The oxidation process from magnetite to hematite through maghemite was investigated by X – ray di ff raction (XRD) and X – ray absorption spectroscopic techniques. The XRD pattern of magnetite heated at 100 °C for 3 h showed small re fl ections of maghemite with partially ordered distribution of vacancy (space group P 4 1 32 or P 4 3 32). Thereafter, the XRD pattern of magnetite heated at 250 °C for 3 h exhibited extra re fl ections corresponding to the tetragonal maghemite with fully ordered distribution of vacancy (space group P 4 1 2 1 2 or P 4 3 2 1 2). Di ff raction peaks of hematite occurred from the magnetite heated at 250 °C, in which maghemite and hematite coexisted with magnetite. Di ff raction peaks of magnetite subsequently disappeared at 300 °C. Instead, maghemite and hematite dominated the XRD pattern, but the amount of maghemite reduced from 300 °C. The maghemite completely disappeared at 500 °C, and hematite fi nally dominated the XRD pattern. Rietveld fi tting results clearly showed that the a lattice parameter and site occupancy factor of Fe at the octahedral site continuously decreased at the temperatures from 25 to 300 °C. The X – ray absorption near edge structure (XANES) result showed that the Fe 3+ / Σ Fe increased up to 300 °C and remained constant until 500 °C, indicating that Fe 2+ in oxidized magnetite was completely oxidized to Fe 3+ at 300 °C. Furthermore, the intensities of radial structure function (RSF) peaks at 1.7 and 3.1 Å corresponding to the Fe – O bonds in octahedral site and the Fe – Fe interaction between the octahedral sites reduced continuously from 25 to 300 °C. The fi tting results of the fi rst shells indicated that the coordination number and site occupancy factor at the octahedral site continuously decreased at the temperature range from 25 to 300 °C, which were approximately consistent with those of Rietveld fi tting analysis. The a lattice parameter of the oxidized magnetite displayed a linear trend between stoichiometric magnetite and stoichiometric maghemite with a relationship of a = 0.0985 x + 8.3397 ( x = Fe 2+ /Fe 3+ ). It was clearly con fi rmed that during the magnetite oxidation, Fe was continuously removed from the octahedral sites, which resulted in the formation of maghemite with partially ordered distribution of vacancy. Just after magnetite oxidation was completed, the vacancy ordering further progressed by the di ff usion of Fe 3+ within the structure, leading to the formation of maghemite with fully ordered distribution of vacancy.
{"title":"Study on magnetite oxidation using synchrotron X–ray diffraction and X–ray absorption spectroscopy: Vacancy ordering transition in maghemite (γ–Fe2O3)","authors":"Ibuki Kinebuchi, A. Kyono","doi":"10.2465/jmps.210304","DOIUrl":"https://doi.org/10.2465/jmps.210304","url":null,"abstract":"The oxidation process from magnetite to hematite through maghemite was investigated by X – ray di ff raction (XRD) and X – ray absorption spectroscopic techniques. The XRD pattern of magnetite heated at 100 °C for 3 h showed small re fl ections of maghemite with partially ordered distribution of vacancy (space group P 4 1 32 or P 4 3 32). Thereafter, the XRD pattern of magnetite heated at 250 °C for 3 h exhibited extra re fl ections corresponding to the tetragonal maghemite with fully ordered distribution of vacancy (space group P 4 1 2 1 2 or P 4 3 2 1 2). Di ff raction peaks of hematite occurred from the magnetite heated at 250 °C, in which maghemite and hematite coexisted with magnetite. Di ff raction peaks of magnetite subsequently disappeared at 300 °C. Instead, maghemite and hematite dominated the XRD pattern, but the amount of maghemite reduced from 300 °C. The maghemite completely disappeared at 500 °C, and hematite fi nally dominated the XRD pattern. Rietveld fi tting results clearly showed that the a lattice parameter and site occupancy factor of Fe at the octahedral site continuously decreased at the temperatures from 25 to 300 °C. The X – ray absorption near edge structure (XANES) result showed that the Fe 3+ / Σ Fe increased up to 300 °C and remained constant until 500 °C, indicating that Fe 2+ in oxidized magnetite was completely oxidized to Fe 3+ at 300 °C. Furthermore, the intensities of radial structure function (RSF) peaks at 1.7 and 3.1 Å corresponding to the Fe – O bonds in octahedral site and the Fe – Fe interaction between the octahedral sites