Cordilleran Section - 113th Annual Meeting - 2017

Paper No. 22-4
Presentation Time: 9:35 AM


GARCIA, Michael O., Department of Geology and Geophysics, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, JICHA, Brian R., Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706, MARSKE, Jared P., Department of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822 and PIETRUSZKA, Aaron J., U.S. Geological Survey, Denver Federal Center, Denver, CO 80225,

Reliable estimates for lava accumulation rates are essential for interpreting magma fluxes to intraplate volcanoes and inferring the thermal and compositional structure of mantle plumes. Kīlauea Volcano’s (Hawai‘i) 1.7-km-deep SOH-1 scientific drill hole provides an opportunity to assess the lava accumulation rate and duration of the early shield stage for Hawaiian volcanoes. New 40Ar/39Ar ages were determined for four SOH-1 tholeiitic samples. Combining these results with two previous 40Ar/39Ar ages and the age of the drill-site surface flow, and correcting sample depth to remove intervening dikes, yields a good correlation (R2 = 0.97) for a 4.4 m/k.y. accumulation rate, which may have increased to 5.9 m/k.y. during the last 50 k.y. These rates contrast with a predicted 40% decrease during the last 200 k.y. from a simple shield volcano growth model. Mauna Loa, a massive shield volcano that buttresses the north flank of Kīlauea, may have contributed to this nearly constant lava accumulation rate. Extending the correlation to the base of the SOH-1 core indicates that Kīlauea’s tholeiitic volcanism probably started by 240 ka. Assuming an ~400 k.y. duration for the preshield stage, Kīlauea is much older than some previous estimates (ca. 600 ka versus 150–275 ka) and has been vigorously erupting tholeiitic lavas for at least the past 200 k.y. During this period, it has been competing with Mauna Loa for the higher-temperature output of the Hawaiian mantle plume, which is contrary to previous models. New models that assess the magmatic output and thermal history of the Hawaiian mantle plume need to consider a steep increase in magma supply during the transition from preshield to shield stages to explain the near constant lava accumulation rate during early shield growth.