Crust-mantle recycling

Bouman C, Elliott TR (1999) Li isotope compositions of Mariana arc lavas Implications for crust-mantle recycling. Ninth Goldschmidt Conf Abst, LPI Contribution 971, Lunar Planetary Institute, 35 Bouman C, Elliott TR, Vroon PZ, Pearson DG (2000) Li isotope evolution of the mantle from analyses of mantle xenoliths. J Conf Abst 5 239... 

Moriguti T, Nakamura E (1998b) Across-arc variation of Li isotopes in lavas and implications for crust/mantle recycling at subduction zones. Earth Planet Sci Lett 163 167-174... 

Ader M, Coleman ML, Doyle SP, Stroud M, Wakelin D (2001) Methods for the stable isotopic analysis of chlorine in chlorate and perchlorate compounds. Anal Chem 73(20) 4946-4950 Ben Othman D, White WM, Patchett J (1989) The geochemistry of marine sediments, island arc magma genesis, and crust-mantle recycling. Earth Planet Sci Lett 94 1-21 Beneteau KM, Aravena R, Frape SK (1999) Isotopic characterization of chlorinated solvents-laboratory and field results. Organic Geochemistry 30(8A) 739-753... 

Ben Othman D., White W. M., and Patchett J. (1989) The geochemistry of marine sediments, island arc magma genesis, and crust-mantle recycling. Earth Planet. Set Utt. 94, 1-21. 

Rapp R. P. and Watson E. B. (1995) Dehydration melting of metabasalt at 8-32 kbar implications for continental growth and crust-mantle recycling. J. Petrol. 36, 891-932. 

However, the results do provide a perspective, which is summarized in Figure 7. Integrating the crust-mantle recycling fluxes of Figure 4b over... 

Schubert, 1984) for no mantle recycling and about twice that much for the alternative where about one-half of the juvenile crust contributes to the orogenic buildup of the continents, while the other half is recycled into the mantle. 

First, the total amount of crust-to-mantle recycling is defined by R, the time-integrated recycling mass flux over Earth history expressed as a fraction of present-day crust mass ... 

Second, it is assumed that the recycling mass flux and its ancillary trace species fluxes are at any time dependent on the amount of crust in existence at that time. This dependence can take the form of various functions, and a variable geometry parameter E is introduced, which describes the crust to mantle recycling flux (t)recycimg function of crust mass in existence. 

Crust-mantle chemical mass-balance models offer important constraints on compositional variations in the mantle, but their constraints on the size of the various reservoirs involved depend critically on uncertainties in the estimates of the bulk composition of the continental crust, the degree of depletion of the complementary depleted mantle, and the existence of enriched reservoirs in Earth s interior, for example, possibly significant volumes of subducted oceanic crust. This last item was left out of the mass-balance models that suggested that the upper and lower mantle are chemically distinct. Chapter 2.03 makes it clear that much of the chemical and isotopic heterogeneity observed in oceanic volcanic rocks reflects various mixtures of depleted mantle with different types of recycled subducted crust. With this realization, and excepting the noble gas evidence for undegassed mantle, some of the characteristics of what was once labeled... 

FIGURE 4.6 A plot of eNd versus time for samples of Proterozoic crust from North America and Europe (grey boxes). The age of the samples was fixed from their U-Pb zircon age. The Nd-isotope compositions are interpreted as mixing between a depleted mantle source, indicative of juvenile crust, and recycled Archaean crust. The % curves indicate the proportion of reworked Archaean crust incorporated into Proterozoic crust and hence the proportion of truly juvenile crust formed (data from Patchett Arndt, 1986) after Rollinson (2006). 

A number of models have been proposed which link crustal evolution with the mantle Nd-isotope evolution curve, the most realistic of which is probably the transport-balance model of Nagler and Kramers (1998). This model is based upon their empirically derived Nd-isotope mantle evolution curve and assumes that the upper mantle melts to form basaltic oceanic crust, which is then reprocessed to form continental crust. An important aspect of the model is that it also includes crustal recycling, such that as the volume of continental crust grows with time, proportionately some crust is recycled back into the mantle through erosion and subduction. 

Kramers (2003) calculated major and minor (noble gas) volatile element abundance patterns in the Outer Earth Reservoir (the atmosphere, hydrosphere, oceanic and continental crust, and recycled components in MORB-source mantle). These are presented, normalized to solar abundances, together with data for chondrites in Fig. 5.6. The following observations can be made ... 

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