Summary of Ge150 Geology of New Zealand, Fall Quarter

Paper 1:

Walcott, R. I.

1998. Modes of Oblique Compression: Late Cenozoic Tectonics of the South Island of New Zealand.

• Both compression and strike slip movement is occurring along the Australia-Pacific plate boundary which runs through the South Island of New Zealand ? Since 6.4 Ma, 90 km of compression has caused the uplift of the Southern Alps and this provides an ideal place to study the early stages of a continental collision zone
•  230 km of strike slip motion has also occurred since 6.4 Ma
• This 90 km of compression has been accommodated in various ways along the boundary:
• 1. In the south, the deformation due to the subduction of the Australian Plate under Fiordland is distributed up to 200 km from the plate boundary, resulting in minor crustal thickening and a small amount of uplift and erosion.
• 2. In the north, excess continental lithosphere is accommodated by major continental overthrusting events along with subduction of the lower lithosphere.
• 3. In the central South Island, accommodation of excess crust is by crustal thickening and erosion.
• Large earthquakes are know to have occurred along the northern and southern parts of the Alpine Fault; however, it is unknown whether great earthquakes can occur on the central segment.

Paper 2:

Kamp, Peter J. J.

1986. The mid-Cenozoic Challenger Rift System of western New Zealand and its implications for the age of Alpine Fault inception.

• Challenger Rift - Middle Eocene to early Miocene 1,200 km long and 100-200 km wide continental rift system
• Four phases of rifting occurred during this time:
• 1. infra-rift subsidence - slow subsidence and accumulation of coal measures and shallow marine transgression sequence
• 2. active axial trough subsidence - formation of steep sided central troughs and deposition of submarine fan sequence
• 3. expanded subsidence and collapse of rift shoulders
• 4. incipient seafloor spreading
• Rifting propagated from north and south to the center of the rift ? Northern segment of Challenger Rift linked with seafloor spreading center in the Norfolk Basin (just west of the South Fiji Basin), and the southern part of the rift linked with the SEIR
•  The age and pattern of rift disruption suggests that the Alpine Fault was formed during the early Miocene (23 Ma); however plate reconstructions predict Alpine Fault inception by the late Eocene.
• The Australia and Pacific plates did not become separate plates until the early Miocene

Paper 3:

Kamp, Peter J. J.

1986. Late Cretaceous-Cenozoic Tectonic Development of the Southwest Pacific Region.

•  This paper presents a tectonic model of the SW Pacific which integrates the continental geology of NZ with seafloor spreading anomalies.
•  The continental geology provides two major constraints:
• 1. The Alpine Fault was not active until 23 Ma
• 2. There has been only 500 km of dextral displacement on the Alpine Fault since its inception
• Because seafloor spreading in the Tasman Sea was much faster than spreading on the Pacific Antarctic Ridge, it is proposed that:
• 1. the Campbell Fault moved as a transform fault from 110-72 Ma.
• 2. the Bounty Trough rifted obliquely
• 3. the Campbell Plateau rotated 25 degrees counterclockwise during the late Cretaceous breakup of Gondwana
• The latest Cretaceous to early Eocene (A32-A24) was a time of quiescence and there is no evidence for a plate boundary through NZ at this time.
•  When the eastward propagating SEIR reached the Tasman Spreading Center 51 Ma, it continued to propagate in to the southern part of the South Island of NZ - initiating late Eocene-Oligocene continental rifting
•  At the same time, southward propagation of the Norfolk Spreading Center caused continental rifting along a similar trend in the North Island
• This model has two important implications regarding motion between E and W Antarctica:
• 1. During the Cretaceous, Marie Byrd Land was no more than 200 km north of its present position
• 2. If the Alpine Fault did not form until the late Eocene, there must be a late Cretaceous to early Tertiary plate boundary within Antarctica

Paper 4:

Bishop, Daniel J.

1992. Extensional tectonism and magmatism during the middle Cretaceous to Paleocene, North Westland, New Zealand.

•  Offshore seismic reflection data west of Greymouth show a large WNW-ESE trending, segmented half-graben structure over 40 km long and up to 15 km wide
•  Seismic interpretation suggests this structure was formed during the Cretaceous and represents a 20% extension ? Structures containing late Cretaceous to Paleocene deposits generally trend NNE-SSW, perpendicular to the earlier structure
•  Seismic data along with published radiometric and fission track ages from basement and Cretaceous igneous rocks show three periods of tectonism and magmatism:
• 1. 125-90 Ma - NNE-SSW directed extension, uplift, plutonism, and minor volcanism
• 2. 90-80 Ma - decreased extension and emplacement of numerous dikes

3. 80-60 Ma - breakup uconformity, volcanism, continued dike intrusion, and initiation of NNE- SSW trending transtensional basins

Paper 5:

Norris, R. J., and I. M. Turnbull.

