Argon geochronology of Kilauea's early submarine history

Submarine alkalic and transitional basalts collected by submersible along Kilauea volcano's south flank represent early eruptive products from Earth's most active volcano. Strongly alkalic basalt fragments sampled from volcaniclastic deposits below the mid-slope Hilina Bench yield 40Ar/39Ar ages from 212 ± 38 to 280 ± 20 ka. These ages are similar to high-precision 234 ± 9 and 239 ± 10 ka phlogopite ages from nephelinite clasts in the same deposits. Above the mid-slope bench, two intact alkalic to transitional pillow lava sequences protrude through the younger sediment apron. Samples collected from a weakly alkalic basalt section yield 138 ± 30 to 166 ± 26 ka ages and others from a transitional basalt section yield 138 ± 115 and 228 ± 114 ka ages. The ages are incompatible with previous unspiked K-Ar studies from samples in deep drill holes along the east rift of Kilauea. The submarine birth of Kīlauea volcano is estimated at < 300 ka. If the weakly alkalic sequence we dated is representative of the volcano as a whole, the transition from alkalic to tholeiitic basalt compositions is dated at ∼ 150 ka.