DSpace Collection: 1984-09
http://hdl.handle.net/2115/34910
1984-092024-03-29T07:30:14ZThe Iwanai Nappe in the Kamuikotan Tectonic Belt, Sothern Hokkaido, Japan
http://hdl.handle.net/2115/36731
Title: The Iwanai Nappe in the Kamuikotan Tectonic Belt, Sothern Hokkaido, Japan
Authors: Jolivet, Laurent; Cadet, Jean-Paul
Abstract: The Sarugawa ultramafic mass is interpreted as a nappe here called the "Iwanai Nappe", resting, with its sedimentary cover, on a unit reworking ophiolitic rocks and Cretaceous Yezo deposits. The Iwanai Nappe has been emplaced toward the south-west from an area situated east of the "Yezo Syncline". The age of movement is inferred to be Eocene, contemporaneous with the beginning of the strike-slip movement in Hidaka belt. This structure is a good explanation for the Lower Cretaceous facies distribution in the concerned area.1984-08-31T15:00:00ZJolivet, LaurentCadet, Jean-PaulThe Sarugawa ultramafic mass is interpreted as a nappe here called the "Iwanai Nappe", resting, with its sedimentary cover, on a unit reworking ophiolitic rocks and Cretaceous Yezo deposits. The Iwanai Nappe has been emplaced toward the south-west from an area situated east of the "Yezo Syncline". The age of movement is inferred to be Eocene, contemporaneous with the beginning of the strike-slip movement in Hidaka belt. This structure is a good explanation for the Lower Cretaceous facies distribution in the concerned area.Tonalite Complexes in the Abukuma Axial Metamorphic Belt, Japan
http://hdl.handle.net/2115/36730
Title: Tonalite Complexes in the Abukuma Axial Metamorphic Belt, Japan
Authors: Uchiyama, Koji
Abstract: In an effort to examine the natures and origin of tonalitic intrusive masses lying between Takanuki and Gozaisho metamorphic units in the Abukuma axial metamorphic belt a study has been made of the Usuki tonalite complex, which crops out in the Takanuki district, as the typical one of the intrusive masses. Two-thirds of the compelx is represented by the lithofacies of tonalite proper, with which migmatitic and granodioritic lithofacies are intimately associated. The host rocks of the migmatitic facies are biotite schist and amphibolite of both metamorphic units. The plagioclases formed in the neosomes of the migmalitic facies are fairly similar to those shown in tonalite proper; they are indicalive of having been under overwhelming conditions of plagioclase formation la king place in the facies of tonalite proper, the conditions prevailing in the whole extent of the complex. Meanwhile, the granodioritic facies is of metasomatic replacement origin, which is considered to be a stable lithofacies according to the behaviour of its plagioclase. An examination of chemical characters of these lithofacies indicates that the lithofacies of granodiorite and tonalite proper are in a stable state of equilibrium. On the other hand, most of the neosomes seem to represent an unstable or transitional state of the lithofacies which deviated from the standard rock species. Based on the geological and petrological evidence obtained through the detailed survey of the whole Takanuki district, the writer has arrived at the conclusion that the present tonalite which derives from crustal materials, did not come about from the partial melting of basic rocks. He dose not agree to the currently accepted view concerning the origin of the early Precambrian voluminous trondhjemite-tonalite suite. Initially, it was formed beneath the central zone of the Takanuki metamorphic belt by the granilization of the Takanuki metamorphics at a deep level during the movement of the main stage of the Abean orogeny. Succeedingly, the granitized materials at that level were rejuvenated and mobilized into the fracture zone formed between the Takanuki and the Gozaisho metamorphics during the subsequent stage of the orogeny. Measured data on lead isotope ratios of rocks of all types in the district also support the above conclusion.1984-08-31T15:00:00ZUchiyama, KojiIn an effort to examine the natures and origin of tonalitic intrusive masses lying between Takanuki and Gozaisho metamorphic units in the Abukuma axial metamorphic belt a study has been made of the Usuki