Ikuo Katayama - Profile on Academia.edu (original) (raw)
Papers by Ikuo Katayama
Garnet shapes within Kimberlite xenoliths record the tectonic evolution of a cratonic root
AGUFM, Dec 1, 2013
Japan Geoscience Union, Mar 10, 2016
Apollo program installed some seismometers on the moon and the seismic data provided us the much ... more Apollo program installed some seismometers on the moon and the seismic data provided us the much information about the moon interior. Analysis of moonquake data supports the following: The moon
Journal of the Geological Society of Japan, 2017
Rheological structures for continental and oceanic plates were calculated using the laboratory-ba... more Rheological structures for continental and oceanic plates were calculated using the laboratory-based frictional and flow laws. Our results show that Peierls creep becomes the dominant mechanism for plastic deformation at low temperatures and high stresses under both dry and wet conditions. When Peierls creep, rather than dislocation-accommodated power-law creep, is the dominant mechanism, there is a lower maximum mechanical strength, and a shallower depth to the brittle-plastic transition in our model. The rheology of continental lithosphere is complex, but may feature a weak lower crust sandwiched between a strong upper crust and mantle. Extensive deformation of this weak zone may explain crustal duplication in continental collision zone. The thick continental lithosphere beneath craton is stable for billions of years. This is partly because partial melting has depleted these regions of water, causing an increase in the mechanical strength of the continental lithosphere. The depth of brittle-plastic transition at island arcs, which we inferred from the maximum depth of seismicity, suggests that the fore-arc regions are enriched in water, but that the back-arc regions are depleted. The rheological structure of oceanic plate is dependent on the age of the plate, and the thickness of oceanic lithosphere is largely consistent with a dry rheology. A relatively thin elastic thickness found for the oceanic lithosphere in the Mariana and Bonin arcs may be explained by local weakening as a result of hydration along outer-rise faults.
Lunar and Planetary Science Conference, Mar 1, 2011
It is thought that plate tectonics is a product of the localized brittle failure in the lithosphe... more It is thought that plate tectonics is a product of the localized brittle failure in the lithosphere and viscous flow in the asthenosphere, and strength profile is a key to understand tectonics of terrestrial planet (Burgmann and Dresen, 2008). Physical properties, such as temperature and pressure and stress, and the chemical compositional layering between crust and mantle result in a strong rheological layering in the planet interior. It has been estimated by previous experiments that the brittle-ductile transition occurs in the planet interior and deformation mechanisms can be changed with increasing depth. In the present study, we evaluate rheological variation in the crust-mantle transition based on new series of deformation experiments, and discuss why plate tectonics doesn't exist in the other terrestrial planets except the Earth. In case of the earth, two different models on the strength profile in the continental crust have been proposed. The first is the "jelly sandwich" model that had been embraced for the past two decades. This model is that a weak middle and lower crust are sandwiched between strong upper crust and strong mantle lithosphere just like a jelly sandwich (e.g., Chen and Molnar, 1983). The second one is the "creme brullee" model, in which the upper mantle is significantly weak, and consequently region for viscous deformation continues into the mantle depth (Jackson, 2002). These two models of strength profile are given by extrapolating frictional strength and viscous flow law of each material to temperature and pressure corresponding to interior of the Earth. In this study, we performed experiment to directly determine the relative strength between plagioclase and olivine without any extrapolating of flow law; the crustal materials consist predominantly of plagioclase that largely control deformation of the crust, whereas deformation of the upper mantle is largely controlled by olivine. These samples are together sandwiched between alumina pistons in simple shear geometry and we used the hot-pressed samples and performed deformation experiments using solid-medium deformation apparatus. The experimental conditions were ranging 1GPa and 400-800 degrees, corresponding conditions to Moho of the Earth under water-rich conditions. The experimental results show that plagioclase and olivine are expected to show almost no difference in strength at temperatures of the continental Moho of the Earth, ca. 500-600 degrees. Moreover, we found the change of relative strength contrast between plagioclase and olivine at low temperature; plagioclase becomes stronger than olivine at 400 degrees. Plagioclase is generally believed to be weaker than olivine (Brace and Kohlstedt, 1980). However, our experimental results indicate that olivine can be weaker than plagioclase (Azuma et al., 2010). In materials with a relatively strong chemical bonding such as silicates, Peierls mechanism becomes dominant at low temperatures (Tsenn and Carter, 1987). Based on deformation mechanism map, deformation of olivine could be controlled by this type of flow mechanism under our low temperature experiments. Thereby, the strength contrast between plagioclase and olivine are reversed. Consequently, our result of this experiments supported "creme brullee" model (e.g., Jackson, 2002), as continental strength profile and showed us that flow law can not be applied for low temperature conditions. In the future, we are going to conduct experiments under dry condition to evaluate strength profile of terrestrial planets like dry Venus. Venus has been thought as a similar planet to the Earth because of closet to the Earth in mass, density, size (Taylor and McLennan, 2008). However, Venus has extraordinary crustal features and plate tectonics does not seem to work. This can be a result of different rheological property on the Venus. We are going to report our new result of deformation experiments under dry conditions, and their tectonic difference.
