Showing papers in "New Zealand Journal of Geology and Geophysics in 1990"
TL;DR: In this article, the authors present the stratigraphic relationships and distribution of 36 named late Quaternary (≤c. 50 000 yr B P) silicic tephra formations, erupted from 4 volcanic centres (Okataina, Taupo, Maroa, and Tuhua).
Abstract: The stratigraphic relationships and distribution of 36 named late Quaternary (≤c. 50 000 yr B P.) silicic tephra formations, erupted from 4 volcanic centres—Okataina, Taupo, Maroa, and Tuhua (Mayor Island)—are presented. The stratigraphy and status of several other named late Quaternary tephras are also discussed. This compilation brings together all the data, currently scattered through many publications, to make tephrostratigraphy more accessible and more easily used. The nomenclature of tephra formations is discussed and some rationalisations are suggested. The term “tephrology” is suggested as an appropriate title for the field of tephra studies. The deletion of grain-size (ash, lapi1li), shape (breccia), and lithologic (pumice) terms from all formation names is recommended, as is standardisation on a “Tephra Formation” formal Several tephra layers not previously formally named, or without designated type sections, are defined. The dominant ferromagnesian mineral assemblage of each tephra for...
442 citations
TL;DR: A c. 700 km2 area of northern Fiordland (South Island, New Zealand) is described in which Early Cretaceous high-pressure metamorphic rocks and virtually unmetamorphosed plutonic rocks occur as mentioned in this paper.
Abstract: A c. 700 km2 area of northern Fiordland (South Island, New Zealand) is described in which Early Cretaceous high-pressure metamorphic rocks and virtually unmetamorphosed plutonic rocks occur. The dominant rocks are orthogneisses developed from synmetamorphic basic-intermediate intrusive complexes, the youngest and most widespread of which is the Early Cretaceous Western Fiordland Orthogneiss (WFO). The latter has undergone granulite facies metamorphism and occurs throughout much of western Fiordland. In the study area, the WFO protolith intruded a country rock of amphibolite facies metasediments and orthogneisses. Fragments of the country rock are rafted within WFO and are represented by George Sound Paragneiss and Rafted Granitoid Gneisses. External country rock is represented by Arthur River Complex and Jagged Gneiss (possibly related to the Anita Ultramafites); it may also include Indecision Creek Complex and Mount Anau Complex. The George Sound Paragneiss is correlated with the Central Fiordla...
91 citations
TL;DR: In this article, a dextrally offset late Pleistocene glacial moraine and river terraces are used to preserve a cumulative record of the local variability of finite strain within the Hope Fault zone.
Abstract: An earthquake in 1888 generated surface rupture on the Hope Fault at Glynn Wye, North Canterbury, New Zealand, where earlier displacements are preserved as dextrally offset late Pleistocene glacial moraine and river terraces. The moraine and terraces are located at the eastern end of a >1 km wide sag basin named Poplars Graben, developed at a releasing bend in the Hope Fault. The offset landforms at Poplars Graben are fortuitously located to preserve a cumulative record of the local variability of finite strain within the Hope Fault zone. The landforms are of near-equal age (17 000 ± 2000 years), but the measured fault displacements across these features are different. Variations in displacement along the fault result from the total being partitioned into vector components of strike-parallel, strike-normal, and vertical slip, which are systematically related to changes in fault strike. This exemplifies the importance of understanding the geometry and kinematics of faults and fault systems when ev...
89 citations
TL;DR: In this paper, the thermoluminescence method was used to date dune sand from two sections in the southwestern North Island of New Zealand, and the results confirm that coastal dunes were migrating inland during the last stadial of the Otira Glaciation.
Abstract: Samples of dune sand from two previously described sections in the southwestern North Island have been dated by the thermoluminescence method. At the first site, Koputaroa Phase dune sand immediately underlying Aokautere Ash ( = Oruanui Ash 14C dated at c. 22 590 yr B.P.) was dated at 24 200 ± 3700 yr. At the second site, Holocene dune sand was dated at 3000 ± 500 yr. Factors influencing the error limits of the thermoluminescence dates are discussed. The results confirm that coastal dunes were migrating inland during the last stadial of the Otira Glaciation and indicate that the thermoluminescence method could usefully be applied in the dating of upper Quaternary deposits in this region.
