New Zealand Journal of Geology and Geophysics abstracts

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Mid-Cretaceous oroclinal bending of New Zealand terranes

J. D. BRADSHAW
S. D. WEAVER
R. J. MUIR

Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand

Abstract  Recently published results and new data suggest that the Jurassic-Cretaceous magmatic rocks of the Median Tectonic Zone of New Zealand, and the Cretaceous Separation Point Batholith that locally intrudes it, were emplaced subparallel to the Mesozoic Gondwana margin. Together, they provide a valuable piercing point on the Alpine Fault for 118 Ma. They also lie almost exactly parallel to mean extension lineations in exhumed metamorphic core complexes and extension directions indicated by fault-bounded Cretaceous sedimentary basins and dike swarms in the overlying cover. Continental extension and subsequent breakup in the Tasman Sea and the eastern Bounty Trough was towards the northeast, almost perpendicular to the overall trend of the Gondwana margin but parallel to the margin-related rocks in the central sector. Together, these relationships suggest almost 90deg. of rotation and major dextral shear. New geochronology now constrains the rotation to the period between the intrusion of the Separation Point Batholith at 118 Ma and the initiation of Cretaceous sedimentary basins at c. 101 Ma. Much of the rotation was probably completed before the intrusion of the Buckland Granite at 110 Ma. The relationships suggest that a prominent dextral "Z" bend developed in the basement terranes of New Zealand and in the continental margin in the mid Cretaceous, and this may have influenced the site of the later Neogene plate boundary.

Keywords  Alpine Fault; Cretaceous; continental breakup; oroclinal bending; tectonics

New Zealand Journal of Geology and Geophysics, 1996, Vol. 39: 461-468

0028-8306/96/3903-0461 $2.50/0 (c) The Royal Society of New Zealand 1996

PDF file of entire paper: medium quality (815K); (scanned from paper original: notes about this process)

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