Japan Geoscience Union, Apr 7, 2014
Venus has been regarded as a twin planet to the Earth, because of density, mass, size and distanc... more Venus has been regarded as a twin planet to the Earth, because of density, mass, size and distance from the Sun. However, the Magellan mission revealed that plate tectonics is unlikely to work on the Venus. The plate tectonics is one of the most important mechanism of heat transport and material circulation of the Earth, consequently, its absence might cause the different tectonic evolution between Earth and Venus. Rheological structure is a key to inferring mantle structure and convection style of planet interiors because the rock rheology controls strength and deformation mechanism. In previous study, the behavior of Venusian lithosphere has been inferred from the power-law type flow law of dry diabase. They indicated that lower crust can be weaker than upper mantle, which might result decoupling at the crust-mantle boundary (Moho depth) and mantle convection without crustal entrainment. However, the power-law creep cannot be applicable to infer the rheological structure at Moho depths, because the dislocation-glide control creep (Peierls mechanism) is known to become dominant at relatively low temperatures in materials with a relatively strong chemical bonding such as silicates. In this study, we conduct two-phase deformation experiments to directly investigate rheological contrast between plagioclase (crust) and olivine (mantle) and discuss the difference between these planets in terms of rheological behaviors. Moreover, one-dimensional and two-dimensional numerical calculation is performed to evaluate the influence of the strength contrast on the Venusian tectonics. Our experiments using solid-medium deformation apparatus directly determine the relative strength between plagioclase (crust) and olivine (mantle) without any extrapolating of flow law. The experimental conditions were ranging 2GPa and 600-1000 degrees under dry conditions. The experimental results show that olivine is expected to always be stronger than plagioclase. This result contradicts to that inferred from powerlaw creep of olivine and plagioclase, suggesting that Peierls mechanism could be dominant deformation mechanism in both olivine and plagioclase at relatively low temperatures. In the case of the Earth, rheological structure of oceanic lithosphere is constrained well by Byerlee's law and power-law type flow law. The oceanic crust and mantle lithosphere are strongly coupled mechanically because the Moho has no strength contrast, so that they could move and subduct together into the deep. In contrast, our experimental results imply that large strength contrast exists at Moho in Venus, resulting decouple of the motion between the crust and mantle lithospheres because the weak lower crust acts as a lubricant. Also one-dimensional numerical calculations show us that the surface velocity becomes more sluggish in the model with larger strength contrast (from two-digit to four-digit difference in viscosity) at Moho. Therefore the crustal part is less likely to be involved to mantle convection when strength contrast gets larger and larger. In fact, two-dimensional simulations suggest that the crustal portion cannot subduct with the mantle lithosphere if the strength contrast exists at Moho
Deformation microstructures of experimentally deformed glaucophane
한국암석학회 학술발표회 논문집, May 1, 2015
Earth, Planets and Space, Jan 3, 2017
