Abstract
Rb-Sr ages were determined on 20 whole-rock samples of granitic rocks from the Marumoridistrict, northernmost part of the Abukuma Plateau. The rocks are divided into two groups onthe basis of Rb-Sr isotopic nature; five samples of granitic rocks near the Marumori Bridge, which is hereby named the Marumoribashi granite, give a Rb-Sr whole-rock isochron age of 111.6±2.4 Ma with an initial 87Sr/86Sr ratio of 0.70645±0.00009, whereas all other samples give an age of 106.4±3.5 Ma with an initial ratio of 0.70553±0.00010. Thus the Marumoribashi granite isslightly but significantly older than and genetically different from other granitic rocks of theMarumori district. The mineral isochrons with biotite, K-feldspar, plagioclase and whole-rock give ages of 98.8±4.5 Ma for a sample of the Marumoribashi granite and 99.3±2.0Ma for that of the other group, both of which are identical to each other and slightly younger than the whole-rock ages.
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Schedule a callMore From: The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
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