Rock and pillar geology, Central Otago, New Zealand

Dickie, Benjamin John, 1978-

The Rock and Pillar Range, Central Otago, is an anticlinal box structure, formed during regional contraction in the Late Cenozoic. All Tertiary sediments have been eroded off the top of the range to expose basement Otago Schist. A sequence of Terrestrial Tertiary sediments; Dunstan Formation, Bannockburn Formation, Wedderburn Formation and Maniototo Conglomerate, at the base of the range have also been buckled in the late Cenozoic contraction. Several outcrops of Miocene basaltic lava flows of the Waipiata Volcanics overlie both the Dunstan and Bannockburn Formations. The Dunstan Formation in this area contains four different populations of quartz sand grains, which originate.from two different provenances; the Haast Schist and a granitic source. Striking E-W across the north end of the range for approximately 11 km is a -14 ° northdippingfault, the Pig Burn Fault (PBF) (new name)that juxtaposes low-grade schist in the hangingwall against high-grade schist in the footwall, indicating normal displacement. The hangingwall block is characterised by extensive brittle fracturing of the schist, which ranges from textural zone (TZ) 1 to 3A, and vertical extension veins filled with carbonate that strike parallel to the fault. The footwall block comprises TZ 3B schist and a -50 m thick mylonite zone adjacent to the fault. Displacement on the fault is estimated at -35 km dowri dip to the north. this is a very low-angle normal fault of regional extent, which shows most of the characteristic features, as described above, of a metamorphic core complex. The timing of this event is uncertain but must predate or partly overlap with cutting of the regional W aipounamu Erosion Surface during the Late Cretaceous. Limited ·structural· data suggests the probability that the very low-angle normal faulting formed along a zone of earlier reverse movement. There are similarities between the features and positions of the Pig Burn Fault and the Hyde-Macraes Shear Zone that suggest that they may be the same structural contact.

vi, 110, [4] p. : ill. (some col.), maps (some col., some folded) ; 30 cm.

1999Dickie

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