The evolution of Mars has been greatly influenced by temporal changes in its rheological structur... more The evolution of Mars has been greatly influenced by temporal changes in its rheological structure, which may explain the difference in tectonics between Mars and Earth. Some previous studies have shown the rheological structures of Mars calculated from the flow law of rocks and the predicted thermal structure. However, the Peierls mechanism, which is the dominant deformation mechanism at relatively low temperature, and the evolution of water reservoirs on Mars were not considered in such studies. In this paper, we apply the Peierls mechanism to refine the rheological structure of Mars to show a new history of the planet that considers the most recent reports on its evolution of water reservoirs. Considering the Peierls creep and the evolution of water reservoirs, we attempt to explain why the tectonics of Mars is inactive compared with that of Earth. On early Mars, the lithospheric thickness inferred from the brittle-ductile transition was small, and the lithospheric strength was low (~200-300 MPa) under wet conditions at 4 Gya. This suggests that plate boundaries could have developed on the early "wet" Mars, which is a prerequisite for the operation of plate tectonics. Our results also imply that the lithospheric strength had significantly increased in the Noachian owing to water loss. Therefore, plate tectonics may have ceased or could no longer be initiated on Mars. At the least, the tectonic style of Mars would have dramatically changed during the Noachian.
Water history in the Mars’ interior inferred from elastic thickness
Japan Geoscience Union, Mar 14, 2018
Japan Geoscience Union, Apr 7, 2014
Apollo program (Passive Seismic Experiment) investigated a number of seismic events in moon (e.g.... more Apollo program (Passive Seismic Experiment) investigated a number of seismic events in moon (e.g., Nakamura 2003). These seismic events (moonquakes) are classified to four categories; thermal moonquake, shallow moonquake, impact moonquake and deep moonquake (Latham et al., 1969). In kinds of moonquake, deep moonquake is especially interesting because the occurrence depth of deep moonquake (700?1200 km) is obviously in plastic deformation region where frictional behavior and fracture does not occur. Analysis of PSE (Passive Seismic Experiment) data and modelling in previous studies suggest that the partial melt layer underlies near the occurrence depth of deep moonquake (Weber et al., 2011). Therefore partial melt possibly is one of important factor on the deep moonquake. Here we show the results of frictional experiments using a borneol?diphenylamine which can be adjusted in melt fraction and dihedral angle (Takei 2000). When dihedral angle is 30o, frictional coefficient becomes small with decrease of melt fraction. Although frictional coefficient is significantly decreased when dihedral angle is 0o, frictional coefficient does not depend on melt fraction. When dihedral angle of partial melt is 0o, frictional behavior is fully dominated by partial melt. Partial melt is considered to have the three effects on the shear strength. First, our frictional experiments found that partial melt decrease frictional coefficient. Second, partial melt behave as the pore pressure. Third, partial melt extracts the water from the surrounded rocks, and induces the shear localization (the stress concentration). Considering these effects of partial melt on frictional behavior, partial melt might be one of important factors on deep moonquake.
