ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The partition of Ni between olivine and monosulfide-oxide liquid has been investigated at 1300–1395° C, $$f_{O_2 }$$ =10−8-9−10−6.8, and $$f_{S_2 }$$ =10−2.0−10−0.9, over the composition range 20–79 mol. % NiS. The product olivine compositions varied from Fo98 to Fo59 and from 0.06 to 3.11 wt% NiO. The metal/sulfur ratio of the sulfide-oxide liquid increases with increase in $$f_{O_2 }$$ , decrease in $$f_{S_2 }$$ , and increase in NiS content. The Ni/Fe exchange reaction has been perfectly reversed using natural olivine and pure forsterite as starting materials. The FeO and NiO contents of olivine from runs equilibrated at the same $$f_{O_2 }$$ and $$f_{S_2 }$$ form isobaric distributions with NiS content, which, to a first approximation, are dependent at constant temperature and total pressure on a variable term, −0.5 log ( $$f_{S_2 }$$ / $$f_{O_2 }$$ ). The Ni/Fe distribution coefficient (K D3) exhibits only a weak decrease from 35 to 29 with increase in $$f_{O_2 }$$ from the IW buffer to close to the FMQ buffer. At $$f_{O_2 }$$ values higher than FMQ, the sulfide-oxide liquid has the approximate composition (Ni,Fe)3±xS2∶K D3≈58. The present K D3 vs O/(S+O) data define a trend which extrapolates to K D3≈20 at 10 wt% oxygen in the sulfide-oxide liquid. The compositions of olivine and Ni-Cu sulfides associated with early-magmatic basic rocks and komatiites are consistent, at 1400° C, with a value of -log ( $$f_{O_2 }$$ / $$f_{S_2 }$$ ) of about 7.7, which is equivalent to ≈0.0 wt% oxygen in the hypothesized immiscible sulfide-oxide liquid. Therefore, K D3 would not be reduced significantly from the 30 to 35 range for sulfide-oxide liquids with low oxygen contents.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00371375
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