EXPLORATION OPPORTUNITIES, EAST COAST BASIN, NEW ZEALAND

2000 ◽  
Vol 40 (1) ◽  
pp. 39
Author(s):  
J.B. Frederick ◽  
E.J. Davies ◽  
P.G. Smith ◽  
D. Spancers ◽  
T.J. Williams
Keyword(s):  
New Zealand ◽  
Late Miocene ◽  
Joint Venture ◽  
East Coast ◽  
High Amplitude ◽  
Petroleum Exploration ◽  
Early Miocene ◽  
Seismic Survey ◽  
Seismic Events ◽  
Submarine Fan

The Westech-Orion Joint Venture holds onshore Petroleum Exploration Permit 38329 and offshore PEPs 38325, 38326 and 38333 in the East Coast Basin, New Zealand. The Joint Venture holds 24,117 km2 covering Hawkes Bay and the Wairarapa shelf.The Westech-Orion Joint Venture has drilled six exploratory wells and five appraisal wells in the onshore East Coast Basin over a two year period. All wells encountered significant gas shows, with two wells discovering hydrocarbons in potentially commercial volumes. Each well was drilled on the crest of a seismically mapped structure, characterised by asymmetric folding over a northwest dipping thrust fault.Prior to this drilling program, the reservoir potential of the Wairoa area was inferred to be dominated by turbidite sandstones of the Tunanui and Makaretu formations (Mid-Late Miocene). The new wells show that the Mid Miocene and parts of the Early and Late Miocene pinch out across the 'Wairoa High'.One of the primary onshore reservoirs is the Kauhauroa Limestone (Early Miocene), a bryozoan-dominated, tightly packed and cemented limestone with dominantly fracture porosity. The other primary reservoir is the Tunanui Sandstone (Mid Miocene), which in well intersections to date comprises medium-thickly bedded sandstone, with net sand typically 40%. The sands have high lithic content, and are moderately sorted and subangular-subrounded.Abnormally high formation pressures were encountered in all wells, ranging up to 3,400 psi at 1,000 m. Crestal pressure gradients commonly exceed 70% of the lithostatic pressure gradient, despite the relative proximity to outcrop. The overpressure may reflect relatively young uplift of fossil pressures, with insufficient time for pressure equilibration within a generally overpressured system.The prospectivity of the area has been highgraded by recent maturation and reservoir studies in Hawkes Bay and by gas discoveries in Westech-Orion wells onshore northern Hawkes Bay. Maturation studies identified nine kitchen areas with oil migration commencing in the Late Miocene. Seismic stratigraphy and correlation with onshore wells identified offshore submarine fan deposits of Eocene, Early Miocene, Mid Miocene and Pliocene age.A 594 km2 exploration 3D seismic survey was acquired in Hawke Bay in April 1999, and 685 km of 2D seismic were acquired in March 2000. Preliminary interpretation of the 3D survey has yielded five prospects, each covering 20–90 km2. One prospect is a lowstand fan identified by stacked mounding and bidirectional downlap, correlated with the onshore Mid Miocene Tunanui Sandstone. High amplitude seismic events of Mid-Late Miocene ages are inferred to be pulses of submarine fan development, in places associated with direct hydrocarbon indicators (DHIs). High amplitude seismic events in the Pliocene include a package of high amplitude seismic reflectors interpreted as structurally trapped DHI truncated by a major unconformity.

Exploring New Zealand's marine territory

2011 ◽  
Vol 51 (1) ◽  
pp. 549 ◽  
Author(s):  
Chris Uruski
Keyword(s):  
New Zealand ◽  
Deep Water ◽  
Seismic Data ◽  
East Coast ◽  
Sedimentary Basins ◽  
Petroleum Exploration ◽  
Seismic Survey ◽  
Data Set ◽  
Eastern Australia ◽  
Deep Water Part

