Fault-angle Depression Research Articles

Stratigraphy, provenance and localisation of the titanomagnetite placer at Waikato North Head, South Auckland, New Zealand

The sequence of coastal and river sands of Pleistocene to Holocene age at the north head of the Waikato River is ~80-m thick; the sands are located in a fault-angle depression at the southern end of the Awhitu Peninsula, a 40-km-long coastal sand barrier. The sequence at Waikato North Head (WNH) consists of three main formations: Awhitu Sands, Hood Sands and Mitiwai Sands. The Waiuku Black Sand member of the Hood Sands and the Entrican Sand member of the Mitiwai Sands contain titanomagnetite-rich dune sands, which are currently mined by New Zealand Steel and constitute a giant placer deposit that has a total resource of ~90 Mt Fe. A tephra at the top of the Awhitu Sands is correlated with the ~1000 ka Waiuku (Potaka) tephra. The Mitiwai Sands overlie the 1.85 ka Taupo Pumice. Comparison of electron probe microanalyses (EPMA) of titanomagnetites in heavy mineral separates of surface and drill-hole samples indicated that the bulk of the titanomagnetite in the Waiuku Black sand and the Entrican Sand is derived from andesitic rocks of the Taranaki Volcanoes 220 km to the south. The Waiuku Black Sand may correlate with an influx of andesitic clasts and mafic minerals in the cover beds of the ~400 ka Ararata Terrace in south Taranaki. There is also a contribution of titanomagnetite and minor ilmenite from the ignimbrites of the Taupo Volcanic Zone (TVZ), particularly in the Lower Hood and Entrican sands. Automated mineralogy data collected on selected sand samples contain silicate and resistate minerals that indicate other potential sources in addition to the Taranaki andesites and TVZ ignimbrites. Minor olivine was likely derived from the late Pleistocene basalts of the South Auckland volcanic field, whereas almandine and epidote were likely sourced from metasedimentary rocks of the Murihiku and Waipapa terranes. The formation of the giant placer at WNH was a multistage process involving (1) a supply of titanomagnetite-bearing sand eroded from the late Pleistocene–Holocene andesites of the Taranaki volcanoes that was transported northwards along the coast by the prevailing longshore drift; (2) concentration of titanomagnetite by wave action on beach faces and collection in a coastal embayment on the northern side of a headland of basement rocks at Port Waikato; (3) further concentration by wind action into dune sands during interglacial low sea levels; and (4) preservation by coeval subsidence in a fault-angle depression on the down-thrown north side of the Waikato Fault.

The Reporoa Caldera, Taupo Volcanic Zone: source of the Kaingaroa Ignimbrites

The Reporoa Caldera occupies the northern end of the Reporoa Depression, previously described as a tectonic fault-angle depression. Earlier confirmation of the topographic basin as a caldera had been hindered by the lack of an associated young pyroclastic flow deposit of large enough volume to have caused caldera collapse. New exposures on the eastern margin of the Reporoa basin reveal thick lithic lag breccias (>30 m) interbedded within the 0.24 Ma Kaingaroa Ignimbrites. These ignimbrites were previously attributed to the adjacent Okataina Volcanic Centre. Lag breccia thicknesses and maximum clast sizes decrease rapidly outward from the caldera rim, and discrete breccias are absent from ignimbrite sections more than 3 km from the rim. The lithic lag breccias, together with structural and geophysical evidence, confirm Reporoa Caldera as the source of the c. 100 km3 Kaingaroa Ignimbrites, adding another major rhyolitic volcanic centre to the seven previously recognized in the Taupo Volcanic Zone. Other, older, calderas may also be present in the Reporoa Depression.

The stratigraphy and structure of the Mt Bruce area, northern Wairarapa, North Island, New Zealand

Abstract A sequence of terrestrial and estuarine to upper bathyal sediments of the Mangaoranga Formation accumulated in the Mt Bruce sub-basin during transgression over Torlesse Supergroup rocks during late Miocene (Tongaporutuan) time. The Moles Mudstone is defined as a new member ofthe Mangaoranga Formation; it consists of mudstone, lignite and conglomerate deposited in estuarine conditions. Conglomerate overlying the Moles Mudstone accumulated locally in a fault-angle depression, establishing an alluvial fan adjacent to a coastline, with its more distal parts deposited offshore. Subsequent deposition of progressively finer grained sediments (from sands and silts to muds) records continuing basinal subsidence and a marine transgression across the Mt Bruce area. Upper-bathyal conditions were widespread by late Tongaporutuan time. The folded Miocene sediments are preserved as infaulted outliers within a zone cif dextral shear bounded by the Wellington and Wairarapa Faults. They are unconformably overlain by aggradational river gravels of Pleistocene age.

Basement structure and sediment thickness beneath the continental shelf of the Hauraki Gulf and offshore Coromandel region, New Zealand

Abstract The basement structure and sedimentary history of the continental shelf east of the northern section of North Island, New Zealand, is interpreted from geophysical data collected by petroleum companies. Interpretation of magnetic data shows the basement to be composed of both igneous and nonigneous rocks in the vicinity of the Coromandel Peninsula and Great Barrier Island; further north the basement is almost entirely nonigneous. From seismic reflection data, basement in the region can be seen to have undergone extension, being faulted into a series of fault-angle depressions and grabens. Sea-floor expression indicating continued development of the fault-angle depressions is found locally, especially in the Tauranga Harbour — Cuvier Island region. Outside the Hauraki Gulf, the sedimentary section overlying basement is separated into two units by an unconformity of unknown age. The lower unit is probably late Tertiary — Quaternary sediments and the upper unit is probably late Quaternary sediments. Within the Hauraki Gulf, the poor quality of seismic reflection data precludes analysis of the sedimentary section.

Análisis de la carta geomorfológica de la cuenca del Mapocho

The Mapocho basin (Central de Chile) is divided into two morphotectonic styles by the Mapocho fracture. ln the northern section, of the Santiago depression an intense monoclinal warping anda deep alveolar excavation evidence important uplift of the western border. ln the southern section, the asymetry is stronger than the former one and inverse, giving a fault angle depression. This fracturation of the depression's bottom has affected both the conditions of sedimentation and the drainage patterns, causing antecedence phenomena and antagonistic effects between tectodynamics and external morphogenesis. Concerning present tectonics and seismicity, the presence both of different tectonic compartments and depositional landforms in the depression, is possibly more important than the faults themselves in the explanation of the distribution of seismic intensities. ln the northern section of the depression there is a characteristic combination between alluvial cones and "glacis" (bahadas). Moreover, marshy terraces correspond to bad drainage conditions. ln the southern section, in exchange, the central compartments are occupied by proximal cones and dista1 terraces. Slopes are presented as slope systems anda new classification supported on the structure and the external dynamics is used. At the same time, the concept of dissection balance allows relate slopes and talweg dynamics. Therefore, it can be known if the more important morphogenetic processes are present or ancient. So, the fluvial landforms at the depression's bottom are inherited. In the present conditions it is unlikely the transport of coarse sediments from the high mountain toward the depression. Moreover, the torrentialand sheet wash morphologic systems are also inherited. Present through put of material from active slopes toward beds and depressions is possible only during heavy storms of rain y years.

Gravity models across the Transantarctic Mountain Front near New Harbour, McMurdo Sound, Antarctica

Abstract A Bouguer gravity map for the Transantarctic Mountains and McMurdo Sound, from Granite Harbour south to the Dailey Islands, reveals a short wavelength gravity anomaly near New Harbour, superimposed on the regional east-west gravity gradient. Gravity models of this anomaly associate it with baseme'nt rocks dipping eastwards just offshore beneath relatively lower density Cenozoic sediment infilling McMurdo Sound. Off the Bowers Piedmont Glacier, the dipping basement is interpreted as the eastern flank of a fault ridge striking subparallel to the coastline. This ridge and the adjacent fault-angle depressions are considered to be products of fault block rotation and collapse contemporaneous with subsidence of the Ross Sea and the rise of the Transantarctic Mountains.

Cenozoic Basin Development in Hispaniola: ABSTRACT

Four distinct generations of Cenozoic basins have developed in Hispaniola (Haiti and Dominican Republic) as a result of collisional or strikeslip interactions between the North America and Caribbean plates. First generation basins formed when the north-facing Hispaniola arc collided with the Bahama platform in the middle Eocene; because of large post-Eocene vertical movements, these basins are preserved locally in widely separated areas but contain several kilometers of arc and ophiolite-derived clastic marine sediments, probably deposited in thrust-loaded, flexure-type basins. Second generation basins, of which only one is exposed at the surface, formed during west-northwesterly strike-slip displacement of southern Cuba and northern Hispaniola relative to central Hispani la during the middle to late Oligocene; deposition occurred along a 5-km (3-mi) wide fault-angle depression and consisted of about 2 km (1 mi) of submarine fan deposits. Third generation basins developed during post-Oligocene convergent strike-slip displacement across a restraining bend formed in central Hispaniola; the southern 2 basins are fairly symmetrical, thrust-bounded ramp valleys, and the third is an asymmetrical fault-angle basin. Fourth generation basins are pull-aparts formed during post-Miocene divergent strike-slip motion along a fault zone across southern Hispaniola. As in other Caribbean areas, good source rocks are present in all generations of basins, but suitable reservoir rocks are scarce. Proven reservoirs are late Neogene shallow marine and fluvial sandstones in thi d generation basins. End_of_Article - Last_Page 503------------

Structure of NZMS1 N153 Eketahuna sheet district and tectonics of Northern Wairarapa, North Island, New Zealand

Abstract The Eketahuna district lies within the Axial Tectonic Belt in North Island, New Zealand and it overlies a subducting Pacific slab. It was strongly deformed during the late Cenozoic. The district contains several major NNE-trending faults, some of which have significant late Quaternary dextral displacements. The dextral Wellington Fault, in the west, is active along its entire trace in the sheet district, but other major faults are active along only parts of the traces, usually in the south. Many NNE-trending faults (synthetic faults) diverge from the major faults at c. 10-30°. Between the major NNE-trending faults, Late Miocene, Pliocene, and early Quaternary strata, thicker than suggested from gravity models, are commonly tilted to the northwest at 15-25° to form fault-angle depressions. Where the major NNEtrending faults are closely spaced, the strata between them usually dip steeply southeastwards. Most cross faults trend normal to the NNE-trending faults. Within fault blocks bounded by major NNEtrending faults, large folds vary in trend from parallel to c. 40° from the major faults. Parallelism of fault/fold trends may indicate that free slip occurred along the bounding faults whereas en echelon folds may indicate that shear strain was not entirely dissipated along these boundary faults. The orientations of drag folds adjacent to some of the major NNE-trending faults indicate that vertical components of faulting occurred along many of the major faults. On the structural contour map the following faults and folds, active during the late Cenozoic and/or Quaternary, are described and named (see Appendix 1): Cliff Road, Faulkner Road, Kaitawa, Newman, Nirvana, Rongokokako, Rongomai, and East and West Taiko (faults); Arakoa, Hinemoa, Kaiparoro, Kameru, Peep-o-day, and Rongomai (folds). The structure of the Eketahuna district has resulted from late Cenozoic dextral faulting and compressive forces, presumably caused by the underthrusting of the Pacific plate beneath the southern part of the North Island.

Seismic refraction studies in the northern Hauraki Gulf, New Zealand

Abstract The seismic velocity structure of sediments and basement rocks underlying the continental shelf between Cape Rodney and the Moko Hinau Islands has been determined by seismic refraction measurements. A penetration of some 5 km was achieved along a 50 km reversed profile using 80 explosions on the sea floor. Jurassic greywacke rocks occur at shallow depths of 100–200 m beneath most of the central part of the profile. These basement rocks are downfaulted by about 2 km to the south-west in the south-western part of the profile; the 13-km-wide fault-angle depression between the coast and the major fault is infilled by a sequence of unconsolidated (?) Quaternary sediments and consolidated, older sediments. The unconsolidated sediments, which are characterised by a seismic velocity of 1.61 km/s, reach a thickness of more than 650 m in the eastern part of the depression and are underlain by a 500–800-m-thick layer of consolidated sediments with a mean velocity of 3.3km/s. The highstanding basement rocks in the central part are dissected by a graben 5 km wide and 250 m deep, infilled with unconsolidated sediments. The volcanic Pleistocene-Pliocene Moko Hinau Islands at the north-eastern end of the profile rest upon a 430-m-thick pedestal of volcanic rocks with a velocity of 3.1–4.0 km/s. The highstanding greywacke rocks in the central part have a rather high velocity of 5.0 km/s which increases to 5.95 km/s at 2.4 km depth. It is likely that the fault-angle depression and the graben are features belonging to the northern extension of the Hauraki Rift.

Geophysical study of the Hauraki Depression, North Island, New Zealand

Abstract Geophysical data show that the southern part of the Hauraki Depression is a rift structure. In W—E cross section it is made up of a fault angle depression, a median horst, and a graben. A maximum thickness of about 3 km of Quaternary and Tertiary sediments fill the two depressions. The fault angle depression and the graben are bounded at the eastern side by major normal faults which dip about 70 ± 10° to the west, namely, the recently discovered Kerepehi Fault in the centre and the Hauraki Fault which forms the eastern boundary of the depression. A minor hinge fault (Firth of Thames Fault) probably runs along the western boundary. Transverse faults cross the depression causing horizontal offsets of the major normal faults of up to 3 km. Recent rifting of the southernmost part is indicated by active faulting and by shallow earthquake activity beneath the depression (focal depth ≤ 12 km). The chemistry of numerous hot springs implies that high temperatures (250–300°c) occur at depths of less than 5...

Gravity models of the Wairarapa region, New Zealand

Abstract Two-dimensional and three-dimensional gravity models of the Mesozoic basement topography in the Wairarapa show that the major feature is the Wairarapa Trough, aligned SSW—NNE through the area. The Trough has two arms, one north of Eketahuna and the other south of Carterton. All three features are fault-angle depressions, bounded to the west by the West Wairarapa, Wellington, and Dry River Faults, respectively, and reaching their greatest depths at these faults. A structural contour map of the Mesozoic surface in the Wairarapa shows that the basement is covered by more than 3000 m of Cenozoic material. The West Wairarapa Fault is shown to be reverse in the south, with a dip as low as 15°. The other faults are apparently near-vertical.

STRUCTURAL AND STRATIGRAPHIC EVOLUTION OF THE TARANAKI BASIN, OFFSHORE NORTH ISLAND, NEW ZEALAND

The Taranaki Basin contains the only commercial gas and condensate fields in New Zealand. Thirteen offshore wells have been drilled, three of which delineated the Maui Field while six deep tests have been drilled onshore, one of which discovered the Kapuni Field. The geology of the Taranaki Basin is synthesised into a transgressive stratigraphic framework which was modified by two tectonic phases, initial rifting and foundering, followed by wrench faulting. The basin consists of the Western Platform and Taranaki Graben Complex. The former was a relatively stable block throughout most of the Tertiary, only affected during Late Cretaceous to Eocene times by normal block faulting. The latter is bounded to the east by the Taranaki Fault Zone which was mainly active during the Miocene. To the west, the Graben Complex generally shallows across a series of en-echelon steep normal to reverse faults which often show drastic changes in throw over short distances.Upper Cretaceous coal measures were deposited in fault angle depressions. Marine sediments were deposited in western areas by Paleocene times. A regressive phase occurred during Eocene times when coal measures were deposited in southern and eastern areas. Quartzose sandstones of these coal measures are the reservoirs in the Kapuni and Maui Fields. In Late Eocene to Oligocene times, regional submergence recommenced and mainly calcareous sediments were deposited: pelagic -rich sediments in the west, neritic limestones, sandstones and mudstones in the south and east. With the development of the Taranaki Graben Complex from the Miocene onwards, sedimentary sequences consist of graben -fill mudstones and flysch, and prograding wedges comprising the continental shelf.

Stratigraphy and depositional environment of the Kyeburn Formation (Cretaceous), a wedge of coarse terrestrial sediments in Central Otago

Abstract The Cretaceous Kyeburn Formation is a 4000-m thick terrestrial sequence dominated by coarse detritus, which was deposited in a fault-angle depression. The distribution of lithofacies, direction of fining and of increasing pebble roundness, nature of clasts, imbrication, and orientation of channels, indicate derivation of the sediment from the southwest and southeast, where the sequence is today bounded by the Dansey Pass and Waihemo Faults. Breccias close to the boundary faults represent talus deposits; alluvial fan, flolodplain, and lacustrine deposits occur in successively more distal (northward) parts of the basin. The more distal part of the sequence has scattered carbonaceous material and is dominantly grey in colour; the more proximal part is largely red because of a hematite stain, possibly formed by post-depositional oxidation of mafic minerals.

Seismic measurements in Wellington harbour

Abstract Seismic surveys in Wellington Harbour (Port Nicholson) show that the greywacke basement under the harbour is an undulating erosional surface which has been depressed to a depth of about 400 m in the northwestern part. For most of the harbour the basement lies at a depth of 200 to 300 m. The depression is likely to be a fault-angle depression caused by tilting in a westerly direction. No signs of faults or fault-block structures were found in the basement under the harbour. A ridge of basement rocks with high seismic velocity crosses the harbour and crops out at Somes Island and Miramar Peninsula. It is inferred that this ridge and other morphological features in the Wellington area aligned approximately north-south are not of tectonic origin but are erosional features. The seismic velocity structure of rocks in the direct vicinity of the transcurrent Wellington Fault, aligned along the northwestern side of the harbour, is not known in detail. The crush zone of the Wellington Fault is, however, li...

THE GEOMORPHOLOGICAL DEVELOPMENT OF THE YAMAGATA BASIN

The Yamagata Basin is a fault basin belonging to the “Median Groove” which lie in a A row on the west side of the Ohu Mountains, the backbone range of Northeast Honshu. The A eastern margin of the Basin is fringed by the steep scarp of the Ohu Mountains, which are truncated by the Yamagata fault, and the western margin is bounded by a vague fault running the eastern side of the Shirataka Hill-lands (Fig. 1). Therefore, in the eastern half of the Basin floor there are three large fans, that is, Mamigasakigawa, Tachiyagawa and Mida regawa fans formed by consequent rivers flowed from the Ohu Mountains. Based on the analysis of landform and underground geology of the Basin by columnar profiles of many boring wells and the results of some physical observations (seismic, electric and gravity methods), geomorphological development of the Basin are summarized as follows.1) In the present Yamagata Basin and its environs two small pliocene basins, the Aterazawa and the Nakayama pliocene basins, were situated in parallel (Fig. 1). They are synclinal basins belonging to the folded structure of NNE-SSW trend, which is the main direction of the geologic structure in Northeast Honshu. The northern end of them are bounded by the Nishikawa-Hozawa fracture zone of NW-SE trend, which is an another direction of the geologic structure in Northeast Honshu. At the pliocene, the present outline of the Yamagata Basin has not yet formed.2) The first significant depression along the Yamagata fault had happened in the late pliocene or early pleistocene, when another fault basins of the “Median Groove” were formed. The depressed area of the Yamagata Basin was expanded to the east and the north of the Nakayama pliocene basin. The base rocks in the eastern part of the Yamagata Basin lie 400 meters or more in depth and lie deeper than those in the western part (Fig. 9). According to such a bottom profile and the piedmont topography of the Basin, it is said that the Basin has been formed as a fault-angle depression. Moreover the base rocks in the southern half of the Basin lie deeper than those in the northern half (Fig. 1 and 4). The difference of bottom depth seems to be brought by the differential movement between the northern and southern blocks being divided by the Nishikawa-Hozawa fracture zone.3) The basin deposits of the Yamagata Basin are composed of many alternative layers of gravel, sand and clay, and are classified into the lower and upper parts at the depth of about 200 meters (Fig. 9). The lower part of the basin deposits consists mostly of coarse materials containing granitic and liparitic gravels, and rarely of fine materials such as clay and silt. Accordingly it is assumed that at early stage of depression the Basin has not been covered with a lake and filled up with fluvial deposits carried from the Ohu Mountains. Apexes of fans formed in the Basin the Basin at this stage had coincided with the base of the Yamagata fault scarp.4) The upper part of the basin deposits distributed in the central and western part of the Basin is characterized by thick layers of lacustrine deposits. They are interfingered with four layers of fanglomerates (I, II, III and IV-layers from the upper) in the eastern part of the Basin, respectively (Fig. 9). Ratio of andesitic gravels contained in the fanglomerates increases suddenly at the IV-layer. It is caused by the great eruption of Zao volcanic group situated southeast of the Basin. In the midst of the deposition of the IV-layer, the Basin changed into a great lake, in which clay and silt were thickly deposited, owing to a heavy depression. By the depression the deposition of fanglomerates under the Yamagata fault scarp also become active. But the range of deposition did not expand into the Basin but retreated upward to respective upstream valley, over the fault line.

Notes on the geology of the Esk Valley, Canterbury

Abstract Two new occurrences of Tertiary rocks in the Esk Valley each consist of about 2,000 ft of steeply dipping beds (35–45°) of which the lower 500 ft consists of marine sediments and volcanic rocks and the upper 1,500 ft of non-marine greywacke gravel. A third occurrence consists only of about 100 ft of tilted greywacke gravel. These beds range in age from Dannevirke Series (Waipawan to Heretaungan) to lower Nukumaruan, and the tilted greywacke gravels are correlated with the Kowai Gravels of North Canterbury. The occurrences lie in a north-east-trending faultangle depression tilted to the south-east, which can be traced from the Waimakariri River to Grant Stream in the north-east. Undermass rocks consist of steeply dipping (50-80°) north-north-east-trending unrnetarnorphosed greywacke and argillite in which good younging directions from scour casts and graded bedding can be obtained in several places. Two outwash surfaces, of probable Blackwater and possible Avoca ages, are present in the Esk Valley. The Blackwater surface (an be traced back to the outer of two closely spaced moraines in the Nigger Stream, but the Avoca (?) surface is represented only by a high isolated tableland. The inner moraine is tentatively correlated with the Poulter Advance.

Geomorphological Study in Kawasaki Basin, MiYagi Prefecture

The writer studied three basins which belong to the catchment area of the Natori River. The surroun-ding area are the table lands of tertiary formation composed of the Takadate andesite, liparite and the marine and Paleo-lake deposits. The Kawasaki Basin of rectangular form lies between the Takadate and the Akyu table lands, and the slender Hasekura basin and the complicated Tsubonuma-Sugo basin in the latter. Near them the two tectonic lines, named Nagamachi-Rifu and Hisanohama and Iwanuma, run or the east bounding the table lands form the Sendai coastal plain, and another one of importance meaning is the Murata thrust fault in the southwestern part of the Takadate table land. After surveys in the field, the writer concluded as follows. 1) All the three basins are the tilt block basin by Jhonson (or the fault angle depression by Cotton). No fault lines have been informed by geolagist, but the topographical features prove the dislocation. The evidences in the Kawasaki basin are the presence of the terminal facets and the fans and the narrow disturbed zone of the formation along the linear margins of the basin (the two sides of it having the different formation). In the Hasekura basin, the steep and linear northwestern slope is contrary to the gentle and comlicatec southeastern slopes with the terminal facets and the geology and the surface geology differ between then (the gravel bed in the case of the former and the loam in the latter). In the Tsubonuma-Sugo basin, the dislocation is supposed form the displacement of the plane of the surrounding table lands and the steel diffs of the western margin which prolongs to the Murata Fault. 2) The Kawasaki basin and the Tsubonuma-Sugo basin are the lake basin. In the former, two group of the horizontal patches (180m and 220m above sea-level) are dominantly adhered to the hill in the basil and further its corresponding delta sediments and deposits are observed in the western part. In the latter, the thick clay deposit and peat show the fact of the lake at the cottom.