摘要:

A review of the distribution of Tremadoc successions in China is presented in terms of their occurrences in various depositional settings: shelf regions (Tarim, Yangzi and North China), shelf margins (Jiangnam and NE flank of Tarim), slope regions (South‐east China and NE of Tarim) and ocean basin or volcanic arc regions. The biostratigraphical schemes for correlating the Tremadoc rocks of China are outlined. Brief comments are also made on the position of the Cambrian‐Ordovician boundary in China.

ISSN:0812-0099    

DOI:10.1080/08120098408729276

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Hornblende‐bearing xenoliths in the I‐type Petford Granite, north‐east Queensland, show an abundance pattern suggesting redistribution in a convecting magma system and were probably carried up with the host magma. The Petford Granite and xenoliths are chemically cognate, but quartz monzodiorite‐granodiorite bodies (a potential source for the xenoliths) in the adjacent country rocks belong to an independent magma suite. The xenoliths are chemically similar to andesite lavas and dykes 90 km to the NW. They represent fragments of the parental andesite (diorite) of a calcalkaline suite, which fractionated to yield the Petford Granite. They are not source rocks for the granite melt, melt residua, or early cumulates. The fractionated granite melt broke through the earlier envelope of diorite and rose into the upper crust, carrying dioritic fragments with it. Interaction between magma and xenoliths was generally minimal.

ISSN:0812-0099    

DOI:10.1080/08120098408729277

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The late Proterozoic to Palaeozoic evolution of the basin and basement terrains of central Australia cannot be ascribed to conventional basin‐forming models based on thermal or stretching mechanisms. Foreland basin models also are inappropriate. The principal objection to the thermal and stretching models is that the basins are not in isostatic equilibrium, whilst the foreland basin model cannot explain the quasi‐continuous evolution of the basins over periods of several hundreds of millions of years. A mechanical model is developed on the supposition that the crust has been in compression for long periods and that the evolution is determined by the balance of the compressive force, the buoyancy force, surface loading and erosion, and the elastic and viscous forces. The lithosphere is considered as a viscoelastic plate subject to a small irregular load in Late Proterozoic time. Some of the initial deflections caused by this load grow with time at a rate that is a function of the various forces and plate properties. Erosion of the uplifting areas, with the sediments deposited in the downwarps, much enhances the deformation. As bending stresses increase with time, the uplift rates increase and gravity sliding may become important. Failure by thrust faulting is also predicted, the basement being thrust over the basins. This would have occurred early in the Cambrian, corresponding to the Petermann Orogeny. The model predicts further significant deformation in the southern Arunta in Late Palaeozoic time, corresponding to the Alice Springs Orogeny and the final stages of the Ngalia Basin formation. The proposed model predicts a crustal structure that is in broad agreement with the available geophysical data and provides a framework for discussing the geological history of the basin sediments and basement metamorphics.

ISSN:0812-0099    

DOI:10.1080/08120098408729278

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A reconnaissance Sm‐Nd study has been made on three areas of Precambrian rocks in northern Australia. This reveals that the Arunta Inlier was originally formed at 1980 ± 190 Ma. Basement rocks below the Warramunga Group in the Tennant Creek area are conservatively dated at about 2300 Ma, and with reasonable assumptions, may be assumed to be uppermost Archaean. Early Georgetown Inlier rocks were possibly derived ∼ 2500 Ma ago from a depleted mantle source with 6Nd= +4±0.5. The provenance of at least some Georgetown Inlier metasediments appears to be only marginally older. These results suggest that crust of age 2000–2500 Ma may be more widespread in central and eastern Australia than was previously realised.

ISSN:0812-0099    

DOI:10.1080/08120098408729279

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Appreciable variations in seismic activity have been observed along the main earthquake trends in South Australia. In determining the long‐term seismic risk, allowance has to be made for areas of temporary quiescence, which could be the sites of significant earthquakes in the future. Hence, risk maps are often smoothed by grouping seismicity into regions with a uniform activity, the boundaries of which tend to be fairly subjective. In an alternative form of regionalization, activity in localized regions (effectively point sources) is expressed in terms of seismic moment, which is related to strain release or fault displacement, with minimum assumptions made about the extent of the active areas. The frequency of occurrence of ground motions at a given distance from a source region is obtained from the recurrence and attenuation relations, and the contributions from all active source elements are summed to give the risk at a particular site. In this approach, all the available seismicity data can be used, to give the longest possible period of observation. The procedure, which is simple in concept, is applied to South Australian data. The results are comparable to those from a standard Cornell analysis employing relatively large defined areas of seismicity. In the more active areas of South Australia, the seismic risk probably lies within Zone 1 of the Australian earthquake code.

ISSN:0812-0099    

DOI:10.1080/08120098408729280

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Early Devonian Tangerang Formation consists of a sequence of shallow marine conglomerate, limestone and shale interbedded with shallow marine and terrestrial volcaniclastic arenite, tuff and dacitic lava flows. Three distinctive members have been recognized within the formation, namely the Windellama Limestone Member, the Carne Dacite Member and the Aloes Tuff Member. Limestone is confined to the lower part of the formation in the south where it is overlain by an entirely shallow marine sequence of volcaniclastic arenite. The proportion of volcanic material increases northwards and includes fiamme and accretionary lapilli which are considered to represent ashflow and ashfall tuffs that accumulated, together with thick lava flows, on the flanks of subaerial dacitic volcanoes. These volcanoes were situated at the northern end of the Aloes Tuff Member and towards the top of the formation in the Marulan South area. In the south the Tangerang Formation unconformably overlies Ordovician strata and the presence of Lochkovian faunas within the lower part of the formation suggests a lateral interdigitation with the upper part of the Bungonia Limestone. The dacitic lavas and associated volcaniclastic rocks in the upper part of the formation are petrographically identical to rocks in the southern part of the Bindook Volcanic Complex. Thus the Tangerang Formation, which accumulated on an uplifted horst of Late Ordovician flysch on the eastern margin of the Wollondilly Tract, is considered to represent the basal unit of the Bindook Volcanic Complex in the Marulan‐Windellama area. The progressive filling of the Wollondilly Tract to the north of Marulan with volcanic ejecta is reflected in the change in palaeocurrent direction from a dominant northward longshore system to an E‐W onshore‐offshore system during the deposition of the Tangerang Formation.