Around the end of the twentieth century, awareness grew that, in addition to the Taranaki Basin, other unexplored basins in New Zealand’s large exclusive economic zone (EEZ) and extended continental shelf (ECS) may contain petroleum. GNS Science initiated a program to assess the prospectivity of more than 1 million square kilometres of sedimentary basins in New Zealand’s marine territories. The first project in 2001 acquired, with TGS-NOPEC, a 6,200 km reconnaissance 2D seismic survey in deep-water Taranaki. This showed a large Late Cretaceous delta built out into a northwest-trending basin above a thick succession of older rocks. Many deltas around the world are petroleum provinces and the new data showed that the deep-water part of Taranaki Basin may also be prospective. Since the 2001 survey a further 9,000 km of infill 2D seismic data has been acquired and exploration continues. The New Zealand government recognised the potential of its frontier basins and, in 2005 Crown Minerals acquired a 2D survey in the East Coast Basin, North Island. This was followed by surveys in the Great South, Raukumara and Reinga basins. Petroleum Exploration Permits were awarded in most of these and licence rounds in the Northland/Reinga Basin closed recently. New data have since been acquired from the Pegasus, Great South and Canterbury basins. The New Zealand government, through Crown Minerals, funds all or part of a survey. GNS Science interprets the new data set and the data along with reports are packaged for free dissemination prior to a licensing round. The strategy has worked well, as indicated by the entry of ExxonMobil, OMV and Petrobras into New Zealand. Anadarko, another new entry, farmed into the previously licensed Canterbury and deep-water Taranaki basins. One of the main results of the surveys has been to show that geology and prospectivity of New Zealand’s frontier basins may be similar to eastern Australia, as older apparently unmetamophosed successions are preserved. By extrapolating from the results in the Taranaki Basin, ultimate prospectivity is likely to be a resource of some tens of billions of barrels of oil equivalent. New Zealand’s largely submerged continent may yield continent-sized resources.

scholarly journals Environment of Deposition and Paleogeography of the Late Cretaceous Glenburn Formation, Eastern North Island, New Zealand

2021 ◽  
Author(s):  
◽  
James McClintock
Keyword(s):  
New Zealand ◽  
Late Cretaceous ◽  
Large Scale ◽  
East Coast ◽  
Three Dimensional ◽  
Depositional Environments ◽  
Tectonic Deformation ◽  
Turbidity Currents ◽  
Submarine Fan ◽  
Submarine Channels

<p>The Glenburn Formation of the East Coast of New Zealand is a Late Cretaceous sedimentary formation consisting of alternating layers of sandstone, mudstone and conglomerate. The Glenburn Formation spans a depositional timeframe of over 10 Ma, is over 1000 m thick, is regionally extensive and is possibly present over large areas offshore. For these reasons, it is important to constrain the paleoenvironment of this unit.  Late Cretaceous paleogeographic reconstructions of the East Coast Basin are, however, hampered by a number of factors, including the pervasive Neogene to modern tectonic deformation of the region, the poorly understood nature of the plate tectonic regime during the Cretaceous, and a lack of detailed sedimentological studies of most of the region’s Cretaceous units. Through detailed mapping of the Glenburn Formation, this study aims to improve inferences of regional Cretaceous depositional environments and paleogeography.  Detailed facies based analysis was undertaken on several measured sections in eastern Wairarapa and southern Hawke’s Bay. Information such as bed thickness, grain size and sedimentary structures were recorded in order to identify distinct facies. Although outcrop is locally extensive, separate outcrop localities generally lie in different thrust blocks, which complicates comparisons of individual field areas and prevents construction of the large-scale, three-dimensional geometry of the Glenburn Formation.  Glenburn Formation consists of facies deposited by sediment gravity flows that were primarily turbidity currents and debris flows. Facies observed are consistent with deposition on a prograding submarine fan system. There is significant variation in facies both within and between sections. Several distinct submarine fan architectural components are recognised, such as fan fringes, fan lobes, submarine channels and overbank deposits. Provenance and paleocurrent indicators are consistent with deposition having occurred on several separate submarine fans, and an integrated regional paleogeographic reconstruction suggests that deposition most likely occurred in a fossil trench following the mid-Cretaceous cessation of subduction along the Pacific-facing margin of Gondwana.</p>

scholarly journals Early Miocene Thrust Tectonics on Raukumara Peninsula, Northeastern New Zealand

2021 ◽  
Author(s):  
◽  
Geoffrey Jonathan Rait
Keyword(s):  
New Zealand ◽  
Oceanic Crust ◽  
Continental Margin ◽  
East Coast ◽  
Sedimentary Rocks ◽  
Early Miocene ◽  
Thrust Belt ◽  
Late Cenozoic ◽  
Thrust Sheets ◽  
Northern Zone

