Fall, classification and cosmogenic records of the Sabrum (LL6) chondrite
Fall, classification and cosmogenic records of the Sabrum (LL6) chondrite
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Sabrum (LL6) 球粒陨石的坠落、分类和宇宙成因记录
DOI：
10.1111/j.1945-5100.2002.tb00826.x
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发表时间：
2002
影响因子：
2.2
通讯作者：
S. Shome
中科院分区：
文献类型：
--
作者：
S. Ghosh;S. Murty;P. N. Shukla;A. Shukla;R. Mahajan;N. Bhandari;N. Pant;J. Ghosh;S. Shome
摘要-描述了位于Sabrum的一颗印度陨石的岩石学和化学特征。其平均矿物组成为橄榄石(Fa31.4)、斜方辉石(Fs25.1，Wo2.0)、单斜辉石(Wo45En45.6Fs9.4)和斜长石(An10.6Ab83.6Or5.8)。该陨石具有中等激波特征，属于S4类。根据矿物学和化学标准，该陨石被归类为LL6角砾脉球粒陨石。测量了几种宇宙成因的放射性同位素(46Sc、7Be、54Mn、22Na和26Al)、惰性气体(He、Ne、Ar、Kr和Xe)、氮同位素和粒子径迹密度。宇宙成因的~(21)Ne和~(38)Ar的浓度表明它的宇宙线暴露年龄为24.8 Ma。存在少量圈闭的Kr和Xe，与岩石学5/6级一致。橄榄石的径迹密度为(1.3±0.3)×106/cm~2。大多数短寿命同位素的活度都低于太阳周变化的预期活度。~(22)Na/~(26)Al(1·12±0·02)明显异常，比TOAX中子监测数据的˜低2 5%。这些结果表明，流星体轨道末段的宇宙射线通量较低。~(26)Al和~(60)Co的活度和径迹密度表明流星体较小，半径˜为15 cm。
Abstract— The petrographic and chemical characteristics of a fresh Indian meteorite fall at Sabrum are described. Its mean mineral composition is defined by olivine (Fa31.4), orthopyroxene (Fs25.1,Wo2.0), clinopyroxene (Wo45En45.6Fs9.4) and plagioclase (An10.6Ab83.6Or5.8). The meteorite shows moderate shock features, which indicate that it belongs to the S4 category. Based on mineralogical and chemical criteria the meteorite is classified as an LL6 brecciated veined chondrite. Several cosmogenic radioisotopes (46Sc, 7Be, 54Mn, 22Na and 26Al), noble gas (He, Ne, Ar, Kr and Xe), nitrogen isotopes, and particle tracks density have been measured. Concentrations of cosmogenic 21Ne and 38Ar indicate that its cosmic‐ray exposure age is 24.8 Ma. Small amounts of trapped Kr and Xe, consistent with petrologic class 5/6, are present. The track density in olivines is found to be (1.3 ± 0.3) × 106/cm2. Activities of most of the short‐lived isotopes are lower than those expected from solar cycle variation. 22Na/26Al (1.12 ± 0.02) is found to be significantly anomalous, being ˜25% lower than expected from the Climax neutron monitor data. These results indicate that the cosmic‐ray flux during the terminal segment of the meteoroid orbit was low. The activities of 26Al and 60Co and the track density indicate small meteoroid size with a radius ˜15 cm.