Petrology,Mineralogy And Possible Source Regions Of Lunar Meteorites NWA 4884 And NWA 11460

Lunar meteorites are rocks found on Earth that were ejected from the Moon by impacts of asteroids/comets.The distinct chemical compositions are significantly different from Earth's rocks,directly reflecting the key evolution information of the lunar crust.The scientific studies of lunar rocks and soils returned by the Apollo and Luna missions provide a basis of ground truth for the physical and chemical properties of the lunar surface obtained by remote sensing data,which can acquire new knowledge of the evolution of lunar crust.However,these lunar samples were collected from a limited lunar surface(only 4.7%)on the nearside of the Moon.On the other hand,lunar meteorites represent random samples ejected from the Moon far away from previous sample-return sites.The unknown source regions,representative rock types and geochemical characteristics can make the lunar meteorite a very important source of lunar "ground truth" and provide more information for the rock diversity of lunar surface and the evolution of magma.This study focuses on lunar meteorites NWA 4884 and NWA 11460,using EPMA,SEM,LRS and micro-FTIR to study in detail the petrography,mineralogy,shock history,clast heritage,pairing relationships and possible source regions to provide deeper understanding for the evolution of lunar crust.NWA 4884 is classified as a mingled(FeO=11.59 wt.%,Al2O3=19.01 wt.%)lunar basalt-rich breccia,composed of major CPX(25.8 vol.%),OPX(16.6 vol.%),plagioclase(26.6 vol.%),maskelynite(8.1 vol.%),olivine(20.7 vol.%)and many accessory minerals ilmenite,quartz,tridymite etc.We identify a range of lunar lithologies including subophitic basaltic clast,coarse gabbroic clasts(OG1 and OG 2),long-shape pyroxenite,evolved clasts(quartz-bearing gabbro,mesostasis and QNI),anorthosite and various impact melt clasts(including crystalline impact melt,clast-bearing impact melt and impact glass).FTIR spectra of plagioclase grains and Raman spectra of quartz indicate that shock intensities imposed on the whole rock was heterogeneous and yield a range of shock pressure from 17.9 to 48.1 GPa.The overall petrographic and compositional similarity,we propose that QUE 94281 and Yamato 793274 are considered to be the most likely paired stones with NWA 4884.The bulk composition(FeO:9.7?13.0 wt.%,Th:1.1?1.2 ppm)with the lunar global FeO and Th data(0.5°/pixels)of GRS aboard LP show that possible source regions are located at the boundaries of Tsiokovsky impact basin(128.3°E,21.8°S),Mare Fecunditatis(53.3°E,20.8°S)and Mare Orientale(91.3°W,19.3°S).The model ages for three regions are 3.51 Ga,3.68 Ga and 3.45 Ga.NWA 11460 is classified as feldspathic breccia,mainly including CPX(3.8 vol.%),OPX(6.8 vol.%),plagioclase(61.6 vol.%),olivine(28.3 vol.%)and distorted pyroxene(0.3 vol.%).Lithic clasts include anorthosite gabbro,anorthosite troctolhte,feldspathic clasts(gabbro anorthosite,troctolite anorthosite.,anorthosite),mosaic breccia,breccia and a wide range of impact melt clasts.The average chemical composition(FeO:4.96±0.80 wt.%and Al2O3:26.71±1.38 wt.%)reveals that NWA 11460 originated from the lunar highlands.Lithic clasts are generally magnesium-rich characteristic and Mg number of a few clasts can be up to 91.The observation of two mosaic breccia clasts reveal that NWA 11460 has experienced more than twice diagenesis process.However,their parental rocks have different source sites.Parental rocks of C1 clast may be consistent with the ferrous anorthosite,while C17 clast is more magnesium-rich(Fo83 2)possibly corresponding to the magnesium-suite rocks.The pristine rocks of feldspathic clasts within NWA 11460 can be divided into three types:ferrous anorthosite,magnesium-suite rocks and magnesium anorthosite.However,magnesium anorthosite may simply present mixtures of Apollo ferroan anorthosite and Mg-suite rocks formedthrough such as impact gardening or a new unknown rock type.It also indirectly indicates the complex diagenesis history of NWA 11460.Mineralogically and petrographically,NWA 11460 has been subjected to moderate(<20 GPa)and heterogeneous shock pressure.The bulk composition(3.45?6.23 wt.%FeO,0.2?0.3 ppm Th),petrography and mineralogy of NWA 11460 suggest that this meteorite originates from the FHT-An(170.3?178.3°W,32.3?42.80°N)which it is classified as magnesian anorthosites.NWA 11460 belongs to NWA 8046 group and have great pairied relationship.