49 research outputs found
Differentiation in the Early Earth's Interior: Constraints from Isotope Geochemistry and High-Pressure Experiments
No full textWe conducted isotopic model calculations and high-pressure melting experiments in order to estimate the major element composition of the “missing reservoir”, which is a supposed component that should compensate the difference in ¹⁴²Nd/¹⁴⁴Nd ratio between the bulk silicate Earth and carbonaceous chondrite, from which the Earth is assumed to have formed. Our estimation demonstrated that the missing reservoir should have picritic to komatiitic composition, and that it was likely to have been lost from the Earth's surface by a giant impact event at the last stage of the Earth formation
Trace element transport during dehydration processes in the subducted oceanic crust: 2. Origin of chemical and physical characteristics in arc magmatism
No full text
Differentiation in the Early Earth's Interior: Constraints from Isotope Geochemistry and High-Pressure Experiments
No full textExperimental study of clinopyroxenite partial melting and the origin of ultra-calcic melt inclusions
No full textGeomagnetic Anomaly Survey at the Divergent Plate Boundary in Afar Depression, Ethiopia
No full textIn order to expand our knowledge about magnetic structures under a sea-floor spreading center and the formation process of magnetic stripes, we now proceed an on-land geo-electromagentic research plan at the divergent plate boundary in Afar Depression, Ethiopia, where we can directly investigate into a sea-floor spreading center on land. We will introduce our plan and report the progress of geomagnetic and geological surveys we have performed
Petit-spot as definitive evidence for partial melting in the asthenosphere caused by CO2
No full text地球のアセノスフェアは二酸化炭素によって部分的に溶けている : プレートテクトニクスの根幹に関わる論争決着に大きな前進. 京都大学プレスリリース. 2017-02-03.The deep carbon cycle plays an important role on the chemical differentiation and physical properties of the Earth's mantle. Especially in the asthenosphere, seismic low-velocity and high electrical conductivity due to carbon dioxide (CO2)-induced partial melting are expected but not directly observed. Here we discuss the experimental results relevant to the genesis of primitive CO2-rich alkali magma forming petit-spot volcanoes at the deformation front of the outer rise of the northwestern Pacific plate. The results suggest that primitive melt last equilibrated with depleted peridotite at 1.8 - 2.1 GPa and 1, 280 - 1, 290 °C. Although the equilibration pressure corresponds to the pressure of the lower lithosphere, by considering an equilibration temperature higher than the solidus in the volatile - peridotite system along with the temperature of the lower lithosphere, we conclude that CO2-rich silicate melt is always produced in the asthenosphere. The melt subsequently ascends into and equilibrates with the lower lithosphere before eruption
Trace element transport during dehydration processes in the subducted oceanic crust: 1. Experiments and implications for the origin of ocean island basalts
No full textIntermittent Beginning to the Formation of Hydrogenous Ferromanganese Nodules in the Vast Field: Insights from Multi-Element Chemostratigraphy Using Microfocus X-ray Fluorescence
No full text南極からの海洋深層水が「国産コバルト資源」を生み出した --南鳥島周辺に広大なマンガンノジュール密集域が形成された原因を特定--. 京都大学プレスリリース. 2022-01-12.Vast ferromanganese nodule fields have been found on the deep-sea floor of all oceans worldwide. They have received attention because they potentially provide high-grade metal resources to develop future high- and green-technology. However, how these vast nodule fields were formed and developed owing to their widespread nature or tendency to be denser with an increasing number of nodules has not yet been established. In this study, the fine-scale inner structure of nodules of various sizes was analyzed on the basis of chemical mapping using microfocus X-ray fluorescence. We found that nodules distributed in the vast field around Minamitorishima (Marcus) Island have several types of innermost layers, which correspond to different chemostratigraphic layers of nodules that have been previously reported by us in this region. As nodules grow in order from the center to the outside, the different types in the innermost layer indicate a difference in the timing of the beginning of their growth. Moreover, because the differences in the chemical features of each layer reflect differences in the composition of the original deep-sea water, our results imply that the beginning of nodule formation occurred intermittently at each time of a water mass replacement due to new deep-sea currents flowing into this region. We recognized that the northern part of the study area was dominated by large nodules that started to grow in relatively earlier times, while the southern part tended to have many nodules that grew in relatively later times. Based on these observations, we hypothesize that the intermittent beginning of nodule formation is governed by the northward inflow of the deep-sea current that originated from the Lower Circumpolar Deep Water for an extended time to form the vast nodule field. Because patterns in the timing of nodule formation were different in the eastern and western regions, we thus further propose that the topographic framework, i.e., the arrangement of individual large seamounts and the cluster of small knolls and petit-spot volcanoes, strongly regulates the flow path of the deep-sea current, even if the position of the entire seamount changes owing to plate motion. The deep-sea current might supply some materials to be nuclei, resulting in the nodule formation at the beginning of the process
