Southern Kitakami Research Articles

The Triassic Inai Group in the Karakuwa Area, Southern Kitakami Mountains, Japan (Part II):On the "intraformational disturbances" in the Lower TriassicOsawa Formation

The Triassic Inai Group in the Karakuwa Area, Southern Kitakami Mountains, Japan (Part II):On the "intraformational disturbances" in the Lower TriassicOsawa Formation

宮城県，笠貝島はんれい岩体について

The Kasagai-jima gabbroic complex is one of the Mesozoic plutonic masses in the southern Kitakami mountains. The complex is composed mainly of four rock types such as type I, type II, type III and type IV, which have been emplaced successively in this order. The rock of type I is clinopyroxene hornblende gabbro and is enriched in clinopyroxene which have been crystallized before the emplacement. The rock of type II varies from olivine two pyroxene gabbro to hornblende gabbro. This variation is ascribed to the magmatic movement during the consolidation. The rock of type III is clinopyroxenze hornblende gabbro characterized by coarse-grained plagioclase. The rock of type IV is clinopyroxene hornblende gabbro characterized by many gabbroic pegmatite veins, These four rock types are considered to have differentiated from a common magma, of which reservoir was situated perhaps in the lower crust. The chemical composition of the magma is characterized by low alkali content and high Al content, showing the trend of calk-alkali rock series after Daly (1914). The differentiated magmas derived from the reservoir were intruded and solidified in the Inai group. At the later stage of differentiation, the magma was enriched in H2O and formed many gabbroic pegmatite veins. The ball structure existed in the rock type IV was formed at the same stage. The original magma of the Kasagai-jima gabbroic complex is similar in chemical composition to that of the Ojika gabbroic complex. The major differences between both complexes are that the enrichment of H2O in the differentiated magma is recognized only in the Kasagai-jima gabbroic complex, and that the place of emplacement is somewhat deeper for the Kasagai-jima gabbroic complex than another.

Stratigraphy of the Mesozoic formations in the Hashiura area, Southern Kitakami Mountainland, northern Japan

Stratigraphy of the Mesozoic formations in the Hashiura area, Southern Kitakami Mountainland, northern Japan

The Triassic Inai Group in the Karakuwa area, southern Kitakami Mountains, Japan (Part I):Stratigraphy and paleogeography

The Triassic Inai Group in the Karakuwa area, southern Kitakami Mountains, Japan (Part I):Stratigraphy and paleogeography

Compositional dependence of the Mg/Fe2+ distribution coefficient between biotite-hornblende pairs from calc-alkaline granitic rocks.

Five pairs of biotite and hornblende from the rocks of the Senmaya granitic intrusion in the southern Kitakami Mountains were analysed chemically. The apparent distribution coefficient of Mg-Fe2+ between biotite and hornblende is considerably controlled by the My/Fe2+ ratio as well as the AlIV content of hornblende in calc-alkaline granitic rocks from Senmaya district and other various localities in the world. With regard to the chemistry of hornblende coexisting with biotite in granitic rocks, the following facts are established: The relation between the Mg/Fe2+ ratio and any one of the AlIV, (Na+K), (AlVI+Fe3+) and Ti contents shows a good linearlity with a negative gradient; the difference in magnitude between the AlIV and (Na+K+AlVI+Fe3++Ti) contents is ascribed to the effects of the glaucophane-riebeckite and/or richterite substitutions.

Geological and Structural Studies of the Area along the Hizume-Kesennuma Tectonic Line, in Southern Kitakami Massif

Geological and Structural Studies of the Area along the Hizume-Kesennuma Tectonic Line, in Southern Kitakami Massif

Petrology of the tabashine granitic body, Kitakami mountains, northeastern Japan.

To reveal the chemical characters of the Tabashine granitic body, southern Kitakami mountains, thirteen rocks, ten biotites and seven hornblendes were analysed chemically. As a result, the analyses indicate high K2O in rocks, high TiO2 in biotites, and low Al2O3 in both biotites and hornblendes. These chemical features of the Tabashine body are common to the Orikabe and Hirota, while the other adjacent granites called Senmaya, Hitokabe and Kesengawa are different. Judging from the fact that all rock types of the Tabashine body, i. e. gabbroic, granodioritic and adamellitic rocks, show similar features of mineral chemistry, it is considered that they are comagmatic dervatives. On the other hand, the reason why the rocks of the three bodies, Tabashine, Orikabe and Hirota, show similar features and are different from the other adjacent granites of Senmaya, Hitokabe and Kesengawa, is probably that their magmas had the same origin and had been passed under similar physicochemical conditions.

