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Non-volcanic CO 2 Degassing from the Solid Earth

Non-volcanic CO 2 Degassing from the Solid Earth Kerrick, D.M. (2001) Rev. Geophys ., 39 , 565-585. Volcanic Non-volcanic CO 2 emitted from crater everything else or flank of volcano some/most CO 2 emitted includes CO 2 emission

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Non-volcanic CO 2 Degassing from the Solid Earth

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  1. Non-volcanic CO2 Degassing from the Solid Earth Kerrick, D.M. (2001) Rev. Geophys., 39, 565-585 VolcanicNon-volcanic CO2 emitted from crater everything else or flank of volcano some/most CO2 emitted includes CO2 emission derived from metamorphic from buried magma decarbonation reactions CO2 consumed by silicate weathering ~7·1012 mol/y If volcanic discharge ~2-3·1012 mol/y, then non-volcanic discharge ~4-5·1012 mol/y 1 Gt CO2 = 22.7·1012 mol CO2

  2. Carbon in the Crust 1. carbonate minerals: calcite CaCO3 dolomite/ankerite Ca(Mg,Fe)(CO3)2 siderite (Fe,Mg)CO3 host rocks: shales (siderite and/or ankerite) marls = shale + carbonate mixture (calcite + ankerite) siliceous carbonates (calcite + dolomite + quartz) 2. graphite (in most sedimentary rocks) 3. reduced organic matter (from petroleum to coal)

  3. CO2 Release Mechanisms: 1. Mineral-fluid Reactions carbonate minerals: muscovite + siderite + ankerite + quartz = biotite + plagioclase + CO2 muscovite + ankerite + quartz = biotite + calcite + plagioclase + CO2 calcite + quartz = wollastonite + CO2 2. graphite: 2C + 2H2O = CO2 + CH4 3. reduced organic matter: rom = CO2, CH4, CO, ??

  4. CO2 Release Mechanisms: 2. Infiltration-driven Reactions calcite + quartz = wollastonite + CO2 thermally-drive reaction produces pure CO2 fluid most metamorphic fluids have CO2/(CO2+H2O) = 0.05-0.3 decarbonation reactions driven by infiltration of rock by H2O-rich, CO2-poor fluids same for formation of CO2 + CH4 from graphite CO2 released from carbonate minerals and graphite into a flow system that carries CO2 towards the surface

  5. Estimates of Non-volcanic CO2 Fluxes and Discharges Modern a. active geothermal systems b. active metamorphism in collisional mountain belts 2. Ancient a. regional extension and contact metamorphism b. metamorphism in a large igneous province c. metamorphism in a collisional mountain belt flux = J(CO2), (mol CO2)/(unit area·unit time) discharge = D(CO2), (mol CO2)/(unit time) over area of interest

  6. Active Geothermal System: Taupo Volcanic Zone, N.Z. Kerrick, D.M. et al. (1995) Chem. Geol., 121, 285-293

  7. Active Geothermal System: Taupo Volcanic Zone, N.Z. Concept Geothermal fluids in TVZ contain CO2 (likely of metamorphic origin) 2. Elevated heat flow indicates advective heat transport; assume advective transport >> transport by conduction 3. Assume CO2 transported with heat and fluid; CO2 degasses within a few km of the surface; CO2 flux  to heat flux.

  8. Active Geothermal System: Taupo Volcanic Zone, N.Z Calculation 1. DH = ∫cpdT integrated between measured T of the reservoir fluid at depth and T at the surface. 2. J(fluid) = Q/DH, where Q is surface heat flow. 3. J(CO2) = J(fluid)·[CO2], where [CO2] is measured. 4. Perimeter of geothermal system defined by the 20--m resistivity contour  area of discharge, A. 5. D(CO2) = J(CO2)·A. 6. D(CO2) = 0.05-1.1·109 mol/y for ten systems studied.

  9. Active Geothermal System: Taupo Volcanic Zone, N.Z calculation (continued) 7. D(CO2) = 4·109 mol/y for all ten systems studied. 8. D(CO2) for TVZ ≈ 1010 mol/y for all 20 active systems. 9. Assume D(CO2) for circum-Pacific basin ≈ 10-100 TVZ: D(CO2) ≈ 1011 -1012 mol/y for entire basin.

  10. Active Regional Metamorphism: the Himalayas Becker, J. A. et al. (2008) EPSL265, 616-629

  11. Active Regional Metamorphism: the Himalayas concept Hot springs deliver CO2-bearing fluids to surface (likely of metamorphic origin)

  12. Active Regional Metamorphism: the Himalayas concept (continued) 2. CO2 separates from metamorphic fluids during ascent; CO2 dissolves in large volume of groundwater; CO2 degasses from groundwater at or near surface.

  13. Active Regional Metamorphism: the Himalayas calculation Measure [DIC] and [Cl] in spring waters. Estimate amount of degassed CO2 from d13C(DIC): >95%. 3. Calculate average [DIC]/[Cl] = 0.11±0.02 to 0.24±0.09, depending on season. 4. Measure D(Cl) of river discharge: (1.0±0.02)·109 mol/y. 5. Convert to D(DIC) of river discharge: (1.6±0.5)·108 mol/y. 6. Correct for CO2 degassing: D(CO2) ≈ (5.4)·109 mol/y.

  14. Active Regional Metamorphism: the Himalayas calculation (continued) 7. Estimate area of watershed: 4800 km2. 8. Estimate area of Himalayas beneath which active metamorphism occurs: 7.5·105 km2. 9. D(CO2) from metamorphism in the Himalayas: 0.8·1012 mol/y, ≈13% of modern CO2 degassing from the solid Earth. Estimated CO2 drawndown from silicate weathering in the Himalayas ≈ 0.3·1012 mol/y.

  15. Ancient Regional Contact Metamorphism: North American Cordillera Nesbitt, B.E. et al. (1995) Geology23, 99-101 concept Eocene (40-55 Ma) extension causes plutonism/regional contact metamorphism. 2. Meteoric water penetrates to ~10 km. 3. Infiltrating fluid drives decarbonation reactions in rocks with silicates and carbonates 4. Flow system returns CO2 to surface; CO2 separates from aqueous liquid phase at low T.

  16. Ancient Regional Contact Metamorphism: North American Cordillera calculation Regional 2D thermal-hydrologic model of fluid flow: model basin 50 km long, 10 km deep; uniform k = 10-16 to 10-15 m2; basal heat flux 30-90 mW/m2; surface T = 20°C; 1000 m topographic relief. domain-average J(fluid) = 10-3 m3/m2·y (± factor of 10). 2. CO2 content of discharged fluid the same as in fluid inclusions in quartz veins believed to be fluid escape channels: CO2/(CO2 + H2O) = 0.1.

  17. Ancient Regional Contact Metamorphism: North American Cordillera 3. J(CO2) = 3.8·106 mol/km2·y. 4. Area affected ≈ (0.4-2)·106 km2. 5. D(CO2) = (1.5-7.6)·1012 mol/y.

  18. Intrusion of Large Igneous Province: Karoo LIP, S. A. Svensen, H. et al. (2007) EPSL256, 554-566 concept Intrusion of Early Jurassic (182.5±0.4 Ma) mafic sills in Karoo Basin.

  19. Intrusion of Large Igneous Province: Karoo LIP, S. A. concept (continued) 2. Host sediments contain reduced organic matter. Contact metamorphism releases C as CH4 ± CO2 ± CO. 4. Gas reaches surface as hydrothermal eruptions through 1000s of breccia pipes.

  20. Intrusion of Large Igneous Province: Karoo LIP, S. A. calculation 1. Carbon loss calibrated from drill cores through 2 pipes. unmetamorphosed Prince Albert Fm. 0.5-4% TOC unmetamorphosed Whitehall Fm. 2-8% TOC

  21. Intrusion of Large Igneous Province: Karoo LIP, S. A. calculation (continued) 2. D(C)t = FC·A·h·r·S FC = wt. % C lost during metamorphism; A = horizontal area of contact metamorphic aureole; h = thickness of C-rich sediments; r = rock density; S = shape factor (1 for complete loss of C; 0.5 for linear vertical gradient in C loss). t = duration of C release. Whitehall Fm. Prince Albert Fm. h 70 m 70 m FC 4-5% 1.5-3.5% S 0.5 1

  22. Intrusion of Large Igneous Province: Karoo LIP, S. A. calculation (continued) 3. Over the study area (A = 650 km2): D(CO2)t = 3.66D(C)t = 14-24 Gt = (320-550)·1012 mol. Over the western Karoo Basin (A ≈ 50,000 km2): D(CO2)t = (2461-4230)·1012 mol. Extrapolation to entire Karoo Basin (A ≈ 390,000 km2): D(CO2)t = [(1.6-6.3)·105]·1012 mol. Likely t “a few 100,000 y.” For t = 300,000 y, D(CO2) = (0.5-2.1)·1012 mol/y.

  23. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas Kerrick, D.M. and Caldeira, K. (1998) Chem. Geol.145, 213-232 concept Mineral reactions during metamorphism release CO2; CO2 ascends to surface. 2. Ancient metamorphic belts preserve a record of the amount of CO2 lost from rocks. 3. Estimation of the amount, spatial extent, and duration of CO2 loss leads to estimates of J(CO2) and D(CO2).

  24. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas enormity of scale and complexity

  25. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas calculation Measure amount of CO2 lost from each abundant rock type. a. Compare CO2 content of reacted and unreacted rock in same small area (1-100 km2). b. Take average composition of common source rocks and estimate average amount of CO2 lost during metamorphism. average shale: 5 wt. % CO2 lost average marl and siliceous carbonate rock 10-15 wt. % CO2 lost

  26. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas calculation (continued) 2. Estimate area fraction of metamorphosed shale and carbonate rock: (consult experts = wild guess). Estimate depth extent of metamorphosed rock: 30-60 km (1x and 2x average thickness of crust).

  27. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas calculation (continued) 4. Estimate duration of mineral decarbonation reactions: a. Thermochronology: time above ~400°C ~10My.

  28. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas calculation (continued) 4. Estimate duration of mineral decarbonation reactions: b. Thermal models of regional metamorphism. Time spent near maximum temperature several 10s My.

  29. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas calculation (continued) 5. Western Central-eastern Himalaya Himalaya Area (km2) 2·105 ~ 105 % shale 5-10 10-20 % metacarbonates 15-25 5 D(CO2) (mol/y) (0.2-0.8)·1012 (0.2-0.8)·1012 6. For whole Himalayas:D(CO2) ≈ (0.3-2)·1012 mol/y

  30. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas Uncertainties in Flux Calculation Amount CO2 lost by each source rock type. 2. Percent of each source rock type. 3. Area and depth of rocks affected by reaction. 4. Duration (t) of reaction << 10 My? a. Hydrologic model of coupled fluid flow and reaction implies t = 103 - 104 y. b. Radiometric age of metamorphic rock that records metamorphism at 7.2 kbar ~ 27 km is 3.3±0.1 Ma.

  31. Ancient Metamorphism in a Collisional Mountain Belt: Eocene-Oligocene Regional Metamorphism in the Himalayas Uncertainties in Flux Calculation (continued) 5. Loss of CO2 between site of reaction and surface by carbonation reactions.

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