摘要:

In order to investigate the tectonic evolution of the Arunta Block and the Ngalia and Amadeus Basins, a regional north‐south seismic reflection line 420 km long from the Northern Arunta Province to the southern part of the Amadeus Basin, and an east‐west refraction profile over 400 km within the Arunta Block, were recorded by the Bureau of Mineral Resources in 1985. The most significant basement features observed in the reflection data are prominent bands of northerly dipping reflections originating from beneath the Northern Arunta Province and the Ngalia Basin at times of between 4 and 10 s. In this region, reflected energy with frequencies as high as 100 Hz is present at two‐way times of 5–6 s, implying that the rocks have high Q to depths of at least 18 km. The character of the reflections changes markedly with varying frequency, which suggests that they arise by interference phenomena, probably associated with laterally varying lamellar structures. Deep crustal features on the reflection profiles from the Central Arunta Province are less clear, although the refraction data suggest an average crustal thickness of about 55 km. Below the Southern Arunta Province there is a zone of northerly dipping reflectors at depths between 21 and 30 km, which suggests deeply buried rocks of sedimentary origin. Beneath the southern part of the Amadeus Basin, prominent bands of reflections, similar in character to those observed beneath the Southern Arunta Province, occur at times between 6 and 10 s, but have an apparent dip to the south. The reflections from the sediments of the Ngalia and Amadeus Basins are generally weak, except for those below the Missionary Plain in the northern part of the Amadeus Basin where strong, excellent‐quality reflections were obtained. Data from an expanding spread recorded in this area give well‐constrained velocity estimates throughout the 10 km thick sedimentary sequence, thus enabling the local thickness of the basin to be accurately determined.

ISSN:0812-0099    

DOI:10.1080/08120098808729447

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Illite crystallinity (IC), b0values and Si contents of K‐white mica are reported from Early Devonian metapelites at Cobar. The IC studies indicate metamorphic conditions near Cobar to have been transitional between the anchizone and epizone; farther north at the Elura mine they are anchizonal. The b0values vary fromx=0.8995 nm at Elura to 0.9032 nm at the Peak mine south of Cobar, with most in the range 9.011–0.9021 nm, suggesting a change from low‐ to intermediate‐pressure metamorphism from north to south. Si contents of the K‐white micas at the CSA mine near Cobar suggest a pressure of 3 kbar.

ISSN:0812-0099    

DOI:10.1080/08120098808729448

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Side‐scan sonar, seabed photography and surficial sediment sampling document a field of sandwaves at 40–46 m water depth in eastern Bass Strait, Australia. The sandwaves are formed of coarse sand and gravel consisting of 50–92% biogenic carbonate, derived largely from the remains of molluscs, bryozoans and echinoderms. Four different scales of bedform are identified: ripples (0.1–0.3 m wavelength, 0.02–0.04 m high), small crest megaripples (4–5 m, 0.2 m), large trough megaripples (3–12 m, 0.1 ‐0.5 m) and sandwaves (55–1730 m, 2–12 m). The ripples are superimposed on both the megaripples and sandwaves. Large megaripples are present in the troughs between the sandwaves, while small megaripples are superimposed on the sandwave crests. Local tidal currents are non‐rectilinear. Sandwaves and their superimposed smaller bedforms are formed transverse to the ebb flow (from 255°) but subparallel to the flood flow, and trough megaripples are aligned transverse to the flood flow (from 135°). Minor deviations of the sandwave crests from normal to the ebb flow appear to deflect flow locally, resulting in megaripples superimposed upon sandwaves aligning oblique to the sandwave crests.

ISSN:0812-0099    

DOI:10.1080/08120098808729449

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

During the Late Pleistocene, the large and shallow Lake Carpentaria occupied part of the continental shelf linking northern Australia and New Guinea. The former lake lay within the modern Gulf of Carpentaria, between the —53 m isobath and the deepest part of the embayment at — 67 m, and may have been as much as 500 km long, 250 km wide and 15 m deep. The basinal feature is separated from the outer margin of the continental shelf in the northwest by an area of shallower sea floor with a maximum water depth of about — 53 m and referred to as the Arafura Sill. We have investigated the sedimentary record of the shallow substrate, both within and beyond the basin perimeter, by using surficial sediment samples, piston cores, and continuous seismic reflection profiling. Sediments interpreted to be of lacustrine origin occur only within the enclosed basin, and have been covered by a blanketing marine sandy mud deposit approximately 1 m thick. Beneath the lacustrine mud and sandy mud is a cohesive clay and sandy clay unit, subaerially weathered, saline and possibly of estuarine/marine origin. In shallower areas beyond the basin perimeter, the surficial marine sediment blanket directly overlies the subaerially weathered unit. Radiocarbon dates have been obtained from the surficial unit, and from the lacustrine deposits, to obtain a time frame for the Late Quaternary geological history. The existence of Lake Carpentaria has been linked to cycles of channel erosion and back‐filling on the Arafura Sill. Over several cycles of sea‐level change, this has led to a gradual shallowing of the sill, and closure of a previously open basin. In the enclosed depression, Lake Carpentaria was able to exist throughout the period of the last glacial maximum, sustained by fluvial inflow from its large drainage basin.

