| The tectonic evolution of the Moon is a significant part of the lunar evolution history and is one of the main goals of Chinese lunar exploration project.The study of the Moon has made rapid progress since the Apollo era when humans landed on the Moon.However,the understanding of the tectonic evolution of the Moon is still shallow and scattered now,and a comprehensive,systematic and scientific tectonic evolution system of the Moon has not been established.In today's world,the scientific value and strategic significance of the Moon are increasingly highlighted.The understanding of the tectonic evolution of the Moon not only helps to understand the formation and evolution of the Moon and its relationship with the Earth,but also has certain implications for the evolution of the solor system.In this study,a reasonable and scientific evolution model of the lunar tectonics is established by using the existing lunar remote sensing data and achievements to dig the geologic structure and tectonic information of the Moon and explain the geologic structure and tectonic phenomena.In order to determine the structure types of the Moon,the names of the existing lunar structures were systematically summarized based on the previous studies on the structures of the Moon.Meanwhile,the definitions,morphologic features and genetic mechanisms of various structures were analyzed in detail and classified.In view of the problems existing in the process of structure classification,the genesis and morphological characteristics of lunar structure were considered comprehensively.A total of 14 structure types including subsurface fault,surface fault,lunar graben,wrinkle ridge,sinuous rille,crater-floor fracture,lobate scarp,impact fracture,impact crater chain,volcanic vent,dome,mascon,impact crater and impact basin were determined,and the corresponding structure interpretation marks were established.Various structures of the Moon were identified from multi-source remote sensing data,and their distribution characteristics were analyzed.The regional distribution characteristics of wrinkle ridges,sinuous rilles,lunar grabens,crater-floor fractures,volcanic vents,domes and mascons are obvious,while the surface faults and lobate scarps show global distribution.Lunar subsurface fault is an important structure for studying the evolution and dynamic mechanism of stress field in early history of the Moon.The Bouguer gravity gradients were calculated based on the Gravity Recovery and Interior Laboratory gravity data of the Moon.On this basis,lunar subsurface faults were globally mapped.A total of 226 subsurface faults were identified.The basic parameters,including length and orientation were calculated.The total length of all the faults was 37137 km,and the mean length was 164 km.Statistical distribution of lunar subsurface faults ranged differently.The results showed that most of the faults are distributed in the low and middle latitudes,and there are more faults in the northern hemisphere than that in the southern hemisphere of the Moon.Furthermore,in the latitudinal zone the most faults are found where the largest concentration of mare occurs.The area with the largest distribution of faults is the western side of the Procellarum in meridional direction.The rose diagrams of the orientations of faults were drawn globally and at different latitudes and longitudes respectively.All subsurface faults showed a statistical NE-SW and NW-SE preferred orientations.The preferred orientation of faults had no obvious changes at different longitudes,however,it changed significantly at different latitudes.The middle and high latitudes of the southern and northern hemispheres had the same preferred orientations,namely NE-SW and NW-SE,S-W,while the low latitude's orientations were different,that is,NE-SW and NW-SE in the southern hemisphere and N-S in the northern hemisphere.To establish the structure classification system of the Moon based on dynamic mechanism,the stress sources of the internal and external dynamic geological actions and the structure types generated by different stresses during the geological evolution process of the Moon were analyzed.The internal dynamic geologic structures of the Moon include tidal stress structure(subsurface fault),thermal stress structure(volcanic vent,dome,mascon,sinuous rille,crater-floor fracture,lunar graben,wrinkle ridge,lobate scarp)and multi-stress structure(surface fault).Specifically,the thermal stress structure can be further divided into thermal expansion stress structure(volcanic vent,dome,mascon,crater-floor fracture),thermal erosion stress structure(sinuous rille),gravity sedimentation stress structure(lunar graben)and thermal contraction stress structure(wrinkle ridge,lobate scarp).The external dynamic geologic structure only includes impact stress structure(impact crater,impact basin,impact fracture,impact crater chain).The principles of lunar structure classification system,which take genesis and morphology as the leading factor and give consideration to the comprehensiveness of the structure,the extensibility and the operability of the structure classification system,were formulated.Under the guidance of the principles of lunar structure classification,the structure classification system of the Moon was established.The three structures of mare,terra and South Pole-Aitken basin is the current understanding of the lunar global tectonic framework.New interpretation of multi-source remote sensing data indicates that there are more individual tectonic units based on the ternary structures.By combining the typical characteristics of lunar geophysical field,geochemical composition,topography,and main tectonic landforms,which can be used to characterize the main structures of the lunar surface and deep,a comprehensive analysis aimed at exploring the regional differences,and studying the tectonic units of the Moon was performed.The results of the study suggest the existence of six tectonic units: the Northern Plain Tectonic Unit,the Giant Mare Tectonic Unit,the Highland Tectonic Unit,the Mare-Highland Transition Tectonic Unit,the Southern Mountain Tectonic Unit and the South Pole-Aitken Tectonic Unit.There are differences in the boundary of tectonic units identified based on the different data,which indicates that the boundary faults of different tectonic units have different dip directions and dip angles.The tectonic evolution model of the Moon was established by combining the evolution process of the lunar structures and the tectonic units,which was divided into five stages:(1)The solidification of the lunar crust dominated by internal dynamic geological action;(2)the formation of the large basins dominated by external dynamic geological action;(3)the flooding of the mare basalt dominated by internal dynamic geological action;(4)global contraction dominated by internal dynamic geological action;and(5)the stable period with equal emphasis on internal and external dynamic geological actions.Different stages of the geologic structure and tectonic evolution dominated by different dynamic geological actions,but also have different landmark geological events and formed unique structure types.In this study,the types of the lunar structures were determined by analyzing the characteristics of the existing structures.The tidal stress was considered to be the dominant stress in the early stages of the lunar geological evolution(4.5 to 4.2 billion years ago)according to the analysis of the stress source which formed the subsurface fault of the Moon.The classification system of lunar structures was established based on the dynamic geological actions.The dominant dynamic geological actions were different at different stages of the evolution of the Moon,and thus formed different tectonic units and structure types.The evolution model of the lunar tectonics in this study conforms to the evolution process of the lunar dynamics,and makes the characteristics of each stage of the lunar tectonic evolution clearer. |
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