Accretion and Early History of Planetesimals and Planets: The Noble Gas Record     

Rainer Wieler 《Earth, Moon, and Planets》2011,108(1):1-8

Some of the distinct noble gas “components” in meteorites represent a record of processes during and even before solar system formation. This record is difficult to interpret. Often, one of the major problems is to recognize whether a certain noble gas elemental and isotopic pattern has been established in a presolar epoch, later in the solar accretion disk, during meteorite parent body formation or finally as a result of metamorphism on a parent body. It would also appear that noble gases are a preferred tool to deduce the types of matter from which the Earth and other planets accreted—if the respective parent materials are present in our extraterrestrial sample collections at all. However, also this issue is unsettled. Noble gas isotopes originating from the decay of radioactive precursors allow us to study the early and later degassing history of terrestrial planets, although the interpretation often remains model-dependent. This contribution briefly reviews some of the fundamental aspects of the noble gas record in meteorites and planets.  相似文献   

Thermodynamic properties and equation of state of fcc aluminum and bcc iron, derived from a lattice vibrational method     

Michel H. G. Jacobs  Rainer Schmid-Fetzer 《Physics and Chemistry of Minerals》2010,37(10):721-739

We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure–temperature space. This semi-empirical technique is based on either the Mie–Grüneisen–Debye (MGD) approach or an extension of Kieffer’s model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane’s equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet’s universal and the Birch–Murnaghan equation of state. It appears that the MGD and Mie–Grüneisen–Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between –1 and 0 K/GPa.  相似文献   

Symplectite formation during decompression induced garnet breakdown in lower crustal mafic granulite xenoliths: mechanisms and rates     

Júlia Dégi  Rainer Abart  Kálmán Török  Enikő Bali  Richard Wirth  Dieter Rhede 《Contributions to Mineralogy and Petrology》2010,159(3):293-314

The complex microstructure of kelyphitic rims around garnet in lower crustal garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field, Central Pannonian Basin has been studied in order to identify controls on garnet breakdown. Symplectites comprised of a vermicular intergrowth of submicron sized anorthite, orthopyroxene and spinel replace garnet at a sharp reaction front. Based on element distribution maps the transformation of garnet to symplectite is isochemical. Phase diagram calculations indicate that this reaction was induced by a pressure decrease and/or a temperature increase. In site-specific TEM foils prepared by focused ion beam technique and oriented parallel and perpendicular to the reaction front 200 nm wide rods of anorthite and 20 nm wide rods of spinel are identified. The rods are oriented approximately perpendicular to the replacement front and are embedded in an orthopyroxene matrix. The regular spacing of the symplectite phases along the reaction front suggests that their growth is controlled by diffusion. The kinetics of symplectite formation has been modelled based on irreversible thermodynamics. During interaction of the xenolith with the host basalt the microstructure and chemistry of the An–Opx–Spl symplectite was significantly modified and it was partially replaced by an olivine bearing symplectite. In contrast to primary symplectite formation, these processes were metasomatic in nature including addition of sodium, titanium and some trace elements from the basaltic melt and can clearly be discerned from the garnet breakdown. Based on these observations it is inferred that symplectite formation took place within the deep crust during the extension of the Pannonian Basin between 15 and 30 km depth at high temperature (850–1,050°C) prior to the volcanic transport to the surface.  相似文献