1. Volatile fluxes at arc volcanoes: comparing different techniques and evaluating mass balance A. Shaw, D. Hilton, T. Fischer, E. Hauri Arenal Volcano

2. The MARGINS Subduction Factory: 1)How do forcing functions regulate production of magma and fluid from the Subduction Factory? 2)How does the volatile cycle (H 2 O and CO 2 ) impact chemical, physical and biological processes from trench to deep mantle? 3)What is the mass balance of chemical species and material across the Subduction Factory?

3. Outline 1)Different methods for measuring gas fluxes and evaluating mass balance at arcs 2)Comparing fluxes from IBM and Central America 3)How well do PT models predict fluid behavior? 4)Summarize the strengths of different methods, their limitations and future directions

4. Volatile Recycling: Subduction zones cycle material between the Earth’s mantle and its exospheric reservoirs Major Volatiles: CO 2, H 2 O, sulfur species (SO 2 & H 2 S) Trace Volatiles : N 2, noble gases (He, Ne, Ar), H 2, CH 4, …

5. Volatile Recycling: Subduction zones cycle material between the Earth’s mantle and its exospheric reservoirs Major Volatiles: CO 2, H 2 O, sulfur species (SO 2 & H 2 S) Trace Volatiles : N 2, noble gases (He, Ne, Ar), H 2, CH 4, … 5

6. Volcanic output flux estimates: 1)Assumed 3 He flux combined with direct measurements of a volcanic gas (x) relative to 3 He 2)Remote sensing techniques 3)Melt inclusion studies combined with magma production rates

7. Volcanic Sampling 1) Fumaroles 2) geothermal wells 3) water springs 4) bubbling hot springs and mudpots Momotombo volcano

8. Volcanic Sampling 1) Fumaroles 2) geothermal wells 3) water springs 4) bubbling hot springs and mudpots

9. 100 0 400 200 300 500 Site 1039 Costa Rica

10. Sano and Marty (1995); Sano and Williams (1996) Source of gases: three component end-member mixing: L : marine carbonate/limestone (δ 13 C = 0‰, C/ 3 He = 10 13 ) M : mantle (δ 13 C = -6.5‰, C/ 3 He = 2×10 9 ) S : organic-rich sediment (δ 13 C = -30‰, C/ 3 He = 10 13 ) Mass balance: 1) ( 13 C/ 12 C) OBS = M( 13 C/ 12 C) M + L( 13 C/ 12 C) L + S( 13 C/ 12 C) S 2) 1/( 12 C/ 3 He) OBS = M/( 12 C/ 3 He) M + L/( 12 C/ 3 He) L + S/( 12 C/ 3 He) S 3) M+L+S = 1

11. crustal additions

12. 3)A higher slab component was observed in Nicaragua Source of carbon: 1)Dominant source of CO 2 is from a limestone/marine carbonate source (83-86%) 2)L/S of input = 10.5 was essentially indistinguishable from the output (9-6-11.1) – see Hilton’s poster for revised models

13. CO 2 flux estimates: 1)Average CO 2 / 3 He for Central America = 2.3 × 10 10 mol/yr combined with an assumed 3 He flux ~ 3 mol/yr (based on global subaerial flux scaled to arc length): CO 2 flux : 7.1 × 10 10 mol/yr (4% of global volcanic arc flux) 2)Mass balance: this represents 23-28% of the CO 2 input to the arc, using estimates from Li and Bebout, 2005 – a significant fraction is cycled to the deep mantle or is lost in the forearc region – limited by fluid availability? 3)Sediment-derived N flux : 28 × 10 8 mol/yr (Elkins et al., 2006) – completely recycled through the arc

14. Remote sensing: Measure absorption of UV light by SO 2, corresponding to a SO 2 concentration. Wind speed and plume geometry are considered to derive an SO 2 flux. SO 2 flux * x i /SO 2 = flux of x i, the gas of interest Limitation: you need a fairly large flux of gas! 1)Satellite-based measurements 2)COSPEC: correlation spectrometer or miniaturized versions such as the mini-DOAS or FlySPEC Masaya volcano, Nicaragua

15. Ozone Mapping Instrument (OMI) on NASA’s Aura satellite is used to map and quantify sulfur dioxide gas (SO 2 ) emitted by volcanoes Satellite-based remote sensing: 10 000 tons SO 2 /day