ISSN:0812-0099    

DOI:10.1080/08120098808729450

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The Late Permian, intermediate to silicic, calc‐alkaline Drake Volcanics of New England, NSW, consist largely of shallow marine, redeposited volcaniclastic rocks, which host epithermal silver‐gold deposits. Pervasive hydrothermal alteration is widespread. The 200–300 m thick Cataract River Member includes several sedimentation cycles composed of massive pumice breccias, overlain by laminated sandstone and siltstone, interbedded with marine, fossiliferous mudstone. Two distinct groups of clasts within the volcaniclastic beds include: (1) lithics of predominantly intermediate‐composition lavas that have undergone subaerial epiclastic erosion and transportation; and (2) pumice, quartz and plagioclase crystals that have not been reworked by epiclastic processes. The lithic clasts were probably derived locally in a subaerial environment within the Drake Volcanics, and pumice and crystal fragments from contemporaneous centres of silicic volcanism elsewhere in New England. The latter group of clasts was transported to Drake by Plinian airfall or rafting, and fell or was washed on to emergent portions of the Drake Volcanics containing reworked locally derived fragments. Cold‐state mass‐flows produced by slumping, redeposited the mixed volcaniclastic detritus into the marine basin in a series of cyclical units with massive lower parts and laminated upper zones. Modern analogues of the palaeogeographic setting in New England in the Late Permian are provided by the Taupo Zone, New Zealand, and southern Kyushu, Japan.

ISSN:0812-0099    

DOI:10.1080/08120098808729451

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The Wyangala Batholith, in the Lachlan Fold Belt of New South Wales, is pre‐tectonic with respect to the deformation that caused the foliation in the granite, and was emplaced during a major thermal event, perhaps associated with dextral shearing, during the Late Silurian to Early Devonian Bowning Orogeny. This followed the first episode of folding in the enclosing Ordovician country rocks. Intrusion was facilitated by upward displacement of fault blocks, with local stoping. Weak magmatic flow fabrics are present. After crystallization of the granite, a swarm of mafic dykes intruded both the granite and country rock, possibly being derived from the same tectonic regime responsible for emplacement of the Wyangala Batholith. A contact aureole surrounding the granite contains cordierite‐biotite and cordierite‐andalusite assemblages. Slaty cleavage produced in the first deformation was largely obliterated by recrystallization in the contact aureole.

ISSN:0812-0099    

DOI:10.1080/08120098808729452

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Previous reconstructions of Antarctica and Australia were made by fitting the bathymetric outlines of the conjugate margins and aligning pre‐existing structures; the precise position of the continent‐ocean boundary (COB) and the amount and azimuth of pre‐breakup extension were unknown. Seismic and magnetic data collected off Wilkes Land by theS.P. Leeprovide: (1) the basis for a unique fit of the COBs by confirming the fit of the oldest magnetic anomalies; and (2) together with information about the deep crustal structure of the Australian margin, an estimate of the azimuth and amount of pre‐breakup continental extension. By these means, Antarctica and Australia are reconstructed at the mid‐Cretaceous breakup and onset of drift (95 ± 5 Ma) by fitting the conjugate COBs, as determined from seismic and magnetic profiles; and before the mid‐Jurassic (160 Ma) onset of rifting by removing the 360 km of continental extension estimated from the crustal structure of the 700 km wide junction zone.

ISSN:0812-0099    

DOI:10.1080/08120098808729453

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The bulk rock chemistry and O and Sr isotopic composition of the S‐type Cooma Granodiorite, NSW, is compared with the rocks of the surrounding metasedimentary envelope. Major and trace element abundances confirm previous suggestions that the high‐grade metapelitic and metapsammitic gneisses immediately surrounding the granodiorite are the geochemical equivalents of the more distant, low‐grade pelitic and psammatic metasediments. The Cooma Granodiorite can be modelled as a subequal mixture of pelite and psammite and probably represents a partial melt from which a solid residue has not significantly separated.

ISSN:0812-0099    

DOI:10.1080/08120098808729454

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The parentage of felsic gneisses in high‐grade metamorphic terranes is often difficult to determine. Recent workers in the Broken Hill Block of the Willyama Supergroup, western New South Wales, have inferred that most of the felsic gneisses have volcanic, tuffaceous or arkosic precursors. However, megacrystic gneisses in the southern and central parts of the Broken Hill Block have field and chemical characteristics consistent with granitoid precursors. Intrusive granitoids have been reported to occur in the contiguous Olary Block, South Australia, and are common in low pressure metamorphic terranes. Therefore, their presence would be expected at Broken Hill. An intrusive granitoid origin is favoured by local unfaulted transgressive contacts, the sizes and shapes of some of the bodies, the general absence of continuous compositional layering, the presence of aplites, and the common occurrence of K‐feldspar megacrysts. If the megacrystic gneisses have intrusive granitoid precursors, they should not be used in stratigraphic correlation. Furthermore, the origin of layering in some non‐megacrystic gneisses is sufficiently doubtful that their use in stratigraphic correlation is also questionable.

ISSN:0812-0099    

DOI:10.1080/08120098808729455

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Contact metamorphism has been recognized along a 4 km wide belt adjacent to the shallow‐dipping eastern margin of the Arthursleigh Tonalite, an Early Devonian pluton of the Marulan Batholith, eastern New South Wales. In Ordovician psammitic and pelitic rocks three zones of progressive contact metamorphism range from muscovite + biotite + chlorite assemblages in the outer zone to K‐feldspar + cordierite assemblages adjacent to the pluton and in metasedimentary xenoliths. Retrograde phenomena include extensive replacement of metamorphic minerals by ‘sericite’ and chlorite. Calcareous metasediments adjacent to the tonalite typically contain assemblages of quartz + calcic plagioclase + ferrosalite + sphene, or wollastonite + calcite + diopside with minor grossularite and vesuvianite. Thermal effects in volcanic rocks along the western margin of the pluton are confined to recrystallization of the groundmass.

ISSN:0812-0099    

DOI:10.1080/08120098808729456

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor