摘要:

An analysis of the uranium and thorium fractionation processes in various granites implies a direct dependence on processes of magmatic differentiation, the magma source materials, and residual accessory phases; suggesting that no universal, vertical heat‐producing element distribution may be applied to all granite crust. Metaluminous I‐type granites show evidence for downward decreases in heat‐producing elements within the plutons. The heat‐producing element content of I‐type residual source regions is probably similar to that of the most mafic I‐type granites. The fractionation trends of peraluminous S‐type granite indicate that no significant change in heat‐producing elements should occur with depth in the plutons. Geochemical evidence indicates that residual source regions of S‐type granites will contain high concentrations of heat‐producing elements and reside deep in the crust. Anomalously high heat flow in southeastern Australia corresponds to areas of S‐type granites and may be largely due to deep crustal radioactivity, rather than Cainozoic mafic magmatism.

ISSN:0812-0099    

DOI:10.1080/08120098608729354

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Since 1969, a major geochronological investigation has been carried out by the South Australian Department of Mines and Energy on rocks of the Gawler Craton. Isotopic dates define three broad groupings corresponding to the Sleafordian Orogeny 2500–2300 Ma, the Kimba Orogeny 1820–1580 Ma, and the Wartakan Event 1580–1400 Ma. The oldest rocks in the craton belong to the Mulgathing Complex (in the north) and the Sleaford Complex (in the south). They consist of strongly folded and metamorphosed paragneisses (probably sediments and volcanics) intruded by several granites during the Sleafordian Orogeny. The Sleafordian Orogeny was followed by a 500 Ma period of magmatic and tectonic quiescence prior to the Kimban Orogeny. During that time sediments of the Hutchison Group were deposited. The Kimban Orogeny is characterized by complex deformation, high‐grade metamorphism and multiple synorogenic granite intrusion. It concluded atca.1580 Ma, but was followed by postorogenic acidic magmatism, sedimentation and minor deformation (the Wartakan Event). The spectrum of isotopic dates ends atca.1400 Ma, the approximate time of cratonization of the Gawler Craton.

ISSN:0812-0099    

DOI:10.1080/08120098608729355

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Thin‐section studies of previously assumed Pleistocene bioclastic dune calcarenites in the coastal regions of southwestern South Australia reveal a reworked marine microfossil assemblage which appears to have been derived mostly from sediments of Miocene age. Calcretes associated with the calcarenite sequence and aeolian carbonate sediments in inland regions of Eyre Peninsula contain a similar microfossil assemblage, though the microfossil clasts are extensively reworked and recrystallized. None of the samples examined carried microfaunas characteristic of Quaternary sediments such as the Glanville and St Kilda Formations. It is possible that deposition of the dune calcarenites commenced after regression of the Middle Miocene seas which had left a widespread blanket of marine sediments over southern South Australia. In this regard the complete sequence of dune calcarenites may span a longer time period than the Bridgewater Formation. It is likely that continued deposition of dune calcarenites through the Pliocene and Pleistocene either modified earlier dune ridge configurations (in tectonically stable regions such as Eyre Peninsula) or created new ridge systems (in regions of tectonic instability such as southeastern South Australia). Concomitant aeolian reworking of the former coastal dunes produced the extensive inland blankets of carbonate sediments and calcretes, though lacustrine and pedogenic sources of carbonate and calcareous bedrock were locally important.

ISSN:0812-0099    

DOI:10.1080/08120098608729356

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The Warburton Basin is an Early Palaeozoic sedimentary basin underlying the Cooper, Pedirka, and Eromanga Basins in northern South Australia. It extends into the Northern Territory and Queensland and lies within the southwestern edge of the Thomson Fold Belt. The Middle and Late Cambrian Kalladeina Formation is either flat‐lying or gently folded and rests on presumed Early Cambrian Mooracoochie Volcanics of the Gidgealpa Volcanic Arc; the latter may be a northern extension of the Mt Wright Volcanic Arc of northwest NSW. The Ordovician Dullingari Group, a sequence of sandstone, siltstone, shale, and black pyritic shale, was apparently affected by the Benambran Orogeny. The gently dipping ‘Innamincka Red‐Beds’ of ?Cambrian or ?Devonian age is a thick marine sandstone‐shale sequence. Granite at Moomba has been dated by whole‐rock Kb‐Sr at 333–362 Ma which may be the date of the last cooling of an older rock emplacement. Early Cambrian rocks in the Arrowie Basin area, eastern Officer Basin, and at McDills 1 in the Northern Territory may be marginal to the Warburton Basin. Petroleum potential of the Warburton Basin is demonstrated by the presence of hydrocarbons below the pre‐Permian unconformity, while also noting the possibility of Permian sourcing. Reservoir potential has been proved by testing and recovery of gas and gas‐saturated saline water. This interpretation is intended only as a model and is not nearly as complex as will be shown by future drilling. Extrapolation beyond the known facts was needed in order to make a model which is workable. More recent drilling has so far supported the model.

