EVIDENCE FROM RE-OS ISOTOPES FOR PLUME LITHOSPHERE MIXING IN KAROO FLOOD-BASALT GENESIS
EVIDENCE FROM RE-OS ISOTOPES FOR PLUME LITHOSPHERE MIXING IN KAROO FLOOD-BASALT GENESIS
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DOI：
10.1038/359718a0
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发表时间：
1992-10-22
期刊：
影响因子：
64.8
通讯作者：
SHIREY, SB
中科院分区：
文献类型：
--
作者：
ELLAM, RM;CARLSON, RW;SHIREY, SB
有大量的证据表明大陆溢流玄武岩省与地幔柱活动1，2;然而，溢流玄武岩往往有放射性同位素的签名，是在洋岛玄武岩记录的地幔柱来源的范围之外。这些特征更容易归因于大陆岩石圈内的源区，并且有强烈的迹象表明，通常是地幔岩石圈贡献同位素“富集”（低Nd-143/Nd-144）物质3，4。然而，有人反对认为冷的、难熔的地幔岩石圈是玄武岩浆的重要来源的模型。锇-锇系统可能提供新的限制相对重要性的羽和大陆岩石圈地幔（SCLM）在玄武岩成因：样品的SCLM带到表面的捕虏体通常有低的Os-187/Os-188 ratios 6，7，而洋岛玄武岩往往有高于南极洲的Os-187/Os-188，和老大陆地壳甚至更高（更多的放射性）的比率。在这里，我们报告的初始Os-187/Os-188的比例为190万年的苦橄玄武岩从Nuanetsi地区的卡鲁洪水玄武岩省，这是最容易解释为富集SCLM和岩石圈下的材料，最有可能来自地幔柱之间的混合物。
THERE is abundant evidence to link continental flood basalt provinces with mantle plume activity1,2; however, flood basalts often have radiogenic isotope signatures that are outside the range for plume sources as recorded in ocean-island basalts. These signatures are more readily attributed to source regions within the continental lithosphere, and there are strong indications that it is often the mantle lithosphere that contributes isotopically 'enriched' (low-Nd-143/Nd-144) material3,4. There are objections, however, to models that propose cold, refractory mantle lithosphere as an important source of basaltic magma5. The rhenium-osmium system may provide new constraints on the relative importance of plume and sub-continental lithospheric mantle (SCLM) in basalt genesis: samples of SCLM brought to the surface as xenoliths commonly have low Os-187/Os-188 ratios6,7, whereas ocean-island basalts tend to have higher than chondritic Os-187/Os-188, and old continental crust has even higher (more radiogenic) ratios. Here we report initial Os-187/Os-188 ratios for 190-Myr-old picrite basalts from the Nuanetsi region of the Karoo flood basalt province, which are most readily explained as mixtures between enriched SCLM and sub-lithospheric material, most probably derived from a mantle plume.