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首页> 外文期刊>Contributions to Mineralogy and Petrology >Genesis of ilmenite rods and palisades along humite-type defects in olivine from Alpe Arami
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Genesis of ilmenite rods and palisades along humite-type defects in olivine from Alpe Arami

机译：Alpe Arami橄榄石中沿腐殖质型缺陷的钛铁矿杆和木栅的成因

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摘要

Rod-shaped ilmenite inclusions in olivine have been observed in numerous peridotite lenses of the Adula–Cima Lunga unit, Central Alps. The rods are elongated parallel to [010]ol and identical in size, shape and concentration to those reported from garnet peridotite at Alpe Arami (AA). TEM investigation of the rods at AA, Cima di Gagnone (CDG) and Monte Duria (MD) demonstrates that the titanate inclusions correspond to a Mg-bearing ilmenite with exclusively a trigonal crystal structure. No other FeTiO3 polymorphs have been identified. The shape of the ilmenite inclusions concurs with minimum topotactic misfits between the lattices of olivine and Mg-bearing ilmenite. Optical microscopy reveals that the ilmenite rods are not randomly distributed within olivine but have, at all localities, a preferred alignment parallel to (001)ol, forming palisades. TEM images of the ilmenite palisades at AA and CDG show that they are controlled by the presence of (001) planar defects in olivine along which the rods nucleated. The defects have been characterised by high-resolution TEM and identified as 4.4 Å-wide humite-type layers, i.e. (Mg2SiO4)·Mg(OH,F)2, intergrown within olivine. In such layers substitution of up to 50 mol% MgH2 by Ti4+ is possible. Assuming Ti-saturated humite slabs, the maximum density of (001) faults observed at AA, approximately 1900 mm–1, can accommodate about 170 ppm TiO2 in olivine. This represents about half the values obtained by UV-laser ablation ICP-MS and EMPA analysis. Evidence for annealing of the defects, however, suggests that only parts of the defects are still preserved. The formation of ilmenite rods is considered to be a consequence of the breakdown of isolated humite layers in olivine. The apparent TiO2 content in olivine at AA, CDG and MD is regarded as a function of the Ti-humite defect density.
机译：在中部阿尔卑斯山的Adula–Cima Lunga单元的许多橄榄岩晶状体中观察到橄榄石中的棒状钛铁矿夹杂物。这些杆平行于[010] ol 伸长，其尺寸，形状和浓度与Alpe Arami（AA）的石榴石橄榄岩报道的杆相同。对AA，Cima di Gagnone（CDG）和Monte Duria（MD）棒材的TEM观察表明，钛酸盐夹杂物对应于仅具有三角晶体结构的含镁钛铁矿。没有发现其他FeTiO3 多晶型物。钛铁矿夹杂物的形状与橄榄石和含Mg钛铁矿晶格之间的最小全能错配一致。光学显微镜显示钛铁棒并非随机分布在橄榄石中，而是在所有位置都具有平行于（001）ol 的优选排列，形成栅栏。 AA和CDG处的钛铁矿栅栏的TEM图像显示，它们受橄榄石中（001）平面缺陷的存在所控制，棒沿这些缺陷成核。缺陷已通过高分辨率TEM表征，并被识别为4.4Å宽的腐殖岩型层，即（Mg2 SiO4 ）·Mg（OH，F）2 橄榄石。在这样的层中，最多可以用Ti4 +代替50％（摩尔）的MgH2 。假设钛饱和的腐殖质平板，AA观察到的（001）断层的最大密度约为1900 mm-1 ，可以容纳橄榄石中约170 ppm的TiO2 。这大约是通过紫外激光烧蚀ICP-MS和EMPA分析获得的值的一半。但是，对缺陷进行退火的证据表明，仅保留了部分缺陷。钛铁矿棒的形成被认为是橄榄石中孤立的腐殖土层破裂的结果。在AA，CDG和MD处橄榄石中的表观TiO2 含量被认为是Ti-Humite缺陷密度的函数。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2001年第5期|619-628|共10页
  • 作者

    A.-C. Risold; V. Trommsdorff; B. Grobéty;

  • 作者单位

    Institut für Mineralogie und Petrographie ETH Zentrum 8092 Zürich Switzerland;

    Institut für Mineralogie und Petrographie ETH Zentrum 8092 Zürich Switzerland;

    Institut de Minéralogie et Pétrographie Perolles 1700 Fribourg Switzerland;

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