Global mapping of the degree of space weathering on asteroid 25143 Itokawa by Hayabusa/AMICA observations

Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.     

Relaxation method for pounding action between adjacent buildings at expansion joint

Earthquake‐induced structural pounding frequently causes serious damage to buildings, particularly at the expansion joint (hereafter, EXPJ) between adjacent buildings. Because the EXPJ width in existing reinforced concrete buildings is usually very small, typically about 5 cm for school buildings in Japan, collision avoidance cannot be achieved by seismic retrofitting. This paper presents an experimental investigation into an effective method for reducing severe structural damage due to pounding at the EXPJ between narrowly separated buildings. The method involves inserting a shock‐absorbing material such as rubber into the EXPJ gap. The efficiency of the proposed method is evaluated by laboratory shaking tests using two model buildings. Furthermore, a lumped mass model is used to carry out a collision analysis in order to numerically investigate the influence of such a shock‐absorbing material. Both the numerical and experimental results confirm the effectiveness of the proposed approach. The validity of the proposed method is also demonstrated by numerical simulation of adjacent 10‐story steel buildings with an EXPJ width of 5 cm. The force, acceleration and velocity produced by earthquake‐induced structural pounding are found to be remarkably mitigated by inserting a soft shock‐absorbing material into the EXPJ gap. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular clouds and star formation in the Magellanic Clouds and the Milky Way

Star formation is a fundamental process that dominates the life-cycle of various matters in galaxies: Stars are formed in molecular clouds, and the formed stars often affect the surrounding materials strongly via their UV photons, stellar winds, and supernova explosions. It is therefore revealing the distribution and properties of molecular gas in a galaxy is crucial to investigate the star formation history and galaxy evolution. Recent progress in developing millimeter and sub-millimeter wave receiver systems has enabled us to rapidly increase our knowledge on molecular clouds. In this proceedings, the recent results from the surveys of the molecular clouds in the Milky Way and the Magellanic Clouds as well as the Galactic center as the most active regions in the Milky Way are presented. The high sensitivity with unrivaled high resolution of ALMA will play a key role in detecting denser gas that is tightly connected to star formation.     

Carbon isotopic thermometry and geobarometry of sillimanite isograd in thermal aureoles: the depth of emplacement of upper crustal granitic bodies

Carbon isotope fractionation between coexisting calcite and graphite (C ) has been studied in metamorphosed limestones from three thermal aureoles around Cretaceous granitic bodies (i.e., Tanohata, Tono, and Senmaya aureoles) in the Kitakami Mountains, Northeast Japan. C in each aureole decreases toward the granitic bodies, and becomes virtually uniform near the sillimanite isograd for metapelites, although calcite has variable isotopic ratios reflecting the original sedimentary compositions. The relationships indicate that isotopic equilibrium has been attained in metamorphosed limestone of sillimanite grade. Estimated C at the sillimanite isograd is similar in the Tanohata and Tono aureoles, but different in the Senmaya aureole with smaller carbon isotopic fractionations. From the temperature dependence of C and the negative dP/dT of andalusite–sillimanite equilibrium, we conclude that the sillimanite isograd in the Senmaya aureole was under higher temperature and lower pressure than in the other two localities. Temperatures at the sillimanite isograd are estimated by using existing calibrations of carbon isotopic exchange between calcite and graphite, whereas pressures are estimated from carbon isotopic temperatures and the andalusite–sillimanite equilibrium (Holdaway and Mukhopadhyay 1993a). Consistency of the P–T estimates is examined in the light of phase equilibria in the pelitic system. The estimated pressures at the sillimanite isograd are at about 2.1–2.7(±0.2) kbar for the Tanohata and Tono aureoles and less than 1 kbar for the Senmaya aureole, respectively. Geobarometry of sillimanite isograd in thermal aureoles indicates a marked difference in the depth of solidification of upper crustal granitoids: the Senmaya pluton has intruded and solidified at a very shallow level of less than 4 km whereas the Tanohata and Tono plutons are more deep-seated (ca. 8–10 km). The method can also be an effective tool in studying low-pressure type metamorphism in which geothermobarometry using garnet is not always applicable.Editorial responsibility: J. Hoefs     

Eoarchean–Paleoproterozoic zircon inheritance in Japanese Permo-Triassic granites (Unazuki area,Hida Metamorphic Complex): Unearthing more old crust and identifying source terrranes

