Rocks In Japan Research Articles

Alkali–silica reactivity of Japanese rocks

Since 1982, problems relating to the alkali–silica reaction of concrete structures have been occurring in Japan. To identify the aggregates causing the reaction, the reactivity of Japanese rocks and the distribution of reactive rocks in Japan have been studied. Observations of aggregates in concrete structures affected by the alkali–silica reaction, reaction experiments (chemical method: ASTM C 289, mortar bar method: ASTM C 227) on the aggregates in the affected concrete and rocks collected from quarries and outcrops, and geological investigations on the results have been performed. As a result, reaction products were observed around andesite, rhyolite and shale, and a reaction rim was recognized in andesite, rhyolite, sandstone, shale and chert. Deleterious and potentially deleterious rocks defined by the chemical method in concrete, which were affected or possibly affected by the alkali–silica reaction, were porphyrite, andesite, dacite, rhyolite, sandstone, shale and chert. The results of the chemical and mortar bar methods on the rocks from quarries and outcrops indicated the same results as the aggregates in concrete structures; the reactive rocks were basalt, andesite, dacite, rhyolite, sandstone, shale, slate, tuffs, chert and quartz schist. The reactivity of volcanic rocks is controlled by the presence of cristobalite, tridymite and volcanic glass. The presence of these minerals is affected by the formation age of the rocks; pre-Miocene rocks do not have reactivity. Reactivities of sedimentary and metamorphic rocks are controlled by crystallinity and content of quartz.

ＴＢＭの掘削抵抗を利用した岩盤分類 花こう岩の事例

Since tunnel boring machine (TBM) is a full-face machine, the face cannot actually be observed. This is disadvantageous when excavating rock, which has rapidly changing characteristics, as is commonly the case for rock in Japan. Therefore, measuring geological characteristics forward of the face is essential. In the previous paper, a method for estimating the rock strength of face using TBM cutting force, such as thrust, torque and cutting depth, is proposed. In the present study, rock strength along the Hiraya tunnel that mainly consists of granite is estimated from actual excavation data. The length of the tunnel excavated by TBM is 3 km. A full-shielded type TBM having a diameter of 2.6 m was used to excavate the tunnel. Firstly, the estimated rock strength was compared with the characteristics of rock obtained using the bedrock surveys (inflow water, alteration etc.) and Schmidt-hammer rebound hardness. Estimated rock strength was found to agree well with those found using these surveys. Therefore, the reliability of the estimated rock strength was very high. Secondly, the relationship between rock mass classification and the estimated rock strength is examined. The results indicated that the higher the rock mass classification, the higher the estimated rock strength. In case of granite, spacing of rock discontinuities and weathering were determined the rock strength. Therefore, the estimated rock strength provides a useful method for properly selecting a supporting pattern for rapidly changing rock mass characteristics. Thirdly, the relationship between the cutter-head rotational rate and estimated rock strength was discussed because the cutter-head rotational rate of the TBM was variable (4~12 rpm). The lower rotational rate was found to be useful to excavate soft rock.

The Higo High-Grade Metamorphic Rocks in Japan as a Part of the Collisional Terrane Between the Sino-Korean and Yangtze Craton

The Higo High-Grade Metamorphic Rocks in Japan as a Part of the Collisional Terrane Between the Sino-Korean and Yangtze Craton

日本における主な岩石中の放射能

日本における主な岩石中の放射能

Construction and analysis of interpreted fracture planes through combination of satellite-image derived lineaments and digital elevation model data

One application of lineaments interpreted from satellite images is to reveal dominant azimuth sets and distribution density of the derived lineaments for an extensive area. In this analysis, a lineament is treated literally as a straight line in the horizontal plane and any dip of the lineament is not considered. We propose a new method to calculate the azimuth (strike and dip angles) of “fracture” planes through a combination of lineament maps and digital elevation models (DEMs). A “fracture” is created by connecting several lineaments, which appear to belong to the same system, using the criteria of distance and directional angle. The proposed method was applied to mines in an area of Cretaceous granite, an area of Miocene andesite and an area of Quaternary volcanic rocks in Japan. Lineaments in these areas were interpreted from Landsat Thematic Mapper (TM) or SPOT panchromatic images using the segment tracing algorithm (STA). A correlation exists between interpreted “fracture” orientations and (1) the predominant azimuth of joints appearing on the drift walls of a skarn deposit in the granite area and (2) the orientation of main gold veins in the andesite area. Furthermore, interpreted “fractures” are believed to act as conduits for transporting hydrothermal fluids to the surface in a hot spring area. Additionally, the proposed method is capable of calculating the intersection pattern of fractures at an arbitrary level below the ground surface.

