Total Heat Loss of the Earthand

Heat Production in the Continental Crust

Makoto Yamano

Earthquake Research Institute, University of Tokyo, Japan

Measurements of surface heat flow

Total heat loss of the Earthoceanic heat flowcontinental heat flow

Radioactive heat productioncontinental crustisland arc crust

Estimation of the subsurface temperatureinfluence of crustal heat production

Subsurface temperature cannot be directly measured.

Geophysical/geological processes

closely related to

temperature/pressure conditions

Heat flux at the surface

Temperature distribution

Heat flow measurements

Global heat flow data

34,500 measurements

Most of the earth’s surface has not been covered.

Goutorbe et al. (2011)

Estimates of global heat loss (TW)

Continental Oceanic Global

Sclater et al. (1980) 11.5 30.4 42.0

Pollack et al. (1993) 11.8 34.3 44.2

Jaupart et al. (2007) 14 (13–15) 32 (30–34) 46 (43–49)

Davies & Davies (2010) 14.7 31.9 46.7

Oceans Thermal models of oceanic plate

Continents Thermotectonic age Geological characteristics

Thermal evolution of oceanic plate

Lateral heat conduction is negligible.

Oceanic heat flow

t

zTtzT

2erf,

1-dimensional, half-space cooling

At the age of t

Seafloor depth

Surface heat flow

Depth of isotherm

　 (Plate thickness)

（ Age ） 1/2 relations

Sources of uncertainty in oceanic heat flow

Heat flow deficit

for young ages (< 60 Myr)

Attributed to

hydrothermal circulation

Stein and Stein (1992)

Value of C2

ranging from 470 to 510 (mW/m2 Myr1/2)

Higher heat flow for old ages (> 100 Myr)

Sources of uncertainty in oceanic heat flow

Stein and Stein (1992)

Continental heat flow

Morgan and Sass (1984)

No clear relation with the age

Significant contribution of crustal heat production

Ambiguous definition of the thermotectonic age

Furlong and Chapman (2013)

Transient effects of thermotectonic events

Rifting extensional tectonics

Collision convergent tectonics

Estimates of global heat loss (TW)

Continental Oceanic Global

Sclater et al. (1980) 11.5 30.4 42.0

Pollack et al. (1993) 11.8 34.3 44.2

Jaupart et al. (2007) 14 (13–15) 32 (30–34) 46 (43–49)

Davies & Davies (2010) 14.7 31.9 46.7

Estimation from geological and geophysical proxiesGoutorbe et al. (2011)

Continental heat loss: 13.6 ± 0.8 TW

Continental Oceanic Global

Sclater et al. (1980) 11.5 30.4 42.0

Pollack et al. (1993) 11.8 34.3 44.2

Jaupart et al. (2007) 14 (13–15) 32 (30–34) 46 (43–49)

Davies & Davies (2010) 14.7 31.9 46.7

Estimates of global heat loss (TW)

Continental Oceanic Global

Sclater et al. (1980) 11.5 30.4 42.0

Pollack et al. (1993) 11.8 34.3 44.2

Jaupart et al. (2007) 14 (13–15) 32 (30–34) 46 (43–49)

Davies & Davies (2010) 14.7 31.9 46.7

Radioactive heat production in the continental crust

Heat flow-heat productionrelationship

qr: Moho heat flow?b (length scale): 10 to 15 km

I-D depth distribution of crustal heat production

Exposed crustal cross section

Deep borehole

KTB

Archean granitic crustin South Africa

No simple relation with depth?

Crustal heat production may be heterogeneous

Exponential model Heterogeneity model

Furlong and Chapman (2013)

b: thickness of enhanced radiogenic region

Furlong and Chapman (2013)

0.45

Mean Median

Upper crust 2.04 ± 1.83 1.50

Lower crust 0.68 ± 0.62 0.45

Observed heat production values

Heat production in the island arc crust

Hidaka

Ichinomegata

Old accretionary prisms

Hidaka metamorphic belt(exposed island arc crust)

Furukawa and Shinjoe (1997)

Graniticbody

Metamorphic rocks

Furukawa (1995)

Ichinomegata(xenolith)

Kohistan paleo arc

Lower crust: 〜 0.08 μW/m3

Mukai et al. (1999)

Old accretionary prisms in SW Japan (sedimentary rocks)

Yamaguchi et al. (2001)

Terrigenous turbidites 〜 Granitic rocks

Seismogenic zoneMagmatism

Influence of crustal heat production

Surface heat flow

Temperature structure

Heat production

Estimation of the subsurface temperature structure

1-D, steady state

Upper crust(15 km)

2.0

1.5

1.0

Lower crust(15 km)

0.6

0.4

0.2

Heat production(μW/m3)

Steady state

No sediment

Constant A, supposing accretionary prism in SW Japan

Simplified subduction zone

Trench axis

Radioactive heat production, A

Frictional heating, τv

Subduction velocity, v

Dependence on the effective coefficient of friction

Dependence on the radioactive heat production

Constrained by the surface heat flow observation

Various combinations can reproduce the observed heat flow.

Influence on the plate boundary temperature

・ Global heat loss is quite well estimated.In spite of large areas with no heat flow data

・ Information on crustal heat production is necessary

for better estimation of subsurface temperature structure.

Summary

Continental Oceanic Global

14 (13–15) 32 (30–34) 46 (43–49) TW

・ Distribution of crustal heat production is heterogeneous.No simple heat production vs. depth relationship

Much lower heat production in the lower crust

Median upper: 1.50 lower: 0.45 μW/m3

Island arc crust has similar values