reduced continuously from 25 to 300 °C. The fi tting results of the fi rst shells indicated that the coordination number and site occupancy factor at the octahedral site continuously decreased at the temperature range from 25 to 300 °C, which were approximately consistent with those of Rietveld fi tting analysis. The a lattice parameter of the oxidized magnetite displayed a linear trend between stoichiometric magnetite and stoichiometric maghemite with a relationship of a = 0.0985 x + 8.3397 ( x = Fe 2+ /Fe 3+ ). It was clearly con fi rmed that during the magnetite oxidation, Fe was continuously removed from the octahedral sites, which resulted in the formation of maghemite with partially ordered distribution of vacancy. Just after magnetite oxidation was completed, the vacancy ordering further progressed by the di ff usion of Fe 3+ within the structure, leading to the formation of maghemite with fully ordered distribution of vacancy.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68831138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yuichiro Mori, H. Kagi, S. Kakizawa, K. Komatsu, Chikara Shito, Riko Iizuka-Oku, K. Aoki, T. Hattori, A. Sano‐Furukawa, K. Funakoshi, Hirouyki Saitoh
{"title":"Neutron diffraction study of hydrogen site occupancy in Fe0.95Si0.05 at 14.7 GPa and 800 K","authors":"Yuichiro Mori, H. Kagi, S. Kakizawa, K. Komatsu, Chikara Shito, Riko Iizuka-Oku, K. Aoki, T. Hattori, A. Sano‐Furukawa, K. Funakoshi, Hirouyki Saitoh","doi":"10.2465/jmps.210825","DOIUrl":"https://doi.org/10.2465/jmps.210825","url":null,"abstract":"","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68831656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Compositional variations of talc in peridotites and serpentinites could have significant implications for modeling of geochemical cycles involving the upper mantle but have been scarcely studied. We analyzed chemical compositions of prograde and retrograde talc and associated minerals in thermally metamorphosed serpentinites from Southwest Japan. The analyzed talc has variations of Si, Al, Mg, Fe, and Na contents. Most of the Si, Al, Mg, and Fe variations indicate mechanical mixing with serpentine and chlorite at a submicroscopic scale. Spatial distribution of talc–chlorite mixtures suggests their prograde metamorphic origin. Talc–serpentine mixtures could be formed by retrograde decomposition of talc–olivine assemblage and orthopyroxene at conditions of higher temperature and/or higher Si activity than serpentine–brucite mixtures, which are the typical products of serpentinization of olivine. Talc itself, regardless of prograde or retrograde origin, has compositional variations with Na enrichment as a likely result of solid solution or Na–mica mixing. The Na enrichment suggests that talc could be the most capable reservoir of Na in metamorphosed peridotites and serpentinites.
{"title":"Compositional variation of talc in metamorphosed serpentinites from Southwest Japan","authors":"T. Nozaka, Daisuke Miyamoto","doi":"10.2465/jmps.211112","DOIUrl":"https://doi.org/10.2465/jmps.211112","url":null,"abstract":"Compositional variations of talc in peridotites and serpentinites could have significant implications for modeling of geochemical cycles involving the upper mantle but have been scarcely studied. We analyzed chemical compositions of prograde and retrograde talc and associated minerals in thermally metamorphosed serpentinites from Southwest Japan. The analyzed talc has variations of Si, Al, Mg, Fe, and Na contents. Most of the Si, Al, Mg, and Fe variations indicate mechanical mixing with serpentine and chlorite at a submicroscopic scale. Spatial distribution of talc–chlorite mixtures suggests their prograde metamorphic origin. Talc–serpentine mixtures could be formed by retrograde decomposition of talc–olivine assemblage and orthopyroxene at conditions of higher temperature and/or higher Si activity than serpentine–brucite mixtures, which are the typical products of serpentinization of olivine. Talc itself, regardless of prograde or retrograde origin, has compositional variations with Na enrichment as a likely result of solid solution or Na–mica mixing. The Na enrichment suggests that talc could be the most capable reservoir of Na in metamorphosed peridotites and serpentinites.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"23 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68831863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Nagashima, D. Nishio–Hamane, Shuichi Ito, Takahiro Tanaka
