Geological and petrological studies on the Tanzawa mountainland (4)

Concluding the previous papers of the authors, adding some new data especially on the mode of occurrence and anorthite contents of a number of plagioclases in each plutonic and metamorphic rocks, the authors made it clear that the complexed sequences of plutonism and metamorphism of the Tanzawa mountainland is genetically related as successive phenomena of three stages of plutonism and metamorphism. Thev are as follows. First phase; activity of gabbro series of plutonic rocks which accompanies metamorphism leading to the formation of amphibolite and greenschist. Second phase; formation of main rock types of diorite series from earlier gabbroic rocks. This is accompanied by earlier diaphthoresis and later hornfelsization. Third phase; the intrusion of trondhjemite dikes and the formation of pools of the last diorite series, which seem to be broadly synchronous with the cleavage formation and zeolite facies metamorphism. Such sequence of plutonism and metamorphism in the deeper zone of the Tanzawa mountainland is tectonically related with the deposition of each stratum in the upper zone. Examining the pebbles of plutonic and metamorphic rocks from various strata, with previous data of the anthers on the areal extension of each phase of metamorphism on each stratum, the following correlation was possible, i.e., the first phase metamorphism predates the deposition of the upper part of the Misaka series, the second phase metamorphism predates the deposition of Ashigara bed and postdate the upheaval and denudation of a part of the lower part of the Misaka series, and the third phase metamorphism synchronizes or postdates the deposition of Ashigara bed and postdates the upheaval and denudation of a main part of the lower part of the Misaka series.