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191.
Abstract— Many solar system processes involve a metallic liquid, and the composition of the metallic liquid, such as the liquid's concentrations of S, P, and C, will influence the partitioning of elements during such processes. We present a method for parameterizing solid metal‐liquid metal partition coefficients for siderophile (metal‐loving) elements as a function of the metallic liquid composition. Our parameterization method is based on an older theory of Jones and Malvin (1990), which stated that the metallic liquid is composed of metal and non‐metal‐bearing domains, and the domains are the dominant influence on the partitioning behavior. By revising the means by which the metal domains are calculated, our revised parameterization method is able to match experimental partitioning data from the Fe‐Ni‐S, Fe‐Ni‐P, Fe‐Ni‐S‐P, and Fe‐Ni‐C systems. Mathematical expressions were derived for the solid metal‐liquid metal partitioning of 13 siderophile elements. Elements that are chalcophile (S‐loving), P‐loving, or C‐loving prefer the non‐metal‐bearing domains in the metallic liquid and, consequently, aren't fit by the parameterization method presented here. Possible applications for our parameterization method include modeling the crystallization of iron meteorites, planetary differentiation, and the solidification of Earth's inner core. 相似文献
192.
Abstract– We have examined Fe/Mn systematics of 34 type IIA chondrules in eight highly unequilibrated CO, CR, and ordinary chondrites using new data from this study and prior studies from our laboratory. Olivine grains from type IIA chondrules in CO chondrites and unequilibrated ordinary chondrites (UOC) have significantly different Fe/Mn ratios, with mean molar Fe/Mn = 99 and 44, respectively. Olivine analyses from both these chondrite groups show well‐defined trends in Mn versus Fe (afu) and molar Fe/Mn versus Fe/Mg diagrams. In general, type IIA chondrules in CR chondrites have properties intermediate between those in UOC and CO chondrites. In most UOC and CR type IIA chondrules, the Fe/Mn ratio of olivine decreases during crystallization, whereas in CO chondrites the Fe/Mn ratio does not appear to change. It is difficult to interpret the observed Fe/Mn trends in terms of differing moderately volatile element depletions inherited from precursor materials. Instead, we suggest that significant differences in the abundances of silicates and sulfides ± metals in the precursor material, as well as open‐system behavior during chondrule formation, were responsible for establishing the different Fe/Mn trends. Using Fe‐Mn‐Mg systematics, we are able to identify relict grains in type IIA chondrules, which could be derived from previous generations of chondrules, including chondrules from other chondrite groups, and possibly chondritic reservoirs that have not been sampled previously. 相似文献
193.
一个关于临界地城的临界区域判别的方法 总被引:2,自引:0,他引:2
由临界地震的概念和外推Bowman等人关于孕育未来的地震半径的思想,发展出一个临界圆重叠方法来地寻找未来强震的临界区域位置,模拟实验的对比检验表明这种方法是有效的,使用主震前一定时间内地震目录,这个方法能找出临界区域,而未来震中位置将位于临界区域内或其边缘。使用新西兰和中国新疆南部的中强震目录检验,该方法可以在震前较准确地定位出强城的临界区域位置,使用中国1995年至1999年8月的小震目录,给出 相似文献
194.
Rhian H. JONES John M. SAXTON Ian C. LYON Grenville TURNER 《Meteoritics & planetary science》2000,35(4):849-857
Abstract— We have measured O‐isotopic ratios in a variety of olivine grains in the CO3 chondrite Allan Hills (ALH) A77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites. Oxygen‐isotopic ratios of olivines in this chondrite are variable from δ17O = ?15.5 to +4.5% and δ18O = ?11.5 to +3.9%, with Δ17O varying from ?10.4 to +3.5%. Forsteritic olivines, Fa<1, are enriched in 16O relative to the bulk chondrite, whereas more FeO‐rich olivines are more depleted in 16O. Most ratios lie close to the carbonaceous chondrite anhydrous minerals (CCAM) line with negative values of Δ17O, although one grain of composition Fa4 has a mean Δ17O of +1.6%. Marked O‐isotopic heterogeneity within one FeO‐rich chondrule is the result of incorporation of relic, 16O‐rich, Mg‐rich grains into a more 16O‐depleted host. Isolated olivine grains, including isolated forsterites, have similar O‐isotopic ratios to olivine in chondrules of corresponding chemical composition. This is consistent with derivation of isolated olivine from chondrules, as well as the possibility that isolated grains are chondrule precursors. The high 16O in forsteritic olivine is similar to that observed in forsterite in CV and CI chondrites and the ordinary chondrite Julesburg and suggests nebula‐wide processes for the origin of forsterite that appears to be a primitive nebular component. 相似文献
195.
Nickpoint recession in the Buchan karst, southeastern Australia, has resulted in the formation of an underground meander cut-off system in the Murrindal River valley. Three nickpoints have been stranded in the surface channel abandoned by the subterranean piracy, and these can be correlated with river terraces and epiphreatic cave passages in the nearby Buchan River valley. The presence of palaeomagnetically reversed sediments in the youngest cave passage in the Buchan valley implies that the topographically lowest nickpoint in the Murrindal valley is more than 730 ka old, and the other nickpoints are probably several million years old. The nickpoints are occasionally active during floods, but the diversion of most surface flow underground has slowed down their retreat to the extent that they have been effectively stationary for several million years. Underground nickpoint migration has been by both incision within major phreatic conduits and their abandonment for lower-level passages. The nickpoints are all present in the upstream part of the cave system, but have not migrated past the sink in the river channel, despite the long period of time available for this to happen. The sink is characterized by collapsed limestone blocks; these filter out the coarse bedload from the river channel. As a result, erosion within the cave passages is dominantly solutional and therefore slower than in the surface channel, where it is mostly mechanical. In addition, to transmit a drop in base level the cave system requires the removal of a larger volume of rock than for the surface migration of a nickpoint, because any roof collapse material in the subsurface system must be removed. These factors have slowed the migration of the base-level changes through the subsurface system, and may be a general feature in caves that have diffuse sinks as their main inputs. 相似文献