Refractory metal nuggets within presolar graphite: First condensates from a circumstellar environment
Refractory metal nuggets within presolar graphite: First condensates from a circumstellar environment
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太阳系前石墨中的难熔金属块：来自星际环境的第一批凝结物
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发表时间：
2013
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通讯作者：
M. Jadhav
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作者：
T. Croat;T. Berg;T. Bernatowicz;E. Groopman;M. Jadhav
透射电子显微镜（TEM）研究发现，在四种不同的太阳前石墨中存在富含Os， Ru， Mo的难熔金属块，来自高密度（HD） Murchison （MUR）和低密度（LD） Orgueil （ORG）分数。微观结构和化学数据表明，这些是天然气的直接冷凝物，而不是后来通过溶解形成的。太阳前难熔金属金块（pRMN）的组成是可变的（例如，从8 < Os原子% < 77），但遵循相同的化学分异趋势，作为分离难熔金属金块（mRMNs）之前在陨石中发现（Berg etal . 2009）。从这些成分中，我们可以推断出与气体的最后平衡温度为1405-1810 K（例如，Berg等人2009年在大约100 dyne cm - 2压力下），这意味着宿主石墨在大致相同的范围内形成（与预测一致），并且当被石墨捕获时，pRMNs从化学上与气体分离。此外，pRMN的组成证明了HD石墨比LD石墨在更高的温度下形成。与分离的mRMNs相似的化学和相位表明，mRMNs也直接由气体凝聚而成，尽管来自早期的太阳星云而不是前太阳环境。尽管prmn本身太小，无法检测到同位素异常，但NanoSIMS对其宿主石墨的同位素测量证实了这些组合的前太阳起源。两个含有pRMN的LD石墨显示出超新星（SN）起源的证据，而HD石墨中pRMN的恒星起源尚不清楚，因为只有较少诊断的12C富集可检测到（HD石墨通常如此）。
Transmission electron microscope (TEM) investigations have revealed Os, Ru, Mo‐rich refractory metal nuggets within four different presolar graphites, from both the high‐density (HD) Murchison (MUR) and low‐density (LD) Orgueil (ORG) fractions. Microstructural and chemical data suggest that these are direct condensates from the gas, rather than forming later by exsolution. The presolar refractory metal nugget (pRMN) compositions are variable (e.g., from 8 < Os atom% < 77), but follow the same chemical fractionation trends as isolated refractory metal nuggets (mRMNs) previously found in meteorites (Berg et al. 2009). From these compositions one can infer a temperature of last equilibration with the gas of 1405–1810 K (e.g., Berg et al. 2009 at approximately 100 dyne cm−2 pressure), which implies that the host graphites form over roughly the same range (in agreement with predictions) and that the pRMNs are chemically isolated from the gas when captured by graphite. Further, the pRMN compositions give evidence that HD graphites form at a higher T than LD ones. Chemical and phase similarities with the isolated mRMNs suggest that the mRMNs also condense directly from a gas, although from the early solar nebula rather than a presolar environment. Although the pRMNs themselves are too small for detection of isotopic anomalies, NanoSIMS isotopic measurements of their host graphites confirm a presolar origin for the assemblages. The two pRMN‐containing LD graphites show evidence of a supernova (SN) origin, whereas the stellar origins of the pRMNs in HD graphite are unclear, because only less‐diagnostic 12C enrichments are detectable (as is commonly true for HD graphites).