{"title":"Ferriprehnite, Ca2Fe3+(AlSi3)O10(OH)2, an Fe3+ analogue of prehnite, from Kouragahana, Shimane Peninsula, Japan","authors":"M. Nagashima, D. Nishio–Hamane, Shuichi Ito, Takahiro Tanaka","doi":"10.2465/jmps.210127","DOIUrl":"https://doi.org/10.2465/jmps.210127","url":null,"abstract":"","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68831059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Enami, Shuaimin Huang, M. Tsuboi, Yuki Wakasugi
*Institute for Space–Earth Environmental Research, Nagoya University, Nagoya 464–8601, Japan **Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464–8601, Japan ***Department of Applied Chemistry for Environment, School of Science and Technology, Kwansei Gakuin University, Sanda 669–1337, Japan †Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Sanda 669–1337, Japan
{"title":"Petrological and mineralogical contrasts of basic lithologies between eclogite and non–eclogite units along the Kokuryo River of the Sanbagawa belt, Central Shikoku, Japan","authors":"M. Enami, Shuaimin Huang, M. Tsuboi, Yuki Wakasugi","doi":"10.2465/jmps.181107a","DOIUrl":"https://doi.org/10.2465/jmps.181107a","url":null,"abstract":"*Institute for Space–Earth Environmental Research, Nagoya University, Nagoya 464–8601, Japan **Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464–8601, Japan ***Department of Applied Chemistry for Environment, School of Science and Technology, Kwansei Gakuin University, Sanda 669–1337, Japan †Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Sanda 669–1337, Japan","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2020-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41644296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
James Cesar Avisado Refran, T. Ohba, C. Arcilla, T. Hoshide, M. Balangue-Tarriela
Manguao Basalt is a Plio–Pleistocene basaltic lava flow located on the northeastern edge of Palawan Island, Philippines. The absence of active trenches surrounding the Palawan Continental Block (PCB) poses a challenge regarding the nature and origin of magmatism in the region. This study presents the petrographic and geochemical character of Manguao Basalt, as well as provides insights to the melt formation beneath the PCB. Manguao Basalt samples are olivine–phyric with minor pyroxenes, set in a plagioclase–dominated microcrystalline groundmass. Average bulk–rock major element composition of Manguao Basalt shows similarities to common olivine basalt tholeiite. Petrographic observations of the phenocrysts, however, show the unusual precedence of pyroxenes in the crystallization sequence. Calculated formation temperatures and pressures of the modal assemblage are consistent with this idea of early pyroxene formation. Simulations of mantle melting using the MELTS program show the formation of pyroxene–saturated primitive liquids. The evolution of these primitive liquids reaches similarities with Manguao Basalt composition at 1230–1260 °C. Simulations of equilibrium and fractional crystallization demonstrate the formation of olivine or orthopyroxene as the first crystals. However, the simulations done at equilibrium conditions are more consistent with the observed mineral chemistry of pyroxene phenocrysts in Manguao Basalt. Hence, maintaining the equilibrium between the source and melt is crucial for replicating the observed pyroxene chemistry. Magmatic underplating provides an excellent model for visualizing the melting and crystallization processes beneath the PCB. The model is also consistent with the narrative of other magmatic units in northern Palawan (e.g., Capoas Granite). The significant findings of this study contribute to the understanding of the tectonic evolution of the PCB.
