月球撞击玻璃的~（40）Ar/~（39）Ar年龄：Ar扩散率、化学成分、形状和尺寸之间的关系
40Ar/39Ar ages of lunar impact glasses: Relationships among Ar diffusivity, chemical composition, shape, and size
摘要：
月球撞击玻璃是月球撞击坑形成过程中产生的淬火熔融物，不仅有可能提供月球局部和区域地质的成分信息，而且还有可能提供随时间推移的撞击通量信息。本文介绍了73个新的40 Ar/39 Ar分析的结果，良好的特点，无夹杂物的月球撞击玻璃，并表明，尺寸，形状，化学成分，放射性40 Ar保留的分数，和宇宙射线暴露（CRE）年龄是重要的40 Ar/39 Ar调查这些样品。具体来说，对阿波罗14号、16号和17号着陆点的月球撞击玻璃的分析表明，放射性40 Ar的保留是月球风化层形成后热历史、大小和化学成分的强烈函数。根据本文提出的关系，月球撞击玻璃的成分和尺寸足以保留90%的放射性Ar在750 Ma的宇宙射线暴露在时间积分温度高达290 K已被确定，并可能产生可靠的40 Ar/39 Ar年龄的形成。此外，约50%的撞击玻璃球的形成年龄小于500 Ma，而约75%的月球撞击玻璃碎片和球体的形成年龄小于2000 Ma。观测到的月球撞击玻璃的年龄-频率分布可能反映了两个过程：（i）由于随年龄的增长而自发破碎，从而减少了保存;（ii）从最终月球轰击的尾端保存了一批残留的撞击玻璃，其40 Ar/39 Ar年龄高达3800 Ma。描述了一种用于选择和分析月球撞击玻璃的协议。
英文摘要：
Lunar impact glasses, quenched melts produced during cratering events on the Moon, have the potential to provide not only compositional information about both the local and regional geology of the Moon but also information about the impact flux over time. We present in this paper the results of 73 new 40Ar/39Ar analyses of well-characterized, inclusion-free lunar impact glasses and demonstrate that size, shape, chemical composition, fraction of radiogenic 40Ar retained, and cosmic ray exposure (CRE) ages are important for 40Ar/39Ar investigations of these samples. Specifically, analyses of lunar impact glasses from the Apollo 14, 16, and 17 landing sites indicate that retention of radiogenic 40Ar is a strong function of post-formation thermal history in the lunar regolith, size, and chemical composition. Based on the relationships presented in this paper, lunar impact glasses with compositions and sizes sufficient to have retained 90% of their radiogenic Ar during 750 Ma of cosmic ray exposure at time-integrated temperatures of up to 290 K have been identified and are likely to have yielded reliable 40Ar/39Ar ages of formation. Additionally, ~50% of the identified impact glass spheres have formation ages of <500 Ma, while ~75% of the identified lunar impact glass shards and spheres have ages of formation <2000 Ma. The observed age-frequency distribution of lunar impact glasses may reflect two processes: (i) diminished preservation due to spontaneous shattering with age; and (ii) preservation of a remnant population of impact glasses from the tail end of the terminal lunar bombardment having 40Ar/39Ar ages up to 3800 Ma. A protocol is described for selecting and analyzing lunar impact glasses.
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