摘要:

The weighted mean values of the234U/238U and the230Th/234U ratios in ore samples collected above the modern water table of the Yeelirrie uranium deposit in Western Australia are 1.38 ± 0.10 and 0.83±0.28, respectively. The relatively larger variability in the latter ratio is evidence for the translocation of uranium subsequent to deposition. Daughter product separation is due to differences in the mobilities of the thorium and uranium species. Factors involved in interpreting the observed ratios, in terms of the dynamics of the accumulation of the deposit, are assessed in terms of an open system model. The observed disequilibria provide a quantitative basis for the evaluation of hypotheses developed from geological and other considerations.

ISSN:0016-7614    

DOI:10.1080/00167618108729174

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The Mount Boreas‐type granite and spatially associated syenitic granitoid of Western Australia yield Pb‐Pb ages of 2370±100 Ma and 2760 ± 210 Ma, respectively. Th‐Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U‐Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (< 3μg/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete‐hosted uranium deposits. The possibility remains that the Mount Boreas‐type granite that has been completely weathered during the Tertiary could have been a source for the calcrete‐type uranium deposits in W.A. Although the Mount Boreas‐type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (∼ 20μg/g)and are associated with large roll‐type and other low temperature‐type uranium deposits.

ISSN:0016-7614    

DOI:10.1080/00167618108729175

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The Mesozoic forerunner of the western margin of Australia has been regarded tectonically as an ancient analogue of the multiple rift‐valley system of East Africa, which comprises two arms: volcanic on the E, and virtually non‐volcanic on the W. The abundance of widespread volcanics recently dredged and cored along the outermost margin, which corresponds with the volcanic arm of the East African system, contrasts with the apparent scarcity of volcanics inshore, in the inner arm of the rift system. We tested the possibility that volcanogenic material has been overlooked inshore by a petrographic study of the Late Jurassic to earliest Cretaceous Yarragadee Formation of the Perth Basin; only rare possible pyroclasts of quartz and glass (probably emplaced by air‐fall from the volcanic outer arm) were found, confirming the contrast in volcanism between the arms. This petrological evidence, together with the appropriate range of composition of the volcanism, from silicic to mafic, including alkaline and peralkaline members, reinforces the analogy with East Africa.

ISSN:0016-7614    

DOI:10.1080/00167618108729176

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Palaeomagnetic results are presented for two young volcanoes in southeastern Australia. Directions for the basalt and lava spatter, erupted near the beginning and end of activity at Mt Gambier respectively, are identical and suggest there was no long break in activity. The direction for basalt at Mt Schank differs from that of Mt Gambier by several degrees, and indicates that the two volcanoes differ in age, probably by three centuries or more. Directions for both volcanoes are much shallower than the present‐day geomagnetic direction at the locality. Palaeomagnetic field strength estimates, from baked ash at Mt Gambier and baked sand at Mt Schank, are higher than the present‐day field strength. Comparisons with other late Pleistocene and Holocene results suggest that ages for Mts Gambier and Schank are either greater than 7000 years or between 5000 and 1000 years. These conclusions are consistent with published radiocarbon ages from charcoal in fossil soil horizons sealed beneath ash deposits.

ISSN:0016-7614    

DOI:10.1080/00167618108729177

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A reconnaissance traverse across Victoria yields 160 K‐Ar dates on igneous rocks from 94 localities. These are supplemented by Rb‐Sr dating in critical cases, and major‐element analyses (some new) on a proportion of the samples. All dates quoted in text and tables, new and previously‐published, have been revised in terms of the latest decay‐constant conventions.

ISSN:0016-7614    

DOI:10.1080/00167618108729178

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Three types of pediment have been recognised. The first are cut bedrock surfaces, veneered (and hence smoothed and protected) by coarse alluvial debris. Characteristically developed in the Brachina area of South Australia, they form in the piedmont zone in areas of mixed sedimentary outcrop and in areas where there are large variations in river and stream discharge, including occasional high floods. They are not restricted to any conventionally defined climatic region or regions, though their development is favoured by stream regimes characteristic of arid and semiarid lands.

ISSN:0016-7614    

DOI:10.1080/00167618108729179

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The sedimentary record from Lake George provides the longest relatively continuous Quaternary continental sequence yet available from Australia, and may record one of the longest Upper Cainozoic lacustrine records in the world.

ISSN:0016-7614    

DOI:10.1080/00167618108729180

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A spinel lherzolite body outcrops as a fault block on the north coast of East Timor. The most common rock‐type in this body is a clinopyroxene‐poor lherzolite, but there are smaller proportions of clinopyroxene‐rich lherzolite and harzburgite. The dominant mineral assemblage is olivine, orthopyroxene, clinopyroxene, spinel and calcic amphibole. Low‐temperature hydrous minerals are restricted in distribution.

ISSN:0016-7614    

DOI:10.1080/00167618108729181

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

From new data on coastal and continental shelf morphology, sediments, stratigraphy and chronology, it is possible to formulate a general model of late Quaternary marine sedimentation, for New South Wales and southern Queensland. This model integrates various factors influencing deposition in coastal and shelf environments, in relation to glacio‐eustatic sea level oscillations.

ISSN:0016-7614    

DOI:10.1080/00167618108729182

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Explosions at two large open cut mines (Leigh Creek and Iron Baron) were used as sources of seismic energy to record along two linear profiles, parallel and approximately transverse to the axis of the Adelaide geosyncline in South Australia. Records at approximately 120 sites were obtained out to distances of the order of 350 km with Kinemetrics PS‐1A portable seismographs, using smoked paper and a recording speed of 4 mm/s. Times of blasting were determined from records at some of the permanent stations of the University of Adelaide seismograph network. Station spacing was normally 5 km, but at large distances from the source this increased to the order of 10 km.

ISSN:0016-7614    

DOI:10.1080/00167618108729183

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor