The tectonic and thermal evolution of Hawke's Bay Basin, New Zealand

Open Access
Author:
Legg, Matthew James
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 18, 2010
Committee Members:
  • Kevin Patrick Furlong, Thesis Advisor
Keywords:
  • tectonics
  • petroleum exploration
  • hydrocarbon maturation
  • apatite fission track
Abstract:
As part of an active plate boundary throughout the Neogene, the thermal evolution of the East Coast Basin along the Hikurangi margin reflects the transition from tectonic extension to convergence. Combining the stratigraphic (burial/exhumation) history of the region as recorded in the Oputouma-1 well with Apatite Fission Track (AFT) ages and track length distributions, and vitrinite reflection (Ro) results from well samples, I have assessed the tectonic framework of the basin incorporating improved models of plate motions, and the thermal effects of plate boundary evolution (e.g. heat flow effects of extension, subduction emplacement, thrusting). We have used a time-dependent numerical (finite-difference) thermal modeling approach that explicitly includes effects of crustal heat production distributions, variable thermal properties of different lithologies, burial and exhumation, regional extension prior to 30 Ma, and the effects of subduction emplacement and ongoing subduction from 25 Ma - present. The vertical section comprised of well samples extending more than 3.5 km below the surface provides substantial constraints on the range of viable tectonic and thermal histories for the basin. Model results indicate the following: (1) Once subduction begins beneath the Hawke’s Bay region, AFT ages and Ro values are locked-in. Modeling results place the timing of the start of subduction at ~ 25 Ma. (2) The level of organic maturation indicated by the Ro values in conjunction with AFT ages and track lengths requires a relatively high heat flow regime during the Eocene-Oligocene, consistent with the plate tectonic history of the region that implies that New Zealand was undergoing extension during that time. (3) Although there is stratigraphic evidence of Miocene burial and exhumation, little additional thermal maturation occurred during this time. Our thermal models indicate that most organic maturation and hydrocarbon production would occur prior to the ca. 25 Ma initiation of subduction, raising the question of whether appropriate reservoir structures and seals existed at that time.