Geological map of New Zealand 1:50,000 Sheet N36AC Akaroa West

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Sewell, R.J.; Weaver, S.D. 1990 Geological map of New Zealand 1:50,000 Sheet N36AC Akaroa West. Lower Hutt: New Zealand Geological Survey. Geological map of New Zealand 1:50,000 N36 1 fold. map + 1 booklet

Abstract: The Akaroa West 1:50 00 geologic map (sheet N36AC) covers the eastern-central region of Banks Peninsula. Akaroa Harbour marks the eroded crater of the Akaroa Volcano - the younger of two large Upper Miocene composite volcanoes which dominate the geology of the peninsula. The northwestern part of the sheet includes the eastern flanks of the Lyttelton Volcano. Volcanic material between the two main centres chiefly represents products of an intermediate stage in the migration of volcanism southeast from the Lyttelton to the Akaroa centre. Volcanic rocks in the area are dominantly of mildly alkalic to transitional tholeiitic chemistry. The oldest rocks (Lyttelton Volcanic Group) form the main cone of the Lyttelton Volcano (Lyttelton 1; c. 11.0-10.4 Ma), and are unconformably overlain by a suite of lavas (Mount Pleasant Formation) which mark a late phase of eruption (Lyttelton 2; 10.4-9.7 Ma). The present day topography is the result of deep excavation of radial drainage initially established during the volcanic period. Upper Quaternary loess and volcanic-derived sediments blanket the area and pose potential slope stability problems, particularly after periods of heavy rain. Postglacial sediments of the Christchurch Formation form minor beach, estuarine, swamp, bayhead and valley floor deposits in the area. The only significant economic deposits are aggregate and loess for roading, although small quantities of building stone have been obtained from Port Levy. The area is one of moderate earthquake and tsunami risk. (auths)

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