Determination of boron and other elements in volcanic rocks by prompt gamma-ray analysis. An application to magma genesis in Kyushu island, SW-Japan

Neutron induced prompt gamma-ray activation analysis (PGAA) is applied for determining boron contents in volcanic rocks, which is an important element in the discussion of material circulation in volcanic arc systems. To evaluate the recycling of oceanic crust in Kyushu, we analyzed boron and other trace element contents in basaltic rocks from the area. The basalts from volcanic front have high B/Nb (2.9-3.7), B/Zr (0.1-0.2) and B/Sm (2.8-6.0) ratios, whereas those ratios in the basalts from backarc are extremely low (<0.5; <0.1; 0.5-1.7), respectively. This indicates that the recycling of subducted oceanic crust to the arc crust is limited in the volcanic front. (author)