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Abstract

AAPG Bulletin, V. 86, No. 10 (October 2002),Copyright ©2002. The American Association of Petroleum Geologists. All rights reserved.

Appraisal of (U-Th)/He apatite thermochronology as a thermal history tool for hydrocarbon Previous HitexplorationNext Hit: An example from the Taranaki Basin, New Zealand

P. V. Crowhurst,1 P. F. Green,2 P. J. J. Kamp3

1CSIRO Petroleum Resources, P.O. Box 136, North Ryde, New South Wales, 1670, Australia; email: [email protected]
2Geotrack International Pty. Ltd., 37 Melville Rd., Brunswick West, Victoria, 3055, Australia; email: [email protected]
3Department of Earth Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand; email: [email protected]

AUTHORS

Peter Crowhurst works at CSIRO Petroleum in Sydney on development of the (U-Th)/He thermochronology technique. Peter graduated with a B.Sc. (hons.) degree from Adelaide University, Australia, an M.Sc. degree at Monash University, Australia, and a Ph.D. project at La Trobe University, Australia, which involved redefining the tectonic history of northern Papua New Guinea. He also worked in the mineral Previous HitexplorationNext Hit industry, mainly for BHP Minerals in Australia and Papua New Guinea.

Paul Green is technical director of Geotrack International, a private company specializing in thermal history reconstruction in sedimentary basins and its application to hydrocarbon Previous HitexplorationNext Hit. He has a Ph.D. from the University of Birmingham, Great Britain, and has held research positions at the University of Birmingham, the University of Melbourne, Australia, and University College London. He is the author of more than 100 published papers on fission-track analysis and related topics and is a member of AAPG, the Petroleum Previous HitExplorationNext Hit Society of Australia, and the Petroleum Previous HitExplorationNext Hit Society of Great Britain.

Peter Kamp is professor of earth sciences at the University of Waikato in Hamilton, New Zealand. His research interests are in the analysis of sedimentary basins, particularly those of Late Cretaceous-Cenozoic age in New Zealand. Another major research interest involves the techniques of fission-track analysis and (U-Th)/He thermochronometry. His research applications involve the thermal history of sedimentary basins and the exhumation history of basement provinces-mountain belts.

ACKNOWLEDGMENTS

We thank Ken Farley of the California Institute of Technology for providing software for modeling helium diffusion and the (U-Th)/He age system in apatite. AFTA is the registered trademark of Geotrack International. P. J. J. Kamp acknowledges research funding from the New Zealand Foundation for Research, Science and Technology.

ABSTRACT

The Taranaki Basin contains most of New Zealand's commercial hydrocarbon reserves. The southern parts of the Taranaki Basin underwent inversion during the late Miocene, with published AFTA (apatite fission-track analysis) and vitrinite reflectance data suggesting approximately 2.5-3 km of section eroded from the structure on which the Fresne-1 well was drilled, consistent with estimates from reconstructions based on seismic sections. The well-constrained tectonic and thermal history framework for this well section, established by earlier studies, provides an ideal test bed for the thermochronological technique of apatite (U-Th)/He dating. Helium ages determined in apatites from the earlier AFTA study decrease from about 6 Ma at about 400 m depth to about 1 Ma at 2465 m. Although these results are qualitatively consistent with late Miocene cooling, quantitative modeling of (U-Th)/He ages based on best-fit thermal histories derived from new AFTA analyses (using improved methods) suggests that cooling was protracted, involving accelerated cooling during the Pliocene, possibly indicating a discrete Pliocene inversion phase. Integration of AFTA and (U-Th)/He dating can provide improved thermal history constraints in sedimentary basins, particularly on cooling rates and/or resolution of multiple thermal events. By independently defining the timing of peak maturation in relation to formation of potential trapping structures, this information offers the potential for improved assessment of hydrocarbon prospectivity and reduced Previous HitexplorationTop risk.

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