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Isotope Geochemistry of Volcanic Rocks from the Barton Peninsula, King George Island, Antarctica

2022-03-24T07:11:24Z

Title: Isotope Geochemistry of Volcanic Rocks from the Barton Peninsula, King George Island, Antarctica Authors: Jeong Hwang; Zheng Xiangshen; Dongbok Shin; Lee, Jong Ik; Edward M Ripley Abstract: C, O, H, S and Sr isotopes were investigated to characterize the isotopic composition of the Paleocene？Eocene volcanic rocks in Barton Peninsula, King George Island, Antarctica. The analyzed samples of volcanic rocks cover a range from basalt to andesite. The δ13C and δ18O values of calcite in volcanic rocks range from -7.5‰ to -3.2‰ and 0.4‰ to 5.1‰, respectively. The homogenous δ13Ccal and depleted δ18Ocal values relative to primary magmatic values reflect the effect of high temperature alteration of volcanic rocks. The δ18O of volcanic rocks ranges from -1.1‰ to 7.2‰, and the majority of values are significantly lower than those of primary magmatic values. The low δ18OWR values are compatible with high temperature alteration. The initial values of 87Sr/86Sr of volcanic rocks span a narrow range from 0.703 312 to 0.703 504 which belong to the present mid-oceanic ridge basalt. The values of 87Sr/86Sr of volcanics in the Barton Peninsula are similar to those determined in the Fildes Peninsula, King George Island. The δDWR and H2O contents of volcanic rocks range from - 74‰ to -66‰ and 0.67 wt.% to 2.74 wt.%, respectively. The higher δDWR and H2O wt.% of volcanic rocks relative to fresh basalts also result from high temperature alteration. Sulfur isotope compositions of the volcanic rocks range from -12.5‰ to -7.0‰;these values may represent fractionation from basalt to andesite. The δ13C and δ18O values of calcite in volcanic rocks range from -7.5‰ to -3.2‰ and 0.4‰ to 5.1‰, respectively. The homogenous δ13Ccal and depleted δ18Ocal values relative to primary magmatic values reflect the effect of high temperature alteration of volcanic rocks. The δ18O of volcanic rocks ranges from -1.1‰ to 7.2‰, and the majority of values are significantly lower than those of primary magmatic values. The low δ18OWR values are compatible with high temperature alteration. The initial values of 87

Petrography of TIL 08007 CM chondrite

2022-03-24T07:13:18Z

Title: Petrography of TIL 08007 CM chondrite Authors: Lee, Hyung Woo; Kwon, Sung-Tack; Lee, Jong Ik; Yoo, In Sung; Ahn, Insu Abstract: CM 콘드라이트는 태양계 초기에 생성된 C-콘드라이트의 세부 그룹이며 시원적인 운석으로 보고되어 있다. CM 콘드라이트는 태양계 성운에서 모체가 되는 소행성단계로의 집적과정 혹은 소행성 내에서 존재했을 수성변질(aqueous alteration)작용에 의한 다양한 암석학 및 광물화학적인 증거들을 포함하고 있음이 알려져 있다. 본 연구의 대상인 TIL 08007은 제3차 남극운석탐사에서 회수된 발견운석으로 기존연구에서 암석학적 특성과 전암 산소동위원소 조성으로 CM 콘드라이트에 해당하며 암석학적인 분류상 수성변질작용을 경험한 유형-2로 분류하였다. TIL 08007를 구성하는 콘드률, 기질, 규산염질 암편들에서 나타나는 다양한 이차광물들과 일부 콘드률을 둘러싸고 있는 FGR(fine-grained rim)의 수성변질작용과 관련된 특징들을 광학현미경과 주사전자현미경을 이용하여 관찰하였다. 콘드률 및 규산염질 암편은 20.4 vol.%을 차지한다. 일부 콘드률의 내부는 사문석화작용이 진행되었음이 보여주며 황-산화물도 관찰된다. 콘드률 반정 내에 함유되어 있는 금속철(Fe-Ni metal)은 <0.1 vol.%로 변질작용에 의한 철-산화물로 일부 치환되어 나타나기도 한다. 기질부는 79.5 vol.%를 차지하며 tochilinite와 cronstedtite를 포함하는 이차광물로 구성된 PCP(poorly characterized phase)를 포함한다. FGR은 콘드률, 규산염 암편을 둘러싸고 있으며 주변의 기질보다 작은 입자크기를 보이며 일부에서 Fe, S 함량에 따른 다층구조가 관찰된다. 추후 전자현미분석(EPMA)을 통해 TIL 08007의 각 구성성분에서 관찰되는 이차광물 및 FGR 구성광물에 대한 정량분석을 수행할 예정이다.

