We report results of petrologic and mineralogical studies of 25 unequilibrated ordinary chondrites(19 Chinese Antarctic meteorites)using electron microprobe,scanning electron microscopy(SEM)and energy-dispersive X-ray spectrometry(EDS)techniques.With increasing degree of thermal metamorphism,chemical zoning of olivine was erased;plessite was transformed into intergrowths of coarser-grained kamacite and Ni-rich metal;Cr exsolved from ferroan olivine,produced needle-like crystals and coarsened into equant chromite grains;and feldspar crystallized during devitrification of glass and recrystallization of matrix.These features can help to identify different metamorphic grades.Based on the scheme by Sears et al(1982),we subdivided type 3 Chinese Antarctic ordinary chondrites into petrologic type 3.3 to 4(3 type 3.3,3 type 3.4,1 type 3.5,2 type 3.6,2 type 3.7,5 type 3.8,3 type 4).This classification scheme is a quite effective way to subdivide Antarctic meteorites.Additionally,we propose to revise the chemical groups of GRV 020032 and GRV 020104 to L and H,respectively.
Miller Range (MIL) 05035 and LaPaz Icefield (LAP) 02224 are unbrecciated lunar basalt meteorites. In this report, we studied their petrography and mineralogy and made in situ uranogenic Pb/Pb dating of Zr-rich minerals. Petrography and mineralogy of these two lunar meteorites are consistent with previous investigations. The zirconolite Pb/Pb age of MIL 05035 is 3851±8 Ma (2σ), in excellent agreement with previous reports. This age suggests that MIL 05035 could be paired with Asuka 881757, a low-Ti mare basalt meteorite. The magmatic event related to MIL 05035 was probably due to the late heavy impact bom- bardment on the moon around 3.9 Ga. One baddeleyite grain in LAP 02224 shows a large variation of Pb/Pb age, from 3109±29 to 3547±21 Ma (2σ), much older than the whole-rock age of the same meteorite (~3.02±0.03 Ga). The other baddeleyite grain in LAP 02224 has an age of 3005±17 Ma (2σ). The result indicates that the minimum crystallization age of LAP 02224 is ~3.55 Ga and the younger ages could reflect late thermal disturbance on U-Pb system.
