Total Heat Loss of the Earth and 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 Earth oceanic heat flow continental heat flow Radioactive heat production continental crust island arc crust Estimation of the subsurface temperature influence 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) ContinentalOceanicGlobal Sclater et al. (1980) Pollack et al. (1993) Jaupart et al. (2007)14 (13–15)32 (30–34)46 (43–49) Davies & Davies (2010) Oceans Thermal models of oceanic plate Continents Thermotectonic age Geological characteristics

Thermal evolution of oceanic plate Lateral heat conduction is negligible. Oceanic heat flow

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 C 2 ranging from 470 to 510 (mW/m 2 Myr 1/2 ) 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) ContinentalOceanicGlobal Sclater et al. (1980) Pollack et al. (1993) Jaupart et al. (2007)14 (13–15)32 (30–34)46 (43–49) Davies & Davies (2010)

Estimation from geological and geophysical proxies Goutorbe et al. (2011)

Continental heat loss: 13.6 ± 0.8 TW ContinentalOceanicGlobal Sclater et al. (1980) Pollack et al. (1993) Jaupart et al. (2007)14 (13–15)32 (30–34)46 (43–49) Davies & Davies (2010)

Estimates of global heat loss (TW) ContinentalOceanicGlobal Sclater et al. (1980) Pollack et al. (1993) Jaupart et al. (2007)14 (13–15)32 (30–34)46 (43–49) Davies & Davies (2010)

Radioactive heat production in the continental crust Heat flow-heat production relationship q r : 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 crust in 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 MeanMedian Upper crust2.04 ± Lower crust0.68 ± 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) Granitic body Metamorphic rocks Furukawa (1995)

Ichinomegata (xenolith) Kohistan paleo arc Lower crust: 〜 0.08 μW/m 3 Mukai et al. (1999)

Old accretionary prisms in SW Japan (sedimentary rocks) Yamaguchi et al. (2001) Terrigenous turbidites 〜 Granitic rocks

Seismogenic zone Magmatism 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) Lower crust (15 km) Hea t production (μW/m 3 )

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 ContinentalOceanicGlobal 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/m 3 Island arc crust has similar values