scholarly journals Occurrence, chemistry and tectonic significance of alkali basaltic rocks in the Miura Peninsula, central Japan.

1990 ◽  
Vol 96 (2) ◽  
pp. 101-116 ◽  
Author(s):  
Hidetsugu TANIGUCHI ◽  
Yujiro OGAWA
Keyword(s):  
Central Japan ◽  
Basaltic Rocks ◽  
Tectonic Significance

Sadanagaite and subsilicic ferroan pargasite from thermally metamorphosed rocks in the Nōgō-Hakusan area, central Japan

1989 ◽  
Vol 53 (369) ◽  
pp. 99-106 ◽  
Author(s):  
Takayuki Sawaki
Keyword(s):  
High Alumina ◽  
Contact Aureole ◽  
Unit Cell Parameters ◽  
Central Japan ◽  
Cell Parameters ◽  
Basaltic Rocks ◽  
Crystalline Limestone ◽  
Facies Zone ◽  
Reaction Zones ◽  
Type Substitution

AbstractHigh-alumina subsilicic calcic amphiboles, including sadanagaite and subsilicic ferroan pargasite, are found in rock samples from the contact aureole in the Nōgō-Hakusan area, central Japan. They occur in the reaction zones between dark fragments and the surrounding crystalline limestone of the pyroxene hornfels facies zone. The dark fragments which underwent K-metasomatism are originally basaltic rocks. The sadanagaite and subsilicic ferroan pargasite have high Al2O3 (16–19 wt. %) and K2O (3.6–4.3 wt. %) contents. The Si value ranges from 5.38 to 5.64 and the total Al ranges from 3.10 to 3.43 when cation ratios are calculated on the basis of O = 23. The calculated unit cell parameters of sadanagaite are a 10.00 (1), b 18.06 (2), c 5.355 (4) Å, β 105.52(7)°, V 932(1) Å3. The A-sites of the amphiboles is occupied almost entirely by K and Na; the amphiboles are saturated with the edenite component. The amphiboles show a larger extent of tschermakite-type substitution [(Mg,Fe)Si⇌AlAl] than does ordinary pargasite. Sadanagaite is probably stable at the temperature above the upper amphibolite facies.

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