A high resolution 40Ar/39Ar lava chronology and edifice construction history for Tongariro volcano, New Zealand

Detailed mapping and geochronological investigations of edifice-forming materials reconstruct the growth history of Tongariro volcano, New Zealand, and subdivide the edifice into thirty six distinct units which are organised into twelve formations and constituent members. Twenty nine new 40Ar/39Ar age determinations, along with published K/Ar ages combined with volume estimates, petrographic observations and rock chemistry provide an integrated history of the volcano's growth through edifice-forming lavas and pyroclastic deposits. The oldest lava (512 ± 59 ka, 2 s.d.) is a small inlier of basaltic-andesite on Tongariro's NW sector that may reflect a nearly buried independent volcano. The next oldest material that can be confidently attributed to a Tongariro source is 304 ± 11 ka andesite, incorporated as boulders in late Pleistocene ejecta from the Tama Lakes area. In-situ lavas at Tongariro date from 230 ka to present, including numerous flows erupted during glacial periods and building the edifice unevenly due to emplacement against valley-filling ice bodies. Tongariro has a total edifice volume of ~90 km3, 19 km3 of which is represented by exposed map units, with glacial deposits amounting to