ISSN:0812-0099    

DOI:10.1080/08120098408729281

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Chromium‐rich aluminous and ferruginous metamorphic rocks at Mount Martin, Western Australia, can be shown on textural and compositional evidence to have been formed from komatiitic flows and pyroclastics. They were apparently altered initially to quartz‐kaolinite ± siderite assemblages, most probably by weathering processes. Metamorphism has produced a variety of mineral assemblages composed variously of quartz, kyanite, andalusite, sillimanite, chloritoid, chlorite, paragonite, muscovite, siderite, biotite, gedrite, almandine, cummingtonite, hornblende and plagioclase, with rutile, ilmenite, pyrite, millerite, polydymite, gersdorffite, pyrrhotite, pentlandite and chromite as accessory minerals. Geothermometry and geobarometry on these samples give substantial support to placing the aluminosilicate triple point at about 500°C and 4kb (400 MPa) pressure.

ISSN:0812-0099    

DOI:10.1080/08120098408729282

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The geomorphological career of J. T. Jutson falls into two distinct, though not quite temporally separate, parts. For about eight years during the second decade of this century, he was a full‐time professional with the West Australian Geological Survey. During this period he was mainly concerned with landform evolution in arid and semiarid regions, and after only three years with the Survey produced what was to be hismagmum opus: An Outline of the Physiographical Geology (Physiography) of Western Australia.Though¦ essentially a synthesis based on the observations and experience of such colleagues as Talbot, Woodward and Maitland, Jutson's was a seminal work, for in it he anticipated many landscape interpretations concerning planation surfaces, hillslope behaviour (and particularly the conditions conducive to scarp retreat), etch planation and the antiquity of landscapes. After his retirement from professional geology, forced partly by financial stringencies in the Survey, partly by Jutson's congenital deafness, he returned to Melbourne and to the law. For about 30 years until his retirement in 1952 he earned his living as a solicitor, and was only a weekend geomorphologist who used his leisure time mainly on coastal studies in the Port Phillip Bay area, but occasionally extending his interests interstate and notably to the Sydney region. It is for this part‐time work, concerned with shore platforms, that Jutson is best known today, for he realised that the sea is capable of producing not one but several platforms simultaneously and moreover that they may extend well beyond the tidal range, with all that that implies for the interpretation of the chronological development of shorelines, for studies concerned with recent relative movements of land and sea. Important as is Jutson's coastal work, his earlier contributions concerning major questions of landscape evolution will, we suggest, in the long term be seen to be more significant, for he anticipated many concepts that are regarded as of more recent derivation and moreover arrived at his conclusions in as rational a manner as is possible in the art of scientific research.

ISSN:0812-0099    

DOI:10.1080/08120098408729283

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

New U‐Pb zircon ages, combined with previous Rb‐Sr data, provide a geochronological framework for the Tennant Creek Inlier of Northern Australia. Ages of 1870± 20 Ma and 1846± 8 Ma are advanced for the igneous crystallization of the Tennant Creek and Cabbage Gum Granites, respectively. A lower concordia intercept age of 248 ± 27 Ma is thought to relate to zircon dilation and Pb loss resulting from late Palaeozoic uplift, alteration and/or erosion. If previously analysed volcanics from the Bernborough Formation also lost Pb at that time, they have a primary age of 1870 ± 15 Ma. This provides a temporal estimate for deposition of the Warramunga Group, the major geological component of the Tennant Creek Inlier. At any single site, Rb‐Sr total‐rock ages are younger than U‐Pb zircon ages, possibly up to 400 Ma so for the Cabbage Gum Granite. Previously reported Rb‐Sr total‐rock ages of about 1650–1660 Ma probably define igenous crystallization of several other felsic magmas. Granite emplacement thus occurred both before and after the main 1810 Ma tectonothermal event and accompanying mineralization.

ISSN:0812-0099    

DOI:10.1080/08120098408729284

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Deposition of Late Carboniferous and Early Permian continental conglomeratic strata along the western edge of the New England Orogen was continuously accompanied by silicic volcanism. Disconformable relationships exist locally between the Early PermianGlossopteris‐bearingrocks and the Late CarboniferousRhacopteris‐bearingrocks but have negligible stratigraphic significance since erosional surfaces are common within the older sequence and probably also occur in the younger sequence. The western volcanic terrain which had supplied ignimbrites, airfall deposits and volcanogenic detritus eastward during the Late Carboniferous still had some active centres in the Early Permian, though eruptions waned in scale and changed in style to include effusion of lavas. Proximal Early Permian volcanics comprised of lithic‐rich ignimbrites and lavas at Boggabri are the remnants of one such centre. After eruptions had ceased, denudation of this and other remaining centres contributed volcanogenic detritus, including ‘flint clay’ clasts, to coal measure sediments (Greta equivalent) accumulating in the flanking low‐lying areas of the incipient Gunnedah Basin. There is no evidence in support of easterly provenance for these Early Permian coal measures nor for movement on the Mooki Thrust at this time.

ISSN:0812-0099    

DOI:10.1080/08120098408729285

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor