摘要:

The migmatites of the Palmer area, in the core of the Mt Lofty Ranges metamorphic belt, are considered to have formed by partial melting of quartzo‐feldspathic schists and gneisses, rather than by metamorphic segregation as formerly suggested. Large‐ and small‐scale tectonic structures indicate that the Cambrian Kanmantoo Group rocks in the Palmer area have undergone three deformations during the Delamerian Orogeny and that these are similar to those described elsewhere in the Mt Lofty Ranges. The relationships of the migmatitic veins to these structures indicate that some partial melt was present during a large part of the structural history: some veins formed before and after the first folding event, and some formed during or after the third folding event even though the metamorphic grade appears to have been waning in areas more distant from the highest grade ore. The early onset of partial melting is consistent with previously reported evidence that thermal activity in the belt began before penetrative deformation.

ISSN:0812-0099    

DOI:10.1080/08120098408729297

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Previously Punchbowl, Signature and Dogleg Caves low down in the Goodradigbee valley at Wee Jasper, NSW, could only be inferred to be younger than Early Miocene basalts on the plateau to the west. Five main quasi‐horizontal cave levels, with discrete bodies of fluvial sediment at more frequent intervals, invited application of magnetostratigraphy to this sequence of passages, which are successively younger downwards, in the hope of more precise dating. Thirteen sites at 10 altitudes over a range of 31 m were sampled at 2–8 points each. The lower third of the system yielded normal polarity and so formed since 0.73 Ma. Treating the palaeomagnetic data conservatively, the upper two thirds, yielding dominantly reversed polarities, can be regarded as forming between the Brunhes‐Matuyama boundary and the Jaramillo. However, this implies a drastic change in rate of lowering of local karst base level and valley incision for which there is no morphological support. Assuming a linear rate of vertical cave development, the cave began to form about 2.0 Ma; weak expression of Matuyama palaeomagnetic events to match this can be discerned and this dating is preferred. On either interpretation, the age of the system has thus been made more precise by an order of magnitude. The longer history fits better with modern ideas on the great age and slow rate of change of the plateaux of south‐eastern Australia.

ISSN:0812-0099    

DOI:10.1080/08120098408729298

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

It has been suggested by Wellman (1981,Geol. Soc. Aust. J.28, 311–321) that the geodetic surveys of south‐eastern Australia carried out in the late nineteenth century and again from 1970 to 1980 are indicative of substantial crustal deformation with strain rates of the order of 50 x 10‐9yr‐1. A re‐evaluation of the data does not confirm this conclusion. Several difficulties with Wellman's analysis have been identified. (i) The geodetic observations made at both epochs do not always meet the high standards required for crustal deformation studies. (ii) The strains have been estimated for parts of the network whose geometries do not meet first‐order standards. (iii) The strain has been evaluated from a comparison of the nineteenth century survey with a network adjustment which incorporated the surveys at both epochs. (iv) The observed angles of the nineteenth century survey have been compared with angles computed from the Geodetic Model of Australia (1980). This model is inappropriate for evaluating crustal deformation. (v) Deflections of the vertical and skew normal corrections have been ignored. (vi) Two different methods have been used in the adjustment of the two surveys making up the 1970–1980 network. (vii) No realistic statistical analysis of the results has been attempted.

