摘要:

Interbedded sandstones and red mudstones of the Upper Devonian Merrimbula Group on the south coast of N.S.W. were mildly deformed during the Carboniferous in a ‘transitional’ tectonic regime. A remarkable variety of structures was developed. Tectonic shortening of about 10% was accommodated by the development of kink‐like monoclines and box folds with very wide‐spaced (few cm) cleavage in sandstones, spaced (few mm) ‘reticulate’ cleavage in siltstones, and a penetrative slaty cleavage in mudstones. Solution transfer played an important role in cleavage formation. Faults and conjugate shear zones, followed by regional joints, were developed in competent beds. Abundant quartz veins occur in bedding planes, faults and shear zones. The low strain allows certain kinematic and dynamic conclusions: the structures are geometrically congruent, were developed under high fluid pressures at a high level in the crust, and are related to a single, long deformational episode under essentially horizontal E‐W compression, possibly accompanied by shearing along bedding planes associated with local décollement. The stress configuration contrasts with that necessary for the wrench faulting and extensional rifting postulated for the period immediately prior to the deposition of the Merrimbula Group.

ISSN:0016-7614    

DOI:10.1080/00167618308729256

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Rare mafic dykes, which intrude 1000 Ma high‐grade metamorphic rocks of the northern Prince Charles Mountains‐Mawson Coast area, are compositionally distinct from abundant early to middle Proterozoic tholeiite dykes, which are confined to Archaean or early Proterozoic terrains in the southern Prince Charles Mountains and elsewhere in East Antarctica, and which have therefore proved useful as stratigraphic markers. The younger dykes (and extrusive rocks) are a composition‐ally heterogeneous group with a wide range of ages (at least Cambrian to Eocene), although most are of K‐rich alkaline composition or have alkaline affinites. Their strong enrichment in highly incompatible elements (Rb, Ba, Th, Nb, K, Pb, Th and U) relative to less incompatible elements (La, Ce and P) suggests derivation by partial melting of more enriched mantle source regions than those of most of the Proterozoic tholeiite suites. However, unlike the latter, many incompatible element ratios have been significantly affected by fractional crystallisation and possibly also by the presence of residual minor phases during low degrees of melting.

ISSN:0016-7614    

DOI:10.1080/00167618308729257

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Australia's Eastern Highlands are a conspicuous manifestation of a tectonic regime that has been previously shown to go back at least 65 Ma. This review of the Mesozoic stratigraphy of eastern Australia gives evidence of a very different regime before 95 Ma, related to the presence of a plate boundary close to the present east coast of the continent.

ISSN:0016-7614    

DOI:10.1080/00167618308729258

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The Lower Permian Byro Group and lower Coolkilya Sandstone of the Carnarvon Basin comprise a 1400 m thick, marine‐shelf sequence of sandstone, siltstone and shale. The sequence is repetitive and is characterised by six facies:1.black‐shale facies (representing the lower offshore environment);2.grey‐siltstone facies (upper offshore environment);3.bioturbated‐sandstone facies (transitional environment);4.laminated‐to‐burrowed facies (lower shoreface environment);5.hummocky‐cross‐stratified sandstone facies (middle shoreface environment); and6.swaley‐cross‐stratified sandstone facies (middle to upper shoreface environment).

ISSN:0016-7614    

DOI:10.1080/00167618308729259

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

This paper continues a survey of Sm‐Nd age relationships at the margins of the Yilgarn Block, Australia's largest Archaean craton. Model ages have been determined along an irregular transect extending approximately 120 km from the extreme SW of the Western Gneiss Terrain of the Yilgarn Block through the western extremity of the Albany‐Fraser Province, a major Proterozoic mobile belt. The ages demonstrate the significance of the Manjimup and Pemberton Lineaments as major crustal discontinuities. The sequence of ages across the lineaments strongly supports accretionary models of Precambrian crustal evolution, although some aspects of the age sequence can also be interpreted as mixing trends. Within the Western Gneiss Terrain, the Manjimup Lineament marks a change from older (c. 3.1 Ga) to younger (c. 2.7 Ga) Archaean gneisses. Further south the Pemberton Lineament, marking the northern tectonic boundary of the Albany‐Fraser Province, defines a change from Archaean (c. 2.7 Ga) to Proterozoic (c.2.1 Ga) mantle differentiation ages. The one exception within the mobile belt is a sample of granulite from Windy Harbour, the age of which (3.1 Ga) implies that the Proterozoic crustal material of the Albany‐Fraser Province is sharply terminated to the west as well as to the north. The ages determined within the Albany‐Fraser Province, together with those previously reported for the Gascoyne Province, point to the existence of a major crust‐forming event surrounding a considerable portion of the Yilgarn Block about 2 Ga ago.

ISSN:0016-7614    

DOI:10.1080/00167618308729260

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Measurements of 18 closely spaced beach profiles spanning Warilla Beach, N.S.W., over a 5‐year period, have been examined for the onshore‐offshore sediment exchanges by empirical orthogonal function (EOF) analysis. Each profile was divided into slices of beach corresponding with berm, upper swash, upper and lower intertidal zones. The first EOF mode represents onshore‐offshore movement and contains at least 67.6% of the variance for each profile. The southern half of the beach is backed by a rockwall. Variances on this section range from 81.0% to 95.1%, whereas away from the wall the variances range from 67.6% to 88.4%. The second most important mode is a swash‐function mode representing sediment exchange between the lower‐intertidal zone and the upper beachface. The variance of this mode ranges from 3.9% to 23.2% for the 18 profiles. Other modes were identified, viz., the berm function mode (where sediment is exchanged between the berm and the rest of the beachface), the mean‐sea‐level mode (where exchange is through a pivotal point near mean‐sea‐level), and a secondary‐swash mode. Sediment exchanges occur generally at 24, 12 and 6 month periods.

ISSN:0016-7614    

DOI:10.1080/00167618308729261

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The Ordovician palaeogeography of southeastern Australia was an east‐facing mafic volcanic island arc separated from the Gondwanan continent by a marginal sea, probably floored by oceanic crust. By mid‐Silurian the palaeogeography had changed to an almost wholly ensialic configuration, with meridional horsts and grabens east of the Wagga Metamorphic Belt and widespread silicic magmatism. By extending a previously postulated match between the modern Andaman Basin and parts of southeastern Australia in the Late Ordovician, the transition from the Late Ordovician to Late Silurian palaeogeography can be explained. The entire Ordovician and Silurian interval can be understood in terms of a relatively simple and constant plate geometry involving southeastern Australia in regional dextral shear.

ISSN:0016-7614    

DOI:10.1080/00167618308729262

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Fluid inclusion homogenisation temperatures from the magnesites of the Celia Dolomite and the Coomalie Dolomite of the Rum Jungle area of the Pine Creek Geosyncline, N.T., indicate that temperature is a major control of the two distinctive morphological forms. The rhombohedral form recrystallised in association with fluids that homogenised mainly at temperatures less than 150°C, whereas the bladed (tabular) form developed by recrystallisation at a higher temperature. Previously the two forms have been interpreted as pseudomorphs after halite and gypsum, respectively.

ISSN:0016-7614    

DOI:10.1080/00167618308729263

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Field studies in the Eucalyptus area, northeastern Yilgarn Block have shown intrusive and extrusive rocks in an Archaean greenstone sequence to be comagma‐tic, and have suggested the sequence of subsequent granitoid intrusion and gold mineralisation. Andesitic volcanic rocks and related subvolcanic granodiorite porphyry and epiclastic sediments were followed by tholeiitic basalt with gabbro/dolerite sills and dykes, which were in turn succeeded by high‐Mg basalt with associated peridotite intrusions. Large, irregular gabbro and peridotite intrusions, which are inferred to represent subvolcanic magma chambers, occur in lower stratigraphic levels, whereas comformable subvolcanic sills occur in higher stratigraphic levels. Granodiorite plutons were followed by adamellite plutons; at least some gold mineralisation was contemporaneous with granitoid emplacement.

ISSN:0016-7614    

DOI:10.1080/00167618308729264

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A late‐Tertiary age, as well as the commonly accepted mid‐Tertiary age, is proved for widespread silcretes in S.A. This is demonstrated by stratigraphic relationships with palynologically dated sequences, and evidence of erosion of silcretes. The age limits are Early Eocene to Early Miocene and Medial Miocene to Early Pleistocene, probably Late Pliocene. The late‐Tertiary silcrete dominates the duricrusted landscape flanking the north of the Willouran and Flinders Ranges, and forms patches throughout the Tarkarooloo Lobe (Lake Frome area). Silica type varies according to the material cemented; chalcedony and opal are more common in finer grained, less permeable, clayey clastics, and micro‐ to crypto‐crystalline quartz ('grey billy’ or ‘terrazzo') in porous permeable arenites and regoliths.

ISSN:0016-7614    

DOI:10.1080/00167618308729265

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor