Update from the Mantle Group · SCLM beneath the Superior Craton Geotherm: 41mW/m2 At ~2700 Ma...

METAL EARTH Advisory Board Meeting

Update from the Mantle Group

J. Czas, A. Vezinet

D.G. Pearson, S. Shirey

Archean continental crust Adrien Vezinet – Part 2

The lithospheric mantleJanina Czas – Part 1

Outline

Unconventional approaches to the study of metal endowments

The lithospheric mantleAge, composition and metal endowment

J. Czas, A. VezinetD.G. Pearson

Collaborators: S.B. Shirey, P. Waterton, D.J. Schulze,C. Veglio, C. Lawley (GSC)

The Lithospheric Mantle

Why is it important to study the lithospheric mantle?

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The Lithospheric Mantle

Why is it important to study the lithospheric mantle?

Metal endowment derived from Earth’s mantle

Where do our samples come from?

Cratonic lithospheric mantle

- 50 – 250 km

- 500 – 1300 oC

- Record geochemical conditions

at the time of eruption

window into the deep & past

Where do our samples come from?

Cratonic lithospheric mantle

- 50 – 250 km

- 500 – 1300 oC

- Record geochemical conditions

at the time of eruption

window into the deep & past

Metals in the lithospheric mantle

Role of lithospheric mantle in metal endowment

Age of the lithospheric mantle

Timing and location of metals storage and transport

Key QuestionsKirkland Lake Peridotite

1 cm

Sulphide

Superior Craton

WATWawa-AbitbiTerrain

Kirkland Lake (kimberlites 147 158 Ma)

Wawa(lamprophyres 2685 - 2744 Ma)

after Percival et al., 2012

Superior Craton

Unique opportunity to study the lithosphere beneath major gold deposit

Kirkland Lake Kimberlites

Lawley et al. unpublished

Superior Craton

Schaeffer and Lebedev, EPSL 2014

Midcontinent Rift

Perturbations in S-wave velocity model at 100km

Superior Craton

WATWawa-AbitbiTerrain

Kirkland Lake (kimberlites 147 158 Ma)

Wawa(lamprophyres 2685 - 2744 Ma)

after Percival et al., 2012Midcontinent Rift

Kirkland Lake Kimberlites

SCLM beneath the Superior Craton

Geotherm: 40mW/m2

At ~150 Ma(Hasterok and Chapman, 2011)

Wawa websterites

Kirkland Lake peridotites

Kirkland Lake Kimberlites

SCLM beneath the Superior Craton

Geotherm: 41mW/m2

At ~2700 Ma(Hasterok and Chapman, 2011)

Wawa websterites

Kirkland Lake peridotites

Kirkland Lake Kimberlites

SCLM beneath the Superior Craton

Wawa websterites

Kirkland Lake peridotites

Blocking Temperature

Conventional Isotopes

The age of the lithospheric mantle

187Re

187Os

melt

Residual mantle

The age of the lithospheric mantle

TRD = Minimum age (Re depletion)

Re/Os=0

187Re

187Os

Residual mantle

Age of the Superior cratonic mantle

Summary

Lithospheric mantle beneath Wawa & Kirkland Lake

Difference in age (data) and composition

Emerging picture

Olivine can host metal elements

Depth dependent metal concentration in lithosphere

Potential effects of large scale metasomatism

(Midcontinent Rift)