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The Archean crust: nature, composition and evolution through time
J. Czas, A. Vezinet, D.G. Pearson,March, 1st 2019
Collaborators from UofA: Y. Luo , C. Sarkar & R.A. Stern
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The Archean crust
Why investigating the continental crust, even the non-endowed parts,
and deciphering its evolution?
2
The Archean crust
Why investigating the continental crust, even the non-endowed parts,
and deciphering its evolution?
2
“[…] how secular changes in Earth’s
evolution have resulted in differential
metal endowment in space and time.”
The Archean crust
Why investigating the continental crust, even the non-endowed parts,
and deciphering its evolution?
2
How can the community produce high(er) quality
spatially resolved isotopic data?
A zircon insight
The Archean crust
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The Archean crust
A zircon insight
3
Arctic Resources Lab, UofA – 193 nm ArF excimer Laser(20 standard 1” mounts holder)
The Archean crust
Which tools?A laser ablation system & an ion probe (O isotopes)
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The interpretation of the zircon isotopic signatures is however disputed
On the difficulty to determine accurate isotopic composition
5
The interpretation of the zircon isotopic signatures is however disputed
6
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
6
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
6
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
6
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
6
𝜺𝑯𝒇(𝑺𝒂𝒎𝒑𝒍𝒆) =( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑺𝒂𝒎𝒑𝒍𝒆
( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑬𝒂𝒓𝒕𝒉− 𝟏 .104
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
6
𝜺𝑯𝒇(𝑺𝒂𝒎𝒑𝒍𝒆) =( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑺𝒂𝒎𝒑𝒍𝒆
( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑬𝒂𝒓𝒕𝒉− 𝟏 .104
Positive e value
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
7
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
7
𝜺𝑯𝒇(𝑺𝒂𝒎𝒑𝒍𝒆) =( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑺𝒂𝒎𝒑𝒍𝒆
( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑬𝒂𝒓𝒕𝒉− 𝟏 .104
Negative e value
On the difficulty to determine accurate isotopic composition
The interpretation of the zircon isotopic signatures is however disputed
7
𝜺𝑯𝒇(𝑺𝒂𝒎𝒑𝒍𝒆) =( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑺𝒂𝒎𝒑𝒍𝒆
( ൗ𝟏𝟕𝟔𝑯𝒇 𝟏𝟕𝟕𝑯𝒇)𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑬𝒂𝒓𝒕𝒉− 𝟏 .104
Negative e value
On the difficulty to determine accurate isotopic composition
The Laser Ablation Split Stream protocol
8
9
The Laser Ablation Split Stream protocol
The interpretation of the zircon isotopic signatures is however disputed
Alteration
On the difficulty to determine accurate isotopic composition
10
Ion probe ⇒ Oxygen isotope measurements
CL/BSE imaging ⇒ Micro-structures
Laser Ablation Split Stream ⇒ Concurrent U-Pb/Hf isotope
measurements
Laser Ablation Single Stream ⇒ Trace element measurements
(REE, HFSE, LILE)
An extensive analytical workflow,
Analytical Protocol
11
which enables thorough filtering of the dataset
Analytical Protocol
Ion probe ⇒ Oxygen isotope measurements
CL/BSE imaging ⇒ Micro-structures
Laser Ablation Split Stream ⇒ Concurrent U-Pb/Hf isotope
measurements
Laser Ablation Single Stream ⇒ Trace element measurements
(REE, HFSE, LILE)
An extensive analytical workflow,
11
which enables thorough filtering of the dataset
Analytical Protocol
An extensive analytical workflow,
Pristine CL & BSE zircon domains,
95% ≤ Concordance ≤ 105%
Uncertainty in the 207Pb/206Pb apparent age < 1%,
Uncertainty in the ε(Hf)initial ≤ 3 ε
f206Pbc ≤ 0.1%,
[Ca] < 100 ppm,
[Ba] < 0.4 ppm.
Ion probe ⇒ Oxygen isotope measurements
CL/BSE imaging ⇒ Micro-structures
Laser Ablation Split Stream ⇒ Concurrent U-Pb/Hf isotope
measurements
Laser Ablation Single Stream ⇒ Trace element measurements
(REE, HFSE, LILE)
11
Pristine CL & BSE zircon domains,
95% ≤ Concordance ≤ 105%
Uncertainty in the 207Pb/206Pb apparent age < 1%,
Uncertainty in the ε(Hf)initial ≤ 3 ε
f206Pbc ≤ 0.1%,
[Ca] < 100 ppm,
[Ba] < 0.4 ppm.
which enables thorough filtering of the dataset
Analytical Protocol
An extensive analytical workflow,
Identification of secondary alteration
processes
Ion probe ⇒ Oxygen isotope measurements
CL/BSE imaging ⇒ Micro-structures
Laser Ablation Split Stream ⇒ Concurrent U-Pb/Hf isotope
measurements
Laser Ablation Single Stream ⇒ Trace element measurements
(REE, HFSE, LILE)
11
Some results
12
The Eoarchean Saglek Block
Vezinet et al., 2018 (EPSL)Vezinet et al., in revision (Geology)
The scientific community agrees that our protocol is
suited for the identification of the least disturbed zircon
domains.
Some results – North Atlantic craton
The Assean Lake crustal complex
14
Some results – Superior Province
The Assean Lake crustal complex
15
Some results – Superior Province
The Assean Lake crustal complex
16
Some results – Superior Province
Some results
17
Work in Progress:• Writing up the Assean
Lake results• Archean Zircon standard• Xenotime standard
Synthetic Baddeleyite Reference Material
• Rutile (U–Pb+TE) from crustal xenoliths
Conclusion - Opportunities in UofA
18
Conclusion - Opportunities in UofA
18
Conclusion - Opportunities in UofA
Outstanding environment for enhancing our knowledge of the Archean lithosphere. 19
Conclusion - Opportunities in UofA
Outstanding environment for enhancing our knowledge of the Archean lithosphere. 19
20
Thank you for you attention
36
The Assean Lake area (Superior Province, Canada)
Some results
Collaborators from UofA: Y. Luo , C. Sarkar & R.A. Stern
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