Chemical and Textural Re-equilibration in the UG2 Chromitite Layer of the Bushveld Complex, South Africa
Chemical and Textural Re-equilibration in the UG2 Chromitite Layer of the Bushveld Complex, South Africa
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南非 Bushveld 杂岩体 UG2 铬铁矿层的化学和结构再平衡
DOI：
10.1093/petrology/egy058
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发表时间：
2018
影响因子：
3.9
通讯作者：
Trumbull R.B.
中科院分区：
文献类型：
--
作者：
Veksler I.V;Sedunova A.P;Darin A.V;Anosova M.O;Reid D.L;Kaufmann F;Hecht L;Trumbull R.B.
矿物化学和全岩成分的变化进行了详细的研究，在毫米到厘米的间隔，在两个垂直钻芯剖面通过含铂的UG 2铬铁矿层在西部和东部肢体的布什维尔德复杂，南非。分析方法包括电子探针和LA-ICP-MS分析的主要造岩矿物，斜方辉石，斜长石和间隙单斜辉石。一个配置文件还研究了同步辐射源XRF。统计分析的晶体粒度分布的铬铁矿也进行了不同层次的铬铁矿层和相邻的硅酸盐岩石。研究结果为UG 2层和接触带硅酸盐岩中晚期岩浆化学和结构的再平衡提供了新的证据。铬铁矿的晶体尺寸分布意味着该矿物在主要铬铁矿层内的广泛粗化，这消除了主要沉积特征的任何纹理证据，如晶体的补给或机械分选，如果这些特征最初存在的话。铬铁矿中的矿物成分不同于那些在邻近的硅酸盐岩石，在一般协议的化学再平衡的预测与演变，残留的熔体（被困的液体移位效应）。详细地说，地球化学数据意味着，然而，传统的被困的液体转移模型有缺点，由于物质运输的影响，由化学梯度之间的模态对比层的晶体糊状物进行再平衡反应。在这种梯度的存在下，选择性的开放系统的条件下，碱金属和氢，因为它们在硅酸盐熔体中的较高的扩散速率可能会举行。间隙熔体中组分的不同流动性也可以通过使矿物在一层中结晶并在另一层中溶解来锐化原始模态分层。详细的微量元素配置文件同步加速器X射线荧光光谱显示不均匀的垂直分布的不相容元素，这意味着渗透性的铬铁矿层可能是显着的，即使在最新阶段的间隙结晶。
Variations of mineral chemistry and whole-rock compositions were studied in detail, at millimetre to centimetre intervals, in two vertical drill core profiles through the platiniferous UG2 chromitite layer in the western and eastern limbs of the Bushveld Complex, South Africa. Analytical methods included electron microprobe and LA-ICP-MS analyses of the main rock-forming minerals, orthopyroxene, plagioclase and interstitial clinopyroxene. One profile was also studied by synchrotron-source XRF. Statistical analysis of crystal size distribution of chromite was also performed at different levels in the chromitite layer and in adjacent silicate rocks. The results provide new evidence for chemical and textural late magmatic re-equilibration in the UG2 layer and in the silicate rocks at the contact zones. The chromite crystal size distributions imply extensive coarsening of that mineral within the main chromitite seam, which has erased any textural evidence of primary deposition features such as recharge or mechanical sorting of crystals, if those features originally existed. The mineral compositions in chromitite differ from those in adjacent silicate rocks, in general agreement with predictions of chemical re-equilibration with evolved, residual melt (the trapped liquid shift effect). In detail, the geochemical data imply, however, that the conventional trapped liquid shift model has shortcomings, due to the effects of material transport driven by chemical gradients between modally contrasting layers of crystal mush undergoing re-equilibration reactions. In the presence of such gradients, selective open-system conditions may hold for alkalis and hydrogen because of their higher diffusion rates in silicate melts. Differential mobility of components in the interstitial melt can also sharpen the original modal layering by causing minerals to crystallise in one layer and dissolve in another. Detailed trace element profiles by synchrotron XRF reveal an uneven vertical distribution of incompatible elements which implies that the permeability of the chromitite layer may have been significant, even at the latest stages of interstitial crystallization.
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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
Bushveld 杂岩体 UG-2 铬铁矿层中亲铜元素和铂族元素的分布
影响因子：
5.8
作者：
S. Hiemstra
通讯作者：
S. Hiemstra
Bushveld 杂岩体 UG2 铬铁矿层铂族元素含量和矿物学的横向变化
影响因子：
1.8
作者：
C. Penberthy;R. Merkle
通讯作者：
R. Merkle
DOI：
--
发表时间：
1964
期刊：
影响因子：
--
作者：
C. Smith
通讯作者：
C. Smith
南非布什维尔德杂岩体 UG2 黑云岩及其层状伟晶岩的蚀变和交代作用——特征、时间和起源。
DOI：
--
发表时间：
2009
期刊：
影响因子：
--
作者：
R. J. Voordouw;N. Beukes
通讯作者：
N. Beukes