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Lead concentration and isotopic composition in five peridotite inclusions of probable mantle origin

Earth and Planetary Science Letters
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https://doi.org/10.1016/0012-821X(73)90139-8

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Abstract

The lead content of five whole-rock peridotite inclusions (four lherzolites and one harzburgite) in alkali basalt ranges from 82 to 570 ppb (parts per billion). Approximately 30–60 ppb of this amount can be accounted for by analyzed major silicate minerals (olivine ≤ 10 ppb; enstatite 5–28 ppb; chrome diopside ∼400 ppb). Through a series of acid leaching experiments, the remainder of the lead is shown to be quite labile and to reside in either glassy or microcrystalline veinlets or accessory mineral phases, such as apatite and mica. The lead isotopic composition of the peridotites (206Pb/204Pb= 18.01–18.90;207Pb/204Pb= 15.52–15.61;208Pb/204Pb= 37.80–38.86) lies within the range of values defined by many modern volcanic rocks and, in particular, is essentially coextensive with the abyssal tholeiite field. In all but one instance, isotopic differences were found between the peridotite and its host alkali basalt. Two of the peridotites clearly demonstrated internal isotopic heterogeneity between leachable and residual fractions that could not simply be due to contamination by the host basalt. However, there is no evidence that these ultramafic rocks form some layer in the mantle with isotopic characteristics fundamentally different from those of the magma sources of volcanic rocks.

    Publication type Article
    Publication Subtype Journal Article
    Title Lead concentration and isotopic composition in five peridotite inclusions of probable mantle origin
    Series title Earth and Planetary Science Letters
    DOI 10.1016/0012-821X(73)90139-8
    Volume 20
    Issue 1
    Year Published 1973
    Language English
    Publisher Elsevier
    Description 13 p.
    First page 54
    Last page 66
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