Occurrence of the Nakanodake Composite Intrusion in the north area of Yoneyama, Niigata, central Japan

Yoneyama Research Group, Masataka AIZAWA
Earth Science (Chikyu Kagaku)  
The early Pleistocene Nakanodake Composite Intrusion composed of basaltic rock core surrounded by hornblende andesite, exposed at the northern foot of the Mt. Yoneyama, central Japan. The boss dimension of this intrusion is 1.6 km in diameter. Basaltic rock comprises of mafic minerals, including clinopyroxene and orthopyroxene. Andesite can be classified into two types: hornblende-rich type and hornblende-poor type. The former includes a minor amount of pyroxene in the groundmass, whereas
more » ... ne is invariably present in the later. Hornblende is replaced by clinopyroxene, magnetite, and feldspar either partially or entirely. Then the hornblende-poor type andesite gradually changes into basaltic rock. It was observed those hornblendes became unstable, and were decomposed by injection of basaltic magma.
doi:10.15080/agcjchikyukagaku.72.2_111 fatcat:ufvhcdab7ngxxmvms56zigiv7q