ISSN:0812-0099    

DOI:10.1080/08120098608729357

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The surficial deposits of the upper Pieman and Boco valleys of western Tasmania are the result of four glaciations. These glacial episodes are partly differentiated on a morphostratigraphic basis and partly on a chronostratigraphic basis by the application of age‐dependent weathering criteria. The most useful relative‐dating measures are weathering rind thicknesses, percentage absorption of water, specific gravity of rock clasts, degree of till matrix weathering, and post‐depositional modification of glacial landforms.

ISSN:0812-0099    

DOI:10.1080/08120098608729358

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Zircon U‐Pb age determinations made by ion microprobe show conclusively that the crystallization age of the Logue Brook Granite is 2612 ± 5 Ma, not 2905 ± 35 Ma as has been inferred from its chondritic uniform reservoir (CHUR) Sm‐Nd model age. It follows that the initial143Nd/144Nd of the Logue Brook Granite was appreciably lower than that predicted by the CHUR model for 2612 Ma (i.e. higher than CHUR for 2905 Ma). The dispersion of Sm‐Nd model ages in the Darling Range Batholith probably reflects not variation in emplacement age, but variation in143Nd/144Nd arising from components of the batholith's source rocks that experienced one or more prior episodes of rare‐earth element fractionation. It is re‐emphasized that Sm‐Nd model ages do not provide direct estimates of crystallization ages.

ISSN:0812-0099    

DOI:10.1080/08120098608729359

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The St Marys Porphyrite crops out in the St Marys district of eastern Tasmania and is a felsic, quartz porphyrite body which contains the only known extrusive rocks associated with the widespread Devonian granitoids of Tasmania. It consists of a thick (1400 m) sheet of predominantly dacitic, welded, ash‐flow tuff together with a high‐level, vesiculated part of the volcanic feeder. The boundary between these subdivisions is an extension of the eastern boundary of the nearby Catos Creek dyke, a deeper unvesiculated level of the feeder. In the St Marys Porphyrite, the boundary is interpreted as a subsidence fault which threw the extrusive rocks down against their feeder, whilst in the Catos Creek dyke, it was the locus of early magma emplacement as well as of major movement. Ash‐flow tuff in the St Marys Porphyrite is particularly rich in crystal fragments (up to 58% by volume). Its matrix becomes progressively more recrystallized with height above the base of the sheet, thus indicating rapid emplacement and cooling as a single unit. This resulted in poor preservation of tuffaceous textures except near the base. Individual ash‐flows are generally difficult to identify, but flows or parts of flows are locally defined by variations in the proportions of metasedimentary lithic fragments and strongly recrystallized pumice(?) fragments (schlieren). Rb‐Sr isotopic data and major trace and rare earth element chemistry strongly support comagmatism of the St Marys Porphyrite with both Catos Creek dyke and Scamander Tier dyke, which is part of the early I‐type phase of magmatism in the Blue Tier Batholith. Thus, the age of emplacement of the porphyrite body (388 ± 1 Ma) precisely limits the age of early magmatism in the Blue Tier Batholith. It also limits the age of earlier deformation in the country rocks (Mathinna Beds).

ISSN:0812-0099    

DOI:10.1080/08120098608729360

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The Cainozoic Lake Bunyan Basin occupies part of the Cooma‐Canberra corridor, a lowland which is bounded in the W by the Murrumbidgee Fault escarpment and in the E by N‐S trending ranges. The Murrumbidgee and Numeralla Rivers are the main streams entering the basin. Lake Bunyan covered an 8 km wide strip of this lowland from near Bredbo to 30 km SE in the vicinity of Cooma. It formed when the Murrumbidgee River became fault‐dammed 5 km S of Bredbo, during the late Oligocene or early Miocene, and it was finally breached in the late Miocene. Five sedimentary facies were identified in the Lake Bunyan sequence. A marginal facies of stratified gravels, sands and sandy clays unconformably overlies bedrock or weathered bedrock at the base of the sequence and also overlaps other facies. A lignitic facies is thin and often interbedded with clay. A volcanogenic facies is up to 50 m thick, has strong red colours, and consists of stratified clays and gravels, the latter containing volcanic debris. A 40 m thick clay facies occurs in the upper part of the sequence and is very fine grained. A diatomite facies at the top of the sequence is up to 13 m thick. The sediments of Lake Bunyan generally occur below the present 780 m contour and were deposited over a vertical interval of at least 210 m. The occurrence of Lake Bunyan, when considered with fault‐dammed Lake George and scarp‐producing movements along the Berridale Wrench Fault, indicates Cainozoic tectonics in the South East Highlands of NSW that were episodic, localized and not synchronous.

ISSN:0812-0099    

DOI:10.1080/08120098608729361

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The five Members of the Miocene Lake Bunyan which make up the Bunyan Formation are described in detail, their palaeoenvironmental implications considered, and possible correlations discussed. The Rose Valley Member comprises a range of lake edge and bottom sediments. The Cooma Creek Member consists of thin lignite seams interbedded with clay and probably developed in shallow lake margins containing heath and swamp species. The Cloyne Member consists of sediments containing volcanic and other lithic debris which is weathered to kaolinite and goethite; rapid deposition is indicated at a time of local volcanism. The Rosebrook Member represents a very quiet depositional environment, but the high crystallinity of the fine‐grained, kaolinitic clay may result from synthesis within the lake. The Bonnie Doon Member diatomites are cyclical deposits formed in response to both annual and longer term cycles. Considerable variation in lake water levels is indicated including dry lake phases when soils developed. Much of the clay in the sediments would have been derived from deep weathering profiles of the Monaro Surface. The source of the volcanic debris in the Cloyne Member is uncertain but this material could not have been associated with Monaro Basalts (54–36 Ma). Absence of rainforest taxa in pollen assemblages of the Cooma Creek Member indicates a cooler, drier climate for the Lake Bunyan Basin than occurred in other parts of the region during the Miocene. The Lake Bunyan sedimentary sequence is another example of continental sedimentation in the Eastern Highlands of Australia during the Miocene. There is a corresponding gap in the sedimentary record of marginal basins such as the Murray. There is also a general absence of substantial sedimentation in the Eastern Highlands during the Oligocene and earlier epochs of the Cainozoic.

ISSN:0812-0099    

DOI:10.1080/08120098608729362

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Vertical movements within mountainous terrain may be indicative of either active tectonism or of passive isostatic rebound of the crust to the erosion of the highlands. During the active orogenic phase, the landscape evolution is controlled largely by the tectonic process but once this ceases or is reduced in intensity, the erosional unloading and concomitant rebound becomes the dominant landscape‐forming process. It is this latter phase that is examined here. It is argued that the southeastern highlands are a residual of the Palaeozoic Lachlan Fold Belt, rather than having been rejuvenated in Tertiary time. It is concluded that the erosional rebound model explains many of the recent geomorphological observations that attest to little landscape evolution since the early Tertiary. The model adopted is of a mountain range that is initially in local isostatic equilibrium but which responds regionally to the erosional unloading. The crust or lithosphere is modelled as a viscoelastic layer so that rebound is not instantaneous. The rate of erosion at any time is assumed to be proportional to elevation above sealevel with a time constant of the order 108years. For a given present‐day topography the elevations, erosion, rebound, stress and gravity can be computed throughout time as a function of model parameters. The time by which the rebound phase became the dominant process is 200–250 Ma ago and the elevations at that time were about 75% greater than present values. An erosion time constant of 200 Ma produces average Tertiary erosion rates of a few metres/million years, rates that are consistent with geomorphological observations in several areas of south‐eastern Australia.

ISSN:0812-0099    

DOI:10.1080/08120098608729363

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor