南极普通球粒陨石风化等级的重新厘定

The reclassification of weathering degree of Antarctic ordinary chondrites

在南极格罗夫山普通球粒陨石的风化等级划分中出现了和Wlotzka(1993)标准矛盾的现象。部分普通球粒陨石的金属和陨硫铁氧化不足20%,然而硅酸盐却发生了蚀变。如果考虑金属的氧化量,这种风化程度应为W1,如果考虑硅酸盐的蚀变,这种风化程度应为W5。对于存在如此大的差异本文给出了折衷的解决办法——对金属和硅酸盐同时进行风化等级划分。金属的风化等级划分为W_m0-W_m4五个,硅酸盐风化等级划分为W_s0-W_s3四个。依据新方案,GRV 021588、021636、021772和021957等4块无法用Wlotzka(1993)标准来确定风化等级的陨石的风化等级均为W_m1-W_s1。而陨石GRV 023312的风化等级为W_m3-W_s0,其相当于Wlotzka(1993)标准中的W3。

There is a contradiction when categorizing some ordinary chondrites （OCs） from Grove Mountains （GRV）, Antarctica, according to Wlotzka＇ s criteria. That is only a minor of metal and troilite （ less than 20% ） were replaced by oxide while silicates being partly weathered, especially along cracks. The weathering degree of these OCs are all W1 if categorized by the oxidation of metal and troilite; however, they should be W5 by the weathering degree of silicates. Therefore, we propose new criteria to categorize the weathering degree of these OCs, in which the weathering degree of metal and silicates are categorized into 5 and 4 progressive stages （they are Win0, Wm1, Win2, Wm3 and Win4 for metal and Ws0, Ws1, Ws2 and Ws3 for silicates）, respectively. Consequently, meteorites GRV 021588, GRV 021636, GRV 021772 and GRV 021957 which can＇ t fit Wlotzka＇ s criteria are all Wm1-Ws1. Furthermore, GRV 023312 is Wm3-Ws0 type, which is the same with W3 in Wlotzka＇ s criteria.