The postshield and previously inferred rejuvenated-stage history of Haleakala?? volcano is reevaluated on the basis of 52 new K-Ar ages, 42 from the postshield Kula Volcanics and 10 from the overlying Ha??na Volcanics. Postshield extrusion was robust from 0.93 to 0.76 Ma. A period of low extrusion rate or volcanic quiescence occurred between 0.76 and 0.65 Ma, well within Kula time. A chemical change to increasingly alkalic lava occurred at this time as the volcano changed from broadly hawaiitic to basanitic in its eruptive products and robust extrusion resumed. A slightly longer period of low extrusion rate or quiescence occurred after ca. 0.4 Ma, but only trifling change in geochemical character is observed. Geochemically, the Ha??na Volcanics unit, chiefly basanitic, overlaps greatly with the upper part of the Kula Volcanics; there is a weak tendency to slightly more alkaline character among the Ha??na Volcanics. The age of the Kula/Ha??na boundary is ca. 0.15-0.12 Ma; thus, volcanic quiescence of only ???0.03 m.y. separates the two formations, much shorter than the previously known limit of 0.25-0.30 m.y. The brevity of this hiatus, coupled with coincident vent loci and broadly similar geochemical characteristics for the Ha??na and the upper part of the Kula Volcanics, indicates that the Ha??na Volcanics unit comprises deposits of postshield-stage volcanism that has waned substantially since ca. 0.4-0.3 Ma. Haleakala?? has not yet begun a classically defined rejuvenated stage. Our findings support recent numerical modeling of plume-lithosphere interactions that predict that Haleakala?? is near the end of its postshield growth.
Additional Publication Details
New K-Ar ages and the geologic evidence against rejuvenated-stage volcanism at Haleakala??, East Maui, a postshield-stage volcano of the Hawaiian island chain