scholarly journals Radiometric ages of granitic rocks in Outer Zone of Southwest Japan and its extension; 1968 summary and north-shift hypothesis of igneous activity

1968 ◽  
Vol 74 (9) ◽  
pp. 485-489 ◽  
Author(s):  
Tamotsu NOZAWA
Keyword(s):  
Outer Zone ◽  
Granitic Rocks ◽  
Southwest Japan ◽  
Igneous Activity ◽  
Radiometric Ages ◽  
Shift Hypothesis

scholarly journals K-Ar ages of granitic rocks from the Outer Zone of Southwest Japan

1967 ◽  
Vol 1 (3) ◽  
pp. 131-137 ◽  
Author(s):  
Ken Shibata ◽  
Tamotsu Nozawa
Keyword(s):  
Outer Zone ◽  
Granitic Rocks ◽  
Southwest Japan

Le massif granitique de Kongolo (Cameroun)

1950 ◽  
Vol S5-XX (4-6) ◽  
pp. 121-124
Author(s):  
J. Gazel
Keyword(s):  
Chemical Analysis ◽  
West Africa ◽  
Granitic Rocks ◽  
French West Africa ◽  
Igneous Activity

Abstract The alkaline granitic rocks of the Kongolo massif in Cameroun differ from other granites of the region. They represent post-tectonic igneous activity and exhibit striking analogies with younger granites of French West Africa and Nigeria. A chemical analysis is appended.

scholarly journals Igneous activity and fractional crystallization of the Abire granodiorite in the Okuizumo area, San^|^apos;in zone, Southwest Japan

2013 ◽  
Vol 119 (3) ◽  
pp. 190-204
Author(s):  
Chika Iwata ◽  
Atsushi Kamei ◽  
Katsuhiko Iwata ◽  
Tomoyuki Shibata ◽  
Asuka Mitani
Keyword(s):  
Fractional Crystallization ◽  
Southwest Japan ◽  
Igneous Activity

Geochronology in the Lake Superior region

1968 ◽  
Vol 5 (3) ◽  
pp. 715-724 ◽  
Author(s):  
S. S. Goldich
Keyword(s):  
World Wide ◽  
Lake Superior ◽  
Decay Constants ◽  
Minnesota River ◽  
The Past ◽  
Daughter Nuclide ◽  
Igneous Activity ◽  
Radiometric Ages ◽  
Minnesota River Valley

During the past 10 years many radiometric ages have been determined on minerals and rocks in the Lake Superior region. The oldest known rocks are the granitic gneisses in the Minnesota River Valley, which have been dated at 3300 to 3550 m.y. ago. Both K–Ar and Rb–Sr methods have been applied to samples from a number of the metasedimentary formations in the region. The ages, however, appear to be the time of folding or of metamorphism rather than of deposition for which only limits or ranges can be given from the ages for associated igneous and metamorphic rocks.Although considerable progress has been made, significant uncertainties remain in the decay constants and in the analytical measurements. More serious problems, however, are geologic ones, such as the effects of metamorphism and of weathering on the parent–daughter nuclide ratios. Both analytical and geological considerations must enter into any proposal for a time classification of the Precambrian.A three-fold division of the Precambrian with time boundaries at 2600 and 1800 m.y. serves well for the Lake Superior region. In addition, the Keweenawan igneous activity is well dated at approximately 1100 m.y. ago. Terms such as Keweenawan, Huronian, and others are best used locally, and time units of a Precambrian classification that might have world-wide utility should not be tied closely to geographic localities. A single radiometric method, as for example K–Ar largely on micas, is not a satisfactory basis for a classification.

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