Behavior of trace elements concentrated at grain-boundaries during partial melting of Peridotites

橄榄岩部分熔融过程中微量元素在晶界富集的行为

• 批准号: 63460053
• 负责人: SUZUKI Kazuhiro
• 金额: $ 5.5万
• 依托单位: Nagoya University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1988
• 资助国家: 日本
• 起止时间: 1988 至 1989
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-63460053/
• 关键词: Grain-boundary; Magma; Partial melting; Trace element; Peridotite; Basalt; Incompatible element; 希土類元素; チタナイト

The distribution of the incompatible elements in mantle peridotites was examined by means of electron microprobe analysis, water leaching and in situ partial melting to explain the contents of potash and other incompatible elements in basaltic magmas. The mineral chemistry can hardly account for the chemistry of the parental peridotites. The enrichment of incompatible elements along grainboundaries is confirmed by the EPMA step analysis across boundaries of the constituent minerals. The boundary enrichment is demonstrated also by the EPMA analysis of the surfaces of the constituents before and after acid washing. AIKbeta emission spectrum of the surfaces suggests that atoms on mineral surfaces are less tightly bonded with surrounding atoms than those in minerals. ahd hence they are leached out easily. To estimate the amount of incompatible elements stored on the surfaces, elements were leached out through repeated washing of samples with deionized water at 20, 75 and 160ﾟC and the leac … More hing solutions were analyzed with an ion chromatographic analyzer. The accumulated amount of leached elements tends to become almost constant at each temperature, but increases with increase in temperature. The potash leached out from 1g sample at 160ﾟC amounts to 63.3-255mug, about 40-80 % of the whole-rock abundance. Thus, we find that most of the unaccountable elements in peridotites is stored on the grain-boundaries. The grain-boundary enrichment of potash and other incompatible elements should be particularly important in partial melting of peridotites. To examine this, chips of peridotites were heated at 1100-1370ﾟC in a gas-mixing furnace. Glass veins, 3-30 mum in width, are formed along grain-boundaries of the constituents at every temperatures. Glass makes up 4-8 vol.% at 1300ﾟC, and shows a basaltic composition. This result leads us to a conclusion that the abundance of incompatible elements in the melt at the small degree of melting is governed mainly by the grain-boundaries, because the grain-boundaries can melt first. The present study demonstrates that basaltic magmas can be generated from kaersutite- and/or phlogopite-free mantle peridotites. Less

通过电子探针分析、水浸和原位部分熔融等方法研究了地幔橄榄岩中不相容元素的分布，以解释玄武质岩浆中钾盐和其他不相容元素的含量。矿物化学很难解释母橄榄岩的化学。跨组成矿物边界的 EPMA 步进分析证实了不相容元素沿晶界的富集。酸洗前后成分表面的 EPMA 分析也证明了边界富集。表面的 AIKbeta 发射光谱表明，矿物表面的原子与周围原子的结合不如矿物中的原子紧密。因此它们很容易被滤出。为了估计表面上储存的不相容元素的量，通过在 20、75 和 160°C 的温度下用去离子水反复清洗样品来滤出元素，并用离子色谱分析仪分析沥滤液。浸出元素的累积量在每个温度下趋于几乎恒定，但随着温度的升高而增加。在160℃下，1g样品浸出的钾含量为63.3-255mug，约占全岩丰度的40-80%。因此，我们发现橄榄岩中大部分无法解释的元素都储存在晶界上。钾盐和其他不相容元素的晶界富集对于橄榄岩的部分熔融尤其重要。为了验证这一点，将橄榄岩碎片在气体混合炉中加热到 1100-1370°C。在每种温度下，沿着成分的晶界都会形成宽度为 3-30 微米的玻璃纹。 1300°C 时玻璃含量为 4-8 vol.%，呈玄武岩成分。这一结果使我们得出这样的结论：小熔化程度熔体中不相容元素的丰度主要受晶界控制，因为晶界可以先熔化。本研究表明，玄武岩岩浆可以由不含钙镁矿和/或金云母的地幔橄榄岩产生。较少的

项目成果

Suzuki, K. ( Adachi, M. & Yamamoto, K ): "Possible effects of grain-boundary REE on the REE distribution in derivative melts at partial melting." Geochem. J.

铃木 K.（安达 M.

飯山敏道: "変成過程における物質移動実験および理論的研究" 〔地球内部に於ける物質移動と変化〕・岩鉱特別号.4号. 199-208 (1989)

Toshimichi Iiyama：“变质过程中的传质实验和理论研究”[地球内部的传质和变化] / Iwane Special Issue.4 (1989)。

SUZUKI Kazuhiro: "Possible effects of grain-boundary REE on the REE distribution in derivative melts at partial melting" Geochem.J.(in submitted).

SUZUKI Kazuhiro：“晶界稀土元素对部分熔化时衍生熔体中稀土元素分布的可能影响”Geochem.J.（已提交）。

ENAMI Masaki: "Quartz pseudomorphs after coesite in eclogites from Shandong province,east China" Am.Mineral.(in press). 75. (1990)

ENAMI Masaki：“中国东部山东省榴辉岩中柯石英后的石英假晶”Am.Mineral.（印刷中）。

Ohtani, E. ( and Suzuki, K ): "Structural change of albite (NaAlSi308) melt quenched at high pressure: density and AlKbeta X-ray emission." Min. Pet. Econ. Geol. (Gannko Gakkaisi), Vol. 11, 385-390, 1989.

Ohtani, E.（和 Suzuki, K）：“高压淬火钠长石 (NaAlSi308) 熔体的结构变化：密度和 AlKbeta X 射线发射。”