Classification Of 104 Meteorites Collected In Grove Mountains, Antarctica, And A Comparative Study Of Ca-, Al-rich Inclusions (CAIs) From Various Groups Of Chondrites

Ca-, Al-rich inclusions (CAIs) are the earliest assemblages of the solar nebula, and they contain information of early solar nebula. They are the probe of studying the origin and evolvement of early solar nebula, and are mainly found in carbonaceous chondrites. In this Ph.D. work, we first assigned the chemical-petrographic types of these new Antarctica meteorites; and then searched for CAIs in three of the new carbonaceous chondrites of CV, CO and CM groups. Lastly, we compare the CAIs among various groups of chondrites. The dissertation includes three main parts as follows: (1) Petrography, mineral chemistry of 104 new Antarctica meteorites and their classification; (2) Petrography, and mineral chemistry of Ca-, Al-rich inclusions from various groups of chondrites; (3) The comparative study of Ca-, Al-rich inclusions in various groups from chondrites and their cosmochemical significance.(1) 104 meteorites that collected in Grove Mountains region, Antarctica, by the 19^th Chinese Antarctic Research Expedition (CHINARE) were classified. The classification was base on the data of electron probe microanalyses, petrography and mineralogy. There are 4 carbonaceous chondrites, including 2 CM2, 1 CO3 and 1 CV3; 6 of them are unequilibrated ordinary chondrites, including 3 H3 and 3 L3; 92 meteorites are equilibrated ordinary chondrites, including 24 H-group (13 H4, 10 H5, 1 H6), 64 L-group (2 L4, 44 L5, 18 L6) and 4 LL-group (3 LL4, 1 LL5). Another 2 meteorites are stone-irons.～40 % meteorites experienced severe shock metamorphism, as indicated by the presences of shock-induced melt veins and pockets. These heavily shocked meteorites provide us with natural samples for study of high-pressure polymorphs of minerals.(2) The study of petrography, and mineral chemistry of Ca-, Al-rich inclusions from various groups of chondrites. We found a number of Ca-, Al-rich inclusions from four new GRV carbonaceous chondrites, and conducted a detailed petrography and mineral chemical study on them. CAIs from Allende(CV3), Murchison(CM2) and ordinary chondrites were also studied in order to compare with those from other chondrites. 1) Three CAIs and several amoeboid olivine aggregates (AOAs) were found in GRV 022459(CV3) chondrites, and all CAIs are Type-A inclusions. Another 62 CAIs were found in 4 polished thin sections of Allende (CV3) chondrites, including 40 Type As, 20 spinel-pyroxene-rich inclusions, a fragment of the spinel-hibonite-rich, and a hibonite-roch inclusion. 2) 13 CAIs were found in GRV 021579(CO3), including 4 Type A-like (Type A: melilite-spinel-rich CAI; Type A-like: alterred Type A), 8 spinel-pyroxene-rich inclusions and 1 spinel spherule. 3) 11 CAIs were found in GRV 020025 (CM2), including 6 Type A-like, 4 spinel-pyroxene-rich inclusions and 1 spinel spherule. And 17 CAIs were found in two sections of Murchison (CM2), including 9 Type A-like, 7 spinel-pyroxene-rich inclusions and 1 spinel-fassaite fragment. 4) 24 CAIs were found in 10 sections of ordinary chondrites, including 14 Type A-like, 9 spinel-pyroxene-rich inclusions and 1 fassaite fragment.Melilite was partially replaced by anorthite and hedenbergite in CAIs from GRV 022459 (CV3), and spinel in these CAIs is typical of FeO-rich. CAIs in Allende (CV3) and GRV 021579 (CO3) are alterred too, with most melilite replaced by fine-grained feldspathoids. Phyllosilicates are commonly found in the alteration assemblages of CAIs from Murchison and GRV 020025 CM2 chondrites. All CAIs in the ordinary chondrites are heavily altered, mainly consisting of fine-grained alteration assemblages without melilite.(3) The comparative study of Ca-, Al-rich inclusions from various groups of chondrites. CAIs from various groups of chondrites have the distinct alteration features. However the precursor assemblages of the most CAIs were Type A (or A-like) and spinel-pyroxene inclusions in all of these chondrites. Although theabundances of CAIs are greatly different among the meteorites, they have similar size distributions. Both Type A-like and spinel-pyroxene-rich inclusions are fluffy assemblages of concentrically zoned objects. The Type A-like inclusions are similar to fluffy Type A inclusions in other carbonaceous chondrites, except that almost all of melilites in the former are replaced by fine-alteration products. Simlar petrography and mineralogy of CAIs in various chemical groups of chondrites argue for a same reservoir of CAIs, consistent with previous studies of oxygen isotopes, Al-Mg isotopic systems and rare earth elements. There are distinct differences of the solar nebular conditions between the CAI reservoirs and accretion locations of various chondrites. During and/or after formation, CAIs were probably transported into different locations where various groups of chondrites accreted. The CAIs were altered due to changing of the nebular conditions. The significantly low abundances and much more fragments of CAIs in the ordinary and enstatite chondrites probably suggest a farther distance to the CAI reservoirs in comparison with carbonaceous chondrites.