New Zealand Journal of Geology and Geophysics abstracts

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Late Tertiary deformation in Cannington Basin, South Canterbury, New Zealand: evidence from seismic and gravity data

S. LANGDALE*
T. A. STERN

School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand

*Present address: Indo-Pacific Energy (NZ) Ltd, 284 Karori Road, Wellington, New Zealand.

Abstract  A maximum subsidence and shortening rate of 0.2 +/- 0.05 mm/yr is calculated for the Pliocene-Pleistocene section of Cannington Basin, South Canterbury, New Zealand. This estimate is based largely on geophysical data. Strong, coherent seismic reflections down to 1.0 s two-way travel time were recorded within the basin. Seismic velocities within the basin range from 1.9 to 4.4 km/s, and seismic refraction data show a depth of c. 1200 m to a basement with a velocity of 5.6 +/- 0.1 km/s. Within the top 600 m of the sedimentary section, seismic velocities are <=2.3 km/s, which we interpret to be the Pliocene-Pleistocene section. Residual gravity anomalies within the basin are as low as -20 mgal and are asymmetrically disposed to the eastern side of the basin against a sharp topographic scarp--the Brothers Fault. About 300 m of topographic relief is present on this 30-40 km long scarp. We propose that the Brothers Fault has been active from the Pliocene until the present as a reverse fault with dip inferred to vary between 80deg. and 50deg.. This interpretation is based on the steepness of the residual gravity anomalies across the Brothers Fault scarp, the seismically interpreted thickness of Pliocene-Pleistocene sediments across the fault, and the observations of tilting of late Pliocene sediments on the hills that flank the eastern margin of Cannington Basin.

Keywords  gravity; seismic surveys; reverse faults; deformation; Alpine Fault

New Zealand Journal of Geology and Geophysics, 1998, Vol. 41: 247-257

0028-8306/98/4103-0247 $7.00/0 (c) The Royal Society of New Zealand 1998

PDF file of entire paper: medium quality (1749K); (scanned from paper original: notes about this process)

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