Properties of iron alloys under the Earth's core conditions

The Earth's core is constituted of iron and nickel alloyed with lighter elements. In view of their affinity with the metallic phase, their relative high abundance in the solar system and their moderate volatility, a list of potential light elements have been established, including sulfur, silicon and oxygen. We will review the effects of these elements on different aspects of Fe–X high pressure phase diagrams under Earth's core conditions, such as melting temperature depression, solid–liquid partitioning during crystallization, and crystalline structure of the solid phases. Once extrapolated to the inner–outer core boundary, these petrological properties can be used to constrain the Earth's core properties.     

东南极拉斯曼丘陵镁铁质麻粒岩的变质作用演化

拉斯曼丘陵（Larsemann Hills）位于东南极普里兹构造带的中部,研究该区麻粒岩的变质作用演化对于理解普里兹带的构造属性至关重要。通过对该区含石榴石镁铁质麻粒岩转石详细的岩相学观察表明,峰期前进变质阶段矿物组合（M1）由角闪石+斜方辉石+单斜辉石+斜长石+黑云母+钛铁矿±石英±磁铁矿组成,其峰期矿物组合（M2）为石榴石+斜方辉石+单斜辉石+角闪石+钛铁矿±磁铁矿±石英,而代表后期与降压有关的叠加变质组合（M3）为斜方辉石+斜长石+单斜辉石+黑云母+钛铁矿±磁铁矿。矿物化学分析,结果显示其中石榴子石和斜方辉石具有弱的成分环带特征。利用THERMOCALC软件在NCFMASHTO体系下对该麻粒岩进行了详细的热力学模拟,结合传统温压计和平均温压计算结果,得出不同阶段温压条件分别为650~750℃/5.5~6.5kb （M1）,850~950℃/8~8.5kb （M2）,800~900℃/5.5~7.5kb （M3）。其变质作用演化为典型的峰期后近等温减压的（ITD）顺时针P-T轨迹。通过区域上镁铁质麻粒岩的对比分析,我们认为该镁铁质麻粒岩可能来源拉斯曼丘陵基岩露头。结合已有的年代学资料,表明该镁铁质麻粒岩的峰期变质事件可能对应于晚元古代格林威尔期构造事件,而后期退变质作用与早古生代的泛非期构造事件有关,意味着泛非期普里兹带可能是陆内造山带。     

Tracing exhumation record in high-pressure micaschists: A new tectonometamorphic model of the evolution of the eastern part of the Fore Sudetic Block,Kamieniec Metamorphic Belt,NE Bohemian Massif,SW Poland

The Kamieniec Metamorphic Belt comprises a volcano-sedimentary succession exposed within a collision zone between the Saxothuringian and Brunovistulian crustal domains of the European Variscides. The studied rocks recorded two metamorphic episodes. The first episode, M₁, occurred at conditions of c. 485 ± 25 °C and 18 ± 1.8 kbar related to burial within a subduction zone. The subsequent episode, M₂, was linked to the final phases of exhumation to mid-crustal level, associated with pressure and temperature (P–T) conditions ranging from c. 520 ± 26 °C and 6 ± 0.6 kbar through 555 ± 28 °C and 7 kbar ± 0.7 to ~590 ± 30 °C and 3–4 ± 0.4 kbar. The documented deformation record is ascribed to three events, D₁ to D₃, interpreted as related to the burial and subsequent exhumation of the Kamieniec Metamorphic Belt. The D₁ event must have witnessed the subduction of the Kamieniec Metamorphic Belt rock succession whereas the D₂ event was associated with the exhumation and folding of the Kamieniec Metamorphic Belt in an E-W-directed shortening regime. A subsequent folding related to the D₂ event was initiated at HP conditions, however, the planar fabric produced during a late stage of the D₂ event, defined by a low-pressure mineral assemblage M₂, indicates that the D₂ final stage was synchronous with the onset of the M₂ episode. Consequently, the entire D₂ event seems to have been associated with the exhumation of the Kamieniec Metamorphic Belt to mid crustal level. The third deformation event D₃, synchronous with the M₂ episode, marked the last stage of the exhumation, and was linked to emplacement of granitoid veins and lenses. The latter resulted in heating and rheological weakening of the entire rock succession and in the formation of non-coaxial shear zones.     

http://www.sciencedirect.com/science/article/pii/S1674987114001601

Data from a migmatised metapelite raft enclosed within charnockite provide quantitative constraints on the pressure-temperature-time[P-T-t) evolution of the Nagercoil Block at the southernmost tip of peninsular India.An inferred peak metamorphic assemblage of garnet,K-feldspar.sillimanite,plagioclase,magnetite,ilmenite,spinel and melt is consistent with peak metamorphic pressures of 6-8 kbar and temperatures in excess of 900℃.Subsequent growth of cordierite and biotite record high-temperature retrograde decompression to around 5 kbar and 800 C.SHRIMP U-Pb dating of magmatic zircon cores suggests that the sedimentary protoliths were in part derived from felsic igneous rocks with Palaeoproterozoic crystallisation ages.New growth of metamorphic zircon on the rims of detrital grains constrains the onset of melt crystallisation,and the minimum age of the metamorphic peak,to around560 Ma.The data suggest two stages of monazite growth.The first generation of REE-enriched monazite grew during partial melting along the prograde path at around 570 Ma via the incongruent breakdown of apatite.Relatively REE-depleted rims,which have a pronounced negative europium anomaly,grew during melt crystallisation along the retrograde path at around 535 Ma.Our data show the rocks remained at suprasolidus temperatures for at least 35 million years and probably much longer,supporting a long-lived high-grade metamorphic history.The metamorphic conditions,timing and duration of the implied clockwise P-T-t path are similar to that previously established for other regions in peninsular India during the Ediacaran to Cambrian assembly of that part of the Gondwanan supercontinent.     

带相敏检波器的线性可变差动变压器(LVDT)读出电路的设计

本文简单介绍了LVDT、相敏检波器和三角波发生器的工作原理及自行设计的一种实用的LVDT相敏检波读出电路。     

Ab initio study of the high-pressure behavior of CaSiO3 perovskite

Using density functional simulations, within the generalized gradient approximation and projector-augmented wave method, we study structures and energetics of CaSiO₃ perovskite in the pressure range of the Earths lower mantle (0–150 GPa). At zero Kelvin temperature the cubic CaSiO₃ perovskite structure is unstable in the whole pressure range, at low pressures the orthorhombic (Pnam) structure is preferred. At 14.2 GPa there is a phase transition to the tetragonal (I4/mcm) phase. The CaIrO₃-type structure is not stable for CaSiO₃. Our results also rule out the possibility of decomposition into oxides.

Mercury's integral phase curve: Phase reddening and wavelength dependence of photometric quantities

We present results of a five-filter photometric study of Mercury's integral phase curve in the Johnson-Cousins UBVRI system, performed with the 0.90-m Westerlund Telescope in Uppsala, Sweden. CCD observations were made of the integrated disk for the phase angle range 22-152°, and the study is the first to cover the extended visible spectrum of Mercury. The observations are analyzed with Hapke's semi-empirical radiative transfer-based light-scattering model and photometric quantities are derived. A statistically significant phase reddening effect of is determined for Mercury based on color index observations, which is similar to that of the Moon. Phase coefficients fit to integral absolute magnitude data and Hapke models in combination with color index data provide a phase reddening effect of which does however not provide statistically significant evidence for its presence. Phase coefficients indicate that phase reddening may be decreasing in magnitude with wavelength. As for the case with the Moon, the value of the phase integral increases with wavelength, but at an eight times higher rate. This value is consistent with the difference in the rate of change in the spectral slope-emission angle relation for the two bodies. We attribute these differences with Mercury's redder spectral slope and an increase with wavelength of the backscattering lobe amplitude in the double Henyey-Greenstein particle phase function formulation. The normal albedo of integral Mercury at 1064 nm, pertinent to the return pulse energy of the BepiColombo laser altimeter (BELA), is estimated to 0.23±0.06 with a range of 0.13-0.33 for 99% of the surface.