Relationship between Failure Process of Creep Test and Conventional Compression Test on Soft Rocks-- Studies on the creep mechanism under compressive load of rocks (Part-2) --

For the rock engineering projects, it is necessary to correctly estimate the mechanical properties of the rock, namely, the stress-strain relations and strength properties, the time-dependent deformation properties and so on. In our previous studies, the drained creep tests under uni-axial compressive load were carried out on some soft rocks in Japan, such as Ohya-Ishi and Kimachi-sandstone. In these experiments, the axial and lateral strains and the acoustic emission activity were observed in the loading time intervals of several minutes ∼ one month. Also, the thin sections for microscope examination conducted on the specimens, which had loaded during the prescribed time or until some region of the creep process. In this study, the creep process and mechanism were discussed by using these experimental data, and the relationship between the failure process of creep loading and conventional uni-axial loading of rock were discussed by the specially planned testing programs of the experiment.by these results, it can be said that the residual compressive strength of the creep loaded rock specimen is almost the same as that of the intact rock, when the axial strain rate is in the decreasing condition, but the residual strength decreases the value when the axial strain rate passes the minimum value and in the increasing condition. Consequently, the failure process of the creep and conventional uni-axial loading are closely connected with each others；the changing point of the residual strength of the creep loaded rock which coincides to the minimum point of the axial strain rate, corresponds to the strength failure point of the rock under the conventional uni-axial compressive loading.

Characterization of organic matter in the Miocene turbidites and hemipelagic mudstones in the Niigata oil field, central Japan

The Teradomari Formation, a principal petroleum source rock in Japan, consists of turbidite (Et) and hemipelagic (Ep) mudstones of a Bouma sequence at the type section in Niigata Prefecture, central Japan. Maceral composition of immature kerogen shows characteristic differences between Et and Ep mudstones. Et kerogen consists mainly of vitrinite and non-fluorescent amorphous organic matter (NFA) both of terrestrial origin, while Ep kerogen mainly consists of weakly fluorescent amorphous organic matter (WFA) of marine plankton origin. Elemental analysis, Rock-Eval pyrolysis, FTIR spectra and stable carbon isotope ratios support the differences in maceral composition between Et and Ep kerogens. The carbon isotopic ratios of WFA from Ep kerogen, separated by centrifugation specific gravity method, were almost the same as for bulk Ep kerogen. This supports the case for their origin from marine plankton indicated by maceral analysis

The cessation of igneous activity and uplift when an actively spreading ridge is subducted beneath an island arc

Abstract Ridge subduction and the resulting formation of a slab window interrupts volcanic arc‐type igneous activity and causes uplift of the arc system. These implied diachronous relationships are examined by comparison of the temporal and spatial positions of ancient migrated trench‐trench‐ridge triple junctions and the distribution of subduction‐related igneous and metamorphic rocks in Japan.

The squeezing potential of rock around tunnels: Theory and prediction with examples taken from Japan

Large deformations of surrounding media around tunnels are often encountered during excavations in rocks with squeezing characteristics. These deformations may sometimes continue for a long period of time. Predictions of deformations of tunnels in such grounds are urgently needed, not because of stability concerns, but also of their sevicability. In the present study, the squeezing phenomenon of rock around tunnels and its mechanism and associated factors are first clarified by carefully studying failures of tunnels, and a survey of tunnels in squeezing rocks in Japan is presented and its results are summarised. Then, a practical method is proposed to predic the squeezing potential and deformation of tunnels in squeezing rock and this method has beeen applied to actual tunnelling projects, where squeezing problems were encountered, to check its applicability and validity. Finally, an extension of this method to the time-dependent behaviour of squeezing rocks is given and an application of this method to an actual tunnel is presented.

