Heat flow and heat production in the Canadian Shield Jean-Claude Mareschal, GEOTOP-UQAM-McGill, with a little help from my friends… Claude Jaupart, Clement.

Heat flow and heat production in the Heat flow and heat production in the Canadian Shield Canadian Shield

Jean-Claude Mareschal, Jean-Claude Mareschal, GEOTOP-UQAM-McGill,GEOTOP-UQAM-McGill,

with a little help from my friends…with a little help from my friends…Claude Jaupart, Clement Gariepy, Claude Jaupart, Clement Gariepy,

Christophe Pinet, Laurent Guillou-Frottier, Christophe Pinet, Laurent Guillou-Frottier, Li Zhen Cheng, Frederique Rolandone, Li Zhen Cheng, Frederique Rolandone,

Claire Perry, Chloe Michaut, Gerard Claire Perry, Chloe Michaut, Gerard Bienfait, Raynald Lapointe, …Bienfait, Raynald Lapointe, …

Measuring heat flowMeasuring heat flow Canadian Shield Canadian Shield Heat flow in the Canadian ShieldHeat flow in the Canadian Shield Interpretation: crustal heat production, Moho, Interpretation: crustal heat production, Moho,

and basal heat flowand basal heat flow Sudbury siteSudbury site

Determining continental heat flowDetermining continental heat flow

Measuring heat flowMeasuring heat flow

Heat flow map of the southern Canadian Shield

In continents, radioactivity of crustIn continents, radioactivity of crustis large component of surface heat fluxis large component of surface heat flux

Heat flux integrates total crustal heat production Heat flux integrates total crustal heat production

In steady state:In steady state:

Zm

m dzzAQQ0

0 )(

Q0 = surface heat flowQm = mantle heat flow (at depth of Moho)A(z) = crustal heat productionZm = Moho depth

Linear heat flow heat production relationship?Linear heat flow heat production relationship?Example of the Trans Hudson OrogenExample of the Trans Hudson Orogen

Model of crustal heat Model of crustal heat production based on linear production based on linear relationship between heat relationship between heat flux and heat productionflux and heat production

In Shield, heat flux and In Shield, heat flux and surface heat production surface heat production data do not fit a linear data do not fit a linear relationshiprelationship

No such relationship for No such relationship for the entire THO nor for the entire THO nor for individual belts. individual belts.

No linear relationship for No linear relationship for any province of the any province of the Canadian Shield. Canadian Shield.

Mantle heat flow in the Canadian Shield Mantle heat flow in the Canadian Shield

QQss = Q = Qmm + ∫ A dz with A(z) estimated from exposures of + ∫ A dz with A(z) estimated from exposures of

different crustal levels (i.e. Kapuskasing area) different crustal levels (i.e. Kapuskasing area) Lowest values QLowest values Qss = 22 mW m = 22 mW m-2 -2 => Q => Qmm < 18 mW m < 18 mW m-2-2

Exposed crustal section Kapuskasing QExposed crustal section Kapuskasing Qss=33 mW m=33 mW m-2 -2 => Q => Qmm

=13 mW m=13 mW m-2-2

Grenville <QGrenville <Qss> = 41 mW m> = 41 mW m-2-2 <A> =0.75 <A> =0.75 µW mµW m-3-3 Q Qmm = 13 = 13

mW mmW m-2-2

Crustal modelsCrustal models

Heat Flow and Gravity profilesHeat Flow and Gravity profiles

Gravity and Heat flow profilesGravity and Heat flow profilesMonte-Carlo inversionMonte-Carlo inversion

Spatial variations in Moho heat flux?Spatial variations in Moho heat flux?

Downward continuation to base of lithosphereDownward continuation to base of lithosphere

δδQQbb = = δδQQmm exp(2 exp(2ππz/z/λλ))

=> => δδQQmm < 3 mW/m < 3 mW/m22

Regional heat flow heat production relationshipRegional heat flow heat production relationship=>on regional scale heat flux uniform below 10km=>on regional scale heat flux uniform below 10km

Heat productionHeat productionof stable continental crustof stable continental crust

Archean cratonsArchean cratons <Q> = 42 mW m<Q> = 42 mW m-2-2 zzmm = 38 km = 38 km

<A<Acc> = .75 > = .75 μμW mW m-3-3

Average continental Average continental crustcrust

<Q> = 55 mW m<Q> = 55 mW m-2-2 ; ; zzmm = 40 km; = 40 km;

<A<Acc> = 1. > = 1. μμW mW m-3-3

These estimates of average crustal heat production are slightly higher than those of Taylor and McLennan (1985).

