Growth of subcontinental lithospheric mantle beneath Zimbabwe started at or before 3.8 Ga: Re-Os study on chromites
Growth of subcontinental lithospheric mantle beneath Zimbabwe started at or before 3.8 Ga: Re-Os study on chromites
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津巴布韦下方次大陆岩石圈地幔的生长开始于 3.8 Ga 或之前：对铬铁矿的 Re-Os 研究
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发表时间：
1997
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影响因子：
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通讯作者：
M. Prendergast
中科院分区：
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作者：
T. Nägler;J. Kramers;B. Kamber;R. Frei;M. Prendergast
对津巴布韦克拉通太古宙（2.7 ~ 3.5 Ga）超镁铁质侵入岩中铬铁矿的Re-Os同位素分析结果表明，铬铁矿现今平均187Os/188Os比值为0.1066，明显低于硅酸盐大地值。源储层被解释为反映津巴布韦次大陆岩石圈地幔（SCLM）。在非洲南部、西伯利亚和怀俄明克拉通的捕虏体研究的基础上，先前已经假设太古宙的SCLM的Re枯竭。然而，由于我们的样品受到年龄的限制，Re-Os数据也揭示了太古宙SCLM随时间的演变。这些结果表明，津巴布韦SCLM在3.8 Ga之前就开始从软流圈地幔中分离出来，并在整个太古代近似连续地生长。这一结果与目前正演模拟的SCLM数据相吻合。
Re-Os isotope results on chromites separated from age-constrained Archean (2.7 to 3.5 Ga) ultramafic intrusions in the Zimbabwe craton show that chromites average a present-day 187Os/188Os ratio of 0.1066, significantly below the bulk silicate Earth value. The source reservoir is interpreted to reflect the Zimbabwean subcontinental lithospheric mantle (SCLM). Archean Re depletion of the SCLM has previously been postulated on the basis of xenolith studies from southern Africa, Siberia, and the Wyoming craton. Because our samples are age constrained, however, the Re-Os data also shed light on the evolution of the Archean SCLM through time. They indicate that the Zimbabwean SCLM began to be separated from asthenospheric mantle before 3.8 Ga and grew quasi-continuously throughout the Archean. This result is reconciled with present-day SCLM data in forward modeling.