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首页> 外文期刊>Contributions to Mineralogy and Petrology >Ilmenite composition in the Tellnes Fe–Ti deposit, SW Norway: fractional crystallization, postcumulus evolution and ilmenite–zircon relation
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Ilmenite composition in the Tellnes Fe–Ti deposit, SW Norway: fractional crystallization, postcumulus evolution and ilmenite–zircon relation

机译：挪威西南部Tellnes Fe-Ti矿床中的钛铁矿组成：分步结晶，后积云演化和钛铁矿-锆石关系

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摘要

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of a ferrodioritic Fe-Ti-P rich melt. Stage 1 is characterized by ilmenite-plagioclase cumulates, partly stored in the lower part of the ore body (Lower Central Zone, LCZ), and stage 2 by ilmenite-plagioclase-orthopyroxene-olivine cumulates (Upper Central Zone, UCZ). The concentration of V and Cr in ilmenite, corrected for the trapped liquid effect, (1) defines the cotectic proportion of ilmenite to be 17.5 wt% during stage 1, and (2) implies an increase of D V Ilm during stage 2, most likely related to a shift in fO2. The proportion of 17.5 wt% is lower than the modal proportion of ilmenite (ca. 50 wt%) in the ore body, implying accumulation of ilmenite and flotation of plagioclase. The fraction of residual liquid left after crystallization of Tellnes cumulates is estimated at 0.6 and the flotation of plagioclase at 26 wt% of the initial melt mass. The increasing content of intercumulus magnetite with stratigraphic height, from 0 to ca. 3 wt%, results from differentiation of the trapped liquid towards magnetite saturation. The MgO content of ilmenite (1.4–4.4 wt%) is much lower than the expected cumulus composition. It shows extensive postcumulus re-equilibration with trapped liquid and ferromagnesian silicates, correlated with distance to the host anorthosite. The Zr content of ilmenite, provided by in situ analyses, is low (<114 ppm) and uncorrelated with stratigraphy or Cr content. The data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of ZrO2 from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process.
机译：挪威西南部Rogaland Anorthosite省Tellnes钛铁矿矿床中的钛铁矿的主要元素和微量元素XRF以及原位LA-ICP-MS分析，限制了富铁铁性Fe-Ti-P熔体的两阶段分步结晶模型。第1阶段的特征是钛铁矿-斜长石堆积物，部分储存在矿体的下部（下部中央区域，LCZ），第2阶段的特征是钛铁矿-斜长石-邻位吡咯-橄榄石累积物（上部中央区域，UCZ）。钛铁矿中的V和Cr的浓度已针对捕集的液体效应进行了校正，（1）定义阶段1中钛铁矿的共晶比例为17.5 wt％，（2）表示DV Ilm 的增加sup>在第2阶段中，很可能与fO2的变化有关。 17.5 wt％的比例低于钛铁矿的模态比例（约50 wt％），这意味着钛铁矿的堆积和斜长石的浮选。在Tellnes结晶后，残留的残留液体分数估计为0.6，斜长石的浮选为初始熔体质量的26 wt％。地层间积间磁铁矿的含量从0到大约增加。 3％（重量）是由于捕获的液体向磁铁矿饱和度的分化所致。钛铁矿的MgO含量（1.4-4.4 wt％）远低于预期的积云组成。它显示了大量的积云后重新平衡，其中包含了被捕获的液态硅酸铁和镁铁硅酸盐，这与到寄主钙铁矿的距离有关。原位分析提供的钛铁矿Zr含量低（<114 ppm），与地层或Cr含量无关。数据表明，锆石电晕在钛铁矿的亚固相渗出ZrO2 形成的钛铁矿周围观察到。 920±3 Ma的U-Pb锆石年龄可能记录了该析出过程。

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