Bridging the gap: 40Ar/39Ar dating of volcanic eruptions from the ‘Age of Discovery’

Many volcanoes worldwide still have poorly resolved eruption histories, with the date of the last eruption often undetermined. One such example is Ascension Island, where the timing of the last eruption, and consequently, the activity status of the volcano, is unclear. Here, we use the Ar-40/Ar-39 dating technique to resolve ages of the three youngest lava flows on the island, which are hawaiites and mugearite with 1.5 - 1.9 wt% K2O. In dating these lavas, we provide the first evidence of Holocene volcanic activity on Ascension (0.51 +/- 0.18 ka; 0.55 +/- 0.12 ka; 1.64 +/- 0.37 ka), determining that it should be classed as an active volcanic system. In addition, we demonstrate that the Ar-40/Ar-39 method can reproducibly date mafic lava flows younger than 1 ka, decreasing the gap between recorded history and geological dating. These results offer new prospects for determining patterns of late-Holocene volcanic activity; critical for accurate volcanic hazard assessment.