矿物尺度的球粒微量元素地球化学
Chondrule trace element geochemistry at the mineral scale
摘要：
我们报告微量元素分析的矿物相球粒从碳质陨石（Vigarano，Renazzo和Acfer 187），进行了激光烧蚀电感耦合等离子体质谱。这三颗陨石的结果都是相似的。中稳态具有10-20 X Cl的稀土元素（REE）浓度。低钙辉石的轻稀土（LREE）和重稀土（HREE）分别接近0.1 × CI和1 × CI。橄榄石的重稀土元素浓度为0.1-1 x CI，轻稀土元素浓度为10-2 x CI。粗粒橄榄石晶体往往有最分馏的稀土元素模式，平衡分配的指示。在大多数富含辉石的球粒中，低钙辉石往往具有最低的REE浓度。I型球粒似乎经历了显著程度的分批结晶（与分步结晶相反），这需要低于1-100 K/h的冷却速率。这将填补火成岩CAIs和II型球粒之间的空白。稀土元素丰度和辉石模式之间的关系可以理解为由于向球粒熔体中添加二氧化硅而稀释，如Libourel等人（2006）的气体-熔体相互作用情景。快速冷却速率（1000 K/h的顺序），这似乎记录低钙辉石，与橄榄石的更多样化的记录相比，可能指向一个非线性的冷却历史，或表明形成的辉石丰富的球粒边缘是一个事件不同的内部结晶。
英文摘要：
We report trace element analyses from mineral phases in chondrules from carbonaceous chondrites (Vigarano, Renazzo and Acfer 187), carried out by laser ablation inductively coupled plasma mass spectrometry. Results are similar in all three meteorites. Mesostasis has Rare Earth Element (REE) concentrations of 10-20 x CI. Low-Ca pyroxene has light REE (LREE) concentrations near 0.1 x CI and heavy REE (HREE) near 1 x CI respectively. Olivine has HREE concentrations at 0.1-1 x CI and LREE around 10-2 x CI. The coarsest olivine crystals tend to have the most fractionated REE patterns, indicative of equilibrium partitioning. Low-Ca pyroxene in the most pyroxene-rich chondrules tends to have the lowest REE concentrations. Type I chondrules seem to have undergone a significant degree of batch crystallization (as opposed to fractional crystallization), which requires cooling rates slower than 1-100 K/h. This would fill the gap between igneous CAIs and type II chondrules. The anticorrelation between REE abundances and pyroxene mode may be understood as due to dilution by addition of silica to the chondrule melt, as in the gas-melt interaction scenario of Libourel et al. (2006). The rapid cooling rate (of the order of 1000 K/h) which seems recorded by low-Ca pyroxene, contrasted with the more diverse record of olivine, may point to a nonlinear cooling history or suggest that formation of pyroxene-rich chondrule margins was an event distinct from the crystallization of the interior.
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