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首页> 外文期刊>Contributions to Mineralogy and Petrology >Sr and Pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the Bushveld Complex, South Africa: microdrilling and progressive leaching evidence for sub-liquidus contamination within a crystal mush
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Sr and Pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the Bushveld Complex, South Africa: microdrilling and progressive leaching evidence for sub-liquidus contamination within a crystal mush

机译：南非布什维尔德（Bushveld）复杂结构中斜长石和邻苯并二甲苯之间共存的Sr和Pb同位素不平衡：晶体糊中亚液相线污染的微钻和渐进浸出证据

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Progressive leaching of plagioclase for Sr isotopes and microdrilling for Sr and Pb isotopes from grains of plagioclase and orthopyroxene from the Critical Zone and the Lower Zone indicates that these minerals are not in isotopic equilibrium. Leaching suggests Critical Zone plagioclase either lost Rb or had a more radiogenic Sri rim relative to the core, whereas plagioclase from an Upper Zone sample is isotopically homogeneous for Sri. Microdrilling analyses of plagioclase from the Lower and Critical Zones consistently have a higher initial 87Sr/86Sr (Sri) and a less radiogenic modeled 238U/204Pb composition (μ2) than coexisting orthopyroxene. The range of calculated Sri for plagioclase and orthopyroxene is 0.70506–0.70662(34) and 0.70290–0.70654(36), respectively. The average difference in Sri between mineral pairs was 0.00095. The range of calculated μ2 for plagioclase and orthopyroxene is 9.42–10.30 (average 9.7) and 9.83–15.75 (average 10.1), respectively. The range of measured 208Pb/206Pb for plagioclase and orthopyroxene is 34.757–36.439(33) and 36.669–41.845(85), respectively. One orthopyroxenite without evidence for more than one population of crystal size distribution, nonetheless had Sri = 0.70654 (36) with calculated μ2 of 10.32 for larger grains as compared with Sri = 0.70290 (32) and calculated μ2 of 9.97 for smaller grain-size fractions. Isotopic results from this study demonstrate that whole-rock isotopic data may not provide the appropriate level of detail necessary to address some processes in the Bushveld Complex. However, systematic changes have the potential to elucidate the timing of contamination with regard to other processes (crystal aging, compaction-driven recrystallization, and mineral exsolution) occurring within a slowly cooled crystal–liquid–vapor mush system.
机译：从临界区和下部区的斜长石和邻苯二酚晶粒逐步浸出斜长石，获取Sr同位素，并微钻Sr和Pb同位素，表明这些矿物未达到同位素平衡。浸出表明临界区斜长石或失去了Rb或相对于核心具有更多的放射源Sr i 边缘，而上部区样品的斜长石酶在同位素上对Sr i 是同质的。下部和临界区斜长石的微钻分析始终具有较高的初始 87 Sr / 86 Sr（Sr i ）和放射源模型较少 238 U / 204 Pb组成（μ 2 ）比邻位邻苯二甲醚更常见斜长石和邻位邻苯二酚的Sr i 的计算范围分别为0.70506–0.70662（34）和0.70290–0.70654（36）。矿物对之间Sr i 的平均差为0.00095。斜长石和邻位吡咯的μ 2 计算范围分别为9.42–10.30（平均9.7）和9.83–15.75（平均10.1）。斜长石和邻位邻苯二酚的 208 Pb / 206 Pb的测量范围分别为34.757–36.439（33）和36.669–41.845（85）。一种没有证据表明存在多于一个晶体大小分布的正辉石，尽管如此，Sr i = 0.70654（36），与Sr相比，较大晶粒的μ 2 计算得出的10.32 i = 0.70290（32），对于较小粒度级分，计算得出的μ 2 为9.97。这项研究的同位素结果表明，全岩石同位素数据可能无法提供解决Bushveld复杂过程中某些过程所必需的适当细节水平。但是，系统变化有可能阐明在缓慢冷却的晶体-液体-蒸汽糊剂系统中发生的其他过程（晶体时效，压实驱动的重结晶和矿物析出）的污染时机。

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