Crust recycling

Puchtel I. and Humayun M. (2000) Platinum group elements in Kostomuksha komatiites and basalts implications for oceanic crust recycling and core-mantle interaction. Geochim. Cosmochim. Acta 64, 4227-4242. 

For any given crust mass v. time curve, the two parameters R and E determine the bulk crust formation and the crust recycling (erosion) fluxes through time, as... 

Following this result, the total amount of crust recycled by erosion into the mantle would be about 60% of the present crust mass (R 0.6). This is not in conflict with any known geochemical data. An apparent contradiction exists with a maximum value of 30% derived from the mass balance of Ar in the atmosphere and K in the continental crust by Coltice et al. (2000). The argument used by these workers was based on the assumption that the amount of Ar in the atmosphere and the continental crust combined is equal to or greater than that generated over geological time by the amount of K that has ever been in the continental crust by (equation (3)... 

Zinc is a bluish-white, lustrous metal which tarnishes in air. It is present in the earth s crust as sulfide (sphalerite), carbonate, or silicate ores, to the extent of only 78 ppm, making it the 23rd most abundant element.2 The metal is obtained from its ores by roasting and subsequent reduction with coke or by electrolysis. Approximately 8.36 million metric tons of zinc were produced worldwide in 2002 of this amount, two-thirds were from ores, while one-third was obtained from recycled zinc.3 The ease of mining and refining of the ore and the subsequent low price of the metal (ca. 1.2 kg-1 in 1998)3 have made zinc the third most popular non-ferrous metal (after aluminum and copper). 

The increment of crust newly formed at t is created at a rate g for the juvenile part, and, for the recycled part, as the negative of the erosion rate. Therefore... 

Mantle composition can also be assessed through examination of lavas from other oceanic settings. In a study of well-characterized Hawaiian lavas, Chan and Frey (2003) found a total range indH i that overlaps the range for MORE, +2.5 to +5.7. Other data from Kilauea volcano substantiate this range (Tomascak et al. 1999b). The Hawaii data, when compared with other isotopic and elemental parameters, suggested incorporation of recycled altered oceanic crust into the source of the Hawaiian plume (Chan and Frey 2003). 

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... 

Seafloor spreading eventually pushes oceanic crust into subduction zones where the hydrothermal sediments and rock are recycled back into the mantle. A small fraction of these deposits is uplifted, or obducted, onto land. These rescued deposits are termed ophiolites. Because of their metal enrichments, they serve as major ore bodies and have been mined for various precious metals, such as copper, for thousands of years. 

The pre-human natural rate at which rivers were carrying secondary minerals into the ocean was 1.4 x lO g/y. Assuming that these solids have an average settled density of 1.6g/cm, this input would have filled the ocean basins (volmne= 1.37 x 10 cm from Figure 2.1) within 157 million years. This has not happened because the sediments are recycled through the crust and the upper mantle (Figure 1.2). 

Ludden, J. Hynes, A. 2000. The Lithoprobe Abitibi-Grenville transect two billion years of crust formation and recycling in the Precambrian Shield of Canada. Canadian Journal of Earth Sciences, 37, 459-476. 

Since hthium and boron isotope fractionations mainly occur during low temperature processes, Li and B isotopes may provide a robust tracer of surface material that is recycled to the mantle (Elhott et al. 2004). Heterogeneous distribution of subducted oceanic and continental crust in the mantle will thus result in variations in Li and B isotope ratios. Furthermore, dehydration processes active in subducdon zones appear to be of crucial importance in the control of Li and B isotope composition of different parts of the mantle. For the upper mantle as a whole Jeffcoate et al. (2007) gave an estimated 8 Li-value of 3.5%o. 

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