- Title
- The geodynamic significance of the Gilmore Fault Zone, Lachlan Orogen: structural characteristics, kinematic history and timing
- Creator
- Bell, Michael
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Masters Research - Master of Philosophy (MPhil)
- Description
- Recent tectonic evolution models for the Lachlan Orogen are evaluated by examining a key region located at the boundary between the central and eastern provinces; the Tumut trough and western boundary, the Gilmore Fault Zone (GFZ). This distinct structural boundary separates the Ordovician Macquarie Arc volcanics and Silurian-Devonian Tumut trough of the eastern province from Ordovician meta-sediments and ~430 Ma old S-type granites of the Wagga Omeo Metamorphic Belt (WOMB) in the western province. The research focuses on the timing of movement of the GFZ, and the tectonic controls on the dynamics of the Tumut trough, by U-Pb zircon age determination of key stratigraphic and magmatic units in the region. This is augmented with 40Ar/39Ar age determination of synkinematic minerals within high-strain deformation zones, where the kinematic evolution had been determined. The initial focus of the research was to develop a new regional basement map, which was achieved by merging and revising current available regional geology maps and reconstructing associated time-space plots. This map provided the regional tectono-stratigraphic context to choose appropriate samples for age determinations. The major results from this thesis are as follows: (1) Conglomerates and associated shear zones, including the Yiddah and Manna Formation (conglomerates), cannot be correlated without U-Pb age constraints from detrital zircons; (2) The deep marine meta-sedimentary rock of the Trigalong Formation are Early Devonian, not Late Ordovician, which requires the Tumut trough was a deep water basin at this stage; (3) the Bumbolee Formation is Early Devonian, unconformably overlying deformed Silurian sediments - not Ordovician as previously assumed; (4) the Blowering Formation is Early Devonian, not middle Silurian as assumed; (5) the GFZ has a protracted history of sinistral re-activation, from ~415 Ma to 360 Ma, with significant E-W shortening at ~400 Ma; (6) Repeated extension-contraction events (tectonic switching) occurred from Ordovician to Carboniferous. At broadest scale, the orocline model for the Lachlan Orogen appears to be consistent with the information presented, but the geological history is more complex than proposed in that model. In particular, the Tumut Trough appeared to have had two distinct phases of opening, in the middle-Silurian and Early Devonian, separated by a period of intense deformation associated with the Bindian orogeny at ~420 Ma. Also, repeated periods of extension and contraction are evident along the Gilmore Fault, beginning at ~430 Ma with dextral opening of the Tumut trough, but followed by repeated periods of contraction associated with sinistral strike slip deformation at ~415 Ma, 400 Ma, 390 Ma and 360 Ma. Periods of dextral extension are inferred to occur at ~430 Ma, 420-415 Ma, and ~370 Ma, associated with distinct phases of magmatic activity. These periods of repeated extension and contraction are consistent with a tectonic switching model for Lachlan fold belt tectonic evolution.
- Subject
- Gilmore Fault Zone; Lachlan Orogen; geochronology; Ar-Ar; U-Pb
- Identifier
- http://hdl.handle.net/1959.13/1433468
- Identifier
- uon:39260
- Rights
- Copyright 2020 Michael Bell
- Language
- eng
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