11:00 〜 13:00
[SCG57-P05] 四万十帯大正層群の炭酸塩濃集スポット
キーワード：四万十帯、炭酸塩鉱物、カルサイト、炭酸塩濃集スポット
Because the trench sediment deposits deeper than carbonate compensation depth (CCD), carbonate mineral is uncommon within accretionary prism except a crack-sealed vein. Some carbonate concentration spots (CCS) were found within sandstone at sandstone dominant Taisyo Group at Shimanto Belt.
Sandstones are usually suffered pressure-solution deformation and have lower porosity less than 5%. The CCS is indistinguishable from the surrounding sandstone in outcrop, and only hydrochloric acid can reveal the distribution of it. The CCS penetrates sandstone layer with irregular shape. The size of the CCS is from several cm to one mater, and boundary between the CCS and surrounding sandstone is sharp. High content of carbonate mineral more than 60 % was observed within CCS, and there are very rare of micro carbonate patches at surrounding sandstone of CCS. Many silicate sand grains within CCS were dissolved, and they were emplaced by carbonate. Some grains having pressure-solution deformation suffered carbonate emplacement. The δ¹³C_VPDB of the calcite within CCS is from -5.1 to -1.9, and this is similar with the value of δ¹³C_VPDB of crack sealed vein at surrounding sandstone (Uchida et al., 2021).
These imply that the silicate grain dissolvable fluid flows within sandstone layer. Fluid flow may have been caused at late stage of diagenesis after pressure-solution deformation.
Reference
Fluid source of seismogenic accretionary body based on calcite isotope ratio. Shimanto complex, Shikoku, southwest Japan , Natsuki Uchida, Masafumi Murayama, Yuki Matsubara, Arito Sakaguchi, J.Geol.Soc.Japan, Vol.127, No.12, p.701-708, December 2021.
Sandstones are usually suffered pressure-solution deformation and have lower porosity less than 5%. The CCS is indistinguishable from the surrounding sandstone in outcrop, and only hydrochloric acid can reveal the distribution of it. The CCS penetrates sandstone layer with irregular shape. The size of the CCS is from several cm to one mater, and boundary between the CCS and surrounding sandstone is sharp. High content of carbonate mineral more than 60 % was observed within CCS, and there are very rare of micro carbonate patches at surrounding sandstone of CCS. Many silicate sand grains within CCS were dissolved, and they were emplaced by carbonate. Some grains having pressure-solution deformation suffered carbonate emplacement. The δ¹³C_VPDB of the calcite within CCS is from -5.1 to -1.9, and this is similar with the value of δ¹³C_VPDB of crack sealed vein at surrounding sandstone (Uchida et al., 2021).
These imply that the silicate grain dissolvable fluid flows within sandstone layer. Fluid flow may have been caused at late stage of diagenesis after pressure-solution deformation.
Reference
Fluid source of seismogenic accretionary body based on calcite isotope ratio. Shimanto complex, Shikoku, southwest Japan , Natsuki Uchida, Masafumi Murayama, Yuki Matsubara, Arito Sakaguchi, J.Geol.Soc.Japan, Vol.127, No.12, p.701-708, December 2021.