HOW OLD IS KīLAUEA VOLCANO? INSIGHTS FROM 40AR/39AR DATING OF THE 1.7–KM–DEEP SOH-1 CORE

Reliable estimates for lava accumulation rate are essential for interpreting the thermal and geochemical structure of mantle plumes. The continuously cored, 1.7–km–deep, SOH-1 scientific drill hole on Kīlauea's lower east rift zone provide an opportunity to assess lava accumulation rate and the duration of the early shield stage of Hawaiian volcanism. Four new ⁴⁰Ar/³⁹Ar ages were determined for tholeiitic rocks from the core. Combining these ages with two previous ⁴⁰Ar/³⁹Ar ages (Teanby et al., 2002) and the drill site surface flow age (Moore and Trusdell, 1991), and correcting sample depth to remove dikes, yields a good correlation (R² = 0.95) for a 4.5 m/kyr lava accumulation rate. Fitting a 2^nd order polynomial curve (R² = 0.986) to these data shows the rate increased to 6.4 m/kyr during the last 50 ka. An increasing rate is contrary to the simple shield volcano growth model, which predicts a 40% decrease during the last 200 kyr for Kīlauea (DePaolo and Stolper, 1996). Kīlauea's growth is constrained on the north by neighboring Mauna Loa, which may have caused an increasing lava accumulation rate. Extending this curve to the base of the SOH-1 core indicates Kīlauea's tholeiitic volcanism started before 250 ka. These results conflict with a recent re-interpretation for the start of tholeiitic volcanism (<100 kyr; Lipman and Calvert, 2013). Combining the new ⁴⁰Ar/³⁹Ar results with a previous model for the duration of Hawaiian preshield stage volcanism (~400 kyr; Garcia et al. 2006), indicates that the lifespan of Kīlauea is ~650 kyr. This age agrees with a dynamic model estimate (~600 kyr; DePaolo and Stolper, 1996) but conflicts with a recent estimate of ~300 kyr based on alkaline rocks collected on the submarine south flank of Kīlauea (Lipman and Calvert, 2013). Our results suggest that Kīlauea is undergoing a period of vigorous tholeiitic volcanism and is growing faster than it is sinking isostatically, unlike shield-stage Mauna Loa volcano.

DePaolo & Stolper 1996, J. Geophys. Res. 101, 11,643–54; Garcia et al. 2006, Chem. Erde 66, 81-108; Lipman & Calvert 2013, Geosphere 9, 1348–83; Moore & Trusdell 1991, USGS Misc. Invest. Map I-2225; Quane et al. 2000, J. Vol. Geoth. Res. 102, 319–338; Teanby et al. 2002, Phys. Earth Planet. Int. 131, 101-130.