ISSN:0812-0099    

DOI:10.1080/08120098408729299

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Broken Hill deposit, western NSW, is an intensely deformed and metamorphosed submarine exhalative deposit, with associated hydrothermal alteration and exhalites, formed in a lineament‐controlled rift. The sulphide and enclosing silicate rocks at Broken Hill have undergone the same complex deformational and metamorphic history. High‐grade metamorphism and coeval deformation were accompanied by mass movement of sulphides with fold hinges, sulphide brecciation, development, of sulphide and silicate porphyroblasts, coarsening of grainsize, development of sulphide‐bearing pegmatites, attainment of surface‐tension equilibrium between coexisting minerals, and the formation high‐grade metamorphic mineral assemblages comprising sulphides, pyroxenes, pyroxenoids, garnets, spinels and feldspars. At the waning stage of high‐grade metamorphism, ore breccias were formed, sulphide minerals (e.g. galena, chalcopyrite, pyrrhotite) were mechanically injected into transgressive fractures, and further redistribution took place by secondary hydrothermal processes. Exsolution and replacement of earlier prograde silicate and sulphide minerals formed many new minerals. Secondary hydrothermal processes formed pegmatoid masses, transgressive veins (quartz, sulphide and silicate) and cavities. Retrogression of the sulphide rocks occurred in shear zones, which transgressed and displaced prograde ore, resulting in brecciation, plastic flow, sulphide injection and retexturing. Ag, As, Sb, Cu and Pb moved from prograde ore into shear zones, and prograde minerals underwent decomposition to other sulphides, exsolution and replacement. Secondary hydrothermal processes formed transgressive quartz, sulphide and carbonate veins. The orebodies are transgressed and displaced by minor fault zones. Sulphide rocks were fractured and retextured and new phases formed by decomposition, exsolution and replacement. Sequential precipitation of carbonates and other phases on fault planes and in crystal‐lined cavities is characteristic. The oxidised zone of the Broken Hill orebody is characterized by telescoped mineral assemblages, collapse structures, solution features, overgrowths, boxworks after cerussite, greatly variable depth of oxidation, and the lack of a supergene zone—all indicative of a long history of multiple rejuvenation of the weathering of the Broken Hill deposit. The Willyama Supergroup has undergone Proterozoic erosion and it is possible that the secondary zone at Broken Hill is Palaeozoic in age.

ISSN:0812-0099    

DOI:10.1080/08120098408729300

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Five generations of structure (D1‐D5) have been recognized in the Early Archaean supracrustal gneisses in the Fyfe Hills‐Khmara Bay region in Enderby Land, East Antarctica. The D1,D2and D3events comprise the Napier structural episode. They resulted in pervasive deformation during Archaean granulite facies metamorphism, and predated the intrusion of the Middle Proterozoic Amundsen dykes. The Napier metamorphic culmination was broadly coeval with, but outlasted both, D1and D2. D3occurred during waning granulite facies metamorphism. The D4and D5events comprise the Rayner structural episode, the effects of which are largely restricted to amphibolite facies retrograde shear zones in which the Amundsen dykes are deformed. The Napier Structural Episode is characterized by: (i) mesoscopic, isoclinal, recumbent, F1folds which formed during intense deformation accompanying the prograde burial of the gneissic sequence; (ii) large scale, tieht to isoclinal, reclined F2folds formed at deep crustal levels; and (iii) large scale, non‐cylindrical, asymmetric, upright F3folds formed in response to differential vertical movements during the final stages of stabilization of the gneissic sequence. The development of a pervasive mesoscopic gneissic layering associated with the Napier structures is attributed to a variety of processes, only some of which are related to deformation mechanisms. The Rayner structures are restricted to amphibolite grade high strain zones which formed in response to displacements between essentially rigid blocks of granulite. Progressive localization of D4and D5structures within the retrograde zones, ultimately resulting in the development of pseudotachylite, reflects deformation at successively higher crustal levels during the excavation of the gneissic sequence.

ISSN:0812-0099    

DOI:10.1080/08120098408729301

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The distribution of trace fossils in the upper part of the Adelaidean succession (Farnell Group) of the Barrier Range near Fowlers Gap is reviewed. Of the main, stratigraphically distinct assemblages, the older from the Fowlers Gap Formation, contains only a few, simple, non‐diagnostic, sinuous and branching trails, and is assumed to be of latest Precambrian age. The assemblage in the succeeding Lintiss Vale Formation has a high diversity, mainly of simple behavioural types produced by worm‐like animals and molluscs, but lacking arthropod traces. It therefore represents a latest Precambrian or an earliest Cambrian assemblage. A third ichnofauna with simple, sinuous and branching trails is recorded from the Wonominta Beds of the Warratta inlier west of Tibooburra. The occurrence of these trails indicates that at least in the northern areas of ‘basement’ Wonominta outcrop the rocks are no older than latest Precambrian (i.e. the age of the earliest indubitable traces of animal activity) and, judging from the size of some of the trails and longitudinal ribbing on others, are more likely to represent younger deposits of Cambrian or even Early Ordovician age. A fourth assemblage including trace fossilsPlanolitesandChondritesis reported from the ‘flysch‐like’ Copper Mine Range Beds west of White Cliffs. This association has not been described, previously from ‘flysch‐like’ deposits older than Early Cambrian.

