Cbb球粒的热历史和喷出物羽流的冷却率分布
Thermal History Of Cbb Chondrules And Cooling Rate Distributions Of Ejecta Plumes
摘要：
有人提出，一些陨石，CB和CH陨石，含有在吸积过程中由于原行星碰撞而形成的物质。它们的熔滴（球粒）和FeNi金属被认为是在撞击羽流中蒸发和冷凝形成的。我们观察到，在CBB陨石的SO（骨架橄榄石）球粒有一个水泡状的纹理和富集难熔元素没有发现在正常球粒。由于纹理需要完全熔化，它们的最高液相线温度1928 K代表了推定羽流的最低温度。动态结晶实验表明，SO织构只能通过结晶过程中短暂的再加热事件产生部分溶解的橄榄石。在平滑粒子流体动力学（SPH）模拟中形成的喷出物羽流（Asphaug等人，2011年）作为自适应网格细化（AMR）代码FLASH4.3的3D建模的基础。与流体细胞一起移动的示踪粒子用于测量原位冷却速率。它们的冷却速率在峰值温度时约为10，000 K/hr，在羽流的密集区，1400-1600 K的冷却速率约为100 K/hr。一小部分细胞被认为是在任何一个时间加热，加热尖峰解释压缩的气体包裹在一个不均匀的斑片状羽。这些温度波动与结晶实验中所需的温度波动相当。对于第一次，我们发现实验和模型之间的协议，支持专门为CBB球粒的形成羽模型。
英文摘要：
It has been proposed that some meteorites, CB and CH chondrites, contain material formed as a result of a protoplanetary collision during accretion. Their melt droplets (chondrules) and FeNi metal are proposed to have formed by evaporation and condensation in the resulting impact plume. We observe that the SO (skeletal olivine) chondrules in CBb chondrites have a blebby texture and an enrichment in refractory elements not found in normal chondrules. Since the texture requires complete melting, their maximum liquidus temperature 1928 K represents a minimum temperature for the putative plume. Dynamic crystallization experiments show that the SO texture can be created only by brief reheating episodes during crystallization giving partial dissolution of olivine. The ejecta plume formed in a smoothed particle hydrodynamics (SPH) simulation (Asphaug et al., 2011) served as the basis for 3D modeling with the adaptive mesh refinement (AMR) code FLASH4.3. Tracer particles that move with the fluid cells are used to measure the in situ cooling rates. Their cooling rates are ~10,000K/hr briefly at peak temperature and, in the densest regions of the plume, ~100 K/hr for 1400-1600 K. A small fraction of cells is seen to be heating at any one time, with heating spikes explained by compression of parcels of gas in a heterogeneous patchy plume. These temperature fluctuations are comparable to those required in crystallization experiments. For the first time, we find agreement between experiment and models that supports the plume model specifically for the formation of CBb chondrules.
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