17:15 〜 19:15
[SGC37-P10] Spectroscopic analysis of microdiamonds from Kokchetav, Kazakhstan: Towards the elucidation of the origin of deep mantle fluids through the noble gas isotope analysis
キーワード：ダイヤモンド、マイクロダイヤモンド、C-O-H fluid、FT-IR、ラマン分光
Ultrahigh-pressure metamorphic rocks from Kokchetav, Kazakhstan, contain large amounts of very fine (tens to hundreds of micrometers) metamorphic diamonds (microdiamonds) (e.g., Sobolev & Shatsky, 1990). The presence of such diamond-bearing ultrahigh-pressure metamorphic rocks is considered evidence for the eventual recycling to the surface of some of the continental crustal material that was subducted with the oceanic plates into the Earth's deep interior (>100 km). However, the factors that drive the processes by which continental crustal materials, less dense than oceanic crust and mantle, are subducted to deeper regions such as diamond-forming sites and eventually recycled to the surface are poorly understood.
Seno and his research group pointed out that fluids may be essential in driving this large-scale circulation of crustal material. Deep fluids act as lubricants that promote the subduction of continental crust by being delivered to plate boundaries in continental collision zones (Seno & Rehman, 2011) and also play a role in causing detachment and uplift of the crust from the slab by weakening the adhesion between the crust and the peridotite that makes up the slab (Seno, 2008). On the other hand, infrared spectroscopic analysis has confirmed the presence of water and carbonate in microdiamonds, suggesting the close involvement of fluids (C-O-H fluids such as carbon dioxide (carbonate), methane, and water) in the formation of diamonds in ultrahigh-pressure metamorphic rocks (e.g., DeCorte et al., 1998). Therefore, the study of volatiles trapped in diamonds is important for revealing the origin of diamond-bearing ultrahigh-pressure metamorphic rocks, as well as the subduction and recycling processes of continental crustal materials.
In this study, we will analyze noble gas isotopes using a noble gas mass spectrometer on microdiamonds separated from ultrahigh-pressure metamorphic rocks. By combining the results with information on inclusions based on spectroscopic analysis, we aim to identify the origin of fluids trapped in diamonds and to reveal the mechanisms controlling the subduction of continental crust deep into the mantle and its recycling using a geochemical approach. As a first step toward noble gas isotope analysis of diamonds, we attempted to identify diamond inclusions (carbonates, fluids, etc.) by micro-Raman spectroscopy and micro-FTIR spectroscopy. Similar infrared spectroscopic analyses performed in previous studies have selected only huge grains (e.g., 100-300 μm; DeCorte et al., 1998), and the results may not represent Kokchetav microdiamonds. Therefore, we focused on diamonds with smaller grain sizes (30-50 μm) and aimed to perform micro-Raman and micro-FTIR spectroscopic analyses on individual diamonds. In the poster, we will present the sample preparation and the results of these analyses and compare them with previous studies on inclusions in microdiamonds.
Seno and his research group pointed out that fluids may be essential in driving this large-scale circulation of crustal material. Deep fluids act as lubricants that promote the subduction of continental crust by being delivered to plate boundaries in continental collision zones (Seno & Rehman, 2011) and also play a role in causing detachment and uplift of the crust from the slab by weakening the adhesion between the crust and the peridotite that makes up the slab (Seno, 2008). On the other hand, infrared spectroscopic analysis has confirmed the presence of water and carbonate in microdiamonds, suggesting the close involvement of fluids (C-O-H fluids such as carbon dioxide (carbonate), methane, and water) in the formation of diamonds in ultrahigh-pressure metamorphic rocks (e.g., DeCorte et al., 1998). Therefore, the study of volatiles trapped in diamonds is important for revealing the origin of diamond-bearing ultrahigh-pressure metamorphic rocks, as well as the subduction and recycling processes of continental crustal materials.
In this study, we will analyze noble gas isotopes using a noble gas mass spectrometer on microdiamonds separated from ultrahigh-pressure metamorphic rocks. By combining the results with information on inclusions based on spectroscopic analysis, we aim to identify the origin of fluids trapped in diamonds and to reveal the mechanisms controlling the subduction of continental crust deep into the mantle and its recycling using a geochemical approach. As a first step toward noble gas isotope analysis of diamonds, we attempted to identify diamond inclusions (carbonates, fluids, etc.) by micro-Raman spectroscopy and micro-FTIR spectroscopy. Similar infrared spectroscopic analyses performed in previous studies have selected only huge grains (e.g., 100-300 μm; DeCorte et al., 1998), and the results may not represent Kokchetav microdiamonds. Therefore, we focused on diamonds with smaller grain sizes (30-50 μm) and aimed to perform micro-Raman and micro-FTIR spectroscopic analyses on individual diamonds. In the poster, we will present the sample preparation and the results of these analyses and compare them with previous studies on inclusions in microdiamonds.