[Objective]With the successful landing of Tianwen-1 in Utopia Plain,China's Mars exploration has en-tered a new historical stage.At present,many scholars have studied the history of water activities and sedimentary system of Mars through remote sensing,spectral imaging,satellite images and other technologies.However,scholars at home and abroad have not reached a unified consensus on the research of quantitative parameters such as the scale,discharge and precipitation of surface water on Mars.Compared with the alluvial fan on Mars,the fluvial fan has a larger area and a more stable channel supply,which makes it easier to observe than the alluvial fan.Moreover,the relative stability of the sedimentary process makes it possible to study the history of water activities and surface water runoff through fluvial fan.[Methods]According to the comparability between Mars and the earth,using the sat-ellite images of Google,through the identification and all-round measurement of fluvial fans around the world,a data set integrating 345 modern fluvial fan deposits of the earth is established.Based on the above identification and analy-sis,the earth's fluvial fans are unevenly distributed in the world,showing the characteristics of regional division and latitude zoning.Central Asia and western China are the main development areas of fluvial fans,and 30°～50°N is the main development zone of fluvial fans.At the same time,the external shape of the earth's fluvial fan is mainly con-trolled by climate and local topography,and the direct control factors that affect the development area of fluvial fan include latitude,slope,catchment area,annual runoff,piedmont distance,etc.Based on the above factor analysis,through the neural network training of 345 fluvial fan samples,a nonlinear neural network prediction model of fan body is established.Combined with the fan characteristics of the data set,the Martian river fan is identified,and the surface water runoff during the development period of the Martian river fan is obtained by using the neural network prediction model,so as to infer the water source of Mars.[Results]The results show that a typical fluvial fan deposit with an area of about 84.35 km2 was identified near Holden crater in the southern highland of Mars.There are two wa-tersheds in the upper reaches of the fluvial fan,which correspond to two catchment area,with the area of the second catchment area being 698.4 km2 and the area of the first catchment area being 5 262.3 km2.According to the classifi-cation of the earth's fluvial fan,Holden fluvial fan has developed into three stages,which belongs to unrestricted flu-vial fan.Compared with the Andkhoy fluvial fan in Afghanistan,the only significant difference is that the Holden flu-vial fan has an inverted topography,that is,the ancient river channel undergoes diagenesis such as cementation and compaction under the action of water flow,thus forming an erosion-resistant surface.By projecting the correlation be-tween the development area of Mars Holden fan and four parameters,such as latitude,slope,catchment area and piedmont distance,on the parameter relationship diagram of the earth's unrestricted fan,most of the parameter points are located in the normal range,which indicates that the relationship between each parameter and area of Mars Holden fluvial fan is roughly the same as that of the earth's fluvial fan.However,the relationship between the area of the first catchment area and the fan area is obviously beyond the scope of the earth fluvial fan,so it can be inferred that the Holden fluvial fan of Mars is mainly controlled by the secondary catchment area,and there is a sediment un-loading area inside the first catchment area.It is worth noting that,compared with the Earth,although the latitude controls the area within the scope of the earth's fluvial fan,the area of the Holden fluvial fan on Mars is smaller at the same latitude.Based on the neural network prediction model of the unrestricted fluvial fan area of the earth,by input-ting the area of Holden fluvial fan on Mars and other factors,the annual average surface water runoff required for the formation of this fan can be predicted in a reverse way to be 1.882 8×106 m3.[Conclusions]According to the compara-tive analysis with the runoff of the earth fluvial fan,it is found that the runoff in this area of Mars is not composed of a single precipitation,and it is speculated that it is from a variety of sources of precipitation and meltwater from snow-capped mountains(glaciers).Therefore,it is speculated that the circulation of atmospheric water and surface water on Mars occurred during the late Noah period to the early Western period due to the brief warming of the climate.In many piedmont areas of the southern highlands,surface runoff produced by precipitation and melting water of snow-capped mountains(glaciers)carries eroded sediments from local highlands into adjacent depressions.Due to the sud-den flat terrain,the river channel diverges from the apex to the downstream,and a large number of sediments begin to unload,which promotes the formation of Martian fluvial fan deposits.
维普
万方数据