<p>Raukumara Peninsula lies at the northeastern end of the East Coast Deformed Belt, a province of deformed Late Mesozoic-Late Cenozoic rocks on the eastern edges of the North Island and northern South Island of New Zealand. Late Cenozoic deformation in this province is associated with westward subduction of the Pacific Plate, which started at about the beginning of the Miocene. Early Miocene tectonism on Raukumara Peninsula took place in a hitherto little-known thrust belt, the East Coast Allochthon. The configuration, evolution and origin of this thrust belt are the subjects of this thesis. The thrust belt extends 110 km from the thrust front in the southwest to the northeastern tip of Raukumara Peninsula. Internal structures strike northwest, perpendicular to the present trend of the continental margin but parallel to the Early Miocene trend suggested by plate reconstructions and paleomagnetic studies. The structure and kinematic evolution of the thrust belt were investigated by detailed mapping of three key areas in its central part and by analysis of previous work throughout the region. Gross differences in structure lead to the division of the belt into three zones: southern, central and northern. Deformation in the southern and central zones (the southwestern two-thirds of the system) was thin-skinned, involving southwestward transport of thrust sheets above a decollement horizon at the top of the Maastrichtian-Paleocene Whangai Formation. The decollement is exposed in the northwest due to southeastward tilting accompanying post-Miocene uplift of the Raukumara Range. Deformation in the northern zone involved reactivations of northeast-directed Cretaceous thrusts as well as southwestward emplacement of allochthonous sheets. Stratigraphic relationships show that thrusting took place during = 6 m.y. in the earliest Miocene. The 18 km wide southern zone is an emergent imbricate fan of rocks detached from above the Whangai Formation in a piggy-back sequence and transported less than about 18 km at rates of 2.6-3.6 mm/yr (plus-minus 20%-100%). The central and northern zones include rocks older than Whangai Formation. The sheets of the central zone and the southwest-directed sheets of the northern zone make up three major allochthonous units: the Waitahaia allochthon, consisting predominantly of mid-Cretaceous flysch above the Waitahaia Fault and equivalent structures, at the bottom of the thrust pile; the Te Rata allochthon, of Late Cretaceous-Early Tertiary continental margin sediments above the Te Rata Thrust, in the middle; and the Matakaoa sheet, an ophiolite body of mid-Cretaceous-Eocene basaltic and pelagic sedimentary rocks, at the top and back of the thrust belt. The Waitahaia allochthon was emplaced first and was subsequently breached by the Te Rata Thrust. The mid-Cretaceous rocks of the Waitahaia allochthon are mostly overturned, a result of the southwest-directed Early Miocene thrusting overprinting a Cretaceous structure of predominantly southwestward dips. The Te Rata allochthon comprises a complex pile of thrust sheets and slices with a general older-on-younger stacking order but with common reversals. Synorogenic sedimentary rocks occur within it. The complexity of internal structure of these two allochthons suggests they have undergone more than the 50% shortening estimated for the southern zone. The minimum southwestward displacement of the Te Rata allochthon is 60 km. The minimum displacements of the Waitahaia and Matakaoa allochthons are 55-195 km and 115-530 km respectively, depending on whether the Te Rata allochthon originally lay in front of the original position of the Waitahaia allochthon or was originally the upper part of the Waitahaia allochthon, and on the amounts of internal shortening of the allochthons. Over the = 6 m.y. period of thrusting, these estimates imply displacement rates for the Matakaoa sheet of 19-88 mm/yr. The average plate convergence rate at East Cape for the period 36-20 Ma is estimated at 25-30 mm/yr; the rate for the Early Miocene-- when subduction was active--may have been faster. Reasonable displacement rates for the Matakaoa sheet would result if the Te Rata allochthon was originally the upper part of the Waitahaia allochthon and if both allochthons have been shortened somewhat less than 50%. The emplacement mechanism of the Matakaoa ophiolite is elucidated by comparison with Northland, northwest along strike from Raukumara Peninsula, onto which correlative rocks were emplaced at the same time. The thinness of the Northland ophiolite bodies, their composition of rocks typical of the uppermost levels of oceanic crust, and the start of andesitic volcanism accompanying their obduction show that they were emplaced as a thin flake of oceanic crust which peeled off the downgoing slab during the inception of southwestward subduction. The reason the ophiolites were initially peeled from the slab is probably that their upper levels prograded southwestward over sediments of the Northland-Raukumara continental margin. In such a situation, initial compression would have led to formation of a northeast-dipping thrust at the volcanic/sediment interface; this thrust would then have propagated back into the downgoing plate with continued convergence, allowing the ophiolites to climb up the continental slope pushing the allochthonous sedimentary sheets ahead of them.</p>