U–Pb zircon geochronology of two Permo-Triassic granites (samples OT-52 and OT-272 with ages of 229 ± 8 Ma and 256 ± 2 Ma, respectively) in the Unazuki area, Hida Metamorphic Belt, southwest Japan, revealed the presence of Eoarchean to Paleoproterozoic inheritance. Inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions. In OT-52, dark in CL, low Th/U zircon domains have a mean ²⁰⁷Pb/²⁰⁶Pb age of 1940 ± 17 Ma, which is consistent with an age of 1937 ± 6 Ma for anatexis in the Precambrian Busan gneiss complex in Korea. Eoarchaean inherited zircons with ²⁰⁷Pb/²⁰⁶Pb ages from ca. 3750 to 3550 Ma are common in OT-272 but are few in OT-52, suggesting a source from rocks with affinities to those in the Anshan area in the northeast China part of the North China Craton. On the other hand, a Hida Metamorphic Belt metasedimentary gneiss into which the granites were intruded contains ca. 1840, 1130, 580, 360, 285 and 250 Ma zircons (Sano et al., 2000). These ages suggest that the Unazuki Mesozoic granites did not originate from proximal Hida Metamorphic Complex rocks, but instead from unrelated rocks obscured at depth. The predominance of Eoarchean to Paleoproterozoic age components, and the marked lack of 900–700 Ma components suggest that the source was the (extended?) fringe of the North China Craton, rather than from Yangtze Craton crust. The Mesozoic evolution of Japan and its linkages to northeast Asia are discussed in the context of these results.     

The complex age of orthogneiss protoliths exemplified by the Eoarchaean Itsaq Gneiss Complex (Greenland): SHRIMP and old rocks

Field studies integrated with cathodoluminescence petrography and SHRIMP U–Pb dating of zircons from >150 orthogneisses and metatonalites from the Eoarchaean Itsaq Gneiss Complex (southern West Greenland) shows that only a minority contain ≥3840 Ma zircons, whereas the majority carry only younger ones. Rocks containing ≥3840 Ma zircons vary from very rare single-phase metatonalites to more common complexly banded tonalitic migmatites. The former metatonalites have simple oscillatory-zoned ≥3840 Ma zircon with limited recrystallisation and overgrowth, whereas the more common migmatites have much more complicated zircon populations with both ≥3840 Ma and 3650–3600 Ma oscillatory-zoned zircon, more extensive recrystallisation and widespread complex core-rim multiple growth relationships.     

Role of Iron(III) and Aluminum Hydroxides in Concentration/reduction of Au(III) Complexes

Abstract: The adsorption of gold on iron(III) and aluminum hydroxides from solutions containing Au(III) complexes has been studied as a function of pH and chloride concentration at 30C. Iron(III) hydroxide was more effective in adsorbing gold from solution than aluminum hydroxide. However, both hydroxides controlled the behavior of Au(III) complex with very similar manner. The most effective gold adsorption occurred in aqueous solution with near neutral pH and low Cl concentration. In this solution condition, Au(III) complexes were mainly dissolved as AuCl₂(OH)₂^- and AuCl(OH)₃^-, and the surface charge for both hydroxides was positive. In addition, the adsorbed Au(III) complexes were spontaneously reduced to elemental gold in spite of the absence of a specific reducing agent.
The results of this study suggest that adsorption and spontaneous reduction of gold complexes on the surface of hydrous metal oxides with positive charge play an important role in gold precipitation in subsurface environment.     

祁连山七一冰川物质平衡的最新观测结果

祁连山七一冰川观测结果表明, 2001/2002年度和 2002/2003 年度冰川物质平衡分别为-810mm和-316 mm水当量, 冰面出现显著的减薄状态. 和过去的观测结果相比较, 20 世纪 70 年代为较大的正平衡, 年平均为360 mm水当量; 80年代年平均为4 mm水当量, 基本接近零平衡状态. 到近两年亏损强烈, 为所有观测资料中负平衡值最大的年份, 零平衡线也达到最高位置. 物质平衡出现较大的负值和零平衡线位置升高的状况, 强烈反映了祁连山冰川对气候变暖过程的响应. 如果气候变暖趋势继续, 冰川物质平衡负值将增大、冰面减薄和雪线的升高, 冰川将继续呈现萎缩状态.