雨海地区晚雨海世—爱拉托逊纪月海玄武岩充填过程研究

The Filling Process of Mare Basalts from Late Imbrian to Eratosthenian in Mare Imbrium

月海玄武岩是月球四大岩类之一,主要充填于月球大型撞击盆地之中。月海玄武岩充填过程的研究,对于了解撞击盆地充填过程和月海玄武岩充填规律及活动规模,揭示月球的热演化历史具有重要意义。本文综合利用嫦娥一号LAM数据、CCD影像数据和Clementine UVVIS数据,对雨海地区的地形地貌、岩石化学组成进行了提取和分析,对雨海地区月海玄武岩进行了单元划分,并运用撞击坑尺寸-频率分布法对各月海玄武岩单元进行了表面年龄的估算。结果表明,雨海地区月海玄武岩随着时代变新钛和铁元素更加富集,总体上从晚雨海世至爱拉托逊纪由低钛低铁玄武岩向高钛高铁方向演化;月海玄武岩充填活动具有多期次性,每期月海玄武岩的充填流动大体上保持由南向北方向,并且活动规模逐步减小,相对年轻月海玄武岩对早期月海玄武岩的覆盖范围不断减小。正是这种玄武岩流动与覆盖关系和充填过程造成了雨海地区从南向北地势的逐渐降低,以及较老月海玄武岩在较北部地区出露。最后,根据雨海地区月海玄武岩单元在地形地貌、岩石化学组成与表面年龄上的相关性,我们提出雨海地区月海玄武岩经历了多期次逐层填充过程,且每期由南向北流动、规模逐步减小。

Mare basalts, one of the rock types in the Moon, occur mainly in the large impact basins. The fillingprocess of mare basalts including the flowing patterns and the scales has implications for understanding the evolution of the impact basin and thermal evolutional history of the moon. In this paper, the charateristics of topography and chemical compositions of rocks in Mare Imbrium were extracted using combination of CE-1 LAM data, CCD data and Clementine UVVIS data. Then mare basaltic units were defined, and surface ages of the defined basaltic units were evaluated using the Crater Size-Defrequency Distribution measurements. Relationships among topography, chemical compositions and surface ages of mare basaltic units in Mare Imbrium indicate that the younger in surface ages of the basaltic units, the more enrichment in Titanium and Iron, exactly from low Titanium, low Iron in Late Imbrium to high Titanium, high Iron in Eratosthenian. The filling process is multi-staged with northward stepwise almost in every stage in Mare Imbrium. With the scales of mare basalts minishing gradually, the extent of relatively younger basaltic unit covering older one becomes smaller and smaller. It is the relationship between filling process and coverage that results in topographic changes and distribution of the surface ages of basaltic units. Therefore, a mode of multi-staged with northward stepwise almost in every stage and gradual minishing scales was suggested.