The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Shotaro Akaho - One of the best experts on this subject based on the ideXlab platform.
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Progressive Evolution of whole rock composition during metamorphism revealed by multivariate statistical analyses
Journal of Metamorphic Geology, 2018Co-Authors: Kenta Yoshida, Tatsu Kuwatani, Takao Hirajima, Hikaru Iwamori, Shotaro AkahoAbstract:The geochemical Evolution of metamorphic rocks during subduction-related metamorphism is described on the basis of multivariate statistical analyses. The studied dataset comprises a series of mapped metamorphic rocks collected from the Sanbagawa metamorphic belt in central Shikoku, Japan, where metamorphic conditions range from the pumpellyite–actinolite to epidote–amphibolite facies. Recent progress in computational and information science provides a number of algorithms capable of revealing structures in large datasets. This study applies k-means cluster analysis (KCA) and non-negative matrix factorization (NMF) to a series of metapelites, which is the main lithotype of the Sanbagawa metamorphic belt. KCA describes the structures of the high-dimensional data, while NMF provides endmember decomposition which can be useful for evaluating the spatial distribution of continuous compositional trends. The analyzed dataset, derived from previously published work, contains 296 samples for which 14 elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P, Rb, Sr, Zr and Ba) have been analyzed. The KCA and NMF analyses indicate five clusters and four endmembers, respectively, successfully explaining compositional variations within the dataset. KCA indicates that the chemical compositions of metapelite samples from the western (Besshi) part of the sampled area differ significantly from those in the east (Asemigawa). In the west, clusters show a good correlation with the metamorphic grade. With increasing metamorphic grade, there are decreases in SiO2 and Na2O and increases in other components. On the other hand, the compositional change with metamorphic grade is less obvious in the eastern area. Endmember decomposition using NMF revealed that the Evolutional change of whole rock composition, as correlated with metamorphic grade, approximates a stoichiometric increase of a garnet-like component in the whole–rock composition, possibly due to the precipitation of garnet and effusion of other components during Progressive dehydration. Thermodynamic modelling of the Evolution of the whole–rock composition yielded the following results: (1) the whole-rock composition at lower metamorphic grade favours the preferential crystallization of garnet under the conditions of the garnet zone, with biotite becoming stable together with garnet in higher-grade rock compositions under the same P-T conditions; (2) with higher-grade whole–rock compositions, more H2O is retained. These results provide insight into the mechanism suppressing dehydration under high-pressure metamorphic conditions. This mechanism should be considered in forward modelling of the fluid cycle in subduction zones, although such a quantitative model has yet to be developed. This article is protected by copyright. All rights reserved.
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Progressive Evolution of whole‐rock composition during metamorphism revealed by multivariate statistical analyses
Journal of Metamorphic Geology, 2017Co-Authors: Kenta Yoshida, Tatsu Kuwatani, Takao Hirajima, Hikaru Iwamori, Shotaro AkahoAbstract:The geochemical Evolution of metamorphic rocks during subduction-related metamorphism is described on the basis of multivariate statistical analyses. The studied dataset comprises a series of mapped metamorphic rocks collected from the Sanbagawa metamorphic belt in central Shikoku, Japan, where metamorphic conditions range from the pumpellyite–actinolite to epidote–amphibolite facies. Recent progress in computational and information science provides a number of algorithms capable of revealing structures in large datasets. This study applies k-means cluster analysis (KCA) and non-negative matrix factorization (NMF) to a series of metapelites, which is the main lithotype of the Sanbagawa metamorphic belt. KCA describes the structures of the high-dimensional data, while NMF provides endmember decomposition which can be useful for evaluating the spatial distribution of continuous compositional trends. The analyzed dataset, derived from previously published work, contains 296 samples for which 14 elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P, Rb, Sr, Zr and Ba) have been analyzed. The KCA and NMF analyses indicate five clusters and four endmembers, respectively, successfully explaining compositional variations within the dataset. KCA indicates that the chemical compositions of metapelite samples from the western (Besshi) part of the sampled area differ significantly from those in the east (Asemigawa). In the west, clusters show a good correlation with the metamorphic grade. With increasing metamorphic grade, there are decreases in SiO2 and Na2O and increases in other components. On the other hand, the compositional change with metamorphic grade is less obvious in the eastern area. Endmember decomposition using NMF revealed that the Evolutional change of whole rock composition, as correlated with metamorphic grade, approximates a stoichiometric increase of a garnet-like component in the whole–rock composition, possibly due to the precipitation of garnet and effusion of other components during Progressive dehydration. Thermodynamic modelling of the Evolution of the whole–rock composition yielded the following results: (1) the whole-rock composition at lower metamorphic grade favours the preferential crystallization of garnet under the conditions of the garnet zone, with biotite becoming stable together with garnet in higher-grade rock compositions under the same P-T conditions; (2) with higher-grade whole–rock compositions, more H2O is retained. These results provide insight into the mechanism suppressing dehydration under high-pressure metamorphic conditions. This mechanism should be considered in forward modelling of the fluid cycle in subduction zones, although such a quantitative model has yet to be developed. This article is protected by copyright. All rights reserved.
