Lunar highland meteorite Dhofar 026 and Apollo sample 15418: Two strongly shocked, partially melted, granulitic breccias
Lunar highland meteorite Dhofar 026 and Apollo sample 15418: Two strongly shocked, partially melted, granulitic breccias
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DOI：
10.1111/j.1945-5100.2004.tb00120.x
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发表时间：
2004-09
影响因子：
2.2
通讯作者：
B. Cohen;O. James;L. Taylor;M. Nazarov;L. Barsukova
中科院分区：
文献类型：
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作者：
B. Cohen;O. James;L. Taylor;M. Nazarov;L. Barsukova
摘要：对月球陨石Dhofar 026的研究，以及与阿波罗样品15418的比较表明，Dhofar 026是一个强烈冲击的麻粒角砾岩（或几乎完全由麻粒角砾岩碎屑组成的破碎角砾岩），经历了相当大的冲击后加热，可能是由于热量从外部扩散到岩石中，更热的来源。冲击波将斜长石转变为镁铝榴石，表明冲击压力在30 - 45 GPa之间。冲击后的加热使岩石的温度升高到约1200 °C;结果，镁铝榴石失透，并发生了广泛的部分熔融。熔化集中在辉石富集区;所有辉石熔化。随着岩石冷却，部分熔体结晶成细粒亚蛇绿-嵌晶结构。样本15418是一个强烈冲击的麻粒角砾岩，具有类似的历史，但这一历史的证据比Dhofar 026保存得更好。Dhofar 026以前被解释为撞击熔融角砾岩的事实强调了详细的岩相学研究在解释具有复杂纹理的月球岩石中的重要性。在过去的研究中，“冲击熔融”这个名称只适用于岩石，其中的熔融部分是由冲击诱导的完全熔融形成的。然而，最近，这个名字也被应用于含有熔融物的岩石，这些熔融物是通过传导热传递加热岩石而形成的，假设撞击是热量的最终来源。我们强烈建议将“撞击熔融物”这一名称仅限于大部分熔融物是由冲击诱导熔融形成的岩石，以避免因将同一名称用于不同过程熔融的岩石而造成混淆。
Abstract— Studies of lunar meteorite Dhofar 026, and comparison to Apollo sample 15418, indicate that Dhofar 026 is a strongly shocked granulitic breccia (or a fragmental breccia consisting almost entirely of granulitic breccia clasts) that experienced considerable post‐shock heating, probably as a result of diffusion of heat into the rock from an external, hotter source. The shock converted plagioclase to maskelynite, indicating that the shock pressure was between 30 and 45 GPa. The post‐shock heating raised the rock's temperature to about 1200 °C; as a result, the maskelynite devitrified, and extensive partial melting took place. The melting was concentrated in pyroxene‐rich areas; all pyroxene melted. As the rock cooled, the partial melts crystallized with fine‐grained, subophitic‐poikilitic textures. Sample 15418 is a strongly shocked granulitic breccia that had a similar history, but evidence for this history is better preserved than in Dhofar 026. The fact that Dhofar 026 was previously interpreted as an impact melt breccia underscores the importance of detailed petrographic study in interpretation of lunar rocks that have complex textures. The name “impact melt” has, in past studies, been applied only to rocks in which the melt fraction formed by shock‐induced total fusion. Recently, however, this name has also been applied to rocks containing melt formed by heating of the rocks by conductive heat transfer, assuming that impact is the ultimate source of the heat. We urge that the name “impact melt” be restricted to rocks in which the bulk of the melt formed by shock‐induced fusion to avoid confusion engendered by applying the same name to rocks melted by different processes.