Two new species and a new subspecies of Tetraclitella (Cirripedia: Thoracica) from the Cainozoic of Australia and New Zealand and a consideration of the significance of tubiferous walls

Zootaxa ◽  
2008 ◽  
Vol 1897 (1) ◽  
pp. 43-52 ◽  
Author(s):  
JOHN S. BUCKERIDGE
Keyword(s):  
New Species ◽  
New Zealand ◽  
Calcium Carbonate ◽  
Late Miocene ◽  
Early Miocene ◽  
Shell Wall ◽  
New Subspecies ◽  
Thermal Maximum ◽  
Two New Species

A tubiferous cirripede Tetraclitella judiciae sp. nov., previously known only from two isolated and incomplete shell wall plates identified as Tetraclitella sp. cf. T. purpurascens (Wood, 1815), is described from the early Miocene of Victoria, Australia; a further taxon, Tetraclitella purpurascens miocenica subsp. nov., occurs in the late Miocene-Pliocene of Victoria, and specimens from the early Miocene of New Zealand, previously recorded as Tetraclitella sp. cf. T. purpurascens (Wood, 1815) are redesignated as Tetraclitella nodicostata sp. nov. Tetraclitella is the first cirripede genus known to have had tubiferous walls. Incorporation of chitinous stringers within the shell wall of early tetraclitids (e.g. Epopella) may have facilitated the development of the tubiferous shell wall, which permitted sessile barnacles to maximise the shell strength to calcite ratio: in doing so, these chitinous stringers not only reduced the diversion of energy required to extract calcium carbonate from seawater, but improved the effectiveness of the shell wall in resisting predators. It is also argued here that the presence of chitin within the shell increased resistance to both corrasion and corrosion, the latter becoming an increasing problem for calcareous shelled organisms following a drop in the pH of seawater after the PalaeoceneEocene Thermal Maximum.

Are bright spots always hydrocarbons? A case study in the Taranaki Basin, New Zealand

2020 ◽  
Vol 8 (4) ◽  
pp. SR45-SR51
Author(s):  
Peter Reilly ◽  
Roberto Clairmont ◽  
Heather Bedle
Keyword(s):  
New Zealand ◽  
High Amplitude ◽  
Seismic Survey ◽  
Bright Spot ◽  
Temporal Region ◽  
Cross Sectional ◽  
Seismic Amplitude ◽  
Bright Spots ◽  
Seismic Amplitudes ◽  
Seismic Anomalies

In the shallower regions of the 3D Nimitz seismic survey, there exist multiple interesting bright seismic amplitude anomalies. These anomalies, or funny looking things, occur in a confined spatial and temporal region of the seismic. They have a concave-up seismic appearance along the cross section. Bright seismic amplitudes can be a direct hydrocarbon indicator, or they can be representative of strong lithologic contrasts and/or acquisition artifacts. We have set out to investigate misinterpreted seismic anomalies along cross-sectional lines. Therefore, we apply seismic attributes to indicate that these bright spot features, which we interpret to be submarine gullies looking along time-slice intersections, can possibly be mistaken for hydrocarbon anomalies in a cross-sectional view. However, we cannot fully rule out the presence of hydrocarbons because it is common for gas sands to create similar anomalies. Previously drilled wells within the survey (Korimako-1 and Tarapunga-1) point to a lack of hydrocarbon potential in the subsurface. Although it is possible that these bright spots are due to hydrocarbon presence, we develop a more likely hypothesis: The lithology of the interfluve sediments is similar to the gully-margin drapes but differs from the gully sediment fill. Funny looking thing (FLT): Submarine gullies Seismic appearance: High-amplitude spotted features Alternative interpretations: Lithologic anomalies, gas seeps, bright spots Features with a similar appearance: Gas accumulation, sediment fills in limestone paleocaves Formation: Giant Foresets Formation Age: Pleistocene Location: Taranaki Basin, New Zealand Seismic data: Nimitz 3D (cropped volume) Analysis tools: Curvature, instantaneous frequency, and sweetness attributes; well reports

