Geology topics

Takahiro Tagami

Publications and source records attributed to Takahiro Tagami.

4 recordsLinked to original sources

USGS2006

New K-Ar ages for calculating end-of-shield extrusion rates at West Maui volcano, Hawaiian island chain

Thirty-seven new K–Ar ages from West Maui volcano, Hawai‘i, are used to define the waning stages of shield growth and a brief episode of postshield volcanism. All but two samples from shield-stage strata have reversed polarity magnetization, so conceivably the exposed shield is not much older than the Olduvai Normal-Polarity subchron, or about 1.8 Ma. The oldest ages obtained are in the range 1.9–2.1 Ma but have large analytical error. Shield volcanism ended about 1.35 Ma, and postshield volcanism followed soon thereafter, persisting until about 1.2 Ma. Exposed shield-stage strata were emplaced at a rate of about 0.001 km 3 per year, a rate smaller than historic Hawaiian magmatic rates by a factor of 100. Stratigraphic accumulation rates are similar to those measured previously at Wai‘anae volcano (O‘ahu) or the upper part of the Mauna Kea shield sequence (Hilo drill core, Hawai‘i). These rates diminish sharply during the final 0.3–0.5 m.y. of the shield stage. Hawaiian shield volcanoes begin waning well before their last 0.5 m.y. of life, then end quickly, geologically speaking, if West Maui is representative.

Hawaii↗

USGS2006

Youngest volcanism about 1 million years ago at Kahoolawe Island, Hawaii

Young volcanic deposits in Kahoolawe Island, cutting up through the caldera-filling lava, colluvium and talus in the west wall of Kanapou Bay, had long been stratigraphically considered the rejuvenated-stage products. New K-Ar ages, combined with magnetic polarity data, show that young volcanism was at about 0.98-1.04 Ma and indicate no substantial quiescence between the filling of the caldera and the young volcanism. This result, and the tholeiitic characteristics of the young deposits, suggest they are a component of late shield-stage volcanism. ?? 2005 Elsevier B.V. All rights reserved.

Hawaii↗

USGS2003

Rejuvenated-stage volcanism after 0.6-m.y. quiescence at West Maui Volcano, Hawaii: New evidence from K-Ar ages and chemistry of Lahaina Volcanics

West Maui's rejuvenated-stage Lahaina Volcanics were erupted from four discrete sites. New KAr ages indicate two pulses of volcanism, the older about 0.6 Ma and the younger about 0.4 Ma. Compositionally the lava flows are entirely basanitic, but each pulse is diverse. The underlying postshield-stage Honolua Volcanics were emplaced by about 1.2 Ma on the basis of previously published ages. Therefore the duration of volcanic quiescence prior to rejuvenation is about 0.6 m.y. at West Maui, much longer than estimated previously. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS2003

New K-Ar ages and the geologic evidence against rejuvenated-stage volcanism at Haleakalā, East Maui, a postshield-stage volcano of the Hawaiian island chain

The postshield and previously inferred rejuvenated-stage history of Haleakalā volcano is reevaluated on the basis of 52 new K-Ar ages, 42 from the postshield Kula Volcanics and 10 from the overlying Hāna 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 Hāna 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 Hāna Volcanics. The age of the Kula/Hāna boundary is ca. 0.15–0.12 Ma; thus, volcanic quiescence of only &sim;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 Hāna and the upper part of the Kula Volcanics, indicates that the Hāna Volcanics unit comprises deposits of postshield-stage volcanism that has waned substantially since ca. 0.4–0.3 Ma. Haleakalā has not yet begun a classically defined rejuvenated stage. Our findings support recent numerical modeling of plume-lithosphere interactions that predict that Haleakalā is near the end of its postshield growth.

Hawaii↗