SIMS matrix effects in oxygen isotope analysis of olivine and pyroxene: Application to Acfer 094 chondrite chondrules and reconsideration of the primitive chondrule minerals (PCM) line
SIMS matrix effects in oxygen isotope analysis of olivine and pyroxene: Application to Acfer 094 chondrite chondrules and reconsideration of the primitive chondrule minerals (PCM) line
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DOI：
10.1016/j.chemgeo.2022.121016
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发表时间：
2022-07
期刊：
影响因子：
3.9
通讯作者：
Mingming Zhang;K. Fukuda;M. Spicuzza;G. Siron;A. Heimann;Alexander Hammerstrom;N. Kita;T. Ushikubo;J. Valley
中科院分区：
文献类型：
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作者：
Mingming Zhang;K. Fukuda;M. Spicuzza;G. Siron;A. Heimann;Alexander Hammerstrom;N. Kita;T. Ushikubo;J. Valley
研究了橄榄石和辉石二次离子质谱（西姆斯）分析中氧同位素的仪器偏差（这里用偏差 * 表示，相对于San卡洛斯橄榄石，SC-OI的偏差）。使用了16种橄榄石（Fo 0 -100）、9种斜方辉石（En 70 - 100 Wo 0 -3）和3种单斜辉石（En 28 - 49 Wo 45 -50）标准物质（RM）。在镁橄榄石（Fo ≥60）RM中，偏差 * 值几乎不变（在0 ± 0.5‰以内），但随着Fe摩尔分数的增加而系统地降低，直到~ −10‰（Fo 0）。对于Fo ≥60的橄榄石，偏差 * 的会话间变异性≤0.3‰，但对于更多富铁成分（≤1.5‰），偏差 * 的会话间变异性稍大。斜方辉石RM的偏差 * 值范围很窄（−1.7‰至−2.6‰），显示会话间的变化≤0.3‰;相应地，溅射率也很低，类似于Fo ≥60的橄榄石。单斜辉石RM偏差 * 值（-0.2 ‰至+1.2‰）的变化更大，并且具有更大的会话间变异性（≤0.8‰），这似乎与溅射率无关。相同RM的偏倚 * 在不同分析设置的会话之间略有变化（对于Fo ≥60 ≤0.6‰，对于铁橄榄石高达2‰），因此，作为Fo，En，在西姆斯中，通过分析多个RM，可以确定Wo和Wo。使用具有扩展组成范围的新的橄榄石和辉石RM套件来校正氧期间的仪器偏差。未分组的Acfer 094球粒陨石球粒中橄榄石和低钙辉石的三同位素分析，原始球粒矿物（PCM，δ 18 O vs. δ 17 O）线最初来源于此。PCM线被认为是早期太阳系中两个极端的原始氧同位素库的混合趋势。然而，这个新的数据集，更好的分析精度和仪器偏差校正，允许两个氧同位素的趋势，以明确确定。一种是在PCM线上或PCM线以上的球粒，可能与普通的球粒陨石（OC）类物质有关。第二种趋势是由该球粒陨石中的主要球粒人口代表，其定义了δ 17 O =（0.968 ± 0.022）× δ 18 O −（3.46 ± 0.10）（MSWD = 2.0）的回归线，与碳质陨石中球粒的最新氧同位素数据一致（即，CV、CK、CO和CM）。我们认为，这条回归线代表了两个氧同位素水库（可能是16 O丰富的固体和16 O-贫H2O冰）在太阳系外的混合，并可能导致同位素水库的独立演变后，“木星鸿沟”建立。
The instrumental bias (here expressed as bias*, the difference relative to San Carlos Olivine, SC-Ol) of oxygen isotopes in secondary ion mass spectrometry (SIMS) analyses of olivine and pyroxene were investigated. Sixteen olivine (Fo0–100), nine orthopyroxene (En70–100Wo0–3), and three clinopyroxene (En28-49Wo45–50) reference materials (RMs) were utilized. The values of bias* are nearly invariant (within 0 ± 0.5‰) among magnesian olivine (Fo ≥60) RMs but decrease systematically with increasing Fe molar fraction down to ~ −10‰ (Fo0). The session-to-session variability of bias* for Fo ≥60 olivines is ≤0.3‰ but becomes slightly larger for more Fe-rich compositions (≤1.5‰). Orthopyroxene RMs have a narrow range of bias* values (−1.7‰ to −2.6‰) that show session-to-session variability ≤0.3‰; correspondingly, the sputter rates are similarly low and resemble those of Fo ≥60 olivines. Clinopyroxene RMs bias* values (−0.2‰ to +1.2‰) are more variable and have larger session-to-session variability (≤0.8‰), which appear to be independent of sputter rates. Bias* of the same RMs change slightly from session to session with different analytical settings (≤0.6‰ for Fo ≥60 and as much as 2‰ for fayalite) so that equations of bias* as a function of Fo, En, and Wo should be determined for each SIMS session by the analyses of multiple RMs.The new suite of olivine and pyroxene RMs with expanded composition range were used to correct the instrumental biases during oxygen three-isotope analysis of olivine and low-Ca pyroxene in chondrules of the ungrouped Acfer 094 chondrite, from which the primitive chondrule minerals (PCM, δ18O vs. δ17O) line was originally derived. The PCM line is considered to be a mixing trend of two extreme primary oxygen isotope reservoirs of solids in the early solar system. However, this new dataset, with better analytical precision and instrumental bias correction, allows two oxygen isotope trends to be clearly identified. One is represented by chondrules that plot on or above the PCM line, likely linked to ordinary chondrite (OC)-like materials. A second trend is represented by the major chondrule population in this chondrite that defines a regression line of δ17O = (0.968 ± 0.022) × δ18O − (3.46 ± 0.10) (MSWD = 2.0), consistent with recent oxygen isotope data of chondrules in carbonaceous chondrites (i.e., CV, CK, CO, and CM). We propose that this regression line represents a mixing of two oxygen isotope reservoirs (possibly16O-rich solids and16O-poor H2O ice) in the outer solar system and likely resulting from the separate evolutions of isotope reservoirs after the “Jupiter divide” built up.