Heat flow vs Age in the Shield? Heat flow vs Age in the Shield?

Archean (>2.5Ga)Archean (>2.5Ga) Slave Province Slave Province

52mW m52mW m-2-2

Superior Province Superior Province 41mW m41mW m-2-2

Proterozoic (0.6-2.5Ga)Proterozoic (0.6-2.5Ga) Wopmay orogen (reworked Wopmay orogen (reworked

Archean) 90mW mArchean) 90mW m-2-2 ? ? Trans Hudson orogen Trans Hudson orogen

(juvenile crust only) (juvenile crust only) 37mW m37mW m-2-2

Thompson Belt (reworked Thompson Belt (reworked Archean in THO) Archean in THO) 57mW m57mW m-2-2

Grenville Province Grenville Province 42mW m42mW m-2-2

Appalachians (400Ma) have higher heat flow(55mW m-2)because of radioactive granitic intrusions

Sudbury sitesSudbury sites

Copper Cliff 51 mWmCopper Cliff 51 mWm-2-2 3.2 3.2 µWmµWm-3-3

Falconbridge Falconbridge 46 mWm46 mWm-2-2 0.8 0.8 µWmµWm-3 -3

Lockerby Lockerby 63 mWm63 mWm-2-2 3.3 3.3 µWmµWm-3 -3

Sudbury 1 Sudbury 1 47 mWm47 mWm-2-2 1.4 1.4 µWmµWm-3 -3

Elliott Lake (100km W) 60 Elliott Lake (100km W) 60 mWm mWm-2-2

Systematic sampling for hpe (Schneider et al., Systematic sampling for hpe (Schneider et al., Geophys. Res. Lett., 14Geophys. Res. Lett., 14, 264-267, 1987), 264-267, 1987)

Lockerby hpe

depth U(ppm) Th(ppm) K(percent) A(uW/m2) 1.000 8.190 40.000 3.530 5.197 2.000 7.680 33.900 4.180 4.706 3.000 7.510 33.600 3.580 4.585 4.000 7.570 37.700 3.590 4.884 5.000 2.660 10.000 0.990 1.467 6.000 0.440 1.590 1.120 0.328 7.000 8.050 39.300 2.920 5.055 8.000 8.050 35.300 2.970 4.784 9.000 1.710 13.200 3.660 1.694 10.000 2.450 21.100 3.360 2.401 11.000 4.390 19.400 3.380 2.785 12.000 7.330 33.000 3.460 4.486 13.000 6.850 39.200 3.400 4.785 14.000 4.600 32.600 2.950 3.709 15.000 3.660 24.700 4.140 3.034 16.000 2.140 14.300 3.630 1.878 17.000 8.040 23.200 3.450 3.991 18.000 8.240 26.500 2.580 4.189 19.000 5.770 28.700 4.160 3.854 20.000 3.430 23.600 2.540 2.749 mean 5.438 26.544 3.180 3.528 std 2.624 10.810 0.859 1.406

ConclusionsConclusions

Most of the heat flux in stable continents Most of the heat flux in stable continents comes from crustal radioactivitycomes from crustal radioactivity

Important variations in crustal radioactivity Important variations in crustal radioactivity (mostly in shallow part of the crust) (mostly in shallow part of the crust)

Crustal radio-activity relatively high and Crustal radio-activity relatively high and variable in Sudbury basinvariable in Sudbury basin

Heat flow vs Age?Heat flow vs Age?

No relationship between No relationship between heat flow and ageheat flow and age

Active belts with high Active belts with high heat flow (not steady heat flow (not steady state). state).

Wopmay ???Wopmay ??? At 2.5 Ga, Slave had At 2.5 Ga, Slave had

very high heat flow very high heat flow

Differentiation indexDifferentiation index

AAss = average surface heat production = average surface heat production

AAcc = average crustal heat production = average crustal heat production

AAcc = (q = (q00 – q – qmm) / Z) / Zmm

ZZmm = Moho depth = Moho depth

Usually DUsually Dii > 1, but for Flin Flon belt > 1, but for Flin Flon belt

DDii=0.4=0.4

m

ms

c

si QQ

zAAA

D

0

Differentiation index vs average crustal heat productionDifferentiation index vs average crustal heat production

Higher heat production Higher heat production leads to more leads to more differentiated crust.differentiated crust.