Infrared microspectroscopy analysis of water distribution in deformed and metamorphosed rocks

Infrared microspectroscopy has been applied to thin sections of various deformed and metamorphosed rocks in order to investigate water content of quartz in these rocks. The broad IR band absorbance around 3400 cm −1 probably due to fluid-inclusion molecular water (H 2O) was used to calculate water contents. Deformed granitic rocks from the Yanazawa-Kamimura area near the Median Tectonic Line (MTL) showed an increase of water content in quartz from about 300 ppm to 2500 ppm toward the MTL with increasing degree of deformation. Metacherts from Sambagawa metamorphic rocks (Asemigawa route) showed a systematic decrease of water content in quartz from about 1000 ppm to 200 ppm with increasing metamorphic degree from chlorite, garnet, albite-biotite to oligoclase-biotite zones. An Archaean metachert from the Napier Complex (granulite facies) has only 40 ppm water. Comparing this with an Inuyama unmetamorphosed chert sample having water contents of 3500 to 7000 ppm (a starting point of metamorphism), the systematic decrease of water in quartz with increasing metamorphic grade may extend from unmetamorphosed cherts to the highest-grade metacherts. Water contents in high-pressure metamorphic rocks in Japan are mostly of the order of 500 ppm (300–700 ppm), except for those from Kurosegawa with a water content as high as 1700 ppm. These results represent an exploratory analysis of intragranular water contents in quartz in various deformed and metamorphosed rocks. Further micro FT-IR studies of the distribution of water in crustal rocks will provide a quantitative basis for examining the geochemical cycle of water in the earth's crust.

日本の主な岩石中の放射能 （線量）

日本の主な岩石中の放射能 （線量）

Formula omitted] analysis of K-feldspars from Cretaceous granitic rocks in Japan: Significance of perthitization in Ar loss

40 Ar 39 Ar spectrum ages have been determined for five K-feldspars from Cretaceous granitic rocks in Japan. Three samples yield flat age spectra, giving plateau ages of 60.1 ± 1.1 Ma (94.3% of integrated 39Ar) for the Naegi granite of the Sanyo Belt, and 101.9 ± 2.5 Ma (95.5%) and 103.3 ± 1.7 Ma (96.1%) for granitic rocks from northeast Japan. The results suggest that these granitic rocks experienced a simple and rapid cooling history. Two feldspars from granitic rocks of the Ryoke Metamorphic Belt in the vicinity of the Median Tectonic Line give two plateau ages each: 61.1 ± 1.0 Ma (46.0%) and 66.0 ± 1.1 Ma (32.4%) for low-temperature steps; and 64.6 ± 1.0 Ma (51.6%) and 71.2 ± 1.1 Ma (65.4%) for high-temperature steps, though plateau ages for high-temperature steps are less well defined. This age pattern may suggest a later thermal event related to the Median Tectonic Line. The cooling rates calculated from KAr ages of coexisting mineral pairs range from 17° to 32°C Ma −1 for granitic rocks from the Sanyo and Ryoke Belts, whereas mineral ages for granitic rocks from northeast Japan are nearly equal, suggesting a very rapid cooling. Diffusion parameters of K-feldspars calculated from the 39Ar release yield activation energy, E, ranging from 22.3 to 53.4 kcal mol −1, and D 0 a 2 ranging from 0.0297 to 1.73·10 5 s −1. The closure temperatures are calculated to be from 115° to 331°C. The activation energy and closure temperature are inversely correlated to the degree of perthitization, which is the decisive factor for Ar loss from K-feldspar.

