A gravity survey of the Cromwell to Bendigo area, Otago

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Broadbent, M.; Bennie, S.L. 1981 A gravity survey of the Cromwell to Bendigo area, Otago. [s.l.]: [s.n.]. Report / Geophysics Division 174 35 p.

Abstract: A gravity survey of the Cromwell to Bendigo area of the Clutha valley, Central Otago was conducted in 1977 to aid planning of hydro electric development. A LaCoste and Romberg gravity meter and barometric levelling were used during the survey. Isostatic gravity anomalies, calculated from the field data using standard Geophysics Division procedures, were partitioned into regional and residual components along section lines by graphical methods. The residual anomaly profiles were interpreted in terms of locally two dimensional distributions of the densities 2.7, 2.2, and 1.9 mg/m3, which were associated primarily with schist, wet Tertiary and Quaternary sediments, and dry sediments respectively. Much of the western side of the investigated part of the Clutha valley was deduced to contain more than 400 m of sediments overlaying schist. The western edge of the valley was inferred to be associated with faulting changing from reverse to normal from south to north. The dip of the top of the schist under the sediments on the eastern side of the valley is broadly consistent with the slope on the exposed hillsides. The structure of the valley is consistent with the area having experienced northwest-southeast extension followed by northwest-southeast compression, since the mid-Miocene period