82 citations
TL;DR: In this paper, it is recommended that strandline ages should be used for reporting the age of marine terraces, based on height spacings of terraces of last interglacial age.
Abstract: Since the 1950s, the study of marine terraces in New Zealand has undergone a major change in emphasis. From studies focussing on altimetric correlations with the (then) standard Mediterranean sequence, and constrained by the four-glaciation model, there has been a change to greater appreciation of tectonic deformation, increasing use of numerical-age dating methods, and acceptance of the New Guinea sea-level record (augmented with oxygen isotope records in deep-sea cores), as a global standard. Shoreline datums are defined and discussed following the recommendations of Gage in 1953. Dating techniques as well as methods of regional and international correlation are reviewed. It is recommended that strandline age be used for reporting the age of marine terraces. The assignment of marine terrace ages based solely on height spacings is reviewed and found to be unreliable in the absence of other dating methods. Estimates of uplift rates based on marine terraces of last interglacial age are presented. ...
76 citations
TL;DR: The M s 7.8 Hawke's Bay earthquake of 1931 February 3 (New Zealand local time) was felt throughout most of New Zealand andcaused extensive damage at Napier, Hastings, and throughout Hawke Bay as mentioned in this paper.
Abstract: The M s 7.8 Hawke's Bay earthquake of 1931 February 3 (New Zealand local time) was felt throughout most of New Zealand andcaused extensive damage at Napier, Hastings, and throughout Hawke's Bay. Surface deformation accompanying the earthquake resulted in a >90 km long, 17 km wide asymmetric dome trending northeast and extending from southwest of Hastings to northeast of the Mohaka River mouth. Maximum uplift of 2.7 m occurred near the mouth of the Aropaoanui River close to the location of major aftershock activity, while maximum subsidence of 1 m was recorded at Hastings, to the southeast of the steeper, southeast-facing side of the dome. Observed surface faulting of about 15 km in length was confined to the southwestern end of the dome where near-surface rocks had sufficient strength and suitably oriented pre-existing fractures to accommodate slip. Elsewhere, the elastic nature of the rocks resulted in surface folding above a buried causative fault. Fault scarps with up to 4.6 m vertical separat...
70 citations
TL;DR: In this article, it is suggested that a large seismic event related to the last major movement on the Alpine Fault occurred in the middle 17th to early 18th century, and the mean ages calculated at 266 +90, -60 years.
Abstract: Stratigraphic sections through sag ponds developed along the Alpine Fault trace between Milford Sound and John O'Groats River record drastic changes in sedimentation. Swamp or forest-floor material has been inundated by up to 0.5 m of cataclasite-derived sand and gravel. Two events, inferred to represent degradation of newly created scarps on the Alpine Fault, occurred at, or later than, 230 ± 50 yr B.P., and 1980 ±60 yr B.P., respectively. At John O'Groats River, large silver beech trees growing on the Alpine Fault scarp have been topped at heights of 8–15 m above ground level by movement on the fault. Unbroken beeches have mean ages calculated at 266 +90, -60 years. On a regional scale, a colluvial fan-forming event at Kaipo River and rotational slumping at Gorge Plateau are broadly synchronous with inferred fault movements near John O'Groats River. It is suggested that a large seismic event, related to the last major movement on the Alpine Fault, occurred in the middle 17th to early 18th century.
55 citations
TL;DR: The Wellington Fault is one of the major active dextral strike-slip faults of southern North Island as discussed by the authors, and it is estimated to have a slip rate from 3.7 m to 900 m. Quaternary stratigraphic studies and fault mapping along the southern part of the fault in Upper Hutt have provided some data on slip rates and recurrence intervals.