16. Power Law Distribution of (SO 2 ) fluxes N = af -c (N= #volcanoes with flux  f) F = f 1 + f 2 + f 3 + …….+ f N {(c/(1- c))(N+1)(N/(N+1)) 1/c } SO 2 flux estimates for arc systems: Hilton et al., 2002 after Brantley & Koepenick (1995) F = 2.5 x 10 10 mol SO 2 /yr Mather et al., 2006 Compiled new flux data from Nicaragua with published data since 1997 4360 Mg/day or 2.5 ± 0.8 × 10 10 mol SO 2 /yr 12% of global volcanic SO 2 flux

17. Estimate primary volatile contents of melts and combine with magma production rates to derive fluxes Melt inclusion studies: 100  m

18. Analytical methods: 1)Pre-eruptive H, C, S, Fl and Cl contents are measured by SIMS 2)Major elements by electron microprobe (Fe-Mg exchange) 3)SEM imaging of inclusions (crystallization and size) 10  m

20. Izu-Bonin: evidence for slab-derived fluids addition of fluids MORB (ppm)

21. Fractional crystallization: Volatile concentrations are thought to increase with fractional crystallization due to their incompatibility Fractional crystallization

22. Volatile loss through degassing degassing

23. Vapor saturation curves: pressure of entrapment Melt inclusions from Nijima volcano were trapped at the deepest depth (15km), based on solubility based vapor saturation curves

24. Degassing style: 1)Open style degassing: exsolved vapor is lost 2)Closed system: vapor re-equilibrates with melt

25. Source estimates: 1200 ppm 3831 ppm 1)Highest concentration sample: 1200 ppm CO 2 2)Extrapolating back for 5% vapor exsolution: 3831 ppm CO 2 after Newman and Lowerstern, 2002

26. Volatile budgets for CO 2 : Izu-Bonin output calculated assuming a magma production rate of 60 km 3 /Ma/km along with pre-eruptive CO 2 contents and a trench length of 1050 km Methodoutput (10 9 mol/yr) % of sed input % of total input Izu-Boninhighest content of MI: 1200 ppm 4.812.55 Modeled pre- degassing value: 3831 ppm 15.439.915 Central AmericaRemote sensing584123 He-C relationships 715028

27. P-T controls on the volcanic output Phase equilibria predicts little CO 2 recycling at cold subduction zones high T low T H 2 O (wt %) CO 2 (wt %) Kerrick and Connolly, 2001

28. Subduction was modeled by stepwise variation of pressure and temperature along a path prescribed by a selected thermal model for a given arc Revised modeling considered the effect of fluid flow (pervasive vs. channelized) (Gorman et al., 2006) Thermodynamic modeling of decarbonation

29. Modeled output fluxes of CO 2 match fluxes derived by direct gas measurements (Shaw et al, 2003) and remote sensing (Hilton et al, 2002) Output fluxes for the Izu-Bonin are also in very good agreement with melt inclusion derived estimates – less CO 2 recycling A significant amount of CO 2 is released in the fore-arc (Gorman et al., 2006) Pervasive infiltration model

30. CO 2 recycling: 1)We find relatively low CO 2 recycling efficiencies at the Izu- Bonin (5-15%) and Central America (23-28%) arc systems. 2) Implication is that either a significant fraction of C is being supplied to the deep mantle, or that CO 2 loss in the fore-arc is substantial – as models suggest. 3)Decarbonation is indeed more limited in cooler regimes such as the Izu-Bonin arc as compared to Costa Rica.

31. Limitations and future directions for volatile fluxes: CO 2 : focus on the fore-arc (and back-arc) flux – melt inclusion from the volcanic arc for Central America SO 2 : measured using various techniques - outputs can be quantified, but inputs are poorly constrained H 2 O: melt inclusions are the only method for quantifying fluxes, due to additional water meteoric waters fluxed through the volcanic system – H isotopes can be used to identify source N 2 : direct gas measurements combined with isotopic analyses – ion probe techniques for N in glasses are very difficult Cl: both melt inclusions and direct gas measurements – what can the isotopes tell us? Source vs. degassing?

32. Acknowledgements: Margins-NSF, Guillermo Alvarado, Carlos Ramirez (ICE-UCR), Willi Strauch (INETER) Kohei Kazahaya, Masaaki Takahashi, Noritoshi Morikawa (GSJ), Aya Shimizu (University of Tokyo)