摘要:

The sediments immediately adjacent to the Wyangala Batholith show direct evidence of two periods of folding. The first visible folds are tightly appressed structures which transpose the bedding to produce a new layering. The plunge of these folds is variable but there is no information to distinguish between superposition on an older generation of folds, and development in a heterogeneous strain field, as mechanisms to explain this variation. The first folds are deformed by a strain‐slip cleavage which is axial plane for a second generation of folds. Geometrical analysis shows that large (macroscopic) structures exist and can be related to one or the other of the two generations of small scale folds. The general absence of transposition on a large scale introduces limitations into the use of geometrical techniques and, in one area, large errors result in the determination of the plunge of macroscopic folds.

ISSN:0016-7614    

DOI:10.1080/00167616508728582

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

A northwest‐trending, sinistral wrench fault having a horizontal component of movement of approximately seven miles, transects the Berridale Batholith of the Snowy Mountains of New South Wales. The displacement has been determined by matching the displaced segments of two granite intrusions and their associated contact aureoles.

ISSN:0016-7614    

DOI:10.1080/00167616508728583

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

The experimental data available are sufficient to justify a tentative diagram for the system Or‐Ab‐An‐SiO2at 5,000 bars Ph2o. In this diagram the SiO2‐saturated plane is projected onto the Or‐Ab‐An face of the tetrahedron. When the normative feldspars of granitic rocks are plotted on this diagram they fall into a low‐temperature trough, whereas when they are plotted on the Or‐Ab‐SiO2diagram the majority fall into the Or field.

ISSN:0016-7614    

DOI:10.1080/00167616508728584

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

Rb‐Sr age measurements are reported for acid volcanic rocks, a tuffaceous siltstone, and two granites, all of Precambrian age, from the northwest division of Western Australia. The lava samples are from four localities within the Woongarra Volcanics, a formation situated near the top of the “Proterozoic” Hamersley Group, formerly a part of the “Nullagine Beds”. On field evidence these samples are of the same age, so that the Rb‐Sr data have been interpreted as giving approximately 2,100 m.y. for this age, assuming a variation in initial Sr87Sr86of 0.700 to 0.720. The tuffaceous siltstone, from the overlying Wyloo Group, has a maximum indicated age of 1,850 m.y. This value is subject to uncertainty since only one sample was analysed, but nevertheless it is significantly younger than the Woongarra Volcanics, in accordance with its strati‐graphic position, and it is likewise consistent with concordant total‐rock and mineral ages of 1,720 m.y. measured in the Boolaloo Granite, which is intrusive into the Wyloo Group. Owing to suspected later metamorphism only broad limits of 2,300 to 3,000 m.y. can be set for the age of an “Archaean” granite which is older than the oldest “Proterozoic” sediments. Two unpublished U‐Pb and Rb‐Sr ages from the same area communicated to the authors are also reported.

ISSN:0016-7614    

DOI:10.1080/00167616508728585

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

A sequence up to 40,000 ft thick of unmetamorphosed and only slightly deformed sedimentary and volcanic rocks occurs in the Carpentaria Province of Northern Australia. Metamorphic and granitic rocks form the basement to this sequence, and K‐Ar and Rb‐Sr age measurements show that the basement granites are about 1,800 ± 50 m.y. old. Associated in space and time with the granitic rocks are acid volcanics which form the basal unit in the overlying sequence. Glauconites in sedimentary rocks from this succession yield dates ranging from 1,600 m.y. in the Tawallah Group, the second lowest unit, to about 1,390 m.y. in the Roper Group, the uppermost unit. Plagioclase and pyroxene from dolerites intrusive into the Roper Group give K‐Ar dates ranging from 1,100 to 1,280 m.y.; the older date provides a younger limit to the age of the Roper Group. Following slight folding the Wessel Group was deposited unconformably on the Roper Group; a single glauconite from the topmost formation of the Wessel Group yields concordant Rb‐Sr and K‐Ar dates of 780 ± 20 m.y.

ISSN:0016-7614    

DOI:10.1080/00167616508728586

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

During the Middle Palaeozoic, the Tasman Geosyncline extended to northeastern Queensland, including the area between Cape York Peninsula and Ingham. The geosyncline was here represented by the Hodgkinson Basin, in which the Hodgkinson Formation forms the main geosynclinal deposit. Meta‐morphic rocks of doubtful age, exposed along the coast within the geographical limits of the Hodgkinson Basin, are called Barron River Metamorphics (green‐schist facies of metamorphism) and Barnard Metamorphics (amphibolite facies). They have hitherto been thought to have formed tectonic land during the Middle Palaeozoic geosynclinal sedimentation—hence to be older than the Hodgkinson Formation—and their ages were estimated to be Early Palaeozoic (Barron River Metamorphics) and Precambrian (Barnard Metamorphics). Recent field work suggests that the two units may both be the metamorphic equivalents of the Hodgkinson Formation: it is concluded that they formed an integral part of the Tasman Geosyncline during the Middle Palaeozoic, and were metamorphosed during the Late Palaeozoic orogeny under conditions of high temperature and relatively low pressure. This idea is supported by geological examples from other places of the world, and by the latest views on the relationships between metamorphosed and unmetamorphosed rock sequences in orogenic belts. The picture thus obtained appears to harmonize with the circum‐Pacific area in general, where this type of metamorphism (andalusite‐sillimanite association) is rather common.

ISSN:0016-7614    

DOI:10.1080/00167616508728587

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

Three Lower Carboniferous marine faunal zones and one faunal assemblage are recognized in the Gresford‐Dungog district, New South Wales following a faunal and stratigraphical study of the region. In ascending order they are the?Thomasaria voiseyiAssemblage Zone, theSchellwienellacf.burlingtonensisFauna, theWerriea australisAssemblage Zone and theDelepinea aspinosaAssemblage Zone. They are correlated with the Lower Carboniferous zones of Germany as follows:?Thomasaria voiseyiAssemblage Zone—Cu IIα,Schellwienellacf.burlingtonensisFauna—Cu IIα to Cu IIβ;Werriea australisAssemblage Zone—Cu IIδto Cu IIIα; andDelepinea aspinosaAssemblage Zone— Cu IIIαto Cu IIIβ.

ISSN:0016-7614    

DOI:10.1080/00167616508728588

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

The Hervey Group (Upper Devonian), central New South Wales, consists of 10,000 ft of orthoquartzites, protoquartzites, lithic sandstones and quartz siltstones. The predominantly fluvial sequence is subdivided into the Beargamil, Nangar and Cookamidgera Sub‐Groups. More than 500 petrographic analyses of sandstones show that the percentage of unstable rock fragments and poly‐crystalline quartz in the sandstones increases with increase in grainsize. Mineral facies maps drawn from these analyses show that polycrystalline quartz, and quartzose sedimentary rock fragments increase westwards and southwards for all sequences of the Hervey Group, indicating derivation of this detritus from a southern landmass. The distribution of rock fragments and feldspar also indicates that minor source areas existed to the southeast and northeast. The red sediments of the basal Beargamil Sub‐Group belong to an arkosic facies derived from nearby basement highs of granite, acid volcanics, and sedimentary rocks. The sediments become increasingly quartz‐rich upwards in the section indicating that the basement highs were gradually covered. The Nangar Sub‐Group consists of cyclothems of coarse orthoquartzites that are cross‐stratified and grade upwards into finer sandstones with more lithic detritus, and red silt‐stones. These sediments are inferred to have been deposited on a large flood‐plain, and the cyclothems to have originated by offlap deposition of migrating river channels. The siltstones were probably mainly deposited in backswamp areas, large ox‐bow and inland lakes, and mudflats that were frequently exposed to the atmosphere. Sedimentation ceased as the streams became sluggish and the floodplain ceased to sink relative to the southern landmass. The sediments of this last phase consist of the dominantly poorly‐sorted, red sandstones and siltstones of the Cookamidgera Sub‐Group.

ISSN:0016-7614    

DOI:10.1080/00167616508728589

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

ISSN:0016-7614    

DOI:10.1080/00167616508728590

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor

摘要:

Metalliferous Deposits

ISSN:0016-7614    

DOI:10.1080/00167616508728591

出版商:Taylor & Francis Group    

年代:1965

数据来源: Taylor