Geological Evolution Of Lunar Imbrium Region

The Mare Imbrium region is located in the northwest of the near side of the moon,central latitude and longitude of geographical coordinate of which is35°N,17°W.As the second largest mare on the moon,it is also the typical representative of mare in the three major tectonic units of the moon,It gathers here a wealth of production heat element on the moon,the old and young basalts on the moon are distributed here,and it is the second most exposed to basaltic rock on the moon after Oceanus Procellarum.This area has experienced many stages of magmatic,volcanic activities and the impact action,which is also an ideal area to study the basalt surface age,origin,activity scale,filling process/ time,composition evolution and the thernal evolution history of the moon.Because of lacking multi-source remote sensing data for deep fusion research,it is a debate on the the origin,formation,geological evolution research of Mare Imbrium region,and so on.Therefore,it is very necessary to study the geological evolution process of this area by using the lunar multi-source remote sensing data.This paper closely focuses on the main line of geological evolution as the research object in the Mare Imbrium region,high spatial resolution,high precision and multi-band lunar component data,topography data and gravity field and other multi-source remote sensing data of fusion methods are used,to expand on initial boundary recovery of multi-ring structures of Mare Imbrium Basin,information extraction and analysis of morphology feature,compilation of rock type distribution map,maria rock chronology,impact and magmatism of geological events,gravity field and deep structure and other geological events,which are studied detailedly respectively,The formation and geological evolution process of Mare Imbrium Basin region is understood with a new perspective.By using lunar LOLA laser elevation data,mountain shadow data and GRAIL free air gravity field and other multi-source data,the initial boundaries of Mare Imbrium Basin are determined.The results show that Imbrium basin is a three ring structure with the eccentric circle,the diameter measurement of three ring structure is 1500 km,1100km and665 km from the outside to the inside,Wherein the inner boundary of which is drawn based on the boundary of the mascon,the middle ring is mainly drawn from Montes AlpsSinus Iridum block of the boundary,the outer ring is drawn from the north shore of Mare Frigoris-Montes Apennine-Montes Caucasus-Montes Carpathian as the main boundary.By making use of the Chang'E-1 IIM reflectance spectral dataset fusion LP gamma-ray spectrometer of inversion of Th element content,it is divided into11 categories of rock types in this area based on previous research results on lunar rocks in this area.Wherein non-mare rock is divided two types of high rock and non-mare basalt,which are divided into 6 categories according to their sub-class standards.The highland rocks are divided into four categories,ferroan anorthosite,Mg-suite,Mg-spinel anorthosite and KREEP rock respectively.The non-mare basalts are divided into two categories, high alumina(Al)mare basalt and KREEP basalt respectively;mare rocks are divided into five categories,which are very low titanium,low titanium,middle titanium,high titanium and very high titanium basalt respectively,and the distribution map of the rock type is compiled in the Mare Imbrium region, as a whole,it is found that the overall evolution of the basalt composition in this area is the regularity of enrichment and evolution from(very) low titanium,low iron to(very) high titanium,high iron basalt direction.With the help of CE-2 image data combined with Clementine UVVIS of multi spectral data,impact crater size-frequency measurements(CSFD)are used to determine surface age of geological unit of basalt in this area,61 geological units of basalts are divided in all,the surface age range of which concentrates on 2.21 Ga ~ 3.76 Ga. the results show that mare magmatic activity in this area is more intense at 3.0Ga ~3.6Ga,then mare magmatism strength has an obvious downward trend at 2.2Ga ~3.0Ga.Through common constraint from the composition and geochronology features of basalts,this paper divides the basaltic magmatic activity into four filling stages:very low titanium mare basalt(3.18Ga~3.76 Ga,I:3.4Ga)-low titanium mare basalt(2.80Ga~3.32 Ga,?:3.0Ga)- medium titanium mare basalt(2.56Ga~3.16 Ga,?:2.7Ga)-(very)high titanium mare basalt(2.21Ga~2.64 Ga,?:2.4Ga).It has a certain correlation between the elevation,roughness characteristics and the basalt unit lithology and surface age of the area.There is a certain negative correlation between the roughness and different titanium contents of mare basalt; The different surface ages of basalt generally show a negative correlation with the elevation,lunar optical maturity of distribution characteristics in the area,and a positive correlation with the lunar surface roughness distribution,It provides the morphology and material composition of evidence for revealing late basaltic magma activities of evolution in the Mare Imbrium region.Based on the statistical analysis of the latest lunar crater database,it