日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 H (地球人間圏科学) » H-CG 地球人間圏科学複合領域・一般

[H-CG32] 堆積・侵食・地形発達プロセスから読み取る地球表層環境変動

2019年5月26日(日) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:清家 弘治(産業技術総合研究所・地質調査総合センター)、山口 直文(茨城大学 広域水圏環境科学教育研究センター)、成瀬 元(京都大学大学院理学研究科)、高柳 栄子(東北大学大学院理学研究科地学専攻)

[HCG32-P06] Implications for paleoenvironment and tectonic setting of Khujirt area, Northern Mongolia

*Bat-Orshikh Erdenetsogt1Ariunbold Erdene2 (1.National University of Mongolia、2.ErdGeo LLC)

キーワード:sedimentology, geochemistry, Mongolia

Khujirt is a syncline that hosts Jurassic coal deposit in Northern Mongolia. Nine coal samples collected from exploration borehole were selected for analyses of major oxide and trace and REE elements of coal ash. The analyses were performed at Central Geological Laboratory in Ulaanbaatar, Mongolia according to appropriate international standards.

The average value of CAI for the samples is 82.8±1.6, reflecting intensive weathering in the source area. The plotted data on A-CN-K diagram displays that rocks in coal were sourced mainly from Early Permian andesite and basalt and Early Paleozoic granodiorite, which borders Khujirt syncline. It is also supported by AlO2O3/TiO2 (avg. 18.4±0.3) and TiO2/Zr (63.4±2.4) ratios. To infer tectonic setting, two multi-dimensional discrimination diagrams were used. The results suggest that the tectonic setting of Khujirt was foreland basin that was probably formed by closure of Mongol-Okhotsk Ocean. This finding is consistent with generally accepted tectonic history of the region. Low Rb/Sr (0.02-0.04) and high Sr/Cu (13.8-30.6) ratios of the studied samples indicate that arid climate condition was dominant during the deposition of Khujirt peat accumulation. This conclusion is supported by C-values of the samples range from 0.1 to 0.3 as well. Due to arid condition, salinity was high reflecting substantially high Sr/Ba ratio varying from 1.7 to 2.7.