Subdivision of petrologic type of unequilibrated ordinary chondrites from Antarctica

• Main Authors: Yun, Jiang, Weibiao, Hsu
• Format: Article in Journal/Newspaper
• Language: English
• Published: Polar Research Institute of China - PRIC 2009
• Subjects: Space; Antarctic; Advances in Polar Science; Antarc*; Antarctica; Polar Science
• Online Access: http://library.arcticportal.org/2380/; http://library.arcticportal.org/2380/1/A0090204.pdf

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; Crex solved 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.