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IASPEI/IAVCEI/IAGA/IAPSO/IAMAS/IAHS/IAG/IAC S http://www.iaspei.org/commissions/IHFC.html International Heat Flow Commission Global Heat Flow Database W. Gosnold - Custodian Base http://www.heatflow.und.edu/ Data Base “You know, for a minute there, I could have sworn I felt Earth’s crust cooling.” Source: Omni magazine (1980s) OUTLINE •Global heat flux •Heat flow compilations •Heat flow estimates •IHFC Database •Heat flow methodology •Distribution of U, Th, K •Limitations and precautions on heat flow data •Hydrologic signals •Transient signals •Climate Change •Microclimate •46 TW or 31 TW Global Heat Flow • • • • • Average solar flux at TOA: 1365 W m‐2 Average solar flux at the surface: 400 W m‐2 Global heat flow from Earth’s interior: 92* mW m‐2 Total surface heat flux from Earth’s interior: 47±2TW Heat flow research has focused on: – – – – Tectonics Thermal history of the planet Thermal history of petroleum source rocks Geothermal energy • For geoneutrino research, we should also consider “reduced heat flow.” q = q0 +AD Heat Flow Compilations • • • • • Lee and Uyeda (1965) Simmons and Horai (1968) Jessop, Hobart, and Sclater (1975) Pollack, Hurter, and Johnson, 1993 Gosnold and Panda, 2002 The global heat flow database of the IHFC contains > 22,000 observations. Global distribution of heat flow data. 38,347 data points from Davies and Davies, 2010. 955 Global Reduced Heat Flow Sites: Heat Production Dark Blue: 0 – 0.6; Light Blue: 0.6 – 1.2; Light Green 1.2 – 2.2; Yellow Green: 2.2 – 3.6; Red: <3.6 Variability in Surface Heat Flow • Tectonic age • Transition between heat flow provinces • Crustal radioactivity • Long period transients • Climate change • Variability due to surface features: – – – – Microclimate Topography Hydrology Structure Global Heat Flow Estimates • • • • Pollack, Hurter, and Johnson (1993) 44.2 TW±1 TW Hofmeister and Criss (2006) 33.2 TW±1 TW Jaupart et al. (2007) 46.0 TW ±3 TW Davies and Davies (2010) * 46.7 TW ±2 TW 1984 Global heat flow map by Pollack and Chapman (1984) Davies & Davies (2010) GIS approach with 93,030 surface geology polygons Heat flow in southern hemisphere shields averages approximately 61.4 mWm‐2, but heat flow in northern hemisphere shields averages 37 mWm‐2. • Brazil 64.8 mW m‐2 (86) • Africa 52.3 mW m‐2 (145) • Australia 68.1 mW m‐2 (157) • N. America 33.1 mW m‐2 (315) • Fennoscandia and East European Craton 35 ‐ 40 mW m‐2 (1,352) IHFC Database Continents and Oceans http://www.heatflow.und.edu/ Africa csv file Asia csv file Antarctica csv file Australia csv file North America Global data csv file RTF format Europe csv file South Continental North Pacific Indian Ocean Marine Data America Data csv file csv file csv file csv file csv file South Pacific csv file North Atlantic Ocean csv file South Atlantic Ocean csv file Black Sea csv file Mediterranean Red Sea Sea csv file csv file IHFC Database Countries North America & South America http://www.heatflow.und.edu/ Argentina csv file Bermuda csv file Bolivia csv file Brazil csv file Canada csv file Chile csv file Columbia csv file Cuba csv file Ecuador csv file Greenland csv file Mexico csv file Panama csv file Peru csv file Puerto Rico csv file USA csv file IHFC Database Canada Data Descriptive Number Code CAN001 B A A CAN002 B A A CAN003 B A A CAN004 B A A CAN005 B A B CAN006 B A C CAN007 B A B CAN008 B A A CAN009 B A A CAN010 B A G http://www.heatflow.und.edu/ Site Name WINNIPEG COCHRANE KAPUSKAS HEARST JACKFISH OSKWIN R MINCHIN ENGLISH NIELSEN L DUFAUL Latitude (degrees) (+N, ‐S) 49.8019 49.1006 49.4167 49.6844 48.8514 51.8181 50.7019 49.635 55.3853 48.35 Longitude (degrees) Elevation (+E, ‐W) (meters) ‐97.1192 232 ‐80.935 250 ‐82.3689 230 ‐83.5336 260 ‐86.9681 280 ‐89.5858 340 ‐90.4689 395 ‐91.3175 420 ‐77.6833 3 ‐79.05 300 IHFC Database Temp. Minimum Maximum Number Gradient Depth (m) Depth (m) Temps. Number (mK m‐1) Conductivities Conductivity W m‐1 K‐1 205 610 20 11 56 2.72 300 469 22 15 42 2.51 300 605 41 10 76 2.64 300 654 47 15 89 3.14 150 610 59 14 55 2.91 200 606 52 9 56 2.69 150 605 58 14 58 3 150 612 59 14 60 3.02 120 1042 35 58 IHFC Database Number of Heat Prod. Heat Flow Number Reference Year of mW m‐2 of Sites Number Publication Heat Prod. μW m‐3 13 1.4 38 1 1 71 6 1.3 43 1 2 71 10 0.5 33 1 2 71 10 1.8 52 1 2 71 15 1 41 1 3 78 12 0.2 25 1 3 78 17 0.9 42 1 3 78 41 2 40 1 3 78 13 1.3 26 1 1 71 0.6 42 1 4 77 http://www.heatflow.und.edu/ References at end of file • “CAN 1 JESSOP,A.M., AND JUDGE, A.S, “ FIVE MEASUREMENTS OF HEAT FLOW IN SOUTHERN CANADA. " CAN. J. EARTH SCI., 8, 711‐716, 1971.” • “CAN 2 CERMAK, V., AND JESSOP, A.M.," HEAT FLOW, HEAT GENERATION AND CRUSTAL TEMPERATURE IN THE KAPUSKASING AREA OF THE CANADIAN SHIELD.“ TECTONOPHYSICS, 103, 19‐32, 1971." • "CAN 3 JESSOP, A.M., AND LEWIS, T.J., " HEAT FLOW AND HEAT GENERATION IN THE SUPERIOR PROVINCE OF THE CANADIAN SHIELD. " TECTONOPHYSICS, 50, 55‐77, 1978." • "CAN 4 LEWIS, T.J., AND BECK, A.E.," ANALYSIS OF HEAT FLOW DATA‐‐ DETAILED OBSERVATIONS IN MANY HOLES IN A SMALL AREA. " TECTONOPHYSICS, 41, 41‐59, 1977." Codes • 1 Geographic area: (A‐F = Continents; N‐S = Oceans) • 2 Tectonic setting: (Archean, Mesozoic, Cenozoic; Ridge, Trench, Shelf) • 3 Temperature measurements: (Borehole, Mine, Lake; Probe Type, Ocean Bottom Borehole) • 4 Conductivity measurements: (Divided bar, Estimated; Needle Probe, Not Specified) • 5 Corrections: (Climate, Topography; Hydrology, Sedimentation) • 6 Quality: Author’s comments Code examples • BABABA – – – – – – North America Proterozoic Borehole Divided Bar Topographic correction High quality • EHACEB – – – – – – Europe Geothermal Area Borehole Estimated from literature Corrected for water circulation Medium quality We can calculate heat flow as the product of temperature gradient and thermal conductivity Fourier’s law of Heat conduction q = λΓ A common method for determining heat flow is to use a plot of thermal resistance vs. temperature (Bullard method). This uses the entire length of the temperature measurements. 2 Ma 66 Ma 251 Ma 570 Ma Thermal conductivity varies with rock type, composition, grain size, grain orientation, density, porosity, composition of pore fluid, & temperature. 2 Ma 66 Ma 251 Ma In a conductive environment with constant heat flow, the temperature gradient varies with thermal conductivity. The blue, green and brown T‐z profiles were measured; the red was calculated. n Tz = ∑ i =1 570 Ma qzi λi Resistance reading in KΩ Light aluminum reel for transport 600 m 4‐conductor shielded cable Metering wheel for depth measurement Divided bar thermal conductivity Copper Warm end ΔT1 Lexan Copper ΔT3 Core sample Copper Lexan ΔT3 Copper Cold end Thermocouples Radioactive Heat Source Turcotte & Schubert (1982) Rate of Heat Production (w m-3) Conc. kg/kg Total Heat Production (W) K 3.58E-09 2.57E-04 5.49E+12 U 2.32E-08 2.57E-08 3.56E+09 Th 2.69E-05 1.03E-07 1.65E+13 2.20E+13 McDonough & Sun (1995) Rate of Heat Production Conc. kg/kg Total Heat Production K 3.58E-09 2.40E-04 5.13E+12 U 2.32E-08 2.03E-08 2.81E+09 Th 2.69E-05 7.95E-08 1.28E+13 1.79E+13 Lyubetskaya and Korenaga (2007) Rate of Heat Production Conc. kg/kg Total Heat Production K 3.58E-09 1.90E-04 4.06E+12 U 2.32E-08 1.73E-08 2.40E+09 Th 2.69E-05 6.30E-09 1.01E+12 5.07E+12 Anderson (2007) Rate of Heat Production Conc. kg/kg Total Heat Production K 3.58E-09 1.51E-04 3.23E+12 U 2.32E-08 1.96E-08 2.71E+09 Th 2.69E-05 7.65E-09 1.23E+12 4.46E+12 Birch et al., (1968) observed a linear relation between heat flow and radioactive heat production with characteristic values of slope and zero intercept for tectono‐ physiographic provinces. The intercept on the heat flow axis ,Q0, is inferred to represent heat flow from the mantle. The IHFC database contains 14,239 continental points. Only 955 have radioactivity data for reduced heat flow calculations. 0 100 km 200 300 Th/U = 3.27±1.86 n = 150 Th/U = 3.27±1.86 n = 150 Total gamma‐ray intensity U, Th, K Potassium gamma‐ray Uranium gamma‐ray Thorium gamma‐ray “It is not so much the things I don’t know that cause me problems as the things I know that are not so.” Paraphrased after Mark Twain A fundamental assumption is that the temperature gradient is vertical and heat flow calculated from the gradient is vertical heat flow. Topography and complex structure with thermal conductivity contrasts or transient sources and sinks such as water flow invalidate this assumption. AAPG Geothermal Map of North America, Blackwell and Richards, 2004 Climate change & unknown transients The effect of a 2 degree shift in mean annual surface is shown for three different periods: Red curves: one year Green curves: ten years Blue curves: 100 years Three temperature vs. depth observations at a site in North Dakota during the past 23 years show continual warming of the ground surface. The surface energy flux required to heat the subsurface as observed is approximately 40 mW m‐2. The critical question is what is the source of the surface energy flux. The site is remote, the surface is flat, and land use has not changed. Initial Conditions q = 60 mW m‐2, λ = 2.5 W m‐1 K‐1, Γ = 24 mK m‐1 Temperature disturbance due to clearing forest 1000 ybp. 2 °C difference from measurements in forest and cleared areas in northern Minnesota, USA. Temperature disturbance due to clearing forest 1000 ybp. 2 °C difference from measurements in forest and cleared areas in northern Minnesota, USA. 1000 y after forest cleared. Open space is 2 °C warmer. Vertical lines simulate 2 km boreholes for T‐z measurements. Temperature disturbance due to clearing forest 1000 ybp superimposed on preexisting temperature profile. Surface temperature (MJJA) record based on pollen analyses in upland lakes in southern Manitoba, CA (J. C. Ritchie, 1983) Temperature vs. depth profiles based on diffusion of surface temperature into subsurface at 500 y intervals during past 12,500 y. Temperature vs. depth profiles based on diffusion of surface temperature into subsurface during past 12,500 y. Surface temperature based on pollen analysis from upland lakes in southern Manitoba. The effect of postglacial warming on the thermal gradient is subtle. 40 35 30 Deg C 25 20 Steady-state T-z 3 Deg T-z 5 Deg T-z 10 Deg T-z 15 Deg T-z 15 10 5 0 0 400 800 Depth (m) 1200 1600 •LSQ analyses of 200 m segments of a temperature log from the Williston basin all appear linear. •The geothermal gradient increases systematically with depth. •The surface intercept on the temperature scale decreases systematically with depth. •Does the change in surface temperature show the amount of warming that has occurred at the surface? •If so, the minimum warming has been at least 12 K. WDG3 The normal temperature vs. depth profile in a thick clastic sedimentary section has a convex curvature due to the increase in thermal conductivity with depth caused by compaction which reduces porosity. Porosity varies with depth as Φ=Φ0e-cz c is a constant and z is depth Thermal conductivity, K, varies with porosity and as a function of the conductivity of the solid rock and water as K = Kr1‐ΦKwΦ If heat flow is constant, the temperature at depth is calculated as T = T0 + ΣΓizi where Γi = q/Ki Diapositiva 62 WDG3 The normal temperature vs. depth profile in a thick clastic sedimentary section is show by the blue curve. Convex curvature in the curve is due to the increase in thermal conductivity (green curve) with depth caused by compaction which reduces porosisty (red curve) Will Gosnold; 05/02/2008 Post glacial warming effect on the temperature gradient for 3 deg and 15 deg warming displayed as a percentage . Any temperature gradient taken from a depth less than 1500 m will yield a low estimate of heat flow. WDG4 Three equilibrium T‐z profiles that penetrate the thick shale section in the Williston Basin show curvature suggesting either a thermal conductivity decrease with depth or a heat flow increase with depth. Interestingly, calculations of the theoretical T‐z profiles for normal compaction, red curve, and for the effect of 15 degrees of warming since the Pleistocene combine to produce a T‐z profile (Glacx) that matches the observed profiles. Diapositiva 64 WDG4 All three equilibrium T-z profiles that penetrate the thick shale section in the Williston Basin show curvature suggesting either a thermal conductivity decrease with depth or a heat flow increase with depth. Interestingly, calculations of the theoretical T-z profiles for normal compaction and for the effect of 15 degrees of warming since the Pleistocene combine to produce a T-z profile that matches the observed profiles. Will Gosnold; 05/02/2008 46 TW or 31 TW? At issue is the accuracy of models of heat flow vs. age. q = 510 t ‐.5 q = 480 t ‐.5 q = 473 t ‐.5 Heat flow in conductive environments is predictable and the heat flow map of North America demonstrates this predictability on the continents and in the ocean basins. High heat flow: young crust and recent tectonics Low heat flow: old thermally stable crust Variation in conductive heat flow within heat flow provinces on the continents is due to variation in radioactive heat production. q = q0+ AD Heat flow within ocean basins correlates with age. Side‐by‐side comparison of marine and continental heat flow suggests the presence of non‐conductive and transient signals in marine environments and in young tectonic environments. Bullard’s Law "Never take a second heat flow measurement within 20 km of the original for fear that it differ from the first by two orders of magnitude." 2‐D finite‐difference heat flow model • Temperature profile for the ridge crest and intraplate from D.H. Green • Temperature at base of intraplate lithosphere 1370 C • Thermal conductivity profile from Hofmeister (1999) and van den Berg, Yuen, and Steinbach (2001) • Half‐spreading velocities of 1, 2.5, 5,&10 cm y‐1 Surface Temperature 0 C T = 1370 T = 1410 Base of Lithosphere = 1370 C Surface Temperature 0 C T = 1370 T = 1410 Base of Lithosphere = 1370 C Temperature and heat flow gradient from ridge crest to 19 Ma (474 km @ 2.5 cm y‐1) 0 1400 1300 -20,000 1200 1100 1000 Depth (m) -40,000 900 800 -60,000 700 600 -80,000 500 400 -100,000 300 200 -120,000 100 0 40000 80000 120000 Age (y/100) 160000 0 46 or 31 TW Summary • The amount of data available from the IHFC database will be increased this year • Use of the database is the responsibility of the user – there are many uncorrected noise signals • U, Th, K contribute as much as half of surface heat flow on continents • Surface heat flux is 46 TW ± 2 TW • Watch for revisions to heat flow in northern hemisphere that could increase total heat flux