Geology of the Tinui district

Mapping Intimacies ◽

10.26686/wgtn.16958449.v1 ◽

2021 ◽

Author(s):

◽

Michael Robert Johnston

Keyword(s):

New Zealand ◽

East Coast ◽

Late Quaternary ◽

Upper Jurassic ◽

Mobile Belt ◽

Late Cenozoic ◽

Complex Reconstruction ◽

History Of ◽

Early Cenozoic ◽

Strike Slip Movement

The Tinui District is assumed to be typical of the more deformed part of the New Zealand Mobile Belt. It contains an unusually complete stratigraphic record, rocks representing most stages from Upper Jurassic to Recent being present. Although the rocks are strongly deformed, the complex diapiric structures that occur in the northeast of the mobile belt are absent. The stratigraphy is described in terms of formations which are then used to infer the paleogeography for eight periods of time. An attempt is made to treat the structure according to its development with time. The main conclusion is that there was a change in the strike of the fold axes and in the sense of movement of the faults. Strong folds, striking approximately northeast, are Paleocene in age and weak folds, striking approximately north, are post-Miocene. There are two fault trends, one NNE and the other ENE. The ENE striking faults were dominant in the Early Cenozoic and the NNE striking faults were dominant in the Late Cenozoic. The sense of movement on the NNE faults changed from sinistral to dextral. The change in the direction of the axes and in the sense of movement on the faults can be expressed as a change in the direction of maximum horizontal shortening, which is inferred to have changed with time. It is also found that the rates of tilting, and probably faulting, have not been constant with time, but occurred as bursts (disturbances) in the Paleocene, Early Miocene Late Pliocene, and Late Quaternary. The Mesozoic part of the geological history of the Tinui District is scrappy and far less complete than the Cenozoic part. In order to place the Tinui District in a broader setting, the central part of the New Zealand landmass in the Cenozoic, called the New Zealand Mobile Belt, is discussed in some detail. The mobile belt consists of fault blocks which form a geanticline along the New Zealand landmass and a geosynclinal trough between the east coast and the Hikurangi Trench. It is shown that a clear distinction has to be made between tilting and uplift. A main feature of the New Zealand Mobile Belt is the dextral faulting, on major NNE striking faults, in the Late Cenozoic. A major reversal in the direction of maximum horizontal shortening was found in the Tinui District to have taken place at the beginning of the Miocene or in the Oligocene. The reversal indicates that the dextral faulting of the New Zealand Mobile Belt may have started at that time, and that earlier strike-slip movement had been sinistral. This conclusion contradicts existing reconstructions of the New Zealand landmass with time, and a more complex reconstruction is required to satisfy the tectonics of the Tinui District.

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Geology of the Tinui district

10.26686/wgtn.16958449 ◽

2021 ◽

Author(s):

◽

Michael Robert Johnston

Keyword(s):

New Zealand ◽

East Coast ◽

Late Quaternary ◽

Upper Jurassic ◽

Mobile Belt ◽

Late Cenozoic ◽

Complex Reconstruction ◽

History Of ◽

Early Cenozoic ◽

Strike Slip Movement

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Geodetic strain and the deformational history of the North Island of New Zealand during the late Cainozoic

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1987.0009 ◽

1987 ◽

Vol 321 (1557) ◽

pp. 163-181 ◽

Cited By ~ 207

Keyword(s):

New Zealand ◽

Subduction Zone ◽

East Coast ◽

Late Quaternary ◽

Plate Boundary ◽

Boundary Zone ◽

Metamorphic Belt ◽

Volcanic Region ◽

The North ◽

Plate Boundary Zone

The subduction zone under the east coast of the North Island of New Zealand comprises, from east to west, a frontal wedge, a fore-arc basin, uplifted basement forming the arc and the Central Volcanic Region. Reconstructions of the plate boundary zone for the Cainozoic from seafloor spreading data require the fore-arc basin to have rotated through 60° in the last 20 Ma which is confirmed by palaeomagnetic declination studies. Estimates of shear strain from geodetic data show that the fore-arc basin is rotating today and that it is under extension in the direction normal to the trend of the plate boundary zone. The extension is apparently achieved by normal faulting. Estimates of the amount of sediments accreted to the subduction zone exceed the volume of the frontal wedge: underplating by the excess sediments is suggested to be the cause of late Quaternary uplift of the fore-arc basin. Low-temperature—high-pressure metamorphism may therefore be occurring at depth on the east coast and high-temperature—low-pressure metamorphism is probable in the Central Volcanic Region. The North Island of New Zealand is therefore a likely setting for a paired metamorphic belt in the making.

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Early Miocene Thrust Tectonics on Raukumara Peninsula, Northeastern New Zealand

10.26686/wgtn.16947481 ◽

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

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.

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Population Genetics of New Zealand Nemadactylus macropterus (tarakihi) and Characterisation of their Mitochondrial Genome

10.26686/wgtn.17142476.v1 ◽

2021 ◽

Author(s):

◽

Alexander Halliwell

Keyword(s):

Genetic Diversity ◽

New Zealand ◽

Genetic Structure ◽

East Coast ◽

Demographic History ◽

Variable Region ◽

Sequencing Data ◽

Commercial Catch ◽

History Of ◽

Hyper Variable Region

Nemadactylus macropterus, commonly known as tarakihi in New Zealand is highly regarded by commercial and recreational fishers and considered a taonga by iwi and customary fisheries. For many years N. macropterus was New Zealand’s second most important commercial catch and is currently the third most valuable inshore commercial finfish fishery in which 90% is consumed by the domestic market. However, despite the apparent importance, relatively little is known about the population structure of the N. macropterus. In 2017 the first fully quantitative stock assessment was conducted on the east coast N. macropterus fisheries as one stock. Alarmingly, the east coast fishery was estimated to be 15.9% of the unexploited spawning biomass and predicted to have been declining for the past thirty years. In an effort to rebuild the fishery, several rebuild plans have been purposed and commercial catch limits have been reduced. In order to rebuild and successfully manage a viable future N. macropterus fishery, an understanding of demographic connectivity and genetic connectivity among N. macropterus populations is essential. The overall goal of this thesis research was to investigate the population genetic structure, genetic diversity and demographic history of N. macropterus using fish sampled from around New Zealand. This was achieved by analysing hyper variable region one of mitochondrial DNA for 370 N. macropterus collected from 14 locations. No genetic differentiation was observed among the 14 locations, an indication that N. macropterus have a panmictic genetic structure. Furthermore, N. macropterus display a relatively high level of genetic diversity and appear to have a large stable population with a long evolutionary history. The Bayesian skyline analysis indicates the N. macropterus historic population has gone through two expansions. The mostly likely cause of this is an expansion before and after the last glacial maximum. The genetic diversity and demographic history of N. sp was also studied using samples collected from around the Three Kings Islands of New Zealand. The complete mitochondrial genome of N. macropterus was reconstructed from bulk DNA sequencing data and a set of specific mtDNA primers were developed to amplify hyper variable region one. The DNA sequencing data provided by these primers with the addition of published control region sequences was used to reconstruct the Nemadactylus phylogeny.

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