Geodynamics, magmatism, and degassing of the Earth

Azbel, I. Ya.; Tolstikhin, Igor

doi:10.1016/0016-7037(90)90202-v

Cited by 49 publications

(7 citation statements)

References 53 publications

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“…The oceanic potassium budget (Figure 11) consists of supply from rivers (both dissolved and suspended load), sediment loss by deposition, diagenesis of seafloor sediments, K 2 O gain from oceanic crust during high‐temperature alteration, and K 2 O loss to oceanic crust during low‐temperature alteration. The mantle potassium budget, which is related to mantle thermal regime and 40 Ar [ Sleep , 1979; Sleep and Wolery , 1979; Jochum et al , 1983; Azbel and Tolstikhin , 1990], consists of loss to magmas during MORB, arc, and hot spot volcanism and plutonism, and gain during subduction of sediments and igneous oceanic crust. Neither budget need be in short‐term or long‐term balance.…”

Section: Subduction Fluxesmentioning

confidence: 99%

Subduction fluxes of water, carbon dioxide, chlorine, and potassium

Jarrard

2003

Geochem Geophys Geosyst

327

324

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[1] The alteration of upper oceanic crust entails growth of hydrous minerals and loss of macroporosity, with associated large-scale fluxes of H 2 O, CO 2 , Cl À , and K 2 O between seawater and crust. This agedependent alteration can be quantified by combining a conceptual alteration model with observed agedependent changes in crustal geophysical properties at DSDP/ODP sites, permitting estimation of crustal concentrations of H 2 O, CO 2 , Cl À , and K 2 O, given crustal age. Surprisingly, low-temperature alteration causes no net change in total water; pore water loss is nearly identical to bound water gain. Net change in total crustal K 2 O is also smaller than expected; the obvious low-temperature enrichment is partly offset by earlier high-temperature depletion, and most crustal K 2 O is primary rather than secondary. I calculate crustal concentrations of H 2 O, CO 2 , Cl À , and K 2 O for 41 modern subduction zones, thereby determining their modern mass fluxes both for individual subduction zones and globally. This data set is complemented by published flux determinations for subducting sediments at 26 of these subduction zones. Global mass fluxes among oceans, oceanic crust, continental crust, and mantle are calculated for H 2 O, Cl À , and K 2 O. Except for the present major imbalance between sedimentation and sediment subduction, most fluxes appear to be at or near steady state. I estimate that half to two thirds of subducted crustal water is later refluxed at the prism toe; most of the remaining water escapes at subarc depths, triggering partial melting. The flux of subducted volatiles, however, does not appear to correlate with either rate of arc magma generation or magnitude of interplate earthquakes.

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Section: Subduction Fluxesmentioning

confidence: 99%

Subduction fluxes of water, carbon dioxide, chlorine, and potassium

Jarrard

2003

Geochem Geophys Geosyst

327

324

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“…The models developed by Allegre and coworkers (1986) and by Zhang & Zindler (1989) and Azbel & Tolstikhin (1990) assume that the upper and lower mantle reservoirs are and always have been very well isolated from each other (with the possible exception of some He exchange). The atmosphere is the complement to a degassed upper mantle, whereas the lower mantle remains relatively undegassed.…”

Section: Interpretations and Modelsmentioning

confidence: 99%

Noble Gases in the Earth's Mantle

Farley

Neroda

1998

Annu. Rev. Earth Planet. Sci.

208

103

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Noble gas isotopic ratios in mantle-derived samples require variability in the timeintegrated ratio of volatile to lithophile elements in the Earth. Documentation of mantle 3 He/ 4 He variability is becoming increasingly complete, but for the heavier noble gases, the picture is still partly clouded by the effects of atmospheric contamination of mantle samples. Nevertheless, clear variations in mantle Ne, Ar, and Xe isotopic ratios exist, are apparently correlated with 3 He/ 4 He, and may be the product of varying degrees of mantle degassing. However, uncertainties in noble gas geochemical behavior and several conflicting observations leave open other possibilities. Recent Ne isotopic data are particularly important because they require that the atmosphere has not been closed to exchange with space. Derivation of much of the atmosphere from a source other than degassing of the mantle is a strong possibility that complicates efforts to model the geochemical evolution of the Earth.

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“…Since Ozima and Kudo (1972) first demonstrated that comparison of 40Ar/36Ar between the at mosphere and the mantle implies a mantle degassing time, a number of authors (e.g., Tolstikhin 1975, Hamano and Ozima 1978, Fisher 1978, Allegre et al 1987, Azbel and Tolstikhin 1990, Zhang and Zindler 1989 have constructed histories of mantle degassing based on the differences between atmospheric and man tle noble gas isotopic ratios. The most important radiogenic components are 40Ar, 4He, and 129Xe.…”

Section: Introductionmentioning

confidence: 99%