中部モンゴルツアガンツアイルウルの深成岩の地質学的岩石学的研究

Geological, petrographical and geochemical characteristics of the Baidrag granite pluton from the Tsagaan Tsahir Uul area can be summarized as following; The granitic complex is composed of two types of granites, distinguished by its biotite content. The modal abundance of biotite varies gradually between the two rock types. Major and trace element geochemical characteristics of the granitic rocks are similar, but they differ by SiO_2 content. FeO, CaO, Sr, and Ba contents of the biotite granite are slightly higher than those of the two mica granite. Both granites are medium to high potassium calc alkaline, and have peraluminous chemical features. Studied mineralogical composition and major and trace element geochemistry show that the granitic rock of Tsagaan Tsahir Uul area has volcanic arc granite (VAG) characteristics.論文Articl

Rb-Sr features of the impact-melted LL-chondrites from Antarctica:Yamato-790723 and Yamato-790528

Rubidium and strontium abundances as well as Sr isotopic compositions were analyzed for the impact-melted meteorites (LL-chondrite : Yamato-790723 and -790528) from Antarctica to clarify their Rb-Sr features and to date the impact events. The samples were separated according to the magnetic property. The less magnetic and glass-rich portions of Y-790723 approximate an isochron of 1.27±0.19 Ga. The obtained age should indicate the impact event. The magnetic portions and fine-grained one largely deviate from the isochron. Y-790528 is rather depleted in K_2O and Rb, but not in Na_2O; this may be due to scarcity of the K-rich fragments. The ^Sr/^Sr ratios of the separated portions from Y-790528 are low and less variable. The five less magnetic portions of the Y-790528 chondrite seem to form the isochron of 4.36±0.76Ga as the time of the impact event. The large errors may have derived from local reset of the Rb-Sr chronometer and incomplete separation into the portions

Rb-Sr isotopic study of Yamato-794046 chondrite and its inclusion

The Yamato-794046 H chondrite and its inclusion were dated by the Rb-Sr method as part of a consortium study of unique inclusions in ordinary chondrites. Although the inclusion recorded an approximate 3.9 Ga-melting event, the age of the impact event of the host chondrite was unclear. The inclusion is not depleted in volatile elements such as Rb and the alkalis, even though the host is depleted. Therefore, when they were impacted, they should have been in different places. The host might have been impacted under low confining pressures, and the inclusion, in contrast, was melted under relatively high confining pressures

ロシア・東部バイカル地域におけるマントル進化

The genesis of major groups of xenoliths from the Late Cenozoic volcanic rocks of the eastern part of Baikal Rift System is considered on the basis of petrology and mineral chemistry. Reconstructed mantle sections beneath the Vitim field appear to be more complex than beneath the Udokan field due to significant modification by hydrous metasomatic melts. Peridotite xenoliths from the Miocene picrobasalts represent garnet and spinel depth facies. Pyroxenite xenoliths are interpreted as products of three types of the melt. The first forms Cr-diopside pyroxenites, it is an interstitial melt migrating through peridotite, and it is similar to melts described in peridotite massifs as undergoing percolative fractionation. Textural and compositional relationships indicate melt segregation and fractionation under the high-pressure conditions towards Al-rich pyroxenites and - at shallower levels - towards sp-websterites. The second and third melt types form the hydrous veins and megacrystic pyroxenites, respectively. Both were crystallized in larger channels relative to the first melt type, whereby the amphibole- and phlogopite-bearing assemblages may represent smaller channels on a scale of dozen centimeters. Three series of peridotite xenoliths from Pliocene basanites were determined: (1) high-T garnet and spinel lherzolites, (2) low-T spinel lherzolites and harzburgites, (3) low-T titaniferous spinel lherzolites. Protogranular peridotites of the Series 1 represent primitive to moderately depleted mantle from the depths 60-80km at T=1100-1250℃. Trace element patterns in clinopyroxenes are indicative of low degree partial melting of the primitive mantle. Peridotites of the Series 2 correspond to the depths 40-50km at T=800-900℃. Titaniferous peridotites enriched in pyroxenes and spinel were newly detected. They have a mosaic equigranular texture and are suggested to be a rare type of melt/mantle interaction. T-estimations within 750-850℃ projected to a geotherm allow to interprete their correspondence to the uppermost mantle section (40-50km depth). High Ti content (TiO_2=0.55% in the bulk rock) may characterize a metasomatizing melt generated from ilmenite- and/or phlogopite-bearing source. Clinopyroxene REE patterns (La/Yb)_n=0.01-0.08) reveal an evidence for MORB-like composition of coexisting melt. Xenoliths from the Pliocene basanites of Kuas Lake (Udokan field) show variation of unhydrous depletion and enrichment of lower lithosphere. Xenoliths correspond to spinel facies and may be divided into lherzolite, harzburgite and dunite, and websterite groups. Depleted nodules contain clinopyroxene enriched in LREE and depleted in HFSE. This enrichment is explained by reactive percolation of small melt fraction and accompanying melting of peridotites. Harzburgite-dunite veins seem to be located at the lower part of mantle column and have been formed by olivine-producing reaction with increasing of melt fraction. Lherzolite and websterite are located at the middle and upper part of column and have been formed by pyroxene-producing reaction with decreasing of melt fraction.論文Articl

中国河北省張家口地区万全県漢淖坎玄武岩の地球化学的研究

Geological, petrographical and geochemical characteristics of the Baidrag granite pluton from the Tsagaan Tsahir Uul area can be summarized as following; The granitic complex is composed of two types of granites, distinguished by its biotite content. The modal abundance of biotite varies gradually between the two rock types. Major and trace element geochemical characteristics of the granitic rocks are similar, but they differ by SiO_2 content. FeO, CaO, Sr, and Ba contents of the biotite granite are slightly higher than those of the two mica granite. Both granites are medium to high potassium calc alkaline, and have peraluminous chemical features. Studied mineralogical composition and major and trace element geochemistry show that the granitic rock of Tsagaan Tsahir Uul area has volcanic arc granite (VAG) characteristics.論文Articl

シベリアの新生代火山活動

論文Articl

Rb-Sr age of an impact event recorded in Yamato-791088 H chondrite

The age of the impact event is recorded in Yamato(Y)-791088,a high-iron type chondrite and has been dated using the Rb-Sr chronometer. A brief mineralogical characterization was made of the chondrite as well. The obtained impact age is 1024±47Ma. When Y-791088 recorded the impact event, it might not have been on the surface of the parent body, but rather deep. Therefore, some sulfide was not vaporized and Rb was not lost during the impact. Metal phases were once homogenized and plessite, consisting of two phases, is really scarce. After the impact, the parental body could not have lasted long before separating into pieces