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首页> 外文期刊>Contributions to Mineralogy and Petrology >Trapped intercumulus liquid in the Main Zone of the eastern Bushveld Complex, South Africa
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Trapped intercumulus liquid in the Main Zone of the eastern Bushveld Complex, South Africa

机译：南非东部布什维尔德综合体主区的积聚的积水

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Lateral variations in the amount of trapped intercumulus liquid in the Main Zone of the eastern Bushveld Complex are constrained by new Sr-isotopic, whole-rock and mineralogical data from three profiles that are separated laterally by ca.100 km and represent thicknesses of 551-1,127 m of Main Zone gabbronorites below the Pyroxenite Marker. An analysis of the An-contents (100 X Ca/(Ca + Na)) of plagioclase cores within the Thornhill (north), Roossenekal and Stoffberg (south) profiles show similar systematic, up-section variations from An_(66) to An_(59). In contrast, both the An-contents of bulk plagioclase separates and the Mg-numbers (100 X Mg/(Mg + Fe_T)) of orthopyroxenes show pronounced lateral variations from Thornhill (An_(67-61); Mg#_(67-61)), through Roossenekal (An_(64-58); Mg#_(64-55)) to Stoffberg (An_(59-55); Mg#_(59-50)). These mineralogical variations are interpreted to be the result of reaction between cumulus minerals and an increasing amount of trapped liquid from north to south. Modelling of the trapped liquid shift of orthopyroxene compositions suggests that the amount of trapped liquid in the cumulates increased from near 0 percent at Thornhill, through 10-30 percent at Roossenekal to 30-45 percent at Stoffberg. A two- to eightfold southward increase in whole-rock concentrations of P, Ti, Y, Zr and Ba is consistent with the trapped liquid model. However, the 14-fold increase in Rb from Thornhill to Stoffberg is too great to be accounted for by trapped liquid alone, but can be explained by local assimilation of partial melts of the country rock. Constant initial ~(87)Sr/~(86)Sr isotopic ratios of Main Zone plagioclase separates (0.7081-0.7085) in all the three profiles do not preclude assimilation of adjacent basaltic to rhyolitic country rock with initial ratios between 0.6924-0.7096. The southward increase in the amount of trapped liquid is ascribed to an increased cooling rate by enhanced heat loss and partial assimilation of country rock xenoliths in the distal cumulate sequence at Stoffberg.
机译：东部布什维尔德综合体主要地带的积聚的积屑间液体的横向变化受到新的Sr同位素，全岩石和矿物学数据的约束，这些数据来自横向分布约100 km的三个剖面，代表了551-在辉石岩标记下方的1,127 m主区辉长岩。对Thornhill（北部），Roossenekal和Stoffberg（南部）剖面中斜长石核心的An含量（100 X Ca /（Ca + Na））进行分析，显示出从An_（66）到An_相似的系统的向上剖面变化（59）。相比之下，块状斜长石的An含量分开，邻位邻苯二酚的Mg值（100 X Mg /（Mg + Fe_T））与Thornhill（An_（67-61）; Mg #_（67- 61）），通过Roossenekal（An_（64-58）; Mg #_（64-55））到Stoffberg（An_（59-55）; Mg #_（59-50））。这些矿物学上的变化被解释为是积云性矿物与从北向南越来越多的被困液体之间反应的结果。对邻位邻苯二酚组合物的截留液体迁移进行建模表明，堆积物中的截留液体量从Thornhill的近0％增加到Roossenekal的10％至30％到Stoffberg的30-45％。 P，Ti，Y，Zr和Ba的全岩浓度向南增加了2到8倍，这与捕集的液体模型一致。但是，从Thornhill到Stoffberg的Rb增加14倍，这太大了以至于不能仅通过捕获的液体来解释，但是可以用乡村岩石的部分熔体的局部同化来解释。在所有三个剖面中主区斜长石分离物的初始〜（87）Sr /〜（86）Sr同位素常数均恒定（0.7081-0.7085）并不排除初始比率在0.6924-0.7096之间的相邻玄武质与流纹岩性乡村岩石的同化。在斯托夫贝格，累积的热量向南增加的原因是，由于热量损失的增加以及乡村岩石异种岩在远端累积序列中的部分同化，冷却速度增加了。

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