Rheological structure in Mars and its time evolution
AGU Fall Meeting Abstracts, Dec 1, 2014
Microstructures of experimentally deformed blueschist
Water-rich Martian mantle can account for the elastic thickness in Amazonian era
AGUFM, Dec 1, 2016
Rheological behavior of glaucophane and lawsonite in experimentally deformed blueschists
EGUGA, Apr 1, 2016
Evolution of rheological structure of Mars
Japan Geoscience Union, Mar 10, 2016
Date of deformation in the Kamila shear zone of Kohistan arc determined by SIMS U-Pb zircon analyses of deformed-undeformed dykes
Missing plate tectonics in Venus caused by rheological contrast at Moho
Mechanism of moonquakes inferred from rheological structure of moon interior
Fabric and petrological characteristics of peridotite xenoliths in Kimberley, South Africa
ABSTRACT This work focuses on high-temperature deformation processes associated with melt/fluid r... more ABSTRACT This work focuses on high-temperature deformation processes associated with melt/fluid rock interactions in peridotites of the mantle wedge. We used peridotite xenoliths from two localities with slightly different geological settings from northeast Japan (Ichinomegata) and southwest Japan (Oki-Dogo). In the context of back-arc spreading (Japan sea opening), Ichinomegata peridotites preserved the last stage of spreading, while Oki-Dogo ones preserved the middle stage of spreading. Olivine CPO of Ichinomegata peridotites are consistent with slip on (010)[100] and {0kl}[100]. The angle between the [100] maximum concentration and the foliation decreases with increasing fabric strength, indicating that these samples record a strain gradient related to back-arc spreading. The mineral chemistry of Ichinomegata peridotites shows a typical residual peridotite trend, depleted in LREE (light rare earth element). However, their strong Th-U positive anomaly indicates a possible metasomatic origin associated to the subduction of the Pacific plate. Olivine CPO of Oki-Dogo peridotites are consistent with the (010)[100] slip system. Samples have low Mg# and show relatively high concentration in [010]. The chemical composition of Oki-Dogo peridotites show that they were affected by various degree of metasomatism by melt, which might be related to back-arc spreading. Geochemical study of these samples shows that they underwent a reactive percolation of melt/fluid. However, fabrics do not show strong evidence of deformation synchronous to reaction of melts or fluids. From infrared analysis, olivine from the both xenoliths contains low water content, which are similar to those observed in spinel peridotite xenoliths from other subduction zones and probably record dehydration during exhumation of the xenoliths. These measured water contents are not sufficient to change the dominant slip direction of in olivine from [100] to [001].
Journal of Geography (Chigaku Zasshi), 2021
In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle sampl... more In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle samples in order to address the unanswered question of what constitutes the Earth's mantle. However, in the 21st century, it is widely accepted that the uppermost mantle is mainly com posed of peridotite. Now, the challenge of mantle drilling is to understand crucial unsolved issues of earth science. Today's Earth is different from other planets due to the existence of life and plate tectonics. It is emphasized that mantle drilling is the only way to obtain the oceanic crust
Water in clinopyroxene from the deeply subducted crust: An evidence for water transportation into the mantle
Garnet shapes within Kimberlite xenoliths record the tectonic evolution of a cratonic root
AGUFM, Dec 1, 2013
Japan Geoscience Union, Mar 10, 2016
Apollo program installed some seismometers on the moon and the seismic data provided us the much ... more Apollo program installed some seismometers on the moon and the seismic data provided us the much information about the moon interior. Analysis of moonquake data supports the following: The moon
Journal of the Geological Society of Japan, 2017
Rheological structures for continental and oceanic plates were calculated using the laboratory-ba... more Rheological structures for continental and oceanic plates were calculated using the laboratory-based frictional and flow laws. Our results show that Peierls creep becomes the dominant mechanism for plastic deformation at low temperatures and high stresses under both dry and wet conditions. When Peierls creep, rather than dislocation-accommodated power-law creep, is the dominant mechanism, there is a lower maximum mechanical strength, and a shallower depth to the brittle-plastic transition in our model. The rheology of continental lithosphere is complex, but may feature a weak lower crust sandwiched between a strong upper crust and mantle. Extensive deformation of this weak zone may explain crustal duplication in continental collision zone. The thick continental lithosphere beneath craton is stable for billions of years. This is partly because partial melting has depleted these regions of water, causing an increase in the mechanical strength of the continental lithosphere. The depth of brittle-plastic transition at island arcs, which we inferred from the maximum depth of seismicity, suggests that the fore-arc regions are enriched in water, but that the back-arc regions are depleted. The rheological structure of oceanic plate is dependent on the age of the plate, and the thickness of oceanic lithosphere is largely consistent with a dry rheology. A relatively thin elastic thickness found for the oceanic lithosphere in the Mariana and Bonin arcs may be explained by local weakening as a result of hydration along outer-rise faults.