Edward R. Laws - One of the best experts on this subject based on the ideXlab platform.
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Transsphenoidal surgery [2] (multiple letters)
Journal of Neurosurgery, 2002Co-Authors: Richard L. Rovit, Giuseppe Lanzino, Edward R. Laws, William T. CouldwellAbstract:The development of new scientific concepts and techniques is usually the result of a Progressive Evolution. The transsphenoidal approach to pituitary lesions is no exception. Several pioneers contributed to its development and its eventual and nearly unconditional acceptance. In this historical vignette, the contributions of three master surgeons, Theodor Kocher, Oskar Hirsch, and Norman Dott. are reviewed.
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Pioneers in the development of transsphenoidal surgery: Theodor Kocher, Oskar Hirsch, and Norman Dott
Journal of neurosurgery, 2001Co-Authors: Giuseppe Lanzino, Edward R. LawsAbstract:✓ The development of new scientific concepts and techniques is usually the result of a Progressive Evolution. The transsphenoidal approach to pituitary lesions is no exception. Several pioneers contributed to its development and its eventual and nearly unconditional acceptance. In this historical vignette, the contributions of three master surgeons, Theodor Kocher, Oskar Hirsch, and Norman Dott, are reviewed.
William T. Couldwell - One of the best experts on this subject based on the ideXlab platform.
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Transsphenoidal surgery [2] (multiple letters)
Journal of Neurosurgery, 2002Co-Authors: Richard L. Rovit, Giuseppe Lanzino, Edward R. Laws, William T. CouldwellAbstract:The development of new scientific concepts and techniques is usually the result of a Progressive Evolution. The transsphenoidal approach to pituitary lesions is no exception. Several pioneers contributed to its development and its eventual and nearly unconditional acceptance. In this historical vignette, the contributions of three master surgeons, Theodor Kocher, Oskar Hirsch, and Norman Dott. are reviewed.
Yadong Wang - One of the best experts on this subject based on the ideXlab platform.
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Late Neogene magnetostratigraphy in the western Qaidam Basin (NE Tibetan Plateau) and its constraints on active tectonic uplift and Progressive Evolution of growth strata
Tectonophysics, 2013Co-Authors: Weilin Zhang, Xiaomin Fang, Chunhui Song, Erwin Appel, Maodu Yan, Yadong WangAbstract:Abstract The Qaidam Basin as the largest intermontane basin of the NE Tibetan Plateau is the ideal place to provide constraints on depositional and tectonic patters. To determine its tectonic deformation history and Progressive Evolution of growth strata we conducted paleomagnetic study on the late-Neogene stratigraphic section in the western Qaidam Basin. A magnetostratigraphic study of the well exposed 805 m Qigequan section at the Qigequan anticline in the western Qaidam Basin reveals twelve pairs of normal and reversed polarity zones which can be readily correlated with chrons C1n-3Ar of the Geomagnetic Polarity Time Scale (GPTS). From this correlation we can conclude that the Shizigou and the Qigequan formations were formed at > 6.9 Ma–2.5 Ma and 2.5–~ 0.4 Ma, respectively. Accumulation rates determined from our chronology, together with the occurrence of unconformities suggest four phases of tectonic uplift which began at about 3.6 Ma, 2.5 Ma, 1.1 Ma and 0.8 Ma. The results also suggest that offlap growth strata according to the limb rotation model on the anticlinorium started to occur at ~ 8.2 Ma. They Progressively become younger from the frontal region of the Altyn Tagh Mts. (~ 8.2 Ma) to the southwestern basin (~ 2.5 Ma) and to further east of the Qaidam Basin (
Giuseppe Lanzino - One of the best experts on this subject based on the ideXlab platform.
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Transsphenoidal surgery [2] (multiple letters)
Journal of Neurosurgery, 2002Co-Authors: Richard L. Rovit, Giuseppe Lanzino, Edward R. Laws, William T. CouldwellAbstract:The development of new scientific concepts and techniques is usually the result of a Progressive Evolution. The transsphenoidal approach to pituitary lesions is no exception. Several pioneers contributed to its development and its eventual and nearly unconditional acceptance. In this historical vignette, the contributions of three master surgeons, Theodor Kocher, Oskar Hirsch, and Norman Dott. are reviewed.
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Pioneers in the development of transsphenoidal surgery: Theodor Kocher, Oskar Hirsch, and Norman Dott
Journal of neurosurgery, 2001Co-Authors: Giuseppe Lanzino, Edward R. LawsAbstract:✓ The development of new scientific concepts and techniques is usually the result of a Progressive Evolution. The transsphenoidal approach to pituitary lesions is no exception. Several pioneers contributed to its development and its eventual and nearly unconditional acceptance. In this historical vignette, the contributions of three master surgeons, Theodor Kocher, Oskar Hirsch, and Norman Dott, are reviewed.
