tracers ??
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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

The dynamic earth: sea floor spreading and subduction of oceanic plates

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Study objects: island arc volcanic rocks from the Sunda-Banda subduction zone

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Which radio-tracers can be applied ?

Isotope Half-life [years] Suitable time span

230Th

76000 2000 – 200000

231Pa

33000 1000 - 100000

226Ra

1600 100 - 6000

210Pb

22 3 - 100

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

U-Th-Ra fractionation during melt differentiation

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.5 1.0 1.5 2.0 2.5 3.0

Ra > U > Th Ra > Th > U

IAB: (this study) alkali basalts: (ref 2) MORB: (ref 1)

226Ra / 230Th activity ratio 238U / 230Th activity ratio

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Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Thank you for your attention