Carbonates in fractures of Martian meteorite Allan Hills 84001: Petrologic evidence for impact origin

Abstract— Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg-rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO₃-FeCO₃-CaCO₃ plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process. The heterogeneous distribution of carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg-rich microdisks appear to be incompatible with growth from an externally derived CO₂-rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg-rich fluid that was squeezed along fractures. Carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate. We infer that carbonates in fractures formed from grain boundary carbonates associated with plagioclase that were melted by impact and dispersed into the surrounding fractured pyroxene. Carbonates in fractures, which include those studied by McKay et al. (1996), could not have formed at low temperatures and preserved mineralogical evidence for Martian organisms.     

Solution Chemistry and the 36~(th) International Conference on Solution Chemistry (36 ICSC) in Xining,China

<正>Solution chemistry covers a broad and interdisciplinary area in chemistry,physics,biology,pharmaceutical,and medical sciences,as well as various application fields. With the advent of new theories,analytical methods,computers,and technology,the research area of solution chemistry has now been widely and deeply     

Possible Sources of Forecast Errors Generated by the Global/Regional Assimilation and Prediction System for Landfalling Tropical Cyclones. Part Ⅱ: Model Uncertainty

This paper investigates the possible sources of errors associated with tropical cyclone (TC) tracks forecasted using the Global/Regional Assimilation and Prediction System (GRAPES). In Part I, it is shown that the model error of GRAPES may be the main cause of poor forecasts of landfalling TCs. Thus, a further examination of the model error is the focus of Part II. Considering model error as a type of forcing, the model error can be represented by the combination of good forecasts and bad forecasts. Results show that there are systematic model errors. The model error of the geopotential height component has periodic features, with a period of 24 h and a global pattern of wavenumber 2 from west to east located between 60°S and 60°N. This periodic model error presents similar features as the atmospheric semidiurnal tide, which reflect signals from tropical diabatic heating, indicating that the parameter errors related to the tropical diabatic heating may be the source of the periodic model error. The above model errors are subtracted from the forecast equation and a series of new forecasts are made. The average forecasting capability using the rectified model is improved compared to simply improving the initial conditions of the original GRAPES model. This confirms the strong impact of the periodic model error on landfalling TC track forecasts. Besides, if the model error used to rectify the model is obtained from an examination of additional TCs, the forecasting capabilities of the corresponding rectified model will be improved.     

Origin of a unique impact-melt rock—the L-chondrite Ramsdorf

Abstract— We have studied a unique impact-melt rock, the Ramsdorf L chondrite, using optical and scanning microscopy and electron microprobe analysis. Ramsdorf contains not only clast-poor impact melt (Begemann and Wlotzka, 1969) but also a chondritic portion (>60 g) with what appears at low magnification to be a normal, well-defined chondritic texture. However, detailed studies at high magnification show that >90 vol% of the crystals in the chondritic portion were largely melted by the impact: the chondrules lack normal microtextures and are ghosts of the original features. The only relics from the precursor chondrules are olivine crystals, which have the highest melting temperature (～1620 °C). Pyroxene-rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine-rich melts. Fine-grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts, probably because pyroxene-rich melts are significantly more viscous. Complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of Ramsdorf formed directly from petrologic type 3–4 material by strong shock. We infer that Ramsdorf was largely melted by shock pressures of ～75–90 GPa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling. Quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes. Ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture.     

The Meteoritical Bulletin,No. 97

Abstract– In this edition of The Meteoritical Bulletin, a total of 506 newly approved meteorite names with their relevant data are reported. These include 354 from northwest Africa, 31 from the Americas, 15 from Antarctica (Koreamet), 85 from Asia, 20 from Australia, and 1 from Europe. Among these meteorites are 2 falls, Grimsby (Canada) and Santa Lucia (2008) (Argentina). Also described are a CM with low degree of alteration, new ungrouped chondrites and achondrites, and 4 Martian meteorites.     

Lateral variations in the lithology and organic chemistry of a black shale sequence on the Mesoarchean seafloor affected by hydrothermal processes: The Dixon Island Formation of the coastal Pilbara Terrane,Western Australia

The Dixon Island Formation of the coastal Pilbara Terrane, Western Australia is a 3.2 Ga volcanic–sedimentary sequence influenced by syndepositional hydrothermal activity formed in an island‐arc setting. We documented lateral variations in stratigraphy, hydrothermal alteration, and biological activity recorded in the sedimentary rocks (over several kilometers), with the aim of identifying areas of biological activity and related small‐scale structures. The Dixon Island Formation comprises volcaniclastics, black chert, and iron‐rich chert within seven tectonic blocks. Based on detailed geological mapping, stratigraphic columns, carbon isotope composition, and organic carbon (C_org) content, we found lateral (>5 km) variations in stratigraphy and carbon isotope compositions in a black chert sequence above the Mesoarchean seafloor with hydrothermal activity. Two felsic tuff layers are used as stratigraphic marker beds within a black chert sequence, which was deposited on altered volcanic rocks. The black chert sequence in each tectonic block is 10–20 m thick. Thickness variations reflect topographical undulations in the paleo‐ocean floor due to faulting. Early‐stage normal faults indicate extensional conditions after hydrothermal activity. Black chert beds in the topographically subsided area contain higher C_org contents (about 0.4 wt%) than in areas around the depression (<0.1 wt%). Carbon isotope compositions for the black chert vary from ?40 to ?25‰, which are similar to values obtained for a black chert vein within the komatiite–rhyolite tuff sequence (underlying the black chert sequence). Those for other rock types in the Dixon Island Formation are ?33 to ?15‰. Results indicate that deformation occurred soon after the final stages of hydrothermal activity. After this early‐stage deformation, organic‐rich sediments were deposited over an area several kilometers across. The organic‐rich sediments indicate stagnant anoxic conditions that resulted in the deposition of siliceous and organic matter from hydrothermal vein systems. When hydrothermal activity terminated, normal faulting occurred and organic matter was deposited from the sea surface and silica from the seafloor.     

Geochemistry of diogenites: Still more diversity in their parental melts

Abstract— We report on the major and trace element abundances of 18 diogenites, and O‐isotopes for 3 of them. Our analyses extend significantly the diogenite compositional range, both in respect of Mg‐rich (e.g., Meteorite Hills [MET] 00425, MgO = 31.5 wt%) and Mg‐poor varieties (e.g., Dhofar 700, MgO = 23 wt%). The wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips. The behavior of incompatible elements in diogenites is more complex, as exemplified by the diversity of their REE patterns. Apart from a few diogenite samples that contain minute amounts of phosphate, and whose incompatible element abundances are unlike the orthopyroxene ones, the range of incompatible element abundances, and particularly the range of Dy/Yb ratios in diogenites is best explained by the diversity of their parental melts. We estimate that the FeO/MgO ratios of the diogenite parental melts range from about 1.4 to 3.5 and therefore largely overlap the values obtained for non‐cumulate eucrites. Our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean. Instead, they point to a more complex history, and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean.     

SLIDING MODE CONTROL OF BUILDINGS WITH ATMD

In the present paper, the application of the sliding mode control (SMC) scheme is discussed in a systematic manner for controlling the vibration of tall buildings with an Active Tuned Mass Damper (ATMD) installed at the top floor. It is shown that the application of the SMC theory for buildings with ATMD may lead to large responses in the building due to the interaction effect from the ATMD caused by the comparatively large response of the ATMD. Based on the theory of compensators, a method is proposed which eliminates the interaction effect from the ATMD to the building and thus prevents large response in the building. The results are demonstrated through simple numerical examples of building–ATMD system subjected to initial condition loading as well as two different types of external excitations. © 1997 by John Wiley & Sons, Ltd.