Japan Geoscience Union Meeting 2016

Presentation information

Oral

Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG56] Petrology, Mineralogy and Resource Geology

Thu. May 26, 2016 1:45 PM - 3:15 PM 201B (2F)

Convener:*Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Akira Miyake(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Nobutaka Tsuchiya(Department of Geology, Faculty of Education, Iwate University), Satoshi SAITO(Graduate School of Science and Engineering, Ehime University), Chair:Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Akira Miyake(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University)

2:15 PM - 2:30 PM

[SCG56-11] New occurrences of silica clathrate minerals in Sakhalin

*Koichi Momma1, Kenichiro Tani1, Ritsuro Miyawaki1 (1.National Museum of Nature and Science)

Keywords:silica clathrate minerals, methane seep, chemosynthetic community

Silica clathrate minerals are rare minerals containing various gas molecules (CH4, C2H6, CO2, H2S, N2 etc.) in their cage-like framework structures constructed of pure silica. Three types of silica clathrate minerals have been hitherto known in nature. They are structurally analogous to gas hydrates. In fact, the three minerals, melanophlogite, chibaite, and bosoite are isostructural with three types of natural gas hydrates, i.e., sI, sII, and sH hydrates, respectively. The source of gas molecules in silica clathrate minerals is also considered to be common with one type of natural gas hydrates having thermogenic origin.
We recently noticed two specimens of quartz pseudomorphs from Sakhalin in old mineral collection of the National Museum of Nature and Science. They are labeled as quartz pseudomorphs after fluorite or apophyllite because they have truncated octahedral shape. However, they look identical to quartz pseudomorphs after chibaite occurred in Chiba and Nagano prefectures. These specimens motivated us to field investigation of Sakhalin. The two specimens are from “Souni misaki” (Kuznetsova) and “Bisyasan”, the most southwest part of Sakhalin where Miocene sedimentary rocks and volcanic rocks are exposed. Unfortunately, we could not approach these places during the field survey in 2015 but we discovered new locality of melanophlogite at Nevelsk. Melanophlogite is associated with fossils of various chemosynthetic shells in calcareous concretion of mudstone of Miocene age. The concretions are abundantly distributed as veins or pipes mostly parallel to the bedding plane, or some of them look like isolated nodules of diameters up to several meters. Among these concretions, melanophlogite only occurs in the one containing massive amount of shells and voids. Melanophlogite occurs in these voids as aggregates of cubic crystals of sizes up to 0.1 mm, associated with chalcedony and small quartz crystals.