ISSN:0812-0099    

DOI:10.1080/08120098408729302

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Glacial pavements associated with tillites of presumed Permian age near Moyhu, north‐east Victoria, Australia, provide further evidence for glaciation in the region, and indicate an ice‐movement direction close to true north. This is near normal to ice‐movement directions (either from the west or the east) previously inferred from the likely provenance of clasts in the tillites, among the more conspicuous of which are Early Devonian fossiliferous sandstones formerly thought to be derived from the Mount Ida Formation, 140 km west near Heathcote, central Victoria. A more southerly source for the Early Devonian fossiliferous sandstones now seems appropriate; the faunal assemblages are not incompatible with sources in Tasmania or Antarctica.

ISSN:0812-0099    

DOI:10.1080/08120098408729303

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Arunta Inlier is a 200 000 km2region of mainly Precambrian metamorphosed sedimentary and igneous rock in central Australia. To the N it merges with similar rocks of lower metamorphic grade in the Tennant Creek Inlier, and to the NW it merges with schist and gneiss of The Granites‐Tanami Province. It is characterized by mafic and felsic meta‐igneous rocks, abundant silicic and aluminous metasediments and carbonate, and low‐ to medium‐pressure metamorphism. Hence, the Arunta Inlier is interpreted as a Proterozoic ensialic mobile belt floored by continental crust. The belt evolved over about 1500 Ma, and began with mafic and felsic volcanism and mafic intrusion in a latitudinal rift, followed by shale and limestone deposition, deformation, metamorphism and emergence. Flysch sedimentation and volcanism then continued in geosynclinal troughs flanking the ridge of meta‐igneous rocks, and were followed by platform deposition of thin shallow‐marine sediments, further deformation, and episodes of metamorphism and granite intrusion.

ISSN:0812-0099    

DOI:10.1080/08120098408729304

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Arunta Inlier is part of a major ensialic Proterozoic mobile belt in central Australia. It comprises three latitudinal tectonic Provinces (Northern, Central and Southern) which have markedly different lithological, metamorphic and structural histories, and are bounded by major deformed zones. Tectonic activity migrated back and forth within the Inlier, and gradually lessened in intensity and extent. Large‐scale movements were localized along the bounding deformed zones from early on. Deformation and metamorphism were concentrated in the Central Province at about 1800–1750 Ma, and then at about 1700 Ma moved to its margins. Subsequent activity at 1700–1600, 1500–1400, 1050–900 and 400–300 Ma was concentrated in the Southern Province and in a belt which extended NW across the entire Inlier from the E part of the Southern Province. The tectonic evolution of the Arunta Inlier resulted from six cycles of crustal extension and compression. The first (before 1800 Ma), and possibly the second (1800–1750 Ma) caused rifting and then limited subduction of subcrustal lithosphere. The later cycles suggest repeated thermal activity and thrust‐faulting in relatively narrow crustal belts above a long‐lasting elongate plume in the mantle.

ISSN:0812-0099    

DOI:10.1080/08120098408729305

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The south‐eastern part of the Litchfield Complex in the Northern Territory has two distinct metamorphic units, both containing mafic and metasedimentary members. These are intruded by gabbros, ultramafics, and anatectic granitoids. Superficially there is a correlation between these metamorphic units and the adjacent, compositionally similar, low grade rocks in the Pine Creek Geosyncline to the E. It is proposed, however, that the two metamorphic units are not corelatives because their metamorphic and deformational histories are markedly different, nor do they relate to the low grade rocks to the E. The most intensely deformed, metamorphic unit could also be allocthonous to account for its complex history. On the basis of recent work in the Pine Creek Geosyncline, it is proposed that the allocthonous unit is Archaean basement which was involved in westward thrusting of parts of the geosynclinal sequence (the Burrell Creek Formation). The least deformed of the metamorphic units may equate to older units in the geosyncline. A correlation between the Litchfield Complex and the Early Lamboo Complex of the Halls Creek Province is made.

ISSN:0812-0099    

DOI:10.1080/08120098408729306

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor