FIELD CHARACTERISTICS, PETROGRAPHY, AND GEOCHRONOLOGY OF THE HOHONU BATHOLITH AND THE ADJACENT GRANITE HILL COMPLEX, NORTH WESTLAND, NEW-ZEALAND

Detailed geological mapping, petrography, geochemistry, and geochronol ogical studies in the Hohonu Batholith, North Westland, have identifie d 10 granitoid plutons emplaced during three intrusive episodes. The e arliest episode is represented by a single dated Paleozoic pluton, Sum mit Granite (new) (381.2 +/- 7.3 Ma), which is correlated with a discr ete pulse of Mid-Late Devonian plutonism recognised in the Karamea Bat holith. The undated Mount Graham Granite (new) is also likely to be Pa leozoic, based on chemical and petrographic characteristics. The bulk of the batholith (seven plutons) was emplaced in the mid Cretaceous (1 14-109 Ma) and comprises two related, yet distinct, geochemical suites , which correlate with the previously defined Rahu Suite. The plutons identified are (from north to south): Pah Point Granite; Jays Creek Gr anodiorite (new); Uncle Bay Tonalite; Te Kinga Monzogranite; Deutgam G ranodiorite; Turiwhate Granodiorite (new); and Arahura Granite (new). Mid-Cretaceous plutonism in the Western Province is considered to be t he result of crustal thinning and extension following overthickening d uring collision of the Early Cretaceous Median Tectonic Zone volcanic arc. Late Cretaceous alkaline activity is represented by the emplaceme nt of the A-type French Creek Granite at 81.7 +/- 1.8 Ma, contemporane ous with intrusion of a major swarm of doleritic-lamprophyric dikes-th e Hohonu Dike Swarm. These events correlate with the first appearance of oceanic crust in the Tasman Sea. The Granite Hill Complex is a suit e of amphibolite facies gneisses occurring as an uplifted wedge betwee n the Alpine Fault and the Hohonu Batholith. These gneisses are consid ered to represent an extension of the Eraser Complex to the south. A d etailed understanding of their geological affinities and history is ye t to be established.