Granites of Japan Nakajima, Takashi
Chishitsugaku zasshi,
8/2018, Letnik:
124, Številka:
8
Journal Article
All the granitoids in the Japanese Islands are Phanerozoic and of arc-type. They are part of the Late Mesozoic Circum-Pacific granite superprovince. Most of the Japanese granitoids were formed when ...the Japanese Islands belonged to the Eurasian continent, as the growing front of the continent. They are mostly of I-type, and S-type granitoids are very small in amount. The origin of these granitoids is mostly partial melt of mantle-derived mafic lower crust of arc without an involvement of ancient cratons or their derivatives. The granitic magmatism was quite episodic. 80% of their surface exposure area is occupied with 50-130Ma, Paleogene to Cretaceous granitoids. In Southwest Japan, they constitute three arc-parallel granitic provinces called Ryoke, San-yo and San-in belts. A transect from the Ryoke to San-yo belt represents the hypothetical crustal cross section of the Cretaceous Eurasian continental margin. The Hidaka belt in Hokkaido is another example of a crustal cross section, exposing the deep Kuril arc at Miocene. On the fore-arc side of the Southwest Japan, 13-15Ma, Middle Miocene granitic rocks are exposed sporadically but widely. The magmatism was very short-lived, supposed to be generated in an unusual tectonic setting related to back-arc opening and incipient subduction of the Philippine Sea plate. Middle Miocene and still younger granitoids are exposed in the Izu Collision Zone. The Quaternary granitoids of ~1Ma are exposed at the Central Highlands in central Japan. Jurassic and Triassic granitoids occur in the Hida belt, which is the most back-arc side unit of the Japanese Islands. Paleozoic granitoids are rare. They are exposed as geologically isolated small bodies or tectonic blocks.
We have undertaken a detailed study of the geology and depositional environments of the Bandodani Formation in the Upper Cretaceous Izumi Group of Shimada-jima Island, north Tokushima, Shikoku, ...Japan. Shimada-jima Island is a well-known locality for the occurrence of the trace fossil Archaeozostera, which had treated as the ancestor of the Zosteracea seagrass. We have delineated the stratigraphic position of the Archaeozostera-bearing interval in the Bandodani Formation distributed in Shimada-jima. Furthermore, we have constrained the depositional conditions suitable for the habitat of the Archaeozostera-animals in submarine fan systems. Facies analysis has revealed that the Bandodani Formation mainly comprises repeating channel-fill and inter-channel deposits, which were deposited in the frontal splay setting of a submarine fan system. Furthermore, a large-scale coarsening-upwards trend is observed throughout the formation and can be interpreted as the result of a prograding submarine fan system. In the studied section, the occurrence of Archaeozostera is restricted to the mud-dominated lowermost interval. This implies that the Archaeozostera-animals preferred relatively stable bottom conditions that were free from severe physical disturbances caused by abrupt and frequent aggradation and/or degradation of the seafloor associated with the sedimentation of the turbidites. Moreover, the ‘Archaeozostera-bearing interval’ represents a useful marker horizon to identify the contemporaneous stratigraphic interval.
The thermal maturity of the Izumi Group within the Izumi Mountains and the Asan Mountains of southwestern Japan was characterized using vitrinite reflectance and Rock-Eval Tmax data. Mean random ...reflectance and Rock-Eval Tmax values range from 0.69 to 2.64%, and from 432 to 548°C, respectively, indicating that the thermal maturity of the entire Izumi Mountains area increases towards the north, compatible with thermal diagenesis previously reconstructed based on zeolite facies distribution. The three-dimensional thermal structure of the study area was estimated by multiple regression analysis of the surface maturity data collected from the western and central parts of the Izumi Mountains, assuming that the altitude of each sample reflected the vertical maturity gradient. This analysis yielded a thermal maturity isograd striking aat N78°E that dips 23° to the south, and has a maximum temperature gradient of 23–26°C/km. The higher maturity of the eastern Izumi Mountains can be attributed to the influence of regional uplift in this area. Three hypothesized processes can explain the thermal structure of the Izumi sedimentary basin: tectonic block tilting of the Izumi Group around the Median Tectonic Line (MTL), influence of heat sources near the Izumi belt, and differential subsidence rates between the northern margin and the depocenter of the Izumi sedimentary basin.
Amphibolites from the Ryoke metamorphic belt, SW Japan were deformed initially by cataclasis and subsequently by dissolution–precipitation creep. Initial cataclastic deformation produced a rather ...weak shape-preferred orientation (SPO) of brown amphibole grains with small aspect ratios as well as a poorly developed amphibole lattice-preferred orientation (LPO) with n
α (≈
a100) axes scattered subnormal to the foliation and n
γ or
c001 axes scattered around the lineation. During later deformation by dissolution–precipitation creep, preferential dissolution at grain boundaries subparallel to the foliation and simultaneous compaction normal to the foliation have likely produced a distinct SPO of elongate brown amphibole grains subparallel to the foliation as well as their LPO such that their n
γ or
c axes are scattered around the lineation, while n
α (≈
a) and n
β (=
b010) are spread along a girdle normal to the lineation. Also during this deformation green amphibole precipitated as isolated grains or in pressure shadow regions around brown amphibole grains. Nucleation and anisotropic growth of isolated green amphibole grains according to the orientations of the principal stress directions produced an LPO of these grains such that their n
α (≈
a) are oriented normal to foliation, n
β (=
b) within the foliation normal to the lineation and n
γ (or
c) axes are parallel to the lineation. In addition, there is an associated SPO. Growth of green amphibole in pressure shadow regions around brown amphibole grains occurs either syntaxially or anisotropically according to the orientations of the principal stress directions.
Two new oribatid mite species of Haplozetidae were collected from litter, humus and soil at Izumi city in Kagoshima Prefecture, south Japan. One of them, Acutozetes izumiensis sp.n. was collected ...from the Arasaki district of Izumi city known as only migration area of cranes in Kyushu. The other, Peloribates fumotoensis sp.n. was collected from one of the places of the samurai residences where was the center of administrative block called Fumoto in the Edo period opened out about 400 years ago.
Dawsonite has been recently re-discovered in the Cretaceous Izumi Group, Southern Osaka Prefecture, the area where this mineral was first described in Japan. Dawsonite commonly occurs as thin ...veinlets that are strongly associated with aragonite. Marginal fringes of aragonite and dawsonite are found along mudstone walls of thick calcite-dominated veins that cut across the dawsonite-aragonite veins. The dawsonite-aragonite association is characterized by a large number of cavities of varying sizes, suggesting their precipitation in an open space formed by the forcible invasion of a CO2-rich fluid. Thin-section observations reveal that the CO2-rich fluid hardly reacts with mudstone. The order of formation of carbonate veins (from the dawsonite-dominated regime to the calcite-dominated regime) is generally concordant with the changes in the fluid chemistry and precipitated phases predicted on the basis of a geochemical simulation to the quartzofeldspathic CO2 reservoir in CO2 geological storage.
Shikoku, Japan, is an island located on the forearc region of the western sector of the Southwest (SW) Japan arc that was formed by subduction of the Philippine Sea plate beneath the Eurasian plate. ...Noble gas isotope analyses were carried out for 30 bubbling gas samples and spring water samples collected in Shikoku. In addition, chemical and carbon isotope analyses were conducted for six gas samples. Observed
3He/
4He ratios were 0.17
R/R
A to 3.56
R/R
A, showing that several samples contain mantle helium components, although some samples contain helium of crustal origin. Geographical distributions of
3He/
4He ratios show that high
3He/
4He ratios originate mainly from two areas: one along the Median Tectonic Line (MTL), a major active fault in Japan; the other coinciding with a region in which non-volcanic long-period tremors occur, about 30 km deep Obara, K., 2002. Nonvolcanic deep tremor associated with subduction in southwest Japan. Science 296, 1679-1681. This fact indicates that fluids liberated from the slab in the forearc region cause deep tremors and fracturing within the crust, thereby easing the transfer of fluids to the surface that are mixed with mantle helium to the surface. An active fault system can also provide an efficient path for mantle helium transfer.
The Hardy integral inequality is one of the most important inequalities in analysis. The present paper establishes some new Copson-Pachpatte （C-P） type inequalities, which are the generalizations of ...the Hardy integral inequalities on binary functions.
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