Tectonic map of Central Otago based on Landsat imagery

Abstract

Low sun angle Landsat imagery permits analysis of late Cenozoic deformation of Central Otago because of preservation of the deformed Tertiary peneplain developed on schist and greywacke together with the contrast in Landsat expression between basin sediments and older rocks. The degree of embayment of fault-controlled mountain fronts in Central Otago by erosion and alluvial-fan development permits determination of relative age of faulting using Landsat, but late Quaternary fault scarps within structural depressions are only rarely visible. Landsat shows that Cenozoic structures of Central Otago may be visualised on two scales. The smaller scale structures are individual northeast-or northwest-trending, fault-bounded ranges and basins, 5-20 km wide. Sets of ranges and basins are grouped into northwest-elongated structural provinces, 40-60 km wide. From northeast to southwest, starting at the Waitaki River, these include ( l) a set of northwest-trending ranges with very few basins south to the Waihemo, Stranraer, and Hawkdun Faults; (2) a set of northeast-trending ranges and basins; and (3) step-faulted schist highlands with very few basins. Northwest elongation of these provinces is parallel to bedrock trends including fold axes in schist and the ophiolite belt. These provinces may represent different responses of crustal rocks to contractile strain across the plate boundary.

Frontal accretion and thrust wedge evolution under very oblique plate convergence: Fiordland Basin, New Zealand

“…The boundary to the south is dominated by the 023°‐striking Puysegur–Fiordland subduction zone, and to the north by the Southern Alps and 050–055°‐striking Alpine Fault. Oblique convergence is being accommodated across a 260‐km wide zone, exceeding the width of the southern South Island (Walcott, 1998), by a combination of very oblique subduction of the Australian Plate beneath Fiordland (Christoffel & van der Linden, 1972; Davey & Smith, 1983; Smith & Davey, 1984; Anderson & Webb, 1994; Eberhart‐Phillips & Reyners, 2001), strike‐slip deformation on the offshore Alpine Fault (Lebrun et al ., 2000; Barnes et al ., 2001), and thrust faulting both within the offshore Fiordland Basin (Collot et al ., 1995; Delteil et al ., 1996a; Wood et al ., 2000) and onshore east of Fiordland (Yeats, 1987; Norris et al ., 1990).…”

Geometry of the folded Otago peneplain surface beneath Ida valley, Central Otago, New Zealand, from gravity observations

“…The deformed peneplain surface is useful because it highlights the shapes of these basins and ranges (Cotton 1917;Yeats 1987;Stirling 1990;Bishop 1994;Jackson et al 1996;Markley & Norris 1999). Sediments associated with renewed uplift suggest that this second and ongoing episode of folding and faulting began within the past few million years (Youngson et al 1998).…”

Structure and neotectonics of the Blackstone Hill Antiform, Central Otago, New Zealand

“…Some have mapped range-scale northeast-striking reverse faults along ridge margins (Fig. 15A;Mutch 1963;Madin 1988;Yeats 1987, although he did not show surface faulting on Blackstone Ridge). At the surface, however, the peneplain and schist basement are warped around the axis of the Blackstone Hill Antiform rather than offset discontinuously along a range-scale fault.…”

“…The structural style of these late Cenozoic ranges is poorly understood. Many workers have inferred the existence of range-scale northeast-striking reverse faults along ridge margins to explain uplift, particularly for the Pisa and Dunstan Ranges west of Blackstone Hill (e.g., Mutch 1963;Yeats 1987;Madin 1988). In the field, however, range-scale faults defining the range front are elusive (e.g., Norris et al 1987).…”