{"title":"Deep crustal crystallization of tholeiitic melt: Insights from Manguao Basalt, Palawan, Philippines","authors":"James Cesar Avisado Refran, T. Ohba, C. Arcilla, T. Hoshide, M. Balangue-Tarriela","doi":"10.2465/jmps.191211","DOIUrl":"https://doi.org/10.2465/jmps.191211","url":null,"abstract":"Manguao Basalt is a Plio–Pleistocene basaltic lava flow located on the northeastern edge of Palawan Island, Philippines. The absence of active trenches surrounding the Palawan Continental Block (PCB) poses a challenge regarding the nature and origin of magmatism in the region. This study presents the petrographic and geochemical character of Manguao Basalt, as well as provides insights to the melt formation beneath the PCB. Manguao Basalt samples are olivine–phyric with minor pyroxenes, set in a plagioclase–dominated microcrystalline groundmass. Average bulk–rock major element composition of Manguao Basalt shows similarities to common olivine basalt tholeiite. Petrographic observations of the phenocrysts, however, show the unusual precedence of pyroxenes in the crystallization sequence. Calculated formation temperatures and pressures of the modal assemblage are consistent with this idea of early pyroxene formation. Simulations of mantle melting using the MELTS program show the formation of pyroxene–saturated primitive liquids. The evolution of these primitive liquids reaches similarities with Manguao Basalt composition at 1230–1260 °C. Simulations of equilibrium and fractional crystallization demonstrate the formation of olivine or orthopyroxene as the first crystals. However, the simulations done at equilibrium conditions are more consistent with the observed mineral chemistry of pyroxene phenocrysts in Manguao Basalt. Hence, maintaining the equilibrium between the source and melt is crucial for replicating the observed pyroxene chemistry. Magmatic underplating provides an excellent model for visualizing the melting and crystallization processes beneath the PCB. The model is also consistent with the narrative of other magmatic units in northern Palawan (e.g., Capoas Granite). The significant findings of this study contribute to the understanding of the tectonic evolution of the PCB.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47727362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
CO 2 distribution in M 12 and M 14 cages of CO 2 – rich melanophlogite from Fortunillo, was studied using synchrotron powder X – ray di ff raction. Original and two heat – treated samples at 500 and 1000 °C were studied at room temperature. The di ff raction patterns of these samples can be indexed as a cubic cell ( Pm (cid:1)3 n ). For the non – heated sample, CO 2 occupancy for M 14 cage is close to unity, whereas about 0.85 for M 12 cage. For the 500 °C – heated sample, the occupancies for M 14 and M 12 cages are reduced to 0.79 and 0.57, respectively. Present study showed that CO 2 has preference to M 14 cage, but substantial CO 2 occupies M 12 cage. The electron distributions obtained by MEM analysis clearly reveal orientationally ordered CO 2 distribution in M 12 and M 14 cages. Present result is also used to clarify a recently proposed interpretation for the splitting of CO 2 Raman vibrational peak for the heat – treated melanophlogite.
{"title":"CO2 distribution in CO2–rich melanophlogite from Fortunillo, Tuscany, Italy","authors":"M. Kanzaki","doi":"10.2465/jmps.200611","DOIUrl":"https://doi.org/10.2465/jmps.200611","url":null,"abstract":"CO 2 distribution in M 12 and M 14 cages of CO 2 – rich melanophlogite from Fortunillo, was studied using synchrotron powder X – ray di ff raction. Original and two heat – treated samples at 500 and 1000 °C were studied at room temperature. The di ff raction patterns of these samples can be indexed as a cubic cell ( Pm (cid:1)3 n ). For the non – heated sample, CO 2 occupancy for M 14 cage is close to unity, whereas about 0.85 for M 12 cage. For the 500 °C – heated sample, the occupancies for M 14 and M 12 cages are reduced to 0.79 and 0.57, respectively. Present study showed that CO 2 has preference to M 14 cage, but substantial CO 2 occupies M 12 cage. The electron distributions obtained by MEM analysis clearly reveal orientationally ordered CO 2 distribution in M 12 and M 14 cages. Present result is also used to clarify a recently proposed interpretation for the splitting of CO 2 Raman vibrational peak for the heat – treated melanophlogite.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47780426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kohei Chiba, Misaki Takahashi, E. Ohshima, T. Kawamata, K. Sugiyama
A mixture of metavivianite, vivianite, and spheniscidite was obtained from an aqueous solution of FeSO 4 ·7H 2 O and (NH 4 ) 2 HPO 4 at temperatures between 50 and 60 °C. The oxidation sequence of partially oxidized vivianite toward santabarbaraite or a solid solution between β – Fe 2 (PO 4 )O and Fe 4 (PO 4 ) 3 (OH) 3 , without passing through metavivianite, was also demonstrated.
{"title":"The synthesis of metavivianite and the oxidation sequence of vivianite","authors":"Kohei Chiba, Misaki Takahashi, E. Ohshima, T. Kawamata, K. Sugiyama","doi":"10.2465/jmps.200417","DOIUrl":"https://doi.org/10.2465/jmps.200417","url":null,"abstract":"A mixture of metavivianite, vivianite, and spheniscidite was obtained from an aqueous solution of FeSO 4 ·7H 2 O and (NH 4 ) 2 HPO 4 at temperatures between 50 and 60 °C. The oxidation sequence of partially oxidized vivianite toward santabarbaraite or a solid solution between β – Fe 2 (PO 4 )O and Fe 4 (PO 4 ) 3 (OH) 3 , without passing through metavivianite, was also demonstrated.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2020-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43809730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the fi rst report of okhotskite in a lawsonite – blueschist – subfacies metachert of the Hakoishi subunit, Kurosegawa Belt, Kyushu, Japan, which was metamorphosed at peak temperatures and pressures of 200 – 300 °C and 0.6 – 0.8 GPa. This okhotskite – bearing assemblage is particularly notable because it formed at higher pressures than that of previously documented okhotskite with available pressure estimations. Textural relationships indicate that okhotskite formed during peak metamorphism in equilibrium with piemontite, Na pyroxene, mag-nesioriebeckite, braunite, and hematite. Okhotskite shows a signi fi cant variation in Fe:Mn ratio (Fe tot /Mn tot = 0.13 – 0.56) and a following average empirical formula; (Ca 7.62 Mn 2+0.16 ) Σ 7.78 (Mn 2+2.71 Mg 1.29 ) Σ 4.00 (Mn 3+4.13 Fe 3+2.26 Al 1.36 V 3+0.23 Ti 0.02 ) Σ 8.00 Si 11.86 O 44.02 (OH) 16.98 . Raman spectra of okhotskite are reported for the fi rst time and show characteristic peaks at 362, 480, and 563 cm − 1 . The stability relationships between okhotskite and other Mn – bearing minerals, such as piemontite, sursassite, spessartine, braunite, and Mn – bearing lawsonite, are examined using a revised Schreinemakers ’ analysis. The obtained petrogenetic grid provides tight constraints on the P – T relation-ship of natural mineral assemblages observed in Mn – bearing cherts within epidote – blueschist – grade and lawsonite – blueschist – grade. Furthermore, this petrogenetic grid predicts that the assemblage of okhotskite and Mn – bearing lawsonite should be stable at higher pressures. The higher – pressure stability suggests that highly oxidized Mn – bearing metacherts can transport water and bu ff er oxygen in the deeper parts of subduction zones, given that okhotskite and Mn – bearing lawsonite contain high water contents (6.9 and 11.3 wt% H 2 O, respec-tively) and trivalent manganese.
本文首次报道了在日本九州黑川带白石亚单元中，在200 ~ 300℃、0.6 ~ 0.8 GPa的峰值温度和压力下变质的褐煤-蓝片岩-亚相变质岩中发现的霍霍钛矿。这个含霍霍钛矿的组合特别值得注意，因为它形成的压力比以前记录的有可用压力估计的霍霍钛矿高。构造关系表明，霍霍钛矿形成于与片辉石、钠辉石、镁辉石、褐灰岩和赤铁矿平衡的峰变质过程中。鄂霍茨钛矿Fe:Mn比值变化显著(Fe tot /Mn tot = 0.13 ~ 0.56)，平均经验公式如下:(Ca 7.62 Mn 2+0.16) Σ 7.78 (Mn 2+2.71 Mg 1.29) Σ 4.00 (Mn 3+4.13 Fe 3+2.26 Al 1.36 V 3+0.23 Ti 0.02) Σ 8.00 Si 11.86 O 44.02 (OH) 16.98。本文首次报道了霍霍钛矿的拉曼光谱，其特征峰位于362、480和563 cm−1。利用修正后的Schreinemakers分析方法，研究了霍霍钛矿与其他含锰矿物(如片铁矿、苏长石、辉钼矿、白钨矿和含锰lawsonite)之间的稳定性关系。所得的岩石成因网格对绿帘石-蓝片岩品位和褐铁矿-蓝片岩品位含锰燧石中观察到的天然矿物组合的P - T关系有严格的约束。此外，该成因格网预测，在较高的压力下，霍霍钛矿和含锰铁榴辉石的组合应该是稳定的。高压力稳定性表明，高氧化的含锰元岩可以在俯冲带的深层输送水和氧，因为霍霍钛矿和含锰的lawsonite含有高含水量(分别为6.9 wt%和11.3 wt%的h2o)和三价锰。
{"title":"A new occurrence of okhotskite in the Kurosegawa belt, Kyushu, Japan: the okhotskite + Mn–lawsonite assemblage as a potential high–pressure indicator","authors":"Wataru Yabuta, T. Hirajima","doi":"10.2465/jmps.190831","DOIUrl":"https://doi.org/10.2465/jmps.190831","url":null,"abstract":"We present the fi rst report of okhotskite in a lawsonite – blueschist – subfacies metachert of the Hakoishi subunit, Kurosegawa Belt, Kyushu, Japan, which was metamorphosed at peak temperatures and pressures of 200 – 300 °C and 0.6 – 0.8 GPa. This okhotskite – bearing assemblage is particularly notable because it formed at higher pressures than that of previously documented okhotskite with available pressure estimations. Textural relationships indicate that okhotskite formed during peak metamorphism in equilibrium with piemontite, Na pyroxene, mag-nesioriebeckite, braunite, and hematite. Okhotskite shows a signi fi cant variation in Fe:Mn ratio (Fe tot /Mn tot = 0.13 – 0.56) and a following average empirical formula; (Ca 7.62 Mn 2+0.16 ) Σ 7.78 (Mn 2+2.71 Mg 1.29 ) Σ 4.00 (Mn 3+4.13 Fe 3+2.26 Al 1.36 V 3+0.23 Ti 0.02 ) Σ 8.00 Si 11.86 O 44.02 (OH) 16.98 . Raman spectra of okhotskite are reported for the fi rst time and show characteristic peaks at 362, 480, and 563 cm − 1 . The stability relationships between okhotskite and other Mn – bearing minerals, such as piemontite, sursassite, spessartine, braunite, and Mn – bearing lawsonite, are examined using a revised Schreinemakers ’ analysis. The obtained petrogenetic grid provides tight constraints on the P – T relation-ship of natural mineral assemblages observed in Mn – bearing cherts within epidote – blueschist – grade and lawsonite – blueschist – grade. Furthermore, this petrogenetic grid predicts that the assemblage of okhotskite and Mn – bearing lawsonite should be stable at higher pressures. The higher – pressure stability suggests that highly oxidized Mn – bearing metacherts can transport water and bu ff er oxygen in the deeper parts of subduction zones, given that okhotskite and Mn – bearing lawsonite contain high water contents (6.9 and 11.3 wt% H 2 O, respec-tively) and trivalent manganese.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2020-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45938378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Suo metamorphic complex in the Chugoku Mountains of southwest (SW) Japan represents Jurassic high pressure (P )/temperature (T ) type metamorphic rocks. Its high–grade part is exposed in the Nichinan area, where barroisite–bearing mafic schist occurs as ~ 50–m thick layers in pelitic schist. These mafic layers contain the common matrix assemblage barroisite + epidote + albite + quartz + titanite + phengite. Relic minerals (garnet, glaucophane, aegirine–augite, Si–rich phengite and rutile) of early–stage parageneses are preserved within albite porphyroblasts. The textural relations combined with pseudosection modeling suggest a clockwise P–T trajectory from epidote–blueschist facies through the garnet + clinopyroxene stable conditions to epidote– amphibolite facies. Two distinct phases of high–strain ductile deformation (D1 and D2) can be recognized in the area, and they are related to early and late stages of exhumation. Albite porphyroblasts initially grew statically between D1 and D2 at ~ 520–530 °C and ~ 0.8 GPa, and further retrogressive growth of albite rims and chlorite at the expense of barroisite is synchronous with D2. The lithological association, deformation structures and metamorphic conditions of the Jurassic Suo metamorphic complex are very similar to those of the Cretaceous Sanbagawa metamorphic complex, suggesting they have comparable exhumation processes as coherent–type high–P/T metamorphic complexes.
{"title":"Structural and paragenetic evolution of garnet–bearing barroisite schist from the Suo metamorphic complex, SW Japan","authors":"M. Eto, S. Endo","doi":"10.2465/jmps.200127","DOIUrl":"https://doi.org/10.2465/jmps.200127","url":null,"abstract":"The Suo metamorphic complex in the Chugoku Mountains of southwest (SW) Japan represents Jurassic high pressure (P )/temperature (T ) type metamorphic rocks. Its high–grade part is exposed in the Nichinan area, where barroisite–bearing mafic schist occurs as ~ 50–m thick layers in pelitic schist. These mafic layers contain the common matrix assemblage barroisite + epidote + albite + quartz + titanite + phengite. Relic minerals (garnet, glaucophane, aegirine–augite, Si–rich phengite and rutile) of early–stage parageneses are preserved within albite porphyroblasts. The textural relations combined with pseudosection modeling suggest a clockwise P–T trajectory from epidote–blueschist facies through the garnet + clinopyroxene stable conditions to epidote– amphibolite facies. Two distinct phases of high–strain ductile deformation (D1 and D2) can be recognized in the area, and they are related to early and late stages of exhumation. Albite porphyroblasts initially grew statically between D1 and D2 at ~ 520–530 °C and ~ 0.8 GPa, and further retrogressive growth of albite rims and chlorite at the expense of barroisite is synchronous with D2. The lithological association, deformation structures and metamorphic conditions of the Jurassic Suo metamorphic complex are very similar to those of the Cretaceous Sanbagawa metamorphic complex, suggesting they have comparable exhumation processes as coherent–type high–P/T metamorphic complexes.","PeriodicalId":51093,"journal":{"name":"Journal of Mineralogical and Petrological Sciences","volume":"115 1","pages":"416-427"},"PeriodicalIF":0.7,"publicationDate":"2020-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45277361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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