Re-identification of G35.6−0.4 as a supernova remnant

G35.6−0.4 is an extended radio source in the Galactic plane which has previously been identified as either a supernova remnant or an H  ii region. Observations from the Very Large Array Galactic Plane Survey at 1.4 GHz with a resolution of 1 arcmin allow the extent of G35.6−0.4 to be defined for the first time. Comparison with other radio survey observations show that this source has a non-thermal spectral index, with   S ∝ν^{−0.47±0.07}  . G35.6−0.4 does not have obvious associated infrared emission, so it is identified as a Galactic supernova remnant, not an H  ii region. It is  ≈15 × 11 arcmin²  in extent, showing partial limb brightening.     

Experimental phase and melting relations of metapelite in the upper mantle: implications for the petrogenesis of intraplate magmas

We performed a series of piston-cylinder experiments on a synthetic pelite starting material over a pressure and temperature range of 3.0–5.0 GPa and 1,100–1,600°C, respectively, to examine the melting behaviour and phase relations of sedimentary rocks at upper mantle conditions. The anhydrous pelite solidus is between 1,150 and 1,200°C at 3.0 GPa and close to 1,250°C at 5.0 GPa, whereas the liquidus is likely to be at 1,600°C or higher at all investigated pressures, giving a large melting interval of over 400°C. The subsolidus paragenesis consists of quartz/coesite, feldspar, garnet, kyanite, rutile, ±clinopyroxene ±apatite. Feldspar, rutile and apatite are rapidly melted out above the solidus, whereas garnet and kyanite are stable to high melt fractions (>70%). Clinopyroxene stability increases with increasing pressure, and quartz/coesite is the sole liquidus phase at all pressures. Feldspars are relatively Na-rich [K/(K + Na) = 0.4–0.5] at 3.0 GPa, but are nearly pure K-feldspar at 5.0 GPa. Clinopyroxenes are jadeite and Ca-eskolaite rich, with jadeite contents increasing with pressure. All supersolidus experiments produced alkaline dacitic melts with relatively constant SiO₂ and Al₂O₃ contents. At 3.0 GPa, initial melting is controlled almost exclusively by feldspar and quartz, giving melts with K₂O/Na₂O ~1. At 4.0 and 5.0 GPa, low-fraction melting is controlled by jadeite-rich clinopyroxene and K-rich feldspar, which leads to compatible behaviour of Na and melts with K₂O/Na₂O ≫ 1. Our results indicate that sedimentary protoliths entrained in upwelling heterogeneous mantle domains may undergo melting at greater depths than mafic lithologies to produce ultrapotassic dacitic melts. Such melts are expected to react with and metasomatise the surrounding peridotite, which may subsequently undergo melting at shallower levels to produce compositionally distinct magma types. This scenario may account for many of the distinctive geochemical characteristics of EM-type ocean island magma suites. Moreover, unmelted or partially melted sedimentary rocks in the mantle may contribute to some seismic discontinuities that have been observed beneath intraplate and island-arc volcanic regions.     

Penetrometry of granular and moist planetary surface materials: Application to the Huygens landing site on Titan

The Huygens probe landed on the then unknown surface of Titan in January 2005. A small, protruding penetrometer, part of the Surface Science Package (SSP), was pushed into the surface material measuring the mechanical resistance of the ground as the probe impacted the landing site. We present laboratory penetrometry into room temperature surface analogue materials using a replica penetrometer to investigate further the nature of Titan’s surface and examine the sensor’s capabilities. The results are then compared to the flight instrument’s signature and suggest the Titan surface substrate material consists of sand-sized particles with a mean grain size ～2 mm. A possible thin 7 mm coating with mechanical properties similar to terrestrial snow may overlie this substrate, although due to the limited data we are unable to detect any further layering or grading within the near-surface material. The unusual weakening with depth of the signature returned from Titan has, to date, only been reproduced using a damp sand target that becomes progressively wetter with depth, and supports the suggestion that the surface may consist of a damp and cohesive material with interstitial liquid contained between its grains. Comparison with terrestrial analogues highlights the unusual nature of the landing site material.     

On mini-halo encounters with stars

We study, analytically and numerically, the energy input into dark matter mini-haloes by interactions with stars. We find that the fractional energy input in simulations of Plummer spheres agrees well with the impulse approximation for small and large impact parameters, with a rapid transition between these two regimes. Using the impulse approximation, the fractional energy input at large impact parameters is fairly independent of the mass and density profiles of the mini-halo; however, low-mass mini-haloes experience a greater fractional energy input in close encounters. We formulate a fitting function which encodes these results and use it to estimate the disruption time-scales of mini-haloes, taking into account the stellar velocity dispersion and mass distribution. For mini-haloes with mass     on typical orbits which pass through the disc, we find that the estimated disruption time-scales are independent of mini-halo mass, and are of the order of the age of the Milky Way. For more massive mini-haloes, the estimated disruption time-scales increase rapidly with increasing mass.     

Processing and preliminary interpretation of noisy high-resolution seismic reflection/refraction data across the active Ostler Fault zone,South Island,New Zealand

In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1–2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N–S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ～ 800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ～ 50° west-dipping primary fault plane.     

大别山超高压榴辉岩流变强度——来自高温高压实验的证据

利用Griggs型 5GPa高压仪器 ,在柯石英稳定域围压条件下 ( >3GPa)完成大别山超高压榴辉岩流变学实验 ,建立了榴辉岩流变状态本构方程 (流动律 ) : ε=Aexp( -Q/RT)σn ,应力指数 (n)为 3 .4 ,活化能 (Q)为 4 80kJ/mol,结构常数 (A)为 10 3.3.实验结果表明 :( 1)作为两相矿物组成的榴辉岩 ,其流变学强度在很大程度上取决于强相矿物 (石榴石 )和弱相矿物 (绿辉石 )含量比例 ;( 2 )天然榴辉岩塑性变形机制是以位错蠕变为主 ;( 3 )根据实验成果比较榴辉岩和上地幔方辉橄榄岩流变学强度相当 ,两者耦合在大陆深俯冲 10 0km左右深度发生拆沉作用可能性很小 ,与上地幔上隆 (upwelling)作用有关的造山期后伸展作用对超高压岩石折返更具有重要意义 .     

Brightness predictions for comets

Daniel W E Green, Brian G Marsden and Charles S Morris write with the aim of illuminating the issue of cometary light curves and brightness predictions, following the publication in this journal last October of the letter by John McFarland (2000).     

Transitional basalts from the eastern Australian tertiary province

Study of Tertiary volcanic rocks from Mt. Tamborine in S. E. Queensland, Australia, suggests that some basalts from the large Tweed vent are intermediate in character between true tholeiites and well documented alkaline basalts of the Australian Tertiary province. Geochemical evidence and comparison with synthetic systems suggests that the transitional lavas are derived by continuous fractional crystallization during the ascent of a parent magma produced by substantial partial melting of the upper mantle at moderate depths and pressures. Alkaline basalts that underlie the transitional basalts are the result of relatively rapid, intermittent extrusion of magma generated by a smaller degree of partial melting of the upper mantle. This interpretation resolves the difficulties posed by an apparent inversion of the usual stratigraphic relationship of tholeiites capped by alkali basalts, and is in accord with recent seismic studies of the continental margin of eastern Australia.