Lunar and Planetary Science Conference, Mar 1, 2011
It is thought that plate tectonics is a product of the localized brittle failure in the lithosphe... more It is thought that plate tectonics is a product of the localized brittle failure in the lithosphere and viscous flow in the asthenosphere, and strength profile is a key to understand tectonics of terrestrial planet (Burgmann and Dresen, 2008). Physical properties, such as temperature and pressure and stress, and the chemical compositional layering between crust and mantle result in a strong rheological layering in the planet interior. It has been estimated by previous experiments that the brittle-ductile transition occurs in the planet interior and deformation mechanisms can be changed with increasing depth. In the present study, we evaluate rheological variation in the crust-mantle transition based on new series of deformation experiments, and discuss why plate tectonics doesn't exist in the other terrestrial planets except the Earth. In case of the earth, two different models on the strength profile in the continental crust have been proposed. The first is the "jelly sandwich" model that had been embraced for the past two decades. This model is that a weak middle and lower crust are sandwiched between strong upper crust and strong mantle lithosphere just like a jelly sandwich (e.g., Chen and Molnar, 1983). The second one is the "creme brullee" model, in which the upper mantle is significantly weak, and consequently region for viscous deformation continues into the mantle depth (Jackson, 2002). These two models of strength profile are given by extrapolating frictional strength and viscous flow law of each material to temperature and pressure corresponding to interior of the Earth. In this study, we performed experiment to directly determine the relative strength between plagioclase and olivine without any extrapolating of flow law; the crustal materials consist predominantly of plagioclase that largely control deformation of the crust, whereas deformation of the upper mantle is largely controlled by olivine. These samples are together sandwiched between alumina pistons in simple shear geometry and we used the hot-pressed samples and performed deformation experiments using solid-medium deformation apparatus. The experimental conditions were ranging 1GPa and 400-800 degrees, corresponding conditions to Moho of the Earth under water-rich conditions. The experimental results show that plagioclase and olivine are expected to show almost no difference in strength at temperatures of the continental Moho of the Earth, ca. 500-600 degrees. Moreover, we found the change of relative strength contrast between plagioclase and olivine at low temperature; plagioclase becomes stronger than olivine at 400 degrees. Plagioclase is generally believed to be weaker than olivine (Brace and Kohlstedt, 1980). However, our experimental results indicate that olivine can be weaker than plagioclase (Azuma et al., 2010). In materials with a relatively strong chemical bonding such as silicates, Peierls mechanism becomes dominant at low temperatures (Tsenn and Carter, 1987). Based on deformation mechanism map, deformation of olivine could be controlled by this type of flow mechanism under our low temperature experiments. Thereby, the strength contrast between plagioclase and olivine are reversed. Consequently, our result of this experiments supported "creme brullee" model (e.g., Jackson, 2002), as continental strength profile and showed us that flow law can not be applied for low temperature conditions. In the future, we are going to conduct experiments under dry condition to evaluate strength profile of terrestrial planets like dry Venus. Venus has been thought as a similar planet to the Earth because of closet to the Earth in mass, density, size (Taylor and McLennan, 2008). However, Venus has extraordinary crustal features and plate tectonics does not seem to work. This can be a result of different rheological property on the Venus. We are going to report our new result of deformation experiments under dry conditions, and their tectonic difference.
