Experimental study on the effects of H2O upon crystallization in the Lower and Critical Zones of the Bushveld Complex with an emphasis on chromitite formation
Experimental study on the effects of H2O upon crystallization in the Lower and Critical Zones of the Bushveld Complex with an emphasis on chromitite formation
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H2O 对 Bushveld 杂岩下区和临界区结晶影响的实验研究，重点是铬铁矿的形成
DOI：
10.1007/s00410-020-01733-w
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发表时间：
2020
影响因子：
3.5
通讯作者：
Veksler
中科院分区：
文献类型：
--
作者：
Veksler
Bushveld杂岩下部和临界带的镁铁质-超镁铁质层状岩石被认为是由通常标记为B1的母岩浆形成的，SiO2含量为55 wt.%，约12重量%的MgO Cr_2O_3浓度为0.15wt.%。先前在300 MPa和名义干燥条件下的实验研究表明，该组合物在1250 ° C和1300 °C之间的液相线上具有斜方辉石，并且在1166 °C及以下，矿物由斜长石和单斜辉石结合。本研究的目的是调查可变添加的H2O（2，4和6重量%）的影响在起始组合物中）对液相线和亚液相线相平衡的影响。主要关注的是铬尖晶石的溶解度和铬之间的熔体和结晶相的分配。在300 MPa和1100-1300 °C的温度区间内，在内部加热压力容器（IHPV）中进行了六个实验。氧化还原条件不受控制，H2O组分的热分解，随后氢通过容器壁扩散，导致运行产物的明显氧化。根据尖晶石-熔体平衡实验数据，用SPINMELT 2.0软件计算了实验中的有效氧值。根据计算，H2O添加在等温系列的实验增加fO 2由0.8-1.6对数单位的水平，在名义上干运行。总体而言，实验表明，H2O的添加抑制硅酸盐的结晶，使橄榄石-斜方辉石包镶平衡向更高的橄榄石稳定性移动（橄榄石在1175 °C下首次出现在含H2O的组合物中），并增加尖晶石固溶体中磁铁矿组分的比例。添加4 wt.%在1200 °C下将H2O添加到起始组合物中导致斜方辉石的完全熔融，这留下Cr-尖晶石作为唯一的液相线相。在1125 °C下等量的H2O导致斜长石、斜方辉石和单斜辉石的完全熔融，这仅留下橄榄石和尖晶石稳定，并将液体质量分数从标称干燥组合物中的0.62增加到0.9。这项研究的结果似乎支持这样的想法，铬铁矿层在布什维尔德复杂的临界区形成的硅酸盐累积的水化熔融事件。
Mafic–ultramafic layered rocks of the Lower and Critical Zones of the Bushveld Complex are believed to have formed from a parental magma usually labelled B1 with SiO2content at 55 wt.%, MgO at about 12 wt.% and Cr2O3concentration at 0.15 wt.%. Previous experimental study at 300 MPa and nominally dry conditions showed that this composition had orthopyroxene on liquidus between 1250 and 1300 °C, and the mineral was joined by plagioclase and clinopyroxene at and below 1166 °C. The objective of this study was to investigate the effects of variable additions of H2O (2, 4 and 6 wt.% in starting compositions) on liquidus and sub-liquidus phase equilibria. Main attention was given to the solubility of Cr-spinel and Cr distribution between melt and crystalline phases. Six experiments were carried out in the internally heated pressure vessel (IHPV) at 300 MPa and in the temperature interval 1100–1300 °C. Redox conditions were not controlled and thermal dissociation of the H2O component followed by hydrogen diffusion through container walls resulted in a noticeable oxidation of run products. The effective values offO2in experiments were calculated using SPINMELT 2.0 software bases on the regression of experimental data on the spinel-melt equilibrium. According to the calculations, H2O additions in isothermal series of experiments increasedfO2by 0.8–1.6 log-units from the level in a nominally dry run. Overall, the experiments showed that H2O additions suppressed crystallization of silicates, shifted olivine-orthopyroxene peritectic equilibrium towards higher olivine stability (olivine first appears in H2O-bearing compositions at 1175 °C) and increased the proportion of magnetite component in spinel solid solution. The addition of 4 wt.% H2O to the starting composition at 1200 °C resulted in complete melting of orthopyroxene, which left Cr-spinel as the only liquidus phase. Equal amount of H2O at 1125 °C leads to complete melting of plagioclase, orthopyroxene and clinopyroxene, which leaves only olivine and spinel stable and increases the liquid mass fraction from 0.62 in the nominally dry compositions to 0.9. The results of this study appear to support the idea that chromitite layers in the Critical Zone of the Bushveld Complex were formed by episodes of hydration melting of silicate cumulates.
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DOI：
10.1007/978-94-017-9652-1_1
发表时间：
2015
期刊：
--
影响因子：
--
作者：
J. Scoates;C. Wall
通讯作者：
J. Scoates;C. Wall
影响因子：
4.6
作者：
Antony, P. M. A.;Kondratyeva, O.;Diederich, N. J.
通讯作者：
Diederich, N. J.
层状侵入体中的挥发性流体超压和坑洞的形成
影响因子：
1.2
作者：
A. Boudreau
通讯作者：
A. Boudreau
Bushveld 和 Rum 层状侵入体中的交代铬铁矿矿层
影响因子：
4.5
作者：
Edmond A. Mathez;R. Kinzler
通讯作者：
R. Kinzler
影响因子：
3.9
作者：
I. Veksler;D. Reid;P. Dulski;J. Keiding;Mathias Schannor;L. Hecht;R. Trumbull
通讯作者：
I. Veksler;D. Reid;P. Dulski;J. Keiding;Mathias Schannor;L. Hecht;R. Trumbull