Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHPM belt, NW China: Implications for ultradeep-origin and hydroxyl defects in mantle garnets
Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHPM belt, NW China: Implications for ultradeep-origin and hydroxyl defects in mantle garnets
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DOI：
10.2138/am.2005.1684
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发表时间：
2005-05
影响因子：
3.1
通讯作者：
Shuguang Song;Lifei Zhang;J. Chen;J. Liou;Y. Niu
中科院分区：
文献类型：
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作者：
Shuguang Song;Lifei Zhang;J. Chen;J. Liou;Y. Niu
摘要在北方柴北缘超高压变质带的石榴橄榄岩中发现了两种类型的角闪石出溶纹层。角闪石薄片严格地在四个方向上取向，对应于等距形式{111}（即，八面体平面）。通过透射电子显微镜（TEM）的观察表明，角闪石薄片与主体石榴石拓扑一致，并具有9.8至10 μ m的晶格。间距。电子探针分析表明，这些出溶角闪石薄片富含Na和Ti。TEM观察和重新计算的组合物表明，定向角闪石lamericum exsolved从原来的supercrystalmajorites与高浓度的Na 2 O（0.3重量%）和羟基（高达1000 ppm的重量）。这些结果意味着，主机石榴石橄榄岩形成深度大于200公里，石榴石可以是一个重要的水库的水在这样的深度在地幔。
Abstract Two types of amphibole exsolution lamellae were discovered in garnet from a few garnet peridotites from the North Qaidam ultrahigh-pressure metamorphic belt, northern Tibet, NW China. The amphibole lamellae are strictly oriented in four directions corresponding to the isometric form {111} (i.e., octahedron planes) of garnet. Observations by transmission electron microscopy (TEM) show that amphibole lamellae are topotaxtially concordant with the host garnet and possess 9.8 to 10 Å lattice .c.-spacing. Electron-microprobe analysis reveals that these exsolved amphibole lamellae are high in Na and Ti. The TEM observations and recalculated compositions indicate that the oriented amphibole lamellae exsolved from original supersilicic majorites with high concentrations of Na2O(0.3 wt%) and hydroxyl (up to 1000 ppm by weight). These results imply that the host garnet peridotites were formed at depths greater than 200 km and that garnet can be an important reservoir of water at such depths in the mantle.