Carbonaceous Matter in Permian Slates from the Southern Kitakami Mountains

Carbonaceous Matter in Permian Slates from the Southern Kitakami Mountains

Rb-Sr geochronology of the Hikami granite, Kitakami mountains, Japan.

Whole-rock samples of the Hikami granite from the southern Kitakami mountains in Northeast Japan give a Rb-Sr age of 339 ± 12m.y with an initial 87Sr/86Sr ratio of 0.7079 ± 0.0003, indicating that the granite intruded in the late Devonian to early Carboniferous time. A slightly high initial 87Sr/86Sr ratio for the Hikami granite suggests that the granite assimilated some amount of older crust. The Tsubonosawa gneiss, which is contained in the Hikami granite as xenolithic masses, gives an isochron age of 334m.y with an initial 87Sr/86Sr ratio of 0.7129. The results show that the Sr isotopic homogenization occurred among the whole masses of the gneiss at the time of granite intrusion. A higher initial 87Sr/86Sr ratio suggests that the gneiss originated in the Precambrian time. Granite boulders from the Devonian Ono formation do not define any isochron, whereas the sandstone from the Silurian Kawauchi formation gives an apparent age of 264m.y. The whole-rock systems of boulders and sandstone may have remained open with respect to Rb and Sr, probably because of their involvement in sedimentary process. The Rb-Sr isotopic data for the Cretaceous Tono and Kesengawa granites confirm the evidence that almost all igneous rocks in Northeast Japan, irrespective of age, have low initial 87Sr/86Sr ratios, reflecting a distinctive nature of crust in Northeast Japan.

Geology of the Kamiyasse area, Southern Kitakami Mountains

Geology of the Kamiyasse area, Southern Kitakami Mountains

Magma types of volcanic rocks and crustal history in the Japanese pre-Cenozoic geosynclines

Magma types and temporal variations of the volcanic rocks erupted in the Japanese pre-Cenozoic geosynclines are examined using the petrochemical data of almost 550 new analyses. It is assumed that the alteration of these rocks was isochemical in nature. The characteristic rock type is basalt, but some variations of rock type are observed in certain areas: 1. (1) In western Japan, the parental magmas of Permian age are mostly inferred to be alkali basalt series and high-alkali tholeiite rock series. The rocks of low-alkali tholeiite are few if any. High-alumina basalts are observed in limited localities. 2. (2) The rocks of the Mikabu metamorphic belt, probably products of Permian submarine volcanism, lack any appreciable high-alumina basalt. These petrochemical features support the conclusion that the geosynclinal basalt from western Japan is much closer to the oceanic basalt than are the Japanese Cenozoic volcanics (Sugisaki et al., 1970). 3. (3) The changes of rock characteristics in the southern Kitakami area with time show that the magma has progressively changed since the Devonian from alkali basalt, high-alkali tholeiite and low alkali tholeiite, through high-alumina basalt and high-alkali tholeiite rock series finally to low-alkali tholeiite rock series. The several magma types show significant differences in both major and minor elements: 1. (1) the Japanese Paleozoic geosynclinal tholeiite is the petrochemical equivalent of the abyssal tholeiite of the Mid-Atlantic Ridge and East Pacific Rise, which was studied by several authors: Engel et al. (1965), Gast (1968), Hart (1969), and Miyashiro et al. (1970). 2. (2) the geosynclinal tholeiite was differentiated in a manner similar to that of the abyssal tholeiite. The weathering effect of sea-water was not significant in the geosynclinal basalts, implying that the volcanic rocks were confined under thick sediments soon after the eruption. These lithologic changes in the Japanese pre-Cenozoic geosynclines may record: 1. (1) the genesis of the geosynclines. 2. (2) the variations in crustal thicknesses in the early stage of the geosynclines; and (3) the crustal evolution (continental and oceanic) of the Japanese Islands.

Stratigraphy of the Permian System in the Area of Toyoma Town, Southern Kitakami Massif, Japan

Stratigraphy of the Permian System in the Area of Toyoma Town, Southern Kitakami Massif, Japan

Permian-Triassic Boundary in the Japanese Islands

In the southern part of the Kitakami Mountainland, North-east Japan, the Permian-Triassic boundary is often well exposed, where the Upper Permian Toyoma Slate and the Lower Triassic basal member of the Inai Group are intimately associated. There, T. Kobayashi once inferred the Tate epeirogeny and later Y. Onuki the Otani orogeny at the Permian-Triassic interval. N. Kanbe who dealt with the gradual transition between the topmost Permian and basal Triassic limestones in Kyûusyû, stated, referring to the Permian-Triassic boundary in the Kitakami Mountainland, “the crustal movement occurred at the Permian-Triassic transition was no more than gentle undulation, although erosion took place at emerged part”.On the other hand, F. Ueda. after his many years' field studies. declared in his paper. “The geological structure of the Permian and Triassic in the Toyoma and Maiya district, southern Kitakami Massif, North-east Japan” (in Japanese), 1963, that he could trace a fairly large overthrust sheet of Permian formations in the Toyoma-Maiya district, Tome-gun, Miyagi Prefecture, along the east side of the Kitakami-gawa.The Permian system of the district, approximately trending N-S, consists of, in descending orderToyoma Slate, lacking fusulinids, Yamazaki Conglomerate (Usuginu Conglomerate), Yabeina zone, Tenzinnoki formation, Parafusulina matsubaishi zone (corresponding to the Neoschwagerina-Verbeekina zone of the other regions in Japan), Nisikori formation, upper part, Parafusulina zone, lower part, Pseudoschwagerina zone.His geological and tectonic maps (Pls. I, VII) show the overthrust sheet built essentially of Upper (eastern) layer of the Toyoma Slate, Middle (intermediate) layer of the Yamazaki Conglomerate, Lower (western) layer of the Yamazaki Conglomerate and Tenzinnoki formation closely folded together.The upper layer, the Toyoma Slate, is unconformably overlain by the Hineusi formation thought to be contemporaneous with the Lower Triassic Hiraiso formation of the Inai Group ; the boundary of the two formations is said to be strongly undulated, indicating an intense erosion interval.The boundaries on the maps, between the overthrust sheet and its superjacent Hineusi formation and subjacent foundation structure, as well as these between its three component tectonic layers are parallel to each other in broad sense, though variously undulated in themselves.The foundation of the overthrust sheet is built of the Nisikori, Tenzinnoki, and Yamazaki formations ; these formations are closely folded and in general overturned to east, but partly to the opposite direction, perhaps under the influence of the westward shift of the overthrust sheet.Now assuming Ueda's conception about his overthrust sheet as well established, there arises another question regarding to the geological age of this tectonic event. Ueda dated it at the Permian-Triassic interval, based on the fact that whereas the Permian system of the overthrust sheet and its foundation is extremely complicate in structure, the Triassic Inai Group is tranquil in its general behaviour. Furthermore, the tectonic lines separating six transverse segments of the overthrust sheet from each other do not extend into the overlying Triassic deposits, and there is also no trace of any significant relative shifting nor shearing between the Toyoma Slate and the Hineusi formation.There are, however, certain geological features incongruent with Ueda's view, mentioned below.

Some Permian Fossils from Southern Kitakami. I

Some Permian Fossils from Southern Kitakami. I

ON THE VOLCANIC ROCKS IN THE JAPANESE PALEOZOIC, THIRD REPORT, PERMIAN

Permian deposits widely developing in the southern Kitakami mountains have been divided into the Sakamotosawa series, the Kanokura series and the Toyama subsystem in ascending order. Volcanic rocks and their associated pyroclastic sediments are rather rare in the Permain deposits of those mountains, however, there exist thin liparitic or dacitic tuffs and “schalstein” in the Sakamotosawa series ranging from the Pseudoschwagerina to the lower half of the Parafusulina zone in age. Except for the Sakamotosawa series, volcanics and their pyroclastics have never been found in the Permian systems in that area The Kanokura series is further diyided into, in ascending order, the Kattisawa and Iwaisaki stages. Lepidolina multiseptata horizon of the Iwaisakistage may be possibly correlative to the middle to upper Neoschwagerina zone, while the Lepidolina gigantea horizon of the same stage may be nearly equivalent to the Yabeina globosa zone. Outside the Kitakami mountains, a large amount of volcanic rocks and their...

Paleozoic Formations in Shimoarisu Village, Southern Kitakami Massif, Northeast Honshu, Japan

Paleozoic Formations in Shimoarisu Village, Southern Kitakami Massif, Northeast Honshu, Japan

On the Permian System of the Maiya District in the Southern Kitakami Massif, Japan

On the Permian System of the Maiya District in the Southern Kitakami Massif, Japan

A New Species of Posidonia from the Inai Series (?) in the Southern Kitakami Mountainland, Japan

宮城縣本吉郡志津川町琵琶崎東方海岸の轉石中の Posidonia を研究結果, Aniso-Ladinicより記載されたる Posidonia pannonica に類似せる1新種なる事判明し Posidonia japonica と命名す。本化石を含む轉石は其の岩質と産地より井内統上部より將來せるものと推察す。

A New Species of Conularia from Southern Kitakami, Japan.,

A New Species of Conularia from Southern Kitakami, Japan.,