Fuchsia pollen from the tertiary of Australia

1990 ◽  
Vol 3 (4) ◽  
pp. 739 ◽  
Author(s):  
PE Berry ◽  
JJ Skvarla ◽  
D PartridgeA ◽  
MK Macphail
Keyword(s):  
New Zealand ◽  
Late Miocene ◽  
Temperate Forests ◽  
Early Miocene ◽  
Late Oligocene ◽  
Early Oligocene ◽  
Extant Genus ◽  
Early Tertiary ◽  
New Localities

Pollen of Diporites aspis, corresponding to the extant genus Fuchsia, is reported from Late Oligocene to Early Miocene strata in two new localities in Australia. They extend the range of Diporites pollen in Australia from the Otway Basin in Victoria to the Capricorn Basin offshore Queensland, and they bring to six the number of Diporites specimens in Australia, from five different sites. These reports establish the presence of Fuchsia in Australasia from at least the Early Oligocene, when mesic forests were widespread across Australia. Fuchsia reached New Zealand by the Late Oligocene and has survived there until the present, but is not known to have survived in Australia past the late Miocene. These results support the hypothesis of an early Tertiary origin of the genus in southern temperate forests.

Seismic and sequence stratigraphic interpretation of the area of influence of the Magdalena submarine fan, offshore northern Colombia

2013 ◽  
Vol 1 (1) ◽  
pp. SA53-SA74 ◽  
Author(s):  
Andrea F. Cadena ◽  
Roger M. Slatt
Keyword(s):  
Late Miocene ◽  
Early Miocene ◽  
Early Pleistocene ◽  
Third Order ◽  
Submarine Fan ◽  
Sequence Stratigraphic ◽  
Level Increase ◽  
Thrust Sheets ◽  
Area Of Influence ◽  
Global Frontier

The area of influence of the Magdalena submarine fan, offshore northern Colombia, is a global frontier basin with sparse well control and only publically available 2D seismic from which to conduct exploration surveys. We have conducted a 2D seismic stratigraphic study to advance knowledge of the tectonostratigraphic evolution of this area and, furthermore, optimize exploration concepts to include stratigraphy and sedimentology to enhance such opportunities. Eight third-order seismic sequences from the early Miocene to Holocene comprise the stratigraphic record. Seismic character, thickness, and sedimentary processes vary in each sequence based on the area of deposition. Three geomorphologic areas are subject to deposition: the Tayrona depression, the undeformed central Magdalena fan and deformed wedges on either side of the fan. From oldest to youngest, sequences I to V represent bathyal paleo-environments that were deformed during the late Miocene Andean phase. Deformation of these sequences is thin skinned thrust sheets, where the main basal detachment corresponds to Oligocene shale. This deformation continued until the middle Pliocene, when sequence VI and VII were deposited on the Magdalena Fan mainly as mass transport and channel-levee deposits. Sequence VIII represents the record from early Pleistocene to the present time. From early Pliocene to present, erosion was mainly the product of submarine fan activity and bypass in areas of high slope, whereas for older deposits, erosion was caused by exposure to subaerial conditions. Superimposed on the third-order sequences are fourth-order sequences, which reveal a relative (tectonic-eustatic) sea level increase from Early Miocene to middle Late Miocene (Tortonian) time, followed by a lowstand event that extended until Holocene time. Potential reservoirs embedded within the sequences include sheet sands, channel fills, and levee-overbank. Other components of the petroleum system such as a mature source rock are still under debate.

EXPLORATION IN THE EAST COAST BASIN, NEW ZEALAND

1972 ◽  
Vol 12 (1) ◽  
pp. 39
Author(s):  
W.C. Leslie ◽  
R.J.S. Hollingsworth
Keyword(s):  
New Zealand ◽  
Oil And Gas ◽  
East Coast ◽  
Geological Structure ◽  
Seismic Survey ◽  
Porosity And Permeability ◽  
Rugged Topography ◽  
Complex Geological Structure ◽  
Petroleum Development ◽  
Made In

