The Ina irregular mare patch, an ∼2 3 km summit depression on an ancient ∼22 km diameter shield volcano, displays two very enigmatic units: (1) dozens of dark convex-upward mounds and (2) a very rough, optically immature floor unit with very sharp morphologic contacts between the two. Controversy surrounds the age interpretation of Ina; superposed impact crater size–frequency distributions (CSFDs) suggest an age of ∼33 Ma, consistent with the presence of sharp contacts between the units and indicating that mare volcanism continues to today. Models of the terminal stages of volcano summit pit crater activity suggest an age coincident with the building of the shield, ∼3.5 Ga; these models interpret the CSFD age and sharp contacts to be due to an extremely porous lava lake floor and extrusion and solidification of magmatic foams. We present robotic–human exploration mission concepts designed to resolve this critical issue for lunar thermal evolution.

Ina 不规则母马斑块是一座直径约 22 公里的古老盾状火山上约 2 3 公里的山顶洼地，显示出两个非常神秘的单元：(1) 数十个黑色的向上凸起的土丘和 (2) 一个非常粗糙、光学不成熟的地面两者之间具有非常尖锐的形态联系的单位。争议围绕着伊娜的年龄解释；叠加撞击坑大小频率分布 (CSFD) 表明年龄约为 33 Ma，与单元之间存在尖锐接触一致，并表明海马火山活动一直持续到今天。火山顶坑火山口活动的末期模型表明，其年龄与地盾的形成相吻合，约 3.5 Ga；这些模型将 CSFD 年龄和尖锐接触解释为由于极其多孔的熔岩湖底以及岩浆泡沫的挤压和凝固。