A pebble of greenstone with pumpellyite vein and pumpellyite grains in the Cretaceous formations of the Sanchu graben, Kanto Mountainland

Abstract

A pebble of greenstone with pumpellyite vein was found in the basal conglomerate of the Upper Cretaceous Sanyama formation (Gyliakian) of the Sanchu graben, Kanto Mountainland. Petrographic study of the pebble shows clearly that the pumpellyite vein had been formed in the greenstone before the deposition of the conglomerate. Detrital fragments of pumpellyite were also found in sandstone of all the Cretaceous formations (Aritan-Gyliakian) of the area. The pebble carrying pumpellyite and the fragments of pumpellyite would have been supplied from the Sanbagawa metamorphic terrain and the North belt of the Chichibu terrain, which are located to the north of the Sanchu graben, at the time of deposition of the Cretaceous sediments. Then, the Sanbagawa -metamorphism should have been completed before the deposition of the Cretaceous sediments. Then, the Sanbagawa metamorphism should have been completed before the deposition of the Cretaceous sediments of the Sanchu graben.