月球雨海地区玄武质岩浆充填活动期次的重新厘定及地质意义

雨海盆地是月球上研究程度最高的多环结构盆地,月球上古老的和年轻的玄武岩在盆地中均有分布,因此雨海是研究月海玄武岩岩浆活动的理想区域。为了更合理的厘定雨海地区的玄武质岩浆演化历史,本文主要结合岩石学、年代学等工作对本区玄武岩的充填期次进行重新划分。利用嫦娥一号IIM光谱数据进行岩石类型分布图编制,初步划分了5类不同钛含量的月海玄武岩;基于高分辨率100m LRO宽视角影像数据通过撞击坑尺寸-频率定年法(CSFD)对本区玄武岩单元模式年龄进行厘定,共划分35个玄武岩单元,发现本区在3.49~2.23Ga均有玄武质岩浆充填活动,具有多期次性。在建立不同类别玄武岩、形貌特征与模式年龄的对应关系基础上,将玄武岩充填划分为4个期次:极低钛玄武岩(3.49~3.20Ga)、低钛玄武岩(3.29~2.83Ga)、中钛玄武岩(3.13~2.52Ga)、(极)高钛玄武岩(2.92~2.23Ga)。本区地形地貌高程特征与不同表面年龄的玄武岩单元之间总体上呈现出一定的负相关性。因此在本区玄武质岩浆期次划分考虑上,不仅要考虑玄武岩的成分特征,更要考虑结合与玄武岩演化密切相关的年代学及形貌学特征,利用形貌、成分数据和年代学信息来共同约束玄武质岩浆期次划分及演化历史。

Redefinition and geological significance of periods of basaltic magma filling in lunar Mare Imbrium

Imbrium basin is the most studied multi-ring structure on the moon. The ancient and young basalts on the moon are all distributed here. Therefore, Imbrium is an ideal area for the research on filling periods of mare basalt magmatism. In order to determine the evolution history of basaltic magma more reasonably in Mare Imbrium, a main combination of petrology, chronology and other analysis are made in this paper, aiming to make a re-division with the filling stages of mare basalt of Mare Imbrium. By making use of the Chang'E-1 IIM spectral dataset to draw distribution diagram of the rock type in this area, 5 different titanium contents of mare basalts are initially divided. Besides, with the help of LRO image data of wide viewing angle with high resolution of 100m, impact crater size and frequency distribution measurements (CSFD) are used to re-determine the age of the mare basalt in this area and 35 basalt units are divided, It is found that 3.49~2.23Ga of the area has a filling activity of basaltic magma occurring in several stages. On the establishment of the relationship between different types of mare basalts, morphology and the model ages, this paper divides the basalt filling into four stages: very low titanium mare basalt (3.49~3.20Ga), low titanium mare basalt (3.29~2.83Ga), medium titanium mare basalt (3.13~2.52Ga), (very) high titanium mare basalt (2.92~2.23Ga). The topographic features of the terrain and the different surface ages of the basalt units are negatively correlated. Therefore, in consideration of the stage division of basaltic magma in this area, not only the composition of mare basalt should be considered, but also the characteristics of the chronology and morphology which are closely related to basalt evolution should be combined with. Only by making use of morphology, composition data and chronology information as a common constraint can determine the stage division and evolution history of the basaltic magma.