School of Earth Sciences - Theses
Permanent URI for this collection
Search Results
1 - 5 of 5
-
ItemThe structural evolution, tectonics and hydrocarbons of the offshore Otway Basin, SE Australia( 2003)The offshore Otway Basin is part of Australia's passive southern margin, in which two separate rift-phases between the Tithonian? and Maastrichtian formed numerous depocentres. The research presented has analyzed and described the structural styles in the offshore Otway Basin and constructed a model of the basin's evolution since the Late Jurassic. The Otway Basin has been divided into four structural zones from north to south. Zone I comprises the onshore area and most of the shelf along the margin. Deep halfgraben developed during the first rift phase with characteristic horst and graben in Palaeozoic basement. To the south, zone I is bound by the Hinge Zone. Structural zone II covers the entire deepwater part of the Otway margin, characterized by a very thick Late Cretaceous section with pervasive Turonian faulting in the east and saucer-shaped depocentres in the west. Large halfgraben controlled deposition of the post-Turonian sedimentation in the eastern Otway Basin. Negative flower structures document strike-slip faulting. Strongly thinned lower laminated continental crust underlies this zone, limited to the south by the Outer Margin Highs. Domino faulting formed halfgraben and less commonly graben in Structural Zone III, the Outer Margin Highs. The base of the Outer Margin High sediments represents a regional decollement surface and domino faulting occurred along a second-generation decollement. Structural zone III is limited to the south by the continent-ocean-boundary with oceanic crust in structural zone IV. In the Shipwreck Trough, halfgraben died out against an accommodation zone which developed into the Shipwreck Fault with strike-slip offset .The regional stress regime indicate sinistral strike-slip movement along this fault zone. In the southwest Shipwreck Trough, four Turonian to early Coniacian syn-rift phases can be distinguished formed through footwall collapse to the north of the Hinge Zone. Differences in the amount of extension in the basin are accommodated along strike-slip faults such as the Shipwreck Fault. Sedimentation rates between 89 and 83 Ma increased whilst extension rates declined. Since approximately 83Ma sedimentation rates declined exponentially in phase with extension rates. Regionally, rapid Turonian extension formed a wide graben system between Antarctica and Australia. With the serpentinization of exhumed mantle peridotite in the Outer Margin Highs during the Coniacian in the east and Turonian in the west, the crustal deformation mechanism changed from mainly pure shear to simple shear along the newly established decollement. Fast spreading since the Mid Eocene caused gravitational collapse of the margin. Changes in heat flow possibly correlate with a change in deformation style in the continental crust. Parallel developments of sedimentation-rate and extension-rate suggest that most of the subsidence was structurally related. The Shipwreck Trough hydrocarbon fairway probably continues south into the Sorrell Basin. Possible stagnant conditions in deeper water offshore across the Hinge Zone might have enhanced the organic content of the Belfast Mudstone creating potential oil source rocks. Deepwater lntra-Paaratte reservoirs are not proven, but the alternating reflective to non-reflective seismic facies might indicate interbedded sands and shales. Large rollover anticlines would make excellent traps in the deepwater Otway Basin.
-
ItemAustralian lineament tectonics: with an emphasis on northwestern Australia( 1994-08)Australia is transected by a network of systematic continental-scale lineaments that are considered to be zones of concentrated, aligned tectonic activity which have apparent continuity over vast distances. The influence of lineaments on the rock record can be identified in many types of data-sets, and existing data reveals previously undescribed basement influences. Several continental-scale lineaments can be traced offshore with apparent continuity for hundreds to thousands of kilometres, two of which are seen to cross the Tasman Sea in offshore eastern Australia. Geological and chronological evidence demonstrates that many of the lineaments have been zones of reactivation since at least the Early Proterozoic (- 1880 Ma) and that they appear to cross major terrane boundaries. Alternative models for their origin are a) a pre-existing lineament network maintained in an ancient basement underlying the entire continent; b) lateral propagation of crustal-scale structures; c) alignment of genetically unrelated lineaments giving the appearance of continuity. Australian deep-seismic profiles show that continental-scale lineaments are zones of crustal-scale structure which in some cases transect the crust-mantle boundary. Lineaments demonstrate many faulting styles, e.g. listric extensional (G3), planar moderate-angle thrusts (G2 l), and sub-vertical thrusts (G 17). In some cases the structural style varies laterally along the length of the lineament. (For complete abstract open document)
-
ItemThe tectonic evolution of the Songpan Garzê Fold Belt, Southwest China( 2001)Structural observations suggest that all pervasive deformation of the Songpan Garzê Fold Belt occurred continuously and progressively during the Indosinian Orogeny (c.230-200 Ma), and prior to widespread post-tectonic magmatism c.195-180 Ma. Development of the arcuate structural grains and discrete high-grade metamorphic complexes that characterise the southeast Songpan Garzê Fold Belt can be explained entirely in terms of this progressive Indosinian deformation. Likewise, all greenschist-amphibolite facies Barrovian-style metamorphism within the southeast Songpan Garzê Fold Belt is correlated with Indosinian orogenesis. Thermodynamic modelling of micaceous, garnet- and aluminosilicate-bearing metamorphic assemblages, all of which define Indosinian-aged tectonic fabrics, suggests a continuous textural evolution that occurred under the influence of a simple clockwise P-T-t path. There is no structural or metamorphic evidence to substantiate the pervasive Yenshanian (Jurassic-Cretaceous) or Himalayan (Tertiary-Recent) orogenic overprints that previous studies of the terrane have inferred. The distribution of progressive structure and locally variable timing relationship between progressive deformation and peak metamorphism imply that Indosinian deformation occurred diachronously across the southeast Songpan Garzê Fold Belt. Such deformation was characterised by the westward migration of progressive structural ‘fronts’, towards the interior of the terrane, in response to lateral growth of the transpressive interface between the Songpan Garzê Fold Belt and adjacent Yangtze Craton. In contrast, consistent timing relationships between peak metamorphism, basement anatexis and the diapiric exhumation of high-grade metamorphic rocks suggest that the thermal maturation of the terrane was spatially and temporally uniform across the southeast Songpan Garzê Fold Belt. Post-Indosinian modification of the Songpan Garzê Fold Belt was limited to brittle strike-slip dissection, predominantly focussed into the discrete west-northwest-trending Xianshui He and Kunlun fault zones. Sinistral displacement of these two fault zones, from at least the Miocene onward, transported two large tracts of the terrane towards the southeast, effectively intact. This displacement was absorbed by reactivation of the Longmen Mountains Thrust Nappe Belt and transpressive exhumation of the Min Shan Uplift Zone. Modification of the Songpan Garzê Fold Belt did not accommodate any significant vertical distortion that might have contributed to isostatic rebound of the present-day 4500-metre Tibetan Plateau. Nevertheless, uplift of the greater Songpan Garzê Fold Belt occurred from at least the Neogene onward, accommodated by reactivation of the Songpan Garzê/Yangtze interface and present-day boundary of the northeast Tibetan Plateau. New 40Ar/39Ar and Rb/Sr thermochronology from southeast Songpan Garzê Fold Belt identifies two discrete cooling episodes: 1) late-Triassic-Jurassic cooling from peak-metamorphic conditions of >500° C to temperatures of around 350° C; and 2) rapid Tertiary-Recent cooling to near-surface temperatures. Both cooling episodes are interpreted to record erosional exhumation of the terrane. Whilst Mesozoic cooling is correlated with limited post-Indosinian rebound of the thin-skinned Songpan Garzê accretionary wedge, Tertiary-Recent cooling is thought to reflect an isostatic potential associated with Himalayan Orogenesis in central Asia. Surprisingly, this latter event does not seem to have been coupled to the rapid Neogene uplift of the Tibetan Plateau. Tertiary-Recent exhumation, uplift and structural modification of the Songpan Garzê Fold Belt are inferred to have been bolstered by a pervasively thickened viscous lower crust. This thickening is attributed to penetrative east-directed deformation of deeper lithosphere beneath the detached thin-skinned veneer of the Songpan Garzê Fold Belt. Such an interpretation favours penetrative deformation of the mid-lower crust as the dominant mechanism by which India/Eurasia intracontinental convergence was absorbed - not lateral escape or extrusion of eastern Asia - and highlights the role that the Yangtze Craton has played throughout Mesozoic and Tertiary orogenesis: acting as a rigid backstop to penetrative deformation of the more plastic Songpan Garzê Fold Belt.
-
ItemMetamorphism of granulite facies metapelites( 2004)This thesis involves a study of metamorphism and partial melting in granulite facies metapelites from three regions, the Larsemann Hills and the Rauer Group of east Antarctica, and Fishery Bay in southern Eyre Peninsula of South Australia. Along with the metamorphic study, $^40Ar/^39Ar$ thermochronological dating was also undertaken for the first two areas to constrain the timing of tectonothermal events and syn- to post-tectonic cooling history. (From Abstract)
-
ItemStructural and thermal evolution of the Gulf Extensional Province in Baja California, Mexico: implications for Neogene rifting and opening of the Gulf of California( 2009)The Gulf of California in western Mexico is a prime example of a young passive margin that is currently undergoing the transition from continental rifting to seafloor spreading. With less than ~25 km of the width of the original continental surface area submerged, the northern Gulf Extensional Province represents a key area to assess the history of strain localisation during the early stages of continental extension. Geological mapping revealed that the basins and ranges of the Sierra San Felipe, located in the hanging wall of the Main Gulf Escarpment, are bounded to the east by an en-echelon array of left-stepping moderate- to low-angle normal faults that represent the next dominant set of normal faults from the break-away fault in direction of transport. Structural displacement estimates suggest up to ~4.5–9 km of broadly east-directed extension on the Las Cuevitas, Santa Rosa and Huatamote detachments. Fault kinematics suggest a transtensional stress regime with NE- to SE-directed extension and permutating vertical and N–S subhorizontal shortening. Clockwise vertical-axis block rotations and constrictional folding of the detachments were an integral part of the late Miocene to Pleistocene deformation history of the San Felipe fault array. This overall constrictional strain regime is indistinguishable from the present-day deformation in the Gulf Extensional Province and indicates that the fault array formed during a single phase of integrated transtensional shearing since rifting began in the late Miocene. Apatite fission track (AFT) and (U-Th)/He results of Cretaceous crystalline basement samples from the Sierra San Felipe record a three-stage Cenozoic cooling history. Moderate cooling (~4–7ºC/m.y.) during late Paleocene to Eocene times is attributed to progressive down-wearing and bevelling of the ancestral Peninsular Ranges. Beginning at ~45–35 Ma, a period of tectonic quiescence with cooling rates of ≤1ºC/m.y. marks final unroofing of the basement and the development of a regional Oligocene to Miocene peneplain. Thermal modelling of samples from the footwall of the Las Cuevitas and Santa Rosa fault systems indicates that accelerated cooling began at ~9–8 Ma. This cooling pulse is attributed to tectonic denudation of the footwall and implies that faulting initiated synchronously on both detachments at ~9–8 Ma. Late Miocene deformation occurred distributed throughout the Sierra San Felipe, but started waning after the Pacific-North America plate boundary had localised into the Gulf of California by ~4.7 Ma. During a late Pliocene structural reorganisation in the northern Gulf, the locus of extension shifted from the Tiburón to the Delfín basins, thereby initiating strike-slip faulting on the Ballenas fracture zone, a transform fault located approximately 1.5–4.5 km offshore in central Baja California. This is consistent with low-temperature thermochronometric data from two horizontal transects perpendicular to the strike of the transform, which document a pronounced late Pliocene to Pleistocene heating event that is related to the structural and/or magmatic evolution of the transform fault. During reheating, maximum paleotemperatures reached >100–120ºC near the coast, but did not exceed ~60ºC some 5–8 km further inland. Highly non-systematic overprinting patterns are best explained by circulating hydrothermal fluids, which are most likely associated with magmatic leaking along the transform fault. AFT and (U-Th)/He ages from a vertical profile collected on the Libertad escarpment, which forms part of the Main Gulf Escarpment in central Baja, pre-date Neogene extension and indicate that rift-related denudation was insufficient to expose samples from temperatures higher than the sensitivity zones of the two systems. One sample from the base of the escarpment however, records a middle to late Miocene hydrothermal overprint and suggests that extension in central Baja California likely initiated before ~10–8 Ma.