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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?
?
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 unpublished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)