Lunar meteorites are fragments of the Moon that escaped the gravity of the Moon following high-energy impacts by asteroids,subsequently fell to Earth.An inventory of 165 lunar meteorites has been developed since the discovery and identification of the first lunar meteorite,ALHA 81005,in 1979.Although the Apollo samples are much heavier in mass than lunar meteorites,the meteorites are still an important sample supplement for scientific research on the composition and history of the Moon.Apart from a small amount of unbrecciated crystalline rocks,the majority of lunar meteorites are breccias that can be classified into three groups:highland feldspathic breccia,mare basaltic breccia,and mingled(including fledspathic and basaltic clasts)breccia.The petrography of lunar rocks suggests that there are a series of rock types of anorthosite,basalt,gabbro,troctolite,norite and KREEP in the Moon.Although KREEP is rare in lunar rocks,KREEP components have been found in the increasing number of lunar meteorites.KREEP provides important information on lunar magmatic evolution,e.g.,the VHK KREEP clasts in SaU 169 may represent the pristine lunar magma(urKREEP).Six launching pairs of lunar meteorites have been proposed now,along with ten possible lunar launching sites.In addition,symplectite is often found in lunar basalts,which is a significant record of shock metamorphism on the lunar surface.Furthermore,isotopic ages and noble gases not only provide information on crystallization processes in lunar rocks and the formation of lunar crust,but also provide insight into shock events on the lunar surface.
Meteorites are the extraterrestrial rocks,which provide insights into the origin and evolution of the solar system.During the past half century,a great number of meteorites has been discovered on the Antarctic Ice Sheet,confirming that the Antarctica is the most important meteorite concentration area on the earth.Since the first four Antarctic meteorites were found in Grove Mountains in 1998,a total of 9834 meteorites have been collected by four subsequent expeditions.It opens a new field of meteorite study in China,and also accumulates a great deal of scientific samples for China.Recently,classification of Grove Mountains meteorites has been carried out for 6 years,and made following progresses:(1)2433 meteorites,which include many special meteorites,e.g.Martian meteorites,ureilites and carbonaceous chondrites,have been classified.(2)the Antarctic meteorite curation and the sample sharing system are set up preliminarily.(3)the classification procedure,the management of meteorite samples,and the application procedure for the Antarctic meteorites are completed after the systematic classification during these years.(4)young generation researchers on meteorite are trained through the cooperation of many universities and institutes on meteorite classification.
Ureilites are a common group of achondrites with a high abundance of carbon.They probably have a genetic relationship with chondrites,hence provide an insight into origin and evolution of terrestrial planets.A new meteorite-rich region,Grove Mountains(GRV),was found by the Chinese Antarctic Research Expedition,with discovery of 9834 meteorites.Of 2433 meteorites classified,9 ureilites have been identified.In this paper,we report petrography of 6 of these ureilites.Four ureilites contain graphite and exhibit triangle conjunction and common reduced margins of olivine.GRV 052382 probably experienced heavy shock metamorphism followed by fast cooling,as indicated by mosaic texture or fine-grained granular texture of olivine.GRV 022931 was highly reduced of these ureilites,with olivine as isolated grains in abundant carbonaceous matrix.All 9 ureilites are monomict,and are classified into subtype II(with medium FeO content,Fa15-18)and subtype I(with high FeO content,Fa>18)based on compositions of the cores of olivine.The diverse mineral compositions and petrography of these ureilites suggest that they are not paired and reveal a multi-event history of the parent body.Partial melting of the parent body produced carbon-rich magma,followed by crystallization of graphite and silicates.Later,graphite was partially inverted to diamond by shock events.Reburial of the shocked debris experienced various degree of thermal metamorphism.Finally,these rocks were excavated from the parent asteroid and ejected into Earth-cross orbit by another impact event.