tonalite complex, which crops out in the Takanuki district, as the typical one of the intrusive masses. Two-thirds of the compelx is represented by the lithofacies of tonalite proper, with which migmatitic and granodioritic lithofacies are intimately associated. The host rocks of the migmatitic facies are biotite schist and amphibolite of both metamorphic units. The plagioclases formed in the neosomes of the migmalitic facies are fairly similar to those shown in tonalite proper; they are indicalive of having been under overwhelming conditions of plagioclase formation la king place in the facies of tonalite proper, the conditions prevailing in the whole extent of the complex. Meanwhile, the granodioritic facies is of metasomatic replacement origin, which is considered to be a stable lithofacies according to the behaviour of its plagioclase. An examination of chemical characters of these lithofacies indicates that the lithofacies of granodiorite and tonalite proper are in a stable state of equilibrium. On the other hand, most of the neosomes seem to represent an unstable or transitional state of the lithofacies which deviated from the standard rock species. Based on the geological and petrological evidence obtained through the detailed survey of the whole Takanuki district, the writer has arrived at the conclusion that the present tonalite which derives from crustal materials, did not come about from the partial melting of basic rocks. He dose not agree to the currently accepted view concerning the origin of the early Precambrian voluminous trondhjemite-tonalite suite. Initially, it was formed beneath the central zone of the Takanuki metamorphic belt by the granilization of the Takanuki metamorphics at a deep level during the movement of the main stage of the Abean orogeny. Succeedingly, the granitized materials at that level were rejuvenated and mobilized into the fracture zone formed between the Takanuki and the Gozaisho metamorphics during the subsequent stage of the orogeny. Measured data on lead isotope ratios of rocks of all types in the district also support the above conclusion.Petrology of the Horoman Ultramafic Rocks in the Hidaka Metamorphic Belt, Hokkaido, Japan
http://hdl.handle.net/2115/36729
Title: Petrology of the Horoman Ultramafic Rocks in the Hidaka Metamorphic Belt, Hokkaido, Japan
Authors: Niida, Kiyoaki
Abstract: The Horoman ultramafic massif, covering more than 8×10 km in the Hidaka Metamorphic Belt, is an "alpine-type" peridotite which is a gently warped sheet about 3,000 m in thickness. The massif exhibits a conspicuous layered structure which consists of layers of dunite, lherzolite, plagioclase lherzolite, and a small amount of gabbro and pyroxenite. Coexisting minerals from all the rock types of the layered ultramafic to mafic sequence were analysed by EPMA. The ferromagnesian minerals show large compositional variations in accordance with lithological change in the series of dunite → lherzolite → plagioclase lherzolite → gabbro. Forsterite content of olivine varies successively from Fo92.5 to Fo64.5. Enstatite content of orthopyroxene also varies from En93.0 to En85.5. Large and continuous compositional variation was also obtained for clinopyroxenes, e.g. Ca46Mg51Fe3 from dunite, Ca48Mg48Fe4 from lherzolite, Ca49Mg46Fe5 from plagioclase lherzolite, Ca50Mg44Fe6 from the margin of gabbro, and Ca38Mg39Fe23 from the center of gabbro. Al and Ti contents of clinopyroxcncs and pargasitic amphiboles increase with decrease of the Mg/ Mg + Fe ratio. The mineralogical characteristics indicate that the Horoman layered sequence represents a magmatic series formed by fractional crystallization. The gabbroic seams in the plagioclase lherzolite and the layers of gabbro were probably formed by crystallization of residual liquid which were slightly alkaline in chemical nature. The Horoman ultramafic rocks are strongly modified by deep-seated deformation and recrystallization, and additionally by mylonitization during the up-thrusting intrusion into the Earth's crust. The primary composition of minerals, obtained by step-scanning EPMA analyses are recognized as a distinct and uniform compositional plateaus at the cores of