Numerous oil and gas seeps have been known in the East Coast Basin of New Zealand since the last century; however, no commercial discovery has been made in the region. Although a number of wells was drilled earlier, the present phase of systematic geological and geophysical exploration was begun by BP Shell Todd Petroleum Development Limited in 1957 and by 1970 had resulted in the drilling of five wells. These wells indicated the presence of thick marine mudstones and siltstones of Cretaceous through Tertiary age, but failed to find any suitable reservoir beds. This, plus complex geological structure and rugged topography are major problems of the region, particularly in the northern portion.Beaver Exploration subsequently became interested in the area because of the presence of a porous Pliocene coquina limestone (known as the Te Aute Beds) cropping out in the Southern Hawke's Bay region. This unit was considered to be a good drilling target if it occurred adequately sealed in the deeper parts of the basin. In an effort to determine this, Beaver conducted a Seismic Survey with the object of tracing the limestone from outcrop into the subsurface, where hopefully it would be found structurally closed.The survey was successful and three drill sites were chosen. In two of these the drill penetrated the Te Aute Beds which had excellent porosity and permeability but were water filled; in the third well the reservoir was missing. Correlations between the seismic and the drilling results indicated that the Te Aute Beds are probably mappable at least over some parts of the Southern Hawke's Bay region. The problem now is to find these beds in areas where they are less likely to be water flushed.

Globoconella Pseudospinosa, N. Sp.: a New Early Pliocene Planktonic Foraminifera from the Southwest Pacific

2018 ◽  
Vol 48 (4) ◽  
pp. 288-300 ◽  
Author(s):  
Martin P. Crundwell
Keyword(s):  
New Zealand ◽  
Late Miocene ◽  
East Coast ◽  
Planktonic Foraminifera ◽  
Ocean Drilling Program ◽  
Late Pliocene ◽  
Early Pliocene ◽  
Southwest Pacific ◽  
Project Site ◽  
Stratigraphic Ranges

Abstract Studies of topotypes of Truncorotalia crassaconica from the East Coast Basin of New Zealand and populations of Tr. crassaconica at Ocean Drilling Program Site 1123 and Deep Sea Drilling Project Site 284 in the southwest Pacific revealed two morphospecies. One of these is a late Pliocene species, Truncorotalia crassaconica s.s., that has low, slit-like apertures with thin, smooth apertural lips. The other is Globoconella pseudospinosa n. sp., an early Pliocene form with arched apertures and pustulose apertural lips. The short stratigraphic ranges of both species are potentially useful as biostratigraphic markers for the subdivision of Plio-Pleistocene stages in New Zealand and the temperate southwest Pacific. Populations of Gc. pseudospinosa, with mostly sinistrally coiled specimens, occur throughout the lectostratotype of the New Zealand Opoitian Stage at Mangapoike River in the East Coast Basin and are confined to the early Pliocene (Opoitian) at sites 1123 and 284, between 4.57 and 4.10 Ma. Small populations of Tr. crassaconica s.s., with mostly dextrally coiled specimens, occur in the late Pliocene (Waipipian Stage) between 3.53 and 2.98 Ma. Sporadic occurrences of relatively rare, mostly sinistrally coiled specimens of Tr. aff. crassaconica occur earlier at sites 1123 and 284 in the late Miocene to Pliocene between ca. 5.5 and 3.53 Ma. These specimens are distinguished in having open umbilici and almost straight umbilical sutures, similar to the late Miocene specimens of Truncorotalia crassaformis.

scholarly journals Early Miocene Thrust Tectonics on Raukumara Peninsula, Northeastern New Zealand

2021 ◽  
Author(s):  
◽  
Geoffrey Jonathan Rait
Keyword(s):  
New Zealand ◽  
Oceanic Crust ◽  
Continental Margin ◽  
East Coast ◽  
Sedimentary Rocks ◽  
Early Miocene ◽  
Thrust Belt ◽  
Late Cenozoic ◽  
Thrust Sheets ◽  
Northern Zone

