标题： 40Ar/39Ar年龄的月球撞击玻璃：Ar扩散率、化学成分、形状和大小之间的关系 显示英文标题

标题： 40Ar/39Ar ages of lunar impact glasses: Relationships among Ar diffusivity, chemical composition, shape, and size

摘要： 月球撞击玻璃是在月球撞击事件中产生的淬火熔体，它们不仅有可能提供关于月球局部和区域地质的成分信息，还能提供随时间变化的撞击通量信息。 本文介绍了73个经过良好表征、不含包裹体的月球撞击玻璃的新40Ar/39Ar分析结果，并证明尺寸、形状、化学成分、放射性40Ar的保留比例以及宇宙射线暴露（CRE）年龄对于这些样品的40Ar/39Ar研究非常重要。 具体而言，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40Ar的保留是月壤中形成后的热历史、尺寸和化学成分的强函数。 根据本文提出的相互关系，已经识别出具有足够成分和尺寸的月球撞击玻璃，在750 Ma的宇宙射线暴露期间，其在最高290 K的时间积分温度下能够保留90%的放射性Ar，这些玻璃很可能提供了可靠的40Ar/39Ar形成年龄。 此外，所识别的撞击玻璃球体中有约50%的形成年龄小于500 Ma，而所识别的月球撞击玻璃碎片和球体中有约75%的形成年龄小于2000 Ma。 观测到的月球撞击玻璃年龄频率分布可能反映了两个过程：(i) 随着年龄增加，由于自发碎裂导致的保存减少；以及(ii) 保存了终端月球轰击末期剩余撞击玻璃种群，其40Ar/39Ar年龄可达3800 Ma。 本文描述了一种选择和分析月球撞击玻璃的协议。 显示英文摘要

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.