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?

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The Archean crust

Why investigating the continental crust, even the non-endowed parts,

and deciphering its evolution?

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“[…] 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?

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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

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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

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The interpretation of the zircon isotopic signatures is however disputed

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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

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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

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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

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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,

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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)

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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)

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Some results

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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

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Some results – Superior Province

The Assean Lake crustal complex

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Some results – Superior Province

The Assean Lake crustal complex

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Some results – Superior Province

Some results

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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

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Conclusion - Opportunities in UofA

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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

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Thank you for you attention

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The Assean Lake area (Superior Province, Canada)

Some results

Collaborators from UofA: Y. Luo , C. Sarkar & R.A. Stern