5:15 PM - 6:45 PM
[HSC07-P14] Physical properties of Neogene basalt to basaltic andesite: Differences between lava and volcaniclastic rocks
Keywords:Geological CO2 storage, Porosity, Basalt, Basaltic andesite, Neogene, Bulk rock chemistry
Recently, CCS (Carbon Dioxide Capture and Storage) initiatives have considered to store CO2 not only in sandstone, but also in mafic volcanic rocks such as basalt. As basalt have high divalent cations of Fe, Mg, and Ca, it is expected to mineralize CO2 better than sandstone. The terms “basalt” and “volcanic rock” encompass a broad classification of various lithofacies, including lava and volcaniclastic rocks, characterized by diverse properties such as vesicularity, sorting, grain size, and other features. Characteristics of rocks for CO2 geological storage are important information, and are thought to be various by lithofacies.
In this study, we investigated the characteristics of Neogene basalt to basaltic andesite lava and its volcaniclastic rocks, distributed in Motegi Town, Tochigi Prefecture, Japan. We collected five samples for each rock: two lavas (basalt and basaltic andesite) and three lapilli tuff samples. Then, we observed thin sections and measured effective porosity, bulk rock chemistry for the samples All of the samples are dense, dark gray colored, and are containing transparent to slightly white plagioclases minerals. Results of the observation of thin sections, plagioclases and altered orthopyroxenes are seen as phenocryst for lava samples The groundmass show intersertal texture, with plagioclases, orthopyroxenes, clinopyroxenes, and opaque minerals. And the crystallinity differs slightly between the two lava samples. The lapilli tuff samples contain many subangular clasts of lava (~1mm). White plagioclases of about 2 mm are found in matrix. In the observation of thin sections, plagioclases, altered orthopyroxenes and clinopyroxenes, opaque minerals, and brown altered minerals are seen.
The results of effective porosity measurements showed differences between the lava and lapilli tuff samples. The effective porosities of lava samples are ~2.8% to 3.2%, while that of tuff breccia samples are ~27% to 30%. Our results suggest that it is important to consider not only terms such as “basalt” and “volcanic rock” but also lithofacies such as “lava” and “volcaniclastic rocks” for considering potential for geological CO2 storage.
In this study, we investigated the characteristics of Neogene basalt to basaltic andesite lava and its volcaniclastic rocks, distributed in Motegi Town, Tochigi Prefecture, Japan. We collected five samples for each rock: two lavas (basalt and basaltic andesite) and three lapilli tuff samples. Then, we observed thin sections and measured effective porosity, bulk rock chemistry for the samples All of the samples are dense, dark gray colored, and are containing transparent to slightly white plagioclases minerals. Results of the observation of thin sections, plagioclases and altered orthopyroxenes are seen as phenocryst for lava samples The groundmass show intersertal texture, with plagioclases, orthopyroxenes, clinopyroxenes, and opaque minerals. And the crystallinity differs slightly between the two lava samples. The lapilli tuff samples contain many subangular clasts of lava (~1mm). White plagioclases of about 2 mm are found in matrix. In the observation of thin sections, plagioclases, altered orthopyroxenes and clinopyroxenes, opaque minerals, and brown altered minerals are seen.
The results of effective porosity measurements showed differences between the lava and lapilli tuff samples. The effective porosities of lava samples are ~2.8% to 3.2%, while that of tuff breccia samples are ~27% to 30%. Our results suggest that it is important to consider not only terms such as “basalt” and “volcanic rock” but also lithofacies such as “lava” and “volcaniclastic rocks” for considering potential for geological CO2 storage.