日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG49] ハードロック掘削科学~陸上掘削から深海底掘削、そしてオマーン~

2019年5月28日(火) 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:道林 克禎(名古屋大学大学院環境学研究科地球環境科学専攻地質・地球生物学講座岩石鉱物学研究室)、高澤 栄一(新潟大学理学部地質科学科)、秋澤 紀克(東京大学 大気海洋研究所 海洋底科学部門)

[SCG49-P06] The evolution of melt inclusions in podiform chromitite in Oman

*YAO Yuan1 高澤 栄一2,3Oman Drilling Project Phase 2 Science Party (1.新潟大学大学院、2.新潟大学理学部、3.JAMSTEC)

キーワード:melt inclusion、Oman、chromitite

Melt inclusions are tiny inclusions which trapped in the host magmatic minerals. After trapping, the host mineral can be considered as a closed and isolated system (Roedder, 1984). Thus, melt inclusions behave as time capsules, which record the liquid line of descent of magmatic systems (Frezzotti, 2001). Therefore, melt inclusions can provide important information of the primary melts (Kent, 2008).

We studied the melt inclusions in chromite from a chromitite deposit mine in the north of Maqsad and the core sample from the Oman drilling project phase 2. The silicate inclusions range in diameter from 5μm to 200μm, contain pargasite, tremolite, aspidolite, high Cr# (=Cr/[Cr+Al] atomic ratio) chromite, diopside, enstatite, forsterite, grossular, albite, titanite, pentlandite, apatite, chlorite, wollastonite and serpentine. We found the high Cr# chromite occurs as lining of the inclusion, moreover the daughter minerals precipitated in the high Cr# chromite lining. Those phenomenon can be explained by the crystallization of chromite on the wall of inclusion. In addition, this is the first report about the necking down of melt inclusion in chromitite. The necking down of inclusions is an originally large, liquid-filled inclusion divided into smaller inclusions. If the necking down happens after the phase change of inclusion, the compositions of smaller inclusions probably are inhomogeneity. Last year, we conducted the high temperature homogenized experiments, the result showed that the homogenized quenching glass are heterogeneous. We consider the inhomogeneity of inclusions perhaps caused by the necking down. Based above all, we suggest the composition of homogenized inclusion can not represent the parental melt.

To summarize, we suggest before analysis and experiment of inclusions in chromite, the origin and the evolution of inclusions should be carefully studied.

Reference
Frezzotti, M. (2001). "Silicate-melt inclusions in magmatic rocks: applications to petrology." Lithos 55 (1-4): 273-299.
Kent, A. J. R. (2008). "Melt Inclusions in Basaltic and Related Volcanic Rocks." Reviews in Mineralogy and Geochemistry 69 (1): 273-331.
Roedder, E. (1984). Fluid inclusions, Walter de Gruyter GmbH & Co KG.