The footwall of a normal fault in the North D'Aguilar block in eastern Australia contains blueschist blocks within a serpentinite matrix melange. The melange contains mass‐flow deposits and was derived by erosion and redeposition of oceanic lithosphere exposed on the ocean floor by faulting. In mid‐Carboniferous time, the melange was metamorphosed in the epidote‐blueschist facies, mylonitized, and underplated to the hanging‐wall of a subduction zone. An S‐type granitoid, intruded at ∼306–307 Ma, was probably derived by partial melting of subducted metasediments during the peak of a greenschist facies overprint that accompanied transposition of an early high‐P/low‐T fabric. Mylonitic rocks below the normal fault absorbed a component of top‐to‐the‐west simple shear related to movement on that originally west dipping fault, and resulted in juxtaposition of very low‐grade accretionary sequences above polydeformed blueschists in a metamorphic core complex. At deeper levels in the footwall of the fault, bulk deformation was approximately irrotational. Later, the low‐angle fault was folded, and its displacement was transferred westward into a more planar fault splay. The juxtaposition of high‐P serpentinite melange against upper plate rocks probably reflects the mechanical weakness of serpentinite in deformed oceanic sequences, and the role serpentinite plays in strain softening that concentrates deformation along major extensional shear zones.
A synclinal depositional system in eastern Australia (Taroom Trough, Bowen Basin) was affected by folds and thrusts, but the structural style associated with this deformation is not fully understood. Using gridded aeromagnetic data and 2‐D seismic reflection data, we conducted a structural analysis that unravels the geometry and kinematics of major thrust faults in the eastern‐central part of the Taroom Trough. Major structures are the east dipping Cockatoo, Miles, and Taroom faults and west dipping Burunga and Glebe faults. Our results show that west dipping thrusts have a listric geometry that produced gentle hanging‐wall anticlines. A north striking gentle symmetric syncline and anticline pair is also observed to the west of the Burunga Fault. These observations indicate that the deformation in the central Taroom Trough was controlled by décollements in the basement rocks. The décollements and resultant structures were likely developed in response to mild contraction of the synclinal depositional system during the last phase of the Permian‐Triassic Hunter‐Bowen Orogeny (HBO). The last phase of the HBO also resulted in the reactivation of preexisting east dipping Cockatoo and Miles faults. The bulk longitudinal strain, however, in the eastern‐central Bowen Basin was low (~2.8% shortening), with the deformation restricted to a relatively narrow zone. In contrast, deformation in the northern Bowen Basin was distributed in a wider fold‐thrust belt that accommodated a higher amount of strain. This change in the pattern of deformation along the eastern part of the Bowen Basin could possibly be explained by along‐strike variations in the rates of trench advance.
More than 6,000 boreholes were compiled to develop a consistent regional scale stratigraphic framework for the Permian Rangal, Baralaba and Bandana coal measures (CMs) within the Bowen Basin. Coal beds and tuff horizons were used as stratigraphic markers, supported by chemostratigraphy and age dating. Results corroborate the general subdivisions of these different coal measures relative to basin location, but increase resolution on migrating depocentres in response to foreland loading and subsidence on coal thickness and splitting patterns. In the north, the Rangal CMs comprise two main seams, correlated as Leichhardt and Vermont. The Yarrabee Tuff is consistently present and splits the Vermont seam. The main Leichhardt seam exhibits relatively simple offset stacking relationships with the underlying Vermont and overlying Phillips seams. In the southwest, the Bandana CMs comprise two to three significant seams—the Aries-Castor, Pollux (Leichhardt equivalent) and Orion—along with the Pisces containing the Yarrabee Tuff. Seams exhibit complex Z splitting and vertical interburden stacking. Locally super-thick seams (crabs) form from convergence of thinner split seams in areas of relative stability over basement highs. In the Taroom Trough, the Baralaba CMs show the greatest response to loading, as seams thin and split along the eastern margin. The variability in the splitting patterns, coupled with the coal measures total thickness, corroborate the extension of the final basin depocentre northward, which was not preserved.
First and foremost I would like to thank my supervisor, Dr Rod Holcombe, for suggesting the topic for this thesis and for supporting my application for Ph.D. candidature. He has given his continuous support, interest and patience throughout the duration of the project, which has benefitted from his many discussions, ideas, and very thorough reviewing of the manuscript.Thanks are due to Drs Tim Little, Chris Fielding, Chris Stephens and Richard Schon from the Department of Earth Sciences for many interesting discussions and information regarding special aspects of the project. Prof. Robin Offler from the University of Newcastle has been particularly helpful with practical and interpretative assistence during the white mica crystallinity study. This project was carried out with funding from an Australian Postgraduate Research Award.I declare that the work as presented in this thesis is original to the best of my knowledge and belief, except as acknowledged in the text, and that this material has not been submitted, either in whole or in part, for a degree at this or any other university. Renate Sliwa v Granodiorite clasts in Marumba Beds Permian-Tr iassic intrusions Late Triassic volcanicsGranitoid geochemistry I-TYPE VERSUS S-TYPE STRUCTURAL SETTING OF CARBONIFEROUS GRANITOIDS Deformation in the Gallangowan assemblageCorrelation with the Claddagh-Manumbar pluton LIST OF FIGURESTectonic elements of the New England Fold Belt in eastern Australia 2Interpretation of the easternmost section of the Eromanga-Brisbane deep seismic profile 3Simplified geology of the New England Orogen in southeast Queensland. 4Location and access of study area 6Previous mapping in the central North D'Aguilar Block. 8Simplified geological compilation map of southeast Queensland. 11Previous correlation schemes for tectonostratigraphic units in the D'Aguilar Blocks. 13Unmigrated seismic reflection profile across the Clarence-Moreton Basin. 15Simplified geological map and crossection of the northern NDB. 25Simplified geological map and crossection of the southern NDB. 26Simplified geological map of the study area. 29CIPW-normative compositions of Mt Mia serpentinite. 37T AS classification diagram and AFM diagram for mafic greenschist samples. 38Ternary classification diagram for pyroxene microprobe data. 38Stereographic projections of S1/S2 and L' in the Jimna Phyllite. 49Rose diagram of combined joint and kink fold orientations in the Jirrma Phyllite. 49Detailed geological traverse along Summ er Creek. 53Stereo graphic projections of S 1 and L10 in the Booloumba Beds. 54Stereo graphic projection of the eastern and western succession of the Amamoor Beds. 56Stereo graphic projection of slaty cleavage in Cambroon Beds. 66 T AS classification diagram and AFM diff erentiation diagrams for Triassic volcanics. 73Total magnetic intensity map of the central NDB. 86Structural framework for the northern NDB. 88Simplified geological map showing the division of the field area. 90Distribution histograms of illite crystall inities and b0 -spacings for...
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