Abstract: The Wellington Fault is one of the major active dextral strike-slip faults of southern North Island. Quaternary stratigraphic studies and fault mapping along the southern part of the fault in Upper Hutt have provided some data on slip rates and recurrence intervals. Horizontal offsets of terrace risers and channels on terrace surfaces range from 3.7 m to 900 m. Increasing numbers of loess units, separated by paleosols, on successively older fluvial terraces in the Upper Hutt and Kaitoke Basins, provide a means of dating the terraces and, together with displacement measurements, a means of estimating horizontal slip rates on the Wellington Fault. At Emerald Hill, a terrace with an estimated age of 14 ± 4ka is dextrally offset by 104± 10m(after correcting for tread width differences of the terrace on either side of the fault). An older terrace estimated to be about 70 ± 5 ka is offset by 437 ± 20 m, and a 940 ± 40 m offset is associated with a terrace about 140 ± 10 ka. These displacement/age pairs...
54 citations
TL;DR: The Haast Schist comprises a polygenetic metamorphic suite derived from Caples, Aspiring, and Torlesse terrane lithologies as mentioned in this paper, which has been ascribed previously to either the Caples or Torlese terranes.
Abstract: The Haast Schist comprises a polygenetic metamorphic suite derived from Caples, Aspiring, and Torlesse terrane lithologies. High-grade Alpine Schist, occurring immediately east of the Alpine Fault, has been ascribed previously to either the Caples or Torlesse terranes. Chemical analyses are presented of schist suites from (1) the Whitcombe River area, including samples that both stratigraphically overlie and structurally underlie the Pounamu Ultramafics, and (2) the lower Haast River, west of a greenschist-rich sequence correlated with the Aspiring terrane. Discriminant function analysis of these suites, and of published data from the Fox-Franz Josef area, indicates that the Alpine Schist has Torlesse affinities. This conclusion is also supported by ratio-ratio plots of trace elements. A Torlesse terrane affiliation is also suggested for a small population of psammitic schists from within the Aspiring terrane. The Aspiring terrane sequence at Haast River, like the Pounamu Ultramafic Belt to the n...
50 citations
TL;DR: Taupo Tephra layers have been identified using mineralogy, glass chemistry, and radiocarbon dates as mentioned in this paper, and two layers contain cummingtonite, amineral diagnostic of Okataina Volcanic Centre and these are identified as Whakatane and Rotoma Tephras.
Abstract: Peat bogs occur along the crests of the main axial ranges of the North Island of New Zealand. The bogs provide ideal sites for palynological investigations and have also preserved a number of tephra layers from andesitic and rhyolitic volcanoes to the west and north. The tephra layers have been identified using mineralogy, glass chemistry, and radiocarbon dates. Taupo Tephra and Waimihia Tephra are ubiquitous and easily identified by thickness and grain size. Other Taupo Volcanic Centre eruptives identified are Mapara, Hinemaiaia, Motutere, Opepe, and Karapiti Tephras. Two layers contain cummingtonite, amineral diagnostic of Okataina Volcanic Centre, and these are identified as Whakatane and Rotoma Tephras. Karapiti Tephra (c. 10 000 yr B.P.) is the oldestrhyolitic tephra layer identified and dates the formation of the deepest bogs. Andesitic tephra is dispersed throughout the northern and western peat bogs and forms several distinct layers. It is characterised by a mineralogy dominated by augite...
48 citations
TL;DR: Taxonomic information can be recovered from tectonically deformed fossils by analyzing the strain and then restoring the fossils to their original shapes as mentioned in this paper, using trilobites and graptolites as examples of two kinds of fossils.
Abstract: Taxonomic information can be recovered from tectonically deformed fossils by analysing the strain and then restoring the fossils to their original shapes. Trilobites and graptolites are used as examples of two kinds of fossils—the first with known original angles and the second with a known original dimension. The first kind enables the shape and orientation of the strain ellipse to be determined; three graphical methods are outlined. The second kind enables, in addition, the actual strains in the bedding plane to be determined, and a method using graptolite thecal spacing is described. Best results for determining actual strains are obtained when both angles and dimensions are used, and a new method using graptolites is described. Five methods of restoring the original shape of fossils are briefly outlined.
TL;DR: In this paper, 13 tephra layers interbedded with peat, and abasal peat horizon, in four pairs of cores provide radiocarbondated reference horizons that indicate vertical displacement on the Kerepehi Fault at Kopouatai bog, Hauraki Lowlands.
Abstract: Thirteen tephra layers interbedded with peat, and abasal peat horizon, in four pairs of cores provide radiocarbondated reference horizons that indicate vertical displacement on the Kerepehi Fault at Kopouatai bog, Hauraki Lowlands. Progressive offset of the horizons with time shows that vertical fault movement, downthrown to the west, has been occurring for the past c. 10 700 radiocarbon years at an approximately uniform rate of c. 0.13 mm/yr. Step functions indicate faulting events (earthquakes) at c. 1400, c. 5600, c. 6800, and c. 9000 years ago, a mean recurrence interval of c. 2500 years. These findings support geophysical and geological evidence that the Hauraki Depression is an active rift, and show that active faulting occurs along the northern as well as southern extensions of the Kerepehi Fault. If such earthquakes occur randomly in time, and based on the return period of 2500 years, there are 2%, 18%, and 33% probabilities of a major earthquake affecting the Kerepehi Fault at Kopouatai ...
TL;DR: The 15-20 km wide zone of active late Quaternary extensional faulting (the Taupo Fault Belt-Whakatane Graben), within the Taupo Volcanic Zone, extends offshore at least 43 km towards White Island, Bay of Plenty.
Abstract: The 15–20 km wide zone of active late Quaternary extensional faulting (the Taupo Fault Belt-Whakatane Graben), within the Taupo Volcanic Zone, extends offshore at least 43 km towards White Island, Bay of Plenty Within the offshore Whakatane Graben, as defined by the White Island Fault and newly named Rurima Fault, some 50 normal faults displacing post-18 ka transgressive sediments are newly mapped from high-resolution 35 kHz seismic profiles The faults strike northeast, appear laterally discontinuous over distances of >10 km, generally dip to the northwest, and bound faultblocks tilted to the southeast Of these, four newly named faults—the Ohiwa, Nukuhou, Pukehoko, and Rangitaiki—show large and repeated movements within the last 18 ka Post-18 ka seismic stratigraphy, tephrostratigraphy, and 14C dating indicate relative vertical fault displacement rates vary from 02 to 28 mm/yr An extensional block model relating fault geometry, vertical displacements, and extension indicates that absolute
TL;DR: A study of the late Cenozoic tectonic geomorphology of a 700 km2 area of remnant peneplain comprising the Old Man Range and Garvie Mountains, Central Otago, has shown the Peneplain to have had a maximum regional Miocene paleorelief of 500 m/10 km, and to be underlain by a low-angle schistosity (dipping 0-20°) as discussed by the authors.
Abstract: A study of the late Cenozoic tectonic geomorphology of a 700 km2 area of remnant peneplain comprising the Old Man Range and Garvie Mountains, Central Otago, has shown the peneplain to have had a maximum regional Miocene paleorelief of 500 m/10 km, and to be underlain by a low-angle schistosity (dipping 0–20°). As much as 1500 m vertical displacement of the peneplain is evident from preserved Tertiary sediments at varying altitude. Sedimentology of mid-Pliocene (Waipipian) quartzose sediments found at 1200 m suggests that reworking of older Miocene sediments (Manuherikia Group) has occurred during early stages of uplift. Mapping reveals a consistently low angle relationship between schistosity and peneplain attitude, and dominance of distributed deformation (flexure) over faulting. Topography and schistosity are sympathetically warped into northerly trending fault-bounded folds (tectonic blocks). Joint orientations are related to orientations of major faults (Nevis-Cardrona Fault System and Old Ma...
Abstract: Two classes of basement rock are recognised on the Campbell Plateau: silicic to intermediate plutonic rocks, and quartzose metasedimentary rocks. The plutonic rocks, from Auckland Island and petroleum exploration wells Pakaha-1, Tara-1, and Pukaki-1, are petrologically similar to granites from southern Stewart Island, Snares Islands, and western South Island and produce similar Cretaceous K-Ar ages. Granodiorite from Bounty Island (K-Ar age 189 Ma) is petrologically comparable with rocks in the Foveaux Strait area. Metasedimentary rocks from Campbell Island, the sea floor near Bounty Islands, and petroleum wells Kawau-1A, Hoiho-1C, and possibly Rakiura-1, are comparable with early Paleozoic metasedimentary rocks (e. g., Greenland Group) on the West Coast of the South Island, as well as Robertson Bay Group of northern Victoria Land and other Antarctic suites, and basement from DSDP hole 281 on the South Tasman Rise. They are distinct compositionally from late Paleozoic and Mesozoic metasedimentary...
TL;DR: New mosasaur specimens of Piripauan-Haumurian (Campanian-Maastrichtian) age are described from the Mangahouanga Stream, North Island, New Zealand, including two distinctive adult skulls and one incomplete cranial and postcranial specimen.
Abstract: New mosasaur specimens of Piripauan-Haumurian (Campanian-Maastrichtian) age are described from the Mangahouanga Stream, North Island, New Zealand. These include two distinctive adult skulls and one incomplete cranial and postcranial specimen. A new genus and species Rikisaurus tehoensis is recognised and a new species of Mosasaurus, M.flemingi, is described. A further specimen is identified as aff. Prognathodon overtoni. Two fragmentary specimens are also described (as aff. Moanasaurus mangahouangae and gen. and sp. indet.), along with an isolated adult limb bone (gen. and sp. indet.) of a type not previously collected in New Zealand.
TL;DR: Petrographic and geochemical data confirm the source of granitic detritus in the Hawks Crag Breccia of the lower Buller Gorge to be the Early Cretaceous Buckland, Blackwater, and Steele Plutons, presently disposed to the south and southwest as discussed by the authors.
Abstract: Petrographic and geochemical data confirm the source of granitic detritus in the Hawks Crag Breccia of the lower Buller Gorge to be the Early Cretaceous Buckland, Blackwater, and Steele Plutons, presently disposed to the south and southwest. Detritus in the Hawks Crag Breccia in the Fox River and Bullock Creek may also be derived from the Buckland Pluton, but the provenance of the granitic detritus in this formation in the Pike Stream remains unclear. However, granitic clasts in the Ohika Formation were derived from Paleozoic granites of the Karamea Suite, of which potential source plutons are presently widely distributed to the WNW (Orowaiti River), the north (Britannia Pluton), and to the east (Dunphy Granite). Clasts derived from the deformed basement of the Paparoa Metamorphic Core Complex first appear in the upper part of the Ohika Formation, indicating initial unroofing of the complex at that time. The indicated source directions are consistent with a northwest-southeast trend for the two d...
TL;DR: The first-order geodetic triangulation of New Zealand, completed between 1925 and 1949 by the Department of Lands & Survey, has been reobserved in part between 1976 and 1984 along a series of narrow belts, as a contribution to to the national Earth Deformation Programme of the Royal Society.
Abstract: The first-order geodetic triangulation of New Zealand, completed between 1925 and 1949by the Department of Lands & Survey, has been reobserved in part between 1976 and 1984 along a series of narrow belts, as a contribution to to the national Earth Deformation Programme of the Royal Society of New Zealand. This has provided a set of data of uniformly high quality, which has been analysed by the method of simultaneous reduction, to yield a continuum model of horizontal deformation for the region between Christchurch and Auckland. This spans the Hikurangi Margin, the southern extension of the Tonga-Kermadec boundary of the subducting Pacific plate that terminates at the Chatham Rise. The continuum model of deformation comprises the 16 terms that specify the horizontal derivatives of the horizontal velocity field of orders 2–4, and their error covariance matrix. Between Hawke Bay and Chatham Rise the pattern of shear-strain rate shows a consistent azimuth of the axis of maximum relative shortening of...
TL;DR: The Torlesse terrane greywacke turbidites with intercalations of red rocks that occur in various combinations of metabasalt, chert, and coloured (red, green, grey) argillite as mentioned in this paper.
Abstract: The Wellington peninsula is composed of Torlesse terrane greywacke turbidites with intercalations of red rocks that occur in various combinations of metabasalt, chert, and coloured (red, green, grey) argillite. The red rocks define 2 km-scale folds (the Rimurapa inverted syncline and Evans Bay Syncline) in the Wellington peninsula. The best known example of red rocks crops out at a point called Red Rocks on the coast about 8 km south of Wellington City. Radiolarians in cherts at Red Rocks indicate a Late Permian age, whereas radiolarians from phosphorite and a probable hydrozoan fossil (Heterastridium) in grey argillite of the turbidite sequence indicate a Late Triassic (Carnian-Norian) age. Radiolarians from phosphatic concretions in grey argillite interbedded with turbidites elsewhere in the Wellington peninsula also indicate a Late Triassic age. The fossil ages indicate a 40–50 Ma age difference between the red rocks and the enclosing turbidites. In addition to their older age, the red rocks: ...
TL;DR: In this paper, the porosity of exhumed mudstone sequences of Wairarapa has been derived from density measurements, and can be used to estimate prior depth of greatest burial, to within about 100 m.
Abstract: The seismic velocities and porosities of mudstones and other fine-grained sedimentary rocks can be used to estimate burial history. The porosity of exhumed mudstone sequences of Wairarapa has been derived from density measurements, and can be used to estimate prior depth of greatest burial, to within about 100 m, by the linear regression function, greatest depth of burial = ™111 porosity +4975, or the exponential function, greatest depth of burial=™8636 log porosity + 14384. The velocity trend of the exhumed mudstones of southeastern Wairarapa is not as good an indicator of burial history, as it has only a poor fit to the regression function, greatest depth=2666 velocity ™3331. However, fully loaded, fine-grained sedimentary rocks (mainly mudstones) still under lithostatic pressure in North Island oil wells have a good fit to the velocity-depth regression functions, depth = 1026 velocity ™1419 or, depth=6617 log velocity ™1403. This relationship can be used to calculate the thickness of sediment ...
TL;DR: The Maungataniwha Sandstone as mentioned in this paper contains a diverse, dominantly marine vertebrate and invertebrate fauna, but includes terrestrial vertebrates, invertebrates, and plants.
Abstract: The Maungataniwha Sandstone is a remarkably thick (c. 400 m), poorly bedded, transgressive, sandstone-dominated unit of Campanian-Maastrichtian age (late Piripauan to early Haumurian). It was deposited during continued slow subsidence, and possibly records onlap over a dissected coastal plain and/or stacking of several minor transgressive and regressive cycles. It contains a diverse, dominantly marine vertebrate and invertebrate fauna, but includes terrestrial vertebrates, invertebrates, and plants. Marine fossils were probably not significantly transported or mixed prior to burial, and indicate deposition in a fully marine, nearshore, shallow water, moderate to high energy environment, possibly within an estuary, bay, or inlet. Three benthic invertebrate assemblages are recognised, and these may correspond to different habitats within such an environment. A nearby river mouth or delta is implied by the abundance of terrestrially derived material. Information on environment of deposition from sed...
TL;DR: In this paper, heavy mineral distribution has been studied to help determine provenance and distinguish lithostratigraphic units in Cretaceous and Cenozoic sedimentary basins.
Abstract: South Island heavy mineral distribution has been studied to help determine provenance and distinguish lithostratigraphic units in Cretaceous and Cenozoic sedimentary basins. Most Cretaceous and Cenozoic sediments reflect derivation from local basement rocks, chiefly granitoids of the Karamea and Golden Bay terranes and older sedimentary rocks of the Karamea, Torlesse, Caples, Murihiku, and Maitai terranes. The granitoid rocks in Fiordland are characterised by both hornblende and biotite, but in Westland and west Nelson biotite predominates. Biotite is also dominant in most sedimentary rocks of the Karamea terrane (Greenland Group and Preservation Formation). Torlesse and Caples samples are characterised by epidote and “semi-opaque debris”, which are also prominent in derived sediments. Much of the Torlesse is biotite rich, reflecting its granitic (Karamea Suite) source, but in derived sediments biotite is not prominent, probably because it did not withstand recycling. Caples terrane samples conta...
TL;DR: Radiocarbon dating of a sequence of terraces at Ballantrae Research Station, near Woodville, provides the first dates for alluvial deposits of Ohakean age to the east of the southern Ruahine Range.
