(TMJ) Quartz-rich Metamorphic Suite -- Tanzawa Mountains, Kanto, Japan


(TMJ) Quartz-rich Metamorphic Suite -- Tanzawa Mountains, Kanto, Japan


The Tanzawa Mountains in Japan were created in an arc-arc collision, when the Izu-Bonin-Mariana Arc was subducted beneath the Honshu Arc. This eventually accreted into the Tanzawa Mountains. The samples in this collection were found in and around the Tanzawa Mountains. The suite includes hornfels, amphibolites, quartz diorite, granophyres, and other basaltic rocks. The samples range from fine to coarse grained. An interesting feature found on many of the samples was a flow-like swirl of minerals in the thin section, visible in XPL. The quartz diorite samples had crystalline, powdery substances on them, which were analyzed using a Scanning Electron Microscope (SEM). The chemical compositions of the mentioned powdery substances were calcium, aluminum, silicon, and oxygen.


Western Minerals, Inc.

Spatial Coverage

The samples were found in the Tanzawa Mountains of Kanto, Japan.

Temporal Coverage

The Tanzawa Mountains were formed during the late Pliocene.


Start here:
Kawate, S., and Makoto, A., 1998, Petrogenesis of the Tanzawa plutonic complex, central Japan; exposed felsic middle crust of the Izu-Bonin-Mariana Arc: Island Arc, v. 7, p. 342-358,
link: http://dx.doi.org/10.1111/j.1440-1738.1998.00194.x.

  • This paper explains the chemical variation and high SiOpercentage of rocks within Tanzawa region, and describes in some depth the tectonic events that uplifted the Tanzawa Mountains.  

Additional resources:

Kitamura, K., Ishikawa, M., and Arima, M., 2003, Petrological model of the northern Izu-Bonin-Mariana Arc crust; constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan: Tectonophysics, v. 371, p.213-221, 
link: http://dx.doi.org/10.1016/S0040-1951(03)00229-4

  • This paper researchs the variations in acoustic impedance between different hornblende-gabbroic rocks from Tanzawa, Japan. 

Mikami, K., 1953, Metamorphic rocks in the southeastern margin of the Tanzawa quartz-diorite mass: Science Reports of Yokohama National University, v. 2, p. 34-49

  • This paper studies the chemical analysis of amphibolites resulting from contact metamorphism of the quartz-diorite mass in the Tanzawa Mountains.

Tani, K., Dunkley, D. J., Kimura, J., Wysoczanski, R.J., Yamada, K., and Tatsumi, Y.,2010, Syncollisional rapid granitic magma formation in an arc-arc collision zone: Evidence from the Tanzawa plutonic complex, Japan: Geology [Boulder], v. 38, p.215-218, 
link: http://dx.doi.org/10.1130/G30526.1

  • This paper discusses the collison that exposed the gabbroic rocks of the Tanzawa plutonic complex, and overall gives the reader an in-depth sturctural history of the Tanzawa Mountains. 

Yoshimura, T., 1997, Ca-Al silicates in low-grade metavolcanic rocks from southern Tanzawa Mountains, Central Japan: Journal of Mineralogy Petrology and Economic Geology,  v. 92, p. 363-378,
link: http://dx.doi.org/10.2465/ganko.92.363.

  • This paper explains prevalence of greenschist facies within the Tanzawa Mountain region, and gives the mineral composition of rocks from southern region of Tanzawa Mountains.




Items in the (TMJ) Quartz-rich Metamorphic Suite -- Tanzawa Mountains, Kanto, Japan Collection

Hornfels, Green Diopside bearing
Rock Sample:
The sample is metamorphic. It is green to light-green in color. There are very course grained tabular zones of metamorphism (12x4cm) and light to dark layering with non-uniform shapes and patterns. The grains are aphanitic. The…

Hornfels, Dark Brown
Rock Sample:
The sample is fine-grained, and the majority of the rock is dark grey in color. There is a 2.5x4cm white crystal formation on the upper edge of the sample. There are fractures running through the sample. There is some chemical…

Hornblende Porphyrite Dike
Rock Sample:
The sample is pinkish gray with brown to green phenocrysts. There are fine-grained to medium-grained phenocrysts (0.5~5mm in length). There is a dark-brown to orange coating, which is evidence of chemical weathering due to oxidation. …

Quartz Diorite
Rock Sample:
The sample has black to green phenocrysts with a greenish white matrix. It has phaneritic grains with a aphanetic matrix. Phenocrysts are coarse to fined grained ranging from 0.1~1cm in size. There is a chalk like powder on the…

Quartz Diorite with Laumontite Vein
Rock Sample:
The sample color has a cream colored matrix with dark green phenocrysts. The sample contains Laumontite, which is a mineral in the zeolite group. There is a white talc-like substance on upper part of sample. Phenocrysts are medium to…

Quartz Diorite
Rock Sample:
The samples color has a white matrix with dark green phenocrysts. It is phaneritic. There is evidence of chemical weathering due to the presence of a dark brownish orange film on the sample--may be oxidation. There is a sandy smooth…

Quartz Diorite
Rock Sample:
The color of the crystals within the sample is half-white and half-black in color. The internal part of the sample feels rough, but the outside layer of the sample feels more like a fine-grained. This could be due to erosion on the…

Amphibolite, with some anthophyllite
Rock Sample:
The sample is a dark greenish blue with brown layering. On one side of the sample there is a sand-like residue that is tan in color. The sample is aphanitic and possesses micro-folds. The sample appears to have experienced some…

Rock Sample:
The sample is very dark grey with light grey foliations.
The sample displays thin layering, some areas of chemical weathering, and microfoliations. It is aphanitic. There is quartz- like residue on the outside of the sample. It has…

Rock Sample:
The sample color is mainly light grey to white. There is a lime green layer as well as some dark grey and brown groupings. It is pegmatic and experiences non-congruent foliation and Y-shaped fractures. There are dark brown to orange…

Rock Sample: The color is a shiny dark grey with a bluish tint. Some parts of the sample are a more dark turquoise. Some faces are lighter and or darker than other faces. There is also a face with a brownish color and another face with a tannish…

Rock Sample:
The sample color is light brown to dark brown in color with white residue through out the surface. The rock has a light green tint. There is a greasy luster to the sample. There are large white veins and planes of cleavage that follow…

Dolerite Sill
Rock Sample:
The rock is dark green throughout, with a mineral forming white specks. The white mineral does not react with hydrochloric acid. The texture is very rough, and the rock's edges are sharp. Large flat phenocrysts (~ ≤10mm). The…

Basaltic Tuff Breccia of Actinolite Greenschist
Rock Sample:
The sample is brown to white to green in color. It is porphyritic and has foliations that fan out. There are also wide fractures (≤1mm in length). There is a brownish orange coating which is evidence of chemical weathering. There…

Pumpellyite Prehnite Basaltic Tuff Breccia
Rock Sample:
The color is mainly a very dark green to dark grey. Some parts of the rock exhibit greasy luster. There are some tannish white spots and some slightly larger dark brown spots. The tannish white mineral reacts with acid. There are dark…

Basaltic Tuffaceous Conglomerate
Rock Sample:
The overall matrix is a dark green blue but there are many different colored clasts that give it a mixture of colors. The color of the clasts range from brick red, pink, white, and green (non-reactant to acid). The texture of the rock…

Clay and Stilbite Matrix in Sandstone
Rock Sample:
The sample appears to be a conglomerate of crystals.The color is tan to dark green. The rock has low specific gravity . There are green, white, and brownish-orange clasts. There are some minor fractures on the outside of the sample. …

Andesite Tuff
Rock Sample:
The color is mainly blue and black. The sample is aphanitic and the cross section of the sample reveals very fined grained phenocrysts (~1mm in diameter). The colors of the phenocrysts range from white, blue, black, or green.
It has…

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