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首页> 外文期刊>Contributions to Mineralogy and Petrology >Dihedral angle measurements and infiltration property of SiO_2-rich melts in mantle peridotite assemblages
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Dihedral angle measurements and infiltration property of SiO_2-rich melts in mantle peridotite assemblages

机译：地幔橄榄岩组合物中富含SiO_2的熔体的二面角测量和渗透性能

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Petrological and experimental studies demonstrated that nepheline-normative, SiO_2-rich melts can be present in the upper mantle at pressures < = 1.5 GPa. To evaluate the role of such melts in mantle processes and magma genesis, we carried out two types of experiments: (1) melt distribution experiments to characterize the grain-scale distribution of a small fraction of typical SiO_2-rich mantle melt (SRMM) in polycrystalline olivine (Ol)at 1,180 deg C, 1.2 GPa; and (2) an infiltration experiment to test the ability of SRMM to impregnate and metasomatise neighbouring non-molten mantle rocks. The median dihedral angles at O1-O1-SRMM contacts are equal to approx = 50 deg, implying that melt should be interconnected at all melt fractions. Complications arise, however, in the investigated system because Ol-liquid interfacial energy is anisotropic, and we estimate that the connectivity threshold in the SRMM-O1 system is approx = O.3 vol percent Regarding the very low volume fraction of SRMM in peridotites, we conclude that these melts either occur as isolated pockets or form a network of grain edge channels with a low degree of connectivity due to a large number of dry grain edges. Even in the case where an interconnected network exists, their large viscosities should prohibit the extraction of SRMM from peridotite sources. The infiltration experiment also points to a very reduced mobility of SRMM in the upper mantle. In this experiment, a slice of synthetic dunite was immersed into a magma reservoir made of 60 wt percent SRMM+ 40 wt percent Ol, and subjected to 1,180 deg C-1.2 GPa for 113 h: despite this long duration, the SiO_2-rich liquidwas unable to infiltrate measurably the dunite. Our experiments do not support the hypothesis that SRMM represent agents of mantle metasomatism.
机译：岩石学和实验研究表明，在压力小于等于1.5 GPa的上地幔中可能存在富于霞石的富SiO_2熔体。为了评估这类熔体在地幔过程和岩浆成因中的作用，我们进行了两种类型的实验：（1）熔体分布实验，以表征一小部分典型的富含SiO_2的地幔熔体（SRMM）的晶粒度分布。 1,180摄氏度，1.2 GPa的多晶橄榄石（Ol）; （2）渗透实验以测试SRMM浸渗和交代邻近的非熔融地幔岩石。 O1-O1-SRMM接点的正二面角大约等于50度，这意味着熔体应该在所有熔体部分互连。但是，在研究的系统中会出现复杂问题，因为Ol-液体界面能是各向异性的，我们估计SRMM-O1系统的连通性阈值约为= 0.3 vol％。关于橄榄岩中SRMM的体积分数非常低，我们得出的结论是，由于大量的干粮边缘，这些熔体要么以孤立的小袋形式出现，要么形成了谷物边缘通道的网络，连通度较低。即使在存在互连网络的情况下，其较大的粘度也应禁止从橄榄岩源中提取SRMM。渗透实验还指出，SRMM在上地幔中的流动性大大降低。在该实验中，将一片合成的榴n石浸入60％SRMM + 40 wt％Ol制成的岩浆储层中，并经受1,180℃-1.2 GPa的作用113 h：尽管如此长的时间，富含SiO_2的液体仍不能使渗入的榴n岩可测量。我们的实验不支持SRMM代表地幔交代作用的假说。

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