Chlorine isotope evidence for crustal recycling into the Earth's mantle
John, Timm, Layne, G.D., Haase, K.M. and Barnes, J.D. (2010) Chlorine isotope evidence for crustal recycling into the Earth's mantle Earth and Planetary Science Letters, 298 . pp. 175-182. DOI 10.1016/j.epsl.2010.07.039. Date online first: 30 August 2010
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Subduction of oceanic lithosphere is a key feature of terrestrial plate tectonics. However, the effect of this
recycled crustal material on mantle composition is debated. Ocean island basalts (OIB) provide direct insights into the composition of Earth's mantle. The distinct composition of the HIMU (high 238U/204Pb)- and EM (enriched mantle)-type OIB mantle sources may be due to either recycling of oceanic crust and sediment into the mantle or metasomatic processes within the mantle. Chlorine derived from seawater or crustal fluids potentially provides a tracer for recycled material. Previously reported δ37Cl values for mid-ocean ridge
basalts (MORB) range from ca. −3.0 to near 0‰. In contrast to MORB, we find a larger variation in OIB glasses representing HIMU- and EM-type mantle sources based on replicate SIMS analyses with δ37Cl values ranging from −1.6 to +1.1‰ for HIMU-type and −0.4 to +2.9‰ for EM-type lavas. These δ37Cl values correlate positively with 87Sr/86Sr ratios for both the HIMU- and EM-type samples. The negative δ37Cl values of some HIMU-type lavas overlap with those of altered oceanic lithosphere, which is assumed to be present
in the HIMU source. The EM lavas have high 87Sr/86Sr and primarily positive δ37Cl values. We hypothesize that subducting sediments may have developed high δ37Cl values by expelling 37Cl-depleted pore fluids, thus accounting for the positive δ37Cl values recorded in the EM-type lavas.
|Keywords:||Geophysics; chlorine isotopes; crustal recycling; SIMS; subduction zone; ocean island basalt; mantle chemistry|
|Research affiliation:||OceanRep > SFB 574 > C1
OceanRep > SFB 574
|Date Deposited:||13 Jul 2010 13:07|
|Last Modified:||06 Jul 2012 15:04|
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