Ion microprobe analyses of oxygen three‐isotope ratios of chondrules from the Sayh al Uhaymir 290 CH chondrite using a multiple‐hole disk
Ion microprobe analyses of oxygen three‐isotope ratios of chondrules from the Sayh al Uhaymir 290 CH chondrite using a multiple‐hole disk
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DOI：
10.1111/j.1945-5100.2011.01198.x
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发表时间：
2011-06
影响因子：
2.2
通讯作者：
D. Nakashima;T. Ushikubo;Rudraswami N. Gowda;N. Kita;J. Valley;K. Nagao
中科院分区：
文献类型：
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作者：
D. Nakashima;T. Ushikubo;Rudraswami N. Gowda;N. Kita;J. Valley;K. Nagao
摘要-离子微探针是唯一能够测定单个微小的外星粒子(直径≤100μm)中高精度稳定同位素比率的技术，但这些小样本面临着特殊的分析挑战。我们研制了一种新的多孔(三孔和七孔)样品保持盘，其中包含一个未知样品和一个标准颗粒的环氧盘被浇铸和抛光。使用圣卡洛斯橄榄石标准颗粒进行的氧两同位素分析的性能测试表明，如果微粒分别位于七孔和三孔圆盘的孔中心半径500μm和1 mm内，则新的多孔圆盘可以准确分析微小颗粒。利用新研制的七孔球粒陨石，用离子探针分析了Sayh al Uhaymir(SAU)290CH球粒陨石中8个镁隐晶球粒(直径约100μm)的氧三同位素比值。8个球粒陨石中有5个具有接近相同的氧同位素比值(Δ17O=−2.2±0.6‰；2SD)，这与CH/CB和CB球粒陨石中的镁隐晶球粒的氧同位素比值基本一致，暗示了一种成因关系，即共同(可能是碰撞)加热事件的形成。其他三个球粒陨石具有不同的氧同位素比值(Δ17O值从−6.4‰到+2.2‰)。鉴于在CH/CB球粒陨石中观察到的I型斑状球粒陨石的Δ17O值变化相似，这三个球粒陨石可能是在太阳星云中形成的，类似于I型斑状球粒陨石。
Abstract– The ion microprobe is the only technique capable of determining high‐precision stable isotope ratios in individual tiny extraterrestrial particles (≤100 μm in diameter), but these small samples present special analytical challenges. We produced a new sample holder disk with multiple holes (three holes and seven holes), in which epoxy disks containing a single unknown sample and a standard grain are cast and polished. Performance tests for oxygen two‐isotope analyses using San Carlos olivine standard grains show that the new multiple‐hole disks allow accurate analysis of tiny particles if the particles are located within the 500 μm and 1 mm radius of the center of holes for seven‐hole and three‐hole disks, respectively. Using the new seven‐hole disk, oxygen three‐isotope ratios of eight magnesian cryptocrystalline chondrules (approximately 100 μm in diameter) from the Sayh al Uhaymir (SaU) 290 CH chondrite were analyzed by ion microprobe at the University of Wisconsin. Five out of eight chondrules have nearly identical oxygen isotope ratios (Δ17O = −2.2 ± 0.6‰; 2SD), which is consistent with those of magnesian cryptocrystalline chondrules in CH/CB and CB chondrites, suggesting a genetic relationship, i.e., formation by a common (possibly impact) heating event. The other three chondrules have distinct oxygen isotope ratios (Δ17O values from −6.4‰ to +2.2‰). Given that similar variation in Δ17O values was observed in type I porphyritic chondrules in a CH/CB chondrite, the three chondrules may have formed in the solar nebula, similar to the type I porphyritic chondrules.