THE WEAK THERMAL EVOLUTION OF THE PRIMITIVE HYDROUS ASTEROIDS RECORDED IN DEHYDRATED CM CARBONACEOUS CHONDRITES

2022-03-24T07:12:02Z

Title: THE WEAK THERMAL EVOLUTION OF THE PRIMITIVE HYDROUS ASTEROIDS RECORDED IN DEHYDRATED CM CARBONACEOUS CHONDRITES Authors: T. Nakamura; A. Nakato; Lee, Jong Ik; Ahn, Insu; T. Noguchi Abstract: The variety of thermal evolution process in the primitive hydrous asteroids can be understood from the study of dehydrated carbonaceous chondrites [e. g., 1]. We are studying more than 40 samples of CM and CM-like carbonaceous chondrites in order to identify and characterize samples having been dehydrated by heating. Synchrotron XRD analysis indicates that matrix phyllosilicates in PCA91084, Y-86695, LAR 06318, ALH 84033, DOM 03183, ALH 83100, and MIL 05152 are decomposed mainly to amorphous phases and secondary olivine and pyroxene are not crystallized. The results suggest that these samples suffered weak heating. The interpretation is confirmed by low maturation grade of organics measured by micro-Raman spectroscopy, low analytical totals of matrices and detection of ~0.3 wt% Cr2O3 in large ferroan olivines in type-II chondrules measured by FE-EPMA. TEM observation of matrices of some samples shows that the degree of crystalline-to-amorphous transformation varies between samples and thus the temperature of heating differs between samples. Oxygen isotopic ratios of all seven samples were analyzed by laser-fluorination mass spectrometer. The results show that Y-8665, DOM 03183, ALH 83100, and MIL 05152 distribute on the CM-CO line, while PCA91084, ALH84033, and LAR06318 are plotted on the CCAM line. Based on FE-SEM and TEM observations,matrices of the latter three samples are abundant in small primary silicates: they suffered low degree of aqueous alteration.

PETROLOGICAL FEATURES OF A NEW UREILITE (NWA6235) FROM FEZZOU, MOROCCO

2022-03-24T07:12:05Z

Title: PETROLOGICAL FEATURES OF A NEW UREILITE (NWA6235) FROM FEZZOU, MOROCCO Authors: T. Endo; K. Nagao; Y. Sawada; D. L. Dettman; Ahn, Insu; Y. Sampei; M. Kusakabe; H. Nishido; Lee, Jong Ik Abstract: A ureilite-like meteorite (NWA 6235), about 6cm x 5cm x 5cm and 216g, with a dark brown to black fusion crust, was collected at Fezzou, Morocco (30°55.68'N, 4°51.50'W). This study of petrographical analyses of NWA 6235 is based on microscopy, areal compositional mapping and mineral chemistry by EPMA (X-ray microanalyzer) and cathodoluminescence (CL). In addition, carbonaceous matter was analyzed using pyrolysis gas chromatography (py-GC) and mass spectrometry (py-GC/MS), and Raman icrospectorometric analysis. C-N-S elemental analysis and stable carbon and oxygen isotope analyses of powdered samples were also performed. NWA 6235 consists mainly of olivine and pigeonite with minor amounts of enstatite, augite, graphite, diamond, metallic iron, iron oxide, limonite and Fe-Cr-Ni sulfide as a mesostasis. The meteorite shows ureilite texture with triple junctions between olivine grains.