is found that this area has a total of 32 craters with chronological of attribute information.It has an exposure of different frequencies from the age of Nectarian to Copernican,From the northeast/northwest- southwest of Mare Imbrium region,the impact crater has the spatial distribution pattern of the gradual transition from the age of the early/late Imbrian to Eratothenian;crater frequency of Eratothenian to early Imbrian of geological period is much higher than that of Copernicus or Nectarian;In this paper,the time evolution series of the impact events experienced by Mare Imbrium region are preliminarily determined in different times,which are roughly as follows : Imbrium basin( 3.85Ga) —Cassini(3.80Ga~3.85Ga)—Sinus Iridum and Plato(3.76Ga~3.85Ga)—Archimedes(3.76Ga~3.80Ga)—Timocharis,Lambert and Euler(0.80Ga~3.16Ga)—Aristillus and Autolycus(0~0.80 Ga).Based on the interpretation of the bouguer gravity field data from GRAIL,this study finds that the mare plain area of the bouguer gravity anomaly value is generally relatively high compared to ring mountain domain of upland.The lunar topography elevation and bouguer gravity anomaly of the Mare Imbrium region have a negative correlation in the spatial distribution;through the analytical continuation results for the bouguer gravity anomaly on different upward continuation heights,the research shows that upward continuation of bouguer gravity anomaly value and the range gradually become a smaller trend with the increase of the upward continuation height(1km-100km),the range of its value decreases from 67 mGal ~ 577 mGal to 107 mGal ~ 526 mGal.and the gravity anomaly characteristics is gradually becoming more and more smooth.The continuation effect of the bouguer gravity anomaly obtained on the upward continuation height between20 km and 100 km is relatively good,the results should be able to reveal the characteristics of the gravity field in the deep structure of regional anomaly for Mare Imbrium area.Based on Euler deconvolution of deep structure feature of inversion result for this area,the research shows that there are two deep fault structures in different depths,tectonic movement properties,genetic mechanism and evolution process in the central Imbrium basin,namely :(1) fault structure of compressional thrust forms to be gradually inclined and extended to the outward within the 40 km depth of Imbrium basin,it forms in the late stage of the moon from paying equal attention to the two kinds of evolution process of internal and external dynamic of lunar geological processes,it provides a migration path for the different stages of the basaltic magma intrusion,eruption and overflow to the lunar surface;(2)the fault structure forms to be gradually inclined and extended to the inward below the 40 km depth of Imbrium basin,it forms in the early stage of the moon from the main evolution process of the internal dynamic of lunar geological processes,it provides a channel for the generation,differentiation and migration of deep magma in the early stage of the moon.Based on the establishment of longitudinal profile of deep faults in this area,it provides an evidence for revealing the tectonic geological of evolution process and the determination of major lunar geological events in the Mare Imbrium area.Based on the main traditional recognition of faults on the plane contour grid chart of bouguer gravity anomaly,in combination with the euler inversion result of the analytic signal,which identify and divide the deep fault structures in this area,a total of 30 tectonic faults are deduced and divided in this paper,its formation mechanism should be related closely to the large impact event of Mare Imbrium.Based on the establishment and classification of the horizontal bouguer gravity profile of deep fault structure in the Mare Imbrium,it also provides an important evidence for revealing the larges-scale impact role and other lunar geological events,even the process of geological evolution in the Mare Imbrium region.Combined with the understanding of the whole geological evolution of the moon,according to the evolution process of geological dynamics of the moon,In this paper,the history of geological evolution in the Mare Imbrium area is mainly divided into three stages:(1)Large pre-Imbrium magmatism of event stage of deep magma ocean generation,differentiation and evolution in the early moon,from the main evolution of the internal dynamic of lunar geological process,the time span of which is 3.85 Ga ~4.60Ga;(2)Impact stage of geologic event of the Imbrium basin and evolution stage of the mare magmatism of basaltic mare magma eruption,filling and overflow,from payingequal attention to the evolutions of internal and external dynamic of lunar geological processes,and the time span is 2.21Ga~3.85Ga;(3)Small impact event of evolution stage of post-Imbrium period,from the main evolution of the external dynamic of lunar geological process,and the time span is 0~2.21 Ga.Therefore,the Mare Imbrium area is formed by the interaction of the magma and the impact geologic event in different lunar geochronology.It provides an important reference for revealing the origin and geological evolution process of the entire moon.