Volatile fluxes at arc volcanoes:
This presentation is the property of its rightful owner.
Sponsored Links
1 / 32

Volatile fluxes at arc volcanoes: comparing different techniques and evaluating mass balance PowerPoint PPT Presentation


  • 43 Views
  • Uploaded on
  • Presentation posted in: General

Volatile fluxes at arc volcanoes: comparing different techniques and evaluating mass balance A. Shaw, D. Hilton, T. Fischer, E. Hauri. Arenal Volcano. The MARGINS Subduction Factory: How do forcing functions regulate production of magma and fluid from the Subduction Factory?

Download Presentation

Volatile fluxes at arc volcanoes: comparing different techniques and evaluating mass balance

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

Volatile fluxes at arc volcanoes: comparing different techniques and evaluating mass balance

A. Shaw, D. Hilton, T. Fischer, E. Hauri

Arenal Volcano


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

  • The MARGINS Subduction Factory:

  • How do forcing functions regulate production of magma and fluid from the Subduction Factory?

  • How does the volatile cycle (H2O and CO2) impact chemical, physical and biological processes from trench to deep mantle?

  • What is the mass balance of chemical species and material across the Subduction Factory?


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

  • Outline

  • Different methods for measuring gas fluxes and evaluating mass balance at arcs

  • Comparing fluxes from IBM and Central America

  • How well do PT models predict fluid behavior?

  • Summarize the strengths of different methods, their limitations and future directions


Volatile recycling

Volatile Recycling:

Subduction zones cycle material between the Earth’s mantle and its exospheric reservoirs

Major Volatiles: CO2, H2O, sulfur species (SO2 & H2S)

Trace Volatiles : N2, noble gases (He, Ne, Ar), H2, CH4, …


Volatile recycling1

Volatile Recycling:

Subduction zones cycle material between the Earth’s mantle and its exospheric reservoirs

Major Volatiles: CO2, H2O, sulfur species (SO2 & H2S)

Trace Volatiles : N2, noble gases (He, Ne, Ar), H2, CH4, …

5


Volcanic output flux estimates

Volcanic output flux estimates:

  • Assumed 3He flux combined with direct measurements of a volcanic gas (x) relative to 3He

  • Remote sensing techniques

  • Melt inclusion studies combined with magma production rates


Volcanic sampling 1 fumaroles 2 geothermal wells 3 water springs 4 bubbling hot springs and mudpots

Volcanic Sampling1) Fumaroles2) geothermal wells3) water springs4) bubbling hot springs and mudpots

Momotombo volcano


Volcanic sampling 1 fumaroles 2 geothermal wells 3 water springs 4 bubbling hot springs and mudpots1

Volcanic Sampling1) Fumaroles2) geothermal wells3) water springs4) bubbling hot springs and mudpots


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

0

100

200

300

400

500

Site 1039Costa Rica


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

  • Source of gases: three component end-member mixing:

  • L : marine carbonate/limestone (δ13C= 0‰, C/3He = 1013 )

  • M : mantle (δ13C = -6.5‰, C/3He = 2×109)

  • S : organic-rich sediment(δ13C = -30‰, C/3He = 1013)

  • Mass balance:

  • 1) (13C/12C)OBS = M(13C/12C)M + L(13C/12C)L + S(13C/12C)S

  • 2) 1/(12C/3He)OBS = M/(12C/3He)M + L/(12C/3He)L + S/(12C/3He)S

  • M+L+S = 1

Sano and Marty (1995); Sano and Williams (1996)


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

crustal

additions


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

  • Source of carbon:

  • Dominant source of CO2 is from a limestone/marine carbonate source (83-86%)

  • L/S of input = 10.5 was essentially indistinguishable from the output (9-6-11.1) – see Hilton’s poster for revised models

  • A higher slab component was observed in Nicaragua


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

  • CO2 flux estimates:

  • Average CO2/3He for Central America = 2.3 × 1010 mol/yr combined with an assumed 3He flux ~ 3 mol/yr (based on global subaerial flux scaled to arc length): CO2 flux : 7.1 × 1010 mol/yr (4% of global volcanic arc flux)

  • Mass balance: this represents 23-28% of the CO2 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?

  • Sediment-derived N flux : 28 × 108 mol/yr (Elkins et al., 2006) – completely recycled through the arc


Remote sensing

Remote sensing:

  • Satellite-based measurements

  • COSPEC: correlation spectrometer or miniaturized versions such as the mini-DOAS or FlySPEC

Masaya volcano, Nicaragua

Measure absorption of UV light by SO2, corresponding to a SO2 concentration. Wind speed and plume geometry are considered to derive an SO2 flux.

SO2 flux * xi/SO2 = flux of xi, the gas of interest

Limitation: you need a fairly large flux of gas!


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

Satellite-based remote sensing:

10 000 tons SO2/day

Ozone Mapping Instrument (OMI) on NASA’s Aura satellite is used to map and quantify sulfur dioxide gas (SO2) emitted by volcanoes


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

SO2 flux estimates for arc systems:

Power Law Distribution of (SO2) fluxes

N = af-c (N= #volcanoes with flux ³ f)

F = f1 + f2 + f3 + …….+ fN{(c/(1-c))(N+1)(N/(N+1))1/c}

F = 2.5 x 1010 mol SO2/yr

Hilton et al., 2002 after Brantley & Koepenick (1995)

Mather et al., 2006

Compiled new flux data from Nicaragua with published data since 1997

4360 Mg/day or 2.5 ± 0.8 × 1010 mol SO2/yr 12% of global volcanic SO2 flux


Melt inclusion studies

Melt inclusion studies:

Estimate primary volatile contents of melts and combine with magma production rates to derive fluxes

100mm


Analytical methods

Analytical methods:

  • Pre-eruptive H, C, S, Fl and Cl contents are measured by SIMS

  • Major elements by electron microprobe (Fe-Mg exchange)

  • SEM imaging of inclusions (crystallization and size)

10mm


Izu bonin evidence for slab derived fluids

Izu-Bonin: evidence for slab-derived fluids

addition

of fluids

MORB

(ppm)


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

Fractional crystallization:

Volatile concentrations are thought to increase with fractional crystallization due to their incompatibility

Fractional

crystallization


Volatile loss through degassing

Volatile loss through degassing

degassing


Vapor saturation curves pressure of entrapment

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


Degassing style

Degassing style:

  • Open style degassing: exsolved vapor is lost

  • Closed system: vapor re-equilibrates with melt


Source estimates

Source estimates:

  • Highest concentration sample: 1200 ppm CO2

  • Extrapolating back for 5% vapor exsolution: 3831 ppm CO2

3831 ppm

1200 ppm

after Newman and Lowerstern, 2002


Volatile budgets for co 2

Volatile budgets for CO2:

Izu-Bonin output calculated assuming a magma production rate of 60 km3/Ma/km along with pre-eruptive CO2 contents and a trench length of 1050 km


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

P-T controls on the volcanic output

Phase equilibria predicts little CO2 recycling at cold subduction zones

low T

high T

H2O (wt %)

low T

high T

CO2(wt %)

Kerrick and Connolly, 2001


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

Thermodynamic modeling of decarbonation

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)


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

Pervasive infiltration model

(Gorman et al., 2006)

Modeled output fluxes of CO2 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 CO2 recycling

A significant amount of CO2 is released in the fore-arc


Co 2 recycling

CO2 recycling:

  • We find relatively low CO2 recycling efficiencies at the Izu-Bonin (5-15%) and Central America (23-28%) arc systems.

  • Implication is that either a significant fraction of C is being supplied to the deep mantle, or that CO2 loss in the fore-arc is substantial – as models suggest.

  • Decarbonation is indeed more limited in cooler regimes such as the Izu-Bonin arc as compared to Costa Rica.


Limitations and future directions for volatile fluxes

Limitations and future directions for volatile fluxes:

CO2: focus on the fore-arc (and back-arc) flux – melt inclusion from the volcanic arc for Central America

SO2: measured using various techniques - outputs can be quantified, but inputs are poorly constrained

H2O: 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

N2: 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?


Volatile fluxes at arc volcanoes comparing different techniques and evaluating mass balance

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


  • Login