Zealand Geosyncline Research Articles

Magnetic anomalies across Campbell Plateau, New Zealand

Magnetic measurements over the Campbell Plateau, New Zealand, show the existence of a linear positive anomaly belt which extends for 900 km along an approximately east-west trend. This anomaly belt is considered to be a continuation of the Stokes Magnetic Anomaly occurring through New Zealand and associated with rocks of the New Zealand Geosyncline. If this is so, a transcurrent fault with a dextral displacement of about 330 km and aligned in a northeast-southwest direction must occur between the eastern end of the Stokes Magnetic Anomaly and the western end of the anomaly belt across Campbell Plateau.

Interpretation of magnetic anomalies across the Campbell Plateau, south of New Zealand

Magnetic anomalies over the Campbell Plateau show up a linear belt of positive anomalies extending for 900 km with an approximate east?west trend. This belt is identified as part of the Stokes Magnetic Anomaly System which extends throughout New Zealand and is associated with rocks of the New Zealand Geosyncline. The system defines a trans-current fault with a dextral displacement of 330 km which can be traced from the SW tip of the Campbell Plateau to the Bounty Trough in the north. Restoration of this Campbell Fault requires the Bounty Trough to be a rift feature, probably associated with Indian-Pacific plates' movements during the Miocene or Oligocene. The extension of this boundary may have been a subduction zone running from the NE tip of the Campbell Plateau past the North Cape of New Zealand to the Norfolk Ridge, along what is now the southern margin of the South Fiji Basin.

The Otago schist megaculmination: Its possible origins and tectonic significance in the Rangitata orogen of New Zealand

In South Island, New Zealand, the Otago schist, 30,000 square km in extent, consists mainly of greenschist facies quartzo-feldspathic metagreywacke and meta-argillite with minor metavolcanics and metacherts. Before metamorphism the sediments were probably Carboniferous to Jurassic; the flanking, steeply dipping greywackes are Triassic in the northeast and southeast, and Permian in the west and southwest. Regional metamorphism culminating in the Late Jurassic was accompanied by pervasive deformation generating a variety of interrelated folds on all scales. The scarcity of distinctive reference units makes recognition of macroscopic structures difficult, and much progress has depended on observations of vergence of mesoscopic folds interpreted as defining macroscopic folds having axial plane separation of between 2 km and 6 km. At least two phases of synmetamorphic deformation are distinguishable locally, but regionally have an overlapping multiphase relationship. The regional schistosity structure is an irregular flat-crested antiform trending S and SE. The internal megascopic structure defined by the mesoscopic folds, appears to consist of a stack of nappe-folds facing east and northeast, which pass into reclining isoclinal folds in the west, southwest and north-east, and is interpreted to be a megaculmination. Mineral and textural metamorphic zones were developed during deformation, and a relatively simple regional pattern established at a late stage by continuing recrystallisation. The Otago schist originated in a complex sequence of Paleozoic—Mesozoic plate interactions near the southwest Pacific margin of Gondwanaland. It included part of a volcaniclastic frontal arc-basin assemblage (Murihiku and Caples Terranes) lying north or northeast of an older crystalline foreland, and a quartzo-feldspathic assemblage of plutonic-metamorphic provenance lying further to the northeast (Torlesse Terrane). Parts of these terranes underwent mainly greenschist facies metamorphism during Late Jurassic subduction-collision to form the Haast Schist Terrane of which the Otago schist is a major part. The earliest Torlesse sediments are thought to have prograded as a vast fan complex onto oceanic crust from the southwesterly crystalline foreland in the Carboniferous, then in the Permian were separated from their source by a spreading zone which thereafter isolated them from the sedimentary province of the newly developing arc system. Tectonic recycling of these sediments at a Permian to Jurassic oceanic subduction zone is considered to have developed the westward progradation features and the products of limited vulcanism found in the present Torlesse Terrane. The New Zealand Geosyncline appears to have consisted of a spreading zone between two inwardly facing convergent zones, one flanked by a foreland to the southwest, the other wholly oceanic. The metamorphic climax of the Rangitata Orogeny was the result of the medial spreading zone passing into the westerly subduction zone, so permitting the convergent zones to collide, with the Torlesse sediments caught between them. The mantle system driving the spreading zone appears to have continued to function, and soon after the collisional climax caused Late Jurassic—Cretaceous rifting of the sialic edge of Gondwanaland, igneous activity, differential shear of the New Zealand region, and initiation of the Alpine Fault. It subsequently commenced sea-floor spreading in the Tasman Sea, and later in the southwest Pacific Ocean.

Mesozoic tectonics, North Island, New Zealand

The Kawhia synclinorium along the western margin of North Island, New Zealand, is a relatively simple open structure with a subvertical to steeply east-dipping axial surface and contains a Triassic-Jurassic shelf or arc-trench gap sequence. It is bounded to the east by a narrow zone of serpentinite and ultramafic rock corresponding to the magnetic Junction anomaly. In the Waipapa and Torlesse terranes east of the Junction anomaly, three deformation phases can be recognized: (1) formation of melange and imbrication of strata, with fold axes trending across the now-dominant basement grain and fold vergence predominantly toward the south; (2) strongly asymmetric folding and imbrication and further melange formation on horizontal axes parallel to the present structural grain; folds verge to the east, and beds in the axial ranges have rotated to vertical and overturned attitudes; and (3) open folding on steeply plunging axes. Phases 1 and 2 are part of the Early Cretaceous Rangitata orogeny or predate it. There is no evidence yet for the age of phase 3 structures. It is hypothesized that the rocks of the Waipapa and Torlesse terranes were imbricated and accreted in a suture zone east of the Junction anomaly. Phase 1 structures were formed oblique to the trend of the New Zealand geosyncline because of a strike-slip component of movement transmitted to the sedimentary column only before and during early decollement. Age patterns in the Torlesse and Waipapa terranes indicate that simultaneously with accretion the clastic apron prograded from south to north.

Paleogeographic and paleotectonic models for the New Zealand geosyncline in eastern Gondwanaland: Discussion and reply

Paleogeographic and paleotectonic models for the New Zealand geosyncline in eastern Gondwanaland: Discussion and reply

Paleogeographic and paleotectonic models for the New Zealand geosyncline in eastern Gondwanaland: Discussion and reply

Paleogeographic and paleotectonic models for the New Zealand geosyncline in eastern Gondwanaland: Discussion and reply

Multistage ore genesis in the New Zealand geosyncline a history of post-metamorphic lode emplacement

Epigenetic gold-quartz and scheelite-quartz lodes in Otago and other parts of the New Zealand geosyncline crosscut quartzofeldspathic and metavolcanic rocks of the pumpellyite-actinolite and greenschist facies. The lodes, which commonly strike north-west, are spatially associated with a 30 km wide belt of metavolcanic schists, with associated piemontite and sideritic schists, which parallels the axis of the geosyncline. Oxygen isotope and uncorrected fluid inclusion data for Glenorchy and Bendigo material give the range 230–350°C for lode formation, over 100°C lower than the metamorphic temperature of the country rock, and this indicates that substantial uplift and unloading had occurred prior to the hydrothermal emplacement of the lodes. A model is developed to account for the origin of the lode mineralization. A recent oxygen isotope study of the Glenorchy lodes suggested that the ore-bearing fluid was derived from rocks at depth over 150°C hotter than the lode formation temperature, and this is consistent with an origin by dehydration reactions at the greenschist to amphibolite transition. Hydraulic fracturing, induced by rapid uplift and unloading of the pile, allowed fluid migration to higher crustal levels where ore-deposition occurred. The spatial association of the lodes with the metavolcanic suite suggests that metals were derived by trace-leaching from the volcanic suite at the water source, or during migration, whilst tungsten may have been leached from associated manganiferous metasediments which commonly contain high anomolous concentrations of tungsten. Ore deposition occurred in response to lowering of temperature and pressure during fluid migration, and wall-rock interactions, particularly where lower oxygen fugacities were imposed by wall-rocks on the hydrothermal phase.

Magnetic Anomalies, Bathymetry and the Tectonic Evolution of the South Pacific since the Late Cretaceous

Summary Bathymetric and magnetic anomaly data indicate that the South Pacific Ocean floor between New Zealand and Antarctica formed since late Cretaceous time by sea-floor spreading at the Pacific-Antarctic Rise and the southern portion of the East Pacific Rise. Following the initial breaking apart of the Campbell plateau from Antarctica, the Pacific plate moved away from the Antarctic plate at a fast rate of about 90 mm/yr. Between approximately 60 and 40 My ago, (anomalies 25 and 13) after spreading within the Tasman Sea had stopped, and during which Australia began to drift away from Antarctica, the direction of relative plate motion in the South Pacific changed and the average rate decreased to 40 mm/yr. During the re-alignment inany of the minor transform faults disappeared and the two that form the Eltanin fracture zone system changed in direction, offset and spacing in a predictable way. The pole of rotation moved nearer to the region. The topography of the sea-floor created during this interval was rough, presumably because of the slow rate of spreading. Since this time, the pole of rotation has been moving farther away and the spreading rate has been increasing. The present relative velocity of the plates ranges from about 60 mm/yr in the south-west to about 100 mm/yr in the north-east. Using reconstructions of Australia and Antarctica and preliminary evidence of the sea-floor spreading history of the Tasman Sea, we reconstructed the surrounding continental fragments at various times since the late Cretaceous. Bending of the ' New Zealand Geosyncline ' appears to have occurred entirely after about 40 My ago, and at the same time the southern portion of the Tasman Sea floor probably formed by slow spreading near the present Macquarie Rise, between the Pacific and Indian plates. Relative motion between East and West Antarctica of about 500 km seems to be required between about 80 and 40 My ago.

An association of the Late Triassic bivalvesHalobia, Manticula, andMonotisin the Torlesse rocks of North Canterbury

Abstract Patches containing Halobia sp. cf. hochstetteri and Manticula problematica or Monotis richmondiana occur within a 100-mm-thick zone in a limestone block in the Esk Head Melange. Lithological and stratigraphic information suggest that the species lived virtually contemporaneously, and that the mixture of patches is probably secondary and due to penecontemporaneous slumping. Evidence for overlap of the range-zones of the species should be searched for in the Hokonui and Alpine Assemblages of the New Zealand Geosyncline.

Paleogeographic and Paleotectonic Models for the New Zealand Geosyncline in Eastern Gondwanaland

New Zealand geosyncline stratigraphy accords with a paleogeographic model whereby late Paleozoic–Mesozoic sedimentation occurred between continental forelands. Such a model fits into a reassembly of eastern Gondwanaland and supports the hypothesis that Late Jurassic–Early Cretaceous tectonism in this region was related to relative motion of the Australian continent.

Geology of the pre-Cenozoic basement of the Taranaki-Cook Strait-Westland area, New Zealand, based on recent drillhole data

Abstract Nine wells drilled in the Taranaki-Cook Strait-Westland area intersected pre-Cenozoic basement or basement-derived material. Petrological examination of cores and cuttings from these wells suggests that the Rotoroa Igneous Complex, the Separation Point Batholith, the NW Nelson Paleozoic metamorphic rocks, and possibly the Karamea Batholith extend from the South Island in a N-NNE direction beneath the Cenozoic cover. The trend of these rocks parallels the western margin of the New Zealand Geosyncline, supporting the suggestion that they constituted a foreland region during the development of the Geosyncline in the North Island, and were an important source of clastic material within it.

Multiphase deformation and its relationship to metamorphic crystallisation at Haast River, South Westland, New Zealand

Abstract The temporal and spatial relationships between multiphase folding, faulting, dike swarm intrusion, and metamorphic crystallisation are discussed for a suite of meta-morphic rocks from the Haast River area (S87, S98), South Westland. Metamorphic reconstitution is sufficiently far advanced in the map area that most structures developed contemporaneous with sedimentation in the New Zealand Geosyncline are now obliterated. The oldest recognisable mesoscopic structures, representing the initiation of Rangitata Orogenic movements in this area, are tight mesoscopic, isoclinal F1 folds. Macroscopic folds of the same generation are considered to be recumbent isoclinal folds or nappes. In localised areas F1 folds are refolded by a second synmetamorphic folding phase, F2. The hinge zone of a macroscopic, isoclinal, F2 antiformal fold has been located and mapped out in the eastern sector of the map area. Although metamorphic temperatures were maintained at high values during F1 and especially F2 deformation,...

Stratigraphy, lithology, structure, and metamorphism of Permian, Triassic, and Tertiary rocks between the Mararoa River and Mount Snowdon, western Southland, New Zealand

Abstract An area in western Southland underlain by Permian, Triassic, and Tertiary rocks is mapped and described geologically. New stratigraphic, lithologic, and petrographic data are presented, and several new mapping units are proposed. These latter include Upukerora Formation, a predominantly coarse-grained, volcanogenic sedimentary unit which occurs at the base of the Bryneira Group; Key Summit Volcanic Sandstone a characteristically massive green rock which underlies large portions of Bryneira Group outcrop north of the present area ; Snowdon Formation, a resistant conglomeratic and tuffaceous unit belonging to the Murihiku Supergroup; and the Annick and Waiau groups, Tertiary sediments of the Te Anau Basin. Several previously defined units are also mapped, described and in some cases, revised: Red Mountain, Livingstone, Howden, Anneal, Tapara, Winton, and Countess. Bryneira and Murihiku rocks comprise sparsely fossiliferous, richly volcanogenic geosynclinal strata which accumulated adjacent to an island arc. Red Mountain-Livingstone rocks are interpreted to be ancient oceanic crust and upper mantle upon which Bryneira sediments were deposited, the latter possibly filling in a frontal arc basin or inactive oceanic trench. The Snowdon Formation appears to overlie, possibly with mild unconformity, Bryneira strata, and was probably deposited in a frontal arc basin (arc-trench gap). Structurally, the area comprises the southern end of the Key Summit Regional Syncline. Red Mountain-Livingstone-Bryneira rocks lie entirely within the nearvertical to overturned east limb of the regional syncline; Red Mountain-Livingstone rocks comprise a tectonic melange throughout most of the area mapped. Snowdon Formation rocks lie near, or within, the axial portion of the syncline A newly recognised strike-slip fault, the Mararoa Fault, truncates the southern extent of Bryneira outcrop. This fault strikes northeasterly and has dextral offset probably exceeding 2–3 km. The Hollyford and Upukerora fault systems are shown to extend south from the Eglinton Valley area (Grindley 1958) into the present area. Lower-grade metamorphism has extensively altered mineralogy and microscopic texture of Permian and Triassic rocks. In addition some Tertiary strata of the Te Anau Basin contain authigenic zeolites. Authigenic hydrous Ca-Al-silicate minerals within Permian and Triassic rocks include lawsonite, laumontite, prehnite, pumpellyite and epidote. Areas within and transitional to five metamorphic zones are mapped on the basis of these minerals, and the zones are correlated with mineral facies of Coombs (1968). The mineral lawsonite is especially abundant and is taken to indicate moderately high pressure-low temperature conditions of recrystallisation. Metamorphism probably occurred during deep in-folding and tectonic pinching of the western margin of the New Zealand Geosyncline during the late Jurassic-early Cretaceous Rangitata Orogeny.

Tungsten concentrations in plants and soils as a means of detecting scheelite-bearing ore-bodies in New Zealand

Plant and soil sampling was carried out across scheelite-bearing ore-bodies at six areas of different geological, vegetational, climatic and topographical environments in the South Island of New Zealand. The feasibility of using the concentration of tungsten in plants and soils to locate the scheelite was investigated for all the areas. These regions may be classified into two main groups according to their lithology and vegetation. The first group, comprising Clenorchy, Paradise, Macrae's Flat and Top Valley, is underlain by the schists of the New Zealand geosyncline, has a low rainfall and a predominantly shallow-rooted vegetation such as tussock grass and bracken. In these areas soil sampling was generally more effective than plant sampling, although the latter sometimes gave sharper anomalies. The areas of the second group, Barrytown and Canaan, are both underlain by predominantly granitic material, have a high rainfall, rugged topography and a predominantly beech forest vegetation. In these areas, although soil sampling was in general satisfactory, tree-trunk sampling was found to have certain advantages in locating extensions of known scheelite-bearing reefs.

Fossils in mélanges

So-called ‘tectonic’ melanges in many parts of the world seem to contain a disproportionately high number of fossils relative to the enclosing rocks. This is particularly true of melanges in ‘greywacke type’ terrains, in particular the Esk Head Melange1 in the otherwise sparsely fossiliferous Torlesse Zone of the Alpine Assemblage2 in the New Zealand Geosyncline, the melange belts of the Franciscan Assemblage of California (M. C. Blake, jun., personal communication), and the Liptrap Formation of southern Victoria, Australia. In addition, the fossils contained in melange belts commonly contain shallow water forms, and in extreme cases even terrestrial fossils (D. L. Jones, personal communication).

Suggestions towards a high-level nomenclature for New Zealand rocks

Abstract Rangitata Sequence is suggested as a comprehensive term for “the rocks of the New Zealand Geosyncline”. It is subdivided into the Hokonui and Alpine Assemblages, the former including the Murihiku Supergroup, and the latter the Torlesse (greywacke) Zone and Haast Schist Zone. Pre-Rangitata rocks are referred to the Tuhua Sequence and post-Rangitata rocks to the Kaikoura Sequence. These terms are convenient labels for the major elements of the geologic column in New Zealand; as they are not members of the strict lithostratigraphic hierarchy, they allow great flexibility and avoid the need for premature lithostratigraphic formalisation. The same terms may also be used with Geosyncline, Orogeny, and Orogenic Belt; they thus introduce great economy into the major tectonostratigraphic nomenclature of New Zealand.

Alpine-type Serpentinites from the Auckland province—I. The Wairere Serpentinite

Abstract The Wairere Serpentinite, exposed over 650 m along the trace of the Waipa Fault near Piopio, lies close to the boundary of the marginal and shelf facies of the New Zealand Geosyncline and hence close to Hatherton and Sibson's magnetic junction anomaly. The body shows faulted contacts against Hokonui, Te KuitI, Mahoenui, and Mokau rocks. Emplacement is believed to have occurred as a diapiric process, in response to a compressive stress system, penecontemporaneously with deposition of the Otorohanga Limestone (Lower Waitakian). The limestone suffered folding and formation of pinch and swell structures, local brecciation and recrystallisation, slickensiding, and jointing. Aragonite is widespread both at contacts and on shear planes throughout the serpentinite. Movement continued well into the Miocene with brecciation of Mokau sediments.

Geotectonics and the New Zealand Geosyncline

ONE interpretation of the New Zealand Geosyncline (Carboniferous-Jurassic) envisages a pair of elongate north or northwest trending sedimentary realms—the Hokonui realm (facies belt) lying to the northeast of a granitoid foreland and the Torlesse realm further to the northeast facing the Pacific1,2. The Hokonui realm is characterized by moderately fossiliferous, structurally simple marine and subsidiary non-marine sediments. Andesitic volcanics and volcanic derived elastics are typical; granitoid foreland derived material is subsidiary and concentrated in near-shore western sections. The Torlesse realm is said to be characterized by deep water, “redeposited” or turbidite sediments. It is characterized by an acid plutonic detrital suite which is said to be derived from the western granitic foreland and transported across the Hokonui realm either in submarine canyons or by some other “by-pass” mechanism.

Structure and Petroleum Potential of Eastern Chatham Rise, New Zealand

Paleozoic-Mesozoic metamorphic rocks and Mesozoic to Tertiary sedimentary sequences exposed on the Chatham Islands have been correlated with sequences shown by marine seismic profiling to underlie the eastern Chatham Rise. The offshore sedimentary sequence appears to be more complete than that exposed onshore. Provinces of igneous intrusion have been delineated by magnetic profiling. Characteristic horst and graben basement topography of the eastern Chatham Rise is consistent with regional arching and flexural fracturing. The grabens contain thickened Mesozoic-Tertiary accumulations, whereas only thin Tertiary deposits may drape the horsts. Reinterpretation of the geologic history of the eastern Chatham Rise leads to a new paleogeographic reconstruction of the New Zealand region. In this new interpretation, the New Zealand geosyncline is considered to have existed between foreland blocks partly comprising the Campbell Plateau and Lord Howe Rise. Late in Mesozoic time, the framework of crustal blocks became fragmented, and during northward drift a dismembered eastern block commenced relative clockwise rotation. The triangular oceanic basin so developed assumed the character of a sphenochasm. The petroleum source, reservoir, and trap potentials of the presumed prospective offshore sections are assessed by comparison with sequences of similar age in the Chatham Islands and New Zealand. The petroleum potential of the area relates to the development of source-bed and reservoir rocks principally in sedimentary-drape and/or combination traps around basement-horst structures.

The shoshonitic association in the upper Mesozoic of Tasmania

Abstract During the Late Mesozoic, igneous activity in Tasmania produced a number of small intrusive bodies and swarms of dykes. Typical examples of these rocks are found on the West Coast and around Cape Portland and Cygnet. The rocks belong to a shoshonitic association and they form part of a more extensive petrographic province that extends from Tasmania into eastern Australia. It is proposed that the magmas from which these rocks were derived evolved at depth beneath the stabilised western margin of the New Zealand Geosyncline. The composition of this magma which formed in a relatively stable environment, contrasts with the more basic magma that erupted during the period of crustal tension that accompanied the break up of the Australian segment of Gondwanaland during the past 200 m.y.