Abstract: Radiocarbon dating of deposits from a sequence of terraces at Ballantrae Research Station, near Woodville, provides the first dates for alluvial deposits of Ohakean age to the east of the southern Ruahine Range. Here these terraces have been vertically offset by the active trace of the Wellington Fault. To the west of the trace, upthrown aggradational deposits are dated at c. 13 000 yr B. P. To the east of the trace, younger aggradational deposits dated at c. 10 500 yr B. P. have inundated and buried the downthrown older terrace surfaces. Vertical offsets and rates of offset were calculated for the Ohakean terrace surfaces along this section of the Wellington Fault. Scarp heights range from 19 m to 10 m. Minimum rates of vertical offset vary from 1.23 mm/yr to 0.76 mm/yr.
TL;DR: The middle Cretaceous (Motuan) Mangapokia Formation near Te Awaiti, southeast North Island, New Zealand, is a complexly deformed, weakly metamorphosed, submarine fan turbidite sequence that represents the youngest part of the Torlesse accretionary wedge as discussed by the authors.
Abstract: The middle Cretaceous (Motuan) Mangapokia Formation near Te Awaiti, southeast North Island, New Zealand, is a complexly deformed, weakly metamorphosed, submarine fan turbidite sequence that represents the youngest part of the Torlesse accretionary wedge. Two fold events, several episodes of shear fractures, and local development of melange fabric were associated with Cretaceous subduction and accretion. F1 folds occur within melange fragments and predate regional stratal disruption and melange formation. The melange fragments were rotated during formation of melange. Isoclinal to tight, predominantly asymmetric, overturned, mesoscopic F2 folds developed during accretion but after pervasive stratal disruption and melange formation. Fold axes trend northeast-southwest and plunge variably to the northeast or southwest. Two later fold events are post-Torlesse, probably late Cenozoic responses to Miocene-Recent subduction at the Hikurangi Margin. Mesoscopic and macroscopic, upright, predomin-antly clo...
TL;DR: In the absence of a fringing reef the Pacific Harbour coast of southern Viti Levu has evolved primarily under the influence of waves generated by the prevailing southeasterly trade winds as discussed by the authors.
Abstract: In the absence of a fringing reef the Pacific Harbour coast of southern Viti Levu has evolved primarily under the influence of waves generated by the prevailing southeasterly trade winds. By c. 3800 yr B.P., a coastal embayment had been partially enclosed by the formation of a gravel storm beach ridge. Subsequent barrier progradation followed only when longshore sediment was transported into the area from the developing Navua/Deuba Delta to the east, resulting in the accretion of a sandy beach ridge sequence. The estuary/lagoon system enclosed by the barrier was converted into a freshwater swamp in which up to 4 m of peat accumulated. Evidence indicates that Holocene sea levels in the area are unlikely to have exceeded c. 0.6 m above the present level, which is consistent with most evidence from elsewhere in Viti Levu. However, hydro-isostatic processes may explain the apparent inconsistency between the attainment of modern sea level at c. 4000 yr B.P. in the Pacific Harbour and Labau areas of so...
TL;DR: The Nukumaru Fault traces typically consist of discontinuous, subparallel scarps, up to 1.5 km long and up to several metres high, consistent with a component of dextral horizontal movement as mentioned in this paper.
Abstract: Wave-cut platforms of late Quaternary marine terraces between Hawera and Marton in Wanganui Basin are vertically displaced by several faults. The faults are probably high-angle normal, and strike generally northeast. Of the four faults that are known to displace surfaces of different age, two show increasing displacements with increasing age, and two show no change with age. Fault traces typically consist of discontinuous, subparallel scarps, up to 1.5 km long and up to several metres high. Some scarps display a left stepping, en echelon pattern, consistent with a component of dextral horizontal movement, though horizontal displacement of terrace risers is not evident. Average rates of vertical movement on the faults vary between 0.02 and 0.2 mm/yr, much less than rates of vertical and horizontal movement documented for many other faults in New Zealand. One fault, the Nukumaru Fault, shows a constant rate of vertical movement averaging 0.07 mm/yr for the last 2.2 million years. The faults are tentatively interpreted as bending-moment faults, associated with folding.
TL;DR: In this article, the early Miocene Gore Lignite Measures were exposed at Landslip Hill and measured in 113 horizontal log moulds, showing a preferred north-south alignment, parallel with the n-southpaleocurrent direction indicated by three trough cross-stratification axes.
Abstract: Silcreteexposed at Landslip Hill forms part of the Early Miocene Gore Lignite Measures. The silcrete, well known for its diverse fossil megaflora of leaves and cones, is up to 8 m thick and consists of silica-cemented alluvial channel and channel-margin deposits. Five sedimentary facies are differentiated: quartz pebble conglomerate; trough cross-stratified coarse grained sandstone; planar laminated fine and medium grained sandstone; mottled sandstone pervaded by root structures; and mud-clast conglomerate. Measurements of 113 horizontal log moulds show a preferred north-south alignment, parallel with the north-southpaleocurrent direction indicated by three trough cross-stratification axes. Field and petrological observations indicate cementation started soon after deposition. Secondary silica consists of spherulitic and granular chalcedony, microcrystalline quartz, and syntaxial quartz overgrowths. Although sandstone in places shows intergranular “pressure solution” textures, the plant fossils a...
TL;DR: In the Marlborough Schist and Permian-Triassic Pelorus Group as discussed by the authors, Mesozoic rocks were thrust over an Oligocene sedimentary sequence, which is now exposed as erosional inliers.
Abstract: In the Marlborough Sounds area near Picton. multiple deformation during the Miocene produced early (D1 north-northeast-trending folds, and north- and east-striking thrusts. Later folding (D2 about east-west axes led to the formation of basin and dome interference structures. During D1, Mesozoic rocks of the Marlborough Schist and Permian-Triassic Pelorus Group were thrust over an Oligocene sedimentary sequence. which is now exposed as erosional inliers. Thrust transport from west to east is inferred from fibre striations. Striation-derived M-axis data, calcite grain fabric studies, and the maximwn shortening direction of north-northeast-trending folds suggest that thrusting developed in association with approximate west-east compression. Thrust motion resulted in progressive late Cenozoic stacking of the basement sequence in this area, with considerable shortening and thickening of the Marlborough Sounds region.
Abstract: Coastal sections between Whiritoa and Whangamata, eastern Coromandel, New Zealand, have exposed a Late Miocene volcanic and pyroclastic sequence which has been interpreted using a caldera facies model. The present-day coastline transects the middle of the caldera, which has been named here the Tunaiti caldera. The sequence comprises: (1) precaldera andesite and dacite lavas; (2) caldera-forming dacitic eruptions and interbedded plinian tuffs; (3) a variety of tilted and deformed moat deposits including extrusive and intrusive preresurgent rhyolitic volcanics, diatomaceous lake sediments, and postcollapse mesobreccias; (4) intracalderaresurgent biotite rhyolite domes and flows; (5) postcaldera dikes and lavas of hornblende rhyolite; and terminated with (6) postcaldera dacite lavas. There is a trend in composition with time from early andesites and dacites through to voluminous intracaldera rhyolites, which reverted to less silicic, small volume ring-fracture rhyolites and dacites. Incompatible ele...
TL;DR: In this paper, the authors identify three petrologically distinct granitoids, namely, Steele Granodiorite, Blackwater Granite and Buckland Granite, which were intruded in that order into the Charleston Metamorphic Group and Greenland Group in mid-Cretaceous times.
Abstract: Mapping in the central Paparoa Range, West Coast of the South Island, New Zealand, has led to the recognition of three petrologically distinct granitoids. These are Steele Granodiorite, Blackwater Granite, and Buckland Granite, which were intruded in that order into the Charleston Metamorphic Group and Greenland Group in mid-Cretaceous times. Mineralogy, whole-rock chemistry, and Sr isotopic composition suggest that all three granitoids belong to the intermediate I/S-type Rahu Suite. Rb-Sr whole-rock geochronology provides an intrusive age of 116 ± 6 Ma for Buckland Granite, but is unable to establish the intrusive age of the other two granitoids. Significant1y younger muscovite ages (103–112 Ma) and biotite ages (92–99 Ma) indicate immediate postintrusive uplift of all three granitoids in the order of 0.5-1.0 mm/a. Fieldevidence suggests that Buckland Granite was intruded in several batches. The wide range of initial 87Sr/86Sr (0.7058–0.7094) indicates at least two isotopically different source ...