School of Earth Sciences - Theses
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ItemThe tectonic history of the Ruker Province, southern Prince Charles Mountains, East Antarctica: implications for Gondwana and RodiniaPhillips, Glen ( 2006-12)Within the Ruker Province of East Antarctica, there is evidence for several key geological events that have occurred coincidently with periods of dynamic earth evolution. A detailed evaluation of the tectonic history of the region is therefore required. This research focuses on the tectonic development of the Ruker Province. The main aspects of this research can be summarised as follows: (1) an evaluation of the gross crustal architecture of the region through the development of a new stratigraphic and structural framework; (2) new U-Th-Pb (LA-ICPMS) age data from detrital zircon grains extracted from thick metasedimentary units that comprise a major component of the Ruker Province; (3) new 40Ar/39Ar data from metamorphic minerals to determine the cooling history of the province; (4) mineral equilibria modelling of metamorphic mineral assemblages to constrain pressure-temperature (P-T) conditions during key orogenic events; (5) a kinematic analysis of brittle/ductile deformation features. Ideas developed from these new data provide inferences on the assembly and dispersion of the late Proterozoic super-continents Rodinia (c. 1000 Ma) and Gondwana (c. 500 Ma).
ItemA new perspective on melt inclusions: development of novel in-situ analytical protocolsPAUL, BENCE TIMOTHY ( 2006-08)Novel techniques for in-situ lead isotope analysis of melt inclusions using multicollector inductively coupled plasma mass spectrometry, and parallel Faraday cup and ion counter detection have been developed. These provide for measurement of the critical 204Pb isotope, which has been unavailable in melt inclusion Pb isotope studies, but requires on-line determination of 200Hg to correct for 204Hg isobaric interferences. External standardisation allows for effective mass fractionation correction and ion counter gain calibration. An off-line Tau correction was applied and standard glass analyses suggest that this correction provides more accurate and precise results.
ItemContinental tectonics and landscape evolution in south-central Australia and southern TibetQuigley, Mark Cameron ( 2006-09)The Indo-Australian Plate is actively deforming at its margins and within its interior. In south-central Australia, more than 3000 km from the closest active plate boundary, a geomorphically rugged and apparently youthful mountain range has developed, rising up to 1.1km above the adjacent flat-lying outback plains. These ‘Flinders’ and ‘Barrier’ Ranges are seismically active and bound by major reverse fault scarps with clear evidence for Plio-Quaternary displacements, implying that young and active intraplate tectonism has played a fundamental role in their development. Palaeoseismic investigations and optically stimulated luminescence (OSL) chronology indicate faulting occurred in response to a series of large magnitude (~M6.6 to M7.3) palaeo-earthquakes with recurrence intervals of ~1:20,000 to~1:80,000 yrs and long-term fault slip rates of ~50 m Myr-1. Geomorphic observations and 10Becosmogenic nuclide dating indicate surprisingly high and spatially variable rates of bedrock erosion from fault-affected catchments in the Flinders Ranges. Slowly eroding bedrock summit surfaces have been uplifted up to 12 m in the last 60,000-100,000 years relative to more rapidly eroding valley floors and bounding piedmonts, indicating Late Quaternary increases in elevation and relief in response to intraplate tectonism and erosion. However, both facies changes and sediment aggradation-dissection cycles in alluvial fan sequences are out-of-synch within dividual tectonic events, indicating that an aspect of climate (aridification, changing flood frequency-magnitude distributions) has governed the spatial-temporal distribution of range front sedimentation.
ItemThe low-temperature thermochronology of cratonic terranesBelton, David X. ( 2006)Cratonic terranes present many problems for geologists attempting to define those regions of the continental crust that are the core of today's continents. Inherent in the term is the great passage of time, and typically, the term defines consolidated Archaean or Proterozoic crust (Park and Jaroszewski, 1994). Cratons are further distinguished on the basis of tectonic activity. Marshak and his colleagues (1999) suggest that the lack of penetrative deformation or metamorphism is a useful definition but they further narrow this with the restriction of a Precambrian timeframe. Central to either view is the assumption of stability and perhaps senescence. And, since many aspects of geological research involve the detection of stratigraphic, structural or mineralogical change, stability implies a lack, or at least a minimum, of change. Thus the absence of these traditional markers of geological evolution or change, related to these processes, presents significant challenges in the study of cratons. This is particularly so in shield areas - those cratons with exposed basement rocks (Park and Jaroszewski, 1994). The extraordinary age of shield rocks and their apparent preservation at the surface, has encouraged research into the mechanics of landscape development and the individual evolution of landforms in the landscape, particularly by geomorphologists. From within this environment many thought provoking ideas have been proposed to explain the breadth of observations pertaining to almost every aspect of landscape process in these terranes. According to Summerfield (1991) the models of Davis, Penck, King and Budel have had the most impact in this field. The ideas presented by these workers remain a cornerstone in our understanding of the earth's surface, but in detail and in practice, the models have been shown to be antiquated. Nevertheless, landform evolution models such as those of L.C. King (1967) have held sway in southern Africa and elsewhere long after the underlying assumptions have been shown to lack validity. The purpose of this thesis is to investigate key aspects of landscape evolution in two regions, central Australia and southern Africa, where models have been espoused, arguing for extraordinary surface stability or alternatively a simple erosional history or pediplanation. Contemporary thermochronological techniques now permit us to investigate these regions in previously unavailable detail. The primary technique used in this work was apatite fission track analysis and an introduction to the fundamentals of the method is given in Chapter 1. The theoretical and practical aspects of the fission track method provided the basis for an innovative approach presented in Chapter 2. TASC is a scheme for analysing the raw fission track data so as to extract additional information about the rock's thermal history prior to undertaking traditional inverse modelling techniques. This method (recently described by the author in Ehlers et al., 2005) proved to be a powerful complement to the routine fission track analysis undertaken as part of the Australian and African case studies. Although first proposed for geological use in the 1960's, the fission track technique really only gained serious application with a number of technical and theoretical breakthroughs in the 1980's. Since then, growing understanding of the processes of annealing and how they might be modelled has allowed the technique continue developing. Chapter 3 is a discussion of this topic that expands on material previously published by the author and colleagues (Gleadow et al., 2002) and presents additional new work. Nevertheless, despite it's wide application in tectonic and basin studies amongst others, there remain many improvements to be made and problems to be solved. As part of this project, research into several areas presented the author with opportunities to contribute toward improvement in the apatite fission track technique, that have the potential to aid the study of cratonic terranes. The chlorine content of apatite has a profound influence on the sensitivity of the mineral for recording thermal events. Few current annealing models are capable of comprehensively addressing the variation of chlorine and other trace elements that appear to play a role in the annealing process. This issue is addressed in Chapter 4 where a universal annealing model is proposed to deal with the wide chemical variability observed in real apatites. For this theme, a fresh consideration of established empirical mathematical models was undertaken and all the current published annealing data was considered. Modern inverse modelling is based on a series of robust, but nonetheless empirical, equations that have withstood the test of time. However, with the aim of developing a more realistic and thus predictive model, Chapter 5 introduces an alternative, physicochemical to modelling the thermal annealing of fission tracks. This work attempts to draw firmer links between the processes of fission track formation, the mechanics of diffusion and the predicted response to variable temperature regimes. The first of the case studies is presented in Chapter 6 and is a comprehensive investigation of the long-term landscape evolution of the Davenport Ranges in the central Australian Craton. The study employs traditional petrographic methods as well as thermochronology and combines cosmogenic isotope analysis in an assessment of early landscape models. This chapter expands on work previously published by the author and co-workers (Belton et al., 2004) and has implications for our understanding of landscape evolution in the broader context of the Australian Craton. In order to maximise temperature sensitivity in slow cooled terranes, the relatively new thermochronological technique of (U-Th)/Helium analysis of apatite was tested on a suite of central Australian samples. The inconclusive results of this experiment prompted an investigation into the possible causes, and an important baseline study was conducted (Chapter 7). The study has implications for routine application of this new thermochronometer in cratonic and other terranes. More importantly the research identified a potential new thermochronometer with an even greater temperature sensitivity and near surface application for use in future landscape studies. Chapter 8 documents a larger, craton-wide study of the Mesozoic to recent landscape evolution of the Zimbabwe Craton. This work builds on material presented in earlier chapters and provides a broader view of the nature of crustal cooling, structural reactivation and landform development in the cratonic setting of southern Africa.
ItemLate quaternary rivers and lakes of the Cadell Tilt Block region, Murray Basin, southeastern AustraliaSTONE, TIM ( 2006)A record of climatic, hydrological and tectonic change spanning the last glacial cycle (-130,000 years) has been obtained from alluvial, aeolian and lacustrine sequences in the Cadell Tilt Block region of the central Murray Basin. Optically stimulated luminescence (OSL) is the principal method of chronological control, with a total of 50 new luminescence ages. Two AMS radiocarbon (^14C) ages are supplementary. Soils are used for relative dating of landforms beyond the range of OSL and ^14C. The result is the largest corpus of late Quaternary ages ever produced for the region. The chronology of the Lake Tyrrell lunette sequence has been revised from previously published interpretations. Beach sediments ~13.5 m above the present lake floor were deposited by Lake Chillingollah, a marine oxygen isotope stage (MIS) 5 (~ 130,000- 75,000 years ago) megalake. The megalake dried because of decreasing winter rainfall and fragmented into a groundwater discharge system. A silty clay dune deflated from the Lake Tyrrell floor ~27,000 years ago ended a long period of pedogenesis and buried evidence for Aboriginal visits to the lakeshore. The earliest evidence for aridification along the Murray River is an episode of riverine source-bordering dune formation in early MIS 4 (~72,000 years ago). The event is a minimum age for the initiation of construction of the Barmah Fan, which accreted in response to uplift of the Cadell Tilt Block. Fan sedimentation on the foot wall close to the fault scarp appears to have accelerated between 65,000 and 45,000 years ago. The Green Gully palaeochannel on the uplifted block was abandoned by the Murray River soon after this period, which culminated in an episode of riverine source-bordering dune formation ~40,000 years ago. The Goulburn River was not defeated by uplift. An older prior stream on the uplifted block, with undatable strong red-brown earth soil profiles along its margins, is not a course of the Goulburn. Instead, the Goulburn River was deflected to the southwest where it developed the Tallygaroopna meander belt ridge. This course had been deflected by ~65,000 years ago. Vertical aggradation of the ancestral Goulburn continued until ~23,000 years ago. Riverine source-bordering dunes were beginning to form again when a clay plug filled the palaeochannel. The Tallygaroopna meander belt ridge is visible beneath the floor of Lake Kanyapella on LIDAR DEM imagery. Downstream it follows the course of Gunbower Creek. Lake Kanyapella is not fault-dammed or fault-controlled because it post-dates formation of the ridge. The lake formed ~34,000 years ago and was sustained by flows from the Tallygaroopna palaeochannel for ~10,000 years. A model of lake formation is proposed based on vertical bedload aggradation. That is, the lake emerged because the Goulburn River had fully-aggraded and could no longer channel its flood flows. This long-term ponding may be of wider palaeohydrological significance. Riverine source-bordering dunes form only at the end of the lacustral period. The Goulburn River avulsed from the meander belt ridge at the end of the Last Glacial Maximum (~18,000 years ago). The Kotupna palaeochannel was rapidly entrenched and back-filled, with riverine source-bordering dunes emplaced along its course in a geological instant. The harsh climate of the LGM was adapted to by the Kow Swamp people who developed robust physical morphologies in response to the cold conditions. Gracilization of the population is related to post-glacial climatic amelioration, which increased gene flow. Robust humans are rare after the LGM. Palaeochannel morphology is not climatically-controlled. Kotupna-type bars were deposited along the Bullatale Creek course of the Murray River in the Holocene, without any concomitant source-bordering dune formation. The Barmah Choke reach of the Murray River is relatively straight because it is a modern avulsion, not an inert Holocene river course. This avulsion happened only ~550 years ago, effectively shutting down the depositional system that constructed the massive Wakool Fan. This event ended a 75,000 year long avulsion sequence.