Regional variations in volatile composition: Isotopic evidence for carbonate recycling in the Central American volcanic arc

Snyder, G. T.; Poreda, Robert J.; Hunt, Andrew G.; Fehn, Udo

doi:10.1029/2001gc000163

Cited by 78 publications

(76 citation statements)

References 84 publications

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“…Fischer et al (2002) and Zimmer et al (2004) showed that the slab-derived contribution of N 2 to arc magmas in most of Costa Rica is <50% of the total, reflecting offscraping of N-rich hemipelagic sediments beneath Costa Rica. Along-arc variations in N 2 and CO 2 sources have also been observed by Snyder et al (2001) and Snyder et al (2003) in Central America and by Clor et al (2005) and Jaffe et al (2004) in the Sangihe arc, Indonesia and have been explained by crustal contributions, variations in subducted sediment composition, forearc devolatilization, and offscraping of oceanic sediments prior to subduction.…”

Section: Along-arc Variationsmentioning

confidence: 91%

“…To date, gas discharges have been examined for helium, carbon, and nitrogen in Guatemala and Costa Rica Hilton et al, 2002;Shaw et al, 2003;Zimmer et al, 2004), and for helium and carbon in Nicaragua (Shaw et al, 2003) and along the entire length of the CAVA (Snyder et al, 2001). Snyder et al (2003) investigated the sources of nitrogen and methane in geothermal fluids along the Central American Arc.…”

Section: Introductionmentioning

confidence: 99%

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Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Elkins

Fischer

Hilton

et al. 2006

Geochimica et Cosmochimica Acta

114

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We report new chemical and isotopic data from 26 volcanic and geothermal gases, vapor condensates, and thermal water samples, collected along the Nicaraguan volcanic front. The samples were analyzed for chemical abundances and stable isotope compositions, with a focus on nitrogen abundances and isotope ratios. These data are used to evaluate samples for volatile contributions from magma, air, air-saturated water, and the crust. Samples devoid of crustal contamination (based upon He isotope composition) but slightly contaminated by air or air-saturated water are corrected using N 2 /Ar ratios in order to obtain primary magmatic values, composed of contributions from upper mantle and subducted hemipelagic sediment on the down-going plate. Using a mantle endmember with d 15 N = À5& and N 2 /He = 100 and a subducted sediment component with d 15 N = +7& and N 2 /He = 10,500, the average sediment contribution to Nicaraguan volcanic and geothermal gases was determined to be 71%. Most of the gases were dominated by sediment-derived nitrogen, but gas from Volcán Mombacho, the southernmost sampling location, had a mantle signature (46% from subducted sediment, or 54% from the mantle) and an affinity with mantle-dominated gases discharging from Costa Rica localities to the south. High CO 2 /N 2 exc. ratios (N 2 exc. is the N 2 abundance corrected for contributions from air) in the south are similar to those in Costa Rica, and reflect the predominant mantle wedge input, whereas low ratios in the north indicate contribution by altered oceanic crust and/or preferential release of nitrogen over carbon from the subducting slab. Sediment-derived nitrogen fluxes at the Nicaraguan volcanic front, estimated by three methods, are 7.8 · 10 8 mol N/a from 3 He flux, 6.9 · 10 8 mol/a from SO 2 flux, and 2.1 · 10 8 and 1.3 · 10 9 mol/a from CO 2 fluxes calculated from 3 He and SO 2 , respectively. These flux results are higher than previous estimates for Central America, reflecting the high sediment-derived volatile contribution and the high nitrogen content of geothermal and volcanic gases in Nicaragua. The fluxes are also similar to but higher than estimated hemipelagic nitrogen inputs at the trench, suggesting addition of N from altered oceanic basement is needed to satisfy these flux estimates. The similarity of the calculated input of N via the trench to our calculated outputs suggests that little or none of the subducted nitrogen is being recycled into the deeper mantle, and that it is, instead, returned to the surface via arc volcanism.

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Section: Along-arc Variationsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Elkins

Fischer

Hilton

et al. 2006

Geochimica et Cosmochimica Acta

114

View full text Add to dashboard Cite

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“…It has been argued that geothermal well sam- ples are the most pristine samples since they originate from deep reservoirs (1^2 km depth) and are less prone to near-surface boiling and degassing [14]. To test this hypothesis we sampled at two di¡erent geothermal well sites on the £anks of active volcanoes^Momotombo and Miravalleŝ and compared the results to other sampling media (fumaroles in Momotombo's crater and bubbling hot spring gas on Miravalles' £ank).…”

Section: Integrity Of Resultsmentioning

confidence: 99%

“…A clear conclusion is that all water spring samples show evidence of crustal contamination : low 3 He/ 4 He values, low X values, extreme N 13 C values (313.4 to 31x) and generally high CO 2 / 3 He ratios. Such samples are thus considered highly susceptible to near-surface fractionating processes, which have modi¢ed C isotopes to extreme values (see [14] for further details).…”

Section: Integrity Of Resultsmentioning

confidence: 99%

“…This region has been the focus of numerous geochemical studies (e.g. [1,6,9,13,14]) since there are striking changes in subduction forcing param-eters (e.g. faulting style of incoming plate, slab dip, crustal thickness) whose in£uence can be assessed at a relatively ¢ne scale given the narrow spacing of volcanoes (V25 km) compared with that found in other arc settings (40^70 km) [1].…”

Section: Geologic Setting and Backgroundmentioning

confidence: 99%

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Contrasting He–C relationships in Nicaragua and Costa Rica: insights into C cycling through subduction zones

Shaw

Hilton

Fischer

et al. 2003

Earth and Planetary Science Letters

166

160

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We report 3 He/ 4 He ratios, relative He, Ne, and CO 2 abundances as well as N 13 C values for volatiles from the volcanic output along the Costa Rica and Nicaragua segments of the Central American arc utilising fumaroles, geothermal wells, water springs and bubbling hot springs. CO 2 / 3 He ratios are relatively constant throughout Costa Rica (av. 2.1U10 10 ) and Nicaragua (av. 2.5U10 10 ) and similar to arcs worldwide (V1.5U10 10 ). N 13 C values range from 36.8x (MORB-like) to 30.1x (similar to marine carbonate (0x)). 3 He/ 4 He ratios are essentially MORBlike (8 þ 1 R A ) with some samples showing evidence of crustal He additions^water spring samples are particularly susceptible to modification. The He^CO 2 relationships are consistent with an enhanced input of slab-derived C to magma sources in Nicaragua ((L+S)/M = 16; where L, M and S represent the fraction of CO 2 derived from limestone and/or marine carbonate (L), the mantle (M) and sedimentary organic C (S) sources) relative to Costa Rica ((L+S)/ M = 10). This is consistent with prior studies showing a higher sedimentary flux to the arc volcanics in Nicaragua (as traced by Ba/La, 10 Be and La/Yb). Possible explanations include: (1) offscraping of the uppermost sediments in the Costa Rica forearc, and (2) a cooler thermal regime in the Nicaragua subduction zone, preserving a higher proportion of melt-inducing fluids to subarc depths, leading to a higher degree of sediment transfer to the subarc mantle. The absolute flux of CO 2 from the Central American arc as determined by correlation spectrometry methods (5.8U10 10 mol/yr) and CO 2 / 3 He ratios (7.1U10 10 mol/yr) represents approximately 14^18% of the amount of CO 2 input at the trench from the various slab contributors (carbonate sediments, organic C, and altered oceanic crust). Although the absolute flux is comparable to other arcs, the efficiency of CO 2 recycling through the Central American arc is surprisingly low (14^18% vs. a global average of V50%). This may be attributed to either significant C loss in the forearc region, or incomplete decarbonation of carbonate sediments at subarc depths. The implication of the latter case is that a large fraction of C (up to 86%) may be transferred to the deep mantle (depths beyond the source of arc magmas). ß

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Rheology of magnesite

et al. 2014

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We deformed two natural magnesite aggregates (grain sizes of 1 versus 100 μm) over a wide range of temperatures (400-1000°C) and strain rates (10 À7 -10 À4 /s) in order to determine the deformation mechanisms of magnesite and their respective flow laws. Experiments using fine-grained magnesite were performed in a Heard gas confining medium rock deformation apparatus at a constant effective pressure (= confining pressure À CO 2 pressure) of 300 MPa. Experiments using coarse-grained magnesite were performed in a Griggs piston-cylinder rock deformation apparatus at a constant effective pressure of 900 MPa. At low temperatures (T < 600°C, strain rate = 10 À5 /s) both magnesite aggregates deform by crystal plastic mechanisms predominated by dislocation glide. At higher temperatures the coarse-grained magnesite deforms by dislocation creep and the fine-grained magnesite deforms by diffusion creep. The strain rate and temperature dependence of the strength of magnesite deforming by low-temperature plasticity, dislocation creep, and diffusion creep can be described by power law flow laws with stress exponents (n) of 19.7, 3.0, and 1.1 and activation enthalpies of 229, 410, and 209 kJ/mol, respectively. The strength of the low-temperature plasticity data can also be described using an exponential flow law with α = 0.022 MPa À1 with an activation enthalpy of 233 kJ/mol. Extrapolation of the flow laws to natural conditions indicates that magnesite is generally stronger than calcite and dolomite assuming similar grain sizes. However, its strength is orders of magnitude lower than olivine at all conditions in the Earth's mantle and may promote deep-focus earthquakes through ductile instabilities.

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Regional variations in volatile composition: Isotopic evidence for carbonate recycling in the Central American volcanic arc

Cited by 78 publications

References 84 publications

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Contrasting He–C relationships in Nicaragua and Costa Rica: insights into C cycling through subduction zones

Rheology of magnesite

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