241 research outputs found
The Basic Plutonic Rocks of the Hidaka Metamorphic Belt, Hokkaido. Part II : The Ameyama Layered Gabbros in the Tokachi Province
No full textThe occurrence of cumulus gabbro in the Hidaka Metamorphic Belt has been noted in the Western Zone of the Metamorphic belt as cumulus series of dunite-wehrlite-troctolite-olivine gabbro-anorthosite and various amphibolites which were obducted westward (Miyashita and Hashimoto, 1975). Besides the Western Zone gabbro series, many small bodies of cumulus gabbros have been known as fault bounded blocks throughout the whole metamorphic belt in the Axial and Eastern zones (Hashimoto, 1975). The Ameyama gabbro which occurs as an outlier of the metamorphic belt, is described and is compared with the Western Zone gabbros. Diabase which is accompanied by the Ameyama gabbro is also described. The chemical characteristic of the diabase show that it is nearly the same as the Hidaka Western Marginal Zone diabases but a slight difference in the trend of differentiation is revealed
Origin of the sheeted dike complex at superfast spread East Pacific Rise revealed by deep ocean crust drilling at Ocean Drilling Program Hole 1256D
No full textSuperfast spread (22 cm/a) upper oceanic crust drilled at Ocean Drilling Program site 1256 comprises a thick sequence of extrusive lavas underlain by a thin region of sheeted dikes. The sheeted dikes at this site are characterized by the intimate association of in situ hyaloclastic fragmentation and hydrothermal alteration. Lithostatic and magmastatic pressure estimates reveal that there is no effective level of neutral buoyancy within the extrusive layer to trap dikes in the crust. This results in a situation that favors the extrusion rather than intrusion of magma. Fractures created by magmas rising in dikes were the loci of intense hydrothermal circulation and provided the pathways for subsequent dike intrusions. Magma-rich conditions expected for fast spreading ridge segments give rise to a rapid increase in magmatic pressure, which can result in dike intrusion even under only small deviatoric stress. This allows for the emplacement of narrow dikes in the upper crust, with magmas more likely to extrude, and hence the high extrusive/intrusive ratio for Site 1256. <br/
Magma Chamber Models beneath Ocean Ridges with Reference to the Spreading Rates and the Mode of Fractional Crystallization
No full textMetamorphosed Dolerite Intrusives from the Western Zone of the Hidaka Metamorphic Belt, Hokkaido
No full textMetamorphosed dolerite intrusives in ultramafic tectonites, cumulates, and metagabbros are first described from the Western Zone of the Hidaka Metamorphic Belt. The dolerite intrusives ranging from a few cm to 30m in thickness occur as a dyke or sheet. Most of the dolerite intrusives are metamorphosed into amphibolite or metadolerite in various degrees. The metamorphic grade attains generally up to the amphibolite facies, and partly to the hornblende granulite facies in the ultramafic tectonites. Primary textures and minerals are well preserved in some metamorphosed intrusives. After mylonitization of the ultramafic tectonite the dolerite magma is considered to have intruded into the tectonites and into the already consolidated cumulate and gabbro complexes. Petrochemical and mineralogical data indicate that all of the dolerite intrusives are co-magmatic and are formed by crystallization of an olivine tholeiite magma which is highly undersaturated in silica and less differentiated
The Hidaka Shear Zone (Hokkaido, Japan): Genesis during a right‐lateral strike‐slip movement
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Metamorphosed Dolerite Intrusives from the Western Zone of the Hidaka Metamorphic Belt, Hokkaido
No full textCrustal Lithology and Stratigraphy of Remnant Arcs Induced from Ophiolitic Rocks in the Idonnappu Zone Acceretionary Complex (Hokkaido,Japan): Comparison with Philippine Sea Remnant Arcs
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