1993. Cenozoic Basins Adjacent to an Evolving Transform Plate Boundary, Southwest New Zealand. South Pacific Sedimentary Basins.

•  Several small marine basins formed during the middle to late Cenozoic in southwest NZ in conjunction with the formation of the oblique transform boundary between the Pacific and Australian plates.
•  The basins are located east and south of the Fiordland Complex
• Cretaceous and Eocene - largely non-marine, late Eocene composed of fluvial sands and coal measures
•  latest Eocene and early Oligocene - extensional marine basins formed with thick deposits of redeposited sediment
• late Oligocene - shallow water limestones covered surrounding areas while deep-water mudstones accumulated in the deep parts of the basins
•  early Miocene - tectonism uplifted parts of the basins and caused other areas to subside
• late Miocene - extensive reverse and strike-slip faulting ? Accretion of terranes during the Cretaceous caused major crustal discontinuities which controlled the Cenozoic basin development history in southwest NZ.

Paper 6:

Rait, Geoff, Frank Chanier and David W. Waters.

1991. Landward- and seaward-directed thrusting accompanying the onset of subduction beneath New Zealand.

•  A ~5 m.y. episode of deformation accompanied the onset of subduction beneath the north island of NZ
•  This deformation was characterized by:
• 1. numerous subhorizontal thrust sheets with tens of km of displacement
• 2. landward and seaward thrusting which is different from typical structures along active trenches - predominantly seaward directed imbricate thrusts and folds.
•  These structures suggest varying degrees of delamination and high degrees of coupling between the overriding and downgoing plates.
•  Delamination of the downgoing plate occurred adjacent to Northland and Raukumara Peninsula, and
• ophiolites? (possible pieces of an oceanic plateau) were pushed up onto the shelf

Paper 7:

Holt, W. E., and T. A. Stern.

1994. Subduction, platform subsidence, and foreland thrust loading: The late Tertiary development of Taranaki Basin,

• This paper uses borehole, seismic, and gravity data to look at deformation of continental lithosphere along the Miocene collisional zone in New Zealand
• South Taranaki Basin is a foreland basin structure resulting from thrust loading of a foreland that initially had a water depth of 1-2 km.
• Deformation is manifested in three ways:
• 1. long wavelength (>500 km) platform subsidence due to mantle convection
• 2. 100-200 km scale deformation due to crustal thrusting along the eastern boundary of the Taranaki Basin
• 3. ~10 km scale ductile thickening that is evident in the deep seismic section of the Taranaki Basin
•  The complete load on the Taranaki foreland is in three parts
• 1. submarine-topographic load
• 2. intracrustal load
• 3. loading due to infilling of sediments
•  The Eocene section in the Taranaki Basin is very thin and there is no evidence for subsidence or rifting in this region during this time period

Paper 8:

Yan, Chun Yeung and Loren W. Kroenke.

1993. A Plate Tectonic Reconstruction of the Southwest Pacific, 0-100 Ma.

• This paper is accompanied by a CD-ROM with an animation of plate motions in the SW Pacific.
• The animation is based on a hotspot reference frame
• As I recall, watching this animation raised more questions than it answered. ? The animation shows numerous episodes of extension and compression as well as right and left lateral strike slip motion through central NZ. Several of these episodes are not supported by geological observations.

Paper 9:

Beggs, J. M.

Depositional and Tectonic History of the Great South Basin. South Pacific Sedimentary

• mid Cretaceous - the Great South Basin began to form by extension of the Gondwana margin oblique to the basement grain
•  late Cretaceous - spreading between the Campbell Plateau and West Antarctica began, and the basin began to subside more rapidly and its southern and eastern margins experienced a marine transgression
•  middle Eocene - carbonate sedimentation became dominant over clastic sedimentation as the NZ landmass subsided and was transgressed.
•  Four stratigraphic sequences are recognized in the basin:
• 1. Hoiho Sequence - rift phase deposits composed mainly of terrestrial coarse clastics and coal measures; deposited in NS trending basins
• 2. Pakaha Sequence - late Cretaceous and Paleocene thick terrestrial and marginal marine clastics in the north; fine grained calcareous clastics overlying a widespread basal sandstone in the central and eastern parts of the basin
• 3. Rakiura Sequence - late Paleocene to Oligocene chalk in the eastern and central parts of the basin; marginal marine clastics along the western margin
• 4. Penrod Sequence - Miocene and younger thin sequence of carbonate deposits over most of the basin with a shelf sequence along the NW margin.
• Hoiho-Pakaha boundary marks the beginning of seafloor spreading between West Antarctica and the Campbell Plateau
•  Pakaha-Rakiura boundary marks the cessation of spreading in the Tasman Sea
•  Rakiura-Penrod boundary is associated with the initiation of movement between the Pacific and Australian plates