CONSTRAINTS ON EARTH EVOLUTION FROM ANTIMONY IN MANTLE-DERIVED ROCKS

Citation
Kp. Jochum et Aw. Hofmann, CONSTRAINTS ON EARTH EVOLUTION FROM ANTIMONY IN MANTLE-DERIVED ROCKS, Chemical geology, 139(1-4), 1997, pp. 39-49
Citations number
36
Categorie Soggetti
Geochemitry & Geophysics
Journal title
ISSN journal
00092541
Volume
139
Issue
1-4
Year of publication
1997
Pages
39 - 49
Database
ISI
SICI code
0009-2541(1997)139:1-4<39:COEEFA>2.0.ZU;2-Z
Abstract
We have analyzed Sb in a variety of mantle-derived volcanic rocks, per idotites, and in the CI chondrite Orgueil by spark source mass spectro metry. Concentrations vary from 0.02 to 0.8 ppm in oceanic basalts (mi d-ocean ridge basalts, MORB; oceanic island basalts, OIB). Antimony is a moderately;siderophile element which behaves like the incompatible lithophile element Pr during igneous processes in the mantle. Both MOR B and OIB samples have similar Sb/Pr ratios of about 0.02, which are d ifferent from those in continental-crustal rocks. Antimony resembles P b in that it behaves like a highly incompatible element during formati on of continental crust, whereas it behaves only moderately incompatib le during formation of oceanic basalts (MORB or OIB). Consequently, Sb /Pb ratios of oceanic basalts agree within error limits with those of the continental crust and with the CI chondritic value, indicating tha t Sb/Pb is not strongly fractionated during crust-mantle-core differen tiation. From the Sb/Pb ratios we estimate a Sb concentration of 11 +/ - 5 ppb for the primitive mantle. An alternative estimate for the prim itive-mantle abundance is obtained by assuming the Sb/Pr ratio of the primitive mantle to be intermediate between the MORB-OIB value (0.02) and that of the continental crust (0.05). This approach yields Sb = 8 +/- 4 ppb for the primitive mantle. Antimony is depleted in the bulk s ilicate Earth by a factor of 45. The volatility-corrected depletion fa ctor of 7 is similar to other moderately siderophile elements. (C) 199 7 Elsevier Science B.V.