<p>Raukumara Peninsula lies at the northeastern end of the East Coast Deformed Belt, a province of deformed Late Mesozoic-Late Cenozoic rocks on the eastern edges of the North Island and northern South Island of New Zealand. Late Cenozoic deformation in this province is associated with westward subduction of the Pacific Plate, which started at about the beginning of the Miocene. Early Miocene tectonism on Raukumara Peninsula took place in a hitherto little-known thrust belt, the East Coast Allochthon. The configuration, evolution and origin of this thrust belt are the subjects of this thesis. The thrust belt extends 110 km from the thrust front in the southwest to the northeastern tip of Raukumara Peninsula. Internal structures strike northwest, perpendicular to the present trend of the continental margin but parallel to the Early Miocene trend suggested by plate reconstructions and paleomagnetic studies. The structure and kinematic evolution of the thrust belt were investigated by detailed mapping of three key areas in its central part and by analysis of previous work throughout the region. Gross differences in structure lead to the division of the belt into three zones: southern, central and northern. Deformation in the southern and central zones (the southwestern two-thirds of the system) was thin-skinned, involving southwestward transport of thrust sheets above a decollement horizon at the top of the Maastrichtian-Paleocene Whangai Formation. The decollement is exposed in the northwest due to southeastward tilting accompanying post-Miocene uplift of the Raukumara Range. Deformation in the northern zone involved reactivations of northeast-directed Cretaceous thrusts as well as southwestward emplacement of allochthonous sheets. Stratigraphic relationships show that thrusting took place during = 6 m.y. in the earliest Miocene. The 18 km wide southern zone is an emergent imbricate fan of rocks detached from above the Whangai Formation in a piggy-back sequence and transported less than about 18 km at rates of 2.6-3.6 mm/yr (plus-minus 20%-100%). The central and northern zones include rocks older than Whangai Formation. The sheets of the central zone and the southwest-directed sheets of the northern zone make up three major allochthonous units: the Waitahaia allochthon, consisting predominantly of mid-Cretaceous flysch above the Waitahaia Fault and equivalent structures, at the bottom of the thrust pile; the Te Rata allochthon, of Late Cretaceous-Early Tertiary continental margin sediments above the Te Rata Thrust, in the middle; and the Matakaoa sheet, an ophiolite body of mid-Cretaceous-Eocene basaltic and pelagic sedimentary rocks, at the top and back of the thrust belt. The Waitahaia allochthon was emplaced first and was subsequently breached by the Te Rata Thrust. The mid-Cretaceous rocks of the Waitahaia allochthon are mostly overturned, a result of the southwest-directed Early Miocene thrusting overprinting a Cretaceous structure of predominantly southwestward dips. The Te Rata allochthon comprises a complex pile of thrust sheets and slices with a general older-on-younger stacking order but with common reversals. Synorogenic sedimentary rocks occur within it. The complexity of internal structure of these two allochthons suggests they have undergone more than the 50% shortening estimated for the southern zone. The minimum southwestward displacement of the Te Rata allochthon is 60 km. The minimum displacements of the Waitahaia and Matakaoa allochthons are 55-195 km and 115-530 km respectively, depending on whether the Te Rata allochthon originally lay in front of the original position of the Waitahaia allochthon or was originally the upper part of the Waitahaia allochthon, and on the amounts of internal shortening of the allochthons. Over the = 6 m.y. period of thrusting, these estimates imply displacement rates for the Matakaoa sheet of 19-88 mm/yr. The average plate convergence rate at East Cape for the period 36-20 Ma is estimated at 25-30 mm/yr; the rate for the Early Miocene-- when subduction was active--may have been faster. Reasonable displacement rates for the Matakaoa sheet would result if the Te Rata allochthon was originally the upper part of the Waitahaia allochthon and if both allochthons have been shortened somewhat less than 50%. The emplacement mechanism of the Matakaoa ophiolite is elucidated by comparison with Northland, northwest along strike from Raukumara Peninsula, onto which correlative rocks were emplaced at the same time. The thinness of the Northland ophiolite bodies, their composition of rocks typical of the uppermost levels of oceanic crust, and the start of andesitic volcanism accompanying their obduction show that they were emplaced as a thin flake of oceanic crust which peeled off the downgoing slab during the inception of southwestward subduction. The reason the ophiolites were initially peeled from the slab is probably that their upper levels prograded southwestward over sediments of the Northland-Raukumara continental margin. In such a situation, initial compression would have led to formation of a northeast-dipping thrust at the volcanic/sediment interface; this thrust would then have propagated back into the downgoing plate with continued convergence, allowing the ophiolites to climb up the continental slope pushing the allochthonous sedimentary sheets ahead of them.</p>

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