ABSTRACT

Isotopic compositions of lead and strontium and concentrations of lead, uranium, thorium, rubidium, and strontium were measured in a suite of volcanic rocks, ranging from basalt to rhyodacite in composition, and in granite and gabbro xenoliths from a traverse across northern Honshu. The observed ²³⁸U/²⁰⁴Pb (μ) ratio ranges from 2.4 in tholeiitic basalt at the east end of the traverse to 11.6 in alkalic basalt from the west end. The isotopic composition is slightly less radiogenic to the west. The ⁸⁷Sr/⁸⁶Sr ratios of most of the samples fall within the range observed in oceanic basalts, but the granite xenolith and the rhyodacite are slightly more radiogenic.