摘要:

Pseudotachylite veinlets occur in the Mawson charnockite along mylonite zones that exhibit intracrystalline plastic deformation. The veinlets intruded along fractures propagated between paired mylonites, and contain orthopyroxene and plagioclase microlites and a magmatic foliation. Although the angular shape of charnockite porphyroclasts in pseudotachylite veinlets implies brittle deformation during fracture propagation, intracrystalline plastic deformation took place before and after pseudotachylite generation. Microprobe analyses indicate that the pseudotachylite veinlets crystallized from a silica‐ and alkali‐rich melt which formed during total rock melting of charnockite in the mylonite zones. The metamorphism and melting of charnockite porphyroclasts was a consequence of their inclusion in this melt. Fe‐rich and alkali‐poor aggregates, probably after melt and possibly after glass in the pseudotachylites, are interpreted to be the result of the incomplete digestion of orthopyroxene and biotite porphyroclasts.

ISSN:0812-0099    

DOI:10.1080/08120099008727900

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Rb‐Sr whole rock analyses describe the isotopic system of the Mount Edgar Batholith in the Archaean Pilbara Block, Western Australia. The batholith comprises a complex gneiss terrain intruded by ‘older’ variably deformed granites, minor aplite, and a ‘younger’ post‐tectonic granite, the Moolyella Suite. The ‘older’ granites occur as six suites with isotopically indistinguishable individual isochrons; the pooled mean age is 3202 ± 17 Ma with initial87Sr/86Sr ratios in the range 0.7010–0.7025. This age is taken to record timing of granite emplacement, although it may represent a metamorphic resetting. If the latter is correct, resetting took place in the greenschist to lower amphibolite facies, less than 100 Ma after batholith formation. Localized Rb‐Sr resetting and aplite dyke emplacement record a ∼3000 Ma event also detected in other parts of the Pilbara Block. The ‘younger’ Moolyella suite is dated at ∼2800 Ma, but appears to have undergone minor isotopic disturbance.

ISSN:0812-0099    

DOI:10.1080/08120099008727901

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Lapstone Structural Complex forms the most prominent topographic feature in the Sydney region. The complex consists of a number of related folds and faults, trending generally north‐south, which together form a large south‐plunging structure between Kurrajong Heights and Lapstone. The east‐facing escarpment of the Blue Mountains, formerly called the Lapstone Monocline, varies in its character, being sometimes a single monocline, sometimes a double monocline and sometimes a normal or high‐angle reverse fault. Faulting west of Kurrajong and at Glenbrook is part of a series of overlappingen echelonfaults, west‐side down, and sometimes overturned, rather than a single fault. This fault system forms the west side of the complex. Significant minor structures associated with major features include thrusts, minor folds, joint systems, tectonic breccias, sedimentary injections and igneous dykes. Many of the minor structures show a marked parallelism with the major structures.

ISSN:0812-0099    

DOI:10.1080/08120099008727902

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A variety of trace fossils including human, avian and macropodid footprints are preserved in two coastal settings of different ages near Clare Bay, South Australia. Macropodid and other tracks occur in laminated littoral sediments of Late Pleistocene age (ca.110 000 years BP). They are preserved beneath a former prograding coastal fore‐dune complex now being exposed by shoreline erosion and regression. Human footprints, together with tracks of emus, kangaroos and wallabies, are present a few kilometres inland on the margin of a coastal saline lake. They originated about 5000 years ago, when soft dolomitic and calcitic marls formed from groundwater seepage and evaporation around gypseous lake margins. Preservation resulted from subsequent lithificat ion of the marl. The footprints have been subject to continuing exposure since formation but are remarkably well preserved.

ISSN:0812-0099    

DOI:10.1080/08120099008727903

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In the upper Barnard River district in the southern New England Fold Belt, unconformable contacts separate Early Permian clastic sedimentary rocks from Devonian spilites to the west of the Peel Fault and from chert and siliceous argillite of probable Middle Palaeozoic age to the east of the Peel Fault. In the Comboyne district, 110 km to the east, a similar contact between Early Permian and older rocks occurs. At each locality several thousand metres of pre‐Permian erosion is indicated, with uplift, possibly a product of back thrusting, immediately west of the Peel Fault and subduction accretion farther east. Uplift may not everywhere have been synchronous, and the unconformities need not relate to a discrete episode of deformation. Early Permian rocks from either side of the Peel Fault in the upper Barnard River have a common provenance and contain compositionally distinctive detrital augite which is indistinguishable from that in the Devonian spilites, indicating limited post‐Carboniferous movement only on the fault. Although the fault separates depositional realms of contrasting character in the Devonian and Early Carboniferous, it does not mark a major Early Permian facies boundary.

ISSN:0812-0099    

DOI:10.1080/08120099008727904

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Zircon U‐Th‐Pb and mineral K‐Ar and40Ar/39Ar isotopic studies indicate that the maximum deposition age of the Mt Narryer quartzite (which contains detrital zircons up to 4200 Ma old) is 3280 Ma, or by association with other sequences possibly 3100 Ma. This postdates a major episode of high‐grade metamorphism, granite emplacement and deformation at 3300 Ma, which affected adjacent gneiss terranes and which previously had been considered to have affected metasediments and basement gneisses alike. Prograde metamorphism of the Narryer metasediments to amphibolite facies evidently took place during a younger event culminatingca2700 Ma, prior to injection of granite sheetsca2650 Ma in age, by which time the present tectonic framework had been assembled.

ISSN:0812-0099    

DOI:10.1080/08120099008727905

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ephemeral saline lakes form along the eastern shore of Spencer Gulf where beach ridges isolate areas of the high supratidal zone. The region is semi‐arid with rainfall averaging about 320 mm/year and with an evaporation rate of 2000 mm/year. Lacustrine sediments in the lake studied contain abundant discoidal gypsum with a calculated δ34S value of +14.9‰ indicative of precipitation from non‐marine, porewater sulphate (δ34S, +13.4‰). Sulphur, deuterium and oxygen isotope distributions and distinctive K/Br and Mg/K ion ratios indicate that groundwaters from landward of and within the lake are non‐marine in origin. The marine‐terrestrial groundwater interface is mobile; after heavy rains, continental‐derived brines flow seaward as far as the high intertidal zone.

ISSN:0812-0099    

DOI:10.1080/08120099008727906

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Gravity anomaly trends from the southern margin of Australia and its associated ‘margin basins’ support the hypothesis that margin formation has been related to two distinct phases of lithospheric extension. Seismic data indicate that extension with a northwest to southeast orientation led to formation of the Eyre Sub‐basin in the pre‐Late Jurassic (Oxfordian): the gravity trends indicate that extension probably took place throughout the region west of the Otway Basin. Extension with a north‐northeast to south‐southwest orientation created the Gippsland Basin in the Early Cretaceous and, as indicated by the gravity, appears to have extended across the entire Otway‐west Tasmania‐South Tasman Rise portion of the margin.

ISSN:0812-0099    

DOI:10.1080/08120099008727907

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The formation of shoreline gypseous dunes is a major event in the Quaternary history of many playas in central Australia. The dunes probably were formed during a period of high regional water table when abundant gypsum was deposited in a near‐shore groundwater seepage zone and deflated on to the shoreline dunes. Ten samples from two sites at Lake Amadeus, a major playa in the region, provided coarse (90–125μ) quartz grains for thermoluminescence (TL) dating. Both regeneration TL and additive TL were measured. A well defined regeneration curve is basically consistent with the additive curves. Three methods, alpha counting, analyses of radioactive isotope concentrations and on‐site gamma scintillometer measurements, were used to evaluate the dose rates, giving consistent results. Although the equivalent doses of the samples scatter from 25 Gy to 71 Gy, the TL ages of all samples from the two sites cluster in the range 45–60 ka.

ISSN:0812-0099    

DOI:10.1080/08120099008727908

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120099008727909

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor