ESR dating of volcanic and baked rocks

Abstract

Volcanic rocks of Pliocene to Pleistocene age are developed in the mountainous region of the central part of Japan. We determined the age of the rocks by electron spin resonance (ESR). Four specimens were dated: granite (IK) and sediment (UN) which were baked by basalt lava flows whose KAr age was reported to be 1.4–2.0 Ma, and felsic pyroclastic flow deposits (TK, NM). The Al centre is found in quartz grains extracted from all samples. The ESR ages of 0.77 and 1.3 Ma are obtained from the Al centre in quartz of IK and UN, respectively. The dacitic pyroclastic flow deposit (NM) whose ESR age is obtained to 0.37 Ma, seems to be correlated with dacite lava in the same region, whose KAr age is 0.5 ± 0.1 Ma. The ESR ages of TK are determined as 0.084 and 0.098 Ma from the Al and Ti centres, respectively.