摘要:

Debris avalanches are rapid flowages of incoherent, unsorted mixtures of rock and soil material which move in response to gravity. On the southern and eastern slopes of Mt Hagen, a minimum area of 105 km2has been covered by chaotic deposits of matrix‐supported clasts which form conical hills. The mean minimum thickness of the deposit is of the order of 30 m and the minimum volume is 3.2 km3. No source area for the avalanche can now be discerned on Mt Hagen but the headwaters area of the Gumants River seems the most likely. This absence of evidence of a source area and tephras overlying the deposit indicate that the debris avalanche occurred at least 80–100 ka and probably more than 400 ka. Emplacement of this avalanche may have contributed to the reversal of the Wahgi drainage.

ISSN:0812-0099    

DOI:10.1080/08120098608729366

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Some recent models of the history of the east Australian continental margin suggest that the continental drainage divide has migrated to the west during the Cainozoic, whereas other models suggest a stable divide. All recent models of the history of the highlands (as distinct from the margin) imply a stable divide. Detailed data from Cainozoic channels in the proximal and distal reaches of the Lachlan and Wollondilly Rivers indicate divide stability in their proximal reaches for much of the Cainozoic, and at least throughout the Neogene in their distal reaches. Models of Tasman Sea formation, therefore, must incorporate a relatively stable Australian hinterland.

ISSN:0812-0099    

DOI:10.1080/08120098608729367

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The Coolgarra Batholith in north‐east Queensland is composed of the Go Sam and Nettle granite suites which were emplaced approximately 314 Ma ago. Initial87Sr/86Sr ratios of the Nettle Suite appear to be marginally above 0.710, a value characteristic of a wide range of Late Palaeozoic felsic igneous rocks in the region. This suite appears to have been derived from an extensive isotopically homogeneous crustal source distinct from rocks which crop out in the Palaeozoic Hodgkinson Basin or Precambrian Georgetown Inlier. Higher and more variable initial87Sr/86Sr ratios (0.727–0.744) of the Go Sam Suite are attributed to a combination of magmatic and hydrothermal processes. Isotopic data, thus, cannot be used to constrain the nature of the Go Sam source rocks. Tungsten (with or without tin) mineralization is associated with the Nettle Suite plutons, with which it shares a common age, whereas the Go Sam Suite is characterized by prominent tin mineralization. One tin occurrence is the same age as, or only slightly younger than, the Nettle Suite tungsten (with or without tin) mineralization. Another tin deposit yields an age of 301 Ma, suggesting the presence of a significantly younger granite at depth.

ISSN:0812-0099    

DOI:10.1080/08120098608729368

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The recent discovery of dickite, intimately associated with ordered and disordered kaolinite, in quartzose sandstones and conglomerates of the Illawarra Coal Measures is of interest since in terms of the phase rule the co‐existence of two or more of these polytypes is evidence of either an unstable or metastable assemblage. A study has, therefore, been undertaken of the host rocks and accompanying strata in an attempt to gain insight into the mechanism of formation of the dickite and the reason for its development in preference to either of the other generally more abundant polytypes. From the results it would appear that although much still remains unresolved, the dickite is authigenic and precipitated from migrating groundwaters. Due probably to unusually low concentrations of silica in the groundwaters the rate of precipitation was inordinately slow and this apparently facilitated growth of relatively coarse crystals and development of the most stable phase.

ISSN:0812-0099    

DOI:10.1080/08120098608729369

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Multiple230Th/234U age determinations on a uniform diameter calcite stalagmite from a Tasmanian cave show that it was deposited between 109 000 and 76 000 years BP at a constant rate of 4.3 cm per 100 years. Except for the first 9000 years, deposition occurred under conditions of oxygen isotope equilibrium enabling it to be used for palaeotemperature studies. Measurements of18O/16O ratios of calcite and d/h ratios of fluid inclusions indicate that mean annual temperatures at the site were nearly always lower than at present from 100 000 to 76 000 BP. A positive relationship is found between mean annual temperature and the18O/16O content of calcite. This is uncommon and represents the first such relationship recorded from the Southern Hemisphere. The stalagmite shows evidence of having grown during two distinct temperature phases. From 100 000 to 97 000 years BP mean annual temperatures were between 4°C and 6°C compared with a present day value of 9.5°C. At about 97 000 years BP there was a rapid transition to milder conditions with mean annual temperatures oscillating around 8°C until the record terminates at 76 000 years BP.

ISSN:0812-0099    

DOI:10.1080/08120098608729370

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The Mt Windsor Subprovince encompasses the dismembered remnants of a thick volcanic and sedimentary succession predominantly of Late Cambrian and Early Ordovician age located within the northern part of the Tasman Orogenic Zone. The succession is divided into four formations which together comprise the Seventy Mile Range Group. Its lower part, Puddler Creek Formation, comprises immature terrigenous clastic strata lacking in volcanics but hosting numerous penecontemporaneous dolerite sills and dykes. Its upper part, Mt Windsor Volcanics, Trooper Creek Formation and Rollston Range Formation, is dominated by acid and intermediate volcanics and volcaniclastics. The group has been dismembered, deformed and in part metamorphosed by emplacement of the Middle Ordovician Ravenswood Granodiorite Complex which is regarded as having been diapirically emplaced. Stratigraphic relationships and reconnaisance geochemistry suggest that the volcanics comprise a consanguineous series ranging from basaltic andesite to rhyolite with the silicic varieties volumetrically predominant. The volcanics are calc‐alkaline in type, typical of active continental margins. Silicic stocks and dykes intruding the Puddler Creek Formation are regarded as hypabyssal equivalents of the volcanic series. Facies relationships and thickness variations suggest that the source of the volcanics was generally from the east. The Seventy Mile Range Group is regarded as having been deposited in a back‐arc basin floored with continental crust and broadly of north to south orientation. The Mt Windsor Subprovince is thought to be a remnant of an active margin terrane which extended the entire length of eastern Australia and represents the earliest developmental stage of the Tasman Orogenic Zone. The concept of a discrete Early Palaeozoic Thomson Orogen in north‐eastern Australia is rejected.

ISSN:0812-0099    

DOI:10.1080/08120098608729371

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098608729372

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098608729373

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098608729374

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098608729375

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor