We present experimentally determined trace element partition coefficients (D) between pyrochlore-group minerals (Ca2(Nb,Ta)2O6(O,F)), Ca fersmite (CaNb2O6), and silicate melts. Our data indicate that pyrochlores and fersmite are able to strongly fractionate trace elements during the evolution of SiO2-undersaturated magmas. Pyrochlore efficiently fractionates Zr and Hf from Nb and Ta, with DZr and DHf below or equal to unity, and DNb and DTa significantly above unity. We find that DTa pyrochlore-group mineral/silicate melt is always higher than DNb, which agrees with the HFSE partitioning of all other Ti–rich minerals such as perovskite, rutile, ilmenite or Fe-Ti spinel. Our experimental partition coefficients also show that, under oxidizing conditions, DTh is higher than corresponding DU and this implies that pyrochlore-group minerals may fractionate U and Th in silicate magmas. The rare earth element (REE) partition coefficients are around unity, only the light REE are compatible in pyrochlore-group minerals, which explains the high rare earth element concentrations in naturally occurring magmatic pyrochlores.

中文翻译：

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微量元素在烧绿石，微晶石，铁矿和硅酸盐熔体之间分配。

我们目前通过实验确定的烧绿石族矿物（Ca2（Nb，Ta）2O6（O，F）），钙钛矿（CaNb2O6）和硅酸盐熔体之间的微量元素分配系数（D）。我们的数据表明，烧绿石和铁矿能够在SiO2欠饱和岩浆演化过程中强烈地分离痕量元素。烧绿石有效地分离了Nb和Ta中的Zr和Hf，其中DZr和DHf小于或等于1，而DNb和DTa明显大于1。我们发现DTa的烧绿石族矿物/硅酸盐熔体总是比DNb高，这与所有其他富含Ti的矿物质（如钙钛矿，金红石，钛铁矿或Fe-Ti尖晶石）的HFSE分配相符。我们的实验分配系数还表明，在氧化条件下，DTh高于相应的DU，这意味着烧绿石类矿物可能会分馏硅酸盐岩浆中的U和Th。稀土元素（REE）的分配系数约为1，只有轻稀土元素与烧绿石族矿物相容，这解释了天然岩浆烧绿石中稀土元素的浓度很高。