Rotation of fragments in catastrophic impact

The rotation of fragments produced by catastrophic impacts into basalt targets was investigated using framing camera records taken by Fujiwara and Tsukamoto (1980, Icarus44, 142–153). Most of the cores have low rotation rates, of the order 1 rev · sec^?1 or less. Many spall fragments have high rotation rates in the strong shear field produced in the target material by impact.     

A DETAILED CHEMICAL STUDY ON THE BARWISE CHONDRITE

Six fragments of the Barwise meteorite were analyzed for REE and eleven other elements (Al, Ca, Mg, Mn, Na, K, Cr, Fe, Co, Ni and Ba). In addition, two fragments were analyzed for Si and Mg. The chondrite-normalized REE patterns of six fragments studied show interesting systematic variations. Three fragments with relatively high La abundances show a negative Ce anomaly. Since the meteorite in question is a find, it could be suspected that the observed REE fractionations are due to terrestrial contamination. To examine this point, a soil sample from the find site was also analyzed for REE and major chemical elements. It is considered that several facts, especially, the relationships between La and SiO₂ and between SiO₂ and MgO, suggest the pre-terrestrial fractionation rather than the terrestrial contamination. Unexpectedly, it is shown that the REE fractionation observed in the investigated fragments correlates with the metal-silicate and the Fe-Co-Ni fractionations. In this connection, large metal grains were investigated for Fe, Co and Ni contents. A suggestion is presented that this chondrite was formed through the melting of the surface of a planetesimal and the subsequent collision, although the possibility of terrestrial contamination might not be ruled out.     

Basalts and serpentinite from the Puerto Rico Trench, 2. Rare-earth geochemistry

Seven tholeiitic basalts from the Puerto Rico Trench walls (three from the south wall and four from the north wall) were investigated for rare-earth abundances. All these rocks, with the exception of a pigeonite-bearing rock (RC8-RD1–12), were found to possess similar rare-earth features. Their rare-earth patterns resembled those of usual abyssal basalts, and showed no Eu anomalies. There is no difference between the rare-earth abundances of fine-grained and coarse-grained rocks. It is clear that the pigeonite-bearing rock (RC8-RD1 type 2) differs in origin from the abyssal basalts. The rocks with rare-earth patterns similar to that of RC8-RD1–12 are found among the Japanes “geosynclinal” basalts (Tanaka and Sugisaki, 1973).A serpentinite from the same trench was also analyzed for the same elements. The resultant rare-earth pattern suggests that the relevant original rock was separated from a magma having the same relative rare-earth abundances as a chondritic meteorite. The markedly high Eu positive anomaly of this serpentinite is also discussed.     

Dating of Japanese Quaternary tephras by ESR and luminescence methods

Electron spin resonance (ESR) and red thermoluminescence (RTL) methods were applied to quartz of eight Japanese Quaternary tephras ranging from 30 to 900 kyr, which have independent ages from other dating methods. The ESR ages were consistent for younger samples, while those from the Ti–Li center are older than those for the Al center for older samples. RTL ages are consistent with the age references and are roughly consistent with Al center ages. The dose response of the Ti–Li center after heating at 260 °C for 15 min implies that thermally unstable component is created in Ti–Li center by irradiation, leading to possible overestimations in the dose values.     

Concentrations of 222 Rn, Its Short-Lived Daughters And 212 Pb And Their Ratios Under Complex Atmospheric Conditions And Topography

Atmospheric activity concentrations of ²¹²Pb and short-lived ²²²Rndaughters, together with meteorological elements, have been observed continuously atthree sites at Kamisaibara Village in Japan. In addition, atmospheric activity concentrationof ²²²Rn, equilibrium-equivalent concentration of ²²²Rn and conditionsof the lower atmosphere were observed for three intensive observation periods at Akawase,one of the three sites in Kamisaibara Village. The equilibrium-equivalent concentration of²²²Rn is almost the same as the atmospheric activity concentration of short-lived²²²Rn daughters.The activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughtersand their ratio were low in the daytime owing to convective mixing, and high at nightowing to the surface-based inversion during periods of no precipitation. Their variationshave several patterns corresponding to the scale of the drainage wind or weak mixing.Mechanical mixing due to strong winds through both day and night during the first andsecond observation periods made the atmospheric activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughters continuously low. However, their ratios werecontinuously high during the first period yet continuously low during the second period.This difference can be explained by the effect ofextraction of ²²⁰Rn and ²²²Rndue to strong winds and snow cover. There were also cases in which the ratio of theatmospheric activity concentration of ²¹²Pb to that of the short-lived ²²²Rndaughters at night was equal to or less than the ratio in the daytime. Thisinverse trend, asin the periods of no precipitation mentioned above, is considered to be due to near-neutralconditions on these nights.We find a difference in the ratio of the equilibrium-equivalent concentration of²²²Rn (the activity concentration of short-lived ²²²Rn daughters) tothe activity concentration of ²²²Rn during the first observation period and thatduring the second. The difference can be explained by snow cover on the ground. Wealso find differences among the ratios of the activity concentration of the short-lived²²²Rn daughters to that of ²²²Rn during the three observation periods.These differences can be explained by the submergence of paddy fields.     

Optical dating of a Japanese marker tephra using plagioclase

The luminescence characteristics of volcanic plagioclase from an andesitic tephra (Hakone-Tokyo pumice, Hk-TP) from Japan were studied in order to assess if optical dating of plagioclase could be applied to Quaternary tephra. The tephra was shown to contain two kinds of plagioclase grains, labradorite which had a smooth surface and bytownite with a rough surface. The aliquots consisting of smaller grains contained more bytownite; these showed higher luminescence sensitivity and a higher fading rate compared to the larger-grained aliquots containing only labradorite. The fading rates of both OSL and IRSL signals were similar for each grain size. However, the OSL signal showed severe thermal transfer which made it difficult to use for dating. Using the IRSL signal from grains ranging from 150 to 212 μm, an age was obtained in agreement with the independent evidence, once a small fading correction had been applied.     

青藏高原草甸下垫面湍流强度相似性关系分析

利用“全球能量水循环之亚洲季风青藏高原试验(GAME／Tibet)”1998年加强期(IOP)的观测资料，分析研究了青藏高原草甸下垫面上的无量纲风速、温度及湿度方差相似性，并与HEIFE戈壁沙漠和绿洲及海洋下垫面作了比较，得到了一些有关青藏高原草甸下垫面上动力及热力学参数的有益的结论。     

Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: Comparison with an independent chronology

There are only a few luminescence dating studies of loess sediments in Japan, but interleaved with these deposits are many well-described tephras of known age based on ¹⁴C and fission track analysis; these independent age controls provide an opportunity to test the reliability of loess luminescence ages. This study provides such a comparison at two sites in central Honshu, the largest island in the Japanese archipelago. Samples were collected from sequences of interleaved volcanic tephra and loess deposited on a Middle Pleistocene river terrace in the Niigata Prefecture and on an Early to Middle Pleistocene dissected fluvial surface at in the Tochigi Prefecture, Honshu. Equivalent doses (D_e) were estimated from fine grains (4–11 μm) using both polymineral IR-OSL and (post-IR) blue-OSL, and quartz blue-OSL. The blue-stimulated luminescence signals could be represented by up to three exponentially decaying components; only the most light sensitive of these components was used in the final D_e estimation. Almost all the estimates of D_e from polymineral IR-OSL are smaller than those from polymineral (post-IR) blue-OSL and quartz blue-OSL, whereas the latter two are in good agreement. The blue-light stimulated luminescence ages using the most light sensitive component are shown to be in good agreement with the independent control, up to 500 ka. Although the IR-OSL signals underestimate the known age, a simple laboratory fading test is found empirically to correct for this underestimation. We conclude that the most rapidly blue-stimulated luminescence signals from quartz extracted from our loess samples give reliable ages, and that future loess dating studies should concentrate on these signals.