Research On The Scale And Flux Variation Of The Late-stage Basalts In Mare Imbrium Based On Remote Sensing Data

The basaltic volcanism is one of the most important geologic processes of the Moon.Lunar volcanism produced plenty lunar basalts on the Moon,whose volume reflects the size and the degree of partial melting of the source region.Research on the scale of late-stage basalts of the Mare Imbrium helps us to analyze the source of lunar volcanism and its eruption style,further can be used to deduce the tectonic activities of the Moon in the past.The Eratosthenian volcanism deposited large scale of basalts in Mare Imbrium,which has never been sampled before.But these basalts are believed to have unique compositions and spectra,which are quite different from other lunar basalts.Based on whether there are apparent lava fronts,this paper divided the late-stage basalts in Mare Imbrium into two groups:Upper Eratosthenian basalts(UEm)and Lower Eratosthenian basalts(LEm).Using a variety of remote sensing data and different methods(topographic profile and crater excavation method),this paper studied the thickness,distribution and flux variation of these basalts in Mare Imbrium.This paper mapped the thickness and estimated the volume of late-stage basalts.Besides,this paper acquired the areal flux variation of several UEm basalts.The results can be listed as follows.(1)The results show that the UEm is 13-33 m thick with several layers of individual lava(7-15 m)inside.This means that at the very last phase of Eratosthenian Period,Mare Imbrium experienced many phases of small eruption.Thus we deduce that lunar volcanism in Mare Imbrium during late stage was still quite active.(2)The estimated thickness of LEm is 14.49-43.61 m,with a trend that thickness reducing from north to south.It is believed to be connected with the different source of late-stage basalts in Mare Imbrium.Besides,the measured thickness(?40 m)of late-stage basalts around Chang'E-3 landing site is quite close to the result(?42 m)acquired by Ground-penetrating radar carried on Chang'E-3.(3)Adding the volume of exposed UEm basalts(?539.38 km3),the volume of exposed LEm basalts(?6055 km3)and the volume of young basalts underlying UEm(?556.2 km3)together,the total volume of the late-stage basalts in Mare Imbrium is?7150 km3.It's far lower than that of the Schaber's estimation(?4×104 km3).The volume of the exposed UEm basalts accounts for only about 1/10 of the volume of the exposed LEm basalts,which means that basaltic eruption decreases with time during the Eratosthenian Period in Mare Imbrium.(4)Besides,we estimated the decrease of the areal flux of Em5-Em7:Em5(249.56 km2/Ma),Em6(39.49 km2/Ma)and Em7(46.89 km2/Ma).These results indicate that the basaltic volcanism receded with time during the Eratosthenian Period.