Geophysical survey of the Paringa River valley, South Westland
Kilner, Jeremy William
The Paringa River valley runs perpendicular to the Alpine Fault, the dominant structural feature of the South Island, New Zealand. Previous geological mapping has contributed much to the understanding of South Westland geology, but a number of questions about the geology, structure and evolution of Paringa River region have been left unanswered. In this study a review of this region's geology was undertaken, together with new gravity and magnetic surveys of the Paringa River valley. Work included modelling the basement profile beneath the river flats, identifying origins and evolution of specific valleys, completing the geological map of the region and analysing Western Province intrusives in the Paringa River valley. Mapping of Blackwater Creek showed amphibolite facies, quartzofeldspathic protomylonites with a prominent S-C fabric exposed in Blackwater Creek grading eastwards into schist at the eastern margin of exposure. Pseudotachylytes discovered within the protomylonites indicated minor, high stress seismic ruptures at depth within the Alpine Fault zone. The geochemical analyses of Paringa Western Province intrusives indicated the South Westland region may have paired Paleozoic I- and S-type granitoids which parallel the well-recognised Cretaceous paired plutonic belts. Intruded lamprophyre dykes are thought to be associated with the same subduction episode as the granitoid plutons. The magnetic survey unfortunately did not contribute to increased understanding of the region. The gravity survey provided valuable data, although the normal uncertainties in interpretation of gravity data were compounded by the two-dimension modelling in an area of rapidly changing basement topography. Gravity modelling of the Paringa River valley and the NE trending valley indicated significantly deep (400-600 m) U-shaped, glacially excavated valleys. The Alpine Fault was imaged in the gravity profiles beneath the valley fill, concurring with Simpson's (1992) mapping of the Alpine Fault trace. The Paringa River is postulated to have drained through the NE trending valley northwards before switching to its present southwards course in response to progressive strike-slip offset along the Alpine Fault. This proposal forms the basis of a theory of sequential reoccupation of drainage west of the Alpine Fault.
Advisor: Norris, Richard; Gorman, Andrew
Degree Name: Bachelor of Science with Honours
Degree Discipline: Geology
Publisher: University of Otago
Research Type: Dissertation
Description: [iv], 104 leaves : ill., maps ; 30 cm. + 1 CD-ROM (4 3/4 in.) and 1 map (folded). Notes: CD-ROM and map in pockets inside back cover. University of Otago department: Geology. Thesis (B. Sc. (Hons.))--University of Otago, 2005. Includes bibliographic references.