南极-艾肯盆地溅射物建造识别及对月球早期演化的意义研究

The SPA (South Pole-Aitken) basin, formed at about 4.2–4.3 Ga, is the oldest and largest impact basin on the Moon. It is one of the inflection points in lunar evolution history and marks the transition from endogenic-dominated lunar magma ocean period to the stage when both endogenic and exogenic processes were equally important. The ejecta deposits formation of SPA basin represents the earliest lunar rock-stratigraphic unit originated from exogenic process, which makes it the role of a “Golden Spike” in newly proposed lunar time scale system. However, because of the post geologic processes, the ejecta deposits have been heavily degraded, and are destroyed or overlaid to a large degree by post impact ejecta, the SPA ejecta deposits have not been found at all. In previous study, we identified the Sternfeld-Das region at north of SPA basin showing SPA ejecta signal and has the conditions to be preserved from being entirely removed. On the base of previous results, this project will investigate the multiple-source image, topography, spectroscopy, gravity and radar data to obtain the information about the surface geology, tectonics and compositions, and subsurface structure and buried tectonics for the area of interest. By using of the results derived from datasets, priori knowledge about basin ejecta deposits, and ejecta thickness model, the geologic units of the investigation area will be carefully identified and mapped. While in the study of the data invertion results and geologic units, the ultimate goal is searching for and identifying the ejecta deposits of SPA basin. In addition, the geologic cross-section of target region will be made by synthetically analyzing the results of stratigraphic elements, topography variation, ejecta deposits thickness, subsurface structure. The ejecta deposits Formation of SPA basin will be identified and shown in the geologic map and cross-section, which can provide with support for revealing the early evolution history of the Moon and for the lunar time scale system.

约42–43亿年前形成的南极艾肯盆地（SPA）是月球上最大最古老的撞击盆地，是月球由以内动力地质作用为主的岩浆洋时期演化到内外动力地质作用并重的转折点，其溅射物建造是月球最古老的外动力成因岩石地层单元，是新提出的月球地质年代表的 “金钉子”。然而，撞击、挖掘、覆盖等后期地质作用致使SPA盆地溅射物受到严重改造，难以识别。研究发现，SPA北部的斯坦菲尔德-达斯区具有SPA溅射物信号且有被保留下来的条件。课题将对该区域通过形貌、光谱、重力场和雷达等多源遥感数据分析，得到研究区的表面地质特征、物质成分、次表层结构和隐伏构造等要素；结合典型盆地溅射物特征、分布模型等，识别地质单元并进行精细的地质填图，搜索并识别SPA溅射物；综合地层要素、地形、溅射物厚度、次表层结构等信息，创建研究区地质剖面，建立SPA盆地溅射物建造，为重建月球早期演化历史和地质年代划分提供参考和依据。

作为月球上最大最古老的撞击盆地，南极艾肯盆地（SPA）是月球动力学演化的转折点，标志着月球由以内动力地质作用为主的岩浆洋时期，演化到撞击作用和岩浆作用等内、外动力地质作用并重的转折点。SPA盆地的溅射物建造是月球最古老的外动力成因岩石地层单元，是新提出的“三宙六纪”月球地质年代表的 “金钉子”。本项目针对SPA盆地的地质背景和演化历史，结合撞击模拟的研究发现，聚焦SPA北部后期改造较弱的斯坦菲尔德-达斯区，通过形貌、光谱、成分等多源遥感数据分析，得到研究区的表面形貌特征、地质要素、物质成分等信息。在此基础上，结合典型盆地溅射物特征与分布模型等知识，识别了主要地质单元并建立了地质剖面图。通过分析带有SPA盆地挖掘出的月幔低钙辉石信号的矿物信息，以哥白尼纪达斯撞击坑为典型露头，建立了代表SPA盆地溅射物建造的岩石-地层单元——达斯建造。.达斯建造作为外动力地质作用形成的最早的地层单元，是“三宙六纪”月球地质年代表中艾肯纪的地层下限，在重建月球的演化历史和地层学研究中具有重要意义。通过本项目研究成果，进一步完善了新的月球地质年代表，为月球地质研究提供了重要的基础研究资料。未来对达斯建造的进一步探测和研究将为揭示SPA盆地的撞击过程和月球的早期演化提供重要信息，因此它也为将来月表着陆探测和采样返回提供了一个重要的目标区域。根据模型预测，SPA盆地溅射物覆盖了全月表，达斯建造作为地层“金钉子”为在月表其它区域研究早期外动力地质作用地层单元提供了关键信息。