large, porphyroclastic, primary grains. The equilibration temperatures were calculated for the orthopyroxene-clinopyroxene pairs of primary porphyroclasts, using the Opx-Cpx geothermometer. The temperatures range from 900℃ to 1,100℃. The estimates for the neoblastic pyroxene pairs are slightly lower, ranging between 850℃ and 1,000℃. The rocks might have re-equilibrated under the subsolidus conditions in the upper mantle.1984-08-31T15:00:00ZNiida, KiyoakiThe Horoman ultramafic massif, covering more than 8×10 km in the Hidaka Metamorphic Belt, is an "alpine-type" peridotite which is a gently warped sheet about 3,000 m in thickness. The massif exhibits a conspicuous layered structure which consists of layers of dunite, lherzolite, plagioclase lherzolite, and a small amount of gabbro and pyroxenite. Coexisting minerals from all the rock types of the layered ultramafic to mafic sequence were analysed by EPMA. The ferromagnesian minerals show large compositional variations in accordance with lithological change in the series of dunite → lherzolite → plagioclase lherzolite → gabbro. Forsterite content of olivine varies successively from Fo92.5 to Fo64.5. Enstatite content of orthopyroxene also varies from En93.0 to En85.5. Large and continuous compositional variation was also obtained for clinopyroxenes, e.g. Ca46Mg51Fe3 from dunite, Ca48Mg48Fe4 from lherzolite, Ca49Mg46Fe5 from plagioclase lherzolite, Ca50Mg44Fe6 from the margin of gabbro, and Ca38Mg39Fe23 from the center of gabbro. Al and Ti contents of clinopyroxcncs and pargasitic amphiboles increase with decrease of the Mg/ Mg + Fe ratio. The mineralogical characteristics indicate that the Horoman layered sequence represents a magmatic series formed by fractional crystallization. The gabbroic seams in the plagioclase lherzolite and the layers of gabbro were probably formed by crystallization of residual liquid which were slightly alkaline in chemical nature. The Horoman ultramafic rocks are strongly modified by deep-seated deformation and recrystallization, and additionally by mylonitization during the up-thrusting intrusion into the Earth's crust. The primary composition of minerals, obtained by step-scanning EPMA analyses are recognized as a distinct and uniform compositional plateaus at the cores of large, porphyroclastic, primary grains. The equilibration temperatures were calculated for the orthopyroxene-clinopyroxene pairs of primary porphyroclasts, using the Opx-Cpx geothermometer. The temperatures range from 900℃ to 1,100℃. The estimates for the neoblastic pyroxene pairs are slightly lower, ranging between 850℃ and 1,000℃. The rocks might have re-equilibrated under the subsolidus conditions in the upper mantle.Formation of Fractures in Komagatake Volcano, Hokkaido
http://hdl.handle.net/2115/36728
Title: Formation of Fractures in Komagatake Volcano, Hokkaido
Authors: Katsui, Yoshio; Komuro, Hiroaki
Abstract: Fractures developed in the atrio of Komagatake Volcano, Hokkaido, are classified into three main types. 1) 1929 fractures along the atrio margin, 2) 1929 concentric fractures, and 3) the 1942 major fissure. The former two fractures were formed by settling and compaction due to welding as well as settling of the 1929 pyroclastic deposits, respectively. These fractures were strongly controlled by the older topography. The 1942 major fissure extending across the atrio for 1.6 km in NW-SE, was initially produced by doming due to the excess magma pressure, and enlarged by explosions and subsequent collapse of the wall.1984-08-31T15:00:00ZKatsui, YoshioKomuro, HiroakiFractures developed in the atrio of Komagatake Volcano, Hokkaido, are classified into three main types. 1) 1929 fractures along the atrio margin, 2) 1929 concentric fractures, and 3) the 1942 major fissure. The former two fractures were formed by settling and compaction due to welding as well as settling of the 1929 pyroclastic deposits, respectively. These fractures were strongly controlled by the older topography. The 1942 major fissure extending across the atrio for 1.6 km in NW-SE, was initially produced by doming due to the excess magma pressure, and enlarged by explosions and subsequent collapse of the wall.