Japan Geoscience Union, Apr 7, 2014
Venus has been regarded as a twin planet to the Earth, because of density, mass, size and distanc... more Venus has been regarded as a twin planet to the Earth, because of density, mass, size and distance from the Sun. However, the Magellan mission revealed that plate tectonics is unlikely to work on the Venus. The plate tectonics is one of the most important mechanism of heat transport and material circulation of the Earth, consequently, its absence might cause the different tectonic evolution between Earth and Venus. Rheological structure is a key to inferring mantle structure and convection style of planet interiors because the rock rheology controls strength and deformation mechanism. In previous study, the behavior of Venusian lithosphere has been inferred from the power-law type flow law of dry diabase. They indicated that lower crust can be weaker than upper mantle, which might result decoupling at the crust-mantle boundary (Moho depth) and mantle convection without crustal entrainment. However, the power-law creep cannot be applicable to infer the rheological structure at Moho depths, because the dislocation-glide control creep (Peierls mechanism) is known to become dominant at relatively low temperatures in materials with a relatively strong chemical bonding such as silicates. In this study, we conduct two-phase deformation experiments to directly investigate rheological contrast between plagioclase (crust) and olivine (mantle) and discuss the difference between these planets in terms of rheological behaviors. Moreover, one-dimensional and two-dimensional numerical calculation is performed to evaluate the influence of the strength contrast on the Venusian tectonics. Our experiments using solid-medium deformation apparatus directly determine the relative strength between plagioclase (crust) and olivine (mantle) without any extrapolating of flow law. The experimental conditions were ranging 2GPa and 600-1000 degrees under dry conditions. The experimental results show that olivine is expected to always be stronger than plagioclase. This result contradicts to that inferred from powerlaw creep of olivine and plagioclase, suggesting that Peierls mechanism could be dominant deformation mechanism in both olivine and plagioclase at relatively low temperatures. In the case of the Earth, rheological structure of oceanic lithosphere is constrained well by Byerlee's law and power-law type flow law. The oceanic crust and mantle lithosphere are strongly coupled mechanically because the Moho has no strength contrast, so that they could move and subduct together into the deep. In contrast, our experimental results imply that large strength contrast exists at Moho in Venus, resulting decouple of the motion between the crust and mantle lithospheres because the weak lower crust acts as a lubricant. Also one-dimensional numerical calculations show us that the surface velocity becomes more sluggish in the model with larger strength contrast (from two-digit to four-digit difference in viscosity) at Moho. Therefore the crustal part is less likely to be involved to mantle convection when strength contrast gets larger and larger. In fact, two-dimensional simulations suggest that the crustal portion cannot subduct with the mantle lithosphere if the strength contrast exists at Moho
Deformation microstructures of experimentally deformed glaucophane
한국암석학회 학술발표회 논문집, May 1, 2015
Earth, Planets and Space, Jan 3, 2017
The evolution of Mars has been greatly influenced by temporal changes in its rheological structur... more The evolution of Mars has been greatly influenced by temporal changes in its rheological structure, which may explain the difference in tectonics between Mars and Earth. Some previous studies have shown the rheological structures of Mars calculated from the flow law of rocks and the predicted thermal structure. However, the Peierls mechanism, which is the dominant deformation mechanism at relatively low temperature, and the evolution of water reservoirs on Mars were not considered in such studies. In this paper, we apply the Peierls mechanism to refine the rheological structure of Mars to show a new history of the planet that considers the most recent reports on its evolution of water reservoirs. Considering the Peierls creep and the evolution of water reservoirs, we attempt to explain why the tectonics of Mars is inactive compared with that of Earth. On early Mars, the lithospheric thickness inferred from the brittle-ductile transition was small, and the lithospheric strength was low (~200-300 MPa) under wet conditions at 4 Gya. This suggests that plate boundaries could have developed on the early "wet" Mars, which is a prerequisite for the operation of plate tectonics. Our results also imply that the lithospheric strength had significantly increased in the Noachian owing to water loss. Therefore, plate tectonics may have ceased or could no longer be initiated on Mars. At the least, the tectonic style of Mars would have dramatically changed during the Noachian.
