摘要:

Comparison of bulk chemistry confirms the comagmatic nature of the New South Wales leucitite belt and the olivine leucitite at Cosgrove, Victoria. This relationship was previously implied by general mineralogical, petrographical, and age similarities, as well as the meridional trend of the occurrences. Differences of a minor nature occur between the N.S.W. and Victorian rock types, the latter being less potassic and magnesian (poorer in leucite and olivine) and more calcic (richer in clinopyroxene). Trace‐element compositions for the Cosgrove leucitite are within the ranges recorded for the N.S.W. belt.

ISSN:0016-7614    

DOI:10.1080/00167617808729047

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Macquarie Island offers a rare opportunity to investigate outcropping ocean crust. In this study, palaeomagnetic samples were collected from 32 sites. After frequency demagnetization, 15 of these sites were found to be stable. Stable sites were from lavas, dykes, and gabbros, representing different depths of formation in the oceanic crust.

ISSN:0016-7614    

DOI:10.1080/00167617808729048

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Four distinct sedimentary facies have been recognized within the upper Precambrian Nuccaleena Formation in the central Flinders Ranges of South Australia. Three dolomite facies, containing tepee structures within either well‐laminated or stromatolitic dolomite, were deposited within supratidal and intertidal environments, whilst an interbedded shale and dolomite facies originated under very shallow submerged conditions.

ISSN:0016-7614    

DOI:10.1080/00167617808729049

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Rubidium‐strontium total‐rock geochronology of granulite‐facies gneisses in the western Musgrave Block, Central Australia records distinct metamorphic and earlier events. The Tomkinson Ranges are subdivided into two regions with similar relative geological sequences of events, but different primary ages and lithologies; the boundary between the regions is the latitudinally‐trending Hinckley Fault. A 90‐km traverse along regional strike in the northern region produces consistent 1550 m.y. ages. Sampling at several structural levels over a slight range of metamorphic grade in the southern region reveals a single regional isochron with a 1330 m.y. age. Both ages are interpreted as the time of supracrustal genesis of the rocks. Subsequently, granulite‐facies metamorphism occurred throughout the area at 1200 m.y.: attribution of this age to the metamorphism is based upon evidence for outcrop scale isotopic homogenization, and the dating of a granitoid intrusion contemporaneous with the metamorphism.

ISSN:0016-7614    

DOI:10.1080/00167617808729050

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The major features of the geology and geomorphology of the semi‐arid, tropical Torrens Creek area of North Queensland are described. The evolution of the landscape through the late Cainozoic is discussed with reference to three phases of landscape instability and erosion, each separated by phases of stability during which weathering and soil formation proceeded. These erosional periods were probably initiated by episodic uplift of the Great Divide region. Tentative correlations with landscape events in the nearby Nulla Basalt Province suggest that soil profile development probably occurred during late Pliocene (2.3–2.0 m.y. ago), mid‐Pleistocene (1.3–1.1 m.y. ago), and in Quaternary (less than 0.1 m.y. ago) times.

ISSN:0016-7614    

DOI:10.1080/00167617808729051

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The Bathurst batholith is a complex of massive granitic intrusions cutting across deformed early and middle Palaeozoic rocks of the Lachlan Fold Belt of New South Wales. An adamellite from Dunkeld, near the western edge of the batholith, has yielded K‐Ar ages of 304 ± 4 m.y. (total‐rock) and 301±6 m.y. (biotite).

ISSN:0016-7614    

DOI:10.1080/00167617808729052

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The Lower Permian Snapper Point Formation at its type locality in the southern Sydney Basin is interpreted as a regressive sequence of a linear clastic shoreline. Lithologies, sedimentary structures, and palaeocurrent patterns suggest a prograding barrier‐beach environment. Barrier foot, bar nucleus, bar crest, and back‐bar are distinguished. Abundant trace fossils aid the recognition of minor facies. The thickness of sediments deposited in the protected inshore environment may be explained by progradation into rising relative sealevel, but rates of sealevel rise or land subsidence were ultimately exceeded by the rate of sediment supply. Up‐sequence changes in the character of the sedimentation units and biofacies may therefore reflect an evolution from a barrier profile to an open mainland beach.

ISSN:0016-7614    

DOI:10.1080/00167617808729053

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The Wonaminta Block is bounded on its eastern and western margins by Lower Cambrian or upper Vendian intrusive and extrusive igneous rocks. The extrusive rocks include pillow lavas. Low‐grade metamorphism has not influenced the distribution of P2O3, Zr, Y, and Nb, but remobilization of Ti has occurred in rocks containing Ti within the oxide phases rather than in the silicate phases. Immobile trace‐element discrimination techniques indicate that the basalts on the western margin of the Wonaminta Block are alkaline whereas those on the eastern margin are tholeiitic. The possibility that these rocks represent petrological variants across an arc system is discussed.

ISSN:0016-7614    

DOI:10.1080/00167617808729054

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A downward‐facing refolded fold in the aureole of the Bathurst Granite displays evidence for three phases of folding. This, and structural anomalies in other Lachlan Fold Belt granitoid aureoles, may be caused by granitoid emplacement. Alternatively they may be records of early deformations, preserved in the granitoid envelopes from the obliterating effects of later deformations. Various causes for the three fold phases are considered, including soft‐sediment deformation, orogenies, and kinking as a result of granitoid emplacement. A unique solution is not yet possible. Unrecognised structural complexities may be widespread in the Hill End Synclinorial Zone.

ISSN:0016-7614    

DOI:10.1080/00167617808729055

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The Reid's Mistake Formation represents the stratigraphic interval that separates the Lower and Upper Pilot Coals within the Boolaroo Sub‐Group of the Newcastle Coal Measures. At Swansea Head it consists mainly of intercalated cherts and claystones with minor amounts of sandstone. The cherts, which frequently have a vitroclastic texture, are composed of chalcedony and analcime with or without feldspars and clay whereas the claystones consist of chalcedony and mixtures of mixed‐layer clay minerals. The intergradation between these rock types indicates that the entire sequence was derived from a common source, either acid volcanics of the New England fold belt or, more likely, contemporaneous ash showers. The detritus apparently accumulated in a flood basin environment where the climate was arid giving rise to saline conditions and the breakdown of the volcanic materials to clay minerals and chalcedony. During protracted periods of desiccation however, sodium ions were concentrated and the pH rose accordingly, sufficient to promote conversion of the clay minerals in the uppermost layers to analcime.

ISSN:0016-7614    

DOI:10.1080/00167617808729056

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor