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Carbonate subduction

A possibly troubling feature of our models is that we implicitly predict a secular trend in the isotopic composition of carbonates. This would occur because the carbonate subducted would presumably have the isotopic composition of sea water, whereas CO2 currently outgassed at midocean ridges is isotopically lighter. One way to avoid this problem is to presume that carbonates and reduced carbon are subducted in the same proportions as they are produced. Because the mantle emits some reduced gases and subducts oxidized ferric iron (Lecuyer Ricard 1999), some reductant must be subducted lest the continents grow secularly more reduced. The natural candidate, perhaps the only viable candidate, is reduced carbon, which is notably refractory and already known to be subducted. This is a reasonable expectation, and it is consistent with what is known of arc volcanoes today (see above), but it is unmotivated by our model. [Pg.254]

Taking our conclusions at face value, there are two issues that need to be addressed. One issue is how our model breaks down at early times if carbonate subduction were inhibited by a hotter mantle. In our model the subduction of carbo-natized oceanic crust closes the mantle s CO2 cycle. Factors that inhibit carbonate subduction have the effect of stranding CO2 in surface reservoirs. Although the capacity of the permeable layer of oceanic basalt to store CO2 is large (c. 3 X 10 moles), it falls well short of the global... [Pg.254]

Oxidation of the surface by methane loss and carbon subduction... [Pg.295]

The subducted organic carbon that returns to the surface as CO2 is an oxygen source as is the deeply subducted organic carbon that was ultimately derived from igneous CO2 as oxygen source. The current organic carbon subduc-tion flux is (0.2-0.6) x 10 mol per year, 1 /5 of the total carbon subduction flux of (1-3) X 10 mol per year. [Pg.68]

The degassing of CO2 from primordial carbonates is not improbable. However, carbonates are very rare in meteorites. Hence this was probably not a dominant source of CO2 in the early earth and may have become dominant in the volcanic source due to carbonate subduction. [Pg.57]

Carbon flux by volcanic gas from island arc and by hydrothermal solution from island arc and back arc is estimated as 0.15 x 10 mol my, and (1-6) X 10 mol my, respectively (Shikazono 1995). These fluxes are smaller than subduction flux (3.7 x 10 mol my ). Therefore, it is considered that most carbon subducts to mantle. This subduction flux ((3—4) x 10 mol my ) seems larger than hydrothermal and volcanic gas flux from mid-oceanic ridge (d-2) X 10 mol my ). Therefore, it seems likely that the amoimt of carbrni in mantle reservoir increases with time and the large amounts of carbon stored in mantle may degass intermittently associated with superplume activity (Shikazono 1995). [Pg.159]

Sano and Williams (1996) calculated present-day volcanic carbon flux from subduction zones to be 3.1 x 10 mol/year based on He and C isotopes and C02/ He ratios of volcanic gases and fumaroles in circum-Pacific volcanic regions. Williams et al. (1992) and Brantley and Koepenich (1995) reported that the global CO2 flux by subaerial volcanoes is (0.5-2.0) x lO mol/m.y. and (2-3) x 10 mol/m.y. (maximum value), respectively. Le Guern (1982) has compiled several measurements from terrestrial individual volcanoes to derive a CO2 flux of ca. 2 x 10 mol/m.y. Le Cloarec and Marty (1991) and Marty and Jambon (1987) estimated a volcanic gas carbon flux of 3.3 X 10 mol/m.y. based on C/S ratio of volcanic gas and sulfur flux. Gerlach (1991) estimated about 1.8 x 10 mol/m.y. based on an extrapolation of measured flux. Thus, from previous estimates it is considered that the volcanic gas carbon flux from subduction zones is similar to or lower than that of hydrothermal solution from back-arc basins. [Pg.417]

Sano, Y. and Williams, S.N. (1996) Fluxes of mantle and subducted carbon along convergent plate boundaries. Geophy.s. Res. Udt., 23, 2749-2752. [Pg.428]

It is well documented that carbon dioxide in vesicles of MORE is derived from the upper mantle. In island arcs and subduction-related volcanism major portions of carbon may derive from limestones and organic carbon. Sano and Marty (1995) demonstrated that the C02/ He ratio in combination with the 8 C-value can be used to distinguish between sedimentary organic, limestone, and MORE carbon. Using this approach Nishio et al. (1998) and Fischer et al. (1998) concluded... [Pg.121]

Nishio Y, Sasaki S, Gamo T, Hiyagon H, Sano Y (1998) Carbon and helium isotope systematics of North Fiji basin basalt glasses carbon geochemical cycle in the subduction zone. Earth Planet Sci Lett 154 127-138... [Pg.261]

In the case of subducting area, however, Van Soest, Hilton, and Kreulen (1998) called attention to the importance of the arc crust carbon in the C/He flux the crustal... [Pg.211]

Much of the chemical, mineralogical, and isotopic data on which our ideas of the evolution of Earth s surface environment are based come from analysis of sedimentary carbonates. Unfortunately because of the increased susceptibility of the sedimentary carbonate mass to alteration and destruction by the processes of weathering, subduction, and metamorphism, much original information is lost from the rock record with increasing age of the carbonate mass. We are left with a biased record of the preserved sedimentary carbonate rock mass. The Precambrian Eon, which includes more than 85% of Earth history, contains only about 25% of the mass of sedimentary carbonates in existence ... [Pg.596]


See other pages where Carbonate subduction is mentioned: [Pg.1049]    [Pg.231]    [Pg.270]    [Pg.348]    [Pg.67]    [Pg.1049]    [Pg.231]    [Pg.270]    [Pg.348]    [Pg.67]    [Pg.14]    [Pg.440]    [Pg.452]    [Pg.270]    [Pg.273]    [Pg.291]    [Pg.294]    [Pg.23]    [Pg.188]    [Pg.265]    [Pg.268]    [Pg.400]    [Pg.501]    [Pg.534]    [Pg.645]    [Pg.712]    [Pg.209]    [Pg.119]    [Pg.122]    [Pg.235]    [Pg.14]    [Pg.193]    [Pg.65]    [Pg.66]    [Pg.259]    [Pg.304]    [Pg.421]    [Pg.422]    [Pg.423]    [Pg.553]    [Pg.575]    [Pg.582]   
See also in sourсe #XX -- [ Pg.254 ]

See also in sourсe #XX -- [ Pg.59 ]




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