Water history in the Mars’ interior inferred from elastic thickness
Japan Geoscience Union, Mar 14, 2018
Japan Geoscience Union, Apr 7, 2014
Apollo program (Passive Seismic Experiment) investigated a number of seismic events in moon (e.g.... more Apollo program (Passive Seismic Experiment) investigated a number of seismic events in moon (e.g., Nakamura 2003). These seismic events (moonquakes) are classified to four categories; thermal moonquake, shallow moonquake, impact moonquake and deep moonquake (Latham et al., 1969). In kinds of moonquake, deep moonquake is especially interesting because the occurrence depth of deep moonquake (700?1200 km) is obviously in plastic deformation region where frictional behavior and fracture does not occur. Analysis of PSE (Passive Seismic Experiment) data and modelling in previous studies suggest that the partial melt layer underlies near the occurrence depth of deep moonquake (Weber et al., 2011). Therefore partial melt possibly is one of important factor on the deep moonquake. Here we show the results of frictional experiments using a borneol?diphenylamine which can be adjusted in melt fraction and dihedral angle (Takei 2000). When dihedral angle is 30o, frictional coefficient becomes small with decrease of melt fraction. Although frictional coefficient is significantly decreased when dihedral angle is 0o, frictional coefficient does not depend on melt fraction. When dihedral angle of partial melt is 0o, frictional behavior is fully dominated by partial melt. Partial melt is considered to have the three effects on the shear strength. First, our frictional experiments found that partial melt decrease frictional coefficient. Second, partial melt behave as the pore pressure. Third, partial melt extracts the water from the surrounded rocks, and induces the shear localization (the stress concentration). Considering these effects of partial melt on frictional behavior, partial melt might be one of important factors on deep moonquake.
Rheological structure in Mars and its time evolution
AGU Fall Meeting Abstracts, Dec 1, 2014
Microstructures of experimentally deformed blueschist
Water-rich Martian mantle can account for the elastic thickness in Amazonian era
AGUFM, Dec 1, 2016
Rheological behavior of glaucophane and lawsonite in experimentally deformed blueschists
EGUGA, Apr 1, 2016
Evolution of rheological structure of Mars
Japan Geoscience Union, Mar 10, 2016
Date of deformation in the Kamila shear zone of Kohistan arc determined by SIMS U-Pb zircon analyses of deformed-undeformed dykes
Missing plate tectonics in Venus caused by rheological contrast at Moho
Mechanism of moonquakes inferred from rheological structure of moon interior
Fabric and petrological characteristics of peridotite xenoliths in Kimberley, South Africa
ABSTRACT This work focuses on high-temperature deformation processes associated with melt/fluid r... more ABSTRACT This work focuses on high-temperature deformation processes associated with melt/fluid rock interactions in peridotites of the mantle wedge. We used peridotite xenoliths from two localities with slightly different geological settings from northeast Japan (Ichinomegata) and southwest Japan (Oki-Dogo). In the context of back-arc spreading (Japan sea opening), Ichinomegata peridotites preserved the last stage of spreading, while Oki-Dogo ones preserved the middle stage of spreading. Olivine CPO of Ichinomegata peridotites are consistent with slip on (010)[100] and {0kl}[100]. The angle between the [100] maximum concentration and the foliation decreases with increasing fabric strength, indicating that these samples record a strain gradient related to back-arc spreading. The mineral chemistry of Ichinomegata peridotites shows a typical residual peridotite trend, depleted in LREE (light rare earth element). However, their strong Th-U positive anomaly indicates a possible metasomatic origin associated to the subduction of the Pacific plate. Olivine CPO of Oki-Dogo peridotites are consistent with the (010)[100] slip system. Samples have low Mg# and show relatively high concentration in [010]. The chemical composition of Oki-Dogo peridotites show that they were affected by various degree of metasomatism by melt, which might be related to back-arc spreading. Geochemical study of these samples shows that they underwent a reactive percolation of melt/fluid. However, fabrics do not show strong evidence of deformation synchronous to reaction of melts or fluids. From infrared analysis, olivine from the both xenoliths contains low water content, which are similar to those observed in spinel peridotite xenoliths from other subduction zones and probably record dehydration during exhumation of the xenoliths. These measured water contents are not sufficient to change the dominant slip direction of in olivine from [100] to [001].
Journal of Geography (Chigaku Zasshi), 2021
In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle sampl... more In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle samples in order to address the unanswered question of what constitutes the Earth's mantle. However, in the 21st century, it is widely accepted that the uppermost mantle is mainly com posed of peridotite. Now, the challenge of mantle drilling is to understand crucial unsolved issues of earth science. Today's Earth is different from other planets due to the existence of life and plate tectonics. It is emphasized that mantle drilling is the only way to obtain the oceanic crust
Water in clinopyroxene from the deeply subducted crust: An evidence for water transportation into the mantle