月球东海盆地综合解析与撞击初始条件的研究

Comprehensive analysis of the lunar Orientale Basin and research of the initial impact condition

东海是月球上最年轻的多环撞击盆地,关于其形成机制的研究很多,但成果大都基于正撞击的机制提出的,虽然有部分学者提出东海是斜撞击的,但缺乏具体撞击参数。本文通过多源数据融合,综合分析LRO影像数据、LOLA地形数据、M^3高光谱数据和IIM高光谱数据,对东海地区的地貌特征、物质成分进行了较为系统的解译,发现在东海中央熔融区存在一条与东海撞击方向垂直的中央隆起区域(中央隆起线),其也是中央熔融区粗糙部分与光滑部分的分界线,结合撞击坑成坑理论,认为其可能是撞击过程冲击波作用引起的堆叠作用形成的。同时利用GRAIL数据及对该地区的重力异常的成因进行了分析,认为异常是由于压强、温度及岩石粘度的改变引起局部莫霍面抬升和中央熔融物的形成而出现的,进而估算出熔融物占盆地内物质的25%,约为1.1×10~6km^3。同时,对GRAIL数据的剖面分析结果也支持了本文的斜撞击理论。最后,综合多方面的信息和撞击理论获取东海盆地构造分布图,并根据中央隆起线、溅射物及线性构造的分布特征等,提出东海盆地理论上是由一直径在50~100km的撞击体以10~30km/s的速度自东偏北约20°~30°方向以20°~30°的角度斜撞击月表而形成的。这可为研究更早期的月球撞击坑提供理论参考。

Orientale Basin is the youngest muhi-ring basin on the moon. Previously, there are a lot of researches about formation theories of Orientale Basin,but most of them are based on the vertical impact formation mechanisms. However, some scholars provide the image that Orientale Basin is an oblique impact, but there are no detail parameters. By comprehensively analyzing the LRO WAC image data, LOLA, M3 and IIM, we interpret the topographic feature and material compositions of the Orientale Basin. Then combining the formation theory of impact craters, we suggest that it has a central uplift ridge （central uplift line） in the melt zone, which divides the center into the smooth and rough parts. It is perpendicular to the impact trajectory of Orientale Basin and caused by the shock wave putting during the impact process. Then using the GRAIL data, we discuss the reasons of the region gravity anomalies of Oriental Basin, proposing it is the result of local Moho uplifting and the formation of the impact melt, which is caused by the change of pressure, temperature and viscosity of the rock. We got the volume of the melt, which is about 1.1 ~ 106km3 and 25% of the basin materials. Finally we merge the multi-source data together, mapping an Oriental Basin ejecta units map. Basing on the structures of ejecta units, the line structure, secondary craters, the central uplift line and formation theories of oblique impact, we propose that Orientale Basin is formed by a 50 - 100km diameter impactor oblique impacting the lunar at the velocity of 10 - 30km/s, with 20° to 30° impact horizontal sextant angle and east to northeast about 20 -30°NE-SW direction. This work can provide theoretical reference for the study more early lunar craters.