The 40Ar/39Ar chronology and eruption rates of Cenozoic volcanism in the eastern Bering Sea Volcanic Province, Alaska

The eastern sector of the Bering Sea Volcanic Province, Alaska, consists of a number of large late Cenozoic volcanic fields that occur in a broad region inboard from the Aleutian arc front to the Arctic Circle. We estimate that about 750 km 3 of magma were erupted in the volcanic centers that we have studied, all within the past 6.0 Ma. Several discrete eruption episodes have been identified with the new 40Ar/39Ar data at circa 6.0 Ma (Imuruk volcanic field), circa 3.5 Ma (Teller volcanic field), circa 2.5-1.5 Ma (St. George Island), circa 1.0 Ma (St. Lawrence Island), and the youngest activity which started at circa 0.7 Ma and continued throughout region until historic times. Combining age information with volume estimates reveals that the intensity of volcanic activity in the Bering Sea Volcanic Province has increased through time, with only about 15% of lava erupted before 3 Ma and about 30% of all late Cenozoic magma erupted within the last 500 ka. Eruption rates also increase toward more recent times, from the 6 Ma Imuruk basalts, which erupted at the rate of similar to 70 +/- 15 m(3) km(-2) yr(-1), to the <= 0.7 Ma Nunivak Island and St. Michael volcanic field basalts, which erupted at a rate of similar to 165 +/- 25 m(3) km(-2) yr(-1). High volumes of erupted lava accompanied by high eruption rates for the youngest volcanic rocks suggest significant changes in the melting rates, which are best explained by either an evolving tectonic regime or significant changes in the melting processes.