Thermal history of the Taranaki Basin, New Zealand

The Taranaki Basin is a Cenozoic active-margin basin located adjacent to the Pacific/Australian plate boundary. The study of its thermal regime is important because (1) the late Cenozoic tectonic history resulted in thermal transients that are large and can be identified, analyzed, and their possible causes interpreted. (2) Half of the basin (Western Platform) is outside the region disturbed by plate boundary deformation and half (Eastern Mobile Belt) is within it. The Western Platform thermal regime can be used as a standard against which the Eastern Mobile Belt thermal regime can be compared for analysis of transient thermal signals. (3) It contains the only known commercial hydrocarbon reserves in New Zealand.; Average surface heat flow for the basin is 57 mW m{dollar}sp{lcub}-2{rcub}{dollar}, but varies from 45 to 75 mW m{dollar}sp{lcub}-2{rcub}{dollar}. Much of this variation is accounted for by the transient thermal effects of burial and exhumation. On the Taranaki Peninsula, magmatism may have also affected the thermal regime. Heat flow, apatite fission track, and vitrinite reflectance data from a region of anomalously high heat flow on the northern peninsula suggest that heat flow was elevated there in the last 1 m.y. and is possibly the result of upper crustal igneous intrusion.; Thermal modelling results reveal anomalies that are not seen in the present-day heat flow distribution. Apparent basal heat flow (at 40 km depth) needed to satisfy the temperature constraints is uniform across the Western Platform, but for parts of the Eastern Mobile Belt it is {dollar}>{dollar}20 mW m{dollar}sp{lcub}-2{rcub}{dollar} less, even where surface heat flow is comparable between the regions. Thermal modelling shows that a combination of low heat-producing crust and the heat sink effects of crustal thickening in the Eastern Mobile Belt can account for the thermal anomalies.; Hydrocarbon generation modelling suggests that generation and expulsion may have occurred since the early Tertiary. The early generation affected only source rocks that were buried to depths of greater than {dollar}sim{dollar}2.5 km during the early rifting phase of basin development, but may have generated volumes of liquid hydrocarbon that either escaped the Taranaki system, were matured to gas, or are trapped elsewhere in the basin. The bulk of the hydrocarbons discovered to date were generated and expelled in mid-Miocene to Recent times, which is coincident with the timing of known hydrocarbon trap formation.