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Page 1: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Janots et al., 2007

Page 2: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 3: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Spear and Pyle, 2010

Page 4: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Spear, 2010

Page 5: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Spear, 2010

Page 6: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Kelsey et al., 2008

Page 7: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 8: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 9: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 10: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 11: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

“Coupled dissolution-reprecipitation is a well-established chemical reaction, driven by a minimization in the Gibbs free energy. In this process, a mineral phase, in the presence of a reactive fluid, is replaced either by an altered composition of the same phase or by an entirely new phase (Putnis, 2002)”.

Page 12: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

ABSTRACT Electron-microprobe (EMP) U-Th-Pb dating on polyphase and discordant monazitesfrom polymetamorphic granulites of the Andriamena unit (north-central Madagascar)reveals inconsistent chemical ages. To explain these drastic variations, transmission electronmicroscopy (TEM) foils were prepared directly from thin sections by using the focusedion beam technique. The most important result of the TEM study is the demonstrationof the presence of small (;50 nm) Pb-rich domains where large variations inEMP ages occur. We suggest that radiogenic Pb was partially reincorporated in monaziteduring the recrystallization at 790 Ma. Because the excited volume of EMP is ;4 mm3,U-Th-Pb dating yielded various apparent older ages without geological significance. Inaddition, TEM analysis of the foils revealed the presence of an ;150-nm-wide amorphouszone along the grain boundary of monazite and its host quartz. This Fe-Si-Al–rich phasemay have formed as a result of fluid activity at 500 Ma, and the phase’s amorphous statemay be due to the irradiation from U and Th decay in the monazite. This demonstratesfor the first time the enormous potential of the TEM investigations on site-specific specimensprepared with the focused ion beam technique for the interpretation of geochronologicaldata.

“The most important result of the TEM study is the demonstration of the presence of small (50 nm) Pb-rich domains where large variations in EMP ages occur. We suggest that radiogenic Pb was partially reincorporated in monazite during the recrystallization…”

Page 13: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

B. Budzyn (2009)

M-21

Page 14: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Assemblage: monazite, muscovite, albite, amorphous SiO2

Reagents: CaF2

Na2Si2O5

Experimental conditions 4.5 kbar, 450°C for a Duration: 16 days.

See: Budzyn (2009)

Experiment: hydrothermal apparatus

Page 15: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

The monazite chosen for the experiment was taken from a heavy-mineral sand deposit at Cumuruxatiba, Bahia State, Brazil D.

Moderately rounded, semi-euhedral, relatively transparent, inclusion-free, 100 – 500 mm, amber-colored grains.

The monazite grains were hand-picked out of the heavy mineral sand, crushed to 50 – 150 mm size fragments and then washed in ethanol in an ultrasonic bath.

Starting monazite

ThO2: 7-8 wt %,

UO2: 0.5-0.75 wt%

Page 16: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Assemblage: monazite, muscovite, albite, amorphous SiO2

Reagents: CaF2

Na2Si2O5

Experimental conditions 4.5 kbar, 450°C for a Duration: 16 days.

See: Budzyn (2009)

Page 17: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

M-21

5m

Page 18: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

M-Y

Page 19: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

M-X

ThO2= ~7wt%

ThO2= ~8wt%

5m

Page 20: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

M-Z

5m

Page 21: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

M-21

Bkg-1

Bkg-2

Bkg-3

5m

Page 22: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 23: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Brazil Monazite

Pristine Unaltered core Altered domains

Oxide MX MX

Weight Gr1 core Hi-Th-Rt LoThLo-Bk2

CaO 1.40 0.90 0.05

P2O5 29.64 29.24 28.48

ThO2 7.05 7.03 1.77

UO2 0.480 0.735 0.007

Y2O3 0.84 1.49 0.08

La2O3 12.490 12.686 15.576

Ce2O3 28.77 28.74 34.16

Nd2O3 12.28 12.43 13.71

Pr2O3 3.06 3.07 3.49

Sm2O3 1.694 1.436 1.148

Gd2O3 1.590 1.423 0.902

Dy2O3 0.349 0.432 0.044

PbO 0.129 0.144 -0.002

Total 100.8 101.2 100.5

Page 24: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Brazil Monazite

Pristine Unaltered core Altered domains

Oxide MX MX

Weight Gr1 core Hi-Th-Rt LoThLo-Bk2

CaO 1.40 0.90 0.05

P2O5 29.64 29.24 28.48

ThO2 7.05 7.63 1.77

UO2 0.480 0.735 0.007

Y2O3 0.84 1.49 0.08

La2O3 12.490 12.686 15.576

Ce2O3 28.77 28.74 34.16

Nd2O3 12.28 12.43 13.71

Pr2O3 3.06 3.07 3.49

Sm2O3 1.694 1.436 1.148

Gd2O3 1.590 1.423 0.902

Dy2O3 0.349 0.432 0.044

PbO 0.129 0.144 -0.002

Total 100.8 101.8 100.5

Page 25: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Brazil Monazite

Pristine Unaltered core Altered domains

Oxide MX MX

Weight Gr1 core Hi-Th-Rt LoThLo-Bk2

CaO 1.40 0.90 0.05

P2O5 29.64 29.24 28.48

ThO2 7.05 7.63 1.77

UO2 0.480 0.735 0.007

Y2O3 0.84 1.49 0.08

La2O3 12.490 12.686 15.576

Ce2O3 28.77 28.74 34.16

Nd2O3 12.28 12.43 13.71

Pr2O3 3.06 3.07 3.49

Sm2O3 1.694 1.436 1.148

Gd2O3 1.590 1.423 0.902

Dy2O3 0.349 0.432 0.044

PbO 0.129 0.144 -0.002

Total 100.8 101.8 100.5

Page 26: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Brazil Monazite

Pristine Unaltered core Altered domains

Oxide MX MX

Weight Gr1 core Hi-Th-Rt LoThLo-Bk2

CaO 1.40 0.90 0.05

P2O5 29.64 29.24 28.48

ThO2 7.05 7.63 1.77

UO2 0.480 0.735 0.007

Y2O3 0.84 1.49 0.08

La2O3 12.490 12.686 15.576

Ce2O3 28.77 28.74 34.16

Nd2O3 12.28 12.43 13.71

Pr2O3 3.06 3.07 3.49

Sm2O3 1.694 1.436 1.148

Gd2O3 1.590 1.423 0.902

Dy2O3 0.349 0.432 0.044

PbO 0.129 0.144 -0.002

Total 100.8 101.8 100.5

Page 27: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

CaO

P2O5

ThO2 UO

2

Y2O3

La2O3

Ce2O3

Nd2O3

Pr2O3

Sm2O3

Gd2O3

Dy2O3

PbO

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

Page 28: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
Page 29: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Th or U + Ca = 2 REE

Page 30: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Th + Si = REE + P

Page 31: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010
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Page 34: Janots et al., 2007. Spear and Pyle, 2010 Spear, 2010

Compiled and modified by G. Dumond from Hoffman (1988), Tella et al. (2000), Ross (2002), Hajnal et al. (2005), van Breeman et al. (2005; 2007), Rainbird and Davis (2007), Berman et al. (2007), & http://www.lithoprobe.ca/transects

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