Thermal history of the early Miocene Waitemata Basin and adjacent Waipapa Group, North Island, New Zealand (vol 42, pg 169, 1999)

Apatite fission track (AFT) and vitrinite reflectance (VR) data for early M iocene outcrops from the Waitemata Basin reveal that the basin sequence was subjected to shallow burial before denudation. AFT results suggest that th e total sediment thickness within the basin was II km and maximum paleotemp eratures during burial never exceeded c. 60 degrees C. Statistical analyses of the detrital AFT ages distinguish four dominant sources of sediment sup ply: contemporaneous volcanism; metagreywacke rocks of the Waipapa Group; t he Northland Allochthon; and an unidentified source south of the basin. The apatite and zircon fission track results from the Waipapa Group rocks ( Gondwana Terrane) adjacent to the basin suggest two discrete phases of acce lerated cooling: the first during the early Cretaceous (c. 117 Ma) and the second during the mid Cretaceous (c. 84 Ma). These events probably reflect key stages in the tectonic development of the New Zealand microcontinent du ring the Cretaceous period, the earlier event being related to the climax o f compressional deformation (Rangitata Orogeny) and the latter to extension al tectonism associated with the opening of the Tasman Sea. Waipapa Group r ocks now exposed at the surface cooled from maximum paleotemperatures of c. 250 degrees C at an estimated rate of c. 180-36 degrees C/m.y., involving substantial denudation.