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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >P-T phase relations of silicic, alkaline, aluminous liquids: new results and applications to mantle melting and metasomatism
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P-T phase relations of silicic, alkaline, aluminous liquids: new results and applications to mantle melting and metasomatism

机译：硅，碱，铝液体的P-T相关系：地幔融化和交代作用的新结果和应用

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摘要

We report new experimental results obtained under nominally anhydrous conditions at 1.0-1.5 GPa on a synthetic melt whose composition is typical of extreme-composition xenolith glasses. These results demonstrate that part of this extreme compositional range is in equilibrium with a lherzolitic assemblage (olivine, orthopyroxene, and clinopyroxene on the liquidus), extending our earlier findings [D.S. Draper, T.H. Green P-T phase relations of silicic, alkaline, aluminous mantle-xenolith glasses under anhydrous and C-O-H fluid-saturated conditions, J. Petrol. 38 (1997) 1187-1224] showing saturation with harzburgite minerals (olivine and orthopyroxene on the liquidus). The new results strengthen the view that such liquids can readily coexist with upper mantle rocks. Our results also bear on the current debate regarding the nature of low-degree mantle melts between proponents of the diamond-aggregate technique [who argue for comparatively silica- and alkali-rich low-degree melts; e.g., M.B. Baker, M.M. Hirschmann, M.S. Ghiorso, E.M. Stolper, Compositions of near-solidus peridotite melts from experiments and thermodynamic calculations, Nature 375 (1995) 308-311; M.B. Baker, M.M. Hirschmann, L.E. Wasylenki, E.M. Stolper, M.S. Ghiorso, Quest for low-degree mantle melts, Nature 381 (1996) 286] and those favoring the sandwich technique [who question the value of the diamond-aggregate work and argue that near-solidus melts must be nepheline- and olivine-normative; T.J. Falloon, D.H. Green, H.St.C. O'Neill, C.G. Ballhaus, Quest for low-degree mantle melts, Nature 381 (1996) 285; T.J. Falloon, D.H. Green, H.St.C. O'Neill, W.O. Hibberson, Experimental tests of low degree peridotite partial melt compositions: implications for the nature of anhydrous near-solidus peridotite melts at 1 GPa, Earth Planet. Sci. Lett. 152 (1997) 149-162]. Our results support aspects of both views. The sandwich-technique view is supported, for example, because all our liquids coexisting with mantle minerals are nepheline- and olivine-normative; and our olivine-liquid Fe-Mg exchange K_D values fall on a trend similar to that supported by those workers. The diamond-aggregate view is supported, for example, because we find equilibrium between highly silicic, alkaline liquids and mantle minerals, showing the effect of high alkali contents to allow high silica contents at silica activities buffered by magnesian olivine and orthopyroxene at low pressure [M.M. Hirschmann, M.B. Baker, E.M. Stolper, The effect of alkalis on the silica content of mantle-derived melts, Geochim. Cosmochim. Acta 62 (1998) 883-902]. Additionally, the melting trends put forward by the sandwich-technique workers include revised low-degree melt compositions, as reported by Hirschmann et al., and our compositions fall on extensions of these trends. These new analyses also yield an olivine-liquid K_D that more closely follows the trend of K_D vs. melt alkali contents. The views of both sides of this controversy appear to permit, under certain conditions, the existence of small amounts of melt in the upper mantle with compositions similar to the extreme-composition xenolith glasses that are the focus of our work. On the basis of our new results, we conclude that extreme-composition xenolith glasses can act as agents of cryptic metasomatism in the upper mantle.
机译：我们报告了在标称无水条件下在1.0-1.5 GPa的合成熔体上获得的新实验结果，该熔体的成分是极端成分异种石玻璃的典型特征。这些结果表明，该极端组成范围的一部分与亮晶石组合（液相线中的橄榄石，邻比邻苯二酚和斜向比邻四烯）处于平衡状态，扩展了我们先前的发现[D.S.德雷珀在无水和C-O-H流体饱和条件下，硅质，碱性，铝质幔-铝酸盐玻璃的绿色P-T相关系。 38（1997）1187-1224]显示了Harzburgite矿物的饱和度（液相线中的橄榄石和邻苯二茂）。新的结果强化了这样的观点，即这种液体很容易与上地幔岩石共存。我们的研究结果还引起了关于钻石凝集技术支持者之间低度地幔熔体性质的争论[他们争论说，二氧化硅和碱的低度熔体含量较高;例如M.B.贝克，M.M. Hirschmann，硕士Ghiorso，E.M.Stolper，根据实验和热力学计算得到的近固相橄榄石熔体的组成，Nature 375（1995）308-311;和Nature 375（1995）。工商管理硕士贝克，M.M.赫希曼（L.E.） Wasylenki，E.M. Stolper，M.S. Ghiorso，《寻找低层地幔熔体》，《自然》（Nature）381（1996）286]和那些支持夹层技术的人[他们质疑钻石骨料的价值，并认为近固相熔体必须是霞石和橄榄石规范的。 T.J. Falloon，D.H. Green，H.St.C.奥尼尔（C.G.） Ballhaus，《探索低度地幔融化》，《自然》 381（1996）285; T.J. Falloon，D.H. Green，H.St.C.奥尼尔（W.O.） Hibberson，低度橄榄岩部分熔体成分的实验测试：对地球上1 GPa无水近固相橄榄石熔体性质的影响。科学来吧152（1997）149-162]。我们的结果支持两种观点。例如，支持三明治技术的原因是，我们与地幔矿物共存的所有液体都是霞石和橄榄石规范的。并且我们的橄榄石-液体Fe-Mg交换K_D值的下降趋势类似于那些工人所支持的趋势。例如，钻石聚集的观点得到支持，因为我们发现高硅含量的碱性液体和地幔矿物之间达到平衡，显示出高碱含量的作用，使得在镁质橄榄石和邻二甲苯在低压下缓冲的硅石活动中，硅石含量较高[ MM赫希曼（M.B.） Baker，E.M. Stolper，碱对地幔衍生熔体二氧化硅含量的影响，Geochim。宇宙猫Acta 62（1998）883-902]。此外，如Hirschmann等人的报道，三明治技术工人提出的熔化趋势包括修订后的低度熔体成分，而我们的成分是这些趋势的延伸。这些新的分析还产生了橄榄石-液体K_D，它更接近K_D与熔融碱含量的趋势。在一定条件下，该争论双方的观点似乎都允许在上地幔中存在少量熔体，其成分类似于我们工作重点的极端成分异种石玻璃。根据我们的新结果，我们得出结论，极端组成的异种石玻璃可以充当上地幔中隐性交代作用的媒介。

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