Subsolidus and melting phase relations of basaltic composition in the uppermost lower mantle
Subsolidus and melting phase relations of basaltic composition in the uppermost lower mantle
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DOI：
10.1016/s0016-7037(02)00847-5
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发表时间：
2002-06-01
影响因子：
5
通讯作者：
Fei, YW
中科院分区：
文献类型：
--
作者：
Hirose, K;Fei, YW
用多砧装置测定了22 ~ 27.5GPa下洋中脊玄武岩固相线上和固相线下的相关系和元素分配。固相线矿物组合随压力变化显著;在22 GPa下，镁铝钙钛矿和硅镁钙钛矿相结合，在23 GPa下，钙钛矿相结合，在25.5GPa下，富CaAl 4Si 2 O 11的CAS相结合，以及镁钙钛矿、硅镁钙钛矿、钙钛矿、CF相结合（约在NaAlSiO_4-MaAl（2）O（4）的结合处）和NAL相（[Na，K，Ca]（1）[Mg，Fe ~（2+）]（2）[Al，Fe ~（3+），Si]（5.5-6.0）O ~（-12））。液相线相是Ca-钙钛矿，并且在27.5GPa下随着温度降低而出现斯钛铁矿、CAS相、NAL相、Mg-钙钛矿和CF相。部分熔体在27至27.5 GPa显着贫化SiO2和CaO和丰富的FeO和MgO相比，在较低的压力下形成的，反映了狭窄的稳定性（Fe，Mg）富相（镁或镁钙钛矿）高于固相线温度。除了在13至18 GPa的高压下，玄武岩组合物具有比橄榄岩组合物更低的熔融温度（Yasuda等人，1994年），因此可以优先在地球内部融化。热的太古宙地幔柱中可能含有具碎屑的玄武质壳，它们可能在最上部的下地幔中熔化。在这种情况下，钙钛矿在熔体和固体之间的微量元素分配中起主导作用。这与部分熔融的橄榄岩组合物的情况下，其中镁橄榄石是在这个深度的液相线相显着的对比。版权所有（C）2002 Elsevier Science Ltd.
The phase relations and the element partitioning in a mid-oceanic ridge basalt composition were determined for both above-solidus and subsolidus conditions at 22 to 27.5 GPa by means of a multianvil apparatus. The mineral assemblage at the solidus changes remarkably with pressure; majorite and stishovite at 22 GPa, joined by Ca-perovskite at 23 GPa, further joined by CaAl4Si2O11-rich CAS phase at 25.5 GPa, and Mg-perovskite, stishovite, Ca-perovskite, CF phase (approximately on the join NaAlSiO4-MaAl(2)O(4)), and NAL phase ([Na,K,Ca](1)[Mg,Fe2+](2)[Al,Fe3+,Si](5.5-6.0)O-12) above 27 GPa. The liquidus phase is Ca-perovskite, and stishovite, a CAS phase, a NAL phase, Mg-perovskite, and a CF phase appear with decreasing temperature at 27.5 GPa. Partial melt at 27 to 27.5 GPa is significantly depleted in SiO2 and CaO and enriched in FeO and MgO compared with those formed at lower pressures, reflecting the narrow stability of (Fe,Mg)-rich phases (majorite or Mg-perovskite) above solidus temperature. The basaltic composition has a lower melting temperature than the peridotitic composition at high pressures except at 13 to 18 GPa (Yasuda et al., 1994) and therefore can preferentially melt in the Earth's interior. Recycled basaltic crusts were possibly included in hot Archean plumes, and they might have melted in the uppermost lower mantle. In this case, Ca-perovskite plays a dominant role in the trace element partitioning between melt and solid. This contrasts remarkably with the case of partial melting of a peridotitic composition in which magnesiowustite is the liquidus phase at this depth. Copyright (C) 2002 Elsevier Science Ltd.