Paleointensities for 10–22 ka from volcanic rocks in Japan and New Zealand

Eight volcanic rocks from Japan and New Zealand in the age range 10–50 ka B.P. were studied using the Thellier method paleointensity experiment and yielded five successful results for 10–22 ka. Samples from the Shikotsu, Kuttara and Daisen volcanoes in Japan were taken from pyroclastic flows (both welded and non-welded) and a pumice fall deposit. One of the two New Zealand rocks is a rhyolite lava from the Taupo Volcanic Zone. Four sites out of seven located on rocks that are not usually subjected to Thellier's experiment yielded successful results, which indicates that volcanic products such as pyroclastic flows and rhyolite lavas are as good a material as basalt and andesite lavas for application of the paleointensity experiment. One paleointensity from New Zealand at 9.9 ka is very large, at about 100 μT, and provides support for the paleointensity high found in Europe and Japan [1,2]. The other four paleointensities for 14–22 ka are smaller than the present-day value, and this agrees with the idea of a broad paleointensity minimum for the period 10–50 ka that was suggested by McElhinny and Senanayake [3]. It is also noted that the variation curve of absolute paleointensity from the volcanic rocks is reasonably similar to the relative paleointensity curves from marine and lake sediments which were summarized by Tauxe [4].

The squeezing potential of rocks around tunnels; Theory and prediction

The deformational behaviour of tunnels, which underwent large deformations, socalled squeezing, have been recently receiving great attention in the field of rock mechanics and tunnelling. Contrary to rockbursting phenomenon in which the deformation of the medium takes place instantaneously, the deformation of the surrounding rock in squeezing phenomenon takes place slowly and gradually when the resulting stress state following the excavation exceeds the strength of the surrounding medium. Although there are some proposals for the definition of squeezing rocks and prediction of their squeezing potential and deformations of tunnels in literature, it is difficult to say that they are concise and appropriate. In the first half of this paper, the squeezing phenomenon of rock about tunnels and its mechanism and associated factors are clarified by studying carefully observed failures in-situ and laboratory model tests. Then, an extensive survey of tunnels in squeezing rocks in Japan is presented and the results of this survey are summarised. In the second half of the paper, a new method is proposed to predict the squeezing potential and deformations of tunnels in squeezing rock. Then, the method is applied to actual tunnelling projects, where squeezing problems have been encountered, to check its validity and applicability. As a concrete example, an application of the method to predict the squeezing potential and deformations of the rock along a 300 m long section of an actual tunnel was made.

加圧式回転ディスク型反応装置を用いた酸処理における鉱物の反応特性の解析

In acidizing, it is important to make a suitable plan for the characteristics of the objective reservoir. Particularly, since most reservoir rocks in Japan contain a large amount of feldspar and clay, acidizing needs to be carefully designed considering the prevention of secondary formation damage. To do this, the characteristics of acid reaction on the minerals which constitute reservoir rocks in practical fields should be fully understood.The reaction characteristics of hydrochloric acid on calcite were measured using a rotating disk apparatus. This apparatus was originally designed by D. R. BOOMER and has been generally used to investigate the acid reaction kinetics on minerals. The measurements were made on combinations of acid concentration of 7.5, 15 and 25% and disk rotational speeds of 50, 100, 300 and 500rpm at room temperature and 100°C under a pressure of 7 MPa. The results indicated that the reaction of acid on calcite was diffusion limited, and the effective diffusion coefficient could be obtained from the experiments at room temperature.The final purpose of the study is to develop numerical models of matrix acidizing and fracture acidizing. This rotating disk apparatus was proved to be used to get the information on the acid reaction parameters.

Paleointensity high at 9000 years ago from volcanic rocks in Japan

Six paleointensities were determined from young lava flows of Fuji and Oshima Volcanoes whose ages are around 8000 to 15000 years B.P. Two lava flows which have well‐defined ages at 8970±390 years B.P. and 9260±430 years B.P. give large paleointensities of 67±12 and 65±6 μT, respectively. Another lava flow of less accurate age also gives large paleointensity of 63±6 μT. The new paleointensity data are consistent with the trend of averaged paleointensity variation in Japan for the last 9000 years. They form a peak of paleointensity high at around 9000 years B.P. comparable to the well‐documented one at 2000 years B.P. This suggests that there exists a dominant component with a characteristic period of about 7000 years in paleointensity variation. Large paleointensity at about 8000–10000 years ago is also reported in France and Iceland. Paleointensity variation averaged every 1000 years for the last 14000 years is quite similar in Europe and Japan. The sine‐curve‐like variation of paleointensity observed in both Europe and Japan probably reflects the nature of the dipole moment if we consider much difference of longitude between the two regions.

Strontium isotope systematics and metallogenesis of skarn deposits in Japan

In order to understand skarn petrogenesis, we determined the strontium isotope compositions of 168 skarns and 43 host or surrounding rocks in Japan. Most skarns have low Rb/Sr ratios (<0.1) and formation ages younger than 120 Ma, indicating negligible contents of 87 Sr due to a decay of 87 Rb. Multiple analyses of skarns from three representative base metal deposits demonstrate that their 87 Sr/ 86 Sr ratios vary only slightly (<0.001) within single mines, irrespective of time and position, indicating that even a single skarn sample can give a representative 87 Sr/ 86 Sr ratio on a single mine scale. On the other hand, skarns from 78 ore deposits in Japan reveal regional variations in the 87 Sr/ 86 Sr ratio ranging from 0.705 to 0.726. The variations are best classified by the ore metal type; skarns of the copper-iron type are rich, whereas those of the lead-zinc type are deficient, in Sr derived from the intrusions responsible for skarn formation. In many cases, Sr was derived from the original carbonate and aluminous rocks replaced by the skarns. Given that host limestones have relatively uniform 87 Sr/ 86 Sr ratios (0.7081 + or - 0.0007), the variability in the strontium isotope composition of skarns may be attributed to the difference and/or the amount of the involved aluminous rocks which have a wider range in the 87 Sr/ 86 Sr ratio. This is consistent as a whole with the occurrence of skarn deposits; copper-iron deposits form in geologic settings dominated by and often in contact with cogenetic large plutonic batholiths, whereas most lead-zinc deposits occur where sedimentary or igneous rocks with higher amounts of 87 Sr are common and form nearer and often distant from smaller hypabyssal dike or stock intrusions. An Sr isotope signature derived from the associated magmatic fluid is perceptible only in some skarns of the copper-iron type. The original magmatic fluid may have been modified isotopically when it encountered aluminous rocks and limestones and leached Sr from them.

きょう炭層岩石のスレーキング特性 ＩＩＩ きょう炭層岩石の力学的諸特性に及ぼす水分の影響

Coal measure rocks in Japan tend to deteriorate their mechanical properties by the presence of water. Most rocks around roadways and workings in the coal mines are liable to be exposed to water from the strata and other sources. Therefore, knowledge of the effect of water on the mechanical properties of coal measure rocks is of great ignificance for strata control in coal mining operations such as the maintenance of roadway and the face support and for the utilization of these rocks as back filling materials.In the present paper durability of coal measure rocks for water is investigated by means of three different kinds of slaking tests. The practical applicability of these tests to coal measure rocks is discussed and the contributory factors to slaking and their correlation with other properties such as uniaxial compressive strength and montmorillonite content are also investigated.

Relation between physical anisotropy and microstructures of granitic rock in Japan : Kudo, Y; Hashimoto, K I; Sano, O; Nakagawa, K Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V1, P429–432. Publ Rotterdam: A A Balkema, 1987

Relation between physical anisotropy and microstructures of granitic rock in Japan : Kudo, Y; Hashimoto, K I; Sano, O; Nakagawa, K Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V1, P429–432. Publ Rotterdam: A A Balkema, 1987

Phosphate minerals in chert from Toyoda, Kochi, City, Japan. .

Wavellite, variscite, planerite and cacoxenite were found in chert from Toyoda, Kochi City, as the first occurrence of aluminum phosphate assemblage in sedimentary rocks in Japan. They were formed on walls of fractures therein under a near surface condition. The phosphate ion came from nearby fluorapatite seam after the decomposition by sulphuric acid generated from pyrite in the intercalated slate after oxidation. The chemical analyses of wavellite, variscite, planerite and cacoxenite indicate wavellite to be a high fluorine material, variscite to be a nearly ideal one, planerite to be a copper-bearing one, and cacoxenite to be a highly aluminian material, respectively. The X-ray powder studies on variscite and fluorapatite specify the former to be Messbach-type and the latter to be very close to end member. Under such a near surface condition, different geochemical behaviours of Al from Fell leads to the formation of aluminum phosphates without any essential Fe3+.