摘要:

The Mt Manypeaks Adamellite is a composite, regionally concordant pluton at least 22 km long and 3 km wide, associated with Precambrian amphibolite facies gneisses of the Albany‐Esperance Block, and situated about 35 km east of Albany, Western Australia. The pluton is surrounded by a granitised aureole, and shows structural and mineralogical harmony with the country rocks. Contacts vary from grada‐tional to sharp. Hence field relations are consistent with syn‐ or late‐kinematic emplacement in the catazone. The normative composition of the pluton corresponds with the thermal trough in the system An‐Ab‐Or‐Q‐H2O at 7 kb PH2O, suggesting an origin involving crystal‐melt equilibria. The pluton is believed to have formed almostin situby partial anatexis of the country rocks at 700–750°C and a depth of about 25 km during the orogenic episode responsible for regional metamorphism and deformation.

ISSN:0016-7614    

DOI:10.1080/00167617308728811

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

The South Australian seismograph network has been extended since 1968 so that most earthquakes of Richter magnitudeML≥ 1.9 within the state are located accurately. Recurrence relations have been derived which define the seismicity of the known active areas. The seismic energy release has also been used to indicate the spatial variation in earthquake activity. Epicentre trends have been noted, and may be related to hypothesized movements on intracontinental plate boundaries.

ISSN:0016-7614    

DOI:10.1080/00167617308728812

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

In southern India the older Precambrian is overlain unconformably in the Cuddapah Basin by the Cuddapah and Kurnool Systems. The former is tilted and unmetamorphosed in the west but eastwards becomes strongly folded and metamorphosed. It contains lavas and sills, particularly in the lower two groups, is intruded by dolerites and at Chelima by diatremes of kimberlitic affinities related to those intruding the older gneisses west of the Cuddapah Basin in the Wajrakarur area. The Kurnool System lacks any igneous rocks; its basal conglomerate is diamondi‐ferous.

ISSN:0016-7614    

DOI:10.1080/00167617308728813

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

The pre‐Devonian sedimentary and volcanic sequence exposed along the south coast of New South Wales has previously been divided into three stratigraphic groups: (1) Upper Ordovician graptolite‐bearing slate which is conformable with (2) interlayered thinly‐bedded greywacke and pelite of undifferentiated Ordovician age and (3) Cambrian successions of interlayered chert, pelite and volcanic rock at Bate‐mans Bay and Narooma. The main bases for this subdivision are a change in rock types between (1) and (2), and the unconformity between (2) and (3) formerly proposed on the basis of changes in rock type and fold style across the boundary. New structural data are presented which refute the presence of the unconformity, and conformity of (2) and (3) with the fossiliferous slates is established.

ISSN:0016-7614    

DOI:10.1080/00167617308728814

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Age determinations have been made on three occurrences of Fitzroy Lamproite using the potassium‐argon isotopic dating method. Within each body, well‐crystallised minerals gave consistent ages. It is inferred from these results that the three Fitzroy Lamproite bodies were emplaced 17.0 ± 0.2, 19.5 ± 0.6, and 20.8 ± 2.0 m.y. ago, in the Early Miocene.

ISSN:0016-7614    

DOI:10.1080/00167617308728815

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Palaeolatitude data obtained from palaeomagnetic studies of Australian formations are described and compared with the palaeoclimatic zones inferred from geological observations. The two techniques produce results which agree for most of the Palaeozoic. Only for the Early Cambrian (and late Proterozoic) and Mesozoic do the climatic indicators appear to contradict the palaeolatitude evidence. It is pointed out that each of these geological intervals follows immediately a period of widespread glaciation.

ISSN:0016-7614    

DOI:10.1080/00167617308728816

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Discordant uranium‐lead isotope measurements are reported for a sample of Nabarlek pitchblende. These are compared with earlier measurements on uranium minerals from the South Alligator River area. New interpretations suggest that regional uranium mineralisation took place either 710 or 815 m.y. ago; the lower of these calculations is based on the assumption of modern episodic lead loss, and the higher assumes lead loss by continuous diffusion.

ISSN:0016-7614    

DOI:10.1080/00167617308728817

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

During the Late Mesozoic, igneous activity in Tasmania produced a number of small intrusive bodies and swarms of dykes. Typical examples of these rocks are found on the West Coast and around Cape Portland and Cygnet. The rocks belong to a shoshonitic association and they form part of a more extensive petrographic province that extends from Tasmania into eastern Australia.

ISSN:0016-7614    

DOI:10.1080/00167617308728818

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Recharge to the Quaternary aquifers beneath the Northern Adelaide Plains was estimated to be 3.9 x 106m3/year using the environmental tritium concentration of water samples taken from suitably sited boreholes. Recharge to the Tertiary aquifers was estimated to be 0.4 x 106m3/year, by the same isotopic techniques. These results may be compared with a total recharge by leakage through the beds of streams which cross the plain, estimated by the South Australian Department of Mines to be 6.4 x 106m3/year.

ISSN:0016-7614    

DOI:10.1080/00167617308728819

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Despite the palaeoecological emphasis of recent stromatolite research outside the USSR, controversy still exists regarding the environmental restriction of these organosedimentary structures and some analogies with modern occurrences have been maintained too rigidly. Palaeo‐environments should be determined where possible by a combination of all biological and sedimentological evidence. In South Australia, Precambrian carbonate rocks contain widespread stromatolites. The absence of independent biological environmental indicators necessitates a reliance on general stratigraphic and sedimentological data for the interpretation of regional palaeogeography and local environmental conditions. The Skillogalee Dolomite contains one predominant form of stromatolite almost throughout its extent, and it chiefly grew as biostromes in littoral and lagoonal settings on an extensive, level, carbonate‐depositing platform, probably of restricted access to the open sea. The interspace and associated sediments show evidence of varying energy conditions, degree of oxidation and possibly salinity, but the same stromatolite persists, although there is some modification of morphology in the higher energy environments. The Umbera‐tana Group has basinal shale and siltstone in its lower part, but during a subsequent widespread regression, the marginal parts of the basin were shallowed sufficiently to allow the growth of stromatolites, probably in water depths ranging from shallow subtidal to low supratidal. In addition, in the northern central part of the basin, offshore banks of shallow water limestone may have been related to areas of diapiric activity. The stromatolites of the Umberatana Group most often occur as bioherms of varying sizes intimately associated with ooid and intraclast grainstones, cross‐bedded sandy limestone, and, in marginal areas, penecontemporaneous dolomite. Different forms may occur in sequences of seemingly indistinguishable litho‐facies. These observations strengthen the view that stromatolite morphology is at least partly biologically controlled, the defined taxa being largely independent of the local environment.

ISSN:0016-7614    

DOI:10.1080/00167617308728820

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor