Conversion of K-Ar dates with modern constants : implications for recalculation of dates reported in Kawano and Ueda using constants reported by Steiger and Jager

This report describes details of a procedure used to convert from K-Ar dates with old constants reported in the relevant literature to K-Ar dates with modern decay constants and the isotopic ratio of potassium reported by Steiger and Jager. Nearly 300 K-Ar dates published by Kawano and Ueda in the 1960s have been recalculated using this procedure. These data are useful for comparing dates reported by Kawano and Ueda to recently obtained K-Ar dates reported by others

Antarctic micrometeorite collection at a bare ice region near Syowa Station by JARE-41 in 2000

We collected Antarctic Micrometeorites (AMMs) at a bare ice field near Syowa Station in the austral fall and spring seasons of 2000. The facility for the AMMs collection introduced by the 39th Japanese Antarctic Research Expedition (JARE-39) was improved to increase the filtering rate of the melt water. The filtering rate became 4-5 times quicker than the previous system, ∿1000 liter/hour, by the addition of a new water pump in parallel with the previous pump. About 50 tons of melt water were formed, of which about 40 tons were filtered using this new system, and 18 holes were made in the bare ice region in 23 days. We obtained particles in which abundant micrometeorites should be included

Search for Antarctic meteorites in the bare ice field around the Yamato Mountains by JARE-41

The wintering party (November 14,1999-March 28,2001) of the 41st Japanese Antarctic Research Expedition (JARE-41) conducted a meteorite search in the bare ice field around the Yamato Mountains. The period of the travel was 89 days. Departure from Syowa Station was on October 27,2000,entrance into the bare ice field on November 17,2000,leaving the bare ice field on January 10,2001,and arrival at Syowa Station on January 23,2001. The 6 men party (field leader : Y. Shimoda, and sub-leader : N. Imae) of JARE-41 collected about 3500 meteorites. The total sample weight was about 196kg. The average meteorite weight was 55g. The most frequent weight was in the bin of 3.2-10g of the weight histogram. The heaviest meteorite collected on the present expedition was an iron meteorite of 50.5kg. This is also the heaviest meteorite among the Yamato bare ice region since the first expedition in 1969 (JARE-10). The iron meteorite was found on the northwest region of JARE IV Nunataks. Compared with other areas, relatively large meteorites were found here. The number of meteorites on the bare ice region around Minami-Yamato Nunataks, which is the most famous meteorite concentration area, was large but the weight of each meteorite was lighter compared with other areas. Sublimation rate, which must be one of the most important factors for the concentration of meteorites, was measured at the near YM175 (71°44.4′S, 35°54.7′E, 2138m) using two independent methods. Both the stake method and the empirical formula method gave nearly comparable values in average; 50-80 and 130.8mg cm^d^, respectively, which are larger than that at Mizuho Station. Sublimation using the stake method was measured at 8 points. Precise GPS measurements for 20 days at YM175 showed that the bare ice is moving 3cm to the west and 2cm upward. This suggests that the upward movement is nearly balanced with the sublimation of ice. However, in order to consider the annual balance, longer measurements are needed

K-Ar biotite ages of the coarse-grained granites from the Inada area, Ibaraki Prefecture: Evaluation of suitability for a new K-Ar dating standard

K-Ar ages have been determined on biotite fractions of three coarse-grained granites from the Inada area, Ibaraki Prefecture. Ages are 65.0 +/－ 2.3 Ma for Inada-I, 63.7 +/－ 2.2 Ma for Inada-II and 62.1 +/－ 2.8 Ma for Inada-III. The Inada-II sample is a better candidate than the other two samples as a K-Ar dating standard on the basis of thin section observation and K-Ar dating results. However, a chlorite removal step is necessary to make the new dating standard

Yamato nakhlites: Petrography and mineralogy

We carried out the petrographical and mineralogical study of new Yamato nakhlites, Yamato 000593 (Y000593), Y000749 and Y000802, with electron probe microanalyser and Fourier transform infrared microspectrometer. Euhedral pyroxenes (En_Fs_Wo_) are the predominant phase with a modal proportion of 75-80 vol% and occur as elongated grains (～1mm x 0.5mm) with thin Fe-rich rims. The chemical composition of the augite cores comprising most of the volume of these pyroxene crystals is homogeneous and nearly identical with those in other nakhlites. Fe-rich rims are present in contact with the mesostasis. Anhedral ferroan olivines (Fa_; 8-18 vol%, ～0.5 mm) and subhedral titanomagnetites (Ab_Or_). Minor phases in the mesostasis are pyrrhotite (Fe_S; smaller than 20μm), apatite (smaller than 20μm), titanomagnetite, Ca-poor pyroxene, fayalitic olivine (Fa_), tridymite and iddingsite. We distinguish these Yamato nakhlites from other nakhlites based on the chemical compositional ranges of the cores and rims of olivine and pyroxene phenocrysts. We suggest that the chemical variations of these minerals for the Yamato nakhlites are intermediate between those of NWA817 and others (Nakhla, Governador Valadares, and Lafayette). The study by Fourier transform infrared microspectrometer of altered phases both on rims and fractures in olivine phenocrysts and in mesostasis revealed the existence of OH-bearing minerals, which might be mixtures of montmorillonite (70%) and goethite (30%). The existence of bubbles in an OH-bearing phase in olivine grains in contact with the fusion crust suggests that the alteration occurred before atmospheric entry (i.e. Martian origin)